Facies anatomy and early diagenesis of carbonate rocks

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Carbonate sedimentary rocks such as limestone are largely made of marine fossils. These components that formed in the marine environment long ago tell us much about the very ancient oceans of our planet and thus the history of our world. The limestones are, furthermore, significant archives of the evolution of marine life through time, amongst the nation's most prolific hydrocarbon reservoirs deep underground, and critical aquifers for fresh water and so human wellbeing. The aim of the science proposed here is to understand how marine carbonate sediments form in the ocean today (facies anatomy) and how they are then transformed into rock (early diagenesis) throughout the vastness of geologic time. These findings are then used to generate predictive scientific models that can be used by earth scientists to interpret ancient rocks at the earth’s surface or deeply buried underground. Specifically the focus is on the most poorly understood of these sediments and rocks specifically cool-water and high latitude marine carbonates and related deposits, the processes of early chemical alteration, both terrestrial and marine that change them, and the perplexing origin of 1 billion year old Precambrian carbonates.Much of the planned research will take place on and adjacent to the southern Australian continental shelf, the largest area of cool-water carbonate deposition in the modern world. Expanding on previous NSERC-supported research in the region, the following questions will be addressed: 1) how is the composition of cool-water seafloor sediment related to the nature of the overlying seawater and how does this govern the chemistry of these deposits, 2) the same sediments are blown into spectacular marginal marine sand dunes and how does the composition these dunes reflect their source, the offshore marine environment, 3) do these offshore sediments somehow contribute to the formation of widespread marginal marine calcareous soils and what are the processes involved, and 4) what is the genesis of large marginal marine carbonate lakes under this semiarid climate adjacent to the Southern Ocean? These questions will be addressed via an integrated field program utilizing extensive onland mapping, and sampling and geochemical analysis, marine research, and computer modeling. Funds are also requested to investigate very ancient limestones, specifically 1) to understand how Paleozoic (550-225 million year old) marine carbonate sand bodies were formed and 2) to determine, via the nature of carbonate sedimentation, how the global ocean evolved during the Neoproterozoic (~800 million years ago) a period of global glaciation just before the evolution of complex animals. The end users of this research range from scientists such as paleontologists, paleoceanographers, and sedimentary geologists unraveling the rock record, to Canadian geoscientists searching for buried hydrocarbon reservoirs and mineral deposits to researchers monitoring marine environmental change.