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1.
松辽盆地东缘下白垩统营城组二段火山碎屑岩的发育特征 总被引：1，自引：0，他引：1
通过精细的野外剖面测量,发现松辽盆地东缘营城组二段中发育熔岩、凝灰岩和凝灰质砂岩。凝灰岩包括熔结凝灰岩、岩屑晶屑凝灰岩、灰球泥粒凝灰岩和角砾凝灰岩。这表明作为火山活动间歇期的营城组二段沉积期依然存在一定规模的火山活动,其沉积作用具有独特的火山和沉积双重控制的特点,区别于正常的沉积作用。营城组二段是一套介于火山岩和陆源碎屑岩之间的过渡岩性,物源既有来自同期火山喷发,也有来自营城组一段和营城组下段以及更老的地层的风化剥蚀。由于存在火山物质和陆源剥蚀物质的双重物源及存在火山物质堆积和沉积作用的双重机理,这套岩石在类型上具有特殊性。存在特殊的火山-沉积作用类型,主要为冲积平原上热碎屑流河道沉积、冲积平原泛滥盆地上热基浪沉积、冲积平原泛滥盆地上空落火山灰云沉积。 相似文献
2.
《地学前缘》2017,(1):265-275
中国白垩纪大陆科学钻探松科2井连续获取营城组岩心365.32m,岩心直径为214mm,岩心收获率达98.47%,是迄今直径最大,收获率最高且保存最为完整的营城组岩心,这些宝贵资料为营城组研究提供了前所未有的机遇。营城组时期与Aptian-Albian对应。通过对松科2井营城组岩心的精细描述,揭示了营城组火山-沉积序列及其建造过程。营城组主要包括沉积岩与火山岩两大岩类,共计17种岩石类型,其中沉积岩9种(砾岩、粗砂岩、中砂岩、细砂岩、粉砂岩、粉砂质泥岩、泥岩,含角砾凝灰质砂岩、凝灰质砂岩)、火山岩类8种(流纹岩、流纹质角砾集块岩、流纹质角砾集块熔岩、流纹质熔结凝灰熔岩、流纹质含角砾熔结凝灰熔岩、隐爆角砾岩、安山质集块熔岩与凝灰岩)。沉积相为扇三角洲相,具体分为扇三角洲平原亚相、扇三角洲前缘亚相与前扇三角洲亚相,分流河道微相、扇间沼泽微相,水下分流河道微相、河口砂坝微相与静水泥质沉积微相。火山岩相包括爆发相和喷溢相,具体分为空落亚相、热碎屑流亚相、喷溢相中部亚相和上部亚相。沉积岩与火山岩交替出现于营城组中,主要发育3期沉积岩与3期火山岩,自下而上形成3个完整的沉积-火山旋回,即沉积岩Ⅰ-火山岩Ⅰ、沉积岩Ⅱ-火山岩Ⅱ和沉积岩Ⅲ-火山岩Ⅲ。这一发现对于重新认识营城组时期构造-火山-盆地充填规律,可能具有重要启示。文中精细的描述资料为今后相关的深入研究提供了迄今最精准的基本地质素材。 相似文献
3.
爆发相火山岩是火山碎屑不同形式的组合体,根据火山碎屑的类型和组合方式可以划分为空落亚相、热基浪亚相、热碎屑流亚相和溅落亚相共4个亚相,每个亚相都有其独特的判别标志.克拉美丽滴西地区爆发相火山岩的岩心、普通薄片、铸体薄片以及测井资料研究发现,该区域岩性复杂,爆发相火山岩主要赋存在滴西10井区和滴西14井区范围内,岩性以火山凝灰岩、火山角砾岩、熔结凝灰岩和熔结火山角砾岩为主.爆发相的储集空间以基质溶孔、粒内溶孔、构造裂缝和溶蚀缝为特征.爆发相各亚相中,以熔结凝灰岩为主的热碎屑流亚相和以火山凝灰岩为主的空落亚相为优质储集体发育部位,主要影响因素为构造作用和流体的溶蚀作用.这项研究为判别其他相似地区爆发相火山岩能否成为有效储层提供参考意义. 相似文献
4.
松辽盆地营城组古火山机构的剖析——以东南隆起区三台珍珠岩山为例 总被引：2，自引：0，他引：2
三台地区下白垩统营城组一段岩石类型有隐爆角砾岩、角砾熔岩、熔结角砾岩、珍珠岩、流纹岩和凝灰岩,所属岩相为火山通道相、侵出相、喷溢相、爆发相。厘定古火山口位置的依据主要是通过分析隐爆角砾岩和珍珠岩的岩性岩相及其分布。整个火山机构划分为中心相组、近源相组和远源相组。中心相组即火山口相,主要包括火山通道相和侵出相,近源相组主要包括喷溢相,远源相组主要包括爆发相。相序（以火山口为基点）为火山通道相隐爆角砾岩亚相-侵出相中带亚相-侵出相内带亚相-喷溢相下部亚相-喷溢相中部亚相-爆发相热碎屑流亚相。近源相组较中心相组储层物性优越。其中喷溢相上部亚相是储层物性最好的岩相带。 相似文献
5.
束鹿凹陷碳酸盐角砾岩的成因研究 总被引：1，自引：0，他引：1
碳酸盐角砾岩一般为内源或构造等成因,陆相沉积环境极难形成。研究发现束鹿凹陷古近系角砾岩为陆相成因。束鹿凹陷角砾岩分布于沙河街组三段中下部,在凹陷的东西斜坡地带呈裙状发育,是一种以碳酸盐岩碎屑为主的沉积岩。岩石类型为角砾岩及少量含砾泥灰岩,角砾岩具有以颗粒支撑为主,块状构造、粒序构造或其它层理构造不明显,角砾大小混杂,没有出现方向的优选,砾岩层单层厚度较大等特点;含砾泥灰岩为杂基支撑,具正粒序构造,并可见倒三角形状角砾。碳酸盐角砾岩中无论角砾还是填隙物都主要由棱角状及次棱角状碳酸盐碎屑颗粒构成,其母岩为盆地周围奥陶系及寒武系碳酸盐岩。研究认为束鹿凹陷沿缓坡分布的角砾岩属陆源非粘性碎屑流沉积产物。 相似文献
6.
河南信阳—安徽庐江断裂带中,出露有中生代裂隙式喷溢形成的火山岩体。在火山岩中具有多期多次活动形成的熔结火山角砾岩。有趣的是,在河南信阳东部的大石窝一带,熔结火山角砾岩体长达几十千米,宽几千米。在采石场和采石坑中竟没有一条断裂或节理;熔结火山角砾岩中的角砾大小不一,多为0.5cm～5cm之间,没有层理;令观者称奇。 相似文献
7.
以松辽盆地东南缘营城组二段两类火山碎屑岩(沉凝灰岩、凝灰质砂岩)为研究对象, 进行了火山碎屑粒度特征、碎屑组成和火山碎屑岩相研究.结果显示, 火山碎屑搬运除受火山作用激发控制外, 还受牵引流、重力流以及牵引流和重力流的双重机制影响.火山碎屑微观特征、成因分析和岩相分析认为, 本区火山碎屑堆积主体为热基浪堆积和热碎屑流堆积, 部分为空落堆积.火山碎屑组成特征为晶屑含量多, 玻屑和岩屑含量少, 且岩屑仅在较粗粒级颗粒组成中存在.研究认为, 本区发育的火山碎屑为沉积环境中的再搬运火山碎屑, 共识别出4种火山碎屑岩相, 河流故道上的热基浪, 河流故道上的热碎屑流, 冲积平原上的热基浪和空落相.建立了松辽盆地东南缘露头区营城组二段河流-冲积平原沉积环境的再搬运火山碎屑岩相模式. 相似文献
8.
吉林龙岗火山群火山碎屑基浪堆积特征与成因机理 总被引：9，自引：0，他引：9
吉林龙岗火山群火山碎屑基浪堆积是中国少数保存较好的、近代喷发的低平火山区之一。基于岩性、岩相与相序的识别与分析,火山碎屑基浪堆积序列由分选性和磨圆度较差的玄武质砂、砾和火山灰构成的毫米级-厘米级厚高频率韵律有序叠置而成,堆积物中发育大量的块状层理、似丘状层理、低角度板状交错层理、槽泊层理、平行层理、冲蚀槽等堆积构造。横向上低平火山由内至外其碎屑粒度、堆积构造、厚度存在着一定规律变化,与易混淆的火山岩区地面流水沉积和火山碎屑流堆积物存在明显的差别。岩浆射汽喷发晚期往往伴随斯通博利式喷发和夏威夷式熔岩流,三者构成一个完整火山活动旋回。 相似文献
9.
以松辽盆地东南缘营城组二段两类火山碎屑岩(沉凝灰岩、凝灰质砂岩)为研究对象,进行了火山碎屑粒度特征、碎屑组成和火山碎屑岩相研究.结果显示,火山碎屑搬运除受火山作用激发控制外,还受牵引流、重力流以及牵引流和重力流的双重机制影响.火山碎屑微观特征、成因分析和岩相分析认为,本区火山碎屑堆积主体为热基浪堆积和热碎屑流堆积,部分为空落堆积.火山碎屑组成特征为晶屑含量多,玻屑和岩屑含量少,且岩屑仅在较粗粒级颗粒组成中存在.研究认为,本区发育的火山碎屑为沉积环境中的再搬运火山碎屑,共识别出4种火山碎屑岩相,河流故道上的热基浪,河流故道上的热碎屑流,冲积平原上的热基浪和空落相.建立了松辽盆地东南缘露头区营城组二段河流-冲积平原沉积环境的再搬运火山碎屑岩相模式. 相似文献
10.
11.
ROBERTO SULPIZIO DANIELA MELE PIERFRANCESCO DELLINO LUIGI LA VOLPE 《Sedimentology》2007,54(3):607-635
Small-scale pyroclastic density currents (PDCs) associated with the AD 472 (Pollena) eruption of Somma-Vesuvius, Italy, were generated by both magmatic and phreatomagmatic explosive fragmentation. The resulting deposits were emplaced under flow boundary conditions dominated by varying combinations of grain interaction, fluid escape and traction processes. Stratigraphic and lithofacies analysis of these PDCs offers a new perspective on the en masse versus progressive aggradation debate for PDC deposition. In particular, the analyses indicate that PDCs were density stratified with a basal underflow dominated by grain interactions. The underflows comprised trains of self-organized granular pulses of variable thickness and magnitude, depending on the overall particle concentration and fluid turbulence. A change in gradient between the upper and lower slopes of the volcano promoted deposition and the different pulses aggraded sequentially (stepwise). In this model each pulse stops en masse and the whole deposit aggrades progressively. Particle concentration, density, mean velocity, and flow height were assessed for the studied PDCs using differaent methods for massive and stratified deposits. The calculated mobility of the flows was 0·2 to 0·3, in the expected range for small-scale PDCs. 相似文献
12.
The Udo tuff cone, Cheju Island, South Korea: transformation of pyroclastic fall into debris fall and grain flow on a steep volcanic cone slope 总被引：1，自引：0，他引：1
The Udo tuff cone of Cheju Island, South Korea, is a middle Pleistocene basalt tuff cone that has formed by early Surtseyan-type eruptions and later drier hydroclastic eruptions. The tuff cone comprises steep (20–30°) and planar beds of lapillistone, lapilli tuff and tuff that can be grouped into seven sedimentary facies (A-G). Facies A and B comprise continuous to lenticular layers of grain-supported and openwork lapillistone that are inversely graded and coarsen downslope. They suggest emplacement by grain flows that are maintained by gravity-induced stress and grain collisions. Facies C includes poorly sorted, crudely bedded and locally inversely graded lapilli tuff, also suggestive of rapid deposition from highly concentrated grain flows. Facies D includes thinly stratified and mantle-bedded tuff that was probably deposited by fallout of wind-borne ash. Other facies include massive lapilli tuff (Facies E), chaotic lapilli tuff (Facies F) and cross-bedded tuffaceous sandstone (Facies G) that were deposited by resedimentation processes such as debris flow, slide/slump and stream flow, respectively. The grain flows that produced Facies A, B and C are interpreted to have originated from falling pyroclasts, which initially generated highly dispersed, saltating avalanches, in which momentum was transferred by the particles themselves. This transport mechanism is similar to that of debris fall. As the slope gradient was too low to maintain a highly dispersed flow, the debris fall decelerated and contracted due to a decrease in dispersive pressure. The mode of momentum transfer changed to one of collision because contraction of the debris fall resulted in an increase in particle concentration. This transport mechanism is similar to that of common grain flows. Grain segregation occurred in several ways. Initial segregation of ash from lapilli occurred due to their differing terminal fall velocities, and their contrasting degrees of sliding friction with the bed. Percolation of ash into interstices of lapilli during flow (kinematic sieving) augmented further segregation of ash from lapilli. The latter process, along with a dispersive pressure effect, gave rise to vertical inverse size grading. Downdip inverse grading was produced by particle overpassing. 相似文献
13.
Emplacement of small‐volume (<0·1 km3) pyroclastic flows is significantly influenced by topography. The Arico ignimbrite on Tenerife (Canary Islands) is a characteristic small‐volume pyroclastic flow deposit emplaced on high relief topography. The pyroclastic flow flowed down pre‐existing valleys on the southern slopes of the island. In proximal areas deep (up to 100 m) valleys acted as efficient conduits for the pyroclastic flow, which was mostly channelled; in this particular area the ignimbrite corresponds to a homogeneous, moderately welded deposit, consisting of flattened pumices in an abundant ashy matrix with a relatively low lithic fragment content. In intermediate zones significant changes occur in the steepness of the slope and, although still channelled, here the pyroclastic flow was influenced by hydraulic jumps. In this area, two different units can be clearly distinguished in the ignimbrite: the lower unit is composed of a lithic‐rich ground‐layer deposit that formed at the turbulent, highly concentrated head of the flow; the upper unit consists of a well welded pumice‐rich deposit that occasionally reveals a basal layer formed by shearing with the lower part. This division into two units is maintained as far as distal areas near the present‐day coastline, where the slope is very gentle or null and the ignimbrite is not channelled. The ground layer is not found in distal areas. The ignimbrite here only consists of the upper unit, which is occasionally repeated due to a surging process provoked by the lower flow speed, as the pyroclastic flow spread out of the channelled zone. A theoretical model on how topography controlled the deposition of the Arico ignimbrite is derived by interpreting the observed lithological and sedimentological variations in terms of changes in topography and bedrock morphology. This new model is of general applicability and will help to explain other deposits of similar characteristics. 相似文献
14.
Pyroclastic surge is a dilute and turbulent flow of volcanic gas and tephra that is commonly generated during explosive volcanic eruptions and can threaten lives along its flow paths. Assessing its travel distance and delineating future volcanic hazards have therefore been major concerns of volcanologists. Historical eruptions show that most pyroclastic surges travel a few tens of kilometres or less from their sources. Aeolian or aquagene processes have therefore been evoked for the emplacement of supposed surge deposits much beyond this distance. Here we show that a Cretaceous tuff bed in Korea was emplaced by an exceptionally powerful pyroclastic surge that flowed as far as the most powerful pyroclastic flows that formed the low-aspect-ratio ignimbrites (LARI). This has significant implications for interpreting ancient volcanic eruptions and delineating volcanic hazards by pyroclastic surges, and casts intriguing questions on the eruption dynamics and physics of long-runout pyroclastic surges and their distinction from LARI-forming pyroclastic flows. 相似文献
15.
The Ilchulbong tuff cone, Cheju Island, South Korea 总被引：3，自引：0，他引：3
The Ilchulbong mount of Cheju Island, South Korea, is an emergent tuff cone of middle Pleistocene age formed by eruption of a vesiculating basaltic magma into shallow seawater. A sedimentological study reveals that the cone sequence can be represented by nine sedimentary facies that are grouped into four facies associations. Facies association I represents steep strata near the crater rim composed mostly of crudely and evenly bedded lapilli tuff and minor inversely graded lapilli tuff. These facies suggest fall-out from tephra finger jets and occasional grain flows, respectively. Facies association II represents flank or base-of-slope deposits composed of lenticular and hummocky beds of massive or backset-stacked deposits intercalated between crudely to thinly stratified lapilli tuffs. They suggest occasional resedimentation of tephra by debris flows and slides during the eruption. Facies association III comprises thin, gently dipping marginal strata, composed of thinly stratified lapilli tuff and tuff. This association results from pyroclastic surges and cosurge falls associated with occasional large-scale jets. Facies association IV comprises a reworked sequence of massive, inversely graded and cross-bedded (gravelly) sandstones. These facies represent post-eruptive reworking of tephra by debris and stream flows. The facies associations suggest that the Ilchulbong tuff cone grew by an alternation of vertical and lateral accumulation. The vertical buildup was accomplished by plastering of wet tephra finger jets. This resulted in oversteepening and periodic failure of the deposits, in which resedimentation contributed to the lateral growth. After the eruption ceased, the cone underwent subaerial erosion and faulting of intracrater deposits. A volcaniclastic apron accumulated with erosion of the original tuff cone; the faulting was caused by subsidence of the subvolcanic basement within the crater. 相似文献
16.
火山碎屑岩是爆破性火山喷发行为的直接产物,不同的碎屑成分、粒度及结构反映了不同岩相的堆积动力学过程,对火山碎屑岩岩石学和岩相组合的研究发展成了以物理火山学为代表的现代火山学研究体系。作为火山爆发碎屑物质的集合,其中不同成因类型的火山碎屑物往往可以直接对应不同阶段火山作用动力学参数特征。火山碎屑物3个最基本的堆积物成因类型是火山碎屑降落物、火山碎屑流和火山碎屑涌浪。火山喷发时碎屑化过程主要涉及挥发分的出溶和岩浆碎屑化过程以及不同火山流体内部的碎屑化过程。对于岩浆喷发、射汽岩浆喷发以及射汽喷发的直接产物,火山碎屑岩在组成上都包含了岩浆破碎的同源碎屑、火山通道裹进的异源碎屑以及火山流体在地表流动时捕获的表生碎屑。火山碎屑定义为爆破性火山喷发的直接行为产物,而包括坡移、滑坡体、火山泥石流等火山降解过程的表生碎屑与熔岩流在自生、淬碎碎屑化过程产生的碎屑则被定义为火山质碎屑。火山岩岩相的建立,为20世纪80年代后期向火山学研究阶段的转变奠定了基础。在地质研究的基础上探索火山活动过程和控制机制的经验模型、实验模拟和数值模拟研究,其中流体动力学的介入对理解火山喷发的基本过程具有里程碑式的推动意义。由此形成的火山学是研究火山与火山喷发的形成机理、喷发过程和产物特性的科学。 相似文献
17.
Grain size variations in ignimbrites and implications for the transport of pyroclastic flows 总被引：11，自引：0，他引：11
R. S. J. SPARKS 《Sedimentology》1976,23(2):147-188
Ignimbrite flow units commonly show reverse grading of large pumice clasts and normal grading of large lithic clasts. Ignimbrites show coarse-tail grading, in which particles beneath a critical diameter, ranging from 64 to 2 mm, are ungraded. Above this size the larger the clast diameter the more pronounced the segregation. The grading is consistent with the theoretical settling rates of particles in a dispersion with a high particle concentration. Ignimbrite flow units show a reversely graded, fine grained basal layer which is attributed to the action of boundary forces during flow. Ignimbrites are commonly associated with cross-stratified pyroclastic surge deposits and fine ash fall deposits formed in the same eruption. The fine ash fall deposit is depleted in crystals and is thought to be the deposit of the fine turbulent cloud observed making up the upper parts of nuées ardentes. Pyroclastic flows are postulated to be dense, poorly expanded partly fluidized debris flows. Only its fine grained components can be fluidized by gas. Pyroclastic flows are believed to behave as a dispersion of larger clasts in a medium of fluidized fines, which acts as a lubricant similar to water in mud-flows. Poor sorting in ignimbrites is attributed to high particle concentrations not turbulence. Many pyroclastic flows may be laminar in their movement with apparent viscosities, deduced from the lateral grading of large lithic clasts, in the range 101?103 poise. 相似文献
18.
实验模拟侧向遮挡对低密度火山碎屑流的影响——对日本云仙岳火山1991年火山碎屑流的启示 总被引：1，自引：1，他引：0
本文将颗粒驱动重力流实验流体与自然界低密度火山碎屑流进行标度化研究,探讨低密度火山碎屑流的流动行为。通过在矩形流体交换水箱中放置占水箱宽度1/4、1/2、3/4比例的侧向遮挡障碍物,调查了颗粒驱动重力流实验流体在遇到侧向遮挡前后的运动模式、流体前锋速度减速特征和颗粒堆积分布特征。实验结果显示出不同比例的部分遮挡对低密度火山碎屑流影响的复杂性。实验表明,1/4比例的部分遮挡能够提高低密度火山碎屑流在通过之后的流速,并增加通过遮挡的颗粒堆积总量,能够解释日本云仙岳火山1991年6月3日喷发形成的碎屑流流动特征。在侧向遮挡比例为1/2时,~100T的时间内流体前锋减速,并在~100T之后加速（T为无量纲时间）;通过遮挡的堆积物总量明显减少。通过3/4比例的侧向遮挡之后,颗粒实验流体前锋持续减速,颗粒堆积总量减少。 相似文献
19.
《Gondwana Research》2002,5(3):721-733
During the late stages of the Brasiliano orogenic cycle (Lower Cambrian), the Camaquã Basin was gradually filled by the alkaline-trending, bimodal volcanic rocks of the Acampamento Velho Alloformation. This volcanic package consists of two facies associations: the lower one composed of andesites and basaltic andesites, and the upper one of rhyolitic rocks. The rhyolitic association comprises alternating pyroclastic rocks (lapilli, tuffs and welded tuffs) in the middle section and flows at the top. Geochemical evidence, especially trace elements and REE, confirmed the stratigraphic succession proposed herein for the volcanic rocks, as well as their co-genetic relationships and the fractional crystallization of the felsic sequence. The Acampamento Velho Formation seems to have been generated in an extensional regime preceding the collision of the Rio de la Plata and Kalahari continental plates. This extensional regime probably occurred during subduction of the Adamastor oceanic plate beneath the Rio de la Plata plate in a retroarc setting. 相似文献
20.
Depositional processes in a kimberlite crater: the Upper Cretaceous Orapa South Pipe (Botswana) 总被引：1，自引：0，他引：1
THOMAS M. GERNON MATTHEW FIELD † R. STEPHEN J. SPARKS Associate Editor: Vern Manville 《Sedimentology》2009,56(3):623-643
The Orapa A/K1 Diamond Mine, Botswana, exposes the crater facies of a bilobate kimberlite pipe of Upper Cretaceous age. The South Crater consists of layered volcaniclastic deposits which unconformably cross‐cut massive volcaniclastic kimberlite of diatreme facies in the North Pipe. Based on the depositional structure, grain‐size, sorting and composition of kimberlite in the South Crater, six units are distinguished in the ～70 m thick stratiform crater‐fill sequence and talus slope deposits close to the crater wall, which represents a multistage infill of the volcanic crater. Monolithic basalt breccias (Unit 1) near the base of the crater‐fill are interpreted as rock‐fall avalanche deposits, generated by the sector collapse of the crater walls. These deposits are overlain by a basal imbricated lithic breccia and upper massive sub‐unit (Unit 2), interpreted as the deposits of a pyroclastic flow that entered the South Crater from another source. Vertical degassing structures within the massive sub‐unit show evidence for elutriation of fines and probably were formed after emplacement by fluidization due to air entrainment. Units 3 and 5 are thinly stratified deposits, characterized by diffuse bedding, reverse and normal grading, coarse lenticular beds, mudstone beds, small‐scale scour channels and load casts. These units are attributed to rapidly emplaced sheet floods on the crater floor. Units 3 and 5 are directly overlain by poorly sorted volcaniclastic kimberlite (Units 4 and 6) rich in basalt boulders, attributed to debris flows formed by the collapse of crater walls. Unit 7 comprises medium sandstones to cobble conglomerates representing talus fans, which were active throughout the deposition of Units 1 to 6. The study demonstrates that much of the material infilling the South Crater is derived externally after eruption, including primary pyroclastic flow deposits probably from another kimberlite pipe. These findings have important implications for predicting diamond grade. Results may also aid the interpretation of crater sequences of ultra‐basic, basaltic and intermediate volcanoes, together with the deposits of topographic basins in sub‐aerial settings. 相似文献