REVUE DE MICROPALEONTOLOGIE最新文献

Based on sediment traps moored in the southern Ionian Sea (Eastern Mediterranean), this paper documents nassellarian radiolarian occurrences (54 species). Several taxa are reported and illustrated for the first time for the Mediterranean Sea (i.e., Trisulcus triacanthus, Tricerapyris damaecornis, Archiperidium longispinum and Artostrobus joergenseni). Emphasis was placed on the documentation of various ontogenetic stages for some of the encountered species. We also provide a review of the biogeographical distribution for all the confidently identified species, in order to shed light on the provenance of radiolarian fauna in the eastern Mediterranean Sea. Interestingly, despite a majority of warm-water radiolarians, we frequently encountered temperate to cold-water radiolarian species, such as Artobotrys borealis, Artostrobus joergenseni and Archiperidium longispinum.

Sedimentary and paleontological records can be powerful means of reconstructing ecological and physical environmental changes, by using a variety of records extending proxies to extend chronologies beyond the reach of instrumental or manual records. Ostracods are often used as paleoenvironmental proxies. Estimating the population age structure could be a useful tool for assessing the influence of some environmental parameters on death assemblages and for determining the autochthoneity or allochthoneity of the species that make up the thanatocoenosis. In the literature, several methods based on population age structure have been proposed to distinguish autochthonous and allochthonous components of life/death ostracod assemblages.

The Adult:Juveniles ratio analysis of a rich and well-preserved ostracod assemblage from one site in the circalittoral zone of Pontine Archipelago, in the central-eastern Tyrrhenian Sea, is presented. The new Specific Population Stage Index (SPS) is proposed, built upon the measurements of all growth stages in the assemblage. The population structure using the new SPS Index on three different grain sizes is tested against a list of putative in situ and transported ostracod specimens. The analysis on the small grain size (maximum heigth >63 µm) proved the most effective in describing the putative life ostracod assemblage, whereas in the largest grain size (maximum height >180 µm) the young instars of the smaller species are under-represented. This includes species generally under-represented in the fossil record of the Mediterranean, probably due to sample processing bias and not to the rarity of the species itself. Assessing the autochthoneity of modern/fossil assemblages has great potential for acquiring baseline information on ecosystems before the onset of human activities, making this an extremely powerful approach essential to evaluating anthropogenic impacts. This approach seeks to identify the in situ life assemblages within an ostracod population to ensure that paleoenvironmental interpretations are not biased by transported allochthonous elements.

Orbitolina tibetica was described by Cotter in 1929 from the Lhasa terrane of the Tibetan Himalaya, presumably from the Langshan Fm. Since Schroeder (1963), this species has been mainly included in the synonymy of Palorbitolina lenticularis (Blumenbach, 1805). New and detailed images from the type material of O. tibetica reveal that the illustrated specimens in the original description are undiagnostic except one axial section showing the megalospheric embryo, designated herein as lectotype. This section shows that O. tibetica Cotter, 1929 is identical to Mesorbitolina parva (Douglass, 1960) thus becoming its senior synonym and reinstating the new combination Mesorbitolina tibetica (Cotter, 1929) introduced by Zhang (1982, 1994). Consequently, the type-level of M. tibetica (Cotter) cannot be late Barremian-early Aptian, but has to be late Aptian. Tibetella tibetica Zhang, 1994 from the Albian Langshan Fm. with its tripartite embryo is redescribed and also reassigned to Mesorbitolina Schroeder, 1962. As there is neither a junior nor a senior synoym for this new combination, Mesorbitolina zhangi nomen novum is proposed as a replacement name for Tibetella tibetica Zhang, 1994 to avoid a secondary homonymy with M. tibetica (Cotter, 1929).

This study is based on larger benthic foraminifera that dominate the Lower Miocene shelf carbonates of the Qamcheqai section, NW Iran. During the time of deposition, the investigated area was positioned on the Eurasian side of the Tethyan Seaway between the Eastern and Western Tethys. Seven porcelaneous and hyaline perforated species were determined, including Praebullalveolina curdica, Peneroplis evolutus, Androsina cf. diyarbakirensis, Sivasina egribucakensis, Miogypsina cf. intermedia, Operculina complanata, and Amphistegina bohdanowiczi. The presence of Miogypsina cf. intermedia, and Praebullalveolina curdica allowed to correlate the assemblage with SBZ 25 Zone, indicating a Burdigalian age. The results of this study extend the paleogeographic distribution of the endemic taxa Androsina and Sivasina eastwards as far as Central Iran.

Among large benthic foraminifera, Balkhania genus is one of the most valuable taxon that has been used to better constrain the biostratigraphy of the Lower Cretaceous successions along the Tethyan carbonate platforms. The species Balkhania balkhanica is considered as biostratigraphical index for the Barremian-Aptian interval. This study is focused on the B. balkhanica-bearing intervals of the Tirgan and Taft formations from two sections, deposited on the carbonate platform of the Iranian Tethyan margin (Kopet-Dagh Basin, NE Iran and Yazd Block, Central Iran). The age of the studied sections has already been determined in previous works. In present research, morphology and stratigraphical and ecological distribution of the recorded specimens are interpreted. According to the morphological changes, two morphotypes of B. Balkhanica have been introduced. Small-size morphotype is recorded in the Upper Valanginian to Upper Hauterivian interval of the Tirgan Formation. The Upper Barremian to Lower Aptian successions are mostly associated with larger sized specimens having a coarse quartz agglutinated wall, and named arenaceous morphotype. Their wall is in contrast to the Turkmenistan type specimens having a calcite microgranular-agglutinated wall. Inherent evolutionary factor suggests an evolutionary trend of this species from smaller to larger sized specimens during the Late Valanginian to Early Aptian. A preliminary study of the depositional environment also indicates an environmental control for this type of morphological variation. It suggests that the small-size morphotype mostly occurred in an under-stress shallow-water environment, while the larger size morphotype was associated with deeper and more stable outer-shelf environments.

Results from the International Ocean Discovery Program (IODP) Site U1512 in the Great Australian Bight offer insights into climate immediately after the peak of the Cretaceous hothouse. Lower Turonian to Santonian deposits yield a unique high-resolution micropaleontological record of the Australo-Antarctic Gulf that is dominated by agglutinated foraminifera. The complex paleoenvironment at Site U1512 illustrates a constantly changing marine setting characterized by the interplay of runoff from the vast Ceduna River system to the north and varying degrees of influence of the Indian Ocean.

A common element in the agglutinated foraminiferal assemblage is the genus Haplophragmoides, which represents between 20 and 40% of the total benthic foraminiferal assemblage, and its occurrence seems particularly common in intervals with higher terrestrial influx. Like many agglutinated foraminiferal assemblages, the agglutinated taxa at Site U1512 suffer from preservational issues. In addition to effects during early diagenesis, like the degradation of organic cement, the delicate planispiral taxa especially experienced extensive deformation, which can affect the correct identification of taxonomically relevant features. Among the six species of Haplophragmoides that represent most of this genus at Site U1512, we identify and describe three new species: H. petaliformis n.sp., H. tenellulus n.sp., and H. antarcticus n.sp.

On Mount Rettenstein (Northern Calcareous Alps, Austria) a 95-m-thick Lower Jurassic succession of grey siliceous limestone and marl allowed us to study well-preserved and diverse radiolarian assemblages. The succession crossing the Sinemurian–Pliensbachian boundary yielded seven productive radiolarian samples, five of which were assigned to the Upper Sinemurian and two to the Lower Pliensbachian. In this article, we present 24 species and nine genera belonging to the order Entactinaria, and 66 species and 27 genera to the order Spumellaria. One genus (Tetractoma Cifer nov. gen.) and six species are described as new: Charlottalum austriacum Cifer nov. sp., Crucella optima Cifer nov. sp., Hexapyramis? sphaericus Cifer nov. sp., Paronaella triangularis Cifer nov. sp., Pseudoheliodiscus rotaformis Cifer nov. sp., and Tetractoma tollmanni Cifer nov. gen. nov. sp. In the Sinemurian, by far the most abundant genus amongst either Spumellaria and Entactinaria is Gorgansium. The Pliensbachian samples are, on the other hand, dominated by the genera Archaeocenosphaera and Praeconocaryomma. Compiled stratigraphic and geographic ranges as well as synonymies, descriptions and remarks are provided.

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.