Origin of mud in turbidites and hybrid event beds: Insight from ponded mudstone caps of the Castagnola turbidite system (north-west Italy)

The partitioning of different grain-size classes in gravity flow deposits is one of the key characteristics used to infer depositional processes. Turbidites have relatively clean sandstones with most of their clay deposited as part of a mudstone cap or as a distal mudstone layer, whereas sand-bearing debrites commonly comprise mixtures of sand grains and interstitial clay; hybrid event beds develop alternations of clean and dirty (clay-rich) sandstones in varying proportions. Analysis of co-genetic mudstone caps in terms of thickness and composition is a novel approach that can provide new insight into gravity flow depositional processes. Bed thickness data from the ponded Castagnola system show that turbidites contain more clay overall than do hybrid event beds. The Castagnola system is characterized by deposits of two very different petrographic types. Thanks to this duality, analyses of sandstone and mudstone composition allow inference of which proportion of the clay in each of the deposit types was acquired en route. In combination with standard sedimentological observations the new data allow insight into the likely characteristics of their parent flows. Clean turbidites were deposited by lower concentration, long duration, erosive, muddy turbidity currents which were more efficient at fractionating clay particles away from their basal layer. Hybrid event beds were deposited by shorter duration, higher-concentration, less-erosive sandier flows which were less efficient at clay fractionation. The results are consistent with data from other turbidite systems (for example, Marnoso-arenacea). The approach represents a new method to infer the controls on the degree of clay partitioning in gravity flow deposits.     

南海北部深海盆地上中新统浊积砂体物源分析*

IODP367/368航次在南海北部深海盆地多个站位发现上中新统厚达数百米的大规模深海浊积岩。采用碎屑锆石U-Pb年龄谱系分析方法对U1500站上中新统浊积砂体进行源汇对比分析。研究结果表明U1500站上中新统浊积岩碎屑锆石年龄谱系与其西侧琼东南盆地和北侧珠江口盆地中新世沉积物特征类似。多维排列分析(MDS)结果也显示,该站位样品与珠江口盆地、琼东南盆地沉积物关系密切,表明南海北部深海盆地内厚达数百米的上中新统浊积砂体为南海北部物源和南海西部物源混合堆积形成。南海西部陆源输入物质以浊流搬运的方式,沿中央峡谷从西到东搬运至南海东部深海盆地;南海北部珠江物源以重力流的形式,经南海北部陆坡峡谷搬运至深海盆地中,两种来源的沉积物在深海盆地发生混合沉积,形成U1500站厚达数百米的浊积砂体。南海北部深海盆地厚层浊积砂体物质来源的准确识别,对深刻理解南海新生代盆地的构造演化、沉积物充填过程、物源演变以及古地理特征均具有重要意义。     

Mass-transport deposits on the Rosetta province (NW Nile deep-sea turbidite system, Egyptian margin): Characteristics, distribution, and potential causal processes

In the Nile deep-sea turbidite system (NDSTS), the province fed by the Rosetta branch of the Nile delta is characterised by the recurrent activity of gravity processes. Seven mass-transport deposits (MTDs) were recognised from the upper to the mid slope, downstream from imbricated scars (~ 30 km-long, ~ 200 m high) running along the shelf edge nearby the Rosetta canyon. Extending on surfaces between 200 and 5000 km², with estimated volumes from 3 to 500 km³, these MTDs represent about 40% (up to 90% locally) of the total Pleistocene–Holocene sedimentary thickness. Three types of MTDs can be distinguished on the basis of their scale. Each has also a distinctive internal configuration and distribution within the Rosetta depositional setting. Age estimates of two MTDs point towards relationships between climate and submarine mass failures through sea-level changes, sediment supply, or a combination of both. Additionally, the presence of gas in the sediment and earthquake shaking may have concurred to trigger large-scale failures on the low slope angles (1°–2°) of the Rosetta area.     

A point-sourced calciclastic submarine fan complex (Eocene Anotz Formation, western Pyrenees): facies architecture, evolution and controlling factors

A complete transect of a fossil carbonate ramp slope has been reconstructed using outcrop data from the Lower-Middle Eocene Anotz Formation in the western Pyrenees. The Anotz Formation contains four calciclastic (mostly bioclastic) members encased within hemipelagic marl/limestone alternations, each calciclastic member representing a submarine fan system. Individual fans are composed of a gullied upper slope, a leveed feeder channel, a channelized lobe area, an unconfined lobe zone and a peripheral lobe fringe that grades downcurrent into basinal deposits. Quantitative data on the dimensions and degree of lateral continuity and vertical connectivity of the Anotz calciclastic fan elements are presented. These data provide information for a better understanding of the intrinsic nature of calciclastic submarine fans and to model their reservoir potential. The long-term evolution of the Anotz carbonate slope was generally progradational, as evidenced by the four discrete episodes of calciclastic-fan development. The location of the fans was controlled by the synsedimentary tectonic activity of the Pamplona fault, which created a slope valley along which the reworked shallow-water calciclastic sediments were funnelled. In addition, episodic basinward tilting of the shallow-water carbonate ramp, linked to the development of the South Pyrenean foreland basin, switched on and off the process of calciclastic resedimentation and determined the growth or abandonment of the fan systems.     

顺倾边坡岩层滑移弯曲临界长度及其影响因素分析

基于顺倾边坡岩层滑移弯曲的弹性微分方程及其精确解,应用能量原理建立了岩层滑移弯曲失稳的临界长度计算式,归纳出主要影响因素,并应用优势分析法探讨了各影响因素的主次关系。分析结果表明：岩层单层厚度、滑移面力学性质、岩体弹性模量和坡角是影响顺倾边坡岩层滑移弯曲的主要因素,其影响程度由大到小依次为岩层单层厚度、滑移面的力学性质、岩层倾角和弹性模量。     

江苏高邮凹陷深凹带古近系戴南组地震沉积学

江苏高邮凹陷石油地质条件优越,但构造复杂,沉积类型多样,砂体沉积厚度薄,横向变化快。根据地震沉积学基 本原理与方法,在等时层序地层格架内,运用90°相位转化、分频处理、属性优选及地层切片等关键技术,对高邮凹陷深凹 带戴南组储集砂体进行了识别与描述。通过对典型地层切片进行精细地质解释与标定,明确各沉积体系发育特征及其演化 规律,并最终建立了适用于断陷湖盆沉积充填的沉积模式。     

冻土斜坡模型试验相似分析

南水北调工程、青藏铁路建设工程等一系列工程的实施,将进一步影响和加剧青藏高原多年冻土区斜坡稳定性问题,冻土区边坡开挖及斜坡稳定性是工程活动中必须解决的问题之一,冻土斜坡稳定性研究在国内尚属空白。通过相似模型试验对高原多年冻土区斜坡在自然和人类活动影响下的失稳机制和活动规律进行分析,是开展研究的重要手段。根据相似理论第一定律,对冻土斜坡模型试验进行了相似分析,应用积分类比法推导并建立了冻土斜坡模型试验的相似指标和相似判据,得出在用原状土作模型介质时,6个相似常数减少为2个相似常数,即cτ和cl。模型与原型的时间比例尺是由几何比例尺决定的,即cτ=c2l,仅有一个相似参数为自变量,另一个为因变量。据此对青藏高原多年冻土区青藏公路沿线K3035处冻土斜坡进行了相似模型设计和冻融模型试验。模型再现了K3035处7°斜坡在4个冻融循环条件下,坡体中部(水平、垂向)4#位移伸张计质点位移曲线随时间的变化特征。实验表明,斜坡土体中部在第一次冻融循环中已有滑动迹象,随着滑坎进一步后退和靠近观测基准点,必然出现一次较大的位移,直至周边土体出现滑塌为止。模型试验结果与现场观测资料相比较是令人满意的。     

鄂尔多斯盆地南缘铜川地区三叠系延长组长9段浊积岩特征及对有机质富集的影响

通过岩芯观察、岩石薄片粒度分析,在鄂尔多斯盆地南缘铜川地区三叠系延长组9段识别出了浊积岩,并揭示了其垂向上典型鲍马序列组合及沉积特征。同时,对鄂尔多斯盆地延长组长9段的油页岩、富有机质泥岩等样本进行TOC、热解测试,分析了该段浊积岩特征及对有机质富集的特征及影响。结果表明:半深湖--深湖区油页岩、泥岩干酪根类型以Ⅱ1型为主,浊积岩上下层位的泥岩、泥页岩、粉砂质泥岩等干酪根类型主要为Ⅲ型和Ⅱ2型。长9段浊积岩对含油页岩段的有机质富集具有一定影响,浊积岩AB及ABC序列对底部沉积的泥岩、泥页岩有机质含量影响最大,其有机碳含量相对较低;浊积岩DE序列对底部沉积的泥岩、泥页岩有机质含量影响相对较小,有机质含量相对较高。     

广西那坡盆地火山岩-碳酸盐岩混杂型滑塌堆积:特殊的弧前域构造指相标志及其大地构造意义

本文详细调查揭示,位于中越边境地区的那坡弧前盆地北部边缘发育17处滑塌堆积,有些表现为火山岩-碳酸盐岩块混杂型滑塌堆积,即由火山岩滑塌块体和碳酸盐岩滑塌块体无序堆积而成;有些只是具软沉积变形特征的薄层碳酸盐岩滑塌块体;还有些是砂屑灰岩滑塌块体与碳酸盐岩(或钙质)浊积岩组合以及单一的碳酸盐岩浊积岩或碳酸盐岩碎屑流。碳酸盐岩质块体流和碎屑流一般夹于大型或巨型滑塌块体间,而碳酸盐岩(或钙质)浊积岩和块状砂岩等一般发育于滑塌堆积的远端,有的覆盖于滑塌块体之上。无论是时代还是地球化学组成,滑塌堆积中的具枕状构造的火山岩块与盆地北侧富宁县架街一带的早-中三叠世弧火山岩完全一致。具软沉积变形特征的薄层碳酸盐滑塌岩块中发育有厚30cm左右的风暴沉积层,暗示这些滑塌岩块是发育于火山弧边缘的或其上的局部的碳酸盐岩台地(主要为潮坪-潟湖相)沉积。与全球不同造山带弧前盆地对比表明,这些滑塌堆积是一种发育于构造活动强烈的弧前盆地边缘的特殊的事件沉积,可作为识别弧前域大地构造相单元的普适性沉积标志,也可用以分析断定俯冲增生造山极性。本文对碳酸盐岩滑塌块体的原始层理和软沉积变形的滑塌褶皱轴面方位测量统计揭示火山弧斜坡大体向南西方向(232°~240°)倾斜,滑塌堆积远端浊积岩古水流测量与校正结果揭示沉积物搬运方向为南或南西向,这表明华南地块与北越地块之间的古特提斯分支洋盆在早三叠世期间是向北俯冲消化减的。