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U-Th dating of lake sediments: Lessons from the 700 ka sediment record of Lake Junín, Peru

Chen, Christine Y. and McGee, David and Woods, Arielle and Pérez, Liseth and Hatfield, Robert G. and Edwards, R. Lawrence and Cheng, Hai and Valero-Garcés, Blas L. and Lehmann, Sophie B. and Stoner, Joseph S. and Schwalb, Antje and Tal, Irit and Seltzer, Geoffrey O. and Tapia, Pedro Miguel and Abbott, Mark B. and Rodbell, Donald T. (2020) U-Th dating of lake sediments: Lessons from the 700 ka sediment record of Lake Junín, Peru. Quaternary Science Reviews, 244 . Art. No. 106422. ISSN 0277-3791.

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Deep sediment cores from long-lived lake basins are fundamental records of paleoenvironmental history, but the power of these reconstructions has been often limited by poor age control. Uranium-thorium (U-Th) dating has the potential to fill a gap in current geochronological tools available for such sediment archives. We present our systematic approach to U-Th date carbonate-rich sediments from the ∼100 m drill core from Lake Junín, Peru. The results form the foundation of an age-depth model spanning ∼700 kyrs. High uranium concentrations (0.3–4 ppm) of these sediments allow us to date smaller amounts of material, giving us the opportunity to improve sample selection by avoiding detrital contamination, the greatest factor limiting the success of previous U-Th dating efforts in other lake basins. Despite this advantage, the dates from 174 analyses on 55 bulk carbonate samples reveal significant scatter that cannot be resolved with traditional isochrons, suggesting that at least some of the sediments have not remained closed systems. To understand the source of noise in the geochronological data, we first apply threshold criteria that screen samples by their U/Th ratio, reproducibility, and δ²³⁴U_(initial) value. We then compare these results with facies types, trace element concentrations, carbonate and total organic carbon content, color reflectance, mineralogy, and ostracode shell color to investigate the causes of open system behavior. Alongside simulations of the isotopic evolution of our samples, we find that the greatest impediment to U-Th dating of these sediments is not detrital contamination, but rather post-depositional remobilization of uranium. Examining U-Th data in these contexts, we identify samples that have likely experienced the least amount of alteration, and use dates from those samples as constraints for the age-depth model. Our work has several lessons for future attempts to U-Th date lake sediments, namely that geologic context is equally as important as the accuracy and precision of analytical measurements. In addition, we caution that significant geologic scatter may remain undetected if not for labor intensive tests of reproducibility achieved through replication. As a result of this work, the deep sediment core from Lake Junín is the only continuous record in the tropical Andes spanning multiple glacial cycles that is constrained entirely by independent radiometric dates.

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Chen, Christine Y.0000-0002-9580-6925
Additional Information:© 2020 Elsevier. Received 8 December 2019, Revised 3 June 2020, Accepted 8 June 2020, Available online 17 August 2020. This research was supported by a grant from the International Continental Scientific Drilling Program (ICDP) and grants from the U.S. National Science Foundation (McGee, EAR-1404414; Rodbell, EAR-1402076; Abbott, EAR-1404113; Stoner, EAR-1400903) and the National Science Foundation of China (Cheng, #41888101). CYC was supported by an NSF Graduate Research Fellowship during the execution of this research. We are grateful to Lake Junín Drilling Project members for their contributions to fieldwork and data collection, the ICDP for financial and logistical support, the authorities of the Reserva Nacional Junín for their assistance, and DOSECC Exploration Services (USA) and GEOTEC (Peru) for drilling expertise. We thank LacCore for access to facilities, core curation, color reflectance data, and data management. We thank Doug Schnurrenberger, Amy Myrbo, Shane Loeffler, Darren Larsen, Mark Shapley, Bryan G. Valencia, Angela Rozas Davila, James Bartle, and Cecilia Oballe for their logistical assistance during drilling; Kristina Brady and Anders Noren for their work managing and coordinating this project; Liam Glennon for assisting with XRD analyses; Ben Hardt for providing lab assistance at MIT; and Sarah Katz and Naomi Levin for collecting modern water samples used for uranium isotope analysis. CYC also thanks resources for making graphics accessible to those with color vision deficiencies by Wong (2011) and Martin Krzywinski (; and P. Donut for companionship and support with revisions. We also gratefully acknowledge Jay Quade, Tim Lowenstein, Kristin Bergmann, C. Brenhin Keller, Adam Maloof, Noah Anderson, Marjorie Cantine, Adam Jost, Christopher Kinsley, Gabi Serrato Marks, Josh Murray, and Ruth Tweedy for reading the initial draft and providing helpful comments. We also gratefully acknowledge two anonymous reviewers for their constructive feedback, Ana Moreno for refereeing our manuscript, and Antje Voelker for the invitation to submit this paper to Quaternary Science Reviews. Datasets and tools. Datasets and tools related to this article can be found in the Appendix and the following open-access data repository hosted at Zenodo (operated by CERN): Products available for use include • U-Th data tables for the PLJ-1 and 1996 core (with all digits preserved where possible, for reproducibility and data longevity); • sample locations and corresponding elemental concentrations, carbon coulometry, color reflectance, and ostracode paleoecological data; • the radiometric-based age-depth model generated by Bacon; and • a spreadsheet for simulating the uranium isotopic evolution of a sample that has undergone open system behavior with respect to uranium and/or a sample of mixed composition (impure carbonate). Author contributions. Following the Contributor Roles Taxonomy (CRediT; Brand et al., 2015), we provide a statement of the diverse contributions to this published work. Christine Y. Chen: Conceptualization, Methodology, Software, Validation, Formal Analysis, Investigation, Writing - Original Draft Preparation, Writing - Review and Editing, Visualization, Project Administration. David McGee: Conceptualization, Methodology, Resources, Writing - Review & Editing, Supervision, Funding Acquisition. Arielle Woods: Methodology, Writing - Review & Editing. Liseth Pérez: Methodology, Investigation, Writing - Review & Editing. Robert G. Hatfield: Writing - Review & Editing. R. Lawrence Edwards: Conceptualization, Resources, Writing - Review & Editing. Hai Cheng: Investigation. Blas L. Valero-Garcés: Investigation, Writing - Review & Editing. Sophie B. Lehmann: Writing - Review & Editing. Joseph S. Stoner: Writing - Review & Editing. Antje Schwalb: Methodology, Resources, Writing - Review & Editing. Irit Tal: Investigation. Geoffrey O. Seltzer: Conceptualization. Pedro Miguel Tapia: Project Administration. Mark B. Abbott: Conceptualization, Writing - Review & Editing, Supervision, Project Administration, Funding Acquisition. Donald T. Rodbell: Conceptualization, Writing - Review & Editing, Supervision, Project Administration, Funding Acquisition. A more specific description of contributions is as follows: GOS laid the foundation for this work in the 1990s (Siegel et al., 2005). MBA, DTR, and DM conceived of the project and secured funding. CYC and DM formulated the research goals and methodology. CYC collected, processed, and analyzed the U-Th samples from the PLJ-1 splice; made comparisons to the other datasets; designed and implemented the model for uranium isotopic evolution; and prepared the original draft and figures, all with supervision from DM. IT assisted with processing of U-Th analyses. RLE oversaw U-Th dating of the 1996 piston core, which was conducted by HC. BLVG provided the stratigraphic core description. DM collected the elemental ICPMS concentration data. CYC initiated the ostracode work with LP, who analyzed the ostracodes with input from AS. DTR analyzed carbon coulometry and mineralogy XRD data. RH and JS analyzed paleomagnetic data. CYC made the age-depth model, with input from AW, SL, RGH, DM, JSS, MBA, and DTR. CYC, AW, RGH, JSS, PMT, MBA, and DTR contributed to the fieldwork campaign. DM, AW, LP, RGH, RLE, BLVG, SL, AS, MBA, and DTR provided manuscript feedback. All authors provided expertise. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Errata:Christine Y. Chen, David McGee, Arielle Woods, Liseth Pérez, Robert G. Hatfield, R. Lawrence Edwards, Hai Cheng, Blas L. Valero-Garcés, Sophie B. Lehmann, Joseph S. Stoner, Antje Schwalb, Irit Tal, Geoffrey O. Seltzer, Pedro Miguel Tapia, Mark B. Abbott, Donald T. Rodbell, Corrigendum to “U–Th dating of lake sediments: Lessons from the 700 ka sediment record of lake Junín, Peru” [Quat. Sci. Rev. 244 (2020) 106422], Quaternary Science Reviews, Volume 248, 2020, 106615, ISSN 0277-3791,
Funding AgencyGrant Number
International Continental Scientific Drilling Program (ICDP)UNSPECIFIED
National Natural Science Foundation of China41888101
NSF Graduate Research FellowshipUNSPECIFIED
Subject Keywords:Quaternary; Paleoclimatology; South America; U-Th series; Sedimentology; Lakes lagoons & swamps; Geochronology; ICDP; Age model
Record Number:CaltechAUTHORS:20200925-104735278
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Official Citation:Christine Y. Chen, David McGee, Arielle Woods, Liseth Pérez, Robert G. Hatfield, R. Lawrence Edwards, Hai Cheng, Blas L. Valero-Garcés, Sophie B. Lehmann, Joseph S. Stoner, Antje Schwalb, Irit Tal, Geoffrey O. Seltzer, Pedro Miguel Tapia, Mark B. Abbott, Donald T. Rodbell, U-Th dating of lake sediments: Lessons from the 700 ka sediment record of Lake Junín, Peru, Quaternary Science Reviews, Volume 244, 2020, 106422, ISSN 0277-3791,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105558
Deposited By: George Porter
Deposited On:25 Sep 2020 19:31
Last Modified:16 Nov 2020 21:53

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