12 Landscape Evolution in Mid-Continental Settings

Thursday, 7 April 2022
1:30 PM - 5:30 PM
North Meeting Room 201/202

CATACLYSM ON THE CONTINENT: OFFERING A NON-CLASSICAL SOLUTION FOR THE GEOMORPHOLOGY OF ENIGMATIC SURFICIAL SEDIMENTARY FORMATIONS BLANKETING NORTH AMERICA

Paper number: 12-11
Program: Theme Sessions
Time: 4:00 PM – 4:15 PM

Authors

Abstract

We observe in North America significant surficial sedimentary deposits which are poorly constrained temporally and morphologically: the Upland Gravels of Maryland and Virginia; the Pinehurst Formation of the Carolinas, where a nearly continuous deposit extends across intervening terraces and scarps; the Cypresshead Formation in Georgia; the Blackwater Draw Formation of the High Plains; the source material for the Nebraska Sand Hills. The surface of these formations shows evidence of ongoing reworking, but studies of deeper extents of these deposits often mention difficulties in determining their provenance while testing gradualistic eolian, fluvial, glacial, lacustrine, or marine sedimentary processes. Marine deposition may be appropriate, but they contain no fossils. Flood deposits on interfluvials is reasonable, but they show no sorting or channeling. On elevated terrain, workers implicate eolian activity but delivering coarse clastic sediments upslope from distant drainage mandates powerful winds or unexpected tectonic activity. Large (up to 7 km diameter) but shallow (1-10 m) hydrologically closed ovoid depressions are found to dimple these formation’s surficial expression, seemingly without deforming or altering the antecedent strata they rest upon. Our survey finds these dimples in prodigious quantities on regions of low relief. They may represent diagnostic markers of the questioned deposits.

A non-classical solution is argued for the depositional mechanism of these deposits, informed by the work of Daniels, Wheeler and Gamble from the 1970's. In their reports the ovoid dimples are asserted to be topological artifacts created during the final stages of deposition of the strata they are formed within.

Invoking a cataclysmic event 788 ka, we speculate a subaerial deposition delivered as geophysical mass flows of pulverized regolith from a cosmic impact, repaving large extents of the continent. The attendant dimples’ catchments would affect the continent’s landscape evolution by buffering precipitation and allowing it to drain into aquifers rather than into antecedent drainage.

The hypothesis would be falsified if the application of isotopic burial dating to the stratigraphic contact between the sediments in question and well dated sub adjacent strata disallows coeval depositions ~ 800 ka.

Geological Society of America Abstracts with Programs. Vol. 54, No. 4

doi: 10.1130/abs/2022NC-374889

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