Surface exposure geochronology using cosmogenic nuclides : applications in Antarctic glacial geology

• Main Author: Brook, Edward J.
• Format: Thesis
• Language: English
• Published: Massachusetts Institute of Technology and Woods Hole Oceanographic Institution 1993
• Subjects: Geochronometry; Radiocarbon dating; Glaciers; Antarctic; Ross Sea; McMurdo Sound; East Antarctic Ice Sheet; Transantarctic Mountains; Sirius; Taylor Glacier; Arena Valley; Antarc*; Ice Sheet
• Online Access: https://hdl.handle.net/1912/5578

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and Woods Hole Oceanographic Institution September 1993 Cosmogenic 3He, 26A1, and 10Be have been measured in a variety of Antarctic glacial deposits in the McMurdo Sound-Dry Valleys region. The goals of this project were to provide age constraints for Antarctic glacial events, to investigate production mechanisms of 3He, lOBe, and 26 A1 in terrestrial rocks, to constrain the importance of loss of 3He from quartz due to diffusion, and to refine methods of exposure-age dating. Moraines deposited in Arena Valley by the Taylor Glacier, an outlet glacier of the East Antarctic Ice Sheet, have exposure ages from ~120 kyr to 2 myr. 10Be and 3He ages of 122 ± 29 and 134 ±54 kyr, respectively, for the Taylor II moraine are consistent with deposition during isotope stage Se (~ 120 kyr) and with aerial expansions of the East Antarctic Ice Sheet during interglacial periods. Mean 10Be exposure ages for older moraines in the valley are 362 ± 26 kyr (Taylor III), 1.1 ± 0.1 myr (Taylor IVa) and 1.9 ± 0.1 myr (Taylor IVb). Because these older moraines were deposited at most ~200m above the Taylor II limit their ages suggest that major ice sheet advances during the last 2 myr have been broadly similar in magnitude to changes during the last glacial-interglacial cycle. 10Be ages for stratigraphically older drift deposited by the Taylor Glacier allow extension of this conclusion to ~ 3 myr. lOBe measurements in high altitude, pre-Pleistocene glacial deposits in the Dry Valleys preclude rapid uplift of the Transantarctic Mountains (400-1000 m/myr) suggested by controversial biostratigraphic studies of Sirius Group tills. Comparison of measured lOBe concentrations in Sirius Group deposits with those predicted with a model of the effects of uplift on 10Be production suggests minimal uplift of the Transantarctic Mountains over the last 3 myr. 3He, 10Be and 26A1 ages for the "late Wisconsin" Ross Sea ...