Lake Towuti on Sulawesi Island, Indonesia, is located within the heart of the Indo-Pacific Warm Pool. This tropical lake is surrounded by ultramafic (ophiolitic) rocks and lateritic soils that create a unique ferruginous depositional setting. In order to understand modern sediment deposition in Lake Towuti, a set of 84 lake surface sediment samples was collected from across the entirety of the lake and samples were analyzed for their physical, chemical, mineralogical and biological constituents. End-member analyses were carried out to elucidate modern sediment origin, transport and depositional processes. This study found that allochthonous sediment, characterized by the concentrations of the elements Mg, Fe, Si and Al, as well as the clay and serpentine minerals, is dominated by fluvial supply from five distinct source areas. Granulometric data and the occurrence of organic matter of a terrestrial origin suggest that, in the southern and north-eastern parts of the lake the near-shore sediments may additionally be influenced by mass wasting. This is due at least partly to the particularly steep slopes in these areas. Furthermore, sediment composition suggests that sediment transport into deeper parts of the lake, particularly in the northern basin, is partly controlled by gravitational and density-driven processes such as turbidity currents. Directional sediment transport by persistent lake currents, in contrast, appears to be less important. Organic matter deposition in the ultra-oligotrophic lake, albeit limited, is dominated by autochthonous production, but with some contribution of fluvial and gravitational supply. Biogenic silica deposition, primarily from diatom frustules and sponge spicules, is very limited and is concentrated in only a few areas close to the shoreline that are characterized by shallow waters, but away from the areas of high suspension loads at the mouths of the major inlets. The results of this study build upon current and published work on short piston cores from Lake Towuti. Conversely, the results will support the interpretation of the depositional history and past climatic and environmental conditions derived from the composition of much longer records, which were obtained by the Towuti Drilling Project in May 2015 and are currently under investigation.
Bibliographical noteFunding Information:
The Towuti Drilling Project was partially supported by grants from the International Continental Scientific Drilling Program (ICDP), the US National Science Foundation (NSF), the German Research Foundation (DFG, grant no. ME 1169/ 26), the Swiss National Science Foundation (SNSF; 20FI21_153054/1 and 200021_153053/1), Brown University, Genome British Columbia, and the Ministry of Research, Technology and Higher Education (RISTEK). PT Vale Indonesia, the US Continental Drilling Coordination Office, the GeoForschungsZentrum Potsdam, and DOSECC Exploration Services are acknowledged for their logistical assistance to the project. This research was carried out with permission from RISTEK, the Ministry of Trade of the Government of Indonesia, the Natural Resources Conservation Center (BKSDA) and the Government of Luwu Timur of Sulawesi. We like to thank Hannah Jauss, University of Cologne, for her competent help in the FlowCam analyses. Special thanks are due to Paul Hamilton for diatom identification and information about their preferred living conditions, to Doug Haffner for providing unpublished chemical data of the water column, and to Rachel Sheppard for providing unpublished mineralogical and spectral data of the surface sediment samples. We are also grateful to two anonymous reviewers and editors Peir Pufahl and Ola Kwiecien for their comments and suggestions, which greatly helped to improve the manuscript.
© 2018 The Authors. Sedimentology © 2018 International Association of Sedimentologists
Copyright 2019 Elsevier B.V., All rights reserved.
- Indo-Pacific Warm Pool (IPWP)
- Lake Towuti
- modern sedimentation
- provenance analysis
- redox conditions
- tropical lake
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