Universität zu Köln

Obert, J. Christina, Muenker, Carsten, Staubwasser, Michael, Herwartz, Daniel, Reicherter, Klaus and Chong, Guillermo (2022). Th-230 dating of gypsum from lacustrine, brackish-marine and terrestrial environments. Chem. Geol., 607. AMSTERDAM: ELSEVIER. ISSN 1872-6836

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Abstract

Gypsum is an important environmental archive in hyperarid settings, but its application in earth sciences has been hampered by the limited availability of suitable dating methods. Here we re-evaluate the potential of 230Th/ U dating for sedimentary gypsum as well as anhydrite samples in different depositional environments. We provide a robust analytical protocol based on a simple dissolution using nitric acid followed by a two-column separation procedure using anion exchange resin. Isotope analyses were performed using MC-ICPMS and a mixed 229Th-233U-236U tracer. We applied the method to a suite of samples that likely reached secular equilibrium as well as to three suites of younger (<300 ka old) samples, two from the Atacama Desert in Chile and one from a drill core of a saline playa lake in southern Spain. We employed a selective sampling approach targeting the least visually altered and clearest parts of the samples largely devoid of detritus and analysed multiple subsamples. The results demonstrate the general applicability of the 230Th/U method to gypsum as well as anhydrite, and recrystallization of gypsum to anhydrite does not significantly affect the U-series isotope system. However, there is evidence for open-system behaviour, which needs to be carefully assessed. Our results suggest that alpha-recoil processes as well as uptake or loss of uranium are important processes biasing the results of gypsum dating. Furthermore, we see signs of multiple-phase contamination in our case studies involving detrital components and authigenic phases. Based on these results we propose geochemical criteria in to identify biased 230Th/U gypsum ages. The application of our protocol to a suite of selenite samples deposited by brine outflows on the lowest terrace of Cerro Soledad (Atacama Desert, Chile) provides a mean age of 212 +/- 8 ka, indicating a relatively humid climate interval with local rainfall in this area that is coinciding with marine isotope stage 7C. Selenites deposited in the paleo-lake Soledad system (Atacama Desert, Chile) yield 230Th/U ages ranging from 250 to 320 ka, in agreement with previous age estimates for the drainage of this paleo-lake obtained by cosmogenic nuclide dating. Application to a suite of gypsum crystals recovered from a drill core in the Laguna de Fuente de Piedra (South Spain) shows good agreement with their stratigraphic context, however, multiple-phase contamination produces larger age uncertainties for these ages.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Obert, J. Christina UNSPECIFIED UNSPECIFIED UNSPECIFIED Muenker, Carsten UNSPECIFIED UNSPECIFIED UNSPECIFIED Staubwasser, Michael UNSPECIFIED UNSPECIFIED UNSPECIFIED Herwartz, Daniel UNSPECIFIED UNSPECIFIED UNSPECIFIED Reicherter, Klaus UNSPECIFIED UNSPECIFIED UNSPECIFIED Chong, Guillermo UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-672687
DOI:	10.1016/j.chemgeo.2022.121019
Journal or Publication Title:	Chem. Geol.
Volume:	607
Date:	2022
Publisher:	ELSEVIER
Place of Publication:	AMSTERDAM
ISSN:	1872-6836
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language MEJILLONES PENINSULA; ATACAMA DESERT; ISOTOPE RATIOS; URANIUM; PALEOCLIMATE; SALAR; DISSOLUTION; CHRONOLOGY; EVAPORITES; ANHYDRITE Multiple languages Geochemistry & Geophysics Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/67268