Late Eifelian Kačák Episode in the epeiric Belarusian Basin: Role of terrestrial-marine teleconnections

Abstract The uppermost Eifelian Kostyukovichi Formation corresponds to a distinct marine transgressive-regressive cycle in predominantly continental to restricted-marine Middle Devonian succession of the intracratonic Belarusian Basin in a near-equatorial area of SE Euramerica. The presence of the conodont ensensis Zone points to the correlation with the global Kacak Episode whose onset coincided with the eustatic If transgression. The comprehensive study of the Kostyukovichi Fm. in 18boreholes included sedimentological, palaeontological (conodonts, palynoflora, vertebrates) and geochemical analyses (C, O and Nd isotopes in carbonates and bioapatite). The results demonstrate that the sedimentation was characterized by intermittent hypoxic conditions and salinity fluctuations; it was controlled by increasing terrigenous and freshwater influx from the northern Scandinavian Land with carbonate sedimentation limited mostly to the early stage and southern part of the basin. The palynological study and occurrence of phytoclasts document terrestrial plant expansion, while the abundance of diverse fish taxa attests to the proliferation of vertebrates. These bioevents are attributed to transgression, climate humidization, and expansion of aquatic environments in surrounding land areas. Regional review suggests that such attributes of the Belarusian Kacak Episode as the initial If transgression, marine hypoxia, land plants blooms, carbonate decline and terminal regression, are characteristic also for other palaeogeographic settings of the episode worldwide. The Kacak Episode is here explained as a result of complex interrelations of various terrestrial and marine processes and events initiated by a global warming resulting in eustatic transgression and climate humidization. It is proposed that the important component of the terrestrial-marine teleconnections was the late Eifelian plant expansion presumably connected with the proliferation of progymnosperm arborescent plants with deepened root systems. It contributed to transiently increased denudation rates and, indirectly, to the development of marine hypoxia. The episode was terminated by the low-amplitude regression related to the enhanced CO2sequestration and resulting climatic cooling.