Cambroclaves from the Cambrian of Sardinia (Italy) and Germany: constraints for the architecture of western Gondwana and the palaeogeographical and palaeoecological potential of cambroclaves

摘要

Cambroclaves represent a group of problematic microfossils previously known from strata close to the Early/Middle Cambrian boundary of only a few palaeogeographic regions (Kazakhstan, China, Australia). Because of their frequent occurrence as disarticulated remains, they have hitherto been assumed to be provincially restricted microfossils of unclear palaeobiological affinity. Discoveries of cambroclaves from the Early to early Middle Cambrian of southern (Sardinia) and central (Germany) Europe point to a much wider distribution during their short stratigraphic range, and imply closer palaeogeographic relations between the European shelf of western Gondwana and the areas from which cambroclaves were previously known. These relations are also supported by the common occurrence of other small shelly fossils. These facts support the existence of a widespread uniform facies belt (shelf) around parts of Gondwana during the Early-Middle Cambrian time interval, and contradict the interpretation of the European depositional areas as isolated basins or as distinctly separate Cambrian terrines. The western Gondwana cambroclaves occur in carbonate successions indicative of special palaeoecological conditions. The specimens are limited to distinct layers formed during transgressive phases that opened inner and partly restricted platform areas to open-marine and more distal (deeper subtidal) environments, possibly accompanied by a transition from a rather arid to more humid climatic conditions. Because of the short stratigraphic window of occurrence and of distinctive facies characteristics, cambroclaves are palaeoecologically and palaeobiogeographically useful, and consequently contribute important evidence for both the reconstruction of the Perigondwana realm and the relations to other palaeocontinents in the Cambrian.