Ri-μi/μm-Ci dependent oblateness of deformed pebbles in the Baraitha conglomerate,Central India and tectonic implications

Strain analysis of the Baraitha conglomerate is attempted by direct measurements on extracted pebbles and by micrometric analysis. The overall deformation is of flattening type, with thek value lower by more than half in the matrix than in the pebbles. The viscosity contrast between pebbles and matrix (μ _i/μ_m) is in the ratio of 2:1 and the bulk deformation appears to be strongly controlled by C_i (concentration of pebbles expressed as percentage). The total shortening (≃35%) in the Baraitha conglomerate is comparable with the shortening accomplished in the folding of the overlying Bijawar Group volcanosedimentary sequence. The bulk strain axesX _t, Y_t andZ _t, as determined from the analysis of the deformed conglomerate, are unsymmetrically oriented with reference to folds formed by oblique flexural-slip with neitherX _t norY _tcoincident with the fold hinges. The lack of transection of folds by cleavage again suggests flattening deformation. The extension in theY _tdirection is greater in the matrix than in the pebbles.     

内蒙古大青山煤田晚古生代砾岩的沉积特征

大青山煤田晚古生代地层中有 1 4层沉积砾岩。其中,晚石炭世地层中赋存 8层,二叠世 6层。通过对这些砾岩层的野外测量、室内岩矿鉴定等综合分析研究,查明晚石炭世的砾岩几乎全是稳定的单成分砾岩,石英砂岩和燧石质砾石的含量高达 93 %以上,砾石最大扁平面均向南倾,倾角在 5° - 1 0°之间,与砾岩伴生的粗粒石英砂岩发育大型低角度双向交错层理,萨胡环境判别参数等特征表明晚石炭世砾岩为滨海环境下的产物。二叠世的砾岩则主要是复杂成分的砾岩,尤其是早二叠世晚期及晚二叠世初期形成的 2层砾岩中砾石种类达 1 5种,以中酸性火山岩和火山碎屑岩砾石为主,并含较多量的变质岩和中酸性侵入岩砾石,砾岩层各种特征表明二叠世砾岩为河流相产物。大青山煤田晚古生代沉积砾岩的形成与北部造山带的隆升密切相关,它们是前陆盆地的沉积产物。     

大兴安岭北部绣峰组下部砾岩的形成时代及其大地构造意义

对漠河盆地南缘绣峰组下部砾岩的野外观察，发现其碎屑物除了主要来源于被前人置于新元古代的花岗岩外，还含有火山岩砾石；与上部砂岩之间被断层分隔而不是连续沉积。作为该砾岩主要源岩的花岗岩中的锆石蒸发法年龄为354-164Ma，锆石SHRIMP定年揭示其最后一次岩浆活动可能发生在早侏罗世(180-190Ma)；全岩-长石-黑云母内部Rb-Sr等时线年龄为177～191Ma，黑云母Ar-Ar年龄为171～175Ma，表明该岩基在中侏罗世还深埋地下没有出露地表。其中的火山岩砾石的岩石学和岩石化学特征与区域上晚侏罗世塔木兰沟组火山岩类似。结合区域地质资料，推测该砾岩的形成时代不是中侏罗世，而可能是早白垩世；漠河盆地是与蒙古-鄂霍茨克造山带有关的前陆盆地，而不是侏罗纪陆内断陷盆地。     

Quantitative finite strain and kinematic flow analyses along the Zagros transpression zone, Iran

The Ghouri area in southwest Iran exposes a cross section through the Zagros orogenic belt. The area provides an opportunity to investigate quantitative finite strain (Rs), kinematic vorticity number (W_k), proportions of pure shear and simple shear components, sense of shear indicators, steeply plunging lineations, and other moderate to steeply plunging stretching lineations in a transpressional zone. Based on a classical strain analysis of deformed microfossils with oblate strain ellipsoid shape, the Zagros orogenic belt is classified as a pure-shear dominated zone of transpression, but asymmetry of shear-sense indicators suggests that a significant component of simple shear was involved along the deformation zone boundaries. The long axes of the microfossils and stretched pebbles of a deformed conglomerate were used to indicate the stretching direction in this zone. The stretching lineations have a steep to moderate plunge but a constant strain magnitude. Characteristics of dextral inclined transpressional kinematics in the Zagros continental collision zone were quantified and indicate an estimated k-value < 1, an angle between the maximum horizontal axis of the instantaneous strain ellipsoid and the zone boundary (θ = 32°), asymmetrical dextral shear-sense indicators, and an angle of relative plate motion (α = 25°).     

库车前陆盆地上侏罗统-下白垩统砾岩特征与构造演化关系

库车前陆盆地充填有上侏罗统喀拉扎组砾岩、下白垩统底部亚格列木组砾岩和下白垩统上部巴什基奇克组砾岩,通过对这三套砾岩区域分布特征、岩石学特征、砾态特征、厚度变化特征的详细描述与此三套砾岩沉积古环境的差异对比研究,认为库车前陆盆地中部库车河地区及西部卡普沙良河地区这三套砾岩成份复杂多样,具低成份与结构成熟度;所代表的气候演化特征由早到晚依次为:干旱、半干旱→温暖、湿润→干旱、炎热气候;所反映的沉积相为冲积扇、浊积扇和季节性辫状河沉积。砾岩与构造关系的结果分析表明,喀拉扎组砾岩是晚侏罗世构造活动的标志,亚格列木组砾岩为早白垩世初逆冲推覆活动的开始,巴什基奇克组砾岩则是早白垩世末构造宁静期的沉积响应产物。     

阿尔金山脉新生代剥露历史——前陆盆地沉积记录

新疆且末县江尕勒萨依盆地位于阿尔金山脉的北西山前,其内连续沉积了中生代一新生代地层。盆地内古新统一始新统为河流相沉积;渐新统至中新统为山麓河流相灰色砾岩和棕色砂岩;上新统为山麓洪积相砾岩夹泥岩;下更新统全为砾岩层。岩性组合特征及其砂岩碎屑、砾石组分变化规律,反映出阿尔金山脉的新生代剥蚀历史：古近纪早、中期,阿尔金山脉的地形高差小,古生界双峰式火山岩首先被剥蚀;至渐新世末一中新世早期,山脉高差加大,基底元古宇开始出露地表被剥蚀;中新世末期,山脉高差进一步加大,剥蚀速率加快;至第四纪早期西域砾岩开始沉积时,地形高差加剧,中、古元古界开始暴露被剥蚀。区域资料分析表明,阿尔金山脉在新生代具有多期次阶段性隆升的特征,存在3期次快速隆升事件：渐新世末一中新世早期、中新世晚期(大约8Ma)和第四纪早期。     

北票盆地侏罗纪砾岩沉积特征及对区域构造演化的指示

陆相盆地充填沉积物中砾岩沉积特征分析是示踪物源及反演源区构造演化背景的重要手段之一。通过对辽西北票盆地侏罗系的砾岩层沉积特征及砾岩的分散型式分析发现，北票盆地砾岩的沉积特征明显受到火山作用的影响，物源主要以盆地前期或同期火山岩及西缘前中生代沉积地层和变质岩系为主，砾石成分组成自下向上表现出一定的规律性变化，与盆地两次大的火山－沉积作用旋回有很好的对应关系，表现为从沉积早期以火山岩砾石为主向晚期以沉积岩及变质岩砾石为主的演化过程。早侏罗世晚期及晚侏罗世晚期砾岩主要为复成分砾岩，松散堆积，填隙物主要为泥砂质．分散型式为混合型，应为盆地在侏罗纪经历的两次大的逆冲推覆作用的沉积响应。中侏罗海房沟组巨厚的粗砾岩沉积对应于盆地西缘的一次快速隆升事件。     

粤北丹霞盆地晚白垩世丹霞组沉积相及古气候意义

粤北丹霞山作为世界自然遗产"中国丹霞"的典型代表,在地貌方面已经积累了丰富的研究成果,但是对丹霞地貌成景地层(晚白垩世红层)的沉积环境和古气候的研究较少。通过对巴寨剖面丹霞组的野外观测、砾石统计、室内砂岩样品薄片鉴定及粒度分析,进行详细的沉积相研究。巴寨剖面丹霞组出露巴寨段和锦石岩段,前者以砾岩为主,发育粒序层理及平行层理、底侵蚀面、叠瓦状构造等,而后者以发育大型交错层理的风成砂岩夹古土壤为特征。在盆地其他位置,可见丹霞组白寨顶段砾岩地层。研究结果表明,在巴寨剖面的晚白垩世丹霞组红层中,可以识别出正粒序层理砾岩、逆粒序层理砾岩、平行层理砾岩、无沉积构造砾岩、大型交错层理风成砂岩、中—薄层砂岩、古土壤7种岩相。巴寨段砾石大小主要为0.5～9.5 cm,成分以脉石英、石英砂岩及砖红色砂岩为主。锦石岩段砂岩粒径为0.03～0.5 mm,分选性好,以跳跃组分为主,指示风成环境。丹霞组从巴寨段到锦石岩段沉积物粒度变细、沉积速率由快变慢,指示了由河流主导的冲积扇沉积体系向沙漠沉积体系的转变,反映了古气候向干热变化,锦石岩段的风成砂岩可能与东亚中纬度地区晚白垩世Campanian期古气候广泛的干旱化有关。丹霞组沉积末期(白寨顶段),古气候条件再次变湿,降水增加,河流将粗粒碎屑物再次搬运到盆地发生沉积,新的冲积扇叠覆在锦石岩段风成砂岩—古土壤序列之上。     

辽宁兴城龙回头盆地海房沟组地层序列 及沉积环境研究

[摘 要]龙回头盆地是位于辽宁省葫芦岛南的小型中生代盆地,盆地内充填中侏罗统海房沟组,本文以研究盆地内海房沟组地层序列及沉积环境为目的,在盆地内进行实测剖面、砾岩成分统计、砾岩粒径统计、砂岩粒度分析等工作,在海房沟组内发现植物化石(Podozamitaceae gen.indet.)及煤线,认为盆地内海房沟组与锦西南票盘道沟海房沟组及北票海房沟村海房沟组岩石地层序列可以对比。对砾岩的研究结果表明,盆地内砾岩普遍具有短距离搬运、快速堆积的特点,并通过分析剖面内砾岩、砂岩、粉砂岩及泥岩的岩石组合特征,认为盆地内海房沟组属山前盆地冲积扇相。     

四川大邑-汶川地区侏罗-第三系砾岩特征及沉积环境

龙门山中南段四川大邑、崇州、都江堰、汶川地区，侏罗系、白垩系、第三系发育良好，划分为侏罗系白田坝组、千佛岩组、沙溪庙组、遂宁组、莲花口组及五龙沟砾岩一组至三组；白垩系天马山组、夹关组和灌口组；下第三系名山组和上第三系（上部包括部分第四系）的大邑砾岩等岩石地层单元。各个地层单元中几乎都有砾岩沉积。概述了该区砾岩的时空分布及特征，按沉积环境将砾岩划分为冲积扇砾岩、河道滞留砾岩及湖滨砾岩等，最后讨论了物源区及其时空演化。     

云南省南涧地区下白垩统南新组砾岩层 砾组特征及其物源意义

该文通过对哀牢山构造带西侧云南省南涧地区下白垩统南新组砾岩层的砾性、砾度、砾态和砾向等的详细研究与分 析,结合盆地基岩地层特点和周边构造带的岩性组合特征,发现南新组砾岩总体上具有砾石成分复杂、分选性较差、磨圆程 度中等-较好（次圆状-圆状）、风化程度较低等特征;探讨了砾岩层本身的性质、物质来源,以及砾石沉积时盆地的水动力条 件、气候环境、古地貌特征和构造条件。认为南新组砾岩层为半干旱-干旱古气候条件下的一套冲积扇-辫状河相粗碎屑沉 积,具有快速堆积的特点;砾岩层沉积前砾石遭受了较强的物理化学作用。根据盆地基岩及周边地层岩性特点和砾石扁平面 倾向统计,砾石的主要来源是盆地内部的基底地层及其东缘的哀牢山构造带。     

新疆富蕴盆地下石炭统“底砾岩”特征及其大地构造意义

研究表明新疆富蕴盆地早石炭世黑山头组、南明水组主要为一套滨、浅海相沉积,地层之间发育多套砾岩层,呈透镜体状,横向上延伸不远,为河流入海时形成的一系列水下河道沉积,而并非前人所认为的萨吾尔造山运动形成的构造底砾岩。砾岩层横向特征的对比及交错层理、波痕等古流向数据,表明地层沉积时期水体古流向总体自北西向南东(介于93°~125°),物源区位于盆地北西方向。研究区内黑山头组与南明水组之间为连续沉积,整合接触,并非准噶尔地块与西伯利亚板块的碰撞形成的构造不整合面。     

New data on hydrocarbons in auriferous conglomerates of the Witwatersrand ore region, Republic of South Africa

Genesis of deposits in the world’s largest Witwatersrand auriferous region (South Africa) remains a debatable issue over several decades. Based on geological and mineralogical-geochemical investigations, we previously proposed a sedimentary-exhalative hypothesis for its origin. In the present communication, we have attempted to develop and scrutinize this concept based on the study of organic matter in ore and nonore conglomerates, quartz in conglomerate pebbles, and fluid inclusions in quartz from pebbles and cement of ore and nonore conglomerates.     

Sedimentology and tectonic implications of Cretaceous fan-delta conglomerates, Queen Charlotte Islands, Canada

The Honna Formation, of Coniacian age, consists of several hundred metres of polymictic clast-supported conglomerate associated with sandstone and mudstone. Five conglomerate facies are recognized: ungraded beds; inverse graded beds; normal graded beds; inverse-to-normal graded beds; and parallel-stratified beds. These facies are interpreted as the deposits of subaqueous cohesionless debris flows and/or high-density turbidity currents. The depositional environment was a deep-water, gravelly fan that draped a fault-controlled, basin-margin slope. The fan is inferred to have passed upslope directly into an alluvial fan (unpreserved); hence, the name fan delta can be applied to the overall depositional system. This type of fan delta, of which the Brae oilfield in the North Sea is an example, is defined here as a deep-water fan delta. The lack of a shelf is in marked contrast to other types of fan delta. Three facies associations are recognized in the Honna Formation: subaqueous proximal-fan conglomerates, distal-fan turbiditic sandstones, and pro-fan/interfan mudstones with thin sandy turbidites. The proximal fan is envisaged as an unchannelled gravel belt with a downslope length of at least 20 km; such a long subaqueous gravel belt lacks a known modern analogue. The distal fan was an unchannelled sandy extension of the proximal gravel belt. It is postulated that the Honna Formation accumulated in a foreland basin which migrated westwards from the Coast Mountains where the Wrangellia-Alexander terrane was colliding with North America. In this model, the Honna fan delta was sourced by a (west-verging) thrust sheet whose sole-thrust was the Sandspit Fault immediately to the east. Deep-water fan deltas appear to develop preferentially when eustatic sea-level is relatively high, so that the‘feeder’ alluvial fan is small, and gravelly throughout. In petroleum exploration and field development, care should be taken to distinguish deep-water fan deltas from base-of-slope (canyon-fed) submarine fans, because the two systems differ significantly in terms of coarse-sediment distribution.     

渤海中部古近系沙河街组有利砾岩类储层特征

渤海湾盆地是我国重要的含油气盆地,其中古近系沙河街组发育储集性较好的砾岩储层。通过对储层岩石薄片显微鉴定、物性分析、扫描电镜分析、阴极发光分析等,明确了沙河街组有利的砾岩储层的岩石学、储集性和成岩作用特征。砾岩类型多样,其中云质砾岩的储集性最好。砾岩储层物性较好,平均孔隙度为16.1%,平均渗透率为217.93m D。主要孔隙类型为原生孔,原生孔类型主要为砾石间残余原生孔和生物碎屑体腔孔,其次是溶蚀孔。砾岩储层成岩作用类型与砾岩填隙物成分关系密切,以砂岩为主要填隙物的成岩作用中有显著的长石溶蚀作用,以碳酸盐岩为主要填隙物的则具有多期白云石和方解石等胶结物,最有利的成岩作用是早期白云石衬垫和长石的溶蚀作用。     

Texture and structure of resedimented conglomerates: examples from Książ Formation (Famennian—Tournaisian), southwestern Poland

The Famennian-Tournaisian conglomerates and sandstones of the Ksiaz Formation are interpreted as marine resedimented deposits. Matrix- and clast-supported conglomerate beds are equally common, and two textural sequences (motifs) have been recognized: (I) matrix-rich conglomerate → pebbly sandstone → sandstone, and (II) clast-supported conglomerate → sandstone. Variation in clast type partly controls motif type, and therefore, to some extent, matrix percentage in the conglomerates generally. Grading is extremely common in both clast- and matrix-supported conglomerates: inverse (19%), inverse-to-normal (14%) and normal (26%). The studied succession, itself part of a 4 km thick, fan delta, basin-fill sequence, is organized into large (110–150 m) and small-scale (5–30 m) sequences, both of which show (1) upward coarsening and thickening, (2) upward trend of sandstones and pebbly sandstone → matrix-rich conglomerates → clast-supported conglomerates and (3) a less clear upward tendency of massive and normally graded beds → inversely graded beds. Variation in matrix percentage in beds is therefore also partly controlled by fan processes, during the progradation of fan bodies and lobes. It is predicted that individual resedimented conglomerate beds or motifs show general downfan trends in thickness, texture and structure opposite to those evident in the vertical sequences.     

Tectono-sedimentary evolution of the Miocene Oued Dayr Formation (Ghomaride Complex,Internal Domain of the Maghrebian Rif Belt,Morocco)

This work deals with sedimentological, petrographic, and structural analyses of a middle Miocene late-orogenic sedimentary cycle, denoted Oued Dayr Formation, recognized in the Rifian sector of the Maghrebian Chain (Morocco). The analyzed Formation (75 m thick) starts with 15–20 m of light colored polymict conglomerates, with minor sandstone beds, lying on the Paleozoic basement and Mesozoic cover of the Ghomaride Nappe. Facies analysis indicates a fining-upward deposition in a marine environment characterized by increasing deepening, reflecting a subsidence rate that exceeds sedimentary supply. Petrographic analysis points out that sandstones are represented by litharenites originated by erosion of recycled orogen. The conglomerates pebbles and cobbles consist of Alpine low- to high-grade metamorphic rocks as metarenites, phyllites, mylonitic quartzites, micaschists, augen gneisses deriving from the exhumed deep metamorphic basement, the overlying metasedimentary of the Sebtide Nappes and of sedimentary rocks as sandstones, jaspes, limestones, and shales deriving from the Ghomaride Nappes and their sedimentary cover. Data reveal mixed provenance indicating that the Oued Dayr Formation was fed by the Internal Nappes stack of the Maghrebian Chain. Structural analysis shows that the Oued Dayr Formation accumulated in a Thrust-Top basin, during an early extension (D₀ phase), recorded by synsedimentary normal faults within middle Langhian deposits on the rear of the Internal Nappes stack. Subsequent ductile and brittle compressional (D₁, D₂, D₃) and extensional (D₄) deformation phases occurred during and/or after the stacking, exhumation, and early unroofing of Sebtide Complex coeval with the opening of the western Mediterranean back-arc basins since middle Miocene time.     

准南前陆盆地燕山期构造活动及其成藏意义

准南前陆盆地燕山期盆地格局的演变、沉积中心有规律的迁移、沉积特征(与构造活动相关的砾岩及其分布)显示晚侏罗世—早白垩世早期、晚白垩世是准南前陆盆地燕山期构造活动相对活跃的时期。晚侏罗世—早白垩世早期的喀拉扎砾岩、白垩系清水河组底砾岩为一套形成于邻近高地附近的剥蚀产物或冲积产物,其分布特征及成因是晚侏罗世—早白垩世早期局部挤压和构造隆升较为活跃的产物,也是盆地边界萎缩、盆山格局发生变化的重要证据,同时天山明显隆升并导致天山南北早白垩世沉积环境的巨大差异。准南前陆盆地烃源岩大量生排烃、圈闭形成、油气运聚成藏与燕山期构造活动关系密切;燕山期发育的储层是准南前陆盆地的主要油气储层,晚侏罗世—早白垩世早期砂砾岩和不整合分布也在一定程度上控制了油气分布,是今后寻找有利隐蔽油气藏、岩性地层油气藏的重要目标之一;燕山期古构造及其形成时间与油气成藏期的良好匹配决定其油气成藏的有效性。     

黑龙江东部林口地区下白垩统穆棱组 砾岩的成因及其意义

大三江地区是中国东部重要的油气资源接替区,早白垩世时期该地区曾为一个统一的盆地,之后盆地遭受破坏分解。如何确定当时的盆地边界进而恢复盆地原型,是该地区亟待解决的关键地质问题之一。前人对盆地边界的确定大都以理论推测为主,缺乏实际证据。本次工作在黑龙江林口地区发现一套穆棱组底部砾岩,对砾石进行成分及分选特征、沉积特征等的统计与分析,结合古水流恢复和地震解释资料,认为该套砾岩整体为冲积扇相,以河道砾岩沉积和漫流砾岩沉积为主,物源主要来自盆地西部的张广才岭。结合地震资料分析,认为研究区穆棱组时期的沉积模型为冲积扇相向滨浅湖亚相的直接过渡。本研究不仅为大三江盆地西部边界的确定提供了直接证据,同时也为该地区今后的油气勘探指明了方向。     

辽西北票盆地中侏罗统海房沟组砾岩沉积特征与成因

通过对总长2 705 m两条剖面的实测、40块薄片鉴定、419个砾石统计及其粒度分析,确定了辽西地区北票盆地中侏罗统海房沟组砾岩的沉积特征及成因。研究表明：辽西北票盆地海房沟组主要岩性为一套冲积扇相的复成分砾岩,并夹一套喷溢相下部亚相安山质角砾熔岩和另一套爆发相空落亚相安山质角砾凝灰岩、热碎屑流亚相安山质角砾凝灰熔岩;海房沟组沉积物源来自研究区SSW向的太古宇变质岩及结晶基底和下侏罗统兴隆沟组火山岩的全面快速隆升剥蚀。结合构造背景,通过对北票组与海房沟组界线的研究和岩性岩相的鉴定,确定海房沟组冲积扇相的复成分砾岩是燕山运动二期挤压伸展构造运动的重要产物,两套中酸性火山岩的出现是两次火山喷发的重要标识。