Effect of barite-bound Sr on detrital Sr isotope systematics in marine sediments
Wu, Jiawang; Liu, Zhifei; Michard, Annie; Tachikawa, Kazuyo; Filippidi, Amalia; He, Zhiwei; Hennekam, Rick; Yang, Shouye; Davies, Gareth R.; de Lange, Gert J.
(2022) Chemical Geology, volume 587, pp. 1 - 19
(Article)
Abstract
In marine sediments, the Sr content and isotope composition (87Sr/86Sr) of the terrigenous detrital component are widely used to track changes in provenance and related transport and weathering processes. Accurately separating detrital-Sr from other sedimentary Sr-phases is a prerequisite for such studies. Conventionally, it is assumed that Sr in the
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carbonate-free residue corresponds to detrital Sr alone. However, the decarbonated residue may contain barite with significant Sr content and a non-detrital 87Sr/86Sr composition; this may substantially affect the measured Sr signal. To examine this chronically overlooked phenomenon, the Mediterranean Sea is an ideal area because 1) detailed provenance studies have been done using Sr and 87Sr/86Sr of the residual fraction, and 2) enhanced levels of barite repeatedly occurred in association with distinct, organic-rich sapropel sediments. Here, we use the most-recent sapropel S1 interval to evaluate the effect of barite-bound Sr in the residual fraction after decarbonation. A total of 130 samples were taken from 10 cores in the eastern Mediterranean Sea (EMS) and 1 core in the western Mediterranean Sea. This selection represents a geographic and bathymetric coverage of the EMS and permits the basin-wide comparison between organic-rich and -lean sediments. After decarbonation using 1 M HCl solution, the residual sediments were subject to NH4Cl extraction (2 M, pH 7), known to selectively dissolve barite. Our results demonstrate the presence of Sr-bearing barite after traditional carbonate removal and its effect on the derived “detrital” Sr signature. This barite-Sr effect is considerable for samples with barite-Ba >400 μg/g in bulk sediment. The impact of barite is prominent if accompanied by a detrital provenance background of high 87Sr/86Sr (>0.713) or low Sr/Al (<1.0 mg/g). In such cases, removal of remaining barite is required to obtain an unbiased detrital Sr signal. We recommend an improved procedure for detrital Sr separation in marine sediments, with an additional NH4Cl leaching step to eliminate any remaining barite after decarbonation. This approach is particularly important for areas/times of high biological productivity, where sediments are often characterized by abundant barite content.
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Keywords: Barite, Barium (Ba), Marine sediments, Mediterranean Sea, Provenance, Sapropel, Sr isotopes, Strontium (Sr), Taverne, Geology, Geochemistry and Petrology
ISSN: 0009-2541
Publisher: Elsevier
Note: Funding Information: Many thanks are given to the captain & crew, scientists & technicians on board the cruises listed in Table 1 for core collections. We are indebted to Anja Reitz, Arrian Rutten, Caroline Slomp, David Gallego-Torres, Enno Schefuß, Patrick van Santvoort, Rinske Knoop, and Sanela Gusic for sediment processing and data analyses. We also thank Dineke van de Meent-Olieman, Helen de Waard, Ton Zalm, and Coen Mulder at Utrecht, Peijun Qiao, Hui Li, Pengfei Liu, Juan Xu at Tongji, as well as Richard Smeets and Mathijs van de Ven at VU Amsterdam for laboratory assistance and analyses. Philipp Böning and Caroline Slomp are acknowledged for comments on an earlier manuscript. We are grateful for the critical but constructive comments given by Matthew Fantle and six anonymous reviewers that all were very useful to improve our initial manuscripts. The efficient handling and guideline of Editor-in-Chief Michael Böttcher are highly appreciated. This work is financially supported by National Key R&D Program of China ( 2018YFE0202402 ), National Natural Science Foundation of China ( 41806064 , 42006060 ), and China Postdoctoral Science Foundation (2019T120352, 2018M640418). European Programmes MARFLUX ( MAST1-90022C ), PALEOFLUX ( MAS2-CT93-0051 ), and SAP ( MAS3-CT97-0137 ) are acknowledged for partially funding the cruises. The shiptime and logistics granted by CNR and NWO are appreciated. This study is part of JW's PhD project, funded by the CSC–UU PhD Program (CSC No. 201206260116 ; USES contribution 146). Funding Information: Many thanks are given to the captain & crew, scientists & technicians on board the cruises listed in Table 1 for core collections. We are indebted to Anja Reitz, Arrian Rutten, Caroline Slomp, David Gallego-Torres, Enno Schefuß, Patrick van Santvoort, Rinske Knoop, and Sanela Gusic for sediment processing and data analyses. We also thank Dineke van de Meent-Olieman, Helen de Waard, Ton Zalm, and Coen Mulder at Utrecht, Peijun Qiao, Hui Li, Pengfei Liu, Juan Xu at Tongji, as well as Richard Smeets and Mathijs van de Ven at VU Amsterdam for laboratory assistance and analyses. Philipp Böning and Caroline Slomp are acknowledged for comments on an earlier manuscript. We are grateful for the critical but constructive comments given by Matthew Fantle and six anonymous reviewers that all were very useful to improve our initial manuscripts. The efficient handling and guideline of Editor-in-Chief Michael Böttcher are highly appreciated. This work is financially supported by National Key R&D Program of China (2018YFE0202402), National Natural Science Foundation of China (41806064, 42006060), and China Postdoctoral Science Foundation (2019T120352, 2018M640418). European Programmes MARFLUX (MAST1-90022C), PALEOFLUX (MAS2-CT93-0051), and SAP (MAS3-CT97-0137) are acknowledged for partially funding the cruises. The shiptime and logistics granted by CNR and NWO are appreciated. This study is part of JW's PhD project, funded by the CSC–UU PhD Program (CSC No. 201206260116; USES contribution 146). Publisher Copyright: © 2021 Elsevier B.V.
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