Szabó János szerk.: Fragmenta Mineralogica Et Palaentologica 19. 2001. (Budapest, 2001)
The Leithakalk is well known from the Middle Miocene of Austria and Hungary. The Leithakalk of the Rüster Bergland deposited during the Middle Badenian (Sandschaler Zone), the Buliminen-Bolivinen Zone is only represented in the upper layers of the limestones around St. Margarethen (FUCHS 1965). The depositional environment of the Leithakalk usually was composed of diverse shallow-water and nearshore facies types in patchy, mosaic-like distribution. The local bottom topography caused variable water energy conditions that led to the development of diverse facies types and deposition of different sediments (HÁMOR 1970, 1985). NÉMETH (1999) recognised maerl, calcarenite and rhodolitic Leithakalk types in the subsurface succession of the Ortaháza region (SW Hungary). Miocene carbonate sediments in Central Europe have traditionally been regarded as indicative of a tropical-subtropical depositional environment (HÁMOR 1985). LELKES & STUDENCKI (1990) and RANDAZZO et al. (1999) suggested more temperate climatic conditions for the Badenian age based on the low diversity of hermatypic corals, lack of calcareous green algae, abundance of a foramol biological association dominated by red algae, and other peculiarities. As CARANNANTE et al. (1988) pointed out, "foramol-type sediments are very abundant on temperate shelves, but they also are present in shallow tropical or subtropical waters where reef corals and calcareous green algae are not developed because of particular environmental or ecological conditions". According to DÜLLO (1983), the Material £ "foraminiferal debris facies types" of St. Margarethen area were formed in a shallow-water environment without reefs. The Vienna Basin, along with the rest of the Paratethys, underwent a complex tectonic history (FODOR 1995); extensive volcanic activity and regional current system changes characterised the region in the Middle Miocene (RANDAZZO et al. 1999). In the Middle Badenian the Central Paratethys retained a marine connection with the Mediterranean through the "TransTethyan-Trench-Corridor" in today's Slovenia (RÖGL 1998, 1999), which assured normal marine salinity conditions for the Vienna Basin and the entire Central Paratethys. In the Vienna Basin marked facies differentiation took place during the Early Badenian: Baden clay deposited in the basinal part and Leithakalk developed as marginal sediments (TOLLMANN 1955). Extensive carbonate platforms could not be formed due to environmental constraints; smaller marine basins were depositional sites instead (RANDAZZO et al. 1999). Fluvial sediments were transported into the Vienna Basin through smaller deltas in the west (SAUER et al. 1992). A complex basinal geometry, with narrow straits and bays separated by islands and peninsulas characterised the region by that time (RANDAZZO et al. 1999). According to a conceptual paleoenvironmental reconstruction by RANDAZZO et al. (1999), western Hungarian carbonate basins were characterised by patch reefs and rhodolite pavements seawards, while river deltas and volcanic activity influenced the coastal environment. d Methods The type specimen of Heterodelphis leiodontus (Inv. number: Ob-258, Geological Museum of the Geological Institute of Hungary, MAFI) lying on two limestone blocks was used for the study. The embedding limestone was split into two parts during excavation, breaking the dolphin skeleton approximately along the mediansagittal plane (Plate I: A). As a consequence, the skeleton lies on two halves of the limestone block that complement each other (table 5 and 6 in PAPP 1905). This resulted in the unfavourable condition of most intact bone surfaces being covered by the embedding limestone. Thus, all vertebrae and the right flipper bones exhibit their outlines only. Since the breakage of the skeleton did not occur accurately along the mediansagittal plane (as concluded e.g. from the condition of the skull), intact bones are expected inside the limestone. The distal part of the rostrum, the complete caudal region of the vertebral column, posterior lumbar vertebrae and pelvic bones as well as the sternum are missing. The broken surfaces of the rostrum bones and the posteriormost preserved vertebra are clearly visible on the cutting surfaces of both halves of the limestone block. This indicates that the missing parts were lost during excavation and not during the embedding. Five thin sections were prepared perpendicular to the bedding. Thin sections No. 1-3 originate from the lower block, No. 4—5 from the upper block, numbered from below. The thin sections were studied under pétrographie microscope and cathodoluminoscope. Xray was used to trace bony elements inside the limestone blocks. Stable isotope ratios 8 13 C and ô 18 0 were measured in two samples taken from the upper and lower part of the upper and lower limestone blocks, respectively. Results The skeletal assemblage Vertical extension of the exposed Leithakalk in St. Figure 1, after DÜLLO 1983). Shark teeth, cetacean Margarethen is about 30 m (see lithologie section in remains and sirenian rib fragments represent the known
