Gastropods from upper Pliensbachian–Toarcian (Lower Jurassic) sediments of Causses Basin, southern France and their recovery after the early Toarcian anoxic event
2015
A gastropod fauna has been studied from upper Pliensbachian – upper Toarcian deposits of
two sections of the Causses Basin (southern France) in order to investigate the mode of
recovery after the early Toarcian anoxic event. The fauna consists of 15 species, one of
which is new ( Bathrotomaria kronzwilmesorum sp. nov.). Their
stratigraphical distribution shows two peaks of diversity – in the Bifrons Zone (Bifrons
Subzone) and in the Aalensis Zone (Mactra Subzone) – which reflect brief times during
which the oxygen content and bottom consistency favoured the settlement of a relatively
diversified fauna. In the Variabilis–Pseudoradiosa zones, gastropods are only represented
by two species. This probably indicates more severe and unstable environmental conditions,
only allowing the survival of gastropod taxa with wide adaptive capacities. The very low
species diversity and the discontinuous and slow faunal recovery were probably determined
by physiographic factors. The Causses area was a small basin confined by exposed lands and
open towards the central part of western Tethys. Gastropods described here occur
exclusively in the Toarcian – early Aalenian communities of the European epicontinental
seas, whereas species from the central region of western Tethys are absent. Geographic
isolation and marginal location of the Causses Basin restricted faunal exchange with the
western European epicontinental seas, preventing fast recovery after the anoxic event.
Gastropods of the central region of the western Tethys were probably unable to settle and
colonize that area due to the strongly different environment.
Keywords:
- Correction
- Source
- Cite
- Save
- Machine Reading By IdeaReader
100
References
9
Citations
NaN
KQI