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
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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
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PA
CI
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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)
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*
*
*
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
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>60-
40 M
a: O
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of
Wes
t P
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Bas
in30
-17
Ma:
Sp
read
ing
of
the
Par
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Vel
a B
asin
24-8
Ma:
35-
deg
. Clo
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ise
rota
tio
no
f th
e P
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pp
ine
Sea
Pla
te
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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
