engleski

Pontian environments from the Croatian part of the Pannonian Basin based on dinocysts and facies analysis

In this work, the succession of environments and dinocysts assemblages is analyzed from the youngest Miocene deposits from the southern margin of the Pannonian Basin. Palynological and facies analysis were carried out on the deposits from two surface profiles on the northern slopes of Krndija Mt. and southern slopes of Dilj Mt. The oldest investigated deposits are massive marls, which are calcite-rich in the lower part and silt-rich in the upper part of the succession. They are deposited in deep, distal, brackish-lacustrine environment. In the lower marls dinocyst assemblage is dominated by Spiniferites validus correlative with assemblages from Hungarian Spiniferites validus zone, used in biozonation of the Paratethys by Magyar et al. (1999), and in the description of the proposed stage or substage Transdanubian (Sacchi & Horváth, 2002). Maximum CaCO3 (79%) was measured in sample which contain less phytoclasts in palynofacies suggesting decreased terrigenous influence, and dinocysts assemblage dominated by forms with thinner wall, and membranous: Galeacysta etrusca and Spiniferites cruciformis. Based on the dinocysts diversity and abundance, maximum flooding was recognised. At that time endemic Paratethyan taxa migrated into the Mediterranean, which might be used for the correlation of Paratethyan with Mediterranean sediments (Bakrač, 2005). It should be pointed out that this is the oldest founding of the Spiniferites cruciformis. Middle part of the investigated succession consists of the alteration of sands, silts and marls deposited in transition from deeper into shallower lacustrine environment (prodelta-deltaic slope). More proximal environment is confirmed by proximate dinocysts with thicker wall: Impagidinium globosum, "Virgodinium asymmetricum", Chytroeisphaeridia tuberosa and Brigantedinium sp. Deposition of sands and silts from the upper part of the succession took place in relatively shallow brackish-lacustrine environment (delta-front). Palynofacies is dominated by inertinite in these sediments, which suggests a relatively coarse-grained high-energy facies (Tyson, 1995). Silty, clayey, and sandy deposits from the uppermost part of the succession were accumulated in delta plain environment. Described vertical succession of the Pontian deposits shows a coarsening-upward trend, while alteration of the environment shows shallowing and infilling of the depositional area. All of this indicates generally regressive trend of sedimentation, which resulted from the progradation of clastic system from the north (Kovačić, 2004) contemporaneously with decreasing of the subsidence rate, and even the basin inversion (Jamičić, 1995). During this regressive deposition an episode of short-living transgression was documented only by dinocysts, which is of great importance for the correlation of Paratethyan, and possibly with Mediterranean sediments.

Pontian; Pannonian Basin; Croatia; lake; delta; dinocysts; sedimentology

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