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

2015年春季，在热带太平洋湖泊Towuti湖（印度尼西亚苏拉威西岛）开始了一项广泛的科学钻探项目。国际科学小组的目标是在过去的5到6个冰期-间冰期旋回（大约5到6个）中调查其古环境、构造和进化生物学历史。650000年)。对过去6万年的浅层沉积物岩心进行的现场前研究表明，过去在湿（暖）期和干（冷）期之间的环境变化动态是由物理和化学性质指示的。因此，在三个地点钻孔至海底以下174 m的深度，将本研究扩展到早期湖泊沉积物。除取心外，还在两个钻井地点进行了井下测井，以确定现场条件下的关键参数。本项目将对采集的测井资料进行分析，得出古环境指标。合适的参数很可能是磁化率和钾含量，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，将比较和合并所有工作组取得的成果，以获得最全面的情况。此外，还将利用旋回地层学方法研究潜在的气候敏感参数。这使我们能够推导出托乌提斯湖过去的年龄深度模型，该模型将与岩心材料（热层）的定年结果相结合进行解释。由于事件沉积（如温层）偶尔会扰乱平静的远洋沉积，因此对托乌提斯湖沉积物进行旋回地层学研究可能很困难。然而，土耳其凡湖的经验表明，将这些事件从记录中去除后，旋回地层方法可以成功地应用。对整个项目组有用的其他目标有：(a)构建连续的岩性剖面，例如，填补岩心记录中的数据空白；(b)识别作为关键年龄控制点的地下层；(c)校正可能受压力释放影响的取心深度；(d)使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.