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1.
The Furongian (Late Cambrian) Kurchavinskaya Formation of October Revolution Island, Severnaya Zemlya Archipelago, Arctic Russia , contains two distinctive morphotypes of the trace fossil Cruziana, both of which we assign to Cruziana semiplicata. A wider form shows characteristics typical of this ichnospecies with inner and outer lobes and marginal ridges. A narrow form has only an inner lobe with siculate, often interfering scratch‐marks, and rare, narrow marginal ridges. This narrow form, which shows characters in common with Cruziana tortworthi, probably represents burrowing in a strongly head‐down orientation. The record from October Revolution Island provides additional evidence that the palaeogeographical distribution of Cruziana semiplicata is not restricted to Gondwana, but also extend to parts of Baltica and North Kara. Cruziana semiplicata is known from the Furongian and Tremadocian of Gondwana, whereas on Baltica it is known only from the Furongian. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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3.
Stanis&#x;aw Or&#x;owski 《Geological Journal》1992,27(1):15-34
Abundant and varied trilobite trace fossils are recognized and described in the Cambrian sequence of the Holy Cross Mountains. Cruziana and Rusophycus are stratigraphically significant and some of the described traces may be used as local index fossils. The first recognition of the Cruziana barbata ichnozone in Poland is made and it occurs in the uppermost Middle Cambrian. A new position for the Middle/Upper Cambrian boundary is established. Three new ichnospecies are described: Cruziana magna, C. regularis and Rusophycus crebus. 相似文献
4.
The Variscan belt of western Europe is part of a large Palaeozoic mountain system, 1000 km broad and 8000 km long, which extended from the Caucasus to the Appalachian and Ouachita mountains of northern America at the end of the Carboniferous. This system, built between 480 and 250 Ma, resulted from the diachronic collision of two continents: Laurentia–Baltica to the NW and Gondwana to the SE. Between these two continents, small, intermediate continental plates separated by oceanic sutures mainly have been defined (based on palaeomagnetism) as Avalonia and Armorica. They are generally assumed to have been detached from Gondwana during the early Ordovician and docked to Laurentia and Baltica before the Carboniferous collision between Gondwana and Laurentia–Baltica. Palaeomagnetic and palaeobiostratigraphic methods allow two main oceanic basins to be distinguished: the Iapetus ocean between Avalonia and Laurentia and between Laurentia and Baltica, with a lateral branch (Tornquist ocean) between Avalonia and Baltica, and the Rheic ocean between Avalonia and the so‐called Armorica microplate. Closure of the Iapetus ocean led to the Caledonian orogeny: a belt resulting from collision between Laurentia and Baltica, and from softer collisions between Avalonia and Laurentia and between Avalonia and Baltica. Closure of the Rheic ocean led to the Variscan orogeny by collision of Avalonia plus Armorica with Gondwana. A tectonic approach allows this scenario to be further refined. Another important oceanic suture is defined: the Galicia–Southern Brittany suture, running through France and Iberia and separating the Armorica microplate into North Armorica and South Armorica. Its closure by northward (or/and westward?) oceanic and then continental subduction led to early Variscan (430–370 Ma) tectonism and metamorphism in the internal parts of the Variscan belt. As no Palaeozoic suture can be detected south of South Armorica, this latter microplate should be considered as part of Gondwana since early Palaeozoic times and during its Palaeozoic north‐westward drift. Thus, the name Armorica should be restricted to the microplate included between the Rheic and the Galicia–Southern Brittany sutures. 相似文献
5.
Delia Rösel Steven David Boger Andreas Möller Birgit Gaitzsch Matthias Barth Jeffrey Oalmann Thomas Zack 《地学学报》2014,26(1):64-71
Provenance studies from Cambro‐Ordovician sediments of the North Gondwana passive margin typically ascribe a North African source, a conclusion that cannot be reconciled with all observations. We present new U‐Pb ages from detrital rutile and zircon from Late Ordovician sediments from Saxo‐Thuringia, Germany. Detrital zircons yield age populations of 500–800 Ma, 900–1050 Ma and 1800–2600 Ma. The detrital rutile age spectra are unimodal with ages between 500 and 650 Ma and likely represent, together with the 500–800 Ma and 1800–2600 Ma zircon populations, detritus sourced predominantly from North Africa. In contrast, the c. 950 Ma zircons, which are persistently found in Cambro‐Ordovician sediments of North Gondwana, have no obvious African source. We propose that these zircons are sourced from the Rayner Complex–Eastern Ghats regions of Antarctica and India. An Indo‐Antarctic source indicates either continental‐scale sedimentary transport from central Gondwana to its peripheries or multiple cycles of sediment reworking and redeposition. 相似文献
6.
Cruziana及其相关的遗迹化石是由底栖三叶虫在沉积物表面停歇、爬行所留下的遗迹,一般认为产于潮下带至浅海陆棚环境,具有古水深指示意义。然而,本文通过对昆明民富二村下奥陶统红石崖组顶部含Cruziana rugosa遗迹化石群落层位的沉积环境分析却发现,Cruziana rugosa遗迹化石群落的沉积环境为潮上带—潮间带,说明三叶虫可以在短暂暴露环境中活动。三叶虫的这种适应性活动可能为节肢动物从海洋走向陆地做好了进化准备。 相似文献
7.
BAI Zhongkai Lü Xiuxiang LIU Xiaoping XIE Qilai LI Jianjiao WU Jianjun 《《地质学报》英文版》2012,86(2):313-319
Based on the analysis of trace fossils collected from the typical outcrop of the Lower Cambrian Wusongger Formation in the Kalpin area, ten ichnospecies of six ichnogenus were identified in the upper member of the Wusongger Formation, with most of them being found for the first time. The trace fossils are described seriatim. The ichnospecies are mainly represented by such common trace fossils as Ophiomorpha nodosa, Helminthopsis hieroglyphica, Helminthopsis ichnosp., Planolites beverleyensis, Planolites vulgaris, Planolites montanus, Palaeophycus striatus, Palaeophycus curvatus?, Cochlichnus anguineus and Rituichnus elongatum. The trace fossils are of high diversity and low abundance, and can be diagnosed as the Cruziana ichnofacies. They can be interpreted as having formed in a shallow water environment. 相似文献
8.
Biostatigraphical significance of trilobites of the Middle and Upper Ordovician in the eastern Baltic area is discussed, based
on a new material from numerous outcrops from Leningrad Region. The study of the Middle and Upper Ordovician trilobites in
the Mednikovo, Viivikonna, Gryazno, Khrevitsa and Elizavetino formations allows establishing two trilobite interval-zones.
The zone of Chasmops odini in the upper part of the Uhaku and Kukruse stages, and the zone of Chasmops marginatus in the lower
part of the Haljala Stage (the Idavere Substage). The upper part of the Haljala Stage (J~ohvi Substage) is characterized by
the occurrence of Rollmops wenjukowi. Distribution and biostratigraphical significance of some trilobite taxa (Asaphus (Neoasaphus) lepidus, Illaenus intermedius, Toxochasmops maximus) is discussed. 相似文献
9.
We report a Middle Ordovician metagranitoid from the northern margin of the Anatolide‐Tauride Block, the basement of which is generally characterized by voluminous Latest Proterozoic to Early Cambrian granitoids. The Ordovician metagranitoid forms an ～400‐m‐thick body in the marbles and micaschists of the Tav?anl? Zone. The whole sequence was metamorphosed in the blueschist facies during the Late Cretaceous (c. 80 Ma). Zircons from the metagranitoid give a Middle Ordovician Pb‐Pb evaporation age of 467.0 ± 4.5 Ma interpreted as the age of crystallization of the parent granitic magma. The micaschists underlying the metagranitoid yield Cambro‐Ordovician (530–450 Ma) and Carboniferous (c. 310 Ma) detrital zircon ages indicating that the granitoid is a pre‐ or syn‐metamorphic tectonic slice. The Ordovician metagranitoid represents a remnant of the crystalline basement of the Anatolide‐Tauride Block and provides evidence for Ordovician magmatism at the northern margin of Gondwana. Prismatic Carboniferous detrital zircons in the micaschists indicate that during the Triassic, the northern margin of the Anatolide‐Tauride Block was close to Variscan terranes. 相似文献
10.
A new species of afghanodesmatid, Cardiolaria benicioi, is recorded from Sandbian strata of northwestern Argentina. This species confirms the strong paleobiogeographic relationships between the western Argentina basin and other peri-Gondwanan areas. The Mid-Late Ordovician distribution of bivalves fit well into the Mediterranean Province defined upon brachiopod and trilobite faunas. Similitudes between Tremadocian and Floian bivalves from the western Gondwana and the peri-Gondwanan areas indicate that such ‘Mediterranean’ paleobiogeographic patterns can be traced back well into the Early Ordovician. 相似文献
11.
《Proceedings of the Geologists' Association. Geologists' Association》2017,128(3):438-446
Pteraspidomorphi are Ordovician to Devonian, jawless vertebrates devoid of paired fins that have developed a variety of phenotypes of mostly demersal aquatic animals of the neritic province. Some, however, were active swimmers in the water column or near to the surface. They show many convergences in adaptive variations with the other ossified agnathan vertebrates or ostracoderms, that is the osteostracans, galeaspids and pituriaspids. They are traditionally known as Old Red Sandstone (ORS) fish, and have been interpreted as fresh-water inhabitants. However, recent palaeoecological and sedimentological analyses have shown that they were near-shore, shallow-marine fishes in the Ordovician, that they occupied marine environments on the Silurian Baltic platform and a wide variety of environments in the Devonian, including those of the ORS (lagoonal, estuarine, deltaic, and open platform). Their peak of diversity was reached in the Early Devonian, and they all disappeared before the Frasnian-Famennian boundary biotic crisis. Within Earth sciences, they are used in biostratigraphy, palaeoecology, and palaeobiogeography. They are good tools for dating siliciclastic sedimentary series of the Silurian and Devonian, including the ORS, and they are good markers of the margins of Ordovician to Devonian palaeocontinents (Laurentia, Baltica, Siberia, Gondwana). 相似文献
12.
A new locality bearing ichnofossils of the Cruziana Assemblage Zone-Ⅲ from the Mussoorie syncline,Lesser Himalaya,is located in rocks of Member-B of the Dhaulagiri Formation,Tal Group,exposed along the Maldewta-Chhimoli fresh road cut section.The site yielded ichnofossils Bergaueria perata,Cochlichnus anguineus,？Diplocraterion isp.,Dimorphichnus obliquus,diplichnitiform Cruziana bonariensis,Diplichnites gouldi,Glockeria isp.,Helminthopsis isp.,Monomorphichnus lineatus,Phycodes palmatum,Palaeophycus striatus,Planolites beverleyensis,Planolites montanus,Treptichnus cf.T.pedum,scratch marks and an undetermined worm impression.An Early Cambrian age （Cambrian Series 2） is assigned to the ichnofossil-bearing strata based on the stratigraphic position between the Drepanuroides and Palaeoolenus trilobite zones.A revised Cambrian ichnofossil zonation is presented for the Tal Group of the Mussoorie syncline.Together with their occurrence on rippled surfaces,and the lateral displacement of some trackways （due to current action）,a sub-aqueous shallow-marine depositional setting is proposed for the rocks of Member-B. 相似文献
13.
Dunes and bars are common elements in tide‐dominated shelf settings. However, there is no consensus on a unifying terminology or a systematic classification for thick sets of cross‐stratified sandstones. In addition, their ichnological attributes have hardly been explored. To address these issues, the properties, architecture and ichnology of compound cross‐stratified sandstone bodies contained in the Lower Cambrian Gog Group of the southern Canadian Rocky Mountains are described here. In these transgressive sandstones, five types of compound cross‐stratified sandstone are distinguished based on foreset geometry, sedimentary structures and internal heterogeneity. These represent four broad categories of subtidal sandbodies: (i) compound‐dune fields; (ii) sand sheets; (iii) sand ridges; and (iv) isolated dune patches; tidal bars comprise a fifth category but are not present in the Gog Group. Compound‐dune fields are characterized by sigmoidal and planar cross‐stratified sandstone in coarsening‐upward and thickening‐upward packages (Type 1); these are mostly unburrowed, or locally contain representatives of the Skolithos ichnofacies, but are intercalated with intensely bioturbated sandstone containing the archetypal Cruziana ichnofacies. Sand‐sheet complexes, also composed of compound dunes, cover more extensive subtidal areas, and comprise three adjacent subenvironments: core, front and margin. The core is characterized by thick‐bedded sets of cross‐stratified sandstone (Type 2). A decrease of bedform size at the front is recorded by wedges of thinner‐bedded, low‐angle and planar cross‐stratified sandstone (Type 3) exhibiting dense Skolithos pipe‐rock ichnofabric. The margin is characterized by interbedded sandstone and mudstone, and hummocky cross‐stratified sandstone. Sand‐sheet deposits exhibit clear trends in trace‐fossil distribution along the sediment transport path, from non‐bioturbated beds in the core to Skolithos ichnofacies at the front, and a depauperate Cruziana ichnofacies at the margin. Tidal sand ridges are large elongate sandbodies characterized by large sigmoid‐shaped reactivation surfaces (Type 4). Sand ridges display clear ichnological trends perpendicular to the axis of the ridge, with no bioturbation or a poorly developed Skolithos ichnofacies in the core, a depauperate Cruziana ichnofacies in lee‐side deposits, and Cruziana ichnofacies at the margin. While both tidal ridges and tidal bars migrate by means of lateral accretion, the latter occur in association with channels while the former do not. Because tidal bars tend to occur in brackish‐water marginal‐marine settings, their ichnofauna are typically of low diversity, representing a depauperate Cruziana ichnofacies. Isolated dune patches developed on sand‐starved areas of the shelf, and are represented by lenticular sandbodies with sigmoidal reactivation surfaces (Type 5); they typically lack trace fossils, but the interfingering muddy deposits are intensely bioturbated by a high‐diversity fauna recording the Cruziana ichnofacies. The variety of sandbody types in the Gog Group reflects varying sediment supply and location on the inner continental shelf. These, in turn, governed substrate mobility, grain size, turbidity, water‐column productivity and sediment organic matter which controlled trace fossil distribution. 相似文献
14.
M. Chandra Singh P. Kundal R. A. S. Kushwaha 《Journal of the Geological Society of India》2010,76(6):573-586
Oligocene-Miocene deposits of Bhuban and Boka Bil Formations, Surma Group, Manipur Western Hill consist of well preserved
ichnofossil assemblages. These formations are represented by eight lithofacies such as Massive sandstone (Sm), Rippled marked
argillaceous sandstone (Sr), Wavy laminated sandstone-siltstone-silty shale (Sw), Laminated shale (Fl), Massive mudstone (Fm),
Trough cross-bedded sandstone (St), Lenticular laminated sandstonesiltstonesilty shale (Sll) and Laminated to massive sandstone-siltstone
(Ssc). Fifteen ichnospecies were identified, which further categories into Skolithos, Cruziana, and Skolithos/Cruziana ichnofacies. Overall distribution pattern and behavioural nature of the ichnoassemblage and sedimentological attributes suggests
that the sediments of Bhuban and Boka Bil Formations were deposited under frequent fluctuating sea level, moderate to strong
energy condition, subtidal to lower intertidal environment, rich in organic nutrients. 相似文献
15.
The Marwar Supergroup of the Bikaner-Nagaur Basin is composed of sediments deposited from the late Neoproterozoic (Ediacaran) to Upper Cambrian. The Nagaur Sandstone Formation of the Nagaur Group (uppermost division of the Marwar Supergroup) preserves trace fossils significant for establishing Early Cambrian biostratigraphic zones and depositional facies. Fifteen ichnospecies (and eight ichnogenera) identified in the Nagaur Sandstone Formation include “Treptichnus” pedum, Cruziana cf. tenella, Cruziana isp., Diplichnites ispp. A, B, and C, Gyrophyllites isp., Lockeia isp., Merostomichnites isp., Monomorphichnus gregarius isp. nov., Monomorphichnus isp., Planolites isp., Psammichnites isp., Rusophycus bikanerus isp. nov., Rusophycus cf. carbonarius, Rusophycus isp. and radial trace fossils.These trace fossils belong to ethological categories pascichnia, repichnia, cubichnia, and fodinichnia and represent arthropod and worm-like burrowing biota. The assemblage and a regional comparison with contemporaneous trace fossils in the eastern Gondwanan realm suggest that the sequence in the study area belongs to the Cruziana tenella Ichnozone and to Stage 2 (upper part of Terreneuvian), however the Middle Cambrian is not excluded. The trace fossil assemblage belongs to the archetypal Cruziana ichnofacies. Cross bedded sandstone, mud cracks and rainprints in the ichniferous strata of the Nagaur Sandstone Formation indicate deposition in an intertidal sand flat with channels that was exposed episodically. 相似文献
16.
RAGHAVENDRA P TIWARI CHINMOY RAJKONWAR LALCHAWIMAWII PAUL LALNUNTLUANGA JEHOVA MALSAWMA VICTOR Z RALTE SATISH J PATEL 《Journal of Earth System Science》2011,120(6):1127-1143
A detailed ichnological study performed on the Bhuban Formation, Surma Group (Lower to Middle Miocene) of Mizoram, India reveals
the occurrence of rich and diverse trace fossils. These have been collected from the two localities in Aizawl, i.e., Bawngkawn
and Ropaiabawk, where sandstone—shale sequence is well exposed. Total 20 ichnospecies of 14 ichnogenera have been identified
which include Arenicolites isp., Cochlichnus anguineus, Helminthopsis abeli, Laevicyclus mongraensis, Ophiomorpha borneensis, Palaeophycus tubularis, Palaeophycus heberti, Palaeophycus sulcatus, Palaeophycus alternatus, Pholeus abomasoformis, Pholeus bifurcatus, Planolites beverleyensis, Planolites annularis, Polykladichnus irregularis, Rhizocorallium isp., Skolithos linearis, Taenidium satanassi, Teichichnus rectus, Thalassinoides horizontalis and Thalassinoides paradoxicus. Ethologically these ichnogenera display dwelling and feeding activities of the infaunal organisms. Arenicolites, Ophiomorpha, Polykladichnus and Skolithos are the members of the Skolithos ichnofacies while Palaeophycus, Planolites, Rhizocorallium and Thalassinoides are the members of the Cruziana ichnofacies. The presence of Skolithos ichnofacies indicates sandy shifting substrate and high energy conditions in foreshore zone while the Cruziana ichnofacies indicate unconsolidated, poorly sorted soft substrate and low energy condition in the shoreface/offshore zone.
These ichnogenera indicate foreshore to shoreface-offshore zone of shallow marine environment for the deposition of the rocks
of the Bhuban Formation of Mizoram. 相似文献
17.
The Blåhø Nappe on the island of Fjørtoft, which represents an isolated portion of the Seve Nappe Complex in the Western Gneiss Region, Norway, has been suggested to have experienced two deep burial cycles during the Caledonian orogeny. However, evidence on this multiple burial process by the derivation of a pressure–temperature–time (P–T–t) path has never been given in the literature. In this study, the ‘diamondiferous’ kyanite–garnet gneiss from the Blåhø Nappe on Fjørtoft was revisited to determine if such a process was correct. Two types of garnet, porphyroblastic garnet‐1 and fine‐grained garnet‐2, were recognized in the gneiss. The core of garnet‐1 is poor in Ca and documents P–T conditions of 1.2–1.3 GPa at c. 880°C based on pseudosection modelling. The inner rims of garnet‐1 and the core of garnet‐2 are both richer in Ca, recording P–T conditions of 1.35–1.45 GPa and 770–820°C. Application of conventional geothermobarometry on the outer rim of garnet‐1 and the rim of garnet‐2 yielded retrograde P–T conditions of 0.75–0.90 GPa and 610–685°C. These estimates define an anticlockwise P–T path at pressures below 1.5 GPa. Accessory monazite was dated with the electron microscope. Relicts of detrital monazite in the gneiss point to Sveconorwegian and possibly also Cryogenian provenance for the detritus of the sedimentary protolith. Metamorphic monazite in the gneiss records a wide age range from 460 to 380 Ma, with a peak c. 435 Ma and a shoulder at 395 Ma. These data suggest that the original (Ediacaran?) Baltica margin sediment (gneiss protolith) was transported to the base of an overlying plate during the early Caledonian (pre‐Scandian) orogeny. A long residence time of the metasedimentary rock at this base caused its heating to 880°C and homogenization of the early garnet chemistry. The late Caledonian (Scandian) collision between Baltica and Laurentia led to further burial, during which the studied gneiss was close to the former surface of the downgoing continental plate and, thus, cooled. The reconstructed P–T–t path confirms the multiple burial history of the Blåhø Nappe but contradicts previous ideas of deep burial of the Fjørtoft gneiss to more than 100 km. 相似文献
18.
Richard A. Fortey 《Geological Journal》2006,41(2):243-253
A deep‐water trilobite fauna has been discovered in the otherwise graptolitic Mydrim Formation near Clarbeston Road, Pembrokeshire, south‐west Wales. Associated graptolites indicate an early Caradocian age. The trilobites comprise three species with eyes reduced or absent, representing an atheloptic assemblage with benthic life habits, which appeared during a short period of relative oxygenation of the Welsh Basin. The trilobite Platycalymene dilatata (Tullberg) is redescribed from the type material from Sweden, and new material from Wales is assigned to this species. Two new species are described in addition. Rorringtonia multisegmentata sp. nov. possesses twelve thoracic segments, which has implications for the classification of the Rorringtoniidae within the Aulacopleuroidea. Trinucleus conollyi sp. nov. differs from T. fimbriatus in the proliferation of the radial sulci. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
19.
《地学前缘(英文版)》2016,7(5)
Belonechitina capitata, a typically middle to late Ordovician chitinozoan index taxon was for the first time recovered from the northeastern Kumaon region, a part of Garhwal-Kumaon Tethys basin of the Himalaya, India. This species is of great biostratigraphic importance and has already been reported from Avalonia, Baltica and northern Gondwana. The study area was during Ordovician, part of a lowpalaeolatitudinal Gondwana region. The vesicles of recovered forms are black and fragmentary. This is principally attributed to intense tectonic activity during the Himalayan orogenic movement which resulted into high thermal alteration. The chitinozoans are found along with melanosclerites. 相似文献
20.
M. Janák E. J. Krogh Ravna K. Kullerud K. Yoshida R. Milovský T. Hirajima 《Journal of Metamorphic Geology》2013,31(6):691-703
We report the first finding of diamond in crustal rocks from the Tromsø Nappe of the North Norwegian Caledonides. Diamond occurs in situ as inclusions in garnet from gneiss at Tønsvika near Tromsø. The rock is composed essentially of garnet, biotite, white mica, quartz and plagioclase, minor constituents include kyanite, zoisite, rutile, tourmaline, amphibole, zircon, apatite and carbonates (magnesite, dolomite, calcite). The microdiamond, identified by micro‐Raman spectroscopy, is cuboidal to octahedral in shape and ranges from 5 to 50 μm in diameter. The diamond occurs as single grains and as composite diamond + carbonate inclusions. Diamond vibration bands show a downshift from 1 332 to 1 325 cm?1, the majority of Raman peaks are centred between 1 332 and 1 330 cm?1 and all peaks exhibit a full width at half maximum between 3 and 5 cm?1. Several spectra show Raman bands typical for disordered and ordered graphite (sp2‐bonded carbon) indicating partial transformation of diamond to graphite. The calculated peak P–T conditions for the diamond‐bearing sample are 3.5 ± 0.5 GPa and 770 ± 50 °C. Metamorphic diamond found in situ in crustal rocks of the Tromsø Nappe thus provides unequivocal evidence for ultrahigh pressure metamorphism in this allochthonous unit of the Scandinavian Caledonides. Deep continental subduction, most probably in the Late Ordovician and shortly before or during the initial collision between Baltica and Laurentia, was required to stabilize the diamond at UHP conditions. 相似文献