We present an integrated work based on calcareous nannofossil and
benthic foraminiferal assemblages, and geochemical analyses of two Upper
Pliensbachian-Lower Toarcian sections located in the central-South
France. The studied sections, Tournadous and Saint-Paul-des-Fonts,
represent the proximal and the distal part, respectively, of the
Jurassic Causses Basin, one of the small, partly enclosed basins
belonging to the epicontinental shelf of the NW Tethys. At the
transition from Late Pliensbachian to Early Toarcian, the Causses Basin
recorded an emersion in response to the global sea-level fall. Our data
indicate severe environmental conditions of marine waters, including
salinity decrease and anoxia development, occurring in the Early
Toarcian. The acme of this deterioration coincides with the Early
Toarcian Anoxic Event (T-OAE) but, due to the restricted nature of the
basin. anoxia persisted until the end of the Early Toarcian. mainly in
the deeper parts of the basin. The micronutrients and organic
organic-matter fluxes were probably high during the entire studied time
interval, as shown by nannofossil and foraminiferal assemblages.
However, nannoplankton production drastically decreased during the
T-OAE, as demonstrated by very low nannofossil fluxes, and only taxa
tolerant to low-saline surface waters could thrive. At the same time,
benthic foraminifers temporarily disappeared in response to sea-bottom
anoxia. Our study demonstrates that environmental changes related to the
T-OAE are well-recorded even in small, partly enclosed basins of NW
Europe, like the Causses Basin. Within this area, the effects of global
changes. like sea sea-level and temperature fluctuations, are modulated
by local conditions mainly controlled by the morphology of the basin.
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