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SEDIMENTARY ROCKSSEDIMENTARY ROCKS

SEDIMENTSEDIMENT ––unconsolidatedunconsolidated ((““looseloose””) ) granular geologic materialgranular geologic material

SEDIMENTARY ROCKSEDIMENTARY ROCK ——lithifiedlithified granular granular geologic materialgeologic material

SEDIMENTSEDIMENT

Comes from:Comes from:–– Physical weatheringPhysical weathering which creates particles which creates particles –– Chemical weatheringChemical weathering which creates solutions which creates solutions

Sediment is unconsolidatedSediment is unconsolidated

Sedimentary ProcessesSedimentary Processes

ParticlesParticles are transported and deposited; are transported and deposited; solutionssolutions are transported and precipitatedare transported and precipitated

Weathered and eroded material transported from Weathered and eroded material transported from higher to lower places higher to lower places

SEDIMENTSEDIMENT

TransportationTransportation–– Grain sizeGrain size–– RoundingRounding–– SortingSorting

http://www.uwrf.edu/~iw00/101gr/rounding.gif

Sediment sorting by a riverSediment sorting by a river

Sorting = process by which particles having a particular size or characteristic are selected or concentrated. Which processes result in poorly-sorted sediment?

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Sedimentary ProcessesSedimentary Processes

ENVIRONMENTS of depositionENVIRONMENTS of deposition–– MarineMarine-- most abundantmost abundant–– TerrestrialTerrestrial

Common Depositional EnvironmentsCommon Depositional Environments

Marine shoreline and nearMarine shoreline and near--shore shore environmentsenvironments

River River

Braided streamBraided stream

Anastamosing channels—caused by sediment overload

Sediment moves downstream via migrating bars and in suspension during flood events

Alluvial fan deposits (terrestrial)Alluvial fan deposits (terrestrial)

Badwateralluvial fanMarli Miller

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SEDIMENTSEDIMENT

Particle sizeParticle size–– Gravel Gravel (> 2 mm)(> 2 mm)-- Pebbles, cobbles, bouldersPebbles, cobbles, boulders–– Sand Sand (2 mm to 1/16 mm)(2 mm to 1/16 mm)

–– Silt Silt (1/16 mm to 1/256 mm)(1/16 mm to 1/256 mm)

–– Clay Clay (< 1/256 mm)(< 1/256 mm)

•• Deposition Deposition ClayClay--sizedsized particle vs. particle vs. clay mineralclay mineral

ClasticClastic

TYPES OF SEDIMENTARY TYPES OF SEDIMENTARY ROCKS ROCKS

Clastic Clastic –– fragments accumulatefragments accumulateChemical Chemical –– precipitates accumulateprecipitates accumulateOrganic Organic –– biogenic, lumped w/ biogenic, lumped w/ chemchem in bookin book

Common Sedimentary Rocks (Clastic)Common Sedimentary Rocks (Clastic)

CONGLOMERATECONGLOMERATE--–– From GRAVELFrom GRAVEL-- coarse coarse roundedrounded fragmentsfragments……

BrecciaBreccia–– From GRAVELFrom GRAVEL-- coarse coarse angularangular fragmentsfragments……

SANDSTONESANDSTONE--–– From SANDFrom SAND-- (1/16 mm to 2 mm)(1/16 mm to 2 mm)……

SHALESHALE--–– From SILT or CLAY (mud)From SILT or CLAY (mud)–– Most common sedimentary rockMost common sedimentary rock

ConglomerateConglomerateBrecciaBreccia

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SandstoneSandstone

Bondi Beach

<=Ss thin

section

Note: can’t see grains—feels smooth to the touch; if it contains some silt particles, then call it either a silty shale or mudstone (if 50/50 silt/clay)

LithificationLithification

CompactionCompactionCementationCementation–– Cement deposited by Cement deposited by groundwatergroundwater–– Cement most commonly calcite (CaCOCement most commonly calcite (CaCO33))–– Less commonly silica (SiOLess commonly silica (SiO22))–– Iron oxide (hematite) when redIron oxide (hematite) when red

Lithification (compaction and cementation)Lithification (compaction and cementation)

Lithification of ShaleLithification of Shale Shale outcropShale outcrop Bedford Shale, Cuyahoga River valley, Ohio, Mississippian age

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Chemical sedimentary rocksChemical sedimentary rocks

Bioclastic limestone

ChalkChalk

A soft marine limestone formed from the tests of many tiny

protozoans, mainly foraminifers (aka “forams”)

Other Sedimentary RocksOther Sedimentary RocksCOALCOAL–– partial decay of plantspartial decay of plants–– important fossil fuelimportant fossil fuel

SEDIMENTARY STRUCTURESSEDIMENTARY STRUCTURES

BEDDINGBEDDING--–– Bedding planeBedding plane——an an interuptioninteruption in depositionin deposition

Principle of Original HorizontalityPrinciple of Original HorizontalityPrinciple of SuperpositionPrinciple of Superposition

Bedding in sandstone and shale, Utah

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Bedded chert from CA coast ranges Peat layers, lahar deposits, and tephra east of EnumclawPeat layers, lahar deposits, and tephra east of Enumclaw

Still sediment—not yet lithified!

Coal beds in Puget Group sedimentary rocks near AshfordCoal beds in Puget Group sedimentary rocks near Ashford

Channel fillChannel fill Sharon Conglomerate, Cuyahoga River valley, Ohio

~315 ma

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Tilted beds

What does the principle of “original horizontality” tell you about the

history of these sedimentary strata?

Lava over sediment:Lava over sediment:Tieton Andesite lava flow (1 Tieton Andesite lava flow (1 Ma) from Goat Rocks Ma) from Goat Rocks volcano over fluvial gravel volcano over fluvial gravel along US 12 west of Nachesalong US 12 west of Naches

SEDIMENTARY STRUCTURESSEDIMENTARY STRUCTURESThese features are indicators of processes and These features are indicators of processes and environmentsenvironments

CROSSCROSS--BEDDING (BEDDING (\\\\\\\\\\\\):):–– Deposited by sand dunes via wind (terrestrial) Deposited by sand dunes via wind (terrestrial) –– Deposited by river dunes (ex: in deltas)Deposited by river dunes (ex: in deltas)

GRADED BEDDINGGRADED BEDDING–– Caused by Caused by turbidity currents or by pulsing flow (glacial turbidity currents or by pulsing flow (glacial

outwash)outwash)MUD CRACKS MUD CRACKS RIPPLE MARKS RIPPLE MARKS ≈≈ ≈≈ ≈≈ ≈≈FOSSILSFOSSILS

MSOffice1

How crossbeds formHow crossbeds form——migrating dunes!migrating dunes!

Crossbedded sandstone

Zion National Park. Festooned cross beds deposited by wind.

Planar cross bedsPlanar cross beds

Sharon Conglomerate, lower Pennsylvanian Age (~315 Ma), Cuyahoga River valley, Ohio; braided stream environment

Slide 39

MSOffice1 , 2/13/2008

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Crossbeds in dipping layers of Ohanapecosh formation, volcaniclastic rocks; SR 165 west of Mt. Rainier

Turbidity currentsTurbidity currents

D:\digital_content\animations_library\0009.swf

Deposited by one turbidity current

Miocene Hoh Fm. Beach 4, Olympic CoastMiocene Hoh Fm. Beach 4, Olympic CoastUpside down graded beds!

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Mud up to 3 ft thick sits in fields, around homes and on roads in and around Curtis —and it's starting to dry up. Occupants of this Ceres Hill Road home are burning their furniture and belongings destroyed by the flood. STEVE RINGMAN / SEATTLE TIMES

Modern mud Modern mud crackscracks

Ancient mud Ancient mud cracks in shalecracks in shale

RipplesRipples

Current ripples in wet sediment, Current ripples in wet sediment, Baja CABaja CA

Ripple marks in sandstone, Capitol Ripple marks in sandstone, Capitol Reef National Park, UtahReef National Park, Utah

Ripple marks in tilted Puget Group sedimentary rocks Ripple marks in tilted Puget Group sedimentary rocks of Eocene age near of Eocene age near WilkesonWilkeson WAWA

Pat Pringle, photo

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FossilFossil

……the remains of an organism the remains of an organism preserved in rock. May consist of preserved in rock. May consist of original mineral matter, petrified original mineral matter, petrified organic material, or an impression left organic material, or an impression left behind.behind.

Above: Fossil fish from Eocene Green River Shale in western Wyoming

www.fossilmuseum.net

Trilobite - species Chancia, order Ptychopariida, Cambrian Addy Quartzite, WA; David Morgan photo; www.westernta.com

Fossil flower: Eocene, Republic WAFlorissantia uilchenensis

Ammonites (Cephalopods)

Photos courtesy of R, Weller, Photos courtesy of R, Weller, Cochise CollegeCochise College

http://www.mmf.selcuk.edu.tr/personel/falkaya/paleolab/bivalvia.htm

Inoceramus

cyanocacteria

www.fossilmuseum.net

Marrella: Burgess Shale, Univ. of Calgary

Wiwaxia, Pam Gore, gpc.edu

Brachiopod

Fossil Fossil metasequoiametasequoia leaf from rocks leaf from rocks several miles east of Packwood, several miles east of Packwood,

Oligocene ageOligocene age

Dinosaur footprints, USGS

http://paleo.cc/paluxy/ovrdino.htm Glen

Kuban’s site

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Subfossil Douglas fir buried by Round Pass lahar Subfossil Douglas fir buried by Round Pass lahar from Mount Rainier along the Nisqually River (2.6 ka)from Mount Rainier along the Nisqually River (2.6 ka)

Misc. Sedimentary FeaturesMisc. Sedimentary Features

SortingSortingRoundnessRoundnessOrientation: random vs. preferredOrientation: random vs. preferredColorColor

SortingSorting Preferred orientationPreferred orientation——shows current directionshows current directionImbrication = strong current

<= Current direction = right to left

ColorColor

Red = oxidation (ex: hematite, Red = oxidation (ex: hematite, ““red bedsred beds””——most of these are subaerial)most of these are subaerial)Green = near oxidation/reduction margin Green = near oxidation/reduction margin (ex: (ex: glauconiteglauconite, chlorite), chlorite)Black = reducing conditions (ex: pyrite, Black = reducing conditions (ex: pyrite, MnOMnO22, organic matter), organic matter)

A function of size and composition

Finer grained = truer colors

Weathering & matrix cement also influenceRock UnitsRock Units

FORMATIONFORMATION--–– A geologic unit extensive enough to show on a A geologic unit extensive enough to show on a

mapmap–– Distinctive from neighboring rock unitsDistinctive from neighboring rock units–– Named locally, ex: Ohanapecosh FormationNamed locally, ex: Ohanapecosh Formation

CONTACTSCONTACTS–– Sedimentary contacts Sedimentary contacts –– bounding surfaces bounding surfaces

between two sedimentary unitsbetween two sedimentary units

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UnconformitiesUnconformities——missing time!missing time!

Angular unconformityAngular unconformity –– horizontal beds horizontal beds atop tilted bedsatop tilted beds……DisconformityDisconformity –– horizontal beds atop other horizontal beds atop other horizontal beds, but missing time in horizontal beds, but missing time in betweenbetween……NonconformityNonconformity –– sedimentary rocks atop sedimentary rocks atop igneous or metamorphic rocksigneous or metamorphic rocks

Angular unconformity

Monument Creek, Grand CanyonMonument Creek, Grand Canyon

Bob Webb, photo, 1986

Granite Rapid, Grand CanyonGranite Rapid, Grand Canyon

Bob Webb, photo, 1986

Grain size, sorting, and angularity in

Tenino Sandstone

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Troutdale Formation Wildcat Creek bedsUS 12 near Rimrock Lake

Centralia Coal Mine—Skookumchuck

Formation