Late Cenomanian Early Turonian Research Articles

Quantitative Interpretation of the Petrophysical Properties of Selected Wells for the Mishrif Formation in Nasiriyah Oilfield, Southern Part of Iraq

One of the oil field's main reservoirs is the Mishrif Formation, which is found in the Nasiriyah oilfield in the southern part of Iraq (Late Cenomanian-Early Turonian). It was one of the three oil wells selected for this study. To extract various petrophysical parameters for open wells indicated by gamma ray, density, neutron, self-potential, acoustic, and resistance, a variety of well logs were analyzed. The qualitative interpretation of the logs allowed for the identification of different types of rocks, the boundaries and thicknesses of the strata, the depths of the formation, and the zones that contained water and hydrocarbons. The quantitative interpretation, which assesses the reservoir's attributes by computing its porosity, the quantity and distribution of the shales, the levels of water and oil saturation, and other elements, that are necessary to evaluate the reservoir’s units in the research wells. The features of the study wells and the used logs were reported, to make clear how these features were distributed among the sample wells. The collected petrophysical characteristics were handled and shown as charts. There are two types of units within the Mishrif Formation: reservoir-containing CR-I, MA, CR-II, and MB. In most wells, reservoir units are made up of hard, low-porous rocks that are positioned between highly porous reservoir units. For a few wells, the MA unit had low residual and mobile hydrocarbon percentages, whereas the MB unit had large percentages, while the hard rocks had significant percentages of water saturation.

Late Cenomanian–early Turonian ammonite successions of north Eastern Desert, Egypt: biostratigraphy and paleobiogeographic implications

The upper Cenomanian-lower Turonian sequence of Egypt yield a remarkably diverse and plentiful ammonite fauna. Three stratigraphic sections located on Wadi Araba, north of the Southern Galal Plateau were investigated. Lithostratigraphically, the measured sections are subdivided from base to top into the Malha (pre-Cenomanian), Galala (Cenomanian) and Maghra El Hadida (Turonian) formations. Over a hundred well-preserved and nearly complete ammonite internal molds were collected. The studied ammonites are systematically classified as Vascoceratidae, Pseudotissotiidae, Acanthoceratidae and Engonoceratidae. Vascoceratidae and Pseudotissotiidae comprise 75% of the identified ammonites. Twelve ammonite species have been identified. Six late Cenomanian-early Turonian ammonite biozones are proposed herein: Neolobites vibrayeanus, Vascoceras gamai, Vascoceras cauvini, Vascoceras proprium, Choffaticeras segne, and Wrightoceras munieri. The identified ammonite biozones are correlated with NW European standard zonation and the Tethyan biostratigraphical schemes was performed. The first occurrences of Vascoceras proprium, as well as the first occurrences of the inoceramids Mytiloides kosmati and Mytiloides puebloensis define the Cenomanian-Turonian boundary. The diversity and abundance of studied fossil groups varied dramatically over the C/T transition. In the latest Cenomanian, all identified Cenomanian species had become extinct. Only three species have reached the Turonian time. The paleobiogeographic implications of the descried ammonites are thoroughly discussed. The paleogeographic distribution of the studied ammonite fauna shows that the majority of the described species are restricted to the shallow shelf of the southern Tethys.

First record of Oceanic Anoxic Event 2 in the Eastern Carpathians: implications for chemostratigraphic and biostratigraphic correlations

This study aims to investigate a marlstone and claystone succession located at the southern end of the Eastern Carpathians, a region where oceanic anoxic event 2 (OAE2) has not been pointed out so far. Toward the upper half of this succession, a 17-cm-thick black shale was identified. The investigated depositional interval lies within the late Cenomanian–early Turonian, encompassing the UC3d up to UC7 nannofossil zones. The δ13C values fluctuated between 2.06‰ and 3.89‰, showing a positive isotope excursion that was assigned to OAE2. The δ13C isotope curve displays the following intervals: pre-excursion, first build-up, trough, second build-up, plateau, and post-excursion. Within the second build-up interval of OAE2, a substantial shift in CaCO3 values, accompanied by high concentrations of total organic carbon and a significant decline in the abundance and diversity of calcareous nannofossil assemblages, was observed. The nannofossil turnover related to OAE2 climax revealed predominance of Watznaueria barnesiae and temporary disappearance from the record of surface-water higher fertility taxa, such as Biscutum constans, Zeugrhabdotus erectus, and Discorhabdus ignotus. Above OAE2, peaks of Eprolithus floralis, followed by increased abundance of Eiffellithus turriseiffelii and Nannoconus spp., were identified. In the lower part of the studied succession (i.e., the upper Cenomanian UC3d nannofossil subzone), during the pre-excursion characterized by low δ13C values and less negative δ18O values, a small group of nannofossils more related to mid- and high-paleolatitudes, such as Crucibiscutum salebrosum, Repagulum parvidentatum, and Seribiscutum primitivum, is present, always showing a low abundance.

Deciphering multi-phase inversion tectonics in the southern Dezful Embayment: insights from the Rag-e-Sefid Oilfield, SW Iran

ABSTRACT Identification of inversion tectonics and inverted structures is very important in petroleum exploration and production due to the positive or negative impacts they can exert on the hydrocarbon traps. In order to characterize the occurrence of multi-phase inversion tectonics and its effect in the Rag-e-Sefid Oilfield, located in the southern Dezful Embayment (SW Iran), this research describes the structural style and deformation history through structural and tectono-sedimentary analyses. The results obtained from the interpretation of seismic profiles and the investigation of the geometry of the sedimentary layers across the growth structures indicate that the Rag-e-Sefid anticline is created from multiple fault-propagation folds. The final shape and geometry of the Rag-e-Sefid anticline are affected by the Rag-e-Sefid and Nourooz-Hendijan-Izeh Faults activity. The deformation history in the north-western part of the Rag-e-Sefid anticline is older than the south-eastern part of it. The Rag-e-Sefid Fault set in the north-western and south-eastern parts of the Rag-e-Sefid Oilfield experienced activity at least during seven and four tectonic phases, respectively. Multiple fault-propagation folding and the fold axis rotation in the north-western part of the Rag-e-Sefid anticline controlled by the presence of several décollement surfaces and the occurrence of inversion tectonics along the pre-existing basement structures. Three-phase inversion tectonics along the Nourooz-Hendijan-Izeh Fault and the Rag-e-Sefid Fault set in the north-western part of the Rag-e-Sefid Oilfield occurred at the Late Devonian-Carboniferous (positive inversion), Permian-Early Triassic (negative inversion), and Late Cenomanian-Early Turonian (positive inversion) boundaries and modified the evolutionary history of the sedimentary basin. The inversion affected hydrocarbon trap development at the Late Cretaceous and controlled their current conditions in the southern Dezful Embayment. Based on the hydrocarbon migration in these regions from the Late Miocene to the present day, the N-S trending (Pan Africa trend) north-western part of the Rag-e-Sefid anticline has a larger share of oil and gas compared to the NW-SE trending (Zagros trend) south-eastern part. The results of this study could add data to worldwide examples of the positive impact of tectonic inversion on the hydrocarbon traps development in the foreland of a collisional orogen.

Impact of inversion tectonics on the spatial distribution of hydrocarbon traps in the NW Persian Gulf and the southern Dezful Embayment, SW Iran

Inversion tectonics has a major impact on distribution of fault-controlled hydrocarbon traps in the fold-and-thrust belts. In order to characterize the spatial distribution of several fault-controlled hydrocarbon traps adjacent to the Nourooz-Hendijan-Izeh Fault, this study describes the structural and tectono-sedimentary evolution of the fault based on the geological interpretation and tectono-sedimentary analysis of seven seismic sections in the Bahregansar, Hendijan, Tangu, and Rag-e-Sefid oilfields in the NW Persian Gulf and the southern Dezful Embayment. The results indicate that the Nourooz-Hendijan-Izeh Fault is a segmented pre-existing basement fault with steep dip, which reactivated to at least seven tectonic phases. Three-phase inversion tectonics along the Nourooz-Hendijan-Izeh Fault occurred at the Late Devonian-Carboniferous (positive inversion), Permian-Early Triassic (negative inversion), and Late Cenomanian-Early Turonian (positive inversion) boundaries and modified the evolutionary history of the sedimentary basin. Inversion affected hydrocarbon trap development at the Late Cretaceous and controlled their current conditions in the NW Persian Gulf and the southern Dezful Embayment along the northeastern margin of African-Arabian plates. Considering the hydrocarbon migration at the Late Miocene in these regions up to now, the N–S trending anticlines (Arabian trend) have a larger share of oil and gas in their hydrocarbon traps and lower hydrocarbon exploration risk than the NW-SE trending anticlines (Zagros trend). Mild to moderate inversion structures can be considered as preferred petroleum exploration targets.

Geochemistry and Zircon U‐Pb Dates of Felsic‐Intermediate Members of the Late Cretaceous Yüksekova Arc Basin: Constraints on the Evolution of the Bitlis–Zagros Branch of Neotethys (Elazığ, E Turkey)

AbstractDuring the Late Cretaceous in the Eastern Mediterranean, the northern branch of the southern Neotethys was closed by multiple northward subductions. Of these, the most northerly located subduction created the Baskil continental arc at around 82–84 Ma. The more southerly and intra‐oceanic subduction, on the other hand, produced an arc‐basin system, the Yüksekova Complex, as early as the late Cenomanian–early Turonian. The abundant and relatively well‐studied basaltic rocks of this complex were intruded by dykes, sills and small stocks of felsic–intermediate rocks, not previously studied in detail. The intrusives collected from five different localities in the Elazığ region of eastern Turkey are all subalkaline, with low Nb/Y values. Most of them have been chemically classified as rhyodacites/dacites, whereas a small number appear to be andesites. In normal mid‐ocean‐ridge basalt (N‐MORB)‐normalised plots, the intrusives are characterised by relative enrichments in Th and La over Nb, Zr, Hf, Ti and high field strength elements (HREEs), indicating their derivation from a subduction‐modified source. While their relatively high, positive εNd(i) values (+6.4 and +7.2) might suggest a depleted mantle source for their ultimate origin, somewhat radiogenic Pb values indicate a sedimentary contribution to the source of the rocks. The overall geochemical characteristics indicate their generation in an oceanic arc setting. The zircon U‐Pb Laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) data obtained from five felsic‐intermediate rock samples yielded intrusion dates of 80–88 Ma. This suggests that the Elazığ oceanic arc‐related intrusives are slightly younger than those of the Yüksekova arc‐basin system, but coeval with the Baskil continental arc. However, the felsic–intermediate intrusives show different geochemical characteristics (oceanic arc‐type, with a lack of crustal contamination) to those of the Baskil continental arc. This indicates that these two igneous systems are unrelated and likely developed in different tectonic settings. This, in turn, supports a geodynamic model in which the northern strand of the southern Neotethys was consumed by multiple northward subductions.

Late Cretaceous marine reptiles from Malyy Prolom in Ryazan Oblast, Central Russia

During the Cenomanian–Turonian transition (~94 Ma), what is today Central Russia formed part of the northern epicontinental margin of the Tethys Ocean. Diverse marine vertebrate faunas inhabited these palaeoenvironments, but their fossils are incompletely documented. Here, we report the discovery of marine reptile remains, recovered together with pterosaur, chondrichthyan, and actinopterygian fish material from a basal-most glauconitic sand and gravel layer of the Dmitrov Formation. These strata are exposed in an active quarry near the village of Malyy Prolom in the Shatsky District of Ryazan Oblast, Central Russia. The Dmitrov Formation deposits are middle–upper Santonian, but unconformably contact the underlying lower–middle Cenomanian Yakhroma Formation via a condensed boundary horizon that contains the vertebrate fossils with bivalve shell fragments and siliceous and phosphatic clasts. Such sedimentary characteristics indicate a high-energy shoreface setting where the vertebrate teeth and bones were likely reworked during cyclical regressions commencing in the latest Cenomanian–early Turonian. Time-averaging is also evidenced by the mixed occurrences of brachauchenine pliosaurids, elasmosaurid and polycotylid plesiosauroids, ophthalmosaurid ichthyosaurians similar to Pervushovisaurus, and a possible yaguarasaurine mosasauroid. These taxa are typical of Cenomanian–Turonian assemblages from across the northern peri-Tethys, and represent components of what were probably palaeobiogeographically widespread marine reptile faunas.

New Constraints on Global Geochemical Cycling During Oceanic Anoxic Event 2 (Late Cretaceous) From a 6‐Million‐year Long Molybdenum‐Isotope Record

AbstractIntervals of extreme warmth are predicted to drive a decrease in the oxygen content of the oceans. This prediction has been tested for the acme of short (<1 million years) episodes of significant marine anoxia in the Phanerozoic geological record known as Oceanic Anoxic Events (OAEs). However, there is a paucity of data spanning prolonged multimillion‐year intervals of geological time before and after OAEs. We present a Mo‐isotope record from limestones and marlstones of the Eagle Ford Group, South Texas, which was deposited in the southern Cretaceous Western Interior Seaway of North America during a 6‐million‐year period encompassing OAE 2 (Late Cenomanian–early Turonian: ∼94 Ma). Mo‐isotope compositions from deposits that formed in euxinic (sulfidic) conditions before OAE 2 allow the paleo‐seawater composition to be constrained to 1.1%–1.9%. This range of values overlaps previous estimates of up to ∼1.5% for the peak of OAE 2 determined from similarly sulfidic sediments deposited in the restricted proto‐North Atlantic Ocean. Mo‐isotopes thus varied by less than a few tenths of per mil across one of the most extreme intervals of global deoxygenation in the Late Phanerozoic. Rather than a limited change in oceanic deoxygenation, we suggest that the new data reflect changes to global iron cycling linked to basalt‐seawater interaction, terrestrial weathering and expanded partially oxygenated shallow shelf‐seas that played a key role in the burial of isotopically light molybdenum, thus acting as a counterbalance to its removal into sulfidic sediments.

Insights into the Pore Structure of Strong Heterogeneous Carbonates in the Mesopotamian Basin

The Cretaceous Late Cenomanian-Early Turonian Mishrif Formation carbonates in the Mesopotamian Basin are characterized by complex pore systems, resulting in strong reservoir quality heterogeneity. Major factors that constitute the complexity of pore structure are types, geometries, and topologies of pores and pore-throats. These factors and the effect of pore structure on reservoir quality were investigated by integration of thin sections, petrographic image analyses, porosity, permeability, and mercury injection capillary pressure measurements. Eight matrix-related and three matrix-unrelated pore types, which are dominated by secondary pores, are identified in the Mishrif carbonates. Pore sizes range from a few microns to more than 1 cm and vary greatly both in the same and in different pore types. Pore shapes range from better circularity and simple boundaries to irregular complex boundaries and similar for the same pore type. Pore-throat radii (PTR) range from 3 nm to 124 μm, and micro pore-throats occur in all carbonates in different proportions. Pore-throat systems show strong heterogeneity and are classified into six classes based on their size distribution characteristics. Carbonate porosity is not solely correlated with pore sizes because pore abundance is another independent factor to determine porosity. Permeability is controlled by PTR rather than pore sizes, and R40 (PTR corresponding to the 40th percentile of mercury saturation) is the most correlated PTR to permeability. There is no apparent correlation between pore size and PTR except for the interparticle pores. Both pore sizes and PTR distributions can reflect reservoir microscopic heterogeneity due to their positive correlations for all pore types other than micropores (pore diameter less than 30 μm).

Palaeoecology and facies analysis of benthic communities in mid-Cretaceous successions in the Sinai platform, Egypt

Within the Aptian-Cenomanian formations of Sinai successions in Egypt, lateral and vertical changes occur in the numerous benthic communities. Microbenthos such as Orbitolina foraminifera and calcareous algae are widespread in the Aptian-Albian deposits in North Sinai, whereas oysters and gastropods are common in the Cenomanian siliciclastic deposits in South Sinai. In order to establish the biostratigraphy, 90 benthic and planktonic foraminifera species have been identified from the studied succession. Based on the stratigraphic distribution of the identified species the studied succession could be subdivided into three planktonic foraminiferal zones: Pseudothalmanninella ticinensis zone (Late Albian), Rotalipora cushmani zone (Middle-Late Cenomanian), and Whiteinella archaeocretacea zone (Late Cenomanian-Early Turonian). This work discusses the first record of the Albian dasycladalean alga Holosporella sugdeni (Elliott) from Sinai and reports on Montiella elitzae (Bakalova) from the Albian Risan Aneiza Formation. The occurrence of Orbitolina (Conicorbitolina) conica distinguished the Albian-Cenomanian boundary in the North Sinai sequences. The benthic communities of the studied successions indicated a faunal shift from an algal-orbitolinid foraminifera community around the Aptian-Early Albian to a rudist community during the Middle Albian and an oyster-gastropod community during the Cenomanian. This faunal shift coincided with the major sea transgression that covered North Sinai until the Middle Albian and reached South Sinai during the Cenomanian. The identified Cenomanian gastropods included Neoptyxis olisiponensis, Nerinea gemmifera, and Tylostoma bussoni. Many oyster species distinguished the Cenomanian deposits, such as Ceratostreon flabellatum, Rhynchostreon mermeti, Rhynchostreon suborbiculatum, and Costagyra olisiponensis. Identifying the benthic fauna and facies indicated a shallow inner to middle ramp environment. Stable carbon and oxygen isotope data from the Cenomanian oyster shells indicate an inner ramp environment. Comparing the carbon isotope values of the oysters with those previously recorded from the rudists may explain the different trophic levels of both groups.

The Cenomanian–Turonian boundary event in Egypt: Foraminiferal turnover and carbon isotopic change

This study deals with the integration between geochemical data (carbon isotope and, total organic carbon) and foraminiferal turnover to track the Oceanic Anoxic Event 2 (OAE2) from the OCT-A8st1 well, which located in October field, central part of Gulf of Suez, Egypt. The studied well is subdivided into two formations, namely the Galala (Early–Late Cenomanian) and Abu Qada (Late Cenomanian–Early Turonian). Concerning the foraminiferal assemblage, agglutinated foraminifera dominate the Galala Formation, while planktonic taxa only occur within a few levels in the Abu Qada Formation. Due to the absence of keeled planktonic forms, the biostratigraphic framework is established on the integration between benthonic and planktonic foraminifera. Three biozones are recognized, including Thomasinella aegyptia–Merlingina cretacea Interval Zone (Early–Middle Cenomanian), Thomasinella fragmentaria–Praebulimina aspera Interval Zone (Middle–Late Cenomanian), and Whiteinella archaeocretacea Taxon Range Zone (Late Cenomanian–Early Turonian). Therefore, the Cenomanian–Turonian boundary interval (CTBI) is placed within the lower part of the Abu Qada Formation, which is characterized by the presence of black shales and low richness of both foraminifera and ostracods. A remarkable increase in TOC values is observed close to the CTBI. Also, the carbon isotope curve shows a distinctive positive δ13C anomaly at the same level of the maximum TOC. The comparison between the recorded δ13C data and those obtained from other sections worldwide, indicates that the base of the Turonian is placed directly above the δ13C excursion. Furthermore, the recorded foraminiferal community shows evidence for the deepening of the environment and extension of the oxygen minimum zone during the CTBI. This conclusion is based on a sequence of bioevents starting with the disappearance of some agglutinated benthic foraminifera, followed by the dominance of opportunistic groups including buliminids, whiteinellids and heterohelicids. Consequently, the studied well may be considered as a local reference section for OAE2.

Biostratigraphy correlation, of Cretaceous successions in Kuh-e-Rahmat and Kuh-e-Sabz sections, NE Shiraz, Zagros (SW Iran)

Two stratigraphic sections (Kuh-e-Rahmat and Kuh-e-Sabz) of Upper Cretaceous strata in the Interior Fars region (SW of Iran) were selected. Lower Cretaceous succession of Kuh-e-Rahmat was consisted of Dariyan, Kazhdumi Sarvak and Ilam Formations. The lower contact of the Sarvak Formation with Kazhdumi Formation is described as a transitional type whereas the upper contact of Sarvak Formation was not clear. Stratigraphic distribution of microfossils reveals three biozones in this section: 1: Palorbitolina lenticularis (Aptian), 2: Orbitolina concava and Hemicyclamina sigali (late Albian-early Cenomanian), 3: Stomiosphaera conoidea (Late Cenomanian-Early Turonian). Kuh-e-Sabz lithologic aspect consists of two rock units such as: Sarvak Formation and thin-bedded limestone of lower part of Ilam Formation. The lower contact of the Sarvak Formation was not clear whereas the upper contact with Ilam Fm. was exposed as an erosional disconformity including oxidized zone. Vertical distribution of investigated taxa supports three biozones: 1: Taberina bingistani zone (middle Cenomanian), 2: Praelveolina cretacea zone (late Cenomanian), 3: Dicyclina schlumbergeri zone (Santonian-Campanian). The Sarvak Formation of Kuh-e-Rahmat was deposited in an inner shelf paleoenvironment (as open marine facies) because of well distributed of pelagic fauna, while Kuh-e-Sabz section mostly shows reef facies (back reef-fore) along the platform including agglutinated and porcelaneous foraminifera which reflects an inner shallow platform (0-50m).

Regional 1D hydrocarbon maturation modelling of the Cenomanian–Turonian Lokpanta Shale, southern Benue Trough, Nigeria: Implications for the origin of Niger Delta deep sea oils

Basin modelling, constrained by geochemical data from eight wells, was carried out, across the late Cretaceous and Early Palaeogene sediment packages of south-eastern Nigeria sedimentary basins. The study was aimed at establishing the sediment burial history, thermal maturation of the source rock and timing of hydrocarbon generation. The Late Cenomanian to Early Turonian Lokpanta Shale, which is the basal unit of the Eze-Aku Formation in the Eze-Aku Group, consists of alternating dark grey to black shales, marl and siltstones. The upper sections are mainly alternating sandstones, shales and limestones. This unit is the key petroleum source rock for the basin. Numerical 1D basin model of the study area revealed that the Cenomanian to Turonian times was the main phase of rifting in the Benue Trough evidenced by rapid subsidence. Subsidence rates varied widely in all the wells studied, ranging from 29–61 m/Mya (million years ago) and averaging 44 m/Mya. Subsidence rates also varied widely through geological time from the Cretaceous to the Palaeogene. The Cenomanian–Turonian and the Maastrichtian ages recorded the highest subsidence rates (169.75 and 168.28 m/Mya, respectively). These phases of rapid subsidence correspond to the main phase of rifting (Cenomanian–Turonian) and periods of increased sediment supply (Campanian and Maastrichtian), due to rapid erosion and unroofing of the structurally inverted Benue Trough, post-Santonian. Vitrinite reflectance values (1.87–4.78% Ro) indicated that the Lokpanta source rock (Late Cenomanian–Early Turonian) is mature to overmature. The vitrinite maturation profiles and the geochemical data suggested the generation of hydrocarbon before the Santonian compressional uplift of the Abakaliki–Benue Trough with its resultant sediment folding, which displaced the depo-centre from the Abakaliki Basin to the Anambra and Afikpo platforms. The subsequent erosion and non-deposition in the Abakaliki Basin raised the Lokpanta Shale above the oil generative window. The renewed sedimentation in the Campanian resulted in sagging due to sediment load creating the Anambra Basin. The lack of an effective trapping mechanism in the pre-Santonian may imply that hydrocarbon generated before the uplift migrated away, probably to upper and/or lower horizons (observed as oil shows in the region); some of which may be contributing to the Niger Delta crude. This is evidenced by the correlation of the Niger Delta deep sea samples to the Cretaceous (Lokpanta Shale) source rock and occurrence of biomarkers of Cretaceous origin (ab-hopanes and oleananes in the Opuama Channel complex, northern depobelt, Niger Delta).

High-resolution bio- and chemostratigraphy of an expanded record of Oceanic Anoxic Event 2 (Late Cenomanian–Early Turonian) at Clot Chevalier, near Barrême, SE France (Vocontian Basin)

A newly located exposure of the Niveau Thomel, an organic-­‐rich level at the Cenomanian–Turonian boundary, provides a highly expanded record of Oceanic Anoxic Event (OAE) 2, excepted for the lower relatively condensed glauconite-­rich part of the section. The new locality, close to Barreme in the Vocontian Basin, SE France, is developed in deep-­water hemi-­pelagic facies (shales, marls, marly limestones, variably enriched in organic matter) and provides an improved understanding of palaeoceanographic events associated with OAE 2. Investigation of the biostratigraphy (nannofossils and planktonic foramininfera), organic and inorganic geochemistry (bulk carbonate δ18O, total organic carbon (TOC), bulk organic, biomarker-specific and carbonate δ13C, major and trace elements, and Rock-­Eval data) has allowed characterization of the sediments in great detail. The combined study further constrains the detailed relationship between bio-­ and chemostratigraphy (particularly with respect to the details of the well-­displayed positive carbon-­‐isotope excursion) for this interval. The section also provides new evidence, in the form of a positive oxygen-­isotope excursion and an offset between carbonate and organic-­carbon carbon-­isotope records, which confirms the importance of cooling accompanied by a drop in dissolved CO2 in near-­surface waters during the Plenus Cold Event that characterized the early part of OAE 2. Evidence for increased oxygenation of bottom waters, together with elevated concentrations of redox-­sensitive and chalcophilic elements registered elsewhere through the level of the Plenus Cold Event, may be reflected in enhanced concentrations of iron (in glauconite) and nickel in coeval strata from the Clot Chevalier section.

Paleoceanographic Significance of Cerium Anomalies During the OAE 2 On the NW African Margin

Abstract Upper Cenomanian–lower Turonian carbonates from the Preafrican Trough (South Morocco) and Agadir Basin contain biological (benthic and planktonic organisms) and chemical (redox-sensitive trace metals) markers indicating the occurrence of dysoxic conditions with a significant increase in productivity in shallow-water areas on the NW African margin during the Oceanic Anoxic Event 2. The geochemistry of carbonate rocks from three sections along a W-E transect, perpendicular to the margin, is studied here to elucidate the origin of the increased productivity and to test the applicability of cerium anomalies as markers of redox-sensitive and/or indicators of paleoenvironmental or paleoceanographic conditions. The rare earth element (REE) data show typical seawater patterns and negative Ce/Ce* anomalies which appear to indicate the persistence of oxic conditions during the late Cenomanian–early Turonian. This interpretation is in contradiction with that inferred from chemical data (ratios of various redox-sensitive elements to aluminum) and paleontological assemblages. To resolve this paradox, our data are compared with current oceanographic data and examined using a geochemical model that simulates the REE patterns of seawater, specifically the cerium anomaly. There is a satisfactory agreement between measured and calculated REE values for the three studied sections which allows us to distinguish Cenomanian and Turonian water masses. Taking all these geochemical data together, we suggest that the Cenomanian–Turonian stratigraphic interval in the Preafrican Trough and the Agadir Basin records a change of water mass during a transgressive event on an upwelling margin. The intense upwelling of nutrient-rich waters explains the high marine productivity throughout the studied area during the Turonian. The dissolved-oxygen concentrations in waters are not straightforwardly recorded in the trace-metal contents of carbonates. Nevertheless, these data can be deconvoluted by taking account of the saturation state of seawater and the role of particles. Even if negative cerium anomalies in carbonates are classically correlated with dissolved-oxygen concentration, this study proposes that they are also dependent, possibly to a large extent, on particle concentration and water-mass circulation. This would explain why several proxies are required to reconstruct paleo-redox conditions in carbonate facies.

Cenomanian–Turonian depositional history of a post–Gondwana rift succession in the West Beni Suef Basin, Egypt

The structural and stratigraphic evolution of rift basins has been documented globally from modern systems, outcrop and subsurface datasets. Extensive fragmentation and break-up of Gondwana during the Cretaceous created a complex suite of rift basins in the Northern Africa. The Beni Suef rift basin straddles the River Nile and is infilled by a thick Mesozoic–Tertiary succession. Cenomanian–Turonian deposition commenced with the sandstone-dominated Bahariya Formation. Depositional environments transitioned stratigraphically from fluvial-marine to shallow marine and finally to mixed clastic and non-clastic shelfal deposits of the Abu Roash Formation. Sedimentation styles were tectonically controlled showing transgressive-to-regressive depositional cycles developed over the Gondwana rift systems. Cycles were controlled by short-lived, small-scale tectonic oscillations of the platform, resulting in four depositional sequences. Deposition environments in the Cenomanian transitioned from shallow marine to deeper marine shelfal deposits and finally to a coastal environment. During Late Cenomanian–Early Turonian, rapid platform submergence resulted in a transgressive facies succession, topped by deltaic deposits. In the Middle–Upper Turonian, two sequences formed with an intervening short-lived period of lower relative sea level. Relative sea-level oscillations were partly in phase with the global sea-level changes, controlled by local tectonics induced by the fragmentation of Gondwana during the Late Cretaceous.

The Cenomanian–Turonian transition in the carbonate platform facies of the Western Saharan Atlas (Rhoundjaïa Formation, Algeria)

Microfacies, fossil macroinvertebrates and microfossil assemblages (foraminifera and ostracods) and δ13C from the Rhoundjaia Formation (Ksour Mountains, Western Saharan Atlas, Algeria) were studied. During the Late Cenomanian–Early Turonian, the Ksour Basin was an isolated platform at mid to outer shelf depths. The neritic conditions were interrupted by pelagic conditions in transgressive intervals. This deepening of the palaeoenvironment is reflected by changes in the foraminiferal assemblages. The composition of benthic and planktic foraminiferal assemblages, characterized by low diversity and abundance of low oxygen tolerant species, reflects a carbonate platform with biotic stress conditions (oxygen and nutrient fluctuations and sea-level changes). Planktic foraminiferal assemblages are dominated by opportunists such as Muricohedbergella and Planoheterohelix, which colonized new ecospace on the shelf during the transgression. The Oceanic Anoxic Event 2 (OAE2) is not represented by organic rich facies but does coincide with the successive proliferation of different opportunist organisms such as microgastropods and small echinoid (hemiasterids) and the heterohelicid shift. The continuous presence of trace fossils (Thalassinoides and Planolites-like) and benthic macroinvertebrates allows us to exclude anoxic conditions during the Whiteinella archaeocretacea Zone. The proliferation of Planoheterohelix indicates the record of eutrophic conditions and the transition from oxygenated to poorly oxygenated waters during stratified open marine settings at the time of maximum flooding. The subsequent increase in thin-shelled bivalves and cytherellid ostracods would confirm the stress conditions at the time of the δ13C isotopic excursion in the upper part of the W. archaeocretacea Zone. The Lower Turonian is represented by a shallowing upward trend in the Ksour Basin. Comparison of the taxonomic composition of the planktic foraminiferal assemblages (phenogram and class diagram) indicates the high degree of relationship of the Ksour Basin with the Northeast Sicily Basin, Central Tunisia Basin and Egypt. This work sheds light on the impact of the OAE2-related environmental perturbation in environments where anoxic conditions were not reached, as well as the response of the fossil assemblages to the biotic crisis.

STRATİGRAPHY AND STRUCTURE OF THE SOUTHEASTERN PART OF PİRAMAGROON ANTİCLİNE, SULAİMANİ AREA, NORTHEAST IRAQ

The Piramagroon anticline (or Pira Magrun Mountain) elongates directly to northwest of Sulaimani city, Northeast Iraq and its southeastern part contains two other anticlines, named Harmetool and Yakhyian anticlines in addition to their complementary synclines and many other smaller folds. The anticline has experienced intense search for oil in the last few years and a well is drilled to depth of 3000 meters without reaching oil or gas. In the present study, the southeastern part has been studied stratigraphically and structurally and the previous studies are critically reviewed which may help reveal the reason for absence of oil in the area. The stratigraphy of the anticline has been differentiated and Kometan, Gulneri and Dokan, Balambo and Sarmord formations are plotted on a geological map and stratigraphic column and the nannofossils are used for aging of intervals that their ages are no determined previously. The thickness of the Gulneri Formation is 2-4m and the nannofossils analysis showed that its age is Late Cenomanian-Early Turonian. Lithology and bedding styles of the Dokan and Upper part of the Balambo formations are very similar to Kometan Formation and they can be differentiated either by fossils or by using Gulneri Formation as marker bed. The outcrop of the Gulneri Formation is helpful for differentiation since it is soft and can be recognized easily in the field by its darker color. The structure of the anticline is relatively complex as it consists mainly of asymmetrical anticlines with southwest vergen in few places while it changes to overturned folds in others and are deformed by reverse fault. The anticlines are shaped by detachments on the Gulneri and Sarmord formations and other older soft rocks. The resulted anticlines have style of multi-detachment fold or multi-detachment faulted fold .

Late Cretaceous (Cenomanian-Turonian) ammonites from southern Morocco and south western Algeria

On the basis of nine lithostratigraphical profiles, 23 cephalopods taxa (nautilus and ammonites) are described from the Preafrican Trough and the Kem Kem region. Among them, a new species is proposed: Spathites (Jeanrogericeras) asflaensis nov. sp. This fauna is placed in its biostratigraphical framework and correlated with the standard zonation of the late Cenomanian–early Turonian. Moreover, stratigraphic correlations are proposed for the whole Maghreb from the Tarfaya Basin in the west to central Tunisia in the east. Selected taxa reveal the paleogeographical context of the western Tethys; a complex distribution of emerged areas and epicontinental seas impacted by an important marine trangression that constantly modified the costaline.

Authigenic siliceous-carbonate concretions in Cenomanian–Turonian carbonates of southern Croatia; geochemical and biotic record

Numerous regular and irregularly shaped concretions were discovered in southern Croatia within the Upper Cretaceous carbonate deposits, which consist mostly of bioclastic wackestones and packstones. The size of the concretions varies from 2 to 25 cm in diameter for the regular, and up to 40 cm in length for the irregular ones. The concretions have different internal structures and compositions, which vary from those of the host rocks. Some concretions are entirely siliceous, while others exhibit alternating opal silica and carbonate-rich zones. Silica is derived from opal-A secreting marine biota, mostly sponges, whose spicules can be found within the concretions and in the surrounding limestones. The regular shape and alterations of zones are the result of the diffusive supply and fast “consummation” of silica at the growth site. Determined fossil community and bitumen found in the surrounding limestones indicate deposition in the oxygen-depleted deep-marine environment of the Adriatic Carbonate Platform, which belongs to the Sveti Duh Formation (latest Cenomanian–Early Turonian). The carbon isotope composition of the concretions corresponds to the globally known Cenomanian–Turonian ‘Oceanic Anoxic Event’ (OAE 2).