Selected Late Paleozoic and Triassic limestone exposures were studied on northern Palawan Island, Philippines, with regard to microfacies, stratigraphy and ...
FACIES
43
39-78
PI. 6-16
8 Figs.
3 Tab.
ERLANGEN 2000
Late Paleozoic and Late Triassic Limestones from North Palawan Block (Philippines): Microfacies and Paleogeographical Implications Wofgang Kiessling and Erik FI0gel, Erlangen KEY-WORDS: MICROFACIES ANALYSIS - CARBONATE RAMPS AND PLATFORMS - REEFS - PALEOGEOGRAPHY PHILIPPINES (PALAWAN) - CARBONIFEROUS - MIDDLE PERMIAN - LATE TRIASSIC CONTENTS Introduction 2 Geological background 3 E1 Nido (Carboniferous and Middle Permian) 3.1 Introduction 3.2 Lithologic and stratigraphic summary 3.3 Tectonic summary 3.4 Sedimentology and microfacies 3.4.1 Paglugaban Formation 3.4.2 Bacuit Formation 3.4.2.1 Lithology 3.4.2.2 Stratigraphy 3.4.2.3 Depositional environment 3.4.3 Minilog Formation: Carbonate ramp and alatoconchid bivalve/richtho feniid buildups 3.4.3.1 Lithology 3.4.2.2 Biostratigraphy 3.4.3.3 Facies differentiation 3.4.3.4 Microfacies (MF P I - MF P 6) 3.4.3.5 Paleontological criteria 3.4.3.6 Facies interpretation of the Minilog Formation 3.4.4 I .iminangcong Formation 3.4.4.1 Lithology and stratigraphy 3.4.4.2 Diagenesis of manganese-rich cherts 3.5 Notes on the Late Paleozoic outcrops in the El Nido area 3.6 Biogeographic and paleogeographicconstraints 3.6.1 Carboniferous 3.6.2 Permian 4 Busuanga area, Calamian Group Islands (Late Triassic) 4.1 Introduction 4.2 Lithofacies and tectonics of cherts and clastics 4.3 Limestone outcrops on and around Busuanga (Coron Formation): Carbonate platforms and reel.,; 4.3.1 Islands off northwestern Busuanga Island: Reef and platform facies (MF Tr 1 - MF Tr 2) 4.3.1.1 Malajon Island 4.3.1.2 Kalampisanan 4.3.2 Southern Busuanga: Platform lacies (MFTr 3- MFTr t 3) 4.3.2.1 Busanaga (Mt. lli) and Sanget Island 4.3.2.2 Busuanga: Hills NE Coron Town 4.3.2.3 Coron Island south of Busuanga 4.4 Comparisons 5 Paleogeographical implications References
SUMMARY
1
Selected Late Paleozoic and Triassic limestone exposures were studied on northern Palawan Island, Philippines, with regard to microfacies, stratigraphy and facies interpretation. Although some of the outcrops were already reported in literature, we present the first detailed microfacies study. Late Paleozoic carbonates in the E1 Nido area are represented by widley distributed Permian and locally very restricted Carboniferous limestones. Of particular interest is the first report of Carboniferous limestones in the Philippines dated by fossils. Fusulinids indicate a 'Middle' Carboniferous (Moscovian-Kasimovian) age of the Paglugaban Formation only known from Paglugaban Island. The Permian Minilog Formation consists mostly of fusulinid wackestones and dasycladacean wacke-/packstones. Fusulinid datings (neoschwagerinids and verbeekinids) provide a Guadalupian (Wordian-Capitanian) age. The depositional setting of the Middle Permian carbonates corresponds to a distally steepened ramp with biostromes built by alatoconchid bivalves locally associated with richthofeniid brachiopods. Late Triassic limestones occur in isolated exposures on and around Busuanga Island (Calamian Islands). The age of the investigated carbonates is Rhaetian based on the occurrence of Triasina hantkeni M.mzoN. Microfacies data indicate the existence of reefs (Malajon Island) and carbonale pIatforms (Kalampisanan Islands, Busuanga Island, Coron Island). Reef boundstones are characterized by abundant solcnoporacean red algae, coralline sponges and corals. Platform carbonates yield a broad spectrum of microfacies types, predominantly wacke- and packstones with abundant involutinid foraminifera and some calcareous algae. These facies types correspond to platform carbonates known from other parts of Southeast Asia (Eastern Sulawcsi and Banda Basin; Malay Peninsula and Malay Basin). The Philippine platfi)rm carbonates were deposited on and around seamounts surrounded by deeper water radiolarian cherts.
Addresses: Dr. W. Kiessling*, Prof. Dr. E. Fl/igel, lnslitut ftir Pal~iontologie, Universit/.it Erlangen-Ntirnberg, Loewenichstrasse 28, D-91054 Erlangen. Fax: 004%9131 852 2690. Mail: el]uegel~1 pal.uni-crlangen.de *Current address: Department of Geophysical Sciences, University of Chicago, 5734 South Ellis Avenue, Chicago IL 60637, USA
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The new data on facies and age of the Philippine Permian and Triassic carbonates contradict a close paleogeographical connection between the North Palawan Block and South China and arise problems for the currently proposed origin of the North Palawan Block at the paleomargin of South China. We hypothesize that North Palawan was part of the Indochina Block during the Carboniferous and Permian, separated from the Indochina Block during the Middle Permian and collided with the South China Block in the Late Cretaceous. 1 INTRODUCTION The Philippines are mostly considered as a Cenozoic archipelago (e.g. HASmMO~O1981, WIEDICKE1987) whereas the Mesozoic and Paleozoic history is little understood. The lack of knowledge is related to the scattered occurrences of pre-Jurassic sediments, the intense weathering of sedimentary rocks and the difficult access to outcrops due to tropical vegetation and karstic overprint. Contract work for Shell Philippines Exploration by one of the authors (W.K.) allowed sampling of Permian and Triassic limestones in northern Palawan (Fig. 1). The study was limited to some selected outcrops in the North Palawan Block (HoLLOWAV1981, 1982). Complex tectonics, intense karstification, and time constraints did not allow to measure detailed continuous sections. Despite these limitations and an often poor preservation of facies diagnostic features, the available biostratigraphic and microfacies data are sufficient to check the facies development through time and to use these criteria in the evaluation of paleogeographical models. The study intends to document the microfacies and stratigraphy of Late Paleozoic and Triassic limestones formed adjacent to Southeast Asian terranes, and to discuss the preTertiary history of the North Palawan Block. The material of our study is deposited in the Forschungsinstitut Senckenberg Frankfurt/Main. 2 G E O L O G I C A L BACKGROUND Lying west of Cebu, between Minoro Island and the Malaysian territory of North Borneo, Palawan is bordered by the Sulu Sea in the east and the South China Sea in the west. Palawan can be geologically subdivided into a south/ central and a northern part, which show a different sedimentary and tectonic evolution. North Palawan consists mainly of Upper Paleozoic and Lower Mesozoic metamorphic and sedimentary rocks, while South/Central Palawan is largely built up of basic magmatics (ophiolitic sequences) and a Cretaceous to Tertiary sedimentary cover. North Palawan is considered as part of a continental fragment that has been termed 'North Palawan Block' by HOLLOWAY(1981, 1982) and 'North Palawan Continental Terrane' by ENCARNACION& MUSAKA(1997). While most of the Philippine Archipelago represents an island arc system with a geologic history not older than Cretaceous (HA~LXON 1979, HtrrcHn~SON1989), the North Palawan Block contains
abundant Permian sediments and an Upper Paleozoic metamorphic basement. The North Palawan Block is considered to form the continental margin of the South China Plate during the Paleozoic and Mesozoic. Most authors agree that the North Palawan Block derived from the mainland of Asia and was separated from South China not earlier than middle Oligocene during the opening of the South China Sea (TAYLOR & HAVES 1980, HOLLOWAY 1981, 1982, WOLFE 1984, I~r 1991, ECARNAC10Nt~ MUKASA1997, .ALMASCOet al. 2000). The southern margin of China was an Andeantype active margin during the Mesozoic. Lithospheric extension is first recorded in the Late Cretaceous (HoLLOWAY 1981, 1982). A first spreading ridge was developed near the end-Paleocene, but major extensional tectonics did not affect the North Palawan Block prior to the end-Eocene. North Palawan was attached to South Palawan along a major transform fault during the Mid-Miocene (Ro & PIGO~ 1986).
3 EL NIDO (CARBONIFEROUS AND MIDDLE PERMIAN) 3.1 Introduction E1 Nido is a municipiality located at the northwestern tip of the Province of Palawan (Fig. 1). The limestone outcrops around El Nido (Bacuit Bay) are scattered over an area of some 100 km 2 (Figs. 1 and 3). The impressive landscape formed by karst towers on the islands of Bacuit Bay (P1. 6/ 1) has attracted tourists for many years, but the geological knowledge of the area is still limited. The area was first studied by HASHIMOTO& SATO (1973), who defined three formations (Fig. 2): 1. Bacuit Formation (base): Slightly metamorphic siliciclastic rocks and cherts with minor tufts. 2. Minilog Formation: Bedded to massive more or less reerystallized limestones. 3. Liminangeong Formation (top): Bedded cherts. Together with a fourth formation not exposed in the Bacuit Bay, these formations form the Malampaya Sound Group. HASHIMOa'O& SATO(1973) assigned a Middle-Late Permian age to the Bacuit Formation, a Middle Permian age to the Minilog Formation and a Middle Triassic age to the Liminangcong Formation. A new stratigraphic unit, the Paglugaban Formation, was recognized in samples from Paglugaban Island (see 3.4.1). Our field work was limited to less than three weeks, not permitting more than a coarse facies mapping and sampling of major exposures. During the field work, all major and some smaller islands in the E1Nido archipelago were visited and sampled (Fig. 3; chapter 3.5). Age and/or facies diagnostic fossils were recognized in thin sections of almost 70 % of more than 100 samples, allowing the definition of facies types and a stratigraphic subdivision of the Minilog Formation.
3.2 Lithologic and Stratigraphic Summary The Paglugaban Formation defined herein (Fig. 2) is only known from Paglugaban Island, south of Minilog
41
Fig. 1. Sketch map of Palawan (Philippines) showing the investigated areas. El N ido consists predominantly of Middle Permian limestones except of isolated Carboniferous outcrops on Paglugaban Island. The Busuanga area yields Triassic carbonates in addition to abundant cherts. Island (Fig. 3). The sequence consists of carbonate breccias and bioclastic limestones. The majority of limestones is completely recrystallized, but two samples with moderatcly preserved fusulinid foraminifera could bc recovered in the central part of the island. The samples yield 'Middle' Carboniferous (late Moscovian-early Kasimovian) fusulinids (Pseudofusulinella sp.; det. D. Vachard). Although it is possible that Carboniferous fusulinids wcrc reworked, the overall stratigraphic and tectonic context suggests that Palugaban is largely composed of Carbonifcrous limestones, separatcd from the Permian limestones by a large oblique strike slip fault. Nevertheless, the occurrence of Carboniferous carbonates within the mostly Permian sequence of northern Palawan is difficult to explain. No evidence :for latest Carboniferous and Early Permian sediments was found suggcsting a major sedimentation break (unconformity ?) in this interval. Furthermore, the Bacuit Formation underlying the Minilog Formation is a siliciclastic-tuffaceous and cherty sequence of partly Middle Permian age. Our data arc currently too limited to propose a tectonic model for the origination of Carboniferous limestones in the Middle Permian sequence, but their presence can not be neglected. The type locality of the Bacuit Formation is Manmcgmeg Bay south of El Nido (formerly Bacuit). The Bacuit Formation includes sandstones, tuffitic shales and cherts. The total thickness was estimated exceeding 1500 m (BuReAU OF M~ES ANDGEOSCiENCES1972). Conodonts in cherts indicate a Middle Permian age (I-I_a.SHtr~IOTO& SATO 1973). This age coincides with the proposed age of the overlying Minilog Formation, although a conformable contact is evident in places. The type locality of the Minilog Formation is Minilog
Island h)cated in the center of the study area (Fig. 3). It consists of gray and black recrystallized, thick-bedded or massive limestones. The thickness is supposed to be between 100 and 300 m (WoLd'ARTet al. 1986), but the complex tectonics hinder reliable estimations. HASHi~aOTO& SAm (1973) provided a preliminary subdivision of the Minilog Formation based on fusulinids, They distinguished a lower horizon with Verbeekina cf. verbeeki (GEINITZ),ParaJusulina sp. and Maklaya sp., and an upper horizon with Neoschwagerina sp. and Verbeekina sp. Later additional findings of bIankinetla sp. were reported (HAsiliMOTO1981). The paleontological data of WOLI:ARret al. (1986) indicate an agc range of the Minilog Formation from the Middlc Permian (based on foraminifera) to Early/Middle Triassic (based on conodonts) with a possible continuous scdimentation. Our new data are basically in accordance with HASmMO'rO& SAro (1973). No evidence for Triassic age was found in the Minilog Formation of Bacuit Bay, but we did not look for conodonts. The Minilog Formation is conformably overlain by the Late Permian to Middle Triassic (to Late Jurassic ?) Liminangcong Formation in the southern par Lof Bacuit Bay. The type locality is Liminangcong coast some 15 km south of lhc study area. The Liminangcong Formation consists predominantly of variably colored radiolarian cherts with admixtures of tuff and black shales. In Bacuit Bay, the formation is limited to the southern parts, but is widely exposed in other parts of North Palawan, especially on Busuanga Island. FONTAINE(1979) reported a maximum thickness of lt)00 m on the Calamian Group Islands. Poorly preserved conodonts (H.~,SinMoro & Saro 197311 suggest a Middle Triassic age for samples from South Guntao Island (Fig. 3).
42
Fig. 2. Provisional biostratigraphic section in El Nido and Busuanga, northern Palawan (Philippines).
these folds have an average wave length of about 10 km. Generally, the western limbs of the chevron-type folds are oriented N-S as in Matinloc and Ilnamuyod islands, while eastern flanks are rather aligned in NW-SE direction (Guntao and Pangalusian islands, east of Cadlao Island). Locally, parasitic folds of these anti- and synclinorium-type megastuctures are often observed in the field, with wave lengths varying between 10 and 200 m. Synsedimentary deformations, mostly extensional, are present in the Minilog Formation. They may be the result of a Late Permian NNE-SSW extension. Steeply dipping sets of parallel fractures are related to folding, hence being contemporaneous with the folding episode. They represent longitudinal and cross-axial extensional fractures, and longitudinal and cross-axial shear fractures. Extensive shearing zones normally coincide with axial planes, sometimes being perpendicular to them. Subsequent right-lateral strike-slip faulting was usually observed along these planes. Oblique thrusting is evident along the contact between the Bacuit Formation and the overlying Minilog Formation, possibly also contemporaneous with the major folding phase. Weak metamorphism has partially affected the limestones along major shear zones. The sequence of tectonic events can be summarized as follows: 1) N-S synsedimentary extension (late Middle Permian), 2) NE-SW compression, 3) N-S compression and NNW-SSE dextral shearing, 4) N-S to NNE-SSW extension.
3.4 Sedimentology and Microfacies 3.4.1 Paglugaban Formation The name Paglugaban Formation is here proposed for a sequence consisting of brecciated, partly dolomitized limeThe lithological sequence is strongly folded and faulted, stones with intercalations of bedded bioclastic wackestones as a result of an ENE-WSW to NE-SW oriented main with foraminifera, crinoids and brachiopods. The carboncompressional event, on which other possible tectonic epi- ates are strongly recrystallized. The thickness of the formasodes were superimposed (SoECItTING in KIESSLING t~ tion corresponds to several tenths of meters. Type locality is SOECHTING1995). Owing to the rotation of the North Palawan the central part of Paglugaban Island south of Minilog Block the original stress direction was different (HAs~OTO Island. Underlying and overlying formations are unknown. & SATO1973). Axial planes are generally trending in NNWAccording to Forke (pers. comm. 1997) some fusulinids SSE direction, and the fold axes plunge some 10 to 45 defrom Paglugaban Island (Fig. 2; Nd 65-66) south of Minilog grees either to the north or to the south. On a regional scale, Island point to a Middle Carboniferous (MoscovianKassimovian) age. D. Vachard (pers. comm.) determined the fusulinids (P1.7/1-3) as PseudoFusulinids Samples Plate fusulinella THOMPSONor Kanmeraia OZAWA.The Afghanella sp. Nd 46 PI. 7/10 fusulinids are associated with smaller foraminColania sp. Nd 97, ?99, 100 ifera (Endothyra or Neoendothyra, Tuberitina Nankinella sp. Nd 9 sp. (P1. 8/6, 8). See chapter 3.4.1. Neoschwagerina sp. Nd 67, 71,97, 99, ?100, 102 Neoschwagerina ex gr. Nd 42, 43, 46, 55, 67, 100 PI. 7/5-7 Age: The foraminiferal assemblage with craticulifera (SCHWAGER) Pseudofusulinella indicates a Middle CarbonifParafusulina sp. Nd 42, 99, 100, 112 PI. 7/4 erous, late Moscovian to early Kasimovian age. Pseudofusulina sp. Nd 71 PI. 7/8
3.3 Tectonic Summary
Schwagerina sp. Sumatrina sp. Verbeekina sp. Verbeekina verbeeki (GEINITZ) Yabeina ? sp.
Nd Nd Nd Nd Nd
67, 99, 17, 46, 99
71,86, 97 ?100, 112 98 67
PI. 7/12 PI. 7/11 PI. 7/9
Table 1. Age diagnostic fusulinids in the Minilog Formation of Bacuit Bay.
3.4.2 Bacuit Formation 3.4.2.1 Lithology The Bacuit Formation in Bacuit Bay is characterized by the absence of bedding traces and a chaotic mixture of different lithologies. Black silty tuffaceous shales, locally altered to green-
43
Fig. 3. Geological map of the El Nido area and sample sites. The Paglugaban Formation represents the l'irsl evidence o[ Middle Carboniferous sediments in the Philippines. The Minilog Formation includes the Middle Permian ramp carbonates described in this paper. Type localities are underlined. schists, are the most common lithology. Incorporated are intensely fractured sandstone clasts and blocks ranging in size from 2 mm to 30 m. The intensively deformed shales are black or dark brown. The TOC content is low (0.42 to 0.92 % in the samples Nd 16, 23 and 39 from Dilumacad Island, Cadlao Island and Entalola Island; cf. Fig. 3). Sandstone fragments and lenses occur almost everywhere within the shales. Contrary to the
field impression, suggesting that this feature might be the result of primary lens-bedding, it seems more reliable that an original intcrbedding of shales and sandstones was completely destroyed by tectonic strain. Arguments favoring this opinion are the well-defined interlayering in less tectonized areas (PI. 6/5) and metamorphic criteria in thin sections. The lithofacies spectrum of the coarser siliciclastics
44
ranges from laminated siltstones to coarse-grained sandstones (graywackes, litharenites). Porphyroblastic growth of quartz and feldspar within the tuffaceous sandstones is common. The sandstones are mostly feldspathic litharenites and lithrudites. The lithic components comprise cherts, basic volcanics, shales and rare sandstones as well as recrystallized limestones amd occasionally metamorphic clasts. Chert is less common in the Bacuit Formation and occurs commonly in lenses and fragments. However, on northern Cadlao Island, a continuous chert sequence, up to 20 m thick, is known. On southern Cadlao a 15 x 15 m sized chert block was found floating in a matrix of black siliceous shales. Most cherts are greenish gray, but red cherts and other variations also are present. The cherts are strongly recrystallized. Radiolarians are rare; WOLVA~Tet al. (1986) failed to isolate any. 3.4.2.2 Stratigraphy Except for rare recrystallized radiolarians in some chert samples, no fossils were found in thin sections, and hence no biostratigraphic dating is possible. The contact to the overlying Minilog Formation is almost in all places a tectonic one. A probably conformable contact is only exposed on Dilumacad Island (Helicopter Island; Fig. 3) documented by a dark, strongly deformed, tuffaceous and silicified shalesandstone sequence overlain by light-gray, in the lowermost part brecciated massive limestones. 3.4.2.3 Depositional environment Lithology and sedimentary structures point to a deep marine environment. The sandstones and shales show evidence of turbiditic sedimentation, with classical Bouma sequences developed (P1. 6/5). The cherts are basinal radiolarites with almost no terrigenous input. They are interpreted as pelagic (oceanic ? radiolarites deposited in a
more distal environment than the shales and sandstones. The chaotic mrlange seen today is due to intense shearing tectonics and folding on a convergent plate boundary. 3.4.3 Minilog Formation: Carbonate ramp and alatoconchid bivalve/richthofeniid buildups 3.4.3.1 Lithology The Minilog Formation covers most of the area exposed in Bacuit Bay and forms spectacular karst towers. It consists of dark-gray, coarsely bedded to massive limestones. Occasionally dolomites occur. Intense recrystallization makes the recognition of facies difficult, both in the field and in thin sections. Additionally, folding and faulting causes problems in tracing facies laterally or vertically. The thickness of the Minilog Formation was estimated to be 100-300 m by WOLFART et al. (1986). Our estimation is 250 m for the anticline of Cadlao Island. 3.4.3.2 Biostratigraphy Our data indicate a Middle Permian age for nearly all limestones in Bacuit Bay except for a few samples from Paglugaban Island. The most characteristic Permian genera are Neoschwagerina, Verbeekina (identified already by Hashimoto 1981) andAfghanella sp. (P1.7/10) indicating an age not younger than the late Guadalupian (Kobayashi 1999). The best age constrain is given by the occurrence of Neoschwagerina craticulifera(ScnwAcER) - P1. 7/5-7, Verbeekina verbeeki (GFJNrrz)- P1.7/10 and Colania douvillei (OZAWA), three zonal marker index species (cf. O'rA 1977, VACHARDet al. 1995, I-InuSERet al. 2000) characterizing the Middle Permian (Murgabian-Midinian; approximately the Wordian to Capitanian interval in today' s chronostratigraphy,
Plate
6 Permian and Triassic sedimentary rocks in northern Palawan Island and Busuanga, Philippines: Field aspects (see Fig. 3 for locations)
Fig. 1.
Typical view of karstic Middle Permian limestone outcrops (Minilog Formation) in the Bacuit Bay, Mainland, west of E1 Nido. Mound-like geometry of Permian limestones near Panayan Point at the southern tip of Matinloc Island. Mound structure might be deceived by folding and karstic overprint. Height of the 'mound' about 10 m. Permian biostromal facies with abundant thick-shelled alatoconchid bivalves in alternation with organic-rich limestones and fusulinid wackestones with rare platy shells. Southern Matinloc Island. Sample location Nd 6869. Cross-sections of richthofeniid brachiopods in the biostromal facies of southern Matinloc Island. Sample location Nd 68-69. Folded sequence of sandstones, siltstones and shales of the Permian Bacuit Formation, with evidence of turbiditic sedimentation. Only the members B to E of the Bouma sequence are developed. North Cadlao Island. Sample location Nd 50. Upper Triassic reef exposed on Malajon Island. Thickness of exposed reef about 30 m (base not shown in the photograph). Fasciculate corals (Retiophyllia-type) in the Triassic reef facies on Malajon Island. Height of picture about 60 cm. Upper Triassic megalodontid bivalves in lagoonal platform facies on Coron Island. Sample location Bs 55-57. Sphinctozoid coralline sponges (Neoguadalupia sp.) in the Upper Triassic reef facies of Malajon Island. Width of picture about 1 m.
Fig. 2. Fig. 3.
Fig. 4. Fig. 5
Fig. 6. Fig. 7. Fig. 8. Fig. 9.
Plate
6
45
46 GLENISTERet al. 1999). The occurrence of Neoschwagerina ex,gr, craticulifera defines a Murgabian (Wordian) age (KoBAYAS,I 1997). HASrUMOTO & SATO (1973) mentioned two successive horizons occurring in the Minilog Formation: The lower horizon is supposed to be oolitic and found at the east coast of Matinloc Island and the east coast of Minilog Island. The upper bituminous horizon occurs along the south coast of Minilog Island, west of Cudugman Point on the mainland and at the west coast of Entalola (Inabalabamalaki) Island (cf. Fig. 3). However, there is no distinct difference in facies and foraminiferal fauna between these 'horizons'. Oolitic facies is not present in the Permian limestones of Bacuit Bay. It appears, that circular outlines of dasycladacean and gynmocodiacean algae have been mistaken for ooids. Therefore, although some age differences are reasonable considering the thickness of the Minilog Formation, no clear separation into lithostratigraphic members is evident. 3.4.3.3 Facies differentiation Five facies types were differentiated in the field. All facies types are widely distributed in Bacuit Bay, but the fusulinid wackestone facies is by far the most dominant. However, the facies types can only be traced where recrystallization is moderate and thus can only be seen in specific localities. Listed in decreasing areal exposure the following types are present: Facies type 1: Fusulinid wacke-/pack-/grainstones. Fusulinid tests are densely packed; the assemblages seem to be diverse. They are associated with medium-sized gastropods and crinoids. This facies covers vast areas of Bacuit Bay. Facies type 2: Dasycladacean wacke-/packstones. Algal fragments are abundant. They are in places the only fossils but occur also associated with smaller foraminifera, especially miliolids. Facies type 3: Alatoconchid bivalve/richthofeniid facies. This facies is the most outstanding in the field (P1. 6/3). Large white and completely recrystallized calcite 'plates' are arranged more or less parallel to bedding. The often densely packed plates reach a length up to 30 cm (sometimes possi-
Plate
Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig.
1. 2. 3. 4. 5. 6 7. 8. 9. 10. 11. 12.
7
bly 50 cm). Most shells represent giant clams and belong to alatoconchid bivalves. In a few localities, it is evident that some of the shells are brachiopods related to richthofeniids (P1.6/4, PI. 9/7; Fig. 4). Facies type 4: Gastropod and oncoid facies. Gastropods occur in association with oncoids (formed around bivalve shells and brachiopods, MF P 4a) or as the dominating fossils (MF P 4b). A mound-like geometry of the gastropod-bearing buildup indicates hydrodynamic accumulation of shells. Dolomitization is widespread in this facies. Facies type 5: Mudstones. True mudstones (yielding very rare radiolarians) are very scarce. Very often, a mudstone texture is deceived by intense recrystallization, resulting in the formation of fine-grained calcite marble. 3.4.3.4 Microfacies (MF P 1 to MF P 6) The major facies types identified in the field are confirmed by thin section analysis. Microfacies criteria allow the definition of subfacies and an environmental interpretation of the limestones. MF P 1: Fusulinid float-, wacke- and packstones (P1. 10/! ) Description: This microfacies is characterized by abundant fusulinids associated with Climacammina and other smaller foraminifers floating in a micritic matrix rich in shell debris. When recrystallization and pressure solution are moderate, nearly all fusulinid tests are complete. Therefore, the fusulinids appear to represent in situ assemblages without significant reworldng. However, many samples exhibit strong compaction and stylolitization causing fragmentary preservation and diagenetic packing of the fusulinids. The diversity of both fusulinids and smaller foraminifera is fairly high; more than thirty taxa were identified (Tab. 1 and 3). Calcareous algae are rare. Rugose corals (PI. 9/9) associated with fusulinid limestones were only found in one locality on Lagen Island (Nd 101; Fig. 3). Two subfacies can be differentiated according to the amount of fusulinids and smaller foraminifera: Subfacies 1a is characterized by the dominance of fusuiinids forming the bulk of the limestone. In Subfacies lb smaller foraminifera
Age diagnostic fusulinid foraminifers of the Minilog Formation (Figs. 4-12). The dominance ofneoschwagerinid taxa and the occurrence of verbeekinid species indicate a Middle Permian (Guadalupian) age of most samples (Figs. 3-12) except for few samples from Panglugaban Island (Panglugaban Formation, Figs. 1-3) which are dated as Middle Carboniferous. Bacuit Bay (El Nido), North Palawan, Philippines
Pseudofusulinella assemblage. Late Moscovian-Early Kasimovian. Paglugaban Island. Nd 66, x 16 Pseudofusulinella sp. Slightly oblique section. Nd 66. x 25 Pseudofi~sulinella sp. Parallel section. Nd 66. x 25 Parafusulina sp. and palaeotextulariid foraminifera (left). Shimisu Island. Nd 42. x 19.5 Neoschwagerina ex gr. craticulifera (ScHWAGER).Shimisu Island. Axial section. Nd 43, x 16 NeoschwageHna ex gr. craticulifera (ScHwACER). Detail of Fig. 5. Nd 43. x 50 Neoschwagerina ex gr. craticulifera (ScHWAGER).Shimisu Island. Parallel section. Nd 46. x 31 Pseudofusulina sp. Oblique axial section. Matinloc Island. Nd 71. x 12.5 Yabeina sp. or Lepidolina sp.. Poorly preserved axial section. Lagen Island. Nd 99. x 16 Afghanella sp. Shimisu Island. Nd 46. x 25 Verbeekina verbeeki (GEtN1TZ).Entalola Island. Nd 67. x 12.5 Verbeekina sp. Entalola Island. Nd 67. x 12.5
Plate
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~
- Fusulinids
Fig. 4. Characteristic organization of the Middle Permian bivalve/ richthofeniid biostromes as seen on southeastern Matinloc Island (Nd 68-69, cf. Fig. 2; P1.6/3). The base of the biostrome is formed by fusulinid wacke-/floatstones. These are overlain by a layer with large bivalves and richtofeniid brachiopods and a subsequent imbricating alatoconchid shell layer indicating a current to the north (right). The overlying thick bed is a fine-grained phylloid algal bindstone, rich in organic matter. It contains common trilobite fragments pointing to a deeper water setting of this facies. A capping layer with bivalve shells is overlain by bioclastic wackestones with scattered algae, followed by a crinoid-rich wackestone. Total thickness 1.2 m. predominate over fusulinids per volume. Calcareous algae occur in subfacies lb; a particular feature is the presence of calcispheres (P1.9/6). A continuum exists in facies transition from MF P la to MF P lb to MF P 2. Increasing amount of algae usually goes- to the expense of the fusulinid content. Interpretation: The fusulinid limestones represent lowenergy open-shelf deposits. The fairly high diversity of the
Plate Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig.
1. 2 3. 4. 5. 6. 7. 8. 9.
Fig. Fig. Fig. Fig.
10. 11. 12. 13.
foraminifera and other biota points to an unconstrained water exchange with the open sea, whereas the absence of significant reworking indicates a low-energy environment. Occasional reworking of semi-lithified sediment is only evident in samples from southeastern Tapiutan Island (Nd 52, 53) where dark rounded clasts of fusulinid wackestones are embedded within a fight matrix of the same composition. Although similar textures can also be achieved through differential recrystalfization, actual reworking is proven by broken fusulinids at the clast margins. MF P 2: Algal facies (PI. 10/2) Description: Calcareous algae, predominantly dasycladaceans (Mizzia and others; cf. Tab. 2; P1. 9/1-2) are the most prominent constituents. In the field the algae are sometimes weathered out showing well-preserved structures. They are commonly densely packed and often are the only identifiable fossils. Other fossils are gastropods, shell fragments and rare echinoderms (mostly crinoids). The transitional facies to MF P 1b may contain some fusulinids. Wacke- and packstone textures prevail. The facies is best exposed on the east coast of Minilog Island (Nd 6 to Nd 9). Two subfacies were differentiated according to the association of the algae. Subfacies 2a is characterized by packstone texture and the distinct predominance ofdasycladacean algae (P1. 10/2). Subfacies 2b is defined by prevailing wackestone textures and the abundance of miliolid and other smaller foraminifera associated with dasycladacean algae. Interpretation: Although the dense packing may be largely attributed to compaction, an originally dense growth of the algae is reasonable. Relatively low diversity, high abundance of algae and the association with euryhaline organisms indicate a shallow, restricted lagoonal environment. The environment of Subfacies 2b was probably slightly more restricted than in Subfacies 2a. MF P 3: Alatoconchid bivalve/richthofeniid biostromal facies (P1.6/3-4, 10/3-6) Description: Significant amounts of the sediment are formed by large platy recrystallized shells, up to >30 cm in
8 Smaller Foraminifera (Fig. 1-11) and calcareous algae (Fig. 12-13) of the Minilog Formation (Fig. 1-5, 7, 913) and Paglugaban Formation (Fig. 6, 8). Bacuit Bay (El Nido), North Palawan, Philippines
Tetrataxis sp. (top) and Climacammina sp. Shimisu Island. Nd 43. x 25 Tetrataxis conica EHREr~ERG.Shimisu Island. Fusulinid pack-/wackestone facies. Shimisu Island. Nd 44. x 50 Palaeotextularia sumatraensis LANGE.Fusulinid pack-/wackestone facies. Shimisu Island. Nd 44. x 50 Climacammina cf. valvulinoides L~'~CE. Shimisu Island. Nd 42. x 25 Deckerella sp. Shimisu Island. Nd 43. x 31 Endothyra or Neoendothyra sp. Middle Carboniferous. Paglubagan Island. Nd 66. x 62 Pseudolangella sp. Minilog Island. Nd 7. x 30 Tuberitina sp. 'Middle Carboniferous'. Paglubagan Island. Nd 66. x 50 Paraglobovalvulina mira RErrL~GER. Grainstone. Cadlao Island. Oncoid-gastropod-peloid facies. Nd 22b. x 25 "Pseudoentothyra "sp. Shimisu Island. Nd 45. x 50 Lasiodiscus sp. Minilog Island. Dasycladacean packstone facies. Nd 9. x 12.5 Compacted staffellid foraminifera and gymnocodiacean alga (Permocalculus sp.). Minilog Island. Nd 72. x 25 Agathammina sp. and algal fragment. Minilog Island. Nd 72. x 25
Plate
8
49
50
Fig. 5. Field sketch of alatoconchid bivalves. Shell thickness appears exaggerated due to cutting effect. The large valves are very flattend along the dorsal-ventral axis, exhibit wing-like flanges and have a sharp crest on the dorsal surface at the anterior end. These criteria reminds on Saikraconcha (Saikraconcha) tuniensisYANCEY & Bo~z White: recrystallized calcitic shell; black: wackestone infilling of the shell interior. Length of specimens 20 cm. lengths. Most 'plates' are alatoconchid bivalves. Alatoconchidae are characterized by unusually large flattend shells and wide, alate wing-like extensions of the valves (RuN~NEGAR& GOBBETT1975, YANCEY• BOYD 1983). The shell walls exhibit a thinner dark gray outer part and a thicker white inner part. Associated with the bivalve shells are phylloid algae and diverse mollusk fragments. Some shells represent richthofeniid brachiopods (Pl. 6/4) as proved by the shape of the valves and the internal structure ( Nd 68 and 69, Matinloc lsland; P1.6/4, 9/7). A richthofeniid nature is also likely in other places as indicated by the often cylindrical cross sections of the shells. The biostromal facies was found at April Beach south of El Nido, on Shimisu Island, on southern Matinloc Island, on southeastern Entalola Island, on the mainland west of Cudugman Point and on eastern Binagboyotan Island. Only on southeastern Matinloc Island and on Shimisu Island, there is evidence of richthofeniids closely associated with alatoconchid bivalve shells.
Plate Fig. 1. Fig. Fig. Fig. Fig. Fig. Fig.
2. 3. 4. 5. 6. 7.
Fig. 8. Fig. 9.
9
Interpretation: Two subfacies can be differentiated. The typical biostromal facies (Subfacies 3a) is characterized by abtmdant thick bivalve shells occurring in association with brachiopods. Alatoconchid beds have been referred to as reefs (TERM1ERet al. 1973), but the shell form is poorly adapted to reef-top environments. The bivalves are believed to have been epifaunal, with the flat ventral shell surface oriented parallel to a loose sediment surface (KocHANSKVDEVIDE 1978, YANCEu& BOW 1983). The abundance of the shells in specific locations points to a gregarious life habit leading to the formation of laterally limited biostromal beds by baffling and trapping of fine-grained sediment. Imbrication structures (PI. 6/3; Fig. 4) and dense packing of the shells indicate a significant current activity. Good outcrops exhibit a prevailing current to the north. In many places, the biostromal facies exhibits a distinct vertical sequence (Fig. 4) characterized by foraminiferal floatstones (MF P 1) overlain by the biostromal facies s.s. with large shells and some phylloid algae. The capping facies is usually a dasycladacean wacke-/packstone, but sometimes also a crinoid-rich bioelastic wackestone. Subfacies 3b is a fine-grained phylloid algal bindstone, occurring often associated with Subfacies 3a, but also separately. It contains high amounts of bitumen and exhibits a high microporosity. The phylloid algae are associated with shell fragments (bivalves, brachiopods, trilobites). The trilobites possibly indicate a slightly deeper water depositional environment (upper slope ?). MF P 4: Oncoid-gastropod-peloid facies (P1. 10/7-9) Description: This facies was encountered predominantly in northwestern Matinloc and northwestern Tapiutan. It is characterized by the abundance of gastropods and a predominantly sparitic matrix. Well-exposed facies successions indicate shallowing-upward cycles starting with oncoid grainstones containing abundant gastropods and bivalve (?) shells at the base, grading to gastropod-peloid packstones and peloidal grainstones. MF P 4 is the only facies type exhibiting synsedimentm3r dolomitization, most commonly associated with the gastropod-peloid Subfacies 4b. Dolomitization increases with increasing abundance of peloids. This points to a
Algae and other fossils of the Middle Permian Minilog Formation. Bacuit Bay (El Nido), North Palawan, Philippines Dasycladacean algae (Macroporella apachena JOHNSONand Mizzia sp.). Packstone. Algal thalli are strongly deformed. MF P 2a. Minilog Island. Nd 8. x 25 Pseudovermiporella nipponica (ENDO). Shimisu Island. Nd 44. x 50 Strongly deformed phylloid alga (Anchicodium sp.). Matinloc Island. Nd 59. x 12.5 Recrystallized algal blade, encrusted by brachiopod shell. Shimisu Island. Nd 44. x 12.5 Bivalve shell and compacted neoschwagerinid fusulinids. Matinloc Island. Nd 55. x 25 Dasycladacean calcispheres in foraminiferal-algal wackestones. Shimisu Island. Nd 45. x 100 Brachiopod shell. The vesicular structure repesents a peripheral section through the body chamber and proves an assignment to richthofeniids. Alatoconchid bivalve/richthofeniid facies, MF P 3. Shimisu Island. Nd 44. x 20 Ostracods (arrows) in strongly recrystallized gastropod-ostracod wackestone. Matinloc Island. Nd 59. x 25 Rugose colonial coral: Waagenophyllum sp. Note fracturing and shearing. Lagen Island. Nd 101. x 4
Plate
9
51
52
Algae
cf.Archaeofthophyllum sp. Permocalculus sp. Mizzia velebitana SCHUBERT Macroporella apachena JOHNSON Pseudovermiporella nipponica (ENDo) Anchicodium sp. Shamovella sp.
Samples Nd 44 Nd 8, 72 Nd 6, 8, 9, 44, 69, 75 NO 8 Nd 9, 38, 44, 75 Nd 59 Nd 22b, 66
Figure PI. 8/12 PI. 9/1 PL. 9/1 PI. 9/2 PI. 9/3 PI. 10/9
Table 2. Calcareous algae and Problematica in the Minilog Formation of Bacuit Bay. Smaller Foraminifera Agathammina sp. Cribrogenerina sp. Climacammina cf. valvulinoides LANGE Dagmarita sp. Deckerella sp. Endothyra or Neoendothyra sp. Hemigordius sp. Lasiodiscus sp. Lunacammina sp. Pachyphloia sp. Palaeotextularia sumatraensis LANGE Paraglobivalvulina mira RE]TLINGER Pseudoendothyra sp. Pseudolangella sp. Robuloides lens REICHEL Tetrataxis sp. Tetrataxis conica EHRENBERG Tuberitina sp.
Sample Figure Nd 9, 72, 86 PI. 8/13 Nd 100 Nd 42, 44, 100, 112 PI. 8/4 Nd 44 Nd 43, 67 PI. 8/5 Nd 66, 86, 97 PI. 8/6 Nd 9 Nd 9 PI. 8/11 Nd 100 Nd 6, 7 Nd 44 PI. 8/3 Nd 22b PI. 8/9 Nd 45 PI. 8/10 Nd 6, 7 PI. 8,7 Nd 86 Nd 43 PI. 8/1 Nd 44 PI. 8/2 Nd 66, 97 PI. 8/8
Table 3. Characteristic smaller foraminifera in the Minilog Formation of Bacuit Bay. synsedimentary dolomitization in a sabkba environment. Some dolomitization, however, is related to faulting and probably late diagenetic. Interpretation: Differences in the depositional environments are indicated by two subfacies types. Subfacies 4a (P1. 10/7), found in northwestern Matinloc, is characterized by Plate Fig. 1. Fig. 2. Fig. 3. Fig. 4. Fig. 5. Fig. 6.
Fig. 7.
Fig. 8. Fig. 9. Fig. 10.
10
large oncoids associated with foraminifera, shells, phylloid algae and abundant gastropods resting in a sparitic matrix. The oncoids are of the 'Osagia' type and were formed around shell tYagments and gastropods. A rugose coral fragment was found encrusted by microbial layers. This facies corresponds to Standard Microfacies 13 (WmsoN 1975) and to the Osagia-oncoid community described by FLiP,EL (1977). It represents the most shallow and agitated environment in the E1 Nido area, but was formed within a restricted, lagoonal environment as indicated by low diversity and the dominance of gastropods. Subfacies 4b (P1.10/8) is characterized by the strong dominance of gastropods. Ostracods and peloids are common. The texture ranges from wackestone to grainstone. The presence of micrite and a local thickening of the limestone beds suggest that the gastropods were bio-accumulated and affected by winnowing. MF P 5: Fine-grained cortoid grainstone facies (P1. 10/9) Description and interpretation: This type was only encountered in one locality (Nd 22, southwestern Cadlao Island). It is characterized by abundant cortoids and peloids associated with
miliolid foraminifera, gastropod fragments and rare Shamovella (formerly Tubiphytes). Texture and low diversity indicate a lagoonal, moderately agitated envirormaent. MF P 6: Mudstone facies (PI. 10/10) Description and interpretation: Mudstones were encoun-
Microfacies types of the limestones of the Middle Permian Minilog Formation. Bacuit Bay (El Nido), North Palawan (Philippines) MF P 1: Fusulinid wackestone, the most widespread facies type in the studied area. Neoschwagerinids (bottom), ParafusuIina (top) and palaeotextulariids within a pelmicritic matrix. Shimisu Island. Nd 42. x 12.5 MF P 2a: Dasycladacean wacke-/packstone, strongly dominated by Mizzia. Minilog Island. Nd 8. x 12.5 MF P 3: Alatoconchid bivalve facies. Some shells exhibit irregular laminated microstructures structures known from thick-shelled bivalves. Shimisu Island. Nd 44. x 12.5 MF P 3: Packed shell bed. The parallel arrangement of the shells and the absence of encrustations indicate reworking by currents. Lagen Island. Nd 108. x 12.5 MF P 3: Packed shell bed formed by bivalves. Lagen Island. Nd 108. x 12.5 MF P 3: Alatoconchid bivalve facies. Tip of a thick brachiopod valve in fusulinid wackestone. Note the distinct difference in microfacies left and right of the shell caused by the strong deformation of the limestone. Matinloc Island. Nd 55. x 12.5 MF P 4a: Oncoid grainstone facies. The microfacies is characterized by strong biogenic encrustations of bivalve shells, gastropods and chaetetid sponges, resulting in the formation of disc-shaped cyanobacterial oncoids. Matinloc Island. Nd 58. x 16 MF P 4b: Gastropod facies, characterized by hydrodynamic accumulations of gastropod shells. Matinloc Island. Nd 59. x 12.5 MF P 5: Fine-grained cortoid grainstone facies. The dominating constituents are smaller foraminifera and small coated grains associated with rare Shamovella (left). Cadlao Island. Nd 22. x 12.5 MF P 6: Mudstone facies. Deeper marine mudstone with radiolarians. Arrow points to a possible Albaillellaria. Cadlao Island.Nd 24. x 50
Plate
lO
53
54
tered in different places, but only in southern Cadlao Island and northern Tapiutan Island, facies diagnostic fossils were found. The Cadlao mudstones (Nd 24) are directly overlying a sedimentary melange (shales and cherts) of the Bacuit Formation, pointing to a possible shallowing-upward sequence and lateral facies transition from MF P 6 to shales of the Bacuit Formation. The Tapiutan mudstones (Nd 87) were only found as clasts within a sparite-cemented breccia. Filaments, sponge spicules and radiolarians are the only biogenic constituents indicating a deeper marine depositional environment. The presence of possible Albaillellaria may point to a real deep-water environment with water depths of more than 200 m (HokDWORTH 1966). 3.4.3.5 Paleontological criteria Algae are very abundant in MF P 2, but the diversity is usually low (Tab. 2). The association is dominated by dasycladaceans. Mizzia velebitana (ScmmERT) is the most common species (P1.9/1), followed by Pseudovermiporella nipponica (ENDo) - P1. 9/2. Other algae are rare. Foraminifers are most abundant in the Permian limestones of the El Nido area. Fusulinids are the most prominent group (P1. 7), but smaller foraminifera (P1. 8) are also common. Table 3 provides a list of the taxa encountered. Smaller foraminifera occur in all shallow-marine facies types but are more abundant in MF P 1 and in MF P 4 than in other facies types. Radiolarians occur together with filaments and sponge spicules and were only found in two localities (Nd 24, 87). Owing to the strong calcification no radiolarians could be extracted from the limestones. Rugose corals were found in two localities. Coral fragments occur in the oncoid facies MF P 4a of northern
Plate
Fig. 1 Fig. 2.
Fig. 3.
Fig. 4. Fig. 5. Fig. 6. Fig. 7.
Fig. 8.
11
Matinloc Island, and small colonies of waagenophyllid corals on northern Lagen Island. The colonies (P1.9/9) can be assigned to Waagenophyllum sensu stricto (pers. comm. H.W. Fltigel 1998). Brachiopods are very common in thin sections. Most of the brachiopods found in the field belong to the Strophomenida; whole specimens of productid brachiopods were discovered on Shimisu Island. Of particular importance is the discovery of abundant richthofeniids (P1.6/4, 9/7) on southeastern Matinloc Island and on Shimisu Island in association with alatoconchid bivalves. Trilobites were only identified in thin sections. They are only common in bituminous limestones rich in fine shell debris and possible phylloid algae. 3.4.3.6 Facies interpretation of the Minilog Formation The ~adual changes in water depths reflected by the microfacies types point to the deposition of the sediments of the Minilog Formation within a carbonate ramp system. B athymetry ranges from sabkha to bathyal (probably > 200 m) without any indication of a prominent shelf break. The strong prevalence of inner to mid-ramp environments indicates a gently dipping but distally steepened ramp. The algal facies (MF P 2) and the oncoid-gastropod-peloid facies (MF P 4) are assigned to inner ramp environments. MF P 4b represents the most shallow and restricted environment. The dasycladacean limestones (MF P 2) originated slightly more offshore. The transition towards MF P 1 (fusulinid limestones) indicates that MF P 2 and MF P 1 were laterally linked. However, although MF P 1 appears to have partly formed in an agitated environment (MF lb), the majority of the fusulinid limestones (MF P 1a) probably originated from below fair-weather wave base. Hence MF P 1 can not be
Microfacies Tr 1 (reef facies) of the Upper Triassic (Rhaetian) limestones of the Coron Formation. Malajon Island, northwestern Busuanga area, North Palawan (Philippines) MF Tr 1a: Solenoporacean algal boundstone. The dome-shaped thalli of the alga exhibit discontinuous growth as shown by irregularly shaped micritic zones (arrows). SE Malajon island. Bs 18. x 1.25 MF Tr 1b: Solenoporacean-coralline sponge boundstone characterized by close intergrowth of red algae and sponges. Depending on the original skeletal mineralogy, solenoporaceans (aragonite) are poorly and sponges (probably Mg-calcite) are well preserved. NE Malajon Island. Bs 20. x 1.25 MF Tr 1c: Coralline sponge-coral boundstone. The framework consists of sponges (predominantly inozoans), encrusted by foraminifers (arrows), in association with corals. The rock is strongly brecciated. Northeastern Malajon Island. Bs 20. x 7.5 MF Tr I c. Coralline sponge-coral boundstone. Cryptic niches with Baccanella sp. These microbial structures are common features in protected shadowed parts of Triassic reefs. SE Malajon Island. Bs 17 B. x 16 MF Tr l c: Coralline-sponge-coral boundstone. Cross section of Retiophyllia sp. Fasciculate corals can be recognized in the field, but records are rare in thin sections. NE Malajon Island. Bs 21. x 10 MF Tr lc: Coralline sponge-coral boundstone. Chaetetid sponge (base) intergrown with inozoid sponge. NE Malajon Island. Bs 21. x 10 Gosaukammerella sp., a strophomenid brachiopod, attached to a coralline sponge. The tubular 'spines' of the pedicle valve are anchored within the meshes of an inozoid sponge. The fossil is widely distributed in crypt habitats of Upper Triassic reefs of the Western Tethys but has not been detected until now in records of East Tethyan and Panthalassan reefs. E Malajon Island. MF Tr la. Bs 19. x 32 Gosaukammerella sp. The brachiopod is characterized by a convex pedicle valve fixed on a sponge by symmetrically re'ranged tubular outgrowth structures ('spines') of the foliated lamellose ventral valve. E Malajon Island. Bs 19. x 50
Plate
11
55
56
assigned to a particular setting on the carbonate ramp but covered large areas within an inner to mid-ramp envh'onment. By contrast, the alatoconchid bivalve/richthofeniid biostrome facies (MF P 3) was deposited in a temporarely agitated environment as indicated by imbrication textures and worn shells. The bathymetric sequence of microfacies types can be summarized from shallow to deep as follows: MF P 4b (gastropod-ostracode wackestone) - > MF P 6 (cortoid grainstone) - > MF P 4a (oncoid-gastropod-peloid wackestone) - > MF P 2b (dasycladacean wackestone) - > MF P 2a (algal-foraminiferal wackestone) - > MF P lb (foraminiferal wackestone) - > MF P 3a (alatoconchid bivalve/richthofeniid biostromal facies) - > MF P 3b - > MF P la (fusulinid wacke-/packstone) - > MF P 5 (radiolarian mudstone). 3.4.4 Liminangcong Formation 3.4.4.1 Lithology and stratigraphy Cherts are found below as well as above the Minilog Formation, but only in the overlying sequence they reach an extensive thickness. There is a conformable contact of the Liminangcong Fonaaation with the older Minolog Formation. The contact is marked by a thick transitional sequence. It appears that the carbonate ramp drowned through an increase in plankton productivity, which in turn was related to an increased input of nutrients into the sea water. By that, the algal-controlled carbonate production (calcareous algae, symbionts in fusulinids) was not capable to keep up with relative sea level rise and the ramp drowned. The cherts exhibit quite different facies in the E1 Nido area, but all cherts contain radiolarians. There are black, green, red and white cherts. For the red and white cherts oxidizing conditions are probable, whereas a reducing environment is assumed for the black and green cherts. The beginning of the chert sedimentation has been dated as Late (today corresponding to Middle)Permian by CrnZNG (1989). Cherts are known to continue up to the Middle Triassic in the Bacuit Bay area (HAsntMOTO& SA'rO 1973). 3.4.4.2 Diagenesis of manganese-rich cherts Near Pangawan Point and Cudugman Point on the mainland (Fig. 3), in other parts of Busuanga Island as well as in Plate Fig. 1. Fig. 2. Fig. 3. Fig. 4. Fig. 5 Fig. 6. Fig. 7.
12
other Calamian Group Islands, stratiform manganese deposits associated with thecherts were found (CRuz 1947, FONTAINE 1979). Their origin was attributed to submarine volcanic activity but this interpretation has been questioned (GERVAOO & FERNANDEZ1967). Study of chert thin sections resulted in the recognition of the following diagenetic and tectonic events: - 'Normal' alteration of siliceous ooze to microcrystalline quartz - Small vertical straight fractures and lining with manganese ore or quartz. Some of the pore space created by the fracture event is still open - Large oblique and curved fractures. Cementation of open fractures with quartz. Filling of the remaining pore space with ore - Very thin straight conjugate fractures (oblique), all fined with manganese ore - Wide open fractures, marginally lined with ore and cemented with quartz. Remaining pore space is sometimes still left in the center; secondary pore space is created by weathering or remobilization of the ore. Therefore, it can be concluded, that ore formation originated quite early, but remobilization of the ore was common and associated with almost every tectonic event. 3.5 Notes on the Late Paleozoic Outcrops in the E! Nido Area
The observations made on the various islands and the mainland of the El Nido area are summarized below. For the locations see Fig. 3. M i n i l o g Island
Limestone exposures were studied in the north, east and south of Minilog Island. 20-50 cm bedded, rarely massive dark gray limestones predominate everywhere. The northern tip of Minilog Island consists of miliolid foraminiferalcalcisphere wackestone representing MF P 2 b (sample Nd 1). The limestones in the northern part of the east coast yield smaller foraminifera and echinoderms (Nd 4). To the south (west of a large tourist resort) the limestones are predominantly composed ofdasycladacean wacke- and packstones (Nd 6, 8, 9) with a variable content of smaller foraminifera including miliolids and fusulinids. Recrystal-
Microfacies Tr 2 (reworked reef and platform material) of Upper Triassic limestones of the Coron Formation. Malajon Island, northwestern Busuanga area, North Palawan (Philippines). Polymict floatstone consisting of reworked fossils (corals, shells, sponges) and microfacially different rounded and angular clasts. Eastern Malajon Island. 13. x 7.5 Cross section of a coral (Stylophyllopsis sp.). x 10 Uvanella ? (Sphinctozoid sponge) sp. Bs 13. x 8 Thrombolitic bindstone clast (bottom left), rounded coral fragment (right), and bored bivalve shell (center). Bs 13. x 1.25 Detail of thrombolitic growth fabric. Note the white cement rims around the microbial peloids and micritic growth boundaries.. Bs 13. x 1.25 Grainstone clast. Dominant grains are cortoids. Duostominid foraminifers are rare. Bs 13. x 1.6 Detail of the grainstone fabric. Recrystallized, peripherally micritized grains and duostominid foraminifer. Bs 13. x 32
Plate
12
57
58
lized dolomites are also present showing traces of fusulinids (Nd 5). Wackestones with smaller foraminifera are sometimes intercalated in the algal limestones (Nd 7). Macrofossils are represented by large bellerophontid gastropods and brachiopods. In southern Minilog Island (Dalabakan Beach), wackestones with poorly preserved fusulinids occur; the limestones are strongly fractured and brecciated (Nd 10).
Binagboyotan Island The outcrops studied in the southern part of the island exhibit exclusively calcite marbles intruded by abundant calcite veins. Recrystallized biostromal facies with a thickness of 20 and 50 cm was observed in two horizons. Cadlao Island Cadlao is the largest island in the E1Nido area. It contains large outcrops of the Bacuit Formation and the thickest exposures of the Minilog Formation. At southern Cadlao an interesting section has been observed: The top of the Bacuit Formation is represented by black siliceous shales with sandstone and chert clasts. The largest clast is an approximately 6 x 6 m folded chert block. The chert (radiolarite) is thin-bedded (0.5 to 4 cm) and exhibits typical pinch and swell structures. The Bacuit Formation is overlain by light gray micritic limestones with sponge spicules and radiolarians (MF P 5; P1. 10/10). The limestones are comonly silicified. The mudstones are succeeded by darker foraminiferal wackestones and finally foraminiferal-cortoid grainstones. In the southeast of Cadlao, another contact between the Bacuit and the Minilog Formations is exposed at Honda Bay. The uppermost Bacuit Formation consists of black siliceous shales with chert and sandstone blocks and N-S trending coarse-grained sandstone beds with up to 25 % feldspar. Fine plant debris is abundant in siltstones (Nd 109). The contact with the overlying limestones is a tectonic one. The micritic nature of the basal limestones and their content of replacement cherts suggest a deeper marine depositional environment of the lowermost beds of the Minilog Formation. The east coast of Cadlao is mainly composed of medium-
Plate Fig. 1.
Fig. 2. Fig. Fig. Fig. Fig. Fig.
3. 4. 5. 6. 7.
Fig. 8.
13
bedded (8-35 cm) recrystallized limestones with some poorly preserved brachiopods. The underlying Bacuit elastics are massive to thick-bedded sandstones with a thickness of 80 m. Shale-silt layers occur occasionally between the sandstone beds. The sandstones are litharenites with up to 60 % of lithic grains (Nd 48). The contact to the overlying limestones is tectonically overprinted. The basal limestones of the Minilog Formations are light gray recrystallized mudstones. Sandstone-shale alternations at the north coast of Cadlao provide the only firm evidence for turbiditic sedimentation in the tightly folded Bacuit Formation. B to E members of the Bouma-sequence can be observed (PI. 6/5).
Dilumaead Island (Helicopter Island) The Bacuit Formation is widely exposed along the east coast of this island. All exposures are strongly fractured. Sandstone blocks, black pyritic cherts and silicified limestones float within a matrix of black siliceous shales with organic debris. Sandstones are fine- and coarse-grained feldspathic litharenites with some calcite content (Nd 14, 15). It appears, that coarse sandstones become increasingly abundant up-section. However, the scarcity of exposures make this statement equivocal. The estimated thickness of the Bacuit Formation is 100 m, with no base exposed. The contact with the overlying limestones is concordant at several places, but is always tectonically overprinted. Strongly sheared and brecciated limestones occur at the base of the limestone sequence. They often contain dolomitic clasts (Nd 19). Entalola (Inabalamaki) Island Comparatively well preserved facies was encountered at the west coast of this island. Large gastropods and green algae, brachiopods, foraminifera and echinoderm fragments rest in a dark wackestone matrix. Algal-foraminiferal wackestones with Pseudovermiporella are common (Nd 38). A small outcrop of the overlying (?) cherts is in tectonic contact with the limestones along a strike slip fault. The dark brecciated cherts most probably belong to the Liminancong
Microfacies Tr 3 (open marine lagoon) and Tr 4 (restricted lagoon) of Upper Triassic platform carbonates (Coron Formation). Kalampisanan Island, northwestern Busuanga area, North Palawan (Philippines). MF Tr 3: Oncoid floatstone, characterized by porostromate oncoids, coated grains, grapestones and peloids, floating in a micritic and partly winnowed (grainstone) matrix. Elet Island, Kalampisanan Islands, northwestern Busuanga. Bs 30. x 1.25 MF Tr 3: Aulotortus sinuosus WEYNSCHENK.Age-diagnostic foraminifer (Late Norian and Rhaetian). Bs 30. x 64 MF Tr 3: Porostromate oncoid composed of Garwoodia. Bs 30. x 50 MF Tr 3: Porostromate oncoid composed of Rivularia and sessile foraminifera. Bs 30. x 40 MF Tr 3: Gymnocodiacean or dasycladacean alga. Bs 30. x 16 MF Tr 3: Grainstone matrix with micritized grapestone intraclasts and few foraminifers. Bs 30. x 25 MF Tr 4: Fine-grained algal filament grainstone. Most of the peloid-like grains are disintegrated algal/ microbial fragments. Additionally variously sized oncoids occur. Note the irregular fenestral texture. Kalampisanan Islands. Bs 31. x 2.5 MF Tr 4: Broken and mititized algal filaments resembling 'Tubiphytes' gracilis SCH~,FER• SENOWBARIDARYAN. Bs 31. X 32
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60 Formation. Thin-bedded biostromal limestones andfusulinid wacke-/packstones occur at the east coast (Nd 67). The rocks of the biostromal facies exhibit up to 6 cm long and 0.5 cm thick calcitic shells arranged parallel to bedding.
wackestones with some foraminifera are present. Biostromal facies with thick shells, fusulinids, smaller foraminifera and brachiopods occur at Seven Commando Beach (Nd 110, Nd 111).
Goitongoan Island (Turtle Island) The limestones exposed on this island are completely recrystallized and best described as brecciated marble. Only in one of the four samples studied (Nd 34-37b) a few smaller foraminifera occur.
Mainland west of Cudugman Point Immediately west of Cudugman Point dasycladacean packstones with smaller foraminifera and large silicified bellerophontid gastropods are common (Nd 75). These limestones overlie a 0.5 m thick biostromal brachiopod facies. A maior shear zone is developed 300 m west of Cudugman Point, separating the limestones of the Minilog Formation from cherts of the Liminangcong Formation. Close to the shear zone red silicified limestones are common (Nd 76). The che~ts are unconformably underlain by recrystallized wacke- and packstones. Farther to the west a gradual transition from pure limestones to pure white cherts of the Liminangcong Formation is exposed. The cherts of the basal Liminiangcong Formation represent silicified limestones (Nd 80). To the south and west of Pangawan Point, however, actual radiolarites predominate. These are greenish gray and yellow (Nd 90, 93), rarely black (Nd 94) and bear significant stratiform Fe-Mn ore deposits (Nd 91, 92).
Inamogol Island Exposures were only studied along the west coast of the island. Recrystallized light gray limestones predominate. One sample yields poorly preserved fusulinids (Nd 82). Rare gastropods and crinoid fragments could be observed in the field. Lagen Island A major SE-trending shear zone is developed in the northwest of this island. All limestones axe completely recrystallized, often silicified and dolomitized. Several moderately preserved microfacies types could be recognized along the north coast: Fusulinid wackestones with Verbeekina (Nd 98, 100, 102) underlie the biostromal facies. Additionally, the unique occurrence of colonial rugose corals (Waagenophyllum) was noted (Nd 101 ), which is associated with strongly bituminous foraminiferal-algal wackestones (Nd 99). Poorly preserved fusulinid mudstones and silicified gastropod-crinoid limestones occur at the east coast of the island. In a bay of southern Lagen Island dark gray to black bituminous biostromal facies was encountered. The 'calcitic plates' are densely packed (Nd 105, 107, 108). Poorly preserved fusulinid mudstones are associated with this facies. Mainland near E! Nido village The limestones immediately south of El Nido village are strongly sheared throughout their thickness. Mudstones and
Plate
Fig. 1. Fig. 2.
Fig. 3.
Fig. 4. Fig. 5. Fig. 6.
14
Malpaeao Island Near the northwestern tip of the island a 80 cm thick biostromal horizon of calcitic shells and a thick sequence of fusulinid wackestones (Nd 112) was found. Recrystallized limestones predominate along the west coast of Malpacao Island. Matinloe Island Near Nicolasa Neck a variety of facies types occur. Bivalve floatstones, dasycladacean wackestones with abundant thalli ofMizzia, neoschwagerinid packstones and foraminiferal wackestones are present at the southern end of Nicolasa Neck (Nd 54-57). To the north of Nicolasa Neck, immediately south of a small chapel, a sequence of oncoid grainstones, gastropod-ostracod wackestones and dolomites was observed. A sequence of thick-bedded dolomites with some dedolomites was found south of Nicolasa Neck along
Microfacies Tr 5, Tr 6 (inner platform), and Tr 7a, Tr 7b (restricted lagoon) of Upper Triassic platform carbonates (Coron Formation). Northwestern Busuanga (Figs. 1-2) and southern Busuanga (Figs. 3-6), North Palawan (Philippines). MF Tr 5: Intraclastic packstone with strongly recrystallized grains (foraminifera, grapestones) and large micritic fecal pellets. Kalampisanan Islands. Northwestern Busuanga mainland. Bs 32. x 17 MF Tr 6: Foraminiferal packstone consisting of densely packed tests of strongly recrystallized foraminifers and few gastropods. The fimestone is strongly tectonized. Note the abundmlt calcite-filled cracks. Kalampisanan Islands. Northwestern Busuanga mainland. Bs 34. x 19 MF Tr 6: Involutinid foraminiferal wackestone. The microfacies is characterized by variously sized foraminifera floating in a pelmicritic matrix. Note the destruction of fossils by sheming. Southern coast SE Concepcion. Bs 26. x 2.7 MF Tr 7b: Ostracod wackestone. Note the geopetal infilling of the shells with 'vadose crystal silt'. Hills NE Coron Town. Bs 43. x 13 MF Tr 6: Triasina hantkeni MAJZON. Southern coast. Bs 26. x 21 MF Tr 7a: M udstone. Euhedral dolomite crystals within the microsparitic matrix occur close to fractures and stylolites. Hills NE Coron Town. Bs 45. x 43
Plate
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62
the east coast of Matinloc Island (Nd 64, 73, 74). Occasionally, some bioclastic wackestones with dasycladacean algae, brachiopods and ostracods occur. Alatoconchid bivalve/richthofeniid biostromes: The best preserved Permian facies successions of the El Nido area were observed in southern Matinloc Island. Biostromes (MF P 3) are common. Some of the he shells at this locality can be firmely assigned to richthofeniid brachiopods (PI. 6/4). The biostromes occur in two different facies associations: 1. Algal-foraminiferal wacke-/packstones (Nd 72) - biostromal facies - algal wackestones, 2. Foraminiferal wackestones, packstones and rarely gainstones (Nd 71) - biostromal facies (Nd 68, 69) - foraminiferal-crinoid wackestones. Both sequences agree to the pattern described by FLAJS& H0SSr,mR (1999) from Late Permian richthofeniid buildups of Chios Island, Greece. Highly porous and bituminous wackestone lenses with trilobites occasionally appear in foraminiferal packstones (Nd 70). Bellerophontid gastropods are common above the biostromal successions.
Paglugaban Island A breccious dolomitic limestone with up to 3.5 cm large recrystallized clasts is exposed in the central part of the island (Nd 65). Up to 30 cm thick cherty layers occur parallel to bedding but appear to be linked to flatense shear fractures. The dolomitic sequence is at least 20 m thick. It is overlain by crinoidal limestones followed by fustdinid wackestones (Nd 66) of Moscovian-Kasimovian age. Some 20 m up section another breccia horizon is exposed exhibiting light and dark limestone clasts with in stylolitic contacts (stylobreccia). The only recognizable fossils are disarticulated crinoid columnals and brachiopods. According to SOECm1NC~ (in KmSSLfNG& SOECHTtNC1995), a large sinistral strike slip fault separates Paglugaban from Shimisu Island.
Plate Fig. 1.
Fig. Fig. Fig. Fig.
2. 3. 4. 5.
Fig. 6. Fig. 7.
Fig. 8. Fig. 9.
15
Shimisu (= Binanlaogan) Island In some places the east coast of the island displays well preserved facies and fossils, Abundant fusulinids, productid brachiopods, gastropods, and thick calcitic shells float within a micritic matrix. The fossils are rarely fragmented. Bedding is nearly vertical and striking north-south. The limestones are predominantly fusulinid wacke-/packstones with calcareous algae, calcispheres, smaller foraminffers, and thick shells of unknown affinity (Nd 42-44). The shells occasionally form biostromal beds (MF P 3a). Three shell-rich horizons can be traced. Near the northern tip of Shimisu Island fusulinid wackestones with Verbeekina verbeeki (GEtyiTz)were encountered (Nd 45, 46).
Tapiutan Island Recrystallized wackestones with some fusulinids and dasycladacean algae and large crinoid stems (lengths up to 4 cm) occur in the southeastern part of the island. At one locality dark pebbles were observed floating in a light gray wackestone matrix (Nd 52). Near the northernmost tip of Tapiutan Island (Binangculan Bay) restricted lagoonal facies predominates comprising gastropod floatstones (Nd 83), algal wackestones (Nd 88) and rare fusulinid wackestones. Dasycladacean algae appear to be well preserved on weathered surfaces, but are poorly recorded in thin sections. Richthofeniid brachiopods occur in loose boulders.
3.6 Biogeographie and Paleogeographic Constraints 3.6.1
Carboniferous
The only report of suspected Carboniferous fossils in the Philippines is from southwestern Mindoro (EAs'roN & MELENDRES 1964) with reworked corals in Pliocene conglomerates. On Palawan, the only sedimentary rocks with a
Microfacies Tr 8 and Tr 9 (inner platform) and Tr l0 (oolite shoal ?) of Upper Triassic platform carbonates (Coron Formation). Coron Island, Southern Busuanga, North Palawan (Philippines). MF Tr 8a: Poorly sorted involutinid foraminiferal wacke-/packstone. Foraminifers are strongly recrystallized. Distinct differences in the size and outline of the tests point to a taxonomically diverse assemblage. Rare fossils are gastropods (center top). The matrix is a fine-grained peloidal packstone. N Coron Island. Bs 52. x 1.25 MF Tr 8a: Aulotorms cf. tenuis (KRISTAN-TOLLMANN).NW Coron Island Bs 49. x 32 MF Tr 8a: Aulotortus cf. communis (KRISTAN).NW Coron Island. Bs 49. x 20 M f T r 8a: Triasina sp. N Coron Island. N Coron island. Bs 55. x 12.5 MF Tr 8a: Additional rare elements in this microfacies are fra~nents of dasycladacean algae (Macroporella). N Coron Island.Bs 55. x 12 MF Tr 8a: Burrowed foraminiferal packstone. Note the differences in size, morphology and preservation of foraminiferal tests and the association with thin pelecypod valves. N Coron Island. Bs 52, x 8 MF Tr 8b: Colonial corals are very rare in the foraminiferal wackestones. The coral most probably represent Parastraeomolpha RONtEWlCZ,a genus known until now only from the Northern Alps. NW Coron Island. Bs 50. x 5 MFTr 9: Fine-grained bioclastic packstone with dasycladacean and shell debris. NW Coron Island Bs 51. x 10 MF Tr 10: Oolitic grainstone. The tangentially structured ooids are strongly micritized. Note deformed ooids (center left). N Coron Island. Bs 54. x 32
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supposedly Permo-Carboniferous age are the Barton Metamorphics, described as a moderately metamorphosed clastic sequence with thin limestones lenses (HAsHIMOTO 1981). The dating of this sequence is, however, only based on the supposed stratigraphic relation to the overlying (?) Bacuit Formation; no fossils were found so far. The occurrence of possibly autochthonous Carboniferous limestones is thus unique in the Philippines. The closest well-dated exposures of Middle and Late Carboniferous limestones are known from Thailand (IGo 1972, FONTAfNEet al. 1982, UENO et al. 1994, 1995, 1996, Fontaine 1995), eastern Peninsula Malaysia, southwestern Kampuchea and northwestern Sarawak (FoN'rAtNE et al. 1990, UENO 1999). Similar to Palawan, records of the latest Carboniferous and Early Permian are rare in northern Thailand. 3.6.2 Permian Although Middle Permian limestones are very widespread in South East Asia (FONTAINE1986), Permian fossils have first been described from the Philippines only some 35 years ago (ANDAL 1966). Fusulinids and algae were reported from Permian limestone pebbles in a Jurassic conglomerate on Mindoro (ENDo 1968, KOmE et al. 1968, HANZAWA & HASH1MOTO1970). Permian foraminifera are also known from Carabao Island north of Panay (FoNTA1NE et al. 1983) and a small group of islands northeast of Busuanga (FONTAINEet al. in FONTAINE1986). However, the outcrops in Bacuit Bay form by far the largest continuous exposure of Permian limestones in the Philippines. The Permian carbonates in Bacuit Bay are of typical Tethyan type. Similar carbonate facies and fusulinid assemblages are known from the Mediterranean region to China and Southeast Asia. The neoschwagerinid-verbeekinid association recognized in the Philippines characterizes a specific faunal province covering parts of Southeast Asia, southern China, Indochina and various parts of the Permian accretionary complex of southw'~stern Japan (KoBAYASHI
Plate Fig. 1. Fig. 2. Fig. 3.
Fig. 4. Fig. 5. Fig. 6.
16
1997a, 1997b; ZAw 2000). The large Tethyan province has been interpreted as result of a loss in provinciality during the Middle Permian (ARcrmOLO & SHI 1996). However, the fossils found in the Philippines provide a complicated picture in detail. Although taxonomically similar algae, foraminifera, gastropods, and corals are widespread in other areas of the Tethys, richthofeniid brachiopods have been rarely mentioned from South East Asia. According to the distributional maps by RUDWICK& COWEN(1967) and FLAJS & H0SSNER (1999), the closest localities with richthofeniid brachiopods are Timor and Thailand. No indications of mass concentrations of richthofeniids are known from Southeast Asia up to now, whereas R i c h t h o f e n i a reefs are well recorded from the Mediterranean Tethys (FLAJSet al. 1996a, b), and strophomenid brachiopod mounds occur in the Deleware Basin in USA (SENOWBAPd-DARY,~& RIGBY1996). The Alatoconchidae are a distinctive Permian group (Artinskian to Capitanian). Guadalupian (predominantly Midian) occurrences associated with neoschwagerinid assemblages are known from central Afghanistan (TER~,nERet al. 1973), Tunisia (BoYo & NEWEt~ 1976), Oman ( P ~ v u T 1993) and Croatia (KoCHANSKY-DEv1D~1978, 1987). Together with the fusulinacean family Verbeekinidae and the coral family Waagenophyllidae the Alatoconchidae define the Tethyan faunal province (YANCEY& BOVO 1983). The absence or scarcity of typical shallow-water Permian dwellers in the working area is additionally striking. Of particular interest is the complete absence ofcoralline sponges and the extreme rareness of S h a m o v e l l a - taxa which are common constituents of coeval shelf and reef carbonates in other parts of Asia. Current plate tectonic reconstructions place El Nido at around 6 ~ southern paleolatitude (Golonka, pers. comm. 1996), facing the open Panthalassa Ocean (Fig. 6). It is difficult to understand why this ideal position for modem reef growth did not lead to more pronounced reef growth in the Permian. Open ocean reefs are quite rare in the Middle and Late Permian and the few examples known (e.g. Japan:
Microfacies Tr 1 l, Tr 12 (deeper water environment)) and Tr 13 (slope environment ?) of Upper Triassic limestones on Coron Island, southern Busuanga, North Palawan (Philippines). MF Tr 11. Fine-grained, bun'owed peloidal packstone consisting of variously sized peloids and coated shell debris. NW Coron Island. Bs 53. x 40 MF Tr 12. Mudstone with calcitized radiolarians and sponge spicules. Note irregularly dispersed pyrite (black). N Coron Island. Bs 57. x 32 MF Tr 13. Polymict limestone breccia consisting of angular and rounded clasts exhibiting different microfacies (ooid-oncoid grainstone: center, calcite marble: top center, mudstones: dark gray) floating within a finely brecciated matrix. N Coron Island. Bs 56. x 8 MF Tr 13. Polymict breccia. Note coarse-grahled calcite marble (left) und the well-rounded limestone pebble (right). N Coron Island. Bs 56. x 10 MF Tr 13. Polymict breccia. Angular dolomite marble clast associated with oncoid grainstone pebbles. N Coron Island. Bs 56. x 7.5 MF Tr 13. Polymict breccia. Grainstone clast. Larger grains are micrite oncoids. Smaller grains are ooids. The dark color of the grains is accentuated by organic matter distributed within abundant lmcroborings in the oncoids. N Coron Island. Bs 56. x 7.5
Plate
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66
Fig. 6. Paleolatitudinal distribution of Middle and Late Permian reefs recorded from East Asia (map from Golonka, pers. comm. 1997). 1 - Mountains, 2 - Land, 3 - Shel f, 4 - Carbonate Platforms, 5 - Reefs of unknown thickness, 6 - Reefs less than 10 m thick, 7 - Reefs with a thickness between I0 ahd I00 m, 8 - Reefs more than 100 m thick. Note that only major carbonate platforms are indicated. East Thailand and Cambodia correspond to the Sibumasu Block, West Thailand to the Indochina Block. SANO& KANMERA1996) differ substantially in biotic composition from the typical Middle/Late Permian reefs in the Delaware Basin, South China and the Mediterranean Tethys. The East Asian 'reefs' facing the western margin of the Middle/Late Permian Panthalassa Ocean are coral reefs and biostromes in Japan (KAWAMURA& MACHIYAMA1995) and an algal-sponge reef in Sumatra (FoWrAINE 1982). Assuming that the surface water of western oceanic margins was similar depleted in nutrients in the Permian as today, the limited reef growth in this setting suggests that Permian reef builders were not as well adapted to oligotrophic conditions as modern coral-algal reefs. The strong concentration and great thickness of reefs in intracratonic basins, closely associated with landmasses, supports this view. hi agreement with WooD (1993), we therefore speculate that Middle
Permian reef growth had quite different ecological controls as compared to m o d e m coral-algal reefs. The absence or scarcity of typical Permian reef builders (coralline sponges, Shamovella, Archaeolithoporella) in the El Nido area may thus be explained by limited nutrient availability.
BUSUANGA AREA, CALAMIAN GROUP ISLANDS (LATE TRIASSIC) 4.1
Introduction
The Calamian Group Islands are the northern islands of the Province Patawan. The main island is Busuanga followed in size by Culion Island and Coron Island. Busuanga Island and the surrounding archipelago consist mainly of
67
Fig. 7. Simplified geological map of Busuanga Island and adjacent islands. Late Triassic reef limestones occur on Malajon Island. The other sampling sites of the Coron Formation exhibit various parts of inner and outer platform carbonates.
radiolarian cherts and isolated Triassic limestones (Fig. 7). The mainland of Busuanga is almost exclusively composcd ofcomplicately folded red radiolarites of the Limanangcong Formation. They have been dated as Early Permian to Late Jurassic by means of radiolarians (CHENr 1989, 1992; Yt~li 1990, KtESSUNG1996, YEH& CH~NCi1996). Chert deposition may have been continuous throughout the interval, although firm age assignments only exist for the Late Permian, Ladinian/Carnian to earliest Jurassic, late Early Jurassic to early Middle Jurassic and Kimmeridgian/early Tithonian. The wide age range of these cherts is in strong contrast to the previously published stratigraphic relationship of the sequence. The stratigraphic compilation of WOI.VAWrct al. (1986) for whole Palawan declared a simple stratigraphic sequence with the Middle Triassic Liminangcong Formation overlying the Permian to Early Triassic Minilog Formation and being itself overlain by the Late Triassic Coron Formation. Considering the new age data, the stratigraphic and sedimentological relationship has to be regarded as much more complex than previously believed (cf. Fig. 2). 4.2 Lithofacies and Tectonics of Cherts and Clastics
Due to a monotonous sequence a lithofacies differentiation is very limited on Busuanga. The cherts comprise four distinct lithologies: 1) dark red to violet, even and thin-
bcdded ribbon chcrts, 2) light green, uneven thin to thickbedded cherts, 3) light yellow, white and pink sandy, thickbedded to massive cherts, and 4) greenish gray, yellow and red chert breccias. Due to strong tectonics, the vertical sequcnce of these lithologies is difficult to understand. Additionally, the lithologies appear repeatedly in different horizons. Intercalations of tuffaceous shaly and sandy horizons could be more useful for lithostratigraphy. They were mapped by the Pililippine Bureau of Mines and Geo-Sciences (BGM 1984) as sandstone intercalations, sometimes with large areal exposures. However, from our field data there is no evidence for a thickness of more than 50 m and the lateral continuity never exceeds 201) m. The Liminangcong Formation is unconformably overlain by a tuffaceous shale, siltstone and sandstone sequence, named King Ranch Formation by the BGM. The King Ranch Formation (probably equivalent to the Guinlo Formation of IL~,SN1Mo'ro & SA~r~ 1973) is a deep marine turbiditic sequence. Radiolarian bearing cherts and siltstones are intercalated with sandstones rich in plant debris. Some coal layers are present. Although a Cretaceous age for the King Ranch Formation was suggested on the BGM map, no constrains on age are currently available. The radiolarian cherts are most intensely folded. The trend of major folds is NW-SE to NNW-SSE. Large anticlines follow this trend and built the characteristic morphol-
68
ogy of Busuanga Island. The strike of the fold axes is approximately perpendicular to the elongation of Palawan Island which is related to Tertiary tectonics. The Busuanga folds are, therefore associated with a pre-Tertiary NE-SW compression.
4.3 Limestone Outcrops on and around Busuanga (Coron Formation): Carbonate Platform and Reefs Limestone outcrops are very rare on Busuanga. Only in the southeast there are isolated limestone exposures in contact to underlying cherts. However, many limestone outcrops are to be found on islands and peninsulas surrounding Busuanga Island. Limestones were studied on the islands off Salvacci6n (NW Busuanga) and off Coron Town (Coron Island, S Busuanga). The limestones occur in tectonic contact with the cherts or in isolated outcrops. According to FON'r,'aNE(1979) all limestones are of Late Triassic, probably Rhaetian age. WOLFARTet al. (1986) defined the Coron Formation ('crystalline, reefal, oolitic or conglomeratic limestone either laterally interfingering with a shale-sandstone sequence or underlain by that sequence') using mostly the published data, and gave an age range from Early Norian to Rhaetian. The occurrence of Triasina hantkeni MAJZONandAulotortus sinuosus WEYNSCHENKin our samples points to a (late) Rhaetian age of the Philippine platform carbonates (Triasina hantkeni zone; cf. GRGASOV1C1997). 4.3.1 Islands off northwestern Busuanga Island (Microfacies MF Tr 1 - MF Tr 6) There are two limestone areas off northwestern Busuanaga (Fig. 5): One is Malajon Island (locally called Black Island) and the other is an island group north of Malajon, close to the village Buluang (Kalampisanan Islands). Both localities exhibit different facies. 4.3.1.1 Malajon Island Facies: The limestones of Malajon represent reefs. The reefal nature is not evident on the first view, since thick bedding is widespread. However, as indicated by massive limestones exhibiting domal geometries (P1.6/6: Bs 13a, b), and shown by the high abundance and diversity of reefframework building organisms (P1. 11; Bs 14a, Bs 15) welldefined reefal buildups can be proved. They are covered by thin-bedded limestones and connected to each other by thick-bedded limestones representing the inter- and backreef facies. Individual reefs are relatively small (maximum height and width 40 m), but widespread. Most of the reef limestones show boundstone and rudstone textures. Floatstones are rare. The preservation of fossils is poor to moderate. Reef-building organisms are calcareous red algae, coralline sponges and corals. Similar biota occur as reworked constituents within the bedded facies. Stratigraphy: HASHIMOTOet al. (1980) found conodonts indicative of a Late Anisian to Early Norian age. This is in contrast to the Rhaetian age given by FOm~NE (1979) and FONTAINEet al. (1979) after studying some foraminifera. The age diagnostic foraminifera Triasina hantkeni MAJzO~ was
reported by FONTAINEet al. (1979) andVAcHARD& FONTAINE (1988). The association of fossils found in our thin sections agrees with that of other Late Norian-Rhaetian reef carbonates, but no specific age diagnostic fossil was recognized in samples of the reef facies. Microfacies: Most samples are boundstones, in addition a few floatstones occur. The following microfacies types have been differentiated: MF Tr 1 Boundstone (P1. 11/1-8) Description: Reef limestone, characterized by closely intergrown sponges, corals and solenoporacean red algae, forming a framework, and intensive biogenic encrustations consisting of foraminifera (Planiinvolutina, Bullopora and others), tube-like fossils and low-growing sponges. Three subfacies can be differentiated according to the dominating group of reefbuilders: MF Tr la: Solenoporacean boundstone with cm-sized domal-shaped algal thalli exhibiting discontinuous growth and borings (P1. 11/1) as well as encrustations by sponges. Sample Bs 18. MF Tr lb: Solenoporacean-coralline sponge boundstone with abundant boundstone clasts (P1.11/2). Solenoporacean algae are strongly recrystallized. The algae occur in close association with sponges. Coralline sponges include inozoid, sphinctozoid and chaetetid forms. Their preservation depends on their primary mineralogy as shown in PI. 11/2. Additional rare fossils are echinoderms, gastropods and foraminifers. Samples Bs 16, 20. MF Tr lc: Coral-coralline sponge boundstone (P1. 11/46). The colonial corals are strongly recrystallized and intensively encrusted by sponges and foraminifera (Planiinvolutina). Baccanella occurs in the micritic matrix (PI. 11/ 4). Cayeuxia-type fossils are rare. Sample Bs 21 yields abundant microfacially differentiated clasts indicating a transition to the floatstone type of MF Tr 2. Samples Bs 17a, 17b, 19, 21. Interpretation: This MF type characterizes the autochthonous reef facies. Of particular interest is the occurrence of the facies-diagnostic strophomenid brachiopod Gosaukammerella in sample Bs 19 (P1. 11/7-8). This brachiopod is a common member of the cryptic dweller guild in the autochthonous central framework of Upper Triassic reefs in the Western Tethys (Northern Calcareous Alps, Western Carpathians, Southern Alps/Slovenia, Western Sicily, Chios Island/Greece and Southern Turkey), Oman and Central Iran (SENoWBARI-DARYAN& FLOGEL1996), but has been not yet recorded from the Eastern Tethys or Panthalassa Ocean until now. Cavity-dwelling brachiopod-coralline sponge associations are known from crypt habitats of modern reefs (JACKSONet al. 1971). The Philippine micromorphic brachiopod is distinctly smaller than Gosaukammerella eomesozoica (FLOGEL).The tubular 'spines' are anchored within the sponge meshwork (P1. 11/7). MF Tr 2: Polymict floatstone (P1. 12/1-7) Description: This type is characterized by various angular and subangular mm-sized clasts and fragmented fossils floating in a micritic matrix. The clasts comprise various
69
microfacies, including laminated thrombolitic bindstones (P1. 12/4-5), cortoid grainstones (P1. 12/6-7) and sponge boundstones (P1. 12/1). Common redeposited fossils are corals and coralline sponges. In addition echinoderms, gastropods and shells occur. Most reef builders arc poorly preserved and can only be differentiated according to group level. Corals include Stylophyllopsis- and Retiophyllia-type taxa (P1. 12/2). Sponges are represented by mostly indeterminable inozoid and sphinctozoid taxa (P1.12/3). Sponges and corals show complex encrustations composed of agglutinated foraminifera, tube-like fossils of unknown affinities and low-growing sphinctozoid sponges. Sample Bs 13. Interpretation: The admixture of clasts derived from various depositional environments (protected lagoon: thrombolitic bindstone; winnowed platform: cortoid grainstone; reef: sponge boundstones) indicates reworking and transport of material to low-energy environments within the reef area. 4.3.1.2 Kalampisanan Islands 9 km to the north of Malajon Island, there is a small limestone island group, named in this paper after the largest island. The limestone exposures continue to the mainland, where they are in tectonic contact to red and greenish gray cherts. Facies: Field evidence and thin sections reveal the existence of two facies types: 1) Low-energetic lagoonal wackestones with megalodontid bivalves, crinoids and other echinoderms, 2) high-energetic lagoonal pack-/grainstones with grapestones and cortoids. Stratigraphy: The only evidence for a Late Triassic age is given by the presence of large megalodonts resembling Paramegalodus. Microfacies: Samples Bs 29-35; R 27. The samples reveal four microfacies types: MF Tr 3: Oncoid float-/grainstone (PI. 13/1-6) Description: Characteristic features are large porostromatc and fenestral oncoids associated with cortoids. Porostromatc taxa include various types belonging to calcareous green algae and cyanobacteria (cf. D~,XGAS'rANet al. 1997, 1998; Dm~,GASTAY & RZCHrF.R 1999): Garwoodia (P1. 13/3), Hedstroemia, Riwdaria (P1. 13/4). Additional fossils are rare coral fragments and calcareous algae. The taxonomic assignment of the alga shown on PI. 13/5 is difficult. At the first look, the oblique section reminds on Griphoporetla, a wide-spread Norian-Rhaetian alga (cf. BARAVrOtO et al. 1993, PUGLn~SE1997). But the arrangement of the branches also shows similarities with Asterocalculus, a recently described gymnocodiaccan alga (SoKAc & G~GASOWC1998). Micritized bioclasts, grapestone intraclasts and involutinid foraminifera occur within grainstone textures (P1. 13/6). Aulotortus sinuosus WEYNSCHENK(PI. 13/2) indicates a Late Norian-Rhaetian age. Sample Bs 30. Interpretation: Porostromate algae and filamentous cyanobacteria are common constituents of open and restricted lagoonal environments. The association of the Porostromata with involutinid foraminifcrs and grapestoncs characterizes an open marine lagoon.
MF Tr 4: Fine-grained algal filamcnt grainstone (PI. 13/7-8) Description: Most micritic peloid-like constituents arc broken, fragmented and micritized filaments of Porostromata. An irregular fenestral texture is indicated by ram-sized sparfilled voids (PI. 13/7). Oncoids, agglutinated foraminifera, ostracods and echinoderm fragments are very rare. Sample Bs 31. Interpretation: The abundance of algal filaments in association with fenestral structures and the scarceness of reefderived fossils point to a restricted, tidally influenced cnvironment, MF Tr 5: Intraclastic wacke-/packstone (P[. 14/l) Main criteria are sparry grains (probably recrystallized grapestones), large fecal pellets (PI. 14/1) and some agglutinated foraminifers. Sample Bs 32. MF Tr 6: Involutinid foraminiferal packstone (PI. 14/2-3) Description: Fractured foraminiferal packstone with densely packed, abundant involutinids and rare gastropods. The foraminifera are strongly recrystallized. A few sections can be attributed to Aulotortus. The limestone exhibits microcrack sets (P1. 14/2). Sample Bs 34. Interpretation: See MF Tr 8.
4.3.2 Southern Busuanga (Microfacies MF Tr 7- MF Tr I3) In southern Busuanga limestone outcrops cover large areas. The largest is Coron Island, which is entirely composed of carbonates. Limestones are also found on Sangat Island and its prolongation to the mainland (Mount Ili), at the Maquinit hot spring and at three hills on Busuanga mainland closc to the old airport NE of Coron town. 4.3.2.1 Busuanga (Mt. Ill) and Sangat Island The limestones are probably in fault contact with cherts. They arc mostly bioclastic wackestones with ostracods and foraminifera (mostly miliolids). Triasina hantkeni in sample Bs 26 indicates an Late Norian to Rhaetian agc. The depositional environment was a protected lagoon. Microfacies: Sample Bs 24 is a poorly preserved bioclastic wackestone with few agglutinated foraminifers, sparry bioclasts and some echinoderms and shells. Sample Bs 25 is similar in texture, but exhibits additionally strongly bored gastropods. Sample Bs 26 (PI. 14/3, 5) is a strongly fractured invol utinid foramin iferal wackeston e with Triasina hantkeni MA_IzoN, and yielding a few dasycladacean fragments and corresponding to MF Tr 6. 4.3.2.2 Busuanga: Hills NE of Coron Town, close to the old airport Only Mr. Batu (12 ~ 00' 533 N, !20 ~ 13' 976 E) was studied in detail. Micritic limestones with a thickness of some 50 m overlie red radiolarian cherts unconformably. Most limestones are mudstones and wackestones exhibiting intensive stylolitization, sometimes leading to a stylomottled fabric. Microfacies: The samples exhibit two subfacies types:
70 MF Tr 7a: Mudstone (P1. 14/6) The limestone is strongly stylolitized and fractured and except for very rare foraminifera unfossiliferous. The matrix is microspar. Patches of euhedral dolomite rhombs are closely associated with stylolites. Samples Bs 44, 45. MF Tr 7b: Ostracod wackestone (PI. 14/4) This type is characterized by abundant smooth-shelled ostracods and rare gastropods occurringwithin a fine-grained, homogenous micrite matrix. The interior of the shells is geopetally filled with gray 'crystal silt' pointing to vadose overprint. Sample Bs 43. Interpretation: Both subfacies types indicate low-energy, restricted lagoonal environments. 4.3.2.3 Coron Island south of Busuanga Microfacies and fossils were studied a) in thin sections of the samples Bs 49-57 from the northwestern part of the island (cf. Fig. 7) and b) in 12 samples (CRN 1-16) collected by Kirkland Consulting in various places of the island.. MS Tr 8: Involutinid foraminiferal wacke-/packstones (P1.15/1-7) Description: This microfacies is characterized by abundant to very abundant involutinid foraminifera and a peloidal micritic matrix. Two subfacies are differentiated: MF Tr 8a: Burrowed wacke-/packstones. Strongly recrystallized involutinids occur together with smaller sparry shells which probably are also foraminifers. Involutinid foraminifers include Triasina cL hantkeni MAJZONand various species ofAulotortus (P1. i5/2-3). Dasyclads are represented by fragments of Macroporella and Griphoporella. In addition thin isolated valves ofpelecypods and some echinoderms occur. Gastropods and other shells are strongly bored. The borings are filled with micrite corresponding to the surrounding sediment. The matrix is a fine-grained peloidal packstone (P1.15/1). Some constituents are silicified (Bs 52). Samples Bs 49, Bs 52, Bs 55, Bs 55 I, Bs 55 I1. MF Tr 8b: Foraminiferal wackestone with colonial corals (cf. Paraso'aeomorpha RONtHWlCZ:P1. 15/7), involutinid recrystallized foraminifers and fine debris. Bs 50. MF Tr 9: Fine-grained bioclastic packstone (P1 15/9) This type is characterized by abundant very small sparry bioclasts. Many of them are probably recrystallized foraminifers, but there occur also dasycladacean fragments. Sample Bs 51. Interpretation of the involutinid foraminiferal facies (MF Tr 6, Tr 8 and Tr 9): Late Triassic involutinid foraminifera flourished both in platform and shallow basinal settings (PEELER1978). The abundance of involutinid tests increases from near-reef back-reef environments to high-energy sand shoal environments characterized by the association of calcareous algae and foraminifera, to muddy inner platform environments (HoHENEGOEa& LoBrrZER1971, HOHENEGGER & PILLER 1975, SENOWBARI-DARYAN& SCI-I,~FER 1979, GAZDZlCKI 1983). In contrast, size of the tests and wall thickness decrease from near-reef outer platform to inner
platform environments. The abundance of thin-shelled involutinids seen in MF Tr 6 (Kalampisanan Islands, sample Bs 34) can be interpreted as storm-induced accumulations within an protected inner platform area. MF Tr 8a (Busuanga: Coron Town area) corresponds approximately to the 'pellet-mud facies' recognized in the Alpine Upper Triassic platforms, as shown by the fine-grained peloidal matrix and the variously sized involutinids in association with few dasycladacean algae. MF Tr 9 (Coron Town area) shows characteristic criteria of the autochthonous inner platform 'mud facies' (abundance of very small involutinids and fine shell debris). MF Tr 9 also shows strong similarities with Norian/Rhaetian carbonates from the Sinta Ridge (Banda Sea, Indonesia), interpreted as back-reef lagoon sediments (VrLLENEt:VEet al. 1994: Fig. 4/10), and Late Norian-Rhaetian platform carbonates in eastern Sulawesi (MART1NIet al. 1997), considered being deposited in protected subtidal platform areas (cf. Fig. 8). MF Tr 10: Well-sorted oolithic grainstone (P1. 15/9) Description: Abundant well-sorted micritized ooids, in association with peloids and very rare ostracods. Rare foraminifers are represented by Glomospirella, Tetrataxis, Reophax, Ammobaculites and Duostomina. Sample Bs 54. Interpretation: Texture and foraminiferal assemblage agree with the criteria of the 'oolite facies' differentiated by HOrn~NEC,aER & PILLER(1975) in Late Triassic platform carbonates of the Northern Alps. The microfacies indicates high-energy conditions, normal marine salinity and a farreef position of the depositional environment. MF Tr 11: Fine-grained burrowed peloidal packstone (P1. 16/1) Criteria are abundant peloids, associated with some gastropods and echinoderms and few ostracods. Burrows are infilled with peloids, fecal pellets and rounded clasts. Sample Bs 53. MF Tr 12: Fractured and brecciated mudstone with radiolarians (P1. 16/2) Description: This microfacies differs distinctly from the other types studied because of the association of sponge spicules, radiolarians and fine-grained bioclastic debris. Sample Bs 57. Interpretation: Open-marine deeper water environment. MF Tr 13: Poorly sorted, polymict carbonate breccia (P1. 16/ 3-6) Description: Large angular and rounded clasts float within a fine-grained brecciated matrix. The larger clasts are oolithic grainstones and calcite marbles. Sample Bs 56. Interpretation: The co-occurrence of angular and rounded clasts of different microfacies and preservation as well as the finely brecciated matrix indicate redeposition of already lithified and partly silicified carbonates, perhaps at the slope. Some of the samples provided by Kirkland Consulting (CRN 3, 13, 15, ?17) are bioclastic mud- to wackestones with radiolarians > ostracods > filaments > sponge spicules
71
Fig. 8. Paleolatitudinal position of Norian-Rhaetian reef and platform carbonates recorded from East Asia (modified from KIESSt,INGet al. 1999). See Fig. 6 lot legend. Note that more reefs occur in the southern belt as compared with the Thailand-Malaysia-Philippines region.
> echinoderm fragments, pointing to a deeper marine bathyal depositional environment and corresponding to MF Tr 12 described above. Other facies types are breccias with diverse litho- and bioclasts (CRN 2, 8, 12). Thc most important components of these resedimented limestones are foram iniferal-bivalve-gastropod wackestoncs and cortoid grainstones. Additional components are red chert fragments. This facies type corresponds to MF Tr 13 and indicates multiple reworking of open platform material and possibly downslope transport into a basin. Interpretation: Field observations indicate that the shallow-water limestones of Coron Island are largely olistoliths of a proximal slope, although some in situ lagoonal successions are certainly present. Evidence is provided by adjacent polymict breccias and radiolarian mudstone in the vicinity. Oolitic and peloidal grainstones found in the field are only
clasts, incorporated in a micritic or breccious matrix. We interpret Coron Island as a carbonate platform yielding lagoonal mud- and wackestones, oolite bars and small coral reefs. The margins of the platform largely agree with the prcsent day outlinc of thc island. Most of the sample sites represent proximal slopc settings that distally interfinger with basinal cherts. 4.3 Comparisons Records of Upper Triassic carbonate platforms and reefs in South East Asia are rare as compared with Permian shallow-marine carbonates (TAMUrA 1975, VACHArD & FONTaIN~!1988). Norian-Rhaetian platform and/or reef limestones were reported from Scram (WmcK~nS 1937, ALSIlAIBANIet al. 1984), Bum (PIGRAM&. PANGGABEAN1984),
72 Timor (WANNER1907, VINASSADE REGNY1915, KRISTANTOLLMANN1986), the Banda Sea (V1LLENEUVEet al. 1994), eastern Sulawesi (CoRNgEet al. 1994, MAR~NXet al. 1997), the Malay Basin (FONTAINEet al. 1990), from drilling in Singapore (FONTAINE& WOON 1993), and from the ShanMergui terrane in Northwest Thailand (KEMPERet al. 1976, VACHARD1986, 1988a, b, FLOGEL1988, FOrCrAINE& TAYnWANIT1992, CHONGLAKMANI1999). These carbonates were distributed in two different paleolatitudinal belts (KIESSLIN~ et al. 1999) around about 30~ (Timor, Bum, Seram, East Sulawesi) and between the paleoequator and 10~ (Peninsular Malaysia and Malay Basin, Singapore, northwestern Thailand and Malajon Island/Philippines; Fig. 6). Some of the basic facies types recognized in North Palawan are also developed in various parts of Indonesia, particularly on the fragmental Late Norian and Rhaetian platforms with coral reefs and megalodontid limestones known from eastern Sulawesi, the Sinta ridge in the North Banda Sea, on Buru Island, Western Scram and Misool. These platforms were probably formed on the same continental block of the Banda Sea, yet somewhat isolated from the Australian sheff and later dismembered during the Miocene (CoRNC_Eet al., 1994, 1999). In the Kolonodale-Beteleme region (Sulawesi), the lowermost part of the sequence consists of outer platform to basinal carbonates of uppermost Sevatian (Late Norian) to Late Rhaetian age. The upper reefal part of the sequence is composed of algal-coral boundstones and foraminiferalpeloidal as well as bioclastic grainstones and packstones of latest Rhaetian age (Triasina hantkeni biozone). The depositional pattern of this part is similar to that of the Palawan platform carbonates with regard to the dominating microfacies types and the abundance of involutinid foraminiferal limestones. MF Tr 10 (oolitic grainstone) corresponds precisely to MF 6 described by MAR'nNI et al. (1997), and MF Tr 8 (involutinid foraminiferal wacke-/packstone) to MF 4 of Sulawesi. The Kolonodale patch reefs were formed by lowdiverse fasciculate corals and various coralline sponges in bioclastic sand areas. In contrast, in the reefs of Malajon Island, coralline sponges and solenoporacean red algae appear to be of greater importance as framebuilding fasciculate corals (traces of which, however, were recognized in the field (P1. 6/7). Shallow-marine carbonates are rare in the Southeast Asian mainland and their age is still a matter of discussion (KmJc & HtrVEN1998). The Late Triassic platform and reef limestones recorded from the Malay Peninsula and from offshore Malay Basin are similar to the carbonates studied in Palawan with regard to the composition of the foraminiferal association of the platform carbonates, but differ in the reef facies, which is differentiated into black limestones with abundant inozoid sponges and various encrusters, and gray massive limestones with corals. The reef mounds of the Malayan Sotong limestone were formed within a protected environment, the Malajon reefs probably on the outer platform. Late Triassic platform carbonates known from northwestern Thailand yield a characteristic assemblage of involutinid foraminifera, similar to carbonates in Burma,
northwestem Malaysia (GAzDZICKI& SMrr 1977) and Sumatra (VAcrtARD1988b) as well as in other Indonesian islands. This points to a widespread distribution of the involutinid foraminiferal facies recognized also on Majon Island. Taxonomic data of Upper Triassic reef and platform carbonates in South East Asia are rather poor except for foraminifera. Many foraminifera appear to be cosmopolitan indicating close relations between Western Tethyan and Asian assemblages (cf. GAZDZICKI1983, VACHARD1988b). However, the taxonomic composition of foraminiferal associations, corals and coralline sponges also show high percentages of endemism as revealed by the reef faunas described from eastern Timor and Scram Island, and foraminifera and algae of platform carbonates in Indonesia and Thailand. An interesting point is the absence of typical reefdiagnostic foraminifera (SENOWBARI-DARYAN& SCH,~t~ER 1979, FLf~GEL1981, AL-SHAmANI et al. 1984, VACHARD 1988b) in the Philippine reef carbonates.
5 P A L E O G E O G R A P H I C IMPLICATIONS According to TAYLOR• HAYES(1981, 1983), HOLLOWAY (1981) and KUDRASSet al. (1986) North Palawan as well as the Dangerous Grounds and the Reed Bank in the South China were an integral part of the South China Plate until the mid-Oligocene. This interpretation is challenged by our data, at least for the area investigated. Although we do not question that North Palawan was part of Eurasia in the early Cenozoic and separated from China during the Oligocene and Miocene (ENARCIONet al. 1995, HALL1996), we raise some doubts that it was part of the South China Block in the Late Paleozoic and early Mesozoic. The following discussion is focused on the implications of the Middle Permian and Late Triassic carbonates described in this paper for the paleoposition of northern Palawan. Comparison with Southern China: Problems arise regarding the proposed origin of the North Palawan Block at the margin of South China if the sedimentary evolution of both areas is compared. No marine Middle Permian platform/ramp carbonates are known from mainland of South China in Eastern Fukien and in the Hong Kong area (HOLLOWAY1981, 1982). Fossiliferous Permian carbonates only have reported from eastern Guandong NE Hongkong. If North Palawan is likely to have formed part of the eastern margin of the South China Plate, it should show particular affinities to the widespread Middle Permian in South China (FAN et al. 1990). However, this is obviously not the case. The reason is likely the large Cathaysia landmass that isolated the Permian platforms of central and western South China from the vast Panthalassa Ocean (WANG& J1N 2000). Late Triassic platform carbonates are absent in this part of southern China (Nanling area). By the Late Triassic, most of southernmost China exhibit nonmarine and marginal marine facies (siliciclastics with coals; WANGet al. 1981) as result of major regressions. The Jurassic sequence is only represented by Early Jurassic terrigenous sediments in eastern Guandong.
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Owing to the considerable differences between the lithostratigraphic development of the Permian and Triassic on Taiwan and southernmost China on one side and North Palawan on the other side, a close paleogeographical connection of North Palawan Block and South China is, therefore, unlikely. The Late Triassic deltaic sandstones with plant remains reported from the offshore Dangerous Grounds in the South China Sea (KUDRASSet al. 1986) may indicate a more proximal setting of this region as compared with the Palawan platforms. North Palawan was suggested to be a continental fragment based on the presence of a metamorphic basement (Barton Metamorphics) and granitic intrusives with trace elements and zircons indicative of continental crust (ENCARNACION~; MUKASA1997). However, monzonitic and granitic intrusives of North Palawan yield Miocene ages whereas the granites in Goangdong and Fuijn arc mostly Mesozoic and subordinately Paleozoic in age (HOHNDORFet al. 1992, L1 2000). The Palawan palcomagnetic data provided by ALMASCOet al. (2000) would agree with a South China origin of th North Palawan Block, but the data are inconsistent and point to pervasive Cretaceous and Recent remagnetization.
age with the carbonates of the Busuanga area are known from the Sibumasu and Indochina terranes (Western and southern Thailand, Peninsular Malaysia and Malay Basin; FONTAINEct al. 1990, FOYrAINE& TANTJWAN~T1992), but are more common in the Eastern Indonesian terranes (see Chapter 4.4) which were positioned during the Late Triassic outbord of northeastern Gondwanaland (see Fig. 6). Tectonic events:The Late Paleozoic to Late Jurassic sequence in North Palawan was clearly affected by postJurassic compressional events, judging from the style of deformation in all rocks of this age. The supposely Late Cretaceous Boayan-Caruray Clastics (WOLVARTct al. 1986) are also affected by weak metamorphism and a similar folding pattern (I-IASHrMOTO& SATO1973) as the Malampaya Sound Group, but unconformably overlain by non-metamorphic Eocene limestones (WoI.VARTet al. 1986). Thus a regional tectonic event around the Cretaceous-Tertiary boundary can be inferred for North Palawan which is much younger than the suggested mid-Jurassic to mid-Cretaceous subduction-rclated deformation at the margin of the South China Block (HOt.LOWA'r1981, 1982).
Middle Permian foraminiferal carbonates: Middle Permian carbonates yielding aNeoschwagerina ex. gr. craticulifera association are widely distributed in the western and eastern Tethys as well as in the Circum-Pacific regions (KoBAYASm1997a). Neoschwagerinid and verbeekinid faunas are known from most of the major terranes now forming South East Asia including the central, but not the southernmost part of the South China Block and the lndochina (Indosinia) Block. Both foraminiferal groups are absent or less common in shelf carbonates of the Sibumasu (ShahThai) Block (UENo 1999). Paleogeographic reconstructions place the Sibumasu Block south of the paleoequator, separated from the amalgamated Indochina and South China blocks to the north by the Paleotethys (METCAH'~ 1994). Middle Permian cm'bonate platforms with reefs developed in Thailand at the western rifted margin of the I ndoch in a Plate (Pha Nok Khao Platform: EI. TABAKll& UTHA-AROON 1998) and the eastern margin of the Shah Thai Plate (Khao Khwang Platform: WIELC~OWSKV& YOUNG 1985, DAWSON 1993). The platforms were separated by the siliciclasticdominated Nam Duk Basin. Both, platforms and basins became parts of fold and thrust belts bordered by suture zones The age of suturing is controversial (TAN1996). Most authors favour a Triassic age (BuNoPAS 1981, METCAI.FE 1994, SASrUDAet al. 2000) but a Middle to Late Permian closing of the Paleotethys in central Thailand is discussed as well (HELMCKEet al. 1983, INGAVA'r-HI:.;LMCKE& Ht._'I.MCKLr 1994). As compared with the Middle Permian carbonates of Northern Palawan, the platforms in Thailand comprise a distinctly broader facies spectrum ranging from restricted environments to interior and outer platforms but there exist some similarities with regard to the dominance of skeletal foraminiferal wackestones. Late Triassic platform and reef carbonates: Late Triassic platform and reef limestones compareable in biofacics and
(1) The Middle Permian limcstones of the El Nido area as well as the Late Triassic carbonates of Busuanga exhibit no striking affinitics to coeval sediments formed in southernmost China. (2) Some of the differences in the tectonosedimentary evolution between North Palawan and South China may be explained by a more distal position of North Palawan. However, the continuous chert deposition surrounding the Middle Permian and Late Triassic shallow-water platforms points to an oceanic setting (scamounLs ?) during thc Permian, Triassic and Jurassic. (3) The facies pattern of the Middle Permian carbonates in central Thailand, known from the Paleotethys margins adjacent to the Siburnasu Block and the lndochina Block, differs from that of the dcpositional patterns represented by the Minilog Formation in North Palawan. (4) Although the Late Triassic involutinid foraminifcral facies of Palawan exhibits some similarities with facies types described from southern Thailand and eastern Peninsular Malaysia, distinct differences in the biotic composition of the reefs point to a setting distant from the lndochina Block margins. (5) We speculate that North Palawan was part of the lndochina Block in the Carboniferous and Permian, separated from the Indochina Block during the Middle Permian (as indicated by synsedimentary Permian extensional tectonics), and collided with the South China Block in the Late Cretaceous.
Conclusions:
Acknowledgments We thank Shell Philippines Exploration B.V. for the permission to publish results of contract work. Some Permian samples have becn analyzed for fusulinids by Ong (Simon Petroleum Technology). H. Forke (Forschungs-
74
institut Senckenberg, Frankfurt) assisted in the identification of microfossils. Laboratory work in the Institute of Paleontology in Erlangen was supported in the context of project F1 42/70 ('Triassic reefs') funded by the Deutsche Forschungsgemeinschaft (DFG). The compilation of reef data was part of the D F G projects F1 42/75-1, F1 42/80-1. The paper was reviewed by Daniel Vachard (Lille) and O. Weidlich (Berlin). W e are especially grateful to D. Vachard for very helpful suggestions.
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