Calcareous nannoplankton, planktonic foraminiferal, and carbonate carbon isotope stratigraphy of the Cenomanian–Turonian boundary section in the Ultrahelvetic Zone (Eastern Alps, Upper Austria) |
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Authors: | Michael Wagreich Ana-Voica Bojar Reinhard F Sachsenhofer Stephanie Neuhuber Hans Egger |
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Institution: | aDepartment of Geodynamics and Sedimentology, Center for Earth Sciences, University of Vienna, A-1090 Vienna, Austria;bInstitute of Earth Sciences, Karl-Franzens University, A-8010 Graz, Austria;cDepartment Angewandte Geowissenschaften und Geophysik, MU Leoben, A-8700 Leoben, Austria;dGeological Survey of Austria, Neulinggasse 28, A-1030 Vienna, Austria |
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Abstract: | Ultrahelvetic units of the Eastern Alps were deposited on the distal European continental margin of the (Alpine) Tethys. The Rehkogelgraben section (“Buntmergelserie”, Ultrahelvetic unit, Upper Austria) comprises a 5 m thick succession of upper Cenomanian marl-limestone cycles overlain by a black shale interval composed of three black shale layers and carbonate-free claystones, followed by lower Turonian white to light grey marly limestones with thin marl layers. The main biostratigraphic events in the section are the last occurrence of Rotalipora and the first occurrences of Helvetoglobotruncana helvetica and Quadrum gartneri. The thickest black shale horizon has a TOC content of about 5%, with predominantly marine organic matter of kerogen type II. Vitrinite reflectance and Rock-Eval parameter Tmax (<424 °C) indicate low maturity. HI values range from 261 to 362 mg HC/g TOC. δ13C values of bulk rock carbonates display the well documented positive shift around the black shale interval, allowing correlation of the Rehkogelgraben section with other sections such as the Global Boundary Stratotype Section and Point (GSSP) succession at Pueblo, USA, and reference sections at Eastbourne, UK, and Gubbio, Italy. Sediment accumulation rates at Rehkogelgraben (average 2.5 mm/ka) are significantly lower than those at Pueblo and Eastbourne. |
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Keywords: | Cenomanian-Turonian boundary Northwestern Tethys Carbon isotopes Oxygen isotopes Nannofossils Organic geochemistry |
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