MISSISSIPPIAN CONTINENTAL MARGINS OF THE CONTERMINOUS UNITED STATES

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Abstract
The paleogeography, paleotectonics, and paleoceanography of continental margins and shelfedges around the present western, southern, and eastern sides of the conterminous United States are reconstructed for a brief span (about 1.5 m.y.) of Mississippian time. The time is that of the middle Osagean anchoralis-latus conodont Zone (latest Tour- naisian, Mamet foram zone 9). At this time, a shallow tropical sea covered most of the southern North American continent and was the site of a broad carbonate platform. Bordering this platform were three elongate foreland troughs, each containing several bathymetrically distinct starved basins on their inner (continentward) sides. The foreland troughs were bordered on their outer sides by orogenic highlands or a welt that formed in response to successive collisions or convergences with North America by Africa and Europe to the east, by an oceanic plate to the west, and by South America to the south. During a eustatic rise of sealevel that accompanied the orogenies and culminated during the anchoralis-latus Zone, the carbonate platform prograded seaward while the troughs subsided and carbonate sediments were transported over the passive shelfedges to intertongue with thin carbonate foreslope deposits and thin (~10 m) phosphatic basinal sediments. Simultaneously, thick (~500 m) flysch and deltaic terrigenous sediments, such as the Antler flysch on the west and the Borden deltaic deposits on the east, were shed into the outer parts of the foreland basins from active margins along orogenic highlands. This Mississippian reconstruction provides a unique opportunity to compare and contrast passive and active shelfedges of a Paleozoic continent during a high stand of sealevel. The passive shelfedges can be recognized and mapped by application of a six-part sedimentation and paleoecologic model developed for the shelfedge of the Deseret starved basin in Utah, Idaho, and Nevada.

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