Comparative ecological analysis of Toarcian (Lower Jurassic) benthic faunas from southern France and east-central Spain

摘要: Toarcian (Lower Jurassic) argillaceous-marly sediments of southern France (Causses) and east-central Spain (Barranco de la Puta section) were deposited in mid to lower shelf settings. They contain a low moderately diverse, autochthonous fauna benthic macroinvertebrates dominated by bivalves gastropods, the case Causses, brachiopods Barranco section. Five associations are recognized at latter locality four former. In species diversity, evidence seasonal mass mortality, presence opportunistic bivalve Parvamussium pumilum, local dominance soft bottom coral Thecocyathus mactrus dark-grey, fine-grained sediment point high rates sedimentation, turbidity, intermittently lowered oxygen values soupy substrate conditions. These factors, together with eutrophic water masses, main environmental parameters governing faunal distribution. Soupy conditions thought be largely biologically produced activity infaunal depositfeeders, chiefly nuculoid bivalves. section, abundant brachiopods, higher carbonate content sediment, intermittent in-situ reworking winnowing an influence storm-induced currents, shallower depositional depth, rate somewhat firmer substrate. As consequence, is epifaunal suspension-feeders. Compared maximum average sizes from elsewhere Jurassic, most distinctly smaller, feature interpreted as stunting. Brachiopods, contrast, reach normal size. The lack nuculids, scarcity deposit-feeders general, stunting oligotrophic environment. Lowered appear have played only very limited role shaping distribution pattern. Many differences between both areas can explained different trophic regimes that reflect considerably run-off consequently input terrigenous dissolved nutrients basin Causses. This turn possibly regional climate; humid more arid eastcentral Spain.