Carbonate recrystallisation and organic matter maturation in heat-affected sediments from the Shaban Deep, Red Sea.

Botz, Reiner, Schmidt, Mark , Kus, Jolanta, Ostertag-Henning, Christian, Ehrhardt, Axel, Olgun, Nazli, Garbe-Schönberg, Dieter and Scholten, Jan (2011) Carbonate recrystallisation and organic matter maturation in heat-affected sediments from the Shaban Deep, Red Sea. Open Access Chemical Geology, 280 (1-2). pp. 126-143. DOI 10.1016/j.chemgeo.2010.11.003.

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Supplementary data:

Abstract

Parasound profiles across the Shaban Deep in the Red Sea indicate turbiditic transport of surface sediments from the topographic hight (basalt ridge) into the interior of the deep. This is supported by petrographical and (isotope-) geochemical evidence in the East Basin of the Shaban Deep where the presence of variable mixtures of authochtonous and allochthonous sediment compounds had been found.

The uppermost 170 cm of both sediment cores 17008-1 and 17009-3 reveal “normal” stable oxygen isotope values for the planktonic foraminifera G. ruber near -1 ‰ which is indicative for carbonate formation in Red Sea surface water around 27°C. However, below 182 cm in core 17008-1 highly variable δ 18O values for G. ruber between 0.26 and -10.68 ‰ occur which are not the result of temperature-controlled oxygen isotope fractionation between foraminiferal carbonate and Red Sea surface water. The lowest δ18O values of -10.68 ‰ measured for highly-altered foraminifera shells suggests carbonate precipitation higher than 90°C.

Organic petrographical observations show a great diversity of marine-derived macerals and terrigenous organic particles. Based on petrographical investigations sediment core 17008-1 can be subdivided in intervals predominantly of authochtonous character (i.e. 1, 3, 5 corresponding to core depths 0-170 cm, 370-415 cm, 69-136 cm), and allochthonous/thermally altered character (e.g. 2, 4 corresponding to core depths 189-353 cm, 515-671 cm). Allochthonous/thermally altered material displays a wide to an extremely wide range of maturities (0.38-1.42 % Rr) and also natural coke particles were found.

Similarily, the organic geochemical and pyrolysis data indicate the predominance of well-preserved, immature algal and bacterial remains with a minor contribution of land plant material. Sediments below 170 cm (core 17008-1) contain contributions of re-sedimented pre-heated material most likely from the area of the basaltic ridge. This is documented by individual coke particles reduced hydrogen indices and elevated Tmax values up to 440°C.

An “oil-type” contribution (evidenced by mature biomarkers, hopene/hopane ratios, elevated background fluorescence, n-alkane distribution) is also present in the sediments which most likely originated at greater depth and impregnated the surface sediments.

The heat source responsible for recrystallisation of foraminiferal carbonate and maturation of organic particles in Shaban Deep sediments most likely is attributed to modern basalt extrusions which now separate the Shaban Deep subbasins.

Document Type: Article
Keywords: Geochemistry; Red Sea; carbonate diagenesis; sediments; turbidite; organic matter maturation
Research affiliation: Kiel University
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.chemgeo.2010.11.003
ISSN: 0009-2541
Projects: Future Ocean
Expeditions/Models/Experiments:
Date Deposited: 01 Dec 2010 09:46
Last Modified: 07 Dec 2017 12:42
URI: http://oceanrep.geomar.de/id/eprint/10255

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