The transition from a closed to an open lake in the Pannonian Basin System (Croatia) during the Miocene Climatic Optimum: Sedimentological evidence of Early Miocene regional aridity

Abstract

In the area of the North Croatian Basin, as the south-western part of the Pannonian Basin System, a lake that was characterized by mainly dolomite deposition evolved in the late Early Miocene. The dolomites precipitated directly from the water body, and are associated with tuffites and marls, together with minerals such as analcime, hydrous Ca-bearing magnesium carbonate, and natrolite. This indicates deposition in a shallow, hydrologically closed lake of highly alkaline waters controlled by an arid climate in the first stage of its evolution. The second evolutionary stage is represented by the intercalation of sandstones as a result of gravity flows, and dolomites that reflect changes of hydrologically open and closed lacustrine environments controlled by the frequent alternation of humid and arid climates. The third stage, that probably commenced in the Middle Miocene, indicates the formation of a long-lived, hydrologically mostly open lake, characterized by deposition of siliciclastics by gravity flows. The whole lacustrine depositional sequence coincides with the Miocene Climatic Optimum generally characterized by hot and warm, and humid climates. However, the evolution of the closed lake that is correlative with similar lakes in northern Bosnia and central Serbia, indicates the existence of an arid zone in the region that was confined by areas characterized by a more humid climate in the late Early Miocene.