A new species of polycotylid plesiosaur (Reptilia: Sauropterygia) from the Lower Turonian of Utah: Extending the stratigraphic range of Dolichorhynchops

Recent work in the Tropic Shale by the Museum of Northern Arizona reveals a high biodiversity for plesiosaurs along the western margin of the Cretaceous Western Interior Seaway during the Cenomanian and the Turonian. This paper describes a new species of polycotylid plesiosaur from the Tropic Shale, Dolichorhynchops tropicensis, which adds to the known biodiversity from this time period. The identification is based on two specimens, a well-preserved, nearly complete skeleton including the skull and an additional specimen with only fragmentary skeletal elements. The material shares several synapomorphic characters with Dolichorhynchops, including the shape of the temporal fenestrae, the shape of the sagittal crest, the trend of the ectopterygoids, the morphology of the teeth, and the number of teeth within the mandibular symphysis. D. tropicensis differs from other species of Dolichorhynchops in a greater size range of the teeth, moderately constricted dorsal vertebrae, angled anterior processes on the coracoids, and the presence of well-defined facets on the propodials. The specimens are of Early Turonian age (based primarily on ammonite biostratigraphy and bentonite marker beds), and their discovery extends the known stratigraphic range for Dolichorhynchops back by approximately seven million years. This suggests that Dolichorhynchops tropicensis and Trinacromerum bentonianum, a closely related polycotylid, co-existed in the Western Interior Seaway.     

广东小良水土保持观察站花岗岩风化壳磁化率特征及其与生态环境演替的关系

广东小良水土保持科学研究观测站位于北回归线上，是联合国“人与生物圈”定点观察站。本文在野外考察和系统采样的基础上，分别分析了同一花岗岩风化壳上光板地（生态破坏）剖面和生态恢复剖面样品的矿物学、磁化率特征，探讨它们与生态环境演替的关系。结果表明，在不同生态环境下的两剖面，其磁性矿物类型与粒度均不同，磁化率变化规律差异显著。其中，光板地剖面主要载磁矿物为赤铁矿、针铁矿等矿物，磁化率值很低，与含水量之间相关性较差，基本无超顺磁矿物的存在；生态恢复剖面主要载磁矿物为磁铁矿和磁赤铁矿，低频磁化率值较高且与含水量之间具有良好的相关性，频率磁化率随剖面深度增加而递减，表明超顺磁矿物浓度的变化趋势，反映了生物因素对风化壳剖面的影响和改造。通过两剖面的对比研究说明生态系统的参与对风化壳结构的改变非常显著，磁化率特征可以作为表征这种改变的良好的替代指标。     

Stratigraphical architecture at the muddy margin of the Cretaceous Western Interior Seaway, southern Utah

The Tropic Shale and correlative Tununk Shale Member of the Mancos Shale accumulated during Cenomanian-Turonian time, within prodeltaic environments near the western margin of the Western Interior Seaway of North America. Stratigraphical and sedimentological analysis has revealed a detailed history of relative sea level change in the thick, fine grained succession. The Tropic and Tununk shales were deposited during the Greenhorn second-order sea level cycle, over a time span of about 2–5 million years. In southern Utah, six depositional sequences are superposed upon the record of this long term sea level change. The sequences developed during third-order relative sea level cycles of hundreds of thousands of years duration and are composed of at least 37 parasequences, arranged in retrogradational, aggradational and progradational parasequence sets. The Tropic Shale and Tununk Shale Member accumulated just basinward of the axis of maximum subsidence of a foreland basin. Stratal geometries and facies distribution patterns in the succession indicate that in southern Utah the Greenhorn cycle was tectonically controlled. During the Greenhorn transgression and highstand, rapid rates of tectonic subsidence trapped terrigenous sediment to the west of the study area, in the more proximal foreland. At this time, hemipelagic facies accumulated at relatively slow rates in southern Utah and type 2 sequences developed during third-order sea level cycles. In contrast, during the Greenhorn regression rates of thrust-induced subsidence in the proximal foreland basin evidently slowed, and deltaic clinoforms prograded across the study area. At least one forced regression occurred in southern Utah at this time, and type 1 sequences developed. The formation of type 1 sequence boundaries in the upper part of the Tropic Shale and Tununk Shale Member points to episodes of base level fall and indicates that the six third-order sea level cycles recorded in the succession were not the result of changes in sediment supply alone. The third-order cycles may have been a consequence of episodic tectonism. The timing of these cycles, however, suggests that development of sequences and parasequences in the Tropic Shale and Tununk Shale Member may have been related to orbital forcing in the Milankovitch band. Glacioeustasy or climatically related fluctuations in the amount of groundwater stored on continents may explain these high frequency sea level changes.     

中国南方海相油气勘探研究新进展

中国南方海相油气勘探研究取得６个方面的进展；１．重塑了华南板块的四个构造演化阶段，将华南板块划分出三个构造区，一个火山岩区和两个造山带，并了南方构造格架与演化对油气地质条件的控制．２．分析了华南板块南北两个大陆边缘沉积盆地的二级超旋回层序，凝缩层段及其与烃源岩发育的关系，并重点分析了区域性四套主力烃源岩的特点；３．提出了华南板块北南两个前陆盆地带的发育对中国南方海相油气的后期保存起着重要的作用。     

川东地区华蓥山海相三叠系不同类型岩石对海水信息的保存性评估

通过对川东地区华蓥山海相三叠系不同岩石类型样品的微观组构、阴极发光和微量元素等分析表明:川东地区华蓥山海相三叠系不同的岩石类型样品具有不同的抵抗成岩蚀变能力,其对海水信息的保存程度也不一致;钙质泥岩所记录的有关信息已基本不能代表海水,多数微晶灰岩所记录的有关信息可以较好地代表海水,而粉晶白云岩只有部分样品可以代表海水的...     

Geomorphology and sedimentary/biosedimentary structures of the intertidal environment along the coast of Kuwait,north-western Arabian Gulf

The coast of Kuwait can be divided into nine intertidal geomorphological subunits, of which four are found along the northern muddy shoreline and five along the southern sandy shoreline. In the north the coast is characterized by wide intertidal mudflats, bounded landward by an extensive coastal sabkha which is partly covered by sand drifts. The upper part of the intertidal environment is covered with a mixture of aeolian sands and muddy sediments of marine origin. A number of shallow tidal channels dissect the intertidal flats and small sand bars occur near the low water line. In contrast, the southern shore is characterized by relatively steep sandy beaches fronted by narrow to moderately wide rocky intertidal platforms which are partly covered by sand, bioherms, skeletal debris and algal mats. In some areas the rocky surface is dissected by numerous small gulleys and shallow channels. Multiple sand bars lying either parallel or diagonal to the shoreline are developed near the low water line. This southern intertidal environment is bounded landward by a sandy berm and a wave-cut cliff.Ripple marks are developed almost parallel to the shoreline, showing different flow directions. Energy levels are moderate to high along the southern shore, but low along the northern shore. In the south, waves induced by winds blowing mostly from the north-east and south-east form the dominant energy source, whereas tidal and wind-driven currents are the only tangible process acting along the northern shore.     

桦甸盆地桦甸组油页岩段地球化学特征及地质意义

桦甸盆地位于敦密断裂带之上,是我国著名的古近纪含油页岩断陷盆地。其中桦甸组油页岩段发育厚层的泥岩沉积。长期以来对该段油页岩特征研究较多,但对其物源区特征和构造背景研究甚少。对油页岩段厚层泥岩进行系统的地球化学分析结果表明：泥岩中w(SiO₂)整体较低,K₂O/Na₂O值较高(大于1),w（MgO+Fe₂O^T₃）为3.91%~11.66%,Al₂O₃/（Na₂O+K₂O）为3.77~6.29,表明泥岩中含有一定的铁镁质组分和较多的稳定组分。微量元素PAAS标准化分配曲线显示不同样品之间元素富集、亏损趋势不一致,同时稀土元素标准化曲线呈现出稀土含量变化较大、轻稀土富集和明显Eu负异常,表明油页岩段沉积时期存在多个物源。泥岩风化蚀变指数为74~82,Th/U值多集中在4.65~6.07,表明泥岩源区经历了相对中等的风化作用。Th/Sc和Zr/Sc值表明泥岩基本受源岩成分控制。由源岩和构造背景判别图解,并结合前人研究资料得知:桦甸盆地油页岩段母岩主要来自于海西期和燕山期花岗岩以及少量的燕山期中酸性喷发岩;源岩形成于大陆边缘造山带,为大陆岛弧火山岩系。     

塔西台地寒武纪沉积环境演化与海陆耦合

碳酸盐岩台地作为陆地与深海间的过渡带,其沉积记录了海洋和邻近陆地的演化。结合已有的沉积学工作,对塔里木盆地西部台地寒武系碳酸盐岩进行全岩及酸不溶物地球化学研究。塔西台地寒武纪主要发育局限台地、局限-蒸发台地或蒸发台地相沉积。碳酸盐岩的地球化学特征主要受沉积环境和成岩作用影响,对研究区寒武系白云岩来说,其元素组成极易受沉积微相的控制,氧同位素组成则很可能已被成岩作用改造,仅原生、准同生白云岩的Sr/Ba、Fe/Mn和C同位素可反映沉积相演化对应的古盐度、离岸距离等沉积环境特征的变化,酸不溶物化学蚀变指数（CIA值）则指示邻近陆地的化学风化强度与气候特征。寒武纪时期,塔西台地在相对海平面较高时发育局限台地相沉积,以水体盐度较低、沉积环境离岸较远和生物活动相对较弱为特征,陆地化学风化强度适中,气候温暖湿润;在相对海平面较低时发育蒸发台地相沉积,具有水体盐度较高、沉积环境离岸较近和生物活动相对较强等特点,陆地化学风化强烈,气候炎热极端;在相对海平面适中时发育局限-蒸发台地,沉积环境和邻近陆地的特征介于前述二者之间。沉积相演化对应的较长周期的海陆演化可能主要受全球海平面升降及宏观气候变化控制,具体表现为相对海平面升降所导致的海相沉积环境的变化,以及气候变化引起的陆地化学风化强度的变化。寒武纪塔西台地所处区域的海洋-陆地演化具有高度耦合的特征。     

Weathering of the New Albany Shale, Kentucky: II. Redistribution of minor and trace elements

During weathering, elements enriched in black shale are dispersed in the environment by aqueous and mechanical transport. Here a unique evaluation of the differential release, transport, and fate of Fe and 15 trace elements during progressive weathering of the Devonian New Albany Shale in Kentucky is presented. Results of chemical analyses along a weathering profile (unweathered through progressively weathered shale to soil) describe the chemically distinct pathways of the trace elements and the rate that elements are transferred into the broader, local environment. Trace elements enriched in the unweathered shale are in massive or framboidal pyrite, minor sphalerite, CuS and NiS phases, organic matter and clay minerals. These phases are subject to varying degrees and rates of alteration along the profile. Cadmium, Co, Mn, Ni, and Zn are removed from weathered shale during sulfide-mineral oxidation and transported primarily in aqueous solution. The aqueous fluxes for these trace elements range from 0.1 g/ha/a (Cd) to 44 g/ha/a (Mn). When hydrologic and climatic conditions are favorable, solutions seep to surface exposures, evaporate, and form Fe-sulfate efflorescent salts rich in these elements. Elements that remain dissolved in the low pH (<4) streams and groundwater draining New Albany Shale watersheds become fixed by reactions that increase pH. Neutralization of the weathering solution in local streams results in elements being adsorbed and precipitated onto sediment surfaces, resulting in trace element anomalies.Other elements are strongly adsorbed or structurally bound to solid phases during weathering. Copper and U initially are concentrated in weathering solutions, but become fixed to modern plant litter in soil formed on New Albany Shale. Molybdenum, Pb, Sb, and Se are released from sulfide minerals and organic matter by oxidation and accumulate in Fe-oxyhydroxide clay coatings that concentrate in surface soil during illuviation. Chromium, Ti, and V are strongly correlated with clay abundance and considered to be in the structure of illitic clay. Illite undergoes minimal alteration during weathering and is concentrated during illuvial processes. Arsenic concentration increases across the weathering profile and is associated with the succession of secondary Fe(III) minerals that form with progressive weathering. Detrital fluxes of particle-bound trace elements range from 0.1 g/ha/a (Sb) to 8 g/ha/a (Mo). Although many of the elements are concentrated in the stream sediments, changes in pH and redox conditions along the sediment transport path could facilitate their release for aqueous transport.     

Compound-specific isotopic analyses: a novel tool for reconstruction of ancient biogeochemical processes

Patterns of isotopic fractionation in biogeochemical processes are reviewed and it is suggested that isotopic fractionations will be small when substrates are large. If so, isotopic compositions of biomarkers will reflect those of their biosynthetic precursors. This prediction is tested by consideration of results of analyses of geoporphyrins and geolipids from the Greenhorn Formation (Cretaceous, Western Interior Seaway of North America) and the Messel Shale (Eocene, lacustrine, southern Germany). It is shown (i) that isotopic compositions of porphyrins that are related to a common source, but which have been altered structurally, cluster tightly and (ii) that isotopic differences between geolipids and porphyrins related to a common source are equal to those observed in modern biosynthetic products. Both of these observations are consistent with preservation of biologically controlled isotopic compositions during diagenesis. Isotopic compositions of individual compounds can thus be interpreted in terms of biogeochemical processes in ancient depositional environments. In the Cretaceous samples, isotopic compositions of n-alkanes are covariant with those of total organic carbon, while delta values for pristane and phytane are covariant with those of porphyrins. In this unit representing an open marine environment, the preserved acyclic polyisoprenoids apparently derive mainly from primary material, while the extractable, n-alkanes derive mainly from lower levels of the food chain. In the Messel Shale, isotopic compositions of individual biomarkers range from -20.9 to -73.4% vs PDB. Isotopic compositions of specific compounds can be interpreted in terms of origin from methylotrophic, chemautotrophic, and chemolithotrophic microorganisms as well as from primary producers that lived in the water column and sediments of this ancient lake.     

Differential diagenesis of strontium in archaeological human dental tissues

The investigation of prehistoric human migration from the measurement of Sr-isotope ratios within preserved tissue is critically dependent on the preservation of biogenic Sr. A number of recent studies have involved isotope ratio measurements on samples of archaeological tooth and bone, but doubt remains as to the extent of diagenesis in various skeletal tissues and the effectiveness of procedures designed to decontaminate them. The authors have compared Sr abundance and isotope ratios in enamel and dentine from archaeological teeth in order to assess the integrity of the biogenic Sr signal preserved within the respective tissues. It is concluded that enamel appears, in most cases, to be a reliable reservoir of biogenic Sr, but that dentine, and by implication bone, is not. The diagenesis of dentine is highly variable even between burials within a single site. For the majority of teeth, dentine diagenesis was not simply by addition of soil-derived Sr, but involved substantial, sometimes complete, turnover of the original biogenic material. It is suggested that, for most of the samples investigated, current decontamination techniques may not have been effective in isolating biogenic Sr from dentine. Similar considerations are likely to apply to archaeological and fossil bone, but the possibility arises to use dentine and enamel measurements to assess the effectiveness of decontamination procedures which may then be used for bone.     

Selective preservation of soil organic matter in oxidized marine sediments (Madeira Abyssal Plain)

In ocean margin sediments both marine and terrestrial organic matter (OM) are buried but the factors governing their relative preservation and degradation are not well understood. In this study, we analysed the degree of preservation of marine isoprenoidal and soil-derived branched glycerol dialkyl glycerol tetraethers (GDGTs) upon long-term oxygen exposure in OM-rich turbidites from the Madeira Abyssal Plain by analyzing GDGT concentrations across oxidation fronts. Relative to the anoxic part of the turbidites ca. 7-20% of the soil-derived branched GDGTs were preserved in the oxidized part while only 0.2-3% of the marine isoprenoid GDGT crenarchaeol was preserved. Due to these different preservation factors the Branched Isoprenoid Tetraether (BIT) index, a ratio between crenarchaeol and the major branched GDGTs that is used as a tracer for soil-derived organic matter, substantially increases from 0.02 to 0.4. Split Flow Thin Cell (SPLITT) separation of turbidite sediments showed that the enhanced preservation of soil-derived carbon was a general phenomenon across the fine particle size ranges (<38 μm). Calculations reveal that, despite their relatively similar chemical structures, degradation rates of crenarchaeol are 2-fold higher than those of soil-derived branched GDGTs, suggesting preferential soil OM preservation possibly due to matrix protection.     

Taphonomic history of a ‘duck-bill’ dinosaur (Dinosauria: Ornithopoda) from the Cerro del Pueblo Formation (Upper Cretaceous,Campanian) Coahuila,Mexico: Preservational and paleoecological implications

The Cerro del Pueblo Formation in the state of Coahuila, Mexico is becoming recognized worldwide due to its abundant and diverse fossil material. While most previous paleontological work from this rock unit has been directed towards taxonomic investigation, this study is directed towards the taphonomy of a “duck-billed” dinosaur (Ornithischia: Hadrosauridae). The hadrosaur skeleton is represented by several skull bones, vertebrae and ribs, a scapula, pubis, and various appendicular elements. The following taphonomic parameters were considered: (1) bone frequency; (2) hydraulic equivalence; (3) degree of bone articulation; (4) abrasion; (5) weathering; (6) breakage; (7) tooth marks; and (8) trampling activities. The low degree of weathering and abrasion suggests that the specimen experienced a short time of subaerial exposure and underwent a short transportation distance before deposition. Burial occurred within a perimarine lagoonal environment. Furthermore, the lack of hydraulic equivalence with the rock matrix, a high degree of disarticulation and a chaotic distribution of the bones in the fossiliferous bed, suggest that it was transported as a “bloated carcass”. The finding of distinct types of tooth marks evidence some sort of predator/scavenging activities on the specimen. Finally, an almost vertical orientation of various bones and the presence of spiral fractures may indicate that these elements were trampled by other animals.     

龙门山泥盆纪腕足化石锶同位素组成特征及其古环境意义

生物成因的海相碳酸盐岩中Sr同位素组成与演化是目前研究古海平面变化、造山运动以及古气候变化的主要工具,在海相地层定年及全球等时对比研究中发挥着重要作用。对四川龙门山泥盆纪剖面腕足化石Sr同位素组成进行了研究。保存鉴定结果显示：腕足化石壳体结构保存完整;阴极射线照射下壳体不发光或部分壳体呈微弱橙黄色;大多数壳体微量元素Mn〈250μg／g、Sr〉400μg／g。表明腕足化石保存完好,后期成岩作用影响微弱。锶同位素结果显示：龙门山泥盆纪sr同位素演化同全球泥盆纪Sr同位素演化基本一致,表明龙门山泥盆纪Sr同位素演化受全球性变化影响。早泥盆世较高Sr同位素比值（甘溪组0．708437）可能是受加里东造山运动的影响,大量古陆的出露,风化作用的加强所致。其后的缓慢下降可能受海平面上升古陆面积缩小的影响。中泥盆世Sr同位素组成低值平台显示着幔源Sr和陆源Sr（风化作用较弱）输入量之间的平衡。随后的Sr同位素组成的上升可能是受中泥盆世开始温度上升的影响,致使风化作用的加强所致。     

罗平生物群的发现与研究进展——据云南1:5万罗平县等四幅区调和专题调查成果

成都地质调查中心云南区调项目组2007年在罗平县中三叠统关岭组二段中发现了罗平生物群。罗平生物群是三叠纪的化石宝库,化石包含了脊椎动物和无脊椎动物。脊椎动物以海生爬行类和鱼类为主。无脊椎动物以节肢动物为主,伴生有双壳类、腹足类、菊石、棘皮动物、腕足类、牙形石、有孔虫和植物类化石。牙形石研究显示罗平生物群处于Nicoraella kockeli牙形石带,时代上属于中三叠世安尼期Pelsonian亚期。罗平生物群保存在一个局限的台盆环境中。其化石的特异保存很可能与底层水缺氧和微生物席的密封作用有关。罗平生物群目前是研究三叠纪海洋生态系统复苏的最好的一扇窗口,也是三叠纪海生鱼类和节肢动物化石保存最好的产地之一,为研究二叠纪末大绝灭后海洋生态系统复苏以及中生代海洋生态系统的演化历史提供了新材料。     

试论动物非矿化组织的保存

动物非矿物化组织在特异埋葬条件下可保存为化石。缺氧和快速埋葬有利于非矿化组织的保存，但不能阻止微生物的破坏作用。无菌环境下可保存软躯体组织，但在构造变动和古气候变迁等因素的影响下会彻底破坏，不可能在地质历史时期长期存在。最稳定的保存形式是与成岩作用有关的保存类型和以碳化有机质薄膜形式的保存类型。与动物非矿化组织保存有关的常见成岩自生矿物有磷酸盐矿物、碳酸盐矿物和黄铁矿等。其中，磷酸盐矿物在成岩作用过程中结晶最早，可以保存动物的微细构造。这些矿物可以矿化交代动物的肉质和角质使其成为矿化实体；也可以呈假形、铸型或铸模等形式保存。布尔吉斯页岩保存类型中，非矿化组织以碳化有机质薄膜或含水的颧硅酸盐矿物两种形式保存。前可能与粘土矿物吸附有机质、阻止酶的降解作用有关，后可能由自生粘土矿物的交代作用造成。     

Sedimentary organic matter in condensed sections from distal oxic environments: examples from the Mesozoic of SE France

A detailed analysis of sedimentary organic matter (or palynofacies) was carried out on thermally immature to early mature Upper Jurassic and Hauterivian condensed intervals in deep-sea carbonate–marl alternations outcropping in the Vocontian Basin (SE France). All the condensed sections studied are characterized by intense bioturbation and very low organic carbon content (< 0·25 wt.%), indicative of oxic depositional conditions. Oxic condensed sections display variable palynofacies signatures, which are best illustrated by: (1) the ratio of continental to marine constituents; (2) the ratio of opaque to translucent phytoclasts (i.e. woody debris) and (3) the preservation of palynomorphs (based on fluorescence intensity and morphological preservation state in transmitted light microscopy). Both of the ratios increase with the degree of palynomorph degradation, which shows that phytoclasts, especially the opaque ones, become relatively concentrated in the most degraded facies. These observations lead to the classification of oxic condensed sections into three organic facies types showing different degrees of preservation and palynofacies signatures. Type 1 organic facies display intense degradation and are characterized by high values of the ratio of continental to marine fraction. They record unfavourable depositional environments for preservation of organic matter. Type 2 organic facies are most common and are characterized by a decreasing value of the ratio of continental to marine fraction. Type 3 organic facies display the same trend of the ratio of continental to marine fraction as type 2, but the palynomorph assemblage is better preserved. Type 1 and type 3 organic facies are relatively rare. Recognizing these organic facies types is important when analysing the relationship between sedimentary organic matter and sequence stratigraphy, because it allows the use of the appropriate palynofacies parameters. In particular, the use of the ratio of continental to marine constituents, usually a very good indicator of regressive–transgressive trends, becomes questionable in highly degraded intervals. Moreover, distinguishing between well-preserved or highly degraded palynofacies in condensed intervals provides valuable information on the oxicity of the depositional environment.     

Relationships between lithology and diagenesis in a limeston—marl facies transition: an electron microprobe study

A 3 km long lateral facies transition from Oligo-Miocene skeletal grainstones into packstones and mudstones displays systematic variation in carbonate skeletal fragment alteration and secondary carbonate mineral composition. Within the skeletal grainstone end-member all aragonitic grains have dissolved, all Mg-calcite skeletal fragments have altered to calcite, and calcite has been precipitated as both void-filling spar and as syntaxial overgrowths on echinoid fragments. Within the transitional grainstone-packstone lithologies some skeletal fragments show preservation of their original mineralogy, while calcite, ferroan calcite spar and dolomite have precipitated in void spaces. Within the packstone-mudstone end-member of the transition, aragonitic grains have been preserved and Mg-calcite skeletal fragments have retained most of their magnesium. Thin, originally porous grainstone layers within the pack-stone-mudstones contain sideroplesite and ferroan calcite spar in void spaces, and iron has been incorporated in skeletal fragments which were originally Mg-calcite. In these grains iron has been incorporated at the expense of magnesium until the grains approach the composition of the surrounding ferroan calcite cement. The lateral variation in diagenetic alteration across this facies transition is a function of differing groundwater movement and composition, controlled ultimately by the composition, porosity and permeability of the host lithologies.     

基于扫描电镜图像和微观渗流模型的云冈石窟砂岩风化特征分析

风化作用、岩石微观结构、岩石微观渗流特性定量关系的研究是石窟文物有效保护的重要基础,砂岩风化作用严重影响了岩体上石窟文物的有效保护。本次研究使用扫描电镜（SEM）获得云冈石窟不同窟体砂岩的微观图像,根据图像增强和图像分割技术得到了岩石中颗粒和孔隙的数字特征参数,从微观角度建立了反映孔喉连接特性的渗流模型,得到了不同窟体岩石的局部水力传导系数,分析了数字特征参数、水力传导系数、风化作用之间的关系。结果表明,风化作用对石窟砂岩微观结构具有很大影响;砂岩孔隙平均长轴长度大小对应的风化程度分别是全风化或强风化、中等风化、微风化或未风化,长度分别为大于40 μm、25～35 μm、15～25 μm;风化程度越高、水力传导系数越大,随着风化程度的增高、水力传导系数的范围为1 × 10?9～1 × 10?4 cm/s;水力传导系数与孔喉尺寸、孔喉连通性密切相关;孔喉半径比增大时、水力传导系数也增大。     

Architecture and preservation in the fluvial to marine transition zone of a mixed-process humid-tropical delta: Middle Miocene Lambir Formation,Baram Delta Province,north-west Borneo

The interaction of river and marine processes in the fluvial to marine transition zone fundamentally impacts delta plain morphology and sedimentary dynamics. This study aims to improve existing models of the facies distribution, stratigraphic architecture and preservation in the fluvial to marine transition zone of mixed-process deltas, using a comprehensive sedimentological and stratigraphic dataset from the Middle Miocene Lambir Formation, Baram Delta Province, north-west Borneo. Eleven facies associations are identified and interpreted to preserve the interaction of fluvial and marine processes in a mixed-energy delta, where fluvial, wave and tidal processes display spatially and temporally variable interactions. Stratigraphic successions in axial areas associated with active distributary channels are sandstone-rich, comprising fluvial-dominated and wave-dominated units. Successions in lateral areas, which lack active distributary channels, are mudstone-rich, comprising fluvial-dominated, tide-dominated and wave-dominated units, including mangrove swamps. Widespread mudstone preservation in axial and lateral areas suggests well-developed turbidity maximum zones, a consequence of high suspended-sediment concentrations resulting from tropical weathering of a mudstone-rich hinterland. Within the fluvial to marine transition zone of distributary channels, interpreted proximal–distal sedimentological and stratigraphic trends suggest: (i) a proximal fluvial-dominated, tide-influenced subzone; (ii) a distal fluvial-dominated to wave-dominated subzone; and (iii) a conspicuously absent tide-dominated subzone. Lateral areas preserve a more diverse spectrum of facies and stratigraphic elements reflecting combined storm, tidal and subordinate river processes. During coupled storm and river floods, fluvial processes dominated the fluvial to marine transition zone along major and minor distributary channels and channel mouths, causing significant overprinting of preceding interflood deposits. Despite interpreted fluvial–tidal channel units and mangrove influence implying tidal processes, there is a paucity of unequivocal tidal indicators (for example, cyclical heterolithic layering). This suggests that process preservation in the fluvial to marine transition zone preserved in the Lambir Formation primarily records episodic (flashy) river discharge, river flood and storm overprinting of tidal processes, and possible backwater dynamics.