Late Eocene impact ejecta; geochemical and isotopic connections with the Popigai impact structure

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doi: 10.1016/S0012-821X(00)00225-9
Author(s): Whitehead, J.; Papanastassiou, D. A.; Spray, J. G.; Grieve, R. A. F.; Wasserburg, G. J.
Author Affiliation(s): Primary:
University of New Brunswick, Planetary and Space Science Centre, Fredericton, NB, Canada
California Institute of Technology, United States
Natural Resources Canada, Canada
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, 181(4), p.473-487. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. Calif. Inst. Technol., Div. Geol. and Planet. Sci., Contrib. No. 8726(1057); Geol. Surv. Can., Contrib. No. 200038. 47 refs.; illus., incl. 2 tables, sketch map
Summary: Late Eocene microtektites and crystal-bearing microkrystites extracted from DSDP and ODP cores from the Atlantic, Pacific, and Indian oceans have been analyzed to address their provenance. A new analysis of Nd and Sr isotopic compositions confirms previous work and the assignment of the uppermost microtektite layer to the North American tektites, which are associated with the 35.5 Ma, 85 km diameter Chesapeake impact structure of Virginia, USA. Extensive major element and Nd and Sr isotopic analyses of the microkrystites from the lowermost layer were obtained. The melanocratic microkrystites from Sites 216 and 462 in the Indian and Pacific oceans possess major element chemistries, Sr and Nd isotopic signatures and Sm-Nd, TCHUR, model ages similar to those of tagamite melt rocks in the Popigai impact structure. They also possess Rb-Sr, TUR, model ages that are younger than the tagamite TCHUR ages by up to ∼1 Ga, which require a process, as yet undefined, of Rb/Sr enrichment. These melanocratic microkrystites are consistent with a provenance from the 35.7 Ma, 100 km diameter Popigai impact structure of Siberia, Russia, while ruling out other contemporaneous structures as a source. Melanocratic microkrystites from other sites and leucocratic microkrystites from all sites possess a wide range of isotopic compositions (ε(143Nd) values of -16 to -27.7 and ε(87Sr) values of 4.1-354.0), making the association with Popigai tagamites less clear. These microkrystites may have been derived by the melting of target rocks of mixed composition, which were ejected without homogenization. Dark glass and felsic inclusions extracted from Popigai tagamites possess ε(143Nd) and ε(87Sr) values of -26.7 to -27.8 and 374.7 and 432.4, respectively, and TCHUR and TUR model ages of 1640-1870 Ma and 240-1830 Ma, respectively, which require the preservation of initially present heterogeneity in the source materials. The leucocratic microkrystites possess diverse isotopic compositions that may reflect the melting of supra-basement sedimentary rocks from Popigai, or early basement melts that were ejected prior to homogenization of the Popigai tagamites. The ejection of melt rocks with chemistries consistent with a basement provenance, rather than the surface ∼1 km of sedimentary cover rocks, atypically indicates a non-surficial source to some of the ejecta. Microkrystites from two adjacent biozones possess statistically indistinguishable major element compositions, suggesting they have a single source. The occurrence of microkrystites derived from a single impact event, but in different biozones, can be explained by: (1) diachronous biozone boundaries; (2) post-accumulation sedimentary reworking; or (3) erroneous biozonation. Abstract Copyright (2000) Elsevier, B.V.
Year of Publication: 2000
Research Program: DSDP Deep Sea Drilling Project
ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 12 Stratigraphy, Historical Geology and Paleoecology; Alkaline earth metals; Asia; Atlantic Ocean; Biostratigraphy; Biozones; Cenozoic; Commonwealth of Independent States; Cores; Correlation; Deep Sea Drilling Project; Ejecta; Eocene; Foraminifera; Geochemistry; Globigerinacea; Globorotalia; Globorotaliidae; Impacts; Indian Ocean; Invertebrata; Isotope ratios; Isotopes; Major elements; Marine sediments; Metals; Microfossils; Microkrystites; Microtektites; Nd-144/Nd-143; Neodymium; North American strewn field; Ocean Drilling Program; Pacific Ocean; Paleogene; Popigay Structure; Porticulasphaera; Protista; Provenance; Radioactive isotopes; Rare earths; Rotaliina; Russian Federation; Samarium; Sediments; Sm-147/Nd-144; Sr-87/Sr-86; Stable isotopes; Strewn fields; Strontium; Tektites; Tertiary; Turborotalia; Upper Eocene
Record ID: 2000073435
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands

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