Iron is the most abundant redox-sensitive element on the Earth's surface, and the oxidation state, mineral host, and crystallinity of Fe-rich phases in sedimentary systems can record details of water-rock interactions and environmental conditions. However, we lack a complete understanding of how these Fe-rich materials are created, maintained, and oxidized or reduced in sedimentary environments, particularly those with mafic sources. The catchment of Lake Towuti, Indonesia, is known to contain a wide range of abundant crystalline Fe oxide, and the lake has a long sedimentary history. Here, we study a ∼100 m long drill core from the lake to understand patterns of sedimentation and how young iron-rich sediments are affected by diagenesis through geologic time. We use visible/near infrared and Mössbauer spectroscopy, X-ray diffraction, bulk chemistry measurements, and statistical cluster analysis to characterize the core sediment. We find that the core sediment can be divided into three statistically different zones dominated by Mg serpentine, Al clay minerals, and Fe2+ carbonate, respectively. The entire core is rich in nanophase Fe, and elemental correlations and Fe mineralogy vary between these zones. The nanophase Fe is highly complex with both ferrous and ferric components, and contributes to, but does not dictate, variations in sediment color. We propose that the distinctive zones are the result of structural basin changes (notably river capture and shifting drainage patterns), and diagenetic overprinting caused by deep burial of reactive Fe. This complex record has implications for disentangling depositional and diagenetic trends in other mafic lacustrine systems.
Bibliographical noteFunding Information:
Funding for laboratory experiments were provided by Brown University Presidential Fellowship and NASA Astrobiology Institute (MIT team, award NNA13AA90A). Sample collection during the Towuti Drilling Project was supported by grants from the International Continental Scientific Drilling Program (ICDP), the US National Science Foundation (NSF‐EAR #1401448), the German Research Foundation (DFG; ME 1169/26), the Swiss National Science Foundation (SNSF; 20FI21_153054/1 & 200021_153053/1&2), Brown University, Genome British Columbia, and the Ministry of Research, Technology, and Higher Education (RISTEK). PT Vale Indonesia and the US Continental Drilling Coordination Office are acknowledged for the 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. Mössbauer analyses were funded by Brown University SSERVI. The authors are very grateful to D. Murray and J. Orchardo for assistance with the ICP‐AES. Grant Rutherford and Sarah Martinez assisted in laboratory work and data collection. Sample material was provided in part by the National Lacustrine Core Facility (LacCore). The authors are grateful to E. Rampe, R. Smith, and an anonymous reviewer for extremely helpful comments that improved the quality of this manuscript.
© 2021. American Geophysical Union. All Rights Reserved.
- Fe oxides
- nanophase material
- redox-stratified lake
- sediment color
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