Stratigraphic Concepts Research Articles

The Miocene to Quaternary evolution of the Vienna Basin (northeastern part): geodynamics, eustasy, stratigraphy and depositional systems

Long-term research of the Vienna Basin (Central Europe) has resulted in multiple stratigraphic concepts, although these are at least in part mutually exclusive. This contribution aims to reconsider the available information on the northeastern Vienna Basin, located in Slovakia, to create a consistent stratigraphic model. Lithostratigraphic correlations based on benthic taxa – widely used elsewhere – are omitted, since these include inherently diachronous palaeoecological zones. This presumption of diachroneity is further supported by the evidence of shelf-slope scale clinoforms. The following sequences were identified: (1) the Early Miocene wedge-top basin, genetically unrelated to the subsequently formed Vienna Basin – Eggenburgian–Ottnangian cycles are still obscured, and the Karpatian includes two transgressive–regressive cycles; (2) Middle Miocene early Badenian rifting including the Kúty Fm lowstand and Lanžhot Fm, together with the Devínska Nová Ves Fm, comprising transgression and a highstand; (3) Middle Miocene late Badenian rifting including lowstand offshore Jakubov Mbr and transgressive littoral Stupava Fm, followed by the highstand offshore Studienka Mbr passing to normal regressive Matzen delta; (4) Middle Miocene Sarmatian rifting including the basal Kopčany and Radimov Mbrs, the offshore transgressive to regressive Holíč Fm and the highstand normal regressive deltaic Skalica Fm; and (5) supposed Late Miocene rifting with Lake Pannon transgression resulting in the lacustrine Bzenec Fm, followed by the highstand normal regressive deltaic Čáry and alluvial Gbely Fms.

Geometrical characterization of fracture systems using point clouds and SELF-Software: example of the Añisclo anticline carbonate platform, Central Pyrenees

Natural fracture systems contribute significantly to rock mass anisotropies. Characterizing these systems is essential for understanding processes of fluid flow, energy exploration and storage, slope stability or tectonic processes that can affect the permeability or compaction of the material, as well as reflect its temporal evolution. This work presents a set of automatic and supervised algorithms integrated into the open-access software solution SEFL, designed to characterize fracture systems using remote sensing data sets. The software implements various strategies to quantify geometrical parameters with deterministic or stochastic descriptions, facilitating a detailed characterization of the fracture system for numerical simulations. Geological outcrops provide direct access to the rock masses and discontinuities, offering analogies with materials that are otherwise inaccessible for its direct study. The digital acquisition of the terrain using high-resolution techniques, such as Terrestrial Laser Scanner (TLS) or photogrammetry to obtain point clouds, enabled post-field studies, particularly for fracture systems that are complex, inaccessible, or large in scale. Additionally, SEFL offers a tool based on the concept of fracture stratigraphy to identify mechanical units, which are essential frameworks for measuring and calculating fracture properties. This new methodology has been applied to study the fractured Eocene limestone outcrop at the hinge of the Añisclo anticline (South-Central Pyrenees, NE Iberia) which has been digitally acquired and characterized. SEFL output data interpretations revealed an outcrop characterized by over two thousand modelled fractures, five fracture sets, fourteen fracture stratigraphic units, and 1-2 fractures/m.

Sequence Stratigraphy and Depositional Environment of the ‘Perahu’ Sand, Bekasap Formation, ‘DAP’ Field, Central Sumatera Basin

Abstract The ‘DAP’ Field is one of the oil and gas fields within the Central Sumatera Basin that is proven to have hydrocarbon reserves. One of the proven reservoirs in the ‘DAP’ Field is the ‘Perahu’ Sand, Bekasap Formation. This study aims to determine the depositional environment and facies distribution focusing on the ‘Perahu’ Sand, Bekasap Formation through a sequence stratigraphic approach. The research was based on an integrated analysis of sedimentary facies from one core data and a key well log to interpret the facies association. Then the key well is correlated to eight other well logs with the help of sequence stratigraphic concept to determine the depositional facies distribution and succession at the study interval. Lithofacies that are identified from core data were interpreted as floodplain, tidal channel, mud flat, mix flat, and sand flat, hence the depositional environment of ‘Perahu’ Sand was interpreted to be a tide-dominated estuarine. The parasequence set level of Bekasap Formation was interpreted to be in a transgressive system tract, with the ‘Perahu’ Sand divided into three flooding surfaces that is FS3, FS4, and FS5. The FS3 distribution consists of tidal-fluvial channel, crevasse splay and floodplain facies. The FS4 distribution consists of two tidal channels and one sand flat facies. The FS5 distribution consists of one sand flat facies. The depositional trend of the ‘Perahu’ Sand shows a northeast to southwest trend, with basinward toward southwest.

Permian–Triassic Boundary in Sedimentary Succession of the Barents Sea

Abstract —The Permian–Triassic (P–T) boundary records the most dramatic events in Phanerozoic history. The character of the boundary differs greatly, so it has been the subject of great discussion. The Barents Sea separates regions having markedly different expressions of the P–T boundary, and it can give an insight into the conditions of formation of this boundary in different parts of the European North. This contribution is based on a combination of regional projects from the Russian and Norwegian sectors, including seismic data across the Barents Sea and well data in marginal zones. Application of new seismic data and the sequence stratigraphy concept provides a novel approach to correlation and interpretation of the P–T boundary beneath the Barents Sea. The study has revealed a distinct regional sequence boundary corresponding to the P–T boundary with conformable and unconformable bedding. Three major types of this stratigraphic boundary are recognized. The distinct “erosional” type of the P–T boundary, with a significantly reduced Permian section, exists in the southeast (Timan–Pechora Basin). The conformable “overcompensated” type of boundary with an additional Lower Triassic section is interpreted in the central part of the Barents Sea. Westward, beneath the Norwegian sector, a relatively conformable “condensed” type of P–T boundary predominates. In addition to these types associated with regional paleostructural and depositional trends, the superposed “structural” subtype caused by local growth of structures at the Permian–Triassic boundary is identified.

The Anthropocene's stratigraphic reality and the humanities: a response to Finney and Gibbard (2023) and to Chvostek (2023)

AbstractThe Anthropocene Epoch is a crucial conceptual breakthrough not only for stratigraphy but also for the humanities. The question, raised by Chvostek (2023), is how best to create engagement between the sciences of the Anthropocene and the study of values, hopes and power in the world's many cultures past and present. In response, this piece makes three points. First, it discusses some of the collaborations that have already taken place between humanists of various kinds and the scientists providing the stratigraphic evidence for the Anthropocene Epoch. Second, it notes that the ‘Anthropocene’ remains, at core, a stratigraphic concept and that the new epoch is now well supported by physical evidence. Third, it shows that the recent idea of an Anthropocene ‘event’ (Gibbard, 2022) does not invite engagement with the humanities. The overall argument is that the integrity of expertise must be maintained even while we encourage the cross‐disciplinary understanding crucial to addressing our global environmental challenge.

Highlighting relationships between sand thicknesses, reservoir-seal pairs and paleobathymetry from a sequence stratigraphic perspective: An example from Tortonian Serravallian deposits, onshore Niger Delta Basin

The utilization of sequence stratigraphic concepts in identifying sands and their spatial continuity in distinct gross depositional settings is key, especially in frontier settings where data paucity is a common challenge. In the Baka field, onshore Niger Delta, detailed reservoir correlation guided by sequence stratigraphic framework analysis showed the distribution of sand and shale units constituting reservoir-seal pairs (RSP) correlatable across the field. Within the 3rd-order packages, it is observed that the lowstand systems tract (LST) and highstand systems tract (HST) contain more RSPs and thicker 4th- and 5th-order sands than the transgressive systems tract (TST). In terms of bathymetry, it is noted that irrespective of systems tracts, the RSP Index (RI) decreases from the proximal shallow/inner shelf settings to the more distal outer shelf areas. Amongst all three systems tracts, intervals interpreted as lowstand prograding complexes contain the best developed sands and highest RSP. Sand development within the LSTs has been controlled by a pronounced growth fault regime accompanied by high subsidence and sedimentation rates. This is linked to the basinward migration of the sands during prolonged sea-level fall, creating significant accommodation space for sand deposition. On the other hand, the TSTs known to mark periods of progressive sea-level rise and landward migration of sandy facies, show thinner sands enclosed in much thicker, laterally extensive, and better-preserved deeper marine shales. Interpreted seismic sections indicate intense growth faulting and channelization that influenced the syn- and post-depositional development of the sand packages across the field. The initial timing of deformation of sub-regional faults in this area coincides with periods of abrupt falls in sea level. This approach could be useful for predicting sand-prone areas in frontier fields as well as possible reservoir-seal parameters required for some aspects of petroleum system analysis and quick-look volume estimation.

Chapter 9. Application of sequence stratigraphy to the evaluation of selected North Sea Jurassic hydrocarbon fields and carbon capture, utilization and storage (CCUS) projects

Abstract The application of sequence stratigraphic concepts and methods augments the efficient development of North Sea hydrocarbon fields with Jurassic reservoirs. In particular, the approach provides enhancements to the development of robust reservoir zonations, more accurate assessments of the extent and continuity of reservoir zones and flow units, clearer identification and prediction of the most productive reservoir intervals, improved understanding of field-wide pressure barriers or baffles to fluid flow, and enhanced reservoir models. In addition, carbon capture and storage (CCS) projects in Jurassic rocks will benefit from the adoption of a sequence stratigraphic approach by enhancing the understanding of storage unit architecture, connectivity and top seals. In this chapter, these applications are discussed with reference to around 20 case studies from the North Sea Basin.

Chapter 2. Sequence stratigraphic concepts and methodologies

Abstract This chapter reviews sequence stratigraphic concepts and methodologies and presents an approach that is most applicable to the North Sea Jurassic, based on the concept of genetic sequence stratigraphy. The concept of depositional sequences, comprising rock units bounded by unconformities, has been developed from the late nineteenth century up to the present day. Many different studies have been carried out on North Sea Jurassic sequence stratigraphy, from the early 1980s to the present day and involving a range of different approaches. Many authors have adopted the J sequence approach that was first published in the early 1990s; however, a number of alternative North Sea Jurassic sequence schemes have also been described. A close relationship existed between tectonics and sequence boundary development, particularly during the Middle–Late Jurassic in the North Sea region. Several of the major unconformities that are known to be of regional extent can be directly related to significant tectonic phases. Other sequence boundaries, for which a tectonic control is not evident, for example, particularly in the Early Jurassic, were potentially driven by glacio-eustatic cycles, which may have been controlled by orbital forcing cycles.

Chapter 10. Sequence stratigraphy in the exploration for North Sea Jurassic stratigraphic traps

Abstract The application of sequence stratigraphic concepts and methods significantly enhances the evaluation of stratigraphic traps. In this chapter, five examples of, as yet undrilled, potential UK North Sea Jurassic combination stratigraphic traps, from the East Shetland Platform, South Viking Graben, Inner Moray Firth and Central Graben, are discussed and the potential application of sequence stratigraphic methods in their evaluation considered.

Geological map of Antony Karol Giedroyc of the territory of Lithuania in the context of geological cartography of the 19th century

The history of geological cartography of the present territory of Lithuania starts with a map published by Jean Etienne Guettard in 1764 and followed by maps by Stanisław Staszic in 1806, Ignacy Domeyko in 1837, and Frederic Dubois de Montpereaux in 1830. A new period of investigations and compilation of geological maps starts about 1840 and is closely related with the development of stratigraphic knowledge; therefore, this period marks the beginning of mapping using the stratigraphic concept (Helmersen 1841). The Geological Committee in St. Petersburg, founded in 1882, at the very beginning of its activities started the compilation of a geological map including the present territory of Lithuania. The works of Antony Karol Giedroyc (Antanas Karolis Giedraitis) were published in 1895 (Giedroyc 1895), and the volume included a map which displays the occurrences of Quaternary and Pre-Quaternary (Tertiary, Cretaceous, and Jurassic) sediments and rocks. The map is constructed on the basis of direct observations and descriptions of outcrops and exposures of Quaternary sediments and Pre-Quaternary rocks carried out by the author, also based on evidence by local people. The main occurrences (provinces) of Pre-Quaternary rocks mapped by Giedroyc are confirmed by the modern geological mapping of the 20th century; therefore, the map of Giedroyc (1895) is regarded as a pioneering work of modern geological mapping using international stratigraphic standards.

Integration of Sequence Stratigraphy and Petrophysical Analysis for Reservoir Characterization: A Case Study of “ED” Field, Offshore Niger Delta

Sequence stratigraphic concept for continental settings was assessed to analyze the depositional systems of the formations penetrated by wells in ‘ED’ Field. Identification and delineation of three sequences and their bounding surfaces was carried out using well logs. Three hydrocarbon bearing reservoirs labelled as ED-R-1000, ED-R-2000 and ED-R-3000 were delineated. Computation of petrophysical properties of reservoir rocks was executed using well established relationship. The stratigraphy comprising of an alternation of sands and shales typically was of the Agbada Formation. The petrophysical analysis results give a good indication of the reservoirs’ capability of accumulating hydrocarbon in their interstitial pore spaces. Three stratigraphic surfaces were used to sub-divide the study field into three (3) depositional sequences and further subdivide the sequences into three system tracts. They are 1154ft(m), 382ft(m) and 738ft(m) thick respectively. The depositional environment of the study field includes distributary channel fill, regressive to transgressive shoreface delta, delta front and storm dominated shelf. The best quality reservoir will be found in the lowstand system tract while TST is a good sealing rock in the study field. Keywords: Stratigraphy, Depositional sequence, Petrophysical, Well logs. DOI: 10.7176/JEES/13-1-05 Publication date: January 31 st 2023

The supply-generated sequence: A unified sequence-stratigraphic model for closed lacustrine sedimentary basins with evidence from the Green River Formation, Uinta Basin, Utah, U.S.A.

Abstract Closed lakes and oceans are stratigraphically distinct systems. However, closed-lake stratigraphy is often interpreted using conventional sequence stratigraphic concepts which were generated for marine settings. As a consequence, lacustrine stratigraphy has long been vexing and applied on an ad-hoc basis. To remedy this, we present a novel, unified sequence stratigraphic model for hydrologically closed (endorheic) basins: the Supply-Generated Sequence (SGS) Model. This model was generated to interpret our outcrop-based correlation—the largest to date at ∼ 30 km—across the Sunnyside Interval member of the middle Green River Formation in Nine Mile Canyon near Price, Utah, USA. The SGS model is based on the fundamental sedimentological and hydrodynamic differences between closed lakes and marine settings wherein the relationship between water discharge and sediment discharge is highly correlated. The SGS model divides packages of genetic lacustrine strata by bounding correlative surfaces, conformable or unconformable, separating facies and surfaces associated with low clastic supply (e.g., carbonates, mudstones, or exposure surfaces) from facies characteristic of relatively higher amounts of clastic supply (subaerial channelized sandstones, subaqueous siltstones, and pedogenic mudstones). We use the SGS model to correlate regional sequences at a higher resolution than previous interpretations and find the greatest amount of clastic deposition occurs during periods of lake-level rise, indicating that the SGSs are characteristically transgressive. Additionally, this model removes the implicit and explicit base-level assumptions of previous sequence stratigraphic models while being agnostic to the source of increased sediment discharge and therefore generalizable to other closed lacustrine settings. We use the high-resolution supply-generated sequences (meters thick) to argue for a climatic origin of the cyclic Sunnyside interval deposits based on sequence durations (40–50 kyr), and aligning sequences with recognized early Eocene transitory hyperthermal event timing and their associated climatic shifts across the region, increasing riverine discharge of sediment and water.

Stratigraphic Forward Modeling Assists Carbonate-Reservoir Characterization

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 202775, “Application of Stratigraphic Forward Modeling to Carbonate-Reservoir Characterization: A New Paradigm From the Albion Research and Development Project,” by Jean Borgomano, Aix-Marseille University, and Gérard Massonnat and Cyprien Lanteaume, TotalEnergies, et al. The paper has not been peer reviewed. _ Improving carbonate-reservoir prediction, field development, and production forecasts, especially in zones lacking data, requires novel reservoir-modeling approaches, including process-based methods. Classical geostatistic modeling methods alone cannot match this challenge, particularly if subtle stratigraphic architectures or sedimentary and diagenetic geometries not directly identified as properties with well data control the reservoir heterogeneity. Stratigraphic forward-modeling approaches can provide pertinent information to carbonate-reservoir characterization. The complete paper describes a modeling package tested and calibrated with high-resolution stratigraphic outcrop models. It allows valid prediction of carbonate facies associations mimicking the spatial distribution mapped along the Urgonian platform transects. Background Classical carbonate-reservoir characterization protocols rely mainly on 3D geostatistical models based on well data, allowing the realization of 3D numerical grids of reservoir properties. These geostatistic property models are supported by deterministic geological interpretations such as stratigraphic well correlations that are commonly based on sequenced stratigraphic concepts and carbonate sedimentological interpretations. The stratigraphic framework obtained from these deterministic interpretations has a critical effect on further static and dynamic reservoir models because it constrains the spatial stationarity of the geostatistic property simulations or imposes discrete flow units or barriers. These deterministic carbonate sequence stratigraphic and associated sedimentological interpretations, however, introduce significant biases, uncertainties, and imprecisions in reservoir models and furthermore are not validated by process-based modeling approaches as one should expect from any scientific protocol. This lack of validation represents a fundamental scientific gap in classical reservoir-characterization work flows that is generally avoided in other scientific domains such as physics by iterations combining experimentation and process-based models to verify deterministic interpretations and hypothesis. The paradox is that this virtuous scientific method is applied at the ultimate stage of the reservoir flow modeling with the classical “flow history matching,” implying the following strong hypothesis (Fig. 1a): If the dynamic model obtained from the upscaled static model matches the dynamic history and the flow records of the studied field and carbonate reservoir, then the geological model, including the deterministic stratigraphic and sedimentary interpretations, is validated. Reservoir flow and dynamic behavior certainly are controlled by initial geological conditions, but those are not dependent on flow processes. According to fundamental scientific principles, geological interpretations and deterministic models must be validated by geological process-based models. To fill this scientific gap in the presented carbonate-reservoir characterization approach, the authors introduce process-based stratigraphical and sedimentological models that are calibrated on pertinent, well-studied outcrop analogs.

Detrital zircon U-Pb-Hf isotope record of conglomerates in the southern Aravalli orogen, NW India: Implications for stratigraphy, provenance and Archean to Paleoproterozoic crustal evolution

The inconsistent stratigraphic framework of the Proterozoic successions in the Aravalli orogen, NW India hinders the detailed reconstruction of its geodynamic evolution during the Archean to Paleoproterozoic. In this study, we present new results of combined U-Pb-Hf isotope data of detrital zircon grains of two conglomerate samples from the southern Aravalli orogen, presently assigned to the upper unit of the Aravalli Supergroup. The youngest concordant zircon grains in both the conglomerates yield concordia ages of 1735 ± 13 Ma (n = 2) and 1736 ± 15 Ma (n = 2), respectively, interpreted as maximum ages of deposition. Older zircon grains mostly reveal Neoarchean to Paleoproterozoic age clusters at 2560–2550, 1870–1860 and 1760–1740 Ma, and minor Paleoarchean ages between 3558 ± 17 Ma and 3239 ± 14 Ma, corresponding to known magmatic events in the Aravalli orogen. Most detrital zircon grains show subchondritic εHft values (+6 to −20), signifying minor reworking of late Hadean/Eoarchean crust during the Paleoarchean, and substantial reworking of Paleo-to Neoarchean crust during the late Neoarchean and Paleoproterozoic, with only minor juvenile input. The maximum depositional ages indicate that the investigated conglomerates were deposited either synchronous or after the emplacement of extension-related A-type granites, which intruded the Aravalli orogen between 1733 ± 9 Ma and 1703 ± 5 Ma. Furthermore, the data suggest that the conglomerates do not belong to the upper Aravalli unit as envisaged by previously published stratigraphic concepts. Instead, these were deposited earlier, during opening of a rift-related basin, grading from a terrestrial into a marine environment, contemporaneous with other sedimentary successions exposed in the North Delhi basin, which are presently assigned to the North Delhi Supergroup. The compiled zircon age-Hf isotope data additionally provide evidence for a series of late Hadean to Archean juvenile crust formation events in hinterland of the Aravalli orogen at 4200–3300 Ma for east Indian cratonic blocks and 3550–3100 Ma for northern and southern cratonic nuclei, and 2700–2500 Ma all over India. Substantial crustal reworking took place during the late Neoarchean at 2500 Ma, and the late Paleoproterozoic at 1850 Ma and 1730–1700 Ma.

The Arapey group: confining basalts of the Guarani aquifer in Uruguay

With the increasing demand of drinking water for agricultural use, takes special importance the geological and hydrogeological knowledge of the infrabasaltic aquifer known as Guaraní Aquifer in the South Cone. The different stratigraphic concepts historically managed for the geological formations of the top of Gondwana Supergroup in Uruguay, carrying great volumes of groundwater with thermal potential, agricultural use (irrigation) and urban supply are discussed. Geological units of Guaraní Aquifer are described: Buena Vista, Cuchilla Ombú, Tacuarembó and Rivera Formations. Geometry and thickness of its confining unit - Arapey group - condition the economic possibilities of taking advantages using groundwater from Guaraní Aquifer. Such group has been divided - according to lithostructural criteria - on six formations for which a brief description is given. A preliminary tridimensional geometry of Arapey group´s basaltic lava and its relation with Guaraní Aquifer is showed. This geometry is related to the basaltic thickness to cross in a borehole in order to obtain groundwater with an error margin of about 30 meters. This is very relevant, specialy in lithosol zones of the basaltic area, where the installation of irrigation systems would mean a sustancial agrarian improvement in these areas.

Strontium isotope stratigraphic insights on the end-Permian mass extinction and the Permian-Triassic boundary in the Dolomites (Italy)

The Dolomites (Southern Alps, Italy) is a most significant region to investigate the evolution of shallow-marine ecosystems during the end-Permian mass extinction (EPME). Shallow-marine ecosystems are complex places from an oceanographic viewpoint and combine high biological productivity and ecological diversity. Therefore, establishing the timing and correlation of globally recognisable events in this region are fundamental to interpreting the biological crisis that followed.We took advantage of the Strontium Isotope Stratigraphy (SIS) concept to correlate our stratigraphic succession, ranging from the upper Bellerophon (Bulla Member, upper Changhsingian) to the lower Werfen (Tesero Member, upper Changhsingian - lower Induan) Formations of the Dolomites, to the Meishan (Zhejiang Province, China), the Global Stratotype Section and Point (GSSP) for the Permian–Triassic boundary. We integrated new and previously published 87Sr/86Sr data from well preserved brachiopods and show that the topmost part of the Bellerophon Formation (the Bulla Member) correlates with beds 24 e-f of the GSSP section, while the Tesero Member, where the Permian-Triassic boundary is located, is characterised by more radiogenic Sr isotope ratios than expected. Differences in Sr isotope ratios may be due to small-scale variations in local paleoenvironmental and paleogeographic conditions/settings. Continental weathering of sedimentary or igneous rocks, distance from terrestrial environment and nearby occurrence of radiogenic rocks might also produce locally variable Sr isotope signatures especially in shallow water environments complicating the application of SIS principles.

Reconsidering Carboniferous–Permian continental paleoenvironments in eastern equatorial Pangea: facies and sequence stratigraphy investigations in the Autun Basin (France)

The late Carboniferous–early Permian represents a key period in the Phanerozoic history, given the major global geodynamic and climate modifications. The aim of this work is to better understand the context and characteristics of the sedimentation recorded in the continental environments of eastern equatorial Pangea at this time, through the example of the Autun Basin (northeastern Massif Central, France). The Autun Basin contains the historical stratotype of the Autunian continental stage, and its stratigraphy was recently improved by accurate numerical ages. This basin formed in an extensional tectonic context during the latest stages of the Variscan orogeny, and it is essential to study its paleoenvironmental evolution to provide new insights into the sedimentary evolution of contemporaneous surrounding basins. Using field and subsurface data, we propose a refined sedimentological model for the Autun Basin, relying on updated facies interpretations, organic matter content fluctuations, and sequence stratigraphy concepts and correlations. The continental environments of the lower sedimentary succession of the Autun Basin, previously considered to be fluvial and lacustrine, are herein re-interpreted as mainly lacustrine, comprising fine-grained organic matter-rich deposits, and supplied by coarser-grained deltaic siliciclastic sediments, without preservation of strict fluvial sedimentation. The determination of the sequence stratigraphy cycles, strengthened by the quantification of the organic matter content, and reflected by the temporal succession of progradational and retrogradational trends, is used to determine new correlations between several sections, as well as to reconstruct the paleoenvironment evolution at the Carboniferous–Permian transition. This study provides evidence that the sedimentation area of the Autun Basin at the time of its filling was much larger than the preserved basin area, and suggests connections with contemporaneous neighboring French basins, pointing to a large sedimentary system in the northeastern Massif Central area rather than narrow and isolated basins.

Mapping of Genetic Sequences of the Cambrian Series in the Jbel Saghro Massif, Eastern Anti-Atlas, Morocco: Implications for Eustatic and Tectonic Controls

In this paper, a sedimentological and sequence stratigraphy analysis was performed on Lower and Middle Cambrian deposits of Jbel Saghro, Eastern Anti-Atlas. The field data analysis and the application of sequence stratigraphy concepts were used to classify sedimentary processes and depositional environment, and to define the Lower to Middle Cambrian basin’s detailed geometry. The Cambrian sedimentation of northeastern Saghro indicates a deltaic environment, which is composed of two depositional sequences. These sequences are made of a transgressive system-tract with retrograding sediments and a highstand system tract with prograding sediments. In response to sea-level change, these system-tracts were formed by several genetic units, and limited by various stratigraphic surfaces. The genetic unit stacking-patterns combined with the study of synsedimentary tectonics enabled to follow the sedimentary record’s Spatio-temporal evolution and its three-dimensional geometry. The study area deposits display significant dissimilarities in thickness. The western part shows a Lower Cambrian hiatus and an important reduction of the thickness in the Middle Cambrian deposits. However, the marine trend (progradation/retrogradation) remains similar in the study area. This suggests the same eustatic origin of all genetic sequences and variations in their preservation rate. This configuration is the result of differential subsidence that affected the Anti-Atlas during the Cambrian.

Depositional environment characterization in deltaic system by utilizing core, well log and seismic attribute data, Northern Malay Basin

The heterogeneity of shallow marine facies is quite hard to be solved. However, integrating all the data is essential to determine the details of facies distribution, whereas facies characterization is an important part that should be done before the petrophysical characterisation. This study aims to evaluate the reservoir depositional facies distribution using seismic well log and core data based on sequence stratigraphy concept, seismic interpretation, and seismic attributes, thus reducing the risk of oil exploration and improving the success rate. To ensure the objective is achieved, sequence stratigraphy interpretation has been done using integrating well log, core, and seismic data to identify the depositional environment. Distribution of coal helps to create well log correlation. Lithofacies and fluid have been interpreted according to core, test and log patterns, such as; gas sand, brine sand, shale, and coal. Based on the characteristic of logs, biostratigraphy and core data, five depositional environments have been interpreted in this study including in-distributary channel, delta plain (flood plain shale), crevasse splay, delta front shale (prodelta), and mouth bar. The interval of the target area is generally influenced by regression systems where on the lower formation is dominated by the transition depositional environment and changed to be dominant of delta plain.

Understanding along-strike variability in controlling mechanisms of paleoenvironmental conditions and stratigraphic architecture: Ordovician successions in the Alborz Mountains of Iran at the northern Gondwana margin

Changes in stacking patterns of facies, stratal architecture and shoreline trajectory along depositional strike are mainly dependent on along-strike differences in factors such as physical processes (rivers, waves, tides), tectonics, eustatic changes, sediment supply, and local physiography. The lower-upper Ordovician successions (Lashkerak Formation) deposited in a Peri-Gondwana shallow continental shelf have been interpreted using the sequence stratigraphic concepts. This approach allowed to highlight main differences along-strike in the co-existing depositional systems (coastal plains, estuaries, deltas, and shoreline to shelf systems) in the Alborz basin along the northern edge of Gondwana. On the basis of sedimentary and ichnological characteristics, the siliciclastic successions are divided into four facies associations: (i) Wave-dominated estuarine, (ii) Wave-dominated shoreface-offshore complex, (iii) Mixed fluvial (F)- and wave (W)-influenced delta (Fw and Wf), and (iv) Tide-dominated, fluvial-influenced delta (Tf). Six third-order depositional sequences (DS1-DS6) were recognized, each of them are bounded by unconformities and pronounced shifts in the facies. Along depositional strike (NE/SW- a distance of c. 150 km), significant intrabasinal changes in sediment supply produced evident lateral changes in the shoreline trajectory and stratal architecture, of the DS1-DS3 (Tremadocian-Floian), may be attributed to differences in physical processes (rivers, waves, tides activity) and topographic irregularities derive probably by different rates of subsidence in the basin. During the deposition of the DS1-DS3, a significant along-strike differences in the composition of ichnological suites and the lifestyle of benthonic organisms, dependent on the relative supremacy of wave, storm, river, and tidal processes. Sedimentary supply and processes are the main controlling factors for the stratigraphic architecture rather than the tectonic activity between Tremadocian and Floian. While during the Darriwilian-Katian interval (DS4-DS6), the tectonic activity predominates with the beginning of extensional phases related to the rifting in the Alborz basin causing the activation of syn-depositional normal faults and the development of block-faulted craton-ward margin. Typically, differential subsidence due to extensional tectonic activity causes the uplift of tectonic blocks west of the Alborz Basin into the emerging areas, on one hand, and simultaneous deepening-upward stacking patterns (i.e., increased subsidence rates) in the hanging-wall depocenters of east of the Alborz Basin, on the other hand. This outcrop-based study suggests that the identification of genetically related depositional units in a larger paleogeographic context is fundamental for understanding along-strike variability in controlling mechanisms of the spatial distribution and stratigraphic architecture of coexisting and linked depositional systems.