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1.
Early Cretaceous Palynological Assemblages of the Shuangliao Fault Depression, Songliao Basin and their Geological Implications 总被引：2，自引：1，他引：1
The pollen and spores found in the Early Cretaceous strata of two cores from the Shuangliao Fault Depression were studied systematically, and two palynological assemblages have been recognized. Assemblage Ⅰ from the Yingcheng Formation is named Paleoconiferus-Pinuspollenites; the assemblage is characterized by an extremely high content of Paleoconifer pollen. Assemblage Ⅱ from Member 1 of the Denglouku Formation is named Cicatricosisporites-Cyathidites-Pinuspollenites; the assemblage is characterized by the abundant presence of Laevigati spores, but less Paleoconifer pollen. According to the palynological data and zircon U-Pb dating, the geological age of the Yingcheng Formation is thought to be Aptian-Albian, and that of the Denglouku Formation is thought to be Early Albian. On the basis of the composition of each assemblage, we can infer that during the depositional period of the Yingcheng Formation, the paleovegetation was mainly conifer forest, the paleoclimate was consistent with the temperate climate of today, and the paleoenvironment was humid feature. During the depositional period of Member 1 of the Denglouku Formation, the paleovegetation was mainly conifer forest and shrubs, the paleoclimate was consistent with the subtropical climate of today, and the paleoenvironment was humid. The results significantly improve our understanding of the stratigraphy in the Shuangliao Fault Depression, provide biostratigraphic evidence for the division and correlation of Early Cretaceous strata in the Shuangliao Fault Depression, and provide new data for analyzing paleovegetation and paleoclimate in the Songliao Basin. 相似文献
2.
Palynological assemblages of non-marine rocks at the Permian–Triassic boundary, western Guizhou and eastern Yunnan, South China 总被引：1，自引：0，他引：1
Yuanqiao Peng Jianxin Yu Yongqun Gao Fengqing Yang 《Journal of Asian Earth Sciences》2006,28(4-6):291-305
Marine and non-marine facies of the Permian–Triassic boundary stratigraphic set (PTBST) are well developed in South China. Palynological assemblages enable subdivision and correlation of the Permian–Triassic boundary (PTB) rocks. Three palynological assemblages are recognized across the PTBST in two terrestrial PTB sections in western Guizhou and eastern Yunnan, South China. Assemblage 1 (Xuanwei Formation) is a Late Permian palynological assemblage dominated by ferns and pteridosperms, with minor gymnosperms. Most taxa are typical long-ranging Paleozoic forms, but the appearance of Lueckisporites confirms a Late Permian age for this assemblage. Assemblage 2 (PTBST) is marked by an abrupt decrease in palynomorph abundance and diversity, and thriving fungal/algal(?) spores. Assemblage 2 is still dominated by ferns and pteridosperms, with a few gymnosperms, but is characterized by a mixed palynoflora containing both Late Permian and Early Triassic elements. Most taxa are typical Late Permian ones also found in Assemblage 1, however, some taxa of Early Triassic aspect, e.g. Lundbladispora and Taeniaesporites, appeared for the first time. In Assemblage 3 (top Xuanwei Formation and Kayitou Formation), the proportion of gymnosperm pollen increases rapidly, exceeding that of ferns and pteridosperms, but the abundance of palynomorphs is still low. Typical Early Triassic taxa (such as Lundbladispora, Aratrisporites and Taeniaesporites) are present in greater abundance and confirms an Early Triassic age for this assemblage. 相似文献
3.
本文描述了松辽盆地探井揭露的深层地层序列及其所产的5个牛物门类化石组合特征.9个孢粉组合是Monosulcites-Cyathidites组合、Pinaceae-Cyathidites-Osmundaeidites组合、Classopollis-Piceites组合、Lophotriletes-Cicatricosisporites组合、Paleoconiferus-Lygodiumsporites组合、Cyathidites-Leiotriletes-Clavatipollenites组合、Cicatricosisporites-Leiotriletes-Polyporopollenites组合、Leiotriletes-Schizaeoisporites-Classopollis组合和Trilobosporites-Cyathidites-Tricolpollenites组合.3个藻类组合是Vesperopsis-Australisphaera组合、Balmula granorugosa组合和Vesperopsis zhaodongensis组合.2个介形类组合是Cypridea unicostata-Limnocypridesadscondida组合和Mongolocypris limpida-Paracandona planiuscula组合.4个植物组合是Elatocladus submanchurica-Ginkgoites orientalis组合、Acanthopteris gothani-Pterophyllum组合、Sphenopteris johnstrupii-Coniopteris nympharum组合和Platanus septentrionalis-Protophyllum undulaturn组合.3个大孢子组合是Minerisporites sp.组合、Ricinospora leavigata-Galamospora sp.组合和Arcellites组合.还介绍了叶肢介、轮藻、双壳类和鱼类化石的产出情况.结合同位素资料认为：大庆群时代为中侏罗世,火石岭组可能为贝里阿斯期,沙河子组为凡兰吟期-欧特里夫期,营城组为欧特里夫期-巴列姆期,登娄库组为巴列姆期-阿普第期早期,泉头组一-二段为阿普第-阿尔卑期,并对各组沉积环境进行了初步分析. 相似文献
4.
A palynological record recovered from successions of Coniacian to early Campanian age (89.1–83.5 Ma) was obtained from the lacustrine sequences of the SK-I south core (SK-Is) in the Songliao Basin, northeastern China. The palynoflora is dominated by bisaccate gymnosperm pollen, followed by spores of pteridophytes, and just minor amounts of angiosperm pollen. Based on the relative abundance of the different spore and pollen taxa through the core, the succession was subdivided into three palynological assemblages. The results indicate two opposite trends for climate change, a minor warming trend (from 89.1 to 85.7 Ma) followed by a rapid cooling trend (85.7–83.5 Ma). The first warming trend reached its maximum at 85.7 Ma, which is inconsistent with results from the marine realm (which instead show a minor cooling trend based on several proxy records). However, the second cooling phase is consistent with global changes from various and abundant palaeoclimate proxies from marine deposits. We interpret the climatic changes within the studied interval (89.1–83.5 Ma) as a consequence of the shifting climate from a hot/super greenhouse to a temperate greenhouse. 相似文献
5.
青海省同仁县古浪堤中上三叠统古浪堤组孢粉组合及其地层意义 总被引：3，自引：0，他引：3
经过对青海同仁县古浪堤组实测剖面的17块样品做孢粉分析, 在6个层位样品中见有孢粉化石30属41种, 据此在该剖面自下而上划分2个孢粉组合:Dictyophyllidites-Di-saccus组合和Verrucosisporites-Di-saccus组合.上述孢粉组合中的孢粉的优势属为Dictyophyllidites, Cyathidites, Verrucosisporites和Chasmatosporites, Protopicea, Pinuspollenites.其中, Dictyophyllidites频繁出现于欧亚、北美、大洋州的晚三叠世和早侏罗世组合, Aratrisporites在南半球大量发育于中三叠世, Asseretospora在澳大利亚的分布时期是中三叠世-早侏罗世.前人于黄南的阿龙江上游及柴陇沟北, 古浪堤组产卡尼期的菊石Protrachycerassp.及双壳类Eumorphotis (Asoella) cf.illyrica.综合而言, 该地区古浪堤组时代厘定为中-晚三叠世, 古植物群生长于暖温带-亚热带河控三角洲环境. 相似文献
6.
《China Geology》2022,5(3):439-456
This study identified two palynological assemblages, namely Bayanhuasporites-Cycadopites-Protoconiferus and Cicatricosisporites-Cedripites-Perinopollenites, in the Tongbomiao Formation in the Hongqi Sag in the Hailar Basin, Inner Mongolia, China for the first time. The former is distributed in the lower part of the Tongbomiao Formation and is characterized by abundant gymnosperm pollen and diverse fern spores. Among them, the gymnosperm pollen is dominated by Paleoconifer (4.98%–31.62%) and Cycadopite (8.55%–25.23%) pollen grains and also includes other pollen grains such as Classopollis, Parcisporites, Erlianpollis, Callialasporites, and Jiaohepollis. The fern spores in the former palynological assemblage contain Bayanhuasporite (0–8.96%), Granulatisporites (0.93%–6.97%), and some important Cretaceous genera, such as Cicatricosisporites, Concavissimisporites, Densoisporites, Hsuisporites, Foraminisporis, and Leptolepidites. The Cicatricosisporites-Cedripites-Perinopollenites palynological assemblage is distributed in the upper part of the Tongbomiao Formation. Gymnosperm (77.30%), Pinaceae (31.9%), and Paleoconiferus (19.02%) pollen predominate this palynological assemblage, and Quadraeculina, Erlianpollis, and Jiaohepollis pollen are also common in this assemblage. The fern spores in this palynological assemblage include abundant Cicatricosisporites (4.29%). Besides, Concavissimisporites, Aequitriradites, and Leptolepidites are also common in this palynological assemblage. No angiosperm pollen has been found in both palynological assemblages. The identification of both palynological assemblages provides important evidence for the biostratigraphic correlation between the Hailar Basin and its adjacent areas. It also enables the reconstructions of the Berriasian-Valanginian (Early Cretaceous) vegetation and the paleoclimate on the eastern Mongolian Plateau during 141–132 Ma. The vegetation reconstructed on the palynological data of the represented by Hailar Basin in eastern Mongolian Plateau (141.6–141.4 Ma), form conifer forest or conifer broad-leaved mixed forest to conifer forest with shrubs and grassland, the climate belongs to warm temperate and warm-subtropicalt, the highest temperature is estimated to reach 35–38°C. Form 132.3 Ma, the vegetation type is conifer forest, and its paleoclimate is sub-humid warm temperate, the highest temperature is estimated to reach 24–29°C.©2022 China Geology Editorial Office. 相似文献
7.
华北地块东北缘红庙子盆地鹰嘴砬子组孢粉化石 总被引：1，自引：1，他引：0
报道华北地块东北缘地区红庙子盆地鹰嘴砬子组的孢粉化石,建立了Cicatricosisporites-Abietineaepollenites-Piceites组合,该组合的主要特征为:以裸子类双气囊花粉和海金沙科孢子为主,含一定量裸子类无气囊花粉,未见被子类花粉,孢粉组合特征可与松辽盆地沙河子组对比。一些具有早白垩世时代意义的孢粉化石,如Cicatricosisporites sp.,Cicatricosisporites undulates和Cicatricosisporites implexus的出现,表明鹰嘴砬子组的地质时代为早白垩世。根据孢粉化石资料,推测华北地块东北缘地区在鹰嘴砬子组沉积时期古植被面貌以松科和杉科组成的松柏类针叶林为主,林下生长着真蕨类。古气候相当于湿润-半湿润的亚热带气候。 相似文献
8.
9.
利用地层序列中火山碎屑岩、凝灰岩及其火山岩锆石U-Pb同位素测年,对晋东北地区侏罗纪地层时代进行了重新厘定。取得了以下主要认识:(1)确认宁武—静乐盆地下侏罗统永定庄组的存在;(2)宁武—静乐盆地天池河组可以与鄂尔多斯盆地安定组相对比,归属于中侏罗统;(3)浑源盆地髫髻山组应归属于中侏罗统上部,该套火山岩地层在整个燕—辽地区具有穿时性;(4)广灵盆地中侏罗统窑坡组底部厚层砾岩的沉积时代可能与燕山造山带的南大岭组相当,应该属于早侏罗世至中侏罗世早期构造运动的产物。通过地层序列的重新厘定,确认了159.0~(152.77±0.63)Ma区域角度不整合的存在,该期构造运动可能与侏罗纪东亚大陆多向汇聚产生的远程效应有关。 相似文献
10.
The evolution of the Cretaceous basins of the Brazilian northeastern hinterland was associated with the Gondwana rifting and opening of the South Atlantic Ocean. The first marine ingression in northeastern Brazil occurred in the late Aptian and was recorded as the Santana Group of the Araripe Basin, which is currently an isolated basin, located hundreds of kilometers away from the Brazilian marginal basins. Bellow the first upper Aptian marine deposits, an important section of fossiliferous limestone (Lagerstätte) was deposited and preserved in the Crato Formation transitioning upward into evaporites of the Ipubi Formation. The direction of the marine ingression is controversial, with several possibilities being suggested, mainly due to the absence of other areas of upper Aptian marine sections within the hinterland. Serra do Tonã is a sedimentary mesa with scarped edges where the upper part of the Marizal Formation crops out, displaying laminated limestones, litho- and chrono-correlated with those of the Crato Formation, is preserved. Therefore, this mixed upper Aptian section, at the North Tucano Basin (Serra do Tonã), is a unique occurrence of utmost importance to the definition of sedimentary events and paleogeographical reconstruction of northeastern Brazil during the late Aptian. A detailed stratigraphic analysis allowed the definition and characterization of two upper Aptian depositional sequences bounded by regional disconformities. Both sequences are dominantly transgressive and carbonate-siliciclastic in composition. The lower sequence comprises the basal portion of the Marizal Formation and consists of a succession of fluvial sandstones, ending on a laterally continuous thin interval (<15 m) of interbedded shales and limestones bearing exposure features and paleosols on the top. The limestones show a diversity of microfacies, including microbialites, organized in high-frequency deepening-upward cycles. The recognized sequence stratigraphic architecture resembles the lower part of the Barbalha Formation in the Araripe Basin, positioned in the same palynological zone, suggesting the correlation of the shale-carbonate interval in the Serra Tonã with the Batateira Beds in the Araripe Basin. The upper sequence also exhibits a fining upward pattern, with a vertical succession starting with sandstones and shales deposited in fluvial and deltaic environments, culminating upward in laminated limestones and lacustrine shales. The stratigraphic succession is very similar to the upper portion of the Barbalha Formation in the Araripe Basin, and the laminated limestones are lithostratigraphically classified as the Crato Formation. These limestones also comprise several microfacies, organized in a transgressive-regressive cycle with the maximum flooding surface positioned on relatively deep-water carbonates. Fluvial paleocurrent directions, which are similar to those of the Araripe Basin, suggest that both basins were part of the same continental paleodrainage, flowing to the south, where the South Atlantic proto-ocean was located. Fish fossils found in shales of the Marizal Formation, further south in the Central Tucano Basin and in the same stratigraphic interval of those of the lower sequence, were interpreted as marine forms. Indeed, some of them were considered to have Tethyan affinity, probably coming from an incipient Equatorial Atlantic gateway, supporting the interpretation based on the paleocurrents. The limestones at the top of the Serra do Tonã, which are also found in inselbergs in the Jatobá Basin, are relicts of a once extensive cover of Aptian carbonate deposits, now restricted because of uplifting and erosion events from the Late Cretaceous to the Cenozoic. 相似文献
11.
Stratigraphy of the Triassic?Jurassic Boundary Successions of the Southern Margin of the Junggar Basin, Northwestern China 总被引：2，自引：1，他引：1
SHA Jingeng Vivi VAJDA PAN Yanhong Linda LARSSON YAO Xiaogang ZHANG Xiaolin WANG Yaqiong CHENG Xiansheng JIANG Baoyu DENG Shenghui CHEN Siwei PENG Bo 《《地质学报》英文版》2011,85(2):421-436
The Triassic?Jurassic (Tr?J) boundary marks a major extinction event, which (~200 Ma) resulted in global extinctions of fauna and flora both in the marine and terrestrial realms. There prevail great challenges in determining the exact location of the terrestrial Tr?J boundary, because of endemism of taxa and the scarcity of fossils in terrestrial settings leading to difficulties in linking marine and terrestrial sedimentary successions. Investigation based on palynology and bivalves has been carried out over a 1113 m thick section, which is subdivided into 132 beds, along the Haojiagou valley on the southern margin of the Junggar Basin of the northern Xinjiang, northwestern China. The terrestrial Lower Jurassic is conformably resting on the Upper Triassic strata. The Upper Triassic covers the Huangshanjie Formation overlaid by the Haojiagou Formation, while the Lower Jurassic comprises the Badaowan Formation followed by the Sangonghe Formation. Fifty six pollen and spore taxa and one algal taxon were identified from the sediments. Based on the key-species and abundance of spores and pollen, three zones were erected: the Late Triassic (Rhaetian) Aratrisporites?Alisporites Assemblage, the Early Jurassic (Hettangian) Perinopollenites?Pinuspollenites Assemblage, and the Sinemurian Perinopollenites?Cycadopites Assemblage. The Tr?J boundary is placed between bed 44 and 45 coincident with the boundary between the Haojiagou and Badaowan formations. Beds with Ferganoconcha (?), Unio?Ferganoconcha and Waagenoperna?Yananoconcha bivalve assemblages are recognized. The Ferganoconcha (?) bed is limited to the upper Haojiagou Formation, Unio?Ferganoconcha and Waagenoperna?Yananoconcha assemblages are present in the middle and upper members of the Badaowan Formation. The sedimentary succession is interpreted as terrestrial with two mainly lake deposit intervals within Haojiagou and Badaowan formations, yielding fresh water algae and bivalves. However, the presence of brackish water algae Tasmanites and the marine?littoral facies bivalve Waagenoperna from the Badaowan Formation indicate that the Junggar Basin was influenced by sea water caused by transgressions from the northern Tethys, during the Sinemurian. 相似文献
12.
<正>Precambrian tectonic history of Zhejiang,Fujian,and Jiangxi provinces of south China is important for understanding the tectonic evolution of South China but its magmatic activity, petrogenesis,stratigraphic sequence of the Mamianshan Group is still strongly controversial.Here we present new sensitive high resolution ion micro-probe(SHRIMP) U-Pb zircon geochronological data for the Mamianshan Group and petrographical data to constrain the tectonic framework of the regions.Our results showed that the SHRIMP U-Pb zircon age of green schists of the Dongyan Formation is 796.5±9.3 Ma,the Daling Formation is 756.2±7.2 Ma,and mica-quartz schist of the Longbeixi Formation is 825.5±9.8 Ma.These data indicate that the Mamianshan Group was formed not in the Mesoproterozoic,but in the Neoproterozoic and its stratigraphic sequences should be composed of Longbeixi,Dongyan,and Daling Formations from the bottom to the top.Rocks from this Group, from Zhejiang,Fujian and Jiangxi provinces,constituted the upper basement of the Cathaysia Block that overlay the lower basement of the Mayuan Group.Detailed petrographic studies demonstrate that the amphibole schists of the Dongyan Formation in the Mamianshan Group were formed within an intra-arc rift setting rather than a continental rift as previously suggested.Rather,this island-arc type formation was developed by collision and/or subduction between various blocks resulting from the breakup of the supercontinent Rodinia at c.850-750 Ma.The Zhuzhou conglomerate,distributed near Dikou Town,Jian'ou City,Fujian Province and previously considered as evidence of the Mesoproterozoic Dikou movement,is shown here not to be the basal conglomerate above the angular unconformity between the upper and lower basements.Our conclusions have important implications for understanding the Precambrian tectonics of South China. 相似文献
13.
鄂尔多斯盆地东北部内蒙古伊金霍洛旗乌兰木伦地区是我国重要的能源矿产地,含煤岩系赋存在侏罗系延安组中,延安组岩石组合以灰白色砂岩、灰色粉砂岩、灰色泥岩为主,夹多层煤层;延安组上覆直罗组以灰色、灰绿色砂岩、灰色粉砂岩、紫红色泥岩为主。通过对乌兰木伦地区武家塔露天煤矿剖面延安组和直罗组孢粉化石分析,在延安组中识别出Cyathidites-Lycopodiumsporites-Neoraistrickia-Cycadopites孢粉组合带,以桫椤科、石松科孢子繁盛,紫萁科孢子和单沟/原始沟类、松柏类两气囊花粉发育,卷柏科孢子及柏科花粉较常见为主要特征,时代为中侏罗世早期(阿林期—巴柔期)。根据延安组孢粉母体植物的生态环境分析,本区在这一沉积时期的气候属于温暖湿润的亚热带—温带型气候。直罗组孢粉化石较少,主要见Cyathidites minor,Osmundacidites parvus,Concentrisporites fragilis,Cycadopites spp.等。综合地层岩性、孢粉组合及古植被分析,延安组到直罗组沉积时期总体上呈现从温暖湿润的亚热带—温带型向半干旱—干旱炎热型的气候... 相似文献
14.
四棵树凹陷位于准噶尔盆地南缘西段乌苏市境内,蕴含丰富的油气和煤炭资源。由于匮乏化石证据,制约四棵树凹陷侏罗纪地层的地质时代的确定。对西山窑组沉积环境和孢粉分析研究,恢复重建了其古环境,探讨了本区中西山窑时期的植被演替及环境演变。西山窑组岩性以泥质细砂岩、浅灰绿色泥岩、粉砂岩、泥岩为主。通过对孢粉化石分析研究,建立了Cyathidites minor—Osmundacidites —Cycadopites—Disacciatrileti（COCD）孢粉组合。组合中蕨类植物孢子与裸子植物花粉含量大体相当,蕨类植物孢子以紫萁科的Osmundacidites为主,桫椤科孢子也有一定含量,其他常见分子包括Deltoidospora、Neoraistrickia等,裸子植物以松柏类两气囊花粉含量为主,均为我国侏罗纪常见属种。通过对西山窑组孢粉植物群的分析,认为西山窑组孢粉组合时代属于中侏罗世早期,该孢粉植物群总体上反映了温暖湿润的热带—亚热带气候特点,植被类型以针阔混交林为主。 相似文献
15.
侏罗系、白垩系间是显生宙唯一还没有定义系级GSSP的界线。生物演替在Thithonian期与Berriasian期之间不存在明显变化,很难找到可以进行全球对比的标志。作为中生代生物年代地层学主要划分依据的菊石类生物,亦受生物区系影响而难作为侏罗系、白垩系界线的标志。微体化石具有优势。近期,国际上趋于将瓮虫类Calpionella alpina带之底、钙质超微化石Nannoconus steinmannii minor和N.kamptneri minor二者的始现面作为侏罗系、白垩系界线,对应于极性带M19n.2n内部,年龄为145 Ma。国际地层划分与对比以海相为标准。中国侏罗系、白垩系以陆相地层发育为特征,与海相对比颇具难度。以陆相生物为标志的界线划分产生了地区性的生物年代地层格架,也形成了地方生物地层与国际年代地层对比的错位,导致中国陆相侏罗系、白垩系界线成为地学界争议的问题。本文认为,在综合考虑不同学科研究结果的同时,问题解决的实质是客观认识陆相生物对比的缺陷,结合考虑非生物的标准,如磁性地层、旋回地层和同位素测年的精度,获得超越相区的对比结果。基于陆相生物特点,着眼于宏观演化阶段来识别界线位置是问题解决的初期阶段。燕辽生物群与热河生物群是代表侏罗纪和白垩纪的两大生物演化类群,其间年龄可为土城子组顶部的139 Ma。这是为全方位研究而铺设的临时工作界线。今后将土城子组作为侏罗纪、白垩纪过渡地层而加大研究力度,有可能在该组顶部或其内部发现界线生物标志和同层位绝对年龄值,或许会使其向目前国际推荐年龄(145 Ma)更靠近一步;也不排除GSSP未定的国际侏罗系、白垩系界线年龄会向年轻方向变化,趋于139 Ma的Valanginian阶底界位置。 相似文献
16.
塔里木盆地侏罗纪孢粉植物地理区系 总被引：1，自引：0，他引：1
塔里木盆地南部地区侏罗纪的孢粉化石 ,可分为 5个孢粉组合 :1) Cyathidites- Classopollis组合 ;2 ) Disac-ciatrileti- Cyathidites- Classopollis- Quadraeculina组合 ;3) Disacciatrileti- Cyathidites- Classopollis- N eoraistrackia组合 ;4) Disacciatrileti- Cyathidites- Classopollis组合 ;5 ) Cyathidites- Classopollis- Disacciatrileti组合。这些组合与塔北地区的组合明显不同 ,与我国华南亚区侏罗纪孢粉组合基本一致 ,属于华南侏罗纪孢粉植物地理亚区的范畴 ,而塔北地区的组合与我国华北亚区侏罗纪孢粉组合大体一致 ,属于华北侏罗纪孢粉植物地理亚区的范畴。因此 ,塔里木盆地侏罗纪孢粉植物地理分区界线应划在盆地的近中间 ,从西北向东南延伸 相似文献
17.
滇中新元古代澄江组层型剖面锆石U-Pb年代学及其地质意义 总被引：1，自引：0，他引：1
澄江组是华南新元古代地层中的重要地层单元之一,其确切沉积时限对于建立和完善华南新元古代区域地层格架具有关键意义。对滇中澄江组层型剖面顶部的凝灰岩夹层进行高精度SHRIMP锆石U-Pb定年研究,获得3组有效的206Pb/238U加权平均年龄值,其分别为(819±14)Ma(MSWD=0.15)、(781±11)Ma(MSWD=0.24)和(725±11)Ma(MSWD=0.65)。其中,最年轻的一组年龄值(725±11)Ma被解释为澄江组顶部凝灰岩夹层的形成时间,可以代表滇中澄江组的顶界年龄,从而进一步确认澄江组的沉积时限为800～725 Ma。结合相关研究资料,证实澄江组与开建桥组、莲沱组的沉积时限基本相当,三者与下冰期长安组不存在对比关系,而应与冰期前板溪群的上部进行对比。此外,推测两组年龄值较老的锆石可能是与新元古代罗迪尼亚(Rodinia)超大陆裂解有关的幕式岩浆活动的记录。 相似文献
18.
通过对新发现于新疆塔里木盆地西部上白垩统乌依塔克组有孔虫化石的时代分析，认为该组的时限为晚上伦期—赛诺期，综合分析各类化石的时代特征，本区土伦阶和赛诺阶的界线应划在Ｍｉｇｒｏｓ－Ａｍｍｏｂａｃｕｌｉｔｅｓ组合和Ｐａｒａｒｏｔａｌｉａ－Ｎｏｎｉｏｎｅｌｌａ组合之间。 相似文献
19.
Outcrop-based sequence stratigraphic analysis and palynological biofacies were used to define depositional sequences and their bounding surfaces, and build a sequence stratigraphic model for the Upper Cretaceous succession of the Afikpo Sub-basin. Four unconformity-bounded third-order depositional sequences were identified. Sequence 1 comprises the Nkporo Formation and is subdivided into lowstand system tract (LST) representing an incised valley fill and transgressive systems tract (TST) consisting of estuarine and marine shales and mudstones. The base of the sequence is an angular unconformity correlated to the 77.5 Ma sequence boundary (SB) and the maximum flooding surface (MFS) is dated at 76 Ma. Sequence 2 is diachronous and straddles the lithostratigraphic boundary of the Nkporo and Mamu formations. The upper SB is dated at 71 Ma while associated MFS is dated at 73.5 Ma. Sequence 3 consists of the upper Mamu Formation and the Ajali Formation. The upper SB of sequence 3 is at 68 Ma while the MFS is dated at 69.8 Ma. Sequence 4 is the topmost depositional sequence belonging to the Nsukka Formation. The upper SB is placed at 66.5 Ma. The MFS within this sequence is dated at 67.8 Ma. The sequences encompass from tidally influenced bay head delta and central estuarine environments to coastal and shallow marine shelf environments. Stratigraphic architecture and facies types show that sequence development was controlled to a great extent by eustatic sea level variations though differential subsidence rates encouraged differential rates of sediment supply and rates of sea level change along different segments of the shoreline. 相似文献
20.
滇中昆阳群一直是华南前寒武纪地质研究的热点之一,其地层序列、时代与区域对比长期存在争议。通过对滇中易门县小街乡普家村-岔河水库剖面禄表组2个凝灰岩样品进行SHRIMP锆石U-Pb定年,获得禄表组凝灰岩的锆石206Pb/238U年龄为878.5±4.7Ma和878.0±4.0Ma,首次证实禄表组的形成时代为新元古代中期。禄表组凝灰岩SHRIMP锆石U-Pb年龄的获得,有利于正确认识昆阳群的划属关系,并为西南地区青白口纪地层格架的建立和对比提供可靠的年代学依据。 相似文献