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.

本数据集的钻探点位位于南极洲（Antarctica）罗斯海（Ross Sea）的麦克默多湾（McMurdo Sound）北部，钻孔CRP-2/2A（drillhole CRP-2/2A）瞄准维多利亚地盆地（Victoria Land basin）西缘，通过获取连续岩心（continuous core）与井下测井（downhole logs）资料，研究新近纪（Neogene）至古近纪（Palaeogene）的气候与构造演化历史。项目背景、具体研究目标、采用方法及迄今取得的成果已由罗伯茨角科学团队（Cape Roberts Science Team, 1999）进行了系统总结。
CRP-2A钻孔的钻进深度达625米海底以下（meters below seafloor，缩写mbsf），渐新世（Oligocene）至第四纪（Quaternary）沉积物的平均岩心回收率为95%。多数井下测井仪器（downhole logging tools）均下至钻孔底部。钻探作业完成后的首批测量为温度与盐度测量（temperature and salinity measurements），该测量分两阶段完成，分别下探至166 mbsf及钻孔底部。尽管钻探作业结束后尚未达到温度平衡状态（equilibrium temperature state），但温度剖面（temperature profiles）数据为地层温度（formation temperature）与流体运移（fluid movement）研究提供了极具价值的重要资料。
整体平均温度梯度（temperature gradient）为24 K/km，略低于DVDP、MSSTS及CIROS钻孔的温度梯度。通过温度与盐度的下降特征，至少可在150 mbsf和580 mbsf两处深度检测到活性渗透带（active permeable zones），表明存在冷水流入现象。CRP-2钻孔中由异常（anomalies）特征所指示的流体运移驱动力目前仍未明确。