Abstract

Middle and Upper Devonian rocks of the eastern midcontinent make up a thick clastic wedge with carbonates of the Onondaga Limestone and its equivalents immediately below. The entire sequence demonstrates the origin and filling of a foreland basin in response to the Acadian Orogeny.

Stratigraphic subdivision and correlation of the succession, though originally based on lithologic criteria, is increasingly based on conodont, ammonoid, brachiopod and paleobotanic zonation. Event stratigraphy involving subregional unconformities and thin beds of pyroclastics is a recent development promising greatly increased resolution in correlation.

Basin-filling proceeded with development of a west-facing clinoform/ramp and multiple transgressive/regressive episodes. Through time, nonmarine facies were deposited at locations first in the northeast and later toward the south and west. Marine facies were progressively displaced to the west and southwest. Effectively, the land area expanded at the expense of the adjacent Catskill Sea which shallowed as it was displaced.