Abstract

The Gulf Coast geosyncline extends from Alabama southwestward to the northeastern part of Mexico, and contains Mesozoic and Cenozoic sediments on the order of 60,000 feet thick. Cenozoic clastics ranging from 10,000 to 50,000 feet or more thick cover an area of approximately 250,000 square miles.

Two stable arches and three embayments are aligned transverse to the axis of the geosyncline, and largely determine the shape of its northwestern limb. These features reflect Paleozoic and pre-Cambrian structures and alignments. The greatest thickness of sediments known for each Cenozoic stratigraphic unit is found in one of the embayments.

During the Cenozoic, rate of sedimentation was never uniform throughout the geosyncline. At some places, deposits accumulated in depocenters or along depoaxes to much greater thicknesses than elsewhere. Area of maximum sedimentation for Eocene was in southwestern Texas, but gradually shifted northeast-ward until area of maximum sedimentation for Miocene and younger was in southern Louisiana.

The gentle southeastward dip of most Cenozoic stratigraphic units is modified by zones called "flexures," downdip from which the rate of dip and thickening of beds is accentuated. Most flexures are accentuated by contemporaneous normal faults of regional extent. Each succeeding younger "flexure" is located seaward, or downdip, from the preceding older one. This results in the cross sectional shape of the geosyncline being asymetrical, with its axial plane dipping landward at an angle of approximately four degrees.