Extensional Collapse and Growth Faulting in a Late Mississippian Incised Paleovalley in the Central Appalachian Basin

Joseph Allen, Concord University
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Abstract

Soft-sediment deformation spans a continuum from delocalized features driven by processes such as liquefaction, to localized growth faults and fault-related folds in semi-consolidated sediment. This study examines the latter in an unusually well-exposed system of listric normal faults imprisoned within a >190-m-long, 10-m-high incised paleovalley in the Upper Mississippian Bluestone Formation at the margin of the Appalachian fold-thrust belt in southern West Virginia. Within the paleovalley, listric faults displace fluvial sandstones and overlying floodplain mudstones. Hanging wall sandstones are folded into a rollover geometry that shows stratal growth up-dip in interfluvial red mudstones and very thin-bedded sandstones. Fault-system slip is interpreted using a soft domino model where faults were broadly synchronous and kinematically linked through ductile strain in each hanging wall. Down-dip, the fault system is buttressed by a multistory stack of channel-form, quartzose sandstones. Modeling the system as pre-lithified sediment shows the quartzose channel sands had higher elastic moduli and fault frictional strength and were more resistant to brittle faulting and ductile soft-sediment folding in listric hanging walls than more mud-rich sands that dominated sedimentary fill in the incised valley. Local depositional conditions are interpreted to control the geometry of soft-sediment fault slip since (a) faulting is restricted to the boundaries of the incised paleovalley; (b) listric faults strike subparallel to the paleovalley margin; (c) net fault displacement is subperpendicular to the paleovalley margin; and (d) the multistory stack of channel-form sandstones provided a mechanical backstop controlling the downdip extent of the fault system.

Session

Deformation in the upper crust