Correlation of Lignites in the Midway and Wilcox Groups of Southern Alabama and Eastern Mississippi

Abstract

The Gulf Coast Paleogene section represents one of the world's most continuous records of cyclic nonmarine through marine sedimentation. Microfossil research has demonstrated the completeness of downdip marine sections; however, the continuity of updip, nonmarine, and marginal marine sections remains relatively uncertain. Lignites occur throughout the Gulf Coast low Paleogene, but to date have not been adequately characterized with the detail necessary for high-resolution correlation. Lignite characteristics, stratigraphic position within Paleogene depositional cycles, and their mode of origin can be used in correlating nonmarine deposits (highstand system tract) to downdip marine deposits (transgressive system tract). Samples were collected for east-central Mississippi and west-central Alabama and analyzed. Principle constituents, comprising over 50%, are inaperturate forms in Midway Group samples and tricolporate forms in Wilcox Group samples. Secondary components, 10-20%, of triporate and monolete/trilete forms occur in both groups. Triporate forms are approximately 25% more abundant in the Wilcox Group samples, whereas monolete/trilete forms remain relatively constant in both groups. Minor components ([le]5%) of bivesticulate, tricolpate, polycolpate, polyporate, and polycolporate forms are present, but show distinct percentage variations between each group. Inaperature forms are present only in the Midway Group and monoporate forms exist only in the Wilcox Group. These group-specific forms,more » combined with the differences in primary and secondary forms and abundances, allow samples to be formationally assigned base on palynomorpbic signature.« less