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Postimpact heat conduction and compaction-driven fluid flow in the Chesapeake Bay impact structure based on downhole vitrinite reflectance data, ICDP-USGS Eyreville deep core holes and Cape Charles test holes

By
MaryAnn Love Malinconico
MaryAnn Love Malinconico
U.S. Geological Survey, 926A National Center, Reston, Virginia 20192, USA
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Ward E. Sanford
Ward E. Sanford
U.S. Geological Survey, 431 National Center, Reston, Virginia 20192, USA
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J. Wright Horton, Jr.
J. Wright Horton, Jr.
U.S. Geological Survey, 926A National Center, Reston, Virginia 20192, USA
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Published:
January 01, 2009

Vitrinite reflectance data from the International Continental Scientific Drilling Program (ICDP)–U.S. Geological Survey (USGS) Eyreville deep cores in the central-crater moat of the Chesapeake Bay impact structure and the Cape Charles test holes on the central uplift show patterns of postimpact maximum-temperature distribution that result from a combination of conductive and advective heat flow. Within the crater-fill sediment-clast breccia sequence at Eyreville, an isoreflectance (~0.44% Ro) section (525–1096 m depth) is higher than modeled background coastal-plain maturity and shows a pattern typical of advective fluid flow. Below an intervening granite slab, a short interval of sediment-clast breccia (1371–1397 m) shows a sharp increase in reflectance (0.47%–0.91% Ro) caused by conductive heat from the underlying suevite (1397–1474 m). Reflectance data in the uppermost suevite range from 1.2% to 2.1% Ro. However, heat conduction alone is not sufficient to affect the temperature of sediments more than 100 m above the suevite. Thermal modeling of the Eyreville suevite as a 390 °C cooling sill-like hot rock layer supplemented by compaction-driven vertical fluid flow (0.046 m/a) of cooling suevitic fluids and deeper basement brines (120 °C) upward through the sediment breccias closely reproduces the measured reflectance data. This scenario would also replace any marine water trapped in the crater fill with more saline brine, similar to that currently in the crater, and it would produce temperatures sufficient to kill microbes in sediment breccias within 450 m above the suevite. A similar downhole maturity pattern is present in the sediment-clast breccia over the central uplift. High-reflectance (5%–9%) black shale and siltstone clasts in the suevite and sediment-clast breccia record a pre-impact (Paleozoic?) metamorphic event. Previously published maturity data in the annular trough indicate no thermal effect there from impact-related processes.

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GSA Special Papers

The ICDP-USGS Deep Drilling Project in the Chesapeake Bay impact structure: Results from the Eyreville Core Holes

Gregory S. Gohn
Gregory S. Gohn
U.S. Geological Survey, Reston, Virginia, USA
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Christian Koeberl
Christian Koeberl
Department of Earth & Planetary Sciences, Rutgers University, USA
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Kenneth G. Miller
Kenneth G. Miller
Museum für Naturkunde–Leibniz Institute at Humboldt University Berlin, Germany
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Wolf Uwe Reimold
Wolf Uwe Reimold
Museum für Naturkunde–Leibniz Institute at Humboldt University Berlin, Germany
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Geological Society of America
Volume
458
ISBN print:
9780813724584
Publication date:
January 01, 2009

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