Cross Lamination Research Articles

Geological History Reconstruction using Stratigraphic Analysis: A Case Study of Kampung Baru, West Sumatra

The reconstruction of geological history includes the development of rocks and volcanic deposits on a depositional pattern consisting of various types of sedimentary materials accumulated over a long time, which involves depositional changes. Depositional changes require geological comprehension in analyzing and understanding the geological processes involved in their evolution. For this reason, stratigraphic analysis is a very relevant approach to discussing rock layers, including significant environmental changes during their geologic history. The purpose of this research is to find out the geological processes that have contributed to the formation of the earth in the past. The method in this research is a stratigraphic analysis carried out from field observation data carried out directly at the outcrop. Deposition began with the re-deposition of the Pre-Tertiary (Triassic)-aged Porphyry Quartz Dasite Formation. In the Late Oligocene Epoch, the Sawahtambang Formation was deposited, which formed in the braided river characterized by the presence of sedimentary structures in the form of lamination and cross lamination. In the Early Miocene to Middle Miocene, the transgression process occurred, where the change in deposition was caused by the supply of larger land sediments that caused the deposition of the Ombilin Formation to be deposited in the marine environment of the Transition-Nerritic Edge based on the bathymetry results. The research results are expected to enable geological information to gain in-depth knowledge and experience about the history of deposition and assist in geological modeling.

Face bonding strength of cross laminated northern hardwoods and softwoods lumber

Producing cross-laminated timber (CLT) has opened a new market for the lumber industry in North America, while few hardwood species have been studied in the U.S. for CLT production. Combining hardwood species in mixed hardwood CLT or in hybrid CLT can be a solution to boost the market of the undervalued hardwoods. However, the knowledge gap on bonding hardwoods needs to be filled to provide evidence of feasibility. This study focused on the face bonding properties of the cross laminations made of seven hardwood species and two softwood species from the Great Lakes region using two commercial structural adhesives, the phenol resorcinol adhesive (the Resorcinol) and the melamine urea formaldehyde adhesive (the Melamine). A total of 45 combinations of the selected species were studied for the bonding strength (shear under compression) and the percentage of wood failure. For single species samples, the bond strength was positively related to the specific gravity of wood and the bond strength of hardwoods was 33% and 82% stronger than that of softwoods bonded with the Resorcinol and the Melamine respectively. The mixed hardwoods showed higher bonding strength (the Melamine: 5.45 MPa, the Resorcinol: 5.28 MPa) than mixed softwoods (the Melamine: 2.8 MPa and the Resorcinol: 2.7 MPa). Among the Resorcinol bonded mixed combinations, 54% had a percentage of wood failure less than 80%, while the Melamine bonded had only 4 out of 22 which had a percentage of wood failure less than 80%. The overall bonding strength of the hybrid combinations was 5% weaker than that of the mixed hardwoods. All hybrid combinations bonded with the Melamine met the 80% wood failure criterium, but some bonded with the Resorcinol had a percentage of wood failure less than 80%. Anatomical features, especially pore distribution, played a key role in the bonding performance. However, the Melamine adhesive consistently achieved over 80% wood failure across all pore distribution types.

Transparent Bamboo with Multiple Light Transmittance levels, Fiber Textures, and Colors Based on the Gradient Structure of Bamboo

Transparent bamboo (TB) is a new type of biomass and light transmitting material with potential to serve as a substitute for transparent wood. However, the potential of the bamboo structure in preparing transparent composites is underexplored. Inspired by the functional gradient structure of bamboo, we used a simple and efficient two‐step strategy to prepare TB with different transmittance levels, fiber textures, and colors. We evaluated the performance of single‐ and multilayer TB with various fiber volume contents prepared using different lamination methods. We found that the optical and mechanical properties of TB differed with the fiber volume content and the lamination method used. TB composed of veneers with low fiber volume showed the highest light transmittance (44.6%), whereas TB composed of veneers with high fiber volume had the highest tensile strength (45.7 MPa). In terms of water resistance, cross lamination inhibited expansion in width (water absorption rate, 16.37–21.26%) and thickness (thickness swelling rate, 10.22–21.74%). The lamination structure and fiber volume content in the preparation of TB should be selected according to the specific application scenarios. The graded utilization of bamboo veneer with a fiber gradient can effectively realize the rational allocation of bamboo resources and promote sustainable development.This article is protected by copyright. All rights reserved.

Effects of grain size and small-scale bedform architecture on CO2 saturation from buoyancy-driven flow

Small-scale (mm-dm scale) heterogeneity has been shown to significantly impact CO2 migration and trapping. To investigate how and why different aspects of small-scale heterogeneity affect the amount of capillary trapping during buoyancy-driven upward migration of CO2, we conducted modified invasion percolation simulations on heterogeneous domains. Realistic simulation domains are constructed by varying two important aspects of small-scale geologic heterogeneity: sedimentary bedform architecture and grain size contrast between the matrix and the laminae facies. Buoyancy-driven flow simulation runs cover 59 bedform architecture and 40 grain size contrast cases. Simulation results show that the domain effective CO2 saturation is strongly affected by both grain size and bedform architecture. At high grain size contrasts, bedforms with continuous ripple lamination at the cm scale tend to retain higher CO2 saturation than bedforms with discontinuous or cross lamination. In addition, the “extremely well sorted” grain sorting cases tend to have lower CO2 saturation than expected for cross-laminated domains. Finally, both a denser CO2 phase and greater interfacial tension increase CO2 saturation. Again, variation in fluid properties seems to have a greater effect on CO2 saturation for cross-laminated domains. This result suggests that differences in bedform architecture can impact how CO2 saturation values respond to other variables such as grain sorting and fluid properties.

Physical and Mechanical Properties of Novel Multilayer Bamboo Laminated Composites Derived from Bamboo Veneer.

Compared with wood, bamboo has a special fiber gradient structure. Bamboo fibers have attracted attention as reinforced polymer composites. This study investigated the effects of lamination and fiber volume on the physical and mechanical properties of bamboo laminated composites (BLCs). Six types of BLC were derived by parallel and cross laminating bamboo veneers with high, middle, and low fiber volumes. The results indicated that the laminated structure and fiber volume significantly influenced the BLC properties. Microstructural analysis showed that parallel lamination and low fiber volume were more conducive to resin penetration and enhanced the bonding strength. Both the bending and tensile strengths of the cross lamination were lower than those of the parallel lamination. BLCs made of veneers with high and middle fiber volumes and parallel lamination had the maximum bending and tensile strengths (145.1 and 101.53 MPa, respectively). When tested for water resistance, parallel and cross lamination inhibited expansion in the thickness (TSR, 0.56-2.14%) and width (WSR, 0.07-1.61%) directions, respectively. Laminated structures and veneers with varying fiber volume contents should be chosen according to the specific application scenarios. This study provides a reference for selecting an appropriate BLC structure and fiber volume based on application.

In-plane mechanical properties of birch plywood

There is an increasing demand for engineered wood products in modern structures. Birch plywood is promising in structural applications, due to the combined advantages of its superior mechanical properties and the cross lamination configuration. However, the off-axis mechanical properties of birch plywood have not been thoroughly investigated. The aim of this paper is to establish a comprehensive experimental dataset that could serve as the input in the analytical or numerical models to design birch plywood under various load conditions. Specifically, tensile, compressive and shear tests were conducted under five different angles to the face grain, i.e., from 0° (parallel) to 90° (perpendicular) to the face grain, with an interval of 22.5°. The stress–strain relationships, failure modes, strength and elastic properties of birch plywood are highly dependent on the load-to-face-grain angle. The strength and the elastic properties are also predicted by various analytical and empirical models. Parametric analyses are performed to study the influence of the interaction coefficient F12 in Tsai-Wu failure criterion and the Poisson’s ratio νxy in the transformation model on the predicted strength and modulus respectively. Lastly, the possibilities of predicting the on-axis shear modulus based on the off-axis uniaxial tests are discussed in this paper.

The negative impact of Ophiomorpha on reservoir quality of channelized deposits in mixed carbonate siliciclastic setting: The case study of the Dam Formation, Saudi Arabia

Several studies have documented the role of burrows with coarse-grained filling in enhancing the reservoir quality of a tight rock matrix. However, very few studies have shown the inverse case where burrows (i.e., Ophiomorpha) exert a detrimental role on the reservoir quality of permeable strata. Documenting such a scenario in the rock record is essential to fully understand the role of burrows in shaping the reservoir quality of sedimentary strata. This study integrates results from field observation and laboratory analysis to document and contribute to the understanding of the impact of Ophiomorpha on reservoir quality (porosity and permeability) of tidal channel deposits in a mixed carbonate siliciclastic setting (Dam Formation, Saudi Arabia). The results showed that the Ophiomorpha consists of shafts (diameter range from 1 cm to 24 cm) that have porous, sand-dominated fillings (porosity of 25%) with quartz (65%) and feldspars (10%); and a dolomitized wall. In the studied outcrops, Ophiomorpha penetrated the entire tidal channel at the flanks and extended laterally to the channel axis for more than 40 cm. In the computer tomography (CT) scans of the samples collected from the tidal channel deposits, Ophiomorpha exhibited a three-dimensional boxwork pattern that intersected the lamination and cross lamination of the tidal channel deposits. These observations suggest that the textural and mineralogical characteristics of Ophiomorpha walls may negatively impact the petrophysical properties of the tidal channel deposits, as the petrographic analysis showed that the wall of Ophiomorpha has very low visual porosity (<1%). The presence of the Ophiomorpha wall can act as a permeability baffle within the tidal channel sandstone due to its textural and mineralogical contrast compared to the surrounding matrix and burrow-fill. The relationship between the bulk porosity and the percentage of the Ophiomorpha wall in the samples confirms this suggestion. The measured bulk porosity on 1.5-inch plugs showed a strong negative correlation with the volume percentage of Ophiomorpha wall in the sample (Coefficient of determination [R2] of 0.79). The presence of the wall in the samples also influences the measured bulk permeability in three different ways. Firstly, the measured bulk permeability is high (>2800 mD) when the volume percentage of the wall in the samples is low (<5%). Secondly, the measured bulk permeability is moderate (∼100 mD) when the volume percentage of the wall is high (>40%), but the wall does not completely block the permeability pathways. Thirdly, the measured bulk permeability is low (≤0.1 mD) when the volume percentage of the wall in the samples is high (∼40%), and the wall acts as a permeability barrier in the samples and blocks their permeability pathways. These results suggest that due to its textural and mineralogical characteristics, the presence of Ophiomorpha may modify permeability anisotropy of the tidal channel by modifying the relationship between vertical and horizontal permeability. They also provide insight into the potential negative impact of bioturbation in similar biogenically modified reservoirs, where Ophiomorpha is the dominant element introducing heterogeneity in an otherwise isotropic fabric.

Sequence Stratigraphy of the Fatha Formation in Shaqlawa Area, Northern Iraq

A surface section of the Fatha Formation (Middle Miocene) was studied in the Shaqlawa area, Erbil, Northern Iraq. It consists of siliciclastic silt, evaporates, and carbonates in a mixed siliciclastic silt composition. The Fatha Formation in the study area can be divided into two members of variable thickness based on rocky differences. Depositional settings ranged from shallow open-marine and restricted-hypersaline to supratidal and continental (sabkha, fluvio-deltaic, and exposure). It is bounded below by a type one sequence boundary above the Eocene Pila Spi Formation and marked by conglomerates. The upper sequence boundary with the Injana Formation is conformable. Thirteen sedimentary facies were distinguished in the Fatha Formation within the Shaqlawa region of northern Iraq and include sandstone to mudstone, wavy bedded sandstone to mudstone, Flaser bedded sandstone to mudstone, Marl, sandstone, cross lamination sandstone, Trough cross bedded sandstone, Planar cross bedded sandstone, marly limestone lithofacies, bioclastic grainstone to packstone microfacies, bioclastic lime mudstone to wackestone microfacies, lime mudstone-wackestone microfacies, and gypsum lithofacies. The depositional environment of the formation was inferred based on the facies association concepts. The succession formation can be divided into several third-order cycles, which reflect fluctuations in the relative sea-level rise. High-frequency cycles of transgressive System Tract and Highstand System tract. Fundamental to the evolution of the sequence, in this case, is the local tectonic component.

Lithofacies and petrography of Miocene Murree Formation, Peshawar basin, NW Pakistan: implications for provenance and paleoclimate

The Miocene Murree Formation is an enormous sedimentary deposit and is considered as foreland basin sediments of Himalayas, extending EastWest throughout the foothills of Himalayas. Lithofacies analysis was performed to establish the depositional environment, the following lithofacies were identified: clast-supported massive gravel (Gcm), sandstone with planar cross lamination (Sp), sandstone trough cross lamination (St), sandstone with horizontal lamination (Sh), sandstone with ripple cross lamination (Sr), sandstone with low-angle cross lamination (Sl) and mud and silt massive with roots bioturbation (Fr). These lithofacies depict shallow channel depth, deposition on the distal part of point bar, natural levees and flood plain of a meandering river. The modal composition data indicates that the Murree sandstone is arkosic to lithic wacke. The mineralogical and textural data suggests that sandstone is compositionally submature to immature and texturally immature to submature. The debris of rock fragments proposes diverse sources for Murree Formation. The ternary plots of detrital quartz type of the current study designate plutonic provenance. The high percentage of unstrained monocrystalline quartz (Qnu) relative to undulatory monocrystalline quartz (Qu) and polycrystalline quartz (Qp) proposes plutonic source area for Murree Formation. The paleoclimate plot discloses semi-humid–humid environment.

Dactyloidites ottoi en depósitos marinos someros de la Formación Coris, Mioceno, Costa Rica

Dactyloidites ottoi traces associated with medium grained, mature, siliceous sandstone facies, with planar and curved parallel lamination and HCS cross laminations were developed in shallow marine environments (upper shoreface) of the Coris Formation (Miocene). High-energy environmental conditions were caused by waves, storms, tides and currents. Episodic sedimentation with high-energy erosive events caused by storms alternating with low-energy deposition with organic matter input favored sediment rework by organisms. These ichnofossils are infrequent in the sedimentary record and they had not previously been reported in Costa Rica. They are constituted by elongated elements which radiate from a central shaft and create a series of rosetted or fan-shaped tiered galleries. The organism that created these structures is yet unknown, however, several studies coincide that it must have been a feeding fodichnia trace produced by a worm-like organism which is part of the Cruziana Icnofacies.

The lithofacies and depositional paleoenvironment of the Bima Sandstone in Girei and Environs, Yola Arm, Upper Benue Trough, Northeastern Nigeria

The Benue Trough is a contiguous intracontinental basin that formed part of the mega west and central African rift system (WCARS). The Cretaceous sedimentary succession preserved up to 6 km thick. The Aptian-Albian Bima Sandstone non-conformably overlies the Precambrian basement rock and the sandstone is the oldest Cretaceous succession in the Upper Benue Trough. This paper aimed at understanding its lithofacies and depositional environment in Girei and environs within Yola arm of the Upper Benue Trough. From the field studies, 13 lithofacies were identified; massive matrix supported and gravel dominated facies (Gmm), matrix supported gravel (Gmg), clast supported gravel (Gci), gravel stratified (Gh), and gravel stratified trough cross-bedded sandstone (Gt), sand, fine to very coarse grained trough crossbedded sandstone (St), sand, fine, medium, coarse to very coarse grained group planar cross-bedded sandstone (Sp), low angle planar crossbedded sandstone (Sl), sand, fine to coarse grained ripple cross laminated sandstone (Sr), sand, very fine, pebbly coarse grained horizontal bedded sandstone(Sh), Sand, fine to coarse grained massive sandstone (Sm), Convuluted sandstone (Sc), silt and mud (Fsm), and mudstone (Fm). The Bima Sandstone in the study area is sub-divided into proximal alluvial fan facies are composed of Gmm, Gmg, Gci, and Fsm, lithofacies, while the mid and distal fan facies are sequentially characterised by Gh, Gt, St, Sp, Sl, Sr, Sm, Sc, and Fm lithofacies. The alluvial fan facies are matrix supported and are restricted to the basin margin, and it may represent the basal part of the outcrop lithosections, the lack of internal organization of these lithofacies reflects high-strength viscous debris flow and it speaks volume of emergence of stream near the upland, however, the Gci facies probably indicate advancement of stream influence and reduction of gravity, the associated Fsm facies could be a backswamp and/or abandoned channel deposits. The mid fan facies have basal surface that is concave-upward in transverse crossection, well-developed thick amalgamated trough crossbedded sandstone (St) facies, theses attribute represent deep channel deposits, high flow regime, and continuous creation of accommodation space, it also points towards deep perennial sand braided river system. The distal fan facies is composed of amalgamated planar cross-bedded sandstone (Sp) associated with horizontal bedded sandstone (Sh), ripple cross lamination (Sr) and mudstone (Fm) facies with better developed floodplain deposit, pointing towards the influence of steady periodic high flow with topographic difference and it reflects shallow perennial sand-bed braided river. The lithofacies of the Bima Sandstone in Girei and environs, within the Yola arm generally show architectural stacking pattern that is generally thinning and fining upward indicating inactivity and/or fan retrogradation, and the depositional paleoenvironment varies from alluvial to braided river setting. The mid to distal fan facies of the Bima Sandstone can serve as good reservoir for hydrocarbon while the mudstone which is the floodplain deposit can serve as the seals and/or traps for the accumulated hydrocarbon.

Facies Architecture Analysis for Paleo-environment Evaluation in “Tom” Oil Field, Eastern Niger Delta, Nigeria

The cored section of reservoir C, well 4 of the drilled five wells that penetrated three reservoirs A, B and C in “TOM” oil field, Eastern Niger Delta was analysed and described on the basis of lithofacies, sedimentary structures and trace fossil records by using core data and wireline log motifs, with the aim of carrying out thorough geological core analysis to interpret the depositional environment of the oil field. The lithofacies are sandstones with interbedded mudstones and siltstones, the dominant sedimentary structures are parallel to ripple cross laminations, hummocky and swaley cross stratifications, sandy hetherolitics, planar to low angle cross bedding with traces of Teichichnus and Ophiomorpha burrows. The gamma-ray log motifs were noted and used to further constrain the character of the sedimentary facies and depositional environment of the field. A tidal incised – fluvial dominated shallow marine (lower, middle, upper shoreface) comprises of tidal channel sands and tidal flat of the coastal shelf depositional setting in the marginal marine mega depositional environment had been inferred for the “TOM” field.&#x0D; Keywords: Shoreface, Reservoir, Lithofacies, Structures

Volcanic reconstruction of the Paleoproterozoic Stroud Breccia: Understanding the transition from a primitive to mature arc and its impact on VMS ore-formation, Snow Lake, Manitoba, Canada

The Stroud Breccia is a ≤400 m thick package of dominantly felsic volcaniclastic rocks within the Paleoproterozoic Snow Lake arc assemblage. It stratigraphically overlies the ore-interval for the Anderson, Stall and Rod volcanogenic massive sulfide (VMS) deposits at Snow Lake, Manitoba, Canada and occupies the stratigraphic interval between the underlying primitive arc Anderson sequence and the overlying mature arc Chisel sequence.The Stroud Breccia is interpreted to be a product of subaqueous pyroclastic and effusive, dominantly rhyolitic, volcanism, and concomitant subsidence. It consists of felsic tuff to lapilli-tuff, crystal-rich felsic tuff, felsic lapillistone, felsic tuff breccia, mafic tuff to lapilli-tuff, heterolithic tuff breccia to breccia and rhyolite. The finer felsic volcaniclastic units are characterised by angular or broken quartz crystals, angular lithic rhyolite lapilli, and pumice. Fine ash, broken crystals and pumice suggest they were deposited by eruption-fed density currents associated with a phreatomagmatic eruption. The coarser felsic volcaniclastic units are characterized by blocks of strongly quartz-feldspar porphyritic rhyolite and pumice and are interpreted to have been deposited during the reworking of pyroclastic debris flow deposits on the seafloor during mass wasting events at fault scarps. Planar and cross laminations, graded beds and bomb sag structures suggest the mafic tuff to lapilli-tuff unit was deposited by a combination of subaqueous eruption-fed density currents and eruption driven ballistically emplaced ejecta, likely through subaqueous tephra jetting.Lithofacies analyses, and geochemistry has allowed comparison between the felsic volcanic rocks of the Stroud Breccia and those that host the Anderson, Stall and Rod VMS deposits. Detailed mapping has led to the identification of synvolcanic faults, defining basins and volcanic vents, that indicate that the process of incipient rifting of the Anderson sequence primitive arc continued during emplacement of the Stroud Breccia. These structures also define magma and fluid pathways critical in controlling the formation of the Anderson VMS deposits, meaning they represent deep-seated and long-lived structures that can be used as vectors to mineralization at depth.

Modern Analogue of Shaly Sand Reservoir on Coastal Plain in Selat Baru, Bengkalis Island, Indonesia

Coastal environment is one of main reservoir depositional system in the oil industry and becomes the main challenges in defining its characteristic, especially in lateral correlation. Research conducted in Bengkalis Island which has a unique characteristic of coastal depositional environment that affected by a tidal system related to modern analogue for reservoir characterization. The method used for this research is analysing lithofacies from drilled core data, surface sampling, and lateral measurement from foreshore to the tidal limit. It is confirmed from core data that research area consists of sand, shale, and peat with lamination, cross laminations sedimentary structure and also filled with organism activity, which clustered into eight lithofacies. By integrating the core data with surface sampling and lateral measurement, it is interpreted that facies is changing only in near distance (about 30 – 40 m) with sloping 1 – 2 degrees in the surface, so by defining the same characteristic on lithofacies, correlation can clearly define on a shaly sand reservoir in the tidal coastal environment.

Multifunctional Stretchable Conductive Woven Fabric Containing Metal Wire with Durable Structural Stability and Electromagnetic Shielding in the X-Band.

Elastomeric, conductive composite yarns have recently received attention around the opportunity for them to offer special protective fields. A straightforward approach for fabricating tri-component elastic-conductive composite yarns (t-ECCYs) containing stainless steel wire (SSW) was proposed previously. This work mainly focuses on the electromagnetic shielding effectiveness (EMSE) of weft-stretchable woven fabric containing t-ECCY over the X-band under different testing conditions, e.g., single step-by-step elongation, cyclic stretch and lamination events. Results showed that a woven cotton fabric with weft yarn of t-ECCY not only exhibited superior weft stretch-ability to a higher elongation (>40%) compared with a pure cotton control but also had an acceptable 15-cyclic stability with 80% shape recovery retention. The t-ECCY weft fabric was effective in shielding electromagnetic radiation, and its EMSE was also enhanced at elevated elongations during stretch at parallel polarization of EM waves. There was also no decay in EMSE before and after the t-ECCY fabric was subject to 15 stretch cycles at extension of 20%. In addition, a 90° by 90° cross lamination of t-ECCY fabric remarkably improved the EMSE compared to a 0°/90° one. The scalable fabrication strategy and excellent EMSE seen in t-ECCY-incorporated fabrics represent a significant step forward in protective fields.

Grouping porosity permeability in deep marine sediment to analogue oil and gas reservoir: A case study Brebes Central Java

Study area is located in Rambatan river and Ciseureh river Malahayu Brebes Central Java. Porosity and permeability are very important to oil and gas industry. Porosity is a measure of the void spaces in a rock and is a part of the total volume rock. Permeability is defined as the ability of a rock to transmit fluids. Deep-water gravity flow or deep marine reservoir are important exploration targets worldwide and there is complicated when little subsurface data available. Porosity and permeability analysis from outcrops data may considered as the data used in this study. The result from four measuring section show there is thin intercalated limy sandstone, marl, and calcareous shale. 14 outcrop samples was carried out the helium porosimetry for porosity permeability value and was examined thin section analysis for fabric discussion, and 2 samples was calcimetry analysis. Lithology are generally contains many foraminifera from very fine to fine grained and mostly moderate grained on inner-outer fan environment. Sedimentary structure represent slope sedimentary structure such as graded bedding, lower lamination, slump bedding, ripple, convolute ripple, cross lamination, and trace fossil as feature of deep-marine deposits. 8 samples from 14 samples limy sandstone are likely to be good reservoirs.

Rapid subsidence and preservation of fluvial signals in an otherwise wave-reworked delta front succession: Early-mid Pliocene Orinoco continental-margin growth, SE Trinidad

Outcrops of the early-mid Pliocene Orinoco Delta succession on the Atlantic-facing Trinidad continental margin demonstrate facies and stratigraphic architecture of a shelf margin developed in a setting of high sediment supply (Orinoco River) and unusually rapid, sediment accumulation/subsidence (averaging >1 km/My). The studied Moruga clastic wedge of the Orinoco margin consists of a series of topset to deepwater clinoforms with channelized sandstones, river- and mixed-process delta front, wave-dominated delta front, shoreface, prodelta-offshore transition-shelf, upper-slope turbidite channels and mass-transport deposits. The succession is sand-prone and generally consists of coarsening- and thickening-upward delta-front lobes with hummocky/swaley and wave-ripple stratified sandstones indicating dominant storm wave reworking of the delta, particularly when the delta lobes had reached outer shelf sites after long shelf transits. The lower parts of distributary channels are well preserved and characterized by cross-bedded to parallel-laminated sandstones with mud clast lags. The upper parts of channel fills were wave reworked during transgressions, creating hummocky/swaley cross-stratified strata. River-dominated and mixed-process (wave and tide) delta-front deposits occur commonly within stacked, coarsening-upward units. The river-dominated delta front deposits exhibit parallel-laminated to current ripple-laminated intervals with normally graded thin beds changing upward to parallel and low-angle cross lamination, but mixed-process delta front deposits also contain wave and bidirectional current ripples as well as discrete intervals of hummocky/swaley cross-stratification. The preservation of the channel-base as well as river- and mixed-process delta-front deposits in the otherwise storm wave-dominated Atlantic-facing setting suggests some sheltering of the coastal morphology, and possibly low-frequency of large storms, but it is more likely that the unusually rapid subsidence (at rates competing well with Icehouse rates of eustatic sea-level change) and burial of deposits may have prevented the fluvial and tidal signals from being completely reworked by the storm waves in the studied outcrop area. This study demonstrates an example of how the interactions of river-, tide- and wave-generated facies impacted stratigraphic architecture of a rapid subsiding shelf margin built by shelf-edge deltas with high sediment supply.

Foam Generation in Flow Across a Sharp Permeability Transition: Effect of Velocity and Fractional Flow

Summary Foam reduces gas mobility and can help improve sweep efficiency in an enhanced-oil-recovery (EOR) process. For the latter, long-distance foam propagation is crucial. In porous media, strong foam generation requires that the local pressure gradient exceed a critical value (▿Pmin). Normally, this happens only in the near-well region. Away from wells, these requirements might not be met, and foam propagation is uncertain. It has been shown theoretically that foam can be generated, independent of pressure gradient, during flow across an abrupt increase in permeability (Rossen 1999). The objective of this study is to validate theoretical explanations through experimental evidence and to quantify the effect of fractional flow on this process. This article is an extension of a recent study (Shah et al. 2018) investigating the effect of permeability contrast on this process. In this study, the effects of fractional flow and total superficial velocity are described. Coreflood experiments were performed in a cylindrical sintered-glass porous medium with two homogeneous layers and a sharp permeability jump in between, representing a lamination or cross lamination. Unlike previous studies of this foam-generation mechanism, in this study, gas and surfactant solution were coinjected at field-like velocities into a medium that was first flooded to steady state with gas/brine coinjection. The pressure gradient is measured across several sections of the core. X-ray computed tomography (CT) is used to generate dynamic phase-saturation maps as foam generates and propagates through the core. We investigate the effects of velocity and injected-gas fractional flow on foam generation and mobilization by systematically changing these variables through multiple experiments. The core is thoroughly cleaned after each experiment to remove any trapped gas and to ensure no hysteresis. Local pressure measurements and CT-based saturation maps confirm that foam is generated at the permeability transition, and it then propagates downstream to the outlet of the core. A significant reduction in gas mobility is observed, even at low superficial velocities. Foam was generated in all cases, at all the injected conditions tested; however, at the lowest velocity tested, strong foam did not propagate all the way to the outlet of the core. Although foam generation was triggered across the permeability boundary at this velocity, it appeared that, for our system, the limit of foam propagation, in terms of a minimum-driving-force requirement, was reached at this low rate. CT images were used to quantify the accumulation of liquid near the permeability jump, causing local capillary pressure to fall below the critical capillary pressure required for snap-off. This leads to foam generation by snap-off. At the tested fractional flows, no clear trend was observed between foam strength and fg. For a given permeability contrast, foam generation was observed at higher gas fractions than predicted by previous work (Rossen 1999). Significant fluctuations in pressure gradient accompanied the process of foam generation, indicating a degree of intermittency in the generation rate—probably reflecting cycles of foam generation, dryout, imbibition, and then generation. The intermittency of foam generation was found to increase with decreasing injection velocities and increasing fractional flow. Within the range of conditions tested, the onset of foam generation (identified by the rise in ▿P and Sg) occurs after roughly the same amount of surfactant injection, independent of fractional flow or injection rate.

Hinterland setting and composition of an Oligocene deep rift-lake sequence, Gulf of Tonkin, Vietnam: Implications for petroleum source rock deposition

Abstract Most SE Asian oil accumulations are sourced from Paleogene lacustrine mudstones. Even so, the mechanisms controlling formation of these source rocks are not fully understood. Bach Long Vi Island, located in the northwestern South China Sea, offers a unique opportunity to study these mechanisms. A continuous, 800 m thick, organic rich and highly oil-prone, lacustrine section was investigated in outcrop and in a continuously cored section. The Oligocene deep-lake succession formed in the Bach Long Vi Graben that connects the Beibuwan Basin with the Yinggehai-Song Hong Basin. Petrography, detrital zircon U-Th-Pb geochronology and heavy mineral assemblages of sandstone intervals document a locally derived sediment source isolated from the Red River. Orientations of ripple cross lamination in gravity flow sands indicate axial sediment transport along the graben. Combined with the local structural configuration, this suggests that sediments were derived from the Qixi High through a relay ramp located about 10 km south of the island. Rare earth and major elements, detrital zircon ages, sandstone petrography and garnet composition, suggest a dominantly Ordovician – Silurian aged felsic and metasedimentary hinterland. The limited sediment supply from the small hinterland allowed tectonic subsidence to keep pace with graben infill. This promoted the establishment of a long-lived, deep lake favorable for source rock generation. In addition, heavy mineral and geochemical data document an unusually high content of detrital phosphate minerals in the investigated section indicative of a phosphate-rich hinterland. Tropical leaching resulted in an extraordinary high phosphorus input into the lake that catalyzed a high organic productivity and promoted the generation of highly prolific, oil-prone source rocks. The study documents that hinterland size and composition play a primary role in lacustrine source rock deposition. Comparable petroleum source rocks are likely to exist in other ancient rift basins surrounded by small, phosphate-rich hinterlands sheltered from significant sediment input.

Geology of the area between Bardibas and Sindhuli Madi, Sub-Himalaya, Central Nepal

The Siwalik Group (Sub-Himalaya) is the east-west extending youngest mountain belt formed by the sediments derived from the rising Himalaya on the north. The Siwalik Group is separated from the Lesser Himalaya to the north by the Main Boundary Thrust (MBT), and the Indo-Gangetic Plain to the south by the Main Frontal Thrust (MFT). The study was carried out mainly along the Ratu Nadi, Kamala Nadi river sections and was lithostratigraphically divided into the Lower Siwalik, Middle Siwalik, and Upper Siwalik, from the bottom to the top section, respectively. The Lower Siwalik is composed of fine-grained greenish grey calcareous sandstone (subarkose and lithic arenite), variegated mudstone, and calcareous siltstone. The Lower Siwalik is exposed due to the Marine Khola Thrust in the Gadyauli Khola, and sandstone there is more indurated and non-calcareous. The Middle Siwalik is mainly comprised of the medium- to coarse-grained salt-and-pepper sandstone (arkose and subarkose) with large cross lamination, calcareous sand lenses, convolute bedding, dark grey siltstone and mudstone. Plant fossils are also present in the finely laminated clay bed of the Middle Siwalik along the Ratu Nadi section. The Upper Siwalik comprises of mud- to sand-supported pebble to cobble conglomerates.