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1.
Dorothy Hill 《International Journal of Earth Sciences》1959,47(2):590-629
The known palaeontological and stratigraphical evidence is used as a basis for the construction of maps of the continents showing the extent of their inundation by the sea in Sakmarian time in the Upper Palaeozoic. In the northern hemisphere apart from India the evidence is sufficiently reliable to give reasonable maps, and the great extent of the inundations suggests that the climate would be considerably modified from that of today; no undoubted Sakmarian glacials occur there. In Southern continents and India, the Gondwana biogeographical province has made correlation with the northern continents controversial, but reasons are given for assuming that Gondwana glacial deposits were at least in part Sakmarian; the resultant maps show that the Gondwana land surfaces were but little reduced in area, and that the main glacials (except for India) lie within a belt between 40 S and 20 S. Present lack of knowledge of Sakmarian conditions in Antarctica makes reconstructions of climatic belts too hazardous for possible use in enunciating or checking hypotheses of continental drift and polar wandering. 相似文献
2.
柴达木盆地北缘中生代盆地性质研究——对大柴旦凹陷的解剖 总被引：3，自引：0，他引：3
柴达木盆地北部地区的中生代地层是柴达木盆地油气勘探的重点层系之一.利用地震剖面解释成果和野外地质资料绘制了侏罗纪与白垩纪的地层残余分布图和断裂分布图;利用平衡剖面对地震剖面进行了平衡恢复.恢复了侏罗纪与自垩纪的原始与剥蚀后形态.通过对中生代各期(主要是侏罗纪和白垩纪)残余地层、断裂的分布和地震剖面构造演化的综合分析,认为柴达木盆地北部地区中生代经历了三个不同性质的盆地演化阶段:早侏罗世为伸展环境下的(箕状)断陷盆地,主要表现为一系列小型断陷盆地群;中侏罗世-早自垩世为伸展型坳陷盆地;晚白垩世末盆地受挤压整体隆升,形成古隆起. 相似文献
3.
H. Zöllner K. Reicherter P. Schikowsky 《International Journal of Earth Sciences》2008,97(5):1013-1027
The pre-Alpine structural and geological evolution in the northern part of the North German Basin have been revealed on the
basis of a very dense reflection seismic profile grid. The study area is situated in the coastal Mecklenburg Bay (Germany),
part of the southwestern Baltic Sea. From the central part of the North German Basin to the northern basin margin in the Grimmen
High area a series of high-resolution maps show the evolution from the base Zechstein to the Lower Jurassic. We present a
map of basement faults affecting the pre-Zechstein. The pre-Alpine structural evolution of the region has been determined
from digital mapping of post-Permian key horizons traced on the processed seismic time sections. The geological evolution
of the North German Basin can be separated into four distinct periods in the Rerik study area. During Late Permian and Early
Triassic evaporites and clastics were deposited. Salt movement was initiated after the deposition of the Middle Triassic Muschelkalk.
Salt pillows, which were previously unmapped in the study area, are responsible for the creation of smaller subsidence centers
and angular unconformities in the Late Triassic Keuper, especially in the vicinity of the fault-bounded Grimmen High. In this
area, partly Lower Jurassic sediments overlie the Keuper unconformably. The change from extension to compression in the regional
stress field remobilized the salt, leading to a major unconformity marked at the base of the Late Cretaceous. 相似文献
4.
深水海底峡谷内部的粗粒碎屑沉积物不仅可以作为良好的油气储层,也可以较为完整地记录海洋地质环境变迁的相关信息,是目前海洋地质领域研究的热点.为揭示南海北部珠江口外峡谷体系沉积演化过程及其控制因素,利用多波束测深和高分辨率二维多道地震数据,对珠江口外峡谷体系地形特征、沉积充填特征、形成发育过程和控制因素进行研究.研究发现珠江口外峡谷呈三段式发育:上段为NW-SE走向,宽度超过30 km,侵蚀强度不大,横截面为不规则形态;中段为E-W走向,宽度开始变窄（25~30 km）,横截面呈U型;下段为NW-SE走向,宽度达到最大（25~45 km）,横截面呈U型,中段和下段以沉积作用为主.珠江口外峡谷体系沉积演化主要分为3个阶段:早期阶段（23~15.5 Ma）,水道?海底扇阶段（15.5~11.6 Ma）和峡谷?海底扇/块体流阶段（11.6~0 Ma）.揭示了该峡谷珠江口外峡谷体系的发育和演化主要受构造运动、海平面变化和沉积物供给的控制作用,通过以上分析,将对南海北部海洋灾害地质、深水沉积体系研究及油气资源勘探有重要的指导意义. 相似文献
5.
Disperse and punctual studies; absence of integration of data ranging from local to regional focus; interpretations based only on lithostratigraphic features; and interpretation of data premised on an allochthonous origin of the Caribbean plate, are some of factors that increase the confusion and uncertainty in understanding the Sinú-San Jacinto Basin. The sedimentary record of Upper Cretaceous to Eocene has been traditionally interpreted as the record of deep-water settings. However, recently these sediments have been related to shallow marine and deltaic settings. Second problematic point is about the deposition environment of the Oligocene to Late Miocene succession. Some studies suggest canyons, turbidites and sediments deposited in deep-water settings. However, recent studies propose deltaic and shallow marine settings. The last stratigraphic problem is related to the controversial fluvial vs. shallow marine interpretations of the Pliocene sediments. Based upon seismic stratigraphic analysis in recent and reprocessed 2D seismic data, integrated with well data, we propose chronostratigraphic charts for the northern, central and southern zones of the Sinú-San Jacinto Basin. Twenty seismic facies based on amplitude, continuity, frequency and geometry of seismic reflectors and twelve seismic sequences were recognized. The seismic stratigraphic analysis in this study suggests that the sediments of Upper Cretaceous to Paleocene/Eocene were associated to continental to shallow marine settings. Lagoons, coastal plain and carbonate platform dominated during this period. The Oligocene to Middle Miocene record was characterized by deep-water deposition, whereas the Late Miocene to recent sedimentation was characterized by falling base level, characterized by deltaic and fluvial deposits. Five syn-rift sequences with wedge-shaped geometry were identified in this study. Three Triassic to Jurassic syn-rift sequences were characterized by seismic facies typical of fluvial to lacustrine and flood plain sedimentation. Two Cretaceous to Paleocene syn-rift sequences were characterized by seismic facies related to lagoons to coastal plain settings. Normal high-angle faults with a northeast-southwest direction related to rifting processes controlled the development of these sequences. The sheet-drape post-rift section was characterized by passive margin settings in the northern part of the Sinú-San Jacinto Basin and by diachronic tectonic inversion of older normal faults during Cenozoic, predominantly in the central and southern zones. The stratigraphic record related to the Mesozoic to Early Cenozoic rifting; the shallow marine sedimentation during Eocene and the tectono-stratigraphic continuity across the northern Colombia and northwestern Venezuela is coherent and well explained by the in situ origin of the Caribbean plate and is not explained by the “allochthonous” model. 相似文献
6.
松辽盆地北部白垩系由3个超层序组、8个超层序、28个沉积层序组成。断陷湖盆期发育3个超层序和6个沉积层序,以火山岩与粗碎屑岩组合为特征。断拗转化期形成1个超层序和4个沉积层序,以中粗碎屑岩为特征。典型的大型拗陷湖盆期,可识别出3个超层序和15个沉积层序,以湖泊、三角洲相中细碎屑岩沉积为主,水进体系域和高水位体系域沉积时期半深湖-深湖相暗色泥岩广为发育。湖盆萎缩期,可识别出1个超层序和3个沉积层序,以湖泊、三角洲相中粗碎屑岩沉积为主。超层序组界面包括白垩系基岩顶面、营城组顶界面和嫩江组顶界面,与燕山运动各主要幕次形成的区域不整合面相对应,区域构造运动对其起着重要的控制作用。超层序界面可以是上述超层序组界面,也可由平行不整合面和剥蚀界面构成。超层序界面处沉积间断的时间较长,河道下切、地层缺失、暴露等沉积现象发育,与岩石地层单位界面一致。沉积层序界面处沉积间断的时间相对超层序界面要短,与岩石地层单位界面往往不一致。超层序界面在地震剖面上最明显的特征是出现削截、上超和顶超等反射终止现象,岩性、测井曲线也发生剧烈变化。 相似文献
7.
The Rashidpur structure is located in the southern part of the Surma Basin, Bangladesh. This paper presents an integrated
interpretation of seismic and other geophysical data considering the available geologic information in terms of hydrocarbon
potential of this structure. The study area lies within a gravity high and a high magnetic intensity. Fifteen seismic sections
of the study area have been analyzed to interpret the subsurface geology, structure and stratigraphy. Based on the analysis
of seismic sections and correlation with well data, four prominent reflecting horizons have been identified. The litho-stratigraphy
of the Rashidpur structure is prepared on the basis of well information. The lithological sequences encountered in the Rashidpur
structure range in age from Miocene to Plio-Pliestocene. The gas producing sands of the structure are within Bokabil to Bhuban
Formations of the Miocene age. The seismic study indicates that the Rashidpur structure is a narrow, NS elongated anticline
affected by a major reverse fault on the eastern flank. It is an asymmetrical anticline with the axis swinging slightly to
the east on the northern plunge and thus attaining a slight concavity to the east. There are various geophysical indications
of hydrocarbons in this structure. 相似文献
8.
Mohammad Abdelfattah Sarhan 《Arabian Journal of Geosciences》2017,10(18):399
Mapping based on the interpreted seismic data covering the Abu Gharadig Basin in the northern Western Desert has revealed that the deposition of the Upper Cretaceous succession was controlled by dextral wrench tectonics. This dextral shear accompanied NW movement of the African Plate relative to Laurasian Plate. Structural depth maps of the Cenomanian Bahariya Formation and the Turonian-Coniacian D and A members of Abu Roash Formation display a clear NE-SW anticline dissected by NW-SE normal faults. This anticline represents one of the en echelon folds characterizing the wrench compressional component. The interpreted normal faults reflect the extensional T-fractures associated with the wrenching tectonics. The interaction between the aforementioned NE-SW anticline with the NW-SE extensional faults further confirms the effect of the Upper Cretaceous dextral wrench tectonic. However, the influence of this wrench tectonics was gradually diminishing from the Cenomanian up to the Coniacian times. The NW-SE compressional stress of the dextral wrench compressional component during the Cenomanian up to Coniacian age was greater in NW direction than the SE direction. Three mapped structural closures which are predicted to be potential hydrocarbon traps belonging to the Bahariya Formation and Abu Roash D Member, and are recommended to be drilled in the study area, with potential reservoirs. The regularity of the en echelon array of both anticlines and normal faults within the wrench zones suggests additional closures may be located elsewhere beside the study area. 相似文献
9.
详细描述了北羌塘乌兰乌拉湖地区白垩纪地层剖面，将区内白垩系划分为错居日组和桑恰山组。沉积相分析表明，乌兰乌拉湖地区错居日组主要为冲积扇至河流相沉积，岩性及厚度变化较大，而桑恰山组为湖泊、湖三角洲至河流相沉积。初步认为错居日组为早日垩世地层，桑恰山组为早白垩世晚期至晚白垩世地层。 相似文献
10.
J. R. INESON 《Sedimentology》1985,32(5):659-670
Isolated exotic blocks of late Jurassic age occur within an undeformed succession of marine Lower Cretaceous back-arc basin deposits on the west coast of James Ross Island, Antarctica. These flat, tabular slabs range up to 200 × 800 m in cross-section and lie concordant with the enclosing Cretaceous strata. Although mainly undeformed, one block displays a range of emplacement-related deformation structures, comparable in many respects to tectonic fabrics produced by simple shear. Emplacement by submarine block gliding is proposed, possibly as the final phase in the evolution of a composite mass transport event. Derivation of such gigantic slabs requires the existence of a steep, highly unstable basin margin during the early Cretaceous. In more complex terranes, differentiation between gravity slides and thrust slices can be difficult. Clearly, internal and marginal disruption of an allochthonous unit is not diagnostic since structures developed within a lithified block during submarine gliding may closely mimic tectonic fabrics. Where contact relationships are ambiguous, emplacement by gravity sliding is suggested by the increasing intensity of internal disruption towards the basal margin and by the style of deformation, reflecting simple shear under low overburden. 相似文献
11.
Summary ¶The Campanian continental margin is characterised by asymmetric half grabens and large-volume volcanic deposits. Vesuvius and Campi Flegrei are active volcanoes located along the coast of Naples Bay along one of these half grabens. The interpretation of an extensive set of seismic reflection data allowed to reconstruct the stratigraphy and structural pattern in Naples Bay and their relationships with volcanism. The stratigraphic succession is characterised by a complex architecture due to the presence of 157Ka old submarine and subaerial vents, pyroclastic flow units associated to the Campanian Ignimbrite and the Neapolitan Yellow Tuff, and numerous tuff cones younger than 12Ka. These volcanic units occur within marine sediments deposited during the late Quaternary sea level oscillations. The structural pattern is characterised by late Quaternary NE- trending normal faults, NW-trending transtensional faults, E–W trending left-lateral faults and WNW-ESE directed folds. The overall fault kinematics and the evaluated very high displacement rates are consistent with an E-trending left-lateral transtensional shear zone located between 41° and 40°N latitude. The relationship between volcanism and tectonics in the Bay of Naples is explained with block rotation associated with this shear zone. Finally, tectonic and stratigraphic data argue against the occurrence of a caldera in the Bay of Naples.Received June 24, 2002; accepted November 8, 2002 相似文献
12.
R. P. Chapman 《Mathematical Geology》1978,10(2):195-224
Univariate and multivariate statistical methods were evaluated using published multi-element stream sediment data from southwestern and northern New Brunswick. The statistical distributions of elements do not obey Ahrens' law of lognormality; eleven of thirteen elements investigated for the Bathurst-Jacquet River area are not lognormally distributed at the 0.05 level of significance. The distributions are positively skewed and leptokurtic and consist of aggregate populations which represent mineral deposits, bedrock, and many other physiographic factors; some of these populations are normally distributed. The efficiency of the Pearson correlation coefficient varied and was compared to nonparametric correlation. Various methods of factor analysis were evaluated and the structure of the factors was similar to the subjective groupings derived from the correlation matrices. Comparison of correlation coefficients and factor models derived from the log-transformed and untransformed Bathurst-Jacquet River data showed that background associations were enhanced by the log transformation at the expense of associations representing mineralization. Q-mode factor matrices could not be satisfactorily interpreted without recourse to the mapping of the factor loadings. The maps produced were inferior to simple concentration maps. An iterative technique was developed for discriminant analysis to refine the sample training groups representing mineralized and background terrain; repeated discriminant analysis after misclassified samples were eliminated altered the inherent character of the training groups. Trend surface analysis was found to give goodness of fits of the trend equations comparable to the fits expected from random numbers. The method was mathematically inappropriate for the type of data used. The goal of exploration geochemical statistical analysis should be to discriminate and sort populations representing mineralized and background populations by classification or filtering techniques. 相似文献
13.
Prof. G. Bellieni Prof. P. Comin-Chiaramonti Dr. L. S. Marques Prof. A. J. Melfi Prof. E. M. Piccirillo Prof. D. Stolfa 《Mineralogy and Petrology》1984,33(1):25-47
Summary Basalt sills (up to 200 metres thick) of tholeiitic and transitional chemistry are widespread in the Paleozoic sedimentary rocks of the Paranà basin. They closely correspond in composition to the overlying Lower Cretaceous flood basalts, and are systematically characterized by pigeonite.All sills underwent low-pressure evolurionary processes (ca. 1 kb; max. depth of intrusion about 3000 metres), essentially throughin situ crystallization of plagioclase, pyroxene, magnetite, and olivine, leading to the formation of quartz-alkali feldspar intergrowths. Mass-balance calculations indicate that differentiation proceded essentially under closed system conditions and imply a major role of Ca-rich pyroxene (liquidus phase) consistent with petrographic data.Bulk rock compositions of the sills distinguish the Paranà Lower Cretaceous magmatism into northern and southern regions characterized by high- and low-TiO2 contents, respectively.
With 11 Figures 相似文献
Die Entwicklung von Basalt-Gängen aus dem Paranà-Becken, Brasilien: Ergebnisse der Untersuchung von Bohrkernen
Zusammenfassung Basaltische Sills von tholeiitischer und Ubergangszusammensetzung sind in paläozoischen Sedimentgesteinen des Paranà-Beckens weit verbreitet. Sie können bis zu 200 m mächtig werden. In geochemischer Hinsicht sind sie mit den darüberliegenden Plateau-Basalten unterkretazischen Alters eng verwandt und durch das Auftreten von Pigeonit charakterisiert.Alle Sills haben in niedrigen Druckbereichen (maximale Intrusionstiefe ca. 3000 m) eine Kristall-Fraktionierung durchgemacht, wahrend der es hauptsächlich zurin situ-Kristallisation von Plagioklas, Pyroxen, Magnetit und Olivin kam. Dies führte zur Bildung von Verwachsungen aus Quarz und Alkalifeldspat. Massenbilanz-Berechnungen zeigen, daß die Differentiation im wesentlichen in einem geschlossenen System stattfand, und bestätigen die petrographischen Beobachtungen, nach denen Ca-reicher Pyroxen als Liquidus-Phase eine bestimmende Rolle spielte. Die chemische Pauschalzusammensetzung der. Sills untermauert die Annahme einer Trennung des Paranà-Magmatismus in eine nördliche und eine südliche Zone, welche jeweils durch hohe bzw, niedrige TiO2-Gehalte gekennzeichnet sind.
With 11 Figures 相似文献
14.
The Camden Syncline and the Lapstone Structual Complex are two major geological features of the central Sydney Basin. We have interpreted over 500 km (45 lines) of an unpublished recenty reprocessed seismic dataset as a means to elucidating the evolution of both features. Major horizons observed in the seismic data have been described and correlated with significant tectonic events that shaped the formation of the greater Sydney–Gunnedah–Bowen Basin; namely Early Permian extension, mid-Permian passive thermal subsidence and Late Permian to mid-Triassic foreland loading. Horizon mapping shows that the Camden Syncline is a broad north-northeast plunging structure whose western limb is truncated by the north–south trending faults and folds of the Lapstone Structural Complex. Furthermore, isochron maps reveal that the Late Permian to mid-Triassic sedimentary succession thickens towards the axis of the Camden Syncline, thus confirming it's role as a depocentre during this period of basin evolution. No abrupt thickening is observed in the Late Permian to mid-Triassic sedimentary succession in the vicinity of the Lapstone Structural Complex indicating that the Lapstone Structural Complex was formed subsequent to the deposition of the Permian–Triassic Sydney Basin sedimentary succession. Furthermore, our interpretation of the reprocessed seismic data confirms that the major structural style of the Lapstone Structural Complex is that of west dipping reverse faults and east facing monoclines. 相似文献
15.
The Bosworgey granite cusp forms an apical portion of the concealed northern extension of the Tregonning-Godolphin granite ridge. It is characterised by unusually high values of B, P, Mn, Fe, As, Cu, Nb, Ta, Bi, Sn, W, U and S which are present largely as tourmaline, apatite, pyrite, arsenopyrite, chalcopyrite, bismuth, columbite, cassiterite, wolframite and uraninite; and low levels of Zr, Hf, Ti and REE present in zircon, ilmenite and monazite. The granite is classified as Sn and W specialised (Tischendorf, 1974) and it belongs to the ilmenite series of Japanese workers. The classification of Chappell and White (1974) (S and I type granites) is shown to be inapplicable to Cornubian rocks although the Bosworgey samples show characteristics of S type granites. The accessory mineral assemblages are typical of high temperature lodes (cassiterite, wolframite, arsenopyrite, chalcopyrite) and the assamblage is concluded to be the cusp analogue of hypothermal lodes produced by extreme differentiation and concentration of volatiles. It is speculated that such granites could provide the parent material for the mesothermal crosscourse mineralisation (pitchblende, bismuth, pyrite, galena, sphalerite). 相似文献
16.
John W. Morse Dwight K. Gledhill Karen S. Sell Rolf S. Arvidson 《Aquatic Geochemistry》2002,8(1):3-13
In sediments from the continental slope of the Northern Gulf of Mexico, generally,the degree of iron pyritization (DOP) is low (<0.1) and dissolved sulfide is belowdetection limits (5 M), whereas dissolved Fe is typically about 50 to100 M. Therefore, the dissolution of kinetically reactive iron minerals generallydominates over the rate of sulfide production in sediments throughout this region.However, in sediments where hydrocarbons have been added via seepage from thesubsurface, dissolved-Fe is undetectable, DOP can approach 1, and high concentrationsof dissolved sulfide (up to 11 mM) are commonly present. Even though thesesediments have high total reduced sulfide (TRS) concentrations (typically 150 to370 mol gdw-1), their average C/S ratio is about 4 times that of normal marine sediments reflecting the major input of hydrocarbons. DOP is significantly (20%) higher when calculated using reactive-Fe extracted by citrate dithionite than by cold 1N HCl. This difference is primarily due to the greater extraction efficiency of the cold HCl method for silicate-Fe. TRS tends to rise to a maximum, and remains close to constant even at high (mM) dissolved sulfide concentrations. These TRS concentrations, therefore, represent the size of the ``kinetically' reactive-Fe pool during early diagenesis. 相似文献
17.
中建海底峡谷具有分段性,但分段的关键地貌特征、各段沉积充填及其控制因素缺乏精细描述和系统论证.综合利用高分辨率二维和三维地震资料,结合水深地貌数据,对中建海底峡谷地貌及沉积特征进行了详细分析,总结了其南北段沉积过程的主控因素.中建海底峡谷呈NW向顺直展布于广乐隆起与西沙隆起之间,以华光礁附近的地貌高点为拐点被分为南北两段.中建海底峡谷北段沉积体系包括重力流沉积（水道、席状沉积、滑塌体）和底流沉积（漂积体、环槽、谷槽）,南段以重力流水道和海底扇为主.北段沉积体系受底流和重力流交互作用控制,底流自中中新世开始出现,改造重力流水道,使其出现侧向迁移或翼部不对称现象,上新世以后重力流作用减弱,底流作用增强,沉积物波和漂积体广泛发育;峡谷南段水道表现出侵蚀-沉积-废弃的沉积旋回,未见底流沉积现象.相对海平面变化导致碳酸盐生产率变化影响物源供应,从而控制水道沉积演化,碳酸盐台地的“高位溢流”作用决定水道在高水位时发育. 相似文献
18.
Alastair H. Ruffell 《Cretaceous Research》1995,16(6)
Non-marine strata of Early Cretaceous age ('Wealden facies') are found at outcrop in the type localities of the Wessex Basins, southern England (and adjacent subsurface) and in extensive and thick successions filling the North Celtic Sea Basin. Sedimentology, paleontology, petrology and geochemistry have traditionally been used as evidence in determining the climatic, tectonic and sea level controls on Wealden facies, sedimentary processes and stratigraphy. Analysis of seismic data, through seismic facies and sequence stratigraphic analysis, allows direct comparison of the Wealden in these basins and new interpretations to be made of the tectonic and depositional influences. In the north-eastern end of the North Celtic Sea Basin, tectonic controls on seismic facies can be demonstrated and are related to coarse-grained fan-delta horizons documented in core. In the south-western North Celtic Sea Basin, adjacent to the Cretaceous proto-Atlantic, tectonic controls are less apparent, and changes in relative sea level were probably more important in controlling the preservation of stratigraphic sequences. Where the non-marine Lower Cretaceous succession is imaged clearly, the stratigraphic similarity between parts of the North Celtic Sea and the Weald and Channel Basins suggests a wider control by relative sea-level fluctuations. However, important variations in seismic facies within the basins indicate localized, dominant tectonic control. The recognition of a very distinctive 'lower' Wealden seismic facies, observed as undulatory (?channelized) and downlapping reflections, is contrasted with either the parallel or synsedimentary fault-dominated 'upper' Wealden facies. These seismic characteristics reflect the previously recognized climatic/tectonic change from Hastings to Weald Clay Group environments. The debate on tectonics versus eustacy is further complicated: palaeoclimate appears to be a third process responsible for stratigraphic variation. 相似文献
19.
The lead isotopic compositions of galena in Early Proterozoic gold deposits have been determined for three districts in northern Sweden and central Finland. The deposits are hosted by a variety of 1870–1890 Ma Svecofennian host rocks including the volcanosedimentary succession within the Skellefte District island arc in Sweden as well as I-type tonalites at Jörn (Sweden) and Pohjanmaa (Finland). The deposits are epigenetic in relation to these Svecofennian rocks and are part of a goldbearing metallogenetic belt, which can be followed for 600 km parallel to the southwestern margin of the Archaean Domain. In spite of these epigenetic relationships, the lead isotopic data indicate that the deposits are not dramatically younger than the 1870–1890 Ma Svecofennian host rocks (probably not exceeding 10–20 million years). Two principal lead sources were activated when the gold deposits were formed. The most significant source is represented by the I-type tonalites, which constitute a relatively primitive ( = 9.3) and widely distributed source in the entire metallogenic belt. In addition, the volcanic components in the westernmost part of the Skellefte District constitute an extremely primitive ( <9.0) source, which only locally was an important contributor to the epigenetic deposits in this metallogenetic belt. The significantly different lead isotopic composition estimated for these sources indicates that the volcanic rocks in the western part of the Skellefte District were not comagmatic with the I-type tonalites recognized at Jörn and central Finland. 相似文献
20.
Impact of dynamic sedimentation on facies heterogeneities in Lower Cretaceous peritidal deposits of central east Oman 总被引：1，自引：0，他引：1
This study, based in the Haushi‐Huqf area of central east Oman, aims to characterize the controls on facies distribution and geometries of some of the best preserved examples of Lower Cretaceous tidal flat facies within the Tethyan epeiric platform. Field, petrographic and geochemical data were acquired from the Barremian–Aptian Jurf and Qishn formations that crop out in a 500 × 1000 m2 butte, thus allowing for pseudo three‐dimensional quantitative data acquisition of the dimensions and spatial distributions of discontinuity surfaces and sedimentary bodies. The interpretation presented here suggests that the main processes impacting sedimentation in the Lower Cretaceous peritidal environment of the Haushi‐Huqf were transport and erosion processes related to storm waves and currents. The vertical evolution of the carbonate system is organized into six types of metre‐scale depositional sequences, from subtidal dominated sequences to supratidal‐capped sequences, which are bounded by regional discontinuity surfaces. At subaerial exposure and submarine erosion surfaces associated with a base level shift, sedimentary horizons along the entire depositional profile are cut by scours possibly created by storm events. Chemostratigraphy allows correlation between the Haushi‐Huqf and the age‐equivalent sections logged in the interior of the platform in Oman. The correlation suggests that the change from subtidal to intertidal depositional sequences during the late highstand is coeval with the development of rudist dominated shoals on the shelf. This study is the first to discuss the controls on Lower Cretaceous peritidal carbonate cyclicity of the Arabian epeiric platform. The results presented here also offer a unique quantitative dataset of the distribution and dimensions of peritidal carbonate shoals and storm scours in a regional sequence stratigraphic context. 相似文献