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 31 毫秒
1.
Two new Permian‐aged formations ‘Kariz Now Formation’ and ‘Aliyak Formation’ are proposed for a 65–150 m‐thick succession in the Kariz Now area, with the type section for both (79.5 m thick) located 9 km northeast of Aliyak village ca. 100 km southeast of Mashhad city, northeastern Iran. The lower Kariz Now Formation is composed of siliciclastics. The age of this Formation is poorly constrained but its correlation with the Shah Zeid Formation in the Central Alborz suggests a possible Asselian‐Hermagorian age for the Kariz Now Formation, which implies a hiatus of Yakhtashian–mid Midian (Artinskian–mid Capitanian) age between the siliciclastics of the Kariz Now Formation and carbonates of the disconformably overlying Aliyak Formation. There is also the possibility of a potential correlation of this Formation with the Kungurian Faraghan Formation in the Zagros area. The succeeding Aliyak Formation is mostly composed of carbonate rocks capped by a thin basaltic lava flow. The Aliyak Formation is unconformably overlain by dolostones that are correlated with the Middle Triassic Shotori Formation. Samples were collected from the Kariz Now and Aliyak formations, but fossils were only recovered from the Aliyak Formation. These include calcareous algae, small foraminiferans, fusulinids, crinoid stems and brachiopods. The recovered fusulinid assemblage from the Aliyak Formation is consistent with that of the upper Capitanian Monodiexodina kattaensis–Codonofusiella erki and Afghanella schencki–Sumatrina brevis zones of the Zagros Mountains and with the upper part of the Ruteh Fm in the Alborz Mountains. Although not radiometrically dated, the basaltic lava flow most probably corresponds to similar basaltic lava flows occurring in the uppermost part of the Ruteh Formation in Central Alborz. Thus, the Permian in the studied region developed in a basin that extended westward as far as the Central Alborz. A late Capitanian age for the Aliyak Formation implies it correlates with the Capitanian KS5 in Al Jabal Al‐Akhdar in Oman, with Aliyak Unit 5 potentially representing the Permian maximum flooding surface MFS P25. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

2.
Data on the composition, inner structure, and magma sources of giant batholith in the Central Asian Orogenic Belt are analyzed with reference to the Khangai batholith. The Khangai batholith was emplaced in the Late Permian–Early Triassic (270–240 Ma) and is the largest accumulations (>150000 km2) of granite plutons in central Mongolia. The plutons are dominated by granites of normal alkalinity and contain subalkaline granites and more rare alkaline granites. The batholith is hosted in the Khangai zonal magmatic area, which consists of the batholith itself and surrounding rift zones. The zones are made up of bimodal basalt–trachyte–comendite (pantellerite) or basalt-dominated (alkaline basalt) volcanic associations, whose intrusive rocks are dominated by syenite and granite, granosyenite, and leucogranite. Both the batholith and the rift zones were produced within the time span of 270–240 Ma. Although the rocks composing the batholith and its rift surroundings are different, they are related through a broad spectrum of transitional varieties, which suggests that that the mantle and crustal melts could interact at various scale when the magmatic area was produced. A model is suggested to explain how the geological structure of the magmatic area and the composition of the magmatic associations that make up its various zones were controlled by the interaction between a mantle plume and the lithospheric folded area. The mantle melts emplaced into the lower crust are thought to not only have been heat sources and thus induced melting but also have predetermined the variable geochemical and isotopic characteristics of the granitoids. In the marginal portions of the zonal area, the activity of the mantle plume triggered rifting associated with bimodal and alkaline granite magmatism. The formation of giant batholiths was typical of the evolution of the active continental margin of the Siberian paleocontinent in the Late Paleozoic and Early Mesozoic: the Khangai, Angara–Vitim, and Khentei batholiths were formed in this area within a relatively brief time span between 300 and 190Ma. The batholiths share certain features: they consist of granitoids of a broad compositional range, from tonalite and plagiogranite to granosyenite and rare-metal granites; and the batholiths were produced in relation to rifting processes that also formed rift magmatic zones in the surroundings of the batholiths. The large-scale and unusual batholith-forming processes are thought to have occurred when the active continental margin of the Late Paleozoic Siberian continent overlapped a number of hotspots in the Paleo- Asian Ocean. This resulted in the origin of a giant anorogenic magmatic province, which included batholiths, flood-basalt areas in Tarim and Junggar, and the Central Asian Rift System. The batholiths are structural elements of the latter and components of the zonal magmatic areas.  相似文献   

3.
The Solonker suture zone has long been considered to mark the location of the final disappearance of the PaleoAsian Ocean in the eastern Central Asian Orogenic Belt(CAOB). However, the time of final suturing is still controversial with two main different proposals of late Permian to early Triassic, and late Devonian. This study reports integrated wholerock geochemistry and LA-ICP-MS zircon U-Pb ages of sedimentary rocks from the Silurian Xuniwusu Formation, the Devonian Xilingol Complex and the Permian Zhesi Formation in the Hegenshan-Xilinhot-Linxi area in central Inner Mongolia, China. The depositional environment, provenance and tectonic setting of the Silurian-Devonian and the Permian sediments are compared to constrain the tectonic evolution of the Solonker suture zone and its neighboring zones. The protoliths of the silty slates from the Xuniwusu Formation in the Baolidao zone belong to wacke and were derived from felsic igneous rocks with steady-state weathering, poor sorting and compositional immaturity. The protoliths of metasedimentary rocks from the Xilingol Complex were wackes and litharenites and were sourced from predominantly felsic igneous rocks with variable weathering conditions and moderate sorting. The Xuniwusu Formation and Xilingol Complex samples both have two groups of detrital zircon that peak at ca. 0.9–1.0 Ga and ca. 420–440 Ma, with maximum deposition ages of late Silurian and middle Devonian age, respectively. Considering the ca. 484–383 Ma volcanic arc in the Baolidao zone, the Xuxiniwu Formation represents an oceanic trench sediment and is covered by the sedimentary rocks in the Xilingol Complex that represents a continental slope sediment in front of the arc. The middle Permian Zhesi Formation metasandstones were derived from predominantly felsic igneous rocks and are texturally immature with very low degrees of rounding and sorting, indicating short transport and rapid burial. The Zhesi Formation in the Hegenshan zone has a main zircon age peak of 302 Ma and a subordinate peak of 423 Ma and was deposited in a back-arc basin with an early marine transgression during extension and a late marine regression during contraction. The formation also crops out locally in the Baolidao zone with a main zircon age peak of 467 Ma and a minor peak of 359 Ma, and suggests it formed as a marine transgression sedimentary sequence in a restricted extensional basin and followed by a marine regressive event. Two obvious zircon age peaks of 444 Ma and 280 Ma in the Solonker zone and 435 Ma and 274 Ma in Ondor Sum are retrieved from the Zhesi Formation. This suggests as a result of the gradual closure of the Paleo-Asian Ocean a narrow ocean sedimentary environment with marine regressive sedimentary sequences occupied the Solonker and Ondor Sum zones during the middle Permian. A restricted ocean is suggested by the Permian strata in the Bainaimiao zone. Early Paleozoic subduction until ca. 381 Ma and renewed subduction during ca. 310–254 Ma accompanied by the opening and closure of a back-arc basin during ca. 298–269 Ma occurred in the northern accretionary zone. In contrast, the southern accretionary zone documented early Paleozoic subduction until ca. 400 Ma and a renewed subduction during ca. 298–246 Ma. The final closure of the Paleo-Asian ocean therefore lasted at least until the early Triassic and ended with the formation of the Solonker suture zone.  相似文献   

4.
The closure of Palaeotethys that led to the collision of the Cimmerian blocks with the southern Eurasian margin causing the Eo-Cimmerian orogeny during the Early Mesozoic is still controversially discussed. The Triassic Nakhlak Group in Central Iran is a key sedimentary succession for better understanding the closure of Palaeotethys and the Eo-Cimmerian orogeny in the Middle East. The Nakhlak Group is composed of the Alam (Olenekian to Middle Anisian), Baqoroq (?Upper Anisian to Middle Ladinian) and Ashin (Upper Ladinian to ?Carnian) formations, which consist mainly of volcaniclastic sandstones, mixed siliciclastic conglomerates, and marine carbonates. Here we present for the first time detrital zircon UPb ages from the Nakhlak Group to unravel its provenance and constrain its palaeotectonic position within the Palaeotethyan realm. Most detrital zircons from the Nakhlak Group are euhedral and subhedral with Permian–Triassic ages (ca. 280–240 Ma) suggesting sediment supply from Permian–Triassic magmatic rocks of the Silk Road Arc. Minor zircon populations show pre-Permian Palaeozoic ages, with age peaks at ca. 320 Ma and 480 Ma, which are probably derived from the basement on which the magmatic arc developed. Neoproterozoic–latest Mesoproterozoic (ca. 550–1100 Ma) and Palaeoproterozoic (ca. 1800–2200 Ma) zircon grains are anhedral (rounded). The latter are prominent in the upper Baqoroq Formation (Middle Ladinian) suggesting recycling of older sedimentary rocks. Sandstone petrography points toward an additional metamorphic provenance for this formation. This short-lived provenance change can be explained by tectonic uplift in the source area that led to erosion of metamorphosed rocks with a northeast Gondwanan affinity. It clearly indicates that northeast Gondwana-derived continental fragments likely belonging to the Cimmerian blocks already arrived at the southern Eurasian margin in pre-Late Triassic time. Current palaeotectonic models of the closure of Palaeotethys and the Eo-Cimmerian orogeny in the Middle East during the Triassic may need to be revised.  相似文献   

5.
藏北羌塘果干加年山的东部出露有一处花岗岩岩体,其主要岩性为黑云母二长花岗岩和花岗细晶岩岩脉,侵入晚三叠世望湖岭组和晚石炭世—早二叠世展金岩群之中。锆石LA-ICP-MS U-Pb年龄测定结果表明,该花岗岩的形成时代为晚三叠世（210.3Ma±2.6Ma）,略晚于区域上高压变质带的变质峰期年龄和望湖岭组底部流纹岩的年龄。岩石地球化学数据显示,该花岗岩岩体属高钾钙碱性过铝质花岗岩,形成于后碰撞环境,是岩石圈碰撞加厚之后减压过程中岩浆活动的产物,说明在210Ma左右果干加年山地区的构造环境开始由碰撞阶段向板内阶段转化,进入了后碰撞阶段。  相似文献   

6.
胡培远  李才  杨韩涛  张海波  于红 《地质通报》2010,29(12):1825-1832
藏北羌塘果干加年山的东部出露有一处花岗岩岩体,其主要岩性为黑云母二长花岗岩和花岗细晶岩岩脉,侵入晚三叠世望湖岭组和晚石炭世—早二叠世展金岩群之中。锆石LA-ICP-MS U-Pb年龄测定结果表明,该花岗岩的形成时代为晚三叠世(210.3Ma±2.6Ma),略晚于区域上高压变质带的变质峰期年龄和望湖岭组底部流纹岩的年龄。岩石地球化学数据显示,该花岗岩岩体属高钾钙碱性过铝质花岗岩,形成于后碰撞环境,是岩石圈碰撞加厚之后减压过程中岩浆活动的产物,说明在210Ma左右果干加年山地区的构造环境开始由碰撞阶段向板内阶段转化,进入了后碰撞阶段。  相似文献   

7.
南祁连盆地在晚三叠世时期处于陆相沉积,上三叠统阿塔寺组碎屑岩十分发育。盆地三叠系砂岩的岩性及岩相特征与二叠系非常相似,但是源岩构造背景、物质组成及物质来源与二叠系有所差异。根据地球化学主量元素、微量元素分析结果,上三叠统阿塔寺组源岩构造背景活动性较强,以活动性较强的大陆岛弧及活动大陆边缘为主,源岩物质组成以长英质火成岩为主。结合区域地质构造背景判断,南祁连盆地上三叠统阿塔寺组沉积物源区以北物源为主,以南物源为辅,中祁连的前震旦系及下古生界变质结晶岩系及花岗岩为其主要物源。  相似文献   

8.
The thrust nappe played an important role in the Mesozoic tectonic evolution of the middle part of the Central Asian Orogenic Belt(CAOB). However, the timing, structural style and kinematic processes of the thrust nappe remain controversial, particularly the detail of the thrust nappe in the Guaizihu region(110 km east of Ejinaq). In this study, we investigate new field mapping, seismic sections, geochronology and low-temperature thermochronometric dating to provide constraints on the history of...  相似文献   

9.
The Alpine Haselgebirge Formation represents an Upper Permian to Lower Triassic evaporitic rift succession of the Northern Calcareous Alps (Eastern Alps). Although the rocksalt body deposits are highly tectonised, consisting mainly of protocataclasites and mylonites of halite and mudrock, the early diagenetic history can be established from non-tectonised mudrock bodies: Cm-sized euhedral halite hopper crystals formed as displacive cubes within mud just during shallow burial. The crystals were deformed by subsequent compaction. Later, migrating fluids led to the replacement of halite by anhydrite retaining the shapes of deformed halite cubes. Polyhalite formed from subsequent enhanced fluid migration. Mudrock provided water by dewatering, while potassium and magnesium were dissolved from primary salt minerals. When these fluids interacted with sulphates, polyhalite precipitated. 40Ar/39Ar analyses date the polyhalite from within the retaining shapes of deformed halite hopper-shaped cubes from two localities to ca. 235–232 Ma (Middle Triassic). At this time, ca. 20–25 Ma after sedimentation, polyhalite crystallised at shallow levels.  相似文献   

10.
The Kuznetsk Basin is located in the northern part of the Altai–Sayan Folded Area (ASFA), southwestern Siberia. Its Late Permian–Middle Triassic section includes basaltic stratum-like bodies, sills, formed at 250–248 Ma. The basalts are medium-high-Ti tholeiites enriched in La. Compositionally they are close to the Early Triassic basalts of the Syverma Formation in the Siberian Flood basalt large igneous province, basalts of the Urengoi Rift in the West Siberian Basin and to the Triassic basalts of the North-Mongolian rift system. The basalts probably formed in relation to mantle plume activity: they are enriched in light rare-earth elements (LREE; Lan = 90–115, La/Smn = 2.4–2.6) but relatively depleted in Nb (Nb/LaPM = 0.34–0.48). Low to medium differentiation of heavy rare-earth elements (HREE; Gd/Ybn = 1.4–1.7) suggests a spinel facies mantle source for basaltic melts. Our obtained data on the composition and age of the Kuznetsk basalts support the previous idea about their genetic and structural links with the Permian–Triassic continental flood basalts of the Siberian Platform (Siberian Traps) possibly related to the activity of the Siberian superplume which peaked at 252–248 Ma. The abruptly changing thickness of the Kuznetsk Late Permian–Middle Triassic units suggests their formation within an extensional regime similar to the exposed rifts of Southern Urals and northern Mongolia and buried rifts of the West Siberian Basin.  相似文献   

11.
Abstract

This article reports the depositional environment and provenance for the Tianquanshan Formation in the Longmuco–Shuanghu–Lancangjiang suture zone, and uses these to better understand the tectonic evolution of this region. Zircons in the andesite of the Tianquanshan Formation yielded concordia ages of 246, 247, and 254 Ma, indicating that the Tianquanshan Formation formed during the late Permian–Early Triassic. The Tianquanshan Formation consists of flysch and ocean island rock assemblages, indicating that the Longmuco–Shuanghu–Lancangjiang Palaeo-Tethys Ocean continued to exist as a mature ocean in the late Permian–Early Triassic. The detrital zircons in the greywackes of the Tianquanshan Formation yielded peak ages of 470–620, 710–830, 910–1080, 1450–1660, and 2400–2650 Ma, indicating the provenance of the Tianquanshan Formation was either Indian Gondwana or terranes that have an affinity with Indian Gondwana in the Tibetan Plateau (i.e. the Southern Qiangtang, Lhasa, and Himalayan terranes). The Ordovician quartzites, Carboniferous sandstones, Carboniferous–Permian diamictites, and the Upper Permian–Lower Triassic greywackes in the Southern Qiangtang, Lhasa, and Himalayan terranes all contain detrital zircons with youngest ages of ca. 470 Ma, indicating their source areas have been in a stable tectonic environment since the Ordovician, and this inference is supported by the continuous deposition in a littoral–neritic passive margin in these regions from the Ordovician to the lower Permian. Combining the present results with regional geological data, we infer that the Southern Qiangtang, Lhasa, and Himalayan terranes were all in a stable passive continental margin along the northern part of Indian Gondwana during the long period from the Ordovician to the early Permian. At early Permian, because of the opening of the Neo-Tethys Ocean, the tectonic framework of this region underwent a marked change to a rifting and active environment.  相似文献   

12.
A suite of the fossil-rich marine-land interbedded strata(Nanshuangyashan Formation) is distributed at the eastern margin of the Jiamusi massif in the eastern Heilongjiang Province, NE China. The authors had recently discovered a suite of arkose beneath the marine-land interbedded strata, which overlays unconformably on the Permain granite in the eastern margin of the Jiamusi massif. The LA-ICP-MS zircon U-Pb dating indicate that all detrital zircons from the analysed four arkose samples show the four population ages of 800 Ma, 538–481 Ma, 269–250 Ma and 223–215 Ma. The former three population ages are widely recorded in the Jiamusi-Khanka massif and the Songnen massif. The later group is the minimal age population in the analyzed samples, limiting the sedimentation time of the arkoses occurred after the Late Triassic. At present, the minimal age population is not recorded in the Jiamusi massif, but the granites with the ages of 228–210 Ma are widely distributed in the Songnen-Zhangguangcai Range massif and the Khanka massif. The predominantly Permian zircons are characterized by oscillatory zoning and euhedral shapes, with variable zircon ε_(Hf)(t) values(-5.5 to +11.2), indicating that they were derived from mixture sources, possibly mixed with components of the Songnen-Zhangguangcai Range massif and the Jiamusi-Khanka massif. These results, combined with regional analyses, indicate that the closing of Mudanjiang ocean and Panthalassa ocean possibly existed from Early Permian to Late Triassic.  相似文献   

13.
ABSTRACT

The Upper Triassic Langjiexue Group, which lies immediately south of the Yarlung-Tsangpo Suture Zone in the Shannan area of southeastern Tibet, represents an important part of the Tethyan Himalayan Sequence (THS). Its provenance and palaeogeography have been the subject of debate. We present new data on petrographic composition, whole-rock geochemistry, and detrital zircon U–Pb geochronology to constrain the provenance of the Langjiexue Group. The dominance of quartz grains and felsic volcanic lithic fragments suggests that the sandstones are litho-quartzose. The trace element geochemical signatures (V–Ni–Th*10, Co/Th–La/Sc, Eu/Eu*–Th/Sc) suggest derivation from felsic igneous sources. The detrital zircon age spectra display three major peaks: a Meso-to-Neoproterozoic peak (1200–900 Ma, 7–18%), a Neoproterozoic-to-Late Cambrian peak (750–500 Ma, 32–65%), and a Late Carboniferous-to-Late Triassic peak (300–200 Ma, 11–33%). The maximum depositional age of early Carnian (236–235 Ma) is obtained by calculating weighted average ages of the youngest zircons (≤250 Ma). The youngest age cluster (300–200 Ma) is incompatible with sources from neighbouring terranes, including the South Qiangtang terrane, Lhasa terrane, THS, and Higher Himalayan Crystalline. Correlations of the Permian–Triassic zircons with those of time-equivalent strata in northwest Australia, west Burma, and the Banda Arc unveil a potential connection to the Tasmanides along the convergent margin of eastern Australia. The New England Orogen (300–230 Ma) could have supplied the Langjiexue Group with magmatic materials via continent-scale drainage systems or a submarine fan complex. This scenario provides a new perspective into the transport of detritus from distal orogens to sedimentary basins thousands of kilometres away.  相似文献   

14.
In Central Iran, the mixed siliciclastic?carbonate Nakhlak Group of Triassic age is commonly seen to have a Cimmerian affinity, although it shows considerable resemblances with the Triassic Aghdarband Group in far northeastern Iran, east of Kopeh-Dagh area, with Eurasian affinity. The Nakhlak Group is composed of the Alam (Late Olenekian?Anisian), Baqoroq (Late Anisian??Early Ladinian), and Ashin (Ladinian??Early Carnian) formations consisting mainly of volcanoclastic sandstone and shale and fossiliferous limestone. The Baqoroq Formation contains also metamorphic detritus. Sandstone petrofacies reflect the detrital evolution from active volcanism to growing orogen and again active volcanism. Textural and modal analyses of volcanic lithic fragments from the Alam Formation reflect the eruption style and magma composition of a felsic to intermediate syn-sedimentary arc activity. The detrital modes of the Baqoroq Formation sediments suggest a recycled orogenic source followed by arc activity in a remnant fore-arc basin. The sandstone samples from the Ashin Formation demonstrate a continuity of felsic to intermediate arc activity. Major and trace element concentrations of the Nakhlak Group clastic samples support sediment supply from first-cycle material and felsic magmatic arc input. The enrichment in LREE, the negative Eu anomalies, and the flat HREE patterns indicate origination from the old upper continental crust and young arc material. The chemical index of alteration (CIA ～51–70 for sandstone and 64–76 for shale samples) indicates medium degrees of chemical weathering at the source. Petrographical and geochemical evidence together with facies analysis constructed the following depositional conditions for the Nakhlak Group sediments: In the Olenekian, a fore-arc shallow to deep marine depositional basin developed that later was filled by recycled and arc-related detritus and changed into a continental basin in the Anisian. Ladinian extension let to a deepening of the basin. With respect to the similarities between the Nakhlak and Aghdarband (NE Iran) groups and unusual present-day position of the Nakhlak Group with no stratigraphic connection to the surrounding area, the development of first a fore-arc basin and later change into a back-arc depositional basin in close relation with the Aghdarband basin at the southern Eurasian active margin in the Triassic are here proposed. Understanding the basin development recorded in the Nakhlak Group provides constraints on the closure history of Palaeotethys and of the tectonic evolution of early Mesozoic basins at the southern Eurasian margin before the Cimmerian Orogeny.  相似文献   

15.
黄云飞  张昌民  朱锐  易雪斐  瞿建华  唐勇 《地球科学》2017,42(10):1736-1749
二叠纪-三叠纪之交重大地质转折期,海相地质记录指示全球发生了一系列显著的生物和环境事件, 但是,该时期陆相古气候、古风化作用等方面的研究还很薄弱,争议较大.为了恢复新疆准噶尔盆地玛湖凹陷上二叠统乌尔禾组至中三叠统克拉玛依组的古气候、物源特征等, 本研究对玛湖凹陷钻井岩心中的泥岩样品开展了全岩主量和微量元素测试,采用多种化学风化指数判定源区风化程度及古气候条件,通过多种地球化学比值及图解来恢复源岩岩性及其构造背景.化学蚀变指数(Chemical Index of Alteration, CIA)、化学风化指数(Chemical Index of Weathering, CIW)、Parker风化指数(Weathering Index of Parker, WIP)和斜长石蚀变指数(Plagioclase Index of Alteration, PIA)等多种化学风化作用指标均指示,玛湖凹陷自晚二叠世至早三叠世发生显著的风化作用变化,由低等程度的化学风化作用转变为中等程度的化学风化作用,某些季节可能会较为温暖湿润,且在整个早三叠世保持大致稳定,在早三叠世晚期稍减弱,这与锶同位素反映的全球风化作用变化趋势一致.中三叠世时的化学风化作用与早三叠世相比,并未降低,反而稍有增加,这可能代表了地区性事件.早三叠世化学风化作用显著增强的原因可能在于全球变暖、植被破坏及季节性降雨增加等.此外,上二叠统乌尔禾组至中三叠统克拉玛依组的物源岩性主要为长英质火成岩,源岩形成时的构造背景可能为大洋岛弧环境.   相似文献   

16.
四川盆地中三叠统雷口坡组勘探已近40年,但迄今为止只发现了两个大中型气藏.近年来,雷口坡组钻井油气显示活跃,展示了良好的勘探前景.四川盆地中三叠统气藏储层主要位于底部雷一段、顶部雷三一雷四段,天然气主要来源于上二叠统龙潭组和上三叠统须家河组烃源岩,各气藏天然气组分特征也不尽相同,储集空间均以各类次生溶蚀孔隙为主,多为低...  相似文献   

17.
Late Olenekian assemblages in the western Panthalassa have been recovered from bedded radiolarian chert sequences of an accretionary complex, the Ashio belt. These faunas are documented and considered in terms of radiolarian diversity and faunal turnover during the latest Permian to Middle Triassic time. The fauna includes 30 radiolarians belonging to Spumellaria or Entactinaria, with two relicts from the Late Permian. This late Olenekian fauna is markedly different from Permian and Asisian faunas, respectively, and is herein named the Minowa fauna. Study of the literaure indicates that radiolarian provinces were significantly disconnected between the western Panthalassa and eastern Tethys during late Olenekian time. Furthermore, 121 of 143 species disappeared during late Olenekian time, and in turn 118 new species appeared in the western Panthalassa around the Olenekian-Anisian boundary. It is concluded that faunal turnover occurred at least three times between the latest Permian and Middle Triassic.The first turnover is the Poalaozoie-type radiolarian extinction at the Permain-Triassic boundary,the second is the diversification of spheroidal Spumellaria and Entactinaria between early and late Olenekian time, and the third is a faunal turnover from the Minowa fauna to the true Mesozoic-type radiolarian famas that are characterized by mulit0segmented Nassellaria.  相似文献   

18.
The Middle Permian to Lower Triassic Buday’ah section, exposed in the Oman Mountains, is the first deep-sea section to be described in the Neotethys. The oceanic sediments were deposited along the southern Tethys margin in the newly formed Hawasina Basin. It is one of the few places where true Tethyan Permian radiolarites are exposed that allow the documentation of CCD evolution through time. The succession begins as oceanic crust pillow basalt with red ammonoid-rich pelagic limestone occurring both above and within inter-pillow cavities; the new occurrence of Clarkina postbitteri hongshuiensis indicates a late Capitanian age for the carbonate. The sharp change to overlying late Capitanian to Changhsingian radiolarite reflects rapid subsidence about 10 Myrs after initial continental breakup that resulted in the formation of the Neotethys Ocean. New conodonts indicate that the Permian-Triassic boundary succession occurs in the first platy lime mudstone beds above a Changhsingian siliceous to calcareous shale unit. The platy lime mudstone beds include an Upper Griesbachian bloom of calcite filled spheres (radiolarians?) that marks a potential world-wide event. New conodonts indicate an early Olenekian age for overlying grey papery limestone that are devoid of both macrofossils and trace fossils indicating that recovery from the Late Permian extinction has not yet progressed within this deep-water environment.δ13Corg, isotope values have not been disturbed and they show a negative shift just below the Permian-Triassic transition and a second one at the parvus zone level above. The Buday’ah succession may represent the most distal and probably deepest Permian and Lower Triassic depositional sequence within the basin.  相似文献   

19.
Regional mapping (1:50,000) and U-Pb and K-Ar geochronology in the El Indio region refines the knowledge of the distribution, lithostratigraphy, and age of the sedimentary, volcanic, and intrusive rocks that comprise the regionally extensive Pastos Blancos Group which is equivalent to the Choiyoi Group of the Argentine Frontal Cordillera. The Pastos Blancos Group (which we elevate to Group status herein) includes at least two diachronous volcanic–sedimentary sequences: an older felsic volcanic and volcaniclastic unit, the Guanaco Sonso sequence, that is Permian in age, and a younger bimodal volcanic and volcaniclastic unit, the Los Tilos sequence that is Middle Triassic to Early Jurassic. Sedimentary rocks of the Los Tilos sequence are transitional upward into the overlying Early to Middle Jurassic shallow marine limestones of the Lautaro Formation.Intrusions that make up the regionally extensive Permian to Early Jurassic plutons of the Chollay and Elqui-Limarı́ batholiths that were previously mapped as a single plutonic association, the Ingaguás Complex, include in the El Indio region at least three discrete intrusive units. These include: Early Permian (280–270 Ma) biotite granites, Early to Middle Triassic (242–238 Ma) silica-rich leucocratic granites and rhyolitic porphyries that made up the bulk of the Chollay Batholith, and a younger Late Triassic–Early Jurassic unit (221–200 Ma) of mainly intrusive rhyolitic porphyries, extrusive domes, and subordinate mafic intrusions and both felsic and mafic dikes, which are coeval with volcanic rocks of the Los Tilos sequence.Our data show that latest Paleozoic to Early Jurassic intrusive, volcanic, and sedimentary rocks in the El Indio region of the High Andes of Chile between 29–30°S likely formed during extension driven processes after the cessation of Carboniferous–Early Permian subduction along the western edge of Gondwana. These processes began by Late Permian time, but instead of recording a single and protracted magmatic event, as has been previously suggested, rocks that belong to the Pastos Blancos Group and the Ingaguás Intrusive Complex record at least three discrete periods of silicic to bimodal magmatism which occurred during the Middle Permian to Early Jurassic interval.  相似文献   

20.
冀北三叠系二马营组分布于下板城—平泉一带,主要为一套河流相红色砂泥岩组合,时代原定为中三叠世。通过1∶5万区域地质调查,首次在二马营组上部发现凝灰岩夹层,并进行了LA-ICP-MS锆石U-Pb定年,获得其206Pb/238U年龄加权平均值为234.2±2.6Ma(MSWD=3.2),综合古生物化石、后期脉岩、地层接触关系等依据,将二马营组沉积时限重新厘定为中—晚三叠世。结合区域地质资料,认为冀北三叠系二马营组凝灰岩夹层的形成可能与西伯利亚板块与华北板块碰撞造山有关,该凝灰岩层作为有效的地质事件标志层,记录了当时构造背景下华北陆块北缘的一次火山活动。  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