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 362 毫秒
1.
The paleogeographic evolution of Late Paleozoic basins located in southern South America is addressed. Three major types of basins are recognized: infracratonic or intraplate, arc-related, and retroarc. Intraplate basins (i.e., Paraná, Chaco-Paraná, Sauce Grande-Colorado, and La Golondrina) are floored by continental or quasi-continental crust, with low or moderate subsidence rates and limited magmatic and tectonic activity. Arc-related basins (northern and central Chile, Navidad–Arizaro, Río Blanco, and Calingasta–Uspallata basins and depocenters along Chilean Patagonia) show a very complex tectonic history, widespread magmatic activity, high subsidence rates, and in some cases metamorphism of Late Paleozoic sediments. An intermediate situation corresponds to the retroarc basins (eastern Madre de Dios, Tarija, Paganzo, and Tepuel-Genoa), which lack extensive magmatism and metamorphism but in which coeval tectonism and sedimentation rates were likely more important than those in the intraplate region. According to the stratigraphic distribution of Late Paleozoic sediments, regional-scale discontinuities, and sedimentation pattern changes, five major paleogeographic stages are proposed. The lowermost is restricted to the proto-Pacific and retroarc basins, corresponds to the Mississippian (stage 1), and is characterized by shallow marine and transitional siliciclastic sediments. During stage 2 (Early Pennsylvanian), glacial–postglacial sequences dominated the infracratonic (or intraplate) and retroarc basins, and terrigenous shallow marine sediments prevailed in arc-related basins. Stage 3 (Late Pennsylvanian–Early Cisuralian) shows the maximum extension of glacial–postglacial sediments in the Paraná and Sauce Grande-Colorado basins (intraplate region), whereas fluvial deposits interfingering with thin intervals of shallow marine sediments prevailed in the retroarc basins. To the west, arc-related basins were dominated by coastal to deep marine conditions (including turbiditic successions). In the Late Cisuralian (stage 4), important differences in sedimentation patterns are registered for the western arc-related basins and eastern intraplate basins. The former were locally dominated by volcaniclastic sediments or marine deposits, and the intraplate basins are characterized by shallow marine conditions punctuated by several episodes of deltaic progradation. Finally, in the Late Permian (stage 5), volcanism and volcaniclastic sedimentation dominated in basins located along the western South American margin. The intraplate basins in turn were characterized by T–R cycles composed of shallow marine, deltaic, and fluvial siliciclastic deposits.  相似文献   

2.
Tectonic activity, sea-level changes, and the climate controlled sedimentation in Late Paleozoic basins of western Argentina. The role of each factor is investigated from the geologic record of the Río Blanco and Paganzo basins using three hierarchical orders of stratigraphic bounding surfaces. First-order surfaces correspond to regional unconformities, second-order ones to local unconformities with a lesser regional extent, and third-order surfaces represent locally extended sedimentary truncation. Using this methodology, the Carboniferous–Permian record of the Paganzo and Río Blanco basins may be divided into two megasequences, four sequences, and 12 stratigraphic sections. Megasequences are bounded by regional unconformities that result from tectonic events important enough to cause regional paleogeographic changes. Sequences are limited by minor regional extension surfaces related to local tectonic movements or significant sea-level falls. Finally, stratigraphic sections correspond to extended sedimentary truncations produced by transgressive events or major climatic changes. Sequence I is mainly composed of marine deposits divided into basal infill of the basin (Section 1) and Tournaisian–Visean transgressive deposits (Section 2). Sequence II is bounded by a sharp erosional surface and begins with coarse conglomerates (Section 3), followed by fluvial and shallow marine sedimentary rocks (Section 4) that pass upward into shales and diamictites (Section 5). The base of Sequence III is marked by an extended unconformity covered by Early Pennsylvanian glacial sedimentary rocks (Section 6) that represent the most important glacial event along the western margin of Gondwana. Postglacial deposits (Section 7) occur in the two basins and comprise both glaciolacustrine (eastern region) and transgressive marine (central and western regions) deposits. By the Moscovian–Kasimovian, fluvial sandstones and conglomerates were deposited in most of the Paganzo Basin (Section 8), while localized volcanic activity took place in the Río Blanco Basin. Near the end of the Carboniferous, an important transgression is recorded in the major part of the Río Blanco Basin (Section 9), reaching the westernmost portion area of the Paganzo Basin. Finally, Sequence IV shows important differences between the Paganzo and Río Blanco basins; fluvial red beds (Section 10), eolian sandstones (Section 11), and low-energy fluvial deposits (Section 12) prevailed in the Paganzo Basin whereas volcaniclastic sedimentation and volcanism dominated in the Río Blanco Basin. Thus, tectonic events, sea-level changes and climate exerted a strong and complex control on the evolution of the Río Blanco and Paganzo basins. The interaction of these allocyclic controls produced not only characteristic facies association patterns but also different kinds of stratigraphic bounding surfaces.  相似文献   

3.
Increasing evidence of Permian volcanic activity along the South American portion of the Gondwana proto-Pacific margin has directed attention to its potential presence in the stratigraphic record of adjacent basins. In recent years, tuffaceous horizons have been identified in late Early Permian–through Middle Permian (280–260 Ma) sections of the Paraná Basin (Brazil, Paraguay, and Uruguay). Farther south and closer to the magmatic tract developed along the continental margin, in the San Rafael and Sauce Grande basins of Argentina, tuffs are present in the Early to Middle Permian section. This tuff-rich interval can be correlated with the appearance of widespread tuffs in the Karoo Basin. Although magmatic activity along the proto-Pacific plate margin was continuous during the Late Paleozoic, Choiyoi silicic volcanism along the Andean Cordillera and its equivalent in Patagonia peaked between the late Early Permian and Middle Permian, when extensive rhyolitic ignimbrites and consanguineous airborne tuffaceous material erupted in the northern Patagonian region. The San Rafael orogenic phase (SROP) interrupted sedimentation along the southwestern segment of the Gondwana margin (i.e., Frontal Cordillera, San Rafael Basin), induced cratonward thrusting (i.e., Ventana and Cape foldbelts), and triggered accelerated subsidence in the adjacent basins (Sauce Grande and Karoo) located inboard of the deformation front. This accelerated subsidence favored the preservation of tuffaceous horizons in the syntectonic successions. The age constraints and similarities in composition between the volcanics along the continental margin and the tuffaceous horizons in the San Rafael, Sauce Grande, Paraná, and Karoo basins strongly suggest a genetic linkage between the two episodes. Radiometric ages from tuffs in the San Rafael, Paraná, and Karoo basins indicate an intensely tuffaceous interval between 280 and 260 Ma.  相似文献   

4.
Tectonic activity, sea-level changes, and the climate controlled sedimentation in Late Paleozoic basins of western Argentina. The role of each factor is investigated from the geologic record of the Río Blanco and Paganzo basins using three hierarchical orders of stratigraphic bounding surfaces. First-order surfaces correspond to regional unconformities, second-order ones to local unconformities with a lesser regional extent, and third-order surfaces represent locally extended sedimentary truncation. Using this methodology, the Carboniferous–Permian record of the Paganzo and Río Blanco basins may be divided into two megasequences, four sequences, and 12 stratigraphic sections. Megasequences are bounded by regional unconformities that result from tectonic events important enough to cause regional paleogeographic changes. Sequences are limited by minor regional extension surfaces related to local tectonic movements or significant sea-level falls. Finally, stratigraphic sections correspond to extended sedimentary truncations produced by transgressive events or major climatic changes. Sequence I is mainly composed of marine deposits divided into basal infill of the basin (Section 1) and Tournaisian–Visean transgressive deposits (Section 2). Sequence II is bounded by a sharp erosional surface and begins with coarse conglomerates (Section 3), followed by fluvial and shallow marine sedimentary rocks (Section 4) that pass upward into shales and diamictites (Section 5). The base of Sequence III is marked by an extended unconformity covered by Early Pennsylvanian glacial sedimentary rocks (Section 6) that represent the most important glacial event along the western margin of Gondwana. Postglacial deposits (Section 7) occur in the two basins and comprise both glaciolacustrine (eastern region) and transgressive marine (central and western regions) deposits. By the Moscovian–Kasimovian, fluvial sandstones and conglomerates were deposited in most of the Paganzo Basin (Section 8), while localized volcanic activity took place in the Río Blanco Basin. Near the end of the Carboniferous, an important transgression is recorded in the major part of the Río Blanco Basin (Section 9), reaching the westernmost portion area of the Paganzo Basin. Finally, Sequence IV shows important differences between the Paganzo and Río Blanco basins; fluvial red beds (Section 10), eolian sandstones (Section 11), and low-energy fluvial deposits (Section 12) prevailed in the Paganzo Basin whereas volcaniclastic sedimentation and volcanism dominated in the Río Blanco Basin. Thus, tectonic events, sea-level changes and climate exerted a strong and complex control on the evolution of the Río Blanco and Paganzo basins. The interaction of these allocyclic controls produced not only characteristic facies association patterns but also different kinds of stratigraphic bounding surfaces.  相似文献   

5.
The Permian system of the Palaeozoic Erathem is divided into three series, the Early Permian Cisuralian Series, the Middle Permian Guadalupian Series, and the Late Permian Lopingian Series. The Cisuralian Series encompasses the Asselian to Kungurian stages which constitute the basal part of the Gondwana supersequence I. In India, they are represented lithostratigraphically by the Talchir, Karharbari, and Barakar formations. This paper presents the palynological results from the Barakar Formation of the Upper Cisuralian Series from Manuguru which lies in the southeastern part of the Godavari basin. The succession studied comprises 35 subsurface samples from bore hole 1007 represented by clay, shale, sandstone, and coal. The palynofloras in this sequence have a homogenous composition demonstrating that not many significant floral changes took place through the considered stratigraphic range. The entire sequence is characterized by the dominance of nonstriate bisaccate genus Scheuringipollenites and sub-dominance of striate bisaccate genus Faunipollenites(=Protohaploxypinus). The other pollen genera among the nonstriate bisaccates are Rhizomaspora, Primuspollenites, Ibisporites, and Platysaccus. The striate bisaccates include Striatites, Striatopodocarpites, and Stroterosporites. The taeniate taxa are represented by Lueckisporites and Lunatisporites. The common monosaccate genera include Caheniasaccites, Potoniesporites, and Barakarites. Spores are less common and include Latosporites, Brevitriletes, Horriditriletes, Microbaculispora, and Callumispora. They characterize the palynofloral composition of the Lower Barakar Formation. The correlation of this assemblage with some of the biostratigraphic palynozones proposed previously for the Cisuralian sequences of the Paraná Basin of South America, Kalahari Karoo Basin of South Africa, Ruhuhu Basin of Tanzania, East Africa as well as palynoassemblages from South Victoria Land and Dronning Maud Land, Antarctica and Collie Basin of west Australia point out to their Early Permian (Late Sakmarian–Early Artinskian) age. Palynomorphs such as Botryococcus sp., Tetraporinia sp., Balmeela sp. and Leiosphaeridia sp. are also recorded which suggest that these sediments were deposited during post-glacial near shore, cool and humid environment.  相似文献   

6.
The Paraná Basin (1 600 000 km2) is the largest intracratonic basin in southern South America and contains a thick (1300 m) Permo-Carboniferous glacial succession (the Itararé Group). This paper describes over 1700 m of drill core recovered during recent exploration for oil and gas. Itararé Group sediments consist of massive and stratified diamictites interbedded with massive and graded sandstones, and massive and laminated mudstones. Facies are interpreted as the product of sediment gravity flows in a glacially influenced marine basin. Three stratigraphic formations can be defined across the basin, each consisting of a lowermost sandstone-rich member overlain by a diamictite-rich member. Examination of Itararé Group rocks both in core and outcrop shows that depositional processes were influenced by active faulting and downslope resedimentation on relatively steep and unstable substrate slopes. Primary glacial deposits such as tillites and associated striated pavements occur along the present eastern outcrop belt which probably coincided with the eastern basin margin during deposition of the Itararé Group. Ice masses fringing the eastern (southern African) and western (Bolivian) basin margins supplied sediment to the basin in the form of fluvio-glacial deltas, fans and floating ice tongues. This sediment was then resedimented downslope as debris flows and turbidites. Both stratigraphic relationships and the regional distribution of facies types identify a clear pattern of basin subsidence and step-wise expansion by outward faulting within Late Proterozoic mobile belts. The position of successive basin margins can be related to specific lineament structures in the underlying basement. Asymmetric expansion of the Paraná Basin occurred along the northern and southern basin margins during deposition of the Itararé Group; this expansion probably reflects shallow crustal adjustments activated by collisional movements along the Andean margin of South America during the Hercynian Orogeny.  相似文献   

7.
Index species useful for correlations with the International Stratigraphical Column are rare or absent in the Pennsylvanian–Permian strata of the Paraná Basin in Brazil, preventing accuracy in geochronologic assignments. Besides, absolute datings are very scarce in comparison with other Gondwana basins. This paper presents palynological data from an outcrop on the surroundings of the Candiota coal mine, southmost Brazil, from several levels of the Rio Bonito and Palermo formations. The presence of certain index species of spore–pollen allowed the recognition of two Permian palynozones: the Vittatina costabilis and the Lueckisporites virkkiae zones. Furthermore, U–Pb in zircons from a volcaniclastic level interbedded in the coal strata of the former unit was analyzed through LA-MC-ICP-MS method, providing a new absolute age dating of 281.4 ± 3.4 Ma (Cisuralian, Early Permian). This dating is assumed as the oldest occurrence of the L. virkkiae Zone in Paraná Basin, which contains index species that are widespread in other Gondwana basins. A well distributed surface boundary occurs in this section also, allowing local and regional correlations. These new biostratigraphical and geochronological data are integrated, in order to offer a deep analysis on the stratigraphical significance for correlations across the Occidental Gondwana.  相似文献   

8.
The late Carboniferous to Triassic tectonic history of eastern Australia includes important periods of regional-scale crustal extension and contraction. Evidence for these periods of tectonism is recorded by the extensive Pennsylvanian (late Carboniferous) to Triassic basin system of eastern Australia. In this study, we investigate the use of U–Pb dating of detrital zircons in reconstructing the tectonic development of one of these basins, the eastern Galilee Basin of Queensland. U–Pb detrital zircon ages were obtained from samples of stratigraphically well-constrained Cisuralian and Lopingian (early and late Permian, respectively) sandstone in the Galilee Basin. Detrital zircons in these sandstones are dominated by a population with ages in the range of 300–250 Ma, and ages from the youngest detrital zircons closely approximate depositional ages. We attribute these two fundamental findings to (1) appreciable derivation of detrital zircons in the Galilee Basin from the New England Orogen of easternmost Australia and (2) syndepositional magmatism. Furthermore, Cisuralian sandstone of the Galilee Basin contains significantly more >300 Ma detrital zircons than Lopingian sandstone. The transition in detrital zircon population, which is bracketed between 296 and 252 Ma based on previous high-precision U–Pb zircon ages from Permian ash beds in the Galilee Basin, corresponds with the Hunter–Bowen Orogeny and reflects a change in the Galilee Basin from an earlier extensional setting to a later foreland basin environment. During the Lopingian foreland basin phase, the individual depocentres of the Galilee and Bowen basins were linked to form a single and enormous foreland basin that covered >300 000 km2 in central and eastern Queensland.  相似文献   

9.
We present four SHRIMP U–Pb zircon ages for the Choiyoi igneous province from the San Rafael Block, central–western Argentina. Dated samples come from the Yacimiento Los Reyunos Formation (281.4 ± 2.5 Ma) of the Cochicó Group (Lower Choiyoi section: andesitic breccias, dacitic to rhyolitic ignimbrites and continental conglomerates), Agua de los Burros Formation (264.8 ± 2.3 Ma and 264.5 ± 3.0 Ma) and Cerro Carrizalito Formation (251.9 ± 2.7 Ma Upper Choiyoi section: rhyolitic ignimbrites and pyroclastic flows) spanning the entire Permian succession of the Choiyoi igneous province. A single zircon from the El Imperial Formation, that is overlain unconformably by the Choiyoi succession, yielded an early Permian age (297.2 ± 5.3 Ma), while the main detrital zircon population indicated an Ordovician age (453.7 ± 8.1 Ma). The new data establishes a more precise Permian age (Artinskian–Lopingian) for the section studied spanning 30 Ma of volcanic activity. Volcanological observations for the Choiyoi succession support the occurrence of explosive eruptions of plinian to ultraplinian magnitudes, capable of injecting enormous volumes of tephra in the troposphere–stratosphere. The new SHRIMP ages indicate contemporaneity between the Choyoi succession and the upper part of the Paraná Basin late Paleozoic section, from the Irati up to the Rio do Rasto formations, encompassing about 24 Ma. Geochemical data show a general congruence in compositional and tectonic settings between the volcanics and Paraná Basin Permian ash fall derived layers of bentonites. Thickness and granulometry of ash fall layers broadly fit into the depletion curve versus distance from the remote source vent of ultraplinian eruptions. Thus, we consider that the Choiyoi igneous province was the source of ash fall deposits in the upper Permian section of the Paraná Basin. Data presented here allow a more consistent correlation between tectono-volcanic Permian events along the paleo-Pacific margin of southwestern Gondwana and the geological evolution of neighboring Paleozoic foreland basins in South America and Africa.  相似文献   

10.
通过对南美洲28个主要含油气盆地石油地质特征的系统梳理,全面总结了南美洲的油气地质特征:①发育两个时代、两种类型的烃源岩;②储层类型单一,油气集中赋存在白垩系和古近系-新近系两个层系中;③发育4种成藏模式,即西缘前陆盆地发育陡坡短距离垂向运移成藏模式和缓坡长距离侧向运移成藏模式、东缘被动陆缘盆地发育盐上"断层+盐刺穿"运移成藏模式和盐下"烃源岩内浊积砂体+潜山"运移成藏模式;④油气分布平面上呈两带展布、两中心富集的规律。同时,以成藏组合为基础评价单元完成了南美地区资源评价。预测南美洲待发现可采资源量约为214 065MMBOE。主要集中分布在东缘海上被动陆缘盆地群和西缘陆上前陆盆地群两个领域。东委内瑞拉盆地、马拉开波盆地、桑托斯盆地和坎波斯盆地是预测资源量较大的4个盆地。  相似文献   

11.
国际二叠纪年代地层划分新方案   总被引：15，自引：0，他引：15  
王向东 《地质论评》1998,44(5):478-488
国际二叠纪地层分会已就二叠系的统和阶的划分,命名及下界的层位达成统一意见,提出新的二叠系年代地层表,该表由３个最佳的区域性地层序列组成,即代表下二叠统的俄罗斯和哈萨克坦乌拉尔地区的乌拉尔统（ＣｉｓｕｒａｌｉａｎＳｅｒｉｅｓ）上二叠下部和上部的美国西南部的瓜德鲁普统（ＧｕａｄａｌｕｐｉａｎＳｅｒｉｅｓ）和中国华南地区的乐平统（ＬｏｐｉｎｇｉａｎＳｅｒｉｅｓ）。新表为建立二叠系内部界线的全球层型及点位  相似文献   

12.
Terrestrial Middle Triassic strata occur throughout continental Africa and are particularly well exposed in South Africa, Tanzania, Zambia, and Namibia. The youngest age for all these African deposits is widely accepted as early Middle Triassic (Anisian). Fossils collected recently from the uppermost strata of the upper Omingonde Formation in Namibia highlighted the presence of Chiniquodon, a carnivorous cynodont previously only found in Ladinian-Carnian aged rocks of South America. In addition, work in progress indicates that a large archosaur, originally reported as Erythrosuchus, also discovered from levels close to the top of this unit, is in fact a rauisuchian, a group of archosaurs well known from Ladinian-Carnian beds of southern South America. Here we present the first record of the tuskless dicynodont Stahleckeria potens from the top of the upper Omingonde Formation in central Namibia. This taxon was up until now only known from the Ladinian Dinodontosaurus Assemblage Zone of the Santa Maria Formation in southern Brazil. Thus, compelling evidence for a Ladinian age for the upper levels of the upper Omingonde Formation is provided by two therapsid and one archosaur taxa. The tetrapod fauna of the upper Omingonde Formation partially fills the gap of the well-documented hiatus (Ladinian gap), prevalent throughout the Karoo basins of south and central Africa. The presence of the same therapsid taxa in the Namibian Waterberg Basin and the Paraná Basin of Brazil during Middle Triassic suggests that these basins were biogeographically linked through a series of interconnecting lowlands, with no major ecological, climatic and/or physical barriers.  相似文献   

13.
Conchostracan fossils are abundant and relatively diversified in the Rio do Rasto Formation (Passa Dois Group, Paraná Basin, southern Brazil), but leaiids (‘Leaia pruvosti’ [Reed, F.R.C., 1929. Novos Phyllopodos Fósseis do Brasil. Boletim do Serviço Geológico e Mineralógico do Brasil 34, 2–16]) were previously found at only one locality of the formation in the northern Santa Catarina State. New specimens of the Family Leaiidae, collected from two outcrops in central Paraná State near the top of the formation, stimulated a revision of related taxa. Both the new and the previously known leaiids are herein assigned to Hemicycloleaia mitchelli [Etheridge Jr., R., 1892. On Leaia mitchelli Etheridge. Proceedings of the Linnean Society of New South Wales 7, 307–310] based on the presence of three carinae and subovate shape. This species was originally recorded in the upper Tatarian (Wuchiapingian, Late Permian) of Sydney Basin, eastern Australia and therefore corroborates the interpretation that the leaiid bearing strata of the Rio do Rasto Formation cannot be younger than Permian. H. mitchelli possibly was one of the most widespread, eurytopic and conservative Late Paleozoic conchostracans of Gondwana (although records from Africa, India and Antarctica must still be confirmed) and it was also found in the Tatarian of Russia. The sudden disappearance of leaiids after their apparent success is consistent with the hypothesis about the biotic crisis around the Permo-Triassic boundary.  相似文献   

14.
The palynological record from the Permian part of the Çakraz Formation from the Çamdağ area of NW Turkey has been investigated in order to obtain a more precise age assessment than achieved in previous studies. The ‘Late Permian’ age and a possible age range beginning in the Roadian (mid Permian) were discussed before for sections of palynomorph‐bearing strata occurring within the formation. These deposits are now assigned to the late Cisuralian/Guadalupian and considered to be not older than early Kungurian, and not younger than Capitanian. The new age assessment was conducted via a long‐distance, intercontinental palynostratigraphic correlation from NW Turkey to South America, where results of radiometric datings were linked to some siliciclastic sections by absolute ages to the chronostratigraphy. Common conspicuous taxa in pollen‐dominated assemblages from both regions are Lueckisporites and Vittatina such as Lueckisporites virkkiae, L. latisaccus, L. stenotaeniatus, Vittatina corrugata, V. subsaccata and V. wodehousei. These species co‐occur in strata of the northern as well as southern palaeohemisphere settings (NW Turkey and S America). Thus, Lueckisporites latisaccus, L. stenotaeniatus and Vittatina corrugata are, as well as L. virkkiae or V. subsaccata, considered as being cosmopolitan. Due to the more precise palynological dating of part of the Çakraz Formation and surrounding deposits they are here broadly correlated with Permian continental successions from the Southern Alps, Italy, including the Val Daone Conglomerate and the Verrucano Lombardo/Val Gardena Sandstone (Gröden) red beds, and the Rotliegend deposits of Germany. These results support some earlier views regarding the age and stratigraphic equivalences with European deposits. The new age for the Çakraz Formation also supports recent considerations as middle Permian (part Guadalupian), and as Cisuralian for the lower parts of the formation, such as the fossil‐bearing section with plants and tetrapod traces further east in NW Turkey, where the unit also crops out. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

15.
The Sierra de San Luis forms the southern tip of the Eastern Sierras Pampeanas in central Argentina. Two narrow belts of low-grade phyllites and quartz arenites, i.e. the San Luis Formation, have accommodated part of the strain-related differential exhumation of the medium- to high-grade metamorphic domains that constitute to the basement complex of the sierra. Eleven phyllite samples were subjected to the K/Ar fine-fraction dating technique. Results are interpreted in relation to the Kübler index of the illites, which indicate epimetamorphic conditions for the majority of the samples. Obtained ages between 330 and 290 Ma cover a period of compressional tectonics in the late Mississippian (Visean/Serpukhovian boundary) followed by the subsidence during the formation of the Paganzo Basin in the provinces of La Rioja and San Luis. These tectonic movements are coincident with the Toco orogeny in northern Chile and southern Bolivia. This suggests that the older K/Ar ages document the compressional stage and that younger ages record the cooling of the basement during the subsequent extensional uplift of the basement.  相似文献   

16.
Two ash fall beds (tonstein) sampled from the post-glacial Permian deposits of the Paraná Basin have provided new U–Pb radiometric age constraints for this stratigraphic interval. The zircon grains were recovered from tonstein layers interbedded with fine-grained and carbonaceous lithologies in the middle portion of the Rio Bonito Formation. In both samples, the dominant population is interpreted as generated by explosive volcanism, as having formed immediately before the eruption. Based on 238U/206Pb, the selected zircon grains from the dominant population have weighted mean ages of 290.6 ± 2.8 Ma and 281.7 ± 3.2 Ma, corresponding to the Sakmarian and Kungurian ages in the Cisuralian epoch, respectively. These ages constrain the time of the deposition of the tonstein horizons and have important stratigraphic implications for the Late Paleozoic evolution of both the Paraná Basin and the southwestern region of Gondwana. The results presented here and the radiometric data already published suggest that deposition of the post-glacial coal-bearing deposits of the Rio Bonito Formation was probably initiated before the Early Permian. Thus, we infer that the climate had already ameliorated by this period in order to allow for the formation and accumulation of peat in this region of Gondwana.  相似文献   

17.
 The giant Mercosul aquifer system consists of Triassic-Jurassic eolian-fluvio-lacustrine sandstones confined by Cretaceous basalt flows, and it covers about 1,195,500 km2 (461,583 miles2) in South America. The aquifer system encompasses all of the Paraná Basin and part of the Chaco-Paraná Basin and is one of the world's largest. The eolian Botucatu Sandstone and its equivalents form an important part of this system. Maps of structure, thickness of overlying rocks, and water temperature, and a potentiometric map, all based on 322 wells, define hydrogeologic characteristics and provide the basis for establishing guidelines for the long-term equilibrium use of this important multinational aquifer system. The Mercosul aquifer system is divided into two domains – the larger and better understood Paraná Basin and the smaller and less well understood Chaco-Paraná Basin. Most of the northern part of the Paraná Basin has axially-directed groundwater flow, whereas the southern part of the aquifer discharges mostly to the southwest into the Corrientes Province of Argentina, with negligible discharge into the Atlantic Ocean. The Mercosul aquifer system is conservatively estimated to have been flushed at least 180 times since deposition. Various factors are responsible for this flushing, including appreciable rainfall since the end of the Cretaceous Period, probable uplift of the basins' borders in Late Cretaceous time, simple basin geometry, long-term riverine and groundwater flow to the southwest (ancestral and present Paraná River Systems), and stable cratonic setting. Key hydraulic properties of the Mercosul aquifer system are compared to those of the eolian Jurassic Navajo-Nugget System of the western United States. The results demonstrate the importance of tectonics and climate on the evolution of sub-continental aquifer systems. Received, September 1997 / Revised, December 1998 / Accepted, January 1999  相似文献   

18.
西北地区铝土矿均为碳酸盐岩古风化壳沉积型,其主要矿床式有：新疆阿依里式,分布于塔里木地块北缘西段,形成于晚石炭世;陕西天桥则式,分布于鄂尔多斯地块的东缘北段、南缘东段,形成于晚石炭世;甘肃大台子式,分布于鄂尔多斯地块的西缘南段,形成于早二叠世;陕西关坪式,分布于扬子地块北缘,形成于中二叠世。对比分析表明,西北已知有铝土...  相似文献   

19.
U–Pb dating and Hf-isotope provenance analysis of detrital zircons from the glaciogenic lower Permian Grant Group of the Canning Basin indicate sources principally from basement terranes in central Australia, with subordinate components from terranes to the south and north. Integrating these data with field outcrop and subsurface evidence for ice sheets, including glacial valleys and striated pavements along the southern and northern margins of the basin, suggests that continental ice sheets extended over several Precambrian upland areas of western and central Australia during the late Paleozoic ice age (LPIA). The youngest zircons constrain the maximum age for contemporaneous ice sheet development to the late Carboniferous (Kasimovian), whereas palynology provides a minimum age of early Permian (Asselian–Sakmarian). Considering the palynological age of the Grant Group within the context of regional and global climate proxies, the main phase of continental ice sheet growth was possibly in the Ghzelian–Asselian. The presence of ice sheets older than Kasimovian in western and central Australia remains difficult to prove given a regional gap in deposition possibly covering the mid-Bashkirian to early Ghzelian within the main depocentres and even larger along basin margins, and the poor evidence for older Carboniferous glacial facies. There is also no evidence for extensive glacial facies younger than mid-Sakmarian in this region as opposed to eastern Australia where the youngest regional glacial phase was Guadalupian.  相似文献   

20.
内蒙古巴彦敖包二叠纪放射虫化石的发现   总被引：15，自引：0，他引：15  
在内蒙古中部达尔罕茂明安联合旗北西靠近国境线的巴彦敖包地区硅质岩中首次发现早二叠世晚期—中二叠世早期的放射虫化石,放射虫化石包括4个属的6个比较种和若干个未定种:Pseudoalbaillella cf.lomentaria,P.cf.rhombothoracata,P.cf.scalprata,P.cf.longicornis,Latentifistula cf.patagilaterala,Ruzhencevisponguscf.uralicus,Stigmosphaerostylus sp.等。该区系索伦山蛇绿构造混杂岩带的东延部分,该动物群的发现提供了索伦山蛇绿构造混杂岩带最终混杂堆积的时间为中二叠世早期的证据。  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