内蒙古西胡里吐盆地有机质特征及其与铀矿化的关系

在砂岩型铀矿床中 ,有机质与铀矿化之间有着较为密切的关系。西胡里吐盆地的有机质主要是以松柏类和蕨类等高等植物残体为母质的腐殖型有机质。通过镜质体反射率、有机质碎屑的颜色、粘土矿物X 衍射和古地温恢复等分析测试发现 ,有机质的成熟度较低 ,处于未成熟—低成熟早期阶段。有机质的类型和成熟度决定了其在热演化中产生了大量腐殖酸并保存在地层中。褐煤、腐殖酸、残余植物碎屑和地沥青等是现存有机质的主要类型。除大量产出的煤层外 ,有机质主要呈碎屑状和细分散状分布于地层之中。 70 %的岩石中有机质的丰度在 0 1 %～ 3 % ,对铀矿化的形成较为有利。铀与有机质的紧密共生以及二者之间的正相关性 ,表明了有机质在西胡里吐盆地铀矿化形成中所起的重要作用。有机质中的腐殖酸与铀矿化的关系最为密切 ,有机粘土复合体、蚀变岩屑、植物碎屑和地沥青等吸附剂对铀的吸附均与腐殖酸有关。腐殖酸吸附铀后可以将铀还原 ,还可以与铀酰离子等进行络 (鳌 )合形成铀酰腐殖酸盐 ,并最终引起铀的沉淀富集。     

Determination of elemental affinities by density fractionation of bulk coal samples from the Chongqing coal district, Southwestern China

The occurrence and distribution of major and trace elements have been investigated in two coal-bearing units in the Chonqing mining district (South China): the Late Permian and Late Triassic coals.The Late Permian coals have higher S contents than the Late Triassic coals due to the fixation of pyrite in marine-influenced coal-forming environments. The occurrence of pyrite accounts for the association of a large number of elements (Fe, S, As, Cd, Co, Cu, Mn, Mo, Ni, Pb, Sb, Se, and Zn) with sulphides, as deduced from the analysis of the density fractions. The marine influence is probably also responsible for the organic association of B. The REEs, Zr, Nb, and Hf, are enriched by a factor of 2–3 with respect to the highest levels fixed for the usual worldwide concentration ranges in coal for these elements. The content of these elements in the Late Permian coal is higher by a factor of 5–10 with respect to the Late Triassic coal. Furthermore, other elements, such as Cu, P, Th, U, V, and Y, are relatively enriched with respect to the common range values, with maximum values higher than the usual range or close to the maximum levels in coal. The content of these elements in the Late Permian coal is higher than the Late Triassic coal. These geochemical enrichments are the consequence of the occurrence, in relatively high levels, of phosphate minerals, such as apatite, xenotime, and monazite, as deduced from the study of the density fractions obtained from the bulk coal.The Late Triassic coal has a low sulphur content with a major organic affinity. The trace element contents are low when compared with worldwide ranges for coal. In this coal, the trace element distribution is governed by clay minerals, carbonate minerals, and to a lesser extent, by organic matter and sulphide minerals.Major differences found between late Permian and Triassic coals are probably related to the source rocks, given that the main source rock of the late Permian epicontinental marine basin is the Emeishan basalt formation, characterised by a high phosphate content.     

三水盆地古近系(土布)心组黑色页岩中黄铁矿的形成及其控制因素

黄铁矿是富有机质沉积的特征矿物。根据TOC/S、TOC/DOP、S/Fe关系以及S TOC Fe多重线性回归分析结果对三水盆地古近系〖HT5”,6”〗土〖KG-*3〗布〖HT5”SS〗心组红岗段黑色页岩中沉积黄铁矿的形成及其控制因素进行了分析。土布心组红岗段黑色页岩的黄铁矿有成岩黄铁矿和同生黄铁矿两种成因组分。红岗段下部（亚段A）有机碳含量普遍较低,底部水体以弱氧化条件为主,硫酸盐还原作用发生于沉积物/水界面以下,黄铁矿为成岩成因,其形成主要受有机质的限制。红岗段中上部（亚段B和C）的沉积条件变化频繁,其有机碳含量变化幅度大。富有机质（TOC>4%）岩层形成于缺氧的底部水体条件下。水体中可含H2S,碎屑铁矿物在埋藏之前即与之在水体中反应形成同生黄铁矿。这一过程不受有机质的限制,而是受活性铁与H2S接触时间的限制。同时,由于大量淡水输入导致硫酸盐浓度的降低,从而对硫化物形成有一定的限制作用。对于低有机质（TOC<4%）样品,黄铁矿由同生和成岩组分组成。其中以成岩黄铁矿为主,其形成过程主要受有机质限制,而同生黄铁矿受铁矿物与H2S接触时间的限制。     

Effects of humic substances on Fe(II) sorption onto aluminum oxide and clay

We studied the effects of humic substances (HS) on the sorption of Fe(II) onto Al-oxide and clay sorbents at pH 7.5 with a combination of batch kinetic experiments and synchrotron Fe K-edge EXAFS analyses. Fe(II) sorption was monitored over the course of 4 months in anoxic clay and Al-oxide suspensions amended with variable HS types (humic acid, HA; or fulvic acid, FA) and levels (0, 1, and 4 wt%), and with differing Fe(II) and HS addition sequences (co-sorption and pre-coated experiments, where Fe(II) sorbate was added alongside and after HS addition, respectively). In the Al-oxide suspensions, the presence of HS slowed down the kinetics of Fe(II) sorption, but had limited, if any, effect on the equilibrium aqueous Fe(II) concentrations. EXAFS analyses revealed precipitation of Fe(II)–Al(III)-layered double hydroxide (LDH) phases as the main mode of Fe(II) sorption in both the HA-containing and HA-free systems. These results demonstrate that HS slow down Fe(II) precipitation in the Al-oxide suspensions, but do not affect the composition or stability of the secondary Fe(II)–Al(III)-LDH phases formed. Interference of HS with the precipitation of Fe(II)–Al(III)-LDH was attributed to the formation organo-Al complexes HS limiting the availability of Al for incorporation into secondary layered Fe(II)-hydroxides. In the clay systems, the presence of HA caused a change in the main Fe(II) sorption product from Fe(II)–Al(III)-LDH to a Fe(II)-phyllosilicate containing little structural Al. This was attributed to complexation of Al by HA, in combination with the presence of dissolved Si in the clay suspension enabling phyllosilicate precipitation. The change in Fe(II) precipitation mechanism did not affect the rate of Fe(II) sorption at the lower HA level, suggesting that the inhibition of Fe(II)–Al(III)-LDH formation in this system was countered by enhanced Fe(II)-phyllosilicate precipitation. Reduced rates of Fe(II) sorption at the higher HA level were attributed to surface masking or poisoning by HA of secondary Fe(II) mineral growth at or near the clay surface. Our results suggest that HS play an important role in controlling the kinetics and products of Fe(II) precipitation in reducing soils, with effects modulated by soil mineralogy, HS content, and HS properties. Further work is needed to assess the importance of layered Fe(II) hydroxides in natural reducing environments.     

Pyritization of iron and trace metals in anoxic fjord sediments (Nordåsvannet fjord,western Norway)

The accumulation and storage of trace metals in coastal sediments is an environmental concern. It is, therefore, important to understand better how these metals are bound or released under different redox conditions. This study of Fe and trace metal fixation under continuously anoxic conditions in the bottom sediments and the lower water column of the Nordåsvannet fjord in western Norway contributes further to such understanding. It allows investigation of both an end member redox state and one important mechanism of Fe and trace metal accumulation in sediments, the pyritization of Fe and trace metals. Pyrite formation occurs both in the water column and in the sediments of the Nordåsvannet fjord and favours the fixing of Fe and trace metals in the bottom sediments of the fjord. Thus, these sediments act as a continuous sink for Fe and trace metals. The DOP, and the degrees of trace metal pyritization for Mo, Ni and Cr correlate with organic matter content. While it is generally thought that Fe is the factor limiting pyrite formation in anoxic environments, this study found that degrees of pyritization of Fe (DOP) are clearly below 100%, and the availability of metabolizable organic matter is limiting pyrite formation. This is an important finding, because it indicates that increased supply of organic and mineral matter by higher runoff from land would further enhance the fixation of these metals in the fjord sediments, as would higher organic matter availability from increased productivity due to higher nutrient supply. The metals stored in the bottom sediments could be released into the biogeochemical cycle if redox conditions were to change from anoxic to suboxic or oxic. The fjord would then become a source rather than a sink for these metals.     

临沧超大型锗矿床的沉积环境、成岩过程和热液作用与锗的富集

临沧超大型锗矿庆的形成与其沉积、成岩和热液作用有密切联系。详细研究了矿床煤岩产出特征、煤岩组成、无机矿物、微量元素、腐殖体反射率,认为该矿床中的锗主要源于盆地西缘的白云母花岗岩的风化作用。在沉积作用阶段,锗被湖水中的低等生物和腐殖酸富集,为形成矿化煤打下基础。临沧褐煤经历了泥炭化阶段、早期成岩阶段和热液改造阶段。泥炭化阶段,沉积物中锗被凝胶体吸附和配合。早期成岩阶段,与腐残酸结合的锗,在碱性还原条     

沉积环境对页岩气储层的控制作用——以渝东北地区五峰组-龙马溪组为例

以"沉积控相,相控储层"为研究思路,基于野外露头剖面实测与室内实验测试,以及前人的研究成果,探讨渝东北地区上奥陶统五峰组-下志留统龙马溪组沉积环境对页岩气储层的控制作用。研究表明,渝东北地区五峰组-龙马溪组富有机质泥页岩主要发育于滞留浅海陆棚相中,沉积中心页岩厚度可达70~80m,有机碳含量(TOC)最高可达7.56%,平均3.09%。静水缺氧还原沉积环境岩石类型主要以富含有机质的含碳质含粉砂泥(页)岩、含碳质含硅质泥(页)岩、含硅质泥(页)岩、含碳质泥(页)岩、含粉砂泥(页)岩及硅质泥(页)岩为主。页岩矿物成分以石英(平均达62.76%)和黏土矿物(平均达22.61%)为主。缺氧还原环境下沉积的大量黄铁矿形成的黄铁矿晶间孔、黏土矿物层间微孔隙、有机质生烃形成的微孔隙以及脆性矿物控制形成的微裂缝为页岩气提供了良好的储集空间。沉积环境控制的储层发育特征的研究可为页岩展布、有机质丰度、储集空间及其之后有利区评价等研究提供基础。     

The glauconite–Fe‐illite–Fe‐smectite problem: a critical review

Iron silicate minerals are a significant component of sedimentary systems but their modes of formation remain controversial. Our analysis of published data identifies end‐member compositions and mixtures and allows us to recognize controls of formation of different mineral species. The compositional fields of glaucony, Fe‐illite, Fe–Al smectites are determined in the M⁺/4Si vs. Fe/Sum of octahedral cations (M⁺ = interlayer charge). Solid solutions could exist between these phases. The Fe–Al and Fe‐rich clay minerals form two distinct solid solutions. The earliest phases to be formed are Fe–Al smectites or berthierine depending on the sedimentation rate. Reductive microsystems appear in the vicinity of organic debris in unconsolidated sediments. The Fe is incorporated first in pyrite and then in silicates after oxidation. Potassium ions diffuse from the sea‐water–sediment interface. If not interrupted, the diffusion process is active until reaction completion is reached, i.e. formation of Fe‐illite or glauconite or a mineral assemblage (berthierine–nontronite) according to the available Al ion amounts in the microsystem. Mixed‐layer minerals are formed when the diffusion process is interrupted because of sedimentation, compaction or cementation. Despite the common belief of their value as palaeoenvironment indicators, these minerals can form in a variety of environments and over a period of millions of years during sediment burial.     

Metal Speciation in Water of the Flooded Mine “Arsenic” (Karelia,Russia): Equilibrium-Kinetic Modeling with a Focus on the Influence of Humic Substances

Equilibrium-kinetic modeling allows investigating metal behavior in the water–rock-organic matter system with time to evaluate anthropogenic effects on the environment. In the article, the interactions of stagnant mine drainage water of the flooded mine “Arsenic” with ore and gangue minerals were simulated using different organic matter incorporation approaches. If the model is closed to humic substances (no additional organic matter input), most fulvic acids are bound in the Fe fulvate complex. While under the removal of Fe fulvate from the model, the Cu fulvate becomes prevalent, the contribution of the fulvate complexes with Zn, Mg, and Ca also increases. This scenario simulates the organo-mineral complexes behavior well and allows identifying the sequence of metal binding to organic ligands as follows Fe?>?Cu?>?Zn?>?Mg?>?Ca. The second scenario imitates the constant input of organic matter to the model (open system regarding humic substances). The dissolved metal concentrations in the model solution are extremely high in comparison to the mine drainage water. This scenario demonstrates that excessive input of organic matter leads to the accumulation of the metals in a dissolved form and blocks the secondary mineral formation despite the faster dissolution of the primary minerals under a more acidic pH than in the first scenario. However, despite the differences between the model solution and the mine drainage water, this scenario is useful to address specific issues associated with changes in natural and anthropogenic conditions. Both scenarios show the importance of organic matter incorporation to the equilibrium-kinetic models.

     

Organic petrology, mineralogy and depositional environment of the Kipra lignite seam, Maritza-West basin, Bulgaria

The aim of the present study is to provide additional information about the properties and depositional environment of the Kipra lignite seam, which was deposited during the regressive stage of development of the Maritza-West basin. Petrographical and mineralogical data, along with ash yields and sulphur contents of 24 samples from a seam profile, have been used to study the vertical variation of the depositional settings during peat accumulation and subsequent coalification.The Kipra lignite is characterized by high ash yields and sulphur contents. It formed in a rheotrophic, low-lying mire with alkaline pH value. Vegetation with low preservation potential dominated within the palaeomire. During peat formation, frequent changes of the water level controlled the depositional environment. During the deposition of units 1 and 2, high water energy caused the transportation of high amounts of inorganic material into the mire, resulting in the formation of weakly gelified mineral-rich lignite. The organic matter from units 3 and 4 is characterized by enhanced gelification, which probably reflects the decreasing energy of the system. Good positive correlation between sulphur contents and the GI values was established in units 4, indicating that the gelification of the tissues was probably mainly controlled by the bacterial activity. In contrast, the gelification of the samples from unit 3 of the Kipra seam was probably governed by the redox conditions. The organic matter deposited under relatively wet conditions, in which the thermal and oxidative destruction of the tissues, was limited.A variety of major, minor and accessory minerals are present in Maritza-West lignite. The mineral composition is dominated mainly by pyrite, gypsum and calcite, and to a lesser extent limonite, quartz, kaolinite, montmorillonite, illite, chlorite and plagioclase. Jarosite, hematite, halloysite, mica, K-feldspar, aragonite, siderite, and dolomite were also determined in very low concentrations. These minerals formed syngenetically and epigenetically. The syngenetic stage is characterized mainly by the formation of pyrite, carbonates, silicates and sulphates, whereas the Fe-oxyhydroxides, partially the carbonates and almost all silicates are of detrital origin. During the epigenetic stage, carbonates, sulphates, clay minerals, pyrite, and Fe-oxyhydroxides were formed. Alteration products like gypsum, jarosite, limonite, chlorite, kaolinite, illite, mica, and calcite were generated due to the transformation of detrital and authigenic minerals.     

“灰成分端元分析法”及其在聚煤环境分析中的应用

“灰成分端元分析法”是以SiO₂ -Al₂O₃ 、CaO -MgO及Fe₂O₃-SO₃ 分别作为三角图端元进行聚煤环境分析的一种新方法。其原理是 :灰成分与煤中矿物质种类与含量具有成因上的相关关系 - -据SiO -Al₂O₃端元特征,可以判断介质的总体运动方向;由CaO -MgO端元特征,可以判断泥炭沼泽受海水影响的程度;由Fe₂O₃ -SO₃ 端元特征,可以判断聚煤环境的氧化还原条件。该方法用于研究河东煤田 10 # 煤的聚煤环境,收到了良好效果,证明其不失为传统聚煤环境分析方法的一个有益补充。     

含油气盆地中粘土矿物的穆斯堡尔效应及应用--以柴达木盆地第三系为例

本文主要讨论了柴达木盆地第三系粘土矿物的穆斯堡尔效应,分析了有关粘土矿物的响应特征及铁离子的赋存状态,测定了Fe2+/Fe3+值,并依据该比值对研究区的沉积环境和沉积相作了判别。表明含油气盆地中粘土矿物的铁穆斯堡尔效应不但可用来鉴别含铁的粘土矿物类型,而且在沉积环境和沉积相的判别中具有重要的应用价值。     

Geochemistry and origin of elements in some UK coals

Twenty-four UK coals ranging in rank with 4.6%–37.6% volatile matter were analysed for 46 major and trace elements. The samples were obtained from the UK Coal Bank and are representative of the major UK coal fields. The major element distributions are interpreted in terms of the mineralogical variations—quartz and kaolinite are largely responsible for the Si and Al, carbonates for Ca and Mg and pyrite for Fe. Also exerting an influence in some samples are siderite, Al-phosphate minerals and illite. Based on statistical relationships with the major elements, Rb, Cr, Th, Ce, Zr, Y, Ga, La, Ta, Nb and V are thought to be mainly present in the clay minerals, and As, Mo, Sb, Tl, Se and Bi and Pb are probably present in pyrite. Strontium and Ba are concentrated in a restricted number of samples related to the phosphate minerals. Germanium is the only element for which a major organic association can be demonstrated. Elements with an indirect association with the organic matter are Na, Cl, and Br in porefluids and possibly Te. The ash content is controlled mainly by the detrital input and the trace elements related to the ash content are therefore those elements associated with the clay minerals. Variations with rank would appear to be mainly related to the moisture content (porefluids). The trace elements associated with the quartz and clay minerals are thought to be dominantly detrital in origin. The non-detrital elements, essentially those contained in pyrite, are thought to have been incorporated in the depositional environment from waters with enhanced salinities through seawater ingress, hence there are positive relationships between S and trace element concentrations.     

鸡西煤的无机地球化学研究

鸡西煤田是东北地区重要的炼焦煤基地，由于受成煤环境的影响，原煤灰分较高，影响了煤炭精细加工利用和环境。采用Ｘ射线衍射、红外光谱等分析方法对鸡西煤的无机地球化学特征研究显示，煤中的主要矿物为石英、方解石、粘土矿物、黄铁矿和菱铁矿等，它们分别以不同的状态赋存于有机质中。煤灰的主要成分为ＳｉＯ２和Ａｌ２Ｏ３，其主要源自流水带入泥炭沼泽的石英和粘土等同生矿物。元素分析表明，煤中硫、磷及微量元素锗和镓等含量较低。     

Use of laser ablation ICP-MS to determine trace element distributions in coals, with special reference to V, Ge and Al

Laser ablation ICP-MS has been used to produce element profiles from polished coal samples. The elements analysed (V, Ge, Ni, Cu, Zn, Sr and Ba) were those known to have an organic association, with the addition of Al and Fe as controls on the clay and pyrite abundances. The element profiles were compared with the petrography and a statistical analysis was also carried out. Sporinite was found to have low trace element concentrations, inertinite higher concentrations of detrital elements and vitrinite higher concentrations of V, Ge and Al. The relationships between these elements are explored and all are thought to be present in the organic matter and not as minerals. It is thought that these elements became concentrated during diagenesis, with the possibility that some of the Al could be residual. The Cu/Ni ratio in the pyrite is relatively constant, suggesting constant ionic proportions during diagenesis, and possibly a seawater source.     

Chemical coagulation of humic substances: A comparison of natural aquatic versus soil-extracted materials

Aquatic humic substances can be removed by chemical coagulation during water treatment. Hydrolyzing metals such as Al(III) and Fe(III), as well as commercially available cationic polyelectrolytes, can effectively remove humic substances prior to chlorination, thus reducing the formation of trihalomethanes. Synthetic waters, produced by adding soil-extracted fulvic acids to distilled water containing a clay source and various salts, have some merit in approximating the behavior of aquatic humic substances during chemical coagulation; however, caution must be exercised in the interpretation and applicability of the results.     

Pyrite-organic matter relationships: Currant Bush Limestone,Georgina Basin,Australia

The relationship between the TOC (total organic carbon) and S (pyritic sulphur) contents of some organic-rich (TOC 3–14%) silty limestones and calcareous siltstones from the Cambrian Currant Bush Limestone of the Georgina Basin, Australia, is similar to that of euxinic sediments, but could also indicate deposition in a non-saline environment. However, such conditions are not easily reconciled with the shallow equatorial epeiric sea in which the formation is considered to have been deposited. The relationship can alternatively be explained by the relatively low Fe content of the sediment being the main limiting factor in pyrite generation, coupled with a slightly increased degree of pyritization with increased TOC. The relationship between the TOC and S contents of organic-poor (TOC 0.2–2.4%) samples from the same formation is similar to that of normal marine sediments, but the Fe content is probably also the major controlling factor on pyrite generation. These interpretations demonstrate that in using TOC and S contents to aid in reconstruction of depositional environments, it is important to check whether Fe content could have been the limiting factor in the formation of pyrite, even in sediments with only moderate carbonate contents.     

Zeolites in Tertiary coal from the Çayirhan mine, Beypazari, Turkey

The study focuses on the mineralogy of the upper coal seam accumulated at the top of the Çoraklar Formation (Miocene), Beypazari, Turkey. This coal seam is laterally extensive and averages 3.0 m thick, varying from 1.0 to 4.9 m. Analcime and clinoptiolite comprise up to 80% of the mineral matter (which also includes feldspars, quartz and pyrite and traces of dolomite, clay minerals and apatite) in the coal from the Cayirhan mine. Zeolites were formed when sodium-rich solutions altered aluminosilicate epiclastic material derived from contemporaneous volcanic activity. The allocthonous organic matter accumulated as a result of detrital plant and epiclastic material from an adjacent fresh-water environment being washed into a saline lake in sufficient quantities to form peat with a high mineral matter content (29.7% mean mineral matter content in raw coal). Subsequent syngenetic alteration of the volcanic glass incorporated into the peat resulted in zeolite formation. Alteration of sodium-rich epiclastic material by sodium-rich solutions resulted in the formation of analcime, whilst alteration of calcium-rich epiclastic material by sodium-rich solutions resulted in the formation of clinoptilolite.     

Sulfide minerals in Seelyville Coal III,Chinook Mine,Indiana

Sulfide minerals in coal bed III at the Chinook Mine, Indiana, are pyrite, marcasite, and rarely sphalerite. Pyrite occurs as framboids concentrated mainly in exinite, as bands or lenses in vitrinite and clay partings, as cell fillings in fusinite, and in cleats. Marcasite normally occurs in association with clusters of pyrite framboids within micro-organic remains. Sphalerite occurs exclusively in fusinite associated with cleat pyrite. The iron sulfides, which are of authigenic origin, were formed during the biochemical stage of coalification during the accumulation and compaction of peat. The factor that limited their formation in such an environment was the availability and reactivity of iron. Chemical heterogeneity in the peat swamps where the sulfides formed existed even on a microscopic scale. The iron sulfides were commonly precipitated in localized micro-environments that were favorable for their formation. The metamorphic stage of coalification did not affect the iron sulfides significantly, although it may have been responsible for the recrystallization of pyrite framboids and minor deformation of pyrite in fusinite and its local mobilisation.     

Depositional environments of the Senonian chert, phosphorite and oil shale sequence in Israel as deduced from their organic matter composition

In the Upper Cretaceous sequence of the Negev (southern Israel) the organic matter in phosphorites and cherts differs from that associated with oil shales in its higher content of humic substances and lower kerogen content, and in its more intensive microbial alteration. The n-alkane distribution pattern of the oil shales, phosphorites and cherts indicates that marine biota, probably algae, are the main organic precursors of their organic matter. In some of the oil shales, however, some contribution of terrestrial organic matter is also evident. Similar high phytane/pristane ratios indicate that the organic matter in the oil shales as well as in the phosphorites and cherts accumulated under reducing conditions. The main differences in the organic matter composition are attributed to early diagenetic processes rather than to different biotic precursors or to late modifications due to temperature-induced maturation. The depositional model suggested for the sequence involves upwelling conditions at the boundary between the deep Tethys and the shallow shelf, which induced high organic productivity deep into the inner shelf. Bottom water circulation enabled intensive microbial alteration of the organic matter, followed by a winnowing process leading to phosphorite formation. Since humification is considered an oxygen-consuming reaction, these processes favoured the formation of oxygen-enriched humic substances and the oxidation of humic substances already present. These humic substances are relatively resistant to further alteration and their conversion into kerogen is thus retarded. Subsequently, syndepositional tectonic activity resulted in the introduction of less saline water, restriction of bottom-water circulation and the establishment of a density stratification in the water body. Consequently, aeration of the bottom layer and the sediments was inhibited, microbial alteration was reduced and later winnowing processes were prevented. Such conditions favoured the formation of kerogen directly, rather than through humic substances, and also favoured the preservation of most of the organic matter in the form of oil shale deposits instead of phosphorites.