Constraining the Timing and Magnitude of Orogenesis by Basin Response: Two Examples from North America

Abstract:

The timing and extent of orogenic events are often determined by investigations of the ancient hinterlands, which can be heavily eroded and overprinted, presenting incomplete chronicles. A complimentary approach leverages the sedimentary response to orogenesis, especially the flexural effects recorded by basin subsidence. In this study, we use geohistory analysis, flexural modeling, and sedimentary stacking patterns to provide additional input to the analysis of mountain belts.

We evaluated the Appalachian foreland with 20 geohistories and 7 flexural profiles from Newfoundland to Mississippi and find the distribution and magnitude of four Paleozoic orogenies is spatially variable. A major Middle to Late Ordovician flexural subsidence event that corresponds to the Taconic Orogeny is identified along the entire orogen, terminating before the Black Warrior Basin. This subsidence is synchronous, which differs from other existing models. A middle Silurian to basal Devonian subsidence event (~Salinic Orogeny) is restricted to the central and northern U.S. Appalachians, and coincides with the deposition of a thick evaporitic section and major subsidence in the Michigan Basin. Flexural models indicate up to ~3 km of topographic relief (each) for the Taconic, Salinic and Acadian orogens.

In the Upper Cretaceous of the U.S. Western Interior, there is significant along-strike variation in depth/subsidence of the Turonian foredeep, as indicated by 40 geohistories, 9 flexural models, and a regional isopach map. Based on flexural models, the load topography reaches a maximum of 2 km in the area of the Wyoming Salient/Wasatch Culmination. Moreover, the best evidence of a significant forebulge occurs distal to this area, with truncation and a facies omission. To the south and north, the coeval modeled topography is <1 km. From the basin response, we posit variable relief/shortening in the distal thrust belt, consistent with published structural reconstructions.