Integrated, High-Resolution Magneto-, Bio-, and Chemostratigraphy of the Cretaceous-Paleogene Sediments of the James Ross Basin, Antarctica

KIRSCHVINK, J.; TOBIN, T.; WARD, P.; STEIG, E.; OLIVERO, E. B.; SMITH, D.; BONIFACIE, M.; EILER, J.; RAPALINI, A.; HILBURN, I.

Iguazu, Brasil

Simposio; 2010 Meeting of the Americas; 2010

American Geophysical Union

On Seymour Island, Antarctic Peninsula, strata of the Haslum CragSandstone and López de Bertodano Formation preserve about 900meters of fossil-rich marine fine-grained sediments of Maastrichtian andDanian age. Although previous biostratigraphic analyses have revealedfive ammonite assemblages through these formations, the onlychronostratigraphic tie points within the sequence have been theCretaceous-Paleogene boundary and a few Sr isotope measurements ondimitobellid belemnites. The lack of diagenetic alteration as indicated byabundant presence of aragonic shells preserving iridescent nacre, and thecomplete presence of all ammonites, argues that this is one of the highestresolutionK/T boundary sections known. Previous investigators haveavoided paleomagnetic work in the James Ross Basin due to theproblems of the generally unconsolidated sediments being disrupted bypermafrost cycling. However, we discovered that every ~ 10m or sothroughout the sequence there are usually horizons of early-diageneticcalcareous concretions that are laterally-continuous and demonstrablyundisturbed by such post-depositional soft-sediment processes.Paleomagnetic and rock-magnetic study of these concretions reveals astable, two-component natural remanent magnetization, usually with a softcomponent removed by low-temperature and low alternating-fielddemagnetization. A more stable, two-polarity characteristic componentremains after this, which has a good match to the global geomagneticpolarity time scale. Using the improved chronology implied from thismagnetostratigraphy, and isotopic data from molluscan fossils thatpreserve iridescent nacre, we present a new high-resolution isotopicrecord for the prelude to this extinction event.DE: [0444] BIOGEOSCIENCES / Evolutionary