Tectonic Evolution Of Basin Research Articles

Effects of basin tectonic evolution on multi-phase dolomitization: Insights from the Middle Permian Qixia Formation of the NW Sichuan Basin, SW China

The platform-marginal shoal carbonates of the Middle Permian Qixia Formation in the NW Sichuan Basin, as important ultra-deep (>5000 m) hydrocarbon reservoirs, experienced multi-phase dolomitization and recrystallization during the long-term and complex basin tectonic evolution; however, there is no consensus on the dolomitization mechanism. Four types of dolomites have been identified: medium- and coarsely-crystalline dolomites within patchy dolomitized limestone (LD) at the top of the carbonate strata, massive medium to coarsely-crystalline dolomites categorized as porous dolomites (MD1) and tight dolomites (MD2) at the bottom of the carbonate strata, and cement coarsely saddle dolomites (SD) in the vugs and fractures. All dolomites exhibit similar REESN patterns to the host limestone with an obviously positively Ce anomaly, and show Sr isotopes falling in the range of Permian seawater. However, the LD dolomites display a higher Sr but lower Mn concentration, and more positive δ13C and δ18O than other types of dolomites. The petrographic and geochemical results suggest the dolomites of the Qixia Formation replaced precursor grainstone by the seawater-derived fluids. A comprehensive dolomitization model is proposed, incorporating seawater-reflux, intermediate-burial and tectonic-squeegee, and hydrothermal dolomitization for forming different types of dolomites. LD dolomites are early diagenetic products after selective dissolution under a near-surface or shallow burial environment, in which the weak-evaporated Permian seawater mixed with minor meteoric water accounting for dolomitizing fluids. MD1 and MD2 dolomites are likely to form due to the residually buried seawater for widely dolomitization driven by the Late Triassic tectonic compression. Subsequently, the dolomitic strata underwent hydrothermal modification due to rejuvenation of the thrust belt to enable saddle dolomites filling pre-forming porosity. This study integrates outcrop, petrographic, geochemical and dating analysis with paleogeography and tectonic events, providing a new perspective to establish a conceptual model for multi-phase dolomitization as an analog in comparative tectonic settings worldwide.

High-resolution sequence stratigraphy applied to reservoir characterization of the Brazilian Cretaceous pre-salt section, Campos Basin: Guidelines for geological modeling and reservoir management

The giant accumulations in the pre-salt section of the Brazilian sedimentary basins stand out among the recent world discoveries of oil and gas provinces. The purpose of this case study was to provide inputs to refined 3D geological modeling and reservoir management by characterizing a pre-salt reservoir in the Marlim and Voador fields in the Campos Basin using high-resolution sequence-stratigraphic methodology. This methodology was strong enough to combine different data types, such as seismic and well data, into a high-resolution chronostratigraphic framework. The investigation classified the geological record of the reservoir within a sequence-stratigraphic framework with at least five hierarchies. The 1st- and 2nd-order sequences relate to distinct phases of the Basin's tectonic evolution. Sequences of carbonate lake sedimentation within the post-rift tectonic configuration, where the reservoir is found, were attributed to multiscale transgressive-regressive (T-R) cyclicity. Lake T-R cycles observed in any hierarchical setting are generally governed by faciological tendencies that determine petrophysical features. Regressive tracts produce a more significant proportion of facies with high porosity, whereas transgressive tracts produce facies with reduced porosity. The proposed detailed stratigraphic zoning satisfactorily explains the depletion behavior of the reservoir, revealing that high-resolution sequences condition the fluid flow. Several recommendations for 3D geological modeling, development planning, and reservoir management are made based on these results. The detail highlighted in this study is fundamental in searching for additional oil reserves, production factors, and final recovery.

Pismanta geothermal play in the iglesia basin related to transverse fault systems in the andean orogen

The intermontane Iglesia Basin constitutes the northern Uspallata-Calingasta-Iglesia tectonic depression that holds the Pismanta geothermal field, genetically connected with the basin evolution and structure. Understanding the local structure associated with this geothermal field and linking this system to the regional tectonics is essential to characterize thermal water rising in this area. To address this issue, we carried out a field-based structural analysis and an examination of sedimentary outcrops at the Pismanta area. Also, we linked surface structural data to the subsurface basin structure by means of a previously interpreted seismic reflection line. Our integrated analysis reveals that the Pismanta geothermal field is located in an area of favorable lithology at the intersection of WNW- and NNE-trending thrust faults. These jointly developed a permeability anomaly zone at the Pismanta locality that allows hot underground water rising from deep sedimentary sequences. This observation explains why the thermal springs are only locally concentrated in the study area; a key aspect that was not taken into account in previous models for the Pismanta geothermal field. These results and the overall basin tectonic evolution allowed us to define a new and more complex structural geothermal play model at the Pismanta field.

Characteristics and origin of continental marginal fault depressions under the background of preexisting subduction continental margin, northern South China Sea, China

Based on the new seismic and drilling data and the recent related research results, this paper systematically analyzes the diversity and complexity of evolution process of crustal lithosphere structure and basin structure in the Pearl River Mouth Basin on the northern margin of the South China Sea. Three types of detachment faults of different structural levels exist: crust-mantle detachment, inter-crust detachment and upper crust detachment. It is considered that different types of extensional detachment control different subbasin structures. Many fault depressions controlled by upper crust detachment faults have been found in the Zhu I Depression located in the proximal zone. These detachment faults are usually reformed by magma emplacement or controlled by preexisting faults. Baiyun-Liwan Sag located in the hyperextension area shows different characteristics of internal structure. The Baiyun main sag with relative weak magmatism transformation is a wide-deep fault depression, which is controlled by crust-mantle detachment system. Extensive magmatism occurred in the eastern and southwest fault steps of the Baiyun Sag after Middle Eocene, and the crust ductile extensional deformation resulted in wide-shallow fault depression controlled by the upper crust detachment fault. Based on the classical lithosphere extensional breaking and basin tectonic evolution in the Atlantic margin, it is believed that the magmatic activities and pre-existing structures in the Mesozoic subduction continental margin background are important controlling factors for the diversified continental margin faulted structures in the northern South China Sea.

Mesozoic-Cenozoic tectonic events of eastern Junggar Basin, NW China and their significance for uranium mineralization: Insights from seismic profiling and AFT dating analysis

For sandstone-type uranium deposits, an unobstructed recharge-runoff-discharge (RRD) groundwater system strongly constrained by tectonic events is one of the most important cornerstones for uranium mineralization. Junggar Basin, located in NW China, is proposed to be an intracontinental Mesozoic basin with great sandstone-type uranium metallogenic potential but no large uranium deposits so far. Compared with other uranium-bearing basins in Northern China, the Junggar Basin experienced episodic strong tectonic events in the Meso-Cenozoic era, resulting in more intense stratigraphic deformation and dislocation, so the detailed analysis of tectonic evolution and ore-controlling structures is indispensable to deciphering the uranium mineralization process in the region. This study interprets the seismic profiles and analyzes the apatite fission track (AFT) thermochronological signatures of the Jurassic Toutunhe Formation detrital sediments in the eastern Junggar Basin, which reveals that the Junggar Basin experienced four tectonic events: the Middle Triassic-Early Jurassic episodic uplift of basin margin (ca. 240–180 Ma), the Late Jurassic or Early Cretaceous modest deformation and uplift within the basin (ca. 140 Ma), the Late Cretaceous-Paleocene rapid uplift (ca. 100–60 Ma), the Eocene-Present episodic rapid uplift (ca. 38–0 Ma). On this basis, the tectonic couples comprising tectonic window and structural pattern is dissected. The ore-controlling structures that can build the good RRD system are identified, such as Jurassic slope in the eastern Luliang Uplift, Jurassic hanging wall of fault propagation fold, Neogene foredeep of the foreland basin, and so on. Meanwhile, the rapid uplifts in ca.100–60 Ma and ca.38–0 Ma are ascertained as the key tectonic events constrained uranium mineralization. Afterward, a uranium metallogenic model based on the thread of basin tectonic evolution is established, which is of great significance for further deployment of uranium exploration in the basin.

Multi-dimensional scaling of detrital zircon geochronology constrains basin evolution of the late Mesoproterozoic Paranoá Group, central Brazil

Some of Proterozoic basin data are commonly difficult to assess due to the complexity of tectonic processes and lack of volcanic rocks and fossil record. The Mesoproterozoic Paranoá Basin in Central Brazil was investigated through stratigraphic framework integration, depositional environmental analysis and with detrital zircon and statistical analysis. Paranoá Group was evolved in three phases: i) Proto-Basin Stage represents the basal succession, including the transition from the continental environment (alluvial fans) to shallow water platform conditions; ii) Expansion Basin Stage, which includes the most significant sediment thickness and the essential contrasting depositional environment, including tide-dominated platform, storm dominated platform, supratidal and foreshore conditions and iii) Final Basin Stage represents the shallower environment condition, including mix siliciclastic – carbonate successions. The stages are related to different depositional space creation mechanisms: mechanical subsidence to the Proto-Basin Stage, thermo-flexural subsidence to the Expansion Basin Stage, and flexural subsidence to the Final Basin Stage. The detrital zircon data allied with multidimensional scale were crucial to constrain the basin's tectonic evolution. For the basal succession, the maximum depositional age is ∼1.5 Ga with the local crystalline basement (Aurumina Suite tonalitic and granodioritic gneiss). The source areas changed during the expansion stage, in which the sedimentary successions accumulated during this stage present maximum depositional age of ∼1.3 Ga and a widespread distribution pattern. In the final phase, the maximum depositional age is ∼1.1 Ga, including a complex distribution of ages representative of different source areas. The new and compiled data presented in this study provide new insights about the Goiás-Pharusian opening and implications on the configuration in the western margin of the São Francisco Craton.

Differences in the Tectonic Evolution of Basins in the Central‐Southern South China Sea and their Hydrocarbon Accumulation Conditions

AbstractTo reveal the causes of differences in the hydrocarbon accumulation in continental marginal basins in the central‐southern South China Sea, we used gravity‐magnetic, seismic, drilling, and outcrop data to investigate the tectonic histories of the basins and explore how these tectonic events controlled the hydrocarbon accumulation conditions in these basins. During the subduction of the Cenozoic proto‐South China Sea and the expansion of the new South China Sea, the continental margin basins in the central‐southern South China Sea could be classified as one of three types of epicontinental basins: southern extensional‐foreland basins, western extensional‐strike slip basins, and central extensional‐drift basins. Because these basins have different tectonic and sedimentary histories, they also differ in their accumulated hydrocarbon resources. During the Cenozoic, the basin groups in the southern South China Sea generally progressed through three stages: faulting and subsidence from the late Eocene to the early Miocene, inversion and uplift in the middle Miocene, and subsidence since the late Miocene. Hydrocarbon source rocks with marine–continental transitional facies dominated by II–III kerogen largely developed in extremely thick Miocene sedimentary series with the filling characteristics being mainly deep‐water deposits in the early stage and shallow water deposits in the late stage. With well‐developed sandstone and carbonate reservoirs, this stratum has a strong hydrocarbon generation potential. During the Cenozoic, the basin groups in the western South China Sea also progressed through the three developmental stages discussed previously. Hydrocarbon source rocks with lacustrine facies, marine‐continental transitional facies, and terrigenous marine facies dominated by II2–III kerogen largely developed in the relatively thick stratum with the filling characteristics being mainly lacustrine deposits in the early stage and marine deposits in the late stage. As a reservoir comprised of self‐generated and self‐stored sandstone, this unit also has a high hydrocarbon generation potential. Throughout those same three developmental stages, the basin groups in the central South China Sea generated hydrocarbon source rocks with terrigenous marine facies dominated by III kerogen that have developed in a stratum with medium thicknesses with the filling characteristics being mainly sandstone in the early stage and carbonate in the late stage. This reservoir, which is dominated by lower‐generation and upper‐storage carbonate rocks, also has a high hydrocarbon generation potential.

Dual‐system tract pattern: Significance for foreland basin reservoir prediction (Jurassic, Central Junggar Basin, West China)

The Junggar Basin is a typical superimposed system characterized by multilateral steep thrusts and extrusions and one of the primary petroliferous basins in Western China. To date, geologists have been most interested in the basin's tectonic evolution and petroleum geology characteristics. Based on field outcrops, lithologic combinations, logging curves, and seismic reflection characteristics, we present a systematic study of the sequence stratigraphy pattern for the Jurassic central Junggar Basin. Herein, we identify the central Junggar area as having a “dual” characteristic sequence framework composed of a lowstand system tract (LST) and a transgressive system tract (TST), which is distinguishable from the traditional three system tract (LST, TST, and highstand system tract [HST]). In each third‐order sequence, the LST consists of conglomerate or pebbly sandstone deposits, displaying the characteristics of braided channel and fan delta. The TST consists of siltstone, argillaceous siltstone, and mudstone, displaying fine‐grained, shore‐shallow lacustrine deposits. It is considered that the combination of multiphasic thrust extrusion and subsequent, steady deposition is likely responsible for the dual‐system tract. The forming process of the dual‐system tract pattern could divide into four stages: the quiet stage of tectonic activity, the early stage of compression, the continuous stage of compression, and the rapid rebound stage. Additionally, two reservoir predictive models are proposed: the progradational predicting model on the edge of the depression and truncated and pinchout predicting model on the palaeo‐uplift. We conclude that the coarse clastic unit of the LST has bright prospects for oil and gas exploration within the superimposed system in Western China.

Well path design by integrating the analysis of wireline logs and the interpretation of seismic data for a fractured basement reservoir in Cuu Long Basin, Viet Nam

Abstract Cuu Long Basin, which is located in southeast offshore Viet Nam, has a number of well fractured granitic basement reservoirs. Though dozens of wells have been drilled in the pre-Tertiary basement, the actual number of wells in which hydrocarbons were discovered is approximately 30% of the total. Therefore, understanding fracture characteristics in the fractured basement is very important and plays a critical role in designing the well path. This study proposes a method to optimize well path design in the fractured granitoid basement rock. Available information, including basin tectonic evolution, basin geological characteristics, seismic interpretation, and wireline logs, especially image and sonic logs, are analyzed in order to understand the fracture characteristics and the distribution of fractures in the study area, which is referred to as Thuy Trieu Do (TTD) structure. There are two key factors related to the flow in basement of TTD structure, namely are solution-enhanced fractures and faults interpreted from seismic images. Solution-enhanced fractures from images are considered to be open fractures that contribute to flow. Within the TTD basement, the solution-enhanced fractures trend in the east-west and sub east-west directions. Faults interpreted from seismic images are complex with different fault directions, having been active in several tectonic phases. They are evaluated and classified, then the faults those are NE-SW 60–70°, E-W, and sub E-W 80–280° have potential in creation fault-related fractures of solution-enhanced fracture type. Fractures are mostly distributed in fracture zones along the fault zone. By displaying faults and fractures together both along the well path and on rose diagrams, combined with production logs analysis, it appears that surrounding faults have increased fracture density and the presence of solution-enhanced fractures in every flow zone. The above relationships were taken in analyses for the next well design in the TTD structure. In this study, for optimal well path design in the fractured basement reservoir, a systematic procedure of interpretation of various geophysical data in Cuu Long Basin has been proposed, and this approach is expected to be applicable to other fractured reservoirs in Viet Nam.

The seawater osmium isotope record of South China Sea: Implications on its history and evolution

The South China Sea is the largest marginal basin in the world, and is located in the confluence of three major tectonic plates (Pacific-Philippine Sea, Indo-Australia, Eurasia). Its tectonic history and evolution throughout the Cenozoic has been the subject of much discussion with regards to its mechanism, timing, and relationship to neighboring geological features. We conducted the first Re-Os isotope study of the South China Sea cores recovered from ocean drilling (ODP-Ocean Drilling Program and IODP-International Ocean Discovery Program) and from Philippine oil exploration wells in order to investigate whether or not the basin's tectonic evolution will be reflected in the seawater Os isotope record. These cores represent the northern and southern conjugate margins of the South China Sea, and should have complementary records of the tectonic events in the basin. We found three important negative anomalies in the South China Sea's seawater Os isotope record at 35–33Ma, 26–23Ma, and ~13–6Ma, which are temporally related to tectono-magmatic events. At the northern margin, the record starts with the lowest (187Os/188Os)i values of 0.37 and 0.32 for the oldest samples, which then progresses to more radiogenic values for younger sediments. The trend is consistent with the start of seafloor spreading at ~33Ma that saw the peak in the flux of mantle-derived material, which later slowed down until the second peak between 26 and 23Ma. However, these unradiogenic values also mark the Eocene-Oligocene Transition and more likely implies South China Sea connectivity to global ocean circulation since pre-Oligocene. In both margins, slight to marked decrease in (187Os/188Os)i values deviate from the global trend and coincides with the ridge jump at ~23Ma. In the southern conjugate margin, (187Os/188Os)i show a general decreasing tendency opposite that of the northern margin and the global trend starting from Mid- to Late Miocene (~13–6Ma). Mass balance modeling suggests that the two younger negative excursions may be accounted for by mantle and hydrothermal Os inputs of ~372mol/my at ~23Ma and post ~13Ma. We suggest that the post ~13Ma protracted decrease in (187Os/188Os)i values for the southern margin reflects localized input of mantle-derived lithogenic Os from the Luzon Arc combined with post-spreading magmatic intrusions, and possibly gradual changes in paleoceanographic condition at the southern East Sub-basin.

Restoration of Eroded Thickness of the Neogene Strata in the Western Qaidam Basin and Its Significance for Oil and Gas Occurrence

AbstractDuring the Pleistocene, the western Qaidam Basin has largely experienced strong structural reconstruction and strong erosion. First, the eroded thickness of Neogene strata was restored approximately by the stratigraphic profile comparison method and plane trend surface restoring method; then, accurate calculation of erosion was recovered using vitrinite reflectance, and the erosion that was restored by the trend surface restoring method was corrected; finally, a distribution map of cumulative erosion was produced. This study marks an important achievement in that one of the most important parameters of basin tectonic evolution, sedimentary evolution, and oil and gas accumulation history has been obtained, and that a basic geological problem has been solved in the Qaidam Basin. The areas with high erosion and low erosion are shown in the map and a close relation between the distribution of oil and gas fields and erosion was recognized. Large and medium oil and gas fields are mainly distributed in areas with medium and low erosion. It is difficult to form large‐scale oil and gas accumulation in areas in which erosion is more than 2000 m. The mechanism of the relation between oil and gas distribution and erosion is explained. This study will be of use in predicting the distribution of oil and gas.

Tectonosedimentary evolution model of an intracontinental flexural (foreland) basin for paleoclimatic research

Intracontinental flexural (foreland) basin sediments are now frequently used as archives for detailed paleoclimatic and sedimentary environmental reconstruction, fossil and stratigraphic correlation, and tectonic evolution and uplift of basin and orogen. However, sedimentologic characteristics vary considerably in time-space with the evolution of flexural basin, apt to cause misinterpretation of climatic change and stratigraphic correlation. Based on high resolution fossil mammal and magnetostratigraphic constraints and sedimentary facies analysis, here we took the Linxia Basin at the front of the NE Tibetan Plateau as a case to demonstrate and figure out a model how sedimentology and stratigraphy vary temporospatially with the evolution of such flexural basin. The results show that the Linxia Basin is a type intracontinental foreland basin subjected to two phases of flexural deformation exerted by the West Qin Ling (Mts.) and NE Tibetan Plateau to the south. Phase I began latest at the beginning of the Miocene (23.3Ma), indicated by a balanced fast flexural subsidence and mostly fine sediment infilling giving rise to the early underlying unconformity. It manifests as an obvious sediment wedge with high filling rate, thickening toward mountains and an occurrence of a mountains-parallel big river – shallow lake system along the foredeep, suggesting a less high mountain topography. In the late Phase I, from ~13Ma to 8Ma, the subsidence and thickening rates began to decrease, accompanied by faults and deformation propagating gradually into the basin, causing gradual basinward migration of the foredeep and its accompanying river-lake system. Since ~8Ma in Phase II, the West Qin Ling and NE Tibetan began to uplift rapidly and thrust/load onto the Linxia Basin, causing strong mountain erosion, thrust-fold belt propagation and basin overfilling. This forced the mountains-parallel river - lake system to turn to the mountains-perpendicular alluvial - braided river system, and finally to an outflow system by the Quaternary onset of the Yellow River in the basin. Concurrent are rapid rotation of the basin, occurrence of growth strata and late unconformities, widespread expansion of boulder conglomerates, great decreasing and increasing sedimentation rates above and before the hanging wall of the fault-fold system and new supplementary provenance from the thrust-fold system. This demonstrates that in stable climate, same lithologic units such as distinct lacustrine sediments and alluvial conglomerates will migrate basinwards with the foredeep moving into basin, causing a great diachroneity and often misleads to recognize the same lithologic unit in space as one unit in time. A dynamic model is presented that should help to avoid such pitfalls in tectonic basin evolution, especially concerning stratigraphic correlation and paleoclimatic change research.

Paleogeographic framework and provenance features during Late Triassic Chang 9 time of the Yanchang Formation, Ordos Basin, China

The Chang 9 interval at the lower part of the Upper Triassic Yanchang Formation in the Ordos Basin is a new discovery sequence for strategy replacement in the oil exploration field. By conducting a comprehensive study of outcrop sections, well drilling, drill cores, well loggings, and test data, based on the relevant research achievements of some predecessors, and combined with the analysis of geological background of this basin, it is considered that the Ordos Basin is a broad and shallow lake basin with terrigenous clastic deposition during Late Triassic Chang 9 time. The lake basin had been supplied with multiple drainage systems and provenances. The lake water in this basin is inland freshwater to brackish water. Sedimentary framework is characterized by the development of “a lake surrounded by multiple deltas” pattern. On the basis of paleocurrent analysis, distribution of sedimentary facies and sand bodies, and the quantitative analysis results of rock fragment components and trace elements of Chang 9 sandstone, it is recognized comprehensively that the Chang 9 provenances have a close connection with the basin tectonic evolution and paleogeographic background. The provenance of the Ordos Basin in Chang 9 time can be divided into five provenance systems: i.e., the northeast, north, northwest, southwest, and south provenance systems. Characteristics of rock fragment and trace element assemblages are documented in the individual provenance systems, respectively. It is inferred that terrigenous clastic sediments in Chang 9 interval mainly originate from the old lands around the basin. Parent rocks in these provenances are composed of a variety of rocks dominated by metamorphic rocks.

The Evolution and Instruction of Strontium Isotope in the Geothermal Water of Basin Type

Combined with the Guanzhong basin tectonic evolution, the data of Sr content,87Sr/86Sr ratio and hot water hydrochemistry has been used to study the supply origin and flow path of deep geothermal water in the Guanzhong central region. The Sr isotope study result shows that when accepting recharge, the geothermal water in the northwest and southeast of Xianli terrace both mainly come from northwest direction. A small amount supply source of geothermal water in the Xi 'an city is from Qinling mountain and the principal supply source comes from the west and north direction, however, geothermal water of Chang’an accepts supply from the north of Qinling mountain. Keywords: geothermal water; strontium isotope; basin type; indicating significance

Tectonic evolution of Cretaceous extensional basins in Zhejiang Province, eastern South China: structural and geochronological constraints

Widespread Cretaceous volcanic basins are common in eastern South China and are crucial to understanding how the Circum-Pacific and Tethyan plate boundaries evolved and interacted with one another in controlling the tectonic evolution of South China. Lithostratigraphic units in these basins are grouped, in ascending order, into the Early Cretaceous volcanic suite (K1V), the Yongkang Group (K1-2), and the Jinqu Group (K2). SHRIMP U-Pb zircon geochronological results indicate that (1) the Early Cretaceous volcanic suite (K1V) erupted at 136–129 Ma, (2) the Yongkang Group (K1-2) was deposited from 129 Ma to 91 Ma, and (3) the deposition of the Jinqu Group (K2) post-dated 91 Ma. Structural analyses of fault-slip data from these rock units delineate a four-stage tectonic evolution of the basins during Cretaceous to Palaeogene time. The first stage (Early to middle Cretaceous time, 136–91 Ma) was dominated by NW–SE extension, as manifested by voluminous volcanism, initial opening of NE-trending basins, and deposition of the Yongkang Group. This extension was followed during Late Cretaceous time by NW–SE compression that inverted previous rift basins. During the third stage in Late Cretaceous time, possibly since 78.5 Ma, the tectonic stress changed to N–S extension, which led to basin opening and deposition of the Jinqu Group along E-trending faults. This extension probably lasted until early Palaeogene time and was terminated by the latest NE–SW compressional deformation that caused basin inversion again. Geodynamically, the NW–SE-oriented stress fields were associated with plate kinematics along the Circum-Pacific plate boundary, and the extension–compression alternation is interpreted as resulting from variations of the subducted slab dynamics. A drastic change in the tectonic stress field from NW–SE to N–S implies that the Pacific subduction-dominated back-arc extension and shortening were completed in the Late Cretaceous, and simultaneously, that Neo-Tethyan subduction became dominant and exerted a new force on South China. The ongoing Neo-Tethyan subduction might provide plausible geodynamic interpretations for the Late Cretaceous N–S extension-dominated basin rifting, and the subsequent Cenozoic India–Asia collision might explain the early Palaeogene NE–SW compression-dominated basin inversion.

Tectonic Evolution of the Wanan Basin, Southwestern South China Sea

AbstractQuantitative studies on the extension and subsidence of the Wanan Basin were carried out based on available seismic and borehole data together with regional geological data. Using balanced cross‐section and backstripping techniques, we reconstructed the stratigraphic deposition and tectonic evolution histories of the basin. The basin formed from the Eocene and was generally in an extensional/transtensional state except for the Late Miocene local compressoin. The major basin extension ocurred in the Oligocene and Early Miocene (before ∼16.3 Ma) and thereafter uniform stretch in a smaller rate. The northern and middle basin extended intensely earlier during 38.6–23.3 Ma, while the southern basin was mainly stretched during 23.3–16.3 Ma. The basin formation and development are related to alternating sinistral to dextral strike‐slip motions along the Wanan Fault Zone. The dominant dynamics may be caused by the seafloor spreading of the South China Sea and the its peripheral plate interaction. The basin tectonic evolution is divided into five phases: initial rifting, main rifting, rift‐drift transition, structural inversion, and thermal subsidence.

Salt tectonics and basin evolution in the Gabon Coastal Basin, West Africa

The Gabon Coastal Basin is a typical saliferous basin located in the middle portion of the West African passive continental margin. Complex salt tectonics make sedimentary sequences and structural frameworks difficult to interpret and can lead to difficulties in construction of balanced cross-sections and reconstruction of basin evolutionary processes. Sedimentary facies and salt structural patterns displaying zonation are based on seismic reflection profiles and drilling data. Two near-vertical fault systems, NW-SE and NE-SW, caused basin to be subdivided E-W zoning and N-S partitioning. Scarp slopes and extension faults formed in the Hinge belt III zone where salt diapir piercement occurred and numbers of salt pillars, salt stocks and salt rollers developed under transtension of coupled near-orthogonal fault systems. The zone east of Hinge belt III is characterized by small-scale salt domes and salt pillows. To the west are large-scale salt walls and salt bulge anticlines caused by diapirism promoted by tension and torsion that also resulted in formation of numerous salt pillars, salt stocks and salt rollers. Our modeling of salt tectonic structures indicates that they were produced by plastic rheological deformation of salt under regional stress fields that varied during three distinct phases of extension, compression and re-activation. Hinge belt III was active from Coniacian to Early Eocene, which was a critical period of formation of salt structures when many extension-related salt structures formed and salt diapirism controlled the distribution of turbidite fans. Rootless extrusion-related salt stocks developed throughout the Late Eocene to Early Oligocene as a result of local ephemeral low-intensity tectonic inversion. Post Oligocene salt diapirism was weak and salt tectonics had a weak influence on sedimentation. Balanced cross-sections of two saliferous horizons crossing different tectonic units from east to west reveal that the basin tectonic evolution and sediment filling processes can be divided into three stages containing seven episodes of rifting, transition and drifting.

Thermal history of the Aragón-Béarn basin (Late Paleozoic, western Pyrenees, Spain); insights into basin tectonic evolution

Organic and inorganic thermal indicators throughout the Late Paleozoic sedimentary fill of the Aragon-Bearn Basin in the western Pyrenees, integrated with stratigraphic and structural data, point to a two-stage tectonic evolution:(i) High heat flow values and widespread magmatic intrusions driven by deeply rooted strike-slip faults characterized the first stage. This regime accompanied the rapid and localized deposition of the lower sedimentary succession and ended with uplift and erosion.(ii) The second stage was characterized by lower heat flow values, shallower strike-slip faults active during the deposition of an upper transgressive sedimentary succession and minor magmatic intrusions.The lower portion of the succession (Unidad Gris, Unidad de Transito and Unidad Roja Inferior, mainly Stephanian-Early Permian in age) records maximum temperatures between 170°C and 220°C as shown by clay mineral-based geothermometers (KI between 0.40 and 0.52°?2?, conversion of mixed layer illite-smectite to discrete illite), vitrinite reflectance (about 2.5%), and total homogenization temperatures from host-rock quartz cements between 160 and 180°C.The upper portion of the succession (Unidad Roja Superior, mainly Upper Permian in age) records maximum temperatures between 100-110° and 150°C as indicated by KI values between 0.57 and 0.94°?2?, illite content in mixed layer illite-smectite of 85-92%, and fluid inclusions in host-rock quartz-calcite cements.Local thermal maturity anomalies affected selected portions of the Late Paleozoic sedimentary succession with organic matter and clay minerals reaching respectively Ro%: 4.2-4.7% and KI up to 0.32°?2??in the lower sequence, and Ro% 2.9% in the upper sequence. These localized anomalies with respect to the basin thermal signature are the result of contact metamorphism related to the emplacement of magmatic intrusions across the sedimentary fill during two different magmatic events.

Studies on Main Factor Coupling and Its Control on Coalbed Methane Accumulation in the Qinshui Basin

There are many factors controlling coalbed methane (CBM) accumulation. So, it is fundamental for CBM exploration and development to identify these factors and investigate their control mechanism. Through statistical analysis of experimental and field test data, the basin tectonic evolution, sedimentary environments and hydrodynamic conditions are comprehensively analyzed, and the gas control mechanism of three main factors (structure, sedimentation and hydrodynamic force) is discussed. Results show that the tectonic evolutions complicated the process of CBM reservoir formation. Multi-episode tectonic stress fields with different features reform the physical properties of coal seams that make areas with high structural principal stress difference convert to high permeability reservoir areas. The mudstone cap rock develops well in shallow water delta system. The coal seams are thick and distributed stably in deltaic plain swamp, and their abundant vitrinite, micropores and strong adsorption capacity are favorable for CBM accumulation. Appropriate hydrodynamic condition may carry secondary biological gas into the gas reservoir to supply gas source, and it is also the main force of methane carbon-isotope fractionation during CBM drainage and production. The methane carbon-isotope fractionation is available to identify the yield stability of CBM well.

Preliminary K-Ar geochronology of lavas from southern Lau Basin

In this short note, we report the ages of five lava samples from a segment of the Eastern Lau Spreading Center (ELSC) and three samples from the Valu Fa Ridge (VFR) in the southern Lau Basin. These samples were collected in situ fromthe axes and flanks of the spreading centers in the basin. These ages provide a key to better understanding the spreading mode, crustal formation and overall tectonic evolution of the basin. Except for two basaltic andesites and one andesite, the lavas analyzed are basalts. The ages of the lavas from ELSC range from (1.45±0.15) Ma to (0.74±0.04) Ma whereas those from VFR range from (0.50±0.06) Ma to (0.32±0.27) Ma, and the basalts give the oldest ages. The relatively younger ages of the VFR lavas are consistent with proposed tectonic evolution of the southern Lau Basin, i.e., VFR is a propagating extension of ELSC. The occurence of older lavas close to or on spreading axes in the southern Lau Basin implies the complex tectonic evolution of the basin. These results underscore a need for further detailed geophysical and geological studies in the southern Lau Basin, in order to better clarify the crustal accretion tectonic evolution in this area.