Non-marine carbonate rocks including cave, spring, stream, calcrete and lacustrine-palustrine sediments, are susceptible to early diagenetic processes. These can profoundly alter the carbonate fabric and affect paleoclimatic proxies. This review integrates recent insights into diagenesis of non-marine carbonates and in particular the variety of early diagenetic processes, and presents a conceptual framework to address them. With ability to study at smaller and smaller scales, down to nanometers, one can now observe diagenesis taking place the moment initial precipitates have formed, and continuing thereafter. Diagenesis may affect whole rocks, but it typically starts in nano- and micro-environments. The potential for diagenetic alteration depends on the reactivity of the initial precipitate, commonly being metastable phases like vaterite, Ca-oxalates, hydrous Mg‐carbonates and aragonite with regard to the ambient fluid. Furthermore, organic compounds commonly play a crucial role in hosting these early transformations. Processes like neomorphism (inversion and recrystallization), cementation and replacement generally result in an overall coarsening of the fabric and homogenization of the wide range of complex, primary microtextures. If early diagenetic modifications are completed in a short time span compared to the (annual to millennial) time scale of interest, then recorded paleoenvironmental signals and trends could still acceptably reflect original, depositional conditions. However, even compact, non-marine carbonate deposits may behave locally and temporarily as open systems to crystal-fluid exchange and overprinting of one or more geochemical proxies is not unexpected. Looking to the future, relatively few studies have examined the behaviour of promising geochemical records, such as clumped isotope thermometry and (non-conventional) stable isotopes, in well-constrained diagenetic settings. Ongoing and future in-vitro and in-situ experimental approaches will help to investigate and detangle sequences of intermediate, diagenetic products, processes and controls, and to quantify rates of early diagenesis, bridging a gap between nanoscale, molecular lab studies and the fossil field rock record of non-marine carbonates.
Bibliographical noteThe authors would like to warmly thank several colleagues and students studying non-marine carbonates for the numerous discussions during conferences, lab and field time that helped in the preparation of this paper. Amongst them Prof. G. Arp, Prof. E. Capezzuoli, Dr. H. Claes, L. DeMott, Dr. A.-E. Held, Dr. D. Jaramillo-Vogel, Dr. C. Kanellopoulos, Dr. M. Rogerson, Prof. R. Swennen and Dr. D. Wacey. Prof. A. Gandin, Dr. P. Homewood, Dr. D. Jaramillo-Vogel, Dr. A. Martin-Pérez, Dr. M. Mettraux and Dr. M. Vanden Berg are in particularly thanked for several of the images included in the petrography figures. Field work in Yellowstone National Park (research permit YELL-2014-SCI-3060) took place with the support of Prof. B.W. Fouke and was partly made possible by TOTAL E&P (project FR5585). Fieldwork in Angola was funded by TOTAL S.A. (project number: FR00004261) and was performed in close collaboration with CNRS – CEREGE. Fieldwork in Ethiopia was financed by the SNSF funded project SERENA (project number 200021_163114). Mono Lake fieldwork was undertaken and samples collected under permit from CA State Parks collection and with the kind support of Mono Lake Tufa State Natural Reserve and the Mono Lake Committee. The first author is financially supported by an SNSF Ambizione Grant (project number 154810), including field work at Edipsos hot springs in Greece, in collaboration with Dr. C. Kanellopoulos (Institute of Geology and Mineral Exploration, Greece). The manuscript greatly benefited from critical and constructive reviews by A. Immenhauser and E. Verrecchia.
- continental carbonates
- isotope geochemistry
- primary fabric