Shelly fossils from the Early Cambrian (Toyonian) Wirrealpa, Aroona Creek, and Ramsay Limestones of South Australia

Abstract

Small shelly fossils from the Wirrealpa and Aroona Creek Limestones, Flinders Ranges, and the temporally equivalent Ramsay Limestone, Yorke Peninsula, South Australia, are described and assessed. These formations, deposited during a widespread marine transgression, have traditionally been assigned an early Middle Cambrian age based on lateral facies relationships, lithostratigraphic interpretation, and age diagnostic trilobites. However, new data from regional sequence stratigraphy and mounting paleontological evidence suggest that a late Early Cambrian age (equivalent to the Toyonian Stage from the Siberian Platform) is more appropriate for these units. Twenty-four taxa, including a number of problematica, poriferans, coeloscleritophorans, palaeoscolecidans, “conodontomorphs,” hyolithelminthes, hyoliths, mollusks, and inarticulate brachiopods, are reported herein; many of these have not previously been reported from the Cambrian of South Australia. The enigmaticChalasiocranos exquisitumn. gen. and sp., known from disarticulated tuberculate cone-shaped phosphatic sclerites, andProtomelission gatehousein. gen. and sp., a problematic, perhaps colonial organism, known from phosphatic plates, are especially notable. The genusKaimenellais formally included in the Palaeoscolecida, and two species (includingK. dailyin. sp.) are recognized.