Facies characteristics and architecture related to palaeodepth of Holocene fjord–delta sediments

Lithofacies characteristics and depositional geometry of a sandy, prograding delta deposited as part of the Holocene valley‐fill stratigraphy in the Målselv valley, northern Norway, were examined using morpho‐sedimentary mapping, facies analysis of sediments in exposed sections, auger drilling and ground penetrating radar survey. Various lithofacies types record a broad range of depositional processes within an overall coarsening‐upward succession comprising a lowermost prodelta/bottomset unit, an intermediate delta slope/foreset unit containing steeply dipping clinoforms and an uppermost delta plain/topset unit. Bottomset lithofacies typically comprise sand‐silt couplets (tidal rhythmites), bioturbated sands and silts, and flaser and lenticular bedding. These sediments were deposited from suspension fall‐out, partly controlled by tidal currents and fluvial effluent processes. Delta foreset lithofacies comprise massive, inverse graded and normal graded beds deposited by gravity‐driven processes (mainly cohesionless debris flows and turbidity currents) and suspension fall‐out. In places, delta foreset beds show tidal rhythmicity and individual beds can be followed downslope into bottomset beds. Delta plain facies show an upward‐fining succession with trough cross‐beds at the base, followed by planar, laminated and massive beds indicative of a bedload dominated river/distributary system. This study presents a model of deltaic development that can be described with reference to three styles within a continuum related primarily to water depth within a basin of variable geometry: (i) bypass; (ii) shoal‐water; and (iii) deep‐water deltas. Bypass and deep‐water deltas can be considered as end members, whereas shoal‐water deltas are an intermediate type. The bypass delta is characterized by rapid progradation and an absence of delta slope sediments and low basin floor aggradation due to low accommodation space. The shoal‐water delta is characterized by rapid progradation, a short delta slope dominated by gravity‐flow processes and a prodelta area characterized by rapid sea‐floor aggradation due to intense suspension fallout of sandy material. Using tidal rhythmites as time‐markers, a progradation rate of up to 11 m year^?1 has been recorded. The deep‐water delta is characterized by a relatively long delta slope dominated by gravity flows, moderate suspension fall‐out and slow sea‐floor aggradation in the prodelta area.     

Controls on late Quaternary incised‐valley dimension along passive margins evaluated using empirical data

Incised valleys are canyon‐like features that initially form near the highstand shoreline and evolve over geological time as rivers erode into coastal plains and continental shelves to maintain equilibrium‐gradient profiles in response to sea‐level fall. Most of these valleys flood during sea‐level rise to form estuaries. Incised‐valley morphology strongly controls the rate of creation of sediment accommodation, valley‐fill facies architecture and the preservation potential of coastal lithosomes on continental shelves, and affects coastal physical processes. Nonetheless, little is known about what dictates incised‐valley size and shape and whether these metrics can be used to explain principal formation processes. The main control on alluvial channel morphology over human time scales is discharge; this is based on numerous empirical studies and is well‐constrained because all variables are easily measured at this short time scale. Knowledge of long‐term river evolution over a complete glacio‐eustatic cycle, on the contrary, remains largely conceptual, experimental and based on individual systems because variables that are thought to drive morphological change are not easily quantified. In spite of this difficulty, existing models of incised‐valley formation at the coast suggest that valley evolution is driven largely by downstream forcing mechanisms, highlighting sea‐level and shelf gradient/morphology as the dominant controls on valley incision. Although valleys are cut by rivers, whose channels are a direct reflection of discharge, little empirical data exist in coastal areas to address the degree to which valley evolution is governed by upstream controls. The late Quaternary is the best time period to examine because it provides the most complete sedimentary record and many variables, including sea‐level, tectonics, substrate lithology and drainage network characteristics, are accurately constrained. Here, 38 late Quaternary valleys along the coast of two different passive continental margins are compared, which suggests that valley shape and size are governed primarily by upstream, intrinsic controls such as discharge. Valley width, depth and cross‐sectional area are found to be predictable at the highstand shoreline and are scaled with the size of their drainage basin, which has important implications for estimating sediment discharge to continental shelves and deep water environments during periods of low sea‐level.     

沟系土壤地球化学测量在内乡韭菜沟矿区勘查中的应用

通过在韭菜沟矿区的沟系土壤地球化学测量工作,发现了一批有价值的地球化学异常,结合地层、岩性、构造等有利控矿因素,对金、银、砷、汞、锑地球化学异常区的找矿潜力进行分析,说明砷、汞、锑异常对金矿化有一定的指示意义。进一步明确找矿方向,缩小找矿范围,圈定了3个找矿靶区,对各靶区实施山地工程验证,取得了较好的找矿效果,证明沟系土壤地球化学测量方法在地质勘查中具有明显的找矿效果,为进一步的地质工作提供了科学依据。     

湟水谷地农业生态经济系统的能值分析——以西宁市为例

运用能值理论与分析方法,采用净能值产出率、环境负荷率、能值密度、人均能值用量、能值产投比及可持续性指数、系统稳定性指数及优势度指数等重要能值指标对位于湟水谷地的西宁市1990-2008年间农业生态经济系统的能值结构作了深入地分析.结果表明:湟水谷地农业生态系统由1990-2004年的低效率开发阶段逐步转变为2005-2...     

金沙江石鼓-宜宾段河谷-水系演化研究综述与讨论

有关金沙江形成演化研究的历史已有百年之久,近十年来更是地学界研究热点之一,产出成果颇为丰硕。该文在对一个多世纪以来有关金沙江研究成果分析基础上,勾绘出金沙江石鼓-宜宾段上新世以来的河谷形成演化过程,基本观点为:全新世之前该区存在数条并列南流水系;上新世末-早更新世初,湖泊广泛发育;早更新世中后期,金沙江经丽江-鹤庆,于金江街附近汇入昔格达古湖;早更新世末期,昔格达古湖被切穿泄空,金沙江下游袭夺连通;中更新晚期,石鼓以南的东西向隆起使金沙江南流受阻,被动袭夺至水洛河,并于三江口与下游川江连通,至此形成真正具有现代意义的金沙江。     

近断层地震下楼层竖向加速度影响因素分析

现阶段基于性能的抗震设计思想不仅关注结构自身体系的安全,而且保护非结构构件在地震作用下使用功能完好.对于工业建筑结构,生产设备在地震作用下受损会影响震后功能恢复.加速度敏感型非结构构件一般采用楼层加速度指标来量化其地震损伤程度.以三个不同高度的钢抗弯框架规则结构体系为研究对象,采用与竖向目标谱匹配的近断层非脉冲和脉冲地...     

滇石林地质公园喀斯特山地天然林和人工林凋落物与死地被物的动态特征

对云南石林地质公园景区及其保护区内喀斯特山地典型森林类型凋落物组成与数量及其动态,地表死地被物现存量与持水特性等进行了研究。结果表明,本区域保护较好的滇青冈(Cyclobalanopsis glaucoides)林的年凋落量达7.26 t/hm2;而以团花木新姜子(Neolitsea homiantha)为主的次生林只有1.98 t/hm2;云南松(Pinus yun-nanensis)人工林和干香柏(Cupressus duclouxiana)人工林年凋落量分别是2.49 t/hm2和4.07 t/hm2。这些森林的凋落节律相似,都呈明显的“双峰型”。在地表死地被物现存量方面,干香柏林因其叶片难以分解而具有较高的地表现存量,为13.59 t/hm2,随后依次为滇青冈林(7.57 t/hm2),团花新木姜子次生林(5.02 t/hm2)和云南松人工林(4.83 t/hm2),死地被物的持水量与其现存量的大小顺序一致。根据森林年凋落量与死地被物现存量的数量关系,表明保护较好的滇青冈林内枯枝落叶的分解率明显大于次生林和人工林,周转期也短,涵养水分能力也较强。因此,应加强对喀斯特山地自然森林的保护,同时也注意对现有人工林的改造,引进一些阔叶树种,提高群落结构的整体效应。     

滇西纵向岭谷区河谷形态特征、发育规律及成因

为了揭示滇西纵向岭谷区河谷形态特征及其发育规律,采用1∶5万DEM图件,利用ARCG IS软件提取研究区41个河谷断面的有关基础数据,据此计算了河谷横断面的宽深比、半高宽深比、断面面积、凹度、不对称系数及河谷纵剖面特征的指标。结果表明,纵向岭谷区北部河谷横断面的宽深比很小,其宽深比在4~16间,但沿流向往南有明显增大的趋势,最大达到24。这是由于北部的构造抬升作用强从而引起该区更强列的河流下蚀作用的结果。河谷横断面的凹度显示大多数河谷属于"V"型谷,表明研究区的河流仍然以下切过程为主。谷宽不对称系数及谷面不对称系数揭示了研究区河谷横断面主要是左倾型河谷,即河谷断面上河道左部谷坡较缓,这是强势西南季风在河流左岸迎风坡形成强降水带和在河流右岸背风坡形成弱降水带的雨水差异侵蚀引起的。河谷纵剖面具有明显的下凹特性,凹度在1.40~1.65间。河道比降具有沿程变小的趋势,并遵循指数衰减关系,平均比降在1.22‰~1.85‰间。在纵向岭谷区北部,响应构造抬升作用的西强东弱的现状,河流主河道的比降具有从西向东变小的趋势。     

GIS的AHP型脆弱性指数法在李雅庄矿底板突水评价中的应用

山西霍州矿区李雅庄煤矿石炭系太原组K₂灰岩岩溶发育,加之区内断裂构造发育,水文地质条件较为复杂。为解决上组2号煤底板太灰突水评价难题,采用GIS的AHP型脆弱性指数法,首先建立煤层底板突水主控因素体系,并通过GIS对主控因素数据进行采集及归一化处理,建立子专题图层,然后运用AHP法确定各主控因素的权重比例,提出煤层底板突水脆弱性的分区方案。与传统突水系数法相比,脆弱性指数法能较为全面地反映不同区域的相对脆弱关系,其评价结果更实际、可靠。     

底板梳状定向钻孔套铣打捞技术研究与应用

为解决底板梳状定向钻孔卡钻事故中采用常规\