Punctuated succession of Paleogene mollusks in the northern Gulf Coastal Plain

Abstract

Occurrence data for 2,876 molluscan species (including species, subspecies, variations, and unnamedforms) in the northern Gulf states of Texas, Louisiana, Mississippi, andAlabama show a punctuated succession through the Paleogene stratigraphic sequence. These occurrence data are readily divisible into five successional cycles that correspond both to stratigraphic groups and to cycles of marine transgression and regression. The base of each cycle contains a fauna with a high percentage of species making their first appearance and coincides with a marine transgression. This percentage decreases through the cycle as the percentage of species making their last appearance increases. Each cycle is concluded by a marine regression. Individual cycles represent a background normal rate of speciation and extinction events. Punctuations between cycles represent major extinction events produced by marine regression and accompanying increased shelf sedimentation from advancing delta complexes.