Hot‐spring Systems Geobiology: abiotic and biotic influences on travertine formation at Mammoth Hot Springs, Yellowstone National Park, USA

Abstract

Multiple abiotic and biotic factors combine in nature to influence the formation of calcium carbonate limestone deposits. Systems Geobiology studies of how micro-organisms respond to, or sometimes even control, the coupled effects of environmental change and mineralization will permit more accurate interpretation of the fossil record of ancient microbial life. Mammoth Hot Springs in Yellowstone National Park, USA, serves as a natural laboratory for tracking how the dynamic interplay of physical, chemical and biological factors come together to form hot-spring limestone (called 'travertine'). Systematic downstream correlations occur at Mammoth Hot Springs between travertine deposition (geomorphology, crystalline structure and geochemistry), microbial communities (mat morphology, pigmentation, and phylogenetic and metabolic diversity) and spring-water conditions (temperature, pH, geochemistry and flow). Field-based microscale and mesoscale experimentation indicates that microbes directly influence travertine growth rate and crystalline structure. At the macroscale, time-lapse field photography and numerical modelling suggest that travertine terrace geomorphology is influenced strongly by hydrology, heat dispersion and geochemistry. These results from Mammoth Hot Springs allow establishment of a conceptual framework across broad spatial and temporal scales in which to track how multiple geological and biological factors combine to control CaCO 3 crystal precipitation and the resulting formation of travertine deposits.

Comparative study of the Pleistocene Cakmak quarry (Denizli Basin, Turkey) and modern Mammoth Hot Springs deposits (Yellowstone National Park, USA)

“…The Apron and Channel Facies are typified by gently sloping deposits of 10e100 mm aragonite needles that encrust filamentous, microbial mats (called "streamers"), forming sinuous travertine pavement deposits ( Fig. 2; Fouke, 2011). Inactive hot-spring streamers are either found as, in place pavements or they prograde laterally over the downstream Pond Facies terracettes (Fig.…”

“…In the active MHS system, a sequence of five travertine depositional facies have been described along upstream-to-downstream "primary flow path" transects (Fouke et al, 2000;Veysey et al, 2008;Fouke, 2011). As the spring water cools (73 Ce25 C), degasses CO 2 (pH 6e8) and rapidly precipitates travertine (0.1e5 mm/day), a consistent downstream succession of facies forms: i.e.…”

“…Unique microbial communities are associated with each facies based on 16S rRNA gene sequence clone library construction, with 90þ% partitioning in phylogenetic diversity observed between the microbial communities inhabiting each facies (Fouke et al, 2003). A detailed summary of the travertine depositional facies and fabrics has previously been presented (Fouke et al, 2000;Fouke, 2011) and they are briefly summarized here as a basis for the MHS facies map.…”

“…Different travertine depositional facies models of modern spring systems have been proposed to describe the complex textural and geometric variations of ancient spring deposits (Guo and Riding, 1998;Fouke et al, 2000;Capezzuoli et al, 2014;Claes et al, 2015;Della Porta, 2015) and to accurately reconstruct the environmental conditions under which ancient deposits originally formed and evolved (Chafetz and Folk, 1984;Veysey et al, 2008;Fouke, 2011;Gandin and Capezzuoli, 2014;Sotohian and Ranjbaran, 2015). A facies, as summarized by James and Dalrymple (2010), is a 'body of (sedimentary) rock characterized by a particular combination of lithology and physical and biological structures that bestow an aspect that is different from the bodies of rock adjacent.…”

“…As a result, travertine facies are characterized by the substrate on which they grow (i.e., plant branches, roots, fragments or microbial filaments) and the different crystal (or grain) fabrics, including crystal type, size, shape, mineralogy and organization. The facies will reflect physical, chemical and (micro)biological conditions and processes that characterized, or played a role in the original depositional environment (Takashima and Kano, 2008;Fouke, 2011;Okumura et al, 2012;Gandin and Capezzuoli, 2014).…”