GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 106-9
Presentation Time: 9:45 AM


MATEO, Paula1, KELLER, Gerta1, ADATTE, Thierry2, BITCHONG, André2, SPANGENBERG, Jorge3, VENNEMANN, Torsten4, HEIZLER, Matthew5, HODGES, Kip6, MCDONALD, Christopher7, HOLLIS, Chris8 and STINNESBECK, Wolfgang9, (1)Department of Geosciences, Princeton University, Guyot Hall, Princeton, NJ 08544, (2)Institute of Geology and Paleontology, University of Lausanne, Anthropole, Lausanne, CH-2000, Switzerland, (3)Idyst, University of Lausanne, UNIL-Mouline, Bâtiment Géopolis, Lausanne, 1015, Switzerland, (4)Institute of Earth Surface Dynamics, University of Lausanne, Geopolis - CH-1015 Lausanne - Suisse, Lausanne, 1015, Switzerland, (5)New Mexico Geochronology Research Laboratory, New Mexico Bureau of Mines & Mineral Resources, 801 Leroy Place, New Mexico Tech, Socorro, NM 87801-4796, (6)School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85282, (7)School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, (8)GNS Science, Avalon, 5010, New Zealand, (9)Institute of Earth Sciences, Heidelberg University, Im Neuenheimer Feld 234-236, Heidelberg, 69120, Germany,

The age of the Chicxulub impact is still controversial. Impact spherules found at or near the Cretaceous-Paleogene boundary (KPB) in the North Atlantic, Caribbean, Belize and Guatemala are reworked in early Danian sediments above a KP hiatus [1-3]. But, in NE Mexico and Texas where impact spherules are beyond erosion by the Gulf Stream, they are found in late Maastrichtian sediments with the primary spherule layer predating the KPB by ~100 ky [4,5]. Recent discovery of pristine Chicxulub impact glass spherules on Gorgonilla Island, Colombia [6], and re-sampling of the section sheds new light on this controversy. Sediments consist of radiolarian-rich marls alternating with volcanic-rich turbidites depleted in calcite. Three closely spaced ~2 cm-thick spherule beds, two discontinuously present, overlie a late Maastrichtian erosion surface and have a similar mineralogical composition as the turbidites, suggesting spherule re-deposition marked by decreasing grain size and repetition of beds due to slumping. Spherule beds contain reworked Maastrichtian species and clay clasts with early Danian planktic foraminifera typical of zone P1a(2) about 150-200 ky after the KPB indicating re-deposition during the early Danian. Study of radiolaria is in progress. δ13Corg.carb values show no negative shift near the spherule bed, confirming a KPB hiatus, as also indicated by absence of significant Ni and Co enrichments. δ18O by laser ablation of spherules have a wide range of values (8.5 to 10.4‰) typical of andesitic-dacitic (~8‰) and rhyolitic glass (9 to 10‰), suggesting melt contaminated with sedimentary material. While these analyses confirm an impact origin, spherules with higher SiO2 content also have higher d18O values, indicating crystal fractionation processes or assimilation of sedimentary material. Preliminary 40Ar/39Ar dating of Gorgonilla impact spherules is currently underway at two laboratories.

[1] Keller et al., 2003. J Geol Soc London 160, 1-13. [2] Keller et al., 2013. Geol Mag 150, 885-907. [3] Mateo et al., 2016. Palaeogeogr Palaeoclimatol Palaeoecol 441, 96-115. [4] Keller et al., 2007. Earth Planet Sci Lett 255, 339-356. [5] Keller et al., 2009. J Geol Soc London 166, 393-411. [6] Bermudez et al., 2016. Terra Nova 28(1), 83-90.