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首页> 外文期刊>Newsletters on stratigraphy >The onset of Oceanic Anoxic Event 2 on the Arabian Shelf - mechanisms between organic matter deposition, sea-level, and palaeoceanography (Shilaif Basin, United Arab Emirates)
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The onset of Oceanic Anoxic Event 2 on the Arabian Shelf - mechanisms between organic matter deposition, sea-level, and palaeoceanography (Shilaif Basin, United Arab Emirates)

机译：The onset of Oceanic Anoxic Event 2 on the Arabian Shelf - mechanisms between organic matter deposition, sea-level, and palaeoceanography (Shilaif Basin, United Arab Emirates)

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摘要

In the late Cenomanian, palaeoenvironments on the Arabian Shelf were characterised by shallow-marine carbonate build-ups and extensive intra-platform basins. The hemipelagic carbonate succession of the Shilaif Basin (Abu Dhabi, United Arab Emirates) offers a continuous sedimentological record from a palaeoequatorial latitude. Carbon-isotope records from these shelf carbonates that span across the Cenomanian-Turonian boundary interval are characterised by low carbonate delta C-13 values that predate the positive carbon-isotope excursion related to Oceanic Anoxic Event 2. It is to date uncertain whether this late Cenomanian negative delta C-13 shift is diagenetically linked to the preservation of organic matter or if it indicates a global signal related to palaeoenvironmental change at the onset of OAE 2. To better understand the cause of this anomaly and to improve our understanding of global palaeoclimatic changes at the onset of OAE 2, we present a multiproxy study on two continuous successions from across the Shilaif Basin. The work includes high-resolution bulk carbonate carbon-isotope records, bio- and cyclostratigraphy, characterisation of organic matter, and elemental concentrations. The integration of available data provides precise chronostratigraphic control between sections and allows for reconstructions of detrital sediment influx, relative sea-level change, differential accumulation rates, and changes in redox conditions. Findings confirm a pronounced light carbonisotope anomaly preceding the characteristic heavy excursion relating to OAE 2. Orbital cyclicities obtained from core-scan greyscale images are in agreement with nannofossil biostratigraphy and suggest a duration of approximately 528-678 kyr for the negative and 194-250 kyr for positive delta C-13 CIEs in the late Cenomanian. The intra-basinal correlation presented in this study further supports evidence for a palaeoceanographic origin of the negative CIE, which appears to be unrelated to diagenetic processes. Integration of results suggests peak sea-levels in the late Cenomanian and a significant increase in surface-water productivity preceding the positive carbon-isotope excursion diagnostic for OAE 2. Organic matter preservation is asynchronous and was probably controlled by restriction, initiating from the South of the Shilaif Basin approximately 550-650 kyr before the positive CIE. Maximum organic matter preservation in the North coincides with the latest Cenomanian OAE 2 carbon-isotope excursion, suggesting open water exchange with the Neotethys. During OAE 2, the sedimentary record and present proxies suggest high-frequent changes in sea-level and sediment oxygenation possibly related to the 'Plenus' event.

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