High-resolution Sequence Stratigraphic Framework Research Articles

Seismic sedimentology analysis of meter-scale thin sand bodies in the Jurassic Qigu Formation, Yongjin area, Junggar Basin

Seismic sedimentology is an interdisciplinary field that integrates sedimentary geology and geophysics to accurately characterize the spatial and temporal distributions of sedimentary systems. This paper focuses on the Qigu Formation in the Yongjin area of the Junggar Basin, China. The objectives are to establish a high-resolution sequence stratigraphic framework and to clarify the types of sedimentary systems present. Various technical methods, including 90° phase adjustment, attribute clustering, red-green-blue attribute fusion, stratal slicing, and seismic phase-controlled waveform indication inversion, are employed to restore the vertical evolution history of the sedimentary system and quantitatively characterize the spatial-temporal distribution of the thin sand bodies in the Qigu Formation. The results revealed that the Qigu Formation is divided into a third-order sequence, consisting of a lowstand systems tract and a lacustrine transgressive systems tract. During the lowstand systems tract, a thick channel sand body developed in the delta front, exhibiting a non-muddy, intermittent normal grading structure. The lacustrine transgressive systems tract features thin, discontinuous channel sand bodies with mud layers, also forming an intermittent normal grading structure. Two distinct types of delta fronts are identified: the first, formed during the lowstand systems tract, is characterized by branching subaqueous distributary channels in a shallow-water environment. The second, associated with the lacustrine transgressive systems tract, displays a network-like distribution of subaqueous distributary channels in a relatively deeper-water environment.

A high-resolution sequence stratigraphic framework for the eastern Ellis Bay Formation, Canada: A record of Hirnantian sea-level change

Anticosti Island (Québec, Canada) contains one of the thickest Ordovician/Silurian boundary sections in the world, providing a fossiliferous and well-preserved record of the Late Ordovician mass extinction; however, the absence of a comprehensive correlation framework for the island prevents the full incorporation of data from across Anticosti into a global understanding of the extinction event. Here, we combine sedimentological, stratigraphic, and chemostratigraphic data to develop a sequence stratigraphic framework for the Ellis Bay and lowermost Becscie formations along the northeastern shore of Anticosti Island. These formations record six fourth-order (∼100−400 k.y.) depositional sequences bounded by regionally traceable unconformities. Evidence of subaerial weathering and exposure at many of these unconformities is subtle and has long gone unrecognized, which highlights the complexity of correlation in this and other stratigraphically thin icehouse records. Quartz pebble lags that mantle these surfaces punctuate the otherwise fine-grained, mixed carbonate−siliciclastic strata of the Ellis Bay Formation and provide the means to trace unconformities across localities; these surfaces are also marked by depleted carbon isotopic values, meteoric cement, microkarst, and incised valleys. This sequence stratigraphic framework provides the first correlation framework for exposures from the eastern end of this classic Ordovician/Silurian boundary section, and thus enables the integration of paleobiological, stratigraphic, and geochemical data into a basin-wide perspective of the Late Ordovician mass extinction. Critically, comparison to sequence stratigraphic frameworks from coeval sections suggests that other regions may be incomplete at the level of the fourth-order cycles recorded on Anticosti Island and may contain similarly cryptic unconformities.

Depositional and diagenetic controls on reservoir properties along the shallow-marine carbonates of the Sarvak Formation, Zagros Basin: Petrographic, petrophysical, and geochemical evidence

As the second important oil reservoir of Iran, shallow-marine carbonates of the Sarvak Formation were deposited in a tectonically active setting, under a warm and humid paleoclimatic condition. This study focuses on sedimentological, geochemical, and petrophysical analysis of this formation in the Abadan Plain, Zagros Basin. Petrographic studies have resulted in the recognition of five microfacies deposited in lagoon, patch-reefs and their taluses, shoal, and open marine environments. They represent a ramp-like depositional model for the Sarvak Formation. Two third-order depositional sequences are differentiated and dated as Cenomanian–Turonian, according to the results of biostratigraphic analysis. Effects of intensive meteoric diagenesis are recorded beneath the two paleoexposure surfaces (Cenomanian–Turonian boundary, and middle Turonian). They include pervasive dissolution (karstification), collapsed brecciation, silicification, recrystallization, and development of paleosols. Additionally, decreased values of δ18Ocarb and δ13Ccarb and a sharp inverted-J pattern in the δ18Ocarb vs. δ13Ccarb cross plot indicate major meteoric phases. The most decreased values of δ18Ocarb (−7 ‰) and δ13Ccarb (−8.6 ‰) are measured from the meteoric cements and paleosols. Reservoir quality evaluation revealed that the best reservoir zones of the Sarvak Formation are developed within the rudist-dominated facies with intensive meteoric dissolution. They are concentrated within the regressive systems tract of the Cenomanian sequence. Fractured and dolomitized mud-dominated facies provided the speed/baffle zones in transgressive systems tracts, and highly compacted/cemented facies formed the barrier units. It could be concluded that the facies characteristics and meteoric diagenetic processes had major controls on reservoir quality of the Sarvak Formation, in the Abadan Plain. These controlling factors are predictable in a high-resolution sequence stratigraphic framework.

Sedimentary microfacies characteristics within the high-resolution sequence framework of the Fuyu oil layer in the New North region

The Xinbei Oilfield has gone through decades of exploration and development, and lithological oil and gas reservoirs with stronger concealment are currently the focus of research. It is urgent to implement the sedimentary microfacies and sand body distribution characteristics of the Fuyu oil layer in the Xinbei area, providing a new theoretical basis for predicting the "sweet spot" of facies control in the area. Using core, logging, and logging data from the study area, a high-resolution sequence stratigraphic framework of the Fuyu oil layer was established. The distribution characteristics of sedimentary microfacies within the sequence framework were analyzed. The study showed that the Fuyu oil layer in the study area was divided into one long-term base level cycle of rising half cycle, four medium-term base level cycles, and 13 short-term base level cycles; In the area, river controlled shallow water delta plains and front sediments are developed, and a total of 10 types of sedimentary microfacies have been identified. Among them, the (underwater) distributary channel sand body, as the dominant reservoir sand body, extends along the southwest to northeast direction. As the A/S value increases, four stacking styles are developed vertically, including vertical shear stacking, staggered shear stacking, horizontal shear stacking, and isolated distribution. In the horizontal, the locally developed wide channel sand body composite zone gradually transitions into a single channel.

High-resolution sequence stratigraphic framework for the late Albian Viking Formation in central Alberta

High-resolution sequence stratigraphic frameworks detail the changes in the orientation and distribution of systems tracts in a basin, making it possible to identify areas encompassing reservoir units that have been previously overlooked. The Viking Formation is a stratigraphically complex unit that accumulated in a shallow foreland basin (Western Canada Sedimentary Basin) during the Lower Cretaceous (late Albian). To date, the Viking Fm has only been described using a low-resolution allostratigraphic framework. Herein, we present a high-resolution sequence stratigraphic framework, and discuss the utility of this framework to further petroleum exploration.Two hundred and ten cores that intersect the Viking Fm were logged and these data were used to develop a facies model for the various sequences of the Viking Fm through central Alberta. The formation is mapped and described using Depositional Sequence IV nomenclature, which includes the recognition and correlation of deposits attributed to one of four systems tracts: falling-stage, lowstand, transgressive and highstand. Four depositional sequences are identified and the architecture of deposits in each sequence are discussed. By carefully mapping these deposits in a high-resolution context, we: i) delineate and refine the mapping of regional trends; ii) correlate valley incision to lowstand shorelines; and iii) provide additional criteria for identifying future reservoir units in a mature basin.Based on the high-resolution sequence stratigraphic framework, four additional stratigraphic plays are identified including: forced regressive shorelines, incised valleys, lowstand shorelines and trangressively incised shorefaces, and new lateral facies relations that potentially could produce reservoir compartmentalization. These additional play types are not the typical reservoirs explored for in the Viking Fm and may have been overlooked as non-prospective.

High resolution sequence stratigraphic analysis of Qingyi section in Hei-258 area

In order to solve the problems of unclear division of the delta front pre delta facies belt of the first member of Qing Dynasty in Hei-258 area of Daqingzijing in the south of Songliao Basin and the lack of a unified fine isochronous stratigraphic framework in the whole region, the types and genesis of the cycle interface of the first member of Qing Dynasty are summarized by using the core data of a coring well and the logging data of more than 70 wells, combined with the theory of high-resolution sequence stratigraphy and sedimentology, Establish a high-resolution sequence stratigraphic framework and summarize the control of base level cycle on sedimentary evolution. The results show that the delta front subfacies are the main subfacies in the first member of Qinghe formation in Hei-258 area, and a small amount of pre delta deposits are developed in the northeast of the study area in some periods. The types of cycle interfaces are mainly Lake flooding surface of different levels, conversion interface from progradation to retrogradation or retrogradation to progradation, lithologic catastrophe interface, etc., and the short-term cycles are classified into three categories according to the structural style. The above understanding can provide a theoretical basis for the distribution range of sedimentary facies belt and the establishment of high-resolution sequence stratigraphic framework in Daqingzijing area.

Lithofacies Types, Assemblage Characteristics, and Sedimentary Evolution Model of Lacustrine Shale in Dongyuemiao Formation of Fuxing Area

The identification and classification of lithofacies’ types are very important activities in shale oil and gas exploration and development evaluation. There have been many studies on the classification of marine shale lithofacies, but research on lacustrine shale lithofacies is still in its infancy. Therefore, in this study, a high-resolution sequence stratigraphic framework is established for the lacustrine shale of the Jurassic Dongyuemiao Formation in the Fuxing area using detailed core observations, thin section identification, XRD analysis, major and trace element analysis, wavelet transform analysis, and detailed identification and characterization of the fossil shell layers in the formation. In addition, the lithofacies’ types and assemblages are identified and characterized, and the lithofacies’ characteristics and sedimentary evolution models in different sequence units are analyzed. The significance of the lithofacies assemblages for shale oil and gas exploration is also discussed. The results show that the shale of the target interval can be divided into 8 parasequence sets; further, 9 types of lithofacies and 6 types of lithofacies assemblages are identified. The 9 lithofacies are massive bioclast-containing limestone shoal facies (LF1), thick-layered fossil shell–containing limestone facies (LF2), layered mud-bearing fossil shell–containing limestone facies (LF3), laminated fossil shell–containing argillaceous shale facies (LF4), laminated fossil shell–bearing argillaceous shale facies (LF5), argillaceous shale facies (LF6), massive storm event–related bioclast-containing facies (LF7), massive argillaceous limestone facies (LF8), and massive mudstone facies (LF9). The sedimentary evolution models of different lithofacies are established as follows: Unit 1 (LF1-LF6) of the Dong-1 Member corresponds to the early stage of a lake transgressive system tract, and Units 2–4 (LF4-LF7) correspond to the middle to late stage of the lake transgressive system tract, which was an anoxic sedimentary environment. The Dong-2 Member (LF7-LF8) and the Dong-3 Member (LF5+LF9) correspond to a lake regressive system tract, which was an oxygen-rich sedimentary environment. Based on the characteristics of the shale lithofacies, sedimentary environment, and the quality of the reservoir, the lithofacies assemblage of LF4–LF7 in Unit 4 is the most favorable type for oil and gas exploration, followed by the lithofacies assemblage in Unit 2; the lithofacies assemblage in the Dong-2 and Dong-3 Members are the worst.

Carbon isotope and sequence stratigraphy of the upper Isachsen Formation on Axel Heiberg Island (Nunavut, Canada): High Arctic expression of oceanic anoxic event 1a in a deltaic environment

Abstract The Early Cretaceous oceanic anoxic event (OAE) 1a documents a major perturbation of the global carbon cycle with severe consequences for the ocean-climate-biosphere system. While numerous studies over the past decades have provided a relatively detailed picture of the environmental repercussions of OAE 1a at low and mid-latitudes, studies from high latitudes, in particular the High Arctic, are limited. In this study, we present a high-resolution carbon isotopic and sequence stratigraphic framework for the lower to lower upper Aptian interval of the Isachsen Formation of the High Arctic Sverdrup Basin (Canada). These data enable us to precisely locate the stratigraphic position of OAE 1a in a deltaic sedimentary environment. The carbon isotope record allows, for the first time, identification of the different carbon isotope segments (CISs) of OAE 1a in the Sverdrup Basin and thereby correlation of the High Arctic record with sections from lower latitudes. Based on this improved chemostratigraphy, we revise the age of upper Paterson Island, Rondon, and Walker Island Members, important regional lithostratigraphic marker units. Whole-rock geochemical data record two episodes of marine incursion into the Sverdrup Basin during OAE 1a (CISs Ap3 and Ap6), which are interpreted as regional maximum flooding surfaces. This information is used in conjunction with detailed sedimentological logs and geochemical grain-size proxies to refine the sequence stratigraphic framework for the upper Isachsen Formation. We propose that transgressive-regressive cycles in the Sverdrup Basin were controlled mainly by the combined effects of eustatic sea-level changes and regional tectonic uplift, potentially related to the emplacement of Alpha Ridge, which culminated at ca. 122 Ma during CIS Ap9.

Evolution and controlling factors of the gravity flow deposits in the Miocene sequence stratigraphic framework, the Lower Congo—Congo Fan Basin, West Africa

To understand the evolution of the Miocene gravity flow deposits in the Lower Cong—Congo Fan Basin, this paper documents the Miocene sequence stratigraphic framework, the depositional characteristics and the controlling factors of the gravity flow system. Based on the establishment of high-resolution sequence stratigraphic framework, lithofacies characteristics and sedimentary units of the gravity flow deposits in the region are identified by using seismic, well logging and core data comprehensively, and the sedimentary evolution process is revealed and the controlling factors are discussed. The Miocene can be divided into four 3rd-order sequences (SQ1—SQ4). The gravity flow deposits mainly include siliciclastic rock and pelite. The main sedimentary units include slumping deposits, mass transport deposits (MTD), channel fills, levee-overbank deposits, and frontal lobes. In the Early Miocene (SQ1), mainly gull-wing, weakly restricted to unrestricted depositional channel-overbank complexes and lobes were formed. In the early Middle Miocene (SQ2), W-shaped and weakly restricted erosional-depositional channels (multi-phase superposition) were subsequently developed. In the late Middle Miocene (SQ3), primarily U-shaped and restricted erosional channels were developed. In the Late Miocene (SQ4), largely V-shaped and deeply erosional isolated channels were formed in the study area. Climate cooling and continuous fall of the sea level made the study area change from toe of slope-submarine plain to lower continental slope, middle continental slope and finally to upper continental slope, which in turn affected the strength of the gravity flow. The three times of tectonic uplifting and climate cooling in the West African coast provided abundant sediment supply for the development of gravity flow deposits. Multistage activities of salt structures played important roles in redirecting, restricting, blocking and destroying the gravity flow deposits. Clarifying the characteristics, evolution and controlling factors of the Miocene gravity flow deposits in the Lower Congo—Congo Fan Basin can provide reference for deep-water petroleum exploration in this basin.

Classification of paralic channel sub-environments in an ancient system using outcrops: The Cretaceous Gallup system, New Mexico, U.S.A.

ABSTRACTDistinguishing trunk channels and delta-plain distributary channels in ancient systems can be difficult due to poor or incomplete data (e.g., limited outcrop or sparse well data). Accurate channel classification is required to reconstruct the plan view of channel networks in a paralic fluvio-deltaic system and to quantify source-to-sink systems. Channel formative mechanisms, such as allogenic versus autogenic and avulsion versus bifurcation, also remain equivocal. In this paper we classify channel types and quantify their discharge and dimensions in an ancient paralic depositional system of the Late Cretaceous Gallup system, New Mexico, in a recently developed high-resolution sequence stratigraphic framework. Six key facies associations are identified and integrated into a detailed facies architectural analysis using bedding diagrams from two outcrop cliffs. Backwater lengths are calculated and used for interpretation of channel forming mechanisms and classification of channel types. Two types of channels are interpreted in the study area: meandering fluvial avulsive distributary channels formed in the upstream backwater region in an upper delta plain with a paleodischarge of 280–410 m3/s, and terminal distributary channels in a subaqueous lower delta plain with a paleodischarge of 80–190 m3/s. The results show that upper-delta-plain fluvial distributary channels are formed by erosive avulsion and resemble fluvial meandering rivers characterized by laterally accreting point bars and a wide range of paleocurrents, whereas terminal distributary channels are formed by both avulsion and bifurcation and show more aggradation with lateral confinement and relatively larger width-to-depth ratios of individual channel stories. The quantification of channels and their depositional system provides new data from a well-known ancient system for the global database and comparison with other modern and ancient systems.

Application of seismic sedimentology in lithostratigraphic trap exploration: A case study from Banqiao Sag, Bohai Bay Basin, China

A method of identifying lithostratigraphic traps based on seismic sedimentology is proposed. We first establish a 3D high-resolution (fifth-order) sequence stratigraphic framework by using the stratal slices. Then, the reservoir distribution and reservoir-seal assemblage are investigated within the high-resolution sequence framework. This method turns the interpretation of lithostratigraphic traps from traditional seismic facies-based approach to the dynamic analysis of high-resolution seismic geomorphic information. We divide the lower Sha-1 member in the Banqiao Sag, Bohai Bay Basin, East China, into fourth- and fifth-order sequences by applying our method. The fifth-order sequence corresponding to Sha1-2 shows that the fan delta-distal subaqueous fan depositional system can be observed at the bottom of Sha1-2. The bounding fault and paleogeomorphology control the deposition of sand, whereas the sand bodies in the fan delta and distal subaqueous fan are developed near the bounding fault and the open lake basin, respectively. We then predict the sand thickness based on the well logs and seismic amplitudes. Moreover, according to the structural features, at least four lithostratigraphic traps are identified. These traps form a good reservoir-seal assemblage with overlying mudstones deposited during the period of lacustrine level rising. The drilling results in Trap-3 suggest that, our method can be a method of choice for effectively identifying the lithostratigraphic traps, a significant measure for hydrocarbon exploration.

High Resolution Sequence Stratigraphic Division and Isochronous Framework Establishment in Wuerxun-baer Sag

High-resolution sequence stratigraphy and related technical methods have been widely used in the analysis of complex and changeable continental petroliferous basins in China in recent years. At present, the main fields of oil and gas exploration in Hailaer Basin have been transferred to lithologic reservoirs, so it is very important to find lithologic traps and analyze the favorable formation conditions of lithologic traps. The tectonic evolution, sequence stratigraphic framework and tectonic control over the sedimentary system of Nantun Formation have been studied in depth by predecessors. However, the division accuracy of Nantun Formation can only reach the level of system tract, and the distribution characteristics of sand bodies and source-reservoir allocation under high-resolution sequence framework are seldom studied. Therefore, on the basis of predecessors’research, the author synthetically uses the related technology and methods of high-resolution sequence stratigraphy, and according to the sequence boundary characteristics reflected by drilling, core, seismic and logging data, establishes the high-resolution sequence stratigraphic framework through fine division and correlation of base-level cycles at various levels. The distribution law of sand body under its control and the source-reservoir allocation relationship favorable to lithologic trap formation are studied in order to have important guiding significance for further tapping the potential of lithologic reservoir.

Sequence stratigraphic analysis of the Surma Group in X Gas Field, Surma Basin, Bengal Delta

This study builds a high-resolution sequence stratigraphic framework for the Surma Group in the X Gas field. At first, electrofacies and depositional sequences were interpreted from wire line logs. Then, the field wide configurations of these sequences have been identified in seismic using reflection terminations (of flap, onlap, top lap and down lap relationship). Finally, wire line log and seismic interpretations were integrated to establish sequences stratigraphic framework in the Surma Group.
 Electrofacies analysis has revealed four major facies associations namely: (i) Bell shaped fining upward facies corresponds to retrogradational shoreface to tidal flat deposits, (ii) Funnel shaped coarsening upward facies corresponds to progradational shoreface to tidal flat, (iii) Cylindrical aggradational facies interpreted as stacked channel and (iv) Symmetrical or Bow shaped facies corresponds to heterolithic unit. The succession of Surma group of about 3100+ m has been divided into twelve depositional sequences. With exception of depositional sequence 1, 11 and 12, most of them are composed of three system tracts: sandy lowstand system tract, shaley transgressive system tract and heterolithic to shaley highstand system tract. Repetitive occurrence of incised valley, shoreface sand as well as tidal channel sand separated by transgressive system tract shelfal mud resulted in sand-shale alternation in the Surma Group. The lower depositional sequences (up to sequence-6) are shale dominated and equivalent to the Lower Surma Group. The upper six sequences are sand dominated, have more channel incisions and sequence boundary representing the Upper Surma Group

High-resolution Palaeogene sequence stratigraphic framework for the Cuu Long Basin, offshore Vietnam, driven by climate change and tectonics, established from sequence biostratigraphy

The chronostratigraphy of the Cuu Long Basin, offshore Vietnam to the south of the Mekong Delta, is poorly understood, especially for the Palaeogene succession. This paper utilises a comprehensive biostratigraphic database from 46 exploration wells to establish a high-resolution sequence biostratigraphic framework for the Oligocene and upper Eocene based on the identification of 36 transgressive-regressive depositional cycles. They are shown to be climate-driven and correlate to 406 kyr ‘heartbeat of the Oligocene’ eccentricity cycles. Their occurrence has been rigorously cross checked against seismic across the basin. This re-evaluation requires the repositioning of the Oligo-Miocene boundary in the Cuu Long Basin from the C seismic pick to the BI.1 seismic pick.By integrating sequence biostratigraphic and seismic datasets, the Oligocene can be seen as characterised by two types of depositional sequence. Firstly, thin and repetitive depositional packages, here termed ‘Sequences’ but perhaps better visualised as parasequences, the deposition of which was controlled by cyclically changing climate. Secondly, much thicker packages, each comprising a succession of parasequences separated by unconformities, and which tie to the main seismic divisions within the Oligocene/upper Eocene and were driven by tectonics. The latter are visualised as 3rd order sequences, with the parasequences forming 4th order sequences.Correlating the succession of parasequences to the 406 kyr ‘heartbeat of the Oligocene’ isotope cycles allows accurate ages to be proposed for each parasequence boundary, and in doing so an accurate time framework is established for the basin. The first sediments may have been deposited during the latest middle Eocene (Seismic group F/G) at the same time as or just prior to the initial stage of faulting prior to the opening of the South China (East Vietnam) Sea, with deposition of seismic group E commencing at about 36.6 Ma during the late Eocene. Unconformities reflecting 3rd order sequence boundaries are dated at 33.4 Ma, 29.8 Ma and 27.4 Ma.

Shallow-marine depositional sequences in a transgressive mixed siliciclastic-carbonate system: The Early Jurassic Marrat Formation from central Saudi Arabia

A high-resolution sequence-stratigraphic framework is proposed for the Marrat Formation (Early to Middle Toarcian of Saudi Arabia) by presenting new outcrop and shallow core sedimentological data located along a 280 km long N-S transect south of Riyadh and westward subsurface correlations based on gamma-ray wireline logs (200 km Ar Riyadh to Khurais Field). This extended spatial cover allows the identification of a northward thickening of sedimentary successions due to syndepositional differential subsidence. Basically, these successions formed on a low-energy falt-topped platform with limited accommodation space in which mainly retrogradational and aggradational stacking patterns were recorded. Overall, the evolution from continental meandering fluvial deposits at the base of the formation to tidal or wave-dominated siliciclastic and carbonate inner-platform deposits indicate a progressive marine transgression that reached its maximum during the Middle Toarcian bifrons Zone. In details, we identify two 3rd-order sequences that onlap southward onto the Triassic−Jurassic unconformity. Higher-energy siliciclastic shoreline facies were deposited in the upper transgressive systems tract of depositional sequences during periods of high accommodation space. The carbonate units consist of platform mud-dominated facies and are well-developed during the maximum marine transgressions of the two Marrat sequences. Continental red shales and fluvial sandstone deposited in a humid and warm environment during the Toarcian bifrons Zone (sublevisioni Subzone) indicate a higher terrigenous input interrupting the two maximum transgressive sequences. The sequences were likely produced by global sea-level changes but also appear to have been influenced by local climate changes with humid and warm conditions during periods of regression and more arid conditions during transgressions. This study serves as an outcrop analog, provides guidelines for hydrocarbon exploration and improves seismic interpretations. Overall, these new facies analyses, wireline log data, stratigraphic interpretations, and regional correlations contribute to a broader understanding of the Early Jurassic successions of the Arabian Platform.

Late Pennsylvanian glaciation: Evidence of icehouse conditions from Canyon and cisco units, Midland Basin, Texas

Abstract The late Paleozoic has long been recognized a time of significant continental glaciation associated with high-frequency, high-amplitude glacioeustasy. Although, precise assessment of glacioeustatic amplitudes are difficult to extract from the stratigraphic record, best approximations may be possible by analyzing spatial and temporal distributions of depositional facies utilizing several wells across the study area. We used detailed sedimentologic description and depositional facies analysis from 12 wells and applied rigorous cycle stacking pattern analysis, exposure surfaces recognition and wireline logs to correlate timelines across the wells. On the basis of the high-resolution sequence stratigraphic framework built for the Scurry Area Canyon Reef Operators (SACROC) field, a highly-resolved glacioeustatic curve was generated for latest Desmoinesian to the latest Virgilian. Our eustatic curve suggests that the Missourian and Virgilian stages of the late Pennsylvanian are characterized by high frequency, high-amplitude eustatic fluctuations. The Missourian stage was a period dominated grainstone-capped cycles that are isopachous and conformable. These cycles reflect a eustatic amplitude of at least 37 m with an average duration of 100 ka suggesting the dominance of short-term eccentricity signal. The Virgilian stage is far more complicated and is characterized by highly shingled cycles compared to the Missourian stage. Deeper water phylloid boundstone and calichified shoal complex grainstones are juxtaposed next to each other which suggests a stronger eustatic amplitude (>40 m) compared to the Missourian stage. Although the eustatic amplitude of the Virgilian cycles is similar to those of the Missourian cycles, they have a longer frequency (343 ka) representative of long-term eccentricity. We conclude that the late Pennsylvanian stratigraphy of the SACROC field in the Midland Basin records extensive continental glaciation during the Missourian stage and increased and reached an acme during the Virgilian stage.

Sequence stratigraphy in the middle Ordovician shale successions, mid-east Korea: Stratigraphic variations and preservation potential of organic matter within a sequence stratigraphic framework

The Jigunsan Formation is the middle Ordovician shale-dominated transgressive succession in the Taebaeksan Basin, located in the eastern margin of the North China platform. The total organic carbon (TOC) content and some geochemical properties of the succession exhibit a stratigraphically distinct distribution pattern. The pattern was closely associated with the redox conditions related to decomposition, bulk sedimentation rate (dilution), and productivity. To explain the distinct distribution pattern, this study attempted to construct a high-resolution sequence stratigraphic framework for the Jigunsan Formation. The shale-dominated Jigunsan Formation comprises a lower layer of dark gray shale, deposited during transgression, and an upper layer of greenish gray siltstone, deposited during highstand and falling stage systems tracts. The concept of a back-stepped carbonate platform is adopted to distinguish early and late transgressive systems tracts (early and late TST) in this study, whereas the highstand systems tracts and falling stage systems tracts can be divided by changes in stacking patterns from aggradation to progradation. The late TST would be initiated on a rapidly back-stepping surface of sediments and, just above the surface, exhibits a high peak in TOC content, followed by a gradually upward decrease. This trend of TOC distribution in the late TST continues to the maximum flooding surface (MFS). The perplexing TOC distribution pattern within the late TST most likely resulted from both a gradual reduction in productivity during the late TST and a gradual increase in dilution effect near the MFS interval. The reduced production of organic matter primarily incurred decreasing TOC content toward the MFS when the productivity was mainly governed by benthic biota because planktonic organisms were not widespread in the Ordovician. Results of this study will help improve the understanding of the source rock distribution in mixed carbonate–siliciclastic successions within a stratigraphic framework, particularly for unconventional shale reservoirs.

Chemostratigraphy of the Cenomanian-Turonian shallow-water carbonate: new correlation for the rudist levels from north Sinai, Egypt

The present study aims to provide carbon-isotope curves for the Cenomanian to Turonian rudist-dominated successions in north Sinai. The high-resolution carbon-isotope curves obtained from north Sinai sections provide new insight for calibrating the age of rudists as well as for evaluating the effects of the oceanic anoxic event 2 (OAE2) on rudist communities. The primary goals are (1) to provide a high-resolution sequence stratigraphic framework for the Cenomanian-Turonian succession, (2) to use rudist and ammonite biostratigraphic data to distinguish the stratigraphic levels of the rudist species, and (3) to integrate the chemostratigraphic (δ13C) profile and the rudist levels to improve the biostratigraphy based on the rudist distributions and the carbon-isotope data. The recognition of three ammonite zones through the Cenomanian-Turonian succession was utilized to identify four temporally significant rudist levels indicative of the Lower Cenomanian, Middle Cenomanian, Upper Cenomanian, and Middle Turonian, respectively. Most of the rudists occur in the highstand deposits of medium-scale sequences. Carbon- and oxygen-isotopic analyses were carried out on both rudists and surrounding carbonate units. Based on the variations in the carbon-isotope signals, 12 chronostratigraphic segments were identified in the studied sections. The Cenomanian carbon-isotope segments (C23–C30) were obtained from the Halal Formation at Gabal Yelleg and Gabal Maaza sections, while the Turonian segments (C30–C34) were measured from the Wata Formation at Gabal Yelleg section. The carbon-isotope record from the studied sections is consistent with the trends documented in previous studies of the Tethyan realm. The Cenomanian-Turonian boundary is placed at the onset of falling carbon-isotope values (δ13C) from 2.61 to −0.25‰ in the upper part of OAE2 with the carbon-isotope segment C30 at Gabal Yelleg. The negative shift in δ13C values (C33) occurred in the Middle Turonian lowstand deposits characterizing the global sea level fall during this interval.

Sequence stratigraphy and ichnology of Early Cretaceous reservoirs, Gadvan Formation in southwestern Iran

The siliciclastic Gadvan Formation from Abadan Plain, southwestern Iran, is highly bioturbated and allows relationships between changes in ichnocoenoses within a depositional system to be documented and placed in a high-resolution sequence stratigraphic framework. Relying on the sedimentary and ichnological characteristics, the siliciclastic succession is divided into two facies associations: a wave-dominated offshore-shoreface complex and a tide-river influenced delta. The first includes facies that have been deposited in shelf-offshore, upper offshore, lower shoreface and upper/middle shoreface environments, the latter includes facies that have been deposited in prodelta and delta front. Integrated ichnologic and sedimentologic studies of the Gadvan Formation, allow distinction between prodelta and delta front and open marine deposits. With the identification of maximum flooding and ravinement surfaces as bounding surfaces of the stratal units, detailed analysis on systematic changes in the stacking pattern (cycle thickness, cycle type, and facies proportion) are made. Eight ichnocoenoses could be differentiated in the studied sections. The positions of the ichnocoenoses within genetically related stratal units (genetically related ichnocoenoses), indicate three large-scale cycles (DS1 to DS3, from oldest to youngest). The cyclical nature of the Gadvan Formation is attributed to low-amplitude eustasy in greenhouse conditions formed under interaction of eustatic high-frequency cycles and longer term tectonically driven sea-level variations during the long-term transgressive sea-level trend of the early Cretaceous. Stratigraphic architectural style of sequences DS1 to DS3 (which includes scarce evidence of lowstand deposits, partial or total truncation of the HST, and predominance of thick transgressive deposits), is remarkably similar to long-term transgressive sea-level trend of the Early Cretaceous across the Arabian Plate. This study suggests a more relatively seaward position of the siliciclastic successions of the Gadvan Formation of Abadan Plain than the Mesopotamian Basin (upper Zubair Formation equivalent in western Iraq and Kuwait), which would be concordant with the prevailing view of an easterly prograding coastline across the Arabian Plate.This study reveals important sedimentological and ichnological features and permits the development of predictive models for the paleoenvironmental and sequence stratigraphical significance of trace fossil assemblages that can be readily compared or translated to analogous depositional systems worldwide. The ichnological analysis is based on cores and can be especially applied to evaluate the applicability of current ichnological models to the study of Cretaceous reservoirs of western Iraq, Kuwait and western Saudi Arabia.

The High Resolution Sequence Stratigraphic Isochronous Framework in Threezhao Peripheral Zone

In detailed study on sedimentary characteristics of Fu Yang reservoir around Threezhao area, based on the theory of high resolution sequence stratigraphy of the base level cycle isochronous contrast, regard short-term base-level cycle as the minimum isochronous contrast comparing unit, this paper has carried on the fine high-resolution isochronous contrast of the reservoir in the studied area, and the high resolution[1] sequence division of different orders of base-level cycle of Fuyu oil layer and Yangdachengzi oil layer. The Fuyu reservoir is divided into one complete long-term base-level cycle and three complete medium-term base-level cycle; while Yangdachengzi reservoir is divided into a long-term base-level rise hemicycles and 3 middle-term base-level rise hemicycles. According to mud logging, well logging and core analysis data, the sands group stratified mark of the Fuyu reservoir has been determined.