Evolution of a Late Carboniferous Fluvio-Lacustrine System in an Endorheic Basin: Multiproxy Insights from the Ludwikowice Formation, Intra-Sudetic Basin (SW Poland, NE Bohemian Massif)

Fluvio-lacustrine systems are highly dynamic continental environments, often developing in tectonically controlled, endorheic basins where sedimentation reflects the interplay of fluvial processes, lake-level fluctuations, climate, and subsidence. The main aim of this paper is to reconstruct the depositional architecture and paleogeographic evolution of the Ludwikowice Formation (Intra-Sudetic Basin, NE Bohemian Massif), which preserves a high-resolution record of a late Carboniferous (late Gzhelian) fluvio-lacustrine system. The formation developed as a fining-upward megacyclothem documenting the transition from proximal alluvial and fluvial fan deposits to distal, organic-rich lacustrine facies referred to as the Lower Anthracosia Shale (LAS). This study integrates lithological data from 92 archival boreholes with high-resolution sedimentological, geochemical, petrological, palynological, and magnetic susceptibility analyses from two fully cored reference sections (Ścinawka Średnia PIG-1 and Rybnica Leśna PIG-1) and selected exposures. Nine facies associations (FA1–FA9) have been identified within the formation, including fluvial, sandy to muddy floodplain, aeolian, playa lake margin/coastal mudflat, nearshore, delta plain, subaqueous delta front and subaqueous fan, prodelta, and open lake. The succession shows progressive thickening into narrow, NW–SE-trending depocenters associated with possible strike-slip faulting. Geochemical and isotopic data indicate alternating hydrologically open and closed lake conditions, while magnetic susceptibility reflects climatically driven variations in detrital influx and microbial activity. Organic petrography and palynofacies analyses reveal redox-controlled maceral associations. The Ludwikowice Formation constitutes a detailed archive of Late Paleozoic environmental change and provides new insights into sedimentation and organic matter preservation in intramontane endorheic basins. Our results highlight the response of fluvio-lacustrine systems to climatic and tectonic factors and provide a framework for interpreting analogous successions throughout the stratigraphic record.