In situ tektite glass and upper Eocene impact stratigraphy of the Southeastern United States

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Author(s): Harris, R. Scott; Roden, Michael F.; Schroeder, Paul A.; Duncan, Mack S.; Anderson, John R.; Gullett-Young, Cheryl; Elliott, W. Crawford
Author Affiliation(s): Primary:
Georgia State University, Geosciences, Atlanta, GA, United States
University of Georgia, Geology, United States
Georgia Perimeter College, Science, United States
Benjamin E. Mays High School, United States
Volume Title: 2010 AAPG annual convention & exhibition; abstracts volume
Source: Abstracts: Annual Meeting - American Association of Petroleum Geologists, Vol.2010; AAPG 2010 annual convention & exhibition, New Orleans, LA, April 11-14, 2010. Publisher: American Association of Petroleum Geologists and Society for Sedimentary Geology, Tulsa, OK, United States
Note: In English. 5 refs.
Summary: Harris et al. [1] report the occurrence of shocked quartz grains at the base of the Twiggs Clay Member of the upper Eocene Dry Branch Formation in east-central Georgia. They conclude that the grains are ejecta from the ca. 35.5 Ma Chesapeake Bay impact and that the horizon represents the likely stratum from which the Georgia tektites (georgiaites) have been reworked. During subsequent investigations [2, 3], we have identified the first in situ specimens of impact glass in the ejecta layer. They are clear to yellowish-brown vesicular tektite fragments 0.3 to 1.2 mm long. Although their major element compositions (wt%: SiO2=63.8, Al2O3=15.4, TiO2=1.1, FeO=4.6, MgO=2.0, CaO=4.4 Na2O=5.7, K2O=2.9) are similar to low-silica microtektites from both the southern Caribbean and DSDP Site 612 (New Jersey slope), refractory element ratios suggest that they melted from the same target materials as other relatively proximal glasses (i.e., DSDP Site 612 and georgiaites). Plotting [ln(MgO/SiO2)]/TiO2 vs. [ln(SiO2/Al2O3)]/TiO2 distinguishes that group from more distal (northern Gulf of Mexico) and most distal (bediasites and Barbados) glasses in the North American strewn field. The differences probably reflect the vertical variability in sedimentary cover sequences near ground zero. The identification and correlation of the Chesapeake Bay ejecta horizon in the Southeastern US provides a convenient benchmark for stratigraphic studies in addition to providing important clues to impact processes--shock metamorphism, melt production and distribution, and regional environmental effects--in a major marine impact. We are investigating possible glasses and shock-deformed minerals in upper Eocene strata from Alabama to North Carolina that may record the Chesapeake Bay event and/or other impacts associated with a protracted comet [4] or asteroid [5] shower during the late Eocene. [1] Harris, R. S. et al. (2004) Geology, 32, 717-720; [2] Harris, R. S. et al. (2007). The Late Eocene Earth: Hothouse, Icehouse, and Impacts--Abstracts with Program and Field Trip Guide (GSA Penrose Conference), 32-33; [3] Harris, R. S. et al. (2009) Lunar Planet. Sci. Conf., XL, #2502; [4] Farley, K. A. et al. (1998) Science, 280, 1250-1253; [5] Tagle, R. and Claeys, P. (2004) Science, 305, 492.
Year of Publication: 2010
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Atlantic Ocean; Caribbean Sea; Cenozoic; Chesapeake Bay impact structure; Correlation; DSDP Site 612; Deep Sea Drilling Project; Dry Branch Formation; East-central Georgia; Eastern U.S.; Ejecta; Eocene; Framework silicates; Georgia; IPOD; Impactites; Impacts; Leg 95; Metamorphic rocks; Metamorphism; North Atlantic; Paleogene; Quartz; Shock metamorphism; Silica minerals; Silicates; Southeastern U.S.; Stratigraphic units; Tektites; Tertiary; Twiggs Clay; United States; Upper Eocene
Coordinates: N384912 N384913 W0724625 W0724626
Record ID: 2013006399
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data supplied by American Association of Petroleum Geologists, Tulsa, OK, United States