Paleoenvironmental indications and cyclostratigraphic studies of sediments from tropical Lake Towuti obtained from downhole logging

2015年春天，在热带太平洋湖泊托乌蒂湖(印度尼西亚苏拉威西)启动了一项广泛的科学钻探项目。国际科学党的目标是调查其在过去五到六个冰川-间冰期旋回(约.65万年)。对过去6万年浅层沉积岩心的现场研究表明，过去湿(暖)期和干(冷)期之间的环境变化动态由物理和化学性质指示。因此，在三个地点向下钻了174米深的钻孔，以将这项研究扩展到早期湖泊沉积物。除了取心外，还在两个钻井现场进行了井下测井，以确定现场条件下的关键参数。在这个项目中，将对获得的测井数据进行分析，以得出古环境指标。合适的参数很可能是磁化率和K含量，但使用铀浓度和高分辨率电阻率变化将进行测试。在最后的多代理研究中，将对所有工作组取得的成果进行比较和合并，以得出最全面的情况。此外，还将通过旋回地层学方法研究潜在的气候敏感参数。这使得能够推导出Towutis湖过去的年龄深度模型，该模型将与岩芯物质(盖层)测年结果相结合进行解释。由于事件沉积(例如，Tephra层)偶尔会扰乱平静的远洋沉积，因此可能很难对Towutis湖沉积物进行旋回地层学研究。然而，土耳其凡湖的经验表明，在将这些事件从记录中删除后，旋回地层学方法可以成功地应用。对整个项目组有用的其他目标是：(A)建造连续的岩性剖面，例如缩小岩心记录中的数据空白；(B)查明作为关键年龄控制点的特弗拉地层；(C)校正可能受压力释放影响的取心深度；(D)利用地震钻孔测量校准地震剖面(将走时转换为深度)。

An extensive scientific drilling project was started at Lake Towuti, a tropical pacific lake (Sulawesi, Indonesia), in spring 2015. The objectives of the international science party were to investigate its paleoenvironmental, tectonic, and evolutionary biological history over the past five to six glacial-interglacial cycles (approx. 650,000 years). Pre-site studies on shallow sediment cores, spanning the past 60,000 years, have shown that the dynamic of past environmental changes in between wet (warm) and dry (cold) periods are indicated by physical and chemical properties. Therefore, boreholes were drilled down to a depth of 174 m below sea floor at three sites to extend this study to the early lake sediments. In addition to coring, downhole logging was carried out at two drill sites to determine crucial parameters under in situ conditions. In this project, the acquired logging data will be analyzed to derive paleoenvironmental indicators. Suitable parameters are most likely magnetic susceptibility and K contents but the use of U concentrations and high resolution resistivity variations will be tested. Within a final multi-proxy study, the achieved results from all working groups will be compared and merged to achieve the most comprehensive picture. Potential climate-sensitive parameters will additionally be studied by cyclostratigraphic methods. This enables to derive an age-depth model for Lake Towutis past which will be interpreted in conjunction with results from dating of core materials (tephra layers). Because of event deposits (e.g. tephra layers) which occasionally disturb the quiet pelagic sedimentation, cyclostratigraphic studies might be difficult to perform on Lake Towutis sediments. However, experiences from Lake Van in Turkey have shown that cyclostratigraphic methods can be successfully applied after removing these events from the records. Additional objectives, useful for the entire project group, are: (a) construction of a continuous lithological profile, e.g. to close data gaps in the core record, (b) identification of tephra layers that are crucial age control points, (c) correction of coring depths, which might be affected by pressure release, and (d) calibration of seismic profiles (transformation of travel time into depth) using seismic borehole measurements.