Sedimentary Basins Research Articles

A case-history tutorial describing the incorporation of geophysical, petrophysical and geological constraints to generate realistic geological models of the Matheson Study Area, Ontario

The model that is used to explain potential-field data is highly dependent on the constraints applied in the modelling process. Many studies demonstrate the necessity of constraining gravity and magnetic models. However, typically they do not demonstrate the individual enhancements that come as a consequence of integrating each constraint into the geophysical model. In this paper, we show that when there are no constraints, it is possible to find an inverse model that is consistent with gravity data, but the model is unrealistic, as one sedimentary basin is too deep. Adding a depth weighting constraint can ensure the depth is correct, but all other features have the same depth, which is unrealistic. Including densities from a density compilation makes the densities at surface realistic, but the dips are all close to vertical and the thicknesses are similar, which is unrealistic. In this case, the inversion is believed to have found a local minimum close to the starting model. Reflection seismic data was used to constrain a two-dimensional (2D) modeling exercise (on multiple profiles) to determine the geometry of one sedimentary sub-basin. These 2D models were then combined to build a realistic three-dimensional (3D) starting model. An inversion from this model fixed the densities of each lithology, but allowed the thicknesses of the layers to vary. The resulting model was realistic, with the dips and thicknesses away from the seismic constraints being consistent with geological expectations. Although the fit to the data was much better than the previous model, it was poorer than hoped. If the densities were then allowed to vary within a realistic range of values, the fit could be improved so that both the fit to the data and the geologic model are realistic.

Geochemistry and mineralogy of the shale-hosted vanadium Van Property deposit, Mackenzie Mountains, Northwest Territories

Abstract Shales and mudstones are fine-grained rocks formed in sedimentary basins throughout Earth’s history. These lithologies are increasingly important targets for mineral deposit exploration since they can have economic resources of critical minerals including vanadium (V), an essential component of redox-flux batteries in solar cells. However, many Paleozoic shale-hosted V deposits are metamorphosed and deformed. This commonly obscures primary features including V-bearing host phases and the original composition of organic material. In this study, we present geochemical and mineralogical data from the Paleozoic Van Property deposit, Northwest Territories, Canada, to show that V can be released from organic matter during metamorphism and incorporated in clay phases such as illite. The siliceous argillites at the Van Property hosts up to 0.69% V2O5 and were metamorphosed to (sub-)greenschist facies. Their mineralogy is dominated by quartz with minor graphite, illite, muscovite, pyrite, sphalerite, rutile, and carbonates. Although, some illite (i.e., high-V illite) can have up to 13 wt% V2O3 and rutile can have up to 4.4 wt% V2O3, mass balance calculations are insufficient to explain V enrichment at the Van Property utilizing only illite and rutile. The third V host is inferred to be carbonaceous matter in which V accumulated syn-deposition on the seafloor. Subsequent metamorphism led to the demetallation of V-bearing geoporphyrins and the release of vanadyl ions (VO2+), some of which were then incorporated into high-V illite and rutile. This process of V enrichment highlights the role of organic matter in scavenging V from superficial reservoirs and the importance of metamorphism on subsequent V release and its incorporation into inorganic phases. The geochemistry of siliceous, V-rich argillites at the Van Property is also compared to other V-enriched shale and mudstone deposits, highlighting the diversity of shale-hosted V deposits, and emphasizing the need for further research to close the knowledge gaps related to variations in composition, mineralogy and V enrichment processes.

Automated high-precision alignment of geologic maps with well orientation

The 3D reflection seismic interpretation entails the creation of structure maps of subsurface horizons across extensive areas, often spanning tens of thousands of square kilometers within sedimentary basins. To be correlated with well measurements, maps made from 3D reflection seismic are routinely assigned the correct depth at well control points. However, integrating orientation information measured from wells remains a challenge due to the absence of upscaling guidelines. We address the scale-dependent nature of geologic structure and well orientation information in subsurface mapping, particularly focusing on integrating kilometer-scale seismic interpretation with centimeter-scale well-measured dip and azimuth data. Our pioneering methodology streamlines this integration process through three essential steps: first, transforming well dip and azimuth into a gradient representation; second, smoothly extending gradient differences between the map and well within a user-defined radius of influence; and third, constructing an updated horizon map by bicubic spline interpolation to ensure automated and high-precision alignment. In addition, a structure-oriented interpolation technique is introduced to preserve faults and local structures during orientation correction. Application of the methodology to a 3D reflection seismic horizon demonstrates its effectiveness in automating the complex task of tying subsurface maps to well orientation information. This not only reduces the need for manual interventions but also introduces a new perspective on subsurface mapping. It provides a robust framework that enhances the accuracy and reliability of geologic interpretation, offering significant advancements beyond previous efforts in the literature.

Three-dimensional model and environmental fragility in the Guarani Aquifer system, SE-Brazil

The Guarani Aquifer System (GAS) is a vast transboundary continental sedimentary basin in southern South America, encompassing sedimentary rocks and basalt flows across Uruguay, Paraguay, Argentina, and Brazil. It serves as a crucial water resource for urban supply and irrigation. This study aims to propose geophysical, geometric, and fragility models of the GAS in a critical exploitation area, utilizing geological data, geophysical logs, geomorphometry, and information from tubular wells. The models define distinct geophysical ranges for each formation and identify contacts between sedimentary and basaltic rocks. Integration of horizontal and vertical spatial distributions of geophysical and geological data forms a 3D model, revealing basaltic flows and intrusions distribution in fragile areas between formations, and potentially connecting aquifer layers. Natural fragility zones, characterized by high fracture densities, are observed in the central-east region, while outcrop and recharge areas of the main aquifer hydrofacies are found in the north. The 3D model highlights similarities between the topography of the Botucatu Formation (KJb – eolian sandstones) and the potentiometry of GAS at local scales, and overexploitation zones in Ribeirão Preto's city center. The assessment prioritizes areas at risk and conservation strategies for sedimentary aquifers, emphasizing interactions between surface and groundwater and addressing issues of overexploitation, identifying high-impact risks on GAS hydrodynamics and water quality.

Petrophysical Evaluation of Arkoses Reservoirs Based on Well Logs and Plug Samples: A Case Study From Alagamar Formation, Southeastern Portion of Onshore Potiguar Basin, Brazil

The Potiguar Basin is a sedimentary basin located in northeastern Brazil. It covers about 48,000 km² and extends from onshore to offshore. The onshore basin is thought to have formed during the Late Cretaceous, as a result of the opening of the Equatorial South Atlantic Ocean, filled with a thick sequence of sedimentary rocks, including sandstones, shales, and limestones, which were deposited in a variety of processes, including marine, deltaic, and fluvial. The study area is in the southern portion of the basin and the reservoir is composed of arkose sandstones deposited by alluvial fan and fluvial systems of the Upanema Member of the Alagamar Formation, which belongs to the post-rift phase of the Potiguar Basin. Recently, new drilling campaigns revealed a reservoir heterogeneity in these deposits, which requested a new petrophysical approach. Using conventional well logs and petrophysical laboratory analysis of plug samples, this study evaluated the best way to calculate the effective porosity, and shale volume and to understand the stratigraphic controls in the distribution of these properties. Three reservoir zones were mapped: the basal one, Zone 3, has disconnected sand bodies, low porosity, and high shale content; Zone 2 has better petrophysical properties, lateral distribution, and connectivity between the fans and Zone 1 is the better reservoir zone with larger sand bodies, higher porosity values, and well-connected fans.

Drainage reorganization and alluvial architecture of endorheic basins: The Lower Cretaceous record of the Chubut Group in the Golfo San Jorge Basin (Patagonia, Argentina)

The size, shape, and organization of depositional systems in endorheic basins are controlled by the tectonic and climatic history of the sedimentary basin and its boundaries. We evaluate the changes in the alluvial architecture of the Matasiete (Aptian) and Castillo (Albian) formations of the Chubut Group (Cretaceous) in the endorheic Golfo San Jorge Basin (Patagonia, Argentina) analyzing a ∼150 km transect along the San Bernardo Fold Belt, subsurface data, and coeval fluvial successions of the Los Adobes Formation in the nearby Cañadón Asfalto Basin. The Aptian Matasiete Formation represents an externally-sourced, high-accommodation fluvial system with its headwaters in the current Cañadón Asfalto Basin, flowing toward the alkaline lake of the Pozo D-129 Formation through N–S oriented sedimentary corridors of tectonic origin. Low sinuosity, fixed channels with ribbon geometries (mean thickness 7.3 m, W/T ratio 14) are encased in red-colored floodplain fines, whereas stratigraphic intervals rich in resedimented tuffs contain braided rivers with W/T ratio up to 90. Deposition of the overlying Albian Castillo Formation occurred in a W-E elongated basin disconnected from the Cañadón Asfalto Basin, comprising aggradational, volcaniclastic floodplain deposits and smaller-scale fluvial channels of narrow-sheet geometries (mean thickness ∼ 3m, mean W/T ratio 45). The Castillo Formation shows spatial variation in fluvial styles and channel sizes, with intermittent to ephemeral rivers of small scale near the headwaters and seasonal, perennial rivers in downstream positions. Alluvial architecture changes between the Matasiete and Castillo formations reflect changes in the configuration of the basin boundaries, subsequent re-organization of the channel networks, and variable supply of volcaniclastic particles to drainage catchments of different hierarchy that evolved in areas with large variation of the preserved thickness. Comparable geomorphic scenarios in the Okavango Macrobasin show multiple base levels (lacustrine, ephemeral pans), several drainage catchments of variable orientation, scale, and behavior (perennial, intermittent to ephemeral), and exotic rivers adjacent to minor-scale courses.

Gravity field and crustal structure of the Eastern Arm of Sulawesi and the Banggai Archipelago, Eastern Indonesia

The occurrence of extensive ophiolite masses and the development of the Batui-Balantak foreland thrust-fold belt on the Eastern Arm of Sulawesi can be attributed to the geologic process in the Neogene period when the Sulawesi Island Arc and the Banggai-Sula collided. Following the convergence, crustal fragments were further adjusted on a regional scale. This adjustment involved the rotation of crustal fragments into strike-slip faults on Sulawesi Island and the formation of extensional faults in the Banggai Archipelago. The analyses of the gravity field in the region of the eastern Sulawesi and Banggai Archipelago have yielded models that can potentially be interpreted as a representation of the underlying crustal structure in the region. The models can also be understood in a way that has consequences for tectonics. The tectonic episodes have played a significant role in the formation and development of sedimentary basins within the region. The primary objective of this study was to investigate the crustal structures of the Eastern Arm of Sulawesi and the Banggai Archipelago by means of analyzing gravity profiles. The findings of the analysis suggest that there is a slight thickening observed in the crustal block beneath the central portion of the eastern arm region. In addition, this area exhibits significant fracturing and severe attenuation. Furthermore, the crustal block has a dipped north-eastward trend in response to the ascent of the Molucca Sea oceanic crust.

Tridactyl dinosaur footprints from the Triassic Sambaíba formation of northern Brazil

Some new tridactyl footprints have been recorded in the Malhada Vermelha farm locality, municipality of Fortaleza dos Nogueiras, state of Maranhão, northern Brazil, from the Sambaíba Formation, Parnaíba Sedimentary Basin. The specimens are fifteen isolated, in situ, mesaxonic tridactyl tracks preserved in six sandstone slabs as concave epireliefs. Abundant MISS evidence is preserved in the track-bearing blocks. The footprints are referred to as Grallator isp., linking them with an theropodian origin. The footprint-bearing levels were accumulated in shallow environments influenced by a tidal flat. The occurrence and interpretation of these findings bring a new approach to sedimentary subenvironments in the Sambaíba Formation.

West Barents Sheared Margin Composite Tectono-Sedimentary Element, Norwegian–Greenland Sea and Fram Strait

The West Barents Sheared Margin developed in response to break-up and initial opening of the NE Atlantic and links to the Arctic Eurasia Basin. It consists of three first-order segments: (1) a southern sheared margin segment bounding the deep SW Barents Sea basins; (2) a central rifted margin segment west of Bjørnøya; and (3) a northern initially sheared margin segment that was later exposed to oblique extension west of Svalbard. The geometry of the margin included releasing, as well as restraining, bends that inflicted substantial impact on the deformation along the sheared margin. In light of structural, stratigraphic and sedimentological investigations in recent years, the first-order three-fold subdivision of the Barents shear margin has been strengthened and expanded on. It has become even clearer that this subdivision reflects the margin geometry and the shifting far-field and local stress configurations. Prior to the final stages of rifting and break-up of the NE Atlantic in the Paleogene, the study area was part of a broad and extensive basin province comprising deep sedimentary basins. The line of break-up cut diagonally across the regional basin province so that different parts of it are now located in the mid-Norwegian margin, in the NE Greenland margin and in the SW Barents Sea. These areas share a long and complex history of multiple rift phases throughout Late Paleozoic and Mesozoic times, and information from these areas is integrated into the description of the West Barents Sheared Margin Composite Tectono-Sedimentary Element. The marginal basins in the SW Barents Sea are the least explored area on the Norwegian continental shelf and sporadic exploration activity has had limited success. A petroleum potential still exist that will be elaborated in renewed upcoming activity.

Spatial heterogeneity in nutrient utilization during the end-Devonian ocean anoxic event: a case study of the Western Canada sedimentary basin

The Devonian-Carboniferous (D-C; 359 Ma) boundary is marked by widespread deposition of organic-matter-rich black shales associated with the Hangenberg mass extinction event. The Exshaw Formation spans the D-C boundary in the Western Canada Sedimentary Basin (WCSB) and includes the basal Exshaw Shale deposited under broadly anoxic waters. The sediments at the base of the Exshaw Shale were deposited synchronously during a transgressive event across the WCSB, spanning the geographic variability of the basin. The variable Corg content of the shale was affected by local nutrient upwelling and paleotectonic features impacting water depth and circulation. To characterize the link between paleogeography and nutrient cycling, geographic (N = 20 locations) and stratigraphic (N = 6 locations) trends of δ13Corg and δ15Nbulk were examined throughout the WCSB, representing a range of depositional settings. The δ15Nbulk values range between 0.0 and 6.3‰ and δ13Corg from −29.5 to −26.8‰. Phytoplankton production in focused upwelling zones acquired a relatively 15N-depleted signature through isotopic fractionation during nutrient assimilation, and the residual nutrient pool was 15N-enriched. The advection of surface waters away from the location of upwelling supported additional phytoplankton growth and the deposition of sediments with higher δ15N values. The stratigraphic sections include black laminated and burrowed mudrock sequences that record changes in paleoredox conditions, water depth, and tectonism over time. Up-core from the base of the Exshaw, the Corg content decreases and simultaneously δ15Nbulk increases, suggesting a decrease in eutrophic conditions. Variable δ13Corg and δ15Nbulk trends demonstrate that there is no “type” isotopic profile spanning the D-C boundary in the WCSB.

New constraints from in-situ U-Pb ages and fluid inclusions of calcite cement and structural analysis on multiple stages of strike-slip fault activities in the northern Tarim Basin, NW China

Dating the activity of complex faults and fracture systems is crucial for creating reliable geological models for various tectonics and subsurface engineering applications. This study presents a comprehensive study integrating U–Pb fracture cement dating, trace elements, and fluid inclusion temperature analysis with seismic analysis of faults, fault diagenesis, and burial history studies to better constrain faulting and fracture activities in an intra-cratonic strike-slip fault system in the northern Tarim Basin. Seismic profiles indicate at least three distinct phases of fault activity corresponding to the Middle Ordovician, Permian, and Paleogene periods. Fracture cementation and crosscutting relationships corroborate the identification of three fracturing stages. U–Pb dating of fractured cement has widely detected Middle Ordovician and Early Permian age intervals. Fluid inclusion homogenization temperatures from the fractured cements, ranging across < 50 °C, 70–130 °C, and 150–180 °C, correspond to three episodes of rapid subsidence during the Ordovician, Permian, and Neogene, respectively. These results suggest three phases of fault/fracture reactivation in the Middle Ordovician (prior to 470 Ma), Early Permian (prior to 295 Ma), and Cenozoic. The fault/fracture reactivation in the Ordovician is closely related to the regional tectonic transition from extension to compression, while fault and fracture reactivation in the Early Permian may be related to hydrothermal activity associated with large-scale igneous province and oil emplacement. Fault/fracture activity in the Cenozoic may be related to a reduction in subsidence, gradual reduction of geothermal gradients, and massive oil emplacement. This research underscores the significance of integrating geochemical and subsurface datasets for accurately determining the timing of faulting and fracturing in sedimentary basins.

The thermal structure of the Colombian lithosphere: A regional and basin-scale analysis

It is well-established that the thermal state of the lithosphere strongly influences various regional and local geological processes, including crustal deformation, hydrocarbon maturation, hydrogen generation, and geothermal phenomena. Moreover, the thermal structure exhibits high sensitivity to tectonic features, a property of particular significance in Colombia, where three main tectonic plates converge, and lithospheric tearing has been documented. In this contribution, we focus on elucidating the impact of plate architecture on the thermal field in central-eastern Colombia at both shallow and deep levels. To accomplish this, we constructed a series of two-dimensional profiles and derived a numerical solution of the heat equation using the conservative finite difference method. As constraints, we incorporate an inferred distribution of rocks in the deep crust and upper mantle based on global and local lithospheric thickness models. Material parameters for the various rocks, both exposed and inferred, were obtained from the literature. Additionally, we used superficial heat flow estimates and apparent geothermal gradients compiled by the Colombian Geological Survey.Our results suggest a significant influence of the lithospheric Caldas tear on the thermal state of Colombia, with the breaking off occurring in the Nazca plate under the Eastern Cordillera range around 5°N. The modeled asthenospheric heat flow remains approximately 25 mWm−2, except in the northern Eastern Cordillera range, where the background heat flow increases rapidly to 40 mWm−2. Consequently, our model predicts partial melting in the lower crust to the north and a thermally unstable lower crust to the south of the Caldas tear. The material parameters that best fit the surface data suggest the presence of a basement moderately enriched in radioactive elements in the Eastern Llanos basin. After accounting for compaction, we also confirm a strong influence of the tectonic setting on the thermal state of sedimentary basins.

Land use/cover drive functional patterns of bacterial communities in sediments of a subtropical river, China

The bacterial community in sediment serves as an important indicator for assessing the environmental health of river ecosystems. However, the response of bacterial community structure and function in river basin sediment to different land use/cover changes has not been widely studied. To characterize changes in the structure, composition, and function of bacterial communities under different types of land use/cover, we studied the bacterial communities and physicochemical properties of the surface sediments of rivers. Surface sediment in cropland and built-up areas was moderately polluted with cadmium and had high nitrogen and phosphorus levels, which disrupted the stability of bacterial communities. Significant differences in the α-diversity of bacterial communities were observed among different types of land use/cover. Bacterial α-diversity and energy sources were greater in woodlands than in cropland and built-up areas. The functional patterns of bacterial communities were shown that phosphorus levels and abundances of pathogenic bacteria and parasites were higher in cropland than in the other land use/cover types; Urban activities have resulted in the loss of the denitrification function and the accumulation of nitrogen in built-up areas, and bacteria in forested and agricultural areas play an important role in nitrogen degradation. Differences in heavy metal and nutrient inputs driven by land use/cover result in variation in the composition, structure, and function of bacterial communities.

Lithostratigraphy and Petrography of Mesozoic Sedimentary Rocks of Lemi Area, North Shewa, Central Ethiopia

The Mesozoic sedimentary basins in Ethiopia, particularly the Central Ethiopia, and Blue Nile Basin within the central main Ethiopian rift region are characterized by a diverse range of volcano-sedimentary rocks dominated by sedimentary sequences. The lithostratigraphy and petrology of Mesozoic sedimentary rocks of Lemi area, North Shewa, in Central Ethiopia within the Blue Nile basin, is described based on detailed field observations, lithostratigraphic analysis, petrographic examinations. The lithological units identified during fieldwork include Mudstone, Sandstone, and Basaltic rock formations. The sandstone unit in the study covers an estimated average thickness is 237 meters with intercalations of thinly bedded mudstone. The average thickness of each sandstone units (coarse (23 meters), medium (90 meters) and fine-grained (115 meters) sandstone unit) are varying from place to place within the study area. The stratigraphic section logs in four each block (Geza Washa, Dalota, Ruka, and Gosh Wiha) shows coarsening upward indicating the depositional environment transition from deep marine to the fluvial environment. The results of the study reveal the geological history and paleoenvironmental conditions of the Mesozoic sedimentary rocks in the Lemi area. This study contributes to our understanding of the geological processes that have influenced the formation of the Lemi area and provides valuable interpretations of regional geology.

Potencial petrolífero remanescente do Brasil - Estado da arte 2023

Petroleum and its byproducts will continue to be humankind’s primary energy source for at least 50 years. Brazil is already one of the main suppliers of this raw material and will continue as such for the next decades. Several large sedimentary basins in Brazil are practically untouched by exploration, especially in the deep and ultra-deep water realms. There are also large tracts of unexplored areas in basins that already have discoveries, reserves and hydrocarbon production. The objective of this work is to make predictions about the remaining petroleum potential of the Brazilian basins. The predictions are made based on the big data bank acquired by the petroleum industry in Brazil in the last 83 years, based on the most updated concepts in petroleum geology, and mainly on my 45 years of experience as an explorationist. Our final forecast for the remaining petroleum potential of Brazil lies in the range of 50-100 billion barrels of oil equivalent recoverable (boer) (prospective resources, already identified or not, but still needed to be discovered). The basins that will contribute the most to realizing this potential are Santos/Campos, Pará-Maranhão/Foz do Amazonas/Barreirinhas, Pelotas and Paraná; besides, in a lesser scale, but still significant, Sergipe-Alagoas, Espírito Santo, Camamu-Almada, Solimões and Parnaiba. We are perfectly aware that Geology is a complex and astounding science. New data, innovative new technologies and creative concepts never formulated can quickly destroy these predictions, for better or worse.

The effects of changing channel retention: Unravelling the mechanisms behind the spatial and temporal trends of suspended sediment in the Rhine basin

The effects of changing channel retention: Unravelling the mechanisms behind the spatial and temporal trends of suspended sediment in the Rhine basin

A NEW MID-MIOCENE WOOD FROM OCNA DEJ SALT MINE

Ocna Dej is an iconic locality for salt mining in Transylvania, being located in the north - north-western area of the Middle Miocene sedimentary basin of Transylvania. In this salt the fossils are rare and refer strictly to plant remains (fragments of wood, pine cones, etc.). A sample of charred wood collected from the area of Ocna Dej salt deposit of Middle Badenian age (Wielician) was submitted to a microscopic study for a taxonomic assignation. It was identified as Cupressinoxylon sp. aff. Thujoxylon sp. as a remain of the synchronous vegetation. This wood type is found for the first time in Ocna Dej salt and could contributes to the paleo-environmental reconstruction of this area. Obviously, wildfires occurred at that time around the marine sedimentary basin of Transylvania.

Fracture stratigraphy in oil-rich shale of the Upper Xiaganchaigou Formation (upper Eocene), western Qaidam Basin

Natural fractures in wells from oil-rich shale of the Upper Xiaganchaigou Formation in Qaidam Basin, the largest Cenozoic sedimentary basin in the Tibetan Plateau, vary systematically by stratigraphic position, allowing reconstruction of fracture generation processes during regional tectonic deformation. Compacted fractures, layer-bounded fractures, and low-angle (or bed-parallel) fractures were widely identified in oil-rich shale cores obtained from vertical wells. The layer-bounded fractures can be subdivided into two sets: one prevalent in light-colored (low gamma-ray) stiff layers and arrested by dark-colored (high gamma-ray) compliant layers, the other set primarily confined to the dark-colored compliant layers. The strikes of layer-bounded fractures, revealed by horizontal well FMI logs, are dominantly N60°-80°E and N10°-30°E within the light and dark intervals respectively. These strikes are consistent with natural hydraulic fracturing of the light layers during the Oligocene and the dark layers during the Middle Miocene-Holocene, based on a regional anticlockwise rotation of the compressional strain orientation. The abutment of layer-bounded fractures against low-angle (or bed-parallel) fractures in dark layers implies that the low-angle fractures were hydraulically fractured under a vertical least compressive stress during the Early Miocene, which produced the most intense tectonic compression. Layer-bounded fractures generally remain unmineralized in the dark layers but were mineralized in the light layers, suggesting that fractures confined in light layers would not decrease the sealing capacity of the shale oil system and fractures confined in dark layers can increase the pore space of shale oil storage. The Oligocene and Early Miocene fractures represented mechanical flaws that affected the initiation of Middle Miocene-Holocene fractures, implying that all natural fractures may alter hydraulic fracture stimulations to some extent.

Firmgrounds and hardgrounds in the Coniacian carbonate platform of the Iberian basin: Origin and model for development of omission surfaces in tidal environments

Distinctive erosional and omission surfaces occur at several stratigraphic levels in the tidal carbonates of the 3rd-order Coniacian sequence (Iberian Basin). They are ancient analogs of omission surfaces developed on lithified carbonates in subaerial and coastal settings. Omission surfaces consist of (i) firmground Glossifungites ichnofacies (Balanoglossites-Thalassinoides); and (ii) hardground Trypanites ichnofacies (scalloped and planar surfaces and Gastrochaenolites-Entobia surfaces). Firmgrounds are also related to erosion or ferruginous crusts. Hardground surfaces are related to bioerosion, dissolution and physical erosion. Grain size and textural features in Balanoglossites and Thalassinoides firmground surfaces are essentially the same, suggesting that even bathymetry could be similar. Several stages in hardgrounds consist of different, scalloped or planar surfaces related to bioerosion, dissolution and physical erosion. Gastrochaenolites-Entobia borers represent a major change in the trace fossil associations and imply different processes in their origin, being originated at slightly different depths with Gastrochaenolites representing shallower environments. The studied field sections display a cyclicity on the scale of meters that tentatively reflects the presence of 4th-order parasequence sets. Two kinds of sedimentary discontinuities have been used for correlation: omission surfaces and ferruginous crusts representing regional sea level falls and rises. Part of the described surfaces does not appear to have been previously recognized in older carbonate deposits. Their common presence of similar surfaces along modern coasts and in karst terrains, as well as their abundance in the Coniacian sequence, suggests that they might also be abundant in the geologic record in other sedimentary basins for defining palaeoshorelines.

Prediction of reservoir properties and fluids using rock physics techniques in the Rio Del Rey Basin, Cameroon

The application of rock physics modeling has been a breakthrough in oil and gas industry and has greatly managed exploration and interpretation risk. In the Rio del Rey Basin, the rock physics method was used to ascertain the reservoir's characteristics and relate them to the elastic characteristics. Using conventional techniques to connect to the elastic properties and assess various rock physics diagnostics, the estimated petrophysical parameters were water saturations, porosity, and shale volume. By connecting the saturated bulk modulus to its porosity, the bulk modulus of the porous frame, the bulk modulus of the mineral matrix, and the bulk modulus of the pore filling fluids, the Gassmann fluid replacement modeling was used to simulate various fluid scenarios. Finally, an evaluation was conducted on rock physics boundaries and cement models. The reservoirs are rated as extremely good based on the results. The rock physics model generated showed the friable sand model is a suitable model for the said basin and the rock physics bounds that were evaluated indicated that the sediments are deposited below the critical porosity and less compacted thereby depicting a soft sand model. Conventional petrophysical study would not be able to reveal the clustering of the gas sands from the brine sand and the shale zone in connection to the geologic trend as demonstrated by the rock physics template. The anticipated model will be useful to extrapolate the study to other sedimentary basins in Cameroon and estimate porosity from the impedance acquired from seismic data throughout the basin.