兰州-民和盆地早白垩世的沉积环境分析

兰州－民和盆地早白垩世充填了巨厚的陆源碎屑物,笔者通过对碎屑物组合方式的研究,陆盆内为冲积扇相→湖泊相→湖控三角洲相序的充填序列;通过对陆盆的基底特征,古流向、物源区和陆盆演化的分析,揭示了盆地的沉积特征。     

Metallogeny,structural, lithological and time controls of ore deposition in anoxic environments

Accumulation of metals in anoxic environments occurs by sorption and precipitation from seawater, fossil brines or hydrothermal solutions. Metals can be remobilized during subsequent metamorphic and magmatic processes and form ore deposits. This type of mineralization is governed chiefly by the type of tectonic setting of the anoxic environment. Carbonaceous sediments of passive margins contain only subeconomic concentrations of uranium, vanadium and molybdenum. Cubearing black shales and the submarine-exhalative type of mineralization are confined to the environments of continental rifts and aulacogens or to back-arc basins of active margins. Metamorphogenic deposits are mainly connected with collision margins but they may also occur in other types of tectonic environments. The formation of Cu-bearing black shales was controlled by period of low sea-level during the break-up of supercontinents in the Earth's evolution. Increased contents of uranium and vanadium accumulated in black shales in periods of sealevel highstands. Lithological control is apparent in deposits of Cu-bearing and uraniferous black shales. On the contrary, the occurrence of polymetallic mineralization does not depend on the lithological maturity of carbonaceous sediments.     

Alluvial Fan-lacustrine Sedimentation and its Tectonic Implications in the Cretaceous Athgarh Gondwana Basin, Orissa, India

The Athgarh Formation is the northernmost extension of the east coast Upper Gondwana sediments of Peninsular India. The formation of the present area is a clastic succession of 700 m thick and was built against an upland scarp along the north and northwestern boundary of the basin marked by an E-W-ENE-WSW boundary fault. A regular variation in the dominant facies types and association of lithofacies from the basin margin to the basin centre reveals deposition of the succession in an alluvial fan environment with the development of proximal, mid and distal fan subenvironments with the distal part of the fan merging into a lake. Several fans coalesced along the basin margin, forming a southeasterly sloping, broad and extensive alluvial plain terminating to a lake in the centre of the basin. Aggradation of fans along the subsiding margin of the basin resulted in the Athgarh succession showing remarkable lateral facies change in the down-dip direction. The proximal fan conglomerates pass into the sandstone-dominated mid-fan deposits, which, in turn, grade into the cyclic sequences of sandstone-mudstone of the distal fan origin. Further downslope, thick sequence of lacustrine shales occur. The faulted boundary condition of the basin and a thick pile of lacustrine sediments at the centre of the basin suggest that tectonism both in the source area and depositional site has played an important role throughout the deposition of the Athgarh succession of the present area. The vertical succession fines upward with the coarse proximal deposits at the base and fine distal deposits at the top, suggesting deposition of the succession during progressive reduction of the source area relief after a single rapid uplift related to a boundary fault movement.The NW-SE trending fault defining the Son-Mahanadi basin of Lower Gondwana sediments are shear zones of great antiquity and these were rejuvenated under neo-tensional stress during Lower Gondwana sedimentation. The E-W-ENE-WSW trending fault of the Athgarh basin, on the other hand, define tensional rupture of much younger date. In the Early Cretaceous period, there was a reversal of palaeoslope in the Athgarh basin (southward slope) with respect to the Son-Mahanadi basin (northward slope). During the phase drifting of the Indian continent and with the evolution of Indian Ocean in the Early Cretaceous period, the tectonic events in the plate interior was manifested by formation of new grabens like the Athgarh graben.     

Sodium - a geochemical indicator of emerald mineralization in the Cordillera Oriental, Colombia

Emerald-bearing deposits in the Cordillera Oriental are structurally controlled, localized at the intersection of two fault systems. At these intersections zones of intense fracturing affected by sodium and carbonate metasomatism host the emerald mineralization. Albitization, carbonatization and hydrothermal leaching of potassium and trace metals are characteristics of the metasomatically altered Cretaceous black shales which compose the emerald-bearing tectonic zones.Stream sediments collected in areas which have metasomatically altered shales in the drainage basin have a low K/Na ratio. It is possible to use this ratio, or the sodium content of the sediments, to locate areas worthy of further exploration.     

西藏南部晚侏罗世—白垩纪沉积与构造背景探讨

根据岩石组合特征、沉积构造和沉积相序的分析,结合岩石化学测试数据和粒度分析结果,将西藏南部的晚侏罗世一白垩纪地层划分为5个沉积区,从南往北依次为:喜马拉雅陆棚-外陆棚沉积区;拉轨岗日斜坡沉积区;雅鲁藏布深海盆地沉积区;日喀则弧前盆地沉积区;拉萨弧间盆地沉积区。进一步确定了西藏南部沉积与构造演化的时空关系。     

西藏比如盆地竟柱山组沉积-火山岩形成环境及构造意义

上白垩统竟柱山组为一套冲积扇-扇三角洲沉积体系的粗碎屑岩,间夹由英安岩、安山岩、石英粗安岩和流纹岩组成的中酸性火山岩。火山岩呈层状、似层状产出,与碎屑岩均呈整合接触关系。地球化学特征表明,竟柱山组火山岩形成于岛弧构造环境,是挤压背景下地壳增厚熔融的产物。竟柱山组沉积-火山岩的形成环境揭示了比如盆地的性质在晚白垩世已由弧后盆地转换为前陆盆地。     

Mesozoic to Cenozoic retroarc basin evolution during changes in tectonic regime,southern Central Andes (31–33°S): Insights from zircon U-Pb geochronology

The southern Central Andes of Argentina and Chile (27–40°S) are the product of deformation, arc magmatism, and basin evolution above a long-lived subduction system. With sufficient timing and provenance constraints, Andean stratigraphic and structural records enable delineation of Mesozoic-Cenozoic variations in subsidence and tectonic regime. For the La Ramada Basin in the High Andes at ∼31–33°S, new assessments of provenance and depositional age provided by detrital zircon U-Pb geochronology help resolve deformational patterns and subsidence mechanisms over the past ∼200 Myr. Marine and nonmarine clastic deposits recorded the unroofing of basin margins and sediment contributions from the Andean magmatic arc during Late Triassic to Early Cretaceous extension, thermal subsidence, and possible slab rollback. Subsequent sediment delivery from the Coastal Cordillera corresponded with initial flexural accommodation in the La Ramada Basin during Andean shortening of late Early Cretaceous to Late Cretaceous age. The architecture of the foreland basin was influenced by the distribution of precursor extensional depocenters, suggesting that inherited basin geometries provided important controls on later flexural subsidence and basin evolution. Following latest Cretaceous to early Paleogene tectonic quiescence and a depositional hiatus, newly dated deposits in the western La Ramada Basin provide evidence for a late Paleogene episode of intra-arc and proximal retroarc extension (development of the Abanico Basin, principally in Chile, at ∼28–44°S). Inversion of this late Paleogene extensional basin system during Neogene compression indicates the southern Central Andes were produced by at least two punctuated episodes of shortening and uplift of Late Cretaceous and Neogene age.     

贵州赤水地区晚白垩世古流向特征及构造意义

贵州赤水地区位于四川盆地西南缘,晚白垩世时期该地区沉积了一套厚达1300m的陆相地层。本文通过地表露头的古流向野外观测和室内分析,详细研究赤水地区晚白垩世沉积充填过程及构造意义。赤水地区晚白垩世早期辫状河的古流向为自北东向南西,表明碎屑物源主要来自盆地北侧和东侧。根据物源、地层分布及区域地质背景推断,赤水地区晚白垩世的陆相沉积盆地属于陆内前陆盆地,陆内造山带位于盆地东侧。晚白垩世陆内前陆盆地的形成,可能受控于此阶段华南的构造挤压事件形成的陆内造山作用。     

吐鲁番-哈密盆地陆源碎屑沉积环境及物源分析

吐鲁番-哈密盆地从晚二叠世到晚第三纪经历了复杂的,多旋回的沉积构造演化历史,造成主要地层间均以不整合为界。盆地内沉积相类型丰富,沉积环境随时间的推移而发生改变。在晚石炭世,盆地北部为浅海环境;到晚二叠世,沉积环境由海相转变为陆相,并在上二叠统下部形成大量冲积相或河流相粗碎屑沉积;在三叠纪,沉积物主要形成于冲积相或河流-湖泊环境中,古气候则由干旱转为温暖湿润。早、中侏罗世,沉积环境以湖泊-沼泽相为主;到晚侏罗世,则以辫状河流相为主及干旱气候为特征。在白垩纪,盆地的沉积范围大为缩小,以湖泊环境为主;第三纪,沉积范围则扩大到整个盆地,沉积相以辫状河流及冲积相为特征,沉积气候干旱,局部地区接受了盐类沉积。古流向分析显示,吐-哈盆地具有复杂的沉积搬运体系。在盆地南侧,沉积物搬运方向总是由南向北,表明觉罗塔格山是盆地的主要物源区;而在盆地北侧,博格达山自晚侏罗世开始隆起,构成盆地的另一新的物源区,沉积物搬运方向由北向南。在白垩及第三纪,博格达山成为盆地的主要物源区。     

新疆塔县达布达尔地区二叠系神仙湾组杂砂岩沉积构造背景分析

新疆塔县达布达尔地区二叠系神仙湾组位于塔阿西构造混杂岩带南侧,总体为一套深海复理石建造,主要以杂砂岩为主。源区岩石没有经过充分的搬运、分选,成熟度比较低。杂砂岩的稀土元素特征表现为轻稀土元素富集和Eu亏损明显的特征,与典型的后太古宙页岩和上地壳非常相似。微量元素含量也接近于大陆上地壳值,说明杂砂岩中的物源来自上地壳。沉积环境分析表明,杂砂岩母岩原岩为大量长英质火成物质和少量沉积物,其形成于深海厌氧环境。大地构造背景分析表明,杂砂岩物源区的构造背景以大陆岛弧为主,兼具活动大陆边缘的性质。结合区域地质构造背景,认为下-中二叠统神仙湾组为裂陷盆地沉积。     

Uppermost Cretaceous–Lower Tertiary Ulukışla Basin,south-central Turkey: sedimentary evolution of part of a unified basin complex within an evolving Neotethyan suture zone

The Ulukışla Basin, the southerly and best exposed of the Lower Tertiary Central Anatolian Basins, sheds light on one of the outstanding problems of the tectonic assembly of suture zones: how large deep-water basins can form within a zone of regional plate convergence. The oldest Ulukışla Basin sediments, of Maastrichtian age, transgressively overlie mélange and ophiolitic rocks that were emplaced southwards onto the Tauride microcontinent during the latest Cretaceous time. The Niğde-Kirşehir Massif forming the northern basin margin probably represents another rifted continental fragment that was surrounded by oceanic crust during Mesozoic time. The stratigraphic succession of the Ulukışla Basin begins with the deposition of shallow-marine carbonates of Maastrichtian–Early Palaeocene age, then passes upwards into slope-facies carbonates, with localised sedimentary breccias and channelised units, followed by deep-water clastic turbidites of Middle Palaeocene–Early Eocene age. This was followed by the extrusion of c. 2000 m of basic volcanic rocks during Early to Mid Eocene time. After volcanism ended, coral-bearing neritic carbonates and nummulitic shelf sediments accumulated along the northern and southern margins of the basin, respectively. Deposition of the Ulukışla Basin ended with gypsum deposits including turbidites, debris flows, and sabkhas, followed by a regional Oligocene unconformity.The Ulukışla Basin is interpreted as the result of extension (or transtension) coupled with subsidence and basic volcanism. After post-volcanic subsidence, the basin was terminated by regional convergence, culminating in thrusting and folding in Late Eocene time. Comparisons of the Ulukışla Basin with the adjacent central Anatolian basins (e.g. Tuzgölü, Sivas and Şarkişla) support the view that these basins formed parts of a regional transtensional (to extensional) basin system. In our preferred hypothesis, the Ulukışla Basin developed during an intermediate stage of continental collision, after steady-state subduction of oceanic crust had more or less ended (“soft collision”), but before the opposing Tauride and Eurasian continental units forcefully collided (“hard collision”). Late Eocene forceful collision terminated the basinal evolution and initiated uplift of the Taurus Mountains.     

新生代酒西盆地沉积特征及其与祁连山隆升关系的研究

酒西盆地普遍缺失上白垩统-始新统,在渐新世晚期开始接受沉积,并形成厚约3．9km的中下第三系一第四系河流相沉积约,不整合覆盖于下白垩统上。渐新统火烧沟组仅在盆地北部出露,往盆地南部尖灭,古流向向南,其物源区应在北部,可能和阿尔金断裂的活动有关。白杨河组全盆均有分布,北祁连山中也有沉积。山中-盆内沉积相由山麓相转变为河湖相,变化明显;古流向大致向北,说明当时祁连山开始隆升,成为白杨河组的物源区。对酒西盆地中、新生界的重矿物进行了系统分析,白杨河组重矿物绝对含量的脉动增加明显,显示白杨河组沉积物源发生变化,原因可能是北祁连山开始隆升,酒西盆地的沉积物源由北转向南侧的祁连山。重矿物的相对含量以及ATi,GZi和ZTR特征值也指示了白杨河组时期矿物成熟度低,构造活动强烈,可能对应着北祁连山的开始隆升。     

Cretaceous sedimentary basins in Sichuan,SW China: Restoration of tectonic and depositional environments

This study documents sediment infill features and their responses to the tectonic evolution of the Sichuan Basin and adjacent areas. The data include a comparison of field outcrops, well drillings, inter-well correlations, seismic data, isopach maps, and the spatial evolution of sedimentary facies. We divided the evolutionary history of the Sichuan Cretaceous Basin into three stages based on the following tectonic subsidence curves: the early Early Cretaceous (145–125 Ma), late Early Cretaceous to early Late Cretaceous (125–89.8 Ma), and late Late Cretaceous (89.8–66 Ma). The basin underwent NW–SE compression with northwestward shortening in the early Early Cretaceous and was dominated by alluvial fans and fluviolacustrine sedimentary systems. The central and northern areas of the Sichuan Basin were rapidly uplifted during the late Early Cretaceous to early Late Cretaceous with southwestward tilting, which resulted in the formation of a depression, exhibited southwestward compression, and was characterized by aeolian desert and fluviolacustrine deposits. The tectonic framework is controlled by the inherited basement structure and the formation of NE mountains, which not only affected the clastic supply of the sedimentary basin but also blocked warm-wet currents from the southeast, which changed the climatic conditions in the late Late Cretaceous. The formation and evolution of Cretaceous sedimentary basins are closely related to synchronous subtle far-field tectonism and changes in climate and drainage systems. According to the analysis of the migration of the Cretaceous sedimentation centers, different basin structures formed during different periods, including periods of peripheral mountain asynchronous thrusting and regional differential uplift. Thus, the Sichuan Cretaceous sedimentary basin is recognized as a superimposed foreland basin.     

Submarine fan and slope-apron deposition in a Cretaceous Forearc Basin: The Gürsökü Formation (Kavak–Samsun, N. Turkey)

The Late Cretaceous Gürsökü Formation represents the proximal fill of the Sinop–Samsun Forearc Basin that was probably initiated by extension during the Early Cretaceous. The succession records sedimentation in two contrasting depositional systems: a slope-apron flanking a faulted basin margin and coarse-grained submarine fans. The slope-apron deposits consist of thinly bedded turbiditic sandstones and mudstones, interbedded with non-channelized chaotic boulder beds and intraformational slump sheets representing a spectrum of processes ranging from debris flow to submarine slides. The submarine fan sediments are represented by conglomerates and sandstones interpreted as deposited from high density turbidity currents and non-cohesive debris flows. The occurrence of both slope apron and submarine fan depositional systems in the Gürsökü Formation may indicates that the region was a tectonically active basin margin during the Late Cretaceous.     

下扬子地区青龙群上部角砾岩成因问题

1989—1990年,安徽省地质科学研究所与德国下萨克森州不伦瑞克大学地质古生物研究所在下扬子地区合作进行了中三叠统的蒸发岩沉积特征及含钾性评价的研究,对下扬子地区青龙群上部(东马鞍山组)地表角砾岩层进行了详细的野外地质工作。我们认为这套以往一直被看作盐溶倒塌成因的角砾岩,主要是碎屑流沉积的结果,有少量构造角砾岩、膏溶崩坍角砾岩。碎屑流沉积发育于长江北岸的宿松、安庆、巢湖、无为和长江南岸的贵池、铜陵、繁昌、南京、镇江、溧阳等地,呈北东—南西向带状展布,分布广泛、规模大,最大沉积厚度超过百米以上,十分引人注目。     

Sedimentary response to a tectonically induced sea-level fall in a shallow back-arc basin: the Mulichinco Formation (Lower Cretaceous), Neuquén Basin, Argentina

This study examines the sedimentary response to a tectonically driven relative sea‐level fall that occurred in the Neuquén Basin, west‐central Argentina, during the late Early Valanginian (Early Cretaceous). At this time the basin lay behind the emergent Andean magmatic arc to the west. Following the relative sea‐level fall, sedimentation was limited to the central part of the Neuquén Basin, with the deposition of a predominantly clastic, continental to shallow marine wedge on top of basinal black shales. This lowstand wedge is called the Mulichinco Formation and consists of a third‐order sequence that lasted about 2 Myr and contains high frequency lowstand, transgressive, and highstand deposits. Significant variations in facies, depositional architecture, and internal organization of the sequence occur along depositional strike. These variations are attributed mainly to tectonic and topographic controls upon sediment flux, basin gradient, fault tilting, and shifting of the depocentre through time. These controls were ultimately related to asymmetrically distributed tectonic activity that was greater towards the magmatic arc in the west. The superposition of fluvial deposits directly upon offshore facies provides unequivocal evidence for a sequence boundary at the base of the Mulichinco Formation. However, the Mulichinco sequence boundary is marked by shallow, low erosional relief and widespread fluvial deposition. The surface lacks prominent valleys traditionally associated with sequence boundaries. This non‐erosive sequence boundary geometry is attributed to the ramp‐type geometry of the basin and/or rapid uplift that limited stratigraphic adjustment to base‐level fall. Significant along‐strike facies changes and a low‐relief sequence boundary are attributes that may be common in tectonically active, semi‐enclosed basins (e.g. shallow back‐arc basins, foreland basins).     

Clay Mineral Associations in Triassic–Lower Cretaceous Rocks of the Dal'negorsk Key Section, Southern Sikhote Alin

Investigation of the Triassic–Lower Cretaceous rocks of the Dal'negorsk key section (southern Sikhote Alin) revealed the following successive associations of authigenic clay minerals: (1) sericite–chlorite (Lower Triassic); (2) mica–chlorite (Anisian–Norian); (3) chlorite–mica (Rhaetian–Lower Jurassic); and (4) smectite–chlorite–mica (Upper Jurassic–Lower Cretaceous). These four associations reflect the primary composition of terrigenous admixture in the siliceous sediments and, hence, serve as important indicators of paleosedimentation conditions. The first association represents a product of the erosion of metamorphic rock complexes. The second one reflects the onset of volcanic activity within the sedimentation basin coinciding in time with a vigorous bloom of siliceous plankton (radiolarians) and short-term appearance of specific (anoxic) carbonaceous sediments in the sequence. The third association characterizes the epoch of minimal supply of the basin with volcanic and terrigenous clastic materials and the dominant accumulation of almost pure planktonogenic sediments. The fourth association marks the change of marginal-marine conditions for pelagic ones and is expressed in a significant input of pyroclastic and clastic materials and the formation of distal flysch deposits.     

西藏札达盆地上新统古格组和托林组的厘定与层序地层划分

根据札达盆地剖面中地层的接触关系、沉积旋回、沉积体系和岩相岩性特征,可将上新统河湖相地层划分为2个组、5个沉积相、8个岩段。古格组(N22g)一岩段为砾岩,属河流相沉积;二、三、五岩段以细碎屑岩为主,属浅湖相沉积;四岩段以含粘土质细碎屑岩为主,属深湖相沉积。托林组(N21t)一、二、三岩段为一套砾岩、含砾中粗粒钙质长石岩屑砂岩和中细粒砂岩的碎屑岩,为典型冲(洪)积扇沉积物。ESR法和古地磁法测年结果表明,古格组形成时代为上新世晚期(4.40～2.47Ma);托林组形成时代为上新世早期(5.44～4.40Ma)。札达盆地为一同生断陷盆地,在上新世时期的构造运动过程中,盆地演化经历了水进体系域—湖泊扩张体系域—湖泊收缩体系域3个发展阶段。     

塔里木盆地库车坳陷白垩纪层序地层格架及古地理演化

白垩纪的库车坳陷是一个干旱气候条件下的内陆坳陷,其中只发育下白垩统,为一套干旱红层地层,进一步划分为亚格列木组、舒善河组、巴西盖组和巴什基奇克组。该套干旱红层,包括洪积扇砾岩、间歇性河流砂砾岩、风成砂岩和沙漠湖紫红色泥岩等沉积。这些沉积在地层记录中常以一种特别的旋回性形式产出,在不整合面及其相关面之上首先沉积的是洪积扇砾岩和间歇性河流砂砾岩所构成的冲积沉积物,向上逐渐演变为沙漠湖红色泥岩,在成湖初期或湖退期发育了滨湖相风成砂岩,它们构成了一个较为典型的沙漠沉积体系。从冲积沉积到湖泊沉积构成总体向上变细的沉积相序组合。按照地层记录的旋回性进行三级沉积层序划分,将库车坳陷下白垩统划分为5个三级沉积层序即SQ1至SQ5。下白垩统的顶和底界面均为间断时间很长的区域不整合面,由它们所限定的下白垩统本身则构成一个二级构造层序,在二级构造层序内三级沉积层序常常形成有规律的叠加形式,下部的SQ1和上部的SQ5发育较多的冲积粗碎屑物,中部SQ2至SQ4则以湖泊相沉积为主。与海相地层不同,库车坳陷白垩系中由三级层序和二级层序所代表的地层记录中的中周期和长周期旋回的主要控制因素是幕式构造沉降,沉降初期由于地形高差大而以发育冲积粗碎屑物为主,均衡沉降期则与成湖期相对应从而发育较多的细粒沙漠湖沉积。以沉积物的时间演化序列和沉积相的空间展布形式所代表的规律性入手,建立库车坳陷下白垩统的层序地层格架,在层序地层框架内,系列层序地层格架栅状图和相应的古地理图较为清晰地反映出早白垩世库车坳陷的古地理面貌,以及相应的沉积岩相古地理演变过程。     

辽东苏子河盆地聂尔库组沉积相与沉积环境研究

辽东苏子河盆地是早白垩世形成的小型断陷盆地,盆地内发育了相对连续的陆相沉积,是研究白垩纪陆地环境及气候演化的理想地区。早白垩世晚期沉积的聂尔库组地层出露连续,沉积现象典型。通过分析聂尔库组沉积岩类型、沉积构造、古生物化石及垂向沉积序列,可识别出扇三角洲相和湖泊相,其中扇三角洲相包括扇三角洲平原亚相、扇三角洲前缘亚相和前扇三角洲亚相,湖泊相主要为滨浅湖泥砂沉积。研究表明,聂尔库组形成于断陷盆地边缘陡坡带,属于间歇性洪水控制的扇三角洲—湖泊沉积体系,经历了扇三角洲—湖泊—扇三角洲的沉积环境变化,代表了断陷湖盆由深陷扩张期—抬升收缩早期的沉积充填过程。根据沉积岩与沉积相特征,结合古生物、特殊沉积、黏土矿物及地球化学资料,认为早白垩世晚期辽东地区总体与当时全球"温室气候"的大背景相一致,处于高温干旱/潮湿的气候条件,但这种高温气候具有不均一性,存在气候波动。