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1 TotalFinaElf Exploration UK PLC, Geoscience Research Centre, 30 Buckingham Gate, London, SW1E 6NN, UK
2 Department of Earth Sciences, Open University, Milton Keynes MK7 6AA, UK
3 Institute of Geography and Earth Sciences, University of Wales Aberystwyth, Aberystwyth, Ceredigion SY23 3BD, UK
Carbonate platforms are open systems with natural boundaries in space and time. Across their spatial boundaries there are fluxes of energy (e.g. light, chemical energy in compounds, and kinetic energy in currents and mass flows) and matter (e.g. nutrients, dissolved gases such as CO2, and sediment — especially, of course, carbonates). Internally, these fluxes are regulated by myriads of interactions and feedbacks (Masse 1995), and the residue is consigned to the geological record. The most distinctive aspect of carbonate platforms is the predominant role of organisms in producing, processing and/or trapping carbonate sediment, even in Precambrian examples.
Because of evolutionary changes in this strong biotic input, it is harder to generalize about carbonate platforms than about most other sedimentary systems. Evolution has altered both the constructive and destructive effects of platform-dwelling organisms on carbonate fabrics, with profound consequences for facies development. Moreover, changing patterns in the provision of accommodation space (e.g. between greenhouse and icehouse climatic regimes) have also left their stamp on facies geometries, in turn feeding back to the evolution of the platform biotas. Hence simplistic analogies between modern and ancient platforms may give rise to misleading interpretations of what the latter were like and how they formed. Although a number of carbonate platform and reef specialists have warned of the dangers of such misplaced uniformitarianism (e.g. Braithwaite 1973; Gili et al. 1995; Wood 1999), it remains depressingly commonplace in the literature on ancient carbonate platforms. The endless quest in the literature for an allpurpose definition of ‘reefs’
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