OBERHAUSERELLIDAE (BENTHIC FORAMINIFERA) OUTBURSTS DURING THE ENVIRONMENTAL PERTURBATIONS AT THE TRIASSIC-JURASSIC BOUNDARY: PALAEOECOLOGICAL IMPLICATIONS

The Oberhauserellidae (particularly, the transitional form Praegubkinella racemosa) have been considered as the benthic ancestor stock of Jurassic planktonic Favusellacea (Conoglobigerina, Globuligerina). In 2003, Hart et al. questioned if such Oberhauserellidae from the early Toarcian of northwestern Europe were mero-planktic forms, implying that it was a “first” experimentation of a planktic mode of life, linked to anoxic stressful conditions. The distribution and abundance of robertininid foraminifera (Oberhauserella spp. and Reinholdella sp.) at Doniford section (southwestern England), during the major perturbations of the Triassic–Jurassic (Tr–J) boundary were investigated. In addition, geochemical and sedimentological analyses (δ¹³C and Total Organic Carbon) were made to understand better the palaeoecological preferences of these organisms as well as their environmental affinities. Results have been correlated with the distribution of Oberhauserella sp. and Praegubkinella turgenscens across (1) the Tr–J boundary in the Northern Calcareous Alps, and (2) the Pliensbachian–Early Toarcian interval from Yorkshire (UK), indicating a close link between Oberhauserellidae occurrences and environmental stress conditions, such as oxygen depletion. The planktic or mero-planktic mode of life of Oberhauserellidae are further discussed. Finally, since Favusellacea are differentiated from Oberhauserellidae by different important morphological features pertaining of both gross architecture and wall ultrastructure, we conclude that a direct evolutionary line between both groups cannot be demonstrated at present.