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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 67 (1983)

Issue: 3. (March)

First Page: 503

Last Page: 503

Title: Alternating Carbonate and Siliciclastic Deep-Water Facies in Tectonic Evolution of Northwest Palawan Margin (Philippines), South China Sea: ABSTRACT

Author(s): R. G. Lighty, M. T. Roberts, M. H. Link, K. P. Helmold, T. F. Moslow, D. W. Jordan, R. M. Slatt

Article Type: Meeting abstract


Shifting Mesozoic and Cenozoic tectonic events controlled the deposition of thick alternating sequences of deep-water carbonate and siliciclastic sediments on the northwest margin of the North Palawan crustal block.

Highly deformed Jurassic to Lower Cretaceous rocks at the base of the section may have originated in a fore-arc region along the South China margin. This convergent margin shifted into a broad extensional region in the Late Cretaceous or early Paleogene. The Late Cretaceous through the early Eocene is generally a time of hiatus in the rock record, but rocks of this age may occur in half grabens under the northwest Palawan slope.

Late Eocene to mid-Oligocene dolomites and limestones were deposited in restricted to open marine environments as the rifted Mesozoic terrain subsided. During sea-floor spreading from the mid-Oligocene to early Miocene in what is now the central South China Sea, extensive carbonate deposition of reefs, platform lagoons, and deep-water sediments draped the trailing (northwest) edge of the southward-drifting North Palawan block. Over 1 km (3,300 ft) of diverse deep-water carbonate facies was deposited in an upper slope to basin setting. Turbidites were derived from reefal sources dominated by benthic forams, coral, and coralline algae. Mudstones formed by off-bank transport and settling of platform lagoon muds differ from normal pelagic deposits rich in planktonic forams. Deep-water car onate units show a continual up-section decrease in abundance of reef- and lagoon-derived sediment and are abruptly overlain by deep-water siliciclastics.

Seismic profiles indicate late early Miocene tilting and partial emergence of the North Palawan block, during which clastic sediments prograded around and over relict carbonate platforms and deposited thick deep-water sequences on the northwest Palawan slope. These siliciclastics were deposited in submarine fan complexes as sand-rich middle to inner fan channels, outer fan lobes, and pelitic interchannel and interlobe deposits. After crossing the submerged carbonate terrain, turbidites were axially confined to a northeast-trending trough and formed a stratigraphic wedge several hundred meters thick against the slope of the relict platforms. Eroded shallow-water carbonate lithoclasts were commonly incorporated within siliciclastic turbidites. Turbidite sandstones are texturally submatu e feldspathic litharenites and subarkoses, and indicate a source terrain of quartzo-feldspathic sediments and metasediments, chert, volcanics, and acid-intermediate plutonic rocks. Petrologic studies thus support seismic and dip-meter interpretations that these sediments were derived from emergent pre-Tertiary rocks of the North Palawan crustal block.

Regional uplift in the middle Miocene was followed by mid to upper miocene subsidence, producing additional siliciclastic wedges on the northwest margin. The last regional uplift event, latest (?) Miocene, was characterized by wrench and reverse faulting. Miocene tectonism may have resulted from collisions of the North Palawan block with now adjacent terrains in the South Palawan, Mindoro-Panay, and North Sulu Sea regions. The northwest Palawan margin has been tectonically quiescent since the early Pliocene, marked again by carbonate deposition of reefs and flanking deep-water deposits.

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