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The upper reservoir zone of the Lower Cretaceous Kharaib Formation (46–54 m thick in the studied wells) is regarded as the upper portion of a third-order depositional sequence comprising higher-order cycles. Whereas the third-order sequence interpretation is clearly supported by the upward-shoaling trend of the reservoir zone, relationships defining the component cycles have not previously been documented and are the focus of the present study. Core descriptions from four wells in a single oilfield reveal little evidence of facies changes or trends of facies patterns indicative of high-frequency depositional cycles. Cycle boundaries could possibly be represented by the repetitive pattern of coarse beds (rudstone and floatstone) 0.1–2 m thick, commonly having sharp basal contacts and gradational upper contacts with enclosing packstone to wackestone. Because the coarse beds do not appear correlative between wells, however, we prefer the alternative interpretation that they reflect episodic storm events which locally redistributed detritus, sourced from a patchwork of low-relief lithosomes, across the flat surface of the epeiric Kharaib platform–lagoon. Although the existence of high-order eustatic fluctuations during upper Kharaib deposition is well established, low-amplitude variations in water depth may not have touched down on the sea floor to significantly affect sediment textures in contrast with the dominant storm signal.Reservoir sub-zones used for production operations, but previously suggested to be fourth-order parasequence sets, are defined by dips in porosity-log profiles, reflecting thin (approximately 1 m) intervals of increased stylolite frequency. These boundaries are thus diagenetic in character, but their correlation over tens to hundreds of kilometers indicates an underlying depositional control. We suggest that the link between sea level and diagenesis is depositional-clay content, which facilitates stylolitic dissolution. Profiles of bulk-rock alumina analyses in the studied cores show subtle indications of higher clay content at the sub-zone tops. Much greater clay peaks mark the third-order sequence boundaries, resulting in the “dense” (very low porosity) zones above and below the studied reservoir zone and the increased stylolite frequency in the upper and lower several meters of the zone. Possible factors promoting clay influx across a carbonate shelf during falls in sea level include increased stream gradients and more humid climate.

Ancient marine evaporites are commonly far more extensive than any known modern evaporite system. This is true not only for basin-central saline giants, but also for evaporites that occur in basin-margin settings, and the origin of these basin-margin systems is unclear. Extensive basin-margin evaporites of the Middle Jurassic Gypsum Spring Formation are well exposed along the eastern flank of the Bighorn Basin in Wyoming, USA, and a facies and sequence stratigraphic analysis was undertaken to understand the origin of these evaporites and associated deposits. The Gypsum Spring Formation was deposited on a northwestward-dipping mixed evaporate–carbonate–siliciclastic ramp, with facies and depositional environments that include distal ooid shoal grainstone, open-marine shallow-subtidal peloidal–skeletal wackestone to packstone, restricted shallow subtidal laminated lime mudstone, peritidal dolostone and microbialite, as well as red mudstone and gypsum deposited on mud flats, sabkhas, and salinas. Three depositional sequences are present, with the J-1, J-1a, and J-1b sequence boundaries characterized locally by chert-pebble lags, silicified horizons, and iron-rich paleosols. Evaporites accumulated in a basin-margin position, with 1–6 m beds of gypsum forming in salinas and sabkhas, and nodular anhydrite and gypsum forming in red mudstones deposited on sabkhas and mud flats. The limited lateral extent of salina-type gypsum beds and the variable number of these beds among the exposures indicates substantial autocyclic control on the formation of salinas. Salinas are well developed in the TST of the J-1 sequence, and sabkhas and mud flats are well developed in the J-1 HST, the J-1a HST, and the J-1b TST. The great lateral extent of the Gypsum Spring evaporites reflects the original expanse of the depositional environment in which they formed, and is not the result of diachroneity of a narrow evaporite-precipitating belt, such as the modern-day coastal sabkhas of the Trucial coast. The great lateral extent of Gypsum Spring evaporites suggests that they were precipitated mainly from continental brines on an expansive desert mudflat.

Late Ordovician mud-mounds in the Boda Limestone, Siljan area, central Sweden, consist mainly of massive spiculitic stromatactis limestone similar to other well-known Paleozoic mud-mounds. The mound cores are predominantly formed by spiculite and ostracod-rich mudstone and/or wackestone, and networks of spar-filled syndepositional cavities. The mounds of the Boda Limestone are specific in two ways: (1) large parts of the lower mound cores are formed by a Palaeoporella framestone and/or bafflestone with signs of early recrystallization and cementation; and (2) the stromatactis facies is accompanied by masses of limestone with non-stromatactis cryptocrystalline patches. Cryptocrystalline patches are filled with massive, fibrous low-Mg calcite, have cloudy, transitional margins, contain randomly spaced skeletal grains and dolomitic micro-inclusions, and are interpreted as recrystallized patches of the original host lime mud. Models of formation of Paleozoic mud-mounds generally hypothesize accretionary processes that are based on sponge biomass degradation and associated diagenetic processes. In the Boda Limestone Palaeoporella skeleton disintegration, early recrystallization, and additionally, cementation were essential for the mound formation. The Boda mounds exemplify that formation of Paleozoic mud-mounds reflects a spectrum of different essentially diagenetic accretionary mechanisms. This diversity should be taken into account in future discussions about Paleozoic mud-mound formation. The new name Osmundsberget Formation is given for a Hirnantian succession of brachiopod-rich limestone above the Boda Limestone. The Osmundsberget Formation occurs only in direct geographical vicinity to the mud-mounds.

Lake Turkana, northern Kenya, serves as a long-lived end-member extensional basin that preserves a volcanically mediated, mixed siliciclastic and carbonate system. Stratigraphic data from the southeastern margin of Lake Turkana reveal a suite of carbonate facies assemblages. Lithologies of this system include mudstone, siltstone, sandstone, conglomerate, diatomite, carbonate mudstone, wackestone, grainstone, packstone, and boundstone. The boundstones are subdivided into framestones (stromatolites or oncoids) and display upward growth from a nucleus where found in association with cobbles and shells and bindstones (laminar tufa) where not. Three discrete, large (up to 7.5 m high), stacked, mounded boundstones are interpreted as subaerial spring deposits based upon overall shape, surficial texture, and orientation with respect to mapped faults and the distribution of modern springs. Petrographic analysis reveals peloids, ostracods, microbial sheaths, gastropods, pelecypods, diatoms, and detrital grains that include quartz, volcanic glass, and volcanic lithic fragments. All grains are micritized, and fossils tend not to retain their original microstructure. Some lithologies have porosities as high as 39%, and permeability averages 4 mD as a result of the dominance of moldic porosity and microporosity. The combination of lithologic data and facies associations is combined to produce a depositional model that is useful for comparison with ancient rift basins that host economic quantities of hydrocarbons. The controlling factors for carbonate development in Lake Turkana include the structural framework, water depth, and lake chemistry.

Carbonate mounds are widespread in many places around the world and are especially well exposed in the Cantabrian Mountains, northern Spain. This study focuses on the composition and growth dynamics of two large mound complexes well exposed near the village of Puebla de Lillo, 70 km northeast of Leon, and evaluates the impact of sea level, accommodation, and siliciclastic input on mound growth. The mound substrate consists of bedded dark skeletal bindstone. The core facies exhibits patchy growth forms of alternating massive microbial–algal boundstone and skeletal and nonskeletal wackestone, reflecting the overall mound internal composition of smaller coalescent bodies. Microbial activity, as inferred from the volumetrically important clotted peloids, appears to be the main factor leading to the high accumulation rate in the cores. The steeply dipping flanks presumably resulted from early cementation and subsequent lithification and stabilization induced mainly by microbial activity. In the intermound strata, carbonate beds and small mounds alternate with fine-grained sandstone, siltstone, and shales. The intermound carbonates consist of skeletal and intraclastic mudstone to wackestone, whereas algal–microbial boundstone is a minor component. Overall, facies transition from the mound core towards the flanks or the mound-capping beds is gradual. However, the volume of bioclasts and intraclasts increases towards the flank and capping facies, inversely to amount of clotted peloids or micrite. The substrate and the cores of the two mound complexes likely formed in the photic zone, as inferred from the common calcareous algae. Carbonate precipitation favored by microbial activity and algal growth along with gain in accommodation space led to mound-core accretion. The growth of the small mound complexes was most likely stopped by recurrent sea-level fall and siliciclastic input. The large, high-relief mound complex actually kept growing until reaching shallow-water and high-energy conditions. Unlike many late Paleozoic counterparts, these mounds were not subaerially exposed during growth. The great thickness and the aggradational mound growth are indicative of a high subsidence rate. At a later stage, however, siliciclastic input also buried the large mound complex. Rapid subsidence, sea-level fluctuations, and siliciclastic input were thus decisive factors controlling carbonate production. This study reveals that mound complexes nucleated and grew on preexisting paleohighs, maintaining consistent growth in these specific settings. Paleohighs, recurrent sea-level fluctuations (presumably linked to glacio-eustasy), and episodic siliciclastic input are the principal factors that controlled the shape, size, and growth evolution. Furthermore, the internal architecture as a mosaic of juxtaposed small bodies composing the complexes represents an important finding for better understanding of mound growth and, thus, for better constraining reservoir heterogeneity, particularly for upper Paleozoic deposits.

The Lower Cretaceous (Berriasian) Valdeprado Formation (Cameros Basin, northern Spain) contains more than 900 m of laminated carbonates and pseudomorphs after sulfates. Traditionally, many sedimentary packages of different ages and lithologies have been interpreted as deep-water deposits based essentially on the abundance of laminations and the absence of subaerial exposure features. In contrast, the Valdeprado Formation provides an example of a shallow-water deposit dominated by laminations with scarce evidence of subaerial exposure, and gives criteria to solve the challenge of distinguishing shallow-water and deep-water, ancient laminated deposits. The two most abundant facies all along the Valdeprado Formation are: a) parallel-laminated limestone, formed by alternating carbonate mudstone and calcite and quartz pseudomorphs after displacive gypsum, and b) graded-laminated limestone, consisting of quartz, mica, ostracodes, and pseudomorphs after detrital gypsum grains at the base, which changes gradually upwards to carbonate mudstone. Parallel-laminated limestone and graded-laminated limestone could have been deposited in either deep or shallow environments as a result of salinity fluctuations driven by alternation of flooding and evaporation and by sediment resuspension processes, respectively. Subaerial exposure features, such as desiccation mudcracks, are scarce in most of the succession, except in a few meter-scale stratigraphic intervals where they are very abundant. Interestingly, in these intervals desiccation cracks are present at the tops of several successive laminae (up to 25 mudcracked laminae per meter of deposit), indicating that, at least during those periods of time, deposition occurred in shallow water bodies that were desiccated frequently. In the upper part of the stratigraphic section, parallel-laminated and graded-laminated limestones are associated with current-ripple and wave-ripple cross-laminated arenites, and ostracode mudstone to wackestone with centimeter-size pseudomorphs after lenticular gypsum, and abundant desiccation mudcracks and tepees, which also suggest sedimentation in shallow-water environments. Moreover, the laminated carbonates display continuous, parallel layering, and the same facies along the 40-km-long outcropping area. These deposits are directly interbedded with, and pass laterally to, siliciclastic sandy–muddy flat deposits in the western area of the basin, without clinoforms, slump structures, or slide masses in between. All of these features suggest deposition in shallow, perennial carbonate–sulfate water bodies and their peripheral mudflats, developed in a flat-bottomed basin with no marked gradients.

“Barrier reefs, when encircling small islands, have been comparatively little noticed by voyagers; but they well deserve attention. In their structure they are little less marvelous than atolls, and they give a singular and most picturesque character to the scenery of the islands they surround.” (Darwin 1842, p. 2) Sediment sampling revealed six modern sedimentary facies in the barrier-reef system around the volcanic island of Bora Bora including mixed skeletal packstone, peloidal packstone, Halimeda-rich packstone to grainstone, coralgal grainstone, wackestone, and mudstone. Whereas sediments rich in corals and coralline algae are abundant on reefs and carbonate shoals, mud-rich sediments with mollusks and foraminifera occur in deep lagoons (15–40 m). Carbonate mud is composed largely of aragonite needles, probably derived from codiaceans like Halimeda, and coccoliths in moderate abundances. Despite the proximity to a volcanic island, the content of siliciclastics in the sediments is low (< 10% on average), which is a consequence of the absence of permanent water courses. In addition to skeletal grains, non-skeletal grains (cemented fecal pellets; aggregates) occur in high abundance (30–50%) in shallow lagoons (< 5 m) on the eastern side of Bora Bora. This observation opposes the widely-held concept that non-skeletal carbonate grains are abundant on platforms from the Atlantic Ocean but virtually missing in recent Indo-Pacific reefs and carbonate platforms. In Bora Bora, non-skeletal grains and aggregates apparently form in warm, shallow (< 5 m), moderately agitated areas with relatively low sedimentation rates. In addition, early cementation is probably favored by elevated alkalinity and pH in surface waters in this part of the south Pacific. In the same area, some 900 km to the southwest of the study area, ooids and peloids have recently been discovered in the shallow lagoon of Aitutaki, Cook Islands. More occurrences of abundant non-skeletal grains probably exist in the Indo-Pacific region; however, too few locations have been systematically studied. A comparison of the new Bora Bora data with other modern reefs and platforms shows that sediment occurrence and distribution exhibits basic patterns in that marginal areas are dominated by coarse-grained coralgal sediment whereas lagoons and platform interiors are characterized by mollusk, foram, Halimeda, and non-skeletal grains, and fines. Still, grain abundances may vary significantly among locations, and again suggest the need for more studies in order to fully understand the factors controlling occurrence and distribution of modern sediments.

The problematic organism Donezella emerged worldwide as one of the main carbonate mound builders in the middle Carboniferous. Donezella is composed of thin (70–160 μm in diameter), bifurcating (45 to 90 degrees) tubes. Microfacies analysis of a Donezella buildup from the Wapanucka Formation, Frontal Ouachita thrust belt, Oklahoma, U.S.A., was undertaken to examine the role of Donezella in a carbonate buildup. Donezella is the predominant biotic component of the Wapanucka buildup, and the buildup is composed of irregular pockets of boundstone dominated by Donezella, worm tubes, peloids and micritic crusts, siliceous sponge spicules, less common siliceous sponge boundstone, and peloidal wackestone with other bioclasts. In the lower part of the buildup, Donezella colonies are robust, convex upward, and up to several centimeters in diameter. These colonies are composed of delicately branching Donezella with an enclosed constructional pore system. These robust, upward-growing Donezella structures formed a substrate for other binders; therefore it appears that, on a microscale, Donezella, together with siliceous sponges and worm tubes, played the role of a constructor. Donezella occurs as a long, semicontinuous row of thalli when encrusting other framework grains, and encrusts siliceous sponges, Donezella colonies, corals, and worm tubes; thus, it also acted as a member of the binder guild. Deciphering these various roles of Donezella is a crucial first step toward documenting a possible spectrum of Donezella-dominated lithologies that constitute key elements in carbonate buildups in the Early to Middle Pennsylvanian.

Carbonate buildups are a common feature in Mississippian sections worldwide. Yet despite intense study, questions remain about depositional processes that form such structures and their interrelations, if any, to each other. Carbonate buildups located in siliciclastic basins are particularly understudied and poorly understood. This study focuses on a new exposure of buildups in the siliciclastic-dominated Fort Payne basin (Osagean) of south central Kentucky. It represents a first attempt to combine field and petrographic descriptions of facies in the buildup interval of the Fort Payne with the concepts of sequence stratigraphy to gain better insight into their depositional histories. The buildup interval is composed of five distinct facies. Two of these, the fossiliferous green shale and the tabular crinoidal packstone-grainstone, represent the background sedimentation during buildup nucleation and growth. The remaining three facies make up the buildups themselves. The shaly packstone marks the inception of buildup growth, the massive wackestone represents the core of the buildups, and the crinoidal grainstone is a buildup-flank facies deposited near the end of buildup growth. The buildups of the Fort Payne Formation grew during the transgressive phase of one third-order sequence in the early Osagean. The time at which buildup growth ceased cannot be determined precisely with available data but likely occurred either at the maximum flooding surface or during the early highstand. Three commonly used depositional models, abbreviated as the lithoherm model, the baffling model, and the microbial model, are evaluated with respect to the Fort Payne buildups. None of the models is deemed adequate to explain all of the features of the buildups. Rather, a combination of all three seems to be required to account fully for all of the characteristics noted in this study. This multi-faceted depositional model compares favorably with other Carboniferous buildups worldwide, suggesting commonalities that transcend the properties of the basins in which they grew.

Upper Paleozoic shallow-water (algal) bioherms were sensitive to changes in accommodation, and thus preserve potentially high-resolution records of the (glacio)eustatic and tectonic perturbations that prevailed during late Paleozoic time. Detailed field and petrographic study of a high-relief (> 100 m), well-exposed mound complex of the western Orogrande basin (New Mexico) indicates that it consists of a series of stacked high-frequency sequences bounded by surfaces of paleo-subaerial exposure. Facies within and proximal to this complex include (1) boundstones (cement-, algal-, peloidal-, and foraminiferal-rich variants) within mound-core regions, (2) packstones (skeletal-, foraminiferal-, algal-, and peloidal-rich debris) within mound-flank regions, and (3) auxiliary facies (oncoidal wackestone, algal bindstone, carbonate mudstone) formed in low-relief off-mound regions. Sequence stacking in this system was the result of high-frequency, high-amplitude glacioeustasy that prevailed during late Paleozoic time. Paleorelief on subaerial exposure surfaces records glacioeustatic amplitudes in excess of 80-100 m; preserved paleoslopes locally exceeding 40° (compactionally corrected) indicate that the mounds were cemented geologically instantaneously and not easily eroded, even at lowstands. Timing of stratal accretion within a given sequence varied significantly as a function of both spatial and temporal position within the biohermal complex. Stratal accretion in mound-nucleation stages produced late-falling-stage ("catch-down") sequences both on- and off-mound. During the "acme" phase of mound growth in this complex, accretion occurred during sea-level rise and maximum inundation phases, nearly pacing production of short-term (glacioeustatic) accommodation and producing an anomalously thick, near keep-up sequence in the mound-core region. Subsequent sequences of the mound core nucleated atop significant paleobathymetric relief, accreted during maximum inundation to incipient fall, and therefore display thicknesses that likely reflect long-term accommodation potential. In a shallow-water biohermal system capable of accretion rates commensurate with production of short-term accommodation space, very thick near keep-up sequences are laterally offset from one another in progradational, retrogradational, or random shifting patterns owing to the limits of short-term accommodation production in any given locality. Sequence thicknesses in shallow-water biohermal systems vary substantially laterally as a result of variable sedimentation (accretion) rates as well as other environmental factors. Accordingly, sequence thicknesses should never be used as faithful and consistent proxies for calculations of accommodation space or eustatic magnitudes.

Distribution of recent sedimentary facies is significantly different in four closely spaced, isolated carbonate platforms off the coasts of Belize and Yucatan (SE Mexico). These differences are largely controlled by variations in submarine topography, which are likely the result of differential subsidence and karstification from platform to platform. A variety of depositional styles and patterns is found in platform interiors that developed during the same Holocene sea-level rise. Composition and texture of surface sediment samples were used to define four major sediment types and to distinguish nine depositional environments within the platforms. Facies maps are based on analysis of 454 sediment samples and high-resolution satellite imagery. Glovers Reef is characterized by a circular facies distribution. The nearly continuous reef margin is composed of a coral-red coralline algae-Halimeda grainstone. Mixed nonskeletal (peloidal)/skeletal wackestones and packstones are present in shallow lagoon parts (< 5 m water depth) behind the margin. The deep interior, from 5 to 18 m water depth, is characterized by mollusk-foram-Halimeda wackestones with over 860 patch reefs of coral-red algae-Halimeda-mollusk packstones. Lighthouse Reef also has a coral grainstone and coral-red algae-Halimeda grainstone rim, but the facies distribution in the interior is strongly asymmetrical. The 8-m-deep eastern lagoon is floored by mollusk-foram-Halimeda wackestones and packstones; the 3-m-deep western lagoon has the mixed peloidal/skeletal wackestone to grainstone facies. A linear trend of coalescing patch reefs and skeletal grainstone facies separates the two lagoons. Banco Chinchorro is similar to Lighthouse Reef, inasmuch as facies distribution patterns of the interior are strongly asymmetrical. Mollusk-foram-Halimeda wackestones-grainstones are present in eastern lagoon areas, whereas shallow (< 5 m) western parts of the lagoon are composed of mixed peloidal/skeletal grainstones, packstones, and wackestones. Most of Turneffe Islands is protected on the east by Lighthouse Reef. Accordingly, Turneffe has a narrower reef and skeletal grainstone rim than the other two platforms. Restricted interior lagoons are up to 8 m deep, and are enclosed by wide mangrove rims and surface sediments dominated by Halimeda-rich wackestone rich in organic matter. Coral patch reefs are absent. In contrast, the unprotected northernmost part of Turneffe has a wide reef and grainstone rim and the open lagoon area consists of mollusk-foram-Halimeda wackestones-packstones with abundant patch reefs.

The sequence stratigraphic architecture of Mississippian strata from the Sacramento and San Andres Mountains, south-central New Mexico, illustrates the combined effects of relative sea-level change and progressively increasing depositional gradients on sedimentary processes and resultant stratal geometries along the outer parts of a carbonate ramp-to-basin transition. Mississippian strata can be subdivided into three progradational sequences (Sequences 1-3) and a fourth, basin-restricted, onlapping sequence (Sequence 4). Sequences 1-3 contain wackestone- to mudstone-dominated transgressive systems tracts that are overlain by packstone- to grainstone-dominated progradational systems tracts. Progradational systems tracts created distinct ramp-to-basin transitions (outer ramp margin) that are characterized by basinward stratal thinning and a concomitant change to muddy lithofacies. Sequence 4 consists of onlapping, fining-upward stratal packages of peloidal-skeletal grainstone that grade upward to laminated, spiculitic lime mudstone. The outer-ramp-margin facies of Sequences 1 through 3 gradually steepened the outer ramp profile until the cumulative effects of the steepening caused the depositional gradient to surpass an "equilibrium grade" (i.e., the gradient at which deposition and erosion/bypass are about equal). Once the depositional gradient exceeded the equilibrium grade for the caliber of sediment supplied to the outer ramp margin, widespread submarine erosion and sediment bypass on the outer ramp was initiated, resulting in deposition of basin-restricted strata of Sequence 4. Similar relationships and inferred processes have been recognized in progradational siliciclastic shelf deposits and are collectively described by previous workers as "slope readjustment". The Mississippian ramp-to-basin transition in south-central New Mexico illustrates how sediment deposition, dispersal, and erosion responded to evolving depositional gradients and in turn controlled resultant, large-scale stratal geometries.

The Oligo-Miocene Gambier Limestone is a poorly lithified, fine-grained, bryozoan-rich grainstone/wackestone and marl. Allochems in these rocks, which are typical of many modern and ancient cool-water carbonates, were originally calcite (LMC), Mg-calcite (IMC and HMC) and minor aragonite, but most are now neomorphosed to LMC. With the exception of calcretes, most limestones have < 5% cement, 13C and 18O values from 0 to +1.5o/oo, and preserved 87Sr/86Sr ratios that indicate that neomorphism occurred in seawater rather than meteoric or evolved pore waters. Marine diagenesis of the limestones was facilitated by their slow accumulation rates, which were ca. 15 mm/ky based on Sr-isotope stratigraphy, relatively fine grain size, and high porosities which locally reach 50%. The Sr and Mg contents of grainstones are significantly lower than in the original sediments, whereas a less porous marl has higher Sr and Mg contents. The grainstones have about 300 ppm Sr and 6000 ppm Mg, consistent with slow abiotic precipitation of calcite under near-equilibrium conditions with seawater, which is the thermodynamic drive for this diagenesis. The higher Sr and Mg content of the marl results from variable preservation of original allochems of biotic calcite. The results from this study and others on modern cool-water carbonates indicate that the extent of diagenesis varies with lithology, but much neomorphism occurred in seawater, with minimal effects from meteoric waters. As such, the chemical characteristics of seawater may be effectively preserved in some ancient cool-water carbonates.