Foraminiferal Packstone Research Articles

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.

Microfacies Analysis and Depositional Environment of the Mishrif Formation at Selected Wells in E Oilfield, Southren Iraq

The Mishrif Formation is an important succession that was deposited during the Cenomanian–Early Turonian. More than 79 thin sections of core in addition to well log data for the Mishrif Formation from 2 boreholes within the E oilfield (E-1, and E- 2) were used to determine the different associations facies to interpret the depositional environment of the Mishrif Formation. Six major microfacies were diagnosed the Mishrif Formation, Mudstone, Wackestone, Packstone, Grainstone, Boundstone, and Rudstone and ten submicrofacies include: Bioclastic Packstone submicrofacies with rich Echinodermat, Coral and Rudist fragment and high Dolomitization, Rudstone submicrofacies with large Rudist fragment and vug porosity , Boundstone submicrofacies with very large coral, Plankton Foraminiferal Packstone submicrofacies withe Globigerinelloides and Calcispheres, Bioclastic Wackestone to Packstone submicrofacies with dolomite and calcareous algae, Peloidal Packstone with coral, pillites, pieces of Rudist and Separate-Vug pore, Bioclastic Packstone to Grainstone submicrofacies, Peloidal to Bioclastic Packstone submicrofacies, Benthonic Foraminiferal Mudstone submicrofacies, Rudist fragmented Mudstone. These microfacies were deposited in restricted, shoal, shallow open marine, rudist bioherm, and deep marine environments.

Implication of the diagenetic evolution, litho- and microfacies types on the storage capacity of the carbonate rocks in West Esh El Mallaha area, SW onshore Gulf of Suez, Egypt

The present study shed the light on the main litho- and microfacies of the Upper Cretaceous- Miocene sequence exposed at West Esh El Mallaha area (Egypt) with more focus on the carbonate rocks. Delineating the implication of the recorded facies and the diagenetic processes on the storage capacity of the entire sequence is among the prime targets of this study. The studied Esh El Mallaha sequence includes the Nubia, Duwi, Dakhla, Tarawan, Esna, Thebes, Abu Gerfan, Gharamul and Gemsa Formations, from older to younger respectively. The carbonate rocks exposed in the studied sequence were deposited in shallow marine, lagoonal outer ramp and environments with high energy and/or open marine conditions. These depositional environments are represented by ten microfacies types: lime-mudstone, foraminiferal wackestone, bioclastic wackestone, algal wackestone/packstone, foraminiferal packstone, bioclastic packstone/grainstone, phosphatic packstone/grainstone, oolitic and bioclastic grainstone, oyster rudstone and bafflestone. Aggrading neomorphism, calcite cementation (drusy calcite, pseudosparite, and poikilotopic calcite), silicification (silica cementation in the form of amorphous silica, micro-quartz, chalcedony and spherulitic quartz), compaction, clay mineral alteration, dissolution, fracturing and dolomitization are the main diagenetic processes recorded in the studied section.The storage capacity of the different rock units were primarily obliterated by multi-cementation phases by calcite, silica and/or clay minerals. Nonetheless, fracturing, dissolution and dolomitization enhanced the storage capacity and can be considered the main storage capacity-enhancing features in the studied sequence. These diagenetic features are more abundant in the studied Duwi, Thebes, Abu Gerfan and Gharamul Formations. This achievement indicates that the studied Upper Cretaceous- Miocene carbonate sequence may be promising in its subsurface extensions in the Gulf of Suez and other analogues in Egypt.

Improving carbonate reservoir characterization by applying rock typing methods: a case study from the Nam Con Son Basin, offshore Vietnam

Understanding the permeability-porosity relationships is the key to improving reservoir prediction and exploitation especially in carbonate reservoirs, which are known for their complex textural and diagenetic variation. Rock type classifications have long been proven to be an effective technique for establishing permeability- porosity relationships, enhance the capability to capture the various reservoir flow behavior and prediction for uncored reservoir zones. This study highlights some of those practical and theoretically-correct methods, such as Hydraulic Flow Unit (HFU); Global hydraulic element (GHE), Winland’s R35 method, Pittman method, Lucia method. They are proposed and tested for identification and characterization of the rock types using a database of 555 core plugs from the Miocene carbonate reservoir in the Nam Con Son basin. It is a large isolated carbonate build-up structure which were deposited within a shallow marine platform interior and are dominated by coral, red algal and foraminiferal packstones, wackestones and grainstones. Hydrocarbons in this reservoir have been found in the upper most part of the late Miocene formation. Conventional core data were first used to define and display the cross plot of permeability and porosity. Different charts and cutoff thresholds were used to classified, defined number of rock type and the linear and non-linear equations were established. The predicted core permeability was calculated using different methods and compared with the actual core permeability for each rock type. The predicted reservoir rock type and permeability predictions of HFU method was recognized to give better matching of measured core permeability with coefficient of more than 89%.

Topography, sedimentology, and biochronology of carbonate deposits on seamounts in the JA area, northwestern Pacific Ocean

AbstractSedimentological and biochronological analyses were undertaken on carbonate deposits from 20 seamounts belonging to the Marcus–Wake Seamount Group, the Magellan Seamounts, and the Marshall Islands Seamounts in the JA area, northwestern Pacific Ocean. Deposition of carbonates on the JA seamounts varied markedly with age. The oldest carbonate deposits are Lower to middle Cretaceous shallow‐water limestones containing mollusks (including rudists), scleractinian corals, and calcareous sponges. Upper Cretaceous and Paleocene carbonates are rare, and no Oligocene carbonates may exist. In contrast, Eocene foraminiferal packstones are widespread, and Miocene–Pleistocene foraminiferal ooze covers the JA seamounts. The limited occurrence of Paleogene carbonate deposits on the JA seamounts is consistent with global observations (i.e., a paucity of Paleogene carbonates). The Cretaceous–Eocene carbonates have been phosphatized, whereas Miocene and later limestones have not. This fact, along with the results of previous studies, suggests that carbonate rocks on seamounts were phosphatized globally during the Oligocene. Upwelling of nutrient‐rich bottom waters during this time is likely responsible for the limited occurrence of Oligocene carbonate rocks on the JA seamounts. The thicknesses of the pelagic caps, which consist mainly of Miocene and younger foraminiferal oozes, varies among the seamounts and depends at least partly on the topography of the top of the seamount.

Diagenetic overprint on porosity and permeability of a combined conventional-unconventional reservoir: Insights from the Eocene pelagic limestones, Gulf of Suez, Egypt

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

Characteristics of Carbonate Facies and Depositional Environment of Tapak Formation in the Ajibarang Area, Central Java, Indonesia

The limestone of Tapak Formation is well exposed in the Ajibarang area and its surroundings, Central Java, Indonesia. Very intensive mining activity is a very serious threat to this limestone. Hitherto, the geological study on this limestone is still very limited. The objective of this study was to investigate the characteristics of these limestone facies and their sedimentation. This research consists of field and laboratory (petrography and micropaleontology) analysis. The results showed that the limestone of the Tapak Formation consisted of three facies: planktonic packstone, algal foraminifera packstone, and foraminifera algal packstone. Planktonic packstone facies are composed of bioclastic fragments in a micro matrix. The fragments were dominated by planktonic foraminifera consisting of a genus of Globigerina, Globigerinoides, Globorotalia, and Orbulina. Benthic foraminifera and radiolarians were also identified. Sedimentation from planktonic packstone facies was estimated to occur in the deep marine environment. Algal foraminiferal packstone facies are composed of bioclastic fragments in a micro matrix. Large algae and large foraminifera dominated the fragments. Algae were from the type of red algae, consisting of Lithophyllum, Corallina, and Rhodolite. Foraminiferal algal packstone and algal foraminiferal packstone that were observed in the studied area were characterized by the abundance of large foraminifera and interpreted to be deposited in the upper reef slope. We interpreted that the limestone in the study area was deposited in the upper reef slope to the lower reef slope environments. We hope that the information we provided here is useful for petroleum system study in Central Java, Indonesia.

Source Rocks’ Potentiality of the Sargelu Formation (Middle Jurassic) in the Taq Taq Oilfield, Kurdistan Region, Iraq

Thirty rock samples were selected from the well Tq-1 that penetrated the Jurassic beds in the Taq Taq Oilfield to be studied the source rock potentiality of the Sargelu Formation. The formation is characterized by three types of microfacies, namely, foraminiferal packstone, grainstone microfacies, fossiliferous packstone microfacies, and foraminiferal wackestone which were deposited in an environment extending from middle to outer carbonate ramp. An average of 3.03 wt.% of total organic carbon was obtained from a Rock Eval pyrolysis analysis carried out on 24 selected rock samples. The petrographic analysis for such organic matters revealed that they are of kerogen types III and IV and they are currently in a post-mature state. Pyrolysis parameters showed that limited generation potential was remained for these sources to expel generated hydrocarbons. The palynological study showed that Amorphous Organic Matter forms the highest percentage of organic matter components with more than 70%, followed by phytoclasts with 10 – 25 % and palynomorphs of less than 10%. The organic matters within the Sargelu Formation are deposited at the distal part of the basin under suboxic to anoxic condition. The color of the organic matter components, examined under transmitted light, showed Thermal Alteration Index values between 3+ and 4-. Such values may indicate that these organic matters are thermally at the end of the liquid oil generation zone and beginning of condensate-wet gas generation zone. The thermal maturity of the Sargelu Formation depending on the calculated VRo% revealed that the formation in the studied oilfield is currently at the peak of the oil generation zone. The Sargelu Formation in the studied field is considered as an effective source rock, as it has already generated and expelled hydrocarbons.

Depositional environment of Eocene oil shales of Wadi Shallala Formation from northern Jordan

Oil shale deposits of the mid-Eocene Wadi Shallala Formation in northern Jordan consist of organic-rich limestones and chalks. These organic-rich deposits are exposed at the surface near Wadi Ash Shajara, in a 12-m-thick outcrop. For this study, a total of 21 oil shale samples were analysed for bulk elemental geochemistry, inorganic geochemistry, organic geochemistry and microfacies analysis. Three microfacies types were recognised: pelagic mudstone/wackestone, foraminiferal packstone and bioclastic packstone/wackestone. The observed cyclicity of these microfacies in the study area indicates fluctuations in depositional conditions in Neo-Tethys during the mid-Eocene. A shallow-water, calm, restricted marine environment with limited water circulation and low energy currents evolved into a deeper-water environment with open circulation at or just below the wave base. Wadi Shallala Formation in Wadi Ash Shajara composes mainly of chalk (CaCO3 = ~92 wt%) with a TOC of up to 5 wt % and comprises abundant calcareous nannofossils, foraminifera and ostracods as well as non-clastic components like calcitic fragments. The sulphur content of the analysed samples is significant (1.24 wt %) and is associated with the organic matter. Redox-sensitive elements (Fe, Ni, Zn, S and Zr) are enriched in the oil shale samples, indicating an anoxic depositional environment fluctuating between euxinic and sub-euxinic. These fluctuations in depositional conditions of the basin are a result of many factors such as climate, and tectonisms affected deposition of oil shales during Middle Eocene time.

An integrated multi-proxy study of cyclic pelagic deposits from the north-western Tethys: The Campanian of the Postalm section (Gosau Group, Austria)

The Upper Cretaceous Postalm section in the Northern Calcareous Alps (Austria) exposes pelagic deposits of the northwestern Tethys whose cyclostratigraphy and palaeoenvironments were examined in this study.The section displays rhythmic deposits of Santonian to late Campanian age (Gosau Group). The Santonian/Campanian transition is characterised by condensed greyish carbonates, while the younger deposits are composed of reddish foraminiferal packstones displaying distinct limestone-marl alternations. A biostratigraphic framework based on planktonic foraminifera and calcareous nannofossils is supported by carbon and strontium isotope stratigraphy as well as magnetostratigraphy. The carbon isotope data allow to correlate the Postalm section to other Tethyan reference sites and to identify δ13C events, such as the Late Campanian Event. Spectral analyses of three independently assessed proxies (δ13C, Fe content and the thickness of limestone/marl couplets) in the upper, continuously exposed section part identified 17 to 18 405 ka cycles spanning the mid to upper Campanian (Contusotruncana plummerae to Gansserina gansseri Zones or CC21/UC15c to CC23a/UC16 nannofossil zones).

Sedimentary facies and paleoenvironmental interpretation of the Oligocene larger-benthic-foraminifera-dominated Qom Formation in the northeastern margin of the Tethyan Seaway

The well-exposed outcrops of the Bujan, northern Abadeh, and Varkan stratigraphic sections of the Qom Formation in the Iranian part of the “northeastern margin” of the Tethyan Seaway were characterized by abundant biogenic components dominated by foraminifers, coralline red algae, and corals. The Qom Formation is Rupelian–Chattian in age in the study areas. Based on the field investigations, depositional textures, and dominant biogenic components, fifteen (carbonate and terrigenous) facies were identified. These facies can be grouped into four depositional environments: open marine, open lagoon, restricted lagoon, and continental braided streams. The marine facies were deposited on a ramp-type platform. The euphotic inner ramp was characterized mainly by imperforate foraminifera, with co-occurrence of some perforate taxa. These facies passed basinward into a mesophotic (middle) ramp with Neorotalia packstone (F5), coral, coralline algae, perforate foraminiferal packstone (F4), and coral patch reefs (F7). The deeper, oligophotic ramp facies were marly packstones with planktonic and hyaline benthic foraminifera, including large lepidocyclinids and nummulitids. The abundance of perforate foraminifera and the absence of facies indicating restricted lagoonal or intertidal settings suggest that the Varkan section was deposited mainly in open marine settings with normal salinity. The prevalence of larger benthic foraminiferal and red algal assemblages, together with the coral facies, indicates that carbonate production took place in tropical–subtropical waters.

Middle Eocene regressive phase evident in the uppermost part of the Harudi Formation, Kachchh Basin, western India

The present study focuses on the presence of gypsiferous foraminiferal packstone (GFP) facies which defines the top of the Lutetian aged Harudi Formation and separates it from the overlying Bartonian aged Fulra Limestone Formation. This facies has been reported from Harudi and Lakhpat areas of Kachchh District and may serve as a regressive stratigraphic boundary between the Harudi and Fulra Limestone Formations that had been previously considered as conformable succession. Here, the gypsum, halite and iron oxide minerals (hematite and/or goethite) are precipitated as secondary minerals in the desiccation cracks developed in the foraminiferal packstone facies. The precipitation of gypsum, halite and hematite/goethite along with desiccation cracks is suggestive of the oxidizing condition and would have been possible in supratidal environment under warm and dry semi-arid to arid climatic conditions. Thus, it is inferred that the cracks would have been formed during subaerial exposure of the foraminiferal packstone facies during relative sea-level fall.

Shipworm bioerosion of lithic substrates in a freshwater setting, Abatan River, Philippines: Ichnologic, paleoenvironmental and biogeomorphical implications

Teredinid bivalves, commonly referred to as shipworms, are known for their propensity to inhabit, bioerode, and digest woody substrates across a range of brackish and fully marine settings. Shipworm body fossils and/or their borings, which are most allied with the ichnotaxon Teredolites longissimus, are found in wood preserved in sedimentary sequences ranging in age from Early Cretaceous to Recent and traditionally they have been regarded as evidence of marginal marine or marine depositional environments. Recent studies associated with the Philippine Mollusk Symbiont International Collaboration Biodiversity Group (PMS-ICBG) expedition on the island of Bohol, Philippines, have identified a new shipworm taxon (Lithoredo abatanica) that is responsible for macrobioerosion of a moderately indurated Neogene foraminiferal packstone cropping out along a freshwater reach of the Abatan River. In the process of drilling into and ingesting the limestone, these shipworms produce elongate borings that expand in diameter very gradually toward distal termini, exhibit sinuous or highly contorted axes and circular transverse outlines, and are lined along most of their length by a calcite tube. Given their strong resemblance to T. longissimus produced in wood but their unusual occurrence in a lithic substrate, these shipworm borings can be regarded as incipient Gastrochaenolites or, alternatively, as Apectoichnus. The alternate names reflect that the borings provide a testbed for ideas of the appropriateness of substrate as an ichnotaxobasis. The discovery of previously unrecognized shipworm borings in lithic substrates and the co-occurrence of another shipworm (Nausitora) in submerged logs in the same freshwater setting have implications for interpreting depositional conditions based on fossil teredinids or their ichnofossils. Of equal significance, the Abatan River study demonstrates that macrobioerosion in freshwater systems may be just as important as it is in marine systems with regard to habitat creation and landscape development. L. abatanica serve as ecosystems engineers in the sense that networks of their abandoned borings provide habitats for a variety of nestling invertebrates, and associated bioerosion undoubtedly enhances rates of mechanical and chemical degradation, thus influencing the Abatan River profile.

Paleo-environmental reconstructions of the Upper Cretaceous-Paleogene successions, Safaga, Egypt

The Late Cretaceous-Early Eocene sedimentary sequences in the Central Eastern Desert of Egypt were studied in three shallow boreholes (Wassief, Um El-Huaitat, and Mohamed Rabah). This study focuses on an integrated investigation of biostratigraphy, lithostratigraphy and some geochemical parameters, to provide important clues to the relative sea-level changes and to interpret the prevailed depositional conditions.Micropaleontological study on planktonic foraminifera allows to identify eight zones, ranging in age from Late Cretaceous to Early Eocene. Three hiatal surfaces have been recognized as evidenced by missing formaniniferal zones: The first spans the Late Maastrichtian-Danian regional unconformity. The second one is recorded in the Late Paleocene. The third one is located at the Late Paleocene-Early Eocene (Thanetian-Ypresian) boundary. The environments of the study foraminiferal parameters range from the non-marine to outer neritic-upper bathyal.Petrographically, thirteen Microfacies Types (MFT) have been recorded. Three MFTs constitute the siliciclastic facies; MFT-1; silty to sandy mudstone, MFT-2; organic-rich silty mudstone, and MFT-3; fine-grained sandstone/glauconite intercalations. Two MFTs represent a phosphorite facies which are MFT-4; phosclast packstone to phosclast grainstone and MFT-5; phosooid packstone to phosooid grainstone. Eight MFTs characterize the carbonate facies; MFT-6; non-fossiliferous lime-mudstone, MFT-7; phosphatic foraminiferal pack/grainstone, MFT-8; bioclastic foraminiferal packstone, MFT-9; bioclastic foraminiferal wackestone, MFT-10; glauconitic phosphatic foraminiferal Wack-Packstone, MFT-11; non-fossiliferous dolomitic mudstone, MFT-12; dolomitic glauconitic lime-mudstone, and MFT-13; dolomitic bioclastic wackestone. The depositional environments of the study microfacies range from the terrestrial to open marine outer neritic-upper bathyal.Geochemical parameters have been used to improve the litho- and biostratigraphic framework: the major oxides, TOC wt.% and the Chondrite-normalized REE. Based on the vertical distribution of CaO/P2O5, TiO2/CaO and cerium (Ce)-anomaly, changes in paleo-bottom water redox conditions were reconstructed and correlated with relative sea level changes. Prior to the major transgression during deposition of the Duwi Formation under reducing marine conditions, the prevailing oxic to sub-oxic bottom water terrestrial conditions during deposition of the Quseir Formation.

Lithofacies, paleoenvironment and high-resolution stratigraphy of the D5 and D6 members of the Middle Jurassic carbonates Dhruma Formation, outcrop analog, central Saudi Arabia

This study characterizes the lithofacies, paleoenvironment and stratigraphic architecture of the D5 and D6 members of carbonates Dhruma Formation outcrops in central Saudi Arabia. The study integrates detailed lithofacies analysis based on vertical and lateral profiles, in addition to thin-sections petrography to reveal the high-resolution architecture framework. Nine lithofacies types (LFTs) were defined namely: (1) skeletal peletal spiculitic wackestone (15%), (2) peloidal echinoderm packstone (19%), (3) fissile shale (36%), (4) peloidal spiculitic echinoderm pack-grainstone (5%), (5) cross-bedded peloidal skeletal oolitic grainstone (7%), (6) oolitic grainstone (2%), (7) intraformational rudstone (<1%), (8) skeletal peloidal foraminiferal packstone (12%) and (9) skeletal foraminiferal wackestone (4%). These lithofacies types were grouped into five major carbonate paleoenvironments that range from distal-to-proximal carbonate ramp setting. The detailed stratigraphic analysis revealed around 53 cycles and cycle sets with 5th to 6th orders magnitude, and thickness ranges from a few centimeters up to 6 m with an average of 1.5 m. Those are stacked to form four high-frequency sequences with thickness range from 1 m up to 14 m. The latter were grouped into a single depositional sequence of 3rd order magnitude. The architectural analysis also shows that the potential reservoir units were intensively affected by muddy-textured rocks which act as reservoir seals. These variations in the stratigraphic sequences in Middle Jurassic Dhruma Formation and its equivalents could be attributed to the eustatic sea-level changes, climate, tectonics, and local paleoenvironments. This study attempts to provide detailed insight into reservoir heterogeneity and architecture. The analog may help to understand and predict lithofacies heterogeneity, architecture, and quality in the subsurface equivalent reservoirs.

Facies characteristics and depositional environments of the middle Eocene (Lutetian) Harudi Formation, Kachchh, Western India

The 8.5 m thick, 1.4 km long and 0.35 km wide, ESE–WNW oriented cliff section (N 23°31′32″ E 68°41′00″) exposed across Harudi–Baranda road is extensively studied for its facies characteristics and based on that depositional environments of the middle Eocene (Lutetian) Harudi Formation are deciphered in the present study. Two cycles of grey mudstone alongwith nodular limestone–coquina limestone-gypsiferous mudstone facies in the lower part of the succession suggest sedimentation in coastal quiet-water lagoonal to tidal flat environments, while glauconitic shale, bioclastic packstone and gypsiferous foraminiferal packstone facies in the upper part suggest sedimentation on middle- to inner-shelf and tidal flat depositional environments. In all, three shallowing upward cycles have been identified in the studied outcrops and based on that lagoonal-middle shelf-inner shelf-tidal flat depositional environments are suggested for the middle Eocene Harudi Formation.

Biostratigraphy and facies analysis of the Upper Cretaceous–Danian? platform carbonate succession in the Kuyucak area, western Central Taurides, S Turkey

The Upper Cretaceous succession outcropping in the Anamas–Akseki Autochton, consists of approximately 500 m thick purely platform carbonate sediments. It begins with Cenomanian limestones intercalated with limestone breccias (Unit-1) containing mainly Pseudorhapydionina dubia, Pseudonummoloculina heimi, Spiroloculina cretacea (Assemblage I) and unconformably overlies the Lower Cretaceous (Barremian–Aptian) limestones with Vercorsella laurentii, Praechrysalidina infracretacea and Salpingoporella hasi. The Cenomanian limestones include foraminiferal packstone–wackestone, peloidal packstone–wackestone and mudstone microfacies deposited in restricted platform conditions. The Cenomanian succession is truncated by an unconformity characterised by locale bauxite deposits. Immediately above the unconformable surface, dolomitic limestones and rudistid limestones (Unit-2) are assigned to the upper Campanian based on the benthic foraminiferal assemblage (Assemblage II) comprising mainly Murciella gr. cuvillieri, Pseudocyclammina sphaeroidea, Accordiella conica, Scandonea samnitica and Fleuryana adriatica (smaller-sized populations). The upper Campanian limestones composed of dominantly foraminiferal-microbial packstone–wackestone microfacies deposited in shallow water environment with low energy, restricted circulation. The following limestones of the Unit-2 is characterised by sporadic intercalation of “open shelf” Orbitoides, Omphalocyclus, Siderolites assemblage (Assemblage III), assigned to the Maastrichtian, in addition to pre-existing “restricted platform” species. In the upper part of this biozone, the Rhapydionina liburnica/Fleuryana adriatica concurrent range subzone (Assemblage IIIb) is distinguished by the presence of Valvulina aff. triangularis, Loftusia minor as well as the nominal species. The Maastrichtian limestones with sporadically open marine influence consist of bioclastic (rudist-bearing) packstone–floatstone, foraminiferal packstone–wackestone with rudist fragments and peloidal/intraclastic packstone–wackestone microfacies deposited in shallow subtidal–subtidal (lagoonal) environments. The Upper Cretaceous succession passes upwardly into 70 m thick limestones and clayey limestones (Unit-3) which do not contain rudists and pre-existing foraminiferal assemblage with one exception Valvulina aff. triangularis. Variable amounts of ostracoda, discorbids, miliolids, dasycladacean algae and Stomatorbina sp. (Assemblage IV) occur into mud-rich microfacies suggesting restricted conditions with low water energy. A probable Danian age is proposed for the Unit-3 based on the occurrence of Valvulina aff. triangularis and Stomatorbina sp. which were previously recorded from Danian of peri-Tethyan platforms.

Early Eocene evolution of carbonate depositional environments recorded in the Čikola Canyon (North Dalmatian Foreland Basin, Croatia)

The stratigraphic succession in the Cikola Canyon (part of the North Dalmatian Foreland Basin) was studied in detail to describe both the sedimentological characteristics and fossil assemblages of the Lower Eocene deposits during the initial stage of the foreland basin formation. The North Dalmatian Basin now represents a part of the Outer Dinarides, and was developed in front of the evolving Dinaric structures by tectonic deformation and marine transgression of an emerged and denuded Mesozoic Adriatic Carbonate Platform (AdCP). During the initial phase, a distal ramp of a foreland basin was formed, characterised by carbonate sedimentation, lasting until the Middle Eocene. In a studied section more than 300 m thick, porcelaneous foraminifera, Alveolina, Orbitolitesand complex miliolids (Idalina, Periloculina) prevail, associated with conical agglutinated forms, nummulitids and red algae. These samples belong to the SBZ 11–12 (Ypresian), according to occurrences of Alveolina decastroi, Alveolina cremae, Alveolina multicanalifera and Coskinolina liburnica. Two main lithological units have been described: 1) mudstones to wackestones with sporadic occurrences of ostracods and charophyceae, deposited in restricted lagoonalsettings with several episodes of freshwater influences, and 2) foraminiferal packstones to grainstones with complex miliolids, alveolinids, corallinacean algae and nummulitids, deposited within inner and middle ramp settings. Palaeogene deposition of ramp carbonates in the Outer Dinarides area was mainly controlled by the continuous compressional tectonics, and the deposits today appear in more or less discontinuous outcrops. Palaeogene transgression occurred at different times over various parts of the former carbonate platform area, and subsequent carbonate sedimentation was characterised by deposition in similar environments during different time intervals over spatially restricted carbonate ramps controlled by synsedimentary tectonics.

High-resolution stratigraphy and facies architecture of the Upper Cretaceous (Cenomanian–Turonian) Eagle Ford Group, Central Texas

Rock-based studies of the Eagle Ford Group of Central Texas demonstrate that mudrock deposition is more complicated than previously supposed. X-ray diffraction, x-ray fluorescence, total organic carbon (TOC), and log data collected from eight cores and two outcrops demonstrate that bottom-current reworking and planktonic productivity are primary depositional controls, acting independently from eustatic forcing. Central Texas Eagle Ford facies include (1) massive argillaceous mudrock, (2) massive foraminiferal calcareous mudrock, (3) laminated calcareous foraminiferal lime mudstone, (4) laminated foraminiferal wackestone, (5) cross-laminated foraminiferal packstone–grainstone, (6) massive bentonitic claystone, and (7) nodular foraminiferal packstone–grainstone. High degrees of lateral facies variability, characterized by pinching and swelling of units, lateral facies changes, truncations, and locally restricted units, are observed even at small lateral scales (50 ft [15 m]). At 10 mi (16 km) and greater lateral spacings, core and geochemical data significantly underestimate intraformational facies variability. Approximately 73% of units can be successfully correlated across a distance of 500 ft (152 m), 35% are traceable across 1 mi (1.6 km), and only 16% of beds are correlative across 10 mi (16 km). Geochemical proxies (enrichment in molybdenum and other trace elements) indicate that maximum anoxia occurred within the Bouldin Member despite being composed of the most calcareous and high-energy facies. Comparison of total gamma ray (GR) logs to computed GR logs is requisite, because GR alone may provide misleading determination of facies, TOC content, depositional environment, and sequence stratigraphic implications.

Sequence biostratigraphy and paleoenvironmental reconstruction of the Oligocene-early Miocene deposits of the Zagros Basin (Dehdasht area, South West Iran)

The Asmari succession is a predominantly carbonate-lithostratigraphic unit corresponding to an Oligocene-Lower Miocene shallow and homoclinal ramp system that developed in the southwest of the Zagros Basin. The sedimentation occurs within a transition from a mixed carbonate–siliciclastic to carbonate-dominated depositional environment. Carbonate production in this system is dominated by diverse benthic foraminifera, coralline algae, mollusks, bryozoans, echinoids, and corals. Based on fossil content and texture, 16 different facies types have been distinguished that accumulated in three interpreted paleoenvironments: The euphotic inner ramp is characterized by two facies zones: an inner and an outer shallow water zone. The inner shallow water zone is characterized by the occurrence of imperforated foraminifera together with mollusks in restricted parts (foramol assemblage). The outer shallow water zone is dominated by wackestones-packstones with benthic foraminifera and coralline red algae, minor mollusks, bryozoans, echinoids, and small epiphytic biota (LB-foralgal assemblage). The higher-energy parts on platform margin are represented by ooids, scattered corals, and robust foraminifera-rich grainstones (coralgal assemblage). The middle ramp is characterized by small coral patch reefs that developed in mesophotic conditions, and larger foraminiferal packstone facies often associated with coralline red algal debris (LB-foralgal assemblages) characterize the sediments of the deeper oligophotic zone, whereas the outer ramp facies–aphotic zone–are represented by bryozoans, mollusks, and echinoid association (bryomol assemblage). This facies passes basinward into wackestone, packstone, and rarely mudstone with pelagic and small benthic foraminifera, sponge spicule, and echinoid fragments (echinofor assemblages). Changes in the depositional facies and cycle stacking patterns indicate four transgressive–regressive sea-level cycles from the bottom to the top of the section. These depositional sequences have been separated by type 2 sequence boundaries. Sea-level fluctuations that cause changes in light penetration which may produce shifts from aphotic to oligophotic and euphotic conditions are an important factor in skeletal production and spatial distribution of carbonate factories. The presence of non-skeletal grains (ooids and ploeids), the occurrence of Porites patch reefs, and the existence of LBF such as Heterostegina, Operculina, Amphistegina, Archaias, and Lepidocyclina in the larger foraminifera associations together with Lithoporella mellobesioides and Spirolithon in coralline red algae assemblage all suggest that carbonate sedimentation took place in tropical waters under oligotrophic to slightly mesotrophic conditions.