REVUE DE MICROPALEONTOLOGIE最新文献

The current Special Issue of Revue de Micropaleontologie, entitled “Updating Micropaleontology and Stratigraphy in Greece and Eastern Mediterranean” includes contributions from the T1S1 special Session [conveners Maria Triantaphyllou (NKUA), Dimitris Kostopoulos (AUTH), George Iliopoulos (UPAT)] organized by the Hellenic Committee for Paleontology and Stratigraphy at the 15th Conference of the Geological Society of Greece (May 2019, Athens, Greece).

The current study performs a detailed micropalaeontological analysis, in terms of ostracods, benthic foraminifera and calcareous nannoplankton, in order to reconstruct the palaeoenvironmental history of the sedimentary sequence exposed in the central part of Corinth Isthmus. Twenty one samples from two lateral sections were studied, on both sides of a westwards dipping normal fault at the west end of the central horst, which are part of the same stratigraphical sequence. The calcareous nannofossil analysis provided for the first time dating evidence for the upper Corinth Marl sequence, revealing that Section A (at the footwall block of the fault/the upper part of the Corinth Marl) is attributed to the Early Pleistocene /Calabrian (nannofossil biozone MNN19f) and that Section B (at the hanging wall of the fault) is assigned to the Middle Pleistocene /Chibanian (MNN20). Both parts of the studied sequence not only differentiate in age but bear notably separated species composition of the main ostracod assemblages as well. The combined study of ostracod and benthic foraminiferal microfaunas indicated that at least since Early Pleistocene the Corinth Marl deposits at the central part of Corinth Isthmus corresponded to a shallow, restricted, oligohaline lagoon with salinity alternations expressed as layers enriched in nannofossil content. Towards Middle Pleistocene the lagoon presented increased salinity and signs of shoaling. The studied sequence closes upwards with a bed of Middle Pleistocene age, rich in marine molluscs and corals indicating a radical environmental change: the opening of the lagoon and the establishment of a shallow marine coastal environment.

The author erects a new genus for the Quaternary artiscin radiolarian species Spongoliva ellipsoides Popofsky 1912. The genus Spongoliva Haeckel 1887 is a nomen dubium because none of its six species has been illustrated and, above all, its type species is Eocene in age, an epoch when the artiscins had not yet appeared.

Larger Benthic Foraminifera (LBF) from five localities in Greece were studied in order to define the morphological features of various nummulitid forms and to describe the foraminiferal assemblages in different geotectonic environments. The selected sites belong to molasse-type formations in Kirki/Thrace Basin and Vasiliki Trikala/Mesohellenic Trough, and carbonate deposits in Alpine Pindos, Ionian and Tripolis geotectonic units.

Taxonomic studies combined with biometric data, when possible, enabled us to identify different morphotypes. In the molasse-type deposits of Thrace Basin (Kirki Thrace), N. perforatus was found along with N. maximus and Assilina exponens suggesting correlation with biozone SBZ 16/17, while in the Mesohellenic Trough deposits (Vasiliki Trikala) the association included N. perforatus group, Operculina gomezi group and Silvestriella tetraedra, indicating a Bartonian age, SBZ 17-18A. In outcrops found within Pindos unit (Perivoli Grevena) three different assemblages have been observed in the microbreccious olistholiths, suggesting three distinguished deposits forming quasi-continuous succession spanning from early to middle and up to late Eocene. The Ionian unit (Manoliasa Ioannina) presented a mixed redeposited fauna including late Eocene, early Paleogene and planktonic foraminifera clasts. Finally, the Tripolis unit (Dervenakia and Tripolis) association was interpreted as Bartonian in age, defined by the presence of Operculina gomezi group and N. perforatus group.

This study deals with the integration between geochemical data (carbon isotope and, total organic carbon) and foraminiferal turnover to track the Oceanic Anoxic Event 2 (OAE2) from the OCT-A8st1 well, which located in October field, central part of Gulf of Suez, Egypt. The studied well is subdivided into two formations, namely the Galala (Early–Late Cenomanian) and Abu Qada (Late Cenomanian–Early Turonian). Concerning the foraminiferal assemblage, agglutinated foraminifera dominate the Galala Formation, while planktonic taxa only occur within a few levels in the Abu Qada Formation. Due to the absence of keeled planktonic forms, the biostratigraphic framework is established on the integration between benthonic and planktonic foraminifera. Three biozones are recognized, including Thomasinella aegyptia–Merlingina cretacea Interval Zone (Early–Middle Cenomanian), Thomasinella fragmentaria–Praebulimina aspera Interval Zone (Middle–Late Cenomanian), and Whiteinella archaeocretacea Taxon Range Zone (Late Cenomanian–Early Turonian). Therefore, the Cenomanian–Turonian boundary interval (CTBI) is placed within the lower part of the Abu Qada Formation, which is characterized by the presence of black shales and low richness of both foraminifera and ostracods. A remarkable increase in TOC values is observed close to the CTBI. Also, the carbon isotope curve shows a distinctive positive δ¹³C anomaly at the same level of the maximum TOC. The comparison between the recorded δ¹³C data and those obtained from other sections worldwide, indicates that the base of the Turonian is placed directly above the δ¹³C excursion. Furthermore, the recorded foraminiferal community shows evidence for the deepening of the environment and extension of the oxygen minimum zone during the CTBI. This conclusion is based on a sequence of bioevents starting with the disappearance of some agglutinated benthic foraminifera, followed by the dominance of opportunistic groups including buliminids, whiteinellids and heterohelicids. Consequently, the studied well may be considered as a local reference section for OAE2.

Living coccolithophores collected from a yearly time interval, January to December 2016, at the SP1 station of the Thessaloniki Bay, an enclosed coastal environment located in the inner part of the Thermaikos Gulf (Northwestern Aegean Sea) were analyzed to determine their seasonal variation and evaluate the effects of environmental factors on their density, species composition and distribution. Our results showed that coccolithophores constituted a significant component of the phytoplankton community and were characterized by the dominance of few opportunistic species, as an impact of eutrophic environmental conditions. Temperature seasonal cycle and the variations in nutrient inputs from riverine and/or anthropogenic sources seem to control the seasonal pattern of coccolithophores. Emiliania huxleyi with densities as high as ∼4.0 × 10⁵ cells l⁻¹ predominated during the late spring–early summer, whereas a strong dominance of Gephyrocapsa oceanica with densities ∼2.0 × 10⁵ cells l⁻¹ was observed during the late summer and the autumn. Emiliania huxleyi appeared to dominate the coccolithophore assemblages once more during the winter; while Helicosphaera carteri was continuously present during the wintertime (exceeding ∼2.7 × 10³ cells l⁻¹). Emiliania huxleyi was entirely represented by morphotype type A in the studied samples. Morphometric analysis of E. huxleyi coccoliths indicated that the population is dominated by lightly calcified forms, although an increase of more heavily calcified coccoliths was observed during late autumn-early spring in line with the well-documented seasonal succession pattern of E. huxleyi type A forms in the Aegean Sea.