浙江桐庐晚奥陶世内潮汐沉积

本文论述了在中国首次发现的内潮汐沉积的特征及其形成环境。该内潮汐沉积发现于浙江省桐庐县桐君山地区上奥陶统上部,具有典型的对偶层双向递交层序。据其岩类组合和层序特征,可将其定为韵律性砂泥岩薄互层相。其中发育有特征的脉状、波状和透镜状层理。其沉积特征表明形成于开阔的深水斜坡环境,这种对偶层双向递交层序可能为内潮汐的大潮和小潮周期性变化的结果。     

塔里木盆地塔中32井中上奥陶统内潮汐沉积

塔里木盆地塔中32井的中、上奥陶统钻遇厚度为1 462 m。它是一套巨厚的深灰色泥岩、页岩与灰色砂岩、粉砂岩互层夹少量灰岩的地层。其中深灰色泥岩、页岩最多；砂岩和粉砂岩主要分布于上部和下部，中部砂岩和粉砂岩较少；鲕粒灰岩数量少，主要夹于深灰色泥页岩中。这些砂岩和鲕粒灰岩既可单独成层，但更常见它们与深灰色泥页岩组合成薄互层。薄互层中发育脉状、波状和透镜状层理，并普遍发育交错层理和双向交错纹理。这些特征表明砂岩和鲕粒灰岩为深水斜坡上的内潮汐沉积的产物。这些内潮汐沉积进一步划分为4种类型：双向交错纹理细砂岩型、单向交错层和双向交错纹理中-细砂岩型、韵律性砂泥岩薄互层型和鲕粒灰岩型。它们具有5种垂向沉积层序，在剖面上常形成多旋回韵律性沉积组合。     

塔中地区中晚奥陶世内波、内潮汐沉积

现代海底普遍发育由内波、内潮汐引起的深水牵引流,内波、内潮汐不仅可形成各种厘米级的深水牵引流沉积构造,还可建造千米级的大型沉积物波。这种大型沉积物波既可沿斜坡向下迁移,也可沿斜坡向上迁移。在古代地层记录中已发现各种厘米级的内波、内潮汐沉积单元,但尚未发现内波成因的大型沉积物波。塔中地区中上奥陶统碎屑岩段内发育内波及内潮汐形成的各种牵引流沉积构造单元。通过详细的岩心观察,识别出 4种内波、内潮汐沉积微相类型及 5种基本垂向沉积层序。此外,通过地震剖面分析,在研究区中上奥陶统陆坡相中识别出顺坡向上迁移的大型沉积物波,该沉积物波的特征与现代海底发育的沉积物波的特征类似,运用内波理论可对其成因进行合理的解释。     

中国地层记录中的内波及内潮汐沉积研究

内波及内潮汐沉积是深水沉积研究中的一个非常年轻的研究领域,从首次发现内潮汐沉积至今仅 ２０年时间,中国学者在这期间做了不懈的努力,取得了不少研究成果。简要地论述了中国在内波及内潮汐沉积 研究方面的历程和取得的主要成果;重点介绍了已发现的内波及内潮汐沉积的特征、沉积层序、微相类型和沉 积模式;指出了当前该研究领域中存在的问题,认为应及时并尽可能地将海洋物理学的相关研究成果应用在内 波及内潮汐沉积研究中,进而利用地层记录中内波及内潮汐的沉积特征反演内波及内潮汐的物理特征,同时尽 可能地开展内波及内潮汐沉积的水槽实验研究,探索其沉积机理。     

哥伦比亚安第斯波哥大海槽下白垩统海底扇、水道堤沉积

松潘－甘孜造山带的西康群占我国陆地国土面积６．２５％，主体为一套复理石建造，南美波哥大海槽下白垩统沉积地质特征与西康群很相似，为配合地矿部目前开展的“第二次填图计划”，特节译此文，供西康群研究及专题“造山带与非史密斯地区填图方法”参考     

内潮汐沉积研究及其存在的问题

内潮汐沉积是深水沉积研究中的一个非常年轻的研究领域,自1990年发现首例内潮汐沉积以来,沉积学工作者做了 大量不懈的努力,不仅发现了一系列内潮汐沉积实例,而且还对已发现的内潮汐沉积的特征、垂向序列和沉积模式进行了 总结,同时还认为内潮汐沉积可能成为油气潜在的良好储层。但是到目前为止,发现的内潮汐沉积的研究实例十分有限, 因此,内潮汐沉积研究中还存在一系列的尚待解决的问题。首先是内潮汐沉积的鉴别标志和识别方法尚不完善;其次是目 前尚缺少现代内潮汐沉积的典型实例研究,难以全面认识内潮汐对沉积作用的影响;第三是沉积学研究尚未将海洋物理学 的相关研究成果应用在内潮汐沉积的研究中,也未开展相关的内潮汐沉积实验模拟研究,更未利用地层记录中内潮汐沉积 特征反演内潮汐的物理特征,从而制约了内潮汐沉积的形成过程、形成机理、形成条件和形成环境的研究;第四是对内潮 汐沉积的研究意义认识不足。在下一步的研究中,应结合海洋物理学的相关研究成果对现代内潮汐沉积进行观察和研究, 同时开展相关的内潮汐沉积的实验模拟研究,并对古代内潮汐沉积进行反演研究。此外,还应将理论研究与油气等资源研 究相结合,从而更好地促进内潮汐沉积研究的发展。     

塔里木盆地塔东凸起西部中上奥陶统地震层序与海底扇沉积

根据区域地震资料研究塔里木盆地塔东凸起西部中上奥陶统层序地层格架及沉积演化, 在中上奥陶统识别出了2个地震层序, 发现了叠置的丘状前积反射地震单元, 综合岩心观察、岩屑录井和薄片资料, 确认为海底扇沉积体.海底扇沉积主要由块状砂、砾岩, 递变层理砂岩, 平行层理砂岩, 砂纹层理粉砂岩, 变形或包卷层理粉砂岩, 水平层理泥质粉砂岩或粉砂质泥岩, 块状或递变的粉砂质泥岩和泥岩等岩相组成, 形成于中扇和外扇环境, 物源来自研究区南部的岛弧带.海底扇的发现对于塔东凸起乃至整个塔里木盆地中上奥陶统油气勘探具有重要意义.      

河口湾潮坪潮汐水道发育特征及地质意义——以钱塘江为例

河口湾中的砂体是有利的油气储集层,但复杂的水动力变化导致古代河口湾识别困难。通过对现代钱塘江河口湾的研究表明,河口湾潮坪环境潮汐水道可以成为识别古河口湾的一种辅助标志。基于野外实地观测,结合卫星地图对潮坪环境潮汐水道的发育特征进行了详细的描述,并探讨了它的地质意义。结果表明:1）泥坪潮汐水道横截面形态主要有“V”型及宽缓的透镜状,平面上由海向陆可划分为曲折的A段、平直的B段和树状分叉的C段;2）砂坪潮汐水道横截面形态主要有“U”型和阶梯型,平面上由海向陆可划分为曲折或平直的A'段和树状分叉的B'段,A'段的平直与曲折主要受控于砂坪潮道规模的大小;3）在砂质潮坪中常见炭屑层、包卷层理、液化流痕、垮塌构造、波痕等特殊的沉积构造;不同形态和规模的潮坪潮道主要受控于潮坪坡度、沉积物粒度、河口湾形态及相对海平面高低的影响,高坡度、低海平面有利于完整序列潮道的发育;4）不同类型河口湾潮坪潮道的特征及其伴生的特殊沉积构造可以为确定地质历史时期的古河口湾及其演化提供参考。     

鄂尔多斯地区南缘奥陶纪层序地层及海平面变化

鄂尔多斯地区南缘奥陶纪可划分为１２个层序（ｓｅｑｕｅｎｃｅｓ）．本区奥陶纪地壳演化正处于重要关键时期，早奥陶世（冶里－亮甲山期、马家沟期、峰峰期）为被动大陆边缘，划分为７个层序．海平面突然上升，尔后逐渐下降．中、晚奥陶世（赵老峪期、上店期）演化为主动大陆边缘，可划分为５个层序．海平面就鄂尔多斯地区整体而言发生大规模海退，露出海面．但就鄂尔多斯地区南缘则海水突然加深，随后海平面渐渐下降．晚奥陶世卡拉道克世末鄂尔多斯地区海水全部退出．     

米钵山组复理石中的内潮汐沉积

贺兰拗拉谷米钵山组复理石由具有递变层理、双向交错层理、单向交错层理、复杂多向交错层理、飘逸层理和波痕构造的韵律性砂岩、粉砂岩、泥岩薄互层组成。根据双向沉积构造等典型物性特征识别出5种内潮汐沉积微相,即飘逸层理砂泥岩韵律性薄互层微相,单向交错层和交错纹理砂岩粉砂岩微相,双向交错纹理和羽状交错纹理砂岩粉砂岩微相。结果表明：研究区复理石为深水牵引流（内波、内潮汐）、重力流以及原地沉积复合成因;经典的鲍玛序列是有待商榷的;重力流与牵引流存在流态转化。     

内蒙古桌子山中奥陶统拉什仲组深水水道沉积

内蒙古桌子山中奥陶统拉什仲组发育一套典型的浊流沉积。通过详细的野外观察和室内岩石薄片鉴定,分析了拉什仲组的岩石类型及其组合关系,划分出5种岩相类型及3个深水水道复合体。在此基础上,综合分析了拉什仲组水道复合体沉积特征,建立了拉什仲组深水水道沉积模式。研究表明,下部水道复合体砂岩具有向上变细变薄的特征,水道侧向迁移加积趋势明显,可能位于深水水道的弯曲带;而中部及上部水道复合体水道砂体侧向延伸稳定,二者上部均为一套粉砂岩、页岩薄互层沉积,水道复合体以垂向加积作用为主,可能发育于水道末端。     

塔中地区中—上奥陶统内波内潮汐沉积与油气勘探

现代海底普遍发育由内波、内潮汐引起的深水牵引流,内波、内潮汐不仅可形成各种小规模、分散的深水牵引流沉积,而且还可建造千米级的大型沉积物波。在古代地层记录中已发现各种厘米级的内波、内潮汐沉积单元,但尚未发现内波成因的大型沉积物波。通过对塔中地区中—上奥陶统碎屑岩段岩心观察和地震剖面的系统分析,发现了该岩段内由内波和内潮汐作用形成的各种牵引流沉积构造单元。已识别出4种内波、内潮汐沉积微相类型及5种基本垂向沉积层序,同时还在研究区中一上奥陶统陆坡相中识别出了内波成因的大型沉积物波。这些内波、内潮汐沉积具有较好的油气潜能,是该区中—上奥陶统潜在的油气勘探新领域。     

宁夏中奥陶统香山群徐家圈组内波、内潮汐沉积类型

内波、内潮汐沉积是深水沉积研究中一个非常年轻的研究领域,自发现到现在仅仅20年时间,对其沉积类型的研究目前尚未涉及。以宁夏香山群徐家圈组中的内波、内潮汐沉积为对象,详细描述了深水环境中形成的双向交错层理、单向交错层理、复合流层理及具有波状纹层、束状纹层和交错纹层透镜体的交错层理,并探讨了其成因机制,识别出了短周期内波沉...     

Terrane sutures in the Maine Appalachians,USA and adjacent areas

Terrane sutures in the Maine Appalachians and adjacent areas are recognized as melange dominated, deformed accretionary prisms of Ordovician age, and as a broad synmetamorphic transcurrent fault zone of probable Late Silurian-Early Devonian age. Although the accretionary prisms are associated with present day aeromagnetic and Bouguer gravity anomalies, they are probably not associated with present day crustal penetrating boundaries. The geology of the accretionary prisms indicates subduction-obduction dominated regimes during which (1) the Gander and Boundary Mountain (Dunnage) terranes amalgamated and (2) the composite Boundary Mountain-Gander terrane accreted to the Laurentian margin. The Penobscottian orogeny produced and deformed the older of the two accretionary prisms. This accretionary prism indicates that the Penobscottian was a continuous or perhaps diachronous event which spanned the late Cambrian to early Late Ordovician. The younger accretionary prism was produced and deformed during the Taconian orogeny during late Middle to early Late Ordovician. Initial deformation of this accretionary prism may have overlapped the waning stages of the Penobscottian. Portions of the Taconian arc locally overlie the Penobscottian accretionary prism. A synmetamorphic fault zone lies within Precambrian(?) to Ordovician(?) bimodal metavolcanic and metapelitic rocks assigned here to the Avalon terrane. This zone is several kilometres wide and is interpreted to be the postsubduction suture between the Avalon and Gander terranes, and may, in part, represent a fossil transform fault system. The fault zone contains phyllonites as well as shear zones which generally record dextral motion. The phyllonites were previously interpreted as a stratigraphic unit, whereas the shear zones span or are contained within mappable compositional units. Formation of and movement along these phyllonites and shear zones ceased before the intrusion of Early Devonian plutons. Not all faults in south-western Maine are related to the suture. Younger dip and/or strike-slip and thrust faults are approximately parallel to, or may lie within, the older shear zones and they complicate the recognition of the older faults.     

鄂尔多斯盆地西缘奥陶系拉什仲组深水水道沉积类型及演化

深水水道沉积是深水区重要沉积类型之一,对其形成机制研究不仅能提高深水沉积认识,还能为油气勘探提供帮助.以露头资料为基础,对鄂尔多斯盆地西缘奥陶系拉什仲组深水水道形成机制进行了详细研究.拉什仲组岩性以灰绿色页岩及砂岩为主,另见少量的粉砂岩及砾岩.槽模、交错层理、粒序层理及变形构造等发育.总体反映深水沉积环境,重力流沉积较为发育.其中,深水水道沉积极为典型.根据形态、结构及沉积方式等,将研究区深水水道沉积划分为限制型和非限制型水道沉积.前者包括复合型及垂向加积型水道沉积,后者由迁移型及孤立型小水道沉积组成.复合型水道沉积厚约7.5 m,岩性以粗砂岩为主,底部见砾岩,水道轴部沉积、次级水道及水道-堤岸复合体沉积发育,可分为早期、中期和晚期.垂向加积型水道沉积宽为12.4 m,厚为1.3 m,宽深比为9.54,以中砂岩及细砂岩为主,水道内部以层状砂岩充填为主.迁移型水道沉积宽为6.9~12.3 m,厚为0.23~0.73 m,宽厚比14.11~53.48,以中-细砂岩为主,具有明显的北西向迁移特征;孤立型小水道沉积宽为0.5~0.6 m,厚为0.15~0.25 m,宽厚比为2.4~3.33,多为细砂-粉砂岩组成,透镜状,规模小.重力流爆发初期,能量高,侵蚀作用强,发育复合型及垂向加积型水道沉积;重力流中-后期,能量逐渐降低,迁移型水道沉积开始发育;在重力流后期及末期,其能量进一步降低,发育孤立型小水道沉积.而在空间位置上,复合型及垂向加积型水道沉积多发育在斜坡中上部,中部及下部发育迁移型水沉积道,斜坡脚及深海盆地以孤立型小水道沉积最为发育.      

Physico-chemical environment of pedogenic carbonate formation in Devonian vertic palaeosols, central Appalachians, USA

The morphology and geochemistry of pedogenic carbonate found in vertic claystone palaeosols in the Devonian Catskill Formation in central Pennsylvania preserve a record of the physical and chemical environment of carbonate precipitation. The carbonate is characterized by three distinct petrographic generations. Pedogenic rhizoliths and nodules are the earliest precipitated generation, and typically consist of dull red-brown luminescent micrite. Clear, equant calcite spar cement fills voids in the centres of rhizoliths, as well as circumgranular cracks and septarian voids in nodules. Early spar cements are non-luminescent to dull luminescent, whereas later spar cements exhibit bright yellow-orange luminescence. Late stage pedogenic fractures are always occluded with very bright yellow-orange luminescent spar cements. The incorporation of progressively higher concentrations of Mn (up to 34000 ppm) into successively younger calcite spar cements, without concomitant increases in Fe, suggests carbonate precipitation from an evolving meteoric water in which Mn²⁺ became increasingly mobile over time. The increased mobility is possibly due to decreasing Eh, resulting from oxidation of organic matter after rapid soil burial on the floodplain. The amount of Fe²⁺ available for incorporation into calcite was limited because most iron was immobile, having been earlier oxidized and bound to the palaeosol clay matrix as a poorly crystallized ferric oxide or oxyhydroxide mineral. Carbon isotope compositions of pedogenic carbonate correlate with the inferred depth of carbonate precipitation. Rhizoliths preserved below the lowest stratigraphic occurrences of pedogenic slickensides are consistently depleted in ¹³C relative to nodules, which formed stratigraphically higher, within the zone of active soil shrink and swell processes. Nodular carbonate, precipitated in proximity to deep cracks in the soil, is enriched due to increased gas exchange with isotopically heavy atmospheric CO₂. Accordingly, rhizolith compositions will most accurately estimate palaeoatmospheric levels of CO₂; the use of nodule compositions may result in overestimation of P_CO2 by as much as 30%.     

深水内波、内潮汐沉积类型及其油气意义

深水内波、内潮汐沉积可归纳为水道型和非水道型两种基本沉积类型。水道型沉积常发育双向递变层序和单向递变层序,单砂层较厚,它不仅是油气的良好储层,而且常与深水重力流沉积和深水背景泥岩沉积一起构成有利的地层或岩性圈闭,应当列为深水沉积区油气勘探的重点目标。非水道型深水内波、内潮汐沉积一般发育由砂泥频繁薄互层所构成的对偶层双向递变层序和对偶层单向递变层序,单砂层很薄,油气勘探意义可能不大。广泛分布的大型沉积物波(分为粗、细粒两种)和水道口附近的内潮汐砂坝,是两种比较特殊的内波、内潮汐沉积建造。根据现有研究实例和沉积成因水流理论分布范围等,建立了深水内波、内潮汐综合沉积模式。     

Cambrian- Ordovician Deep - Water Deposits in Southwest Jiangxi, China

The Cambrian-Ordovician rocks in southwestern Jiangxi are mainly composed of deep-water deposits, in which 5 facies have been recognized: sandstone facies, sandstone-mudstone facies, siltstone-mudstone facies, mudstone (slate)facies, and chert facies. They are of turbidity current origin and are related to pelagic and hemipelagic deposits. In the light of facies distribution, the Cambrian-Ordovician deposits can be classified into 3 facies associations formed in middle fan, outer fan and deep-sea plain environments respectively. The 3 different orders of vertical cycles in the stratigraphic sequence are considered to be controlled by factors such as sea-level fluctuation, basin subsidence and submarine fan progradation. The tectonic setting of the sedimentary basin is interpreted as passive continental margin based on the chemical composition analysis of the sandstone.