Rifting Phase Research Articles

The Influence of Pre‐existing Basement Faults on the Cenozoic Structure and Evolution of the Proximal Domain, Northern South China Sea Rifted Margin

AbstractIn this paper, we investigate the structure of the Cenozoic rift basin in the proximal domain of the northern South China Sea (SCS) margin, with an emphasis on the influence exerted by pre‐existing basement faults on rift development. Results of our work indicate that the overall rift architecture of the proximal domain of the northern SCS margin is associated with extensional faults arranged in two main structural trends, WNW‐ to EW‐trending and ENE‐trending. Structural evidence presented in this paper suggests that extensional faults of the two main structural trends mainly reactivated two pre‐existing basement fault systems mapped in previous works, a WNW‐ to EW‐striking thrust fault system (PFS1) and an ENE‐striking thrust fault system (PFS2). During the first rifting phase, both pre‐existing fault systems were reactivated; however, strains and depocenters were mainly localized on the ENE‐striking normal fault system that reactivated the PFS2. On the contrary, in the second rifting phase, extension was mainly accommodated by WNW‐ to EW‐striking normal faults that reactivated the PFS1, while most of the earlier ENE‐striking normal faults became inactive or less active. These different degrees of reactivation of the two pre‐existing fault systems during the two rifting phases suggest a clockwise rotation of the regional extension direction from NNW‐SSE in the Syn‐rift stage 1 to N‐S in the Syn‐rift stage 2. This study implies that apart from Cenozoic tectonic processes, pre‐existing structures have also played a key role during rifting evolution across the SCS margin.

Climatic signals in lacustrine deposits of the Upper Yacoraite Formation, Western Argentina: Evidence from clay minerals, analcime, dolomite and fibrous calcite

AbstractAuthigenic clays are an important control on reservoir quality in lacustrine carbonates but remain challenging to predict. Lacustrine depositional systems respond to climatic variations in rainfall, surface runoff and groundwater input, and evaporation, and result in rapid and frequent changes in lake volume; this is expressed through changing water depth and shoreline position. In the upper portion of the Early Palaeocene Yacoraite Formation of the Salta Basin in Argentina, extensive lacustrine deposits were deposited during the sag phase of rifting. Prior high‐resolution stratigraphic studies have suggested that climatic factors control microbial carbonate sequences within a ‘balanced fill’ lake, with variation in the lake level having a major influence on facies association changes. This study characterizes the evolution of facies and mineralogy within the Yacoraite Formation, focusing on the distribution of clay minerals, making a link between the high, medium and low‐frequency sequence stratigraphic cycles. The low‐frequency transgressive hemicycle of the upper portion of the Yacoraite Formation is comprised of abundant siliciclastic facies, suggesting a wetter period. Microbialites occurring in this interval are coarse‐grained and agglutinated. Detrital clay minerals such as illite and chlorite and associated siliciclastic sediments were input to the lake during high‐frequency transgressive periods. During high‐frequency regressive hemicycles, sedimentation was dominated by carbonate facies with Ca‐rich dolomite and the authigenic clays are comprised of chlorite/smectite mixed‐layers. By contrast, the low frequency regressive hemicycle records fine‐grained agglutinated microbialite with horizons of fibrous calcite, more stoichiometric dolomite, barite and authigenic magnesian smectite. This indicates elevated ion concentrations in the lake under intense evaporation during an arid period. Understanding the conditions that are favourable for formation and preservation of authigenic clays within the lacustrine environment can improve understanding of reservoir quality in comparable economically important deposits.

Sedimentological and petrographic evolution of a fluvio‐lacustrine environment during the onset of volcanism: Volcanically‐induced forcing of sedimentation and environmental responses

AbstractThis work focuses on the transition from the Las Leoneras to Lonco Trapial Formations, in the lower part of the Early Jurassic succession of the incipient rift phase of the Cañadon Asfalto Basin (western part of Chubut Province – Patagonia, Argentina). Twenty lithofacies have been identified and grouped into seven facies associations on the basis of field characteristics (sedimentological and lithological) and optical microscope analysis, from two localities representing proximal and distal locations in the basin. The spatial relationship between all the lithofacies provided a four‐dimensional reconstruction of the palaeoenvironmental evolution, showing how the original, clastic sedimentation in alluvial/fluvial and lake environments was modified by short‐lived volcanic events during three volcanic cycles, and how the environment reacted after the input of huge amounts of volcaniclastics. Progradation of small deltas and subaqueous lobes, retrogradation caused by rising lake levels, and frequent erosion of valleys were typical processes in this environment. When explosive volcanism began, the original tectono‐climatic control on sedimentation was replaced by the volcanic control, and the volcanically‐forced sedimentation broke the equilibrium among production, delivery and accumulation of sediments. The nature of the volcanic eruptions and the different propensity of volcanic lithofacies to produce particles of different size and types (lithics, crystals and glass) are also analyzed. The role of volcanism in the production and transport of great volumes of sediments across sedimentary systems needs to be carefully re‐examined, and the analysis on the variability in the composition of volcaniclastic deposits must take into account that volcaniclastic particle types may not simply reflect a linear deepening in the dissection of magmatic arcs through time but are often controlled by the style of the eruptions and the lithological variation of the volcanic products.

Crustal structure and erosion of the Lofoten/Vesterålen shelf, northern Norwegian margin

The Norwegian continental shelf has been through several rift phases since the Caledonian orogeny. Early Cretaceous rifting created the largest sedimentary basins, and Early Cenozoic continental breakup between East Greenland and Europe affected the continental shelf to various degrees. The Lofoten/Vesterålen shelf is located off Northern Norway, bordering the epicontinental Barents Sea to the northeast, and the deep-water Lofoten Basin to the west. An ocean bottom seismometer/hydrophone (OBS) survey was conducted over the shelf and margin areas in 2003 to constrain crustal structure and margin development. This study presents Profile 8-03, located between the islands of Lofoten/Vesterålen and the shelf edge. The wide-angle seismic data were modeled using forward/inverse raytracing to build a crustal velocity-depth transect. Gravity modeling was used to resolve an ambiguity in seismic Moho identification in the southwestern part. Results show a crustal thickness of ~31 km, significantly thicker than what a vintage land station based study suggested. Profile 8-03 and other OBS profiles to the southwest show high sedimentary velocities at or near the seafloor, increasing rapidly with depth. Sedimentary velocities were compared to the velocity-depth function derived from an OBS profile at the Barents Sea margin, tied to a coincident well log, where there is little erosion. Results from this profile and the crossing Profile 6-03 (Breivik et al. 2017) indicate three major erosion episodes; Late Triassic-Early Jurassic, tentatively mid-Cretaceous, Late Cretaceous–early Cenozoic, and a minor late glacial erosion episode off Vesterålen.

Tectono-sedimentary signature of the second rift phase in multiphase rifts: A case study in the Lufeng Depression (38–33.9 Ma), Pearl River Mouth Basin, south China sea

Compared to first rift phase (RP1) or single rift basins, the relationship between fault behaviours and depositional architecture during the second rift phase (RP2) remains insufficiently understood in multiphase rifts. This study attempts to provide implications for tectono-sedimentary signatures during the RP2 in multiphase rift evolution, according to an integrated analysis of 3D seismic reflections, wire logs and cores from the Lufeng Depression in the Pearl River Mouth Basin, South China Sea. The four recognised third-order sequences, ESQ1-4, define a two-stage tectono-sedimentary evolution, including an early (ESQ1-2) and a late stage (ESQ3-4) of the RP2 (38–33.8 Ma) in the Lufeng Depression. Fan-deltaic, braided deltaic sandstone-prone and lacustrine mud-prone deposits are interpreted from the basin margin towards to the central areas. During the early stage of the RP2, two relatively steep dipping E-W striking faults in the northern area were very active, undergoing rapid reactivation with a high displacement, while other faults were less active, had low displacements with respect to the extension direction and possibly represent pre-existing fault geometries. Two tectono-depositional signatures are identified during the early stage of the RP2: 1) facilitation of newly captured axially-dominated deltaic systems in the rapidly reactivated fault propagated areas, as a more uniform distribution of connected and elongated depocentres establishes an axial-supply drainage catchment; 2) sustained previous drainages from the end of the RP1 showed an increase of dip-slope sourced systems in low-displacement faulted-controlled areas, i.e. these areas lack fault-controlled topographic re-organisation but show establishment of a hanging dip-slope. The late stage of the RP2 is characterised by a low-accommodation basin as faulting activities totally waned, and thus large-sized shallow-water deltaic systems and long-distance transported sandstones are promoted. This study highlights the distinctive stratigraphic architectures and associated sediment dispersal patterns induced by progressive fault activity during the RP2 cycle. Furthermore, the proposed depositional signatures may be used as a reference when studying less data-rich multiphase rifts elsewhere.

About this title - Sweden: Lithotectonic Framework, Tectonic Evolution and Mineral Resources

The solid rock mass of Sweden forms a natural field laboratory revealing insight into the westward growth and reworking of one of the planet's ancient continental nuclei. Three major geological units are exposed in different parts of the country: the western part of the Fennoscandian Shield, mainly sedimentary rocks deposited on this crystalline rock mass and the Caledonide orogen. This volume synthesizes the tectonic evolution of Sweden over more than 2500 million years from the Neoarchean to the Neogene. Following an introduction describing the lithotectonic framework of the country and the organization of the volume, the tectonic evolution is addressed essentially chronologically. Different phases of intracratonic rifting, accretionary orogeny, continent–continent collisional orogeny and platformal sedimentation are identified. Sweden is one of Europe's major suppliers of metals, and the country's mineral resources are also presented in the context of the lithotectonic framework. Sweden: Lithotectonic Framework, Tectonic Evolution and Mineral Resources has been designed to interest a professional geoscientific audience and advanced students of Earth Sciences.

Seismic tectono-stratigraphic analysis of the Aptian pre-salt marginal system of Espírito Santo Basin, Brazil

The Aptian sedimentary sequence of Mucuri Member, lower Mariricu Formation, constitutes the pre-salt of Espírito Santo Basin. Proximal successions are dominantly clastic consisting of fluvial and coastal sediments deposited within the margins of a wide lake, thus corresponding to the marginal deposits of lacustrine carbonate reservoirs located in distal portions of the basin. Economic interest for oil is centered on such distal reservoirs, consequently proximal sections lack detailed studies. The Espírito Santo Basin is located near pre-salt official polygon, with oil exploration active for over six decades. The main objective of this study is the tectono-stratigraphic analysis of the clastic Mucuri Member, Aptian sag succession of the Espírito Santo Basin. Leading methodology is a seismostratigraphic characterization based on 220 2D lines, 1 3D volume, 103 well log data and 1 cored well. Four seismostratigraphic units were identified, delimited by three conformable horizons. Unit-bounding reflectors coincide with gamma ray maxima or minima interpreted to reflect shale or anhydrites deposited in deep water environments, corresponding to lacustrine maximum flooding surfaces. The structural framework is characterized by minor faults in the north onto shallow basement platforms, and in the south by half-graben bounded by normal faults developed during the rift phase. The Mucuri Member records an enlargement in depositional area from its base to top unit witnessing an overall lacustrine base level rise during depositon. The geometry of depositional area was initially influenced by the paleorelief of the preceding rift basins. The seismic units record a decrease in thickness as remnant topography was gradually filled and the upper units extended beyond the rift boundaries, covering a larger area. The Early Cretaceous Mucuri Member composes the first post-rift sequence of Espírito Santo Basin marked by the cessation of fault activity and the onset of thermal subsidence.

SISMOESTRATIGRAFIA DA FASE RIFTE DA PORÇÃO SUL DA BACIA DE CAMAMU

O trabalho consiste na interpretação regional de 91 linhas sismicas 2D pós-empilhadas do sul da Bacia de Camamu. A análise é auxiliada pela interpretação de perfis geofísicos de 21 poços e um cubo sísmico 3D. A metodologia do trabalho fez uso da estratigrafia de sequências aplicada às bacias rifte e contemplou a confecção de sismogramas sintéticos de dados de poços para correlação com as linhas sísmicas. Atributos sísmicos foram utilizados na identificação de terminações estratais, superfícies estratigráficas e feições estruturais, como falhas e superfície do embasamento. O mapeamento estratigráfico da supersequência rifte evidenciou discordâncias internas segmentando-a em sequências de terceira ordem associadas o caráter episódico do tectonismo sofrido pelas bacias durante o período de rifteamento. A análise de tratos de sistemas só foi possível de ser realizada na região proximal da Bacia devido ao grande número de poços disponíveis para amarração. Como resultados da interpretação foi possível confeccionar mapas de espessura sísmica das sequências e juntamente com a análise estrutural, compreender os principais sistemas sedimentares atuantes nos diferentes estágio de rifteamento da bacia. Foram mapeadas além das discordância que delimitam a fase rifte (DSR e DPR), quatro discordâncias internas (DR2, DR3, DR4 e DR5), totalizando cinco sequências deposicionais de terceira ordem (Rifte 1, 2 ,3,4 e 5). A separação em tratos tectônicos pela superfícies estratigráficas só foi possível na região proximal devido ao grande número de poços e à boa confiabilidade das amarrações. A ZTS favoreceu uma maior criação de espaço principalmente durante a deposição do primeiro rifte.

Hydrocarbon potential of Late Palaeozoic residual basins in the Central Asian Orogenic Belt: Insights from the tectonic evolution of the Yinggen‐Ejinaqi Basin, Inner Mongolia, China

The Yinggen‐Ejinaqi Basin (YEB) is located in the central‐southern part of the Central Asian Orogenic Belt (CAOB). Tectonically, the basin is situated at the intersection between the eastern and western CAOB, where Late Palaeozoic strata were well exposed. Hence, it offers a great opportunity to study the deep strata of the eastern CAOB. In this paper, based on extensive studies of Upper Palaeozoic field outcrops and reanalysis of associated geochemical and geochronological data in previous research, the local stratigraphic correlation is established, and the tectonic evolution, sedimentary filling, sedimentary characteristics, and petroleum system of the YEB are discussed. It is revealed that: (a) The filling characteristics of the Upper Palaeozoic strata in YEB are closely related to the closure of the Paleo‐Asian Ocean (PAO). YEB underwent subduction‐related compression during the initial extensional phase of the fore‐arc basin from the Viséan to the Serpukhovian (late Early Carboniferous). During the Bashkirian–Sakmarian interval (Late Carboniferous to Early Permian), it was in subduction‐related fore‐arc and postarc rifting phases. During the Artinskian–Capitanian (Early‐Middle Permian) times, it was in an intracontinental rifting‐depression phase. During the Wuchapingian (Late Permian), it was in an intracontinental compressional phase. Tectonostratigraphy, tectonic evolution, and hydrocarbon potential assessments of the study area show that the Zhusileng Hangwula‐Tost Ul tectonic zone (ZHTUTZ) and southwestern part of Querrshan‐Atasbogd tectonic zone (QATZ) are identified as the main prospective areas for the exploration in the YEB. (b) According to the tectonostratigraphic analysis, tectonic evolution and hydrocarbon system of Carboniferous–Permian in the YEB, the YEB has similar attributes to the basin province in western CAOB (e.g., Santanghu and Junggar basins) and eastern CAOB (Erlian, Songliao Basin). To explore commercial oil and gas in the deeper strata (Carboniferous–Permian) of the eastern CAOB basins, further tectonostratigraphic analyses and comprehensive assessment on hydrocarbon potentials are necessitated in the near future.

Gravity and Magnetic Constraints on the Crustal Structure of the Ceará Plateau, Brazilian Equatorial Margin

The Brazilian Equatorial Margin is a transform passive margin with long fracture zones and several seamounts, including the largest one, the Ceara Plateau. This is a complex and poorly recognized area, with few available geophysical data. Gravity and magnetic data from the Equant I Project, seismic published lines and other previous studies are used to make several models and analyses. We recognized gravity and magnetic anomalies related to a denser, magnetized basement, internally comprised of two magmatic highs. Through gravity and magnetic forward modeling, we estimated the basement surface between 800 and 6000 m and the Mohorovicic discontinuity about 22-23 km below the Ceara Plateau. We also present and discuss the position of the continent-ocean boundary 40 km away from the continental shelf, placing the plateau at the oceanic crust domain, and the area of the transitional crust, with an extension of 40-50 km, formed during the rifting phase of the Atlantic Ocean opening.

The Influence of Structural Inheritance and Multiphase Extension on Rift Development, the NorthernNorth Sea

AbstractThe northern North Sea rift evolved through multiple rift phases within a highly heterogeneous crystalline basement. The geometry and evolution of syn‐rift depocenters during this multiphase evolution and the mechanisms and extent to which they were influenced by preexisting structural heterogeneities remain elusive, particularly at the regional scale. Using an extensive database of borehole‐constrained 2D seismic reflection data, we examine how the physiography of the northern North Sea rift evolved throughout late Permian‐Early Triassic (RP1) and Late Jurassic‐Early Cretaceous (RP2) rift phases, and assess the influence of basement structures related to the Caledonian orogeny and subsequent Devonian extension. During RP1, the location of major depocenters, the Stord and East Shetland basins, was controlled by favorably oriented Devonian shear zones. RP2 shows a diminished influence from structural heterogeneities, activity localizes along the Viking‐Sogn graben system and the East Shetland Basin, with negligible activity in the Stord Basin and Horda Platform. The Utsira High and the Devonian Lomre Shear Zone form the eastern barrier to rift activity during RP2. Toward the end of RP2, rift activity migrated northward as extension related to opening of the proto‐North Atlantic becomes the dominant regional stress as rift activity in the northern North Sea decreases. Through documenting the evolving syn‐rift depocenters of the northern North Sea rift, we show how structural heterogeneities and prior rift phases influence regional rift physiography and kinematics, controlling the segmentation of depocenters, as well as the locations, styles, and magnitude of fault activity and reactivation during subsequent events.

Plate tectonic control on the formation and tectonic migration of Cenozoic basins in northern margin of the South China Sea

The tectonic evolution history of the South China Sea (SCS) is important for understanding the interaction between the Pacific Tectonic Domain and the Tethyan Tectonic Domain, as well as the regional tectonics and geodynamics during the multi-plate convergence in the Cenozoic. Several Cenozoic basins formed in the northern margin of the SCS, which preserve the sedimentary tectonic records of the opening of the SCS. Due to the spatial non-uniformity among different basins, a systematic study on the various basins in the northern margin of the SCS constituting the Northern Cenozoic Basin Group (NCBG) is essential. Here we present results from a detailed evaluation of the spatial-temporal migration of the boundary faults and primary unconformities to unravel the mechanism of formation of the NCBG. The NCBG is composed of the Beibu Gulf Basin (BBGB), Qiongdongnan Basin (QDNB), Pearl River Mouth Basin (PRMB) and Taixinan Basin (TXNB). Based on seismic profiles and gravity-magnetic anomalies, we confirm that the NE-striking onshore boundary faults propagated into the northern margin of the SCS. Combining the fault slip rate, fault combination and a comparison of the unconformities in different basins, we identify NE-striking rift composed of two-stage rifting events in the NCBG: an early-stage rifting (from the Paleocene to the Early Oligocene) and a late-stage rifting (from the Late Eocene to the beginning of the Miocene). Spatially only the late-stage faults occurs in the western part of the NCBG (the BBGB, the QDNB and the western PRMB), but the early-stage rifting is distributed in the whole NCBG. Temporally, the early-stage rifting can be subdivided into three phases which show an eastward migration, resulting in the same trend of the primary unconformities and peak faulting within the NCBG. The late-stage rifting is subdivided into two phases, which took place simultaneously in different basins. The first and second phase of the early-stage rifting is related to back-arc extension of the Pacific subduction retreat system. The third phase of the early-stage rifting resulted from the joint effect of slab-pull force due to southward subduction of the proto-SCS and the back-arc extension of the Pacific subduction retreat system. In addition, the first phase of the late-stage faulting corresponds with the combined effect of the post-collision extension along the Red River Fault and slab-pull force of the proto-SCS subduction. The second phase of the late-stage faulting fits well with the sinistral faulting of the Red River Fault in response to the Indochina Block escape tectonics and the slab-pull force of the proto-SCS.

Structural analysis and tectonic evolution of the Komombo basin, south Egypt; an example of interior Cretaceous rift

Structural geometry of the Komombo basin was demonstrated using 2D seismic data. Komombo basin appears as two, left-stepping, en-echelon half grabens separated by a NNE oriented broad anticline dissected by NNE oriented oblique-slip faults. The developed fault pattern in the Komombo basin is a typical, non-collinear fault system which encompasses several segments of NW, N–S and WNW orientations. Komombo basin shows along strike variation in the fault pattern. Its southern part is further subdivided into several intrabasinal troughs and highs bounded by synthetic down-dip and antithetic up-dip fault systems, while the northern part is characterized by a synthetic SW dipping step fault pattern producing small eastward rotated half-grabens. The two fault patterns are separated by N–S shear zone.The architecture of the Komombo basin is developed through two extensional phases. The first phase occurred during the Barressian- Hautervian (a NE-SW directed extension), producing predominantly NNW-SSE to NW oriented normal faults. The first phase was followed by a tectonically quiescent period during Barremian-Early Aptian. The rifting resumed during Late Aptian-Late Albian (phase II) under similar stress condition. A group of small NW oriented faults were developed during the second phase as indicated by Late Aptian-Late Albian growth in their hanging walls.The seismic reflection data and D-z graph display dip-linkage between the NW oriented faults that developed during the two rift phases. The Late Aptian-Late Aptian fault system nucleated in a vertical isolation from the Barressian-Hautervian fault system as indicated by the displacement minima observed at the Late Barremian-Early Aptian thick shale.

Sedimentary basins of the East Siberian sea and the Chukchi sea region and the adjacent area of Amerasia basin: seismic stratigraphy and stages of geological history

Abstract The seismic stratigraphy scheme for the shelf basins of the East Siberian Sea and the Chukchi Sea region and the adjacent deep-water part of the Amerasia basin has been developed, and mega-sequences (or tectonostratigraphic units) with proposed age of 125100, 10080, 8066, 6656, 4645, 4534, 200 Ma are distinguished. Zhokhov foredeep basin of the Late Jurassic‒Neocomian age is distinguished between the New Siberia and De Long islands. Three main phases of rifting are identified on the shelves in the region with ages of 125100, 6656 and 4537 Ma. The main phase of continental rifting occurred in the Podvodnikov and Toll basins 125100 Ma. The typical clinoform accumulation of sediments occurred at the edge of the shelf 6620 Ma. We identified three syntectonic epochs of the formation of clinoform complexes with ages of 6645, 4534 and 3420 Ma. The phase of uplifting and compression in the region of Wrangel Island happened 66 Ma. The relatively monotonous tectonic setting with approximately the same thickness of the sedimentary cover began from 20 Ma.

Crustal structure, tectonic subsidence and lithospheric stretching of the princess Elizabeth trough basin, East Antarctica

Abstract This paper considers crustal structure, seismic stratigraphy, thermal evolution and lithospheric stretching of the deep-water basin located on the East Antarctic passive margin in the Princess Elizabeth Trough. Seven of the Middle Jurassic to Quaternary seismic sequences was identified based on interpretation of multichannel seismic data. The information about seismic stratigraphy and crustal thickness (calculated from gravity data) along the section crossing the Princess Elizabeth Trough was used for numerical modeling of the thermal regime of the lithosphere, tectonic subsidence of the crystalline basement and lithospheric stretching. Modeling shows that calculated tectonic subsidence is possible only under the assumption of crustal extension before the deposition (during the crustal doming at the early rift phase). Maximum stretching factor in the basin ranges from 1.1 to 2.0 for the period which preceded the deposition and 2.8 for the period of the rift-related deposition.

Sedimentary Basins of the East Siberian Sea and the Chukchi Sea and the Adjacent Area of the Amerasia Basin: Seismic Stratigraphy and Stages of Geological History

The seismic stratigraphy scheme for the shelf basins of the East Siberian Sea and the Chukchi Sea region and the adjacent deepwater area of the Amerasia basin has been developed, and mega-sequences (or tectonostratigraphic units) with the conventional ages of 125‒100, 100‒80, 80‒66, 66‒56, 46‒45, 45‒34, 34‒20, 20‒0 Ma are distinguished. Zhokhov foredeep basin of the Late Jurassic‒Neocomian age is distinguished between the New Siberia and the De Long islands. Three main phases of rifting are identified on the shelves in the region with ages of 125–100, 66–56, and 45–37 Ma. The main phase of continental rifting occurred in the Podvodnikov and Toll basins at 125‒100 Ma. The typical clinoform accumulation of sediments occurred at the edge of the shelf at 66–20 Ma. We identified three syntectonic epochs of the formation of clinoform sequences with the ages of 66–45, 45–34, and 34–20 Ma. The phase of uplifting and compression in the region of Wrangel Island happened at ≈66 Ma. The relatively monotonous tectonic setting with approximately the same thicknesses of the sedimentary cover began at 20 Ma.

Testing of Permian – Lower Triassic stratigraphic data in a half-graben/tilt-block system: evidence for the initial rifting phase in Antalya Nappes

Testing of Middle Permian – Lower Triassic stratigraphic data from the Antalya Nappes in a half-graben/tilt-block system has revealed the presence of episodic rifting events separated by periods of tectonic quiescence. Following a period of uplift during the Permian (Late Artinskian to Roadian), the basement rocks have been activated by displacement faults and several depocenters in half-graben-like asymmetrical basins began to be filled with Roadian to Wordian continental clastic deposits intercalated with coal and marine rocks. The Early Capitanian time was a period of tectonic quiescence. The second event occurred in Middle to Late Capitanian times and produced basaltic volcanic rocks intercalated in the shallow marine fossiliferous carbonate successions. Following the Lopingian (Wuchiapingian and Changhsingian) and Permian–Triassic boundary interval representing a long tectonic quiescence, the last rifting episode started with an abrupt facies change in the late Griesbachian. Variegated shales, limestones, volcanics, talus breccia, and debris flow deposits were laid down in a half-graben/tilt-block system. As normal faulting has become active, the deposition continued on the subsiding hanging wall side. The stratigraphic gap increased in magnitude as the erosional truncation has incised deeply the footwall side. This initial rifting phase in the Antalya Nappes is prior to the onset of a stronger and more continuous rifting event that occurred in the Anisian–Carnian interval including a variety of deepwater clastic and carbonate deposits, radiolarites containing sometimes blocks and clasts derived from the basin margins, and volcanic rocks carrying intraoceanic setting character.

Crustal Structure, Tectonic Subsidence, and Lithospheric Stretching of the Princess Elizabeth Trough Basin, East Antarctica

This paper considers crustal structure, seismic stratigraphy, thermal evolution and lithospheric stretching of the deep-water basin located on the East Antarctic passive margin in the Princess Elizabeth Trough. Seven of the Middle Jurassic to Quaternary seismic sequences was identified based on interpretation of multichannel seismic data. The information about seismic stratigraphy and crustal thickness (calculated from gravity data) along the section crossing the Princess Elizabeth Trough was used for numerical modeling of the thermal regime of the lithosphere, tectonic subsidence of the crystalline basement and lithospheric stretching. Modeling shows that calculated tectonic subsidence is possible only under the assumption of crustal extension before the deposition (during the crustal doming at the early rift phase). Maximum stretching factor in the basin ranges from 1.1 to 2.0 for the period which preceded the deposition and 2.8 for the period of the rift-related deposition.

Impact of a pre‐existing transverse drainage system on active rift stratigraphy: An example from the Corinth Rift, Greece

AbstractModels to explain alluvial system development in rift settings commonly depict fans that are sourced directly from catchments formed in newly uplifted footwalls, which leads to the development of steep‐sided talus‐cone fans in the actively subsiding basin depocentre. The impact of basin evolution on antecedent drainage networks orientated close to perpendicular to a rift axis, and flowing over the developing hangingwall dip slope, remains relatively poorly understood. The aim of this study is to better understand the responses to rift margin uplift and subsequent intrabasinal fault development in determining sedimentation patterns in alluvial deposits of a major antecedent drainage system. Field‐acquired data from a coarse‐grained alluvial syn‐rift succession in the western Gulf of Corinth, Greece (sedimentological logging and mapping) has allowed analysis of the spatial distribution of facies associations, stratigraphic architectural elements and patterns of palaeoflow. During the earliest rifting phase, newly uplifted footwalls redirected a previously established fluvial system with predominantly southward drainage. Footwall uplift on the southern basin margin at an initially relatively slow rate led to the development of an overfilled basin, within which an alluvial fan prograded to the south‐west, south and south‐east over a hangingwall dip slope. Deposition of the alluvial system sourced from the north coincided with the establishment of small‐scale alluvial fans sourced from the newly uplifted footwall in the south. Deposits of non‐cohesive debris flows close to the proposed hangingwall fan apex pass gradationally downstream into predominantly bedload conglomerate deposits indicative of sedimentation via hyperconcentrated flows laden with sand‐ and silt‐grade sediment. Subsequent normal faulting in the hangingwall resulted in the establishment of further barriers to stream drainage, blocking flow routes to the south. This culminated in the termination of sediment supply to the basin depocentre from the north, and the onset of underfilled basin conditions as signified by an associated lacustrine transgression. The evolution of the fluvial system described in this study records transitions between three possible end‐member types of interaction between active rifting and antecedent drainage systems: (a) erosion through an uplifted footwall, (b) drainage diversion away from an uplifted footwall and (c) deposition over the hangingwall dip slope. The orientation of antecedent drainage pathways at a high angle to the trend of a developing rift axis, replete with intrabasinal faulting, exerts a primary control on the timing and location of development of overfilled and underfilled basin states in evolving depocentres.

Base‐salt relief controls salt‐related deformation in the Outer Kwanza Basin, offshore Angola

AbstractSalt‐influenced passive margins are widespread and commonly hydrocarbon‐rich. However, they can be structurally complex, with their kinematic development being poorly understood. Classic models of salt tectonics divide such margins into updip extensional, mid‐slope translational and downdip contractional kinematic domains. Furthermore the faults, folds, and salt walls associated with each kinematic domain are typically assumed to form perpendicular to the maximum principal stress, which in gravitationally driven systems means broadly perpendicular to base‐salt dip. We use high‐resolution 3D seismic reflection data from the Outer Kwanza Basin, offshore Angola to show that these models cannot explain the diversity of salt structures developing on passive margins, especially those defined by considerable relief on the base‐of‐salt surface. Overburden seismic‐stratigraphic patterns record the basinward translation and rotation, allowing us to reconstruct the origin and evolution of the salt structures. We show structures in the transitional domain of the Outer Kwanza Basin display three dominant trends, each characterised by different structural styles: (a) salt walls perpendicular to the overall base‐salt dip, (b) salt walls parallel to the base‐salt dip and (c) salt walls oblique to the base‐salt dip. We show that each set of walls has a unique history, with synchronous phases of extension and compression occurring in adjacent structures despite their close spatial relationship. Our analysis suggests that, in the Outer Kwanza Basin, the structural evolution of the salt and overburden is predominantly controlled by translation over relief on the base‐salt surface formed above fault scarps associated with a preceding phase of rifting. Changes in the downdip volumetric flux and velocity of the salt over topographic features can cause local extension or contraction of the salt and its overburden, associated with local acceleration or deceleration of the salt, respectively. This interaction with base‐salt relief creates locally variable stress fields that deform the salt and its overburden, overprinting the broader, margin‐scale salt tectonics typically associated with gravity gliding and spreading.