Lithic Arenites Research Articles

Microfacies and Sedimentary Environments of Nfayil Formation (Middle Miocene) in Karbala Using Stable Isotope

A surface section of the Nfayil Formation (Middle Miocene) was studied approximately 80 km from the holy city of Karbala. The study area includes the Malutiyat area's Nyfail Formation (Middle Miocene age). The Nfayil Formation contains marls interbedded with limestones, as well as marly limestone. Fieldwork and petrographic analysis are being conducted on Miocene sediments from the Karbala region. Details obtained from textural and faunal properties aided in the designation of microfacies zones, which led to environmental subdivisions as a ramp. The carbonate lithic arenite sandstone has a significant amount of carbonate fragments. Microfacies characteristics of the whole successions showed skeletal and non-skeletal grains. The oysters, an index fossil of the Nfayil Formation are found in the lower part of the Nfayil Formation. The stable isotopes 18O/16O and 13C/12C in carbonates are analyzed to define the depositional characters and the basin paleo depth. The studied samples have negative δ18O isotope values (average -11.79 %). The carbon isotope composition is of positive values (average 2.16‰), The Z values, higher than 120, reflect the marine sediments of the formation. Four facies were identified, (Lime mudstone Microfacies, Sandy Lime mudstone Microfacies, Peloidal Bioclastic Packstone-Wackestone Microfacies, Bioclastic Wackestone Microfacies) and based on them, the formation environment was determined (restricted marine, and shallow open marine environments).

Petrographic and geochemical study of Precambrian and Paleozoic rocks in the western Anti-Atlas belt, Morocco: Facies, weathering, provenance and economic exploitation

Detrital and volcanic-detrital rocks from the Ifni Buttonhole and Lakhssas Plateau were analyzed to determine their provenance, compositional maturity, and alteration source. Geochemically, the sediments were classified as arkoses, lithic arenites, grauwackes, sandstones, lithic arenites, and Fe-rich sands, indicating low compositional and mineralogical maturity. A high average SiO2 concentration and low Al2O3 were consistent with a low abundance of shale and clay components. The geochemical signatures of the detrital and volcano-detrital (RDVD) rocks indicate that they have undergone a moderate to low degree of chemical alteration. The CIA study also suggests that the granitic, granodioritic rocks represent the source provenance which, during weathering and transport, supplied the detritus to the supra-crustal units. The major trace element data suggest that these rocks are largely derived from felsic igneous rocks, namely granitoids, with a minor contribution from intermediate sources. The carbonate rocks do not represent a wide variety of facies: dolomitic limestone, calcareous limestone, and calcaro-dolomitic chert. Calcitic and dolomitic samples show a linear increase in SiO2, regardless of their CaO/LOI ratio values, which remain relatively constant. The highest SiO2 contents are observed in the calc-dolomitic chert. Geochemical analysis of RDVD from the Ifni buttonhole determined their origin, maturity, and alteration. Major oxides decreased with higher silica content, indicating quartz control. Samples, formed under semi-arid conditions, show maturity under stable deposition. They suggest a felsic, recycled source, with moderate alteration and zircon enrichment during recycling. In the study area, limestones and dolomites serve as materials applicable in the building sector, suitable for all types of concrete. The Taliwine Formation harbors Lower Cambrian dolomites and limestones, ideal for mosaic aggregates. Described as variable in color, compact, homogeneous, very hard, and resistant to alteration, the plutonic rocks form prominent peaks. They exhibit both subalkaline characteristics in granitoids and an alkaline trend in dolerite dykes. Most samples display minimal alteration, indicating the reliability of their major element compositions for geochemical analyses. These granitoids constitute valuable deposits for ornamental and building rock purposes.

Diagenesis, Provenance, Tectonic Setting and Palaeoclimate of the Eocene Kopili Sandstone, Assam, India: A Petrographic Study

Abstract The Eocene Kopili Sandstone outcropping in the North Cachar Hills (NCHs) of Assam, India, was petrographically studied to unravel its diagenetic features, provenance, tectonic setting and palaeoclimate conditions. The modal analysis of the Kopili Sandstone reveals that the detrital mineralogy is dominated by quartz (48.78 to 83.70 %), with variable amounts of rock fragments (0.37 to 7.35 %), feldspar (0.37 to 8.33 %), micas (0.36 to 7.84 %) and subordinate amount of heavy minerals. The matrix and cement content varies from 9.88 to 21.50 % and 1.12 to 19.41 % respectively. The Kopili Sandstone is classified as quartz arenite to sub lithic arenite. Compaction, cementation, dissolution and replacement are the observed diagenetic processes in the studied sandstones. Diagenetic transformations are manifested in the fractured detrital grains, overgrowth of quartz, corrosion of grain boundaries of quartz, modification of grain boundaries, and silica and iron oxide cement precipitation in the interstices of the framework grains. The provenance is of granite-gneissic rock terrain. The detritus in the depositional basin is derived predominantly from craton interior with minor input from recycled orogen. The study discerns humid palaeoclimate conditions for the Kopili Sandstone.

Geochemical assessment of mineral sequestration of carbon dioxide in the midcontinent rift

AbstractThis study examines the potential of Midcontinent Rift rocks to facilitate long‐term CO2 sequestration by providing the necessary Ca and Mg for carbonate mineralization. Surface samples were collected from the Oronto and Bayfield‐Jacobsville Groups around Lake Superior and used for petrography and X‐ray diffraction to determine their mineral composition. Also, X‐ray fluorescence was also used to assess their bulk chemical composition. The samples were then exposed to CO2 and deionized water in Teflon‐lined vessels at 90°C, and the resulting leachate fluids were analyzed for the cation released during the testing. SEM microscopy was used to examine the samples for potential mineralization of carbonate minerals. The Oronto Group sediments consist primarily of feldspathic to feldspathic lithic arenites with a chlorite‐dominated matrix, and the primary porosity is blocked by calcite and hematite cement. The Bayfield–Jacobsville sequences are porous quartz arenites to feldspathic quartz arenites that do not contain significant accumulation of Ca‐, Mg‐, and Fe‐bearing minerals. The leachate fluids obtained from Oronto Group samples exhibit a maximum Ca release rate (5.2 × 10−4 mole/cm2.day), indicating rapid calcite cement dissolution and increased porosity and permeability. SEM/EDS microanalysis revealed areas where pore‐filling calcite was preferentially dissolved. Longer‐term rock‐water reactions resulted in induced carbonate mineralization, as evidenced by calcite crystals observed in a sample reacted for 102 days. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd.

Lower Permian Košna conglomerates of the Velebit Mt. (Croatia): modal composition, provenance and depositional environment

The multicoloured ‘Košna’ conglomerates are investigated in the area of the Košna Voda spring, in the Brušane area of Velebit Mt., Croatia. The studied conglomerates consist of red-coloured matrix and clasts of various lithologies (sandstones, limestones, chert and quartz pebbles) and sizes, suggesting provenance from different areas. Average clast size and their percentage was determined by the Udden-Wentworth classification with estimation of the matrix content. Clasts and matrix lithological and mineralogical characteristics were determined using petrographic, ore microscopy, and X-ray diffraction analysis. Sandstone clasts in the studied conglomerates are classified as lithic arenites, subarkoses and arkoses. Limestone clasts are mostly wackestones to packstones with foraminifera, ostracods, echinoid and bryozoan fragments that derive from late Carboniferous/early Permian shallow-marine limestones. Calcispheres and incipient growth forms of Microcodium are also present, suggesting different sediment sources and resedimentation processes. Fragments of fusulinid foraminifera were identified in the matrix of the ‘Košna’ conglomerates. Based on the analyses performed, and field observations, the ‘Košna’ conglomerates are described as early Permian (Cisuralian) polymictic clast-supported to matrix-supported conglomerates and breccia-conglomerates that share structural and textural similarities with conglomerates from other areas in the Dinarides, as well as in the Eastern and Southern Alps. The ‘Košna’ conglomerates are younger than the Sakmarian and are comparable with the Trogkofel limestones of the Carnic Alps and the Karavanke Mts. in Slovenia. We suggest that the studied deposits originated from the uplifted Variscan Mountains during the Variscan and Saalian orogenic movements, and were finally deposited from tractive flows and occasional debris flows in a shallow marine environment of the Palaeo-Tethys, possibly in fan deltas.

Gravity flow deposits in Mesozoic sediments of Chukotka microplate (North‐East Russia)

AbstractIn the Mesozoic succession of the Anyui–Chukotka fold system (North‐East Russia), five stratigraphic intervals were recognised that have an abundance of gravity flow deposits. These are the Olenekian (Lower Triassic), Upper Carnian, Upper Norian, Oxfordian–Kimmeridgian and Valanginian. The Triassic gravity flow deposits formed on the south‐facing, passive margin of the Chukotka microplate and consist of greywackes and lithic arenites. Palaeocurrent data indicate that the flows were directed towards the south‐east. The Olenekian gravity flow units consist of clast‐rich sandstone deposited on the continental slope, and clast‐poor sandstone deposited at the base of the slope. Upper Carnian mud‐poor sandstones were deposited at the base of the slope and the Norian thin‐bedded turbidites were upper to mid‐slope deposits. The continental margin was affected by tectonism and was uplifted in the latest Triassic–earliest Jurassic, possibly due to the initiation of the southward translation of the Arctic Alaska–Chukotka microplate. Following an Early–Middle Jurassic uplift of the area, sedimentation resumed in the Late Jurassic and earliest Cretaceous. Several syn‐orogenic depressions (Rauchua, Pegtymel, Pevek, Myrgovaam and Kytepveem) developed on the south‐western margin of the Chukotka microplate, and deposition in these basins included gravity flow deposits at various times. In both the Oxfordian–Kimmeridgian and Valanginian successions, gravity flow deposits included arkosic and subarkosic sandstones with a northern source area of granitoid complexes and deformed Triassic strata. The intervening Tithonian–Berriasian gravity flow deposits consisted mainly of thin‐bedded turbidites. These sediments had a southern source, which included a volcanic arc that had accreted to the southern margin of the Chukotka microplate.

Provenance, diagenesis, and depositional environment of Miocene Kamlial Formation, Azad Jammu and Kashmir, Sub Himalayas, Pakistan: Evidences from field observations and petrography

Petrographical characterization and field observations were caried out to evaluate Kamlial Formation in Bagh district, Azad Jammu and Kashmir. Based on detailed petrography, the lithic arenite consisted of quartz (20–25%), feldspar (7–11%), rock fragments (20–37%), cementing materials (11–21%), and accessory minerals. Grains are mostly angular to subrounded and poorly to moderately sorted. The analysis revealed that the lithic arenite is mineralogically immature; also, the current activity during the time of deposition was low. Polycrystalline quartz indicates that the sandstone was derived from metamorphic source, while monocrystalline quartz indicates a granitic origin. Quartz having an angular shape suggests the source rock was near the depositional site, while quartz having a rounded shape represents long transportation. The presence of feldspar in the lithic arenite suggests the rocks were deposited at high relief or cold temperatures. Primary porosity in sandstone was reduced by calcite cements around the grain, while secondary porosity was developed by fracturing of quartz and feldspar. Tectonic uplift in the study area was demonstrated by fractured quartz and mica in thin sections. Field observations of various sedimentary structures were observed such as load casts, ripple marks, and mud cracks, etc. The presence of conglomerates and load casts in the study area indicates that the Kamlial sandstone was deposited by fluvial and shallow marine environment. Furthermore, the ripple marks indicate that the tidal flat environment controlled the deposition of the sediments.

Classification and Provenance of Lower and Upper Cretaceous Sandstones of the Bornu Basin, Ne Nigeria

Representative sandstone samples from different formations such as the Bima Group (Lower, Middle and Upper Bima Sandstones), Yolde Formation and Dumbulwa Member of the Pindiga Formation in the study area were classified on the basis of their mineralogical compositions for sandstones. Samples 4, 5, 7, 24, 27, 28, 34, 35, 36, 38, 40 and 41a are classified as arkosic arenites due to the high percentage of feldspars and quartz than rock fragments in majority of the samples, whereas samples 12, 21, 25 are classed as lithic arenites because rock fragments have higher mineral aggregate than feldspar. The compositional maturity of the sandstones was identified, the matured is composed of arkosic arenites and the immature ones are related to lithic arenites.

Explainable deep learning for automatic rock classification

As deep learning (DL) gains popularity for its ability to make accurate predictions in various fields, its applications in geosciences are also on the rise. Many studies focus on achieving high accuracy in DL models by selecting models, developing more complex architectures, and tuning hyperparameters. However, the interpretability of these models, or the ability to understand how they make their predictions, is less frequently discussed. To address the challenge of high accuracy but low interpretability of DL models in geosciences, we study rock classification from thin-section photomicrographs of six types of sedimentary rocks, including quartz arenite, feldspathic arenite, lithic arenite, siltstone, oolitic packstone, and dolomite. These rocks’ characteristic framework grains and grain textures are their distinguishing features, such as the rounded or oval ooids in oolitic packstone. We first train regular DL models, such as ResNet-50, on these photomicrographs and achieve an accuracy of over 0.94. However, these models make classifications based on features like cracks, cements, and scale bars, which are irrelevant for distinguishing sedimentary rocks in real-world applications. We then propose an attention-based dual network incorporating both global (overall photomicrograph) and local (distinguishing framework grains) features to address this issue. Our proposed model achieves not only high accuracy (0.99) but also provides interpretable feature extractions. Our study highlights the need to consider interpretability and geological knowledge in developing DL models, in addition to aiming for high accuracy.

Climato-tectonic evolution of siliciclastic sandstones on Puerto Rico: from lithic arenites to quartz-arenitic sands in an oceanic island-arc setting

Abstract Siliciclastic sandstone composition on the island of Puerto Rico, part of the Greater Antilles, was influenced by both tectonic setting and climate. Cretaceous through Eocene volcanic and plutonic rocks on Puerto Rico formed in an oceanic-arc setting. Sandstones deposited during arc volcanism are quartz-poor lithic and feldspatholithic arenites, whose geochemistry largely matches that of the oceanic-arc volcanic and plutonic rocks on Puerto Rico. After cessation of volcanism on Puerto Rico during collision of the Greater Antilles island arc with the Bahamas Bank, an Oligocene through Holocene overlap assemblage was deposited unconformably above the arc deposits in the North Coast and South Coast basins of Puerto Rico. The overlap assemblage consists of some siliciclastic material, but largely shallow-water carbonate deposits. Siliciclastic deposition in the overlap assemblage reflects the volcanic-arc source, plus quartz derived from plutons exposed during uplift. In the Pleistocene and Holocene (and possibly earlier), poorly consolidated quartz-arenitic sands with SiO2 values from 92 to 98% were deposited in the overlap assemblage. On geochemical tectonic-affinity diagrams, the lithic sandstones plot, as expected, in or near the fields for oceanic-arc provenance. However, the quartz-arenitic sands plot incorrectly in the passive-margin field when considering major elements, and correctly in or near the oceanic-arc field when considering trace elements. Trace elements in the quartz-arenitic sands are largely found in refractory minerals, whereas major elements in feldspars and lithic fragments are effectively removed by intense tropical weathering. Hence, future use of tectonic-affinity diagrams should rely on trace-element geochemistry. Sandstones derived from the Sierra Nevada continental arc in California have QFL quartz fractions below 60%, even though the source magmatic arc has significant modal quartz. This observation suggests a “climate cap,” which does not “allow” formation of more quartzose sediments. In contrast, tropical weathering on Puerto Rico removes this climate cap allowing the creation of quartz-arenitic sands from a source rock containing limited quartz. It is remarkable that quartz-arenitic sands occur on Puerto Rico, sourced from a provenance area containing extremely limited quantities of modal quartz (estimated at less than 5%) in an oceanic-arc environment bounded by two active subduction zones. Quartz-arenitic sands and sandstones are not uniquely continental or of cratonal origin; chemical weathering is fundamentally important for the origin of first-cycle quartz-arenitic sands.

Facies analysis, biostratigraphy, and provenance of the late Neogene Seulimeum Formation, Northwest Aceh basin, Sumatra (Indonesia)

A sedimentological, biostratigraphic, and petrographical investigation was conducted on exposed sedimentary rocks in the Seulimeum Formation in the Northwest Aceh Basin, Sumatra. Sedimentary facies analysis suggests a deep-marine depositional environment consists of an inner fan, middle fan, and outer fan to basin plain deposits. New foraminiferal data designated a late Miocene to early Pleistocene age for the studied rock unit, equivalent to N17 to N21 zone, with paleobathymetry in the bathyal environment. Petrographically, the sandstone of the Seulimeum Formation is included as subarkose, sublithic arenite, and lithic arenite, or classified as litho-quartzose, feldspatho-litho-quartzose, and litho-feldspatho-quartzose. Provenance analysis suggests that the origin of the sandstones is from the arc orogen sources. Furthermore, it is concluded that the development of the GSF zone in the late Neogene controls the formation of the deep-marine depositional setting. The west-south-west part of the fault is the footwall part (the Barisan Mountains), as the main high area of sedimentary source material consisting dominantly of the Woyla Group, with some contributions from Bentaro volcanic and Paleogene to early Neogene sediments. Our findings also suggest that the beginning of the Great Sumatran Fault, which corresponds with the uplift of the Barisan Mountains in the northern part of Sumatra, took place in the late Miocene, between 8.6 and 5.9 Ma.

Lithostratigraphy of the Paleogene Deccan Intra-, Intertrappeans of the Saurashtra, Western India and their Prevalence in Large Igneous Provinces

Abstract The periphery of the Deccan Volcanic Province (DVP) of India comprises sedimentary succession deposited during the waning phase of volcanism across the Cretaceous-Paleogene boundary which preserves the continental biota. The Saurashtra Peninsula, a part of the Saurashtra-Kachchh sub-province, exposes thick intertrappean sedimentary successions, systematically described to understand the stratigraphic framework with respect to the lava flows and their geographic distinctness. The thickness of the exposed sections is measured, and contact and continuities are marked, revealing two different, small geographically isolated but adjacent, coeval basins, named the Ninama Basin and Chotila Basin, initially comprising fine grain sediment, followed by thick conspicuous limestone and chert deposits respectively. Formal lithostratigraphic unit names are proposed for both basins: Ninama Basin comprises lithic arenite, fossiliferous limestone, bedded siltstone, mudstone and claystone, and is divided into Sukhbhadar Formation and Ninama Limestone. Chotila Basin comprises calcareous sandstone, bedded siltstone, silty shale and mudstone, claystone and chert divided into Rangpar Formation, Chotila Chert, and Bamanbor Formation. Lithology and palynofossil evidence suggest restricted continental environments with varying salinities during the Paleogene.

Provenance and Paleoclimate Analysis of Sandstone from Meluhu Formation in Kendari, Southeast Sulawesi.

The Meluhu Formation consists of quartz sandstone, red shale, siltstone, and mudstone at the bottom part, and alternating black shale, sandstone, and thin limestone in the upper part. Petrographic components composition can reveal the litho-tectonic setting of a region. The composition of sandstone can be done by determining and counting the proportion of a quartz minerals, feldspar, and rock fragment from thin sections using petrographic analysis. This result can guide to depositional setting and paleoclimates of a region. The Provenance and paleoclimates studies of Meluhu Sandstone are still relatively new. The purpose of this study was to find out the provenance and paleoclimate of sandstone of Meluhu Formation which is exposed in 14 sites along Kendari and adjacent area. The method used to make petrographic observations followed by data processing using the point counting method. The sandstone in this study area was classified into sublitharenite, lithic arenite, arkose, subarkose, and greywacke. The origin of rock was interpreted as located in the recycled orogenic province, interior craton, and undissected arc. The paleoclimate that occurred in the formation of these siliciclastic rocks was arid to humid. Keywords: Meluhu Formation, provenance, paleoclimate, sandstone.

Petrological, petrophysical and petrothermal study of a folded sedimentary succession: the Oliana anticline (Southern Pyrenees), outcrop analogue of a geothermal reservoir

The Oliana anticline (Southern Pyrenees) has been characterized as an outcrop analogue of a geothermal reservoir using field data (stratigraphy and fracturing) and petrological, petrophysical and petrothermal analyses. Five lithofacies were established including conglomerates, hybrid arenites, lithic arenites, carbonates and evaporites. Petrophysical measurements indicate widely dispersed values of bulk density, connected porosity, permeability and velocity of compressional acoustic waves. Connected porosity is the factor that mostly influences bulk density, compressional wave velocity and permeability. In turn, diagenetic processes (such as dissolution and cementation) and fracturing, coupled with petrological features such as mineral composition, matrix content and grain size, are the most critical factors controlling rock porosity along the Oliana anticline. Thermal conductivity measures reveal a compositional control on the thermal properties of rocks. Thermal characterization of the structure reveals a low conductive area that matches the carbonate and evaporite succession of the anticline core and a highly conductive zone associated with the detrital succession of the fold limbs. The Oliana anticline has been classified as a petrothermal system due to the low permeability values of the studied sedimentary succession. Despite such classification, this contribution provides a useful exploration tool for future studies of non-conventional geothermal and CO2 storage sites located in folded sedimentary successions in the proximal domain of foreland basins.

The critical role of recycling of post-Grenvillian, Neoproterozoic sediments for Phanerozoic Laurentian clastic systems: evidence from detrital-zircon and -monazite geochronology and textures

ABSTRACT Lithic and quartz arenites of the Central Appalachian Basin deposited by late Paleozoic Laurentian fluvial systems are widely interpreted to be sourced by recycling of late Precambrian and early Paleozoic clastic sequences in the Appalachian Orogen. U-Pb and (U-Th)/He age distributions for detrital-zircon and Th-Pb age distributions for detrital-monazite, detrital-zircon and monazite textures (including detrital diagenetic monazite, which prove recycling), sandstone petrology, heavy-mineral abundances, and other detrital proxies are all accounted for by the following: 1) lithic arenite is directly sourced from late Neoproterozoic metasediments in the proximal Appalachian fold and thrust belt via transverse drainages, 2) the late Neoproterozoic sediments were recycled from early Neoproterozoic, post-Grenvillian clastic sequences, 3) Cambrian quartz arenites along the Laurentian margin were recycled from Neoproterozoic sequences with local cratonic input, 4) although dominated by sediment of ultimate Grenvillian age, quartz arenites require ∼ 40% of Paleoproterozoic and Archean input, interpreted to be recycled from late Neoproterozoic to Devonian clastic sequences of the northern Appalachians and/or southern (Scottish–Irish) Caledonides in the distal reaches of a longitudinal drainage system. Ordovician to Mississippian clastic sequences and their metamorphosed equivalents in the Appalachian crystalline core were also likely sediment sources. Quartz arenite does not result from mixing of lithic arenite with other sources because of differences in textural and compositional maturity, and in heavy-mineral characteristics. Input from the Laurentian craton, commonly cited as the source for Paleoproterozoic and Archean detrital zircon in the eastern Laurentian clastic systems, is untenable here because of: 1) the presence of Paleozoic monazite derived from Appalachian Neoproterozoic and early Paleozoic metasediments, 2) abundant detrital chromite, and 3) abundant Paleozoic detrital muscovite. Multiple recycling explains all observed sedimentologic and mineralogic characteristics of the two lithic types. Incorporation of published detrital-zircon data for Paleozoic to modern clastic sequences in eastern Laurentia reveals that Grenville-age zircons experienced at least five and potentially ten recycling events since entering the clastic system in the Neoproterozoic. Recycling also explains the abundance of quartz pebbles in conglomerates of the quartz-arenite lithofacies, and the range of detrital-muscovite 40Ar/39Ar ages in quartz arenites of the Appalachian Basin.

Provenance and Origin of the Sand Dunes Sediments in the Na’ama Area / Southeast Tikrit City Northern Iraq

Study of three Barchan sand dunes in Na'ama area southeast Tikrit city have been carried out for (10) samples, the investigation included petrographical, mineralogical and geochemical aspects of the sand dunes from grain size point, the sand grains are commonly sub-rounded to sub-angular forming about (98.8%) with (1.2%) of mud. Petrographically, the sand are sub-litharenite to lithic arenite and mineralogical analysis indicated that most of sand dunes are mainly consist of quartz and carbonate rock fragments in addition to rare feldspar and mica where quartz prevail the mineralogy of all sand dunes due to the selective wind sorting which concentrates more quartz grains, and to the aeolian weathering activity which has depleted the feldspar grains through subaerial collisions. Fine grained mean grain size, very well to moderately sorted, near symmetrical skewness with leptokurtic distribution are characterized the sand dunes in the study area. These statistical parameters show that the sand dunes are extremely controlled by sedimentary sources (Injana Formation sediments). Also, the rarities of organic materials within the sand dunes indicate to the rarity of coverage plant within the seasonably moved sand dunes.
 Several transparent heavy minerals are identified in the sand dunes such as Tourmaline, Hornblende, Olivine, Chlorite, Ankerite and Zircon with well rounded edges due to the transportation, in addition to opaque heavy minerals of iron oxide like Magnetite, Hematite and Chromite concentrated within sand fraction. Atomic absorption analysis distinguished many types of major and trace elements in the sand dunes too. These heavy minerals and trace elements refer to that the sand dunes were derived from ancient igneous and metamorphic rocks which eroded and deposited later within Injana Formation

Revised stratigraphy in the eastern Meguma terrane, Nova Scotia, Canada, and variations in whole-rock chemical and Sm–Nd isotopic compositions of the Goldenville and Halifax groups

As a result of new geological mapping, the Goldenville and Halifax groups in the eastern Meguma terrane have been divided into formations. They have a total stratigraphic thickness of about 7750 m and correspond to only the upper half of the Goldenville Group and lower half of the Halifax Group in the northwestern and southeastern areas of the terrane. The revised stratigraphy combined with compiled and new whole-rock major and trace element and Sm–Nd isotopic analyses enable more detailed documentation of the chemical changes with stratigraphy that were demonstrated in previous studies. Based on chemical compositions, the protolith compositions of the analysed samples range from lithic arenite to wacke to shale. Major and trace element characteristics are consistent with deposition in an active continental margin, basins associated with island arcs, or most likely at a passive continental margin with volcanic rocks in the source area. Chemical compositions show a scattered but overall increasing abundance of lithophile elements such as La and Th with stratigraphic position. Epsilon Nd(t) values become increasingly negative up-section, and depleted mantle model ages become increasingly older. The data are consistent with increased mixing between sediments derived from Mesoproterozoic upper crustal sources and sediments derived from a magmatic arc. These data are consistent with published detrital zircon patterns which show increasing amounts of ca. 2 Ga zircon with decreasing age, and with a source area comprising a Pan-African (800–540 Ma) volcanic arc and/or active margin magmatism and mainly Eburnean crust, most likely in the West African craton.

Diagenesis and reservoir quality of Oligocene Barail Group of Upper Assam Shelf, Assam and Assam Arakan basin, India

The Oligocene Barail deltaic sandstones are the main oil reservoirs in Upper Assam Basin. Nonetheless, the diagenetic alterations and their impact on reservoir quality on Barail sandstones are virtually unknown. The present study aims to know the ways diagenesis plays the role for the invariable hydrocarbon production from these clastic reservoirs within the Barail Group. Samples representing the lower unit of Barail Group known as Barail Main Sand (BMS) and the upper unit known as Barail Coal Shale (BCS) were studied using a combination of petrographic, scanning electron microscopy (SEM), X-ray diffraction (XRD) of clay and wireline log techniques. The average framework composition of BMS is Q49.42F4.18R14.75 while the BCS are composed of Q51.33 F3.89 R14.04. The BMS are moderately hard, fine to medium grained, sub angular to sub rounded, moderately well sorted, dominantly of lithic arenite type and porosity value ranges from 10 to 22.01%. The sandstones of BCS Unit are moderately hard, light grey, fine to very fine grained and usually have low porosity except the channel sands. Both the BMS and BCS have undergone various diagenetic alterations which are observed as mechanical compaction, authigenesis of cements and clays, dissolution and alteration of unstable clastic grains. The identified clay minerals are kaolinite, illite and chlorite. Smectite is occasionally observed as mixed layered smectite-illite clay. The diagenetic alterations along with the clay minerals occupying as pore-filling and lining cements have critically influenced the reservoir quality of both BMS and BCS units of Barail Group. Proper treatment of these clay minerals could aid in the prevention of formation damage to a large extent.

Assessment of Bholari River Sand for its Geotechnical Characterization as Fine Aggregate

Present study is aimed at assessment of Bholari river sand for its geotechnical characterization and suitability as fine aggregate which is being quarried in Jamshoro district, Sindh, Pakistan. For this purpose, sand samples (n=11) were collected from quarry sites and main river channel. Physical properties reveal that Bholari sand is mainly coarse to fine in size (0.2 mm-5 mm). Average values of fineness modulus, specific gravity, bulk density and void content of collected samples are 2.58, 2.56, 1659.90 kg/m3 and 35.12% respectively which varied within the corresponding permissible ranges of ACI (American Concrete Institute). Carbonate content of about 57.59% is also in agreement with corresponding range for fine aggregate. Petrographic examination revealed that Bholari River sand mainly comprises of quartz and rock fragments with subordinate limestone fragments. As per classification of Dott (1964), Bholari sand is lithic arenite where quartz (50%) occurs as main mineral followed by rock fragments (30%), feldspars (15%) and other opaque minerals (5%). Texturally, the sediments are angular (77%) to sub-round (33%). All these physical properties lie within the range set by National Highway Authority (NHA) and American Standard of Testing Material (ASTM). It is concluded that Bholari River sand is suitable for use in concrete mixed with cement and asphalt.

SANDSTONES PETROGRAPHIC STUDY OF WALAT FORMATION CIBADAK AREA, SUKABUMI: THE IMPLICATIONS FOR THE PROVENANT TYPE

The Walat Formation is an Paleogen siliciclastic sedimentary rock formed in the Bogor Basin. Outcrops of this formation are widespread in the Cibadak area such as in Gunung Walat, the Sand Bongkok Complex, Aseupan Sand, and the Cicareuh River. Several studies have been done before on this formation. However, studies on provenance with petrographic methods are still rarely conducted, especially in the research area. This is the basis of this study. The data used in this study consisted of field data and previous research literature. The location of field data collection is located in the south of Gunung Walat, precisely in the Holcim Educational Forest (HEF) using the measured stratigraphic method. A total of 18 sandstone samples were using the petrographic. From one existing track, three facies were identified, namely Sp (planar-cross-bedded sand), Gh (clast supported, horizontally stratified gravel), and Fl (laminated sand, silt, and mud). This facies distribution is based on lithology, grain size, and sedimentary structure. Petrographic data indicate that the sandstones of the Walat Formation are mostly lithic arenite, sublithic arenite, and lithic-graywacke. Comparison of QFL composition shows that all sandstones come from orogenic deposits with Q compositions (78.51% - 97.74%), F (0 - 1%), and L (2.26% - 21.13%) meanwhile, QmFLt comparisons show originating from quartz recycled (three samples), transitional recycled (11 samples), and lithic recycled (four samples).