A genetic classification of carbonate platforms based on their basinal and tectonic settings in the Cenozoic

Abstract

This paper reassesses the usefulness of the morphological classification of carbonate platforms into rimmed shelves and ramps. Whilst the existing classifications have value in describing platform margin morphology at any one time, the terms rimmed-shelf and ramp are less successful at categorising the entire morphology and stratigraphy of carbonate platforms. Research on Cenozoic carbonate platforms from a range of different tectono-stratigraphic settings indicates that the basinal and tectonic setting of a platform can be used to erect a first-order, genetic classification of carbonate platforms. The basinal and tectonic setting of carbonate platforms is shown to control their occurrence, the overall 3-D platform morphology, the large-scale stratigraphic features and depositional sequences. Climate, ocean chemistry and biological evolution control grain types, facies and some elements of platform margins but not the larger-scale features considered in this new classification. From a review of well-exposed outcropping and seismically imaged Cenozoic platforms, it is proposed that eight types of carbonate platform can currently be recognised and characterised based on their basinal and tectonic setting: Fault-Block, Salt Diapir, Subsiding Margin, Offshore Bank, Volcanic Pedestal, Thrust-Top, Delta-Top and Foreland Margin carbonate platforms. These eight types are described using information from Cenozoic platforms worldwide and the controls on their development are discussed. Many platform types (e.g. Subsiding Margin, Offshore Bank, Salt Diapir, Thrust-Top and Foreland Margin) are typical of particular classes of sedimentary basins, others (e.g. Fault-Block, Volcanic Pedestal and Delta-Top) are more widespread in their occurrence and occur in a range of basin types. The value of this classification is that it is genetic rather than morphological; the classification reflects the entire morphology and large-scale stratigraphy of the platform and the controls on its development. In addition, the platform models can be used to understand the details of less well exposed, or seismically imaged platforms so that they can be characterised and understood in terms of tectono-sedimentary processes. Conversely, the classification also provides valuable information on basin evolution, as carbonate platforms house information on palaeoenvironments, sea-level change and are sensitive recorders of the tectonic environment.