Surface Occurence of Cretaceous Beds in the Southeastern States: ABSTRACT

Abstract

The Cretaceous sedimentary rocks of the eastern Gulf region crop out in a crescentic band around the southwestern end of the plunging Appalachian Highlands in a belt 500 miles long and up to 75 miles wide. Their maximum thickness at the outcrop is estimated to be about 2,100 feet. The oldest beds of the eastern Gulf Coastal Plain, the Vick formation, crop out in a small area in central Alabama. The age of the Vick is uncertain, being post-Paleozoic and pre-Tuscaloosa. It is probably Jurassic or Lower Cretaceous. Above the Vick formation the Upper Cretaceous formations can be correlated fairly closely with the Texas section, the sequence being divisible into several groups of related formations. The formations equivalent to the Woodbine of Texas include the Cottondale, Eoline, and possibly the Coker formation, the three lower formations of the Tuscaloosa group. These crop out in an arc extending from Marion County in northwestern Alabama to the Coosa River Valley in east-central Alabama. The formations equivalent to the Eagle Ford formation are the Gordo formation at the top of the Tuscaloosa group and the McShan formation, formerly considered the lower part of the Eutaw formation. These extend from the Tennesee River Valley on the north into Georgia on the east. The Austin equivalents include the restricted Eutaw formation and the basal formations of the Selma group, the Mooreville chalk and its sandy equivalents, the lower part of the Coffee sand in northeastern Mississippi and southern Tennessee and the Blufftown formation in eastern Alabama and western Georgia. End_Page 1963------------------------------ Above the beds of Austin age the Cretaceous sequence in the eastern Gulf region may be divided most naturally into two sequences: the lower correlated with Taylor marl and the lower part of the Navarro group and the upper correlated with the upper part of the Navarro. The lower of these two sequences consists of the Demopolis chalk, its sandy northern partial equivalent of the Coffee sand, and its eastern equivalent, the Cusseta sand, and the Ripley formation, which overlies all three units. This stratigraphic sequence extends from southern Illinois to west-central Georgia. The upper beds of the Cretaceous include the Prairie Bluff chalk and its two sandy equivalents, the Owl Creek formation on the north and the Providence sand on the east. These formations extend from southern Tennessee as far at least as central Georgia, broken in west-central Alabama by overlap by the overlying Midway beds. Near the ends of the crescentic belt the sequence of deposition is broken by extensive overlaps. As may be expected, internal, progressive overlap is common in all the formations, but extensive overlap indicating crustal warping is especially notable at the base of each of the larger groups discussed. End_of_Article - Last_Page 1964------------