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1.
The 35.7 ± 0.2 Ma old Popigai crater, Siberia, with a diameter of about 100 km is one of the best preserved large terrestrial impact structures. The heterogeneous target at the impact site consists of Archean to Lower Proterozoic metamorphic rocks of the crystalline basement, Upper Proterozoic quartzites and other clastic deposits, as well as Cambrian to Cretaceous clastic sediments and sedimentary rocks, including carbonate rocks. Moreover, Proterozoic and Permo-Triassic dolerite dykes are found in the target area. We report major element, Sr and Nd isotope data for 13 of these target rocks and for various types of impactites. The 15 analysed impactite samples include tagamites (impact melt rocks), suevites and impact glass from small veins. Furthermore, two impact breccias and two impact glass-coated gneiss bombs were analysed. We discuss the relation of these impactites to the target lithologies, and evaluate on the basis of literature data the relation of microkrystites (and associated microtektites) in Upper Eocene sediments to the Popigai event.The impactites have SiO2 abundances ranging from 59 to 66 wt.% and show significant variations in the content of Fe, Ca, and Ti. They have present day 87Sr/86Sr ratios between 0.7191 and 0.7369. Their Sr model ages TSrUR range from 1.9 to 2.3 Ga. The 143Nd/144Nd ratios for the impactite samples cluster between 0.5113 and 0.5115. The Nd model ages TNdCHUR range from 1.9 to 2.1 Ga.In an εCHUR(Nd)-εUR(Sr) diagram, the impactites and Upper Eocene microkrystites (and associated microtektites) plot in a field delimited by Popigai target lithologies. The impactites are restricted to the field of crystalline basement rocks and Upper Proterozoic quartzites, but they show different isotopic signatures in different crater sectors. Impactites and Upper Eocene microkrystites plot in different, only partly overlapping clusters. The leucocratic microkrystites and microtektites have a higher affinity to the post-Proterozoic rocks in the target area than the impactites. Seemingly, the melanocratic microkrystites originated mostly from crystalline basement. This data alignment supports the assumption that Popigai is the source crater for all three types of ejecta. For the first time, clear relations are established of the geochemically variable Upper Eocene microkrystites and associated microtektites to specific target lithologies at Popigai crater. Finally, the observed range in Sr and Nd isotope parameters determined for impact melt lithologies that originated during the Popigai event show a much higher variability than known from other craters. This result indicates that mixing of impact melt which later formed tagamite sheets and glass particles in different impact breccias, was incomplete at the time of ejecta dispersal.  相似文献   

2.
Impact melt samples from drill hole B1-59 at the 3.8 km diameter Brent crater (Ontario) have been analysed for siderophile trace elements indicative of meteoritic contamination. Samples from the basal melt zone at 823–857 m depth are enriched in Ir, Os, Pd, Ni, Co, Cr and Se over basement, with the abundance pattern suggesting a chondritic projectile for Brent. From a Ni-Cr correlation of 10 melt samples an L or LL chondrite is inferred. The contribution of an ultramafic country rock (alnoite) in the melt is too small to significantly influence its NiCr ratio. Glass-rich breccias from the allochthonous breccias filling the crater also contain a meteoritic component. Interelement ratios (e.g. NiCr) are, however, fractionated relative to the melt zone samples. This, as well as the low Au content of all Brent samples, is probably a product of alteration.Additional data on impact melts from the 65 km diameter crater Manicouagan still did not reveal a meteoritic component, as also for the Mistastin crater (28 km diameter) where Cr analyses set an upper limit of 1% of an achondritic projectile component in the melt. Irghizites (tektite like glasses) from the Zhamanshin impact structure have been found to contain high Ni and Co concentrations, and our data show that Ir is also enriched. It is however not possible to define the projectile-type. Enrichment of an Ivory Coast tektite in Ir is confirmed. There are large differences in siderophile element concentrations among tektites, with otherwise similar chemical composition.There are now four known craters formed by chondrites (Clearwater East, Lapparjärvi, Wanapitei, and Brent), with Brent being the smallest of these. For smaller craters the projectiles appear to be limited to iron or stony-iron meteorites, because of atmospheric destruction of relatively small stony meteorites. It appears, however, that all major classes of meteorites are represented among the projectiles at terrestrial impact craters.  相似文献   

3.
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4.
A large number of specimens of Seymouriamorph amphibian, family Discosauriscidae, were collected from the south slopes of the Kuramanskiy Khrebet, Mt. Sarytaypan, 10 km northeast of the settlement of Adrasman, Tadzhik S.S.R. Deposits yielding the fossils consist of about 70 m of effusive sedimentary rocks, the top third being tuffs, tuff sandstones, and tuff breccias, and the remainder being alternating fine-grained sandstones, argillites, and siltstones, of gray, greenish, pink, and black colors. The beds overlie 800 m of tuff lavas and tuff breccias and are overlain by 200 m of-tuff breccias. Fossil leaves are abundant in the lower half of the beds in all lithologic types, but the vertebrates are confined to about 1 m of adjoining layers of fine-grained gray to pink sandstone, and almost black argillite. The fossils consist of complete impressions of skeletons, which will yield much anatomical information. Two genera are represented, the most abundant referrable to the Central European form Discosauriscus. The other is related to the European Leptoverpeton but may be new. These specimens permit correlation of the Sarytaypan deposits with Lower Permian' bedsgqn Czechoslovakia and Germany. Larval forms are by far the most abundant, but the presence of adults affords a reliable comparison of growth stages. New and detailed information of the development of the spinal column will also be forthcoming from further study of the growth stages. Presence of gills in the larvae reaffirms the persistence of an aquatic larval stage in the morphologically reptile-like Seymouriamorpha. — N. Hotton III.  相似文献   

5.
Lithium (Li) abundances and isotope compositions were determined in a representative suite of tektites (moldavites, Muong Nong-type tektites and an australite, Ivory Coast tektites and bediasites), impact-related glasses (Libyan Desert Glass, zhamanshinites and irghizites), a glass fragment embedded in the suevite from the Ries impact crater and sedimentary materials in order to test a possible susceptibility of Li to fractionation during hypervelocity impact events and to de-convolve links to their potential parental sources. The overall data show a large spread in Li abundance (4.7-58 ppm Li) and δ7Li values (−3.2‰ to 26.0‰) but individual groups of tektites and impact glasses have distinctive Li compositions.Most importantly, any significant high-temperature Li isotope fractionation can be excluded by comparing sedimentary lithologies from central Europe with moldavites. Instead, we suggest that Li isotope compositions in tektites and impact-related glasses are probably diagnostic of the precursor materials and their pre-impact geological histories. The Muong Nong-type tektites and australite specimen are identical in terms of Li concentrations and δ7Li and we tentatively endorse their common origin in a single impact event. Evidence for low-temperature Rayleigh fractionation, which must have operated prior to impact-induced melting and solidification, is provided for a subset of Muong Nong-type tektites. Although Li isotope variations in most tektites are broadly similar to those of the upper continental crust, Libyan Desert Glass carries high δ7Li ?24.7‰, which appears to mirror the previous fluvial history of parental material that was perhaps deposited in lacustrine environment or coastal seawater. Lithium isotopes in impact-related glasses from the Zhamanshin crater define a group distinct from all other samples and point to melting of chemically less evolved mafic lithologies, which is also consistent with their major and trace element patterns.Extreme shock pressures and the related extreme post-shock temperatures alone appear not to have any effect on the Li isotope systematics; therefore, useful information on parental lithologies and magmatic processes may be retrieved from analyses of Martian and lunar meteorites. Moreover, lack of significant Li depletion in tektites provides further constraints on the loss of moderately volatile elements during the Moon-forming impact.  相似文献   

6.
《International Geology Review》2012,54(10):1858-1867
The foraminifer Tournayella Dain, 1953, formerly believed to be restricted to the Tournasian, is found in the upper part of the Frasnian, western Ural Mountain province. The Frasnianform is a subgenus of Tournayella and is here named T. (Eotournayella) jubra, n. sg., n. sp., monotypic. Eotournayella seems to be transitional from the ammodiscids to the tournayellids and to be ancestral to or to contain marks of characteristic structures in certain tournayellid stocks.—L.G. Henbest  相似文献   

7.
The latest Cambrian deposits of the Malyy Karatau in Kazakhstan contain nautiloid cephalopods associated with trilobites. Four new species of nautiloids are described and assigned as follows: Ellesmeroceratidae — Tamdoceras n. gen; T. lisogorae n. sp.; T. logicameratum n. sp.; Protocycloceratidae — Chabactoceras n. gen.; C. balashovi n. sp. — C. R. Palmer.  相似文献   

8.
The Bosumtwi crater, Ghana, was excavated in phyllites and greywackes with subordinate microgranite dykes and quartz veins of the 2000 Ma old Lower Birimian System with a granodiorite intrusion at Pepiakese on its northeastern side. New major and trace element analyses are presented for 7 phyllites, 5 greywackes, 2 microgranites, 3 Pepiakese intrusion rocks and 1 suevite using XRF and INNA.Means and standard deviations were calculated using all available modern analyses for each element in the Bosumtwi target rocks, Bosumtwi suevite glasses and Ivory Coast tektites. Good agreements between the means were found for the three groups with the suevite glasses and tektites having more limited compositional ranges than the target rocks. Least squares mixing between target rock types shows that the best fits to the tektite and suevite glass compositions require components of about a third or a quarter from the Pepiakese intrusion and some extra silica, derived from quartz veins, as well as the metasediments.The new data provide evidence for vapour phase fractionation of P2O5 and Na2O in the tektites in addition to the previously reported Pb and Rb. Evidence for a meteoritic component in the tektites was found to be equivocal since the target rocks are probably a sufficient source of the meteorite indicator elements Ni and Ir.  相似文献   

9.
Tabulate corals, including new species of Cyrtophyllum (C. elegantum, C. altaicum, C. vulgaris), Propora (P. proheliolitoides), and Plasmoporella (P. altaica) aid in defining Upper Ordovician strata of Gornyy Altay region; in addition, new species of Heliolites (H. pachycanaliculoides), Favosites (F. karagemensis), Pachyfavosites (P. bazhenovae), Squameofavosites (S. karagemensis, S. altaicum), and Hexismia (H. asiatica) form part of a rich Late Silurian fauna within the same region.—T. E. Bolton  相似文献   

10.
《International Geology Review》2012,54(10):1860-1863
Putrya describes the new species Streblus galicianus, S. mjatliukae, S. pseudobeccarii, and S. granulosus from upper Tortonian (Miocene) deposits in Ciscarpathia.—M. A. Buzas  相似文献   

11.
The new subfamily Galliaecytherideinae is established in Cytherideinae Sars, 1925 for Galliaecytheridea, Lyubimovina, Palaeocytheridella, Asciocythere, Rubracea and Procytheridea. Lyubimivina is removed as a subgenus Palaeocytheridella and given generic status. Morphologic, phylogenetic and geographic justifications for the above actions are discussed. — I. G. Sohn.  相似文献   

12.
One new species for each of the following genera is described: Taxopora Sokolov (Upper Wenlock), Scoliopora Lang, Smith, and Thomas (Ludlow), Rachopora Sokolov (Givetian), Placocoenites Sokolov (Givetian), and Tyrganolites Tchernychev (Givetian). — D. J. McLaren.  相似文献   

13.
The 1.07?Myr old Bosumtwi impact structure (Ghana), excavated in 2.1-2.2?Gyr old supracrustal rocks of the Birimian Supergroup, was drilled in 2004. Here, we present single crystal U-Pb zircon ages from a suevite and two meta-graywacke samples recovered from the central uplift (drill core LB-08A), which yield an upper Concordia intercept age of ca. 2145?±?82?Ma, in very good agreement with previous geochronological data for the West African Craton rocks in Ghana. Whole rock Rb-Sr and Sm-Nd isotope data of six suevites (five from inside the crater and one from outside the northern crater rim), three meta-graywacke, and two phyllite samples from core LB-08A are also presented, providing further insights into the timing of the metamorphism and a possibly related isotopic redistribution of the Bosumtwi crater rocks. Our Rb-Sr and Sm-Nd data show also that the suevites are mixtures of meta-greywacke and phyllite (and possibly a very low amount of granite). A comparison of our new isotopic data with literature data for the Ivory Coast tektites allows to better constrain the parent material of the Ivory Coast tektites (i.e., distal impactites), which is thought to consist of a mixture of metasedimentary rocks (and possibly granite), but with a higher proportion of phyllite (and shale) than the suevites (i.e., proximal impactites). When plotted in a Rb/Sr isochron diagram, the sample data points (n?=?29, including literature data) scatter along a regression line, whose slope corresponds to an age of 1846?±?160?Ma, with an initial Sr isotope ratio of 0.703?±?0.002. However, due to the extensive alteration of some of the investigated samples and the lithological diversity of the source material, this age, which is in close agreement with a possible "metamorphic age" of ～?1.8-1.9?Ga tentatively derived from our U-Pb dating of zircons, is difficult to consider as a reliable metamorphic age. It may perhaps reflect a common ancient source whose Rb-Sr isotope systematics has not basically been reset on the whole rock scale during the Bosumtwi impact event, or even reflect another unknown geologic event.  相似文献   

14.
Six new species of the genus Bythocytheremorpha, including B. centroscrobiculata, B. aksuensis, B. bicornis, B. (?) abnormis, B. torulosa, and B. ilyini, are reported and described from beds of Upper Cretaceous age (Cenomanian through Santonian) of the southwestern part of the Gissar Range, located in the southeast of Soviet Central Asia. These relatively primitive Cretaceous ostracods, which possess an intricately sculptured carapace, seem to have lived in a shallow, warm, marine environment. — R. H. Benson.  相似文献   

15.
A new graptolite genus is described from lower Wenlockian rocks on the Molyud-Vozh river in the northwest Urals. Uralograptus closely resembles Cyrtograptus but lacks the spiral coiling of the main part of the rhabdosome. U. insuetus, the type species, was collected from the zone of Oktavites spiralis (Geinitz). --B.S. Norford.  相似文献   

16.
A new species is described, Tunguskocrinus ivanovae, representing a new genus and family of the superfamily Homocrinicae. The crinoid was found in Middle Ordovician rocks in Siberia.—P. M. Kier.  相似文献   

17.
The classification of the tribe Bereselleae of the family Dasycladaceae is discussed in some detail. The genera Beresella, Samarella and Dvinella are placed in the tribe with Trinodella, being treated as a subgenus of Dvinella. A number of new species are described: four in Beresella, six in Dvinella subgenus Dvinella and two in Dvinella subgenus Trinodella. The stratigraphic occurrence of the tribe in the Carboniferous at a number of localities on the Russian Platform is represented and a strong generic-facies association is pointed out. A pattern of variation in morphological form with sediment type is also discussed. — W. Adey.  相似文献   

18.
《International Geology Review》2012,54(10):1844-1846
Kurgalimova discusses the displacement of the aperture and the modification of its shape in the genera Gaudryina, Belorussiella, and Paragaudryina. The species G. navarroana Cushman, B. intermedia sp. nov., and P. pseudonavarroana (Balakh.) occur in fairly distinct stratigraphic position in lower to middle Eocene deposits of the southeastern part of the Turgay depression, South Emba and Bukhara Province.—M.A. Buzas  相似文献   

19.
The author discusses the conceptual bases of the pelecypod family Allorismidae and of the Carboniferous genera Allorisma, Allorismiella, Edmondia, Edmondiella, and Pseudedmondia. There is an extensive discussion of the hinge line structures of Allorisma based on Russian specimens, and four species of the genus from the Carboniferous of the Moscow area are described. Astaf'yeva-Urbaitis overlooked Wilson's 1959 paper in which Allorisma was shown to be a junior synonym of Edmondia; as a result Astaf'yeva-Urbaitis' nomenclature is faulty. Wilson replaced Allorisma with the new generic name Wilkingia. — J. Pojeta, Jr.  相似文献   

20.
A new species of Caytonia, C. orientale, and a new genus and species Chankanella vachrameevi are described from Neocomian-Aptian coal bearing strata in the Primor'ye Territory, Suifun basin. The new species of Caytonia is differentiated from C. sewardii Thomas and C. canadensis (Berry) Bell on the basis of size and slight morphological variances. Only one specimen of a megasporophyll was available for study. Leaves found in the same stratum and attributed to the new species differ from other species of Sagenopteris chiefly in the greater length of the petioles of the leaflets. Chankanella vachrameevi is described as a Sagenopteris-like leaf. It differs from Sagenopteris in having a larger number of leaflets and in lacking anastomoses of veins in the leaflets. It is compared with Lesleva Lesquereux. Its leaflets are compared with Thinnfeldia pinnae, and the leaves of Tersiella Radczenko, Linquifolium and Protophyllocladus. — F. M. Hueber.  相似文献   

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