Jour. Geol. Soc. Japan, Vol. 107, No. 5, p. 316-336, May 2001

Malampaya Sound Group : a Jurassic-Early Cretaceous accretionary complex in , North Block ()

Abstra.et

Lawrence R. Zamoras' Busuanga Island is considered an accretionary complex primarily composed of Middle Permian to Jurassic chert and Atsushi Matsuoka** (Liminangcong Formation), Middle Jurassic to Early Cretaceous elastics (Guinlo Formation) and limestone units of various ages, Received November 1, 2000. with minor melange bodies (Bicatan Melange), collectively Accepted February 27, 2001. called as the Malampaya Sound Group. These rocks are Graduate School of Science and Techno- regarded as off scraped sedimentary deposits from a subducted logy, Nugata University, Niigata 950-2181, oceanic plate that developed imbricate structure during the Japan. Jurassic-Early Cretaceous accretion. The lithologic transition Department of Geology, Faculty of Sci- from chert to siliceous mudstone to terrigenous elastics ence, Nngata University, Niigata 950-2181, indicates facies change from pelagic to terrigenous condition Japan. brought by a plate movement from an open ocean to the subduction zone. The siliceous mudstone units, which mark the end of chert deposition and the beginning of clastic deposition, are classified into three different ages in Busuanga Island, and found to be younging from north to south. This provides a major basis for de亜ning three belts composing Busuanga Island :the Northern, Middle and Southern Busuanga belts. The Northern Busuanga Belt is composed of Middle Permian to Middle Jurassic (probably Aalenian) chert followed by Batho- nian-Callovian (JR4-JR5) siliceous mudstone and Callovian (JR5) terrigenous elastics. T顛e Middle Busuanga Belt has its topmost chert deposit at Bajocian-lower Bathonian (JR4), siliceous mudstone interval from upper Bathonian to lower Oxfordian (JR5-JR6), and terrigenous elastics at Oxfordian (JR6). The Southern Busuanga Belt shows the transition from lower-middle Tithonian (JR8) chert to upper Tithonian- Bernasian (KRl) siliceous mudstone. The subsequent deposi- tion of terrigenous elastics, supposedly overlying the siliceous mudstone, is considered occurring within the Lower Cretaceous. The off scrape accretion period of these three belts probably occurred during the Middle Jurassic for the Northern Busuanga Belt, Late Jurassic for the Middle Busuanga Belt and Early Cretaceous for the Southern Busuanga Belt. These chert-clastic sequences of the Malampaya Sound Group are also found correlative with the Togano Group of the Southern Chichibu Terrane of SW Japan.

Key words : Busuanga, North Palawan Block, Liminangcong Formation, Gumlo Formation, Malampaya Sound Group, chert- clastic sequences, accretionary complex, radiolarian, Jurassic, Bicatan Melange, Togano Group

framework. After a few decades of continuous geo- Introduction logic works particularly in Japan, the NE-SW trend- The progressive studies on chert-clastic sequences ing subduction zone along the eastern margin of that eventually established the Mesozoic accretion- Asian landmass during the Mesozoic, as earlier pro- subduction complexes in East Asia have attained the posed by Hamilton (1979), has finally become evident essential role in understanding the region's tectonic in the stratigraphy and geologic structure of the

◎ The Geological Society of Japan 2001 316 Jour. Geol. Soc. Japan, 107 (5) Accretion complex in Busuanga, Philippines 317

Fig. 1. (A) The North Palawan Block言n the western central Philippines. (B) The and location of the study area. (C) The Jurassic accretionary complex in East Asia (Isozaki et al.∴1988 ; Matsuda and Isozaki, 1991 ; Mizutani and Kojima, 1992 ; Kojima and Kametaka, 2000)I The dashed lines indicate the probable location of the North Palawan Block before the mid-Oligocene opening of the (Holloway, 1982).

region. Following its acceptance, geologic research- coveries in mid 1980's, Isozaki et al. (1988) proposed the ers worldwide did substantial review on recognized subduction-accretion framework for the North chert-clastic complexes in this modern tectonic per- Palawan Block quite similar to the then newly spective. Heretofore, ongoing developments on tec- recognized subduction-accretion complexes in SW tonic studies in East Asia in collaboration with radio- Japan. Faure and Ishida (1990) further proposed that larian works successfully amassed sufficient amounts the North Palawan Block is an olistostrome with its of data whereby terrane correlation within the region chert and limestone bodies serving as olistoliths set in have already become possible. Middle-Late Jurassic mudstone matrix. In the ab- The chert-clastic complex in the North Palawan sence of follow-up geologic, structural or tectonic Block (Fig. 1 A) has long been intended for review and works during the last decade, however, our modern further research to complement the progress of study theory on the Mesozoic events transpiring the North in the region's chert-clastic complexes especially in Palawan Block remained unsubstantiated. Japan. That the structural framework of Busuanga Nevertheless, radiolarian works in Busuanga Island Island considered as an array of parallel folded struc- continuously increased particularly during the last tures oriented NE-SW in the western side and NW-SE decade. These works such as Cheng (1989, 1992), in the central and eastern portion (Bureau of Mines Tumanda (1991a, 1991b, 1994), Yeh (1992), Yeh and and Geosciences (BMG), 1984) needs to be reviewed to Cheng (1996, 1998), Tumanda-Mateer et al. (1996), and ascertain its comparability with East Asian chert- Zamoras and Matsuoka (2000a) have gradually clastic complexes. Following the tectonic dis- portrayed general characteristics of the chert-clastic Lawrence R. Zamoras and Atsushi Matsuoka 2001-5

or biostratigrapmc zone assignments particularly for Jurassic samples are referred from the zonal scheme for the Western Pacific and Japan proposed by Matsuoka (1995). Succeeding sections are the revi- sion of the Upper Paleozoic-Mesozoic stratigraphy of the North Palawan Block and the characterization of the chert-clastic sequences including the subdivision of Busuanga Island into three belts. Later discus- sions include the geologic structure of the ac- cretionary complex, its formative process, and its cor- relation with corresponding complexes in Japan. The area covered in this study is the easily accessi- ble central portion of Busuanga Island (Fig. 1B). Unlike the east and western sides of Busuanga Island the central portion manifests simple topographic con- figuration quite reflective of its geologic structures as Fig.2. Sample locations of previous radiolarian works. C : Cheng (1989, 1992), I : Isozaki et al. (1988), T : well as lithologic distribution. This significantly Tumanda (1991a), Y : Yeh (1992), YC: Yeh and Cheng guides in planning for an appropriate mapping strate- (1996, 1998), Z : Zamoras and Matsuoka (2000a). gy. Its road network connecting villages to Coron town generally cut across the chert-clastic sequences, sequences in Busuanga Island (see Fig.2). The which favorably provide us exposures for data gath- reports on the occurrence of Permian, Triassic and ermg. An approximate total of 20km of north-south Jurassic chert sequences, and Jurassic elastics as well, section can be traced across central Busuanga Island can already give an impression of apparent continui- from Buyod Point to Coron. ty. In fact, Tumanda (1991a) had already proposed a Outline of the geology in Busuanga Island radiolarian biostratigraphic zonation of the Middle Permian to Lower Jurassic chert sequences. These The North Palawan Block is considered a continen- developments in radiolarian research have already tal fragment (Hashimoto and Sator1973 ; Hamilton, offered potentially important contribution to the nee- 1979) which integrates the northern half of Palawan essary further studies in Busuanga Island or in the Island, the Calamian Islands, the Reed Bank, SW North Palawan Block. Mmdoro, NW and Tablas Islands (Holloway, In this work the general scope covers the Permian, 1982 ; McCabe et al, 1982). Its stratigraphy shows a Tnassic and Jurassic stratigraphy of the. North distinct sequence of Upper Paleozoic to Mesozoic sed- Palawan Block but the emphasis remains on the Ju- lmentary rocks not found in the younger Philippine rassic portion. The significance of the Jurassic por- Island arc. This evidence combined with magnetic tion is that it is the stage when the lithologic transi- anomaly data from the South China Sea (Taylor and tion from chert to elastics occurred, not observed in Hayes, 1980) firmly supports the model that the North the Triassic and Permian sequencesin North Palawan. Palawan Block originated from the Asian mainland.

This transition specifically indicates a paleoenviron- Its southward drift was driven by a sea一且oor spread- mental change typical to those with pelagic settings ing from mid-Oligocene to early Miocene based on that gradually approach toward a continent, the South China Sea's east-west trending magnetic linea- formational process theory of accretion-subduction tions dated 32-17Ma (Taylor and Hayes, 1980). Hollo- complexes. In this advanced stage of chert-clastic way (1982) further elaborated the crustal movement of sequence studies, understanding the complex litho- the North Palawan Block with palinspastic recon- logic and radiolarian assemblages would not be as struction of tectonic plates from the Jurassic ac- crucial as experienced by earlier researchers. The cretion-subduction setting, through the incipient development of well-defined accretion-subduction stage of crustal migration when the South China Sea models for East Asia has significantly facilitated our opened, and負nally its collision with the Philippine understanding of the North Palawan Block's tectonic Island arc system. Recent studies on Mesozoic ac- framework. cretion-subduction widely believe that the North This paper attempts to present the geology of Palawan Block was positioned alongside with SW Busuanga Island and its role m understanding the Japan s accretion subduction complexes and Taiwan Upper Paleozoic to Mesozoic stratigraphy and tecton- m between (e.g., Isozaki etal, 1988 ; Matsuda and ics of the North Palawan Block. It starts with a brief Isozaki, 1991 ; Mizutani and Kojima, 1992 ; Isozaki, presentation of radiolarian data from selected 1997 ; Kojima and Kametaka, 2000) (Fig. 1C). samples, followed by detailed geological, paleontolog- There are about five major stratigraphic works con- ical and age descriptions of selected areas. The ages ducted in the North Palawan Block : Hashimoto and Jour. Geol. Soc. Japan, 107 (5) Accretion complex in Busuanga, Philippines 319

Sato (1973), BMG (1981), Wolf art et al. (1986), Isozaki et 1. Bicatan Peninsula aL (1988) and JICA-MMAJ (1990) in cooperation with A good geologic section of roughly 6km is exposed BMG. These works gradually developed more com- along the western coast of Bicatan Peninsula, north of plex stratigraphy following the discovery of new data Decabobo village. The strata dip variably from NW from expanded areas of the North Palawan Block. in the central portion, to NE in the northern and However, these stratigraphic columns are made prior southern portion but it can be generalized as north- to the inception of the Mesozoic accretion-subduction ward dipping. This long coastal section shows rela- framework as the encompassing explanation of the tively better or clearer exposure since the outcrops chert-elastics-limestone complex. Certain modific- are fresh and the strata are cut perpendicular to the ations are proposed in this present work including coastline. The chert appears as white-colored with revised geologic map and section, redefinition of black layers in the north, while it is red-colored far- lithostratigraphic units and revision of its strati- ther south. Its radiolarian occurrences between graphic column. The formational names, Limmang- Buyod Point and Dipalirong Point are not well cong Formation for the chert sequences and Gumlo represented due to notably poor preservation. Two Formation for the clastic sequences, are retained samples collected near Buyod Point, B10-02 and B 10- while the sporadic limestone bodies are treated in one 05 contains poorly to moderately preserved radiolan- category as limestone units. These Paleozoic- ans of probably Middle Triassic radiolanans. These Mesozoic sequences are collectively referred to as the include Spinotriassocampe annulata (Nakaseko and Malampaya Sound Group (see Fig. 7). Further dis- Nishimura), S. carnica Kozur and Mostler, Pentac-

cussion on this appears in later section. tinocarpus awaensis (Nakaseko and Nishimura) and‾ Triassocampe spp. Another chert sample B 17-21 taken Geological and paleontological descriptions near Dipalirong Point is also considered Tnassic for selected areas based on the presence of Tnassocampe sp.

Geologic studies for chert-clastic sequences pnmar- A limestone-basalt-chert melange is observed about ily require radiolarian analysis to stratigraphically 2km south of Buyod Point at the foot of another distinguish one chert or clastic outcrop from another. unnamed peak. This melange body is composed of Recognizing which chert is Permian, Triassic or Ju- highly indurated micritic limestone and basalt with rassic in the field has been regarded difficult as no minor che止Its components range in size from reliable physical distinctive characteristics associate pebble to boulder. Limestone clasts generally have with these different ages. The radiolarian occur- larger size and basalt of smaller size. Occasionally, rence in Busuanga Island therefore offers indispensa- the pebble size component shows a mixture of lime- ble data in the analysis of its geology. stone and basalt serving as the matrix of the cobble In this study, the samples collected from the central sized limestone. The proportion of basalt and lime- portion of Busuanga Island generally yield fair radio- stone varies from limestone-dominated, equal larian contents. The siliceous mudstones generally limestone-basalt proportion to basa虹dominated. In contain well preserved radiolarians in remarkable ab- limestone-dominated portion, the limestone clasts undance much better than chert and terrigenous tend to amalgamate and, in the process, swallow the mudstone samples. Most chert samples contain basalt resulting to a massive limestone appearance, recrystallized forms while terrigenous clastic samples while the basalt components are reduced to forming have fewer radiolarian occurrences. Table 1 shows vein-like structures. At the base of this melange, can the partial list of identified radiolarian species from be observed a bedded chert block of probably Permian selected samples, mostly Jurassic. Figures, descnp- age (B 10-13). Below the bedded chert block, a chaot- tions and elaborate characterization of these assem- ic array of parallel oriented volcaniclastics and lime- blages will appear in another paper in the near future. stone in shear contact with one another. In the The sections investigated are grouped into seven basalt-dominated portion, cobble-sized fragments areas namely (1) Bicatan Peninsula, (2) Decabobo-San described as olivine basalt are contained in a volcani- Nicolas, (3) Buwang, (4) Guadalupe-Mabintangin, (5) clastic matrix. In one horizon, lensoid shaped pebble Decalachiao-Maricaban-Cabilauan, (6) Pangarawan limestone clasts are set oriented parallel m green River and (7) southern Busuanga (see Fig. 3 for loca- basaltic matrix. In the lowermost portion of the out- tions ; Fig. 4 for the geologic map). Included in the crop also appears amygdaloidal basalt as clasts. discussion of each section are the lithologic descnp- Another melange type is observed in two outcrops tion, geologic structure, radiolarian data and age. in Buyod area, south of the limestone-basalt-chert Certain emphasis is given to Jurassic sections, which type. The first outcrop appears sandwiched between are discussed in terms of biostratigraphic zonations sandstone and chert strata. It is basically composed unlike the more generalized Triassic and Permian sec- of 2-3 cm thick sandstone layers, set in a dark green to tions. black mudstone matrix. Recurrence of similar me- lange type is observed at its south after an interval of 320 Lawrence R. Zamoras and Atsushi Matsuoka 2001-5

Ta′ble 1. Partial list of radiolarians from selected samples. For sample locations refer to Figs. 3,.5 and 6.

LOCATION CATANECABOBO-BUWANGUADAECALACH-ANGARAWANSOUTHERN PENNSULA.NICOLAS BⅢABILAUAN,VER BUSUANGA

巴 2≡B=s AGE reL 巴QIド.e▲L5 s n ..●inLnmin..惑in㊥【L0のN～㊥◎㊥in【Linぐ､▲NLn--㊥㊥◎㊥㊥▼.帝d,CM㊥ T5B=B=EEQ=BEAaE≡つロ・oQ=Q=≡蝣o負.【巳Q=【:B=B=a:QEn=iB=B=B=a:0=QEa:BEtcB=B=g隻nEn=D=a: さ.･,】,..,【･■,⊃.､22つ.つ⊃,･.,.･,..,･.,■,.,.,⊃..,.,..,･.,.･,.,..,･.1･.〉->.,l,.つ.,.つ

*fr s SAMPLENUMBER′ginト.†inN▼●N◎○-○CDO▼▲～q.r<》蝣*◎卜ぐ0､10⊂〉N○○▼lN▼-早ぐ可<1⊃J-¢〉?qIO30○ト.○㊥○ぐ､lC13寸?帝等-㊥～rCDq守ト.○ ▼●.▼I.▼...... ▼I.d▼●>､.･--.▼●IA▼.h.44*4.▼.*- J}めJ-> -.-.読良a- SPECIES ○ト.ド.卜`ト.tbin◎◎～.●Lhぐ蝣*Ⅵ～Tf～0●C､●LhN-撃等ub▼.-uS さ等iu†rLhqm 【千n.【-nE-B.L▼nld-3a▼.)<1lH<▼.a▼▲)m▼.d､..a)<▼.【nmEBJDa)

Fig. 3. Location of the sections or areas and sampling points. Samples from previous works included in the discussion are indicated : T for Tumanda (1991a) and ∇ Y for Yeh (1992).

a chert sequence. It contains thinly layered compo- Peninsula in alternation with chert horizons portrays nents composed of sandstone and occasionally chert similar structural features common in the central por- The matrix is composed of highly sheared dark green tion of Busuanga Island, although no apparent topo- to black mudstone, which resembles slate. The graphic features correspond to its occurrence. The samples from this area have no diagnostic radiolan- elastics that appear structurally underlying the ans, instead, opaque materials with radiolarian shapes Bicatan Melange consistently dip NW, but their con- have been observed. These two types of melange tact is unknown. SampleBIO-17, black mudstone, will be referred to as the Bicatan Melange. contains poorly to moderately preserved radiolarians The frequent occurrence of the elastics m Bicatan including Dictyomitrella (?) kamoensis Mizutani and 322 Lawrence R. Zamoras and Atsushi Matsuoka

L雨用喝C佃a Bica転用軸噂e 晦亘壷F乱朗 Formation (Chert) L押esl｡博Bas融 ****悔触Be!l tmLのdefy GLl油q Form融ion Chert Type ､､. ヽ､ら-･). 〈Cま童steき ¥ Raa

Kido, and Eucyrtidiellum sp., probably of JR4-JR5 ance of Albaillella sp. and Pseudoalbaillella sp. Its (Middle Jurassic) age. Two samples, B17-14 and B17 contact with the adjacent JR5 (upper Bathoman to -15, from a mudstone outcrop similarly contain Callovian) elastics is unknown. The Patic Range sec- Tricolocapsa plicarum Yao, Dicolocapsa conoformis tions farther SW similarly exhibit wavy structures of Matsuoka, Archaeodictyomitra suzukii Aita and Mm- thinly bedded red chert. Its sampleB19-12 ab- fusus sp., which also probably represent JR4-JR5 undantly yields moderate to well preserved Middle (Bajocian to Callovian). In Lukib village, appears Triassic radiolarians, among them Triassocampe bedded sandstone of up to 50cm thick, dipping north. campanilis (Kozur and Mostler) and Pseudostylo- Another outcrop of terrigenous mudstone-sandstone sphaera japonica (Nakaseko and Nishimura). sequence can be observed in Punot area, wherein mas- 3. Buwang area sive and highly fractured sandstone intercalates with The road between the villages of San Nicolas and black mudstone. SampleB17-26 taken from the Borac crosses a mountain range via a 250-m high mudstone outcrop is highly terrigenous with rare ra- saddle composed of elastics, which lies between two diolarian occurrence but the presence of Tricolocapsa roughly 400-m high chert peaks (Fig. 5). The consid- tetragona Matsuoka indicates upper JR 4 to lower JR 5 erably weathered outcrop in the saddle area appears (Bathonian). Its occurrence in this locality was previ- rather complex, as different sedimentary rocks crop ously reported in Tumanda (1991 a). out with vague lithologic contacts. Three sedimenta- 2. Deca.bobo-Sa.n Nicola.s ry rock types are encountered in the saddle area : South of Bicatan Peninsula follows a section from muddy chert, mudstone, and sandstone. The muddy Decabobo to San Nicolas village transecting three chert is mint green and relatively soft, with undefined mountain ranges namely, Decabobo Range, bedding structure. Its radiolarian content from Kalebaong Range and Patic Range all composed samplesB24-01 to B24-04 is high but poorly pre- mainly of chert. These mountain ranges alternate served. The bluish gray siliceous mudstone samples with narrow valleys all presumably composed of clas- B24-07 and A 15-19 contain moderately preserved ra- tics. From the northern end of this section, along the diolarian assemblage characterized by frequent occur- Maluwatan River, east of Decabobo village, limited rence of Stylocapsa (?) spiralis Matsuoka, Stichocapsa occurrence of black mudstone with fine-grained sand- robusta Matsuoka and T. conexa indicative of JR6 stone intercalation appears. Massive medium- (upper Callovian-Oxfordian). grained sandstone also occurs in interval with the In another outcrop of at least 50m below the saddle mudstone-sandstone intercalation. SampleB 18-02, pass, occurs thinly bedded greenish chert with weak dark gray to brown mudstone is highly terrigenous laminations and dipping north with varying dip with rare radiolarian occurrence. The presence of angles. SampleA15-20 contains moderately pre- Tricolocapsa conexa Matsuoka is insufficient for age served radiolarians such as Hsuum medium determination, but the occurrence of JR5 elastics at (Takemura), Bipedis sp., Canesium sp. aff. C. lenticum its north and south suggests that its age is also JR5. Blome, indicative of JR2 (upper Pliensbachian- At the NW end of Decabobo Range, a blue-gray to Toarcian). SampleB24-30, reddish when fresh black finely laminated chert (A15-01) yields many having Parvicingula sp. aff. P. nanoconica Hon and saturnaliids such as Kozurastrum sp. aff. K. quin- Otsuka, also belongs to JR2. Farther down, chert guespinosa (Kozur and Mostler) and Kozurastrum sp. sample B24-23 shows the occurrence of Laxtorum (?) suggesting a Late Triassic age. At the SW side of jurassicum Isozaki and Matsuda, and Parahsuum Decabobo Range, a light brown NE dipping siliceous grande Hori and Yao, indicating JR3 (Aaleman). mudstone contains T, tetragona, T. conexa, T. plica- Sample B24-17, a pinkish maroon chert sample with rum, Stylocapsa tecta Matsuoka indicative of JR5 0r 負ne bed-parallel strands, contains Tympaneides upper Bathonian to Callovian age (A 15-07, A15-C charlottensis Carter, Hexasaturnalis hexagonus (Yao), This clastic body appears in fault contact with the Tritrabssimplex Kito and De Wever and L. (?) base of the Decabobo Range chert, and serving as the jurassicum, also indicative of JR 3. footwall of the thrust chert unit. The samples co主 This JR2, JR3 and JR6 chert-clastic sequence is Iected south of the siliceous mudstone, B 19-06 and B bounded in the northby Permian chert sequence. An 19-07 (mudstone samples) have no radiolanans but outcrop around 200m north of the saddle pass along terrigenous materials. the steeply sloping road, crops out generally thickly Two chert mountain ranges stretched parallel to bedded chert, which is part of the northern chert peak. Decabobo Range follow at its SW after the elastics, Its samplesB24-14 and B24-16 contain Pseudo- namely, the Kalebaong Range and the Patic Range. albaillella fusiformis (Holdsworth and Jones) and Chert exposures across Kalebaong Range exhibit Albaillella levis Ishiga, Kito and Imoto, respectively, wavy beds with widely varying dip directions. indicating Middle and Late Permian. This chert Samples B19-10 (dark blue chert) and B19-ll (red body is apparently in thrust fault contact over the chert) indicate Middle Permian based on the appear- younger JR6 elastics and JR2 to JR3 chert at its 324 Lawrence R. Zamoras and Atsushi Matsuoka 2001-5

E= brown, gray and black color ; bed thickness ranging N from 3 to 6cm;and laminated, with minor fine- grained sandstone occurrence. SampleB21-02 con- tains palynomorphs and very few radiolanans. It is highly probable that this particular outcrop is the same Mabintangm section sampled and reported by Fontaine (1979) as having abundant Late Triassic- Early Cretaceous palynomorph, Classopollis. Despite the low radiolanan occurrence, a well preserved S. (?) spirahs has been found with T. conexa, and Protunuma sp. that strongly correlates with the Guadalupe clastic section. Fontaine (1979) assumed that this JR6 clastic out- crop in Mabmtangin conformably overlies the chert sequence composing Mt. Dalara. Our且eld data con- forms to this view although the chert samples owing to poor preservation hardly verify their biostra五 graphic relationship. A section across the Pina Mountains north of this locality along a north-bound stream reportedly reveals a chert sequence of wide age range from Late Permian, Tnassic to Early Juras- sic (Tumanda, 1991a, 1991b). Apparently this gener- ally north-dipping Pma Mountain chert sequence is in fault contact with the adjacent southern Upper Juras- Fig. 5. A section of the road connecting San Nicolas sic elastics in the Mabintangm area. and Borac villages in the elevated Buwang area (Fig. 3) 5. Decalachiao-Maricaban-Cabilauan showing the Permian and Jurassic chert exposures generally northeast-dipping. The Lower-Middle (JR 2- At least lkm NW of Decalachiao village, a clastic JR3) chert sequence exhibits wavy fold structures sequence of mudstone and sandstone appears as a often parallel to the road and outcrop surface resulting road section. The light brown siliceous mudstone to repetitive age trend of samples along the road. The commonly features trace fossils having black lensoid Middle (?) Jurassic (JR5?) chert and the Upper outlines oriented parallel to the bed. A moderately Jurassic (JR6) elastics m the saddle portion. The fault structure is considered a contact between the preserved JR 5 (late Bathoman-Callovian) radiolarian lower section of the Northern Busuanga Belt (Permian assemblage is observed m sampleA05-04 having T. chert) and the upper section of the Middle Busuanga plicarum, T. conexa, S. tecta and Parvicingula dhi- Belt (Jurassic chert-clastic sequence). menaensis Baumgartner. The upsection of this sili- ceous mudstone appears to be represented by the nearby massive arkosic sandstone although contact is south. not exposed. A fault contact probably exists be- 4. Guadalupe-Mabintangin tween this clastic sequence and the Upper Permian A continuous section of roughly 200m long clastic chert (A 05-19) which contains Albaillella protolevis sequence crops out along a small headwater tributary Kuwahara and A, levis. Minor occurrence of basalt near the Guadalupe area, revealing an alternation of has also been noted adjacent to the Permian chert but mudstone, sandstone and pebbly sandstone. These its exposure is highly weathered. different types of elastics appear in repetitive manner In the coastal Maricaban village a terrigenous and their dip direction is widely variable. Mudstone mudstone-sandstone sequence is exposed. This clas- commonly intercalates with thinly bedded 貢me- tic body appears belonging to a separate stratigraphic grained sandstone. Coarse-grained massive sand- unit NW of that in Decalachiao as they are intervened stone intervals along the sequence range m total by a chert horizon. Maricaban sample A05-14 con- thickness from around 30 to 70m with bed thickness tarns T. conexa, S. tecta, T. plicarum, D. (?) kamoensis, of 1 to 3m. Several samples were collected mostly A. suzukii, T. tetragona, P. dhimenaensis and Hsuum from the mudstone beds, but most of these are highly brevicostatum (Ozvoldova), an assemblage signifying terrigenous with rare radiolanan occurrence. Sam- JR5 zone that closely resembles that in Decalachiao piesI〕 14-21 and A08-01 contain S. (?) spirahs, mdicat- siliceous mudstone. Another chert horizon in the ing JR 6 (upper Callovian-Oxfordian). north, the Balnek Mountain Range, bound the clastic In Mabmtangin.another clastic outcrop, roughly 8 m sequence of Maricaban. This chert unit is sampled thick, is exposed along the NE tributary of the Bacbac from Binian Point but no diagnostic radiolarians have River. It is composed of mudstone, characterized by been found. Jour. Geol. Soc. Japan, 107 (5) Accretion complex in Busuanga, Philippines 325

Fig. 6. The Pangarawan River section exposing the lithologic transition from chert to elastics of the Middle Busuanga Belt. Locations of B15-05 to B15-08 show the topmost portion of the chert sequence of JR4 (Bajocian-lower Bathonian). Two siliceous mudstone samples B15-03 of JR5 (Bathonian-Callovian), and A03-02 (or 990303-02 in Zamoras and Matsuoka, 2000 a) of JR6 (upper Callovian-Oxfordian) represent the transitional fades. Samples B 15-10 to B 16-04 belong to the terrigenous clastic facies of JR 6.

In the NW tip of the long narrow Cabilauan Island, pearance of NE-dipping black mudstone interbedded a NE dipping blue-gray colored chert has been ob- with thick sandstone layers. Sample B15-03 taken served of at least lOm outcrop thickness, with gener- from a siliceous mudstone outcrop in this locality ally thin beds of 2cm in average. Two samples, Bll yields a JR 5 (late Bathonian to Callovian) assemblage -04 and Bll-05 from this site show JR2 (upper of T. tetragona, T.plicaγurn, T. conexa, P. dhime- Pliensbachian-Toarcian) radiolarian assemblage such naensis, A. suzukii, Hsuum maxwelli Pessagno, Amphi- as p. nanoconica, Parvicingula spp., Bipedis sp., pyndax tsunoensis Aita and Protunuma turbo Matsuoka. Eucyrtidiellum spp. and abundant multicyrtid forms. At the NW end of the Mapuyawen Range chert where 6. Pangarawan River it seems to taper out, appears chert outcrop that ap- At least 6-km stretch of the Pangarawan River was parently plunges beneath the Tulbuan Plain. Its traversed starting from the headwaters in the vicinity chert sample B 15-07 described as black with average of abandoned Mapuyanen Mines down to Incal Range thickness of 3cm contains abundant but poorly to foothills (see Fig. 6). It is revealed along the section moderately preserved radiolarians such as Parahsuum incised by the river that a Jurassic clastic sequence stanleyense (Pessagno), P. officerense (Pessagno and exists in the Tulbuan Plain but already overlain by a Whalen), Higumastra winteri Baumgartner and Kito, Quaternary chert conglomerate, which often reaches Eucyrtidiellum unumaense (Yao) and Parahsuum spp. up to lOm of thickness. From the headwaters of the Another sample, B 15-08, approximately lOm strati- river, the Jurassic elastics started appearing past the graphically above B 15-07, characterized as muddy bridge near the Busuanga Airport road with the ap- chert, abundantly contains moderately to well pre- 326 Lawrence R. Zamoras and Atsushi Matsuoka 2001-5

served JR4 (Bajocian-early Bathoman) radiolarians Protovallupus spp. and H. maxwelh. Approximately 3 such as Mirifususfraguis Baumgartner, Hsuum m above A04-ll, another siliceous mudstone sample hisuikyoense Isozaki and Matsuda, Tricolocapsa (?) (A04-18) shows very similar assemblage. The occur- fusiformis Yao, Archicapsa (?) pachyderma (Tan), T. rence of P. carpatica associated with E. pyramis inch- plicarum, H. winten, Parvicingula spp. and Sethocapsa cates that the biohorizon of these samples has already spp. This rich assemblage without T. conexa occur- crossed the KR 1 or the P. carpatica Zone of Matsuoka rence is considered a representative of JR4, which is (1995) but still within Tithoman. The presence ofH. also the most likely age of B15-07. The remarkable maxwelli, which supposedly disappeared around the change m hthologic character from black chert (B 15- end of Kimmeridgian, will be further studied. 07) to muddy chert (B 15-08) in this sequence suggests Sample B25-22, a greenish gray chert taken from a transitional stage of its paleoenvironmental condi- the Tagumpay area along the road to Maqumit, con- tion. tarns moderate to well i⊃reserved radiolanans with About loom downstream appears the clastic se- Parahsuum (?) grande Hon and Yao, Eucyrtidiellum (?) quence described as concordantly NE dipping gray- quinatum Takemura, Hsuum matsuokai Isozaki and colored siliceous mudstone. This is the sample loca- Matsuda, Parahsuum sp. cf. P. levicostatum Takemura tion of the siliceous mudstone A 03-02 (or 990303-02) in and P. sp. cf. P. cruciferum Takemura. This assem- Zamoras and Matsuoka (2000 a) that has been assigned blage probably represents the JR3 (Aalenian) of to JR6 (upper Callovian to lower Oxfordian) based on southern Busuanga. Sample B20-47 from Dipulao the common appearance of S. (?) spirahs, S. tecta, D. area, between Km Posts 4 and 5 along the Coron- conoformis, Guexella nudata (Kocher) and G. sp. aff. G. Salvacion road contains Unuma sp. cf. U. echinatus nudata. The stratigraphic upsection over sample A 03 Ichikawa and Yao, Parahsuum izeense (Pessagno and -02 is a long sequence of highly terrigenous mudstone- Whalen), Bernoullius rectispinus rectispmus Kito, De sandstone mterbeds characterized by poor radiolarian Wever, Danehan and Cordey, Eucytidiellum sp. aff. E. occurrence. The appearance of S. (?) spirahs being qumatum, H. medium, Zartus sp. and Tnllus sp. This the essential zonal indicator is last observed in sample sample is indicative of JR2-JR3 (upper Toarcian to B15-12. Althoughit has not appeared in all succeed- lower Aaleman), probably slightly older than B 25-22. ing samples along this section, the terrigenous clastic In the Nagbanl area, near Km Post 23 along the portion is entirely considered JR6. Sample B16-04, Coron-Salvacion Road, another muddy chert sequence the last sample along this river traverse, containing S. appears. Sample B30-10 contains moderately to well tecta, T. conexa, H. maxwelli, Protunuma sp., D. con- preserved S. (?) spiralis, A. tsunoensis, S. funatoensis, oformis, G. nudata and Zhamoidellum ventricosum S. oblongula, among others, indicative of JR6 Dumitrica, is also considered part of the upper section (Oxfordian). In another outcrop, near Km Post 24, a of the elastics. chert exposure was sampled (A 13-28) containing well 7. Southern Busuanga preserved JR5 (Callovian) radiolarian assemblage, Three sampling localities represent Southern such as T. conexa, S. tecta, A. suzukn, H. brevicostatum, Busuanga namely, Nagbanl-Bintuan m the west, and T. plicarum and common E. ptyctum. This sampled Dipulao and Tagumpay areas in the east. In these chert outcrop however appears to be part of a trans- southern portions of Busuanga Island, the chert se- ported large block as it is in contact with a soil hon- quences include Middle and Upper Jurassic, not en- zon at its base. But since it is the only chert sample countered m the northern portions. Sample AO4-03, that represents JR5 in Southern Busuanga Belt, its brown chert (gray-colored when fresh), contains JR 8 analysis has become important. (Tithoman) assemblage based on Mirifusus guada- Revision of the Upper Paleozoic to lupensis Pessagno, Ristola altissima altissima (Rust), Mesozoic stra.tigra.p血y Loopus pγimitivus (Matsuoka and Yao) and Archaeo- dictyomitra apiarium (Rust). Near the topmost chert The new geologic and paleontologic data gathered horizon, sample AO4-06A (about 120cm above A04- m this study from the central Busuanga Island have 03) contains well preserved radiolarians such as provided adequate bases for the revision of the Upper Cinguloturris carpatica Dumitrica, Mirifusus dianae Paleozoic to Mesozoic stratigraphy of the North minor Baumgartner and M. guadalupensis, likewise Palawan Block m general. The lithologic transition representing JR8 (Tithonian). Just above the top- from chert to siliceous mudstone and to terrigenous most chert horizon, a siliceous mudstone sample, A 04 elastics coupled with the gradually younging succes- -ll, yields well preserved radiolanans namely, C. sion of radiolarian assemblages has clearly defined the caゆatica, M. dianae minor, Solenotryma ichikawai relationship between the chert and the elastics. This Matsuoka and Yao, Pseudodictyomitra carpatica discovery leads to the integration of the chert se- (Lozyniak), L. primitivus, Eucyrtidiellum pyramis quences of various ages as a single unit that is over- (Aita), Pantanellium oligoporum (Vmassa), Bistarkum lam by the clastic sequences, also considered as one irazuense (Aita), A. apiarium, R. altissima altissima, unit (Fig. 7). Associated limestone occurrences, sepa- Jour. Geol. Soc. Japan, 107 (5) Accretion complex m Busuanga, Philippines 327

H ashim oto & BM G ,1981 W olfartetal., Isozakietai., JICA -M MA J, T his W ork AG ∈ Sato,1973 1986 1988 1990 日日岬 岬

∽ Serpentine& Serpentine Malam payaSoundGroup =〉 Upper 0 G abbroic pOGkS Gabbro 1⊥l Boayan 0 g ＼＼ elastics メ ＼ OJ BE ト ◇ o Low er /

メ/ ＼ノ/､. メ ; Form ation 【= Forma屯on,.'Ll 重 ｣ ⊃ く= ◎ 雲= i' E 竃 Upper M inilog Minilog ｣ .ど L碓 ヨ Form ation Form ation ｣ Mnilog ? 管 Bacu旺 I Formation ‡ Formation ｣ C .< ≡ ≡ Bacu江 Bacurt Bacuit M iddle Form ation Formation a: Form ation uJ EL 朝 岬 - ? ? - Low er き 義 Barton Metam orphics S at Barton l算 ∈ d】 【ピ M etam orphics < 5 〇 C> ㌢ ,

Fig. 7. Previous stratigraphic columns for the Upper Paleozoic and Mesozoic of North Palawan as compared with the modified version in this present work. The limestone units include (Upper and Lower) Minilog Formation (Hashimoto and Sato, 1973 ; Wolf art et al., 1986 ; Amiscaray, 1987), Malajon Limestone (Hashimoto et al., 1980), Coron Limestone (Wolf art et al, 1986), and Hi and Imorigue Limestones (Bassoullet, 1983 ; Beauvais, 1983 ; Fontaine etal.,1983).

rately studied and de負ned by several previous work- tion (elastics) and the limestone units ; and a minor ers, are regarded belonging to one category. Al- unit, the Bicatan Melange. though most of these limestones are not part of the 1. Malampaya Sound Group current study, their inclusion in the stratigraphy is Author : Hashimoto and Sato (1973). considered essential to represent a comprehensive Original Definition : A collective name for Bacuit Upper Paleozoic to Mesozoic stratigraphic column. Formation, Minilog Formation, Liminangcong Forma- But no additional fossil data on the limestones are tion and Gumlo Formation. included in this paper since this work focuses on the Redefinition : A collective name for Limmangcong chert-clastic sequences. Melange bodies have also Formation, Guinlo Formation, limestone units and been encountered but their occurrence is rather limit- melange bodies (such as the Bicatan Melange). ed to a few localities, thus, considered minor. Hence Distribution : This group was originally identi負ed in this paper considers three major units namely ; the northern Palawえn Island, Linapacan Island and Liminangcong Formation (chert), the Gumlo Forma- Island. Subsequent correlation of the chert 328 Lawrence R. Zamoras and Atsushi Matsuoka 2001-5

sequence in Busuanga Island as part of the dred meters. Liminangcong Formation (BMG, 1981) had also ex- Contacts : Stratigraphically underlying unit un- panded the distribution of this group. known ; Guinlo Formation conformably overlies. Age : Liminancong Formation, Middle Permian Fossils : At least 500 radiolarian species have al- through Jurassic ; Guinlo Formation, Middle Jurassic ready been described or encountered based on this to Early Cretaceous ; limestone units, Permian to Late ongoing work and previous radiolanan works of Jurassic. Isozaki et al. (1988), Cheng (1989, 1992), Tumanda (1991 2. Liminangcong Formation a, 1991b, 1994), Yeh (1992), Yeh and Cheng (1996, 1998), Author : Hashimoto and Sato (1973) ; further works Tumanda-Mateer et al. (1996). Occurrence of radio- include BMG (1981), Wolf art et al. (1986), Isozaki et al. larians in chert samples normally depends on the (1988). degree of preservation ; abundant when the preserva- Historical review : Following the discovery of Per- tion is moderate to good, rare or absent when mian and Jurassic cherts in Busuanga Island, the recrystallization or any form of alteration prevails. Liminangcong Formation of Hashimoto and Sato Age : Middle Permian to LateJurassic. Most of the (1973), which was originally considered as Middle Tn- chert exposures in the Calamian Islands are of Trias- assic chert, was subdivided into Liminangcong Chert sic age. Middle to Late Permian and Jurassic chert for the Triassic portion, and Busuanga Chert for the outcrops are rather occasional and less extensive. Jurassic portion (JICA-MMAJ, 1990), while Bacmt For- Tumanda (1991 a) de負ned four interval zones (I.Z.) for mation was adopted for the Permian chert (Wolf art et the Middle to Upper Permian ; Folhcucullus mona- al., 1986). Isozaki et al. (1988) considered the Permian canthus I.Z., F. scholasticus I.Z., Latentifistula simi- to Jurassic chert sequences as a single unit, licutis I. Z. and Neoalbaillella ornithoformis I. Z. ; eight Liminangcong Chert. interval zones for the Lower to Upper Tnassic, Original definition : Bedded hematite-bearing chert Pactarentinia koikei I.Z., Hozmadia altipedana I.Z., containing radiolarians ; intercalated with slumping Pseudostylosphaera japonica I. Z., Triassocampe dewe- bed, black slate and reddish tuff layers ; occasionally veri I. Z., Emiluvia cochleata I. Z., Capnuchosphaera I. Z., banded. Capnodoce I.Z. and Livarella I.Z. For the Jurassic Redefinition : Bedded chert sequences of highly portion, seven out of eight zones of the Jurassic radi- varied characteristics, commonly intercalated with olarian biostratigraphy for the Western Paci且c and clayey layers, distributed in the northern part of Japan (Matsuoka, 1995) have been certainly repre- Palawan Island and the Calamian Islands. sented by chert samples from various locations, Original type locality : Liminangcong Coast, namely, Parahsuum simplum Zone (JRl), Trillus Palawan Island. Present study is mainly based on elkhornensis Zone (JR 2), Laxtorum (?) jurassicum Zone the data from the Calamian Islands as its chert and (JR 3), Tricolocapsa plicarum Zone (JR 4), Tncolocapsa clastic exposures have better radiolarian contents and conexa Zone (JR5), Stylocapsa (?) spiralis Zone (JR6) preservation. and Loopus primitivus Zone (JR 8). Lithology : This dominantly chert unit is charac- 3. Guinlo Forma.tion terized by color variations ranging from deep red, Author : Hashimoto and Sato (1973) ; further works maroon, flesh color, light green, dark or light gray, by BMG (1981) and Wolf art et al. (1986). beige, white to black that often differ from the actual Historical review : From Gumlo Point, Palawan interior color. Conspicuous color banding is occa- Island, where Hashimoto and Sato (1973) described sionally encountered with deep red color m the mid- this unit, BMG (1981) extended the Guinlo Formation layer portion and lighter shades such as light green or to Busuanga Island referring to the extensive light brown at the upper and lower margins of each mudstone-sandstone-conglomerate succession. This bed. Its bed thickness ranges from less than 1 to 30 was modified as King Ranch Formation (BMG, 1984) cm ; older chert sequences are relatively thicker than with the same reference to the clastic sequence m younger chert sequences. It occasionally exhibits Busuanga and later considered it as a matrix of an lamination with varying laminar thickness as well as olistostrome (Faure and Ishida, 1990). distinctness. Its degree of induration also varies Original definition : Unfossihferous white coarse- from the relatively softer muddy chert to highly m- grained massive sandstone with conglomerate inter- durated chert. The clayey intervals appear light beds (Hashimoto and Sato, 1973). gray to light brown color with common thickness of Redefinition : A succession of siliceous mudstone less than 1 cm, but occasionally reach more than 2cm. and terrigenous interbeds of mudstone, sandstone and This unit is generally highly folded and commonly conglomerate, distributed in northern Palawan Island faulted. and the Calamian Islands. Thickness : Its apparent thickness is at least 2000m Type locality : Guinlo Point, Palawan Island is the based on the chert sequence across Mt. Dalara. How- original type locality for the Guinlo Formation. ever, its actual thickness is probably only a few hun- However, many subsequent studies of this unit refer 329 Jour. Geol. Soc. Japan, 107 (5) Accretion complex in Busuanga, Philippines

to the exposures in Busuanga Island where strati- sequence in Tagumpay. The terrigenous mudstone graphic and paleontologic data are better. In this and sandstone, which presumably overlie this KR 1 study as well, all data from the elastics are gathered siliceous mudstone is assigned to middle-upper KR 1 from Busuanga Island. or much younger zones within the Lower Cretaceous. Lithology : The siliceous mudstone is characterized 4. Limestone units as moderately indurated, light brown to light gray, 2- Historical review : A number of limestone bodies 5cm bed thickness and primarily composed of radio- occur sporadically around the Calamian Island Group larians, terrigenous quartz and clay minerals. It and in the northern Palawan Island with ages ranging serves as the base of the elastics and right on top of from Middle Permian to Late Jurassic. Among the the chert sequence. The terrigenous mudstone por- previously studied are Middle Permian to Lower- tion appears gray to black dominated by siliciclastics Middle Triassic Minilog Formation, Triassic Malajon with dark organic matters frequently including Limestone, Upper Triassic-Lower Jurassic Coron palynomorphs. It is moderately or highly indurated Limestone and Upper Jurassic limestone from Hi with 1-5cm thick beds. Its radiolarian content is Island and Imorigue Island (Hashimoto and Sato, 1973; substantially lower compared to siliceous mudstone. Fontaine, 1979 ; Hashimoto et al, 1980 ; Bassoullet, The sandstone portion is generally characterized as 1983 ; Beauvais, 1983 ; Wolf art et al., 1986 ; Amiscaray, highly indurated, massive or thickly bedded (40 cm to 1987). 5m), medium to coarse-grained with arkosic composi- Lithology : Minilog Formation, described as black or tion. The coarser facies of the elastics composed of white limestone, more or less recrystallized, partly bedded and oolitic, with its lower horizon appearing pebble conglomerate is not frequently encountered compared to mudstone and sandstone. Mudstone- as black partly oolitic limestone and the upper hon- sandstone intercalation is observed common m the zon as black massive, somewhat bituminous lower or mid stratigraphic sections while the massive (Hashimoto and Sato, 1973) ; Minilog Formation, sub- sandstone portion predominates in the upsection. sequently described as wackestone and biomicrite Thickness : Maximum thickness is approximately (Amiscaray, 1987) ; Coron Limestone, described as 2000 m along the Pangarawan River section. massive to bedded, light to dark gray, crystalline, Contact : Conformably overlying the Limmangcong reef al, oolitic or conglomeratic (Wolf art et al, 1986) ; Formation ; also commonly in fault contact with the Hi Limestone as wackestone to packstone (Bassoullet, lower stratigraphic sections of Liminangcong Forma- 1983). tion ; no overlying unit was observed in the study Distribution : The limestone units furthermore m- area. elude the Coron Limestone (, south of Fossils : At least 200 radiolarian species have been Busuanga Island), Minilog Formation (Bacuit Bay m encountered based on this work plus Tumanda- the northern part of Palawan Island), Malajon Lime- Mateer et al. (1996) and Zamoras and Matsuoka (2000 stone (Malajon Island, west of Busuanga Man鋸, Hi a). Palynomorphs earlier reported by Fontaine (1979) Limestone (Hi Island, south of Culion Island or east of have also been encountered in our samples. Linapacan Island) and Imorigue Limestone (nearby Age : Middle Jurassic to Early Cretaceous. JR4 NE coast of Palawan Island). Contacts : In fault contact with either the Limmang- (Bajocian to early Bathonian) age is the probable age of the elastics in the Bicatan Peninsula containing cong Formation or the Guinlo Formation. Fossils : The lower section of the Minilog Forma- poorly preserved radiolarians such as T. plicarum, D. (?) kamoensis, A. suzukii and Eucyrtidiellum sp. The tion contains Verbeekina verbeeki (Geinitz), Neoschwa- JR 5 (late Bathonian to Callovian) radiolanan assem- gerina megasphaerica Deprat, N. margaritae Deprat, N. blage is represented by T. tetragona, T. conexa, T. craticulifera (Schwager), Nankinella orbiculana Lee, plicarum and P. turbo, observed in siliceous and Yabeina globosa (Yabe), among other large forami- terrigenous mudstones from various locations. The nifera (Amiscaray, 1987) ; the upper section of the JR 6 (latest Callovian to Oxfordian) assemblage, basi- Minilog Formation contains conodont species such as cally indicated by the occurrence of S. (?) spiralis, has Acodina sp., Gladiogondolella cf. tethydis (Hucknede), been observed in both siliceous and terrigenous parachirognathus sp. and Spathognathodus gondolel- mudstone. The JR 8 (early-middle Tithonian) assem- loidea (Bender) (Wolf art et al., 1986) ; Malajon Lime- blage, represented by L. primitivus, M. guadalupensis, stone with conodont Epigondolella abneptis R. altissima altissima and A. apiarium, is encountered (Huckriede) (Hashimoto et al., 1980) ; Coron Limestone in Tagumpay which is considered as the topmost with Sphinctozoa [Porifera], Girvanella, Dasycla- chert section of the Southern Busuanga Belt. The daceae [Algae], Hemigordius-Triasina [Foramimfera] KR 1 (late Tithonian-Berriasian) assemblage includes and pelecypod Paramegalodus (Wolf art et al, 1986) ; Hi protovallupus spp., M. dianae minor, P. carpahca, L. Limestone contains foraminifera such as, Pseudo- primitivus, S. ichikawai and E. pyramis as observed cyclammina lituus (Yokoyama), Protopenerophs sp., from a siliceous mudstone section overlying the chert Salpingoporella johnsoni (Dragastan), Pycnopondium 330 Lawrence R. Zamoras and Atsushi Matsuoka 2001-5

lobatum (Yabe and Toyama), Nautilocuhna oohthica mudstone with texture resembling a now structure. Muhl (Bassoullet, 1983) ; Ptychochaetetes ponticus Likewise, no radiolarians have been recovered from (Deninger), Cladocoropsis mirabilis Felix and Clado- the mudstone matrix. Its apparent thickness is about coropsis memoγia-naumanni (Yabe) (Beauvais, 1983). 100 m. Age: The lower section of Minilog Formation - Comparison : This unit probably occurs in other Middle to Late Permian based on high occurrence of parts of Calamian Islands and north Palawan. Simi- many fusulinid species (Amiscaray, 1987) ; the upper lar melange reportedly occurs m northern Palawan section of Minilog Formation - Lower to Middle Trias- Island (Faure and Ishida, 1990). sic (late Scythian to early Anisian) based on conodont Chert-clastic sequence in Busuanga Island assemblage of Acodina sp., G. cf. tethydis, Parachi- rognathus sp. and S. gondolelloidea (Wolf art et al., 1986) The age analysis of the chert-clastic sequences ; Malajon Limestone - Lower Norian based on the across parallel alternating mountain ranges and index fossilE. abneptis (Hashimoto et al, 1980) ; Coron narrow valleys using radiolarians has proven that Limestone - Rhaetian based on the occurrence of these constitute a series of similar sedimentary se- Paramegalodus (Wolf art et al, 1986) ; Hi Limestone quences that progressively differ in age. Their age Late Jurassic (Kimmeridgian) based on the associa- differences are distinguished through the age of the tion of P. lituus, Protopeneroplis sp., S. johnsoni, P. lithologic transition from chert to elastics. In lobatum and N. oolithica (Bassoullet, 1983) ; Imongue determining a transition age, clear chert-to-clastics Limestone - Late Jurassic based on P.ponticus sections are ideally important. But m areas where no

(Deninger), C. mirabilis Felix and C. memona-nau- such outcrop has been found its transition age assign一 manni (Yabe) (Beauvais, 1983). ment is at least based on the siliceous mudstone. 5. Bicatan Melange {new name) The lowermost section of the Limmangcong Forma- Type locality : Buyod area, Bicatan Peninsula, tion is Middle Permian (see Fig. 7) while the topmost Busuanga Island. section shows progressively youngmg age : probably Definition : Composed of either the limestone-basalt- JR3 (Aalenian) in the north, JR4 (Bajocian-early chert melange or the sandstone-chert-mudstone me- Bathonian) in the middle and JR8 (Tithonian) m the lange. south of Busuanga Island. Consequently, t`he sili- Lithology : ceous and terrigenous elastics (Guinlo Formation), 1. Limestone-basalt-chert melange : This is des- which overlie the chert sequences, range from JR4- cribed as poorly layered melange composed of highly JR5 (Bajocian to Callovian) in the north, to JR5-JR6 indurated micritic limestone and basalt with minor (late Bathonian to early Oxfordian) m the middle, and bedded chert. Its components range in size from to JR8-KR 1 (Tithonian to Bernasian-early pebble to boulder. Limestone clasts generally have Valanginian) in the south (Fig. 8). This progressive larger size and basalt smaller size. The pebble size younging in age for lithologic transitions becomes component composed of limestone and basalt occa- essential basis in delineating three distinct belts com- sionally serves as the matrix of the cobble-sized lime- posing the accretionary complex of Busuanga Island stone. The proportion between limestone and basalt (Fig. 4).

conspicuously varies from limestone-dominated to 1. Three belts of the a′ccretiona.ry complex in basalt-dominated. The coarser limestone-dominated Busuanga Island portion occurs in the upper section while the finer (1) Northern Busuanga Belt basalt-dominated portion occurs at the base of the This belt covers the areas of Bicatan Peninsula, section. The limited chert component, of probably Maricaban, Decalachiao, Cabilauan Island, Decabobo, Permian age, appears immediately above the basalt- Patic Range, and the mountain ranges north of the dominated portion. The basalt-dominated portion is Buwang section. As shown in the geologic section composed of volcaniclastics ; occasionally with oh- (Fig. 4) the Northern Busuanga Belt appears to include vine basalt cobble-sized fragments contained m simi- more chert-clastic sequences than the Middle and larly basaltic matrix. Its apparent thickness is ap- Southern Busuanga belts. Its representatives for the proximately 100 m. Middle to Upper Permian portion are the sections m 2. Sandstone-chert-mudstone melange : It is basical- Kalebaong, Buwang, and Decalachiao. Its Middle ly composed of layered sandstone and minor chert Tnassic section is represented by exposures in Patic slabs oriented parallel in a mudstone matrix. The Range and Buyod Point while its Upper Tnassic is sandstone slabs are described as gray-colored, fine- found m Decabobo Range. The only Jurassic chert grained, well sorted, well indurated and with thick- section representing the Northern Busuanga Belt is m nessranging from 1 to 5cm. The chertslabs vary m Cabilauan Island with JR2 (late Pliensbachian- color from dark gray to brown, thickness from 3 to 5 Toarcian) assemblage. cm, well indurated without radiolarians. The matrix As its chert-to-clastics transition exposure has not is described as highly sheared dark green to black been encountered yet言ts topmost chert sequence is Jour. Geol. Soc. Japan, 107 (5) Accretion complex m Busuanga, Philippines 331

Southern Busuanga Be旺 r: ≡ alangiman L∪$◎ B= ◇ C 〉..｣Berriasia KRl (PC) Middle Busuanga Be旺 T仙oman I [監輝喝umpay JR8 (Lp AO4-06A i K狛nmend-JR7 (Hm ) Northern Busuanga Be旺 .〔AO8-01 A04-03 A man ≡B15-12 ⊃ B21-｡2監River) < B30-10 (Nagbaril-Bi血an) OxfordianJR6 (Ss) fAO3-02(PangarawanR.) Calovian 蝣41A15-19(Buwangsaddle) g JR5 (Tc)

‡ < U pper ≡ Q= 田 M iddle CL

Fig. 8. Reconstruction of the oceanic plate stratigraphy for the three belts of the Malampaya Sound Group in Busuanga Island. Plotted samples for the Middle Busuanga Belt include the San Nicolas Road and Pamatpatan samples of Tumanda (1991a) to represent the Triassic to Permian portion. Southern Busuanga Belt samples include the Malbato samples of Tumanda (1991a) and Uson Island samples of Yeh (1992) to represent the Tnassic portion (See Fig. 3 for sample locations). assumed as Aalenian, while the siliceous mudstone geologic map (Fig. 4). The thrust-fault contact be- portion begins probably from JR4 (Bajocian-lower tween two chert-clastic sequences in Buwang (Fig. 5), Bathonian) to JR 5 (upper Bathonian-Callovian). The as indicated by juxtaposed Permian chert and Juras- JR 5 siliceous and terrigenous mudstones m northern sic elastics言s also considered a continuation of this outcrops of Busuanga Island such as those found boundary. south of Decabobo Range, Decalachiao and Maricaban The best section of chert-to-clastics transition so far have become its distinctive characteristic. The ab- discovered is the one exposed along the Pangarawan sence of JR6 0r younger radiolarian assemblage m River. Despite its discontinuous outcrops, the these elastics essentially distinguishes the Northern lithologic transition can be observed from black chert Busuanga Belt from the subsequent belts. to siliceous mudstone, and to terrigenous mudstone- (2) Middle Busuanga Belt sandstone interbeds. It is accompanied by a remark- The appearance of S. (?) spiralis in the terrigenous able change from JR4 (Bajocian-early Bathoman) ra- elastics in the mid-portion of Busuanga Island has diolarian assemblage in chert to JR 5 (late Bathoman- become the distinctive marker for the Middle Callovian) assemblage in siliceous mudstone. The Busuanga Belt. This radiolarian, the principal inch- upsection of the siliceous mudstone further proves to cator of JR6 or Stylocapsa (?) spirahs Zone for the have JR 6 (late Callovian-early Oxfordian) assemblage upper Callovian-lower Oxfordian age, has been en- based on S. (?) spiralis. The succession of terrigenous countered in the elastics of Buwang, Mabintangm, elastics of mudstone and sandstone follows wherein 5. Guadalupe and Pangarawan River or Tulbuan Plain. ?)spiralis can also be found. Terrigenous mud- Between the Patic Range and San Nicolas, the bound- stones containing S. (?) spiralis have been observed in ary between the Northern Busuanga Belt and the Pangarawan, Guadalupe, Mabintangin and Buwang Middle Busuanga Belt has been located. The basis of (Fig. 8). which is that the age of the terrigenous mudstone in Cheng (1989) and Tumanda (1991a) have already the north of Patic Range is JR5, while m the south it studied the lower stratigraphic sections of this belt is JR6. This boundary runs subparallel to the NW-SE particularly the Permian to Tnassic exposures along trends of the chert-clastic sequences as shown in the the San Nicolas Road. Other sections m Tumanda 2001-5 332 Lawrence R. Zamoras and Atsushi Matsuoka

the southern areas of Busuanga Island, however, (1991a) such as Pamatpatan and Mabintangin-Pina Mountains are also considered part of the Middle terrigenous elastics have not been encountered yet. Probable sites of the Early Cretaceous elastics south Busuanga Be五 Based on Tumanda (1991a), the of Mt. Dalara and Balolo River valley are covered by Middle to Upper Permian section of this belt is ex- posed along the San Nicolas and Mabintangin-Pma Quaternary chert conglomerate. Mountains sections. The upper Lower and lower The Lower to lower Middle Jurassic of the Southern Middle Triassic are represented by the Pamatpatan Busuanga Belt is found in the Tagumpay (JR 1 and JR section, south of Tulbuan Plain while subsequent m- 3) and Dipulao (JR2-JR3) chert sections. The JR5 terval zones from mid-Middle Triassic to Upper Trias- and JR 6 chert samples from Nagbaril-Bintuan repre- sic are found along the San Nicolas Road section. sent the upper Middle Jurassic and lower Upper Ju- From the same section Tumanda (1991a) further rassic of the Southern Busuanga Belt. For the Trias- defined the earliest Jurassic Interval Zone, Parahsuum sic portion, the Upper Triassic samples of Yeh (1992) from Uson Island and Tumanda (1991a) from the simplum I. Z., which is equivalent to JR 1 orParahsuum simplum Zone of Matsuoka (1995). A stratigraphic Malbato section are considered representative of the continuation of the JR 1 San Nicolas section is appar- lower section of the Southern Busuanga.

ently shown by the JR2 (upper Pliensbachian- Discussions Toarcian) and JR 3 (Aalenian) chert samples from the Buwang section. The occurrence of JR4 (Bajocian- 1. Geologic Structure lower Bathonian) chert along the Pangarawan River, The linear topographic features exhibiting elon- which is the topmost chert for the Middle Busuanga gated narrow mountain ranges and valleys m Belt, more or less completes the representation of the Busuanga Island were previously interpreted as a chert sequence for this belt. simple sequence of folded structures (BMG, 1984). (3) Southern Busuanga Belt The chert mountain ranges accordingly constitute the It represents the youngest group of accreted se- core of anticlines, and the intermittent valleys are quences in Busuanga Island. The JR8 (lower-middle synclines with overlying clastic deposits, serving as Tithonian) chert and the KRl (late Tithonian- the upsection of the chert-clastic sequence. Subse- Berriasian) siliceous mudstone in Tagumpay high- quent contentions to such model were earlier hinted in the works of Isozaki et al. (1988) and Faure and light the distinction of the Southern Busuanga from the Middle and Northern Busuanga belts. Its occur- Ishida (1990), both proposing more complex Mesozoic rence has clearly established the younging polarity of scenarios for the North Palawan Block. Isozaki et al. Busuanga Island's accretionary complex from north (1988) considered the chert and limestones as priman- to south. ly oceanic deposits, then secondarily peeled off from The boundary between the Middle and the South- the subducting oceanic plate, and subsequently ern Busuanga belts is tentatively located south of juxtaposed with trench-fill turbidites and olisto- Mount Dalara in the east, and SW of Wayan-Balaw stromes (sandstone/mudstone) in an ancient subdue- Mountain Ranges in the west. Both west and east tion zone. Its lithologic assemblage and mode of oc- boundary traces presumably meet across Bacuit currence are accordingly similar to the Paleozoic and Island (Fig. 4). The distinctive characteristic of the Mesozoic subduction complexes in SW Japan and Southern Busuanga Belt is that its chert sequences are North America. much youngerincluding JR5, JR6 and JR8 ages. In In this work Busuanga Island is considered as an the Northern and Middle Busuanga belts, JR5 and JR accretion-subduction complex composed of juxta- 6 are already represented by clastic sequences while posed accreted chert-clastic sequences, in line with the no JR8 sequence has been found. Moreover, the proposal of Isozaki et al. (1988). Each constituent lithologic transition of the Southern Busuanga Belt sheet in this complex is characterized by a chert se- from chert to siliceous mudstone occurs in JR8 quence in the lower section and clastic sequence m the (Tithonian), much younger than the JR3-JR4 upsection. The strata dip generally northward, with (Aalenian-Bajocian) and the JR4-JR5 (Bathoman) its topmost section in fault contact with the base transition ages of the Northern and Middle Busuanga (chert) of the adjacent sheet at its north, and its lower- belts, respectively. most section in fault contact with the top of the The lithologic transition from chert to siliceous subsequent sheet at its south. Such feature charac- mudstone in Tagumpay is accompanied by moderate- terizes the imbricate framework of the Malampaya ly to well preserved JR8 (Tithonian) radiolanans. Sound Group in Busuanga Island, resulting to appar- This siliceous mudstone probably extends up to the ent alternation of chert and elastics sequences. earliest Cretaceous as shown in the stratigraphic 2. Formative process of the Malampaya Sound column of the Southern Busuanga Belt (Fig. 8). The Group terrigenous elastics over the siliceous mudstone The general succession from chert to elastics m should therefore have an Early Cretaceous age. In North Palawan is interpreted as a facies change fol- Jour. Geol. Soc. Japan, 107 (5) Accretion complex in Busuanga, Philippines 333

lowing the gradual plate movement from a remote during the subduction stage wherein these deposits oceanic environment toward the subduction zone. underwent off scraping from the subducting oceanic Its Middle Permian to Upper Jurassic chert sequences plate and juxtaposed with chert-clastic sequences in record a long depositional history re且ective of a long an imbricate manner. duration of pelagic environment, as previously The Bicatan Melange most probably originates recognized by Isozaki et al. (1988). Before the deposi- from the chert-clastic sequences and limestone units tion of the elastics occurred, the travelling oceanic of the Malampaya Sound Group, and from the basaltic plate must have originated from a considerably far basement of these sedimentary rocks. The develop- distance across a very wide paleo-ocean to accumulate ment of this melange most likely conforms to the such thick chert sequences from Middle Permian up to model of Moore and Byrne (1987) for melange forma- Middle or Upper Jurassic. The beginning of clastic tion in accreting sediments. Accordingly, the accre- deposition as represented by the siliceous mudstone tion process at the subduction zone causes strata! marks its transition from pelagic to hemipelagic con- disruption of the submarine accretionary prisms that dition. This lithologic transition indicates the near initiates progressive deformation of the young poorly approach of the travelling oceanic plate toward the consolidated sediments. Such mechanism is ex- subduction zone. The subsequent deposition of emplified by the Shimanto accretionary complex of terrigenous elastics reflects its final transition from SW Japan wherein at the base of its constituent chert- hemipelagic to turbidite deposition, while the coarsen- clastic sequences, progressive deformational history ing from terrigenous mudstone into sandstone indicating gradual underthrusting of sediments have signifies the closer approach to the continental been recorded (Mackenzie et al, 1987 ; Kimura and margin (Matsuoka, 1984 ; Matsuda and Isozaki, 1991). Mukai, 1991). The two types under the Bicatan Me- It therefore implies that the off scrape accretion lange distinguished through lithologic components event of the oceanic chert-clastic sequences occurred are considered undergoing the same tectonic process. immediately or even simultaneously with the deposi- The limestone-basalt-chert melange originates from tion of the terrigenous elastics. With the Malampaya the progressive deformation of its component maten- Sound Group in Busuanga Island exhibiting three als without the elastics, whereas the sandstone-chert- belts distinguished by different ages of lithologic tran- mudstone melange is from a chert-clastic sequence sition, three events of accretion are apparently m- without limestone and basaltic units involved. dicated. The accretion timing of the Northern 3. Correlation between Jurassic accretion com- Busuanga Belt probably took place in the late Middle plexes of North Palawan and SW Japan Jurassic based on its JR5 terrigenous elastics. The In the conceptualized Jurassic accretionary com- Middle Busuanga Belt's accretion would be m the Late plex along the East Asian margin, the North Palawan Jurassic based on its JR6 terrigenous elastics while Block has been considered the southernmost continiト the Southern Busuanga Belt could have accreted ation so far discovered. As shown in Fig. 1C, this during the Early Cretaceous as indicated by the KR 1 narrow zone has been traced from eastern Russia, NE base of the siliceous mudstone. These events appar- China, NE and SW Japan and the Ryukyus, with the ently illustrate progressive accretion of chert-clastic metamorphic complex in Taiwan as originally part of sequences. it (Isozaki etal., 1988 ; Matsuda and Isozaki, 1991 ; Modern interpretations of limestone bodies Mizutani and Kojima, 1992 ; Isozaki, 1997 ; Kojima and associated with chert-clastic sequences fall under the Kametaka, 2000). Hence, it is highly probable that off scrape model for oceanic deposits during the sub- the North Palawan Block, which originated from the duction stage (Isozaki et al, 1988 ; Matsuoka, 1992). southern part of China or in the vicinity of Taiwan Prior to subduction, these limestone bodies, as ll- (Taylor and Hayes, 1980 ; Holloway, 1982), can prove a lustrated by Sano and Kanmera (1988), originally close correlation to other Jurassic accretion com- developed as shallow facies deposits or carbonate plexes in East Asia. build-ups on oceanic seamounts that radially grade Among the many chert-clastic sequences m SW away from the seamounts into chert as distal facies. Japan, it has been found that the Malampaya Sound Such scenario quite explains the sporadically dis- Group closely correlates with the Togano Group or tributed limestone bodies around the North Palawan Subterrane of the Southern Chichibu Terrane (Fig. 9). Block. The Minilog, Malajon, CoronJIi and Imongue The Togano Group is characterized by chert-clastic limestones are hereby interpreted as originally car- sequences forming a northward dipping imbricate bonate build-ups that formed independently on structure (Matsuoka and Yao, 1990 ; Matsuoka, 1984, isolated seamounts of a past ocean. The range of 1992). It is subdivided into丘ve belts, namely, Ogawa their respective ages falling within Middle Permian to Belt, Kobiura Belt and Nishiyama Belt (I, II, III). Late Jurassic may imply that seamount carbonate These belts have different ages of lithologic transition setting coexisted with the Middle Permian to Late from chert to siliceous mudstone to coarse elastics, Jurassic pelagic setting of the chert sequences. It is and observed younging from north to south. The 334 Lawrence R. Zamoras and Atsushi Matsuoka 2001-5

Southern Busu酌ga Bek H Va 山 Il nil ¥ n in i◎ B= KR l(Pc) ○ .｣ Ber Tth JR8 (Lp) k Kim JR7(Hm) ⊃a 0Xf JR6 (Ss) Civ g JR5 (Tc) 描 ㊥ Bth ∽ lt) JR4 (Tp) < 蝣g Baj B= s =⊃ Aal JR3 (Li) ll Toa JR2 (Te) h PIb a◎ ..メSin JR l (Ps Het Uj Rha ≦ ◎I. n= 負【L. Nor ト■⊃

(a) Maiampaya Sound (b) Togano Group Group

Sandstone Si liceous Chert M udstone M udstone Shale

Fig. 9. Correlation between the Malampaya Sound Group and the Togano Group of the Southern Chichibu Terrane, SW Japan, (a) The Malampaya Sound Group composed of the Northern, Middle and Southern Busuanga belts characterized by the north-to-south youngmg polarity, (b) The Togano Group composed of Ogawa, Kobiura and Nishiyama (I, II, III) belts (Matsuoka, 1984 ; 1992).

systematic younging of the lithologic transition from Summa.ry Middle Jurassic in the Ogawa Belt to Upper Jurassic in the Nishiyama Belt III remarkably coincides with 1. The revised Upper Paleozoic-Mesozoic stratigra- lithologic transition ages of the three belts of the phy of the North Palawan Block includes three major Malampaya Sound Group. This similarity strongly lithostratigraphic units namely, Limmangcong For- indicates that the Malampaya Sound Group and the mation, Guinlo Formation and limestone units, with Togano Group have about the same accretion timing minor melange bodies (Bicatan Melange) collectively and formative process. called as the Malampaya Sound Group. Beside the similarities in lithology, sequence, struc- 2. The linear topographic features of Busuanga ture and age, the fauna! assemblages between the two Island, exhibited by alternating narrow mountain regions show close affinity. Zamoras and Matsuoka ranges and valleys, actually manifest an imbricate (2000a) observed remarkable similarity of the late structure formed through juxtaposition of off scraped Callovian-early Oxfordian radiolarian assemblage chert-clastic sequences. from a siliceous mudstone in the Tulbuan Plain of 3. The chert-clastic sequences m Busuanga Island Busuanga to those from the Sakawa area (Matsuoka, generally exhibit lithologic transition from chert to 1983) and Mt. Irazu area (Aita, 1987) in Shikoku, SW siliceous mudstone to terrigenous elastics. Japan. Based on these available data, therefore, we 4. There are three belts defined in Busuanga Island believe that the Malampaya Sound Group is correla- based on the age of lithologic transition : (a) Northern tive to the Togano Group of the Southern Chichibu Busuanga Belt, (b) Middle Busuanga Belt, (c) Southern Terrane. This correlation further confirms that the Busuanga Belt. These belts feature a north-to-south North Palawan Block is a southern extension of the youngmg polarity. Mesozoic accretionary complex of the East Asian 5. The close correlation between the Malampaya margin and SW-NE Japan. Sound Group in Busuanga Island and the Togano Group of the Southern Chichibu terrane in SW Japan is strong evidence that the North Palawan Block is a Jour. Geol. Soc. Japan, 107 (5) Accretion complex in Busuanga, Philippines 335 southern extension of the Mesozoic subduction com- relation to Asia Mainland and role m evolution of South plexes of eastern Russia, NE and SW Japan and the China Sea. Bull. Amer. Assoc. Petrol. Geol, 66, 1355-1383. Isozaki, Y., 1997, Jurassic accretion tectonics of Japan. The Ryukyus. Island Arc, 6, 25-51. Acknowledgements Isozaki, Y., Amiscaray, E.A. and Rillon, A., 1988, Permian, Triassic and Jurassic bedded radiolanan cherts m North Our sincere thanks to the National Institute of Palawan Block, Philippines : Evidence of Late Mesozoic Geological Sciences, University of the Philippines for subduction-accretion. Rep. No. 3 IGCP Proj. 224 : Pre- Jurassic Evolution of Eastern Asia, 99-115. the assistance rendered to us especially in the prepara- JICA-MMAJ, 1990, Mineral deposits and tectonics of two tion for our負eldworks in Busuanga Island, and to the contrasting geologic environments in the Republic of members of the Earth History Seminar (Nugata Um- the Philippines. 1-121. versity) for their comments. We would like to dedi- Kimura, G. and Mukai, A., 1991, Underplated units in an cate this article to the late Prof. Wataru Hashimoto accretionary complex : Melange of the Shimanto Belt of the eastern Shikoku, southwest Japan. Tectonics, 10, 31- who conveyed his interest in our work and comments 50. on our scientific results presented in an abstract Kojima, S. and Kametaka, M., 2000, Jurassic accretionary (Zamoras and Matsuoka, 2000 b). complexes m East Asia.Mem. Geol. Soc. Japan, no. 55, 6ト 72.* References Mackenzie, J.S., Needham, D.T. and Agar, S.M., 1987, Pro一 gressive deformation in an accretionary complex : An Aita, Y., 1987, Middle Jurassic to lower Cretaceous radiolan- example from the Shimanto belt of eastern Kyushu, an biostratigraphy of Shikoku with reference to selected southwest Japan. Geology, 15, 353-356. sections in Lombardy Basin and Sicily. Sci. Rep. Tohoku Matsuda, T. and Isozaki, Y., 1991, Well-documented travel Univ., Second Ser. (Geol), 58, 1-91. history of Mesozoic pelagic chert in Japan : from remote Amiscaray, E.A., 1987, Permian Fusulinids and other micro- ocean to subduction zone. Tectonics, 10, 475-499. fossils from northwestern Palawan. Rep. 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Faure, M. and Ishida, K｡ 1990, The Mid-Upper Jurassic Mizutani, S. and Kojima, S., 1992, Mesozoic radiolanan bio- olistostrome of the west Philippines : a distinctive key- stratigraphy of Japan and collage tectonics along the marker for the North Palawan block. Jour. SE Asian eastern continental margin of Asia. Palaeogeogr. Earth Sci, 4, 61-67. Palaeoclimatol. PalaeoecoL, 96, 3-22. Fontaine, H., 1979, Note on the geology of the Calamian Moore, J.C. and Byrne, T., 1987, Thickening of fault zones : A Islands, North Palawan, Philippines. ESCAP-CCOP mechanism of melange formation in accreted sediments. NewsL, 6, 40-47. Geology, 15, 1040-1043. Fontaine, H., David, P., Pardede, R. and Suwarna, N., 1983, Sano, H. and Kanmera, K., 1988, Paleogeographic reconstruc- Marine Jurassic in Southeast Asia. ESCAP-CCOP Tech. tion of accreted oceanic rocks, Akiyoshi, southwest Bull, 16, 3-30. Japan. Geology, 16, 600-603. Hamilton, W., 1979, Tectonics of the Indonesian region. U. S. Taylor, B. and Hayes, D.E., 1980, The tectonic evolution of the Geol. Surv. Prof. Pap., no. 1078,上338. South China Sea Basin. In Hayes, D.E., ed., The tectonic Hashimoto, W. and Sato, T., 1973, Geologic structure of North and geologic evolution of Southeast Asian Seas and Palawan and its bearing on the geological history of the islands. Geophys. Monogr., ser. 23, 23-56. Philippines.In Kobayashi, T. and Toriyama, R., eds., Geol. Tumanda, F., 1991 a, Permian to Jurassic radiolanan bio- Paleont. SE Asia, 13, 145-161. stratigraphy of Busuanga Island, Palawan, Philippines. Hashimoto, W., Takizawa, S., Balce, G.R., Espintu, E.A. and Doc. Sci. dissertation, Inst. Geosci., Umv. Tsukuba, 1-212. Baura, C.A., 1980, Discovery of Triassic conodonts from Tumanda, F., 1991 b, Radiolarian biostratigraphy m central Malajon and Uson Islands of the Calamian Island Group, Busuanga Island, Palawan, Philippines. Jour. Geol. Soc. Palawan Province, the Philippines, and its geological Phils., 46, nos. 1-2, 49-104. significance. Proc. Japan Acad., 56, ser. B, 69-73. Tumanda, F., 1994, Permian radiolaria from Busuanga Island, Holloway, N. EL, 1982, North Palawan Block, Philippines - Its Palawan, Philippines. Jour. Geol. Soc. Phils., 49, 119-193. 336 Lawrence R. Zamoras and Atsushi Matsuoka 2001-5

Tumanda-Mateer, F., Sashida, K. and Igo, H., 1996, Some Yeh, K. and Cheng, Y., 1998, Radiolarians from the Lower Jurassic radiolarians from Busuanga Island, Calamian Jurassic of the Busuanga Island, Philippines. Bull. Natn. Island Group, Palawan, Philippines. In Noda, H. and Mus. Nat. Set (Taiwan), no. ll, 1-65. Sashida, K., eds., Prof. Hisayoshi Igo Commemorative Zamoras, L.R. and Matsuoka, A., 2000a, Early Late Jurassic Volume on Geology and Paleontology of Japan and radiolarians from the clastic unit in Busuanga Island, Southeast Asia, 165-192. North Palawan, Philippines. Sci. Rep., Niigata Unw., Ser. Wolf art, R., Cepek, P., Gramann, F., Kemper, E. and Porth, H., E (Geology), no. 15, 91-109. 1986, Stratigraphy of Palawan Island, Philippines. Newsl. Zamoras, L. R. and Matsuoka, A., 2000 b, Late Callovian-early Stratigr., 16, 19-48. Oxfordian radiolarians from the clastic unit m Busuanga Yeh, K., 1992, Triassic Radiolaria from Uson Island, Philip- Island, North Palawan, Philippines. Paleont. Soc. Japan pines. Bull. Natn. Mus. Nat. Sci. (Taiwan), no. 3, 51-91. Abst. (The 2000 Annual Meeting), 41. Yeh, K. and Cheng, Y., 1996, Jurassic radiolarians from the northwest coast of Busuanga Island, North∵Palawan * : in Japanese with English abstract Block, Philippines. Micropaleontology, 42, 93-124.

(要 旨)

Zamoras, L.R. and Matsuoka, A., 2001, Malampaya Sound Group : a Jurassic-Early Cretaceous accretionary complex in Busuanga Island, North Palawan Block (Philippines).Jour. Geol. Soc. Japan, 107, 316-336. (ローレンス R.ザモラス･松岡 篤, 2001,マランパヤサウンド層群-フィリピン北パラワン地塊のジュラ紀-白亜紀古世付加体.也 質雑, 107, 316-336.) ブスアンガ島は,ペルム紀からジュラ紀にわたるチャート(リミナンコン層)とジュラ紀中世 から白亜紀古世にわたる砕屠岩幾(ギンロ層)から主として構成される付加体(マランパヤサウ ンド層群)よりなる.マランパヤサウンド層群は,全体として北に急角度で傾斜する覆瓦構造を なしている.同層群はチャート･砕層岩シーケンスの剥ぎ取り付加によって形成されたと考えら れる.放散虫の生層序学的検討により,チャートから珪質泥岩に移化する層準は,北から南に向 かって系統的に若くなる年代極性をもつことが明らかになった.この年代の違いに基づき,ブス アンガ島のマランパヤサウンド層群分布域を,北帯,中帯,南帯の3帯に区分した.同層群の付 加年代は,ジュラ中世から白亜紀古世にわたる.マランパヤサウンド層群は,西南日本南部秩父 テレーンの斗套野層群に対比される. Fig. 1. The lin棚r t叩Oglm tic expressi別且of the ch-も-cuastse 柵qu棚ce,s sh阜wing 丑腫rt mou雨且in蹄Ⅲg鞘(Bat強ek M机良itams) W…血i雨erva玩㊥f narrow vaIieys r哩細碑xitrng池亀C'l耳鼻f･藁C事.

?ォfSU'

The丸転Iampaya Sound Gro明日s predo汀mi待待mv掴m- posed c酌血YULiminang-ecme抽rrnatioi:亘elastics (ixuinlo Formatie恨) and scattered lime雨one i】壷拍that cha撒cter- ize the North Palaw且n Block (Zamora整an達Mats*沌k孔 20机上In宕he Caiamian Isl鋸ids (gr的押Ig勘1紺ang勘 Coro且, Cmil硝 払nci otheI, smaller i融andil 沌e

壬壷Iir拍堀eO堀Ff)rmati皿is repres輔ted by Perm*鋸x to Late Jurassic c!h肝玉the Gttmlo F反raation is repres路ted b写′ Middle亮且転Jut且ssie tくま鑑arまV eretaee日払S Cl鋸ti相. The commm甜C(忠ssion丘om elaertよo cl離ti甜with. ge.r.ト er礼Ilv conformable contact is thus referred t揖且s a eh朗事 d且前ic sequence.壬n Buman胆 Imea再opogra画ic 押tterx蟻revea｢血e par且IIc｢di雨ib融ion of chert-c'h猶玩 sequer).舘s di押1堀揮n群aHy NW in the west, arid∴醐Hn ォ 血e c裡tr且接点d ea雨ern pc雨ions. This cherレclastic repe- litiol} indica砲台且f貢mforie且七e structure typ昔払I to融isc.rape aecret/io丑compl路es.

> Fig.望. Gk'ologul nヽ叩of the (〕よ雨用tian Islands (BusmⅢ押詳uli帝n. C冊Y刷imd §mallei｢ isl甘tids).

Xi Fig. 4. Typical thinly bedded Triassic chert sequence (p盆雨of血e Lfon…nancottg

Pig. 5, Lat虚Triassie l〕oron him磨stoue viewed m Cayangan Lake m Coroii lslalld.

Fig誹. ng.前Iascan鋼醜mhl噂鞘 refle雨ive of lagoml且I enヽ壷onmen一 間ォfgf!冒KlaBggffuBliB相即蘭h事昆雨脚鐙は The pel靴yP帝d f㊥ssils profoaもIy melud愈Paru榊egal専d融融衰ch w乱事 r叩Or転d by Woifart et粛I. {li>88}.

Wolfart,私A eepek, PっGramami, F,, Kemper.私and Por恥且. 1粥私Stra七.igr叩hy ofPai且wan IさIand, Fhiii押iries. Ne購i. S柄油gr., lP), 19-48. Zamoras, L薫.津nd M融硯fjkaグAリ豆001, Maiampaya S朝雨Gmup: a Jx鋤鍋i臣.振rlv C撒fcacems aecre七iolaary compl唐笠m Bu鈍anga I血nd. North FalaWan mock ('Phi毎pm即), J軸γ-, Q路上S肱J叩an,相等318-338.

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