Palaeoenvironments of the late Triassic Rhaetian Sea: Implications from oxygen and strontium isotopes of hybodont shark teeth

The oxygen and strontium isotopic composition of 125 teeth of the hybodont sharks Lissodus and Hybodus from various late Triassic (Rhaetian) bone bed localities in the Central European Basin are used as environmental and ecological tracers for the shallow epicontinental Rhaetian Sea. The preservation of tooth enameloid was ascertained by cathodoluminescence microscopy. Mean delta O-18(p) values differ regionally across the Rhaetian Sea with values of 18.6 +/- 0.6 parts per thousand. near the western gate, 16.1 +/- 0.8 parts per thousand in the east, 15.4 +/- 0.6 parts per thousand in the southeast, and 17.7 +/- 0.9 parts per thousand., in the south. The delta O-18(p) values in the eastern Rhaetian Sea are 4-5 parts per thousand lower relative to Tethyan seawater, while teeth from the southern and western parts close to the marine gates are less fractionated. The strontium isotopic composition of teeth from most localities is more radiogenic in comparison to late Triassic seawater. The observed spatial delta O-18(p) trend in the Rhaetian Sea indicates a shift from marine to brackish conditions in the south and west towards extensively brackish conditions with salinities of less than 16 parts per thousand in the east, thus confirming the existence of two marine gates. Brackish conditions persisted throughout early Rhaetian times, and were maintained by increased fluvial discharge from the Vindelician-Bohemian and Fennoscandian Highs as a result of enhanced atmospheric moisture availability in the course of the Rhaetian transgression. The delta O-18(p) values of Lissodus and Hybodus indicate euryhaline behaviour of Rhaetian hybodonts by exceeding modern shark intraspecific variability. The lack of accordance in delta O-18(p) values between different isotopically conspicuous localities in the Rhaetian Sea contradicts a basin-wide migration pattern. Differences between co-site taxa might indicate some degree of niche partitioning. (C) 2012 Elsevier B.V. All rights reserved.