Architecture of the evaporite accumulation and salt structures dynamics in Tiddlybanken Basin,southeastern Norwegian Barents Sea     

Muhammad Hassaan  Jan I. Faleide  Roy H. Gabrielsen  Filippos Tsikalas 《Basin Research》2021,33(1):91-117

An extensive, reprocessed two‐dimensional (2D) seismic data set was utilized together with available well data to study the Tiddlybanken Basin in the southeastern Norwegian Barents Sea, which is revealed to be an excellent example of base salt rift structures, evaporite accumulations and evolution of salt structures. Late Devonian–early Carboniferous NE‐SW regional extensional stress affected the study area and gave rise to three half‐grabens that are separated by a NW‐SE to NNW‐SSE trending horst and an affiliated interference transfer zone. The arcuate nature of the horst is believed to be the effect of pre‐existing Timanian basement grain, whereas the interference zone formed due to the combined effect of a Timanian (basement) lineament and the geometrical arrangement of the opposing master faults. The interference transfer zone acted as a physical barrier, controlling the facies distribution and sedimentary thickness of three‐layered evaporitic sequences (LES). During the late Triassic, the northwestern part of a salt wall was developed due to passive diapirism and its evolution was influenced by halite lithology between the three‐LES. The central and southeastern parts of the salt wall did not progress beyond the pedestal stage due to lack of halite in the deepest evaporitic sequence. During the Triassic–Jurassic transition, far‐field stresses from the Novaya Zemlya fold‐and‐thrust belt reactivated the pre‐salt Carboniferous rift structures. The reactivation led to the development of the Signalhorn Dome, rejuvenated the northwestern part of the salt wall and affected the sedimentation rates in the southeastern broad basin. The salt wall together with the Signalhorn Dome and the Carboniferous pre‐salt structures were again reactivated during post‐Early Cretaceous, in response to regional compressional stresses. During this main tectonic inversion phase, the northwestern and southeastern parts of the salt wall were rejuvenated; however, salt reactivation was minimized towards the interference transfer zone beneath the centre of the salt wall.  相似文献   

Analytic models for orogenic collapse     

Margarete A. Jadamec  Donald L. Turcotte  Peter Howell   《Tectonophysics》2007,435(1-4):1-12

The temporal and spatial distribution of the aftershock sequences of the Ruwenzori (February 5, 1994, Mb (5.8)), Masisi (April 29, 1995, Mb (5.1)) and Kalehe (October 24, 2002, Mb (5.9)) earthquakes have been studied. It has been found that most of the aftershocks of the Ruwenzori earthquake are located on the eastern flank of the main escarpment and those of the Masisi earthquake are confined to the northwest of Lake Kivu margin where earthquake occurrence of swarm-type was normally observed. The Kalehe earthquake occurred in the central part of Lake Kivu and it was the largest earthquake observed in the Lake Kivu basin since 1900. The rate of decrease in aftershock activity with the time has shown that the p-value for Ruwenzori and Masisi earthquake equals 0.6, somehow smaller than that found in other geotectonic zones where p is close to 1. The p-value of the Kalehe earthquake is a normal value equal to 1.From an area delimited by spatial distribution of aftershocks, the linear dimension of the fault was estimated. The fault area determined in this study correlates well with those of previous studies which occurred in the Western Rift Valley of Africa including the Tanganyika and Upemba Rift.  相似文献   

Stress Changes due to Recent Seismic Events in the Central Apennines (Italy)     

Andrea?Tallarico  Stefano?SantiniEmail author  Michele?Dragoni 《Pure and Applied Geophysics》2005,162(12):2273-2298

The Central Apennines, Italy, are characterized by moderate seismic activity on normal faults, oriented in directions parallel to the Apenninic chain. The subject of this study is the Umbria-Marche Apennines, a segment approximately 200-km long, where three main seismic events occurred in the last three decades. The 1979 Norcia earthquake was a M_w = 5.8 event, taking place at the south end of the considered segment. The 1984 Gubbio earthquake was a M_w = 5.6 event which took place at the north end. The 1997-1998 Colfiorito sequence constituted 8 main shocks with magnitudes M_w between 5 and 6 and epicenters located between the Gubbio and the Norcia earthquake areas. A model made of an elastic half-space is considered, in which the seismic sources are represented by rectangular dislocations which have the appropriate values of source parameters, and in which the static stress field produced by each event is calculated. The analysis of the Coulomb stress change (ΔC) as a function of time shows that the coseismic stress transfer and fault interaction played an important role in the region during the past three decades: 7 earthquakes of the 9 considered took place where ΔC>0. Such an interaction has been confirmed by the analysis of the aftershocks in the Colfiorito zone post September 26, 1997: about the 61% of the aftershocks considered took place where ΔC>0. The comparison between the ΔC^s due to the coseismic stress transfer and the rate ΔĊ^t due to the tectonic stress allows us to quantify the time advance of the earthquakes. The ΔC^s pattern shows positive values in two areas that can be regarded as historical seismic gaps.  相似文献   

Deglaciation sequences in the Permo-Carboniferous Itararé Group, Paraná Basin, southern Brazil     

Fernando Farias Vesely  Mario Luis Assine 《Journal of South American Earth Sciences》2006,22(3-4):156

The Late Carboniferous–Early Permian Itararé Group is a thick glacial unit of the Paraná Basin. Five unconformity-bounded sequences have been defined in the eastern outcrop belt and recognized in well logs along 400 km across the central portion of the basin. Deglaciation sequences are present in the whole succession and represent the bulk of the stratigraphic record. The fining-upward vertical facies succession is characteristic of a retrogradational stacking pattern and corresponds to the stratigraphic record of major ice-retreat phases. Laterally discontinuous subglacial tillites and boulder beds occur at the base of the sequences. When these subglacial facies are absent, deglaciation sequences lie directly on the basal disconformities. Commonly present in the lowermost portions of the deglaciation sequences, polymictic conglomerates and cross-bedded sandstones are generated in subaqueous proximal outwash fans in front of retreating glaciers. The overlying assemblage of diamictites, parallel-bedded and rippled sandstones, and Bouma-like facies sequences are interpreted as deposits of distal outwash fan lobes. The tops of the deglaciation sequences are positioned in clay-rich marine horizons that show little (fine-laminated facies with dropstones) or no evidence of glacial influence on the deposition and likely represent periods of maximum ice retreat.  相似文献   

Calculation of equilibrium distributions of chemical species in aqueous solutions by means of monotone sequences     

Thomas J. Wolery  Lester J. Walters Jr. 《Mathematical Geology》1975,7(2):99-115

A numerical method for the calculation of equilibrium distributions of chemical species in aqueous solutions of electrolytes is presented. This method is constructed by transforming the problem of determining the set of unknown concentrations satisfying the mass balance and mass action equations into the equivalent problem of finding the limits of certain well-behaved mathematical sequences in a multivariable direct iteration scheme. The total (analytical) concentrations are taken as the starting estimates, and the recursive equations are constructed from the starting equations. It is shown that the sequences so constructed are both monotonic and bounded, hence convergent in an orderly fashion by a mathematical axiom. Each unknown free ion concentration (that is, each limit) is approached simultaneously from above and from below, being effectively sandwiched in an ever tightening manner. Strict error bounds therefore are easily constructed. The method has been found to be exceedingly efficient in practice, with the error bound (maximum fractional error in taking the upper estimate as the final answer) decreasing in an approximately exponential fashion with respect to iteration number, commonly 0.5–1.5 orders of magnitude per iteration. Correction for nonideality is presented, and the possibility of this giving rise to more than one solution is discussed in connection with three examples of natural waters of low-, medium-, and high-ionic strengths.  相似文献   

日本绒螫蟹放流群体12S rRNA序列研究   总被引：5，自引：2，他引：3  

高天翔  王溪宏  张秀梅 《海洋湖沼通报》2000,(1):47-51

参考果蝇与蚤状溞序列进行了日本绒螯蟹放流群体的线粒体DNA 12S rRNA基因片段的引物设计、PCR扩增及序列测定,得到457bp的碱基序列,其A、T、G、C含量分别为158bp(34.57%)、178bp(38.95%)、51bp(11.16%),70bp(15.32%),与果蝇与蚤状相同基因片段序列含量相似.  相似文献   

天山玛纳斯河源鹿角湾冰川地貌与冰期序列   总被引：1，自引：0，他引：1  

鞠远江  刘耕年 《冰川冻土》2005,27(6):907-912

在鹿角湾冰川区40 km²的考察范围内,共发育了18个冰斗.按斗底高度的不同,可以将18个冰斗分成3个高度等级,分别代表了3次雪线高度不同的冰进.冰斗朝向以偏北为主,说明水热条件对冰斗发育是限制因素.18号冰斗和2号冰斗朝向偏南,说明其所代表的冰进阶段水热条件组合有利于冰川的长期存在,从而发育了大规模的向阳冰斗.鹿角湾冰川共发育了10道保存比较完整的冰碛垄,按冰碛垄表面特征和产出位置,结合测年资料,将10道冰碛垄划分为5套冰碛地层.对冰碛垄上所采冰碛土样品进行年代测试的结果是:冰碛丘陵上组地层属于小冰期沉积,较早的两次冰进结束时间为(680±60)a BP和(250±60)a BP;冰碛丘陵组地层属于新冰期沉积,3次冰进结束年代分别为:(4.2±0.4)ka BP,(2.9±0.3)ka BP,(1720±60)a BP;末次冰期晚期结束年代为1.1~1.2 ka BP.其它几次冰进阶段未能取得可信的测年数据.  相似文献   

Stratigraphic record of continental breakup,offshore NW Australia—Discussion     

Tiago M. Alves  Marcos Fetter  Cathy Busby  Tiago A. Cunha  Nathalia H. Mattos 《Basin Research》2023,35(1):470-482

Reeve et al. (2022) address the stratigraphic record of continental breakup by focusing on a set of stratigraphic unconformities from a proximal sector of the NW Australian continental margin, inboard from the Exmouth Plateau. They suggest that such unconformities can potentially document a well-defined three-stage process: end of the syn-rift phase, formation of a wide continent-ocean transition zone (COTZ) and generation of ‘true’ Penrose-type oceanic crust. We counterargue that continental breakup is a protracted event that can only be understood via seismic- and chronostratigraphic correlations of strata, and their composing sequences, across and along rifted margins. Tying proximal stratigraphic unconformities to magnetic anomalies outboard from the study area in Reeve et al. (2022) is open to question. In parallel, we suggest that age resolutions of ca. 1 Ma are not achievable using the micropaleontological data presented in Reeve et al. (2022), with an important reworking of microfossil assemblages potentially occurring during the erosional process forming local and regional unconformities. Our discussion addresses these points in more detail.  相似文献   

Characteristics of geochemical weathering of L3 and S3 loess-paleosol section in the Hengshan area,Shaanxi Province北大核心CSCD     

杨宇哲  岳大鹏  赵景波  王晓宁  刘怡婷  刘蓉 《地理科学进展》2023,(2):364-379

The Hengshan area in Shaanxi Province is located at the transitional junction of the Loess Plateau and the Mu Us sandy land in China. It is sensitive to environmental changes and has formed a unique paleoaeolian sand loess paleosol sequence. In this study, the L3 and S3 loess paleosol strata of the Liushumao section in Hengshan were selected for the analysis of the element content and related geochemical parameters in soil samples, to systematically explain the chemical weathering intensity and environmental evolution information recorded by the element geochemical index parameters during the L3 loess accumulation and S3 paleosol development in the Hengshan area. The results show that the major elements in the Liushumao section are mainly SiO2, Al2O3 and CaO. There are differences in the content of major elements in loess layers (L3-1, L3-2), paleosol layers (S3-1, S3-2), and aeolian sand layers (L3F, S3F). The contents of Al2O3 and Fe2O3 are the highest in the paleosol layer of the section, the content of CaO is the highest in the loess layer, and the content of Na2O is the highest in the aeolian sand layer. The CIA and Na/K values of the section samples reveal that the loess-paleosol layer are in the stage of primary chemical weathering, and the aeolian sand layer has not entered the stage of chemical weathering. The high values of CIA, Rb/Sr ratio, and magnetic susceptibility in the Liushumao section indicate the strengthening of weathering and pedogenesis, the relatively warm and humid climate in this period, the increasingly strong summer monsoon, and the fixed contraction of the Mu Us sandy land. The high values of the ratio of silicon and aluminium (Sa) and > 63 μm particle content indicate the occurrence of strong winter monsoon, which led to the activation and expansion of the sandy land under the effect of dry and cold climate. One extremely cold period, two cold periods, and a relatively warm period occurred in the L3 loess accumulation period, while two warm periods and one cold period occurred in the S3 paleosol development period. The change of element geochemical indicators in the Liushumao section revealed that the climate change in the Hengshan area was mainly affected by the change of strength of the East Asian winter and summer monsoon, which is generally consistent with other climate change records in North China. The study results provide more evidence for exploring the climate and environmental changes in the transitional area of the Loess Plateau and Mu Us sandy land in China. © 2023, Editorial office of PROGRESS IN GEOGRAPHY. All rights reserved.  相似文献   

2011年云南盈江Ms5.8地震及其余震序列重定位   总被引：2，自引：0，他引：2       下载免费PDF全文

房立华  吴建平  张天中  黄静  王长在  杨婷 《地震学报》2011,33(2):262-267

使用川滇地区三维走时表和三维速度模型,利用单纯形法对2011年3月10日云南盈江Ms5.8地震进行了重新定位.震中位置为97.901°E,24.677°N;震源深度13.1 km.使用双差定位方法对其余震序列进行了重定位.余震呈现明显的时空分布特征:余震主要分布在大盈江断裂的两侧及中段和北东段的转折处,余震带长度约12...  相似文献