Cross-laminated Sandstones Research Articles

Depositional system of Halang Formation from Ci Mande and Panaruban River outcrop: an interpretive based on lithofacies and trace fossil

This paper focuses on confusing various theories of Middle to Late Miocene sedimentary rocks, especially the Halang Formation in the CiMande and Panaruban River Banyumas Central Java. Previous studies revealed miscellaneous conclusions regarding the depositional system of this formation. This research was conducted with field observations, consisting of 2 measured stratigraphy section. Lithofacies and trace fossils are identified by making detailed vertical records of outcrops. The lithofacies association are: B1 is Massive Sandstone, B2a is Parallel Laminated Sandstone, B2b is cross-laminated sandstone, C2 is interbedded sandstone and shale, D1 is Siltstone, E1 is Mudstone, and F2 is Coherent deposits. Four variations of trace fossils include Thallasinoides, Skolithos, Chondrites and Rhizocorallium. It is classified into Skolithos Ichnofacies and Cruziana Ichnofacies in the lower shoreface. Skolithos and Cruziana ichnofacies association in the submarine fan due to local sediments preserved trace fossils are not ultimately consolidating. Based on the facies association, it has characteristics resulting from the turbidite mechanism, which was deposited in the deep marine fan environment precisely in parts of suprafan lobes on midfan. Conversely, the presence and diversity of trace fossils indicate that these sediments were deposited in shallow marine. The conclusion is that the sediment in which the trace fossils are preserved has been partially lithified, and the deposition reworked by gravity in the suprafan lobes on the midfan.

Sedimentological and Geochemical Characterization of the Early Cambrian Eastern Yunnan, Southwestern China

The accurate reconstruction of the early Cambrian paleoclimate and paleoceanographic conditions on the Yangtze Plate is crucial for understanding the ancient environment during the Cambrian Explosion. It is also a key factor in understanding the ecological habits of organisms during the Cambrian Explosion. The study utilized field outcrops, thin section analysis, and major and trace elements to investigate the sedimentary environment, provenance, paleoweathering, and paleoclimate of the Lower Cambrian Hongjingshao (HJS) Formation (Cambrian Stage 3, ~515 Ma) in the Yangtze Basin, eastern Yunnan, SW China. The HJS sandstones are composed of 10 lithofacies, including massive and weakly bedded gravel supported by coarse sandstone (Gm), trough cross-bedded sandstone (St), planar cross-bedded sandstone (Sp), ripple cross-laminated sandstone (Sr), horizontal bedded sandstone (Sh), scour-fill sandstone (Se), massive sandstone (Sm), fine to medium sandstone with thin bed muddy siltstone (Fl), muddy siltstone (Fsc), and mudstone (Fm). On the basis of these lithofacies, channel fill and over-bank deposits in delta and shallow shelf depositional environments are suggested for HJS Formation. The major elements-based provenance discriminant function and mineral composition indicate that felsic rocks from the recycled orogen and continental block are the main sediment source terrane for the HJS sandstones of the study area. CIA, PIA, and CIW values range from 71.29 to 93.72, indicating an intermediate to intense chemical weathering and semiarid to humid climate conditions in Cambrian Stage 3. The research findings have clarified the paleoclimate and paleoceanographic environment of the Early Cambrian in the Yangtze region, which is of significant importance for understanding the early biological and ecological marine environment in the study area.

The edge of a Permian erg: Eolian facies and provenance of the Lyons Sandstone in northern Colorado

ABSTRACT Facies of the Permian Lyons Sandstone are described and interpreted based on analyses of 23 cores from Larimer and Weld counties, Colorado. Here, the Lyons Sandstone consists of very fine- to medium-grained sandstone with minor silt and mudstone interbeds. The unit has five recurrent siliciclastic facies that can be grouped into two facies associations (FA). FA1 consists of (1) high-angle, cross-laminated sandstone (Facies 1; interpreted as eolian dune remnants); (2) low-angle, cross-laminated and horizontally laminated sandstone (Facies 2; interdune); and (3) chaotically bedded to folded sandstone (Facies 3; lower dune flanks). FA2, in contrast, is mainly (4) wavy- to irregularly laminated silty sandstone (Facies 4; wet to damp interdune); and (5) massive to wavy-laminated silt-rich mudstone (Facies 5; ponded water areas between dunes) with minor amounts of high-angle, cross-laminated sandstone (Facies 1) and low-angle, cross-laminated and horizontally laminated sandstone (Facies 2). FA1 is hypothesized to have been produced in an eolian system akin to those that might exist in the dune-dominated portion of an erg, whereas FA2 was deposited in the intermittently wet portion of this eolian system, perhaps along erg margins or in flat dune-adjacent settings that were impacted by the water table. Isopach data suggests that the study area is on the fringe of a larger Lyons system that spans > 100,000 km2, and was deposited close to the Ancestral Rockies—a paleogeography consistent with deposition in erg to erg-margin paleoenvironments. Detrital zircon populations from nearby Colorado Front Range outcrops and from 12 correlative eolian units are dominated by small, well-rounded Paleoproterozoic and Mesoproterozoic grain populations that are remarkably similar between units, signaling a well-mixed system that also received an influx of distally sourced sediment from the Appalachian orogen. Detrital zircon-based maximum depositional ages of the Lyons Sandstone and its equivalents are internally consistent with deposition of the unit during the latest Artinskian to Kungurian.

Sedimentological study of Bima sandstone in Dumne and Environs, Yola Sub-basin, Upper Benue Trough, Northeastern Nigeria.

Field mapping was carried out on Bima sandstone from Dumne and its environs with the aim to understand the geology and determine the paleoenvironment of deposition. The integrated (outcrop study with granulometric and pebble morphometric) studies were used to achieve this aim. Based on outcrop studies, nine (9) lithofacies were identified from the proximal alluvial fan facies to the mid-fan braided river: massive, matrix-supported, gravel-dominated facies (Gmm); matrix-supported gravel (Gmg); clast-supported gravel stratified (Gh); gravel stratified trough cross-bedded sandstone (Gt); trough cross-bedded sandstone (St); planar cross-bedded sandstone (Sp); ripple cross-laminated sandstone (Sr); massive sandstone (Sm) and silt and mud (Fsm). The outcrop sampled materials were subjected to granulometric and morphometric analyses. The result of the granulometric shows that the Bima sandstones of the study area have an average graphic mean (Mz) of 0.82 (coarse grains), an inclusive graphic standard deviation (δi) of 1.33 (poorly sorted), a graphic kurtosis (K) of 1.11 (leptokurtic), and an inclusive graphic skewness (Ski) of 0.17 (positive skewed). The result of the pebble morphometrics shows that the grains have an average elongation ratio (ER) of 0.80, coefficient of flatness (FI) of 60.6%, oblate–prolate index (OPI) of 0.35, maximum projection sphericity index (MPSI) of 0.77 and roundness (ρ) of 0.43. The roundness versus elongation ratio plot indicates a fluvial to transitional environment. Several bivariate and ternary plots that include the granulometric and pebble morphometric data suggest a river environment for the Bima sandstone in the studied area.

Implication of the micro- and lithofacies types on the quality of a gas-bearing deltaic reservoir in the Nile Delta, Egypt

The Messinian Qawasim sequence, as one of the most important reservoirs in the Egyptian Nile Delta, represents a typical gas-bearing deltaic reservoir sequence. It aims at delineating the implication of the litho- and microfacies associations on the reservoir characteristics of the different stages of the fluvial deltas including the prodelta, proximal/distal delta front, and the delta plain depositional sequences. The studied reservoir sequence was divided into two units; upper and lower clastic units. The petrophysical properties of these two units were studied on the borehole scale using the gamma-ray, caliper, sonic, density, neutron, and resistivity logs to estimate the reservoir parameters including the total and effective porosities, water saturation, shale volume, and the net-pay thickness. For more details, they are also examined on the plug-scale using the core dataset including helium porosity, density, permeability, and fluids saturations, where the flow zone indicator, the reservoir potentiality index, the reservoir quality index, and the average reservoir pore radius were then estimated. The entire sequence is divided into five reservoir rock types (RRT1-RRT5) where, the best quality is assigned to the first RRT (the upper reservoir unit), and the lowest quality is assigned to the RRT5 of the lower reservoir unit. Based on core description and the petrographical studies five lithofacies and four microfacies have been identified. The lithofacies are (1) laminated mudstones/siltstones, (2) ripple laminated sandstones, (3) cross-laminated sandstones, (4) cross-bedded sandstones, and (5) pebbly massive sandstones. These lithofacies are primarily composed of four microfacies; sublithic arenites, subarkose arenite, glauconitic quartz wacke, and sandy mudstone/siltstone. Based on this study, the pebbly massive and the cross-bedded sandstones of the upper unit which is composed of the sublithic and subarkose arenites (RRT1-RRT2) have the best reservoir quality. On the other hand, the lowest quality is assigned to the RRT5 (sandy mudstone/siltstone microfacies) which is represented on the macro scale by the laminated mudstones/siltstones lithofacies. The integration between multi-scale datasets (core-well, petrography, well logs, and seismic) gives a precise picture of the deltaic Qawasim reservoir rock units in the Nile Delta. This workflow has never been applied to the deltaic system in the onshore Nile delta and North Africa. Thereby, this study is considered a standard case study for the deltaic sequences and its proposed workflow is applicable to the Nile Delta elsewhere and worldwide for similar reservoir sequences.

The primary depositional structures of the Upper Bima Member from Fufore and environs, Yola Arm of the Upper Benue Trough, Northeastern Nigeria: implications for paleoenvironment

Primary depositional structures are important parameters that can provide the means of unraveling the processes and process responses in sedimentary depositional settings. This paper is aimed at determining the paleoenvironment of the Upper Bima Member in Fufore and environs using the primary depositional structures. This research was carried out in two phases which involved fieldwork that dealt with logging the outcrops sections and desk work whereby the logged sections and other field data are digitized, remodeled and analyzed using relevant computer programs. The result of the study shows that the Upper Bima Member is composed of five lithofacies succession; trough cross-bedded sandstone facies (St), planar cross-bedded sandstone facies (Sp), horizontal bedded sandstone facies (Sh), ripple cross-laminated sandstone facies (Sr), and mudstone facies (Fm). These lithofacies gave rise to two facies associations; sand dominated and fine-grained facies dominated facies association. The cross-stratified facies show an overall paleocurrent trend in the NW direction. These facies succession represent both shallow perennial and ephemeral sand-bed in a braided river depositional environment.

LOWER CAMBRIANRUSOPHYCUSFROM ELLESMERE ISLAND, ARCTIC CANADA: ICHNOFOSSIL OF A PREDATORY, NON-TRILOBITE ARTHROPOD

ABSTRACTCruziana and Rusophycus are commonly assumed to be trilobite trace fossils, although associated exoskeletons are almost invariably absent from host strata. In the lower Cambrian Dallas Bugt Formation of Ellesmere Island, Arctic Canada, high-energy, cross-laminated sandstones locally with dense populations of large Skolithos are overlain by thin-bedded, bioturbated, argillaceous, medium-grained glauconitic sandstones of lagoonal aspect, yielding Rusophycus along with an assortment of other “worm” burrows. Some specimens of Rusophycus are located over small Skolithos shafts and the bottoms of Arenicolites, suggesting a predator-prey relationship. Many preserve the impression of a strongly vaulted carapace with a broad, triangular dorsal outline between 1 cm and 7 cm across. A blunt anterior “prow” projects slightly forward and arches dorsally, forming a keyhole-shaped notch. The arthropod dug into the sediment up to 5 cm deep with an antero-posterior angle of up to ∼ 45° from the sea floor; in some cases it dug obliquely laterally and rarely sideways. Retroverse scratches—preserved in hyporelief as sharp-crested ridges—suggest about 20 pairs of endopodites tipped by a pair of small claws typically dug in unison, the anterior ones starting with a V-angle of 140° and decreasing posteriorly to 90°, in rare cases more tightly. Limb length increased posteriorly, although none extended beyond the carapace. Leg muscles were strong enough to rake through the muddy sand and pull inwards either straight or in a slightly forward-curving arc, but were also slightly flexible to wiggle around obstacles. Some specimens show subsequent re-burrowing which produced cross-cutting and opposed scratches. No evidence for exopodite brushings is present. Successive carapace imprints and scratches organized in transverse rugae in some specimens suggest repeatedly plunging and digging as the arthropod pulled backward in the sediment. This was likely aided by a stout trunk and a fan-shaped uropod-like structure flanking the telson which increased grip and leverage. A pair of eye stalks may have projected from the anterior notch, and these could have been retracted during digging, but there is no evidence for antennae. The tracemaker was not a trilobite but an unrelated crustacean-like arthropod, although there is no known late early Cambrian body fossil to which it can be ascribed. The specimens are classified as Rusophycus jenningsi (Fenton and Fenton, 1937) and a neotype is selected for this ichnospecies from the Gog Group near where it was first collected. Its range extends from the southern Canadian Rocky Mountains north along depositional strike to Victoria Island and northwest to Ellesmere Island and northern Greenland. Two new ichnofamilies are established: Rusophycidae and Cruzianidae.

Sedimentary and diagenetic characteristics of the Z21 field in the Huizhou depression, Pearl River Mouth basin, South China Sea

The Huizhou Depression in the Pearl River Mouth basin has prospective hydrocarbon potential, with Miocene sandstones as its main oil and gas-bearing reservoir. The sandstones in Miocene formation of the Z21 offshore oil–gas field composed of medium-grained, moderately sorted subarkose and lithic arkose. In this study, a total of six depositional lithofacies, namely Massive fine- to medium-grained sandstone (Sm), ripple cross-laminated fine-grained sandstone (Sr), parallel-laminated siltstone and claystone (Fl), lenticular siltstone (Sl), parallel-bedded fine-grained sandstone (Sp), wavy laminated siltstone (Sw), and two depositional systems, namely nearshore sand bar (SB) and sand sheet (SS) were identified based on core observations and seismic study. Distributions of the porosity (13.9%) and permeability (35.8 mD) reveal that the Miocene sandstones have characteristics of low porosity and low permeability, with high heterogeneity. The sedimentary system, primary texture and diagenesis jointly control the reservoir quality. Sandstones with sand bars as well coarse-grained tend to exhibit a higher quality. Mechanical compaction and calcite (average 6.81%) cementation are the major determinants to reductions in porosity and permeability. The total clay minerals (average 5.27%) generally lead to reduction of porosity, whereas chlorite coatings and illite within a certain content range may enhance the preservation of porosity in eodiagenesis. Dissolution of feldspar and debris contribute significantly to improving the reservoir quality.

Foraminiferal stratigraphy and palaeoenvironment of a storm-influenced marine shelf: Upper Aptian – lower Albian, Svalbard, Arctic Norway

This study presents the first record of foraminifera from the Lower Cretaceous Carolinefjellet Formation on the Svalbard archipelago, Arctic Norway. The Svalbard foraminiferal assemblages are dominated by agglutinated forms with a subordinate calcareous component. Several stratigraphically important species are recognised, and four assemblage zones are established: 1) Serovaina loetterlei Zone of middle Aptian or lower, 2) Ammobaculites wenonahae Zone of the middle Aptian, 3) Gaudryina tailleuri Zone of the upper Aptian, 4) Verneuilinoides borealis Zone of the lower Albian. The assemblages exhibit characteristic Boreal features, previously reported from the North Slope of Alaska, Arctic Canada, Western Siberia, and older Mesozoic strata in Svalbard. The study therefore allows for Circum-Arctic correlations and the extensions of stratigraphic ranges of several Boreal species.The investigated succession exhibits a large-scale fining-upwards trend. The lower part (the Dalkjegla Member) is characterised by abundant hummocky cross-stratified and wave-ripple cross-laminated sandstone beds, indicating deposition on a storm-dominated shelf. The upper part (the Innkjegla Member) is dominated by mudstones containing strata-bound siderite concretions and carbonate-cemented sandstone beds, suggesting deposition under more quiescent, middle to outer shelf conditions. An upwards increase in trace fossil diversity and degree of bioturbation, in concert with expanding foraminiferal diversity and morphogroup variability, reflects a long-term deepening of the shelf with fluctuating oxygen conditions. In combination with XRF data, diversity statistics, and morphogroup application, the present study thus sheds a new light on higher frequency palaeoenvironmental changes in upper part of the Carolinefjellet Formation.

Sedimentology, petrography, and deposition of the Upper Cretaceous Codell Sandstone in the Denver Basin

We integrate new and previous stratigraphic and petrographic data for the mid-Turonian Codell Sandstone to interpret its provenance, depositional characteristics, and environments. Our focus is on sedimentologic, X-ray diffraction, and X-ray fluorescence analyses of cores and thin sections spread throughout the Denver Basin, augmented by interpretation and correlation of well logs, isopach maps, outcrops, and provenance data. Although we treat the Codell as a single mappable unit, it actually consists of two geographically disjunct sandstone packages separated by a southwest-northeast-trending gap, the NoCoZo, short for No Codell Zone. The Codell is everywhere capped by a significant unconformity and across much of the northern Denver Basin rests unconformably on the underlying shales of the Carlile Shale. In the southern Denver Basin, the Codell commonly contains two parasequences, each of which becomes less muddy upward. Biostratigraphic and geochonologic data suggest that the unit represents deposition over a relatively brief time, spanning ~0.4 Ma from ~91.7 to ~91.3 Ma. The Codell is predominantly a thin (<50 ft) sheet-like package of pervasively bioturbated coarse siltstone and very fine-grained sandstone dominated by quartz and chert grains 50 to 100 μm in diameter. The unit is more phosphatic than the underlying members of the Carlile Shale, and its grain size coarsens to medium-grained in the northern part of the basin. An unusual aspect of the Codell across our study area is the generally excellent grain sorting despite the presence of an intermixed clay matrix. This duality of well sorted grains in a detrital clay matrix is due to the bioturbation that dominates the unit. Such burrowing created a textural inversion that obscures most of the unit’s primary sedimentary structures, except for thin intervals dominated by interlaminated silty shale and very fine sandstone. A relatively widespread and unburrowed example of this bedded facies is preserved in a thin (<10 ft) interval that extends across most of the northern Denver Basin where it is informally called the middle Codell bedded to laminated lithofacies. Sparse beds with hummocky or swaley cross-stratified and ripple cross-laminated fine-grained sandstone are present locally in this bedded facies. We hypothesize that Codell sediments were derived from a major deltaic source extending into the Western Interior Seaway from northwestern Wyoming, and that the Codell was deposited and reworked southward on the relatively flat floor of the Seaway by waxing and waning shelf currents as well as storms and waves. Codell sediments were spread across an area of more than 100,000 mi2 in this epeiric shelf system that spans eastern Colorado, southeastern Wyoming, western Kansas, parts of Nebraska and beyond.

Re-examining models of shallow-water deltas: Insights from tank experiments and field examples

Shallow-water deltas remain enigmatic in terms of placing the observed facies within a coherent process-based depositional model. Here we report tank experiments on mouth-bar formation from shallow water pure and stratified jets that, combined with recent flume experiments on bedforms, suggest new interpretations of field observations from shallow-water delta outcrops.Our experiments imply that the height, geometry and bedforms of the mouth bars depend on the jet properties and grain size of the supplied sediment. Pure jets with very coarse-grained sediment formed a high and steep mouth bar that is characterised by steep angle-of-repose cross bedding with related avalanche processes (grain flows) on the lee side. The experiments with stratified jets imply that mouth-bar deposition and growth are dominated by supercritical density flows that evolve from the initial jets on the lee side of the growing mouth bar. In stratified jets with very coarse-grained sediment, deposition on the mouth-bar lee side was both from grain-flow avalanches and density flows. While deposition on the upper lee slope was dominated by grain flows, a concentric field of low relief, asymmetric, downflow-migrating bedforms evolved on the lower slope and beyond the mouth bar. In the stratified jet with medium-grained sediment a very low relief mouth bar formed within a concentric field of low, asymmetric, downflow-migrating bedforms covering the entire lee slope and the area beyond.Many previous field studies show that mouth bars deposited from dense stratified jets (hyperpycnal flows) are characterised by a distinct facies assemblage of coarse-grained cross-stratified or low-angle cross-stratified sandstone passing downslope into finer-grained plane-parallel, or “quasi-parallel” laminated sand and into climbing-ripple cross-laminated sandstone. Comparison to flume and tank experiments suggests that the proximal coarse-grained planar and trough cross-stratified sandstones could represent deposition by supercritical dunes that pass downslope into antidunes, characterised by sinusoidal stratification and/or low-angle cross stratification. The repeated vertical transition between antidune deposits and climbing-ripple cross-laminated sandstone may indicate the superposition of ripples onto antidunes in finer-grained sediments, indicating ripple formation under supercritical flow conditions. Similar bedforms/sedimentary structures have previously been interpreted as hummocky cross-stratification or swaley cross-stratification and attributed to combined flows in storm-dominated settings, which probably in some cases must be revised.

Bioturbation, heavy mineral concentration, and high gamma-ray activity in the Lower Cretaceous McMurray Formation, Canada

In the Lower Cretaceous McMurray Formation (Alberta, Canada), many intervals of intensely bioturbated (Bioturbation Index = 5–6) fine-grained sediments are characterized by high gamma-ray (GR) readings. Several methods, including sedimentary facies analysis, thin-section petrography, handheld spectral gamma-ray, portable X-ray fluorescence, X-ray diffraction, inductively coupled plasma-mass spectrometry, microprobe of K-feldspar, energy dispersive spectroscopy, and detrital zircon geochronology by laser ablation-inductively coupled plasma-mass spectrometry, were used to investigate the interval of interest in core samples. The mineralogical analysis shows that these intervals are enriched in heavy mineral grains, and particularly in zircons. The content of radioactive elements is variable. Thorium is commonly elevated up to three times, uranium nil to two times, and potassium content usually remains normal. The studied intervals consist of interbedded, bitumen-saturated cross-bedded and/or ripple cross-laminated sandstone (high-energy deposits) and light-gray bioturbated mudstone (low-energy deposits), commonly addressed as inclined heterolithic strata (IHS). IHS represent tidally influenced, brackish-water, upper point-bar deposits. The zircon grains become concentrated while hydraulic processes interact with bioturbation: the burrowing animals cause significant sediment mixing that allows the lightest sediment particles to go back into the suspension. Additionally, bioturbation increases the surface roughness along the sediment-water interface and, causes more turbulent flow, allowing for quartz and other light grains to be removed by traction and/or saltation, while dispersed heavier zircon grains become trapped and concentrated in open burrows.So far, this study is the first to demonstrate the importance of bioturbation in the enrichment of zircon grains in IHS. The interaction of bioturbation and hydraulic processes explains the apparently counter-intuitive enrichment of heavy minerals in a low-energy depositional setting. This scenario likely applies to numerous intervals characterized by similar GR and/or zirconium spikes across the McMurray Formation. Furthermore, it can be expected that in other sedimentary basins and stratigraphic units, similar studies will demonstrate that the proposed mechanism is universal.

Architectural analysis of an Early Cambrian braided-river system on the north Gondwana margin: The lower sandstone of the Lalun Formation in the Shirgesht area, central Iran

The Lalun Formation (Early Cimmerian), up to 867 m thick, was studied in the Shirgesht area, Central Iran. It was laid down across the northern edge of Gondwana, where fluvial sandstones were covered by marine shales, carbonates and sandstones. The Lower Sandstone unit of the formation is dominated by sand-rich braided river deposits (97%) with a general scarcity of fine-grained deposits (3%), and the unit consists nine lithofacies (Se, Spb, Sm, Sp, St, Sh, Sr, Fl and Fm). Common sedimentary structures in the succession include planar and trough cross-bedded, plane-laminated and ripple cross-laminated sandstone, and mudcracks in laminated and structureless mudstone. Architectural elements are defined as channel forms and fills (CHs and CHm), sheet sandstone bodies (SB, DA, and LS) and mudstone bodies (FF). The Early Cambrian fluvial system was operating in a non-vegetated setting, and it is probable that the major flooding of the system took place on a seasonal basis. Six orders of surfaces are identified in the outcrops. The highest order surface (sixth-order) includes the lower contact of the Lalun Formation (Lower Sandstone), which was laid down on the Zaigun Formation, and the upper contact of the Lower Sandstone with estuarine deposits of the Middle Shale, denoting a marine transgression. The paleoflow direction is consistent with the reconstructed position of the Lalun Formation during the Cambrian and indicates that sediment was transported eastward to northeastward in the northern part of the Gondwana margin. The petrographic analysis suggests craton interior and transitional continental sources under seasonal humid conditions, consistent with the reconstructed position of Iran along the northeast margin of the Arabian Shield.

The Silurian glaciation in the eastern Parnaíba Basin, Brazil: paleoenvironment, sequence stratigraphy and insights for the evolution and paleogeography of West Gondwana

Glacial strata are excellent stratigraphic markers in Paleozoic basins worldwide. The eastern Parnaíba Basin in northern Brazil is a highly favorable setting for studying episodes related to the Ordovician-Silurian glaciation. Previous studies in this region led to the recognition of unequivocally glaciogenic sediments associated with pre- and postglacial deposits, favoring the understanding of lower Paleozoic events that occurred in West Gondwana. Outcrop-based facies and stratigraphic analyses of the ~170 m-thick siliciclastic succession of the Serra Grande Group indicate fluvial, glacial, and coastal depositional systems. Seventeen sedimentary facies are grouped into seven facies associations (FAs): FA1, interpreted as intermediary sheet braided plain deposits that consist of tabular cross-bedded coarse-grained sandstones and conglomerates; FA2-FA4, which correspond to subaqueous glacial deposits comprising massive to stratified diamictites, cross-laminated sandstones, diamictites and organic matter-rich black shales with dumpstone and dropstone structures; FA5-FA6, constituting organic matter-rich black shales, fine- to medium-grained sandstones with sigmoidal cross-bedding and occurrences of the ichnotaxon Arthrophycus interpreted as delta front deposits; and FA7, composed of medium- to coarse-grained pebbly sandstones interpreted as channelized braided plain deposits. This interpretation partially confirms the previous paleoenvironmental interpretation discounting the presence of subaerial alluvial fan and outwash plain deposits for this unit. The sequence stratigraphy of the Serra Grande Group is refined mainly using the coherent interpretation of the key surfaces and comparing the systems tracts with the global sea-level curve, providing a more robust third-order sequential evolutionary model that includes three depositional sequences. The Middle Ordovician sheet braided deposits are the lowstand sediments of Sequence 1 truncated by an extensive unconformity that possibly removed the transgressive and highstand strata. This unconformity generated by glacial dynamics represents 23 Myr during the Late Ordovician to early Silurian. The second sequence started with the advance of ice sheets in marginal areas of the basin, causing the deposition of ablation diamicton during the lowstand. The postglacial transgression is marked by ice-rafted debris from icebergs deposited onto organic matter-rich mud in the shoreface-offshore zone. The maximum flooding during the middle to late Silurian was succeeded by the highstand phase marked by the progradation of deltaic deposits. Biological activity is marked by the presence of polychaetes that reworked the marine seafloor. The Early Devonian featured extensive sea-level fall and renewed continental drainage with the formation of a braided plain marking a lowstand phase of Sequence 3. These new interpretations allow the global correlation of the Serra Grande Group and provide an improved understanding of the role of ice sheets and postglacial transgressions that affected West Gondwana during the Ordovician-Silurian periods.

Facies Analysis, Markov Model and Linking of Sub-environments in the Early Permian Barakar Coal Measures of Godavari Gondwana Basin of Southeastern India

Abstract The early Permian Barakar coal measures Formation of Gondwana Supergroup in the Godavari basin comprise siliciclastic fluvial facies of passive continental margin. The lithofacies relationship and their sequences are analyzed quantitatively using embedded Markov Chain analysis along with improved binomial probability method. Summarized lithofacies sequence show the following order: (CGSD= Matrix supported conglomerate, gritty to pebbly / coarse-grained tabular and trough cross bedded sandstones) →(MGSD= Medium grained trough and planar cross bedded sandstones)→(FGSD= Fine-grained parallel and ripple drift cross-laminated sandstones)→ (SH= Shale/inter-bedded sandstone-shale and gray shale)→ (C=coal/shaly coal and carbonaceous shale)→ (CGSD= Matrix supported conglomerate, gritty to pebbly/coarse-grained planar and trough bedded sandstones). These repetitive cycles accumulated in a low sinuosity, high gradient braided streams which became moderately sinuous at places. The lithofacies relationships showing fining upward tendency suggest a progressive upward decline in current competency. The sequence is considered as the classical example of a sand dominated braided river. The lateral changes in lithofacies association indicate shifting of subenvironments from stream channel, overbank levee and peat forming back swamp to flood plains of fluvial system. It is suggested that the channel wandering along with differential intra-basinal tectonism and subsidence controlled cyclic repetition during early Permian sedimentation in the Godavari basin.

The facies analysis of a fan delta by integrating multiple discipline data — A case study of the KL-A oilfield, Bohai Bay Basin, China

The third member of the Shahejie Formation (Es3) is the main hydrocarbon exploration target in the KL-A oilfield, Bohai Bay Basin, East China. The facies classification is an essential step in mapping the depositional system of Es3 within the Bohai Bay Basin. The facies model is important for identifying the “sweet” lithology within the reservoirs. We characterize the facies of Es3 by integrating cores, well logs, and seismic data. The analysis indicates that the Es3 consists of fan delta deposits. The analysis using well logs and cores indicates that there are five different lithofacies for the Es3 Formation: massive sandstone, horizontally bedded sandstone, trough cross-bedded sandstone, ripple cross-laminated sandstone, and massive mud. The microfacies of Es3 include distributary channel, distributary mouth bar, interdistributary bay, and lacustrine mudstone deposits. The sweet lithologies for hydrocarbon accumulation within the KL-A oilfield include the coarse- and fine-grained sand developed within the channels and distributary mouth bar. We use seismic rms amplitude strata slices to determine the horizontal distribution of facies of the fan delta. The correlation between rms amplitude and well logs indicates that relatively low rms amplitude anomalies on the strata slices can be used as an indicator for sandstone within the KL-A oilfield.

Integrated sedimentological, ichnological and sequence stratigraphical studies of the Koti Dhaman Formation (Tal Group), Nigali Dhar Syncline, Lesser Himalaya, India: paleoenvironmental, paleoecological, paleogeographic significance

Integrated ichnology, sedimentology and sequence stratigraphy of the Lower Quartzite Member to the Arkosic Sandstone Member of the Koti Dhaman Formation (Cambrian Series 2, Stage 4), Tal Group, Nigali Dhar Syncline, Lesser Himalayan lithotectonic zone are presented. Trilobite traces of Gondwanan affinity i.e., Cruziana salomonis, Cruziana fasciculata, Rusophycus dispar and Rusophycus burjensis are recorded along with Arenicolites isp. and Skolithos isp. from the Lower Quartzite Member. A rich and diverse ichnoassemblage attributed to the Cruziana ichnofacies is described for the first time from the Arkosic Sandstone Member of the same formation. Seven ichnofossil assemblages, i.e., Cruziana-Rusophycus, Planolites-Palaeophycus, Cruziana problematica, Diplichnites, Cochlichnus anguineus, Bergaueria perata and Psammichnites gigas have been recognized in the Lower Quartzite to Arkosic Sandstone members of the Koti Dhaman Formation. Seven sedimentary facies i.e., sandstone–shale facies (FT1), cross-bedded (trough and planar) sandstone (FT2), bedded sandstone facies (FT3), shale facies (FT4), shale–sandstone facies (FT5), shale-rippled sandstone facies (FT6) and planar and trough cross-laminated sandstone (FT7) and four facies associations FA1-FA4 are identified in the Koti Dhaman Formation. The formation contains shallowing upward parasequences of a tidal flat complex. Overall, two major events are recognized: i) the break in sedimentation between the Lower Quartzite Member and the overlying Shale Member probably related to forced-regressive event and ii) the facies shift from FT6 to FT7 of the Arkosic Sandstone Member represents an erosive transgressive event; the surface is interpreted as wave ravinement surface, which also serves as a sequence boundary. Integrated ichnology, sedimentology and sequence stratigraphic studies indicate that the Lower Quartzite Member was deposited in a shallow subtidal sand sheet complex and tidal flat complex; the Shale Member was deposited in a mud flat setting of a tidal flat complex, and the Arkosic Sandstone Member in a mixed-flat (tidal flat complex) to sand sheet complex front and margin (subtidal sand sheet complex). Overall, the lower to middle part of the Koti Dhaman Formation represents a tide-dominated shallow subtidal–intertidal to mud-flat subenvironments of the tidal flat complex. A palaeogeographic reconstruction of lower Cambrian (516–514 Ma) is presented based on the distribution of trilobite traces from the Lesser Himalaya and the Bikaner–Nagaur area of Peninsular India (eastern Gondwana), Egypt, Jordan, Turkey (western Gondwana) and Canada (Avalonia).

Rainfall-induced landslide in the active frontal fold–thrust belt of Northwestern Himalaya, Jammu: dynamics inferred by geological evidences and Ground Penetrating Radar

Landslides are the most established geological hazards in the frontal fold–thrust belt of Northwestern Himalaya comprising of Siwaliks and Murree strata. The continuous rainfall from 2 to 6 September, 2014 caused a massive landslide at village Sadal in Udhampur district of Jammu and Kashmir state. The landslide occurred in the early morning of September 6, 2014, destroying entire Sadal habitation comprising 45 houses, and killing 41 people and more than 500 domestic animals. Google earth images of pre and post-landslide events along with the field measurements show the kinematics of upper and lower parts of the slide. Horizontal and vertical components of displacement and mode of failure suggest the landslide as of complex nature. The shallow subsurface geophysical imaging through Ground Penetrating Radar (GPR) survey shows the failure plane composed of friable mudstone bed underlain by massive mudstone and overlain by cross-bedded sandstone. The depth of debris material above the failure plane ranges from 6 m at Site S1a-b to 10 m at Site-S2b and 20 m at Site S3a. The velocity analysis of Site-3 shows four thick layers represented from bottom to surface by L1—sandstone (V = 0.16 m/ns, travel time = 356.36 ns), L2—mudstone (V = 0.17 m/ns, travel time = 288.48 ns), L3—massive mudstone (V = 0.19 m/ns, travel time 220.68 ns), and L4—cross-laminated sandstone (V = 0.20 m/ns, travel time = 77.58 ns) overlaying the failure plane. The study shows the landslide occur along the western limb of a fold identified during the present work. We mapped an old landslide on the same limb which shows 5–6 m-thick subsurface debris material with thick rock fragments involved in the landslide process. The detailed geological and geophysical investigations suggest that both the landslides were triggered by extreme rain fall events.

Integrating traditional field methods with emerging digital techniques for enhanced outcrop analysis of deep water channel-fill deposits

The development of emerging digital technologies that allow the collection and analysis of field data represents a significant innovation in field-based geological studies. The integration of these digital techniques with traditional sedimentological field methods facilitates considerable improvements in outcrop characterization. An example of this integrated modern approach for geological data collection is employed for the detailed characterization of a turbidite channel-lobe system of the Gorgoglione Flysch Formation in Southern Italy. The study area, exposed above the village of Castelmezzano, has been measured and described in detailed stratigraphic sections, providing data for both sedimentological analysis and correlation of the stratigraphy. In order to gain a complete perspective on the exposure and stratigraphic elements, analysis of physical outcrop data was enhanced by the use of high-resolution Gigapixel imagery and 3D photogrammetric outcrop reconstructions. The Santa Maria section has been assessed in terms of vertical and lateral facies stacking arrangements and subdivided into two component facies associations separated by a prominent concave-up erosional boundary. The lower facies association, interpreted as a frontal lobe complex, consists of tabular, thick-bedded coarse sandstones interbedded with persistent heterolithic packages of thin-bedded sandstones and mudstones, and minor soft-sediment deformed strata. The upper facies association represents the infill of a channel-form and consists of a basal conglomerate, passing gradually upwards into massive amalgamated sandstones overlain by large-scale cross-laminated sandstones. The excellent exposure of the Santa Maria section records the complete evolution of a channel-lobe system, transitioning from frontal lobe deposition through channel incision and bypass, to progressive backfilling. This study shows how facies characterization, stratigraphic correlations and reconstruction of the depositional architectures have been substantially enhanced by the use of emerging digital techniques for geological data collection.

Pedogenic Mud Aggregates Preserved In A Fine-Grained Meandering Channel In the Lower Permian Clear Fork Formation, North-Central Texas, U.S.A.

Abstract: The Lower Permian Clear Fork Formation of north-central Texas is among few examples from the rock record where mud aggregates are well-preserved as the main sediment component of a meandering channel. This rare occurrence provides an excellent opportunity to evaluate the origin and depositional setting of aggregates, as well as the conditions responsible for their preservation. At the study site, lateral-accretion deposits define an exhumed point bar composed of thick mudstone layers rich in aggregates, interbedded with thin layers of ripple cross-laminated sandstone. Petrographic analysis indicates that red-brown and gray aggregates constitute > 68% of the mudstones, with minor quartz, feldspar, ferruginous grains, and dolomite rhombs. When size estimates are corrected for 2D sections and for ∼ 17% flattening during compaction, the aggregates are of fine-sand size and more than twice the size of associated quartz grains, which were probably size-limited on the distal plain. Despite the difference in grain size and density, the aggregates and quartz populations were both entrained at very low velocities ranging from 1.2 to 1.5 cms –1 . Based on their relatively uniform size, variation in iron-oxide content, and association with small ferruginous concretions, the aggregates formed by reworking of associated vertic paleosols. In the absence of discrete smectite, their formation probably reflects a minor swelling-clay component in illite, Fe-rich chlorite, and mixed-layer clays, as indicated by glycolation results. Deficiency in smectite is probably a result of parent-rock composition, rather than burial illitization in this shallowly buried formation. In modern floodplains, aggregates typically lose their pelleted texture during shallow burial. Their excellent preservation at the study site is attributed mainly to the lack of swelling clays in the mud aggregates and their rapid incorporation into a migrating point bar, set within a “compartment” of indurated paleosols that limited compactional effects. Some early cementation by dolomite, gypsum, and barite of the aggregate-bearing and associated beds would have enhanced rigidity.