Sedimentology and palaeoenvironmental analysis of a karstic shallow carbonate lake (Early-Middle Miocene, Sinj Basin, Croatia)

Abstract

In the Early to Middle Miocene, the post-orogenic intramontane lacustrine Sinj Basin that belonged to the Dinarides Lake System evolved in the area of the External Dinarides. A composite 770 m thick stratigraphic column was measured spanning the basin's stratigraphy. Eight facies were differentiated. Four facies are almost entirely composed of freshwater carbonate deposits. Carbonate facies are divided into calcareous mudstone, charophytic micritic limestone, calcisiltite and coquina facies. They are interpreted to belong to a prograding carbonate bench on a gently inclined lake margin. In addition, tuff/clays, carbonate conglomerate, carbonate breccia and coal were differentiated. The tuff/clays are the result of remote volcanic eruptions, while the coarse-grained sediments belong to subaqueous shallow stream channels or were deposited by gravity flows. The coal at the top of the measured succession, mostly of allochthonous origin, was deposited as a fen forest peat, representing the final stage of the lake. The formation of the Sinj Basin might have been triggered by dissolution of Permo-Triassic evaporites, within the mostly carbonate basement but also by breakdown and collapse of Mesozoic and Palaeogene carbonate rocks and coalescence of contiguous sinkholes. The non-tectonic interpretation of the basin genesis is a novel hypothesis explaining the origin of one of the Dinarides intramontane basins and is in contrast to previous considerations that evolution of the Sinj Basin was controlled by strike-slip or extensional tectonics.