TEMPORAL AND SPATIAL DIFFERENTIATION OF EARLY SILURIAN PENTAMERIDE SHELLY COMMUNITIES: EXAMPLES FROM ANTICOSTI ISLAND, EASTERN CANADA

The Early Silurian carbonate succession of Anticosti Island, eastern Canada, contains a rich and diverse pentameride brachiopod fauna. Multivariate analyses of 93 samples (total 17318 specimens) confirm a high degree of temporal segregation but only moderate spatial differentiation of the Virgiana, Pentamerus, Stricklandia, Ehlersella, Microcardinalia, and Clorinda communities. The Virgiana Community is of low diversity or nearly monospecific, with disarticulated, damaged valves stacked as coquinas and common hummocky cross stratification; articulated shells either in situ or in life position are rare. This implies a substrate settings above the normal storm wave base (BA2). Pentamerus communities span a wide range from BA2 to BA4 settings; the Pentamerus palaformis Community usually occurs in soft, micritic mudstone, with intact shells in life position or in situ; whereas the Pentamerus oblongus Community is preserved predominantly in shelly packstone or grainstone, similar to the Virgiana Community. The stricklandiid communities have a high beta-diversity, dominated by various species of Stricklandia, Ehlersella, and Microcardinalia, with a taphonomic range similar to that the Pentamerus communities. The Clorinda Community is characterized either by a sparse distribution of complete shells of the eponymous taxon, or by its association with overwhelmingly abundant, minute rhynchonellide shells. This is in agreement with its widely accepted BA5 assignment. The Pentamerus communities and the stricklandiid communities have a largely overlapping BA range, but a clear stratigraphic segregation. Thus the temporal successions between the two types of communities were not likely controlled by water depth, water turbulence, or substrate sediments, but by other paleoecological factors (such as water temperature).