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Abstract:
Investigating the gas hydrate and hydrocarbon distribution of the Tuaheni Landslide Complex (TLC) was one of the main targets of IODP expedition 372 on the Hikurangi Margin east of New Zealand's North Island. Site U1517 was drilled into the creeping part of the TLC to depths of 205 mbsf passing through the base of the slide mass at shallower depth and the BSR just above the base of the hole. Logging while drilling (LWD) and pore water data reveal the occurrence of gas hydrates at roughly 105 – 160 mbsf with high saturations in thin coarse-grained sediments. Infrared imaging was used to quickly sample and freeze gas hydrate-bearing core sections in liquid nitrogen. Macroscopically, no gas hydrates could be observed. Coarse layers of the preserved core sections are investigated in on-shore labs using microscopy to look for gas hydrates, gas chromatography to measure degassed core sections, and Raman Spectroscopy to measure gas hydrate compositions – if applicable. Further, a large number of slightly overpressurized voids could be sampled throughout the length of the sediment core before cutting the core liners. This allows for a very good characterization of the gas composition with depth. Gas and isotopic composition of light hydrocarbons above, within and below the gas hydrate-bearing sediments were determined. The gas composition shows a close relationship with the gas hydrate occurrence.
