Productivity Fluctuations and Orbital Cyclicity During Onset of Early to Middle Turonian Marine Red-Bed Formation (Austrian Eastern Alps)
Published:January 01, 2009
Ines Wendler, Jens Wendler, Stephanie Neuhuber, Michael Wagreich, 2009. "Productivity Fluctuations and Orbital Cyclicity During Onset of Early to Middle Turonian Marine Red-Bed Formation (Austrian Eastern Alps)", Cretaceous Oceanic Red Beds: Stratigraphy, Composition, Origins, and Paleoceanographic and Paleoclimatic Significance, Xiumian Hu, Chengshan Wang, Robert W. Scott, Michael Wagreich, Luba Jansa
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A section from the Ultrahelvetic units of Upper Austria comprises the transition from light-gray, upper-bathyal to middle-bathyal carbonates of Early Turonian age towards red-colored carbonates of the Middle Turonian. The total-organic-carbon content is very low throughout the section, but benthic foraminifera associations, especially high abundance of Tappanina laciniosa, indicate repeated phases of enhanced organic-matter flux and decreased oxygen concentrations at the seafloor. The overlying reddish layers are enriched in iron oxides and hydroxides and pyrite and may represent paleo-redox fronts that were related to periods of well oxygenated bottom waters, reduced sedimentation rates, and degradation of organic matter in the underlying sediments. Cyclic sedimentary packages consist of four marlstone-limestone couplets with upward-increasing bedding thickness, red carbonates at the base, and a gray limestone bed at the top. Based on carbon isotope stratigraphy, these packages reflect the 400 kyr eccentricity cycle, with the four marlstone-limestone couplets representing the 100 kyr cycle. Three 400-kyr-cycle boundaries are preceded by horizons with high T.laciniosa abundance and are followed by a paleo-redox front and red-bed deposition. Thus, there is indication of the temporary presence of a local oxygen-minimum zone during enhanced production at the end of each 400 kyr cycle, possibly linked to sea-level fluctuations. Organic-carbon fluxes seem to have decreased immediately above the cycle boundaries. Recycling of organic carbon could be responsible for the distinct carbon-isotope minima at the base of each cycle. Accumulation rates based on our orbital model suggest a switch from relatively uniform sedimentation rates in the Early Turonian to cyclic fluctuations of sedimentation rates in the Middle Turonian. The occurrence of three 400 kyr cycles between the main carbon-isotope excursions points to a 1.2 Myr periodicity, which may reflect the Earth’s long obliquity cycle. A long-term increase in bottom-water aeration from the Early to the Middle Turonian is evident from the increasing dominance of red sediments.
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Cretaceous Oceanic Red Beds: Stratigraphy, Composition, Origins, and Paleoceanographic and Paleoclimatic Significance
The occurrence of marine red beds has been known for at least 140 years, since Stúr (1860) and Gümbel (1861) first described them from the Púchov beds in the Carpathians and the Nierental beds in the Eastern Alps. A few biostratigraphic and sedimentological studies followed, particularly in European countries. However, detailed investigations on paleoceanographic and paleoclimatic implications related to Cretaceous marine red beds were initiated by Prof. Chengshan Wang, Dr. Xiumian Hu, and their colleagues. This collection of papers resulted from two collaborative research projects funded in part by UNESCO/IUGS International Geosciences Project IGCP 463 and IGCP 494. The IGCP 463 “Upper Cretaceous Oceanic Red Beds: Response to Ocean/Climate Global Change” (2002-2006) was led by Prof. Chengshan Wang (China University of Geosciences, Beijing, China), Prof. Massimo Sarti (Universitá Politecnica delle Marche, Italy), Dr. Robert Scott (University of Tulsa and Precision Stratigraphy Associates, USA), and Prof. Luba Jansa (Dalhousie University, Canada). The objective of IGCP 463 was to study major paleoceanographic phenomena recorded by sedimentary sequences in the world oceans. Cretaceous deposition changed several times from widespread organic-carbon-enriched shales that indicate a dysoxic to anoxic deep ocean environment, to mostly reddish clays and marls deposited in an oxic marine environment during the Late Cretaceous.