REVUE DE MICROPALEONTOLOGIE最新文献

This study presents the first data on radiolarian fauna from Miocene deposits of the submarine Vityaz Ridge (SVR) and paraxial zone of the Kuril-Kamchatka Trench. Twenty-two dredge samples were studied, and 214 radiolarian taxa were identified. Taxonomic composition allowed their assignment to Miocene assemblage zones, including Lipmanella japonica conica-Gondwanaria dogieli, Pentactinosphaera hokurikuensis, Dendrospyris sakaii, Eucyrtidium inflatum Subzone a, Lychnocanoma magnacornuta, and Lychnocanoma parallelipes zones. These radiolarian assemblages correlate with studied sequences of many deep-sea cores in the northern Pacific and some sections of onshore Japan. As a result, we designed a biostratigraphic scheme of Miocene radiolarians for the SVR and reconstructed the environmental conditions in this area. In particular, two Miocene climatic optima that were previously established in the northern Pacific were identified in the Middle and Upper Miocene sediments of the southern plateau and Middle Miocene sediments of the northern plateau of the SVR.

Palynological analysis of 200 ditch cuttings of wells M6 and M7 from the western Niger Delta yield a diverse assemblage of pollen, spores, freshwater algae, foraminiferal wall linings and dinoflagellate cysts. Based on pollen and spore marker species, the wells date middle – late Miocene (P720-P860). The regular occurrence of dinoflagellate cysts enhances the subdivision of the sequences into eight and seven tentative dinoflagellate cysts assemblage zones for the M6 and M7 wells respectively. The proposed Niger Delta Dinoflagellate Cysts (C-I) zones are viz: the Lingulodinium machaerophorum Assemblage zone; Homotryblium spp./Sumatradinium spp. Assemblage zone; Operculodinium centrocarpum Assemblage zone; Nematosphaeropsis labyrinthus Assemblage zone; and the Protoperidinium spp./Selenopemphix spp. Assemblage zone. The boundaries are marked by remarkable dinocysts events such as first downhole occurrences or highest stratigraphic occurrences, supplemented with last downhole occurrences or lowest stratigraphic occurrences as the samples were ditch cuttings. The common presence of dinoflagellate cysts and the dominance of Nematosphaeropsis labyrinthus and Impagidinium spp. indicate open marine conditions during the deposition of the studied section.

Reconstructing ocean plate stratigraphy (OPS) and revealing the places of origin and ages of oceanic rocks of the Jurassic–Early Cretaceous accretionary complex in Eastern Asia are important to clarify the accretion process and the paleogeography and tectonic setting of the Panthalassa Sea during the Paleozoic to Mesozoic times. In this context, many geological investigations of the Middle Jurassic–Early Cretaceous units of the Northern Chichibu accretionary complex (except for an Early Jurassic one) and Mikabu Unit have been performed. In this study, geological mapping, faunal analysis of radiolarians, and geochemical analysis of basaltic rocks were conducted for the Hebiki Unit of the Northern Chichibu accretionary complex to obtain prime geological information such as its stratigraphy, ages, and origin of basaltic rock. The Early Jurassic Hebiki Unit consists of chaotic mélange, which contains sandstone, siliceous shale, chert, and basaltic rocks as blocks in a highly sheared shale matrix. Late Permian and Late Triassic radiolarians were newly identified from chert blocks in this study. Based on the radiolarian evidence from this study and previous ones that identified Jurassic radiolarians from siliceous shale, the OPS of the Hebiki Unit are reconstructed as follows: Upper Permian and Upper Triassic (upper Carnian to Rhaetian) chert, and Lower Jurassic (Pliensbachian) siliceous shale in ascending order. Meanwhile, the basaltic rocks of the Hebiki Unit are divided into two types in terms of the major and trace element composition and REE profiles: low and high Nb/Zr types. The low and high types are interpreted as oceanic island basalt (OIB) and mid-ocean ridge basalt (MORB), respectively. Considering the reconstructed OPS of the four tectonostratigraphic units (Kashiwagi, Kamiyoshida, Sumaizuku, and Hebiki) of the Northern Chichibu accretionary complex, the four units are considered to have accreted successively.

Larger benthic foraminifera such as orbitolinids are particularly important in Lower and mid-Cretaceous biostratigraphy of neritic deposits of the Arabian Plate. These data are supplemented by a few non-orbitolinid taxa. Among these, two new species are described herein as Voloshinoides simplex and Cribellopsis? kharaibensis from upper Barremian–lowermost Aptian inner platform limestones of the Kharaib Formation and the Hawar Member cropping out in Wadi Rahabah, United Arabian Emirates. V. simplex sp. nov. represents the oldest and most primitive species of the genus Voloshinoides Barnard and Banner, exhibiting a simple and poorly developed exoskeleton. C.? kharaibensis represents a rather small species exhibiting a primitive marginal zone that lacks intercalary beams. The assignment of the taxonomic status is provisional awaiting some structural clarifications. While C.? kharaibensis is restricted to the upper Barremian Kharaib Formation, V. simplex reaches into the lower part of the lowermost Aptian Hawar Member.

The study by Gheiasvand and Bartolini (2023) treated Balkhania balkhanica and Torinosuella peneropliformis as morphotypes of a single species, Balkhania balkhanica, leading to incorrect conclusions about its characteristics. Their analysis overlooked key aspects of the life cycle, morphotypes, ecological roles, and paleogeographical distribution of B. balkhanica due to a misunderstanding of foraminiferal systematics. Notably, its megalospheric forms can reach a maximal diameter of 5.2 mm, whereas its microspheric forms may reach up to 15 mm. Its stratigraphic range is limited to the Barremian-early Aptian interval. Although B. balkhanica and Choffatella decipiens share equivalent ecological niches, they are not found together in the same strata. Ch. decipiens has a much wider distribution, over most of the Tethys realm, whereas Balkhania balkhanica is primarily found in the northern Tethys platforms, with the notable exception of Lebanon in the southern Tethys platforms.

This paper describes a new monospecific polycystine radiolarian genus and its single species so far, Pirumosphaera armandae, found in the Southwest Pacific and Indian sectors of the Southern Ocean. The new spumellarian form is rarely found as a complete specimen, as only its first and second shells are commonly found. However, partially complete specimens suggest that the test of this species is made of four shells. The most diagnostic feature of the species is the peculiar shape of the first shell which protrudes through the second shell, a characteristic that does not conform to any other Quaternary spumellarian genus. Based on the distinct and unique relationship between the first and second shells, the species is assigned to the newly established Pirumosphaera genus.

To mitigate ecological and health risks, implementing a comprehensive multidisciplinary monitoring strategy is imperative. This approach aims to effectively identify and record potential declines in water quality and ecological conditions. Utilizing cost-effective and efficient monitoring tools is crucial, especially for developing nations. Despite the previously reported uMlalazi River's pristine status within a protected natural reserve at South Africa's eastern coast, our findings challenge the assumption of its cleanliness, emphasizing the need for ongoing proactive monitoring. Here we reassess the pollution levels and ecological status of aquatic life of the river, and use this to enhance the indicator value of microfauna in South Africa. We analysed 25 surface sediment samples from the uMlalazi estuary, covering a salinity range from oligohaline to euhaline, with a focus on marginal marine Ostracoda and Foraminifera as potential indicators. All samples contained Ostracoda and Foraminifera, with the exception of two. Among the identified ostracod species, there were 17 species belonging to 14 genera. Typical taxa are the brackish water species Perissocytheridea estuaria, Sulcostocythere knysnaenis, and Australoloxoconcha favornamentata. We identified 19 Foraminifera species from 16 genera, with dominant taxa such as Ammonia sp., Quinqueloculina sp., and Miliolinella sp. Three distinct assemblages were observed: A) Ammonia sp. and Quinqueloculina sp., with very low diversity and abundances in general, located along the river course at stations exceeding Pollution Load Index (PLI), which indicates deterioration of sites quality; B) Ammonia sp., Quinqueloculina sp., and Sulcostocythere knysnaenis associated with higher salinity and lower PLI; C) Ammonia sp., Quinqueloculina agglutinans, and Cribroelphidium articulatum located in mudflats with minimal PLI. Our findings align with the commonly observed diversity trend, which indicates reduced species diversity corresponding to elevated pollution levels. Notably, the examined samples revealed a range of Foraminiferal Abnormality Index (FAI) up to 23%, exhibiting anomalies such as multiple tests, changes in coiling, and abnormal chamber shapes. Geochemical analysis indicates that the catchment is subjected to substantial anthropogenic pressure, as evidenced by elevated concentrations of heavy metals, sulphur, and microplastic. Sugarcane farming, urban sewage, titanium mining, and fish farming are the primary sources of pollution in the catchment area. Ongoing investigations in South African estuaries are expanding our dataset and will contribute to a better understanding of the species-specific responses of Ostracoda and Foraminifera to anthropogenic pressure.

Choffatella singularis was described from the Hauterivian of the Paris Basin based on abundant isolated specimens and oriented thin-sections enabling a very detailed description. Although an alveolar wall-structure was mentioned in the original description, the new species was assigned to Choffatella Schlumberger that lacks this feature, instead displaying a fine and regular choffatellid subepidermal network. This feature instead would refer to Pseudocyclammina Yabe and Hanzawa that however has a different apertural type. To accommodate Ch. singularis into the current classification of agglutinated benthic foraminifera and its basic criteria, the new genus Magniezjanninius is established including the new combination M. singularis (Magniez-Jannin).

This study deals with the taphonomy of siliceous microfossils preserved in trace fossils. With this objective, we chose to study trace fossils (Tasselia ordamensis) from the Oligocene Okubo Mudstone Member of the Nishinoomote Formation (Kumage Group), exposed on Tanegashima Island, Kagoshima, southwest Japan. Specifically, we examined microfossil distribution patterns, their mode of occurrence, and state of preservation, within the infill of the trace fossil and as well as from the surrounding host mudstone. This has enabled us to establish that there is a significant siliceous microfossil preservation advantage within trace fossils in mudstones that have been subject to burial diagenesis. The following three conclusions can be made

(1) Relatively well-preserved radiolarian and diatom fossils are distributed unevenly within the trace fossil infills and most of them are interpreted to be derived from passive infilling sediment that was not affected by feeding and excretion activities of the trace maker. (2) Comparing preservation from inside and outside of the trace fossils, the radiolarians from inside the trace fossil are much better preserved than those from outside. (3) Microfossils that were transported into the trace fossil within infill sediment were protected from subsequent burial compaction and diagenesis by preferential cementation to produce a concretion of the trace fossil, and this has enabled the siliceous microfossils to be relatively well-preserved. These results support the idea that trace fossils offer significant microfossil preservation potential. Trace fossils may also be considered as natural archives of valuable micropaleontological records that would usually be lost during burial, compaction and diagenetic processes. Taphonomic analysis of siliceous microfossils within the infills of trace fossils, such as Tasselia ordamensis, has the potential to reveal significant new paleontological insight from sedimentary rocks throughout the fossil record.