The carbonate factory continuum, facies mosaics and microfacies: an appraisal of some of the key concepts underpinning carbonate sedimentology

Abstract

Our understanding of where and how carbonate sediments are produced and accumulate has changed considerably in recent years and a more complex framework is emerging. The earlier concept invoking a limited range of productivity-depth models has now evolved into an appreciation that there is a continuum of different types of productive sites over wide depth ranges, influenced by complex factors and not simply water depth or temperature. Studies of the nature of lithofacies ordering in the stratigraphic record, and most recent studies of the spatial distribution of Holocene environments, raise the issue that at the lithofacies scale the sedimentary record represents, in part, the product of complex and mobile facies mosaics. Many of these mosaic elements are not depth dependent and can change through time as a consequence of subtle environmental changes. As the rates of change typically exceed rates of accommodation space creation, individual sites are likely to have sediments of different environments superimposed and mixed (palimpsest). Recent studies showing the extent that dissolution is capable of skewing sediment compositions suggest that many ancient microfacies are unrepresentative of their original sediments, and there is a need for a more critical approach to interpreting microfacies in terms of identifying habitats and especially water depth. The carbonate factory is spatially and temporally highly variable and is not simply a uniform production line. This fact, coupled with the likely importance of selective early dissolution, may in part explain why accumulation rates estimated from ancient strata are lower than the production rates measured over short time periods.