Facies Belts Research Articles

Supradetachment to rift basin transition recorded in continental to marine deposition; Paleogene Bandar Jissah Basin, NE Oman

AbstractA transition from supradetachment to rift basin signature is recorded in the ~1,500 m thick succession of continental to shallow marine conglomerates, mixed carbonate‐siliciclastic shallow marine sediments and carbonate ramp deposits preserved in the Bandar Jissah Basin, located southeast of Muscat in the Sultanate of Oman. During deposition, isostatically‐driven uplift rotated the underlying Banurama Detachment and basin fill ~45° before both were cut by the steep Wadi Kabir Fault as the basin progressed to a rift‐style bathymetry that controlled sedimentary facies belts and growth packages. The upper Paleocene to lower Eocene Jafnayn Formation was deposited in a supradetachment basin controlled by the Banurama Detachment. Alluvial fan conglomerates sourced from the Semail Ophiolite and the Saih Hatat window overlie the ophiolitic substrate and display sedimentary transport directions parallel to tectonic transport in the Banurama Detachment. The continental strata grade into braidplain, mouth bar, shoreface and carbonate ramp deposits. Subsequent detachment‐related folding of the basin during deposition of the Eocene Rusayl and lower Seeb formations marks the early transition towards a rift‐style basin setting. The folding, which caused drainage diversion and is affiliated with sedimentary growth packages, coincided with uplift‐isostasy as the Banurama Detachment was abandoned and the steeper Marina, Yiti Beach and Wadi Kabir faults were activated. The upper Seeb Formation records the late transition to rift‐style basin phase, with fault‐controlled sedimentary growth packages and facies distributions. A predominance of carbonates over siliciclastic sediments resulted from increasing near‐fault accommodation, complemented by reduced sedimentary input from upland catchments. Hence, facies distributions in the Bandar Jissah Basin reflect the progression from detachment to rift‐style tectonics, adding to the understanding of post‐orogenic extensional basin systems.

Stratigraphy and sedimentology of distal-alluvial and lacustrine deposits of the western-central Ebro Basin (NE Iberia) reflecting the onset of the middle Miocene Climatic Optimum

Stratigraphic and sedimentological study of distal alluvial and lacustrine deposits in the Plana de la Negra-Sancho Abarca area (western-central Ebro Basin, NE Iberia) within the early and middle Miocene allows five main lithofacies to be characterized and mapped within two tectosedimentary units, construction of a sedimentary facies model and discussion on allogenic controls on sedimentation. In this area, the boundary between tectosedimentary units T5 and T6 appears to be conformable and is marked by the change from dominant clastics to carbonates. Correlation of the studied outcrops with nearby sections that already had magnetostratigraphic and biostratigraphic data allows the studied succession to be dated from C5Dr to C5Cn (Burdigalian-Langhian), placing the boundary T5/T6 at ca. 16.1-16.05Ma. Seven vertical facies sequences document deposition of distal alluvial clastics and palustrine and lacustrine carbonates. Sandstones and mudstones represent low-sinuosity channels and lateral and terminal splays by unconfined flows runnig across the alluvial plain, associated to the Pyrenean-derived Luna fluvial system. The carbonates contain charophytes, ostracods, bivalves and gastropods, indicating deposition in 2-4m deep lakes. Laminated carbonate facies record reworking of shore carbonates and the influx fine-siliciclastic sediment offshore. Abundant bioturbation and desiccation features indicate episodic submergence and subaerial exposure. Four main episodes of alluvial and associated palustrine/lacustrine facies belt shifts are identified. Alluvial deposition in the studied T5 unit is related to low lake level conditions, rather than to a Pyrenean uplift. The maximum extent of the freshwater carbonates occur at the base of unit T6. This is consistent with conditions of increasing humidity of the Middle Miocene Climatic Optimum.

Phosphorites, glass ramps and carbonate factories: The evolution of an epicontinental sea and a late Palaeozoic upwelling system (Phosphoria Rock Complex)

AbstractThe Permian Phosphoria Rock Complex of the western USA contains an enigmatic assemblage of bioelemental rocks (i.e. phosphorites and cherts) that accumulated in a depositional system with no modern analogue. This study utilizes detailed sedimentological, stratigraphic and petrographic examination to evaluate the genetic relations of phosphorites, spiculitic chert and carbonates of the Ervay cycle (depositional sequence) and propose a unified oceanographic model for their deposition. The Ervay cycle contains three marine and one terrestrial facies association, each of which composes the bulk of a single lithostratigraphic unit. The marine facies associations include: (i) granular phosphorites (Retort Member); (ii) spiculitic cherty dolostones (Tosi Member); and (iii) marine to peritidal carbonates (Ervay Member). Red beds and intercalated gypsum (Goose Egg Formation) accumulated in the vast desert adjacent to the sea. The three marine members are chronostratigraphically distinct, successive and conformably stacked. They are not coeval facies belts. They reflect the progressive evolution of the epicontinental sea from the location of: (i) authigenic phosphogenesis (lowstand to transgression); to (ii) a glass ramp with biosiliceous (sponge) deposition (transgression); to (iii) a carbonate ramp (regression). This succession of switching biochemical sediment factories records the evolution of sea‐level, nutrient supply, upwelling, oxygenation and dissolved Si. Intense upwelling, potentially coupled with aeolian input, led to sedimentary condensation and phosphogenesis. Decreased upwelling intensity during transgression increased oxygenation sufficiently for a siliceous sponge benthos. Sponges were favoured over biocalcifiers due to elevated dissolved silica and a low carbonate saturation state. The cessation of sponge dominance and transition to a carbonate ramp occurred due to decreasing upwelling intensity, Si drawdown and an increased carbonate saturation state. These results provide insight into the role of Si loading in faunal turnover on glass ramps and highlight how differences in dissolved Si utilizers in pre‐Cretaceous versus post‐Cretaceous upwelling systems influence the resultant deposits.

Depositional sequences and microfacies of Lower Carboniferous strata in the Marsel block of the Chu-Sarysu Basin, Southern Kazakhstan

The sequence development and evolution of Lower Carboniferous strata in the Marsel block of the Chu-Sarysu Basin, Kazakhstan have been established through detailed sedimentological analysis of cores, petrophysical data, and new seismic interpretations. Four depositional sequences and eighteen parasequences were classified in the Lower Carboniferous strata. Each depositional sequence is composed of a transgressive systems tract (TST) and highstand systems tract (HST), roughly coinciding, respectively, with the following four stratigraphic intervals (1) lower Tournaisian (C1t) through lower Visean (C1v-1) strata; (2) middle Visean (C1v-2) strata; (3) upper Visean (C1v-3) strata; and (4) Serpukhovian (C1sr) strata. Parasequences are bounded by an instantaneous drowned punctuated surface (C1t and C1v) or instantaneous exposed punctuated surface (C1sr). In addition, petrographic studies have led to the recognition of 20 microfacies, distributed on the major depositional facies zones of the outer ramp (Mf1, Mf6, Mf20), middle ramp (Mf3–5, Mf8–13), and inner ramp (Mf2, Mf4, Mf7, Mf9, Mf12, Mf14–19). They are grouped into seven facies associations corresponding to widespread deposits of tidal flats (MA3, MA5), shallow shoals (MA6), and shallow lagoons (MA4) in the inner ramp; deposits of restricted lagoons (MA1) and local patch shoals (MA7) in the middle ramp and a relatively small outer ramp deposits (MA2). SQSQ All the microfacies and their associations are grouped into the following 6 major facies belts: outer ramp; restricted lagoon, and patch shoals in the middle ramp; and shallow shoals, restricted lagoon, subtidal to intertidal and supratidal in the inner ramp. The interpretation of these facies belts suggests a shallow warm-water tropical-subtropical depositional environment on a passive continental margin ramp. Facies correlation between wells in sequence framework suggests that the strata may be divided into four sequences (SQ1, SQ2, SQ3, SQ4). SQ1 and SQ2 are dominated by lagoon facies and outer ramp facies in the northwest area in the TST, and tidal flat facies in the HST; SQ3 is characterized by restricted to semi-restricted lagoon facies in the TST and local patch shoal facies and mixed tidal flat facies in the HST; SQ4 is marked by restricted lagoon facies in the TST and evaporitic lagoon, tidal flat, and shallow shoal facies in the HST. The research results can be used for investigating the development and distribution of potential reservoirs in the Lower Carboniferous strata of the Chu-Sarysu Basin; the reservoirs in the HST of late Visean and Serpukhovian in the northern and southeastern part of the platform interiors may be of premium quality.

Interpretation of Depositional Environment of Rho Field Using Sequence Stratigraphic Analysis, Shallow Offshore Depobelt, Niger Delta

Candidate Maximum Flooding Surfaces (MFS) identified on Rho-1, Rho-2 and Rho-3 were the basis of correlation across the wells for sequence Stratigraphic analysis in the field. Three (3) candidate MFS which include MFS-1, MFS-2 and MFS-3 were identified using the method adopted by Okoli [1]. Erosional surfaces were also delineated in wells from the observed stacking pattern between a sequence from Galloway model (1989) leading to the correlation of SB-1 and SB-2 across the wells. Using the Galloway model, four (4) depositional sequences were inferred SEQ (1-4). In the first sequence (SEQ 1), deposition occurred in a transgressive episode. Depositional environment was interpreted from electrofacies and revealing stacked sequences of reservoirs predominantly composed of fluvial channels which incised the Upper and Lower Shorefaces on a delta front system. In SEQ 2, looking at the aggradational pattern of the sequence, the formed channels were under the influence of both tidal and fluvial systems. In SEQ 3 and 4, based on electro-facies, the stacked reservoir sands were deposited predominantly in a shoreface/delta front environment and channel incisions in a wave subjugated high energy deltaic setting.
 The entire well section showed deposition in a regressive phase. Proposed conceptual models were generated using Petrel software and could be used as an input reconstruction of subsurface geological models. Indicating correct orientation of geo-bodies and facies belts (pinch outs of sands and shales), depositional dips and gross permeability architecture.

Distribution rules, main controlling factors and exploration directions of giant gas fields in the Sichuan Basin

Over the past decade, great progresses have been made in natural gas exploration in the Sichuan Basin, where several large gas fields (such as Anyue) have been discovered. With the increase of data and the deepening of exploration, new knowledges have been gained in geological theory, thus it is necessary to further analyze the distribution characteristics and main controlling factors of large gas fields, thus to put forward new exploration directions for large gas fields. Therefore, based on the statistics on the geological parameters of 20 large gas fields discovered in this basin, the distribution rules, formation conditions and main controlling factors of large gas fields were analyzed, and the follow-up exploration directions were proposed. The following results were achieved. (1) Large gas fields are developed in different tectonic regions in the Sichuan Basin, mostly in the low and gentle tectonic belts in the central Sichuan Basin. Large gas fields are developed in seven series of strata in longitudinal stratigraphic sequences, which are dominated by the reef-shoal large gas fields formed in the Upper Permian Changxing–Lower Triassic Feixianguan Fms. (2) There are four sets of source rocks contributing to the formation of large gas fields, mostly from the assemblage of Xujiahe Fm source rocks. (3) Reservoirs in the large gas fields are dominated by porous carbonates and tight sandstones; large gas fields are mostly structural–lithological ones and normal pressure ones. (4) The development of marine large gas fields are mainly controlled by intracratonic rifts and paleo-uplifts. The controlling effect of intracratonic rifts is mainly from three aspects, namely the hydrocarbon generation center of source rocks, high-energy facies belts on the platform edges, and lateral sealing for hydrocarbon accumulation. The controlling effect of the paleo-uplifts mainly acts from another three aspects: intra-platform high-energy facies belts, karstic dolomite reservoirs and long-term hydrocarbon accumulation. The structures of foreland basins controlled the development of the continental large gas fields from four aspects: tectonic setting, source and reservoir assemblage, trap type and fracture distribution. In conclusion, a total of 5 domains with 14 favorable zones are the follow-up exploration directions of large gas fields in the Sichuan Basin.

Factors controlling the development of tight sandstone reservoirs in the Huagang Formation of the central inverted structural belt in Xihu sag, East China Sea Basin

By means of thin section analysis, zircon U-Pb dating, scanning electron microscopy, electron probe, laser micro carbon and oxygen isotope analysis, the lithologic features, diagenetic environment evolution and controlling factors of the tight sandstone reservoirs in the Huagang Formation of Xihu sag, East China Sea Basin were comprehensively studied. The results show that: the sandstones of the Huagang Formation in the central inverted structural belt are poor in physical properties, dominated by feldspathic lithic quartz sandstone, high in quartz content, low in matrix, kaolinite and cement contents, and coarse in clastic grains; the acidic diagenetic environment formed by organic acids and meteoric water is vital for the formation of secondary pores in the reservoirs; and the development and distribution of the higher quality reservoirs in the tight sandstones of the Huagang Formation are controlled by sediment source, sedimentary facies belt, abnormal overpressure and diagenetic environment evolution. Sediment provenance and dominant sedimentary facies led to favorable initial physical properties of the sandstones in the Huagang Formation, which is the prerequisite for development of reservoirs with better quality later. Abnormal high pressure protected the primary pores, thus improving physical properties of the reservoirs in the Huagang Formation. Longitudinally, due to the difference in diagenetic environment evolution, the high-quality reservoirs in the Huagang Formation are concentrated in the sections formed in acidic diagenetic environment. Laterally, the high-quality reservoirs are concentrated in the lower section of the Huagang Formation with abnormal high pressure in the middle-northern part; but concentrated in the upper section of Huagang Formation shallower in burial depth in the middle-southern part.

Distribution Characteristics and Main Controlling Factors of Oil and Gas in the Bohai Sea Area

Liu, Y.; Cao, Q., and Zhang, Q., 2019. Distribution characteristics and main controlling factors of oil and gas in the Bohai Sea area. In: Li, L.; Wan, X., and Huang, X. (eds.), Recent Developments in Practices and Research on Coastal Regions: Transportation, Environment and Economy. Journal of Coastal Research, Special Issue No. 98, pp. 243–246. Coconut Creek (Florida), ISSN 0749-0208.In the Bohai Sea, structural oil and gas reservoirs account for the highest proportion of proven oil and gas reserves, followed by composite oil and gas reservoirs. In large and medium-sized oil and gas fields, which account for one-third of the total oil and gas fields, the proven oil and gas reserves account for 83% of the total reserves. Low uplift, middle sag uplift, and uplift structural belts have the most proven oil and gas reserves. Vertically, more than half of the proven oil and gas reserves are concentrated in the Neogene strata. More than 90% of the proven oil reserves and 85% of the proven gas reserves are distributed in shallow-middle reservoirs less than 3,000 M. The distribution of oil and gas in the Bohai Sea is the result of the interaction of a series of geological processes, such as source rocks, sedimentary systems, tectonic and fault systems development, and evolution. Oil and gas migrate and accumulate in short distance around hydrocarbon-rich sags; favorable sedimentary facies belts, high-quality lithofacies, and good physical properties determine the development of high-quality reservoirs in the Bohai Sea.

Reservoir characteristics of and potential analysis to Lower Palaeozoic shale in Xiuwu Basin, Lower Yangtze Plate

ABSTRACT In order to evaluate reservoir characteristics and gas potential of organic-rich shale in Bottom-Lower Cambrian Hetang Formation and Upper Ordovician Xinkailing Formation, Xiuwu Basin, Jiangxi Province, Lower Yangtze Plate of China, researches regarding reservoir characteristics of organic-rich shale thickness, moderate burial depth, abundance and maturity of organic matter, fracturability, organic-matter pores and absorption performance have been conducted to Hetang Formation and Xinkailing Formation through field survey, shallow drilling, analysis to hydrocarbon-generation potential, scanning electron microscopy, measuring specific surface area and isothermal adsorption experiments. The results show that (1) Hetang Formation reservoir, although with extremely rich material basis, is of unfavorable hydrocarbon generation conditions due to late-stage thermal maturity, besides of undeveloped micropore structure, reservoir space development mainly by macroscopic crack, so further exploration should focus on locating favorable areas of low maturity and developed cracks, which is considered distributing in the core of Yanshan-Lingangshan-Shiziyan Mountains syncline; (2) Xinkailing Formation reservoir is of better organic matter abundance, pore development and absorption performance than Xinkailing Formation and hence further exploration should focus on surveying favorable areas of better sedimentary facies belt and stable structure for major breakthrough in shale-gas exploration, which is considered distributing in Wuning-Lixi and Jinkou-Tuolin areas.

Algae, calcitarchs and the Late Ordovician Baltic limestone facies of the Baltic Basin

The Late Ordovician succession of the Baltic Basin contains a characteristic fine-grained limestone, which is rich in calcareous green algae. This limestone occurs in surface outcrops and drill-cores in an extensive belt reaching from Sweden across the Baltic Sea to the Baltic countries. This limestone, which is known in the literature under several different lithological names, is described and interpreted, and the term “Baltic limestone facies” is suggested. The microfacies, from selected outcrops from the Åland Islands, Finland and Estonia, consists of calcareous green algae as the main skeletal component in a bioclastic mudstone-packstone lithology with a pure micritic matrix. Three types of calcitarch, which range in diameter from c. 100–180 μm, are common. Basinward, the youngest sections of the facies belt contain coral-stromatoporoid patch reefs and Palaeoporella-algal mounds. The Baltic limestone facies can be interpreted as representing the shallow part of an open-marine low-latitude carbonate platform.

Geological conditions of natural gas accumulation and new exploration areas in the Mesoproterozoic to Lower Paleozoic of Ordos Basin, NW China

Based on field outcrop investigation, interpretation and analysis of drilling and seismic data, and consulting on a large number of previous research results, the characteristics of ancient marine hydrocarbon source rocks, favorable reservoir facies belts, hydrocarbon migration direction and reservoir-forming law in the Ordos Basin have been studied from the viewpoints of North China Craton breakup and Qilian-Qinling oceanic basin opening and closing. Four main results are obtained: (1) Controlled by deep-water shelf-rift, there are three suites of source rocks in the Ordos Basin and its periphery: Mesoproterozoic, Lower Cambrian and Middle-Upper Ordovician. (2) Controlled by littoral environment, paleo-uplift and platform margin, four types of reservoirs are developed in the area: Mesoproterozoic– Lower Cambrian littoral shallow sea quartz sandstone, Middle-Upper Cambrian–Ordovician weathering crust and dolomitized reservoir, and Ordovician L-shape platform margin reef and beach bodies. (3) Reservoir-forming assemblages vary greatly in the study area, with “upper generation and lower storage” as the main pattern in the platform, followed by “self-generation and self-storage”. There are both “upper generation and lower storage” and “self-generation and self-storage” in the platform margin zone. In addition, in the case of communication between deep-large faults and the Changchengian system paleo-rift trough, there may also exist a “lower generation and upper reservoir” combination between the platform and the margin. (4) There are four new exploration fields including Qingyang paleo-uplift pre-Carboniferous weathering crust, L-shape platform margin zone in southwestern margin of the basin, Ordovician subsalt assemblage in central and eastern parts of the basin, and Mesoproterozoic–Cambrian. Among them, pre-Carboniferous weathering crust and L-shape platform margin facies zone are more realistic replacement areas, and Ordovician subsalt assemblage and the Proterozoic-Cambrian have certain potential and are worth exploring.

Sequence Control Factors and Hydrocarbon Accumulation Pattern of Es3 in Kenxi Slope Zone of Bohai Bay Basin

Xu, X.-Y.; Wang, W.-F.; Li, X.-S., and Chen, H., 2019. Sequence control factors and hydrocarbon accumulation pattern of Es3 in Kenxi slope zone of Bohai Bay basin. In: Gong, D.; Zhu, H., and Liu, R. (eds.), Selected Topics in Coastal Research: Engineering, Industry, Economy, and Sustainable Development. Journal of Coastal Research, Special Issue No. 94, pp. 91–95. Coconut Creek (Florida), ISSN 0749-0208.Based on outcrops, rock cores, seismic, well logging, and other data, the study traces the evolutions of sequence stratigraphy, the types of sedimentary facies and sequence development control factors of Es3 in the Kenxi slope zone of Bohai Bay basin. The findings show that the stratum in this area can be divided into three third-order sequences, eleven fourth-order sequences and seven system tracts; the types of sedimentary facies include fan delta, sublacustrine fan, semi-deep lake, and deep lakes, etc.; sedimentary facies belt, lithologic trap patterns, hydrocarbon migration and preservation conditions are the core factors controlling lithologic reservoirs in this area. The exploration prospect in this area have been predicted. It is believed that there is a large exploration potential in the upper Es3 sub-member, the south of well K25-1 of the west Kenxi prominence.

Microfacies, geochemistry and sequence stratigraphy of the Sarvak Formation (Mid Cretaceous) in the Kuh-e Siah and Kuh-e Mond, Fars area, southern Iran

During Middle Cretaceous (Late Albian-Early Turonian) period, the Sarvak Formation prevailed in the coastal Fars area (Zagros), southern Iran. This formation is one of the main hydrocarbon reservoirs in the Zagros Basin which has gradually been deposited on the Kazhdomi Formation and unconformably covered by the Laffan shales. This study used thin section descriptions and geochemical analyses to determine the depositional environment of the Sarvak carbonates. Based on the petrographic studies, fifteen microfacies were recognized. These microfacies were deposited in the lagoon, shoal, back reef, reef, fore-reef, shallow open marine and deep open marine facies belts. Facies analysis indicates that the Sarvak limestones were deposited in a carbonate ramp environment which changed to the rimed shelf environment towards the top of the sequence. The minor elements (such as Sr and Mn) and petrographic studies indicate that microfacies could be separated from each other by using trace element values. The aragonite was original carbonate mineralogy These carbonates were affected by the meteoric diagenesis in a semi-closed system. Six transgressive-regressive third-order sequences have been identified. The sequence boundaries have been determined with a sudden change in the depositional and important diagenetic processes related to the relative sea level fall. The maximum flooding surfaces have been recognized by the high value gamma ray log and abundant bioturbation related to the deep facies which separates TST from RST.

Sediment‐supply‐dominated stratal architectures in a regressively stacked succession of shoreline sand bodies, Campanian Desert Member to Lower Castlegate Sandstone interval, Book Cliffs, Utah–Colorado, USA

AbstractStrongly progradational regressive stacks of shallow marine sandstones are ubiquitous in modern and ancient coastal depositional systems. Many ancient examples form prolific hydrocarbon and freshwater reservoirs in the subsurface. One of the best areas in the world to study progradational shallow marine successions is the Campanian Book Cliffs of Utah and Colorado, where the Desert Member to Lower Castlegate Sandstone interval served as a foundational data set for early sequence stratigraphic models. A strongly progradational stack of 17 parasequences comprises the Desert–Castlegate interval. Parasequences are 6·5 to 20·7 m thick. Normally regressive coarsening‐upward successions are abundant, as are flat‐topped, rooted foreshore sandstones. Conformable facies contacts mark the transition between the laterally adjoining nearshore terrestrial and shallow marine deposits which are genetically, temporally and spatially linked. The width of the shoreface to inner shelf facies belts varies from 4·8 to 19·9 km per parasequence, with a mean of 12·6 km. Solitary tongue shoreline trajectories are all very low to low angle ascending regressive, varying from +0·0004° to +0·171°. Stacked shoreline system trajectories are also dominantly low angle ascending regressive, with only two descending regressive trajectories, one of which intersects the depositional slope. The predominance of ascending regressive shoreline trajectories and normal regression, rarity of high frequency sequence boundaries, regressive surfaces of marine erosion and descending regressive shoreline trajectories, and absence of third‐order sequence boundaries, incised valley fill deposits and no prolonged and regionally extensive sediment bypass, all point towards increasing sediment supply as the dominant driver of the Desert–Castlegate stratal architectures, while reduced accommodation (i.e. decreasing tectonic subsidence) played a secondary role.

GEOCHEMISTRY AND MICROFACIES OF THE RUTEH FORMATION IN THE RUTEH AREA, CENTRAL ALBORZ, IRAN

To understand microfacies, depositional environment and geochemistry of Upper Permian rocks in Alborz region, the type sections of Ruteh Formation were studied. During the Permian, the Alborz region was a part of the east-west trending Paleotethys sea. Stratigraphic studies indicate that the Ruteh Formation in Ruteh section is composed of thin to massive limestone, argillaceous limestone interbedded with shale, is overlain by distinct laterite horizon of the Elika Formation and is underlain by the disconformity by the Dorud Formation. Facies analysis and petrographic studies led to the recognition of 11 microfacies in Ruteh section. These facies were deposited in 4 facies belts such as tidal flat, lagoon, shoal and open marine sub-environment. The Permian calcareous algae in the Ruteh Formation are widespread and well documented to determine the environment and microfacies of Permian deposits. Cementation and dolomitization are the main diagenetic processes in Ruteh Formation. Based on petrographic (size and fabric) studies, 4 dolomite types such as dolomicrite, dolomicrospar, dolospar, and dolomite cement were recognized. Seawater was the main source of Mg for early diagenetic dolomite (type 1), while Mg for late diagenetic dolomite (types 2,3,4) probably were sourced by shale pressing processes and pressure solution. Major and minor element studies led to there cognition of aragonite mineralogy. The geochemical study illustrates that these carbonates were affected mostly by meteoric diagenesis, which is occurred in a semi-close to open diagenetic system.

Sedimentary evolution of the marine Agua de la Mula Member (Agrio Formation, Lower Cretaceous) in the central Neuquén Basin: Source areas and paleogeographic considerations from a distal setting

The Agua de la Mula Member (Upper Hauterivian–Lower Barremian) of the Agrio Formation represents the infill of a mixed siliciclastic–carbonate low-gradient ramp system comprising both hydrocarbon sand reservoirs and a source rock interval considered as potential unconventional shale play. The present study analyzes the unit in offshore settings (Loma La Torre section) where high-quality, laterally continuous exposures allowed the recognition of muddy subaqueous clinoforms prograding northwestward. The muddy-dominated facies throughout the entire section represent an overall evolution from distal outer-ramp to inner-ramp settings associated with tidal flat deposits. Based on previous sedimentological studies and paleogeographic reconstruction, four facies belts are refined for the unit in the central Neuquén Basin: (1) shallow marine and deltaic facies to fluvial deposits documented in the subsurface (mainly siliciclastic); (2) mid-ramp to inner-ramp with subordinated outer-ramp settings (mainly siliciclastic); (3) outer-ramp to distal mid-ramp settings with muddy subaqueous clinoforms (mixed siliciclastic–carbonate); and, (4) basinal to outer-ramp areas (carbonate-dominated). In addition to the main sediment input from the south and southeastern margin of the basin, sedimentological and stratigraphic approaches suggest a sediment supply from the eastern and northeastern regions. Sporadic ash-fall deposits also indicate that the coetaneous magmatic arc was active. In fact, LA-ICP-MS U–Pb zircon ages from two tuff layers recorded in the study section yield an age interval of less than 1 m.yr., which allowed us to estimate the sedimentation and progradation rates of a clinoform set. Finally, four asymmetrical sequences are recognized comprising thin (carbonate–siliciclastic) transgressive systems tracts and thick regressive (highstand) systems tracts with stacked parasequences of shallowing-upward siliciclastic-dominated facies. These sequences are correlated with the four (4th-order) sequences previously defined in proximal settings. The observations suggest that sea-level changes were relatively synchronous events and, according to the present knowledge, controlled not only by orbital mechanisms but also by tectonism.

Tectono-sedimentary controls on Lower Cretaceous carbonate platforms of the central Zagros, Iran: An example of rift-basin carbonate systems

Abstract This study focuses on the variations in facies characteristics, depositional environments, and sedimentary sequences of the Fahliyan Formation carbonate succession (Neocomian–Barremian) as one of the petroliferous units in the Middle East. Four surface and subsurface sections were selected from the Dezful Embayment and Izeh Zone of the central Zagros, SW Iran. A shoal-algal facies dominated homoclinal ramp is proposed as the general depositional setting of this formation. It shows remarkable variations in facies belts, their abundance and thickness in the study area. Four third-order depositional sequences are differentiated in studied outcrops of the Izeh Zone. Interaction of tectonics, eustasy, and sedimentation (carbonate production) rates are discussed for depositional sequences and three tectono-sedimentary models are presented for the Fahliyan Formation that correspond to depositional sequences I to III of this formation. Variations in thickness, facies, diagenesis, and allochemical grains are discussed for each tectono-sedimentary model. Comparison of the acquired results with the proposed models of active tectonic basins suggests a fault-block platform in an extensional rift basin for the Fahliyan Formation in the study area.

Characteristics and Mechanism of Upper Permian Reef Reservoirs in the Eastern Longgang Area, Northeastern Sichuan Basin, China

Abstract As a typical kind of lithologic reservoirs, reef reservoirs are generally featured by their large single-well reservoir thickness, good reservoir physical properties, and high gas well productivity. The Upper Permian Changxing Formation is an important natural gas exploration target in the Sichuan Basin, which hosts a large reef gas reservoir and is mainly distributed along the Kaijiang-Liangping Trough. Comprehensive analyses are implemented to investigate reservoir characteristics and identify controlling factors of reef reservoirs in Changxing Formation in the Eastern Longgang Area, Northeastern Sichuan Basin, including core, logging, and seismic data analyses. Changxing Formation reservoirs in the study area mainly occur in the reef-shoal complex, which are featured by wide distribution, large thickness and generally good physical properties. Reservoir rocks are dominantly composed of bioclastic dolomite and silty-fine dolomite (with grain phantom structure), while the main reservoir space consists of residual intergranular pores, intergranular dissolution pores, and karst vugs. In the seismic profiles, typical mound-shaped chaotic reflections can be clearly seen. It is suggested by the main reservoir development controlling factor analysis that the distributions of reef reservoirs are typically controlled by sedimentary facies belts, while the scale of the reef-shoal complex is determined by the pene-sedimentary micro-paleo-geomorphology. Dolomitization can not only significantly preserve the primary pores but also enhance the permeability of rocks. Moreover, karstification is the key to high-quality reef-shoal reservoirs.

High resolution linkage of channel-coastal plain and shallow marine facies belts, Desert Member to Lower Castlegate Sandstone stratigraphic interval, Book Cliffs, Utah-Colorado, USA

AbstractThe Campanian Desert Member and Lower Castlegate Sandstone in the Book Cliffs of east-central Utah to western Colorado, USA, has served as a foundational data set in the development of sequence stratigraphy. Contrary to previous work, no third-order sequence boundaries are recognized. These were originally thought to partition the neighboring coastal plain and shallow marine facies belts into separate systems tracts, unlinked in time or space. In contrast, adjoining channel-coastal plain and shallow marine facies belts are genetically-, temporally-, and spatially-related. Evidence includes the (i) synchronous, strongly progradational stacking patterns within each facies belt, (ii) gradational and conformable transitions between adjoining facies belts, accentuated by the ubiquity of flat-topped, rooted foreshore sandstones passing upwards into carbonaceous-rich-mudstone-dominated coastal plain, (iii) parasequence-scale interfingering of coastal plain-channel and foreshore-shoreface deposits, with channels, white caps and coals embedded within stacked shoreface parasequences, (iv) regional correlation of coals and flooding surfaces, and (v) near orthogonal paleocurrent relationship between channels and shorelines. Terminal channels incise into proximal foreshore-shoreface sandstones in most Desert-Castlegate parasequences. Incisions are generally confined to the parasequence in which the channels are nested, rarely cutting deeper. These shoreface-incised channels are cut and filled at a parasequence-scale, and are bounded above by the same flooding surface that caps each foreshore-shoreface package. The ubiquity of ascending regressive shoreface trajectories and near absence of descending regressive trajectories that intersect depositional slope argues against any significant sea level fall. Increased rates of sediment supply, driven by autogenic and/or allogenic processes, likely generated the strongly progradational Desert-Castlegate great tongue of sandstone.

Facies, sedimentary environments and sequence stratigraphy of Cretaceous deposits in the northwest of Azerbaijan, Iran

The Cretaceous deposits in Morakan, located in the northeast of Khoy, a town in western Azerbaijan province, Iran, are primarily made up of carbonate rocks. These deposits, which are of 717 meters thick, lie on the clastic facies of Jurassic and are covered with beneath the pelagic beds of the Upper Cretaceous. To investigate the facies, sedimentary environment and sequential stratigraphy of these successions, a stratigraphic section was made in the south of Morakan village. Carbonate facies in this section have deposited in open marine, bar, lagoon, and tidal flat facies belts. The study of these facies and comparing them with old and modern sedimentary environments reveals that these succes-sions have deposited in a carbonated platform of rimmed shelf type. The study of the vertical succes-sion of microfacies shows four main sequences in the form of system tracts of TST and HST, which are made up of shallowing and deepening parasequences. The first lower boundary of the sequences is the type SB1 unconformity, and other identified sequences are the type SB2 unconformity.