Seismic Stratigraphic Identification of Eustatic Cycles in Late Triassic, Jurassic, and Early Cretaceous Rocks--Gulf of Mexico and West Africa: ABSTRACT

Abstract

ABSTRACT Seismic stratigraphic techniques permit identification of Late Triassic, Jurassic, and Early Cretaceous eustatically controlled sequences in strata from the North American Gulf Coast and West Africa. Several distinct sequences are remarkably persistent from the Florida Panhandle around the perimeter of the Gulf Coast into northern Mexico, a distance of over 1,500 miles. Their identification requires the integration of seismic data with lithologic, environmental-facies, biostratigraphic, radiometric, and well log information. A comparison with strata of comparable age in offshore West Africa indicates the same sequences can be recognized there. The sequences in North America and Africa are interpreted to be eustatically controlled because they occupy the same time-stratigraphic positions and display coastal onlap patterns similar to those previously recognized by us elsewhere in the world. Gulf Coast eustatic cycles and the formations occurring within them are: (1) Late Triassic--Eagle Mills Formation; (2) Early Jurassic--known only from southern Mexico and not identified in the study area; (3) Middle Jurassic (Bajocian-Bathonian)--Werner Anhydrite-Louann Salt interval; (4) Late Middle Jurassic (Callovian)--Norphlet Formation; (5) Late Jurassic (Oxfordian-Kimmeridgian)--Smackover-Buckner-Haynesville Formations; (6) Late Jurassic-Early Cretaceous (Tithonian-Berriasian)--most of the Cotton Valley Group; and (7) Early Cretaceous (Valanginian)--a restricted wedge seen only in a basinward position. West African eustatic cycles are (1) Late Triassic; (2) Early Jurassic; (3) Middle Jurassic; (4) Early Late Jurassic (Oxfordian-Kimmeridgian); (5) Late Jurassic-Early Cretaceous (Tithonian-Berriasian); and (6) Early Cretaceous (Valanginian). Further refinement may show additional sequences in Middle Jurassic and Late Jurassic intervals.