Retrogradational Stacking Pattern Research Articles

Quantitative facies analysis of a fluvio-aeolian system: Lower Triassic Buntsandstein Group, eastern France

Understanding the factors that control the temporal and spatial evolution of the Lower Triassic Buntsandstein Group, eastern France, is important not just for palaeoenvironmental reconstruction but also because it is an important reservoir for the lithium-rich geothermal brines in the Upper Rhine Graben region. The interval of interest in this study, the Lower Grès Vosgien Formation (LGV), is made up of c. 200 m of clastic deposits of mixed fluvial and aeolian origin. Given the proximity between the outcrops and the areas of mineral and heat exploration, this region offers a unique opportunity for quantitative analysis and correlation between outcrops and reservoirs. The LGV is the thickest Formation in the Buntsandstein Group. However, hitherto, no detailed architectural analysis has been published to reveal the controlling factors of its depositional elements. In this study, high-resolution facies analysis was applied to thirteen outcrops, and a core, to quantify fluvial and aeolian depositional architectures, and to comprehend palaeoenvironmental conditions during their deposition. Two facies associations were identified. The fluvial channel facies association, composed mainly of sandstones deposited in poorly confined, occasionally ephemeral channels, corresponds to 93 % of the total thickness. The analysis of >800 sets of strata characterised by lower-, transitional-, and upper-flow regime sedimentary structures, distributed within different architectural elements, enabled the distinction of temporal and spatial variabilities, and an estimate of fluvial palaeohydraulic characteristics. The wind- and water-laid facies association, which accounts for 7 % of the total thickness, records an architecture controlled by a fluctuating water-table level, and ephemeral floods. Results revealed that aeolian dunes and sand sheets accumulated in distinct temporal moments. The vertical trends, recorded in the core, indicate an upward increase in the frequency of intercalations between the two facies associations, and a decrease in the occurrences of thicker cross-bedded sandstone sets of fluvial origin, which, associated with the overall retrogradational stacking pattern of the LGV, is interpreted as the preserved record of a large distributive fluvial system (DFS). The occurrence of laterally extensive aeolian deposits, overlying fluvial deposits, is often associated by authors with periods of relatively more arid conditions at a regional scale. However, evidence indicates channel belt avulsion as an alternative interpretation for the establishment of the two facies associations. The findings enhance the knowledge about the depositional controlling factors in braided fluvial and aeolian systems, and improve predictive models that account for reservoir heterogeneity in accumulated successions of this type.

Carboniferous to Triassic polyphase tectonic transition in the western North China craton: A retroarc basin response to termination of the middle segment of the Paleo-Asian Ocean

Knowledge of the closure of the archipelago-type southern Paleo-Asian Ocean has been limited by uncertainty regarding whether the Alxa tectonic belt was isolated from the North China craton by an ocean around the Helanshan tectonic belt. Newly released seismic reflection profiles across the Alxa-Ordos border showed that the Alxa tectonic belt and Ordos Basin were located in a paleogeographically linked basin throughout the Paleozoic, indicating that the Tianshan and Solonker sutures were contiguous. The ca. 320−285 Ma successions in the Helanshan tectonic belt and surroundings, fed by a northeasterly Inner Mongolia continental arc source, display a retrogradational stacking pattern along with diabase sill emplacement. This inferred retroarc extensional setting was coeval with asthenospheric upwelling and thinning of the continental arc driven by retreating subduction of the Paleo-Asian Ocean. The subsequent ca. 280−260 Ma sedimentary hiatus coincided with magmatic flare-up, crustal thickening, and retroarc foreland formation in the Inner Mongolia continental arc, indicating a geodynamic transition from retroarc extension to compression in the mid-Permian. Then craton-scale drainage reorganization occurred during the Early Triassic (ca. 250−230 Ma), manifested by the discharge of the Middle Triassic fluvial system southeastward to the central Ordos Basin; this was steered by southeastward expansion of the Alxa tectonic belt during the final termination of the Paleo-Asian Ocean. Postcollision lithospheric adjustment since ca. 230 Ma resulted in vigorous alkaline magmatism and supracrustal stretching in the Inner Mongolia continental arc as well as mafic magmatism and rifting in the study area. Hence, Carboniferous to Triassic polyphase tectonic transitions in the western North China craton were retroarc basin expressions related to complicated subduction-closure processes in the southern Paleo-Asian Ocean.

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

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

A multi-scale assessment of shoreline changes at an undeveloped beach in southern Brazil

This research aims to investigate shoreline variability at an undeveloped beach in southern Brazil on interannual and millennial scales. The long-term coastal evolution was investigated by GPR, whereas the interannual scale shoreline changes were analyzed by the Digital Shoreline Analysis System (DSAS). Simultaneously, a supervised Maximum Likelihood image classification was applied to the dune systems to differentiate vegetation from sand. The results show that the coastline in the Praia das Cabras region is retreating at different scales. The stratigraphic record in GPR shows that the coast has a retrogradational stacking pattern behavior in geological time. At the same time, the results obtained from the digital shoreline analysis revealed that the coast has suffered short-term erosion in the analyzed period, and this is attributed to natural causes. Another point is the higher values of erosion in the extreme parts of the study area, which are related to the presence of washouts. There is also a differentiation in the stage of the dunes and vegetation between the northern and southern parts of the stretch. The northern area is more densely vegetated and has a continuous foredune ridge with incipient dunes forming a ramp, whereas in the southern part, the vegetation is more dispersed, with interrupted dunes forming nebkhas. Between 2019 and 2023 there was a recovery of the dune field, by filling in the blowouts and minimizing the indentations, forming a more homogeneous foredune line.

Limnogeology of the Agua de la Zorra Formation (Middle–Upper Triassic), Cuyana Basin, NW Argentina: Emphasising lacustrine carbonates

Lacustrine systems are complex and highly sensitive in responding to allogenic factors like tectonics, climate and volcanism but also present within lake processes that are difficult to disentangle. The Agua de la Zorra Formation (Middle–Upper Triassic) outcropping in the Paramillos de Uspallata sub-basin, Cuyana rift Basin (SW Gondwana), is composed of deltaic–fluvial–lacustrine–volcaniclastic deposits. The lacustrine system presents carbonate deposits, as almost every other sub-basin within the Cuyana rift. This makes it an exceptional case for analysing limnogeological questions in an extensional tectonic regime linked to volcanism (basalt flow and tuff deposits) and studying lacustrine carbonate in that particular setting. This study focuses on a high-resolution stratigraphic, sedimentologic, petrographic and limnogeological investigation of the Agua de la Zorra depositional system to understand its evolution through space and time; and to reconstruct the development of the carbonate factory within the palaeolake. Stratigraphic correlation of five sedimentary logs across the sub-basin allowed the identification of a deltaic–lacustrine facies association and a progradational–retrogradational stacking pattern interpreting the palaeolake as an overfilled lake basin type. Five facies associations represent a delta front, prodelta, lake margin, lake centre and volcanic episodes. The stratigraphic analysis allowed interpreting that volcanic episodes were diachronous during the evolution of the Agua de la Zorra system; the development of a well-established axial fluvial system upsection and the coeval migration of the highest accommodation point and lake centre northwards. Carbonate deposits are part of the lake margin subenvironment and immediately overlie volcanic basalts and are laterally linked to altered sandstones in contact with basalts. Their microfabric is characterised by fibro-radial spar mosaics and laminated carbonate, interpreted as inorganic authigenic calcite precipitation. This and their restricted extent support that alkaline lava flows in contact with the palaeolake water column triggered carbonate precipitation. Stratigraphic, sedimentologic, limnogeological and petrographic analyses strongly support volcanism and tectonics as the main allogenic factors controlling the Agua de La Zorra lacustrine system evolution.

Fault growth and orthogonal shortening in transtensional supradetachment basins: Insights from the ‘Old Red’ of western Norway

AbstractFor basins that evolve adjacent to large‐magnitude normal faults, tectonic controls on sedimentation involve isostatic back rotation of an exhuming footwall and, commonly, the evolution of kilometre‐scale extension‐parallel folds. Based on observations from classic localities in western Norway, we propose a three‐stage evolution scenario for transtensional supradetachment basins where the basins become progressively re‐arranged because of core complex exhumation and subsequent orthogonal shortening. Extension‐parallel transverse synclines initially form due to a normal displacement gradient, but when displacements accumulate beyond a certain magnitude, the hanging wall increasingly responds to core complex exhumation and the original depocentre, formed close to the original area of maximum displacement, will become inverted and dismembered above the core complex. Two new synclinal depocentres will develop along the flanks. Because these synclines form by extensional fault growth rather than by shortening, they will be associated with widening of the basin and onlap onto basement at high angles to the maximum elongation trend with overall grain‐size decrease and retrogradational stacking patterns. Further, because these synclines grow away from the evolving core complex, sedimentary units will become asymmetrically distributed inside each syncline in such a way that the oldest deposits in the syncline will be preserved on the flank most proximal to the core complex. In transtensional environments, a third evolutionary stage may involve constrictional strain where extension‐parallel folds and reverse faults produced by orthogonal shortening enhance or interact with other structures. Ultimately, initial extensional sub‐basins may become warped across extension‐parallel folds. Hanging wall deformation will be manifested in shifting accommodation patterns, with depocentres that generally migrate in the direction of the detachment fault. Accommodation patterns initially related to megafault growth may conceptually evolve into depocentres controlled by orthogonal shortening.

Sedimentary–tectonic interaction on the growth sequence architecture within the intraslope basins of deep-water Niger Delta Basin

This paper presents a 3D seismic-based case study from the deep-water Niger Delta Basin to investigate sedimentary–tectonic interaction on growth sequence architecture within the thrust-related intraslope or piggyback basins. Gravitational contraction in the lower continental slope had yielded a series of thrust faults and associated folds in the study area, which formed several piggyback basins. These basins were filled by a suite of growth sequences with varying stratigraphic architecture. Analysis of the 3D seismic data recognized three primary seismic facies types respectively as: convergent, draping and chaotic, which contain seven subtypes. These facies types are combined to form different filling successions for convergent or chaotic growth sequences. The convergent growth sequences mainly occur in the deep section of basin fills during strong gravitational deformation, and always began with convergent-baselapping strata succeeded by convergent-thinning strata, representing pond-to-bypass transition in the ponded-basin accommodation space. The chaotic growth sequences mainly occur in the shallow section of basin fills in response to weak gravitational deformation, and usually began with debris-flow deposits succeeded by channel-levee complexes, reflecting dominant erosion-bypass processes in the slope accommodation space. A dynamic fill-and-spill model considering relationship between episodic sedimentation rate and structural growth rate is proposed to explain the formative mechanisms of growth strata units and associated successions. Interaction between glaciation or deglaciation and sea-level change and gravitational deformation history are suggested to be the factor which resulted in the complex stratal stacking patterns, including progradational or retrogradational stacking patterns within convergent growth sequences, and progradational stacking patterns within chaotic growth sequences.

Late Pleistocene to Holocene glacio-eustatic history as recorded in the Pescara paleovalley system (Central Italy, Adriatic basin)

A buried paleovalley system, about 50 m deep and 2 km wide, is documented from the Pescara coastal plain. Based on stratigraphic, sedimentological, paleontological, chronological and geotechnical data, the paleovalley profile and 3D facies architecture of the paleovalley fill (PVF) were reconstructed.The lowermost PVF is a laterally extensive fluvial gravel body, up to 13 m-thick, that represents the lowstand systems tract (LST; pre-11.3 ka cal BP). Above lowstand deposits, the transgressive systems tract (TST), 21 m-thick, shows a deepening-upward trend, from freshwater/inner-estuarine to brackish/outer-estuarine facies associations (11.3–8.0 ka cal BP). The upper part of the succession (highstand systems tract – HST) shows a shallowing-upward tendency from paludal to fluvio-deltaic deposits.Seven millennial-scale parasequences (Ps) were identified within the Pescara Holocene (TST + HST) succession. Transgressive Ps1-3 exhibit a distinctive retrogradational stacking pattern. Highstand Ps4-7 are aggradationally-to-progradationally stacked. During the aggradational phase (P4), the estuary was gradually filled and swamp environments spread onto the valley interfluve. Because of subsequent progradation (Ps5-7), delta plain conditions established. In the research core, TST parasequences show higher accumulation rates (up to 9.4 mm/y) than HST ones (1.3–1.8 mm/y). Thus, the study area evolved from a region of sediment storage (11.3–8.0 ka cal BP) into a sector of prevalent sediment bypass (last 8.0 ky).Major early Holocene flooding events were possibly triggered by Melt-Water Pulses (MWPs) 1B, 1C and 1D. The eustatic rise linked to MWP-1B reasonably caused the P1 flooding event (11.3 ka cal BP). Post-MWPs 1C and 1D sea-level rises likely provoked the complete drowning of the paleovalley system and the subsequent maximum landward migration of the shoreline (about 8.0 ka cal BP).This study provides new evidences, in terms of sedimentary response, of the poorly-documented MWPs 1C and 1D, and the first documentation of MWP-1B eustatic effects in an onshore sector of the Central Adriatic.

Impact of sedimentation, climate and sea level on marine sedimentary pyrite sulfur isotopes: Insights from the Valle di Manche section (Lower-Middle Pleistocene, southern Italy)

Variations in the isotopic composition of sulfur in sedimentary pyrite (δ34Spyr) are often used to reconstruct global sulfur biogeochemical cycling and Earth's surface oxidation state over Earth history. Recent work, however, has shown that δ34Spyr is strongly impacted by local depositional conditions, which both confounds attempts to reconstruct global sulfur cycling and provides a new proxy for investigating local paleoenvironmental conditions. We present a chemostratigraphic record of δ34Spyr in a detailed paleoenvironmental and sequence stratigraphic framework spanning the Early-Mid Pleistocene transition from the Crotone Basin (Calabria, Southern Italy). Bulk δ34Spyr data parallel transgressive-regressive cycles and enable the differentiation of progradational and retrogradational stacking patterns, where δ34Spyr values decrease toward −50‰ in outer shelf deposits during late transgression and become more positive and variable in prograding sedimentary units accumulated in shallower environments. In parallel with the observed variations in δ34Spyr, complementary data on organic carbon abundance and isotopic composition and total nitrogen abundance document changes in terrestrial delivery of sediment to the basin, as a consequence of glacial-interglacial eustatic sea-level changes, regional climate and local tectonics. The chemostratigraphic record of δ34Spyr appears sensitive to variations in sedimentation rates and local erosional surfaces and therefore may represent a powerful tool to assess stratal stacking patterns for sequence stratigraphic interpretations of siliciclastic successions. These results highlight the role of local conditions in controlling sedimentary δ34Spyr records and illustrate how isotopic data can be used to reconstruct key parameters of the sedimentary environment that might not otherwise be accessible, especially in deep-time strata.

Late Paleozoic glacial to postglacial stratigraphic evolution of the Rio do Sul depocenter, Itararé and Guatá groups, Pennsylvanian-Cisuralian, southern Brazil

The transition from the Late Paleozoic Ice Age (LPIA) to fully postglacial conditions in SW Gondwana is under increasing discussion due to either the radiometric ages of its boundary or the stratigraphic nature of this transition. The record of this transition in the Paraná Basin is found in the glacial and glacially influenced deposits of the upper Mafra and Rio do Sul Formations (upper Itararé Group) and postglacial strata of the Rio Bonito Formation (Guatá Group). Here we address the depositional architecture and stratigraphic evolution of these deposits in the Rio do Sul depocenter, eastern Paraná Basin, Brazil, the main area of subsidence in the basin during this transition in Pennsylvanian-Cisuralian time, bringing an opportunity to examine the characteristics of glacial to postglacial transition. Analyses of facies, stratigraphic logs, stratigraphic correlations, and paleocurrent dispersal trends allowed us to define three evolutionary stages. The first stage registers glacial advance from the south-southwest represented by an erosive surface and subglacial tillites. Gravitational deposits covered the tillites in response to ice retreat (upper Mafra Formation), and the Lontras Shales (lower Rio do Sul Formation) correspond to the marine maximum flooding. The second stage comprises co-genetic deepwater (Rio do Sul Formation) to shallow (Rio Bonito Formation, Triunfo Member) progradational deposits after the Lontras Shale maximum flooding. Paleocurrent data and glacially related features point to glaciated source areas located to the NE, E, and SE for the Rio do Sul depocenter during this stage. The third stage corresponds to retrogradational stacking pattern upon a fluvial subaerial unconformity (incised valley), starting with fluvio-deltaic beds (Triunfo Member), followed by fine-grained deposits of the Paraguaçu Member of Rio Bonito Formation. No features related to glacial influence characterize this third stage. As previously suggested, tectonic uplift likely drove the additional NE source and created the space that allowed the transitional contact between Rio do Sul and Rio Bonito formations in the Rio do Sul depocenter.

Facies analysis and sequence-stratigraphic control on reservoir architecture: Example from mixed carbonate/siliciclastic sediments of Raha Formation, Gulf of Suez, Egypt

Mixed carbonate-siliciclastic systems are complex, and their development can sometimes be difficult to understand, given the various responses to each sub-environment to specific forcing, such as variation in sediment supply, climatic conditions, or available accommodation. This work integrates a detailed facies, associated with a depositional environment reconstruction, all of which is placed in a sequence stratigraphy framework in order identify the different controls on the reservoir architecture of the Upper Cretaceous (Cenomanian) Raha Formation, Gulf of Suez. The study utilized outcrop data from Gabal Ekma and Gabal Nezzazat, as well as subsurface data from five wells drilled through the October oil field.Our findings revealed that the Raha Formation succession is subdivided into eleven facies associations (FA) deposited as one depositional sequence. The Abu Had Member of the Raha formation consists of mixed siliciclastic/carbonate packages, arranged in a retrogradational stacking pattern, which were deposited during a period of pulsative shoreline regression. As a result of the transgression, the siliciclastic input in the system increased, potentially due to increased precipitation and weathering in the hinterland of the study area. The upper part of the Raha Formation belongs to the Mellaha Sand Member, which is mostly composed of bioturbated quartz arenite with bioturbation, and is the main reservoir in the October Field. It was deposited during a period of shoreline progradation as testified by its progradational stacking pattern.The reservoirs of the Raha Formation can be divided into five distinctive types (G, C, Q, P, and M), based on the factors controlling the permeability (Diagenetic criteria and compositional framework). The outcrops-subsurface correlations indicated that these reservoirs in the Mellaha Sand Member are laterally extensive, and thicken from 25 m in the SE to 91 m northwestwards. It is predicted that these reservoir intervals thicken toward the unexplored areas northern of October Field. Pore-filling cement and detrital matrix decreased the permeability and the reservoir quality to minimum while, the grain coating prevented the collapse of the reservoir quality. Pore-filling cement and detrital matrix decreased the permeability values, consequently lowering the reservoir quality to minimum, whereas the grain coating prevented the collapse of the reservoir quality, retaining the highest permeability values in the overall pore system. The aforementioned study provides significant insight into the understanding of depositional facies and sequence-stratigraphic control on reservoir architecture. Additionally, it provides insights for further exploration activities in these mixed carbonate/siliciclastic intervals along the Gulf of Suez and adjacent basin, and the improved understanding of these reservoirs units could also be applied to future Carbon Capture and Storage projects.

Crowded Rosselia ichnofabric in estuarine settings recording early transgressions in lowermost Permian post-glacial Gondwana (Rio Bonito Formation, Paraná Basin, S Brazil)

Ichnology has widely been used in paleoecological, paleoenvironmental, and evolutionary analysis. Rosselia is a dwelling burrow of infaunal, detritus-feeding terebellid polychaetes and is common in Phanerozoic shallow-marine deposits. The crowded Rosselia ichnofabric (CRI, i.e., a dense occurrence of Rosselia) provides itself in this study as a valuable guide to recognizing high-energy and high-frequency shoreface settings but is poorly recorded in estuarine settings. This study aims (1) to interpret the occurrence of Rosselia and the accompanying ichnofauna in the early Permian postglacial estuarine deposits of the Rio Bonito Formation (Paraná Basin) in southern Brazil and (2) to evaluate the potential of the CRI as an ichnomarker of transgressive events in estuarine settings. The study area presents a glacially incised paleovalley (the Capané paleovalley) near Caçapava do Sul town in the south of Brazil and exhibits 8 facies associations that tell the depositional history of the paleovalley-fill sediments. The succession indicates a confined and retrogradational stacking pattern and constitutes two high-frequency depositional sequences. The CRI is recurrent in three distinct intervals of Sequence 1; it occurs in both the sandy to clayey heterolithic facies and the sandstone facies. The CRI indicates relatively high-energy sedimentation that is likely associated with the storm events influencing the paleovalley during a marine transgression. The Rosselia specimens are either vertical or inclined to the bedding plane. The causative tubes vary from 5 to 10 mm in diameter and the spindle diameter ranges from 20 to 90 mm. Most of the specimens are preserved as funnel-shaped burrows; however, spindle-shaped burrows also occur. The density of burrows is high (60–80 per m2), representing a crowded Rosselia ichnofabric (CRI). The CRI reflects the high energy and the high frequency of the storm surges that impacted the Capané paleovalley estuary during the Early Permian. This scenario inhibited the presence of other tracemakers that colonized the surrounding subenvironments of the paleovalley, resulting in the preservation of a monotypic R. socialis assemblage in the storm-related deposits. These results provide new insights about the distribution of CRI in shallow marine environments and reinforce its value as a stratigraphic ichnomarker of high-energy, high-frequency storm deposits also in estuaries impacted by large-scale episodic marine incursions.

Shoreline trajectory and stratal stacking patterns: Relation to sediment partitioning and types of deep-lacustrine deposits

This study utilizes drilling data to investigate shoreline trajectory, associated stratal stacking patterns and their relationships to sediment partitioning within the Lower Triassic in the Mahu Sag, northwestern Junggar Basin. Accretionary transgression occurred with changing of shoreline trajectory, sediment partition and basin-margin morphology. Two main types of shoreline trajectory and their associated stratal stacking patterns were recognized: (1) slightly rising trajectory, which has low trajectory angle (0.065°–0.072°) and is associated with retrogradational to aggradational back-stepping stacking patterns with low slope relief, and (2) moderately rising trajectory, which has relatively higher trajectory angle (0.09°–0.27°) and is associated with aggradational to retrogradational stacking patterns with moderate slope relief. The rising shoreline trajectory is associated with a fan-delta system with facies belts that migrate landward and are fining-upward, which is characterized by thick plain and thin front architecture. In vertical, the ascending trajectory developed with upward decreasing of sediment grain-size, muddy matrix changed to sandy matrix and even changed to clast supported in conglomerates. In planar, shoreline trajectory angle variations exist associated with different delta-front processes and different prodelta/deep-lacustrine deposits. Shoreline trajectory angle variations generated by sediment partition represents the relations between aggradation and retrogradation which determines the basin-margin growth pattern and morphology. It also indicates the vertical succession of basin-margin deposits and the preservation potential of deposits generated in various depositional environments. The results of this study show that shoreline trajectory could be a good indicator for basin-margin process and reservoir interpretation.

Stratigraphic Architecture of the Karoo River Channels at the End-Capitanian

The main Karoo Basin of southern Africa contains the continental record of the end-Triassic, end-Permian, and end-Capitanian mass extinction events. Of these, the environmental drivers of the end-Capitanian are least known. Integrating quantitative stratigraphic architecture analysis from abundant outcrop profiles, paleocurrent measurements, and petrography, this study investigates the stratigraphic interval that records the end-Capitanian extinction event in the southwestern and southern main Karoo Basin and demonstrates that this biotic change coincided with a subtle variation in the stratigraphic architectural style ∼260 Ma ago. Our multi-proxy sedimentological work not only defines the depositional setting of the succession as a megafan system that drained the foothills of the Cape Fold Belt, but also attempts to differentiate the tectonic and climatic controls on the fluvial architecture of this paleontologically important Permian succession. Our results reveal limited changes in sediment sources, paleocurrents, sandstone body geometries, and possibly a constant hot, semi-arid paleoclimate during the deposition of the studied interval; however, the stratigraphic trends show upward increase in 1) laterally accreted, sandy architectural elements and 2) architectural elements that build a portion of the floodplain deposits. We consider this to reflect a long-term retrogradational stacking pattern of facies composition that can be linked to changes on the medial parts of southward draining megafans, where channel sinuosity increased, and depositional energy decreased at the end-Capitanian. The shift in the fluvial architecture was likely triggered by basin-wide allogenic controls rather than local autogenic processes because this trend is observed in the coeval stratigraphic intervals from geographically disparate areas in the southwestern and southern main Karoo Basin. Consequently, we propose that this regional backstepping most likely resulted from tectonic events in the adjacent Cape Fold Belt.

Coeval deposition of transgressive and normal regressive stratal packages in a structurally controlled area of the Viking Formation, central Alberta, Canada

AbstractVariability in accommodation and sedimentation rates within a basin generates significant deviations in the along‐strike stratal stacking patterns of systems tracts. This variability can lead to coeval depositional units that record the juxtaposition of transgressive (retrogradational) and regressive (progradational) stratal stacking patterns. In scenarios where transgressive and regressive units are deposited concurrently, challenges arise when attempting to correlate and place systems tracts into a sequence stratigraphic framework. In these scenarios, the maximum flooding surface records a high level of diachroneity, with the position of the surface variable throughout the stratigraphic column. In this study, Viking Formation (late Albian) deposits in the Western Canada Sedimentary Basin, central Alberta, Canada, preserve significant along‐strike variability of palaeoshorelines that developed in response to autogenic processes as well as allogenic controls that were active during deposition. Specifically, structural reactivation of Precambrian basement structures during Viking deposition led to significant variability in depositional environments along the palaeoshoreline. The incremental basement reactivation of the Precambrian Snowbird Tectonic Zone influenced sedimentation patterns and the creation of anomalous zones of accommodation in localized areas of the basin. Across fault boundaries and within the anomalously thick strata, both progradational and retrogradational stacking patterns occur within broadly contemporaneous deposits, complicating the correlation of stratigraphic units. While the concomitant deposition of transgressive and regressive units has been documented in a number of modern marine analogues, the concept is rarely applied to ancient successions. By identifying along‐strike variabilities in shoreline geometries and incorporating the autogenic and allogenic controls that were active during deposition, a more accurate sequence stratigraphic framework can be proposed.

Facies distribution, paleoenvironment and sequence stratigraphy model of the Oligo-Miocene Asmari Formation (Fars Province, south of Iran)

The Oligocene (Rupelian-Chattian) to Miocene (Aquitanian)-aged Asmari Formation is considered one of the most significant petroliferous reservoirs in the Middle East. The Oligocene-Miocene Asmari Formation represents diverse facies patterns in different parts of Zagros, so analysis of its facies in different provinces of the Zagros Basin is necessary. In this study, the sedimentary depositional sequences of Asmari Formation in the Firuzabad (south of Shiraz) and Bastak (west of Bandar-Abbas) sections in the Zagros Basin (Fras Platform) have been analyzed for distinguishing facies characteristics, interpreting the paleoenvironment and determining dominant depositional sequences. Based on field investigations and laboratory studies, 13 microfacies have been determined; these are organized in 3 facies associations containing outer ramp (open marine), mid ramp, and inner ramp (shoal, lagoon, and tidal flat). Sedimentary characteristics, arrangement, and comparison of horizontal and vertical facies indicated that the successions of the Asmari Formation sediments were deposited in a homoclinal ramp-like platform with a gentle slope and the deeper part of the basin located in the Firuzabad section. Analysis of detailed facies frequency showed that the outer ramp is the most frequent facies association in the Firuzabad and the inner ramp (lagoon subenvironment) is the most frequent facies association in the Bastak. Sea level variations during Oligo-Miocene time resulted in creation of two third-order depositional sequences in both sections. The depositional sequences consist of transgressive systems tract and highstand systems tract. In all the identified sequences, transgressive systems tract (TST) demonstrate retrogradational stacking pattern with deepening-upward trend while highstand systems tract (HST) indicate progradational stacking pattern with shallowing-upward trend.

High‐resolution sequence stratigraphy of the Middle Triassic Sunset Prairie Formation, Western Canada Sedimentary Basin, north‐eastern British Columbia

AbstractThe Middle Triassic Sunset Prairie Formation has been recently identified between the Lower Triassic Montney Formation and the Middle Triassic Doig Formation in the Western Canada Sedimentary Basin. Due to its recent recognition, the Sunset Prairie Formation has yet to be incorporated into sequence stratigraphic frameworks of the Triassic. Through the investigation of 25 cored wells, facies characteristics, vertical facies stacking and lateral facies distributions have been identified and described. Sequence stratigraphic surfaces were identified in core and extrapolated to geophysical wireline log signatures of 248 wells within the basin. The Sunset Prairie Formation can be divided into three, upward‐coarsening parasequences that exhibit a retrogradational stacking pattern. All parasequences of the Sunset Prairie Formation are truncated at their tops by the Doig phosphate zone. The Sunset Prairie Formation truncates the underlying Montney Formation, suggesting that the stratigraphic interval is unconformity bound by sequence boundaries and their correlative conformities. The addition of the Sunset Prairie Formation reveals a discrete sequence of transgressive deposits previously unaccounted for within the Triassic sequence stratigraphic framework of the Western Canada Sedimentary Basin.

Geomorphological and stratigraphic analysis applied to coastal management

Many of the current conflicts related to inadequate planning of coastal land use are due to the lack of public knowledge about coastal dynamics. With the objective of supporting Integrated Coastal Management actions and increasing public knowledge, this study presents results obtained from the application of Remote Sensing and Ground Penetrating Radar (GPR) to demonstrate the medium and long term behavior of the Cigana Beach barrier evolution in southern Brazil. The stratigraphic record enables definition of the Holocene retrogradational stacking pattern of the coastal barrier at the study area. On a more recent scale, the average of shoreline changes obtained from the aerial photos of 1938 and 1978 shows a historical erosion trend. The proposed use of the mean high tide line in 1831 to legally designate Federal Lands in coastal areas does not consider coastal dynamics and generates an overlap of public jurisdictions. Due to lack of information on a local scale, and the consequent missing application of coastal management tools for decision-making to resolve land use conflicts, incorporation of the knowledge generated in this work into municipal management instruments is suggested.

Syn‐rift sequence development in a fault‐controlled embayment (Early Permian Irwin River Coal Measures, Northern Perth Basin, Western Australia)

AbstractStratigraphic patterns and sequence development in tectonically active extensional basins remain poorly documented in comparison with passive‐margin settings. Rift basin fills are generally characterized by coarsening‐upward trends in response to the rapid creation of accommodation by extensional faulting, and the progressive filling of graben during more quiescent periods. The Early Permian Irwin River Coal Measures in the Northern Perth Basin (Western Australia) record a complex stratigraphic arrangement of conglomerate, sandstone, mudstone and coal, and have been attributed to delta plain depositional environments that developed in a cool–temperate climatic setting during syn‐rift activity. Sedimentary analysis of outcrop and core data from the fault‐bounded Irwin Terrace is used to distinguish nine facies associations reflecting deposition in braided rivers, fixed‐anastomosed channel belts, tide‐influenced coastal environments and storm‐affected distal bays. The broader depositional system is interpreted as a morphologically asymmetrical tide‐dominated embayment with a fluvial and wave influence. The stratigraphic architecture of the Irwin River Coal Measures was strongly influenced by the evolving rift basin margin. Fault reactivation of the major basin‐bounding Darling Fault in the early syn‐rift phase caused footwall uplift and the inception of transverse palaeo‐valleys occupied by braided fluvial systems. Fault block subsidence during the subsequent balanced, backstepping and drowning phases resulted in a dominantly retrogradational stacking pattern indicating progressive flooding of marginal‐marine areas and culminating in deposition of distal marine elements. In the active rift basin, it is proposed that preservation of a shallow‐marine syn‐rift sequence was promoted by the geomorphological confinement of the embayed system increasing tidal current acceleration and hampering transgressive ravinement. The proposed sequence model demonstrates that transgressive successions can develop in the early syn‐rift phase in response to footwall uplift and tectonic subsidence. The syn‐rift sequence recording the filling of an embayment on a rift basin margin may be applied in similar tectonic and/or depositional contexts worldwide.

Rift activity and sequence stratigraphy of the Oligocene Dongying Formation in the Nanpu Sag, eastern China: Implications for rift sequence stratigraphy in lacustrine basins

Rifting plays an important role in accommodation variations in rift basins. However, fluvial discharge as another important factor affecting lacustrine rift sequence stratigraphy is not well explored. In this work, seismic and well data are used to investigate the stratigraphic features, rift activity, and effect of fluvial discharge in the Nanpu Sag, Bohai Bay Basin. The syn‐rift deposition of the Dongying Formation (28.5–23.8 Ma) is divided into four sequences (SQ1, SQ2, SQ3, and SQ4), and the rift‐related subsidence rate along two parallel boundary faults is calculated. The results indicate that the rift activity weakens from SQ1 to SQ4 and that the two parallel boundary faults consist of a total of four fault segments. As the fault segmented, three propagation folds formed intrabasin highs on which the Beipu, Laoyemiao, and Gaoliu outlets developed. Well logs and 3D seismic data show that from SQ1 to SQ3, retrogradational stacking patterns occur in Beipu, Laoyemiao, and the hanging‐wall ramp, while progradational stacking patterns occur in the Gaoliu outlet. In SQ4, the sequence stacking patterns are progradation‐dominated. By evaluating channel erosion and sediment supply, the fluvial discharge can be estimated, and the result indicates that the Gaoliu outlet has the strongest fluvial discharge from SQ1 to SQ3 with strong channel erosion, and in SQ4, the fluvial discharge of each outlet is comparable and relatively low. The high fluvial discharge of the Gaoliu outlet from SQ1 to SQ3 is considered to be the primary reason for the lake level rise in the intervals between the pulses of rift activities. Sequence stacking patterns and depositional trends in our study intervals are not in line with the rift subsidence rate; this indicates that rifting is not the only factor controlling the rift sequence stratigraphy and variations in the accommodation of lacustrine rift basins. While the Gaoliu outlet has predominant fluvial discharge from SQ1 to SQ3, progradational parasequence sets deposit in the Gaoliu outlet. In contrast, the retrogradational parasequence sets occurred in the Beipu outlet, Laoyemiao outlet, and the hanging‐wall ramp. As the fluvial discharge of the Gaoliu outlet decreased in SQ4, the fluvial discharge in each outlet became low, and the stacking patterns were dominated by progradation. Consequently, this research suggests that fluvial discharge is a significant factor controlling the accommodation creation in lacustrine rift basins, and a sequence model which gives a full consideration of fluvial discharge is constructed for lacustrine rift basins.