Basal Wenlock biofacies from the Girvan district, SW Scotland

Abstract

Synopsis Basal Wenlock shelly biofacies from the Knockgardner Formation (middle Straiton Group) of the Girvan district are dominated by brachiopods and trilobites assigned, respectively, to the Howellella–Protochonetes and the Podowrinella faunas. The Podowrinella fauna is consistently developed across the Midland Valley in Llandovery–Wenlock boundary rocks but the association is not known outside Scotland. In contrast the Howellella–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 Scotland both associations occur in nearshore, commonly storm-dominated sediments. The contrasting distributional patterns of the mobile and sessile benthos may reflect the differing life strategies of both the larval and adult stages in each group. Lithofacies within the upper Llandovery–lower Wenlock Straiton Group are revised within the regressive framework of the region.