Microfacies analysis and cyclostratigraphy of the upper cretaceous- lower paleogene succession of Bir Dakhl section,north eastern desert,Egypt

The Bir Dakhl section which is located in the southern Galala plateau, north eastern desert was sampled for microfacies analysis of the upper Cretaceous–lower Paleogene succession. Microfacies analysis led to the recognition of eight mixed clastic-carbonate facies types (black shale lithofacies MF-1, pure shale lithofacies MF-2, sandy shale lithofacies MF-3, marly shale lithofacies MF-4, mudstone microfacies MF-5, foraminiferal wackestone microfacies MF-6, bioclastic wackestone microfacies MF-7, and bioclastic packstone microfacies MF-8) of the studied interval. These microfacies can be grouped into three depositional environments: inner, middle and outer ramp. The interpreted depositional environments have been suggested to range from neritic to middle bathyal (~ 700 m). Based on cyclostratigraphy, five deepening upward cycles and three shallowing upward cycles have been differentiated in Bir Dakhl section.     

Sedimentary facies and diagenetic features of the Early Cretaceous Fahliyan Formation in the Zagros Fold-Thrust Belt,Iran

The Early Cretaceous Fahliyan Formation (middle part of the Khami Group), is one of the important reservoir rocks in the Zagros Fold-Thrust Belt. The Zagros Fold-Thrust Belt is located on the boundary between the Arabian and Eurasian lithospheric plates and formed from collision between Eurasia and advancing Arabia during the Cenozoic. In this study area, the Fahliyan Formation with a thickness of 325 m, consists of carbonate rocks (limestone and dolomite). This formation overlies the Late Jurassic Surmeh Formation unconformably and underlies the Early Cretaceous Gadvan Formation conformably at Gadvan Anticline. The formation was investigated by a detailed petrographic analysis to clarify the depositional facies, sedimentary environments and diagenetic features in the Gadvan Anticline. Petrographic studies led to recognition of the 12 microfacies that were deposited in four facies belts: tidal flat, lagoon, and shoal in inner ramp and shallow open marine in mid-ramp environments. The absence of turbidite deposits, reefal facies, and gradual facies changes show that the Fahliyan Formation was deposited on a carbonate ramp. Calcareous algae and benthic foraminifera are abundant in the shallow marine carbonates of the Fahliyan Formation. The diagenetic settings favored productioning a variety of features which include cements from early to late marine cements, micritization, dolomitization, compaction features, dissolution fabric, and pores. The diagenetic sequence can be roughly divided into three stages: (1) eugenic stage: marine diagenetic environment, (2) mesogenic stage: burial environment, and (3) telogenic stage: meteoric diagenetic environment.     

Facies Analysis, Sequence Stratigraphy and Diagenetic Studies of the Jurassic Carbonates of the Kohat Basin, Northwest Pakistan: Reservoir Implications

The present study deals with the depositional facies, diagenetic processes and sequence stratigraphy of the shallow marine carbonates of the Samana Suk Formation, Kohat Basin, in order to elucidate its reservoir quality. The Samana Suk Formation consists of thin to thick-bedded, oolitic, bioclastic, dolomitic and fractured limestone. Based on the integration of outcrop, petrographic and biofacies analyses, the unit is thought to have been deposited on a gentle homoclinal ramp in peritidal, lagoonal and carbonate shoal settings. Frequent variations in microfacies based sea-level curve have revealed seven Transgressive Systems Tracts (TSTs) and six Regressive Systems Tracts (RSTs). The unit has undergone various stages of diagenetic processes, including mechanical and chemical compaction, cementation, micritization, dissolution and dolomitization. The petrographic analyses show the evolution of porosity in various depositional and diagenetic phases. The fenestral porosity was mainly developed in peritidal carbonates during deposition, while the burial dissolution and diagenetic dolomitization have greatly enhanced the reservoir potential of the rock unit, as is further confirmed by the plug porosity and permeability analyses. The porosities and permeabilities were higher in shoal facies deposited in TSTs, as compared to lagoonal and peritidal facies, except for the dolomite in mudstone, deposited during RSTs. Hence good, moderate and poor reservoir potential is suggested for shoal, lagoonal and peritidal facies, respectively.     

Facies and depositional settings of the Middle Eocene-Oligocene carbonates in Kutch

Middle Eocene Fulra Limestone and Oligocene Maniyara Fort Formation represent platform carbonate deposits of Kutch at the north-western margin of India. These carbonates contain larger benthic foraminifera, including Alveolina, Assilina, Discocyclina, Lepidocyclina, Miogypsina, Nummulites and Spiroclypeus. This study presents paleodepositional and paleobathymetric interpretations for both formations using benthic foraminifera in combination with lithological association, sedimentary structures and early diagenetic features. The six carbonate facies comprising the Fulra Limestone indicate a depositional spectrum ranging from bar-lagoon to mid-ramp depositional conditions. It records several shallowing upward cycles, leading to emergence and formation of paleokarst. The four carbonate facies of the Maniyara Fort Formation represents deposition within the inner ramp setting in bar-lagoon and patch-reef environment, while intervening fine siliciclastics correspond to episodes of relative sea level fall. Nummulitic accumulations form low-relief bars within the fair weather wave base in both the formations. The depositional setting of the Paleogene carbonate in Kutch broadly resembles Eocene platformal deposits in the circum-Tethys belt.     

The inner ramp facies of the Thanetian Lockhart Formation,western Salt Range,Indus Basin,Pakistan

The Lockhart Formation from a major carbonate unit of the Paleocene Charrat Group in Upper Indus Basin, Pakistan represents a larger foraminiferal–algal build up deposited in a cyclic sequence of the carbonate ramp. The foraminiferal–algal assemblages of the Lockhart Formation are correlated here to larger foraminiferal biostratigraphic zone, i.e. Shallow Benthic Zone (SBZ3) of the Thanetian Age. Inner ramp lagoon, shoal and fore shoal open marine are three main facies associations represented by wackstone and packstone foraminiferal–algal deposits. These facies are present in a cyclic order and displayed a retrograding carbonate ramp indicating the Thanetian transgressive deposits associated with eustatic sea level rise. The correlation of the microfacies of the Lockhart Formation (Upper Indus Basin) and facies of the Dungan Formation (Lower Indus Basin) provide detailed configuration of the depositional setting of the Indus Basin during the time interval represented by the Thanetian Zone SBZ3.     

Sedimentary and organic facies investigation of the Gurpi Formation (Campanian–Paleocene) in southwest of Zagros,Iran

The Gurpi Formation in the southwest of Iran has been studied for microfacies and bulk organic geochemistry in order to elucidate its depositional environment and petroleum source rock characteristics. The obtained results ended up with four types of organic facies and three types of microfacies through the formation. Three microfacies types differentiated including Pelagic mudstone Wackstone, microbioclast Packstone and bioclastic Packstone reflect a distal outer ramp or basinal environment. Combination of palynofacies and organic geochemistry resulted in differentiation of four organic facies corresponding to organic facies B, BC, C and CD of Jones 1987. Detailed organic facies shows that the formation is characterized by low values of TOC, high percentages of amorphous organic matter and black phytoclasts, rare marine algae thereby representing a mixture of terrestrial and marine kerogen that confirm the formation was deposited in a distal anoxic to oxic condition. The formation shallows upward to the Microbioclast Packstone facies below the Lopha Member reaching its minimum depth in boundstones of this member in uppermost Campanian and then is followed by stagnant condition and high contents of organic matter in suboxic to anoxic condition that favoured accumulation of organic matter in early Maastrichtian. Organic geochemical and petrographical data indicate that the formation is not potentially suitable for petroleum production except for the minor interval (organic facies 2) in early Maastrichtian. Tmax values vary between 340 and 440 °C confirming immaturity trends indicated by Rock-Eval data.     

Lithologic and diagenetic attributes of the Sharwayn (Maastrichtian) and Umm Er Radhuma (late Paleocene–Eocene) formations and their significance to the K-T unconformity, Jabal Samhan area, Dhofar, Sultanate of Oman

The boundary separating Maastrichtian Sharwayn Formation from late Paleocene Eocene Umm Er Radhuma (UER) Formation in Dhofar, southern Oman, is characterized by a regionally extensive unconformity. The Jabal Samhan escarpment, north of Marbat-Sadh transect, preserves this unconformable boundary. This paper addresses the lithologic and diagenetic differences of the strata across the boundary and discusses their significance and link to the development of the upper Maastrichtian to lower Paleocene unconformity. The upper part of the Sharwayn Formation is characterized by lower thickly bedded, bioclastic, and peloidal mudstone to wackestone lithofacies overlain by a thick ledge (~5.5 m) of medium to coarse crystalline, (sucrosic) dolostone. Poorly preserved outlines of the framework grains suggest an original peloidal and bioclastic grainstone texture for the dolostone unit. The contact with the overlying UER Formation is sharp. The UER Formation is characterized by thickly bedded, bioclastic mudstone to wackestone overlain by coarse-grained, foraminiferal grainstone. The dolomitization process of the dolomite unit at the top of the Sharwayn Formation is envisaged to a shallow subsurface mixed meteoric and sea water diagenetic realm. This interpretation is supported by an inferred timing of dolomitization of latest Maastrichtian (post-Sharwayn Formation) to early Paleocene (pre-EUR Formation), preservation (although poorly recognizable) of the original depositional texture and diagenetic features that postdate the sucrosic dolomite. Pervasive dolomitization of the dolomite unit was controlled by its original grainstone texture, which permitted efficient percolation of the dolomitizing fluids. Correlation between the reference section of the formation and the section studied in this work raises the thickness of the formation to 28.5 m (relative to a thickness of 22 m at the reference section). Analysis of the new composite section suggests that deposition of the formation took place in a shallowing-upward setting where low-energy subtidal sediments (the lower limestone unit) were succeeded by a high energy sand shoal (upper dolomitized unit).This shallowing-upward succession is attributed to a third-order sea-level drop. The later is also recognized in many parts of the Arabian Peninsula, as well as globally, and interpreted as eustatic sea-level fluctuation.     

Microfacies, diagenesis, and depositional environments of the Tertiary carbonates of Usfan Formation in Haddat Ash Sham area, Western Arabian Shield, Saudi Arabia

The studied carbonates are present within the middle part of the Tertiary siliciclastic dominated succession in Haddat Ash Sham area. This succession consists of conglomerates, sandstones, siltstones, mudstones, and ironstones arranged in upward coarsening and fining cycles of intermittent depositional environments ranging from fluvial coastal plain to shallow marine. The carbonates represent deposition in slightly restricted depositional environments during periods of very low clastic input. The studied two carbonate sections show a pronounced lateral and vertical changes from predominantly dolostones in the west to mixed dolostones and limestones in the east. Both sections began by egg yellow dolomitic lime mudstones and fine crystalline dolomite which indicate the formation of dolomite by late depositional to early diagenetic recrystallization of precursor Fe and Mg lime mud. During this time period, the western part of the study area continues in the deposition of Fe and Mg lime mud in slightly restricted depositional environments and formation of interbedded fine and coarse crystalline dolostones in coarsening-upward cycles. In the eastern part, the depositional environments become deeper and more circulated with short-lived periods of fluctuation in sea level and hence the deposition of foraminiferal wackestone, bioclastic packstones, and bioclastic rudstone in coarsening and shallowing-upward cycles. Both the western and eastern parts of the study area are terminated by characteristic yellow coarse crystalline phosphatic dolomite which indicate ultimate stages of shoaling and increasing the level and concentration of phosphorous in the restricted water and hence the formation of in situ and reworked phosphatic components. The diagenetic processes affected the dolostones and limestones microfacies associations include: dolomitization of Fe and Mg-rich lime mud, hematitization, calcitization, gypsification, and phosphatization of dolomite. Neophormation and recrystallization of micritic matrix and micritic intraclasts as well as shell fragments are the main diagenetic processes affected the limestones.     

Biostratigraphy,Depositional and Diagenetic Processes in Carbonate Rocks from Southern Lebanon: Impact on Porosity and Permeability

Carbonate rocks contain prolific hydrocarbon reserves all over the world, particularly in the Middle East. For exploration and production strategies, it is essential to understand carbonate reservoirs in terms of their internal characteristics, depositional environment, relative age, diagenetic processes and impact on petrophysical properties. This study has been performed on exposed Cretaceous, Paleocene and Miocene marine carbonate sedimentary sequences in two localities (Maghdoucheh and Qennarit) near the city of Sidon (Southern Lebanon). It represents the first comprehensive study that takes into consideration the carbonate reservoir facies, diagenetic history and reservoir quality in the area. Rocks at Maghdoucheh are mainly dominated by limestone beds showing sedimentary structures and erosive bases alternating with microfossil-rich silty marls, related to a shallowing upward sequence in a restricted marine platform environment. Shells of benthic foraminifera and mollusks dominate the fossil assemblage extracted from the studied rocks. The microfossil and nannofossil assemblage detected in the Maghdoucheh sections indicates a middle Miocene age. Rocks at Qennarit are composed of mudstone/wackestone limestone beds rich in planktonic foraminifera and nannofossils related to open marine conditions. Based on the nannofossil content, rocks from Qennarit 1 and 2 are Paleocene and Cretaceous in age, respectively. Four main types of microfacies have been identified, i.e. (1) microbioclastic peloidal calcisiltite, (2) pelagic lime mudstone and wackestone with planktonic microfossils, (3) grainstone/packstone with abundant foraminifera and (4) fenestral bindstones, mudstones and packstones with porostromate microstructures. The porosity-permeability (poro-perm) analysis of representative samples reveals moderate to good porosity but very low permeability. This is mainly due to the presence of large moldic pores that are isolated in nature. The diagenetic features are dominated by micritization and dissolution (both fabric selective and non-fabric selective). Among all diagenetic features, dissolution in both localities contributes to porosity enhancement, while micritization, cementation, compaction and the filled fractures have negative impacts on permeability; hence the overall reservoir quality.     

湖北省栖霞组沉积环境-沉积旋回及层序地层划分

根据岩石结构、构造及生物碎屑含量等特征,将本区栖霞组分为3类微相:A.生物碎屑灰岩;B.灰泥岩;C.具水平层纹的含炭质泥质细生物屑灰岩(泥灰岩).在剖面上,这3类微相组合成CA、CB或以C微相为主的韵律.不同韵律纵向上有规律的叠置常构成厚约10余米的沉积旋回.根据沉积旋回在垂向上的更替,在本区栖霞组内可识别出4次较大的海平面变化,周期约3My.通过与同期泛大陆北方各大陆上所发育的旋回层的对比,作者认为本区栖霞组内的4次海平面变化属三级海平面变化,对应4个三级层序,为全球冰川性海平面变化的结果,可与同期北美大陆上海平面变化曲线对比.     

重庆开县上二叠统长兴组红花生物礁成礁模式

通过对红花生物礁露头的精细解剖和微相分析,研究了礁的内部构成和成礁模式。红花生物礁发育3期礁体旋回：礁A、礁B和礁C。礁A由生屑泥晶灰岩和骨架岩构成;礁B由生屑泥晶灰岩、粘结岩、骨架岩和生屑灰岩构成;礁C由粘结岩、骨架岩和生屑灰岩构成。红花生物礁造礁生物有钙质海绵、钙藻类、苔藓虫和水螅类,附礁生物为有孔虫、腕足类、双壳类、腹足类和棘皮动物等。单个礁体内,由下往上的生物演化为：腕足类+双壳类+有孔虫组合→钙藻类→钙质海绵+水螅类+钙藻类+苔藓虫组合→生物碎屑;岩性演化为：生屑泥晶灰岩→粘结岩→骨架岩→生屑灰岩。礁B的生屑滩内生屑间为泥晶充填,生屑分选、磨圆较好,是由相邻的高能生屑滩侵蚀搬运到礁B侧翼低能区沉积形成。3期礁都发育在碎屑滩上,礁A为低能环境下形成的礁,礁B和礁C在礁A形成的高地上成礁,为高能环境礁;单个礁体的完整成礁模式为：在浅滩之上,钙藻类大量生长、粘结吸附颗粒固结基底,钙质海绵和钙藻类在硬质基底上繁茂生长,形成具有抗浪格架的生物礁,礁体暴露水面死亡后遭波浪、水流改造形成生屑滩。     

羌塘盆地昂达尔错地区白云岩成岩结构特征及其成因意义

通过薄片、阴极发光、背散射和扫描电镜等特征分析,根据白云石的晶体颗粒的形态、大小、晶面、接触关系等特征,兼顾白云石的成因信息,将羌塘盆地昂达尔错地区古油藏中白云石划分为粉-细晶曲面它形结构、粉-细晶曲面它形雾心亮边结构、细-中晶直面半自形-自形结构、细-中晶直面半自形-自形雾心亮边结构、细-中晶直面半自形-自形环带结构、中-粗晶曲面它形结构。成岩结构特征反映了成岩期不同成岩流体作用叠加的多成因模式,包括准同生阶段蒸发咸化海水成因、浅埋藏阶段蒸发咸化海水的回流或下渗扩散交代成因、中-深埋藏阶段埋藏白云石化成因以及深埋藏阶段与构造运动相关的热液交代成因。白云岩中常见的残余粒屑结构和藻纹层结构反映出原始的浅滩相、潮坪相及生屑滩相等高能沉积环境更有利于该区白云岩的形成,原始的沉积微相控制着白云岩化作用的发育和白云岩的空间展布。     

Facies, depositional environment and diagenetic processes of the early Mid-Miocene Jeribe Formation, Central and Southern Iraq

The Jeribe Formation (Early Middle Miocene) in the central and southern Iraq consists mainly of shallow marine carbonates. Many microfacies have been identified: mudstone, wackestone, packstone, and grainstone with seven submicrofacies. Four major depositional cycles were determined. Microfacies developments and their distribution are controlled by cyclicity and relative sea level fluctuations. The Allochems in the Jeribe Limestone Formation are dominated by bioclasts. Peloids, ooids, and intraclasts are less abundant. The fossils are represented by benthonic forams and very rare planktonic forams. Calcite and dolomite are the predominant mineral components of Jeribe Formation. The carbonates of Jeribe have been affected by a variety of diagenetic processes such as compaction, dissolution, cementation, neomorphism, dolomitization, anhydritization, and silicification. By using the lithofacies association concepts, the depositional model of the Jeribe Formation environment was built. The Jeribe was deposited in open to restricted platforms which indicated lagoonal environment with warm and restricted-open circulation and the lower part (in well Hemrin-2) was deposited in foreslope environment.     

Facies analysis and depositional environments of the Bhander Limestone (Precambrian), southeastern Rajasthan and adjoining Madhya Pradesh,India

Special interest is attached to the Bhander Limestone because it is the only calcareous formation in the very thick elastic sequence of Precambrian age, designated informally as the “Upper” Vindhyan. The sedimentology of the Bhander Limestone was studied in the Mandalgarh-Singoli area of southeastern Rajasthan and adjoining Madhya Pradesh with a view to interpreting the depositional environments of the formation. This study has an important bearing on the exploration for oil in India and presents one of the few examples of Precambrian limestones of which thorough modern sedimentological analysis has been made.The Bhander Limestone comprises micritic limestones, crystalline dolostones, siltstones and shales that show desiccation structures (horizontal fenestrae, bird's-eye structures, mud cracks), very shallow small channels filled with flat-pebble breccia, algal lamination, palisade structure, and occasional ripple marks, ripple lamination and micro-cross-lamination. The major petrographic constituents are micrite, intraclasts, sparry-calcite cement, pseudospar and replacement dolomite. Seven environmentally significant microfacies have been recognized: micrite, silty micrite, graded micrite, dolomitized micrite, neomorphosed micrite, intrasparrudite and intramicrudite.The Bhander Limestone Formation has been divided vertically into four lithofacies: red argillaceous micritic limestones (lithofacies A), interlaminated blue micritic limestones and red dolomite (lithofacies B), olive calcareous shales (lithofacies C), and black micritic limestones (lithofacies D). Each lithofacies is characterized by certain megascopic sedimentary features and microfacies. The various lithofacies have been interpreted as representing deposition in the different subenvironments of a generally low-energy, marginal marine environment comprising tidal flats and lagoons. The vertical changes from one lithofacies to another are interpreted as reflecting the change from one subenvironment to another brought about by the landward shifting of the boundaries of these subenvironments in response to a transgression.     

Combination Patterns and Depositional Characteristics of Ordovician Carbonate Banks in the Western Tarim Basin,China

The combination patterns and depositional characteristics of the carbonate banks are investigated based on outcrop sections, thin sections, and carbon isotopes of Ordovician in the western Tarim Basin, China. Four carbonate bank combination patterns are deposited in the Ordovician, western Tarim Basin, including: Reef-Bank Complex (RBC), Algae-Reef-Bank Interbed (ARBI), Thick-Layer Cake Aggradation Bank (TLCAB), and Thin-Layer Cake Retrogradation Bank (TLCRB). All combination patterns show clear periods vertically. The RBC is mainly composed of reefs and bioclastic banks, and the dimension of the RBC depends on the scale of the reefs. Bioclastic banks deposits surround the reefs. The range of the ARBI is determined by the scale of algae-reefs, algae peloid dolomite microfacies and algal dolomite microfacies deposit alternating vertically. TLCAB and TLCRB are deposited as layer-cakes stacking in cycles and extending widely with cross bedding developed. The grains of TLCAB and TLCRB are diverse and multi-source. With the impacting of relative sea level change, biological development and geomorphology, the ARBI, TLCAB or TLCRB, RBC are successively developed from the Lower Ordovician Penglaiba Formation to the Middle Ordovician Yijianfang Formation. The depositional environment analysis of Ordovician indicates that the RBC and ARBI can form effective oil and gas reservoirs, and the TLCAB and TLCRB have the potential to form the huge scale oil and gas reservoirs and to be the crucial targets of exploration for the Ordovician carbonate banks in the future.     

An insight into the Eocene tide-dominated estuarine system: implications for palaeoenvironmental and sequence stratigraphic interpretations

This article describes a complete sedimentary succession of an ancient macrotidal tide-dominated estuarine system based on the detailed outcrop study. The Eocene siliciclastic sedimentary facies of Ameki Group in the south-eastern Nigeria provides a record of the sedimentary response to an initial regression, followed by marine incursion (transgression) into the Niger Delta Basin. These sedimentary successions are analogues to the subsurface petrolific Niger Delta lithostratigraphic units. Seven facies associations (FA 1 to FA 7) are documented in the study area and the sediments are interpreted as fluvial channel, tidally influenced fluvial channel, tidal channel, tidal flats, supratidal, tidal sand bar and estuarine embayment (open estuarine) deposits. The occurrence of low diversity ichnofaunal assemblages and/or localised high-density monospecific ichnofossil assemblages indicates brackish-water condition typical of estuarine settings. The suites of assemblages include Scoyenia, Skolithos, Cruziana, mixed Skolithos-Cruziana, Glossifungites, Psilonichnus and Teredolites ichnofacies. A complete depositional sequence is encountered in the Eocene Ameki Group which consists of the lowstand, transgressive, highstand and falling stage systems tracts. This depositional succession was most probably controlled by relative sea level changes, sediment supply, accommodation and regional tectonics which affected the development of Niger Delta Basin.     

Primary depositional and diagenetic features in the banded iron formation and associated iron-ore deposits of Noamundi,Singhbhum district,Bihar, India

The Banded Hematite Jasper (BHJ) Formation of Noamundi region in Bihar, belonging to the lower part of the Iron Ore Group of early Precambrian age (c. 2900–3200 Ma), exhibits numerous primary depositional and diagenetic features, both in BHJ as well as the associated iron ore deposits. Observed primary depositional features include banding and bedding of different geometric-types, surface-markings including interference ripple-marks, current crescents, linear markings, scour-and-fill structures, etc. and within-mass microstructures such as spherulites, granules, discs and maculose cylindrical bodies. Diagenetic features, such as fabric changes, micro-dessication structures, gravity-density features, etc. and motion-and-disruption features of various kinds are also seen. The significance of various features in terms of probable mode and environments of deposition of BHJ and the iron ore beds has been considered. In general, shallow water environment of deposition in a region proximal to the shoreline with a rather steep paleoslope of the shelf has been surmised.     

重庆万盛中二叠统碳酸盐岩微相研究

重庆市万盛区中二叠统碳酸盐岩分布广泛，露头发育良好，发育有10种微相类型，即灰泥石灰岩、筵粒泥灰岩、球粒生物碎屑粒泥灰岩、生物碎屑内碎屑泥粒灰岩、荷叶藻泥粒灰岩、鲕粒内碎屑泥粒岩/颗粒岩、小有孔虫泥粒灰岩、生物碎屑泥粒灰岩、绿藻颗粒灰岩和生物碎屑颗粒灰岩。综合分析表明，研究区中二叠统形成于滨岸、局限台地和开阔台地环境，据此建立了沉积相模式。     

Acervulinid macroid and rhodolith facies in the Eocene Nummulitic Limestone of the Dauphinois Domain (Maritime Alps,Liguria, Italy)

The Eocene Nummulitic Limestone of the Dauphinois domain in the Argentina Valley (Maritime Alps, Liguria, Italy) is characterized by the local presence of carbonate ramp facies rich in acervulinid macroids, rhodoliths and larger foraminifera. The development of these particular facies is mainly controlled by palaeomorphology of the substratum, tectonics, type and amount of terrigenous supply and global sea level changes.

The Upper Cretaceous to Eocene succession outcropping in the Argentina Valley shows differences in facies and age if compared to the typical succession of the Maritime Alps:

• the Cretaceous substratum is younger (early Maastrichtian) and is followed by an unconformity that is interpreted as a submarine discontinuity surface;
• the first Eocene carbonate deposits are older (late Lutetian);
• the Nummulitic Limestone is characterized by the development of carbonate facies deposited in a deep infralittoral-circalittoral setting of a carbonate ramp, sheltered from terrigenous input; in these facies encrusting foraminifera (Solenomeris) replace calcareous red algae in nodules similar to rhodoliths (acervulinid macroids);
• the Nummulitic Limestone is thicker than usual, reaching 110–160 m of thickness.

The Eocene tectonostratigraphic evolution can be summarized as follow: (1) synsedimentary tectonic activity that causes the development of a carbonate ramp with an adjacent structural trough where ramp-derived bioclastic material is deposited (late Lutetian); (2) interruption of the tectonic activity and uniform deposition of deep circalittoral sediments, characterized by deepening upward trend (late Lutetian?); (3) regression indicated by an abrupt shallowing of the depositional setting (Bartonian); and (4) deepening of the depositional setting, ending with the drowning of the carbonate ramp (late Bartonian).The evolution of the Eocene Argentina Valley succession is strongly influenced by tectonics related to the Alpine foreland basin development, but locally, and during definite time intervals, the global sea level changes could be recorded by the sediments during periods of stasis in tectonic activity. The regressive events recognized in the studied succession could be related to the sea level fall reported in the global sea level curve during the Bartonian.     

Facies mosaic and diagenetic patterns of the early Devonian (Late Pragian–Early Emsian) microbialite‐dominated carbonate sequences,Qasr Member,Jauf Formation,Saudi Arabia

The Al‐Jawf area of northern Saudi Arabia provides spectacular outcrops of Early Devonian carbonate bioherms in the Wadi Murayr and Dumat Al‐Jandal areas. These carbonate bioherms belong to the Qasr Member of the Late Pragian–Early Emsian Jauf Formation (~405 Ma) and are surrounded by a bioclastic carbonate succession. The Qasr Member is the first major carbonate unit of the Palaeozoic succession in Saudi Arabia that mainly consists of microbialite carbonates and metazoan reefs exhibiting distinct mound features. These bioherm complexes and their associated carbonate facies are pervasively dolomitized. Stratigraphic, petrographic and geochemical analyses were conducted to determine the facies distribution and interpret their depositional and diagenetic processes. A total of 11 facies are identified from a range of depositional environments within a carbonate platform system, ranging from tidal flats, lagoon, shoal, patch reefs to reef front. The main diagenetic processes are carbonate cementation and dolomitization. Dolomitization occurred as both fabric preserved (mostly in grain‐dominated facies) and fabric destructive (mud‐dominated facies). The microbialites and coralline sponges facies show poor reservoir with visual porosity less than 5%, but this succession may have a potential to serve as a good source for the underlying and overlying facies. Ooid and peloidal grainstone facies show fair to good visual porosity that locally exceeds 10% with intergranular porosity as the dominant type. However, in the most studied samples, vuggy and intraparticle porosities are observed as the dominant type. Copyright © 2015 John Wiley & Sons, Ltd.