XRF core-scanning signal interpretation in Miocene carbonate and siliciclastic contourite deposits (IODP sites U1387 and U1475)

Jens.Gruetzner [ at ] awi.de


Contourites are deposits formed by along-slope bottom currents and are therefore sensitive to changes in current velocity, sediments supply and paleoceanographic conditions. They are typically associated with high accumulation rates making these archives ideal for paleoenviromental reconstructions. Nevertheless, they are also occasionally affected by winnowing of fine particles and erosion/deposition of allochthonous material, which alters the grain-size and mineralogy. These processes can, as such, promote significant bias in proxy interpretation compared with other pelagic deposits. X-ray fluorescence (XRF) core-scanning is ideal to assess elemental variations in these high accumulation rate sequences. The comparison between lithological changes, Natural Gamma Ray and other parameters with XRF scanning data, along with statistical analysis can provide very useful information to support improved proxy interpretation. Using this approach at Site U1387, (detrital contourite system at Gulf of Cadiz), results indicate that the Zr/Al ratio represents a promising proxy for bottom current speed and show the transition from a hemipelagic to a contouritic system during the Miocene/Pliocene transition. Carbonate content and Ba/Al ratio appear to represent paleo-productivity variations and later to be completely overprinted by current activit y. At Site U1475 (carbonate contourite system at Agulhas Plateau) Zr content is just one artifact associated with high Sr content and the Ca/Sr ratio appears to be a more promising proxy for contourite reconstruction that is influenced by carbonate dissolution by deep corrosive waters. Comparing both locations we can conclude that proxies associated with the continuous background sediment settling over the seafloor (e.g. planktonic foraminifera) do not appear to be severely biased in countourite systems.

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XRF Core Scanning 2017, 20 Mar 2017 - 24 Mar 2017, National Taiwan University, Taiwan.
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Jiménez-Espejo, F. , Gruetzner, J. , Bahr, A. , Sierro, F. J. , Ohkouchi, N. , Hall, I. R. , Hemming, S. R. and LeVay, L. J. , Expedition 361 Scientists (2017): XRF core-scanning signal interpretation in Miocene carbonate and siliciclastic contourite deposits (IODP sites U1387 and U1475) , XRF Core Scanning 2017, National Taiwan University, Taiwan, 20 March 2017 - 24 March 2017 .

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