Extensive non-marine depositional setting evidenced by carbonate minerals in the Ediacaran clastic series of the western East European Craton

Abstract

The Ediacaran sedimentary rocks on the East European Craton (EEC) comprise chiefly siliciclastic deposits of the Volyn and Valdai series that have commonly been regarded as deposits in a shallow epicontinental sea on Baltica. However, an intermittent fresh-water sedimentary setting was also indicated for some part of the paleocontinent. Surprisingly, although Baltica was positioned in low latitudes during the Ediacaran period, no carbonate sequences have formed on the EEC. Systematic and detailed mineralogical, petrographic and stable isotope evaluation of carbonate minerals occurring in the Ediacaran sedimentary rocks of the western EEC stretching from the Arkhangelsk area at the White Sea to the Ukraine-Moldova borderland near the Black Sea show that continuously marine or sea water-influenced depositional conditions existed only in the marginal parts of the area: Podillya, Moldova, and the Arkhangelsk area. In contrast, a fully continental depositional setting stretched in the central part (St. Petersburg area, Lithuania, E Belarus) with intermittent periods of marine or brackish-water conditions only in E Belarus. SW Belarus and Volyn were influenced by marine or brackish environments. Highly 13C-enriched early-diagenetic calcite from Poddillya and pedogenic siderite from the St. Petersburg area attest for bacterial methanogenesis operating during the Kotlinian period both in marine and continental environments, respectively. This shows that not only marine, but also terrestrial biosphere was already very productive at the end of the Ediacaran. The δ18O composition of meteoric, marine hypersaline, burial, and hydrothermal fluids was reconstructed by integration of mineralogical, petrographic and stable isotope data for various types of Ediacaran carbonates from the western EEC. Moreover, the range of δ18O values for Ediacaran marine carbonate was constrained by setting the lower limit at −5‰, which is the maximum value for pedogenic siderite, and the upper limit at +2‰, which is the minimum value for carbonates associated with saline fluids.