首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 105 毫秒
1.
Excellently preserved organic-walled and silicified microfossils are first found in the Lower Riphean Ust-Il’ya and Kotuikan formations of the Billyakh Group in the northern slope of the Anabar Uplift (the Fomich River basin). Similar assemblages were previously known only from sections located southward in the Kotuikan River basin, and taxonomic composition of organic-walled microbiotas from the Ust-Il’ya and Kotuikan formations became a corner stone in competitive microphytological models that are based on different approaches. In their composition and general appearance, microbiotas from the Kotuikan and Ust-Il’ya formations in the Fomich River basin are similar to microbiotas reported from the Kotuikan River basin, although northern sections of the above formations characterize deeper sedimentation settings than in localities known before. The Ust-Il’ya and Kotuikan assemblages of organic-walled microfossils include sphaeromorphic Chuaria circularis and Leiosphaeridia, two-layer vesicles the genus Simia, filamentous Plicatidium and Taenitrichoides, and some others. The silicified microbiota from the lower Kotuikan Subformation is largely composed of akinetes of Anabaena-like cyanobacteria Archaeoellipsoides, spherical Myxococcoides grandis, and short trichomes Filiconstrictosus and Orculiphycus representing initial germination stages of Anabaena-like cyanobacterial spores. Acanthomorphic acritarchs known from lithology-similar Lower and Middle Riphean (Mesoproterozoic) formations of Australia and China have not been observed in the Ust-Il’ya and Kotuikan microbiotas, which are probably of older age. The found microbiotas outline substantially wider distribution area of organic-walled and silicified microfossils, supplement microphytological characteristics of Riphean sediments in the Anabar Uplift, provide information on taxonomic composition of microbiotas from a wider spectrum of facies, and specify relationships between Early and Middle Riphean assemblages of microorganisms from different continents.  相似文献   

2.
A relatively diverse microbiota, preserved in-situ, has been discovered in cherty stratiform stromatolites of the middle Proterozoic Wumishan Formation (c. 1200–1300 Maold), Jixian Group, in the Ming Tombs area of Beijing. This microfossil assemblage consists of two parts: (1) the mat-building and mat-dwelling benthos which mostly belong to “long-lasting” taxa and are mostly common with those of other Proterozoic microbiotas; and (2) allochthonous elements including some plankton and peculiar structures which are either new forms first described here or taxa shared with some contemporaneous or penecontemporaneous microbiotas elsewhere. The latter may have more stratigraphic significance.Bivariate analysis on two characters measured (length and width) has been used in the classification of the elongate microfossils, and the results demonstrate that biometrical methods are effective in the taxonomy of some Precambrian microfossils.The following new taxa are described:Archaeoellipsoides obesus sp. nov., Archaeoellipsoides conjunctivus sp. nov., Bactrophycus oblongum gen. et sp. nov., Bactrophycus dolichum gen. et sp. nov., Callosicoccus crauros gen. et sp. nov.  相似文献   

3.
It is demonstrated on the basis of the first monographic study of multiple and taxonomically variable organic-walled microfossils from the Ust’-Il’ya Formation of the Anabar Uplift that both prokaryotic and eukaryotic forms are present in the composition of this microbiota. They are divided into four formal groups on the basis of the specifics of the morphological indicators of the identified taxa. The review of the data on the isotopic age of hosting deposits showed that the Ust’-Il’ya Formation is of the Early Riphean in age which are currently evaluated as 1750 ± 10–1400 Ma. Relatively large and morphologically complex eukaryotic forms present in the Ust’-Il’ya Formation served in due time as the basis for an erroneous conclusion on the Late Riphean age of the specified formation and the overlying Lower Kotuikan Subformation of the Anabar Uplift. The paper provides a global comparative analysis of the Early Riphean microbiotas, demonstrates the position of the Ust’-Il’ya and Kotuikan microbiotas amidst the microbiotas of the same age, and shows that the relatively large acanthomorphic acritarchs Tappania, Valeria, Dictiosphaera, Satka, and Shuiyousphaeridium appeared in the geological history already during the Early Riphean Erathem. Moreover, the paper discusses the recently published data on the distribution of aerobic and anaerobic conditions in the Early Riphean paleobasins and provides the conclusion on the impact of the lateral change of these conditions on the taxonomic composition of the microbiota.  相似文献   

4.
New finds of siliceous microfossils, mainly diatoms, are reported from hard limestone levels in the Campanian cherty Mishash Formation, Negev, Israel. Twenty taxa were recognized, of which Melosira campaniensis and Trinacria negeviensis are new species. Representatives of Ebridians are reported for the first time from Cretaceous sediments. Calcareous nannofossils are usually few and poorly preserved. The diversity of the micro- and nannofossil assemblages vary through the succession and points to fluctuations in the palaeoenvironmental conditions from restricted to more normal marine. The moderate preservation of the opaline microfossils within the limestones is probably the result of early diagenetic lithification.  相似文献   

5.
ABSTRACT This paper presents high-precision U–Pb ages and initial Hf isotopic compositions of zircon from mafic to felsic rocks of the Kohistan Arc Complex, Pakistan. Three magmatic pulses tapping geochemically different reservoirs are distinguished. Partial melting of mantle with MORB-type isotopic characteristics generated 99–92-Ma-old magmas. Plutonism around 85 Ma tapped a more fertile mantle source, most likely consisting of a >600-Ma-old metasomatically enriched mantle, or of mantle contaminated by an old sedimentary component; 82-Ma-old felsic peraluminous dykes have MORB-type isotopic compositions considered to be inherited from remelting earlier magmas in the deep base of the arc. The isotopic results demonstrate several and rather rapid changes in melt source region during arc development. They also show that there was subordinate continental influence and negligible importance of slab components for the Hf budget during the generation of the Kohistan Arc Complex.  相似文献   

6.
The oldest filament- and colonial coccoid-containing microbial fossil assemblage now known is described here from drill core samples of stromatolitic cherty limestones of the Neoarchean, approximately 2600-Ma-old Campbell Group (Ghaap Plateau Dolomite, Lime Acres Member) obtained at Lime Acres, northern Cape Province, South Africa. The assemblage is biologically diverse, including entophysalidacean (Eoentophysalis sp.), probable chroococcacean (unnamed colonial coccoids), and oscillatoriacean cyanobacteria (Eomycetopsis cf. filiformis, and Siphonophycus transvaalensis), as well as filamentous fossil bacteria (Archaeotrichion sp.); filamentous possible microfossils (unnamed hematitic filaments) also occur. The Campbell Group microorganisms contributed to the formation of stratiform and domical to columnar stromatolitic reefs in shallow subtidal to intertidal environments of the Transvaal intracratonic sea. Although only moderately to poorly preserved, they provide new evidence regarding the paleoenvironmental setting of the Campbell Group sediments, extend the known time-range of entophysalidacean cyanobacteria by more than 400 million years, substantiate the antiquity and role in stromatolite formation of Archean oscillatoriacean cyanobacteria, and document the exceedingly slow (hypobradytelic) evolutionary rate characteristic of this early evolving prokaryotic lineage.  相似文献   

7.
A new fossil microbiota yielding eukaryotic Tappania is described from the Mesoproterozoic Kamo Group of the Central Angara Basin, Siberian Craton. The assemblage also includes Valeria, Satka, Lophosphaeridium, Pulvinosphaeridium, Miroedichia, Osculosphaera, Tasmanites, Obruchevella, Glomovertella, as well as branching and anastomosing filamentous microfossils of putative fungal affinities and peculiar short trichomes, that together substantially increase the biodiversity of the Tappania Association. Stratigraphic position and geochronological constraints indicate a relatively young Late Mesoproterozoic age of the Tappania-bearing sediments. There appears to be a continuity between the Tappania Association and the Neoproterozoic microbiota, the latter being firmly rooted in the Late Mesoproterozoic.  相似文献   

8.
Middle Ordovician acritarchs, including enigmatic, spore-like microfossils, are recorded from the Labrado and Capillas formations, of the Sierras Subandinas (Capillas River Section, Sierra de Zapla), northwestern Argentina. The Sierras Subandinas represent the outermost exposures of the Central Andean Basin that display an alternation of shallow-marine deltaic systems and estuarine environments, where relative sea-level fluctuations are frequent. The scarcity of fossils in the section, due to the marginal marine settings and frequent subaerial exposures, hinders the biostratigraphic constraining of these sedimentary successions. Based on the palynological assemblages, a probably Dapingian age is interpreted for the upper Lagunilla Member of the Labrado Formation, whereas the lower part of the Capillas Formation is assigned to the Darriwilian. Acritarchs from the lower part of the Capillas Formation indicate clear affinities with the “peri-Gondwana province”. However the lack of Frankea, a marker taxa for the Middle Ordovician, could be related either to the intermediate paleolatitudinal position of the Central Andean Basin or to local paleoenvironmental conditions. The facies analysis and the distribution of palynomorph assemblages throughout the studied section, suggest that organic-walled microfossils are influenced by local paleoenvironmental conditions. A probable non-marine origin is proposed for the spore-like microfossils co-occurring within the acritarch assemblages.  相似文献   

9.
The microfossils studied are discovered for the first time in the Riphean-Lower Vendian deposits, which have been recovered in 2002 by the Kel’tminskaya-1 deep parametric borehole in the Vychegda depression, the northeastern margin of the East European platform. The sampled interval of core section (4825–2347 m) consists of three units: the lower (depth range 4825–3995 m, 5 samples) and middle (depth range 3687–2961 m, 17 samples) carbonate successions overlain by sandstone-siltstone beds (depth range 2907–2347 m, 58 samples). Based on lithological criteria and/or composition of stromatolites, the carbonate successions are correlative with the Yshkemes and Vapol formations of the Upper Riphean of the Timan ridge succession, while the overlying, mostly siltstone succession was correlated with the Vychegda Formation of the southern Timan according to similarity in lithology and mineral composition. Microfossils found in 56 samples occur at 20 microphytological levels and represent different microbiotas. The Yshkemes and Vapol microbiotas of low diversity characterize six lower levels and represent one assemblage, while the diverse and abundant Vychegda microbiota typical of fourteen upper levels is divisible into three successive assemblages. The Vapol stromatolites Inzeria djejimii and Poludia polymorpha along with giant Chuaria and Navifusa present in the Yshkemes-Vapol assemblage suggest that their host deposits correspond to the upper Upper Riphean. The Vychegda assemblages, each of peculiar biostratigraphic specifics and unique in composition, consist of different morphotypes, primarily of large acanthomorphic acritarchs Cavaspina, Polyhedrosphaeridium, Cymatiosphaeridium, Asterocapsoides, and Tanarium, which are known in Scandinavia, Siberia, China, Australia, and India only in the Lower Vendian microbiotas of the Perthatataka type. The comprehensive microphytological characterization of the Lower Vendian in the Vychegda depression and earlier data on the Middle-Upper Riphean microbiotas from the adjacent Mezen syneclise enable a high-resolution biostratigraphic subdivision of the Riphean and Vendian successions in the vast region under consideration.  相似文献   

10.
The Vendian (Ediacaran) beds of the Zavkhan Basin, in the upper part of the Tsagaanolom Formation (<632 ± 14 Ma), yielded a new “Zavkhan” association of algae, microfossils, and problematic organisms, which is established in the series of alternating chert-carbonate shale with phosphorite interbeds. This association is distinct in the predomination of large (250 μm and over) sphaeromorphic microfossils of the genera Tasmanites, Archaeooides, and Leiosphaeridia, whereas acanthomorph acritarchs are represented by rarely found Cavaspina sp. and Tanarium sp. Multicellular algae included fragments of encrusting or foliate thalli with pseudoparenchymatous structure of polygonal cells characteristic of Rhodophyta algae (Thallophycoides sp.), and cordlike thalli of Vendotaenid algae Tyrasotaenia podolica. These layers of siltstone contain imprints of the problematic Vendian macrofossil Beltanelliformis brunsae. In their stratigraphic position, chemostratigraphic data, and fossil assemblage, the “Zavkhan” association can be assigned to the Upper Vendian.  相似文献   

11.
Characteristic latest Neoproterozoic and Early Paleozoic acritarchs and associated organic-walled microfossils are recorded from the sediments of Marwar Supergroup encountered in BGW-A well (Bikaner-Nagaur Basin) from 1123–481 m depth. Six distinct acritarch assemblages, broadly comparable with globally known Ediacaran (Vendian) and Cambrian assemblages are recognised. The recovered microfossils provide precise age for different units of the Marwar Supergroup whose ages, till now, were poorly understood due to absence or paucity of invertebrate and other mega and microfossils.  相似文献   

12.
A sample of chert from North Pole in the Archaean Pilbara block of Western Australia contains carbonaceous filaments that resemble microfossils. These occur in alternating light and dark laminae that look stromatolitic. However, the filaments are too simple in form for their origin to be determined, so they should be regarded as dubiofossils, perhaps biogenic, perhaps inorganic. Their host laminae were inorganically precipitated in a concordant fissure and thus cannot be stromatolitic. This fissure is younger than the surrounding silicified sediments of the ca. 3500 Ma old Warrawoona Group and possibly formed towards the end of the uplift and associated fracturing of the North Pole Dome, perhaps ca. 2750 Ma ago. The filaments are therefore contaminants in secondary chert.The filament-bearing rock was collected less than a metre from one of the localities (B) from which Awramik et al. reported early Archaean microfossils and possible microfossils. Their filaments from this locality were almost identical to those described here and were found in similar laminae. This suggests that their locality B filaments may also be contaminants in secondary chert. Other filaments found by Awramik et al. at North Pole come from an imprecisely located sample site (locality A) where the rock relationships are unknown. Since the host laminae of these filaments are not demonstrably primary and as cryptic concordant fissures filled with secondary minerals are common in locality A rocks, the filaments from this sample site could be contaminants too. Those that were assigned to Archaeotrichion should be treated as dubiofossils. Thus, the filaments described by Awramik et al. may not be fossil bacteria in ca. 3500 Ma old stromatolites, as they proposed, and are not necessarily the oldest known fossil organisms, as has been claimed.  相似文献   

13.
New materials obtained in the Pacific during cruises of the R/V Gelendzhik carried out by the State Scientific Center Yuzhmorgeologiya in 2000–2001 make it possible to specify the geologic and geomorphologic structure of Alba Guyot and clarify lithological and paleontological characteristics of lithotectonic rock complexes ranging from the Early Cretaceous to Pleistocene in age. Based on macro-and microfossils from sedimentary rocks several “transgressive” phases are distinguished in the guyot development: Cenomanian-Turonian, late Campanian-Maastrichtian, late Paleocene-middle Eocene, and Late Cenozoic. Finds of Paleogene molluscan and coral remains, together with planktonic foraminifers, imply relatively shallow sedimentation settings on Alba Guyot during the early Paleocene.  相似文献   

14.
Nora Noffke   《Earth》2009,96(3):173-479
The identification of fossils or biogenic sedimentary structures in rocks of Archean age is difficult, because similar lithological features could rise from purely physical or chemical processes alone. Therefore it is important to define criteria that serve the secure definition of a fossil or structure in question as of biological origin. Such criteria have been established for stromatolites and microfossils.This contribution discusses the 6 criteria of biogeneicity of ‘microbially induced sedimentary structures’ (MISS). Those structures are found in sandy deposits of early Archean age to the present, and rise from the interaction of benthic microbiota with physical sediment dynamics. The six criteria for their biogeneicity are: (i) MISS occur in rocks of not more than lower greenschist facies; (ii) in stratigraphic sections, MISS correlate with turning points of regression–trangressions; (iii), MISS correlate with a characteristic depositional facies that enhances the development and the preservation of microbial mats; (iv), the distribution of MISS correlates with the ancient average hydraulic pattern; (v), the geometries and dimensions of fossil MISS correspond to that of the modern ones; (vi), the MISS include at least one of 9 specific microtextures.  相似文献   

15.
Lower Kundelungu black argillites and silty dolomicrites from the Ndola area contain a rich microfossil assemblage, of which several forms can be attributed to the form-genus Fibularix Pflug, 1965. The same assemblage has also been found in fine-grained, mildly metamorphosed sedimentary rocks from Kalengwa and Karibarembi (North-Western Province). These findings support the Kundelungu correlation of the Kalengwa and Karibarembi successions.Three new species of Fibularix are described and illustrated. Seven types of sphaeromorphs are described and illustrated, though treated informally. Some sphaeromorphs are detached parts of Fibularix chains.The Lower Kundelungu microfossils resemble very closely some palynomorphs that occur in the Brioverian (Late Precambrian) of France, in the Libby Formation (Belt) of the northwestern United States, and in other formations of Late Precambrian age.  相似文献   

16.
The occurrence, types, morphology, and mineralogical characteristics of tube microfossils were studied in gossanites from twelve VHMS deposits of the Urals. Several types of tube microfossils were recognized, including siboglinids, polychaetes and calcerous serpulids, replaced by a variety of minerals (e.g. hematite–quartz, hematite–chlorite, carbonate–hematite) depending on the nature of the substrate prior to the formation of the gossanites. Colonial hematite tube microfossils (~ 150 μm across,1–2 mm long) are composed of hematitic outer and inner walls, and may exhibit a cellular structure within their cavities. Spherical forms are saturated with Fe-oxidizing bacteria inside the tubes – probably analogues of trophosomes. Colloform stromatolitic outer wall surfaces are characterized by the presence of numerous interlaced filaments of hematite (2–3 μm diameter, up to 1–2 mm long). Between tube microfossils, the hematitized cement contains bundles of hematitized filaments with structures similar to the hyphae of fungi. Hematite–chlorite tube microfossils are scattered in gossanites, mostly as biological debris. They are typically 30 to 300 μm in diameter and 1 to 5 mm long. The layered structure of their tube walls is characterized by hematite–quartz and chlorite layers. Abundant filamentous bacteria coated by glycocalix and chlorite stromatolite are associated with hematite–chlorite tubes. The carbonate–hematite tube microfossils (up to 300 μm across, 2–3 mm long) occur in carbonate-rich gossanites. The tubes are characterized by fine (~ 10 μm thick) walls of hematite and cavities dominated by relatively dark carbonate or hematite. Carbonates may be present both in walls and cavities. Stromatolite-like leucoxene or hematite–carbonate aggregates were also found in association with tubes. Randomly oriented filaments are composed of ankerite. Single filaments are composed of individual cells, typically smaller than 100 nm across, similar to that of magnetotactic bacteria.Three dimensional tomographic images of all types of tube microfossils demonstrate a clear wavy microlayering from outer and inner walls, which may reflect segmentation of the tube worms. The traces of burrowing or fragments of glycocalix with relict spheres are typical of tube microfossils from gossanites.The carbon isotopic composition of carbonates associated with tube microfossils from hematite–quartz, hematite–carbonate, and hematite–chlorite gossanites average − 7.2, − 6.8, –22.8‰, PDB, respectively. These values are indicative of a biogenic origin for the carbonates. The oxygen isotopic composition of these carbonates is similar in all three gossanite types averaging + 13.5, + 14.2, + 13.0‰ (relative to SMOW), and indicative of active sulfate reduction during the diagenetic (and anadiagenetic) stages of the sediments evolution. The trace element characteristics of hematite from tube microfossils are characterized by high contents of following trace elements (average, ppm): Mn (1529), As (714), V (540), W (537), Mo (35), and U (5). Such high contents are most likely the result of metal and metalloid sorption by fine particles of precursor iron hydroxides during the oxidation of sulfides and decomposition of hyaloclasts via microbially-mediated reactions.  相似文献   

17.
Approximately 500-Ma-old orthogneisses are widespread in the eastern part of the Variscan belt and are commonly interpreted to have intruded mica-schist series of assumed Neoproterozoic age. New SHRIMP zircon ages of quartzofeldspathic metavolcanogenic rocks of the mica schist series in the eastern part of the Karkonosze-Izera Massif (SW Poland) indicate that they are late Cambrian/early Ordovician rather than Neoproterozoic in age, based on the zircon age spectra distributed mainly between ca. 500 and 660 Ma (with a few Proterozoic inherited minimum ages of ca. 970 and 1,825 Ma). Younger zircon dates, dispersed between ca. 412 and 464 Ma, are interpreted as a result of Pb-loss likely caused by subsequent metamorphism. Consequently, the felsic metavolcanogenic rocks appear to be roughly contemporaneous with the intrusion of ca. 500-Ma-old orthogneiss protoliths (with the pooled concordia age of 487 ± 8 Ma interpreted as the best approximation of the protolith intrusive age). Field relationships, petrological and geochemical features of the felsic and mafic rocks studied support a model in which the accompanying mica schist series are not the original country rocks to the ca. 500 Ma granite intrusions, and indicate that their recent close proximity is the result of tectonic juxtaposition. However, both the mica schists enclosing the bimodal metavolcanic rocks, and the orthogneisses, are interpreted to represent a Cambro-Ordovician passive continental margin sequence being part of the Saxothuringian domain. They are tectonically overlain to the east by HP/T metamorphic units, comprising MORB-type metaigneous rocks, and delineating a tectonic suture separating the Saxothuringian block in the west from an assumed continental block (Tepla-Barrandian) to the south-east.  相似文献   

18.
贵州瓮安陡山沱组球状化石元素地球化学浅析   总被引：3，自引：0，他引：3       下载免费PDF全文
唐烽  高林志  尹崇玉  王约 《地质论评》2011,57(2):175-184
本文利用电子探针微区分析技术(EPMA),首次分析了采自贵州瓮安北斗山磷矿区陡山沱组外壁呈瘤状及多边形板片状的磷酸盐化球状化石的元素地球化学含量,包括常量元素氧化物含量和部分稀土元素含量,经初步对比发现:具瘤状及板片状外壁的两类球状化石,由内至外常量元素含量的变化趋势大体相似,表明归人同一生物大门类的可能性较大;与磷块...  相似文献   

19.
The ?eské st?edoho?í Mts. is the dominant volcanic center of the Oh?e (Eger) rift zone. It hosts the Roztoky Intrusive Complex (RIC), which is made up of a caldera vent and intrusions of 33–28-Ma-old hypabyssal bodies of essexite–monzodiorite–sodalite syenite series accompanied by a radially oriented 30–25-Ma-old dike swarm comprising about 1,000 dikes. The hypabyssal rocks are mildly alkaline mostly foid-bearing types of mafic to intermediate compositions. The dike swarm consists of chemically mildly alkaline and rare strongly alkaline rocks (tinguaites). The geochemical signatures of the mildly alkaline hypabyssal and associated dike rocks of the RIC are consistent with HIMU mantle sources and contributions from lithospheric mantle. The compositional variations of essexite and monzodiorite can be best explained by fractional crystallization of parent magma without significant contributions of crustal material. On the other hand, the composition of monzosyenite, leuco-monzodiorite and sodalite syenite reflects fractional crystallization coupled with variable degrees of crustal assimilation. It is suggested that the parent magmas in the Oh?e rift were produced by an adiabatic decompression melting of ambient upper mantle in response to lithospheric extension associated with the Alpine Orogeny.  相似文献   

20.
First finds of microfossils from the silicified microphytolitic carbonates of the Uluntui Formation in the southwestern Baikal region are described. They are represented by remains of the cyanobacterial community that formed microphytolites. These microfossils are accompanied by acritarchs probably belonging to green algae. The silicified microfossils are sufficiently well preserved despite complete and repeated recrystallization of host primary carbonate rocks. Main phases of secondary mineralization are related to hydrothermal-metasomatic processes, which were likely provoked by collisional events on the southern flank of the Siberian Craton in the Silurian.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号