ABSTRACT

The South Bosco-Duson-Ridge area is located in the Oligocene and Miocene oil- and gas-producing trends of Acadia and Lafayette Parishes, Louisiana. Wells drilled to sufficient depth encounter three facies: first, a Pliocene and Miocene near-shore to continental massive sand facies; then, an early Miocene and Oligocene continental-shelf facies of alternating sands and shales; and finally, a thick bathyal shale facies of Oligocene age. Oil- and gas-production in this area is almost entirely confined to sands in the continental-shelf facies.

Structurally, the South Bosco-Duson-Ridge feature is a faulted, elongate anticline that trends normal to the regional strike of the beds. All faults are normal and are either down-to-the-basin or up-to-the-basin. The former are regional in extent and trend parallel to the regional bed strike. The up-to-the-basin faults are compensating faults confined to the South Bosco-Duson-Ridge complex. The fault throw generally increases gradually with depth. All the faults "die-out" upward in the section in or before reaching sediments of early Miocene age.

Strata thicken into the downthrown sides of the faults and thin toward the crest and over the structurally highest portions of the structure. The amount of thickening or thinning generally increase gradually with depth. Thus, fault movement and anticlinal folding were contemporaneous with sedimentation, acted more or less continuously from Oligocene into Miocene time, and were greatest in intensity during Oligocene time.

The South Bosco-Duson-Ridge structure probably originated from faulting and anticlinal folding on the continental slope during Oligocene time. Structural growth was greatest when the structure was located in the unstable environment of the hinge line (or shelf edge). Structural activity continued during the deposition of the neritic sediments of the Oligocene and early Miocene but at a steadily reduced rate. The structure was buried by a great thickness of near-shore and continental massive sands during Miocene and Pliocene time.