Cretaceous Tectonic Events Research Articles

New insights into tectonostratigraphy and structural style of the Late Cretaceous sediments of Gongola Basin, Northern Benue Trough, NE Nigeria

Tectonostratigraphy of the Gongola Basin is still least understood. This study aims to present a new insight into tectonic evolution and structure of Gongola Basin based on field geology. The study revealed that sedimentation processes commenced in the depression created by tectonic subsidence as a result of Early Cretaceous tectonic events, which affected the basin and subsequently, reactivated the Santonian/Maastrichtian compression. The sediments were affected by Santonian and Maastrichtian compressions resulting in syn-sedimentary deformation and post-depositional faulting and folding. The imprints of dextral strike-slip faults and reverse faults on pre-Maastrichtian and Maastritchtian sediments formed as a result of reactivation of the pre-Santonian and Santonian faults. Active rifting phase followed by uplift and subaerial exposure as in Gombe inlier, and adjacent areas such as Teli Fault, Kaltungo, Burashika inliers followed by subsidence allowing for initial deposit of continental sediments and later, marine ingression which causes a change from continental to marine environments during Cenomanian. Eustatic adjustment in Late-Cenomanian to Early-Turonian led to first major transgression and short-regressive phase in middle Turonian-early Santonian. Mid-Santonian compression folded the sediments and was followed by subaerial erosion of parts of the folded sediments. Another eustatic adjustment in Late-Santonian-Campanian led to a short-lived transgression. A gradual retreat of the sea in the Maastrichtian resulted in progradation of Gombe Sandstone. Late Maastrichtian compression in end-Cretaceous tectonic event folded and tilted Gombe Sandstone, responsible for the angular unconformity that existed between Gombe Formation and overlying Paleocene sediments of Kerri-Kerri Formation, mostly restricted to NW of the basin.

Kinematic analysis of fault-slip data in the Nanling Tectonic Belt and Cretaceous to Paleogene tectonic evolution of the Central South China Block

• Six tectonic events were inversed from fault-slip analysis in the Nanling Tectonic Belt. • Four Cretaceous tectonic events resulted from the Paleo-Pacific subduction . • Two Paleogene tectonic events were due to the far field effect of the India-Asia collision. Cretaceous tectonic events and Cenozoic geodynamics of the central South China Block are still under debate. A long-term extensional regime or two extension-contraction tectonic cycles were proposed for the Cretaceous tectonic evolution. While Cenozoic geodynamics of the central South China Block were ascribed to the Pacific subduction or the far field effect of the India-Asia collision. Kinematic analysis of fault-slip data were carried out for the Cretaceous to Paleogene Chaling-Yongxing Basin and the Lianshan-Yangshan Domain in the Nanling Tectonic Belt. Kinematic analysis of fault-slip data (409 groups of faults and striations) reveal four Cretaceous tectonic events and two Paleogene tectonic events. i) The early Early Cretaceous extensional regime is represented by a NW-SE horizontal minimum principal stress and a vertical maximum principal stress, which generated NE-striking boundary normal faults of Early Cretaceous basins. ii) The late Early Cretaceous strike-slip regime is characterized by a N-S horizontal maximum principal stress and a E-W horizontal minimum principal stress, which led to tectonic inversion of Early Cretaceous extensional basins and nearly N-S-striking folding of the Lower Cretaceous. iii) The early Late Cretaceous extensional regime is represented by a NW-SE horizontal minimum principal stress and a vertical maximum principal stress, which activated the NE-striking boundary normal faults of Late Cretaceous basins. And iv) the latest Late Cretaceous strike-slip regime is characterized by NW-SE horizontal maximum principal stress and a NE-SW horizontal minimum principal stress, which led to tectonic inversion of Late Cretaceous extensional basins and NNE-striking folding of the Upper Cretaceous. Orientations of maximum or minimum principal stresses imply that two extension-contraction tectonic cycles during the Cretaceous resulted from the Paleo-Pacific subduction. Two Paleogene tectonic events are v) the strike-slip regime characterized by NE-SW horizontal maximum principal stress and a NW-SE horizontal minimum principal stress, and vi) the subsequent extensional regime represented by a NE-SW minimum principal stress and a vertical maximum principal stress. The former generated NW-striking reverse faults and reactivated strike-slipping of NE- and NW-striking conjugate faults whereas the latter formed NW-striking normal faults in the Lower Paleogene clastic rocks. Orientations of maximum or minimum principal stresses indicate that two Paleogene tectonic events in the central South China Block were attributed to the far field effect of the India-Asia collision and subsequent stress relief.

Tectonothermal events in the central North China Craton since the Mesozoic and their tectonic implications: Constraints from low-temperature thermochronology

The North China Craton (NCC) experienced important tectonic events during the Meso-Cenozoic as implied by many geological studies. Combined with existing low-temperature thermochronological data, new apatite fission track (AFT) and zircon (UTh)/He data from the Lüliangshan and Taihangshan mountains in this study reveal that the central NCC experienced tectonothermal events during the Meso-Cenozoic, i.e., ca. 150 Ma, 110–80 Ma, 50–40 Ma and 30–20 Ma. The Late Jurassic event caused the formation of the Lüliangshan basement-involved anticline. The main folding and thrusting in the central NCC developed in the Mesozoic instead of the Cenozoic and resulted from the low-angle subduction of the Paleo-Pacific ocean plate beneath the Eurasian Plate during the Late Jurassic; and the Late Cretaceous tectonic event stopped the Early Cretaceous extension across the eastern Asia, thrusting and sinistral strike-slip faulting occurred across the central NCC, which was possibly caused by a collision along the southeastern boundary of eastern Asia. The early Cenozoic event in central NCC was coeval with an event occurring throughout eastern Asia and may have been a regional response to changes in the movement direction and velocity of the Pacific Plate, and this event may have resulted in the formation of rift basins in the eastern NCC. The whole central NCC experienced uplift during this period in isostatic readjustment to this extension.

Dynamic background of Early Cretaceous tectonic thermal events and its control on various mineral accumulations such as oil and gas in the Ordos Basin

Dynamic background of Early Cretaceous tectonic thermal events and its control on various mineral accumulations such as oil and gas in the Ordos Basin

New zircon U-Pb geochronological and geochemical data reveals the earliest Cretaceous tectonic shift event in the Lanqi Basin, Inner Mongolia, northern China

New zircon U-Pb geochronological and geochemical data reveals the earliest Cretaceous tectonic shift event in the Lanqi Basin, Inner Mongolia, northern China

Cretaceous intracontinental rifting at the southern Chatham Rise margin and initialisation of seafloor spreading between Zealandia and Antarctica

Passive continental margins are commonly classified as magma-poor and magma-rich types. Related breakup processes are often associated with far-field tectonic stresses or upwelling mantle plumes. The Chatham Rise east off New Zealand records a sequence of Late Cretaceous tectonic events, which include subduction and collision of the oceanic Hikurangi Plateau to subsequent continental rifting and breakup. The mechanisms triggering the change in tectonic forces are poorly understood but address open questions regarding the formation of passive margins. We acquired wide-angle seismic reflection/refraction, multi-channel seismic and potential field data along three profiles crossing the southern Chatham Rise margin and SE Chatham Terrace to the oceanic crust in order to image and understand the crustal structure and breakup mechanisms. Variations in crustal thickness along the highly faulted Chatham Rise are most likely related to the collision with the Hikurangi Plateau. Our data indicate that the SE Chatham Terrace represents a broad continent-ocean transition zone (COTZ), which we interpret to consist of very thin continental crust affected by magmatic activity. Along the southern Chatham Rise margin, features of both, magma-poor and magma-rich rifted margins are present. We suggest that passive rifting initiated at 105–100 Ma related to slab dynamics after the Hikurangi Plateau collision. We revise the onset of seafloor spreading south of the eastern Chatham Rise to ~88 Ma from the extent of our inferred COTZ. Geographically extensive, but low-volume intraplate magmatism affected the margin at 85–79 Ma. We suggest that this magmatism and the onset of seafloor spreading are a response to upwelling mantle through a slab window after 90 Ma. After 85 Ma, spreading segments became connected leading to the final separation of Zealandia from Antarctica. We interpret the southern Chatham Rise margin as a unique hybrid margin whose tectonic history was influenced by passive continental rifting and mantle upwelling.

Late Paleozoic – Mesozoic tectonic evolution of the Eastern Taimyr-Severnaya Zemlya Fold and Thrust Belt and adjoining Yenisey-Khatanga Depression

Combined structural, thermochronological and geochronological studies were carried out to unravel the complex late Paleozoic – Mesozoic tectonic evolution of the eastern Taimyr – Severnaya Zemlya Fold and Thrust Belt, along with the adjoining Yenisey-Khatanga Depression and Olenek Fold Zone. New detailed field mapping, a fault and fold geometry and kinematic study, and paleostress reconstruction were undertaken for key areas within the Central and Southern Taimyr domains and the Olenek Fold Zone. Thirty seven samples were used for apatite fission track (AFT) analysis along with two samples for U-Pb zircon granite dating, and three samples for Ar-Ar metamorphic muscovite dating.The late Paleozoic (Early Carboniferous – Permian) tectonic event is recognized only in a relatively narrow zone including the Northern Taimyr Domain and part of the Central Taimyr Domain. It started in the Early Carboniferous (Visean) and is synchronous with the earliest stages of collision in the Uralian Orogen. Our results reveal a widespread distribution of latest Triassic – earliest Jurassic and Cretaceous deformations. The latest Triassic – earliest Jurassic tectonic event significantly overprinted the Northern and Central Taimyr domains and original unaltered late Paleozoic AFT ages are identified only locally. New completely reset AFT cooling ages group at 195-180 Ma, in reasonable agreement with structural data. Older Neoproterozoic and late Paleozoic Ar-Ar ages of metamorphic muscovite are retained, demonstrating that the dated rocks were not heated above 300 °C. An Early Cretaceous tectonic event is inferred from both the structural study and ca. 115–125 Ma AFT cooling ages, and is most widespread in the Southern Taimyr Domain, Olenek Fold Zone and adjoining parts of the Yenisey-Khatanga Depression, modifying older geological structures. A younger Late Cretaceous tectonic event at ca. 100-60 Ma is also inferred from AFT cooling ages, but its distribution is poorly constrained.Our study reveals that the distribution of late Mesozoic tectonic events has been significantly underestimated in previous structural studies of the region. The latest Triassic – earliest Jurassic and Cretaceous tectonic events are easily correlated with those in the Pai-Khoi – Novaya Zemlya and northern Verkhoyansk fold and thrust belts.

Petrographic and geochemical characterization of the Upper Cretaceous coal and mudstones of Gombe Formation, Gongola sub-basin, northern Benue trough Nigeria: Implication for organic matter preservation, paleodepositional environment and tectonic settings

Under-exploration of the Upper Cretaceous petroleum systems in the Northern Benue Trough Nigeria has been attributed largely to lack of subsurface samples and non-integration of organic and inorganic geochemical methods. Recent access to surface sampling from Maiganga coalfield revealed a need for detailed evaluation of the sedimentary facies types for better understanding of the hydrocarbon potential of the area. Detailed maceral point count, Py-GC, CHNSO as well as major oxides and trace element (ICP-MS) analysis were used to characterize the Gombe Formation coals and the mudstones for determination of the organic matter origin, preservation, paleodepositional environment, tectonic setting and paleoclimatic condition during sedimentation. Evaluation based on the maceral composition, TPI, GI values, plot of trace elements V versus Ni and sedimentary succession suggest deposition of predominantly terrigenous organic matter (45 to 73% huminite maceral) in an upper deltaic setting for the Maiganga facies. The maceral analysis associated with Py-GC studies indicates that the sedimentary facies of Gombe Formation have potential to generate liquid hydrocarbon. This can be estimated from an average of 21.50% liptinite content and the ternary plot of the Py-GC pyrolysate m(+p) xylene, n-octene and phenol suggesting presence of Type II and Type II/III kerogen within the basin. Assessment of the paleodepositional environment based on the trace elements composition indicates a moderate stratified water column and salinity within a relatively sub-oxic to oxic conditions during sedimentation. The major oxide composition as well as the binary plots of SiO2 versus (Al2O3+K2O+Na2O) and log SiO2 versus (K2O/Na2O) for the shales and mudstones revealed a predominance of semi-arid to slightly humid-warm paleoclimatic conditions and a passive continental margin setting. This is in accordance with the Cretaceous tectonic events of the West and Central Africa which affected the petroleum system in the entire Benue Trough.

Total exhumation across the Beichuan fault in the Longmen Shan (eastern Tibetan plateau, China): Constraints from petrology and thermobarometry

The deep structure and deformation mechanisms of the Longmen Shan thrust belt (Sichuan, China), at the eastern border of the Tibetan plateau, were largely debated after the devastating Mw 7.9 Wenchuan earthquake (2008). Recent geophysical studies and field investigations have been focused on the active motion of the major Beichuan fault, which ruptured during the earthquake. However, the total exhumation across the fault still remains unclear. In the hanging wall of the Beichuan fault, the South China block is exhumed in the Pengguan massif. Close to the Beichuan fault, the rocks of the Pengguan massif underwent greenschist facies metamorphism associated with brittle-ductile deformation. No metamorphism is observed in the footwall of the fault. In this study, we characterize and date the metamorphic history recorded in the hanging wall of the Beichuan fault in order to constrain the depth and timing of exhumation of the rocks of the Pengguan massif along the fault. A high-resolution petrological approach involving chemical analyses and X-ray maps was used to analyze the micrometric metamorphic minerals. The P-T conditions of the greenschist facies metamorphic event were estimated by an inverse multi-equilibrium thermodynamic approach. The results, 280±30°C and 7±1kbar, suggest that the rocks of the Pengguan massif were exhumed from ca. 20km depth. Our results underline the importance of the thrusting component in the long-term behavior of the Beichuan fault and provide a minimal depth at which the fault is rooted. In situ laser ablation 40Ar/39Ar dating of metamorphic white mica revealed that the greenschist overprint occurred at 135–140Ma.The Pengguan massif was therefore partially thrusted along the Beichuan fault during the Lower Cretaceous, long before the Eocene-Miocene exhumation phase which is well-constrained by low-temperature thermochronology. Our results provide the first independent depth information for the exhumation history of the Pengguan massif and reveal a previously undocumented Lower Cretaceous tectonic event that marks the onset of the thick-skinned deformation in the external domain of the Longmen Shan (East of the Wenchuan Fault).

Controls of Late Jurassic-Early Cretaceous tectonic event on source rocks and seals in marine sequences, South China

Thermal evolution of source rocks and dynamic sealing evolution of cap rocks are both subjected to tectonic evolution. The marine sequences in South China have experienced superposed structural deformation from multiple tectonic events. To investigate the effectiveness of preservation conditions, it is of great importance to understand the controls of key tectonic events on the dynamic evolution of cap rocks. This paper discusses the controls of Late Jurassic-Early Cretaceous (J3-K1) tectonic event on source and cap rocks in marine sequences in South China based on the relationships between J3-K1 tectonic event and the burial history types of the marine sequences, the hydrocarbon generation processes of marine source rocks, the sealing evolution of cap rocks, the preservation of hydrocarbon accumulations, and the destruction of paleo-oil pools. The study has the following findings. In the continuously subsiding and deeply buried areas during the J3-K1 period, marine source rocks had been generating hydrocarbons for over a long period of time and hydrocarbon generation ended relatively late. At the same time, the sealing capacity of the overburden cap rocks had been constantly strengthened so that hydrocarbons could be preserved. In the areas which suffered compressional deformation, folding and thrusting, uplifting and denudation in J3-K1, the burial history was characterized by an early uplifting and the hydrocarbon generation by marine source rocks ended (or suspended) during the J3-K1 period. The sealing capacity of the cap rocks was weakened or even vanished. Thus the conditions for preserving the hydrocarbon accumulations were destroyed. The continuously subsiding and deeply buried areas during the J3-K1 period are the strategic precincts of the petroleum exploration in marine sequences in South China.

Is the Jurassic (Yanshanian) intraplate tectonics of North China due to westward indentation of the North China block?

Terra Nova, 24, 333–338, 2012AbstractThe northern mountains of Beijing are the type locality of the Mesozoic Yanshanian orogen. Our structural study emphasizes the importance of dextral strike‐slip for the formation of this intracontinental belt. The South‐ and North‐directed thrusts are positive flower structures rooted in strike‐slip faults. This transpressional tectonics developed from Late Triassic to Late Jurassic‐Early Cretaceous through three deformation phases coeval with syntectonic sedimentation, separated by two transtensional episodes coeval with magmatism. The Late Jurassic–Early Cretaceous tectonic event is also recognized in several places of North China. Strike‐slip faulting controls the deformation of the northern border of the North China block in the Yanshan‐Yinshan belt. Simultaneously, East‐directed thrusts and folds develop along N‐S elongated ranges in Helanshan, Shanxi highlands and Taihangshan. The Jurassic tectonics of the North China Block is interpreted in a unitary way as the result of the westward underthrusting of the North China block below the Alashan block.

The Structural Framework of the Erlangping Group in North Qinling, Central China

As one major unit of the North Qinling tectonic belt, and being located in the north side of the UHP belt between the Yangtze block and the North China block, the Erlangping Group has become one hot research spot because it still keeps records of both plate and inner-continent evolution histories. Three aspects of the Erlangping Group are reviewed. (1) Research history are concluded into three stages, including the determination of rock assemblages before the late 1980s, the regional metamorphism laws solution in the 1990s, and the formation time and tectonic background discussion in the 2000s. (2) Five major controversies and frontier scientific problems have been offered, such as, the deformation ages determination, the Cretaceous tectonic event definition, the determination of the deformation mechanisms and conditions, the kinematic and dynamic nature of the Zhuyangguan-Xiaguan shear zone, and the reconstruction of the evolution and exhumation history. (3) Structural framework of the Erlangping Group is divided into five parts according to our field and laboratory study, including the Erjingou slab, the Damiao-Wantan shear zone, the Huoshenmiao slab, the Xiaozhai-Erlangping shear zone, and the Baoshuping slab. Only the Xiaozhai-Erlangping shear zone has clear kinematic marks of left lateral slip.

Discovery of a dismembered metamorphic sole in the Saga ophiolitic mélange, South Tibet: Assessing an Early Cretaceous disruption of the Neo-Tethyan supra-subduction zone and consequences on basin closing

Blocks of strongly foliated garnet- and clinopyroxene-bearing amphibolites have recently been discovered in the Saga ophiolitic mélange, South Tibet. The Saga ophiolitic mélange is a sheared serpentinite matrix mélange that crops out along the Yarlung Zangbo Suture Zone (YZSZ), South Tibet. The YZSZ is the youngest and the southernmost of all sutures stretching across the Tibetan Plateau and contains the remnants of the Neo-Tethys ocean that once separated India from the Lhasa block. The garnet- and clinopyroxene-bearing amphibolite blocks are interpreted as parts of a dismembered sub-ophiolitic metamorphic sole. They are made mainly of hornblende, diopside and garnet and were strongly metasomatized during retrogression. Thermobarometry and 40Ar/39Ar dating on hornblende indicate that they were metamorphosed to peak conditions in excess of 12kbar and 850°C between 132 and 127Ma. Major and trace element geochemistry suggest an N- to E-MORB-type protolith, although a back- or inter-arc basin setting cannot be ruled out. This data supports a model in which the back-arc YZSZ ophiolites (central segment) were trapped in a fore-arc setting by the inception of a subduction at the back-/inter-arc ridge. The cause of this important Early Cretaceous tectonic event might be the presence of an oceanic plateau or hot-spot tracks in the Neo-Tethys, the collision of the Lhasa and Qiangtang blocks in the North and/or the onset of northward movement of the Indian continent in the South. The proposed conceptual model provides an explanation for the absence (or rarity) of Late Cretaceous ophiolites along the YZSZ which are mostly of Late Jurassic to Early Cretaceous age.

Alpine tectonic evolution of a Jurassic subduction-accretionary complex: Deformation, kinematics and 40Ar/ 39Ar age constraints on the Mesozoic low-grade schists of the Circum-Rhodope Belt in the eastern Rhodope-Thrace region, Bulgaria-Greece

Deformation of the Circum-Rhodope Belt Mesozoic (Middle Triassic to earliest Lower Cretaceous) low-grade schists underneath an arc-related ophiolitic magmatic suite and associated sedimentary successions in the eastern Rhodope-Thrace region occurred as a two-episode tectonic process: (i) Late Jurassic deformation of arc to margin units resulting from the eastern Rhodope-Evros arc–Rhodope terrane continental margin collision and accretion to that margin, and (ii) Middle Eocene deformation related to the Tertiary crustal extension and final collision resulting in the closure of the Vardar ocean south of the Rhodope terrane. The first deformational event D 1 is expressed by Late Jurassic NW-N vergent fold generations and the main and subsidiary planar-linear structures. Although overprinting, these structural elements depict uniform bulk north-directed thrust kinematics and are geometrically compatible with the increments of progressive deformation that develops in same greenschist-facies metamorphic grade. It followed the Early-Middle Jurassic magmatic evolution of the eastern Rhodope-Evros arc established on the upper plate of the southward subducting Maliac-Meliata oceanic lithosphere that established the Vardar Ocean in a supra-subduction back-arc setting. This first event resulted in the thrust-related tectonic emplacement of the Mesozoic schists in a supra-crustal level onto the Rhodope continental margin. This Late Jurassic-Early Cretaceous tectonic event related to N-vergent Balkan orogeny is well-constrained by geochronological data and traced at a regional-scale within distinct units of the Carpatho-Balkan Belt. Following subduction reversal towards the north whereby the Vardar Ocean was subducted beneath the Rhodope margin by latest Cretaceous times, the low-grade schists aquired a new position in the upper plate, and hence, the Mesozoic schists are lacking the Cretaceous S-directed tectono-metamorphic episode whose effects are widespread in the underlying high-grade basement. The subduction of the remnant Vardar Ocean located behind the colliding arc since the middle Cretaceous was responsible for its ultimate closure, Early Tertiary collision with the Pelagonian block and extension in the region caused the extensional collapse related to the second deformational event D 2. This extensional episode was experienced passively by the Mesozoic schists located in the hanging wall of the extensional detachments in Eocene times. It resulted in NE-SW oriented open folds representing corrugation antiforms of the extensional detachment surfaces, brittle faulting and burial history beneath thick Eocene sediments as indicated by 42.1–39.7 Ma 40Ar/ 39Ar mica plateau ages obtained in the study. The results provide structural constraints for the involvement components of Jurassic paleo-subduction zone in a Late Jurassic arc-continental margin collisional history that contributed to accretion-related crustal growth of the Rhodope terrane.

The Cretaceous tectonic event in the Qiangtang Basin and its implications for hydrocarbon accumulation

The tectonic event during Cretaceous and its relationship with hydrocarbon accumulation in the Qiangtang Basin is discussed based on zircon U-Pb dating and the study of deformation, thermochronology and hydrocarbon formation. LA-ICPMS zircon U-Pb dating indicates that the tectonic event took place during the Early-Late Cretaceous (125–75Ma). The event not only established the framework and the styles of structural traps in the basin, but also led to the cessation of the first hydrocarbon formation and the destruction of previous oil pools. The light crude oil in the basin was formed during the second hydrocarbon formation stage in the Cenozoic, and ancient structural traps formed during the Cretaceous event are promising targets for oil and gas exploration.

Block tilting of the North Provence early Cretaceous carbonate margin: stratigraphic, sedimentologic and tectonic data

AbstractIn the western part of the Castellane tectonic arc, the so-called “ Provence platform area “, corresponding to the foreland of the Alpine nappes (figs. 1–2), is marked by Tithonian-Berriasian shallow water carbonates capped by hemipelagic sediments deposited from the Valanginian up to the Aptian-Albian. A detailed biostratigraphic study of the Berriasian succession, based on calcareous algae and foraminifera, allows us to distinguish a Lower to Middle Berriasian, with Clypeina sulcata, Clypeina isabellae and Holosporella sarda, from an Upper Berriasian with Pfenderina neocomiensis, Danubiella cernavodensis, Falsolikanella campanensis and Macroporella praturloni (fig. 3). We performed a field survey of 30 sites located from Quinson to the west, and Escragnolles to the east (figs. 4–5) including the study of measured stratigraphic sections and the collection of samples for biostratigraphic interpretations. These stratigraphic investigations show that below the Valanginian beds, the Berriasian platfom carbonate succession, is locally incomplete, i.e. Upper Berriasian beds are frequently absent. During the Early and Middle Berriasian, depositional environments are marked by a strong bathymetric instability, with frequent subaerial exposure events, and a significant marine restriction; by contrast, during the Late Berriasian, the overall biological diversity increases and water agitation as well, which means a significant marine opening towards the basin. The Upper Berriasian hiatus is consequently regarded as the result of a Berriasian/Valanginian and/or a lowermost Valanginian erosion (fig. 6). The spatial distribution of complete or truncated Berriasian successions identifies east-west bands, in each band truncated series are located northward and complete series are located southward. Bands are limited by thrust or strip faults interpreted as palaeofaults reactivated during the Alpine orogeny (fig. 7). These fault-bounded blocks, 3 to 10 km in width, known as the Aiguine, La Palud-sur-Verdon, Carajuan-Audibergue and Peyroulles-La Foux blocks, are southerly rotated by 1 to 2o. We regard this structural architecture as the result of basinward tilting of blocks. Due to their rotation, the uplifted parts were eroded whereas the depressed parts were protected against erosion (fig. 8). Such a dynamic behavior reflects a distensive tectonic regime, which has been active at least during the Valanginian, that is after the drowning of the North-Provence carbonate platform. These structural events are considered as the regional expression of the Neocimmerian tectonic phase coupled with an enhancement of the Atlantic rifting. The orientation of the major Alpine structural elements (folds and faults) of the Castellane arc, is mostly inherited from these early Cretaceous tectonic events.

Brittle deformation relating to the Carboniferous–Cretaceous evolution of the Lambert Graben, East Antarctica: A precursor for Cenozoic relief development in an intraplate and glaciated region

Stress inversions of kinematic data measured from brittle deformation structures exposed in the southern Prince Charles Mountains have been carried out to elucidate the drivers of intracontinental deformation responsible for the development of the Lambert Graben, East Antarctica. Four palaeostress fields ( D1– D4) were identified from these data, which when coupled with pre-existing geochronological and sedimentological evidence, provide a clear deformation framework. The architecture of the Lambert Graben is dominantly defined by north–south trending D2 and northeast–southwest trending D3 faults that formed respectively during: (1) Carboniferous–Permian intracontinental extrusion and (2) Cretaceous transtensional tectonics related to the dispersion of East Gondwana. Interestingly, sub-ice topography in the southern Prince Charles Mountains and further south towards the Gamburtsev Mountains is defined by bedrock lineaments that parallel the orientations of the main fault arrays. Previous work shows that the development of relief in the southern Prince Charles Mountains is Tertiary in age and probably not associated with Carboniferous–Permian or Cretaceous tectonic events. Based on a clear spatial link between the orientations of faults and bedrock lineaments, we suggest that inherited fault zones were integral in accommodating uplift driven by plate flexure as a response to crustal unloading during glacial incision.

Linking the Sulu UHP belt to the Korean Peninsula: Evidence from eclogite, Precambrian basement, and Paleozoic sedimentary basins

Considerable debate on whether and how the Sulu Orogenic Belt extends eastward to the Korean Peninsula has remained over the past decade. New results reported here include the following: (1) an eclogite and retrograded eclogite-bearing complex (Hongseong Complex) is discovered in South Korea, in which the eclogite occurs as lenses in circa ∼ 810–820 Ma granitic gneiss. SHRIMP zircon dating of the eclogite yields ∼ 230 Ma for the metamorphic age and ∼ 880 Ma for the protolith age; (2) The basement of the Rangnim, Gyeonggi and Yeongnam massifs have affinities to the basement of the North China Block (NCB). However the Gyeonggi Massif encloses a minor amount of large or small slabs of the Hongseong Complex that are similar to the rocks of the Sulu Belt. (3) Two main Paleozoic basins within the Rangnim and Gyeonggi massifs have a similar Paleozoic tectono-stratigraphy to the NCB. (4) The Imjingang and Ogcheon belts do not exhibit any metamorphic characteristics of collisional orogenic belts. Based on these facts, we propose a crustal-detachment and thrust model and suggest that the collision belt between the Yangtze Block (YB) and NCB (Sino–Korea Craton) is preserved along the western margin of the Korean Peninsula. The lower part of the UHP metamorphosed lithosphere of the YB was subducted under the Korean Peninsula and not uplifted to the surface. The lower crust of the YB (the Hongseong Complex) was detached from the subducted lithosphere and thrust over the Korean Peninsula, and inserted into the basement rocks of the Gyeonggi Massif. The upper crust of the YB possibly was detached from the lower crust and overthrusted along the Honam and Chugaryong shear zones. The Imjingang and Ogcheon belts possibly represent the detached upper crust of YB and their present occurrences are controlled by a Mesozoic strike–slip shear structure. All these detached lower and upper crustal slabs were strongly deformed during the Late Jurassic and Early Cretaceous tectonic event leading to their present geological distribution and characteristics.

Delimitation of the Paranapanema Proterozoic block: A geophysical contribution

This study focuses on the basement structure of the Parana Basin in South America, based on geological and geophysical data. It is a large intracratonic basin formed from the Late Ordovician until the Cretaceous, when a sequence of continental flood basalts eruptions covered the entire basin, preceding the break-up of Western Gondwana. Isostatic modeling was applied to large gravity surveys comprising more than 12,000 gravity stations. The residual Bouguer anomaly pattern, representing the crustal contribution of the crystalline basement, as well as the sedimentary and volcanic layers of the basin, reveals similarities between the basement gravity signature and the exposed rock. The stress patterns of the Late Ordovician and Cretaceous tectonic events present a geographically coincident maximum, and the correlation between gravity highs and the main attenuation (beta factor) suggests the presence of some preexistent suture zones. The resultant mosaic of gravity blocks and the location of major faults give support to the presence of an important Proterozoic cratonic feature, here referred to as Paranapanema block.

The early Ordovician Majiagou reservoir of the Jingbian Field, Northwest China: Karstic peritidal dolomite

The Jingbian Field is located in the central part of the Ordos Basin in the west part of the North China Platform. It is the largest gas field discovery in China in the 1980’s. The field is an example of production from a paleogeomorphic trap formed by karstification of Lower Ordovician peritidal dolomites. In terms of gas potential, the Majiagou Formation is the more important stratigraphic unit. It is composed of six members, the uppermost member (O1m6) has been largely removed by prolonged Caledonian karst erosion, leaving the underlying (O1m5) member to provide the main pay for the field. In spite of the 163 wells drilled the field presents many problems and uncertainties because of the poor seismic definition of the pay zones and the great reservoir heterogeneity of the karst system. Statistical data from more than 30 wells show a poor correlation between individual well-flow rates and thickness of the karstic zone or distance of wells, relative to a paleeochannel. This suggests karstification is not the most important factor controlling productivity. The release of organic acids (during maturation of the source rock) and fracturing in response to Cretaceous tectonic event appear to be key factors responsible for the productivity of the Majiagou-5 (O1m5) reservoir in terms of modifying and enlarging the pore network. Carboniferous clays provide an effective updip seal through the infill of karst-breccia zones. High productivity is prominent along structural axes where karstic fractures, solution vugs and caverns are interconnected by vertical to sub-vertical fractures. On the basis of pore-type the Majiagou-5 Member reservoirs can be divided into four reservoir types, each allowing differentiation of reservoir quality through characteristic porosity-permeability ranges and capillary-pressure curves. Key aspects which affect the commerciality of the field are still uncertain but with recent test wells producing gas with water, considerations should focus on the mechanism of weak edge-water drive and the need to predict fracture zones.