ABSTRACT

Recent discoveries in the Hackberry of southwest Louisiana have created new interest in the high-risk, deep Hackberry section. Petrographic examination of three conventional cores and hundreds of sidewall cores, together with previously completed isopach studies, has established that the lower Hackberry sandstones are turbidites. Within the area, the lower Hackberry sandstone interval has two depositional patterns: an updip north-south channel pattern, and a downdip blanket-type sandstone pattern. Cores in the lower Hackberry have the following graded sequence from bottom to top: (1) coarse-grained conglomeratic sandstone which grades upward into finer laminated sandstones; (2) cross-bedded and convoluted sandstone; (3) siltstone; and (4) finely laminated shale. The sandstone is bimodal and trimodal, commonly containing 30-50% clay matrix. The microfaunal assemblage within the lower Hackberry cyclic sequence indicate depth ranges of 300 to 3000 feet (Zones 5 and 6).

Because of the turbidite nature of the sediments, production within the channels has been small, except where the channels have been deflected around salt domes. In such channels, the turbidity currents lost velocity, and important sandstone bodies were deposited, reworked, and locally winnowed. In the downdip area where the channels spread out into a blanket pattern, production is controlled by the topographic and structural configuration of the unconformity surface on and around which the turbidity currents deposited sediments.