GSA 2020 Connects Online

Paper No. 145-10
Presentation Time: 4:00 PM


THEILEN, Brittany M.1, SIMMS, Alexander R.1, GERNANT, Cameron1, ZURBUCHEN, Julie1 and DEWITT, Regina2, (1)Department of Earth Science, University of California, Santa Barbara, 1006 Webb Hall, Santa Barbara, CA 93106, (2)Physics, East Carolina University, Howell Science Complex, Rm C-209 1000 E. 5th Street Greenville, NC 27858, Greenville, NC 27858

The grain-size and roundness of beach deposits may record changes in past wave climates as well as other processes acting on beaches. Here, we examine changes in grain-size and roundness of two sets of raised beaches on opposite sides of the Antarctic Peninsula (AP): Joinville Island along the Eastern AP (EAP), and Livingston Island along the Western AP (WAP). Overall, the 9 beaches on Livingston Island are stratified with poorly sorted clasts compared to Joinville Island’s better sorted 21 stratified lower and 15 unstratified upper beaches. The overall increase in roundness on the Joinville beaches is interrupted at beaches 5, 13-15.5, and 28. Beaches 5 and 28 are, respectively, less and more rounded than the general trend. The less rounded beach 5 sediments may represent a period of shorter open water conditions with an increase in sea ice. The opposite could hold true for beach 28. The decrease in roundness from beaches 15.5 to 13 coincides with the onset of the Neoglacial time period ~2.5 cal kyr BP. The presence of sea-ice or glacial activity could hinder clast rounding or introduce new angular material to the beaches during this cooler period. The only apparent trend in sedimentary characteristics on Livingston Island beaches reflects the type of beach deposits. Strand plains deposited by normal swash processes exhibit sub-angular to sub-rounded sediments while beach ridges formed during storms contain sub-rounded to rounded deposits. Ground penetrated radar profiles through the beach ridges suggest they bury older strand plain deposits. Therefore, we suggest Livingston beach ridges consist of recycled, older strand plain sediments deposited by storms, resulting in more rounded deposits.