Mg isotope fractionation during microbial dolomite formation in the Khor Al‐Adaid sabkha, Qatar
Year: 2026
Type: article
Abstract: The processes governing dolomite [CaMg(CO 3 ) 2 ] formation remain among the most debated topics in sedimentary geology. Although primary dolomite can precipitate at low temperatures in certain modern environments, its scarcity today contrasts sharply with its abundance in ancient rocks—a discrepancy known as the ‘dolomite problem’. Dolomite typically forms through two pathways: (1) primary precipitation during early diagenesis, often influenced by microbial activity and organic matter and (2) secondary replacement of preexisting carbonates during burial at higher temperatures. In this study, we investigate Mg isotope fractionation in a modern sabkha in southern Qatar to evaluate its potential as a tracer of dolomite formation processes. We analysed δ 26 Mg and δ 44 Ca in surface‐ and pore waters, authigenic clays and organic‐ and leached dolomite‐containing fractions. Ca isotopes reveal an ~1‰ fractionation between pore water–organic matter and dolomite, consistent with a two‐step, biologically mediated formation pathway. Contrary, only minor 26 Mg enrichment in the organic fraction relative to pore water suggests that Mg isotopes alone provide limited evidence for such microbial mediation. Dolomite δ 26 Mg values (~−2.15‰) align with predictions for temperature‐dependent inorganic precipitation. Overall, the results indicate that microbial activity probably influences dolomite formation indirectly by altering local water chemistry rather than having a distinct Mg isotopic fractionation. These findings refine the application of Mg isotopes as proxies for dolomite genesis and offer new insights into carbonate diagenesis in saline environments.
Source: The Depositional Record
DOI: 10.1002/dep2.70072
Institutions: University of California, Santa Cruz, University of Göttingen, The Ohio State University, GFZ Helmholtz Centre for Geosciences, Federal Institute For Materials Research and Testing, Instituto Andaluz de Ciencias de la Tierra, University of Toronto, University of Toronto Scarborough, University of Basel, Qatar University, Universidad de Granada, Vrije Universiteit Amsterdam
Language: English
Subfield: Paleontology
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,400
Funders: Qatar Foundation, Ministerio de Ciencia, Innovación y Universidades, Canada Foundation for Innovation, Deutsche Forschungsgemeinschaft, Fonds National de la Recherche Luxembourg, Nederlandse Organisatie voor Wetenschappelijk Onderzoek, University of Toronto, Ministerio de Ciencia y Tecnología, Qatar National Research Fund, Natural Sciences and Engineering Research Council of Canada, Agencia Estatal de Investigación
Awards: G1105844351, G1175115578, G1360567091, G1385313657, G2262748287, G2894603144, G294895050, G300979063, G3480869486, G4124119072, G425668148, G4371122427, G4575350107, G4633207564, G464105488, G4839063796, G4840891477, G491712853, G4919812829, G5080475149, G5234035111, G5635532810, G593054264, G638187646, G6396138059, G7084143925, G7395345766, Thermochromic hydrogel for phase-transitioning window applications, G7549035430, Eine neue Sichtweise auf das Dolomitproblem basierend auf stabilen Mg, Ca und Sr Isotopen, G7805626310, G7863371703, G7957821110, G8154206437, G8497050386, G8522895693, G8667377315, G8706746236
OpenAlex ID: W7153174738