Abstract
Middle to Late Jurassic belemnites from the Spiti and Zanskar valleys in the Indian Himalayas were used for stable isotope (δ13C, δ18O) 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 δ18O value of seawater, but most likely varied between 17.6 °C to 27.6 °C in the Kimmeridgian and Tithonian with average values between 22 °C to 24 °C. 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.
Highlights
Since many decades, stable oxygen isotope (δ18O) analyses of fossil shells have been used to reconstruct the temperature development throughout Earth’s history, including the Jurassic period (e.g. Epstein et al 1951; Urey et al 1951; Bowen 1963; Stevens and Clayton 1971)
Specimens from the outcrops in the Zanskar Valley were excluded from temperature reconstructions and only eight belemnite rostra were analysed for comparison
7 Conclusions Fossils collected from the Middle to Upper Jurassic succession of the Spiti and Zanskar valleys in the Indian
Summary
Stable oxygen isotope (δ18O) analyses of fossil shells have been used to reconstruct the temperature development throughout Earth’s history, including the Jurassic period (e.g. Epstein et al 1951; Urey et al 1951; Bowen 1963; Stevens and Clayton 1971). Alberti et al Journal of Palaeogeography (2021) 10:24 suggest that low-latitudinal regions of western Gondwana (e.g. Egypt, Algeria) showed comparatively stable temperatures throughout the Middle and Late Jurassic, while eastern Gondwana experienced a concurrent temperature decrease (Fürsich et al 2005; Alberti et al 2017, 2019, 2020a; Sadji et al 2021). The latter has been found in fossil records from Madagascar and western India (Kachchh), but data are still sparse in the Late Jurassic. While the Kumaon outcrops ( referred to in the literature as Malla Johar, Niti, and Laptal) are situated in a restricted border-region and were not accessible during the present project, sections within the Spiti and Zanskar valleys were measured and sampled (Fig. 1)
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