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Pleistocene-Holocene Boundary and Wisconsinan Substages, Gulf of Mexico

By
John H. Beard
John H. Beard
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Published:
January 01, 1973

Late Pleistocene-Holocene climatic fluctuations and environmental conditions in the Gulf of Mexico are reflected by changes in the vertical distribution of planktonic foraminifers in the bottom sediments. The events are related closely by radiocarbon dates to continental Wisconsinan glacial-interglacial substages. The almost inverse relationship between abundances of two species, Globorotalia menardii (warm) and Globorotalia inflata (cold), allows recognition of three major episodes of climatic cooling during the Wisconsinan. Moreover, minor fluctuations of climate are reflected in detail by the combined distributional patterns of warm- versus cold-water planktonic species. Paleotemperature curves quantitatively derived from the frequency ratio of warm- versus cold-water species from the Gulf of Mexico are strikingly similar to the oxygen-isotope curve of Emiliani (1966) from the Caribbean for about the last 75,000 yrs.

Morphologic changes in the Globorotalia menardii group and the withdrawal of cold-water species, such as Globorotalia inflata, from the Gulf of Mexico characterize two climatically distinct assemblages. The older assemblage corresponds to the late Pleistocene and is characterized by Globorotalia menardii flexuosa (warm) and by Globorotalia inflata (cold). Withdrawal of Globorotalia inflata occurred between 4,000 and 11,000 yrs ago and corresponds closely to an incursion of abundant

Globorotalia tumida, Globorotalia ungulata, and other warm-water species. This faunal boundary is interpreted to represent the transition from the last glacial to postglacial conditions in the Gulf of Mexico. Assuming a constant average rate of deposition for pelagic sediment, the age estimated for the boundary agrees very closely with that of the radiocarbon bracketed date of 7,000 yrs B.P. of Frye and others (1968) for the Wisconsinan-Holocene boundary.

Paleontologie events and paleotemperature curves from the Gulf of Mexico correlate almost exactly with those from the Caribbean and adjacent Atlantic. Widely differing opinions expressed by several authors on Wisconsinan nomenclature in the marine section are based on correlations using different paleontological criteria and different geochemical dating methods. Carbon-14 determinations reported in this study indicate ages considerably younger than other published dates for what certainly appears to be a paleontologically equivalent unit. Climatic events recognized in the Gulf of Mexico can be correlated rather precisely on the basis of radiocarbon dates with the continental Wisconsinan glacial-interglacial substages and, therefore, development of an independent nomenclature for the marine section is neither necessary nor desirable.

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Contents

GSA Memoirs

The Wisconsinan Stage

Robert F. Black
Robert F. Black
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Richard P. Goldthwait
Richard P. Goldthwait
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H. B. Willman
H. B. Willman
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Geological Society of America
Volume
136
ISBN print:
9780813711362
Publication date:
January 01, 1973

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