Succession Of Sandstones Research Articles

Sedimentary Structures and Petrography of Rocks within Akpoha Area of the Afikpo Basin Southeastern Nigeria; Constraints on Provenance

Sedimentary structures and petrographic studies of Akpoha area in Afikpo/Abakiliki basin was undertaken in an attempt to understudy and determining constraints in depositional processes in the area . The major outcrops in the area are alternating succession of sandstones and shales striking in a NE-SW direction primarily as a result of folding due to past orogeny in the area. The sandstone outcrops at Akpoha are highly indurated due to age, compaction and tectonism and occur in ridges within the shale unit. The studied shale outcrops were poorly laminated and low in fossil content.Sedimentary structures identified include;Wavy/ripple lamination, Mud cracks, Parallel lamination and Fissility.The results of the petrographic modal analysis from thin section studies show that the sandstone consists predominantly of quartz (55 - 64%); feldspar (22 - 30%) and rock fragment (1 – 9%). The sandstones were immature, poorly to moderately sorted with angular to sub-angular grain shapes which gives clear indication of high energy of sediment deposition and short transport history from provenance.The abundance of well preserved sedimentary structures is an indication of prolong calmness of tectonic/orogenic activities in the area. The fissility observed in shale outcrops and the high induration of the Akpoha sandstones was as a result of compaction from overburden pressure before uplift and exposure.

Characterization of a marine mudstone confining unit at a proposed CO2 storage hub: Kemper county energy facility, Mississippi, USA

Cretaceous and Tertiary strata across Mississippi, Alabama, and the adjacent continental shelf constitute a widespread succession of sandstone, mudstone, and carbonate that have proven to be important objectives for deployment of geologic CO2 storage technology in saline formations. Analyses of stratigraphy, sedimentology, and reservoir properties indicate that the Cretaceous-age Paluxy Formation, Washita–Fredericksburg interval, and lower Tuscaloosa Group may provide a 1.4 gigatonne storage opportunity at the Kemper County Energy Facility in east-central Mississippi. The marine Tuscaloosa shale is a widespread reservoir seal in the deep subsurface of Mississippi and Alabama, and detailed geologic investigation of the shale includes integrated analysis of geophysical well logs and core that have yielded a multiscale analysis of the confining strata. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), quantitative X-ray diffraction (XRD), and permeability analyses from core were used to interpret microfabric, pore types, mineralogy and fluid properties within mudstone of the east-central Mississippi Embayment. This study has importance for identifying potential migration of fugitive CO2 into or across the shale. Results indicate that mudstone in the marine Tuscaloosa shale is an effective confining unit that is a key component of the storage complex in Kemper County. Water saturation in the marine Tuscaloosa shale units promotes rock ductility and contributes to low permeability, which is on the order of 10–100 nanodarcies (nD) as determined by pressure-decay permeametry. Accordingly, the marine Tuscaloosa shale is interpreted to prevent significant cross-stratal migration of injected CO2 from deeper sandstone reservoirs.

A Pliocene lacustrine system in the Nellis basin, southern Nevada, USA: implications for the Colorado River drainage system

ABSTRACT Lacustrine basins and the sediments in them provide a critical component of regional tectonic development and climate history. Each sub-basin in the landscape records the interplay between active tectonism and shifting climate. Many of the basins in southern Nevada that contain deposits of the Muddy Creek Formation were closed fluvio-lacustrine systems during the latest Miocene and into the Pliocene. They were subsequently integrated into the regional Colorado River system. Lacustrine deposits of the Muddy Creek Formation are exposed along the trace of the Las Vegas Valley shear zone in the Nellis Dunes Recreation Area (NDRA), northeast of Las Vegas, Nevada. The Muddy Creek Formation in NDRA consists of approximately 130 m of mixed carbonates and clastics, and new tephrochronology suggests an early to late Pliocene age (∼ 4.7 to ∼ 2.6 Ma) for the lowermost lacustrine deposits and an unknown, but younger, age for the uppermost spring-fed lacustrine deposit. These sediments were deposited in an arid to semiarid lake (Lake Nellis) and alluvial floodplain system based on the interpretation of lithologies and facies associations. The stratigraphic succession coarsens upward and reflects establishment of a lacustrine carbonate system overlain by a clastic succession of peripheral lake sediments of alluvial and floodplain origin. The peripheral lake deposits consist of spring-fed and fluvial wetland mudflats of brown claystone and siltstone. This brown claystone is capped by a succession of yellow and red sandstones deposited by fluvial and minor eolian processes. The second, and youngest, freshwater limestone, likely disconformably, overlies the yellow and red sandstones, and is thought to be temporally and depositionally distinct from the underlying Muddy Creek deposits. The transition from the lower lacustrine carbonates to clastic fluvial channel and flood-plain deposits indicates desiccation of Lake Nellis and possibly occurs soon after ∼ 2.7 to ∼ 2.6 Ma based on the ages of tuffs occurring in the uppermost limestone and marl beds. This is consistent with an interpreted increase in regional aridity after ∼ 2.8 Ma (Smith et al. 1993). The second limestone deposit at the top of the section represents an even younger spring-fed lacustrine deposit of unknown age. Throughout the lower carbonate section, three tuffs were identified, and geochemically correlated, using a discriminant-function analysis, to the tuff of Napa (≤ 4.70 ± 0.03 Ma), the Putah Tuff (∼ 3.3 Ma), and the lower tuffs of the Badlands (∼ 2.7 to ∼ 2.6 Ma). The timing of deposition of Lake Nellis sediments postdates the integration of the three major lake systems in this region (Lake Grand Wash, Lake Hualapai, and Lake Las Vegas) into the Colorado River drainage (5.6–4.9 Ma), and also postdates the full integration of the river to sea level (4.8–4.63 Ma) (Howard et al. 2015; Crow et al. 2021). Lake Nellis represents an isolated lake basin that was one, and maybe the last, lacustrine system to be fully integrated into the Colorado River drainage in this region.

Depositional Environment and Reservoir Prospect Analysis of Barail Sandstone Exposed in the Northeastern Part of Bangladesh

The study characterized the Oligocene Barail sandstone in the Surma Basin from a reservoir perspective. Data were collected by direct field observations; rock samples were collected from outcrops for detailed sedimentological, petrographic, and geochemical analysis. Collected sedimentary logs are analyzed to delineate the facies associations, sandbody architecture, and depositional environment. A total of ten facies were identified, which were further grouped into three facies associations: FA1: Tidal-influenced multistorey channel-fill deposits, FA2: Fluvial multistorey channel-fill deposits, and FA3: Overbank deposits. Facies analysis suggests that the Barail sandstone was deposited in the tidal-influenced paralic to fluvial depositional settings, and channel body dimensions increase towards the top. A petrographic study shows that these sandstones are mostly litharenite (Q70F4L26) in type, and sediments were derived from quartzose recycled orogens. The average porosity of the sandstones is 16.9%; the pore spaces are of both primary and secondary origin and are mostly interconnected. Porosity distribution in the fluvial multistory channel-fill deposits (FA2)—the upper part of the sandstone succession, is less heterogeneous, while that in the tidal-influenced channel-fill deposits (FA1), occurs in the lower part is more heterogeneous. Both the depositional process and diagenesis influenced the porosity of Barail sandstones. Geochemical analysis suggests that the sandstones are chemically stable and moderately matured. The study demonstrates that the Barail sandstones may be a good petroleum reservoir. The Dhaka University Journal of Earth and Environmental Sciences, Vol. 12(1), 2023, P 69-88

Geochemistry and petrology of the Chandarpur-Raipur sandstones: Implications for the evolution of the Chattisgarh Basin, Central India

Depositional processes and stratigraphic evolution of the Chattisgarh basin exhibit a synergistic relation between sedimentation and tectonics. To interpret the sedimentation history and basin evolution, multiproxy approach including field studies, petrography, geochemical, and multivariate statistical analyses of the sandstones of Chandarpur and Raipur groups is employed. The study provides a detailed analysis of the time-connoted petrography and geochemistry of the sandstone units from each formation of the Chandarpur-Raipur sequence of Chattisgarh basin. The sandstones grade from immature wacke through submature arkose to mature quartzarenite from the bottom up the section. These sandstones are broadly characterized by felsic provenance, arid-humid palaeoclimate, and weak-intense palaeoweathering at the source. The assemblage of wacke-arkose-sublitharenite of the basal Lohardih Formation is characteristics of fan delta environment and represents initiation of rifting and basin formation stage. Subarkoses from the younging up sequence of Lohardih-Chaporadih-Kansapathar formations reflect prograding shelf environment that represents craton interior field of the continental block provenance and passive marginal tectonic setting, indicating gradual stabilization of the basin. Quartzarenites from Kansapathar Formation and stratigraphically younger Devsagar Member of Charmuria Formation also represent broadly similar provenance and tectonic setting indicating stable craton interior provenance in a passive marginal setting. Petrographic and geochemical analyses of some of the Kansapathar-Devsagar sandstones suggesting recycled orogen provenance, however, may be attributed to the orogenic activity and/or role of younger bimodal volcanic rock during rejuvenation of multistage basin opening faults. Rifting stage was followed by subsidence stage as indicated by the presence of black limestone capping the sandstone successions. Initiation of basin formation ∼1400 Ma and sedimentation can be correlated with the late-stage fragmentation of the supercontinent Columbia. The basin probably closed ∼1000 Ma during the assembly of the next supercontinent Rodinia. It is estimated that ∼87% of the 2.2-km-thick sedimentary succession in the eastern Chattisgarh basin, were already deposited within this time frame (∼1405 and ∼1007 Ma). The basin is correlatable with other Mesoproterozoic basins of Peninsular India like Vindhyan, Cuddapah basins, as well as with basins like Xiong’er rift basin of North China Craton, Espinhaco basin of eastern Brazil, that are related to the Columbia-Rodinia Supercontinent cycle.

Submarine-Channel Element Architecture Demonstrates Facies Heterogeneity in Both Strike and Dip Views: Miocene Modelo Formation, Lake Piru, California, USA

Submarine channels deliver vast quantities of sediment into ocean basins and the deposits left by these systems host important archives of paleoenvironmental change and are major targets for hydrocarbon production and carbon sequestration. However, similarities between channel subenvironments often make their identification difficult, particularly because some subenvironments are transitional or quite variable. While large channel complexes can often be resolved on seismic data, only outcrop data yields high-resolution detail of their internal heterogeneity. This study integrates 10 measured sections with drone-based photography to document lateral and vertical changes in depositional architecture in a well exposed outcrop of a submarine-channel element in the Miocene Modelo Formation at Lake Piru, California. The channel-element architecture is well constrained by erosional-surface mapping and lateral and vertical facies changes. The 3-dimensionality of the outcrop provides a unique example to demonstrate this heterogeneity in both strike (i.e., cross-sectional view) and dip orientations (i.e., longitudinal view). This channel element has a predictable vertical facies succession of thin sandstones and mudstones, mass transport deposits and amalgamated sandstones. The element is capped by a siliceous mudstones that provide a unique marker of hemipelagic deposition and the presence of an abandonment surface. The amalgamated sand packages are thickest in axial locations and thin over a distance of 500 m in the dip direction, but thin over 150 m in the strike direction toward two locations along the same margin. This thinning is used to constrain the dimensions and sinuosity of the channel element. We interpret a channel-element width of 550 m, a thickness of 29 m and an aspect ratio of 19:1, which is in agreement with previously published ranges of channel-element dimensions. With the documentation of lateral facies heterogeneity in orientations slightly oblique to both strike and dip, this study provides important data for understanding channelized sediment gravity flow dynamics in submarine channels and aids in evaluating reservoir-model volume and connectivity estimates.

Soft-sediment deformation structures in the Mesoproterozoic Kaimur Sandstone, Vindhyan Supergroup (Central India), and their seismotectonic implications

The unequivocal identification of soft-sediment deformation structures (SSDS) is a significant attribute to constrain the effect of transient geological events in the spatio-temporal evolution of ancient sedimentary basins. This paper reports and discusses, for the first time, the occurrence of several cm- to dm-scale SSDS within sandstone successions of the Mesoproterozoic Kaimur Group (Vindhyan Supergroup), exposed at the Hanumandhara Hill of Chitrakoot-Satna border region, Madhya Pradesh State, India. The SSDS are confined to a deformed interval comprising seven individual sedimentary units of variable composition and texture, which are sandwiched between nearly horizontally undeformed sandstone beds. The SSDS consist of load structures (load casts, flame structures, pseudonodules and ball-and-pillow structures), contorted lamination, convolute lamination, boudins and pinch-and-swell structures, deformed cross-stratification, slump structures, clastic injections, fluid escape structures, and syn-sedimentary fractures/faults. The present study suggests that the formation of these SSDS is essentially related to a combination of processes (gravitational instability, liquefaction, fluidization, and fluid escape) predominantly induced by seismic shocks. In addition, the restricted occurrence of fractures/faults in these deformed layers emphasizes the passage of seismically-induced Rayleigh waves. Considering the observed types of SSDS, their lateral homogeneity and geographic distribution along with the geodynamic framework of the Vindhyan Basin, the whole area can be tentatively attributed to having experienced moderate- to high-magnitude (M ≥ 5) seismicity. The present study combined with earlier reports of seismically-induced SSDS, from other regionally disposed formations belonging to the Lower (e.g., Kajrahat Limestone, Chopan Porcellanite, Koldaha Shale, Rohtas Limestone, and Glauconitic Sandstone of the Semri Group) and Upper (e.g., Bhander Limestone of the Bhander Group) Vindhyan Supergroup, respectively, provides evidence for the constant regional-scale seismo–tectonic activity within the Paleo-Mesoproterozoic Vindhyan Basin. Importantly, this observation further suggests that the intracratonic basins can be active tectonically contrary to the earlier propositions.

Orogens and detritus: unravelling the Mesoproterozoic tectonic geography of northern Australia through coupled detrital thermo- and geo-chronometers

This study presents detrital muscovite 40Ar/39Ar data from the Mesoproterozoic Roper Group and overlying informally named successions, in the Beetaloo Sub-basin, northern Australia. Detrital muscovite chronology reveals tectono-thermal processes within source regions and provides new constraints on the basin provenance, revising previous interpretations based on detrital zircon data. Detrital thermo- and geochronology, together demonstrate three main periods when the basin paleogeography was altered that correspond to the evolving tectonic history of the North Australia Craton (NAC) through the Mesoproterozoic. The first is characterised by an increased sediment contribution from source regions that lay along the eastern margin of Proterozoic Australia. These source regions are interpreted to have formed the uplifted rift-shoulders between Proterozoic Australia and Laurentia at ca 1.45 Ga. After that, sediments derived from eastern Proterozoic Australia sources become less voluminous up-section. The youngest analysed formation from the Roper Group, the Kyalla Formation, was predominately from sources to the south of the basin, representing another modification of basin geography. This is interpreted to result from the closure/subduction of the Mirning Ocean as the West Australian Craton (WAC) approached and collided with the NAC, resulting in an uplift of the southern margin of the NAC, at ca 1.35–1.31 Ga. The uppermost Mesoproterozoic to lower Neoproterozoic sandstone successions that overlie the Roper Group were derived from the Musgrave Province. Coupled detrital zircon and muscovite data imply a rapid cooling at ca 1.20–1.15 Ga that is interpreted to reflect syn-orogenic exhumation during the Musgrave Orogeny. Furthermore, data from the Beetaloo Sub-basin suggest that the changed basin tectonic settings reshaped basin geography and result in distinctive detrital zircon and muscovite geochronology records. In this study, we used the detrital U–Pb zircon and muscovite 40Ar/39Ar age data from the Beetaloo Sub-basin and a range of other basins deposited in different tectonic environments, including the convergent, collisional and extensional settings, to reconstruct the basin tectonic geography and illustrate various tectonic controls on basin formation in different tectonic backgrounds. KEY POINTS Detrital muscovite 40Ar/39Ar data provide thermochronological constraints on basin provenance, complementing previous interpretations based on detrital zircon data. Spatial and temporal variation of provenance reconstructs the basin tectonic geography, reflecting the Mesoproterozoic tectonic history of the North Australia Craton. Coupled thermo- and geochronology constrain tectonic settings of basin deposition.

Petrographic and Lithofacies of Injana Formation Berman Inticline Northern Iraq

This study is including Petrographic and Lithofacies investigation of Injana Formation North Iraq. The Formation composed of succession of sandstone, siltstone and claystone cycles. The grain size analysis and indicated that the sandstone composed of medium to coarse grains, minor percent silt and clay. The petrographic indicated that the quartz with percent monocrystalline (11-30%) and polycrystalline (4-10%) type , while the feldspar forming mostly of Plagioclace feldspar (2-7.88%) and K-feldspar (5.20-11%). The rocks and fragments mostly of carbonate with percent (15.20- 22.20%) derived from outcrop rocks especially from Fatha and Pilaspi Formation in the area. The recognized clay mineral are; Montmorellonite, palygorskite, kaolinite and chlorite

Paleoenvironmental, paleoclimatic, and organic matter assessment of the hybrid Kharita Formation (Albian) in the Abu Gharadig Basin, Egypt: Integration between palynology, organic petrography, and organic geochemistry

The Early Cretaceous (Albian) was a time of equatorial to polar temperature warming and increased environmental perturbations of the global carbon cycle and oceanic anoxia, which resulted in the widespread accumulation of organic carbon-rich sediments. During the Albian, the southern margin of the Tethys Ocean was characterized by marginal to shallow water conditions with minor phases of enhanced stratification and bottom water anoxia in northern Egypt. At this time, accumulation of the thick siliciclastic succession of sandstones versus shale intercalations of the Kharita Formation took place in the Abu Gharadig Basin. The Kharita Formation is investigated for palynological composition and palynofacies analysis, organic matter characterization, hydrocarbon generation potential, and thermal maturity assessment based on 30 and 26 drill cuttings samples from the BED2-3 and BED2-1x wells, respectively. A rich palynological assemblage of herbaceous hygrophilous plants, including pteridophyte spores and water ferns, along with Elaterates and Afropollis pollen indicated warm humid climate conditions. Furthermore, abundant occurrences of Araucariaceae and Cheirolepidiaceae, including Araucariacites, Inaperturopollenites, and Classopollis, reinforcing warm climatic conditions and their climax in areas near coastal vegetation. Statistical cluster analysis identified two palynofacies assemblages (PFA) based on stratigraphic variation in the particulate organic matter (POM). The PFA-1 characterized all samples of the BED2-3 and some intervals of the BED2-1x wells and comprised moderate abundances of phytoclasts and amorphous organic matter (AOM) that defined a kerogen Type II, whereas the PFA-2 was recorded only in the BED2-1x well and is dominated by phytoclast fragments of kerogen Type III. The geochemical screening revealed, based on the low average values of TOC (1.2 wt%), S2 (1.8 mg HC/g rock), and HI (146 mg HC/g TOC), that the Kharita Formation is characterized by a kerogen Type III of gas-prone hydrocarbon but with low generation potential. Tmax and vitrinite reflectance measurements along with greenish-to golden-yellow liptinite macerals indicated that the thermal maturity of preserved organic matter is still in the immature to the early mature stage of the oil window. Inconsistency in kerogen types between PFA-1 and geochemical deductions was interpreted in terms of microscopic investigations of the recovered AOM. Morphologic characteristics observed that most AOM particles were of terrigenous origin due to the impact of biodegradation and transformation of phytoclast particles into AOM, confirming a kerogen Type III of gas-prone hydrocarbons instead of Type II that was elucidated by palynofacies ternary diagrams. The occurrence of coaly matter in the BED2-1x infers closer proximity to fluvio-deltaic sources during deposition of the lower part of the Kharita Formation than in the BED2-3.

Dinosaur tracks from the Sítio Pereiros ichnosite, Triunfo Basin (Lower Cretaceous) and the dinosaur diversity in the Rio do Peixe basins, Northeastern Brazil

The dinosaur tracks in the Rio do Peixe basins (Lower Cretaceous, Rio da Serra-Aratu stages) occur in at least 39 individual tracksites through approximately 98 stratigraphic levels in the western part of the State of Paraíba, Brazil. The Triunfo basin (one of the four Rio do Peixe basins) is a 480 km2 asymmetric graben, located in the counties of São João do Rio do Peixe, Uiraúna, Poço, Brejo das Freiras, Triunfo, and Santa Helena, controlled by a NE transcurrent fault system. To date, only four isolated footprints and two incomplete trackways have been identified in the Antenor Navarro Formation. Among the isolated footprints, three probably belong to theropods. One incomplete trackway consists of just two digitigrade, rounded digits, suggesting they were made by a small ornithopod. In this study we describe a new ichnosite, located at Sítio Pereiros, São João do Rio do Peixe county, Paraíba State. The one and a half meter thick succession of fine-grained sandstones, siltstones, mudstones and shales with ripple marks, climbing ripples and mud cracks of the Sousa Formation reveals a bedding plane with three trackways, with a total of 19 tridactyl, mesaxonic footprints. These trackways are interpreted as produced by theropods, two large and one smaller. In these beds there are also ostracods, spinicaudatans (conchostracans), and fragments of microvertebrates (fish scales, teeth and bones). The Sítio Pereiros ichnosite represents a deposition in a floodplain area, with temporary aerial exposure of the superficial sediments in which tracks were impressed. The ichnofauna from this locality increases knowledge of the theropod fauna from the Triunfo basin and the distribution of the dinosaur tracks throughout the interior basins of Northeastern Brazil.Description of these new theropod tracks permits evaluation of the behavior of these three theropods, including inferences about trackmaker speed and the type of gait of the three animals, and also of their possible size. This is the 40th ichnosite in the Rio do Peixe basins, extending analysis of the types of trackmaker associations present at such ichnosites, as well as the dinosaur diversity represented at each of them. New interpretations are presented about the environments, and the relationship between the various groups represented in this region during the Early Cretaceous.

New microbiostratigraphic data (calpionellids and calcispheres) from the tithonian of central Chile, type section (Río Tinguiririca) of the baños del Flaco Formation

This work presents new biostratigraphic data based on calpionellids and calcareous dinoflagellate cysts for the Tithonian in Central Chile. This stratigraphic interval is mostly represented by a thick marine succession of limestone and sandstone known as Baños del Flaco Formation. This formation originated in the shallow-water setting of a carbonate ramp and correlates with other well-studied units in the Neuquén basin of Argentina. Calpionellids and calcareous dinogflagellate cysts are studied on the Chilean side of the Andes for the first time. The recognition of several calpionellids and calcareous dinogflagellate cyst species within the lower Baños del Flaco Formation allowed the identification of a preliminary microbiostratigraphic zonation. Calcareous dinoflagellate cysts include eleven species that defines the Colomisphaera tenuis, and Colomisphaera fortis zones, whereas six chitinoidellid species allowed the identification of the Chitinoidella and Crassicollaria zones, with the Slovenica, Boneti and Remanei subzones. These new microbiostratigraphic data suggest a latest early to earliest late Tithonian age for the studied interval.

Stratigraphic palynology and micropaleontological study of the Cretaceous-Paleogene succession of the Nani-1 well of the Anambra and Niger Delta basins: Implications for hydrocarbon exploration

Integrated palynological and micropaleontological analyses were carried out on the Nani-1 well drilled into the Anambra and Niger Delta basins of Nigeria. The study is aimed at reconstructing biozones and paleoenvironments of deposition, as well as deducing the sequence stratigraphic framework of the Cretaceous-Paleogene successions of an area containing key elements for hydrocarbon exploration. Encountered lithofacies succession of sandstone, siltstone, dark-grey to black shale, and coal beds comprises six lithostratigraphic units, namely the Nkporo Group (Campanian-Maastrichtian), Mamu Formation (Middle Maastrichtian), Ajali Formation (Middle-Late Maastrichtian), Nsukka Formation (Late Maastrichtian), Imo Formation (Danian-Thanetian) and Ameki Group (Eocene). Fourteen dinoflagellate zones (A-N) and seven pollen and spore subzones (A1-G1) are recognized based on the first occurrence of two or more species. Two major stratigraphic events are documented: (1) dinoflagellate cyst (dinocyst) zone G at 880 m depth marked by first appearance of Danea aff. californica and Danea cf. mutabilis in association with Cordosphaeridium fibrospinosum, and the last occurrence of Danea aff. californica and Phelodinium magnificum place the Cretaceous-Paleogene (K/Pg) boundary in the lowermost part of the Imo Formation; and (2) a hiatus characterized by a starved section observed at 380 m directly overlain by the Early Eocene assemblages of the Ameki Group indicates a sequence boundary at Imo/Ameki Boundary. Thus, a chronostratigraphic chart is developed for parts of the Anambra Basin and the Niger Delta. Six depositional environments which include marginal to shallow marine, marshy lagoon to estuarine, shallow neritic and tidally influenced fluvial channel are identified, and palynostratigraphic evidences indicate that fresh water palynomorphs are present in the Lower Maastrichtian strata. Four sequence boundaries and four maximum flooding surfaces are also identified within the Maastrichtian–Early Eocene sediments. The paleoenvironmental reconstruction shows that possible hydrocarbon reservoirs in the basin are the marine sandstone facies of the Nkporo Group and Mamu Formation. Their shale members constitute potential source rocks, while the overlying shale units of the Nsukka and Imo formations may provide regional seals for hydrocarbon habitation.

Mudstone Baffles and Barriers in Lower Cretaceous Strata at a Proposed CO2 Storage Hub in Kemper County, Mississippi, United States

The Cretaceous and Tertiary deposits in Mississippi, Alabama, and the adjacent continental shelf constitute a widespread succession of sandstone, mudstone, and carbonate that has proven to be an important target for geologic CO2storage in the onshore Gulf of Mexico basin. Integrated analysis of stratigraphy, sedimentology, and reservoir properties based on cores and geophysical well logs indicates that the Paluxy Formation and Washita- Fredericksburg interval present gigatonne-class storage opportunities. The distribution, geometry, and composition of the area is a direct reflection of the original depositional environments, and understanding these factors is essential for understanding the geologic storage potential of the Paluxy Formation and Washita-Fredericksburg interval at the Kemper County energy facility in Mississippi. Geologic characterization of the Mississippi Embayment at the energy facility focused primarily on characterizing the confinement potential of the storage complex. Integration of core analyses and geophysical well logs has yielded a high-resolution stratigraphic analysis of storage reservoirs, baffles, barriers, and seals. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), and quantitative X-ray diffraction (XRD) was used to characterize microfabric, pore types, and mineralogy within mudstone of the east-central Mississippi Embayment at the Kemper County energy facility. Mudstone beds in the Paluxy Formation and Washita-Fredericksburg interval have variable thickness and continuity. High water saturation in the Cretaceous mudstone units influences swelling smectite clay and mudrock permeability based on pulse decay analysis is 1–96 nD. These low permeability values indicate that the mudstone units are effective baffles, barriers, and confining intervals that make significant migration of injected CO2out of the storage complex unlikely. The numerous baffles and barriers within the target reservoir intervals, moreover, favor the retention of multiple CO2in plumes within the abundant stacked sandstone bodies.

Subduction-controlled temporal and spatial variations in early Palaeozoic sedimentary and volcanic record of the Mongol-Altai Domain

The early Palaeozoic volcano–sedimentary evolution of the Khovd and Gobi-Altai zones of the Mongol–Altai Domain was investigated by quantitative petrographic analysis of sediments, whole-rock geochemistry of volcanic rocks, and U–Pb zircon dating. Three evolutionary stages were identified in the Khovd Zone: (1) Cambrian–mid Ordovician basaltic (Nb/Yb = 0.09–1.25) and rhyodacitic (Nb/Yb = 4.36) volcanism and sedimentation of immature greywackes in the fore-arc basin in front of the juvenile continental arc, (2) late Ordovician flysch-type sedimentation accompanied by a volcanic gap coincided with Barrovian metamorphism in footwall sequences reflecting a compressional stage, and (3) Silurian–Devonian within-plate bimodal volcanism (with a strong asthenospheric imprint; Nb/Yb = 4.45–20.34) followed by mature siliciclastic deposition interpreted as transformation of the former fore-arc region into a back-arc domain associated with HT metamorphism. In the Gobi-Altai Zone the three stages were: (1) Cambro–Ordovician marginal greywacke–sandstone succession adjacent to a mature continental arc (mafic rocks Nb/Yb = 0.71–4.36), (2) Silurian siliciclastic sedimentation associated with migration of the volcanic gap and Barrovian metamorphism, and (3) Lower Devonian deep-marine sedimentation followed by shallow-marine carbonate sedimentation, initially accompanied by calc-alkaline basalts (Nb/Yb = 0.74–4.57) and andesites to rhyolites (Nb/Yb = 0.69–4.87), evolving in the mid–late Devonian to within-plate alkali basalts (Nb/Yb = 11.05) thus reflecting back-arc basin development. These temporal and spatial variations in the Mongol-Altai Domain are interpreted as a diachronous sequence of retreating and advancing subduction modes instead of juxtaposition of suspect terranes as proposed in previous studies.

Channel, dune and sand sheet architectures of a strait-adjacent delta, Rifian Corridor, Morocco

Abstract Sea straits are elongated zones where geographical constriction can amplify marine currents. Sediment deposits that formed in sea straits are relatively well studied and robust models of tidal strait depositional systems have been developed. However, models of strait-adjacent systems remain uncommon. In this study, we present such a model which is based on detailed outcrop descriptions of Miocene deposits that formed adjacent to the Rifian Corridor, an ancient sea strait that existed in what is now northern Morocco. The kilometre-scale outcrops at the Ben Allou locality (30 km north of Fez, Morocco) contain a succession of claystones, siltstones and sandstones that formed under a sea strait-adjacent process regime characterized by marine current constriction, tidal amplification and reduced wave activity. Detailed descriptions of the sandstone's sedimentary architectures reflect a development from mud drape-bearing sand sheets in the proximal regions of the system to stacked cross-strata and channel forms nearer to the basin depocentre. In the deep, distal reaches of this system, sediment grain sizes are generally fine (silt and clay) and are sparsely interbedded with sandy turbidites. These results confirm existing models which show that proximal strait-adjacent deposits tend to be tide dominated, and wave and fluvial influence can be overprinted by tidal processes. Some insights into the formation of tidal dunes are discussed. For example, it is shown that compound tidal dunes may not be preserved differently than simple tidal dunes, which is relevant for predicting sedimentary architectures and fluid flow properties of ancient tide-dominated successions.

Palynology of the Freshwater East Formation (Upper Silurian, Pridoli), Pembrokeshire, South Wales, UK

Upper Silurian (Pridoli) cryptospores and trilete spores are described from the type section of the Freshwater East Formation in Pembrokeshire, South Wales. This formation is the oldest stratigraphical division of the Lower Old Red Sandstone succession south of the Ritec Fault in the Anglo-Welsh Basin. It represents an incised valley fill sequence composed predominately of red dryland alluvial sediments inter-bedded with four tidally-influenced green-grey heterothithic units. The sequence is well known for the occurrence of an early land plant Cooksonia flora. The spore assemblages are dominated by cryptospores (67%), particularly laevigate monads and dyads. Trilete spores are less abundant but are diverse in composition and provide the principal means of accurately dating the sequence. Eleven cryptospore taxa and thirty one trilete taxa are identified. Two new species Cymbohilates richardsonii and Velamisporites edwardsae are erected. The Freshwater East microflora contains a distinctive complex of Chelinospora taxa, here named the Chelinospora lavidensis assemblage. It represents a previously unrecognised assemblage within the Pridoli succession of the Anglo Welsh Basin. An accurate age for this assemblage has been determined by correlation with the Upper Silurian succession of the Cantabrian Mountains in northwest Spain, where a continuous spore succession through the Pridoli Series has independent biostratigraphical age control from chitinozoans. The Freshwater East assemblages are correlated with the upper part of the Chelinospora hemiesferica (H) Biozone, which is dated by the chitinozoans Margachitina elegans and Pseudoclathrochitina carmenchui as early mid Pridoli in age. Rare occurrences of small spiny acritarchs, sphaeromorph acritarchs and prasinophyte phycomata in two of the Freshwater East assemblages support the sedimentological data that the grey-green heterolithic beds were deposited in tidally-influenced fluvial and estuarine environments.

TO EXPLAIN THE NATURE OF CORE POROSITY USING RESULTS OF PETROGRAPHY ANALYSIS

The Permian to Triassic Tirrawarra Sandstone succession in the Cooper Basin of CentralAustralia is characterized by its low permeability. Ambient core porosity averages8.96% and ambient permeability 0.9 mD. Most samples studied have permeabilities lessthan 3mD. Despite its overall poor reservoir characteristics, the Tirrawarra Sandstone isone of the major oil and gas targets in Australia. A total of 17 core plugs from 6 wellswere studied petrographically using optical petrography, SEM and XRD. These resultswere integrated with core analysis data.Petrographic study revealed the diagenetic events, mainly mechanical and chemicalcompaction, cementation and alteration have modified the reservoir quality. Ductile componentssuch as rock fragments, clay and matrix influence mechanical compaction, whichare the main cause of reservoir quality reduction. Quartz cementation and clay distributionalso affected the porosity, but particularly permeability. Mechanical compaction aswell as quartz cementation have reduced and blocked pore-throats to isolate intergranularpores. The alteration of feldspar to kaolin has changed intergranular porosity tomicroporosity. Illite occurs as either cement, alteration of rock fragments or kaolinite. Allof these diagenetic events also affect fluid movement in the reservoir.This paper presents the evaluation of the determination of effectiveness of porosity inthe delivery of gas from sandstone reservoir in the Cooper Basin using integrated petrographyanalysis and core measurements.

PETROLOGY AND GEOCHEMISTRY OF THE LATE CRETACEOUS PAB FORMATION, WESTERN SULAIMAN FOLD- THRUST- BELT, PAKISTAN: IMPLICATIONS FOR PROVENANCE AND PALEO-WEATHERING

Late Cretaceous sandstone succession of the Pab Formation in western Sulaiman Fold Thrust belt Pakistan was investigated for petrology and bulk rock chemistry to determine its source terrain, paleo-weathering and tectonic setting. The formation is mainly comprised of sandstone with reddish to maroon color shale and arenaceous limestone. Texturally, the sandstone is fine to coarse grained, sub-angular to well-rounded and moderately to well sorted. The sandstone is petrologically and geochemically classified as quartz arenite to sub lithic arenite. The detritus was mainly derived from plutonic acidic source. QtFL and QmFLt suggests that recycled orogeny and Craton Interior setting were major sources of sediments. Geochemical models support that the detritus was derived from quartzose sedimentary source terrain, suggest deposition in a passive continental margin setting. Average values of chemical indices are CIA 59% CIW 67% and CIV 12.70%, which suggest moderate to high degree of chemical weathering in source area, that may reflect humid climate condition in the source area. The petrographic study and geochemical models demonstrate that the Pab Formation is mostly composed of mature sandstone from acidic plutonic and low-grade metamorphic rocks terrain in recycled and Craton Interior setting deposited on western passive margin of Indian plate in Tethys Ocean.

Assessing Thermal Maturity through a Multi-Proxy Approach: A Case Study from the Permian Faraghan Formation (Zagros Basin, Southwest Iran)

This study focuses on the thermal maturity of Permian deposits from the Zagros Basin, Southwest Iran, employing both optical methods (Thermal Alteration Index, Palynomorph Darkness Index, Vitrinite Reflectance, UV Fluorescence) and geochemical analyses of organic matter (Rock Eval Pyrolysis and MicroRaman spectroscopy) applied to the Faraghan Formation along two investigated Darreh Yas and Kuh e Faraghan surface sections. Furthermore, an integrated palynofacies and lithofacies analysis was carried out in order to integrate the few studies on the depositional environment. The Faraghan Formation, which is widely distributed in the Zagros area, generally consists of shale intercalated with sandstones and pebble conglomerates in the lower part, followed by a succession of sandstone, siltstone and shaly intercalations and with carbonate levels at the top. The integrated palynofacies and lithofacies data confirm a coastal depositional setting evolving upwards to a shallow marine carbonate environment upwards. Rock Eval Pyrolysis and Vitrinite Reflectance analysis showed that the organic matter from samples of the Darreh Yas and Kuh e Faraghan sections fall in the mature to postmature range with respect to the oil to gas generation window, restricting the thermal maturity range proposed by previous authors. Similar results were obtained with MicroRaman spectroscopy and optical analysis such as Thermal Alteration Index and UV Fluorescence. Palynomorph Darkness Index values were compared with Rock Eval Pyrolysis and vitrinite reflectance values and discussed for the first time in the late stage of oil generation.