The Chenier Plain of southwestern Louisiana is a low coastal marshland characterized by numerous relict beach ridges, or cheniers, which parallel the shore and rise generally 5-10 feet above the marsh level. From analyses of cores along a north-south line of section through Creole, Louisiana, it has been possible to identify four faunal zones and seven distinct sedimentary facies in the post-Pleistocene deposits which underlie the plain. The faunal zones, named after the dominant foraminifers, are: the Streblus, Streblus-Elphidium, Quinqueloculina, and Trochammina zones. The sedimentary facies consist of varying proportions of sand, silt, and clay which, together with their contained fauna, clearly reflect the environments of deposition, including marsh, bay, mudflat, ope gulf, and beach.

The relict beaches or cheniers are lenticular sand and shell bodies similar to certain shoestring sands of older rocks which commonly serve as oil reservoirs; thus, they hold special interest for the petroleum geologist. They are biconvex in section, average less than 1,000 feet across, and extend as uninterrupted coastwise ridges up to 30 miles in length. They average about 10 feet in thickness and are characterized by a smooth, generally arcuate seaward front and irregular landward margin. These deposits rest on shallow gulf-bottom mud and are overlapped by organic marsh clay. Should the ridges eventually be buried by such deposits, they will form potential stratigraphic traps. The characteristic shape, trend, and dimensions of the chenier sands, together with their distinctive sedi entary and faunal properties should aid materially in identifying similar potential reservoirs in the subsurface.

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