Tectonostratigraphic Framework Research Articles

The development of the eastern Orpheus rift basin, offshore eastern Canada: A case study of the interplay between rift-related faulting and salt deposition and flow

The salt-rich Orpheus rift basin, part of the eastern North American (ENAM) rift system, formed during the Late Triassic to Early Jurassic prior to opening of the Atlantic Ocean. Using a dense grid of 2D seismic-reflection lines, data from nearby wells, and information from adjacent ENAM rift basins, we have established a tectonostratigraphic framework, identified key structural elements, and reconstructed the deformation history for the eastern part of the basin. Our work shows that a series of E-striking, S-dipping faults with normal separation bound the basin on the north. Deformation within the basin is complex with forced folds above deep-seated intrabasin faults, detachment folds, detached thrust faults, and salt diapirs. The synrift evaporite sequence consists of an older massive salt unit that underlies a younger unit with two distinct interfingering facies. Facies A, consisting of salt and interbedded sedimentary rocks (likely shales), developed near the border-fault system and its relay ramps. Facies B, consisting of massive salt with few interbedded sedimentary rocks, developed toward the basin center. The youngest synrift unit accumulated exclusively within minibasins near the northern border-fault system. Based on location, this youngest synrift unit likely consists of coarse-grained and poorly sorted alluvial-fan or talus-slope deposits shed from the footwall. All synrift units are intruded by igneous sheets likely associated with the Central Atlantic Magmatic Province and, thus, are mostly Late Triassic in age (or possibly older). The border-fault system profoundly affected deposition within the eastern Orpheus rift basin by providing pathways for clastic sediment input into the salt-rich basin. These depositional patterns subsequently influenced deformation associated with lateral salt flow during minibasin formation. In regions with interbedded salt, detachment folds and thrust faults developed, whereas salt walls and stocks developed in regions with more massive salt.

‘Block and basin’ style rift basins: sedimentological insights from the Mississippian Fell Sandstone Formation

The block and basin tectonostratigraphic framework for the northern Pennine (rift) Basin, within which buoyant granite intrusions core intra-basin fault-bounded blocks, has long held traction. However, many of the elements of this framework are rooted in primitive tectonic models and, perhaps unsurprisingly, corresponding depositional models often reflect this. Using sedimentological and sedimentary provenance approaches, the synrift (Mississippian) fluvio-deltaic Fell Sandstone Formation and age-equivalent strata within the northern Pennine Basin are examined. Highlighted divergences from classically depicted models relate to occurrences of pre-Carboniferous basement domes or monoclines, which are unbounded by major vertically displacing (>100 m) fault systems. Such structures in the northern Pennine Basin are all granite-cored and their origins are associated with their buoyancy and flexural isostatic processes. One such basement dome, the Cheviot Block, confined and deflected the Fell Sandstone fluvio-deltaic system from the west, causing locally elevated net sand content and variations in the dominant palaeodrainage direction. Central parts of the Alston Block, which forms a regional monocline along an east–west axis, were comparatively uplifted because of flexural isostatic responses to granite intrusions. The findings presented are at variance not only with classically depicted depositional models for the region, but also with more general depictions of dominantly normal fault-driven rift basin systems. Supplementary material: Tables of data locations with derivation, trace element data and major element (oxide) data are available at https://doi.org/10.6084/m9.figshare.c.5733257

Chronology of thrust propagation from an updated tectono-sedimentary framework of the Miocene molasse (western Alps)

Abstract. After more than a century of research, the chronology of the deformation of the external part of the western Alpine belt (France) is still controversial for the Miocene epoch. In particular, the poor dating of the foreland basin sedimentary succession hampers a comprehensive understanding of the deformation kinematics. Here we focus on the Miocene molasse deposits of the northern subalpine massifs, southern Jura, Royans, Bas-Dauphiné, Crest, and La Bresse sedimentary basins through a multidisciplinary approach to build a basin-wide tectono-stratigraphic framework. Based on sequence stratigraphy constrained by biostratigraphical, chemostratigraphical (Sr isotopes), and magnetostratigraphical data between the late Aquitanian (∼ 21 Ma) and the Tortonian (∼ 8.2 Ma), the Miocene molasse chronostratigraphy is revised with a precision of ∼ 0.5 Ma. The Miocene molasse sediments encompass four different paleogeographical domains: (i) the oriental domain outlined by depositional sequences S1a to S3 (∼ 21 to ∼ 15 Ma), (ii) the median domain characterized by sequences S2 to S5 (∼ 17.8 to ∼ 12 Ma), (iii) the occidental domain in which sequences S2a to S8 (∼ 17.8 to ∼ 8.2 Ma) were deposited, and (iv) the Bressan domain where sedimentation is restricted to sequences S6 to S8 (∼ 12 to ∼ 8.2 Ma). A structural and tectono-sedimentary study is conducted based on new field observations and the reappraisal of regional seismic profiles, thereby allowing the identification of five major faults zones (FZs). The oriental, median, and occidental paleogeographical domains are clearly separated by FZ1, FZ2, and FZ3, suggesting strong interactions between tectonics and sedimentation during the Miocene. The evolution in time and space of the paleogeographical domains within a well-constrained structural framework reveals syntectonic deposits and a westward migration of the depocenters, allowing for proposing the succession of three deformation phases at the western Alpine front. (i) The first is a compressive phase (P1) corresponding to thrusting above the Chartreuse oriental thrust (FZ1), which was likely initiated during the Oligocene and rooted east of Belledonne. This tectonic phase generated reliefs that limited the Miocene transgression to the east. (ii) The second is a ∼ WNW–ESE-directed compressive phase (P2) lasting between 18.05 ± 0.25 Ma and ∼ 12 Ma, with thrusts rooted in the Belledonne basal thrust. Thrusts were activated from east to west: the Salève (SAL) and Gros Foug (GF) thrusts and then successively FZ2, FZ3, FZ4, and FZ5. Along two WNW–ESE balanced cross sections the amount of horizontal shortening is of ∼ 6.3 to 6.7 km, corresponding to average shortening rates of ∼ 1.2 km Myr−1 and migration of the deformation toward the west at a rate of ∼ 2.9 km Myr−1. During ∼ 6 Myr, the Miocene Sea was forced to regress rapidly westwards in response to westward migration of the active thrusts and exhumation of piggyback basins atop the fault zones. Phase P2 thus deeply shaped the Miocene paleogeographical evolution of the area and appears as a prominent compressive phase at the scale of the western Alps from the Swiss molasse basin to the Rhodano–Provencal one. (iii) The third is a ∼ 300 m phase of uplift in the Bas-Dauphiné (P3) of probable Tortonian age (∼ 10 Ma), which would have induced southward sea retreat and been coeval with the folding of the Jura in the north and possibly with back-thrusting east of the Chartreuse massif.

Cross-border stratigraphy of the Northern, Central and Southern North Sea: a comparative tectono-stratigraphic megasequence synthesis

Abstract The Devonian–Recent tectono-stratigraphic history of the Northern, Central and Southern North Sea is here reviewed at a regional scale and four novel cross-border pseudo-Wheeler diagrams are presented to summarize the stratigraphic evolution of the cycles of basin fill and uplift/erosion. In this scheme, six first-order megasequence boundaries have been defined, characterized by extensive and long-lasting erosional hiatuses and major coastal regressions: (1) Caledonian (or Base Devonian) Unconformity; (2) Variscan–Saalian (or Base Permian) Unconformity; (3) Mid Cimmerian (or Intra-Aalenian) Unconformity; (4) Late Cimmerian (or Base Cretaceous) Unconformity; (5) Atlantean (or Near-Base Tertiary) Unconformity; and (6) Eridanos (or Mid-Miocene) Unconformity. These surfaces have been linked to regional causal factors ranging from orogenesis-related compressional uplifts, in either active plate margin settings (1) or foreland basin settings (2), to intra-plate dynamically supported uplifts associated with the development of mantle plumes (3, 5 and 6) and the end-of-rifting and associated widespread erosion of tilted fault block crests (4). The aforementioned megasequence boundaries punctuate the geodynamic evolution of the North Sea area and facilitate the subdivision of the entire the North Sea sedimentary basin fill into six megasequences, named here A–F. All of the lithostratigraphic units of the North Sea (formations and members) have been described within the context of this first-order tectono-stratigraphic framework. The correlation powers of certain stratigraphic markers are also compared and contrasted, together with the potential cross-border equivalence of sedimentary units on different sides of the political median lines.

Tectonostratigraphic framework in the eastern Korean continental margin, East Sea: Implication for evolution of the Hupo Basin

AbstractIntegrating seismic interpretation facilitates the discernment of tectonostratigraphic evolution in the eastern Korean continental margin, East Sea. The sedimentary succession of this margin is divided into three major seismic units based on distinct unconformities. These unconformities and their associated seismic characteristics indicate that the eastern Korean continental margin has experienced four evolutionary stages through extensional and subsequent two‐phase tectonic inversions. Early Miocene back‐arc opening of the East Sea triggered the extension of NNW–SSE and N–S trending rifts, resulting in non‐marine to deep‐marine deposition of typical rift‐related linked sedimentological systems in the eastern Korean continental margin. In the early Late Miocene, changes in plate motion and the subduction mode of the Japanese island (NW–SE compression) caused the positive inversion of extensional fault‐bounded half‐grabens in the eastern Korean continental margin, and the Hupo Basin was likely created by the regional flexural response. During this depositional period, hemipelagic sedimentation accompanied by episodic gravity‐controlled slope failures was predominant in the deep‐water environment. The subsidence of the Hupo Basin was enhanced by crustal shortening (E–W compression) that was induced by subduction initiation at the western margin of the Ulleung Basin during the late Early Pliocene (ca. 3.8 Ma). At that time, sedimentary environment gradually became shallower with time and coarse‐grained terrigenous input into the Hupo Basin began so that shallow‐ to deep‐marine sedimentation occurred. In the Quaternary period, the uplift of the Hupo Bank and coeval subsidence of the Hupo Basin were maintained by continued compressive neotectonics. The shallow‐ to deep‐marine deposition continued, but greater quantities of coarse‐grained terrestrial sediment were transported into the Hupo Basin due to combined effects on tectonics and eustasy. Based on the tectonostratigraphic reconstruction developed in this study, we propose that the Hupo Basin is likely a Late Miocene–Quaternary compression‐related basin induced by crustal or thrust loading.

Tectono-stratigraphic evolution of the Permo-Triassic succession in the fars platform of Iran: Implications for future exploration of the Paleozoic petroleum system

• Salt tectonics has influenced the Paleozoic petroleum system of the Fars Platform. • Withdrawal synclines control the thickness/facies of the Permo-Triassic sequences. • Considerable potential exists for stratigraphic traps in this petroleum system. Using a new tectono-stratigraphic framework, this paper investigates the Paleozoic petroleum system of the Fars Platform (Southwest Iran). The essential elements and processes of this prolific petroleum system were strongly impacted during both syn -rift and post-rift phases. Extensive erosion during the syn -rift phase led to the local removal of the Latest Ordovician-Earliest Silurian Sarchahan source rock and deposition of continental clastic sediments which acted as important carrier rocks during hydrocarbon migration. During the post-rift phase, syn -depositional salt tectonics predominantly controlled the stratigraphy of the Permo-Triassic strata. The salt- withdrawal synclines not only controlled the facies and thickness of the reservoir-seal couplets, but also promoted hydrocarbon generation from the Silurian source rock in the resulting depocenters. These hydrocarbons could migrate toward structurally higher areas through areally-continuous carriers of the Lower Permian Faraghan Formation and from huge accumulations below efficient evaporitic seals. This model can better explain the present-day distribution of Paleozoic accumulations in the Fars Platform and sheds new light on the remaining potential (in stratigraphic traps) within the Paleozoic petroleum system.

The Appalachian area as a tectonostratigraphic analogue for the Barents Sea shelf

AbstractThe US Appalachian Basin and the Arctic Norwegian and Russian Barents Sea shelf (BSS) areas are two strategic provinces for the energy industry. The Appalachian Basin is a well‐studied, mature, onshore basin, whereas the offshore BSS is still considered a frontier area. This study suggests that the Appalachian Basin may be an appropriate analogue for understanding the BSS and contribute to development of a tectonostratigraphic framework for the area. Although the Appalachian and BSS areas reflect different times and settings, both areas began as passive margins that were subsequently subjected to subduction and continent collision associated with the closure of an adjacent ocean basin. As a result, both areas exhibited multi‐phase subduction‐type orogenies, a rising hinterland that sourced sediments, and a foreland‐basin sedimentary system that periodically overflowed onto an adjacent intracratonic area of basins and platforms with underlying basement structures. Foreland‐basin sedimentary systems in the Mid‐to‐Late Palaeozoic Appalachian Basin are composed of unconformity‐bound cycles related to specific orogenic pulses called tectophases. Each tectophase gave rise to a distinct sequence of lithologies related to flexural events in the orogen. In this study, similar sequences are recognised in both BSS foreland‐basin and adjacent intracratonic sedimentary sequences that formed in response to the Late Palaeozoic–Mesozoic Uralian–Pai–Khoi–Novaya Zemlya Orogeny, suggesting that the processes generating the sequences are analogous to the tectophase cycles in the Appalachian Basin. Hence, this pioneering use of the Appalachian area and its succession as large‐scale tectonostratigraphic analogues for the BSS may further enhance understanding of Upper Palaeozoic to Middle Jurassic stratigraphy across the BSS.

Cenozoic uplift of the Fátima Basin, NE Brazil

The Fátima Basin is a small Cretaceous interior basin that was formed within the continental Borborema Province in northeastern Brazil. Its formation was related to the opening of the southern Atlantic Ocean. This study investigates the hypothesis of post-rift tectonic reactivation within this basin through an integrated set of geophysical (aeromagnetic), surface (outcrops), and subsurface (boreholes) data to model the tectono-stratigraphic framework of the basin. An analysis of several morphometric parameters, including the slope index, relief aspect, stream profiles, asymmetry factor (AF), stream-gradient index (SL), and valley floor width-to-height ratio (VF) was used to identify possible tectonic adjustments related to post-rift stress fields. The integration of geophysical and subsurface data showed that the basin possesses a half-graben geometry with the main basin axis trending NE-SW. Two families of topographic lineaments were identified: 1) NE-SW, corresponding to the main shear zones and faults of the Pre-Cambrian basement, and 2) NW-SE, representing faults and fractures in the adjacent basement and the sedimentary cover. A digital elevation model revealed that the maximum topographic elevation was 950 m, associated with deposits of the Paleozoic Tacaratu Formation located over the hinge line of the flexural margin of the basin. The AF values in the basin ranged between 25 and 76, and first- and second-order SL index anomalies were frequent, especially in the faulted border, the southeast sector, and the northeast sector. Analyses of the main river channels revealed VF values of around 1, which indicate active incisions in the river valleys. We suggest that the basin was subjected to differential uplift during the Cenozoic, which strongly affected the southeast and northeast sectors. Based on the exhumation of the Tacaratu Formation deposits, we estimate that the basin experienced approximately 500 m of uplift that influenced the erosion of Cretaceous deposits and adjacent basement rocks.

Tectonic and Stratigraphic Evolution Based on Seismic Sequence Stratigraphy: Central Rift Section of the Campos Basin, Offshore Brazil

The rift section of the Brazilian basins represent the sedimentary record associated with the first stages of Gondwana break-up in the Early Cretaceous phase (Berriasian to Aptian). The rift succession of the Campos Basin constitutes one of the main petroleum systems of Brazil’s marginal basins. This interval contains the main source rock and important reservoirs in the Lagoa Feia Group deposits. The Lagoa Feia Group is characterized by siliciclastic, carbonate and evaporite sediments deposited during the rift and post-rift phases. Despite the economic relevance, little is known in stratigraphic terms regarding this rift interval. To date, most studies of the Lagoa Feia Group have adopted a lithostratigraphic approach, while this study proposes a tectonostratigraphic framework for the deep-rift succession of the Campos Basin (Lagoa Feia Group), using the fundamentals of seismic sequence stratigraphy. This work also aims to establish a methodological and practical procedure for the stratigraphic analysis of rift basins, using seismic data and seismofacies, and focusing on tectonicstratigraphic analysis. The dataset comprised 2D seismic lines, core and lithological logs from exploration wells. Three seismic facies were identified based on reflector patterns and lithologic data from well cores, providing an improved subdivision of the pre-, syn- and post-rift stages. The syn-rift stage was further subdivided based on the geometric patterns of the reflectors. Tectonics was the main controlling factor in the sedimentary succession, and the pattern and geometry of the seismic reflectors of the syn-rift interval in the Campos Basin allowed the identification of three tectonic systems tracts: (i) a Rift Initiation Systems Tract; (ii) a High Tectonic Activity Systems Tract and (iii) a Low Tectonic Activity Systems Tract.

Kosyu–Rogov Composite Tectono-Sedimentary Element, Northwestern Russia

Abstract The Kosyu–Rogov Composite Tectono-Sedimentary Element (CTSE) is one of the last exploration frontiers left in the European part of Russia. A sedimentary section up to 15 km thick comprises several working petroleum systems. Multiphase structural development created various trapping configurations and numerous reservoir–seal pairs. There are several mature source rocks including the world-class Domanik bituminous shale in the area. The past exploration efforts fell short of delivering the expected volumes of oil and gas reserves. This was mainly due to an underestimation of the technical difficulties related to exploration in the complex tectonic settings and an inadequate understanding of the petroleum system development. They were in unfavourable conditions for the presence of a reservoir and hydrocarbon retention. A revision of the tectonostratigraphic framework of the Kosyu–Rogov CTSE shows new high-impact exploration opportunities. The large petroleum potential of the area was confirmed by the discovery of the Nertseta oilfield, the largest oil find in Russia, in 2016.

Multi-scale tectono-stratigraphic analysis of pre- and syn-rift sequences in the Rio do Peixe Basin, NE Brazil

Intracratonic rift basins developed in Northeastern Brazil during the Early Cretaceous, recording the continental rifting stage that preceded the development of the passive margins along the South Atlantic. The Rio do Peixe Basin is a remarkable example of this set of basins. It comprises four well-exposed NE-to E-W-trending half-grabens, the larger of which, the Brejo das Freiras and Sousa Half-grabens, being connected by a complex rift-related structural high, the Santa Helena Step. The basin also represents a unique case in the region where Lower Devonian strata underlies the Lower Cretaceous Rift Sequence, as a remnant pre-rift Paleozoic basin. This work covers part of the Sousa Half-graben and the Santa Helena Step, combining outcrop, wells and 3D seismic data to improve analysis of the tectono-stratigraphic framework of both the pre- and syn-rift sequences. The Lower Devonian Sequence comprises a deltaic system, which delta front to prodeltaic deposits characterize a transgressive systems tract, followed by delta plain deposits of a regressive systems tract. The base of the Lower Cretaceous Rift Sequence is defined by a low-angle unconformity recognizable at both surface and subsurface. This sequence displays interfingered contacts between its coeval units and is subdivided into four tectonic systems tracts related to the beginning of extension and periods of high and low tectonic activity. The southern termination of the Brejo das Freiras Fault performs an important depositional control in the Santa Helena Step, which at this place didn't developed high escarpments and acted as source area for fluvial fans. In the strike ramp and flexural margin of the Sousa Half-graben, fluvial distributary systems predominate and the basement contact is characterized by NE- and E-W-trending oblique slip normal faults. Finally, our study emphasizes the association of the structural framework with the Neocomian NW-SE rifting extension responsible for the South Atlantic opening.

Dictyodora-Nereites dominated ichnofauna in the Silurian−Devonian turbidite-like deposits of central-western Gondwana (San Rafael Block, Argentina): New stratigraphic and bathymetric constraints

The Río Seco de los Castaños Formation (San Rafael Block) holds one of the few middle Palaeozoic (Silurian−Devonian) records worldwide of a Nereites-Dictyodora dominated ichnofauna with sedimentological features such as oscillatory and combined-flow deposits. This record is associated with microbial mats in fine-grained intervals between turbidite-like deposits documented above the storm wave base. In this work, a detailed sedimentological study permitted to divide the unit into two informal sections separated by an erosional unconformity attributed to a sea level fall. Prograding turbidite-like sand-grained deposits document gravitational turbulent flows. The tectonostratigraphic framework allowed to disregard a submarine fan, whereas the unconformity does not support an autocyclic deltaic evolution. Palaeocurrents and palaeoslope indicators to the SW suggest a high source area to the NE, that contrasts with the well-established E-W trend of most of the units of similar age in the Cuyania terrane. Deposition was probably deflected by subaqueous highs with the development of mini-basins most likely structurally controlled.The ichnological analysis allowed to recognise ichnotaxa and intergradation cases between ichnospecies previously unknown for the unit, adding to the most diverse record of Dictyodora and Nereites in central-western Gondwana. Chondrites intricatus, Chondrites targionii, Chondrites?, Dictyodora zimmermanni, and specimens resembling Dictyodora liebeana are recorded for the first time. Nereites missouriensis is documented in intergradation with Nereites jacksoni, whereas Dictyodora scotica is recognised in intergradation with Dictyodora atuelica and Dictyodora tenuis. A decrease in ichnodiversity throughout the section could be related to variation in environmental parameters between the lower and upper sections. The ichnofacies assignment is discussed in terms of ethological categories and ichnodiversity. Some of the defined ichnoassemblages are assignable to a non-standard record of the Nereites Ichnofacies, and one in particular to the Nereites Ichnosubfacies, while another shows some characteristics coincident with the Zoophycos Ichnofacies. A transitional case between ichnofacies for the ichnological content of the unit as a whole, as previously reported in other units, cannot be disregarded.

New insights into the deep-water Otway Basin – Part 2. Tectonostratigraphic framework revealed by new seismic data

The inboard areas of the Otway Basin, particularly the Shipwreck Trough, are well explored and a petroleum-producing province. However, outboard in water depths greater than 500m, the basin is underexplored with distant well control and sparse 2D reflection seismic data coverage. The presence of a successful petroleum province onshore and in shallow waters raises the question as to whether these plays may extend further outboard into the deep-water areas. In the deep-water area, structural complexity and poor imaging of events in the legacy seismic data have resulted in interpretation uncertainty and consequentially a high-risk profile for explorers. The 2020 Otway Basin seismic program acquired over 7000-line km of 2D reflection seismic data across the deep-water Otway Basin. In addition, over 10000km of legacy 2D seismic data were reprocessed to improve the tie between the inboard wells and the new seismic grid. This new dataset provides the first clear insight into the structural and stratigraphic framework of this frontier area, including better imaging of the sedimentary section and the lower crust, increased structural resolution and improved calibration of the outboard seismic reflectors via ties to the inboard wells. Interpretation of the new data has led to an improved assessment of the structural elements and the extension of regional supersequences into the deep-water areas. These refinements have been used as input into petroleum systems modelling work and will provide a foundation for future work to understand petroleum prospectivity, including the distribution of source, reservoir and seal facies.

Understanding reservoir heterogeneity using variography and data analysis: an example from coastal swamp deposits, Niger Delta Basin (Nigeria)

Abstract For efficient reservoir management and long-term field development strategies, most geologists and asset managers pay special attention to reservoir chance of success. To minimise this uncertainty, a good understanding of reservoir presence and adequacy is required for better ranking of infill opportunities and optimal well placement. This can be quite challenging due to insufficient data and complexities that are typically associated with areas with compounded tectonostratigraphic framework. For the present paper, data analysis and variography were used firstly to examine possible geological factors that determine directions in which reservoirs show minimum heterogeneity for both discrete and continuous properties; secondly, to determine the maximum range and degree of variability of key reservoir petro-physical properties from the variogram, and thirdly, to highlight possible geological controls on reservoir distribution trends as well as areas with optimal reservoir quality. Discrete properties evaluated were lithology and genetic units, while continuous properties examined were porosity and net-to-gross (NtG). From the variogram analysis, the sandy lithology shows minimum heterogeneity in east-west (E–W) and north-south (N–S) directions, for Upper Shoreface Sands (USF) and Fluvial/Tidal Channel Sands (FCX/TCS), respectively. Porosity and NtG both show the least heterogeneity in the E–W axis for reservoirs belonging to both Upper Shoreface and Fluvial Channel environments with porosity showing a slightly higher range than NtG. The vertical ranges for both continuous properties did not show a clear trend. The Sequential Indicator Simulation (SIS) and Object modelling algorithm were used for modelling the discrete properties, while Sequential Gaussian Simulation (SGS) was used for modelling of the continuous properties. Results from this exercise show that depositional environment, sediment provenance, topographical slope, sub-regional structural trends, shoreline orientation and longshore currents, could have significant impacts on reservoir spatial distribution and property trends. This understanding could be applied in reservoir prediction and for generating stochastic estimates of petrophysical properties for nearby exploration assets of similar depositional environments.

Structural Controls on Slope Failure Within the Western Santa Barbara Channel Based on 2‐D and 3‐D Seismic Imaging

AbstractThe Santa Barbara Channel, offshore California, contains several submarine landslides and ample evidence for incipient failure. This region hosts active thrust and reverse faults that accommodate several mm/yr of convergence, yet the relationships between tectonic deformation and slope failure remain unclear. We present 3‐D and 2‐D multichannel seismic reflection (MCS) data sets, multibeam bathymetry, and chronostratigraphic constraints to investigate the controls on slope failure. Splay faulting along the North Channel Deformation Trend (NCDT) coincides with a distinct zone of compressional uplift and onlapping of steeply dipping Quaternary strata. The NCDT is spatially correlated with seafloor fissures, and 3‐D seismic analyses reveal an intricate system of en echelon reverse faults that offset sediments younger than ~25 ka. Localized uplift zones are located between faults, one of which underlies the Gaviota landslide headscarp. We observe a direct relationship between slope failure and along‐strike variations in the tectonostratigraphic framework. Based on geophysical properties at Ocean Drilling Program (ODP) Site 893, we predict a trend in compaction and porosity reduction in the basin that drives pore fluids up‐dip, toward the zone of onlap above the NCDT, thus reducing slope stability. This interplay between tectonic, sedimentary, and fluid‐flow processes along the NCDT has created a confluence of preconditioning factors, with Gaviota and Goleta landslides being distinguished from the surrounding slopes by their position above the NCDT. The distribution of seafloor fissures suggests sections of the slope remain unstable and are prone to future landsliding. These results provide insights into the processes and 3‐D feedbacks that lead to slope instability along other convergent margins.

Sedimentary evolution and stratigraphy of the ~765–740 Ma Kansuki-Mwashya platform succession in the Tenke-Fungurume Mining District, Democratic Republic of the Congo

The origin of the Mwashya Conglomerate at the base of the Mwashya Subgroup in the Lufilian Belt is uncertain since it is considered as either a tectonic or as a sedimentary breccia. At Tenke Fungurume Mining District (TFMD) in the Democratic Republic of the Congo, the Mwashya Conglomerate is marked by an iron-bearing polymictic conglomerate embedded between the Kansuki and Kamoya formations. In this paper, the Kansuki-Mwashya platform succession at TFMD was investigated to shed light on the origin of this conglomerate, the depositional evolution and the tectonostratigraphic framework of the platform. Lithofacies analysis revealed that the Mwashya Conglomerate is a periglacial olistostrome, which was formed around ~765–745 Ma. A pre-Sturtian age for this conglomerate is supported by the Kamoya Formation, which is here interpreted as a post-glacial cap carbonate sequence. The Kansuki-Mwashya platform succession consists of a protected coastal lagoon adjacent to a tidal flat environment, both bordered by a barrier shoal. This paper concludes that the Kansuki-Mwashya platform succession was driven by rifting pulses, occurring gravity flows on instable slope, superimposed upon the ~750–717 Ma long-lasting Sturtian glacial period.

Chapter 19 Regional context and tectonostratigraphic framework of the early–middle Paleozoic Caledonide orogen, northwestern Sweden

Abstract The Scandian mountains in northwestern Sweden are dominated by the eastern part of the Scandinavian Caledonides, an orogen that terminated during the middle Paleozoic with Himalayan-style collision of the ancient continents of Baltica and Laurentia. In this foreland region, far-transported higher allochthons from an exotic continental margin (Rödingsfjället Nappe Complex) and underlying mostly oceanic-arc basin character (Köli Nappe Complex) were emplaced at least 700 km onto the Baltoscandian margin of Baltica. The thrust sheets below the Iapetus Ocean terranes were derived from the transition zone to Baltica (Seve Nappe Complex), comprising mainly siliciclastic metasedimentary rocks, hosting abundant metamorphosed c. 600 Ma mafic intrusions. They preserve evidence of subduction (eclogites, garnet peridotites and microdiamonds in host paragneisses), starting in the late Cambrian; exhumation continued through the Ordovician. Underlying allochthons derived from the outer margin of Baltica are less-metamorphosed Neoproterozoic sandstone-dominated successions, also intruded by Ediacaran dolerite dykes (Särv Nappes); they are located tectonically above similar-aged metasandstone and basement slices, devoid of dykes (Offerdal and Tännäs Augen Gneiss nappes and equivalents). Lowermost allochthons (Jämtlandian Nappes and equivalents), from the inner Baltoscandian margin, provide evidence of Cryogenian rifting, Ediacaran–Cambrian drifting and platformal sedimentation, followed by foreland basin development in the Ordovician and Silurian.

Geochemical characteristics and genetic origin of crude oil in the Fushan sag, Beibuwan Basin, South China Sea

Abstract The Fushan sag is an important petroleum-bearing unit in the Beibuwan Basin, South China Sea. However, genetic relationship between oil and source rocks has not been well understood. In this work, 43 mudstone samples and 22 crude oil samples in the sag were collected for molecular geochemical and isotopic analyses to investigate this relationship. The geochemical data shows that the mudstones in Liushagang formation have poor to good oil generation potential with TOC ranging from 0.45 to 2.19 wt% and the kerogen is mainly type Ⅱ. Two types of crude oils were identified in this study. The first type of Group A oils including the subgroup A1 and subgroup A2 has the characteristics of low maturity with low saturated hydrocarbon content and lighter δ13C values in the Huachang uplift. The source rocks for the Group A oils were deposited under suboxic to oxic and freshwater environment containing more terrestrial higher plant and less angiosperm. The subgroup A1 oils in Els11 reservoirs are separated from subgroup A2 in the Els12 reservoirs by relatively lower maturity. The subgroup A1 and subgroup A2 oils are closely related to the Els1 to Els21 and Els12 to Els21 source rocks, respectively. While the second type of oils including Group B and Group C oils has higher level of maturity with higher saturated hydrocarbon content and heavier δ13C values. The source rocks of Group B oils were deposited in a freshwater environment with lower salinity, and more angiosperms and terrestrial higher plants input than those of Group C oils. Two subgroups are divided in the Group B oils, of which subgroup B1 oils have higher maturity and their source rocks were deposited in lower salinity with more terrestrial higher plant input than that of subgroup B2 oils. The subgroup B1 oils occurring in the Els31 reservoirs from the Huachang uplift are likely related to Els31 source rocks, while subgroup B2 oils in the Els22 reservoirs from the southern slope area of the Bailian subsag is linked with mixed source of Els22 and Els31 mudstones. The Group C oils are distributed in Els22 and Els31 reservoirs in the Huachang uplift and their oil source are from Els32 mudstones. Two petroleum plays are likely divided by the mfs in Els2 based on the oil-source correlation in the sag. Group B and Group C oils belong to the lower play, and Group A oils only occur in the upper play. The distribution and accumulation of different groups of oils are mainly controlled by the special two-layered tectonostratigraphic framework and the transport ability of fault zone in the sag. This study clarifies the types of oils, as well as the oil-source correlation and the spatial distribution of different groups of oils. The results could benefit the further petroleum exploration and resource evaluation in the sag.

Reservoir rock typing and zonation in sequence stratigraphic framework of the Cretaceous Dariyan Formation, Persian Gulf

This study delineates reservoir and non-reservoir zones in the Lower Cretaceous Dariyan Formation as units that are characteristic of the stratigraphic section representative of portions of the Persian Gulf offshore area. Reservoir rock types are categorized by textural and diagenetic properties. Static flow zones were delineated by porosity and permeability measurements of cored intervals. Electrofacies were prepared from clusters of petrophysical data to define reservoir zones for areas lacking wells with cored intervals. The attributes of these reservoirs are integrated into a sequence stratigraphic framework. This research indicates that rock types and reservoir zones of the Dariyan Formation differ in the studied fields located to the west and to the east in the Persian Gulf. These differences are interpreted to have resulted from a differing tectono-stratigraphic framework that controlled depositional facies and subsequent diagenesis. For example, reservoirs associated with the lower and upper carbonate units of the Dariyan Formation have different lithofacies and diagenetic modifications that resulted from deposition at two intrashelf basins at areas to the northwest and to the southeast in the Persian Gulf, and subsequent exposure to meteoric water flows during subaerial exposure.

Tectonostratigraphic framework and depositional history of the deepwater Ulleung Basin, East Sea/Sea of Japan

AbstractThe Ulleung Basin, East Sea/Japan Sea, is a Neogene back‐arc basin and occupies a tectonically crucial zone under the influence of relative motions between Eurasian, Pacific and Philippine Sea plates. However, the link between tectonics and sedimentation remains poorly understood in the back‐arc Ulleung Basin, as it does in many other back‐arc basins as well, because of a paucity of seismic data and controversy over the tectonic history of the basin. This paper presents an integrated tectonostratigraphic and sedimentary evolution in the deepwater Ulleung Basin using 2D multichannel seismic reflection data. The sedimentary succession within the deepwater Ulleung Basin is divided into four second‐order seismic megasequences (MS1 to MS4). Detailed seismic stratigraphy interpretation of the four megasequences suggests the depositional history of the deepwater Ulleung Basin occurred in four stages, controlled by tectonic movement, volcanism, and sea‐level fluctuations. In Stage 1 (late Oligocene through early Miocene), syn‐rift sediment supplied to the basin was restricted to the southern base‐of‐slope, whereas the northern distal part of the basin was dominated by volcanic sills and lava flows derived from initial rifting‐related volcanism. In Stage 2 (late early Miocene through middle Miocene), volcanic extrusion occurred through post‐rift, chain volcanism in the earliest time, followed by hemipelagic and turbidite sedimentation in a quiescent open marine setting. In Stage 3 (late middle Miocene through late Miocene), compressional activity was predominant throughout the Ulleung Basin, resulting in regional uplift and sub‐aerial erosion/denudation of the southern shelf of the basin, which provided enormous volumes of sediment into the basin through mass transport processes. In Stage 4 (early Pliocene through present), although the degree of tectonic stress decreased significantly, mass movement was still generated by sea‐level fluctuations as well as compressional tectonic movement, resulting in stacked mass transport deposits along the southern basin margin. We propose a new depositional history model for the deepwater Ulleung Basin and provide a window into understanding how tectonic, volcanic and eustatic interactions control sedimentation in back‐arc basins.