Sequence Stratigraphic Architecture Research Articles

Sedimentological and sequence-stratigraphic analyses of the Tithonian Hith Anhydrite Formation in the Dahal Hit outcrop, Saudi Arabia

The Dahal Hit cavern in Central Saudi Arabia is the only locality where the Tithonian Hith Anhydrite Formation is exposed in the Middle East. In 2010, a 28.5-m interval in the 90-m-thick Hith Formation was logged and described in the cavern as part of a study to evaluate its sedimentological and sequence-stratigraphic architecture and to identify potential high-permeability layers within the seal of the world’s most prolific petroleum system. Seven facies types were interpreted as reflecting sabkha (subaerial) or salina (subaqueous) settings, and their vertical stacking patterns revealed that the logged interval consists of three transgressive–regressive cycles and part of a fourth cycle. The cavern was revisited in 2016 but only to find that the water level had risen by about 50 m rendering further geological studies impossible. The higher level of the water suggests that the cavern was flooded by the flow in the subsurface of treated sewage water released into a former quarry. The quarry is situated about 10 km southeast of the cavern, and the storage of water in it started in 2008. The flow pathways to the Dahal Hit cavern are apparently well-connected karsts, caverns, and high-permeability flow zones present in dolomite layers.

Quaternary stratigraphic architecture of the Pearl River Mouth continental shelf, northern South China Sea: Unraveling stratigraphic imprints of tectonism, paleoceanography, and climate change

The complexity of continental shelf stratigraphy is determined by the interactions among various global or local factors. However, their specific roles are still poorly understood. Using a newly-acquired grid of single-channel seismic reflection profiles, combined with piston cores, shallow boreholes, and industrial wells, this study investigates the sequence stratigraphic architecture and evolution of the Quaternary continental shelf offshore the Pearl River Mouth (PRM), northern South China Sea (SCS). Three types of bounding surfaces have been identified according to their stratal terminations: erosional surfaces (ESs), flat-lying surfaces (FSs), and locally dipping surfaces (LDSs). Given the limited extent of LDSs, we utilized ES/FS couplets to subdivide the upper Quaternary section into six high-frequency sequences (SQ6–SQ1) and their corresponding systems tracts. Within each sequence, regional progradational clinoforms (RPCs) prevail across the entire shelf and are accompanied by downstepping shoreline trajectories, which we interpreted as deposits of falling-stage systems tract. RPCs are interrupted by intercalated sheeted units (ISUs) characterized by high-amplitude and continuous seismic reflections, which may consist of transgressive and lowstand deposits. In younger sequences particularly SQ2 and SQ1, progradational-aggradational clinoforms (PACs) with ascending shoreline trajectories are well developed but confined to the shelf margin, indicating efficient sedimentation during lowstand.Our results revealed significant spatial and temporal variability in stratigraphic architectures of the PRM shelf. Along the SW–NE direction, the stratigraphic pattern changes from progradation to retrogradation and back to progradation, resulting in three sectors with distinct shoreline trajectories. Retreating shoreline trajectories and retrogradational stacking patterns are preferentially present in areas adjacent to the Dongsha Rise, which are jointly influenced by several local factors such as tectonism and intense marine processes. Temporally, a dramatic change in stratigraphic patterns can be observed across a key surface ES4, dated ca. 0.8 Ma. Below ES4, fluvial incisions are scarce and RPCs are overall low-angle and capped with relatively thick ISUs. Also, no lowstand PACs were observed. Above ES4, large-scale incised valley networks appear, together with increased scale and dominance of RPCs and PACs. This stratigraphic imprint is attributed to the Mid-Pleistocene Transition (MPT), which caused a noticeable increase in periodicity, amplitude, and asymmetry of glacio-eustatic cycles. The increased scale of RPCs and PACs after the MPT may reflect increased sediment input due to high denudation rate under intensified monsoon climate.

Growth and demise of a Paleocene isolated carbonate platform, northwest Sirte Basin, Libya: Sequence stratigraphic architecture and controlling factors

Growth and demise of a Paleocene isolated carbonate platform, northwest Sirte Basin, Libya: Sequence stratigraphic architecture and controlling factors

Integrated analysis of a mixed carbonate-siliciclastic reservoir in the Iranian Asmari intra-shelf Basin: Insights from well data, seismic profiles, and outcrops

A multidisciplinary approach (facies analysis, biostratigraphy, cyclostratigraphy, and seismic stratigraphy) was employed in this case study to assess the depositional geometry and sequence stratigraphic architecture of a mixed carbonate-siliciclastic reservoir in the Oligo-Miocene Asmari intra-shelf basin (SW Iran). The integration of both the surface and subsurface datasets provides an excellent opportunity for this analysis. Previously, this reservoir was assumed to consist of flat-lying strata with no significant gradient, primarily because of the emphasis on the lithostratigraphy correlation technique and, to some extent, biostratigraphy resolution. However, these aspects have been discussed and improved in this study. Subsurface data, including well data and seismic data, correspond to the southern flank of the Asmari Basin (Kupal Oil Field), which was compared with the exposed sections (Lar and Dashtak anticlines), exceptionally found in its northern counterpart. The Oligo-Miocene rock successions studied here are Chattian-Burdigalian in age and comprise 14 sedimentary facies distributed along different settings of a depositional profile, ranging from deep-water basin (F.1, F.2) and shallow-water carbonate platform (F.3 to 13) to continental settings (F.14). Using cyclostratigraphy, 19 significant timelines were identified along the oil field and calibrated with age dating and seismic data. The integration of well-to-seismic data ties and outcrop observations allowed for the identification of five seismic facies and four seismic packages. Consequently, the combination of these techniques and methods established a sequence stratigraphy architecture comprising four 3rd-order depositional sequences (sequence. I, II, III, IV). The transgressive system tract (TST) and highstand system tract (HST) are the main packages identified within these sequences. Due to the resolution of seismic data and the spatial position of the Oligo-Miocene depositional setting in the Kupal Oil Field, Lowstand system tract (LST) can only be observed in the sequence. I. within this sequence, three 4th-order depositional sequences (cycles. I-a, I-b, I-c) were hierarchically nested into the HST package.

Tecono-stratigraphy of Paleogene Zhu-3 depression of the Pearl River Mouth Basin, South China Sea: Implications for syn-rift architecture in multiphase rifts

In multi-phase rift basins, the links between fault activities and sequence stratigraphic architectures are still poorly understood compared to single-rift basins. The purpose of this work is to give implications for tectono-stratigraphic signatures in multiphase rifts based on seismic data from the Zhu-3 Depression in the Pearl River Mouth Basin, China. Stratigraphically, three composite sequences (CS1-3) defined by major unconformities in the Paleogene successions of the Zhu-3 Depression are interpreted, with each one subdivided into two or three third-order sequences. Regional unconformities and basin configurations indicate two episodic rift phases, termed rift phase 1 (formed CS1), and rift phase 2 (formed CS2) followed by a lithospheric breakup phase (formed CS3). From rift phase 1 to rift phase 2, the basin evolved from small-sized, independent half-grabens into relatively large-scale grabens and finally a dish-like basin configuration. Fault displacement and stratigraphic stacking patterns revealed three distinctive structural stages of rift phase 1: rift initiation (WC-SQ1), rift development (WC-SQ2), and rift termination (WC-SQ3) stages. However, an immediate decrease in fault activity was recorded in the rift phase 2. Immediate strain localization under rotated extension fields during episodic rift phases led to variabilities in tectono-stratigraphic architectures. In turn, this transition may likely contribute to interpreting the depositional pattern from balanced infill during rift phase 1 to an overfilled pattern during rift phase 2 as well as the breakup stage in response to possible enhanced sediment supply. This work enhanced our understanding of additional hydrocarbon evaluations in the Zhu-3 Depression, South China Sea.

Lower Eocene carbonate ramp clinoforms of the southern Tethys; Zagros Foreland Basin, SW Iran: Sequence stratigraphy architecture, basin physiography and carbonate factory controlling parameters

AbstractExcellent cliff exposures in the Khush‐Ab and Chenareh anticlines (Zagros Foreland Basin, SW Iran) offer a good opportunity to document stratal geometries, paleofacies heterogeneity, depositional architecture and depositional cycles of the Lower Eocene sedimentary basin system. These unique outcrops containing six logged sections have been studied across a large‐scale transect, covering ca. 10 km of continental (Kashkan Formation), carbonate‐dominated platforms (Taleh‐Zang Formation) and submarine fan to basin‐floor settings (Amiran and Pabdeh formations). Field observations of the bedding geometries revealed a set of NE–SW oriented carbonate ramp clinoforms (clinoformal units 1–4) with sigmoidal cross‐sectional shapes and an internal fore‐stepping architecture. Based on detailed facies analysis, six facies associations (FA) were identified (FA.I to FA.VI), which are interpreted to have been deposited laterally in the continental, proximal to distal and deep‐water settings of a distally steepened carbonate ramp. According to the stratal stacking pattern, bounding surface, facies architecture and internal makeup of carbonate clinoforms, four H‐F‐cycles (cycle I–IV) corresponding to a lower hierarchical rank (fourth‐order cycle) were recognized and nested within the regressive stacking pattern (HST) of a higher hierarchical rank (third‐order sequence). These H‐F‐cycles are arranged in three segments (bottomset, foreset and topset) of each clinoformal unit. Higher rank transgressive blocks (TST) discriminated each clinoformal unit by up‐deepening sets of the H‐F‐cycle V. In total, five third‐order depositional sequences were identified. The sequence, stratigraphic framework and internal makeup of this carbonate platform indicate that these carbonate sloping successions are the type of accretionary carbonate ramp clinoforms that display an ascending ramp‐slope break trajectory. Evolutionary episodes of biogenic communities, climatic change, local tectonic movements, physical processes (e.g. waves and storms) and water depth gradient are major forcing parameters that controlled the carbonate factory and depositional geometry of this Lower Eocene succession; however, carbonate‐producing organisms and eustatic sea‐level fluctuations played the first role, and local tectonic movements in response to tectonic activities of the Zagros Foreland Basin played the second role. As a result, Taleh‐Zang carbonate platforms are rich in diverse assemblages of LBFs without fragments of coral and red algae, which appear to be a consequence of a hothouse state that diminishes the global thermal gradient, weakens pycnoclines and thereby limits the turbulence.

High-resolution geologic modeling and CO2 flow simulation of a realistic clastic deltaic 3D model derived from a laboratory flume tank experiment

Carbon sequestration in geologic reservoirs is a proven method for reducing carbon dioxide (CO2) emissions from industrial point sources. Subsurface deltaic deposits are attractive candidates for CO2 storage projects due to their common occurrence as host to significant hydrocarbon and hydrologic resources, and are highly prospective for subsurface storage of large volumes of CO2. This research informs subsurface passive margin deltaic reservoir characterization and fluid flow performance for geologic carbon storage. The objective of this research is to create a high-resolution geocellular digital model that honors both the large-scale stratigraphic architecture and local vertical and lateral facies heterogeneity represented in deltaic environments of deposition. We present a novel approach to reservoir model generation by utilizing a previously generated meter-scale physical flume sand tank analog experiment to represent realistic deltaic stratigraphic architectures and facies distributions. The result is an extremely high-resolution geologic model that can be used for a variety of applications, including single and multiphase fluid flow simulation. An application is presented using the example model to simulate buoyant fluid (CO2) migration and resulting saturation distribution. Results emphasize the importance of recognizing sequence stratigraphic architectures in deltaic depositional settings for predicting CO2 migration and retention (storage capacity).

Sequence stratigraphic architecture, evolution, and geological controls of an Eocene isolated carbonate platform, NE Sirte Basin, Libya

The sequence stratigraphic architecture, evolution, and controlling mechanisms of a lower and middle Eocene isolated carbonate platform in the Sirte Basin in north-central Libya were interpreted from two- and three-dimensional (2D and 3D) seismic and well data. The platform contains six stratigraphic surfaces that divide the platform sedimentary successions into two stratigraphic sequences, namely Sequence 5 and Sequence 6, and five systems tracts. The five systems tracts vary in thickness and differ in depositional systems. The lowstand systems tract (LST) of Sequence 5 forms at the base of the focus interval and is composed of a basin floor fan system with hummocky to undulated seismic facies. The highstand systems tracts (HST) of Sequence 5 has the greatest thickness and comprises a well-defined slope system showing a funnel-shaped trend and suggesting progradational stacking pattern. The LST of Sequence 6 contains a middle ramp system formed during the lowest sea-level. The two transgressive systems tracts (TST) are the thinnest, several meters thick, and separating the LST from the HST. Log curves show an overall funnel-shaped motif through all three depositional systems, indicating a progradational stacking pattern. The main factor controlling the platform growth and demise is sea-level fluctuations. Additional factors, such as, subsidence, antecedent topography, and prevailing currents have also contributed to the evolution of the platform. Sea-level changes coupled with subsidence create accommodation for the platform growth and terminate deposition by drowning. The pre-existing topography creates a topographic relief and influences the growth pattern of the platform. Prevailing local currents influence the direction of platform progradation. This study provides insights on the evolution of isolated carbonate platform in a rift setting, which can help predict the lithofacies and depositional systems of economic significance.

Controls of allogenic factors on the development of fluvial sequence stratigraphic architecture: A case study

Controls of allogenic factors on the development of fluvial sequence stratigraphic architecture: A case study

Sequence stratigraphic architecture of the Lower Triassic Montney Formation, northeastern British Columbia, Canada

Sequence stratigraphic architecture of the Lower Triassic Montney Formation, northeastern British Columbia, Canada

Quantifying controls on the occurrence of nonmarine fossils

Abstract Although numerous studies have described differential preservation of nonmarine fossils in channel and floodplain facies, quantitative comparisons are lacking. We present measurements of the probability of occurrence of plant, mollusk, and vertebrate fossils in the Campanian Judith River Formation of north-central Montana, USA. The data reveal little difference in the probability of occurrence among higher taxa in channel and floodplain facies, except for plants, which have a higher probability in floodplain deposits. This surprising result supports more recent models in which many organisms are buried initially in floodplain deposits, but those deposits are subsequently exhumed by migrating rivers, and finally buried in those channels. Comparisons across systems tracts revealed intriguing patterns in which plants have a higher probability of occurrence in high-accommodation systems tracts in channel and floodplain deposits, and vertebrates have a higher probability of occurrence in channels of the low-accommodation systems tract. These results confirm that sequence-stratigraphic architecture should be considered in interpretations of the nonmarine fossil record. This probability of occurrence method has promise for many other comparisons of fossilization potential.

Depositional environment and sequence stratigraphy architecture of continuous Upper Permian and Lowermost Triassic deep marine deposits in NW and SW Iran

The end-Permian mass extinction, the greatest biotic crisis through the Phanerozoic, caused a severe loss of marine organisms in terms of abundance and diversity. Knowing sea level fluctuations, environmental conditions and the sequence stratigraphic architecture of the Upper Permian deposits will enable us to reconstruct events before the mass extinction and across the Permian/Triassic boundary in a regional and global context. The Upper Permian deposits are examined in well-known sections in Julfa, NW Iran and Abadeh in SW Iran using microfacies analyses, depositional environment interpretation and sequence stratigraphic framework. Detailed petrographic examination and microfacies analyses show third- and fourth-order cycles both in Wuchiapingian and Changhsingian deep-water distally deposited strata of Julfa and Abadeh sections. Considering Iranian tectonics during Permian through Triassic time, there was rifting accompanied by drift and subsequent subsidence. Tectonics was a main factor that influenced the depositional environment and sequence stratigraphic framework in the study areas. According to previous studies, since subsidence increased in a North to SW direction during Middle Permian through Triassic time, this effect is seen in lithologic characteristics of the Wuchiapingian with more mid-ramp settings in Julfa Beds in Julfa area, compared to the more outer-ramp settings of the Unit 6 of the Hambast Formation in Abadeh area. Tectonic subsidence influence was also responsible for creating the fourth-order cycles within third-order cycles despite the absence of common glacial events to create high-frequency cycles in Iran during the Lopingian. The Lopingian successive deepening in Iran caused the faunal changes which is evident in decreasing trend of body size and biodiversity in brachiopods and ammonoids and also marks the beginning of the transgressive system tracts during this time interval.

Predicting sequence stratigraphic architecture and its implication for hydrocarbon reservoir potential of the uppermost Silurian through Lower Devonian Winduck Interval, central Darling Basin of western New South Wales, SE Australia

This paper provides the results of lithostratigraphy and depositional environment of the uppermost Silurian through Lower Devonian Winduck Interval section from three areas widely distributed in the central Bancannia Trough from Bancannia South 1 well, the southern Pondie Range Sub-basin from Pondie Range 1 well and the northwestern part of the Blantyre Sub-basin from two wells, the Booligal Creek 1 and 2. These wells were studied using wireline log, core and cutting data to predict sequence stratigraphic architecture and its implication for hydrocarbon sandstone reservoir potential. This study necessitated the use of detailed facies prediction relationships and geometry of lithostratigraphic concepts for the purpose of establishing a sequence stratigraphic architecture framework of the studied areas. Two units were established, lower and upper Winduck Interval, within the Winduck Interval identified by lithological data examination and wireline log characteristics of the sediments from the four wells in the study area. Results of the lithology type analysis showed that the Winduck Interval is interbedded richly in sandstone and siltstone complex deposits. This paper presents a clear picture of the sequence stratigraphic model, as well as that of the three third-order depositional sequences (DS1, DS2 and DS3, respectively) that are identified from changes in systems tracts patterns (composed of lowstand, transgressive and highstand), vertical and lateral facies sequence thickness changes and the lithostratigraphic units distribution in the Winduck Interval section. Potential reservoir prospectivity targets are identified in lowstand system tracts and highstand system tracts deposits consisting of sandstone facies and thin silts, while the transgressive system tracts deposits consist of shales and some interbedded shaly siltstones, many having excellent potential source and seal properties. The contribution of sequence stratigraphy as an approach to understanding lithostratigraphy of the Winduck Interval has important significance in regard to future hydrocarbon reservoirs exploration across the central Darling Basin.

Hyperextension and polyphase rifting: Impact on inversion tectonics and stratigraphic architecture of the North West Shelf, Australia

Restoration of interpreted 2D deep seismic lines across Australia's North West Shelf indicates that rifting style changed significantly during multiple phases of extension and continental breakup. Early phase rifting during the Neo-Proterozoic and Early Paleozoic, characterised by low-angle detachment faults, crustal-scale necking and hyperextension of the crust (Metamorphic Core Complex Mode), was localised over pre-existing Proterozoic orogenic belts formed adjacent to major cratonic blocks. Subsequent extensional events in the Late Paleozoic and Mesozoic reactivated these low-angle rift fault systems. However, a series of narrow rift basins (Narrow Rift Mode), bound by high-angle normal faults that cut into the upper mantle, also began forming due to changes in the rheological architecture of the lithosphere following previous extension, crustal thinning and post-rift cooling. Wide rift mode extension, wherein extensional deformation was distributed over broad areas, may have occurred prior to, or in conjunction with, the development of more localised narrow rifts (dual mode rifting) in areas such as the Northern Carnarvon and Browse basins. Extensional deformation progressively localised into the narrow rift basins, which in some cases, matured into seafloor spreading centres during breakup, typically outboard of the major low-angle detachment fault systems. The resulting general structural architecture evolution is consistent with several other hyperextended margins from around the world.The rift events were punctuated by periods of thermal sag, often in conjunction with pulses of compressional deformation associated with plate-scale tectonic events. Structural restoration of 2D regional seismic lines shows a marked difference in the way the different polyphase rift basin elements responded to shortening. Low-angle detachment faults were relatively well oriented for reactivation under compression, leading to the development of inversion anticlines and associated convergent unconformities towards the inboard basin margin. In contrast, high-angle normal fault systems associated with the pre-existing narrow rift basins were poorly oriented for reactivation during compression and tend to be characterised by minor wrench/flower structures, generally with relatively limited uplift and erosion on the basin margins. Regional in-plane compressional stresses also worked in combination with vertical loading due to thermal decay to downwarp the lithosphere, forming broad rapidly subsiding synclinal basins above axes of the pre-existing rift basins. The evolving structural architecture developed during the compressional events had significant impacts on the associated sequence stratigraphic architecture.

Depositional environment and sequence stratigraphy of the Upper Cretaceous Aruma Formation, NE Riyadh, Saudi Arabia

The Campanian to Maastrichtian Aruma Formation represents a distinctive depositional system of the carbonate-dominated ramp along the Arabian plate. Sedimentologic characteristics and stratigraphic relations are integrated with carbon and oxygen stable-isotope data to interpret the depositional environments in a sequence stratigraphic framework. One siliciclastic facies association (FA1) and eight carbonate microfacies (MF 1–8) belonging to four facies belts (FB1–4) were identified. Facies characteristics support accumulations on a carbonate ramp environment that extends from offshore/outer ramp to middle and inner ramp settings. Stable-isotope data are correlated to the oscillating global sea-level curve and global excursions’ events in order to refine the sequence stratigraphy of the Aruma Formation. Carbon-isotope chemostratigraphy shows remarkable long-time excursions, which are correlated to the two global negative excursions (Late Campanian event “LCE” and Campanian–Maastrichtian boundary event “CMBE”) as well as the positive δ13 C excursion of Middle Maastrichtian event “MME” and the uppermost negative δ13 C excursion toward the K–Pg boundary. The negative shift in the δ13 C values associated with relatively positive values in the δ18 O herald three marked sea-level falls, which can be coincided with global sequence boundaries. The merged surfaces TS1/SB1 and TS2/SB2 can be correlated to the Campanian events KCa3 (80 Ma) and KCa6 (75.4 Ma), respectively. The coplanar surface TS3/SB3 matches well with the Maastrichtian event KMa3 (69.4 Ma). The positive values of δ13 C and/or negative values of δ18 O coincide with periods of maximum transgressions. The minor pulses are mostly attributed to cyclic fourth-order sequences. The established sequence stratigraphic architecture and depositional model of the outcrop data herein will be useful in regional correlations with analogous subsurface successions along the Arabian plate and enhancement of potential petroleum explorations.

The effects of strong sediment-supply variability on the sequence stratigraphic architecture: Insights from early Toarcian carbonate factory collapses

Standard sequence stratigraphy interpretations are commonly built upon the premise of fairly constant sediment supply, leaving vast uncertainties about sequence architecture and sea-level change recorded during major paleoenvironmental disturbances, usually associated with carbonate productivity collapse and increased siliciclastic sediments supply. During relative sea-level rise, this process is referred to as drowning event. However, drastic collapse of carbonate productivity during relative sea-level drop remains poorly documented. The Pliensbachian/Toarcian boundary in Morocco provides an outstanding example of such a case, referred here to as poisoning event. Using bio-, chemo- and high-resolution sequence stratigraphic approaches on horizontal seismic-scale outcrop data, we characterize the architecture of vertically and laterally mixed siliciclastic/carbonate systems. During poisoning event, the standard sequence Lowstand-Transgressive-Highstand system tracts is altered into Highstand-Transgressive-Falling Stage system tracts with little or no evidence for Highstand deposits. Noteworthy, it is important to note that poisoning and drowning events can be confused together in sedimentary records where the shoreline trajectory cannot be clearly tracked, as it has often been the case in previous Pliensbachian/Toarcian studies. The outcome of this study calls thus for a closer re-examination of other carbonate factory collapse event attributed to drowning events without an unambiguous knowledge of their coeval shoreline trajectory.

Sequence stratigraphy of the Andaman Basin, northern Indian Ocean

Andaman Basin, a poly history basin in the northeastern Indian Ocean, preserves the sedimentary record from Late Cretaceous to Recent with several stratigraphic breaks. Studies from outcropping sedimentary succession, integrated with subsurface data from drilled wells in the offshore, have enables to work out a sequence stratigraphic framework of the sedimentary succession in the basin.The succession comprises of three first-order sequences viz., Late Cretaceous – Eocene, Oligocene and Neogene. These have been related to basin forming tectonic events related to accretionary prism formation and subduction in Paleogene, Oligocene uplift and renewed subduction in Neogene, respectively. Excellent bio-stratigraphic control and field evidence have enabled identification of unconformities of various magnitudes, which in turn has enabled mapping second-order sequence. The 3 second-order sequences within first-order Late Cretaceous–Eocene sequence are: Late Cretaceous-Early Paleocene, Late Paleocene-Middle Eocene and Late Eocene sequence. The Oligocene first-order sequence related to the major uplift and emergence of the main Andaman Island chain, contributed >2000m of flysch sediments. Three second-order sequences within the first-order Neogene sequence are Early Miocene - early Middle Miocene, Middle Miocene - Middle Pliocene and Late Pliocene - Pleistocene sequences separated by unconformities of various magnitude. Each sequence is discussed with respect to its extent, nature of sequence boundaries, sedimentary fill and sequence stratigraphic surfaces to understand the sequence stratigraphic architecture of the basin.

Influence of sediment supply rate on sequence stratigraphic architecture change: A case study from the Kaiping Sag, northern South China Sea

The sequence stratigraphic architecture change is mainly controlled by three factors: basement subsidence or uplift, sea level change and sediment supply. However, the internal mechanism of the influence of the sediment supply on the sequence stratigraphic architecture change is not clear. In this paper, the Middle-Upper Miocene sequences in Kaiping Sag, northern South China Sea are taken as an example to discuss this issue. First, we divide and correlate the sequence through the comprehensive analysis of drilling and seismic data, and restore the seven seismic sequences in the study interval to their original form of sedimentary stage through the original form structural section restoration technique. Then, based on the original form structural section, the vertical changes of sequence stratigraphic architecture are recognized and the basement subsidence rate and sediment supply rate are estimated. Furthermore, through the correlation analysis between the sediment supply rate and the sequence stratigraphic architecture change, how the sediment supply rate affects the sequence stratigraphic architecture changes is recognized. The results show that the stratigraphic frameworks of the seven sequences are all LST-TST-HST-FRST combination, but the scale of systems tracts of each sequence varies greatly, which is quite different from the sequence stratigraphic architecture of the adjacent Baiyun Sag. The second-order cycle sea level change, basement subsidence, regional tectonic uplift and special paleogeographic environment (Kaiping Sag is located in the lateral edge of the trough zone) in the study area jointly lead to the variation of sediment supply rate in time and space, and this variable sediment supply rate is the main driving force for the change of sequence stratigraphic architecture in Kaiping Sag.

Paleo-facies distribution and sequence stratigraphic architecture of the Oligo-Miocene Asmari carbonate platform (southeast Dezful Embayment, Zagros Basin, SW Iran)

A facies and sequence stratigraphic analysis was made of the Oligo-Miocene Asmari carbonate platform situated in the east and southeast of the Dezful Embayment (Zagros Basin, SW Iran). This study provides new paleofacies and depositional sequence distribution models for the eastern part of the Dezful Embayment and discusses the impact of the factors controlling sediment deposition being eustatic sea-level changes and tectonic processes. The petrographic study reveals that the variations in facies cover three depositional settings, e.g. open marine, lagoon and tidal flats. In total, six depositional sequences (DS) were identified within the sedimentary sequence of the Asmari Formation. DS1 and DS2 were deposited during the Rupelian (Oligocene) within deeper open marine platform settings. Sediments forming DS3 and DS4 were deposited during the Chattian in a carbonate platform environment within an open lagoon to protected lagoon setting. The Miocene DS5 and 6 sequences, Aquitanian and Burdigalian in age, were deposited in shallower environments compared to other DS's, within protected lagoon to tidal flat settings. A comparison with the sedimentary development in other parts of the Dezful Embayment showed that the deposition of the Asmari strata started earlier (Early Rupelian) in the eastern, south-eastern and north-eastern part of the basin. In the western and central parts of the Dezful Embayment it began in the Late Rupelian or even Rupelian/Chattian. The eastern and south-eastern parts of the Dezful Embayment displayed a platform margin setting during the Rupelian while the north-eastern and central areas showed a basin setting. During the Early Chattian, clastic sediments originating from the Arabian Plate were deposited in the west, southwest, northwest and centre of the basin in response to a sea-level lowstand. The two very thin sandstone units occurring in the Late Aquitanian succession across the west of the Bibi Hakimeh oilfield are the only sandstone layers related to a sea-level lowstand throughout E/SE of the Dezful Embayment. During the Chattian the sediments in the eastern parts of the Dezful Embayment were deposited in a proximal inner ramp setting, and corals and coralline red algae (mainly Lithophyllum sp. and Lithothamnion sp.) dominated the carbonate platform in the east, while imperforate benthic foraminifera (e.g. Peneroplis sp., Archaias sp.) and rare perforate benthic foraminifera (e.g. Neorotalia sp., and Amphistegina sp.) were the most frequent sediment contributors in the southeast of the basin (Bibi Hakimeh area). At the same time, sedimentation occurred on a distal inner to mid-ramp settings through the central areas of the Dezful Embayment. A eustatic fall in sea-level and tectonic processes resulted in the isolation of the basin. During the Aquitanian two exposure horizons formed in the western and central Dezful Embayment basin while the eastern part only displays one. During the Burdigalian, sedimentation in the entire Dezful Embayment occurred within an innermost, very shallow ramp setting. The current study shows that sea-level fluctuations and sometimes combined with regional tectonic processes controlled the variability in platform geometry and paleofacies distribution of the Oligo-Miocene sediments across the basin.

Depositional environments and sequence stratigraphy of post-last glacial maximum incised valley-fill, Malay Basin, northern Sunda Shelf

The alternating submergence and subaerial exposure of the low-gradient, shallow Sunda Shelf of southeast Asia during Quaternary interglacial-glacial cycles played an important role in ocean circulation and monsoonal climate through the interchange of Indian Ocean and Pacific Ocean waters. The Quaternary stratigraphic development of this margin is, however, poorly understood. This study uses a multi-proxy approach (AMS radiocarbon, bulk sediment magnetic susceptibility, X-ray fluorescence spectrometry, and foraminiferal assemblage data) to characterize environmental change and late Pleistocene to Holocene sequence stratigraphic architecture in 16 cores from the northern Sunda Shelf off the east coast of Peninsular Malaysia.Five chronostratigraphic units are recognized. Unit 1 is an inner shelf deposit dating from a late Pleistocene sea-level highstand (the highstand systems tract of the pre-LGM base-level cycle). Units 2–4 represent different paleoenvironmenal components of the transgressive systems tract (TST) of the most recent base-level cycle. Unit 2 is a late Pleistocene shallow open embayment deposit that formed during the post-LGM inundation of the paleo-Chao Phraya River valley as sea level rose. Unit 3 is composed of late Pleistocene to early Holocene paralic peat and organic-rich mud and is capped by a transgressive ravinement surface. Unit 4 is a shallow shelf unit deposited during the early Holocene transgression on the Sunda Shelf prior to ca. 6500 cal yr BP (the onset of the regional Holocene sea-level highstand). Unit 5 represents the mid-Holocene to recent highstand systems tract (HST) deposited from ca. 6500 cal yr BP to present.The incised paleovalleys of the paleo-Chao Phraya River and its tributaries provide more accommodation space for sediment accumulation than the surrounding shelf. However, the thinness of the Holocene sedimentary record, 2–3 m in the incised valleys compared to <1 m over the adjacent shelf, indicates that the LGM incised valleys were almost filled by fluvial and coastal plain sediments before open marine conditions returned near the beginning of the Holocene. The multi-proxy approach of this study elucidates the geologic response of this shelf to sea-level rise and the sequence stratigraphic development of tropical, siliciclastic-dominated shallow shelf depositional sequences.