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Late Cretaceous-Miocene foraminiferas were recovered from the BG-1 well in the offshore Eastern Dahomey Basin. Four (4) lithostratigraphic units comprising Ogwashi-Asaba, Upper Araromi, Lower Araromi and Afowo Formations have been delineated and assigned based on the textural characteristics of the sediments. Forty-nine (49) foraminiferal species were identified, with a total count of 47 calcareous species (96%) comprising both planktonic and benthic forms and two arenaceous forms (3%). Seven (7) foraminiferal zones were recognised and dated from the Upper Cenomanian to Late Miocene age. The Globotruncana aegyptica zone, marked by the disappearance of the Maastrichtian forms at 3060 ft, coincided with the appearance of the Early Paleocene benthic forms such at the Anomalinoides umboniferus- Anomalinoides midwayensis zone. The Cretaceous-Paleogene (K-Pg) boundary was recognised at 3060 ft. Seven MFSs and SBs dated from the Upper Cenomanian and Upper Miocene ages were identified in the sequence stratigraphic analysis. The stacking patterns of the lowstand and highstand systems tracts reveal the interplay of progradational and aggradational parasequence signatures of siltstones and sandstone lithologies. The paleodepositional sedimentary packages of the BG-1 well are recognised from the Inner-Neritic to Bathyal environment. The sequence stratigraphic integration of lithofacies and foraminifera assemblages in this study has created a model of the distribution of the elements in the hydrocarbon system of the offshore Eastern Dahomey basin. Therefore, this study will underscore the critical role of sequence biostratigraphy in enhancing the accuracy and efficiency of exploration and development efforts in the hydrocarbon industry.

The Xujiahe Formation in the upper Triassic is characterized by 5 members (Member-1 to Member-5), representing three cycles from coarse to fine. The overall facies architecture of Xujiahe Formation implies deposition in a braided delta environment. High resolution sequence stratigraphy was performed based on outcrops, core observations, well logs and seismic interpretations. The Xujiahe Formation is interpreted as a 3rd sequence, comprising a transgressive systems tract (TST) and a regressive systems tract (RST). Within this 3rd sequence, six 4th sequences are recognized. The TST(FS1–FS4) mostly comprises subaqueous distributary channel fills ,distal bars, and shallow-lake facies, capped by the Belt Child mudstone that includes the maximum flooding surface(MFS). The RST(FS5–FS6) mainly contains subaqueous distributary channel deposits. Based on thin-sections, high-pressure mercury-intrusion analyses, the sandstone cements primarily consist of chlorite, calcite , secondary quartz and dolomite, filling pores. This study reveals quality reservoirs are mainly distributed in the lacustrine transgression and retrogradation strata in the base-level rising stage and in the stable period of the transition from base-level decline to base-level rise, but are seldom developed in the lacustrine retrogradation strata in base-level falling stage. The variation of accommodative space and sediment supply controls the vertical sand body assemblage, the distribution of sand body and the distribution characteristics of high-quality reservoirs in the study area.

Glaucony occurrences have been reported both from exposed transgressive and overlying highstand system tracts. However, its occurrences within highstand deposits are often invoked as the result of underlying condensed section reworking. Detailed textural, mineralogical and geochemical reports of glaucony grains in highstand deposits remain elusive. The northern Gulf of Cadiz shelf (SW Iberia) offers a unique opportunity to investigate late Holocene glaucony authigenesis in a well-documented time-stratigraphic context, where transgressive deposits are locally exposed on the seafloor and are laterally draped by highstand muddy deposits. In this study, glaucony grains extracted from a core retrieved from a highstand muddy depocenter off the Guadiana River were investigated by means of digital microscopy, X-ray diffraction (XRD), and electron microscopic methods (FESEM-EDX and TEM-HRTEM). To better constrain the glaucony origin (autochthonous vs. allochthonous) in highstand muddy deposits, glaucony grains from surficial samples—taken from exposed transgressive deposits—were also investigated. Glauconitization in the studied core can be largely attributed to the replacement of faecal pellets from c. ~4.2–1.0 cal. ka BP. Both XRD and TEM-HRTEM analyses indicate that glaucony consists mainly of an R1, with a minor presence of R0, smectite-rich (nontronite) glauconite-smectite mixed-layer silicate, made up of 35–75% glauconitic layers and 65–25% of interstratified smectite layers. At the mineral lattice level, minor individual 7Å layers (berthierine) were also identified by HRTEM. Shallow radial cracks at the pellet surface, along with globular and vermiform-like biomorphic to low packing density lamellar-flaky nanostructures, mineralogical properties, and K-poor content (average 0.4 atoms p.f.u.) indicate a scarcely mature glauconitization process, attesting to formation of the grains in situ (autochthonous). Glaucony grains from exposed transgressive deposits, i.e., in the tests of calcareous benthic foraminifera, do not share a genetic relationship with the grains investigated in the highstand deposits, thus supporting the autochthonous origin of glaucony within the highstand deposits. Our combined dataset provides evidence of a multiphase history for autochthonous glaucony formation in the Guadiana shelf, as its genesis is traced to both transgressive and highstand conditions. While eustatic sea-level changes favoured glaucony formation under transgressive conditions, factors such as protracted low sediment supply and the establishment of a strong nutrient-rich upwelling system in the study area promoted glaucony development during late Holocene highstand conditions.

The Sergipe–Alagoas Basin, in northeastern Brazil, has extensive exposures of carbonate rocks that may be studied as analogues to hydrocarbon reservoirs. The outcrops are equivalent to the pre-salt and post-salt reservoirs of the Campos and Santos basins, the most important hydrocarbon exploration targets nowadays in Brazil. Outcrops and well logs of the Riachuelo Formation, the most important for analogue studies of Cretaceous marine carbonate reservoirs of the Campos Basin due to the great variability of facies, are described and interpreted to identify the depositional cycles and stratigraphic sequences. Three unconformities formed during the initial drift phase of the basin are recognized. The depositional setting of the studied section changes from a siliciclastic-dominated continental to shallow-marine mixed siliciclastic-carbonate at the base to a shallow-marine carbonate platform in the upper part. The transgressive–regressive (T–R) sequence model was used for the stratigraphic analysis, leading to a stratigraphic framework of three third-order T–R sequences, with an estimated duration of approximately 2.0, 4.5 and 1.5 Ma, respectively. Consequently, the higher frequency cycles identified in the well logs represent a timing of circa 140,000 years, and are interpreted as fourth-order depositional cycles.

Shale reservoirs, the most important unconventional resource, are difficult to characterize. Shale formations require detailed interpretation of geological, petrophysical, and geochemical analyses, and an integration of these disciplines. In terms of geological interpretation, the commonly used sequence stratigraphy analysis includes a lithofacies analysis. The application of sequence stratigraphy to shales facilitates the ability to relate between lithofacies and mineral composition, petrophysical parameters, and kerogen contents, which are affected by depositional setting. The classification of lithofacies is indispensable for reservoir quality prediction. In this study, porosity, permeability, and TOC content largely depend on lithofacies, and their correlation coefficient is relatively high. The sequence stratigraphic interpretation shows that organic carbon content usually increases within the maximum flooding surfaces and decreases stepwise. However, the relationship between total organic carbon contents and systems tract is less direct and redox dependent.

Effective shale gas exploration is hindered by the need for obtaining high-resolution correlations between shale strata and the need for classifying shale facies. To address these issues, chemostratigraphy, sequence stratigraphy, and shale gas geology methods were integrated to develop a new method known as “chemical sequence stratigraphy,” which was successfully applied to the Wufeng–Lower Longmaxi Formations in the upper Yangtze region. Well Huadi 1 was used as a case study, and detailed data were acquired. Multivariate statistical analyses were applied to three defined indices having different genetic significance, namely: terrigenous input intensity (TII), authigenic precipitation intensity (API), and organic matter adsorption and reduction intensity (OARI). By analyzing the trends of these three indices, the Wufeng–Lower Longmaxi Formations were divided into five fourth-order chemical sequences (from bottom to top): LCW, MCL1-1, MCL1-2, MCL1-3, and MCL1-4. The geochemical facies were named and classified using the chemical sequence stratigraphic framework. The enrichment factor (EF) transformation of elements was conducted to determine whether an element is rich or deficient. The results showed that the favorable geochemical facies in the well were EF-Al deficient, EF-Ca rich, and EF-V rich. The organic matter content and rock brittle strength were then used as chemical parameters, and it was predicted that the LCW and MCL1-1 chemical sequences most likely comprised shale gas sweet spots. This conclusion is consistent with the drilling results and indicates that our proposed method is effective and reliable. This method is further applied to the Changning Shuanghe section, the Shizhu Liutang section, and sections in the Xindi 1 well in the upper Yangtze region. The comparative study of these four sections showed that LCW and MCL1-1 are the key chemical sequences for shale gas exploration and development in the Wufeng–Lower Longmaxi Formations within the Upper Yangtze region.

As an example of an epeiric carbonate ramp depositional system, the world‐class outcrops of the Middle Jurassic Dhruma Formation were studied in the Oman Mountains (Sultanate of Oman). An integrated approach was followed: facies analyses were combined with quantitative sequence‐stratigraphic methods as well as bio‐ and chemostratigraphy. Depositional environments range from peritidal to lagoonal and ‘shoal‐like’ environments. A conspicuous four‐level hierarchy of cyclicity was identified. This is substantiated by facies trends and specific cycle indicators such as various types of discontinuity surfaces, biofacies changes, and a suite of quantitative‐ and semi‐quantitative sequence‐stratigraphic methods like facies stacking pattern plots, facies percentage, bed‐thickness and bio‐component diversity plots, as well as diagrams representing the environmental range and facies belt width per high‐frequency sequence. Potential reservoir facies are present in the form of peloidal and oolitic grainstones; potential baffle/seal facies as vastly extensive mudstones and marls. A transition from peritidal to low‐energy lagoonal deposits to increasingly high‐energy deposits can be observed towards the top of the Dhruma Formation representing a landward shift of the depositional environment. This study may be useful as outcrop analogue for the hydrocarbon‐bearing parts of the Dhruma in the subsurface of the Arabian Plate and for similar epeiric carbonates elsewhere. The Middle Jurassic Dhruma Formation in outcrops of the Oman Mountains as an example of an epeiric carboante ramp depositional system. Sequence‐stratigraphic analysis with the help of quantitative‐ and semi‐quantitative methods.

This work deals with the plankton stratigraphy of the subsurface Upper Cretaceous-Palaeogene succession of theEast Bahariya Concession based on planktonic foraminifera and calcareous nannofossils. The examination of the cuttings from five wells: AQSA-1X, KARMA-E-1X, KARMA-3X, KARMA-NW-1X and KARMA-NW-5X is biostratigraphically evaluated. It is possible to identify the planktonic foraminifera as well as the calcareous nannofossil biozones. The analyses of calcareous nannofossils revealed the presence of several hiatuses. Information obtained from well data such as seismic facies analysis for the studied area has enabled classification of the Upper Cretaceous Palaeogene succession into five major 2nd order depositional sequences, separated by four major depositional sequence boundaries (SB1, SB2, SB3 and SB4). The Upper Cretaceous-Palaeogene succession in the East Bahariya is dividedinto 17 systems tracts. These systems tracts are: 7 System tracts of probable Cenomanian age, (the sequence stratigraphic framework as well as the cycles and system tracts of the Cenomanian Bahariya Formation match well with thoseof CATUNEANUet al., 2006); 4 System tracts of Turonianage, 2 System tracts of Campanian-Maastrichtian ageand 4 System tracts of Eocene age.

Some aspects on the age and correlation of the upper Barremian-lower Aptian stratigraphic units of the NW Maestrat Basin were uncertain prior to this study, due to the differing lithostratigraphy of the marginal Oliete subbasin compared to the more depocentral Galve and Morella subbasins. New magnetostratigraphic, ammonite and sedimentological data presented in this study refine the age and sequence stratigraphy of the upper Barremian-lower Aptian succession, enabling a direct and precise correlation across these subbasins. Three third-order TR sequences are identified. The lower boundary of Sequence 1 corresponds to a transgressive surface found on top of the continental red beds of the lower Morella Fm. These beds are equivalent in age to the continental succession of the upper Blesa Fm. (Fm. (Oliete subbasin). The boundary between the M1 and M0r magnetozones (latest Barremian) is found above this surface, in the lower part of the Alacón Fm. Sequence 1 includes the lower part of the Alacón Fm., which passes basinwards to the upper Morella and Xert formations. Sequence 2 corresponds to the upper part of the Alacón Fm and basinwards to the Cap de Vinyet and Barra de Morella members of the Forcall Fm. The boundary between the M0r and C34n magnetozones (earliest Aptian) is found towards the lowermost part of Sequence 2. Sequence 3 includes the Josa Fm and its offshore equivalents, the Morella la Vella Mb. and the Villarroya de los Pinares Fm. Additionally, the overall facies distribution in successive depositional stages is reconstructed, describing the lateral transition from marginal protected to open marine areas. The improved chronostratigraphic framework presented here will enable more accurate correlations with other subbasins of the Maestrat Basin, and the reconstructed sedimentary evolution may be useful for the interpretation of other Lower Cretaceous successions of the Tethys.

Landscapes respond to climate, tectonic motions and sea level, but this response is mediated by sediment transport. Understanding transmission of environmental signals is crucial for predicting landscape response to climate change, and interpreting paleo‐climate and tectonics from stratigraphy. Here we propose that sediment transport can act as a nonlinear filter that completely destroys (“shreds”) environmental signals. This results from ubiquitous thresholds in sediment transport systems; e.g., landsliding, bed load transport, and river avulsion. This “morphodynamic turbulence” is analogous to turbulence in fluid flows, where energy injected at one frequency is smeared across a range of scales. We show with a numerical model that external signals are shredded when their time and amplitude scales fall within the ranges of morphodynamic turbulence. As signal frequency increases, signal preservation becomes the exception rather than the rule, suggesting a critical re‐examination of purported sedimentary signals of external forcing.