Neritic Conditions Research Articles

Paleocene – Late Oligocene dinoflagellate cysts biostratigraphy, onshore Niger Delta

A new biostratigraphic biozonation for the Paleocene to Late Oligocene succession of the onshore Niger Delta has been developed based on the identification of significant stratigraphic dinoflagellate cyst events. This study is aimed at applying rarely used dinoflagellate cysts events in dating, correlating and inferring the paleoenvironment of penetrated sedimentary successions in the studied area. Palynological processing and analysis were carried out on two hundred and twenty ditch cutting samples recovered from two exploration wells (BN-1 and FJ-1) located in the Greater Ughelli and Northern Depobelts of the onshore Niger Delta respectively. Abundant and diverse dinoflagellate cysts recovered included marker Peridinales species Apectodinium sp., Palaeocystodinium australinum, and Gonyaulacales such as Areosphaeridium arcuatum, Cordosphaeridium gracile, Tuberculodinium vancampoae, Polysphaeridium zoharyi and Hystrichokolpoma rigaudiae. Three dinoflagellate cysts Palynological Zones - DPZ 100 (Early to Late Paleocene), DPZ 200 (Early to Late Eocene) and DPZ 300 (Late Eocene to Late Oligocene) are proposed herein. The biozones were subdivided into ten subzones based on the Top occurrence, Quantitative Tops and Quantitative base as well as ACME events of dinoflagellate cysts marker taxa which are used to date the rock sequence to be Paleocene to Late Oligocene. Abundant and diverse shallow outer neritic to inner neritic dinoflagellate cysts are identified from thick grey soft shales at the lower section of the studied wells. The upper section show significant reduction in dinocysts assemblage dominated by inner (coastal) neritic taxa. This dinocysts occurrence and distribution suggests inner (coastal) neritic paleoenvironment at the upper sections which deepened into shallow outer neritic conditions at the lower intervals of the studied wells. The thick brown to grey shales at the lower section and the medium to fine grained, moderately well sorted sandstone interbeds at the middle section of the studied wells are interpreted to be potential source and reservoir rocks respectively. These datasets are useful for correlating possible hydrocarbon source rocks and potential reservoir carrier beds in the Gulf of Guinea.

Palynostratigraphy and palaeoenvironment of the Danian sediments from the Nsukka Formation of the Anambra Basin at the vicinity of Ikpankwu, southeastern Nigeria.

Detailed investigations of biostratigraphy of the Nsukka Formation in the Ikpankwu area are paramount due to the fluctuation of depositional environment, fossil flora abundance and diversity interchange, and lateral facies change dynamics from the southern to northern sections of this formation. The microflora assemblages, chronostratigraphic age and depositional paleoenvironment of index palynomorphs suggest a Danian age for the studied strata, based on global dinoflagellate cyst events. The persistent abundance of monocolpate assemblages and the biostratigraphic resolution attained, suggest that the studied sediment interval is continuous. The marker species of terrestrial microflora (Constructipollenites ineffectus, Echitriporites trianguliformis, Foveotriletes margaritae, Longapertites group, Proxapertites group, Retidiporites magdalenensis, Scabratriporites annellus, Spinizonocolpites group, Syncolporites marginatus) and dinocysts (Carpatella cornuta, Danea californica, Fibrocysta licia, Kenleyia pachycerata, Spiniferella cornuta subsp. kasira), compared with several reference sections from the tropical to subtropical province, engineered a refined geologic age and paleoenvironment of deposition of the sediments. These dinocysts taxa are global Danian index fossils which are valuable in the identification of earliest Palaeocene sequence of the formation. The depositional paleoenvironment alternately fluctuates from continental setting to marginal marine inner neritic and outer neritic conditions, based on the presence of land-derived miospores and dinocysts. These macroenvironments are the products of effective vacillating depositional environment systems between the lower and upper deltaic plains, oscillating from tidal flat, lagoon, tidal bar to nearshore open marine influenced settings. Lycopodiaceae-Zlivisporis blanensis fern spore with fragile perispore substantiate the autochtonous vegetation and least transport and palynomorph hydrodynamic system inherent in the predominant pollen and spore species and close proximity to fresh water settings visible in medium to coarse grained sandstone units of the middle section. These microenvironment syntheses of the Nsukka Formation revealed a confirmed and pronounced transgressive systems tract (TST), articulated in the shale sample from the Ikpankwu section of the Nsukka Formation, Anambra Basin. The palaeoenvironments and palynostratigraphic dynamics illustrate that overall progradation was trailed by sporadic retrogradation of the delta with a high biostratigraphic resolution system indicative of continuous biological imprints of the terrestrial and marine microflora of the Nsukka Formation during the Danian.

New Tithonian-Berriasian morphospecies of the genus Stomiosphaera Wanner (calcareous dinoflagellate cysts) from the Vaca Muerta Formation, Neuquén Basin, Argentina

Five new morphospecies of calcareous dinoflagellate cysts belonging to the genus Stomiosphaera Wanner, are described from the Tithonian–Berriasian Vaca Muerta Formation, in the Neuquén Basin, Western Argentina: Stomiosphaera triangulata sp. nov., Stomiosphaera quadrata sp. nov., Stomiosphaera subechinata sp. nov., Stomiosphaera subspinosa sp. nov., and Stomiosphaera gracilis sp. nov. Their stratigraphic distribution is discussed, particularly that of Stomiosphaera subechinata sp. nov. (Tithonian – lower Berriasian), which was previously assigned to Stomiosphaera echinata Nowak, a species that in the Tethys domain appears for the first time in the upper Valanginian. Likewise, possible assignments to the genera defined from three-dimensional observations are proposed, and eutrophic neritic conditions are interpreted for the time in which these species appear in the Neuquén Basin.

Paleobiogeographic affinities and paleoecological significance of paleogene ostracods from Eastern Benin Basin, Southwestern Nigeria

Ditch cutting samples from the studied section of the RC-4 Hole, eastern Benin (Dahomey) Basin were studied for their ostracod content. 3671 ostracod fauna belonging to 22 species were recovered and analysed with a view to determining ostracod paleobiogeographic affinities and paleoecological conditions within this part of the basin during the Paleogene. Ostracod assemblages of the studied section bear close affinities to those of some North and West African basins. Species such as Bairdia ilaroensis, Leguminocythereis spp., Bairdia malzi, Paracosta kefensis, Xestoleberis tunisiensis, Buntonia jordanica, Aegyptiana duwiensis and Leguminocythereis lokossaensis identified from the RC-4 hole suggest shallow neritic conditions. Paracosta kefensis and Paracosta parakefensis occur in high abundance indicating marine upwelling conditions. Many of the species recovered in this study have also been identified from Iullemeden and southern Tethys basins (e.g. Sirte Basin) suggesting ostracod migration from Benin Basin (Gulf of Guinea) to southern Tethys basins through the Paleogene shallow Trans – Saharan Seaway. A distinct ostracod turnover at the top of the limestone unit (Ewekoro Formation) is related to the Paleoceneo Eocene Thermal Maximum (PETM) – a climatic phenomenon characterised by 5 – 8 C global temperature rise at the end of the Paleocene.

Organic Matter Assessment and Paleoenvironmental Changes of the Middle Jurassic Main Source Rocks (Khatatba Formation) in the North Western Desert, Egypt: Palynofacies and Palynomorph Perspectives

The Middle Jurassic in the north Western Desert, Egypt, was a time of complex tectonics and increased environmental perturbations attributed to the predominant sedimentation of organic carbon-rich fine siliciclastic and carbonate deposits of the Khatatba Formation. Although some studies have addressed the hydrocarbon potential and source rock characteristics of the Khatatba Formation, a regional-scale investigation of the prevalent paleoenvironmental conditions and organic matter characteristics is still necessary. In this study, the Khatatba Formation is investigated for detailed palynofacies analysis and palynomorph composition to assess organic matter kerogen types and reconstruct the depositional paleoenvironmental patterns on a regional scale. For this purpose, 116 drill cuttings were collected from five wells in the Matruh, Shushan, and Dahab-Mireir Basins. Moderately diverse assemblages of spores, pollen, and dinoflagellate cysts are reported. Age-diagnostic dinoflagellate cysts, including Adnatosphaeridium caulleryi, Dichadogonyaulax sellwoodii, Korystocysta gochtii, Wanaea acollaris, and Pareodinia ceratophora, along with occasional records of Systematophora areolate and Systematophora penicillate, defined a Bajocian–Callovian age. Based on particulate organic matter (POM) composition, four palynofacies assemblages (PFAs) are identified. PFA-1 is the most common within the Khatatba Formation in the five studied wells. It contains high proportions of phytoclast fragments versus low contents of amorphous organic matter (AOM) and palynomorphs and is defined by a gas-prone kerogen Type III. PFA-2 is comprised of moderate abundances of AOM and phytoclast characteristics of oil-prone kerogen Type II. PFA-3 is dominated by phytoclasts and moderate to low proportions of AOM and palynomorphs of kerogen Type III, whereas PFA-4 consists of AOM and palynomorphs defining kerogen Type II. PFA-1 indicates predominant deposition in proximal active fluvio-deltaic sources to marginal marine conditions with enhanced contributions of terrestrial/riverine influx. PFA-2 and PFA-3 reveal deposition under an enhanced dysoxic to anoxic proximal inner neritic shelf due to the abundant occurrences of spores and coastal to shallow marine dinoflagellate cysts. PFA-4 suggests deposition under enhanced suboxic to anoxic distal inner neritic conditions because of enhanced AOM and abundant proximate and some chorate dinoflagellate cysts. Thus, the Middle Jurassic experienced a predominantly marginal to shallow water column in this part of the southern margin of the Tethyan Ocean where the Matruh, Shushan, and Dahab-Mireir Basins were located.

Biostratigraphy, palaeoecology, and palaeobiogeography of the Middle–Late Eocene ostracods, north‐west Fayoum area, Egypt

The present study focuses principally on the late Middle Eocene–early Late Eocene ostracods from two successions (Garet Umm Rigl section and Qasr El Sagha sections), in the northwestern portion of Fayoum area, Egypt. Stratigraphically, the studied successions are classified into three formations (from base to top), the Gehannam, Birket Qarun, and Qasr El Sagha (Temple Member). The recorded ostracod assemblage contains 33 species belonging to 20 genera and 9 families. According to their stratigraphic ranges, three local biozones are recognized, Asymmetricythere yousefi–Loxoconcha pseudopunctatella, Reticulina heluanensis–Leguminocythereis sadeki, and Trachyleberis nodosus nodosulcatus–Ruggeria (Keijella) glabella. The comparison of the proposed biozones with their equivalents inside Egypt denotes a Middle–Late Eocene age for the studied sections. Based on the character of investigated ostracods, three ecozones are distinguished. An inner–outer neritic environment is suggested for the first ecozone, inner‐middle neritic conditions for the second, while shallow water conditions are proposed for the third ecozone. In addition, this paper represents an attempt to detect the palaeobiogeographic provinces of Eocene ostracods by means of multivariate analyses (principle component analysis, Q‐mode cluster analysis and similarity index). These analyses are applied on a matrix composed of some selected Eocene species from 10 regions located at the southern Tethys and western Africa. The results identify three distinctive provinces, North Africa (Algeria, Tunisia, Libya, and Egypt), the Middle East (Jordan and Israel) and West Africa (Senegal, Togo, Ivory Coast and Nigeria). The distinctive affinities between these provinces suggests ostracod migration along the southern Tethys during the Eocene age.

OSTRACODS FROM THE LATE TRIASSIC (NORIAN) OF YUKON, CANADA: NEW TAXONOMIC AND PALAEOBIOGEOGRAPHIC INSIGHTS

The present work investigates the significance of Late Triassic ostracods from the Yukon Territory, Canada, and adds to the scientific knowledge of the taxonomy of these organisms during the Norian, which remain poorly documented and understood. Fifteen limestone samples representing distinct marine palaeoenvironments cropping out at Lime Peak, Stikinia terrane, provided 90 species, including 9 newly described: Alatobairdia? sohni n. sp., Bairdia aksala n. sp., B. taan n. sp., B. yukonensis n. sp., Cornutobairdia yukonella n. sp., Lobobairdia whitella n. sp., Mirabairdia canadia n. sp., Hungarella limella n. sp., Leviella riedeli n. sp. Most assemblages point to neritic conditions in the photic zone. A similarity analysis demonstrates the distinct composition of reef-related and algae-related ostracod assemblages. The ostracod-algae associations in Lime Peak reveal that the affinity of Bairdiidae for algae (Dasycladaleans in the case of Lime Peak) was already established in the Norian. A faunal link is identified during the Norian between eastern and western Panthalassa and Japan, in line with studies on other taxa. The flux of species between eastern Panthalassa and Tethyan areas appears very unbalanced in the Late Triassic with most migrations originating from the Tethys. Further data from other Middle and Upper Triassic Panthalassan localities and stages (i.e. Ladinian and Carnian) are needed to confirm whether this apparent trend is due to sampling bias or reflects real dispersal fluxes.

Palaeoenvironmental changes based on foraminifera during the late Holocene at the Beagle Channel, Argentina.

A foraminiferal faunal study was carried out in a Holocene marine section from Arroyo Baliza, located on the northwest coast of the Beagle Channel, to contribute to the knowledge of the palaeoenvironmental conditions during the marine Holocene event. Foraminiferal assemblage was represented by 32 species distributed among 21 genera. The assemblage was dominated by Elphidium macellum (Fichtel & Moll) Elphidium alvarezianum (d'Orbigny), Cribroelphidium excavatum (Terquem) and Buccella peruviana (d'Orbigny), accompanied by Cibicides fletcheri Galloway & Wissler and Cibicidoides dispars (d'Orbigny) in low proportion. The predominance of Peridiniales dinocysts in the marine palynomorphs assemblage, suggested inner neritic conditions with cooler and more nutrient-rich waters. The distribution of the foraminiferal species was variable throughout the section indicating palaeoenvironmental changes in Arroyo Baliza between 3499-2595 cal yr BP. A gradual passage from high energy, cold and well-oxygenated marine waters towards a shallower environment with low energy and low to moderate salinity of the waters were linked to the regressive phase. This study complements and supports the previous palynological data from this section, which reflects an increase in number and diversity of dinocyst species indicating marine environmental conditions during the late Holocene as it exists today in the Beagle Channel.

The Danian Sea: Dinoflagellate cysts assemblages from Neuquén Basin, Roca Formation (Argentina) and its comparison with other southern South America localities

The study section at the Casa de Piedra locality (Neuquén Basin) is located near the Colorado River, southwestern sector of La Pampa province, Argentina. The section is assigned to the Roca Formation, which records a shallow marine environment linked with Atlantic transgressions. It includes a new record of dinoflagellate cysts of the Danian Sea, in northern Patagonia. Most of the recognized taxa have a Late Cretaceous – Danian stratigraphic range in the Southern Hemisphere. The great similarity with the dinoflagellate cysts recorded in the uppermost Pedro Luro Formation, Colorado Basin allowed inferring a Late Danian age for the Roca Formation in the Casa de Piedra section. This age is also supported by the presence of Vozzhennikovia apertura (FAD: 65.10 Ma) and Cerodinium diebelli (LAD: 61.05 Ma) and by other micofossils data including foraminifers and nannofosils. The sedimentary facies and the dinoflagellate cysts identified suggest a neritic environment ranging from marginal-marine with scarce fluvial influence to outer neritic conditions. Taking into account the sporomorphs content, the paleoenvironment conditions would be similar to those of the North-west and Colorado Basins for the Danian, with a forest of Ulmaceae (Verrustephanoporites simplex) and montane forest (Podocarpaceae, Rutaceae). The sporomorph assemblages indicate warm paleotemperatures (subtropical-tropical). The high similarity of dinoflagellate cyst records between Roca and Pedro Luro Formations would suggest a probable link between Neuquén and Colorado basins during Danian times. This connection has been postulated by several authors and could be related to the Neuquén embayment through the Huincul fault.

Early and middle Miocene paleobathymetry of the Vienna Basin (Austria)

The Vienna Basin (VB) originated during the early Miocene and represents one of the largest onshore oil and gas field in Europe. The VB is composed of several horst and graben structures forming different subbasins, each with its own geodynamic evolution and deviating paleobathymetric developments during the Miocene. We present an analysis of water depth evolution along a NE-SW transect by applying a transfer function for benthic foraminifers. We document dramatic changes in the depth profile through time, which coincide with shifts of prevailing tectonic regimes. Bathyal conditions were established during the early Miocene piggy-back stage and the early middle Miocene extensional phase. A clear shallowing trend from upper bathyal to inner neritic conditions occurred during the middle Miocene extensional tectonic phase.All lowstand systems of relative sea level in the VB coincide with global Mi-events. The observed maxima of the relative sea level in the VB are vaguely in phase with the global record from the Ottnangian (late early Miocene) to the middle Badenian (middle Miocene) but exceed the range of global sea level rise by three to four times, suggesting a strong tectonic amplification. Fluctuations of the relative sea level during the late Badenian and Sarmatian (Serravallian, middle Miocene) range well within the global signal, documenting ceasing influence of tectonics.

Paleoecologic implications of foraminiferal assemblages in the Upper Cretaceous-Paleogene strata, eastern Dahomey (Benin) Basin, southwestern Nigeria

The paleoecologic conditions of eastern Dahomey (Benin) Basin during Late Campanian-Eocene were investigated using foraminifera as proxies. Twenty-four (24) samples obtained from four (4) exploration boreholes and three (3) exposed outcrop sections were subjected to conventional micropaleontological processing techniques. Thirty-one (31) species of foraminifera (25 benthic and 6 planktic species) were identified from the samples. The recovered assemblages consist predominantly of Paleocene calcareous benthic species such as Anomalinoides midwayensis, Anomalinoides umboniferus, Eponides pseudoelevatus, Gavellina guineana, and Cibicides succedens. Sparse occurrence of Late Cretaceous agglutinated benthic species comprising Ammobaculites coprolithiformis and Textularia hockleyensis was also recorded. The Upper Cretaceous strata are either devoid of microfauna or contain few agglutinated taxa suggestive of continental to brackish water settings. The development of calcareous benthic foraminiferal assemblages in Paleogene strata of the study area signaled the incursion of open marine neritic conditions. Influx of sandy sediments at some horizons in the studied boreholes resulted into increased pore-water oxygenation leading to poor preservation of benthic foraminifera at these horizons. Planktic/benthic (P/B) ratio analysis of the foraminiferal assemblages suggests paleo-water depth not exceeding 65 m.

Middle Eocene dinoflagellate cysts from the Tsoul section, eastern External Rif, Morocco: biostratigraphy and paleoenvironmental interpretations

This palynological study is carried out on the Eocene sediments in the Tsoul section, which is located in the Taza region, Tsoul Unit, eastern External Rif, northeastern Morocco. It aims their age assessment and paleoenvironmental interpretations, based on palynological data. The palynological content is diverse, well preserved and rich in organic-walled dinoflagellate cysts (dinocysts), whereas spores and pollen are rare. We identified 117 dinocyst species (including some reworked species), among which 6 species and 1 acme are good biostratigraphic markers of the Bartonian (middle Eocene). The main dinocyst bioevents that are used to assign the studied section to the Bartonian include the lowest occurrences (LOs) of Glaphyrocysta semitecta, Impagidinium dispertitum, Lentinia serrata, Membranophoridium aspinatum and Operculodinium divergens, the highest occurrence (HO) of Castellodinium compactum and the acme of Polysphaeridium spp. Regarding the paleoenvironment, the studied section was deposited in a marine environment, characterized by a low productivity inferred from the scarcity of peridinioid cysts and by important environmental changes ranging from restricted inner neritic (lagoon) conditions, inferred from the dominance of Homotryblium and Polysphaeridium, to outer neritic open marine conditions inferred from the dominance of Spiniferites.

The marine palynology of the Upper Cretaceous Abu Roash ‘A’ Member in the BED 2-3 borehole, Abu Gharadig Basin, Egypt

This study presents a high-resolution palynological analysis for the Abu Roash ‘A’ Member in the hydrocarbon-rich Abu Gharadig Basin, North Western Desert, Egypt. Thirty-one rock samples, spanning the upper Coniacian to lower Campanian Abu Roash ‘A’ Member (180 m) from the Badr El Din (BED) 2-3 borehole, were investigated. Highly diverse and well-preserved assemblages of organic-walled dinoflagellate cysts were recorded. A total of 220 species belonging to 123 genera were identified from different levels throughout the studied succession. The marine dinoflagellate cysts represented herein by 160 species allowed three palynological assemblage zones to be recognised. These include the Satyrodinium haumuriense-Isabelidinium belfastense-Odontochitina operculata Assemblage Zone (early Campanian), Dinogymnium acuminatum-Nelsoniella aceras-Odontochitina porifera Assemblage Zone (Santonian), and Cyclonephelium filoreticulatum-Spinidinium echinoideum Assemblage Zone (late Coniacian). Approximately 17 species representing 14 dinoflagellate cyst genera are identified for the first time in the Cretaceous record of Egypt. A comparison to published palynological data from neighbouring areas reveals that several significant events are synchronous throughout the Western Desert, suggesting a common similarity of water masses. Palynofacies and palynomorph analyses of the whole samples led us to define two palynofacies assemblages, which indicate that the Abu Roash ‘A’ Member was deposited during a successive oscillation of sea level from distal inner to middle neritic conditions. A sequence stratigraphic framework assessment was carried out to trace the relative response of the sedimentological organic matter distribution to the changes of sea level. Four third-order transgressive–regressive sequences (SQ2–SQ5) and two incomplete transgressive–regressive sequences (SQ1 and SQ6) are constructed through the Abu Roash ‘A’ Member.

Miocene Glacial Dynamics Recorded by Variations in Magnetic Properties in the ANDRILL‐2A Drill Core

AbstractDuring the 2007 ANtarctic geological DRILLing (ANDRILL) campaign in the Ross Sea, Antarctica, the AND‐2A core was recovered through a stratigraphic succession spanning 1,138.54 m of Neogene sedimentary rocks that include an expanded early to middle Miocene sequence. The study reported here focuses on the magnetic properties of the interval from 778.63 m below sea floor (mbsf) to 1,138.54 mbsf, which comprises a time interval spanning 1.5 Myr, from ~18.7 to ~20.2 Ma. We recognize three main pulses of increased input of magnetic materials to the drill site between 778.34–903.06, 950.55–995.78, and 1,040–1,103.96 mbsf. Trends in the magnetic mineral concentration dependent parameters mirror changes in the proportion of sediments derived from McMurdo Volcanic Group rocks. We suggest that these pulses in magnetic mineral concentration reflect changes in sediment transport processes associated with changing glacial conditions at the drill site that included (1) subglacial and grounding zone proximal settings, (2) hemipelagic and neritic conditions with abundant sediment‐rich icebergs, and (3) grounding zone‐distal environment that was covered by land‐fast multiyear sea ice or a fringing ice shelf. The magnetic minerals record preserved in the AND‐2A core supports other data that indicate a highly dynamic and variable coastal environment during the early Miocene, where glaciers retreated inland under warm climatic conditions and advanced beyond the drill site across the continental shelf when cold climate prevailed.

Middle Eocene to early Oligocene dinoflagellate cyst biostratigraphy and paleoenvironmental interpretations of the Ben Attaya section at Taza, eastern External Rif, Morocco

The palynological study was carried out on middle Eocene to early Oligocene sediments from the Ben Aattaya section, located in the Taza region, eastern External Rif, northeastern Morocco. The palynological content is dominated by dinoflagellate cysts (dinocyst), while spores and pollen are rare. Very known dinocyst event markers were used for dating the Ben Attaya section. The first occurrences (FO) of Cerebrocysta bartonensis, Glaphyrocysta semitecta, Lentinia serrata, Operculodinium divergens indicate the Bartonian. The FOs of Deflandrea heterophlycta, Schematophora speciosa, Stoveracysta ornata were used to recognize the Priabonian. While the FOs of Chiropteridium lobospinosum and Wetzeliella gochtii, as well as the last occurrences (LO) of Achilleodinium biformoides, Charlesdowniea coleothrypta subsp. coleothrypta, Enneadocysta pectiniformis, Glaphyrocyst semitecta, Hemiplacophora semilunifera, Lentinia serrata, Operculodinium divergens, Rhombodinium perforatum, Schematophora speciosa and Stoverocysta ornata highlight the Rupelian. The changes in relative abundances of selected dinocyst groups and sporomorphs (pollen and spores) suggest a lagoonal to coastal inner neritic marine environment during the Bartonian and Priabonian, which was interrupted by a short phase of outer neritic conditions at the basal part of the section and ended by a marked decrease in the sea level, probably due to a regression during the Priabonian. The Rupelian deposits indicate a middle neritic marine environment marked by a progressive rise during the transgression.

Palynological and palaeoenvironmental analyses of the upper Albian-Cenomanian succession in Gindi Basin, Egypt: Implication for transgressive/regressive systems tracts

The current contribution illustrates the advantage of the use of quantitative palynological data to palaeoenvironmentally differentiate the similar-looking monotonous, thick clastic interval of the Kharita, Bahariya and Abu Roash “G” units in Gindi Basin, Egypt. The present study aims also to the utilization of the upper Albian-Cenomanian quantitative palynological and palynofacies data and their integral interpretation in a sequence stratigraphic context. The recovered palynomorph assemblages with moderately diverse sporomorphs and dinoflagellate cysts, show poor to fair preservation. Around 47 species of pollen grains, 37 of dinoflagellate cysts and 36 species of pteridophytic spores have been recorded from two sections encountered in El Sagha-1A and BRE 6-1 wells drilled in Gindi Basin; however, achritarchs, microforaminiferal test linings and freshwater algae are impoverished and sparsely documented through the studied intervals. Based on the first downhole appearances (FDAs) of the recovered marker taxa, the encountered Abu Roash “G”, Bahariya and the upper Kharita units are palynologically dated as late Cenomanian, early-middle Cenomanian and late Albian, respectively. Relative sea level fluctuation is particularly relevant and deduced from various palynological parameters mainly the terrestrial:marine (T:M) ratio and the palynological marine index (PMI). Based on the vertical stratigraphic distribution of the palynofacies along with the relative variations of the terrestrial versus marine palynomorphs, five complete (SQ1-SQ5) third order transgressive-regressive sequences and incomplete one are defined in El Sagha-1A in comparison to six complete (SQ2-SQ7) and one incomplete (SQ1) are constructed in BRE 6-1. Reliance on distinctive palynofacies assemblages, differentiated based on the relative composition of particulate organic matter constituents, four depositional palaeoenvironments were interpreted for the studied intervals. The Kharita and Bahariya formations were elucidated to be deposited in fluctuating marginal-shallow and proximal inner neritic marine environments. However, the sea level remarkably showed a continued rising which brought the inner-middle neritic conditions of the Abu Roash “G” Member during late Cenomanian.

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.

Sequence stratigraphy of the Raha Formation, Bakr Oil Field, Gulf of Suez, Egypt: Insights from electrical well log and palynological data

The current paper provides a high resolution sequence stratigraphic study of the Raha Formation from the productive Bakr Oil Field, central Gulf of Suez, Egypt. Sixty cutting rock samples spanning the Cenomanian from three wells (Bakr-114, B-115 and B-109) in the Bakr Basin, were palynologically investigated. The documented palynomorphs assemblage of either terrestrially-derived sporomorphs or marine inhabited dinocysts, allowed two palynological zones as well as their encompassing depositional palaeoenvironment to be recognized. These zones are Afropollis jardinus–Crybelosporites pannuceus Assemblage Zone (early-middle Cenomanian) and Classopollis brasiliensis-Tricolpites sagax Assemblage Zone (late Cenomanian). Detailed analysis of the particulate organic matter compositions suggested that the depositional palaeoenvironment of the Raha Formation was fluctuating between supratidal and distal-inner neritic conditions, due to successive oscillations of the Neo-Tethyan Ocean during the Cenomanian.The pronounced peaks of particulate organic matter versus gamma ray are markedly used in delineating the depositional sequences of the Raha Formation and their bounding surfaces. The Raha Formation probably corresponds to a second-order depositional sequence, which can be further subdivided into eight third-order depositional sequences, of which six are complete and two are incomplete ones. These depositional sequences are significantly synchronized based on a simple 2-D correlation model between the three wells. According to the hierarchical duration system, the Cenomanian herein was approximately attributed to 6 Myr, each of which has lower order depositional sequences that took approximately 0.9 Myr. Based on the sequence stratigraphic approach together with palynofacies analysis and gamma ray data, a condensed section was defined in the B-115.

Palynological, palaeoenvironmental and sequence stratigraphical analyses of a Turonian-Coniacian sequence, Beni Suef Basin, Eastern Desert, Egypt: Implication of Pediastrum rhythmic signature

Sixteen samples from the “E” to “B” members of the Abu Roash Formation encountered in the Beni Suef Basin, Eastern Desert of Egypt were palynologically analyzed for palaeoenvironmental and sequence stratigraphic investigations. The integrated palynofacies and lithofacies analysis of the studied section indicates deposition of five alternating regressive and transgressive sequences in well-oxygenated, proximal shelf settings. The Abu Roash “E” and the upper “D” to the lower “C” members were deposited during pronounced regressive phases in oxic, shallow marginal marine settings. The upper “B” Member was deposited during a recurring regressive phase but of a lower magnitude in oxic, shallow inner neritic conditions. The lower “D” Member was deposited during a minor transgression phase in dysoxic, shallow inner neritic settings. While the upper “C” to the lower “B” section was deposited during a stronger transgressive episode in a relatively deep, inner neritic environment of prominent dysoxic conditions. This interchange in the depositional setting was documented by the pronounced and concurrent, cyclic nature of the freshwater algae, peridinioid dinoflagellate cysts, pteridophyte spores, and reworked sporomorphs with variable intensities. Their increasing and conversely their diminishing trends clearly reflect alternating regressive-transgressive periods of reduced and relatively normal salinity conditions, respectively. Overall, sedimentation of the studied Abu Roash section indicates a recurring rise in sea level, which accentuated during the earliest Santonian time.The analogous peaking in the Pediastrum signals with those of the pteridophyte spores and reworked taxa indicate a good connection between these Pediastrum signals and the pronounced fluviatile influxes of terrigenous sediments during regressive phases. Accordingly, this can be used to identify regressive sequence boundaries and hence the clastic reservoirs. Even with the small counts recorded herein, we believe high ratios of peridinioid/gonyalulacoid dinocysts are significantly paralleled by peaking signals of freshwater algae and regressive sedimentation phases. This must be preliminary documented here. Probably future palynological studies will be able to fully interpret and address this important Pediastrum rhythmic event in different sequence stratigraphic settings.The palynological parameters, age controlled sporomorph marker taxa, lithology, and gamma ray data were used to differentiate the Abu Roash members into three distinctive 3rd order depositional sequences (AR SQ1, AR SQ2, and AR SQ3). These sequences match well with the global stratigraphic sequences Tu 3, Tu 4, and Co 1 and connect the local rise in sea level to the global eustatic sea level rise.

Dinoflagellate cyst assemblages, biostratigraphy and paleoenvironment of a Paleocene-Early Eocene sedimentary succession in the northern Niger Delta Basin: Comparison with low, mid and high latitude regions

This study represents a contribution to the Late Paleocene-Early Eocene biostratigraphy in a low latitude stratigraphic setting where, published studies are few in comparison with mid- and high latitude regions. We generated data for 62 dinoflagellate cysts from a comprehensive analysis of 33 samples covering a 713-m interval in the Alo-1 Well in the northern Niger Delta (Anambra) Basin, Nigeria. Dinoflagellate cyst recovery in the samples varies from very good to poor, and the specimens are commonly well preserved. We calibrate the dinoflagellate cyst data with recent biozonation schemes for ODP Hole 959D, Côte d'Ivoire-Ghana Transform Margin in the eastern Equatorial Atlantic, which allowed for a valid comparison with published studies in well-dated rock sections in northwestern Europe, the Mediterranean region, New Zealand, and Tasmania. Our observations show that there is better correlation between tropical and mid latitude dinoflagellate cyst assemblages compared to those in high latitude regions.We use the last occurrence and/or last abundance events of dinoflagellate cysts to identify four biostratigraphic zones (zone E to zone H) in the Alo-1 Well. Lithostratigraphic and biostratigraphic analyses suggest a late Selandian age for the contact between the Imo and Nsukka formations. Abundant thermophilic taxa that include the Cordosphaeridium group and Apectodinuim dominate the assemblage recovered in the depositional succession. The late Selandian to early Thanetian sediments are dominated by the Cordosphaeridium group, and are succeeded by abundant to superabundant marker species of Apectodinium in the late Thanetian to Ypresian. The superabundance of Apectodinium is significant because it is indicative of the global intense climatic warming that characterized the late Thanetian to early Ypresian. The Alo-1 Well dinoflagellate cyst data also suggest deposition under proximal, inner neritic conditions that preserved an assemblage dominated by species of Cordosphaeridium, Damassadinium, Ifecysta and Polysphaeridium.