Abstract The hydrocarbon-productive James reef at Fairway field, trending nearly at a right angle to the Lower Cretaceous strandline, has been proven by detailed facies mapping and key well control to have an atoll reef configuration. Facies of the atoll are differentiated into: (I) two northwest trending reefs of algal stromatolite-hydrozoan boundstone (lowermost zone), Chondrodonta wackestone (middle zone), and rudistid boundstone and wackestone (uppermost zone); (2) lenticular bodies of reef-derived skeletal grainstone that flank the reefs; and (3) lagoonal limestones characterized by interbedded miliolid-peloidal grainstone, algal nodule wackestone, and biostromes of rudistid wackestone and Chondrodonta wackestone. The thickest sections of the lagoonal facies lie between the reefs, and the reef facies appear to partially enclose the lagoonal facies. The off-reef facies, which developed contemporaneously with reef growth, consist of argillaceous, skeletal packstone, wackestone, and mudstone.

Abstract: There are three depositional scenarios for Miocene reef development within the Pelagian Region as follows: Carbonate ramps provide an important setting for coral patch reefs, with the additional important development of coralline algal (often rhodolitic) biostromes immediately basinward of the lime-mud dominated patch reefs. Delta tops and chaannels, in total contrast to the clear water carbonates of gently sloping ramps, are the tectonically active zones associated with areas immediately to the south of the Sicilian Alpine fold belt. Here, in association with delta top channels and small offshore culminations above thrust-generated sea floor ridges, localised reefs developed whenever turbidity and siliciclastic sedimentation was reduced. Generally this was coincidental with marine onlap events of relatively short duration. Finally, carbonate shelf slope breaks, there are the monogeneric coral curtain reefs which developed under clear water conditions at basin-facing breaks in slope such as the submarine fault scarps bordering on to the central Mediterranean graben systems. From a palaeoecological viewpoint, the limited range of coral genera present may most conveniently be catalogued on the basis of their respective growth form strategy. These range from slender rods in excess of 1 m long in the coral curtains, to vermiform and ramose bushy growths in the areas of highest siliciclastic sedimentation. Additionally, dome headed corals dominate upper fore-reef and reef crest locations; whereas, undulose growth forms typify lagoonal and ramp patch reefs. Each peculiar reef type is the product of a variable range of parameters including substrate stability, eustatic fluctuations, tectonism and sedimentation rates. These are all considered before proposing several sedimentological models common to the central Mediterranean region and possibly of value elsewhere within Tertiary "Tethyan realm."

Abstract Accurate interpretations of facies in ancient reefs requires both proper “classification” of the reef and an understanding of the sedimentologie and biologic processes active during the formation of the reef. Study of modern reefs provides evidence for the processes affecting facies in reef complexes with a rigid organic framework and steep fore-reef wall, but generally reveals only the incipient products of these processes because most Holocene reefs have been growing for only a few thousand years following the Holocene transgression. Only where underlying topography approximates the profile of a mature reef complex can well developed examples of the sedimentologie facies of a mature reef complex be found in modern reefs. Study of these pseudo-mature reef complexes reveals a sequence of sedimentologie facies (from basin toward land) consisting of: I. distal talus, 2. proximal talus, 3. reef-slope, 4. reef framework, 5. reef-crest, 6. reef-flat, and 7. back-reef sand. Knowledge of the characteristics and distribution of these facies should facilitate facies interpretation in comparable ancient reef complexes. Reef framework forms only a few percent of the volume of a mature reef complex, whereas the vast majority of the complex consists of debris in fore-reef and back-reef facies; the debris being derived largely from the framework. This has particular significance in hydrocarbon exploration because most wells drilled toward the top of a seismicly defined ancient reef complex would penetrate only the back-reef carbonate sand facies. However, this is as it should be because the reef framework facies generally has little preserved primary porosity due to sediment infilling of cavities and extensive marine cementation. The facies of modern reef complexes discussed here exist due to the presence of a significant marginal (as opposed to centrally located) shallow water, wave resistant, rigid organic framework composed largely of scler-actinian corals. Similar facies may be expected in those fossil reef complexes with a more or less comparable organic framework such as the Devonian stromatoporoid/tabulate coral reefs, the Permian algal/sponge/marine cement reefs, and the Neogene coral reefs. However, different facies must occur in ancient reefs that lacked rigid organic frameworks such as the Paleozoic bryozoan and/or crinoid mounds, Late Paleozoic phylloid algal mounds, Cretaceous rudistid banks, and early Tertiary Nummulites banks.