During the larger part of the Upper Cretaceous the northern sector of the Adriatic Carbonate Platform (ACP) was significantly topographically differentiated. Temporarily and spatially shallow subtidal and peritidal enviroments with subaerially exposed areas alternated with deepened lagoons. Simultaneously, NE from the investigated area a land with karst features and bauxite existed. Typical lithofacies with the Murgella latta foraminifera assemblage, which occur everywhere directly above the paleokastic surface, indicate a relatively synchronous transgression in the middle Coniacian. On the contrary, SW from the investigated area shallow-marine sediments of the Sežana formation, occasionally interrupted by sediments of deep lagoons (the Komen and the Pliskovica limestones) sedimented.
We studied about 180 meters thick geological section situated above the passages of the Postojnska jama Cave in the area of Polhovica near Postojna, along the road towards the Pivka jama Cave. The investigated sequences should thus represent an intermediate zone between the inner, often slightly deepened, areas of the northern sector of the ACP and its NE regions which were subaerially exposed at the time considered. We were interested in the sedimentation dynamics and the relative fluctuations of the sea level of this topographically diverse part of the ACP in the Turonian and part of the Coniacian.
In general terms, the sedimentary sequence of the lower part of the section up to about 73 meters) of the Cenomanian-Turonian hemipelagic limestones (not entirely covered by the section) through bioturbeded micritic, rudist and peloidal-foraminiferal limestones of open lagoons. This section also contains bioturbeded peloidal limestone areas between open and closed lagoon through bioturbeded peritidal micritic and fenestral limestones and microbial micritic limestone. This sequence thus represents a gradual shallowing of sedimentary environments. Up to 130 meters, during short transgressive system tract and later during the highstand system tract, peloidal (locally bioturbated) and foraminiferal peloidal limestones which are in places interrupted by individual layers of skeletal micritic limestone alternate. Especially in the upper part of this section, fenestral porosity relatively often occurs, indicating the occasional exposure of the sediment to the intertidal conditions. A sequence of closed lagoon, occasionally interrupted by rudist and peloidal limestone, follows up to 151 meters. In this part of the section, fenestral limestones still occur, and in one place, also limestone with up to 2 cm large algal ball type oncoides. Rarely, in some layers, individual small black pebbles were observed. To the top of the section peloidal-foraminiferal limestone of the open lagoon predominates, where gradually more diverse and larger foraminiferas of the Murgella lata assemblage appear.
Most of the sedimentary sequences discussed were deposited in a very shallow subtidal environment of closed to open lagoon and the intermediate zone during the highstand system tract established after the Cenomanian/Turonian transgression. The above mentioned subaerially exposed and karstified part of the platform may have only "touched" the investigated area at its largest extent in the late Turonian or early Coniacian (commonly intertidal conditions). The foraminiferal peloidal limestone was deposited during the mid-Coniacian transgression on the top of the geological section.
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