Mathematics – Logic
Scientific paper
May 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agusm.p43a..01k&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #P43A-01
Mathematics
Logic
4944 Micropaleontology (0459, 3030), 5420 Impact Phenomena, Cratering (6022, 8136), 1065 Major And Trace Element Geochemistry, 1630 Impacts Of Global Change (1225), 3030 Micropaleontology (0459, 4944)
Scientific paper
In March 2005 NSF-EAR supported the drilling of three holes by DOSECC, along the Brazos River, Falls County, Texas, about 1000 km from the impact crater in order to test earlier observations in NE Mexico and the Chicxulub crater that this impact predates the K-T boundary by about 300,000 years. The new Texas Mullinax cores and new outcrops recovered the most complete K-T sequences known in this area and a stratigraphic record which revealed: (1) the K-T boundary 90 cm above the event deposit that is commonly interpreted as impact tsunami, and (2) the discovery of the original Chicxulub impact ejecta layer 40 cm below the event deposit. Multidisciplinary biostratigraphic, sedimentological, geochemical and mineralogical analyses reveal that in the new Mullinax-1 core and the outcrop the K-T boundary is marked by the global K-T negative /?13C excursion, a major faunal turnover from Cretaceous to Tertiary dominated assemblages and the first appearances of Tertiary species in all microfossil groups (planktic foraminifera, nannofossils, palynomorphs). A major iridium anomaly was earlier reported coincident with these K-T characteristics at the classic Brazos-1 outcrop only 150 m to the east. The underlying 45 cm thick event deposit, interbedded in late Maastrichtian sediments, contains multiple depositional events with burrows, and near the base reworked and altered Chicxulub impact glass spherules in a clast-rich, shelly, glauconitic sandstone. The event deposits infill a channel and overlie an erosional surface. The original impact ejecta layer is in a claystone 40 cm below the event deposit and consists of a 3 cm thick layer of altered impact glass in the lower part of chron 29R and near the base of biozone CF1, which marks the last 300,000 years of the Cretaceous. The new Brazos results confirm the earlier results from NE Mexico and the crater core Yaxcopoil-1 that the Chicxulub impact predates the K-T boundary by about 300,000 years.
Adatte Th.
Baum G. R.
Berner Zsolt
Harting Markus
Keller Gerhard
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