Post-rift Stage Research Articles

Volcanism at the end of continental rifting: The Cretaceous syn-rift to post-rift transition in the Songliao Basin (NE China)

The evolution of volcanism at the latest stages of continental rifting and its transition to the post-rift stage are poorly known. A Cretaceous rifting episode characterized the Songliao Basin (NE China) between 150 and 105–100 Ma. The transition to the post-rifting stage was marked by an increase in the subsidence rate due to thermal contraction. Here we present new major, trace element and Sr-Nd isotopic data on the volcanic rocks sampled in wells located in the Songliao Basin. These rocks are representative of two major eruptive cycles: K1yc1 (115–106 Ma, syn-rift stage) and K1yc3 (105–102 Ma, transition to the post-rift stage). The K1yc1 and K1yc3 rocks were erupted during the late phases of the Songliao rifting and have been found in the two members of the Yingcheng Formation. The K1yc1 rocks consist of trachybasalts, basaltic trachyandesites, and rhyolites. The K1yc3 rocks show a homogeneous rhyolitic composition. Both the K1yc1 and K1yc3 rocks display an alkaline, Within-Plate affinity. The trace element patterns and the isotopic composition of the K1yc1 mafic rocks indicate that they are the product of the fractional crystallization from a parent magma with an OIB signature. The felsic rocks from K1yc1 and K1yc3 have similar major and trace element patterns and originate from fractional crystallization of the K1yc1 trachybasalt and assimilation of upper crust material. The bimodal K1yc1 volcanism is related to fractionation processes producing low amounts of magmas with intermediate compositions. The lack of mafic eruption in K1yc3 is due to the reduction of porosity of the crustal rocks and a transition from ‘hot’ to ‘cold’ crust related to the thermal subsidence from syn-rift to post-rift stage. The late stage of the Songliao rifting volcanism coincides with a shift from a roll-backing phase of the Paleo-Pacific slab to its passive sinking in the asthenosphere.

Characteristics and Main Controls of Tectonic Fractures and Their Contribution to Deep Tight Reservoirs: A Case Study of the Huoshiling-Shahezi Formations in Gudian Half-Graben, Songliao Basin, China

AbstractThe deep volcanic and clastic rocks in the Songliao Basin are typical tight reservoirs with ultralow porosity and permeability. Natural fracture determines the effective reservoirs in the deep strata. Integrated core and thin section observations, image logging, physical property measurement, X-ray diffraction, and seismic attribute analysis were applied to ascertain the characteristics and genetic mechanisms of the tectonic fractures in the Huoshiling-Shahezi Formations of the Gudian half-graben. The contribution of the fractures to deep tight reservoirs was also discussed. Results showed that tectonic fractures are mainly tension, shear, and slip fractures. The density of the fractures in andesitic tuffs with high clay minerals content is significantly higher than that in the other rock types. The main controls of the developmental degree of fractures are tectonism. Three sets of fractures were identified based on the genetic connection between fracture formation and tectonic stress. The NNW-trending tension fractures were formed in the syn-rift stage and successively extended in the post-rift stage. The regional compressional stress drove the formation of the NEE-trending shear fractures and NNW-trending “X” plane-conjugated shear fractures in the postextrusion stage. The averaged porosity and permeability of the reservoirs are generally less than 6.0% and lower than 0.06 mD. The pores can hardly independently provide migration pathways and storage spaces, but the fractures significantly improved the reservoir properties. The fractures were well developed in the regions near the Gudian fault, fault transfer zones, and volcanoes, indicating the distribution of potential reservoirs. Moreover, unraveling the types and orientations of the fractures will provide an essential basis for the analysis of hydrocarbon migration and hydraulic fracture treatments.

Onset of Iberian-European plate convergence: Late Cretaceous flexural response of a hot lithosphere (Aquitaine Basin, France)

The Aquitaine Basin is closely linked to the evolution of the Pyrenees, providing precious evidence of the early stages of the Pyrenean orogeny in the Late Cretaceous. Although the timing and geometry of the Early Cretaceous rifting stage is well constrained in the Pyrenees and surrounding north Pyrenean basins, the subsequent early inversion stage has resisted characterization. In this study, we used well log correlations and interpretation of seismic reflection profiles to determine the Late Cretaceous evolution of the sedimentary record in the Aquitaine Basin, spanning the transition from the postrift stage to the beginning of convergence. We identified two main deformation stages during the Late Cretaceous with radically different basin geometries in the western and eastern portions of the Aquitaine Basin. The western part appears to remain under a thermal subsidence regime, inherited from the postrift stage initiated in the Turonian, with little to no deformation. In contrast, the eastern part records early inversion, as indicated by the presence of a well-defined Campanian flexural basin. Between them, Coniacian and Santonian strata indicate a sharply increasing distinction between a very slowly subsiding North Aquitaine Domain (condensed sedimentation) and a strongly subsiding South Aquitaine Domain. We interpret this development as a consequence of lithospheric buckling resulting from far-field compressive strain between the Eurasia and Africa plates. During the Campanian, northward convergence of the Iberia plate led to the formation of a flexural basin with a narrower, steeper geometry than the subsequent Eocene basin that formed in nearly the same region during the Pyrenean orogeny. We attribute this difference to the development of the foreland over a lithosphere that was not thermally reequilibrated in Campanian time, roughly 10 Myr after rifting. This thermal inheritance resulted in lithosphere of very low rigidity. Sedimentary basins formed during both the Coniacian-Santonian and Campanian to early Maastrichtian were thus accommodated by short-wavelength flexural deformation of the lithosphere, a distinctive deformation pattern that represents an immediate response to the onset of compressive strain.

North America's Midcontinent Rift magma volume: A coincidental rendezvous of a plume with a rift

Abstract The Midcontinent Rift of North America is a ca. 1.1 Ga, 3000-km-long failed rift that nearly split the Precambrian continent of Laurentia. Unlike most continental rifts, which are filled with a mixture of volcanic rocks and sediments, the Midcontinent Rift contains a large volume of flood basalts that were emplaced during both syn- and post-rift stages. Consequently, the Midcontinent Rift, which comprises the Keweenaw large igneous province, is the most significant positive anomaly on gravity maps of central North America. We investigated the mantle conditions required to produce this large volume of flood basalt and the observed two main stages of emplacement. To explore whether these magma volumes required a plume or, instead, could have resulted from the increased ambient mantle temperatures expected for the Neoproterozoic, we used a geodynamic model for a range of ambient mantle and plume temperatures under different scenarios of lithospheric extension. The most favorable scenario for the generation of both syn-rift and post-rift lavas combines a plume with excess temperatures between 175 and 225 °C introduced during the syn-rift phase and ambient mantle potential temperatures between 1393 and 1443 °C, with an initial lithospheric thickness not exceeding 150 km for 3 mm/yr extension rates.

Spatial-temporal evolution of the source-to-sink system in the northwestern South China Sea from the Eocene to the Miocene

The northwestern South China Sea (NW-SCS) presents a spatial-temporal evolution of its source-to-sink (S2S) system, that recorded the movement of the Indochina block and the collision between the Indian and Eurasian plates. However, complex tectonic movements and topographic evolution have led to controversial studies about the spatial-temporal distribution of allogenic materials and autogenic sediments. In this study, we integrated a number of multiscale data to review the S2S system evolution of the northwestern area of the South China Sea from the Eocene to the Miocene. The series include the initial synrift, postrift and thermal subsidence stages. First, we identified the major sediment pathways using seismic profile interpretation. We reconstructed the sediment distribution and lithofacies association within the dispersal sink area based on seismic data, core samples and grain-size analysis. We quantitatively studied the sediment flux and catchment area based on mass balance calculation modeling. Following this, we acquired rare-earth element (REE) data and zircon U–Pb age data from the bedrocks of the continental blocks and the South China Sea Cenozoic basement and rivers in the NW-SCS area to restore the provenance area and evaluate the migration distance by inspecting the heavy mineral assemblages. According to the above studies, three phases of S2S dynamics were identified. 1) The initial rifting stage occurred during the Eocene, and active rifting in the South China Sea induced a major topographic change. A large amount of autogenic slump sediments and a smaller amount of paleo-Red River sediments were injected into the Beibu Gulf Basin (BBGB) and the Yinggehai-Song Hong Basin (YGHB). 2) The postrift stage occurred during the Oligocene. Regional uplift and tectonic inversion probably linked to the clockwise rotation of the Indochina Block, broke the connection between the Beibu Gulf Basin and the Red River catchments. The paleo-Qin River and the paleo-Lian (Nanliu) River brought a large amount of clastic material into the Beibu Gulf Basin from the Cathaysia Block. 3) The thermal subsidence stage occurred during the Miocene: the eastward topographic tilt was enhanced, and the drainage basin entered postrift stage. The development of the Paleo-Red River and its branches, the Lam River and the Ma River, brought distal sediment into the YGHB, while the rivers in the west Cathaysia Block transported sediment into the BBGB. Statistical analysis of the S2S system parameters suggests that the average terrain altitude played a dominant role in determining the S2S system volume during the Eocene, while the dominant role transferred to the sediment supply during the Oligocene and Miocene. • Reconstructs the Source to sink system within NW-SCS from the Eocene to the Miocene. • Reveal the drainage evolution of basins in NW-SCS with multiple dates. • Put out the impact factors to the Source-to-Sink system developed during the rifting process.

Unrecognized post-rifting deposition and uplift history of the Erlian Basin, Northern China: Evidence from seismic reflection data and apatite fission-track thermochronology

Early Cretaceous rift basins in Northeast Asia typically experienced varying degrees of post-rifting thermal subsidence and compressional deformation. However, previous workers believed that only a thin post-rifting sequence was developed in basins west of the Great Xing'an Range, making a proper understanding of the post-rift tectonic history in this part of Northeast Asia difficult. In this study, newly acquired shallow seismic reflection data were utilized to unravel the shallow deformation of the Erlian Basin, which to the west of the Great Xing'an Range contains a thin post-rifting sequence. Furthermore, we used apatite fission-track thermochronology to analyze the post-rifting deposition and uplift processes in the Erlian Basin, for which there are limited stratigraphic records. Our results show that the Erlian Basin experienced a typical post-rifting stage whose sequence from the Albian to the Campanian was not controlled by normal faults. The corresponding sedimentary thickness was up to 2 km, which contradicts the previously reported little or no post-rifting thermal subsidence. The current thin post-rifting sequence is the remaining stratum after 1.4–1.8 km of denudation at the end of the Erlian period. In addition, by further comparing the sedimentary thickness and time-lag in the onset of post-rifting to those of other basins in Northeast Asia, we found two driving mechanisms of rifting in Northeast Asia, which occurred simultaneously: the gravitational collapse and back-arc extension. Moreover, the basins in Northeast Asia experienced a gradual weakening in the compressional deformation from east to west during the Cenomanian to the Coniacian, and an intense compressional deformation in the east of Northeast Asia and large-scale vertical uplift in the west during the Late Cretaceous Campanian to the Eocene.

High-precision geochronology of the Early Cretaceous Yingcheng Formation and its stratigraphic implications for Songliao Basin, China

The Songliao Basin in Northeast Asia is the largest and longest-lived rift basin and preserves a near-continuous continental succession of the most of the Cretaceous period, providing great material to investigate the adaption of the terrestrial systems to the Cretaceous greenhouse climate and tectonic events. However, the paucity of precise and accurate radioisotopic ages from the Early Cretaceous strata of the Songliao Basin has greatly held back the temporal and causal correlation of the continental records to the global Early Cretaceous records. Three tuff layers intercalated in the Yingcheng Formation have been intercepted by the SK-2 borehole, which offer excellent materials for radioisotopic dating and calibration of the chronostratigraphy of the Lower Cretaceous sequence of Songliao Basin. Moreover, the Yingcheng Formation recorded the largest and the last of the two major volcanic events in Songliao Basin, which also represents a turning point in the basin evolution history of Songliao from syn-rift stage to post-rift stage. Here we report high-precision U–Pb zircon geochronology by the CA-ID-TIMS technique on three tuff samples from the Yingcheng Formation of the SK-2 borehole in the Songliao Basin to construct a greatly improved, absolute age framework for the Yingcheng Formation and provide crucial age constraints for the Songliao Lower Cretaceous Strata. The new CA-ID-TIMS geochronology constrained the Yingcheng Formation at 102.571 + 0.320/−2.346 Ma to ca. 113 Ma, correlating to the Albian Stage. Combined with the previous published Songliao geochronology, the Quantou Formation is constrained to between 96.442 + 0.475/−0.086 Ma and 91.923 + 0.475/−0.086 Ma; the Denglouku Formation is constrained to between 102.571 + 0.320/−2.346 Ma and 96.442 + 0.475/−0.086 Ma; the age of the Shahezi Formation is estimated at ca. 113 Ma to ca. 118 Ma, which could extend to ca. 125 Ma in some locations in Songliao Basin. The major unconformity between the Yingcheng Formation and the Denglouku Formation, which represents the transition of the basin from syn-rift to post-rift is thus confined to between 102.571 + 0.320/−2.346 Ma and 96.442 + 0.475/−0.086 Ma. This is roughly contemporaneous with the change in the direction of the paleo-Pacific plate motion from west-southwest to north or northwest in mid-Cretaceous, suggesting their possible connections.

Syn-rift to post-rift tectonic transition and drainage reorganization in continental rifting basins: Detrital zircon analysis from the Songliao Basin, NE China

Tectonic transition from a syn-rift stage to subsequent post-rift stage is an important mechanism in the evolution of extensional basins. The sedimentary infill records the crustal response to this process. We have obtained new detrital zircon U-Pb and Lu-Hf signatures from the Lower Cretaceous stratigraphic successions encompassing the commonly accepted syn- to post-rift transition boundary, the T4 unconformity, in the Songliao Basin, NE China. These constrain the Songliao Basin’s evolution from its center to distal margins, providing insights into the sediment provenance and dispersal pattern over the tectonic transition. Analysis of zircons from the syn-rift (the Shahezi and Yingcheng formations) and immediate post-rift (the Lower and Middle Denglouku Formation) stages reveals Phanerozoic age populations with positive ƐHf(t) values, which were derived from the proximal juvenile mantle-derived melt origin bedrocks of the Songliao Block. In contrast, the overlying samples from the Upper Denglouku Formation deposited in the subsequent post-rift stage contain exotic and ancient zircon populations with ages of 2.5 Ga & 1.8 Ga and complex hafnium signatures, characteristic of a mixed origin. These are interpreted to be transported from distant cratonic terranes via larger drainage networks. It is obvious that the sediment dispersal pattern switched from being a local and hydrologically closed “intraregional” pattern to a “transcontinental” pattern during the transition. The time lag between the development of the T4 unconformity and the drainage reorganization also ensures a distinguishable ∼3 Myr (106103 Ma, Late Albian) transition period of regional extent. During this transition stage, syn-rift faulting was replaced by post-rift thermal subsidence, exhibiting a uniform sag configuration. Our new findings are important for understanding other continental rift basins during syn- to post-rift transition, which often demonstrates a complex interaction between the linkage and integration of sub-basins, and the reorganization of fluvial drainages and catchment systems.

Structural characteristics and mechanism of the Hengshui accommodation zone in the southern Jizhong subbasin, Bohai Bay basin, China

Based on seismic data, we document the differences in the geological structure and evolution on the two sides of the Hengshui Accommodation Zone (HAZ), identify the timing of faulting on faults, and analyze the mechanism of the HAZ. The northern part of the HAZ is characterized by a half-graben controlled by double detachment faults with opposite dips, and the southern part of the HAZ is characterized by a compound half-graben controlled by a single detachment fault with multiple faults. The structural evolution of the southern Jizhong subbasin can be divided into the following five stages: the basement evolution stage; Rift Episode I (Ek-Es4); Rift Episode II (Es3–Es2); Rift Episode III (Es1-Ed); and the Postrift stage (Nm-Ng). Three segments were identified along the HAZ, namely, the Xinle Anticline (XLA), the Ningjin Segment (NJS) and the Hengshui Transfer Fault (HSTF). The XLA is a transverse anticline produced by the fault section of the Taihang Mountain Piedmont Fault (TMPF). The NJS is a transfer fault formed by the differential extension of the Ningjin Fault. As a major part of the HAZ, there are obvious differences in the faults on both sides of the HSTF, and NE-trending Cenozoic faults were mainly on its north side, while the NNE-trending faults formed in the basement stage were distributed on its south side. During the basement evolution stage, NNE-trending basement faults and the HSTF developed by WNW extension. During Rift Episode Ⅰ (Ek-Es4), under the NW extension, NE-trending fault segments formed, and pre-existing faults were reactivated. During Rift Episode Ⅱ (Es3–Es2), pre-existing faults were subjected to oblique extension, and the NE-trending fault segments on both sides of the HSTF grew into the main fault and intersected with the HSTF. From Rift Episode III (Es1-Ed) to the present, some pre-existing faults have been reactivated, and many new secondary faults in the basin have finally produced the present structural pattern. These results suggest that the continuous transfer of the regional stress field during the Mesozoic and Cenozoic was the driving force for the formation and evolution of the HAZ.

Evolution of syn‐ to early post‐rift facies in rift basins: insights from the Cretaceous–Paleocene of the Great South Basin, New Zealand

AbstractEvolution of rift basin fill and geometry depend on the complex interactions between fault growth, sediment supply, base level changes and pre‐existing basement fabric. This study integrates multiple datasets in the Great South Basin (GSB), southeast New Zealand, and provides key insights into the evolution of depositional environments in rift basins, including the interplay between normal faulting, sediment supply and sediment dispersal patterns. It also examines the control of pre‐existing basement fabric on rift geometry and sediment distribution in the syn‐ and post rift successions. The syn‐rift is up to ~5.5 km thick in the GSB, and is underlain by several different basement terranes. Three syn‐rift stages are recognised; c.105–101, 101–90 and 90–83 Ma. During the initial syn‐rift, isolated northeast‐trending graben developed, with resultant alluvial fan/fan delta, fluvial, coastal and lacustrine sediment fill. The balance between sediment supply and accommodation space exerted considerable control on facies, especially the presence of lacustrine facies. During the later stages of syn‐rift, marine transgression occurred and connectivity between the graben developed, with shelfal, shoreface and marginal‐marine facies deposited. With marine transgression across the hinterland, sediment supply was significantly reduced in the northeast of the basin, leading to underfilling of graben, and preservation of rift topography for up to ~20 Myr after the cessation of faulting. In the west, where sediment supply was higher, rift topography was quickly filled. The NW‐trending basement terrane boundaries controlled accommodation space development during the initial stages of graben formation. Later in the syn‐ and post rift stages, these terrane boundaries formed long‐lived sediment input points into the basin, and controlled the position of repeated large deltaic depositional units.

Detachment-controlled subsidence pattern at hyper-extended passive margin: Insights from backstripping modelling of the Baiyun Rift, northern South China Sea

How detachment fault controls the basin subsidence at hyper-extended passive margin remains mysterious. Based on a detailed geological interpretation and backstripping on 29 high-resolution multi-channel seismic profiles, we calculate the basin-scale tectonic subsidence across the Baiyun Rift to study the relationship between tectonic subsidence and detachment faulting. Our results confirm that detachment faulting is the primary factor controlling the syn-rift subsidence. A decaying subsidence rate, or deficit subsidence is observed in the eastern Baiyun Rift from the early to late Eocene, which is in marked contrast to the intensive brittle stretching. We attribute this to the doming of the detachment fault footwall involving the syn-rift magmatism during its hyper-extension process. While in the western Baiyun Rift the average subsidence rate is over 45 m Myr−1 higher than that in the eastern as the response of flexural loading in the late Eocene. During the post-rift stage, the subsidence rate shows a similar oceanward increasing trend, and an anomalous rapid subsidence event during the middle Miocene in the eastern Baiyun Rift, which can be ascribed to the magma-assisted weakened rheological condition of the lithosphere deriving from the syn-rift detachment faulting. We propose that this relationship between subsidence pattern and detachment faulting has global applicability for other hyper-extended rift systems developing detachments and magmatic-related dome structures.

Salt control on the kinematic evolution of the Southern Basque-Cantabrian Basin and its underground storage systems (Northern Spain)

Underground gas storage is one of the solutions required for reducing CO2 emissions and ensure the transition to a renewable power supply. The Hontomín pilot-plant in N-Spain is a well-studied CO2 facility located in the Burgalesa Platform, a fold belt in the Southern Basque-Cantabrian Basin. Previous works agree that crustal extension and evaporite migration controlled the subsidence in the area. The discrepancies lie in the salt expulsion models proposed during syn-rift and post-rift stages and the basin deformation during Cenozoic contraction. The models range from thin-skinned tectonics, basement-involved thrusting, strike-slip faulting, and interference between thick- and thin-skinned thrusting with lateral extrusion. There is multiple working hypothesis often with contradictory predictions of the underground structure. Understanding these structural styles is critical for identify the main salt structures suitable for gas storage in the Burgalesa Platform. We integrate multidisciplinary data from 2D seismic to wellbore, gravity and field data, allowing us to construct three restored cross-sections that illustrate the process of progradational loading and salt expulsion towards the SW during the Early Cretaceous, which led to the development of the Hontomín and other trap structures within the salt overburden. Differential loading occurred diachronously along strike during the Cenozoic, younging to the SE by evacuation of the remaining salt, which caused diapirism and salt welding. We found that most of the structures in the cover were formed by salt migration, whereas Cenozoic shortening caused the rejuvenation of salt-structures and local diapir squeezing. Shortening in the basement is consumed in the frontal thrust that overrides the Duero foreland and in the partial reactivation of the former Mesozoic transfer faults as transpressional faults. The results of this work have implications for a further understanding of the tectonic evolution of the external area of rift structures, and as tectonic analogues in other salt-bearing basins.

Tectonic-Lithofacies Paleogeography and Sizeable Reservoir Potential in the Early Cambrian Postrift Depressed Carbonate Ramp, Tarim Basin, NW China

Abstract The carbonate ramps developed at the postrift depositional stage have become a major field of ultradeep hydrocarbon exploration. Taking the Lower Cambrian Xiaoerblak Formation in the Tarim Basin as an example, the paleotectonic framework and lithofacies paleogeography response, reservoir distribution, and internal architecture difference were systematically analysed based on the data of newly processed 42 2D seismic lines, 9 outcrops, and 22 wells. The results show that (1) the palaeotectonic framework with three palaeohighs and two topographic lows (abbreviated to “TPTT”) dominated the differentiation in the ramp system (association) at the Xiaoerblak depositional stage. High-energy grain shoals and mounds occurred around the palaeohighs, and the sediment composition was further complicated by ancient ocean currents. Three subtypes of ramp are recognized: the slope-plateau ramp dominated by grain shoal on the northern margin of the paleohigh of the southwestern Tarim, homocline ramp dominated by the mound-shoal complex on the Keping-Wensu area lower high, and isolated island type in the Lunnan-Yaha lower high. (2) Xiaoerblak reservoirs mainly occur in the high-energy facies belts in the middle ramps around the palaeohighs because original pores were effectively preserved in early dolomitization and reconstructed at the burial stage. Reservoirs are predicted to mainly distribute in the high-energy mound-shoal zones around three palaeohighs (low uplifts) with an area of 9×104 km2. Different ramp systems show different reservoir properties. There are mainly type II reservoirs (porosity range of 1.8-4.5%, permeability range of 0.5-10×10−3 μm2) with sustained distribution and the largest size in the grain shoals at the slope-plateau ramp, which may be the potential favorable hydrocarbon exploration zone. Based on the example anatomy, the differentiation in the carbonate ramp systems forming at the postrift subsidence stage was structurally dominated. This means that it is crucial to deepen the understanding of the presedimentation palaeotectonic framework for the prediction of promising reservoirs and assessment of reservoir properties.

Cenozoic tectonic evolution of the eastern Liaodong Bay sub-basin, Bohai Bay basin, eastern China — Constraints from seismic data

The eastern Liaodong Bay sub-basin is located in the northeastern Bohai Bay basin, where Cenozoic fault patterns are thought to be largely affected by the movement of the Tan-Lu strike-slip fault zone. Based on three-dimensional seismic data, we identify the initial timing of faulting on normal faults with various orientations in the eastern Liaodong Bay sub-basin, document the structural features and evolution of the fault system and compare the fault patterns with analog models. The basin experienced phases of extensional, strike-slip and inversion-type deformation from the Paleogene syn-rift stage to the Neogene-Quaternary post-rift stage. During the Eocene, the eastern Liaodong Bay sub-basin was in a nearly NNW-SSE oriented extensional setting, with active faults predominantly trending NE-SW to ENE-WSW. During the Oligocene, the eastern Liaodong Bay sub-basin was in a predominantly dextral strike-slip setting. In the study area, the NE-SW trending boundary faults were reactivated, and the reactivated pre-existing internal faults rotated to a more E-W trend. Some of the newly formed extensional faults were orthogonal to the eastern boundary fault F1 and were oriented NW-SE, while others were predominantly oriented E-W. The renewed minor phase of N–S extension during the Miocene caused the reactivation of some pre-existing faults striking NE-SW (boundary faults) and E-W (internal faults); the faults exhibit a bidirectional character in the post-rift section, and the later inversion caused regional compressional deformation. These results suggest that the reactivation of pre-existing faults under phases of extension, strike-slip and inversion provides a more comprehensive explanation for the fault patterns and anticlines observed in the eastern Liaodong Bay sub-basin.

Crustal extension and magmatism along the northeastern margin of the South China Sea: Further insights from shear waves

The northern continental margin of the South China Sea (SCS) is a unique rifted margin that experienced weak magmatism in the syn-rift stage and intense magmatism in the post-rift stage. This area also exhibits a complicated relationship between crustal extension and magmatism. We present the tomographic inversion of seismic P-wave and S-wave velocity models, as well as the Vp/Vs ratio model, in order to delineate the crustal extension and post-rift magmatic features. The velocity structure is created by forward modelling (RayInvr) and travel-time tomographic inversion (Tomo2D). The results suggest that Mesozoic strata near the Dongsha area has a maximum thickness of ~4.6 km with a Vp of 3.5–5.5 km/s, a Vs of 1.9–3.1 km/s, and Vp/Vs ratios of 1.71–1.76, indicating a low porosity and high degree of diagenesis. High-velocity lower crust (HVLC) is imaged in our model, with a Vp of 7.0–7.5 km/s ± 0.05–0.25 km/s and Vp/Vs ratios of 1.70–1.82 ± 0.05. The composition of the HVLC is mainly mafic, we considered it is related to magmatic underplating due to decompression melting caused by crustal extension. The crustal anomalies with high Vp/Vs ratios of 1.80–1.85 ± 0.04 are identified, which are the product of post-rift magmatic intrusions. The seaward increase in continental lower crustal Vp/Vs ratios, suggests an increasing level of mafic intrusion into the continental crust. We attributed crustal hyperextension to increasing fault density, which caused intense magmatic intrusion and thinner HVLC beneath the continent-ocean transition (COT).

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.

The Late Jurassic–Palaeogene Carbonate Platforms in the Outer Western Carpathian Tethys—A Regional Overview

The present work focuses on palaeogeographic reconstruction of shallow-water carbonate deposition in the Outer Western Carpathian Tethys. Platform deposits are preserved only as a component of turbidites and olistostromes, and reconstructions of these platforms are based on clastic material redistributed into slopes and deep basins and occurring among the Outer Carpathian nappes. Similar platforms were also present on the Tethys margins. These reconstructions were performed using the global models of plate tectonics. Several ridges covered by carbonate platforms developed in that area during the latest Jurassic–Palaeogene times. Three main shallow-water facies associations—Štramberk, Urgonian, and Lithothamnion–bryozoan—could be distinguished. The Tithonian–lowermost Cretaceous Štramberk facies is related to early, synrift–postrift stage of the development of the Silesian Domain. Facies that are diversified, narrow, shallow-water platforms, rich in corals, sponges, green algae, echinoderms, foraminifera, microencrusters, and microbes are typical of this stage. The Urgonian facies developed mainly on the south margin of the Outer Carpathian basins and is characterised by organodetritic limestones built of bivalves (including rudists), larger benthic foraminifera, crinoids, echinoids, and corals. Since the Paleocene, in all the Western Outer Carpathian sedimentary areas, Lithothamnion–bryozoan facies developed and adapted to unstable conditions. Algae–bryozoan covers originating on the siliciclastic substrate are typical of these facies. This type of deposition was preserved practically until the final stage in the evolution of the Outer Carpathian basins.

Geochronological and Paleomagnetic Constraints on the Lower Cretaceous Dalazi Formation from the Yanji Basin, NE China, and its Tectonic Implication

The Lower Cretaceous Dalazi Formation in the Yanji Basin, eastern Jilin Province is of particular interest because it contains key fresh water fossil taxa, oil and gas resources, a potential terrestrial Albian–Cenomanian boundary, and regional unconformities. However, the lack of a precise chronology for the non-marine strata has precluded a better understanding of the regional stratigraphic correlation and terrestrial processes. Here, we report magnetostratigraphic and U–Pb geochronologic results of a sedimentary sequence from the Xing’antun section in the Yanji Basin. Thirty-two zircons from the tuff sample were analyzed by secondary ion mass spectrometry (SIMS); the U–Pb zircon dating method yielded a weighted mean of 206Pb/238U age of 105.7 ± 0.8 Ma (2σ, internal error). Paleomagnetic results show that the Dalazi Formation is of normal polarity, which was correlated to the early chron C34n constrained by the SIMS U–Pb zircon geochronologic data, further demonstrating that the terrestrial sedimentary sequence of the upper Dalazi Formation is of late Albian age. The established geochronologic framework allows the regional correlation of the Dalazi Formation in the Yanji Basin to the strata from other terrestrial sequences in northeastern China. The similar geodynamic and geologic background between the Yanji Basin and other terrestrial rift basins in northeastern China suggests that the unconformity between the Dalazi and Longjing formations may represent syn-rift and post-rift stages in the Yanji Basin, and thus the switch from extension to contraction during the mid-Cretaceous, precisely constrained to ~106–101 Ma based on our new chronology and previously published high-precision U–Pb dating of the lower Longjing Formation. It is most likely attributable to the docking of the west Pacific plate along the East Asian continental margin.

Tectonic Switch From Triassic Contraction to Jurassic-Cretaceous Extension in the Western Tarim Basin, Northwest China: New Insights Into the Evolution of the Paleo-Tethyan Orogenic Belt

We use stratigraphic, sedimentological, and borehole data and seismic profiles from the western Tarim Basin to document its Mesozoic tectonic evolution. A nearly 60-km-wide, Triassic fold-and-thrust belt along the southwestern margin of Tarim Basin is unconformably overlain by a Jurassic-Cretaceous sedimentary sequence along a regional angular unconformity. The Lower-Middle Jurassic strata consist mainly of an upward-fining sequence ranging from terrestrial conglomerates to turbidite deposits, which represent the products of an initial rift stage. Palaeocurrent analyses show that sediments for these rift deposits were derived from the paleo-Kunlun and paleo-Tienshan Mountains to the southwest and northern, respectively. The overlying Upper Jurassic-Cretaceous series consist of coarse-grained, alluvial fan to braided river deposits in the lower stratigraphic member, and lagoonal mudstones and marine carbonates in the upper member. These finer-grained rocks were deposited in a subsiding basin, indicating that a significant change and reorientation in the drainage system should have occurred within the basin during the Early Cretaceous. The western Tarim Basin evolved from a syn-rift stage to a post-rift stage during the Jurassic-Cretaceous. A post-orogenic stretch developed due to the evolution of the Paleo-Tethyan orogenic belt in Central Asia is a likely geodynamic mechanism for this major tectonic switch from a contractional episode in the Triassic to an extensional deformation phase in the Jurassic-Cretaceous.

Characteristic of the Bodong segment of the Tanlu Fault Zone, Bohai sea area, eastern China: Implications for hydrocarbon exploration and regional tectonic evolution

In the Bodong segment of the Tanlu Fault Zone (TLFZ), the largest strike-slip fault zone in Eastern China, there are three sags with varying degrees of modification by strike-slip faults. These sags provide an opportunity to examine TLFZ-controlled factors on basin development. The North Bodong sag (NBDS) which was not transformed by TLFZ, entered a rifting stage and post-rifting stage, while the Middle Bodong (MBDS) and South Bodong sags (SBDS) influenced by the TLFZ underwent more complex evolution, including i) a rifting stage, ii) a strike-slipping stage, iii) a structurally quiescent stage and iv) a reactivation stage. There exist two structural changes at about 30.3 Ma and 5.3 Ma, marking the migration of the depocenter and a high activity rate of the TLFZ-related faults. The structural transformation makes hydrocarbon vertically migrate difficult along faults in sag zones, making the slope and the rise zones the main areas for hydrocarbon accumulation due to lateral migration along the unconformity. The differences between the time of the initial rifting of the basin and the strike-slip motion of the TLFZ provides direct evidence for the idea that the Bohai Bay Basin is a rift basin strongly reworked by strike-slip movement. The change from rifting to strike-slip at 30.3 Ma is mainly the result of the combined action of the Indian-Asian collision and the subduction of the Pacific Plate, and the reactivation of the TLFZ at 5.3 Ma is a response to the accelerating subduction of the Pacific Plate.