45th Annual Virginia Geological Field Conference, September 25-26, 201545th Annual Virginia Geological Field Conference, September 25-26, 2015

John HaynesRick DiecchioSteve Whitmeyer

James Madison Univ. George Mason Univ.

Stratigraphy of Silurian Sandstones in Western Virginia from Eagle Rock to Bluegrass

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Figure A. Facies changes in Upper Ordovician and Silurian strata between selected exposures along and near the �eld trip route, including Eagle Rock (Stop 1), Chestnut Ridge (Stop 3) and Williamsville (Stop 4), in and near the Bullpasture River Gorge, and Bluegrass/Forks of Waters (Stop 5). See back cover for stoplocations. The thinning and stratigraphic splitting of the “Eagle Rock Sandstone” into separate sandstonesof the Keefer, McKenzie, and Williamsport formations, and the possible equivalence of the calcareous upper part of the “Eagle Rock Sandstone” with similar sandstones in the Tonoloway, will be the primary focus of this trip.

Front Cover. Deformation in the Keefer facies of the lower “Eagle Rock Sandstone” at Eagle Rock (Stop 1).The prominent pinnacle is one of the resistant quartz arenites in the “Eagle Rock Sandstone” that de�nesthe summit of Crawford Mountain. View is to the southwest looking across US 220 at the southwestend of the bridge over the James River near the town of Eagle Rock.

 45th  Annual  Virginia  Geological  Field  Conference  

 

September  25  –  26,  2015    

Natural  Bridge  Hotel,  Natural  Bridge,  Virginia        

 

STRATIGRAPHY  OF  SILURIAN  SANDSTONES  IN  WESTERN  VIRGINIA  

FROM  EAGLE  ROCK  TO  BLUEGRASS      

John  Haynes  Department  of  Geology  and  Environmental  Science  

James  Madison  University    

Richard  Diecchio  Department  of  Atmospheric,  Oceanic  &  Earth  Sciences  

George  Mason  University    

Steven  Whitmeyer  Department  of  Geology  and  Environmental  Science  

James  Madison  University                      

   

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                   Figure  B.  Age  and  generalized  stratigraphic  relations  of  Upper  Ordovician,  Silurian,  and  Lower  Devonian  strata  at  and  near  the  stops  on  the  field  trip.  Uncertainties  in  upper  and  lower  contacts  of  the  “Eagle  Rock  Sandstone”  and  in  the  extent  of  the  Ordovician  –  Silurian  boundary  are  indicated  by  question  marks.    Based  on  field  work  by  the  authors,  and  the  work  of  Denkler  and  Harris  (1988a,  1988b),  Harris  et  al.  (1994),  and  Cohen  et  al.  (2013).  

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INTRODUCTION     This  year’s  field  trip  will  examine  bedrock  exposures  of  Silurian  strata  in  the  western  Valley  and  Ridge  with  a  principal  focus  being  the  dramatic  facies  changes  that  occur  in  a  SSE  to  a  NNW  direction  of  this  region  (Fig.  A  [inside  front  cover]),  especially  in  the  stratigraphic  interval  above  the  siliciclastics  of  the  Rose  Hill  Formation  and  below  the  carbonates  and  thin  sandstones  of  the  Tonoloway  Limestone  (Fig.  E  [inside  back  cover]).    We  will  examine  Silurian  strata  in  exposures  at  5  stops  in  Botetourt,  Alleghany,  Bath,  and  Highland  Counties  (Fig.  F,  [trip  route  on  back  cover]).     New  findings  based  on  our  recent  and  ongoing  bedrock  mapping  in  Highland  County  (Haynes  and  Whitmeyer,  2010;  Hazelwood  et  al.,  2012;  Haynes  and  Diecchio,  2013)  will  be  a  principal  part  of  today’s  field  trip.    Stratigraphic  highlights  will  include  (A)  the  presentation  of  evidence  that  supports  suggested  new  correlations  of  the  upper  several  meters  of  the  “Eagle  Rock  Sandstone”  at  Eagle  Rock  (Stop  1)  with  the  Wills  Creek  Formation  as  well  as  the  lower  Tonoloway  Limestone  (Stop  3);  (B)  recognition  that  the  quartz  sandstones  in  the  middle  of  the  McKenzie  Formation  exposed  at  Williamsville  in  the  Bullpasture  River   Gorge   (Stop   4)   are   the   middle   sandstone   member   of   the   McKenzie,   which   extends   the   known  exposures  of  this  sandstone;  (C)  recognition  that  the  quartzose  oolitic  grainstones  in  the  lower  McKenzie  Formation  exposed  in  the  Bullpasture  River  Gorge  (Stop  4)  are  the  easternmost  known  exposures  of  the  oolitic   facies  that  comprises  the  upper  beds  of   the  Lockport  Member  of   the  McKenzie  Formation   in  the  subsurface   of   western   West   Virginia;   (D)   a   reinterpretation   of   prior   stratigraphic   findings   and  correlations   in  and  near   the  Bullpasture  River  Gorge   (Stops  3  and  4);   and   (E)   confirmation   that  of   the  Keefer,  McKenzie,  and  Williamsport  equivalents  which  collectively  comprise  the  sandstones  in  the  ~140  m  thick  “Eagle  Rock  Sandstone”  at  Stop  1,  only  the  Williamsport  Sandstone  persists  as  a  quartz  arenite  sandstone   to   the   exposures   in   northernmost   Highland   County   at   Stop   5   near   Forks   of   Water   and  Bluegrass  where,  as  we  will  see,  it  is  only  ~8  m  thick.         Structurally,  we  will  see  deformation  at  several  scales,  from  the  regional  scale  of  folds  and  faults  across  the  Valley  and  Ridge,  to  outcrop-­‐  and  hand  sample-­‐scale  structures  (front  cover).  The  route  of  the  field   trip   will   transect   (and   parallel)   kilometers-­‐scale   folds,   including   the   Rich   Patch,   Warm   Springs,  Bolar,   and   Hightown   (Wills   Mountain)   anticlines.     Individual   stops   will   highlight   fault-­‐related  deformation,  such  as  outcrop-­‐scale  folds  and  faults  at  Eagle  Rock  that  are  related  to  the  Pulaski  Fault,  and  other  smaller-­‐scale  structures.    BACKGROUND  AND  GEOLOGIC  SETTING     In  the  Mid-­‐Atlantic  region,  the  Appalachian  Mountains  are  divided  into  the  Blue  Ridge,  and  Valley  and  Ridge,   and  Appalachian  Plateaus  physiographic  provinces.    Today’s   field   trip   is   entirely  within   the  Valley   and   Ridge   that,   with   its   distinctive   northeast-­‐trending   linear   topography   of   parallel   ridges   and  valleys,   is   a   classic   fold-­‐and-­‐thrust   belt.     In   the   area   along   the   field   trip   route,   the  Valley   and  Ridge   is  underlain  by  a  thick  sequence  of  Cambrian  to  Mississippian  sedimentary  rocks.    These  Lower  and  Middle  Paleozoic  sedimentary  strata  now  exposed  in  the  Valley  and  Ridge  province  of  western  Virginia  have  had  a  long  and  interesting  history  of  deposition,  burial,  lithification,  deformation,  exhumation  and  erosion,  a  second   round   of   burial,   intrusion,   and   uplift,   and   ongoing   erosional   sculpting,   which   collectively   have  produced  the  landscape  we  see  today.    The  ridges  are  held  up  by  mechanically  and  chemically  resistant  quartz  sandstones,  and  the  valleys  are  underlain  by  mechanically  weak  mudrocks  and/or  by  chemically  weak   carbonate   rocks.    With   its   overview   of   the   regional   sedimentology   and   stratigraphy,   and   of   the  regional   deformational   and   structural   relationships,   today’s   field   trip  will   allow  participants   to   have   a  look  at  the  effects  of  several  of  these  processes.         The  earliest  geologic  mapping  in  the  area  of  the  field  trip  route  includes  the  work  of  Darton  (1892,  1899),   Schmitz   (1896),   and   Butts   (1933).     From   that   time   to   the   present,   many   regionally   focused  geologic  studies  (both  stratigraphic  and  structural,  as  well  as  geologic  mapping)  that  are  of  relevance  to  this  field  trip  have  been  carried  out  in  the  area  of  today’s  trip,  including  Butts  (1940),  Woodward  (1941,  1943),   Lesure   (1957),   Deike   (1960),   Folk   (1960),   Hunter   (1960),   Bick   (1962,   1973),   Travis   (1962),  Appalachian  Geological  Society   (1970),  McGuire   (1970),  Patchen  (1974),  Lampiris   (1975),  Patchen  and  

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Smosna  (1975),  Smosna  et  al.  (1977),  Smosna  and  Patchen  (1978),  White  and  Hess  (1982),  Whitehurst  (1982),  Smosna  (1984),  Kulander  and  Dean  (1986),  Rader  and  Gathright   (1986),  Bartholomew  (1987),  Denkler  and  Harris  (1988a),  Diecchio  and  Dennison  (1996),  Brett  et  al.  (1998),  Bell  and  Smosna  (1999),  Haynes   and   Whitmeyer   (2010),   Hazelwood   et   al.   (2012),   Haynes   and   Diecchio   (2013),   Haynes   et   al.  (2014),  Martin  et  al.  (2014),  Swezey  and  Haynes  (2015),  and  Swezey  et  al.  (2015).         Of  the  stratigraphic  studies  on  the  Silurian  of  this  region,  several  deserve  additional  mention.      Dennison  (1970)  made  note  of  two  important  relationships  related  to  Silurian  stratigraphy  in  the  outcrop  belt  of  Virginia  and  West  Virginia.  First,  southwest  of  Roanoke,  the  strata  are  incomplete,  being  cut-­‐out  by  one  or  more  unconformities.  Second,  toward  the  west  and  north  (including  the  area  covered  by  this  field  guide),  where  the  strata  are  more  complete,  the  quartz  arenite  facies  are  dominant  at  the  southeast  basin  margin,  but  become  tongues  to  the  north  and  west  with  some  eventually  pinching.         The  name  “Eagle  Rock  Sandstone”  was  introduced  informally  by  Lampiris  (1975)  to  describe  the  quartz   arenite   unit   that   occurs   between   the   Rose   Hill   Formation   and   the   Tonoloway   Limestone.     The  “Eagle  Rock  Sandstone”   is   thickest  at  Eagle  Rock,  near   the  southeast  basin  margin,  and  thinner   toward  the  southwest,  northwest  and  northeast.     It  thus  thins  into  the  basin  and  along  the  basin  axis.  Lampiris  also   recognized   that   the   “Eagle   Rock   Sandstone”   splits   and   thins   into   tongues   toward   the   west   and  northwest.  These  sandstone  tongues  are  the  emphasis  of  this  field  guide.     It   should   be  mentioned   that   the   surface   exposures   of   distal   or   basinal   facies   in   the   Valley   and  Ridge,  including  those  which  we  will  see  on  this  trip,  are  not  the  limit  of  these  facies.    Basin  center  is  in  West   Virginia,   where  most   Silurian   strata   occur   in   the   subsurface,   and   the   Silurian   strata   continue   to  change   facies  westward   into   the  basin   center,  where   they   contain  more   shale,   limestone  and  dolomite  than  anything  we  will  see  on  this  trip.    These  relationships  are  illustrated  by  Woodward  (1941),  Knight  (1969),  and  Horvath  et  al.  (1970)  in  the  form  of  stratigraphic  cross-­‐sections.    STRATIGRAPHIC  UNITS  OF  INTEREST     Figure  B   shows   the  various  Upper  Ordovician,   Silurian,   and  Lower  Devonian   stratigraphic  units  and  stratigraphic  relationships  in  this  region,  many  of  which  will  be  of  interest  at  the  stops  on  this  trip  as  indicated  at  the  top  of  each  column.    The  stratigraphic  units  are  summarized  below.    Ordovician  Reedsville/Martinsburg  Shale  (300–400  m  thick)     The   type   section  of   the  Reedsville   Shale   is   at  Reedsville   in  Mifflin  County,  Pennsylvania   (Ulrich,  1911),  and  the  type  section  of  the  Martinsburg  Shale  is  at  Martinsburg  in  Berkeley  County,  West  Virginia  (Geiger   and   Keith,   1891).     Darton   (1899)   and   Bick   (1962)  mapped   these   strata   in   Bath   and  Highland  Counties   as   the  Martinsburg   Shale   or   the  Martinsburg   Formation.   In   the   Shenandoah   Valley,   area   the  Martinsburg  Shale   is   a   thick   sequence  of   siliciclastic   turbidites  with  only  a   few   tens  of  meters  of  black  laminated   argillaceous   limestone   at   its   base,   all   deposited   in   open   basin   to   basin   margin   settings.   In  contrast,   the   strata   of   equivalent   age   west   of   the   North   Mountain   front   are   mixed   carbonate   and  siliciclastic  sediments  deposited  in  a  storm-­‐dominated  shelf  setting.  Diecchio  (1991)  recommended  that  the  name  Reedsville  Shale  be  used  for  the  strata  on  the  west  side  of  the  North  Mountain  front,  and  that  the  name  Martinsburg  Formation  should  be  restricted  in  its  usage  to  equivalent  strata  in  exposures  east  of  the  North  Mountain  front,  primarily  in  the  Shenandoah  Valley.    Reedsville  Shale  has  been  used  to  refer  to  these  strata  throughout  most  of  the  field  trip  area  (Rader  and  Wilkes,  2001;  Haynes  and  Whitmeyer,  2010;  Wilkes,  2011;  Haynes  and  Diecchio,  2013).    It  is  the  oldest  formation  shown  in  the  regional  cross  section  (Fig.  A).     Thin,   greenish-­‐gray   to   gray  mudrock  with   thin   interbeds   of   fine-­‐grained   sandstones,   siltstones,  and  bioclastic  limestones  deposited  on  a  storm-­‐dominated  shelf  (Kreisa,  1981)  comprise  this  interval.    A  prominent  brachiopod-­‐rich  biozone  known  regionally  as  the  Orthorhynchula  zone  occurs  in  the  upper  3–4  m  of   the  Reedsville,   and   it   is   a  useful  marker  bed   for   identifying   the   contact  between   the  Reedsville  Shale   and   the   overlying   Oswego   Sandstone   or   Juniata   Formation.     The   Reedsville   is   present   in   the  exposures  at  Stop  1  (Eagle  Rock)  and  Stop  5  (Bluegrass/Forks  of  Waters).  

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Ordovician  Oswego  Sandstone  (8–25  m  thick)     The  Oswego  Sandstone  was  named  by  Prosser  (1888)  for  outcrops  in  Oswego  County,  New  York,  although   a   specific   type   section  was   not   specified.     Darton   (1899)  mapped   these   strata   as   part   of   the  Juniata   Formation.     Butts   (1940)   identified   a   thin   outcrop   of   the   Oswego   Sandstone   in   northwestern  Highland  County,  but  Bick  (1962)  did  not  include  the  Oswego  among  the  stratigraphic  units  he  mapped.    Subsequently,   the   Oswego   has   been   recognized   at   several   exposures   in   this   region   (Dennison   and  Wheeler,  1975;  Diecchio,  1985;  Wilkes,  2011;  Haynes  and  Diecchio,  2013).     Bluish-­‐  to  greenish-­‐gray  to  brown  beds  of  fine-­‐  to  medium-­‐  to  coarse-­‐grained  sublithic  arenites  up  to  1  m  thick,  with  some  cross-­‐bedding   in  places,  and  an  overall   lack  of   fossils  characterize   the  Oswego  Sandstone,   which   was   deposited   in   transitional   to   non-­‐marine   environments   that   probably   included  fluvial,  beach,  and  fan-­‐delta  systems.    A  common  and  distinctive  character  of  these  sandstones  on  a  fresh  surface  is  the  presence  of   limonite  as  small  yellowish-­‐orange  specks.    Thin  interbeds  of  green  mudrock  are  also  generally  present.    The  Oswego  is  present  in  the  exposure  at  Stop  1  (Eagle  Rock),  and  it  is  poorly  exposed  as  float  blocks  at  Stop  5  (Bluegrass/Forks  of  Waters).    Ordovician  Juniata  Formation  (100–250  m  thick)     The  Juniata  Formation  was  named  by  Darton  and  Taff  (1896),  and  a  type  section  was  designated  by  Clark  (1897).    Darton  (1899)  mapped  the  Juniata  Formation  in  this  region,  and  this  stratigraphic  name  has  been  in  essentially  continuous  use  in  this  region  ever  since  (Butts,  1940;  Bick,  1962;  Dennison  and  Wheeler,  1975;  Diecchio,  1985;  Rader  and  Wilkes,  2001;  Wilkes  2011;  Haynes  and  Diecchio,  2013).     Interbedded   reddish-­‐brown   to   yellowish-­‐brown   sublithic   arenites   up   to   1  m   thick,   some   with  cross-­‐bedding,  and  red  mudrocks  are  the  major  lithologies  in  the  Juniata  Formation,  which  was  deposited  in   a   transitional,   perhaps   deltaic,   marine   environment   that   oscillated   from   marine   to   non-­‐marine   as  evidenced  by  the  presence  of  Skolithos  (trace  fossils  of  vertical  burrows)  in  some  of  the  sandstone  beds.    In  many  sections,  the  top  of  the  Juniata  is  characterized  by  several  pink  quartz  to  sublithic  arenite  beds  up  to  ~1.5  m  thick  that  are   transitional  with   the  overlying  quartz  arenites  of   the  Tuscarora  Formation.    The   upper   several   meters   of   the   Juniata,   and   the   Juniata   –   Tuscarora   contact,   will   be   seen   at   Stop   2  (Falling  Spring  Falls),  and  it  is  also  exposed  at  Stop  5  (Bluegrass/Forks  of  Waters).    Silurian  Tuscarora  Formation  (15–25  m  thick)     The   type   section  of   the  Tuscarora  Formation   is   at  Tuscarora  Mountain   in  Pennsylvania.     It  was  named  by  Darton  and  Taff  (1896),  and  Darton  (1899)  mapped  these  strata  in  Bath  and  Highland  Counties  as   the   Tuscarora   Quartzite.     Woodward   (1941)   referred   to   these   strata   regionally   as   the   Tuscarora  Sandstone,  whereas  Bick   (1962)  mapped   them  as   the  Clinch  Sandstone.    Subsequent  publications  have  generally  referred  to  these  strata  as  the  Tuscarora  Formation  in  the  field  trip  area  (e.g.,  Bick,  1973;  Rader  and  Wilkes,  2001).    Tuscarora  is  a  name  that  generally  is  used  east  of  the  New  River,  and  Clinch  is  used  west  of  the  New  River;  however,  they  are  the  same  stratigraphic  unit.     Thick   to   massively   bedded   white   to   grayish-­‐white   to   pale-­‐yellow   to   pale-­‐pink   silica-­‐cemented  supermature   quartz   arenites,   some   with   prominent   crossbeds,   are   the   principal   lithology   of   the  Tuscarora,   which  was   deposited   in   beach,   nearshore,   and   shallow   shelf   environments.     Because   of   its  extreme   durability,   the   Tuscarora   Formation   is   the   dominant   ridge-­‐forming   stratigraphic   unit   of   the  central  Appalachians.    Thin  beds  of  quartz-­‐pebble  conglomerate  occur  in  the  lower  half  of  the  formation  at  many  exposures,  and  at  a  few  locations,  notably  along  the  west  limb  of  the  Wills  Mountain  anticline,  a  thin  black  shale   is  present   in  the  middle  of  the  unit.    Trace  fossils   including  Skolithos  and  Arthrophycus  (single   to   compound  elongate  burrows)   can  be   found   in   some  beds  and  on  some  bedding  planes.    The  Tuscarora  Formation  is  exposed  at  Stops  1  (Eagle  Rock),  2  (Falling  Spring  Falls),  and  5  (Bluegrass/Forks  of  Waters).        

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Silurian  Rose  Hill  Formation  (80–250  m  thick)     The   type   section   of   the   Rose  Hill   Formation   is   at   Rose  Hill   in   the   city   of   Cumberland,   Allegany  County,   Maryland   (Swartz,   1923).     The   earlier   name   for   this   stratigraphic   unit   was   the   Cacapon  Sandstone   (Darton  and  Taff,  1896),   and   in  Bath  and  Highland  Counties   that  name  was  used  by  Darton  (1899).    Woodward   (1941)  noted   that   strata  previously  mapped  as   the  Cacapon  Sandstone   in  western  Virginia  should  be  mapped  as  the  Rose  Hill  Formation,  and  although  Bick  (1962)  mapped  these  strata  as  the   Cacapon  Member   of   the   Clinton   Formation,   subsequent   publications   (e.g.,   Rader,   1984;   Rader   and  Wilkes,   2001)   have   nearly   uniformly   referred   to   this   interval   as   the   Rose   Hill   Formation.     The   name  Cacapon  sandstone  is  still  widely  used  in  this  region  to  refer  to  the  distinctive  dusky-­‐red  to  dark-­‐maroon  hematite-­‐cemented   quartz   and   sublithic   sandstones,   some   of   which   are   ripple  marked.   These   are   the  most   recognizable   lithology   in   the  Rose  Hill   Formation   and   invariably   are   a  major,   and   commonly   the  major,  component  of  colluvial  and  alluvial  deposits  that  blanket  the  dip  slopes  of  ridges  in  this  region  that  are  underlain  by  the  Tuscarora  Formation.    Ironstones  in  the  Rose  Hill  are  part  of  the  regional  iron  ore  facies  that  has  been  exploited  at  places  from  New  York  to  Alabama  for  over  a  century  (Hunter,  1960).     In  addition  to  the  distinctive  dark-­‐maroon  to  purplish  hematitic  sandstones  that  were  deposited  in  beach  or  nearshore  environments,   the  Rose  Hill   typically   includes   thin-­‐bedded  olive   to  gray  mudrocks  and   shales   interbedded  with   reddish   shales   and   siltstones,   and   in   some   exposures   there   are   thin   but  distinctive  sandy  dolomites  present  as  well.    The  Rose  Hill   is  sparsely   to  moderately   fossiliferous,  with  ostracodes,   brachiopods,   and   trilobites,   a   faunal   content   consistent   with   deposition   in   a   more   open  marine   shelf   setting.     The   character   of   the   Rose   Hill   Formation   along   the   field   trip   route   is   relatively  consistent,  as  we  will  see  at  Stops  1  (Eagle  Rock),  2  (Falling  Spring  Falls),  4  (Williamsville;  Fig.  E),  and  5  (Bluegrass/Forks  of  Waters).    Silurian  “Eagle  Rock  sandstone”  (125  m  thick)     The   “Eagle   Rock   sandstone”   was   named   by   Lampiris   (1975),   and   the   as-­‐not-­‐yet   formally  designated   type  section   is   the  series  of  cuts  along  U.S.  220  at  Eagle  Rock   in  Botetourt  County  (Stop  1),  where   the   James   River   has   cut   a   steep-­‐walled   gorge   that   bisects   a   prominent   ridge   into   two   separate  ridges:  Rathole  Mountain   and  Crawford  Mountain.     The   “Eagle  Rock   sandstone”   consists   principally   of  quartz  arenites  to  sublithic  quartz  wackes  (Lampiris,  1975)  deposited  in  beach,  bar,  and  other  nearshore  sandy  environments.    The  name  “Eagle  Rock  sandstone”  has  never  been  formalized,  but  we  all  use  it.    As  is  evident  at  Eagle  Rock  (Stop  1)  and  at  least  a  few  other  exposures  in  the  area,  including  Iron  Gate  and  Panther   Gap   (Lampiris,   1975),   the   “Eagle   Rock   sandstone”   is   widely   agreed   to   include   the   collective  stratigraphic  equivalents  of  the  Keefer,  McKenzie,  and  Williamsport.    Relations  to  younger  strata  are  less  certain;  Lampiris  (1975)  reported  that  conodonts  obtained  from  carbonate  strata  above  the  “Eagle  Rock  sandstone”  support  correlation  of  the  upper  part  of  the  “Eagle  Rock  sandstone”  with  beds  as  young  as  the  equivalent   of   the   upper   Wills   Creek   Formation   and,   in   some   sections,   beds   as   young   as   the   upper  Tonoloway  Limestone.    Each  of  these  younger  stratigraphic  units  is  separable  into  discrete  stratigraphic  units  at  sections  farther  to  the  north  and  northwest  (Fig.  A).    We  will  see  the  “Eagle  Rock  sandstone”  at  Stop  1  (front  cover).    Silurian  Keefer  Sandstone  (<1–8  m  thick)     The   type   section   of   the   Keefer   Sandstone   is   at   Keefer  Mountain,   a   few   kilometers   northeast   of  Hancock   in  Washington   County,   Maryland   (Stose   and   Swartz,   1912).     In   Bath   and   Highland   Counties,  Darton  (1899)  mapped  this  stratigraphic  interval  as  part  of  the  Rockwood  Formation.     The  character  of  the  Keefer  changes  significantly  along  the  route  of  this  field  trip  (Figs.  A,  F),  from  a  massive,  thick,  and  erosionally  resistant  quartz  arenite  that  comprises  the  lower  part  of  the  “Eagle  Rock  sandstone”  at  Eagle  Rock  (Stop  1),  to  a  thinner  but  still  resistant  ledge  of  quartz  arenite  in  the  Bullpasture  River  Gorge  at  Williamsville  (Stop  4),  to  thin  ferruginous  dolomites  and  mudrocks  at  Bluegrass/Forks  of  Waters   (Stop   5).     The   Keefer   seems   to   record   deposition   in   progressively  more  marine   environments  from  south  to  north  along  the  field  trip  route.  

  7  

  In   southern  Highland   and  northern  Bath  Counties   (Stop  4),  Haynes   and  Whitmeyer   (2010)   and  Hazelwood  et  al.  (2012)  found  that  the  Keefer  is  a  mappable  unit,  but  in  west-­‐central  and  northwestern  Highland  County,  Wilkes  (2011)  and  Haynes  and  Diecchio  (2013)  found  that  the  Keefer  is  too  thin  to  map  as  a   separate  unit,   and  so   they   included   it  with   the  underlying  Rose  Hill  Formation.     In  a  petrographic  investigation,  Haynes  et  al.   (2011)  noted   that   little  or  no  quartz  arenite   is  present   in   the  Keefer   in   the  exposure  at  Bluegrass  (Stop  5).    Instead,  there  is  appreciable  ferroan  dolomite  as  well  as  ooids  that  are  composed  of  hematite  and  berthierine  and/or  chamosite,  which  were  described  in  more  detail  by  Hunter  (1960).     We  will  see  the  Keefer  facies  as  the  lower  ~145  ft  of  the  “Eagle  Rock  sandstone”  at  Stop  1  (Eagle  Rock),   as   a   thin   but   discrete   quartz   arenite   sequence   at   Stop   4   (Williamsville;   Fig.   E),   and   as   a   thin  sequence  of  sandy  ironstones  and  mudrocks  at  Stop  5  (Bluegrass/Forks  of  Waters).    Keefer  vs.  “Keefer”     There   is   a   long   history   of   nomenclatural   complexity   to   this   stratigraphic   interval,   as   noted   in   a  subsequent   section   below.     In   its   restricted   stratigraphic   sense,   the   name  Keefer   refers   to   a   white   to  grayish-­‐white  to  pale-­‐pink  to  red  silica-­‐cemented  quartz  arenite,  known  informally  in  this  region  as  the  “true”  Keefer.    From  the  Clifton  Forge  area  southward,  the  name  “Keefer”  has  been  used  to  refer  to  what  is  more  appropriately  referred  to  as  “Eagle  Rock  sandstone”  because  the  thicker  sandstone  includes  units  younger   than   the  Keefer,   as   noted   above   in   the   discussion   of   the   “Eagle  Rock   sandstone.”    Woodward  (1941)   referred   to   these   strata   regionally  as   the  Keefer  Sandstone,   as  did  Hunter   (1960).    Bick   (1962)  mapped  these  strata  as  the  Keefer  Member  of  the  Clinton  Formation.    Perry  (1971)  mapped  these  strata  in  Germany  Valley,  Pendleton  County,  West  Virginia,   as   the  Mifflintown  Formation,  which   included   the  McKenzie  Formation  and  the  Williamsport  Sandstone  as  well.    Helfrich  (1975,  1980)  mapped  these  strata  at   the   Bluegrass   section   in   northern   Highland   County   (Stop   5)   as   the   lower   hematitic  member   of   the  Mifflintown  Formation  and  the  overlying  Cosner  Gap  Member  of  the  Mifflintown  Formation,  and  Helfrich  stated   that   the   Cosner   Gap  Member   is   a   limey   equivalent   of   the   Keefer   Sandstone.     The   Pennsylvania  formation   name   “Mifflintown”   has   not   subsequently   been   used   in   this   region,   and   Rader   and   Wilkes  (2001)  mapped  these  strata  as  the  Keefer  Formation.     At  Stop  1  we  will  discuss  a  historically  significant  stratigraphic  aspect  of   the  Keefer,  specifically,  what   is   true   Keefer   Sandstone   versus   “Keefer   Sandstone”   versus   “Eagle   Rock   sandstone.”   Woodward  (1936)  may   have   been   the   first   to   refer   to   the   thick   sequence   of   sandstones   in   the  Roanoke   area   and  vicinity  (including  Eagle  Rock)  as  Keefer,  and  several  authors  since  then  (e.g.,  Lesure,  1957;  Rader,  1967,  1984;   Appalachian   Geological   Society,   1970;   Patchen,   1974;   Dennison   et   al.,   1992)   have   used   the  expanded   Keefer   or   “Keefer”   as   a   convenient   name   and   useful   mapping   unit,   but   one   that   is  stratigraphically   inappropriate   vis-­‐à-­‐vis   the   North   American   Stratigraphic   Code   (North   American  Commission  on  Stratigraphic  Nomenclature,  1983,  2005),  because  the  restricted  Keefer  is  a  well-­‐defined  stratigraphic  unit,  as  discussed  in  detail  by  Woodward  himself  (1941,  p.  92-­‐106).     It  is  uncommon  now  to  see  “Keefer  Sandstone”  used  in  geologic  reports  about  this  region,  and  we  favor  discontinuing  any  use  of  “Keefer”  entirely,  and  substituting  instead  the  “Eagle  Rock  sandstone”  of  Lampiris  (1975)  as  an  acceptable  alternative  name  (and  one  that  is  far  less  stratigraphically  confusing)  for   this   markedly   thickened   sequence   of   Silurian   sandstones   at   exposures   in   this   area   where   its   use  would  be  appropriate.    This  would  be  analogous  to  the  way  that  the  name  Massanutten  Sandstone  is  used  in   the   northern   Shenandoah  Valley   of   Virginia,   and   the   name   Shawangunk  Conglomerate   is   used   even  farther  north  in  New  Jersey  and  New  York.    “Eagle  Rock”  as  a  stratigraphic  name  is  available,  because  the  term  Eagle  Rock  tuff  in  Idaho,  named  by  Stearns  (1936),  has  been  abandoned  (Stearns  and  Isotoff,  1956).    For   this   to   happen,   though,   the   name   “Eagle   Rock   Sandstone”  will   need   to   be   formally   proposed   as   a  stratigraphic   unit   in   accordance   with   the   North   American   Stratigraphic   Code   (North   American  Commission  on  Stratigraphic  Nomenclature,  1983,  2005).    With  remapping  of  the  bedrock  geology  of  the  Eagle  Rock  quadrangle  by  Haynes  set  to  begin  in  the  fall  of  2015,  there  may  well  be  an  opportunity  in  the  near  future  to  bring  about  this  stratigraphic  change  in  a  formal  way  that  is  in  accord  with  the  guidelines  

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of  the  North  American  Stratigraphic  Code  (North  American  Commission  on  Stratigraphic  Nomenclature,  1983,  2005).    Silurian  McKenzie  Formation  (60–80  m  thick)     The   type   section   of   the  McKenzie   Formation   is   at  McKenzie   Station   on   the   Baltimore   and  Ohio  Railroad  (now  CSX  Transportation)  in  Allegany  County,  Maryland  (Stose  and  Swartz,  1912).    The  unit  was  first   mapped   in   Bath   and   Highland   Counties   as   the   lower   part   of   the   Lewistown   Limestone   (Darton,  1899).    Woodward  (1941)  referred  to  this  stratigraphic  interval  as  the  McKenzie  Formation.    Bick  (1962)  mapped   these   strata   in   Bath   and   Highland   Counties   as   the   “McKensie   [sic]   Limestone”   of   the   Cayuga  Group,   but   the   name   “Cayuga   Group”   has   since   been   abandoned   as   a   lithostratigraphic   term  (http://ngmdb.usgs.gov/Geolex/Units/Cayuga_937.html).     Perry   (1971)   and   Helfrich   (1975,   1980)  mapped   these   strata   in  Highland   and   Pendleton   Counties   as   the  McKenzie  Member   of   the  Mifflintown  Formation,  but  as  noted  above  that  name  has  not  subsequently  been  widely  used,  and  these  strata  have  since   been  mapped   in   this   area   as   the  McKenzie   Formation   (Diecchio   and  Dennison,   1996;   Rader   and  Wilkes,  2001;  Haynes  and  Whitmeyer,  2010;  Haynes  and  Diecchio,  2013).     Where  the  McKenzie  is  recognized  as  a  distinct  stratigraphic  unit  in  the  field  trip  area  (Stops  2–5),  it  is  a  heterogeneous  sequence  of  thin  bedded  and  thinly  laminated  dark-­‐gray  lime  mudstones,  oolitic  and  bioclastic   (primarily   ostracode)   grainstones,   and   tan   to   green   to   blue-­‐green   to   gray   to   black   shales  deposited   in   shallow   shelf   environments   of   varying   energy,   from   higher   energy   settings   where   ooid  shoals  developed,  to  lower  energy  settings  where  muds  and  fine  sands  accumulated.    The  aforementioned  thick   to  massively   bedded  medium-­‐   to   coarse-­‐grained,   silica-­‐cemented,   yellowish-­‐white   quartz   arenite  beds   that   collectively   comprise   the  middle   sandstone  member  are  ~5  m   thick   in   the  Bullpasture  River  Gorge  at  Williamsville  (Stop  4),  and  almost  10  m  thick  along  Muddy  Run  to  the  southwest  (Whitehurst,  1982);  this  sandstone  has  not  yet  been  examined  in  detail  for  sedimentary  structures  and  fossils,  but  it  is  likely   to   have   been   deposited   in   beach   or   barrier   bar   settings   considering   the   fossiliferous   limestones  with  which  it  is  interbedded.     At   Stop   1   (Eagle   Rock),   we   will   see   the   McKenzie,   presumably   the   greatly   thickened   middle  sandstone  member,  as  a  facies  in  the  middle  part  of  the  “Eagle  Rock  sandstone,”  but  at  the  other  stops  we  will   see   a   heterogeneous   sequence   of   oolitic,   bioclastic,   and   laminated   limestones   and   lesser   quartz  sandstones  and  mudrocks  (Stop  4,  Williamsville;  Fig.  E),  and  a  sequence  of  thin  laminated  limestones  and  mudrocks  (Stop  5,  Bluegrass/Forks  of  Waters).    Silurian  Williamsport  Sandstone  (9–10  m  thick)     The   type   section  of   the  Williamsport   Sandstone   is  on  a  branch  of  Patterson  Creek,  1  km  east  of  Williamsport   in   Grant   County,  West   Virginia   (Reger,   1924).     Darton   (1899)  mapped   this   sandstone   as  part  of  the  Lewistown  Limestone.    Butts  (1940)  included  it  as  part  of  the  Wills  Creek  Formation,  which  he  defined  as  all  of  the  strata  between  the  McKenzie  Limestone  below  and  the  Tonoloway  Limestone  above.    Woodward  (1941)  first  identified  this  sandstone  as  a  separate  formation  in  this  region,  which  he  mapped  as  the  Williamsport  Sandstone.         Although  Bick   (1962)  mapped   this   sandstone   as   part   of   the  Wills   Creek  Formation,   subsequent  publications   have   separated   these   strata   in   Highland   County   as   the  Williamsport   Sandstone   (Helfrich,  1975;  Diecchio   and  Dennison,  1996;  Wilkes,   2011);   and  our  mapping  efforts  have  also   shown   that   the  Williamsport   is   a   persistent   and   useful   marker   bed   in   this   area   (Haynes   and   Whitmeyer,   2010;  Hazelwood  et  al.,  2012;  Haynes  and  Diecchio,  2013).     The   Williamsport   Sandstone   is   a   tough,   erosionally-­‐resistant,   silica-­‐cemented   quartz   arenite  deposited  in  beach  to  nearshore  shelf  and  bar  settings,  and  it  commonly  weathers  white  to  tan  to  orange-­‐brown  to  brown,  with  the  latter  colors  seeming  to  be  a  useful  guide  to  identification  at  many  exposures.    Like  the  quartz  arenites  of  the  Tuscarora,  the  “Eagle  Rock,”  and  the  Keefer,  the  Williamsport  is  generally  very  resistant  and  it  makes  prominent  flatirons  on  many  of  the  dip  slopes  in  this  region,  but  because  it  is  typically  medium  bedded  it  commonly  (but  not  always)  breaks  into  smaller  blocks  than  if   it  were  more  

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massively   bedded,   as   the   Tuscarora   tends   to   be.     It   is   common   to   find   some   bedding   planes   with  prominent   ripple  marks,   a   sedimentary   structure   that   seems   to   be   far   less   common   in   the   otherwise  petrologically   similar   quartz   arenites   of   the   Tuscarora,   Keefer,   and   McKenzie   Formations.     In   some  intervals,   isolated   ostracodes   to   ostracode   coquinas   are   present.   On   more   weathered   exposures,   the  ostracodes  are  now   just   shell  moldic  pores   that  are  commonly   lined  by  orange   limonite,  but  ostracode  shells   in   unweathered   samples   are   extensively   pyritized,   and   it   is   the   oxidation   of   this   pyrite   that  contributes  to  the  yellowish-­‐brown  limonite  staining  and  patina  that  is  common  on  the  surface  of  ledges  and  blocks  of  the  Williamsport  throughout  this  region.     The  Keefer  of  Lesure  (1957,  his  Table  8,  p.  39)  includes  52  ft  (15.8  m)  of  “resistant…light-­‐brown  to  grayish-­‐orange”   sandstone   as   its   uppermost   bed,   a   description   that   is   consistent   with   typical  Williamsport   Sandstone   of   this   region,   further   suggesting   that   the   expanded   Keefer,   i.e.,   “Keefer”   of  previous  reports  includes  the  Williamsport.     We  will  see  the  Williamsport  as  a  thick  and  distinctly  yellowish  colored  facies  in  the  upper  part  of  the  “Eagle  Rock  sandstone”  at  Stop  1  (Eagle  Rock),  as  a  sequence  of  ripple-­‐marked  quartz  arenites  with  interbedded  mudrocks  and  thin  limestones  at  Stop  4  (Williamsville;  Fig.  E),  and  as  a  sequence  of  quartz  arenites  with  some  cross-­‐bedding  at  Stop  5  (Bluegrass/Forks  of  Waters).    Silurian  Wills  Creek  Formation  (<1–70  m  thick)     The  type  section  of  the  Wills  Creek  Formation  is  at  Wills  Creek  in  Cumberland,  Allegany  County,  Maryland   (Uhler,   1905).   In   this   region,   Darton   (1899)   included   these   strata   as   part   of   the   Lewistown  Limestone,  and  Butts  (1940)  mapped  them  as  the  Wills  Creek  Formation,  which  he  defined  as  all  of  the  strata  between  the  McKenzie  Limestone  below  and  the  Tonoloway  Limestone  above  (thus  his  definition  would  include  the  Williamsport  Sandstone).    Woodward  (1941)  assigned  these  strata  to  the  Wills  Creek  Limestone.    Bick  (1962)  mapped  them  as  the  Wills  Creek  Formation  -­‐  the  name  that  has  been  used  in  this  region  by  most  authors   since   (e.g.,  Helfrich,  1975;  Diecchio  and  Dennison,  1996;  Wilkes,  2011;  Haynes  and  Diecchio,  2013).     Brown   to   green   mudrocks   comprise   the   principal   Wills   Creek   lithology,   with   interbedded  sandstone,   sandy   limestone,   and   lime   mudstone   present   as   well.     Ripple   marks,   algal   laminations,  desiccation   cracks,   rip-­‐up   clasts,   and   molds   of   evaporite   crystals   are   present   in   some   of   these   beds.    Fossils  are  not  abundant,  but  include  leperditian  ostracodes,  stromatolites,  and  brachiopods.    The  Wills  Creek  was  deposited  in  tidal  flat  to  intertidal  or  very  shallow  subtidal  settings.     The  thickness  of  the  Wills  Creek  Formation  changes  significantly  from  south  to  north  in  the  field  trip   area   (Fig.  A).     It   is   <   3   ft   (1  m)   thick   at  Williamsville   (Stop   4)   but   over   210   ft   (70  m)   thick   at   the  Bluegrass/Forks  of  Waters  exposure  (Stop  5).     We  will  see  the  Wills  Creek  as  a  sequence  of  ostracode  grainstones  and  interbedded  mudrocks  and  laminated  and  in  places  stromatolitic  lime  mudstones,  and  a  thin  but  prominent  quartz  arenite,  at  Stop  5  (Bluegrass/Forks  of  Waters).      Part  of  the  calcareous  upper  “Eagle  Rock  sandstone”  at  Stop  1  (Eagle  Rock)  may  also  be  correlative  with  the  Wills  Creek  Formation.    Silurian  Tonoloway  Limestone  (4–180  m  thick)     The   type   section   of   the   Tonoloway   Limestone   is   at   Tonoloway   Ridge   in   Washington   County,  Maryland  (Ulrich,  1911).    This   thick  sequence  of  predominantly   thin-­‐bedded  and   laminated   limestones  was  mapped  by  Darton  (1899)  as  part  of  the  Lewistown  Limestone.    Swartz  (1930)  mapped  these  strata  as  the  Tonoloway  Limestone  of  the  Cayuga  Group,  whereas  Butts  (1940)  and  Woodward  (1941)  referred  to  these  carbonates  as  the  Tonoloway  Limestone,  the  name  that  is  used  for  this  interval  of  strata  in  this  region   today   (Bick,   1962;  Perry,   1971;  Helfrich,   1975;  Diecchio   and  Dennison,   1996;  Bell   and   Smosna,  1999;  Wilkes,  2011;  Haynes  and  Diecchio,  2013).     At   most   exposures   in   the   mid-­‐Atlantic   region,   the   Tonoloway   Limestone   consists   of   three  unnamed  members  (Woodward,  1941;  Perry,  1971;  Bell  and  Smosna,  1999)  that  are  laterally  persistent  across  Pendleton,  Highland,  and  northern  Bath  Counties:  

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 1.   The   lower   member   of   the   Tonoloway   Limestone   is   up   to   60  m   thick   and   it   consists  primarily  of  thin-­‐bedded  and  laminated-­‐gray  to  black  lime  mudstones,  commonly  peloidal  and   usually   cut   by   many   prominent   orthogonal   fractures;   in   some   of   these   limestones,  there   are   zones   in   which   prominent   pink   to   red   to   reddish-­‐brown   argillaceous   and  dolomitic   partings   are   present.   This   member   also   contains   two   prominent   calcite-­‐   and  quartz-­‐cemented  calcarenaceous  (bioclastic)  quartz  arenites  in  the  area  around  the  gorge  of   the  Bullpasture  River   including  along  Jack  Mountain,  Bullpasture  Mountain,  Tower  Hill  Mountain,   and   Chestnut   Ridge   (Stop   3).     One   outcome   of   the   bedrock   mapping   in   this  region  by  the  authors  (Haynes  and  Whitmeyer,  2010;  Hazelwood  et  al.  2012;  Haynes  and  Diecchio,  2013)  has  been  the  recognition  that   these  two  sandstones,  which  are  up  to  4  m  thick,  were  accidently  correlated  as  tongues  of  the  Clifton  Forge  Sandstone  in  this  area  for  decades  (White  and  Hess,  1982).    Detailed  stratigraphic  work,  especially   in  Highland  and  Bath   Counties,   has   now   shown   that   these   are   indeed   Tonoloway   sandstones,   not   Keyser  sandstones  (Swezey  et  al.,  2015).    Sedimentary  structures  in  the  upper  sandstone  include  cross-­‐bedding   and   scours   that   are   perhaps   consistent  with   an   origin   as   wave-­‐generated  tidal   bundles   (Yang   et   al.,   2008).     The   lower   member   also   contains   a   few   thin   beds   of  ostracode  and  gastropod  packstones   and  grainstones,   and   thin  oolitic   grainstones   in   this  member.     The   lower   member   was   deposited   in   restricted   intertidal   to   supratidal  environments,  with  the  sandstones  being  deposited  in  a  variety  of  beach,  wave-­‐dominated  tidal  flat,  and  –  for  the  lower  sandstone  –  nearshore  shallow  shelf  environments.    2.  The  middle  member  of   the  Tonoloway  Limestone   is  up  to  20  m  thick  and   it  consists  of  thick  to  massively  bedded  bioclastic  grainstones  in  which  abundant  crinoid  fragments  and  lesser  sponge,  brachiopod,  coral,  and  bryozoan  debris  are  most  common,  along  with  sparse  boundstones  and  coral-­‐stromatoporoid  framestones,  that  were  deposited  in  a  open  marine  subtidal  shelf   setting  with  normal  marine  salinities  and  moderate   to  high  current  and/or  wave  energy.    3.  The  upper  member  of  the  Tonoloway  Limestone  is  up  to  100  m  thick  and  it  consists  of  thin-­‐bedded   and   laminated   gray   lime   mudstones   that   have   some   to   abundant   and  prominent  orthogonal  fractures  that  cut  individual  beds;  many  of  these  lime  mudstones  are  also   peloidal,   and   mud   cracked   and   algal   laminated,   and   in   a   few   beds   thin   intraclast  grainstones   and   packstones   are   present.     This   member   also   contains   3–4   thin   beds   of  calcite-­‐cemented  quartz  arenites  up  to  4  m  thick.    At  four  exposures  in  this  region  thus  far  (near  Oak  Flat  on  U.S.  33  in  Pendleton  County,  West  Virginia;  at  the  north  end  of  Burnsville  Cove  along  S.R.  609  in  Bath  County;  just  north  of  the  junction  of  Muddy  Run  Road  and  U.S.  220  in  an  unused  quarry  on  the  east  side  of  U.S.  220  in  Bath  County;  and  in  the  bed  of  the  stream  in  Crizer  Gap  south  of  Millboro  Springs  in  Bath  County),  a  vuggy  bed,  brecciated  in  places,  and  with  rare  “gypsum  daisies”   that  are  now  pseudomorphed  by  calcite,  has  been  identified   in   the   upper  Tonoloway.     This   bed   or   beds,  which   is   likely   laterally   persistent  from   this   region   westward,   was   originally   an   evaporite   horizon   of   mostly   gypsum   or  anhydrite  deposited   in   the   sabkha  environments   that  predominated  during  deposition  of  these   sediments.    The  original   evaporite  minerals  have  now  been  modified  by  diagenetic  processes  and   largely   replaced  by  calcite,  but   some  of   the  original  evaporite   textures  are  still  present  in  some  beds  throughout  the  region.  It  is  almost  certain  that  this  bed(s)  is  an  eastward  extension  of   the  widespread  evaporites  of   the  Salina   facies   in   the  subsurface  of  the  Appalachian  basin  farther  west  (Dennison  and  Head,  1975;  Smosna  et  al.,  1977).    The  contact   with   the   overlying   Keyser   Limestone   is   sharp,   and   in   places   consists   of   an  

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intraclastic  grainstone  and  packstone  (“flat-­‐pebble  conglomerate”)  that  varies  in  thickness  from  0  to  1.4  m  over  short  distances.  

 

                               Figure  C.  Comparison  of  sedimentary  structures  and  overall  appearance  of  sandstones  in  the  upper  “Eagle  Rock  Sandstone”  with  the  sandstone  separating  the  lower  and  middle  members  of  the  Tonoloway  Limestone.    Some   (most?)   of   the   cross-­‐lamination  may   be  wave-­‐generated   tidal   bundles   (cf.   Yang   et   al.,   2008).   1.   Bi-­‐directional  cross-­‐bedding  in  the  upper  “Eagle  Rock  Sandstone”  at  Stop  1.    2.  Cross-­‐laminations  and  moldic  pores   where   calcareous   grains   have   been   removed,   upper   “Eagle   Rock   Sandstone”   at   Stop   1,   scale   in  decimeters.    3.  Scours  and  cross-­‐lamination,  upper  “Eagle  Rock  Sandstone”  at  Stop  1,  scale  in  decimeters.    4.    Rick  Lambert  on  Chestnut  Ridge  near  Stop  3,  by  a  weathered  block  of  the  “upper  Breathing  Cave  sandstone”  with   typical   vuggy   pores   developed   after   dissolution   and   removal   of   lenses   and   laminae   of   carbonate  allochems,   primarily   bioclasts.     5.   Phil   Lucas   showing   the   scale   of   the   prominent   cross-­‐bedding,   and  associated   smaller   scours,   in   the   “upper   Breathing   Cave   sandstone”   at   Chestnut   Ridge   (Stop   3).     6.    Weathered  block  of  the  “upper  Breathing  Cave  sandstone”  on  Bullpasture  Mountain  along  U.S.  250  in  north-­‐central  Highland  County,  with  the  vuggy  weathering  typical  of  this  sandstone  throughout  the  field  trip  area.  

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  We   will   see   the   Tonoloway   Limestone   at   Stops   1   (Eagle   Rock),   3   (Chestnut   Ridge),   and   5  (Bluegrass/Forks  of  Waters).    At  Stop  1  we  will  discuss  the  evidence  that  has  led  us  to  hypothesize  that  some  or  maybe  all  of  the  cross-­‐bedded  calcareous  upper  “Eagle  Rock  sandstone”  at  Stop  1  (Eagle  Rock)  may   also   be   correlative   with   sandstones   of   the   lower   member   of   the   Tonoloway   (Fig.   C,   Tonoloway  sandstones  in  region).    At  Stop  3  we  will  examine  the  middle  member  of  the  Tonoloway  and  the  thin  but  stratigraphically  important  sandstone  that  separates  the  lower  and  middle  members  of  the  Tonoloway  in  this  region  (Fig.  C5).    CORRELATION  OF  SILURIAN  SANDSTONES     Local  and  regional  stratigraphic  relationships  among  the  various  Silurian  sandstones  in  the  area  of  today’s   field   trip   are   complex,   in   particular   those   in   the   Keefer–McKenzie–Williamsport–Wills   Creek–Tonoloway–Keyser  interval.    Correlations  have  been  puzzled  over  by  geologists  in  this  region  for  decades,  even  before  Woodward  aptly  referred  to  the  lower  four  of  these  units  in  the  Eagle  Rock  and  Clifton  Forge  area  as  a  stratigraphic  “tangle  of  Silurian  sandstones”  (Woodward,  1941,  p.  103,  169).         At  Eagle  Rock  (Stop  1),  near  the  eastern  margin  of  the  depositional  basin,  an  amalgamated  125-­‐m-­‐thick   sequence   of   Silurian   quartz   arenites   comprises   the   “Eagle   Rock   sandstone”   (Fig.   A),   the  modern  name  for  Woodward’s  stratigraphic  “tangle.”    It  is  worth  noting  that  in  the  Massanutten  Synclinorium  to  the   northeast   of   the   field   trip   area,   another   thick   Silurian   sandstone,   the   Massanutten   Sandstone,   is  present.  The   stratigraphic   relations  of   the  Massanutten  have  been  understood   for   some   time,   and   it   is  recognized   as   the   collective   equivalent   of   the   Tuscarora   and   Rose   Hill   Formations,   and   the   Keefer  Sandstone  (Roberts  and  Kite,  1978).    That  contrasts  with  the  difficulties  geologists  have  had  in  working  out   the   regional   stratigraphic   relations   of   the   “Eagle   Rock   sandstone”   over   the   decades;   the   problem  being   succinctly   stated   by  Woodward   (1941,   p.,   95):   “...this   thicker   sandstone   presents   a   problem   of  correlation  that  has  not  been  satisfactorily  solved.”     A  few  of  the  many  fundamental  questions  about  these  Silurian  sandstones  that  can  be  asked  as  we  examine  and  discuss  some  of   the  changes   that  are  evident   in  a   southeast   to  northwest   traverse  across  part   of   the   depositional   basin   include:   (1)  What  might   the   subtle   petrographic   details   of   these   quartz  arenites  tell  us  about  the  provenance  of  all  the  sand  that  was  transported  to  the  Eagle  Rock  depocenter?  (2)  What  tectonic  or  eustatic  event(s)  accompanied  or  preceded  the  erosion,  transport,  and  deposition  of  this  quantity  of  quartz  sand?  (3)  Are  any/all  of  these  sandstones  first-­‐cycle  quartz  arenites  (Johnsson  et  al.,   1988)?   (4)  How  does   the   composition  of   the   silt   and  clay   fraction   in   the  mudrocks  vary  across   the  region   (Taylor   and   McLennan,   1985)?   and   (5)   Are   the   upper   calcareous   intervals   of   the   “Eagle   Rock  sandstone”  correlative  with  the  Wills  Creek  Formation  and/or  the  Tonoloway  Limestone,  on  the  basis  of  any  stratigraphic  evidence  in  addition  to  the  conodont  data  reported  by  Lampiris  (1975)?       From  a  tectonic  perspective,  the  stratigraphic  and  sedimentologic  details  that  this  thick  sequence  of  Lower  Silurian  quartz  arenites  preserve  may  ultimately   support  a  basin   rebound  hypothesis   for   the  depositional  environment  of  these  sandstones  (Driese  et  al.,  1991;  Dorsch  et  al.,  1994;  Dorsch  and  Driese,  1995),   as  well   as   the   hypothesis   that   the   Taconic   Orogeny   persisted   into   the   Silurian   (Ettensohn   and  Brett,  2002).  They  may  also  help  improve  our  understanding  of  the  Late  Ordovician  glaciation  (Hambrey,  1985).     Our  recent  and  ongoing  mapping  efforts  in  this  area  (Haynes  and  Whitmeyer,  2010;  Walker  et  al.,  2010;   Haynes   et   al.,   2011;   Hazelwood   et   al.,   2012;   Haynes   and   Diecchio,   2013)   have   led   to   the  development  of  a  working  stratigraphic  model   that  evolves  as  we  continue   to  map  and  trace  out   these  several   Silurian   (and   Lower   Devonian)   sandstones   across   this   region   (Fig.   A),   from   the   area   of  Woodward’s   “tangle”   northward.     In   Bath   County   and   northward   into   southern   Highland   County,   the  individual   sandstones  become  more   stratigraphically  distinct   and   “untangled”  as   the  overall   volume  of  mudrocks  and  carbonates   in   the  section   increases  relative  to  quartz  arenites.    This  change   in   lithologic  ratios   effectively   divides   and   separates  what   at   Eagle   Rock   is   the  massive   and   undifferentiated   “Eagle  Rock   sandstone”   (Stop   1)   into   the   readily   differentiated   Keefer,   McKenzie,   and   Williamsport   quartz  

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arenites  that  comprise  discrete  stratigraphic  horizons  at  other  exposures  such  as  those  in  the  Bullpasture  River  Gorge  at  Williamsville  (Stop  4).        

   Figure  D.  Google  Earth  aerial  views  of  the  Bullpasture  River  gorge  showing  the  ledges  of  resistant  dipping  sandstones,  with  annotations  based  on  mapping  by  the  authors.  The  Bullpasture  River  has  eroded  through  both  the  west  and  east   limbs  of   the  Bullpasture  Mountain  anticline,  down  to  the  stratigraphic   level  of   the  Rose  Hill  Formation.    1.  Exposures  on  the  west  limb  of  the  Bullpasture  Mountain  anticline  in  the  west-­‐central  part   of   the   gorge,   where   northwesterly   dipping   and   erosionally   resistant   ledges   of   the   Williamsport  Sandstone   (the   middle   sandstone   member   of   the   McKenzie   Formation)   and   the   Keefer   Sandstone   make  prominent  rapids  in  the  river.    2.  Exposures  on  the  east  limb  of  the  Bullpasture  Mountain  anticline  just  north  of  Williamsville   (Stop   4)   at   the   eastern   (lower)   part   of   the   gorge,   where   the   now-­‐southeasterly   dipping  ledges  of  the  Williamsport,  McKenzie,  and  Keefer  sandstones  again  make  prominent  rapids  in  the  river.    The  ledges  of  Keefer  and  McKenzie  are  especially  prominent.       Although   each   of   these   sandstones  makes   obvious   ledges   in   the   gorge   of   the   Bullpasture   River  (Stop  4;  Figs.  D,  E),  when  our  mapping   in  this  region  began  we  found  that   identifying  which  sandstone  ledge   was   which   is   no   simple   task.     This   fundamental   stratigraphic   issue   evidently   eluded   previous  geologists  who  worked  in  this  region  as  well  (e.g.,  Bick,  1962),  perhaps  because  no  complete  stratigraphic  column  for   the  gorge  and  nearby  areas   that   is  based  on  one  or  more  measured  sections  has  ever  been  published,   a   situation   that  we  have   rectified   (Fig.  A).    And,  even   though  Bick   (1962)   included  a  partial  measured  section  from  the  gorge  based  on  the  exposures  along  S.R.  678  that  we  will  see  at  Williamsville  (Stop  4),  our  work  has  led  us  to  conclude  that  some  reinterpretation  of  Bick’s  stratigraphic  correlations  is  needed,  and  this  will  be  discussed  at  Stop  4.    One  major  advance  in  our  understanding  of  the  stratigraphic  section   exposed   in   and   around   the   gorge   of   the   Bullpasture   River   is   the   identification   of   a   prominent  sandstone  as  the  middle  sandstone  member  of  the  McKenzie,  a  second  is  the  identification  of  laminated  Tonoloway-­‐like  lime  mudstones  in  the  upper  McKenzie  Formation,  and  a  third  is  the  identification  of  the  Williamsport  Sandstone  in  the  Bullpasture  River  Gorge  exposures,  each  of  which  will  be  seen  at  Stop  4.  

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  In  addition  to  the  sandstones  of  the  Keefer,  McKenzie,  and  Williamsport,  we  will  see  and  discuss  the  calcarenaceous  quartz  arenites  (“calcarenaceous”  refers  to  a  siliciclastic  sediment  in  which  10%–50%  of  the  total  framework  grains  are  carbonate  allochems,  e.g.,  peloids  or  bioclasts;  Pettijohn  et  al.,  1972,  p.  190;   Riley   et   al.,   1997,   p.   437)   of   the   lower  member   of   the   Tonoloway   Limestone.     In   contrast   to   the  predominantly   silica-­‐cemented   quartz   arenites   of   the   Tuscarora,   Keefer,   and   Williamsport   (in   which  quartz  framework  grains  comprise  ≥  95%  of  the  total  framework  grains),  the  calcarenaceous  sandstones  of   the  Tonoloway   include   some  quartz   cement  as  overgrowths,  but  also  a   significant  amount  of   calcite  cement  as  well,  much  as  syntaxial  overgrowths  on  echinoderm  fragments.       For  almost  50  years  these  unnamed  sandstones  in  the  lower  member  of  the  Tonoloway  Limestone  (Stop  3)  were  accidentally  but  mistakenly  identified  in  the  Bullpasture  River  Gorge  and  nearby  areas  as  upper   and   lower   tongues   of   the   Clifton   Forge   Sandstone   (Deike,   1960;   White   and   Hess,   1982).   With  careful  work  that  included  measurements  of  stratigraphic  units  in  and  near  the  Bullpasture  River  Gorge,  the  correct  stratigraphic  position  of  these  sandstones  is  now  clear  (Swezey  et  al.,  2015).        TECTONIC  SETTING  AND  STRUCTURAL  GEOLOGY     Though  the  focus  of  this  field  trip  is  to  highlight  and  differentiate  the  complex  stratigraphy  of  the  region,  one  cannot  ignore  the  dramatic  and  sometimes  complex  deformation  features  that  have  modified  and  enhanced  the  stratigraphic  units.  This  region  is  an  excellent  example  of  thin-­‐skinned  tectonics  at  the  leading   (western)   edge   of   deformation   during   the   Alleghanian   orogeny.   As   such,   this   is   part   of   the  foreland   fold-­‐thrust  belt  produced  by   the  collision  of  western  Gondwana  and  eastern  Laurentia  during  the  assembly  of  Pangaea  (e.g.,  Rodgers,  1970).  Regional-­‐scale,  northeast-­‐striking  anticlines  and  synclines  predominate  throughout  the  area,  bounded  in  the  east  by  the  west-­‐directed  Pulaski-­‐Staunton  and  North  Mountain   thrust   systems,  and  dissipating   in   the  west  at   the  Allegheny  Front.  From  east   to  west,  major  fold   structures   include   the   Rich   Patch   anticline,   Rough   Mountain   syncline,   Warm   Springs   –   Bolar  anticline,   and   Hightown   –   Wills   Mountain   anticline   (Rader   and   Gathright,   1984;   Kulander   and   Dean,  1986;  Rader  and  Wilkes,  2001).  Likely  underlying  these  regional  folds  are  a  series  of  duplexes,  composed  of   Cambrian-­‐Ordovician   clastic   and   carbonate   rocks   (Kulander   and  Dean,   1986;  Mitra   1986).     Smaller  structural   features   include  parasitic   folds,  outcrop-­‐scale   faults,   and   fault-­‐related   folds,  which  appear   to  accommodate  space   limitations  or  opportunities  created  by   larger-­‐scale   folding.  Fault-­‐bend  folds,  ramp  anticlines,   and   fault-­‐propagation   folds   are   abundant,   as   can   be   seen   at   Eagle   Rock   (McConnell   et   al.,  1997);  refer  to  the  Stop  1  description  for  more  details.       Northwest-­‐directed   translation   of   upper-­‐crustal   material   in   this   region   was   typically  accommodated  along  mechanically  weak,   shale-­‐dominated   lithologies,   such  as   the  Millboro,  Needmore,  and  Brallier  Formations.  More  competent  units  (Tuscarora,  Oriskany,  Eagle  Rock  sandstones,  etc.)  were  transported  westward  along  shallowly-­‐   to  moderately-­‐dipping   thrust  surfaces   (e.g.,  Pulaski   thrust)  and  today   form  resistant   topographic  ridges.  Outcrop-­‐scale  contractional  wedge   faults  and  bedding-­‐parallel  faults  occur  in  these  more-­‐competent  units,  especially  in  areas  within  fold  hinges  (Perry,  1978)  or  within  proximal  parts  of  fold  limbs.    

Regional   ridges   and   valleys   tend   to   reflect   the   relative   resistance   of   the   various   lithologies   to  weathering,   such   that   sandstones   form   the   ridges,   and   shales   and   carbonates   form   the   valleys   (e.g.,  Diecchio,  1985,  1986;  Enomoto  et  al.,  2012).  This  commonly  resulted  in  the  classic  inverted  topography  of   the   Valley   and   Ridge   province,   where   anticlines   are   typically   breached,   so   that   the   hinge   region   of  underlying   carbonates   is   topographically   lower   than   the   resistant   limbs   of   stratigraphically   higher  sandstones  (e.g.,  Germany  Valley:  Perry,  1971;  Martin  et  al.,  2014).        

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ACKNOWLEDGEMENTS     Funding   for   the   ongoing  bedrock  mapping   in   the   area   of   Stops   3   and  4   has   come   from   the  U.S.  Geological   Survey   via   EDMAP   Agreement   No.   G09AC00122   to   Haynes   and   Whitmeyer   in   2009-­‐2010  (north  half  of  the  Williamsville  7½-­‐minute  quadrangle),  EDMAP  Agreement  No.  G11AC20278  to  Haynes  and   Whitmeyer   in   2011-­‐2012   (southeast   quarter   of   the   Monterey   SE   7½-­‐minute   quadrangle),   and  EDMAP  Agreement  No.  G12AC20312  to  Haynes  and  Diecchio  in  2012-­‐2013  (west  half  of  the  Monterey  SE  7½-­‐minute   quadrangle).   Much   of   the   stratigraphic   work   reported   herein   was   initiated   by   Haynes   in  support  of   those  mapping  efforts.    Rick  Lambert  of  Monterey,   and  Phil  Lucas  and  Nevin  Davis,  both  of  Burnsville,  have  been  valued  field  companions  since  2009.    Their  willingness  to  take  us  to  many  outcrops  and  subcrops  of  the  limestones  and  sandstones  described  herein  in  Highland  and  Bath  counties  has  been  of  immense  help  as  we  worked  to  figure  out  the  stratigraphic  relationships  of  the  Silurian  throughout  the  region.     As   many   of   the   exposures   in   this   region   are   on   private   property,   their   help   in   maintaining  excellent  landowner  relations  is  also  greatly  appreciated.    Chris  Swezey  of  the  U.S.  Geological  Survey  has  also  been  very  supportive  of  our  efforts  during  this  time  as  well,  and  his  interest  and  time  in  the  field  are  greatly   appreciated.   JMU   geology   students   Kyle   Hazelwood,   Casey  Marshall,   Charles   Covington,   Selina  Cole,   Seldon  Walker,   Tim   Kropp,   Aryn   Hoge,   Craig   Morris,   Elizabeth  Weisbrot,   Sharon   Porter,   Natalie  Caro,   Kimberly   Walsh,   Evan   Bryant,   Timothy   Louie,   Meghan   Moss,   and   Kathyrn   McConahy,   and   GMU  geology  students  Christopher  Johnson  and  Ashley  Hughes,  spent  a  great  deal  of  time  in  the  field  with  us  in  the  area  of   this   field   trip,  and  their  contributions  are  appreciated  as  well.  Thanks  to  L.  Scott  Eaton  and  Lynn  Fichter  for  reviewing  versions  of  this  manuscript.        

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ROAD  LOG  and  Stop  Descriptions    The   field   trip   road   log  begins   in   the  parking   lot   of   the  Natural  Bridge  Hotel,   on  U.S.   11,   in  Rockbridge  County.     All   of   the   field   trip   stops   will   be   on   roadcuts.     Participants   will   need   to   be   mindful   of   field  conditions  and  traffic,  and  to  exercise  prudence  and  good  judgment  while  on  the  outcrops.    Stay  off  the  active  roadway  /  median,  and  always  watch  for  traffic.    High-­‐visibility  safety  vests  MUST  be  worn  at  all  times  while  along  roadways.        

             Cumulative  Trip     Point  to  Point       Mileage              Mileage         Directions  and  Comments      

       0.0                      0.0     Load  buses  at  Natural  Bridge  Hotel    parking  lot.  Exit  parking  lot  and  drive    south  on  U.S.  11.  

         1.8                      1.8     Cross  I-­‐81  and  turn  left  (southeast)  onto    

I-­‐81  S,  toward  Roanoke.    

       9.8                      8.0     Bear  right  onto  exit  ramp  from  I-­‐81  for    U.S.  11,  and  turn  left  (southeast)  on  U.S.  11  

  toward  Buchanan.    

       11.2                      1.3     Turn  right  (west)  onto  S.R.  43  toward               Eagle  Rock.  

         26.0                      14.8     In  Eagle  Rock,  turn  left  (southwest)  onto    

the  James  River  bridge  toward  U.S.  220.    

       26.1                          0.1     Unload  buses,  and  cross  U.S.  220  to    exposures.    

 STOP  1  –  Eagle  Rock    Location:  37.641353  N,  79.806658  W,  Eagle  Rock  7½  minute  quadrangle    Units  (oldest  to  youngest):  Reedsville  Shale,  Oswego  Sandstone,  Tuscarora  Formation,  Rose  Hill  Formation,  “Eagle  Rock  sandstone”,  Tonoloway  Limestone    

Eagle  Rock  is  a  prominent  geologic  locality  that  has  been  examined  and  interpreted  by  geologists  at  least  since  the  early  20th  century  (Butts,  1940;  McGuire,  1970;  Bartholomew  et  al.,  1982;  Spencer  et  al.,  1989;  McConnell  et  al.,  1997).  Prominent  cliffs  and  roadcuts  occur  on  both  the  northeast  and  southwest  sides  of   the   James  River,  where   a  water   gap  bisects   a  prominent   ridge  of   Silurian   sandstones.  We  will  examine  the  excellent  roadcuts  along  southwest  side  of   the  river  that  were  enlarged  when  US  220  was  notably  widened  in  the  early  1980s  (Bartholomew  et  al.,  1982).  This  exposure  is  notable  for  its  structural  complexity,   attributed   to   the   proximity   of   splays   of   the   Pulaski   thrust   fault   that   are   mapped   both  southeast   and   northwest   of   Eagle   Rock   (McGuire,   1970;   Bartholomew,   1987;   Fig.   1-­‐1).   These   thrusts  likely  mark  the  abrupt  termination  of  otherwise  resistant  ridges  of  Silurian  sandstones,  near  here  at  the  southwest  end  of  Crawford  Mountain  and  the  northeast  end  of  Rathole  and  Sheets  Mountains  (Spencer  et  al.,  1989).  McGuire  (1970)  and  Bartholomew  (1987)  both  interpreted  the  leading  edge  of  these  thrusts  as  reaching  the  surface  in  a  cryptic  region  of  Devonian  shales  just  west  of  Crawford  and  Rathole  Mountains.  

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 Figure   1-­‐1.   Cross   section   from   McGuire   (1970)   showing   Eagle   Rock’s   proximity   to   northwest-­‐directed  thrusts  that  are  likely  related  to  the  Pulaski  thrust  system.    Stratigraphic  Relationships  

At  the  south  end  of  the  exposure  are  the  shales  and  sandstones  of  the  Ordovician  Reedsville  Shale  and  Oswego  Sandstone,   and  overlying   them   is   the  ~140   ft   (42  m)   thick   Silurian  Tuscarora  Formation,  which   here   –   as   is   typical   –   consists   of   several   beds   of   silica-­‐cemented   quartz   arenite.     Overlying   the  Tuscarora   is   the   ~83   ft   (25   m)   thick   Rose   Hill   Formation,   with   some   beds   of   hematite-­‐cemented  sandstones  with   the  characteristic  grayish  red   to  purple  color  of  Rose  Hill   ironstones   that  characterize  them  in  the  mid-­‐Atlantic  region.    Above  the  Rose  Hill  is  the  ~412  ft  (125  m)  thick  “Eagle  Rock  sandstone”  that  is  the  focus  of  this  stop.    Overlying  the  “Eagle  Rock  sandstone”  are  intermittent  exposures  of  typical  thin-­‐bedded  and  laminated  Tonoloway  Limestone  that  may  total  about  30  ft  (9  m)  in  thickness,  assuming  there  is  no  faulting  in  any  of  the  covered  intervals.    Above  those  limestones  is  ~5  ft  (1.5  m)  of  calcareous  cross-­‐bedded  sandstone  that  is  identified  as  the  Clifton  Forge  Sandstone,  a  Silurian  member  of  the  Siluro-­‐Devonian  Keyser  Formation.    That  sandstone  is  overlain  by  another  covered  interval,  which  may  be  more  Clifton   Forge   Sandstone,   and   then   there   is   an   ~10   ft   (3   m)   thick   exposure   of   reddish   weathering,  ferruginous   crinoidal   grainstone,   with   numerous   quartz   laminae   and   thin   beds   and   stringers   that  weather  in  relief  up  to  about  0.3  in  (1  cm).      

This  unit  is  identified  here  for  the  first  time  as  the  Devonian  Healing  Springs  Sandstone,  perhaps  with  a  thin  New  Creek  Limestone  at  its  base.    At  nearby  exposures  in  this  area  including  those  at  Crizer  Gap,  Black  Oak  Cave  Hollow,  Millboro  Springs  (Haynes  et  al.,  2014),  and  Deep  Hollow,  the  Healing  Springs  Sandstone  is  distinctive  for  its  wavy  laminae  and  thin  beds  of  calcarenaceous  sandstone,  very  similar  in  appearance  to  this  bed  here  at  Eagle  Rock.    Above  this  unit  is  a  covered  interval  where  the  main  or  one  of  the  main  faults  in  this  exposure  occurs,  as  the  Tuscarora  Sandstone  is  the  next  unit  to  the  north.        

Although   Gathright   and   Rader   (1981)   identified   a   thin   (5   ft.   thick)   exposure   of   cherty   Licking  Creek  Limestone  immediately  above  the  Clifton  Forge  Sandstone  at  this  same  exposure,  i.e.,  downsection  (south)  of  the  fault,  we  have  been  unable  to  find  any  cherty  limestones  along  the  road,  but  there  may  be  Licking  Creek  exposed  higher  on  the  hillside.    Because  the  Healing  Springs  Sandstone  overlies   the  New  Creek  Limestone  or,  where  that  unit   is  absent  as  it   is   in  several  exposures  in  the  immediate  region,  the  Keyser   Formation,   the   stratigraphic   sequence  we   suggest   here   of   Clifton   Forge   Sandstone   overlain   by  Healing  Springs  Sandstone  does  not  necessarily  require  a  fault  or  an  unconformity,  as  does  a  sequence  of  Clifton  Forge  overlain  by  Licking  Creek.  

Gathright   and  Rader   (1981),  who  did  not  use   the  name   “Eagle  Rock   sandstone,”   considered   the  lower  146  ft  (44  m)  of  white  silica-­‐cemented  quartz  arenite  to  be  the  Keefer  Sandstone,  a  60  ft  (18  m)  thick  interval  above  the  Keefer  that  consists  of  red  and  purple  mottled  sandstone  to  be  the  “Bloomsburg”  Formation,   and   the  upper  205   ft   (62  m)  of   sandstones   to  be   the  Wills  Creek  Sandstone.    They  did  not  identify   any   part   of   this   thick   sequence   of   sandstone   as   McKenzie   Formation   equivalents,   nor   as  Williamsport   Sandstone   equivalents.     In   the   guidebook   for   the   16th   Annual   Virginia   Geologic   Field  Conference,  Rader  and  Gathright  (1984)  referred  to  the  entire  sequence  between  the  Rose  Hill  and  the  Tonoloway  as  the  Eagle  Rock  Sandstone  of  Lampiris,  with  Lampiris  (1976)  having  been  the  first  to  use  the  name  “Eagle  Rock  sandstone”  (Fig.  1-­‐2).    

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   Figure   1-­‐2.   Stratigraphic   nomenclature   applied   to   outcrop   at   Eagle   Rock,   Virginia   by   various   workers.  Dennison  and  Lampiris  measured  the  section  on  the  north  side  of  the  James  River,  before  the  section  on  the  south  side  was  exposed.    No  vertical  scale  implied.    

Of  note  is  that  the  upper  65  ft  (20  m)  of  what  Gathright  and  Rader  (1981)  identified  as  the  Wills  Creek  Sandstone  is  a  sequence  of  calcareous  to  calcarenaceous  quartz  arenite,  some  beds  of  which  exhibit  prominent   low   angle   cross-­‐bedding.     Upon   closer   examination   still,   some   of   this   cross-­‐bedding   can  reasonably  be   interpreted  as   tidal  bundles  (Yang  et  al.,  2008)   formed  by  waves  moving  across  a  sandy  tidal  flat  (Figs.  C1,  C2,  C3).      

The  presence  of  silica  cement  vs.  calcite  cement  in  the  sandstones  of  this  region  has  been  used  as  a  guide   to   distinguishing   some   of   the   several   sandstones   from  one   another   (Dennison   et   al.,   1992),   and  although  many  sandstones  of   the  sandstones  are  cross-­‐bedded,   the   three  major  sandstones  of   regional  interest  here  (the  Keefer,  McKenzie,  and  Williamsport  sandstones)  that  probably  comprise  much  of  the  “Eagle  Rock  sandstone”  here  at  Stop  1  are  each  predominantly  a  silica-­‐cemented  sandstone  in  the  central  Appalachians.     So   (1)   the   lack   of   a   thick  Wills   Creek   Formation   here   (Appalachian   Geological   Society,  1970)  and  elsewhere  in  this  vicinity  perhaps  as  far  north  as  central  Highland  County,  (2)  the  presence  in  the  lower  member  of  the  Tonoloway  Limestone  of  cross-­‐bedded  calcarenaceous  sandstones  that  thicken  southward   (Figs.  C4,  C5,  C6),  and   (3)   the  existence  of  only  a   thin  Tonoloway  Limestone  here  at  Stop  1  immediately  above  calcareous  cross-­‐bedded  sandstones,  has  led  us  to  hypothesize  that,  rather  than  these  calcareous  sandstones  being  correlative  with  a  thin  Wills  Creek,  they  may  instead  be  correlative  with  the  lower   and   perhaps   even   the   middle   members   of   the   Tonoloway   Limestone.     The   Tonoloway   thins  significantly  from  north  to  south  in  this  region,  and  its  sandstones  become  prominent  as  well:  at  U.S.  250  on   the   east   flank   of   Bullpasture  Mountain   in   north-­‐central  Highland   County   it   is   496   ft   (150  m)   thick  (Woodward,  1941),   it   is  ~422  ft   (128  m)  thick  near  Burnsville   in  northern  Bath  County  (Swezey  et  al.,  2015),   it   is  ~267   ft   (81  m)   thick  at  Crizer  Gap   in  southern  Bath  County   (Haynes  et  al.,  2014),  and   it   is  ~140  ft  (42  m)  thick  at  Iron  Gate  in  east-­‐central  Alleghany  County  (Lesure,  1957).    So  continued  thinning  toward  Eagle  Rock  is  consistent  with  this  regional  trend,  as  is  the  appearance  of  sandier  intervals.  

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The   146   ft   thick   Keefer   interval   here   at   Stop   1   probably   includes   the   true   Keefer   Sandstone  equivalent  immediately  above  the  Rose  Hill  Formation,  as  well  as  some  of  the  McKenzie  Formation.    The  unnamed  middle  sandstone  of  the  McKenzie  (Patchen  and  Smosna,  1975)  extends  west-­‐northwest  in  the  subsurface   across   several   counties   as   “...a   tongue   of   the   extremely   thick   Middle   and   Upper   Silurian  “Keefer”  Sandstone   in  Virginia....”   (Smosna  and  Patchen,  1978,  p.  2318),   thus   it  would  be  expected   that  the   “Eagle   Rock   sandstone”   here   at   Stop   1   would   include   the   correlative   equivalent   of   the   middle  sandstone  of   the  McKenzie.    Determining  exactly  where   that  might  be   is  complicated  somewhat  by   the  presence  of  reddish  sandstones  that  comprise  the  “Bloomsburg”  interval  of  Gathright  and  Rader  (1981).      But   because   the   Williamsport   Sandstone   is   likewise   “...another   tongue   of   the   “Keefer”   Sandstone...”  (Smosna  and  Patchen,  1978,  p.   2321),   as  well   as   a   thin  marine   tongue  of   the  Bloomsburg,   it  would  be  expected  that  the  “Eagle  Rock  sandstone”  here  at  Stop  1  would  also  include  the  correlative  equivalent  of  the  Williamsport  Sandstone.    Additionally,   the  Wills  Creek  Formation   is   in  most  areas  of   its  occurrence  both   in   the   surface   and   subsurface   of   this   region,   a   heterogeneous   sequence   of   mudrocks,   some  calcareous,  as  well  as  some  thin  limestones  (Smosna  and  Patchen,  1978),  with  only  very  thin  sandstones  (as  we  will  see  at  Stop  5).      

So   correlation   of   a   part   of   the   “Eagle   Rock   sandstone”  with   the  Wills   Creek   rather   than  with   a  thicker  Williamsport   seems   less   supported   than  does  a   correlation  with   the  Williamsport  and  possibly  the   lower   Tonoloway   Limestone;   indeed   Woodward   (1941,   p.   95)   commented   that   “Probably   this  siliceous   unit   of   west-­‐central   Virginia   contains   separable   horizons   as   high   as   the   Williamsport,   with  which  its  upper  portion  is  believed  to  be  equivalent.     Indeed,   it  may  ascend  into  the  Wills  Creek,  which  seems  otherwise  to  be  absent.”    John  Dennison  (Appalachian  Geological  Society,  1970,  p.  140-­‐141)  noted  that   the   “Wills   Creek   Formation   [is]   absent”   at   Eagle   Rock,   and   he   recognized   the   Williamsport  Sandstone,  the  McKenzie  Formation,  and  the  “Keefer”  Sandstone  at  Eagle  Rock  as  well,  at  the  original  and  older  outcrop  that  is  still  present  and  reasonably  well-­‐exposed  and  accessible  along  the  north  side  of  the  James  River.  

There  is  also  the  possibility  that  part  of  the  “Eagle  Rock  sandstone”  may  correlate  with  the  upper  Rose   Hill   Formation   stratigraphically   downsection.     This   suggestion   was   made   by   Charles   Butts,   as  quoted   by   Woodward   (1941,   p.   95);   Butts   stated   that   the   thick   “Keefer”   of   this   area   “....is   laterally  continuous  with  the  Keefer,  and  on  James  River  as  well  as  in  the  southeastern  limb  of  Catawba  Mountain,  Roanoke   County,   Virginia,   thickens   downward   to   replace   the   upper   part   of   the   Rose   Hill”   is   another  hypothesis  to  explain  the  great  thickness  of  the  “Eagle  Rock  sandstone.”      And  indeed  the  typical  shales  of  the  upper  Rose  Hill  are  not  seen  here  at  Stop  1,  so  Butts’s  suggestion  may  likewise  have  merit.      

The   upper   and   lower   contacts   of   the   “Eagle   Rock   Sandstone”   here   at   Stop   1   are   shown  diagrammatically  in  Figure  B  with  these  stratigraphic  relations  as  possibilities.      Structural  Relationships     Interpretative  sketches  of  the  Eagle  Rock  area  have  varied  in  complexity  from  unfaulted  southeast  verging   folds   (Butts,   1940),   to   folds  with   folded   faults   (McGuire,   1970;   Spencer   et   al.,   1989),   to  more  complex  fold  and  fault  relationships  (Bartholomew  et  al.,  1982)  (Fig.  1-­‐3).  The  fold  and  fault  structures  in  evidence  at  Eagle  Rock  are  bounded  to  the  east  and  west  by  west-­‐directed  thrusts  that  may  be  splays  of  the  Pulaski  thrust  system  (McGuire,  1970;  Spencer  et  al.,  1989).  Rader  and  Gathright  (1986)  interpreted  Eagle   Rock   as   a   footwall-­‐derived   horse   block   on   the   leading   edge   of   the   Pulaski   thrust,   above   a  decollement   within   Devonian   shales.   Smaller-­‐scale   structures   are   abundant   and   include   hanging   wall  anticlines,  footwall  synclines,  and  other  detached  folds  that  have  been  interpreted  as  break-­‐thrusts,  fault  propagation   folds,   and   fault  bend   folds   (McConnell   et   al.,   1997).  Many  of   these   smaller-­‐scale   folds   and  faults  are  antithetic  to  the  principal  west-­‐directed  thrusts  that  bound  the  central  area  of  the  roadcut.  

Unfortunately,  the  higher  elevations  of  Eagle  Rock  are  shrouded  in  abundant  foliage,  which  makes  the  upper  parts  of  the  interpretations  in  Figure  1-­‐3  hard  for  us  to  evaluate.  Nevertheless,  the  lower  parts  of   the  outcrop  exhibit  numerous  tantalizing  deformation   features  at  a  variety  of  scales   that  allow  us  to  compare  and  contrast  the  interpretations  of  previous  workers.    

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   Figure  1-­‐3.  A  series  of  sketches  that  interpret  the  stratigraphic  and  structural  relationships  at  Eagle  Rock.    A.   Interpretation   of   Butts   (1940)   showing   continuous,   meters-­‐scale   southeast-­‐verging   folds.   B.   Sketch   by  McGuire   (1970)   showing   folded   faults   in   the  middle   section   of   the   cliff.   C.   Sketch   by   Bartholomew   et   al.  (1982)  highlighting  complex  fold  and  fault  relationships,  some  of  which  are  now  obscured  in  upper  parts  of  the  outcrop.  D.  Sketch  by  Spencer  et  al.  (1989)  showing  faults  bounding  “SD”  carbonate  slices.    

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 Specific  structural  features  that  you  might  want  to  examine  and  compare  among  the  interpretations  in  Figures  1-­‐3  and  1-­‐4,  include:    

-­‐ Possible  thrust  faulting  in  the  Martinsburg  shales  at  the  southeastern  end  of  the  outcrop  that  could  have  thickened  the  section  (e.g.  McGuire,  1970,  but  not  later  interpretations)  

-­‐ Faulting  along  the  Rose  Hill  and  Keefer  contact  (e.g.  Bartholomew  et  al.,  1982)  along  the   left  margin  of  the  distinctive  nose-­‐shaped  fold  (Fig.  1-­‐3c)  

-­‐ Complexities  in  the  Spencer  et  al.  (1989)  sketch  of  the  nose-­‐shaped  fold  (Fig.  1-­‐4a)  that  are  less  apparent  in  the  current  outcrop  exposure  (Fig.  1-­‐4b).  Has  the  roadcut  been  re-­‐excavated  since  1989?  

-­‐ Sense  of  movement  along  the  faults  that  bound  the  northwest  dipping  slices  of  “SD”  (compare  Figs.   1-­‐3c   and   1-­‐3d).   Considering   our   reinterpreted   stratigraphy,   are   all   of   these   faults  necessary?  

-­‐ Subhorizontal  faults  and  fault-­‐propagation(?)  folds  in  the  Tonoloway  carbonates  (SD  slices  in  Fig.  1-­‐3)  

-­‐ Subvertical   faults   in  clastic  rocks  west  of   the  “SD”  section  that  exhibit  hangingwall  anticlines  and  footwall  synclines  (McConnell  et  al.,  1997),  as  well  as  other  small-­‐scale  inter-­‐related  fold  and  fault  structures  (Figs.  1-­‐4c,  1-­‐4d)  

   

   Figure   1-­‐4.   Smaller-­‐scale   deformation   features   at   Eagle   Rock.   A.   Sketch   from   Spencer   et   al.   (1989)   of  complex  folds  around  the  “nose”  area;  compare  with  the  modern  photo  (B)  of  the  same  area.  C.  Subvertical  faults  in  clastic  rocks  at  the  western  end  of  the  roadcut,  interpreted  (in  figure  D)  by  McConnell  et  al.  (1997).          

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               Cumulative  Trip     Point  to  Point       Mileage              Mileage         Directions  and  Comments      

       26.1                          0.0     Load  buses.  Drive  north  on  U.S.  220               toward  Clifton  Forge.  

         39.5                      13.4     Site  of  the  Clifton  Forge  iron  furnace.                 Rainbow  Arch  (anticline  highlighted  by  

the  Juniata  and  Tuscarora  Fms.)  can  be               seen  to  the  east  across  the  river.              40.0                      0.5     Junction  of  U.S.  220  and  U.S.  60.    Turn  right  

          (northeast)  on  U.S.  60.    

       40.8                      0.8     Interchange  with  I-­‐64.    Turn  left  (west)  on  I-­‐64  westbound  toward  Covington.    

         51.8                      11.0     Exit  I-­‐64  onto  Valley  Ridge  Road,  and  turn  

left  (west);  this  is  U.S.  60W  and  U.S.  220N.      Follow  U.S.  220N  toward  Hot  Springs.    

       61.5                      9.7     Unload  buses  at  parking  area  for  Falling  Spring  Falls  along  the  west  side  of  U.S.  220.  

   STOP  2  –  Falling  Spring  Falls    Location:  37.867546  N,  79.947096  W,  Covington  7½  minute  quadrangle    Units:  Juniata  Formation,  Tuscarora  Formation,  Rose  Hill  Formation,  Recent  travertine         Just  north  along   the  highway   is  an  exposure  which  shows   the   redbeds  of   the   Juniata  Formation  beneath   the   Tuscarora   Sandstone   here,   in   contrast   to   the   greenish   lithic   sandstones   of   the   Oswego  Sandstone  that  underlie  the  Tuscarora  at  Stop  1  (Eagle  Rock).    The  Tuscarora  here  is  nearly  vertical,  and  it  makes   a   prominent   hogback  where   it   crosses   Falling   Spring   Creek   on   the   east   side   of   the   highway.      Diecchio  (1985)  measured  a  total  of  504  ft  (154  m)  of  Juniata  at  this  exposure,  and  although  a  thickness  of  the  Tuscarora  here  was  not  obtainable,  a  thickness  of  52  ft  (16  m)  was  measured  at  a  nearby  exposure  to   the  north-­‐northeast,   along   the   summit  of  Warm  Springs  Mountain.    That   thickness   is   approximately  one-­‐third  of  the  ~140  feet  of  Tuscarora  that  is  present  at  Stop  1  (Eagle  Rock),  and  it  indicates  appreciable  thinning  of  the  Tuscarora  in  this  direction  from  Eagle  Rock.    Of  note  however,  is  that  unlike  the  younger  Silurian  sandstones,  especially  the  Keefer  and  McKenzie,  which  thin  to  disappearance  between  here  and  Stop  5  (Bluegrass)  to  the  north-­‐northeast,  the  Tuscarora  Formation  does  not  continue  to  thin,  but  instead  it  thickens  again  toward  the  eastern  panhandle  of  West  Virginia,  where  it  reaches  thicknesses  of  close  to  400  ft  (120  m)  (Smosna  and  Patchen,  1978).     The  waterfall  and  stream  here  are  notable  for  their  unusual  origin  and  geochemistry.    The  entire  stream  emerges   from  multiple  openings  at  what   is  nonetheless  collectively  called  Falling  Spring,  about  0.9  miles  up  the  valley  from  here,  after  traveling  through  Warm  River  Cave  and  gathering  the  flow  from  at  least   four  separate   thermal  springs   in   that  cave,  and  a  separate   thermal  stream  that   flows  though  Mud  Pot  Cave  to  the  north  of  Warm  River  Cave.    The  waters  are  nearly  saturated  in  calcium  carbonate  much  of  

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the  year,   and   these  dissolved  solids  precipitate  out  along   the  stream  as   the  numerous   travertine  dams  and  the  deposits  beneath  the  waterfall  itself.     The   following   description   is   taken   from   Dennen   &   Diecchio   (1984),   Dennen   et   al.   (1990),   and  Diecchio  and  Walton  (2003).    Falling  Spring  Valley  lies  at  the  southern  end  of  Warm  Springs  Valley,  which  coincides  with  the  southern  end  of  the  Warm  Springs  Anticline  (Fig.  2-­‐1).  The  Falling  Spring  Valley  is  a  karst  valley  underlain  by  Lower  and  Middle  Ordovician   limestones.  Around  the  periphery  of  the  valley,  the  underlying  carbonate  strata  transition  stratigraphically  and  geographically  upward  into  the  overlying  Ordovician  clastics  of  the  Reedsville,  Oswego,  and  Juniata  Formations.    Little  Mountain  and  Warm  Springs  Mountain,  which  enclose  the  valley,  are  ridges  underlain  by,  and  held  up  by,  the  Tuscarora  Formation.  

Thermal   and   normal   spring   waters   mix   within   Warm   River   Cave   before   emanating   onto   the  surface.  On   the   surface,   the   spring  water  mixes  with   the   runoff   in   Falling   Spring   Creek   (Fig.   2-­‐1).   The  creek  water  has  its  lowest  pH  upstream  from  the  spring.  The  spring  introduces  higher  pH  water.  Farther  downstream,   pH   increases   due   to   CO2   degassing,   and   the   biggest   increase   is   associated   with   the  turbulence  that  occurs  as  the  water  cascades  over  the  waterfall.  Temperature,  which  plays  a  minor  role,  usually   decreases   downstream   from   the   spring.   Temperature   of   the   spring   itself   varies   annually,  probably   due   to   various   amounts   of   mixing   with   shallow   groundwater.   The   result   is   that   carbonate  solubility  decreases  downstream  from  the  spring,  primarily  due   to   increasing  pH,  and   the  most  abrupt  change  in  solubility  occurs  at  the  waterfall.    

 

 Figure   2-­‐1.   Falling   Spring   Creek   drainage   system.  Heavy   dashed   line   represents   approximate   outcrop   of  Tuscarora  Formation.    From  Dennen  et  al.  (1990).  

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    The   critical   point   where   the   stream   water   becomes   oversaturated   with   respect   to   calcium  carbonate   varies   from   place   to   place   during   the   course   of   the   year.   It   is   farther   upstream   during   dry  seasons,   when   shallow   groundwater   influx   and   surface   runoff   are   minimal,   and   this   is   usually   late  summer   or   early   autumn.   At   these   times,   travertine   precipitation   may   occur   above   the   falls,   and   is  evidenced   by   the   travertine   dams   behind   the   parking   area.   The   greatest   amount   of   precipitation,  however,  typically  occurs  below  the  waterfall,  and  can  be  seen  in  the  form  of  numerous  travertine  dams  and   rim  pools.   A   low,  wide   “stalagmite”   can   usually   be   observed   directly   below  where   the  water   hits.  During  times  of  peak  precipitation,  branches,   leaves,  and  other  debris  can  be   found  coated  with  sparry  deposits.   A   rare,   bryophyte-­‐dominated   spray   cliff   community   at   the   base   of   the   waterfall   aids   in   the  precipitation  of   the   travertine,   apparently  by   further   removing  CO2  during  photosynthesis.    At   times  of  the  year  when  calcification  is  active,  some  of  these  plants  ‘crunch’  when  you  squeeze  them  in  your  hand.     Travertine  deposits,  primarily  in  the  form  of  cascade  deposits,  occur  today  higher  up  on  the  west  slope  of  Little  Mountain,  along  State  Road  640,  as  well  as  below  the  waterfall  to  unknown  depths  (Figs.  2-­‐1,  2-­‐2a).  Along   the   course  of  Falling  Spring  Creek,   travertine  deposits  occur   just  downstream   from   the  ledge  of  Tuscarora  Sandstone  (Fig.  2-­‐2b).  Apparently,  the  resistant  Tuscarora  was  the  site  of  the  earliest  waterfalls  of  cascades.  We  propose  that,  prior  to  dissection  of  the  present  water  gap,  the  Tuscarora  ridge  was  the  feature  that  most  aided  in  the  natural  degassing  of  the  stream  water,  and  localized  the  formation  of  the  ancient  cascade  deposits.    

   Figure  2-­‐2.  A.  West  to  east  profile  (solid  line),  through  Little  Mountain.    Location  indicated  (as  A  –  B  line)  on  Fig.  2-­‐1.    Dashed  line  in  (A)  is  the  same  profile  as  in  (B).    B.  Profile  along  Falling  Spring  Creek.  From  Dennen  et  al.  (1990).    

  25  

               Cumulative  Trip     Point  to  Point       Mileage              Mileage         Directions  and  Comments      

       61.5                          0.0     Load  buses.    Continue  north  on  U.S.  220    through  Healing  Springs,  Hot  Springs,  and    Warm  Springs  to  intersection  with  S.R.  614  (Muddy  Run  Road).    

       82.5                      21.0     Turn  right  (northeast)  onto  S.R.  614    toward  Burnsville.  

         91.6                      9.1     Burnsville,  junction  with  S.R.  609.  Continue  

east  on  S.R.  614  (Tower  Hill  Road).    

       92.8                      1.2     Unload  buses  along  S.R.  614.      STOP  3  –  Chestnut  Ridge    Location:  38.182714  N,  79.627042  W,  Burnsville  7½  minute  quadrangle    Units:  Tonoloway  Limestone  –  (a)  upper  ~1.5  ft  (45  cm)  of  limestones  of  the  lower  member,  with  prominent  pink  partings,  overlain  by  (b)  “upper  Breathing  Cave  sandstone”  between  lower  and  middle  members,  overlain  by  (c)  silty  fossiliferous  lime  mudstones,  wackestones,  and  packstones  of  the  middle  member         Here  we  will  see  one  of  the  thin  but  important  sandstones  of  the  Tonoloway  Limestone,  and  in  this  area  this  particular  sandstone   is  notable   for  being  the  caprock  for  many  extensive  cave  systems  within  Chestnut  Ridge,   the   forested  ridge  to   the  north  of   this  exposure.    This  sandstone,  which   is  almost  12   ft  (3.5  m)  thick  at  this  exposure,  and  another  prominent  and  nearly  equally  as  thick  sandstone  about  80  ft  (24  m)  stratigraphically  downsection,  are  both  in  the  lower  member  of  the  Tonoloway  (Fig.  C5).    These  two  sandstones  are  informally  referred  to  in  this  area  as  the  “lower  Breathing  Cave  sandstone”  and  the  “upper  Breathing  Cave  sandstone”  respectively  (Swezey  et  al.,  2015),   for  their   importance  in  governing  the  development  of  Breathing  Cave,  as  documented  by  Deike  (1960)  and  White  and  Hess  (1982).      For  decades,   these   two   sandstones   were   identifed   in   this   area   as   tongues   of   the   Clifton   Forge   Sandstone,  which  regionally  is  a  middle  member  (there  are  five  members)  of  the  Keyser  Formation  that  overlies  the  Tonoloway   Limestone   in   a   several   state   area.     Detailed   stratigraphic   investigations   in   recent   years,  however,  by  Haynes  and  Phil  Lucas,  Rick  Lambert  (both  of  Highland  County),  and  Nevin  Davis  (of  Bath  County)  (Swezey  and  Haynes,  2015)  have  shown  that  these  are  definitively  Tonoloway  sandstones,  not  Keyser  sandstones.     The  “upper  Breathing  Cave  sandstone”  in  this  area  is  notable  for   its  thickness,   its  cross-­‐bedding,  its  calcarenaceous  character,  and  the  common  presence  of  a  silicified  cherty  zone  that  adds  strength  and  rigidity   in   its  role  as  an   important  caprock  that  protects  many  underlying  cave  passages   from  collapse.    The  cross-­‐bedding  is  attributed  to  sand  movement  in  tidal  channels  and  maybe  a  beach  environment.    In  thin   section   the   numerous   bioclastic   grains   of   bryozoans,   brachiopods,   echinoderms   (mostly   crinoids,  with   syntaxial   overgrowths),   and   trilobites   are   evident,   as   are   the   ubiquitous   monocrystalline   quartz  grains  and  quartz  overgrowths.    The  silicified  zone  has  been  observed  here  along  Chestnut  Ridge  as  well  as  on  Bullpasture  Mountain  to  the  northeast  and  on  Jack  Mountain  to  the  north  and  northwest.      

  26  

  At   this   stop   above   the   “upper  Breathing   Cave   sandstone,”  which   in   this   area  marks   the   contact  between  the  lower  and  middle  members  of  the  Tonoloway  Limestone,  is  a  nearly  complete  exposure  of  the   middle   member   of   the   Tonoloway.     This   member   was   deposited   following   transgression   of   the  Tonoloway  sea  over   the  shallow  shelf   to   intertidal  and  supratidal  environments   that   characterized   the  lower   member,   a   sea   level   change   that   first   produced   a   shelly   beach   or   barrier   and   sand   shoal  environment   (the   “upper   Breathing   Cave   sandstone”)   and   then   an   open  marine   shelf   environment   in  which  stromatoporoids,  corals  (including  Favosites  and  Halysites),  crinoids,  brachiopods,  bryozoans,  and  trilobites   thrived  during  deposition  of   the  middle  member  of   the  Tonoloway.     In   the  exposures  here  at  Stop  3,  many  well-­‐preserved  stromatoporoids  and  corals  especially  can  be  readily  seen,  along  with  some  of  the  characteristic  silt  partings  that  contain  just  enough  iron  to  weather  a  yellowish  brown  to  orange  yellow.       Geologists  who   are   familiar  with   the   Silurian   –  Devonian   carbonates   of   this   area  will   recognize  that   the  middle  member  of   the  Tonoloway  has  a  distinctly   “Keyser”   look   to   it,   i.e.,   it  has   some  nodular  bedding   in   places,   it   contains   an   abundant   and   diverse   open   marine   fauna   of   typical   late   Silurian  character,   and   it   is   comprised  of  mostly  bioclastic  wackestones,   packstones,   and  grainstones,  with   few  lime  mudstones.    Because  of  these  lithologic  characteristics,  it  seems  that  more  than  a  few  geologists  and  others   carrying   out   research   in   this   area   over   recent   decades   have   been   misled   by   this   deceptively  “Keyser-­‐like”  appearance  of  the  middle  member  of  the  Tonoloway.    None  other  than  Charles  Butts  seems  in  retrospect  to  have  made  several  misidentifications  in  a  key  section  to  the  north  of  here,  the  exposure  along  U.S.  250  on  the  east  side  of  Bullpasture  Mountain  (Butts,  1940,  p.  264-­‐266),  and   figuring  out   the  stratigraphy  of  that  section  was  a  key  to  understanding  the  stratigraphic  relationships  of  the  Tonoloway  and   Keyser   throughout   Highland   and   Bath   Counties,   as   well   as   Alleghany   County   farther   south   and  Pendleton  County  in  West  Virginia  to  the  north  (Swezey  et  al,  2015).    At  the  same  time  Butts  was  working  in  Virginia,  Woodward  (1941,  1943)  was  working  primarily  in  West  Virginia  as  well  on  the  Silurian  and  Devonian   stratigraphic   sequences   in   that   state,   but   he   included   some   significant   measurements   from  sections  in  Virginia  as  well,  including  the  Bullpasture  Mountain  section  along  U.S.  250,  which  Woodward  called  his  McDowell   section   (Woodward,  1941,  p.   241;  Woodward,  1943,  p.   215-­‐216).    At   the  U.S.   250  section,  Butts  and  Woodward  report  some  difference  in  the  thickness  of  the  limestones  that  Woodward  identified   as   the   upper   beds   of   the   lower   member   of   the   Tonoloway,   but   it   seems   evident   that   both  recognized  these  beds  as  alternating  thin-­‐bedded  limestones,  with  pink  or  red  coloration.    These  form  the  lower   200   feet   of   Butts’s   595±   feet   of   Keyser,   and   the   entirety   of  Woodward’s   lower  member   of   the  Tonoloway.     The  simplest  explanation  seems  to  be  that  this  is  an  error  by  Butts,  whereby  he  placed  nearly  all  of  the   Tonoloway   at   the   U.S.   250   section   in   the  Keyser.     In   text   that   follows   his  measured   section,   Butts  (1940,  p.  265-­‐266)  makes  the  following  statement:  “The  thickness  of  the  Keyser  obtained  here  is  greater  than  would  be  expected,   and   it   is  probable   that   some  of   the   laminated   limestone,  bed  3,   at   the  base   is  Tonoloway.”         The  middle  member  of  the  Tonoloway  at  the  U.S.  250  section  looks  strikingly  similar  to  the  lower  ~40   feet   of   the  Keyser,  which   is   nonetheless   over   200   feet   upsection   stratigraphically   in   an   unfaulted  sequence.     So   it   is   understandable   how   Butts   might   have   lumped  what  Woodward   recognized   as   the  middle  member  of  the  Tonoloway  with  the  Keyser  on  account  of  lithologic  similarity;  in  fact  Woodward  (1941,  p.  210)  commented  explicitly  on  the  similarity  of   the  middle  member  of   the  Tonoloway  and  the  Keyser.       Haynes’s   thinking   over   the   years   has   been   to   side  more  with  Woodward’s   interpretations   than  with   Butts’s,   for   this   reason:   Butts   was   working   on   the   geology   of   the   entire   Paleozoic   sequence   in  Virginia,  Cambrian  to  Pennsylvanian,  and  so  he  was  more  likely  perhaps  to  make  measurements,  assign  the  units  to  a  stratigraphic  unit,   then  move  on.  By  contrast,  Woodward  seemed  to  have   long  periods  of  time  where  he  was  working   on   a   single   system  of   the  Paleozoic,   i.e.,   the   Silurian   System,   published   in  1941,  then  the  Devonian  System,  published  in  1943.    From  careful  reading  of  both  Butts  and  Woodward  over  many  years,  along  with  much  field  checking  of  many  sections  that  both  geologists  had  visited  and  

  27  

measured,   it   has   seemed   to  Haynes   that  Woodward’s   reports   show  a  much  more  detailed,   and  maybe  more-­‐thought-­‐out,   approach   to   the   stratigraphic   and   faunal/biostratigraphic   complexities   in   the  Paleozoic   systems.   Woodward   describes   literally   dozens   of   measured   sections   from   Pennsylvania   to  Virginia,  with  numerous  sentences  and  paragraphs   that   refer   to  one  or  another  section  or   locality   that  exhibits   some   or   another   feature   of   interest,   and   clearly   Woodward   put   a   lot   of   thought   into   his  discussion  of  the  stratigraphic  relations  of  these  units.     The  “upper  Breathing  Cave  sandstone”  in  the  Tonoloway  exposure  here  at  Stop  3  correlates  quite  well  with  a   thinner   (~2   ft,  or  60  cm,   thick)  calcarenaceous,   cross-­‐bedded,  and  very  porous  weathering  sandstone  in  the  exposure  along  U.S.  250  referred  to  above  (Figs.  C5,  C6),  and  petrographic  study  shows  that   both   sandstones   are   lithologically   similar.     The   lateral   persistence   of   this   “upper   Breathing   Cave  sandstone”  from  here  along  Chestnut  Ridge  north-­‐northeast  to  the  section  on  Bullpasture  Mountain  along  U.S.  250  is  of  interest  relative  to  the  lateral  persistence  of  the  Clifton  Forge  Sandstone,  with  which  it  was  long   thought   to  be   correlative;   this   sandstone  cannot  be   the  Clifton  Forge  Sandstone  or   its   correlative,  because   that  stratigraphic  unit   is   a   facies   equivalent  of   the  Big  Mountain  Shale  Member  of   the  Keyser,  which   along  U.S.   250   is   present,   over   80  meters   stratigraphically   upsection   from   the   sandstone   at   the  contact  of  the  lower  and  middle  members  of  the  Tonoloway  that  we  correlate  with  the  “upper  Breathing  Cave  sandstone”  here  at  Stop  3  and  at  many  other  exposures  throughout  this  area.        

             Cumulative  Trip     Point  to  Point       Mileage              Mileage         Directions  and  Comments      

       92.8                      0.0     Load  buses,  and  continue  east-­‐northeast               along  S.R.  614  across  Tower  Hill  Mountain    

toward  Williamsville.    

       96.4                          3.6     T-­‐intersection  in  Williamsville  with    S.R.  678,  turn  left  (north-­‐northwest)  onto    S.R.  678  (Indian  Draft  Road,  which      

  becomes  Bullpasture  River  Road)    

       96.6                          0.2     Unload  buses  in  large  pullout  along  the    right  (east)  side  of  S.R.  678.  

   STOP  4  –  Williamsville    Location:  38.199591  N,  79.573218  W,  Williamsville  7½  minute  quadrangle    Units:  Rose  Hill  Formation,  Keefer  Sandstone,  Rochester  Shale(??),  McKenzie  Formation,  Williamsport  Sandstone         This  long  exposure  along  S.R.  678  (Fig.  D)  is  at  the  downriver  end  of  the  gorge  of  the  Bullpasture  River,  which  has  formed  where  the  river  has  cut  completely  through  the  structurally  complex  Bullpasture  Mountain  anticlinorium.    Together  with  exposures  in  the  bed  of  the  river  itself  (Fig.  D),  a  composite  but  complete   stratigraphic   section   from   the   Rose  Hill   Formation   upsection   to   the   Needmore   Shale   can   be  measured   (Figs.   A,   D).    We  will   walk   uphill   and   downsection   to   see   a   part   of   this   composite   section,  starting  with   the  Williamsport   Sandstone,   and   going   downsection   through   a   complete   exposure   of   the  heterogeneous  McKenzie  Formation,  then  a  complete  exposure  of  the  Keefer  Sandstone,  with  a  possible  thin   Rochester   Shale   between   the   McKenzie   and   Keefer,   and   then   to   the   shales   and   reddish   purple  sandstones  of  the  Rose  Hill  Formation.    

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  Exposures  in  the  gorge,  both  in  the  riverbed  itself  and  along  the  walls  of  the  gorge,  have  proved  to  be  the  key  to  understanding  the  stratigraphy  of  the  Silurian-­‐  Devonian  sequence  of  the  immediate  area.    Good  exposures  of  the  Rose  Hill  Formation,  the  oldest  unit  in  the  gorge,  up  to  the  Oriskany  Sandstone  and  the   overlying   Devonian   shales,   are   present   and   accessible   on   one   or   both   limbs   of   the   anticlinorium.    When   remapping   of   the   bedrock   geology   of   the   north   half   of   the  Williamsville   7½  minute   quadrangle  began  in  the  summer  of  2009  (Haynes  and  Whitmeyer,  2010),  Haynes  subsequently  spent  many  days  in  the   field,  with  much   of   this   time   spent   striving   to   understand   and  work   out   the   specific   details   of   the  stratigraphy  of  the  entire  Silurian  and  Lower  Devonian  of  this  area.    During  that  time,  it  slowly  dawned  on  Haynes  that  in  all  the  decades  during  which  substantive  and  methodical  field  geologic  investigations  have  been  carried  out   in  this  area,  there  has  apparently  been  not  one  complete  measured  stratigraphic  section   produced   for   the   exposures   in   the   Bullpasture   River   gorge   from   the   Rose   Hill   Formation  upsection  to  the  Needmore  Shale.    Not  one.     This  is  really  quite  surprising  when  one  considers  three  things:  (1)  the  quality  of  exposures  in  the  gorge,  which  is  very  good  for  the  Appalachians;  (2)  the  geologists  who  have  worked  in  this  region  over  the  decades,  and  (3)  how  long  there  has  been  geologic  interest  in  this  area,  back  to  the  reports  of  Swartz  (1930),  Butts  (1940),  and  Woodward  (1941,  1943),   in  which  measurements  of  stratigraphic  sequences  were  included.    The  exposures  in  the  gorge  are  strategically  located  from  a  correlation  point  of  view,  and  they  are  well  positioned  to  help  us  better  understand  some  of  the  long-­‐standing  stratigraphic  unknowns  and  uncertainties  in  the  Silurian  and  Devonian  of  this  area.     In   the   geologic   map   of   the   Monterey   Folio   (Darton,   1899),   there   are   no   detailed   stratigraphic  sections  included,  just  the  general  description  of  the  stratigraphic  units  as  they  were  known  at  that  time,  e.g.,  the  Monterey  Sandstone  (now  the  Oriskany),  and  the  Lewistown  Limestone  (now  all  the  carbonates  from   the   Tonoloway   through   the   Helderberg).     The   later   reports   by   Swartz,   Butts,   Woodward,   et   al.  included   measured   sections   of   Silurian   and   Devonian   numbering   from   several   (Swartz,   1930;   Butts,  1940)   to   dozens   (Woodward,   1941,   1943).     It   is   primarily   from   these   publications   that   much   of   our  current  understanding  of  the  regional  stratigraphy  of  this  area  –  right  or  wrong  –  has  been  derived.    But  in  none  of  those  reports  is  there  a  measured  section  of  the  stratigraphic  sequence  that  is  exposed  in  the  river  bed  and  along  the  sides  of  the  gorge  of  the  Bullpasture  River.     We   know  of   two   partial  measured   sections   based   on   exposures   in   the  Bullpasture  River   gorge.    Hunter   (1960,   p.   387)   included   a   measured   section   named   simply   “Bullpasture   Gorge,   Va.”   that  presumably   was   measured   along   S.R.   678   (Fig.   4-­‐1a);   the   units   that   Hunter   described   were   the  Tonoloway,  Wills  Creek  (he  noted  that  this  might  possibly  include  McKenzie),  Keefer,  and  Rose  Hill.    Bick  (1962,   p.   24)   included   a   measured   section   along   S.R.   678   at   the   west   end   of   the   gorge   north   of  Williamsville  (Fig.  4-­‐1b),  and  it  includes  units  from  the  base  of  the  McKensie  [sic]  up  to  the  Wills  Creek,  but  Bick’s  geologic  map  shows  no  strike  and  dip  symbols  along  the  river,  only  along  S.R.  678,  so  evidently  he  also  did  not  venture  into  the  gorge  itself  to  make  geologic  observations  and  measurements.    As  a  result  of  the  detailed  study  of  the  exposures  in  the  gorge  by  Haynes  and  Whitmeyer  (2010),  and  a  JMU  geology  student  (Covington,  2015),  a  reinterpretation  of  the  stratigraphic  measurements  of  both  Hunter  (Fig.  4-­‐1a)  and  Bick  (Fig.  4-­‐1b)  is  presented  for  discussion.            

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From  youngest   to  oldest  (the  stratigraphic  order  that  we  will  see  these  units   today),  a  summary  of   the  reinterpretations  of  Bick’s  1962  section  is  thus:    

1. What  Bick   (1962)  described  as  bed  2  of  his  Tonoloway  Limestone,   is  a  sandstone   that   is  herein  identified  as  the  Williamsport  Sandstone  (Fig.  E;  Fig.  4-­‐1b)  on  the  basis  of  its  lithologic  character  including   an   interbedded   limestone   bed,   its   sedimentary   structures   including   ripple-­‐marked  bedding  planes,  and  its  sparse  but  important  fossil  content  of  ostracodes,  primarily  as  shell  moldic  pores  now  lined  with  limonite.    

The   Williamsport   Sandstone   persists   laterally   throughout   this   region,   where   we   have  observed  it  to  have  almost  invariably  the  character  as  described  by  Woodward  (1941,  p.  151,   153):   “...the   Williamsport   contains   20   to   30   feet   of   greenish-­‐brown   sandstone   of  medium   texture   and   in  medium-­‐thick   beds.   Zones   of   greenish-­‐gray   to   gray-­‐brown   shale  are   common,   especially   in   the   middle   third   of   the   rock.     Throughout   most   of   its  occurrence...[it]  is  identified  by  the  presence  at  both  top  and  bottom  of  a  3-­‐  to  4-­‐foot  bed  of  fairly   massive   brown   to   green-­‐brown   sandstone,   together   with   an   assortment   of   more  thinly   bedded   argillaceous   sandstones   or   shales   in   the   median   portion.   ...   Williamsport  sandstones  are   seldom  coarse  grained,   and  pebbles  or   conglomeratic  beds  are  normally  lacking.     Grain   size,   however,   is   fairly   even,   and   a   mildly   ferruginous   cement   is   partly  responsible   for   the   dark   colors   of   the   fresh   rock.     Upon   weathering,   the   sandstone  fragments  rarely  grow  friable,  but  commonly  become  somewhat  more  highly  indurated,  so  that  the  rock  usually  supplies  abundant  tough  siliceous  debris  to  the  soil  of  its  outcrop.  ....  Except   for   two   species   of   Leperditia   and   a   pelecypod,   the  Williamsport   appears   to   be  unfossiliferous.”        So  the  reinterpretation  of  this  sandstone  as  the  Williamsport  rather  than  as  a  Tonoloway  sandstone  also  fits  well  with  what  is  observed  in  the  bed  of  the  Bullpasture  River  below  us.    It  is  a  tough,  erosionally  resistant,  silica-­‐cemented  quartz  arenite  that  weathers  variously  white  to  tan  to  orange-­‐brown  to  brown,  and  it  forms  a  distinct  riffle  in  the  river,  more  so  on   the  west   limb  of   the   anticlinorium   than  here   on   the   east   limb,  where   the   outcrop   of  Williamsport  in  the  bed  of  the  river  is  covered  with  blocks  and  boulders  and  other  colluvial  and   alluvial   sediments.     The   thickness   here   as  measured   by   Bick   (1962)   and   Covington  (2015)  of  about  70  feet  (26  m)  is  almost  double  the  typical  thickness  of  the  Williamsport  as  reported  anywhere  else  in  this  region.    This  may  simply  be  an  anomalously  thick  section  of   Williamsport,   or,   given   the   deformation   seen   here,   the   section   may   be   repeated   by  faulting.      

2. What  Bick  (1962)  described  as  bed  1  of  his  Tonoloway  Limestone  and  beds  1  and  2  of  his  Wills  Creek  Formation  are  herein  correlated  with,  and  placed  in,  the  McKenzie  Formation.      

In   retrospect,   it   is   readily   understandable   that  Bick  would   identify   the   thin-­‐bedded   and  planar  to  crinkly  laminated  limestones  (his  bed  1  of  the  Tonoloway  and  the  reinterpreted  bed   6   of   the   McKenzie)   as   Tonoloway   limestones,   because   they  DO   look   a   lot   like   the  typical  limestones  that  characterize  both  the  lower  and  upper  members  of  the  Tonoloway  Limestone  in  this  region.    The  reinterpretation  of  these  limestones  as  McKenzie  limestones,  however,  is  supported  by  examination  of  exposures  just  down  the  hill  behind  us  along  the  banks  of  the  Bullpasture  River,  where  a  normal  section  of  Tonoloway  is  present,  although  relatively  poorly  exposed.        

3. What  Bick  (1962)  described  as  bed  2  of  his  Wills  Creek  Formation  is  a  resistant  quartz  arenite  that  is   herein   correlated   with   the   unnamed   middle   sandstone   member   of   the   McKenzie   Formation  (Patchen  and  Smosna,  1975;  Smosna  and  Patchen,  1978),  and  placed  in  the  McKenzie  Formation.    

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This  sandstone  ledge  makes  a  prominent  low  waterfall  that  drops  about  4-­‐5  ft  in  the  gorge  behind  us,  which  is  known  as  Beaver  Dam  Falls  (Fig.  E;  Fig.  4-­‐1b),  which  is  well  known  to  the  canoeists  and  kayakers  who  enjoy  traversing  the  gorge.    

The  middle  sandstone  member  of  the  McKenzie  was  previously  recognized  as  far  north  as  the  section  along  Muddy  Run  in  central  Bath  County  (Whitehurst,  1982;  Dieccchio,  1986),  and   this   exposure   in   the   Bullpasture   River   gorge   extends   its   known   lateral   extent   into  southern  Highland  County,  and   in   fact  we  have  recognized   it  as   far  north  as  Trimble,   in  central  Highland  County  (Fig.  1-­‐2).    It  is  not  present  either  at  McDowell  or  at  Stop  5  near  Bluegrass,  where  the  McKenzie  consists  primarily  of  calcareous  mudrocks.    

 4. What   Bick   (1962)   described   as   bed   1   of   his   Wills   Creek   Formation   is   placed   in   the   McKenzie  

Formation,  and  beds  1,  2,  and  3  of  his  McKensie  [sic]  Limestone,  are  described  in  more  detail  as  arenaceous  oolitic  grainstones  that  comprise  the  lowest  beds  of  the  McKenzie  Formation  here  in  this  exposure.    These  oolitic  grainstones  are  undoubtedly  also  the  unmeasured  beds  that  Hunter  (1960)  placed  in  the  Tonoloway  Limestone.  

The  ~35  ft  of  Bick’s  bed  1  of  the  Wills  Creek  comprise  a  distinct  unit  in  the  middle  of  the  McKenzie   Formation   as   we   currently   delineate   it,   of   thin   bedded   ostracode-­‐rich  packstones   and   grainstones,   and   interbedded   platy   fine-­‐grained   sandstones,   siltstones,  and  shales,  many  of  which  are  calcareous.        The  dark  gray,  quartzose  oolitic  grainstones  form  prominent  ledges  along  S.R.  678  and  in  the  sides  of  the  gorge,  and  they  comprise  the  basal  beds  of  the  McKenzie  Formation  in  this  area.    Their  presence  here  makes  this  the  easternmost  exposure  known  of  the  oolitic  facies  that  in  the  subsurface  to  the  west  comprise  the  upper  beds  of  the  Lockport  Member  of  the  McKenzie  Formation.    These  exposures  of  oolitic  limestones  in  the  gorge  of  the  Bullpasture  River  and  along  nearby  Tower  Hill  Mountain   form  prominent   ledges  that  total  ~25  ft  (8  m)   in   thickness   here   along   State   Road   678,   which   could   be   of   some   significance   in   the  search  for  hydrocarbons  in  the  Silurian  of  this  region  as  discussed  below.  

   5. Although  not  included  in  Bick’s  1962  section,  Hunter  (1960)  included  in  his  section  the  lower  part  

of  the  exposure  down  to  the  upper  shaly  beds  of  the  Rose  Hill  Formation.    This  interval  is  in  fact  excellent  exposed,  and  they  include  ~30  ft  (9.5  m)  of  sandy  and  shaley  beds  immediately  beneath  the  lowest  oolitic  grainstone  of  the  McKenzie  Formation,  and  above  the  uppermost  obvious  quartz  arenite  of  the  Keefer  Sandstone.    

This   interval   between   the   top   bed   of   the   Keefer   and   the   basal   oolitic   limestones   of   the  McKenzie  may  represent  the  southernmost  tongue  of  the  Rochester  Shale  in  this  region,  a  unit   that   Woodward   (1941)   identified   in   the   section   we   will   see   at   Stop   5  (Bluegrass/Forks   of   Waters).     Hunter   (1960)   measured   29   feet   of   section;   Covington  (2015)  measured  26  feet  (8  m)  of  section  in  this  interval.    Because  the  upper  boundary  of  the  Rochester  Shale  has  traditionally  been  placed  on  the  basis  of  biostratigraphic  changes  in   the   fossil   content   (Woodward,   1941,   p.   107),   a   practice   now   forbidden   by   the   North  American   Stratigraphic   Code   (North   American   Commission   on   Stratigraphic  Nomenclature,  1983,  2005),   these  shaly  beds  are   included   in  the  McKenzie  Formation  at  this  section  until  further  work  might  be  carried  out  at  this  and  other  exposures.  

 6. Below  this  shaley  interval  that  may  or  may  not  represent  the  Rochester  Shale  are  ~30  ft  (9  m)  of  

massive  quartz  arenite  ledges,  the  lower  ledges  in  particular  being  notable  for  prominent  channel  form  structures.    Hunter  (1960)  measured  31  ft  of  Keefer;  Covington  (2015)  measured  33  ft  (10  m)  of  Keefer  (Fig.  E;  Fig.  4-­‐1a).    This  is  the  true  Keefer  Sandstone,  and  its  measured  thickness  here  equals  the  greatest  reported  in  this  region  (Woodward,  1941,  p.  104).    The  Keefer  is  exposed  here  

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in  its  entirety  along  S.R.  678  and  in  the  gorge  behind  us,  where  it  makes  a  prominent  chute  in  the  river   that,   not   unlike   Beaver   Dam   Falls   just   downriver,   is   also   well   known   to   canoeists   and  kayakers  who  enjoy  traversing  the  gorge.  

This  exposure  of  the  Keefer  shows  the  typical  character  of  the  Keefer  in  much  of  the  mid-­‐Atlantic   region,   yet   this   exposure   represents   the   southern   edge   of   an   extensive   area   in  which   the  Keefer   is   greatly   reduced   in   thickness   or   is   absent.       Our   recent   and   ongoing  mapping   in   the   adjacent   Monterey   SE   7½   minute   quadrangle   (Haynes   and   Diecchio,  2013)   shows   that   the   Keefer   is   not   a   mappable   unit   in   that   area,   nor   is   it   even  recognizable  as  a  distinct   ledge-­‐former  as   it   is  here.    As  a  result,   the  McKenzie  and  Rose  Hill  were  lumped  together  on  account  of  a  lack  of  obvious  lithologic  differences  that  could  be   used   to   separate   the   shales   of   the   upper   Rose   Hill   from   the   shales   of   the   overlying  McKenzie.    Farther  north  in  West  Virginia,      

7. Several  tens  of  ft/m  of  the  Rose  Hill  Formation  are  exposed  beneath  the  Keefer  along  S.R.  678,  and  they  include  shales  and  siltstones  as  well  as  the  typical  reddish  purple  sandstones  of  the  Rose  Hill  (Fig.  E;  Fig.  4-­‐1a).    Beyond  where  we  will  examine  the  Rose  Hill  is  a  small  fault  in  these  sandstones  that  will  be  pointed  out  as  we  drive  past  it.  

    With   the   above   reinterpretations,   the   heterogeneous   nature   of   the   McKenzie   at   this   exposure  becomes  apparent,  as  do  the  regional  facies  changes  in  this  interval  from  Stop  1  (Eagle  Rock)  to  here.    The  thick   “Eagle  Rock  sandstone”  has  split   into   three  distinct   sandstones   (Williamsport,  McKenzie,  Keefer),  and  thick  beds  of  limestone  and  mudrock  have  appeared  in  the  intervals  between  these  sandstones.    And  there  is  little  or  no  Wills  Creek  Formation  here.      Potential  Significance  of  the  McKenzie  Oolitic  Grainstones     The  oolitic  grainstones  in  the  McKenzie  Formation  here  along  the  Bath–Highland  County  line  are  stratigraphically  below  the  unnamed  middle  sandstone  member  of  the  McKenzie,  in  contrast  to  the  oolitic  carbonates   in   the   Lockport   Member   farther   west   that   overlie   the   middle   sandstone.     Thus   we   have  concluded  (Haynes  et  al.,  2014)  that  these  oolitic  limestones  represent  an  older  and  earlier  –  perhaps  the  earliest?  –  development  of   the  oolitic   facies   that   in   the  subsurface  of  West  Virginia   to   the  west  of  here  comprises  the  upper  part  of  the  Lockport  Member  of  the  McKenzie  (Patchen  and  Smosna,  1975;  Smosna  and  Patchen  1978;  Smosna,  1984).         Petrographic   study   of   thin   sections   (Fig.   E)   of   these   oolitic   grainstones   and   related   bioclastic  grainstones  from  the  exposures  here  along  S.R.  678  and  from  Lower  Gap  several  miles  to  the  west  of  here  (Haynes  et  al.,  2014)  indicate  that  dolomitization  has  not  been  as  pervasive  in  this  area  as  in  many  of  the  cores  described  by  Smosna  (1984).    Nonetheless,   the  cementation  history  of   these  oolitic  carbonates   is  complex,   with   a   later   diagenetic   ferroan   baroque   dolomite   (Spötl   and   Pitman,   1998)   that   effectively  reduced  any  remaining  interparticle  pore  spaces  in  these  sediments.    The  presence  of  baroque  dolomite  in  these  and  other  Silurian  and  Devonian  carbonate  strata  of   this  region  (Dorobek,  1987;  Haynes  et  al.,  2011)  is  evidence  that  these  strata  have  been  in  the  oil  window  (Spötl  and  Pitman,  1998).    There  is  a  long  history   of   natural   gas   production   in   the   central   Appalachian   basin   from   the   Lockport   oolite   facies  (Patchen  and  Smosna,  1975)  and   from  the  Williamsport  Sandstone  as  well.    Patchen  (1974)  noted  that  thicknesses  of  the  Williamsport  Sandstone  were  inversely  proportional  to  the  thickness  of  the  underlying  McKenzie  Formation.    Given  the  proximity  of  these  McKenzie  exposures  in  the  Bullpasture  River  Gorge  to  the  scattered  gas  production  in  neighboring  Pocahontas  County  (Limerick  et  al.,  2005),  further  study  of  these  units  may  be  warranted  at  some  future  time  for  their  potential  to  assist  in  identification  of  drilling  prospects  in  the  Silurian  of  this  area.        Regional  Stratigraphic  Relations  of  the  Silurian  Sandstones     Figure   A,   a   cross   section  modified   from  Diecchio   (1986)   by   the   addition   of  much   stratigraphic  

  34  

information   obtained   since   2009,   shows   a   major   part   of   the   Silurian   sequence   in   this   area   from  Montgomery   County,   Virginia,   to   Pendleton   County,   West   Virginia.     The   section   in   the   gorge   of   the  Bullpasture  River  is  now  included.         This  cross  section  adds  greatly  to  our  understanding  of  how  the  sandstones  that  are  so  prominent  to  the  south,  as  we  saw  at  Stop  1  (Eagle  Rock),  change  facies  laterally  north  of  Muddy  Run.    The  exposures  here   in   the   gorge   of   the   Bullpasture   have   helped   us   understand   what   happens   in   a   generally   south-­‐southeast   to   north-­‐northwest   direction   to   (1)   the   Keefer   Sandstone,   (2)   the   prominent   –   but   as   yet  unnamed  –  middle  sandstone  member  in  the  McKenzie  Formation,  and  (3)  the  Williamsport  Sandstone,  as  each  of  these  formations  is  traced  northward  into  this  region.    The  exposures  in  the  gorge  also  confirm  how   thin   the  Wills   Creek   Formation   is   in   this   region   (Fig.   A),   and   the   nature   of   its   apparently   abrupt  thinning   south   of   the   exposure   we   will   see   at   Stop   5   (Bluegrass/Forks   of   Waters),   in   northernmost  Highland  County.         Our  stratigraphic  work  in  the  gorge  has  confirmed  which  Silurian  sandstones  are  present  on  both  limbs   of   the   Bullpasture   Mountain   anticline.     The   Williamsport   Sandstone   is   confirmed   (Fig.   E),   and  identification   of   the   next   sandstone   stratigraphically   downsection   is   confirmed   as   the   unnamed  sandstone  member  of  the  McKenzie  Formation  (Fig.  E),  which  forms  the  prominent  ledge  at  Beaver  Dam  Falls  and  which  Whitehurst  (1982)  recognized  in  the  section  along  Muddy  Run  (southwest  of  Burnsville)  as   shown   by   Diecchio   (1986)   and   in   Figure   A.   Recognition   of   this   McKenzie   sandstone   here   in   the  Bullpasture  River  Gorge  and  at  Trimble  in  central  Highland  County  significantly  extends  its  known  extent.    The  stratigraphically  lowest  quartz  arenite  in  the  gorge  is  the  Keefer  Sandstone  (Fig.  E).          Figure   D   shows   annotated   aerial   views   of   the   west   (Fig.   D1)   and   east   (Fig.   D2)   limbs   of   the  Bullpasture  Mountain  anticlinorium  where  the  river  has  cut  through  that  regionally  extensive  structure  to  form  the  gorge,  with  key  stratigraphic  units  identified  by  Haynes  on  the  basis  of  a  two-­‐day  traverse  of  the  gorge  with  Rick  Lambert  and  Phil  Lucas  in  2010.    The  section  here  along  S.R.  678  is  immediately  west  of  these  ledges  in  the  river  that  are  prominent  on  the  aerial  view  in  Figure  D2.    

             Cumulative  Trip     Point  to  Point       Mileage              Mileage         Directions  and  Comments      

       96.6                      0.0     Load  buses  in  pullout  across  from  the    Keefer-­‐McKenzie  contact,  and  continue    north  along  S.R.  678  through  the    Bullpasture  Gorge  into  the  broad  valley  of    the  Bullpasture  River  where  it  flows  along  a  syncline  that  is  floored  with  Devonian      

  shales.      

       99.3                      12.7     Junction  of  S.R.  678  and  U.S.  250  in    McDowell.    Turn  left  (west)  on  U.S.  250    toward  Monterey.    

       104.8                    9.5     Junction  of  U.S.  250  and  U.S.  220  in    Monterey.    Turn  right  (north)  on  U.S.  220.    

         111.2                    6.4     Junction  of  U.S.  220  and  S.R.  642  (Bluegrass  

Valley  Road)  at  Forks  of  Waters.    Turn  left  onto  S.R.  642  toward  Bluegrass.    

         111.9                    0.7     Unload  buses  across  from  low  exposure    

along  right  (north)  side  of  S.R.  642.  

  35  

 STOP  5  –  Bluegrass  and  Forks  of  Waters    Location:  38.483997  N,  79.516853  W,  Monterey  7½  minute  quadrangle    Units:  Juniata  Formation,  Tuscarora  Formation,  Rose  Hill  Formation,  Keefer  Formation  ironstones,  McKenzie  Formation,  Williamsport  Sandstone,  Wills  Creek  Formation,  Tonoloway  Limestone         At  this  long  and  discontinuous  exposure  along  S.R.  642  (Fig.  5-­‐1)  we  will  start  at  the  exposure  of  the  Keefer  and  walk  upsection  along  the  road  to  the  Wills  Creek  –  Tonoloway  contact.    If  there  is  time,  we  may  see  the  Tuscarora  Formation  and  exposures  of  the  Rose  Hill  Formation  as  well.      

   Figure  5-­‐1.  Sketch  of  the  exposure  along  S.R.  642  (VA  642  in  figure)  in  northern  Highland  County  between  Forks   of  Waters   and   Bluegrass   (Stop   5),   showing   formational   boundaries   of   the   stratigraphic   units   and  selected  lithologic  features.    Compare  the  thickness  of  the  Williamsport  Sandstone  here  with  the  “Eagle  Rock  sandstone”  at  Stop  1  (Fig.  A).    The  Williamsport  and  a  thinner  sandstone  in  the  Wills  Creek  Formation  (Fig.  A)  are  the  only  quartz  arenites  at  this  location  that  equate  to  the  stratigraphic  interval  that  is  occupied  by  the  “Eagle  Rock  sandstone”  at  Stop  1;   the  Keefer  and  McKenzie  have  changed   facies   into  other   lithologies  (modified  from  Figure  10  of  Diecchio  and  Dennison,  1996).       The   first   strata   we   will   examine   include   thin   oolitic   and   quartz   bearing   ironstones   that   are  cemented  with  ferroan  dolomite  (Fig.  5-­‐2A).    These  are  a  thin  example  of  the  regionally  extensive  Clinton  iron   ore   lithofacies   of   the   Silurian   in   the   Appalachians   (Hunter,   1960),   and   which   includes   the  Birmingham,  Alabama  ironstones  as  well  as  the  Clinton  ironstones  of  New  York.    Associated  with  these  thin   oolitic   ironstones   are   ~   8   ft   (2.5   m)   of   fine-­‐grained   and   thin-­‐bedded   quartz   sandstones   that  

  36  

represent  and  are  correlative  with  the  Keefer  Sandstone  (Hunter,  1960),  but  which  here   is  really  not  a  sandstone   at   all,   but   a   thin   sequence   of   sandy   ferroan   dolomites,   and   associated   shales   and   oolitic  ironstones.    So  from  Stop  4  (Williamsville)  to  here,  the  ~32  ft  of  massive  quartz  arenites  that  comprise  the   Keefer   Sandstone   has   changed   facies   into   these   thin   and   finer   grained   sandy   dolomites   and  ironstones.    

   Figure  5-­‐2.  Selected  stratigraphic  units  exposed  at  Bluegrass/Forks  of  Waters  (Stop  5).    A.  Thin   ledges  of  sandy  ferroan  dolomite,  oolitic  ironstones,  and  shales  that  constitute  the  whole  of  the  Keefer.    B.  Shaly  lime  mudstones  and  platy   calcareous   shales   in   the  McKenzie  Formation.     C.  Contact  between   the  Williamsport  Sandstone  and  the  underlying  greenish  shales  of  the  uppermost  McKenzie  Formation.      D.  Channel  and  cross-­‐bedding  in  the  Williamsport  Sandstone.    E.  Thin  quartz  arenite  bed  in  the  upper  Wills  Creek  Formation;  this  bed   contains   abundant   ostracode   debris.     F.   Contact   between   the  more   resistant   limestones   of   the   lower  member   of   the   Tonoloway   Limestone   above   and   the   less   resistant   shales   and   shaly   limestones   of   the  underlying  Wills  Creek  Formation.  

  37  

  In   the  mostly   covered   interval   upsection   from   the   ironstones   are   scattered   exposures   of   shaly  limestones  and  calcareous  shales  of  what  Hunter  (1960)  and  Helfrich  (1975,  1980)  identified  as  the  ~25  ft  (7.5m)  thick  Rochester  Shale,  and  above  that  are  the  likewise  poorly  exposed  shaly  limestones  of  the  ~180   ft   (70   m)   thick   McKenzie   Formation   (Fig.   5-­‐2B),   although   an   accurate   measurement   of   the  McKenzie  is  difficult  to  obtain  here.    The  ~24  ft  thick  middle  sandstone  member  of  the  McKenzie  that  is  present  at  Stop  4  and  which  makes  such  a  prominent  ledge  in  the  Bullpasture  River  Gorge  has,   like  the  Keefer   Sandstone   downsection,   changed   facies   into   a   sequence   of   recessively  weathering   fine-­‐grained  limestones  and  mudrocks.         The  contact  of  the  McKenzie  and  the  overlying  Williamsport  Sandstone  is  well-­‐exposed  (Fig.  5-­‐2C),  as  is  the  entirety  of  the  ~30  ft  (9  m)  thick  Williamsport  Sandstone.    The  uppermost  beds  of  the  McKenzie  include  greenish  mudrocks  that  are  not  very  fissile,  but  which  weather  into  small  blocks,  and  which  are  mottled.    These  may  be  paleosols,  but  further  study  is  needed.     The  Williamsport  Sandstone  here  exhibits   its   typical  character   in   thickness,   lithology,  and  color.    Sedimentary  structures   include  a  prominent  channel  with  cross-­‐bedding  (Fig.  5-­‐2D).    A   few  ostracodes  and  ostracode  molds  can  be  found  in  some  of  the  beds.     Above   the   Williamsport   is   a   discontinuous   exposure   of   the   ~215   ft   (65   m)   thick   Wills   Creek  Formation,  which  here  is  a  heterogeneous  sequence  of  limestones,  mudrocks,  and  thin  sandstones  (Fig.  5-­‐2E).     There   are   numerous   sedimentary   structures   in   the   beds   including   gutters,   scours,   domal  stromatolites  and  cryptalgalamination,   small-­‐scale  hummocky(?)   cross-­‐stratification,   load   casts,   ripples  of   various   scales,   ball   and   pillow   structures,   lenticular   bedding,   and   intraclast   (“flat   pebble”)  conglomerates  (Fig.  5-­‐3).    In  the  upper  Wills  Creek  there  is  a  prominent  medium-­‐grained  calcarenaceous  quartz  arenite  that  consists  principally  of  monocrystalline  quartz  grains  and  ostracode  shell  fragments.     The  contact  of  the  Wills  Creek  and  the  overlying  Tonoloway  Limestone  is  abrupt  (Fig.  5-­‐2F),  and  is  placed  at  the  uppermost  shale  and  shaly-­‐weathering  beds  of  the  Wills  Creek;  the  overlying  limestones  of  the  lower  member  of  the  Tonoloway  are  thin  to  medium  bedded  but  massively  weathering  here,  where  they   form  a  nearly   vertical   cliff   along   the   road.     All   of   the  Tonoloway   exposed   along   S.R.   642   to   its  T-­‐intersection   with   U.S.   220   are   limestones   of   the   lower   member;   the   calcarenaceous   sandstone   at   the  contact  of  the  lower  and  middle  members  is  exposed  about  0.3  miles  north  on  U.S.  220  on  a  hillside  on  the  west  side  of  the  highway,  and  there  it  is  about  half  the  thickness  as  what  we  observed  at  Stop  3.        

             Cumulative  Trip     Point  to  Point       Mileage              Mileage         Directions  and  Comments      

       111.9                    0.0     Load  buses  in  pullout  by  Tonoloway    Limestone  on  north  side  of  road,  and    retrace  route  to  McDowell  (east  on    S.R.  642  to  U.S.  220,  turn  south  on  U.S.  220    to  Monterey,  then  turn  east  on  U.S.  250)  Continue  on  U.S.  250  toward  Staunton,  then    turn  south  on  S.H.  262  around  Staunton    to  its  junction  with  I-­‐  81,  then  take  I-­‐81    south  back  to  Natural  Bridge.          

         209.5                    97.6     Arrive  at  Natural  Bridge  Hotel.  

     

 END  OF  ROAD  LOG  

 

  38  

   Figure  5-­‐3.  Sedimentary  structures  in  selected  measured  intervals  of  the  Wills  Creek  Formation  at  Bluegrass/Forks  of  Waters  (Stop  5;  Bryant,  2014).      

  39  

   Figure   5-­‐3   (cont’d).      Collectively,   the  presence  of   stromatolites,  microbial   laminates,  gutters  and  scours,  ripples,   and   wavy   and   lenticular   bedding   suggests   that   deposition   occurred   in   tidal   flat   to   nearshore  environments,  ranging  from  supratidal  to  shallow  shelf.      

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                                                                       Figure  E  (inside  back  cover).  Silurian  stratigraphic  units  in  the  Bullpasture  River  Gorge  at  Williamsville  that  we   will   see   at   Stop   4.     Arrows   indicate   where   in   the   section   the   photographs   were   taken,   and   which  stratigraphic  unit  is  shown.    Top  row:  Williamsport  Sandstone  with  ripple  marks  on  several  bedding  planes  (right  photo).    Second  row:  laminated  limestones  in  the  upper  McKenzie  Formation  that  are  very  much  like  typical   limestones   of   the   lower   and   upper   members   of   the   Tonoloway   Limestone.     Third   row:   Middle  sandstone  member  of  the  McKenzie  Formation,  with  Rick  Lambert  (right  photo)  on  the  middle  sandstone  at  Beaver  Dam  Falls   in   the  bed  of   the  Bullpasture  River.    Fourth  row:  Sandy  oolitic  grainstones  of   the   lower  McKenzie  Formation  in  outcrop  (left  photo)  and  thin  section  (right  photo).    Fifth  row:  Keefer  Sandstone  with  large  scours  (left  photo);  Rick  Lambert  and  Phil  Lucas  (right  photo)  on  the  Keefer  Sandstone  in  the  bed  of  the   Bullpasture   River.     Bottom   row:   Rose   Hill   Formation   with   typical   ferruginous   reddish   purple   quartz  sandstones   along   fault   exposed   on   S.R.   678   (left   picture);   Phil   Lucas   (right   photo)   at   a   cliff   of   Rose   Hill  Formation   along   the   south   bank   of   the   Bullpasture   River   in   the   gorge.     Measured   section   at   left   from  Covington  (2015).      

Figure E.

Figure F. Google Earth aerial map of west-central Virginia showing the �eld trip route outlined in red, and the �eld trip stops indicated with red placemarks and labeled with the stop name. Inset (upper left) shows the regional location.