GEOLOGY OF SAIPAN MARIANA ISLANDS PART 1. GENERAL GEOLOGY

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• Document Creation Date: December 27, 2016
• Document Release Date: October 22, 2013
• Sequence Number: 3
• Publication Date: January 1, 1956
• Content Type: REPORT

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Geology of Saipan
Mariana Islands
Part 1. General Geology
STAT
GEOLOGICAL SURVEY PROFESSIONAL PAPER 280-A
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3
Geology of Saipan
Mariana Islands
Part 1. General Geology
By PRESTON E. CLOUD, Jr., ROBERT GEORGE SCHMIDT, and
HAROLD W. BURKE
GEOLOGICAL SURVEY PROFESSIONAL PAPER 280-A
A study of the nature, field relations, and origin
of the roch succession on this small but complex
western Pacific island, and of its regional setting
and geologic history since _Eocene time
UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1956
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UNITED STATES DEPARTMENT OF THE INTERIOR
Fred A. Seaton, Secretary of the Interior
GEOLOGICAL SURVEY
Thomas B. Nolan, Director
For sale by the Superintendent of Documents, U. S. Government Printing Office
Washington 25, D. C. - Price $3.00 (paper covers)
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qr ?
GEOLOGICAL SURVEY PROFESSIONAL PAPER 280
Geology of Saipan, Mariana Islands
Part 1. General Geology
A. General Geology
By PRESTON E. CLOUD, JR., ROBERT GEORGE SCHMIDT, and HAROLD
Part 2. Petrology and Soils
B. Petrology of the Volcanic Rocks
By ROBERT GEORGE SCHMIDT
C. Petrography of the Limestones
By J. HARLAN JOHNSON
By RALPH J. McCRACKEN
Part 3. Paleontology
E. Calcareous Algae
By J. HARLAN JOHNSON
F. Discoaster and Some Related Microfossils
By M. N. BRAMLETTE
G. Eocene Radiolaria
By WILLIAM RIEDEL
H. Smaller Foraminifera
By RUTH TODD
I. Larger Foraminifera
v v By W. STORRS COLE
J. Echinoids
By C. WYTHE COOKE
D. Soils
Part 4. Submarine Topography and Shoal-Water Ecology
K. Submarine Topography and Shoal-Water Ecology
By PRESTON E. CLOUD, JR.
W. BURKE
Professional Paper 280 is being published in the foregoing sequence of parts and chapters
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CONTENTS
Page
Abstract 1
Introduction 2
Basis and scope of the report 2
Acknowledgments 3
General history of the region 3
Geographic terminology 5
Climate 6
Water resources 6
Land classification
Plants and animals 7
Mineral resources 9
Previous studies 0
Earliest scientific explorations, 1792-1839 9
Mostly dormant interval, 1840-1900 10
Interval 1900-1920 10
Since 1920 13
General comments 14
Regional geology 15
Island arcs of the Philippine Sea margins 15
Affinities of western Pacific borderlands with Asia 18
Origin of the island arcs 90
Geomorphology 20
Introduction and synopsis 20
Nlaterial and structural foundations 21
Prevailing genetic processes and characteristic re-
sults 93
Formation and morphology of benches and
scarps 23
Terrace succession
Terrestrial solution and solution features _ 9.1
General considerations 94
Solution ramparts 95
Caves and sinkholes 95
Lateritic weathering 96
Runoff 96
Stage of development 96
96
Systematic geomorphology
Axial uplands 27
Terraced limestone uplands 27
Volcanic uplands 29
Low limestone platforms 30
Southern platform 30
Eastern platform _______ 31
Northern platform 31
Low terraced benches :31
Magpi benches 31
East coast benches 31
Laulau benches 31
South coast bench and scarp 32
Donni clay hills belt 32
Southeastern coastal fault ridges 32
Hagman ridge 32
Naftali ridge 32
Western coastal plain 33
Coastline, beaches, and offshore features 33
Geologic succession
Introduction and synopsis
Petrographic terminology
Primary volcanic rock types
Rocks and sediments as field associations
Reference to localities
Thickness estimates
Supposed Eocene
Sankakuyama formation
Description of the formation_
Supplementary descriptions of mapped
facies
Massive dacite flow rock_
Vitrophyric and perlitic dacite breccia_
Dacitic tuffs
Mixed dacitic pyroclastics
Eocene
Hagman formation
Description of the formation..
Supplementary descriptions of mapped
facies
Andesite flow rock
Breccia-tuff facies
Conglomerate-sandstone facies
Densinyama formation
Description of the formation
Supplementary descriptions of mapped
fades
Breccia facies
Conglomerate-sandstone facies___ _
Limestone-conglomerate facie-
Matansa limestone
Description of the formation
Supplementary descriptions of mapped
facies
Basal transitional facies
Pink facies
White facies
Oligocene
Fina-sisu formation
Miocene
Tagpochau limestone
Description of the formation
Supplementary descriptions of mapped
subdivisions
Doimi sandstone member
Machegit conglomerate member
Transitional facieq
Tuffaceous facies
Marly facies
Thick residual clays over tuffaceous
and marly facies
Rubbly fades
Equigranular facies _
Tnequigranular facies
Sismondia beds
Page
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IS
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VI
Geologic succession-Continued
Pliocene(?)
Older terrace deposits
Description of the unit
Supplementary descriptions of mapped
subdivisions
Pleistocene
Mariana limestone
Description of the formation
Supplementary descriptions of mapped
subdivisions
Rubbly facies
Thick residual clays over the rubbly
facies
Acropora-rich facies
Massive facies
Halimeda-rich facies
Post-Mariana terrace deposits
Description of the unit
Supplementary descriptions of subdivisions_
Tanapag limestone
Pleistocene and Recent
Younger terrace deposits
Deposits formed by mass wasting
Alluvium and clay wash
Recent
Recently elevated limesands
Marsh deposits
Gravel and sand on emerged fringing-reef
surfaces
Present reef and beach deposits
Structural geology
Introduction and synopsis
Primary structures
Volcanic remnants, protrusive structures, and
lava flows
Other initially dipping deposits
Depositional(?) folds
Tectonic structures
Faults
Joints
Folds
Structures due to compaction, slumping, mass wast-
ing, and collapse
Relation of structure to topography
Historical geology
Introduction and synopsis
The oldest rocks (Eocene?)
? The Eocene core and the beginning of the volcanic
island arc
CONTENTS
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Historical geology-Continued
Oligocene history and the last of the primary vol-
canic rocks
The early Miocene bank sediment complex
Later Miocene and Pliocene
Definition of the fault pattern
Emergence, terrace formation, and renewed
faulting
Pleistocene and Recent
The older Pleistocene and its reef-complex
limestones_
Middle(?) Pleistocene terrace formation and
faulting
Late Pleistocene emergence, fringing-reef forma-
tion, and latest fault movement
Eustatic shifts of sea level and the most recent
events
References cited
Appendix A. Described sections
Mount Achugau section of the Sankakuyaina forma-
tion
Talofofo ridge section of the Densinyama formation._
Tank? cliffs section of the Matansa and Tagpochau
limestones
Introductory remarks
Matansa limestone, white facies
Tagpochan limestone, inequigranular facies_ _ _ _
Lower Tertiary e, Heterostegina borneensis
zone
Unassigned Tertiary e beds
Upper Tertiary e, illiogypsinoides dehaarth
zone
Bafiadero cliffs section of the Tagpochau limestone
Machegit cliffs section, Machegit conglomerate
member of Tagpochau limestone
Appendix B. Economic geology
Introduction
Metallic mineral resources
Manganese ore
Ocher
Iron
Reports of bauxite
Reports of gold and silver
Nonmetallic mineral resources
Phosphate
Quartz sand and other abrasive materials
Clay
Sand and gravel
Building and decorative stone
Engineering construction materials ---
Index
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A
ILLUSTRATIONS
[Plates 1-4 and 25 In pocket; plates 5-24 follow page 1261
PLATE 1. Geologic map and sections of Saipan, Mariana Islands.
2. Generalized geologic map and sections of Saipan, Mariana Islands.
3. Topographic and geomorphic map of Saipan, Mariana Islands.
4. Locality-finding map of Saipan.
5. Sankakuyanca formation.
6. Sankakuyaina and Hagman formations.
7. Hagman and Densinyama formations.
rettetatazdemy___,_...
?
II
s
CONTENTS
PLATE 8. Densinyama formation, Matansa limestone, and Fina-sisu formation.
9. Tagpochau limestone-Donni sandstone member and transitional facies.
10. Tagpochau limestone-transitional, inequigranular, and rubbly facies.
11. Tagpochau limestone-inequigranular facies and soils.
12. Tagpochau limestone, older terrace deposits, and Mariana limestone.
13. Mariana limestone, Tanapag limestone, and existing coastal features.
14. Tanapag limestone and elevated surge channels.
15. Tanapag limestone, 0-foot notch, and Recent beachrock.
16. Matuis uplands, northern platform, terraced benches, and elevated shoreline features.
17. Distinctive terrain of volcanic rocks and limestones, vegetation patterns, and shoreline features.
18. Volcanic rocks and terrain, and elevated and present shoreline features.
19. Elevated and present shoreline features in eastern Saipan.
20. Geomorphic and structural features of southwestern Saipan.
21. Hagman formation, Tagpochau limestone, Mariana limestone, and mass-wasting features.
22. Fault-controlled topography and elevated marine surfaces of south Saipan.
23. Geomorphic features of southwestern Saipan.
24. General structure of the western slope, reef, and lagoon northward from Mount Tagpochau.
25. Map of economic geology of Saipan.
Major structural elements of the Pacific Ocean area
Regional relationships in the western north Pacific
Principal geomorphic subdivisions of Saipan
Illustrations and local stratigraphic ranges of some distinctive genera
Illustrations and local stratigraphic ranges of some distinctive genera
Graphic summary of selected stratigraphic sections
VII
Page
16
17
22
of larger Foraminifera 35
of calcareous algae 36
37
7. Distribution of the genera of larger Foraminifera in the Eocene formations 48
S. Characteristic relations of Tanapag limestone and custatic notches along cast coast north of Talofofo beach 88
9. Structural outline map of Saipan 92
10. Sites of rock and terrain photographs on plates 5-24. Faces plate 5.
TABLES
TAIII.E 1. Temperature and rainfall data for Saipan 6
9. Acreage of outcropping rocks and unconsolidated mantling deposits 21
3. Stratigraphic units of Saipan compared with standard faunal and stage zonation In pocket
4. Average chemical and normative mineral composition of dacites and andesites from Saipan 38
a. Partial list of fossils from the Eocene rocks of Saipan 47
6. Estimated composition of typical sandstones in the conglomerate-sandstone facies of the Hagman formation 51
7. Partial list of fossils from the Tagpochau limestone 65
S. Cuttings from a drilled well at Cha.lan Kiya, Saipan 70
9. Partial list of fossils from the Mariana and Tanapag limestones 80
10. Carbon-14 analyses of Tanapag limestone and Recent calcareous materials 87
11. Summary of the inferred geologic history of Saipan 99
CHART
Summary of the geologic units of Saipan In pocket
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GEOLOGY OF SAIPAN, MARIANA ISLANDS
GENERAL GEOLOGY
By PRESTON E. CLOUD, Jr., ROBERT GEORGE SCHMIDT, and HAROLD W. BURKE
ABSTRACT
Saipan, situated about 15? N. and 146? E., is one of the larger
and more southerly of the Mariana Islands. The 15 small
islands of this chain are strung along an eastwardly convex ridge
for more than 400 miles north to south, midway between Honshu
and New Guinea and about 1,200 miles east of the Philippines.
54
Paralleling this ridge 60 to 100 miles further east is a deep sub-
marine trench, beyond which lies the Pacific Basin proper. To
the west is the Philippine Sea, generally deeper than 2,000
fathoms. The trench coincides with a zone of negative gravity
anomalies, earthquake foci occur at increasing depths westward
from it, and silica- and alumina-rich volcanic rocks characterize
the emergent island chain itself. The contrast between these
features and those of the Pacific Basin proper to the east is held
to favor the conclusion that the Mariana island arc and trench
define the structural and petrographic front of Asia.
Magellan touched at the Marianas in 1521. After him came
adventurers, traders, and priests. They found the temperature
warm and little varied, rainfall seasonal, and resources modest.
Saipan was occupied in 1564, and the name Mariana Islands
was applied to the chain by Sanvitores in 1668. In the late
18th and early 19th centuries the Marianas were visited by the
scientific exploring expeditions of Malaspina, von Kotzebue, de
Freycinet, and Dumont d'Urville. Primarily geologic studies
began at the turn of the 20th century, and there has been an
increasing number of publications on the geology of the region
since 1035.
Although second in size among the Mariana Islands, Saipan has
a land area of only 48 square miles. It consists of a volcanic core
enveloped by younger limestones. From axial uplands that
rise to a maximum altitude of 1,555 feet, the slopes of the north-
south elongated island step down to the sea in a succession of
mainly erosional terraces that become conspicuous away from a
strongly dissected central volcanic area. The lowest bench
and the western coastal plain, however, are in large part of
constructional origin.
The oldest rocks are andesitic inclusions in dacite, but the
island began its decipherable geologic record with the subaerial
accumulation of dacitic pyroclastic and flow rocks known as the
Sankakuyama formation. The Sankakuyama is dated as
Eocene (?) on the basis of late Eocene fossils in overlying strata,
and the presence within it of tridymite and cristobalite---meta-
stable forms of silica that are yet unknown from pre-Cenozoic
rocks.
Over and around the Sankakuyama formation were deposited
the andcsitic pyroclastic and greatly subordinate flow rocks of the
Hagman formation, and both andesites and exposed dacites were
extensively reworked in bordering tropical seas to form the
373761-50-2
Densinyama formation. This consists mostly of conglomerate
and sandstone. The reworked volcanic sediments of the Densin-
yama grade laterally and upward into a 500-foot succession of
warm-water bank limestones known as the Matansa limestone.
All three of these units (Hagman, Densinyama, and Matansa)
have yielded camerinid and discocyclinid Foraminifera distinc-
tive of the upper Eocene (Tertiary b); this indicates relatively
short time span and partial lateral equivalence for them.
The Mariana geanticline presumably originated in early
Tertiary time, before or during Eocene volcanism. Its growth is
believed to have been closely related to the construction of a
central volcanic core, which, on Saipan, presumably continued
into or through Oligocene time.
Rocks believed to be of Oligocene age are the interlayered
andesite flows and marine tuffs of the Fina-sisu formation.
These contain smaller Foraminifera considered indicative of
moderately deep tropical seas. Included also are planktonic
species that imply approximate correlation with the upper
Oligocene Globigerinatella insueta zone of the Caribbean region.
The 4,600 feet or so of Eocene and Oligocene rocks of mainly
volcanic nature that form the core of Saipan are succeeded by
1,500 feet of bioclastic limestones and some coral-algal limestones
and unconsolidated sediments of Miocene, possibly Pliocene, and
Pleistocene to Recent age. The limestones generally contain
Foraminifera and abundant coralline algae of both articulate
and crustose types. Locally they also display reef-building
corals, Halimeda and other calcareous green algae, mollusks,
echinoids, and other fossils. Complicated facies relationships
are characteristic.
The early Miocene Tagpochau limestone, like the late Eocene
Matansa limestone, includes mostly bank-type deposits that
accumulated in a tropical sea Gf shallow to moderate depth. The
general scarcity of significant coral masses suggests depths
mainly a little too great for vigorous reef growth, although
within the zone of photosynthesis and in warm water. At
deeper levels, downslope from the Tagpochau bank deposits,
. reworked tuffaceous sediments accumulated to form the Donni
sandstone member of the Tagpochau. Orbitoid, miogypsinid,
and other larger Foraminifera indicate a Tertiary e age for these
beds and possible approximate equivalence to the Aquitanian of
Europe. Smaller Foraminifera and mollusks indicate early
Miocene in a broad way, without sure ties to specific sections.
Two faunal zones are recognizable on the basis of larger Fora-
minifera, with an intermediate interval of mixing. The lower
zone, characterized by Heterostegina borneensis van der Vlerk, is
referred to the lower part of the Tertiary e beds. The upper
zone, characterized by Miogypsinoides dehaartii van der Vlerk
and Miogypsina s. s. denotes the upper part of Tertiary e.
Neither the Heterostegina borneensis zone nor the Miogypsinoides
1
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2 GEOLOGY OF SAIPAN,
dehaartii zone appears to be related to sedimentary lacks as
mapped.
The Pliocene may be represented by terrace deposits on
benches that truncate Miocene strata at levels above the highest
probable Pleistocene limestones. However, no fossils are known
from these thin terrace sands and gravels.
Younger still than these possible Pliocene terrace deposits is
the Mariana limestone of supposed older Pleistocene age,
reaching to 500 feet above present sea level, and the Tanapag
limestone of late Pleistocene age, restricted to elevations below
100 feet. The Mariana limestone consists of lithified reef-
complex and bank-type or lagoonal deposits; whereas the Tana-
pag is an elevated fringing reef complex. Both contain domi-
nantly modern types of algae, Foraminifera, corals, and mollusks.
Only two new stratigraphic names are introduced for the
succession outlined, the presumably Oligocene Fina-sisu forma-
tion and the lower Miocene Machegit conglomerate member of
the Tagpochau limestone.
Miocene deposits overtopped the volcanic core, and subsequent
fluctuating relationships between land and sea led to the forma-
tion of somewhere between 12 and 25 marine bench surfaces.
Three principal sets of terraces are recognized, according to eleva-
tion and intervals of terrace formation: an upper, late Pliocene(?)
set with surfaces above 500 feet; an intermediate, middle(?)
Pleistocene set between 100 and 500 feet; and a lower, late
Pleistocene set below 100 feet. The rock benches below 100
feet tend to be veneered by, or are parts of, the elevated late
Pleistocene fringing reef complex. The higher terraces were cut
in preexisting rocks by marine erosion. Some are veneered by
stratified Pliocene(?) and Pleistocene nonmarine terrace sands.
The limesands of the western coastal plain seem mostly to
veneer a recently down-faulted part or parts of the lowest con-
structional bench.
A solution notch at 5 to 8 feet above present sea level gives
further evidence of the now widely recognized 6-foot eustatic
stand of the sea that may correlate with a late subpeak of the
postglacial thermal maximum The fall from this eustatic lc \ el
was interrupted by a stillstand at about 2 feet Evidence of
other possible eustatic le els is found at 12 to 15, 40, and about
100 feet above present sea level and probably below it. If the
100 foot level is eustatic it may correlate with the last major
interglacial or interstadial epoch, and deposition of the Tanapag
reef limestone would seem to have been in progress during some
part or parts of the last Pleistocene glacial advance.
Parallel to the long axis of Saipan are steep, north-northeast to
northeast-trending, west-dipping faults, along which dip-slip
movement has been relatively down on the west. A few cross
faults add to the complexity of this pattern, and minor local
folding has taken place. The basic fault pattern may well have
originated in Oligocene time, but the oldest clearly datable
offsets are post-early Miocene and pre-late Pliocene. There-
after four intervals of recurrent fault movement can be recog-
nized and closely dated in the local sequence: post-upper
terrace formation, or late Pliocene(?); post-Mariana limestone
deposition, or early middle(?) Pleistocene; post-intermediate
terrace formation, or late middle(?) Pleistocene; and post-
Tanapag limestone deposition but before the retreat of the sea
from the 6-foot eustatic level, latest Pleistocene or early Recent.
The general shape and location of the island are probably in
significant degree fault-controlled.
Emphasis is placed on the ecologic implications and age signif-
icance of the fossils, and on the origin and historical analysis of
the rock succession and geomorphic features
Descriptions of stratigraphic sections and economic geology
are appended to the report.
MARIANA ISLANDS
INTRODUCTION
BASIS AND SCOPE OF THE REPORT
Following World War II the U. S. Geological Survey
has been engaged in a program of areal studies in the
western north Pacific Ocean under financial sponsorship
of the Corps of Engineers, U. S. Army. As a part of
this program, geological, soils, and ecologic field work
was carried out on and around Saipan (figs. 1, 2; pls.
1, 2) from late September 1948 to mid-July 1949 by the
authors, soils scientists Ralph J. McCracken and Ray
L. Zarza, and briefly by Allen H. Nicol and Jarvis H.
O'Mara. These investigations were supplemented by
the laboratory studies of paleontologists Milton N.
Bramlette, W. Storrs Cole, C. Wythe Cooke, Julia
Gardner, J. Harlan Johnson, William Riedel, Ruth
Todd, and John W. Wells.
Because studies basic to the evaluation of military
problems yielded much purely scientific information, it
was decided to publish separately that information and
the interpretations that are based on it. This chapter
of the resulting report relates to the general geology of
Saipan. It is planned that subsequent chapters will
deal with soils, petrology of the volcanic rocks, petrog-
raphy of selected limestones, discoasters and related
objects, the larger calcareous algae, Radiolaria, Fora in in-
ifera, echinoids, and submarine topography and shoal-
water ecology. The mollusks are being reserved for in-
clusion in a proposed general study of Cenozoic mollusks
of the Pacific islands by H. S. Ladd.
For this chapter, "General geology," Burke pro-
vided the first draft of descriptions of the Matansa
limestone; the equigranular, inequigranular, and tuffa-
ceous facies of the Tagpochau limestone; and the Tanke
cliffs stratigraphic section. This was done in the field
in mid-1949 and Burke is not responsible for subsequent
variations from his original descriptions or for inter-
pretive sections. Schmidt is responsible for basic
description of the Sankakuyama, Hagman, and Densin-
yama formations; the Machegit conglomerate member
of the Tagpochau limestone; the rubbly facies of and
thick residual clays over the Mariana limestone; all
terrace and slump deposits; stratigraphic sections at
Machegit cliffs, Talofofo ridge, and Mount Achugau;
and the petrology and classification of the volcanic
rocks. He shares responsibility for descriptions of the
Fina-sisu formation, for the Dormi sandstone member
and transitional facies of the Tagpochau limestone, and
for the thick residual clays over the Tagpochau lime-
stone. Schmidt and Cloud prepared the Appendix on
economic geology together. Cloud is responsible for
general coordination, for descriptions of geologic units
not attributed to Schmidt or Burke, and for micro-
scopic and palcoecologic studies of the limestones in
all unit descriptions. The writing of all general sections
1
?
GENERAL GEOLOGY
of this chapter was also by Cloud, with Schmidt's
extensive help in general organization, the writing of
paragraphs relating specifically to volcanic rocks, and
in preparation of illustrations. Responsibility for
mapping is indicated on the maps themselves.
Although Saipan includes an area of only 48 square
miles, it displays a varied and complicated succession
of rocks, and recommissance of other islands in the
Marianas suggests that it may provide good exposures of
some rocks not elsewhere well displayed. This itratig-
raphy is described in detail, both because it illustrates
well some of the complexities of "high island" stratig-
raphy and because such a study has not previously
been published for any similar island nearby.
The reader should not be lulled into a sense of finality,
however, by the attempt here made to provide as com-
plete coverage as possible. In spite of intensive efforts
in the field over a period of 9 months, and the laboratory
studies that have been made since then, much could
still profitably be done, both in the field and in the
laboratory. There is need for further study of rock
weathering and solution. Larger megafaunas could
be obtained with intensive collecting?localities in north
Saipan that we had intended to revisit for collecting
were closed because of fire in an ammunition dump
during the latter part of our field work. Offshore and
beach zone studies were incidental to the main project
ashore, and thus incomplete. Even the stratigraphic
succession and subdivision of the rocks have their
points of uncertainty and many of the facies contacts
mapped are highly generalized. Mapping in the thickly
vegetated and precipitous terrain was slow, interpreta-
tion of the complexly intergradational rock units is
difficult, and some possible lines of investigation had to
be foregone or abbreviated for lack of time or means to
follow them up. As for geomorphology, it, is not fea-
sible to go much beyond the incidental observational
data. What is needed here is a unified regional study
of the Mariana Islands as a. whole, carried out under the
continuous field leadership of one person.
In fact, topical studies in the western Pacific, are now
needed more than ever? not only of geomorphology,
but also of stratigrapitie correlation, paleoecology,
structure, the volcanic rocks, and geophysical patterns.
In the hope of bringing Saipan into better focus and of
encouraging further investigation, an effort will be made
in later parts of this report to summarize the present
state of knowledge in some of these fields. It is in-
evitable that time and new evidence will modify or
invalidate some or many of the opinions to be expressed.
ACKNOWLEDGMENTS
We are indebted to so many for help and encourage-
ment with the preparation of this report and the field-
3
work on-which it is based that to attempt to thank all
would be to run the risk of inadvertent omission. Of course
we are sincerely grateful to everyone who aided this
study in any way, but we can specifically acknowledge
only help of an especially extensive or significant nature.
Without the support of Col.' B. C. Snow, then staff
engineer, Marianas-Bonins Command, and Sherman K.
Neuschel, in charge of the Geological Survey's Pacific
program, the fieldwork could not have been accom-
plished.
Rear Adm. C. A. Pownall, then Commander Naval
Forces Marianas, and the personnel under his command
on Guam and Saipan, made it possible for the field party
to supplement its investigations ashore with a program
of marine studies. The success of this operation was
assured by outstandingly fine support from Capt. G.
L. Compo, then Island Commander of Saipan, his
executive officer, Comdr. William Dickey, and Chief
Boatswain Francis X. Jozwick.
Col. H. P. Detwiler, commanding officer of the Army
Garrison Forces on Saipan when the geologic work was
begun there, and Lt. Col. J. P. Davis, first as executive
officer to Col. Detwiler and later himself in command,
provided living and working quarters, vehicles, and
other facilities on Saipan. Mrs. Davis significantly
aided the work of the field party by volunteer service as
collector and compilation draftswoman.
Comdr. F. L. Sheffield, civil administrator on Saipan
during the later geological field work there, arranged
for R. G. Schmidt to visit and study Alamagan. Pagan,
and Agrihan, in the northern Marianas.
Drs. Shoshiro Hanzawa,, Kotora Hatai, and the late
Risaburo Tayama helped to clarify controversial mat-
ters relating to Saipan geology at a 2-day conference
with Cloud and Burke in Sendai, Japan, in July 1949.
Also of help was Dr. Ruiji Endo, who prepared for our
use in the field "A lexicon of geologic names of Saipan
Island," giving translations and page citations of
Tayama's original descriptions.
Temporary members of the mapping party not in-
cluded among authors of reports resulting from this
field work are Ray L. Zarza and Jarvis H. O' lam.
Buenusto Reyes of Saipan also assisted with the field
work.
GENERAL HISTORY OF THE REGION
Midway between Honshu and New Guinea, and
about 1,200 miles east of the Philippines, the convex
eastern margin of the Philippine Sea is festooned by 15
widely separated islands that define a remarkably
symmetrical arc more than 400 miles long.
These are
the Mariana Islands (figs. 1 and 2).
They were first seen by people of European descent
I All military ranks here mentioned refer to those held at time of flelawork.
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4 GEOLOGY OF SAIPAN
on March 6, 1521, when the desperate little squadron
of Fenian de Magalhaes (Magellan), sailing the 13th
parallel westward in the neighborhood of 146? E., "dis-
covered in the northwest a small island, and afterwards
two others in the southwest" (Pigafetta, as translated
by Pinkerton, 1812). According to a translation from
the original logbook of navigator Francisco Albo
(Stanley, 1874, p. 223), "On the 6th [March, 1521]
* * * we saw land, and went to it, and there were two
islands, which were not very large; and when we came
between them, we turned to the S. W., and left one to
the N. W. * * * and there I took the sun, and one of
these islands is in 12%?, and the other in 13? and more
[north latitude]."
Historians have generally agreed that the island at
which Magellan landed and spent three days (Albo,
'in Stanley 1874, p. 223-224) was probably Guam, and
some have even pinpointed his stopping place as Umatac
Bay (southwest Guam). In fact, however, the original
accounts are ambiguous, and Tinian, rather than Guam,
may have been the site of Magellan's landing. Even
Rota is a possibility, as one of Magellan's sailors was
found living there in 1526 (Pinkerton, 1812, P. 324).
Recorded latitude and distance between islands seem
to favor Guam, however, even though the point can-
not be settled conclusively. In any event, Magellan
did sight two or three of the Mariana Islands, landed at
one of them, and opened a route of travel that was
followed by Eltano in 1524, Loaisa in 1526, and many
others in later years.
Magellan found the Marianas inhabited by Microne-
sian people of presumed Indo-Malayan derivation, with
a distinct language and distinctive physical characteris-
tics. Pigafetta, who wrote the history of Magellan's
voyage, observed that some of the men had "black
hair, tied over the forehead, and hanging down to the
girdle," and that these "wore small hats made of palm."
They would have been according to Mr. Elias Sablan of
Saipan, the Chamorri, or nobility, a term that was ex-
tended by later explorers to all natives of the Mariana
group (see also Safford, 1903, vol. 5, p. 291; 1905b, p.
104; Prowazek, 1913, p. 29; Joseph and Murray, 1951,
p. 18).
Chamorro discovery of the Marianas is buried in
legend and disputed as to approximate date. The age
indicated by carbon-14 activity of a shell associated
with pottery 1.5 feet below the surface of the sandy
coastal plain at Chalan Piao in southwestern Saipan
waS originally given as 3,479? 200 years (Libby, 1952,
p. 680), but recent studies of organically precipitated
calcium carbonate suggest a negative correction of 1,500
to 2,000 years on this date (J. L. Kulp, letter of Janu-
ary 15, 1953, to Cloud). In this same excavation
Alexander Spoehr found pottery to a depth of 6 feet,
AIARIANA ISLANDS
about at present sea level. Thus it appeals that man
already had a history of residence in the Mariana Islands
more than 1,500 and perhaps more than 3,500 years
ago-long before Magellan arrived.
The first definitely recorded European occupancy of
Saipan occurred in November 1564 when Adm. Miguel
Lopez do Legaspi landed there and proclaimed Spanish
sovereignty over the Mariana Island group. The
islands, which had been called Islas de los Ladrones by
Magellan, were at this time renamed Las Islas de las
Veins Latinas. It was not until 1668 that the Jesuit,
Diego Luis de Sanvitores, fulfilling a long ambition to
establish a mission in these islands, gave them their
present name in honor of Maria Aim of Austria, Queen
of Spain, widow of Philip IV, and patroness of the
Jesuit order.
The Spanish occupation of the Mariana Islands
lasted more than 200 years (until 1899) and greatly in-
fluenced the language, habits, religious beliefs, and
racial composition of the inhabitants. Go x aliment
was difficult, and although there were enlightened and
thoughtful men among the succession of Spanish gov-
ernors, the accounts of historians indicate that their
efforts were nullified by those who thought that display
of force would insure obedience. Punitive expeditions
against unruly natives, famine, disease, and mass evac-
uations reduced the population from an estimated
70,000 to 100,000 in 1668 to fewer than 4,000 natives
at the time of the first census in 1710. In the next 50
years or so the population fell to fewer than 2,000.
Recovery from this point of near extinction was steady,
however. By 1816 the Chamorro population for the
Marianas was back up to 2,559 in a total of 5,389,
(Prowazek, 1913, p. 24); and by 1898 the total popula-
tion had increased to about 10,000. By this time, how-
ever, pure-blooded Chamorros had all but disappeared
(Joseph and Murray, 1951, p. 23), and the present much
more numerous inhabitants of the 'Marianas are mainly
descendants of mixed blood from this small group.
Caroline Islanders, Japanese, Koreans, and Okinawans
were later numerous in Saipan, Tinian, and Rota where
they apparently rarely interbred with the Chamorros
and are minority strains today.
Throughout Spanish and later times Saipan itself
underwent even more drastic population shifts than the
Marianas as a whole. In 1694 the Spanish governor of
the Marianas, Don Jose de Quiroga y Lossada, had sub-
jugated the natives of Saipan in a series of bloody skir-
mishes from which, it is said by local elders, several of
the present geographic names on Saipan are derived
(Matansa, for massacre, and Kalabera, for skeleton). In
1698 the entire remaining population was removed to
Guam where it could be kept under close surveillance,
and Saipan remained supposedly uninhabited for more
?
GENERAL GEOLOGY
than 100 years, An abortive effort at colonization was
made by Americans and Hawaiians in 1810, a more suc-
cessful attempt by Caroline Islanders in 1815, and the
Chamorros finally began their return in 1816 (Joseph and
Murray, 1951, p. 23). Emigration from the Caroline
Islands to Saipan became active about 1842 (Marche,
1887; 1898, p. 60; Seidel, 1904a, p. 280). Marche
(1898, p. 60) reports that in 1887 two-thirds of Saipan's
small population was Carolinian and the other third
mostly Chamorros not visibly different from those of
Guam. By 1937 the balance between Chamorro and Car-
olinian has swung in the other direction, the native
population of Saipan then being said to include 2,170
Chamorros (as the term is now used) and 796 Carolinians.
In addition, however, the island was occupied by 20,696
Japanese, Koreans, and Okinawans (U. S. Navy, 1944, p.
35). Finally, in September 1948, the total native popula-
tion of 4,962 persons included 3,890 Chamorros and 1,072
Carolinians (Bowers in Freeman, 1951, p. 227). Nearly
half of these were under 16 years of age (Joseph and
Murray, 1951, p. Si).
During the Spanish rule of the Marianas, Guam was
the capital and its Umatac Bay was a world-reknowned
port for exploring expeditions and trading galleons
plying between Mexico and the Philippines. Like the
masters of the galleons, the English privateers and
pirates who preyed on them also stopped here on oc-
casion with their Spanish prizes and prisoners. Among
these were Eaton and Cowley in 1685, William Dampier
in 1686, and Woodes Rogers in 1710. Other early
visitors to the Marianas included the crews of Anson
in 1742, Byron in 1765, Wallis in 1767, Crozet in 1772,
La Perouse from 1785 to 1788, Malaspina in 1792, von
Kotzebue in 1817, de Freycinet in 1819, and d'Urville
in 1828.
Spanish rule of the Mariana Islands ended in 1898-
99. Guam was occupied by American forces in 1898
and later purchased from Spain by the United States.
In 1899 the remaining Mariana Islands were sold to
Germany by the Spanish. During the brief German
occupation of the Marianas (1899-1914) the copra
industry was considerably expanded, food and stock
farming was encouraged, a few schools were established,
and Capuchin priests were substituted for A ugustinians
and Jesuits; but otherwise the handful of German
officials seem to have left things essentially as they had
been under Spanish rule.
Japan seized the Mariana Islands (except Guam)
from Germany in October 1914, and Japanese mandate
over these islands was approved by the League of Na-
tions in 1920. Headquarters for the Japanese mandated
Marianas were on Saipan. Under Japanese rule an
important sugar cane industry was developed in the
.Marianas, phosphate and manganese were mined, and
5
trade with other mandated islands and Japan was en-
couraged. Okinawan and Korean laborers were im-
ported to work the sugar fields. The Japanese segre-
gated the Chamorros and restricted their holdings but
apparently did not interfere with their religious activ-
ities or social customs.
On June 15, 1944, American troops landed on the
southwestern beaches of Saipan, and within 2 months
the 30-year Japanese occupation of the Marianas was
ended (for an account of the campaign see Hoffman,
1950). Guam, which had been taken by the Japanese
on December 9, 1941, was retaken by American troops,
and the United States trusteeship of the remaining
islands, including Saipan, was approved bytheSe7, andcini
l?
Council of the United Nations on April 2, n4
accepted by the U. S. Government on July 18, 1947.2
GEO GRAPHIC TERMINOLOGY
The geographic names used in this report are those
approved by the U. S. Board of Geographic Names as
recommended in a "Preliminary gazetteer of geographic
names for Saipan" (Cloud, 1949). The specific parts
of the Chamorro names are adhered to throughout; but,
in the text itself, the generic parts at most places are
translated to English in the interests of smoother
reading-thus Ogso Tagpochau is written Mount Tag-
pochau and Ogso Talofofo is Talofofo ridge. At
irregular intervals bracketed Chamorro translations
follow the names of geographic features as a form of
translation aid. The maps give the entire approved
name in Chamorro only, together with a translating
key to generic parts.
Translation of Chamorro specific terms is given in
the reference mentioned, and other information may
be found in a Chamorro grammar by W. E. Safford (1903-
1905a, see also Safford 1905b, p. 113-116) and a dic-
tionary by the Capuchin Father Callistus (1910).
Safford also refers to a small Spanish-Chamorro
dictionary nary by Fathee Ibanez del Carmen, published in
18
One matter needs to be clarified. The Chamorro
words for the cardinal directions somehow became
confused between Guam and Saipan (perhaps at the
time of the repopulation of Saipan during the middle
and late 1800's). On Saipan north is Icatan, south is
luchan (san lichan, toward the south; gi lichan, south
of, south from, on the south of), east is haya (pronounced
ha'za), and west is lagu (sometimes given as lago). On
Guam lagu (or lago) means north, haya south, katan
east, and luchan, west. This seem incredible-but the
usage for directions on Saipan was verified at every
opportunity and is sm:ely correct for that island; the
3 Most of tho foregoing information was obtained from references cited. A fuller
and moro recent account of Marianas history is given by Reed (1952).
,?
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6
GEOLOGY OF SAIPAN, MARIANA ISLANDS
usage for Guam is given on the authority of Salford
(1903-1905a, v. 7, p. 315), and Father Callistus (1910,
p. 50, 52, 67, 81) substantiates the double usage. More-
over, Albo's log of Magellan's voyage (Stanley, 1874,
p. 223), as quoted on an earlier page, bears out Safford's
contention (1903, v. 5, p. 291, 307) that the Spaniards
were called gi lago, and their language linolago, be-
cause they first appeared to the natives coming from
a northerly direction.
CLIMATE
Japanese climatic records for Saipan have been sum-
marized in compilations by the U. S. Navy (1944,
p. 3-8) and the U. S. Geological Survey (1944, p. 46-47).
Temperature and rainfall data from the latter reference
are further condensed in table 1.
TA131,E
Saipan is characterized by a tropical oceanic climate.
Recorded mean annual temperature ranges from 78? F
at an altitude of about 676 feet on the central ridge
east of Tanapag to about 85? F in the southwest low-
lands. Recorded deviations from the mean are as low
as 67? on the central ridge and as high as 102? in the
southwest lowlands. The mean annual relative humid-
ity is about 82 percent, with a monthly average between
79 and 86 percent (U. S. Navy, 1944, p. 5). The axial
uplands and east slope of the island, being exposed to
the easterly trade-winds, are cooler and generally less
humid than is its western slope and coastal area.
Average annual rainfall, according to Japanese
records, varies from 81.0 inches in the southwestern
lowlands to 90.7 inches at an altitude of 676 feet on the
central ridge. Mount Tagpochau, which rises to a
1.?Temperature and rainfall data for Saipan (averaged from 9 years of Japanese records)
Temperature (Fahrenheit)
Rainfall (Inches)
Maximum monthly
Mean
Maxt-
Mean
Months with
Rainiest
Less rainy
Mean Absolute
Station
annual
mum
mum
annual
. ? Y?r1,.. 45,3?
,P.4.7;q44.\17ST:frak741-t.
INTERPRETIVE COLUMNAR SECTION
H., rm. tem* torromens no* Onapal
unets too. uonsoatonaa.m?M?ta. 8.4 OM.
101.?????,,, n?neifYIJ ayarar,.. non,
a** any goon vote. a*
GLOSSARY
As the place of
Bahia bay
Bobo aPnng
Danitalo bog
DALAI little
Ilagol Ube
Iloyon large sink
I the. that, dos
!Meta small Island
Kanat "MO
Katan north
Laderan Off or rbff?
INTOnalt lagoon
Lkhan south
Uyang Mire
Og.o mouoL Inounta/n. hilt ndge
Poetton harbor
Pontan 101141
Saban. ItY.Mands 'mostly imorsigrasa/
Sadog fah WALLY. or name to *Inch freak water omits
Oral befell
Sankaktuaina formation
tear., trkattor aorta. undo., elotr rook tonna.
cod aloud ry....o.stae met* Computed gore.. Mode.
LAOfree :nu Wel.. wag to aura ranter
TW **ed da.a. praeiresete rock* Tot doctor NIT
Tto rolrepayear and por.'ofte dartee Vol
ad..* eaderales oatante plug. 404410* to" aer
brawn on areas 14 flag.. Iwo,* toll jont?
Ts! narrow Jan. ft.. reek
S"olla, ...UMW.' contact
Agar:Ts:rip c...ealtc.lowetetta marigt7,,d,cp.7e:r
aggronnolety lacanted
Interfmgenng or intergradat metal ibrattgraphot0111.14
Srporotes Idernallet tneregradoad ....flatter.. bade.
Mad rim det......adle. daftol warn otuireret or
apponrunalely brae. Intrrtal* af ft. roar.* tad.
rate app.,. mato aoroltetts.
U. eon_
Trace of !soh. 0104111X dip
Soltd Otero doononatrobfo rforilood rarer Weer./ ne
apprortmately lactated dated erkeTr concealed u
Ware. ? Mr. P. dm...Armee ado
ha. of serlocal fault
Trace of anticlinal au.
Tormona/ armor trodonates 41940.04 411 apparent oho,
Sold vAerr droloaarrmate donned rarer egerred or