Heterostegina Zone--A Shallow Anahuac (Late Oligocene-Early Miocene) Oil Frontier in Southern Louisiana and Mississippi: ABSTRACT

Abstract

ABSTRACT The Heterostegina (Het) zone (23.6-23.0 ma, N4a -- Globorotalia kugleri zone) is recognized throughout the Gulf Coast as an excellent correlative datum and an erratic, but prolific producer of hydrocarbons. Its late Oligocene-early Miocene? chronozone represents the maximum development of Neogene reefs in the Caribbean/West Atlantic biogeographic province. Although many of the western Gulf Coast Heterostegina reservoirs consist of reefal limestones that grew atop piercement salt domes, eastern Heterostegina equivalents in Louisiana (St. Martin Parish), southern Mississippi, and Alabama (Mobile Bay area) comprise a rimmed accretionary carbonate shelf. The existence of this shelf is confirmed by seismic data as well as by a core from the Sapphire Petroleum Company #1 State well (MS-85-4-OS) located south of Ship Island, Mississippi. Petrographic study of seventeen feet of Anahuac-age core (5660-5677 ft) recovered from the Sapphire well has delineated three carbonate paleoenvironments-in ascending order: 1) shallow-water, windward algal thickets (5671.0-5677.0 ft); 2) bryozoan-mollusc-foraminiferal-algal limestones deposited below fairweather wave base (5664.2-5671.0 ft); and 3) foraminiferal-algal-rhodolitic limestone laid down above fairweather wave base (5660.0-5664.2 ft).