REVUE DE MICROPALEONTOLOGIE最新文献

During the mid-Cretaceous the Arabian Plate underwent a major tectonically-driven stratigraphic reorganization, with the development of a major regional unconformity, often ascribed to the middle Turonian. However, evidence for the age calibration of this unconformity (e.g., from biostratigraphy) is limited. A previously undescribed assemblage of larger benthic foraminifera has been discovered in a section at Khormuj in the Coastal Fars region of the Iranian Zagros. This section lies in the uppermost Sarvak Formation, directly beneath the major unconformity surface. Dominant components of the assemblage are Mangashtia viennoti Henson, and Reticulinella? kaeveri Cherchi, Radoičić and Schroeder. Their presence places the uppermost Sarvak Formation at this locality in the age range (upper?) middle – ?lower upper Turonian, and in the context of evidence from other localities in the region it is most likely upper middle Turonian. This provides new constraint on the timing of the unconformity and stratigraphic organisation, and the tectonic events leading to its creation (e.g., forebulge creation related to ophiolite obduction). The presence of R.? kaeveri is reported for the first time from outside of the Mediterranean region and indicates that this taxon is useful for biostratigraphic calibration. As a result, biozonation schemes for the upper Sarvak Formation can be updated.

Continental clastic red-beds including red and fine- to medium-grained sandstone, pebbly sandstone, and conglomerates are distributed in the Sai Yok area of western Thailand. This rock sequence is known as the Jurassic Kaeng Raboet Formation by Thai geologists. A similar clastic rock succession, approximately 150 m thick, outcropping at Wat Phu Toey, near Ban Tha Sao, was investigated for paleontological analysis. The lithostratigraphy of the sequence in this section consists of Units 1-3 in ascending order. Unit 1 is characterized by pebble-sized chert conglomerates, Unit 2 by medium-grained massive sandstone, and Unit 3 by fine-grained red sandstone and shale with ripple marks and cross-laminations. Several thin layers of chert conglomerate are intercalated in the lower parts of Units 2 and 3. We collected six chert conglomerate samples from this section and distinguished Tournaisian (Lower Carboniferous) to middle Norian (Upper Triassic) radiolarian-bearing chert clasts that have not been not separated as single clasts but treated as one sample. Although the preservation of radiolarians is generally poor, we identified 40 species belonging to 26 genera with one radiolarian gen. et sp. indet. The exact age of the Kaeng Raboet Formation is still equivocal; however, we assigned the age of the red-bed to the Late Jurassic to Early Cretaceous based on the presence of Middle Jurassic foraminifer-bearing limestone clasts in the limestone conglomerate embedded in equivalent formations. The present chert conglomerate, including radiolarian-bearing chert clasts is interpreted to have been derived from the grained siliceous rock bodies of the Mae Sariang Zone and deposited in an alluvial depositional basin and braided river system during the Late Jurassic to Early Cretaceous.

Silurian myodocopes have been demonstrated to be the pioneer pelagic ostracods. Their ecological shift into the water column, during the middle Silurian (Wenlock-Ludlow), is now well documented from sites around the world, but the evolution of this fauna during the late Silurian (Pridoli) remains little studied. We recognise, for the first time, two ecologically distinct myodocope ostracod faunas from the same late Pridoli horizon (possibly ?Wolynograptus bouceki - Skalograptus transgrediens biozones) of southern Spain (Alcaracejos, province of Córdoba). One fauna, associated with black shales, comprises five species belonging to three myodocope families (bolbozoids, entomozoids and cypridinids). The other fauna, recovered from large dark-reddish calcareous nodules and associated with the planktonic crinoid Scyphocrinites elegans, comprises seven myodocope species belonging to the same three families and includes one new species, Calocaria callundosa sp. nov. Although the shale and nodule faunas have two species in common, they are clearly different in terms of diversity, abundance and size of the specimens. The discrepancies between these two assemblages could either be explained by sampling or taphonomic bias, or because they represent faunas with different ecologies. In the latter hypothesis, the myodocope association in the shales could represent the “background” planktonic fauna, while the fauna in the nodules could have lived in the water column in the vicinity of the Scyphocrinites “floating islands”, or scavenge around the dead crinoids on the sea floor. These two diverse assemblages also allow discussions on the temporal and palaeogeographical distributions of these late Silurian myodocope ostracods.

Triassic marine ostracods from south-eastern Asia are poorly known, leading to a profound misreading of their biodiversity on the eastern Tethys margin during this critical interval of the history of life. Here we describe the first Late Triassic ostracod assemblage from the Khao Pathawi Limestone exposed in Uthai Thani Province, central Thailand. It comprises 22 relatively poorly preserved species, their taxonomy is discussed and adds to the scientific understanding of marine ostracods during the Late Triassic. The noticeable lack of the archetypal Triassic Metacopina and ornate Bairdiidae is discussed. Although several of the recovered species might be new to science, it is premature to describe them. Two species are shared with Rhaetian communities described from western and southern Tethyan localities and additional shared species may be confirmed in the future, illustrating the largescale distribution of ostracod taxa during the Late Triassic. Overall, the ostracod assemblage described here is in line with the Norian-Rhaetian age proposed for the Khao Pathawi Limestone.

Palynomorphs and benthic foraminifers are reported from the Upper Holocene Bangkok Clay Formation at a whale-fall excavation site in Samut Sakhon Province, located 15 kilometers from the shoreline of the Gulf of Thailand. The aim of this research is to interpret the paleoenvironment of the whale-trapped layer using bioindicator assemblages. Twenty-two palynomorphs are identified. The palynomorphs are composed of tropical plants and categorized based on their ecological communities into five groups: mangrove, back mangrove, floodplain, terrestrial, and ferns. Of these, mangrove and floodplain pollen assemblages are dominant. The pollen was transported via aeolian and fluvial systems to deposit in the delta system, then wave and tide processes dispersed them to the deeper part of the sea floor. The foraminiferal assemblage is dominated by marine ammonioids and miliolids without agglutinated forms, representing a shallow marine setting with low freshwater influence. The assemblages of foraminifers together with ostracods, gastropods and diatoms suggest sedimentary deposition in shallow subtidal marine environments, where salinity varied from slightly brackish to normal. The terrigenous sediment influx was high; the depositional environment is likely to be the distal part of a prodelta.

We report for the first time a rich and well-preserved marine ostracod and foraminifera association from lower Pleistocene fossiliferous sandstones of the Mida Section (Cap Bon, NE Tunisia).

Micropalaeontological analysis of nine samples taken along an eight-meter exposure revealed 46 ostracod species belonging to 34 genera, 15 species of benthic foraminifera belonging to 14 genera and 8 species of planktonic foraminifera belonging to 4 genera. The ostracod association enabled us to draw a palaeoenvironmental reconstruction of this area during the Gelasian to Calabrian time, highlighting a regressive cycle from circalittoral to shallow infralittoral palaeoenvironments. Planktonic foraminifera were used to constrain the age of the section to the end of Gelasian-beginning of Calabrian. Moreover, the discovery of Bythocythere turgida in the lower part of the section allowed to infer that these sandstones were deposited during the early Pleistocene cold periods.

Well-preserved and diverse radiolarian assemblages were recovered from a continuous 95 m-thick Lower Jurassic succession of grey siliceous limestone and marl on Mount Rettenstein (Northern Calcareous Alps, Austria). A total of seven radiolarian samples across the Late Sinemurian–Early Pliensbachian boundary were studied – five samples were assigned to the Upper Sinemurian and two samples to the Lower Pliensbachian. In total, 188 radiolarian species have been identified. In this article, we present 90 species and 33 genera belonging to the order Nassellaria. One genus and five species are described as new: Katroma hasta Cifer nov. sp., Tipiforma missoniae Cifer nov. gen. nov. sp., Trexus rotundus Cifer nov. sp., Wrangellium mediterraneum Cifer nov. sp., and Zhamoidellum spinosum Cifer nov. sp. In the Sinemurian, the most abundant nassellarian genera are Droltus, Parahsuum and Saitoum. The Pliensbachian yields an entirely different nassellarian assemblage dominated by the genera Zhamoidellum and Lantus. Compiled stratigraphic and geographic ranges as well as a synonymy, descriptions and remarks are provided.

Non-marine ostracods from the Upper Cretaceous of Southern Hemisphere (South America, Africa and India) are studied and discussed for the purpose of establishing a biostratigraphy scheme and their paleogeographic distribution. The paleogeographic analysis performed here reveals ten distinct groupings of species: (1) Neuquén and Paraná basins (Brazil) are characterized by Ilyocypris riograndensis, Neuquenocypris minor, Neuquenocypris tenuipunctata, Wolburgiopsis vicinalis and Vecticypris aff. punctata; (2) Wolburgiopsis neocretacea is characteristic of Los Llanos Formation (Sub-Andean Basin, Argentina) and Neuquén (Argentina) and Parana basins (Brazil); (3) Ilyocypris triebeli is characteristic of Sub-Andean Basins (El Molino Formation, Bolivia; Los Llanos, Ciénaga del Rio Huaco formations, Argentina), and Yacoraite formations (Salta Basin); Neuquén (Argentina), Paraná and Campos basins (Brazil): Ilyocypris triebeli; (4) Neuquén (Argentina), Paraná and Santos basins (Brazil): Fossocytheridea lobulata; (5) Paraná, Santos (Brazil), Congo (R. D. Congo) basins and Lameta Formation (India): Stenocypris cylindrica; (6) Paraná (Brazil) and Congo (R. D. Congo) basins: Paracypria makawensis and Species “K 530 b” Grekoff, 1960; (7) Yacoraite Formation (Salta Basin) and Neuquén Basin (Argentina), Paraná (Brazil) and Congo (R. D. Congo) basins: Ilyocypris argentiniensis; (8) Neuquén (Argentina), Paraná (Brazil) and Congo (R. D. Congo) basins: Alicenula kwangoensis; (9) Paraná Basin (Brazil) and Lameta Formation (India): Candona chuiensis, Cypridopsis huenei, Paracandona jabalpurensis and Paralimnocythere hasuii; (10) Paraná (Brazil), Congo (R. D. Congo) basins and Lameta Formation (India): Periosocypris megistus. Other generic correlations, especially the genera Wolburgiopsis, Neuquenocypris, Virgatocypris, Altanicypris and Talycypridea, reinforce this paleobiogeographical similarities and a Campanian-Maastrichtian age to the Bauru Group (Paraná Basin) and the Kwango Series (Congo Basin), whose age was still in need of refinement.

The present study represents the first attempt to described foraminiferal fauna of the Gucuo Locality and is among the first work to illustrate the Upper Jurassic to Lower Cretaceous benthic foraminifers of South Tibet. The material consists in a combination of unpublished data on the Gucuo Section and published data on the Gyangze; Weimei, and Bandingsi sections.

A total of 239 specimens have been currently recorded in the Upper Jurassic to Lower Cretaceous Menkadun and Gucuo formations of the Gucuo locality. To facilitate further researches on foraminifers from the Tethyan Himalayas, a total of 59 species from 38 genera have currently been repertory and described. Among the recorded specimens, a few species are significant biostratigraphic markers used to identify and constrain the age of four foraminiferal assemblages. The Textularia aff. haeusleri assemblage contains a few numbers of agglutinated species very similar to the one described in the Oxfordian to Kimmeridgian Nupra Formation of the Thakkola Region. The Tithonian Trochammina quinqueloba assemblage is a widespread biostratigraphic horizon recorded in both southern and northern parts of South Tibet, as well as in the Indian and the Proto-Atlantic oceans. The Berriasian to Valanginian Trochammina abrupta assemblage contains typical Early Cretaceous foraminifers. It confirms the Jurassic/Cretaceous boundary should be delineated at the base of the shale Unit of the Gucuo Formation, although it was previously attributed to the base of the volcaniclastic sandstone units using ammonite data. This latest being currently associated to the Valanginian to Hauterivian Ammobaculites crepinae–Textularia bettenstaedti foraminiferal assemblage.

A palaeoecological reconstruction along a southwest to northeast transect of South Tibet, Himalayas, is proposed to understand the composition and dynamic of foraminiferal assemblages along with palaeoenvironmental changes. The morphogroup approach has been selected as the best methods to illustrate both sea-level and oxic changes. The northern tectonic zone of South Tibet is associated with the abundance of deep-water agglutinated foraminifers, which suggests a deep environment beyond the shelf break. The southern tectonic zone of South Tibet is rich in typical species of shallow environment and was located on the neritic shelf. The morphogroup analysis reveals localized, periodic disaerobic conditions on the sea-floor. The Jurassic to Cretaceous Boundary interval was associated with a drop of the sea-level, whereas the rise in diversity and abundance of marginal-sea taxa during the Valanginian to Hauterivian times underline a higher sea-level and a pulse in the development of epeiric seas in the southern part of South Tibet.

The ostracod genus Liuzhinia has been reported from Permian and Triassic marine deposits mainly from the Tethyan area but its classification and history remain obscure. Here we report on the discovery of a rare steinkern of Liuzhinia antalyaensis from the Early Triassic of South China bearing the first known adductor muscle scars, allowing for first insights into its supra-generic classification. We demonstrate that Liuzhinia does not belong to Bairdiidae and propose that the observed muscle scars could illustrate ancestral characters of Paracyprididae or Bythocyprididae. We summarize the diversity of Liuzhinia through time, including the newly described Liuzhinia phetchabunensis Forel & Chitnarin sp. nov. from the Middle Permian of central Thailand, and discuss its geographical distribution and environmental preferences over its stratigraphical range.