Oolitic Grainstone Research Articles

Facies Analysis and Depositional Environment of the Euphrates Formation in Selected Sections, Southwestern Iraq

The current study aims to investigate the microfacies, diagenetic processes, and depositional environments of the twenty-three rock samples from the Lower Miocene Euphrates Formation of two outcrops collected at Bahar-Najaf in Najaf governorate and Al-Shinafiya in Diwaniyah governorate, southern Iraq. Thin sections of these samples were prepared; hence, the nature of microfacies and related depositional environments was established. The formation contains abundant benthonic foraminifers and other fossils like miliolids, echinoderm, coral, gastropods, and pelecypods. Seven distinct microfacies were identified: lime mudstone, miliolid packstone, Pelletal Grainstone, Lime Wackestone, Peloidal Grainstone, Oolitic grainstone Microfacies, and fossiliferous packstone packed with bioclasts. Diagenetic processes evidenced in this study are dissolution, neomorphism, cementation, micritization, and dolomitization. The Euphrates Formation was deposited in a shallow marine setting with fluctuating energy levels, ranging from low-energy lagoons to moderate and high-energy shoals and fore-reef environments. Various microfacies indicate a complex depositional environment on a carbonate platform influenced by biota and sedimentary processes. These observations support the inference that the Euphrates Formation accumulated in shallow open marine, inner barrier, and shoal settings, providing a detailed interpretation of its para-depositional and diagenetic development.

Nubecularia-coralline algal-serpulid-microbial bioherms of the Paratethys Sea-Distribution and paleoecological significance (upper Serravallian, upper Sarmatian, Middle Miocene).

Nubecularia bioherms represent unique bioconstructions that are restricted to the upper Serravallian of the Paratethys and have been reported since the 19th century. They occur in the Central Paratethys in the late Sarmatian and the Eastern Paratethys in the Bessarabian both regional stages of the respective Paratethyan areas. In this study, several locations in the Vienna and Styrian basins of the Central Paratethys were studied out of which four localities were documented in detail (Wolfsthal, Maustrenk, St. Margarethen-Zollhaus, Vienna-Ruzickagasse) to reconstruct their sedimentary setting, their internal composition, and their indications of environmental parameters. The detailed studies included logging of outcrop sections, petrographic, facies and biotic analyses of polished slabs and thin sections and also cathodoluminescence analyses. These concluded that these bioconstructions are not only composed of the foraminifer Nubecularia but represent a complex mixture and interrelationships of Nubecularia, serpulids and microbial carbonate. Four boundstone types can be differentiated: Nubecularia boundstone, Nubecularia-coralline algal boundstone, stromatolitic/thrombolitic boundstone and serpulid-nubeculariid-microbial boundstone. The first 3 types are characteristic of specific localities; the fourth type occurs in all studied locations and represents the terminal association on top of the three other types. The three basal boundstones are predominantly of columnar growth form irrespective of dominance of Nubecularia, coralline algae or microbial carbonate, and the terminal boundstone is widely irregularly organized. The general depositional environment is characterized by cross-bedded oolitic grainstones with abundant quartz grains, miliolid foraminifers and mollusks. Intercalated are microbial carbonates mostly stromatolites but also thrombolites. This indicates a general high water energy environment interrupted by more calm periods when the microbial carbonate was built. The 3 basal types of bioconstructions are interpreted to reflect decreasing food supply and/or oxygenation from Nubecularia over Nubecularia-coralline algal to stromatolitic/thrombolitic boundstone. The serpulid-nubeculariid-microbial boundstone reflects an internal succession with a decrease of the same parameters. Water depth is considered very shallow ranging from 0 to a few meters, and salinity was normal marine to hypersaline. The reconstructed paleoenvironment with dominating oolite shoals and seagrass meadows was not restricted to the Central Paratethys but extended over the entire Paratethys and represented the largest oolite facies area of the entire Cenozoic!

Multidisciplinary Integrated Approach Unlocks Fracture-Characterization Ambiguity

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 213771, “Unlocking Fracture-Characterization Ambiguity: A Multidisciplinary Integrated Approach,” by Ali Abughneej, Mohamed Al-Naqeeb, and Mohammed Al-Ostath, SPE, Kuwait Oil Company, et al. The paper has not been peer reviewed. _ Fracture systems play a significant role in production in the case of tight, low-porosity complex reservoirs. An exploration well in North Kuwait that targeted the Middle Marrat formation encountered uncertainty regarding reservoir compartments in an underexplored field, with minimal offset wells to properly evaluate its potential. A multidomain approach is proposed leveraging different types of expertise to tackle the petrophysical and geomechanical aspects of the fracture system governing the carbonate layer and assess its producibility and qualification for stimulation through hydraulic fracturing. Introduction A comprehensive study was performed on Well A targeting the Marrat formation, a tight, low-permeability carbonate Jurassic reservoir. During the last two decades, the operator has drilled many vertical and deviated wells through this formation. Hydrocarbon production from the closely spaced wells shows a major variation in flow rates, which has been attributed to the presence of uncharacterized fracture clusters as well as the limited understanding of reservoir compartmentalization. To address the challenges of production discrepancy, an innovative multidomain approach was proposed as an integrated solution in an attempt to understand the fracture systems governing the reservoir setting and its compartments and further assess their connectivity and extent to form a perspective on their possible contribution or hindrance to flow. An end-to-end comprehensive work flow was created combining the results of advanced formation evaluation, high-resolution borehole imaging, and state-of-the-art sonic imaging [the 3D far-field sonic (3DFFS) approach], followed by a fracture-stability analysis for the purposes of completion optimization and potential future hydraulic fracture design. Geological Setting Middle Marrat is targeted as the hydrocarbon-bearing zone, consisting of dolomitized oolitic grainstone to packstone facies, reflecting the high-energy inner-midramp shoal depositional environment.

Microfacies and paleoenvironment of microbialites of the Cambrian (Stage 4) Qingxudong Formation in the Huayuan area, northwestern Hunan Province, southern China

After the extinction of Archaeocyatha (sponges), microbial bioherms were well developed in the lower Cambrian of the Yangtze cratonic basin, especially in the Qingxudong Formation (Cambrian (Stage 4)) of the Huayuan area, northwestern Hunan Province, southern China. Herein, four sections from this area were chosen for investigating and analyzing their microfacies and depositional environment. Twelve microfacies types were recognized through petrographic analysis of textural attributes and calcimicrobes (including Epiphyton, Renalcis, Girvanella and Kenella), respectively as: laminated calcareous mudstone (MF1), algal wackestone (MF2), intraclastic grainstone (MF3), algal intrasparrudite (MF4), oolitic algal intrasparrudite (MF5), sparry oolitic grainstone (MF6), Epiphyton framestone (MF7), Renalcis bafflestone (MF8), Kenella bafflestone (MF9), Girvanella boundstone (MF10), thrombolitic boundstone (MF11), and dolomite (MF12). These microfacies represent four major depositional environments: carbonate ramp, carbonate platform, slope and tidal flat. Calcimicrobes played an important role in the transition from carbonate ramp to platform, while the evolution from ramp to tidal flat must be ascribed to sea-level fall during the Cambrian Age 4.

Lithostratigraphy, lithofacies and deposition conditions of the late Olenekian-middle Anisian Alam Formation in the Nakhlak area, central Iran

The present study aims to investigate petrography characteristics and sedimental environments of upper Olenekian–middle Anisian deposits of Nakhlak group in the sedimentary-structural zone of central Iran. To this end, a section of these deposits with a thickness of 720 meters was first selected, and 190 samples were taken from this section for preparing thin sections. Also, quantitative and qualitative laboratory tests were performed and 25 samples of sandstone were selected for point counter analysis. The results indicated that the major deposits of this formation are related to siliciclastic, carbonate, and pyroclastic types, which are in the form of two facies associations. The facies association A at the bottom of the studied section with the thickness of 90 meters has a periodicity of clastic, carbonate, and pyroclastic facies. The clastic facies of this association consists of fine-grained sandstone. In addition, the carbonate facies in association A are characterized by two microfacies consisting of intraclast oolitic grainstone and oolitic grainstone. Further, tuffite is the only pyroclastic facies related to association A, which has a laminate structure, cross-bedding lamination, herringbone bedding, and upward-thinning and thickening cycles. The facies association, B which is deposited later, is more in the middle and top part of the section. The facies association B is 660 meters thick and has a periodicity of clastic and limestone facies. Clastic facies of this association includes four lithofacies such as conglomerate, pebble coarse-grained sandstone, medium-grained sandstone to thin layer siltstone and shale. The carbonate facies consists of four microfacies such as sandy intraclastic wackestone and mudstone. Furthermore, slumping structures, cross bedding, turbulence, boudinage structure, and convolute of sediments, along with the effects of erosional channels are observed in facies B. Field and laboratory studies conducted on this succession indicate the structure of facies association A was deposited in a mixed siliciclastic carbonate ramp. Finally, submarine canyons and submarine fan environments were left by increasing the depth of the facies association B in the deep part of sea and turbidity systems.

Constraining depositional evolution and reservoir compartmentalization in a mixed carbonate-siliciclastic lacustrine system: The Yacoraite formation, Salta Group, NW Argentina

The mixed carbonate-siliciclastic Yacoraite Formation, Salta Group in northern Argentina has been interest of recent studies searching for potential analogues for the South Atlantic pre-sal carbonates. Microbial lacustrine carbonates are important reservoir systems and their characteristics and stratigraphic packaging are a major factor impacting compartmentalization. This study provides sedimentological and facies analyses combined with petrographical, isotope geochemical and petrophysical analyses of lacustrine clastics and carbonates using an example from the Yacoraite Formation (Salta Group) in northern Argentina (Tres Cruces sub-basin).The Yacoraite Formation records the evolution of a lacustrine system responding to basin scale tectonic processes and climatic conditions and is interpreted as a microbially-related mixed carbonate clastic lacustrine system comprising 8 main Facies types, deposited in either a perennial or an ephemeral system. The most dominant architectural elements are: Sandstones with interbedded shales (F1), Shales with interbedded sandstones and siltstones (F2), Thick-bedded oolitic grainstone (F5), Thin-bedded oolitic grainstone-packstone (F6) and Stromatolite boundstone (F8). These facies types allow to differentiate two types of lacustrine environments: Perennial (Stage I) vs Ephemeral (Stage II) intercalated with episodes of continental plains deposition, arranged in three depositional sequences (Yacoraite I, II and III), each recording either transgressive or a regressive-transgressive trend.Carbonate and clastics are arranged in cycles during the Perennial l Stage suggesting that the depositional system responded in patterns attributable to reciprocal sedimentation, whereas, during the Ephemeral Stage 2, spatial coexistence of clastic and carbonate seem to be the case rather that cyclic vertical superposition.Thick-bedded oolitic grainstone and Stromatolites (F5 and F8 respectively) of the perennial lacustrine system show laterally continuous and thick beds with the best reservoir properties. Furthermore, the Sandstones with interbedded shales (F1) are characterized by intermediate values of porosity and permeability, which would not result in permeability barriers. On the other hand, Thin-bedded oolitic grainstone-packstone (F6) of the ephemeral lacustrine system are characterized by a high degree of heterogeneity due to their limited areal distribution and their complex spatial variability with Shales with interbedded sandstones and siltstones (F2).

Tracking depositional and geochemical variations in the Cambrian North China Platform: Insights from sedimentology, geochemistry, and C-O isotopic records

The Cambrian carbonate sequence in North China is of significant global and regional scientific importance due to its continuous and thick exposure and the data on the major environmental changes and biological events of the early Phanerozoic, which can be gleaned from it. While the well-exposed Cambrian outcrops have been utilized to unravel the processes governing these events, few studies have focused on the outcrops' spatio-temporal depositional patterns and geochemical variations. Therefore, our study address, these issues by integrating fieldwork with petrographic and geochemical analyses. In the North China Platform (NCP), the Cambrian carbonate sequence is predominantly composed of six third-order depositional sequences (~370–400 m thick) that can be divided into nine microfacies, representing three primary microfacies associations, namely tidal flat, lagoon, and shoal. In contrast to the standard carbonate sequence stratigraphy model and many other examples of Cambrian platforms, the deposition of oolitic grainstones in the NCP are overlain by the deep-water calcareous mudstone and shale during a period of slow fall of sea-levels. Such a particular style shows a similar trend to the Schlager model of a type III sequence boundary that formed between a highstand systems tract (HST) and a transgressive system tract (TST). Scanning electron microscope (SEM) observations show an abundance of microbial fossils, a nanosphere, and remnants of extracellular polymeric substances (EPS) inside the dark micrite of normal regressive deposits (oolitic grainstone), suggesting the significant role of microbial activity in the formation of ooids. The δ18O isotopic values range from −4.15 to −11.75‰ VPDB, portraying pervasive diagenetic alterations with a variable degree of diagenesis at different localities, and both marine- and burial-related diagenesis. In contrast, the δ13C VPDB values have a very narrow range, from −2 to +2‰ VPDB, suggesting little to no influence of meteoric diagenesis. At the same time, the slight depletion of δ13C isotope values may reflect the role of microbial processes during the genesis of ooids. This study highlights the importance of microbial activity and marine-related diagenetic overprints during the formation of carbonate facies in the Cambrian Period and provides evidence that carbon isotopic excursions observed during different major environmental and biological events in the NCP are related to primary signals and not altered by intensive meteoric diagenesis.

Microfacies Analysis and Stratigraphic Framework of Yamama Formation in Sindbad, Halfaya and Ad'daimah Oil Fields, Southern Iraq

The Yamama Formation represents a part of the Late Berriasian-Aptian sequence, deposited during the Early Cretaceous period within the main shallow marine depositional environment. The studied area covers three oil fields; Sindbad oil field, Halfaya and Ad'daimah oil field, located in southeastern Iraq. Six major microfacies were recognized in the succession of the studied area represented by the Yamama Formation to determine and recognize depositional paleoenvironments. These microfacies are; Peloidal Packstone, Algal Wackestone to Packstone, Bioclastic Wackestone – Packstone, Foraminiferal Bioclastic Wackstone, Packstone, Peloidal – Oolitic Grainstone and Mudstone Microfacies. These microfacies are classified into three standard microfacies and three Facies Zones MFS-18/FZ- 8, SMF 15/FZ-6 and SMF-10/FZ-7, representing the restricted marine, shoal and shallow open marine associations facies, respectively. The Yamama succession in the studied area is divided into three cycles representing three depositional stages of highstand system tracts. These three cycles are characterized by shallowing upward depositional mode where they are deposited in the shallow open marine shoal with semi-restricted associations facies for each cycle. To the northeast of the study area near Halfya-5 well, the shoal association appeared in the lower and middle part of the Yamama succession, and in Da-1 and Sn-2 were three cycles. This case suggests that the paleo high was developed north of the study area, while the open marine was extended to the southern part. The presence of shallow open marine association facies between the Sulaiy and Yamama successions refers to continuous deposition during the same depositional stage in all studied wells. It may mark the end of the Sulaiy succession with the maximum flooding surface (MFS). This first depositional stage is started with the shallow open marine association facies underlain by shoal facies association and then semi-restricted association. The repetition of this cycle in the studied sections symmetrically indicates the harmonic oscillation in sea level during the second and third depositional stages of this sequence. The Halfaya oil field within the Mesopotamian Block and Ad'daimah and Sindbad oil fields within the Basra Blok explain the significant variation in the thickness for this succession between the Halfaya oil field and the other oil fields. This may suggest the occurrence of high depositional subsidence in Basra Blok and uplifting during the Yamama depositional stages. The fact that the studied sections are distinguished by the same cycles, albeit roughly, indicates that the lifting and sit-down processes synchronized sedimentation.

Evaluation of the hydrocarbon source rock and the reservoir characterization of the Minagish Formation using wireline logs

We investigated the Mianagish Formation's potentiality as a Lower Cretaceous source rock and the included reservoir facies zone in the Umm Gudair oil field. The Middle Oolitic grainstone is the only producing zone in the formation. The wireline logs were used to trace the reservoir characteristics and calculate the total percentage of organic carbon (TOC) in the lithotype of the Minagish Formation. The commercial software, thin sections, and laboratory measurements are used to provide an integrated study. Integration of burial history, calculated TOC values, thermal maturity, depositional model, structural elements, and reservoir characterization were used to take a thoughtful look at the Minagish Formation's role in oil production in the field and as Lower Cretaceous source rock for the Cretaceous reservoirs. The reservoir facies are characterized by 16% average clay content, 16.7% average porosity, 420 millidarcys (mD) average permeability, and the average oil saturation is about 62%. The reservoir's quality reaches its maximum at the crest of the anticline in the west, south, and east, whereas the reservoir facies are deposited on the pre-existing structurally high shoal, while the quality decrease away from the shoal into the relatively deep water. The oil feeds the reservoir from the Lower Minagish Formation and maybe the Sulaiy Formation. According to the thermal model, the oil is heavy because of falling the TOC in the early maturation stage. The depositional environment and sequence stratigraphy are similar in the nearby Dharif and Abduliyah oil fields, and the study can be applied.

First hexactinellid spicules from the Late Cambrian olitofish of the Los Sombreros Formation, Tontal Range, San Juan Precordillera, Argentina

A moderately diverse fauna of hexactinellid sponges is described from one Late Cambrian olitofish of the Los Sombreros Formation from Tres Saltos Gulch in the Tontal Range, Western Precordillera, San Juan Province. Argentina. Protospongia sp., Diagoniella? Sp., Kiwetinokia, anchoring spicules, prodiaenes, diagonally arranged spicules and root tuft are present. The preservation degree of the spicules and the patterns allow us to presume that after their death, they were transported not very far from the original sponges oases. The Cambrian oolitic grainstone limestone with spicules conform an olitofish which was transported and resedimented during the Ordovician by gravity flows within a pelitic matrix of the terrigenous-carbonate talus of the Los Sombreros Formation.

Geology and construction: survey of archaeological sites and their natural environments (Gulf of Corinth, Greece)

This study attempts to demonstrate how Greek builders exploited their geological environment during the Archaic to Hellenistic periods. Four major sites in the eastern part of the Gulf of Corinth are compared: the old city of Corinth, the sanctuary of Poseidon at Isthmia, ancient Sikyon and the Heraeum at Perachora. Ancient builders utilised primary topographic features and natural resources to their advantage, thus reducing costs. They preferred local low-density stones sourced from the more recent Corinth syn-rift deposits (calcarenite, oolitic grainstone, sandstones, stromatolites and conglomerates), rather than the pre-rift Mesozoic carbonates. These local stones represent more than 90% of the volume employed for public construction. Greek builders also imported allochthonous high-porosity limestones for their temples. Hard stones, such as marbles, do not appear to have been attractive to ancient builders at any of the studied sites.

Origin of dolomites in oolitic carbonates of the Middle Jurassic Dorgali Formation, eastern Sardinia, Italy: Petrographic and geochemical constraints

The Bathonian-Callovian (Middle Jurassic) Dorgali Formation in eastern Sardinia (Italy) consists of dolomitized oolitic grainstone and records a complex diagenetic history. Petrographic examinations revealed three main phases of replacive (D1, D2) and fracture-filling (D3) dolomites with crystal-size ranges of <4–50 μm (dolomicrite to dolomicrosparite D1), 50–200 μm (eu-to subhedral dolomite D2), and 50–400 μm (sub-to anhedral crystals of dolomite D3). The early D1 exhibits dull luminescence (CL) under cathodoluminoscope, whereas the later D2 shows dull to zoned CL, and D3 consistently zoned CL. The near-micritic grainsize, low Sr contents (136 ± 43 ppm) and estimated δ18O values of the parent dolomitizing fluids (−1.3‰ to −0.9‰ VSMOW) suggest an early-diagenesis origin for D1 at low temperatures of near-surface conditions. In contrast, the larger crystal size and microthermometric measurements of primary two-phase fluid inclusions (Th = 101.7 ± 8.0 °C) reveal that D2 precipitated during later stages at higher temperatures of mid-to deeper burial settings, which is supported by the high calculated δ18O values of D2 parent dolomitizing fluids (10.0‰–10.7‰ VSMOW). Petrographic examinations suggest that the vug- and fracture-filling D3 and coarse calcite cement (C3, up to 2 mm) precipitated at deeper burial conditions, which is consistent with the low δ18O (−5.2 ± 1.0‰ VPDB) and δ13C (−5.1 ± 2.6‰ VPDB) compositions of C3. The similarity in shale-normalized REESN patterns, strong negative Ce anomalies and lack of Eu anomalies, suggest a seawater origin for the parent dolomitizing fluids.

The role of carbonate factories and sea water chemistry on basin‐wide ramp to high‐relief carbonate platform evolution: Triassic, Nanpanjiang Basin, South China

AbstractThe end‐Permian extinction and its aftermath altered carbonate factories globally for millions of years, but its impact on platform geometries remains poorly understood. Here, the evolution in architecture and composition of two exceptionally exposed platforms in the Nanpanjiang Basin are constrained and compared with geochemical proxies to evaluate controls on platform geometries. Geochemical proxies indicate elevated siliciclastic and nutrient fluxes in the basal Triassic, at the Induan—Olenekian boundary and in the uppermost Olenekian. Cerium/Ce* shifts from high Ce/Ce* values and a lack of Ce anomaly indicating anoxia during the Lower Triassic to a negative Ce anomaly indicating oxygenation in the latest Olenekian and Anisian. Uranium and Mo depletion represents widespread anoxia in the world's oceans in the Early Triassic with progressive oxygenation in the Anisian. Carbonate factories shifted from skeletal in the Late Permian to abiotic and microbial in the Early Triassic before returning to skeletal systems in the Middle Triassic, Anisian coincident with declining anoxia. Margin facies shifted to oolitic grainstone in the Early Triassic with development of giant ooids and extensive marine cements. Anisian margins, in contrast, are boundstone with a diverse skeletal component. The shift in platform architecture from ramp to steep, high‐relief, flat‐topped profiles is decoupled from carbonate compositions having occurred in the Olenekian prior to the onset of basin oxygenation and biotic stabilisation of the margins. A basin‐wide synchronous shift from ramp to high‐relief platforms points to a combination of high subsidence rate and basin starvation coupled with high rates of abiotic and microbial carbonate accumulation and marine cement stabilisation of oolitic margins as the primary causes for margin up‐building. High sea water carbonate saturation resulting from a lack of skeletal sinks for precipitation, and basin anoxia promoting an expanded depth of carbonate supersaturation, probably contributed to marine cement stabilisation of margins that stimulated the shift from ramp to high‐relief platform architecture.

Facies Analysis and Depositional Environments of the Ubaid Formation, Western Iraq

The Early Jurassic (Liassic) sequence crops out in numerous anticlines of the high folded zone of north and north-east Iraq and in the Rutba subzone (including Ubaid Formation) in west Iraq. The present study deals with siliciclastic / carbonate rocks of the 58 m-thick Ubaid Formation at Zor Hauran valley in south western Iraq. The formation consists of two parts; the lower part is composed of pebbly coarse sandstone and greenish to yellowish soft marl alternated with marly dolostone, while the upper part is characterized by light brown, well bedded dolostone, with stromatolite structure in some locations. Oval, light to dark brown nodules of chert are also present.&#x0D; A detailed field lithological description and facies analysis of the Ubaid Formation were performed for thin sections. It is composed of five main microfacies; dolomitized mudstone, dolomitized bioclastic wackstone, dolomitized pelloidal packstone, dolomitized oolitic grainstone, and bindstone, in addition to two lithofacies: marl and pebbly sandstone. These facies reflect the deposition from the environment of the lower supratidal to intertidal zone and the encompassing shallow scaffold secured shoal - marine environment with cautious water circulation.

Carbon-isotope stratigraphy of the Middle–Upper Cambrian in eastern Laurentia: Implications for global correlation

The examined interval of the March Point and Petit Jardin formations (total thickness ~130 m) spans the Middle−Upper Cambrian (lower Port au Port Group) at the Belle Isle Strait, western Newfoundland. The deposits consist of dolomitized shallow-water carbonates ranging from microbial mudstones to oolitic grainstones. A multi-technique evaluation proved the petrographic and geochemical preservation of the investigated micritic carbonates. The δ13C and δ18O values (−1.2 ± 1.1‰ VPDB and −6.7 ± 1.3‰ VPDB, respectively) exhibit an insignificant correlation (R2 = 0.16) and similarly the δ13C values with their Mn/Sr ratio (R2 = 0.01). This supports the preservation of at least near-primary δ13C signatures that can be utilized to construct a high-resolution δ13C profile for reliable global correlations. The δ13C profile exhibits two major negative excursions, the lower excursion (~4‰) immediately below the lower boundary of the March Point Formation (Hawke Bay/March Point boundary) and the upper excursion (~2‰) almost at the lower boundary of the Petit Jardin Formation where these excursions are likely associated with short-term sealevel changes. The trilobite biozonation scheme suggests the correlation of the lower excursion with the DICE (Drumian Carbon Isotope Excursion) event and the upper excursion with the base of the SPICE (Steptoean Positive Carbon Isotope Excursion) counterpart and both events have been globally documented on different paleocontinents.

Mixed carbonate-siliciclastic sequence development influenced by astronomical forcing on a distal foreland, Miocene Dam Formation, eastern Saudi Arabia

Given increasing importance of tertiary reservoirs in the Middle East, the Miocene (Upper Aquitanian to mid-Langhian) Dam Formation in eastern Saudi Arabia was cored along a 40 km transect, to develop a high-resolution sequence framework, and examine the role played by astronomical forcing, moderate glacio-eustasy (20- to 40-m sea-level changes), and tectonic deformation in this distal foreland setting. The Dam Formation (up to 80 m thick) contains updip siliciclastics which interfinger downdip with marine carbonates. Siliciclastic facies include paleosol-capped, red mudrock (mudflat), green and gray mudrock (near-shore siliciclastic lagoon), rare mud clast–bearing sandstone (fluvial), and massive very fine to medium sandstone (terrestrial sand sheets, rare tidal channels). Carbonate facies include brecciated carbonates (paleosols), lime/clay-clast quartz wackestone (lag gravel), carbonate laminites and microbial heads and mounds (tidal flat and shallow subtidal), argillaceous quartzose marl (near-shore lagoon), peloid mudstone-wackestone (restricted lagoon), variably quartzose skeletal peloid mudstone to packstone (open lagoon), oolitic grainstone (hypersaline beach, tidal channel), mollusk packstone (hypersaline lagoon border), and foram-mollusk packstone-grainstone (seagrass meadows). The Dam Formation contains eight sequences, each of which contains 2 to 4 parasequence sets or individual parasequences. Sequences and individual parasequences are capped by paleosols and/or erosion surfaces, and microbial laminite caps are rare. Bases of parasequences locally are veneered with ravinement gravel lags or siliciclastics beneath shallowing-upward subtidal carbonates, and lack intercalated deeper water facies. Statistical analysis of core-gamma ray (API) vs depth (m) shows that accumulation rates were ~ 3 to 4 cm/kyr, considerably faster than long-term accommodation rates (~ 1.2 cm/kyr), indicating deposition occurred for only 40% of the time, the remainder of the time being non-depositional during many short-term lowered sea levels, evidenced by the coeval oceanic δ18O curve. Spectral analysis of the core-gamma ray logs show astronomical forcing within the eccentricity, obliquity, and precessional bands. Spectral analysis indicates that the eight Dam sequences (average 10 m thick, range < 5 to 18 m) are a mix of long-term obliquity (~ 1.2 Myr) and long-term eccentricity (400 k.y.) cycles. The 3- to 4.4-m sets/parasequences are short term (~ 100 kyr) cycles, and the 0.7- to 1.25-m parasequences are obliquity and precessional cycles. Given the updip position of the study area, repeated glacio-estutatic sea-level changes caused repeated shallow flooding (< 20 m) and emergence, which generated paleosol-bounded or erosionally capped sequences and parasequences. Although the distal foreland was undergoing synsedimentary deformation and slow but locally variable subsidence, which influenced variable thickness of units, astronomically driven glacio-eustasy was the dominant influence on timing of sequence and parasequence development.

Porosity system analysis and its relation to the permeability of the reservoir zones in the Upper Dalan Member and Kangan Formation: A case study, one of the gas fields in the Zagros Coastal Fars, SW Iran

The studied gas field is located in the Coastal Fars structural zone of the folded Zagros, in the west of Hormozgan Province and on the Gavbandi highland. The Dehram Group forms gas reservoirs in this field. The results of macroscopic and microscopic studies and routine core analysis of the Upper Dalan Member and Kangan Formation show that porosity with an average of 14.51% in the Kangan Formation is more than Upper Dalan Member with an average of 8.29% (certain intervals of the well cores); however, the Upper Dalan Member with an average of 10.8 md (10.8 × × 10−3 μm2) has higher permeability than Kangan Formation with an average of 3.54 md (3.54 × × 10−3 μm2). The Grain-supported facies (in accordance with Ka-2 reservoir zone) of the Kangan Formation has the best reservoir quality with an average of 10.7% effective porosity and 43.3% total water saturation; while in the Upper Dalan Member, mud-supported facies (in accordance with UDL-5 reservoir zone) has the best reservoir quality with an average of 10.2% effective porosity, and 36.7% total water saturation where the dolomitization process has been the most important factor for increasing the reservoir quality in these facies. The porosity type of the Kangan reservoir (oolitic grainstone of shoal facies belt in Ka-2 reservoir zone) is isolated moldic and vuggy those generates high porosity and low permeability values in this formation but in some intervals, the isolated molds and vugs are connected by channel and fracture; therefore increased the value of permeability. The tidal flat facies belt of Upper Dalan member has high porosity and permeability and good reservoir quality in the UDL-2, UDL-5 and UDL-6 reservoir zones, with respect to the tidal flat facies of the Kangan Formation, which is related to dolomitization processes that generate intercrystalline porosity type. Finally, both the depositional environment and diagenetic processes controlled the distribution characteristics of reservoir quality, as seen in the relation between porosity and permeability.

Rock fabric controls on pore evolution and porosity–permeability trends in oolitic grainstone reservoirs and reservoir analogs

Although the general influence of rock fabric on porosity and permeability (Φ–k) within carbonates is well documented, if and how pore evolution and Φ–k scatter quantitatively relate to depositional fabric remains poorly constrained. This project empirically explores this uncertainty within oolitic grainstones from a range of geologic ages and diagenetic histories to understand depositional sediment–pore relationships and how they can evolve with lithification. Integrating data from point counting, digital image analysis, nuclear magnetic resonance, and core analysis of Holocene, Pleistocene, Pennsylvanian, and Mississippian oolitic grainstones reveals quantitative relations among rock fabric, pores, and petrophysical parameters. Oolitic grainstones of similar sedimentology taken from distinct diagenetic scenarios display a unique combination of pore size, shape, spatial distribution, and Φ–k character. Within each scenario, pore attributes and k are correlated more closely with grain size, sorting, and type than with cementation and compaction. Collectively, these results are interpreted to suggest that sedimentology controls the trends or variability within an oolitic succession but that diagenesis defines the absolute values of pore attributes and petrophysical parameters. These findings suggest that petrophysical variability within oolitic reservoirs may closely follow sedimentologic trends, which may be predictable within a stratigraphic framework.

Khurmala Formation (Late Paleocene-Early Eocene) in Halabja area, Kurdistan Region, Iraq

The studied section of Khurmala Formation (Late Paleocene-Early Eocene) is located in the Nawar Mountains on the northern part of the entrance of Sirwan River in Darbandikhan Lake. The section is mostly composed of dolomitic limestone, with occasional occurrence of sparsely fossiliferous limestone which are white, light grey and yellowish grey in color. The thickness of this section is almost 73 m and a total of 52 samples were collected at intervals of 0.5-3.0 m according to the lithological changes. Fifty-two thin sections were prepared and analyzed under a binocular microscope. The microfacies distinguished are Boundstone with corals, Bindstone with coralline red algae and corals, Bioclastic grainstone, Bioclastic oolitic grainstone, Bioclastic packstone, and Wackestone. These facies were interpreted to be deposited mainly in the shoal and lagoon of inner ramp environment. Although the studied section is not rich in fossils and most of them were destroyed by diagenesis processes, the following have been identified: Spongites sp., Cymopolia ellongata, Mesophyllum sp., Sporolithon sp., Idalina sinjarica, Quinqueloculina, Cymopolia sp. and Spongites cf. albanensis Lemoine.

BIOSTRATIGRAFIA CON 1 FORAMINIFERI DEL LIMITE FORMAZIONE A BELLEROPHON FORMAZIONE DI WERFEN FRA RECOARO E LA VAL BADIA (ALPI MERIDIONALI)

In thc Southern Alps the boundary between the marine Upper Permian Bellerophon Formation and the Scythian Werfen Formation was believed to coincide with the Permo—Triassic boundary. Almost everywhere in the area from Recoaro (Vicenza) to the Badia Valley (Northern Dolomites) (Fig, l) the lower part of the Wcrfen Fm. is represented by the Mazzin Member dated as Early Griesbachian (Broglio Loriga et al., 1980, 1982; Mostler et al., 1982). The Mazzin Member begins with the Tesero oolitic Horizon (Bosellini, 1964, 1968), which consists of oolitic grainstones with dolomitized ooids and it ig considered to be trasgressive on the Bellerophon Fm. (Bosellini, 1964; Assereto et al., 1973; Cassinis et al., 1979; Farabegoli &amp; Vicl, 1982; etc.). The Upper Bellerophon Fm. has been correlated with the Caucasian Phisonites—comelicania zone (Assereto et al., 1973), today referred to Lower Dorashamian (Rostovtsev &amp; Azaryan, 1973).