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1.
In order to obtain new sedimentological data for a better understanding of the palaeo geological assembly of the various sedimentary and tectonic complexes of the Northern Apennines, the authors have re-examined and re-analysed the petrography of the main Tertiary graywacke and sandstone sequences of this mountain range. Several hundred thin sections and heavy-mineral preparations have been studied qualitatively and quantitatively. Generally, for all investigated graywackes and sandstones a source area with a more or less uniform petrographic organization can be assumed, since all different components, though in variable distributions, occur in all the studied sequences. Differences in the abundance of the components in the individual graywackes and sandstones are attributable to influences of the source area itself. The distribution of quartz-poor or quartz-free volcanic rocks, quartz—epidote—zoisite schists, and carbonatic cement in the samples and epidote and zoisite in the heavy-mineral preparations indicate, however, a certain palaeogeological succession of the original areas of deposition from the internal to the external parts of the mountain range. 相似文献
2.
The areal distribution of stream sediment and source-rock heavy mineralogy was studied to determine the mineralogical relations between source and derived sediment in the Piney Creek drainage basin of Wyoming. Heavy-mineral distribution in the streams was characterized using factor analysis. The results of analyses show that for an actively degrading stream system, the heavy-mineral composition of stream sediment is controlled to a considerable extent by the composition of local sediment sources and by continuous addition of detritus from bank cutting. Only the most common minerals from upstream sources persist as statistically significant variables downstream. In some cases the heavy-mineral mineral composition of stream sediment can be controlled by comparatively few, or volumetrically rare source rocks, even though more abundant source rocks supply a wide range of heavy minerals. Specific drainage configurations such as lakes and proximity of streams to major sediment sources significantly modify sediment mineralogy immediately downstream. 相似文献
3.
Analysis of heavy-mineral distribution in modern sediments of Willapa Bay, Washington, indicates a dominance of two mineralogic assemblages, one with approximately equivalent amounts of hornblende, orthopyroxene and clinopyroxene, the other dominated by clinopyroxene. The hornblende-orthopyroxene-clinopyroxene suite is derived from the Columbia River, which discharges into the ocean a short distance south of the bay. The clinopyroxene suite is restricted in modern sediments to sands in rivers flowing into the bay from the east. The heavy-mineral distributions suggest that sand discharged from the Columbia River, borne north by longshore transport, and carried into the bay by tidal currents accounts for most of the sand within the interior of Willapa Bay.Three heavy-mineral assemblages are present in the surrounding Pleistocene deposits; two of these are identical to the modern assemblages described above. These heavy-mineral assemblages reflect the relative influence of tidal and fluvial processes on the Late Pleistocene deposits; their relative influences are consistent with those inferred on the basis of sedimentary structures and stratigraphic relations in about two-thirds of the samples examined. The anomalies can be explained by recycling of sand from older deposits. The persistence of the two heavy-mineral assemblages suggests that the pattern of estuarine sedimentation in Late Pleistocene deposits closely resembled that of the modern bay.The third heavy-mineral suite, dominated by epidote, occurs in a few older Pleistocene units. On the north side of the bay, the association of this suite with southwest-directed foresets in crossbedded gravel indicates derivation from the northeast, perhaps from an area of glacial outwash. The presence of this suite in ancient estuarine sands exposed on the east side of the bay suggests that input from this northerly source may have intermittently dominated bay deposition in the past. 相似文献
4.
Henrik Friis 《Sedimentary Geology》1974,12(3):199-213
Exemplified by young Tertiary sandy sediments from Denmark, general aspects of the study of heavy-minerals are discussed. It is demonstrated that three different heavy-mineral associations of the sediments have originated from one single association by successive chemical weathering of amphibole and epidote. Physical processes active during deposition may influence the composition within associations, but differences of this origin are shown to be insufficient to explain the differences between the associations. It has not been possible to demonstrate major influence on the heavy-mineral associations from differences in the composition within the source area, which is assumed to be part of the Scandinavian Shield. 相似文献
5.
The results described relate to an investigation into the nature of Au dispersion in glacial till, undertaken to identify optimum search techniques for use in exploration for Au mineralization.The diversity of Au mineralization, in terms of the host rock lithologies, mineralogy and grain size of the Au, would be expected to give rise to differences in the secondary response in the associated overburden. Common exploration procedures involve the analyses of the heavy-mineral fraction or a particular size fraction of the tills. However, having regard to the expected variable response of Au in associated glacial till, attributed to variations in primary mineralization, effective exploration requires that the methodology employed is capable of locating all types of Au mineralization.Bulk till samples were collected from various sites associated with the Owl Creek deposit near Timmins and the Hemlo deposits. Grain size analyses were carried out on the till samples and on the heavy-mineral concentrates. The concentration of the Au in the various fractions was determined by Instrumental Neutron Activation Analysis.Preliminary results allow a number of provisional conclusions to be drawn:
- 1. (1) Grain size analysis of the −2 mm fraction of tills indicates that the silt and clay fraction constitutes 20–50%, whereas, in contrast, the equivalent heavy-mineral concentrates are dominantly composed of the coarser −500 + 63 μm material.
- 2. (2) The amount of Au present in the heavy-mineral concentrates of tills represents only a minor proportion of the total Au in the original till samples. In addition, the proportion of the total Au recovered in the heavy-mineral concentrate varies from 4 to 15%. Both factors indicate that caution is necessary in interpreting the significance of heavy-mineral Au data.
- 3. (3) Examination of the size distribution of Au within the heavy-mineral concentrate indicates that the majority of the Au is contained in the −125 μm fraction.
- 4. (4) The concentration factor (the original sample weight divided by the heavy-mineral concentrate weight) varies up to 7-fold between samples due presumably to the differing proportions of heavy minerals. Hence, in Au deposits of equivalent economic significance this gives rise to varying Au concentrations in heavy-mineral concentrates according to the quantity of heavy minerals present. Significant interpretation can only be achieved by re-expressing the Au contents of heavy-mineral concentrates in terms of the absolute amount of Au in heavy-mineral concentrates.
- 5. (5) A comparison of the heavy-mineral concentrates produced by different laboratories indicates marked differences in the weight of the heavy-mineral concentrate, the Au concentration of the heavy-mineral concentrate, the total weight of Au in the heavy-mineral concentrate and the size distribution of the Au in the heavy-mineral concentrate.
- 6. (6) Analysis of the −63 μm silt and clay size fraction indicates anomalous Au contents within this fraction of the tills collected from Owl Creek and Hemlo, extending over 500 m down-ice from mineralization at Hemlo.
- 7. (7) Analysis of the −63 μm silt and clay size fraction is suitable for the detection of fine-grained Au deposits that are not amenable to detection on the basis of heavy-mineral concentrate analyses.
- 8. (8) The analysis of the silt and clay fraction reduces the sample representativity problems associated with analyzing coarser fractions.
- 9. (9) A comparison of the Au distribution in heavy-mineral concentrates and the −63 μm fraction of till down-ice from the Owl Creek deposit indicates broadly similar dispersion patterns.
6.
广西宁明组植物化石中黄铁矿及其沉积意义 总被引：1，自引：1，他引：0
对化石中的黄铁矿进行研究,有助于明确生物的化石化过程以及期间的沉积微环境。利用光学显微镜和扫描电镜,对广西宁明组植物化石中保存的黄铁矿进行了分析,发现离散型单晶和成群的莓状体共同保存。单晶绝大多数为无规则至球状体,晶棱不明显,表面可见凹点;少数为八面体,晶棱明显,表面光滑;单晶直径为0.79~1.58 μm;莓状体为圆球状,粒径为7.23~14.95 μm,S/Fe原子个数比的均值为1.54。莓状体的粒径大小和变化幅度均处于低值段,其S/Fe原子个数比值小于2,结果均说明当时植物体上、下表皮间为一种贫氧的水体环境,并在短时间内形成了莓状体。植物化石上、下表皮间由于未保存组织结构,而被大量的、近似层状分布的黄铁矿单晶和莓状体充填,结果支持了化石内莓状体形成与有机质降解之间存在着必然联系。 相似文献
7.
黄河公伯峡古风化花岗岩石英表面结构的工程地质研究 总被引：1，自引：0，他引：1
本文对黄河公伯峡电站古风化花岗岩中的石英表面结构进行了扫描电镜观察。其特征表明是在典型的高能化学环境下形成的,这与现代风化花岗岩石英表表面结构特征明显不同,为鉴定古风化花岗岩提供了依据。 相似文献
8.
MARTIN RAPPOL HENK M. P. STOLTENBERG 《Boreas: An International Journal of Quaternary Research》1985,14(1):33-50
Variations in composition between and within Saalian till types of The Netherlands are demonstrated with reference to grain-size distribution, fine-gravel petrography and heavy-mineral composition. Several factors explain different aspects of the compositional variations. Firstly, a compositional layering results from differences in the amount of local material that has been assimilated in successive till hands. Secondly, a petrographic stratification is present in the erratic components, which is most strikingly expressed by the occurrence of flint-poor till overlying till rich in flints. This feature is interpreted to have been inherited from an englacial debris stratification which is related to the distribution of source rock types in the up-glacier area. Finally, a predominantly lateral variation in till composition is present, reflected best in the assemblages of the indicator pebbles, resulting from deposition by ice streams of different source and direction of flow. 相似文献
9.
《International Geology Review》2012,54(1):65-72
Chert-plus-pyrite pebbles have been known for some time in a number of Witwatersrand conglomerates, but their distribution is highly variable. A wide variety of textures in chert-plus pyrite pebbles are documented here, and these textures place constraints on the origin of such pebbles. Replacement of chert pebbles by pyrite is indicated (pyrite grains and aggregates continue across many pebble boundaries), and both distributional and textural evidence favors a post-burial timing for this process. Significant mobility of sulfur after burial is indicated. Whether this replacement was diagenetic or metamorphic is not certain. 相似文献
10.
《International Geology Review》2012,54(12):1086-1097
Nineteen samples of mélange matrix and volcanogenic sandstone matrix were collected from the Maitai (including the Hawtel), Caples, and Torlesse terranes, South Island, and southernmost North Island, New Zealand, in an attempt to identify contrasting provenances for these lithostratigraphic units. Heavy minerals were concentrated employing water settling columns followed by high-speed centrifugation utilizing bromoform and methyl iodide. Semiquantitative scanning-electron-microscope and quantitative-microprobe investigations of heavy-mineral concentrates support conclusions of previous workers. (1) The Torlesse Complex is a richly quartzofeldspathic, at least partially multicycle, unit derived from an evolved, well-dissected continental margin or mature island arc. It contains a diverse suite of igneous, metamorphic, and sedimentary detritus including widespread traces of clastic zircon, rutile, biotite, barite, almandine, clinopyroxene, Ca-amphibole, staurolite, chromite, and epidote. (2) Mélanges belonging to the Maitai and Caples terranes possess heavy-mineral suites suggestive of somewhat more restricted, first-cycle volcanogenic arc-like provenances, being richer in unstable rock fragments, aluminosilicates, grossular-andradite garnets, and chlorites as well as amphiboles and pyroxenes. Neoblastic hydrous, calcic aluminosilicates and layer silicates suggest that the Hawtel mélange recrystallized at lithostatic pressures of less than 3 kbar, whereas the other investigated terranes were metamorphosed at slightly higher pressures. 相似文献
11.
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. 相似文献
12.
粤北金鸡岭丹霞群砂岩矿物表面结构初步研究 总被引：2，自引：0，他引：2
本文对丹霞群砂岩中的石英、长石、电气石、锆石４种碎屑矿物的表面结构特征作了初步研究，并与现代河流和海岸砂质沉积物中的同类矿物的表面结构特征进行类比。文章指出，由于成岩作用的影响，古代砂岩中的碎屑矿物比现代砂的同类矿物具有更为复杂的表面结构，原因在于成岩环境下，溶解、溶蚀和压溶作用对古代砂岩的矿物表面有更深刻的改造。 相似文献
13.
EL&#;BIETA MYCIELSKA-DOWGIA&#;&#; 《Boreas: An International Journal of Quaternary Research》1993,22(2):165-170
A set of textural features is proposed as a measure of the degree of transformation of alluvial source deposits into aeolian ones. Analysis of grain-size distribution, quartz-grain rounding and frosting. heavy-mineral and overall mineral composition and micromorphology of quartz-grain surfaces in dune and source deposits in Poland. Belgium and Sweden, enabled a variable degree of sediment transformation to be distinguished. The degree of transformation is termed degree of aeolization. It is shown to be dependent upon the total duration of aeolian episodes. The degree of aeolization of the dune deposits investigated is highest in Poland, intermediate in Belgium and lowest in Sweden. 相似文献
14.
淮北煤田南部新生界底部松散沉积物沉积特征及古地理意义 总被引：1，自引：0，他引：1
通过对淮北煤田市部新生界底部松散沉积的沉积特征研究，初步得出结论，位于同一煤田的宿县矿区和临涣矿区的沉积物结构和矿物成份特征差别较大，导致这一差别的主要原因是物源区与岩性的不同，以及古地理条件的差别．在临涣矿区，以石英、长石和少量碳酸盐矿物组合以及以锆石、电气石为主的重矿物组合，反映了来自于矿区北部的中性闪长岩岩体的风化。而以含大量灰岩砾石，和以石英、燧石为辅的碎屑组成则说明了宿县矿区东部、北部奥陶系地层和煤系地层本身遭受了强烈风化。沉积物的复杂结构特征和矿物成份特征反映了基岩地貌南低北高，源区遭受的强烈物理风化作用以及在短距离内快速搬运和多源沉积特征。 相似文献
15.
Joel C. Le Baron Stefan W. Grab Kathleen Kuman 《Journal of African Earth Sciences》2011,59(4-5):384-394
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. 相似文献
16.
17.
The U.S. Geological Survey has conducted geochemical studies in the Indian Pass (CDCA-355), 124 km2, and Picacho Peak (CDCA-355A), 23 km2, Wilderness Study Areas (WSA's) as part of a program to evaluate the mineral resource potential of designated areas in the California Desert Conservation Area. These two WSA's are of particular interest because they lie within a region which has intermittently produced significant quantities of Au since the mid-1800's, and is currently the site of much exploration activity for additional Au resources. Within a 15-km radius of the WSA's, there is one actively producing gold mine, a major deposit which began production in 1986, and one recently announced discovery. In the reconnaissance geochemical surveys of the two WSA's - 177 μm (-80 mesh) stream sediments, heavy-mineral concentrates from stream sediments, and rocks were prepared and analyzed.Four areas of possible exploration interest were identified within the WSA's. The first area is characterized by anomalous W and Bi in nonmagnetic heavy-mineral concentrates, and is underlain primarily by the Mesozoic Orocopia Schist which has been intruded by monzogranite of Oligocene age. Alteration and mineralization appear to be localized near the intrusive contact. The mineralized rock at the surface contains secondary Cu and Fe minerals where the monzogranite intrudes the metabasite horizons of the Orocopia Schist and scheelite where the monzogranite intrudes marble within the Orocopia Schist.The second area is characterized by anomalous As, Sb, Ba, B, and Sr in nonmagnetic heavy-mineral concentrates and by anomalous As in - 177 μm stream sediments. Geologically, this area is underlain by metasedimentary and metavolcanic rocks of Jurassic(?) age; a biotite monzogranite of Jurassic(?) age; and Tertiary volcanic and hypabyssal rocks composed of flows, domes, and tuffs of intermediate to silicic composition. All these rock types are cut by a set of north-south-striking normal faults. The anomalies in the heavy-mineral concentrates are believed to be related to silica-clay alteration observed in the vicinity of some of these faults. 相似文献
18.
渤海海域沙一、二时期混合沉积分布广泛,而在沙三段发现较少,其沉积特征及控制因素尚不明确.以莱南斜坡带沙三下亚段为例,通过壁心、薄片、钻测井、三维地震等多种资料,对研究区混合沉积特征开展综合研究,预测混合沉积平面及垂向的分布,并探讨混合沉积发育的主控因素.研究表明,莱南斜坡带沙三下亚段发育湖相与火山喷发伴生的混合沉积,在垂向发育组分式混合和互层式混合的2类混积样式;发育混积相、辫状河三角洲、火山碎屑岩相等3类沉积相类型,其中,早期陆源碎屑影响较大,发育远岸混积泥晶滩;晚期陆源碎屑影响较弱,但波浪作用增强,发育近岸和远岸共生的混积碎屑滩.温暖湿热的古气候、相对闭塞的浅水环境、同期火山形成的营养物质为混合沉积发育提供了良好条件;西部远物源和东部近物源供给控制了混合沉积发育类型;水下古隆起控制其平面分布位置及富集程度;局部火山活动形成了特殊的混合沉积岩性及其组合.该成果不仅完善和深化了渤海海域混合沉积新认识,对在沙三段寻找类似的混合沉积提供指导,也可为研究区优质动用储量及开发井网部署研究提供参考. 相似文献
19.
Ancient microbialites reflect interactions between microbial communities and environmental conditions. However, evaluating the relative roles of microbial community processes and environmental influences on microbialite morphology and internal fabric in the rock record can be challenging. The Neoproterozoic Beck Spring Dolomite preserves diverse microbialites, and thus provides an opportunity to explore the factors that influenced microbialite development locally. Stromatolitic, thrombolitic and composite microbialites are abundant in subtidal to upper intertidal carbonates in the Beck Spring Dolomite. Thrombolitic and composite microbialites have not been recognized previously in this unit, but compose much of the newly defined thrombolitic member. Stratigraphic relationships demonstrate that these three types of microbialites formed in close spatial and temporal association in subtidal to intertidal environments. The relative proportions and distributions of stromatolitic and thrombolitic microbialites vary with depositional environment; stromatolitic microbialites dominate in deeper intertidal to subtidal facies, whereas thrombolitic textures are more abundant in upper intertidal facies. Composite microbialites, composed of intermingled clotted and laminated textures, formed in all environments but are most abundant in intertidal facies. The broad environmental distribution of stromatolitic, thrombolitic and composite microbialites and the intermingling of textures suggest that laminated and clotted textures reflect diverse microbial community morphologies rather than environmental variations. Furthermore, the ca 750 Ma age of thrombolitic microbialites in the Beck Spring Dolomite requires that they formed without the influence of calcimicrobes or metazoans colonizing and grazing the microbial mat surface. Thus, these thrombolites provide further evidence that the biostratigraphic distribution of thrombolites cannot be uniquely attributed to evolution of calcifying and grazing organisms in the earliest Cambrian, and that older microbial communities were capable of producing clotted textures. 相似文献
20.
Michelle S. Trommelen Martin Ross 《Boreas: An International Journal of Quaternary Research》2014,43(3):557-576
The distribution of basal drag zones (sticky spots) underneath palaeo‐ice streams or lobes is largely unknown. We investigated the centre of the large (300 km long and up to 400 km wide) deglacial Hayes Lobe in NE Manitoba, Canada, by focusing on surficial till and its composition to get insights into dispersal patterns and their potential relationships to areas of basal drag. Subglacial bed roughness is a good criterion to identify areas of basal drag, but till composition may provide important insights across smoother beds. The onset zone of the Hayes Lobe overlies Palaeozoic Carbonate Platform rocks, whereas the majority of the lobe overlies the low‐lying Canadian Shield. We show that, within a 3500‐km2 central area of this lobe, calcareous detritus within the till has been transported over 100 km within subglacial environments of reduced ice‐bed coupling and fast ice flow. Six per cent of samples (n = 782), however, outline 0.2 to 4 km wide spots with a dominantly local composition. The glacial history and composition indicate that the till within these spots contains high inheritance from a pre‐Late Wisconsinan ice‐flow phase, which we suggest was protected beneath sticky spots (low erosion, high strength) during transport of substantial calcareous detritus to the area. Furthermore, our findings show that local till spots are present within streamlined landforms, as well as till blankets or veneers over bedrock. This diverse geomorphology indicates that the process of drumlinization within the deglacial Hayes Lobe does not appear to have been responsible for significant sediment transport or deposition across the study area. The overall record thus indicates potentially complex spatiotemporal shifts between calcareous till deposition, sticky conditions, erosion and drumlinization – which supports the subglacial bed mosaic model. 相似文献