Resolving aspects of past glaciations by dating exposed rock surfaces using aluminum-26 and beryllium-10 produced in situ: Wright Valley, Southern Victoria Land, Antarctica and the southeasternmost ridge of the Appalachian mountains, northeast United States

• Main Author: Macchiaroli, Paola Emilia
• Format: Text
• Language: English
• Published: ScholarlyCommons 1995
• Subjects: Geology; Victoria Land; Wright Valley; Orestes; Wilson Piedmont Glacier; Antarc*; Antarctica
• Online Access: https://repository.upenn.edu/dissertations/AAI9543117

Recent histories of glaciations along the southeasternmost ridge of the Appalachian Mountains, United States and along the Wright Valley, Antarctica were determined from concentrations of $\sp{26}$Al(T$\sb{1/2}$ = 0.7 Ma) and $\sp{10}$Be (T$\sb{1/2}$ = 1.5 Ma) in quartz produced by cosmic-rays. Measurements were made by accelerator mass spectrometry (AMS). The $\sp{26}$Al/$\sp{10}$Be method permits the dating of quartz-rich rocks with exposures $<$ 5 $\times$ 10$\sp6$ years and can distinguish continuous exposures from exposures interrupted by ice or sediment cover. To compare the glacial dynamics along the coastal and inland areas of Wright Valley, seventy-six samples were collected from (1) Mt. Fleming, (2) Mt. Orestes, and (3) terrain adjacent to and protruding through the Wilson Piedmont Glacier (WPG). Exposure times for Mt. Fleming indicate that while the summit has been ice-free for at least 5.5 Ma, the lower slopes have experienced more recent ice cover. Samples from Mt. Orestes reveal an erosion-controlled western slope and an alpine-glaciated southern slope; the summit has been ice free $>$1.9 Ma. The most-recent withdrawal of ice from the terrain adjacent to the WPG began $>$84 ka ago; an earlier period of ice withdrawal occurred $>$260 ka ago. Calculated maximum erosion rates range from 0.02-15.22 mm/ka. Thirty-two samples were collected along the southeasternmost ridge of the Appalachian Mountains from three regions characterized by stratigraphic evidence of glaciation. The $\sp{26}$Al/$\sp{10}$Be exposure times resolve three episodes of deglaciation along the ridge, with exposures northeast of the Wisconsinan terminal moraine (WTM) of $\sim$15 ka, exposures southwest of the WTM of $\sim$40 ka, and exposures farther southwest of $\sim$80 ka. Highly variable $\sp{26}$Al/$\sp{10}$Be ratios are explained by attenuated production at depth, and samples brought to the surface by plucking or block erosion. Plucking and block-erosion models estimate the thickness of rock loss at 300-150 cm northeast of the WTM, and 250-127 cm southwest of the WTM. Re-exposure times (since plucking) average $\sim$14.5 ka northeast of the WTM. Calculated erosion rates do not exceed 35.8 mm/ka.