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From source to sink; glacially eroded, Late Devonian algal "cysts" (Tasmanites) delivered to the Gulf of Mexico during the last glacial maximum

Barry Kohl, B. Brandon Curry and Merrell Miller
From source to sink; glacially eroded, Late Devonian algal "cysts" (Tasmanites) delivered to the Gulf of Mexico during the last glacial maximum
Geological Society of America Bulletin (August 2020) 133 (3-4): 849-866


The source of reworked Devonian algal "cysts" in last glacial maximum (LGM) sediment in the Gulf of Mexico is traced to their host black shales, which ring the southwestern Great Lakes. The source-to-sink pathway includes intermediate storage in fine-grained LGM glacial lacustrine sediment and till. The "cysts" are pelagic chlorophyllous algae (Tasmanites and Leiosphaeridia), collectively referred to herein as tasmanitids. Radiocarbon dates of syndepositional Gulf of Mexico foraminifera, derived from accelerator mass spectrometry, bracket the Gulf of Mexico sediment age with common tasmanitids from 28.5+ or -0.6 to 17.8+ or -0.2 cal kyr B.P. Approximately 1400 km north of the Gulf of Mexico, tasmanitids are abundant in Upper Devonian black shales (New Albany, Antrim, and Ohio Shales) that ring the Michigan, Illinois, and Appalachian intracratonic basins. Tasmanitids were eroded from bedrock and incorporated in glacial sediment dating from ca. 28.0-17.6 cal kyr B.P. by the Lake Michigan, and Huron-Erie lobes of the Laurentide Ice Sheet. The physical characteristics of tasmanitids are ideal for long-distance transport as suspended sediment (density: 1.1-1.3 g/cc, size ranging from 63 mu m to 300 mu m), and these sand-sized tasmanitids traveled with the silt-clay fraction. Thus, the source-to-sink journey of tasmanitids was initiated by subglacial erosion by water or friction, sequestering in till or glaciolacustrine sediment, re-entrainment and suspension in meltwater, and final delivery in meltwater plumes to the Gulf of Mexico. River routes included the Mississippi, Illinois, Ohio, Wabash, Kaskaskia, and many of their tributaries. Reworked Devonian tasmanitids are a previously unrecognized link between their occurrence in deep-water deposits of the Gulf of Mexico and the late Wisconsin glacial history of the Upper Mississippi Valley. We propose that tracking occurrences of tasmanitid concentrations from the source area to sink, along with adjunct proxies such as clay minerals, will facilitate a more refined analysis of the timing and duration of megafloods. This study also demonstrates that isotopically dead carbon, from reworked Devonian tasmanitid "cysts," can contaminate radiocarbon dating of LGM bulk sediment samples toward older ages.

ISSN: 0016-7606
EISSN: 1943-2674
Serial Title: Geological Society of America Bulletin
Serial Volume: 133
Serial Issue: 3-4
Title: From source to sink; glacially eroded, Late Devonian algal "cysts" (Tasmanites) delivered to the Gulf of Mexico during the last glacial maximum
Affiliation: Tulane University, Department of Earth and Environmental Sciences, New Orleans, LA, United States
Pages: 849-866
Published: 20200824
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
Number of pages: 18
References: 109
Accession Number: 2021-004959
Categories: PaleobotanyQuaternary geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sketch maps, 2 plates, 3 tables, sect.
N39°00'00" - N45°00'00", W90°00'00" - W85°00'00"
Secondary Affiliation: University of Illinois at Urbana-Champaign, USA, United StatesThe irf group, Tulsa, OK, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2022, 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: 202104
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