闽南-台湾浅滩陆架沉积砂中石英颗粒表面的微结构

石英颗粒表面微结构的研究是随着电子显微镜应用到地质学上而发展起来的。近年来利用扫描电镜观察石英颗粒表面形态特征及差异来研究沉积物物质来源、搬运方式和沉积环境已在我国开展起来。本文是在对闽南-台湾浅滩陆架的地形、沉积物粒度研究基础上,用JSM-50A扫描电镜观察、研究石英颗粒表面微结构时,发现调查海区的(中砂)沉积物中的石英颗粒具有各种微结构,反映特有的沉积环境。     

四川盆地白垩纪沙漠石英沙颗粒表面特征

石英具有较大的硬度和较高的化学稳定性，因而其颗粒表面特征能很好地反映沉积环境。而通过扫描电镜研究石英颗粒表面微细特征是分析沉积环境行之有效的方法。虽然多数人认为四川盆地白垩纪地层存在沙漠沉积(打儿凼组和夹关组)，但仍有人对沙漠沉积的存在持怀疑态度，并认为是河流成三角洲沉积。过去关于其沉积环境的判别主要是根据沉积结构和构造，并未对其石英沙颗粒表面特征进行过系统分析。笔者对采自四川盆地白垩系不同层位地层的样品进行了石英沙颗粒表面特征系统分析。结果表明，石英沙颗粒表面特征分析可以成功地将石英沙区分为风成和水成沉积。因此，本文从石英沙颗粒表面特征方面进一步肯定了四川盆地白垩纪古沙漠的存在。     

Fracturing mode analysis and relative age dating of faults by surface textures of quartz grains from fault gouges

Surface textures of quartz grains taken from about 250 samples of fault gouges in faults ranging in length from several metres to several tens of metres with the faults extending several tens to several hundreds of kilometres in length, are examined by means of the scanning electron microscope and are categorized into four groups from I to IV, based on the smoothness of the surface, degree of undulation and development of cavities, as mentioned in a previous paper. Based on surface features of quartz grains from faults the geological age of movement of which is known, the groups I to IV are tentatively related to the age of formation of quartz grains and the period of formation of surface textures. This correlation makes it clear that quartz-grain surface textures are an important clue to dating a relative age of faulting. River patterns, striations, granular fracture surfaces, and dimple-like textures are observed to appear on less corroded surfaces of quartz grains from fault gouges. Fractographic analysis of these surfaces of quartz grains should be a clue to revealing the mode of fracture of the fault movement which released the quartz grains into the fault gouge.     

Dating fault activity by surface textures of quartz grains from fault gouges

Surface textures of quartz grains from fault gouges are examined by means of the scanning electron microscope. It is disclosed that the surface morphology of the grains is variable, but quartz grains extracted from one fault gouge sample commonly show a type of texture different from those observed on the grains from the other samples. The surface textures observed under the microscope are tentatively classified into eight types; subconchoidal, orange peel-like, fish scale-like, moss-like, moth-eaten, stalactitic, pot-hole, and coral-like textures. These textures can be classified into four groups. Arranged in the order of their apparent features, it is interpreted that the progressive corrosion of quartz grains by ground water has taken place after faulting. The change of this surface feature can assist in estimating the time elapsed since the last fault activity.     

Significance and origin of surface textures on broken sand grains in deep-sea sediments

The surface textures of fine sand particles from the Deep Sea Drilling Project Leg 39 have been studied via scanning electron microscopy. A large portion of the coarsest fraction of these grains from deep sea cores were formerly fragments of larger sand-sized grains that had been mechanically broken. Surface textures characteristic of previous aeolian and subaqueous environments were preserved in fragments broken from the original larger grain surfaces, thus making palaeo-environmental reconstruction possible. Previously, characteristic mechanical markings had not been observed on deep sea sands; the momentum of grain to grain collisions with respect to fine sands is generally insufficient to initiate mechanical breakage.     

风成沉积物中不同粒径石英颗粒表面机械结构的变化特征

按搬运方式将风成石英颗粒分级,逐级测量并统计表面机械结构的类型、数量和大小,并计算其面积。发现悬移为主的颗粒表面结构的类型、数量最少,仅见少量不规则坑、V形坑,在颗粒表面分布面积最小;跃移搬运为主的颗粒表面结构类型最丰富,不规则坑、蝶形坑、V形坑、新月形坑、贝壳状断口大而深,在颗粒表面的分布面积最大;滚动搬运为主的颗粒表面结构数量最多,以小而浅的不规则坑为主,伴有Ⅴ形坑、贝壳状断口等,在颗粒表面的分布面积大小适中。不同搬运方式在石英颗粒表面形成的结构不同,撞击频率、颗粒大小、搬运速度共同影响表面结构的发育,高撞击频率、大粒径可以形成并承载更多的表面结构,大动能撞击可形成多种类且大尺寸的表面结构。在借助石英颗粒表面结构进行成因判别时需根据粒径大小选择相应粒级的石英颗粒表面结构特征组合,以及结构的数量、大小特征等进行综合判别。     

Circumgranular bassanite in a gypsum crust from eastern Algeria – a potential palaeosurface indicator

Detrital sand grains are surrounded by thin bassanite coatings in the upper part of a coarse-crystalline gypsum crust from the Algerian Sahara. The bassanite developed by topotactic replacement of the surrounding gypsum in the absence of a liquid phase. Heating experiments using a gypsum crystal with sand inclusions produced similar patterns and textures. In one experiment, bassanite developed around quartz and carbonate grains but not along the sides of the heated gypsum crystal. This is the result of differences in heat capacity between gypsum, quartz and calcite. Bassanite formation in the crust from Algeria was not controlled by differences in thermal properties. Instead, the bassanite apparently formed under conditions of thermal equilibrium. The occurrence of bassanite as circumgranular coatings in the crust is interpreted as being related to the availability of submicroscopic space along the contact between the gypsum cement and the enclosed sand grains. The presence of coatings of this type, or derived relict features, is a potential criterion for the recognition of palaeosurfaces.     

图门江下游沙丘粒度分布与石英表面结构研究

图门江下游沙丘粒度频率累积曲线形态全部为双峰,负偏态,粒度变化范围大,平均粒度数值小,标准偏差平均值为0.61;粒度分布特征方法判断沙丘沉积环境以河流成因为主。通过扫描电镜研究其石英颗粒表面结构,机械作用以贝壳状断口、V形坑和次棱角状形态组合为主,化学作用为中等-强烈溶蚀特征;石英颗粒表面结构特征表明沙丘为河口沉积;热释光测年结果表明沙丘受全新世海平面变化的影响,经历海水及风力改造。     

Thin section and S.E.M. textural criteria for the recognition of cement-dissolution porosity in sandstones

Cement-porosity relationships are described from the Lower Triassic Sherwood Sandstone Group and the Middle Jurassic Ravenscar Group in the United Kingdom. Calcite cemented sandstones display a variety of replacement textures, with preferential replacement of grains and of overgrowth faces with high free-surface energy. Dolomite and siderite cemented sandstones display similar textures but replacement is less specific and euhedral overgrowth surfaces are commonly embayed by carbonates. Examination of the more porous sandstones with the scanning electron microscope reveals a range of pitting and embayment textures in authigenic overgrowths and in detrital grains. These range from small ‘v’-shaped notches and pits, through regular and irregular shaped embayments, into large depressions. These textures appear to be morphologically similar to the quartz surfaces seen in thin sections of carbonate cemented sandstones, and are interpreted to have been formed by the dissolution of pore-filling and grain replacive authigenic carbonates. This is confirmed by examination of experimentally exhumed overgrowth surfaces from carbonate cemented sandstones. These textures indicate that part of the intergranular porosity in these sediments is secondary in origin, and has been generated by the dissolution of carbonate cements. The identification of such textures may lead to a more confident interpretation of the nature of intergranular porosity in the subsurface.     

克里雅河沿线沙丘沉积物石英砂表面特征分析

对沙漠内部典型河流沿线沙丘石英颗粒表面微形态特征的系统研究尚少。沿塔里木盆地南缘克里雅河下游丹丹乌里克、喀拉墩、圆沙古城、北方墓地及其北部塔里木河一带的沙丘顶部采到5件表沙样品。扫描电镜观察172颗经能谱挑选的石英颗粒表面微形态,筛析法测定5件样品的粒度。结果表明:1）丹丹乌里克样品以极细沙为主,其余均以细沙为主,各样品几乎不含黏土;2）样品磨圆度特征以次棱和次圆状为主,圆状很少,未见棱状特征,次棱状与次圆状特征之间消长关系显著,沙漠南北边缘样品的次棱状特征出现频率较腹地高;3）颗粒中V形坑频率呈现出沙漠边缘较高腹地低的特征,而沙漠边缘的化学作用结构特征低于腹地。石英砂表面特征结构以机械作用为主,同时伴生化学环境作用特征,可认为克里雅河下游沙物质包括了河流、冰川与戈壁成因及风输送而来的颗粒;颗粒表面特征总体新鲜,沙丘应较年轻。纵穿塔克拉玛干沙漠沉积物样品的表面微形态观察与粒度测定,为该地区沉积环境分析与沙丘砂溯源研究增添了新数据。     

Surface texture analysis of southern Tuli Basin sediments: Implications for Limpopo Valley geoarchaeological contexts

The Hackthorne 1 site (southern Tuli Basin, South Africa) is situated on a sand-covered plateau adjacent to the Limpopo River Valley. Although the site is well known for its Stone Age archaeology, the past environmental contexts (particularly sedimentological/geomorphological) are not well known. We examine the Hackthorne sand grain surface textures, so as to provide some insight on the site specific and regional depositional history. Quartz sands at Hackthorne were collected from surface sands and from underlying weathered calcrete. SEM analysis was performed on sand grains, through which several mechanical and chemical microtextures were identified. Microtextures typical of fluvial environments were found only on grains derived from the plateau calcrete host sediment, whilst the surface sands exhibited only textures associated with aeolian environments. The results indicate that the calcrete host sediment is composed of alluvium, and that the surface sands mantling the Hackthorne Plateau are not deflated from the alluvial deposits in the Limpopo Valley, but may rather be derived from distant aeolian sources. The deposition of aeolian sands is consistent with OSL dates which place sand deposition, or remobilization, at 23 and 15 kya, periods in southern Africa associated with increased aridity.     

First known Cretaceous glaciation: Livingston Tillite Member of the Cadna‐owie Formation,South Australia

A 2 m‐thick diamictite occurs near the base of the Cretaceous Eromanga Basin succession at Trinity Well, at the northern extremity of the Flinders Ranges in South Australia. The diamictite consists of a matrix of silt‐ and clay‐size particles and a framework of sand and coarser materials up to small boulder size. Scanning electron microscope study reveals the presence of numerous quartz grains displaying extreme angularity and surface textures attributed to glacial crushing. Sandy sediments considered as fluvioglacial in origin and a locally developed facies displaying flow structures attributed to solifluction processes constitute the basal 3–5 m of the sequence. In places these directly underlie the diamictite and rest with angularity on Neoproterozoic Adelaidean strata. Conformably above the diamictite at the type locality ‘Recorder Hill’ is a sequence approximately 15 m thick of fine sand and silt units containing lonestones up to ～70 cm diameter and hummocky cross‐stratification. These sediments have been assigned to the Cadna‐owie Formation and are dated on palynology as Berriasian to Valanginian. The occurrence of diamictite containing glacially affected quartz grains contributes to our interpretation that the southern margin of the Eromanga Basin, and at least the adjacent part of the northern Flinders Ranges, were affected by glaciation in the Early Cretaceous. The associated dropstone and solifluction facies and nearby glendonite pseudomorphs after ikaite are further evidence of at least intermittent cold climates at this time.     

白云岩的残余结构及由此引发的孔隙分类问题

对碳酸盐岩的结构分类方法进行了评述,但目前的分类并未对白云岩的残余结构问题进行充分论述.为了能更准确地恢复岩相古地理和进行精细的成岩研究,有必要对残余结构进行细分.白云岩的残余结构是由于原始粒屑结构的灰岩,经白云岩化、重结晶、溶蚀、胶结等成岩作用之后,岩石原始结构遭到不同程度的破坏,但仍残留有部分原始结构信息而形成的....     

The relation between the crystallography of quartz, and upturned aeolian cleavage plates

The relation between the crystallography of artificially abraded quartz sand grains and aeolian surface textures has been studied using an X-ray precession camera and the scanning electron microscope (SEM). Crushed Brazilian quartz was sieved to between 250 and 350 μm, eroded in a paddle wheel device which simulated aeolian action at 8 m s^?1 for 3 h, and photographed with the SEM. A typical grain was selected and over 1100 photographs were combined to create a 3 × 3 m photomosaic; because of the large size, it was possible to observe and measure the angular and linear relations between the various features. After the c axis direction in the grain was determined by precession X-ray analysis, the most important aeolian features were related to the crystallography of quartz. The upturned plates or cleavage plates probably represent traces parallel to r(10ī1) and z(01ī1) cleavages in quartz. Blocky areas appear to be an expression of a cleavage parallel to m(10ī0). In addition, plate spacing on thirty-five experimental, modern, and ancient quartz sand grains is fairly constant. Assuming that abrasion in most sedimentary environments acts in the same manner with respect to quartz crystallography, much of the fine silt and clay in sediments and sedimentary rocks may be the result of cleavage following abrasion parallel to the r and z cleavage planes, while the less common blocky particles are probably the result of cleavage parallel to the m planes.     

A scanning electron microscope study of surface textures of quartz grains from glacial environments

Surface textures of quartz sand grains from several glacial environments at the Feegletscher, Switzerland examined by means of scanning electron microscopy are described. The difference between supraglacial and subglacial material is very slight. At the moment the interpretation of these textures must be done with care until the full statistical relation to environments can be ascertained. This does not necessarily invalidate earlier investigations although it does mean that glacial and extraglacial environments in the vicinity of glaciers are apparently not distinguishable. Examination of surface precipitation features suggests a sequence of events which can be used to help discriminate between different ages of deposits in an area. A similarity between some of the surface debris from moraine samples and those seen in loess and quickclay deposits is also suggested.     

对《西藏高原雅鲁藏布江北岸蛇绿岩带的发现及其地质意义》一文的商榷

综合1：5万区调成果，系统阐述了赣西北地区双桥山群的沉积学特征，认为是一套形成于滨海－半深海环境的重力流沉积体系，基本发育－系列重力流沉积相单元，即块状混杂砾岩相，正递变砾岩相，经典浊积岩相等，对各单元基本层序特征进行了总结论述，并结合地球化学特征及粒度分析成果探讨了沉积环境。     

云南西北部丽江—剑川地区古近纪宝相寺组石英砂颗粒表面特征

石英砂具有丰富的颗粒表面特征,是判别沉积环境的重要标志。利用扫描电镜对云南丽江—剑川地区宝相寺组(E2b)的石英砂颗粒表面特征进行了系统分析:下部样品具水成特征,中部样品具风成特征,上部样品则具经水流改造后的风成特征。结合野外观察结果,从宝相寺组石英砂颗粒表面特征的变化规律可以看出,下部为近源洪积环境、中部为风成沙丘环境、上部为湖泊环境。其中中部样品的石英砂磨圆、分选极好,普遍具有标准的碟形、新月形撞击坑和毛玻璃化表面,是典型的沙漠砂沉积。     

云南西北部丽江—剑川地区古近纪宝相寺组石英砂颗粒表面特征

石英砂具有丰富的颗粒表面特征,是判别沉积环境的重要标志。利用扫描电镜对云南丽江—剑川地区宝相寺组（E2b）的石英砂颗粒表面特征进行了系统分析：下部样品具水成特征,中部样品具风成特征,上部样品则具经水流改造后的风成特征。结合野外观察结果,从宝相寺组石英砂颗粒表面特征的变化规律可以看出,下部为近源洪积环境、中部为风成沙丘环境、上部为湖泊环境。其中中部样品的石英砂磨圆、分选极好,普遍具有标准的碟形、新月形撞击坑和毛玻璃化表面,是典型的沙漠砂沉积。     

云南西北部丽江—剑川地区古近纪宝相寺组 石英砂颗粒表面特征

石英砂具有丰富的颗粒表面特征,是判别沉积环境的重要标志。利用扫描电镜对云南丽江—剑川地区宝相寺组(E2b)的石英砂颗粒表面特征进行了系统分析:下部样品具水成特征,中部样品具风成特征,上部样品则具经水流改造后的风成特征。结合野外观察结果,从宝相寺组石英砂颗粒表面特征的变化规律可以看出,下部为近源洪积环境、中部为风成沙丘环境、上部为湖泊环境。其中中部样品的石英砂磨圆、分选极好,普遍具有标准的碟形、新月形撞击坑和毛玻璃化表面,是典型的沙漠砂沉积。     

四川盆地古近纪沙漠沉积特征及古风向意义

基于前人研究成果,通过野外地质调查、室内分析测试对四川盆地古近系柳嘉组红层沉积物的性质、结构、原生沉积构造及石英颗粒表面结构进行了系统分析,分析结果进一步证明了本区古沙漠的存在.将其沙漠沉积分为沙丘和丘间两种沉积类型,对丘间又细分为干丘间和湿丘间,针对不同的沉积类型也明确了相应的识别标志.通过对沙丘前积层倾向的测量,重...