Abstract

During the Middle and Late Pennsylvanian marine transgressions spread from the southwest along two separate routes: (1) north across Nevada, western Utah, eastern Idaho and Montana to the Dakotas; and (2) east across southern Arizona and New Mexico, then north through the Texas and Oklahoma panhandles, across Kansas, Missouri and Iowa to the Illinois basin and at times across northern Indiana and Ohio to the northern Appalachian area. Western areas were covered by marine waters most of the time, but brief, widespread, transgressions spread east hundreds of miles while only a few inches to a few feet of marine sediment were deposited. Of 13 Desmoinesian transgressions in the Illinois basin, six reached Ohio. Of 14 Missourian inundations of the Illinois basin, seven reached Ohio, and one reached northeastern Pennsylvania. During the Virgilian 25 more or less separate transgressions reached eastern Kansas; four or five remain in Illinois, and none reached Ohio. Sediments of each marine transgression are generally put into distinct cyclothems, but in some places where clastic wedges have nearly disappeared the records of two or more transgressions may locally seem parts of the same one. In other areas where a clastic wedge developed locally during a marine transgression there is an impression of two distinct advances.

Each cyclic succession generally contains widely persistent thin stratigraphic units. It includes underclay, coal, black fissile shale and marine limestone. When studied regionally the cyclothem is found to contain as many as six or seven deltaic wedges which result from local influxes of clastic sediment. They are generally tectonically controlled, and interrupt, rather than cause the cyclic pattern. The persistent units mentioned above may be traced not only across a single basin, but across a series of basins separated by arches or other uplifts.

These widespread shifts in sea level with attendant changes in sedimentational pattern seem to result from eustatic shifts in sea level simultaneously affecting many separate basins. Their causes may be the alternate growth and waning of Gondwana glaciers, or large scale tectonics in any part of the world.