AGE ESTIMATES OF HOLOCENE GLACIAL RETREAT IN LAPEYRÈRE BAY, AN ANVERS ISLAND FJORD
Mead, Kimberly 1988-
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Lapeyrère Bay is located on the eastern side of Anvers Island, off the Western Antarctic Peninsula. Though a large amount of data has been gathered in Lapeyrère Bay, very little has been published on the fjord’s glacial retreat history. The primary purpose of this study is to reconstruct glacial retreat from Lapeyrère Bay using cores for chronology and facies analysis, shallow seismic for mapping facies, and multibeam swath bathymetry for identifying seafloor morphological features. Bathymetric maps display seafloor features including grounding zone wedges and a glacial outwash fan. Core data have documented five sediment facies, interpreted as open-marine, glacial outwash fan, and proximal glacial-marine deposits. This study also seeks to assess the effectiveness of ramped pyrolysis, which dates individual fractions of organic material combusted at successively higher temperatures, by performing ramped pyrolysis 14C dating and carbonate 14C dating on the same cores. Nine carbonate 14C dates and ramped pyrolysis 14C dates from six depths in a proximal 20.3 m drill core yield discordant ages. Ramped pyrolysis ages are younger than carbonate ages, and the difference between both methods increases down-core. Ramped pyrolysis estimates the maximum age of the proximal core as ~4000 years younger than carbonate 14C ages. Two glacial reconstructions were developed to explain the deposition of older foraminifera with modern organic matter. The first scenario is a full deglaciation of Lapeyrère Bay ~14,000-8,500 cal yr BP followed by a re-advance of Iliad Glacier and unnamed glacier. During the subsequent retreat foraminifera, reworked by the glacial fluctuation, were deposited in the glacial outwash fan while modern organic matter fell out of suspension. The second scenario is a full deglaciation between ~14,000-8,500 cal yr BP without subsequent re-advance. In this scenario foraminifera are reworked through turbidite flows and constant re-suspension prior to deposition. The difference in dates yielded by ramped pyrolysis and carbonate 14C methods may indicate the glacial retreat history of other Antarctic bays and fjords are more complex than previously recognized. The “gold standard” of dating Antarctic sediment cores, carbonate 14C dating, may not be as reliable as previously thought.