ESTIMATING MIOCENE TOPOGRAPHY OF THE DINARIC ALPS USING STABLE-ISOTOPE PALEOALTIMETRY

The collision between Eurasia and the Adria microplate of the Alpine-Himalayan orogenic belt led to the formation of the Dinaric Alps and the formation of basins that became known as the Dinaride Lake System. However, the topography of the Dinaric Alps during this process remains poorly constrained, with attendant uncertainties regarding the geodynamic mechanisms that created the range and the climatic conditions that sustained the extensive Dinaride Lake System. To constrain paleo-elevations using stable isotope paleo-altimetry, we collected authigenic lacustrine carbonate samples from ten sections across seven Early to Middle Miocene basins which range from the coast of Croatia to the high-elevation intermontane basins of Bosnia and Herzegovina. In addition, we collected water samples from streams that span across the elevation range of the basins to constrain the modern δ¹⁸O gradient. We find higher δ¹⁸O at the coast and lower δ¹⁸O near the crest of the modern range, resulting in a decrease of approximately -5 ‰ from the coast to the crest over the 2.5 km height origin. However, we observe a different trend in the lacustrine carbonate δ¹⁸O; the highest Miocene δ¹⁸O values are near the crest of the range, with lower δ¹⁸O values at the coast. Given that many of the lacustrine carbonates show a positive correlation between δ¹⁸O and δ¹³C—indicative of evaporative enrichment of ¹⁸O—we suspect that this reversed δ¹⁸O gradient results from substantial evaporation in the Dinaride Lake System. We plan further analysis to measure the Δ¹⁷O of the collected lacustrine carbonates to eliminate the effect of evaporation and thereby constrain the paleotopography of the Dinaric Alps.