豫西焦作地区上石炭统浅海碳酸盐岩中的风暴沉积

焦作太原组灰岩存在至少四种类型的风暴沉积。类型A由下亚段正粒序分壳滞积层和上亚段生物扰动层组成,形成于风暴浪基面附近或之下;类型B由正粒序介壳滞积层、纹理层和痕迹层组成,形成于正常天气浪基面与风暴浪基面之间的下部环境;类型C由下亚段正粒序介壳滞积层和上亚段含少量痕迹化石的粒泥状灰岩组成,类型D仅由下部介壳滞积层和上部粒泥状灰岩组成,偶见痕迹化石,故类型C和D分别形成于正常天气浪基面之下和附近。     

四川龙门山区下泥盆统的介壳岩形成模式及其意义

四川龙门山区(前山)早泥盆世地层中,特别是在白柳坪、甘溪、谢家湾三组地层中,含有相当数量的介壳层。它包括呈两向伸展的介壳毯和三向伸展的介壳层(包括透镜体),据在地层中产出的层位,自身的特点及其与围岩的关系等方面综合分析,表明介壳毯形成于正常波基面向海一侧,介壳岩则是位于波基面以下,正常风暴浪基面附近向海一侧的部位;前者主要为簸扬作用和沉积速率快慢相间的幕式沉积过程的结果,后者则和风暴作用有关,属近积风暴岩,介壳岩的研究不仅对正确划分白柳坪、甘溪、谢家湾三组提供了充分的岩性依据,而且也为正确解释古环境及盆地沉积史提供大量可靠依据。     

川西北江油马角坝地区黄龙组下部风暴沉积特征

川西北江油马角坝地区上石炭统黄龙组下部发育典型的风暴沉积,包括介壳灰岩、砾屑灰岩、瘤块状灰岩、砂屑灰岩和正常沉积灰岩或泥岩等沉积类型,以及冲刷沟槽、瘤块状构造、粒序层理、水平层理、波状层理和生物扰动等沉积构造。根据野外观察和室内显微分析,结合风暴沉积标志组合,在江油马角坝地区2个剖面的黄龙组下部各识别出4层风暴层,并划分出5套风暴沉积组合。组合Ⅰ以冲刷沟槽、介壳滞留层、粗砾滞留层、块状层理、水平层理、波状层理、泥灰岩层和生物富集层为特征,沉积于正常浪基面以上强风暴作用的开阔台地环境。组合Ⅱ以瘤块状构造、粒序层理和块状层理的生物碎屑灰岩为特征,沉积于正常浪基面之上受重力流影响的局限台地环境。组合Ⅲ以冲刷沟槽、粗砾滞留层、粒序层理、块状层理为特征,沉积于浪基面以上持续风暴流作用的开阔台地边缘浅滩环境。组合Ⅳ由冲刷沟槽、正粒序层理和块状层理的生物碎屑灰岩组成,产出于组合Ⅲ之上,表明该组合在前一期风暴未完全结束时又遭到后一期风暴的侵袭,接受浪基面之上的浅滩沉积。组合Ⅴ由冲刷沟槽、粗砾滞留层和泥岩层组成,沉积于晴天浪基面以上缺少物源的极浅水开阔台地环境。以上5种组合风暴岩都发育于台地中上部,与一般的斜坡风暴岩有明显的差别,均属于近源极浅水风暴岩。风暴岩的研究对地层对比、古气候、岩相古地理、沉积盆地演化和油气勘探具有重要的理论和现实意义。     

黔南罗甸沫阳中二叠世茅口组风暴岩沉积特征及地质意义

黔南罗甸沫阳剖面中二叠世茅口组以海相碳酸盐为主,下部地层中发育风暴岩,露头特征明显,主要以介壳灰岩为识别标志。风暴沉积构造包括底面侵蚀构造、截切构造、波痕层理、递变层理、块状层理等。风暴沉积主要包括一个底面构造A和B、C、D、E等四个沉积单元:A.侵蚀底面,代表风暴流对海底沉积物的作用;B.介壳灰岩层,代表风暴浪、风暴涡流沉积;C.粒序层,代表风暴衰减期重力分异沉积或风暴浊流沉积;D.块状层,代表风暴快速悬浮沉积;E.波痕层理段,代表风暴衰减后期沉积。它们共组成4种风暴沉积序列,分别代表不同深度的风暴沉积,反映了不同的风暴沉积作用和风暴流的类型。沫阳地区风暴沉积的沉积特征表明,该区风暴沉积主要发育于风暴浪基面之上的内陆棚沉积环境,风暴强度大,为近源风暴岩。仅个别风暴沉积发育于风暴浪基面之下的外陆棚沉积环境,为风暴引起的浊流沉积,为远源风暴岩。风暴岩类型的正确识别,对确定该区沉积相与深入认识扬子碳酸盐台地南部边缘沉积演化提供参考依据。     

华北燕山裂陷槽中元古代深水藻类生物沉积及其环境

河北平泉燕山裂陷槽中元古代地层中,藻席-藻团-藻丝-藻屑-泥晶薄层交替形成韵律沉积。经对系列标本(薄片)特征及其不同结构类型的对比分析,认为它们是在风暴浪基面之下,具风暴流浊积特征的深水藻类生物沉积系列。浅海叠层石及其他底栖藻类构成了从浅海至半深海上部浅水一个完整的藻类沉积序列,其不同类型的特征则成为鉴别沉积时各环境要素的可靠依据,即依据不同藻类生物沉积类型———藻席、藻团、藻丝及藻层的组合序列变化,作为判别200～400 m半深海浅水环境的依据。     

塔里木盆地苏盖特布拉克地区下寒武统风暴岩及其地质意义

塔里木盆地苏盖特布拉克地区下寒武统肖尔布拉克组发育较为典型的风暴岩。风暴沉积标志主要有冲刷充填构造、风暴砾屑层和丘状交错层理等。在野外实测和室内薄片观察基础上,依据风暴沉积物、沉积位置和沉积标志组合的不同,划分出5种风暴沉积序列。序列Ⅰ为mm级或cm级的递变纹层,截切深水微生物礁,为风暴浪基面以下的深水陆棚远源风暴浊流沉积;序列Ⅱ发育异地型风暴砾屑、粒序段、平行纹层段和水平层理黑色钙质页岩,为风暴浪基面与晴天浪基面之间的缓斜坡下部沉积;序列Ⅲ为风暴成因的生屑、砾屑与平行纹层、丘状纹层的组合,多出现在风暴浪基面与晴天浪基面之间的缓斜坡上部;序列Ⅳ以渠模与复合丘状交错层理的组合为特征,为水体较浅的晴天浪基面附近的沉积;序列Ⅴ由风暴砂砾屑及沉积充填构造、平行纹层段组成,上部单元为正常天气沉积的蓝细菌礁滩垮塌体,为晴天浪基面以上的台地边缘礁滩前缘沉积。风暴层序自下而上的沉积环境演化为深水陆棚→浅水陆棚缓斜坡下部→缓斜坡上部→台地边缘前缘,形成向上变浅沉积特征。风暴岩的发现和研究,对于塔里木早寒武世古纬度与古板块演化、古地理及沉积学研究具有重要意义。     

峡东地区埃迪卡拉系灯影组风暴岩的发现 及其环境意义

本文首次报道了峡东地区埃迪卡拉系灯影组石板滩段地层中的风暴岩。通过详细的剖面观察、测制和室内研究,识别出石板滩段典型的风暴沉积标志,包括各种丘状交错层理、粒序层理、冲刷 充填构造、平行层理及变形层理等。结合各类风暴沉积标志在剖面上的组合关系将研究区风暴岩划分出4个风暴沉积序列类型：其中类型Ⅰ为风暴流成因的滞留沉积与底面的冲刷面、丘状层理、波状层理、水平层理的组合,属形成于正常浪基面附近的近原地风暴岩; 类型Ⅱ为具颗粒流性质的块状内碎屑灰岩与丘状交错层理的组合,常见变形层理,形成于斜坡上部;类型Ⅲ为以渠模、丘状交错层理与水平层理的频繁叠加为特征,出现在风暴浪基面与正常浪基面之间;类型Ⅳ为具粒序层理的砂 砾屑浊积灰岩,形成于风暴浪基面以下,划归为风暴成因的远源浊流沉积。研究区风暴岩的特征表明：风暴层蕴含了强烈的气候信息,风暴频发是灯影期气候转型的重要响应;该时期构造相对活跃、海底地形复杂化是风暴沉积形成的原因之一;研究风暴岩的特征对等时地层对比研究也具有重要意义。     

豫西前寒武纪汝阳群和洛峪群中风暴沉积

豫西前寒式纪汝阳群和洛峪群中广泛发育不同类型的风暴岩,主要包括丘状交错层砂岩、洼状交错层砂岩、浅水浊积岩以及与风暴作用有关的硬底、凝缩层和层间砾岩。不同类型风暴署具有不同的岩相组合及形成过程,并且发育在浅海陆棚的不同沉积带中。由洼伏交错层砂岩为主的相组合代表了滨岸带的下部;丘状交错层砂岩相组合指示风暴浪基面以上的内陆棚;而浅水浊积岩相组合则主要发育在外陆棚沉积区。这种风暴岩的沉积模式可用于详细恢复受风暴影响的古陆棚环境。     

新疆阿克苏寒武系吾松格尔组造迹行为的单调性

除某些蓝细菌之外,绝大多数白云岩中很难出现底栖后生动物化石。位于塔里木板块北部新疆阿克苏地区肖尔布拉克剖面的寒武系第二统吾松格尔组岩性以白云岩为主夹少量灰岩,属广阔浅潮汐带大面积强蒸发高盐度云坪环境而不利于底栖和游泳的后生动物群生存。本文首次报导该层位中一个低分异度的遗迹类群,它们均产出于薄层泥晶灰岩,鉴定遗迹属包括：Chondrites,Helminthopsis,Skolithos,Stelloglyphu,Taenidium,Thalassinoides,其形态均为小型简单的动物潜穴,属于古生代浅海地层中的常见分子;薄层灰岩中还见少量三叶虫和密集产出软舌螺。吾松格尔组白云岩沉积期海水高盐度环境在很大程度上不但抑制实体化石保存的底栖型和游泳型后生动物,也同样抑制没有实体化石保存的后生动物型遗迹造主栖居,遗迹化石的造主和带壳后生动物只能在正常盐度和动荡环境的薄层灰岩沉积期短暂迁移到此。本实例从环境角度诠释生物进化的制约机制,云坪不是后生动物的理想生态条件,这在寒武纪早期生命大爆发过程中就已经显现出来。     

渤海湾盆地东营凹陷利津洼陷古近系沙河街组湖相风暴沉积特征及控制因素*

渤海湾盆地东营凹陷利津洼陷古近系沙河街组第四上亚段风暴岩沉积构造类型丰富,包括风暴侵蚀形成的冲刷面、渠模、截切面构造,风暴涡流形成的撕裂构造,风暴重力流形成的递变、块状层理,风暴浪形成的丘状交错层理、平行层理、浪成沙纹交错层理及风暴后能量衰减阶段形成的准同生变形构造等。通过岩心观察统计,建立了适合于研究区风暴岩的理想垂向沉积序列,包括10个岩相单元,对应着3个主要的风暴作用阶段：风暴涡流作用阶段、风暴浪作用阶段和风暴作用衰减阶段。结合风暴岩沉积特征及沉积动力学机制,将研究区风暴岩归为4种类型：其中Ⅰ型风暴岩发育于正常浪基面之上,为原地侵蚀型风暴岩,Ⅱ型、Ⅲ型、Ⅳ型风暴岩发育于正常浪基面与风暴浪基面之间。根据以上4种风暴岩沉积特征,探讨了研究区风暴岩形成的主控因素,认为风暴岩的形成主要受风暴作用、物源、古地形以及湖平面变化的影响,并总结出4种类型风暴岩发育的有利条件。     

Caractéristiques et signification d'un niveau coquillier majeur à brachiopodes,marqueur événementiel dans l'évolution dévonienne de la Saoura (Sahara du Nord-Ouest,Algérie)

In the Saoura, the brachiopod shell beds, so-called niveau coralligène, correspond to a major shell deposit dated to the Late Emsian. Brachiopods and crinoids dominate the benthic assemblage that contains also corals, bryozoans, trilobites, goniatites, and orthocones. This major level has a large geographic distribution and it is characterized by a wide brachiopod diversity due to time-averaging, taphonomic feedback and alternate bottom conditions changing from soft to shelly and firm. This kind of brachiopod association is linked to a transgressive onlap system. At regional extent, we can correlate this major shell bed to similar shell deposits from the Ahnet-Mouydir, Tindouf, and Zemmour areas. It indicates an important transgressive event underlined by change in the sedimentation from detritic deposits to carbonate sediments. To cite this article: A. Ouali Mehadji et al., C. R. Geoscience 336 (2004).     

青海省南部侏罗纪地层问题讨论

青海省南部侏罗纪海相双壳类异常丰富.根据近年来新测制的地层剖面和化石资料,本文分析了该区双壳类动物群的时代意义,从而确立了本区侏罗系应包括中,上侏罗统;海相侏罗纪沉积大致自巴柔阶到基末里阶.东特提斯区北缘的弧形地带,诸如青海南部、藏东、藏北、滇西,缅甸掸邦和泰国呵叻等地在中,晚侏罗世基本上属于同一个生态环境较特殊的双壳类生物地理分区,双壳类动物群表现出强烈的地方性色彩,特别是淡水双壳类动物群cuneopsis—Psilunio—Lamprotula组合,半咸水动物群Corbula—Neomindon组合以及淡水（微咸水）动物群Peregrinococha组合完全是该区特有的土著分子,从时代对比意义上来说,它们之间可对比度更高.云南和平乡组双壳类动物群和本区相比较后表明,和平乡组沉积时代大致相当于巴柔期（含早巴通期）.缅甸南瑶系中的双壳类动物群时代不应晚于巴通期.藏东和青海南部产出的奇异蛤动物群时代则应不早于基末里期.     

华北石炭纪含煤建造的陆表海堡岛体系特点及其事件沉积

华北石炭纪含煤建造沉积属于陆表海性质,其岩相古地理特点为陆表海多堡岛浑水与清水混合沉积体系。主要成煤古地理条件是位于潮坪上不同类型的泥炭坪环境,因而煤层分布面积广,层位稳定。聚煤期盆地性的重大事件是风暴沉积和火山事件沉积。风暴岩的主要类型是:回流型远源碳酸盐风暴岩和近源碳酸盐风暴岩,搅动型碳酸盐风暴岩;近源型砂岩风暴岩,漫流型砂岩风暴岩和砾屑泥岩风暴岩。风暴沉积影响着煤层的形成与赋存。     

Tempestite facies models for the epicontinental Triassic carbonates of the Betic Cordillera (southern Spain)

This study focuses on storm deposits in the Muschelkalk facies of the Betic Cordillera (southern Spain) and interprets their deposition mechanisms. Three types of storm deposit are distinguished: (i) pot/gutter casts; (ii) tempestite beds; and (iii) storm‐winnowed deposits. Each deposit provides information about the carbonate platform environment in which it was deposited. The tempestite models proposed are: (i) the bypass‐zone tempestite model, occurring in a muddy ramp at the epicontinental basin margin. This model is characterized by potholes and gutters that form in a shoreline bypass‐zone during storms; (ii) the gradient‐current tempestite model in which frequent tempestite beds are related to storm gradient currents. Thickness and grain size decrease towards the deep distal ramp; and (iii) the winnowed deposit tempestite model whereby storm deposits are winnowed and deposited in the same environment with only short lateral transport having occurred. This model evokes more restricted and shallower conditions, lagoons or inland seas. The distribution of all these deposits in the stratigraphic sections studied corroborate the eustatic third‐order cycle identified, although the different features of the storm deposits and their positions in each section indicate a subsidence varying in time and space. In the transgressive stage, the margins of the epicontinental basin were a well‐developed ramp with potholes and gutters. In contrast, during the high sea‐level stage, storm deposits generated tempestite beds or storm‐winnowed deposits in the different areas. The epicontinental carbonate platform with ramp edges evolved into a complex depositional system of coastal and shallow‐marine environments with lagoons and restricted inland seas. Thus, the epicontinental platform underwent substantial change from the Late Anisian to the Late Ladinian and this is reflected in its storm deposits.     

Non-uniform across-shelf variations in thickness, grain size, and frequency of turbidites in a transgressive outer-shelf, the Middle Pleistocene Kakinokidai Formation, Boso Peninsula, Japan

Across-shelf variations in thickness, grain size, and frequency of sandstone beds in a transgressive outer-shelf succession were investigated from the Middle Pleistocene (ca. 0.7 Ma) Kakinokidai Formation on the Boso Peninsula, Japan. The transgressive deposits are generally muddy and contain slumps and slump scars. The intercalated sandstone beds are interpreted to have been formed from turbidity currents as a response to erosion and resuspension of sandridge-complex deposits in the southwestern upslope area during storm events. Mapping of volcanic ash beds and a transgressive surface in the base of the formation permits detailed bed-by-bed correlation of the outer-shelf sandstone beds. Although, overall, thickness, grain size, and frequency of sandstone beds decrease in the downslope direction, some sandstone beds locally thin out and coarsen in association with slump scars in the surrounding muddy deposits. These sandstone beds subsequently thicken and fine, and finally thin out in the farther downslope area. In addition to the local thinning of sandstone beds, the frequency of sandstone beds first decreases and then increases in the farther offshore direction. From this evidence, we concluded that these non-uniform patterns of across-outer-shelf variations in thickness, grain size, and frequency of sandstone beds were caused by the local increases in flow speeds and subsequent expansion and reduced speeds of turbidity currents, along with a local increase in the seafloor gradient that was induced by the development of slump scars in the transgressive outer-shelf floor. These physiographic features in the outer shelf are interpreted not to have permitted monotonous downslope thinning and fining of sandstone beds, compared with the bed-shape models of depletive turbidity currents and with the proximality trend of shelf sandstones from modern and ancient highstand-stage shelf systems.     

Postglacial stratigraphic evolution of a current-influenced sandy shelf: offshore Kujukuri strandplain,central Japan

Sandy shelf sediments are important elements of clastic sedimentary systems because of their wide distribution in the geological record and their significance as hydrocarbon reservoirs. Although many studies have investigated shelf sediments influenced by waves or tidal currents, little is known about shelf sediments influenced by oceanic currents, particularly their lithofacies characteristics and stratigraphic evolution. This study investigated the stratigraphic evolution of shelf sediments off the Kujukuri strandplain facing the Pacific Ocean, which is influenced by the strong Kuroshio Current. Sediment cores were obtained from six locations on the Kujukuri shelf (34 to 124 m water depth) using a vibrocorer. The dominant lithofacies is mud-free sand with low-angle cross-lamination associated with alternating beds of finer and coarser sand with cross-lamination. These display depositional processes influenced by storm waves and the Kuroshio Current, respectively. This finding is consistent with the previously presented modern and historical observations of the Kuroshio Current and estimates of the storm-wave base. Radiocarbon dates show that the sediment succession formed during the last transgressive and highstand stages after 13·1 ka. The depositional processes during the stages represent a transition from storm waves with abundant sediment supply to both storm waves and the Kuroshio Current with sediment starvation mainly due to its trapping in the strandplain. Comparison to other Holocene–Modern shelf systems suggests that the sandy shelf successions are strongly influenced by oceanic currents under conditions of limited riverine input and open coastal geometry. The resultant sand-dominated succession is characterized by reversal of the proximal to distal grain-size trend compared to the fining for most other recognized wave/storm-dominated shelf successions. This is because of seaward increase in the influence of the Kuroshio Current. Thus, shelf deposits are naturally complex, and these may be further complicated by the additional influence of oceanic currents above the usual wave-dominated and tide-dominated end members.     

Postglacial Deposits of the Dal’nyaya Taiga Group: Early Vendian in the Ura Uplift,Siberia. Communication 1. Barakun Formation

Analysis of modern paleontological, isotope-geochemical, and paleotectonic data on Vendian rocks in the Patom Basin (Siberia) is presented. The paper discusses depositional settings and features of the specifics of sedimentogenesis of the Barakun carbonate–terrigenous formation, which matches the lower strata of postglacial deposits of the Dal’nyaya Taiga Group. It is shown that formation of the transgressive Barakun Formation was governed by relatively deep-water (below the storm wave base) distal settings of a low-angle (about 1°) homoclinal ramp. Its formation was related to a more intense sagging of the northeastern part of the Ura Uplift. The formation of breccias and intrusions was fostered by high seismic activity of the paleobasin recorded in plastic deformations along with liquefaction and fluidization of sedimentary beds. The constant seismic destabilization of bottom beds provoked small but frequent landslides without the formation of turbidite flows. The continuous dislocation of sediments toward the depocenter actively governed specifics of the ramp architecture. The unusual behavior of sediments during their long-term thixotropic residence could be related to a high content of organic matter, processes of methanogenesis and, probably, dissemination of gas hydrate compounds.     

重庆城口锰矿床的地质特征及其成因的再认识

城口锰矿是成岩作用的产物,除叠层石外其它如鲕粒、豆粒、球粒等主要源自碳酸盐台地,由合适的海流搬运而来,后被原地生长的微生物韵律性包覆而构成稳定的“滩”。Mn²⁺主要来源于下部富含有机质、形成于深水还原环境之泥岩的粒间水,其极有利于来自陆地和海底喷发的锰质的富集和保存,在成岩作用时受上覆重荷影响使富含Mn²⁺的酸性粒间水被排驱,向压力较小的孔隙度大、渗秀性好的“滩”内转移,使“滩”相弱碱性碳酸盐层的Ca²⁺、Mg²⁺被Mn²⁺交代而成矿。     

元古界会理群凤山营组风暴流沉积特征

四川省会理县洪川桥地区,是会理群凤山营组广泛分布地区之一,出露面积达百余平方公里。在洪川桥凤山营组剖面的上部(洪剖119层—108层),发育一套约845m厚的风暴流沉积。现将其特征及形成机制作一初步分析,以供参考。一、岩性特征风暴流沉积物,主要为灰—深灰色粉砂质粉屑灰岩和部分泥质灰岩。有时两者呈薄的互层出现。一般层厚几毫米到几厘米,沿走向在数十厘米或几米内尖灭,形成一个个薄的透镜     

重庆凉风垭飞仙关组风暴流沉积

本文根据重庆中梁山凉风垭下三叠统飞仙关组中风暴岩的特征,讨论了在风暴作用下的沉积环境中形成一系列独特的沉积物类型和沉积标志。一个完整的风暴流沉积序列,由底部、中部和顶部三个部分六个层段组成。并根据剖面上各单元风暴层各层段发育程度和滞留砾石特点不同,划分出原地型滞留砾石近积风暴岩、异地型滞留砾石近积风暴岩和迭加型近积风暴岩三种类型。