Abstract Outcrop and marine field work on the NW part of the Caicos platform illustrates Pleistocene-Holocene accretion of the Providenciales and West Caicos Islands, the effects of the Holocene transgression on the flooded substrate, and the differentiation of sedimentary provinces in relation to prevailing current direction and inherited topography. A marine field study of 2D seismic (CHIRP) sub-bottom profile data and surface sediment sampling on the shelf north of Providenciales and North Caicos, and on the platform interior south of Providenciales provide an image of the top-Pleistocene surface, the thickness of Holocene sediments, and the present distribution of facies, biogenic components, and grain sizes. A pronounced difference in the composition and grain sizes of Holocene sediments exists between the open shelf north and the platform interior south of Providenciales, but maximum thicknesses of approximately 2 meters are similar. On the back-reef shelf, peloidal nearshore sands grade seaward to coarse skeletal sands, rocky bottoms and reefs. On the platform interior, the sediments are peloidal and skeletal on or near beaches, coarse skeletal grains and rubble near patch reefs, and peloidal grainstones and mud-lean packstones elsewhere in the subtidal environment. Outcrop mapping and Uranium-Thorium age dating of carbonate material from Providenciales and West Caicos provide constraints on island growth and sequence development during the Pleistocene and Holocene. Providenciales has two discontinuous core ridges of eolian and subtidal deposits with ages ranging between 160 and 302 Ka. Cutting the island core and prograding away from it are shingles (up to 4 parasequences) of marine and eolian sediments deposited during 140-90 Ka representing the transgression and high stand of isotopic stages 5e and c. Comparison of the elevation of Pleistocene marine deposits (> 12 m) and published sea level curves for the area indicates the need for uplift or higher sea levels for the island. Holocene eolian ridges, beaches, and strandplains form a discontinuous outer shingle on the island. West Caicos is cored by two eolian cores with similar age sediments (219-136 Ka), followed by reef and beach growth (120-130 ka) and younger Holocene eolian ridges making up the east and northeast extension of the island.

Abstract Carbonate platforms and reefs emerge, grow, and die in response to intrinsic and extrinsic mechanisms forced primarily by tectonics, oceanography, climate, ecology, and eustasy. These mechanisms, or controls, create the physical, biological, and chemical signals accountable for the myriad of carbonate depositional responses that, together, form the complex depositional systems present in modern and ancient settings. If we are to fully comprehend these systems, it is critical to ascertain which controls ultimately govern the “life cycle” of carbonate platforms and reefs and understand how these signals are recorded and preserved. Deciphering which signals produce a dominant sedimen– tological response from the plethora of physical and biological information generated from superimposed regional to global–scale controls is critical to achieving this goal. With this understanding, it may be possible to extract common time–and space–independent depositional responses to specific mechanisms that may, ultimately, be used in a predictive sense.

Abstract The Carbonate Analogs Through Time hypothesis states that “high-confidence, age-specific predictive models for carbonate systems and for reservoir occurrence, composition, stratal attributes, and reservoir properties can be developed by summing the ambient conditions of the carbonate processes and Earth processes at any geologic age.” We term these models age-sensitive patterns or themes. The hypothesis is built upon the cumulative body of knowledge that demonstrates carbonate processes (biotic evolution and mineralogic variation) and Earth processes (tectonics, climate, eustasy, ocean chemistry, and ocean circulation) have varied differentially throughout Phanerozoic time. The concepts of the stratigraphic hierarchy and the Sloss sequences are employed to temporally define and anchor age- specific predictive models. Age-based themes correspond to second-order supersequence scale of stratal packages, and these are fixed in geologic time (Ma). Two products developed are the Phanerozoic Carbonate Trends Chart and the Global Atlas of Carbonate Fields . The Carbonate Analogs Through Time hypothesis defines an approach for developing systematic evaluations and predictive models of Phanerozoic carbonate systems and reservoirs for use in exploration, development, and production businesses. Exploration geoscientists employ a host of concepts, tools, and data to develop predictive models for occurrence and quality of fields and reservoirs. However, as exploration successes decrease, alternative approaches are needed to refresh the exploration mindset. The CATT hypothesis and approach represent a basis for developing an alternative mindset for exploration for carbonate reservoirs. It provides a thought-provoking perspective on known occurrences of carbonate reservoirs, and offers a different way of thinking about predicting where undiscovered carbonate reservoirs may exist. Reservoir engineers require detailed geology-based reservoir parameters for simulations of reservoir / field performance. Such simulations form the bases for field development/depletion plans that carry with them implications of huge capital and operating expense. Thus, it is imperative to provide the best possible input to simulation so that investments are optimal. Typically, the input, if not derived directly from data collected within a field under development, is obtained from “analog” fields. Thus, choosing the most appropriate analog is a critical task. We contend that this approach provides the conceptual basis for choosing the most appropriate analogs for development and production-based reservoir characterization. Further, this approach provides a framework or context for the systematic organization and evaluation of the concepts, facts, and carbonate-reservoir case studies one encounters throughout a career.

Abstract Syndepositional aragonite dissolution at very shallow depths, above the lysocline, is a major process that affects carbonate deposition and skews the composition of carbonate sediments. Such dissolution is capable of altering sediment composition in many settings, and during microfacies analysis it is critical to be aware of this early, selective filtering by identifying taphonomic signatures. These effects are also capable of distorting the trophic composition of fossil biotas, potentially restricting the ability to identify nutrient levels and other controls. The evidence from widespread diagenetic limestones in shale (marl)-limestone rhythms supports the dissolution model, but the source of the precursor aragonite is unresolved; allochthonous aragonite mud is one possible source, but, especially during calcite- sea intervals, another possibility is from the autochthonous aragonitic fauna. Forward models for carbonate sedimentation will need to compensate for aragonite dissolution if realistic models are to be developed, but our knowledge of the environmental distribution and magnitude of aragonite dissolution is still woefully incomplete. Another major consequence of early aragonite loss is that the diagenetic potentials of many carbonate sediments have been changed, drastically reducing secondary porosity potentials long before they are affected by meteoric or burial processes.

Abstract All scales of tectonic deformation influence the location, sizes, shapes, and internal stratigraphy of carbonate platforms that form in active rift settings. Normal and oblique-slip faults bound the tectono-geomorphologic features that are typically found across rift settings. These fault-bounded structural elements can provide substrates for shallow-water carbonate platforms if they are submerged to shallow water depths. Thus, the incremental and long-term growth of tectonic structures, and interactions between surface processes and carbonate depositional systems that develop around or on top of these structures, determines nearly all stratigraphic aspects of syn-rift carbonate platforms.Isolated carbonate platforms are the most common type of platforms in active rift settings because they form on fault–bounded syn-rift highs. Steeply dipping fault scarps and tilted to flat-topped depositional surfaces control where shallow-marine carbonate deposition is possible. Fault scaling laws and rules for fault growth, spacing, and linkage/interaction are important for understanding the internal stratal patterns within syn-rift carbonate platforms. Footwall highs are common nucleation sites for carbonate platforms, although paleo-wind directions and siliciclastic supply to adjacent depocenters also influence facies distributions, platform morphology, and overall stratigraphic development. Active fault displacements and related surface deformations during platform growth can control platform-margin locations, facies distributions across fault-bounded basement highs, siliciclastic–carbonate interactions (especially in updip fault-bounded depocenters), and the internal growth stratal patterns within syn-rift platforms. Wedge-like growth stratal patterns within syn-rift isolated platforms are characteristic of half-graben structural elements and are well documented in outcrop and subsurface examples. Flexural uplift of footwall margins of large, fault-bounded horsts is also documented by stratal relationships from syn-rift isolated platforms that build on horst highs. Syn-rift thermal subsidence may influence where carbonate facies are distributed across the rift system, as well as timedependent accumulation rates for each platform.Syn-rift carbonate platform strata can form important petroleum reservoirs within rift-basin systems. They also provide critical records for understanding the tectonic evolution and depositional history of rift systems.

Abstract Detailed outcrop study of Miocene platform carbonates along the southwestern margin ofthe Gulf of Suez rift, together with an extensive review of comparable systems elsewhere, has generated new tectono–sedimentary models for marine rift–basin carbonate systems. Both syntectonic and post–tectonic platforms are described for various extensional settings in rift basins. Syntectonic platforms are defined as systems deposited during periods associated with active faulting in rift basins. Post–tectonic platforms are defined as carbonate systems deposited after periods of active extensional faulting that develop over preexisting, fault–generated rift topography. Carbonate systems that occupy transfer zones are also defined, which display the effects of active tectonism and intervening phases of tectonic quiescence. These platform types produce recurring tectono–sedimentological signatures recognizable throughout the strati– graphic record. The footwall margins to syntectonic platforms generally develop through the tectonic modification of existing platforms and display features associated with relative sea–level fall such as emergence and, depending upon the prevailing climate, meteoric diagenesis. In addition, fault activity truncates platforms that have prograded across the fault line during preceding phases of tectonic quiescence. Hanging–wall dip–slope margins can be complex, inasmuch as they display the effects of hanging–wall subsidence and up–dip footwall uplift. Down–dip of the fault–block fulcrum, depositional sequences are more likely to be bounded by flooding surfaces and display retrogradational to backstepping depositional sequences, while up–dip of the fault–block fulcrum, sequences may form as a result of forced regression driven by relative sea–level fall. In rift–margin areas, clastic influx is likely to play a more important part in tectonically active hanging–wall dip–slope stratigraphies because of the rejuvenation of adjacent footwall highs. Post–tectonic footwall platforms develop on the uplifted highs of fault blocks during periods of relative tectonic quiescence. Such areas reflect favorable shallow–water sites for carbonate production, because commonly they are isolated from significant clastic drainage fairways. The geometry of a footwall margin is highly variable, because it is inherited from the morphology of the faulted margin. Low– relief footwall margins produce progradational platforms that can bridge the block–bounding fault zone. High–relief blocks produce smaller, aggradational platforms in which the platform margin corresponds to the position of the previous fault scarp. Hanging–wall dip– slope margins commonly have large progradational geometries and typically evolve from ramp–type to rimmed–shelf morphologies through time. Platforms are more likely to form on rotated fault blocks that dip toward the rift margin or upon intrabasinal blocks that are set well away from rift–margin clastic input. In areas of low clastic flux, transfer–zone platforms occur with either faulted (hard linkage) or low–relief and progradational (soft linkage) margins. Such platforms commonly pass laterally into rift–parallel footwall margins to produce complex platform–margin geometries. Hydrocarbon reservoirs in platforms from these settings have a range of tectonic, sedimentary, and diagenetic controls, but the 3D models presented form templates that can be used as analogues for exploration and/or production from fault–block carbonate platforms. The active (syntectonic) and passive (post–tectonic) platform models presented can be used at scales varying from individual depositional sequences to large–scale rift–basin stratigraphies characterized by episodes of tectonic activity and intervening periods of tectonic quiescence.

Abstract In the distal part of the Late Cretaceous Hidalgoan foreland basin in NE Mexico three isolated carbonate platforms nucleated on seafloor topography created by rising passive diapirs. Carbonate facies type and architecture of each platform was distinctly influenced by a combination of both short-term local conditions surrounding individual diapirs and by long-term regional conditions that affected the entire shelf. Local conditions included windward-leeward platform paleogeography, possible elevated nutrient levels at the salt- sediment interface, and halokinesis. Regional conditions included eustatic sea-level changes, foreland-basin tectonism, and siliciclastic sediment supply to the shelf. Maastrichtian carbonate-platform facies are distributed asymmetrically across individual diapirs, reflecting windward-margin versus leeward-margin paleogeographic setting and differential minibasin subsidence related to salt withdrawal. Southern (windward) margins are dominated by steep-sided sponge, coral, and red algal reefs displaying minor fore-reef progradation (< 1.5 km) into the adjacent minibasin, thick carbonate debris-flow beds containing diapir-derived detritus, and pervasive near-diapir halokinetic fracturing. In contrast, northern (leeward) margins are dominated by foraminifera, red algal grainstone banks displaying major progradation (3-4 km) into the adjacent minibasin and lack debris-flow beds or halokinetic fracturing. Carbonate facies at all the diapirs are primarily sand-prone, heterozoan faunal assemblages that are unusual for this period of time and paleogeographic location. The presence of heterozoan faunal assemblages may be in response to high nutrient levels from local methane seeps forming at the salt- sediment interface. Carbonate facies form the bases of angular-unconformity-bounded carbonate-siliciclastic cycles called halokinetic sequences. The cycles reflect local variations in net diapiric-rise rates versus local sediment accumulation rates. Halokinetic sequences vary in number and character between the different diapirs and between the windward and leeward margins of each diapir. On leeward margins, halokinetic sequences are more numerous and carbonate facies are dominated by grainstone banks, whereas on windward margins halokinetic sequences are amalgamated and carbonate facies are dominated by fore-reef debris and debris-flow facies. The isolated carbonate platforms are best developed within the transgressive systems tracts (TST) of third-order deltaic siliciclastic depositional sequences within the regionally marine foreland-basin depositional system. Late Cretaceous to Paleogene Hidalgoan shortening of La Popa foreland basin formed large-wavelength (> 10 km) NW-SE trending salt-cored detachment folds. Diapirs that lie in the hinges of folds were shortened or “squeezed” significantly more than diapirs that lie on the limbs of folds. Squeezed diapirs generated much higher and broader topographic relief in response to higher diapiric rise rates and are correspondingly dominated by extensive, thick, shallow-water (< 15 m deep) sponge, red algal reef and grainstone-bank facies with carbonate strata extending more than 4 km away from the diapir. Age-equivalent carbonate strata on limb diapirs contain thin, deeper-water (> 30 m deep) silty, red algal packstone facies that extend < 2 km from the diapir, reflecting lower carbonate production rates in a deeper-water setting.

Abstract During the Carboniferous a carbonate shelf covered areas of the central U.S, including Kansas, with the outer shelf and shelf margin intermittently extending through southern Kansas and northern Oklahoma. The regional setting resulted in deposition of relatively laterally continuous carbonate and siliciclastic facies belts. Areally sparse subsurface well data and surface exposures have led to the interpretation that most structures on the craton are simply shallow draped anticlines and associated synclines primarily reflecting general aspects of regional structure and depositional and erosional heterogeneity. Models that assume a broad continuous shelf relegate local structure to being minor or non-existent. However, our recent examination of subsurface data, 3-D seismic, and rock properties for oil fields from the Middle Mississippian shelf margin, Middle Pennsylvanian mid-shelf, and Late Pennsylvanian lower shelf indicate that regional- and kilometer-scale structures (e.g., faults, fractures, lineaments) segmented the shelf and shelf-margin areas in Kansas, primarily along Precambrian structures that were reactivated throughout the Phanerozoic. Movement on faults resulted in segmentation expressed as rhombic-shaped structural blocks (1-10s km) with subtle variations in relief (generally meter to ~ 70 m) and slope (near zero to upwards of 2-3 m/km). Regional, down-to-basin block faulting produced linear shelf edges and segmentation of the ramp and shelf profile repeatedly during the Carboniferous. The association of stratal packages and rock properties with structural elements argues that structure exerted continued, but episodic, influence and affected sediment accommodation, depositional patterns, paleotopography, weathering intensity, diagenesis, and later fluid movement, including hydrocarbon emplacement. Results from our study of the “stable” shelf carbonates of the Midcontinent indicate that tectonic events may have had far-reaching effects and caused structural deformation in the interiors of cratons. Sedimentologic and stratigraphic analyses in such settings can benefit by evaluating the possible influence of subtle faulting and fault reactivation on depositional and diagenetic patterns that can significantly influence rock properties and reservoir development.

Abstract A regional study, based on detailed descriptions of 17 outcrops across east-central Idaho and southwestern Montana, provides a dip-oriented cross section in which to better understand the distribution of Upper Mississippian (Chesterian) stratigraphy on the distal margin of the Antler foreland basin. Chesterian strata constitute an eastward-thinning wedge of mixed carbonate and siliciclastic rocks that formed on a west-facing ramp. Foreland-basin tectonism subdivided the ramp into three distinct depositional settings: the western, central, and eastern ramp. The western ramp records nearly continuous Chesterian deposition, whereas the central and eastern ramps have significant unconformities. Mud-rich subtidal carbonate predominates on the western ramp, but this interfingered during the late Chesterian with tidally influenced siliciclastics. The central ramp contains an intraramp basin with deep subtidal siliciclastics and carbonate that formed adjacent to shallower-water facies to the west and east. The eastern ramp has mostly peritidal carbonate and shallow marine to fluvial siliciclastics, but a transgression from the north during the late Chesterian inundated this portion of the ramp with open marine carbonate. New conodont biostratigraphic constraints indicate that these Chesterian strata are a second-order megasequence (10-12 My duration) composed of more than seven third-order depositional sequences (S0-S7), each having a duration of 1-5 My. The sequences are grouped into three composite sequences (I, II, and III) that define long-term changes in accommodation controlled by syndepositional tectonism. Composite sequence I was deposited during a period of tectonic loading that partitioned the ramp via subsidence loading and extension. Composite sequence II records a period of tectonic stabilization and deposition during the most extensive eustatic flooding, whereas composite sequence III is dominated by a localized subsidence event in the Big Snowy Trough. Higher-frequency (fourth- and fifth- order) parasequences are common throughout the study interval, but they are only locally correlative. A change from thick-bedded carbonate- dominated parasequences in the early and middle Chesterian to thinner-bedded mixed carbonate and siliciclastic parasequences in the late Chesterian likely reflects the onset of moderate- to high-amplitude, high-frequency eustatic fluctuations caused by the initiation of Gondwanan glaciation.

Abstract A thick Oligocene succession of shallow-water carbonates exposed in southeast Spain provides an opportunity for studying the controls on platform and off-platform morphology and arrangement of facies successions, including compositional trends. The Oligocene platform of the Costa Blanca progressively onlaps a topographic high. It includes four high-frequency sequences that, together, show an overall upward-deepening trend and a vertical transition from cyclical inner-platform strata at the base to open-marine coralline algalmounded morphologies at the top. The margin is interpreted to have been a steep-sided and possibly faulted margin that shed coarsegrained platformal and older material into the basin. The five defined facies associations (restricted inner shelf, open-marine inner shelf, open-marine middle shelf, open-marine mounded outer shelf, and basin) consist chiefly of heterozoan biotic assemblages (red algae, benthic foraminifera, bryozoans, mollusks) that are in contrast to most other coral-dominated Oligocene strata of the Tethys. Deposition of the Oligocene platform and basin strata occurred contemporaneously with the opening of the Valencia Trough, and postdated and predated contractional events that folded the area. Faulting and increased subsidence associated with this extensional tectonic setting governed the overall platform morphology, deepening-upward trend, and slope-basin sedimentary wedges. The tectonic setting allowed the accumulation of a thick stratigraphic succession and subsequent drowning; it also overprinted the effects of global sea-level fall. The opening of the Valencia Trough may have brought deeper, cooler, and possibly nutrient-rich waters onto the shelf, controlling the heterozoan biotic assemblage. The tectonic setting, biotic assemblages, and deepening-upward characteristics of this Tethyan platform make it a good analog for Cenozoic carbonates of Southeast Asia.

Abstract The spectrum of carbonate-platform types, their heterogeneities, and their architecture is complex. Each platform succession has a distinctive and unique character that is a response to the particular geotectonic context and the physical, chemical, and biological conditions to that specific Phanerozoic window. Each succession has a distinct depositional profile, facies-belt distribution, and platform architecture, and it is expressed by the order of the basic accretional units and their stacking patterns. Critical differences between platform types are often the result of differences in their ecological accommodation. End members include (A) low-relief carbonate ramps that match a shelf equilibrium profile and are composed of either loose, fine-grained sediments produced in shallow, well-illuminated areas but shed downdip, or sediment produced and accumulated (sometimes as a distal bulge) in the deeper part of the depositional profile (poor-light or no-light zones), (B) open-shelf platforms involving large-skeleton metazoans with a marked to moderate capacity to build a platform margin above the shelf equilibrium profile, (C) rigid rimmed platforms with biotic components capable of accumulating to sea level with a maximum ecological accommodation, and (D) platforms with steep, massive and thick marginal slopes characteristic of many Paleozoic and some Mesozoic settings. Interpretation of carbonate platforms and prediction of their facies heterogeneities involves analyzing and integrating geometrically related data. Analysis involves iterative and successive backstripping of sediment accumulation from youngest to oldest. This is reassembled to determine the genetic character of the carbonate sequences, cycles, parasequences, and/or beds as products of changes in physical and ecological accommodation. This reassembly considers the evolution of the biota involved, and the resulting changes in ecological requirements, the hydrodynamic setting, the physical accommodation, and the ecological accommodation (capacity of building up above a certain hydrodynamic energy level). The limits to this analytical strategy are tied to the knowledge of the ecology of ancient biota, while its advantage is that it formulates new questions that lead to more realistic interpretations and enhanced predictions of lithofacies heterogeneities.

Abstract The well-known cyclic carbonate succession of the Middle Triassic Latemar Massif in the Italian Dolomites reveals significant lateral variability in cycle numbers in platform-interior strata. Within an interval of 60 m, a 25% increase in the number of marine flooding surfaces was detected when approaching the several-hundred-meters-wide tepee belt in the backreef area, which represents the maximum elevation of the isolated Latemar buildup. The impact of high-frequency- low-amplitude sea-level fluctuations on this elevated zone resulted in the development of spatially restricted intermittent emergence and marine flooding surfaces bounding small-scale upward-shallowing cycles. It is postulated that these alternations of submergence and subaerial exposure have favored tepee formation. Sediment collecting in the saucer-shaped tepee megapolygons further expedited upward shallowing of small-scale cycles. Conversely, deeper parts of the lagoon remained largely unaffected by high-frequency, low- amplitude sea-level oscillations: marine flooding surfaces disappear and cycles amalgamate. It is concluded that tepee structures are generally confined to topographically elevated areas where low-amplitude sea-level fluctuations were recorded. Lateral variations in cycle stacking pattern should be commonplace in shallow carbonate buildups throughout the geological record, where paleorelief existed in the platform interior.

Abstract The Port Willunga Formation is a cool–water, marine, quartzose, clay–rich, biosiliceous, and calcareous sedimentary succession of Early Oligocene age that accumulated in a series of proximal estuarine paleoenvironments along the eastern side of the St. Vincent Basin, South Australia. Coeval strata in two of the paleo–embayments are interpreted to record deposition during one ~ 3.5 My–long eustatic sea–level fluctuation. Transgressive facies above a ravinement surface comprise quartzose sands (subaqueous marine tidal dunes) that grade upward into fossiliferous floatstones and mudstones (shoreface to shallow basin–floor environments) that accumulated in a protected embayment. Highstand sediments are distinctly cyclic at the meter scale and consist of epifaunal bryozoan–pecten–echinoid clay–rich floatstones that become less fossiliferous but more spiculitic and chert–rich upward in each cycle. Whereas cyclic sediments in one embayment (Willunga) are interpreted to have accumulated on a current–swept, illuminated seafloor, those in the other (Noarlunga) are thought to have been deposited in a lower–energy, sub–photic setting. Cyclicity is interpreted to record the increasing influence of fluvial fresh water in the system during each sea–level fluctuation. Comparison with underlying strata reveals a striking similarity in depositional style and stratigraphic packaging between Late Eocene and Early Oligocene deposits; both are interpreted as paleoestuarine. Differences between the dark, organic–rich, biosiliceous, and low–diversity Eocene highstand deposits and the light, more calcareous, and more diverse Oligocene highstand deposits are interpreted to be due to local depositional controls. An important implication of local controls is that several postulated unconformities in the succession are not due to global eustatic changes but are ravinement surfaces related to estuarine sedimentation dynamics. Such controls, specifically terrestrial climate, hydrodynamic energy, and trophic resource levels were more important in determining sediment composition than eustasy and Southern Ocean cooling. Similar biosiliceous–carbonate sedimentary facies are a recurring feature of cool–water deposition throughout the Phanerozoic.

Abstract Post-Turonian (Late Cretaceous) rudist-bearing limestones of the Nurra region in northwestern Sardinia (northern Tethyan margin) and in the central-southern Apennines and Apulia (central Tethyan domain) have recorded relevant changes in the characteristics of the carbonate platforms following the “middle” Cretaceous crisis events which affected the peri-Tethyan region as well as other regions worldwide. Rudist bivalves became the dominant lithogenetic taxon owing to their proliferation in shallow-water environments and strong dominance of Late Cretaceous carbonate factories. Their inception, evolution, and demise were seemingly controlled by a complex interplay of environmental processes that, acting on a global scale, profoundly modified the Early Cretaceous hydrosphere-atmosphere system and forced Tethyan depositional systems to change their organization, internal architecture, and facies patterns. As a result, wide, open shelves developed where the almost ubiquitous mode of carbonate fixation was that of foramol factories. In this paper, evidence of the remarkable regional variability in the rudist-bearing carbonate platforms of the Mediterranean Tethys is presented. The analysis of the resulting shallow-water facies has demonstrated that, in spite of several stratigraphic similarities and common sedimentological features, some remarkable differences occurred between the northern Tethyan margin and the central Tethyan banks as regards the areal partitioning of the main paleoecologic controlling factors. This resulted in the deposition of rhodalgal successions in Sardinia (northern Tethyan margin) and rudist-rich foramol facies in the Apennine-Apulia (central Tethys) regions, respectively. Such Late Cretaceous carbonate systems can be viewed as geological products which have closely and coherently recorded the globally changing environmental conditions of the oceanic realm. In spite of this, the difference of the facies partitioning in different Tethyan regions according to a latitudinal gradient is interpreted as derived mainly from local variable paleoceanographic and paleoclimatic conditions.

Abstract Devonian reef systems are thought to represent the greatest phase of global reef development in the Phanerozoic. Despite this, ecological and environmental controls on the sedimentary nature of these vast systems have scarcely been investigated and remain enigmatic. The Late Devonian (Frasnian) Alexandra Reef System, exposed in the Northwest Territories of Canada, developed on a ramp that was situated on the western margin of Laurussia. The system consists of two reef complexes. The second reef complex developed basinwards of the first after sea level fell ~ 17 m. In contrast to stromatoporoid (± coral)-dominated reef facies in the first reef complex and the upper part of the second reef complex, reef facies in the lower part of the second reef complex are dominated by stromatoporoid-microbe associations. These include significant renalcid boundstone and stromatolite accumulations that are not found elsewhere in the reef system. It is concluded that the occurrence of the stromatoporoid-microbe reef facies indicates that a shift in the reef environment from oligotrophic to mesotrophic conditions took place. The mechanisms of nutrification were linked to the platform geometry, sea-level position, and oceanographic system, indicating that on carbonate ramps, systems tracts of falling sea level (forced regression) and sea-level lowstand may be particularly susceptible to nutrification. A nutrient-gradient model developed to explain different types of reef facies in the Alexandra Reef System indicates that trophic resources were an important control on the composition of Devonian reef-building communities, and that Devonian reefs and carbonate platforms were not highly susceptible to nutrient-invoked drowning.

Abstract This study applies high-resolution sequence stratigraphy, biostratigraphy, and magnetic susceptibility (MS) stratigraphy to better constrain correlation of upper Middle and Upper Devonian strata and geologic events in western Alberta, Canada. We also explore the potential of MS stratigraphy as a long-range correlation tool and paleoclimatic or oxygen isotope proxy. High-resolution MS data from slope and basin deposits near the isolated Miette and Ancient Wall platforms provide insight into patterns of carbonate- platform development and infilling of the Devonian Alberta basin. Our MS data, combined with conodont and brachiopod biostrati-graphic data and sequence stratigraphy, provides additional control on the relative timing of five major and fifteen higher-frequency MS excursions and nine depositional sequences. Sea-level events that initiated deposition of seven of nine late Givetian-early Famennian third order depositional sequences in western Alberta coincide with Devonian transgressive-regressive (T-R) cycles IIa-2 to IIe. Eight of these form the main sequence stratigraphic architectural units of the isolated Miette and Ancient Wall platforms. Sea- level events were identified based on significant sequence stratigraphic horizons, including exposure and marine flooding surfaces, and were biochronologically calibrated using combined conodont and brachiopod biostratigraphy. Identification of sequence boundaries and differentiation of highstand and lowstand slope and basinal deposits was based on the geometry, mineralogy, and clast content of redeposited carbonate units. The magnetic-susceptibility signature of slope and basin facies is also shown to vary systematically within the sequence stratigraphic framework. Spikes in the MS record coincide with events associated with lowstand or initial transgression. The MS stratigraphy displays a consistent pattern across the Alberta basin, with generally higher MS values toward the east. The MS signature is generally low in the late Givetian and early Frasnian (through MN Zone 9) but displays a major bimodal MS increase in the middle to late Frasnian (MN zones 10-11). MS values return to generally lower levels during the late Frasnian (MN zones 12-13) and early Famennian. This general pattern of increasing followed by decreasing MS is interpreted to indicate variations in delivery of magnetically susceptible terrigenous material. The highest MS values correlate directly to the lithologic change associated with an influx of fine-grained siliciclastics in the Mount Hawk Formation. The generally consistent pattern of MS change across the Alberta basin points toward the utility of MS stratigraphy as a regional correlation tool. Several other positive MS excursions documented here are also associated with increased detrital input and are coeval with decreasing or low oxygen isotope values (increasing or high paleotemperatures) reported from both Laurasia and Gondwana. This relationship implies a paleoclimatic linkage with increasing temperatures and weathering rates resulting in higher detrital input and higher MS values. Published oxygen isotope data are too coarse to conduct high-resolution comparison with our MS data, but the parallel trends noted here suggest that further research on the use of MS as an oxygen isotope or paleoclimate proxy is warranted. The MS signature of coeval Devonian rocks from highly condensed sections in Morocco displays a shape structure similar to our data and reinforces arguments that MS stratigraphy has potential as a long-range correlation tool.

Abstract Shallow-water carbonate systems encompass a spectrum of environments, from reefs to shoals to tidal flats. Although the sedimentologic characteristics of these systems have been studied for many years, new remote-sensing data provide unique, unparalleled perspectives on spatial heterogeneity in Holocene carbonate systems. The purpose of this paper is to describe the structure, content, and utility of a database of remote-sensing images that are included on a companion CD. The twenty-five focus areas include a range of depositional systems from across the globe. The image database for most areas includes three scales of remote-sensing data: one that captures the regional context (Moderate Resolution Imaging Spectroradiometer [MODIS] data, with 250 m 2 pixels), another that illustrates the local setting (Landsat data, with ~ 30 m 2 pixels), and a third that includes high-resolution details of the area (IKONOS or QuickBird data, with 4 m 2 or 2.5 m 2 pixels). These are presented in an interactive, zoomable format, and are supplemented by supporting information on the setting and published work in each area. The overall goal of the database is to provide the suite of new images to a broad audience, rather than to provide a detailed interpretation of any or all areas, or an overview of controls on carbonate depositional systems. These images can be used in several ways. For example, specific examples in the database have been applied as a learning tool in a classroom, and quantitative analysis illustrates enhanced student understanding of spatial complexity in these systems. Additionally, beyond the classroom, these images provide information on depositional models and the scales of depositional heterogeneity in carbonate systems for geologists, reservoir modelers, and geophysicists.

Abstract A geologic model is essential for characterization and modeling of hydrocarbon reservoirs, and depositional facies are a main parameter controlling heterogeneity in porosity and permeability. Quantification of facies attributes (size, shape, orientation, and distribution) can decrease uncertainty in a geologic model and therefore enhance the model’s utility. This study uses Landsat images of modern isolated carbonate platforms to evaluate platform characteristics, facies distribution, and facies attributes, and assess quantitative relationships among these parameters. Facies include fully aggraded reef, partially aggraded reef, reef apron, shallow platform interior, shoals, intermediate platform interior, deep platform interior, forereef and outer platform, and land. Statistical analyses demonstrate the existence of relationships between the configuration and composition of facies tracts on and among carbonate platforms, which become useful predictive tools. In addition, several aspects of reef-belt facies have been quantified, including the abundance by platform size, width and variability, length and variability, and aspect ratio. The results offer insights that could be used for better prediction of facies distribution in ancient platforms and reservoirs.

Abstract Dionisos is a forward stratigraphic modeling package that can be used to analyze the facies distributions in an isolated carbonate platform. Two grainstone distributions are considered and used as “inspiration” for an unconditioned case study: grainstones around the platform margin and grainstones in the platform center. In one experiment a linear rate of sea-level rise is used and the rate is varied to generate a series of models. In a second experiment a cyclic sea-level curve is added, and the amplitude of the cycles is varied to generate a second series of models. Platform-margin grainstone facies patterns develop during times of very shallow water depth on the platform top, and slow changes in bathymetry. Platform-center grainstone facies patterns develop during times of slightly deeper water depth and increasing bathymetry (flooding). Different facies patterns can occur at the same bathymetry, depending on whether water depth is increasing or decreasing. The difference is attributed to the persistence of local depocenters that depended on previous environments (stratigraphic inertia) and the roundness of the platform. In these experiments a platform will be flatter during deepening than during shallowing because of its previous history. Neither of these two factors is reflected in the average bathymetry value but is captured in the rate and sense of flooding. The timing of interpreted sequence boundaries and maximum flooding surfaces is investigated. In some models these surfaces are clearly diachronous, and their timing relative to the accommodation cycle varies depending on the amplitude of the accommodation change. During “greenhouse” times the subtle environmental shifts created by changes in accommodation are more significant than the actual resulting bathymetry change, and the timing of sequences is poorly related to the highs and lows on the accommodation cycle. Conversely, during “icehouse” times bathymetry change is directly driven by the accommodation cycle and the resulting sedimentary cycle is in phase with accommodation.