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Higher Order Cycles, Inferred Chronostratigraphy, and Impact of Multiple Lowstand Previous HitSystemsNext Hit Previous HitTractsNext Hit on Hydrocarbon Exploration, Pletmos Basin, Southern Offshore, South Africa

Gerhard J. Brink

Development of 67 middle Valanginian to middle Campanian cyclic depositional sequences is interpreted to be a response to the interplay of unique tectonics and higher order eustatic Previous HitseaNext Hit Previous HitlevelNext Hit cycles capable of imposing type 1 unconformities. Direct correlation of 16 sequences, within available paleontological age constraints, with Exxon's global third-order cycles encompasses the remaining 51 sequences, which are inferred to be fourth-order and fifth-order cycles. These unconformity bound sequences were grouped into genetic megasequences bound by major type 1 unconformities (third-order or fourth-order falls at the trough of a third-order Previous HitcycleNext Hit) typically displaying evidence of extensive erosion of thick highstand Previous HitsystemsNext Hit Previous HittractsNext Hit.

Lowstand Previous HitsystemsNext Hit Previous HittractsNext Hit are considered to be excellent stratigraphic targets because of updip pinch-out below relict shelf edges. These Previous HittractsNext Hit display similar depositional styles within megasequences both in relation to areal distribution and in geometric and seismic facies characteristics. Principal hydrocarbon plays proposed in this postrift frontier basin exhibit combinations of the following: (1) intensity of type 1 erosion, (2) proximity to persistent, scattered fluvial point sources, (3) superposed lowstand Previous HitsystemsNext Hit Previous HittractsNext Hit (aggradational vs. progradational megasequences) preferentially consisting of deltaic and coastal wedges and/or slope-front fans/submarine channel fill/basin-floor fans, (4) seal enhancement by transgressive Previous HitsystemsNext Hit tract shales and distal highstand Previous HitsystemsTop tra t shales, and potential drape and compactional closure, and (5) the geographic or stratigraphic proximity of marine condensed sections within maturation windows. Using these criteria, three hydrocarbon play fairways can be delineated in the Pletmos basin.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.