Abstract The Ammonitico Rosso of the western Venetian Alps is a 10- to 25-m-thick, red nodular limestone that overlies thick Late Triassic to Middle Jurassic shallow-water carbonates that form the South Trento Platform. Deposition of the Ammonitico Rosso is thought to represent a Middle-Late Jurassic drowning event whereby the South Trento Platform became a deeply submerged plateau. The Ammonitico Rosso is problematic in that it: (1) overlies a platform-wide unconformity that contains complex brecciated fabrics filled by pelagic-rich "Posidonia alpina" sediment and cement; (2) is rich in ammonites and other pelagic fauna; and (3) contains stromatolites, oncolites, and wave-rippled coquinas. Based on new data from the eastern margin of the South Trento Platform, the drowning succession is interpreted to have a shallow origin. These data include: (1) the discovery of two sponge-coral-stromatoporoid patch reefs within oolitic and peloidal grainstone below the unconformity; (2) cavities and fill associated with the unconformity; and (3) diagenetic fabrics and transition from platform interior to platform margin facies in both the Lower and Intermediate members of the Ammonitico Rosso. Faunal and lithologic similarity of sponge-coral-stromatoporoid reefs with other Lower Jurassic reef complexes suggest that these reefs are Late Pliensbachian in age. Cavities and neptunian dikes within back-reef, reef, and fore-reef sediments are filled by P. alpina sediment, rounded lithoclasts, fibrous cement, and crystal silt. Pendant cement and crystal silt found within reef cavities and neptunian dikes overlap deposition of internal sediment. In a west-to-east transect above the unconformity, stromatolitic and oncolitic mudstone/wackestone in the Lower Ammonitico Rosso grades first into thrombolites and stromatolites, then into nodular burrowed wackestone and packstone/grainstone. Packstone and grainstone contain well-preserved ammonites, pelagic bivalves, peloids, belemnites, gastropods, solitary corals, and fibrous cement. In the Intermediate Member, thin-bedded chert-rich limestone grades into event strata (i.e., tempestites) composed of limestone gravel and well-sorted sand, and pelagic-dominated mudstone/wackestone. Gravels are poorly sorted, sometimes imbricated and contain lithoclasts derived from underlying sediments. These lithologies overlie truncation surfaces that include deep irregular excavations, rounded gutters, and gently scoured surfaces and grade upward into sands that possess hummocky, low-angle, and planar cross-stratification. Sands are composed of coarse- to fine-size lithoclasts, peloids, and skeletal grains. Peloidal mud-stone and wackestone contain protoglobigerinids, radiolarians, ammonites, pelagic bivalves, belemnites, crinoids, and solitary corals. Solitary corals are found in growth position on ammonite and belemnite substrates. The drowning succession of the South Trento Platform correlates with long-term eustatic rises and falls of sea level and includes: (1) Upper Pliensbachian deposition and tectonism; (2) a transgressive systems tract and high-stand systems tract (Toarcian); (3) a small-scale type 1 sequence boundary (late Toarcian-Lower Bajocian?); (4) a drowning sequence (Aalenian-Upper Bajocian); and (5) a composite condensed section (Upper Bajocian-Tithonian). The appearance of pelagic organisms on the South Trento Platform and a biotic succession from (1) sponge-coral-stromatoporoid reefs to (2) bioeroded sponge and hermatypic coral reefs to (3) grainstone composed of ahermatypic suspension/detrital feeders and planktic organisms to (4) "stunted" pelagic and benthic faunas to (5) microbial mat (stromatolite) structures indicates progressive paleoecologic deterioration of shallow-water environments. Analogy of these transitions with those observed on modern "drowned" platforms suggests that the demise of carbonate producing benthos was caused by increasing amounts of nutrients and organic matter (i.e., trophic resources) and establishment of oxygen-deficient environments. Faunal transition is coincident with the breakup of Pangea during the Lower-Middle Jurassic, the deposition of organic-rich shale and manganese-rich limestone in periplatform and basinal settings, and eustatic sea-level rise. This suggests that influx of trophic resources was associated with changes in regional circulation patterns and upwelling. Drowning is interpreted to have occurred gradually over time through a combination of eustatic sea-level rise and environmental change.

Abstract The late Paleoproterozoic upper McArthur Group (River Supersequence) is a dominantly shallow marine carbonate platform sequence. Deeper water shaley rocks of the Barney Creek Formation of this Supersequence host the supergiant HYC Zn-Pb-Ag deposit. Three higher order sequences, the Emmerugga Depositional Sequence, the Barney Creek Depositional Sequence, and the Lynott Depositional Sequence, make up the River Supersequence in the southern McArthur basin. Within the Barney Creek Depositional Sequence, there are 26 lithofacies that can be grouped into seven facies associations, each representing specific and coeval sedimentary environments. This complex facies mosaic formed in response to a sinistral transpression event during regional north-south extension. Basin architecture was controlled by major meridional strike-slip structures, such as the Emu, Tawallah, and Hot-Springs faults. Although these structures have a later, postsedimentation history, they also controlled the distribution of the different facies of the Barney Creek Depositional Sequence. North- to northwest-trending segments of these structures were transtensional, whereas structures oriented east of north were transpressional. Transtension resulted in the development of significant local accommodation and sub-basin development and allowed substantial thicknesses of deeper water, fine-grained sediments, which are potential hosts to Zn-Pb-Ag SEDEX deposits, to accumulate. Locally, in platform and slope facies of the Barney Creek Depositional Sequence, the orientation and vergence of kinematic indicators, such as neptunian dikes and intrafolial folds, may indicate the direction to deeper shaley facies.

Abstract Synsedimentary diagenesis in the marine realm is relatively uncomplicated (by comparison with meteoric and burial diagenesis) because it generally operates over short time spans (only years to thousands of years, in most cases) and involves a restricted range of pore fluid chemistries. Nevertheless, through a combination of physical, chemical and biological processes, coupled with access to a nearly unlimited supply of dissolved materials in seawater, marine diagenesis can often bring about remarkable change in carbonate sediments and produce some very complex fabrics. Furthermore, the subsequent overlay of meteoric or burial diagenetic alterations can greatly complicate the recognition of marine diagenetic fabrics in ancient carbonate rocks. That is especially true because the aragonitic or Mg-calcitic cements that result from marine diagenesis are essentially just as unstable in meteoric or burial-stage pore fluids as primary grains of those compositions. The intensity or extent of marine cementation is a function of the supply of solutes from seawater. Solute supply, in turn, depends on sedimentation rates and the effectiveness of water transport from the surface into the interior of a sediment pile. Mechanisms of water movement include, among others, wave forcing, tidal pumping, thermal convection, and diffusive transport. Areas of very slow sedimentation (e.g., hiatus surfaces, low-sedimentation-rate platform interiors, or low-productivity deep sea settings) can have substantial marine cementation (including hardgrounds) because they all have long times of contact between seawater and a thin package of sediment, even with no special mechanism for water pumping. In high-sedimentation rate areas, on the other hand, substantial marine cementation occurs mainly in reef front or coastal settings where wave or tidal action can force seawater through the sediments to a considerable depth. Likewise, atoll margins and steep carbonate platform flanks are sites of extensive marine cementation because of convective water input coupled, in some cases, with low sediment accumulation rates. Hot or cold seeps on the sea floor also represent sites of exceptional water throughput and extensive cementation. Grain and matrix dissolution are widespread in certain marine environments, particularly in cold- and deep-water areas. Modern oceanic waters have an aragonite compensation depth or ACD at roughly 1,500 m (the ACD is the depth below which aragonite does not accumulate because the rate of dissolution exceeds the rate of aragonite supply). Aragonite also is extensively dissolved in cool and cold-water shelf areas. The modern calcite compensation depth (CCD) lies at roughly 4,500 m (but that depth, as well as that of the ACD, varies with latitude, productivity, and other factors, and undoubtedly has varied significantly with geologic time). Bored (biodegraded) grains with cement infill of borings and generation of micrite envelopes (also discussed in the sections on pellets/peloids and sedimentary structures-borings). Isopachous crusts of fibrous to bladed, peloidal, or aphanocrystalline high-Mg calcite cement. The aphanocrystalline crusts consist of equant, less than 4 μ m-sized rhombs that look much like micrite. Isopachous crusts of fibrous aragonite cement within grain cavities and as intergranular cements (predominantly found in warm-water, slightly hypersaline settings and tropical beachrock deposits). Marine-cemented hardground formation in selected areas (see above) — associated, in many cases, with phosphate and glauconite cementation, boring and faunal encrustation, and intraclast formation. Large botryoids of cavity-filling aragonite and high-Mg calcite cement. Internal sediment fills of primary cavities or neptunian dikes in framework-supported sediments. Coastal beachrock and spray-zone cements. Microbe/cement associations in marine methane and thermal seeps. Modern marine cements in warm-water settings consist mainly of high-Mg calcite (~12-18 mol% Mg), but with extensive aragonite as well. In colder-water areas (temperate, polar and deep marine), high-Mg calcite cements predominate, but become scarcer and less Mg-rich at higher latitudes. Many ancient carbonate deposits certainly had aragonite and high-Mg calcite cements, perhaps with secular variations in their abundance (e.g., Wilkinson and Given, 1986 ), but low-Mg calcite marine cements may also have formed at some times. In older limestones, original aragonite and high-Mg calcite cements generally have been converted diagenetically to low-Mg calcite and must be recognized by micro-inclusions, geochemical analysis (especially Mg and Sr contents), relict morphologies or crystal outlines, or, as a last resort, characteristic patterns of preservation or alteration (former aragonitic cements, for example, typically have poor primary fabric preservation.) Characteristic morphologies of marine cements A diagrammatic depiction of some common types of modern marine high-Mg calcite and aragonite cements. Most of these morphologies will be illustrated in this section. Adapted from James and Choquette (1983) .

Abstract The distribution of lithofacies in the Devonian Great Barrier Reef on the Lennard Shelf area is controlled by basement-hosted faults, with the reef and platform facies confined to palaeo-highs, clearly separated from basin facies in the abutting areas. These faults also focused syn-sedimentary deformation along the edge of the platform margin, with zones of sediment and cement-filled neptunian dikes forming above the basement faults and subsequently being reactivated during regional extensional deformation. From the interpretation of geophysical data and field work, the gross structural architecture of the Lennard Shelf is strike-extensive northwest-trending listric normal faults that parallel the basin margin and which show apparent offset on northeast-trending accommodation zones. The Limestone Billy Hills and Pillara Range of the Lennard Shelf are within a structural corridor of regional extent, perpendicular to the trend of the Fitzroy Trough. Meso-scale structures combined with the trend of the fault zone, consistently indicate that deformation is the result of a sinistral oblique-slip zone possibly above basement faults at depth. The deformation occurred within an accommodation zone between offset, regionally extensive northwest-trending normal faults which are parallel to the Fitzroy Trough margin. There is no evidence for compressional tectonics nor penetrative deformation as suggested by some earlier workers.

Abstract The Devonian "Great Barrier Reef" of the Canning Basin developed beside a mountainous landmass of Precambrian rocks (the Kimberley Block) and around islands of Precambrian and Ordovician rocks. Basement topography, commonly fault controlled, was important in localizing the reefal platforms. Growth of the platforms was nearly continuous from late Givetian to late Famennian times, with only rare intervals of brief emergence. The earliest (Givetian) platforms were low-relief banks; later Frasnian and Famennian platforms were usually reef rimmed, with high relief. Upright reef margins predominated in the Frasnian, with intervals of backstepping in the late Frasnian associated with widespread drowning and the development of pinnacle reefs. A brief regression, with minor subaerial erosion of platforms (including mild karstification), occurred at the Frasnian-Famennian boundary, and the succeeding Famennian platforms advanced basinward over their equivalent marginal-slope and basin facies. Platform extinction in the late Famennian resulted from abrupt drowning. The hypothetical curve of relative sea level for the Canning Basin Devonian shows only partial resemblance to the Euramerican eustatic curve. In both areas, rapid rises in relative sea level in the late Frasnian caused widespread drowning of reefal platforms, followed by a brief regression at the Frasnian-Famennian boundary, which coincided with the world-wide mass extinction of metazoan reef builders. The Famennian regressions identified in Euramerica are not recognized in the Canning Basin, where the limestone platforms advanced continuously under conditions of steady rise or stillstand in relative sea level. Earthquakes associated with faulting during growth of the complexes resulted in extensive fracturing of rigid submarine-cemented limestones along the platform margins and upper marginal slopes, leading to the development of neptunian dikes and the collapse of platform margins to form massive debris flows. Contemporary faulting also influenced platform-basin morphology and was responsible for the mountainous topography of the adjoining landmass, which shed masses of boulder conglomerate and other terrigenous sediments interfingering with the reef complexes. Seismic stratigraphic modeling, in comparison with observed seismic records and well data, suggests that the evolutionary model for the Devonian reef complexes deduced from outcrop studies can also be recognized in the subsurface. Three small oil fields are associated with or overlie a well-defined subsurface Famennian platform margin. Recent research involving outcrop, core, seismic, and geochemical studies suggest, however, that the best prospects for future oil discoveries are likely to be in Givetian-Frasnian platforms, which have yet to be adequately tested. Mississippi Valley-type zinc-lead orebodies have been found in Givetian-Frasnian platforms in the outcrop area, and one of these is now being developed. The area is believed to have a good potential for further zinc-lead mining developments.