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This study provided insight into the origin, age, and formation conditions of the Late Oligocene sulfate lithofacies that were deposited in the SW Erzincan Basin throughout a broad region. Primary, secondary gypsum, and anhydrite make up the majority of sulfates, which are interbedded with clastic, volcanic, volcaniclastic and carbonated rocks. During the early-late diagenetic processes, primary gypsum changes into secondary gypsum along with primary anhydrite that is growing within the host-sediment. In the lithofacies, sedimentary structures created by tectonism and diagenesis are commonly found. The distribution of element concentrations shows that continental detrital input has a significant impact. Fe- and Mg-rich clays imply alkaline and hot-humid environmental conditions in the basin. The negative trend relationship of CaO with MgO refers to carbonation in the environment, while Sr, Ba, U, Mo, Ni, Cu and Zn values and Co, Ni/Co (0.98), Co/Zn (11.3), Cu/Zn (1.39) ratios and the high positive correlation of Cu with Al2O3 (r = +0.72) indicate the dominance of biologic factor, high salinity and reducing conditions in sulfates. The presence and values of Fe–Mn-rich alteration zones detected by field, mineralogical and geochemical studies within the gypsum revealed the hydrothermal solution activity in the region. 87Sr/86Sr, 18O/16O, 34S/32S and δ13C isotope data are consistent with Late Oligocene marine sulfates and suggest occasional mixing of freshwater. In addition, the origin and age data revealed by this study; It contributed to the paleogeographic evolution of the northern branch of Neotethys (Inner Tauride Ocean), which extends along the Central and northern-central Anatolia and Eastern Anatolia basins line, which includes Paleogene evaporitic deposits in Turkey, where the study area is located. Accordingly, it is obvious that the Neotethys, which extends along the basins from west to east, is quite shallow (lagoonal and coastal sabkha, etc.) and started to close further east during the Middle-Late Miocene (Erzurum-Pasinler- Horasan, Erzurum-Hınıs-Tekman, Iğdır-Tuzluca lacustrine basins, etc.). [ABSTRACT FROM AUTHOR]

Lithofacies and palynofacies were investigated from deposits of the Laopanga Basin to provide sedimentation conditions and their evolution during the Cenozoic Era. Deposition occurred in an active tectonic setting giving rise to six facies including laminated, reeds/fossils-rich, bubble mat, massive, packed fragmental and botryoidal lithofacies and various microfacies (mudstone, wackestone, packstone, grainstone and floatstone). They record precipitates in the form of travertines, pure sinters and carbonate sinters interfingering with alluvial deposits (conglomerates, sandstones and claystones with silica and carbonate cements) as a result of tectonics and climate fluctuations. Sedimentation has been affected by several erosional events which affected the sedimentary basin. The precipitates suggest different temperature of deposition, ranging between 30 °C to 70 °C, likely related to lateral gradients from proximal to distal deposits. The mixing of sinters and travertines suggests a geothermal upflow and outflow and a probable migration of the spring controlled by tectonics related likely to reactivation of the Precambrian fault during the Cenozoic period. Freshwater algal and fungal remains such as Chomotriletes minor and the fern monolete spores Laevigatosporites sp. point to freshwater inflow from terrestrial habitats. Occurrence of other monolete spores such as Polypodiaceoisporites sp. indicates a similar marshy environment. Microbial communities (i.e. cyanobacteria) including coalesced silica spheres and filamentous bacteria reflect their influence on the chemical deposits, in active hydrothermal systems. The mixed precipitates and alluvial/terrigenous deposits are reported elsewhere as for example in the alluvial deposits in Namibia, Italy and Tunisia, meanwhile, the case ofinteraction between travertine-sinter-terrigenous deposits is exceptional. [ABSTRACT FROM AUTHOR]

Sequence architectures along the margins of rift basins are still poorly documented compared to passive continental margin settings. The Eocene Shahejie Formation on the rift margin of the Dongying Depression records a complex sequence stratigraphic distribution of conglomerate, sandy conglomerate, sandstone and mudstone. These facies have been mainly attributed to fan delta and marginal subaqueous fan depositional settings that developed during segmented fault activity along the rift margin. We utilize three‐dimensional (3D) seismic data, conventional cores, and wireline log data to dissect the overall wedge‐shaped upper sub‐member strata of the Shahejie Formation's fourth member. The study interval is a third‐order sequence formed between 45.4 and 42.5 Ma and contains a lowstand–transgressive systems tract (LST–TST) and a highstand systems tract–falling‐stage systems tract (HST–FSST). We found that the LST–TST developed several huge amalgamated depocenters along the Chennan border fault; whereas, these depocenters gradually diminished or even disappeared during the HST–FSST period, illustrating less significant control by the border fault. Through calculations of strata growth rates, we confirmed that the segmented activity of the border fault influences the stratigraphic distribution and facies evolution during these two periods. Specifically, deep‐water depositional systems, represented by marginal subaqueous fans were widely developed in the LST–TST period and were influenced by overall strong tectonic activity, including retrogradational (R) and aggradational (A) patterns. However, the aggradational to progradational (AP) deltas and progradational to degradational (PD) deltas dominated the generally muted tectonic activity setting during the HST–FSST. Additionally, influenced by localized segmented fault activity, these systems tracts exhibit incomplete vertical development, resulting in spatial variability in stratigraphic stacking patterns. [ABSTRACT FROM AUTHOR]

Objective The exploration direction of the Weixinan Sag in the Beibuwan Basin has shifted from structural traps to lithological traps, and the key problem in searching for lithological traps is to clarify the distribution of sandstones. Methods In this study, the high-frequency sequence division and depositional system of the First Member of the Liushagang Formation in the Weixinan Sag were analyzed using zircon dating, logging, core and seismic data. Results Then, the types and distributions of depositional facies in the First Member of the Liushagang Formation in the Weixinan Sag were clarified. The results show that the First Member of the Liushagang Formation was deposited as a third-order sequence, which can be divided into three system tracts and eight parasequence sets. Based on the analysis of the source to sink systems and sedimentary facies, the sediments in the Weixinan Sag mainly sourced from the Wanshan provenance in the northwest, the Qixi provenance in the east, the Wexinan provenance in the southeast, and the Xinan provenance in the southwest. The First Member of the Liushagang Formation in the Weixinan Sag mainly contains three sedimentary facies types: delta, lacustrine and sublacustrine fan. The lowstand system tract is dominated by mid-deep lake and sublacustrine fan deposits, including turbidity channels, natural levee, and sheet lobes. The expanding system tract mainly contains the sedimentary microfacies of deep lacustrine mud. The highstand system tract consists of front-delta deposition, among which the subaqueous distributary channel and subaqueous distributary interchannel are widely developed, and sedimentary microfacies such as mouth bar and sheet sand are less developed. Conclusion Three types of sublacustrine fan are mainly developed in the B subsag, including the western delta progradation slump type, southern near source fault slope belt type, and eastern far source gentle slope type.Among them, the southern provenance system with large-scale and good reservoir-forming conditions is the most promising target for further exploration.

Research on the interaction between depositional evolution process and marine transgression is critical to understanding the transform mechanism of sedimentary systems and guiding hydrocarbon exploration. The early Miocene witnessed the most significant sea-level rise since the Cenomanian, which resulted in extensive marine-influenced deposits worldwide. However, the relationship between the process of depositional evolution and long-term marine transgressions (>1 Ma) remains poorly understood. The Pearl River Mouth Basin in the South China Sea offers a comprehensive deposition record of the early Miocene marine transgression. This study employs high-quality 3D seismic, well-logging, and core data to investigate the impact of the early Miocene transgression on the evolutionary dynamics of the sedimentary system. The regional sea level exhibited a prolonged rise of at least 100 m during the deposition period of the Miocene Zhujiang Formation, corresponding to the long-term marine transgressive in the South China Sea. Throughout this marine transgression, depositional systems developed in the study area include tidal flats, fan deltas, meandering river deltas, and shallow marine shelf sand bodies. The marine transgression process resulted in a significant change in depositional system types, which can be divided into seven units from Unit 1 at the bottom to Unit 7 at the top. The predominant deposition environment transitioned from tidal flats in Units 1-3 to meandering river deltas in Units 4-5, and finally to shallow marine shelf systems in Units 6-7. In the early stage (Units 1-3), the regional uplifts hindered sea level transgression and caused erosion, leading to the development of small-scale proximal fan deltas. In the middle stage (Units 4-5), these regional uplifts submerged, and meandering river deltas dominated with sediments derived from distant extrabasinal sources. During the late stage (Units 6-7), regional sea levels reached their peak, transforming the entire basin into a shallow marine shelf system. Additionally, this marine transgression significantly influenced the distribution of hydrocarbon resources. Notably, the shallow marine shelf sand bodies in Units 6-7 warrant substantial attention for future exploration. This study outlines the complicated transitional processes within depositional systems during long-term marine transgression events, holding relevance for the global evolution of marginal sea basins.

Jackson, K.; Wang, P.; Pluckhahn, T.J.; Rogers, J.A., and Thompson, V.D., 2023. Stratigraphic framework, paleoenvironments, and Indigenous terraforming of inshore estuarine subbasins in Tampa Bay, Florida, U.S.A. Journal of Coastal Research, 39(5), 779–815. Charlotte (North Carolina), ISSN 0749-0208. Tampa Bay is a karst-controlled estuary system on Florida's central peninsular Gulf of Mexico coast. Although previous work has reconstructed late-Pleistocene environments (ca. 20–11.5 kya) and early marine influence (ca. 8–5.5 kya) in deeper central portions of the bay, the estuarine development of the shallow inshore subbasins remains poorly understood. Across the late Holocene, Indigenous societies terraformed the coastal strand with large volumes of estuarine mollusk shell, and these anthropogenic landforms constitute coastal barriers that partially enclose marginal tidal bayous. This study integrates sediment coring and archaeological excavations to reconstruct the Holocene estuarine evolution of four inshore subbasins within Tampa Bay. This study synthesizes sedimentological, macrofossil, and archaeological data to describe and differentiate seven sedimentary facies and 18 subfacies representing weathered Miocene limestone at the base, overlain by late-Pleistocene freshwater wetland deposits, followed by Holocene estuarine sediments and late-Holocene shell-terraformed settlements. Four stratigraphic cross-sections and >100 radiocarbon assays are utilized to interpret the sequences of inshore estuary development, situate ancient shell-bearing Native settlements within a geologic and paleoenvironmental framework, and resolve elements of mid- and late-Holocene sea-level history. [ABSTRACT FROM AUTHOR]

Abstract The Acque Albule Basin in Tivoli (Rome, Central Italy) represents one of the largest exposures of travertine deposits in the world. A detailed study of the Upper Pleistocene Testina travertine, constituting the poorly lithified top part of the Lapis Tiburtinus travertines, is presented. Fieldwork performed in an area of 10 km2 and petrographic analysis allow the recognition of six geobodies with different geometries, degree of diagenetic alteration and architectural elements, composed of seven lithotypes. The Testina travertine appears in general as a poorly lithified travertine, even if it shows a high degree of cementation. It is mainly characterised by blocky, drusy or bladed microsparite and sparite calcite cements, related to thermal and meteoric phreatic to vadose water circulation, affecting in particular those travertine deposits located in the northern part of the study area. The Testina, neglected until now in the several studies performed in the Acque Albule Basin, shows a progradational trend from the north to the south and is characterised by environments, evidencing deposition on a gentle slope, in an alluvial plain and in a shallow lake, with gradual transitions between low‐energy environments and high‐energy environments. Furthermore, based on correlation between the different geobodies in the overall study area, the Testina travertine depositional system was influenced by tectonic activity in the northern part, by an increasing topographic gradient and water discharge flow in the central part and by flooding events related to the Aniene River in the southern part. This study aims to differentiate such influencing factors facilitating the analysis of other travertine depositional systems and also to aid in the interpretation of subsurface analogues, as in the case of South Atlantic Pre‐Salt reservoirs.

Investigating the deposition evolution and stratal stacking patterns in continental rift basins is critical not only to better understand the mechanism of basin fills but also to reveal the enrichment regularity of hydrocarbon reservoirs. The Pearl River Mouth Basin (PRMB) is a petroliferous continental rift basin located in the northern continental shelf of the South China Sea. In this study, the depositional evolution process and stacking pattern of the Zhu III Depression, western PRMB were studied through the integration of 3D seismic data, core data, and well logs. Five types of depositional systems formed from the Eocene to the Miocene, including the fan delta, meandering river delta, tidal flat, lacustrine system, and neritic shelf system. The representative depositional systems changed from the proximal fan delta and lacustrine system in the Eocene–early Oligocene, to the tidal flat and fan delta in the late Oligocene, and then the neritic shelf system in the Miocene. The statal stacking pattern varied in time and space with a total of six types of slope break belts developed. The diversity of sequence architecture results from the comprehensive effect of tectonic activities, sediment supply, sea/lake level changes, and geomorphic conditions. In addition, our results suggest that the types of traps are closely associated with stratal stacking patterns. Structural traps were developed in the regions of tectonic slope breaks, whereas lithological traps occurred within sedimentary slope breaks. This study highlights the diversity and complexity of sequence architecture in the continental rift basin, and the proposed hydrocarbon distribution patterns are applicable to reservoir prediction in the PRMB and the other continental rift basins. [ABSTRACT FROM AUTHOR]

Sequence stratigraphy and Electrosequence of the Don-Field Central Swamp depobelt of the Niger Delta Basin, was carried out using well logs, biostratigraphic and core data. The aim of this study is to re-characterise and revalidate the reservoirs within the study area and provide an optimum framework for predicting reservoir character, development and reservoir quality distribution. Detailed petrophysical evaluation reveals proficient hydrocarbon reservoir units with variable parameters (i.e. porosity, permeability and shale volume) that can accommodate productive hydrocarbon reserve. Core data analyses revealed heavy minerals like pyrites and glauconites that can be of economic interest. The gamma wireline signatures of the wells show reservoir units that are predominantly blocky in shape indicative of fluvial channels. Fluvial channels are typically associated with coastal and/or marginal marine environments. More so, the aforementioned observations were validated using palaeoenvironmental interpretation of strata penetrated by Well-1, Well-2, and Well-3 via the sidewall core analyses. Sequence stratigraphic surfaces such as maximum flooding surfaces (MFS) and sequence boundary (SB) were observed to show good correlation with palynological and foraminiferal zones. The stacking patterns (i.e. progradation, retrogradation and aggradation) encountered gave acumen into systems tracts (i.e. lowstand system tract (LST), transgressıve system tract (TST) and highstand system tract (HST) interpretation. These system tracts constitute a depositional sequence set of middle—late Miocene age bounded chronologically by MFS of 9.5 Ma, 12.8 Ma, 15.0 Ma, 15.9 Ma and SB of 12.1 Ma, 13.1 Ma, 15.5 Ma, 15.9 Ma. The SB and MFS were delineated based on Shell Petroleum Development Company (SPDC) biozonation scheme: F-zone and P-zone were within P820-P680 and F9500-F9600/F9700 as contained in the biofacies interpreted data of index fossils (Globorotalia foshi S.I; Globorotalia praefohsi; Globorotalia peripheroacuta; Orbulina spp; Praeorbulina sicana; Paragloborotalia mayeri; Neogloboquadrina acostaensis) which corresponded to the alphanumeric code N8–N16 planktonic foraminiferal zones of Blow. [ABSTRACT FROM AUTHOR]

The X Formation, which dates from the Late Cenomanian to the early Turonian, is the largest carbonate reservoir in Iraq's South Mesopotamian Basin. There are two shallowing-up depositional periods in it, which begin with deep water mudstone associated with wackestone, which gradually shallows into rudist and is dominated by big foraminifera shoals and barriers, which are followed by lagoonal and intertidal facies. The identification of five distinct reservoir rock types, including mB2, mB1, CRII, mA, and CRI, was based on a combination of sediment types and diagenetic processes that influenced porosity types. The formation oil geochemical studies point to a Lower Cretaceous marine carbonate source depositional environment that is early mature and anoxic. [ABSTRACT FROM AUTHOR]

Abstract The Early Cretaceous is an important coal accumulation period in China. Abundant coal resources were formed in the southeastern margin of Songliao Basin. Sequence stratigraphy and coal accumulation of the Early Cretaceous in the southeastern margin of Songliao Basin have been studied on the basis of extensive outcrop and borehole data. Based on regional unconformity, basal erosional surfaces of incised valley fills, and abrupt depositional facies-reversal surface, six sequence boundaries have been identified, which subdivide the Early Cretaceous coal-bearing series into 5 third-order sequences. Sequence I corresponds to Huoshiling Formation, sequences II and III correspond to member I and member II of Shahezi Formation. Sequences IV and V correspond to member I and member II of Yingcheng Formation. Sequence I developed at the initial subsiding stage, sequence II and III developed during the stable subsiding stage, while sequence IV and V developed during the basin shrinkage stage. The major coal seams were developed in the sequence II and III, which ensured the relative balance between the increase rate of the accommodation space and the rate of peat accumulation for a longer period, thus forming a thick coal seam.

The Acque Albule Basin in Tivoli (Rome, Central Italy) represents one of the largest exposures of travertine deposits in the world. A detailed study of the Upper Pleistocene Testina travertine, constituting the poorly lithified top part of the Lapis Tiburtinus travertines, is presented. Fieldwork performed in an area of 10 km2 and petrographic analysis allow the recognition of six geobodies with different geometries, degree of diagenetic alteration and architectural elements, composed of seven lithotypes. The Testina travertine appears in general as a poorly lithified travertine, even if it shows a high degree of cementation. It is mainly characterised by blocky, drusy or bladed microsparite and sparite calcite cements, related to thermal and meteoric phreatic to vadose water circulation, affecting in particular those travertine deposits located in the northern part of the study area. The Testina, neglected until now in the several studies performed in the Acque Albule Basin, shows a progradational trend from the north to the south and is characterised by environments, evidencing deposition on a gentle slope, in an alluvial plain and in a shallow lake, with gradual transitions between low‐energy environments and high‐energy environments. Furthermore, based on correlation between the different geobodies in the overall study area, the Testina travertine depositional system was influenced by tectonic activity in the northern part, by an increasing topographic gradient and water discharge flow in the central part and by flooding events related to the Aniene River in the southern part. This study aims to differentiate such influencing factors facilitating the analysis of other travertine depositional systems and also to aid in the interpretation of subsurface analogues, as in the case of South Atlantic Pre‐Salt reservoirs. [ABSTRACT FROM AUTHOR]

The Bahçecik travertines, located in Gümü#hane (NE-Turkey) have been investigated for the first time using a multidisciplinary approach, which included sedimentological (lithofacies, depositional system), petrographic, radiometric 230Th dating, geochemical analysis (stable isotopes), palynomorphs and geophysics (GPR). A carbonate build-up, 12 m thick, was formed with some interruptions, through the middle Pleistocene period. For this study, two travertine sections (F and D) were extensively used to figure out palaeoenvironmental and palaeoclimatic proxies. The main precipitation cycles, separated by palaeosol levels, have been described and interpreted from a sedimentological perspective. The carbonate deposits consist of shrubs, crystalline crust, reed, laminated (micritic), pisoids, oncoids, calcite thin rafts and coated gas bubbles, lithoclasts, and palaeosol levels. The sedimentological fieldwork and petrographic analysis show that the Bahçecik travertines formed in depression depositional and slope depositional systems. Moreover, the first 230Th ages, stable isotopic results and palynofloral data in this study, prove that the Bahçecik travertines might have been affected by climatic and tectonic interruptions. According to dating results, the travertine occurrences began to precipitate during the 353 ka and continued into the 263 ka. Based on the palynological data, an abundance of herbaceous plants species was recorded in the warming period of climate. The thickness ranges from 2 to 12 m of the Bahçecik travertines. This precise thickness and also the presence of two different travertine formations, separated by a palaeosol erosional surface, were recorded by the ground penetrating radar (GPR) geophysical method. [ABSTRACT FROM AUTHOR]

The Early Cretaceous is an important coal accumulation period in China. Abundant coal resources were formed in the southeastern margin of Songliao Basin. Sequence stratigraphy and coal accumulation of the Early Cretaceous in the southeastern margin of Songliao Basin have been studied on the basis of extensive outcrop and borehole data. Based on regional unconformity, basal erosional surfaces of incised valley fills, and abrupt depositional facies-reversal surface, six sequence boundaries have been identified, which subdivide the Early Cretaceous coal-bearing series into 5 third-order sequences. Sequence I corresponds to Huoshiling Formation, sequences II and III correspond to member I and member II of Shahezi Formation. Sequences IV and V correspond to member I and member II of Yingcheng Formation. Sequence I developed at the initial subsiding stage, sequence II and III developed during the stable subsiding stage, while sequence IV and V developed during the basin shrinkage stage. The major coal seams were developed in the sequence II and III, which ensured the relative balance between the increase rate of the accommodation space and the rate of peat accumulation for a longer period, thus forming a thick coal seam. [ABSTRACT FROM AUTHOR]

Abstract This study is a contribution to the understanding of the depositional environment and reservoir architecture of the “Bruks Field,” Niger Delta, Nigeria. The objective is to use sequence stratigraphy and petrophysical evaluation in characterizing the reservoirs encountered in the study area. Well logs from six wells (B001, B002, B003, B009, B010 and B012-ST); biofacies data from wells B001 and B002; and a 3D seismic volume were analyzed to understand the spatial and temporal trends of reservoir sandstones, the environments of deposition, petrophysical properties of the F-sandstone and fault patterns on the structural map of the field. Log correlations show a considerable thickness of sands marked as fluvial. Results also show that the reservoirs are of foreshore, upper shoreface, lower shoreface, tidal channel and channel sands, which were deposited in a shallow marine setting. Two depositional sequences SEQ1 and SEQ2 were delineated with maximum flooding surfaces (MFS) 10.4 and 8.6 Ma, respectively. The depositional sequences are bounded with sequence boundaries (SB) dated 10.6, 10.36 and 7.4 Ma. The F-sand reservoir has an average net to gross thickness of 0.55, effective porosity of 0.29 v/v, permeability of 2506 mD and water saturation of 0.14 v/v. These values depict good reservoir quality, though the sand is deposited in tidal channels with the presence of heteroliths. The delineated faults composed of mainly growth faults, listric fault, antithetic and synthetic faults that formed the hydrocarbon traps for the F-sand.

The geomorphological evolution and sediment dispersal processes of the Liaodong Bay Depression (LBD), a strike-slip and extensional composite basin in the Dongying Formation, were studied using 3D seismic, drilling, and logging data in an attempt to understand the diversity of sand-controlling factors and the complexity of the sand dispersal processes. The LBD was mainly supplied by sediments from the eastern side, which originated in the Yanshan Fold system (comprising the Dashi River, Liugu River, and Lin River systems) and sediments from the western side, which originated from the Jiaoliao Uplift system (comprising the Daqing River and Fuzhou River systems). Different sediment provenances had various sediment supply capacities depending on the composition of the source rocks. Sediments were injected into the basin through the channels identified from two interpreted southwest-to northwest-orientated seismic sections. Strata of the Dongying Formation could be divided into three sequences, and comprised shallow-deep lacustrine deposits, braided river delta deposits, fan delta deposits, and sublacustrine fan deposits. Based on the established sequence stratigraphic framework, the strata thickness distribution and sequence of geomorphological evolution could be restored from 3D seismic data of the LBD. By analyzing the distribution and migration of depocenters and the distribution of channels, sediment pathways in the basin could be determined under high flux sediment supply. In terms of five interpreted seismic sections from north to south, we demonstrated that in addition to immense changes in tectonic depositional style in the eastern areas of the basin, the sediment dispersal processes in different areas exhibited prominent discrepancies in sediment accumulations from diverse depositional systems. Tectonic activities, efficient sediment provenance, distribution of channels, and sequence geomorphology jointly controlled the sediment dispersal processes in the deposition areas and determined the potential reservoir distribution. • Geomorphological evolution and sediment dispersal of a bay depression was studied. • Strata thickness and sequence-geomorphology was restored from 3D seismic data. • Distribution of incised valleys and sediment pathways in the basin were determined. [ABSTRACT FROM AUTHOR]

Many evidences for gas hydrate bearing sediments had been found in the continental slope of the East China Sea, such as bottom simulating reflections (BSRs), undersea gas springs, pyrite associated with methane leakage, mud diapirs/mud volcanos, bottom-water methane anomalies and so on. In this study, six key stratigraphic interfaces including T0 (seafloor), T1 (LGM, 23 kyr B.P.), T2 (2.58 Myr), T3 (5.33 Myr), T4 (11.02 Myr) and T5 (16.12 Myr) were identified, and then five third-order sequences of SQIII1 to SQIII5 were divided. However, T5 in southern continental slope is not found, which shows that the middle-northern Okinawa Trough had begun to rift in the early Miocene, earlier than the southern segment. Four system tracts including lowstand systems tract (LST), transgressive systems tract (TST), highstand systems tract (HST) and falling stage systems tract (FSST) are further divided. The marine erosion interface of 11.02 Myr and regressive unconformity interface of 23 kyr B.P. indicate two large-scale sea level drop events in the research area. Seven typical seismic facies identified in the continental slope are continental shelf-edge deltas, littoral fluvial-delta plains, incised channels or submarine canyons, slope fans, submarine fans or coastal sandbars, littoral-neritic finegrained sediments, mud volcanos and some other geological bodies respectively. The minimum water depth for hydrate occurrence in the Okinawa Trough is 630 m, and the thickness of gas hydrate stability zone in continental slope is between 0 and 590 m. The calculated bottom boundary of hydrate stability zone is slightly deeper than BSRs on the seismic sections. The re-depositional turbidite sand bodies, such as canyon channels, slope fans and submarine fans developed in Quaternary strata, are the predominant hydrate reservoirs. According to developing process, the dynamic accumulation of hydrate systems can be divided into three evolutionary stages including canyon erosion and hydrate stability zone migration stage, sediments destabilizing and methane leakage stage, and channel filling and hydrate re-occurrence stage. [ABSTRACT FROM AUTHOR]

Reservoirs in the Weicheng Oilfield, which occur in Paleogene Shahejie Formation Member 4 (Es4), were formed during the initial and strongly rifting stage of the Dongpu Depression. The geometry and distribution of sands of different types have controlled the heterogeneity of the reservoirs and have resulted in exploration challenges and relatively low recoveries. Based on various static and dynamic geological data including drilling, logging, seismic and production data, the microfacies features and distribution of Es4 were analyzed. Geostatistical three-dimensional (3-D) models and an integrated numerical simulation were constructed to quantify the geometry, spatial distribution and continuity of the reservoir sands and to predict the remaining oil distribution rules. Two depositional systems were recognized in Es4: terminal fans deposits in the lower part and partial shallow-lake deposits in the upper part. The three-dimensional geological model provided insights into the external and internal geometries, distributions and physical properties of the reservoir units. A sedimentary and connectivity feature analysis suggested four types of flow units: Type I units, which are primary sands of distributary channels and bars; Type II units, which are primary sands of proximal overbank and beaches; Type III units, which are sands of distal overbank; and Type IV units, which are mud flats and inter-beach-bar. The numerical simulation reproduced the changing process of the remaining oil, and the areas that have both high remaining oil saturations and reserve abundance, which are controlled by micro-facies and influenced by the structural trend and injection-production relations, comprise the key potential reservoirs: the sand pinch-out area, the imperfect pattern area and structural highs in Type I units and most of the areas in Type II units. [ABSTRACT FROM AUTHOR]

Porosity is one of the most important parameters to assess in-place oil or gas in reservoirs, and to evaluate recovery from enhanced production operations. Since it is relatively well-established to determine porosity using different laboratory and field methods, its value is usually determined at many locations across a reservoir as part of the common practice to capture reservoir heterogeneity and the variability in values. This suite of measurements and the distribution of values are most valuable for probabilistic reservoir assessments, and for spatial modeling if the exact data locations are known. Despite the importance of individual measurements to set the range of values for probabilistic studies, it is not always possible to access these data due to confidentiality. In most cases, commercial or publicly available databases that assessments may rely on usually report only mean values of porosity, like any other reservoir data, or they may not report a value at all. This makes both quantifying the mean value and the uncertainty around it difficult for probabilistic assessments. In this study, the TORIS (Tertiary Oil Recovery Information System) dataset of the National Petroleum Council and the U.S. Department of Energy was used to model porosity and the uncertainty around predicted values. TORIS is an integrated dataset of production data, reservoir properties, and project databases of crude oil reservoirs in the United States. The model presented in the paper was based on ANCOVA (Analysis of Co-Variance) of data from 1038 reservoirs from the TORIS dataset for porosity prediction, validation and testing for quantitative and qualitative parameters that may be readily available in most cases, and to estimate uncertainty around the mean values. This model also explored association of porosity values to different parameters, and to different depositional systems and diagenetic overprint conditions. Furthermore, an ANN (Artificial Neural Network) model was created to compare the predicted values of both models. Results showed that the ANN model was able to represent more of the variability, however it lacked the insights that might be gained from the ANCOVA model. • TORIS dataset was used to model porosity and its uncertainty around the mean values using ANCOVA. • esides quantitative variables, qualitative variables were used. • A regression equation was generated, validated and tested using additional data. • The model can be used to predict porosity when data is scarce. • The model can also be used to generate prediction interval around the mean values for probabilistic assessments. [ABSTRACT FROM AUTHOR]

Different sequence types were formed in various stages associated with tectonic variations and changes of the sediment supply in the rift‐related Wenchang Formation. Based on cores, wire logging, and seismic data, the sequence stratigraphy, depositional systems, and controls on the depositional systems of the Wenchang Formation in the Lufeng Depression were studied. The Wenchang Formation developed braided‐delta, lacustrine, fan‐delta, and nearshore subaqueous fan deposits and represents one first‐order sequence and three second‐order sequences, indicating three stages of tectonostratigraphic evolution. (a) The early syn‐rift sequence (SSQ1) developed fan‐delta and shallow lacustrine deposits. (b) The rift climax sequence (SSQ2) contains the early rift climax systems tract and the middle‐late rift climax systems tract. The early rift climax systems tract formed primarily braided‐delta and shallow lacustrine deposits, whereas the middle‐late rift climax systems tract developed mostly semi‐deep to deep lacustrine deposits. (c) The late syn‐rift sequence (SSQ3) developed braided‐delta and shallow lacustrine deposits. In the SSQ3 transgressive systems tract, retrogradational parasequence sets developed along the southern dip slope because of the weak sediment supply from the Huilu low uplift, whereas westward aggradational–progradational parasequence sets developed along the long axis because of the stronger sediment supply from the Lufeng eastern low uplift. Tectonic activity primarily controlled the early syn‐rift and rift climax deposition; syn‐depositional faults formed the transfer zones and slope break zones. Three types of transfer zones for sedimentary transport into the basin were distinguished, including synthetic approaching transfer zones, strike ramps, and collateral transfer zones. Three types of slope break zones were also recognised, including fault scarp zones controlling fan deltas and nearshore subaqueous fans, fault terrace zones controlling low‐stand fan deltas, and antithetic fault terrace dip‐slope zones controlling braided deltas. [ABSTRACT FROM AUTHOR]

The Qaidam Basin is a Mesozoic-Cenozoic compresso-shearing basin in western China. This basin has been subsiding since the Indosinian orogeny, and the subsidence is a strongly inherited feature in its Quaternary development. Five third-order sequences (SQ1, SQ2, SQ3, SQ4 and SQ5) were recognised using drilling/logging, coring and seismic data analysis. Each sequence was further divided into transgressive systems tract and regressive systems tract based on the maximum flooding surface. A sequence stratigraphic framework was established that revealed the distribution of sedimentary systems. Seven depositional systems, namely, alluvial fan, fan delta, braided-delta, shore lacustrine, shallow lacustrine, semi-deep lacustrine and incised valley depositional system, were identified from 105 well logs and 2 D seismic lines covering 1600 km. The sedimentary system distribution was identified as follows: (1) large-scale alluvial deposit located on the southern slope and adjacent to Kunlun Mountain and Yaber tectonic zone located northeast of the study area; (2) braided-delta deposits southeast of the Sanhu area; (3) widely developed fan-delta sediments on the base of Qigequan Formation in the Yaber tectonic zone; (4) well-deposited shoal lacustrine facies along the depositional strike in the regressive systems tract; (5) widely distributed shallow lacustrine facies; and (6) incised valley with large lateral extension and incision depth as an entity at the front of the Golmud Basin in the Sanhu area. Two different depositional models, namely, east and west models, were built by conducting an integrated analysis of sequence stratigraphy and sedimentary process. In the Sanhu area, the main controlling factors of the sequence architecture and depositional systems associations of the Qigequan Formation are tectonic subsidence and climate change with sediment supply and lake-level fluctuation secondary factors. This case study provides an example of the analyses of sequence stratigraphy and depositional systems in a salinised plateau basin. The approach combines seismic and sedimentary facies analysis to investigate Quaternary deposition and stratigraphy. The low-amplitude tectonic belt on the northern slope and the lithological traps on the southern slope are predicted to be favourable for the lithological gas reservoirs. [ABSTRACT FROM AUTHOR]

The Bohai Bay Basin is the second largest oil-producing basin in China located on the east Asian margin. The Bohai Bay Basin contains numerous depressions, sub-basins, and sags. One of these, the Nanpu Sag, has played a particularly important role in oil and gas exploration in recent years. Four depositional systems are recognized in the Nanpu Sag, fan-delta, braided-river delta, turbidite deposits, and lacustrine systems. In the Paleogene, the Nanpu Sag underwent complex and multi-phased rifting evolution. Two evolutionary phases have been identified: the syn-rift phase and the post-rift phase, the syn-rift stage can be further sub-divided into four episodes. This study reveals the considerable faulting activity and associated strong subsidence that occurred during the deposition of the Dongying Formation in the fourth episode of the syn-rift stage. The depositional systems and the tectonic activity during the fourth episode in the Nanpu Sag have very different characteristics compared to those of other depressions or sub-basins in the Bohai Bay Basin. Boundary fault activity was extremely intense during the deposition of the Dongying Formation, especially the east to west trending faults, including the Xinanzhuang Fault and the Gaoliu Fault. Moreover, the migration of subsidence centers from the Shahejie Formation to the Dongying Formation is a result of the strong down-warping that occurred during the fourth episode of the syn-rift stage. In the Nanpu Sag, the Dongying Formation is of great significance to hydrocarbon exploration, which is affected by both the intensity of fault activity and magnitude of basement subsidence. [ABSTRACT FROM AUTHOR]

Abstract The break-up of Pangea remains one of the most interesting moments in the Earth's history. In the Pyrenees this geological moment is represented by continental successions, giving rise to a magnificent example of the creation of new basins and their sedimentary fill. In this work we present a study based on stratigraphy, sedimentology and synsedimentary tectonics data; on this basis, we define for the first time the different tectono-stratigraphic phases that occurred in the evolution of the incipient continental basin of the Erill Castell-Estac Basin (Southern Pyrenees, NE Spain). Traditionally, four lithostratigraphic units have been defined in the area and grouped into tectono-stratigraphic units, but we propose three sedimentary cycles characterized by fining upward trends and separated by angular unconformities. The first sedimentary cycle (late Carboniferous-early Permian) is strongly related to intense volcanic activity and is characterized by isolated sub-basins. In the upper part of this cycle, fluvial and lacustrine deposits were deposited in a volcanic and transtensive tectonic context. In the second sedimentary cycle (early-middle Permian), the connection between the sub-basins started in a transtensive tectonic context. The main deposits in this cycle are lacustrine and fluvial, relative to playa-lake environments with a minor volcanic influence. Finally, the third sedimentary cycle (Early-Middle Triassic) is represented by meandering fluvial deposits with scarce lacustrine environments and no volcanic influence. The syn-depositional tectonic context is extensional, at the top of this last cycle the first Mesozoic marine incursions are preserved. Detailed description of the evolution of the Erill Castell-Estac Basin provides a new example of the sedimentary filling of strike-slip basins and is a key point to further considerations of the still unknown role of the Carboniferous to Triassic Pyrenean basins in Pangea break-up. [ABSTRACT FROM AUTHOR]

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In this study, we use 3D seismic, well‐log, and core data to investigate the sequence stratigraphy and facies associations of the Paleogene in the Nanpu Sag, Bohai Bay Basin, East China. Three second‐order sequences—SQEs3‐SQEs2, SQEs1, and SQEd—and 12 third‐order sequences are identified. Fan‐delta, braid‐delta, sublacustrine fan, and lacustrine systems are identified. Four types of tectonic‐induced sequence models are distinguished, which consist of fault‐cliff type, fault‐slope type, axial ramp type, and multiple fault‐terrace type. Sequence architecture of third‐order sequences is dominated by thin lowstand systems tracts with thick transgressive systems tracts (TST) and highstand systems tracts (HST). High‐resolution sediment‐partition pattern analysis shows that a large volume of sediments can be delivered into prodelta/deep‐lacustrine environments during transgressive periods and lake‐level highstand. This study also shows that sand/strata ratios in fan‐delta/braid‐delta front of systems tracts scale have a negative correlation with the subsidence rate, which is demonstrated by the finding that higher subsidence rates correspond to lower sand/strata ratios. This result suggests that subsidence rate has a significant influence on high‐frequency sequences. The occurrence of the high volume of sand‐rich deposits developed in TST and HST and relatively high sand/strata ratios within these sequence units reveal that TST and HST could also have a high hydrocarbon potential. The strongly asymmetrical accommodation generated by an early rapid tectonic subsidence and late tectonic quiescence results in sequence architecture variations between passive‐margin basins and rift basins. Different subsidence rates among different structural belts result in sequence architecture variations within different sequence models. [ABSTRACT FROM AUTHOR]

The responses of depositional patterns to extensional faulting during the rift cycle are discussed in this article, based on an integrated analysis of 3D seismic reflections, wire logs and cores from the Early Cretaceous Tanan Depression in the Tamtsag Basin, Mongolia. The synrift succession comprises four third-order sequences (SQ1-4). A four-stage fault evolution is defined, including early synrift SQ1 (initial isolate faults), early synrift SQ2 (rapid fault propagation), climax synrift SQ3 (maximum fault relief) and late synrift SQ4 (minor fault activity) stages. The initial isolated fault stage is defined by separated and small-sized half-grabens associated with short-dispersal alluvium. In contrast, the rapid fault propagation stage is characterised by much longer dispersal systems of fan-delta deposits. As rifting progressed, a considerable increase in the basin subsidence occurred and the maximum fault displacement led to a dustpan basin geometry, the coalescence of depocentres and extensive deep-water deposits. The observed both sediment starvation and balanced-filled patterns in SQ3 indicate that caution must be exercised when attempting to correlate reservoirs and source rocks since variations in basin-filled patterns would be enhanced by the displacement localisation on several major faults during the significant basin formation. During the early period of the climax synrift stage, footwall-sourced systems were prominent, but drainages in prior relay zone sites were mostly decayed or submerged. In response to the subsequent degradation of the footwall sources, axial-sourced braided deltaic systems became more important during the later period. An abrupt decrease of faulting at the end of the rift cycle gave a rise to an increased sediment supply and long-dispersal axially-sourced systems in the Tanan Depression. Petroleum exploration shows that fan-delta front sandstones in SQ2 are the most prospective hydrocarbon reservoirs, whereas the nearshore and offshore sub-lacustrine fan deposits in SQ3 have proved to be secondary potential oil-bearing reservoirs. This study indicates that sediment dispersal patterns would be significantly re-organised by the differential faulting displacement patterns and varied sediment potentials during the different synrift stages. The rapid fault propagation allowed the fault arrays to reach their nearly maximum length during the early period of the basin evolution, while the displacement remained almost constant. This fault growth pattern tends to establish large-scale topographic lows including overlapped transfer zones and hanging dip-slope. Hence, major drainage catchments and long-dispersal depositional systems of sand-rich deposits are facilitated during this early fault propagation stage, which may be a key aspect for the tectono-sedimentary evolution in rift basins. In addition, the fault and sedimentary relationships defined here may be used as a model when studying less data-rich rift basins elsewhere. [ABSTRACT FROM AUTHOR]

This study is a contribution to the understanding of the depositional environment and reservoir architecture of the 'Bruks Field,' Niger Delta, Nigeria. The objective is to use sequence stratigraphy and petrophysical evaluation in characterizing the reservoirs encountered in the study area. Well logs from six wells (B001, B002, B003, B009, B010 and B012-ST); biofacies data from wells B001 and B002; and a 3D seismic volume were analyzed to understand the spatial and temporal trends of reservoir sandstones, the environments of deposition, petrophysical properties of the F-sandstone and fault patterns on the structural map of the field. Log correlations show a considerable thickness of sands marked as fluvial. Results also show that the reservoirs are of foreshore, upper shoreface, lower shoreface, tidal channel and channel sands, which were deposited in a shallow marine setting. Two depositional sequences SEQ1 and SEQ2 were delineated with maximum flooding surfaces (MFS) 10.4 and 8.6 Ma, respectively. The depositional sequences are bounded with sequence boundaries (SB) dated 10.6, 10.36 and 7.4 Ma. The F-sand reservoir has an average net to gross thickness of 0.55, effective porosity of 0.29 v/v, permeability of 2506 mD and water saturation of 0.14 v/v. These values depict good reservoir quality, though the sand is deposited in tidal channels with the presence of heteroliths. The delineated faults composed of mainly growth faults, listric fault, antithetic and synthetic faults that formed the hydrocarbon traps for the F-sand. [ABSTRACT FROM AUTHOR]

The evolution of large-scale paleo-uplifts within sedimentary basins controls the sedimentary provenance, depositional systems and hydrocarbon distributions. This study aims to unravel changes in paleo-geomorphology, interpret sedimentary sequence evolution, and investigate favourable reservoir types and the hydrocarbon distribution during the buried stage of a long-term eroded paleo-uplift, taking the Lower Cretaceous Qingshuihe Formation (K 1 q) in the Junggar Basin as an example. These research topics have rarely been studied or are poorly understood. This study integrates current drilling production data with outcrop and core analyses, drilling well logs, 3D seismic data interpretations, grading data, physical property comparisons and identified hydrocarbon distributions. After more than 20 million years of differential river erosion and weathering in arid conditions, the large-scale Chemo paleo-uplift within the hinterland area of the basin formed a distinctive valley–monadnock paleo-geomorphology prior to the deposition of K 1 q. Since the Early Cretaceous, tectonic subsidence and humid conditions have caused the base level (lake level) to rise, leading to backfilling of valleys and burial processes. Two systems tracts in the target strata of K 1 q, consisting of distinctive depositional systems, can be identified: (1) a lowstand systems tract (LST), which is confined within incised valleys and is mainly composed of gravelly braided rivers and rarely occurring debris flows and (2) an extensive transgressive systems tract (TST), which developed into an almost flat landform and consists of braided river delta to lacustrine depositional systems. Overall, the physical properties of braided river reservoirs in the LST are better than those of the braided river delta reservoirs in the TST. However, the inhomogeneous distributions of carbonate cements cause differences in the physical properties of conglomerate reservoirs in the LST. However, for sandstones in both the LST and TST, coarser grain sizes and better sorting result in better physical properties. Altogether, four types of reservoir can be identified in the study area: Jurassic inner monadnock reservoirs, K 1 q LST stratigraphic onlap reservoirs, LST structural reservoirs and TST structural reservoirs. [ABSTRACT FROM AUTHOR]

In the Quaternary Sarıkavak fluvial tufa deposits, situated in south-western Turkey, different facies have been identified and their mutual relationships have been unravelled. This tufa formation is located at the northern part of Acıgöl Graben. The development of the Sarıkavak tufas represents typical fluvial and fluvio-palustrine environments. In total eight tufa lithofacies have been differentiated, namely: moss tufa facies, oncolitic tufa facies, stromatolitic tufa facies, phytoclastic tufa facies, intraclastic tufa facies, extra-formational clastic tufa facies, sapropelitic tufa facies, and palaeosol. Preliminary U/Th datings indicate that these deposits formed prior to 219 ka and continued until 80 ka (MIS 7 till 5). δ 13 C signatures (0.78‰ to −1.63‰ V-PDB) best can be explained by limestone dissolution processes or respiration from C4 plant vegetation into the soil or both. For that reason, the Sarıkavak tufa deposits can be classified as ‘travitufa’ which precipitated in a distal facies system of travertine occurrences. δ 18 O values (−7.49‰ to −10.83‰ V-PDB) of the whole data set reflect some significant changes, which is interpreted in terms of temperature variations reflecting warm and cold periods among MIS 7 (interglacial), MIS 6 (glacial) and MIS 5 (interglacial). The development of the Sarıkavak tufa deposits are related to the Maymundağı fault that borders the Acıgöl Graben in the north. This fault and its synthetic fault segments play a pivotal role with regard to the palaeo-flow direction of water and control the basin topography. These structural structures are likely responsible for all active and ancient springs in the study area, as well as their respective carbonate precipitates. [ABSTRACT FROM AUTHOR]

The Barra Velha carbonates are widely known for their complexity regarding facies, diagenetic features, and depositional history. The absence of recent analogues representing the depositional setting of these rock formations leaves many uncertainties concerning the sedimentary process that generated them. The present work aims to propose a model for the depositional environment of the Barra Velha Formation based on sedimentary features identified through facies description and interpretation. The employed data consists of 645 m of core descriptions, 2300photomicrographs, 1201 plug samples, and 44 thin sectionsdistributed throughout 34 wells in two Santos Basin oil fields. Fourteen facies were identified and classified into four categories: in situ, microbial, reworked, and altered. The in situ facies are composed of spherulites, shrubs, and mud. Sedimentological evidence points out that spherulites and shrubs precipitated within layers of mud, as a post depositional process. Microbial facies have several characteristics that refer to stromatolites and occur laterally and vertically associated with in situ facies. The spatial association between them indicates that in situ and microbial facies formed in the lower energy portions of the lake. Reworked facies were formed by grain fragmentation and transportation, indicating an energetic lake-littoral zone, where grainstones and packstones formed in the shallowest portions, and wackestones formed in the less energetic portion of the littoral zone. The altered category comprises the weathering profiles. These profiles resemble soils and developed in response to periods of strong evaporation, when lake brines would become dense enough to infiltrate into the groundwaters, leading to the precipitation of the dolocretes in the mixing zone. The spatial distribution of the facies corroborates the sedimentological interpretations. In situ and microbial facies are frequently found in the structurally lower regions of the study area. In contrast, reworked facies and weathering profiles are more common on structural highs. • The Barra Velha Formation comprises 14 facies, that were grouped in 4 categories: in situ, reworked, microbial and altered. • The in-situ facies are composed by spherulites, shrubs and mud, and were formed in the limnetic zone of the lake. • Reworked facies were formed in lake littoral zone, and indicated the occurrence of an energetic lake shoreline. • Microbial facies occur spatially associated with in situ facies indicating that they formed submerged in the lake water. • Altered facies resemble soils and were formed in a palustrine setting due to lake level fluctuations and evaporation. [ABSTRACT FROM AUTHOR]

A foreland basin is a dynamic system whose depositional systems migrate in response to changes in tectonic uplift patterns, sedimentary filling processes and isostatic rebound of the lithosphere. The Paleocene-middle Miocene foreland system of the Llanos foothills and Llanos basin of Colombia includes regional unconformities, abrupt changes in lithology/stacking patterns and flooding surfaces bounding reservoir and seal units. Here we integrate a systematic biostratigraphic study, stratal architecture and tectonic subsidence analyses, regional seismic profiles, and provenance data to define the diachronism of such surfaces and to document the direction of migration of foreland depozones. In a flexurally-deformed basin, sandstone composition, rates of accommodation and sediment supply vary across and along the basin. We show how a coeval depositional profile in the Llanos foothills-Llanos foreland basin consists of litharenites interbedded with mudstones (seal rock, supplied from the orogenic front to the west) that correlate cratonward with organic-rich mudstones and coal (source rock), and to amalgamated fluvial-estuarine quartzarenites (reservoir rock, supplied from the craton to the east) adjacent to a subaerial forebulge (unconformity). This system migrated northward and eastward during the Paleocene, westward during the early-middle Eocene, and eastward during the Oligocene. In the lower-middle Miocene succession of the Llanos basin, identification of flooding events indicates a westward encroaching of a shallow-water lacustrine system that covered an eastward-directed fluvial-deltaic system. A similar process has been documented in other basins in Venezuela and Bolivia, indicating the regional extent of such flooding event may be related to the onset of Andean-scale mountain-building processes.Una cuenca de antepaís es un sistema dinámico cuyos sistemas deposicionales migran en respuesta a cambios en los patrones de deformación, relleno de cuenca y rebote isostático de la litosfera. La cuenca de antepaís de los Llanos Orientales de Colombia incluye registro del Paleoceno-Mioceno medio con discordancias regionales, cambios abruptos de patrones de apilamiento/litologías, y superficies de inundación, limitando unidades reservorios y sellos. En este estudio integramos análisis de bioestratigrafía, arquitectura estratigráfica, subsidencia tectónica, perfiles sísmicos regionales y procedencia para definir el diacronismo de dichas superficies y para documentar la dirección de migración de los sistemas deposicionales en una cuenca antepaís. En una cuenca flexural, la composición de las areniscas, los patrones de acomodación y aporte de sedimentos varían dentro de la cuenca. Este artículo presenta un perfil deposicional entre el Piedemonte hasta la cuenca de los Llanos el cual incluye litoareniscas interestratificadas con lodolitas (roca sello derivada del frente de deformación) que correlacionan hacia el Este con lodolitas carbonosas y carbón (roca fuente). Siguiendo hacia el Este continúan cuarzo areniscas fluvio-estuarino (roca reservorio derivada de áreas cratónicas) adyacentes a la zona de levantamiento flexural, con exposición subaérea (discordancia). Este sistema migró hacia el Norte y Este durante el Paleoceno, hacia el Oeste durante el Eoceno temprano-medio, y hacia el Este durante el Oligoceno. En la sucesión del Mioceno inferior-medio de los Llanos, la identificación de eventos de inundación indica un avance hacia el Oeste de sistemas lacustre someros, cubriendo el sistema fluvio-deltaico que avanzaba hacia el Este desde el Piedemonte. Un proceso similar ha sido documentado en otras cuencas en Venezuela y Bolivia, indicando la extensión regional de este evento de inundación, el cual puede estar relacionado con el inicio del levantamiento de los Andes.

Although the Late Oligocene - Early Miocene Kujung Formation is one of the important exploration targets in the Kangean PSC Block where JAPEX share the interest with Mitsubishi Corporation and Energi Mega Persada, no commercial hydrocarbon accumulation from this formation have been discovered yet in the block. In the Kangean area, the relationship between facies and reservoir quality in the Kujung Formation carbonates are not well understood. In this study, geological survey in Kangean Island and petrological analysis using outcrop samples(totally 88 samples)were conducted to evaluate reservoir qualities of the Kujung Formation carbonates. Our study reveals that the Kujung Formation in the island is divided into 10 facies (F0 - F9) based on lithology, texture, sedimentary structures and bioclastic content. These facies are grouped into 3 facies associations (FA1-FA3) based on large scales depositional environments. Reservoir qualities of the Kujung Formation are generally controlled by pore system related with the facies associations and diagenesis. Since mechanical/chemical compaction during burial diagenesis is the most common effect on shelf slope and outer shelf facies, these sediments have micro porosities or are tight carbonates. These show permeability lower than 2 mD regardless of porosity values. In contrast, moldic/vuggy porosity is abundant in shallow marine facies by calcite cementation in interparticle porosity and dissolution of carbonate grains. These facies show fair to excellent reservoir qualities. Furthermore, results of core plugs and thin-sections analysis and observation indicate that connectivity of secondary pores is critical for enhanced permeability commonly by solution-enlargement. Our study also implies that shallow marine facies are likely to undergo multi-phase subaerial exposure events causing improvement of reservoir quality rather than outer shelf slope and outer shelf facies. [ABSTRACT FROM AUTHOR]

The Zhanhua Depression is a hydrocarbon-rich, fault-generated depression in Bohai Bay Basin, eastern China. Gubei slope zone, located in eastern Zhanhua Depression, is an important oil production region. Drilling cores, logging data, and 3D seismic data were used to identify several depositional system infilling the slope zone, including braided-delta, sublacustrine fans, and deep/ semi-deep lake fine-grained deposits and turbidite, all of which are associated with a lacustrine succession belonging to the 3rd member of Shahejie Formation (Es3). Sedimentary rock of Es3 are composed of mudstone, silty mudstone, fine sandstone, coarse sandstones, and conglomeratic sandstones with various structures including massive bedding, parallel bedding, scour-fill structures, graded bedding, and deformed structures. Sandstone distributed in braided-delta front subfacies, lacustrine fans and some turbidite are favorable reservoir facies. Fault system was an important hydrocarbon migration pathway and sometimes a sealing geologic unit, which played an important role in the formation of commercial oil reservoirs in Gubei slope zone. The commercial oil reservoir is dominantly distributed in ridge-like structures in Gubei slope zone, which give an inspiration that ridge-like structure was probably a very favorable area for hydrocarbon exploration in continental basin slope zone. [ABSTRACT FROM AUTHOR]

The coal-bearing strata of the Upper Paleozoic (from the Taiyuan Formation to the lower member of the Shanxi Formation) are the most important units that have high gas production in the Daniudi gas field, which is a typical tight-sandstone reservoir with high heterogeneity in the Ordos Basin, China. Based on an integrated investigation of well logs, cores, SEM and 3-D seismic data, we delineated the sedimentary facies of the coal-bearing strata and divided the succession into sequenced stratigraphic units of different depositional systems. A sedimentary hiatus was documented for the first time in the study area and forms the sequence boundary between the Lower Pennsylvanian Carboniferous Taiyuan Formation (C t ) and the Upper Pennsylvanian Carboniferous Taiyuan Formation (C t ). The coal-bearing strata in C t are indicative of a barrier coastal deposition system. Tidal channels are identified by their fine-grained, cross-stratified character. The sands in the tidal channels are well sorted, and the quartz content is above 95%. The coalbed located beside the sandstone is thought to be a lagoon. Gas-bearing, coarse-grained sandstone in the coal-bearing strata spanning from the C t to the lower members of the Shanxi Formation (P s) is interpreted as a fluvial-dominated braided delta that is divided into four third-order sequences. The coal-bearing strata are composed of sandstone, mudstone and coalbed from base to top in each sequence. Braided-river deposits form the lowstand system tract (LST) within each sequence. A shelf and lake depositional environment containing dark gray mudstone forms the transgressive systems tract (TST). The highstand systems tract (HST) deposits form the swamp coalbed in each sequence. [ABSTRACT FROM AUTHOR]