Ironstone, phosphorite, and nutrient cycling during Paleozoic biodiversification

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Ironstone and phosphorite are marine chemical sediments of scientific and industrial importance. Ironstone is enriched in Fe, which is not only required for steel production, but also essential for nearly all living things. It is necessary for photosynthesis in plants, part of many proteins, and involved in microbial metabolisms that cycle other nutrient elements. Phosphorite is the most important source of P in fertilizer, and therefore vital for feeding the Earth's burgeoning population. Like Fe, P is also a bioessential element. It forms skeletons, is a building block of DNA, is essential for cellular energy transfer, and limits biologic productivity over geologic timescales. Because the precipitation of ironstone and phosphorite is so closely tied to biology, these deposits are not simply recorders of geologic processes, but intimately involved in Earth system evolution. Four synchronous episodes of ironstone and phosphorite deposition are recognized in the rock record, reflecting coupled cycling of Fe and P in the ocean. Each represents changes in seawater chemistry and circulation related to variability in the feedbacks regulating the Earth system. Previous NSERC Discovery Grants investigated the first and second episodes, with proposed research focused on the third. The goal is to use fieldwork, modern stratigraphic techniques, and chemical tracers to understand ironstone and related phosphorite in Atlantic Canada, USA, Brazil, UK, and Spain. These deposits were part of a system of Fe and P cycling prior to, during, and after the Great Ordovician Biodiversification Event (GOBE; 480 to 445 million years ago), which is the most important sustained increase in marine biodiversity in Earth history. While the Cambrian Explosion produced skeletonized organisms with a range of new body plans, the GOBE records the staggering increase in diversity of these animals. Results also promise to yield new information about the link between ocean-atmosphere composition, Fe and P deposition, and later extinction events 433 and 372 million years ago. Future Discovery Grants will focus on understanding the fourth episode of coupled Fe and P cycling. Significant to Canada is that this research will develop new Fe and P exploration models that can be applied to understand the geology and metallurgy of poorly understood Canadian ironstone and phosphorite deposits. The reinterpretation of ironstone using state-of-the-art models may define previously unknown reserves that are much closer to infrastructure and market than existing ore bodies. When applied to phosphorite this knowledge will enhance Canada's ability to feed itself. Current use of phosphorite is unsustainable, with Peak Phosphorus estimated by 2050 and depletion of current reserves expected in 100 years. Most of these deposits reside in countries with significant political unrest, amplifying the threat to Canadian and global food security.