Pennsylvanian-Lower Permian Shelf Margin Facies in Southwestern United States of America

Abstract

Coal measures of the Appalachians and cyclothemic deposits of the midcontinent Pennsylvanian are well known, but equally characteristic are several types of carbonate buildups produced in the clear and shallow seas around the southern extension of the North American craton. The sections containing these buildups remain lithologically varied because this was a time of general tectonic instability and considerable terrigenous sedimentation. Many of the carbonate-producing organisms which formed these offshore banks, shelf-margin buildups and shelf-interior mounds are unique to the Late Paleozoic. They appear in the Pennsylvanian and evolve continuously in the early Permian and even to the Triassic. They principally include types of algae and foraminifera, with several algal-like forms and certain sponges and stromatoporoids. Very few large frame-building organisms occur.