3rd-order Sequences Research Articles

Late Campanian-Maastrichtian foraminiferal biostratigraphy and paleoecology at Wadi Tarfa (North Eastern Desert, Egypt)

The upper Campanian-Maastrichtian (from Globotruncanella havanensis to Plummerita hantkeninoides zones) foraminiferal assemblages at the Wadi Tarfa section in the Egyptian North Eastern Desert are studied to infer paleoenvironments and relative sea-level changes. The multivariate R-mode hierarchical clustering and the Q-mode Nonmetric Multi-Dimensional Scaling (NMDS) of the benthic foraminiferal dataset have been attempted to quantify the vertical variations in paleobathymetry, oxygenation, and trophic conditions. The inferred foraminiferal-based sea-level curve reveals paleodepth fluctuations ranging from middle neritic to upper bathyal and distinguishes five 3rd order sequences, two in the upper Campanian and three in the Maastrichtian. The development of the inferred relative sea-level curve expresses greater control of the eustasy. Also, the regional impact of the Syrian Arc Orogeny (SAO) subordinately led to amalgamation and repositioning of some sea-level events. The lowermost part (Gl. havanensis Zone) was deposited under stressed, low oxygenated, weakly eutrophic bottom-water conditions. However, well‑oxygenated oligotrophic conditions occurred around the level of the Campanian/Maastrichtian (C/M) boundary, as inferred from the predominance of heavily calcified epibenthic oxic species. We attributed this oligotrophy to the oceanic circulation change and the accompanying climatic cooling experienced at that time. The remainder of the early Maastrichtian through late Maastrichtian experienced an environmental shift toward mesotrophic conditions without considerable oxygenation change. The latest Maastrichtian, however, reveals low-oxic mesotrophic-weakly eutrophic bottom-water conditions, which is likely owed to the Deccan volcanism induced food detritus enrichment.

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.

Biostratigraphy and Sequence Stratigraphy and Depositional Environment of Kolosh Formation in Dohuk Area, Northern Iraq

The present study deals with biostratigraphy, depositional environment and sequence stratigraphy of Kolosh Formation in two sections of Bekher anticline, northeastern Iraq by using the planktonic and benthonic foraminifera. Therefore, (48) species of planktonic foraminifera belonging to (14) genera and (34) species of benthonic foraminifera belonging to (19) genera have been recognized. The detailed planktonic foraminiferal investigation permits the recognition of seven well defined biozones and three subzones; they indicate that Kolosh Formation extends from the Early Paleocene (Danian) to Late Paleocene (Thanetian) age. The depositional environment of the formation was studied throughout relying on the variation in the diversity of planktonic forminifera, as well as throughout the ratio of the planktonic foraminifera to the whole mass of foraminifera, and the ratio of planktonic forminifera to the benthonic formiminifera. The lower part of the formation represents the upper bathyal environment, while the middle part deposited within the outer shelf environment, then deposition basin became within the middle shelf area in the upper parts of the formation. Sequence stratigraphic analysis for the studied sections of Kolosh Formation delineated three sequences which is interpreted as 3rd order sequences, and it is found that the deposition of Kolosh Formation in the Badi section had been occurred in shallower level for most sedimentation intervals compared to the Linwa section which represents a somewhat deeper marine environment.

Palaeoecological analysis of maximum flooding zones from the Tithonian (Upper Jurassic) of the Kachchh Basin, western India

The siliciclastic Jhuran Formation of the Kachchh Basin, a rift basin bordering the Malagasy Seaway, documents the filling of the basin during the late syn-rift stage. The marine, more than 700-m-thick Tithonian part of the succession in the western part of the basin is composed of highly asymmetric transgressive–regressive cycles and is nearly unfossiliferous except for two intervals, the Lower Tithonian Hildoglochiceras Bed (HB) and the upper Lower Tithonian to lowermost Cretaceous Green Ammonite Beds (GAB). Both horizons represent maximum flooding zones (MFZ) and contain a rich fauna composed of ammonites and benthic macroinvertebrates. Within the HB the benthic assemblages change, concomitant with an increase in the carbonate content, from the predominantly infaunal “Lucina” rotundata to the epifaunal Actinostreon marshii and finally to the partly epifaunal, partly infaunal Eoseebachia sowerbyana assemblage. The Green Ammonite Beds are composed of three highly ferruginous beds, which are the MFZ of transgressive–regressive cycles forming the MFZ of a 3rd-order depositional sequence. The GAB are highly ferruginous, containing berthieroid ooids and grains. GAB I is characterized by the reworked Gryphaea moondanensis assemblage, GAB II by an autochthonous high-diversity assemblage dominated by the brachiopods Acanthorhynchia multistriata and Somalithyris lakhaparensis, whereas GAB III is devoid of fossils except for scarce ammonites. The GAB are interpreted to occupy different positions along an onshore–offshore transect with increasing condensation offshore. Integrated analyses of sedimentological, taphonomic, and palaeoecological data allow to reconstruct, in detail, the sequence stratigraphic architecture of sedimentary successions and to evaluate their degree of faunal condensation.

Reservoir quality of the Surmeh (Arab-D) reservoir in the context of sequence stratigraphy in Salman Field, Persian Gulf

The Upper Jurassic Surmeh reservoir in the northern Persian Gulf is a stratigraphic equivalent of Arab-D reservoir that is one of the best Jurassic reservoir rocks of the Arabian Peninsula. In this study, in the first step the palaeontology, sedimentary environment, sequence stratigraphy and reservoir quality of the Surmeh reservoir was investigated in a core-bearing well in Salman oil field. The palaeontological studies reveal a moderately diverse assemblage of benthic foraminifera. Dominated foraminifera include the agglutinated forms and miliolids and there are also fragments of alga, stromatoporoids, corals, bivalves, gastropods and echinoderms. These recorded fauna and flora resulted in distinction of three zones that characterize the age of undifferentiated Kimmeridgian-Tithonian. Based on petrographic observations, along with palaeontological materials, eight microfacies were identified that represent four sub-environments of a carbonate inner ramp including supratidal, intertidal, lagoon and shoal. These studies combined with well log responses resulted in identification of a 3rd order sequence and parts of an incomplete one that is composed of an incomplete HST. These 3rd order sequences comprise four 4th order subordinate sequences.In addition by integration of petrographic analyses, sub-environments energy regimes and petrophysical data, five reservoir zones were identified. Also, based on core porosity and permeability 6 Hydraulic Flow Unit (HFU) with poor to excellent reservoir quality in ascending trend were identified. The reservoir zone I, which belongs to the sabkha and littoral facies, represents the worst reservoir quality (includes HFU1 to HFU3), while the reservoir zone III with best reservoir quality (includes HFU4 and HFU5) comprises the back shoal grain-supported facies. The introduced sequences and reservoir zones in the studied well were propagated to three other wells throughout the Salman Field via using log responses. Also they were correlated with those introduced for Arab-D reservoir in the southern parts of the Persian Gulf providing a correlation framework. This pattern can be used in the next exploration wells which are going to be drilled especially in the northern parts of the Persian Gulf.

The rudist-rich carbonate units in central Tunisia as markers of Late Cretaceous transgressive events

Rudist-rich carbonates are common in central Tunisia. They constitute frequent intercalations in Upper Cretaceous series, particularly within the Cenomanian-Campanian interval. They are generally transgressive upon shallower deposits, such as Lower Cretaceous siliciclastic sediments, or Upper Cretaceous tidal flat deposits. The sequence stratigraphy analysis of the study carbonate series reveals discontinuities and unconformities that mark the boundaries between the identified sequences. These unconformities, which are mainly represented by oxidized hard-grounds with several borings and micro-karstification features, are in relation with a sea level drop or a tectonic uplift of central Tunisia during the Late Cretaceous. Sea-level changes, tectonic movements, and climatic events appear acting a lot for the growth but also for the demise of Upper Cretaceous rudist and coral communities. Globally, the Upper Aptian-Lower Albian shallow-water carbonate deposits are unconformably overlain by Upper Albian-Cenomanian transgressive deposits, locally rich in organic matter, represented by black-shales. This unconformity, which is identified at least in the whole central Tunisia, consists of a regional sequence boundary that announces typical greenhouse conditions and the beginning of a carbonate-rich sedimentation admitting frequent intercalations of rudist-sponge-coral-rich deposits. Above this main regional unconformity, the Upper Cretaceous series show additional sequence boundaries separating 3rd-order sequences. Overall, six transgressive-regressive sequences were identified within the Cenomanian-Campanian interval. The identification of these 3rd-order sequences including rudist-rich deposits has helped a lot to establish correlations at least at regional, north African (Algeria, Egypt), and Tethyan scales (Italy, Germany and other areas). In central Tunisia, Rudist-coral-rich carbonates appear both during shallowing and at the beginning of deepening stages. However, according to our study, they are obviously more common and well represented during transgressions. In this context, they constitute deepening-upward cycles in transgressive systems tracts. For these reasons, they could be considered as markers of most Late Cretaceous transgressive events, essentially the Cenomanian-Turonian and the Campanian global transgressions. Commonly, the Upper Cenomanian-Lower Turonian transgressive event, for example, is globally marked by the deposition of black-shales. However, in shallower environments, more closed to carbonate platforms and their margins, regionally extended rudist-coral-rich carbonates could be used as markers of such transgressive event.

De-risking hydrocarbon exploration in lower Jurassic carbonate systems of Kuwait through forward stratigraphic models

This paper discusses the results of an integrated case study using forward stratigraphic modelling of Lower Jurassic complex carbonate reservoirs along the Eastern Arabian Plate. Traditional stochastic or deterministic modelling techniques do not sufficiently capture carbonate reservoir heterogeneities in sectors with restricted datasets. The methodology applied uses a process-based approach that aims to define carbonate architectural and textural/facies heterogeneity and provides a framework to develop a more consistent conceptual geological model for exploration and field development.Through this communication we test the sensitivity of Lower Jurassic reference case model of complex carbonate systems (Al Wazzan et al., 2020) to various framework and sedimentological/ecological parameters as subsidence, eustacy, carbonate production rates, wave energies and evaporation versus precipitation rates. Results of this work help achieve a more refined and data calibrated model that tackles mainly the 3rd and 4th order sequence stratigraphic evolution of the Marrat Formation. Simulation results point to the main impact of differential subsidence and eustatic sea level changes on the architectural and textural variability along Kuwait with dominantly (1) transgressive onlapping packages of intercalated mudstone/wackestone and anhydritic textures in the Lower Marrat, (2) prograding to aggrading packages in the Middle Marrat localized around the southern, northern, northwestern and westernmost part of onshore Kuwait, and (3) an onlapping transgressive system composed of wackestone and lime mudstone with very restricted shoal patches.This work also highlights (1) the good fit with overall tendencies of the recently published Haq (2018) Jurassic global relative sea level curves, (2) the need to reduce the latter amplitudes of high frequency relative sea level drops to fit the G&G dataset, (3) the good anhydritic prediction using evaporation and precipitation predictions of the General Circulation Models (GCMs) (Sellwood and Valdes, 2006) and finally (4) the need for about 20–30% of additional differential subsidence in zones of thinner continental crust. Finally, a more geologically plausible prediction of the spatial and temporal extent of petroleum systems elements unraveled a new under-explored hydrocarbon potential in West and Central Kuwait.

Seismic geomorphology of shallow-water lacustrine deltas in the Paleocene Huanghua Depression, Bohai Bay Basin, eastern China

The most important sedimentary facies comprising shallow-water lacustrine deltas are distributary channels, and these form abundant ribbon-shaped sand bodies that are excellent petroleum reservoirs. However, distributary channel sandstones are notoriously difficult to correlate and characterize in the subsurface based on well data alone. Here, we show how seismic geomorphology can be used to map lacustrine deltaic sedimentary successions in the First Member of the Kongdian Formation within the Zilaitun Oilfield, Huanghua Depression (China). Using core and wireline logs, this study identified distributary channels as the dominant sedimentary facies. Together with mottled gray-green or maroon mudstones and locally shingled progradational seismic reflection architecture, this indicates that deltas were built in a weakly-oxidized shallow-water lacustrine environment. Next, core observations were linked to seismic data to produce a successive series of stratal slices and root mean square amplitude attribute (RMSAA) maps. The RMSAA maps allowed distributary channel, mouth bar, and beach bar facies to be identified and mapped across the study area. Two patterns of distributary channels emerged from the data: (1) a distributive pattern with a lower concentration of distributary channels; and, (2) an anastomosing deltaic pattern with a high concentration of bifurcated distributary channels. Based on the seismic geomorphological analysis we show that the succession records three phases of delta evolution - retrogradation, aggradation, and progradation - which combine to form 3rd-order sequences. From a petroleum reservoir point of view, the distributive pattern yields narrower, thicker, and less connected sand bodies than the anastomosing pattern. This is consistent with observations from modern shallow-water lacustrine delta systems, providing independent support for the interpretation and highlighting the effectiveness of using seismic geomorphology.

Diagenesis and reservoir quality in high-resolution sandstone sequences: An example from the Middle Jurassic Ravenscar sandstones, Yorkshire CoastUK

A section of the Middle Jurassic Ravenscar sandstones exposed between Cloughton Wyke and Burniston Bay was studied to understand fine-scale variation in reservoir quality that can affect flow properties at the reservoir scale. The study has identified two 3rd-order depositional sequences consisting of twelve 4th-order high-resolution sandstone sequences deposited mostly in a lower delta plain. Although these sandstones exhibit a narrow range in porosity values, however, a sharp disparity exists in their permeability which can have implications at the scale of reservoir development. Diagenetic studies have revealed that mechanical compaction produced the same effect for most of these sandstones. However, dissolution and cementation vary, hence, are mostly responsible for the sharp contrast in their reservoir quality. The distributary channel sandstones developed during normal regression of the area in the FS9 sequence are considered the best reservoir sand bodies. However, these LST sandstones are compartmentalised by authigenic illite, quartz and kaolin into two reservoir segments. The upper portion lacks illite with resultant higher permeability values above 1100 mD (ave. 2217 mD) and classified as reservoir group 4. In contrast, the lower part contains illite with relatively lower permeability values in the range of 300–1100 mD (ave. 879 mD) and classified as reservoir group 3 together with the transgressive crevasse channel sandstones in the FS11 sequence. The presence of illite cement in these sandstones is linked to the occurrence of k-feldspar, hence, facilitated illitization of kaolin in contrast to group 4, which lacks this mineral. The other transgressive sandstones deposited in interdistributary bay, crevasse delta, back-barrier lagoon, lagoon, and estuarine environments which form reservoir groups 1 and 2 have permeability values in the range of 0–50 mD (ave. 6 mD) and 50–300 mD (ave. 184 mD) respectively. These sandstones have complex styles of diagenetic cement with variable higher volumes of total authigenic cement consisting of quartz, kaolin, illite, chlorite and calcite than reservoir groups 3 and 4, hence, have significantly reduced their reservoir potential. Therefore, for effective reservoir development of these sandstone reservoirs in the North Sea and elsewhere in the world with a similar geological setting, detailed reservoir characterisation involving linking lithofacies, sequence stratigraphy and diagenesis at high-resolution are essential for understanding the distribution of reservoir flow properties.

Tectonic and eustatic impact on depositional features in the upper Cretaceous Austin Chalk Group of south-central Texas, USA

The upper Cretaceous Austin Chalk Group in south-central Texas, USA, displays vertical and lateral variations in thickness and facies resulting from an irregular paleotopography of the seafloor and variable preservation of 3rd-order sea-level cycles. During the Coniacian to early Campanian, the tectonic evolution of the San Marcos Arch, a prominent basement feature in the study area, impacted facies and sequence architecture within the Austin Chalk Group. Outcropping sections of the Austin Chalk Group along the margin of the Edwards Plateau in south-central Texas stratigraphically transition between inner and outer ramp environments. The cyclic stacking pattern of facies is recorded in vertical stratigraphic succession as 3rd-order cycles separated by discontinuity surfaces and condensed deposits. Inner ramp facies consist of Thalassinoides-burrowed bivalve wackestone to packstone with minor occurrences of skeletal grainstone. Outer ramp facies comprise Planolites-burrowed foraminiferal chalk and marl with fine skeletal debris. Condensed facies associated with transgressive re-working are characterized by glauconitic packstone with high concentrations of coarse skeletal debris and lithoclasts. Gamma-ray profiles of outcrops investigated in the study area are correlated to subsurface wireline logs of wells drilled along the outcrop and subsurface trend, in order to construct a stratigraphic framework across the San Marcos Arch. This stratigraphic framework is biostratigraphically well constrained and correlated to the type section of the Austin Chalk Group farther north in the vicinity of Austin. The integration of sedimentological and stratigraphic information enables the identification of four regional 3rd-order depositional sequences within the Austin Chalk Group. Thickness maps of each depositional sequence illustrate the tectonic evolution of the San Marcos Arch and its influence on the deposition of the Austin Chalk Group, which is judged as negligible during most of the lower Austin Chalk Group (Coniacian), and started to trigger lateral thickness variations and pinch-outs in the Santonian and early Campanian. Syndepositional tectonic movement played an active role in the geometry of Austin Chalk depositional sequences and should be accounted for in sequence stratigraphic models developed in chalk depositional settings to explain the occurrence of coarser and cleaner facies.

Deep-water channels in the lower Congo basin: Evolution of the geomorphology and depositional environment during the Miocene

Abstract Deep-water channel systems are an important component of the “source to sink” system from continental slope to deep-sea basin. They are also the critical reservoir type in deep-water hydrocarbon exploration. The study of geomorphology evolution, filling processes and controlling factors of the Miocene deep-water channel in the Lower Congo Basin is conducive to deepening our understanding of basin dynamics, and to improving the prediction accuracy of deep-water reservoirs. Based on 3D seismic data, cores, thin sections, well logging data, we study the Miocene seismic stratigraphic characteristics, deep-water sedimentary units, lithofacies and channel types. Using the techniques and means of seismic geomorphology, we discuss the occurrence, development, recession and extinction processes of channel complexes and controlling factors. The Miocene was divided into seven 3rd-order sequences. Each 3rd-order sequence is subdivided into two (lower/upper) seismic stratigraphy units, with initial flooding surface (FS) as the separated boundary. The seismic characteristics of the lower/upper unit suggest the occurrence of alternating turbidite/hemipelagic sedimentary units. Seismic units such as erosional surface, filling channel, levee, lobe, MTD and background slope deposits are described. Fifteen deep-water lithofacies are identified and they are determined to be composed of clay, silt, fine-coarse sand, gravel, and conglomerate. The deep-water channels in the study area are interpreted four types: single-stage erosional channel, single-stage aggradational channel, vertical aggradational channel complexes and lateral migration channel complexes. The different types of channel are the results of interaction of flow energy and accommodation space. On this basis, we propose that tectonic uplift is the driving force for the formation of the deep-water sandy channel system, and that high frequency sea-level fluctuation in West Africa controls the development of third-order sequences and restricts the scale of the deep-water sandstone accumulation. In addition, the avulsion processes controlled by climate variations are the main factors to influence channel complex filling process.

Depositional history and sequence stratigraphy of central Tethyan from the Upper Triassic Nayband Formation, Central Iran

To progress in the knowledge of Upper Triassic evolution of the central Tethys realm, an integrated approach which includes new sedimentological and sequence stratigraphy has described in central Iran. The Nayband Formation of Late Triassic age in central Iran is composed of various rocks of siliciclastic and mixed carbonate–siliciclastic deposits and represents an example of storm-dominated shelf deposition. Based on texture and sedimentary structures of the siliciclastic deposits, 11 lithofacies were identified and classified into three categories, i.e., conglomerate (Gms, Gcm), sandstone (Sp, Se, Sm, Sr, Hcs, Scs, Sh) and mud rock (Fm, F). These mainly consist of alternations of sandstone and shale, and constitute the lower and upper units of the studied section. The mixed carbonate–siliciclastic sediments crop out in the middle unit of the section. Based on field observations and petrographic studies, 12 microfacies were recognized which can be grouped into three depositional environments: shoreface (lower, upper), offshore-transition (proximal, distal) and offshore (upper, lower) on a storm-dominated shelf. Seven 3rd-order depositional sequences have been identified in this section based on field observations, facies analysis and sequence stratigraphy studies. The lower and upper boundaries of this succession are type 1 sequence boundaries (SB1); whereas, other boundaries are type 2 sequence boundaries (SB2). Depositional sequences are composed only of TST, MFS and HST, whereby the transgressive sequences (TST) mainly consist of deeper facies, and regressive sequences (HST) consist of shallower facies. Shelf transport was driven by the available accommodation space on the shelf and therefore was a function of eustatic sea-level fluctuations, but local tectonic activity has also controlled the thickness of the deposits.

Revised stratigraphy of the Eifelian (Middle Devonian) of southern Belgium: sequence stratigraphy, global events, reef development and basin structuration

The Eifelian lithostratigraphic succession of southern Belgium is here revised based on new field investigations and reconsideration of biostratigraphic data. The Couvin Formation is divided into four members: the Villers-la-Tour Member recorded the onset of stromatoporoid biostromes, the Petigny Member is a dark fine-grained limestone that recorded the Choteč event, the Cul d’Efer Member is dominated by stromatoporoid-coral biostromes. These first three members were previously united in the Foulerie Member and correspond to the transgressive and highstand system tracts of the Middle Devonian 3rd-order sequence MD1. The argillaceous and bioclastic successive units of the Abîme Member recorded the sequence MD2. Laterally, this sequence is only composed of siliciclastic deposits of the Vieux Moulin, Station and Cimetière members of the Jemelle Formation. The highstand system tract is the newly introduced carbonate Vierves Member. Large bioherms, newly described as the Wancennes Formation, recorded the first two sequences MD1 and MD2. A major sequence boundary caps the Couvin Formation and is overlaid by the transgressive and diachronous Chavées Member of the Jemelle Formation with a depositional gap increasing eastwards. The highstand system tract of sequence MD3 is recorded in the bioherms of the Tienne Sainte-Anne Member (upper part of the Jemelle Formation), also capped by a sequence boundary. These bioherms probably acted as highs around which the sandy deposits of the Lomme Formation accumulated as lowstand system tract of sequence MD4. The Hanonet Formation and its crinoidal Wellin Member form the transgressive system tracts of sequence MD4 that terminates in the bioclastic and biohermal Trois-Fontaines Formation (Givetian). The Kačák event is identified in the transgressive system tract of this sequence. The geographic distribution of facies and of reefs in particular led to the recognition of at least six sedimentation areas corresponding most probably to synsedimentary faulted blocks here defined as the Eau Blanche, Viroin, Lesse, Ourthe, Condroz and Sambre blocks. These sedimentation areas structured the Namur-Dinant Basin and recorded distinct depositional history and were probably active during the Devonian and Carboniferous interval.

Sedimentology and high-frequency cycles of the late Pleistocene of the Bizerte area (N-E Tunisia)

Quaternary deposits are well known around the Mediterranean basin especially those exposed along the Tunisia Coast. This work focuses on the Pleistocene deposits outcropping along the Bizerte littoral (Northeastern Tunisia) with special attention to coastal deposits and their evolution during the late Pleistocene. The sedimentologic analysis carried on four cross-sections exhibits a complete Quaternary series that begin with basal erosive surface and marine deposits attributed to the last interglacial period. The Pleistocene deposits represent a 3rd-order sequence that is divided into 2 (4th–5th order) shallowing-upward sequences that are interpreted as a response to glacio-eustatic events. The lower sequence consists mainly of shoreface facies which evolve to foreshore and continental facies. The upper sequence shows a dune facies with cross-stratification and continental gastropods (eolian deposit interbedded with red to gray paleosoils). Those eolian deposits and paleosoils levels are related to the highstand system track of the 3rd-order sequence.

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.

High-resolution sequence architecture and depositional evolution of the Quaternary in the northeastern shelf margin of the South China Sea

The northeastern shelf margin of the South China Sea (SCS) is characterized by the development of large scale foresets complexes since Quaternary. Based on integral analysis of the seismic, well logging and paleontological data, successions since ~3.0 Ma can be defined as one composite sequence, consist of a set of regional transgressive to regressive sequences. They can be further divided into six 3rd order sequences (SQ0–SQ5) based on the Exxon sequence stratigraphic model. Since ~1.6 Ma, five sets of deltaic systems characterized by development of wedge-shaped foresets complexes or clinoforms had been identified. High-resolution seismic data and the thick foresets allowed further divided of sub-depositional sequences (4th order) of regression to transgression, which is basically consistent with published stacked benthic foram O-isotope records. Depositional systems identified in the study area include deltaic deposits (inner-shelf deltas and shelf-edge deltas), incised valleys, and slope slumping massive deposits. Since ~1.6 Ma, clinoforms prograded from the southern Panyu Lower Uplift toward the northern Baiyun Depression, shelf slope break migrated seaward, whereas the shelf edge of SQ0 migrated landward. The development of incised valleys in the continental shelf increased upward, especially intensive on the SB3 and SB2. The slumping massive deposits increased abruptly since SB2, which corresponds to the development of incised valleys. The evolution of depositional systems of continental slope mainly controlled by the combined influence of sea level changes, tectonic movements, sediment supply and climate changes. Since ~3.0 Ma, relative sea level of the northern SCS had been experienced transgression (~3.0 Ma BP) to regression (~1.6 Ma BP). The regional regression and maximum transgressions of the composite sequences were apparently enhanced by uplift or subsidence related to tectono-thermal events. In addition, climatic variations including monsoon intensification and the mid-Pleistocene transition may have enhanced sediment supply by increasing erosion rate and have an indispensable influence on the development of the incised valleys and 5 sets of deltaic systems since ~1.6 Ma.

ICHNOFABRICS FROM A CRETACEOUS EOLIAN SYSTEM OF WESTERN ARGENTINA: EXPANDING THE APPLICATION OF CORE ICHNOLOGY TO DESERT ENVIRONMENTS

The Lower Cretaceous (Valanginian) Mulichinco Formation of the Neuquen Basin in western Argentina is host to important hydrocarbon reservoirs, encompassing a wide variety of sedimentary facies, including thick eolian deposits in its lower interval in proximal positions. Ten ichnofabrics are characterized based on the analysis of cores from the El Mangrullo oil field. These ichnofabrics have been grouped in four associations, representing eolian dunes, eolian sand sheets, interdunes, and fluvial sheet floods. In terms of the ichnofacies model, both the Scoyenia and Octopodichnus-Entradichnus ichnofacies are identified. Ichnologic information has been integrated with sedimentologic and sequence-stratigraphic information. The studied succession comprises a 3rd-order depositional sequence that is subdivided into three 4th-order sequences stacked in a backstepping pattern as a result of a rise in the water table. The base of the 3rd-order sequence is represented by the intra-Valanginian unconformity that in this area separates marine deposits below from continental deposits above. Overall the 3rd-order sequence reflects the vertical transition from a dominance of eolian dune deposits to eolian sand sheet and fluvial sheet flood deposits, the latter intercalating with marginal-marine intervals. Application of available conceptual frameworks to understand trace-fossil distribution in desert environments suggests that the eolian Mulichinco ichnofauna indicates a temporal evolution from hyper-arid to arid and semi-arid conditions. The results of the present analysis argue against the common assumption of deserts as barren of life and provide further support to the notion of an archetypal eolian ichnofacies. This study expands the realm of application of ichnology in subsurface to eolian environments by providing a characterization of an ichnofauna from a desert setting based on core analysis.

2D seismic interpretation and hydrocarbon prospects for the Neogene-Quaternary succession in the Temsah Field, offshore Nile Delta Basin, Egypt

This study is concerned with the Neogene-Quaternary subsurface sedimentary succession of the Temsah Field in the northeastern offshore Nile Delta Basin. A sequence stratigraphic analysis based on seismic and available well data enables the subdivision of the investigated succession into two megasequences: the Pre- and Post-Messinian Megasequences. The Pre-Messinian Megasequence encompasses Miocene rock units, whereas the Post-Messinian Megasequence includes Pliocene-Pleistocene rock units. The detailed sequence stratigraphic analysis presented herein subdivides the Pre-Messinian Megasequence into three 3rd-order depositional sequences as follows (from the base to the top): Sequence-1 (Serravallian Sidi Salim Formation), Sequence-2 (Tortonian Wakar Formation), and Sequence-3 (Messinian Rosetta Formation). The Post-Messinian Megasequence is also subdivided into three additional 3rd-order seismic sequences: Sequence-4 (Lower-Middle Pliocene Kafr El-Sheikh Formation), Sequence-5 (Late Pliocene El-Wastani Formation) and Sequence-6 (Pleistocene Mit Ghamr Formation). This study suggests that the sea level underwent six transgressive-regressive depositional cycles during the evolution of the Neogene-Quaternary succession. The greatest relative sea level fall occurred during the Messinian, while the highest identified relative sea level rise occurred during the Lower-Middle Pliocene. The interpreted NW-SE anticline represents a distinctive four-way closure that may form a suitable structural hydrocarbon trap within the sandy intervals of the siliciclastic Sidi Salim and Wakar Formations in the Temsah Field. Moreover, the identified single and multiple buried channels within the Kafr El-Sheikh Formation are recommended for further exploration and possible drilling.

Depositional Environment and Sequence Stratigraphy of the Oligocene-Miocene Deposits North and East of Dehdasht, Izeh Zone, Zagros Basin, Iran

In this study, four well-exposed outcrops of the Asmari Fm in the southeastern part of the Izeh Zone of the Zagros Mountains were measured and sampled. In this region, the Asmari Fm is Oligocene to Early Miocene in age as determined by large benthic foraminifera. Based on depositional geometries, biogenic contents and lateral and vertical variations of facies, three depositional models are proposed to illustrate the evolution of the Asmari carbonate platform. During the Chattian, large benthic foraminifera and coral-coralline red algae were dominant, while through the Early Miocene time interval (Aquitanian-Burdigalian), non-skeletal components along with porcelaneous foraminifera were the most conspicuous elements. These deposits formed a carbonate ramp in the Chattian and a low angle carbonate-ramp during the Early Miocene. Five major 3rd-order depositional sequences have been identified based on stratal stacking patterns and facies relationships. These depositional sequences show systematic progradations from SE to NW into and over the basinal Pabdeh Fm during Oligo-Miocene times.

NORIAN AMMONOIDS FROM THE NAYBAND FORMATION (IRAN) AND THEIR BEARING ON LATE TRIASSIC SEDIMENTARY AND GEODYNAMIC HISTORY OF THE IRAN PLATE

A Middle Norian (Alaunian 2) ammonoid assemblage from north of Esfahan (Central Iran) is described and chronostratigraphically evaluated. Formerly known as Distichites fauna, it represents a geographically widely distributed and stratigraphically important fossil level in the lower part of the Upper Triassic Nayband Formation. The new distichitid ammonoid genus Mesodistichites with the new species M. evolutus are introduced; additional faunal members are Noridiscites nodosus n. sp. and the leiostracean Stenarcestes diogenis and Pinacoceras cf. imperator. The Nayband Formation of the Esfahan region, belonging to the Zefreh-Soh Facies, is lithostratigraphically emended to contain three formally introduced members (Parsefid, Venher and Niazmargh members), which are all of Norian age, whereas Rhaetian sediments are missing. These members are correlated with Norian lithostratigraphic units of the type sequence of the formation in Nayband, eastern Iran. Integration of all Iranian Nayband data allows the recognition of three 3rd order sequences within this formation and the proof of a major pre- or syn-Jurassic unconformity across Central Iran and the Central-East Iranian Microcontinent (CEIM) related to the Main-Cimmerian event. Because of the latter and of major lithostratigraphic and facial differences, we propose to exclude the Nayband Formation from the Shemshak Group. A careful review of the available biostratigraphic data from northern and southern Iran let us further assume that the collision of the Iran Plate with Eurasia occurred in the later Early Carnian and was concurrent to the onset of the Carnian Humid Episode.