A Reconstruction and Discussion of the Effect of Diagenetic Environment on Hydrocarbon Generation Based on Diagenetic Mineral Assemblage in Mudstone

Inorganic minerals in mudstone are composed of clay minerals,carbonate and detrital minerals.Detrital minerals(such as quartz and feldspar)are mainly original deposit.However,clay minerals(kaolinite,illite,and chlorite)and carbonate(calcite and dolomite)are mostly diagenetic minerals.Furthermore,conversion of the four kinds of clay minerals are common.The formation of clay minerals and carbonate is controlled by temperature,pressure,p H,Eh and type of cations during diagenesis.Therefore mineral assemblage can indicate the characteristics and change of diagenetic environment.In addition to inorganic minerals,there are also organic matter of different sources and chemical properties in mudstone.Traditionally,it is considered that evolution of organic matter is controlled by thermal effect.Now studies show that inorganic and organic matter can interact with each other and form clay-organic complexes.This suggest that attention should be paid to the influence of diagenetic mineral assemblage and diagenetic environment on the evolution of organic matter* Samples of mudstone from 1500-4500m of the Palaeogene in the Dongying Depression,China,were collected to investigate the changes of mudstone diagenetic environment.XRD,thin section and SEM were used to detect diagenetic minerals and assemblage characteristics.Results showed that content of detrital minerals,which are floating in mud matrix or preserved as silt laminae,is basically unchanged from shallow to deep strata.Clay minerals which are gathered as argillaceous matrix or preserved as argillaceous laminae have growth and decline relation to carbonate which mainly appear as micropoikilitic ferriferous calcite and ferriferous dolomite.All these characteristics indicate that detrital minerals are exogenetic,whereas carbonate is diagenetic minerals.Based on the SEM analysis of the clay minerals,it was found that smectite present honeycomb and reticulate structure,while illite present filiform and schistose structure and there are growth and decline relationship between them.Nevertheless,hexagonal tabular and stratified kaolinite has the highest content from 2400m to3300m.Rosette and stratified chlorite shows increase trend when the burial depth is deeper than 3300m.These characteristics indicated that clay minerals are diagenetic minerals and there are conversions among the four types.Therefore form shallow to deep,three diagenetic mineral assemblage zones can be divided based on the characteristics of carbonate and clay minerals in mudstone.Namely,smectite+illite/smectite zone in the depth of 2000-2500m;kaolinite+illite/smectite zone in the depth of 2500-3300m and illite+chlorite+carbonate zone below 3300m.Previous studies showed that kaolinite is stable under acidic conditions,while other clay minerals and carbonate are stable under alkaline conditions.Hence according to mineral assemblages feature,it was inferred that diagenetic environment of mudstonehasundergonethechangeof alkaline-acid-alkaline.For the organic matter with different chemical properties in mudstone,the hydrocarbon generation will be different in the acidic and alkaline diagenetic environment even if the conditions of temperature and pressure are the same.Therefore,for hydrocarbon generation we should not only focus on thermal effect,but also pay more attention to the differences of diagenetic environment which have great significance for the understanding of hydrocarbon generation,hydrocarbon expulsion and reservoir formation in mudstone.     

The roles of pedogenesis and diagenesis in clay mineral assemblages: Lower Cretaceous fluvial mudrocks,Nova Scotia,Canada

Clay mineral assemblages in alluvial mudrocks are important for paleoclimatic interpretation and for understanding burial diagenetic cementation in sandstones, but it is commonly difficult to unravel the relative importance of source weathering, pedogenesis and diagenesis in their origin. The clay mineral assemblages in fluvial overbank mudrocks from the Lower Cretaceous Chaswood Formation in central Nova Scotia, investigated by X-ray diffraction analysis of the < 2 µm fraction of 45 samples, include kaolinite, illite, vermiculite, and mixed layer kaolinite/expandable clay and mica/vermiculite. The assemblages vary with depositional facies. Wetland organic-rich mudrocks have large amounts of amorphous material and kaolinite is the dominant clay mineral. In the eastern part of the basin, where overbank mudrocks were episodically uplifted by syn-sedimentary strike-slip faulting, cumulate ultisol and alfisol paleosols are common. In the ultisols, hematite is enriched and kaolinite increases at the expense of illite in the B horizon. Alfisols contain more illite and vermiculite and the B horizon is enriched in goethite. In the western part of the basin, where thin sandstones with abundant diagenetic kaolinite cement are interbedded with the mudrocks, the distinctive clay mineral assemblage of mica/vermiculite mixed layer, vermiculite with 15.5 Å peak, and kaolinite/expandable mixed layer clay with a 17.7 Å peak is interpreted to result from bacterially-mediated oxidation of organic matter below the paleo-water table during early burial diagenesis. Deeper burial diagenesis may lead to slightly higher kaolinite crystallinity. Volcanic ash appears to alter to kaolinite/expandable mixed layer clay with a 7.9 Å peak. Comparison with the continuously subsiding and rapidly accumulated Wessex Formation of southern England, formed at a similar paleolatitude, shows the strong role of pedogenic processes and early diagenesis by meteoric water in development of clay mineral assemblages in the locally tectonically uplifted Chaswood Formation.     

十红滩地浸砂岩铀矿层间氧化带蚀变矿物群

十红滩砂岩型铀矿床是我国大型层间氧化带型砂岩铀矿床之一。层间氧化带型砂岩铀矿含矿砂层在含氧含铀水的渗入径流过程中,由于水介质性状的变化,在与砂体发生水岩作用时形成了完全氧化带、不完全氧化带、还原带和原生带等不同地球化学亚带及其相对应的蚀变矿物群,即完全氧化带为褐铁矿(针铁矿、水针铁矿)、伊利石、蒙脱石、少量黄钾铁矾的蚀变矿物群;不完全氧化带为褐铁矿(针铁矿、水针铁矿)、黄钾铁矾、蒙脱石、伊利石、少量绿泥石、高岭石的蚀变矿物群;还原带为沥青铀矿、黄铁矿、高岭石、绿泥石、少量蒙脱石、伊蒙混层粘土、伊利石和碳酸盐等新生蚀变矿物群;原生带的新生蚀变矿物群以黄铁矿、绿泥石、高岭石为主,有时出现少量碳酸盐、蒙脱石和伊利石等。     

上新世以来伊豆-小笠原海脊黏土矿物的来源与古气候意义

对伊豆-小笠原海脊(ODP 782A孔)上新世以来沉积物中黏土矿物的组成、含量及矿物学特征进行了分析,结果表明:黏土矿物以伊利石(42%)和蒙皂石(42%)为主,绿泥石的平均含量为14%,高岭石的含量最低,平均仅为2%。伊利石的结晶度较好,平均为0.25°Δ2θ;化学指数较低,平均为0.31;表明伊利石主要形成于干冷的气候环境。通过将ODP 782A孔黏土矿物组合特征和含量与周边可能源区对比,并结合伊利石和蒙皂石的矿物学参数特征,我们认为蒙皂石主要来源于伊豆-小笠原海脊周边岛弧火山物质;伊利石、绿泥石和高岭石主要来自亚洲大陆风尘。上新世以来(伊利石+绿泥石)/蒙皂石比值总体上呈增加的趋势,并且在5.3~3.6、3.6~1.6、1.6~0 Ma的三个阶段表现出不同的变化特征,该比值与全球深海δ¹⁸O值所记录的全球变冷、北太平洋ODP 885/886孔风尘通量和灵台黄土沉积速率,以及日本海U1430站伊利石/蒙皂石比值所指示的亚洲内陆干旱变化的总体变化趋势和阶段性变化的时间点大致同步,表明该比值敏感地响应了全球变冷和亚洲内陆的干旱。上新世以来(伊利石+绿泥石)/高岭石比值表现为高/低交替变化,分别与中国灵台黄土磁化率高/低变化相对应,由于黄土磁化率记录了亚洲内陆干/湿变化,因此该黏土矿物比值敏感地响应了亚洲内陆的古气候变化,因而可以作为可靠的亚洲大陆干/湿变化示踪指标。     

Normative mineral composition of high-temperature coal ashes from the Sydney basin coalfields,Australia

Chemical differences in the composition of high-temperature coal ashes of major economic seams of the Sydney Basin were studied using a normative analysis. All chemical data were recalculated to normative mineral assemblages consisting of: quartz, kaolinite and illite. Quartz and clay minerals, the principal constituents of mineral matter occurring in coals, account for most of the variations found in the chemical composition of high-temperature coal ashes between seams of various stratigraphic levels and/or geographic locations. Ternary diagrams based on the quantitative relation of quartz, kaolinite and illite were used to demonstrate these differences.     

Provenance of bar-top sediments at Tons river near Allahabad

The bar-top sediments at the Tons river deposited mainly from the suspension current during waning stage condition of river are collected to study their provenance on the basis of clay mineralogy, heavy minerals and magnetic properties. The clay mineral assemblages in samples predominantly consist of illite, with minor amounts of kaolinite, smectite and chlorite. The clay minerals are contributed due to (i) weathering and decomposition of shales, argillaceous limestones and pyroclastic deposits of upper Vindhyan Groups and (ii) weathering and erosion of Banda plain of Gangetic alluvium. The low ZTR index for the studied samples indicates poor sediment maturity, rapid erosion in the source region and short transportation of detritus. The transparent heavy mineral assemblages in the sediment samples predominantly consist of garnet, with minor amounts of tourmaline, zircon, hornblende, enstatite, hypersthene, rutile, tremolite, kyanite, sillimanite, andalusite, chlorite, epidote, wollastonite, and staurolite. The heavy minerals are dominantly angular to sub-angular with some rounded to sub-rounded grains. The rounded grains indicate multicyclicity and derivation fromVindhyan sandstones. The angular grains are either contributed due to erosion of primary rocks of Bundelkhand gneissic complex and or various Gangetic alluviums. The magnetic properties from sediment samples indicate that the antiferromagnetic minerals (illite, chlorite and smectite) are more concentrated in clay sized particles and it also indicated mixed source rocks for the bar-top sediment of Tons river.     

粘土矿物研究在塔里木盆地石油勘探中的应用

以塔里木盆地粘土矿物的分布特征及其组合形式、演化与形成机理为依据,探讨了粘土矿物在地层划分对比中的应用及其与有机质热演化、成岩阶段的关系和对储层物性的影响。研究表明,在侏罗系和白垩系两个不同古环境中形成的粘土矿物及其组合特征,为地层对比提供了一定的证据。泥岩中伊利石／蒙皂石间层中蒙皂石含量的纵向变化与有机质热演化及成岩阶段的关系不大。对储层物性影响不大但有利于储集性能的是以高岭石为主的粘土矿物组合类型及粘土矿物的早期自生（伊利石／蒙皂石间层矿物）衬垫式以及非自生（伊利石）衬垫式产状。     

Provenance of Clay Minerals in the Amami Sankaku Basin and Their Paleoclimate Implications Since Late Pleistocene

We analyzed the clay mineral assemblages, content and mineralogical characteristics of Hole U1438A sediment recovered from Amami Sankaku Basin during International Ocean Discovery Program (IODP) expedition 351. The results show that the clay minerals are mainly composed of illite (average 57%), smectite (average 26%), chlorite (average 14%) and minor kaolinite(average 3%). The crystallinity of illite in all samples are good (<0.4 Δ° 2θ), and the chemical indexes of illite in all samples are low (<0.4). Both indicate that illite in Hole U1438A formed in cold and dry climate. By comparing clay mineral assemblages of hole U1438A and the potential sediment sources, we suggest that smectite be mainly derived from the volcanic materials around Amami Sankaku Basin. Illite, chlorite and kaolinite are mainly derived from the Asian dust. The ratios of (illite+chlorite)/smectite show a phased increase over the last 350 ka, which is consistent with the cold and drying trend of the Asian continent since late Pleistocene. The high ratios of (illite+chlorite)/smectite and (illite+chlorite)/kaolinite during glacial period indicate that much more Asian dust was input into the Amami Sankaku Basin, which are responded to the aridity of Asian continent and strengthened east Asian Monsoon during glacial period.     

湘中下石炭统粘土矿物组合特征

湖南中部下石炭统是一套以碳酸盐岩为主夹碎屑岩含煤岩系的沉积,根据粘土矿物在下石岩统剖面分布规律,结合各组段岩性岩相特征,可推断出粘土矿物组合特征及其环境分布,从滨岸碎屑沉积到滨外泥质陆棚、滨外浅水碳酸盐陆棚,到深水碳酸盐陆棚和浅海盆地,即从滨岸向盆地方向,高岭石含量急剧减少,伊利石逐渐增加,伊利石/蒙脱石混层矿物和绿泥石则先是增加,然后又趋于减少,其最高含量分别在浅水碳酸盐陆棚和滨外泥质陆棚。测水组含煤岩系粘土矿物以高岭石为主,伊利石次之,并有一定量的绿泥石和伊利石/蒙脱石混层矿物,它们在垂向上的变化反映了沉积环境水介质酸碱度和盐度的变化规律。     

鸡西盆地下白垩统城子河组-穆棱组露头砂岩中的黏土矿物成因探讨

对鸡西盆地下白垩统城子河组—穆棱组露头砂岩中的黏土矿物进行了X-衍射分析。研究结果表明,黏土矿物主要由伊利石,高岭石和伊/蒙混层组成,组合可分为高岭石型与伊/蒙混层和伊利石型两种,根据黏土矿物组合判断露头砂岩处于中成岩阶段A期。下白垩统城子河组—穆棱组煤系地层和泥岩成岩过程中析出的有机酸是高岭石型黏土矿物组合发育的重要原因,而沉积相带水动力条件弱导致砂岩渗滤条件的变差则是伊/蒙混层和伊利石型黏土矿物组合形成的原因。     

Characteristics of Clay Minerals in the Luohe Formation in Zhenyuan Area,Ordos Basin,and its Uranium Prospecting SignificanceEI北大核心CSCD

Industrial uranium orebodies have recently been found through in-depth uranium exploration in the Luohe Formation in the southwestern Ordos Basin, which is an important breakthrough in deep prospecting for sandstone-type uranium deposits. The composition, content and characteristics of clay minerals in the Luohe Formation in the Zhenyuan area were systematically studied by means of thin section identification, scanning electron microscopy, X-ray diffraction and altered mineral spectral scanning. Unlike the most important uranium-bearing rock series in the Zhiluo Formation in the northeast and southwest of the basin, the ore-bearing Luohe Formation sandstone has low contents of clay minerals while the clay mineral assemblages vary in different sand bodies. Among them, the main types of mudstone, oxidized sandstone, calcareous sandstone and mineralized sandstone are illite-smectite mixed-layer mineral and illite, followed by kaolinite and chlorite, the main types uranium-rich sandstone and gray-green sandstone are kaolinite and illite-smectite mixed-layer mineral, followed by illite and chlorite. Even though adsorption of clay minerals, such as chlorite, illite-smectite mixed-layer mineral, kaolinite, and illite may contribute to U enrichment and uranium mineral precipitation, no correlation between clays and uranium minerals have been observed, indicating that clay minerals are not the main factor affecting uranium enrichment during the deep metallogenic process. The study of clay minerals in the Luohe Formation sandstone demonstrated that there are at least two phases of chlorite and one phase of kaolinite in the study area, which respectively represent two phases of alkaline fluid and one phase of acid fluid activities, revealing a fluid phase transition of alkaline-acidic-alkaline. Therefore, the clay minerals can be used as an important indicator for uranium mineralization. © 2020, Science Press. All right reserved.     

安徽池州地区下蜀组沉积环境及成因探讨

采用磁化率、黏土矿物测试及粒度分析等手段,结合区域第四纪地质特征,从气候演变和岩相古地理等角度探讨了安徽池州地区下蜀组的沉积环境及成因。该区下蜀组磁化率曲线呈波峰、波谷旋回特征;黏土矿物以伊利石为主,个别层位以蒙脱石、高岭石、绿泥石为主;粒度以粉砂为主,个别层位以粉砂及中粗砂为主。下蜀组沉积期间存在多次寒冷干燥到温暖潮湿的气候转换,整体为寒冷干燥气候的风成沉积,受古地理位置影响,沿江局部地区夹温暖潮湿气候条件下的长江水系冲积沉积。     

Characterization of a Lacustrine Shale Reservoir and the Evolution of its Nanopores: A Case Study of the Upper Cretaceous Qingshankou Formation in the Songliao Basin,Northeastern China

The Songliao Basin is one of the most important petroliferous basins in northern China. With a recent gradual decline in conventional oil production in the basin, the exploration and development of unconventional resources are becoming increasingly urgent. The Qingshankou Formation consists of typical Upper Cretaceous continental strata, and represents a promising and practical replacement resource for shale oil in the Songliao Basin. Previous studies have shown that low-mature to mature Qingshankou shale mainly preserves type Ⅰ and type Ⅱ1 organic matter, with relatively high total organic carbon(TOC) content. It is estimated that there is a great potential to explore for shale oil resources in the Qingshankou Formation in this basin. However, not enough systematic research has been conducted on pore characteristics and their main controlling factors in this lacustrine shale reservoir. In this study, 19 Qingshankou shales from two wells drilled in the study area were tested and analyzed for mineral composition, pore distribution and feature evolution using Xray diffraction(XRD), scanning electron microscopy(SEM), low-pressure nitrogen gas adsorption(N2-GA), and thermal simulation experiments. The XRD results show that clay, quartz, and feldspar are the dominant mineral constituents of Qingshankou shale. The clay minerals are mostly illite/smectite mixed layers with a mean content of 83.5%, followed by illite, chlorite, and kaolinite. There are abundant deposits of clay-rich shale in the Qingshankou Formation in the study area, within which many mineral and organic matter pores were observed using SEM. Mineral pores contribute the most to shale porosity;specifically, clay mineral pores and carbonate pores comprise most of the mineral pores in the shale. Among the three types of organic matter pores, type B is more dominant the other two. Pores with diameters greater than 10 nm supply the main pore volume;most are half-open slits and wedge-shaped pores. The total pore volume had no obvious linear relationship with TOC content, but had some degree of positive correlation with the content of quartz + feldspar and clay minerals respectively. However, it was negatively correlated with carbonate mineral content. The specific surface area of the pores is negatively related to TOC content, average pore diameter, and carbonate mineral content. Moreover, it had a somewhat positive correlation with clay mineral content and no clear linear relationship with the content of quartz + feldspar. With increases in maturity, there was also an increase in the number of carbonate mineral dissolution pores and organic matter pores, average pore diameter, and pore volume, whereas there was a decrease in specific surface area of the pores. Generally, the Qingshankou shale is at a low-mature to mature stage with a TOC content of more than 1.0%, and could be as thick as 250 m in the study area. Pores with diameters of more than 10 nm are well-developed in the shale. This research illustrates that there are favorable conditions for shale oil occurrence and enrichment in the Qingshankou shale in the study area.     

海南岛周边海域表层沉积物中粘土矿物组合及其气候环境意义

X射线衍射分析结果显示,海南岛周边海域表层沉积物中粘土矿物主要由伊-蒙混层矿物、伊利石、高岭石和绿泥石等组成,其含量分别为34.2%,27.3%,21.1%和17.4%。采用人工判别分区和Q型聚类分析分区相结合的方法,将研究区按粘土矿物的相对含量和分布水深,划分出3个粘土矿物组合区,各分区的矿物组合特点显示它们的赋存现状受控于各种粘土矿物本身的粒度、形态特征、水动力条件和水深等因素。在南海海域首次鉴别出有较高含量的伊-蒙混层矿物存在,根据前人对伊-蒙混层矿物、伊利石和高岭石所指示气候条件的研究结果和本研究区内这些表层粘土矿物的含量、组合特征,判断海南岛及周边区域1 500 a以来一直处于比较温湿的气候环境。     

Clay minerals in SW Indian continental shelf sediment cores as indicators of provenance and palaeomonsoonal conditions: a statistical approach

Two sediment cores from the inner continental shelf of SW India, SK‐148/13 (4.66 m long; from 50 m water depth) and SK‐148/14 (5.37 m long; from 22 m water depth), were studied for provenance and palaeomonsoonal implications. Sediment layers at different depth intervals in these cores were estimated for clay minerals and organic matter content. Five surface sediment samples from the nearby Kali River estuary of the adjacent hinterland were also analysed for clay mineral contents. In both cores and Kali River sediments, smectite is the dominant clay followed by illite, and kaolinite or chlorite. Based on the similarities of the abundances of clay minerals and their relative wt‐% in the inner shelf sediment cores and in surface sediments of the estuary as demonstrated by significance tests, Al‐rich illite, and negligible contribution of clay from the deep‐sea and aeolian sources, it can be inferred that the sediments of the two inner continental shelf cores were derived from the adjacent hinterland. Application of statistical discordancy and significance tests on the down‐core variations in the crystallinity index (CI) of illite and organic matter content in the sediment cores indicates intense monsoonal (high rainfall) conditions at the adjacent hinterland during about 4300–6200 and 9300–10,400 years BP. These inferences are comparable to those from other well‐established palaeomonsoonal indicators such as sedimentation rates and mineral magnetic properties. The CI of illite, an easily determinable and climatically sensitive parameter, can thus be a reliable palaemonsoonal indicator for inner shelf sediment cores. The statistical methodology used in this work highlights the advantages of a quantitative interpretation of the data instead of the conventional qualitative visual examination.     

准噶尔盆地南缘新生界粘土矿物分布及影响因素

根据粘土矿物的相对含量研究了准噶尔盆地南缘新生界砂岩粘土矿物类型、组合特征及纵、横向分布规律及其主要影响因素。划分出无序伊/蒙混层型、部分有序伊/蒙混层型、伊利石+伊/蒙混层型、蒙皂石型以及含坡缕石型等5类粘土矿物组合。按照伊/蒙混层相对含量的变化,粘土矿物纵向上演化呈正常转化型(伊/蒙混层相对含量降低)、反向转化型(伊/蒙混层相对含量增加)和“S”型(伊/蒙混层相对含量呈曲线变化)3种形式。平面上,伊/蒙混层和伊利石这两类主要粘土矿物从湖盆的边缘向中心分别呈现减少和增多的趋势,湖盆边缘相带以无序伊/蒙混层型、蒙皂石型和含坡缕石型为主,湖盆中心则为部分有序伊/蒙混层型和伊利石+伊/蒙混层型组合等类型。上述分布规律的控制因素主要有沉积环境、构造运动及层序发育等。     

台湾海峡表层沉积物中黏土矿物特征及物质来源

利用X射线衍射仪,对比分析台湾海峡及周边表层沉积物的黏土矿物特征,讨论长江、福建和台湾河流对海峡黏土矿物的贡献程度。福建河流（闽江）的黏土矿物以高岭石为主（>40％）,其次是伊利石（30％）和绿泥石,不含蒙脱石;长江和浙闽泥质区的黏土矿物特征是伊利石含量最高（61％～66％）,其次是绿泥石（16％～17％）和高岭石（10％～13％）,少量蒙脱石（6％～9％）。台湾河流（浊水溪）黏土矿物组合为伊利石（>70％）和绿泥石,不含高岭石和蒙脱石为特征。台湾海峡高岭石含量由西向东明显减少,说明高岭石主要来自福建的河流。〖JP2〗台湾海峡50 m等深线以东区域的黏土矿物具有高的伊利石和绿泥石含量,低的蒙脱石和高岭石含量,且伊利石的化学指数和结晶度值都明显低于长江和福建的河流,反映台湾河流的物质来源。在台湾暖流作用下,台湾河流为台湾海峡中北部提供了大量的伊利石和绿泥石。福建近海的黏土矿物主要是由福建河流提供的,但在平潭岛周边海域的黏土矿物可能有长江物质的混合。〖JP〗     

Diagenesis of clay minerals and K-bentonites in Late Permian/Early Triassic sediments of the Sichuan Basin (Chaotian section,Central China)

Detailed clay mineralogical analyses were carried out on Late Permian/Early Triassic carbonate sediments exposed on the Chaotian section (Sichuan Basin, Central China). The clay assemblages are dominantly composed of illite in platform carbonates and clay seams, and illite–smectite mixed-layers (I/S) in tuff layers (K-bentonites) intercalated in the carbonate succession. Detrital and authigenic volcanogenic clay minerals have been partially replaced through illitisation processes during burial, raising questions about diagenetic effects. The precise determination of I/S occurring in K-bentonites shows that the sediments reached a temperature of about 180 °C, which is consistent with (1) previous estimates based on fluid-inclusion homogenisation temperature analysis, (2) the burial depth of the sedimentary series deduced from the post-Palaeozoic geological history of the Sichuan Basin and (3) the new data (T_max) obtained on organic matter indicating the transition between oil and gas windows. The Wangpo Bed, located close to the Guadalupian–Lopingian Boundary, is interpreted either as a volcanic acidic tuff or as a clastic horizon. This controversial origin probably results from mixed volcanogenic and detrital influences. The Wangpo Bed is therefore interpreted as a reworked bentonite as revealed by the occurrence of I/S similar to those found in tuff layers, together with preserved detrital kaolinite.     

Paleoclimate and Paleoenvironment of Gonghe Basin, Qinghai-Tibet Plateau, During the Lastdeglacial: Weathering, Erosion and Vegetation Cover Affect Clay Mineral Formation

With the analysis of the sources and formation mechanism of the clay minerals in the sediment core from the Dalianhai lake in the Gonghe Basin,northeastern Tibet-Qinghai Plateau,clay mineral composition proxies,grain-size and carbonate contents have been employed for high-resolution study in order to reconstruct East Asian Summer Monsoon （EASM） over the northeastern Tibet-Qinghai Plateau during the lastdeglacial.The study also extended to establish a relationship between vegetation cover changes and erosion during the last 14.5 ka with pollen record and clay mineral proxies.Smectite/kaolinite and smectite/（illite＋chlorite） ratios allow us to assess hydrolysis conditions in lowlands and/or physical erosion process in highlands of the Gonghe Basin.Before 12.9 Cal ka BP,both mineralogical ratios show low values indicative of strong physical erosion in the basin with a dominant cold and dry phase.After 12.9 Cal ka BP,an increase in both mineralogical ratios indicates enhanced chemical weathering in the basin associated with a warm and humid climate.The beginning of Holocene is characterized by high smectite/（illite＋chlorite） and smectite/kaolinite ratios that is synchronous as with deposition of many peat laminae,implying the best warm and humid conditions specifically between 8.0 to 5.5 Cal ka BP.The time interval after 5.0 Cai ka BP is characterized by a return to high physical erosion and low chemical weathering with dry climate conditions in the basin.Comparing variations of clay mineral assemblages with previous pollen results,we observe a rapid response in terms of chemical weathering and physical erosion intensity to a modification of the vegetation cover in the basin.     

辽河坳陷古近系碎屑岩储层孔隙演化特征探讨

辽河坳陷古近系的沉积特征是物源多、沉积体系多、砂岩成熟度低及砂体规模小。通过成岩作用和成岩相研究，储层成岩相可划分为4种,即碳酸盐胶结相、自生粘土矿物胶结相、石英胶结相和粘土矿物转化相。这4个相可进一步划分为7个亚相：自生粘土膜胶结亚相、晶粒状碳酸盐胶结亚相、自生高岭石胶结亚相、石英胶结亚相、嵌晶状碳酸盐胶结亚相、伊/蒙混层亚相和伊利石亚相。不同成岩相分布明显受深度控制，具有在垂向相连的展布特征，垂向上可组成6个成岩相带。通过大量的砂岩和泥岩孔渗数据统计分析，建立了6个对应的高孔渗带（ABCDEF）与6个低孔渗带（abcdef），它们与6个成岩相带在空间分布上具有一一对应关系，即A－a、B－b、C－c、D－d、E－e和F－f分别与晶粒状碳酸盐相带、自生高岭石相带、石英胶结相带、嵌晶状碳酸盐相带、伊／蒙混层粘土矿物相带和伊利石相带相对应。可见,不同成岩相带对应不同孔隙度发育带的孔隙演化，并从有机质演化的角度解释了上述对应关系。应用这一规律在鸳鸯沟地区有利储层孔隙预测中取得了较好效果，验证了该区储层孔隙演化特征及其对油气运聚的影响。