Parallel Laminae Research Articles

Twisted-layer boron nitride ceramic with high deformability and strength.

Moiré superlattices formed by twisted stacking in van der Waals materials have emerged as a new platform for exploring thephysics of strongly correlated materials and other emergent phenomena1-5. However, there remains a lack of research on the mechanical properties of twisted-layer van der Waals materials, owing to a lack of suitable strategies for making three-dimensional bulk materials. Here we report the successful synthesis of a polycrystalline boron nitride bulk ceramic with high room-temperature deformability and strength. This ceramic, synthesized from an onion-like boron nitride nanoprecursor with conventional spark plasma sintering and hot-pressing sintering, consists of interlocked laminated nanoplates in which parallel laminae are stacked with varying twist angles. The compressive strain of this bulk ceramic can reach 14% before fracture, about one order of magnitude higher compared with traditional ceramics (less than 1% in general), whereas the compressive strength is about six times that of ordinary hexagonal boron nitride layered ceramics. The exceptional mechanical properties are due to a combination of theelevated intrinsic deformability of the twisted layering in the nanoplates and the three-dimensional interlocked architecture that restricts deformation from propagating across individual nanoplates. The advent of this twisted-layer boron nitride bulk ceramic opens a gate to the fabrication of highly deformable bulk ceramics.

Geometry of sliding lamellae dictates the constitutive properties of nacre-like hierarchical materials

The mechanical properties of nacre (mother-of-pearl), which are superior to those of its constituent materials, derive from a micro-architecture formed by the arrangement into parallel laminae of individual aragonite tiles with surface asperities, bonded by organic interlayers. A mechanical model is developed to determine how the contact profile that defines the geometry of the tile surface affects the constitutive response of hierarchical metamaterials of this type when they are strained in the lamellar plane. We consider the structured character of the deformation, consisting of elastic distortion of the tiles and the inelastic contribution from the disarrangements produced by relative sliding of the lamellar interfaces, which is formulated within the thermodynamic framework for irreversible processes in generalized materials. The resistance to sliding associated with constrained shear-induced dilatation of the tiles and the bridging of the organic interlayers are represented by a generalized cohesive-frictional law, effective at the level of averaged separation plane, providing a phenomenological approach that by-passes the difficulty in analytically solving the contact problem at asperities. The nominal stress–strain curves of the nacreous structure are shown to be highly dependent, qualitatively and quantitatively, on the geometry of the contact profiles. The model not only produces results that are in excellent agreement with experiments on nacre, but it can also describe complex stress–strain curves with pinched hysteresis loops having branches of various shapes, as well as serrated inelastic regimes. The versatility of this theoretical approach offers promise as a design tool for innovative metamaterials.

Study on key influencing factors of competitive adsorption of coalbed methane by carbon dioxide displacement.

The extraction of coal bed methane (CBM) by injecting CO2 into deeply buried unmined coal seams in competition with CH4 adsorption to provide a clean fuel is known as enhanced coal bed methane recovery (ECBM) and has proven to be an effective technological strategy to address global warming. The study of the interaction of coal with CO2 and CH4 under multi-physical field conditions is particularly necessary. In this work, a series of experiments were conducted on a home-made test system to investigate the competing sorption patterns of high and medium ash coal samples subjected to variables such as gas pressure, temperature, nodulation and lateral limit constraints. The results show that there is a sorption isotherm relationship between coal samples and exposure time. The adsorption capacity sorption of CH4/CO2 varied considerably for different ash coal samples. As the CO2 pressure increased from 2.3 to 5.5 MPa, the strain on the coal samples increased from 0.082 to 0.4%. The deformation in the vertical laminae direction is always greater than that in the parallel laminae direction. A correlation coefficient K exists between 1 and 2, and there is an internal expansion pattern in the adsorption deformation of coal. This paper can contribute to the improvement of ECBM efficiency.

Laminar characteristics of lacustrine organic-rich shales and their significance for shale reservoir formation: A case study of the Paleogene shales in the Dongying Sag, Bohai Bay Basin, China

• Six types of the organic-rich shale laminae are reported in the Dongying Sag. • Discontinuous laminae were formed under high-energy hydrodynamic conditions. • Shale laminae containing favorable reservoir storage space are in the order of wavy laminar > lenticular laminar > weak laminar. • Thick and wavy laminae are the most favorable types for shale oil exploration. Shale oil exploration in China has demonstrated that laminated shales are favorable lithofacies for producing shale oil effectively. It is of great significance to study the type and reservoir properties of shales with different laminar structures. In this study, the laminae of Paleogene organic-rich shales in the Dongying Sag, Bohai Bay Basin were divided into two categories and six types based on thin section petrography, scanning electron microscopy (SEM), and geochemical characterization. The laminar types include thin parallel laminae, thick parallel laminae, wavy laminae, lenticular laminae, weak laminae, and sandy laminae. The first three types of laminae have good continuity and were formed under low-energy hydrodynamic conditions. In comparison, the latter three types are discontinuous and were formed under relatively high-energy hydrodynamic conditions with a strong terrigenous input. Significant differences were observed in the reservoir space types, microcracks, and oil-bearing properties among the different laminae. Analyses of porosity and oil saturation further revealed that laminated shales with high laminar continuity exhibit higher porosity, permeability, and oil saturation values than shales with poor laminar continuity. Shales with thick parallel laminar shale and wavy laminar shale possess favorable petrophysical parameters. Thus, from the perspectives of reservoir and oil-bearing properties, laminated shales with high laminar continuity are better than shales with poor laminar continuity for shale oil exploration in the Dongying Sag. The new findings provide a reference for the optimization and evaluation of favorable continental shale oil reservoirs in eastern China.

Facies Analysis Of The Late Eocene Deep-Marine Middle- To Outer-Fan Sequence Of The Crocker Formation In Tenom District, Sabah, Malaysia

The Crocker Formation, Late Eocene to Middle Miocene in age, was deposited in a deep-marine environment by a turbidity current. Most of the facies identified in the field are related to the sedimentary bed-form structures belonging to Bouma sequences. These prominently include unit divisions such as Ta referring to grading sand, Tb for parallel laminae, Tc for cross laminae, Td for mud laminae, and Te referring to hemipelagic mud. Five facies have adequately been identified using Bouma sequence implications, namely Facies 1 (F1: Ta-Tb layers), Facies 2 (F2: Ta-Te layers), Facies 3 (F3: Tb-Te layers), Facies 4 (F4: Tb / Tc-Te layers), and Facies 5 (F5: Td-Te layers). Based on the Crocker Formation facies analysis, three distinct groups of facies associations were recognised: Deep-Marine Channel-Lobe Association (Type A1), Deep-Marine Channel-Levee Association (Type A2), and Distal Lobe Association. These facies associations precisely revealed that the Crocker Formation's depositional environments were likely deposited in the middle-fan with associated outer-fan settings.

A simple scheme for calculating the energy harvesting figures of merit of porous ceramics

Abstract We propose a scheme based on recursively applying analytical formulae for effective properties to a class of porous ceramics for calculating their energy harvesting figures of merit. We approximate the structure of freeze-cast PZT parallel laminae joined by links (or bridges) by a model that can be broken down into two directions along which the structure resembles a laminate. The effective coefficients obtained in the first step of the recursion are then used as input on the second step which gives the final effective moduli. The comparison of those with calculations via Finite Element Method (FEM) on a non-recursive model shows good agreement. Finally, we calculate the piezoelectric and pyroelectric figures of merit and compare them with experimental results. The proposed scheme is a good alternative since it relies only on known simple analytical formulae and has a very low computational cost with respect to other methods that may be applied to such a geometry.

Emplacement of massive deposits by sheet flow

AbstractTurbidity current and coastal storm deposits are commonly characterized by a basal sandy massive (structureless) unit overlying an erosional surface and underlying a parallel or cross‐laminated unit. Similar sequences have been recently identified in fluvial settings as well. Notwithstanding field, laboratory and numerical studies, the mechanisms for emplacement of these massive basal units are still under debate. It is well accepted that the sequence considered here can be deposited by waning‐energy flows, and that the parallel‐laminated units are deposited under transport conditions corresponding to upper plane bed at the dune–antidune transition. Thus, transport conditions that are more intense than those at the dune–antidune transition should deposit massive units. This study presents experimental, open‐channel flow results showing that sandy massive units can be the result of gradual deposition from a thick bedload layer of colliding grains called sheet flow layer. When this layer forms with relatively coarse sand, the non‐dimensional bed shear stress associated with skin friction, the Shields number, is larger than a threshold value approximately equal to 0·4. For values of the Shields number smaller than 0·4 the sheet flow layer disappeared, sediment was transported by a standard bedload layer one or two grain diameters thick, and the bed configuration was characterized by downstream migrating antidunes and washed out dunes. Parallel laminae were found in deposits emplaced with standard bedload transport demonstrating that the same dilute flow can gradually deposit the basal and the parallel‐laminated unit in presence of traction at the depositional boundary. Further, the experiments suggested that two different types of upper plane bed conditions can be defined, one associated with standard bedload transport at the dune–antidune transition, and the other associated with bedload transport in sheet flow mode at the transition between upstream and downstream migrating antidunes.

Two new microscopic ductile kinematic indicators from the Oman Mountains

Two novel shear-sense indicators were observed in different tectonic settings. The first one (“PDT”) occurs in a calcmylonite, associated with extension. The second one (“Dragged Intergrowths”) was discovered in mylonitized plagiogranite (trondhjemite) dikes with vertical to sub-vertical foliation and strike-slip deformation within harzburgite.The calcite mylonite displays shear planes, characterized by parallel laminae which differ in composition. They contain light-colored, calcite, while darker impurities consist of hematite, goethite, and rutile. PDTs are associated with microthrusts. The thrusts form an acute angle with the mylonitic foliation. Thrusting between two microthrusts created pull-aparts, filled with drusy calcite. The shear sense of the PDTs is revealed by (1) shortening and related imbrication of the thrust laminae, (2) pull-apart structures and (3) drag folds at either end of the microthrusts. The indicated shear is confirmed by independent evidences. One PDT is up to ∼0.5 mm wide and 1 mm long.The mylonitized plagiogranite contains a K-feldspar δ-porphyroclast (2 mm long), featuring dragged K-feldspar/quartz intergrowth due to rotation during high-temperature conditions. Bending occurs on either end of the object. The original orientation of the intergrowth was subparallel to the foliation. As a result an “S”-shaped object formed. The deduced shear sense is independently confirmed.

Geological evidence of tsunamis in the past 3800 years at a coastal lowland in the Central Fukushima Prefecture, Japan

We found seven event deposits during the past 3800 years in a total of 16 geological core samples from a coastal lowland in Fukushima Prefecture, about 12 km north of the Fukushima Daiichi Nuclear Power Station. The event deposits consisted of well-sorted and rounded fine to coarse sand with single normal grading structures, parallel laminae, mud drapes, rip-up clasts, and erosional basal contacts. They were distributed about 2 km inland from the current shoreline and commonly became thinner landward. The third and fifth sand layers were characterized by many climbing ripples and parallel and trough-cross bedding that were probably caused by storm surges or some other events during the period of absent beach ridges. The other deposits were characterized by sedimentological features common to tsunami deposits. The top layer appeared to have been deposited by the 2011 Tohoku tsunami, and the second layer might have been resulted from the AD 869 Jogan Tohoku tsunami. The other three tsunami deposits corresponded to tsunami events between the second and fourth centuries AD, the sixth and fourth centuries BC, and the twelfth and ninth centuries BC. The average recurrence interval of the paleo-tsunamis was estimated to be 560–950 years. These dates are mostly consistent with previous studies of the Sendai plain, suggesting that paleo-tsunamis that reached the Sendai plain also reached the coast of Fukushima Prefecture. However, no trace was found from an earthquake around the 15th century, which had been considered as a predecessor of the 2011 Tohoku earthquake (Mw 9.0) in the tsunami deposit surveys in Sendai plain.

Anatomorradiographic Description of the Capybara´s Teeth (Hydrochoerus hydrochaeris)

Background: The capybara (Hydrochoerus hydrochaeris) is the largest South American rodent species alive, and it preferentially inhabits floodable environments. Currently, capybara populations have been increasing owing to lack of predators and increased availability of food. This favors reemergence of Rocky Mountain spotted fever in the state of São Paulo, as these animals can play host to the Cayenne tick (Amblyomma cajennense), a vector of the bacteria that transmit this disease. The objective of this work was to perform anatomical and radiographic analyses on the teeth of capybaras to broaden knowledge on the morphology of this species, as scientific interest on capybaras has been growing owing to reemergence of Rocky Mountain spotted fever.Materials, Methods & Results: Six capybara carcasses from the state of São Paulo, Brazil, were taken to the Laboratory for Animal Anatomy of the School of Agricultural Sciences and Veterinary Medicine of UNESP - Jaboticabal for obtainment of heads by disarticulation of the cervical region. The heads were frozen at -18°C, and then sectioned medially with a band saw to avoid tissue overlap in radiographs. The head halves were radiographed in the Diagnostic Imaging Section at the Veterinary Hospital of UNESP-Jaboticabal in laterolateral projection. After taking the radiographs, the teeth were extracted from the dental arches using anatomical forceps and pliers, placed in 0.1% thymol, and kept at 4°C for up to 30 days. The teeth were dried using an air jet produced by a compressor, and placed in molds made of aluminum foil. The specimens were embedded in alternating layers of clear polymethylmethacrylate and liquid polymerization catalyst until each tooth was completely covered. After 24 h, the molds were removed, and the blocks were sectioned using a band saw. Transversal and longitudinal calcified tooth sections with a thickness of 1.5 mm were prepared. The sections were sanded using an automotive sander with 80-grit sandpaper, and then sanded by hand until a thickness of 0.12 mm was reached. The tooth fragments were removed from the resin, dehydrated in ethanol, clarified in xylene, and placed in a Petri dish containing glycerin for evaluation using a mesoscope and a negatoscope. Capybaras were found to have one incisor, one premolar, and three molar teeth in each dental hemiarch (superior and inferior). All teeth contained large, open roots. The root of the superior incisor is rostral to the root of the premolar tooth, and the root of the inferior incisor lies between the roots of the premolar and the first molar teeth. The inferior incisors are much larger than their superior counterparts, and their ends are chisel-shaped. The pulp cavity extends from the apical region to up to two-thirds of the longitudinal length of the tooth, and the enamel is arranged in layers. The roots of the four molar teeth are large and resemble several aggregated laminae arranged longitudinally - five laminae in the inferior molars, four laminae in the premolar, first and second molars, and 13 or 14 laminae in the third superior molar.Discussion: The dental formula of capybaras is similar to that of guinea pigs, chinchillas, and pacas, but different from that of agoutis. All teeth are aradicular as in guinea pigs and chinchillas because of the great tooth wear owing to feeding. In chinchillas and guinea pigs, the apex of the mandibular incisor tooth is located between the second and the third molar; in capybaras, it is located between the premolar and the first molar. The premolar and molar teeth of capybaras are similar to their counterparts in the paca and to the molars of elephants because they exhibit parallel internal laminae. The teeth of capybaras are similar to those of guinea pigs in terms of number and type of teeth, and similar to those of pacas and elephants regarding external morphology.

The first Dictyoolithus egg clutches from the Lishui Basin, Zhejiang Province, China

ABSTRACT Three clutches and eight additional eggs are described from the Upper Cretaceous Chichengshan Formation in the Lishui Basin of Zhejiang Province, China. The three clutches contain 6–18 partial or complete spherical eggs, 14–18 cm in diameter. The eggshell thickness and reticulate pore system are identical to Dictyoolithus hongpoensisZhao, 1994. However, the eggshell lacks superimposed shell units previously reported in this oospecies. The difference in microstructure most likely results from the reliance on thin section analysis in the original study; furthermore, superimposed shell units are inadequately documented in all Dictyoolithus oospecies due to the absence of scanning electron microscopy (SEM) or low (×45) magnification of SEM imaging. Cladistic analysis and the presence of the following characters support a theropod affinity of Dictyoolithus hongpoensis: relatively narrow spacing of nucleation sites, mammillary cones with blocky calcite cleavage, prismatic columns, and parallel laminae within the shell units. We reevaluate previous assignment of Dictyoolithus eggs to the Dinosauroid-spherulitic Basic Type and advocate discontinuation of Basic Type and Morphotype in fossil egg classification.

Synthesis of 9‐Substituted‐1,8‐Dioxooctahydroxanthenes by an Efficient Iodine‐Catalyzed Cyclization

AbstractNew 1,8‐dioxooctahydroxanthenes with substituents in the 2‐, 3‐, and 9‐positions were obtained by cyclization with iodine from tandem Michael/Michael adducts. The X‐ray molecular structure of the methyl 2‐(1,8‐dioxo‐2,3,4,5,6,7,8,9‐octahydro‐1H‐xanthen‐9‐yl)acetate (3a) was solved and shows the parallel laminae packing of these molecules. Furthermore, we reported the structure of intermediate 4 isolated from this reaction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Palaeoenvironmental implication of resedimented limestones shed from Mississippian–Permian mid-oceanic atoll-type buildup into slope-to-basin facies, Akiyoshi, Japan

For better understanding of long-term environmental changes in a mid-oceanic atoll-type buildup (Akiyoshi Limestone Group), we examined the atoll-derived carbonate sediments that were contemporaneously shed into the spicular chert of slope-to-basin facies (Ota Group) in the Akiyoshi area, southwest Japan. Both of these two units are dated as upper Viséan to Capitanian, and interpreted as having laterally passed into each other on and around a mid-oceanic seamount. The resedimented limestone occurs as slab-like bodies, and isolated and laterally discrete smaller pods, and thin beds and laminae in the spicular chert of the Ota Group. The composite succession (ca. 105 m thick) measured in slab-like bodies is divided into the lower and upper units, each of which consists of the sharp-based calcarenite, siliceous lime–mud/siltstone, and spicular chert with blocks, beds, and laminae of calcarenite and siliceous limestone in ascending order. The calcarenite forming slabs and smaller blocks are massive and dominantly comprises densely packed, coarse crinoid debris and subordinate bryozoan fragments with no or sparse matrix. The siliceous lime–mud/siltstone consists of siliceous sponges spicules, minute calcitic skeletal debris, and peloidal particles, with the matrix of a mixture of lime–mud and microcrystalline quartz. The calcarenite and siliceous lime–mud/siltstone beds and laminae in the spicular chert occasionally contain graded and parallel laminae. The massive calcarenite, and graded calcarenite and siliceous limestone were formed by redeposition mainly of skeletal sands presumably by grain flows with minor debris flows, and by mixing of sponge spicule-rich siliceous sediments and redeposited lime–mud and skeletal debris by muddy turbidites of distal facies, respectively. These redeposited carbonate sediments were exported from the Akiyoshi Limestone Group onto the spicular sediments of slope-to-basin facies. Conodonts, fusulinids, and smaller foraminifers from the resedimented limestone indicate that the redeposition of the carbonate sediments took place dominantly in late Viséan to late Bashkirian, and subordinately in Sakmarian to Capitanian time. The absence of the Moscovian to Asselian resedimented limestone implies much-reduced carbonate shedding during this period. The correlation with the interpreted palaeoenvironmental episodes in the Akiyoshi buildup shows that late Viséan to late Bashkirian and Sakmarian to Capitanian carbonate-shedding events correspond to the times of generally warm climate and high sea-levels in the Akiyoshi buildup. Moscovian to Asselian time, which lacks records of carbonate shedding, nearly corresponds to the Moscovian to Gzhelian cooling and sea-level lowering in the Akiyoshi buildup. We consider that the shedding of carbonate sediments from the Akiyoshi atoll is its depositional response to the warm climate and elevated sea-levels and is compared with a sedimentary system of the highstand shedding of carbonates. Atoll-type carbonates equivalent to the Akiyoshi Limestone Group in the Akiyoshi terrane also show comparable responses of carbonate shedding into slope and slope-to-basin facies.

Fabrication of a new composite orthodontic archwire and validation by a bridging micromechanics model

A new technique based on tube shrinkage is proposed for the fabrication of composite archwires. Compared with a traditional pultrusion method, this new technique can avoid any fiber damage during the fabrication and can provide the archwire with a required curvature in its final clinical usage. The present paper focuses on the technique development and mechanical design and validation in terms of constituent materials by using a micromechanics bridging model. Prototype archwire has been fabricated using fiberglass and an epoxy matrix, with a wire diameter of 0.5 mm and a 45% fiber volume fraction. Tensile and three-point bending tests have shown that the mechanical performance of the prototype composite archwire is comparable to that of a clinical Ni–Ti archwire. Another purpose of the present paper is to provide an efficient procedure for a critical design of composite archwires. For this to be possible, the ultimate load especially flexural load carrying ability of the composite archwire must be assessed from the knowledge of its constituent properties. However, difficulty exists in doing this, which comes from the fact that the failure of the utmost filament of the composite archwire subjected to initially the maximum bending stress does not imply its ultimate failure. Additional higher loads can still be applied and a progressive failure process is generated. In this paper, the circular archwire was discretized into a number of parallel laminae along its axis direction, and the bridging micromechanics model combined with the classical lamination theory has been applied to understand the progressive failure process with reasonable accuracy. Only the constituent fiber and matrix properties are required for this understanding. Nevertheless, the ultimate bending strength cannot be obtained only based on a stress failure criterion. This is because neither the first-ply nor the last-ply failure corresponds to the ultimate failure. An additional critical deflection (curvature) condition must be employed also. By using both the stress failure and the critical deflection conditions, the predicted load-deflection up to the ultimate failure agrees well with the measured data. Thereafter, different mechanical performances of composite archwires can be tailored before fabrication by choosing suitable constituent materials, their contents, and the archwire diameters. Several design examples have been shown in the paper.

Sulfur speciation in kerogens of the Orbagnoux deposit (Upper Kimmeridgian, Jura) by XANES spectroscopy and pyrolysis

Thermally immature, extremely sulfur-rich kerogens from the Orbagnoux deposit have been extensively studied over the last few years for their chemical structure, source organisms and depositional conditions. However, important uncertainties remain concerning sulfur speciation in these kerogens and changes in sulfur functionality that occur upon thermal stress. In the present study sulfur speciation for isolated kerogens from the five facies recognized in the deposit was established via K- and L-edge X-ray Absorption Near Edge Structure (XANES) spectroscopy. A representative sample of the most organic-rich facies of the deposit, the dark parallel laminae, was examined by “direct” pyrolysis at 400 °C and the results compared with those previously derived from “indirect” pyrolysis (carried out under the same conditions but from kerogen pre-heated at 300 °C). XANES examination was performed on the unheated kerogen, the pre-heated kerogen, the insoluble pyrolysis residues and the effluents obtained via these two pyrolyses. Sulphur distribution was also determined via elemental analyses and measurements of evolved H 2S. Identification of the pyrolysis products of the “direct” experiment was performed by gas chromatographic/mass spectrometric analyses, before and after desulfurization, of the crude pyrolysate and of separated fractions and sub-fractions. Substantial quantitative and qualitative differences are thus noted between the “direct” and “indirect” pyrolyses at 400 °C, as a result of the cleavage and aromatization of some sulfide bridges occurring upon pre-heating at 300 °C. Thus, the “indirect” pyrolysis appears somewhat less efficient for the thermal cracking of the macromolecular structure of the kerogen. Nevertheless, it provides more detailed information on the intermolecularly sulfur-linked carbon skeletons that build up the bulk of this structure owing to (i) the release of OSC with higher carbon numbers and (ii) the much easier desulfurization of the molecular aggregates probably due to a lower degree of cross-linking. XANES spectroscopy showed that (i) thiophenes are the main sulfur species in the unheated kerogens and (ii) substantial aromatization of the non-thiophenic sulfur forms occurs upon the thermal treatments.

Turbulence Modulation in Clay-Rich Sediment-Laden Flows and Some Implications for Sediment Deposition

Clay-rich flows are common in many sedimentary environments, ranging from rivers with high suspended sediment concentrations and fluid muds on the continental shelves to deep-ocean density currents. Such sediment-laden flows have fluid-dynamic characteristics which are radically different from their clear-water counterparts. Laboratory experiments demonstrate that an increasing concentration of kaolinite results in a distinct change in velocity and turbulence structure in flows transitional between Newtonian and non-Newtonian behavior. Such transitional flows develop a lower region of reduced velocity that is separated from the overlying flow by a distinct shear layer. Large-scale Kelvin-Helmholtz instabilities are generated along this shear layer and dominate both turbulence production and fluid mixing. These experimental results are used to interpret the formation of parallel laminae in turbiditic muds and propose a model for sediment sorting in a range of clay-rich flows. Non-Newtonian flows with low concentrations of kaolinite (∼ 4% by volume) are devoid of both turbulent and cohesive strength at the shear velocities investigated. Deposition of coarser, noncohesive particles in such flows would be expected to be controlled entirely by differences in settling velocity, and the deposits would therefore be expected to be graded and massive.

Grain Fabric in Cross Laminated Deposits Conformably Superimposed on Parallel Laminae: Flume Experiments and Application to Geologic Records.

Small-scale bed waves under unidirectional currents can be classified into two types; Type I well-developed bed waves formed under a flow with a certain velocity, and sand grains move by avalanche on the lee slope; Type II: immature bed waves with short wavelength and low height formed at the early stage after the flow velocity decreases from the upper-plane-bed-regime, and grains on the bed move as a sheet flow. Experiments demonstrated that Type II bed waves could be preserved in the presence of ambient sedimentation and resulted in small-scale cross-stratifications similar to Type I formed under a relatively slow flow. Grain fabric analyses showed that the dominant direction of long axes of grains in the deposit of Type II bed waves dipped upstream against the lee slope, unlike Type I deposits. It is possible to identify the type of small-scale cross-stratifications by its grain fabric. We found an ancient example of ripples categorized into Type II in a turbidite sequence of the Plio-Pleistocene Kakegawa Group, in Japan.

Modern Analogs for Paleocave Sediment Fills and their Importance in Identifying Paleocave Reservoirs

ABSTRACT Coalesced, collapsed-paleocave reservoirs occur in Lower Ordovician Ellenburger, Arbuckle, and Knox carbonates and less commonly in other Paleozoic strata. One of the most distinctive features of these paleocave systems, on wireline logs and in core data, is sediment fill. Modern analogs of paleocave-sediment fills from several Gulf of Mexico cave systems characterize the texture, fabric, and associated sedimentary structures of these fills. The sediment-fill facies can consist of carbonate and/or siliciclastic debris. Clastic cave sediment, ranging from clay- to cobble-sized material, commonly contains variable amounts of breakdown-derived breccia. Sections of passages can be completely plugged by sediment. Depositional processes include suspension, traction, and mass-flow mechanisms. Sedimentary structures such as parallel laminae, chaotic bedding, cross bedding, graded bedding, and scour are common. Reservoir quality of the sediment-fill facies depends on the texture and mineralogy of the material. Sediment fills are distinctive in core and can be found more than 100 m beneath the unconformity that produced the cave system. On wireline logs, they are characterized by high positive spontaneous-potential and high gamma-ray responses that reflect the terrigenous content in an otherwise carbonate system. Sediment fills, distinctive eatures of paleocave reservoir systems, are important in substantiating the origin of these reservoirs.

Unusual coarse, clastic, wave-dominated shoreface deposits, Pliocene to middle Pleistocene, northern Chile; implications for coastal facies analysis

ABSTRACT Pliocene to mid-Pleistocene shallow-marine strata exposed at Gatico, northern Chile (22° 30 S, 70° 14 W) display unusual characteristics for coarse-grained wave-dominated shoreface deposits. A 15 m2000 m strike section of Pliocene to mid-Pleistocene strata exposed within small, late Pleistocene sea cliffs contain four facies: beach, foreshore channel, upper shoreface, and rip channel. Beach and upper shoreface facies predominate. The latter consists of locally bioturbated, coarse-grained, pebbly sandstone with (1) single sets of planar to tangential cross-strata, up to 3.5 m thick, with reactivation surfaces, and (2) sets of medium-to large-scale cross-strata that were deposited on inclined set surfaces (up to 15°). Some of the inclined set surfaces extend up-dip of cross-set terminations. Inclined parallel laminae and bioturbated beds lie subparallel to the inclined set surfaces. Interpretation of these unusual bedforms has been made through analogy with the present-day microtidal wave-dominated coastline at Gatico, by facies analysis, and by comparison with modern-day wave-dominated shorelines. The large-scale sets of cross-strata record the migration of simple, two-dimensional (2-D) dunes and represent the slipface deposits of nearshore bars. Parallel laminae represent the bar surface. Medium-scale dunes migrated up the inclined set-bounding surfaces, which lie subparallel to older preserved bar surfaces. Paleocurrent data indicate that bar migration was largely directed obliquely onshore towards the southeast. The bar slipface deposits are considered to record the recovery of a nearshore bar immediately following storm conditions. Bar recovery involves re-establishment of a slipface and rapid onshore migration. Erosion surfaces that appear as the extension of lower set boundaries beyond the termination of cross-strata sets, and reactivation surfaces, are considered to be storm-generated. The episodic nature of bar migration is indicated by the development of heavily bioturbated horizons. The small-scale ascending cross-sets may reflect fair-weather conditions with northwestward dune migration up the modified bar slipface. Despite the abundance of barred shorelines around the world at present, their deposits are not widely described from the rock record, suggesting that they are either not preserved or not recognized. The scale and internal characteristics of these nearshore bars closely resemble those of some tide-generated bedforms (e.g., compound cross-strata in marine sediment with bimodal-bipolar paleocurrents and evidence of episodic bedform migration). The similarity of these north Chilean deposits to documented tidal deposits suggests that an element of caution may be required in the identification of tidal deposits from the rock record.

Spectroscopic, kinetic and pyrolytic studies of kerogen from the dark parallel laminae facies of the sulphur-rich Orbagnoux deposit (Upper Kimmeridgian, Jura)

Kerogen isolated from a representative sample of the dark parallel laminae facies of the Orbagnoux deposit, characterized by very high hydrogen and sulphur indices, was examined to derive information on its chemical structure and source organisms. The study of this extremely sulphur-rich material was carried out via a combination of kinetic (Pyromat), spectroscopic (FTIR, solid-state 13C NMR) and pyrolytic (`off-line' pyrolysis) methods. The highly complex pyrolysate obtained consisted chiefly of organic sulphur compounds (OSC). Analyses were focused on the highly polar and/or high molecular weight constituents, including the non-column chromatography (CC)-eluted and non-gas chromatography (GC)-amenable macromolecular components which account for the bulk of the pyrolysate. This study showed that two types of structural units, exhibiting differences both in chemical structure and source organisms, occur in the Orbagnoux kerogen. The predominant type corresponds to macromolecular units based on intermolecularly sulphur-linked, normal, C 14–C 24 hydrocarbon chains with a marked even-over-odd predominance and a sharp maximum at C 18. These chains exhibit a high degree of cross-linking via (poly)sulphide bridges; they probably originated from cyanobacterial lipids, especially n-alcohols. The second type (whose occurrence was recognized in previous studies through analysis of bitumen and of apolar pyrolysis products) is based on longer, normal, hydrocarbon chains, up to C 31, and is characterized by a lower degree of cross-linking. These chains, of algal origin, were likely sourced from lipids of the coccolithophorid Cyclagelosphaera margereli, whose mineral remains built up the bulk of the rock matrix. Both types of units were chiefly formed via the sulphurization of lipids and of diagenetically transformed lipids. Owing to extensive, early, intermolecular sulphurization, such lipids underwent only moderate bacterial degradation, as shown by the nature and distribution of the fatty acids released upon pyrolysis.