2007 GSA Denver Annual Meeting (28–31 October 2007)
Paper No. 116-4
Presentation Time: 1:30 PM-5:30 PM

PHYSICAL PROPERTIES OF THE ICDP-USGS EYREVILLE CORE, CHESAPEAKE BAY IMPACT STRUCTURE

PIERCE, Herbert A. and MURRAY, James B., Reston, VA 20192, hpierce@usgs.gov

During 2005 the International Continental Scientific Drilling Program and the U.S. Geological Survey (USGS) cored the 35.8 million-year-old Chesapeake Bay impact structure (CBIS) near the southern end of the Delmarva Peninsula. The Eyreville A and B hole was cored from 125 to 1,766 m depth with about 90 percent recovery. Borehole logging equipment problems, and a collapsed coastal plain core-hole below 1,099 m, prevented all but temperature and natural-gamma data collection within the drill rods. The lack of physical property information prompted us to select sections of the CBIS core for scanning with the USGS Geotek multi-sensor core logger (MSCL) in Menlo Park, California. Data from the MSCL included density, P-wave velocity, magnetic susceptibility, resistivity, and fractional porosity. Cores were sampled at one-centimeter intervals using core photos to allow visual comparison of data and core. The Exmore resurge sediments (444 to 600 m) have P-wave velocities that average 1,538 m/s, density 1.99 g/cm3, magnetic susceptibility 5.6 (cgs), fractional porosity 0.45, and resistivity 5.7 ohm-m. Slumped Cretaceous sediments (~600 to 1,096 m) have an average p-wave velocity of 1,704 m/s, density 2.22 g/cm3, magnetic susceptibility 2.4, fractional porosity 0.31, and resistivity 10.4 ohm-m. Granite blocks (1,096 to 1,371 m) have an average P-wave velocity of 3,970 m/s, density 2.51 g/cm3, magnetic susceptibility 372.4, fractional porosity 0.15, and resistivity 18.6 ohm-m. Sand and lithic blocks beneath the granite (1,371 to 1,393 m) have an average P-wave velocity of 2,959 m/s, density 2.40 g/cm3, magnetic susceptibility 8.9, fractional porosity 0.26, and resistivity 412 ohm-m. Suevite and lithic breccia (1,393 to ~1,550 m) have an average P-wave velocity of 5,208 m/s, density 2.22 g/cm3, magnetic susceptibility 27.8, fractional porosity 0.32, and resistivity 374 ohm-m. Schist and pegmatite near the bottom of the corehole (1,393 to 1,756 m) have an average P-wave velocity of 4,722 m/s, density 2.50 g/cm3, magnetic susceptibility 21.2, fractional porosity 0.16, and resistivity 244 ohm-m. In detail CBIS physical property variations are complex. Density vs P-wave velocity plots within the granite, for example, show data clusters that suggest that at least five different granite types are present in the core.

2007 GSA Denver Annual Meeting (28–31 October 2007)
General Information for this Meeting
Session No. 116--Booth# 97
The Chesapeake Bay Impact Structure: Results from the 2005–2006 ICDP-USGS Deep Drilling Project (Posters)
Colorado Convention Center: Exhibit Hall E/F
1:30 PM-5:30 PM, Monday, 29 October 2007

Geological Society of America Abstracts with Programs, Vol. 39, No. 6, p. 313

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