13. Impact-Related Processes: ICDP-USGS Deep Corehole in the Central Crater of the Chesapeake Bay Impact Structure
The late Eocene (ca. 35.5 Ma) Chesapeake Bay impact structure is one of Earth's largest and best preserved "wet-target" impact craters. Special characteristics of interest to the impact community include the structure's size (85 km diameter), its rheologically layered water-sediment-rock target, its relative youth and lack of tectonic deformation, its inferred association with the North American tektite strewn field, and its good accessibility beneath post-impact sediments on an intra-plate continental shelf. An international group of scientists, including USGS researchers, has proposed drilling a 2.2-km deep corehole into the center of this impact structure to the International Continental Scientific Drilling Program (ICDP). The proposed coring builds on a recent drilling program conducted in the outer part of the crater by the USGS and affiliated agencies and on available geophysical data for the entire impact structure.
The proposed corehole will be drilled through the covering post-impact sedimentary section, through the entire breccia sequence in the deeper part of the central crater (the moat) that surrounds the central uplift, and into rocks of the crater floor. Drilling is proposed for the late summer and early fall of 2005; samples will be available to project scientists for examination shortly thereafter.
Applications are sought for a postdoctoral fellow to conduct research and to coordinate the sampling program for this international research effort. The postdoctoral research will be conducted within the context of a wide-ranging international research program focused on the ICDP core. The incumbent will conduct research on selected topics from the following subject areas, depending on his/her qualifications and experience:
- Mineralogical studies of high-pressure minerals and shock features in minerals to determine variations in the levels, pressures, and gradients of shock metamorphism in a large complex crater formed in a marine environment.
- Geochemical and isotopic studies of impactites, including melts, to search for evidence of meteorite components and to determine characteristics of the impact projectile.
- Sedimentological studies to understand the physical processes of formation of different impact-breccia types, such as seawater-resurge, tsunami, fallback, and collapse breccias, and of post-impact sedimentation. Sedimentary breccias produced by the catastrophic surge of ocean water back into the collapsing crater are typical of impacts on continental shelves, including the Chesapeake Bay impact structure. The ICDP core and other Project cores will provide samples for the sedimentologic, petrologic, and stratigraphic study of these widespread impact deposits.
- Petrophysical studies involving direct measurements of properties of cored materials, and interpretation of the results in context of borehole and regional geophysical data and numerical models of crater formation.
- Paleomagnetic studies of the core to improve the modeling of regional magnetic anomalies associated with crater features (such as the central-crater margin, moat, and central peak) and to develop a magnetostratigraphy of impactites and post-impact deposits.
- Hydrothermal mineralogical, geochemical, and (or) isotopic studies to understand the thermochemical evolution of a large marine impact crater, including the cooling history and thermal gradients, as well as chemical and environmental implications.
- Hydrogeochemical and (or) isotopic studies to understand the presence, evolution, distribution, and significance of saline ground water in the Chesapeake Bay impact structure.
- Studies to test and implement new technologies for rapid, automated mineralogical and geochemical mapping of drill cores.
In addition to research, the postdoctoral fellow will have important responsibilities as Sampling Coordinator for the ICDP core. This function will provide opportunities to develop world-wide scientific contacts and potential research collaborations. Sampling Coordinator duties will include the tracking of sample requests and sample disbursements, implementation and enforcement of sampling protocols, and curatorship of core. These duties are expected to require one-quarter of the incumbent's time. Experience with core drilling and sampling, and experience on a large scientific drilling project are very helpful.
Proposed Duty Station: Reston, VA
Areas of Ph.D.: Impact processes, mineralogy, geochemistry, sedimentology, petrophysics, paleomagnetism, or ground-water geochemistry.
Qualifications: Applicants must meet one of the following qualifications: Research Geologist
(This type of research is performed by those who have backgrounds for the
occupations stated above. However, other titles may be applicable depending
on the applicant's background, education, and research proposal. The final
classification of the position will be made by the Personnel specialist.)
Research Advisor(s): Gregory Gohn, (703) 648-4382, ggohn@usgs.gov; Wright Horton, (703) 648-6933, whorton@usgs.gov; David Powars, (703) 648-4325, dpowars@usgs.gov; Ward Sanford, (703) 648-5882, wsanford@usgs.gov
Personnel Office contact: Rosetta Alexander, (703) 648-7468, ralexand@usgs.gov
U.S. Department of the Interior, U.S. Geological Survey
URL: http://geology.usgs.gov/postdoc/2006/opps/opp13.html
Direct inquiries to Rama K. Kotra at rkotra@usgs.gov
Maintained by Mendenhall Postdoctoral Fellowship Program Web Team
Last modified: 12:06:18 Tue 24 Aug 2004
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