ABSTRACT

Local Oligocene subsidence during post Nonion struma time created an elongate channel 15 miles long extending north-south from Indian Village to South Manchester and varying in width from 3 to 6 miles. This submarine channel was developed on a slope created by subsidence of the area to the south and subsequently filled with sediments supplied from an updip delta.

The channel floor can be divided into two structural areas: an undip segment of slump-block type faulting and a downdip, deeper water segment characterized by folding and faulting.

The Hackberry section fills the channel and consists of a thick shale sequence with sands concentrated in the lower part of the channel. Association of the sands with pelagic shales containing deep water fauna, the geometry of the sand bodies, and the sequence of primary sedimentary structures strongly suggest the sands were deposited by turbidity currents in deep water.

As Hackberry shale and sand deposition continued the channel was filled and the depositional slope was reduced; thus less sands were carried down slope into the basin in Cibicides hazzardi timem, gradation was achieved and a prograding shallow marine sequence was deposited.

Hackberry sands are productive in the study area producing a condensate rich gas from stratigraphic and structural traps.