Quantifying Biogenic Versus Detrital Carbonates on Marine Shelf: An Isotopic Approach

Type Article
Date 2019-07
Language English
Author(s) Pasquier V.1, 2, Revillon Sidonie2, 3, Leroux EstelleORCID4, Molliex Stephane2, 5, Mocochain L.6, Rabineau MarinaORCID2, 7
Affiliation(s) 1 : Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot, Israël
2 : Laboratoire Geosciences Océan LGO, UMR 6538 (CNRS/Univ Brest/Univ Bretagne Sud), IUEM, Plouzané, France
3 : SEDISOR, IUEM, Plouzané, France
4 : IFREMER, Laboratoire Géodynamique et enregistrement Sédimentaire, Plouzané, France
5 : CRPG, UMR 7358, CNRS-Université de Lorraine, Vandœuvre-lès-Nancy, France
6 : Sorbonne Université, Institut des Sciences de la Terre de Paris (ISTeP), Paris, France
Source Frontiers In Earth Science (2296-6463) (Frontiers Media SA), 2019-07 , Vol. 7 , N. 164 , P. 10p.
DOI 10.3389/feart.2019.00164
Keyword(s) Sr-87/Sr-86(carbonate), detrital carbonate export, source-to-sink, glacial - interglacial, strontium isotope stratigraphy
Abstract

The terrigenous sedimentary budget of passive margins, records variations in past sedimentary fluxes, and thus can be used to infer past variations of Earth surface deformation processes or climate change. Accurate estimates of sediment fluxes over various times and spatial scales are therefore crucial. Traditionally, offshore sediment volume determination only considers siliciclastic accumulation, the carbonate fraction (i.e., CaCO3) being considered only as in situ production. Here we propose a new geochemical methodology to decipher and quantify the number of detrital carbonates in comparison to in situ produced biogenic carbonates. This isotopic approach enables considering the export of detrital carbonates and investigating its effect on sediment budgets. This study, located in the Gulf of Lion, is based on a 300 m long sediment borehole located near the shelf break and covering the last 500 000 years (i.e., five glacial-interglacial periods). Strontium isotope (87Sr/86Sr) of carbonate fractions (0.70809 to 0.70858) are significantly less radiogenic than modern seawater (i.e., 0.7092) and show fluctuations in agreement with stratigraphic and climatic variations. These results suggest an unsuspected high export of detrital carbonates from the catchment area during both glacial (between 55 and 85% of the sedimentary carbonate fraction) and interglacial (between 30 and 50%) conditions. Thus, not only do detrital carbonate fluxes need to be factored into sediment flux calculations, but these results also suggest that detrital carbonate components could potentially have a strong influence on bulk carbonate 87Sr/86Sr ratios when not obtained from micro drilled biogenic carbonates, such as the entirety of the Precambrian Sr chemostratigraphic record.

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