Geochemical investigation and characterisation of Neogene sediments from Valjevo-Mionica Basin (Serbia)

Sediments from the Valjevo-Mionica Basin of Neogene age were investigated in this study using different geochemical methods. The results of the inorganic part analyses suggest that during genesis of the sediments, the contents of Na₂O, B and As changed the most, which indicates that genesis of the investigated sediments was followed by climate changes and volcanic activity. The quantity of other macro- and microelements did not vary significantly. Investigations of the organic substance showed that it is native organic matter, which has been preserved to a significant extent, formed predominantly of algal precursor organisms, which provided good quality, deposited under reducing conditions and that it is at a low maturity level. As it has been established that genesis of the investigated sediments was mostly affected by an arid climate with more intensive salinity, the aim of this study, was also to identify the processes which were the most affected by the change in salinity, as well as biomarkers which are the most sensitive to this change. The results led to the conclusion that the salinity increase in the depositional environment had a primary effect on the preservation of the organic substance and the formation of the mineral searlesite. In addition, it was noticed that besides the Sq/nC₂₆ ratio, the parameters nC₁₇/nC₂₇, CPI and Ph/nC₁₈, are also significantly sensitive to salinity change in a depositional environment in case of immature organic substance deposited under reducing conditions.     

Origin,organic geochemistry,and estimation of the generation potential of Neogene lacustrine sediments from the Valjevo-Mionica Basin,Serbia

This paper reports an investigation of 60 samples of lacustrine sedimentary rocks of Neogene age lying at depths of 0–400 m in the Valjevo-Mionica Basin, Serbia. The goal of the study was to determine the origin and type of primary organic matter (OM), the degree of thermal alteration, the generation potential of OM from the rocks of this basin, and conditions in the sedimentation environment during the formation of the rocks. The potential of OM of the rocks was estimated on the basis of the thermolysis of a representative sample after its preliminary debituminization.     

Pregnanes as molecular indicators for depositional environments of sediments and petroleum source rocks

Steroids with unconventional side chains have increasingly been applied as diagnostic markers for geological source and age assessments. However, one of the most distinctive characteristics, the abnormal abundance of pregnane and homopregnane in ancient sediments and petroleum, remains unresolved. Higher pregnane and homopregnane, as well as C₂₃–C₂₆ 20-n-alkylpregnanes, relative to the regular steranes were observed in samples collected from different petroleum basins in China. These included Precambrian marine carbonate-derived petroleum (NW Sichuan Basin), Lower Paleozoic marine marl derived crude oils (Tarim Basin), and Eocene hypersaline lacustrine carbonate source rocks and associated petroleum (Bohai Bay Basin). However, all of the samples have many common biomarker characteristics, such as pristane/phytane ratios < 1, low amounts of diasteranes and high C₂₉/C₃₀ hopane (∼0.6–1), C₃₅/C₃₄ hopane (mostly ⩾ 1) and dibenzothiophene/phenanthrene (DBT/PHEN, mostly 0.5–1) ratios revealing a contribution from anoxic carbonate/marl source rocks deposited in restricted, clastic-starved settings. We suggest that 5α,l4β,l7β-pregnane and homopregnane, as well as their higher C₂₃–C₂₆ homologues, are geological products derived from steroids bound to the kerogen by a sulfurized side chain. Carbon or carbonate minerals are considered to be natural catalysts for this cracking reaction via preferential cleavage of the bond between C-20 and C-22. Similar distributions occur in the short chain analogues of 4-methylsterane, triaromatic steroid and methyltriaromatic steroid hydrocarbons, providing circumstantial evidence for this proposal. The ratio of pregnane and homopregnane to the total regular steranes and the ratio of C₂₇ diasteranes to cholestanes can be sensitive indicators of sedimentary environments and facies. In general, high diasteranes and low pregnanes (with homologues) indicate an oxic water column or significant input of terrigenous organic matter in clay rich source rocks and some organic lean carbonate rocks. Low diasteranes with high pregnanes implies restricted, sulfur rich conditions, typical of anoxic carbonate source rocks. Furthermore, the two ratios may be useful to assess the variation of mineralogy and openness of source rock depositional settings.     

咸化湖盆混积岩成因机理研究

关于海相及淡水湖盆混积岩的研究已相对完善,而针对咸化湖盆混积岩理论的形成及实践应用却鲜有报道,本文旨在系统地阐述咸化湖盆混积岩的成因机理、沉积模式、分布规律,对比其与一般混积岩沉积特征的异同点,并探讨其与油气富集特征的相关性。本文采用矿物学、微观岩石学分析方法进行混积岩矿物组成、沉积特征、储集空间类型研究,采取地质统计分析方法明确混积岩分布规律,并运用物性分析方法对比不同类型混积岩的储集性能。结合柴达木盆地西北区新近系混积岩研究实例,本文创新性地提出了欠补偿咸化湖盆的混积岩成因类型：机械成因的相混合混积岩和生物成因的藻混合混积岩。相混合又可划分为两种亚类：互层型混合、组构型混合;藻混合亦可划分为两种亚类：藻粘结混合、滑塌再混合。建立了咸化湖盆混积岩的沉积模式：混积岩主要发育于三角洲、水下扇、滩坝等碎屑岩沉积体系与湖相碳酸盐岩沉积体系的过渡相带以及藻灰岩发育区。明确了混积岩的分布规律,可归纳为“盆缘互层型、盆内组构型、藻混合局限分布”。混积岩沉积特征对比分析结果表明,任何环境下混积岩形成的先决条件均为碳酸盐岩的生长和聚集,而不同于淡水湖盆及海相混积岩沉积厚度大,生物含量高等特点,咸化湖盆混积岩单层厚度极薄,并发育特殊的藻混积岩类。综合研究认为,藻混合混积岩与油气储层的相关性要大于相混合混积岩。以上成果可为咸化湖盆混积岩,乃至陆相湖泊混合沉积物的成因类型及油气地质意义研究提供借鉴与参考。     

Biomarker Compounds as Indicators of Paleoenvironments

In an attempt to assess the paleoenvironments of terrestrial sediments,some twenty-two representa-tive Chinese non-marine sediment samples were studied using the molecular organic geochemistry method.The sediment samples stuied include oilshale,shale,mudstone and glauber salt from Tertiary to Cretaceous in age.Judging from geological/geochemical data and paleosalinity data,the samples studied are of lacustrine sedimentary origin and can be divided into three different types:fresh water,brackish and saline/hypersaline lake sediments.The aliphatic fractions were separated from the extracts of the samples and analysed by means of GC and GC/MS instruments,giving a number of parameters such as relative abundances of alkanes and cycloalkanes as shown in the mass chromatograms.     

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.     

Biomarker transformations as constraints for the depositional environment and for maximum temperatures during burial of Opalinus Clay and Posidonia Shale in northern Switzerland

Samples from two argillaceous formations (Opalinus Clay and Posidonia Shale) of near-identical maturity from northern Switzerland were subjected to a geochemical characterisation of organic matter and to confined-system pyrolysis experiments. Throughout the study area, the characteristics of organic matter are similar, indicating a spatially homogeneous sedimentary facies. Posidonia Shale contains marine organic matter deposited in a reducing environment, while a predominantly terrigenous source and a more oxidising environment of deposition was identified for Opalinus Clay. In the western and central parts of the study area, organic maturity is close to the onset of oil generation. In the easternmost part, a higher maturity has been reached due to a deeper burial below thick Tertiary Molasse deposits.Isothermal pyrolysis experiments were conducted at temperatures between 250 and 390 °C over 24 h. Bitumen yields increase along similar pathways for both Opalinus Clay and Posidonia Shale, but the maximum values are displaced by 10–20 °C. Data pertaining to maturity were determined from GC–MS analyses of saturated hydrocarbons, and specific attention was given to C₂₉-sterane and C₃₂-hopane isomerisation ratios. The evolution of these parameters with rising temperature is slightly different in the two formations, which is attributed to the contrasting organic facies. The pyrolysis data, together with literature data from natural basins, were used to calculate kinetic parameters for C₂₉-sterane and C₃₂-hopane, assuming a single-step isomerisation scheme according to the Arrhenius law. The resulting values based on pyrolysis data alone are very similar to those based on the combination of pyrolysis and natural data. Activation energies are similar in both formations, while the frequency factors are up to one order of magnitude higher for Posidonia Shale when compared to Opalinus Clay. For the Benken site, maximum temperature during Cretaceous burial was calculated on the basis of the kinetic data, using the TTI approach. The resulting temperatures of 75–80 °C are 5–10 °C below those derived in the literature from apatite fission-track analysis, vitrinite reflectance and basin modelling.     

Sedimentation History of Neogene Lacustrine Sediments of Suseocka Bela Stena Based on Geochemical Parameters (Valjevo-Mionica Basin, Serbia)

Sediments of the western part of the Valjevo-Mionica basin (Serbia) were examined both geochemically and mineralogically to explain, on the basis of their sedimentological characteristics, the causes of changes in their qualitative and quantitative composition. A total of 62 samples obtained from the drillhole at depths up to 400 m was investigated. Using correlation of the obtained data, six geochemical zones were defined, two of which being specially distinguished by their mineralogical, geochemical and sedimentological characteristics. The first one, upper zone A, consists of banded marlstones interbedded with clay and oil shales and is characterized by presence of analcite and searlesite. These minerals and very high contents of Na2O indicate sedimentation in alkaline conditions with increased salinity in arid climate. That provided pronounced water stratification, as well as higher bioproductivity in the basin and sedimentary organic matter preservation. Therefore, the zone A sediments are characterized by high organic matter contents of the type which provides good potential for production of liquid hydrocarbons. Another specific zone, zone F, contains sediments with very high MgO, K2O and Li concentrations. Their geochemical correlation, as well as almost complete absence of illite in this zone, indicates the presence of interstratified clay mineral type illite-saponite (lithium-bearing Mg-smectite).     

柴西地区上油砂山组咸化湖沼沉积与微生物岩

利用大量岩芯、薄片、地震及分析化验资料,围绕南翼山—大风山地区的上新统上油砂山组(N²₂)咸化湖沼沉积,研究沉积特征及成因机制,建立沉积模式,分析控制因素。研究表明:(1)上新统上油砂山组(N²₂)沉积时期,南翼山—大风山地区为咸化湖沼环境,因咸水与淡水频繁融合,构成独特的生态系统,发育适应性的水生生物与微生物等,由生物、化学、物理沉积作用共同影响,形成咸化沼泽沉积组合。(2)明确了咸化湖沼相识别标志,主要包括沼泽土以及大量近地表暴露标志等,并伴生湖沼相微生物岩与微体化石组合等。(3)沼泽环境共发育7类岩相,进一步分析主要岩相的沉积特征及控制因素。(4)沼泽环境可分为滨岸带、植被带及浸没区,不同环境可形成不同的沉积层序、发育不同沉积岩相组合。咸化湖沼相的沉积层序主要包括退积型准层序,进积型准层序以及加积型准层序等。     

Facies analysis and depositional systems of Cenozoic sediments in the Hoh Xil basin, northern Tibet

A sedimentary succession more than 5800 m thick, including the Lower Eocene to Lower Oligocene Fenghuoshan Group, the Lower Oligocene Yaxicuo Group, and the Lower Miocene Wudaoliang Group, is widely distributed in the Hoh Xil piggyback basin, the largest Cenozoic sedimentary basin in the hinterland of the Tibetan plateau. The strata of the Fenghuoshan and Yaxicuo groups have undergone strong deformation, whereas only minor tilting has occurred in the Wudaoliang Group. We analyze their sedimentary facies and depositional systems to help characterize continental collision and early uplift of the Tibetan plateau. The results indicate fluvial, lacustrine, and fan-delta facies for the Fenghuoshan Group, fluvial and lacustrine facies for the Yaxicuo Group, and lacustrine facies for the Wudaoliang Group. Development of the Hoh Xil basin underwent three stages: (1) the Fenghuoshan Group was deposited mainly in the Fenghuoshan-Hantaishan sub-basin between 56.0 and 31.8 Ma ago; (2) the Yaxicuo Group was deposited mainly in the Wudaoliang and Zhuolai Lake sub-basins between 31.8 and 30.0 Ma ago; and (3) the Wudaoliang Group was deposited throughout the entire Hoh Xil basin during the Early Miocene. The Fenghuoshan and Yaxicuo groups were deposited in piggyback basins during the Early Eocene to Early Oligocene, whereas the Wudaoliang Group was deposited in a relatively stable large lake. The Hoh Xil basin underwent two periods of strong north–south shortening, which could have been produced by the collision between India and Asia and the early uplift of the Tibetan plateau. The study suggests the Hoh Xil region could reach a high elevation during the Late Oligocene and the diachronous uplift history for the Tibetan plateau from east to west.     

Dissolved noble gases in the porewater of lacustrine sediments as palaeolimnological proxies

This paper presents results from the numerical modelling of the transport of atmospheric noble gases (He, Ne, Ar, Kr, Xe), tritiated water and ³He produced by radioactive decay of ³H, in unconsolidated lacustrine sediment. Two case studies are discussed: (1) the evolution of ³H and ³He concentrations in the sediment porewater of Lake Zug (Switzerland) from 1953 up to the present; and (2) the response of dissolved atmospheric noble gas concentrations in the sediment porewater of a subtropical lake to an abrupt climatic change that occurred some 10 kyr before the present. (1) Modelled ³H and ³He porewater concentrations are compared with recent data from Lake Zug. An estimate of the effective diffusion coefficients in the sediment porewater is derived using an original approach which is also applicable also to lakes for which the historical ³H and ³He concentrations in the water column are unknown. (2) The air/water partitioning of atmospheric noble gases is sensitive to water temperature and salinity, and thus provides a mechanism by which these environmental variables are recorded in the concentrations of atmospheric noble gases in lakes. We investigate the feasibility of using noble gas concentrations in the porewater of lacustrine sediments as a proxy for palaeoenvironmental conditions in lakes. Numerical modelling shows that heavy noble gases in sediment porewater, because of their comparatively small diffusion coefficients and the strong temperature sensitivity of their equilibrium concentrations, can preserve concentrations corresponding to past lake temperatures over times on the order of 10 kyr. Noble gas analysis of sediment porewaters therefore promises to yield valuable quantitative information on the past environmental states of lakes.     

Lead isotopes in lacustrine sediments and lichen transplants, contrasting and complimentary indicators of sources

The isotopic composition of lead has proven a powerful tool for the characterization of the types of its sources, and with other information on their identity. Lead is dispersed in the environment through water courses or airborne particulates, and has serious impact on the natural and human environments. Lake sediments record deposition derived mainly from its catchment while lichen represents the fine-grained atmospheric deposition of the site. The records of deposition differ in the scales of grain size, time and space. This investigation aims at comparing and contrasting these two types of records in an area affected essentially by a single visible emission source, and to improve the understanding of the controls on the formation of these records. The visible source is a Cu smelter complex with mining installations within the town of Karabash, in the southern Ural Mountains of Russia and considered one of the most heavily polluted areas in the world.     

Palynology and depositional facet of lower Permian (Artinskian) sediments from New Majri opencast mine,Wardha basin,India

Coal samples and the associated sediments from New Majri open cast mine have been analysed palynologically with the following objectives: to date the sediments on the basis of the palyno-assemblage recognised; to carry out an inter-basinal, intra-basinal and Gondwana wide correlation; to interpret the palaeoenvironment and depositional facet of the coal field on the basis of dispersed organic matter analysis and sedimentary facies analysis. Based on the qualitative and quantitative analysis of the spore and pollen content one palyno-assemblage-Scheuringipollenites and Faunipollenites has been recognised which is typical of lower Barakar Formation. This has been correlated with known palyno-assemblages from Wardha basin and other basins in India, while with the Gondwana continents the assemblage has been broadly correlated with early Permian Australian, African, South America palynofloras as well as early Permian palynoflora of Antarctica. Consequently, a tentative late Early Permian, Artinskian age is proposed for the sediments from New Majri open cast mine. Palynological studies also revealed that the peat forming vegetation was mainly composed of gymnosperms represented by glossopterids (Scheuringipollenites, Ibisporites, Platysaccus, Cuneatisporites, Primuspollenites and Sahnites), conifers (Faunipollenites, Striatites, Striatopodocarpites, Verticipollenites, Distriatites) and cordaites (Parasaccites, Plicatipollenites, Crucisaccites, Divarisaccus, Densipollenites). Spores were represented mainly by filicopsids (Horriditriletes, Brevitriletes, Callumispora) and sphenopsids (Latosporites). The relative abundance of structured organic matter implies the existence of a fairly dense cover of vegetation in the hinterland. Anaerobic, reducing, water logged peat-forming conditions have been inferred by the presence of biodegraded organic matter and amorphous organic matter. The charcoal fragments recovered from the present study area reflects a possible wildfire in the accumulated swamps or a wildfire in the hinterland after which the sediments were flushed by fluvial systems into the swamps. The coalfield exhibits horizontal bedding pattern which may be due to deposition by suspension settling or horizontal accretion. Further the alternating high and low energy regime is noticed in the sandstone-shale intercalated beds overlying the coarse grained yellow sandstone which forms the roof of the coal seam. Comprehensively the sediments are deposited as overbank / levee deposits.     

Geochemistry of Miocene lacustrine sediments from the Sokolov Coal Basin (Czech Republic)

Sediments of the upper part of the Sokolov Formation of the Sokolov Brown Coal Basin consist mostly of brown lacustrine clays and claystones enriched in organic matter (2–18% TOC). The lower portion of the stratigraphic profile is formed mostly by kaolinite–illite clays and claystones, while the montmorillonite content increases in the upper portion. The change in the lithology of sediments is caused by the gradual erosion of the weathering crust in the source areas of the clastic material. Inversion of the weathering profile during erosion is manifested geochemically in a decrease in the Al₂O₃/Na₂O ratio and an increase in the SiO₂/Al₂O₃, Na₂O/K₂O and K₂O/TiO₂ ratios from the base to the top of the studied part of the Sokolov Formation. The amounts of trace elements (La, Ce, Nb, Zr, Cr, V, Sn) also decrease in the same direction. On the other hand, the amounts of Rb and Sr increase. The organic matter of the upper part of the Sokolov Formation consists primarily of Types I and II kerogen. Only near the base of the studied part of the formation, i.e., in the coal stringer, kerogen of Type III prevails. The extremely low degree of thermal maturity permits determination of the source of the organic matter and characterization of its accumulation environment. The organic material in the sediments is predominantly of algae origin. Relatively high amount of pentacyclic triterpanes of the hopane series indicates either the occurrence of cyanobacteria as primary producers or bacterial reworking during sedimentation and diagenesis. Organic matter accumulated under the conditions of a fresh-water lake or lake with slightly elevated salinity, in a dysoxic aqueous environment. The alternation of organic carbon-rich layers with layers low in organic matter is explained in terms of changes in the degree of dysoxia of the aqueous environment and a variation in the intensity of oxidation and mineralization of the organic material.     

Biostratigraphy and depositional environments of subsurface sediments in well Arani-A,Palar basin,Tamil Nadu

The first exploratory well Arani–A was drilled in the Palar basin to a depth of 2400m and terminated within the granitic basement.This well offered the first ever opportunity to understand biostratigraphy, sedimentation history and depositional environment of the entire sedimentary column based on arenaceous foraminifera, spores, pollen and dinoflagellate cyst assemblages. Previous studies on few scattered outcrops around Sriperumbudur, Chengalpattu and Sathyavedu areas have documented palynofossil assemblage of Neocomian–Aptian age. The present study reveals the presence of middle Jurassic (Bajocian-Callovian) sediments (2360-1725 m) resting on the granitic basement. The sediments are interpreted to have deposited under lacustrine/estuarine conditions with high tides providing occasional marine influence. The middle Jurassic sediments are conformably overlain by late Jurassic (Oxfordian–Tithonian) sediments (1725 - 950 m). The late Jurassic sediments have been inferred to have got deposited under fluctuating near shoremarginal marine conditions. There is a 55m thick boulder bed (950 - 895 m) separating the overlying Valanginian sediments. Early Cretaceous (Valanginian-Early Albian) sediments are developed in the interval from 895-50m. The boulder bed possibly corresponds to the missing Berriasian stage of the earliest Cretaceous representing an unconformity of the order of ~5 Ma across Jurassic-Cretaceous boundary. These sediments are inferred to have deposited under shallow inner neritic conditions. The sediments from 50m to surface consist mainly of lateritic sandstone and alluvium. The sedimentary history of Palar basin began in Bajocian stage of middle Jurassic (170-168 Ma) and ended in early Albian stage of early Cretaceous (113-105 Ma). The late Albian marine transgression which facilitated huge sedimentation in Cauvery and Krishna-Godavari basins has bypassed the Palar basin thus adversely affecting the hydrocarbon potential.     

Late cretaceous radiolarians and age of flyschoid sediments in the Struganik section (Western Serbia)

The succession of radiolarian assemblages in the Struganik section of western Serbia is described for the first time. The following radiolarian beds are defined in carbonate flyschoid sequences represented by thin-platy limestones with calcarenite and bentonite clay intercalations (from the base upward): Theocampe urna-Dictyomitra koslovae (presumably lower Santonian); Afens perapediensis-Clathropyrgus titthium (presumably uppermost lower Santonian-basal upper Santonian); Alievium gallowayi-Crucella espartoensis (upper Santonian). The examined assemblages are characterized by high taxonomic diversity. The upper Santonian Alievium gallowayi-Crucella espartoensis Assemblage exhibits significant similarity with the coeval radiolarian assemblage of the Crimean Mountains (Ukraine). Archaeocenosphaera (?) karamatai sp. nov. is described.     

Comparison of ladderane phospholipid and core lipids as indicators for anaerobic ammonium oxidation (anammox) in marine sediments

We investigated anaerobic ammonium oxidation (anammox) in continental shelf and slope sediments of the Irish and Celtic Seas by using anammox specific ladderane biomarker lipids. We used the presence of an intact ladderane phospholipid as a direct indicator for living anammox bacteria, and compared it with the abundance of ladderane core lipids derived from both living and dead bacterial biomass. All investigated sediments contained ladderane core lipids as well as the intact ladderane phospholipid, in agreement with ¹⁵N-labeling experiments, which revealed anammox activity at all sites. Ladderane core lipid and intact ladderane phospholipid concentrations were significantly correlated (R² = 0.957 and 0.464, respectively) with anammox activity over the transect of the continental shelf and slope sediments. In the Irish Sea (50-100 m water depth) highest abundances of the intact ladderane phospholipid were found in the upper 2 cm of the sediment, indicating a zone of active anammox. A sharp decline further down-core suggested a strong decrease in anammox biomass and rapid degradation of the intact lipids. In comparison, ladderane core lipids were 1-2 orders of magnitude higher in concentration than the intact ladderane phospholipid and accumulated as dead cell remnants with depth. In the slope sediments of the Celtic Sea both ladderane core lipids and the intact ladderane phospholipid were found in sediments at water depths ranging from 500 to 2000 m. Here, anammox seemed to be active at greater depths of the sediment (>2 cm). Mean abundances of both intact and core ladderane lipids in whole sediment cores increased downslope, indicating an increasing importance of anammox in deeper slope sediments.     

银川盆地35ka以来古植被演化的类脂分子记录

为了更好地了解干旱-半干旱区的植被类型及其演化规律,利用气相色谱仪对银川盆地冰沟剖面河湖相沉积物中的正构烷烃进行了检测,结果显示其正构烷烃碳数分布范围为C15~C34,奇碳优势明显,以C29或C31为主峰的单峰型为主,但少量样品也出现双峰型分布模式。通过对冰沟剖面正构烷烃分布特征、碳优势指数CPI和L/H（ΣC21-/ΣC22+）指标的详细分析得知其有机质来源以陆生高等植物占主导优势。结合年代数据、有机碳同位素、长链正构烷烃平均链长ACL和C33/(C33+C27)值重建出35.0ka以来银川盆地植被类型以 C3植物为主,并且C3和C4植物的相对比例变化主导受温度制约,而木本和草本植被的演化主要受控于水分条件。     

Relationship between sediments and their igneous source rocks using clay mineral multi-element chemistry: the Cenozoic lacustrine Anloua basin (Adamaoua, Cameroon)

The Cenozoic lacustrine basin of Anloua (Adamaoua, Cameroon), is filled with the weathering products of the surrounding rocks. In order to determine the origin of these sediments, multi-element, especially trace element, analysis of their < 2 μm fraction was undertaken. The chemical compositions of these fractions were compared with those of the rocks surrounding the basin by multivariate statistical analysis and also graphically. A principal component analysis allowed the most discriminant elements to be selected, and a hierarchical ascending classification (HAC) made with these elements divided the samples into groups. Some of these groups contain < 2 μm fractions of both the lake sediments and surrounding rocks. These sediments are determined as deriving by weathering from the surrounding rocks. Some of the other groups contain no samples from the surrounding rocks and their petrographic origin cannot be given. A graphic comparison of the relative amounts of the elements (determined by HAC) from the < 2 μm fractions of the various groups and the rocks surrounding the basin allowed attribution of a petrographic origin for the various sediments analysed by using the fit between the curves.

The clay mineralogy, the amounts of Ti, Zr, and heavy minerals in the < 2 μm fractions and their distribution in the area studied, as well as the presence of angular quartzite pebbles in some sediments gives an indication of the paleogeography of the Anloua basin. There was deltaic input towards the north and a high energy input, possibly torrential, to the west.