ABSTRACT: Depositional History and Genetic Sequence Stratigraphic Framework of the Middle Miocene Depositional Episode South Louisiana

Abstract

ABSTRACT Two widespread, transgressive deposits associated with the faunal tops Amphistegina B (15.5 Ma) and Textularia W (12.0 Ma) defined the middle Miocene depositional episode (MM depisode). Sediment supply coupled with mobile salt, subsidence and sea-level changes produced a mosaic of linked structural and depositional systems. Three distinct structural provinces were identified: the western detachment province is characterized by continuous E-W-oriented faults, with minor salt spreading. The subsided central detachment province was caused by high sediment supply and concomitant salt withdrawal; here, a roller fault system developed. Roller fault systems, linked with the formation of a salt canopy, provided an effective barrier preventing sediments from reaching the basin floor. Depotroughs and isolated salt domes and sheets produced by differential loading composed the third structural province. Four genetic cycles separated by maximum flooding events divided the MM depisode: Genetic Cycle 1 (Amphistegina B-Cibicides opima), Genetic Cycle 2 (Cibicides opima-Cristellaria I), Genetic Cycle 3 (Cristellaria I-Bigenerina humblei), and Genetic Cycle 4 (Bigenerina humblei-Textularia W). Genetic Cycles 1 and 2 are composed of fluvial-dominated platform and shelf margin deltas fed by the ancestral Mississippi fluvial system. During Genetic Cycle 2, collapse of the shelf margin (Harang embayment) originated intraslope fans and a long-lived submarine-fan system farther downdip. During Genetic Cycle 3, the main deltaic depocenter was located in the east and was fed by the ancestral, wave-modified, fluvially dominated Tennessee delta system. During Genetic Cycle 4, progradation of the ancestral Mississippi and Tennessee deltas extended along the northern Gulf shelf margin.