Search

This study investigates the potential of laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) U‐Pb dating for carbonate nodules in the Late Triassic Ischigualasto Formation of northwestern Argentina. We establish a fully characterized paragenetic sequence to guide the analysis of three pedogenic carbonates and compare the U‐Pb ages with published geochronology from volcanic ashes within the sedimentary succession. Our findings demonstrate the importance of interpreting U‐Pb data within a well‐defined paragenetic framework for accurate age interpretation of pedogenic carbonates. We observe variations in U‐Pb isotopic signatures across different generations of carbonate precipitates and identify syn‐pedogenic and early burial calcite cements as most suitable for precise dating. Respectively, these two calcite cements are interpreted as microcodium and crack‐lining calcite cements formed early in the paragenetic sequence during pedogenesis to early burial of the paleosols as they transitioned from the unsaturated vadose to saturated phreatic zone below the water table. The U‐Pb ages obtained from the carbonate nodules agree with the radioisotopic ages of volcanic ashes, supporting the validity of our dating strategy. These results contribute to advancing U‐Pb carbonate geochronology and highlight its increased potential for dating sedimentary records in the terrestrial realm. Future research should focus on replicating similar work on different carbonate nodules within the Ischigualasto Fm and expanding the application of LA‐ICP‐MS U‐Pb dating to other carbonate‐bearing formations, especially in successions with limited absolute ages or where volcanic ashes are sparse or absent. Plain Language Summary: Carbonate minerals that formed in fossil soils can provide valuable insights into past physical, biological, and chemical processes on Earth's surface. Despite their significance in reconstructing ancient climates and environments, determining the age of these fossil soils via uranium‐to‐lead dating has proven challenging. This difficulty arises from factors associated with soil carbonate minerals, including low uranium content, high lead content, complex formation chemistry, multiple formation episodes (generations), and potential for post‐formation chemical alteration. To address these issues, we first identified the order in which carbonate minerals formed within three samples from the Late Triassic Ischigualasto Formation of Argentina. Then, we dated each generation within each sample and compared the results to identify and understand the most optimal sample locations for dating. Analysis of our data shows that carbonate minerals formed due to biological processes near the surface as well as during the burial and submersion of the fossil soils below the water table are the most suitable for dating and approximate the timing of soil formation. Importantly, the ages from these soil carbonate samples align with ages from volcanic ashes found within the Ischigualasto Formation, thus validating our results and the potential to apply our strategy in other locations. Key Points: A well‐defined paragenetic framework is necessary to interpret laser ablation inductively coupled plasma mass spectrometry U‐Pb data for accurate age interpretation of pedogenic carbonatesU‐Pb isotopic signatures vary across generations of carbonate precipitates, with syn‐pedogenic and early burial cements being the most suitable for precise datingSyn‐pedogenic and early burial cements approximate the timing of pedogenesis and transition from the unsaturated vadose to the saturated phreatic zone, respectively [ABSTRACT FROM AUTHOR]

This paper presents a detailed geological map at the 1:20,000 scale of the Tocomar basin in the Central Puna (north-western Argentina), which extends over an area of about 80 km2 and displays the spatial distribution of the Quaternary deposits and the structures that cover the Ordovician basement and the Tertiary sedimentary and volcanic units. The new dataset includes litho-facies descriptions, stratigraphic and structural data and new 234U/230Th ages for travertine rocks. The new reconstructed stratigraphic framework, along with the structural analysis, has revealed the complex evolution of a small extensional basin including a period of prolonged volcanic activity with different eruptive centres and styles. The geological map improves the knowledge of the geology of the Tocomar basin and the local interplay between orogen-parallel thrusts and orogen-oblique fault systems. This contribution represents a fundamental support for in depth research and also for encouraging geothermal exploration and exploitation in the Puna Plateau region. [ABSTRACT FROM AUTHOR]