Benthonic Foraminiferal Assemblages Research Articles

Paleoenvironment, sequence stratigraphy, and sea level change in the upper Maastrichtian–Danian boundary interval in Gabal Aras, east Qena, Nile Valley, Egypt

The Cretaceous–Paleogene (K–Pg) boundary interval at Gabal Aras, Qena region (part of the southern Tethyan margin) was investigated in detail for calcareous nannofossil and foraminiferal (planktonic and benthonic) assemblages to characterize the surface and bottom sea water conditions. The K–Pg boundary is marked by a minor hiatus expressed by the absence of the lowermost Danian P0 and Pα planktonic foraminiferal zones. Benthonic foraminifera assemblages indicate moderately oxygenated bottom sea waters associated with oligo-mesotrophic conditions during early late Maastrichtian, and mesotrophic conditions during the latest Maastrichtian. The benthonic foraminiferal assemblage reflects a decrease in the food supply in the bottom sea water during the early Danian, while well-oxygenated and oligotrophic conditions dominated during late Danian. The late Maastrichtian surface water witnessed a general cooling trend that was interrupted by a warming episode that could correspond to the Late Maastrichtian Warming Event (LMWE). Acme of Thoracosphaera associated with increased abundance of Neobiscutum romeinii were observed within the upper part of NP1 Zone indicating stressful surface water conditions. The increase of the epifaunal foraminiferal taxa and the occurrence of Cruciplacolithus primus throughout NP2 and NP3 zones reflect a progressive return to normal marine conditions. In the framework of sequence stratigraphy, two third-order depositional sequences covering the K–Pg boundary interval were identified, interpreted, and correlated. The obtained sea-level curve was evaluated to assess whether it was controlled by the eustatic sea-level changes, regional tectonics, or both these factors.

Foraminifera from the Aruma Formation of Central Saudi Arabia

The Aruma Formation is well exposed in central Saudi Arabia as a thin northwest-southeast trending outcrop. It consists of a carbonate-dominated succession dated asCampanian to Paleocene. Of the three members, theKhanasir and Hajajah are confirmed as being Cretaceous, but the uppermost Linah Shale Member is assigned a Paleocene age. Dolomitization and differential erosion of the Aruma has left exposures for which the lithostratigraphy can only be confirmed by biostratigraphy. At the study location, the Khanasir Member contains the dasyclad algae Cymopolia tibetica, radiolitid rudist fragments and rare small rotalid and miliolid foraminifera. The HajajahMember is confirmed by the presence of the characteristic larger benthonic foraminiferal assemblage including Loftusia persica, Omphalocyclus macroporus, Rotalia trochidiformis and Fissoelphidium cf. operculiferum of Maastrichtian age. The sparse microfossil assemblages indicate deposition undifferentiated shallow marine, normal salinity, probably lagoon depositional setting.

Foraminiferal evidence of basin submergence in part of Sundarban mangrove delta, India

Sundarban is a largest mangrove forest delta developed along the NE-SW direction covering parts of India and Bangladesh. Little work has been done on Indian part of Sundarban in respect of heterogeneity in channel morphology which could be mostly due to the effect of tilting and basin subsidence. These changes might have played a major role on development of high marshes, which offers a congenial environment for survival of Haplophragmoides wilberti, Jadammina macrescens, Trochammina inflata, and Miliammina fusca. These marsh benthonic foraminiferal assemblages provide a direct evidence of recent past sea level changes. To establish the depositional pattern and their effects rendered by merciless changing environment, 11 pit sections have been excavated along three E-W transects from Indian Sundarban. Depth of these pit sections varies from 2 to 3 m. Generally, top 20 cm sediment (in pit section W-1 to W-11) deposited under the intertidal environment, as indicated by the presence of Ammonia tepida. However, sediment below 20 cm in some of the pit sections (W-3 and W-5) exhibits fresh water signatures as indicated by the presence of Charophytes algae. In other pit sections (W-1, W-2, W-6, W-7, W-8, W-9 and W-11), the intertidal assemblage is noticed just above the upper marshes assemblage and vice versa, signifying that depositional environment is in proximity to the mangrove dominated area as indicated by the presence of marsh benthonic foraminiferal assemblage containing T. inflata, H. wilberti, Haplophragmoides sp., J. macrescens and M. fusca. Bottom sediment in most of the pit sections from south to north have different depositional environment with alternate presence of intertidal to subtidal faunal assemblages. The peculiar presence of intertidal assemblage above the upper marshes assemblages in recent sediment points towards the theory of submergence due to relative rise in the sea level. But the effect of relative sea level rise is not uniform throughout the area because of differential subsidence due to varied rate of sediment supply (0.5 to 3.3 cm/year) and eastward tilting of the basin. Based on the upper marshes benthonic foraminiferal assemblage and radiocarbon age (in W-1 at 100 cm ~ 150 years age), the average subsidence rate as recorded is approximately 0.3 to 0.5 cm/year. Hence, such depositional sequence conjectures that the Indian part of Sundarban is undergoing a phase of submergence concomitant to basin subsidence.

Cretaceous-Tertiary Foraminifera and Palynomorphs from Djega Section and Inferred Paleodepositional Environments, Rio Del Rey Basin, Cameroon, West Africa.

Late Cretaceous-Paleocene foraminiferans and palynomorphs were recovered from the upper section of the Djega outcrop in the Rio del Rey Basin. Only a few planktonic foraminiferan species of the genera Heterohelix and Hedbergella were recovered among an assemblage dominated by calcareous and agglutinated benthonics. Marine dinocysts are curiously absent from among the palynomorph assemblage, which consists dominantly of pollen grains from land plants (angiosperms and gymnosperms) and pteridophytic spores, together with a few fungal remains. Two benthonic foraminiferal assemblages that include the Campanian-Maastrichtian Bolivina afra-Haplophragmoides talokensis and the Paleocene Anomalinoides umboniferus-Eponides pseudoelevatus are well established at this outcrop. The palynomorphs include a few typical Late Cretaceous and typical Paleogene species, while the majority are long ranging forms that straddle the Cretaceous-Tertiary boundary. The foraminiferal and palynomorph biostratigraphic distributions permitted us to recognize the succession of Campanian-Maastrichtian and Paleocene strata and the Cretaceous-Tertiary boundary for the first time in this basin. Lithofacies change from a monotonous thick pile of shales below, succeeded by sandstones, frequently alternating with mudstone, above. This indicates a general fall in sea level during the Early Paleocene earlier reported within this subregion, and the boundary marks the start of the out building of the Niger Delta which the Tertiary Rio del Rey Basin is part of. Both microfossils and lithofacies analyses aided the reconstruction of an open marine, probably middle to inner neritic shallow and transitional intertidal paleodepositional environments for the sediments exposed at this outcrop.

Benthonic foraminiferal biostratigraphy and faunal turnover events during the Late Paleocene-Early Eocene at Darb Gaga, Western Desert, Egypt: Paleoenvironmental and sequence stratigraphic interpretations

The present study depends on qualitative and quantitative analyses for the Late Paleocene-Early Eocene benthonic foraminifera at Darb Gaga area, Baris Oasis, Western Desert, Egypt. The study Late Paleocene-Early Eocene succession consists of two rock units; Esna Formation at base and Thebes Formation (lowermost part) at top. Esna Formation is subdivided into four members stratigraphically arranged as follow: El Hanadi, Dababiya Quarry, Darb Gaga and Abu Had. Dababiya Quarry Member (marker of the P/E boundary) is characterized by the occurrence of glauconitic grains at the base confirming a minor hiatus at the P/E boundary. This hiatus led to the missing of the beds no. 1 & 2 of the five beds (lowermost part) of Dababiya Quarry Member. Four benthonic foraminiferal events are defined during the Late Paleocene-Early Eocene interval. The first one is global event at the Paleocene/Eocene (P/E) boundary, and the remainder events are local and define during the Ypresian (Early Eocene). The first event is characterized by a rapid extinction and abrupt faunal changes for the benthonic foraminiferal assemblages. This event led to the extinction of about 80% of the Paleocene foraminiferal taxa. About 72% of these taxa are temporarily extinct and reappeared soon. This event is characterized by carbonate dissolution which suggesting oxygen deficiency of oceanic bottom waters and food supply changes. Afterwards, a recovery phase of the benthonic foraminifers is directly recorded above this event and probably due to improved depositional environmental conditions. Quantitative analyses of benthonic foraminiferal assemblages at Darb Gaga section, suggest an outer shelf paleoenvironmental setting during the deposition of El Hanadi, Dababiya Quarry and Darb Gaga sediments that changes to inner-middle shelf during the deposition of Abu Had Member and inner shelf of Thebes Formation. This succession is subdivided into four depositional sequences which are bracketed by unconformities and their correlative conformities depending on integrated field investigations, lithofacies and biofacies data. These sequences are controlled by sea-level changes and/or tectonic activities that prevailed during the deposition.

Paleocene–Eocene transition at Naqb Assiut, Kharga Oasis, Western Desert, Egypt: Stratigraphical and paleoenvironmental inferences

This work depends on the study of the lower part of the Esna Formation which encompasses the Paleocene–Eocene (P-E) transition in Egypt as well as at Naqb Assiut section, Kharga Oasis, Western Desert. The Paleocene/Eocene (P/E) boundary is represented by El Dababiya Quarry Member which consists of five distinctive beds (nos. 1–5) at the GSSP. On the other hand, at Naqb Assiut section this boundary is only represented by the upper two beds (nos. 4&5), whereas, the lower three beds (nos. 1–3) are missing due to a hiatus. This hiatus is marked by the occurrence of an irregular surface contains pebbles and phosphatic materials. This hiatus may be related to the echo of Sryian Arc Orogeny at the P/E time. Biostratigraphically; four planktonic foraminiferal zones are defined from base to top as: Acarinina soldadoensis/Globanomalina pseudomenardii and Morozovella velascoensis (late Paleocene), Acarinina sibaiyaensis and Pseudohastigerina wilcoxensis/Morozovella velascoensis (early Eocene). The Acarinina sibaiyaensis Zone which represents the P//E/boundary is characterized by the occurrence of intrazonal hiatus at it's lower part. The benthonic foraminiferal taxa contain abundant representatives of Midway-type fauna (∼91% of the whole assemblages), beside few Velasco-type faunal ones (∼9%), indicating an outer neritic (150–200 m) water depth of deposition during the P–E transition. Quantitative analysis and composition of benthonic foraminiferal assemblages are indicative for various environmental changes around the P/E boundary. They reflected a high diversity, increase of epifaunal taxa, and low-intermediate productivity conditions, which indicates a well-ventilated bottom water and oligo - to mesotrophic conditions during the late Paleocene age. Rapid extinction of about 18% of the entire benthonic foraminiferal species started at the P/E boundary, where the last occurrence of Angulogavelinella avnimelechi is pronounced at the base of this boundary. There is a decline in the preceding faunal characteristics of the late Paleocene and signified an increase in the abundance of agglutinated and buliminid species. These characters are revealed some environmental stressful conditions of low oxygen and increased productivity. During the early Eocene, the environmental conditions are improved leading to the recovery of most benthonic and planktonic foraminifera.

Biostratygrafia osadów miocenu z otworów wiertniczych Busko (Młyny) PIG-1 i Kazimierza Wielka (Donosy) PIG-1 na podstawie otwornic (północna część zapadliska przedkarpackiego)

FORAMINIFERAL BIOSTRATIGRAPHY OF THE MIOCENE DEPOSITS FROM THE BUSKO (MŁYNY) PIG-1 AND KAZIMIERZA WIELKA (DONOSY) PIG-1 BOREHOLES (NORTHERN PART OF THE CARPATHIAN FOREDEEP) Abstract. Micropaleontological study of Miocene deposits from the Busko (Mlyny) PIG-1 and Kazimierza Wielka (Donosy) PIG-1 boreholes, located in the northern part of the Carpathian Foredeep, has allowed taxonomic and biostratigraphic characteristics of foraminiferal assemblages. The samples were taken from clay and clay-marly interbeds in sub-evaporitic, evaporitic and supra-evaporitc complexes. In the Busko (Mlyny) PIG-1 borehole, five foraminiferal assemblages have been defined (Z.b.I–Z.s.V), corresponding with the following foraminiferal zones: Orbulina suturalis / Praeorbulina – Z.b.I (Moravian substage of the Early Badenian), Neobulimina longa – Z.b.II; Velapertina indigena – Z.b.III, Hanzawaia crassiseptata – Z.b.IV (Kosovian substage of the Late Badenian) and Anomalinoides dividens – Z.b.V (Volhynian substage of the Early Sarmatian). In the Kazimierza Wielka (Donosy) PIG-1 borehole, two foraminiferal assemblages have been identified (Z.b.I and Z.s.II), correlated with following foraminiferal zones Velapertina indigena – Z.b.I (Kosovian substage of the Late Badenian) and Varidentella sarmatica – Z.s.II (Volhynian substage of the Early Sarmatian). The third assemblage (Z.s.III), because of poor preservation of foraminifers has been attributed to the Sarmatian stage in general. Lateral replacement of planktonic and benthonic foraminiferal assemblages confirms a significant facies variability of the Late Badenian deposits that accumulated in the northern margin of marine basin in the Carpathian Foredeep.

ABUNDANCE BIOZONES AND COMMUNITY STRUCTURES IN THE UPPER QUATERNARY OF ODP HOLE 994C (BLAKE RIDGE, WESTERN ATLANTIC OCEAN) COMPARED WITH MARINE ISOTOPE STAGES, GLACIAL CYCLES, AND TERMINATIONS

Bathyal and abyssal benthonic foraminiferal assemblages have been thought to undergo community- and species-level regime shifts between glacials and interglacials. Comparisons between communities and oxygen isotope curves are, however, few. Comparisons between multiple aspects of the benthonic foraminiferal community and the oxygen isotope curve are made here for the abyssal Upper Quaternary of ODP Hole 994C (Blake Ridge, western Atlantic Ocean). Presumed allochthonous species were removed from the dataset to give an in situ abyssal assemblage dominated by Brizalina lowmani with subordinate Cibicides wuellerstorfi and other species. The total number N of benthonic foraminifera/20 cm3 sediment sample, the point diversity measured using the information function H, and max(pi) (the proportional abundance of the most abundant species in each sample) all fluctuated between samples. These variables apparently mirrored the oxygen-isotope curve based on planktonic foraminifera, and so show potential for tracking marine isotope stages (MIS). However, neither abundance biozone boundaries nor species-level regime shifts (i.e., points of change in percentage carrying capacity, Kp) coincided or showed consistent associations with terminations (pronounced boundaries between isotopic maxima and minima). Cibicides wuellerstorfi was most abundant towards the base of the section, which might indicate stronger current action. Most abundance biozones (ABs) had a Type 0 community structure, but Type 1 community structure was recorded in ABs from the upper part of Glacial Cycle E (glacial MIS 10) and the lower part of Glacial Cycle D (interglacial MIS 9), for which this community structure may mark an extended period of stress. Peaks in percentage abundance of Uvigerina spp. occurred in glacial MIS 2, 6, and 8, but not in MIS 4, 10, and 12. It is, therefore, recommended that workers be cautious when using glacial-interglacial cycles to explain ecostratigraphic events in abyssal Pleistocene successions, especially in the absence of an oxygen-isotope curve.

Quantifying Assemblage Turnover and Species Contributions at Ecologic Boundaries

Not all boundaries, whether stratigraphical or geographical, are marked by species-level changes in community composition. For example, paleodata for some sites do not show readily discernible glacial-interglacial contrasts. Rather, the proportional abundances of species can vary subtly between glacials and interglacials. This paper presents a simple quantitative measure of assemblage turnover (assemblage turnover index, ATI) that uses changes in species' proportional abundances to identify intervals of community change. A second, functionally-related index (conditioned-on-boundary index, CoBI) identifies species contributions to the total assemblage turnover. With these measures we examine benthonic foraminiferal assemblages to assess glacial/interglacial contrasts at abyssal depths. Our results indicate that these measures, ATI and CoBI, have potential as sequence stratigraphic tools in abyssal depth deposits. Many peaks in the set of values of ATI coincide with terminations at the end of glaciations and delineate peak-bounded ATI intervals (PATIs) separated by boundaries that approximate to glacial terminations and to transgressions at neritic depths. These measures, however, can be used to evaluate the assemblage turnover and composition at any defined ecological or paleoecological boundary. The section used is from Ocean Drilling Program (OPD) Hole 994C, drilled on the Blake Ridge, offshore SE USA.

Integrated stratigraphy and palaeoenvironment of the P/E boundary interval, Rakhi Nala section, Indus Basin (Pakistan)

Marine sedimentary section across the Paleocene/Eocene (P/E) boundary interval is preserved in the Dungan Formation (Lower Indus Basin), Pakistan. Four dinoflagellate zones in the P/E interval of the Rakhi Nala section (Lower Indus Basin) are identified and correlated. The quantitative analysis of the dinoflagellate cyst assemblages together with geochemical data are used to reconstruct the palaeoenvironment across the P/E interval. The dinocyst assemblages allow the local correlation of the Dungan Formation (part) of the Sulaiman Range with the Patala Formation (part) of the Upper Indus Basin and global correlation of the Zone Pak-DV with the Apectodinium acme Zone of the Northern and Southern hemispheres. The onset of the carbon isotopic excursion (CIE) associated with Paleocene Eocene Thermal Maximum (PETM) is used globally to identify the P/E boundary. The CIE for the total organic carbon (fine fraction) δ13CFF is of a magnitude of −1.7‰ is recorded for the first time in the Indus Basin. The Apectodinium acme precedes and straddles the onset of the CIE in the Indus Basin. This Apectodinium acme is also accompanied by a planktonic and benthonic foraminifera “barren zone.” The CIE in the Indus Basin, coupled with the changes in the dinocyst distribution and the benthonic and planktonic foraminifera assemblages, provides evidence of the changes associated with the PETM in this little-known part of the world. The benthonic foraminiferal assemblage indicates bathyal environment of deposition at the time of P/E boundary interval; the presence of dominantly open marine dinoflagellates and high planktonic foraminiferal ratio suggest that the water column at this site was well connected with the rest of the Tethys.

Campano–Maastrichtian foraminifera from onshore sediments in the Rio del Rey Basin, Southwest Cameroon

Campanian–Maastrichtian marine sediments outcrop in five genetically linked sedimentary basins along the West African coast in the Gulf of Guinea, from the Douala Basin in Cameroon to the Anambra Basin in Nigeria. These sediments in the more centrally located Rio del Rey Basin have been the least studied. Therefore, the geologic history of this region has merely been speculative. The Rio del Rey Basin like the adjacent Niger Delta is producing hydrocarbon from the offshore Tertiary sedimentary interval in which all studies have been focused, neglecting the onshore Cretaceous sediments. Outcrops in the basin are rare, small and highly weathered. Samples from some of these sediments have yielded a few Planktonic and dominantly benthonic foraminiferal assemblages. The long-ranging heterohelix and hedbergellids characterized the planktics while the species Afrobolivina afra which is a well known diagnostic taxon for Campanian–Maastrichtian sediments in West African basins clearly dominate the benthic assemblage. Its occurrence in association with other Upper Cretaceous forms such as Bolivina explicata, Praebulimina exiqua, Gabonita lata, Ammobaculites coprolithiformis amongst others, formed the basis on which this age was assigned to the sediments sampled from the Rio del Rey Basin. Hence, this work has undoubtedly established the much needed link in this regional geologic history and correlates these sediments with the Logbaba and Nkporo Formations in the Douala Basin in Cameroon and the southeastern Nigerian Sedimentary Basins. Thus, these units were all deposited during this same geologic period and probably controlled by the same geologic event.

Climatic variability and anthropogenic signatures in the Gulf of Salerno (southern-eastern Tyrrhenian Sea) during the last half millennium

The high-resolution study of sediment core C90-1 m collected at the continental shelf of the Gulf of Salerno (southern Tyrrhenian Sea) provides an excellent opportunity to show paleoenvironmental changes during the last 500 years induced by natural variability and human impact. Based on 210Pb and 137Cs measurements, the sedimentation rate results 0.20 cm/year for the last 100 years. The high sampling resolution (1 cm sample spacing) of core C90-1 m, 105 cm long, provides a time resolution of approximately 5 years/cm. Quantitative changes in the planktonic and benthonic foraminiferal assemblages combined with δ18O G.ruber variations allow to identify regional climatic and oceanographic signals. A significant turnover between herbivorous and opportunistic species and carnivorous planktonic foraminifera after the Maunder event suggests changes in river runoff and/or an increase in coastal flooding events in the studied area. Variations in the microfauna since 1940 yAD document environmental changes induced by the construction of a dam in the Sele River.

Middle and late Cenomanian oceanic anoxic events in shallow and deeper shelf environments of western Morocco

The response of shallow-water sequences to oceanic anoxic event 2 and mid-Cenomanian events 1a and 1b was investigated along the west African margin of Morocco north of Agadir (Azazoul) and correlated with the deep-water sequence of the Tarfaya Basin (Mohammed Beach) based on biostratigraphy, mineralogy, phosphorus and stable isotopes. In the deeper Mohammed Beach section results show double peaks in δ13Corg for mid-Cenomanian events 1a and 1b (Rotalipora reicheli biozone, lower CC10a biozone), the characteristic oceanic anoxic event 2 δ13C excursion (Rotalipora cushmani extinction, top of CC10a biozone) and laminated (anoxic) black shale. In the shallow environment north of Agadir, a fluctuating sea-level associated with dysoxic, brackish and mesotrophic conditions prevailed during the middle to late Cenomanian, as indicated by oyster biostromes, nannofossils, planktonic and benthonic foraminiferal assemblages. Anoxic conditions characteristic of oceanic anoxic event 2 (for example, laminated black shales) did not reach into shallow-water environments until the maximum transgression of the early Turonian. Climate conditions decoupled along the western margin of Morocco between mid-Cenomanian event 1b and the Cenomanian–Turonian boundary, as also observed in eastern Tethys. North of Agadir alternating humid and dry seasonal conditions prevailed, whereas in the Tarfaya Basin the climate was dry and seasonal. This climatic decoupling can be attributed to variations in the Intertropical Convergence Zone and in the intensity of the north-east trade winds in tropical areas.

The significance of iron-stained foraminifera off SE Trinidad, West Indies, western central Atlantic Ocean

AbstractEleven samples of seafloor sediment were taken from water depths of 78–90 m within the Savonette Field, off SE Trinidad, western Atlantic Ocean. This surface sediment is relict, having been deposited during an early Holocene transgression. The samples yielded much iron-stained quartz and a rich assemblage of dead foraminifera, of which 75% of planktonic foraminifera were stained with iron, as was 66.5% of the calcareous benthonic foraminiferal assemblage. The fauna, both iron-stained and unstained, was dominated byCibicidoidesex. gr.pseudoungerianus, and is concluded, despite the proximity of the Orinoco Delta, to be equivalent to a relictCibicidoidesbiofacies in carbonate-rich areas of the Gulf of Mexico. Staining was by limonite and hematite. Differing percentages of calcareous benthonic species had been stained with iron, ANOVA revealing three groups of species within which the mean percentage of iron-stained specimens per sample did not differ: (a)Globocassidulina subglobosaandHanzawaia concentrica; (b)Amphistegina gibbosa, Cassidulina norcrossi australis Cibicioidesex. gr.pseudoungerianus,C. io,Elphidium translucensandQuinqueloculina lamarckiana; and (c)Eponides antillarumandE. repandus. It is concluded that species differ in their susceptibility to iron staining, and that planktonic foraminifera are more susceptible than most benthonic species. Although waters off northern South America are turbid and the photic zone only ~25 m deep, the relict assemblage contained 8.4% algal symbiont-bearing foraminifera (especiallyA. gibbosaandE. translucens) that would be limited to the photic zone. These are thought to have lived at a time early in the Holocene transgression when sequestration of sediment within the Orinoco delta rendered the water sufficiently clear for viable populations of symbiont-bearing foraminifera. Should iron-stained foraminifera prove to be restricted to transgressive systems tracts, this would make them a useful sequence stratigraphic tool.

Benthonic Foraminiferal Biostratigraphy of the Upper Cretaceous (Middle Cenomanian−Coniacian) Sequences of the Bey Dağları Carbonate Platform, Western Taurides, Turkey

Identification of the benthonic foraminiferal assemblages from ten stratigraphic sections from the inner platform limestones of the Middle Cenomanian−Coniacian successions of the Bey Dağları carbonate platform (BDCP) allowed the recognition of one biozone and two subzones. The lower part of the platform limestones (Middle−Upper Cenomanian) is represented by relatively rich benthonic foraminiferal assemblages, while the upper part (Turonian−Coniacian) contains poor assemblages. The benthonic foraminiferal assemblages determined in the BDCP are dominated by long-ranging species. The shorter-ranging, stratigraphical index species have been selected to date the Upper Cretaceous platform limestones of the BDCP based on the distributions of the species in the circum-Mediterranean region. The Pseudolituonella reicheli-Pseudorhapydionina dubia Concurrent Range Zone is defined from the Middle−Upper Cenomanian platform limestones. The biozone includes the Cisalveolina lehneri Subzone and the Coxites zubairensis Subzone of Middle Cenomanian and Upper Cenomanian age respectively. The first occurrences of Moncharmontia apenninica-compressa and Pseudocyclammina sphaeroidea indicate the Late Turonian and the Coniacian respectively. The spread of hemipelagic limestones in the BDCP during the Coniacian shows that neritic accumulation on the BDCP persisted from the Middle Cenomanian to the Coniacian. These data indicate that the global sea level rise at the Cenomanian−Turonian boundary, which caused the general demise of many Tethyan carbonate platforms, did not result in deepening on the BDCP.

秋田県鮎川‐由利原地域の中新統のフィッション・トラック年代

Fission-track dating using both internal and external surfaces of zircons was carried out for ten core samples from the Miocene formations in the Ayukawa-Yurihara district, Akita Prefecture. These samples were collected from the Yashiozawakawa, Nishikurosawa and Onnagawa Formations of eight wells drilled for the petroleum exploration in this area.After the detail examination for grain ages of each sample using histogram, age spectrum and radial plot, fission-track ages are interpretated. The results are summarized as follows.1) Although external fission-track age (20.1 ± 1.3Ma) of andesite in the upper part of the Yashiozawakawa Formation shows the eruption age with some possibility of rejuvenation, internal fission-track age (16.4 ± 0.6Ma) shows the thermal event which probably corresponds to the start of the “graben-fill basalt” activity.2) The most reliable internal fission-track age (12.2 ± 0.4Ma) of acidic tuff in the Nishikurosawa Formation is in harmony with the biostratigraphic age of this formation. The external fission-track age (16.6 ± 0.8Ma) indicates that the provenance of zircons is probably the Hatamura Formation.3) The most reliable fission-track age of tuffs between the O-1 and O-2 benthonic foraminiferal assemblages, 8.6 ± 0.4 Ma of the Ayukawa-kita well, is consistent with Sr isotopic age (about 9Ma) of the O-2 assemblage. The age of the O-1 assemblage is estimated 8.2 Ma based on K-Ar ages of the overlying Fukuyama andesite. Therefore, the O-1 assemblage is correlated with “Blue zone” in Niigata Prefecture, and has a possibility of regional correlation marker.4) This study indicates that the fission-track dating using both surfaces and more than one samples of the same horizon is a valuable method for the use of few and expensive cores.

Quantitative analysis and palaeoecology of Eocene Ostracoda and benthonic foraminifera from Gebel Mokattam, Cairo, Egypt

A detailed study of the ostracod and benthonic foraminiferal assemblages of two sections from Gebel Mokattam (east of Cairo) yielded ostracod species and benthonic foraminiferal species in 25 samples from the Mokattam Group of late middle Eocene age and the Maadi Group of late middle to late Eocene ages. The remaining five samples representing the Gebel Ahmar Formation of Oligocene age, at the top of the succession, are barren of fossils. Cluster analysis, using the Jaccard coefficient of similarity (the group average linkage method), helped distinguish four ecozones of late middle to late Eocene age. Principal coordinate analysis (PCO) applied to the same data led to the distinction of two important environmental factors affecting the distribution of these ostracod assemblages in the study area: turbidity currents–exposure to water depth and oxygenation of water. Analyses of the microfacies and microfaunas indicate deposition in a well-oxygenated, turbid, shallow marine environment except at the base of the sequence, which implies reduced oxygenation. Despite the lack of planktonic foraminifera in the studied sections, however, the identified benthonic foraminiferal assemblage affirms that the age of the Mokattam Group is Biarritzian, while that of the Maadi Group ranges from Biarritzian to Priabonian. The Gebel Ahmar Formation, covering the whole succession, is assigned to the Oligocene. A reduced ostracod migration activity was detected along the shores of Tethys during the middle to late Eocene times.

Benthonic foraminiferal assemblages and microfacies analysis of Paleocene–Eocene carbonate rocks in the Kastamonu region, Northern Turkey

The Kastamonu region, NW Turkey, is known for its rich foraminiferal marine biota and variety of deposits from Paleocene to Eocene times. The focus of this study is on the foraminiferal assemblages and microfacies analysis of the sediments. Usually Paleocene shallow water limestones overlie Maastrichtian rocks conformably. They are characterized by benthic foraminifera such as Laffitteina mengaudi (Astre) Anomalina sp., Eponides sp., Rotalia sp., Mississippina sp., Haurenidae in the lower strata and numerous rotaliid such as Pseudocuvillierina sireli İnan, Rotalia perovalis Terquem, R. trochidiformis (Lamarck), Kathina selveri Smout, Kathina major Smout, Smoutina? subspherica (Sirel), Miscellanea primitiva Rahaghi in the upper strata. The Eocene clayey limestones, limestones and marls, which generally conformably overlie the Paleocene, are commonly characterized by benthic foraminifera of Orbitolites complanatus Lamarck, Asterigerina rotula (Kaufmann), Gyroidinella magna (Le Calvez), Fabiania cassis (Oppenheim), Nummulites minervensis Schaub, Nummulites burdigalensis de la Harpe, Nummulites millecaput Boubee, Assilina placentula (Deshayes), Assilina exponens (Sowerby). Microfacies analyses of the Paleocene–Eocene carbonate rocks were carried out with respect to the distribution of depositional components and biota. The Danian, Selandian and Thanetian units are characterized by reefal (organic buildup), shelf lagoon, shelf and tidal flat paleoenvironments. The Ilerdian units are represented by reefal and shelf lagoon environments, while the Cuisian units are characterized by shelf lagoon and deep shelf settings. The Lutetian units indicate platform margin through fore-slope to deep marine shelf paleoenvironments.

Paleontological evidence of the Campanian to Early Paleocene paleogeography of Baja California

Fossil assemblages of Campanian to Maastrichtian dinoflagellates, invertebrates, mammals, reptilians, and planktonic foraminifera in Baja California are mainly temperate, similar to those found in the North Atlantic, Rocky Mountains and North Pacific regions. Early Paleocene assemblages are mostly subtropical ones. Danian dinoflagellates suggest deposition in a temperate to subtropical province, and benthonic foraminiferal assemblages (Midway type) are common in a region from the Gulf of Mexico to the northeastern coast of the U.S.A. The molluscan assemblages recovered from early Paleocene rocks indicate deposition mostly in subtropical environments. Although these invertebrate assemblages are related to the Caribbean province, dominant mollusks and solitary corals indicate subtropical to warm temperate paleoenvironments. Considering that the dinoflagellate, invertebrate, vertebrate and planktonic foraminiferal assemblages indicate temperate environments, together with paleogeographic models based on plate tectonics, we conclude that at least since the Campanian, Baja California was attached to western Mexico. The peninsula did not move much more than the 300 km needed to close the Gulf of California.

Upper Cretaceous palaeoenvironments and benthonic foraminiferal assemblages of potential source rocks from the western African margin, Central Atlantic

Abstract Upper Cretaceous benthonic foraminiferal assemblages, clay minerals, kerogen types and carbonate microfacies are examined in organic-rich sediments from western African coastal basins along a latitudinal transect extending from southern Morocco to Nigeria. Samples from onshore sections of the Tarfaya Basin, southern Morocco, from DSDP Site 369, from offshore commercial wells on the Casamance Shelf, Senegal, from DSDP Site 367, from ODP Site 959 and from onshore sections of the Benue Trough in Nigeria, are analysed. Organic-rich sediments from these sites are characterized by smectiterich clay mineral assemblages, high amounts of marine organic matter and a typical benthonic foraminiferal biofacies dominated by buliminids and bolivinids. Benthonic foraminifera provide robust proxy indicators of palaeoproductivity and organic matter flux to the seafloor. The palaeobiogeographic distribution of benthonic foraminiferal biofacies can be used to identify areas and stratigraphic intervals of hydrocarbon accumulation. Lower Turonian benthonic foraminiferal assemblages exhibit extremely low diversity and are strongly dominated by a Gabonita biofacies, in contrast to Coniacian to Maastrichtian assemblages, which display higher diversity and contain numerous species of Buliminella, Praebulimina, Afrobolivina, Bolivina and Orthokarstenia . The palaeobathymetric distribution of these high productivity benthonic foraminiferal biofacies reflects the establishment of a productivity driven oxygen minimum zone along the western African shelf, associated with an upwelling system active off coastal Africa during most of the Late Cretaceous. The extent of the high productivity equatorial belt appears to have shifted latitudinally during the Late Cretaceous as sea level and circulation patterns changed. The zone of highest productivity was broadest in the Early Turonian, when it coincided with the maximum sea-level rise and highest atmospheric temperature in the Late Cretaceous.