马尼拉海沟1.4 ka B.P.以来浊流事件沉积及其成因机制*

浊流是远距离沉积物运输的一种重要方式,海底浊流广泛存在于海底峡谷或海沟。马尼拉海沟位于南海东北部,是一条正在活动的板块汇聚边界。独特的地理位置(亚热带—热带)和气候条件(台风频发),使得马尼拉海沟浊流频发,然而,现今对马尼拉海沟的浊流研究甚少。本研究通过对马尼拉海沟北部水深3747 m处重力柱岩心(GEO6)进行高精度的粒度及沉积学特征分析,探讨马尼拉海沟浊流沉积规律。GEO6岩心底部细颗粒沉积物中浮游有孔虫的¹⁴C的AMS年龄为1405 a B.P.。高精度的粒度分析(0.25 cm)和沉积学特征显示: GEO6岩心记录有至少11次浊流沉积(T1-T11),且这些浊流都有明显的底部粒度最粗(砂质粉砂或砂)、向上粒度逐渐变细的正粒序特征,只有T8沉积体为反粒序特征,可能为异重流沉积。结合区域地质资料,本研究认为1.4 ka B.P.以来,研究区频繁的台风带来了大量陆源松散沉积物堆积在马尼拉海沟上游(高屏峡谷),不稳定的构造环境及地震频发导致这些松散沉积物垮塌并向下游马尼拉海沟输送,在海沟内形成频繁发育的浊流沉积体。     

南海北部东沙海底峡谷沉积演化过程及其地质意义

为揭示南海北部东沙海底峡谷沉积演化及其资源效应,利用高分辨率二维多道地震与多波束测深数据,对该峡谷中-上游段的沉积层序、地貌特征及沉积构型展开剖析.东沙海底峡谷上游段表现为6个分支峡谷,中游段则汇聚为2条主峡谷,峡谷头部广泛发育分支水道.峡谷中游段于早中新世晚期开始发育,处于岩浆岩体和构造凸起之间;上游段分支峡谷形成于晚中新世以来,其与峡谷头部分支水道的形成分别受断裂体系和底流作用影响较大.东沙海底峡谷演化分为3个阶段:(1)早中新世晚期-中中新世,峡谷初始发育阶段;(2)晚中新世,峡谷拓展阶段;(3)上新世以来,现代峡谷发育阶段.东沙海底峡谷向马尼拉海沟提供了充足的富有机质沉积物,构成了马尼拉海沟增生楔天然气水合物形成的重要物质基础.      

碎屑流与浊流的流体性质及沉积特征研究进展

受浊流沉积模式(即鲍马序列和浊积扇模式)的驱动和浊积岩思维定势的影响,自1970s浊流与浊积岩的概念逐渐扩大,特别是通过"高密度浊流"术语的引入,以及将水下浊流与陆上河流的错误类比,使得一部分碎屑流与底流的沉积被认为是浊积岩。随着现代观测设备的应用以及详细的岩芯观察,碎屑流(特别是砂质碎屑流)和浊流被重新认识。浊流是一种具牛顿流变性质和紊乱状态的沉积物重力流,其沉积物支撑机制是湍流。碎屑流是一种具塑性流变性质和层流状态的沉积物重力流,其沉积物支撑机制主要是基质强度和颗粒间的摩擦强度。浊流沉积具特征的正粒序韵律结构,底部为突变接触而顶部为渐变接触;碎屑流沉积一般具上、下两层韵律结构,即下部发育具平行碎屑结构的层流段,上部发育具块状层理的"刚性"筏流段。但当碎屑流被周围流体整体稀释改造且改造不彻底时,强碎屑流可变为中—弱碎屑流,相应自下而上可形成逆—正粒序的沉积韵律结构,其中发育有呈漂浮状的石英颗粒和泥质撕裂屑等碎屑颗粒,明显区别于浊流沉积单一的正粒序韵律结构特征。碎屑流沉积顶、底部均为突变接触。浊流的沉积模式为简单的具平坦盆底的坡底模式,而碎屑流则为复杂的斜坡模式。     

水下沉积物重力流与海底扇相模式研究进展

水下沉积物重力流将大量沉积物搬运至海底,形成了地球上最大的沉积体系——海底扇。综合前人研究成果,梳理水下沉积物重力流的基本概念、分类和识别标志,介绍了现代观测的重要结果和海底扇相模式的研究进展。浊流和碎屑流是重力流最主要的两类流体,浊流为逐层沉积,发育正粒序;碎屑流为整体沉积,垂向无序。由浊流转换为碎屑流的重力流称混合流,陆上洪水入海(湖)形成的浊流称异重流。现代观测的结果表明:浊流底部存在高密度层,横向结构并不都是涌浪型,浊流的持续时间可以长达1周。海底扇通常采用组构分析和层级分类进行研究,由水道、天然堤、朵体、远洋—半远洋沉积和块体搬运沉积组成。水道侧向延伸窄,发育侵蚀结构;天然堤由薄层泥—粉砂质浊积岩组成,横向呈楔形变薄;朵体侧向延伸宽,颗粒粒度集中,侵蚀结构较少。水道的层级从低到高依次为水道单元、水道复合体和水道复合体群。朵体的层级从低到高依次为层、朵体元素、朵体和朵体复合体。     

科学与技术并进——近20年来海底峡谷浊流观测的成就和挑战

自1993年至今,美国地质调查局的科学家及其合作伙伴在美国西海岸的Monterey海底峡谷进行了针对现代浊流过程的一系列基础性研究,并成功地在世界上首次实地测量到高精度浊流流速及粒度参数.近20年来的数据和知识积累为解释海底峡谷内沉积物和其他颗粒物质输运的机理,以及浊流在维持深海峡谷中生机勃勃的生态系统所起的重要作用提供了直接依据.通过展示把海底观测应用于海洋沉积动力学研究过程中的成果、经验、教训,以及介绍目前还在讨论中的研究计划,以期达到以下宏观论点:在海洋科学里,只有科学与技术不脱节的科研团队才有希望获得成果和突破.     

南海西部深海平原SA14—34岩心浊流沉积特征

本文对位于南海西部深海平原的SAM-34岩心进行详细的沉积物组分研究，结果表明：该岩心岩性复杂多变，沉积了粘土、粉砂质粘土、砂质粘土、粘土质粉砂、砂质粉砂、砂和粉砂质砂等7种沉积物类型。浊流沉积发育，至少已识别出4个特征明显的浊流层。浊流层厚度为18～120cm，具有粒度较粗呈下粗上细、异地钙质微体生物化石丰富、陆源碎屑矿物含量高、SiO2／Al2O3比值和CaCO3含量高四大特点。并对浊流沉积的物质来源、成因进行了初步分析，认为浊积物主要来自西部陆架一陆坡区，有利的地形、丰富的物源和频繁的海底火山活动诱发的地震是浊流发生的主要原因。     

香港海域全新世地层及风暴潮的建造作用

香港全新世地层中发现有6种沉积构造类型,包括:1)隐构造淤泥层(SM型)、2)砂质粒序层(GS型)、3)层理状沉积层(L型)、4)贝屑粒序层(GSh型)、5)无序贝屑层(USh型)和6)均一粉砂层(SS型)。其中,后5种类型与风暴潮有关。沉积物的粒度分布有7种类型。其中,双峰型粒度分布与风暴潮对海底沉积物的悬浮和再分配密切相关。贝壳的破碎度可指示沉积物受改造的程度。沉积构造受改造的程度主要取决于沉积速率和生物扰动。     

冲绳海槽中全新世的浊流沉积及其控制因素

浊流沉积是陆源物质向深海搬运的主要方式,其发生对于海底扇、峡谷以及深海油气藏的形成具有重要意义。对冲绳海槽3个柱状样岩芯的研究,均发现了发生于7300~7500cal.a B.P.的浊流层。这3个浊流层S1,S2和S3的发生伴随着粒度、粘土矿物以及log(Ti/Ca)的明显变化。浊流沉积层相比正常沉积层具有粗粒组分峰值较高以及下覆的不整合构造,粒度上呈现由粗到细的正粒序构造。伴随着粒度的变化,log(Ti/Ca)也发生明显增大。A7孔位的S2浊流层的底部以及Oki01孔位的S3浊流层的上部含有火山灰层,火山玻璃含量约为80%左右。火山灰层的粒度众数约24~32μm的单峰分布。通过对比其他古气候、古环境指标,发现7300~7500 cal.a B.P.的浊流事件可能与活跃的火山地震作用以及冬季风明显增强有关。     

弯曲海底峡谷中浊流的三维流动及沉积的初步研究

海底浊流的运动及其沉积,是目前浊流研究的热点之一。根据经过验证的基于雷诺平均纳维尔-斯托克斯方程及浮力项修正 k-ε 湍流模型的三维数值计算模型模拟了海底弯曲圆弧形峡谷内的浊流的流动和沉积,结果表明:（1）浊流在运动过程中由于对环境水体的夹带厚度不断增加,浊流厚度一般会超过峡谷深度,溢出峡谷,使浊流产生密度和动量损失;（2）浊流到达弯道部分后,由于离心力的作用会产生剥离,溢出更多的浊流至漫滩区域。浊流剥离的最大处为弯道顶点外岸下游处,其过量密度可达入流的37.5%;（3）对于模拟的横剖面为圆弧型的峡谷内的浊流来说,弯道顶点处的二次流在底部形成一个顺时针的循环圈,靠近峡谷底部从外岸指向内岸;（4）在峡谷中间及弯道顶点内岸下游处形成沉积,在弯道顶点外岸下游处形成侵蚀。这些特征对根据浊流的沉积观察推测其形成环境及油气储层的调查等方面有一定的参考意义。     

滑塌型深水重力流沉积特征及沉积模式:以渤海湾盆地临南洼陷古近系沙三中亚段为例*

综合运用钻井岩心、测录井等资料,通过岩心观察、薄片鉴定和粒度分析等方法,对渤海湾盆地临南洼陷古近系沙三中亚段深水重力流沉积类型及其沉积特征、沉积模式展开研究。研究表明,临南洼陷沙三中亚段深水重力流沉积主要发育滑塌沉积、碎屑流沉积和浊流沉积3种成因类型。滑塌沉积以包卷层理、液化砂岩脉、阶梯状小断层、变形岩层与未变形岩层叠置为典型特征。碎屑流沉积中砂质碎屑流沉积分布较广,以突变的底部接触面、块状层理、泥岩撕裂屑、土黄色泥砾、突变或不规则的上接触面为典型识别标志。浊流沉积则以正粒序层理、底部冲刷面和槽模、薄层砂泥互层、不完整的鲍马序列为典型识别标志。滑塌沉积主要发育在三角洲前缘斜坡根部,在滑塌沉积前方形成碎屑流沉积,碎屑流向前搬运的过程中,流体被稀释逐渐转化成浊流。滑塌型深水重力流沉积整体分为近源沉积、中部沉积和远源沉积3个部分: 近源沉积主要发育具变形构造的滑塌沉积和厚层块状砂质碎屑流沉积;中部沉积主要发育砂质碎屑流沉积及浊流沉积;远源沉积以薄层浊流沉积为主。     

Sedimentary facies of the Nova Scotian upper and middle continental slope, offshore eastern Canada

A detailed survey of the upper and middle Nova Scotian continental slope at 42°50′N and 63°30′W indicates a complex morphology dominated by mass movements on various scales and an immature turbidity current channel. The range of sediment facies is diverse including hemipelagic and turbidite muds, turbidite sands and gravelly sandy muds of debris flow origin. Deformed units, interpreted as slump deposits are also observed. Several facies associations, related to discrete morphological environments, are recognized. Thick turbidite sand units with minor intervening mud beds are characteristic of the high-relief uppermost slope and channel margin. Thinner turbidite sands, deformed slump beds and various mud facies are associated with small-scale, hummocky mid-slope topography. Sand beds are more abundant in the depressions than on intervening hummocks indicating the preferred transport paths of small turbidity currents. At the lower end of the main turbidity current channel, frequent turbidite sand beds with relatively minor mud beds are deposited on a depositional lobe. In areas unaffected by mass movements, alternating bioturbated mud and sandy muds make up the core sequences. A local model of sedimentation is proposed for this area and illustrates that simple models of continental slope sedimentation only apply to a limited range of settings.     

Formation of Hengchun Accretionary Prism Turbidites and Implications for Deep‐water Transport Processes in the Northern South China Sea

Located at the end of the northern Manila Trench,the Hengchun Peninsula is the latest exposed part of Taiwan Island,and preserves a complete sequence of accretionary deep-sea turbidite sandstones.Combined with extensive field observations,a’source-to-sink’approach was employed to systematically analyze the formation and evolutionary process of the accretionary prism turbidites on the Hengchun Peninsula.Lying at the base of the Hengchun turbidites are abundant mafic normal oceanic crust gravels with a certain degree of roundness.The gravels with U-Pb ages ranging from 25.4 to23.6 Ma are underlain by hundreds-of-meters thickness of younger deep-sea sandstone turbidites with interbedded gravels.This indicates that large amounts of terrigenous materials from both the’Kontum-Ying-Qiong’River of Indochina and the Pearl River of South China were transported into the deep-water areas of the northern South China Sea during the late Miocene and further eastward in the form of turbidity currents.The turbidity flow drastically eroded and snatched mafic materials from the normal South China Sea oceanic crust along the way,and subsequently unloaded large bodies of basic gravel-bearing sandstones to form turbidites near the northern Manila Trench.With the Philippine Sea Plate drifting clockwise to the northwest,these turbidite successions eventually migrated and,since the Middle Pleistocene,were exposed as an accretionary prism on the Hengchun Peninsula.     

鄂尔多斯盆地上三叠统延长组长7段深水重力流沉积类型

以鄂尔多斯盆地上三叠统延长组长7段取芯段为主要研究对象,以详细的岩芯观察为基础,以Z43井为例,研究鄂尔多斯盆地延长组长7段深水重力流沉积类型及其特征。研究结果表明,研究区主要发育砂质碎屑流沉积、低密度浊流沉积及混合事件层三种沉积类型。砂质碎屑流沉积整体呈块状,岩性为中—细砂岩,内部可见多个接触面,为多套砂质碎屑流沉积垂向叠置形成。低密度浊流沉积中大部分为中—薄层的正粒序砂岩垂向叠置而成,部分泥质含量较高,表现出砂泥互层的特征。混合事件层主要由下部干净的块状细砂岩与上部富含变形泥岩撕裂屑的砂质泥岩或泥质砂岩成对组合形成,其成因为浊流流动过程中侵蚀泥质基底,黏土物质或泥质碎屑的混入导致浊流向泥质碎屑流转化,最终形成下部浊流沉积上部泥质碎屑流沉积的混合事件层。相近位置不同深度不同类型的深水重力流沉积垂向叠置,指示了复杂多变的重力流流体演化过程。对重力流沉积类型的准确认识,能进一步促进对深水重力流流体转化过程的理解,明确深水重力流沉积分布,为鄂尔多斯盆地深水重力流沉积及常规与非常规油气勘探与开发提供理论指导。     

黔南桂西中三叠统浊积扇、物源及板块构造

引言广布于黔南桂西地区的中三叠世重力流沉积物(面积达7000km~2),由于在黔桂盆地的沉积演化历程中,占有重要地位,因而,历来为世人所注目。近年来,国内先后有许多单位和个人(西南石油学院地质系,1978、1979;张继淹,1985;苟汉成,1985;贺自爱,1956;)曾就这套沉积物形成的地质背景,沉积机理进行过有益的论述。但迄今为止,尚意见纷纭,争论颇     

藏南日喀则群复理石的层序、沉积流体性质和沉积模式分析

日喀则群砂泥质复理石的浊积层序非常发育,包括富泥的粘性高密度浊流、砂质高密度浊流、低密度浊流和Pickering及Hiscott(1986)的限制性泥质高密度浊流的沉积层序。其中,低密度浊流沉积层序的组合与鲍马(Bouma)层序很相似,两者的区别在于沉积的粒度、粒级分布范围、层序厚度和相组合等特征的不同。沉积相序、古流向和物源分析表明,日喀则群复理石盆地的南侧主要发育单向物源的海底扇体系,而盆地北侧以发育双向物源和多种沉积流体的复合沉积为特征。值得指出的是,特殊的浊积类型——限制性泥质高密度浊流沉积的发现为论证日喀则群复理石盆地属残留盆地又提供了一条有力的依据。     

Turbidite Events Recorded in Deep-sea Core IR-GC1 off Western Sumatra: Evidence from Grain-size Distribution

Sediment core IR-GC1, from the abyssal basin of the Indian Ocean off Sumatra, may provide important information on depositional events related to earthquakes and tsunamis. In this study, based on a combination of grain-size analysis with lithological studies and oxygen isotope stratigraphy, seven deep-sea turbidite layers were identified, corresponding to seven turbidity events that occurred at 128–130, 105–107, 98–100, 86–87, 50–53, 37–41 and 20–29 ka. The sediments of the turbidite deposits are characterized by coarse grain sizes, poor sorting, wide kurtosis, bimodal frequency distributions and clear depositional variations. Particle size grading is also an important signature of deep-sea turbidite deposits and can be used as an indicator to identify turbidite layers. Possible triggering mechanisms for the turbidite events include tsunamis, earthquakes, volcanic eruptions and sea-level changes.     

四川盆地西缘早三叠世早期碳酸盐重力流沉积与环境

四川竹园坝?梨园里地区下三叠统飞仙关组地层中,碳酸盐砾屑沉积类型有:碎屑流和浊流;根据岩性组合可分三种组合层序:Ⅰ.碎屑流与半深水泥晶灰岩沉积组合层序;Ⅱ.碎屑流与浊流沉积组合层序;Ⅲ.复合层序?据重力流形成环境,计算了古斜坡坡度,测定了古流向,结合重力流形成及古构造?古地理演化,提出了区内碳酸盐重力流的演化及沉积模式?     

Sustained turbidity currents and their interaction with debrite-related topography; Labuan Island, offshore NW Borneo, Malaysia

The Temburong Fm (Early Miocene), Labuan Island, offshore NW Borneo, was deposited in a lower-slope to proximal basin-floor setting, and provides an opportunity to study the deposits of sustained turbidity currents and their interaction with debrite-related topography. Two main gravity-flow facies are identified; (i) slump-derived debris-flow deposits (debrites) — characterised by ungraded silty mudstones in beds 1.5 to > 60 m thick which are rich in large (> 5 m) lithic clasts; and (ii) turbidity current deposits (turbidites) — characterised by medium-grained sandstone in beds up to 2 m thick, which contain structureless (T_a) intervals alternating with planar-parallel (T_b) and current-ripple (T_c) laminated intervals. Laterally discontinuous, cobble-mantled scours are also locally developed within turbidite beds. Based on these characteristics, these sandstones are interpreted to have been deposited by sustained turbidity currents. The cobble-mantled scours indicate either periods of intense turbidity current waxing or individual flow events. The sustained turbidity currents are interpreted to have been derived from retrogressive collapse of sand-rich mouth bars (breaching) or directly from river effluent (hyperpycnal flow). Analysis of the stratal architecture of the two facies indicates that routing of the turbidity currents was influenced by topographic relief developed at the top of the underlying debrite. In addition, turbidite beds are locally eroded at the base of an overlying debrite, possibly due to clast-related substrate ‘ploughing’ during the latter flow event. This study highlights the difficulty in constraining the origin of sustained turbidity currents in ancient sedimentary sequences. In addition, this study documents the importance large debrites may have in generating topography on submarine slopes and influencing routing of subsequent turbidity currents and the geometry of their associated deposits.