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1.
The analysis of radiolarian assemblages and lithological types of siliceous rocks yielded new data on the structure of different sequences constituting the northern Algan terrane in the Pereval’naya River basin. Three tectonic slices formed by different lithothectonic complexes can be defined in this area. The radiolarian assemblages from the volcanogenic-siliceous slice allow the oceanic section to be dated back to the Kimmeridgian-Valanginian. The tuffaceous-terrigenous slice contains cherts of two types: (1) formed in situ and (2) reworked. The reworked deep-sea cherts yielded Bathonian-Kimmerdgian and Bathonian-Oxfordian radiolarians, while late Aalenian-late Bathonian radiolarian assemblages were extracted from the Kimmerdgian-Tithonian matrix of siliceous rocks.  相似文献   

2.
The East Sakhalin accretionary wedge is a part of the Cretaceous-Paleogene accretionary system, which developed on the eastern Asian margin in response to subduction of the Pacific oceanic plates. Its formation was related to the evolution of the Early Cretaceous Kem-Samarga island volcanic arc and Late Cretaceous-Paleogene East Sikhote Alin continental-margin volcanic belt. The structure, litho-, and biostratigraphy of the accretionary wedge were investigated in the central part of the East Sakhalin Mountains along two profiles approximately 40 km long crossing the Nabil and Rymnik zones. The general structure of the examined part of the accretionary wedge represents a system of numerous east-vergent tectonic slices. These tectonic slices. tens to hundreds of meters thick. are composed of various siliciclastic rocks, which were formed at the convergent plate boundary, and subordinate oceanic pelagic cherts and basalts, and hemipelagic siliceous and tuffaceous-siliceous mudstones. The siliciclastic deposits include trench-fill mudstones and turbidites and draping sediments. The structure of the accretionary wedge was presumably formed owing to off-scraping and tectonic underplating. The off-scraped and tectonically underplated fragments were probably tectonically juxtaposed along out-of-sequence thrusts with draping deposits. The radiolarian fauna was used to constrain the ages of rocks and time of the accretion episodes in different parts of the accretionary wedge. The defined radiolarian assemblages were correlated with the radiolarian scale for the Tethyan region using the method of unitary associations. In the Nabil zone, the age of pelagic sediments is estimated to have lasted from the Late Jurassic to Early Cretaceous (Barremian); that of hemipelagic sediments, from the early Aptian to middle Albian; and trench-fill and draping deposits of the accretionary complex date back to the middle-late Albian. In the Rymnik zone, the respective ages of cherts, hemipelagic sediments, and trench facies with draping deposits have been determined as Late Jurassic to Early Cretaceous (middle Albian), middle Aptian-middle Cenomanian, and middle-late Cenomanian. East of the rear toward the frontal parts of the accretionary wedge, stratigraphic boundaries between sediments of different lithology become successively younger. Timing of accretion episodes is based on the age of trench-fill and draping sediments of the accretionary wedge. The accretion occurred in a period lasting from the terminal Aptian to the middle Albian in the western part of the Nabil zone and in the middle Cenomanian in the eastern part of the Rymnik zone. The western part of the Nabil zone accreted synchronously with the Kiselevka-Manoma accretionary wedge located westerward on the continent. These accretionary wedges presumably formed along a single convergent plate margin, with the Sakhalin accretionary system located to the south of the Kiselevka-Manoma terrane in the Albian.  相似文献   

3.
In the Triassic siliceous formation of Sikhote Alin, carbonaceous silicites occur in the late Olenekian-middle Anisian member (4–20 m) of alternating cherts and clayey cherts (“phtanite member”) near the section base. The silicites are represented by radiolarian and spicule-radiolarian cherts alternating with clayey cherts. They contain up to 8.5% Corg. In the majority of sections, the rocks underwent structural and mineral transformation at the mesocatagenetic stage. The slightly oxidized organic (primarily, marine sapropelic) matter contains quinones, methyl, methylene, and ether groups. The content of neutral bitumens in rocks shows a wide variation range. The carbon isotopic composition in phtanites and clayey phtanites (δ13C from ?27.3 to ?30.2‰) is identical to that in many Paleozoic-Mesozoic bitumens and oils. As compared with other Mesozoic sedimentary rocks of Sikhote Alin, the carbonaceous silicites are enriched in V, B, Mo, Ni, Cu, and Ag. Anomalously high concentrations of Ba are recorded in phtanite rock sections at the Gornaya and Khor rivers and in the vicinity of Khabarovsk. Modal value of the Au content in phtanites and clayey phtanites is three or four times higher than the clarke value in carbonaceous silicites and reaches anomalous values in some sections (e.g., Ogorodnaya River section). Carbonaceous silicites of this section are also enriched in Pt. Positive Au-Corg correlation is recorded in clayey phtanites of the Ogorodnaya River section containing more than 0.5% Corg. In organic fractions, Au and Ag are concentrated in alcohol and alcohol-benzene bitumens, asphalt acids, and asphaltenes. Migration of bitumens from high-carbonaceous clayey phtanites to the pore-fissure space of cherts and phtanites also fostered the concentration of these metals in some low-carbonaceous layers of the member.  相似文献   

4.
In the southwestern part of the South Sakhalin Basin, the main source rocks are early Miocene clayey deposits of the Upper Due Suite, middle Miocene dark gray and black mudstone of the Kurasiy Suite, and, probably, black mudstone of the Bykov Suite of Late Cretaceous age.  相似文献   

5.
The Aptian-Albian sediments of Kotel’nyi Island are represented by a terrigenous coaliferous complex with the apparent thickness of approximately 700 m. The upper two thirds of their section enclose ignimbrites and rhyolitic ash tuffs. The integral thickness of volcanics is 170 m. A new sequence composed largely of acidic volcanics and sedimentary rocks is defined in the upper part of the Cretaceous section. The K-Ar age estimated for ignimbrite glasses is 110–107 ± 2.5 Ma, which corresponds to the first half of the Albian. The fossil flora list is added by several previously unknown forms. The macroflora of Kotel’nyi Island is similar to its Albian counterpart from the Kolyma-Indigirka region and allows Cretaceous sediments from the lower part the Kotel’nyi Island section to be dated back to the Aptian (?)-Albian (except for the terminal Albian). The palynological characteristic of rocks immediately contacting the dated volcanics appeared to be untypical of Albian sediments of Siberia and similar to that of the Late Neocomian palynocomplexes. This is partly explained by erosion and reworking processes. The examined continental sediments accumulated in post-orogenic extension settings. They constitute the lower strata of the Aptian(?)-Tertiary post-orogenic complex filling riftogenic depressions in the New Siberian Islands and Laptev Sea.  相似文献   

6.
The study of the radiolarian ribbon chert is a key in determining the origins of associated Mesozoic oceanic terranes and may help to achieve a general agreement regarding the basic principles on the evolution of the Caribbean Plate. The Bermeja Complex of Puerto Rico, which contains serpentinized peridotite, altered basalt, amphibolite, and chert (Mariquita Chert Formation), is one of these crucial oceanic terranes. The radiolarian biochronology presented in this work is mainly based by correlation on the biozonations of Baumgartner et al. (1995) and O??Dogherty (1994) and indicates an early Middle Jurassic to early Late Cretaceous (late Bajocian?Cearly Callovian to late early Albian?Cearly middle Cenomanian) age. The illustrated assemblages contain about 120 species, of which one is new (Pantanellium karinae), and belonging to about 50 genera. A review of the previous radiolarian published works on the Mariquita Chert Formation and the results of this study suggest that this formation ranges in age from Middle Jurassic to early Late Cretaceous (late Aalenian to early?Cmiddle Cenomanian) and also reveal a possible feature of the Bermeja Complex, which is the younging of radiolarian cherts from north to south, evoking a polarity of accretion. On the basis of a currently exhaustive inventory of the radiolarite facies s.s. on the Caribbean Plate, a re-examination of the regional distribution of Middle Jurassic sediments associated with oceanic crust, and a paleoceanographic argumentation on the water currents, we come to the conclusion that the radiolarite and associated Mesozoic oceanic terranes of the Caribbean Plate are of Pacific origin. Eventually, a discussion on the origin of the cherts of the Mariquita Formation illustrated by Middle Jurassic to middle Cretaceous geodynamic models of the Pacific and Caribbean realms bring up the possibility that the rocks of the Bermeja Complex are remnants of two different oceans.  相似文献   

7.
The Gustav Group of the James Ross Basin, Antarctic Peninsula, forms part of a major Southern Hemisphere Cretaceous reference section. Palynological data, chiefly from dinoflagellate cysts, integrated with macrofaunal evidence and strontium isotope stratigraphy, indicate that the Gustav Group, which is approximately 2.6 km thick, is Aptian–Coniacian in age. Aptian–Coniacian palynofloras in the James Ross Basin closely resemble coeval associations from Australia and New Zealand, and Australian palynological zonation schemes are applicable to the Gustav Group. The lowermost units, the coeval Pedersen and Lagrelius Point formations, have both yielded early Aptian dinoflagellate cysts. Because the overlying Kotick Point Formation is of early to mid Albian age, the Aptian/Albian boundary is placed, questionably, at the Lagrelius Point Formation–Kotick Point Formation boundary on James Ross Island, and this transition may be unconformable. Although the Kotick Point Formation is largely early Albian on dinoflagellate cyst evidence, the uppermost part of the formation appears to be of mid Albian age. This differentiation of the early and mid Albian has refined the age of the formation, previously considered to be Aptian–Albian, based on macrofaunal evidence. The Whisky Bay Formation is of late Albian to latest Turonian age on dinoflagellate cyst evidence and this supports the macrofaunal ages. Late Albian palynofloras have been recorded from the Gin Cove, lower Tumbledown Cliffs, Bibby Point and the lower–middle Lewis Hill members. However, the Cenomanian age of the upper Tumbledown Cliffs and Rum Cove members, based on molluscan evidence, is not supported by the dinoflagellate cyst floras and further work is required on this succession. The uppermost part of the Whisky Bay Formation in north-west James Ross Island is of mid to late Turonian age and this is confirmed by strontium isotope stratigraphy. The uppermost unit, the Hidden Lake Formation, is Coniacian in age on both palaeontological and strontium isotope evidence. The uppermost part of the formation appears to be early Santonian based on dinoflagellate cysts, but strontium isotope stratigraphy constrains this as being no younger than late Coniacian. This refined palynostratigraphy greatly improves the potential of the James Ross Basin as a major Cretaceous Southern Hemisphere reference section.  相似文献   

8.
The marine sedimentary formations of the Middle Albian to Maastrichtian in the Cretaceous Sakhalin Basin (CSB) were investigated. These successions of strata consist of interbedded sandy, clayey and calcareous rocks which are underlain by heterogeneous metamorphosed (up to greenschist facies) Paleozoic to Mesozoic (pre-Aptian) rocks. The studied sections display several different facies reflecting geological settings ranging from an inner shelf to a continental slope. Three depositional complexes bound by regional subaerial unconformities are recognized within the marine successions. Since the Albian, the CSB has been a rapidly subsiding marginal part of the Okhotsk Sea plate. The Naiba Valley succession, corresponding to a sublittoral zone, shows extremely high sedimentation rates up to 190 m/Ma. The stratigraphic distribution of lithofacies indicates that the CSB became shallower from the Middle Albian to the Maastrichtian.  相似文献   

9.
滇西昌宁─孟连带南部地层地质问题   总被引：1，自引：1，他引：1  
滇西孟连以南，整合于南段组浊积岩之上的拉巴群硅质岩含晚二叠世早期放射虫化石，南段组时代不仅限于石炭纪，可能延入二叠纪。二者为晚古生代思茅地块的外陆坡沉积。其西面的南基河杂岩（新名）由层序混乱的晚古生代硅质岩、泥岩和少量砂岩、玄武岩构成。放射虫化石证据表明，硅质岩时代不仅限于晚泥盆世－早二叠世，还延入晚二叠世，而有的砂岩时代为早石炭世，它们是经过强烈构造变动的古特提斯洋的沉积记录。昌宁－孟连带向南可能延至泰国北部的清迈带，而非东北部的难河带。  相似文献   

10.
The data of geochemical study of Late Triassic cherts from tectonic–sedimentary complexes from different structural levels of the Samarka Terrane are reported. It is shown that the concentration and character of distribution of the major petrogenic oxides and minor and rare-earth elements in cherts of the upper and lower structural levels differ significantly, which results from differences in the facies environments of chert deposition. All the geochemical characteristics of cherts show that their deposition proceeded in the pelagic area of sedimentation, but in different parts. The Katen Complex composing the lower structural level is the most distant from the continental margin. The closest is the Amba-Matay Complex composing the upper structural level. Based on the geochemical and biostratigraphic data and the age of accretion of paleooceanic fragments, the length of the subducted oceanic plate (>6000 km) is calculated.  相似文献   

11.
雒昆利 《地层学杂志》2006,30(2):149-156
根据鲁家坪组的岩性、岩相和变质程度的变化以及区域分布特征,原定义所包含的岩石内容过于庞大,混淆了岩石地层单位和年代地层单位。通过对鲁家坪组的命名地点和标准剖面所在地——北大巴山南部的陕西紫阳县鲁家坪村的鲁家坪剖面及其他剖面的详细研究,原鲁家坪组按岩性可分为三段,下段以白云岩为主;中段以厚层硅质岩为主,中段下部的硅质岩中夹磷质白云岩和灰岩,其中产小壳化石Archaeooidessp.、Protohertinasp.、Chan-celloriasp.和Hyolithids,中段上部的硅质岩中夹多层毒重石或重晶石矿层以及砂炭(石煤)和火山岩层,即以硅质岩类为主;上段以黑灰色(风化后为浅灰色)含硅炭板岩和泥灰质含炭板岩为主。根据原鲁家坪组各段岩层的岩性、岩相、岩层层序、厚度和分布范围等,原鲁家坪组的下部的厚层状灰质白云岩和硅质白云岩等与原鲁家坪组中部的厚层硅质岩及硅质板岩,以及上部的板岩和千枚岩和页岩的岩性和岩相差别较大,应从原鲁家坪组划出,暂仍称为灯影组,与三峡地区的灯影组可对比;原鲁家坪组的中上部为鲁家坪组的主体,仍称鲁家坪组。厘定后的鲁家坪组与扬子地台的下寒武统的筇竹寺组(云南)、牛蹄塘组(贵州)和宽川铺组(陕南宁强)可以对比,而与后者的主要区别在于后者的下部以黑色页岩为主、硅质岩岩层薄,而鲁家坪组下部的硅质岩特别发育,厚度大,常常夹有毒重石矿层、砂炭和火山岩等。  相似文献   

12.
滇西昌宁─孟连带南部地层地质问题   总被引：4，自引：2，他引：4  
吴浩若  杜越 《地层学杂志》1994,18(3):221-227
滇西孟连以南，整合于南段组浊积岩之上的拉巴群硅质岩含晚二叠世早期放射虫化石，南段组时代不仅限于石炭纪，可能延入二叠纪。二者为晚古生代思茅地块的外陆坡沉积。其西面的南基河杂岩（新名）由层序混乱的晚古生代硅质岩、泥岩和少量砂岩、玄武岩构成。放射虫化石证据表明，硅质岩时代不仅限于晚泥盆世－早二叠世，还延入晚二叠世，而有的砂岩时代为早石炭世，它们是经过强烈构造变动的古特提斯洋的沉积记录。昌宁－孟连带向南可能延至泰国北部的清迈带，而非东北部的难河带。  相似文献   

13.
The northern part of the Tasman Fold Belt System in Queensland comprises three segments, the Thomson, Hodgkinson- Broken River, and New England Fold Belts. The evolution of each fold belt can be traced through pre-cratonic (orogenic), transitional, and cratonic stages. The different timing of these stages within each fold belt indicates differing tectonic histories, although connecting links can be recognised between them from Late Devonian time onward. In general, orogenesis became younger from west to east towards the present continental margin. The most recent folding, confined to the New England Fold Belt, was of Early to mid-Cretaceous age. It is considered that this eastward migration of orogenic activity may reflect progressive continental accretion, although the total amount of accretion since the inception of the Tasman Fold Belt System in Cambrian time is uncertain.The Thomson Fold Belt is largely concealed beneath late Palaeozoic and Mesozoic intracratonic basin sediments. In addition, the age of the more highly deformed and metamorphosed rocks exposed in the northeast is unknown, being either Precambrian or early Palaeozoic. Therefore, the tectonic evolution of this fold belt must remain very speculative. In its early stages (Precambrian or early Palaeozoic), the Thomson Fold Belt was probably a rifted continental margin adjacent to the Early to Middle Proterozoic craton to the west and north. The presence of calc-alkaline volcanics of Late Cambrian Early Ordovician and Early-Middle Devonian age suggests that the fold belt evolved to a convergent Pacific-type continental margin. The tectonic setting of the pre-cratonic (orogenic) stage of the Hodgkinson—Broken River Fold Belt is also uncertain. Most of this fold belt consists of strongly deformed, flysch-type sediments of Silurian-Devonian age. Forearc, back-arc and rifted margin settings have all been proposed for these deposits. The transitional stage of the Hodgkinson—Broken River Fold Belt was characterised by eruption of extensive silicic continental volcanics, mainly ignimbrites, and intrusion of comagmatic granitoids in Late Carboniferous Early Permian time. An Andean-type continental margin model, with calc-alkaline volcanics erupted above a west-dipping subduction zone, has been suggested for this period. The tectonic history of the New England Fold Belt is believed to be relatively well understood. It was the site of extensive and repeated eruption of calc-alkaline volcanics from Late Silurian to Early Cretaceous time. The oldest rocks may have formed in a volcanic island arc. From the Late Devonian, the fold belt was a convergent continental margin above a west-dipping subduction zone. For Late Devonian- Early Carboniferous time, parallel belts representing continental margin volcanic arc, forearc basin, and subduction complex can be recognised.A great variety of mineral deposits, ranging in age from Late Cambrian-Early Ordovician and possibly even Precambrian to Early Cretaceous, is present in the exposed rocks of the Tasman Fold Belt System in Queensland. Volcanogenic massive sulphides and slate belt-type gold-bearing quartz veins are the most important deposits formed in the pre-cratonic (orogenic) stage of all three fold belts. The voicanogenic massive sulphides include classic Kuroko-type orebodies associated with silicic volcanics, such as those at Thalanga (Late Cambrian-Early Ordovician. Thomson Fold Belt) and at Mount Chalmers (Early Permian New England Fold Belt), and Kieslager or Besshi-type deposits related to submarine mafic volcanics, such as Peak Downs (Precambrian or early Palaeozoic, Thomson Fold Belt) and Dianne. OK and Mount Molloy (Silurian—Devonian, Hodgkinson Broken River Fold Belt). The major gold—copper orebody at Mount Morgan (Middle Devonian, New England Fold Belt), is considered to be of volcanic or subvolcanic origin, but is not a typical volcanogenic massive sulphide.The most numerous ore deposits are associated with calc-alkaline volcanics and granitoid intrusives of the transitional tectonic stage of the three fold belts, particularly the Late Carboniferous Early Perman of the Hodgkinson—Broken River Fold Belt and the Late Permian—Middle Triassic of the southeast Queensland part of the New England Fold Belt. In general, these deposits are small but rich. They include tin, tungsten, molybdenum and bismuth in granites and adjacent metasediments, base metals in contact meta somatic skarns, gold in volcanic breccia pipes, gold-bearing quartz veins within granitoid intrusives and in volcanic contact rocks, and low-grade disseminated porphyry-type copper and molybdenum deposits. The porphyry-type deposits occur in distinct belts related to intrusives of different ages: Devonian (Thomson Fold Belt), Late Carboniferous—Early Permian (Hodgkinson—Broken River Fold Belt). Late Permian Middle Triassic (southeast Queensland part of the New England Fold Belt), and Early Cretaceous (northern New England Fold Belt). All are too low grade to be of economic importance at present.Tertiary deep weathering events were responsible for the formation of lateritic nickel deposits on ultramafics and surficial manganese concentrations from disseminated mineralisation in cherts and jaspers.  相似文献   

14.
On the basis of geological observations and the study of conodont and radiolarian microfauna, a new stratigraphic scheme was proposed for the Mesozoic deposits of the Komsomolsk district of the Amur region. The lower Khorpy Group (T2-J3) consists of two units: the Boktor (T2-J2) and Kholvasi (J2–3). The Boktor Sequence (400 m thick) is represented by pelagic cherts with an admixture of cherty-clayey shales and volcanic rocks. The Kholvasi Sequence (500 m thick) is built up of the predominant siltstones and clayey shales with rare intercalations and lenses of clayey cherts and cherty-clayey shales. The upper Komsomolskaya Group (K1) has a terrigenous composition and includes the Gorin, Pionerskaya, and Pivan formations of 5 km total thickness. It is made up of intercalated sandstones, siltstones, mudstones, and often turbidites (proximal to distal). The rocks contain abundant buchia fauna of Volgian-Valanginian age, as well as carbonized plant detritus and flora of the Early Cretaceous habit. The described complex is characterized by a nappe-fold structure typical of the accretionary prisms in the ocean-continent convergence zones. The predominance of the coherent type of accretionary prisms reflects the simple morphology of the oceanic plate.  相似文献   

15.
Gabbroic bodies in the Bralorne-Gold Bridge area of southwestern British Columbia are associated with the oceanic Bridge River complex of the western Canadian Cordillera, one of the suspect terranes accreted to North America in the Jurassic. The gabbros are locally cut by tonalites and are structurally interleaved with ultramafic rocks, phyllites, graphitic cherts, and carbonate lenses that comprise the lower part of the Bridge River complex. Their late Carboniferous crystallization age overlaps the depositional age of affiliated supracrustal rocks (Mississippian-Jurassic), some of which have been metamorphosed to blueschist facies. Compositionally, the gabbros resemble mafic plutonic rocks of ophiolitic complexes and gabbroic rocks of the nearby Shulaps Range. They display some affinity to oceanic island arc tholeiitic suites. The Bralorne and Shulaps gabbros include cumulates and appear to have been derived from a single, light REE-depleted, peridotitic source by melting and subsequent fractional crystallization/accumulation of various combinations of plagioclase, pyroxenes, and olivine. The tonalites are compositionally distinct from typical ophiolitic plagiogranites, but might be related to the associated gabbros. The gabbroic bodies occur within tectonic slivers derived from the oceanic crust that floored a deep ocean basin that existed during the late Paleozoic and early Mesozoic. The Bridge River complex comprises fragments of oceanic crust that were tectonically incorporated into an east-verging accretionary prism during a middle/late Triassic to Jurassic collisional event.  相似文献   

16.
浙江白垩系上部地层的划分与对比   总被引：13，自引：5，他引：13  
浙江白垩系上部地层可划分为永康群、天台群和衢江群 ,长期以来 ,认为天台群和衢江群不整合覆于永康群之上。通过对代表性盆地岩石地层层序、古生物、同位素年龄资料的综合分析 ,发现三个群的下部地层 (馆头组、中戴组和天台盆地的塘上组 )为下白垩统 ,上部为上白垩统 ;天台盆地塘上组与仙居盆地小平田组为同物异名的早白垩世晚期火山岩层 ,覆于小平田组之上的“塘上组”是两头塘组的下部层位 ;永康生物群和衢江生物群的主要生物化石时代分别为早白垩世晚期和晚白垩世早期 ,但就两个生物群所涵盖的永康群和衢江群生物化石总体而言 ,其时代均应为早白垩世晚期至晚白垩世早期。永康群、天台群和衢江群是早白垩世晚期至晚白垩世时期的同期异相堆积 ,不存在相互叠覆关系。  相似文献   

17.
Alternating radiolarian cherts and mudstones associated with basaltic lavas occur in a olistolith within the Late Cretaceous Bornova Flysch in W Anatolia. Cherts yielded diverse and moderately preserved, Nassellaria-dominated radiolarian faunas of late Bathonian-early Callovian age. Associated volcanic rocks are geochemically classified as remnants of oceanic seamounts. This is so far the first late Middle Jurassic age from the crust of the Neotethyan Izmir-Ankara Ocean in W Anatolia, and suggests that its spreading started earlier. Similar ages were reported from the Vardar and Meliata-Hallstadt Tethyan oceanic branches in Greece and Serbia, which also opened in Late Triassic but closed earlier. Published in Russian in Stratigrafiya. Geologicheskaya Korrelyatsiya, 2009, Vol. 17, No. 3, pp. 70–80. The article is published in the original.  相似文献   

18.
New age and structural data are reported for the siliceous-volcanogenic complexes developed in the lower reaches of the Ussuri River. These complexes, which were previously treated as one stratigraphic unit, are subdivided into the Snarsky tectonostratigraphic complex (end of the Middle Jurassic-Middle Aptian) and the basaltic sequence (supposedly, Campanian-Maastrichtian). The Snarsky Complex is made up of basic volcanics, cherts, siliceous-clayey rocks, as well as subordinate limestones, sandstones, and conglomerates. Its distinctive features are the large amounts of genetically diverse basalts, the abundance of volcanomictic and pyroclastic material in siliceous-clayey rocks, the absence of fragmental rocks typical of the continental convergent zone, and the facies heterogeneity of the deposits. The complex is considered to be the southwestern continuation of the Kiselevka-Manoma terrane. Its origin is presumably related to the tectonic piling of genetically heterogeneous assemblages. The basaltic sequence includes basalts, basaltic andesites, their tuffs, and tuff conglomerates. The tuff conglomerates contain numerous fragments of granites and garnet-bearing felsic volcanics. The sequence was formed on the crystalline paleocontinental basement in the Late Cretaceous.  相似文献   

19.
冰沟蛇绿混杂岩是阿尔金山红柳沟蛇绿混杂岩带的东段部分,岩石组合包括蛇纹岩、方辉橄榄岩、辉石岩和辉长岩等。蛇纹岩具高Mg,Mg/Fe值大于9,低Al、Ca、Na、K为特征,从稀土元素和微量元素特征来看,基性辉长岩和洋壳以及洋中脊玄武岩极为相似,而超基性岩与原始地幔较为接近。辉长岩获得锆石SHRIMP年龄为449.5±10.9Ma。蛇绿混杂岩的围岩为一套巨厚的碎屑岩、火山碎屑岩、火山岩,以及部分碳酸盐岩构成,其中含有具有洋中脊特征的枕状构造玄武岩,以及放射虫硅质岩,放射虫时代为奥陶纪中晚期,与辉长岩的SHRIMP年龄一致。这些证据进一步证实了红柳沟一带存在早古生代洋盆的地质事实。  相似文献   

20.
The model of geological structure of sedimentary cover of the Laptev Sea accepted by most geologists suggests that the lower seismic complex of the cover begins by the Aptian–Albian sedimentary rocks. They can be studied in natural outcrops of Kotelnyi Island. The section of the Tuor-Yuryakh Trough, which exposes the lower part of the Cretaceous complex, is described in the paper. It is composed of continental coaliferous rocks ~100 m thick. The marking beds divide it into five members, which are traced along the western wall of the trough at the distance up to 3 km. The spore–pollen complexes and plant megafossils indicate that almost the entire visible section of the mid-Cretaceous is Albian. Only its lower part no more than 14 m thick can probably belong to the Aptian. Marine facies with Albian foraminifers were found 15 m above the bottom of the Cretaceous complex. The section of the Cretaceous rocks is underlain by the Lower Jurassic marine clays and siltstones. The foraminifer assemblages of this part of the section are typical of the upper Sinemurian–Pliensbachian and fossil bivalves indicate late Sinemurian age of the host rocks. The hiatus ~70 Ma duration has no expression in the section and this boundary can de facto be substantiated only by microfossils. This vague contact between the Lower Jurassic and mid-Cretaceous rocks does not correspond to geophysical characteristics of the bottom of the lower seismic complex of the cover of the eastern part of the Laptev Sea. The latter is described as the most evident seismic horizon of the section of the cover, suggesting unconformable occurrence of the lower seismic complex on a peneplenized surface of lithified and dislocated rocks. This is mostly similar to the bottom of the Eocene sediments, which were observed on Belkovsky and Kotelnyi islands. The paper discusses possible application of our land results for interpretation of the shelf seismic sections of the Laptev Sea. It is concluded that local reasons are responsible for a vague boundary between the Lower Jurassic and mid-Cretaceous sequences in the section studied. Our observations support ideas on possible Aptian–Albian age of the rocks of the basement of the lower seismic complex; however, it is proposed to use also the previously popular idea on the Eocene age of the lower seismic complex of sedimentary cover of the eastern part of the Laptev Sea as one of the possible working scenarios.  相似文献   

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