Sheet-like Geometry Research Articles

Refractive lensing of scintillating FRBs by subparsec cloudlets in the multiphase CGM

We consider the refractive lensing effects of ionized cool ([Formula: see text]) gas cloudlets in the circumgalactic medium (CGM) of galaxies. In particular, we discuss the combined effects of lensing from these cloudlets and scintillation from plasma screens in the Milky Way interstellar medium (ISM). We show that, if the CGM comprises a mist of subparsec cloudlets with column densities of order [Formula: see text] (as predicted by [M. McCourt, S. P. Oh, R. O'Leary, A. M. Madigan, MNRAS 473, 5407-5431 (2018)]), then fast radio bursts (FRBs) whose sightlines pass within a virial radius of a CGM halo will may be lensed into tens of refractive images with a ∼10 ms scattering timescale. When these images are formed, they will be resolved by scintillating screens in the Milky Way ISM and will suppress the observed scintillation. We illustrate this effect in refractive lensing and argue that positive detections of FRB scintillation may constrain the properties of these cool-gas cloudlets, with current scintillation observation weakly disfavoring the cloudlet model. We propose that sheet-like geometries for the cool gas in the CGM can reconcile quasar absorption measurements (from which we infer the presence of the cool gas with structure on subparsec scales) and the unexpected lack of lensing signals from this gas thus far observed.

Multipoint study of the rapid filament evolution during a confined C2 flare on 28 March 2022, leading to eruption

This study focuses on the rapid evolution of the solar filament in active region 12975 during a confined C2 flare on 28 March 2022, which finally led to an eruptive M4 flare 1.5 h later. The event is characterized by the apparent breakup of the filament, the disappearance of its southern half, and the flow of the remaining filament plasma into a new, longer channel with a topology very similar to an extreme ultraviolet (EUV) hot channel observed during the flare. In addition, we outline the emergence of the original filament from a sheared arcade and discuss possible drivers for its rise and eruption. We took advantage of Solar Orbiter's favorable position, 0.33 AU from the Sun, and $83. 5^ west of the Sun-Earth line, to perform a multi-point study using the Spectrometer Telescope for Imaging X-rays (STIX) and the Extreme Ultraviolet Imager (EUI) in combination with the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) and Halpha images from the Earth-based Kanzelhöhe Observatory for Solar and Environmental Research (KSO) and the Global Oscillation Network Group (GONG). While STIX and EUI observed the flare and the filament's rise from close up and at the limb, AIA and HMI observations provided highly complementary on-disk observations from which we derived differential emission measure (DEM) maps and nonlinear force-free (NLFF) magnetic field extrapolations. According to our pre-flare NLFF extrapolation, field lines corresponding to both filament channels existed in close proximity before the flare. We propose a loop-loop reconnection scenario based on field structures associated with the AIA 1600 Å flare ribbons and kernels. It involves field lines surrounding and passing beneath the shorter filament channel, and field lines closely following the southern part of the longer channel. Reconnection occurs in an essentially vertical current sheet at a polarity inversion line (PIL) below the breakup region, which enables the formation of the flare loop arcade and EUV hot channel. This scenario is supported by concentrated currents and free magnetic energy built up by antiparallel flows along the PIL before the flare, and by non-thermal X-ray emission observed from the reconnection region. The reconnection probably propagated to involve the original filament itself, leading to its breakup and new geometry. This reconnection geometry also provides a general mechanism for the formation of the long filament channel and realizes the concept of tether cutting. It was probably active throughout the filament's continuous rise phase, which lasted from at least 30 min before the C2 flare until the filament eruption. The C2 flare represents a period of fast reconnection during this otherwise more steady period, during which most of the original filament was reconnected and joined the longer channel. These results demonstrate how rapid changes in solar filament topology can be driven by loop-loop reconnection with nearby field structures, and how this can be part of a long-lasting tether-cutting reconnection process. They also illustrate how a confined precursor flare due to loop-loop reconnection (Type I) can contribute to the evolution towards a full eruption, and that they can produce a flare loop arcade when the contact region between interacting loop systems has a sheet-like geometry similar to a flare current sheet.

Ultra-Confined Catalytic Growth Integration of Sub-10nm 3D Stacked Silicon Nanowires Via a Self-Delimited Droplet Formation Strategy.

Fabricating ultrathin silicon (Si) channels down to critical dimension (CD) <10nm, a key capability to implementing cutting-edge microelectronics and quantum charge-qubits, has never been accomplished via an extremely low-cost catalytic growth. In this work, 3D stacked ultrathin Si nanowires (SiNWs) are demonstrated, with width and height of Wnw = 9.9 ± 1.2 nm (down to 8nm) and Hnw = 18.8 ± 1.8 nm, that can be reliably grown into the ultrafine sidewall grooves, approaching to the CD of 10nm technology node, thanks to a new self-delimited droplet control strategy. Interestingly, the cross-sections of the as-grown SiNW channels can also be easily tailored from fin-like to sheet-like geometries by tuning the groove profile, while a sharply folding guided growth indicates a unique capability to produce closely-packed multiple rows of stacked SiNWs, out of a single run growth, with the minimal use of catalyst metal. Prototype field effect transistors are also successfully fabricated, achieving Ion/off ratio and sub-threshold swing of >106 and 125mV dec-1 , respectively. These results highlight the unexplored potential of versatile catalytic growth to compete with, or complement, the advanced top-down etching technology in the exploitation of monolithic 3D integration of logic-in-memory, neuromorphic and charge-qubit applications.

The musca molecular cloud: The perfect ‘filament’ is still a sheet

ABSTRACT The true three-dimensional (3D) morphology of the Musca molecular cloud is a topic that has received significant attention lately. Given that Musca does not exhibit intense star-formation activity, unveiling its shape has the potential to also reveal crucial information regarding the physics that dictates the formation of the first generation of stars within molecular clouds. Here, we revisit the shape of Musca and we present a comprehensive array of evidence pointing towards a shape that is extended along the line-of-sight dimension: (a) 3D maps of differential extinction; (b) new non-local thermodynamic equilibrium radiative transfer simulations of CO rotational transitions from a sheet-like, magnetically dominated simulated cloud; (c) an effective/critical density analysis of available CO observations; and (d) indirect consequences that a filamentary structure would have had, from a theoretical star-formation perspective. We conclude that the full collection of observational evidence strongly suggests that Musca has a sheet-like geometry.

Fluvial sedimentation and its reservoir potential at foreland basin margins: A case study of the Puig-reig anticline (South-eastern Pyrenees)

Fluvial fans represent one of the dominant sedimentary systems at the active margins of non-marine foreland basins. The Puig-reig anticline at the north-eastern margin of the Ebro Foreland Basin (SE Pyrenees, Spain) exposes continuous outcrops of Late Eocene-Early Oligocene fluvial deposits, from proximal to medial fluvial fan environments. The proximal deposits are found in the north limb of the anticline, especially in the northwest zone. These deposits are characterised by conglomerates with minor interbedded sandstones, with thick and wide sheet-like geometries with unscoured or variably scoured basal surfaces. These are interpreted to be the deposits of unconfined flash floods and wide-shallow channel streams. The medial deposits, covering the rest of the anticline, consist of interbedded conglomerates, sandstones and claystones. These are interpreted to have been deposited from braided to meandering channel streams and overbank areas. Distal deposits are found towards the south, beyond the anticline, and are characterised by sandstone and clay deposits of terminal lobes and lacustrine deltas. This study assesses the impact of the primary depositional characteristics, diagenesis and deformation of the most heterolithic portion of the system, with implications for increasing our understanding of folded fluvial reservoirs. Diagenetic processes, mainly mechanical compaction and calcite cementation, resulted in overall low intergranular porosity, with limited relatively high porosity developed in sandstone lithofacies in the medial deposits. Deformation associated with thrusting and fold growth resulted in the formation of abundant fractures, with relatively high fracture intensities observed in sandstone lithofacies in the anticline crest. This study shows that post-depositional processes can both improve and diminish the reservoir potential of basin proximal fluvial deposits, through the development of fracture networks and by compaction-cementation. The comparison of the Puig-reig anticline with other similar settings worldwide indicates that foreland basin margin locations may be potential areas for effective reservoirs, even in the case of low intergranular porosity.

Depositional Architecture of Eocene and Cretaceous Reservoirs (Blending Seismic and Well Data) in Mubarik Area, Central Indus Basin, Pakistan

Structural and stratigraphic geometries in the Central Indus Basin of Pakistan are subjects of interest for explorers. The thickening and thinning sequences in conjunction with structural anomalies often provide an environment for hydrocarbon accumulation. Hydrocarbons play a vital role in the energy mix of Pakistan. With the help of well correlation, work on seismicity can be confirmed by marking terminations, depositional extent and thickness variation at different stratigraphic levels. Therefore, this work presents depositional geometries of Eocene and Cretaceous reservoirs [Sui Main Limestone (SML) and B-sand interval of Lower Goru Formation], keeping in view the vertical and lateral resolution of the seismic data and the distance between the wells for correlation. The Eocene SML and Cretaceous B-sand are extensively mapped as isochrones using 20 seismic lines and correlated with ten wells. The results give evidence of a building up of shallow marine shelf carbonate in Eocene SML. The isochrone maps also indicate that Eocene SML has untapped potential east of the study area. The Cretaceous B-sand demonstrates sheet-like geometry of sand-filled delta progrades in the west to southwest direction in a ramp setting. This geometry suggests an updip hydrocarbon potential in Cretaceous B-sand reservoir in the north of the study area. Because of the pinching out behavior and excellent stratigraphic trapping system, these two reservoirs can be considered future exploration targets.

Architecture of coarse-grained gravity flow deposits in a structurally confined submarine canyon (late Eocene Tokaren Conglomerate, Slovakia)

This study documents the coarse-grained fill of an upper slope, late Eocene Tokaren Canyon in the Carpathian Mountains, whose planform geometry and internal architecture were driven by normal faulting of an underlying carbonate platform. Facies analysis hints at a narrow shelf and a direct link to rivers draining a rapidly-uplifting hinterland. The axial part of the canyon consists of several meters thick, amalgamated conglomerate intervals deposited by debris flows and, to a lesser extent, by debris falls, slides and high-density turbidity currents. The sediments form sheets consisting of several tens to several hundreds of meters wide lobes occasionally entrenched by small erosional chutes. The deposits on the higher, fault-bounded blocks closer to the channel margins, include well-developed conglomerate–sandstone packages. They show a sheet-like geometry scattered with small channels. The textural immaturity of the sediment, grain-size caliber, the sediment thickness variation in the canyon, the sedimentary facies and their spatial distribution imply a dominant role of tectonics and sediment supply in the evolution of the canyon.Despite numerous studies of canyons in tectonically active settings, there are surprisingly limited studies on the depositional fill architectures of such canyons based on outcrop analogs. The detailed study of the Tokaren Canyon architecture brings a valuable insight into processes and distribution of proximal canyon fill facies controlled by syn-depositional faulting. It describes the architecture of such coarse-grained depositional system fed directly by rivers and governed by tectonics and supplements the knowledge from such systems obtained by different methodologies.

Grain Size and Heavy Minerals Analysis of Maastrichtian Sandstone, Anambra Basin, Nigeria: Implication for Aquifer Properties

The Maastrichtian sediments of Anambra Basin, south western Nigeria was studied for grain characteristics and maturity of the sediments, so that by combining sedimentological characteristics, maturity and its paleoenvironment of deposition of the Ajali sandstone, in order to ascertain the aquifer properties of the groundwater within the study area and by extension the availability of drinking water for both the urban and rural settlers. Grain size analysis (51 samples) and heavy mineral analysis (15 samples each) were analyzed. The textural parameters show that the Sandstone are medium sand, poorly to moderately sorted, coarse to strongly coarse skewed with mesokurtic to leptokurtic grains. The heavy minerals present in lithologic sand and sandstone units of Ajali Formation are mainly zircon, rutile, tourmaline, apatite, staurolite, and opaque minerals (Goethite, hematite, ilmenite), these heavy minerals found in the sandstone are associated with igneous and metamorphic source which indicates that these maastritchian sediments are from basement complex rock The ZTR index of 67.96% and the values of the kurtosis indicates a sub-mature sandstone to mature sandstone, which gives an excellent aquifer properties. Also, the paleoenvironment of deposition of the Maastrichtian sediments is Fluvial. The sand and sandstone bodies deposited in a fluvial system have sheet-like geometries and due to the differences in the extent of aquifer compartmentalization, Sandstone deposited in fluvial environment normally has better hydraulic conductivity which again reveals a good aquifer property. The sedimentological characteristics for the Sandstone exposed at Fugar and environs, is a coarsening upward sequence (increasing grain sizes) with a progressive increase in sorting. since hydraulic conductivity increases with increasing grain sizes and sorting, hence, excellent aquifer characteristics for the groundwater within the study area. The foregoing revealed that the aquifer geometry and properties of the study areas is favourable for the availability of drinking water for both the Urban and rural dwellers within these communities.&#x0D; Keywords: Aquifer geometry, groundwater, hydraulic conductivity, Anambra Basin

Analysis of coastal-plain fluvial architecture and high-frequency stacking patterns in the Upper Cretaceous Masuk Formation, Utah, U.S.A.: Climate-driven cyclicity?

ABSTRACTMost sequence stratigraphic models are based on the premise that relative changes in sea level (RSL) control stacking patterns in continental-margin settings. An alternative hypothesis, however, is that upstream factors, notably variations in relative water discharge (RQW) or the ratio of water to sediment discharge can influence or control stratal stacking patterns in fluvial systems. Sequence boundaries of RQW-driven systems differ from those driven by base-level fluctuations in that: 1) the depth of incision increases updip, and 2) rates of erosion are spatially uniform, leading to the formation of widespread, planar sequence boundaries. This paper presents an architectural and stratigraphic analysis of the well-exposed Masuk Formation of the Henry Mountains Syncline in southern Utah, an Upper Cretaceous coastal-plain fluvial succession that is interpreted to have been influenced significantly by RQW. Six lithofacies are recognized, three (Facies 1–3) recording floodbasin, mire, and (in one short interval) estuarine environments, and three (Facies 4–6) record different kinds of channel fills on a coastal alluvial plain. Seven major composite channel bodies (Facies 4–6), separated by intervals of non-channel deposits (Facies 1–3), are recognized in the stratigraphic interval. Composite channel bodies display planar, sheet-like geometry and are laterally continuous to a significantly greater extent (&amp;gt; 10 km) than would be expected from purely autogenic channel-belt construction. Together, these intervals record a series of high-frequency sequences, formed along the western margin of the Western Interior Seaway. In each individual sequence is a repetitive facies succession from a basal chaotic sandstone with admixed mudrock and sandstone transitioning upward to a more organized cross-bedded and stratified sandstone. This is interpreted to record cyclical changes from a peaked (flashy) discharge regime to a more normal runoff regime. Paleoflow data indicate a dominance of transverse (eastward-directed) dispersal early in the accumulation of the Masuk Formation, shifting to a pattern of greater axial (northward) dispersal over time. The RQW signal is strong in the lower part of the formation, decreasing upward. This suggests that the relatively short-headed streams draining from the rising Sevier fold–thrust belt were strongly influenced by climatic cyclicity, whereas more distally sourced systems were not. This study provides new insights into the architecture and stacking patterns of coastal-plain fluvial successions, emphasizing the plausible role that climate can play in shaping alluvial architecture in the rock record.

Thickening-upward cycles in deep-marine and deep-lacustrine turbidite lobes: examples from the Clare Basin and the Ordos Basin

Deep-marine and deep-lacustrine reservoirs have been targets for conventional and unconventional oil and gas exploration and development for decades. Thickening-upward cycles in the deep-marine Carboniferous Ross Sandstone Formation outcrops in western Ireland and the deep-lacustrine Triassic Yanchang Formation outcrops in southeast Ordos Basin have been investigated and correlated in this study. Typical thickening-upward cycles consisting of, from bottom to top: (1) laminated shales/shales with interbedded siltstone beds; (2) interbedded sandstones/siltstones and mudstones; (3) structureless massive sandstones, are well recognized in these outcrops and are interpreted as turbidite lobes. A continuously prograding lobe-element model is proposed to explain the repeated stacking of thickening-upward cycles. Thickening-upward cycles developed within deep-marine and deep-lacustrine environments are highly comparable in many aspects, such as sedimentary structures, sheet-like geometries and amalgamation features. A frequent and strong degree of amalgamation is developed within the massive sandstone at the top of each thickening-upward cycle, suggesting a layer-by-layer depositional manner. Field observations and comparison with deep-marine counterparts support the occurrence of turbidity flows in the Yanchang Formation, Ordos Basin.

Improving the pore-ion size compatibility between poly(ionic liquid)-derived carbons and high-voltage electrolytes for high energy-power supercapacitors

Maximizing carbon capacitance in high-voltage electrolytes has gained increasing interests to resolve the low energy storage concern in supercapacitors. Yet the large ion sizes and high viscosity of such electrolytes greatly thwart their compatibility with the pore diameters of carbon electrodes, leading to sluggish charge transport and unsatisfied energy-power outputs. Herein, heteroatom-doped, hierarchical porous carbons are derived from a high-carbon-yield main-chain poly(ionic liquid) bearing NH2+: HSO4− ion pairs and rigid aromatic backbones, followed by tailoring the 3D porous architecture through alkali ion exchange and in-situ activation. The typical sample (PIL-RbC) has sheet-like geometry, electron-rich N/O heterogeneous dopants, and a vast adsorbing surface (3021 m2 g−1). More importantly, PIL-RbC with ion-matching pores (dominated at 0.80 nm) and ion-transport paths (>1 nm pores) shows a superb compatibility with 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid electrolyte, giving a maximized electrode capacitance of 228 F g−1 in a symmetric supercapacitor. The PIL-RbC-based device delivers a high energy density up to 119.4 Wh kg−1 at 397 W kg−1, and maintains 41.7 Wh kg−1 at a high power-output of 19.7 kW kg−1, along with a satisfactory tolerability (91% retention after 10,000 consecutive cycles at 4 V). This strategy sheds light on both synthesizing poly(ionic liquid)-derived heteroatom-doped porous carbons and matching well-designed carbon electrodes with high-potential electrolytes for integrated enhancements in supercapacitor performances.

Carbonate reservoir outcrop analogues with a glance at pore-scale (Middle Jurassic, Lusitanian Basin, Portugal)

Abstract The Middle Jurassic carbonate successions from the Lusitanian Basin (Portugal) show a range of facies deposited across a ramp depositional system, well exposed over large areas. These facies are valuable for understanding reservoirs and related seal and trap configurations, namely in carbonate ramps. This paper documents primarily shallow-water units corresponding to the dominant reservoir-type facies, highlighting their potential as analogues, particularly at outcrop but integrating main macro and micro-scale characteristics. The mid and inner ramp sediments, which include the key studied units, consist of: peloidal-intraclastic, bioturbated, fossiliferous limestones; oolitic, skeletal, and coral-algal limestones, assigned to shoals and barrier-island complex; fossiliferous, oncoidal, fenestral deposits from lagoonal, peritidal and, locally, pedogenic settings; dolostones and dolomitic limestones. Facies with higher potential reservoir features are addressed in more detail, in three broad groups: sandbodies; biostromes; dolostones/dolomitic limestones. The remaining facies are more briefly described. The most widespread reservoir lithofacies are cross-stratified or massive oolitic and bioclastic grainstones to rudstones and coral-dominated biostromes. The larger-scale sandbody units show a dominant sheet-like geometry, but wedges and smaller-scale lensoid units occur, grading into, and interfingering with, other facies types. The reservoir facies are closely associated with, hence often encased by, flow baffle or barrier seal facies, either landwards (lagoonal/peritidal) or seawards (mid-outer ramp). This architecture, coupled with varied diagenetic paragenesis, created a range of stratigraphic and diagenetic traps that may be perceived as play similarities in potential exploration situations. The present reservoir quality is mostly low to moderate, but examples of high/excellent porosities and locally enhanced permeabilities occur. Overall, these units are highly suitable field analogues to clarify processes leading to depositional, diagenetic, fractured and hybrid reservoir types. Moreover, they clearly indicate how shoreface dynamics, shallow-water carbonate factory productivity and diagenesis lead to more complex reservoirs than usually appreciated in mostly homoclinal depositional systems.

Investigation of seismic attributes, depositional environments, and hydrocarbon sweet-spot distribution in the Serbin field, Taylor Formation, Southeast Texas

We have conducted seismic-attribute analysis at the Serbin field — in an area straddling Lee, Fayette, and Bastrop Counties and covering approximately [Formula: see text] (approximately [Formula: see text]) — using new, reprocessed, 3D seismic data to provide additional understanding of depositional environments and better predict the distribution of hydrocarbon sweet spots. We converted the 3D seismic volume into a log-lithology volume and integrated core data to examine the distribution of lithology and interpret depositional environments. By conducting multiattribute analysis, we predicted resistivity (deep-induction log) volume and generated a resistivity map to identify hydrocarbon sweet spots. Our results show that reservoir sandstones in the Serbin field are storm-dominated, shelf-sand deposits. Although individual sandstone beds are lenticular and discontinuous, they collectively constitute a sheet-like geometry, trending northeast to southwest. On the basis of resistivity maps and rock property versus seismic-amplitude crossplots, we differentiated reservoirs in the lower Taylor Formation into two zones: (1) a northwest, high-resistivity, high-acoustic impedance zone and (2) a southeast, low-resistivity, low-acoustic impedance zone. The results also indicated that hydrocarbon sweet spots in the Serbin field are characterized by high resistivity and high impedance. Furthermore, the log-lithology method, although fast and effective, is limited because it cannot take into account sandstone zones having low acoustic impedance.

Magnesium-based basic mixtures derived from earth-abundant natural minerals for CO2 capture in simulated flue gas

Magnesium-based adsorbents with high theoretical CO2 uptakes, moderate regeneration energy, and good cyclic working stability show promise for intermediate-temperature CO2 capture from flue gas stream. Identification of low-cost materials for fabricating highly efficient magnesium-based adsorbents is one significant challenge for their large-scale applications. In this work, magnesium-based basic mixtures derived from earth-abundant natural minerals were employed as CO2 adsorbents. CO2 sorption performance of the adsorbents was evaluated using a fixed-bed reactor. Several kinetic equations were adopted to describe their CO2 sorption kinetic behaviors. Results show that the BM-HM and BM-BR adsorbents calcined from hydromagnesite and brucite possess attractive CO2 uptakes (1.73 and 1.67 mmol CO2/g) at 200 °C. The Avrami fractional kinetic model is expected to accurately predict the equilibrium CO2 uptakes, and the adsorbents show relatively fast CO2 sorption rate. The desired adsorbents exhibit favorable working stability with low loss-in-capacity of 5.65% and 5.33% over 10 repeated cycles. Characterization analyses indicates that the adsorbents own great physicochemical parameters, which will facilitate the diffusion and adsorption of gaseous reactants. Moreover, the dispersion of the basic mixtures in flake and sheet-like geometry can benefit the adsorbents reduced internal diffusion resistance and enhanced MgO utilization efficiency. These are associated with their excellent CO2 sorption performance. The scheme provides significant environmental implications as it will provide an attractive route towards cost-effective CO2 abatement and waste management.

Effect of oxygen substitution and phase on nickel selenide nanostructures for supercapacitor applications

Electrochemical supercapacitors are the eminent technology for the progress of energy storage devices. The current manuscript deals with the formation of oxygen substituted nickel selenide nanostructures and their use as active electrode material for supercapacitor, expecting an enhanced performance owing to their sheet-like geometry, high specific surface area and porous assembly. In this context, Ni(OH)2 (nickel hydroxide) nanostructures were synthesized employing one-pot hydrothermal method and the ion-exchange reaction of Ni(OH)2 nanostructures with selenium resulted in cubic-NiSe2 (nickel selenide) nanostructures. Further, annealing NiSe2 nanostructures at intermediate pressure (10^-3 Torr) has realized the partial oxygen substitution in place of selenium, resulting in NiSe/NiO nanostructures along with phase change from cubic-NiSe2 to hexagonal-NiSe. Supercapacitor electrodes fabricated using NiSe/NiO nanostructures delivered the specific capacitance of 83.5 F g−1 at the scan rate of 2 mV s−1, which is surprisingly more than a double as compared with pristine NiSe2 electrodes (37.4 F g−1). Annealing at intermediate pressure and high temperature significantly enhanced the specific capacitances of the nanostructured electrodes and also accompanied with the good capacitance retention of 94% for 5000 CV cycles.

Lombardi reservoir, San Ardo field, California: Sequence stratigraphy in a deltaic environment associated with local tectoni

The Lombardi reservoir at San Ardo oil field in California is extremely sand rich (>90%) and appears to be a relatively simple reservoir several hundred feet thick. The purpose of this study is to characterize stratigraphic complexities in the Lombardi reservoir that may affect later production and interpret how changes in stratigraphic architecture are tied to local syndepositional tectonism. Two parasequence sets are present in the Lombardi: the reservoir exhibits clinoform geometries along the western edge of the field and stacking patterns within the reservoir change across the field. Based on stacking pattern, core, and correlation studies, two possible sequence boundaries are recognized in the Lombardi sand. A lower sequence boundary is proposed approximately in the middle of the Lombardi sand, and an upper sequence boundary is proposed at the top of the Lombardi sand. In the southern part of the field, the Lombardi sand consists of two progradational parasequence sets, separated by the mid-Lombardi sequence boundary. The upper sequence boundary clearly truncates underlying folded Lombardi sand. Just a few miles (∼5 km) away, in the northwest part of the field, the Lombardi sand consists of a lower progradational parasequence set and an upper retrogradational parasequence set, separated by the mid-Lombardi sequence boundary. The upper sequence boundary at the top of the Lombardi sand shows little evidence of truncation of underlying units and is recognized by onlapping of younger strata. The difference in reservoir architecture between the south and northwest part of the field, a distance of only a few miles (∼5 km), is interpreted to be related to syndepositional uplift accompanying tectonism in the south. In core, the Lombardi sand consists mostly of homogeneous sand and bioturbated sand, arranged in upward-coarsening successions. The Lombardi sand is interpreted to be the product of deltaic deposition based on (1) the presence of homogeneous and laminated sandstones interpreted to represent mass flow deposits and (2) its restricted geographic distribution within the Salinas basin. No evidence of deposition in a wave-dominated or tidal-dominated shoreline is indicated. The interpretation presented here is that the sediments were deposited on the front of a delta emptying into a wave-protected estuary or bay, with minimal tidal effects. Complexities in stratigraphic architecture along the western edge of the field do not currently affect production but will likely become important during later stages of field development. That is, in the developed part of the field, reservoir continuity is not an issue, because of high sand content and sheet-like geometries. However, at the margins of the field, which will be produced in the future, clinoform geometries and sandstone tongues clearly affect reservoir continuity and will create vertical compartments during draining.

Depositional environment reconstruction of the Maragheh Formation, East Azarbaijan, Northwestern Iran

The Maragheh Formation is an important deposit, which yields the savanna-type large mammal assemblage known as the “Pikermian Fauna.” Our high-resolution facies analysis of the interval between the Lower Pumice and the White Tuff demonstrated that debris-flow deposits and paleosols are dominant in the studied sequence. Fluvial channel-fill and small pond facies are the subordinate components in this interval. Most of the channel-fill deposits are interpreted as having been accumulated from ephemeral streams. The wide distribution of the Middle Pumice, the fact that it contains grains with older ages than those of the Lower Pumice, and the presence of “traction carpet” deposits allow the interpretation of the pumice interval as having been deposited from a hyperconcentrated flow probably caused by crater-lake destruction around the peak of Mt. Sahand, which supplied older rocks to the flow. The internal architecture of fluvial channel-fill deposits and the structures of paleosols (rhizoliths, cracks and slickensides: probable Vertic Inceptisols) imply a seasonal climate during deposition of the studied interval. This is consistent with previous environmental reconstructions based on mammal fossils (woodland-dominated savannah) as well as the results of phytolith analysis and δ18O data obtained from northern Iran. However, flood deposits covering the paleosols, showing sheet-like geometry, may not have been affected by large trees on the flood plain: the extent of woodland around the study site appears to have been limited.

Mesoproterozoic delta systems of the Açuruá Formation, Chapada Diamantina, Brazil

Facies analysis, distinct depositional paleoflow directions and grain size ranges suggest that different fluvial systems fed coeval distinct, independent river-dominated and tide-dominated braid delta systems in the Mesoproterozoic Açuruá Formation. The river-dominated delta system is characterized by: (a) vertical stacking of parasequences up to 30m which are characterized by coarsening- and thickening-upward trends; (b) gradationally based vertical succession of prodelta, delta front, distributary channels, and floodplain; (c) grain size of sandstone from delta front and distributary channels varies respectively from very fine to medium and medium to coarse; (d) lacking of wave or tide reworking suggests delta development in a relatively low energy marine basin; (e) paleocurrent readings indicate delta front sandstone bodies shifting laterally towards NE to SE directions. The tide-dominated delta system is characterized by: (a) vertical stacking of parasequences up to 25m which are characterized by coarsening- and thickening-upward trends; (b) gradationally based vertical succession of prodelta, delta front and tide-influenced distributary channels; (c) grain size of sandstone from delta front and tide-influenced distributary channels varies respectively from very fine to coarse and fine to granular; (d) abundance of tide-influenced sedimentary structures suggest tidal dominated delta development; (e) consistent bidirectional paleocurrents with northwards ebb-tide direction and no lobe shifting. The studied braid delta systems belong to a highstand system tract and as such, they exhibit classic parasequence sets with progradational stacking pattern. The facies association variability and overall characteristics of these Mesoproteozoic delta systems are compatible with delta systems of all ages. However, contrary to typically Phanerozoic deltas – which are characterized by progradational clinoforms – the coalescence of the studied braid delta facies associations promoted fairly sheet-like geometry limited by marine flooding surface that more likely resulted from the response of deposition on shallow and wide epeiric sea.

Climatic and paleogeographic significance of eolian sediment in the Middle Permian Dog Creek Shale (Midcontinent U.S.)

Middle Permian fine-grained redbeds of Midcontinent North America are analogous to many Permian units globally. They archive an interesting time in Earth history, but the lack of fossils and the fine grain size have confounded attempts to refine the age and depositional setting, respectively. Here we focus on the Dog Creek Shale and correlatives of Oklahoma and Kansas (paleo-tropical western Pangaea), which are representative of many analogous Permian units across the region and globe, to assess the age, depositional environment, and provenance of siliciclastic material.These mudstone-dominant units have long been interpreted to record marine deltaic or tidal flat deposition based primarily on the presence of evaporites and an inferred relationship with sandstone units southward. However, the uniform grain size, and occurrence of common paleosols, together with the lack of typical deltaic attributes such as hyper/hypo-pycnites, proximal deltaic channels, and large-scale upwardly coarsening trends, in addition to the problematic correlation, complicate this interpretation. Sheet-like tabular siliciclastic units thin northward from the Anadarko foredeep (Oklahoma) onto the Anadarko shelf (Kansas), and undergo lateral facies changes into marginal marine evaporites of the San Andres Formation in the Palo Duro Basin (Texas Panhandle). The fine and uniform grain size, massive bedding, and sheet-like geometry indicate that the siliciclastic units are eolian in origin, but at times were transported by wind and deposited and reworked in mudflats. Abundant Vertisols within the Dog Creek Shale indicate periods of wetting and drying in a low-relief setting. Major detrital zircon age populations reflect a dominantly east to southeasterly Appalachian–Ouachita source, with minor input from derivative sediment from the Ancestral Rocky Mountains to the west and northwest. These data indicate prevailing easterlies, and some westerly and southwesterly winds in western equatorial Pangaea, possibly representing north to south shifting of the Inter-Tropical Convergence Zone (ITCZ), likely associated with monsoonal circulation. The predominance of eolian-transported material and its capture in a series of mudflats and soils indicates that midcontinent North America (western equatorial Pangaea) formed a major sink for large volumes of atmospheric dust in middle Permian time, quite unlike the modern and recent tropics.

THE REDSHIFT DISTRIBUTION OF INTERVENING WEAK Mg II QUASAR ABSORBERS AND A CURIOUS DEPENDENCE ON QUASAR LUMINOSITY

We have identified 469 MgII doublet systems having W_r >= 0.02 {\AA} in 252 Keck/HIRES and UVES/VLT quasar spectra over the redshift range 0.1 < z < 2.6. Using the largest sample yet of 188 weak MgII systems (0.02 {\AA} <= W_r < 0.3 {\AA}), we calculate their absorber redshift path density, dN/dz. We find clear evidence of evolution, with dN/dz peaking at z ~ 1.2, and that the product of the absorber number density and cross section decreases linearly with increasing redshift; weak MgII absorbers seem to vanish above z ~ 2.7. If the absorbers are ionized by the UV background, we estimate number densities of 10^6 - 10^9 per Mpc^3 for spherical geometries and 10^2 - 10^5 per Mpc^3 for more sheetlike geometries. We also find that dN/dz toward intrinsically faint versus bright quasars differs significantly for weak and strong (W_r >= 1.0 {\AA}) absorbers. For weak absorption, dN/dz toward bright quasars is ~ 25% higher than toward faint quasars (10 sigma at low redshift, 0.4 <= z <= 1.4, and 4 sigma at high redshift, 1.4 < z <= 2.34). For strong absorption the trend reverses, with dN/dz toward faint quasars being ~ 20% higher than toward bright quasars (also 10 sigma at low redshift and 4 sigma at high redshift). We explore scenarios in which beam size is proportional to quasar luminosity and varies with absorber and quasar redshifts. These do not explain dN/dz's dependence on quasar luminosity.