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1.
The dinoflagellate cyst, palynofacies and foraminiferal records from the Early Eocene Figols Group of the Spanish Pyrenees exhibit major changes associated with relative sea-level fluctuations and variations in efficiency of the fluvial systems. The mixed siliciclastic-carbonate marine succession exposed in the Merli-Esdolomada area was deposited on the shelf in a tectonically active basin, under oxic conditions, in shallow to moderately deep marine waters (close to the lower boundary of the photic zone) influenced by river discharge from adjacent emerged lands. Sedimentary cycles are mainly recorded by fine-grained deposits. The paleoenvironmental interpretation of palynological and calcareous microfaunal records allows the definition of depositional sequences and enables to trace basinward surfaces identified in more proximal settings by means of sedimentological facies analysis. At the same time, the solid regional stratigraphic framework already available for the Figols Group allows new insights on the paleoecology of extinct taxa.The Merli-Esdolomada section (ME) spans two 3rd order sequences. The upper sequence reflects more marginal marine conditions than the lower one, thus pointing to an overall shallowing trend with time. In the lower sequence the maximum flooding interval is characterised by a rich and diverse microfauna, highest relative abundances of marine phytoplankton and typically neritic dinoflagellate cyst (dinocyst) assemblages dominated by Spiniferites and Cordosphaeridium. The final phase of the highstand systems tract, in proximity of the main sequence boundary, is characterised by a decrease in abundance and diversity of dinocysts, with the dominance of the lagoonal genus Polysphaeridium, and by decreased microfaunal diversity (discorbids, miliolids, larger foraminifers).Palynological records permit the reconstruction of activation and deactivation phases of the fluvial systems, variations in runoff from the hinterland, nutrient delivery to the sea and productivity in surface waters of the Tremp-Graus Basin. The overall abundance of Spiniferites and the scarcity of peridinioid cysts, Lingulodinium, Pediastrum and Botryococcus algae are interpreted to indicate oligotrophic conditions during the deposition of the investigated succession. Recurrent intervals where the temporary disappearance of Spiniferites corresponds to highest relative abundances of Operculodinium and herbaceous debris are the main evidence for river plumes and denote periods of enhanced fluvial discharge reflecting a Milankovitch-type cyclicity. The Rotalia group, which shows abundance peaks of Cuvillierina spp. in the shallower intervals, is often associated with these episodes, thus suggesting for this taxon more tolerance to turbidity than larger foraminifera. Within the maximum flooding zone, a Thalassiphora patula acme corresponding to the local disappearance of Homotryblium is deemed to record the distal expression of a fluvial activation which triggered water salinity stratification. Despite broad morphological similarities, Homotryblium exhibits more cosmopolitan preferences than Polysphaeridium, which is instead confirmed as a lagoonal euryhaline taxon. The increase of Spinizonocolpites pollen toward the top of the Figols Group records the northwestward migration of Nypa mangrove-palms from southern Europe during the mid Early Eocene.  相似文献   

2.
Cenomanian-Turonian ostracodes are reported from the western Colorado Plateau (Western Interior Basin) in the United States. Fifteen genera and twenty species are illustrated, six of which are new: Cytheromorphaperornata nov. sp., Looneyellaleckiei nov. sp., Asciocythereposterangulata nov. sp., Asciocytherearizonensis nov. sp., Cytheropteronclavifragilis nov. sp. and Hourcqiadakotaensis nov. sp. Three ostracode interval zones are proposed that broadly correspond to the existing late Cenomanian through to Middle Turonian Ammonite-zones of Kauffman et al. (1993). Paleoenvironments range from estuarine to coastal plain.  相似文献   

3.
The Tangbian Formation (K2t), the middle part of the Upper Cretaceous Guifeng Group in the Xinjiang Basin, Jiangxi Province, southeastern China is usually regarded as an aqueous sediment. However, based on our study, it is now attributed to an aeolian origin. This new interpretation is supported by considerable evidence, including purple-red, well-sorted and round-grained, medium to fine-grained pure sandstone with little suspension load such as clay, silt and mica, well-developed, thick, large-scale and high-dip tabular planar cross-beddings characterized by aeolian dune foresets, wind-ripple lamination, typical aeolian grain surface textures such as dish-shaped impact scars, crescent-shaped impact scars and frosted surfaces. Our palaeo-current reconstruction proved that the dominant prevailing winds were westerlies and the secondary prevailing winds were northeasterlies with a small amount of south–southeasterlies and north–northwesterlies. Based on the palaeogeography and the global wind belt model, the studied area was located within the westerlies and northeast trades of the northern hemisphere and possibly influenced by the south–southeast and north–northwest monsoons during the Late Cretaceous.  相似文献   

4.
The Paleogene sediments of the southwest Tarim Basin along the West Kunlun Shan in western China include the remnants of the easternmost extent of a large epicontinental sea. This shallow sea once extended across the Eurasian continent before it retreated westward and eventually separated as the Paratethys Sea. Climate modeling results suggest that this sea retreat is an equally important forcing mechanism as the Tibetan plateau uplift in the aridification of the Asian continental interior and the intensification of the Asian monsoon system. The age and paleogeography of the retreat are poorly constrained, hindering the understanding of its cause and paleoenvironmental impacts. This study reports litho- and biostratigraphic results from two sections recording the last major regression out of the Tarim Basin that is expressed by a regional transition from marine clastics and limestones to continental red-beds. Rich micro- and macrofossil assemblages, including benthic foraminifera, ostracods, bivalves, calcareous nannofossils and organic walled dinoflagellate cysts (dinocysts), indicate a shallow, proximal and marine environment. Strong similarity to assemblages known from Central Asia and Europe confirms that surface–ocean connections extended across Eurasia from the Tarim Basin to the western Tethys during the latest Eocene. Moreover, the recovered fossil associations date the last marine sediments as earliest Priabonian in age (~ 37 Ma; overlap between dinoflagellate Mps Interval Zone and calcareous nannofossil Zone CP 14). The retreat of the sea from the Tarim Basin is time-equivalent with the sea level lowstand at the Bartonian–Priabonian boundary but pre-dates both the Oligocene–Miocene regional uplift of the Pamir mountains and Kunlun Shan and the major eustatic sea-level falls of the Eocene–Oligocene Transition (~ 34 Ma) and mid-Oligocene (~ 30 Ma), which are usually held responsible for the sea retreat. Furthermore, a concomitant and significant aridification step occurs at ~ 36.6 Ma (top of chron C17n.1n) as recorded by regional sedimentary records of the Xining Basin along the northeastern Tibetan Plateau, suggesting that the Tarim Sea served as a significant moisture contributor for the Asian interior.  相似文献   

5.
《Palaeoworld》2014,23(3-4):357-369
The analysis of fossil palynomorh assemblages in the Late Miocene freshwater sediments of the Sofia Basin (West Bulgaria) was done to collect data on the vegetation and climate dynamics during the Late Miocene. On the basis of pollen data, we described the main palaeocomunities developed in the region. The mixed mesophytic forests dominated the vegetation in which species of Quercus, Ulmus, Zelkova, Fagus, Carpinus, Betula, Castanea, Corylus, Pterocarya, Carya, Juglans, and Eucommia played important roles. Swamp forests were also recorded, including Taxodiaceae, Alnus, Glyptostrobus, Nyssa, and Myrica. Herbaceous vegetation was distributed in the middle part of the section, with a maximum of 35.5%. The vegetation dynamic passes through several phases, which were associated with changes in paleoclimate and palaeoecological conditions. Coexistence Approach (CA) was applied to palynological data to calculate four climatic parameters. The values of coexistence intervals for mean annual temperatures are 13.6–16.6 °C, with winter temperatures being 3.7–6.6 °C and summer temperatures being 23.6–27.8 °C. Mean annual precipitation ranged most frequently between 828 and 1308 mm. The palaeoclimatic reconstruction illustrates existence of a warm-temperate and relatively humid climate with higher mean annual temperature than the present day climate.  相似文献   

6.
A representative paleoenvironmental reconstruction of continental middle latitude from ca. 2 my to the upper part of Middle Pleistocene (279 ± 77 ky) was obtained from the carbon and oxygen stable isotopes analyzed in ostracode shells (Cyprideis torosa) recovered in the Guadix-Baza Basin (SE Spain), an intramontaneous closed depression filled by alluvial and lacustrine sediments. This study was performed along a 356-m-thick composite section, dated previously by paleomagnetism and the amino acid racemization method. δ13C and δ18O profiles reflected changes in temperature, the evaporation/infill ratio in the water bodies and the amount of rain. δ13C is also affected by changes in plant biomass: periods with high δ13C and δ18O values are associated with warm and dry regimes, and with less vegetation, which, in some cases, coincide with the development of displacive gypsum crystals, whereas low δ13C and δ18O values correlate with cold and humid episodes, which cause more vegetation biomass and, therefore, increasing the input of isotopically light carbon. Intermediate δ18O values are linked to temperate dry or humid episodes when they coincide with high or low δ13C values, respectively. 86 paleoclimatic events were distinguished in the Pleistocene record from the δ13C and δ18O profiles. From both the statistical analysis of the geochemical data and the geological observations, four Cold and Humid Long Periods (low δ18O) and four Warm and Dry Long Periods (high δ18O) were defined. This differs with respect to the paleoclimatological behavior established for the Northern Hemisphere where during cold periods (glacial), no water was available while permafrost conditions persisted, whereas in warm episodes (interglacial), higher precipitation rates occurred. Good correspondences between the Guadix-Baza Basin paleoclimatic record and a marine oxygen-isotope sequence, two continental cores and other long Mediterranean paleoenvironmental records (pollen sequences from Israel) were found, which suggested that climate changes in the Guadix-Baza Basin were in tune with global climatic changes.  相似文献   

7.
《Palaeoworld》2016,25(4):581-599
Six Early Carboniferous brachiopod species in four genera of the Superfamily Spiriferoidea are described from the Qaidam Basin, northwestern China, including a new genus, Qaidamospirifer, and two new species: Grandispirifer qaidamensis and Qaidamospirifer elongatus. Additionally, a new genus, Triangulospirifer, is also proposed to replace Triangularia Poletaev, 2001 that was preoccupied by a Devonian molluscan genus.On the basis of the new material as well as published information, we have reviewed the taxonomic composition and the stratigraphic and palaeobiogeographic distributions of the three previously established genera from the viewpoint of palaeobiogeography. The study reveals that Grandispirifer has a relatively long stratigraphic range from the late Tournaisian to Serpukhovian. During this interval, the genus attained a wide geographical distribution, reaching Northwest China, western Yunnan of West China, Japan, as well as Iran and North Africa. Angiospirifer first occurred in western Europe in the Viséan, and later migrated to North Africa during the late Viséan. In the Serpukhovian, it migrated eastward, reaching the Donets Basin of Ukraine and the Qaidam Basin in Northwest China. Anthracothyrina evolved from Brachythyrina in North Africa in late Viséan, then dispersed north-westward to western and eastern Europe and, further eastward to the Qaidam Basin during the Serpukhovian.  相似文献   

8.
A new genus and new species of lindholmemydid turtle (Cryptodira: Testudinoidea), Shandongemys dongwuica n. g. and n. sp. are described on the basis of a partial skeleton with incomplete shell and skull, complete lower jaws and disarticulated limb bones from the Upper Cretaceous Wangshi Group of Zhucheng, Shandong Province, China. Among Lindholmemydidae, the new species is closely related to Mongolemys elegans from the Late Cretaceous of Mongolia. An incomplete shell from the same locality is referred as Lindholmemydidae indet. Glyptops sp. from the Upper Cretaceous Wang Group of Jingangkou, Laiyang, Shandong is revised and assigned to Lindholmemydidae.  相似文献   

9.
The Albian sediments of the Transdanubian Range in Hungary were deposited in non-marine to fully-marine environments. The studied sections revealed diverse benthic ostracod faunas with moderately-preserved specimens. Forty-six taxa are identified and Cypridea zalanyii n. sp. is newly described. The detailed palaeoecological study of these ostracod faunas provided an opportunity to distinguish eight assemblages. The assemblages include limnic, brackish lagoon, shallow marine, reef and low oxygenated semi-enclosed basin environments in the Northern Tethys region we investigated. This work contributes to the knowledge about Albian non-marine faunas from Europe and explores ecological requirements of brackish faunas.  相似文献   

10.
In this contribution is given a preliminary up-to-date annotated list of all fossil vertebrates from the Turonian-Santonian Adamantina Formation, Bauru Group where it occurs in the Prata paleontological district which is located 45 km to the west of Prata in Minas Gerais State, Brazil. The Adamantina Formation is a reddish sandstone in the Triângulo Mineiro region. These fluviolacustrine sediments were deposited in a semiarid environment. Three fossil vertebrate sites occur in the Prata paleontological district. The diversity of vertebrates in the Adamantina Formation is modest, and its components comprise a mixture of typical austral Gondwana taxa (such as abelisaurids, Aeolosaurus) and boreal Gondwana taxa (such as Carcharodontosauridae). The absence of Laurasian taxa in the upper part of the Bauru Group is noteworthy. Excepting some turtles, crocodylians, and one titanosaurid, most of the specimens discovered in this Group are based on fragmentary and isolated remains, which make it difficult to correctly identify the fossils. For this reason, many of the taxa have only been identified in a preliminary manner. Despite this drawback, the dinosaurs are typical Gondwana forms with no evidence of Laurasian affinities. This is concordant with the idea that the Laurasian dinosaurs entered South America at the end of the Late Cretaceous; i.e. after the Turonian-Santonian, the age of the Adamantina Formation.  相似文献   

11.
Jurassic studies in the Internal Zones of the Betic Cordillera are scarce since this zone is composed mainly of pre-Jurassic metamorphic rocks. Only the “Dorsal” and the Malaguide domains include fossiliferous Jurassic successions, as in Sierra Espuña (SE Spain), which is one of the bigger and well-exposed Jurassic outcrops of the Internal Zones. Collected Ammonite assemblages update and improve the precision of previous biostratigraphic data by the recognition of: the Domerian (= Upper Pliensbachian, in the Mediterranean Domain) Lavinianum (Cornacaldense Subzone), Algovianum (Ragazzoni, Bertrandi, Accuratum and Levidorsatum Subzones) and Emaciatum (Solare and Elisa Subzones) Zones; the Lower Toarcian Polymorphum and Serpentinum Zones; the Middle Toarcian, Bifrons and Gradata Zone; the Upper Toarcian Reynesi Zone; the Lower/Upper Bajocian, the Lower Callovian Bullatus and Gracilis Zones; the Middle/Upper Oxfordian Transversarium, Bifurcatus, Bimammatum and Planula Zones; and the Lower and Upper Kimmeridgian Platynota, Strombecki, Divisum and Beckeri Zones.The paleoenvironmental evolution of the Malaguide Jurassic at Sierra Espuña shows similarities with other Mediterranean Tethyan paleomargins. The biostratigraphic precision along with the litho- and biofacies analyses has enabled the interpretation that the Malaguide paleomargin evolved as a passive margin, developing shallow carbonate platforms, until the Domerian (Lavinianum Zone). Then, the platform broke up (Domerian, Lavinianum Zone-Upper Toarcian, Reynesi Zone) with the beginning of the rifting stage, beginning the development of horst-graben systems and the coeval drowning of the area. This stage ended in the upper Lower Callovian (Gracilis Zone) to the Middle Oxfordian (Transversarium Zone) interval, starting the drifting stage, which accentuated the horst-graben systems, leading to the deposition of condensed nodular limestones in the raised sea bottom.  相似文献   

12.
The Sherwood Sandstone Group in south Devon consists of the Budleigh Salterton Pebble Beds and the Otter Sandstone Formation. The Otter Sandstone Formation comprises four lithostratigraphic sub-units, from the base labelled A-D, and contains tetrapods corresponding to the Perovkan land vertebrate faunachron, and is consequently a key European non-marine Anisian succession. A total of 181 palaeomagnetic specimens from 92 horizons were measured to determine the palaeomagnetic signal. The magnetic properties and characteristic remanence is predominantly carried by haematite, most of which probably formed early in the depositional and diagenetic history. The lower part of the Sherwood Sandstone Group (Budleigh Salterton Pebble Beds and Otter Sandstone Formation, unit A, lower part of unit B) has predominantly normal polarity (magnetozones BS1, BS2 and BS3n) with three thin reversed polarity magnetozones. The lower part of unit B to the lower part of unit C of the Otter Sandstone Formation is predominantly reverse polarity (magnetozones BS3r, BS4 and BS5), but includes three short normal polarity intervals. The upper ca. 50 m of unit C shows a mix of normal and reverse polarity (BS6, BS7) with normal dominating. The ca. 15-m-thick unit D is entirely of normal polarity (BS8n). The magnetostratigraphy allows unambiguous comparison with conodont and ammonite calibrated magnetostratigraphies from elsewhere in Europe. These show that the BS2 and BS3n magnetozones of the Otter Sandstone Formation are lower Aegean to middle Pelsonian (lower to middle Anisian). The BS3r to BS5r magnetozone interval, is middle Pelsonian to lower Illyrian (middle to upper Anisian), and the BS6 to BS8n magnetozone interval is middle Illyrian to lower Fassanian. The top of unit D is correlated to an interval in the middle of the Nevadites Zone (close to the Anisian-Ladinian boundary). Consequently, the Otter Sandstone Formation correlates with the Muschelkalk in the Polish Basin, but is equivalent to only part of the Germanic Basin Muschelkalk. The continuous magnetostratigraphy from the Sherwood Sandstone Group, provides additional details of the polarity pattern through the Pelsonian to Illyrian interval, which appears to be lacking in discontinuous marine sections. A synthesis of adjacent European sedimentary basins in combination with the magnetostratigraphy, suggests that the Budleigh Salterton Pebble Beds are probably Late Spathian to lower Aegean.  相似文献   

13.
14.
A new genus,Oldenlandiopsis, is proposed, based onOldenlandia callitrichoides Griseb., native to the West Indies, southern Mexico, and Central America. Relationships toOldenlandia andLucya, the latter with 6-aperturate pollen, are discussed. The major character differences between the new genus andOldenlandia are in pollen structure, chromosome number, capsule shape and dehiscence, and seed shape and number.  相似文献   

15.
The most extensive latest Cretaceous deposits of the Pyrenees are non-marine facies traditionally called “Garumnian”, which represent the first continentalization of the Pyrenean Foreland Basins. The age and paleogeography of the basal Garumnian facies in the different parts of the Pyrenean Basin has been a matter of debate. Charophyte biostratigraphy and microfacies analysis suggest that the continentalization was diachronous in the Central Southern Pyrenean basins, i.e., between the Àger and Tremp basins, and the emersion progressed from south to north. In the Àger Basin, to the south, the first Upper Cretaceous non-marine rocks are represented by the La Maçana Formation. This unit is mainly formed by freshwater lacustrine limestones organized into hundreds of shallowing-upwards sequences ranging from deeper lacustrine facies, through marginal, well-illuminated environments dominated by characean meadows, and finishing with lakeshores dominated by clavatoracean meadows. The charophyte assemblage from the La Maçana Fm is mainly formed by Peckichara cancellata, P. sertulata, Microchara cristata, M. parazensis, Platychara caudata, and Clavator brachycerus, which belong to the Peckichara cancellata charophyte biozone (Late Campanian). In contrast, in the Tremp Basin, located to the north, the beginning of the non-marine sedimentation is organized into a few cycles of the well-known La Posa Fm. These cycles begin with brackish deposits formed by thick marls with euryhaline molluscs at the base, followed by lignite and brackish to freshwater limestones. The brackish facies are dominated by porocharaceans. The charophyte assemblage of the La Posa Formation is formed by Feistiella malladae, Peckichara sertulata, Microchara cristata, and Clavator brachycerus, which belong to the Septorella ultima charophyte biozone (Early Maastrichtian).  相似文献   

16.
Studying the evolution and biogeographic distribution of dinosaurs during the latest Cretaceous is critical for better understanding the end-Cretaceous extinction event that killed off all non-avian dinosaurs. Western North America contains among the best records of Late Cretaceous terrestrial vertebrates in the world, but is biased against small-bodied dinosaurs. Isolated teeth are the primary evidence for understanding the diversity and evolution of small-bodied theropod dinosaurs during the Late Cretaceous, but few such specimens have been well documented from outside of the northern Rockies, making it difficult to assess Late Cretaceous dinosaur diversity and biogeographic patterns. We describe small theropod teeth from the San Juan Basin of northwestern New Mexico. These specimens were collected from strata spanning Santonian – Maastrichtian. We grouped isolated theropod teeth into several morphotypes, which we assigned to higher-level theropod clades based on possession of phylogenetic synapomorphies. We then used principal components analysis and discriminant function analyses to gauge whether the San Juan Basin teeth overlap with, or are quantitatively distinct from, similar tooth morphotypes from other geographic areas. The San Juan Basin contains a diverse record of small theropods. Late Campanian assemblages differ from approximately co-eval assemblages of the northern Rockies in being less diverse with only rare representatives of troodontids and a Dromaeosaurus-like taxon. We also provide evidence that erect and recurved morphs of a Richardoestesia-like taxon represent a single heterodont species. A late Maastrichtian assemblage is dominated by a distinct troodontid. The differences between northern and southern faunas based on isolated theropod teeth provide evidence for provinciality in the late Campanian and the late Maastrichtian of North America. However, there is no indication that major components of small-bodied theropod diversity were lost during the Maastrichtian in New Mexico. The same pattern seen in northern faunas, which may provide evidence for an abrupt dinosaur extinction.  相似文献   

17.
The morphology and taxonomic value of morphological features of Late Jurassic and Early Cretaceous oysters from northern Siberia are considered. A new species, Deltoideum exoticum Kosenko, sp. nov. is described.  相似文献   

18.
Increased excavation of dinosaurs from China over the last two decades has enriched the record of Asian titanosauriform sauropods. However, the relationships of these sauropods remain contentious, and hinges on a few well-preserved taxa, such as Euhelopus zdanskyi. Here we describe a new sauropod, Yongjinglong datangi gen. nov. et sp. nov., from the Lower Cretaceous Hekou Group in the Lanzhou Basin of Gansu Province, northwestern China. Yongjinglong datangi is characterized by the following unique combination of characters, including seven autapomorphies: long-crowned, spoon-shaped premaxillary tooth; axially elongate parapophyses on the cervical vertebra; very deep lateral pneumatic foramina on the lateral surfaces of the cervical and cranial dorsal vertebral centra; low, unbifurcated neural spine fused with the postzygapophyses to form a cranially-pointing, triangular plate in a middle dorsal vertebra; an “XI”-shaped configuration of the laminae on the arches of the middle dorsal vertebrae; a very long scapular blade with straight cranial and caudal edges; and a tall, deep groove on the lateral surface of the distal shaft of the radius. The new specimen shares several features with other sauropods: a pronounced M. triceps longus tubercle on the scapula and ventrolaterally elongated parapophyses in its cervical vertebra as in Euhelopodidae. Based on phylogenetic analyses Yongjinglong datangi is highly derived within Titanosauria, which suggests either a remarkable convergence with more basal titanosauriform sauropods in the Early Cretaceous or a retention of plesiomorphic features that were lost in other titanosaurians. The morphology and remarkable length of the scapulocoracoid reveal an unusual relationship between the shoulder and the middle trunk: the scapulocoracoid spans over half of the length of the trunk. The medial, notch-shaped coracoid foramen and the partially fused scapulocoracoid synostosis suggest that the specimen is a subadult individual. This specimen sheds new light on the diversity of Early Cretaceous Titanosauriformes in China.  相似文献   

19.
In the eastern Saharan Atlas, particularly in the northern area of Tebessa Province (NE Algeria), the widely outcropping Cenomanian strata display a highly diversified macrofauna, among which bivalves are prominently represented. Twenty-eight bivalve species are here reported for the first time from the Cenomanian of Hameimat Massifs. Based on the stratigraphic distribution of these bivalves, five bivalve zones were recognized, i.e., Costagyra olisiponensis - Gyrostrea delettrei, Rhynchostreon suborbiculatum - Exogyra conica, Ceratostreon flabellatum, Ilymatogyra africana, and Pycnodonte vesicularis vesiculosa - Rastellum carinatum zones. Correlation to the ammonite biozones of the same region as follows: the Costagyra olisiponensis - Gyrostrea delettrei and the Rhynchostreon suborbiculatum - Exogyra conica zones occur respectively in the Sharpeiceras schlueteri and Mantelliceras saxbii subzones of the lower Cenomanian Mantelliceras mantelli Zone. The Ceratostreon flabellatum Zone is correlated with the middle Cenomanian Acanthoceras rhotomagense Zone. The Ilymatogyra africana Zone is correlated with the upper Cenomanian Calycoceras naviculare and the Metoicoceras geslinianum zones. Finally, the Pycnodonte vesicularis vesiculosa - Rastellum carinatum Zone represents the uppermost Cenomanian. Detailed analysis of biometrical and morphological features of these bivalve specimens provides the most reliable tool within the scope of palaeo-environmental reconstitution and the many palaeo-ecological variables that had driven the development and distribution of these macro-invertebrates. Comparison of these new data to those of adjacent south Tethyian areas supports the homogeneity of the Cenomanian bivalve faunas. Such an affinity underlines more vividly the favorable marine communications and currents driving the geographic dispersal of these bivalves during the Cenomanian.  相似文献   

20.
In the Namur-Dinant Basin (Belgium), the last Atrypida and Pentamerida originate from the top of the Upper Palmatolepis rhenana Zone (Late Frasnian). Within this biozone, their representatives belong to the genera Costatrypa, Desquamatia (Desquamatia), Radiatrypa, Spinatrypa (Spinatrypa), Spinatrypina (Spinatrypina?), Spinatrypina (Exatrypa), Waiotrypa, Iowatrypa and Metabolipa. No representative of these orders occurs within the Palmatolepis linguiformis Zone. The disappearance of the last pentamerids, mostly confined to reefal ecosystems, is clearly related to the end of the edification of the carbonate mounds; it precedes shortly the atrypid one. This event, resulting from a transgressive episode, which induces a progressive and dramatic deterioration of the oxygenation conditions, takes place firstly in the most distal zones of the Namur-Dinant Basin (southern border of the Dinant Synclinorium; Lower P. rhenana Zone). It is only recorded within the Upper P. rhenana Zone in the Philippeville Anticlinorium, the Vesdre area, and the northern flank of the Dinant Synclinorium. It would seem that the terebratulids were absent during the Famennian in this basin, probably due to inappropriate facies. Among the 13 species described or briefly discussed (Palmatolepis hassi to Upper P. rhenana zones), Pseudoatrypa godefroidi nov. sp. and Spinatrypina (Exatrypa) marmoris nov. sp. are proposed as new.  相似文献   

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