Oxygen isotope composition of fossil shark teeth as a palaeoclimate proxy

The suitability of oxygen isotope analysis of fossil shark teeth as a proxy for marine palaeotemperature determination is assessed. Shark teeth may be useful for palaeoclimate reconstruction because they are common fossils, generally well-preserved, possess a long geological history, and are readily identified to generic, if not specific level. While many forms are cosmopolitan in habitat, individual taxa are fairly conservative, allowing certain palaeoecological assumptions to be made. Shallow marine shark taxa odontaspids, lamnids and carcharhinids) were collected from the Miocene Upper Marine Molasse of southern Germany. Jurassic shark teeth(hybodont and neoselachian taxa) from a variety of ages and marine palaeo-environments of the northern Europe epeiric sea were also analysed. The rapid growth and replacement of teeth means that the oxygen isotope composition of the tooth hydroxyapatite should not be affected by physiological or ecological changes with time, but instead, reflect temperature and isotopic composition of the water at the time of formation. A series of samples from the separate phosphatic phases (enameloid, orthodentine and osteodentine) of individual teeth was taken, to check for oxygen isotope heterogeneity across a tooth. In addition, several samples from within one sedimentary unit and across several layers were taken to evaluate inter-tooth heterogeneity and possible diagenetic alteration of the phosphate. Crystallinity is determined through XRD and trace element analyses.