Structural style and fault kinematics of the Lower Eocene Rus Formation at Jabal Hafit area,Al Ain,United Arab Emirates (UAE)

The current contribution presents aspects of the structural style and fault kinematics of the Rus Formation that expose at Jabal Hafit, Al Ain, United Arab Emirates. Although the major structure of Jabal Hafit is an anticlinal fold, fractures (joints and faults) are the prominent structure of the study area. The fractures can be interpreted as the distributed effect of deep-seated basement fault reactivation or to be as reactivation of deep-seated basement faults. These fractures were created during two main tectonic stress regimes. The first is a WNW–ESE S _Hmax strike-slip stress regime, responsible for producing E–W to ESE–WNW joints and E–W dextral strike-slip and NNE–SSW reverse faults. This stress is interpreted to be post-Early Eocene in age and related to the second phase of thrusting in the Oman Mountains in the Miocene. The second stress regime is a NNE–SSW S _Hmax transtensional (strike-slip extensive) stress regime that was responsible for N–S to NNE–SSW striking joints and NE–SW sinistral strike-slip and N–S normal faults. This regime is interpreted to be post-Middle Eocene in age. This stress was the response to the collision of the Arabian–Eurasian Plates which began during the Late Eocene and continues to the present day.     

Architecture of the Oman–UAE ophiolite: evidence for a multi-phase magmatic history

The Oman–United Arab Emirates ophiolite is the world’s largest ophiolite. It is divided into 12 separate fault-bounded blocks, of which the northern three lie wholly or partly in the United Arab Emirates. Extensive mapping has shown that the United Arab Emirates blocks contain mantle and crustal sections which correspond to the classic ‘Penrose conference’ ophiolite definition but which are cut by a voluminous later magmatic sequence including ultramafic, mafic and felsic components. Samples from the later magmatic sequence are dated at 96.4?±?0.3, 95.74?±?0.3 and 95.2?±?0.3 Ma; the early crustal section, which has not been dated directly, is thus constrained to be older than c. 96.4 Ma. Petrological evidence shows that the early crustal section formed at a spreading ridge, but the later magmatic sequence was formed from hydrous magmas that produced different mineral crystallisation sequences to normal mid-ocean ridge basalt (MORB). Mineral and whole-rock geochemical analyses show that the early crustal rocks are chemically similar to MORB, but the later magmatic sequence has chemical features typically found in supra-subduction zone (SSZ) settings. The ophiolite in the United Arab Emirates thus preserves clear evidence for two stages of magmatism, an early episode formed at a spreading centre and a later episode associated with the onset of subduction. Similar two-stage magmatism has been recognised in the Oman sector, but the United Arab Emirates contains the most voluminous SSZ magmatism yet described from this ophiolite.     

New Middle Ordovician (Darriwilian) faunas from the Sultanate of Oman

New trilobite material and the first graptolites from outcrop are described from the Am5 member of the Amdeh Formation near Al Fleij in northeast Oman. The sediments in which these faunas occur are interpreted as distal-shelf deposits with storm beds packed with brachiopods and orthoconic nautiloids. The deposits and its faunas are considered of late Darriwilian age and younger than the shallower-water Am5 deposits known from other outcrops. No palynomorphs could be recovered to confirm this due to the increased burial temperature the Al Fleij area has experienced.The trilobites are of considerable palaeo-biogeographic interest as few faunas of this age are known from the Arabian Plate, though their preservation precludes the establishment of new species. They include Isabelinia aff. glabrata, Liomegalaspides sp., Neseuretus tristani, Neseuretinus sp. and the deeper-water forms, Cyclopyge cf. C. bohemica, Arthrorhachis sp. and Brachypleura sp. The graptolites are pendent Didymograptus spp. of later Darriwilian type.Rare elements of the conodonts Nordiora, Amorphognathus and Microzarkodina have been recovered from shell beds that occur interbedded with the faunas. They too indicate a late Darriwilian age and differ from richer, restricted, shallow-water faunas known from the Am5 at other locations, and the more cosmopolitan shelf fauna from the Ayim Member of the Rann Formation of the United Arab Emirates.A coarser, 80 m-thick, terrestrial sequence containing igneous pebbles, included in the Am5 in the 1980s, is shown from the occurrence of fossil plants to be of Permian age and probably equivalent to the Basal Saiq Clastics of Jabal al Akhdar.     

The Albian to Turonian carbon isotope record from the Shilaif Basin (United Arab Emirates) and its regional and intercontinental correlation

The sedimentary record of the Arabian Shelf offers a unique opportunity to study the Cretaceous (Albian–Turonian) greenhouse climate from a palaeoequatorial perspective. In particular, hemipelagic to pelagic carbonate successions from the extensive Shilaif intra‐shelf basin have the potential to produce an excellent record of carbon cycle perturbations during this interval. This study presents a 269 m thick chemostratigraphic (carbonate δ¹³C and δ¹⁸O) record from the Middle Albian to Early Turonian of central Abu Dhabi (United Arab Emirates), representing over 14 Myr of uninterrupted carbonate sedimentation. The Mauddud to Shilaif formations represent outer ramp to basinal intra‐shelf carbonates with variations from laminated organic‐rich to clean bioturbated intervals. Isotopic evidence of the latest Albian Anoxic Event (Oceanic Anoxic Event 1d), Middle Cenomanian Event I and the Cenomanian–Turonian Anoxic Event (Oceanic Anoxic Event 2) are confirmed and biostratigraphically calibrated by means of calcareous nannofossils. The carbon isotope record allows correlation with other regional records and well‐calibrated records across the Tethyan Ocean and represents a significant improvement of the chronostratigraphic framework of the United Arab Emirates (Shilaif) and Oman (Natih) intra‐shelf basins. The study further confirms that low carbon isotope values corresponding to the two source rock intervals in the Shilaif Formation clearly precede the isotopic expressions of Oceanic Anoxic Event 1d and Oceanic Anoxic Event 2.     

Understanding carbonate ramp dynamics using δ13C profiles: examples from the Neoproterozoic Buah Formation of Oman

The Late Neoproterozoic Buah Formation (Nafun Group, Oman) is a carbonate unit outcropping in the Jabal Akhdar and Huqf areas. It is composed mostly of shallow‐water carbonates deposited on a distally steepened carbonate ramp. Correlation of two δ¹³C isotope shifts shows that in the Jabal Akhdar ramp differentiation into fast and slow subsiding areas was followed by lateral progradation. In the Huqf area, however, a uniform scenario of upward shallowing of the facies and lateral progradation is demonstrated by chemostratigraphic timelines cross‐cutting the facies belts. The chemostratigraphic profiles show that the Buah Formation was deposited during sea‐level highstand conditions and that ramp differentiation was due to synsedimentary tectonics. High‐resolution correlation of δ¹³C profiles from the same lithostratigraphic unit (whether Precambrian or Phanerozoic in age) lacking biostratigraphic data can shed light on carbonate systems dynamics, tectonic vs. eustatic controls on depositional sequences and basin subsidence.     

The March 11, 2002 Masafi, United Arab Emirates earthquake: Insights into the seismotectonics of the northern Oman Mountains

A moderate (M 5) earthquake struck the northeastern United Arab Emirates (UAE) and northern Oman on March 11, 2002. The event was felt over a wide area of the northern Emirates and was accompanied by smaller (felt) events before and after the March 11 main shock. The event was large enough to be detected and located by global networks at teleseismic distances. We estimated focal mechanism and depth from broadband complete regional waveform modeling. We report a normal mechanism with a slight right-lateral strike-slip component consistent with the large-scale tectonics. The normal component suggests relaxation of obducted crust of the Semail ophiolite (specifically, the Khor Fakkan Block) while the right-lateral strike-slip component of the mechanism is consistent with shear across the Oman Line. Felt earthquakes are rare in the region, however no regional seismic network exists in the UAE to determine local seismicity. This event offers a unique opportunity to study the active tectonics of the region as well as inform future studies of seismic hazard in the UAE and northern Oman.     

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

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

New Alveolinoidea (Foraminifera) from the Cenomanian of Oman

The first alveolinoidean appearing in the Cenomanian Natih Formation of Oman (Adam foothills and southern edge of Jabal Akhdar) are studied in detail. Morphological analysis results in the creation of one new family, Myriastylidae, two new genera, Myriastyla and Alveocella, and four new species, M. omanensis, M. grelaudae, A. wernliana, and Cisalveolina nakharensis. These four new taxa have a short stratigraphic extension restricted to the uppermost part of Natih E unit and are dated early middle Cenomanian by neighboring foraminifers and ammonite levels.     

Chemostratigraphy of the Tamengo Formation (Corumbá Group,Brazil): A contribution to the calibration of the Ediacaran carbon-isotope curve

The Corumbá Group, cropping out in the southern Paraguay Belt in Brazil, is one of the most complete Ediacaran sedimentary archives of palaeogeographic, climatic, biogeochemical and biotic evolution in southwestern Gondwana. The unit hosts a rich fossil record, including acritarchs, vendotaenids (Vendotaenia, Eoholynia), soft-bodied metazoans (Corumbella) and skeletal fossils (Cloudina, Titanotheca). The Tamengo Formation, made up mainly of limestones and marls, provides a rich bio- and chemostratigraphic record. Several outcrops, formerly assigned to the Cuiabá Group, are here included in the Tamengo Formation on the basis of lithological and chemostratigraphical criteria. High-resolution carbon isotopic analyses are reported for the Tamengo Formation, showing (from base to top): (1) a positive δ¹³C excursion to +4‰ PDB above post-glacial negative values, (2) a negative excursion to −3.5‰ associated with a marked regression and subsequent transgression, (3) a positive excursion to +5.5‰, and (4) a plateau characterized by δ¹³C around +3‰. A U-Pb SHRIMP zircon age of an ash bed interbedded in the upper part of the δ¹³C positive plateau yielded 543 ± 3 Ma, which is considered as the depositional age ( Babinski et al., 2008a). The positive plateau in the upper Tamengo Formation and the preceding positive excursion are ubiquitous features in several successions worldwide, including the Nama Group (Namibia), the Dengying Formation (South China) and the Nafun and Ara groups (Oman). This plateau is constrained between 542 and 551 Ma, thus consistent with the age of the upper Tamengo Formation. The negative excursion of the lower Tamengo Formation may be correlated to the Shuram–Wonoka negative anomaly, although δ¹³C values do not fall beyond −3.5‰ in the Brazilian sections. Sedimentary breccias occur just beneath this negative excursion in the lower Tamengo Formation. One possible interpretation of the origin of these breccias is a glacioeustatic sea-level fall, but a tectonic interpretation cannot be completely ruled out.     

New biostratigraphic data for the Chikkim Formation (Cretaceous, Tethyan Himalaya, India)

The Chikkim Formation as exposed in the Tethyan Himalaya (India) has been studied at its type locality, using planktonic foraminifera for a detailed biostratigraphic elaboration. Divided into two members, the Lower and Upper Chikkim members, this formation ranges in age from Albian to early Maastrichtian(?), and reaches a maximum thickness of 150 m. Examination of thin sections has yielded 34 species of foraminifera in five genus-level assemblages. The Lower Chikkim Member is about 55 m thick; its basal portion is of Albian age based on the presence of Biticinella breggiensis and Planomalina buxtorfi. At 26 m above the base, Whiteinella archaeocretacaea documents OAE 2 (Oceanic Anoxic Event 2), and thus the Cenomanian/Turonian boundary in this section. The carbonate sequence is capped by a Santonian-age hardground with iron oxide crusts and bioturbation. Macrofossils, including belemnites (at the base) and irregular echinoids (upper part), are present. The basal carbonaceous marls of the Upper Chikkim Member yield both large (benthic) rotaliid as well as planktonic foraminifera (Globotruncanita elevata, Gl. stuartiformis, Gl. stuarti, Gansserina gansseri and others), indicating a Campanian age. The co-occurrence of Gl. elevata and G. gansseri in a single thin section results either from condensation or reworking in the basal part of the Upper Chikkim Member. Late Cretaceous index foraminifera such as Gl. elevata document deposition within the Tethyan Realm. The original thickness of the Upper Chikkim Member is uncertain, but would have been around 100 m; the unit appears markedly reduced through weathering at a height of about 5000 m above sea level. Equivalent sediments are exposed in the Zanskar area to the northwest, and in Nepal and Tibet. Cretaceous Oceanic Red Beds (CORBs) are probably missing due to the proximality of these pelagic settings.     

昆明二村下奥陶统红石崖组顶部Cruziana rugosa遗迹化石群落的沉积环境和生态特征

Cruziana及其相关的遗迹化石是由底栖三叶虫在沉积物表面停歇、爬行所留下的遗迹,一般认为产于潮下带至浅海陆棚环境,具有古水深指示意义。然而,本文通过对昆明民富二村下奥陶统红石崖组顶部含Cruziana rugosa遗迹化石群落层位的沉积环境分析却发现,Cruziana rugosa遗迹化石群落的沉积环境为潮上带—潮间带,说明三叶虫可以在短暂暴露环境中活动。三叶虫的这种适应性活动可能为节肢动物从海洋走向陆地做好了进化准备。     

Early Miocene benthic foraminifera and biostratigraphy of the Qom Formation, Deh Namak, Central Iran

A total of 165 samples were collected from the Qom Formation investigated in a stratigraphic section north of Deh Namak, in Central Iran. From these, 35 genera and 47 species of benthic foraminifera were identified. The age of the studied section is Early Miocene (Aquitanian to Early Burdigalian) based on the occurrence of Borelis melo curdica, Meandropsina anahensis, Meandropsina iranica, Elphidium sp. 14, Peneroplis farsensis, and Triloculina tricarinata. The thickness of the Qom Formation is 401 m of which 161.2 m is early Burdigalian in age. Foraminiferal assemblages in the Deh Namak section are referable to the Borelis melo group-Meandropsina iranica Assemblage Zone and Miogypsinoides-Archaias-Valvulinid Assemblage Zone of [Adams, T.D., Bourgeois, F., 1967. Asmari biostratigraphy. Iranian Oil Operating Companies, Geological and Exploration Division, Report1074 (unpublished) 1–37.] described originally from the Asmari Formation.     

Biostratigraphic interpretation and systematics of Alveolina assemblages from the Ilerdian–Cuisian limestones of Southern Eskişehir, Central Turkey

The Ilerdian–Middle Cuisian sedimentary succession of the Seyitgazi region, southern Eskişehir (Central Anatolia, Turkey) is composed of claystones, limestones and clayey limestones. It contains abundant benthic foraminifera, particularly species of Alveolina. From this succession, 28 species of Alveolina d’Orbigny are described and their comparative stratigraphic distribution with the Alveolina species in the Tethyan Eocene is documented. Generally, Ilerdian–Cuisian Alveolina assemblages of the Seyitgazi region have close affinities with coeval Alveolina assemblages described in different studies from the Tethyan Province. The Ilerdian unit of the study area is characterized by Alveolina species such as Glomalveolina lepidula, Glomalveolina minutula, G. karsica, Alveolina vredenburgi, A. ellipsoidalis, A. avellana, A. aff. minervensis, A. dedolia, A. moussoulensis, A. subpyrenaica, A. laxa, A. aragonensis, A. varians, A. ilerdensis, A. trempina, A. citrea, A. pisella and A. decipiens. Likewise, the Early Middle Cuisian unit is represented by G. minutula, A. oblonga, A. schwageri, A. haymanensis, A. canavarii, A. aff. coudurensis, A. ruetimeyeri, A. muscatensis, A. cremae, A. bayburtensis and A. lehneri.     

Trace fossil evidence from the Adigrat Sandstone for an Ordovician glaciation in Eritrea, NE Africa

Trace fossils are described here from the Adigrat Sandstone formation of hitherto uncertain Palaeozoic-Mesozoic age in south-central Eritrea. The formation is subdivided into a lower unit, the Adi MaEkheno Member, and an upper informal unit, Member 2. The formation was deposited on the locally mudcracked top of the glacigenic Edaga Arbi Beds, suggesting that these two rock units were formed in a very short time interval. The Adi MaEkheno Member and the lower part of Member 2 contain trace fossils Arthrophycus alleghaniensis (Harlan), Arthrophycus ?brongniartii (Harlan), Didymaulichnus lyelli (Rouault), Palaeophycus tubularis Hall, Taenidium isp., thin winding ridges, winding ridges and furrows, simple cylinders, and ‘stellate’ forms. A. alleghaniensis is distinctively of Ordovician–Silurian (?Early Devonian) age. The trace fossil association belongs to the Cruziana ichnofacies that indicates a shallow marine environment between the normal and storm wave bases. The trace fossil data and stratigraphic relationships indicate that the Adigrat Sandstone formation and the Edaga Arbi Beds in Eritrea are Ordovician–Silurian in age. The Edaga Arbi Beds are correlated with other Upper Ordovician (Hirnantian) glacial units in northern Africa and the Arabian Peninsula, lending these beds the status of a marker unit in the Lower Palaeozoic stratigraphy of the Horn of Africa. The Jurassic “Adigrat Sandstone” in central-west and eastern Ethiopia cannot be correlated with the Adigrat Sandstone formation in its type area and in Eritrea.     

阿联酋下白垩统舒艾巴组生物礁沉积模式

本文在露头分析和钻井资料研究的基础上,结合区域地质背景,对阿联酋地区下白垩统舒艾巴组生物礁沉积特征进行了分析,确定了该区生物礁的沉积模式及有利储层发育相带。舒艾巴组沉积时期,具备优越的生物礁发育条件,造礁生物主要为厚壳蛤。研究区舒艾巴组碳酸盐台地具有"缓斜坡镶边台地"沉积特征,自盆地边缘向盆地内部,依次发育浅海低能碳酸盐陆架、浅海高能碳酸盐陆架、深水低能碳酸盐陆架、盆地斜坡相和深海盆地相。浅海高能碳酸盐陆架-盆地斜坡相带为生物礁发育带及油气富集区。其中浅海陆架边缘的高能相带为厚壳蛤生物礁发育的最有利区域,储层物性最好,厚壳蛤礁主要形成于早期存在的藻类粘结灰岩台地高点和台地边缘,礁核和礁前为优质储层发育带。研究该区生物礁的沉积模式与分布规律,对该区生物礁储层油气勘探具有重要的指导意义。     

Planktic Foraminiferal Biostratigraphy of the Cretaceous Oceanic Red Beds in Kangmar,Southern Tibet,China

The planktic foraminifera of the Chuangde Formation (Upper Cretaceous Oceanic Red Beds, CORBs) as exposed at Tianbadong section, Kangmar, southern Tibet has been firstly studied for a detailed for a detailed biostratigraphy elaboration. A rich and well-preserved planktic foraminifera were recovered from the Chuangde Formation of the Tianbadong section and the Globotruncanita elevata, Globotruncana ventricosa, Radotruncana calcarata, Globotruncanella havanensis, Globotruncana aegyptiaca, Gansserina gansseri and Abathomphalus mayaroensis zones have been recognized. The planktic foraminiferal assemblage points to an early Campanian to Maastrichitian age for the CORBs of the eastern North Tethyan Himalayan sub-belt, which also provides a better understanding of the shifting progress of the Indian Plate to the north and the evolution of the Neotethyan ocean. The lithostratigraphy of the Chuangde Formation of the Tianbadong section comprises two lithological sequences observed in ascending succession: a lower unit (the Shale Member) mainly composed of purple (cherry-red, violet-red) shales with interbedded siltstones and siliceous rocks; and an upper unit (the Limestone Member) of variegated limestones. The strata of the Chuangde Formation in the Tianbadong section are similar to CORBs in other parts of the northern Tethyan Himalaya area of Asia (Gyangze, Sa’gya, Sangdanlin, northern Zanskar, etc.). The fossil contents of the Chuangde Formation in the sections (CORBs) studied provide a means of correlation with the zonation schemes for those of the northern Tethyan Himalayan sub-belt and the Upper Cretaceous of the southern Tethyan Himalayan sub-belt. Paleogeographic reconstruction for the Late Cretaceous indicates that the Upper Cretaceous Chuangde Formation (CORBs) and correlatable strata in northern Zanskar were representative of slope to basinal deposits, which were situated in the northern Tethyan Belt. Correlatable Cretaceous strata in Spiti and Gamba situated in the southern Tethyan Belt in contrast were deposited in shelf environments along the Tethyan Himalayan passive margin. CORBs are most likely formed by the oxidation of Fe(II)-enriched, anoxic deep ocean water near the chemocline that separated the oxic oceanic surface from the anoxic.     

Biostratigraphy,microfacies and depositional environments of upper Viséan limestones from the Burren region,County Clare,Ireland

The Burren region in western Ireland contains an almost continuous record of Viséan (Middle Mississippian) carbonate deposition extending from Chadian to Brigantian times, represented by three formations: the Chadian to Holkerian Tubber Formation, the Asbian Burren Formation and the Brigantian Slievenaglasha Formation. The upper Viséan (Holkerian–Brigantian) platform carbonate succession of the Burren can be subdivided into six distinct depositional units outlined below. (1) An Holkerian to lower Asbian unit of skeletal peloidal and bryozoan bedded limestone. (2) Lower Asbian unit of massive light grey Koninckopora‐rich limestone, representing a shallower marine facies. (3) Upper Asbian terraced limestone unit with minor shallowing‐upward cycles of poorly bedded Kamaenella‐rich limestone with shell bands and palaeokarst features. This unit is very similar to other cyclic sequences of late Asbian age in southern Ireland and western Europe, suggesting a glacio‐eustatic origin for this fourth‐order cyclicity. (4) Lower Brigantian unit with cyclic alternations of crinoidal/bryozoan limestone and peloidal limestone with coral thickets. These cycles lack evidence of subaerial exposure. (5) Lower Brigantian bedded cherty dark grey limestone unit, deposited during the maximum transgressive phase of the Brigantian. (6) Lower to upper Brigantian unit mostly comprising cyclic bryozoan/crinoidal cherty limestone. In most areas this youngest unit is truncated and unconformably overlain by Serpukhovian siliciclastic rocks. Deepening enhanced by platform‐wide subsidence strongly influenced later Brigantian cycle development in Ireland, but localized rapid shallowing led to emergence at the end of the Brigantian. A Cf5 Zone (Holkerian) assemblage of microfossils is recorded from the Tubber Formation at Black Head, but in the Ballard Bridge section the top of the formation has Cf6 Zone (Asbian) foraminiferans. A typical upper Asbian Rugose Coral Assemblage G near the top of the Burren Formation is replaced by a lower Brigantian Rugose Coral Assemblage H in the Slievenaglasha Formation. A similar change in the foraminiferans and calcareous algae at this Asbian–Brigantian formation boundary is recognized by the presence of upper Asbian Cf6γ Subzone taxa in the Burren Formation including Cribrostomum lecomptei, Koskinobigenerina sp., Bradyina rotula and Howchinia bradyana, and in the Slievenaglasha Formation abundant Asteroarchaediscus spp., Neoarchaediscus spp. and Fasciella crustosa of the Brigantian Cf6δ Subzone. The uppermost beds of the Slievenaglasha Formation contain a rare and unusual foraminiferal assemblage containing evolved archaediscids close to tenuis stage indicating a late Brigantian age. Copyright © 2006 John Wiley & Sons, Ltd.     

Early Cretaceous planktonic foraminifera from the Tethys: the large, many-chambered representatives of the genus Globigerinelloides

This paper deals with the taxonomic revision of the Early Cretaceous large, many-chambered planispiral planktonic foraminifera, historically assigned to the genus Globigerinelloides or alternatively assigned in the 1990s to the genera Globigerinelloides Cushman and ten Dam, Biglobigerinella Lalicker, Blowiella Krechmar and Gorbachik and Alanlordella BouDagher-Fadel. In a previous paper we demonstrated that the morphological and microstructural features used in the literature for distinguishing Blowiella from Globigerinelloides have value only at species level, and the former genus was thus invalidated (being the junior synonym). Moreover, the Late Aptian specimens assigned to Biglobigerinella by some authors, based on the presence of twin last chamber(s), are also included in Globigerinelloides because individuals sharing the same features (number of chambers, growth rate, size of umbilicus, and a finely perforate wall) may or may not possess twin last chamber(s). Meanwhile, Moullade et al. questioned the taxonomic value of Alanlordella, erected by BouDagher-Fadel to accommodate planispiral taxa possessing a macroperforate wall. All the species analysed here possess a finely perforate wall and consequently cannot be assigned to this taxon.The large species of Globigerinelloides retained here, with six or more chambers in the outer whorl, are G. algerianus Cushman and ten Dam, G. aptiensis Longoria, G. barri (Bolli, Loeblich and Tappan) and G. ferreolensis (Moullade).In the sections studied, Globigerinelloides aptiensis was first found close to the Barremian/Aptian boundary, even though this species was recorded in Spain (Rio Argos) in the mid Upper Barremian; very rare, small, seven-chambered individuals here assigned to Globigerinelloides ferreolensis are recorded in the Lower Aptian (just below and within the Selli Level, OAE1a), while a few specimens belonging to Globigerinelloides barri occur in the Globigerinelloides ferreolensis Zone (Upper Aptian). Globigerinelloides aptiensis and G. ferreolensis range up to the Ticinella bejaouaensis Zone while Globigerinelloides barri disappears at the top of the Globigerinelloides algerianus Zone; finally, Globigerinelloides algerianus obviously spans the eponymous total range zone.From an evolutionary point of view, two lineages within the many-chambered Globigerinelloides have been recognized. In the first, already known in the literature, Globigerinelloides aptiensis gave rise to G. ferreolensis, which evolved into G. algerianus; the latter in turn gave rise to Pseudoplanomalina cheniourensis as the final evolutionary member. In the second lineage Globigerinelloides barri originated from G. blowi.