Flooding Surface Research Articles

Pre‐Vegetation Mixed (Wave‐Tide) Energy Trangressive Nearshore Sedimentation: Evidence From the Proterozoic Passive Margin Sequence of NW Himalaya, India

ABSTRACTThe coupled evolution of the Earth's atmosphere–biosphere system through time has caused irreversible changes in the geodynamics as well as surface processes and sedimentation patterns. One such significant change took place in sedimentation in the Palaeozoic (i.e., Silurian) by the appearance of vascular vegetation. While the impact of evolving vegetation on the terrestrial fluvial environment has been relatively well documented, vegetation‐induced effects down the system in marginal or nearshore marine settings have undergone little study. The Meso‐ to Neoproterozoic Rautgara Formation exposed in the Himalayan Orogenic Belt of NW India, offers a chance to study a well‐preserved fluvial–marine transition to nearshore sedimentation before the appearance of vascular vegetation. A detailed sedimentological analysis identifies six genetically linked facies associations (FA) probably deposited in barrier, back‐barrier, and subtidal deltaic environments. Contrary to the other transgressive barrier models (where beach‐barrier overlie the back barrier environments), in the present case, wave‐dominated barrier deposits mostly occupy the basal part of the stratigraphy. In the middle stratigraphic level, back‐barrier deposits lack thick mud flats and show a dominance of sandstone over mudstone. Stacked subtidal sand bar facies association represents the top part of the sequence. Two sequence stratigraphic surfaces, that is, subaerial unconformity and maximum flooding surface, have been identified and the whole succession is interpreted in terms of HST and TST. Barrier and back‐barrier sediments are deposited during HST and TST, respectively. Subtidal deltaic system developed in late TST. The lack of frequent interbedding between the barrier and back‐barrier facies indicates negligible landward migration of the barrier and demonstrates system stability. The barrier system might have resulted from vertical aggradations akin to modern vegetated systems. The study portrays that sandy barrier systems are common in the Proterozoic. Vegetation and thick mud flats are not always essential for the stability of a barrier‐beach system.

Quantifying paleoecological impact of the OAE1a on shallow marine ecosystems from southeastern France

Climate and environmental instability during the early Aptian culminated with the unfolding of the Oceanic Anoxic Event (OAE) 1a, which resulted in the deposition of black shales in deep marine settings and a typical negative spike followed by a positive excursion in δ13C values. In Vercors (southern France) the Urgonian platform developed prior to and coeval to the OAE1a, but the impact of this paleoenvironmental crisis on the ecology of benthic ecosystems is yet to be quantified. We gathered field and petrographic data to identify sequence boundaries and maximum flooding surfaces that are biostratigraphically dated and correlated between four localities within the study area. A composite δ13C curve is built where the C3 to C7 isotope segments from the literature are identified, pinpointing the onset of the OAE1a above the last episode of deposition of Urgonian facies rich in rudist bivalves. Furthermore, thin section point counting data are used to quantify the proportion of allochems in samples and to trace changes in the ecology of ecosystems. The principal component analysis of point counting data helps define ecological tiers: a diversified, photozoan association with rudists, green algae, and benthic foraminifera dominated ecosystems before the OAE1a and up to the C7 segment, while a less diversified heterozoan association with bryozoans and crinoids developed after the OAE1a. To explore the triggers for this change, the principal component analysis of elemental geochemical data highlights an increased nutrient and detrital input as major triggering mechanisms for ecological adjustments and changes in the biodiversity of ecosystems. In particular after the OAE1a, an increase in detrital and nutrient input leads to the replacement of photozoan by heterozoan assemblages more adapted to these stressful conditions. This research directly links paleoenvironmental deterioration to paleoecological changes and quantifies the amount of adaptation of ecosystems.

Recognition of a cryptic maximum flooding surface in shallow marine carbonate sequences using geochemical (Y/Ho) proxy data

ABSTRACTSince diagnostic primary depositional sedimentary structures and depth‐dependent grain‐size trends are rarely preserved, building a comprehensive sequence stratigraphic framework for the vast majority of the Phanerozoic carbonate platform sequences is pending. Among the two most important sequence stratigraphic surfaces, while the subaerial unconformity can be reliably identified by either karst development or the appearance of siliciclastic materials, the demarcation of the maximum flooding surface remains difficult in lithologically uniform shallow marine carbonate sequences. The present study attempts to identify the globally documented maximum flooding surface within the body of the negative carbon isotope excursion of the Palaeocene–Eocene Thermal Maximum recorded in the shallow marine carbonate platform sequences. The results show that, along with the carbonate microfacies, the yttrium to holmium ratio (Y/Ho ratio) of the carbonate fraction reliably records the sea‐level changes. A Y/Ho ratio between 70 and 80 demarcates the stratigraphic position of the maximum sea‐level state (the most open marine condition in the studied interval) and maximum flooding surface in the studied sections. Since the Y/Ho ratios remain relatively stable throughout diagenesis, they can be used for maximum flooding surface identification in shallow marine carbonate platform sequences. The possibility exists that the same method can also be applied to the mixed siliciclastic–carbonate systems.

Study on the relationship between shale organic matter development and paleowater depth—A new understanding of the condensed section

Recent studies dispute the long-standing belief that highly organic-rich shales are predominantly linked to condensed section (CS) at the maximum flooding surface (MFS), proposing instead that they more commonly develop in shallow waters along basin margins. This hypothesis, however, has not been thoroughly investigated. Our study, focusing on the pivotal regions of the Longmaxi Formation and the Chang 7 Member for marine and continental shale exploration in China, integrates sequence stratigraphy with analyses of total organic carbon (TOC) and elemental geochemistry to pinpoint the environments conducive to the formation of organic-rich shales. The most organic-rich intervals, specifically the bottom of the Longmaxi Formation and the mid-to-lower Chang 73 sub-member, are located within the transgressive systems tract (TST), showing higher TOC levels in the middle to lower TST, compared to the CS of the MFS. The formation of high organic matter shale is related to warm, humid, and dysoxic shallow waters with minimal terrigenous influx and high primary productivity. We found a pronounced inverse relationship between organic matter concentration and water depth, with deeper waters promoting the decomposition and recycling of organic matter during sedimentation, thereby diminishing the TOC content. Moreover, volcanic activity also affected the organic enrichment in the Chang 7 Member. With high primary productivity, organic matter tends to accumulate in dysoxic slope zones. Consequently, high-organic content shale intervals are generally situated in shallow, dysoxic water environments, suggesting that the CS of the MFS may actually represent organic-poor intervals with limited source rock potential. The results of this study are of great significance for shale oil and gas exploration in China, and provide a new direction for the discovery of shale oil and gas sweet spots.

Sequence Stratigraphy and Depositional Environment of the ‘Perahu’ Sand, Bekasap Formation, ‘DAP’ Field, Central Sumatera Basin

Abstract The ‘DAP’ Field is one of the oil and gas fields within the Central Sumatera Basin that is proven to have hydrocarbon reserves. One of the proven reservoirs in the ‘DAP’ Field is the ‘Perahu’ Sand, Bekasap Formation. This study aims to determine the depositional environment and facies distribution focusing on the ‘Perahu’ Sand, Bekasap Formation through a sequence stratigraphic approach. The research was based on an integrated analysis of sedimentary facies from one core data and a key well log to interpret the facies association. Then the key well is correlated to eight other well logs with the help of sequence stratigraphic concept to determine the depositional facies distribution and succession at the study interval. Lithofacies that are identified from core data were interpreted as floodplain, tidal channel, mud flat, mix flat, and sand flat, hence the depositional environment of ‘Perahu’ Sand was interpreted to be a tide-dominated estuarine. The parasequence set level of Bekasap Formation was interpreted to be in a transgressive system tract, with the ‘Perahu’ Sand divided into three flooding surfaces that is FS3, FS4, and FS5. The FS3 distribution consists of tidal-fluvial channel, crevasse splay and floodplain facies. The FS4 distribution consists of two tidal channels and one sand flat facies. The FS5 distribution consists of one sand flat facies. The depositional trend of the ‘Perahu’ Sand shows a northeast to southwest trend, with basinward toward southwest.

Evolution of Neoproterozoic siliciclastic Kerur Formation in the light of sequence stratigraphic framework: Badami Basin, Karnataka, India

Field-based sedimentology, state of the art facies analysis and sequence stratigraphic framework analysis have revealed the controls of local and global tectonics, basin-marginal slope, climate and changes in relative sea level (RSL) over the sedimentation pattern and evolution of a Neoproterozoic Kerur Formation within the Badami Group of Kaladgi Supergroup in India. The entire succession shows three major cycles of deposition. Facies study and fluvial architectural elemental analysis suggest considerable variations in depositional environments as well as palaeogeography. A transition from basin-margin alluvial cone deposits to braided system, initially with fluctuating ephemeral flows then to a steadier semi-perennial nature, is discernible within the 1st cycle, in response to decreasing depositional slope with rising water table. The initial alluvial cone and braided ephemeral streams of high slope areas is designated as a product of low accommodation systems tract (LAST), while the semi-perennial system with steadier flows, representing the axial river of the initial rift valley, appears to be a product of high – accommodation systems tract (HAST). The 2nd cycle begins with a perennial and steady braided river system and grades upward to a shallow marine succession, comprising wave-dominated, well-sorted sandstone, with a granular transgressive lag at the base. Thus, the bottommost fluvial interval of the 2nd cycle constitutes the lowstand systems tract (LST). The marine succession represents deposits of outer shelf offshore to foreshore-beach settings and is composed of an initially deepening and fining upward transgressive systems tract (TST), followed by a coarsening and shallowing upward highstand systems tract (HST) with a maximum marine flooding surface (MFS) in between, demarcated by a shale-rich condensed zone. The 3rd cycle, with its prograding alluvial fan and aggrading braided fluvial deposits and restricted occurrence, represents only the low accommodation systems tract (LAST) with a subaerial unconformity at the base. The basin evidently initiated in the western sector, followed by its eastward expansion during the first major rejuvenation of the basin margin faults, after the deposition of the 1st cycle. After the basin-wide deposition of the 2nd cycle, restricted development of the 3rd cycle took place in the western sector only, following the second major rejuvenation of the fault system. The proposed sedimentological model, supported by established geochronological constraints, suggests that the sedimentation in the 1st cycle begins with scree cones, alluvial fans and braided ephemeral channel networks, originated from faulted basin margins within a riftogenic setting possibly related to the global-scale extensional tectonics of Rodinia breakup. After the expansion of the basin, the marine inundation has been correlated to the transgression that possibly took place during the post-rift maturation stages.

Identification of Milankovitch sedimentary cycle in Fengcheng Formation, Mahu depression: a case study of well Maye 1

The sedimentary cycle of Fengcheng Formation in Junggar Basin changes rapidly and is difficult to identify. The low classification accuracy of high-frequency fine-grained sedimentary cycles restricts the exploration of unconventional shale oil and gas. Full-interval coring of well Maye 1 provides a solid foundation for small-layer research. In this paper, the high-frequency sedimentary cycle of Milan kovitch in Fengcheng Formation is studied by means of spectral analysis and wavelet transform, and the shale sweet spot is identified. The long period of eccentricity of 405ka, short period of eccentricity of 100ka and long period of axis slope of 42736a can be used as semi-quantitative basis for the classification of the fourth, fifth and sixth sequences. The Fengcheng Formation can be divided into 2 quaternary sequence cycles, 9 quaternary sequence cycles and 16 quaternary sequence cycles. A long period of eccentricity of 405ka can identify large-scale lake recessional and recessional, and there is a maximum lake flooding surface in the middle of the second Fengcheng Formation, which corresponds to high abundance of organic matter and high hydrocarbon generation potential. The 100ka short period eccentricity can identify the sweet spot layer, and there are 8 sweet spots in the well Maye 1, which is consistent with the results of nuclear magnetic interpretation. The research results provide a semi-quantitative basis for the classification of high-frequency sedimentary cycles and the identification of sweet spots of Fengcheng Formation in Mahu Sag, Junggar Basin.

Seismic sequence stratigraphy of Late Albian-Early Turonian successions in SW Iran: Implication for reservoir characterizations and potential for improved reservoir quality prediction

The Late Albian-Early Turonian succession on the Arabian Platform stands out as one of the world's richest hydrocarbon provinces. This study delves into the Seismic Sequence Stratigraphy (SSS) of these successions to unravel reservoir characterization and characterized potential hydrocarbon plays. Utilizing data from five exploration wells, including well logs, selected core data, biostratigraphical information, and chemostratigraphy analysis, alongside a comprehensive 3D seismic volume, enabled the identification of four 3rd-order sequences and multiple 4th-order sequences within the studied successions. Sequence-1 (DS-I), dating back to the Late Albian age, features mudstone and bioclast wackestone in an open marine environment. DS-I is a key sequence, notably witnessing the disappearance of siliciclastic input from west to east in the study area. DS-II (Early Cenomanian) and DS-III (Mid-Cenomanian) were deposited on carbonate platforms with grain-supported facies in shoal and lagoonal depositional environments.A distinct regional unconformity at the Turonian base, evident on seismic sections, aligns with depleted δ18O values on the Cenomanian-Turonian Boundary. The maximum flooding surfaces of DS-I and DS-II are characterized by continuous reflectors with negative amplitude. Furthermore, the lateral grading of reservoir facies and their intercalation with non-reservoir facies within 4th-order sequences suggest that reservoir facies heterogeneity is strongly influenced by depositional processes at this scale. Potential reservoirs, particularly in the Highstand System Tract (HST) of each 3rd sequence, are highlighted, with DC-III's HST standing out, hosting patch reef facies resulting from local tectonic activities and carbonate build-up movements.

Chemostratigraphy of the Cretaceous Yolde Formation in Yola Sub-Basin, Northern Benue Trough, Ne Nigeria

This research aims to determine the chemostratigraphy of the Yolde Formation. The formation has been inadequately studied systematically in the light of chemostratigraphy. The existing works on the formation either lack representativeness in terms of the proxies used or are subjective during their division procedures. From the field studies, five (5) samples of sandstone and shale units of the Yolde Formation were collected. The samples were analyzed for both major and trace elements using an X-ray fluorescence machine. The following geochemical parameters were studied; Al2O3, Al2O3/Fe2O3, KO2/Al2O3, TiO2/Al2O3, CaO, Cr, Rb/Sc, and Zr. From the studies, six (6) chemozones were identified in the Yolde Formation. Transgressive and regressive depositional sequences were observed with a significant sequence boundary of maximum flooding surface which is a time-significant feature. The chemostratigraphic scheme could not only be comparable to the regional sequence stratigraphic scheme but also more objective and higher resolution. This research gives a systematic chemostratigraphic analysis of Yolde Formation, which testifies to the feasibility and potential of the usage of chemostratigraphy for stratigraphic development.

Mixed siliciclastic-carbonate-tuffaceous sedimentation in a rift lacustrine basin: A case study of the Lower Cretaceous Jiufotang Formation in the Luxi sag, Songliao basin

The Lower Cretaceous Jiufotang Formation lacustrine successions in the rift Luxi sag, Songliao Basin are characterized by mixed siliciclastic-carbonate-tuffaceous and organic-rich deposits. Ten facies were recognized and were formed in fan delta, delta, littoral-sublittoral lacustrine and deep lacustrine environments. A depositional sequence characterized by significant changes in facies and lake regime has been defined, and is divided into lowstand systems tract (LST), transgressive systems tract (TST), and highstand systems tract (HST) that are separated by sequence boundaries, initial flooding surfaces, and maximum flooding surfaces, respectively. During the LST, the delta and fan delta deposits covered the marginal area and extended into littoral-sublittoral lacustrine and deep lacustrine environments, respectively. During the TST, the areas of delta and fan delta decreased and lake areas increased, and the carbonate-dominated shoals and mixed siliciclastic-carbonate shorelines occupied the edge of the Majiapu highland belt. During the HST, the lake areas further expanded, and the fan delta deposits extended into deep lacustrine environments and formed deposits of underflows and turbidites. A depositional model in the rift lacustrine Luxi sag is proposed, incorporating the effects of tectonics and sediment supply, climate and carbonate production, hydrodynamic conditions, and lake-level fluctuations. During the LST, the active tectonic movement, high input of siliciclastic sediments, and subaerial volcanic eruptions resulted in the wide distribution of mixed siliciclastic-tuffaceous sedimentation. During the TST, the brackish lake water controlled by periodic dry and hot climate facilitated the carbonate deposition in shallow water, and tractional currents onto the lake shore carried sediments to form the mixed siliciclastic-carbonate-tuffaceous facies. During the HST, more humid climate and increased runoff allowed formation of widely distributed, mostly oil shale-rich deposits, and the gravity flows carried the sediments into the deeper part of basin to form the mixed siliciclastic-carbonate-tuffaceous facies. The depositional model of mixed deposits in this rift lacustrine basin has been proposed here in order to encourage comparison with other similar basins.

3D static modeling and sequence stratigraphy using well logs and seismic data: An example of Abu Roash G member in Bahga oilfield

This research uses both three-dimensional (3D) modeling and geologic well control to piece back together the architectural parts of the Late Cretaceous formations. The goal is to figure out the sizes, directions, locations, and controls of the layers of the fluvial sandstone reservoirs. Sequence stratigraphy is essential for 3D reservoir modeling and petroleum geology understanding in the Bahga oilfield. The purpose of this work is to create a static model that shows the layers and facies distribution in the reservoir interval. We will use data from nine well logs and 22 seismic lines calibrated by the Abu Roash G Member reservoir core intervals to accomplish this. The petrophysical study discovered three parts in the Abu Roash G Member reservoir rock: channel fill that is affected by tides, channel fill that is dominated by tides (intertidal sands), and channel top with lenticular bedded sandstone. The model's findings point to the existence of an NNW-oriented sand body, which could be a prime location to produce hydrocarbons. The original oil in place (OOIP) is about 3,438,279 Stock Tank Barrels (STB), and the oil reserve reaches up to 1,031,484 (STB). Sequence stratigraphic analysis using seismic and well log information (SB) reveals that the Upper Cretaceous AR/G reservoir of the Bahga field is characterized by third- and fourth-order stratigraphic sequences, which are constrained by three Maximum Flooding Surfaces (MFS) and two Sequence Boundaries. The integration of the derived geological model and sequence stratigraphic results can lower future extraction risk by identifying the locations and trends of the geologic facies with the necessary petrophysical properties for the hydrocarbon accumulations.

Stratigraphy and depositional history of the Aguja Formation (Upper Cretaceous, Campanian) of West Texas, southwestern USA

Abstract Although the Aguja Formation (West Texas, southwestern USA) and its fossil vertebrate fauna have been known for over a century, its basic stratigraphic requisites (type area and type section) have not been formally documented. The formation is herein subdivided into a series of formal members, and a lectostratotype section is proposed. Lithostratigraphic and biostratigraphic subdivisions are documented and integrated with geochronologic data to provide an age model for the formation. Four terrestrial vertebrate biozones are proposed. There are at least four major depositional intervals represented in the Aguja and intertonguing Pen Formations. An initial progradational deltaic succession is recorded by the La Basa Sandstone and lower part of the Abajo Shale Members of the Aguja Formation. A second phase of deposition resulted in a retrogradational shoreface succession that includes the upper part of the Abajo Shale, overlying Rattlesnake Mountain Sandstone Member, and lower part of the McKinney Springs Tongue of the Pen Formation, up to a skeletal phosphate bed interpreted to represent the maximum flooding surface. The third phase of deposition comprises a progradational deltaic succession that includes the upper part of the McKinney Springs Tongue, Terlingua Creek Sandstone Member of the Aguja Formation, and lower part of the Alto Shale Member of the Aguja Formation. This third succession records eastward migration of the strandline and withdrawal of the Western Interior Seaway from the Big Bend region. The fourth phase of deposition comprises a series of aggradational fluvial channel and floodplain successions that form the upper part of the Alto Shale Member and is coincident with redirection of stream flow to the southeast. This interval is much thicker in the central part of the Big Bend region, thins to the southwest and northeast, and likely records initial subsidence in the Laramide Tornillo Basin. The upper part of this succession was also contemporaneous with a series of basaltic pyroclastic eruptions, the westernmost expression of the Balcones igneous province. A dramatic constriction in the southern entrance to the Western Interior Seaway through the Gulf of Mexico occurred during this final phase in deposition of the Aguja Formation and corresponds to a shift of stream flow southeastward and to an outbreak of local pyroclastic eruptions. Regional uplift associated with this episode of magmatism is likely responsible for closing the southern aperture of the Western Interior Seaway.

Sequence stratigraphy of the paleozoic successions in Ghadames Basin, southern Tunisia: Insights from integrated interpretation of well logs and seismic data.

The Ghadames Basin is considered as huge intracratonic structure, which preserved over 4000 m of Paleozoic sedimentary succession deposited over the Precambrian Basement. The present work consists of an integrated interpretation of the Paleozoic interval in the Ghadames basin of southern Tunisia using well logs and calibrated seismic data. Thus, the adopted sequence stratigraphic approach allowed the identification of a total of 3 s-order sequences, bounded by Taconic, Caledonian, and Hercynian unconformities recognized as major tectonic discontinuities in the study area. The determined second-order sequences have been further subdivided into fourteen third-order sequences with their associated systems tracts, which are limited by sequence boundaries (SB), and presenting transgressive surfaces (TS), and maximum flooding surfaces (mfs). Each sequence is characterized by a unique stacking pattern and distinctive facies, thus reflecting the lithology and the corresponding depositional environment. These sequences are composed of claystone and sandstone facies deposited in varying depositional environments, ranging from a shallow marine setting during the Ordovician period to a deep marine environment during the Early Silurian. A complex deltaic environment was evidenced during the Late Silurian involving to a fluvial environment during the Devonian period. The integration of well logs and seismic data proved to be an efficient approach in the delineation of sequence stratigraphy, revealing in detail the spatial distribution and sequence organizations within the study area. These later are controlled by the relative sea level variations, with eustasy is being the dominant factor. The obtained results are mainly correlatable with the sequence stratigraphy of North African basins at a regional scale and Snedden and Lee chart (2010) at a global scale.

The record of marine ingression in western Gondwana from Devonian conodonts in the Amazonas and Solimões basins, Brazil

During the Devonian, the Gondwana supercontinent was in a paleogeographic position in high-latitudes, close to the South Pole. The arrangement of continents, tectonic activity, climate fluctuations, and the evolution of marine life played an important role in the marine ecosystems during this period. Conodont occurrences in high-latitudes are scarce. In the Upper Devonian (Frasnian/Famenian) of western Gondwana, conodonts have been found in anoxic black-shale deposits associated with maximum flooding surface (MFS) of a distal platform, in the Barreirinha Formation of the Amazonas Basin and Jandiatuba Formation of the Solimões Basin, in northern Brazil. The fauna is characterized by low diversity and well-preserved platform and ramiform elements of Mehlina gradata, Ozarkodina sp. aff. O. sannemanni, Cryptotaxis sp. and Polygnathus sp. in the Amazonas Basin and Cryptotaxis sp., Parapolygnathus sp., Pandorinellina sp., and Hibbardella sp. in the Solimões Basin. The conodont faunal association and sedimentary succession suggest a marine ingression in cool water conditions to the Devonian sea of the Amazonian region.

Depositional cyclicity of lower Cambrian strata in the NW Himalayas: Regional sequence stratigraphy of the Indian passive margin

Lower Cambrian (538-512 Ma) strata have been deposited in the northern Hazara, Kashmir, Salt Range and Zanskar-Spiti basins, which were undergoing subsidence during this period. However, the southern part of the Hazara Basin remained uplifted (Muzaffarabad-Hazara paleo-high, MHP) and acted as a sediment source. Unlike the previous work, the present paper provides an integrated sequence stratigraphic framework of the Lower Cambrian in this region, based on outcrop data, petrography, and well, seismic and gravity data, thereby enabling a correlation among the basins. In the NW Himalayas (Pakistan), the Lower Cambrian strata outcrop in the Salt Range, northern Hazara and Kashmir basins were penetrated during drilling in the Salt Basin (Potwar, Punjab Platform and Bikaner-Naguar basins). Lower Cambrian stratal terminations and subaerial/composite unconformities formed towards the Sargodha paleo-high and the MHP. The Jehlum and Abbottabad groups are well preserved in outcrops of clastic and carbonate sequences. The top of the Khewra/Sangargali sandstone marks an erosional surface and separates two sequences – a progradational and a retrogradational/progradational sequence. The progradational sequence began with sandstone deposition (Khewra and Tanaki Boulder Bed/Sangar Gali formation), just after Khewrite volcanism (538 Ma), with fining upward cycles during a falling stage system tract. Sea level dropped further, as marked by an intraformational subaerial unconformity, and the fluvio-deltaic facies of a lowstand system tract was deposited; this was again capped by a subaerial unconformity. Once subsidence began, a transgressive systems tract developed in a marginal marine setting. Further transgression occurred and a widespread tidalflat was established. These subtidal facies marked the maximum flooding surface in Jutana and Abbottabad formations and a highstand system tract was developed. During the late stages of the highstand system tract the clastic Baghanwala and Hazira formations were deposited and subaerial unconformities were formed at the top and bottom of these formations. The Kashmir Basin remained uplifted during the late stages of the highstand systems tract and no deposition occurred until the Danian. The maximum flooding surfaces of the subtidal facies are correlatable on both shoulders of the MHP. The deposition ceased in the Middle Cambrian with the intrusion of the Mansehra type granites.

Sequence stratigraphy of the foraminiferal zones F9700 and F9800 in the Niger Delta: A comprehensive litho-sequence approach

Understanding how variations in relative sea level affect reservoir structure requires a thorough understanding of sequence stratigraphy. A detailed sequence stratigraphic investigation was performed on the OML X field to uncover and establish links between concurrently originating hydrocarbon reservoir deposits. The analysis of major stratigraphic surfaces, such as maximum flooding surfaces and sequence borders, was made possible by the integration of well log and biostratigraphic data. The research region includes two palynological subzones, P850 and P860, discovered in the foraminifera zones F9700 (Haplophragmoides 24) and F9800 (Bolivina 46). The study discovered two distinct chronological limitations, which occurred approximately 6.7 million years ago (Ma) and 5.6 Ma, respectively. Furthermore, two maximum flooding surface events were discovered, estimated to have happened at 6.0 Ma and 5.0 Ma. When well log and biostratigraphic data were combined, it was simpler to identify sequences 1, 2, and 3, which correspond to the LST, TST, and HST. The implementation of this detailed methodology facilitated the identification and linking of hydrocarbon sources inside the high- and low-stand system tracts. The findings of the study demonstrated a good link between well-logged log data and biostratigraphy utilizing well-accepted primary stratigraphic surfaces and depositional histories. Furthermore, using fault interpretation and correlation approaches has enhanced our understanding of reservoir geometry and continuity in the field, making it easier to discover potential reservoirs.

Structural and Stratigraphic Reservoir Characterization of “MONI” Field¸ Niger Delta.

Reservoir characterization of “MONI” field of the Niger Delta has been carried out using well log and seismic data. The study is aimed at delineating structural and stratigraphic features associated with hydrocarbon entrapment of the field. Lithostratigraphic correlation reviewed two main lithologies which are reservoir sands and seal shales. Well log correlation and interpretation across the field indicates – main stratigraphic bounding surface which include two sequence boundaries and one maximum flooding surface. This indicates about three depositional sequences exists in the study area. Stacking patterns (progradation, retrogradation, and aggradation) were delineated and interpreted as lowstand system tract (LST), highst and system tract (HST), and transgressive system tract (TST). The alternation of LST, HST and TST offers good reservoir and seal for the hydrocarbon accumulation. The depositional environment of the reservoirs ranges from subaerial channel deposits, barrier bar, tidal channel sands to delta distributary channel fill. Subaerial channel deposits have a bad reservoir quality, tidal channel sands possess a fair reservoir quality while delta distributary channel fill have a good reservoir quality. Petrophysical analysis shows that three reservoirs delineated have a porosity ranging from 19.37% to 23.62%, permeability ranging from 1408.71 to 1855.36 mD, a Net-to-Gross ranging from 0.46 to 0.88, volume of shale ranging from 11.72% to 24.92%, Water saturation ranging from 37.24% to 47.96% and hydrocarbon saturation ranging from 52.04% to 62.76%. Structural interpretation reviewed four main faults that serves as traps to the accumulation of hydrocarbon. Three hydrocarbon bearing sands were interpreted in the seismic volume. Time and depth structure maps show that the hydrocarbon bearing structure is a fault assisted anticlinal structure. Seismic facies analysis reviewed five facies. The study concluded that structural and stratigraphic features can be used to characterize reservoirs.

Lithostratigraphy and Sedimentation Models of TMG-C4 Well Offshore Eastern Niger Delta

Analysis was carried out in TMG-C4 well by integrating well logs data that revealed three depositional sequences within the Agbada Formation of about 400ft thick. Three systems tracts identified include highstand systems tract, transgressive systems tract and lowstand systems tracts. The highstand systems tract is majorly stacked regressive shoreface sands that occurred in two parasequence sets, whereas the transgressive systems tract is a transgressive unit with both source rock and sealing potentials. The lowstand systems tract shows a boxcar log motif and is identified to be probably channel or barrier bar sand. Major shale units (maximum flooding surfaces) with regional significance mapped are designated MFS. This division is relevant to identifying genetic depositional units. Three genetic sequences occurred in the well. The transgressive shales represent interruptions in the overall regressive sequence that is related to sea-level rise. Three of these shales have been mapped and two of them correspond to the eleven genetic megasequences that occur delta wide. A predominantly marine and deltaic sequences strongly influenced by clastic output from the continent is inferred from the well logs. Paleo water depth is interpreted to fluctuate considerably and deposition occurred within a variety of littoral and neritic environments ranging from nearshore barrier sand complexes to fully marine outer shelf mudstones. The sediments are rapidly deposited within the shallow marine realm and reworked into longitudinal bars by wave action, strong longshore drift and tidal effects. The dominant depositional trend observed in the well shows progradation

Further Development of the Lower Cretaceous Clinoform Model of the North of West Siberia Based on the Sequence Stratigraphy Principles: New Possibilities of Stratification

The clinoform concept of the Lower Cretaceous of Western Siberia was and remains the scientific basis for predicting its oil and gas potential. At the same time, new challenges and new technological opportunities require its further development. The basis for this can be a modern model independent methodology of sequence stratigraphy, the essence of which is to divide the stratigraphic section into a succession of systems tracts by mapping of all sequence stratigraphic surfaces. At the same time, the choice of the type of surfaces limiting the sequence is carried out already at the second stage on the basis of the expression of the surfaces in the stratigraphic section or the preferences of the researcher. The wide development of unconformities in the Western Siberian Lower Cretaceous clinoform complex makes it possible to subdivide clinoforms into four systemic tracts: highstand HST, falling-stages FSST, lowstand LST, transgressive TST. The subdivision is carried out by mapping sequence stratigraphic surfaces based on the analysis of stratal stacking patterns. According to the authors, the boundaries of the sequences in this case should be the tops of the TST – the downlap surfaces (DLS), traditionally interpreted as maximum flooding surfaces (MFS). This ensures the consistency of the proposed approach with the clinoform concept. The named clinoforms of Western Siberia can be considered as genetic sequences of the III order. However, the position of facies in their systems tracts is far from always predictable. For further detailing of facies models, clinoforms – III order sequences should be subdivided into clinoforms – IV order sequences, and subdivide them into systems tracts. But the latter are not always mapped by modern seismic method. Special conditions are necessary for this. Therefore, it is proposed at first to subdivide the III order sequences into systems tracts. Then – to map their thicknesses, and to allocate of their depocenters. Further, within the depocenters (under suitable seismogeological conditions), to define IV-order clinoforms – sequences and their constituent system tracts as a basis for mapping reservoirs and hydrocarbons traps.

Oligocene biostratigraphy, depositional patterns, and stable isotope values in the eastern Zagros basin: Novel insight into the signature of regional and global events

Biostratigraphy, depositional environment, sequence stratigraphy, and paleoclimate iterpretation of the Asmari carbonate reservoir are the subject of the current study. Two, earlier uninvestigated stratigraphic sections are studied and correlated over the eastern Zagros basin. The vertical distribution of foraminifera (benthic and planktic) reveals that the Asmari Formation deposited during the Rupelian-Chattian. Three shallow benthic foraminifera biozones are established, namely the Globigerina-Turborotalia cerroazulensis-Hantkenina Assemblage Zone, the Nummulites vascus-Nummulites fichteli Assemblage Zone, and the Archaias asmaricus- Archaias hensoni-Miogypsinoides complanatus Assemblage Zone. Ten microfacies types associated with the inner, middle and outer ramp of a carbonate platform are identified. Three depositional sequences are recognized in the eastern Zagros basin. The oldest sequence is Rupelian in age, and two others are of Rupelian-Chattian and Chattian in age. Two maximum flooding surfaces occur in the eastern Zagros basin. The isotope startigraphical data show that the more positive values of the δ18O and δ13C coincide with the maximum flooding surfaces, while these values show depletion over the sequence boundaries. The exception is observed at the upper boundary of the succession where the hypersalinity conditions affected the trend. The stable isotope values obtained from bulk samples enable to identify the Oligocene glacial events such as Oi2 and, Oi2a (Rupelian) and Oi2b (Chattian). The examination of the grain associations of the MF3 and MF5 prove these cooling events. We suggest the middle ramp microfacies and MFS2 of Sq.2 as signatures for tracing these cooling events throughout the eastern Zagros basin.