An arid phase in the Internal Dinarides during the early to middle Miocene: Inferences from Mg-clays in the Pranjani Basin (Serbia)

Abstract

Lacustrine strata record long-term variations in climatic and tectonic perturbations during orogen evolution. Here we use the sedimentological record of the early to middle Miocene intramontane lacustrine Pranjani Basin (Serbia) to study tectonic and climatic variations during the evolution of the Dinaridic orogen. Our study focuses on a Mg-clay-bearing succession that belongs to the second depositional cycle. A detailed sedimentological, mineralogical and geochemical study shows that the investigated Mg-clays bearing succession consists of an alternation of smectite- (± analcime or sepiolite), dolomite-sepiolite and sepiolite layers. We interpret this high-order cyclicity to have been driven by variable water availability, i.e. by the interplay between runoff, groundwater influx and evaporation. Furthermore, we relate these pulses in water variability to wet and dry intervals under semi-arid to arid climatic conditions. Dry intervals produced a negative water balance promoting the deposition of sepiolite - and dolomite - dominated facies. Wet intervals and a positive water balance stimulated higher terrestrial input and thus favored the deposition of smectite-dominated facies. Our new data combined with a review of previous studies reveal longer-term basin-wide lake level and chemistry fluctuations, which we relate to closed and open lake phases. We suggest that these phases can be explained by alternating humid and arid phases superimposed on tectonically induced uplift and subsidence. The arid phases led to lake shrinking and deposition of an evaporite-bearing succession. During the intervening humid phase, the lake expanded. In contrast to the lakes formed in the external part of the Dinarides, the lakes that existed in its internal part contain evaporite-bearing successions, indicating that this arid phase was regionally extensive and possibly orographically controlled.