Subsidence Analysis of the Appalachian Foreland Basin

Date

2021-12

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Abstract

The eastern North American margin was subject to a series of four Paleozoic orogenies forming the Appalachian Mountains: The Taconic (ca. 463-445 Ma), Salinic (ca. 430-420 Ma), Acadian (ca. 390-355 Ma), and Alleghanian (ca. 325-260 Ma). The timing and extent of Paleozoic orogenic events are often determined by investigations of the ancient hinterlands, which can be heavily eroded, vegetated, and overprinted, often presenting incomplete chronicles. A complimentary approach leverages the sedimentary response to and basin record of orogenesis. My hypothesis is that the Appalachian Foreland Basin records the spatial-temporal variabilities of the Taconic, Salinic, Acadian, and Alleghanian orogenies through rapid subsidence controlled by the load from accreting landmasses. To test this, I present three new regional cross-sections of the Appalachian Foreland Basin, one along-strike (1000 km) and two in the dip-direction (450 km). These three new cross-sections complement the five regional cross-sections from the central and northern Appalachian Foreland published by the USGS, and fill in gaps in the southern Appalachian Basin. The along-strike cross-section connects the seven dip cross-sections from Tennessee to New York. The along-strike section correlates key formations and examines their thickness variation to constrain the geographic limits of each orogenic event and create basin-wide isopach maps. The isopach maps are tied to multiple 1D basin models that provide quantitative estimates of thrust-related flexural subsidence. The spatial-temporal evolution of deposition, as recorded by thickness variations of key horizons, facilitates examination into the magnitude, timing, extent, and topography of each subsequent orogeny. A network of 1D basin models along the new and existing cross-sections resolve the spatial-temporal variability of each orogeny throughout the basin. The rapid subsidence in the basin is controlled by the orogenic load from accreting landmasses; 2D flexural modeling evaluates the load across the orogen to determine topographic relief, geographic extent, and effective elastic thickness (Te) of each orogeny along strike. The distribution of Salinic and Acadian orogenesis can be evaluated by the occurrence of thick synorogenic foreland deposits of contemporaneous age. Their synorogenic formations are restricted to the north and central Appalachian Foreland, inferring the southern limit of the suturing of the Ganderia and Avalonia microplates.

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Keywords

Appalachian Basin, Appalachian Foreland, Flexural Modeling, cross-section

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