• journal_title：Journal of the Geological Society
• Contributor：Lucia Angiolini ; Flavio Jadoul ; Melanie J. Leng ; Michael H. Stephenson ; Jeremy Rushton ; Simon Chenery ; Gaia Crippa
• Publisher：Geological Society of London
• Date：2009-
• Format：text/html
• Language：en
• Identifier：10.1144/0016-76492008-096R
• journal_abbrev：Journal of the Geological Society
• issn：0016-7649
• volume：166
• issue：5
• firstpage：933
• section：Research Article

Brachiopod carbonate from Early Permian brachiopod shells from low palaeolatitude north Iran and higher palaeolatitude Pakistan Karakorum were screened for diagenesis and analysed for oxygen isotope ratios to derive seawater palaeotemperatures. Screening techniques employed included SEM ultrastructural analysis, cathodoluminescence (CL), image analysis of CL images, trace-element (Sr, Mn, Fe) determinations, and carbon and oxygen stable-isotope determinations. The Karakorum shells were found to be diagenetically altered, but those from north Iran were judged to be pristine. Using data from pristine material, two distinct time slices were analysed: the early and middle Asselian. Two contrasting δ¹⁸O values for seawater (0‰ and +1.0‰ V-SMOW) were used to account for different extensions of the Gondwanan ice caps. The δ¹⁸O data from north Iran indicate a range of seawater temperatures from +24.3 to +30.3 °C (for δ¹⁸O_seawater = 0‰ V-SMOW) or from +30.3 to +35.4 °C (for δ¹⁸O_seawater = +1.0‰ V-SMOW) for the early Asselian. Results for δ¹⁸O from the middle Asselian indicate seawater temperatures of +24.4 to +28.0 °C (for δ¹⁸O_seawater = 0‰) or +29.2 to +32.8 °C (for δ¹⁸O_seawater = +1.0‰). The maximum calculated temperatures in the middle Asselian are about 2 °C lower than those for the early Asselian. The average temperature for both time slices is similar to modern tropical sea-surface temperatures, indicating that low-latitude Early Permian ocean waters in Iran did not undergo significant cooling during the final Glacial III episode of Gondwanan glaciation. This confirms other evidence based on biotic provinces, which suggests that during the Permo-Carboniferous glaciation, the low-latitude warm belt became narrower and confined to the western Tethys and Cathaysian provinces, and was not subject to a reduction in temperature, but rather a reduction in size.