G. Della Porta (2015) - Non marine carbonate build-ups: comparing depositional geometry, fabric types and geochemical signature
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- 2. Non-marine carbonate precipitates • Wide range of carbonate precipitated geobody types, fabrics and flow unit architectures with complex pore systems. • occur in different depositional settings (lakes, spring related) and water physico-chemical properties (high T, high alkalinity and salinity, freshwater, ambient T) • favoured by active tectonics and volcanisms • various types coexist in the same basin (e.g., East African Rift lakes and hydrothermal vents) • all unique case studies.. • but share some common features depending on the scale of observation
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- 4. Limited studies and confused terminology Subaerial spring related non marine carbonates • Travertine (Pedley 1990) or Thermogene travertine (Pentecost 2005): continental carbonates precipitated from thermal water (T >20°C) supersaturated with CaCO3 degassing CO2 while out-flowing from subaerial vents. CO2 derived from deep seated geothermal sources. They are scarce in macrophytes and dominated by heat tolerant microbes. • Calcareous Tufa (Pedley, 1990) or Meteogene travertine (Pentecost 2005): continental carbonates precipitated from ambient temperature freshwater of fluvial-marsh origin and karstic springs, rich in microphytic and macrophytic growths, leaves and woody tissue. Lacustrine carbonates • Lacustrine tufa (Pedley, 1990); meteogene travertine and lake bioherms or build- ups (Pentecost 2005) • Sub-lacustrine spring related saline travertines and saline tufa (Capezzuoli et al. 2014)
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- 15. Non marine carbonate selected case studies Lacustrine shoreline buildups • a) hypersaline Holocene Great Salt Lake, • b) soda lake Miocene Ries Crater, • c) schizohaline Eocene Green River Fm. Sublacustrine springs – thermal or groundwater mixing with lake water - upper Pleistocene-Holocene • a) mildly alkaline Pyramid Lake, • b) saline alkaline Mono Lake. Hydrothermal travertine rift lake (Miocene, Tuscany, Central Italy). Subaerial flowing-water systems : • a) freshwater fluvial systems (tufa Lombardy, Italy), • b) hydrothermal (38-50°C) travertine, Tuscany, Central Italy). 200 km 200 km Pleistocene hot-spring travertine Miocene rift lake with hydrothermal water, Tuscany, Central Italy Miocene algal bioherms, Ries Crater, South Germany Eocene schizohaline lake caddis fly larvae stromatolite bioherms Green River Fm., Utah & Wyoming Holocene hypersaline lake microbial bioherms, Great Salt Lake, Utah Late Pleistocene mildly alkaline lake, mounds, Pyramid Lake, Nevada Pleistocene-Holocene alkaline lake pinnacles, Mono Lake, California Google map images http://maps.google.com/ Fluvial freshwater tufa, Holocene, Lombardy
- 16. Lake shoreline bioherms, Great Salt Lake, Utah • Hypersaline (6-27%); • Extensional, N-S and NE-SW oriented faults ; • Holocene aragonitic laminated and clotted peloidal microbial bioherms at high-energy shorelines associated with ooids; • Buildup distribution controlled by stable substrate, water depth (0.1-5 m depth) and faults; • Buildup shapes: m-scale, dms thick, elongated perpendicular to shoreline or sub-circular and coalesced. Modified after Eardley (1938), Carozzi (1962), Colman et al. (2002) Della Porta (2015, Geol Soc Spec Publ)
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- 21. Sublacustrine spring mounds, Pyramid Lake, NV • freshwater to mildly alkaline (pH 9); • extensional tectonics Basin and Range Province; • Upper Pleistocene-Holocene mounds (dm to 10s m, up to 60-100 m) • isolated, kms spacing, at mixing of groundwater and/or thermal sub-lacustrine springs with lake water; • spatial control by N-S normal and strike-slip faults acting as fluid conduits; • ikaite CaCO3·6H2O, calcite, aragonite 60-100 m Needles Rocks, Pyramid Lake Modified after Henry et al. (2007) Della Porta (2015, Geol Soc Spec Publ)
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- 24. Non marine carbonate selected case studies Lacustrine shoreline buildups • a) hypersaline Holocene Great Salt Lake, • b) soda lake Miocene Ries Crater, • c) schizohaline Eocene Green River Fm. Sublacustrine springs – thermal or groundwater mixing with lake water - upper Pleistocene-Holocene • a) mildly alkaline Pyramid Lake, • b) saline alkaline Mono Lake. Hydrothermal travertine rift lake (Miocene, Tuscany, Central Italy). Subaerial flowing-water systems : • a) freshwater fluvial systems (tufa Lombardy, Italy), • b) hydrothermal (38-50°C) travertine, Tuscany, Central Italy). 200 km 200 km Pleistocene hot-spring travertine Miocene rift lake with hydrothermal water, Tuscany, Central Italy Miocene algal bioherms, Ries Crater, South Germany Eocene schizohaline lake caddis fly larvae stromatolite bioherms Green River Fm., Utah & Wyoming Holocene hypersaline lake microbial bioherms, Great Salt Lake, Utah Late Pleistocene mildly alkaline lake, mounds, Pyramid Lake, Nevada Pleistocene-Holocene alkaline lake pinnacles, Mono Lake, California Google map images http://maps.google.com/ Fluvial freshwater tufa, Holocene, Lombardy
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- 27. Hydrothermal travertine terraced slope geometry § Present-day and Pleistocene subaerial hydrothermal travertine (T=38°) terraced slope (Tuscany, Italy) § mm- to dm layering § fast-flowing slopes vs. stagnant pools 0 . 5 m 60 cm W E N S 0.5 m pisoids pisoids pisoids Clotted micrite dendrites/ shrubs laminated Coated gas bubbles 1 cm Della Porta (2015, Geol Soc Spec Publ)
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- 38. What fabrics are diagnostic of a specific depositional setting and spatial distribution? • None… • similar fabrics in different depositional settings with different spatial distribution. • Clotted peloidal micrite fabrics (biologically induced/influenced) in all studied examples and similar to marine microbialites. • Crystalline dendrites and fans mostly present in hydrothermal travertine, sublacustrine spring mounds and fluvial tufa where supersaturation is from physico-chemical processes (evaporation, cooling, CO2 degassing, water mixing). • Better understanding by combining fabric associations + buildup architecture: • a) spring mounds: columnar and spherical structures with cm-dm concentric layering with crystalline, clotted peloidal and laminated fabrics; • b) hydrothermal travertines: evidence of water flow (terraced systems) and steep slopes.
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- 51. , Enrico Capezzuoli (Siena University) Paiute Tribe, PyramidLake California State Park, Mono Lake Saturnia Travertine Quarry Many thanks to: the project sponsors BG Group, Repsol & Statoil
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