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Late Quaternary volcanic activity in Marie Byrd Land; potential (super 40) Ar/ (super 39) Ar-dated time horizons in West Antarctic ice and marine cores

T. I. Wilch, William C. McIntosh and N. W. Dunbar
Late Quaternary volcanic activity in Marie Byrd Land; potential (super 40) Ar/ (super 39) Ar-dated time horizons in West Antarctic ice and marine cores
Geological Society of America Bulletin (October 1999) 111 (10): 1563-1580

Abstract

Late Quaternary volcanic activity at three major alkaline composite volcanoes in Marie Byrd Land, West Antarctica, is dominated by explosive eruptions, many capable of depositing ash layers as regional time-stratigraphic horizons in the West Antarctic Ice Sheet and in Southern Ocean marine sediments. A total of 20 eruptions at Mount Berlin, Mount Takahe, and Mount Siple are recorded in lava and welded and nonwelded pyroclastic fall deposits, mostly peralkaline trachyte in composition. The eruptions, dated by the (super 40) Ar/ (super 39) Ar laser-fusion and furnace step-heating methods, range in age from 571 to 8.2 ka. Tephra from these (super 40) Ar/ (super 39) Ar-dated Marie Byrd Land eruptions are identified by geochemical fingerprinting in the 1968 Byrd Station ice core. The 74 ka ice-core record contained abundant coarse ash layers, with model ice-flow ages ranging from 7.5 to 40 ka, all of which were previously geochemically correlated to the Mount Takahe volcano. We identify a one-to-one geochemical and age correlation of the youngest (ca. 7.5 ka) tephra layer in the Byrd ice core to an 8.2+ or -5.4 ka (2sigma uncertainty) pyroclastic deposit at Mount Takahe. We infer that the 20-30 ka tephra layers in the Byrd ice core actually were erupted from Mount Berlin, on the basis of age and geochemical similarities. If products of these youngest, as well as the older (super 40) Ar/ (super 39) Ar-dated eruptions are identified by geochemical fingerprinting in future ice and marine cores, they will provide the cores with independently dated time horizons. More than 12 (super 40) Ar/ (super 39) Ar-dated tephra layers, exposed in bare ice on the summit ice cap of Mount Moulton, 30 km from their inferred source at Mount Berlin, range in age from 492 to 15 ka. These englacial tephra layers provide a minimum age of 492 ka for the oldest isotopically dated ice in West Antarctica. This well-dated section of locally derived glacial ice contains a potential "horizontal ice core" record of paleoclimate that extends back through several glacial-interglacial cycles. The coarse grain size and density of the englacial tephra (mean diameters 17-18 mm, densities 540-780 kg/m (super 3) ), combined with their distance from source, indicate derivation from highly explosive Plinian eruptions of Mount Berlin.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 111
Serial Issue: 10
Title: Late Quaternary volcanic activity in Marie Byrd Land; potential (super 40) Ar/ (super 39) Ar-dated time horizons in West Antarctic ice and marine cores
Affiliation: Albion College, Department of Geological Sciences, Albion, MI, United States
Pages: 1563-1580
Published: 199910
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 47
Accession Number: 1999-066501
Categories: Quaternary geologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 9981
Illustration Description: illus. incl. 3 tables, sketch maps
S87°00'00" - S60°00'00", W165°00'00" - W40°00'00"
Secondary Affiliation: New Mexico Institute of Mining and Technology, Socorro, NM, USA, United StatesNew Mexico Bureau of Mines and Mineral Resources, Socorro, NM, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 199922
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