Granulometric and facies analysis of Middle–Upper Jurassic rocks of Ler Dome, Kachchh, western India: an attempt to reconstruct the depositional environment

Grain size analysis is an important sedimentological tool used to unravel hydrodynamic conditions, mode of trans- portation and deposition of detrital sediments. For the present study, detailed grain size analysis was carried out in order to decipher the palaeodepositional environment of Middle–Upper Jurassic rocks of the Ler Dome (Kachchh, western India), which is further reinforced by facies analysis. Microtextures were identified as grooves, straight steps and V-shaped pits, curved steps and solution pits suggesting the predominance of chemical solution activity. Grain size statistical parameters (Graphic and Moment parameters) were used to document depositional processes, sedimen- tation mechanisms and conditions of hydrodynamic energy, as well as to discriminate between various depositional environments. The grain size parameters show that most of the sandstones are medium- to coarse-grained, moderately to well sorted, strongly fine skewed to fine skewed and mesokurtic to platykurtic in nature. The abundance of medi- um- to coarse-grained sandstones indicates fluctuating energy levels of the deposition medium and sediment type of the source area. The bivariate plots show that the samples are mostly grouped, except for some samples that show a scattered trend, which is either due to a mixture of two modes in equal proportion in bimodal sediments or good sorting in unimodal sediments. The linear discriminant function analysis is predominantly indicative of turbidity current de- posits under shallow-marine conditions. The C-M plots indicate that the sediments formed mainly by rolling to bottom suspension and rolling condition in a beach subenvironment. Log probability curves show that the mixing between the suspension and saltation populations is related to variable energy conditions

Petrology and stratigraphy of the Kiowa and Dakota Formations (basal Cretaceous), north-central Kansas

Ph. D. University of Kansas, Geology 1966The Kiowa Foundation (formerly Kiowa Shale) of Early Cretaceous age and the Dakota Foundation of Early(?) and Late Cretaceous age have been studied and mapped on a detailed reconnaissance basis in an area encompassing some 3500 square miles (9100 krn2) in north-central Kansas. Mapping was initiated as a means of unravelling the stratigraphy, an understanding of which is essential to sedimentary petrographic studies. Neither formation had previously been mapped extensively despite long standing as rock-stratigraphic units. The Kiowa Formation is not present in the northern part of the area mapped. Both formations have an involved nomenclatural history. The Kiowa Foundation is a heterogeneous assemblage composed largely of olive-weathering gray illitic shale and abundant sandstone. The Foundation rests on the eroded surface of Permian rocks. Along the eastern fringes of its outcrop belt, the Kiowa Formation contains a diagnostic sequence of siltstone underlain by a heterogeneous assemblage of red-mottled and carbonaceous gray to black mudstone and siltstone. The mudstone contains variable amounts of montmorillonite and kaolinite. The siltstone and the underlying assemblage are designated the Longford Member (new name) of the Kiowa Foundation. Above the Longford Member, the Kiowa Formation contains numerous fossils of marine or brackish-water invertebrates. As in the Dakota Formation above, fossil deciduous leaves locally are abundant. The Dakota Formation is subdivided into two members, the Terra Cotta Clay Member below and the Janssen Clay Member above. The Terra Cotta is made up largely of light-gray kaolinitic mudstone and claystone showing abundant red mottles, but it also contains appreciable sandstone. The Janssen is composed chiefly of gray and dark-gray kaolinitic mudstone and claystone, locally abundant sandstone, and scattered beds of lignite. It contains marine and brackish-water fossils near its contact with the overlying Graneros Shale, into which its upper part grades laterally. The Kiowa Formation was deposited in, and near the margins of, the Early Cretaceous sea that transgressed from southwest· to northeast across Kansas. Part of the Longford Member of the Kiowa Formation is thought to have been deposited on the landward side of the shifting shoreline. The upper part of the formation is thought to include regressive deposits, sedimentation of which heralded deposition of the Dakota Formation. The Dakota Formation is mainly an alluvial plain deposit that developed and extended itself southwestward upon relatively rapid withdrawal of the Kiowa sea. Upward changes in the Janssen Clay Member largely reflect the influence of the transgressing sea in which the Graneros Shale was deposited. Sandstone in the Kiowa and Dakota formations is mature and contains as much as 95 percent detrital quartz, quartzite, and chert, and locally contains molds and casts of pelecypods. Conglomeratic sandstone in the Dakota Formation is coarser grained than conglomeratic sandstone in the Kiowa and contains numerous pebbles of penecontemporaneously reworked mudstone and claystone. Heavy mineral assemblages in both formations are similar and contain zircon, tourmaline, and staurolite as major components. The proportion of staurolite decreases upward in passing from the Kiowa Formation to the Janssen Clay Member of the Dakota Formation. Sandstone in both formations is abundantly cross-stratified. Computation of vector-resultant dip bearings of cross-strata in both formations indicates that the regional slope was inclined to the west-southwest. The heavy mineral suite therefore is attributed in part to source areas lying to the east and northeast, mainly Paleozoic or older rocks. The staurolite probably was derived from rocks in the central Appalachian Mountains. Variations in clay mineralogy are attributed to differential transport and sedimentation. Source areas for the clay minerals are thought to have been generally the same for both formations. The contact selected for mapping the Kiowa and Dakota formations is a sharp, consistent boundary that can be used in most of north-central Kansas and in the type area of the Kiowa Foundation in southwestern Kansas. In many places the contact is disconformable

Automatically extracted Antarctic coastline using remotely-sensed data: an update

The temporal and spatial variability of the Antarctic coastline is a clear indicator of change in extent and mass balance of ice sheets and shelves. In this study, the Canny edge detector was utilized to automatically extract high-resolution information of the Antarctic coastline for 2005, 2010, and 2017, based on optical and microwave satellite data. In order to improve the accuracy of the extracted coastlines, we developed the Canny algorithm by automatically calculating the local low and high thresholds via the intensity histogram of each image to derive thresholds to distinguish ice sheet from water. A visual comparison between extracted coastlines and mosaics from remote sensing images shows good agreement. In addition, comparing manually extracted coastline, based on prior knowledge, the accuracy of planimetric position of automated extraction is better than two pixels of Landsat images (30 m resolution). Our study shows that the percentage of deviation (7 km2 (2005) to 1.3537 × 107 km2 (2010) and 1.3657 × 107 km2 (2017). We have found that the decline of the Antarctic area between 2005 and 2010 is related to the breakup of some individual ice shelves, mainly in the Antarctic Peninsula and off East Antarctica. We present a detailed analysis of the temporal and spatial change of coastline and area change for the six ice shelves that exhibited the largest change in the last decade. The largest area change (a loss of 4836 km2) occurred at the Wilkins Ice Shelf between 2005 and 2010

Phase-space structures I: A comparison of 6D density estimators

This paper reviews and analyses methods used to identify neighbours in 6D space and estimate the corresponding phase-space density. It compares SPH methods to 6D Delaunay tessellation on statical and dynamical realisation of single halo profiles, paying attention to the unknown scaling, S_G, used to relate the spatial dimensions to the velocity dimensions. The methods with local adaptive metric provide the best phase-space estimators. They make use of a Shannon entropy criterion combined with a binary tree partitioning and with SPH interpolation using 10-40 neighbours. Local scaling implemented by such methods, which enforces local isotropy of the distribution function, can vary by about one order of magnitude in different regions within the system. It presents a bimodal distribution, in which one component is dominated by the main part of the halo and the other one is dominated by the substructures. While potentially better than SPH techniques, since it yields an optimal estimate of the local softening volume (and the local number of neighbours required to perform the interpolation), the Delaunay tessellation in fact poorly estimates the phase-space distribution function. Indeed, it requires, the choice of a global scaling S_G. We propose two methods to estimate S_G that yield a good global compromise. However, the Delaunay interpolation still remains quite sensitive to local anisotropies in the distribution. We also compare 6D phase-space density estimation with the proxy, Q=rho/sigma^3, where rho is the local density and 3 sigma^2 is the local 3D velocity dispersion. We show that Q only corresponds to a rough approximation of the true phase-space density, and is not able to capture all the details of the distribution in phase-space, ignoring, in particular, filamentation and tidal streams.Comment: Submitted to MNRAS, 22 pages, 18 figure

Red riding on hood: Exploring how galaxy colour depends on environment

Galaxy populations are known to exhibit a strong colour bimodality, corresponding to blue star-forming and red quiescent subpopulations. The relative abundance of the two populations has been found to vary with stellar mass and environment. In this paper, we explore the effect of environment considering different types of measurements. We choose a sample of $49, 911$ galaxies with $0.05 < z < 0.18$ from the Galaxy And Mass Assembly survey. We study the dependence of the fraction of red galaxies on different measures of the local environment as well as the large-scale "geometric" environment defined by density gradients in the surround- ing cosmic web. We find that the red galaxy fraction varies with the environment at fixed stellar mass. The red fraction depends more strongly on local environmental measures than on large-scale geometric environment measures. By comparing the different environmental densities, we show that no density measurement fully explains the observed environmental red fraction variation, suggesting the different measures of environmental density contain different information. We test whether the local environmental measures, when combined together, can explain all the observed environmental red fraction variation. The geometric environment has a small residual effect, and this effect is larger for voids than any other type of geometric environment. This could provide a test of the physics applied to cosmological-scale galaxy evolution simulations as it combines large-scale effects with local environmental impact.Comment: Accepted for publication in MNRAS; 16 pages; 10 figures; 2 tables

Understanding Arctic aerosols : multi-station climatology of extensive- and intensive-parameter optical retrievals & evaluation of an advanced aerosol transport model versus the multi-station climatology

Abstract : Atmospheric aerosols play a crucial radiative forcing role in climate systems. They influence the radiative balance by either the direct effect of absorbing or scattering of radiation or the indirect affect associated with the impact of their physical and optical properties on cloud droplet or ice nucleation properties. Parameterizing their direct and indirect radiative forcing contributions represents a major challenge to climate modellers. Uncertainties arise in the representation of aerosol microphysics and optical properties: to strengthen the confidence in climate model simulations, aerosol opto-physical property interpretations of robust (climatological scale) measurements in parallel with the validation of aerosol-model simulations are essential. It is accordingly important to understand the physical, chemical, and optical properties of aerosols as well as the processes that govern their formation and transportation mechanisms. Aerosol properties are characterized by their size, shape, chemical nature and concentration. From an optical (UV to near-IR) perspective, the fundamental form of the particle size distribution (PSD) that significantly affects optical measurements is largely represented by two modal components: a fine mode (FM) sub-micrometer (radius) component and a coarse mode (CM) super-micrometer component. Their optical impact is dependent on the PSD, the refractive index (which defines the scattering and absorption impact as a function of their size) and radiation wavelength. In this research project, we focused on Arctic aerosols: this is especially relevant from a climate change perspective given that Arctic temperature changes are roughly twice those of the global average. Our objectives were broken into two phases (corresponding to two peer-reviewed papers). The first phase was an investigation of the seasonal variations of various microphysical and optical aerosol properties over the Arctic using ground-based retrievals of sunphotometer/sky radiometer measurements provided by AERONET/AEROCAN (AEROsol Robotic NETwork/Canadian AEROCAN subnetwork). The second was an investigation into the accuracy of spatio-temporal aerosol model simulations and their success in capturing the seasonal trends of Arctic aerosols. Given the daylight limitations of sunphotometry/sky radiometry, we were constrained to the spring to early fall seasons. In Paper 1, we performed a climatological-scale (seasonal) multi-year study of key extensive (quantity dependent) and intensive (quantity independent) aerosol retrievals from six AERONET Arctic stations. An important original contribution of this paper was an analysis that went beyond the traditional parameters of aerosol optical depth (AOD) and classical Angstrom exponent (spectral slope of the AOD in logarithmic space). The analysis parameters included the PSD, the radius of cardinal features of the PSD such as the peaks of the FM and CM components, the FM and CM AOD, the FM and CM effective radii, and the fine mode fraction (FMF). The originality of the monthly-binned results included robust FM and CM seasonal tendencies from spring to summer (notably a small but robust increase in the radius of the FM peak that was attributed to the influence of large particle summertime smoke and the demonstration of a pan-Arctic (even pan Canadian) springtime, small CM-particle-size (~ 1.3 µm) peak that was attributed to springtime Asian dust. In Paper 2, we compared the simulations of GCT (GEOS-Chem - TOMAS) to the seasonal results of Paper 1. The TOMAS (TwO Moment Aerosol Sectional) aerosol microphysical model provides PSD number and mass concentrations spread across an Arctic domain that included the 6 AERONET stations. We investigated the same seasonal variations as those presented in Paper 1 by (offline) conversion TOMAS outputs to parameters that were analogous to the AERONET products. Specific Paper 1 tendencies such as the small CM-particle-size peak due to Asian dust and the robust spring to summer decrease of the CM AOD were successfully simulated. At the same time, GCT did not capture the spring to summer increase in radius of the FM peak and provided a FM effective radius that was significantly smaller than the values of Paper 1. This, we argued, was likely attributable to a GCT shortcoming in the modelling of small particle (coagulative) growth of smoke particles (problem associated with the coarse GCT lat/long spatial resolution of 4 x 5 degrees).Les aérosols atmosphériques jouent un rôle crucial dans le forçage radiatif des systèmes climatiques. Ils influencent le bilan radiatif soit par l'effet direct d'absorption ou de diffusion du rayonnement, soit par l'effet indirect associé à l'impact de leurs propriétés physiques et optiques sur les propriétés de nucléation des gouttelettes nuageuses ou de la glace. Le paramétrage de leurs contributions directes et indirectes au forçage radiatif représente un défi majeur pour les modélisateurs climatiques. Des incertitudes surgissent dans la représentation des propriétés microphysiques et optiques des aérosols : pour renforcer la certitude dans les simulations des modèles climatiques, les interprétations des propriétés opto-physiques des aérosols de mesures robustes (à l'échelle climatologique) parallèlement à la validation des simulations des modèles d'aérosols sont essentielles. Il est donc important de comprendre les propriétés physiques, chimiques et optiques des aérosols ainsi que les processus qui régissent leurs mécanismes de formation et de transport. Les propriétés des aérosols sont caractérisées par leur taille, leur forme, leur nature chimique et leur concentration. D'un point de vue optique (UV à proche IR), ils sont effectivement bimodaux : leur distribution granulométrique (PSD) est largement représentée par deux composantes modales : une composante submicrométrique (rayon) de mode fin (FM) et une composante grossière (CM) qui est un composant super-micrométrique. Leur impact optique dépend de la PSD, de l'indice de réfraction (qui définit l'impact de diffusion et d'absorption en fonction de leur taille) et de la longueur d'onde du rayonnement. Dans ce projet de recherche, nous nous sommes concentrés sur les aérosols arctiques : cela est particulièrement pertinent du point de vue du changement climatique étant donné que les changements de la température dans l'Arctique sont environ le double de la moyenne mondiale. Nos objectifs ont été divisés sur deux phases (correspondant à deux articles évalués par des pairs). La première phase consistait en une analyse des variations saisonnières de diverses propriétés microphysiques et optiques des aérosols au-dessus de l'Arctique à l'aide d'extractions au sol de mesures de photomètres solaires/radiomètres célestes fournies par AERONET/AEROCAN (AEROsol Robotic NETwork/sous-réseau canadien AEROCAN). La seconde était analyse sur l'exactitude des simulations de modèles d'aérosols spatio-temporels et leur succès dans la capture des tendances saisonnières des aérosols arctiques. Étant donné les limites de la lumière du jour de la photométrie solaire/radiométrie du ciel, nous étions limités aux saisons du printemps et au début de l'automne. Dans le premier l'article, nous avons effectué une étude pluriannuelle à l'échelle climatologique (saisonnière) des principales caractéristiques d'aérosols extensives (dépendantes de la quantité) et intensives (indépendantes de la quantité) de six stations d’AERONET dans de l’Arctique. Une contribution originale importante de cet article était une analyse qui allait au-delà des paramètres traditionnels de la profondeur optique des aérosols (AOD) et de l'exposant d'Angstrom classique (pente spectrale de l'AOD). Les paramètres d'analyse comprenaient la PSD, le rayon des caractéristiques cardinales de la PSD telles que les pics des composantes FM et CM, les AOD FM et CM, les rayons effectifs FM et CM et la fraction de mode fin (FMF). L'originalité des résultats mensuels incluait des tendances saisonnières FM et CM robustes du printemps à l'été (notamment une augmentation faible mais robuste du rayon du pic FM qui a été attribuée à l'influence de la fumée estivale à grosses particules et à la démonstration d'un pan -Printemps arctique (même pancanadien), petit pic de taille de particules CM (~ 1,3 m) attribué à la poussière asiatique printanière. Dans le deuxième l'article, nous avons comparé les simulations de GCT (GEOS-Chem - TOMAS) aux résultats saisonniers du premier article 1. Le modèle microphysique d'aérosol TOMAS (TwO Moment Aerosol Sectional) fournit les densités numériques et les concentrations en masse réparties dans un domaine Arctique qui comprenait le six stations d’AERONET. Nous avons étudié les mêmes variations saisonnières que celles présentées dans le premier article par conversion (hors ligne) des sorties TOMAS en paramètres analogues aux produits AERONET. Les tendances spécifiques du premier article 1 telles que le petit pic de taille de particule CM dû à la poussière asiatique et la forte diminution du printemps à l'été de l'AOD CM ont été simulées avec succès. Au même temps, GCT n'a pas capturé l'augmentation du printemps à l'été du rayon du pic FM et a fourni un rayon effectif FM qui était significativement plus petit que les valeurs de la première recherche. Ceci était probablement attribuable à une lacune de GCT dans la modélisation de la croissance de petites particules (coagulantes) de particules de fumée (problème associé à la résolution spatiale lat/long GCT grossière de 4' x 5')

APOGEE Data and Spectral Analysis from SDSS Data Release 16: Seven Years of Observations Including First Results from APOGEE-South

The spectral analysis and data products in Data Release 16 (DR16; December 2019) from the high-resolution near-infrared APOGEE-2/SDSS-IV survey are described. Compared to the previous APOGEE data release (DR14; July 2017), APOGEE DR16 includes about 200000 new stellar spectra, of which 100000 are from a new southern APOGEE instrument mounted on the 2.5 m du Pont telescope at Las Campanas Observatory in Chile. DR16 includes all data taken up to August 2018, including data released in previous data releases. All of the data have been re-reduced and re-analyzed using the latest pipelines, resulting in a total of 473307 spectra of 437445 stars. Changes to the analysis methods for this release include, but are not limited to, the use of MARCS model atmospheres for calculation of the entire main grid of synthetic spectra used in the analysis, a new method for filling "holes" in the grids due to unconverged model atmospheres, and a new scheme for continuum normalization. Abundances of the neutron capture element Ce are included for the first time. A new scheme for estimating uncertainties of the derived quantities using stars with multiple observations has been applied, and calibrated values of surface gravities for dwarf stars are now supplied. Compared to DR14, the radial velocities derived for this release more closely match those in the Gaia DR2 data base, and a clear improvement in the spectral analysis of the coolest giants can be seen. The reduced spectra as well as the result of the analysis can be downloaded using links provided in the SDSS DR16 web page

The Rise of Massive Red Galaxies: the color-magnitude and color-stellar mass diagrams for z < ~2 from the MUltiwavelength Survey by Yale-Chile (MUSYC)

We present the color-magnitude and color-stellar mass diagrams for galaxies with z_phot < ~2, based on a K < 22 (AB) catalog of the Extended Chandra Deep Field South (ECDFS) from the MUltiwavelength Survey by Yale-Chile (MUSYC). Our main sample of 7840 galaxies contains 1297 M_* > 10^11 M_Sol galaxies in the range 0.2 < z_phot < 1.8. We show empirically that this catalog is approximately complete for M_* > 10^11 M_Sol galaxies for z_phot < 1.8. For this mass-limited sample, we show that the locus of the red sequence color-stellar mass relation evolves as Del(u-r) ~ (-0.44+/-0.02) z_phot for z_phot ~1.3, however, we are no longer able to reliably distinguish red and blue subpopulations from the observed color distribution; we show that this would require much deeper near infrared data. At 1.5 < z_phot 10^11 M_Sol galaxies is ~50% of the local value, with a red fraction of ~33%. Making a parametric fit to the observed evolution, we find n_tot(z) ~ (1+z_phot)^(-0.52+/-0.12(+/-0.20)). We find stronger evolution in the red fraction: f_red(z) ~ (1+z_phot)^(-1.17+/-0.18(+/-0.21)). Through a series of sensitivity analyses, we show that the most important sources of systematic error are: 1. systematic differences in the analysis of the z~0 and z>>0 samples; 2. systematic effects associated with details of the photometric redshift calculation; and 3. uncertainties in the photometric calibration. With this in mind, we show that our results based on photometric redshifts are consistent with a completely independent analysis which does not require redshift information for individual galaxies. Our results suggest that, at most, 1/5 of local red sequence galaxies with M_* >10^11 M_Sol were already in place at z ~ 2.Comment: Accepted for publication in ApJ. 31 pages in emulateapj format; 18 figues (14 in main text). Additional online data available through http://www.strw.leidenuniv.nl/~ent

Coarse-to-Fine Changes of Receptive Fields in Lateral Geniculate Nucleus Have a Transient and a Sustained Component That Depend on Distinct Mechanisms

Visual processing in the brain seems to provide fast but coarse information before information about fine details. Such dynamics occur also in single neurons at several levels of the visual system. In the dorsal lateral geniculate nucleus (LGN), neurons have a receptive field (RF) with antagonistic center-surround organization, and temporal changes in center-surround organization are generally assumed to be due to a time-lag of the surround activity relative to center activity. Spatial resolution may be measured as the inverse of center size, and in LGN neurons RF-center width changes during static stimulation with durations in the range of normal fixation periods (250–500 ms) between saccadic eye-movements. The RF-center is initially large, but rapidly shrinks during the first ∼100 ms to a rather sustained size. We studied such dynamics in anesthetized cats during presentation (250 ms) of static spots centered on the RF with main focus on the transition from the first transient and highly dynamic component to the second more sustained component. The results suggest that the two components depend on different neuronal mechanisms that operate in parallel and with partial temporal overlap rather than on a continuously changing center-surround balance. Results from mathematical modeling further supported this conclusion. We found that existing models for the spatiotemporal RF of LGN neurons failed to account for our experimental results. The modeling demonstrated that a new model, in which the response is given by a sum of an early transient component and a partially overlapping sustained component, adequately accounts for our experimental data