BRINE EXPULSIONS TO PALEOZOIC BASINS: TRIGGER OF CATASTROPHIC GLOBAL CHANGE

Chemostratigraphic investigations during the last decade have resulted in global, deep-time stratigraphic correlation at unprecedented resolution and fostered insights into the inner workings of the ancient ocean-atmosphere system. Increasingly, these studies document dramatic episodes of global climate-oceanic system instability characterized by isotope disturbances of oceanic C, O, S and Sr cycles. Demonstrably, these reorganizations of global climate-ocean chemical systems form the nodes in the evolutionary trajectory of life. Yet, while our understanding of these phenomena is advancing, the underlying trigger(s) have been poorly understood.

We have integrated new paleontological, chemostratigraphic, and sedimentologic observations with recently developed geochemical tools to establish an alternative hypothesis for these dramatic events. Specifically, we propose that massive releases of sedimentary brines, analogous to those responsible for sedimentary-exhalative (sedex) ore deposit formation, triggered events by inducing runaway fertilization and eutrophication through a series of positive feedbacks that initiate perturbations to global ocean-climate systems. Central to this novel model are new ore genesis and fluid flow studies that demonstrate these brine discharges supplied enormous quantities of metals, radiogenic Sr and biolimiting nutrients to the oceans. Strong temporal correlations between brine releases and events, combined with mass balance evidence and oceanographic box modelling, suggest that the flux of radiogenic Sr-rich sedex brines was sufficient to cause observed positive excursions (“spikes”) in the global marine Sr-isotope record. Significantly, the apex of these enigmatic 87Sr/86Sr spikes correlates with periods of highly variable global δ¹³C and δ¹⁸O, global anoxia, metal-rich black shale deposition, climate change, metal-induced teratology of marine organisms, and significant biotic extinctions. Additional new evidence suggests that the flux of key biolimiting nutrients and metals contained in sedex brines may have equaled or exceeded the total modern riverine inputs to the ocean and that massive brine exhalations may have been responsible for dramatic chemical variations within the global ocean.