Skip to Main Content
Skip Nav Destination
GEOREF RECORD

Physical setting and tephrochronology of the summit caldera ice record at Mount Moulton, West Antarctica

Nelia W. Dunbar, William C. McIntosh and Richard P. Esser
Physical setting and tephrochronology of the summit caldera ice record at Mount Moulton, West Antarctica
Geological Society of America Bulletin (August 2008) 120 (7-8): 796-812

Abstract

A site on the shoulder of the ice-filled summit crater of Mount Moulton, located at an elevation of 2800 m in West Antarctica, exhibits a 400-m-long section of exposed blue ice and intercalated tephra layers. A total of 48 tephra layers are observed. Many are thick (up to 10 cm) and coarse (pumice up to 3 cm). Detailed dip measurements and global positioning system (GPS) mapping reveals a simple geometry of parallel tephra layers all exhibiting consistent dips. The simple stratigraphy of the tephra layers suggests that although the local ice is thinned, based on the boudinaged appearance of the thicker tephra layers, it is otherwise undeformed. Local measured ice motion and ablation rates are similar, averaging around 3 cm/yr for the 4-yr measurement period. Most of the Mount Moulton tephra layers are trachytic, and are derived from Mount Berlin, a still thermally active volcano located approximately 30 km away to the west. Eight of the tephra layers at the Mount Moulton site have been directly dated, using (super 40) Ar/ (super 39) Ar geochronology of potassic feldspar phenocrysts, to (in stratigraphic order from top to base of the blue ice section) 10.5+ or -2.5; 24.7+ or -1.5; 92.1+ or -0.9; 104.9+ or -0.6; 118.1+ or -1.3; 135.6+ or -0.9; 225.7+ or -11.6; and 495.6+ or -9.7 ka. The depth-age curve for the Mount Moulton site, based on these radioisotopic ages, is qualitatively similar to that of the Siple Dome ice core, also in West Antarctica. Although not part of the West Antarctic ice sheet, the Mount Moulton site certainly contains some of the oldest known ice in West Antarctica, and provides a long and detailed climate record.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 120
Serial Issue: 7-8
Title: Physical setting and tephrochronology of the summit caldera ice record at Mount Moulton, West Antarctica
Affiliation: New Mexico Institute of Mining and Technology, Earth and Environmental Science Department, Socorro, NM, United States
Pages: 796-812
Published: 200808
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 62
Accession Number: 2008-104164
Categories: Quaternary geologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 2008025
Illustration Description: illus. incl. 2 tables, sketch maps
S76°00'00" - S76°00'00", W135°00'00" - W135°00'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200836
Close Modal

or Create an Account

Close Modal
Close Modal