The carbon and oxygen isotope records of Upper Bajocian-Bathonian calcareous fossils from the Polish Jura Chain

• Autorzy: Wierzbowski H. , Joachimski M.
• Konferencja: International Congress on the Jurassic System (7 ; 06-18.09.2006 ; Kraków, Poland]
• Języki publikacji: EN

Abstrakty

EN

A collection of stratigraphically well-dated calcitic and aragonitic fossils (belemnites, ammonites, nautiloids and oysters), derived from Upper Bajocian - Upper Bathonian clays from the Polish Jura Chain (central Poland), were studied for oxygen and carbon isotopes. The preservation state of the shell material was investigated by means of cathodoluminescence microscopy, trace element geochemistry and X-ray diffraction. Palaeotemperatures calculated from the oxygen isotope composition of calcitic shells (belemnites and oysters) are similar to each other despite the significant spread in 18O values (Fig. 1). The 18O values of calcitic fossils generally vary from -0.1 to +1.1‰ VPDB for the studied interval, which corresponds to palaeotemperatures between +7.9 and +12.4°C (calculated with the equation of Anderson & Arthur 1983). The palaeotemperatures derived from the oxygen isotope composition of aragonitic ammonoid and nautiloid shells are distinctly higher (Fig. 1) with most of the estimates ranging from 15 to 23°C (calculated with the equation of Grossman & Ku 1986). The observed temperature difference may have resulted from different depth habitats of the organisms. The ammonites and nautiloids might have lived in surface waters and the temperature contrast might represent a palaeotemperature gradient between thermally stratified surface and deep waters of the Late Bajocian - Late Bathonian sea in the Polish Jura Chain. The ?13C values for the Upper Bajocian - Upper Bathonian belemnite rostra do not indicate major secular variations (Fig. 1). However, the data show a significant scatter of about 1.5‰. Several oyster shells show considerable higher 13C values (around +3‰ VPDB) compared to coeval belemnite rostra (between 0 and +1.5‰ VPDB). This may point to a metabolic fractionation effect that resulted in disequilibrium fractionation of carbon isotopes within belemnite skeletons (cf. Wierzbowski 2002). The aragonitic ammonite and nautiloid shells show a significant variation in 13C with values ranging from -3.7 to +2.2‰ VPDB. The carbon isotope composition of the oysters and the belemnites may suggest that the ?13C value of ancient seawater bicarbonate (HCO3-) averaged +3‰ VPDB.

Słowa kluczowe

EN

Bajocian; Bathonian; oxygen and carbon isotopes; belemnites; ammonites; nautiloids; oysters

• Wydawca: Państwowy Instytut Geologiczny - Państwowy Instytut Badawczy
• Czasopismo: Volumina Jurassica
• Rocznik: 2006
• Tom: Vol. 4, no. 1
• Strony: 220--222
• Opis fizyczny: Bibliogr. 3 poz.

Twórcy

autor

Wierzbowski H.

autor

Joachimski M.

• Institute of Geological Sciences, Polish Academy of Sciences, ul. Twarda 51/55, PL-00818 Warszawa, Poland,

Bibliografia

• Anderson T. F. and Arthur M. A. 1983. Stable isotopes of oxygen and carbon and their application to sedimentologic and paleoenvironmental problems. In: Arthur M. A, Anderson T. F., Kaplan I. R., Veizer J. and Land L. S. (Eds), Stable isotopes in sedimentary geology. SEPM Short Course, 10: 1-151.
• Grossman E. L. and Ku T-L. 1986. Oxygen and carbon isotope fractionation in biogenic aragonite: temperature effects, Chemical Geology, 59: 59-74.
• Wierzbowski H. 2002 Detailed oxygen and carbon isotope stratigraphy of the Oxfordian in Central Poland. International Journal of Earth Sciences (Geologische Rundschau), 91, 2: 304-314.