BASAL WENLOCK BIOFACIES FROM THE GIRVAN DISTRICT, SW SCOTLAND

Basal Wenlock shelly biofacies from the Knockgardner Formation (middle Straiton Group) of the Girvan district are dominated by brachiopods a nd trilobites assigned, respectively, to the Howellella-Plotochonetes and the Podowrinella faunas. The Podowrinella fauna is consistently de veloped across the Midland Valley in Llandovery-Wenlock boundary rocks but the association is not known outside Scotland. In contrast the Ho wellella-Protochonetes fauna is more variably developed and restricted to the western part of the Midland Valley; but the components of this type of fauna occur in Wenlock and Ludlow rocks elsewhere. In Scotlan d both associations occur in nearshore, commonly storm-dominated sedim ents. The contrasting distributional patterns of the mobile and sessil e benthos may reflect the differing life strategies of both the larval and adult stages in each group. Lithofacies within the upper Llandove ry-lower Wenlock Straiton Group are revised within the regressive fram ework of the region.