SILICIFIED MID-DARRIWILIAN OSTRACODS FROM QUEBEC, CANADA

The Les Méchins locality (Gaspé Peninsula, eastern Canada), on the southern shore of the St. Lawrence River, yielded rich ostracod faunas from various levels in a ca. 15 m thick limestone succession of Middle Ordovician age. The faunas are associated with graptolite faunas from the upper part of the Holmograptus lentus Biozone as shown by the presence of Holmograptus spinosus, Atopograptus sp., Bergstroemograptus crawfordi and Parisograptus forcipiformis, associated with a number of biserial graptolites including Archiclimacograptus decoratus and Archiclimacograptus confertus. Ostracods are common at many levels in the succession, where they are associated with graptolites and conodonts. The specimens are invariably silicified and the preservation is quite variable. In some of the specimens even the fine surface ornamentation is preserved. The ostracod faunas are highly diverse and represent some of the oldest and most diverse ostracod faunas found in North America. Their importance lies in the fact that they can be dated precisely with associated macrofossil assemblages. Ostracods from this interval have never been described in detail, thus, allowing for the first time a glimpse into the diversity of mid-Darriwilian ostracod faunas of eastern North America. The following genera and species are recognized: Jachalipisthia n. sp., Baltonotella sp., Ordovizona aff. O. immanis Becker, 1994, Bromidella? n. sp., Ectoprimitioides n. sp., Duplicristatia? sp., Berounella sp., Budnianella n. sp., Budnianella? n. sp., Parasclerites n. sp., Longiscula? sp. A number of additional faunal elements await taxonomic treatment as most of the species in these faunas appear to be new. The faunas show relationships to Laurentian faunas, as well as to those of Baltica. Jachalipisthia was known previously only from the Argentinian Precordillera, where it occurs in a number of species. Ectoprimitioides is another genus that was recently discovered in the Argentinian Precordillera, but is characteristic for Laurentia. Elements like Ordovizona and Bromidella are more widespread and found in Laurentia and Baltica, while Baltonotella is found worldwide. Berounella is known from the Silurian and Devonian of Baltica and Laurentia. This record would extend its biostratigraphic range considerably.