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1.
Shenghui Deng Yuanzheng Lu Zhong Luo Ru Fan Xin Li Yi Zhao Xueying Ma Rukai Zhu Jingwei Cui 《中国科学:地球科学(英文版)》2018,61(10):1419-1439
The Yanchang Formation is extensively developed in the Ordos Basin and its surrounding regions. As one of the best terrestrial Triassic sequences in China and the major oil-gas bearing formations in the Ordos Basin, its age determination and stratigraphic assignment are important in geological survey and oil-gas exploration. It had been attributed to the Late Triassic and regarded as the typical representative of the Upper Triassic in northern China for a long time, although some scholars had already proposed that the lower part of this formation should be of the Middle Triassic age in the mid-late 20th century. In this paper, we suggest that the lower and middle parts of the Yanchang Formation should be of the Ladinian and the bottom possibly belongs to the late Anisian of the Middle Triassic, mainly based on new fossils found in it and high resolution radiometric dating results. The main source rocks, namely the oil shales and mudstones of the Chang-7, are of the Ladinian Age. The upper part of the Yanchang Formation, namely the Chang-6 and the above parts, belongs to the Late Triassic. The uppermost of the Triassic is missed in most parts of the Ordos Basin. The Middle-Upper Triassic Series boundary lies in the Yanchang Formation, equivalent to the boundary between Chang-7 and Chang-6. The Ladinian is an important palaeoenvironmental turning point in the Ordos Basin. Palaeoenvironmental changes in the basin are coincidence with that of the Sichuan Basin and the main tectonic movement of the Qinling Mountains. It indicates that tectonic activities of the Qinling Mountains are related to the big palaeoenvironmental changes in both the Ordos and Sichuan Basins, which are caused by the same structural dynamic system during the Ladinian. 相似文献
2.
A Middle to Late Triassic (Ladinian–Carnian) radiolarian fauna was discovered in cherts of the Situlanglang Member of the Garba Formation, South Sumatra, which is generally regarded as of Late Jurassic–Early Cretaceous age. This fauna is characterized by the presence of Annulotriassocampe sulovensis, Triassocampe postdeweveri, Spongotortilispinus tortilis, Poulpus piabyx, Canoptum levis and others. This evidence possibly indicates that the deposition of the Situlanglang cherts took place after the collision of the Sibumasu and East Malaya blocks recorded in the Bentong–Raub Suture in Peninsular Malaysia in Late Permian–Early Triassic times. During the Middle–Late Triassic Sumatra and Peninsular Malaysia consisted of submarine horst and graben structures. It is possible that a submarine graben, the Tuhur basin, whose southern boundary was formerly undefined, extends into South Sumatra, to the area in which the Situlanglang cherts were deposited. The Situlanglang Member is proposed to be a rock unit stratigraphically contemporaneous with those of the Middle–Upper Triassic Kualu and Tuhur Formations in North and Central Sumatra. 相似文献
3.
《中国科学:地球科学(英文版)》2015,(4)
Age determinations of the Triassic lithostratigraphic units of the Yanshan belt were previously based on plant fossils and regional correlations of lithologies. The Liujiagou and Heshanggou Formations were assigned as the Lower Triassic, and the Ermaying Formation was regarded as the Middle Triassic. We carried out a geochronologic study of detrital zircon grains from the Triassic sandstone in the Xiabancheng and Yingzi basins in northern Hebei where the Triassic strata are exceptionally well preserved. The results show that the Liujiagou, Heshanggou, and Ermaying Formations are all Late Triassic in age. The ages of detrital zircons also revealed that the upper part of the Shihezi Formation and the overlying Sunjiagou Formation, both of which were thought to be the Middle-Late Permian units, are actually late Early to Middle Triassic deposits. This study combines the upper Shihezi and Sunjiagou Formations into a single unit termed as the Yingzi Formation. We also substitute the widely-used Liujiagou, Heshanggou, and Ermaying Formations with the Dingjiagou, Xiabancheng, and Huzhangzi Formations, respectively. Field observations and facies analysis show that the top of the Shihezi Formation is an erosive surface, marking a parallel unconformity between the Middle Permian and Lower Triassic. The Yingzi Formation is composed mainly of meandering river deposits, indicative of tectonic quiescence and low-relief landform in the Early to Middle Triassic. In contrast, the Dingjiagou, Xiabancheng, and Huzhangzi Formations are interpreted as the deposits of sandy/gravelly braided rivers, alluvial fans, fan deltas, and deep lakes in association with volcanism, thus indicating an intense rifting setting. A new Triassic lithostratigraphic division is proposed according to age constraints and facies analysis, and the results are of significance for understanding the early Mesozoic tectonic evolution of the Yanshan belt. 相似文献
4.
Abstract The Sambosan accretionary complex of southwest Japan was formed during the uppermost Jurassic to lowermost Cretaceous and consists of basaltic rocks, carbonates and siliceous rocks. The Sambosan oceanic rocks were grouped into four stratigraphic successions: (i) Middle Upper Triassic basaltic rock; (ii) Upper Triassic shallow-water limestone; (iii) limestone breccia; and (iv) Middle Middle Triassic to lower Upper Jurassic siliceous rock successions. The basaltic rocks have a geochemical affinity with oceanic island basalt of a normal hotspot origin. The shallow-water limestone, limestone breccia, and siliceous rock successions are interpreted to be sediments on the seamount-top, upper seamount-flank and surrounding ocean floor, respectively. Deposition of the radiolarian chert of the siliceous rock succession took place on the ocean floor in Late Anisian and continued until Middle Jurassic. Oceanic island basalt was erupted to form a seamount by an intraplate volcanism in Late Carnian. Late Triassic shallow-water carbonate sedimentation occurred at the top of this seamount. Accumulation of the radiolarian chert was temporally replaced by Late Carnian to Early Norian deep-water pelagic carbonate sedimentation. Biotic association and lithologic properties of the pelagic carbonates suggest that an enormous production and accumulation of calcareous planktonic biotas occurred in an open-ocean realm of the Panthalassa Ocean in Late Carnian through Early Norian. Upper Norian ribbon chert of the siliceous rock succession contains thin beds of limestone breccia displaced from the shallow-water buildup resting upon the seamount. The shallow-water limestone and siliceous rock successions are nearly coeval with one another and are laterally linked by displaced carbonates in the siliceous rock succession. 相似文献
5.
Anachronistic facies in the Lower Triassic of South China and their implications to the ecosystems during the recovery time 总被引：3，自引：1，他引：2
The end-Permian mass extinction not only severely distressed the Paleozoic ecosystems but also dramatically changed the sedimentary systems, resulting in a peculiar Early Triassic ecosystem and submarine environment during the recovery time following the mass extinction. The Lower Triassic is characteristic of the wide occurrence of various distinctive sediments and related sedimentary structures, such as flatpebble conglomerates, vermicular limestone, subtidal wrinkle structures, microbialite, carbonate seafloor fans, thin-bedded limestone and zebra limestone-mudstone. These sediments were common in the Precambrian to Early Ordovician marine settings, and then they occurred only in some extreme and unusual environments with the expansion of metazoan faunas. However, the Early Triassic witnessed an "anachronistic" reappearance of some distinctive sedimentary records in normal shallow marine settings. The study of these anachronistic facies should be of great importance for the understanding of the unique ecosystem and marine environment through the great Paleozoic-Mesozoic transition. The anachronistic facies characterized by vermicular limestone have been documented in many localities in South China and occur at various horizons of the Lower Triassic. Most types of re- ported distinctive sediments over the world have been observed in the Lower Triassic of South China. This provides an excellent opportunity for understanding the Early Triassic environment and its co- evolution with the biotic recovery. Among the anachronistic facies the vermicular limestone is the most characteristic and common distinctive sediments in the Lower Triassic of South China but has received relatively few investigations. Taking it as a case study, we will detail the variation of vermicular limestone and its stratigraphic distribution in the Three Gorges area, Hubei Province. The investigation on the vermicular limestone and other distinctive sediments from the Lower Triassic of South China further indicates that the appearance of anachronistic facies immediately following the mass extinction and the elimination from normal shallow marine facies with the radiation of Mesozoic marine faunas imply the natural response of the sedimentary systems and ecosystems to the great Paleozoic-Mesozoic transitional events and their induced harsh environments. Therefore, the ups and downs of the anachronistic facies may act as a proxy for the evolution of ecosystems independent of fossil analyses. 相似文献
6.
Guo-Can Wang Robert P. Wintsch John I. Garver Mary Roden-Tice She-Fa Chen Ke-Xin Zhang Qi-Xiang Lin Yun-Hai Zhu Shu-Yuan Xiang De-Wei Li 《Island Arc》2009,18(3):444-466
Triassic turbidites dominate the Songpan–Ganzi–Bayan Har (SGBH) terrane of the northern Tibetan Plateau. U‐Pb dating on single detrital zircon grains from the Triassic Bayan Har Group turbidites yield peaks at 400–500 m.y., 900–1000 m.y., 1800–1900 m.y., and 2400–2500 m.y., These results are consistent with recently published U‐Pb zircon ages of pre‐Triassic bedrock in the East Kunlun, Altyn, Qaidam, Qilian and Alaxa areas to the north, suggesting that provenance of the Bayan Har Group may include these rocks. The similarities in the compositions of the lithic arkosic sandstones of the Bayan Har Group with the sandstones of the Lower‐Middle Triassic formations in the East Kunlun terrane to the north also suggests a common northern provenance for both. A well exposed angular unconformity between the Carboniferous–Middle Permian mélange sequences and the overlying Upper Permian or Triassic strata indicates that regional deformation occurred between the Middle and Late Permian. This deformation may have been the result of a soft collision between the Qiangtang terrane and the North China Plate and the closure of the Paleo‐Tethyan oceanic basin. The Bayan Har Group turbidites were then deposited in a re‐opened marine basin on a shelf environment. Fission‐track dating of detrital zircons from the Bayan Har Group sandstones revealed pre‐ and post‐depositional age components, suggesting that the temperatures did not reach the temperatures necessary to anneal retentive zircon fission tracks (250–300°C). A 282–292 m.y. peak age defined by low U concentration, retentive zircons likely reflects a northern granitic source. Euhedral zircons from two lithic arkoses with abundant volcanic fragments in the southern area yielded a ～237 m.y. zircon fission track (ZFT) peak age, likely recording the maximum age of deposition. A dominant post‐depositional 170–185 m.y. ZFT peak age suggests peak temperatures were reached in the Early Jurassic. Some samples appear to record a younger thermal event at ～140 m.y., a short lived event that apparently affected only the least retentive zircons. 相似文献
7.
The majority of tephra generated during the paroxysmal 1883 eruption of Krakatau volcano, Indonesia, was deposited in the sea within a 15-km radius of the caldera. Two syneruptive pyroclastic facies have been recovered in SCUBA cores which sampled the 1883 subaqueous pyroclastic deposit. The most commonly recovered facies is a massive textured, poorly sorted mixture of pumice and lithic lapilli-to-block-sized fragments set in a silty to sandy ash matrix. This facies is indistinguishable from the 1883 subaerial pyroclastic flow deposits preserved on the Krakatau islands on the basis of grain size and component abundances. A less common facies consists of well-sorted, planarlaminated to low-angle cross-bedded, vitric-enriched silty ash. Entrance of subaerial pyroclastic flows into the sea resulted in subaqueous deposition of the massive facies primarily by deceleration and sinking of highly concentrated, deflated components of pyroclastic flows as they traveled over water. The basal component of the deposit suggests no mixing with seawater as inferred from retention of the fine ash fraction, high temperature of emplacement, and lack of traction structures, and no significant hydraulic sorting of components. The laminated facies was most likely deposited from low-concentration pyroclastic density currents generated by shear along the boundary between the submarine pyroclastic flows and seawater. The Krakatau deposits are the first well-documented example of true submarine pyroclastic flow deposition from a modern eruption, and thus constitute an important analog for the interpretation of ancient sequences where subaqueous deposition has been inferred based on the facies characteristics of encapsulating sedimentary sequences. 相似文献
8.
LI Wei DONG YunPeng GUO AnLin LIU XiaoMing LIU YiQun ZHA XianFeng ZHANG KuaiLe 《中国科学:地球科学(英文版)》2013,56(10):1639-1653
The Qinling Orogenic Belt is divided commonly by the Fengxian-Taibai strike-slip shear zone and the Huicheng Basin into the East and West Qinling mountains,which show significant geological differences after the Indosinian orogeny.The Fengxian-Taibai fault zone and the Meso-Cenozoic Huicheng Basin,situated at the boundary of the East and West Qinling,provide a natural laboratory for tectonic analysis and sedimentological study of intracontinental tectonic evolution of the Qinling Orogenic Belt.In order to explain the dynamic development of the Huicheng Basin and elucidate its post-orogenic tectonic evolution at the junction of the East and West Qinling,we studied the geometry and kinematics of fault zones between the blocks of West Qinling,as well as the sedimentary fill history of the Huicheng Basin.First,we found that after the collisional orogeny in the Late Triassic,post-orogenic extensional collapse occurred in the Early and Middle Jurassic within the Qinling Orogenic Belt,resulting in a series of rift basins.Second,in the Late Jurassic and Early Cretaceous,a NE-SW compressive stress field caused large-scale sinistral strike-slip faults in the Qinling Orogenic Belt,causing intracontinental escape tectonics at the junction of the East and West Qinling,including eastward finite escape of the East Qinling micro-plate and southwest lateral escape of the Bikou Terrane.Meanwhile,the strike-slip-related Early Cretaceous sedimentary basin was formed with a right-order echelon arrangement in sinistral shear zones along the southern margin of the Huicheng fault.Overall during the Mesozoic,the Huicheng Basin and surrounding areas experienced four tectonic evolutionary stages,including extensional rift basin development in the Early and Middle Jurassic,intense compressive uplift in the Late Jurassic,formation of a strike-slip extensional basin in the Early Cretaceous,and compressive uplift in the Late Cretaceous. 相似文献
9.
10.
The volcanic island of Milos, Greece, comprises an Upper Pliocene –Pleistocene, thick (up to 700 m), compositionally and texturally diverse succession of calc-alkaline, volcanic, and sedimentary rocks that record a transition from a relatively shallow but dominantly below-wave-base submarine setting to a subaerial one. The volcanic activity began at 2.66±0.07 Ma and has been more or less continuous since then. Subaerial emergence probably occurred at 1.44±0.08 Ma, in response to a combination of volcanic constructional processes and fault-controlled volcano-tectonic uplift. The architecture of the dominantly felsic-intermediate volcanic succession reflects contrasts in eruption style, proximity to source, depositional environment and emplacement processes. The juxtaposition of submarine and subaerial facies indicates that for part of the volcanic history, below-wave base to above-wave base, and shoaling to subaerial depositional environments coexisted in most areas. The volcanic facies architecture comprises interfingering proximal (near vent), medial and distal facies associations related to five main volcano types: (1) submarine felsic cryptodome-pumice cone volcanoes; (2) submarine dacitic and andesitic lava domes; (3) submarine-to-subaerial scoria cones; (4) submarine-to-subaerial dacitic and andesitic lava domes and (5) subaerial lava-pumice cone volcanoes. The volcanic facies are interbedded with a sedimentary facies association comprising sandstone and/or fossiliferous mudstone mainly derived from erosion of pre-existing volcanic deposits. The main facies associations are interpreted to have conformable, disconformable, and interfingering contacts, and there are no mappable angular unconformities or disconformities within the volcanic succession.Electronic Supplementary Material Supplementary material is available for this article at 相似文献
11.
福建省地体构造划分及构造演化 总被引：2，自引：0，他引：2
本文根据对福建省不同地区的地质特征进行详细的研究对比,划分出闽西北、闽西南、闽东和闽东南四个性质不同的地体,并研究了各地体的之间碰撞拼贴的历史,指出它们主要经历了三个阶段：1、晚元古代,闽西南地体和闽西北地体沿南平-宁化一线发生碰撞拼贴作用,同时伴随海底和陆上火山喷发活动;2、三叠纪,闽东地体沿政和-大埔一线和闽西南、闽西北地体发生碰撞拼贴作用,闽东南地体也随之拼贴在闽东地体之上;3、白垩纪,闽东南地体沿平潭一东山断裂带发生左行走滑运动。 相似文献
12.
The Highway–Reward massive sulphide deposit is hosted by a silicic volcanic succession in the Cambro-Ordovician Seventy Mile Range Group, northeastern Australia. Three principal lithofacies associations have been identified in the host succession: the volcanogenic sedimentary facies association, the primary volcanic facies association and the resedimented syn-eruptive facies association. The volcanogenic sedimentary facies association comprises volcanic and non-volcanic siltstone and sandstone turbidites that indicate submarine settings below storm wave base. Lithofacies of the primary volcanic facies association include coherent rhyolite, rhyodacite and dacite, and associated non-stratified breccia facies (autoclastic breccia and peperite). The resedimented volcaniclastic facies association contains clasts that were initially formed and deposited by volcanic processes, but then redeposited by mass-flow processes. Resedimentation was more or less syn-eruptive so that the deposits are essentially monomictic and clast shapes are unmodified. This facies association includes monomictic rhyolitic to dacitic breccia (resedimented autoclastic facies), siltstone-matrix rhyolitic to dacitic breccia (resedimented intrusive hyaloclastite or resedimented peperite) and graded lithic-crystal-pumice breccia and sandstone (pumiceous and crystal-rich turbidites). The graded lithic-crystal-pumice breccia and sandstone facies is the submarine record of a volcanic centre(s) that is not preserved or is located outside the study area. Pumice, shards, and crystals are pyroclasts that reflect the importance of explosive magmatic and/or phreatomagmatic eruptions and suggest that the source vents were in shallow water or subaerial settings.The lithofacies associations at Highway–Reward collectively define a submarine, shallow-intrusion-dominated volcanic centre. Contact relationships and phenocryst populations indicate the presence of more than 13 distinct porphyritic units with a collective volume of 0.5 km3. Single porphyritic units vary from <10 to 350 m in thickness and some are less than 200 m in diameter. Ten of the porphyritic units studied in the immediate host sequence to the Highway–Reward deposit are entirely intrusive. Two of the units lack features diagnostic of their emplacement mechanism and could be either lavas and intrusions. Direct evidence for eruption at the seafloor is limited to a single partly extrusive cryptodome. However, distinctive units of resedimented autoclastic breccia indicate the presence nearby of additional lavas and domes.The size and shape of the lavas and intrusions reflect a restricted supply of magma during eruption/intrusion, the style of emplacement, and the subaqueous emplacement environment. Due to rapid quenching and mixing with unconsolidated clastic facies, the sills and cryptodomes did not spread far from their conduits. The shape and distribution of the lavas and intrusions were further influenced by the positions of previously or concurrently emplaced units. Magma preferentially invaded the sediment, avoiding the older units or conforming to their margins. Large intrusions and their dewatered envelope may have formed a barrier to the lateral progression and ascent of subsequent batches of magma. 相似文献
13.
River floods influence sedimentary environments and ecosystems from the terrestrial to the deep-marine. This study documents the occurrence conditions of hyperpycnal flows generated by river floods and related organic-matter sedimentation for Holocene sediments of the Niigata Plain, Central Japan, based on detailed sedimentary facies, total sulfur and total organic carbon content, diatom assemblages and organic-matter composition. Holocene sediments of the Niigata Plain consist of sand, mud and gravel that were deposited in estuarine and fluvial systems during a sea-level rise (15 000–6800 years BP) and stillstand (after 6800 years BP) following the Last Glacial Maximum. Hyperpycnites are present in the upper part of the estuarine lagoon sediments. The depositional age is considered to be about 5000 years BP. The hyperpycnites comprise two successions of a top fining-up unit and a basal coarsening-up unit, and include abundant terrigenous organic matter and freshwater diatoms. A large volume of freshwater is inferred to have flowed into the lagoon during deposition of the upper part of the lagoon sediments. In consequence, hyperpycnal flows may have readily formed in the lagoon, because the halocline was weak. The hyperpycnal flows also produced a layer of concentrated terrigenous organic matter in the uppermost part of the hyperpycnites. The abundant organic matter on the estuarine floor is inferred to have produced anoxic bottom conditions owing to oxidative decomposition by benthic bacteria. 相似文献
14.
利用沉积学、层序地层学理论分析和研究沉积相特征,得出探区内发育的储层主要有冲积扇、河流、三角洲、浊积扇和滩坝五大沉积体系,提出了上第三系”水流控砂”、下第三系”坡槽控砂”的沉积模式,得到储层按构造带分布的规律.隐蔽性油气藏以”断导”模式成藏,与储层发育相匹配形成四个大的隐蔽性油气藏群.研究地震储层描述方法的适应性和敏感性,利用正、反演类比方法研究地震反射特征,实现了地震相和沉积相的转换.剖析典型的油气藏类型,分析成功的经验,总结失败的教训,得到了针对河流、冲积扇、三角洲、滩坝和浊积扇的描述流程和配套技术系列. 相似文献
15.
C. Caillat P. Delhavi B. Martel-Jantin R. Michel P. M. Vincent 《Bulletin of Volcanology》1981,44(2):169-176
Study of these submarine pyroclastic flows is important for two reasons:
- From a regional point of view, submarine pyroclastic flows partially explain the origin of widespread argillized glasses in the Eocene sedimentary series of Central Iran, which have diversely been described by earlier workers as Green Tuffs, Tuffaceous Muds, Green Series.
- More generally, in contrast to basaltic volcanism, submarine acid volcanism is still very poorly-known. The mechanism here proposed is as follows: starting with a submarine, highly vesiculated lava containing idiomorphic phenocrysts, gas expansion gives rise to a vitroclastic shardy facies, whereas phenocrysts are fragmented. The whole makes up a gravitational flow that is rich in pumice, glassy shards, broken crystals, and gases; it becomes increasingly turbulent and able to tear-up sea-bottom sediments in its down-stream course. This flow evolves into turbidity currents at its distal reaches.
16.
Mesozoic basin-fill records in south foot of the Dabie Mountains: Implication for Dabie Orogenic attributes 总被引：1，自引：0，他引：1
For the Triassic continental collision, subduction and orogenesis in the Dabie-Sulu belt, a lot of data on petrology, geochemistry and chronology have been published[1]. However, so far no depositional records on the Triassic syn-collisional orogenesis of… 相似文献
17.
At Rakiraki in northeastern Viti Levu, the Pliocene Ba Volcanic Group comprises gently dipping, pyroxene-phyric basaltic lavas, including pillow lava, and texturally diverse volcanic breccia interbedded with conglomerate and sandstone. Three main facies associations have been identified: (1) The primary volcanic facies association includes massive basalt (flows and sills), pillow lava and related in-situ breccia (pillow-fragment breccia, autobreccia, in-situ hyaloclastite, peperite). (2) The resedimented volcaniclastic facies association consists of bedded, monomict volcanic breccia and scoria lapilli-rich breccia. (3) The volcanogenic sedimentary facies association is composed of bedded, polymict conglomerate and breccia, together with volcanic sandstone and siltstone-mudstone facies. Pillow lava and coarse hyaloclastite breccia indicate a submarine depositional setting for most of the sequence. Thick, massive to graded beds of polymict breccia and conglomerate are interpreted as volcaniclastic mass-flow deposits emplaced below wave base. Well-rounded clasts in conglomerate were reworked during subaerial transport and/or temporary storage in shoreline or shallow water environments prior to redeposition. Red, oxidised lava and scoria clasts in bedded breccia and conglomerate also imply that the source was partly subaerial. The facies assemblage is consistent with a setting on the submerged flanks of a shoaling basaltic seamount. The coarse grade and large volume of conglomerate and breccia reflect the high supply rate of clasts, and the propensity for collapse and redeposition on steep palaeoslopes. The clast supply may have been boosted by vigorous fragmentation processes accompanying transition of lava from subaerial to submarine settings. The greater proportion of primary volcanic facies compared with resedimented volcaniclastic and volcanogenic sedimentary facies in central and northwestern exposures (near Rakiraki) indicates they are more proximal than those in the southeast (towards Viti Levu Bay). The proximal area coincides with one of two zones where NW-SE-trending mafic dykes are especially abundant, and it is close to several, small, dome-like intrusions of intermediate and felsic igneous rocks. The original surface morphology of the volcano is no longer preserved, though the partial fan of bedding dip azimuths in the south and east and the wide diameter (exceeding 20 km) are consistent with a broad shield. 相似文献
18.
Milankovitch forcing of bioturbation intensity in deep-marine thin-bedded siliciclastic turbidites 总被引：1，自引：0，他引：1
Thomas G. Heard Kevin T. Pickering Stuart A. Robinson 《Earth and Planetary Science Letters》2008,272(1-2):130-138
Trace fossils have been used to infer a Milankovitch-type control on pelagic and hemipelagic sediments, but there have been no comparable studies in deep-marine siliciclastic turbidite successions. Here, we present the results of a quantitative analysis of trace-fossil abundance and intensity in an essentially continuous, Middle Eocene, 230-m-long (Well A6) core, comprising very thin- and thin-bedded siliciclastic turbidites in the deep-marine Ainsa basin, Spanish Pyrenees. After removing the sediment slides and debris flow deposits, as these represent geologically instantaneous events approximately two orders of magnitude thicker than the typical laminated turbiditic sediments in the core, spectral analysis was conducted on the bioturbation intensity data. Spectral analysis of bioturbation intensity in the A6 core suggests, for the first time from a siliciclastic turbidite succession at a tectonically active plate margin (thrust-top basin in a foreland basin), a cyclicity that is interpreted to reflect the 41-kyr and an ~ 112-kyr (possibly an average of the 95- and 125-kyr) Milankovitch frequencies. We propose that this drove environmental changes in bottom-water conditions in the Ainsa basin, most likely leading to critically varying levels of oxygenation (stratification) of bottom waters. Our age model for the Ainsa basin (~ 4 km of deep-marine sediments in ~ 10 Myr) yields an average sediment accumulation rate of ~ 40 cm kyr− 1, that is consistent with that inferred from the spectral analysis (~ 30 cm kyr− 1) for fine-grained sedimentation. An implication of these results is that global environmental change, probably glacio-eustasy, acted as a driver on deep-marine siliciclastic sedimentation patterns during the Middle Eocene. 相似文献
19.
Abstract The Maizuru terrane, distributed in the Inner Zone of southwest Japan, is divided into three subzones (Northern, Central and Southern), each with distinct lithological associations. In clear contrast with the Southern zone consisting of the Yakuno ophiolite, the Northern zone is subdivided into the western and eastern bodies by a high-angle fault, recognized mainly by the presence of deformed granitic rocks and pelitic gneiss. This association suggests an affinity with a mature continental block; this is supported by the mode of occurrence, and petrological and isotopic data. Newly obtained sensitive high mass-resolution ion microprobe (SHRIMP) zircon U–Pb ages reveal the intrusion ages of 424 ± 16 and 405 ± 18 Ma (Siluro–Devonian) for the granites from the western body, and 249 ± 10 and 243 ± 19 Ma (Permo–Triassic) for the granodiorites from the eastern body. The granites in the western body also show inherited zircon ages of around 580 and 765 Ma. In addition, electron probe microanalysis (EPMA) monazite U–Th–total Pb dating gives around 475–460 Ma. The age of intrusion, inherited ages, mode of occurrence, and geological setting of the Siluro–Devonian granites of the Northern zone all show similarities with those of the Khanka Massif, southern Primoye, Russia, and the Hikami granitic rocks of the South Kitakami terrane, Northeast Japan. We propose that both the Siluro–Devonian and Permo–Triassic granitic rocks of the Northern zone are likely to have been juxtaposed through the Triassic–Late Jurassic dextral strike-slip movement, and to have originated from the Khanka Massif and the Hida terrane, respectively. This study strongly supports the importance of the strike-slip movement as a mechanism causing the structural rearrangement of the Paleozoic–Mesozoic terranes in the Japanese Islands, as well as in East Asia. 相似文献
20.
Deformation of the Circum-Rhodope Belt Mesozoic (Middle Triassic to earliest Lower Cretaceous) low-grade schists underneath an arc-related ophiolitic magmatic suite and associated sedimentary successions in the eastern Rhodope-Thrace region occurred as a two-episode tectonic process: (i) Late Jurassic deformation of arc to margin units resulting from the eastern Rhodope-Evros arc–Rhodope terrane continental margin collision and accretion to that margin, and (ii) Middle Eocene deformation related to the Tertiary crustal extension and final collision resulting in the closure of the Vardar ocean south of the Rhodope terrane. The first deformational event D1 is expressed by Late Jurassic NW-N vergent fold generations and the main and subsidiary planar-linear structures. Although overprinting, these structural elements depict uniform bulk north-directed thrust kinematics and are geometrically compatible with the increments of progressive deformation that develops in same greenschist-facies metamorphic grade. It followed the Early-Middle Jurassic magmatic evolution of the eastern Rhodope-Evros arc established on the upper plate of the southward subducting Maliac-Meliata oceanic lithosphere that established the Vardar Ocean in a supra-subduction back-arc setting. This first event resulted in the thrust-related tectonic emplacement of the Mesozoic schists in a supra-crustal level onto the Rhodope continental margin. This Late Jurassic-Early Cretaceous tectonic event related to N-vergent Balkan orogeny is well-constrained by geochronological data and traced at a regional-scale within distinct units of the Carpatho-Balkan Belt. Following subduction reversal towards the north whereby the Vardar Ocean was subducted beneath the Rhodope margin by latest Cretaceous times, the low-grade schists aquired a new position in the upper plate, and hence, the Mesozoic schists are lacking the Cretaceous S-directed tectono-metamorphic episode whose effects are widespread in the underlying high-grade basement. The subduction of the remnant Vardar Ocean located behind the colliding arc since the middle Cretaceous was responsible for its ultimate closure, Early Tertiary collision with the Pelagonian block and extension in the region caused the extensional collapse related to the second deformational event D2. This extensional episode was experienced passively by the Mesozoic schists located in the hanging wall of the extensional detachments in Eocene times. It resulted in NE-SW oriented open folds representing corrugation antiforms of the extensional detachment surfaces, brittle faulting and burial history beneath thick Eocene sediments as indicated by 42.1–39.7 Ma 40Ar/39Ar mica plateau ages obtained in the study. The results provide structural constraints for the involvement components of Jurassic paleo-subduction zone in a Late Jurassic arc-continental margin collisional history that contributed to accretion-related crustal growth of the Rhodope terrane. 相似文献