Gallium behaviour in some contrasting lateritic profiles from Cameroon and Brazil

In the supergene environment under tropical climates, the behaviour of gallium depends on the physico-chemical conditions which control the evolution stages of the residual mantle and this element is not necessarily linked to aluminum, as was formerly believed. Ga vs. Al correlation is positive in weathering profiles from West Cameroon developed on granodiorite, basalt and trachyte, which essentially result from the leaching of alkalis, alkali-earths and silicon. However, in the upper part of the profile on trachyte, which underwent later aluminization, no significant Ga vs. Al correlation was evidenced. In lateritic and bauxitic profiles from Eastern Brazilian Amazonia developed on basalt and siliciclastic sedimentary rocks, the dissociation between gallium and aluminum is clearly expressed by a negative or lack of Ga vs. Al correlation in the bauxitic horizons, resulting mainly from intense aluminization, as well as in the ferruginous horizons. In turn, Ga vs. Fe correlation is markedly positive in both cases. Thus, when dissolution of early formed Ga-containing gibbsite and kaolinite occurs, aluminum migrates and concentrates in well differentiated zones while gallium tends to be leached out of the profile or is retained by Fe-oxyhydroxides.     

Insights into the high-pressure behavior of kaolinite from infrared spectroscopy and quantum-mechanical calculations

The high-pressure behavior of Keokuk kaolinite has been studied to 9.5 GPa by infrared spectroscopy using synchrotron radiation. The kaolinite-I → kaolinite-II and kaolinite-II → kaolinite-III transformations have clear spectroscopic expression, with discontinuities coinciding with the transformation pressures bracketed by X-ray diffraction (Welch and Crichton in Am Mineral 95:651–654, 2010). The experimental spectra have been interpreted from band assignments derived from density functional theory for the structures of kaolinite-II and kaolinite-III, using as starting models the ab initio structures reported by Mercier and Le Page (Acta Crystallogr A B64:131–143, 2008, Mater Sci Technol 25:437–442, 2009) and unit-cell parameters from Welch and Crichton (Am Mineral 95:651–654, 2010). The relaxed theoretical structures are very similar to those reported by Mercier and Le Page (Acta Crystallogr A B64:131–143, 2008, Mater Sci Technol 25:437–442, 2009) in their theoretical investigation of kaolinite polytypes at high pressure. The vibrational spectra calculated from the quantum-mechanical analysis allow band assignments of the IR spectra to be made and provide insights into the behavior of different OH environments in the two high-pressure polytypes. The single perpendicular-interlayer OH group of kaolinite-III has a distinctive spectroscopic signature that is diagnostic of this polytype (ν = 3,595 cm⁻¹ at 9.5 GPa) and is sensitive to the compression/expansion of the interlayer space. This OH group also has a distinctive signature in the calculated spectra. The spectra collected on decompression are those of kaolinite-III and persist largely unchanged to 4.6 GPa, except for a continuous blue shift of the 3,595 cm⁻¹ band to 3,613 cm⁻¹. Finally, kaolinite-I is recovered at 0.6 GPa, confirming the kaolinite-III → kaolinite-I transformation previously observed by X-ray diffraction, and the irreversibility of the kaolinite-II → kaolinite-III transformation. The ambient spectra collected at the start and finish of the experiment are those of kaolinite-I, and start/finish band frequencies agree to within 6 cm⁻¹.     

云南宁蒗新生代盆地的形成与演化

宁蒗盆地地处扬子古陆块的活动边缘,在构造上亦属吸纳和调节印度-欧亚大陆碰撞应力应变的构造转化带.为了研究云南宁蒗地区新生代盆地形成、演化与区域构造的关系及盆地类型,通过对宁蒗地区开展的数幅1∶ 5万区域地质调查,分析了宁蒗盆地内部及相邻地区的构造格架特征,认为盆地的形成及演化均受控于断裂;通过对宁蒗新生代盆地的沉积建造...     

云南宁蒗新生代盆地的形成与演化

宁蒗盆地地处扬子古陆块的活动边缘,在构造上亦属吸纳和调节印度-欧亚大陆碰撞应力应变的构造转化带。为了研究云南宁蒗地区新生代盆地形成、演化与区域构造的关系及盆地类型,通过对宁蒗地区开展的数幅1∶5万区域地质调查,分析了宁蒗盆地内部及相邻地区的构造格架特征,认为盆地的形成及演化均受控于断裂;通过对宁蒗新生代盆地的沉积建造、控盆构造的时空演化及区域地质背景的研究,认为宁蒗盆地是比较典型的走滑拉分盆地,其演化经历了3个阶段古新世末至始新世初盆地拉分打开阶段、始新世初至始新世末拉分盆地沉积阶段、始新世末至中新世盆地改造阶段。     

Suspended sediment load in the Amazon basin: An overview

In this report the state of knowledge of sediment transport by rivers of the Amazon drainage basin is reviewed. On an annual basis the Amazon river transports about 1200×10⁶ tons of sediment from the South American continent to the ocean, which puts it among the world's largest rivers in this respect. The main source of sediment is erosion in the Andes mountains and this material is progressively diluted with sediment poor runoff from lowland draining tributaries. Almost half of the Amazon river transport is attributable to one tributary, the Rio Madeira (488×10⁶ t/y). The Rio Negro, which drains the N crystalline shield, has a comparable water discharge to the Rio Madeira, but only contributes 7×10⁶ t/y. In general the sediments in transport are about 1% organic carbon by weight and this results in an annual particulate carbon to the oceans of 13×10⁶ t/y. Total carbon transport, particulate plus dissolved, is about twice this amount.     

Mineralogy and geochemistry of lateritic soil profiles in Kerala, India

Lateritic soils near Calicut, Kerala, contain halloysite of intermediate hydration, kaolinite, goethite, gibbsite and quartz. The presence of halloysite is responsible for relatively high plasticity and cation-exchange capacity. Fe-hydroxide colloids along with halloysite contribute to significant phosphate uptake by this soil. Composition of local groundwater is consistent with weathering of sodic plagioclase to gibbsite, kaolinite and metastable halloysite.     

Marine muds along the Guyana coast and their origin from the Amazon basin

The mineralogical composition of clay samples from the Amazon basin and the Guyana coast, including samples collected inland and on the continental shelf, was investigated by X-ray diffraction. Also humus content, specific surface and degree of potassium fixation were determined. The muds from the Guyana coast have virtually the same composition as those of the Amazon but are very different from the Guyanese soils and river muds. This suggests that most Guyanese coastal muds come from the Amazon which is confirmed by a consideration of the quantities involved. The only measurable effect of the sea water on the mud particles moving from the Amazon to Venezuela, which takes from one month up to 1000 years, is a decrease in potassium fixation, indicating that some potassium has been taken up from the sea water. The presence of large amounts of soil chlorite in shelf samples may be due to a prolonged contact with sea water but most probably is the result of subaereal conditions during the Pleistocene.     

梅溪河流域明水中学滑坡形成机理与稳定性评价

明水中学滑坡位于梅溪河左岸,为典型的松散堆积体滑坡。通过分析坡体结构、形态、组成及变形特征等滑坡工程地质条件,认为该滑坡形成大致经历了“崩塌堆积-滑移-趋稳定-复活”4个阶段。运用GEO-SLOPE软件对滑坡变形状态进行定量分析,确定滑坡稳定性。计算结果表明,明水中学滑坡目前整体处于较稳定状态,发生整体滑动的可能性较小,但在天然工况下,滑坡体前缘已接近极限平衡状态,产生滑移的可能性较大。     

Multi-stage evolution of the Xuhuai rift: Insights from the occurrence and compositional profiles of doleritic sills in the southeastern margin of the North China Craton

Various types of igneous suites occurred between 930 Ma and 890 Ma in the North China craton are known to represent a large igneous province (LIP). However, the magma plumbing system of this LIP and its potential consequence to a breakup event are poorly understood. We report morphology, crystal size distribution of plagioclase, and whole-rock and mineral geochemistry profiles of this LIP represented by the two decoupled mafic sill complexes (Niutishan and Pingshan) in the Xuhuai basin. In terms of petrography and whole-rock geochemistry, unlike the lower-level doleritic Niutishan sill, the Pingshan sill is subdivided into an upper and a lower sequence that meets at a Sandwich Horizon but lacks stratification. The significant En reversals present an almost M-shaped profile that differs from a C-shaped profile as previously revealed in the Niutishan sill. Quantitative textural analyses show relatively strong plagioclase orientation in the lower sequence of the Pingshan sill, which is attributed to magma flow. The Pingshan sill is interpreted to have been constructed as multiple magma injections from crustal magma chambers based on the crystal size distribution and the varied crystallization pressure (5.1–7.5 kbar) of clinopyroxene crystals.Similar to the far-field radiating Dashigou dyke swarm (c. 925 Ma), the Niutishan sill is enriched in incompatible elements, which may represent the initiation of the Xuhuai rifting. However, the depleted features of the diamond-bearing Pingshan sill and the other coeval doleritic sills (916–890 Ma) were probably related to the subsequent process switched from continental rifting to lithospheric rupture in the divergent stage of the Wilson cycle. The occurrence of the intrusive rocks evolving from an early radiating dyke swarm to later sill complexes indicates a time-transgressive change from radial to planar patterns, implying that it was the upwelling asthenospheric plume material, instead of plate boundary processes, governed the initial and early evolution of this intracontinental rift.     

Backwater effects in the Amazon River basin of Brazil

The Amazon River mainstem of Brazil is so regulated by differences in the timing of tributary inputs and by seasonal storage of water on floodplains that maximum discharges exceed minimum discharges by a factor of only 3. Large tributaries that drain the southern Amazon River basin reach their peak discharges two months earlier than does the mainstem. The resulting backwater in the lowermost 800 km of two large southern tributaries, the Madeira and Purús rivers, causes falling river stages to be as much as 2–3 m higher than rising stages at any given discharge. Large tributaries that drain the northernmost Amazon River basin reach their annual minimum discharges three to four months later than does the mainstem. In the lowermost 300–400 km of the Negro River, the largest northern tributary and the fifth largest river in the world, the lowest stages of the year correspond to those of the Amazon River mainstem rather than to those in the upstream reaches of the Negro River.     

Facies pattern of the middle Permian Barren Measures Formation, Jharia basin, India: The sedimentary response to basin tectonics

In the Lower Gondwana succession of the Jharia basin of eastern India, the Barren Measures Formation is characterized by the cyclic disposition of fine-grained lacustrine deposits and relatively coarse-grained fluvial deposits. The cyclic variation in the rate of coarse clastic input is attributed to the sedimentary response to basin tectonics. The sandstone-shale alternations of the Barren Measures succession can be correlated with the tectonic cyclothems developed on the hangingwall dip-slope and adjoining trough in a continental half-graben setting. Enhancement of the gradient of the hangingwall dip-slope during reactivation of the basin margin faults led to progradation of the existing fluvial system towards the half-graben trough and deposition of the coarser clastics on the fine-grained lacustrine deposits of the trough. Peneplanation of the hangingwall slope and slow increase in the lake level caused lacustrine transgression and retrogration of the fluvial system on the hangingwall block. The fluvial sediments were onlapped by the fine-grained lacustrine deposits. Episodic rejuvenation of the basin margin faults thus caused development of tectonic cyclothem on the hangingwall block. The paleocurrent pattern indicates that a persistent northward paleoslope was maintained during Barren Measures sedimentation. The inferred depositional settings were much more extensive than the present limit of the outcrop. The faults, presently defining the northern limit of the Barren Measures Formation, were possibly emplaced after Barren Measures sedimentation. The final movement along these fault planes caused preservation of the downthrown hangingwall block and the Barren Measures sediments on the footwall block were eroded during subsequent denudation. The Southern Boundary Fault came into existence after the deposition of the Barren Measures sediments.     

鄂尔多斯盆地马五5亚段沉积微相分布及演化

岩性及沉积环境的差异是鄂尔多斯盆地下奥陶统马家沟组马五5亚段储层非均质性的重要因素,根据岩石类型、沉积构造及颜色等特征及其与沉积微相的关系,研究区马五5亚段可分为盆缘坪和台内盆地两个亚相及缘内（膏）云质洼地、缘内云坪、缘内灰坪、缘内云灰-灰云坪、盆地（膏）云质洼地、灰云-云灰质盆地及灰质盆地等微相。沉积微相平面上表现为,马五5²时期,鄂尔多斯盆地基底抬升,中央古隆起带露出水面;北部地区发育缘内云坪-云质洼地、缘内灰云-云灰坪和灰质盆地;西部地区为缘内云坪-云质洼地、缘内灰云-云灰坪;中部地区为灰质盆地,间夹云灰盆地及盆内云质洼地;马五5¹时期,北部地区主要发育缘内云坪-云质洼地;西部地区为缘内云坪-云质洼地;中部地区为灰质盆地及盆内云质洼地。盆缘坪和台内盆地的低洼处有利于发生同生期后回流渗透白云化作用,对生成较大规模的泥粉晶白云岩具有重要的意义。     

塔里木盆地西部地区中奥陶统一间房组沉积演化及其控制因素

塔里木盆地中奥陶统一间房组沉积演化和沉积层序的发育特征及其控制因素目前还存在争议。选择塔里木盆地西部良里塔格山地区一间房组为研究对象,基于沉积相和高频米级沉积旋回类型的识别及其垂向叠置样式的分析,明确一间房组的沉积演化和沉积层序的发育特征及其控制因素。研究表明：(1)一间房组沉积时期,良里塔格山地区整体为一个碳酸盐岩缓坡沉积体系,主要发育10种岩相类型和2个沉积相带(潮缘—局限潮下带和开阔潮下带);(2)一间房组发育两种高频米级沉积旋回,分别为潮缘—局限潮下沉积旋回和开阔潮下沉积旋回;(3)识别出2个半三级层序,层序界面主要为岩性转换面,其中一个完整的三级层序包括海侵体系域和海退体系域两部分;(4)沉积演化与层序发育的主要控制因素包括古地理格局、沉积微地貌及不同级次的相对海平面变化。其中古地理格局控制着整体的沉积相带分布,沉积微地貌决定着特定岩相(如瓶筐石礁)发育的优势部位,不同级次相对海平面变化则制约着沉积相的时空演化。     

Geochronology of metarhyolites from the Kangbutiebao Formation in the Kelang basin, Altay Mountains, Xinjiang: Implications for the tectonic evolution and metallogeny

The Altay orogenic belt (AOB), situated in the middle part of the Central Asian Orogenic Belt (CAOB), is one of the most important metallogenic belts in China. The Kangbutiebao Formation is a Late Paleozoic stratigraphic unit that hosts many important iron and Pb–Zn deposits. The Kangbutiebao Formation consists of intercalated volcanic and sedimentary rocks that have undergone regional greenschist to lower amphibolite facies metamorphism, and mainly outcrops in three NW-trending fault-bounded volcano–sedimentary basins, including the Maizi, Kelang, and Chonghuer basins. SHRIMP analyses of zircons from three metarhyolites of the Kangbutiebao Fm. in the Kelang Basin yield weighted mean ²⁰⁶Pb/²³⁸U ages of 412.6 ± 3.5 Ma, 408.7 ± 5.3 Ma and 406.7 ± 4.3 Ma, respectively, which can be interpreted as the eruption age of the Kangbutiebao silicic volcanic rocks in the Kelang Basin. These ages indicate that the Kangbutiebao Formation was formed during the Late Silurian to Early Devonian. They also demonstrate that the deposits hosted in the Kangbutiebao Formation were formed after 412–407 Ma. They play a key role in understanding the Paleozoic tectonic evolution and metallogenesis of the southern margin of the Chinese AOB.     

鄂尔多斯盆地南部延长组沉积体系和层序特征

鄂尔多斯盆地南部延长组沉积体系类型形成于不同的地质背景,物源方向和沉积环境也不同,因此沉积特征和分布规律差异较大。以主力含油层段长8油组为例,辫状河三角洲体系主要位于盆地西南缘较陡坡带,砂体为长石砂岩,以槽状层理构造发育、前三角洲中有重力流沉积为特征;重力流沉积主要分布在盆地南部渭北地区的长7油层段,以岩屑砂岩为主,形成于深湖环境中,发育的鲍玛组合层序有ABCE、ADE、AE和BCE型序列;东北方向水系形成了曲流河三角洲体系,主要位于盆地东北缓坡带上,三角洲分流河道伸展距离长,朵体规模大,以长石细砂岩为主,河口砂坝发育。     

δ31Corg perturbations preserved by the interglacial Datangpo Formation in South China with implications for stratigraphic correlation and carbon cycle

Palaeoclimatic and palaeoenvironmental reconstructions of the Cryogenian Period have attracted attention in relation to the debated “Snowball Earth ” hypothesis and the early evolution of metazoan life. The carbon cycle and redox conditions of the Sturtian-Marinoan non-glacial interval have been subjected to much controversy in the past decades because of the lack of a high-resolution stratigraphic correlation scheme. As one of the typical Sturtian-Marinoan interglacial deposits, the Datangpo Fo...     

Erratic shortening from balanced cross-sections of the western Himalayan foreland basin: causes and implications for basin evolution

Balanced cross-sections from the western Himalayan foreland foothill belt reveal a variation in shortening amounts from 22 to 71.3% over a lateral distance of 85 km. The large variation may be attributed to the fact that the method of cross-section balancing considers the initial layering as horizontal, which is an unlikely situation in foreland basins. Simple trigonometric relationships are used to minimize the error in shortening estimates. However, the suggested corrections could not be applied to the Himalayan foreland basin because of unavailability of the required data on initial basin geometry. The study also indicates that shortening rates for the area based on these shortening amounts cannot be used for earthquake prediction.     

鄂尔多斯盆地晚三叠世延长组湖盆演化及石油聚集规律

延长组湖岸线、深湖线及湖盆底形恢复显示,延长组湖盆具有向西南部迁移,再向东北部迁移的演化特点。长6期湖盆底形具有"南陡北缓、西陡东缓"的特点,盆地中心位于庙湾以北、正宁以东、甘泉以南地带,造成盆地东北部为缓坡型三角洲体系,而西南部为陡坡型辫状河三角洲,前缘末端发育浊积扇。延长组划分为5个三级层序,控制了4套生储盖的分布。延长组湖盆演化与石油的聚集关系密切,湖岸线附近的三角洲前缘是油气的主要富集区,深湖区的浊积砂体也具有一定的储集性能和良好的成藏条件。东北部、西南部主要成藏组合及深湖浊积岩的特征表明,可以进一步向盆地腹地扩大勘探。     

四川盆地东北部长兴期沉积相、沉积模式及其演化

笔者根据四川盆地东北部长兴组沉积特点,将其分为台地边缘生物礁相、台地边缘浅滩相、开阔台地相、局限台地相、碳酸盐斜坡相、盆地相和蒸发台地相等7个基本的相带。由于期间经历了一次二级海平面的升降过程,使得长兴组广泛发育海侵生物礁滩,形成了两类最为有利的储集相带。礁滩沉积相带在纵横向上不断迁移、抬升,主要发育于台盆的两侧,呈带状分布,明显受沉积相带控制。主要沉积微相类型有生物粘结云岩微相、亮晶颗粒云岩微相、角砾云岩微相、云泥岩微相、生物粘结灰岩微相、灰泥岩微相、亮晶颗粒灰岩微相和介屑灰岩等,其中对储层最有利的微相类型是角砾云岩微相、生物粘结云岩微相和亮晶颗粒云岩微相。在详细研究分析各沉积相带沉积特点的基础上,探讨了该期沉积相带的空间展布。利用钻井、野外露头、岩心和岩石薄片等资料,对目的层进行了沉积相和沉积微相研究的基础上,建立了研究区的沉积模式以及对沉积模式的演化进行了研究,最后编制了沉积相平面分布。     

伊宁地块石炭纪火山岩及其对构造演化的约束

西天山伊宁地块的构造格局及其演化之认识久存争议,倍受关注。分歧焦点有三:(1)石炭纪有无洋盆存在?(2)若有洋盆,何时闭合?(3)"沟-弧-盆"消亡时究竟是单向俯冲还是双向俯冲?若是单向俯冲,俯冲方向是由北向南或是相反(即俯冲极性)?因此,这些重大地质问题均聚焦于本区的火山岩。石炭纪火山岩是伊宁地块中的最主要建造和指示构造演化的关键层位,争论长久而激烈。本文认为,伊宁地块早石炭世发育弧前-岛弧-弧后盆地钙碱性火山-沉积建造,是塔里木板块北缘的主要组成部分;而晚石炭世碱性系列双峰式火山岩及其沉积组合则是大陆裂谷火山-沉积建造,形成于区域性伸展构造环境,是准噶尔板块与塔里木板块缝合后的陆内建造,因而古洋盆的关闭时限是早石炭世晚期(鄯善运动)。依据区内早石炭世建造的空间分布和变化规律,作者们认为古天山洋盆与当今地学界作为典型的日本沟-弧-盆体系有着极好的相似性和空间分布可对比性。石炭纪火山岩为本区的构造演化研究提供了重要的约束信息。