--> Abstract: Tectonic influences controlling the growth and demise of isolated Oligo-Miocene platforms; East Java Basin, Indonesia

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Tectonic influences controlling the growth and demise of isolated Oligo-Miocene platforms; East Java Basin, Indonesia

John C. Naranjo

Department of Geology and Geophysics, University of Wisconsin-Madison, 1215 W Dayton St.,

Madison, WI 53705

A depositional and tectonic model of early (Eocene to Miocene) evolutionary stages of the East Java Basin is presented from 2-D reflection seismic interpretation (~400 lines), well-log synthesis and analysis, and subsidence profiling. We focus on the prolific growth and sudden demise of the Kujung limestone that has been dated using Sr isotopes to represent deposition during 28.2+0.7 - 23.4+0.7 Ma.

The tectonic history of the East Java Basin, which includes a major portion of the East Java Sea, can be categorized into three major events: crustal compression from subduction during the Cretaceous, crustal extension from wrenching of the Philippine Sea and Eurasian plates during the Paleocene and Eocene, and structural inversion during the Miocene and Pliocene from compression of the Sunda orogeny. Tectonic quiescence during most of the Oligocene- Early Miocene accommodated abundant shallow-water carbonate reservoir formation throughout Southeast Asia. Shallow-water carbonates are represented by prolific mound, reef and platform facies laterally grading into deep-marine off-mound sediments of calcareous mudstone and chalk. The carbonate growth and stratigraphy of the Kujung limestone throughout the early stages (Eocene to Late Miocene) of the East Java Basin appears to have external controls.

Subsidence analyses indicate that carbonate mound growth during the tectonically quiescent Oligocene- Early Miocene was accommodated by subsidence rates of 175+65 m/Ma. A much higher rate compared to the earlier Eocene- Oligocene (60+26 m/Ma; likely due to little overburden of sediments and no major vertical tectonic activity) and the later Mid- Late Miocene (79+36 m/Ma; continuation of quiescent period into structural inversion events).

Interpretation of onshore 2-D reflection seismic data was used to create structure contour maps of Eocene-Miocene seismic stratigraphic intervals. Predicted tectonic reconstructions of the early stages of the East Java Basin are modeled and presented in a series of paleogeographic maps.

Outcrop data, rock samples and measured stratigraphic sections collected at several Late Eocene to Late Miocene exposures in Central and Western Java, August-September 2006, are to be used as a means of calibration for the paleogeographic representations in age, stratigraphy and depositional environment.

AAPG Search and Discovery Article #90060©2006 AAPG Foundation Grants-in-Aid