| Summary: | While mapping the coastal deposits in the Gerlache Strait of the Antarctic Peninsula, we observed several "conspicuous ridges at sea level" (CRASL). Usually, located directly in front of a glacier, these features were only observed in the intertidal zone. Three hypotheses for their origin are considered: 1) recessional moraines, 2) detached spits, and 3) partially submerged pro-talus ramparts. In order to determine which of these hypotheses best explains their origin, we compared the grain size, angularity, sphericity, and petrology of the CRASL deposits with surface samples taken from modern moraine, beach, and talus-slope deposits in the area. In addition to documenting their sedimentological characteristics, their distribution was mapped according to their orientation and shape, throughout the Gerlache Strait. Aerial photos from 1956/1957, 1981, and 2001 were examined for CRASLs. Finally, samples were obtained from raised beach ridges in the study area in an attempt to date using Optically Stimulated Luminescence (OSL). Data from grain size, angularity, sphericity, and petrology suggest that the CRASL deposits are supplied by recessional moraines and are reworked into beach deposits. A model for how the transition occurs was proposed. The distribution maps created indicated that the CRASLs vary in size, occur on both sides of the strait, and have no specific orientation. Furthermore, it was found that the most common type of CRASL is one that is detached and parallel in relation to the coastline. Aerial photos indicated that CRASLs were present in 1956/1957, 1981, and 2001. In addition, it was determined that OSL dating of the beach ridges did not work on the samples obtained. Finally, the prevalence of these features indicates changes in the study area since the beginning of the 20th century and further work to determine their age of formation is needed. Boone Pickens School of Geology
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