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doi:10.2204/iodp.proc.336.202.2014 Methods and materialsX-Ray fluorescence scanningSediment cores were analyzed by XRF scanning. XRF scanning is a semiquantitative method for stepwise geochemical characterization of sediment cores. For detailed description of the method, see Tjallingii et al. (2007). From the chemical data, information about the relative abundances of calcium carbonate and clay can be revealed. The XRF data are merged with visual estimates of foraminiferal sand versus nannofossil ooze. XRF core scanner data were collected every 1 cm using generator settings of 10 kV, a current of 0.2 mA, and a sampling time of 20 s directly at the split core surface of the archive half with the XRF core scanner (AVAATECH SERIEL No. 2) at MARUM–University of Bremen (Germany). All XRF data are reported in XRFDATA in “Supplementary material.” The split core surface was covered with a 4 µm thin SPEXCerti Prep Ultralene1 foil to avoid contamination of the XRF measurement unit and desiccation of the sediment. The data reported here have been acquired by a Canberra X-PIPS silicon drift detector (SDD; Model SXD 15C-150-500) with 150 eV X-ray resolution, the Canberra digital spectrum analyzer DAS 100, and an Oxford Instruments 50W XTF5011 X-ray tube with rhodium (Rh) target material. Raw data spectra were processed by the analysis of X-ray spectra by the iterative least-squares software (WIN AXIL) package from Canberra Eurisys. Lithologic unitsResults of shipboard studies during Expedition 336 indicate varied sediment lithologies ranging from nannofossil ooze to foraminiferal sand with occasional layers containing rock debris from the surrounding basement outcrops (see the “Expedition 336 summary” chapter [Expedition 336 Scientists, 2012]). The purpose of this data report is to augment the shipboard core descriptions by systematic core scanning data and observations in order to provide a more comprehensive account of the sediment lithostratigraphy of North Pond. In addition to XRF scanning results, we used natural gamma ray (NGR) and magnetic susceptibility data (see the “Expedition 336 summary” chapter [Expedition 336 Scientists, 2012]) in characterizing the sediment. We visually identified intervals of foraminiferal sand layers while preparing cores for XRF scanning. Some of these layers were not analyzed by the XRF core scanner, as the poor recovery of the thicker sandy intervals produced a retreated and uneven split core surface, which was unsuitable for X-ray scanning. In the lithologic profiles, visual observations, core scanning data, NGR, and susceptibility were combined to understand the entire sedimentary sequence. Lithostratigraphic units were defined using the following criteria:
These units merely account for geochemical enrichments or lithologic properties but do not indicate the actual presence of distinct mineral phases. |
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