CLAY MINERAL CONTROL OF THE LATE PRECAMBRIAN OXYGEN RISE

Accumulation of oxygen in the earth's atmosphere requires burial of organic matter in marine sediments. Today, the major mode of organic carbon burial is in association with detrital pedogenic clay minerals which serve to protect organic matter against biological oxidation during burial in marine sediments. Since pedogenic clays are formed in biologically active soils that require organic processes, at some point in Earth history before the colonization of land surfaces by terrestrial organisms, this mode of carbon burial and oxygen release must have been inoperative. Multiple independent lines of evidence indicate a significant change in continental weathering and pedogenic clay mineral formation that coincides with colonization of land surfaces by primitive plant-like organisms in the late Precambrian. Here we propose the hypothesis that the enhanced burial efficiency that would have accompanied the shift to the modern mode of detrital pedogenic clay hosted carbon burial would have driven an increase in oxygen levels toward modern values that may have resulted in the advent of the first complex animals. This hypothesis links research in modern marine depositional systems that identifys the first order importance of clay minerals to organic carbon preservation and burial. It offers a new paradigm for organic carbon cycling in the Precambrain before the initiation of a terrestrial clay factory, explains the stepwise rise in atmospheric oxygen into the Phanerozoic and agrees with multiple independent geochemical and mineralogical proxies for a change in weathering regieme at the end of the Precambrian.