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1.
Palynomorphs and nannofossils were examined from the Lower Cretaceous interval of the well North Scarborough-1, drilled on the Exmouth Plateau, North West Shelf of Australia. Integration of the chronostratigraphic information from both fossil groups revealed discrepancies in the age information with the nannofossils suggesting a younger age than dinoflagellate cysts. The nannofossil events have a stronger tie to the global time scale than the dinoflagellate zones which are mainly local. The direct comparison of nannofossil and dinoflagellate events in the same section allows for improved stratigraphic precision and a revised correlation of Australian dinoflagellate zonal ages to the global time scale, GTS12. Global nannofossil ages confirm a Barremian–late Hauterivian age for the Muderongia australis Zone, but the Systematophora areolata to Dissimulidinium lobispinosum Zones appear to be 1–2 my younger than previously estimated.  相似文献   

2.
Sediments of Early Aptian age in Bulgaria can be assigned to four different facies: platform carbonates (Urgonian complex), shallow-water siliciclastics, hemipelagic and flyschoid siliciclastics. The taxonomic analysis of the ammonite faunas of 18 sections from these four different facies resulted in a revision of the existing ammonite zonation scheme so far applied in Bulgaria and adjoining areas. A new biostratigraphic scheme, which bridges the western and eastern Tethys, is thereby proposed for the Lower Aptian of Bulgaria.The Upper Barremian Martelites sarasini Zone is characterized in its upper part by the Pseudocrioceras waagenoides Subzone in the shallow-water sections and by a horizon with Turkmeniceras turkmenicum in the deep-water settings. The Upper Barremian/Lower Aptian boundary is fixed by the first appearance of Paradeshayesites oglanlensis. For the Lower Aptian the following ammonite zones were established (from bottom to top): The Paradeshayesites oglanlensis Zone, the Deshayesites forbesi Zone (= formerly Paradeshayesites weissi Zone) including the Roloboceras hambrovi Subzone in the upper part, the Deshayesites deshayesi Zone including the Paradeshayesites grandis Subzone in the upper part and the Dufrenoyia furcata Zone. The Lower–Middle Aptian boundary has been defined by the appearance of species belonging to the genera Epicheloniceras and Colombiceras.The Lower Aptian ammonite faunas of Bulgaria, allow an interregional correlation with other areas of the Tethyan Realm. The presence of Turkmeniceras in the Upper Barremian enables a correlation with the Transcaspian region, whereas Roloboceras, Koeneniceras and Volgoceratoides found in the middle part of the Lower Aptian are more typical representatives of the ammonite faunas in northern Europe (England, Germany, Volga region).The analysis of the ammonite successions in combination with sedimentological observations enable us to conclude that the marls and marly limestones of the Lower Aptian studied here also cover the interval of the Oceanic Anoxic Event 1a. An interval of thin-laminated clays, rich in organic matter, was identified in the upper part of the D. forbesi Zone (Roloboceras hambrovi Subzone). This interval is characterized by a total lack of benthic faunas.  相似文献   

3.
Palaeotemperatures during the late Barremian–early Aptian (Early Cretaceous) on the Russian Platform have been determined on the basis of oxygen isotope analysis of aragonitic bivalve molluscan and ammonoid shells and belemnite rostra with well-preserved microstructure from the Ulyanovsk area. Those obtained from the planispiral and heteromorph ammonoid shells from the lower Aptian Volgensis–Schilovkensis, Deshayesi–Tuberculatum, and Deshayesi–Renauxianum zones range from 26.7 to 33.2 °C, from 29.2 to 33.1 °C, and from 27.0 to 29.5 °C, respectively. A heteromorph Helicancylus? cf. philadelphius shell from the uppermost lower Aptian Bowerbanki Zone was secreted in highest temperature conditions (32.8–35.2 °C). In contrast, upper Barremian molluscs (bivalve Cyprina sp. and belemnite Oxyteuthis sp.) of the Ulyanovsk area show significantly lower palaeotemperatures: 16.9–18.5 °C and 7.9–17.8 °C, respectively, which is in accordance with known palaeogeographic and palaeobotanical evidences, showing that a distinct climatic optimum seems to have occurred during the late early Aptian, when warm Tethyan water penetrated into the basin. Marked changes in calculated growth temperatures for investigated molluscs from the Russian Platform were most likely connected with both the general warming trend during the late Barremian–early Aptian and local palaeonvironmental conditions. New data from the Bowerbanki Zone of the Russian Platform provide evidence on existence of the positive carbon isotope anomaly (2.4–6‰) at the end of the lower Aptian. There were apparently the three positive C-isotope anomalies during the late Barremian–early Aptian. The onset of mid early Aptian Oceanic Anoxic Event (OAE) 1a seems to coincide with both the beginning of significant warm conditions (followed by short-term cooling) and the abrupt decline in heavy carbon isotope concentrations in marine carbonates, which partly were the likely consequences of the intensive release of CO2 (biased by volcanic activity) and/or dissociation of methane gas hydrate.  相似文献   

4.
Radiolarian biostratigraphic research has been carried out along two continuous sections through the Xialu Chert, one of the accreted sheets included in the Yarlung-Zangbo Suture Zone. Six radiolarian zones have been identified as follows: Laxtorum(?) jurassicum Zone (Aalenian), Tricolocapsa plicarum Zone (Bajocian–lower Bathonian), Stylocapsa(?) spiralis Zone (upper Callovian–Oxfordian), Hsuum maxwelli Zone (Kimmeridgian), Pseudodictyomitra carpatica Zone (upper Tithonian–lower Valanginian), and Turbocapsula costata Zone (Aptian).A reconstructed stratigraphy of the Xialu Chert, based on lithological succession and radiolarian dating, indicates that the chert exhibits a long depositional history, at least from early Middle Jurassic (Aalenian) to late Early Cretaceous (Aptian). The separation of the Lhasa Block from the northern Gondwana margin must, therefore, be dated before the Aalenian. The absence of calcareous sediments in the Xialu Chert indicates that the oceanic basin was deeper than the CCD throughout the depositional history. The transition from chert to siliceous mudstone is recorded sometime in Early Cretaceous, most probably around the Barremian/Aptian boundary. This means that the oceanic plate had already started being consumed at a trench by that time. The accretion of the Xialu Chert occurred after the Aptian time.  相似文献   

5.
Reexamination of the Barremian–Aptian planktonic foraminifers from three sections (Verkhoirechie, mountain Krasnaya, and Marino) allowed the biostratigraphic scheme for Southwest and Central Crimea to be refined and updated. The following standard zones are recognized in the studied sections: Blowiella blowi (upper Barremian), Hedbergella excelsa (upper Barremian–lower Aptian), Leupoldina cabri (lower Aptian), H. luterbacheri, Globigerinelloides ferreolensis, Gl. barri, Gl. algerianus, Hedbergella trocoidea, Paraticinella rohri (upper Aptian). Beds with Hedbergella ruka are recognized in the B. blowi Zone. Foraminifers from the Partizanskoe section, representing the lower Aptian L. cabri and H. luterbacheri zones, are studied. The recognized strata are correlated with ammonite and nannoplankton zones and paleomagnetic data.  相似文献   

6.
This paper deals with the taxonomic revision of the Early Cretaceous large, many-chambered planispiral planktonic foraminifera, historically assigned to the genus Globigerinelloides or alternatively assigned in the 1990s to the genera Globigerinelloides Cushman and ten Dam, Biglobigerinella Lalicker, Blowiella Krechmar and Gorbachik and Alanlordella BouDagher-Fadel. In a previous paper we demonstrated that the morphological and microstructural features used in the literature for distinguishing Blowiella from Globigerinelloides have value only at species level, and the former genus was thus invalidated (being the junior synonym). Moreover, the Late Aptian specimens assigned to Biglobigerinella by some authors, based on the presence of twin last chamber(s), are also included in Globigerinelloides because individuals sharing the same features (number of chambers, growth rate, size of umbilicus, and a finely perforate wall) may or may not possess twin last chamber(s). Meanwhile, Moullade et al. questioned the taxonomic value of Alanlordella, erected by BouDagher-Fadel to accommodate planispiral taxa possessing a macroperforate wall. All the species analysed here possess a finely perforate wall and consequently cannot be assigned to this taxon.The large species of Globigerinelloides retained here, with six or more chambers in the outer whorl, are G. algerianus Cushman and ten Dam, G. aptiensis Longoria, G. barri (Bolli, Loeblich and Tappan) and G. ferreolensis (Moullade).In the sections studied, Globigerinelloides aptiensis was first found close to the Barremian/Aptian boundary, even though this species was recorded in Spain (Rio Argos) in the mid Upper Barremian; very rare, small, seven-chambered individuals here assigned to Globigerinelloides ferreolensis are recorded in the Lower Aptian (just below and within the Selli Level, OAE1a), while a few specimens belonging to Globigerinelloides barri occur in the Globigerinelloides ferreolensis Zone (Upper Aptian). Globigerinelloides aptiensis and G. ferreolensis range up to the Ticinella bejaouaensis Zone while Globigerinelloides barri disappears at the top of the Globigerinelloides algerianus Zone; finally, Globigerinelloides algerianus obviously spans the eponymous total range zone.From an evolutionary point of view, two lineages within the many-chambered Globigerinelloides have been recognized. In the first, already known in the literature, Globigerinelloides aptiensis gave rise to G. ferreolensis, which evolved into G. algerianus; the latter in turn gave rise to Pseudoplanomalina cheniourensis as the final evolutionary member. In the second lineage Globigerinelloides barri originated from G. blowi.  相似文献   

7.
The lower Cretaceous rock units of the Koppeh-Dagh Basin of northeastern Iran were investigated here in terms of biostratigraphy, depositional setting and geochemical analyses to find out if they, alike other parts of the world, are rich in petroleum. For this purpose, a stratigraphic framework is established using calcareous nannofossil and palynological elements. A nannoplankton zonation based on which subzones of the zones CC7 – CC8 of Sissingh(1977) and their equivalent NC6 – NC8 of Roth(1978) was established indicating a Late Barremian–Albian age. Palynological assemblages led us to establish the local palynozone of Odontochitina operculata. A dominantly marginal basin to a transitional zone between shelf and basin under a dysoxic–anoxic condition with low to moderate sedimentation rates coincided with a gradual sea level rise was introduced as the environment of deposition for the strata via interpretation of the palynological parameters and quantitative palynology. The obtained data from Rock-Eval pyrolysis in compilation with palynofacies analysis reveals that the studied succession contains mainly gas-prone type III kerogen. The Spore Coloration Index(SCI) alongside with the Rock-Eval pyrolysis results(low values of HI and TOC) proves that these rock units locally produced natural gas during the time under consideration.  相似文献   

8.
High-resolution clay-mineral analyses were performed on upper Hauterivian to lower Aptian sediments along a platform-to-basin transect through the northern Tethyan margin from the Neuchâtel area (Switzerland), to the Vocontian Trough (France) in order to investigate links between climate change, carbonate platform evolution, and fractionation patterns in clay minerals during their transport.During the Hauterivian, the northern Tethyan carbonate platform developed in a heterozoan mode, and the associated ramp-like topography facilitated the export of detrital material into the adjacent basin, where clay-mineral assemblages are dominated by smectite and kaolinite is almost absent, thereby suggesting dry-seasonal conditions. During the Late Hauterivian Balearites balearis ammonite zone, a change to a more humid climate is documented by the appearance of kaolinite, which reaches up to 30% of the clay fraction in sediments in the Vocontian Trough. This prominent change just preceded the Faraoni Oceanic Anoxic Event and the onset of the demise of the Helvetic Carbonate Platform, which lasted to the late early Barremian.From the Late Barremian onwards, the renewed growth of the northern Tethyan carbonate platform in a photozoan mode and the associated development of a marginally confined platform topography fractionated the clay-mineral assemblages exported into hemipelagic settings: kaolinite particles were preferentially retained in proximal, platform settings, due to their size and their relatively high specific weight. In the inner platform environment preserved in the Swiss Jura, an average of 32% of kaolinite in the clay fraction is observed during the latest Barremian–earliest Aptian, whereas clay-mineral assemblages of coeval sediments from deeper depositional settings are dominated by smectite and show only minor amounts of kaolinite.This signifies that besides palaeoclimate conditions, the morphology and ecology of the carbonate platform had a significant effect on the distribution and composition of clay assemblages during the Late Hauterivian–Early Aptian along the northern Tethyan margin.  相似文献   

9.
Tunisia, Ukraine, Russia, the North Sea area and elsewhere have yielded knowledge that the Early Cretaceous planktonic foraminifera are predominantly members of the Praehedbergellidae. The taxonomy and phylogeny of this family have been revised and refined. New generic and specific taxa have been proposed, new phylogenetic lineages have been described, and many type specimens have been imaged by scanning electron microscopy for the first time.Gorbachikella(Hauterivian–Early Aptian) gave rise toPraehedbergella(Late Hauterivian–Late Aptian), evolvingBlefuscuiana,Lilliputianella, and the planospiralBlowiellain the Barremian. The last gave rise toGlobigerinelloidesin the Aptian, from which the macroperforateAlanlordella(and its descendantPlanomalina) evolved in the Albian.Blowiellawas ancestral to taxa with radially elongated chambers (Claviblowiella, Leupoldina, Schackoina).  相似文献   

10.
Calcareous nannofossil assemblages at Site 641C (Galicia Margin, North Atlantic) were investigated in order to determine changes in fertility and temperature of surface waters. Taxa such as Zeughrabdotus spp. <3.5 μm, Biscutum constans, Discorhabdus rotatorius and Diazomatolithus lehmanii, which thrived in higher fertility conditions, are particularly abundant across the CM0 interval as opposed to those with oligotrophic affinities such as Watznaueria spp. and Nannoconus spp., which are generally reduced in abundance. The abundances of nannoconids are much lower than those observed in Tethyan sections, indicating higher fertility conditions. Slumpings and low recovery prevent the identification of the onset of the “nannoconid crisis”, but a sharp drop in nannoconid abundances, observed prior to the CM0 interval, correlates with the “nannoconid decline” observed in several Tethys sections.The normalized ratio between low and high fertility taxa (Fertility Index) was used to characterize the nannofossil assemblages in terms of productivity changes. The highest values of the Fertility Index were observed across magnetic chron CM0. The paucity of cold water taxa such as Seribiscutum spp. and Repagulum parvidentatum suggests warm water conditions throughout the deposition of upper Barremian–lower Aptian sediments on the Galicia Margin.  相似文献   

11.
The chronostratigraphic framework of the non-marine deposits of the Central Tunisian Lower Cretaceous (Kebar Formation) is reviewed from a biostratigraphic viewpoint. The outcrops located in the Jebel Kebar, Jebel Ksaïra and Jebel Koumine localities provided charophyte assemblages belonging to two biochronozones: Ascidiella cruciata-Pseudoglobator paucibracteatus (upper Barremian–lower Aptian) and Clavator grovesii lusitanicus (upper Aptian–lower Albian). Clavatoraceans from the upper Barremian–lower Aptian in the Tunisian Atlas are reported here for the first time. The assemblage consists of Atopochara trivolvis var. triquetra, Ascidiella iberica var. inflata, Globator maillardii var. trochiliscoides, Globator maillardii var. biutricularis, Echinochara peckii var. lazarii, Clavator harrisii var. harrisii and Clavator harrisii var. reyi. In addition, a new characean species, Mesochara magna nov. sp. Trabelsi and Martín-Closas, is described herein. The results show that the Kebar Formation is diachronous in Central Tunisia, with a more complete record to the north (Jebel Koumine) than in the type locality (Jebel Kebar). Barremian–Aptian diapiric activity is proposed as the factor that controls the diachronous nature of this formation.The late Barremian–early Aptian charophyte assemblages from the Kebar Formation display strong affinities with the contemporaneous floras of the European basins, thus suggesting that intense supraregional floristic exchanges occurred between the Tethyan islands scattered throughout what is now Western Europe and North Africa. The biogeographic distribution of these charophytes leads to the hypothesis that the peri-Tethyan Archipelago acted as an effective bridge for the intercontinental exchanges of these plants between Laurasia and Gondwana.  相似文献   

12.
The 4th Kilian Group meeting (Dijon, France, 30th August 2010) focused on the Aptian and Albian Stages. For the Aptian, a two-fold division of the stage was adopted for the Mediterranean area with a boundary between the Dufrenoyia furcata and Epicheloniceras martini Zones. The main changes to the zonal scheme concern the Lower Aptian with: the introduction of a Deshayesites luppovi Subzone in the upper part of the Deshayesites oglanlensis Zone; the replacement of Deshayesites weissi by Deshayesites forbesi as new index-species of the second interval zone; the introduction of a Roloboceras hambrovi Subzone in the upper part of the D. forbesi Zone; and the subdivision of the D. furcata Zone into the D. furcata and Dufrenoyia dufrenoyi Subzones. For the Albian, the upper part of the Douvilleiceras mammillatum Zone (Lower Albian) is now characterized by a Lyelliceras pseudolyelli Subzone. The main amendments concern the Upper Albian. The base of this substage is defined by the base of the Dipoloceras cristatum Zone. Above it, the Upper Albian zonal scheme comprises in stratigraphic order the Mortoniceras pricei, Mortoniceras inflatum, Mortoniceras fallax, Mortoniceras rostratum, Mortoniceras perinflatum and Arrhaphoceras briacensis Zones.  相似文献   

13.
日本具有4个标志早白垩世的半咸水和淡水软体动物群组合:欧特里沃期—早巴列姆期的立川和菖蒲动物群组合,晚巴列姆期的濑林动物群组合和早阿普特期动物群组合。纯非海相下白垩统大量分布于日本东北部(本州岛北部)的部分地区,以及日本中部、西南部的内带。在日本东北部的部分地区以及日本西南部的外带(四国岛与本州岛中部),从巴列姆阶下部往上有一些海相地层夹在非海相层中,这为研究非海相动物群提供了准确的年代依据。生物组合之间在种一级水平上的区别,主要由环境的差异而引起。1)立川动物群组合(欧特里沃期—早巴列姆期),含有半咸水Hayamina naumanni组合和淡水Megasphaerioides okurodaniensis组合;手取群的Okurodani、Kuwajima和Izuki三个组内的淡水软体动物可与本动物组合相对比;2)菖蒲动物群组合(欧特里沃期—早巴列姆期),含有Eomiodon nipponicus组合;3)濑林动物群组合(晚巴列姆期),含有Costocyrena radiatostriata组合,可与手取群的Kitadani组和日本东北部关门群的Sengoku组以及Monomiyama组的淡水软体动物组合相对比;4)日比原动物群组合(早阿普特期),含有Costocyrena minor组合,关门群Wakamiya组的淡水软体动物可与本动物组合相对比。  相似文献   

14.
The WNW–ESE trending Toulourenc Fault Zone (TFZ) is the western segment of the major Ventoux–Lure Fault Zone, which separates the Provençal platform from the Baronnies Vocontian Basin. The TFZ was subject to polyphased Mid-Cretaceous movements, during the Early Aptian and Middle–Late Albian times. The latter faulting episode generated conglomerates and olistoliths resulting from dismantled faultscarps cutting Barremian–Bedoulian limestones. The deformation is related to compressional wrench faulting (NE–SW sinistral faults; dextral component for the TFZ). It induced the uplift of the northwestern corner of the platform, as indicated by a mid-Cretaceous hiatus (Early Aptian pro parte to Early Albian) narrowly delimited in space. The opening of submeridian grabens within the platform favoured the northward transit of channelised coarse-grained Albian sands originating from a southern area. To cite this article: C. Montenat et al., C. R. Geoscience 336 (2004).  相似文献   

15.
Two cored boreholes in the central part of the North West German Basin recovered a unique section of Upper Barremian to Lower Aptian strata. Calcareous nannofossils show a distinctive shift from boreal endemic assemblages in the Barremian to cosmopolitan ones in the Aptian. This onset of new cosmopolitan species (e.g., Chiastozygus litterarius, Flabellites oblongus, Rhagodiscus angustus, Braarudosphaera sp., Eprolithus sp.) is spread over an interval of 25m, starting well below the early Aptian "Fischschiefer", a dark laminated shale rich in organic matter. These changes in the composition of calcareous nannofossils indicate that major palaeoceanographic changes occurred before the deposition of the Fischschiefer.The distribution pattern of calcispheres allows the differentiation of two sedimentary successions, separated by the Fischschiefer. The lower succession, which includes the sediments below the base of the Fischschiefer, indicates a boreal-pelagic environment. The lower part of the upper successions which includes the Fischschiefer, represents warmer inner shelf conditions. This corresponds to the presence of rich Tethyan-derived nannoconid assemblages and the presence of the planktonic foraminifera Hedbergella in the Fischschiefer. The topmost part of the upper succession (middle Aptian, Hedbergella marl) suggests a change to a pelagic warmer water environment. Two new taxa are introduced: the calcareous dinoflagellate cyst Obliquipithonella laqueata n. sp. and the foraminiferan Choanaella fortunate n. gen. n. sp.  相似文献   

16.
The Upper Barremian to Aptian Almadich Formation (Inner Prebetic Domain of the Betic Cordillera) is composed of hemipelagic sediments deposited on a distal carbonate ramp in the southern Iberian Palaeomargin. Within this facies we have found a thick interval of blue to black shales and marls that is interpreted as deposited under oxygen-depleted conditions. We think that this interval, dated as early Aptian, represents the local record of Ocean Anoxic Event 1a. The integrated biostratigraphic analysis of a section in the Almadich Formation, by means of planktonic foraminifera, calcareous nannofossils and ammonites, enables us to recognize most of the biostratigraphic units based on these three fossil groups and to correlate between them. The Sartousiana, Sarasini, Weissi, Deshayesi and Furcata (ammonite) Zones were identified for the Upper Barremian–Lower Aptian interval. By means of calcareous nannofossil biostratigraphy the Micrantholithus hoschulzii, Hayesites irregularis and Rhagodiscus angustus Zones, plus several additional biohorizons, were identified. A quantitative study performed on a set of 27 Lower Aptian samples has enabled the precise identification of the ‘nannoconid crisis’, the lower limit of which clearly precedes the main anoxic event, and its correlation with other bioevents. Planktonic foraminifera occur consistently throughout the Lower to Upper Aptian of the Cau section and are moderately well preserved. This fact allows us to use the most recent taxonomic framework, based on wall texture, to identify the Blowiella blowi, Schackoina cabri, Globigerinelloides ferreolensis, Globigerinelloides algerianus, Hedbergella trocoidea andTicinella bejaouaensis Zones. Coincident with the anoxic episode, the planktonic foraminiferal assemblages are composed of a significant number of forms with elongated chambers and/or tubulospines assigned to the genera Claviblowiella,Lilliputianella , Leupoldina and Schackoina. Most of the planktonic foraminiferal and nannofossil taxa are illustrated.  相似文献   

17.
The earliest Aptian marine transgression of the Lower Cretaceous across southern England resulted in the collapse of the generally freshwater Barremian environment and the initiation of marine mileux. Salinities passed from fresh-oligohaline to meso- and pliohaline, reaching fully marine conditions during the obsoletum Subzone (P. fissicostus Zone). Newly formed environmental niches were rapidly occupied by ostracod associations. In the Isle of Wight, freshwater Cypridea-rich assemblages in the lower Shepherd's Chine Member (Vectis Formation) were gradually replaced by faunas dominated by Sternbergella cornigera, Mantelliana mantelli and Theriosynoecum fittoni. Marine taxa recorded from the Atherfield Clay Formation migrated predominantly from the Paris Basin and include Asciocythere albae, Schuleridea derooi, Neocythere gottisi, N. bordeti, Cythereis geometrica, Cytheropteron stchepinskyi and Protocythere croutesensis.  相似文献   

18.
《Geodinamica Acta》2013,26(5):349-361
The most widespread blocks within the Cretaceous ophiolitic mélange (North Anatolian ophiolitic mélange) in Central Anatolia (Turkey) are pillow basalts, radiolarites, other ophiolitic fragments and Jurassic-Cretaceous carbonate blocks. The pillow basalts crop out as discrete blocks in close relation to radiolarites and ophiolitic units in Cretaceous ophiolitic mélange.

The geochemical results suggest that analyzed pillow basalts are within-plate ocean island alkali basalts. The enrichment of incompatible elements (Nb, Ta, Light REE, Th, U, Cs, Rb, Ba, K) demonstrates the ocean island environment (both tholeiites and alkali basalts) and enriched MORB. Dated calcareous intrafills and biodetrital carbonates reveal an age span of Callovian—Early Aptian. The thin-shelled protoglobigerinids, belonging to the genus Globuligerina, in the calcareous intrafills between pillow basalt lobes indicates a Callovian—Barremian age interval, most probably, Valanginian to Late Barremian. The volcanic and radiolarite detritus-bearing orbitolinid—Baccinella biodetrital carbonates dated as Late Barremian-Early Aptian in age, were probably deposited around atolls and have a close relationship with the ocean island pillow basalts.

The results collectively support the presence of a seamount on the Neo-Tethyan oceanic crust during the Valanginian—Late Barremian and atolls during the Late Barremian-Early Aptian interval. The presence of an oceanic crust older than that seamount along the Northern Branch of Neo-Tethys is conformable with the geodynamic evolution of the Tethys.  相似文献   

19.
Eight zonal dinocyst assemblages and three bio stratigraphic units ranked as “beds with flora” are first distinguished in the Danian—lower Lutetian interval of the Paleogene succession, penetrated by the reference borehole Novousensk no. 1, where eight standard and one local nannoplankton zones are simultaneously recognized. The direct correlation of nannoplankton and dinocyst zones is used to refine the paleon-tological substantiation and stratigraphic position of regional lithostratigraphic units, ranges of hiatuses, and the correlation with the general stratigraphie scale. The nannoplankton of the Danian NP2 Cruciplacolithus tenuis and NP3 Chiasmolithus danicus zones is characteristic of the Algai Formation (Fm). The nannoplankton of the NP4 Coccolithus robustus Zone and dinocysts of the D3a Alterbidinium circulum Zone from the Tsyganovo Fm characterizes the Danian top. The Lower Syzran Subformation (Subfm) corresponds to the upper part of the NP4 Coccolithus robustus Zone (Neochiastizygus junctus local zone) and to the D3b (part) Cerodinium depressum Zone of the Selandian dinocysts. The latter spans part of the Upper Syzran Subformation, whose characteristic nannofossils are the nannoplankton of the NP5 Fasciculithus tympaniformis Zone and the dinocysts of the D3b (part) Isabelidinium? viborgense Zone of the Selandian. The Novouzensk Fm is represented by a succession of the dinocyst Cerodinium markovae Beds and the standard D4c Apectodinium hyperacanthum Zone of the upper Thanetian. The coccolitophorids of the lower Thanetian NP6 Heliolithus kleinpelli Zone occur at the formation base. The Bostandyk Fm includes successive bio stratigraphie units of the Ypresian. In the dinocyst scale, these are the D5a Apectodinium augustum Zone, the Pterospermella Beds (DEla Zone of the North Sea scale), and zones DBlb-c Deflandrea oebisfeldensis, D7c Dracodinium varielon-gitudum, and D8 Dracodinium politum—Charlesdowniea coleothrypta, while units of the nannoplankton scale correspond to the NP12 Martasterites tribrachiatus and NP13 Discoaster lodoensis zones. The Kopterek Fm yields Lutetian nannofossils: the nannoplankton of the NP14 Discoaster sublodoensis Zone and the dinocysts of the Wetzeliella coronata—Areosphaeridium diktyoplokum Beds. Three meaningful hiatuses are established at the Danian base, Selandian top, and in the lower Ypresian.  相似文献   

20.
During the Barremian–Early Aptian, the Lower Saxony Basin (LSB) of northwest Germany was covered by a shallow epicontinental sea where restricted conditions resulted in the formation of black shales. This study focuses on a 103-m-thick succession of Lower Barremian–Lower Aptian dark claystones and black shales exposed in a temporary road cut in northwest Germany (A39). Calcareous nannofossils and the δ13Corg record have been used to determine the timing of black shale deposition (Hauptblätterton, Blätterton, Fischschiefer events). Redox-sensitive trace elements indicate anoxic conditions with free H2S causing the formation of black shales and dysoxic conditions during deposition of the dark claystones. The palaeoecological reconstructions based on calcareous nannofossils suggest that during the Lower Barremian Hauptblätterton event a stratification of water masses existed, caused by high surface water temperatures and reduced terrigenous run-off. During the deposition of the Upper Barremian clay-Blätterton alternation warm surface water prevailed, accompanied by meso-eutrophic surface water conditions. The formation of the Barremian black shales was mainly caused by restricted conditions related to the palaeogeography and palaeoceanography of the LSB. Global processes associated with the Oceanic Anoxic Event 1a most likely induced the deposition of the Lower Aptian Fischschiefer. High weathering rates, high primary production, and restricted conditions in the LSB led to increased burial of organic matter and thereby to the formation of the Fischschiefer.  相似文献   

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