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doi:10.2204/iodp.proc.319.201.2014

Introduction

At Site C0009 of Integrated Ocean Drilling Program (IODP) Expedition 319 (NanTroSEIZE Stage 2: riser/riserless observatory), riser technology was used for the first time during an IODP drilling operation (see the “Expedition 319 summary” chapter [Expedition 319 Scientists, 2010a]). Drilling at Site C0009 provided in situ data for pore pressure, permeability, minimum principal stress magnitude, and real-time mud gas analyses. On the D/V Chikyu, cuttings obtained during riser drilling were carried by drilling mud from the seafloor into the mud tank, and cuttings were sampled at 5 m depth intervals. The drilling mud used for riser coring, which is a mixture of seawater, clay minerals (e.g., bentonite), polymers, alkaline solutions (e.g., sodium hydroxide), and organic compounds, can affect the results of subsequent analyses. Cuttings must therefore be carefully cleaned before analysis. Clean-up procedures before shipboard analysis were developed during preexpedition trials and are described in the “Methods” chapter (Expedition 319 Scientists, 2010b). Cuttings were recovered throughout the riser-drilled depth range (~700–1600 meters below seafloor [mbsf]) and were washed and analyzed shipboard (e.g., X-ray diffraction, X-ray fluorescence [XRF], and total carbon and nitrogen analysis) as described in the “Expedition 319 summary” chapter (Expedition 319 Scientists, 2010a). Aliquots for these samples were stored immersed in drilling mud at 4ºC at the Kochi Core Center, an IODP core repository. Interaction of the cuttings with the drilling mud during storage might cause, for example, chemical and physical degradation of cuttings with time.

Here we report the results of our study on temporal variations in the chemical composition of cuttings during 33 months of storage in drilling mud.

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