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ABSTRACT: Tropical Climate Variations, Hydrodynamic Regimes, and Rift Tectonics Develop the Sedimentary Architecture, Source Rock Potential, and Reservoir Character Observed in Central Sumatran Basins

Smith-Rouch, Linda
Smith-Rouch Consultants, Lakewood, CO

The dynamic interplay among climate, lake hydrodynamic regime, and tectonics determine source rock and reservoir potential in Central Sumatra rift basins. Sediment distribution and delta depositional systems of these rift lakes were driven by tectonics in the Malay Peninsula, Sunda Platform and the Barisan Mountains. Local rift tectonics (i.e. periods of quiescence) and hydrodynamic regimes strongly influenced the thickness of coal facies within individual rift basins. Paleosol development within the Brown Shale Sequence was enhanced by local hydrodynamic regimes and climate. Tectonic inversion in the northeast section of Central Sumatra controlled the architecture of the Shiapas sands in these basins. Tropical climate and vegetation influence porosity and grain size in fan conglomerates of the lake sequence.

Nested within tectonic pulses are decadal, century, millennial, and Milankovitch climate cycles. Tropical climates are effected by ENSO events that vary in cyclically and intensity. These "events" forced upwelling currents, controlled sea surface temperatures, droughts, precipitation rates, fluctuations in wind and current directions, and fluctuations in the depth of the meteoric boundary layer. Within local rift lakes these high frequency climate cycles control production of organic facies, fossil diversity, oxygen minimum zones, seasonal lake turnover, and paleosol development. Climate cycles might explain some of the diversity expressed within the tectonic rift sequences.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia