南极普里兹湾主要碎屑矿物特征及物源分析

基于南极普里兹湾海域33个表层碎屑沉积物样品的碎屑矿物学分析,对该区的沉积环境与物质来源进行了分析。结果表明该区碎屑重矿物共17种,石榴子石、普通角闪石和磁铁矿为优势矿物,紫苏辉石和赤铁矿为特征矿物。根据矿物组合分布特征,普里兹湾可划分为4个矿物区:Ⅰ区为石榴子石含量占绝对优势、重矿物含量较高的弗拉姆浅滩矿物区;Ⅱ区为石榴子石、普通角闪石含量较高,磁铁矿为特征矿物的普里兹水道矿物区;Ⅲ区为紫苏辉石含量较突出的四女士浅滩矿物区;Ⅳ区为普通角闪石含量明显突出,石榴子石显著减少的深水陆坡矿物区。通过电子探针测试研究区石榴子石结果表明:碎屑石榴子石含有较高的Fe、Mg和较低的Ca、Mn,属主要来源于高级麻粒岩相副变质岩的A型石榴子石。普里兹湾海域的碎屑矿物分布特征是物质来源、海流系统以及冰川活动等多重因素综合作用的产物。     

Geochemistry and provenance of a multiple-stage fan in the Upper Miocene to the Pliocene in the Yinggehai and Qiongdongnan basins,offshore South China Sea

The Yinggehai and Qiongdongnan basins in the northwestern South China Sea preserve a large volume of Cenozoic sediments. However, their sources are still remain controversial and need a further research. This paper uses discriminant diagrams and bivariate plots of major, trace and rare earth elements, combined with heavy mineral data and detrital zircon U-Pb ages to determine the provenance, source area weathering and tectonic setting of the Upper Miocene to Pliocene sediments in the Yinggehai and Qiongdongnan basins, offshore South China Sea. The sandstone samples used in this study are characterized by four features: (i) The studied sandstones are first-cycle deposits, no recycling processes are recorded in these sediments, and there is a low degree of weathering conditions in the source areas. (ii) The sandstones from the DF fan, LD fan and Central Canyon System may have a similar source, being derived from an old upper continental crust mainly composed of felsic igneous source rocks. (iii) Detrital zircon U-Pb ages suggest that Central Vietnam is likely to be the dominant source of the DF fan, LD fan and Central Canyon System. (iv) The tectonic setting of the sandstones in the DF fan, LD fan and Central Canyon System belongs to the continental island arc (CIA) or the active continental margin (ACM) fields.     

基于重矿物地球化学手段的南海东北部陆架沉积物物源研究

物源是研究大陆架沉积物搬运过程、重建陆架古环境以及海洋砂矿资源勘查的重要信息。然而,陆架砂质沉积物普遍经历过多次搬运、分选和混合,这给物源识别带来极大的困难。南海东北部陆架砂质沉积物分布广泛,本文首次采用单矿物化学方法对其物源进行了新的解析。研究区表层砂质沉积物中电气石与角闪石为优势重矿物,两者含量呈现此消彼长的关系。电气石和石榴子石的电子探针数据显示:珠江、韩江沉积物影响海域,火成岩成因的电气石占60%左右,其主要来源为区内广泛发育的燕山期花岗岩的风化产物;莲花山断裂带和长乐-南澳断裂带附近的南海东北部沿岸小河沉积物中变质岩成因的电气石含量显著增高,最高可达70%,其来源为区内与断裂带伴生的变质岩风化物;矽卡岩成因的钙铝榴石在南澳岛以东的陆架沉积物中发现最多,这与华南陆域矽卡岩的分布区吻合。综合分析认为,重矿物的矿物化学方法可以减少分选效应的影响,利用多种矿物的矿物化学分异可以获得多维的信息,为陆架沉积物的物源判定提供便利。     

南海北部陆架表层沉积物重矿物分布特征及物源意义

该文根据2007～2010年间对南海北部陆架采集的292个表层沉积物样品0．063～0．125mm粒级矿物的鉴定和分析结果,研究了该海域表层沉积物重矿物的分布特征和物质来源．结果表明：该海域矿物组成以轻组分矿物为主,平均质量百分数高达98．49％,重组分矿物的含量较低,平均值为1．51％,最高质量百分数仅为10．38％,共发现了60种重矿物．影响南海北部陆架表层沉积物重矿物的含量和分布的首要因素是水动力条件,其次是物质来源,其他因素如沉积环境、矿物自身的变质程度等也在一定程度上影响其分布特征．根据因子分析的因子荷载分布及南海北部陆架的地形地貌,研究区可划分为4个主要矿物组合区和2个亚区．分析结果表明,华南沿海的众多河流特别是珠江的入海泥沙是南海北部陆架表层沉积物的主要物质来源．海南岛东南部海底峡谷区处于相对稳定的沉积环境,胶结于有孔虫壳内的海洋自生黄铁矿含量丰富．     

Mineral provinces and matter provenance of the surficial sediments in the western Philippine Sea: implication for modern sedimentation in West Pacific marginal basin

The characteristics and distribution patterns of detrital minerals (0.063~0.125 mm) in marine sediments provide a significant indicator for the identification of the origin of sediment.The detrital mineral composition of 219 surface sediment samples was analysed to identify the distribution of sediments within the western Philippine Sea. The area can be divided into three mineral provinces: (I) province east of the Philippine Trench, the detrital minerals in this province are mainly composed of calcareous or siliceous organisms, with the addition of volcanogenic minerals from an adjacent island arc; (II) middle mineral province, clastic minerals including feldspar, quartz and colorless volcanic glass, sourced from seamounts with intermediate-acid volcanic rock, or erupting intermediate-acid volcano; (III) province west of the Palau—Kyūshū Ridge, the matter provenance within this province is complex; the small quantity of feldspar and quartz may be sourced from seamounts or erupting volcano with intermediate-acid composition, with a component of volcanic scoria sourced from a volcano erupting on the Palau—Kyūshū Ridge. it is suggested that, (1) Biogenic debris of the study area is closely related to water depth, with the amount of biogenic debris controlled by carbonate lysocline. (2) Volcaniclastic matter derived from the adjacent island arc can be entrained by oceanic currents and transported towards the abyssal basin over a short distance. The weathering products of volcanic rocks of the submarine plateau (e.g.,Benham Plateau) and adjacent ridges provide an important source of detrital sedimentation, and the influence scope of them is constrained by the intensity of submarine weathering. (3) Terrigenous sediments from the continent of Asia and the adjacent Philippine island arc have little influence on the sedimentation of this study area, and the felsic mineral component is probably sourced from volcanic seamounts of intermediate-acid composition.     

Heavy-mineral variability in bottom sediments of the lower Chesapeake Bay,Virginia

Heavy minerals in bottom-sediment samples of the lower Chesapeake Bay show distribution patterns and interrelationships that denote characteristic mineral suites associated with defined geographic provinces. The Baymouth province has a garnet—hornblende—pyroxene suite, which is largely attributed to the influx of littoral and shelf sediments; the Eastern Shore province has a similar suite, derived largely from coastal erosion of the Eastern Shore peninsula. The Northern and Combined River provinces have a zircon—tourmaline—staurolite assemblage, which reflects derivation from an Appalachian Piedmont—Atlantic Coastal Plain sourceland. The Western Shore province is associated with a zircon—epidote—staurolite assemblage, apparently derived jointly from tributary influx and coastal erosion of the western shore. Factor analysis identified two major factors that account for 63% of the total variation in the relative amounts of the seven most common heavy minerals. The dominant factor (44%) is based on a zircon—hornblende—staurolite—pyroxene relationship, which indicates that mineral stability, as influenced by sediment maturity, is a major contributing factor. The second factor (19%) based on a tourmaline—epidote—staurolite—garnet relationship indicates that provenance is another major cause of heavy-mineral variability within the lower bay.     

北极王湾表层沉积物中的粘土矿物及其对物源与古环境变化的指示意义

Kongsfjorden is a typical fjord on the edge of the ice cap of the Arctic Svalbard-Barents Sea. Its inner bay is connected with a modern glacier front along the direction of the fjord axis with a significant gradient change in the parameters of hydrology, sedimentation, and biology. In summer, ice and snow melt-water and floating ice collapse continuously and thus transport the weathering products on the surrounding land into the sea. Thus Kongsfjorden is regards as a natural laboratory for the study of unique sedimentation in polar fjords under modern glacial-sea water conditions. In this study, fifty-two surface sediments were collected in Kongsfjorden for clay mineral analysis to study the sediment source and sediment-transport process. Our results indicate that clay minerals in the surface sediments from Kongsfjorden are mainly composed of illite, chlorite, and kaolinite, and no smectite is found. Rocks from different periods exposed extensively in the surrounding areas of Kongsfjorden provide an important material basis for clay minerals in the Kongsfjorden. Kaolinite may be mainly derived from the fluvial deposits, weathered from reddish sandstones and conglomerates during the Carboniferous Period.Illite is mainly derived from Proterozoic low-grade and medium-grade metamorphic phyllite, mica schist, and gneiss. While chlorite is mainly from Proterozoic low-grade metamorphic phyllite and mica schist. In the direction from the fluvio-glacial estuary to the sea of the glacier front of Kongsfjorden, illite increase gradually,and the content of kaolinite declines gradually. However, the change pattern of chlorite is insignificant, which may be related to the provenance. Kongsfjorden detritus is mainly transported by the fluvio-glacial streams and icebergs into the sea and deposited in the inner bay. Coarse sediments are rapidly deposited in the glacier front,estuary, and near-shore areas. Clay fraction begins to deposit significantly by 200–400 m after flowing into the sea,which due to the crystal behavior of clay minerals, hydrodynamic condition and flocculation. Kaolinite and chlorite on the south of the bay near the Blomstrandhalv?ya Island is mainly affected by ice-rafted detritus and thus can reveal the trajectory of transportation by the floating ice while entering the sea.     

Provenance Signature of Pre-Cambrian and Mesozoic Rocks in the Nearshore Placers of Konkan,Central West Coast of India

Heavy mineral studies of the nearshore placer deposits of the Konkan Coast reveal a dominant assemblage comprised of garnet and kyanite along with other accessory minerals like epidote, olivine and rutile. The heavy mineral assemblage of the study region shows a characteristic suite of 17 types of heavy minerals. Their abundance shows hardly any drastic variation in the four bays studied. Overwhelming presence of minerals like garnet and kyanite in the studied four bays points to the source as metamorphic rocks. The presence of etched garnets, overgrown zircons and etched kyanites corroborate the recycling of paleo-sediments into the bay. Characterization of opaques under the microscope also corroborates the influence of a metamorphic source, rather than the adjoining basaltic rocks. However, the absence of metamorphic rocks in the hinterland suggests the possibility of deposition of sediments predominantly from offshore. Factor analysis results also corroborate the overwhelming influence of metamorphic rocks in the present study region rather than the abutting basalts.     

江苏南通QC_5孔第四系碎屑矿物特征及其地质意义

南通QC_5孔第四系碎屑矿物达40余种。不同重矿物的含量垂向分布与沉积环境有关而呈“波状”变化。重矿物的组合分段大多与第四系中地层界线相对比。第四系碎屑矿物母岩以中酸性火成岩为主。F/Q值之大小是沉积物生成时间长短、古气候冷暖与沉积速率高低综合作用的结果。     

长江口表层沉积物重矿物在不同粒级中的分布与研究意义

在粒度分析基础上,以0.5Φ为间距对长江口表层沉积物的不同粒级分样进行碎屑重矿物分析,并对各粒级重矿物特征与广粒级(1.5Φ～6Φ)进行相似度分析。结果表明,长江口沉积物粒度跨度大,从粗砂到泥(黏土)均有分布,粉砂含量高。样内不同粒级分样重矿物含量、种类和组合均有一定变化,样间表现出较一致的规律性。长江口出现碎屑重矿物30种左右,粗粒级分样中矿物种数为10余种,细粒级分样中重矿物种类增至20多种;3.5Φ～4.5Φ是重矿物种类多、矿物成分复杂的粒级区段。粗粒级(粒径大于3Φ)云母族富集,其重矿物组合为云母+角闪石,随粒级变细(粒径小于4Φ)云母急剧减少;闪石族分布粒级广泛,在3Φ～5Φ粒级含量相对较高;帘石族、稳定矿物尤其是金属矿物在粒径小于3.5Φ粒级逐渐增多。长江口重矿物整体组合为普通角闪石+绿帘石+褐铁矿,榍石为特征矿物。相似度分析表明,长江口沉积物样品中主要粒级与广粒级重矿物特征相近,能代表沉积物整体重矿物特征。长江口碎屑重矿物特征深受粒度分布的影响,其矿物种类、矿物组合和矿物指数及其所蕴含的水动力和物源意义都要结合粒度特征来综合分析。     

Controls on reservoir quality of Lower Cretaceous tight sandstones in the Laiyang Sag,Jiaolai Basin,Eastern China: Integrated sedimentologic,diagenetic and microfracturing data

The Jiaolai Basin (Fig. 1) is an under-explored rift basin that has produced minor oil from Lower Cretaceous lacustrine deltaic sandstones. The reservoir quality is highly heterogeneous and is an important exploratory unknown in the basin. This study investigates how reservoir porosity and permeability vary with diagenetic minerals and burial history, particularly the effects of fracturing on the diagenesis and reservoir deliverability. The Laiyang sandstones are tight reservoirs with low porosity and permeability (Φ < 10% and K < 1 mD). Spatial variations in detrital supply and burial history significantly affected the diagenetic alterations during burial. In the western Laiyang Sag, the rocks are primarily feldspathic litharenites that underwent progressive burial, and thus, the primary porosity was partially to completely eliminated as a result of significant mechanical compaction of ductile grains. In contrast, in the eastern Laiyang Sag, the rocks are lithic arkoses that were uplifted to the surface and extensively eroded, which resulted in less porosity reduction by compaction. The tectonic uplift could promote leaching by meteoric water and the dissolution of remaining feldspars and calcite cement. Relatively high-quality reservoirs are preferentially developed in distributary channel and mouth-bar sandstones with chlorite rims on detrital quartz grains, which are also the locations of aqueous fluid flow that produced secondary porosity. The fold-related fractures are primarily developed in the silt–sandstones of Longwangzhuang and Shuinan members in the eastern Laiyang Sag. Quartz is the most prevalent fracture filling mineral in the Laiyang sandstones, and most of the small-aperture fractures are completely sealed, whereas the large-aperture fractures in a given set may be only partially sealed. The greatest fracture density is in the silt–sandstones containing more brittle minerals such as calcite and quartz cement. The wide apertures are crucial to preservation of the fracture porosity, and the great variation in the distribution of fracture-filling cements presents an opportunity for targeting fractures that contribute to fluid flow.     

Grain size and heavy mineral distribution as related to hinterland and environmental conditions for modern beach sediments from the Gulfs of Antalya and Finike, eastern Mediterranean

Backshore sediment samples from 22 beaches along the Antalya and Finike Gulfs have been studied for their grain size, chemical and heavy mineral composition. Data presented here suggest that well- to moderately-sorted (0.41 Φ–0.92 Φ) medium sand (1 Φ–2 Φ) represents dominant mean grain size in most beaches. In contrast, some beaches from the western part of the Gulf of Antalya (Göynük, Kemer-Kiriş and Beldibi) are composed of pebble- to boulder-size grained beaches which are located close to mouths of short and steep-gradient ephemeral rivers entering the sea from the Western Taurus Mountains. The heavy mineral assemblages are dominated by detrital opaque minerals (14–58% magnetite, chromite, and hematite), pyroxene (8–65% augite), amphibole (3–15% tremolite and actinolite), epidote (3–25%), garnet (2–9% pyrope and almandine) and micas (3–20 biotite, muscovite and chlorite). The very high concentrations of heavy minerals (up to 86% of bulk sediment) together with the significant concentrations of some elements found in beach sediments from the Gulf of Finike and western Gulf of Antalya (Fe: 18.40%; Cr: 10.00%; and Ti: 1.32%) are indicative of ultramafic origin, mainly derived from the ophiolitic rocks of the Antalya–Tekirova nappe on coastal hinterland.     

The fluid regime during fracturing of the Embla field, Central Trough, North Sea

The deep Embla field, located in the Central Trough, North Sea, represents the first oil reservoir in Paleozoic rocks to be developed on the Norwegian shelf. The reservoir consists of braided fluvial and alluvial fan sandstones interlayered with floodplain/lacustrine mudstones and volcanics and intrusives. Extensive fracturing of the reservoir has led to the formation of numerous mineralised veins. Three main types of mineralised fractures can be identified: (1) early diagenetic veins and veins which occur in and around mafic igneous rocks; (2) carbonate-dominated veins; (3) barite, clay minerals and bitumen veins. This article presents fluid inclusion evidence from fracture-filling minerals, suggesting that the fractures were important fluid conduits of both petroleum and brine migration. The petroleum inclusion data are consistent with an undersaturated oil composition. A range in salinity between 23 and 12 wt % NaCl_eq is found for the aqueous inclusions. The variation in salinity indicates mixing between a high saline fluid, related to evaporites, and a fluid with lower salinity. Microthermometry data suggest that the fracturing events occurred at deep basinal levels, at temperatures in excess of 100°C.     

海沧邻近海域表层沉积物中重矿物研究

对厦门海沧邻近海域表层沉积物中的重矿物(0．063～0．125mm粒级)进行了分析和研究，结果表明该粒级的重矿物共计49种，其优势和特征矿物为磁铁矿、赤铁矿、褐铁矿、绿帘石、铁铁矿、角闪石、锆石、红柱石等；重矿物的平均质量分数为9．56％；根据重矿物的分布和含量，并结合主要标志矿物的颗粒百分含量和分布特征，将该海域划分为5个矿物组合区，根据各区的矿物组合类型分析了该海域的物质来源及影响重矿物分布和组合的因素，进而探讨了九龙江河口湾和厦门西港海湾的沉积环境。     

MINERALOGY OF COASTAL DEPOSITS OF NORTH-WESTERN SEA OF JAPAN

Distribution of heavy, light and clay minerals in Late Pleistocene—Holocene deposits from different coastal environments (beaches, lagoons, dunes, relict lakes, ria bays and inlets, open inlets) was analysed. It was established that mineralogical composition of coastal deposits was a result of provenance and its hypergenous changes, transformation of material within transit zone, and accumulative conditions of inshore zone. Contents of stable minerals increase in deposits of the inlets confined to mouths of the small streams and in horizons of the sections, formed during regressive phases. Unstable minerals amount is higher in deposits of inlets, confined to mouths of the large river. The clay mineral fraction of shelf sediments consists mostly of illite. Authigenous pyrites dominate in deposits of ria bays, lagoons and relict lakes, formed during transgressive phases. Volcanic glass, found in deposits, is product of Holocene eruptions of Baegdusan (Baitushen) Volcano.     

沉积矿物学在陆缘海环境分析中的应用

沉积矿物学是进行环境分析的重要手段之一，对矿物在表生环境下的物理、化学行为的研究是正确理解和获取一些重要的替代性环境指标的基础，它可为认识近代地质过程、地表气候过程和海洋环境过程提供定性和定量依据。20世纪90年代以来，海洋矿物学注重于以沉积矿物为指示，研究气候、物质来源、扩散路径和运移方向以及沉积环境等相关内容，并与地球化学相结合，解释区域性环境变化，乃至全球性环境演变等问题，取得了重要进展。对我国这一领域的研究现状作一综述，提出了5项环境示踪的沉积矿物学指标，即：用矿物组合、重矿物含量、磁铁矿、角闪石、长石等矿物示踪物源和物流；用矿物组合、高岭石、伊利石、方解石等指示古气候；用重矿物含量、石英特征等反映水动力条件；用海绿石、自生黄铁矿、铁锰氧化物等揭示氧化－还原环境；用火山玻璃、玄武闪石、蒙脱石等示踪火山和热液活动。但应用沉积矿物学示踪环境，必须运用多种指标进行综合分析。     

单颗粒碎屑矿物在海洋沉积物物源分析中的应用*

单颗粒碎屑矿物可减小源区岩石类型、蚀变过程和程度及搬运与沉积过程对物源信息释读的干扰, 已逐渐成为海洋沉积物物源分析的有力工具, 并取得一定的应用成果。目前, 锆石、石榴石、长石、辉石、角闪石、独居石及磁铁矿等均已被成功用于海洋沉积物物源研究, 并主要利用单矿物主量元素、年代学等方法精确识别物源区地质特征和位置, 但单矿物微量元素、同位素及微区结构及多矿物对比研究的应用尚有不足; 因此, 目前对物源信息的释读难免片面, 物源识别方法和技术也仍未成熟。随着方法的发展和完善, 将可开展诸多深入研究, 如通过锆石、独居石、云母和磷灰石等不同矿物的年代学研究, 示踪研究物源区的时空变化; 通过建立多矿物定量研究模型, 进而定量研究源区蚀变速率和源汇过程中的物质输运通量和过程等。文章总结单颗粒碎屑矿物在物源识别中的应用现状, 并展望其应用前景, 以期引起同行对此研究方法的关注, 进一步促进该方法在海洋沉积物物源分析中的应用和发展。     

琉球群岛以东海区沉积物重矿物分布及来源

琉球群岛东部海区沉积物中富含大量火山碎屑矿物、岛屿岩石遭受风化蚀变形成的普通角闪石以及水生的铁锰微结核,其重矿物种类、特征、组合分区等与火山作用、沉积环境、地形、物质来源等内外生因素密切相关。通过对本区重矿物的种类、特征及组合分区的研究,初步判断位于研究区北部、菲律宾板块向欧亚大陆俯冲而导致的正在活动的的琉球岛弧区为火山碎屑的主要源区,重矿物成分主要为水携成因来源,受同期火山作用控制;少量紫苏辉石来自先期形成的海岭或海底高原(如冲大东海岭、奄美海岭及九州海岭等)上的火山岩系,是经过剥蚀、搬运再沉积的产物;琉球群岛、九州等火山活动产物受海底高地等阻隔而在本区表现为向南或东南影响力逐渐减小;本区地质历史上的及正在进行的岩浆活动主要以基性及中性岩浆为主。此外,流经本区的黑潮对自生铁锰微结核的富集具有重要影响。     

Radioelement distribution in river,beach, and offshore areas and their significance to Chavara placer deposit,Southern Kerala Coast of India

The radioelement and heavy mineral distribution in river, beach and innershelf areas of the southern Kerala coast is related to placer mineral concentration on the beaches at Chavara. Southern Kerala rivers—Neyyar, Karamana and Vamanapuram—transport higher amounts of radioactive elements than the larger Kallada River due to higher radioactive minerals in the hinterland rocks. Coastal configurations and the seasonal longshore current pattern seems to control along-shore distribution of minerals. The proposed model for placer concentration suggests that the energy difference and seasonal current direction along this coast is important.     

Reservoir characteristics and their effects on hydrocarbon accumulation in lacustrine turbidites in the Jiyang Super-depression,Bohai Bay Basin,China

A great difference exists between the hydrocarbon charging characteristics of different Tertiary lacustrine turbidites in the Jiyang Super-depression of the Bohai Bay Basin, east China. Based on wireline log data, core observation and thin-section analyses, this study presents detailed reservoir property data and their controlling effects from several case studies and discusses the geological factors that govern the hydrocarbon accumulation in turbidite reservoirs. The lacustrine fluxoturbidite bodies investigated are typically distributed in an area of 0.5–10 km², with a thickness of 5–20 m. The sandstones of the Tertiary turbidites in the Jiyang Super-depression have been strongly altered diagenetically by mechanical compaction, cementation and mineral dissolution. The effect of compaction caused the porosity to decrease drastically with the burial depths, especially during the early diagenesis when the porosity was reduced by over 15%. The effect of cementation and mineral dissolution during the late-stage diagenesis is dominated by carbonate cementation in sandstones. High carbonate cement content is usually associated with low porosity and permeability. Carbonate dissolution (secondary porosity zone) and primary calcite dissolution is believed to be related to thermal maturation of organic matter and clay mineral reactions in the surrounding shales and mudstone. Two stages of carbonate cementation were identified: the precipitation from pore-water during sedimentation and secondary precipitation in sandstones from the organic acid-dissolved carbonate minerals from source rocks. Petrophysical properties have controlled hydrocarbon accumulation in turbidite sandstones: high porosity and permeability sandstones have high oil saturation and are excellent producing reservoirs. It is also noticed that interstitial matter content affects the oil-bearing property to some degree. There are three essential elements for high oil-bearing turbidite reservoirs: excellent pore types, low carbonate cement (<5%) and good petrophysical properties with average porosity >15% and average permeability >10 mD.