Origin and depositional environment of the china clay deposits of south Kerala

Results of petrographic, mineralogic and granulometric studies of the sedimentary china clay deposits of Trivandrum district in south Kerala are discussed in terms of their origin and depositional environment. While mineralogic data indicate a khondalitic source for the kaolins as against the hitherto postulated leptynitic source, petrographic evidences suggest that most of the kaolinite were transported from the weathering crust and deposited. Granulometric data and SEM scanning of sand grains from the clays indicate their deposition in a fluvial/low energy littoral environment under conditions of subaqueous agitation.     

广西巴马县水晶宫洞穴沉积物特征及其沉积环境

巴马县水晶宫洞内次生化学沉积物景观丰富,类型多样,有石钟乳、石幔、石瀑布、石笋、石柱、石盾等特色景观;尤其是近期仍在发育的洞顶鹅管、卷曲石、石花等是国内外较为罕见的洞穴奇景。据沉积物的沉积类型、物质成分、沉积序次及测年等资料研究表明,水晶宫洞穴沉积物形成于晚第三纪以来。晚第三纪和第四纪早更新世早期,洞内沉积主要为外源水携带的硅质岩、砂岩类砾石沉积形成的钙华砾石层。早更新世中期—中更新世气候温暖湿润,是水晶宫洞穴主要景观的形成期,沉积物景观宏大而壮观,230Th-U系测年得出其分别形成于100～35万年前。晚更新世早期12.5～9万年的末次间冰期主要为温暖气候环境,洞内仅有少量的石笋沉积,且极少保存;9万年后气候环境发生突变,更不利沉积物发育和保存;自4万年后气候环境开始表现为温暖湿润,化学沉积活跃,洞穴沉积物主要由高约50～150 cm的纯白色石笋群和钟乳石组成,为洞穴奇景的形成期,230Th-U系测年得出其分别形成于40 ka BP和7 500 a BP以及1 450 a BP。晚更新世晚期以来形成的洞穴沉积物景观,不仅为水晶宫提供了丰富的旅游资源和价值,同时也为广西重建古气候环境提供了重要的信息载体。      

柴达木盆地别勒滩杂卤石矿床特征及其沉积环境研究

别勒滩是青海察尔汗盐湖固体钾矿的主要分布区段,也是企业固转液开采和生产钾盐的主要矿区,该区段分布着大面积的杂卤石矿(K₂Ca₂Mg[SO₄]₄2H₂O)。文章利用2022年察尔汗盐湖储量核查项目获得的岩芯样品和钻孔资料,通过系统的分析测试,开展别勒滩杂卤石成矿特征及沉积环境研究。文章首次查明别勒滩区段杂卤石矿床分布面积超过150 km²,平均厚度0.8 m,w(K₂SO₄)平均大于5%,计算获得K₂SO₄资源量2089.79×10⁴t。研究认为,别勒滩杂卤石形成于钾石盐、光卤石析出阶段的高浓缩盐湖相沉积环境,周期性淡化带入的大量Ca²⁺和SO₄^2-与卤水中含量较高的K⁺、Mg²⁺离子反应形成了杂卤石矿层。别勒滩杂卤石矿层具有较好渗透性和给水...     

Isometamorphic variations in the reflectance and fluorescence of vitrinite—a key to depositional environment

Petrographic investigations of serial ply samples from five high- to medium-volatile bituminous coal seams from Australia (4) and Canada (1) reveal substantial in-seam variations in the reflectance and monochromatic microfluorescence intensities of the maceral subgroup telovitrinite. The variations consist of one case of reflectance enhancement and fluorescence suppression, and four cases of reflectance suppression and fluorescence enhancement. The single case of reflectance enhancement and fluorescence suppression is due to the oxidation of the vitrinite nuclei at the sequence boundary between the Bayswater and Upper Wynn seams in New South Wales. The four cases of reflectance suppression and fluorescence enhancement result from the syn- and epigenetic absorption by the vitrinite nuclei of hydrogen donated by, presumably, anaerobic bacteria-generated lipids. Two of the coals are marine-influenced: the Liskeard Seam from the Bowen Basin by combined syngenetic and epigenetic effects, and the Greta Seam from the Sydney Basin mainly by epigenetic contact with sea water. For both coals, the results are strong vitrinite reflectance suppression and fluorescence enhancement. The remaining two coals, the Bulli Seam from the Sydney Basin and a coal seam from the Gates Formation in British Columbia, show moderate epigenetic effects on the optical properties of telovitrinite by fresh-water. In the Bulli Seam which was studied in two adjacent localities, the reflectance suppression and fluorescence enhancement of telovitrinite are stronger under sandstone roof than under shale roof. In some cases, the epigenetic effects are superimposed on syngenetic telovitrinite reflectance and fluorescence variations resulting from the cogeneration and mixing of different telovitrinite precursors, for example, autochthonous roots and hypautochthonous or allochthonous shoots. A measure of the degree of dispersal and mixing is the coefficient of variation of telovitrinite reflectance and/or fluorescence. This coefficient correlates well with detrital minerals and dispersed macerals, e.g., inertodetrinite and, to a lesser extent, sporinite. Some comments are made on slitted so-called pseudovitrinite which is regarded as a telovitrinite that was subjected to very weak post-coalification desiccation and possibly oxidation without losing much of its thermoplastic properties.     

Iron–phosphorus relationship in the iron and phosphorite ores of Egypt

Iron and phosphorite ores are very common in the geological record of Egypt and exploitable for economic purposes. In some cases these deposits belong together to the same geographic and geologic setting. The most common deposits include phosphorites, glauconites, and iron ores. Phosphorites are widely distributed as a belt in the central and southern part of Egypt. Sedimentary iron ores include oolitic ironstone of Aswan area and karstified iron ore of Bahria Oasis. Glauconites occur in the Western Desert associated with phosphorites and iron ores. As these ores are exploitable and phosphorus in iron ores and iron in phosphorites are considered as gangue elements, the iron–phosphorus relationship is examined in these deposits to clarify their modes of occurrences and genetic relationship based on previously published results.Phosphorus occurs mainly as carbonate fluorapatite (francolite). Iron, on the other hand, occurs in different mineralogical forms such as glauconites, hematite, limonite and goethite.In P-rich rocks (phosphorites) no relationship is observed between iron and phosphorus, which in turn indicates that the FeP model is unlikely to interpret the origin of the late Cretaceous phosphorites and the association of phosphorites and glauconites in Egypt. In Fe-rich rocks (iron ores and glauconites) also no relationship between iron and phosphorus is observed. The present work, therefore, does not support the hypothesis that there is a genetic relationship between phosphorus and iron in sedimentary rocks.     

Sedimentation, depositional environment and diagenesis of Eocene biosiliceous deposits in Gafsa basin (southern Tunisia)

The sedimentary rocks of the Metlaoui Formation in the Gafsa basin (southern Tunisia), which may be grouped in three units: the basal (Thèlja), middle (Chouabine) and upper unit (Kef Eddour), provide a record of preserved sedimentary, authigenic and biological processes. This paper presents the findings of sedimentological investigations of the biosiliceous deposits of the middle unit. This unit contains either well-preserved (Opal-A) or diagenetically altered (Opal-CT, clinoptilolite, quartz and even clays) diatom frustules. Such diagenetic changes are commonly described in marine and lacustrine biosiliceous deposits. The fossil content of theses diatomaceous layers implies shallow-marine conditions.The opal-rich sediments, and the associated facies record the transgressive transitions associated with high organic productivity, probably enhanced by seasonal input of nutrients, and high sea level stands, and a close association with stratified water column conditions. The formation of bedded diatomaceous sediments is known to require either high organic productivity or anoxic conditions in bottom/intermediate water, and eventually both processes. The initial organic content of the biogenic deposits was impoverished in early stages of sedimentation and diagenesis. A large part of the organic matter could have been destroyed during early diagenetic processes and from further oxidation in outcrops.     

Iron isotope constraints on the metal source and depositional environment of the Neoproterozoic banded iron- and manganese deposits in Urucum,Brazil

The Urucum area of Brazil hosts a series of Cryogenian ironstones intercalated by oxide-dominated manganese layers. The Urucum iron and manganese formations (IF-MnF) are among the largest sedimentary iron and associated manganese deposits of the Neoproterozoic, however, the depositional model and the source of metals for the IF-MnF in this area are highly controversial. In this study, we performed systematic Fe isotope analysis on fresh and geochemically characterized drill core samples of the Urucum iron and manganese formation deposited in the center of the ancient Urucum graben system. The samples have a large variation in Fe isotope composition, with a δ⁵⁶Fe range of −2.04‰ to +0.75‰, and exhibit a general trend of decreasing δ⁵⁶Fe values with increasing manganese contents. The low δ⁵⁶Fe values of the IF and MnF samples reflect Rayleigh fractionation processes of contineous partial oxidation of aqueous Fe(II) prior to deposition at the sampling site. Using a mixing model and previously published Nd isotope data on the same samples, we estimated that benthic (i.e., porewaters released from submarine sediments in the Urucum basin) Fe fluxes provided 7–50% of total Fe in the Urucum IF-MnF, and the rest of Fe source was from low-temperature hydrothermal vents. Based on combined Fe and Nd isotope data of the Urucum IF-MnF, we propose that low-temperature hydrothermal fluids and benthic fluxes of pore waters were mixed and transported by an upwelling current. The fluid subsequently experienced partial oxidation during the transportation process and became enriched in light Fe isotopes. In the Urucum graben basin, the iron- and manganese-rich oxides deposition occurred progressively under increasingly oxidizing conditions, and such process could have operated repeatedly to produce the alternation of iron and manganese formations. The chemical sediments of the Urucum IF-MnF deposits thus reflect the existence of a sharp redox gradient in the marine environment during the late Cryogenian period.     

Paleo-Tsunami deposits on the Red Sea beach, Egypt

The characteristics of the recent tsunami deposits threw light on some sources of deposition on the beach of the Red Sea. The studied area is delineated by latitudes 25°6′ N and 25°9′ N and longitudes 34°50′ E and 34°53′ E; it covers an elongate area of about 12 km² along the Red Sea coast, North Marsa Alam City (4 km). The area is bounded by Wadi Asalay to the north and Wadi Sifayn from the south. For evaluation of the area, a lot of information allows us to interpret the conditions prevailing during deposition of the sediments especially at the coast. To achieve the target, five wells were drilled to study core samples, well logging measurements, and 69 vertical electrical sounding stations were carried out. The studied area and adjacent areas were geologically surveyed to note geological features related to Paleo-earthquakes. From geological and geophysical studies, the dominant rock types at the western portions of the studied area are sandstone, sandy clay, clay, clayey sandstone, and gravels; at the middle portion of the studied area, the rocks are hard, but the eastern side of the area, especially at the beach of the Red Sea, several cycles of depositions of coral reefs occurred with intercalations of clastic deposits such as clay, sand, sandstone, conglomerate, gravels, pebbles, and a lot of fossils and shell fragments. The rocks are characterized by heterogeneous properties and ill-sorted. The area includes large numbers of faults due to highly tectonism of the area. The results indicated that the area has lateral variation of sediments. The carbonate rocks at the beach contain clastic fragments, and carbonate blocks are included within clastic rocks. With increasing the distance from the beach to the west, the sediments are less heterogeneous. The beach of the Red Sea was subjected to Paleo-tsunami waves due to highly Paleo-seismic activity inside the Red Sea and left their signature in geological column especially at the beach. The observation of some geological features such as Paleo-liquefaction and landslides indicate that the area subjected to strong earthquakes related to rifting of the Red Sea.     

Systematic compositional variations in the Cape York iron meteorite

Concentrations of Re, Ir and Au are nearly constant within individual masses of the Cape York IIIAB iron meteorite, but differences between masses can be as large as a factor of 2, the extremes being Savik (5.1 μg/g Ir) and Agpalilik (2.7 μg/g Ir). The S concentration shows a still larger range from 13 mg/g in Agpalilik to 1.4 mg/g in Savik. A relatively large compositional hiatus between Dog and Agpalilik probably reflects inadequate sampling of the original material.Concentrations of Ir vary by ~10% and Au by ~3% between the ends of an 85-cm section from the Agpalilik mass of Cape York, but other sections through Agpalilik show smaller variations. These concentration ranges are much larger than expected from radial crystallization of a moderately large (radius 10 s of km) core. These variations in the Agpalilik mass may reflect dendritic crystallization, or they may have resulted from the process that produced the large concentration range among the Cape York masses.Large gradients in Re and Ir and small gradients in Ni and Au were also observed in samples within 2 cm of a large (100 cm³) troilite nodule. These gradients may reflect rapidly changing solid/liquid distribution coefficients during the final crystallization of S-rich liquid.The compositional trends among the various masses can either be explained by mixing of disparate end members followed by diffusive homogenization on a scale of m, or by dendritic crystallization on the ceiling of the IIIAB magma chamber. The mixing of a solid similar in composition to Savik with a liquid in equilibrium with this solid yields a good match to the observed trends, in which case Agpalilik consists of a mixture of 64% liquid and 36% solids. The bulk S content of the IIIAB core is calculated to be 14 mg/g on the basis of this model.     

Differentiating fluvio-marine depositional environments in the Nile Delta using textural and compositional components

Textural and coarse fraction compositional components are evaluated to distinguish samples from modern environments of the Nile Delta of Egypt. These environments include: river, coastal dune, accretion ridges, beach, neashore, lagoon and prodelta. In this study petrological variables (12 textural and 18 mineralogical, faunal and floral) were considered for each sample. Discrimination was achieved by using simple bar graphs of the raw data for each environment and Q-mode factor analysis. The factor analysis yielded four compositional assemblages: Factor 1 is dominated by terrigenous fine sand; factor 2 consists of biogenic mud; factor 3 contains terrigenous coarse and medium sands; and factor 4 comprises composite silty sand. Discrimination of the seven environments is generally good, with a lower resolution for beach, coastal dune and river sands.Having discriminating the examined environments using Q-mode factor analysis, a graphic model was constructed to help determine the origin of ‘unknown’ samples. As a test, this model is satisfactory in identifying and interpreting the origin of sediments of Holocene age from two additional cores recovered off the delta coast.     

济阳坳陷中生代物源方向与沉积体系

笔者利用砂岩和砾岩的百分含量,稳定矿物和不稳定矿物的含量变化特征及微量元素分布特征,分析济阳坳陷中生界物源方向。研究表明研究区中生界的主要物源来自西北侧和东南侧,内部的局部凸起仅提供部分碎屑物质。依据物源方向、岩心观察、测井及地震等资料对沉积体系进行了综合分析,研究区西北侧发育有冲积扇-辫状河-辫状河三角洲沉积体系,东南侧发育有冲积扇-曲流河(冲积平原)-三角洲沉积体系,内部主要发育有湖泊沉积体系,具有盆大、湖浅、坡缓及浅水型三角洲发育的特点。     

四川雷波矿集区磷矿沉积特征及成矿规律研究

四川雷波地区磷矿属于中国昆阳式海相沉积型磷矿,赋存于下寒武统梅树村阶麦地坪组地层中。通过野外实测剖面,重点研究其岩石学和沉积相特征,在矿集区建立了潮坪沉积体系,判断麦地坪组以潮下带沉积为主,潮间带和潮上带沉积不发育,总体表现为海侵-海退-海侵的垂向沉积组合。沉积相在矿集区呈环带状分布,磷矿层厚度与地层厚度大体呈正相关关系。磷矿床的岩相古地理类型直接影响了磷质颗粒的物理富集过程,其中潮下高能带为磷矿沉积的最有利相带,是今后勘探开发的重点区域。     

超大型金刚石矿床、磷矿床、油气田、油页岩矿床与碳质球粒陨石星子的成因联系

通过对太阳系起源的研究,笔者指出,超大型金刚石矿床、磷矿床、油气田和油页岩矿床,都与碳质球粒陨石星子有成因联系。碳质球粒陨石星子被吸积于原始地球上地幔表层,形成原始富碳区。当地壳形成后,富碳区的岩石圈没有被软流层的对流作用均匀化,并在155—250km深度范围内,碳质聚合成金刚石。随着金伯利岩和钾镁煌斑岩岩浆侵位,金刚石被带入地壳上部形成金刚石矿床。在富碳区,除金刚石矿床外,还形成了超基性岩-碱性岩-碳酸岩富磷杂岩体及超大型,大型磷灰石矿床。富磷杂岩体为超人型磷块岩矿床的形成提供了成矿物质,也为成油生物群的繁殖提供了矿物养料,从而为形成超大型油气、油页岩矿床创造了物质条件。碳质球粒陨石中的有机质在高温条件下合成油气,被封存于大陆岩石圈上地幔部分,在构造条件有利时进入储油构造,促进了超大型油气田的形成。超大型矿床的存在,是岩石圈成矿物质横向不均匀性的反映。     

New data on the stratigraphy and depositional environment for Upper Jurassic and Lower Cretaceous deposits of the Stolbovoi Island (New Siberian Islands)

The section of Mesozoic terrigenous deposits over 1200 m thick has been described, and a new geological map of the Stolbovoi Island southern half has been compiled. The inference has been made that the sedimentary sequence represents a single uniform turbidite complex, which is indivisible into lithological units and which does not show transition to shallow-marine facies either in the visible foot section or visible roof section. The complex accumulated in the foreland basin emerged on the margin of the Novosibirsk-Chukchi continental block during the Anyuian orogeny. The presence of upper Volgian deposits (Upper Jurassic) with a visible thickness of 640 m, Berriasian (Ryazanian) deposits about 100-m thick, and lower Valanginian deposits with a visible thickness of ～200 m has been established on the basis of identification of fossils represented by remains of bivalve mollusks (the genus Buchia). Finds of upper Volgian buchias in the southeastern part of the island are inconsistent with field geological observations of the sequence of deposits. Paleontological data acquired for the island southern part suggest the presence of a transverse thrust fault, along which upper Volgian rocks were thrust over lower Neocomian rocks. The possibility of another interpretation of the data has also been considered. The correlation of the Buchia Beds of the Stolbovoi Island, Nordvik Peninsula, the basin of the Anyui River, and northern California has been carried out. The inference about a close relationship between the biota of the Stolbovoi Island and the North Pacific paleobiogeographic realm has been drawn.     

Limitation of petrographic indices in depositional environmental interpretation of coal deposits

Organic petrology based petrographic indices (Tissue Preservation Index and Gelification Index) is a widely utilized tool in the study of depositional palaeoenvironment of coal. Evaluation of these petrographic indices suggests that, at present, utilize only vitrinite/huminite and inertinite macerals to interpret depositional environment of coal. Liptinite group macerals have important depositional environment implications, but liptinite macerals have not been taken into account in earlier petrographic indices (TPI and GI) formulations. This article examines the limitation of TPI and GI, and proposes improved TPI and GI indices, including the liptinite and inertinite macerals having depositional environment significance.     

Biostratigraphy and seismic data analysis to detect the sequence stratigraphic depositional environment of the Miocene succession: Gulf of Suez (Egypt)

This work comprises a study of the sequence stratigraphy, seismic-facies analysis, biostratigraphy and depositional environments of the northern part of the Gulf of Suez, Egypt, using a set of 24 3D seismic profiles, composite logs and sonic logs from ten wells. The syn-rift formations in the studied ten wells are described lithologically and interpreted based on investigating two seismic profiles. Biostratigraphically, the Miocene fossils are identified to correlate the five planktonic foraminiferal biozones in the examined boreholes (RB-A1, RB-B1, RB-B3, EE85-2 and RB-C1). The sequence stratigraphic analysis suggests that the Miocene succession can be subdivided into two major third order depositional sequences (S1 and S2) separated by the three major sequence boundaries (DSB1, DSB2 and DSB3).     

云南沉积型磷矿成矿特征与资源潜力预测

在典型矿床与区域成矿特征研究的基础上,系统总结云南沉积型磷矿的成矿地质、地球化学和岩相古地理特征,深入分析沉积型磷矿的成矿控制因素,建立了区域成矿模式。在此基础上,运用基于GIS的矿床模型综合地质信息预测方法对云南沉积型磷矿进行综合定位和定量预测,共圈定130个最小预测区,估算未查明的磷矿预测资源量121.98×108t。该成果对云南沉积型磷矿进一步的找矿工作具有重要的指导意义。     

Effect of Aspergillus niger on weathering of phosphorite rock

Weathering mechanism of phosphorite rock by Aspergillus niger has been studied. Ten strains of phosphate-solubilizing fungi were isolated from rhizosphere soils by using dilute plate method in solid inorganic phosphorus culture. According to the size of soluble phosphate circle in the medium, a strain of stronger phosphate-solubilizing fungus was acquired, which was identified as, Aspergillus niger using identification methods of morphology and ITS sequences comparison in Genbank. In liquid culture, incubation in static state, the weathering of apatite rock with the fungus by contrast method： putting apatite powder （200 mesh） in liquid culture medium of flask, inoculation fungus after autoclave （setting sterile control） for studying direct weathering process; putting dialysis bag with apatite powder （200 mesh） in liquid culture medium of flask, inoculation fungus after autoclave （setting sterile control） for studying indirect weathering process.