نبذة مختصرة : The study deals with the biological impacts of sea-Ievel changes on evolution of a Jurassic benthic fossil group (Ornithellida, Brachiopoda). The different time and scale at which the shifts in marine environments occur leads to the recognition of three interacting dynamic systems: environmental, communities, populations dynamics. The analysis is thus divided into a three steps hierarchy: sequence stratigraphy, analysis of the diversity of brachiopod assemblages, and analysis of morphological variations within omithellid populations. Sequence stratigraphy of the Dogger marly and carbonate successions in the Paris basin provides accurate correlations of depositional environments from shallow water carbonate platform to a deeper open marine domain. It also demonstrates the major events of sea-Ievel variation. The main result is the distinction of 2 types of depositional sequences (sequence of platform drowning vs sequences of platform building) depending on the rate of carbonate production vs water depth. The environmental changes involved have strong repercussions upon marine benthic community structures which are taxonomically replaced. The deep marine faunas act as a stable set of populations which periodically invade the previously emergent platform. These remplacements allow to characterize every sequence (especially the TST component) by a specifie brachiopod association. The associations occur within biostratigraphical marker-beds which extend over the Anglo-Paris basin as demonstrated by outcrops and weIl-log correlations. The second step of analysis deals with the structure -in terms of diversity - of major brachiopod shell-beds. Three structures (mono, oligo, polyspecific) are defined by descriptive classification and factor analysis. They corresponds to 3 time-averaging degrees of a few decades, a few thousands to a few 10's of thousands of years, respectively. The condensation allows taphonomic feedback processes which emphasize the epibenthic fauna and especially brachiopods. A model is proposed ...
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