THE SARMATIAN (MIDDLE MIOCENE, PARATETHYS) BRACKISH WATER TURNED INTO FULLY MARINE

The upper Middle Miocene Sarmatian Stage (duration: 1.5 Ma) of the Central Paratethys is generally interpreted as a transition from the marine, subtropical Badenian Sea towards the temperate-freshwater environments of Lake Pannon (Upper Miocene), reflecting brackish conditions. An integrated re-evaluation of Sarmatian deposits in the western Central Paratethys, including all currently available outcrops in the Vienna and Styrian basins as well as some deep wells, brought new inside into this story. After a distinct sea-level drop at the end of the Badenian, the Lower Sarmatian Mohrensternia Zone is dominated by fine-siliciclastic sedimentation and only rarely autochthonous carbonate build-ups of serpulids and bryozoans occur (3rd order TST). Even in this setting, except of some hyposaline coastal environments (tidal flats), most biota point to a normal marine salinity (e.g., the serpulid Hydroides). After a marked drop in sea-level and sedimentation of coarse grained conglomerates even in the basin centers during the lower Ervilia Zone sedimentation switched from siliciclastic to carbonatic. As a result, up to 20 m oolite-sequences of multi-layerd oolites and thick coquina beds were deposited, forming small carbonate platforms. This switch coincides with a dramatic increase in shell-thickness of bivalves reflecting a change in mineralisation of the Sarmatian water body. Similar implications come from "gastropod-sediments" formed by marine to hypersaline cerithiids, foraminifera (Spirolina and abundant thick-walled miliolids), and cementation features (botryoidal cements) pointing into the same direction. The shift from mixohaline to full marine conditions from Lower to Upper Sarmatian is strongly triggered by the ingression of marine waters from the Mediterranean and reflects a 3rd order HST. This ingression coincides well with the appearance of marine taxa unknown from Lower Sarmatian deposits. Correspondingly, complex bryozoan-foraminiferal-algal-microbolite build-ups show their optimum during the Upper Sarmatian Mactra Zone. From these data it is obvious that the generally accepted interpretation of the Sarmatian Sea as a slowly freshening brackish basin has to be rejected and particularly during the Late Sarmatian normal marine to partly hypersaline conditions prevailed.