--> ABSTRACT: Massive Carbonate Biohermal Buildups in the Presence of an Actively Prograding Delta: Mahakam Delta (Indonesia), by H. H. Roberts and J. Sydow; #91021 (2010)

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Massive Carbonate Biohermal Buildups in the Presence of an Actively Prograding Delta: Mahakam Delta (Indonesia) 

ROBERTS, H.H., and J. SYDOW

The modern Mahakam delta of East Kalimantan (Borneo) is prograding across a narrow shelf dominated by bioherms 20-30 m thick constructed by the calcareous green alga, Halimeda. During the Holocene highstand the fluvio-tidal Mahakam delta has prograded onto the inner shelf and constructed a delta platform of approx. 5000 km{2}. Southerly flowing high energy currents from the Makassar Strait (largely Pacific intermediate water) restrict prodelta sediments to the inner shelf and bathe the middle-to-outer shelf regions in nutrient-rich waters. In response, these areas are dominated by individual and compound biohermal buildups composed of aragonitic Halimeda particles in a matrix of foraminifera-rich mixed terrigenous and carbonate mud. Radiocarbon dates on piston cores through 3 separate bioherms define accretion rates ranging from 5.87 cm/yr to 13.89 cm/yr. Seismic relationships indicate that bioherms were initiated on a regional ravinement the formed following sea level rise from the latest Pleistocene glacial maximum. The modern highstand delta is currently down lapping and burying inner shelf bioherms. Seismic data clearly indicate that the sedimentary architecture of the shelf is dominated by vertical stacking of similar depositional sequences related to successive glacioeustatic cycles. 

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.