REVUE DE MICROPALEONTOLOGIE最新文献

A new distinctive calcareous alga Filippoporella barattoloi n. gen n. sp., coming from the rich Lower Palaeogene algal assemblage (partly known from Radoičić, 2004) of the Pločice locality, is described. It is characterized by slightly claviform thallus, bearing whorls with two types of laterals of different form and function. In the lower (older) part of thallus, whorls contain sterile laterals of the Dissocladella-type. Going upwards, globular fertile laterals with several secondaries start to appear, at first irregularly inserted between sterile whorls. In the upper part of the thallus, whorls with different types of laterals alternate quite regularly, giving the appearance to that part of the thallus similar to Chinianella, as distinct from the lower, Dissocladella-type, part. The accompanying algal assemblage points to the uppermost Selandian-Thanetian, which is also confirmed by the accompanying foraminiferal species.

Ostracods are important palaeoenvironmental tools and for this reason the study of their palaeoecology and geographic distribution must be enhanced in the frame of a unified geographic approach. The PLOSTRAC’s project (Study of Pleistocene ostracods from central and southern Greece: Digital imaging of a palaeoenvironmental tool) main aim is to study the Pleistocene ostracods deriving from sedimentary successions from central and southern Greece and provide a bibliographic database of Pleistocene ostracod-bearing sequences in the study area accompanied by SEM pictures of the identified species. This output can be used as a reference point for future studies not only in Greece but also in the Eastern Mediterranean region as well. This work presents new data from brackish and marine Pleistocene sequences in Peloponnesus, the Ionian Islands (Zakynthos and Cephalonia) and Crete. A total number of 166 taxa were identified from the processed samples. The ostracods belong mainly to the families Trachyleberididae and Hemicytheridae. The studied sedimentary sequences cover the entire Pleistocene Age and range between purely brackish to deep marine assemblages. Moreover, according to both the palaeoenvironmental interpretation of the studied sections and the published literature, across Northern Peloponnesus during the Pleistocene mostly brackish to shallow marine conditions prevailed. Moving to the south and also to the Ionian Islands and Crete deep marine palaeoenvironments were observed.

Well-preserved Late Cretaceous (early Cenomanian) radiolarians were recovered from two sections in Crimea: Bodrak River and Sel’-Bukhra Mountain sections. Abundant and diverse representatives of order Spumellaria were recognized and studied. Four new radiolarian species: Becus naidini nov. sp., B. tauricus nov. sp., Praeconocaryomma? bodrakensis nov. sp., and Savaryella? nikishini nov. sp. were described. Moreover, stratigraphical ranges of species Archaeospongoprunum sphaericum Bragina, Crucella lata (Lipman), Patellula cognata O’Dogherty, P. verteroensis (Pessagno), Spongodiscus quasipersenex Bragina were exactly defined (their lower limits are expanded to the lower Cenomanian). The upper limit of stratigraphic range of "Cenodiscus" alievi Pessagno is expanded to the lower Cenomanian. Our results suggest that two rare taxa "Cenodiscus" alievi Pessagno (California Coast Ranges) and Spongodiscus quasipersenex Bragina (West Sakhalin Mountains) are reported for the first time in the Tethyan regions.

The eastern Mediterranean Sea is a partially isolated sea where excess evaporation over precipitation or riverine discharge results in large north to south gradients in temperature and salinity. Eastern Mediterranean Sea surface sediment samples from 28 locations spanning from the North Aegean to the Levantine Sea have been examined for recent planktonic foraminiferal distribution. In addition to determining the relative abundance of 12 species that have been identified, the average intraspecific size along with the size of the overall faunal pattern was also examined. The quantitative analysis performed on >125 μm fraction reveals pronounced and complex changes in planktonic foraminiferal assemblages that do not parallel the intraspecific size variation and sea surface temperature (SST). On the contrary, foraminifera most of the times are slightly larger in the colder and fresher North Aegean and become progressively smaller toward the warmer Levantine Sea. We conclude that the relationship between planktonic foraminifera shell size and abundance or SST are either absent or weaker than previously reported for other regions and that in E. Mediterranean assemblages size may be mainly related to nutrient availability.

The Aptian–Albian boundary has long been difficult to identify along the foreland basin of the Tunisian Atlas, although ammonites occur in the Fahden Formation. The revision of Aptian–Albian series from Jebel Sidi Salem, in the northeastern part of the Tunisian Ridge, provides new data for the recognition of this boundary. The Jebel Sidi Salem section contains a rich succession of planktic foraminifers’ index species which document a complete marine record of Aptian–Albian boundary with no sign of redeposition. Six zones of planktic foraminifera have been identified through the late Aptian to middle Albian; including Globigerinelloides algerianus Zone, Hedbergella trocoidea Zone, Planomalina cheniourensis Zone, Paraticinella eubejaouensis/Ticinella roberti Zone, Hedbergella planispira Zone and Ticinella primula Zone.

The morphological abnormalities caused on the agglutinated foraminifera Ammobaculites texanus CUSHMAN extracted from the Lower Kharga Member of the Dakhla Formation (Upper Maastrichtian) deposits may be caused due to environmental factors such as high organic flux, high terrigenous input and low salinity as indicated by the presence of Ammoastuta together with A. texanus agglutinated foraminifera, which suggested hyposaline environments.

The deformations described in this work are several types of morphological abnormalities, including irregular chamber shape (lobate peripheral outline), abnormal size or shape of the last chambers, high spire giving a spiroconvex test and irregular coiling, and additional chambers (elongated axes of rotation). Some studied species of A. texanus show compaction and the collapse of the inner microgranular layer, the compaction indicates the binding of quartz grains with a deformable substance before cementation.

Climatic oscillations during the Pleistocene were controlled by glacial/interglacial cycles. Such oscillations are commonly imprinted into sediments and fossils from transitional marine environments, as is also the case in Sousaki Basin (Eastern Gulf of Corinth, Greece). Nevertheless, the records become scarcer as we go back in time. During the Lower Pleistocene, Sousaki Basin (Eastern Gulf of Corinth, Greece), was dominated by transitional marine environments. Micropalaeontological analysis has been carried out in sedimentary sequences to identify the evolution of the palaeoenvironments in an area where intense tectonic activity occurred, being at the western end of the Hellenic volcanic arc and at the eastern end of the Corinth rift. The recovered ostracod assemblage revealed a primarily brackish environment. Deposition took place in a coastal lagoon which was subjected to constant salinity changes. The palaeoenvironment in the basin evolved from a delta fan environment to an outer lagoon with possible connection to a sublittoral marine environment at the top. This evolution coincides and therefore is attributed to minor climate oscillations that occurred during the Early Pleistocene.

Abundant specimens of the orbitolinid Dictyoconus turriculus Hottinger and Drobne from Thanetian shallow-water carbonates of the Zagros Zone, SW Iran, allow new taxonomic insights. With a high conico-cylindrical test, lacking a prominent eccentric initial spire and the occurrence of a distinct zone of only primary beams between the marginal zone (with subepidermal network) and central zone, this species always stood out from a morphological perspective among the other species of the genus Dictyoconus Blanckenhorn. However, its generic status was never challenged. The aligned arrangement of the main radial partitions and also of the pillars to a large extent, rules out a possible inclusion of this species in a rigorous classification framework within the genus Dictyoconus Blanckenhorn and therefore, the subfamily Dictyoconinae Moullade because its members display an alternating pattern of the respective structural elements. In addition, intercalary elements also occur and account for the partly irregular pattern, a pattern similar with that of Dictyorbitolina Cherchi and Schroeder. The new genus Schroedericonus is introduced with the new combination Schroedericonus turriculus (Hottinger and Drobne) and assigned to the Dictyorbitolininae Schroeder. As a consequence of this taxonomic review, there are no other species of Dictyoconus in the Paleocene. The distributional pattern of Dictyoconus (upper Cretaceous and Eocene) can be considered as a classical example of iterative evolution.

The paleoenvironmental evolution of Lake Ismarida in Thrace (Northern Greece) is revealed by the combined lithological, micropaleontological (benthic foraminifera, pollen and NPPS), molluscan analyses, magnetic susceptibility measurement and radiocarbon dating of a 5.8-m long sediment core. The mid Holocene evolution of the lake area is evidenced by the documentation of four sedimentary Units in the core ISMR-2, corresponding to four distinct evolutionary stages: (1) during ∼5500-3500 cal yr BP the lake area was a shallow marine environment characterized by an Ammonia beccarii, small rotaliids, miliolids, Bittium reticulatum and Veneridae spp. assemblage, marine dinoflagellate cysts, and low magnetic susceptibility values; (2) during ∼3500-3000 cal BP the environment is gradually tending to more isolated conditions forming an open lagoon, characterized by marine and euryhaline fauna and low magnetic susceptibility values; (3) during 3000 cal yr BP, the open lagoon presented a transition to an oligohaline inner lagoon, characterized by an Ammonia tepida, Haynesina germanica, Aubignyna perlucida, Pirenella conica, Cerastoderma glaucum and Abra spp. assemblage, sedges and aquatic vegetation. This restricted, entirely isolated from the sea inner lagoon could be definitely used as the landmark of the Lake Ismaris from Heorodotus, while describing the march of Xerxes through Thrace in 480 B.C.; (4) since ∼2000 cal yr BP to the present, the Lake Ismarida is formed, characterized by fresh-water indicators and aquatic pollen, Pseudoschizaea and high magnetic susceptibility values. Finally, the progradation of the Filiouris River deltaic deposits resulted to a 4 km wide deltaic plain between Lake Ismarida and the nowadays coastline. Pollen assemblages record the dominance of a rather rich deciduous forest in the area with traces of human presence in the lower part of the sequence, whereas the opening of the plant landscape under the increasing human pressure is evidenced after ∼ 3000 cal yr BP. Finally, an open vegetation pattern, contemporaneous with the retreat of forest vegetation, is evidenced in the area already before 2000 cal yr BP.