Neoproterozoic-Cambrian microbialite record

Abstract

Microbes and the sedimentary record of their activity, microbialites, have existed since the Archaean. During the Neoproterozoic-Cambrian interval, there is a marked shift in the fossil record of microbialites with the widespread proliferation of thrombolites (clotted microbialites) and the appearance and proliferation of dendrolites (microbialites composed of dendritic clusters) alongside stromatolites (laminated microbialites). Calcimicrobes also diversified during this interval. The end of this resurgence coincided with the increase in invertebrate taxa at the end of the Early Ordovician. The ìMicrobialite Resurgenceî has long been recognized but the importance of the Neoporoterozoic microbialite record for deciphering trends of this interval has not been so widely realized. It is critical to note that some of the oldest skeletal invertebrates and calcimicrobes are found in Neoproterozoic microbial reefs. Also, microbe-invertebrate synecology and invertebrate abundance trends during this interval suggests that a simple model that keys the resurgence tied in to a lack of competition from reef-building sponges and corals may not be valid. Current re-evaluation of the environmental conditions, principally the fluctuations in the geochemical conditions of the global oceans and atmosphere, will likely shed new light on understanding the Neoproterozoic-Cambrian microbialite record.