排序方式： 共有6条查询结果，搜索用时 15 毫秒
1
1.
During the last decades, several integrated studies of Tethyan Jurassic/Cretaceous boundary
sections from different countries were published with the objective to indicate problems for the selection
of biological, chemical or physical markers suitable for identification of the Jurassic/Cretaceous
boundary e the only system boundary within the Phanerozoic still not fixed by GSSP. Drawing the
boundary between the Jurassic and Cretaceous systems is a matter of global scale discussions. The
problem of proposing possible J/K boundary stratotypes results from lack of a global index fossils,
global sea level drop, paleogeographic changes causing development of isolated facies areas, as well
as from the effect of Late Cimmerian Orogeny. This contribution summarizes and comments data on
J/K boundary interval obtained from several important Tethyan sections and shows still existing problems
and discrepancies in its determination. 相似文献
2.
Berriasella jacobi is a key ammonite taxon that has been widely used for the definition of the Tithonian/Berriasian boundary and has been widely quoted in the literature as the index species for the lowest zone of the Berriasian Stage. The taxonomic revision of B. jacobi shows that it should be excluded from the genus Berriasella and transferred to the genus Strambergella. Analysis of the literature has convinced us that most specimens illustrated as B. jacobi have been misidentified. New collection at Le Font de Saint Bertrand (Les Combes, Glandage, Drôme, France) shows us the type series corresponds to the microconch form of a dimorphic pair. New integrated data on its stratigraphic distribution causes us to question its value as an index species for the base of the Berriasian. 相似文献
3.
A detailed bed-by-bed sampling within the Pimienta and the Lower Tamaulipas Formations from a section in the Apulco area (Puebla State, Eastern Mexico), allows the delimitation of the Jurassic/Cretaceous boundary. The Late Tithonian was identified by the presence of calpionellids of the Crassicollaria Zone (Colomi Subzone) and calcareous dinocysts of the Proxima Zone. The Tithonian/Berriasian boundary was placed at the acme of Calpionella alpina (small forms) between samples MZT 45–46. The Berriasian was divided into two main units, namely the Calpionella Zone, further subdivided into the Alpina, Ferasini and Elliptica subzones, and the Calpionellopsis Zone, within which only the Oblonga subzone was identified. The vertical distribution of calpionellids and their assemblages in the biozones of this Mexican section fit those from other Tethyan areas. 相似文献
4.
Fluctuation in calpionellid, foraminiferal, and nannofossil diversity and abundance are documented in two successions located in the eastern part of the Upper Jurassic–Lower Cretaceous carbonate platform of the Southern Carpathian area, Romania. The lower part of the studied sections consists of upper Tithonian–upper Berriasian bioclastic limestones. This age is supported by the presence of the calpionellid assemblages assigned to the Crassicollaria, Calpionella, and Calpionellopsis Zones. Based on biostratigraphical data, a gap was identified within the uppermost Berriasian–base of the upper Valanginian (the interval encompasses the Boissieri, Pertransiensis, Campylotoxum, and lower part of the Verrucosum ammonite Zones). Hence, the upper Tithonian–upper Berriasian bioclastic limestones are overlain by upper Valanginian–lower Hauterivian pelagic limestones (the interval covered by the NK3B and NC4A nannofossil Subzones). A detailed qualitative and semiquantitative analysis of the nannoflora was carried out over this interval. To estimate the surface water fertility conditions, the nannoplankton-based nutrient index (NI) was calculated. The fluctuation pattern of NI allow us to recognize four phases in the investigated interval, as follows: (1) phase I (covering the lower part of the NK3B nannofossil Subzone and the upper part of the Verrucosum ammonite Zone, respectively) is characterized by low values of the NI (below 20%), by the dominance of the genus Nannoconus in the nannofloral assemblages (between 60–70%), and moderate abundance of Watznaueria barnesae (up to 23%), while the high-fertility nannofossils constitute a minor component of the assemblages; (2) phase II (placed in the NK3B nannofossil Subzone, extending from the top of Verrucosum ammonite Zone, up to the lower part of the Furcillata ammonite Zone) is characterized by increase of NI above 30%, a decrease of nannoconids (up to 50% at the top), while Watznaueria barnesae increases in abundance up to 27%. The fertility proxies (Diazomatolithus lehmanii, Zeugrhabdotus erectus, Discorhabdus rotatorius, and Biscutum constans) represent again a minor component of the recorded nannofloras (less than 7% in both sections), but they have an ascending trend; (3) phase III (which encompasses the boundary interval of the NK3B and NC4A nannofossil Subzones, corresponding to the upper part of the Furcillata ammonite Zone) contains higher NI values (over 35%, and up 52% towards the base of this phase), an abrupt nannoconid decrease (down to 20%), higher abundance of Watznaueria barnesae (over 30%), while the fertility nannofossils became an important nannofloral component, jointly amounting to almost 20%; (4) phase IV (identified within the NC4A Nannofossil Zone and corresponding to the boundary interval of the Furcillata and Radiatus ammonite Zones) is characterized by a decrease of NI to 25%, a recovery of the nannoconids up to 40%, a decline in abundance of Watznaueria barnesae to 25%, together with a pronounced drop of fertility taxa, which make together no more than 8%. We assume that maximum of eutrophication in the studied interval from the Southern Carpathians was in the Furcillata ammonite Zone. Notably, within the phases 2 and 3, the morphological changes identified in the benthic foraminiferal assemblages (the predominance of flattened morphologies, together with the presence of conical and trochospiral inflated forms), as well as the occurrence of the Zoophycos trace fossils and pyrite framboids, indicate dysaerobic conditions. In the Southern Carpathians, the late Valanginian–early Hauterivian biogeographical changes are coeval with the initiation of the carbonate platform drowning. 相似文献
5.
A revision of the calpionellid bio-chronostratigraphy in Western Sicily (Italy) was carried out, in order to update the taxonomy
of this group, through the identification of some genera (Borziella, Longicollaria, Chitinoidella, Dobeniella, Sturiella, Borzaiella and Praecalpionellites) and species (Remaniella catalanoi Pop, Remaniella duranddelgai Pop, Remaniella colomi Pop, Remaniella borzai Pop, Remaniella filipescui Pop) recorded for the first time in the area. The studied sections, belonging to the Trapanese and Saccense Domains (Western
Sicily), include at the base the upper portion of the Rosso Ammonitico Unit (Upper Tithonian), followed by the Lattimusa Formation
(Lower Cretaceous). The quantitative and biostratigraphic analysis of the calpionellid assemblages allowed us to identify
13 assemblages and to define some important bioevents for the Upper Tithonian–Valangianian interval. The recorded calpionellid
bioevents allowed us to recognize Zone/Subzone schema, which have been correlated with the bio-chronostratigraphy previously
proposed for the Western Tethys.
Editorial handling: M. Chiari (Guest) & J.-P. Billon-Bruyat 相似文献
6.
Mabrouk Boughdiri Houaïda Sallouhi Kamel Malaoui Mohamed Soussi Fabrice Cordey 《Comptes Rendus Geoscience》2006,338(16):1250-1259
The analysis of calpionellid associations from jebels Amar and Jédidi sections in North-Atlasic Tunisia provides, for the first time, a precise biozonation of the Jurassic–Cretaceous transition succession. In the light of the new data obtained and considering recently published results, the age of Upper Jurassic formations is clarified, allowing correlations with the Tunisian ‘Dorsale’ and the North–South Axis successions. Within the Maghrebides' range, sections from the external zones correlated to the Tunisian successions are quite distinctive from their equivalent in the internal zones. Both have evolved in different palaeogeographic domains related to the early structuration of the northwestern and southwestern Tethys margins. To cite this article: M. Boughdiri et al., C. R. Geoscience 338 (2006). 相似文献
1