12 D3. North American Rifts, Faults, and Tectonic Activity

Monday, 10 March 2025
1:30 PM - 5:30 PM
114

ASSEMBLY OF FORELAND AND HINTERLAND ALLOCHTHONS IN THE SOUTHERN APPALACHIANS OF ALABAMA AND GEORGIA: IN-SEQUENCE TO OUT-OF-SEQUENCE THRUSTING AT THE MISSISSIPPIAN-PENNSYLVANIAN BOUNDARY

Paper number: 12-7
Program: Technical Sessions
Time: 3:30 PM – 3:50 PM

Authors

Abstract

A comprehensive analysis of southern Appalachian structural features in Alabama and Georgia reveals an initial pulse of in-sequence (e.g., forward breaking thrusts) Mississippian deformation stretching from the hinterland (Blue Ridge) to the northwestern flank of the foreland fold-and-thrust-belt. That in-sequence deformation was followed by an extensive interval of out-of-sequence, backward breaking thrust faults that developed during the earliest Pennsylvanian through the Permian. The out-of-sequence thrust faults, which stretch from the Sequatchie anticline on the northwestern flank of the foreland fold-and-thrust-belt, southeast to the Brevard fault zone at the eastern Blue Ridge-western Inner Piedmont boundary, dominate the structural architecture of the southern Appalachian orogen in this region. The transition from in-sequence to out-of-sequence thrust faulting at the Mississippian-Pennsylvanian boundary suggests the southern Appalachian orogenic wedge achieved critical taper during the Mississippian, but transitioned to sub-critical taper by the Pennsylvanian. Importantly, the switch from in-sequence to out-of-sequence thrusting occurred during the same time frame as uplift and erosion of the Upper Mississippian-Lower Pennsylvanian Parkwood Formation, subsequent deposition of the Pottsville Formation clastic wedge, and the waning stages of peak metamorphism in the southern Appalachian Blue Ridge (330-320 Ma). The Mississippian-Pennsylvanian boundary also coincides with a significant climatic shift from monsoonal, wet-dry conditions to “ever-wet” conditions in this segment of Pangea. We present evidence for at least 20 out-of-sequence thrust faults spanning the foreland fold-and-thrust-belt and Blue Ridge of Alabama and Georgia that likely developed as a result of climate-tectonic interactions that influenced the topographic slope and critical taper of the southern Appalachian, Alleghanian orogenic wedge. Similar climate-tectonic interactions have been noted in the Eastern Alpine Molasse Basin of Germany.

Geological Society of America Abstracts with Programs. Vol. 57, No. 1

doi: 10.1130/abs/2025SC-408426

© Copyright 2025 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.