Ediacaran-Paleozoic subsidence history of the Volyn-Podillya-Moldavia Basin (W and SW Ukraine, Moldova, NE Romania)

Abstract

Tectonic subsidence history was analysed for the Ediacaran-Paleozoic Volyn-Podillya-Moldavia Basin, by performing 1D backstripping for 21 boreholes located in western and SW Ukraine, Moldova and NE Romania. Tectonic subsidence history is coherent across the area studied. Development of the basin commenced with an Ediacaran phase of extension, initiated with the emplacement of rift-related volcanic rocks and associated with rapid syn-rift tectonic subsidence. During this event, tectonic subsidence increased towards the SW, i.e. towards the edge of the East European Craton, where the Ediacaran rift zone was located. At that time, a rift developed along the whole SW margin of the East European Craton from Scandinavia to the Black Sea. Development of this large extensional basin was related to the latest stages of break-up of the Precambrian supercontinent Rodinia/Pannotia and ultimately the formation of the Tornquist Ocean. The latest Ediacaran to Late Ordovician tectonic subsidence pattern was characteristic of the post-rift thermal sag stage of extensional basins. The SW margin of the newly formed Baltica, including the area studied, became a passive continental margin. The late Cambrian uplift and erosion was presumably related to a far-field effect of contractional events or intra-plate stresses. Since the Late Ordovician, a gradual change to a collisional tectonic setting is observed across the SW margin of Baltica. In the study area, this is indicated by a systematic increase in subsidence rate from Wenlock to Early Devonian time, creating subsidence curves with convex shapes typical of foreland basin development. The Silurian to Early Devonian Volyn-Podillya-Moldavia Basin is interpreted here as a flexural foredeep related to a Caledonian collision zone located further to the SW. The prominent diachroneity in the initiation of the foredeep basin development at a scale of the whole SW margin of Baltica is coherent with a model of oblique collision of Avalonia and Baltica. During the Pragian-Emsian, the basin was part of a system of post-collisional Old Red basins, with subsidence driven presumably by lithospheric isostatic imbalance resulting from the Caledonian collision and development of an accretionary wedge. Middle to Late Devonian short-term phases of rapid subsidence in small depocentres might be regarded as an indication of a transtensional tectonic regime