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Most Upper Jurassic studies of astronomical forcing have focused on deeper-water sections which are relatively continuous. An Upper Jurassic (Kimmeridgian) section on the greenhouse Adriatic Carbonate Platform, Croatia, was studied to determine if astronomical forcing can be recognized in a 5.8 ± 0.1 Myr duration, disconformity-prone shallow platform succession. The succession consists of metre-scale subtidal parasequences intermixed with peritidal parasequences, and intermittent subaerial breccias at sequence boundaries. Ages were constrained by biostratigraphy and δ13C chemostratigraphy, and most sequence boundaries appear to match those of the coastal onlap curve of Haq (2018). Logged sections were converted into depth–rank time series and parasequence–thickness time series. Accumulation rates were statistically evaluated for the rank series against an astronomical-forcing model, and compared with long-term accumulation rates (thickness divided by time). The statistical rates were used to select the ca 100 kyr eccentricity cycle to tune the series. Spectral analysis showed peaks at ca 400 kyr (superbundles) and ca 100 kyr (bundles), along with obliquity (38 kyr and 27 kyr) and precessional (18−22 kyr) cycles (parasequences). The Kimmeridgian sequences are ca 400 kyr, ca 800 kyr and ca 1.1 Myr duration. Sequence scale (0.4 to 1.2 Myr) stratigraphic completeness based on statistical accumulation rates versus long-term rates is ca 60%. This study estimates ca 1 Myr missing time in parasequences stacked into superbundles and 1.6 Myr in four major sequence boundaries. Given that the Kimmeridgian was the hottest time of the Middle and Late Jurassic, aquifer eustasy may have influenced the timing of sequence boundaries, although documented late Kimmeridgian cooling could have triggered a glacio-eustatic component.

The Upper Dalan (Khuff-equivalent) Formation constitutes the principal reservoir of the giant gas fields in the Persian Gulf Superbasin. A sedimentological and sequence stratigraphic analysis was conducted on selected cores from the South Pars, Kish, and Lavan gas fields, offshore Iran, to evaluate a recently proposed method for automatic reservoir zonation, and discuss the predictability of such defined zones. The succession consists of nine evaporite-carbonate lithofacies grouped into three shallow-marine facies associations (shoal, lagoon, and tidal flat) that were deposited on a low-gradient homoclinal ramp. Lithofacies are stacked into two complete long-term (3rd-order?) transgressive-regressive depositional sequences. Sequence boundaries were defined by facies stacking patterns and presence of evaporites and meteoric diagenetic features. The reservoir quality was improved by both early-stage dolomitization and dissolution, whereas pervasive pore-filling anhydrite cementation, compaction, and late-stage over-dolomitization reduced the reservoir quality. Whereas dolomitization overall slightly affected porosity, it significantly increased the permeability in mud-dominated lithofacies. Fibrous and bladed calcite rim cements, as well as micritization of the grain-dominated lagoon and shoal lithofacies, prevented porosity reduction during the early- and late-stage burial by building a stronger framework. Core-plug porosity and permeability measurements were used to calculate the Winland R35, Reservoir Quality Index (RQI), and Flow-Zone Indicator (FZI) values. A novel, fully automated approach, was used to effectively identify the hydraulic flow units (HFUs). The HFUs are sedimentologically distinct units with characteristic combinations of the original rock texture and the subsequent diagenetic overprint, and their subsurface position within the sequence stratigraphic framework may be predicted.

Lower to Middle Eocene organic-rich deep-water limestones of the ∼335-m-thick (1100 ft) Radwany (Thebes-equivalent) Formation represent a source rock and a potential reservoir unit at the October Oil Field in the Gulf of Suez. However, in spite of recent exploration advances, the pore system and diagenetic history of the formation are still poorly understood. This study aims to discriminate porosity types and their vertical distribution, assess the diagenetic processes controlling porosity evolution, and evaluate the unit's overall reservoir potential. To achieve these goals, we utilized an integrated petrographic, mineralogical, geochemical and petrophysical dataset from four offshore wells. At October Oil Field, the Radwany Formation is informally divided into three intervals (from the base up: C, B and A) which are composed of planktonic foraminiferal wackestone, wackestone-packstone and packstone microfacies. Pores include both fabric selective (interparticle, intraparticle and moldic) and non-fabric selective (fracture) types. Visible porosity reaches up to 11.6%, and the highest porosity values are associated with interparticle pores in foraminiferal packstone in interval C. The two overlying intervals have lower porosities but have TOC values of up to 6 wt %. The Nuclear Magnetic Resonance (NMR) analysis yields low amplitudes of short T2 components (max. 52 ms), which suggests the presence of small pores (intraparticle, moldic, fracture, and fissure). Based on the electrical quality index (EQI) rock classification, nine groups were identified, suggesting a high heterogeneity of the formation. The highest EQI values positively correlate with high porosity (visible and estimated) in the lower part of Interval C which is dominated by interparticle/intraparticle porosity, thus reflecting the low tortuosity values of this microfacies. Dominantly low EQI values in Intervals A and B indicate low porosity efficiency and higher tortuosity. Carbonate sediments of the Radwany Formation are interpreted to have undergone a complex series of diagenetic processes. These processes modified the primary pore system either by enhancing the reservoir properties (dissolution and fracturing), or by reducing or destroying porosity (cementation, mechanical and chemical compaction, and minor pyritization, chertification, and asphaltene precipitation). The study highlights the unconventional reservoir potential of the middle and upper parts of the Radwany Formation (intervals B and A) at October Oil Field, and the conventional reservoir potential of interval C. It emphasizes the complexity of diagenetic controls on the porosity evolution in deep-water limestones of the Gulf of Suez, and may provide valuable insight into similar deep-water carbonate systems in rift basin reservoirs elsewhere.

Despite the vast research on various aspects of its stratigraphy, relatively little is known about the source-rock potential of the Upper Jurassic Adriatic platform, southern Croatia. Here a case palynological study has been provided to determine the kerogen type, quality, and thermal maturity, and assess its relative hydrocarbon generative potential. Palynofacies characteristics indicate a low-energy, shallow-marine oxygen-depleted setting. The deposited mud-supported carbonates contain organic matter that is almost entirely composed of a fluorescent amorphous organic matter of planktonic and bacterial origin. A high phycomata/dinocyst ratio suggests relative hydrographic stability in an environment favorable for motile-stage dinoflagellate community with reduced production of dinocysts. The lack of anaerobic degradation and very good preservation of lipoid palynomorphs indicates dysoxic conditions ; the latter also is suggested by a low proportion of algal-phytoplanktic carbohydrates. The lack of oxygen-deficient zone within the water column, coupled with well-preserved lipoid sediment components, suggests that the boundary between the oxygen-rich and oxygen-poor levels was likely located at/near the sediment-water interface. The palyno-organic facies analysis suggests that the organic matter corresponds to the type II (possibly I/II) kerogen (VRo ∼0.3–0.4%) that was protected from degradation before, during and after sedimentation. Well-preserved lipoid components suggest a good hydrocarbon-generative potential, but the low TOC values (

Patch reefs and their surrounding skeletal–peloidal–intraclast grainstone facies are very abundant on modern (sub-) tropical carbonate platforms. Compared to the barrier and fringing reef facies, the processes influencing composition, mineralogy, and stable-isotope record of peri-reefal sediment have received much less attention, despite a potentially significant volume of such sediment in many Phanerozoic carbonate platforms. To better understand the evolution and sedimentary record of patch-reef settings, this study investigates the patch-reef biota (scuba diving surveys) and composition (petrography), mineralogy (X-ray diffraction) and stable-isotope record (mass spectrometry) of peri-reefal sediments at East Beach on the northeastern, windward margin of San Salvador Island, the Bahamas. The macroalgae-dominated ecology is assessed, and a decadal decline in stony coral coverage with a shift to more opportunistic, stress-tolerant species is documented. The most common stony corals on these shallow-water (3–5 m) patch reefs are Diploria strigosa, Porites astreoides, and P. porites, and Halimeda lacrimosa dominates among green algae. Peri-reefal sediment is pure carbonate sand composed of roughly equal volumes of aragonite and high-Mg calcite (HMC), with mean MgCO3 content in HMC of 15.2%. The bulk-sediment isotope record shows very limited variation (δ13C between + 2.3‰ and + 3.2‰, and δ18O between − 0.8‰ and − 0.6‰) and this is consistent with similar modern settings. A lack of very fine particles and an abundance of intraclasts suggest that the environment is strongly influenced by bio- and physical erosion. Fast-growing algae have likely reached an abundance beyond the grazing capacity, which has drastically reduced the space for coral settlement and recruitment, and thus has compromised the patch-reef resilience in this part of the Bahamian Archipelago.

The upper Katian (Upper Ordovician) Red River Formation is a carbonate-evaporite supersequence that formed in the epicratonic Williston Basin of western North America. This study focuses on the upper part of the formation in the southern, US part of the basin. The studied succession is made up of three transgressive-regressive sequences (RR1, RR2, and RR3), each ∼0.5–∼1 m.y. in duration and composed of relatively few meter-scale high-frequency cycles (parasequences). Sequence boundaries are characterized by intraclastic breccia-laminated dolomite successions that have been truncated and capped by evaporite deposits. Subaqueous anhydrites within each sequence represent evaporite Lowstand Systems Tracts (LSTs) that formed during relative sea-level lows that lead to the precipitation of gypsum (later recrystallized into anhydrite) in a quiet, salina-type environment. Transgressive (TST) and early Highstand Systems Tracts (HST) are composed of subtidal facies of predominantly skeletal mudstone to wackestone-packstone with abundant burrow mottling. Late HSTs are predominantly composed of peritidal, porous laminated dolomite. The study illustrates how the sequence stratigraphic framework of carbonate-evaporite deposits from the Williston Basin relates to the Late Ordovician glacio-eustasy, transitional climates, and low basin subsidence in an arid setting.

Secular variations in stable carbon isotope values of marine carbonates are widely used to correlate successions that lack high-resolution index fossils. Various environmental processes, however, commonly may affect and alter the primary marine carbon isotope signal in shallow epicratonic basins. This study focuses on the marine carbon isotope record from the carbonate-evaporite succession of the upper Katian (Upper Ordovician) Red River Formation of the shallow epicratonic Williston Basin, USA. It documents the carbon isotope signal between the two major Ordovician positive shifts in δ13C, the early Katian Guttenberg, and the Hirnantian excursions. Eight δ13C stages are identified based on positive excursions, shifts from positive to negative values, and relatively uniform 13Ccarb values. A correlation between carbon-isotope trends and the relative sea-level changes based on gross facies stacking patterns shows no clear relationship. Based on the available biostratigraphy and δ13C trends, the studied Williston Basin curves are tied to the isotope curves from the North American Midcontinent, Québec (Anticosti Island), and Estonia, which confirms the Late Katian age (Aphelognathus divergens Conodont Zone) of the upper Red River Formation. The differences in the δ13C overall trend and absolute values, coupled with the petrographic and cathodoluminescence evidence, suggest that carbon-isotope record has been affected by the syndepositional environmental processes in the shallow and periodically isolated Williston Basin, and stabilized by later burial diagenesis under reducing conditions and the presence of isotopically more negative fluids.

A new benthic foraminifer is described as Siphodinarella costata n. gen., n. sp. from Coniacian shallow-water platform-interior carbonates of Slovenia and Croatia. The new foraminifer is found in skeletal wackestone in association with small benthic foraminifera, thaumatoporellaceans, and calcimicrobes (Decastronema, Girvanella-type tubes). The existence of an internal siphon in Siphodinarella n. gen. is interpreted as an entosolenian tube and discussed in terms of its generic and suprageneric importance.

The Upper Permian Upper Dalan Formation contains one of the largest gas reservoirs in the world. The formation consists of carbonates with some evaporite intercalations that developed on a gently sloping homoclinal carbonate ramp facing the Late Permian Paleo-Tethys Ocean. This study focuses on the Kish Gas Field (Zagros offshore basin situated between Iran and Qatar), and is based on a 222-m-thick continuous core. Based on the integration of core- and wireline-log data coupled with petrographic analyses of 580 thin sections, three major depositional environments (facies belts) with 11 carbonate microfacies are identified. These include (1) sabkha to tidal flat (laminated to massive anhydrite, dolomudstone with anhydrite nodules, dolomudstone, and intraclastic dolowackestone), (2) lagoon and leeward shoals (bioclastic wackestone/dolowackestone to packstone, and peloid dolopackstone and peloid–bioclastic dolopackstone), and (3) mobile (windward) sand shoal (ooid–peloid dolograinstone, ooid dolograinstone, ooid–intraclast dolograinstone, ooid–bioclast dolograinstone–packstone, and coarse bioclast–intraclast dolograinstone). Diagenetic evolution of the Upper Dalan Formation is associated with evaporative marine, shallow-water normal-marine, meteoric, and burial diagenetic environments. Common diagenetic effects include dolomite and calcite cementation, mechanical and chemical compaction, dissolution, dolomitization, and evaporative (anhydrite) mineralization. Reservoir quality is strongly affected by variations in the original rock fabrics and subsequent diagenetic alterations. The most common pore types include interparticle, moldic, and connected vug (fracture and cavernous). The interparticle porosity–permeability relationship for the studied facies suggests that the reservoir quality is not affected by different crystal sizes and most samples plot in the low porosity and low to high permeability field, or display Lucia class 1 or 2 petrophysical relationships. The study shows that the pervasive pore-filling anhydrite mineralization lead to a significant decrease in porosity and permeability; poikilotopic anhydrite cement reduced matrix porosity, but the pore size was less affected.

Clypeina lagustensis n.sp. has been found in the Lower Tithonian deposits of the Lastovo Island (Dalmatia, Croatia). It is visually similar, obviously related and in some sections appearing almost identical, to Clypeina jurassica FAVRE, from which it differs by visible swellings and thinning of the central cavity, more pronounced distance between neighbouring whorls of fertile branches, and shape and structure of the interverticillate thallus parts, characterized by having well developed, hairy, sterile branches. These, after emerging from the exit pore, divide into several bundles which form a common turf with a calcareous envelope in the proximal part.

The island of Cres is located in the northern part of the Adriatic Sea. The island is built up of predominantly Cretaceous carbonates deposited in north-western part of extensive and long-lasting Adriatic Carbonate Platform. Owing to the influence of synsedimentary tectonics supported by eustatic changes during the latest Albian/Early Cenomanian, different sedimentary environments were established: from shallow intraplatform basin and related slope, across basin margin to protected shallow-platform. During the Early to Middle Cenomanian rudist communities (ichthyosarcolitid/caprinid/radiolitid) flourished along a relatively high-energy intraplatform basin margin. Fair amounts of coarse-grained bioclasts, derived almost exclusively from broken rudist shells, were deposited over a marginal depocenter. Contemporaneously, pithonellid wackestone-packstones containing microbioclasts and planktonic foraminifera were deposited basinward while marginal bioclastic sediments and limestone blocks of the basin margin origin were sporadically deposited within the basin. The opening of the Cres intraplatform basin was aborted and the basin was finally filled up during the Late Cenomanian. Since the Cres intraplatform basin was established at the beginning of the Cenomanian it probably represented the initiation phase in the north-western extension of the later Adriatic Trough development.

Well-exposed Mesozoic sections of the Bahama-like Adriatic Platform along the Dalmatian coast (southern Croatia) reveal the detailed stacking patterns of cyclic facies within the rapidly subsiding Late Jurassic (Tithonian) shallow platform-interior (over 750 m thick, ca 5–6 Myr duration). Facies within parasequences include dasyclad-oncoid mudstone-wackestone-floatstone and skeletal-peloid wackestone-packstone (shallow lagoon), intraclast-peloid packstone and grainstone (shoal), radial-ooid grainstone (hypersaline shallow subtidal/intertidal shoals and ponds), lime mudstone (restricted lagoon), fenestral carbonates and microbial laminites (tidal flat). Parasequences in the overall transgressive Lower Tithonian sections are 1– 4AE5 m thick, and dominated by subtidal facies, some of which are capped by very shallow-water grainstone-packstone or restricted lime mudstone; laminated tidal caps become common only towards the interior of the platform. Parasequences in the regressive Upper Tithonian are dominated by peritidal facies with distinctive basal oolite units and well-developed laminate caps. Maximum water depths of facies within parasequences (estimated from stratigraphic distance of the facies to the base of the tidal flat units capping parasequences) were generally