Fine Sandstone Research Articles

Effects of CO2 on mechanical variability and constitutive behavior of the Lower Tuscaloosa Formation, Cranfield Injection Site, USA

We characterize geomechanical constitutive behavior of reservoir sandstones at conditions simulating the “Cranfield” Southeast Regional Carbon Sequestration Partnership injection program. From two cores of Lower Tuscaloosa Formation, three sandstone lithofacies were identified for mechanical testing based on permeability and lithology. These include: chlorite-cemented conglomeratic sandstone (Facies A); quartz-cemented fine sandstone (Facies B); and quartz- and calcite-cemented very fine sandstone (Facies C). We performed a suite of compression tests for each lithofacies at 100°C and pore pressure of 30MPa, including hydrostatic compression and triaxial tests at several confining pressures. Plugs were saturated with supercritical CO2-saturated brine.Chemical environment affected the mechanical response of all three lithofacies, which experience initial plastic yielding at stresses far below estimated in situ stress. Measured elastic moduli degradation defines a secondary yield surface coinciding with in situ stress for Facies B and C. Facies A shows measurable volumetric creep strain and a failure envelope below estimates of in situ stress, linked to damage of chlorite cements by acidic pore solutions. The substantial weakening of a particular lithofacies by CO2 demonstrates a possible chemical-mechanical coupling during injection at Cranfield with implications for CO2 injection, reservoir permeability stimulation, and enhanced oil recovery.

Brachiopods from the Cisuralian–Guadalupian of Darvaz, Tajikistan and implications for Permian stratigraphic correlations

In this paper, we describe the upper Cisuralian Safetdara and Gundara formations of the Darvaz mountains, North Pamir, which were part of the Kunlun Arc, developed along the active Eurasian margin. The Safetdara Formation comprises massive limestones (mainly cyanobacterial, Tubiphytes and Archaeolithoporella boundstones) alternating with well-bedded bioclastic and oncoidal limestones and an interval of recessive shales. The formation crops out above the Chelamchi Formation consisting of turbiditic siltstones and sandstones with bioclastic silty limestones yielding massive limestone olistoliths. The Gundara Formation consists of fine sandstones at the base, followed by well-bedded marly bioclastic, oncoidal and microbial limestones, bearing a rich silicified brachiopod fauna in life-position. Two new taxa have been identified in this association: the cemented coralliform Gundaria insolita n. gen. n. sp. and the pedicle attached Hemileurus politus n. sp. The inferred environmental setting is that of shoal deposits of warm, shallow, high energy, clear marine waters for the Safetdara Formation. The agglutinated microbial reefs to cluster reefs of the Gundara Formation were probably growing in a muddier, quieter and probably slightly deeper setting.The foraminifers of the Brevaxina Zone suggest a Bolorian age for the top of the Chelamchi Formation, the Safetdara Formation and the base of the Gundara Formation. Kungurian conodonts have been found in the lower part of the Safetdara Formation. The biostratigraphic data from the sedimentary succession of North Pamir, integrated with those already obtained from Southeast Pamir, allow to refine the correlations between the Tethyan regional scale and the International Time Scale. In particular, it seems now clear that the Bolorian and the lower part of the Kubergandian correlate to the Kungurian.

Early Mississippian sandy siltstones preserve rare vertebrate fossils in seasonal flooding episodes

AbstractFlood‐generated sandy siltstones are under‐recognised deposits that preserve key vertebrate (actinopterygians, rhizodonts, and rarer lungfish, chondrichthyans and tetrapods), invertebrate and plant fossils. Recorded for the first time from the lower Mississippian Ballagan Formation of Scotland, more than 140 beds occur throughout a 490 m thick core succession characterised by fluvial sandstones, palaeosols, siltstones, dolostone ‘cementstones’ and gypsum from a coastal–alluvial plain setting. Sandy siltstones are described as a unique taphofacies of the Ballagan Formation (Scotland, UK); they are matrix‐supported siltstones with millimetre‐sized siltstone and very fine sandstone lithic clasts. Common bioclasts include plants and megaspores, fish, ostracods, eurypterids and bivalves. Fossils have a high degree of articulation compared with those found in other fossil‐bearing deposits, such as conglomerate lags at the base of fluvial channel sandstones. Bed thickness and distribution varies throughout the formation, with no stratigraphic trend. The matrix sediment and clasts are sourced from the reworking of floodplain sediments including desiccated surfaces and palaeosols. Secondary pedogenic modification affects 30% of the sandy siltstone beds and most (71%) overlie palaeosols or desiccation cracks. Sandy siltstones are interpreted as cohesive debris flow deposits that originated by the overbank flooding of rivers and due to localised floodplain sediment transport at times of high rainfall; their association with palaeosols and desiccation cracks indicates seasonally wet to dry cycles throughout the Tournaisian. Tetrapod and fish fossils derived from floodplain lakes and land surfaces are concentrated by local erosion and reworking, and are preserved by deposition into temporary lakes on the floodplain; their distribution indicates a local origin, with sediment transported across the floodplain in seasonal rainfall episodes. These deposits are significant new sites that can be explored for the preservation of rare non‐marine fossil material and provide unique insights into the evolution of early terrestrial ecosystems.

The potassic sedimentary rocks in Gale Crater, Mars, as seen by ChemCam on board Curiosity

AbstractThe Mars Science Laboratory rover Curiosity encountered potassium‐rich clastic sedimentary rocks at two sites in Gale Crater, the waypoints Cooperstown and Kimberley. These rocks include several distinct meters thick sedimentary outcrops ranging from fine sandstone to conglomerate, interpreted to record an ancient fluvial or fluvio‐deltaic depositional system. From ChemCam Laser‐Induced Breakdown Spectroscopy (LIBS) chemical analyses, this suite of sedimentary rocks has an overall mean K2O abundance that is more than 5 times higher than that of the average Martian crust. The combined analysis of ChemCam data with stratigraphic and geographic locations reveals that the mean K2O abundance increases upward through the stratigraphic section. Chemical analyses across each unit can be represented as mixtures of several distinct chemical components, i.e., mineral phases, including K‐bearing minerals, mafic silicates, Fe‐oxides, and Fe‐hydroxide/oxyhydroxides. Possible K‐bearing minerals include alkali feldspar (including anorthoclase and sanidine) and K‐bearing phyllosilicate such as illite. Mixtures of different source rocks, including a potassium‐rich rock located on the rim and walls of Gale Crater, are the likely origin of observed chemical variations within each unit. Physical sorting may have also played a role in the enrichment in K in the Kimberley formation. The occurrence of these potassic sedimentary rocks provides additional evidence for the chemical diversity of the crust exposed at Gale Crater.

Microbially induced sedimentary structures from the 1.64 Ga Chuanlinggou Formation, Jixian, North China

The present study documents abundant exceptionally preserved microbially induced sedimentary structures (MISS) from the 1.64Ga Chuanlinggou Formation of the Jixian area, North China Craton. The Chuanlinggou Formation is dominated by black silty shale/mudstone with fine sandstone of the lower part and was likely deposited in a relatively restricted shallow marine environment varying from fair-weather wave action zone to below storm wave action zone. Both wrinkle structures and sand veins are very abundant in the lower and middle parts of the formation. Wrinkled layers are dark colored, densely laminated, and contain floating quartz grains and abundant mica grains, both of which are aligned parallel to bedding plane. Such an arrangement pattern is attributed to the microbe's binding and trapping of MISS. SEM imaging also shows that sticky networks interwoven by filamentous extracellular polymer substances (EPS) and biofilms, with distinct pores, are very pronounced in clay matrix of wrinkled layers, providing direct evidence of microbial activities during the formation of wrinkle structures. In addition, the circularly arranged quartz grains, forming hollow cavities, and vertical channels of quartz grains beneath the laminated layers are unique to the wrinkle structures showing initial forming stage of the sand veins. Sand veins, similar to fills of sand cracks, are usually preserved in silty shales and occasionally occur beneath the winkled surfaces. They were formed due to methane degassing of decay of microbial mats and biofilms. Abundant nano-particles of various EPSs (isolated nanoglobules, paired nanoglobules, dumbbell-shaped nanoglobules, and polyhedron aggregates) are detected in clay matrix close to sand veins, indicating microbial participation in the formation of sand veins. Wide spatial distribution, broadened environmental inhabitation, and extremely high abundance and bed surface density of the MISSs indicate proliferation of MISS-forming microbial mats in Mesoproterozoic times.

A logging identification method of tight oil reservoir lithology and lithofacies: A case from Chang7 Member of Triassic Yanchang Formation in Heshui area, Ordos Basin, NW China

Abstract Based on the observation results of cores, structural analysis, sedimentary microfacies analysis, lithologic analysis and other analytical tests and logging data, the characteristics of lithology and lithofacies of the Member Chang7 tight oil reservoir of the Triassic Yanchang Formation in Heshui area are described and summarized and the criteria for identification of lithology and lithofacies by logging are established. The lithofacies in the Chang7 tight oil reservoir were classified into five types: fine sandstone deposited by sandy debris flow, turbidite fine siltstone, fine sandstone deposited by slump, semi-deep to deep lacustrine mudstone, and oil shale. The lithology and lithofacies in the Chang7 tight oil reservoir were characterized, both qualitatively and quantitatively, with electric logging and imaging logging and several means and methods, the response characteristics of different lithology and lithofacies were summarized through analyzing the image log and conventional log data, and the parameters characterizing sandstone's structures were used to quantitatively characterize the lithology and lithofacies, the criteria for identification of different lithology and lithofacies by logging were established. The vertical and horizontal identification and classification of lithology and lithofacies in a single well was then accomplished by processing the log data from each well, the results of lithology and lithofacies identification tally well with the results of formation testing. In-depth lithology and lithofacies analysis proves to be an important method of tight oil reservoir evaluation and “sweet spot” prediction.

Geology and taphonomy of the base of the Taquaral Member, Irati Formation (Permian, Paraná Basin), Brazil

AbstractThe taphonomy of Early Permian vertebrates from a sandy facies at the base of the Taquaral Member, Irati Formation, was surveyed in order to acquire data for the interpretation of the sedimentary processes and paleoenvironment of deposition. Six outcrops from the Rio Claro municipality and surrounding areas, from the Brazilian State of São Paulo, were investigated. The vertebrate groups are Chondrichthyes (Xenacanthiformes, Ctenacanthiformes and Petalodontiformes), Osteichthyes (Actinopterygii and Sarcopterygii) and Tetrapodomorpha. They occur as loose teeth, scales, spines and bone remains. The sandy facies is characterized by fining upward deposition. The coarser sandstone immediately above the underlying Tatuí Formation is rich in Chondrichthyes. However, the fine sandstone above, immediately beneath the silty shale facies, is devoid of Chondrichthyes, though Osteichthyes scales, teeth and bones were present. The taphonomy is important for inferring sedimentary processes and then the paleoenvironments. The poor sorting of the sandstone and the presence of fossils that are mostly abraded or worn are indicative of a high energy environment. In contrast, the presence of fossils in a good state of preservation, some without abrasion and breakages are indicative of only limited transport. Differences of fossil spatial density, numbers of specimens and taxa may be explained by the dynamics of deposition, from details of the palaeoenvironment can be obtained.

Application of imaging logging in reservoir geological research

With the ability to provide complete profiles of pseudocolor image formation, IL (imaging logging) measures directionally, thereby offering a possible alternative to drilling and coring. This paper, relying mainly on IL information but also referring to formation dip angle logging information, details sandstone lamina dips and identifies sedimentary body dips, and sums up a practical palaeo-provenance direction judgment method using heavy mineral data analysis. By identifying a fine sandstone reservoir through an IL lithological model, a bedding model and a rhyme model, a 1D pseudoresistivity curve (named the 'IL rhythm curve') is, according to IL image analysis, extracted to assist in the interpretation of sedimentary microfacies and to establish an IL single-well facies analysis profile, overcoming an observance difficulty of IL in silty sandstone regions and intuitively displaying whole-horizon sedimentary evolution. As for a glutenite formation, calibrating IL information by rock cores, a single-well facies sequence of IL is established by identifying the Bouma sequence, high-density turbidity succession, the middle fan braided channel, the outer fan mudstone and other microfacies sequences, finely dividing the sedimentary facies sequence about sedimentary stage.

A diversified vertebrate ichnite fauna from the Feitianshan Formation (Lower Cretaceous) of southwestern Sichuan, China

The Bajiu tracksite exposed on a fine sandstone surface at the top of the Feitianshan Formation, close the contact with the overlying Xiaoba Formation, reveals a saurischian dominated ichnofauna consisting of four sauropod and at least eight theropod trackways. The sauropod trackways display a medium-wide gauge pattern characteristic of titanosauriforms, while the theropod trackways can be subdivided into two distinct morphotypes. One is similar to the ichnogenera Eubrontes and Megalosauripus, the other (cf. Dromaeopodus) appears to represent a functionally didactyl dromaeosaur where pedal digit II is represented only by an oval basal pad. A single swim track is possibly attributable to a turtle or crocodylian. Such sauropod-theropod dominated ichnofaunas are consistently typical of the red-bed tracksites in the region and useful for characterizing a fauna that is otherwise poorly known from body fossils. The stratigraphic position and late occurrence of the (typical Jurassic) Eubrontes-Megalosauripus morphotype is well known from other Cretaceous localities in China and seems to reflect a peculiarity in the theropod faunas of East Asia.

Paleoproterozoic microbially induced sedimentary structures from lagoonal depositional settings in northern China

Microbially induced sand cracks/crack-fills occur extensively on the top surface of fine sandstone beds of the Paleoproterozoic Zhaojiazhuang Formation, Changcheng Group (>1.7Ga) around the Cangyan Mountain, Hebei Province, northern China. Detailed field and microscopic petrographical evidence reveal that these sand cracks/crack-fills possibly resulted from dehydration and desiccation of microbial mats. The age and peculiar morphology of these microbially induced sedimentary structures do not allow comparison with trace fossils or purely physical desiccation cracks. The fine sandstone beds on the surfaces of which these microbially induced sedimentary structures formed were deposited in a lagoon/brackish depositional setting (marine to non-marine transitional setting) with episodic injection of marine water. As such, these microbially induced sedimentary structures suggest the colonization of the marine to non-marine transitional settings in the Paleoproterozoic period, and that the search for evidence of early microbial life should be sought in the marine to non-marine transitional settings. These broad habitats suggest these microbes could have been eurytopic organisms capable of adapting to varying extents of salt and oxygen content variations, like their modern counterparts.

Styles of early diagenesis and the preservation potential of onshore tsunami deposits—A re-survey of Isla Mocha, Central Chile, 2 years after the February 27, 2010, Maule tsunami

The style of early diagenesis and preservation of onshore tsunami deposits are poorly constrained. Only tsunami surveys and subsequent re-surveys can fill this information gap. Here we present the results of a first re-survey in 2012 on Isla Mocha following the original survey in 2010 in the wake of the February 27, 2010, Maule earthquake and tsunami in central Chile. As a result of this tsunami, a large number of boulders consisting of clay-rich fine sandstones representing the Miocene age bedrock of the island had been transferred from the tidal to shallow subtidal zone onto the coastal plain. Coarse clastic sediment mixtures of pebbles, granules, and sand entrained at coastal plain terraces and transported up to the maximum runup position c. 600m from the coast by the inflow had been left behind as extensive backflow blankets on the lower coastal plain.In 2012, vegetation had covered the 2010 tsunami deposits. Sediment beyond 200m from the coast had been removed by a combination of surface processes and grazing cattle. Grain-size distributions of the preserved sediment show an increase of the sand fraction at the expense of the coarser grain sizes. Boulders show patterns resembling mud cracks on the surface and evidence of disintegration into smaller fragments and sand. Veneers of dried algae documenting the derivation of the boulders from the tidal zones had flaked off partly or completely from most rock surfaces. At the northern, wind-facing coast of the island, a c. 130m long and 1.2m high beach ridge had accumulated, most likely from reworked tsunami sediment.Boulders deposited by tsunamis are commonly assigned a high preservation potential. We demonstrate for the first time that such boulders may in fact disintegrate rapidly and disappear from the record over short geological time scales, given a lithology susceptible to weathering.The degree of modification to the lsla Mocha tsunami boulders and deposits strongly questions the applicability of inverse models using paleotsunami deposit thickness and grain-size distributions to infer parameters and magnitudes of the causative tsunamis. Inverse models would consequently underestimate tsunami flow parameters and may result in the inference of erroneous transport modes and event magnitudes. Our study gives strong evidence in support of re-survey studies following the deposition of tsunami sediments by tracing and quantifying the changes affecting them.

The Oldest Record ofPaleoparadoxiafrom the Northwest Pacific with an Implication on the Early Evolution of Paleoparadoxiinae (Mammalia: Desmostylia)

Abstract A new specimen of Paleoparadoxia found from a marine lower Miocene deposit in the Chikubetsu area, Hokkaido, Japan, is described. The material consists of a distal part of the scapula, proximal end of the humerus from the right side, as well as a fragmentary rib, preserved in a float of calcareous fine sandstone. The specimen is referred to the order Desmostylia and subsequently to the genus Paleoparadoxia sp. The well preserved shoulder girdle of this specimen provides the first detailed morphology of this anatomical region in Paleoparadoxia. We compared the specimen with a wide range of desmostylid samples to reveal new diagnostic characters for the genus, such as the greater tubercle extending toward the proximal side above the head and the distinct lesser tubercle located on the medial side, projected medially. The lower Miocene Sankebetsu Formation outcrops in the area where the float was found, and the lithology and associated fossil fauna of the float indicate that it was derived from ther...

Depósitos de plataforma mista, Neocarbonífero da Bacia do Amazonas, região de Uruará, estado do Pará

Rochas carbonáticas são amplamente registradas na região oeste e centro-oeste do Estado do Pará, borda Sul da Bacia do Amazonas, correspondentes ao período Neocarbonífero. Esses depósitos são incluídos na sequência pensilvaniana-permiana correspondente a uma super sequência de segunda ordem representada pelo Grupo Tapajós. A Formação Itaituba corresponde à porção transgressiva que precedeu a expressiva continentalização e formação de Pangeia. Essa unidade é constituída de carbonatos fossilíferos, arenito com estratificação cruzada e subordinadamente folhelhos e evaporitos de ambiente marinho costeiro. Dezenove fácies e microfácies foram agrupadas em cinco associações de fácies (AF) correspondentes a depósitos de planície de maré (AF1), canal de maré (AF2), laguna (AF3), barra bioclástica (AF4) e plataforma externa (AF5). A AF1 compreende ciclos de exposição subaérea com formação de gretas de contração e deposição subaquosa, composta de brecha dolomítica, dolomito fino laminado e dolomudstone com terrígenos separados por arenito maciço piritoso e dolomito fino silicificado. A AF2 consiste em arenito fino com laminação cruzada de base reta e recobrimento pelítico nos foresets, siltito argiloso com laminação cruzada, marga com laminação cruzada cavalgante e arenito grosso com estratificação cruzada com recobrimento pelítico nos foresets. Falhas sinsedimentares afetam os arenitos e siltitos. A AF3 é constituída de siltito maciço avermelhado, mudstone fossilífero, floatstone com braquiópode e folhelho negro piritoso maciço. A AF4 é representada por grainstone oolítico fossilífero e grainstone com terrígenos e fósseis de braquiópodes, equinodermas, bivalves, moluscos e subordinadamente artrópodes, briozoários e foraminíferos. A AF5 associa-se a uma plataforma composta de wackestone fossilífero, wackestone fossilífero com terrígenos e mudstone maciço. A assembleia fossilífera é representada por foraminíferos, braquiópodes, bivalves e, subordinadamente, briozoários e equinodermas, que atestam um ambiente costeiro de salinidade moderada e profundidade baixa com intensa proliferação de organismos bentônicos. O modelo deposicional da Formação Itaituba, na região de Uruará, foi atribuído a um sistema lagunar e de planície de maré conectado a um sistema de plataforma marinha carbonática. As lagunas eram bordejadas por planície de maré na porção mais continental e periodicamente supridas por aporte de terrígeno fino (silte) que inibia a precipitação carbonática. Barras bioclásticas cortadas por canais de maré (inlet) separavam a laguna da plataforma rasa com maior abundância de fósseis marinhos bentônicos, registrando o início de uma transgressão marinha neocarbonífera na Bacia do Amazonas advinda de NNW.

Paleomagnetic study of Plio-Pleistocene sediments in the concentrated deformation zone along the eastern margin of the Japan Sea

Paleomagnetic results are presented for a concentrated deformation zone (CDZ) in a convergent plate boundary region along the eastern Eurasian margin. We sampled late Pliocene–early Pleistocene tuffs and clastic sediments of the Sasaoka Formation (∼750 m thick) in northeastern Honshu, Japan, to test whether the late Pliocene–Quaternary crustal deformation within the CDZ along the eastern margin of the Japan Sea was accompanied by rotation about a vertical axis. Rock magnetic experiments suggest that the principal magnetic carrier is magnetite in the fine tuffs, and magnetic iron sulfide in the fine sandstones. Pre-folding characteristic remanent magnetization was confirmed using a positive bootstrap fold test. We obtained 21 acceptable site-mean characteristic directions that include our preliminary published results, and which cover an interval from ca. 2.7 to 1.7 Ma on the basis of magnetostratigraphic correlations. An updated age–depth model is given, and this allowed us to make numerical age estimates for key interbedded tuff beds (tephras). A positive fold test also suggests that the Gojome syncline began to develop after 1.7 Ma, which means the folding began long after the initiation of late Pliocene crustal shortening in northeastern Honshu. After 100% unfolding, the overall mean direction (D = 359.7°, I = 54.9°, α95 = 6.7°) is indistinguishable from the geocentric axial dipole field direction, indicating that the Gojome syncline, the most prominent structural element in the study area, developed without vertical-axis rotation. A comparison of our results with Plio-Pleistocene directions reported from other areas reveals no paleomagnetically detectable rotation in or adjacent to the CDZ, except for local rotation near strike-slip faults in central Honshu.

Boundary between Soil and Saprolite in Alisols in the South of Brazil

Despite numerous studies conducted on the lower limit of soil and its contact with saprolite layers, a great deal of work is left to standardize identification and annotation of these variables in the field. In shallow soils, the appropriately noting these limits or contacts is essential for determining their behavior and potential use. The aims of this study were to identify and define the field contact and/or transition zone between soil and saprolite in profiles of an Alisol derived from fine sandstone and siltstone/claystone in subtropical southern Brazil and to subsequently validate the field observations through a multivariate analysis of laboratory analytical data. In the six Alisol profiles evaluated, the sequence of horizons found was A, Bt, C, and Cr, where C was considered part of the soil due to its pedogenetic structure, and Cr was considered saprolite due to its rock structure. The morphological properties that were determined in the field and that were different between the B and C horizons and the Cr layer were color, structure, texture, and fragments of saprolite. According to the test of means, the properties that support the inclusion of the C horizon as part of the soil are sand, clay, water-dispersible clay, silt/clay ratio, macroporosity, total porosity, resistance to penetration, cation exchange capacity, Fe extracted by DCB, Al, H+Al, and cation exchange capacity of clay. The properties that support the C horizon as a transition zone are silt, Ca, total organic C, and Fe extracted by ammonium oxalate. Discriminant analysis indicated differences among the three horizons evaluated.

Mud-Rich Density-Driven Flows Along an Early Ordovician Storm-Dominated Shoreline: Implications for Shallow-Marine Facies Models

Abstract Dynamic physical and biological seafloor processes shape the three-dimensional stratal architecture of modern and ancient mud-dominated continental shelves. When evaluating a mudstone unit as a potential source, reservoir, or seal, it is imperative to understand the physical, biological, and chemical seafloor processes that control mudstone depositional fabric and diagenesis. This study presents sedimentological, ichnological, and geochemical data of exceptionally preserved mudstone originating from hyperpycnal and possible combined-flow deposits in the Lower Ordovician (Tremadocian) Beach Formation, Bell Island Group, Newfoundland. Seven mudstone facies are described, based on textural, compositional, and ichnological characteristics. Mudstone deposits interpreted to originate from hyperpycnal flows are well cemented, exhibit high chlorite­:illite ratios, and contain sharp grain-size changes, commonly forming beds with tripartite subdivisions. Deposits of wave-enhanced sediment gravity flows are, in contrast, poorly cemented illitic mudstone. These mudstone facies exhibit decimeter-thick wave or combined-flow structures within siltstone and very fine sandstone beds as well as laterally discontinuous, nonbioturbated mudstone layers. Beds of this facies have abundant mudstone-on-mudstone and mudstone-on-sandstone erosional contacts. Low organic carbon loading from the nonvegetated early Paleozoic hinterland, combined with a high reworking frequency on a shallow marine wave-dominated shelf, is inferred to have resulted in high remineralization efficiency, and low preservation potential of reactive organic carbon. Burial efficiency and bioavailability of organic matter are considered to be the critical variables controlling infaunal colonization and bioturbation in mud-dominated open-coastline paleoenvironments. This work demonstrates that ancient fine-grained coastal systems are incompletely incorporated into sequence stratigraphic models owing to their atypical proximal-to-distal facies relationships. It is proposed that the spatial organization of fine-grained sediment and facies architecture in such systems are controlled by: 1) frequency of sediment supply events, 2) direction of mud transport, 3) diagenetic reactivity of minerals and bioavailable organic carbon, and (4) residence time of mineral grains and organic matter close to the sediment–water interface.

Reservoir quality variations within a sinuous deep water channel system in the Niger Delta Basin, offshore West Africa

Submarine fan channel reservoirs exhibit strong heterogeneity not only on channel architecture but also on the qualities of reservoirs, which can exert direct control over the fluid flow and remaining oil distribution during oilfield development. However, the distribution of the variations in the reservoir quality within submarine fan channel systems is poorly understood. This paper, which takes the submarine fan channel reservoirs of the X oilfield in the Niger Delta Basin as an example, aims to study the variations in reservoir qualities and the controlling mechanisms within a sinuous deep-water channel system. The studies are based on the integration of core analysis, well-logging interpretation, seismic inversion and interpretation constrained by channel architecture.The results show that variations in the reservoir quality within a sinuous deep-water channel system are primarily controlled by rock texture, lithofacies (association) and channel architecture under the circumstance of weak diagenesis. (1) The grain sorting and clay content mainly control the reservoir's porosity and permeability, respectively, while the relationship between grain size and the reservoir's properties is complicated because of the strong heterogeneity in the rock textures for different lithofacies. Cross-laminated fine sandstones have the highest porosity because of their good sorting, while massive medium to coarse sandstones have the highest permeability because of their low clay content. (2) Channel fillings are divided into four types (Type I – Type IV), which bear different reservoir qualities according to the lithofacies associations. Within a complete channel system, the channel fill types evolve progressively upward as the dominant gravity flow types evolve, which leads to the vertical differential distribution of porosity and permeability. (3) The relatively high porosity-permeability zones in the plane of a channel belt exhibit two patterns: multiple lenticular strips and single lenticular strips, which are controlled by the channel's architecture.

The Application of Flame Atomic Absorption Spectrometry for Gold Determination in Some of Its Bearing Rocks

A developed method was designed for gold determination directly in organic medium in some sedimentary rocks (fine sandstone, carbonates), pyrite, serpentine and international standard gold sample (MA-1a) using flame atomic absorption spectroscopy (FAAS). Instrumental parameters; burner angle, fuel flow rate, band pass and burner height together with chemical parameters; different media, leaching and interference effect were optimized to improve gold determination. Selective leaching using a new mixture (5% KCN, 5% Na2S2O3 and hydrogen peroxide) offered maximum leaching percentage of gold (>99%) with minimal concentration of accompanying elements. Extraction parameters using methyl isobutyl ketone (MIBK) from 3 M HCl were optimized for more than 99% gold extraction, followed by scrubbing using 0.1 M HCl. Gold was determined directly in organic phase. Beer’s law was obeyed from 0.01 μg/ml to 10 μg/ml. Standard deviation (from 0.017 to 1.05) and percentage error (from 1.5% to 2.5%) using the present developed AAS method were calculated.

Conodont faunas from a complete basinal succession of the upper part of the Wordian (Middle Permian, Guadalupian,West Texas)

In the southern part of the Patterson Hills just to the west of the Guadalupe Mountains escarpment of West Texas, a 29m outcrop of alternating calcareous siltstone and silty limestone with a few thin fine sandstone interbeds displays the overlap occurrence of a narrow morphotype of Jinogondolella nankingensis (herein named J. nankingensis behnkeni) with J. aserrata near its base. The transition of Jinogondolella aserrata to J. postserrata is present near the top of this section and marks the Wordian-Capitanian boundary, therefore displaying a significant portion of the upper part of the Wordian in one short continuous section. Pseudohindeodus brevis n. sp. and H. capitanensis n. sp. are described. Pseudohindeodus ramovsi, Caenodontus serrulatus, Hindeodus wordensis, Sweetina triticum, Jinogondolella palmata, and J. errata also occur in this succession.

The Applicability of Different Fluid Media to Measure Effective Stress Coefficient for Rock Permeability

Effective stress coefficient for permeability (ESCK) is the key parameter to evaluate the properties of reservoir stress sensitivity. So far, little studies have clarified which ESCK is correct for a certain reservoir while rock ESCK is measured differently by different fluid media. Thus, three different fluids were taken to measure a fine sandstone sample’s ESCK, respectively. As a result, the ESCK was measured to be the smallest by injecting nitrogen, the largest by injecting water, and between the two by brine. Besides, those microcharacteristics such as rock component, clay mineral content, and pore structure were further analyzed based on some microscopic experiments. Rock elastic modulus was reduced when water-sensitive clay minerals were encountered with aqua fluid media so as to enlarge the rock ESCK value. Moreover, some clay minerals reacting with water can spall and possibly block pore throats. Compared with water, brine can soften the water sensitivity; however, gas has no water sensitivity effects. Therefore, to choose which fluid medium to measure reservoir ESCK is mainly depending on its own exploitation conditions. For gas reservoirs using gas to measure ESCK is more reliable than water or brine, while using brine is more appropriate for oil reservoirs.