|2011 GSA Annual Meeting in Minneapolis (9–12 October 2011)|
|Paper No. 117-13|
|Presentation Time: 9:00 AM-6:00 PM|
SEARCH FOR EXTRATERRESTRIAL SIGNATURES OF A POSSIBLE IMPACT EVENT IN THE DIAMICTITE/CAP CARBONATE TRANSITIONS AFTER SNOWBALL EARTH GLACIATIONS (STURTIAN, MARINOAN), OTAVI GROUP, NW-NAMIBIA
GYOLLAI, Ildiko1, POPP, Friedrich2, MADER, Dieter1, and KOEBERL, Christian3, (1) Department of Lithospheric Research, University of Vienna, Althanstrasse 14, Vienna, A-1090, Austria, email@example.com, (2) Department of Geodynamics and Sedimentology, University of Vienna, Althanstrasse 14, Vienna, A-1090, Austria, (3) Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria, also of the Natural History Museum, Burgring 7, A-1010 Vienna, Austria|
The idea of this topic is based on earlier results of our group, who in 2004 found an iridium (Ir) anomaly within drill-core-samples from the diamictite/cap carbonate transition in Zambia, which was explained as accumulation of cosmic dust on an ice sheet with low sedimentation rates. The so-called Snowball Earth hypothesis states that the Sturtian (710 Ma) and Marinoan glaciations (635 Ma) were of global extent and may have lasted for several million years. Our samples were collected from conspicuous transition layers on top of the glaciogenic Chuos (Sturtian) and Ghaub (Marinoan) formations of the Neoproterozoic Otavi Group in NW-Namibia.
The mineralogical composition of the samples was studied using the petrographic microscope, X-ray powder diffraction, cathodoluminescence microscopy, and micro-Raman spectrometry. Instrumental neutron activation analyses were utilized for the geochemical study.
Normal impact ejecta are well-known to contain marker minerals, such as Cr- and Ni- spinels, as well as microtektites and a variety of spherules. In our samples, however, only minerals characteristic for the environment of the local carbonate platform, such as quartz, detrital dolomite, mica, clay minerals, and several minerals of a green-schist facies tectono-metamorphic overprint during break-up of Rodinia, e.g., pyrite and chlorite, were found until now. According to the cathodoluminescence studies, all quartz is mostly of diagenetic origin (no CL color) and occurs as fracture-filling mineral with several generations of carbonate-cement (micrite and block cement). In terms of geochemistry, the Fe/Ni, Ni/Cr, Co/Cr ratios are all near or below normal crustal ratios and the concentration of Ir is under the detection limit in bulk samples. However, element concentrations of the bulk samples are highly diluted with carbonate, study of the residue after carbonate dissolving procedure might provide better results.
Thus, at this time we have not been able to confirm the presence of any definitive impact markers in our samples. Before abandoning the impact hypothesis, additional analyses are planned to look for impact evidence in the Snowball Earth cap carbonates. These include the search for geochemical anomalies in terms of trace element measurements of the separated silt fraction, and isotope analyses.
2011 GSA Annual Meeting in Minneapolis (9–12 October 2011)
General Information for this Meeting
|Session No. 117--Booth# 343|
Impact Cratering on the Earth, Moon, and Planets: Remote, Field, and Lab Studies (Posters)
Minneapolis Convention Center: Hall C
9:00 AM-6:00 PM, Monday, 10 October 2011
Geological Society of America Abstracts with Programs, Vol. 43, No. 5, p. 307
© Copyright 2011 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.