Calcareous Siltstone Research Articles

Sandstones and red beds in the Lower Cretaceous Sidi Aich Formation, Chotts Basin (Southern Tunisia): facies, architecture and depositional environments

Abstract The Lower Cretaceous deposits of North Africa represent a terrestrial to shallow-marine sandstone-dominated succession often referred to as the ‘Continental Intercalaire’ and Nubian Sandstone informal groups. The upper Barremian Sidi Aich Formation of the Continental Intercalaire is distinguished throughout the Chotts basin of southern Tunisia by sandstone-dominated sequences within conglomerate, calcareous siltstone and palaeosol red bed occurrences. This paper aims to highlight: (1) the facies distribution, internal architecture and depositional environment of the sandbodies; and (2) the origin, spatial distribution and architecture of the red beds that underlined and topped sandbodies. Strata in the Zimlet El Beida anticlinal structure, Chotts basin, offer a good opportunity for detailed field observations and bed-by-bed logging of three representative lithostratigraphic sections. Detailed sedimentological investigation allows the recognition of several lithofacies grouped into three facies associations indicating tidal flat, tidal channel and tidal bar depositional settings characterizing a transgressive tide-dominated estuarine system that developed during an episode of relative sea-level fluctuations in the Early Cretaceous. The high-resolution petrographic, mineralogical and geochemical analyses of the red beds allow the differentiation of three distinct lithofacies sets including: (1) intraformational conglomerates; (2) calcareous siltstones; and (3) palaeosol. Major red beds comprise detrital grains inherited from the host or parent sediment and authigenic minerals (dolomite, calcite and hematite) precipitated during the diagenetic processes. Grain components have been partially or completely cemented and/or replaced by terrestrial phreatic dolomite. The negative δ 13 C and δ 18 O signatures of the dolomite analyses indicate that the dolomitization processes have been influenced by fluctuations of the groundwater table or climate change from semi-arid to semi-humid conditions. This study, therefore, may provide useful data for the better understanding of the internal architecture of the red beds associated with sandbodies that represent the main and significant potential reservoir within the Lower Cretaceous Continental Intercalaire sandstone-dominated groundwater aquifers of the Chotts basin.

Earth-fill Dam Seepage Safety Risk Assessment: Randugunting Dam, Blora

Earth-fill dam, the most common dam, is constructed primarily using compacted earth materials from surrounding areas. Despite its simplicity, these dams have higher chances of failures caused by seepage or sliding. Randugunting Dam is an earth-fill dam located in the northern part of Blora, Central Java. This dam was built to accommodate irrigation and domestic needs in Blora, Pati, and Rembang Regencies. This study is conducted to monitor and assess the present Randugunting Dam’s seepage condition using Finite Element Analysis (FEA) and calculate the seepage safety factor. Geological and engineering geological mapping are combined by coring data to understand the rock and soil characteristics of the main dam location. The seepage rate analysis is conducted using Finite Element Analysis on GeoStudio 2021 SEEP/W. The results showed that Randugunting’s main dam and reservoir area primarily comprises calcareous siltstone, carbonaceous sandstone, claystone, and limestone. Weathering rates in this area range from slightly weathered to highly weathered. The seepage rate from FEA ranges from 4.39 - 5.31 litre/s and calculation of safety factor along the Randugunting Main Dam is 4.49. Those values are considered to be safe. Installing blanket type of horizontal drain and seepage berm can act as prevention step in the future.

Kasimovian (late Pennsylvanian) cornute rugose corals from Egypt: taxonomy, facies and palaeogeography of a cool-water fauna from northern Gondwana

A strongly endemic Upper Pennsylvanian (Kasimovian) rugose coral association consisting of small, mostly non-dissepimented, simple structured and poorly diversified species is studied from the lower member of the Aheimer Formation (Western side of the Gulf of Suez, Egypt). The unit is composed of grey, silty mudstone intercalated with thin, ferruginous, silty dolostone–limestone and calcareous siltstone beds. Ten taxa from four families were identified. Four species of the Antiphyllinae are new; Actinophrentiscrassithecata n. sp., Lytvolasmaaheimerensis n. sp., L.paraaucta n. sp. and Monophyllumgalalaensis n. sp. Besides, Rotiphyllumexile de Groot, 1963 and Bothrophyllumokense Kossovaya, 2001 were identified; four taxa remain in open nomenclature (Lytvolasma cf. canadense, Zaphrentites cf. parallela, Zaphrentites sp. and Ufimia sp.). Rejuvenation, encrustation and bioerosion phenomena are rare. Attachment structures during mature stages are not evident; attachment scars in the apical parts are also rare. Growth patterns and embedding in the muddy deposits indicates that the corals lived as mudstickers in soft substrate. Recrystallization, dolomitization and ferrugination of open pore spaces inside the corals are the most common diagenetic features. The corals from the lower Aheimer Formation represent a typical cyathaxonid fauna that was adapted to high clastic input and turbid waters in a restricted, sheltered, episodically storm-swept inner ramp environment in an embayment of the southern shelf of the Palaeotethys. A time-averaged ramp model shows a regressive development from a mixed carbonate–siliciclastic open inner ramp setting during the Moscovian to the restricted inner ramp of the lower Aheimer Formation (Kasimovian) and following peritidal to fluvial environments of the Gzhelian. General and local palaeoclimatic considerations indicate cooling. Besides relations to northern Spain that root Egypt in the western Palaeotethys, connections existed via the Donets Basin (and the southern Urals) to the Cordilleran–Arctic–Uralian realm which is a cool water province during the Lower and Middle Permian. The Egyptian fauna appears to be a precursor of the anti-tropical cyathaxonid fauna of the latter time slice and also of the Lower Permian cool-water faunas of the east Cimmerian peri-Gondwana terranes.

Maastrichtian – Paleocene environmental and climatic conditions in Koum Basin (northern benue trough, Cameroon) inferred using a multiproxy approach including sedimentology, mineralogy, and geochemistry

The Koum Basin is one of major intracontinental basins in northern Cameroon. It is part of the Upper Benue Trough and has genetic ties to the West and Central African Rift System. The main purpose of studying the Koum Basin sedimentary deposits was to re-examine the time of the deposition and constrain the palaeoenvironmental and paleoclimatic conditions during deposition. To accomplish this, we used a combination of sedimentologic, palynologic, mineralogic, and geochemical data. Claystone units interbedded with calcareous siltstones dominate sedimentary sequence, including few clay beds, fine to medium-grained sandstone, and rare marl layers. The palynomorph assemblage suggests a previously unknown Maastrichtian – Paleocene age in this basin. The sediments originated from intermediate igneous parent rocks with a relative contribution of felsic rocks. These rocks underwent low detritism (Si/Al: 2.51–4.43; K/Al: 0.11–0.36; Ti/Al: 0.05–0.10) and chemical weathering (CIA: 55–64; PIA: 56–68) in the source region. Consequently, deposits are immature (ICV values > 1) and weakly recycled (Si2O3/Al2O3 ratios ≤5). The organic matter analysis and the palynoflora assemblage, reveal Type III kerogen with significant contributions of Type II-III and type II kerogens, as well as a continental paleo-depositional environment with open rainforest to savannah vegetation. The clay minerals distribution suggests moderate illitization and chloritization processes and thus moderate burial diagenesis at temperatures ranging from 70 to 90 °C, also attested by immature to mature Tmax values (≤436 °C) marginally. The low CIA values and very low kaolinite contents, indicate dry climatic conditions. In addition, two major-element-based discrimination diagrams show that the parent rocks of clastic sediments formed primarily in a continental arc system, with a moderate contribution from the rift system and a low contribution from the oceanic island arc, implying compressional conditions, which is consistent with previous studies on the tectonic background of the region during the late Maastrichtian to Paleocene period.

Diversity of dinosaur tracks and swim traces in a new site in the Upper Cretaceous El Molino Formation, Torotoro National Park, Bolivia

In January 2021, a new site containing dinosaur trackways was uncovered at kilometer 99 during the Anzaldo to Torotoro highway construction. The trackways were found on two beds of ooid and ostracod-bearing quartz arenites of about 160 m2, each separated by roughly 2 m of calcareous siltstone. In the lower layer, five theropod and five sauropod trackways were identified, three trackways of uncertain identity, and three trackways of didactyl tracks. Due to time constraints, only the upper layer containing a rich assemblage of theropod tracks and traces was thoroughly studied before road construction removed the bed. The upper bed contained 493 tracks in 88 trackways. Of those trackways, 21 consisted of a single, isolated track. In addition to tracks, 73 swim traces from 14 trackways were characterized. We distinguished five track morphotypes based on the morphology of the digits and pedal impression. Swim traces occurred in three distinct morphotypes. Invertebrate burrowing and sediment collapse, after the kick-off phase of track formation, partially modified most tracks. Before substrate stabilization, the water level rose, and dinosaurs swam in the area, leaving characteristic swim trackways with their feet scratching the bottom. This report records abundant theropod tracks and swim traces in a fortuitous exposure that is no longer accessible and comments on behavioral and paleoenvironmental implications. This location adds to the significance of the dinosaur track record of the Parque Nacional Torotoro (Torotoro National Park), Bolivia.

Palynology of Permian red-bed successions of Colorado and Wyoming and its influence on Laramide strata

ABSTRACTThe first reported Permian (Kungurian to Roadian) palynomorphs are described from Colorado, recovered from bedded gypsum and rare organic-rich shale intercalated in the red siltstone-dominated Lykins and State Bridge Formations. Surprisingly, these units generally lack the taeniate, saccate pollen that typifies most Permian continental rocks elsewhere, yet they contain abundant terrestrially derived palynomacerals, a low-diversity suite of sphaeromorph and acanthomorph acritarchs, and extremely rare non-taeniate, bissacate pollen grains. Acritarchs, known from one stratigraphic interval, are well-preserved and interpreted to represent autochthonous deposition during a marine incursion into the depocenter. This interpretation is consistent with their occurrence in a gray mudstone that is mantled by a mollusk-dominated coquina that bears conodonts, palaeoniscoid scales, and actinopterygian teeth. In contrast, most studied samples are dominated by wood fragments, charcoal, cuticles, and unidentified phytoclasts—all interpreted to represent dispersed plant cuticle and wood of continental origin. Fossils occur in black paper shale, gray fetid calcareous siltstone, and rhythmically bedded gypsum that is closely associated with thin limestone. Palynofacies analyses suggest that non-acritarch palynomacerals were deposited in dysoxic to anoxic waters that received minimal suspended terrigenous input. When combined with sedimentologic information, these non-acritarch fossils are hypothesized to have been deposited in shallow epicontinental lake-like settings that were periodically alkaline, hypersaline, and/or emergent.

Spatial variability of petrofacies using supervised machine learning and geostatistical modeling: Sycamore Formation, Sho-Vel-Tum Field, Oklahoma, USA

The Sycamore Formation at the Sho-Vel-Tum Field primarily consists of clay-rich mudstones (Mdst) and quartz-rich siltstones. The clay-rich Mdst are mainly composed of clays, quartz grains, some allochems, and detrital organic matter. The siltstones are structureless and are divided into two petrofacies: high porosity and permeability massive calcareous siltstones and low porosity and permeability massive calcite-cemented siltstones. Core and well-log data provide mineralogical, lithologic, and porosity information that is useful to define petrophysical facies (petrofacies) and to create facies logs within the Sycamore Formation. We used the data to establish the Sycamore Formation stratigraphic architecture and to map its spatial variability and reservoir properties. To classify the Sycamore Formation petrofacies in noncored wells, we developed a machine learning-based workflow that compares more than 1800 classification models and selects the best combination of well logs, algorithms, and hyperparameters to predict defined petrofacies. The process includes combinations of well logs that were optimized in four classification algorithms: artificial neural network, K-nearest neighbor, support vector machine, and random forest. To adjust each classifier, we used a grid search and a fivefold cross validation to find the best combination of three hyperparameters to improve results of each algorithm. This workflow allows for the efficient extraction of information from cores at a low cost. After we generated the petrofacies logs in noncored wells, we combined them with multiple constraints to create a 3D petrofacies model for the Sycamore Formation at the Sho-Vel-Tum Field and analyze the stratigraphic and diagenetic controls on petrofacies and its impact in reservoir quality.

Empirical analyses of the excavating method and support system based on engineering geology of the Rukoh Dam Suppletion Tunnel, Pidie Regency, Aceh Province, Indonesia

In the design of the Rukoh Dam Suppletion Tunnel, the rock mass quality had not yet been evaluated. Whereas the evaluation empirically affects the stability and support system of the tunnel. This research aimed to provide recommendations for excavation methods and support systems in tunnel construction based on the RMR and Q-System methodologies. The research investigation was conducted by surface geological mapping and assessing the rock mass quality from drill points. The results showed that the tunnel area consists of calcareous siltstone. Meanwhile, the tunnel axis consisted of poor-quality calcareous siltstone based on the RMR value. Following the Q-value, the quality of the calcareous siltstone ranges from very poor to extremely poor. Based on empirical analysis, the tunnel's excavation methods were the top heading and bench methods with 0.6 to 10.0 hours of stand-up time. The proposed support systems analyzed from RMR and Q-value were rock bolt, wire mesh, shotcrete, and steel sets. This analysis had implications for minimizing the risk of failure at the tunnel site due to poor rock mass quality. Even though an empirical method aids in the design, numerical studies are required to bolster the recommendations.

An eolian dust origin for clastic fines of Devono-Mississippian mudrocks of the greater North American midcontinent

ABSTRACT Upper Devonian and Lower–Middle Mississippian strata of the North American midcontinent are ubiquitously fine-grained and silt-rich, comprising both so-called shale as well as argillaceous limestone (or calcareous siltstone) that accumulated in the Laurentian epeiric sea. Although long recognized as recording marine deposition, the origin and transport of the fine-grained siliciclastic material in these units remains enigmatic because they do not connect to any proximal deltaic feeder systems. Here, we present new data on grain size, whole-rock geochemistry, mineralogy, and U-Pb detrital-zircon geochronology from units across Oklahoma; we then integrate these data with models of surface wind circulation, refined paleogeographic reconstructions, and correlations from the greater midcontinent to test the hypothesis that wind transported the siliciclastic fraction to the marine system. The exclusively very fine silt to very fine sand grain size, clear detrital origin, widespread distribution over large regions of the epeiric sea, Appalachian sources, and paleogeographic setting in the subtropical arid belt far-removed from contemporaneous deltaic feeder systems are most consistent with eolian transport of dust lofted from subaerial delta plains of the greater Appalachian orogen and incorporated into subaqueous depositional systems. Delivery of dust that was minimally chemically weathered to Devono-Mississippian epeiric seas likely provided essential nutrients that stimulated organic productivity in these commonly organic-rich units.

Microscopic Characteristics and Formation Mechanism of Effective Reservoirs in the Xihu Depression, China: The Important Role of the Poikilotopic Calcite Cements in Tide-Dominated Delta Systems

The Xihu depression is an offshore sag located on the East China Sea Shelf Basin, which is currently one of the major oil and gas basins along the coast of China. In this study, an integrated approach using thin sections, scanning electron microscopy (SEM), X-ray diffraction (XRD), cathodoluminescence (CL), high-resolution 3D CT core scanning and stable isotope analysis was applied to examine the diagenetic evolution and investigate the microscopic characteristics and formation mechanisms associated with effective reservoirs. Four types were distinguished: upper conventional reservoirs (UC reservoirs), lower conventional reservoirs (LC reservoirs), “bottom calcium” low-permeability reservoirs (“bottom calcium” reservoirs) and “MI clay” low-permeability reservoirs (“MI clay” reservoirs). Poikilotopic calcite cements play an important role in the diagenetic alterations and reservoir quality evolution, precipitating during early eogenesis, provided a framework that retards the adverse impacts of UC reservoirs by compaction. Conversely, in LC reservoirs, with limited poikilotopic calcite, secondary porosity is mostly due to the dissolution of feldspar or unstable rock fragments. UC reservoirs normally develop in the middle of tidal channels and in subaqueous distributary channels, with the base of the sand-body being extensively cemented by carbonate cements, such as late calcite, Fe-calcite and dolomite, which formed the “bottom calcium” reservoir. Combined evidence from petrographic and geochemical analyses suggests that calcite precipitates from diagenetic fluids of mixed marine and meteoric waters, with additional external sources from calcareous siltstones and bioclasts. The carbon sources of calcite mostly originate from the dissolution of carbonates clacts or bioclasts within sandstone beds or adjacent silty mudstones, while dolomite cements have an isotopic composition that is more comparable to the generation of biogenic methane. This study demonstrates how poikilotopic calcite, developed in tide-dominated delta systems, affects the vertical heterogeneity. The results can be used to improve the reservoir evolution model of tide-dominated delta systems and provide a basic understanding for researchers conducting reservoir studies of similar sedimentary systems. Our results can act as a geological basis for further oil and gas exploration.

Non-calcified warm-water marine macroalgae from the Ordovician strata of Spiti, Tethys Himalaya, India

The calcareous siltstones within the Ordovician section of the Takche Formation near Takche, Spiti region of Tethyan Himalaya, India, contain numerous specimens of non-calcified marine macroalgae in association with brachiopods, gastropods, tentaculitoids, and few trace fossils. The algal remains, representing five genera, are preserved as black or dark brown carbonaceous compression fossils, interpreted as warm-water marine macroalgae, namely, Inocladus sp., Callisphenus? sp., Algites sp. (siphonous algae), Fisherites sp., and Mastopora sp. (non-siphonous). Callisphenus is characterised by a radially symmetrical short pyriform thallus, with a central axis surrounded by short laterals whereas Inocladus sp. is characterised by an unsegmented simple thallus with internal parallel medullary siphons and cortical tubes. These algal remains, probably transported from a more near-shore living niche, co-occur with Cyclocrinitids, Tentaculitoids tube worms, trace fossils and brachiopods, suggesting that deposition of the studied units took place in low energy hydrodynamic conditions influenced by intermittent storm events. The study represents the first diversified macroalgal records from the Ordovician strata in the Tethyan realm of Indian subcontinent.

Stratigraphy and Paleoenvironment(s) of the Late Cretaceous deposits in Ohafia area, Afikpo Basin, Southeastern Nigeria

Lithofacies and biofacies data extracted from three outcropping sections of Nkporo and Mamu Formations’ sediments in Ohafia area were used for paleoenvironmental and sequence stratigraphic interpretations. The five (5) lithofacies distinguished from the sections were Dark-Grey to Black Shale Facies (A), Oolitic Limestone Facies (B), Calcareous Siltstone Facies (C), Sandstone Facies (D) and Heterolithic Facies (E). The attributes of these lithofacies, including lithotype, rootlets, bioturbation, reducing conditions and microfossil contents, were used to discriminate the units into various environments of deposition and paleodepths. The oolithic limestone facies for instance was interpreted as deposits in shallow coastal areas with high turbulence, especially, in warm shallow marine environments. Paleobathymetry of the lithofacies ranged from non-marine through coastal deltaic, shallow inner neritic, inner neritic to middle neritic paleodepths. Micropalaeontological analysis of the sediments revealed a complete absence of planktonic foraminifera while agglutinated benthic assemblages (dominated by Haplophragmoides spp., Textularia spp. and Anomalinoides spp.), calcareous benthic foraminifera (Gavelinella guineana and Planulina nacatochensis), Gastropods, Ostracods, and Arenaceous indeterminate were recovered. The recognition of Bolivina afra-Haplophragmoides talokaense assemblage zone in the Mamu Formation conferred Maastrichtian age to the deposits. The presence of palynological assemblages like the Adallussiella polymorpha were used to assign Late Campanian age for the Nkporo Formation. Sequence stratigraphic analysis using the integration of foraminiferal, paleontological and lithofacies data identified two incomplete depositional sequences. The first sequence identified in the Nkporo Formation, comprised a Highstand systems tract (HST) bounded at the top by a sequence boundary (SB) dated 75 Ma. The SB also marked the beginning of the second depositional sequence that occurred in the successions of the Mamu Formation and comprised of Transgressive systems tract (TST), bounded at the top by a maximum flooding surface (MFS) dated 69.8 Ma. The results of this study have indicated the presence marker beds and constrained stratigraphic surfaces which can be used to map the identified play elements (source, reservoirs, traps and seals) in the study area. The surfaces are thus essential ingredients in basin-wide correlations for improved hydrocarbon exploration and development in the Afikpo and other adjoining inland basins of Nigeria.

Ediacaran cap dolomite of Shennongjia, northern Yangtze Craton, South China

Ediacaran cap dolomites are strong evidence for the glaciation during the Neoproterozoic. Stratigraphic-sedimentological studies combined with δ13C and δ18O isotope analyses are used for defining the processes of post-glacier environmental changes and sea-level rise caused by glacier melting and the reconstruction of the depositional environments for the Doushantuo cap dolomites in Shennongjia, northern Yangtze Craton (YC). Like many other cap dolomites in the YC and worldwide, those in Shennongjia exhibit strongly negative δ13Ccarb excursions, ranging from −7.3 to −2.5 ‰ (averagely from −5.4 to −4.1 ‰). A laminated clast-free calcareous siltstone commonly occurs between the cap dolomite and the underlying diamictites, indicating a low-energy, shallow-water depositional environment, wherein alkaline conditions developed before the deposition of the cap dolomite. The most prominent features of the cap dolomites in Shennongjia are the very thin thickness and monotonous sedimentary structures. The maximum thickness of the cap dolomites from the six sections in Shennongjia is 1.8 m, and the thinnest cap dolomite is 0.4 m with simple laminations. Sedimentary structures such as low-angle cross-bedding, giant wave ripples, sheet-crack cement, and tepee breccias are rare in Shennongjia except in the area near the Three Gorges. These evidences, therefore, point to the deposition of the Shennongjia cap dolomite in restricted shallow-water tidal environments.The space–time distribution of sedimentary facies in Shennongjia and the southeastern areas to Shennongjia indicate that the Ediacaran cap dolomite was formed on a ramp. Accordingly, we propose a sedimentary facies model for the formation of the cap dolomite, covering the inner and middle ramp facies. This model explains the thickness variations and distributions of the cap dolomites at both the local and regional scale, including their sedimentary structures, compositions, and barite occurrences. The model successfully illustrates why the cap dolomites in the Shennongjia area share a unique set of sedimentary features. Finally, the cap dolomite is interpreted as a diachronous deposit (bottom to top), tracking glacioeustatic flooding and recording ocean-wide changes over the time following deglaciation, and a correlation and cause of negative δ13Ccarb excursions in cap dolomites worldwide, particularly in those in the Yangtze Carton, are further discussed.

Diagenetic controls on reservoir quality of a mixed carbonate-siliciclastic system: Sycamore Formation, Sho-Vel-Tum Field, Oklahoma, USA

Reservoir quality (RQ), commonly related to diagenesis, is important to predict formation porosity and permeability. The lack of studies to understand the role of diagenesis on tight reservoirs is a limiting factor for predicting petroleum accumulation in unconventional reservoirs. This study aims to determine the influence of diagenesis on RQ for the mixed carbonate-siliciclastic Sycamore Formation in southern Oklahoma. Additionally, this study assesses other geologic factors such as depositional facies control on diagenesis of the Sycamore.Petrographic observation, geochemical data, and conventional plug analysis from six cores and one outcrop were used to accomplish three objectives: i) reconstruct the paragenetic sequence; ii) determine the role of diagenesis on RQ; and iii) elucidate geological factors that control the diagenetic evolution in the Sycamore strata.Four facies were identified: Massive Calcite-cemented Siltstones, Massive Calcareous Siltstone, Bioturbated Mudstones, and Argillaceous Mudstones. However, this study focuses on the siltstones and their associated diagenetic processes and products. Porosity evolution in the siltstones is affected by cementation and dissolution processes. These diagenetic processes are related to each other; calcite cement decreases permeability during early diagenesis and controls the flow of later diagenetic fluids responsible for feldspar dissolution. Additionally, differences in the supply between a carbonate and siliciclastic material and a change from a carbonate-dominated system to a mixed system through time controls the distribution of calcite cement in the Sycamore.This study allows geologists to understand the diagenetic evolution and to characterize RQ of the Sycamore and similar formations by considering the sediment supply between carbonate- and siliciclastic-dominated systems, changes in stratigraphy, and influx of acidic fluids. Identifying geological controls on diagenesis and defining the influence of diagenesis on RQ in tight formations is important for the exploration and development of unconventional reservoirs, to build predictable porosity and permeability models, and to identify petroleum accumulations.

Excavation method and support system in the diversion tunnel of Tiga Dihaji Dam, South Sumatera, Indonesia based on the rock mass quality

This study determined the excavation method and the support system in the diversion tunnel of Tiga Dihaji Dam, South Sumatera of Indonesia. Investigation performed in this study included surface geological mapping and evaluation of core drilling that are useful for determining rock mass quality. Geological conditions in the tunnel consist of tuffaceous sandstone lying unconformity over interbedded calcareous sandstone and calcareous siltstone. Based on the Geological Strength Index analysis, the excavation method for tuffaceous sandstone by hammer and blasting, and digging and ripping for the interbedded calcareous sandstone and calcareous siltstone. The support system is the installation of rock bolts of 3 m long with spaced 2.5 m on tuffaceous sandstone, 4 - 6 m long with spaced 1 - 1.5 m on interbedded calcareous sandstone and calcareous siltstone, and with shotcrete thickness of 50 -200 mm (Rock Mass Rating). While in the Q-system classification were 2.7 m long rock bolts with spaced 2.7 m on tuffaceous sandstone, 2.7 m long rock bolts with spaced 1 – 2.4 m, and a shotcrete thickness of 25 cm on interbedded calcareous sandstone and calcareous siltstone.

Multiscale Characterization of the Caney Shale — An Emerging Play in Oklahoma

From a hydrocarbon perspective, the Caney Shale has historically been evaluated as a sealing unit, which resulted in limited studies characterizing the rock properties of the Caney Shale and its suitability for hydraulic fracturing. The objective of our research is to help bridge the current knowledge gap through the integration of multiscale laboratory techniques and to characterize the macro- and microscale rock properties of the Caney Shale. We employed an integrated approach for the characterization of the Caney using 200 ft (61 m) of Caney core from a target well in southern Oklahoma. Core observation and petrographic analysis of thin sections were combined to characterize the general rock types and associated fabrics and textures. Mineralogical composition, pore system architecture, and rock fabric were analyzed using x-ray diffraction (XRD), scanning electron microscopy/energy dispersive x-ray spectroscopy (SEM/EDS), and focused ion beam (FIB)-SEM. In addition, rebound hardness and indentation testing were carried out to determine rock hardness (brittleness) and elasticity, respectively. With the integrated multiscale characterization, three mixed carbonate-siliciclastic rock types were identified — mudstone, calcareous siltstone, and silty carbonate — likely representing a spectrum of deposition from low to relatively high energy environments in the distal portions of a ramp system. Silty carbonate contains mostly interparticle pores. The calcareous siltstones and silty mudstones contain a combination of organic matter pores and interparticle pores. Each of the rock types shows unique mineralogical compositions based on XRD. The mudstone lithofacies has the highest clay content and the least carbonate content. Calcareous siltstones show moderate carbonate and clay content. Silty carbonate indicates the highest carbonate content with the least clay content. In an order of mudstone, calcareous siltstone, and silty carbonate, rebound hardness and Young’s modulus show an increasing trend. As a result of rock-fluid interactions, there are potential scaling reactions during completion and production that could ultimately affect permeability and production rates. Overall, the proposed multiscale integration approach is critical for the geologic characterization of most rocks. However, in shale reservoirs dominated by microporosity and microstructure where engineered fractures are expected to provide permeability at a reservoir scale, successful integration is essential. An optimized, integrated geological characterization of the Caney Shale that is well aligned with the engineering designs in drilling, completing, and producing wellbores will ultimately lead to optimal production while providing safe and environmentally responsible operations.

PALEOENVIRONMENTAL IMPLICATIONS OF INVERTEBRATE FECAL PELLETS (EDAPHICHNIUMISP.) AT AN ICHNOFOSSIL-RICH DINOSAUR NESTING LOCALITY, UPPER CRETACEOUS TWO MEDICINE FORMATION, MONTANA, USA

ABSTRACTThe terrestrial feeding trace Edaphichnium lumbricatum is known from the Triassic to the Pleistocene and is characterized by tubular burrows with ellipsoidal fecal pellets, indicating substrate feeding by earthworms or other invertebrates. We describe 11 specimens attributable to Edaphichnium isp. from Egg Mountain, a terrestrial locality with a diverse fossil assemblage from the Upper Cretaceous Two Medicine Formation in Montana, USA, and assess their paleoenvironmental and paleoecological implications. These ichnofossils were recovered from a 1.5 meter stratigraphic succession comprised of calcareous siltstones and limestones with abundant fossil insect pupal cases, representing well-drained paleosols. Although burrows are not always present, three recurring arrangements of Edaphichnium isp. fecal pellets are identified: linearly arranged pellets, horizon-confined pellets, and pellets in clusters dispersed vertically and horizontally throughout the matrix. Two color patterns (light and dark pellets) are also distinguished. Pellets are fine-grained and have a consistently ellipsoidal shape (length:diameter of 1.57), with maximum lengths ranging from 1.9–6.7 mm (mean 4.1 mm) and maximum diameters ranging from 1.0–4.1 mm (mean 2.6 mm). Geochemical analyses indicate pellets are comprised of varying proportions of calcite, plagioclase, and quartz, and are enriched in phosphorus relative to the sedimentary host matrix. Possible trace makers include chafer or other coleopteran larvae, millipedes, and earthworms, suggesting a range of capable trace makers of Edaphichnium-like fecal pellets. Edaphichnium isp. at specific stratigraphic horizons suggests increased organic content in the subsurface, potentially connected to depositional hiatuses. Edaphichnium isp. adds a secondary component to the Celliforma ichnofacies known from Egg Mountain and surrounding strata, and to the array of nesting, feeding, and dwelling traces of wasps, beetles, other invertebrates, mammals, and dinosaurs from the locality.

(Bio)stratigraphic overview and paleoclimatic-paleoceanographic implications of the middle-upper Eocene deposits from the Ica River Valley (East Pisco Basin, Peru)

The Eocene sediment successions of the East Pisco Basin (southern Peru) host an exceptionally rich and well-preserved assemblage of vertebrate fossils. However, due to the dearth of geochronological and biostratigraphic controls as well as of stratigraphic correlations, our understanding of these rocks and their fossil content remains elusive.This paper provides a comprehensive calcareous nannofossil, diatom, and silicoflagellate biostratigraphic framework for the Eocene strata exposed at four localities along the Ica River Valley, permitting a robust chronological calibration of the marine vertebrate fauna entombed therein and a better definition of important appearance/ extinction events. The Paracas Formation, deposited directly on top of the Proterozoic and Paleozoic rocks of the crystalline basement, is formed by a siliciclastic-bioclastic sand-sized deposit (Los Choros member) and calcareous-terrigenous siltstone (Yumaque member) that was deposited from the Lutetian (47.8–41.2 Ma) through the Bartonian (41.2–37.7 Ma) to the early Priabonian (37.7–33.9 Ma). The unconformably overlying Otuma Formation consists of a basal sandstone, followed by calcareous siltstone intercalated by diatomite layers towards the top. In the study area, the Otuma Formation is Priabonian in age and is truncated at the top by an unconformity at the base of the overlying Miocene Chilcatay Formation. Due to the angular nature of the unconformity, the upper Otuma strata reach the Oligocene elsewhere.Average sedimentation rates range from 17 to 24 m/My in the Yumaque member of the Paracas Formation and increase to 147–170 m/My in the Otuma Formation. The microfossil assemblages witness a coastal setting with warm-temperate conditions for the Paracas Formation that become slightly cooler (though still temperate) in the upper Otuma Formation. Diatomaceous layers in the upper Otuma Formation indicate an overall increase in nutrient availability, which could reflect the global reorganization of ocean currents at the Eocene-Oligocene transition. However, the taxonomic composition of the diatom assemblage suggests seasonal rather than persistent upwelling conditions.

Mechanical stratigraphy of Mississippian strata using machine learning and seismic-based reservoir characterization and modeling, Anadarko Basin, Oklahoma

The Sooner Trend in the Anadarko (Basin) in Canadian and Kingfisher counties play primarily produces oil and gas from Mississippian strata. The interval consists of interbedded argillaceous mudstones and calcareous siltstones. Such a contrast in rock composition is linked directly to the mechanical stratigraphy of the strata. Brittle (calcareous siltstones) and ductile beds (argillaceous mudstones) are related to the sequence-stratigraphic framework at different scales. We have used seismic and well-log data to estimate and map the geomechanical properties’ distribution and interpret the mechanical stratigraphy of rocks within the Mississippian strata. First, we defined the parasequences that form the main reservoir zones of the Meramecian-Mississippian strata. Once we established the stratigraphic framework, we estimated and compared rock brittleness index (BI) using two independent laboratory-based measurements from the core. The first method, the mineralogical-derived BI, uses mineralogical composition inverted from Fourier-transform infrared spectroscopy analyses, whereas the second method, the mechanical-derived BI, involves measurements of compressional and shear velocities from core plugs. We use the data from core-plug velocity measurements along with well logs and an artificial neural network approach to establish relationships among the geomechanical properties, well logs, and acoustic impedance values. We then applied these relationships to generate 3D geomechanical models constrained to seismic volumes. The resulting grid distributions illustrate the stratigraphic variability of the properties at the parasequence scale. Overall, brittle strata decrease in thickness and abundance basinward as the frequency of interbedded brittle and ductile zones increases and gradually transitions into thin calcite-cemented siltstones and clay-rich mudstones. Analysis of the production performance of selected horizontal wells drilled within the Mississippian strata indicates that the proportion of brittle and ductile rocks along the well path drilled and the drilled area vertical stacking pattern play a significant role in hydrocarbon production for these Mississippian units.

Mississippian Meramec lithologies and petrophysical property variability, stack trend, Anadarko Basin, Oklahoma

Mississippian Meramec reservoirs of the Sooner Trend in the Anadarko (Basin) in Canadian and Kingfisher Counties (STACK) play are comprised of silty limestones, calcareous siltstones, argillaceous calcareous siltstones, argillaceous siltstones, and mudstones. We found that core-defined reservoir lithologies are related to petrophysics-based rock types derived from porosity-permeability relationships using a flow-zone indicator approach. We classified lithologies and rock types in noncored wells using an artificial neural network (ANN) with overall accuracies of 93% and 70%, respectively. We observed that mudstone-rich rock type 1 exhibits high clay and relatively low calcite, whereas calcareous-rich rock type 3 has high calcite and low clay content with rock type 2 falling in between as a balance between rock types 1 and 3. Results of the ANN were applied to a suite of well logs in noncored wells in which we generated lithology and rock-type logs for the Meramec. We identified that the Meramec consists of seven stratigraphic units characterized as strike-elongate, shoaling-upward parasequences; each parasequence is capped by a marine-flooding surface. The lower three parasequences (lower Meramec) form a retrogradational parasequence set that back steps to the northwest and is capped by a maximum flooding surface. The upper Meramec is characterized by parasequences that form an aggradational to progradational stacking pattern followed again by a retrogradational trend. We predict that the parasequence stacking, associated lithology distribution, and diagenetic cements appear to control the spatial distribution of petrophysical properties (porosity, permeability, and water saturation), pore volume, and hydrocarbon pore volume (HCPV). Calcareous-rich lithologies exhibit lower porosity, permeability, HCPV, and higher water saturation. We deduced that argillaceous-rich lithologies that occur near the maximum flooding surface are the most favorable reservoir intervals because they exhibit relatively higher porosity, permeability, HCPV, and lower water saturation. Productivity could not be directly correlated to rock types as operational and completion factors as well as overpressure and oil phase play important roles on production.