REVUE DE MICROPALEONTOLOGIE最新文献

Calcareous nannofossil biostratigraphy of Alaka well was carried out to identify the biohorizons that exist, ultimately for biozonation, chronostratigraphy and geologic age calibration of the studied interval. The study involved sedimentology analysis, gamma ray description and preparation of two hundred and twelve (212) ditch cuttings, sampled at 9.144m intervals for the study of calcareous nannofossils on smear slides. Sedimentology and gamma ray analyse showed deposition within shallow marine paleoenvironments with alternating minor transgressions in a generally progradational delta setting, accounting for the low calcareous nannofossil occurrences. The calcareous nannofossil assemblages recovered from the slide preparations consist of fourteen (14) species, comprising nine (9) long ranged, non-stratigraphic significant forms and five (5) short ranged stratigraphic significant forms. The biohorizons identified included Base (B) occurrence of Catinaster coalitus at 3578m; Discoaster hamatus at 2874m; Top (T) occurrence of Discoaster hamatus at 2518m and Base absence (Ba) of Reticulofenestra pseudoumbilicus at 2280m. Other biohorizons included Top occurrence (T) of Discoaster bollii at 2435m and Discoaster deflandrei at 3578m respectively. The biohorizons defined boundaries between biozones and showed that the studied interval penetrated four biozones from CNM11 to CNM14 of Backman et al. (2012), NN7 to NN10 of Martini (1971) and CN5b to CN8a of Okada and Bukry (1980). The geologic age of the studied interval ranged between about 11.60 Ma within CNM11/NN7/CN5b zone to about 8.80 Ma within CNM14/NN10/CN8a zone, the standard chronostratigraphy lies within Tortonian stage. Two chronostratigraphic surfaces were mapped in the studied section and comprised one global maximum transgression at 3514m corresponding to 10.5 Ma maximum flooding event, and one localized maximum transgression at 2847m corresponding to 9.5 Ma maximum flooding surface, separated by sea-level lowstand mapped at 3331m and corresponding to 10.35 Ma.

An inventory of 35 species of ostracods (Crustacea) recovered from sediment samples from a shallow embayment nearby the Mu Koh Phetra National Park in the southwestern coast of Peninsular Thailand, Andaman Sea is given. Most of the species are well-known from the Indo-Pacific area and some others are kept in open nomenclature or compared to already know species because because only few specimens were found. Several species may be new to science but have also to be kept in open nomenclature until new material is obtained. The very abundant specimens of this assemblage are mainly disarticulated valves. This contribution adds to our knowledge of the distribution of ostracods in the Andaman Sea and the degree of ostracod relationship between the Indonesian, Indian and West Pacific areas.

Resumé

Un inventaire de 35 espèces d'ostracodes (Crustacea) provenant de sédiments d'une baie peu profonde près du Parc National Mu Koh Phetra sur la côte sud-ouest de la péninsule de Thïlande, Mer d'Andaman, est donné. La plupart des espèces sont bien connues de la zone Indo-Pacifique et certaines sont conservées en nomenclature ouverte ou comparées à des espèces déjà connues en raison du faible nombre de spécimens collectés. Plusieurs espèces semblent nouvelles mais sont aussi conservées en nomenclature ouverte jusqu’à l'observation de nouveau matériel. Les très abondants spécimens qui composent cet assemblage sont principalement des valves désarticulées. Cette contribution accroit notre connaissance de la distribution des ostracodes dans la Mer d'Andaman et de la relation entre les ostracodes des zones indonésiennes, indiennes et ouest-pacifiques.

Palynomorphs from the Toarcian and Aalenian Djigiat Formation of Karachay-Cherkessia in the Kuban River Basin (North Caucasus, southwest Russian Federation) are reported for the first time. Five samples carefully selected for their biostratigraphical content were studied to document the palynological assemblages. Four samples (1, 2, 3, 4) were collected from pieces of rock with key index ammonite specimens, and sample 5 comprises fragments of ammonite shells from a sideritic concretion. Three of these samples (4, 2 and 1) yielded relatively abundant and diverse aquatic microplankton (acritarchs, dinoflagellate cysts, prasinophytes and zygnematalean algae) and terrestrial palynomorphs (pollen and spores); the remaining two samples (3 and 5) were less productive and contained fewer than 50 palynomorph specimens. The study of the dinoflagellate assemblages provided characteristic and key information. These are the uppermost Toarcian Nannoceratopsis Assemblage and the uppermost Toarcian to lowermost Aalenian Parvocysta Suite Assemblage. The former is overwhelmingly dominated by Nannoceratopsis with sparse numbers of the Parvocysta suite, and the latter yielded more diverse and common specimens of Parvocysta and its relatives. This is consistent with the hypothesis that the Parvocysta suite migrated from the Boreal Realm further south into Laurasia during the Toarcian. Certain dinoflagellate cysts such as Mancodinium semitabulatum and Scriniocassis spp., which are typical of Europe and much of Greater Laurasia are absent. Composition of the pollen and spores proved relatively out to be monotonous, and cannot be subdivided. However, in general, the composition of the assemblages of spores and pollen is consistent with the Toarcian–Aalenian transition.

This work introduces one of the first palynostatigraphic study conducted on formations from the Eocene and overlying lowermost Miocene successions (Cunga and Quifangondo formations) exposed in the Onshore Kwanza Basin, Angola.

To improve the Cunga and Quifangondo formations age, new biostratigraphic correlations and palaeoenvironmental interpretations based on qualitative and quantitative analyses of organic walled dinoflagellate cysts from sedimentary rocks sampled in the Cabo de São Brás section were obtained.

Those works have revealed that the Cunga Formation could be assigned to a middle Eocene - early Oligocene age, with a palynomorph signature typical of outer neritic to oceanic environments (dominance of dinocysts with microforaminiferal linings and radiolarian pyritized fragments).

The lower Quifangondo Formation could be assigned to late Oligocene (latest Chattian) - early Miocene (Aquitanian) ages. This assumption is based on the first occurrence of Ectosphaeropsis burdigalensis, and the last occurrence of Deflandrea spp. and Chiropteridium galea. Additionally, the Chiropteridium, Distatodinium, Homotryblium, Hystrichokolpoma and Lingulodinium acme endorses a latest Chattian-early Aquitanian age to these samples. The palynomorph signature of this unit reflects an outer neritic environment.

The latest Oligocene/early Miocene Quifangondo Formation overlaps unconformably on strata of the middle Eocene to early Oligocene Cunga Formation, pointing out a hiatus between the two units.

Abundant ostracods of the genus Hollinella (Palaeocopida) have recently been described from the Early Triassic siliciclastic deposits of the paralic Mide B section, Yunnan Province, South China. These weathered and delicate specimens are preserved on the surface of cracked sediments, often still partly buried and impossible to extract. A small piece of siliciclastic sediments with Hollinella specimens visible on the surface has been investigated by X-ray computed tomography (CT) to search for better preserved and possibly complete specimens still enclosed in the matrix. While surface observations led to the attribution of these specimens to Hollinella panxiensis Wang already known from other Permian-Triassic sections in South China, this non-destructive technique reveals distinctive characters that drive us to introduce the new species Hollinella locula Forel nov. sp. Certain previous identifications of Hollinella panxiensis are re-attributed to Hollinella locula. The taphonomic analysis of this material is refined and confirms the previous interpretation of a low energy thanatocoenosis. This investigation further highlights the strong implications of new imaging techniques in diverse fields of ostracodology, even in the absence of soft parts preservation.

In this study, taxonomic criteria were revised for 64 spumellarians/collodarians from the Upper Miocene that were collected at the Ocean Drilling Program Site 1208. The taxonomic approach employed in this study allowed a relatively wide range of intra-species variation to promote palaeoceanographic studies on Upper Miocene fauna in the future. In addition, the nomenclature of species with controversial taxonomies, for which there is significant biostratigraphic interest, was also revised. One such example is Stylatractus universus Hays, which should be renamed as Xiphosphaerantha angelina (Campbell and Clark). In addition, a new species from the Upper to Middle Miocene core sequences was collected at mid-latitudes of the North Pacific Ocean. This species has been named Didymocyrtis noritoshii and can potentially be used as a biostratigraphic and environmental index in core sequences from the Upper Miocene.

Resumé

Dans cette étude, les critères taxonomiques de 64 spumellaires et collodaires du Miocène supérieur, collectés sur le site de l'Ocean Drilling Program 1208 sont révisés. Mon approche taxonomique utilisée dans le cadre de cette étude fut libérale, permettant une certaine marge de variations intra-espèces dans le but de promouvoir à l'avenir les études paléocéanographiques en se basant sur la faune radiolaire du Miocène supérieur. En permettant ainsi une plus large variation morphologique au sein d'une espèce, les taxonomies sont plus simples que si on applique une variation morphologique avec des critères assez stricts pour séparer les espèces. En outre, la nomenclature des espèces aux taxonomies controversées parmi lesquelles y figure une espèce à certain intérêt biostratigraphique a également été révisée. C’est le cas de Stylatractus universus Hays, que j'ai renommé Xiphosphaerantha angelina (Campbell et Clark). Enfin, une nouvelle espèce a pu être décrite dans les séquences sédimentaires datant du Miocène supérieur. Cette espèce, qui a été qui fut nommée Didymocyrtis noritoshii, pourrait potentiellement être utilisée comme indicateur biostratigraphique et environnemental dans l'océan Pacifique du nord.

Well-preserved Late Cretaceous (early Cenomanian) radiolarians were recovered from two sections in Crimea: Bodrak River and Sel’-Bukhra Mountain. Abundant and diverse Nassellaria were studied and four new species are described: Holocryptocanium pseudoastiense nov. sp., Diacanthocapsa bodrakiense nov. sp., Novixitus riedeli nov. sp. and Rhopalosyringium panovi nov. sp. Herein Archaeodictyomitra (?) speciosa Bragina is newly attributed to the genus Obeliscoites O’Dogherty and Dorypyle ovoidea (Squinabol) is tentatively attributed to the genus Homeoarchicorys Empson-Morin. The stratigraphic ranges of Diacanthocapsa urkutica Bragina, Distylocapsa squama O’Dogherty, Novixitus subtilis Bragina, and Siphocampe altamontensis (Campbell and Clark) are more precisely defined with their lower limits expanded to the lower Cenomanian and the upper limits of Pseudodictyomitra languida O’Dogherty and Thanarla conica (Squinabol) extended to the lower Cenomanian.

Two stratigraphic sections referable to the late Messinian have been identified and studied in eastern Tunisia; the first, south of Cape Bon (Salakta-SAL section), the second in the Sahel region (Wadi el Kebir–OK section). The analysis of the ostracod fauna content (assemblages) has revealed that in some stratigraphic levels some taxa are certainly attributable to the Lago-Mare fauna, while other taxa, observed in subsequent or previous stratigraphic levels, are referable to true shallow-water marine environments. From these latter shallow water marine levels, several ostracods species were recognized; some of which, due to their morphological particularities, have been described as new species.

Consequently, in this article, 24 species belonging to the genera Cytherella, Paijenborchellina, Cimbaurila, Pokornyella, Dorukella, Graptocythere, Capsacythere, Chrysocythere, Okadaleberis, Ruggieria, Cytheretta, and Neomonoceratina are described and illustrated as new.

Quaternary deep-sea ostracods supply invaluable data for the understanding of both hydrological and sedimentary processes in the continental slope. A huge portion of western South Atlantic bathyal regions is still poorly explored with respect to deep-sea ostracod research. This article contributes to the study of the assemblage ostracod of the Upper Pleistocene of five piston cores recovered in the Cone of Rio Grande, Pelotas Basin, Brazil. Taxonomic analysis revealed 21 species belonging to 13 genera: Cytherella, Macropyxis, Argilloecia, Paracytherois, Cytheropteron, Rimacytheropteron, Eucytherura, Loxoconchidea, Xestoleberis, Apatihowella, Henryhowella, Poseidonamicus and Krithe. The assemblages are quite similar to those registered in southwestern Brazilian bathyal regions. A taxon left in open nomenclature is probably a new genus and species. Eucytherura fossapunctata nov. sp. is here described.