1 D2. Recent Advances in Geosciences

Sunday, 20 March 2022
8:00 AM - 12:00 PM
Commonwealth Salon 2

LIDAR-MAPPED GIANT SAND BLANKET AND ABLATED TEKTITES SUGGEST SAME SOURCE

Paper number: 1-1
Program: Technical Sessions
Time: 8:00 AM – 8:20 AM

Authors

Abstract

Two independent geologic signals imply the N. American Great Lakes as a possible large-scale mid Pleistocene cosmic impact region. First, ablated Australasian tektites have well characterized speed and vertical angle reentry conditions per NASA research in the 1960s led by Dean R. Chapman, i.e., “Chapman conditions”. Second, a large conformal blanket of silicate aggregate is detailed via high-accuracy LiDAR. The upper contact of the structurally robust, enigmatic blanket has tens of thousands of repetitive morphologic features conforming to just eight archetype planforms, expressing to the surface as low-relief ovoid basins with rigid systematic co-alignment by region, the Carolina bays.

Dynamically correct assessment of Chapman conditions via A-given-B suborbital analysis (inverse variant of A-to-B suborbital problem) provides launch solutions across Earth’s surface. NASA’s 1960s work omitted this step and assumed lunar origin of tektites, triggering subsequent avoidance of Chapman’s reentry conditions. Distant tektite fall sites and their reentry conditions imply the MIS 20 source as the N. American Great Lakes region.

Carolina bay morphology, systematic regional alignment and structure provide a basis for their assessment as proximal ejecta, per observations of energetic emplacement and lack of both biotic detritus and internal bedding structure. Conic perturbation around baseline trajectories to the center of each bay per ballistic targeting technique solidly recreates bay shapes. Launch conditions of elevation and azimuth are extracted from bay ellipticity and bearing, respectively, also via A-given-B suborbital analysis. Assumed common launch speeds imply launch regions that swarm to the S. W. of Lake Huron for each bay planform group.

The suborbital patterns are consistent with Schultz, Gault (1990) for an oblique impact and resulting hemispheric expansion plume with center marching downrange from N.E.-to-S.W. An impact footprint consistent with Lake Huron’s location and arrangement is inferred by both of the subject geologic signals. The shallow depth of Lake Huron relative to its size, and its rough symmetry about its N.E.-to-S.W bisector are consistent with an oblique cosmic impact per Stickle, Schultz (2012) into the Laurentide ice sheet above the contemporary lake.

Geological Society of America Abstracts with Programs. Vol. 54, No. 3

doi: 10.1130/abs/2022NE-374575

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