Abstract Pennsylvanian (Late Carboniferous)–Early Permian cyclothems are documented for the first time from the shallow-marine carbonate succession on the Yangtze Carbonate Platform, South China. The Zongdi section in southern Guizhou Province comprises bioclast-rich grey limestones with dark-coloured intervals yielding macro- and microfabrics related to emergent events. We recognized 26 depositional sequences (consisting essentially of basal peritidal sediments, middle shallow subtidal sediments and upper peritidal sediments affected by meteoric diagenesis and subaerial exposure) separated by 25 lowstand events. These are interpreted as having been formed by alternating marine transgression and regression resulting from variations in the Gondwanan ice sheets. They are compared with the Midcontinent (Kansas-type) cyclothems in North America. However, the Zongdi cyclothems are relatively thin and consist entirely of very shallow-marine sediments formed above wave base, whereas the Midcontinent cyclothems reflect deposition far below wave base. The Zongdi depositional environment was an upper shelf area, on a platform within the epeiric sea on the South China Craton, where sedimentation occurred in a relatively small (shallow) accommodation space during the highest stands of sea level. They were formed by major (large-scale) transgressions that submerged high-shelf areas, and most of them correspond to the major cyclothems of the North American Midcontinent Basin. The fusuline biostratigraphical framework reveals an uneven stratigraphical pattern of the Zongdi cyclothems, reflecting subtle fluctuations of tectonic subsidence on the epeiric Yangtze Carbonate Platform. Less erosion and karstification on the tops of cyclothems in the Zongdi section, together with the presence of partly calcareous palaeosols, indicates that a dry climate prevailed on the South China Block during the Pennsylvanian–Early Permian when the Zongdi cyclothems were formed.

Abstract The northwestern margin of the northern Appalachian Orogen and adjacent craton is a Lower Paleozoic, low-latitude carbonate platform that originally lay along the northern margin of the Iapetus Ocean. Parts of the platform interior are now exposed in Quebec, but much lies beneath the Gulf of St. Lawrence. Outer-shelf and deep-water deposits crop out in western Newfoundland. The shelf break and upper slope are nowhere exposed, but their nature has been determined from numerous clasts in sediment gravity flows redeposited on the lower slope and now stacked in allochthonous thrust complexes. The relatively thin part of the platform (approximately 2 km) preserved in western Newfoundland lay well inboard of the shelf edge and accumulated on rigid crust that underwent relatively little thermal subsidence. Four separate phases of platform evolution can be differentiated, reflecting the interplay between tectonics, eustasy, and the evolving Lower Paleozoic biota. Phase 1: preplatform shelf, reflects initial siliciclastic deposition and volcanism on rifted crystalline basement, followed by a short period of carbonate sedimentation with archaeocyathan buildups and ooid-sand shoals that was terminated by offlap of thick quartz arenites. Phase 2: narrow, high-energy platform, is characterized by mixed siliciclastic-carbonate, non-bioclastic, peritidal sedimentation throughout and is locally manifest as three Grand Cycles. Contemporaneous deep-water sediment composes basal welded conglomerate overlain by quartzose carbonate turbidites. Phase 3: wide, low-energy platform, is an onlap package of muddy, bioclastic, subtidal and peritidal carbonates arranged in the form of two unconformity-bounded sequences. The adjacent deep-water slope was a narrow belt of debris flows and a wide apron of carbonate and shale, deposited in the lower part of an oxygen-minimum zone. Phase 4: foundered platform, documents the initial uplift, faulting, subsidence, and fragmentation of the platform in a sequence of peritidal to subtidal to deep-water carbonates, reflecting the initial stages of the Taconic Orogeny. The entire sequence is buried by synorgenic flysch and overlain by thrust sheets containing deep-water sediments of phases 1, 2, and 3, as well as oceanic lithosphere and other exotic assemblages. The main control governing platform initiation, thickness, and demise was tectonics. Internal stratigraphy, arrangement of shallow-water facies, and style of deep-water sedimentation were governed by eustasy with a local tectonic overprint. Climate was temperate tropical. The sediments themselves, dominated by periods of bioclastic versus non-bioclastic (ooids, peloids) sedimentation, reflects temporal changes in the early Paleozoic global biosphere.

A bstract Upper Cenomanian limestones exposed in southern and western Istria, Croatia, are rich in radiolitid remains and also containdinosaur footprints. As documented in measured sections at Lovrecica, Ladin Gaj, Grakalovac, and Fenoliga, as well as in a new sectionat Karigador, rudists and dinosaur tracks occur together in peritidal sediments that are organized into shallowing-up cycles. These cycleswere deposited in the interior of the carbonate platform and are commonly capped by intertidal laminites. At these localities, the rudistsare elevator types and mud-supported sediment dwellers that thrived in the soft substrate where dinosaurs made footprints. Dinosaurtracks are preserved in both types of subtidal limestones, and radiolitid congregations are laterally discontinuous in foraminiferal-peloidal limestone. The presence of dinosaur footprints on the upper bedding plane of rudist floatstone implies that the Istrian part of the Late Cenomanian carbonate platform was a shallow, protected platform interior. Dinosaurs strode across the muddy bottom of the shallow-water platformin water depths equivalent to their estimated hip heights. These dinosaur-track-rich levels in Upper Cenomanian shallow marinelimestones of the Adriatic carbonate platform underlines the relevance of dinosaur footprints as a tool for paleoenvironmental reconstruction.

Abstract In west-central Kansas the Cherokee Group of early Desmoinesian, Pennsylvanian age is a mixed siliciclastic and carbonate sequence. It was deposited in environments that were transitional from continental to marginal marine as the sea transgressed over the Mississippian unconformity out of the Hugoton Embayment and onto the Central Kansas Uplift. Sandstones of the Cherokee Group are important oil reservoirs in west-central Kansas, but they are highly variable in properties and in aerial distribution; therefore, they are difficult to predict. Core studies and subsurface analysis using wireline logs reveal two persistent and widespread limestone beds that form useful stratigraphic markers within the Cherokee. They provide a framework for facies analysis and regional mapping that may be useful as a predictive tool for oil exploration. Six basic lithofacies are interpreted from lithologies and sedimentary structures observed in cores obtained from four wells in eastern Ness County: (1) basal Pennsylvanian conglomerate, (2) fluvial sands, (3) fine-grained tidal-flat deposits, (4) shallow marine limestones and shales, (5) shoreline sands and tidal-channel sands, and (6) braided-stream sandy conglomerates. Successions of these facies are equivalent to components commonly observed in Kansas cyclothems. Two transgressive-regressive cycles are identified in the Cherokee, and maximum transgression is correlated with the basal portion of the two widespread limestone beds. Following burial of the Mississippian karstic surface, deposition of peritidal sediments occurred on a uniformly shallow platform. Sedimentation was punctuated by episodes of subaerial exposure and weathering. Clastics derived from the eroding Central Kansas Uplift were probably supplied episodically to the coastal plain by braided streams that were reworked by coastal processes.

Abstract The sequence of deposition of the Upper Jurassic Smackover Formation in updip marginal positions, north of the regional peripheral fault trend in the eastern Gulf Coastal Plain is the result of the combined effects of many variables including paleotopography, eustasy, tectonic subsidence, and carbonate productivity, which have been highly influenced by environmental conditions. Tectonic subsidence is identified as a critical mechanism for the generation of the accommodation space required for the accumulation of thick Smackover sections measured in wells located in areas associated with basement paleohighs that were elevated during the time of Smackover deposition. This study focuses on Vocation Field located in southwestern Alabama, in the eastern margin of the Manila sub-basin, along the western flank of the Conecuh ridge. The structure in Vocation Field is a Paleozoic basement high associated with the Triassic/Jurassic rifting event. The reservoir in the field is the Upper Jurassic Smackover Formation, which overlies siliciclastic deposits of the Norphlet Formation in the margins of the structure and onlaps crystalline basement rocks in updip positions. Based on core and thin section descriptions, four subenvironments have been interpreted for Smackover deposits: microbial reef complex, shallow lagoon, shoal complex, and sabkha-tidal flat. These subenvironments define an overall aggradational to progradational shallowing-upward marine cycle developed in an evaporate-carbonate setting. The reef and shoal complexes are the main and potential petroleum reservoirs. Significant boundstone accumulations have been deposited on the northeastern side of the basement structure due to restricted environmental conditions that favored the establishment and growth of the microbial reefs in that area. Smackover deposition in Vocation Field was initiated as a result of a rapid relative sea level rise (transgressive event) that partially submerged the basement paleohigh and led to the development of microbial reef buildups on the northeastern flank of the structure during the “catch–up” phase of the carbonate system. Changes in the depositional environment and a decrease in the rate of relative sea level rise initiated the “keep-up” phase characterized by the aggradation and finally progradation of shallow subtidal and peritidal sediments of the upper part of the Smackover Formation. According to the depositional model, the microbial boundstones are equivalent to the peloidal wackestones and laminated carbonate mudstones of the middle Smackover accumulated in downdip areas having greater water depths.

Abstract Middle and Upper Ordovician sediments in northwest Georgia and northeast Alabama can be separated into three facies complexes. The northwestern complex is dominated by shallow water and peritidal carbonates, the central complex by red, peritidal clastics, and the southeastern complex by basinal black shales.

Abstract In the central Appalachians, carbonate deposition of the great American carbonate bank began during the Early Cambrian with the creation of initial ramp facies of the Vintage Formation and lower members of the Tomstown Formation. Vertical stacking of bioturbated subtidal ramp deposits (Bolivar Heights Member) and dolomitized microbial boundstone (Fort Duncan Member) preceded the initiation of platform sedimentation and creation of a sand shoal facies (Benevola Member) that was followed by the development of peritidal cyclicity (Dargan Member). Initiation of peritidal deposition coincided with the development of a rimmed platform that would persist throughout much of the Cambrian and Early Ordovician. At the end of deposition of the Waynesboro Formation, the platform became subaerially exposed because of the Hawke Bay regression, bringing the Sauk I supersequence to an end. In the Conestoga Valley of eastern Pennsylvania, Early Cambrian ramp deposition was succeeded by deposition of platform-margin and periplatform facies of the Kinzers Formation. The basal Sauk II transgression during the early Middle Cambrian submerged the platform and reinitiated the peritidal cyclicity that had characterized the pre-Hawke Bay deposition. This thick stack of meter-scale cycles is preserved as the Pleasant Hill and Warrior Formations of the Nittany arch, the Elbrook Formation of the Great Valley, and the Zooks Corner Formation of the Conestoga Valley. Deposition of peritidal cycles was interrupted during deposition of the Glossopleura and Bathyriscus-Elrathina Biozones by third-order deepening episodes that submerged the platform with subtidal facies. Regressive facies of the Sauk II supersequence produced platform-wide restrictions and the deposition of the lower sandy member of the Gatesburg Formation, the Big Spring Station Member of the Conococheague Formation, and the Snitz Creek Formation. Resubmergence of the platform was initiated during the late Steptoean ( Elvinia Zone) with the expansion of extensive subtidal thrombolitic boundstone facies. Vertical stacking of no fewer than four of these thrombolite-dominated intervalsrecords third-order deepening episodesseparatedbyintervening shallowing episodes that produced peritidal ribbony and laminated mudcracked dolostone. The maximum deepening of the Sauk III transgression produced the Stonehenge Formation in two separate and distinct third-order submergences. Circulation restriction during the Sauk III regression produced a thick stack of meter-scale cycles of the Rockdale Run Formation (northern Virginia to southern Pennsylvania), the upper Nittany Dolomite, the Epler Formation, and the lower Bellefonte Dolomite of the Nittany arch (central Pennsylvania). This regressive phase was interrupted by a third-order deepening event that produced the oolitic member of the lower Rockdale Run and the Woodsboro Member of the Grove Formation in the Frederick Valley. Restricted circulation continued into the Whiterockian, with deposition of the upper Rockdale Run and the Pinesburg Station Dolomite in the Great Valley and the middle and upper parts of the Bellefonte Dolomite in the Nittany Arch region. This deposition was continuous from the Ibexian into the Whiterockian; the succession lacks significant unconformities and there are no missing biozones through this interval, the top of which marks the end of the Sauk megasequence. During deposition of the Tippecanoe megasequence, the peritidal shelf cycles were reestablished during deposition of the St. Paul Group. The vertical stacking of lithologies in the Row Park and New Market Limestones represents transgressive and regressive facies of a third-order deepening event. This submergence reached its maximum deepening within the lower Row Park Limestone and extended into the Nittany arch region with deposition of the equivalent Loysburg Formation. Shallow tidal-flat deposits were bordered to the south and east by deep-water ramp deposits of the Lincolnshire Formation. The St. Paul Group is succeeded upsection by ramp facies of the Chambersburg and the Edinburg Formations in the Great Valley, whereas shallow-shelf sedimentation continued in the Nittany arch area with the deposition of the Hatter Limestone and the Snyder and Linden Hall Formations. Carbonate deposition on the great American carbonate bank was brought to an end when it was buried beneath clastic flysch deposits of the Martinsburg Formation. Foundering of the bank was diachronous, as the flysch sediments prograded from east to west.

Abstract Field mapping, facies analysis, and laboratory study have been completed on Upper Devonian to Lower Permian carbonates of the Bolshoi Karatau Mountains, southern Kazakhstan, and of the southern Urals, Russia. These data suggest that: (1) following the Late Devonian extinction event, major shifts took place in the composition and spatial distribution of reef biota and in the mineralogy and stable- isotope composition of abiotic marine precipitates, and (2) the distribution of reservoir-grade porosity is strongly influenced by early-marine cementation, dolomitization, and meteoric-related diagenetic processes. Corresponding shifts in the morphology of carbonate platforms, and the spatial distribution of potential reservoirs, suggest a strong biotic and abiotic influence on platform architecture, cementation patterns, and reservoir development. Importantly, results of this study describe a series of depositional models and associated diagenetic patterns that are comparable to the known distributions of reservoirs in giant carbonate fields of similar age in the subsurface of the North Caspian basin. Upper Devonian (Fammenian) reefs are composed of Girvanella boundstones, algal cementstones, and brachiopod bioherms and form reef-rimmed platforms. Boundstone and slope deposits are cemented by fibrous and radiaxial fibrous calcite; inner-shelf peritidal deposits are extensively dolomitized, and several intervals of karst are present near the Fammenian-Tournaisian boundary. Tournaisian to Lower Visean carbonates lack a defined organic margin and form ramps that contain Waulsortian mud mounds; inner-shelf peritidal facies are partly dolomitized. Middle-Late Visean and Serpukhovian carbonates form rimmed platforms consisting of peritidal shelf lithologies, grainstone margins, resedimented carbonate and microbial boundstone upper slopes, and deep slope mounds. Shelf interiors consist of cyclic, meter-scale peritidal carbonate lithologies that are capped by paleosols and contain intervals of carbonate-clast conglomerates that are interpreted as forming through prolonged periods of exposure. These layered shelf carbonates are both dolomitized and karsted, and their sedimentation and early diagenesis is attributed to climate changes brought about by the onset of glaciation during the Middle-Late Visean. Slope mounds are composed of sponge-bryozoan-Tubiphytes-algae boundstone and cementstone. Radiaxial fibrous calcite infills skeletal growth frameworks and hash layers, and forms thick linings in stromatactis cavities. Thus mound stabilization is achieved through void cementation and the mantling of mud-dominated fabrics. Bashkirian shelf margins consist of donezellid-brachiopod boundstone and cementstone; shelf interiors contain prolific oolitic grainstone. Bashkirian ooids and marine cement were dominantly composed of aragonite and were particularly susceptible to exposure-related diagenesis and indicate that shelf and margin sediments were exposed during lowstands. Lower Permian shelf margins and slope mounds are composed of bryozoan- Tubiphytes -algae boundstone and cementstone, Palaeoaplysina rudstone, and foram-rich lithologies. Incomplete infilling of boundstone and rudstone lithologies by radiaxial calcite and subaerial exposure resulted in the preservation of primary growth and shelter cavities. On the basis of detailed field and laboratory study of outcrop, it is concluded that biota, eustasy, primary mineralogy, and diagenesis exerted strong control on platform architecture and reservoir development in thick, Upper Devonian to Lower Permian carbonates. Following a Late Devonian extinction event, platform architecture exhibits a transition from reef-rimmed to ramp to shoal-rimmed to reef-rimmed carbonate platforms. This transition in platform architecture is interpreted to reflect: (1) the initial replacement of reef-forming skeletal organisms by reef- forming algae and maintenance of reef-rimmed platforms (Fammenian), (2) demise of algal-constructed margins concomitant with biotic recovery and formation of ramps (Tournaisian-Lower Visean), (3) deposition of microbial boundstone in upper slopes and early stabilization of ooid grainstone to form shoal-rimmed platforms (Middle Visean-Serpukhovian) with mound-building organisms relegated to subphotic slope positions, (4) eventual reestablishment of shallow-water benthos capable of forming wave-resistant platform margins (reef-rimmed platforms; Bashkirian), and (5) formation of reef-rimmed platforms with slope-mound complexes (Lower Permian). Marine cement is particularly abundant in slope mounds, resedimented upper-slope deposits, and reefal boundstone at platform margins, where it occurs as frame-filling cementstone and thick isopachous linings in pores. An association between cementstone and trophic biotic assemblages suggests that massive cementation was enabled by upwelling of carbonate-saturated bottom waters. Isotopic compositions of originally aragonitic and calcitic marine cement are enriched in 13 C and 18 O and are in agreement with secular trends defined by other Devonian to Permian carbonates. Thus, early marine cementation plays an important role both in constructing these lithofacies and in reducing most primary depositional porosity. As a result, porosity-enhancing diagenetic processes in the slope and platform margin (e.g., early marine- related dolomitization; leaching) are limited to partial alteration of skeletal fabrics, cements, and micritic matrix. Partial marine cementation of shelf-margin grainstone and a relative absence of marine cement in shelf-interior lithologies allows for extensive development of porosity-enhancing diagenetic processes that are related to small-scale and large-scale relative sea-level fluctuations (e.g., glacio-eustasy). Diagenetic processes that have been mapped and identified by petrographic and geochemical study include marine-related dolomitization, mixing-zone dolomitization, and meteoric leaching. In the field, reservoir development is expressed as: (1) early marine-related dolomitization of shelf-margin oolite and interior lagoonal sediments, which results in formation of intercrystalline and moldic porosity, and thin stratal reservoirs at a scale of meters to tens of meters; and (2) karsting of platform-interior lithologies, which results in formation of vugs, molds, and microporosity, and thin and thick stratal reservoirs at the scale of meters to < 100 meters. The observed changeover from Upper Devonian-Tournaisian meter-scale peritidal carbonate cycles to Visean-Serpukhovian meter-scale carbonate cycles capped by paleosols and carbonate-clast conglomerates is interpreted to reflect a changeover from “greenhouse” to “icehouse” conditions during the Middle to Late Visean. Thus, Visean to Serpukhovian shelf carbonates are characterized by sequential meter-scale layering and early meteoric diagenesis, and Bashkirian reservoirs are more susceptible to diagenetic enhancement due to original aragonite composition. The sequential deposition of Upper Devonian through Lower Permian carbonates results in a thick stack of relatively tight lithologies at platform margins and slopes, and porous lithologies within shelf margins and interiors. Comparison of predicted diagenetic patterns and reservoir geometries based on field studies with observed diagenetic and reservoir attributes of Karachaganak and Tengiz fields suggest that similar diagenetic processes were operative in the North Caspian basin.