Temperature and resistivity profile of drill hole CRP-2A

In the northern part of McMurdo Sound (Ross Sea, Antarctica), drillhole CRP-2/2A targeted he western margin of the Victoria Land basin to investigate Neogene to Palaeogene climatic and tectonic history by obtaining continuous core and downhole logs. The background of the project and its detailed aims, methods used and results so far are summarized in Cape Roberts Science Team (1999). The CRP-2A drillhole extended to 625 mbsf (meters below seafloor) with an average of 95 % recovery of Oligocene to Quaternary sediments. Most of the downhole logging tools were run to the bottom of the hole. The first measurement after drilling operations was the temperature and salinity measurements, which were completed in two phases down to 166 mbsf and down to the bottom of the hole. Although an equilibrium temperature state had not been reached after drilling operations, the temperature profiles provide interesting and important data on formation temperature and fluid movement. The average overall temperature gradient is 24 K/km, somewhat lower than the temperature gradients found in the DVDP, MSSTS, and CIROS boreholes. Active permeable zones could be detected at least at two depths (150 and 580 mbsf) by falling temperatures and salinities, suggesting cold water influx. The driving forces for fluid movements detected by the anomalies in CRP-2 are still unknown.