Relating physical properties from geophysical downhole logging data with clay mineralogy from drill core samples of the ICDP Lake Junín drilling project, Peru
Geophysics
Final Report Abstract
The petrophysical properties of lacustrine sediments of Lake Junín in Peru were studied and compared using borehole logs and from drilled rocks. Lake Junín is located at 4082 m elevation in the Andes and is characterized by a thick sedimentary package in which carbonates and glacial silts alternate with thin peat and organic-bearing mud layers. Several glacial cycles spanned the lake, although it was not covered by glacial ice at any time during the last 700 ka. Our project had three main objectives: i. to reconstruct the sediment record of Lake Junín using cluster analysis; ii. to investigate paleoclimatic implications in order to build an age-depth model and to estimate sedimentation rate using a suite of cyclostratigraphic methods; iii. to link borehole data to the mineralogy and clay mineralogy of selected cores to determine differences in the nature of sedimentation through time. Comparison of the borehole data with the mineralogy and geochemistry of the cores will support and strengthen the interpretation of the borehole data. This project represents a novelty in this field because the use of only downhole logging data in lake drilling for cyclostratigraphic interpretation is quite rare. Furthermore, comparison of the borehole data with the mineralogy and geochemistry of the drill cores will support and strengthen the interpretation of the borehole data. The application of statistical methods (TimeOpt, Astronomical Spectral Misfit-ASM) allowed to derive an age-depth model from downhole logging datasets because the imprint of astronomical climate forcing is detectable in lacustrine sediments. For the age-depth model, we compared the fluctuation of the gamma ray (GR) data with the LR04 benthic isotope stack. By comparing GR and LR04, we found out that the lake was affected by several glacial-interglacial stages (MIS 5 to 17) dating lake deposits back to about 630 ka. We investigated the consistency of cyclic sedimentation behavior and saw that the interval from ~20-80 mblf shows a rather stable cyclicity of ~10 m. By combining the GR with the ASM method we were able to identify cyclostratigraphic records, to reconstruct the age-depth model and estimate the sedimentation rate (~15 cm/ka). The comparison between our findings with those from core analysis is consistent and matches very well. Our results show that this method can be a valid alternative in case of poor or absent core recovery. Borehole data such as magnetic susceptibility (MS), Gamma-ray (GR), Uran-Thorium (U-Th data) were furthermore examined, compared and complemented with mineralogical and geochemical analyses of 68 samples from the cores. A total of six interglacial and six glacial phases could be distinguished. During glacial periods, the borehole data show a high proportion of siliciclastic material with a high MS and Th/U ratio, whereas during interglacial sediments low MS and Th/U ratios are prevalent. In comparison, the mineralogy and geochemistry of the core analyses show a high proportion of clay minerals during the glacial periods, and an absence of clay minerals in the interglacial periods with a concomitant high occurrence of quartz and calcite. In both logging data and core samples, the Th/U ratio is a good indicator of the nature of sediments. Although glacial/interglacial periods were determined using separate and different approaches, our methods show very good agreement. In addition, the relative proportions of K, U, and Th are diagnostic of the depositional environment and the origin of the sediments. They indicate deposition under chemically reducing conditions (sediment relatively unweathered) as well as deeply weathered sediment. Furthermore, U in sedimentary rocks is a sensitive indicator of redox conditions. The occurrence of thin, U-rich marker layers with broad geographic distribution indicates U "fixation" at the seafloor. In contrast, Th tends to be insensitive to redox conditions and persists at the Earth's surface under weathering conditions. Element K is relatively more abundant in unaltered igneous/metamorphic rocks (the sedimentary protolith) than in siliclastic sedimentary rocks of comparable mineralogy. Based on borehole data and core analyses, a relationship between the geologic history of the lake and climate change processes has been demonstrated. The mineralogical and geochemical composition of the rocks, thus also the Th/U ratios from the borehole data reflect glacial/interglacial cyclicity, and can be compared with age dating in the next step.
Publications
- (2018). Investigating core mineralogy and downhole logging data from the ICDP Lake Junín drilling project, Peru. Geophysical Research Abstracts Vol. 20, EGU2018-4298, 2018 EGU General Assembly 2018
Pierdominici S., Schleicher A.M., Kück J., Rodbell D.T., Abbott M.B. and the ICDP Lake Junín Working Group
- (2018). Linking downhole logging data and clay mineralogy analysis in the ICDP Lake Junín drilling Project, Peru. IODP/ICDP Kolloquium 2018 Bochum, 14.-16. März 2018
Pierdominici S., Schleicher A.M., Kück J., Rodbell D.T., Abbott M.B. and the ICDP Lake Junín Working Group
- (2019). Facies characterization based on physical properties from downhole logging data: a case study for the ICDP drilling project Lake Junín, Peru. Geophysical Research Abstracts Vol. 21, EGU2019-4787, EGU General Assembly 2019
Pierdominici, S., Schleicher, A.M., Kück, J., Rodbell, D.T., Abbott, M.B., and the ICDP Lake Junín Working Group
- (2019). Implication (link) of mineralogical composition and climate changes: an example from the ICDP drilling project Lake Junín, Peru. Geophysical Research Abstracts Vol. 21, EGU2019-4826, EGU General Assembly 2019
Schleicher, A.M., Pierdominici, S., Kück, J., Rodbell, D.T., Abbott, M.B. and the ICDP Lake Junín Working Group
- (2019). Petrophysical and mineralogical investigation of lacustrine sediments from Lake Junín (Peru). IODP/ICDP Kolloquium 2019, at University of Köln, 18-20 March 2019
Pierdominici, S., Schleicher, A.M., Kück, J., Rodbell, D.T., Abbott, M.B., and the ICDP Lake Junín Working Group
- (2020). Investigating glacial/interglacial cyclicity from downhole logging data and mineralogical composition: an example from the ICDP drilling project Lake Junín, Peru. vEGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3891
Schleicher A.M., Pierdominici S., Zeeden C., Kück J., Rodbell D., Abbott M.
(See online at https://doi.org/10.5194/egusphere-egu2020-3891) - (2020). Studying glacial/interglacial cycles from downhole logging data and mineralogical composition: an application to the ICDP drilling project Lake Junín, Peru. IODP-ICDP Kolloquium (DFG), virtual
Pierdominici S., Schleicher A.M., Zeeden C., Kück J., Rodbell D.T., Abbott M.B.
- (2020). Studying glacial/interglacial cycles from downhole logging data: an application to the ICDP drilling project Lake Junín, Peru. GeoUtrecht 2020, 24-26 August 2020, Utrecht, The Netherlands
Pierdominici S., Zeeden C., Kück J., Rodbell D., Abbott M.
(See online at https://doi.org/10.48380/dggv-54r7-a519)
