Monocrystalline Quartz Research Articles

Petrographic Studies of the Vihowa Formation, Sulaiman Range, Pakistan: Implications for Provenance

The Vihowa Formation of late to early Miocene is investigated for mineral composition and petrographic characteristics to understand the provenance, diagenesis and depositional environments. Ten representative sandstone samples were collected from various lithological units for petrographic studies. Petrographic results show that the quartz is a major constituent; while the accessory minerals are chlorite, chamosite, palagonite, sphalerite, staurolite, aragonite, hypersthene, glaucophane, monazite, kyanite, epidote, olivine, rutile, ilmenite, hematite, magnetite, zircon, tourmaline and garnet. The tourmaline and rutile showing an igneous source however, the presence of epidote, staurolite and garnet expresses a metamorphic source for studied sandstones. The sandstone is medium to coarse grained having grains dominantly from the meta-sedimentary rocks whereas minor amount of grains from igneous rocks is also observed. Monocrystalline quartz is present in sands derived either from gneiss or granitic rocks, but polycrystalline quartz are from slate and schist. The inclusion of mica and garnet within quartz is observed which indicates a metamorphic source. On the QFL triangular diagram the sandstone of Vihowa Formation is mainly sub-lithic arenite and partly quartz arenite. The Qm-P-K plots indicate that feldspar and quartz are from granitic rocks along with small amount from metamorphic and volcanic rocks. The provenance of sandstone indicates that sediments were mostly deposited by transitional recycled orogeny and mixed magmatic subduction complex.

Lower Paleozoic reservoir zonation into different flow units using turbulence factor and their relations to diagenesis

Surface Lower Paleozoic sandstone samples were collected from southeast central Sinai. These samples subjected to petrophysical measurements which are porosity and permeability. It is known that turbulence factor (β) is a good tool to describe turbulent flow level, hence it was used to detect the flow properties distribution that corresponds to the nature of the pore system, so turbulence factor (β) was correlated with porosity, permeability, and reservoir quality index using many equations, where porosity correlation shows the presence of three groups having same porosity ranges but correspond to different values of turbulence factor, this refers to the presence of different flow zones. Porosity–permeability relation confirmed also the presence of similar three groups, where there are nearly same porosity ranges but with different permeability values. Consequently, samples with nearly same porosity values and representing the three groups were selected for capillary pressure by mercury injection to reveal the flow properties that characterize each group. Capillary pressure results confirmed that each group has their own pore system and flow regime. Petrography was done by optical polarizing microscope (OPM) through thin sections. The results indicated that the studied sandstone is composed mainly of quartz arenite microfacies of fine, angular to subrounded, moderately well sorted monocrystalline quartz grains. There are several features indicating that the investigated sandstones have been subjected to diagenesis processes. Diagenetic events identified in these sandstones include considerable compaction during burial diagenesis at higher temperatures and low flow rates, cementation by clay minerals and iron oxides, dissolution and alteration of unstable clastic grains, and tectonically induced grain fracturing. Unstable clastic grains like feldspars suffered considerable alteration to kaolinite when exposed to meteoric water of low ionic strength near the surface. The distribution of this kaolinite rather than the post-depositional iron oxides in pores of the studied sandstone leaded to differentiating these sandstones into three different flow units. This zonation indicates that the turbulence properties are proportional to the diagenetic effects inside the pores.

サハラ砂漠のエルグの砂より見いだした単結晶石英内部の"Ghost ring"

サハラ砂漠のエルグの砂より見いだした単結晶石英内部の"Ghost ring"

Architecture and quantitative assessment of channeled clastic deposits, Shihezi sandstone (Lower Permian), Ordos Basin, China

Lower Permian Shihezi sandstone in Ordos Basin is the largest gas reservoir in China. Architecture elements of channel, overbank and floodplain facies of braided channel deposits were identified through an outcrops survey, and their proportion of channel facies have been quantitatively estimated from well logging. Characteristics of architecture elements, such as sand thickness, bounding surfaces and lithofacies were investigated through outcrops and core. Petrology of Shihezi sandstone has also been studied in detail. Analysis on sandstone components shows that monocrystalline quartz with approximately 76% bulk volume, and lithic up to 5%–45% bulk volume, are the two main components. Litharenite and lithic quartz sandstone are the main rock types. Compaction is concluded by former researchers as the control factor of low permeability. Examination through thin section reveals that secondary pores developed well in coarse sand. Inter-granular dissolution is included as the positive effect to increasing porosity, and is concluded as the control factor to the generation of net pay. Scale of coarse grained channel fills and channel bar sandstone bodies are quantitatively estimated. Strike-oriented, dip-oriented, and vertical distribution of channel fills and channel bar sandstone bodies have been investigated. The geometry of sand bodies can be depicted as an elongated lens. Subsurface mapping reveals that channel sandstone bodies distribute widely from both lateral and longitudinal cross section profiles, and are poorly connected.

Chapter 5 Arakan Coastal Ranges in western Myanmar, geology and provenance of Neogene siliciclastic sequences: implications for the tectonic evolution of the Himalaya–Bengal System

Supplementary material : Preparation and analysis of samples with appendices are available at https://doi.org/10.6084/m9.figshare.c.3860926 Neogene clastic sequences preserved in the western part of Indo-Myanmar Ranges provide detrital information that document the erosional and unroofing history of the eastern Himalayas and the Burmese Arc during the Indian–Asian collision. All of the sedimentological and provenance data link the syntectonic sedimentation and sequential evolution of the Bengal Basin, a remnant ocean basin south of the eastern Himalayas and, at the time of formation, a palaeo-incised valley in the eastern trough of the Central Myanmar Tertiary Basin. To the east lies the Sagaing Fault and the Mogok Belt, and further east the Shan–Thai Block. Modal analysis of the Lower Miocene sandstones of the Baronga Islands, Arakan Coastal Ranges shows that they are rich in both monocrystalline and polycrystalline quartz, sub-angular to subrounded feldspars and lithic fragments including metamorphic rock fragments with minor basaltic fragments, suggesting the onset of uplift, erosion and unroofing of the eastern Himalayas and Indo-Myanmar Ranges. Since the Early Miocene, sediments were deposited in twin gulfs separated by the uplifted Indo-Myanmar Ranges. In the Middle Miocene there was a major change in the provenance of the Neogene sediments of the Arakan Basin and the Central Tertiary Basin of Myanmar. Since the Early Miocene, basement uplift of the Mogok Belt in the east and the Gangaw Ranges of the upper Irrawaddy Basin in the western part of the Asian Plate, as well as the initiation of river systems, supplied orogenic detritus to the south (Allen et al. 2008; Kyi Khin et al. 2014; Robinson et al. 2014; Licht et al. 2015). Middle Miocene sandstones from both areas are rich in sub-angular monocrystalline quartz, chert and argillites with small amounts of feldspar and metamorphic lithic fragments, suggesting a relatively low …

Middle Cenozoic diachronous shift to eolian deposition in the central Rocky Mountains: Timing, provenance, and significance for paleoclimate, tectonics, and paleogeography

Eolian sedimentation was widespread in the Rocky Mountains (Rockies herein) during the middle and late Cenozoic. Although changes to eolian depositional environment have significance for tectonics, paleoclimate, and paleogeography, little is known regarding the timing of initiation and the provenance of these eolian sedimentary rocks in the Rockies. Here we study the timing of a transition to eolian depositional environments in the central Rockies and the adjacent Great Plains during the middle Cenozoic, and use sandstone petrography and detrital zircon U-Pb geochronology to constrain the provenance of the eolian sedimentary rocks. Our samples have compositions of Qm44F27Lt29 (Qm is monocrystalline quartz, F is feldspar, and Lt is total lithics), Q47F27L26 (Q is total quartz, L is total non-quartzose lithics), and Qm64P28K8 (P is plagioclase and K is potassic feldspar), and zircon age populations of 17–44 , 45–218 Ma, 220–708 Ma, 948–1326 Ma, 1332–1816 Ma, and 1825–3314 Ma. The youngest zircon population was derived from distal volcanism in western and southwestern North America, and the other populations were derived directly from local Precambrian basements on Laramide ranges and recycled from Paleozoic–lower Cenozoic strata distributed along flanks of Laramide ranges and on the Sevier hinterland. The maximum depositional ages, based on the mean U-Pb ages of the youngest clusters of zircon grains, are generally consistent with the available ash radiometric dates for the latest Eocene–early Miocene samples, confirming that detrital zircon maximum depositional ages can be used to constrain depositional ages when ash beds or dateable minerals in ash beds were not present and when synchronous magmatic activity was intense. The occurrence of eolian deposition initiated during the latest Eocene–early Oligocene and became younger eastward, suggesting eastward progressive drying in the central Rockies. The diachronous drying may have resulted from the combined effect of renewed uplift of the Cordilleran hinterland and central Rockies during the late Eocene and global cooling at the Eocene-Oligocene boundary. The provenance data presented here suggest that during the latest Eocene–early Oligocene, the westerlies and possibly the dry summer monsoon winds transported unlithified fluvial sediments and pyroclastic materials eastward and northeastward, and formed massive eolian deposits in the central Rockies and the adjacent Great Plains. The eolian sedimentation continued into the Miocene and largely blanketed the Precambrian basement cores on Laramide ranges. The unlithified Oligocene eolian sediments were further eroded and recycled into the latest Oligocene–Miocene eolian sedimentary rocks.

Detrital mode and whole-rock geochemistry of the Miocene-Pliocene fluvial succession, Pishin Belt, Pakistan: implications on provenance and source area weathering in peripheral foreland basins

Detrital mode and geochemical composition of sandstones and mudstones of the Miocene Dasht Murgha Group (DMG) and Pliocene Malthanai Formation (MF) of the Pishin Belt, northwestern Pakistan, have been examined to identify their provenance and source area weathering. Sandstones of the Dasht Murgha Group and Malthanai Formation are lithic to sublitharenites, rich in quartz, and metamorphic and sedimentary lithic fragments, indicating a recycled orogenic source. LmLvLs plots show that the Dasht Murgha Group is rich in sedimentary and metamorphic lithic fragments (Lm35Lv18Ls47), while samples of the Malthanai Formation are overwhelmingly rich in sedimentary fragments (Lm14Lv10Ls76). Eocene Nisai Formation and Oligocene Khojak Formation within the Pishin Belt were mainly providing the sedimentary/metasedimentary detritus. High content of monocrystalline quartz (DMG 28.21 %; MF 30.7) and higher SiO2/Al2O3 ratios in sandstones (DMG 9.86; MF 11.98) also indicate high maturity of sandstones due to recycling of source terrain in collision orogens. High Cr/Ni (DMG 5.23; MF 6.17) and moderate Cr/V (DMG 3.96; MF 3.88) ratios suggest significant contributions from mafic and ultramafic detritus derived from Muslim Bagh-Zhob Ophiolite. Malthanai Formation has higher CIA and CIW values (68.96 and 77.53) than Dasht Murgha Group (63.87 and 70.93); however, they both indicate low to moderate weathering intensities. Dasht Murgha Group and Malthanai Formation have higher ICV values which indicate abundance of aluminous silicates, hence, showing moderate weathering of the source area. In A-CN-K diagrams, the samples make linear trend towards illite which suggests that the sediments were derived from a tectonically active source going through non-steady-state weathering, where the detritus has been derived from different zones of weathering profiles.

Composition of Pliocene to Quaternary mixed terrigenous and calcareous sandy beds in contourite drift deposits at ODP Site 1119 off New Zealand: Insights into sandy drift development and drift petroleum reservoir characterization

ODP (Ocean Drilling Program) Site 1119 was drilled in drift successions deposited by northward flowing currents on the Canterbury slope, South Island, New Zealand. Pliocene (∼3.9 Ma) to Pleistocene drift accumulation was concomitant with tectonic uplift and sediment supply from the Alpine Fault plate boundary to the west, glacial development and eustatic sealevel change that created cyclicity in sandy input. Sand detrital and biogenic modes of very fine and fine sand fractions from 24 unconsolidated core samples (44 thin sections) were determined. Fine sand fractions contain an average of 52% bioclastic debris, with bioclasts making up 23% of the very fine sand fraction. Foraminifers are the dominant bioclasts, with pelagic more common than benthic varieties. The average proportions of monocrystalline quartz, plagioclase and potassium feldspar are similar in both size fractions (average QmKP of ∼25:12:63). In contrast, the very fine sand fractions have, on average, higher lithic (QFL%L of 16 vs. 3%), mica (Totalgrain%M of 10 vs. 6%), and dense mineral (Totalgrain%D of 8 vs. 5%) content as compared with the fine sand fractions. Younger clinoform drape (Unit I) and older mounded drift (Unit II) seismic facies showed no distinct detrital compositional differences in their sand fractions, though bioclast content ranges higher in the fine sand fraction of Unit II. Albite feldspar, metamorphic rock fragment, and chlorite components in the sand are consistent with a schist provenance. Other components such as biotite, plagioclase, and K-feldspar require a contribution from metasedimentary and volcanic rocks. Thus there is some along-slope mixing during sediment transport by south-to-north flowing currents. Cemented microporous sandstone at the base of the section provides some insight into contourite burial diagenesis. This work provides a better understanding of the compositional variability of sand components of drift successions which are potential hydrocarbon reservoirs elsewhere.

Petrography and geochemistry of the siliciclastic Araba Formation (Cambrian), east Sinai, Egypt: implications for provenance, tectonic setting and source weathering

AbstractCombined petrographic and geochemical methods are utilized to investigate the provenance, tectonic setting, palaeo-weathering and climatic conditions of the Cambrian Araba clastic sediments of NE Egypt. The ~ 60 m thick Araba Formation consists predominantly of sandstone and mudstone interbedded with conglomerate. Petrographically the Araba sandstones are mostly sub-mature and classified as subarkoses with an average framework composition of Q80F14L6. The framework components are dominated by monocrystalline quartz with subordinate K-feldspar, together with volcanic and granitic rock fragments. XRD analysis demonstrated that clay minerals comprise mixed-layer illite/smectite (I/S), illite and smectite, with minor kaolinite. Diagenetic features of the sandstone include mechanical infiltration of clay, mechanical and chemical compaction, cementation, dissolution and replacement of feldspars by carbonate cements and clays. The modal composition and geochemical parameters (e.g. Cr/V, Y/Ni, Th/Co and Cr/Th ratios) of the sandstones and mudstones indicate that they were derived from felsic source rocks, probably from the crystalline basement of the northern fringe of the Arabian–Nubian Shield. The study reveals a collisional tectonic setting for the sediments of the Araba Formation. Palaeo-weathering indices such as the chemical index of alteration (CIA), chemical index of weathering (CIW) and plagioclase index of alteration (PIA) of the clastic sediments suggest that the source area was moderately chemically weathered. On the northern margin of Gondwana, early Palaeozoic weathering occurred under fluctuating climatic conditions.

Petrography and geochemistry of sandstone samples of Vischkuil formation, Karoo Supergroup, South Africa

Petrography and geochemistry of sandstones of Vischkuil formation in the Ecca Group of the Karoo Supergroup of South Africa was investigated to evaluate the petroleum potential of its reservoir rock. The petrographic analysis showed that the sandstones were poorly to moderately sorted with evidence of angular to sub-angular grains. The sandstones are lithic arenite. Diagenetic processes on the sandstone include physical and chemical compaction as seen from the straight grain contacts and dissolution of the quartz grains. There is an evidence of pore space reduction by the rearrangement and cementation by silica, calcite and clay minerals. The petrographic analysis also revealed that there is dominance of monocrystalline quartz grains and evidence of cratonic setting derivation. The chemical alteration index ranged from 52.96 to 65.5 %, an indication of a moderate weathering at the source area before deposition. The samples are texturally immature, which indicate poor storage capacity for fluids.

Deposition of the Upper Rewa Sandstone Formation of Proterozoic Rewa Group of the Vindhyan Basin, M.P., India: A Reappraisal

Abstract The Upper Rewa Sandstone Formation of the Rewa Group in the Vindhyan basin is composed mainly of medium to very fine grained, iron pigmented arenaceous rocks variously interpreted as fluvial, marine or continental deposits. The Upper Rewa Sandstone Formation consists of channelized, laterally shifting sand bodies comprising 1-2 m thick fining upward (FU) sharply/erosionally based cycles. Each shoaling bar cycle is characterized by presence of large scale planar and trough cross-bedding, horizontal bedding showing primary parting lineation, wave and current ripples, herringbone cross-bedding and tidal bundles with double mud-drapes and indicates marine environment of deposition and rule out the possibility of continental sedimentation. However, channelized nature of sand bodies composed of shoaling bar cycles with signatures of wave modification and exposure in the lower part of the succession and well developed horizontally bedded lithofacies showing primary parting lineation and well sorted character of sandstones in the upper part of the succession may imply deposition under subtidal to intertidal setting in estuarine to bordering beach environments. The palaeocurrent study shows polymodal to bimodal and unimodal palaeocurrent patterns. The dominant polymodal palaeocurrent patterns with temporal trends directed towards NW, N and SW also corroborate marine origin and sediment dispersal under combined action of wave and currents. Petrographically, sandstone is quartzarenite and consists of mostly monocrystalline quartz, feldspar, mica, rock-fragments and heavy minerals such as hypersthene, zircon, hornblende, tourmaline, rutile, augite, kyanite and andalusite indicating sediment contribution from mixed sedimentary/metamorphic and igneous source terrain. Qm-F-Lt and Qt- F-Lt plots reveal that the Upper Rewa Sandstone Formation shows continental block province with stable craton (C) and in uplifted basement (B) where C>B.

Mineralogy and grain morphology of the aeolian dune sand of Toshka area, southeastern Western Desert, Egypt

Abstract This work investigates the mineralogical properties and the morphology of aeolian quartz sand in the Toshka dune area, southeastern Western Desert of Egypt. The dunes are composed mostly of subangular to subrounded fine to medium quartz sands together with minor proportions of feldspars and lithic fragments. Significant roundness variations are observed both between different dune types and within the dune sites. Barchan sands are the most rounded, whilst sand shadows are angular and fine. Barchans are also relatively enriched in polycrystalline quartz, where most of these grains are more rounded and more durable than monocrystalline quartz. Roundness characteristics of the Toshka sands are considerably managed by their grain size as medium quartz grains are more rounded than the finer ones. Angularity is a characteristic property of most monocrystalline quartz grains that exhibit undulose extinction. This maintenance of undulose extinction in quartz perhaps as a result of less stability and minimal transport from the source in the vicinity of the dune fields, as shown by the increase of angularity of quartz and short-distance transfer of these grains. These Toshka sand grains also show signs of a fluvial transportation signature. The analysis of grain surface features by scanning electron microscope (SEM) performed on dune sand grains from the Toshka area showed that quartz grains demonstrate a variety of surface textures indicating mechanical and chemical processes developed during transportation of these grains in subaqueous and aeolian environments, respectively, reflecting the mixed mode of formation of these dunes.

Geochemistry and provenance of the Lower Siwaliks from southwestern Kohat, western Himalayan Foreland Basin, NW Pakistan

Equivalent to the Lower Siwalik Group, the Late Miocene Chinji Formation in Pakistan consists of interbedded in-channel sandstone (SSt) and overbank mudstone (MSt) sequences. Twelve sandstone and sixteen mudstone samples from three different sections of the formation in southwestern Kohat, NW Pakistan were analyzed for major elements and selected trace elements. The Chinji sandstones are feldspathic and lithic arenites. They are mostly matrix-supported, moderately to well sorted, and contain angular to rounded framework grains. Authigenic carbonate makes up most of the matrix. The framework grains consist of abundant monocrystalline quartz, alkali feldspar, and lithic fragments with subordinate mica and trace to accessory amounts of heavy minerals including epidote, monazite, apatite, garnet, rutile, and brown hornblende. The lithic fragments consist of sedimentary, volcanic, and low-grade metamorphic rocks.The average concentration of Zr, Nb and Y, and the Ba/Sc and Ba/Co ratios in the studied samples are lower than the corresponding values for the upper continental crust (UCC) and Post-Archean Australian Shale (PAAS) indicating the presence of mafic phases in the source area(s). The high average Cr/Zr and Cr/V ratios of the investigated samples relative to UCC and PASS also support the presence of mafic lihtologies, possibly chromite and ultramafic rocks in the source region. The La/Sc and Th/Sc ratios of the Chingi samples are more like the UCC while the Th/Co and Cr/Th ratios suggest a major contribution from mafic rocks. The average percent differences of the Chinji samples from both the UCC and PAAS in terms of critical silicic to basic trace element ratios (Ba/Co, Ba/Sc, La/Co, La/Sc, Th/Co, Th/Sc, Zr/Cr, and Zr/Sc) suggest a mafic contribution of 23 to 47% (mudstone) and 56 to 69% (sandstone). The lower Th/U, Rb/Sr and Zr/Sc ratios in the studied samples than the corresponding values of the UCC and PAAS suggest negligible recycling for the sediments of the Chinji Formation. Petrographic point count data on the Chinji sandstone indicate sediment derivation from a dissected arc, suture belt, and recycled orogen corresponding to the Kohistan-Ladakh Arc, the Indus Suture Zone, and the Himalayan Tectonic units, respectively. The different source rocks identified on the basis of various petrographic and geochemical parameters occur as part of the mentioned tectonic domains.

Sedimentary facies analysis, mineralogy and diagenesis of the Mesozoic aquifers of the central Perth Basin, Western Australia

Assessment and successful exploration for, and exploitation of, aquifers in the Perth Basin require knowledge of their petrophysical and sedimentological characteristics and geometries. This study provides a sedimentological and lithofacies analysis of core from the Mesozoic Yarragadee Formation, Cadda Formation, Cattamarra Coal Measures, Eneabba Formation and Lesueur Sandstone of Western Australia recovered from Pinjarra-1, Cockburn-1, Gingin-1 and Gingin-2 wells provide insights into changes in depositional environment over time and space in the central Perth Basin. In studied sections, nine different fluvial-dominated lithofacies have been identified in the Yarragadee Formation, Cadda Formation and Cattamarra Coal Measures that occur in similar proportions, whereas the Lesueur Sandstone is dominated by coarse-grained deposits of high energy fluvial systems. Vertical variation in lithofacies on the order of 10 cm to approximately 2 m vertical scale is observed in all formations and wells. Changes in the lithofacies, linked to local depositional environments, are probably associated with fluvial-alluvial to fluvio-deltaic systems that have complex 3D architecture, including braided and to probably meandering systems, and are affected by channel avulsion. Point counting and automated mineral analysis of thin sections of core showed detrital mineralogy dominated by monocrystalline quartz, with rare polycrystalline quartz, a moderate amount of alkali feldspar and very minor amounts of garnet, organic fragments, muscovite and biotite. These data show a lithofacies-dependence of the proportion of minerals, with little variation between equivalent lithofacies from different depths, formations or wells. Grain size and sorting, that have a first order control on porosity, are strongly lithofacies dependent. Individual lithofacies types show a trend of decreasing porosity with depth due to the increasing effects of compaction, quartz overgrowth cementation and authigenic clay mineral development. Lithofacies and depth are the main controls on permeability, and so lithofacies distribution exerts a key control on hydraulic behaviour.

Fabrication and characterization of high density silicon quantum dots in gradient Si-rich carbide films

Gradient Si -rich carbide (GSRC) thin films were deposited on monocrystalline silicon wafers and quartz substrates by magnetron co-sputtering, with subsequent thermal annealing by rapid thermal processing. Fourier transform infrared spectroscopy, Raman spectroscopy, grazing incident X-ray diffraction, transmission electron microscope, and Hall measurements were used to analyze the microstructure and conductivity of the films. It was observed that bonding configurations, microstructure and conductivity properties changes with the annealing temperature from 700°C to 1000°C. The experimental results demonstrate that Si QDs with crystal volume fraction of 72.5%, average size of 4.5 nm, and number density of ~2 ×1012 cm -2 embedded in the amorphous SiC matrix can be formed using a GSRC multilayer structure, with subsequent annealing at 1000°C. The 1000°C annealed thin film possesses a conductivity of ~5 S ⋅ cm -1, which can be attributed to high carrier transport efficiency caused by high Si QD density.

Sedimentology and stratigraphy of the Lower Cretaceous Isachsen Formation: Ellef Ringnes Island, Sverdrup Basin, Canadian Arctic Archipelago

The Lower Cretaceous Isachsen Formation is a widespread, siliciclastic succession up to 1.4 km thick that records the northwestward progradation of fluvio-deltaic environments into the Sverdrup Basin in the Canadian Arctic. Although the Isachsen Formation is a prominent unit with proven oil and gas reserves, detailed outcrop descriptions of its sedimentology and stratigraphy, and correlation of these features to subsurface data are rare. We examined outcrop exposures of the Isachsen Formation on Ellef Ringnes Island in the province of Nunavut in the Canadian Arctic in order to document and interpret the sedimentology and stratigraphy of this unit in the central portion of the Sverdrup Basin. Interpretations are based on observations from over 5000 m of measured stratigraphic sections, local mapping of facies contacts, palynology, and sandstone petrography. Deposits of the Isachsen Formation on Ellef Ringnes Island can be divided into six broadly-defined facies associations that record deposition in braided-fluvial, meandering-fluvial, floodplain, tidally-influenced fluvial, shoreface, and offshore environments. Sandstones within the Isachsen Formation are typically quartzose, commonly with compositions of >90% well-rounded, monocrystalline quartz. Although the sedimentary details between outcrop locations vary, a generalized stratigraphic trend is present within the Isachsen Formation. Where exposed, the base of the unit consists of marginal marine sandstones abruptly overlain by braided stream deposits, which grade into mudstone-rich, meandering-fluvial and floodplain deposits. These nonmarine deposits are overlain by a thin marine mudstone (Rondon Member), which is in turn overlain by marginal marine sandstone and fluvial deposits. The uppermost portion of the Isachsen Formation records a transgression and is overlain by marine mudstones of the Christopher Formation. The stratigraphic succession of the Isachsen Formation in outcrops correlates to data from nearby hydrocarbon exploration wells. Stratigraphically, the Isachsen Formation on Ellef Ringnes Island represents a regressive–transgressive sequence, but contains within it two higher-order regressive–transgressive sequences, which is consistent with observations from elsewhere in the Sverdrup Basin. The detailed descriptions of facies within the Isachsen Formation on Ellef Ringnes Island and their correlation to subsurface data can be extrapolated to other parts of the Sverdrup Basin where data are lacking.

A Petrographic Study of the Three Forks Formation (Upper Devonian), Williston Basin, North Dakota: Based on Thin Section Analysis, XRD and SEM

Deeply buried below 8,000 ft, the Three Forks Formation in North Dakota displays a variety of interesting diagenetic characteristics including dolomitization and hematite precipitation. Samples from three lithofacies are analyzed by thin section and SEM petrography and combined bulk and clay XRD analyses. Key aspects controlling the porosity and permeability of this formation are revealed by focusing on the detail mineralogy, rock type and diagenetic mineral distribution, and overall reservoir quality. Results prove that the Three Forks mineralogy is dominated by dolomite, along with substantial hematite, monocrystalline quartz, and mica flakes with trace feldspar, calcite, and pyrite. Clays mainly consist of illite together with minor chlorite and kaolinite and are associated with the scattered clasts. The reservoir quality is controlled by intercrystalline, rare microvuggy, and microporosity types that result from diagenetic and depositional events. Three stages of the dolomitization process are identified and discussed. Our hypothesis is that dolomitization commenced soon after deposition and was pervasive as no original carbonate texture is detectable.

Petrography and geochemistry of lower carboniferous greywacke and mudstones in Northeast Junggar, China: Implications for provenance, source weathering, and tectonic setting

Northeast Junggar occupies an important position that links East Junggar and Chinese Altai. Numerous magmatic and sedimentary rocks of the Paleozoic in this area recorded the final amalgamation processes of East Junggar and Chinese Altai. This study analyzes the petrological and geochemical characteristics of sandstones and mudstones from the Early Carboniferous Nanmingshui formation in Northeast Junggar. The provenance and tectonic setting of these clastic rocks are discussed. Petrography indicates that the composition and texture maturity of the sandstones are low. The components of the sandstones are mainly volcanic fragments (61–87%), feldspars (9–30%), and monocrystalline quartz (2–18%), with a few polycrystalline quartz and other minerals. Slice observation indicates that the majority of the volcanic fragments of sandstones are basic-intermediate volcanic rocks with a few dacite and felsic plutonic fragments. The detrital modes of the sandstones reflect that these sandstones are derived from undissected arcs. A low to moderate chemical index of alteration and the Al2O3–CaO*+Na2O–K2O diagram reflect a low to moderate weathering degree in the source area. Trace and rare earth element (e.g., La, Th, Hf, Sc, Cr, Co, and Eu) contents and their ratios suggest that the source rocks of the clastic rocks are intermediate-basic rocks with some felsic rocks. Compared with sandstones, the source rocks for mudstones are more felsic. The petrography and geochemistry characteristics of the clastic rocks suggest that the proximal Dulate arc should be the primary source area. Mixing calculations based on REE data suggest that approximately two-thirds of the sandstone fragments are intermediate-basic volcanic rocks. The contents of the major and trace elements, as well as the stratum features, of the clastic rocks manifest that these clastic rocks resemble sedimentary rocks in a back-arc basin. The formation of this back-arc basin is caused by the southward subduction of the Zaysan–Erqis Ocean.

Análisis de proveniencia de las arenas del complejo de dunas parabólicas El Socorro, Baja California, México, mediante una caracterización mineralógica y granulométrica

In this study, fourteen superficial sandy sediment samples and fifteen core samples, taken at 2 to 30 m in depth, were analyzed in order to determine the granulometry and mineralogical features of the dune system named duna costera El Socorro (DCES), San Quintin, Baja California, Mexico. In addition, we investigated the sediment provenance by analyzing twelve samples collected from three nearby arroyos and sand bars. The main components of the DCES are plagioclase and quartz (35 - 39 % and 36 - 58 % plagioclase, and 50 - 56 % and 38 - 60 % monocrystalline quartz for core samples and superficial samples, respectively). The remaining components include scarce lithic fragments and abundant heavy minerals, mostly hornblende and traces of pyroxene, but also small amounts of magnetite and ilmenite (> 1 % in volume). The samples from arroyo El Socorro (south of the DCES) and arroyo Santo Domingo (~45 km north of the DCES) contain 69 and 52 % monocrystalline quartz, respectively, while arroyo San Simon, located north of the DCES,

Integrated provenance record of a forearc basin modified by slab‐window magmatism: detrital‐ zircon geochronology and sandstone compositions of the Paleogene Arkose Ridge Formation, south‐central Alaska

AbstractThis study presents an integrated provenance record for ancient forearc strata in southern Alaska. Paleocene–Eocene sedimentary and volcanic strata >2000 m thick in the southern Talkeetna Mountains record nonmarine sediment accumulation in a remnant forearc basin. In these strata, igneous detritus dominates conglomerate and sandstone detrital modes, including plutonic and volcanic clasts, plagioclase feldspar, and monocrystalline quartz. Volcanic detritus is more abundant and increases upsection in eastern sandstone and conglomerate. U‐Pb ages of >1600 detrital zircons from 19 sandstone samples document three main populations: 60–48 Ma (late Paleocene–Eocene; 14% of all grains), 85–60 Ma (late Cretaceous–early Paleocene; 64%) and 200–100 Ma (Jurassic–Early Cretaceous; 11%). Eastern sections exhibit the broadest distribution of detrital ages, including a principal population of late Paleocene–Eocene ages. In contrast, central and western sections yield mainly late Cretaceous–early Paleocene detrital ages. Collectively, our results permit reconstruction of individual fluvial drainages oriented transverse to a dissected arc. Specifically, new data suggest: (1) Detritus was eroded from volcanic‐plutonic sources exposed along the arcward margin of the sampled forearc basin fill, primarily Jurassic–Paleocene magmatic‐arc plutons and spatially limited late Paleocene–Eocene volcanic centers; (2) Eastern deposystems received higher proportions of juvenile volcanic detritus through time from late Paleocene–Eocene volcanic centers, consistent with emplacement of a slab window beneath the northeastern part of the basin during spreading‐ridge subduction; (3) Western deposystems transported volcanic‐plutonic detritus from Jurassic–Paleocene remnant arc plutons and local eruptive centers that flanked the northwestern part of the basin; (4) Diagnostic evidence of sediment derivation from accretionary‐prism strata exposed trenchward of the basin fill is lacking. Our results provide geologic evidence for latest Cretaceous–early Paleocene exhumation of arc plutons and marine forearc strata followed by nonmarine sediment accumulation and slab‐window magmatism. This inferred history supports models that invoke spreading‐ridge subduction beneath southern Alaska during Paleogene time, providing a framework for understanding a mature continental‐arc/forearc‐basin system modified by ridge subduction. Conventional provenance models predict reduced input of volcanic detritus to forearc basins during progressive exhumation of the volcanic edifice and increasing exposure of subvolcanic plutons. In contrast, our results show that forearc basins influenced by ridge subduction may record localized increases in juvenile volcanic detritus during late‐stage evolution in response to accumulation of volcanic sequences formed from slab‐window eruptive centers.