georefid:2006-066612georefid:2006-066600SEDIS Publication Catalogue

ana.macario@awi.de

http://sedis.iodp.org/pub-catalogue/informationpointOfContact2011-06-23T00:00:00Zhttp://sedis.iodp.org/pub-catalogue/index.php?id=10.2973/odp.proc.sr.195.105.20042006-01-01publicationgeorefid:2006-066612doi:10.2973/odp.proc.sr.195.105.2004Dean, Simon M.University of Southampton, School of Ocean and Earth Sciences, Southampton, United KingdomauthorTexas A&M University, Ocean Drilling Program, College Station, TX, United StatespublisherdocumentDigitalIn: Shinohara, Masanao (editor), Salisbury, Matthew H. (editor), Richter, Carl (editor), Araki, Eiichiro, Barr, Samantha R., D'Antonio, Massimo, Dean, Simon M., Diekmann, Bernhard, Edwards, K. Michelle, Fryer, Patricia B., Gaillot, Philippe J., Hammon, William S., III, Hart, David, Januszczak, Nicole, Komor, Stephen C., Kristensen, Mette B., Lockwood, John P., Mottl, Michael J., Moyer, Craig L., Nakahigashi, Kazuo, Savov, Ivan P., Su Xin, Wei, Kuo-Yen, Yamada, Tomoaki, Proceedings of the Ocean Drilling Program; scientific results; seafloor observatories and the Kuroshio Current; covering Leg 195 of the cruises of the drilling vessel JOIDES Resolution; Apra Harbor, Guam, to Keelung, Taiwan; Sites 1200-1202; 2 March-2 May 2001195Natural gamma ray measurements are made routinely during core logging using the physical property multisensor track. The instrument provides a measure of the natural decay of radioactive elements in the core, expressed in counts per second, which is generally used as a proxy for the clay content of nonmarginal marine sediments. At Site 1201 spikes of increased gamma ray emissions, up to six times the average for the entire core over depth intervals on the order of 20-50 cm, are observed from the sediments within 50 m of the basement contact. The spikes show a strong correlation with sediment color variations, coinciding with red/brown layers within otherwise green/gray-colored sediments. In this paper, the gamma ray spectra obtained from 21 measurements using a 4-hr counting period are analyzed to obtain the absolute concentration of the radioactive elements K (sub 2) O, U, and Th in both the intervals with spikes and the intervals with relatively low count rates. In addition, the concentration of these elements is estimated using the spectra obtained from the routine 20-s counting period measurements and which, although exhibiting a great deal of scatter due to the high statistical uncertainty in the original measurements, are roughly similar to those obtained from the 4-hr counting period. Baseline concentrations for U (1 ppm) and Th (5 ppm) match published averages for the amount present in deep-sea clays; the peak concentrations measured correspond to an additional concentration of 100%-200%. The results are compared to those from downhole logging and shipboard inductively coupled plasma-atomic emission spectrometry measurements. The gamma ray spectra results do not support post-depositional fluid flow through the sediment as the source of the enrichment of radioactive elements. It is more likely that the spikes in the gamma ray emissions are simply the result of interbedding sediments from two different sources, one with relatively high concentrations of K (sub 2) O, U, and Th.completedGeochemistry of rocks, soils, and sedimentsOceanographycolordeep-sea environmentgamma-ray spectrageochemistryICP mass spectraisotopesLeg 195marine environmentmarine sedimentsmass spectraNorth PacificNorthwest PacificOcean Drilling ProgramODP Site 1201Pacific OceanPhilippine Seaphysical propertiesradioactive isotopessedimentsspectravariationsWest PacificX-ray fluorescence spectraurn:org.iodp:exp:195urnlargerWorkCitationcampaignurn:org.iodp:exp:195:site:1201urnlargerWorkCitationstudyurn:org.iodp:exp:195urnlargerWorkCitationcampaignEnglishgeoscientificInformation135.0500135.060019.170019.1800Available only on CD-ROM in PDF format and on the Web in PDF or HTMLapplication/pdfunknownSEDIS Publication Catalogue

ana.macario@awi.de

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