Midway Stage, Sabine Stage, and Wilcox Group

Abstract

Stratigraphic nomenclature for provincial divisions of the lower Tertiary (Paleocene and lower Eocene) deposits of the Coastal Plain of eastern North America is variable in form and usage. Midway group, Wilcox group, and Sabine group, the modern geographic, class nouns most commonly applied to these deposits, are used dually as major divisions (groups) of rocks and as provincial subdivisions (stages) of the Paleocene and Eocene. Initially established as names of lithologic units, stated or implied modern usage of Midway, Wilcox, and Sabine is predominantly in a time-rock sense. Dual usage of Wilcox as a rock-unit name is increasingly common. This failure to differentiate fundamentally between rocks, their times-of-creation, and other rocks originating wholly or in part simultaneously, not only impedes interpretations of the natural geological history of the region but confuses beginners and others who may have only superficial or occasional contact with the terminology. The use of (1) Midway and Sabine stages and their companion units, Midway and Sabine ages, as provincial time-rock and time units of the early Tertiary of the Coastal Plain, based on major fluctuations of the strand line; and (2) Wilcox group for the great mass of lignitic, prominently arenaceous deposits of both Midway and Sabine ages; can clarify the nomenclatural confusion and permit conformity to standard usage of time and time-rock units elsewhere in the world. Type exposures of formations included in the Midwayan, Sabinian, and Wilcox, in Alabama, Louisiana, and East Texas are typical of the units. Additional exposures in these areas are usable as reference sections for comparison and partly for the emendation of stratigraphic data supplied by the type locality.