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 pCO 2 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 pCO 2 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-mthick 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 1 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, whereasthe surficial dolomite crusts and dolomite cements are likely syndepositional precipitates. The investigated precipitates often show δ 13 C 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 CO 2-bearing fluids, likely at high earth surface temperatures.

The influence of microbial mats on travertine precipitation in active hydrothermal systems (Central Italy)

“…The oldest reported terrestrial travertine deposits, attributed to deep‐sourced carbon dioxide fluids at high temperature, are hosted in the Palaeoproterozoic ( ca 2.2 Ga) Kuetsjärvi Sedimentary Formation (Pechenga Greenstone Belt; Fennoscandian Shield; Brasier, 2011; Melezhik & Fallick, 2001; Salminen et al, 2014). These dolomitic travertines and stromatolites might have formed through similar processes to present‐day hydrothermal springs, but they do not contain traces of organic carbon (Salminen et al, 2014). The oldest siliceous deposits attributed to terrestrial thermal springs are known from the ca 3.5 Ga Dresser Formation (Pilbara, Western Australia) and were interpreted as putative geyser environments (Djokic et al, 2017).…”

“…Despite the abundance of Cenozoic terrestrial thermal spring settings with precipitation of siliceous sinter and/or carbonate travertine (Capezzuoli et al, 2014; Jones & Renaut, 2010, 2011; Pentecost, 2005), these deposits are scarce in the pre‐Cenozoic fossil record (Des Marais & Walter, 2019). The oldest reported terrestrial travertine deposits, attributed to deep‐sourced carbon dioxide fluids at high temperature, are hosted in the Palaeoproterozoic ( ca 2.2 Ga) Kuetsjärvi Sedimentary Formation (Pechenga Greenstone Belt; Fennoscandian Shield; Brasier, 2011; Melezhik & Fallick, 2001; Salminen et al, 2014). These dolomitic travertines and stromatolites might have formed through similar processes to present‐day hydrothermal springs, but they do not contain traces of organic carbon (Salminen et al, 2014).…”