P I T I

D E D E D O

Y I G O

MA

NG

IL

AO

M A N G I L A O

TA

LO

FO

FO

IN

AR

AJ

AN

B A R R I G A D A

T A MU N I N G

MONGMONG- TOTO- MAITE

HA

GA

TN

A

HE

I GH

TS

A S A N

S I N A J A N A

Y O N A

UM

AT

AC

A G A T

SA

NT

A

RI

TA

ME

RI Z

O

~o

Ritidian Pt.

Pati Pt.

Facpi Pt.

Orote Peninsula

C H A L A N PAGO-O

RD

OT

A P R A H A R B O R

o~

AG

AT

BA

Y

C O C O S L A G O O N

P H I L I P P I N E

SE

A

OC

EA

N

PA

CI

FI

C

P A G O

B A Y

T A L O F O F O

B A Y

T A R A G U E

T UM

O

N

BA

Y

H A G A T NA

BA

Y

INDEX TOSECTION LOCATION

SAIPAN

TINIAN

ROTA

GUAM

LOCATION DIAGRAM

MARIANAISLANDS

QTmrQTma

TalTt

Tb

Tm

Tub

Tam

Ta

TuTu

QTmm

QTmd

Tbl

TbTj

Qal Qal

QTma

QTma

QTmrQTmr

Qal

TalTal

Ta

Ta

Ta

Tf

Tug

Tug

Tus

Tub

0 1 21 3 4 MILE

GENERALIZED GEOLOGY OF GUAM, MARIANA ISLANDSH.G. Siegrist, Jr. and Mark K. Reagan

Field interpretations assisted by Richard H. Randall and John W. JensonBased on Tracey et al., 1964

2008

Funded byWATER & ENVIRONMENTAL RESEARCH INSTITUTE OF THE WESTERN PACIFIC

through the GUAM HYDROLOGIC SURVEY PROGRAM

1

3

1

2

4

3

1

2

4

COMPOSITE STRATIGRAPHIC SECTIONSComposite stratigraphic sections showing probable vertical bedrock sequence. Maximum limestone section thicknesses, in feet,

shown below in parentheses; formation abbreviations and color consistent with 2008 revision of 1:50,000 geologic map

1 2 3 4

Sections extrapolated from surface geology shown on revised 1:50,000 geologic map of Guam.

Artificial fill—shown only where extensive Reefs—reef platforms of living coral, coralline algae, and reef sediment, raised terraced ramps and pools, and algal encrusted intertidal bedrock outcrops, including basaltic outcrops along the southwest coast and limestone outcrops on the platform margin from Ritidian Point south to Urano Point

Beach deposits (Quaternary)—beach sand and gravel, beach rock in the intertidal zone, and small isolated patches of recently emerged detrital limestone. Sand generally is less than 15 feet above sea level, seldom as much as 30 feet above

Merizo limestone (Quaternary)—emergent Holocene (2,500-4,800 years old) coralgal reef limestones, 2-12 feet thick, capping modern reef flats and platforms. Occurs as intertidal and low-supratidal outcrops. Extensive supratidal outcrops at Tarague (algal-rich), Ylig Point (coral-rich), and Aga Point (detrital-rich). Almost no meteoric diagenetic alteration evidenced in outcrops. Many outcrops, too small to map, occur along SW coast between Merizo and Agat

Alluvium (Quaternary)—alluvial clay deposits, mostly 30-100 feet thick, muck and clay in marshy estuarine deposits on the west coast, scattered sand and gravel bars within deposits near SE river mouths, and clay fill in large sinks in limestone areas

Tarague limestone (Quaternary)—125,000- 135,000 year-old coralgal reef limestone cropping out exclusively in Tarague embayment at +15 to +25 feet elevation. Undergone only partial diagenetic alteration. Rich assemblage of reef corals. Maximum estimated thickness 25 feet

Mariana limestone (Pliocene and Pleistocene)—White, dense, inequigranular, predominantly detrital facies, representing a variety of reef platform and off-reef environments. Coralgal framework, molluscan and Halimeda subfacies locally important. Completely recrystallized, and commonly displays vuggy to cavernous porosity. Dominant rock unit throughout much of northern Guam where it attains thicknesses estimated at between 550 and 600 ft. Major source of quarried aggregate

Hagatna argillaceous member (Pliocene and Pleistocene)—coarse-to fine-grained pale- yellow, tan, or brown fossiliferous detrital limestone containing 2 to 5 percent disseminated clay and as much as 20 percent clay in pockets and cavities; includes undifferentiated lenses of other Limestone facies. Formation typically unconformable upon underlying rocks. Maximum aggregate thickness of formation is as much as 500 feet in some cliffs

Alifan limestone (Miocene and Pliocene)— Massive coarse-to fine-grained recrystallized limstone generally pale pink, buff, or white but locally red, yellow, or brown. Characterized by dominance of sticklike Porites and Acropora and by long calcite tubes formed by burrowing worms or gastrpods. Locally argillaceous above base. Maximum estimated thickness of the Alifan limestone is 150 feet

Talisay member (Miocene)—yellow, green, and red clay and lenticular clayey conglomerate and lignite; gray to green marl containing sticklike Porites and Acropora, and interbedded limestone lenses, 2 to 30 feet thick

Barrigada, Bonya and Janum limestones (Pliocene and Miocene)—Detrital limestones: Janum, pink to tan, somewhat friable, deep-water facies with abundant pelagic forams. Bonya limestone, white, compact, sometimes sandy, well-bedded biomicrite, benthic forams abundant. Frequently displays manganese mineralization. Barrigada limestome, a dead-white, compact to chalky biomicrite featuring coralline red algae, Halimeda, benthic forams as well as corals near the upper contact with the Mariana limestone

Maemong limestone formation (Miocene)—reef facies in central Guam consists of compact white recrystallized limestone containing larger Foraminifera and algae, and corals in position of growth; at some places overlain by the Bolanos pyroclastic member. Outcrop distribution restricted generally to several prominent wooded knolls in the upper Talofofo River valley, many lying within the Talofofo Golfing Resort. The estimated outcrop thickness of the Maemong limestone ranges from less than 10 feet to about 150 feet, although the elevation of the base of the unit is not apparent

MAP SYMBOLS

DESCRIPTION OF MAP UNITS

Basaltic and boninitic dikeFault—Solid where definitely located; dashed whereapproximately located; dotted where concealed

Approximate site of numbered stratigraphic sections shown on accompanying sheet

Umatac formation undifferentiated (Miocene)— unresolved stratigraphic sequences in Umatac formation that encompass sections of Tub, Tug, and/or Tus. Approximate thickness ranges from 200 to 500 feet

Dandan flow member (Miocene)—compact medium- to coarse-grained porphyritic andesite flows separated from the underlying Bolanos pyroclastic member by a flow breccias approximately 10 feet thick; maximum thickness of member 50 feet

Bolanos pyroclastic member (Miocene)— breccias, conglomerates, and sandstones consisting largely of fragmented andesite. These andesites typically have prominant euhedral augite phenocrysts up to 1 centimeter in length and millimeter-scale plagioclase phenocrysts. Limestone clasts are conspicuous in some breccias and conglomerates. Estimated thickness of the Bolanos pyroclastic member ranges from 750 to 1000 feet

Schroeder flow member (Miocene)—basaltic andesite pillow lava with plagioclase, augite and olvine phenocrysts. Volcanic sandstones consisting of clasts derived from the pillow lavas. Interbedded with the uppermost portion of the Schroeder flow member. Estimated thickness of the Schroeder flow member ranges from 100 to 400 feet

Geus River member (Oligocene)—interbedded limestones, sandy and tuffaceous limestones, sandstones and conglomerates. Clasts in sandy units are largely fragmented and altered andesitic volcanics, but also include intraformational limestones including reef limestones not seen in southwestern Guam. Conglomerates with clasts of basalts, andesites and dacites are considered to be near the base of Tug. Estimated thickness of the Geus River member ranges from 250 to 300 feet

Mahlac member of Alutom formation (Eocene and Oligocene)—thin-bedded to laminated friable buff to tan or yellow-tan calcareous formaminiferal shale; maximum known thickness 200 feet

Alutom formation (Eocene and Oligocene)— bedded breccias, conglomerates, sandstones, turbidites, sandy limestones, and micritic to bioclastic limestones. Clasts in the breccias and conglomerates generally are two-pyroxene andesites, although rare olivine phyric basalts and hornblende andesite clasts also are present. Estimated thickness of the Alutom formation ranges from 1850 to 2000 feet

Facpi formation (Eocene)—basal portion consists of high-Ca boninite pillow lavas interbedded with pillow breccias, hyaloclastites, and sandstones of the same lithology. Least differentiated lavas have olivine, augite, and chromite phenocrysts; more differentiated varieties lack chromite and have plagioclase and orthopyroxene phenocrysts. The upper portion consists of pillow lavas, breccias, bedded breccias and conglomerates of arc tholeiitic basalt with olivine, augite, and plagioclase phenocrysts. Boninitic and basaltic dikes cut this formation and are particularly abundant in the region of the Facpi peninsula

Qaf

Qrb

Qrm

Qal

Qt

QTmr

QTma

Tal

Tt

Tm

Tbl

Tu

Tud

Tub

Tus

Tug

Tam

Ta

Tf

Umatac formation (Oligocene-Miocene)Aggregate thickness of formation about 2200 feet

Limestone

Limestone, argillaceous

Limestone, significantmacrofossils

Limestone, significantcoralline framework

Limestone, significant manganese

Limestone, sedimentaryand volcanic (tuffaceous)

Globigerina limestone

Mudstones, siltstones, and shale,sedimentary and volcanic (tuffaceous)

Shale

Cross-bedded strata

Coarse sands and gravel

Conglomerate and agglomerate

Breccia, sedimentaryand volcanic (bedded and random)

Lava flows (pillow lava)

Lava flows(non-pillow lava), (subaerial)

Sill

Major fault

Dike

SYMBOLS

Togcha River ValleyTalofofo Golfing Resort

(QTma+Tal+Tb+Tm=300 feet)SinajanaOrdot

Chalan PagoRoute 4

(QTma+Tal=500 feet)

Mt. Santa RosaBack Gate

Yigo(QTmd+QTmm+Tal+Tb=600 feet) Umatac

Mt. SchroederMerizo area

(Tug=300 feet)

*

*

*

*

GNMN

DECLINATIONDIAGRAM

Mariana Islands Palau Yap Main Islands

Guam Rota Aguijan and Tinian Farallon deMedinilla

Gagel-Tomil, Yap,Maap and RumumgNorthern Islands

Koror and UrukthapelPeleliu and AngaurSaipan

GEOLOGIC FORMATIONS OF HIGH ISLANDS ON THE PHILIPPINE SEA PLATE

Babelthuap

Merizo limestone

Mirakatten limestone (Sugawara)

Rota limestone

Tanapag limestone Tanapag limestone

Ponia limestone

Tarague limestone

Aguijan limestone (Tayama)

Island/submarinevolcanism

Unnamed limestone Peleliu limestone Garim limestone

Mariana limestone Mariana limestone Mariana limestone Mariana limestoneUpper terrace

gravelsPalau limestone

Airai clay/lignite

Alifan limestone

Unnamed limestone

Janum limestone

Barrigada limestone

Talisay shale/lignite

Bonya limestoneFina-sisu

basalt flowsTomil volcanics

Dandan basalticandesite flows

Bolanostuffaceous brecciaagglomerate flows

Geus Riverlimestone (upper)

Schroeder volcanics

Map melangeArakabesan

andesite

Tagpochau limestone Tagpochau

limestone withsandstone member

Maemong limestoneGeus River

limestone (lower)Basaltic sill in

Alutom formationNgeremlengui daciteAimeliik andesite tuff

Ogo andesitesMahlac shale

Alutom volcanicsand volcaniclastics

Matansa limestone

Sabana andesiteDensinyama fm.

Basaltic dikes inFacpi formation

Unnamedvolcaniclastic fm.

Hagman andesitesFacpi formation

Sankakuyamarhyolite Unnamed serpentine

Yap schist/phylliteUnnamed perodotite

PlateRotation

PlateSpreading

VolcanicRidge

EvolutionEpochsPeriods

PALE

OG

EN

EN

EO

GE

NE

Radiometricyears bp

(non-linear)

AGE PHILIPPINE SEA PLATE

106

1.6X106

25X106

53X106

65X106

37X106

5X106 5-0

Ma:

Sp

read

ing

of

the

Mar

ian

a Tr

ou

gh

>60-

40 M

a: O

pen

ing

of

Wes

t P

hili

pp

ine

Bas

in30

-17

Ma:

Sp

read

ing

of

the

Par

ece-

Vel

a B

asin

24-8

Ma:

35-

deg

. Clo

ckw

ise

rota

tio

no

f th

e P

hili

pp

ine

Sea

Pla

te

1.5-

0 M

a: I

slan

d &

su

bm

arin

e vo

lcan

ism

bu

ild E

ast

Mar

ian

a R

idg

e20

-8 M

a: S

ub

mar

ine

& s

ub

aeri

al v

olc

anis

mb

uild

th

e W

est

Mar

ian

a R

idg

e, n

ow

a r

emn

ant

arc

42-3

2 M

a: S

ub

mar

ine

volc

anis

m b

uild

sP

alau

-Kyu

shu

Rid

ge,

no

w a

rem

nan

t ar

c

>50-

38 M

a: 5

0-d

eg. C

lock

wis

e ro

tati

on

of

the

Ph

ilip

pin

e S

ea P

late

Holocene

Pleistocene

Pliocene

Miocene

Oligocene

Eocene

Paleocene

Cretaceous