STENOTHERMAL HABITS OF GLADIGONDOLELLA AND NORIGONDOLELLA: CONSTRAINTS FROM δ18O OF CONODONT APATITE

The stable mineralogy of conodont microfossils (fluorapatite) is a robust archive of palaeoseawater temperatures, which can be estimated from their oxygen isotope compositions. Using secondary ion mass spectrometry (SHRIMP II), multiple spot (30μm) in situ analyses of single conodont specimens enables comparative analyses at species level, which can be useful to discriminate taxon-specific isotopic variability that reflects palaeoecological (eg. biofacies) controls.

Cooler water Gladigondolella and Norigondolella biofacies have been distinguished by careful comparative analyses of different species within and between samples. Gladigondolella consistently yielded high δ¹⁸O_phos values (between ~21 and 21.5‰) compared to coeval eurythermal genera (e.g. Paragondolella and Budurovignathus, 20 and 20.5‰), which have been found in different environments, from marginal to proximal to open ocean settings, during the Middle and early Late Triassic. The consistent behavior of Gladigondolella at different sites and time intervals supports the notion that Gladigondolella was stenothermal, and thus could not tolerate higher SST’s during particularly warm periods so opted to migrate to deeper/cooler waters. A similar behavior is suggested for the genus Norigondolella (Late Triassic), which also preferred cooler conditions (~21‰).