Mathematics – Logic
Scientific paper
May 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agusm.p43a..02p&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #P43A-02
Mathematics
Logic
5420 Impact Phenomena, Cratering (6022, 8136)
Scientific paper
A core spanning the Cretaceous/Paleogene boundary (KTB) interval at Brazos -River, Texas, U.S.A. has been high resolution sampled and analyzed palynologically, with emphasis on organic-walled dinocysts. Stratigraphically, the first appearance date (FAD) of a Danian dinocyst taxon, Membranilarnacia tenella, is about 75 cm above, and the FAD of the global marker taxon for Lower Danian, Damassadinium californicum, is about 108 cm above the top of a distinct "event deposit". Both of the FAD's are in reasonable accordance with the onset of the P0 foraminifera zone at about 90 cm above the top of the "event deposit". The latter represents a lithologically complex unit about 35 cm in thickness, including layers of spherule ejecta at its base that are probably related to the Chicxulub impact event. With respect to relative sea-level changes, the ratio of terrigenous sporomorphs to marine dinocysts (t/m index) as well as the distribution of environmentally diagnostic dinocysts and algae taxa suggest a late highstand to possibly lowstand systems tract for most of the section, modified by parasequence cycles. Starting in the middle to upper P1a foraminifera zone, a distinct transgressive systems tract is indicated by both t/m index changes and the quantitative increase of diagnostic algae. Within the dinocysts fraction, changes in the ratio of tropical-subtropical to warm-temperate peridinioids (tropical/temperate ratio) reflect significant changes in the contribution of respective photic-zone water-masses throughout the section. The ratio is low at the base of the section. Within the proximate pre- and post- "event deposit" intervals it shows prominent peak abundances, followed by the minimum within the P0 foraminifera zone and low values throughout most of the Lower Danian. This is suggestive for considerable paleo- environmental fluctuations starting during pre- "event deposit" times already, finally approaching and stabilizing with new paleo-ecological boundary conditions towards and within the Lower Danian respectively. Based on these changes within photic-zone waters as well as on associated changes in oxygen and carbon stable isotopes of benthic foraminifera a model for paleo-climatical changes across the KTB interval is proposed.
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