-
doi:10.1144/GSL.SP.2005.004.01.21 1974; v. 4; p. 365-378
Geological Society, London, Special Publications
Michael Geoffrey Audley-Charles
Sulawesi
Geological Society, London, Special Publications
serviceEmail alerting to receive free email alerts when new
articles cite this article click here
requestPermission to seek permission to re-use all or part of
this article click here
Subscribe to subscribe to Geological Society, London, Special
Publications or the Lyell Collection click here
Notes
Downloaded by Royal Holloway University of London on 4 August
2010
© 1974 Geological Society of London
http://sp.lyellcollection.org/cgi/alertshttp://www.geolsoc.org.uk/gsl/publications/page417.htmlhttp://sp.lyellcollection.org/subscriptions
-
SULAWESI
MICHAEL GEOFFREY AUDLEY-CHARLES Department of Geology, Imperial
College, Prince Consort Road, London S.W.7
CONTENTS
A. General data on the segment 365
B. Subdivision of the segment 374
C. Structural relationships of the Sulawesi Arcs with
neighbouring regions 376
D. References 377
A. G E N E R A L D A T A ON T H E S E G M E N T
1. T H E SEGMENT STUDIED
The island of Sulawesi--formerly called Celebes--occupies a
critical but very complex position at the junction of the
Alpine-Himalayan and Circum-Pacific chains. It links along strike
with both the Philippine and the Banda orogens, but lies between
the Borneo and the West Irian orogens. The island is one of the
most mountainous in the Indonesian Archipelago and is poorly known
geologically, because of which the present article is largely in
essay form.
Segment: the Sulawesi orogen has a strike length, excluding
small Islands, of about 1300 km. The west margin of the belt
consists of an arc open in the south to the south-east, which
reverses its direction of curvature in the north to form an arc
open to the north-west. In the south it is separated from the Sunda
Shelf by the 2000 m deep Makassar Strait and in the north it is
adjacent to the Celebes Sea. The east margin of the belt abuts
against the Banggai and Sula Islands (part of a stable positive
area called the Sula Spur) and, to the south, against the northern
part of the Banda Sea. The width of the orogenic belt in Sulawesi,
measured between these margins, varies from 500 km to 270 km, and
averages 350 km.
History: the oldest rocks known in Sulawesi are sedimentary
rocks which have been metamorphosed in pre-U. Triassic times. Then,
there seems to have been a period of general uplift and erosion in
Sulawesi. Mesozoic-Cenozoic orogenic movements commenced during U.
Jurassic and L. Cretaceous times with vertical movements, perhaps
associated with some folding, in the Butung Archipelago and the
South-east and South Arms of Sulawesi. It is possible there were
fold movements at the end of the Triassic in the west of Central
Sulawesi and in parts of the East Arm, but palaeontological control
is un- satisfactory and the rocks have been mapped on a
reconnaissance basis only. The first phase of strong folding began
at the end of the Cretaceous and was completed during the L. Eocene
in most parts of Sulawesi and in the Butung Archipelago (Bemmelen
1949). A major phase of folding and thrusting of M. Miocene age is
reported from the East Arm, and may also have occurred in Central
Sulawesi and the North Arm. An important phase of folding (locally
with overthrusting) during the late Pliocene is reported throughout
Sulawesi and the Butung Archipelago.
The stratigraphy and structure of Sulawesi are poorly known, for
the density of reconnaissance geological mapping in the island is
low. All published geological maps appear to be based on surveys
carried out before 1942 (see Roy 1961 ; Tectonic Map of Eurasia
1966; U.S.G.S. 1965). Few topographical maps were available; aerial
photography was not then employed so that many of the published
maps show only the geology of the immediate vicinity of the
traverses. Only three papers dealing with regional geology of parts
of Sulawesi
-
366 S U L A W E S I
I 120"
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . .
iiii•••i!i•i!iiiiii•ii•iiiii!!!•!iiiiiiiiiii•i•ii•iiiiiiiii•i•iiii•i•iiii••iiiiiii••iiiii•ii
iiiii~iiii!!!!i!!!!iii~i~iiiiiiiiiiiii!iii!!!i!i!!iiiiii~ii~!iii!i:::::::::::::::
! ii i i i i i i i i ! ! : : : : : : : : : : : : : : : : : : : : :
: i i i i i i i i i ! i i i ! ! i ! ! ! i i : S a n g ihe I s .
~
i i i i ! ~iiiCELEBES :: : : : : : : : : : : : : : : : : : : : :
: : : : : : : : : : : : : : : : :
••••••••••••i•iii••ii•ii•••••••!••ii•!••••i•ii••i••!••••i•ii••••••••i•••i•iiiiiii••••••
:i. i!:
. . °
: i! i!~ ::" . . . . . . " : : : : : : : : i i : ! i ! i i i : i
! : . . : : : : : : : . - . . . .
" i i i ] i i i : ~ T A L ~ . D IS.
::•:: : : : : : :.i!i. ! !~! i ! ! i " : : : : i~ii i~i" : : : :
: . . . . . . ! i i ! ! : " i i i ! i !~ i
] i ! i ~ ] ] i ~ i~ i i ] ~ i ! ! ! ! ! i i ! i i ] ] i ~ i i i
i i i ] ~ ] i i i i i ~ ! ! ! ! ! ! ! i i i i ! i i i i ~ ] ] i ~ i
i ! ! ~ i i i i i ! i i i i i i i i i i ' :5i:
~iii~iiiii!~iiiiii~ii~iiiiiiiiii~i~i~iii!i~i~i~i~i~iiiiii~i~ii~iiiiii~iiii~:~
. . . . . ~ i ~ ~
=============================================================================
. ! i ! i M,~
: : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :
: : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :
: : : : : : : : .• : : : : : : : : : : : : : : : : : : : : : : : :
: : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :
: : : : : : : : : : : : : : : : . : : : : :
: : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :
: : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :
: . : i i i ! ! # i i i i i i ! ! i ! i i . !~ii! i TIFOF
: : : : : : : • : : : : : . : : : : : : : . . . . . . . . . . .
. . . . . . . . . . . . : i i i i i i i i i i ~ . :~!! ! ! ! ! :" .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . .
: : : : : : : : : : : : : : : . . . . . . . . . . . : ! ] ! ~ i
i i ! : ' . : : : : : : • : : : : : : : : . . . . . . . . . . : : :
: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . : : / ' - ' ! ! i ! ! ! ! : i :
==========================================================
~ : ~ i ~ i : ~
======================================================== :: /~ : :
: : : : : : : ;
. : : C ~ : : ¼ : : : : : : : : : : : : : : : : : : : : • :
:
. . . . . . . . . . . . . . : : : : : : : : : : : : : : : : : :
: : : : : : : : : :
.! i] ~ i i i i ! i i " : : : : ~l: : : : : : :
:iiiii ~ i i i { i : : : : : : • : : : : : : : : :
iiiiiiiii!iiiii+ : : : : : : : : : : : : : : : : ,
! ! i i i ! i i i i i i i i i i i ! i i i lg i l l i i ! i i i i
!
I 130 °
2 5 0 k i n !
PACIFIC
OCEAN o
4HERA
. . . . . . . . . . . . " + " : : : : : : : : : : : : : : : . .
. .
!i!i::!iiii: ~ ' ~ ~ o
. - :..i..:i:::.~ ~, . . . . . . . . . . . . . . . . 4 . . . . .
: : . ' ~ . ' . " . " " .'." •. -. J:::.:"- ~L"-'." -'."
.'..~s.o
• - ; y i y . • ." " ~ . . ' - ~ - . ~ - " • . ' - . ' ~ ' . . '
. . " • . ' . . ' ~ .I . , . . . . . _ , , . . - - - - - " - " - -
." • ." • ." • ." • ." • ." • ." • ." • ." • ." " ~ " " • " : i : i
i : i i i i i i i i i i i ! i ! ! ~ i ! ! ! ! i ! i i ~ ! i ! i i i
~ i ! ! i i i i i i i i i i i i
.'.'..:.'..:.'..:.'..?.':.'.':.'.':.:.::.:,~i,i iiii++!ii!::+!~
::~"'""2 ! " • ." • ." • ." • ." " • " • " . . . . i i i i ! ! i :
' o -,~
• ".:+++++~++++~++++i+!++!++++++++++: . . . . ~ : ~ : : : : : :
: : : : . . . . .
' ~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _
_ . . . . - - . . . . . . . . . . . . . . , , i ~ ~ ~ i : i : . : :
~ i : : ! ! ! i ~ i ~ i ~ i " . . . . . . . . . . . . . . . . . . .
. . . . . . . . . : : . . . . . . . . . . . . + '
:::::::::::::::::::::::::::::::::::::::::::::::: B 4 . S . . q ~
i i ~ . i i i ! ! ! !~ i i ! i i ! ! i i i : " " . . . . . . . . .
. . . . . . . . . . . . . . . . O " ' : : : : : : :
":•:::::::•:::::" : i ! i i i i ! i ! i ! i !~ ! i i ! i i i i ~ :
" • ....
"::i!i~:::'" .!!!!! ii~iii~i!!iiiii!:" . . . . . . . . . . . •
...... ":" . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . .
B U T U N G : ! i i i i i i i i i ~ ! ! i i~ i ! : " . : : i i
i~ ! ! i i i i i i i i i i ~ " .......... ~ ....................
iiiiiiiiiiiil. !ii!!!!!!!!!ii. ' : : : : : : : : : : : : : : : : :
: : K A B A E W A IS. o . . . . . . . . . . . . . . . ::. . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . .
: i i i i i i i i i i i i i i i i! i i:. D : !~!~i~!~:. ~ . :~i
i i i i i i ! i i i i i i : : .:~i!!!!iiiii!~i~!~iiiiiii.~ -
6 . ~ili i i i i i i i i i ! i i i i i i i i~: ~ii! i ! i ! i i
! i i i i i i i~:::: . . . . . . . : : : : :~i i i i i i i i i i i
i i i~:: o .::~ii i i i i ! i i i i ! i i i i i i ! i i i i i i
i~:: . : / i i i " :ii~i!!i'"!'~ . . . . . . . . ! ....... i " ! '
! ' : : . - . : : : : : : : : : : : : : : : ' "
.::i!!!!!ii!ii!ii!!iiiiii!!:::::" ~:
i ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! I .SALAJAR " :
: i i i i i i i i i i i i ! i i i i i i i i i i ! i i i i ! i i i i
i i i i i i i~::'" . . . i i i i ! i i i i i i i i i i i ! i i ! i
! i i i i ! !~::'" . : : ! ! ! i i ! ! ! i i i i i . . . . . . . .
. . . . . . . . . . . . . . .
. : : ! ! ! i ! i ! ! i ! ! i ! ! i ! i i i i i i i i i i i i i
i i i i ! i ! : . O • .... : : : ! i i ! ! ! ! i i ! i i ~ i ! i i
i i ~ i i i ~ ! ! i i i i : : : " " ============================= :
: : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :
: : : : : : : : : . . . . . . . . : : : : : ! ~ ! ! i i i i i ~ i i
i i i i ! i ! ! : : : : : : : : . . . . . . . ~. . .... : : : ! !~
i i i i i ! i i i ! i~ : : : : : . . . . . . . .
~. ~ i i ~ i ~ i ~ i ~ ~ ~ i ~ i i i ~ i ~ i + ~ i ~ + ~ + ~
........ ,,,+~i~iiiiiiiii:i+++~'":: ~ , , _
Figure 1. T h e s t r u c t u r a l zones o f the Su lawes i o r
o g e n i c bel t , the i r c o r r e l a t i o n w i t h those o f
the B a n d a Arcs o r o g e n i c bel t , a n d the i r r e l a t
i o n s h i p w i t h t he S u l a S p u r ( s h o w n b y coar se
d o t t e d o r n a m e n t ) .
-
S U L A W E S I 367
appear to have been published since Van Bemmelen's The Geology
of Indonesia of 1949. A further impediment to understanding the
structural history is the often uncertain age of sedimentary,
igneous and meta- morphic rocks. Many of the published ages of the
Cenozoic strata are based on foraminifera determined before 1948
and names are probably in need of revision to bring them into line
with recent work.
Each of the four arms of Sulawesi appears to have a different
geological history, but it has long been recognized that the North
Arm, the western part of the Central region and the South Arm have
fundamental features in common which distinguish them from the
South-east and East Arms.
The present article has been prepared from a literature review:
the writer has not visited Sulawesi.
2. SHAPE OF THE O R O G E N IN PLAN
33 The Sulawesi orogenic belt (including the North Celebes Arc
and
BORNEO
\FS
"*~"*" ~ e ' . e e " • e " • " j • " • • l ee e' t. oe4 • o°o •
e°e e • • • • • •
TIMOR
i NN,-.'b % - ~ t Figure 2. The distribution of the arcs of the
Sulawesi orogenic belt and Banda Arcs orogenic belt. l = O u t e r
Sunda Arc; 2 = I n n e r Sunda Arc; 3 = O u t e r Banda Arc; 4 =
Inner Banda Arc; 5 = Tukang Besi-Buru Arc; 6 = Salajar-Lucipara
Arc; 7 = East Gelebes Arc; 8 = Western Celebes Arc; 9 = North
Moluccan Arc; 10 = Nor th Celebes Arc; 11 = Ha lmahera Arcs. S =
Sorong Faul t Zone; TA = Tarera-Aidoena Fault Zone; T = Tawael ia
Faul t Zone; FS = Fossa Sarasina.
The area of coarse dot ted o rnament represents the Sula
Spur.
the western part of the Salajar-Lucipara Arc) curves through 270
° and has a strike length of 1900 km, or of 1300 km if those arcs
of small islands are omitted. The lengths of radii of curvature of
the principal arcs are 500 km for the 'outer' arcs (East Celebes
and Tukangbesi Arcs). In the north the curvature of the arcs is
reversed: the radius of the 'inner' North Celebes Arc is 400 km and
that of the 'outer' North Moluccan Arc is 550 km.
3. SURFACE SHAPE OF THE SULAWESI BELT IN ELEVATION
30 Highest 5% of the ground: 2000 to 2500 m above sea level.
Sulawesi is one of the most mountainous islands of the Indonesian
Archipelago. Most of the highest land is in Central Sulawesi, but
all the arms are mountainous and nearly 40% of the land area is
over 500 m above sea level.
33-4 Plio-Pleistocene raised reef limestones have been reported
from the East Arm at various heights. Bemmelen (1949, p. 151)
quoted heights of 400 m, 500 m, 1000 m, and possibly even 2000 m in
the western part of the East Arm (cf. Loczy 1934). An old alluvial
surface 20 to 30 m above the present one occurs on the north coast
of the East Arm and indicates minor subrecent uplift (Koolhoven
1930, p. 207).
4. GEOPHYSICAL DATA
38 Gravity data are available as a map on a scale of
1:10,000,000 with a 50 mgl contour interval for the marine areas
surrounding Sulawesi (Kuenen, Umbgrove & Vening Meinesz 1934).
A revised isogam map for the whole of Indonesia has since been
published (Bruyn 1951). It incorporates the gravity data of Vening
Meinesz and data from land based surveys, is on a scale of
1:10,000,000 and has a contour interval of 25 mgl.
41 There is isostatic inequilibrium over most of Sulawesi and
this is greatest in the East Celebes and North lV[oluccan Arcs.
42-3 As far as can be judged from available data the general
gravity field shows pronounced concordance with the main tectonic
and topographic trends of Sulawesi.
There are several outstanding features of the gravity field:
very strong negative values are coincident with the marine section
of the North Moluccan Arc; strong positive values coincide with
some deeper parts of the surrounding seas, e.g. Celebes Sea and
Banda Sea; strong positive anomalies are coincident with the marine
gulfs which separate the inner and outer arcs of Sulawesi and the
outer arc from Borneo. Bruyn (1951, p. 605) remarked that ' I t is
certainly possible to recognize on the profiles across Sulawesi the
characteristics of a double arc. Here (i.e. all Sulawesi except the
Minahasa section of the North Arm), however, the curvature is
reversed so that the Vening Meinesz
-
368 SULAWESI
minimum is found on the concave side of the arc. No active
volcanoes are present (in the section of reversed curvature). The
high positive values coinciding with the deep water of the Makassar
Strait are comparable with those of the Banda Sea. As soon as the
curvature returns to normal (i.e. the minimum on the convex side of
the arc) active volcanoes reappear, namely Una-Una and those on the
North Arm of Sulawesi and the Sangihe Islands. Here the profiles
show the standard sequence of maximum and minimum axes, troughs and
ridges.'
5. PRESENT-DAY A C T I V I T Y
69 The Sulawesi region is seismically active, and the northern
half is very active. Gutenberg & Richter (1954, pp. 60-61)
commented that seismic activity in the Celebes 'is well above
average for the Pacific belt; intermediate shocks are very numerous
and some of them (notably in northern Celebes) are among the
largest known. Deep shocks are fairly frequent.' Fitch & Molnar
(1970) remarked that 'The occurrence of earthquakes between 300 and
500 km depths in the Banda Sea region is an indication that the
lithosphere is continuous there. This activity may be a consequence
of the marked contortion in the seismic zone.' The difficulty of
interpreting important features of the seismic behaviour of
Sulawesi and the Banda Arcs in terms of regional tectonics was
pointed out by Fitch & Molnar: 'A zone of intense
intermediate-depth activity paralleling the northern peninsula of
Celebes forms the southern terminus of the deep-focus activity
beneath the Philippine arc. There are similarities between the con-
figuration of this zone and the seismic zone beneath the Banda Sea.
Both regions have intense activity extending from the surface
nearly vertically to approximately 200 km. Below 200 km activity is
less, and it is along a plane which dips approximately 45 ° beneath
the respective arcs.' 'East of the Celebes Sea is a complicated
seismic region associated with an island arc paralleling the
northern peninsula of Halmahera. A cross section of the activity in
this region shows that the zone beneath the Celebes Sea dips
towards the west while another zone extending only to intermediate
depth dips towards the south-east. This eastward-dipping zone is
very unusual, and its relation to the tectonics of the region is
not apparent to us.' More recently, further maps of the seismic
epicentres have been published (Fitch 1970). Hatherton &
Dickinson (1969) figured seismic isobaths to the north, south and
east of Sulawesi.
6. T I M E RELATIONS
85 The oldest undeformed rocks in Sulawesi are of Quaternary
age. They are mainly raised reef limestones, alluvium and coastal
plain deposits, many of which are highly fossiliferous.
83 The youngest deformed rocks are late Pliocene in age.
Throughout
Sulawesi and the archipelagos to the north and south Pliocene
rocks have been folded. Palaeontological evidence is not
sufficiently precise to be certain that these movements did not
continue into the Pleistocene (see Bemmelen 1949, pp. 149-52,
389-436; Vlerk & Dozy 1934). Before the age of the tectonic
events in the Cenozoic rocks of Sulawesi can be correlated reliably
with those in other Cenozoic fold belts the faunas need to be
reviewed in the light of the biostratigraphy of Blow (1969). 9t-5
Phases of mobility
10. Plio-Pleistocene uplift: Geomorphological evidence for this
event has been reported from all parts of Sulawesi. The process is
probably still continuing.
9. Late Pliocene phase: This was important and widespread. An
unconformity with gentle folds occurs in the East Arm (Kundig 1956;
Loczy 1933-4; Umbgrove 1938; Bemmelen 1949), in the South Arm
(Umbgrove 1938), in Central Sulawesi (Witkamp 1940; Vlerk &
Dozy 1934), and in the South-east Arm (Umbgrove 1938; Bothe 1927).
In the Butung Archipelago Bothe (1927) and Hetzel (1936) reported
strong folding and thrusting of Pliocene age. The evidence for the
age of these tectonic events rests mainly on the foraminifera
determined at that time. It seems likely that the age of the
folding would still be regarded as Pliocene, but in view of the
anomalous directions of movement, the faunas might profitably be
reviewed in the light of Blow's (1969) work. The movements might
range into the Quaternary.
8. Middle Miocene phase: In the East Arm this is the major
orogenic phase (Kundig 1956) and involved strong folding and
thrusting. The presence of an unconformity between U. and L.
Miocene, which may represent M. Miocene uplift, erosion and
possible folding, was reported from the Gorontalo and Minahasa
sections of the North Arm (Koperberg 1929-30; Bemmelen 1949). An
unconformity between the Oligo-Miocene and the 'Celebes Molasse',
which Umbgrove (1938) regarded as a M. Miocene Tf2 unconformity,
was reported from Central Sulawesi by Witkamp (1940) and may
possibly represent an orogenic phase there. The report of a
transgression in the 'post-Tertiary-f' (i .e.M. Miocene) in the
South-east Arm by Bothe (1927) may be related to M. Miocene or
possibly U. Miocene movements. Local erosion in M. Miocene time in
the Butung Archipelago was reported by Bothe (1927).
7. Lower Miocene: An unconformity at the base of the Miocene
Tondo Beds was reported from Butung (Hetzel 1936; Bothe 1927).
Umbgrove (1938) reported an unconformity of L. Miocene (Te4) age
from Central Sulawesi and the East Arm, but Kundig (1956) made no
mention of this unconformity in the East Arm.
6. Oligocene: An unconformity at the base of the Oligocene is
reported from Central Sulawesi (Bemmelen 1949). In the northern
part of the South Arm the main phase of folding and thrusting is
said to occur in the Oligocene (Rutten 1927; Bemmelen 1949).
-
SULAWESI 369
An unconformity at the base of the L. Miocene Tondo Beds of
Butung (Bothe 1927) may represent Oligocene movements. The
uncertainty results from the lack of a sufficiently diagnostic
microfauna.
5. End-Cretaceous to Eocene phase: In the South-east Arm a major
unconformity is present between the Cretaceous and the Neogene
(Eocene and Oligocene rocks are missing) and represents a period of
strong folding, uplift and erosion (Bothe 1927; Brouwer et al.
1934; Hetzel 1936; Bemmelen 1949). Here and in the nearby
~ _ _ ~ I 250km
CELEBES SEA
TOMINI GULF
UNA UNA I$, ~ GORONTALO TROUGH
o~::~
o -" "~
NORTHERN BANDA SEA
HAKASSAR( oGUNUNGAPI
Figure 3. Location map for the Sulawesi orogenic belt. K.-Z. =
Kolonodale zone. The named zones of Central Sulawesi are taken from
Van Beramelen (1949).
island of Kabaena evidence suggests there was an important phase
of metamorphism (glaucophane facies) penecontemporane- ous with
these end-Cretaceous orogenic movements in the South- east Arm
(Roever 1950, 1953, 1956). A major unconformity between the
Cretaceous Tobelo Beds and the L. Miocene Tondo Beds is widespread
in Butung Archipelago where it is considered to have resulted from
a period of folding, uplift and erosion (Bothe 1927; Hetzel 1936).
The local occurrence in Butung of the Wani Beds of either Eocene or
Oligocene age, unconformable on but folded with the underlying
Cretaceous Tobelo Beds, indicates an important orogenic phase at
the end of the Cretaceous, perhaps extending into Eocene or even
Oligocene time. In the South Arm an important unconformity between
Cretaceous and Eocene strata represents a period of folding and
erosion; in the northern part it marks the onset of andesite
volcanism (Rutten 1927; Brouwer et al. 1934; Bemmelen 1949). Owing
to the lack of precisely diagnostic faunas there is some doubt
about the time limits of these movements. In the East Arm the
actual contact between the Cretaceous and Eocene has not been
observed. Kundig (1956) thought it probable that there was a
depositional gap between the Cretaceous and the Palaeocene, and
that this interval coincided with the main phase of ophiolitic
extrusions. The rapid change from abyssal facies in the Cretaceous
to nerific facies in the Eocene seems to indicate strong vertical
uplift at the end of the Cretaceous in the East Arm. In the western
part of Central Sulawesi an important unconformity resulting from
fold movements and erosion separates Cretaceous and basal Tertiary
strata (which have locally been determined as Eocene) according to
Witkamp (1940) and Bemmelen (1949, p. 409).
4. Intra-Cretaceous phase: In part of the South Arm a siliceous
facies of probable Cretaceous age is overlain unconformably by a
greywacke-sandstone facies that is also thought to be Cretaceous on
the basis of its stratigraphical position and analogous litho- logy
(Rutten 1927; Brouwer et al. 1934; Bemmelen 1949). If these facies
have been correctly identified as Cretaceous there is evidence for
a period of folding and erosion in the southern part of the South
Arm during the Cretaceous.
3. Upper Jurassic--Lower Cretaceous phase ?: The Cretaceous
Tobelo Beds in Butung are in contact with the U. Jurassic Rumu Beds
and with other older Mesozoic formations. It is uncertain whether
this has resulted from tectonic complications or from a
depositional unconformity at the base of the Cretaceous Tobelo Beds
(Hetzel 1936; Bothe 1927; Bemmelen 1949). In the East Arm there is
no unconformity between the Jurassic and Cretaceous but Kundig
(1956) considered that there must have been a phase of great
downwarping during U. Jurassic to L. Cretaceous time, because of
the sudden change in facies from neritic Jurassic to bathyal
Cretaceous.
2. Lower Jurassic phase ?: In the west of the East Arm Loczy
-
370 S U L A W E S I
110" E
/ /
?
0 '
#
. ;~; ' :~
~Si:!:i:i:!:i:i:i:iS~:.',:~:,:.~.~/~:::::::::i:::::"" ~' .~:~;.~
. . . . . . . - . . . . .~ :~- ~...~..,:............. :...~....,.~
.~,..:...:.:,~ ~ . : .. ~...:.:,~: . . . . . ...
................................. ~ ~
i:i:i:i:i:i:i:i:i:i:!:!:i:i:i:i:i:!:ii:i:i:i:?:!:i:i:!:i:i:i:!:
iiiiiii!iiiii!iiiiiiiiiiiiiii i!iiiiiii!i!iiiii!ii
~ , 2 0 0 Isobaths on approximate centre of dipping seismic
zone, in km (after Hatherton & Dickinson 1969)
.~- Negative ~ Zones of isostatic Positive J gravity
anomalies
Region major positive isostatic of gravity anomaly
| 132' E
HALMAHERA
0 0 o
• ..:::: . ' : : ~ : : : - ~
..:::+~:~i:!:i:i:i:i:: .
' : ' : - F : - : ' ~ ' ~ ' : " . " ' - " ' . . . . . . . - " "
' - " : - > : ' : ' F : ' : - ' . : . ' . : . : ' . ' F " " . .
. . " ' " " . : - . ' . : . > ' . ~ . . . .
SERAM
,~:;;~,"
e.-'
Z~
t Lk
A TANIMBAR IPs--
]k Active v o l c a n o 4 0 0 " ~ - - ~ ~ ~ __ . . . . . ._
Faults and f ~ ~ " I o O "iolites postulated submarine
~ ~ M'"~r~ I ~ Granitic intrusions ~ Sula Spur
~ 0 ~ ~ - ~ - I~11 Direction of increasing ~ - n- - grade of
metamorphism ~ Main Islands
~ + ~ ~ ~ ) + ~ . . . - - T --- '~ ~ Direction of thrusting
250kin I II I
! ., I
Figure 4. The regional distribution of seismic and gravity
features of the Sulawesi and Banda Arcs orogenic belts and their
relationship to overthrmting, ophiolites, acid plutonics, and
recent volcanism.
-
SULAWESI 371
(1933-4) considered that the Triassic rocks were folded prioI to
the deposition of Jurassic strata. Umbgrove (1935) suggested that
in the west of Central Sulawesi there was a phase of folding after
the Triassic, followed by erosion after which marine sedi-
mentation recommenced during the Cretaceous. No rocks of definitely
Triassic age have been reported from western Sulawesi, however. So
although it is possible that there were fold movements and erosion
during the Jurassic in these parts of Sulawesi, it cannot be
regarded as proved.
1. Pre-Upper Triassic uplift and erosion appears to have been
widespread in Sulawesi and Butung. There may have been associated
folding but this has not been established. The evidence for these
events has been discussed by Bemmelen (1949).
87-9 The initiation of mobility associated with the
Mesozoic-Cenozoic orogeny could be regarded as the marine
transgression near the beginning of the U. Triassic that appears to
be a widespread pheno- menon in Sulawesi.
81 The oldest rocks deformed for the first time during the
Mesozoic-Cenozoic orogeny are fossiliferous Upper Triassic strata
reported from the East Arm by Loczy (1933-4) and Kundig (1956).
Loczy (1933-4) and Kutassy (1934) regarded some rocks in the
western part as Permo-Carboniferous but Hetzel (1935) referred to
them as 'very doubtful Permo-Carboniferous'. In the east of Central
Sulawesi, fossiliferous U. Triassic was reported to be the lowest
exposed member of a continuous succession up into the Cretaceous
(Umbgrove 1938). Fossiliferous U. Triassic Baito Beds in the
South-east Arm and the Einto Beds in Butung (Bothe 1927) are the
oldest rocks deformed for the first time by this orogeny there.
78 Basement rocks: Crystalline schists of pre-U. Triassic age
have been reported from the south-west of the Gorontalo section of
the North Arm (Koperberg 1929, 1930), from the Neck of the North
Arm (Egeler 1947), from the western and eastern parts of Central
Sulawesi (Kundig 1932, Williams 1937; Brouwer 1941; De Roever 1947;
Bemmelen 1949, fig. 171), from the South-east Arm (Dieckmann &
Julius 1925; Koolhoven 1932; Brouwer et al. 1934; Hetzel 1936;
Bemmelen 1949), from Butung (Bothe 1927; Hetzel 1936) and from
Kabaena (De Roever 1953). From the South Arm they were described as
pre-Cretaceous crystalline schists (Rutten 1927; Brouwer 1934;
Bemmelen 1949). The age of these basement rocks has been determined
from the unconformable relationship of the unmetamorphosed Meso-
zoic (U. Trias or locally Cretaceous) on the metamorphic
basement.
To the east of the Sulawesi orogenic belt very similar basement
rocks to those just described have been reported from the Sula
Islands (pre-Liassic crystalline schists, Brouwer 1921); they are
generally regarded as lateral extensions of the pre-U. Triassic
crystalline schists of the Banggai Islands (Bemmelen 1949; Klompe
1954, 1957; Kundig 1956). There seems to be strong evidence for
regarding, as Klompe (1954) did, the Banggai Islands as belonging
to the Sula Spur. They
thus lie outside the Sulawesi orogenic belt. To the west of the
Sulawesi orogenic belt basement rocks are not known to crop out
within 200 km of Sulawesi.
8. S T R U C T U R A L R E L A T I O N S
m-17 Two major faults have been recognized. The Tawaelia Graben
zone (Brouwer 1947) strikes N-S in Central Sulawesi and probably
extends north along strike to cut the North Arm and southwards
along the west side of the Bone Gulf, passing just east of Salajar.
The age of commencement of movements along this structure is not
known, but it separates zones 2 and 3 and so seems to be an
important feature related to the evolution of the belt. I t appears
to have in- fluenced the distribution of sedimentary facies on
either side since the Cretaceous and it limits the distribution of
metamorphic facies. The extent of its movements are unknown, but it
appears to have acted as a graben during Neogene and probably
earlier times. Mylonite occurs along part of the fault zone where
igneous rocks are present.
The other major faul t -- the Fossa Sarasina--also appears to
behave as a graben in Sulawesi, where it has formed a fault valley.
I t appears to strike NNW into the Makassar Strait. I t may be much
younger than the Tawaelia structure, but its age of initiation is
uncertain. The Fossa Sarasina and other faults in Sulawesi have
been discussed recently by Katili (1970).
9. R E V I E W OF O R O G E N I C D E V E L O P M E N T
132 GEOPHYSICAL EVIDENCE OF OROGENIC STRUCTURE
Fitch (1970) stated that data gathered from shallow focus earth-
quakes from 1961 to 1968 show that thrusting and normal faulting
are the dominant modes of deformation in the Philippines, Sulawesi
and Bands orogenic belts. The conclusion reached by Ritsema &
Veldkamp (1968) that strike-slip faulting is dominant was based on
data that Fitch (1970) claimed was inadequate by modern standards.
Another recent paper is that of Hatherton & Dickinson
(1969.)
Mechanism solutions from submarine seismic zones on the convex
sides of the North Celebes and North Moluccan Arcs show evidence
for underthrusting of lithosphere beneath the island arcs. Fitch
stated that there 'is no evidence from focal mechanisms supporting
the existence of underthrusting along the eastern end of the Sunda
Arc (i.e. the Banda Arcs) even though a well-developed inclined
seismic zone exists beneath the arc in this region . . . the close
approach of the Australian continent may have disrupted the simple
under- thrusting in the region'. Also 'inclined seismic zones
beneath the (Bands, North Celebes and North Moluccan) arcs show
that activity at deep and intermediate depths is in general
confined to narrow slab-like regions of the upper mantle' . He
claimed that seismic evidence from this region and other inclined
seismic zones 'supports
-
372 SULAWESI
the hypothesis that slabs of lithosphere constituting lateral
inhomo- geneities in the upper mantle beneath island arc structures
act as stress guides'.
On the basis of shallow focus seismic activity, Fitch (1970)
defined boundaries of plates of lithosphere that differ in detail
from the plate boundaries proposed by Le Pichon (1968) largely by
the introduction of the Philippine Sea plate (Fig. 5). Fitch has
drawn the tentative boundary of the Pacific and Asian plates
cutting through the East Arm and North Arm of Sulawesi. This
interpretation seems un- satisfactory to the present writer on the
basis of the published accounts of the geology of these
regions.
Figure 5. Plates of lithosphere within the Sulawesi and Banda
Arcs orogenic belts (from Fitch 1970). Plate boundaries are defined
here by shallow focus seismic activity, shown by the solid curve
and by a peeked line where the boundary is poorly defined.
134 THE OVERALL EVOLUTION OF THE SULAWESl OROGENIC BELT
Pre-Upper Triassic history: The oldest rocks in Sulawesi are
pre-U. Triassic crystalline schists with intrusives. The schists
have been produced by regional metamorphism of mainly sedimentary
rocks, the age of deposition and provenance of which are unknown.
The true age of the pre-U. Triassic metamorphism is not known.
Kundig (1956) and Roever (1956) referred to the crystalline
basement rocks as Palaeozoic or pre-Palaeozoic, but apparently
without evidence other than regional considerations. In the South
Arm of Sulawesi the crystalline schists can only be shown to be
pre-Cretaceous in age, but their metamorphism is likely to have
been of the same age as elsewhere. Possible Permian history: The
apparent absence of Permian rocks from Sulawesi is surprising in
view of the extensive Permian marine deposits
in parts of the Banda Arc (Timor and Left). Brouwer (1919)
thought that the crystalline schists in the Lesser Sunda Islands
(e.g. Timor) might, at least in part, be Permian in age on the
basis of a reported gradation between them and fossiliferous rocks
in Left. Bemmelen (1949) doubted the reality of this gradation and
postulated tectonic wedges to explain their association. The field
relations in Left need re-examination. Syn-orogenic
(Triassic-Jurassic) history: L. and M. Triassic strata are not
known in Sulawesi, although their presence was postulated by Loczy
(1933-4). U. Triassic neritic limestones and shales and a paralic
facies occur in zone 4. There may have been a period of erosion in
zones 2 and 3 during the U. Triassic. In zone 4 sedimentation from
the U. Triassic to the L. Cretaceous seems to have been fairly
continuous in shallow marine environments. Relatively gentle fold
movements may have occurred locally during this period.
Syn-orogenic (Cretaceous) history: During the Cretaceous there must
have been considerable downwarping of zone 4 for the facies change
rapidly from neritic to bathyal, suggesting a correlation with the
development of the Outer Banda Arc. In zone 2 Cretaceous deposits
appear to belong to two very different facies; one is
neritic-paralic, the other bathyal and similar to that of zone 4. I
t is possible that tectonic dislocations, presently unrecognized,
may account for this anomalous association. Alternatively, the east
and north of zone 2 may have been downwarped to provide a bathyal
environment similar to zone 4, whilst the west of zone 2 remained
close to sea level producing neritic sedimentation. Another
possibility is that the bathyal environment has been
mis-identified. Perhaps the calcilutites and siliceous deposits
were laid down in a quiet sea of moderate depth in which little
terrigenous sediment entered, so that deposits similar to bathyal
facies were produced. Syn-orogenic (late Cretaceous-L. Eocene)
history: At the end of the Cretaceous and possibly extending into
Eocene times, there was a major orogenic phase which resulted in
folding and local over- thrusting. It has been identified in zones
2, 3 and 4, although its effects appear to vary greatly along the
strike of the zone, e.g. it appears not to have had much influence,
beyond possible uplift, in the East Arm (zone 4). Accompanying this
orogenic phase was a major ophiolite eruption in zone 4.
Greenschist metamorphism probably occurred during this time in
zones 2, 3 and 4. In zones 3 and 4 there was also a
glaucophane-schist metamorphism contemporaneous with this phase.
Granodiorite intrusions into zone 2 occurred at this time as well
as volcanic activity during the Eocene. The direction of folding
and thrusting, as well as the development of ophiolites in a belt
around the Sula Spur, seem to indicate the important role that
feature was playing in the evolution of this region. In addition
the downwarping of zone 4 and perhaps parts of zones 2 and 3 in a
belt around the Sula Spur suggests a direct comparison with the U.
Cretaceous downwarping of the Outer Banda Arc in front of the
Australian shelf. Orogenic movements were widespread in the Banda
Arcs at this time.
-
S U L A W E S I 373
I I
' ' ; : " . ~,~ "' " "1- ': .. . . . . ~"~ , ", ,, .. ~ : ' . .
-~-. : . ! ,
P .~, ,, • _~.. ~. ~ ' + . : ~ - ~ "-- .. :.. .... . + + + ". -
, ; ,-..: t~.~.,-,.- .... • ".-F ± .: "" . "'
. . . . . .~ ~ "l'_Lt---~ ' " . .;'1":i --J:~.'.:'~--~'_ " - ,-
÷ ' r . I . . . . . ":
UNA UNA I S . ~
.. :~- f... GAI
~+ ÷ . ~ . . _ /~--,-- ." •
+ ar','-_~-- " ~
.~ " . : -
• t - , __--
_ SULA IS.
IOOkm i !
Ouat . . . . . y a,,uv,om ~" ~.-.~,.'," :at" Reefs etc
(~ i : ! "" _ ~ P Palaeogene
• . x ~ [ ) f ~'~11 und i f fe ren t ia ted
i ~ B U T U N G IS. ~ In te rmed ia te to basic suite, .!: •
KABAENA IS. . . ~
inc lud ing some in t rus ives I I Q TUKANG PLUTONIC ROCKS
t 0 ~ BESI IS. ~ i" SALAJAR IS. ~ ~ ' ~
Gran i te & granodiorite
Basic rocks, inc lud ing oph io l i tes
V 'i" " Figure 6. Geological sketch map of Sulawesi (redrawn
from a geological map published by the U.S.G.S. 1965). Blank areas
in
Sulawesi and the Sula Islands are areas for which no geological
maps are known.
-
374 SULAWESI
Syn-orogenic (M. Eocene-L. Miocene) history: Eocene to Oligocene
neritic deposits, mainly shelf limestone in zones 3 and 4, are thin
and often absent. This may be due to a period of uplift and erosion
following the folding and introduction of ophiolites. In zone 2 a
paralic facies de- veloped during Eocene to Oligocene times as well
as some lime- stones. The Eocene volcanic activity continued
through Oligocene and into Miocene times.
During the Oligocene the main orogenic phase of folding and
thrusting occurred in the north of the South Arm (zone 2). There
may also have been some fold movements in zone 3 and part of zone
4. Granodiorites and diorites were intruded into zone 2 during
Eocene to Oligocene times. During the L. Miocene shelf limestones
were widely deposited in Sulawesi, in zones 2, 3 and 4.
Syn-orogenic (M. Miocene) history: The main orogenic phase in part
of zone 4 (East Arm), involving folding and thrusting, occurred at
this time. There is a suggestion of some fold movements at this
time in zone 3 and the north of zone 2. The direction of thrusting
was towards the Sula Spur. The M. Miocene was the time of a major
orogenic phase in the Banda Arcs. @n-orogenic (U.Miocene-Pliocene)
history: A molasse facies was de- veloped in zones 2, 3 and 4
during this interval, perhaps as a re- sponse to uplift and erosion
following the M. Miocene folding phase. Very similar behaviour at
this time is found in the Banda Arcs. Locally neritic and littoral
depgsits developed in zones 2, 3 and 4 and in zone 2 volcanoes were
again active and important intrusions of granodiorites occurred.
Syn-orogenic (late Pliocene) history: Towards the end of the
Pliocene there was a widespread period of folding in all parts of
Sulawesi (zones 2, 3 and 4). Thrusts developed in the Butung
Archipelago and the movements appear to be towards the west. This
seems to be an anomalous feature of the regional tectonics and may
indicate the waning importance of the southern part of the Sula
Spur, perhaps associated with its subsidence in that region, where
the sea is now more than 4000 m deep. The U. Miocene to Pliocene
granodiorite intrusions of zone 2 may be associated with this
orogenic phase. In zone 2 there was volcanic activity at this time.
The late Pliocene interval also saw a period of folding throughout
most of the Banda Arc. Post-orogenic (Quaternary) history: The
Quaternary history of zones 2 and 4 appears to have been one of
uplift and erosion, following the late Pliocene fold movements. The
behaviour of zone 3 appears anomalous. The part of zone 3 in
Central Sulawesi seems to have been uplifted and eroded, as were
the Tongian Islands, whilst most of the zone is sub- marine and may
have subsided. Zone 1 subsided during the Quater- nary (Krause
(1966). Zone 5 by analogy with zone 1 also possibly subsided. It
seems likely that in general the Quaternary evolution of the region
has emphasized the relief between the marine and non- marine zones
by adjacent processes of uplift and subsidence. Volcanic activity
has occurred during the Quaternary in the nolthern part of zone 2
and in zone 3 (Una Una).
135 METAMORPHISM IN THE SULAWESI OROGENIG BELT
Metamorphic rocks occur in all the four arms of Sulawesi, in
some small nearby islands such as Kabaena and Butung and in several
parts of Central Sulawesi. The considerable literature on these
rocks has been summarized by Rutten (1927), Brouwer (1947) and
Bemmelen (1949) and the most recent publications are by Egeler
(1947, 1948) and Roever (1947, 1950, 1953 and 1956). The general
conclusions reached by Roever (1953, 1956) are as follows: (1) The
oldest phase of regional metamorphism in Sulawesi occurred before
the U. Triassic and probably produced the epidote-amphibolite
facies of Central Sulawesi (zone 3) and the amphibolite facies of
the South-east Arm, Butung and Kabaena (zone 4). This regional
metamorphic phase, which may even be pre-Palaeozoic according to
Kundig (1956), belongs to an orogeny older than the
Mesozoic-Cenozoic orogeny. (2) A younger regional metamorphic phase
which produced green- schists and glaucophane schist facies in
zones 3 and 4 is probably of late Cretaceous or early Eocene age.
(3) A phase of strong over- thrusting in Kabaena (zone 4), which
was post-Eocene in age (or possibly late Eocene or even mid-Eocene,
as Kundig (1956) suggested for the East Arm) produced dynamic
metamorphism. This dynamic metamorphic phase may have also occurred
contemporaneously in the North Arm (zone 2) (Brouwer et al. 1934)
and in the South-east Arm (zone 4). According to Kundig (1956) the
greenschists and amphi- bolites in the East Arm (zone 4) were
associated with the eruption of the ophiolites.
B. S U B D I V I S I O N OF T H E S E G M E N T
The Sulawesi orogenic belt is here divided into five structural
zones delimited somewhat arbitrarily at the 1000 m isobaths. The
Banggai Islands have been included in the Sula Spur, which is
regarded as a separate structural feature. Zone 1 is wholly
submarine, but has distinct northern and southern parts, the
Celebes Sea Basin (Krause 1966) and the Makassar Strait Fracture.
At the south of the Makassar Strait the sea floor shallows and
opposite Makassar the zone may be cut off" or pinch out. I f zone 1
of the Sulawesi orogenic belt connects with zone 1 of the Banda Arc
orogenic belt, then it must do so at 500 m between the Doang- doang
shoals and the coast near Makassar. There is some geophysical
evidence for regarding this broad ridge between the South A r m - -
Paternoster Islands and east Java as a structural feature
connecting the Western Celebes Arc with the Inner Sunda Arc of
Java. The geo- logical history and igneous activity of these two
regions offer support for this idea. Zone 5 (the Foredeep) will be
considered next, for like zone 1 it is wholly marine. Where zone 5
lies on the convex, outer side of the Banda Arc orogenic belt it is
a deep water zone always over 1000 m
-
SULAWESI
Table 1
ZONES AND ELEMENTS IN SULAWESI
375
Age and fades of the Elements
Zones
1 2 3 4 5
Celebes Sea Basin
W. Celebes Arc and N. Celebes Arc
Intra-Celebes E. Celebes Arcs Zone Arc Foredeep
Western Part of Sula Spur
Quaternary Volcanics Quaternary Littoral and neritic Quaternary
Evidence of subsidence LATE-PLIOCENE OROGENIC PHASE Pliocene
Littoral and neritic Miocene-Pliocene Granodiorite intrusive, U.
Miocene-Pliocene Molasse U. Miocene-Pliocene Paralic U.
Miocene-Pliocene Littoral and neritic U. Miocene-Pliocene Volcanics
MID-MIOCENE OROGENm PHASE Oligo-L. Miocene Volcanics Oligo-L.
Miocene Neritic Eocene-Oligocene Granite, granodiorite and
diorite intrusives Eocene-Oligocene Neritic Eocene-Oligocene
Paralic Eocene Volcanics U. Mesozoic-Eocene Glaucophane schists U.
Mesozoic-Eocene Greenschists U. CRETACEOus-L. EOCENE OROGENIC PHASE
U. Cretaceous-L. Eocene Ophiolites U. Cretaceous-L. Eocene
Granodiorite intrusives U. Mesozoic Bathyal U. Mesozoic Neritic L.
Mesozoic Neritic and paralic
UNCONFORMITY BELOW THE MESOZOIC SUCCESSION Pre-U. Triassic
Basement crystalline schists
X X
X X X
M M M + S x x x x × × x
x x W W S+W x x x x x
x x
x not Obi x only Obi
X X
X X
S S + W W x x only in Obi
x x not Obi x ? in Obi
x Juras, but no Trias
x x x x x x
Note: x =present Principal orogenic phases: S=strong;
M=moderate; W=weak.
and locally over 4000 m deep. In the Sulawesi region zone 5 lies
on the concave side of the inner arc, and its disappearance from
most of the Sulawesi orogenic belt may be associated with this
reversal of geometry. The in terpre ta t ion of the relative
positions of zone 5 and the Sula Spur in the Nor the rn Banda Sea
is open to discussion, however. The identif icat ion of the deeper
water ( > 1000 m) immedi- ately west of the Ha lmahe ra Islands
as the cont inuat ion of zone 5 of the Sulawesi orogenic belt is
one that might not find general acceptance, but it does seem to
occupy the outside of the convex outer arc (of the Nor th Moluccan
Arc). This region between Sulawesi and I r ian Barat is
geophysically complicated (el. Fitch 1970; Ha the r ton &
Dickinson
1969) and geologically poorly documented, so several a l ternat
ive tectonic interpretat ions are possible. Al though few
epicentres of in termediate and deep focus seismic ear thquakes are
reported from this par t of zone 5 (of. Fitch 1970), we may not
expect geophysical analogy with zone 5 of the Banda Arcs, because
the nea rby deep Phil ippine t rench and the volcanoes of Ha lmahe
ra have no equivalents on the convex side of the zone 5 of the
Banda Arcs. Zone 2. The western limits of zone 2 are drawn arbi t
rar i ly at the 1000 m isobath, except south of Makassar where (as
discussed for zone 1 above) the l imit is taken at the 500 m
isobath unti l near the t rench in the Flores Sea. From there the
margins of zone 2 cont inue
-
376 SULAWESI
eastward as part of the Salajar-Lucipara Arc at much greater
depths in the Banda Sea. The inner margin of zone 2 is drawn at the
1000 m isobath until the Banda Sea. This eastern margin coincides
locally with the submarine fault scarp on the east of the South Arm
which extends from the Tawaelia graben in Central Sulawesi to the
east of Salajar. In the north the margin separates the Sangihe
ridge and islands from the Gorontalo Trough and the Sangihe Trough.
The northern part of zone 2 (Northern Celebes Arc) is characterized
by a line of active volcanoes and a zone of epicentres of
intermediate focus earthquakes. Zone 3 may be called the
Intra-Celebes Arcs zone. Mostly it is submarine and is deeper than
1000 m or even than 9000 m. Two land areas are involved in this
zone, one is the Poso zone of Central Sulawesi and the other is the
Tongian Islands and the volcano of Una Una. On Sulawesi the western
margin of the zone is coincident with the Tawaelia graben and its
northern and southern submarine exten- sions. In the south this
zone is continuous with the Intra-Banda Arcs trough (zone 3 of the
Banda Arcs). Zone 3 is coincident with a zone of positive isostatic
gravity anomalies over most of its length in the Sulawesi belt, but
this feature does not continue into zone 3 of the Banda orogenic
belt. Zone 4 is the East Celebes Arc, which to the south and north
continues with structures called the Tukang Besi Arc and the North
Moluccan Arc respectively. At the southern end the arc is inter-
preted to be continuous along strike with the Outer Banda Arc (zone
4 of the Banda Arcs orogenic belt. The zone is characterized in
both the Sulawesi and Banda orogenic belts by a strong zone of
negative isostatic gravity anomalies. The seismic isobaths drawn by
Hatherton & Dickinson (1969) suggest important differences
between zone 4 of the Banda Arcs and part of zone 4 of Sulawesi
(the South- east Arm). Their contours suggest, however, that the
East Arm of Sulawesi may occupy a similar position to an inclined
seismic zone as that indicated for the Outer Banda Arc. The Sula
Spur: Stille (1945) and Klompe (1954) regarded the Sula Spur as a
detached part of the Australian continent. Kundig (1956) referred
to it as a 'small stable intra-orogenic craton'. Wegener (1966)
interpreted it as a structure due to New Guinea penetrating the
region of the Banda Arcs by the north-west drift of Australia
relative to Asia. Fitch (1970) claimed that seismic evidence
suggests the Sula Spur 'currently includes one or more plates of
lithosphere'.
The north margin of the western part of the Sula Spur is drawn
at the 1000 m isobath. Klompe (1954), and others later, took this
margin through the middle of Obi so as to exclude the ophiolites.
The present writer follows Kundig (1956) and Fitch (1970) and
considers on the basis of the geological history, the isostatic
gravity map and the shallow focus seismic activity that the
northern limit of the Sula Spur should be drawn north of Obi.
Eastward from Obi the northern limit is here drawn at the north
edge of the Obi-Pisau-Kafiau-Batanta ridge, which on the basis of
topography, the isostatic gravity anomaly
map and with some support from shallow focus seismic activity
(Fitch 1970), appears to be a more consistent interpretation than
that offered by Klompe (1954).
One problem is the relationship of the possible western
extension of the Sorong Fault zone, to the north edge of the Sula
Spur. Visser & Hermes (1962) suggested the fault extended south
of Obi and south of the Sula Islands. Alternatively it may extend
south of Obi but north of the Sula Islands, so that west of Obi it
could coincide with the north limit of the Sula Spur, or it could
occur north of Obi separating that island from the Halmahera
Islands; this last interpretation might account for a line of
shallow focus seismicity along the postulated extension (Fitch
1970). The south margin of the west part of the Spur presents the
greatest problem; the positive isostatic gravity anomaly extends
south into the north of the Banda Sea where the sea floor drops
rapidly to 4000 m south of the Sula Islands. The present writer
follows Klompe (1954) in drawing this south margin around the
southern limit of the gravity anomaly; this seems to accord most
closely with the tectonic behaviour of the East Celebes Arc and the
Outer and Inner Banda Arcs, although this hypothesis receives no
support from present seismic activity.
C. S T R U C T U R A L R E L A T I O N S H I P S OF T H E S U L
A W E S I A R C S W I T H
N E I G H B O U R I N G R E G I O N S
Sulawesi separates four major geological provinces: to the west
and south-west are the Larger Sunda Islands and their shelf, partly
represented by Borneo and Java; to the south and south-east are the
Lesser Sunda Islands which form the Banda Arcs; to the east is the
Vogelkop and Bomberai of Irian Barat (formerly called west New
Guinea); to the north are the Philippines which form part of the
island chains that mark the boundary of the western Pacific. Each
different part of Sulawesi appears to have geological affinity with
some important aspects of one or more of these four major
geological provinces. On the basis of the linear belt of strongly
negative gravity anomalies that characterize the East and
South-East Arms of Sulawesi, the East Celebes Arc has been regarded
(Kuenen et al. 1934) as an extension of the Outer Banda Arc
(structural zone 4). I t is believed to continue northwards into
the North ~vIoluccan Arc (Visser & Hermes 1962). There is
uncertainty about the correlation on gravity data between Butung at
the south of the South-East Arm and Buru because this part of the
Banda Sea does not display the strong negative gravity values that
characterize zone 4 elsewhere. Westerveld (1955) noted that the
submarine floor of this part of zone 4 was marked by a series of
strong ridges and trenches striking NW-SE, which he suggested
probably marked the sites of transverse faults striking in that
direction. The absence of the strong negative gravity values may be
associated with such faults. The correlation of the Outer Banda Arc
with the
-
SULAWESI 377
East Celebes Arc has also been proposed on the basis of these
lands possessing a Mesozoic (and possibly Palaeozoic) history that
dis- tinguishes them from all the surrounding regions. Umbgrove
(1938) a n d Teichert (1939) referred to this zone 4 as the T i m o
r - - E a s t Celebes Geosyncline, and Teichert thought it an
extension of the Westra l ian Geosyncline of the Carnarvon
basin.
The South A r m of Sulawesi, together with the Palu zone of the
central region and the North Arm, expose granite intrusions and
acid extrusives which suggests some affinity between this zone 2
and the larger Sunda Islands (Borneo, J a v a & Sumatra) . In
contrast, in the East and South-East Arms extensive outcrops of
ultrabasic and basic igneous rocks predominate , which as Brouwer
(1930) observed are characteristic of the Banda Arcs.
The North A r m of Sulawesi is usually regarded as a southerly
extension of the chains of island arcs around the western Pacific.
The Phi l ippine Arc passes south of M i n d a n a o into a submar
ine ridge with islands and then into the Minahasa portion of the
North Arm. This correlation is based on the strong topographical
feature with accompanying chain of active volcanoes (zone 2) which
separates the belt of strong negative gravity anomalies of the
North Moluccan Arc (zone 4) from the strong positive anomalies of
the Celebes Sea (zone 1).
The structural relationship of the South A r m and the western
part of Central Sulawesi (zone 2) to zones 3 and 4 is uncertain.
The south of zone 2 lacks active volcanoes (Neumann van Padang
1951) and strong gravity anomalies in Sulawesi. The acid igneous
rocks of this region have suggested some possible affinity with the
Larger Sunda Islands to the west and south, but Westerveld (1955)
proposed that this region was an extension of the Inner Banda Arc.
He suggested that the southern part of the South A r m was part of
an arc that connected Salajar with the Banda Islands through a
series of submar ine ridges with a few islands such as Komba ,
Gunungap i and the Lucipara Islands. This arc is characterized by
weak positive isostatic anomalies and locally in the Banda and
Flores Seas by active volcanoes. At the present t ime there seems
to be insufficient avai lable geological or geophysical evidence to
support or reject this hypothesis.
Two major strike slip faults, called the Sorong Faul t zone and
the Tarera-Aidoena Faul t zone in I r ian Barat by Visser &
Hermes (1962), m a y through their possible westward extension have
influenced the development of the major arcuate zone of the East
Celebes Arc and its extensions into the Phi l ippine and Banda
Arcs.
Stille (1945) and Klompe (1954) suggested that the region of the
Sula and Banggai Islands where crystalline schists crop out, m a y
repre- sent a detached fragment of the Austral ian continent. The
western par t of this Sula Spur is characterized by a strong
positive gravity anomaly. In Figs. 1, 2 and 4 the eastward
extension of this Spur is shown to include the is land of Obi and a
south-eastward extension is suggested to include Misool and part of
south-western Bomberai . Stille (1945) regarded Misool as part of
the Sula Spur and Bemmelen (1949, p. 458) considered that Misool
does not belong to the Banda Arcs but is par t
of what he called the ' foreland belt ' that included Sula, Ob i
and western Bomberai . Visser & Hermes (1962) and Hermes (1968)
considered that Misool and western Bomberai form part of the Banda
Arc pr in- cipally because they were submerged dur ing most of
Mesozoic time. The present author favours the interpretat ion that
regards Misool and western Bomberai as part of the Sula Spur and
distinct from the Banda Arcs.
Al though the definition of the limits and correlation between
the various structural zones of Sulawesi and the ne ighbour ing
island arcs is open to debate, it is general ly acknowledged
(Umbgrove 1949; Holmes 1965) that Sulawesi represents the junc t
ion of two major Ter t iary orogenic belts, one is the H i m a l a
y a n - I n d o b u r m a n - I n d o n e s i a n orogenic belt and
the other a b ranch of the Circum-Pacif ic orogenic belt.
D. R E F E R E N C E S
BEMMELEN, R. W. VAN. 1949. The Geology of Indonesia. The Hague
(Government Printing Office).
BLOW, W. H. 1969. Late Middle Eocene to Recent planktonic
foraminiferal bio- stratigraphy. In: Bronniman, P. & Renz, H.
H. (Eds.), Proceedings 1st Inter- national Conference on Planktonic
Microfossils, Geneva (1967), vol. 1. Leiden (Brill), pp.
199-421.
BOTHE, A. CH. D. 1927. Voorloopige mededeeling betreffende de
geologic van Zuidoost Celebes. De Mijningenieur, 8, 97-103.
BROUWER, H. A. 1919. Geologisch overzicht van her oostelijk
gedeelte van den Oost- Indischen Archipel. 07aarb. M~inw. Ned.-
Oost-Indig, 1917, 2, 145-452.
- - 1921. Geologische onderzoekingen op de Soela Eilanden.
07aarb. MOnw. Wed.- Oost-Indi~, 1920, 2.
1924. Bijdrage tot de geologic der Obi-eilanden. 07aarb. Mijnw.
Wed.-Oost- Indig, 1923, 63-136.
1930. The major tectonic features of Celebes. Proc. K. ned.
Akad. Wet. 33, 338-43.
- - 1 9 4 1 . Tektonik und Magma in der Insel Celebes und der
indonesische Gebirgstypus. Proc. K. ned. Akad. Wet. 44, 253-61.
- - 1 9 4 7 . Geological explorations in Celebes: Summary of the
results. In'. Geo- logical Explorations in the island of Celebes.
Amsterdam (North-Holland), pp. 1-64.
BROUW~R, H. A., H~TZEL, W. H. & STRAET~R, H. E. G. 1934.
Geologische onderzoe- kingen op het eiland Celebes. Verh. K. ned.
geol.-m~jnb. Genoot. 10, 39-171.
BRUYN, J. W. de. 1951. Isogam maps of Caribbean Sea and
surroundings and of southeast Asia. WldPetrol. Congr. 3,
1,598-612.
DIECKMANN, W. • JULIUS, M. W. 1925. Algemeine geologie en
ertsofzettingen van Zuidoost Celebes. 07aarb. Mijnw.
Wed.-Oost-Indig, 1924, 11-65.
EGELER, C. G. 1947. Contribution to the petrology of the
metamorphic rocks of western Celebes. In: Geological explorations
in the island of Celebes. Amsterdam (North-Holland), pp.
177-346.
- - 1948. On amphibolitic and related rocks from Western Celebes
and the southern Sierra Nevada. California. Proc. If. ned. Akad.
Wet. 51, 100-5
FITCH, T.J. 1970. Earthquake mechanisms and island arc tectonics
in the Indonesian- Philippine region. Bull. Seismol. Soc. Am. 60,
565-91.
FITCH, T.J. & MOLNAR, P. 1970. Focal mechanisms along
inclined earthquake zones in the Indoneslan-Philippine region. 07.
geophys. Res. 75, 1431-44.
GUTENBERG, B. & RICHTER, C. F. 1954. Seismicity of the Earth
and related phenomena. 2nd edn. New Jersey (Princeton University
Press).
-
378 S U L A W E S I
HATHERTON, T. & DICKINSON, W. 1~.. 1969. The relationship
between andesitic volcanism and seismicity in Indonesia, the Lesser
Antilles, and other island arcs. 07. geophys. Res. 74, 5301-10.
HERMES, J. J. 1968. The Papuan geosyncline and the concept of
geosynclines. Geol. Mijnb. 47, 81-97.
HeTZEL, W. H. 1935. Enkele kritische aanteckeningen bij een
recente publicatie over de Geologic van den Oostarm van Celebes. De
Ingenieur in Ned. Ind. 2 (4), IV, 29-31.
1936. Verslag van het onderzoek naar het voorkomen van
asfaltgesteenten op het eiland Boeton. Wet. Meded. Dienst. Mijnb.
Ned.-Oost-Indig, 21.
HOLMES, A. 1965. Principles of physical geology. 2nd edn. London
(Nelson). KATIL~, J. A. 1970. Large transcurrent faults in
southeast Asia with special reference
to Indonesia. Geol. Rdsch. 59, 581-600. KLOMPE, TH. H. F. 1954.
The structural importance of the Sula Spur (Indonesia).
Indones..y. nat. Sci. 110, 21-40. 1957. Pacific and Variscan
orogeny in Indonesia. Indones. ~7. nat. Sci. 113,
43-87. KOOLHOVEN, W. C. B. 1930. Verslag over eene
verkenningstocht in den Oostarm van
Celebes en den Banggai-archipel. aTaarb. Mijnw. Wed.-Oost-Indig,
1929, 187-228. 1932. De Geologic van her Maliliterrein (Midden
Celebes). j?aarb. Mijnw.
Wed.-Oost-Indig, 1930, 3, 127-53. KOPERnERG, M. 1929 & 1930.
Bouwstoffen voor de geologic van de Residentie
Menado. oTaarb. Mijnw. Ned.-Oost-Indig, 1928, 1 and 2. KRAUSE,
D. C. 1966. Tectonics, marine geology and bathymetry of the Celebes
Sea-
Sula Sea region. Bull. geol. Soc. Am. 77, 813-32. KtmN~N, PH.
H., UMBGROVe, J. H. F. & VENING MEINESZ, F. A. 1934.
Gravity,
geology and morphology of the East Indian Archipelago. In:
Gravity expeditions at sea, 1923-1932. Vol. II, The interpretation
of the results. Netherlands Geodetic Commission, pp. 107-94.
KUNDm, E. 1932. Versuch einer petrographischen Characteristik
des Kristallinen Grundgebirges von Celebes. Schweiz. miner,
petrogr. Mitt. 12, 450-507.
1956. Geology and ophiolite problems of east-Celebes. Verb. If.
ned. geol.- m~inb. Genoot. 16, 210-35.
KtrrAss,,', A. YON. 1934. Her Paleozoicum en de Trias van Oost
Celebes. Verb. If. ned. geol.-m~inb. Genoot. 10, 295-305.
Ia~ PICHON, X. 1968. Sea-floor spreading and continental drift.
J. geophys. Res. 73, 3661-705.
LoezY, L. YON. 1933--4. Geologic van Noord Boengkoe en het
Bongka gebied tusschen de Golf van Tomini en de Golf van Tolo in
Oost Celebes. Verb. If. ned. geol.- mijnw. Genoot. 10, 219-27.
NAGASAKA, K. 1971. Terrestrial heat flow in the Celebes Sea and
the Sula Sea. Marine geophys. Res.
NEUM~'~N W~'~ PADANG, M. 1951. Catalogue of the active volcanoes
of the world including solfatarafields. Part 1, Indonesia. (Int.
Ass. Vulc.)
RITSEMA, H. R. & VELDK~'~P, J. 1968. Fault plane mechanisms
of southeast Asian earthquakes. Meded. Verh. If. ned. met. Inst.
76, 63.
ROEVER, W. P. DE. 1947. Igneous and metamorphic rocks in eastern
central Celebes. In: Geological explorations of the island of
Celebes. Amsterdam (North-Holland), pp. 67-173.
1950. Preliminary notes on glaucophane-bearing and other
crystalline schists from south-east Celebes, and on the origin of
glaucophane-bearing rocks. Proc. If. ned. Akad. Wet. 53,
1455-65.
1953. Tectonic conclusions from the distribution of metamorphic
facies in the island of Kabaena, near Celebes. Proc. Pacific Sci.
Congr. (New Zealand, 1949), 7, 2, 71-81.
- - 1 9 5 6 . Some additional data on the crystalline schists of
the Rumbia and Mendoke mountains, south-east Celebes. Verh. K. ned.
geol.-mijnb. Genoot. 16, 385-93.
RoY, B. C. (co-ordinator). 1961. Geological map of Asia and Far
East (1:5,000,000) (ECAFE.)
RUTTEN, L. M. K. 1927. Voordrachten over de geologic van
Nederlandsch Oost-Indig. Groningen-Den Haag (Wolters U.M.).
STXLLE, H. 1945. Die tektonische Entwicklung des hinterindischen
Festlands und Inselgebiete. Geotekt. Forsch. 7, 1-34.
TECTONIC MAP OF EURASIA (SCALE 1:5,000~000). 1966. Moscow (Akad.
nauk SSSK). TEICHERT, C. 1939. The Mesozoic transgressions in
Western Australia. Austr. 3. Sci.
2, 84--6. UMBGROV~, J. H. F. 1935. De Pretertiaire historic van
den Indischen Archipel. Leid.
geol. Meded. 7, 119-55. - - 1938. Geological history of the East
Indies. Bull. Am. Ass. Petrol. Geol. 22,
1 -70 . 1949. The structural history of the East Indies
(Cambridge University Press).
UNITED STATES GEOLOGIC SURREY. 1965. Geologic map of
Indonesia--Eastern half. 1:2,000,000. Misc. geol. Inv. Map.
1--414.
VXSSER, W. A. & HERMES, J. J. 1962. Geological results of
the exploration for oil in Netherlands New Guinea. Verb. If. ned.
geol.-m~]nb. Genoot. 20, 1-265.
VLERK, I. M. VAN DER & DOZY, J. J. 1934. The Tertiary rocks
of the Celebes expedi- tion, 1929. Verh. If. ned. geol.-rn~]nb.
Genoot. 10, 183-217.
VLERK, I. M. VAN DER & UMBGROVE, J. H. F. 1927. Tertiaire
gidsforaminiferen van Nederlandsch Oost-Indie. Wet. Meded. Dienst.
Mijnb. Wed.-Oost-Indi8, 6.
WEGENER, A. 1966. The origin of continents and oceans. 4th edn.
London (Methuen). WP..STERVELD, D.J. 1955. The Lucipara Islands
ridge and a third arc in the Banda
Sea. Geol. Mijnb. 17, 84-8. WILLIAMS, H. W. V. 1937.
Contribution to the petrology of the crystalline schists of
western central Celebes. Doctoral thesis, University of
Amsterdam. WITKAMP, H. 1940. Langs het stroomgebied van de
Lariangrivier (West Celebes).
Tijdschr. If. ned. aardrijksk Genoot. 47, 581-600. WUNDERLIN, W.
1913. Beitr~ige zur Kenntnis der Gesteine yon Sfidost-Celebes.
Samml. geol. Reichsmus. Leiden, Ser. 1, 9, 244-80.