Influence of Late Carboniferous–Early Permian climate change on the sedimentary evolution : a case study of the lacustrine Lower Anthracosia Shales (Intra-Sudetic Basin, SW Poland)

The Anthracosia Shales are lacustrine deposits within the volcano-sedimentary Pennsylvanian– Lower Permian succession of the Intra-Sudetic Basin. Core from the Rybnica Leśna PIG 1 borehole, which penetrated the Lower Anthracosia Shales, was analysed to explore the influence of climate on the evolution of the palaeolake, as distinct from tectonic and volcanic forcing. This reconstruction was made using mineralogical and geochemical proxies (elemental and mineralogical composition, TOC values, presence of framboidal pyrite and siderite). Based on the results, three chemically different intervals previously introduced by Wójcik-Tabol et al. (2021) are described. They represent the following stages of lake evolution: transgression (interval I), open lake (interval IIA and IIB), and termination (interval IIC and III). The initial stage of the lake (interval I) was probably related to a rise in humidity in the Late Pennsylvanian, linked to a southern Gondwana interglacial episode. Interval IIA represents the deepest facies of the Anthracosia Basin, where lake-floor anoxia prevailed. This stage was followed by a gradual lake-level fall recorded in interval IIB, with documented seasonality in humid and warm conditions. Interval IIC represents a stepwise lake regression attributed to aridification, as indicated by proxies showing a decrease in chemical weathering. Turbiditic sandy laminae in interval III reflect the terminal stage of lake infill.