Szabó János szerk.: Fragmenta Mineralogica Et Palaentologica 19. 2001. (Budapest, 2001)
close to the coarse-grained base of the more porous bed. We conclude that the more porous, thinner rock slab is the stratigraphically younger, upper block and the dolphin lies on its right side. The grain-size contrast of the embedding block suggests a rapid sedimentation event. Table 1 — Stable isotope ratios of the embedding rock Sample Ô 13 C 6 18 0 Sample (PDB, %o) (PDB, %o) St. Margarethen, 1 -2.31±0.05 -5.1610.11 St. Margarethen, 2 -2.25+0.11 -5.29+0.07 Stable isotope investigation — Table 1 shows the stable isotope ratios measured in two samples from the vicinity of the skeleton. The depleted carbon reveals meteoric water influence during diagenesis for both samples. Hence, salinity of the palaeoenvironment cannot be calculated and 5 18 0 values cannot be used for palaeotemperature reconstruction. Microscopic observations — The majority of the elongated grains lie roughly parallel to the bedding that indicates the lack of strong bioturbation in the vicinity of the dolphin skeleton. The tendency of increase in grain- and pore-size upwards, observed by macroscopic scale, is clearly visible in the thin sections (Plate I: C, Plate II: D). The grain-size varies between 0.1 and 6 mm. The taxonomic composition of the rock forming flora and fauna is similar in all samples. The bedrock and the overlying sediment represent the same facies type. DÜLLO (1983) distinguished 10 Leithakalk microfacies types. Our samples could be best correlated with his "foraminiferal algal debris facies", with minor differences. Our samples contain locally more bryozoa and serpulids, but do not contain any rhodolites and peloids. The investigated material is more porous and less cemented than the "foraminiferal algal debris facies" type of DÜLLO. The material is weakly cemented bioclastic grainstone and rudstone, containing no mud at all. Halfquantitative measurement of the main components shows the following distribution: red algae 50—60%, foraminifera 3—5%, fragmented bryozoan colonies 5— 10%, bivalve shells 0-2%, echinoid fragments 2-6%, serpulids 0-1%. Very few ostracod shells were found. Micrite mud is absent in the material and there were no peloids observed in the thin sections. Micritic envelope around the bioclastic grains is common. The bioclasts are weakly cemented with the 8—10% calcite. Table 2 — Foraminifer genera identified from the thin sections and their abundances in t he samples. Ecological preferences are based on MURRAY (1976), typical sediments according to NÉMETH (1999). Uncertain occurrences are not listed. (+ found in one sample only; ++ present in at least two samples; +++ present in all samples but not abundant; ++ + + abundant in all samples) Foraminifer genera Abundance Ecological preferences Typical Leithakalk facies Asterigerina sp. ++++ shallow, warm waters ? Elphidium sp. ++++ euryhalin; 1-30°C; 0-50 m depth maerl Textularia sp. +++ normal marine; arctic to tropical; 50—640 m depth calcareous sand Eenticulina sp. ++ euryhalin; subtropical; shallow waters ? Quinqueloculina sp. +++ mainly normal marine; temperate to tropical; 0—40 m depth maerl Spiroloculina sp. ++ euryhalin; subtropical; shallow waters maerl Triloculina sp. + euryhalin; subtropical; shallow waters maerl Explanation to Plate I A Ob-258 on the larger rock slab. Sliding caliper open at 50 mm. B Dashed line indicates the boundary between the fine grained lower part of the larger slab and the more porous parts. The skeleton lies between the two blocks. Scale bar = 50 mm. C General view of the thin section No. 1. The material is weakly cemented bioclastic grainstone. Grain sizes are typically smaller than in the upper part of the embedding b lock. Scale bar =10 mm
