Lower Cretaceous Rocks in Gulf Coastal Plain of United States: ABSTRACT

Abstract

Rocks of Early Cretaceous (Comanchean) age underlie most of the Gulf coastal plain. Their thickness varies from zero at the updip subsurface pinchout in the eastern region and less than 2,000 ft at the outcrop in central Texas to about 7,000 ft at the downdip limit of control. Carbonates make up most of the section west of the East Texas embayment; alternating carbonates, terrigenous clastics, and some anhydrite compose the section in eastern Texas and adjacent parts of Louisiana and Arkansas; and sandstone and shale, with some beds of limestone and anhydrite, represent the Lower Cretaceous in the eastern region. The percentage of carbonates increases seaward in all segments of the Gulf Coast. Deposition was in shallow open-sea to restricted marine, deltaic, coastal-interdeltaic, and coastal-plain End_Page 358------------------------------ environments. Subsidence was generally at the same rate as sedimentation, and all sediments were deposited near sea level. The shoreline fluctuated greatly in the eastern clastic province but shifted little in the western carbonate region after the Early Cretaceous transgression. Deltas were constructed in several segments of the Gulf Coast during earliest Cretaceous, and in the central and eastern regions during several later regressive intervals. The tectonic-sedimentation history of the Gulf Coast Lower Cretaceous was optimum for the development and preservation of abundant organic matter adjacent to deltaic sandstone and porous carbonate rocks, creating favorable conditions for petroleum occurrence. End_of_Article - Last_Page 359------------