Diagenetic processes in cretaceous sandstones from occidental Brazilian Equatorial Margin     

《Journal of South American Earth Sciences》2015

Despite a great interest in Brazilian Equatorial Margin exploration, very little was published on the diagenesis of sandstones from that area. A wide recognition petrographic study was performed to identify the major diagenetic processes that impacted the porosity of Lower Cretaceous sandstones of the Pará-Maranhão, São Luís, Bragança-Viseu and Barreirinhas basins. Arkoses from the Pará-Maranhão Basin show neoformed or infiltrated clay coatings, mica replacement and expansion by kaolinite and vermiculite, and precipitation of grain-replacive and pore-filling quartz, kaolinite, albite, chlorite, calcite, dolomite, siderite, pyrite and titanium oxides. Compaction, quartz and calcite cementation were the main porosity-reducing processes. Barreirinhas Basin lithic arkoses and subarkoses display clay coatings, compaction of metamorphic fragments into pseudomatrix, and precipitation of grain-replacive and pore-filling kaolinite, quartz, albite, chlorite, calcite, dolomite, TiO₂ and pyrite. The main porosity-reducing processes were calcite cementation in the subarkoses, and compaction and quartz cementation in lithic arkoses. Quartzarenites from this basin were early- and pervasively cemented by dolomite. Arkoses and lithic arkoses of the São Luís and Bragança-Viseu basins show clay coatings, pseudomatrix from mud intraclasts compaction, and precipitation of pore-filling and grain-replacive kaolinite, vermiculite, smectite, quartz, albite, chlorite, illite, calcite, dolomite, hematite, TiO₂ and pyrite. Compaction of mud intraclasts and dissolution of feldspars and heavy minerals were the main porosity-modification processes. These preliminary results may contribute to the understanding of the spatial and temporal distribution of the diagenetic processes and their impacts on the porosity of the sandstones from these basins.  相似文献   

http://www.sciencedirect.com/science/article/pii/S1674987114000413     

Dong Feng  Hongwen Deng  Zhan Zhou  Xiaopeng Gao  Longtao Cui 《地学前缘(英文版)》2015,6(4)

Braid-delta depositional systems are widely developed in most continental basins in China. Research indicates that, for different types of braid delta, the facies sequence and association, which are cr...  相似文献   

干、湿环境下中尺度对流系统发生的环流背景和地面特征分析   总被引：10，自引：2，他引：8  

郑淋淋  孙建华 《大气科学》2013,37(4):891-904

对2007～2010 年暖季(6～9 月)发生在江淮和黄淮流域46 个对流天气过程的环流背景和地面特征进行了统计研究。根据整层可降水量小于或大于等于50 mm 将这些个例发生的环境分成干环境(10 个个例)和湿环境(36 个个例)。干环境下发生强对流的天气形势可以分为槽后型和副高边缘型,湿环境下的天气形势可分为槽前型、副高边缘型和槽后型,湿环境下有明显的暖湿区配合。湿环境下槽前型发生的概率最高,地面系统较为复杂,有静止锋、倒槽、冷锋和暖锋,而干环境下在本研究的个例中无槽前型发生。干、湿环境下副高边缘型的对流,从地面到500 hPa 都发生在副高后部的“S”流型的拐弯处,但部分湿环境个例低层有切变线。干环境下槽后型的发生概率较高,而湿环境下发生概率则相对较少。由这些研究表明,干、湿环境下强对流系统的触发和维持机制存在明显的差异。  相似文献   

Bulk organic δ13C and C/N ratios as palaeosalinity indicators within a Scottish isolation basin     

Elizabeth A. V. Mackie  Melanie J. Leng  Jeremy M. Lloyd  Carol Arrowsmith 《第四纪科学杂志》2005,20(4):303-312

Microfossils in isolation basin sediments are frequently used to reconstruct sea‐level change, but preservation problems and non‐analogue situations can limit their usefulness. Here we investigate the potential of stable carbon isotopes (δ¹³C) and C/N ratios from bulk organic matter, as an alternative proxy of salinity within isolation basin sediments from a basin in northwest Scotland. Within the Holocene sediment δ¹³C and C/N are determined largely by the mean weighted values of the predominant source of the organic material. Analysis of modern materials and comparison with the diatom record shows that the marine parts of the sequence are dominated by high δ¹³C and variable C/N. In the fresh water sequences the organic material is a mixture of both freshwater aquatic and terrestrial plant input that have relatively low δ¹³C and high C/N. The application of δ¹³C and C/N ratios in the studied basin in general follow the environmental change recorded by the diatoms and shows the potential of bulk organic matter in the investigation of salinity change in isolation basins. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

High velocities and seismic anisotropy in Pleistocene turbidites off Western Canada     

Earl E. Davis  Ron M. Clowes 《Geophysical Journal International》1986,84(2):381-399

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A method to solve the paleotectonic analysis problem     

Valentine O. Mikhailov 《Mathematical Geology》1993,25(7):949-961

The method to determine the rates of tectonic movements is based on the use of dynamic models of sedimentary basins. A standard dataset should be provided as input information: the present-day position of sedimentary layer interfaces (chronostratigraphic boundaries), land surface and basement, the layer ages, and the uncertainty limits within which the depth of sedimentation of each layer may have differed. In terms of dynamic models, the paleotectonic analysis problem is reduced to the determination of such tectonic rates that, at prescribed reference times, the model surface topography within the assumed limits would be constrained. At the final moment, the interfaces would be brought into agreement with the contemporary geologic cross-section. The analysis the problem of tectonic rates determination has shown that it has no unique solution. One of the ways to obtain the unique solution is to seek it within a prescribed class of functions, for example, the Fourier series. This method differs from the paleotectonic analysis methodology in that it treats the tectonic rates of motion as functions of time and spatial variables. Under certain conditions, it proves feasible to reconstruct the rates of tectonic movements not only within the time intervals represented in the deposited strata, but within periods of erosion as well. It also is possible to take into account the deformation-induced changes in thickness of the layers. The method's application is illustrated with an example of the Terek-Caspian Trough. As follows from the computation, the tectonic movements since the Middle Jurassic may be presented as a sum of two components: an overall slowing-down subsidence whose rate is proportional to the square root of the age, and local movements which follow a regular oscillatory time pattern with a period of 60–70 MY. The character of the local movements is such that the profile appears to break into a northern and southern segment. When one was being uplifted, the other segment was sinking, andvice versa. These two segments are separated by a deep-seated fault. This may have been a result of an external compression on the trough.  相似文献   

Geochemical characteristics of Cretaceous basaltic rocks in South China and constraints on Pacific plate subduction     

CHEN Weifeng  CHEN Peirong  XU Xisheng & ZHANG Min The State Key Laboratory of Mineral Deposit Research  Department of Earth Sciences  Nanjing University  Nanjing  China 《中国科学D辑(英文版)》2005,48(12):2104-2117

The South China, including Yangzi Craton and the Cathaysian Block, belongs to the southern part of East Asia continent. It borders Pacific plate on the east side and Qinling-Dabie Orogen on the north side. During the middle-late Cretaceous, a number of downfaulted red basins (the terrestrial sedimentary basins in Fig. 1) and volcanic- sedimentary basins had been developed in South China[1,2], in which the con-temporaneous basaltic rocks were generally distributed (Fig. 1). Although the …  相似文献   

SWAT模型在伊犁河上游缺资料区的应用          下载免费PDF全文

陆志翔  蔡晓慧  邹松兵  龙爱华  许宝荣 《干旱区地理》2012,35(3):399-407

 在分布式水文模型中,探索产生分布式降水数据的方法是该领域研究的热点之一,发展基于水文物理过程的模型校准方法是实践PUB的热点与难点。基于SWAT分布式水文模型,以资料稀缺的伊犁河上游为研究区域,针对流域的水资源评价关键问题,首先准确描述区域的降水空间分布特征,并基于流域水文过程采用综合流域特征、多时间尺度、多变量和多站点的适宜性模型校准新方法,取得了满意的模拟结果,表明模型较好地再现了流域的水文过程。另外,完善水文机理研究,提高降水及下垫面相关参数的观测水平是改善模型模拟的有效途径。  相似文献   

浑太流域降水极值的统计分布特征   总被引：2，自引：0，他引：2  

胡乃发  金昌杰  关德新  王安志  吴家兵  袁凤辉 《高原气象》2012,31(4):1166-1172

基于浑太流域1966-2006年73个雨量站的日降水资料,建立了逐站年最大日降水量(AnnualMaximum,AM)序列和汛期4-9月日降水量<1.27mm.d-1的最长持续干旱天数(Munger Index,MI)序列,并对其时空分布规律进行了分析。采用广义极值(General Extreme Value,GEV)分布、广义帕雷托(General Pareto,GP)分布、韦布尔(Weibull,WB)分布、约翰逊SB(Jonhson SB,J-SB)分布、Burr分布和对数逻辑(Log-Logistic,L-LG)分布等6种极值分布函数对AM和MI序列进行了逐站分布拟合,结果表明,广泛应用的GEV分布整体拟合程度最好,有50个测站的KS检验统计量Dn<0.09,而未曾推广使用的Burr分布的拟合效果也非常好,有36个测站Dn<0.09。用GEV分布对50年一遇的AM和MI进行了估算,发现流域中心地区极端强降水和极端干旱的程度较高,分别为>208mm.d-1和>47d。  相似文献   

Stratigraphy, depositional environments and level reconstruction of the last interglacial Lake Samra in the Dead Sea basin   总被引：1，自引：0，他引：1  

N. Waldmann  M. Stein  A. Starinsky 《Quaternary Research》2009,72(1):1-185

In this paper we describe the stratigraphy and sediments deposited in Lake Samra that occupied the Dead Sea basin between ∼ 135 and 75 ka. This information is combined with U/Th dating of primary aragonites in order to estimate a relative lake-level curve that serves as a regional paleohydrological monitor. The lake stood at an elevation of ∼ 340 m below mean sea level (MSL) during most of the last interglacial. This level is relatively higher than the average Holocene Dead Sea (∼ 400 ± 30 m below MSL). At ∼ 120 and ∼ 85 ka, Lake Samra rose to ∼ 320 m below MSL while it dropped to levels lower than ∼ 380 m below MSL at ∼ 135 and ∼ 75 ka, reflecting arid conditions in the drainage area. Lowstands are correlated with warm intervals in the Northern Hemisphere, while minor lake rises are probably related to cold episodes during MIS 5b and MIS 5d. Similar climate relationships are documented for the last glacial highstand Lake Lisan and the lowstand Holocene Dead Sea. Yet, the dominance of detrital calcites and precipitation of travertines in the Dead Sea basin during the last interglacial interval suggest intense pluvial conditions and possible contribution of southern sources of wetness to the region.  相似文献