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

QUATERNARY SCIENCE REVIEWS

卷:244

Article

Chen, Christine Y.^1,2  McGee, David²  Woods, Arielle³  Perez, Liseth⁴  Hatfield, Robert G.^5,6  Edwards, R. Lawrence⁷  Cheng, Hai^7,8,9  Valero-Garces, Blas L.^10,11  Lehmann, Sophie B.³  Stoner, Joseph S.⁶  Schwalb, Antje⁴  Tal, Irit²  Seltzer, Geoffrey O.¹²  Miguel Tapia, Pedro¹³  Abbott, Mark B.³  Rodbell, Donald T.¹⁴ 

[1] MIT, Woods Hole Oceanog Inst, Joint Program Oceanog, Cambridge, MA USA

[2] MIT, Dept Earth Atmospher & Planetary Sci, Cambridge, MA USA

[3] Univ Pittsburgh, Dept Geol & Environm Sci, Pittsburgh, PA USA

[4] Tech Univ Carolo Wilhelmina Braunschweig, Inst Geosyst & Bioindikat, Braunschweig, Germany

[5] Univ Florida, Dept Geol Sci, Gainesville, FL USA

[6] Oregon State Univ, Coll Earth Ocean & Atmospher Sci, Corvallis, OR USA

[7] Univ Minnesota Twin Cities, Dept Earth & Environm Sci, Minneapolis, MN USA

[8] Xi An Jiao Tong Univ, Inst Global Environm Change, Xian, Peoples R China

[9] Chinese Acad Sci, Inst Earth Environm, State Key Lab Loess & Quaternary Geol, Xian, Peoples R China

[10] CSIC, Pyrenean Inst Ecol, Avda Montanana 1005, Zaragoza 50059, Spain

[11] CSIC PUC UFRJ, Lab Int Cambio Global, Zaragoza, Spain

[12] Syracuse Univ, Dept Earth Sci, Syracuse, NY USA

[13] Inst Nacl Invest Glaciares & Ecosistemas Montanas, Huaraz, Ancash, Peru

[14] Union Coll, Dept Geol, Schenectady, NY USA

关键词: Quaternary;    Paleoclimatology;    South America;    U-Th series;    Sedimentology;    Lakes lagoons & swamps;    Geochronology;    ICDP;    Age model;   

DOI  :  10.1016/j.quascirev.2020.106422

来源: Elsevier

【 摘 要 】

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 (UTh) 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 similar to 100 m drill core from Lake Junin, Peru. The results form the foundation of an age-depth model spanning similar to 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 delta U-234(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 Junin is the only continuous record in the tropical Andes spanning multiple glacial cycles that is constrained entirely by independent radiometric dates. (C) 2020 Elsevier Ltd. All rights reserved.

【 授权许可】

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