Southeastern Section - 58th Annual Meeting (12-13 March 2009)
Paper No. 16-43
Presentation Time: 8:30 AM-12:30 PM


LYONS, Will and REYNOLDS, Jim, Science & Math, Brevard College, Brevard, NC 28712,

The peninsula Magallanes, centered ~40 km west of El Calafate, Santa Cruz, Argentina (50 24'S 72 53'W), is a quasi-circular feature that exhibits macro-scale radiating and annular drainage features typical of impact structures. The area is situated in Parque Nacional de los Glaciares in strongly deformed Cretaceous back-arc basin strata that were subjected to intense glacial scouring by glaciers descending from the Patagonian Ice Sheet, particularly the Perito Moreno glacier.

After identifying the feature using Google Earth, we travelled to the field site to collect preliminary data to attempt to verify an impact origin for the feature. Standard field and laboratory techniques were applied: 1) identifying the near circular structure through mapping and/or remote sensing, 2) identifying macroscopic evidence of an impact, 3) locating potential shock features, and 4) identifying other petrographic and mineral indicators.

Data were collected in greywacke sandstones along the SW and S borders of the peninsula which were easily accessible by road. Strike and dip measurements on joints were taken at regular intervals along the border, and samples were collected for petrographic analysis. Structural observations of the north side were made from a boat but no landing was attempted.

XRD and petrographic results revealed no high pressure quartz polymorphs. Fault and jointing patterns only marginally correlated with a circle and were more indicative of the strong bedrock deformation. We conclude that the morphology of the structure is a result of glaciation by the surrounding glaciers. Because 1) the Cretaceous strata of the peninsula are quartz-rich greywacke sandstones typical of abyssal fan deposits and 2) much of the surrounding bedrock is interbedded with shale, it is likely the glaciers split around the peninsula's more resistant bedrock. Although the results of this work refuted the original hypothesis, they confirm the origin of the peninsula by glacial differential erosion.

Southeastern Section - 58th Annual Meeting (12-13 March 2009)
General Information for this Meeting
Session No. 16--Booth# 43
Undergraduate Research (Posters)
Hilton St. Petersburg Bayfront Hotel: Grand Bay Ballroom
8:30 AM-12:30 PM, Friday, 13 March 2009

Geological Society of America Abstracts with Programs, Vol. 41, No. 1, p. 46

© Copyright 2009 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.