The Benthic Foraminiferal Record from the Bathyal Gulf of Mexico During the Last Glacial–Postglacial Transition
Richard A. Denne, Barun K. Sen Gupta, 2003. "The Benthic Foraminiferal Record from the Bathyal Gulf of Mexico During the Last Glacial–Postglacial Transition", Micropaleontologic Proxies for Sea-Level Change and Stratigraphic Discontinuities, Hilary Clement Olson, R. Mark Leckie
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Examination of the benthic foraminifera from the northwestern Gulf of Mexico slope (90–95o W; 283–1341 m) reveals widespread changes in their assemblages during the transition from the most recent sea-level lowstand (last glacial maximum) to the current highstand (interglacial). These glacial assemblages are defined by Q-mode cluster and R-mode principal component analyses of both relative abundance and presence/absence data from 61 samples dated at 15 ka. Distinct bathymetric positions can be assigned to the assemblages, except in the case of a deltaic outflow assemblage. They are interpreted to be associated with water masses, and basin-wide changes in water-mass position and chemistry at the glacial–postglacial transition are reflected in assemblage changes. Most important is the switch from North Atlantic Intermediate Water (NAIW), which was found in the Gulf during the last glacial maximum, to Subantarctic Intermediate Water (SAIW), which is found in the modern Gulf. This water-mass shift allowed several species associated with SAIW (e.g., Bulimina alazanensis and Osangularia culter) to reenter the Gulf after the last glacial interval. The position of several water-mass boundaries were found to differ between the two time periods, causing the upper depth limits of some species to change with time. The benthic foraminiferal record in a core (water depth 726 m) shows three faunal events during and after the deglaciation; apparently, these events are related to water-mass shifts at 13 and 11 ka and a change in the substrate organic matter at 4.5 ka.
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Micropaleontology and biostratigraphy play vital roles for deciphering the stratigraphic record produced by changes in relative sea level, interpreting the history of global sea-level change, and testing models for the causes of sea-level fluctuations due to the variable influences of tectonics, glacio-eustasy, and climate. The stratigraphic architecture developed in response to changing eustasy, accommodation space, and sediment supply along continental margins, in epicontinental seas, and on carbonate platforms can be interpreted using the tools of marine micropaleontology. Microfossils provide chronostratigraphic control and a wealth of paleoenvironmental information about depositional environments as well as post-depositional changes to those environments. This volume demonstrates clearly that micropaleontologic proxies of environmental change provide a powerful dimension to the interpretive potential of stratigraphic sequences produced by changes in relative sea level and eustasy. Studies in the volume range from paralic to bathyal environments, span Pennsylvanian through Holocene stratigraphy, encompass a variety of microfossil groups and include a wide spectrum of techniques and paleoenvironmental proxies. The volume has been designed for graduate students and professionals interested in a wide range of subjects.