34 Processes and Landforms of Great Lakes Coasts (Posters)

Friday, 5 May 2023
1:30 PM - 5:30 PM
EC 215

SEDIMENTARY AND GEOMORPHIC RECORDS OF LITTORAL TRANSPORT DURING THE NIPISSING TRANSGRESSION-REGRESSION CYCLE, NORTHEAST COAST OF THE UPPER PENINSULA OF MICHIGAN

Paper number: 34-5
Program: Theme Sessions
Time: 1:30 PM – 5:30 PM

Authors

Abstract

Mid-Holocene aged sediment along the northeast coast of the Upper Peninsula (UP) of Michigan is stratigraphically inset between an older deglacial landscape, and a younger, post Nipissing strandplain landscape. Strandplains of mid-Holocene age sediment extend from Grand Sable eastward to near Whitefish Point as numerous discrete strandplain segments that all record eastward littoral transport. Widths of strandplains reach ~23 km and contain up to 84 beach ridges, which are considered minimum estimates because the basinward boundaries are truncated by modern bluffs and by younger, lower strandplains. The highest level of the Nipissing transgression is recorded by the highest elevation beach ridge, which at the Lonesome Point strandplain segment is approximately in the middle of the strandplain, where sporadic blowouts and parabolic dunes drape the beach ridges. GPR transects at the Lonesome Point strandplain segment image to ~45 m depth, where there is some uncertainty distinguishing between outwash sediment boundaries and the Jacobsville Sandstone. Overlying outwash is a package of littoral sediment 5–7 m thick. The base of the littoral sediment radar facies is a flat-lying, continuous reflection. Internal reflections from a south to north transect (along dip) are semi-continuous to continuous and dip gently northwards, but in places are hummocky. On a west to east transect (along strike) the reflections are more discontinuous and flat-lying. The littoral sediment exposed along a shoreline bluff at the northern end of a GPR transect consists of flat-lying cross- and planar-stratified sand, pebble, and cobble gravel recording eastward sediment transport. Several OSL ages bracket the age of the littoral sediment to ~8–4 ka. With the age and elevation of the Lonesome Point strandplain segment bracketing the age (~4.5 ka) and elevation of the peak Nipissing level, the strandplain records a depositional transgression. The many now abandoned strandplain segments along the northeast UP coastline record massive volumes of sediment transported eastwards during the mid-Holocene.

Geological Society of America Abstracts with Programs. Vol. 55, No. 3

doi: 10.1130/abs/2023NC-386893

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