THE ROLE OF TECTONISM ON NEOPROTEROZOIC TO EARLY PALEOZOIC CLIMATE AND EARLY METAZOAN BIODIVERSIFICATION

Metazoans first evolved and diversified during one of the most dramatic periods of climatic change in Earth history, specifically the transition from the Cryogenian icehouse to the Cambrian hothouse. Determining the driving mechanisms behind these major environmental shifts is critical in order to understand their influence on early Metazoan diversification. Surface and lithospheric processes are major controllers of atmospheric CO₂ and must be constrained through time. Large populations of relatively young detrital zircons result from the rapid erosion of young felsic–intermediate rocks that are common along continental arc systems and therefore can be used as proxies for arc-volcanism and tectonic CO₂ outgasssing. Here we attempt to track variation in the spatial extent of Neoproterozoic–early Paleozoic continental arc-volcanism by evaluating changes in detrital zircon age populations from globally dispersed siliciclastic rocks with depositional ages spanning the Cryogenian to the Devonian. These data show a general paucity in Cryogenian-aged zircon around the onset of the glacial interval, whereas Ediacaran–Cambrian zircons are abundant in all Gondwanan terranes. The low-abundance of Cryogenian-aged zircons represents a major reduction in global arc-volcanism and tectonic CO₂ outgassing, which likely contributed to widespread glaciations during this interval. Late Cryogenian–Ediacaran detrital zircons are abundant in Pan-African-associated terranes and reflect the onset of widespread arc-volcanism and CO₂ outgassing that would have helped bring Earth out of the ‘snowball state’. Large populations of relatively young Cambrian-aged zircons in lower Paleozoic strata across the Gondwanan realm were derived from voluminous igneous bodies during the most spatially extensive period of arc-volcanism of the Phanerozoic. Gondwanan tectonic activity was likely responsible for the high pCO₂ of the Cambrian atmosphere that resulted in widespread oceanic oxygen deficiency and euxinia that drove the high genus-level extinction rates observed during the Cambrian. Cessation of continental margin activity is recorded across the Gondwanan realm during the Ordovician and is coincident with global cooling, a reduction in seawater ⁸⁷Sr/⁸⁶Sr, and the Great Ordovician Biodiversification Event.