A geochemical application of the ITRAX scanner to a sediment core containing eastern Mediterranean sapropel units
J. Thomson, I. W. Croudace, R. G. Rothwell, 2006. "A geochemical application of the ITRAX scanner to a sediment core containing eastern Mediterranean sapropel units", New Techniques in Sediment Core Analysis, R. G. Rothwell
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The ITRAX micro-X-ray fluoresence (XRF) core scanner has been applied in a sediment geochemistry investigation. The core sections selected contain examples of the organic-rich sedimentary units (sapropels) that form periodically in the eastern Mediterranean basin. Sapropels are visually obvious from their dark coloration, but the ITRAX X-radiograph also reveals physical property changes that result mainly from the high pore-water content of sapropels. A consideration of wavelength-dispersive XRF data from discrete samples of the most recent sapropel (S1) was made along with the set of elements reported by the ITRAX instrument’s energy-dispersive XRF system over core sections containing S1. This allowed selection of a suite of eight inter-element ratios or element integrals through which characteristic features of sapropel development and geochemistry were revealed. While recognizing that the measured XRF element integrals from the ITRAX do not have an exact constant relationship with element concentration over changing sediment types, this combination of ratios provides significant information for geochemical interpretation. These include evidence for: (i) the presence of high Corg contents in the visual sapropel from Ba/Ti and Br/Cl ratios; (ii) a thinning of the original sapropel thickness by post-depositional oxidation from Mn/Ti and Cu/Ti ratios; (iii) pyrite authigenesis in the residual visual sapropel from Fe/Ti and S/Cl ratios and the As integral; and (iv) aragonite formation in and around the sapropel from the Sr/Ca ratio. These same ratios were then used to interpret ITRAX data from a deeper section of the same core containing the older sapropel S3, where the same characteristics, including the relict post-depositional oxidative thinning of the original unit, could be identified with only minor differences of detail. Directions of supply of Fe, As and Cu into the sapropels could be inferred from profile shapes.
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Marine sediment cores are the fundamental data source for information on seabed character, depositional history and environmental change. They provide raw data for a wide range of research including studies of climate change, palaeoceanography, slope stability, oil exploration, pollution assessment and control, seafloor survey for laying cables, pipelines and construction of seafloor structures. During the last three decades, a varied suite of new technologies have been developed to analyse cores, often non-destructively, to produce high-quality, closely spaced, co-located downcore measurements. These techniques can characterize sediment physical properties, geochemistry and composition in unprecedented detail. Palaeoenvironmentally significant proxies can now be logged at decadal, and in some cases, annual or sub-annual scales, allowing highly detailed insights into climatic history and associated environmental change. These advances have had a profound effect on many aspects of the Earth Sciences and our understanding of the Earth's history.
In this volume, recent advances in analytical and logging technology and their application to the analysis of sediment cores are presented. Developments in providing access to core data and associated datasets, and advances in data mining technology in order to integrate and interpret new and legacy datasets within the wider context of seafloor studies are also discussed.