Geology of the Abbeville-Perry-South Perry Structure, Vermilion Parish, Louisiana

R.O. Steinhoff

Abstract


The Abbeville-Perry-South Perry structure is located in the Miocene oil- and gasproducing trends of Vermilion Parish, Louisiana. The strata encountered by drilling are primarily Pliocene, Miocene, and Oligocene in age. Wells drilled to sufficient depth encounter three distinct facies : first, a shallow-water massive Pliocene and Miocene near-shore to continental sand facies; then, an intermediate facies of alternating sands and shales from the Miocene continentalshelf environment; and, finally, the thick deep-water shale facies of the early Miocene and late Oligocene. Structurally, the Abbeville-Perry-South Perry feature is a faulted, elongate anticline that trends north-northwest. It is oriented normal to the regional strike of the beds. All faults are normal and include both down-to- the-basin and up-tO-the-basin faults. The former are generally regional in extent; the up-tO-the-basin faults are smaller compensating faults confined tO the Abbeville-PerrySouth Perry structure. The fault throw generally increases gradually with depth. Faults decreasing with depth appear tO "die-out" in the bathyal shales. Individual beds thicken onto the downthrown sides of the faults and thin toward the crest of the structure. The amounts of thickening or thinning generally increase gradually with depth. Thus, fault movement and anticlinal folding were contemporaneous with sedimentation more-or-less continuously from Oligocene tO Pliocene time. These tectOnic movements were greatest during Oligocene and Lower Miocene time. The Abbeville-Perry-South Perry structure probably originated from anticlinal folding and faulting in the region of the continental slope during early Miocene and Oligocene time. As the hinge line (or shelf edge) migrated seaward across the area, the strtlCture became positioned closer tO the shoreline until in Pliocene time it was near the shoreline. Anticlinal growth and fault movement were greatest at the time when the structure was located in the environment of the continental slope and outer continental shelf. The structural activity steadily decreased after Lower Miocene time as the hinge line with its unstable environment continued tO migrate farther basinward.

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