First record of stable isotopes(δ^(13)C, δ^(18)O) and element ratios(Mg/Ca, Sr/Ca) of Middle to Late Jurassic belemnites from the Indian Himalayas and their potential for palaeoenvironmental reconstructions

Middle to Late Jurassic belemnites from the Spiti and Zanskar valleys in the Indian Himalayas were used for stable isotope(δ^(13)C, δ^(18)O) and element(Mg/Ca, Sr/Ca) analyses. Although the Himalayan orogeny deformed and altered a large portion of the collected fossils, cathodoluminescence and scanning electron microscopy in combination with analyses of iron and manganese contents allowed the identification of belemnites believed to still retain their original chemical composition. Results indicate a long-term temperature decrease from the Middle Callovian–Oxfordian to the Tithonian, which is proposed to have been caused by a concomitant drift of eastern Gondwana into higher palaeolatitudes. Reconstructed absolute temperatures depend on the used equation and assumed δ^(18)O value of seawater, but most likely varied between 17.6 ℃ to 27.6℃ in the Kimmeridgian and Tithonian with average values between 22 ℃ to 24 ℃. This way, temperatures were similar to slightly warmer than today at comparable latitudes. The reconstruction of absolute temperatures for the Middle Callovian–Oxfordian was hindered by a larger number of poorly preserved belemnites representing this time interval.

First steps in reconstructing Early Jurassic sea water temperatures in the Andean Basin of northern Chile based on stable isotope analyses of oyster and brachiopod shells

The stable isotope(δ13 C,δ18 O)composition of a collection of Lower Jurassic brachiopods and oysters from the Andean Basin of northern Chile was analyzed.The results allow the first reconstruction of absolute water temperatures for several ammonite zones in the Lower Jurassic of South America.The temperature record starts with comparatively high values in the Late Sinemurian(average:27.0℃;Raricostatum Zone).Just before the Sinemurian–Pliensbachian transition,temperatures dropped to an average of 24.3℃.The lowest temperature value in the dataset was recorded for a brachiopod shell of the latest Pliensbachian Spinatum Zone(19.6℃).No data are available for the Early Toarcian,but results for the late Toarcian show again comparatively warm conditions(average:24.4℃;Thouarsense–Levesquei zones).Even though more material and analyses are necessary to corroborate the recorded temperatures,the present dataset seems to indicate the global nature of the Late Pliensbachian Cooling Event.In contrast,the global warming during the Toarcian Oceanic Anoxic Event has not been recorded due to a lack of Early Toarcian material.Theδ13 C record of brachiopods and oysters documents a gradual increase in values representing background conditions.Oyster shells were used for high-resolution stable isotope analyses and show seasonal temperature fluctuations over a period of around 3 years in the life time of the bivalves.If explained only by temperatures,theδ18 O values point to a minimum estimate for the seasonality in the late Toarcian of slightly more than 3℃.