ICDP-USGS Workshop on Deep Drilling in the Central Crater of the Chesapeake Bay Impact Structure, Virginia, USA September 22-24, 2003 Herndon, Virginia PROCEEDINGS VOLUME Lucy E. Edwards, J. Wright Horton, Jr., and Gregory S. Gohn, compilers Prepared in cooperation with the International Continental Scientific Drilling Program (ICDP) 2004 U.S. Geological Survey Open-File Report 2004-1016 1 Foreword This volume contains the proceedings of the “ICDP-USGS Workshop on Deep Drilling in the Central Crater of the Chesapeake Bay Impact Structure, Virginia, USA,” which was held September 22-24, 2003, in Herndon, Virginia. This workshop was jointly sponsored by the International Continental Scientific Drilling Program (ICDP) and the U.S. Geological Survey (USGS). The proceedings begin with a brief summary of the workshop followed by the list of participants and a copy of the agenda. This proceedings volume contains two sets of abstracts. The first set of 17 abstracts is based on 29 poster presentations that were displayed at the workshop. The second set of 19 abstracts consists of research proposals that were submitted by members of the scientific community following the workshop. The abstracts are given here as submitted by the authors without further edit, except for the correction of some obvious typographical errors. Disclaimer This report is preliminary and has not been reviewed for conformity with the North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although all data and software released on this CD-ROM have been used by the USGS, no warranty, expressed or implied, is made by the USGS as to the accuracy of the data and related materials and (or) the functioning of the software. TABLE OF CONTENTS WORKSHOP SUMMARY .......................................................................................................... 4 LIST OF PARTICIPANTS........................................................................................................... 6 WORKSHOP PROGRAM WITH LINKS TO SLIDE PRESENTATIONS ............................... 8 POSTER PRESENTATIONS WITH LINKS TO ABSTRACTS.............................................. 12 PROPOSALS FOR FUTURE WORK (ABSTRACTS) ............................................................ 47 3 WORKSHOP SUMMARY. Gregory S. Gohn1, J. Wright Horton, Jr.1, and Lucy E. Edwards1, 1U.S. Geological Survey, 926A National Center, Reston, VA 20192, USA ([email protected]). Introduction. The International Continental and geophysical investigations of the Chesapeake Scientific Drilling Program (ICDP) and the U.S. Bay impact structure, summaries of the capabilities Geological Survey (USGS) sponsored a scientific of the ICDP Support Group and drilling capabilities workshop on “Deep Drilling in the Central Crater of of DOSECC, Inc. (Drilling, Observation, and the Chesapeake Bay Impact Structure.” The Sampling of the Earth’s Continental Crust), and workshop was held September 22-24, 2003, in discussion of first-order scientific questions that Herndon, Virginia. The purpose of the workshop could be addressed by deep drilling in the central was to review the results of previous investigations of crater. The first day concluded with an evening the Chesapeake Bay impact structure and to provide a poster session, where voluntary posters by workshop forum for creating scientific and operational plans for participants and USGS drill cores were examined and deep drilling in the structure’s central crater. Over 60 discussed. scientists represented 10 countries at the workshop. The second day began with a review of The late Eocene Chesapeake Bay impact structure sedimentary, climatic, and tectonic studies of middle is among the largest and best preserved of the known Tertiary to Quaternary (postimpact) sediments of the marine impact craters on Earth. This complex crater U.S. Mid-Atlantic continental margin. The morning lies buried at shallow to moderate depths beneath session continued with a lengthy panel and audience postimpact Cenozoic sediments of the Virginia discussion of the scientific objectives and Coastal Plain and adjacent Continental Shelf on the experiments, drilling strategy, site selection criteria, U.S. Atlantic continental margin. The diameter of funding sources, and logistics of a deep drilling the impact structure typically is cited as about 85 km. program in the Chesapeake Bay central crater. In the Principal subdivisions are a 38-km-wide central afternoon, participants divided into three working crater, which may approximate the location of the groups: (1) impact processes and products, (2) impact’s transient crater, and a surrounding 24-km- postimpact geology, and (3) hydrology. The second wide annular trough that primarily records late-stage day concluded with reports from the working groups. gravitational collapse. The third day consisted of moderated audience The coreholes and geophysical studies that discussions of a variety of issues, including the ultimately led to recognition and characterization of identification of standing science teams, drilling and the Chesapeake Bay impact structure began in the logging operations, drill-site and sampling protocols, late 1980’s and continued into the 1990’s. Since core storage, and publications. 2000, the USGS, the Hampton Roads Planning Identification of Scientific Issues. A significant District Commission, the Virginia Department of outcome of the workshop was the identification of Environmental Quality, and collaborating institutions scientific goals for the proposed drilling program. have conducted a second phase of multidisciplinary The goals were limited to research topics that could geophysical, corehole, and hydrologic investigations be addressed by core drilling in the central crater. of the impact structure (see summaries in Poag and Crater Structure and Morphology others, 2004, and Horton and others, in press). • Determine the crater depth Previous investigations have defined the location, • Determine the structural character of the cored size, structure, and inferred origin of the major segment of the central crater architectural elements of the Chesapeake Bay impact Crater Materials structure (Powars and Bruce, 1999; Powars, 2000; • Determine target composition and stratigraphy Poag and others, 2004; Horton and others, in press). beneath crater Collectively, over 2,000 km of seismic-reflection • Determine petrophysical properties of target data have been analyzed (Poag and others, 2004) and materials 8 new coreholes have been drilled, geophysically • Determine target chemistry and mineralogy for logged, and analyzed. However, none of the comparison with North American tektites coreholes were drilled in the central crater. • Search for meteorite component in crater materials Workshop Agenda. The workshop began on to identify projectile type September 22 with welcoming remarks by Charles G. • Determine isotopic ages for all suitable types of Groat, Director of the USGS, and P. Patrick Leahy, material USGS Associate Director for Geology. The first day • Determine fracture depth and distribution of the program featured reviews of previous corehole 4 • Determine the amount and distribution of melt should be submitted to ICDP in January 2004, and • Characterize the types of crater breccias and infer that additional geophysical studies by the USGS were their formative processes needed to provide adequate site characterization. • Quantify the volumes of breccia types and melts Drill-site selection was addressed in several • Determine the character of resurge and tsunami plenary and breakout sessions. These discussions sediments were guided by interpretations of the regional gravity • Determine stratigraphy of the crater fill map and the seismic-reflection profiles that cross the • Conduct paleomagnetic studies of shocked rocks central crater. Consideration was given to three and melt general locations characterized by distinctive gravity anomalies. The three locations are (1) the uplifted • Document levels and gradients of shock deformation central peak, (2) the “moat” or deepest part of the central crater that surrounds the central uplift, and (3) • Document impact damage in fossils the rim of the central crater. Each location addresses Borehole Geophysical Studies a different set of scientific issues with some overlap. • Collect a full suite of borehole geophysical logs for After considering the relative merits of each location determining petrophysical properties for addressing the major scientific questions listed • Directly measure petrophysical properties of core above, the “moat” was the consensus first choice for samples a proposed drill site. The other two locations were • Integrate core and log petrophysical data with consensus scientific choices for a second and (or) regional gravity, magnetic, seismic, and electrical third corehole, if possible, to understand the crater. conductivity surveys and with numerical models Impact - Postimpact Transition and Postimpact References Cited. Events Horton, J.W., Jr., Powars, D.S., and Gohn, G.S., in • Document the impact-produced local biotic crisis press, Studies of the Chesapeake Bay impact and recovery structure—Introduction and discussion, chap. A • Document the physical transition from the high- of Horton, J.W., Jr., Powars, D.S., and Gohn, energy impact environment to the normal shelf G.S., eds., Studies of the Chesapeake Bay impact environment structure—The USGS-NASA Langley corehole,