Lake Towuti (Sulawesi, Indonesia; Fig. 1) is part of the ancient Malili lake system, a group of five tectonic lakes that are estimated to be between 1 – 2 million years old. The lake is hosted by ophiolitic rock and surrounded by lateritic soils; they are the source of iron-rich deposits in the lake sediments.
Within an extensive research initiative of the International Continental Scientific Drilling program (ICDP), the geological- and evolutionary biological history of the lake is being investigated. The ICDP supported Lake Towuti Drilling Project (TDP) is co-funded by US National Science Foundation, German Science Foundation (DFG), Swiss National Science Foundation, Brown University, Genome British Columbia and Ministry of Research, Technology, and Higher Education (RISTEK).
The TDP continues a series of ICDP research projects on lacustrine sediment archives. These lakes cover the climatic history of hundreds of thousands to millions of years and investigations contribute to reconstruct past climate evolution and to predict future climate change. The tropics and, in particular the western Pacific Warm Pool and associated circulation processes in between the atmosphere and the ocean, are very important for the global climate. However, few studies were performed in this critical region up to today. Figure 2 gives an overview about past ICDP projects in tropical- and subtropical regions, marked on a map of the annual mean precipitable (maximal) water.
Lake Towuti is being investigated by an interdisciplinary science team from several countries that combines numerous geoscientific disciplines such as geology, microbiology and geophysics. From May to July 2015 an extensive driling campaign was carried out and three drillsites were cored at water depth up to 200 m below lake floor (mblf). A total of 1000 m of sediment cores were drilled with a high recovery of more than 95% (Fig. 3).
An extensive set of high-quality downhole logging data was acquired by the section Rock Physics & Borehole Geophysics at site 1 and 2. The following tools were applied: spectral gamma ray (SGR), magnetic susceptibility (SUSC), resistivity, dipmeter, borehole televiewer, sonic as well as salinity and temperature. SGR was run through the drillpipe and thereafter, pipes were pulled gradually to maintain the borehole stability. Some pipes were kept in hole to allow other probes to enter. Site 3 could not be logged due to repeated technical failures of the drilling rig and associated delays.
Initial processing of the data at site 1 indicates a remarkable change in SGR values from the bottom of the hole towards a depth of 103 mblf. First lithological interpretation shows the transition from an initial state to lacustrine conditions at according depth. In addition, sharp spikes in the SUSC data (e.g. at 70 mblf) are interpreted to indicate tephra layers; they are important stratigraphic markers and can potentially be dated by, e.g. 40Ar/39Ar methods. Initial sedimentological data indicate that more than 600 kyr of sedimentation history were recovered.
At the end of the drilling campaign, sediment cores were shipped to the core repository “LacCore”, located in Minneapolis (Minnesota, US). LacCore provides cooled storage and enough space for a big sampling party. Sampling took place in November 2015 and January 2016 and the cores were cut, described and sampled. Additional analysis will be performed by LIAG using Nuclear Magnetic Resonanz (NMR) in the petrophysical lab of section Rock Physics & Borehole Geophysics to determine porosity and permeability of these sediments. Lithological units were selected for sampling based on the core description and the data will be jointly evaluated with the physical in-situ data from downhole logging.
A research proposal was submitted to the German Science Foundation (DFG) and its funding decision is expected in March 2016.
2015 - 2018
German Research Foundation