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Thursday, November 14, 2013

Evidence for high salinity of Early Cretaceous sea water from the Chesapeake Bay crater, by W. E. Sanford et al., Nature 503

Nature, 503 (2013) 252-256; doi:10.1038/nature12714

Evidence for high salinity of Early Cretaceous sea water from the Chesapeake Bay crater

Abstract

High-salinity groundwater more than 1,000metres deep in the Atlantic coastal plain of the USA has been documented in several locations12, most recently within the 35-million-year-old Chesapeake Bay impact crater345. Suggestions for the origin of increased salinity in the crater have included evaporite dissolution6, osmosis6 and evaporation from heating7 associated with the bolide impact. Here we present chemical, isotopic and physical evidence that together indicate that groundwater in the Chesapeake crater is remnant Early Cretaceous North Atlantic (ECNA) sea water. We find that the sea water is probably 100–145 million years old and that it has an average salinity of about 70 per mil, which is twice that of modern sea water and consistent with the nearly closed ECNA basin8. Previous evidence for temperature and salinity levels of ancient oceans have been estimated indirectly from geochemical, isotopic and palaeontological analyses of solid materials in deep sediment cores. In contrast, our study identifies ancient sea water in situ and provides a direct estimate of its age and salinity. Moreover, we suggest that it is likely that remnants of ECNA sea water persist in deep sediments at many locations along the Atlantic margin.

http://www.nature.com/nature/journal/v503/n7475/full/nature12714.html

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