Travertine precipitation in the Paleoproterozoic Kuetsjärvi Sedimentary Formation, Pechenga Greenstone Belt, NE Fennoscandian Shield

Abstract

Precambrian travertines, tufas and speleothems either formed rarely or they have not been identified in previous studies. In the absence of high pCO2 soils in Paleoproterozoic, karst solution and speleothem formation occurred by processes distinct from those commonly found in present-day low temperature karst environments. However, the high pCO2 atmosphere could itself have encouraged karst formation. The Paleoproterozoic Kuetsjärvi Sedimentary Formation of the Pechenga Greenstone Belt, NW Russia, includes abundant terrestrial carbonate precipitates. These precipitates were sampled from a drillcore representing a complete section of the ca. 120-m-thick formation and were investigated for C and O isotopes, acid-soluble elemental contents and petrography. The newly obtained results were used to constrain the origins of the precipitates and to illuminate different terrestrial carbonate types. The investigated drillcore includes abundant small-scale cavities and veins, which are commonly filled with dolomite and quartz. Dolomite crusts are found both in the cavities and on bedding/erosional surfaces. Dolomite cements coat uneven surfaces and surficial rock fragments. The surficial dolomite crusts form distinct and discrete layers, whereas the cements do not. The cavity and vein fills are likely post-depositional in origin, whereas the surficial dolomite crusts and dolomite cements are likely syn-depositional precipitates. The investigated precipitates often show δ13C values lower than those reported from their host rocks, suggesting the influence of an external carbon source. Petrographic features and geochemical data suggest dissolution and precipitation of carbonate material originating from deep-sourced CO2-bearing fluids, likely at high earth surface temperatures.