Sequence Stratigraphic Study Research Articles

Interplay of tectonism and eustasy during the Early Permian icehouse: Southern Sydney Basin, southeast Australia

This investigation presents an outcrop‐based integrated study of sedimentological analysis and sequence stratigraphy applied to the Lower Permian sedimentary succession in the southern Sydney Basin, Australia. This succession accumulated in several depositional environments and sub‐environments that range from non‐marine (fluvial) to marine (outer shelf), representing the fill of a sedimentary basin that resembles a fault‐bounded, rift basin. The stratigraphic analysis indicates a deepening‐upward trend, and the sequence stratigraphic approach has established that these sediments can be attributed to the lowstand, transgressive, and highstand systems tracts. Lowstand sediments can be defined by fluvial facies that are located between the subaerial unconformity and the maximum regressive surface. Transgressive facies correspond to estuarine, upper and lower shoreface, and inner and outer shelf depositional environments and are located between the maximum regressive and the maximum flooding surfaces. Highstand bottomset sediments are accumulated above the maximum flooding surface and are represented by outer shelf facies. The stratigraphic architecture indicates the development of an almost complete depositional sequence, mainly developed under the control of tectonically induced subsidence, but also influenced by the high sedimentation rates and the high gradient of the inherited topography. Eustatic sea‐level fluctuations were of minor importance during the deposition of the examined sediments.

The sequence stratigraphy and depositional characteristics of fan‐delta complexes in the Upper Bayingebi Member (Lower Cretaceous) in Chagan Sag, Inner Mongolia, China

The Chagan Sag is a small Early Cretaceous intracontinental passive rift subbasin in the Yingen‐Ejinaqi Basin Group generated on the Tianshan‐Xingmeng Orogenic Belt. The Lower Cretaceous strata contain the Bayingebi, Suhongtu, and Yingen formations deposited during the syn‐rift phase. The Wuliji Structural Zone bounded by a high‐dip syn‐sedimentary fault is an intensively studied area with an extent of ~300 km2 having abundant available subsurface dataset and great hydrocarbon potential. According to well‐ and seismic‐based sequence stratigraphic study, the Upper Bayingebi Member generally corresponds to a complete third‐order transgressive–regressive sequence in the Wuliji Structural Zone. The transgressive system tract gradually thins towards the north, but the regressive system tract covers the entire study area in this third‐order sequence. Further investigations reveal that tectonic subsidence and climate change are two predominant allogenic factors for controlling stratigraphic development in the Wuliji Structural Zone.During the deposition of the Upper Bayingebi Member, transverse gravity flow dominated fan‐delta complexes sourced from the Maodun Subuplift are well developed in the Wuliji Structural Zone. The retrogradational conical fan deltas are mainly located in the southern sector during the transgressive system tract stage, but the progradational Gilbert‐type fan deltas are widely developed during the regressive system tract stage. The sedimentary evolution and stratigraphic architecture are directly linked with preexisting topography, accommodation, and sediment supply. In addition, climate change and vegetation types are thought to be critical controls for fluid properties originated from feeder drainage systems and depositional processes of the construction of fan‐delta complexes in the distinct system tracts.

An interdisciplinary approach to reservoir characterisation; an example from the early to middle Eocene Kaimiro Formation, Taranaki Basin, New Zealand

The Kaimiro Formation is an early to middle Eocene, NE-SW trending reservoir fairway in Taranaki Basin, and comprises a range of coastal plain through to shallow marine facies. A time of regional transgression is observed across the Paleocene–Eocene transition, which is linked to a general global warming trend and to regional thermal relaxation-related subsidence in New Zealand. The earliest Eocene transgressive deposits pass upwards into a series of cyclically stacked packages, interpreted as 3rd and 4th order sequences. Maximum regression occurred within the early Eocene and was followed by punctuated retrogradational stacking patterns associated with shoreline retreat and subsequent regional transgression in the middle Eocene.The Kaimiro Formation is considered a good reservoir target along most of the reservoir fairway, which can largely be attributed to a consistently quartz-rich, lithic-poor composition and reasonably coarse sand grain size. Correlations demonstrate that within the early Eocene the main reservoir facies are channel-fill sandstones overlying candidate sequence boundaries in paleoenvironmentally landward (proximal) settings, and upper shoreface/shoreline sandstones in relatively basinward (distal) settings. Middle Eocene reservoir facies are not represented in distal wells due to overall transgression at this time, yet they form a significant target in more proximal well locations, particularly on the Taranaki Peninsula.Depositional facies is one of the principal controls on sandstone reservoir quality. However, while reservoir facies have been proven along the length of the reservoir fairway, it is evident that diagenesis has significantly impacted sandstone quality. Relatively poor reservoir properties are predicted for deeply buried parts of the basin (maximum burial >4.5 km) due to severe compaction and relatively abundant authigenic quartz and illite. In contrast, good reservoir properties are locally represented in reservoir facies where present-day burial depths are <4 km due to less severe compaction, cementation and illitisation. Within these beds (<4 km) the presence of locally occurring authigenic grain-coating chlorite (shallow marine facies) and/or well-developed secondary porosity are both favourable to reservoir quality, while pervasive kaolinite and/or carbonate are both detrimental to reservoir quality.These results illustrate how an interdisciplinary approach to regional reservoir characterisation are used to help reduce risk during prospect evaluation. Assessment of both reservoir distribution and quality is necessary and can be undertaken through integrated studies of facies, sequence stratigraphy, burial modelling and petrography.

Spatiotemporal sedimentological and petrophysical characterization of El Gueria reservoir (Ypresian) in sFAX and Gulf of Gabes Basins (SE-Tunisia)

El Gueria carbonate Formation (Ypresian) in Tunisia is a proven hydrocarbon reservoir. In the Gulf of Gabes, El Gueria reservoir consists mainly of a nummulitic limestone which is developed in an inner shelf environment. In order to characterize the depositional facies evolution and the petrophysical parameters, and to understand the origin of heterogeneity of El Gueria reservoir, we firstly conducted a sedimentological and a sequence stratigraphy study of this Formation in more than 10 wells especially in P1, then we established a detailed petrophysical study of El Gueria reservoir in P1, P3c and P7d cores.Based on lithostratigraphic and gamma ray correlations of an important number of wells in the study area, a detailed sedimentological study has been established. This latter shows that: (i): The Ypresien deposits are deposited in an inner shelf (El Gueria Formation) in the south and in an outer shelf (Boudabbous Formation) in the north of the study area with the form of horsts and grabens, (ii): 3 distinct members and 7 principal facies within El Gueria Formation have been distinguished. The coupling of data logging and data of the P1 core shows that the El Gueria deposits include 10 transgressive-regressive depositional sequences, while showing from bottom to top a broad regressive tendancy from a subtidal domain during the early Ypresian to an intertidal domain during the middle Ypresian reaching the supratidal environnement during the late Ypresian-early Lutetian.The petrophysical parameters (porosity and permeability) of El Gueria reservoir vary in time and space (laterally and vertically variation) following the deposit environment variation.Particularly, the porosity variation is controlled by eustatic cycles so that high porosities are linked with transgressive phases and low porosities with regressive phases. In addition, the vertical evolution of porosity through the El Gueria reservoir varies following the (i) deposit environments, (ii) type and morphology of nummulites such as large nummulites are more porous than small nummulites and nummilithoclastes (iii) matrix and cement such as micrite are more porous than sparite (iv) microfacies and diagenetic structures (Fractures, stylolithic seals …) such as the fractured wackstone are the most porous and permeable.

Facies and sequence stratigraphy of fluvio-lacustrine deposits: Cretaceous Nubian succession of the Saharan platform (SW Egypt)

The Early to Late Cretaceous Nubian succession of the Mesaha trough (SW Egypt) records fluvial and mudflat/lacustrine deposition in an intracratonic sag. The facies architectures and sequence stratigraphic studies of this succession were carried out through detailed description and interpretation of seven lithostratigraphic sections. The development of depositional sequences in this succession reflects variation in the accommodation-to-sediment supply ratio (A/S). The depositional site of these sediments was located tens to hundred kilometers from contemporaneous shoreline and hence any possible base level effect is not ruled out. Three depositional sequences showing an overall upward fining-coarsening couplet are established. These depositional sequences are separated by regional ferricrete markers (subaerial unconformities). Sequence 1, 20–50m thick, is characterized by amalgamated, multistory, fluvial channel deposits of proximal braidplain, defining degradational system tracts. These are capped by isolated channel deposits, 10m thick, of distal braidplain of transitional/aggradational system tracts. Sequence 2, 12–25m thick, is characterized by mudflat/lacustrine deposits of transitional system tracts passing upward to floodbasin and crevasse/terminal splays of aggradational system tracts. Sequence 3, up to 95m thick, and it is represented by degradational system tracts and consist mainly of prograding braidplain sets of. Paleocurrent trends on fluvial deposits of the depositional sequences 1 and 3 show a unimodal paleoflow to the North to northeast and the source area was located to the south/southwest. Sedimentological evidences indicate humid climate with arid/semi-arid periods during the deposition of the studied Cretaceous Nubian succession.

Petroleum system elements within the Late Cretaceous and Early Paleogene sediments of Nigeria's inland basins: An integrated sequence stratigraphic approach

Sequence stratigraphic studies have been carried out using subsurface well and 2D seismic data in the Late Cretaceous and Early Paleogene sediments of Anambra and proximal onshore section of Niger Delta Basin in the Southeastern Nigeria. The aim was to establish the stratigraphic framework for better understanding of the reservoir, source and seal rock presence and distribution in the basin. Thirteen stratigraphic bounding surfaces (consisting of six maximum flooding surfaces - MFSs and seven sequence boundaries – SBs) were recognized and calibrated using a newly modified chronostratigraphic chart. Stratigraphic surfaces were matched with corresponding foraminiferal and palynological biozones, aiding correlation across wells in this study. Well log sequence stratigraphic correlation reveals that stratal packages within the basin are segmented into six depositional sequences occurring from Late Cretaceous to Early Paleogene age. Generated gross depositional environment maps at various MFSs show that sediment packages deposited within shelfal to deep marine settings, reflect continuous rise and fall of sea levels within a regressive cycle. Each of these sequences consist of three system tracts (lowstand system tract – LST, transgressive system tract – TST and highstand system tract – HST) that are associated with mainly progradational and retrogradational sediment stacking patterns. Well correlation reveals that the sand and shale units of the LSTs, HSTs and TSTs, that constitute the reservoir and source/seal packages respectively are laterally continuous and thicken basinwards, due to structural influences. Result from interpretation of seismic section reveals the presence of hanging wall, footwall, horst block and collapsed crest structures. These structural features generally aid migration and offer entrapment mechanism for hydrocarbon accumulation. The combination of these reservoirs, sources, seals and trap elements form a good petroleum system that is viable for hydrocarbon exploration and development.

Early to middle miocene sequence stratigraphy of well-5 (OML 34), Niger Delta, Nigeria

A sequence stratigraphic study was carried out on ditch cutting samples from well-5 (OML 34) in the Niger Delta in Nigeria. The sequence stratigraphic analysis based on foraminifera content and lithologic descriptions has revealed the following: five systems tracts (two transgressive systems tracts, two highstand systems tracts and one lowstand system tract); two third order maximum flooding surfaces (proposed at 3388 m and 3557 m dated 15.9 Ma and 17.4 Ma respectively) and two sequence boundaries proposed at 3301 m and 3466 m dated 15.5 Ma and 16.7 Ma respectively with the aid of index foraminifers present in the well (Praeorbulina glomerosa, Praeorbulina sicana, Orbulina saturalis and Catapsydrax dissimilis), as a result, three depositional sequences were established from the well intervals. These depositional sequences with the foraminifera species present in the well revealed that the well interval was exposed to two local depositional cycles (cycle 6 and 7), two regional cycles (cycles 2.2 and 2.3) within the TB2 super cycles corresponding to Haq et al. (1988) chronostratigraphic chart.

Facies analysis, sequence stratigraphy and chemostratigraphy of the Sete Lagoas Formation (Bambui Group), northern Minas Gerais State, Brazil: evidence of a cap carbonate deposited on the Januária basement high

ABSTRACT: Sedimentary rocks of the Sete Lagoas Formation, exposed in the left margin of the São Francisco river (Minas Gerais State, Brazil), were deposited on the Januária-Itacarambi basement high. They show both lateral and vertical rock stacking along continuous outcrops, allowing us to carry out detailed facies analysis and sequence stratigraphy studies. Our studies also integrate data from geological mapping, macro and microscopic petrography and high-resolution C and O isotope analysis. Eight facies and four facies associations make up a sequence composed by a transgressive tract in the base, and a high stand tract in the upper portion, separated by a maximum flooding surface. The high stand tract shows a progradation stacking from the basement high apex towards progressively deeper basement areas. This stratigraphic framework, associated with others stratigraphic and isotopic features, indicates that the now exposed Januária basement high also represents a paleo-high during the sedimentation event. Aragonite pseudomorphs and dolomites coupled with δ13C values of -5‰ characterize the basal carbonate of the transgressive tract as a cap carbonate. Records of the Cloudina fossil, recognized in the high stand tract, indicate a Late Ediacaran age for the upper portion of the studied stratigraphic sequence.

Paleoenvironmental Distribution Patterns of Sequence Stratigraphy in the Paleocene-Eocene Deposits of Sekonj Trough Event (Central Iran)

The Paleocene-Eocene successions were studied in Sekonj and Abaregh sections and located in South of Kerman in order to determine the microfacies, depositional environment and sequence stratigraphy. The deposits in the studied area are mainly composed of limestone, sandstone, conglomerate and shale. The obtained data from the field and laboratory observations led to identification of 11 microfacies which represent the coastal, tidal flat, lagoon, barrier and proximal open marine which were deposited in a carbonate-siliciclastic ramp environment. The sedimentology evidences, vertical analysis of microfacies, facies and relative sea level changes represent that the Paleocene-Eocene succession deposits have two 3rd depositional sequences in the studied area. The sequence 2 cannot be recognized completely due to the lack of outcrop. Sequence stratigraphic studies show an upward shallowing trend corresponding to the global sea level changes from the base to the upward of the succession.

Anatomy of a eustatic event during the Turonian (Late Cretaceous) hot greenhouse climate

Sequence stratigraphic studies consider relative change in sea level (as regulated by eustasy, local tectonics and sediment supply) as the main builder of the stratigraphic record. Eustasy has generally been considered as a consequence of the growth and decay of continental ice sheets that would explain large, rapid changes in sea level, even during periods of relative global climatic warmth. However, such a mechanism has become increasingly difficult to envision during times of extreme global warmth such as the Turonian, when the equator-to-pole temperature gradient was very low and the presence of polar ice seems improbable. This paper investigates the timing and extent of sea level falls during the late Cenomanian through Turonian, especially the largest of those events, sequence boundary KTu4, which occurred during the middle to late Turonian peak of the Cretaceous hot greenhouse climate. We conclude that the amplitude of the widespread third-order sea level fall in the middle Turonian that is centered at ~91.8 Ma varies at different locations depending on the influence of dynamic topography on local tectonics and regional climatic conditions. Ice volume variations seem unlikely as a mechanism for controlling sea level at this time. However, this causal factor cannot be ruled out completely since Antarctic highlands (if they existed in the Late Cretaceous) could sequester enough water as ice to cause eustatic falls. To ascertain this requires detailed tomographic imaging of Antarctica, followed by geodynamic modeling, to determine whether high plateaus could have existed to accumulate ephemeral ice sheets. Other mechanisms for sea level change, such as transference between ground water (a small amplitude shorter time scale effect) and the ocean and entrainment and release of water from the mantle to the oceanic reservoir (a potentially large amplitude and longer time scale process), are intriguing and need to be explored further to prove their efficacy at third-order time scales.

Seismic tectono-stratigraphy of fluvio-deltaic to deep marine Miocene silicoclastic hydrocarbon reservoir systems in the Gulf of Hammamet, northeastern Tunisia

Most of hydrocarbon accumulations within the Gulf of Hammamet foreland basins in eastern Tunisia are reservoired within the Upper Miocene Birsa and Saouaf sandstones. It is the case of Birsa, Tazarka, Oudna, Baraka, Maamoura, Cosmos and Yasmine fields. These sandstones constitute oil and gas fields located on folded and faulted horst anticline highs and described as varying from shoreface to shallow marine and typically exhibit excellent reservoir quality of 30 to 35% porosity and good permeability from 500 to 1100 md. In addition, the fracturing of faults enhanced their reservoir quality potential. However, due to the lack of seismic stratigraphic studies to highlight depositional environment reservoir characterization and distribution, petroleum exploration faces structural and stratigraphic trap types and remains on targeting only high fold closures with limited reserve volumes of hydrocarbons. As an example of the Birsa concession case, syn-sedimentary tectonic structuring and geodynamic evolution during Middle to Upper Miocene Birsa reservoir sequences have guided the distribution of depositional environment of sandstone channel systems around horst and grabens by E-W, NE-SW and N-S strike slip flower faults controlling the subsidence distribution combined with the eustatic sea level variations. Seismic sequence stratigraphy study of Miocene Birsa reservoir horizons, based on the analysis and interpretations of E-W and N-S 3D selected regional lines that were compared and correlated to outcrops and calibrated by well data, permitted to highlight the basin configuration and sequence deposit nature and distribution. Sedimentary infilling of the basin from Langhian Ain Ghrab carbonate to Serravallian Tortonian Birsa and Saouaf sandstone and shale formations is organized in four third-order seismic sequences, limited by regional erosional toplap, onlap and downlap unconformity surfaces and by remarkable chronostratigraphic horizons of forced and normal erosive lowstand and highstand system tracts separated by transgressive and maximum flooding surfaces. Reconstructed sedimentary paleo-environment distribution vary from deltaic fluvial proximal deposits in the northern part of the high central Birsa horst to a delta front and prodelta coastal and shelf shore face and shore line channelized deposits in the surrounding borders of grabens. Distal deposits seem to be distributed from upper to lower slope fans and probably to the basin floor on the flanks of the subsiding grabens. Synthetic predictive paleogeographic depositional reservoir fairway map distribution of Lower, Middle and Upper Birsa sandstone reservoirs highlights four main domains of channelized superposed and shifted reservoirs to explore.

Climatically Versus Eustatically Controlled, Sediment-Supply-Driven Cycles: Carbonate–Siliciclastic, High-Frequency Sequences In the Valanginian of the Neuquén Basin (Argentina)

Carbonate–siliciclastic high-frequency sequences are formed by reciprocal sedimentation. In siliciclastic-dominated successions, the carbonate-rich interval is typically associated with transgressive conditions and relatively low terrigenous influx, particularly in distal parts of the marine basin. However, key questions for each individual case are: What sort of depositional system developed during transgressions, and what controls sediment-supply fluctuations? This paper integrates outcrop and subsurface data to present a high-resolution sequence-stratigraphic study of small-scale (2–18 m), carbonate–siliciclastic cycles deposited during the Valanginian in a proximal–distal transect of the Neuquen Basin (western Argentina) and discusses those key issues. Carbonate hemicycles in this study are composed of cross-bedded oolitic–skeletal grainstones and packstones to massive skeletal floatstones, which accumulated in carbonate ramps with high biogenic production in their distal sector (bivalves, serpulids, echinoids), and significant contribution of non-biogenic (ooids) material in inner-ramp settings. Siliciclastic material is present only at the base of the hemicycles, but rapidly diminishes upwards. These carbonate hemicycles have retrogradational staking patterns in proximal sectors and less obvious trends in distal areas. The siliciclastic hemicycles comprise shallowing-upward successions that include mudstones, bioturbated muddy sandstones, sandstones with HCS and SCS, and bioturbated sandstones. These facies were collectively deposited in a storm- and wave-influenced offshore-shoreface depositional system during normal regressions. These shoreface systems were likely fed by littoral drift from riverine inputs located tens of kilometers to the south. The duration of the investigated small-scale, transgressive–regressive cycles can be estimated in 50 to 150 kyr, and they are bounded by marine transgressive surfaces placed at the bases of carbonate hemicycles. The bounding discontinuities together with the sequence architecture do not suggest periods of sea-level falls between cycles, nor high-amplitude relative sea-level changes during a cycle formation. Additionally, the low proportion of mixed sediments suggests rapid changes in the rate between terrigenous supply and carbonate productivity. The resulting sequence architecture cannot be reasonably explained by autocyclic controls or eustatic changes alone. It is argued here that high-frequency changes in sediment supply, driven by orbitally induced climate fluctuations, could be a better explanation for these sequences, particularly in the context of a long-term relative sea-level rise. In this scenario, periods of low siliciclastic influx during extreme arid conditions would develop a negative balance with accommodation and prompt carbonate systems and transgression. On the other hand, during more humid conditions relatively high sediment flux would temporarily overcome long-term accommodation, producing the regressive siliciclastic hemicycles. As this scenario does not require high-frequency sea-level falls, it would satisfactorily explain the observed sequence architecture. The distal Mulichinco carbonate hemicycles would be hard to distinguish from transgressive, fossiliferous-rich deposits that characterize transgressive–regressive cycles in clastic systems. In the Mulichinco case, however, these carbonate hemicycles are recording the onset of carbonate ramps, not the trapping of siliciclastic sediments in transgressive coasts (e.g., filling estuaries). This alternative scenario, ultimately controlled by reciprocal sedimentation, could be common in epicontinental basins developed under arid to semiarid conditions, and its identification could provide additional templates for basin-scale correlations and hydrocarbon exploration within carbonate–siliciclastic small-scale cycles.

An Integrated Appraisal of Burgan Reservoir in Soroosh Oil Field, Using Petrographic and Petrophysical Approaches

The Burgan Formation in northwest of the Persian Gulf is applied to lower part of Albian age Kazhdumi Formation, where is dominated by coarse to medium terrigenous facies. It is the most susceptible siliciclastic unit in the area to hydrocarbon reservoir. This reservoir is studied in a well of Soroosh oil field with best available data to determine its facies characteristics, sequence stratigraphy and reservoir quality. Based on the petrographic results and log data, 7 facies are determined in the formation, which are mainly composed of sandstone and shale. These facies are classified into three facies associations (FA) based on their sedimentological properties and environmental conditions. The first FA consists of sandstone, siltstone and shale, mostly developed in the lower part of formation, and is related to a fluvial environment. The second FA consists of fluvial sandstones and sandwich by marine shales and is related to fluvial-dominated shallow marine setting (estuary to delta). The third FA consists of limestones of chemical and biochemical origin and is related to a marine condition. According to their reservoir quality, these facies associations show a decreasing trend in porosity and permeability values from FA1 to FA3. The first FA is more abundant in the lower part of the Burgan Formation where causes a good reservoir quality trait. FA2, presenting a medium reservoir quality, is more frequent in the middle parts of studied formation and FA3 is found almost in the upper parts. Based on the results from this study, three 3rd order sequences have been identified. Sequences 1 and 3 are partial but the sequence 2 is the main and most complete one of the formation in the studied area. The paleosol horizons are used for relative sea level change analysis of the formation in sequence stratigraphic studies.

Depositional Facies and Sequence Stratigraphic Study in Parts of Benin (Dahomey) Basin SW Nigeria: Implications on the Re-Interpretation of Tertiary Sedimentary Successions

Detailed fieldwork in parts of the Benin (Dahomey) Basin SW, Nigeria has allowed the recognition of sedimentary successions deposited in different continental depositional environments interpreted as fluvial sedimentation characterised by abandoned channels and subaerial exposure features. The lithofacies recognised are: conglomerates, debris flow deposits, very coarse grained sandstone, ferruginous cross bedded sandstone, siltstone, shale/clay and massive sand. The lithofacies were interpreted in terms of sequence stratigraphic elements with the recognition of sequence boundaries characterised by distinct facies dislocations and subaerial exposures. Four depositional sequences (DS I to DS IV) were identified. Depositional sequences (DS I) exhibited a complete regressive–transgressive cycle comprising LST, TST and HST, while DS II to DS IV were incomplete comprising of sediments interpreted as LST deposits. On the basis of the depositional facies and sequence stratigraphic elements, the sediments in the area of study are interpreted as predominantly of Ilaro Formation while fewer exposures are sediments of the Coastal Plain Sands/ Benin Formation. This observation suggests a re-interpretation of the Tertiary sedimentary successions, which hitherto recognised all the sediments in the area of study as Coastal Plain Sands.

Facies, Sedimentary Environment and Sequence Stratigraphy of Dalan Formation in South Fars, Iran —(Qatar-South Fars Arch) Well ASL-A

Dalan Formation is one of the most important gas reservoirs of south and southwest Iran which it belongs to Dehram Group and its age is Middle to Late Permian. The Dalan formation is interpreted as reflecting a major tectono-eustatic event related to the onset of rapid thermal subsidence of the early Neo-Tethys passive margin in Arabia and Iran, and the drowning of its rift shoulders. The Dalan formation consists mainly of medium to thick-bedded oolitic to micritic shallow-marine carbonate, with intercalations of evaporates. This formation overlies the Faraghan formation and extends up into the Lower Triassic kangan formation. The current paper is focused on the facies, sedimentary environment and sequence Stratigraphy study of the Middle to Upper Permian Dalan formation in the West Assaluyeh gas field the subsurface section of well ASL-A. Based on microfacies analysis and significant founa and flora, nineteen major facies in five facies associations including Tidal flat (A), Lagoon (B), Shoal (C), Open marine (D) and Mid ramp (E) were recognized in the Dalan formation. Facies analysis and those comparisons with modern and ancient environments indicated that the Dalan formation was deposited inner to mid parts of a homoclinal ramp. The sequence stratigraphy studies on the Dalan formation in this gas field led to assessment of seven main sedimentary sequences of the third-order in the Assaluyeh field, well ASL-A. The boundary between the third-order sequences with the Faraghan formation and between the Nar and Upper Dalan members are Subaerial Unconformity (SU) and the boundaries between the third-order sequences with each other and also with the Kangan formation are Correlative Conformity (CC). The main diagenetic processes in this formation are dolomitization, dissolution, anhydritization, cementation and compaction which played a significant role in improving reservoir quality. The shoal ooid grainstone facies with intergranular and oomoldic porosity comprise the main reservoir facies of the Dalan formation.

Paleogeography and Sequence Stratigraphy in Dariyan Carbonate Reservoir, NE Shiraz

Zagros Basin is a very important hydrocarbon region in the Iran and World. One of the major reservoirs in this basin is the Lower Cretaceous Dariyan Formation. Based on petrographic studies, 9 microfacies were determined and interpreted as related to lagoon, barrier island and open marine environments. Facies associations show deposition in a carbonate ramp. Sequence stratigraphy studies show two sequences, each one with a transgressive system tract, marked by open marine microfacies, and then a retrogradational highstand, marked by barrier and lagoonal facies. Paleogeography and sequence stratigraphy studies of this formation and correlation of it with other sections may provide useful information about reservoir characterizations.

Microfacies, Sedimentary Environment and Sequence Stratigraphy of the Asmari Formation in Masjed-I-Soleyman Oil Field, Khuzestan Provence, Southwest Iran

The Oligo-Miocen Asmari Formation is the most important oil reservoir in Iran. This study deals with facies associations, sedimentary environments and sequence stratigraphy of this formation in Masjed-I-Solyman oil field by using petrographical studies and statistical analysis. These findings show that studied succession belongs to the upper Asmari Formation (Bordigalian) with nine microfacies assosiations that consist of four wackestone, four packstone and one Boundstone microfacies. These microfacies were deposited in the inner and middle parts of a homoclinal carbonate ramp. Sequence stratigraphy studies express that the succession could be discriminated to four third order sedimentary sequences that would have been deposited under global sea level fluctuation (Eustasy).

Palynology of the Upper Cretaceous (Turonian) Ferron Sandstone Member, Utah, USA: identification of marine flooding surfaces and Milankovitch cycles in subtropical, ever-wet, paralic to non-marine palaeoenvironments

The Upper Cretaceous Ferron Sandstone Member of the Mancos Shale Formation in Utah includes coal and gas deposits and is an important outcrop analogue to study reservoir characterisation of fluvial–deltaic petroleum systems. Numerous sedimentological and sequence stratigraphic studies of the Notom fluvial–deltaic wedge have been conducted recently; however, palynological analyses had not previously been undertaken. Here, we present palynological data from 128 samples collected in the Notom wedge of the Ferron Sandstone Member outcropping in south-central Utah. The purpose of this study is to use palynological analysis to refine the broader depositional environments, evaluate the climatic setting, and to build a biostratigraphic palynological framework. The dominance of terrestrial palynomorphs, especially the high yield of moisture-loving cryptogam spores, indicates a primarily ever-wet depositional environment characteristic of hydromorphic floodplain palaeosols formed in subtropical to tropical climates. Although dinoflagellates are rare, four intervals with occurrences of marine cysts indicate periods of increased marine/tidal influence associated with previously identified flooding surfaces within Milankovitch-scale parasequences of the largely non-marine stratal succession. These flooding surfaces confirm correlations from regional high-resolution sequence stratigraphic studies and allow correlative marine parasequences and systems tracts to be extended within floodplain-dominated stratal successions. The presence of Nyssapollenites albertensis pollen places the interval studied within the Nyssapollenites albertensis Interval Zone (Nichols 1994), constraining the age of the Ferron Sandstone Member to the latter part of the Cenomanian and the early Coniacian. This largely agrees with the bentonite- and ammonite-derived Turonian age proposed in previous studies.

Chemo-stratigraphy as a tool for sequence stratigraphy of the Early Triassic Kangan Formation, North of the Persian Gulf

The Lower Triassic Kangan Formation, which is equivalent to the Upper Khuff, is the main reservoir for natural gas in SW Iran and the northern Persian Gulf. Investigations of this formation in Salman Field indicate that it is composed of 14 facies deposited in tidal flat, lagoon and oolitic barrier settings in the inner part of a carbonate ramp. Vertical variations of microfacies and gamma-ray log profiles show that this formation consists of three depositional sequences (KG3–KG1), each including of transgressive and high stand systems tract and each bounded above and below by type-two unconformities. Carbon and oxygen stable isotope profiles from a well-dated carbonate section were compared with the sedimentological data and results from the sequence stratigraphic study of the Kangan Formation, showing negative and positive peaks coinciding with sequence boundaries and maximum flooding surfaces Boundaries and Maximum Flooding Surfaces, respectively.

Sedimentary facies, depositional environment, and sequence stratigraphy of Oligocene–Miocene shallow water carbonate from the Rig Mountain, Zagros basin (SW Iran)

This study investigates the depositional environment and sequence stratigraphy of the Asmari Formation that is exposed at the Rig anticline in the Izeh zone of the Zagros foreland basin with a thickness of 374 m as a sequence of thin, medium, thick, and massive carbonate rocks. The Asmari Formation is Oligocene–Early Miocene (Burdigalian) in age at the study area. In this area 12 microfacies are distinguished on the basis of their depositional texture, petrographic analysis, and fauna. These facies deposited in four major depositional environment including tidal flat, lagoon, shoal, and basin. The Asmari Formation represents sedimentation on a homoclinal carbonate ramp system. Based on the microfacies analysis, sequence stratigraphic studies, and distribution of planktonic and benthic foraminifera, six third-order sequences, three in Oligocene (Rupelian, Early Chattian, and Late Chattian in age) and three in Miocene (Early Aquitanian, Late Aquitanian, and Early Burdigalian in age), in Rig mountain section were identified.