Lenticular Deposits Research Articles

Spatial distribution and reserve estimation of sand and gravel deposits using geostatistical methods in west Basrah, southern Iraq

Sand and gravel are among the most common natural materials. They are generally used as a raw material in concrete, road construction, mixing with asphalt and filling material, among other uses. Sand and gravel deposits are widespread within the southern and central regions of Iraq. Among these deposits are the alluvial sand and gravel that form the upper part of the Dibdibba Formation in the Al-Rafiya, Al-Tuba, Chwaibda and Safwan blocks in west Basrah, southern Iraq. In this research, grain size distribution for channel samples collected from each block was determined. Thickness of overburden and industrial beds was measured and the stripping ratio (SR) was calculated. Geostatistical interpolation approaches including inverse distance weighting (IDW) and ordinary kriging (OK) were utilised to predict the spatial distribution of sand and gravel deposits and their reserves from borehole data. Data validation using the mean error (ME) and root-mean-square error (RMSE) were applied. The deposits can be characterised as gravelly sand (gS) in the Al-Tuba, Al-Rafiya and Chwaibda blocks, while it is a sandy gravel (sG) in the Safwan block. The overburden gypcrete beds varied between 1 and 3 ​m thick, while the industrial sand and gravel beds which appear as planar and sometimes lenticular deposits ranging between 3 and 8 ​m thick. The SR is generally low, considering the easily removed lightweight material of the overburden bed and the easily extractable fairly flat and near-surface friable sand and gravel deposits. Reserves are estimated as 376.63 Million m3 and 385.97 Million m3 using the IDW and OK approaches, respectively. Based on the least error values of ME and RMSE, we conclude that the OK method is the more accurate spatial interpolation approach for sand and gravel reserve estimation in all blocks compared to the IDW method.

Confirmation of PRDX3 c.568G>C as the Genetic Basis of Punctiform and Polychromatic Pre-Descemet Corneal Dystrophy.

The aim of this study was to report the results of screening peroxiredoxin 3 (PRDX3) and PDZ domain-containing protein 8 (PDZD8) in a previously unreported pedigree with punctiform and polychromatic pre-Descemet corneal dystrophy (PPPCD) to confirm that the PRDX3 mutation c.568G>C is the genetic basis of PPPCD. Ophthalmologic examination of the proband and her affected father was performed with slit lamp biomicroscopy. Saliva was collected from the proband as a source of DNA, after which screening for PRDX3 and PDZD8 was performed. Slit lamp examination of the proband revealed polychromatic deposits diffusely distributed at the pre-Descemet level in both corneas and anterior subcapsular in the crystalline lens of both eyes. The proband's father also demonstrated diffuse pre-Descemetic polychromatic deposits in both eyes but no lenticular deposits. Screening of PRDX3 in the proband demonstrated the c.568G>C (p.Asp190His) variant previously associated with PPPCD and failed to identify any variants in PDZD8. We report the initial confirmation of PRDX3 as the genetic basis of PPPCD in a previously unreported pedigree and expand the phenotype of PPPCD to include polychromatic lenticular deposits.

Improving processes and natural production minerals recycling

The article is devoted to improving the processes of extraction of natural carbon minerals through increased selectivity and reduce dilution, as well as processing of ash-slag wastes to reduce environmental burdens and increasing complexity of extracting minerals. Data are elemental and mineral composition, energy dispersive microanalysis by scanning electron microscope JEOL JCM-6000. As a result of natural objects analysis carbon minerals, with their typing on structural and mineralogical composition, marked by the characteristic difficult structural signs plastoobraznyh and lenticular deposits. A method of treatment of structured development of carbonaceous deposits of minerals based on the improved design of the working body of the harvester, that will increase the efficiency of minerals through mining selectivity. As a result, microanalysis samples ash wastes found the presence of native gold, рlatinum and silver. The application of ways of dressing of secondary raw materials using innovative technologies developed, based on the processes of gravitational and ultrasonic cavitation effects, provide comprehensiveness of allocating valuable components micron level and reduce the pollution of Wednesday.

Quaternary volcanic ash of Kharkiv region

Formulation of the problem. The article is devoted to detail geological and mineralogical description of quaternary volcanic ash in Kharkiv region. The purpose of the article is to ground its origin. Presentation of the main material. Quaternary volcanic ash was discovered in Kharkiv region in the middle of last century. There are a few Late Neo-Pleistocene deposits of volcanic ash in Kharkiv region now. They are located in Kharkiv and near such villages as Russki Tishki, Novoselivka, Levkivka, Donetzke and Krasnokutsk. Such deposits of volcanic ash were found in the neighboring regions of the Eastern Ukraine - Lugansk, Donetsk, Dnieperpetrovsk and some other regions. Volcanic ash forms the elongated lenticular deposits in the loess loam strata. The contact of ash beds is clear with underlying loess and gradual with overlying loess. The ash lies 3-5 m below the surface of loess. These ashes are light-grey with feeble yellow or brown shades. Its thickness is up to 0.4 m. The particles of the ash are volcanic colourless isotropic glass with refraction index 1,517. Its forms are various. Plate isometric and elongated ash particles with even straight or cambered sides are the most widespread. Predominance of 0.005-0.1 mm particles in this ash rocks is confirmed by the results of mechanical analyses. This tephra is badly sorted. Their sort factor is 4.2-5.9. The ash deposits were formed by wind transportation of ash particles to wind shadow zones. The results of X-ray investigation are typical for glass. IR-spectra investigation revealed molecular water and hydroxyl groups in the volcanic ash. Chemical composition of the volcanic ash of Kharkiv region is characterized by the average percentage of SiO2 – 58.88, Al2O3 – 18.79, Na2O – 5.03, K2O – 6.30, Na2O+K2O – 11.33. Relation of Na2O to K2O is 0.80 and Na2O+K2O to Al2O3 is 0.60. It corresponds to trachyte and phonolite and is confirmed by the refraction index of glass particles. The volcanic glass particles are angular and non-rounded. This fact signifies the eolian origin of ash deposits. Moreover, numerous manifestations of volcanic ash scattered in loess loams are found in Kharkiv region. These loams contain only a few per cents of poorly rounded volcanic ash particles. The loess loams with scattered volcanic ash and volcanic ash deposits belong to the same stratigraphic datum - to the Bugskij horizon, which correspond to Wurmian stage. Conclusions. All tephra deposits of Kharkiv region are in the ash plume of the super-eruption, which occurred in Southern Italy about 39280 years ago (Campanian Ignimbrite eruption). Kharkiv objects fill territory in this plume between the ash depositions of Romania and Russian Voronezh region. They are similar to all other tephra localities of this plume. The volcanic ash was taken by air from the Phlegraean Fields though the distance between Kharkiv and this volcano is over 2000 km. Scientific novelty and practical significance. We can affirm that Kharkiv ash deposits are the result of distant ashfall of Phlegraean Fields super-eruption. The volcanic ash is a horizon marker in the Neo-Pleistocene strata and a datum mark for archaeological study of the Paleolithic cultures. Volcanic ash is a remarkable component of Kharkiv region geological monuments. Russki Tishki locality of volcanic ash is the best object in Kharkiv region. It is situated in 22 km north from Kharkiv. These geological sights have been used as objects of scientific tourism and native land study. Their protection is of highly necessity.

Phenothiazine Group Drug Induced Corneal and Lenticular Deposits in a Patient of Severe Depression – A Case Report

Phenothiazine Group Drug Induced Corneal and Lenticular Deposits in a Patient of Severe Depression – A Case Report

Occurrence of Naturally Shaped Lenticular Bed Deposit and Its Influence on the Frictional Pressure Drop during Pipeline Transportation of Low Concentration Slurries

Solid particles can be transported along a pipeline in the form of trains of individually shaped lenticular deposits (LDs) when the concentration of solids is less than 1 vol% and the transport velocity is below the critical value required for full suspension. Such special bed transport, observed as rippled sand dune patterns, may occur in petroleum production lines transporting oil and gas produced from unconsolidated sand reservoirs under turbulent flow conditions, and during sediment transport by rivers and winds. The primary objective of this study was to investigate how the occurrence of lenticular bed deposits affects near-wall turbulent activities at the sand/fluid (“wave-like”) interface and frictional pressure drop during pipeline transportation of solids. Particle image velocimetry (PIV) measurements were used to quantify the velocity field, the turbulence kinetic energy (TKE), and the coherent structures associated with surface morphology change and LD formation near the bed deposits/fluid interface. A 7–8% reduction in frictional pressure drop was consistently observed during the transition from continuous sand bed to LDs. Results also indicate that the formation of naturally shaped LDs reduces the intensity and frequency of near-wall turbulent coherent structures (burst-sweep events). Moreover, TKE associated with flow over the LDs was found to be lower than that of continuous bed and water (only) flow.

Lenticular changes in cerebrotendinous xanthomatosis, a treatable metabolic disorder that is important to recognize

Cerebrotendinous xanthomatosis is a progressive neurodegenerative storage disease characterized by abnormal deposition of cholestanol and cholesterol in multiple tissues, including the lens and brain, and caused by recessive CYP27A mutations. Ophthalmologists have the unique potential to facilitate earlier diagnosis and preventative treatment by recognizing the juvenile cataract phenotype. We highlight the morphology of lens opacities in a family with genetically confirmed disease. Retrospective case series. Two sisters, each visually symptomatic before 10 years of age, had a unique pattern of bilateral fleck deposits throughout the lens with significant posterior capsular cataract. When initially examined at 8 years old, their then asymptomatic younger brother had the same bilateral fleck deposits with minimal posterior capsular opacity; one year later he developed anterior capsular opacity and became symptomatic. Both asymptomatic parents had few but distinct similar flecks localized at the Y-suture while an asymptomatic sister did not. Genetic analysis revealed homozygosity for a novel CYP27A mutation in the three symptomatic siblings, heterozygosity for the mutation in the two parents, and no mutation in the asymptomatic sister. When specifically questioned, the three affected children had had recurrent bouts of diarrhea since early childhood, which is a common feature of the disease. An usual pattern of fleck lenticular deposits were seen in affected children. With time posterior and/or anterior capsular opacity developed and caused visual symptoms. Asymptomatic fleck-like opacities at the Y-suture may be a carrier sign. Such juvenile lenticular findings should raise suspicion for this treatable metabolic disorder.

Juvenile Cataract Morphology in 3 Siblings Not Yet Diagnosed with Cerebrotendinous Xanthomatosis

Cerebrotendinous xanthomatosis is a progressive neurodegenerative storage disease caused by recessive CYP27A1 mutations and is characterized by abnormal deposition of cholestanol and cholesterol in multiple tissues, including the lens and brain. Oral chenodeoxycholic acid is preventive and can be therapeutic, but is not used optimally because the condition typically is diagnosed late or not at all. When affected children demonstrate lens opacities, ophthalmologists have the unique potential to facilitate earlier diagnosis and treatment by recognizing the juvenile cataract phenotype. This study highlights the morphology of lens opacities in a family with genetically confirmed disease. Prospective case series. Four siblings and their 2 parents, who are first cousins. Ophthalmic examination, general physical examination, and exome sequencing guided by homozygosity analysis. Ophthalmic findings, general clinical findings, and results of CYP27A1 candidate gene testing. Two sisters, each visually symptomatic before 10 years of age, had a unique pattern of bilateral fleck deposits throughout the lens with significant posterior capsular cataract. When initially examined at 8 years of age, their then-asymptomatic younger brother had the same bilateral fleck deposits with minimal posterior capsular opacity; 1 year later, he demonstrated anterior capsular opacity and became symptomatic. Both asymptomatic parents had few but distinct similar flecks localized at or near the anterior Y-suture, whereas an asymptomatic sister did not. Genetic analysis revealed homozygosity for a known CYP27A1 mutation (c.1263+1G → A) in the 3 symptomatic siblings, heterozygosity for the mutation in the 2 parents, and no mutation in the asymptomatic sister. When specifically questioned, the 3 affected children had experienced recurrent bouts of diarrhea in early childhood, which is a common feature of the disease. An unusual pattern of fleck lenticular deposits was seen in affected children. With time, capsular opacities (posterior only or posterior and anterior) developed and caused visual symptoms. Such juvenile lenticular findings should raise suspicion for this treatable metabolic disorder, especially when in the context of recurrent diarrhea during early childhood. Asymptomatic fleck-like opacities at or near the anterior Y-suture may be a carrier sign. The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Rapid magma ascent and short eruption durations in the Lake Natron–Engaruka monogenetic volcanic field (Tanzania): A case study of the olivine melilititic Pello Hill scoria cone

The Pello Hill scoria cone displays widely different characteristics dependent on which side of the cone is studied. This follows as a direct result of a strong depositional asymmetry (i.e., the crater rim varies between 14 and 111m in height), preferentially depositing material to the northwestern side of the construct. This is interpreted to reflect sedimentation from a sustained eruption plume (with prevailing winds at the time of the eruption coinciding with the direction of maximum deposition). The scoria deposits on this side of the cone form relatively fine-grained and well-sorted deposits which are laterally continuous over distances of 10's of meters. To all other sides of the vent, deposits are characterized by coarse-grained lenticular deposits rich in mantle xenoliths, occasionally showing inverse grading (consistent with an origin as ballistic ejecta and slight reworking down-slope as grain-flows). The pyroclastic textures are dominated by a moderate vesicularity (~40vol. %) in combination with smooth, fluidal, outer surfaces. Two other features that stands out in comparison with “normal” scoria cones, these are defined by the absence of: (i) inward dipping layers into the crater area, and (ii) no agglutination/welding features can be found in any of the exposed outcrops.Calculated magma ascent rates yields values between 8.5 and 36.0m s–1, which is similar to that previously reported for kimberlitic magmas. Building on these ascent rates, and the volume of the pyroclastic construct (~5×106 m3 DRE), the eruption duration is estimated to less than 6hours (for any vent area larger than 28m2). Therefore, it may not have taken longer time than 9hours from the time the magma started to ascend from upper-mantle depth (90km) and the point at which the eruption halted.Overall, the olivine melilititic Pello Hill scoria cone displays many characteristics that can also be found in the vent-facies deposits of kimberlite eruptions. Therefore, further detailed studies of well-preserved, CO2-rich, olivine melilitite eruptions (such as the provided by the landforms within the LNE-MVF and Pello Hill) could provide a tool to understand the emplacement dynamics of the vent-facies of kimberlitic eruptions.

Limestone interbedded with submarine volcanics: the Early–Middle Miocene Conejo Volcanics, California

Carbonate sedimentation concurrent with submarine volcanism is very rare in the geologic record but is well displayed in the Early to Middle Miocene Conejo Volcanics of the central Santa Monica Mountains of southern California. Limestone occurs as lenticular deposits on the surface of composite flows units, as matrix within breccia of pebble- to cobble-size volcanic clasts, within primary voids extending down from flow surfaces, as lenses between flows within composite flow units, and as neptunian dikes. The common depositional sequence is of limestone lying on a flow and being overlain by hyaloclastic breccia. Limestone is not deposited on hyaloclastic breccia. Limestone deposition was controlled locally by relief on the sea floor that formed as the volcanic rocks accumulated. The limestone is predominantly skeletal packstone; volcanic clasts ranging in size from silt to boulders are locally common. Major constituent fossils are shallow-water bivalve mollusks, barnacles, serpulids, and regular echinoids; most are epifaunal and hard-substrate taxa in contrast to the soft-substrate and burrowing infaunal biota otherwise dominant in Cenozoic strata along the Pacific Coast of North America. The biota is diagnostic of a non-tropical, warm temperate environment. The limestone was deposited within a local basin that formed along the plate boundary at the western margin of the North American Plate. While volcanic rocks accumulated in the basin at bathyal depth, carbonate sediment accumulated on the outer-shelf margin of the basin and was transported intermittently into the basin by gravity flow. Neogene limestone occurs at only a few other sites in southern California. These have an origin that is similar to those in the Conejo Volcanics but differ in occurring with basin fill of diatomaceous sedimentary rocks rather than of submarine volcanics.

Corneal Manifestations of Chronic Systemic Drug Therapy

We report 2 cases of incidental ocular pathology secondary to systemic drug therapy. Two male patients aged 67 and 66 of Malay and Indian origin respectively presented to the eye clinic for routine eye evaluation for diabetic retinopathy. On eye evaluation, both patients were found incidentally to have corneal deposits secondary to chronic ingestion of amiodarone and chlorpromazine respectively. Both these medications are known to have ocular side effects. The Malay patient had additional lenticular deposits secondary to chlorpromazine. These drug-induced deposits can be visually significant and in some cases irreversible. We herein describe the ocular manifestations of amiodarone and chlorpromazine in these 2 patients respectively with the aim to increase awareness and highlight the importance of ophthalmic review for patients on chronic medications with known ocular side effects.

Incremental oil recovery using a horizontal drainhole in the San Andres Formation, Olson field, west Texas

Oolitic carbonates and associated rocks in the San Andres Formation produce hydrocarbons at Olson field, west Texas. Mudstones, dolomitized fusulinid-peloid packstones and wackestones, ooid-peloid grainstones and packstones, and minor siliciclastic sediments occur in the field. The reservoir is stratigraphically compartmentalized by lenticular oolite deposits that are overlain by algal-laminated mudstones and siltstones. Pore-filling anhydrite cement, common in all lithologies, adds to porosity heterogeneity. Interwell communication is poor, as indicated by variable bottomhole pressures and erratic waterflood response.A medium-radius lateral hole was drilled to a total depth approximately 50 ft (15 m) from an offset vertical well. At this depth, the horizontal well intersected a previously existing artificial fracture that occurred in the nearby vertical well. The intersection of this fracture by the lateral borehole had a significant economic impact. The production rate in the vertical well jumped from a few barrels per day to an average of 70 BOPD and less than 20 BWPD. The ensuing years maintained relatively high flow rates. Projected incremental oil recovery is 153,000 bbl, roughly equivalent to production from an average well drilled during the early life of the field.Other unsuccessful horizontal wells have been drilled at Olson field, but they have not targeted preexisting hydrofractures in offset vertical wells. Therefore, the concepts presented in this paper have not been retested. This approach, intentionally drilling a drainhole to intersect a preexisting hydrofracture, could add new life to many older, compartmentalized reservoirs.

Comparison of some sediment-hosted, stratiform barite deposits in China, the United States, and India

Shifts in world barite production since the 1980s have resulted in China becoming the world's largest barite-producing country followed by the US and India. Most barite produced for use in drilling fluids is derived from black shale- and chert-hosted, stratiform marine deposits. In China, Late Proterozoic to Early Cambrian marine barite deposits occur on the oceanic margins of the Yangtze platform, in the Qinling region in the north and the Jiangnan region in the south. Most US ore-grade deposits are in the Nevada barite belt; most commercial deposits occur in Ordovician and Devonian marine rocks along the western margin of the early Paleozoic North American continent. Production in India is predominantly from a single Middle Proterozoic deposit in a sedimentary basin located on Archean basement in Andrah Pradesh. The geologic and geochemical characteristics of the deposits are consistent with origins from a variety of sedimentary-exhalative processes, with biogenic processes contributing to the concentration of some seafloor barite. Linear distributions of clusters of lenticular deposits suggest a geographic relationship to syndepositional seafloor fault zones. Sulfur isotope data of the barite deposits range from values that are similar to coeval seawater sulfate to significantly higher δ 34S values. Strontium isotope values of continental-margin-type deposits in Nevada and China are less radiogenic than those of cratonic-rift deposits (e.g. Meggen and Rammelsberg). Comparison of La n /Ce n ratios of barite in the Qinling region of China with marine chert ratios suggests a relationship to hydrothermal fluids, whereas ratios from the Jiangnan region and Nevada can be interpreted as reflecting a biogenic influence. The California Borderland provides a potential modern analog where hydrothermal barium is being deposited on the seafloor in fault-block-bounded basins. Anoxic to dysaerobic conditions on some marine basin floors result from upwelling, nutrient-rich currents and high productivity in surface waters. In this setting, biogenic processes could contribute to the concentration of barium from hydrothermal sources.

Revision of the late Pleistocene stratigraphy of Bermuda

The Quaternary stratigraphy of Bermuda is one of the world's most complete sedimentary records of interglacial highstands, representing at least the past million years. Yet in terms of the last interglacial (Rocky Bay Formation), marine isotope substage (MIS) 5e, only scanty deposits are preserved. In contrast, MIS 7, generally regarded as a diminutive interglaciation, exposes widespread emergent subtidal deposits of the Belmont Formation indicating a prolonged sea level highstand at ca. +2.5±0.3 m. This “Belmont paradox” has prompted a reexamination of the geology of key sites along the South Shore of Bermuda. This revision of the late Quaternary stratigraphy of Bermuda is based on geological field observations; primarily the questionable origin of red soil-like deposits. It is concluded here that there is no physical evidence of the exposure of the upper Belmont surface for a full glacial cycle (∼70–100 ka), and that interbedded, reddish soil-like, lenticular deposits are the result of colluvial activity during mid-MIS 5e. Reexamination of previously published uranium-series (U/Th) ages indicates that several “+3-m notches” contain a mix of ca. 125 ka and older coral ages. Contrary to previous works, this study favors an early MIS 5e interpretation of the coral ages from the +2.5-m Belmont shoreline, which is further supported by amino acid racemization (AAR) ratios on whole-rock, Poecilozonites, Glycymeris, and Brachiodontes samples from shore and notch deposits. An updated AAR kinetic model demonstrates that the bulk of epimerization occurred during warm interglacial intervals between 130 and 80 ka and the last 10 ka of the Holocene. This revised stratigraphy of Bermuda now falls into accordance with a more general view of middle and late Pleistocene sea level history.

The Midway sequence: a Timiskaming-type, pull-apart basin deposit in the western Wawa subprovince, Minnesota

The Midway sequence is an assemblage of subaerially deposited clastic and volcanic rocks that forms a narrow wedge within Neoarchean greenstone of the western Wawa subprovince of the Superior Province. Volcanic conglomerate in the Midway sequence contains clasts of stratigraphically older greenstone, together with clasts of a distinctive hornblende-phyric trachyandesite that is not represented among the older greenstone flows. The trachyandesite forms flows and pyroclastic units that are interbedded with lenticular deposits of volcanic conglomerate in a manner interpreted to indicate approximately coeval volcanism and alluvial fan - fluvial sedimentation within a linear, restricted, and tectonically active depocentre. The Midway sequence unconformably overlies greenstone on one side and is bounded by a regional-scale, strike-slip fault on the other. Structural analyses show that the Midway sequence was deposited after an early, precleavage folding event (D1) in greenstone, but before the regional metamorphic cleavage-forming D2 deformation. Lithologic and structural attributes are consistent with deposition in a strike-slip "pull-apart" basin. The stratigraphic and structural characteristics of the Midway sequence are generally similar to those of the Timiskaming Group and Timiskaming-type rocks in Canada, and more specifically to those of the Shebandowan Group in the Thunder Bay district. This similarity implies that the latest Archean tectonic and magmatic history of the western Wawa subprovince may have been nearly synchronous over great distances.

Lowstand Fan Model, Basal Complex, Barbados: Utility as a Predictor of Reservoir Geometry and Continuity: ABSTRACT

Lowstand fan deposits on Barbados were studied in outcrop to construct a conceptual reservior model for prediction of facies assemblages. Lowstand fan and wedge deposits are found in terrigenous clastic strata of the Basal Complex of Barbados, and are of Eocene age. The Barbados lowstand fan model consists of five parts, discussed below. (1) Residual lag facies with contrasting texture (conglomerate and coarse-grained sandstone beds interbedded with pebbly mudstone and mudstone) and depositional processes (debris flows, high- and low-density turbidity currents, suspended-load deposits) are interpreted to characterize an area largely of sediment bypass (bypass corridor 1) occurring updip of the lowstand fan. Channel-fill complexes, isolated channel-fills and interchannel deposits are recognized by different types of upward-fining vertical successions and associations of lithologies and compose the lowstand fan proper. (2) Conglomerate, pebbly sandstone and high- and low-density turbiditic sandstone forming hierarchical upward-fining successions, characterize channel-fill complexes in the proximal fan, and are typically amalgamated with other channel-fill complexes. (3) High- and low-density sediment gravity-flow deposits in well-developed hierarchial upward-fining packages characterize amalgamated channel-fill deposits, and are interstratified with mud-rich facies strata representing abandoned channel deposits and interchannel deposits. Together, the amalgamated channel-fill deposits interchannel deposits characterize deposition in the middle fan.more » (4) A residual lag facies, similar to that observed in bypass corridor 1, characterized by cross-bedded lenticular tractional deposits, interbedded with low-density sediment gravity flow deposits, defines bypass corridor 2: this occurs at the transition from the middle fan to the distal fan. (5) Low-density sediment gravity-flow deposits in tabular beds are observed in the distal fan.« less

Proterozoic sedimentation and Pan-African geodynamic development in the Himalaya

The Purana or Proterozoic-Lower Cambrian continental-margin sedimentary succession of the Lesser Himalaya comprises three lithological divisions: a lower argillo-arenaceous group, a middle carbonate succession and an upper argillo-calcareous assemblage. The poorly sorted basal sediments consisting of wacke-slate alternations of the lower group were emplaced by currents, including turbidity currents, which in the early stage flowed northwards from the Aravalli and Satpura mountains of Peninsular India. Lenticular deposits of diamictite within the flysch succession represent submarine slides. Penecontemporaneous basaltic lavas and associated tuffs, interbedded with shallow-water arenites making up the bulk of the upper part of the lower group, were related to rifting of the basins. The overlying dolomites and dolomitic limestones were laid down on a very shallow stable shelf and are characterised by columnar-branching stromatolites and lenticular units of crystalline magnesite and associated talc. Lenticular diamictites towards the top of the upper group of slates and limestone are harbingers of tectonic movements culminating towards the end of the Early Cambrian in an upheaval which abruptly terminated sedimentation throughout the Lesser Himalaya and Peninsular India, and caused a pronounced interruption of sedimentation in the Tethyan domain in the northern Himalaya. The Cambro-Ordovician (500±25 Ma) granites intruding the Lesser Himalayan thrust sheets of Lower Proterozoic metamorphic rocks and the upwarped northern front of the Himalaya signify an important tectonic event that terminated the Purana (Proterozoic-Lower Cambrian) sedimentation in the Indian subcontinent. This seems to be related to the tectonic movements that occurred towards the close of the Late Proterozoic or Early Cambrian.

Plio-Quaternary Seismic Stratigraphy of Ross Sea Eastern Basin (Antarctica): Implications to Glacial History and Basin Evolution

From air-gun and water-gun high-resolution single-channel seismic records, seven seismic units are defined, overlying the Ross Sea Unconformity, in the Plio-Quaternary sequences of the Ross Sea Eastern basin. These units are up to 600 m in thickness and generally thin onshore, disappearing near the western limit of the basin. The units are separated by smooth erosional surfaces characterized by continuous, high-amplitude reflectors. By correlation to DSDP Site 272, seismic units I and II are Pliocene in age, and the overlying units (III or VII) are Quaternary in age. Units I, III, and VII are basinal in extension and the others are confined to the central part of the basin. Thickness of the units ranges from 50 to 120 m, and they are mainly characterized by lenticular and wedge geometrics. Three acoustic facies are discerned: stratified, semitransparent, and chaotic. Wide (7 km) lenticular deposits, containing chaotic facies, are incised by U-shaped channels in seismic units, II, III (both up to 0.5 km wide), and VI (2 km wide), The spatial distribution of these channels indicates a paleodrainage system in which ice streams followed flow paths similar to those of the present. The major geological events that occurred on the continental shelfmore » during Plio-Quaternary time were: (1) the first channel incisions are identified near the boundary of the late Pliocene-Quaternary; (2) the advance and retreat of the ice sheet resulted in widespread erosion processes alternating with deposition of glacial and glaciomarine sediments; (3) the largest depocenter has been always situated in the shelf break environment, near the western limit of the basin; and (4) the only important progradation of the shelf occurred during the late Pliocene, and since then the shelf has been aggradational.« less

Thick iron oxide pans in soils of Taranaki, New Zealand

Thick iron oxide pans are a distinctive feature of some soils in Taranaki, New Zealand, which occur on the ringplain, or on terraces of valleys draining the ringplain of Mount Egmont. The pans tend to form in the boundary area between layers of differing texture within the zone of water table fluctuations. The pans are indurated, brittle, and vesicular, and have a black or reddish brown appearance with a shiny black fracture. They are up to 50 cm thick and form lenticular deposits sometimes several metres across at depths ranging from a few centimetres to about 1 m. Analysis of seven samples of pan gave 34-45% elemental Fe, 3-5% A1 and 4-10% Si, consistent with about 55-70% iron oxides, together with entrapped and adhering soil particles. V and Mo are enriched in the pan samples and probably occur as anionic species strongly adsorbed on the iron oxide surfaces. X-ray powder diffraction, Moessbauer spectroscopy and acid-oxalate dissolution indicate that the dominant iron oxides present are goethite and ferrihydrite. The relative proportion of these two minerals varies widely without any noticeable change in the nature of the pan materials. Microstructures in one sample were examined by scanning electron microscopy. The pans are considered to have formed from the aeration of groundwaters (rich in ferrous ions) moving laterally through the soils. Such groundwaters are formed on Mount Egmont from the reaction of meteoric water, sometimes containing dissolved volcanic carbon dioxide, with ferromagnesian minerals. Positive tests for ferrous ions (using �,�'-dipyridyl as indicator) were obtained from groundwaters presently associated with the pans.

Palaeoecology and significance of barnacles in the mid‐Pliocene Balanus Bed of Tobago, West Indies

AbstractThe Balanus Bed of the Rockly Bay Formation (mid‐Pliocene) of Tobago is a sequence of orange‐brown sands with laterally equivalent muds. The invertebrate macrofauna is dominated by the balanid barnacle Megabalanus tintinnabulum (Linnaeus) sensu lato, with associated oysters, pectinaceans, gastropods, bryozoans, regular echinoids, and rare crabs and sharks. Vertical burrows in muddier substrates are good evidence that this assemblage was living littorally or shallowly sublittorially. Previous analyses of the Rockly Bay Formation of the type area have erroneously suggested that it represents a lenticular deposit. It is now recognized to be a transgressive unit, unconformable on the underlying Mesozoic basalts. The sediment of the Balanus Beds was derived from the in situ weathering of basalts, producing a gradation from sandy (near shore) to muddy substrates. Balanids grew singly on the weathering basalt, but suitable substrates for attachment in the muddy environment were rare, so barnacles are found clustered in close association. The primary substrates for attachment in the muddy environment were disarticulated balanid plates, mollusc valves and small pebbles. Although the base of the Formation is not seen in Rockly Bay, a basal conglomerate overlain by a horizon of dissociated valves of the large ark Anadara patricia (Sowerby) is exposed in nearby Little Rockly Bay. Apart from the two fossiliferous horizons mentioned, the Formation is barren of marine microinvertebrates. The Rockly Bay Formation appears to have formed in response to the mid‐Pliocene rise in sea level. Horizons dominated by balanids may be useful indicators of sea‐level rise, at least in the Neogene, Darwin's ‘Age of Barnacles’.