SPRING DEPOSITS: ARCHIVES FOR PALEOENVIRONMENTAL AND PALEOBIOLOGICAL INFORMATION

Spring deposits record important information about local biological, hydrologic and climatic conditions. Integrated over time, such records may reveal features of the co-evolution of Earth's surface biological and geological systems. Many springs are sites for the mixing of geofluids in strong physical and chemical disequilibrium. This is often reflected in steep geochemical and physical gradients over micro-spatial scales. Mineral precipitation in these environments may be both rapid and pervasive. At the same time, various chemical disequilibria of springs are exploited by a wide variety of microorganisms for redox-based energy production. Thus, most springs sustain both high levels of microbial diversity and productivity. The coexistence of high rates of mineral precipitation and biological productivity provides especially favorable conditions for the capture and preservation of fossil biosignatures. Although the geobiology of spring deposits is presently understudied in relationship to other sedimentary systems, ancient spring deposits have been shown contain important records of past biological and environmental conditions, which integrated over time, may yield new views of the evolutionary history of our planet.

We have been conducting parallel studies of the microbial geobiology, taphonomy and biogeochemistry of modern springs and their ancient analogs, over a broad range of physical, chemical and diagenetic conditions. One major goal of the research has been the development of integrated litho-, bio- and taphofacies models that can be applied in the exploration for ancient spring deposits in the deep terrestrial record, or on other terrestrial planets, like Mars. In this talk, I will compare the geobiological records of modern and ancient spring systems over a broad range of temperature, pH, redox, microbiological and diagenetic conditions. This will help to elucidate the nature of the geologic record of springs and what it reveals about the paleoenvironmental and geobiological evolution of Earth's surface and shallow crust.