Abstract: The Epicontinental System of Western Indonesia as an Analog for Cyclic Stratigraphy in Ancient Tropical Epeiric Seaways

C. Blaine Cecil, Frank T. Dulong, Sandra G. Neuzil, N. Terence Edgar

Pleistocene to Recent sedimentation patterns in the epicontinental system of western Indonesia may help to explain the cyclic stratigraphy of analogous ancient systems. The modern influx of fluvial siliciclastic sediment to the equatorial region of the epeiric sea is highly restricted, apparently the result of dense rain-forest cover within the ever-wet climatic belt of the Intertropical Convergence Zone. Because the modern system is sediment starved, much of the epeiric seaway appears to be erosional or nondepositional, except for reworking of older sediments by strong marine currents. On the poorly drained coastal lowlands, thick (up to 13 m), laterally extensive (>150,000 sq km) peat deposits are forming. The modern peat formation is, therefore, not coeval with aggrading fluvial or marine siliciclastic systems, as is commonly assumed in facies models of ancient systems.

During the last glacial low stand, paleobotanical and alpine glacial data indicate that western Indonesia was covered by a treed savanna under a cooler, drier, and perhaps more seasonal climate. In contrast to the sediment-starved modern system, rivers that traversed the shelf may have been sediment laden, as indicated by placer tin deposits. Offshore reconnaissance coring in the modern system indicates that peat formation was probably not as extensive during the drier intervals. Therefore, the stratigraphy of Pleistocene to Recent sediments in the western Indonesian epicontinental system appears to be the result of climatic and glacioeustatic processes and climate change was the major control on variation in sediment yield.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994