Maastrichtian Research Articles

Benthic foraminifera from the Albian shallow-marine limestones in the Geyik Dağı area (Central Taurides), southern Turkey

AbstractCretaceous carbonates in the Geyik Dağı area (Central Taurides, southern Turkey) are represented by two successions with different paleoenvironmental settings: open shelf to slope succession of Cenomanian to Danian age and inner platform succession of Albian to Maastrichtian age, which is interrupted by a post-Cenomanian disconformity. Outcropped lowermost part of the platform-type one is composed of rudistid limestones corresponding to the Urgonian-type carbonates and belongs to the Geyik Dağı Unit (=Anamas-Akseki Carbonate Platform). It contains a rich assemblage of larger benthic foraminifera including orbitolinid, chrysalidinid, cuneolinid, nezzazatid, and miliolid taxa, which has been illustrated and documented here for the first time from the upper Albian of the Tauride Carbonate Platform. The occurrence of such a diversified foraminiferal fauna indicates a prominent high diversity that took place in the Tauride Carbonate Platform during the late Albian time, which corresponds to a major emersion period in some parts of the platform.

Discussion of the paper by Yahya et al. 2018 entitled “Paleoenvironmental and paleoclimatic conditions during the deposition of the bauxite layer (Upper Cretaceous) using multi-proxy geochemical and palynological analyses, in the Zabirah Area, Northern Saudi Arabia” (Arabian Journal of Geosciences v.11, Article No.15)

Yahya et al. (2018) interpreted the palaeoenvironmental and palaeoclimatic conditions prevalent during the formation of the Late Cretaceous Az Zabirah Bauxite in Northern Saudi Arabia. They suggest that claystones associated with the bauxite profile are of Maastrichtian age based on palynology. This age interpretation is counter to the evidence of decades of detailed mapping and biostratigraphic analyses conducted by specialists from the Bureau de Recherches Geologiques et Minieres (BRGM) that demonstrate an Albian to Cenomanian age for the Az Zabirah Bauxite. This older age is even reported in Yahya et al.’s text quoting BRGM and Arabian American Oil Company palynology reports yet, for reasons that remain obscure, was rejected in favour of an unsubstantiated Maastrichtian age. More recent publications on the Cretaceous stratigraphy of Saudi Arabia were not cited. Furthermore, the palynology presented in the paper does not confirm their age interpretation. A second bauxite horizon, the “Pre-Aruma Bauxite” is present nearby but all descriptions and illustrations in the paper suggest that this is not the studied horizon. Moreover, recent Sr isotope dating suggests that the “Pre-Aruma Bauxite” is older than Middle Campanian. The value of sedimentological, palaeoclimatic and palaeoenvironmental interpretations requires them to be placed in their correct stratigraphic context. The authors have singularly failed to achieve this in their publication.

A diversified Ostracoda (Crustacea) assemblage from the Upper Cretaceous intertrappean beds of Gujri, Dhar District, Madhya Pradesh, India

Two new non-marine ostracod species, named Gomphocythere testudo sp. nov. and Candona phaseolus sp. nov. are described from the intertrappean beds exposed near Gujri village in District Dhar, Madhya Pradesh, Central India along with common Deccan intertrappean ostracod species Cyclocypris sahnii, Cypria cyrtonidion, Paracypretta jonesi, Periosocypris megistus and Stenocypris cylindrica. Presence of five other ostracod taxa, viz., Frambocythere tumiensis anjarensis, Gomphocythere strangulata, G. paucisulcatus, Zonocypris gujaratensis and Eucypris intervolcanus documented earlier from this locality are also present in our sample. Barring the two new taxa, the other ten species are also known to occur in coeval intertrappean and infratrappean beds of eastern, central, southern and western parts of the Deccan volcanic province. A Maastrichtian age is inferred for the fossiliferous horizon based on the ostracod fauna. Biostratinomical assessment of ostracod assemblages was carried out followed by palaeoecological and palaeoenvironmental analyses. The presence of non-marine ostracods in association with terrestrial vertebrate remains, gastropods, and charophytes favours a freshwater depositional environment for the Gujri intertrappean beds and do not provide any evidence for the prevalence of supposed marine conditions along the Narmada lineament in the latest Cretaceous.

‘X’ marks the spot! Sedimentological, geochemical and palaeontological investigations of Upper Cretaceous (Maastrichtian) vertebrate fossil localities from the Vălioara valley (Densuş-Ciula Formation, Hațeg Basin, Romania)

At the beginning of the 20th century, the Croatian-Hungarian palaeontologist Ottokár Kadić discovered a rich Late Cretaceous vertebrate assemblage around Vălioara in the Haţeg Basin, including fossils of several dinosaurs and the lectotype of the eusuchian Allodaposuchus. These fossils were collected from seven main localities and have been housed in the collections of the Mining and Geological Survey of Hungary. However, the collection was mixed after World War II, and this unprovenanced material currently cannot be used for palaeoecological investigations. Nevertheless, the map marking the location of Kadić’s sites has been recently uncovered, showing the positions of the fossiliferous localities, which allows matching these with the historically collected specimens using geochemistry. Based on Kadić’s map, we georeferenced, relocated, and re-excavated these vertebrate-bearing outcrops, and documented their sedimentological context. Detailed stratigraphical investigations of the exposed successions indicate that this Vălioara material represents one of the oldest (earliest Maastrichtian) Late Cretaceous faunal assemblages known from the Haţeg Basin. The vertebrate remains collected during our new excavations around Vălioara represent turtles (Kallokibotion), crocodyliforms (Allodaposuchus, Doratodon, ‘Theriosuchus’, Acynodon), dinosaurs (Zalmoxes, Telmatosaurus, titanosaurs, theropods), and mammals. In order to determine potential geochemical differences among the sites, we selected several specimens with recorded stratigraphic position, measured their trace element compositions, and used these as independent proxies to assess the probable stratigraphic origin of the historical vertebrate fossils. Our detailed sedimentological, geochemical and palaeontological investigations around Vălioara contribute to a deeper understanding of the distribution, evolution and palaeoecology of the Haţeg vertebrate faunas during the latest Cretaceous.

Palynofacies analysis and depositional environments of Upper Cretaceous sediments in the ST‐9H well, offshore South Tano Basin, Western Ghana

Palynofacies analyses were carried out on 43 cutting samples from the ST 9H well in the Tano Basin, with the view of reconstructing the palaeoenvironment of the Upper Cretaceous sediments in the well. The stratigraphic distribution of the palynofacies assemblages defined four palynofacies units. Palynofacies PA reflects deposition in near shore/shallow marine (inner neritic) environment under distal dysoxic‐anoxic shelf condition. Palynofacies PB was deposited in an inner–middle neritic environment under mud‐dominated oxic shelf conditions, Palynofacies PC in an open marine (outer neritic) environment under distal suboxic‐anoxic basin conditions, and Palynofacies PD in a proximal–marginal marine environment under dysoxic‐anoxic basin conditions. These palynofacies assemblages (PA–PD) are characterized by kerogen types II (oil prone), III‐IV (gas prone), II > I (oil prone), and III (gas prone), respectively. Marker dinoflagellate and miospore assemblages recovered from the sediments –are indicative of a Campanian–Maastrichtian age. The palaeofloral association and the perideanacean dinocysts assemblage are typical of Senonian Palme Province and the Malloy suite, respectively. These assemblages are indicative of a warm and humid tropical‐subtropical climatic condition.

Planktonic Foraminifera Biostratigraphy of Shiranish Formation in Piramagroon Anticline, NE Iraq

67 planktonic foraminiferal species were identified from the Shiranish Formation. On the basis of the stratigraphic distribution of the planktonic foraminiferal assemblages recognited of six biozones within the Shiranish Formation representing an age ranging from Middle Campanian – Early Maastrichtian, these zones are from older at base: 6 -Planoglobulina acervulinoides Interval Zone. 5 - Contusotruncana contusa Total Range Zone. 4 -Gansserina gansseri Interval Zone. 3 - Globotruncana aegyptiaca Interval Biozone. 2 -Globotruncanella havanensis Interval Biozone. 1 -Globotruncana ventricosa Interval Biozone

Biostratigraphy and Systematic Palaeontology of Late Cretaceous Heterohelicidae Foraminifera from Kurdistan Region North-eastern Iraq

The biostratigraphical importance and systematic palaeontology of Early Turonian to Early Maastrichtian Heterohelicidae Planktic foraminifera from Kurdistan region, NE Iraq are described. Some 24 species from 11 genera are recorded. Species abundance and diversity increase from the Early Turonian to Early Maastrichtian, perhaps signifying cooler sea temperatures in the Arabian sector of the Tethys Ocean during the Early Maastrichtian. Despite the long biostratigraphical ranges of some species, the importance of the biserial and multiserial Planktic foraminifers in Late Cretaceous biostratigraphy is emphasized. From a biostratigraphic perspective, heterohelicids are important for the definition of the Campanian-Maastrichtian boundary in Kurdistan region, with Planoglobulina species being especially important in this respect, as they are in Iran, Turkey and North Africa.

Biostratigraphy and paleobiogeography of the Gan’kino horizon (Maastrichtian) of the Western Siberia

Research subject. This paper investigates Maastrichtian (Upper Cretaceous) foraminifera complexes present in various parts of the Western Siberia.Materials and methods. The materials of parametric drilling performed in the last century were reviewed in the context of new data. The characteristics of the main ecological microfauna groups in the Gan’kino horizon (Maastrichtian) were clarified by analysing their taxonomic composition, structure and diversity. Results. It was shown that, in the typical Yamal-Tyumen district, the Gan’kino horizon consists of three zones: Spiroplectammina variabilis, Gaudryina rugosa (with subzones Bolivina decurrens, Bolivinoides senonicus and Stensioeina caucasica transuralica), Spiroplectammina kasanzevi, Bulimina rosenkrantzi (with subzones Bolivina plaita, Bulimina rosenkrantzi and Heterostomella foveolata) and Brotzenella praeacuta. Here, the horizon volume is limited to the Maastrichtian stages. The Stensioeina caucasica transuralica and Brotzenella praeacuta zones were found to belong to the Upper Maastrichtian.Conclusions. It was established that, the Early and early Late Maastrichtian was characterized by a gradual increase in the diversity of foraminifera complexes due to immigrants from the Boreal-Atlantic realm. The widespread distribution of foraminifera complexes from the Northern district across the Western Siberia during the Spiroplectammina kasanzevi and Bulimina rosenkrantzi period was associated with the transgression of Arctic waters. The appearance of the foraminifera associations with Heterostomella foveolata reflects a wide levelling of the foraminifera composition throughout the Western Siberia. At the beginning of the Brotzenella praeacuta time, Boreal-Atlantic taxa were widely dispersed across the Western Siberian basin.

The Campanian–Maastrichtian interval at The Naze, James Ross Island, Antarctica: microbiostratigraphic and paleoenvironmental study

A biostratigraphic and paleoenvironmental characterization of the Campanian–Maastrichtian deposits on The Naze (James Ross Island, Antarctica) based on the foraminiferal assemblages, lithofacies analysis, and Hg/total organic carbon (TOC) data was developed. The sedimentary deposits mapped in The Naze region showed an association of four sedimentary lithofacies, including greenish-gray claystone, shales with levels of concretion, bioturbated marl, and sandstone. The sedimentary deposits have been covered by a fifth lithofacies, the James Ross Island Volcanic Group (JRIVG), which consists of pyroclastic rocks interbedded with basalt bodies. The association of agglutinated foraminifera was found to consist mainly of Rzehakina epigona, Trochammina ribstonensis, Gaudryina healyi, Karreriella aegra, Dorothia elongata, Alveolophragmium macellarii, Cyclammina complanata and Spiroplectammina spectabilis, that allow to infer a Campanian–early Maastrichtian age to the studied interval. An association of opportunistic agglutinated foraminifera predominated in this stressful environment. The absence of Hg-TOC unassociated excursions ruled out distal volcanism as a source of environmental stress, while Hg/TOC ratio variability suggested that regional oceanic processes were the major environmental change driver.

New Sedimentological, Magnetostratigraphic, and Biostratigraphic Data on the Campanian–Maastrichtian of Beshkosh Mountain, Southwest Crimea

An integrated study of the Campanian–Maastrichtian deposits of Beshkosh Mountain (Southwest Crimea) was carried out. The finds of cephalopods and dinocysts were studied, and ichnofacies and sedimentological analyses were performed. Isotopic, paleomagnetic, and petromagnetic data were obtained for the first time. New macro- and micropaleontological data made it possible to refine the stratigraphic subdivision of the section and confirm its late Campanian–Maastrichtian age. Paleomagnetic studies have revealed no analogs of magnetic Chron C31r. The only recognizable reversed-polarity magnetozone against the background of the prevailing normal polarity was identified as an analog of Chron C30r. The study of dinocysts revealed a sharp change in their assemblages in the lower part of the section, above which ammonite Pachydiscus (P.) neubergicus neubergicus (Hauer), a marker species of the Campanian–Maastrichtian boundary, was found. An integrated biostratigraphic, magnetostratigraphic, and sedimentological analysis made it possible to recognize the previously unknown unconformity in the Campanian–Maastrichtian boundary interval. Data of stable isotopes are consistent with the proposed hiatus.

Porphyry-related high-sulfidation mineralization early in Central American Arc development: Cerro Quema deposit, Azuero Peninsula, Panama

The 70.74 to 70.66 Ma age range for three molybdenite samples accompanying pyrite- and enargite-bearing assemblages effectively constrains an earliest Maastrichtian age for the high-sulfidation Au-Cu mineralization at Cerro Quema, Panama. The epithermal system was contemporaneous with emplacement of a composite dacite dome complex in a geotectonic setting transitional from mafic, primitive intraoceanic (Azuero Protoarc) to more evolved island arc magmatism (Azuero Arc), during initial construction of the Central American land bridge at the trailing edge of the Caribbean Large Igneous Province (CLIP). The molybdenite ages confirm the rapid evolution of the earliest stages of the Central American Arc, from subduction initiation at 75–73 Ma to arc maturation at 71 Ma. A porphyry connection is apparent at Cerro Quema and characterized by highly contorted, banded, and planar quartz-veinlet stockworks and sheeted zones in pyrophyllite- and sericite-bearing patchy-textured rock. These are cut by ledges of quartz, alunite, and dickite, which implies overprinting of the advanced argillic lithocap onto the underlying porphyry environment. Hydrothermal telescoping resulted from synmineralization uplift congruent with an actively emerging volcanic arc, which the Re-Os molybdenite dates accurately constrain at 71 Ma, presumably as a far-field effect of collision between the leading edge of the CLIP with parts of North and South America.

Morphological changes of the large foraminiferal genus Loftusia during the Maastrichtian and its palaeogeographical inferences from the Zagros and Neotethys basins

This study examines the morphological changes of the Loftusia genus from the Zagros Belt of southern Iran using quantitative data. Eight Tarbur Formation outcrops were investigated in the High Zagros and the Lurestan sub zones. The observed Loftusia species are of mid Maastrichtian age in the High Zagros and the mid to late Maastrichtian age in the Lurestan and Murak areas, and they are often observed in deposits of the lagoon environments with high nutrient conditions. Two (Tang-e Shabi Khoon area) and four (Murak area) cycles were recognized based on the morphological parameter changes of Loftusia species. The correlation of the number of cycles of Loftusia species between the Zagros basin and the different areas of the Neotethys basin indicates that Loftusia species sizes change in time. The obtained data shows that the number of the sedimentary cycles (alternating shale and limestone layers) in the High Zagros zone is more different than the Lurestan zone. The High Zagros zone comprises rich terrigenous shale with higher nutrient flux in comparision to the Lurestan zone and other areas of the Neotethys basins. The number of cycles decreased from the southeast toward the northwest of the Neotethys basin. It is thought changes in Loftusia species in the Zagros basin are related to nutrient input during the Maastrichtian age and were independent of evolutionary trends.The genus Loftusia disappeared in the High Zagros zone at the end of the late Maastrichtian. The subsidence of the basin is associated with the Dena and High Zagros Faults. Due to the activities of those faults, the Tabur Formation was not deposited in the High Zagros zone areas. The genus Loftusia appeared in the southeast region of the Arabian plate during the early Maastrichtian, and migrated to the northwest of the Neotethys during the Maastrichtian.

Late Maastrichtian to Danian organic-walled dinoflagellate cysts and calcareous nannofossils from eastern Austral Basin, Patagonia, Argentina

Late Maastrichtian to Danian dinoflagellate cyst and calcareous nannofossil biostratigraphy was analyzed at the Sur Río Chico borehole, Austral Basin, Argentina. Two stratigraphical intervals from the 965 to 1003 m below ground surface of the drilled section were defined. The co-occurrence of Manumiella bertodano, M. seelandica and M. conorata in the 990–1000 to 1000–1003 mbgs interval, associated with the top of the nannofossil Neprolithus frequens miniporus Zone indicated a late (probably latest) Maastrichtian age. The acme of the presumed heterotrophic Manumiella spp. and the acme of the mesotrophic cool-water nannofossil Prediscosphaera stoveri, together with other cool-water taxa Arkhangelskiella cymbiformis, Kamptnerius magnificus and Nephrolithus frequens may indicate cool nutrient–rich waters in this interval. Finally, the co-occurrence of dinoflagellate cyst taxa Carpatella cornuta, Cerodinium diebelii, Danea californica, Senoniasphaera inornata and Palaeoperidinium pyrophorum linked to the nannofossil NP3 Zone, suggest a middle Danian age for the 965–970 to 985–990 mbgs interval. An acme of P. pyrophorum herein related to the Pp2 of New Zealand, might reflect an episode of cool temperature during the Danian in the Austral Basin. The sedimentary succession is represented by the Campo Bola Formation within which two discontinuities were recognized; the older is of early-late Maastrichtian, and the younger is of the latest Maastrichtian to the earliest Danian. A third discontinuity involving the middle to late Paleocene separates the Campo Bola Formation from the overlain Eocene Man Aike Formation.

An elongate hadrosaurid forelimb with biological traces informs the biogeography of the Lambeosaurinae

AbstractAlthough the fossil record of the Late Cretaceous eastern North American landmass Appalachia is poor compared to that from the American West, it includes material from surprisingly aberrant terrestrial vertebrates that may represent relictual forms persisting in relative isolation until the end of the Mesozoic. One intriguing question is to what extent eastern and western North American faunas interspersed following the closure of the Western Interior Seaway during the Maastrichtian Stage of the Late Cretaceous ca. 70 Ma. Isolated remains from the Atlantic Coastal Plain in New Jersey have been preliminarily identified as the bones of crested lambeosaurine hadrosaurids, a derived clade known from the Cretaceous of Asia, western North America, and Europe, but have not been formally described. We describe the partial forelimb of a large hadrosaurid from the late Maastrichtian New Egypt Formation of New Jersey. The ulna preserves multiple deep scores identifiable as shark feeding marks, and both bones show ovoid and circular marks attributable to invertebrates. This forelimb is very similar to another partial antebrachium from the same area that shows evidence of septic arthritis. Both these specimens and a complete humerus from the same unit are closely comparable to the lower forelimbs of lambeosaurines among hadrosaurid dinosaurs. Although the absence of lambeosaurine synapomorphies observable on the New Egypt Formation forelimbs precludes their definite referral to Lambeosaurinae, they show that a morphotype of large hadrosauromorph with distinctly elongate forelimbs existed in the latest Maastrichtian of eastern North America and allow for a revision of the latest Cretaceous biogeography of crested herbivorous dinosaurs.

The Maastrichtian‐Danian in the SW Zagros Fold‐Thrust Belt (S. Iran): An Integration of Planktonic Foraminiferal Biostratigraphy and Gamma‐Ray Spectrometry

AbstractIn this study, the Maastrichtian‐Danian boundary was measured and sampled in two stratigraphic sections, the north and south flanks of the Dehnow anticline in Coastal Fars, Southern Iran. This boundary was also investigated in the drilled exploratory well‐1 in the same region. The lithology of the Maastrichtian‐Danian deposits consists of glauconitic, phosphatic argillaceous limestones and marlstones. 30 genera and 77 species of planktonic foraminifera have been determined. The recognized biozones are the Gansserina gansseri Interval Zone, and the Contusotruncana contusa Interval Zone, which indicates latest Campanian to middle Maastrichtian age for the upper part of the Gurpi Formation. In addition, the Eoglobigerina edita (P1) Partial Range Zone, Praemurica uncinata (P2) Lowest Occurrence Zone, Morozovella angulata (P3) Lowest Occurrence Zone and Globanomalina psudomenardii (P4) Taxon Range Zone represent a Danian to Thanetian age for the lower part of the Pabdeh Formation. From the absence of the Abathomphalus mayaroensis Interval Zone, Pseudoguembelina hariaensis Interval Zone, Pseudotextularia elegans Interval Zone, Plummerita hantkeninoides Interval Zone, Guembelitria cretacea (P0) Partial Range Zone and Parvularugoglobigerina eugubina (Pα) Total Range Zone, it can be deduced that there is a paraconformity across the Maastrichtian–Danian boundary in the studied area, this hiatus encompassing the late Maastrichtian and the earliest Danian. Danian deposits from the study area contain reworked glauconitized macrofossils, planktonic and benthic foraminifera of the Cretaceous. The obtained surface gamma‐ray spectrometry logs resemble the exploratory well‐1 gamma‐ray wireline log.

Upper Cretaceous-Paleogene stratigraphy and development of the Mímir High, Vøring Transform Margin, Norwegian Sea

Transform margins represent strike-slip type of plate boundaries that form during continental breakup and initial ocean opening. They are often characterized by margin-parallel highs with exposed pre- and syn-rift sequences. The Vøring Transform Margin, offshore mid-Norway, initiated in the earliest Eocene during the opening of the NE Atlantic. Here, 2D seismic reflection data reveal a transform margin high, the Mímir High. The western flank of this undrilled structure is a kilometer-high escarpment where seismic reflections of pre-breakup age are truncated at the seafloor. The aim of this study was to recover seabed rock samples from the outcropping or shallowly buried sedimentary sequences to provide a geological tie to the regional seismic framework, thereby constraining the basin history and tectono-stratigraphic development. Seabed samples were successfully collected from 14 gravity core and Selcore stations and 10 ROV (remotely operated vehicle) sites along a 750 m high sampling profile, recovering clay, shales, sandstones and glacial dropstones. Biostratigraphy results revealed that the ages of the sedimentary rocks follow the stratigraphic order predicted by the initial seismic interpretation, with Upper Cretaceous sediments at the base and lower Eocene sediments at the top. The integrated interpretation shows that the Mímir High area, including parts of the outer Vøring and Møre basins and the proto-Jan Mayen Microplate Complex, were characterized by the deposition of late Campanian to early Maastrichtian, near coastal and shale-dominated sequences with poor source rock qualities. The early Paleocene samples indicate deep marine conditions that abruptly ended by rapid uplift of the Mímir High in the earliest Eocene. Finally, a reworked Pliensbachian palynomorph assemblage in potential early Eocene strata indicate the presence of exposed Mesozoic sequences in the vicinity of the Mímir High. We argue that some of the lower Eocene sediments where deposited within a hypothetical drainage system sourced from Greenland (Traill Ø or Jameson Land) and/or from the Jan Mayen Ridge prior to continental separation, and not the result of recent ice-rafting.

Organic geochemical and palynological studies of the Maastrichtian source rock intervals in Bida Basin, Nigeria: implications for hydrocarbon prospectivity

The Patti Formation which consists of sandstone and shale offers the best potential source beds in the Bida Basin. This inland basin is one of the basins currently being tested for hydrocarbon prospectivity in Nigeria. Fresh samples of shale from Agbaja borehole, Ahoko quarry and Geheku road cut were analysed using organic geochemical and palynological techniques to unravel their age, paleoecology, palynofacies and source bed hydrocarbon potential. Palynological data suggest Maastrichtian age for the sediments based on the abundance of microfloral assemblage; Retidiporites magdalenensis, Echitriporites trianguliformis and Buttinia andreevi. Dinocysts belonging to the Spiniferites, Deflandrea and Dinogymnium genera from some of the analysed intervals are indicative of freshwater swamp and normal sea conditions. Palynological evidence further suggests mangrove paleovegetation and humid climate. Relatively high total organic carbon TOC (0.77–8.95 wt%) was obtained for the shales which implies substantial concentration of organic matter in the source beds. Hydrocarbon source rock potential ranges from 0.19 to 0.70 mgHC/g.rock except for a certain source rock interval in the Agbaja borehole with high yield of 25.18 mgHC/g.rock. This interval also presents exceptionally high HI of 274 mgHC/g.TOC and moderate amount of amorphous organic matter. The data suggests that in spite of the favourable organic matter quantity, the thermal maturity is low as indicated by vitrinite reflectance and Tmax (0.46 to 0.48 Ro% and 413 to 475 °C, respectively). The hydrocarbon extracts show abundance of odd number alkanes C27–C33, low sterane/hopane ratio and Pr/Ph > 2. We conclude that the source rocks were terrestrially derived under oxic condition and dominated by type III kerogen. Type II organic matter with oil and gas potential is a possibility in Agbaja area of Bida Basin. Thermal maturity is low and little, or no hydrocarbon has been generated from the source rocks.

A new ophiacanthid brittle star (Echinodermata, Ophiuroidea) from sublittoral crinoid and seagrass communities of late Maastrichtian age in the southeast Netherlands.

A new species of brittle star, Ophiomitrella floorae, is recorded from the lower two meters of the Gronsveld Member (Maastricht Formation), of late Maastrichtian age (c. 66.7 Ma). These relatively fine-grained biocalcarenites reflect shallow-water deposition in a sheltered setting with a relatively firm sea floor and clear waters, under middle sublittoral and subtropical conditions. Associated echinoderm taxa comprise more robust, sturdy-plated ophiomusaid and ophiodermatid brittle stars and numerous bourgueticrinine sea lilies. The new brittle star described herein belongs to a family whose present-day members are predominantly restricted to bathyal depths. Its small size and the exceptional preservation of a single articulated specimen partially wrapped around the stalk of a bourgueticrinine suggest that O. floorae n. sp. was probably epizoic and specifically associated with stalked crinoids.

Chemical and isotope composition of the oilfield brines from Mishrif Formation (southern Iraq): Diagenesis and geothermometry

This paper focuses on the geochemical composition and isotope geochemistry of brines in the Cenomanian–Turonian carbonate Mishrif reservoir of southern Iraq. Main dissolved constituents, trace elements, δ2H and δ18O, 87Sr/86Sr, mineral saturation indices and thermodynamic calculations were investigated in formation waters from the Mishrif Formation to obtain a better understanding of brine evolution and diagenetic effects over geological time. Previous published δ11B data were also reinterpreted as a geothermometer tool. The results are compared with previous published data for local oilfields and coeval formations in the Arabian Gulf. The Mishrif brine has a marine origin and is diagenetically modified to Ca-excess and Na-deficit. Formation waters are quartz supersaturated and are in equilibrium with chalcedony and calcite-dolomite in the temperatures range of 50–75 °C, which is also confirmed by calcite-water oxygen isotope fractionation and δ11B geothermometer. The potential role of clays in conditioning brine chemistry during diagenetic processes was highlighted by activity diagrams; in particular, their adsorption/exchange effect on sodium could explain the lower temperature obtained by the Na/Li geothermometer (42 ± 6 °C). The δ2H and δ18O values show that oxygen isotope composition of the brines was isotopically more affected by interaction with limestone during diagenesis than seawater evaporation. The main effect is an 18O-enrichment on the brine starting from the SMOW value. Locally, dilution by present-day meteoric water was also detected (Rumaila South), which is shifted towards the local meteoric water line. The strontium isotope ratios range from 0.707713 to 0.707749 and correspond to a marine strontium of late Cenomanian–early Maastrichtian age, except for the Majnoon sample, which shows a more radiogenic value (0.708043). Radiogenic strontium and gypsum and anhydride saturation indices of the Majnoon sample could indicate the contribution of calcium and sulphate from the strontium-rich sulphate minerals of the Cambrian salt domes occurring in the oilfields of southern Iraq. The higher manganese concentration (4 mg/l) and the slightly higher temperature inferred by geothermometers (up to 74 °C) in comparison with present-day could indicate that the Majnoon brine is a hot fluid, probably related to a deeper structure such as the Zagros Foredeep Fault.

Cretaceous succession of the Cambambe basin, Chapada dos Guimarães, Mato Grosso, Brazil

This paper aims to show the filling and stratigraphy of the units that constitute the Cambambe Basin, that is located at the mid-southern portion of the State of Mato Grosso, Brazil. The rocks of this vulcano-sedimentary unit have been deposited during Upper Cretaceous, between the Santonian and Maastrichtian Stages. The scientific literature has been associated these units to different basins, such as the Paraná Basin, the Parecis Basin and the Bauru Basin and also to other different lithostratigraphic units. Such confusion was the motivation to carry out this study in which the description and interpretation of facies associations was the main tool to clarify some of the aspects related to the Cambambe basin evolution. It has been observed five facies: Polymytic Conglomerate (PCF), Oligomitic Conglomerate (OCF), Siltstone and Mudstone (SMF), Litharenite (LF), Quartzarenite Facies (QF). This facies points to an alluvial fan system, with facies associations interpreted as corresponding to three portions: proximal, immature plains and mature plains. Such facies associations corresponds to the lithostratigrphic units that constitutes the Cambambe basin: the lower portion is the Ribeirão Boiadeiro Group, consisting of the interfingering Quilombinho and Cachoeira do Bom Jardim formations and the upper portion is the Cambambe Formation. An erosive unconfomity separates both portions. The sedimentary record exceeds 400 m in thickness and demonstrates a long-term deposition marked by numerous non-deposition surfaces, including paleosols.