Cool-Water Carbonates: an Evolving Paradigm

James, Noel P.¹ (1) Queen'sUniversity, Kingston, ON

The cool-water carbonate paradigm, which states that significant parts of the neritic carbonate record accumulated in cool ocean waters outside the tropics, is now part of mainstream scientific thinking. Because such sediments are composed only of marine organisms, all of whom respond in different ways to varying environmental controls, the precise characterization of resultant sediments in the modern ocean is proving difficult and controversial, whereas their identification in the rock record is variably speculative and puzzling.

Such sediments belong to the heterozoan (foramol) assemblage that is distinct from the photozoan (chlorozoan, chloralagal) assemblage characterized by warm-water (>20°C), light-dependent, and non-biogenic components. In the modern ocean such simple assignments are perturbed by water depth, nature of the photic zone, changing salinities, and varying trophic resources. This is particularly apparent in the transition zone between temperate and tropical realms. Alternatively, carbonates in forbidden polar environments are present, but virtually undocumented.

Whereas Cenozoic and Mesozoic carbonate rocks can be interpreted with confidence based on modern deposits, the consignment of older rocks to cool- or warm-water environments is elusive. Late Paleozoic rocks associated with glacial-marine neritic environments as opposed to those with large benthic foraminifers (fusilinids) can be resolved. In contrast, early and middle Paleozoic carbonates are assigned to the cool-water realm based on the absence of warm-water elements and inclusion of prolific biosiliceous components. The Proterozoic carbonate realm remains largely enigmatic, new research suggests that ooids may be part of the cool-water depositional realm on the early earth.