首页|Chemical isolation and isotopic analysis of terrigenous sediments with emphasis on effective removal of contaminating marine phases including barite
Chemical isolation and isotopic analysis of terrigenous sediments with emphasis on effective removal of contaminating marine phases including barite
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NSTL
Elsevier
The radiogenic isotope composition (e.g. Sr-87/Sr-86 and epsilon(Nd)) of the terrigenous fraction is commonly used to determine the provenance and transport history of sediments. In ocean sediments, the terrigenous fraction must be isolated prior to analysis to avoid contamination by marine phases. While the removal of calcium carbonate, organic matter, biogenic opal, authigenic coatings and adsorbed cations is widely advised, steps to remove all these phases are not consistently employed, and there is no standard procedure for the effective removal of marine barite. Marine barite is found throughout the world's oceans, particularly in regions of high export production, is highly enriched in strontium (Sr) and therefore has the potential to bias measurements of terrigenous Sr-87/Sr-86 towards seawater. Here we present results from sequential leaching experiments on marine sediments from the Atlantic and the Pacific Oceans to quantitatively determine the contaminating effect on Sr-87/Sr-86 and epsilon(Nd) exerted by the presence of barite and develop a protocol to successfully isolate the terrigenous fraction. Our results show that marine barite can skew measurements of terrigenous Sr-87/Sr-86 by >0.01 towards the Sr-87/Sr-86 value of seawater, and we highlight the importance of assessing the location-specific impact of barite contamination on terrigenous Sr-87/Sr-86. Our results show that marine barite can severely contaminate terrigenous Sr-87/Sr-86, even where marine barite accumulation rates are modest (< similar to 5 mg/m(3)/yr and <similar to 20 g C/m(2)/yr, respectively). Barite contains epsilon(Nd) in very low concentrations so barite contamination of terrigenous cm is not a major concern but an important aspect of our protocol is that it has minimal effect on terrigenous epsilon(Nd), allowing Sr-87/Sr-86 and cm to be analysed on identically cleaned aliquots. Our systematic graduated approach will help standardise Sr-87/Sr-86 data, allow for robust comparisons between sites, and will contribute to an improved understanding of the provenance, transport and weathering histories of windblown continental dust and riverine sediments.
NSTL
Elsevier
