Early to Middle Miocene terrestrial paleoenvironmental reconstructions of the Dinarides Lake System (Croatia, Bosnia and Herzegovina)

The Dinarides Lake System (DLS) constituted a set of intramontane freshwater lakes, which expanded during the Early to Middle Miocene in southeastern Europe. Sedimentation between ca. 18-12.5 Ma was contemporaneous with two well-documented climatic phases in marine records: the warm and humid Miocene Climatic Optimum (MCO; ca. 16.9-14.7 Ma) and the subsequent Middle Miocene Climatic Transition (MMCT; ca. 14.7-13.8 Ma). The MMCT was characterized by global cooling and the establishment of permanent Antarctic ice sheets. Here, we aim to reconstruct continental paleoenvironmental and paleoclimate dynamics during the MCO and MMCT in southeastern Europe based on sedimentary records from the DLS.We focus on four former lake basins (Pag, Gacko, Livno-Tomislavgrad, and Bugojno) and build on existing stratigraphic, sedimentological, and geochronological studies, including magnetostratigraphy, biostratigraphy, and the absolute dating of ash layers. We establish stable carbon and oxygen isotope records for the four basins and combine them with petrographic and mineralogical analysis derived from Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD).Our first quantified XRD results show the presence of high-Mg calcite and aragonite in some samples from each section, which indicates little to no diagenesis affecting our samples. δ18O and δ13C values for each lake basin are positively correlated. We interpret the positive correlation to reflect hydrologically closed lake conditions during carbonate precipitation. Additionally, δ18O values display a positive relationship with modern elevations and distance to the coast for two time-equivalent lake records (Pag and Livno-Tomislavgrad) during the onset of the MCO. While the near-coastal Pag section yields mean δ18Ovalues of -9.1 ± 0.1 ‰ (n= 89; V-PDB), the Livno-Tomislavgrad basin (located ca. 50 km off the coast at ca. 750 m elevation) yields δ18O values of -5.0 ± 0.2 ‰ (n= 22; V-PDB). This may indicate that δ18O values are primarily controlled by evaporation in the lake basin located further away from the coast, rather than the isotopic composition of the incoming waters. By combining existing studies with our new data, we aim to reconstruct the terrestrial paleoenvironment and paleoclimate during lake deposition during the MCO and MMCT in southeastern Europe.