Ramp Environment Research Articles

Lithogeochemical characteristics and sedimentary environments of the Uk Formation limestones (upper Riphean, Southern Urals)

The lithogeochemical characteristics of the Uk Formation limestones (Uppermost Unit of the Riphean stratotype section in the Southern Urals) are considered. Data points of limestones (40 samples) accumulated in the middle and inner ramp environments have a quite contrasting distribution on diagrams with parameters (La/Sm)sh, (La/Yb)sh and (Sm/Yb)sh, proposed based on the systematization of a significant amount of analytical data on carbonate sequences formed in various platetectonic (in the broad sense of the word, paleogeographic) environments (according to [Zhang et al., 2017]) was established. The data points of the limestones of the Medved Member of the Uk Formation, which was formed, according to a detailed lithological-facies analysis, in the middle ramp environment, in the indicated diagrams located towards the field of limestones of the open ocean, while the limestones of the Manaysu Member (inner ramp deposits) in their geochemical characteristics are more consistent with the limestones of the near-coastal environments. Thus, the geochemical characteristics of the Uk Formation limestones seem to confirm the conclusions of the previous reconstructions. It has been suggested that in the example we described, the distribution of trace elements in the inner ramp limestones was apparently controlled by fine-grained siliciclastic material coming from the continent, while in the geochemical features of deeper-sea middle ramp limestones the influence of the open ocean environment is already perceptible.

Microfacies, diagenetic processes and reservoir quality of the Aptian carbonate Dariyan Formation, southeast of the Persian Gulf, South Iran

The Aptian carbonate Dariyan Formation (Shu'aiba equivalent) is one of the most important oil reservoirs in the Zagros Basin and the Persian Gulf (South and Southwest of Iran). The Dariyan Formation with mainly carbonate facies overlies the Gadvan (Hawar) Formation and is overlain by the Kazhdumi (Nahr Umr) Formation. Despite the reservoir importance of the Dariyan Formation, it seems that not much detailed work has been done about the facies characteristics, diagenetic processes and reservoir quality of this formation in the east of the Persian Gulf Basin of Iran.By using the new and valuable data obtained from the core, this study focused on the identification of microfacies, diagenetic processes, determining the sedimentary environment, biostratigraphy and reservoir characterization of this formation in one of the wells of Reshadat oilfield in the southeast of the Persian Gulf. The results obtained from microfacies study, led to the identification of seven carbonate and one mixed carbonate-clastic microfacies that were deposited in four facies belts including the inner ramp, middle ramp, outer ramp, and deep basin. Uniform facies changes and the absence of reef-forming organisms such as rudists and its replacement by Lithocodium algae with the ability to form patch reefs indicate the homoclinal carbonate ramp environment. The study of benthic and planktonic foraminifera, as well as algae, led to the identification of five biozones, which indicated the Aptian age for this formation.Based on petrographic study, the Dariyan Formation is affected by diagenetic processes such as Cementation, dissolution, mechanical and chemical compaction, dolomitization, bioturbation and pyritization. Correspondence of porosity and permeability data of the cores and petrophysical logs indicates that the reservoir quality of the Dariyan Formation in the studied field was affected by facies, and diagenesis factors. Reservoir characterization has revealed that the high quality zone is located in the intervals containing Lithocodium algae. In the Lithocodium-bearing facies (boundstone-floatstone) the presence of many interconnected pores and cavities in the skeletal network structure of Lithocodium/Bacinella algae have created a suitable reservoir quality and a permeable facies.

Microfacies Analysis and Diagenesis Processes of Mauddud Formation in selected wells from Ratawi oil field, Southern Iraq

Mauddud Formation was studied in Ratawi oil field, Southern Iraq. The lithology of the formation is limestone in all studied wells (Rt-2, Rt-4, Rt-17 and Rt-19). lower contact of Mauddud Formation with Nahr Umr Formation is gradational, but the upper contact is unconformable with Ahmadi Formation. In this work, 114 thin sections were examined and shows four microfacies (wackestone, packstone, grainstone and argillaceous mudstone), which deposited in the Inner-Mid to Outer ramp environment. The most significant diagenesis processes were micritization, dissolution, cementation, compaction, and dolomitization, which had an impact on the texture and porosity of the Mauddud Formation.

Biostratigraphy and Paleoecology of the Sinjar Formation (Late Paleocene-Early Eocene) in the Dokan and Sinjar Areas, Iraq

Biostratigraphy of the Sinjar Formation is investigated in two sections (Dokan and Sinjar) from northeastern and northwestern Iraq, respectively. Two hundred samples from all the limestones and marl that form the main lithological components of the studied sections were collected. The studied limestones and marl are rich in microfossils. Through thin sections, we were able to identify thirty species of benthic foraminifera and fifteen species of other microfossils (coral, algae, mollusca, bryozoa, and echinoids) at Dokan section, and fifty-one species of benthic foraminifera and thirty species of other microfossils at Sinjar section. 3 biozones were distinguished from both sections 1-Biozone A: Kathina sp.- Lockhartia hunti Assemblage zone (SBZ 5) (Dokan section); (Kathina pemavuti - Lockhartia hunti Assemblage zone (Sinjar section), 2- Biozone B: Idalina sinjarica Total Range zone (SBZ 6-7) and 3-Biozone C: Alveolina globosa- Alveolina pasitisilata Concurrent Range Zone (SBZ8-10). These zones indicate the Late Paleocene –Early Eocene age of the Sinjar formation. The biostratigraphic correlations in the studied sections are based on benthic foraminiferal zonations. Showed the correlation comparison between the biostratigraphic zones of the commonly used benthic zonal scheme around the Late Paleocene -Early Eocene in and outside of Iraq. paleoecological studies suggest that the carbonate sedimentation of the Sinjar Formation thrived in 18-25oC, with mesophotic to oligophobic light, under an oligotrophic to mesotrophic middle ramp environment with normal marine to slightly saline and at water depths from 40 - 80 m. Stable isotopic carbon (δ13C) and oxygen (δ18O) data revealed generally hot conditions with high productivity during the deposition of the Sinjar Formation accompanied by an abrupt change in paleoenvironmental conditions across the Paleocene-Eocene contact.

Tectonic control on the palaeogeographic evolution of thrust‐top basins at the active margin of the Guadalquivir Basin (central Betic Cordillera, S Spain)

AbstractThe Guadalquivir Basin is the foreland basin of the Betic Cordillera (S Spain). Closest to the orogen, several thrust‐top basins evolved during the Late Miocene in the central part of the cordillera. Here, we study the Upper Miocene deposits in five of these satellite basins: Montefrío, Iznájar‐Cuevas de San Marcos, Antequera, Bobadilla Estación and Teba, in order to (1) update the stratigraphic framework, (2) infer a depositional model, (3) establish the relationship between sedimentary record and tectonic context and (4) reconstruct the palaeogeography of the area during the Late Miocene. Upper Miocene sediments mostly consist of mixed carbonate‐terrigenous deposits. Facies characterization allows inferring a sedimentary model corresponding to a ramp with foreshore deposits changing to a shoal belt offshore in the inner ramp. Swaley and hummocky cross‐stratified deposits formed in the transition to the middle ramp, and plane parallel carbonate beds in the distal middle‐outer ramp. Factory facies, dominated by rhodoliths and bryozoans, also occur in the middle‐outer ramp environments. Silts and marls formed in the deepest outer ramp and basin settings respectively. Breccias accumulated at the toe of palaeocliffs and conglomerates and massive coarse sands were deposited in fluvio‐deltaic systems. Conglomerates and sands were also reworked as gravity flows and redeposited offshore. Local facies include rudstones‐grainstones displaying large‐scale trough‐cross bedding formed in a strait in Montefrío, and marls with chalky carbonates deposited in a shallow marine, sheltered lagoon with hydromorphic soils in Bobadilla Estación. The study basins evolved in an N‐S compressive tectonic context responsible of the emersion of the main Betic reliefs. Concomitantly, E‐W and ESE‐WNW extension originated the main depocentres. The influence of the tectonic activity on the sedimentary infills is indicated by the presence of synsedimentary deformations and several diachronic unconformities, which are younger westward. Tectonism, in turn, also controlled the palaeogeographic evolution during the late Tortonian‐early Messinian interval.

Reconstruction of the Yangtze Ramp during Floian to Darriwilian (Ordovician) in South China: Its Morphology, Controlling Factors and Significances

AbstractA robust stratigraphic framework and a coherent depositional ramp model for the Zitai, Dawan, Meitan and Ningkuo formations of Floian–Darriwilian age (Early–Middle Ordovician) in the Yangtze (Daoba, Xiangshuidong, Daling, Gudongkou and Honghuayuan sections) and Jiangnan regions (Nanba section) was created based on lithofacies and major element analysis. Three siliciclastic (LF1–3) and six carbonate (LF4–9) lithofacies are recognized representing sediments that were deposited in mixed siliciclastic and carbonate ramp environment. The intensity of mixed sedimentation and terrigenous input were evaluated using the elemental proxies Intensity of Mixed sedimentation (IM) and Aluminum Accumulation Rate (AlAR), as well as their mean values during certain time intervals. Mixed sediments are most well‐developed along the marginal Yangtze region, strongly impacted by recurrent influx of westerly derived terrigenous materials in response to global eustatic changes and regional tectonic movements, shaping the gently southeast‐dipping morphology. Regular terrigenous influx resulted in periods of enhanced primary productivity on the Yangtze Ramp as evidenced by matching biodiversity peaks in planktonic organisms, i.e., chitinozoans and acritarchs. Brachiopods and other shelly fauna were also able to proliferate as new niches developed along the gently dipping ramp floor with substrate changes. The biodiversification patterns suggest that terrigenous influx controlled in part by regional tectonics played a more important role than previously thought in the development of Great Ordovician Biodiversification Event in South China.

Kasimovian (late Pennsylvanian) cornute rugose corals from Egypt: taxonomy, facies and palaeogeography of a cool-water fauna from northern Gondwana

A strongly endemic Upper Pennsylvanian (Kasimovian) rugose coral association consisting of small, mostly non-dissepimented, simple structured and poorly diversified species is studied from the lower member of the Aheimer Formation (Western side of the Gulf of Suez, Egypt). The unit is composed of grey, silty mudstone intercalated with thin, ferruginous, silty dolostone–limestone and calcareous siltstone beds. Ten taxa from four families were identified. Four species of the Antiphyllinae are new; Actinophrentiscrassithecata n. sp., Lytvolasmaaheimerensis n. sp., L.paraaucta n. sp. and Monophyllumgalalaensis n. sp. Besides, Rotiphyllumexile de Groot, 1963 and Bothrophyllumokense Kossovaya, 2001 were identified; four taxa remain in open nomenclature (Lytvolasma cf. canadense, Zaphrentites cf. parallela, Zaphrentites sp. and Ufimia sp.). Rejuvenation, encrustation and bioerosion phenomena are rare. Attachment structures during mature stages are not evident; attachment scars in the apical parts are also rare. Growth patterns and embedding in the muddy deposits indicates that the corals lived as mudstickers in soft substrate. Recrystallization, dolomitization and ferrugination of open pore spaces inside the corals are the most common diagenetic features. The corals from the lower Aheimer Formation represent a typical cyathaxonid fauna that was adapted to high clastic input and turbid waters in a restricted, sheltered, episodically storm-swept inner ramp environment in an embayment of the southern shelf of the Palaeotethys. A time-averaged ramp model shows a regressive development from a mixed carbonate–siliciclastic open inner ramp setting during the Moscovian to the restricted inner ramp of the lower Aheimer Formation (Kasimovian) and following peritidal to fluvial environments of the Gzhelian. General and local palaeoclimatic considerations indicate cooling. Besides relations to northern Spain that root Egypt in the western Palaeotethys, connections existed via the Donets Basin (and the southern Urals) to the Cordilleran–Arctic–Uralian realm which is a cool water province during the Lower and Middle Permian. The Egyptian fauna appears to be a precursor of the anti-tropical cyathaxonid fauna of the latter time slice and also of the Lower Permian cool-water faunas of the east Cimmerian peri-Gondwana terranes.

Late Paleocene–Early Eocene larger foraminifera from the Galala Plateaus, North Eastern Desert, Egypt: biostratigraphic, paleoenvironmental and paleoecological implications

Two stratigraphic sections are investigated, and a diverse larger benthic foraminiferal assemblage is recorded from the upper Paleocene–lower Eocene Southern Galala Formation at the Galala Plateaus, north Eastern Desert, Egypt. Twenty-eight larger foraminiferal species, belonging to thirteen genera, are identified and their comparative stratigraphic range with the Tethyan zonations of Hottinger (1960) and Serra-Kiel et al. (1998) is documented. Nine shallow benthic zones (SBZ3-6 and SBZ8-12) are designated in the studied interval, involving index zonal markers, e.g., Glomalveolina primaeva (Reichel), G. levis Hottinger, Nummulites atacicus (Leymerie), Alveolina vredenburgi Davies, and A. ellipsoidalis Schwager. Fifty-four thin sections are prepared and analyzed, yielding seven microfacies types in the present study, with larger benthic foraminifera as the dominant biotic components. These microfacies types indicate a deposition in restricted tidal flat inner ramp to open-marine middle ramp environments. The inner ramp environments are dominated by alveolinids, orbitolitids, and in part by miliolids and orthophragminids, reflecting euphotic to mesophotic, meso-oligotrophic, and normal to hyper salinity conditions. The middle ramp environment is characterized by nummulitids, implying meso-oligophotic, oligotrophic, and normal salinity conditions. The studied successions at the Galala Plateaus are devoid of corals in platform stages II and III, similar to the Pyrenean strata from middle latitudes at the northern Tethys, except for small coral patches in both stages in the latter due to the cooler temperature. The Early Eocene (Cuisian) Nummulites accumulations suggest a development on paleohighs in a distal inner ramp environment, and then a transportation by wave and current actions into the surrounding proximal middle ramp environment.

Shallow‐marine calciclastic mass‐transport deposits in an evolving thrust‐top basin: A case study from the North Dalmatian foreland basin, Croatia

AbstractMass‐transport deposits are products of resedimentation phenomena involving a broad spectrum of gravity‐driven processes, and commonly have a high preservation potential in deep‐marine environments. This study documents various types of mass‐transport deposits that are interbedded with intensely bioturbated shallow‐marine calciclastic sediments deposited along a reflective coast during the middle and late Eocene. The sedimentary succession, located in the vicinity of Novigrad in northern Dalmatia, Croatia, comprises sediments deposited in a range of nearshore and carbonate ramp environments, and represents the infill of a thrust‐top (piggyback) basin of the North Dalmatian foreland basin. Five types of mass‐transport deposits, ranging in thickness from 13 cm to 6 m, have been identified: (i) calcilutite and calcarenite slumps; (ii) conglomeratic slump‐debrites with a ‘dough‐like’ appearance; (iii) blocky‐flow deposits bearing large blocks of beachface and/or shoreface deposits; (iv) rockfall deposits comprising scattered blocks of beachface conglomerates and shoreface calcarenites; and (v) ‘classical’ matrix‐supported debrites. Calciturbidites are rare and mainly comprise Ta and Tb divisions. Conglomeratic slump‐debrites are mostly found in association with offshore‐transition deposits, suggesting that mass flows were triggered above the storm‐wave base likely due to a combined effect of: (i) strong earthquakes related to the tectonic development of the basin; (ii) sediment destabilization due to pore‐water overpressure during forced regressions; and (iii) storm‐wave loading affecting the shallow seabed. Progressive deepening likely favoured mass‐flow transformations, although the overall paucity of turbidites suggests relatively short mass‐flow transport distance and turbidity current bypass to deeper realms. Multiple erosion phases and resedimentation processes from the Cretaceous to the late Eocene contributed to the diverse suite of extraformational clasts in the mass‐transport deposits studied. The mass‐transport deposits may be triggered and emplaced in shallow‐marine settings mainly during regressive stages of basin development, as the diverse gravel clast composition suggests significant tectonic influence. Although the mass‐transport deposits reported herein are relatively small, some of their peculiar sedimentary features and occurrence within shallow‐marine calciclastic deposits render them rather unique and suitable for a re‐assessment of the nature and evolutionary continuum of processes involved in subaqueous sediment mass transport, as well as the preservation potential of sedimentary features in high‐energy wave‐reworked environments.

Carbonate Ramp Facies and Porosity Recognition: Case Study of the Late Albian-Early Cenomanian Mauddud Formation in Ratawi Oilfield, Southern Iraq

The carbonate ramp facies of the Late Albian-Early Cenomanian Mauddud Formation were studied in the Ratawi Oilfield, Basra Governorate, south of Iraq using integrated borehole data set that included, core and cutting samples in three drilled wells to analyze the petrography of the Mauddud Formation, two hundred and eighty-one (281) thin sections were prepared and examined for the three selected wells. The results show that the formation is composed of light grey dolomitized limestone and pseudo-oolitic creamy limestone with green to bluish shale. The petrographic observations results show four facies’ associations in the Mauddud Formation. These include: Mid–Ramp environment which is represented by Argillaceous mudstone microfacies, Argillaceous wackestone microfacies and orbitolinid wackestone microfacies; the shallow open marine environment which is assimilated by foraminiferal wackestone microfacies and foraminiferal packstone microfacies; a restricted marine environment that represented by bioclastic fossiliferous wackestone microfacies and miliolid wackestone microfacies and Shoal environment is represented by bioclastic packstone microfacies, bioclastic grainstone microfacies, peloidal foraminiferal pack-grainstone microfacies, and peloidal packstone-grainstone microfacies with diverse skeletal grains. The porosity includes Vuggy, Interparticle, Intraparticle and Fracture porosity.

Simulating reservoir capillary pressure curves using image processing and classification machine learning algorithms applied to petrographic thin sections

Reservoir rock porosity and capillary pressure data are fundamental parameters to understand the physical properties of rocks. Porosity, which shows the rock's void fraction to its bulk volume, can be measured by s techniques such as He-porosimetry, mercury injection capillary pressure (MICP) analysis, point counting analysis, and image analysis. Image analysis has for many years been used to obtain relevant data from digital microscopic images. Segmentation of images is an important technique used to partition an image into distinctive components to extract useful data. When an image is segmented, it is simplified, making it easier to understand its component parts. In this research, two-dimensional (2D) rock thin section image processing is initially applied to determine porosity. To achieve this, the K-means clustering algorithm was used to automatically segment and measure the digital rock porosity. In this regard, one hundred and nine samples were selected from approximately one thousand 2D petrographic thin-section images of the Dorood Oilfield reservoir rocks and were digitally processed and evaluated. The porosity values estimated from the image analysis agree with the porosity derived from whole-rock core analysis with a correlation coefficient of 67 %. Moreover, petrographic studies distinguished five microfacies, which relate to lagoon, shoal, mid and outer ramp depositional environments associated with a carbonate homoclinal ramp. In addition. three distinct Hydraulic Flow Units(HFUs) were determined based on K-means clustering by applying the Elbow method. Based on those clusters, permeability was estimated from HFU porosity distributions with high correlation coefficient (R = 90 %). Pore-throat size distributions and Pc curves were then estimated from thin-section image analysis based on the Pittman equations for different mercury saturation percentages. The estimated Pc curves derived from image analyses show an acceptable correlation with SCAL-derived Pc curves. Comparison between RT/HFU and depositional settings show that RT1/HFU1 belongs to the lagoon and outer ramp depositional settings, RT2/HFU2 belongs to shoal and mid carbonate ramp environments and RT3/HFU3 belongs to a shoal environment.

Stratigraphic Sequence and Diagenetic Effects of the Upper Qamchuqa Formation in Khabaz and Kirkuk Oil Fields, Northern Iraq

The Upper Qamchuqa Formation was deposited in Zagros foreland basin in the north of Iraq during the Late Albian age. Two boreholes from Kirkuk oil field (K-229) and Khabaz oil field (Kz-4) are selected in the current study, where 100 samples of cores and cutting were used to determine diagenetic evolution of the Upper Qamchuqa Formation. Five major sub-environments can be diagnosed within the Upper Qamchuqa sequence, they are: shallow-open marine environment, semi-restricted marine environment, restricted marine environment, shoal and deep outer ramp environment. The diagenesis process are contain the physical or chemical variations in sedimentary rocks and sediments that happen after the deposition, where many diagenetic process effect on the Upper Qamchuqa Formation which are: Micritization, Cementation with three types (blocky, drusy,and syntaxial calcite overgrowth cement ), Dolomitization with three types too (scattered, Pervasive coarsely ,and saddle dolomite), neomorphism, recrystallization, silicification, dissolution and compaction (mechanical and chemical). There are four sedimentary cycles: cycle A extends from the upper part of the underlying Upper Sarmord Formation (TST) to the shallow open marine facies (HST) of the lower part of Lower Qamchuqa in k-229 which ended with shoal facies, cycle B on the other hand, shows a grain dominated facies where the carbonates buildup kept pace with the still relative sea level (keep up) during high stand which deposited under semi-restricted and restricted successively, cycle C shows a marked variation in thickness within the sections (K-229 and Kz-4); it is greatest thickness was noticed at k-229 where its lower part is mostly mud dominated in Kz-4, and cycle D shows a distinct variation in facies change from grain-rich to mud-poor lithology of restricted to semi-restricted facies in the East (k-229) to predominantly restricted marine conditions at the central area (Kz-4).

Study of Hydrocarbon Potentials and Sedimentary Properties of Ispartaçay Formation, Turkey

The idea of the current work was the combination of the organic geochemical analyses, and the study of sedimentology characteristics of the source rock samples collected from the Ispartaçay Formation (Cretaceous period) between the city of Antalya and the city of Isparta, southwestern Turkey. Total Organic Carbon analysis and Rock-Eval pyrolysis were performed on the 24 samples taken from the study area, in order to evaluate quantitatively, and qualitatively organic matter and thermal maturity to determine the potential for hydrocarbon production. As well as studying the petrographic features (component and diagenesis), microfacies analysis, and sedimentary environment of the Ispartaçay Formation. The successions of the Ispartaçay Formation are poor to fair organic matter content and consist of dark grayish limestone, marly limestone, shale, massive cherty limestone, and thin-bedded radiolarian limestone. Total Organic Carbon values indicate that Ispartaçay Formation rocks are fair potential. Besides this, most of the samples from the Ispartaçay Formation contain mature to pot-mature (Type III -Type IV) kerogen. Petrographically, the particle portion of the Ispartaçay sediments is composed mainly of radiolarians, and planktonic foraminifera, In addition to the presence of a proportion of benthic foraminifera, whereas the groundmass is composed of micrite. Generally, the present sediments are subjected to some diagenetic processes like silicification, cementation, and dissolution. The microfacies analysis revealed that the succession of the Ispartaçay Formation is composed of alternations of two major microfacies, namely lime mudstone and lime wackestone microfacies. Depending on the facies and petrographic evidence, Ispartaçay Formation represents sediments deposited in the mid to outer ramp environment.

Biostratigraphy, Microfacies, Sedimentary Environments and Sequence Stratigraphy of the Late Devonian–Carboniferous Deposits at the Anarak Section, Central Iran

AbstractThe Late Devonian–early Carboniferous deposits of the Anarak section in northeastern Isfahan, Central Iran, evaluated based on conodont biostratigraphy, sedimentary environment and sequence stratigraphy. According to the field observations, five lithological units were identified. Investigating the conodont fauna of the Late Devonian–Carboniferous (Mississippian–Pennsylvanian) deposits of Bahram, Shishtu, and Qaleh (Sardar 1) formations in Anarak section led to the identification of 67 species of 18 conodont genera, and accordingly 22 conodont biozones were differentiated. The correlation of sea‐level change curves, regarding to the conodont biofacies with the global sea‐level curve, demonstrates the relative correlation in the mentioned times due to the shallow condition of the central Iran basin compared to the European and American basins. The microfacies analysis led to the identification of 12 microfacies related to the open sea, bioclastic barrier, lagoon and tidal flat sub‐sedimentary environments in a homoclinal carbonate ramp environment. Based on sequence stratigraphy studies, three 3rd order sequences were identified. The first sequence, which is of the Late Devonian (upper part of the Bahram Formation, 32.5 m), the second sequence (12.5 m) is the Late Devonian (uppermost part of the Bahram Formation), and the third sequence (68 m) is the early Carboniferous (the Shishtu I Formation).

Biostratigraphy and Paleoecology of the Anah Formation in Kurdistan Region, Iraq

In the current study, biostratigraphy and paleoecology of the Anah Formation have been investigated.The study area is located in the Sulaimanyah Governorate, Kurdistan Region, Northeast Iraqwhere the Darzila section hasbeen sampled. Twenty-five species of larger foraminifera and skeletal fragments of coral, echinoid spine, pelecypods,and gastropods are described in seven samples collected from the Darzila section. Based on the distribution of the larger-benthic foraminifera andother skeletal grains, two assemblage biozones of the Late Oligocene–Early Miocene age have been recognized. According to the paleoecological parameters,such as temperature, nutrients, depth, and salinity in the study area, the Anah Formation hasdeposited the euphotic zone, abundant imperforate foraminifera are present, sub-tropical waters under oligotrophic to mesotrophic middle ramp environment with normal to a higher salinity inner ramp setting and at water depths that ranged from 40 m to 80 m, anda temperature about 18–25ºC.

Sedimentological, Diagenetic, and Sequence Stratigraphic Controls on the Shallow to Marginal Marine Carbonates of the Middle Jurassic Samana Suk Formation, North Pakistan

This study presents a thorough analysis of the sedimentology, diagenesis, and sequence stratigraphy of the Middle Jurassic Samana Suk Formation in the Hazara Basin of northern Pakistan. Focusing on two sections, namely Mera Rehmat and Por Miana, the research aims to unravel the complex geological processes within the formation. The examination of microfacies reveals nine distinct depositional textures, ranging from mudstone to wackestone, packstone, and grainstone, indicating various inner ramp environments such as open marine, lagoon, and coastal settings. Petrographic investigations shed light on diagenetic processes, including micritization, cementation, dissolution, compaction, neomorphism, and dolomitization. Six cementation types are identified, and the dolomitization patterns vary, providing insights into lagoonal environments and mudstone replacement. Sequence stratigraphic analysis uncovers intriguing patterns within the Samana Suk Formation. The high-stand system tract is characterized by mudstones, pelloidal grainstones, and dolomitized mudstones, indicating periods of high sea level. In contrast, the transgressive system tract displays ooidal grainstones, pelloidal packstones, and pel-bioclastic grainstones, representing transgression and inundation of previously exposed areas. A significant finding is the impact of diagenesis on reservoir quality parameters, specifically porosity, and permeability. Diagenetic processes, cementation types, and dolomitization patterns have significantly altered the pore network, highlighting the importance of considering diagenesis in assessing the Samana Suk Formation as a hydrocarbon reservoir. This research provides a comprehensive understanding of the sedimentology, diagenesis, and sequence stratigraphy of the Middle Jurassic Samana Suk Formation. The findings contribute to our knowledge of similar carbonate reservoirs globally, enhancing the exploration and development of hydrocarbon resources in comparable depositional environments.

The Eocene carbonate platforms of the Ghomaride Domain (Internal Rif Zone, N Morocco): a segment of the westernmost Tethys

The Eocene platform deposits in the Moroccan Ghomarides have been studied. These marine carbonate platforms were located in the westernmost Tethys approximately 30°N and 0°–10°W during the Cuisian to Bartonian. The study includes observations from fossiliferous assemblages (such as larger benthic foraminifera and colonial corals), their palaeoenvironment as well as rock texture and fabric. Eight microfacies were identified that represent different ramp environments in a ‘distally-steepened carbonate ramp’ type of platform. The studied deposits are organised into a transgressive succession composed of three sedimentary cycles: lower Cuisian, middle Cuisian and middle Lutetian to Bartonian. In the lower cycle, photic inner to mid ramp environments in mesotrophic conditions were prevalent. In the second cycle, photic inner ramp (sea-grass) to mid ramp environments in mesotrophic to oligotrophic conditions were observed. The upper cycle, which is more extensive and variable, represents mesophotic mid ramp to aphotic slope environments and changes gradually from oligotrophic to eutrophic conditions. During the Eocene, larger benthic foraminifera were dominant overtaking the zooxanthellate corals in the Tethys regions. Nevertheless, our study and the performed comparison with other Tethyan sectors have revealed that in some areas both coexisted in similar proportions. In some western Tethys regions close to the Atlantic Ocean, coinciding with areas influenced by upwelling currents, larger benthic foraminifera and coral build-ups were replaced by oyster reefs. The Ghomaride Domain represents an intermediate case between fossil assemblages of the northern Tethyan margin and eastern sector of the southern margin of the Tethys, with a dominance of larger benthic foraminifera but with a certain presence of corals as well. A good correlation exists between Eocene warm intervals and carbonate platform deposits in these domains. Contrarily, during cooling ones shallowing and gaps in the sedimentation are registered. Two anomalies have been detected in the Ghomaride Domain during Ypresian and Bartonian times indicating particular climatic conditions or local tectonic interferences.

Palaeobiogeography, palaeoecology, and sequence stratigraphy of the Upper Jurassic carbonate succession of the Lar Formation, central Alborz Zone, Iran

Foraminifera, ammonites, and calcareous dinoflagellates were used for stratigraphy and, together with microfacies, for the assessment of the palaeoenvironmental conditions of the Upper Jurassic deposits in the central Alborz Zone of northern Iran. The Lar Formation (Lar Fm.) in the Polur section is of latest Oxfordian to early Kimmeridgian age. The ammonite Subnebrodites planula and the calcareous dinoflagellate Colomisphaera nagyi have been introduced as new biomarkers of the lower Kimmeridgian in the central Neo-Tethys. The distribution of calcareous dinoflagellates reflects possible dispersal routes along a narrow seaway between the western Neo-Tethys and the Alborz Zone in the central Neo-Tethys. The Terebella-Crescentiella associations of the Lar Fm. represent a low-energy setting under dysoxic conditions in the Central Neo-Tethys Ocean. The benthic foraminiferal assemblages in this formation show a high dominance of infaunal taxa and r-selected strategists. This assemblage is reminiscent of eutrophic conditions and low oxygen levels in the lower part of the Lar Fm. Good preservation of the hexactinellid sponges in the upper part of the Lar Fm. also indicates an oxygen-minimum zone. Three third-order depositional sequences can be distinguished in the study area based on six microfacies. Depositional sequence 1 (DS1) is composed mainly of argillaceous limestone and medium- to thick-bedded limestone, corresponding to an outer ramp-to-middle ramp environment. Depositional sequence 2 (DS2) comprises breccia limestone and thick-bedded limestone facies in its lower part and thin-bedded limestone to massive limestone in its upper part. The breccia limestone facies may be associated with subaerial exposure and reworking of previously deposited sediment during a relative sea level fall. The thin-bedded limestone to massive limestone of DS2 consists mainly of bioclastic mudstone to wackestone (outer ramp). These represent an deep-water outer homoclinal ramp facies. Depositional sequence 3 (DS3) consists mainly of massive limestone to thick-bedded limestone with a bioclastic peloidal microbial Crescentiella packstone (middle ramp). The relative stratigraphic positions of DSs1–3 and sequence boundaries in the uppermost Oxfordian to lower Kimmeridgian of the Polur area show a fair match to the upper Oxfordian to lower Kimmeridgian sequences (JOx7, JOx8, JKi1 and JKi2) on the global sea level curve.

The Bolognano Fm in the south-eastern sectors of Majella and correlation with the north-western domain

This work investigated the evolution of the Bolognano Fm in the southern portion of the Majella Mountain and correlated it with the northwestern sector. Here the Bolognano Fm overlies unconformably the Eocene deposits of the S. Spirito Fm. The first unit is the Burdigalian Bryozoan Calcarenite, overlain by the Hemipelagic limestone to calcareous marls Burdigalian to Langhian in age. Lastly, the Tortonian to early Messinian interval is represented by different units. The first unit, which unconformably overlies the hemipelagic limestone to calcareous marls, is the Bioclastic calcarenites unit, which is fed by sediments produced within a euphotic inner ramp and accumulated in a deep environment. Upwards, the Marly limestones and laminated calcareous marls unit shows a mixing of deep water and shallow skeletal components deposited in an outer ramp. Moving southward, the Coralline algal limestone crops out, identifying a productive middle ramp environment. Lastly, a coral limestone unit was identified, where coral bioconstructions interfinger with seagrass meadows and ooidal shoals, in the euphotic zone. The Marly limestone and laminated calcareous marls testify for a deterioration of environmental conditions due to both global climate change as well as the approaching of the Apennines accretionary wedge, which triggered an increase of terrigenous runoff.

Facies Architecture And Depositional Marine Systems of the Yamama Formation in Selected Wells, Southern Iraq

The Yamama Formation is characterized by a wide geographic extension of southern Iraq. Microfacies analysis of this formation was studied in six wells distributed in six fields: Fayhaa, Sindbad, Siba, Zubair, Ratawi and West Qurna. This research aims to determine paleoenvironments by diagnosing biofacies and lithofacies. Miscellaneous marine fauna of foraminifera and calcareous algae, mainly green algae (dasycladacean.) and skeletal bioclasts from gastropods, pelecypods, bryozoans, sponge spicules, and echinoderms were found. Petrographic studies and well logs interpretations led to the identification of five main Microfacies ( Mudstone, Wackestone, Packestone, Grainestone and Rudstone and twelve submicrofacies (Foraminiferal-Lime mudstone submicrofacies, Argillaceous Lime Mudstone submicrofacies, Planktonic foraminiferal – Lime Wackestone submicrofacies, piculites/ Calcisphers – Lime Wackstone submicrofacies, Benthonic Foraminiferal -Lime wackestone/packestone submicrofacies, Algal (desycladecan) Lime wackestone submicrofacies, Algal-Lime packestone submicrofacies, Bioclastic/ Algal-Lime packestone submicrofacies, Algal/ Foraminiferal- Algal -Lime packstone submicrofacies, Peloidal poorly sorted grainstone with bioclasts submicrofacies, Intraclastic grainstone submicrofacies, Pesudo oolitic-Lithocodium aggregatum grainstone submicrofacies and finally Peloidal-intraclastic, and bioclastic grainstone submicrofacies). Microfacies are deposited in the lagoon, shoal, rudist biostrome and open marine gradient to middle and outer ramp environments. Vertical changes in microfacies with depth were reflected by lateral changes in marine depositional systems and the thickness of the formation. Shoal environments' microfacies are characterized by high thickness, while low thickness characterizes the open marine microfacies. The Yamama Formation was deposited on the low-angle homoclinic carbonate ramp, mainly in the inner and middle ramp, with outer ramp conditions in some parts of the formation.