ABSTRACT

Detailed correlation using well logs combined with seismic data shows that the Miocene succession of central Texas and western Louisiana is highly cyclic. These cycles are vertically stacked to form a hierarchy with durations ranging from 0.4 my. to 2.0 my. Previous quantitative testing of the high-frequency cyclicity in central Texas suggested their glacioeustatic control. The cyclicity in western Louisiana is comparable to that in Central Texas despite their different depositional settings. The Texas section accumulated in a barrier/strandplain-shelf-slope apron depositional system tract, whereas the western Louisiana accumulated in a delta-slope apron depositional system tract.

Cycles with 0.4 - 1.0 my duration bounded by flooding surfaces are the most important ones in hydrocarbon exploration. They typically contain shoreface and delta-front sand facies on the shelf, a submarine channel complex on the upper slope, and turbidite sheets and lobes within intraslope basins. Most of the channel complex and turbidite facies were encapsulated in thick transgressive shales and thus are potentially productive if charged with hydrocarbons. Our research on glacioeustasy shows that these cycles have large fluctuations in the Neogene (up to 90 m). Therefore, the determination of the exact timing of such cycles is vitally important in the current search for deep water prospects.