Skip to Main Content
Book Chapter

Postimpact alteration of sedimentary breccias in the ICDP-USGS Eyreville A and B cores with comparison to the Cape Charles core, Chesapeake Bay impact structure, Virginia, USA

By
Daniel Larsen
Daniel Larsen
Department of Earth Sciences, University of Memphis, Memphis, Tennessee 38152, USA
Search for other works by this author on:
Elizabeth C. Stephens
Elizabeth C. Stephens
Department of Earth Sciences, University of Memphis, Memphis, Tennessee 38152, USA
Search for other works by this author on:
Vladimir B. Zivkovic
Vladimir B. Zivkovic
Department of Earth Sciences, University of Memphis, Memphis, Tennessee 38152, USA
Search for other works by this author on:
Published:
January 01, 2009

In this study, we extend the knowledge of postimpact alteration processes through an investigation of mineralogy and petrology of 24 samples from the Exmore Formation and sedimentary megablock intervals in the Eyreville borehole within the Chesa-peake Bay impact structure and comparisons to similar studies of cored intervals of the Cape Charles borehole. The bulk mineralogical studies reveal quartz, feldspars (microcline and albite), muscovite, smectite-vermiculite clays, and kaolinite with variable quantities of pyrite, zeolites, calcite, and chlorite. X-ray diffraction analysis of the clay (<2 μm) fraction of samples indicates that the clays are dominated by expandable clays with lesser quantities of illite, kaolinite, glauconite, and mixed-layered clays. The expandable clays include smectite, vermiculite, and smectite-vermiculite intergrade varieties; illite interlayering is minimal (generally, <10% illite layers). Thin section and scanning electron microscope petrography in the Exmore breccia show evidence for extensive authigenic expandable clay in the matrix and dispersed pyrite lepispheres and fine calcite rhombs. Grain alteration includes feldspar dissolution and albitization, glauconite recrystallization, and dissolution and expandable-clay replacement of micas. Taken together, the results indicate that low-temperature alteration (maximum temperatures 60–80 °C) is prevalent in the sedimentary clast–rich intervals in the Eyreville cores, and the maximum effects are observed between 600 and 970 m depth.

In comparison, the Exmore Formation from the Cape Charles borehole, 8 km to the southwest and overlying the central peak of the inner crater, shows more advanced authigenesis with Fe-rich chlorite, common quartz overgrowths, and mixed-layered illite-smectite clay with as much as 20% interlayered illite. A low-temperature hydrothermal mineral assemblage is documented in suevite and crystalline-clast breccia at depths of 725–820 m in the Cape Charles borehole.

The fine-grained clastic target material and contained seawater are argued to have limited initial target melting and initial crater-floor temperatures in the Chesa-peake Bay impact structure to an even greater degree than that of other marine craters targeted in consolidated sedimentary substrates. Subsequent hydrothermal circulation was confined to the central uplift and neighboring fractured zones, whereas alteration in the overlying sedimentary breccias involved conductive heat flow, reaction with hypersaline pore fluids, and minor fluid flow into more porous, permeable sedimentary blocks adjacent to the central uplift.

You do not currently have access to this article.

Figures & Tables

Contents

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
Search for other works by this author on:
Christian Koeberl
Christian Koeberl
Department of Earth & Planetary Sciences, Rutgers University, USA
Search for other works by this author on:
Kenneth G. Miller
Kenneth G. Miller
Museum für Naturkunde–Leibniz Institute at Humboldt University Berlin, Germany
Search for other works by this author on:
Wolf Uwe Reimold
Wolf Uwe Reimold
Museum für Naturkunde–Leibniz Institute at Humboldt University Berlin, Germany
Search for other works by this author on:
Geological Society of America
Volume
458
ISBN print:
9780813724584
Publication date:
January 01, 2009

References

Related

Citing Books via

A comprehensive resource of eBooks for researchers in the Earth Sciences

Related Articles
Related Book Content
Close Modal
This Feature Is Available To Subscribers Only

Sign In or Create an Account

Close Modal
Close Modal