Palustrine limestones and calcretes as the sedimentary record of paleoenvironmental changes in a Late Permian semi-arid climate at the SE periphery of the Southern Permian Basin (the Holy Cross Mountains, Poland)

Abstract

An important part of the Upper Permian (Zechstein) sequence in the Holy Cross Mountains (HCM) in Poland comprises continental carbonate facies where dryland and wetland depositional environments dominated the southeastern part of the Southern Permian Basin. Sedimentological and thin-section microfacies analysis of over 860 m of core from seven wells, supplemented with field observations from several outcrops from the HCM area, has allowed recognition of numerous siliciclastic and mixed silici‑carbonate facies which are related to alluvial fan, proximal and distal floodplains, and ephemeral lacustrine environments. Due to climatic seasonality and subsequent groundwater oscillations, the latter were frequently exposed, causing widespread desiccation cracking and pedogenesis. Continuous aggradation controlled by steady tectonic subsidence allowed the deposition and preservation of thick (> 30 m) units with numerous palustrine intervals. In such a low aggradation rate system, vertical and lateral changes in the continental facies associations reflect the climatic evolution from arid to semi-arid and then to sub-humid environments with enhanced climatic seasonality. These facies changes indicate a gradual increase in the water availability towards the Permian-Triassic boundary, which may support the hypothesis of generally increased wetting at the low-latitudes of Pangea, linked with the development of greenhouse conditions and enhancement of the intertropical convergence zone at that time. Continental carbonates are therefore recognised as high-resolution recorders of palaeoclimate and tectonics.