OXYGEN ISOTOPE PROFILES OF UPPERMOST JURASSIC VERTEBRATE TEETH AND OYSTER SHELLS: A RECORD OF PALEOENVIRONMENTAL CHANGES AND ANIMAL HABITATS

摘要

High resolution oxygen isotopes profiles of well-preserved uppermost Jurassic oyster shells and vertebrate (ichthyosaur and fish) teeth from Central Poland were obtained using a microdrill and an ion microprobe (SHRIMP He/MC). Internal variability of delta O-18 values of oyster shells (-1.7 to 1.3 parts per thousand VPDB) collected from the offshore interval of the studied section is greater than that determined previously from bulk oysters. Relatively high delta O-18 values of the studied oysters may be linked to a slight increase in the salinity of the mid-Polish basin. Low delta O-18 values of co-occurring ichthyosaur tooth enamel substantiate endothermy of these reptiles. An observed ontogenetic increase in the ichthyosaur enamel delta O-18 values (from similar to 19.4 to similar to 21.6 parts per thousand VSMOW) may be a result of long distance migrations although the effect of metabolic factors at rising body mass cannot be completely excluded. It is postulated that delta O-18 values of the latest portion of the ichthyosaur tooth enamel can be used for the calculation of ancient water oxygen isotope composition and verification of oxygen isotope temperatures. High delta O-18 values of the enameloid of Caturus lungfishes (23.6 to 26.5 parts per thousand VSMOW) collected from an upper part of the studied section, which was deposited in a restricted lagoonal environment after a marine regression, are probably a result of a high evaporation rate. The fishes could have breathed atmospheric air and withstood episodes of water hypoxia. Internal oxygen isotope records of the shells and teeth are promising proxies for studies of the paleoenvironment and activity of animals.