Editorial preface to special issue: Extreme environments and biotic responses during the Neoproterozoic-Phanerozoic transition

This special issue deals with Extreme environments and biotic responses during the Neoproterozoic-Phanerozoic transition and comprises 23 papers. In this preface, we summarise the major findings and place them in a wider context. Some key discoveries are as follows: (1) After the Marinoan global glaciation (end-Cryogenian), a rise in seawater carbon isotopic composition of dissolved inorganic carbon (δ¹³CDIC), together with various biomarkers, indicate an increase in marine primary productivity, and imply a postglacial increase in atmospheric O₂ level by 3.813.4% of present atmospheric levels. (2) The earliest Cambrian sulfidic ocean was characterized by widespread but low levels of microbial sulfate reduction (MSR) in seawater with active microbial iron reduction in sediment porewaters; this state differs from present day sulfidic water masses, such as those in the Black Sea, which show predominantly MSR in the sediment. Multiple geochemical proxies demonstrate that a dynamic ‘euxinic wedge’ may have existed at mid-water depths, and its expansion/contraction controlled redox variations during the early Cambrian. (3) Studies of Hg concentration and isotope analyses shed new light on the Late Ordovician mass extinction event, and reveal that volatile volcanism probably acted as a trigger for several catastrophes, involving climate change, ocean acidification, and anoxia. (4) Other findings show that primitive foraminiferans may have occurred already prior to the Cambrian Explosion, brachiopod-dominated shell beds were already present in the early Cambrian, and reef-builders diversified during the Middle Ordovician, altering our understanding of Cambrian-Ordovician evolution. The papers in this special issue therefore improve knowledge of the Neoproterozoic-Phanerozoic transition and will be of interest to a broad readership of palaeontologists and earth system scientists.