Regional Tectonic Activity Research Articles

Oxygen level, primary productivity, and water turbulence during the OAE2 interval of Zagros Basin (SW Iran): Benthic foraminiferal variations in the carbonate microfacies

Cenomanian/Turonian boundary (upper Sarvak Formation) benthic foraminiferal assemblages were analyzed to reconstruct oxygen level, primary productivity, and water turbulence in the Izeh Zone, Zagros Basin. The interplay between environmental perturbations during the Oceanic Anoxic Event 2 (OAE2) and regional tectonic activities in the Zagros Basin resulted in formation of various benthic foraminiferal assemblages in the study section. The OAE2 interval at the region of study starts with extinction of rotaliporids at the onset of δ13C positive excursion (peak “a”), which is associated with population of infaunal benthic foraminifera (especially Bolivina alata). The following interval at the onset of Whiteinella archaeocretacea Biozone is characterized by the total absence of benthic taxa and dominance of planoheterohelicids (“Heterohelix shift”) in the black shale strata, indicating expansion of oxygen minimum zone and unhospitable conditions for both benthic and planktic foraminifera. The upper part of OAE2 interval (including δ13C peaks “b” and “c”) coincides with harbinger of Neo-Tethys closure in the Arabian Plate, causing a compressional tectonic regime, and creation of uplifted terrains in the basin. The relative sea level started to locally fall in this succession, which was accompanied by a better ventilation of seafloor, lower TOC contents, and reappearance of benthic foraminifera.

WATERSHED TOPOGRAPHIC CHARACTERISTICS AND CAUSES ANALYSIS OF THE UPPER REACHES OF THE WEIHE RIVER

Abstract. The morphology of watershed is the most intuitive information carrier to reflect regional tectonic activity, surface erosion and morphologic evolution. Active tectonic and fluvial system play a significant role in patterns and characters of regional morphology. Taking twenty-nine tributaries of the upper reaches of the Weihe River as the main study objects, four parameters, such as gully density (GD), basin topography ratio (BTR), roundness ratio (RR), river longitudinal profile fitting exponent (RLPFE), etc., were used to quantitatively analyse the topographic characteristics in this area. To reveal the main cause of the characteristics, the hypsometric integral (HI) were also applied in this area. The results showed that: (1) There is a positive linear function between basin topography ratio (BTR) and mean slope, and the mean values of four indexes in northern channels are smaller than southern channels; (2) The mean HI value is 0.44, indicating that the main topographic characteristics of this area is in maturity, which is in the transitional period of adjustment of the deep erosion and uplift movement; (3) The main cause of this topographic changes is tectonic. These results are consistent with other geological background, and will enrich regional basin morphology research and tectonic activity evaluation, provide important basic data for regional disaster prediction and analysis of soil and water loss.

Geophysical responses and possible geothermal mechanism in the Gonghe Basin, China

In Qinghai Province of China, the Gonghe Basin is characterized as a potential hot dry rock (HDR) area due to the high heat flow rate and high-temperature records from several springs and drillings. However, the regional geothermal mechanism is still disputable and then essential to be discussed for the HDR exploration strategy, even for analysis in other areas. Geophysical methods are useful tools of analysing regional tectonic activities and geological structures, which are related to heat generation and conduction. In this paper, we mainly focus on the geophysical data within different scales. Firstly, we mapped the epicentral distribution along a profile covering Qinghai-Tibetan Plateau and the north part of India. This result shows that the Gonghe Basin was in a relatively stable area where less earthquake happened in deep zones (> 40 km). The geothermic mode should be thereby different from another geothermal field Yangbajain, which has a high frequency of earthquake events in deep zones (> 40 km). Secondly, we focus on the area of the Gonghe Basin and its surrounding area. By using the gravity and magnetic data, we estimated the Moho depth and Curie point depth through the Park-Oldenburg algorithm. The results indicate that the Gonghe Basin was at the gravity gradient zone without noticeable depth gap of Moho interface. The regional aeromagnetic data along with the Curie point depth was in a different trend. The high-value magnetic zone covers the major part of the Triassic igneous rock area. In this case, the heat from the deep zone (> 30 km) might not be the major contributor to the HDR forming here. Referred MT, seismic inversion results, we integrated all geophysical results. Based on this, a conceptual model in the Gonghe basin was then put forward. The low resistivity zones such as the magma capsules or melted granites in the upper-crust might be the significant heat resource for the HDR, although those from lower crust, mantle and the igneous rocks might make some contributions. The heat was conducted through the near-ground fractures and make the Gonghe Basin as a potential geothermal area, also validated by other geochemical evidence.

Facies analysis and depositional environments of the Miocene syn-rift carbonate–siliciclastic rock packages in the northwest Gulf of Suez, Egypt

The Miocene sedimentary successions in the northwest Gulf of Suez allow insight into the syn-rift deposition. These rocks are subdivided into three formations, namely the Sadat Formation coeval with the Gharra Formation (Early Miocene), the Hommath Formation (Middle Miocene), and the Hagul Formation (Late Miocene). The Miocene rocks in the study area are dominated by carbonate-siliciclastic packages. Detailed microfacies analysis permit discrimination of 14 sedimentary microfacies types, which are represented by continental quartz-arenites and sandy siltstones, as well as shallow-marine gypsiferous laminated shales, litharenites, dolomicrites, wackestones, wacke-/packstones, packestones, pack-/grainstones, ooidal/pelloidal pack-/grainstones, grainstones, rudstones, framestones, and bindstones. These microfacies types are stacked into four facies associations that represent fluvial, and inner ramp, shallow marine environments (facies associations for the later are restricted lagoonal/tidal flat, shoal bar, and open-lagoonal/reefal). In terms of sequence stratigraphy, it is possible to distinguish five depositional sequences in the studied Miocene succession. The retrograditional package displays predominance of open lagoon/reefal facies. The aggradational package shows increase in restricted lagoon tidal flat and shoal bar facies. The progradational package marks occurrence of continental (fluvial) facies. The regional tectonic activity related to the rifting of the Gulf of Suez was the leading control of the Miocene sedimentation in the study area.

Minerálne zloženie metapelitovej a metapyroklastickej zložky kryštalických vápencov z lokalít Lubeník a Ochtiná (Slovenská republika)

Crystalline limestones from the localities Lubeník and Ochtiná (Slovak Republic) have been formed by recrystallization of limestones enriched by basaltic tuffogenic material and a minor pelitic component. The regional metamorphism and tectonic activity associated with Alpine orogennesis resulted in origin of various color and textural varieties of crystalline limestones. The recrystallized tuffogene-pelitic material was transformed into the laminar arrangement in crystalline limestones. The original clay-like pelitic component has probably been entirely recrystallized into muscovite. Higher contents of Fe (0.286 - 0.302 apfu) and Mg (0.342 - 0.396 apfu) are present in muscovites from Lubeník compared to those from Ochtiná. Recrystallized tuffogenic material is represented by epidote, titanite, magnetite and fluorapatite inclusions in muscovites. Quartz and albite form part of a calcite matrix in the crystalline limestones.

The Hettangian–Early Pliensbachian Evolution Phase of the Anabar–Lena Sedimentary Basin, Nordvik Facies Region

New data on the structure and formation conditions of the Anabar–Lena sedimentary basin in the Nordvik facies region at the beginning of the Early Jurassic (Hettangian–early Pliensbachian) are presented. Based on a detailed lithofacies analysis, coastal-continental, coastal-marine, and shallow-marine sedimentation conditions were reconstructed. Ichnofacies studies were carried out for the first time: various traces of the vital activity of organisms identified as Scolithos and Cruziana ichnofacies were identified. An analysis of the relationship between individual lithofacies and their associations made it possible to identify a series of different rank cyclites in the section. In the general regressive series, six decameter-scale cyclites corresponding (except the basal, regressive migration regime of cyclogenesis) were established. They are characterized by an asymmetric internal structure, reflecting periods of coastline migration. The reconstructed model of the sedimentary sequence allows one to trace temporal changes in the sedimentation conditions and identify the main events in the sedimentary basin. It is established that the main Early Jurassic evolution phases in the western part of the Anabar–Lena paleobasin are reflected in the structure of the section and are caused by the alternation of transgressive and regressive periods against the background of a gradual attenuation of the regional tectonic activity. The results obtained allow us to significantly refine our understanding of sedimentation evolution in the Anabar–Lena basin. The revealed cyclical nature of the Lower Jurassic sequence can be used for the regional lithostratigraphic correlation.

Clay mineralogy of the upper Miocene-Pliocene red clay from the central Chinese Loess Plateau and its paleoclimate implications

Study of clay mineral is one of effective methods for reconstruction of the paleoclimate and paleoenvironment. Here we represent clay mineral records from an upper Miocene–Pliocene red clay succession in the central Chinese Loess Plateau (CLP). On the basis of the existing age model, we employ X-ray diffraction and scanning electron microscopy to carry out clay mineral analyses, the results indicated that illite was the dominant clay mineral and the contents of smectite, chlorite and kaolinite were minor. From the analysis of contents of clay minerals, illite crystallinity, illite 5 Å/10 Å, smectite/(illite+chlorite) ratio, magnetic susceptibility, summer monsoon intensity and deep-sea δ18O values, the paleoclimatic evolution between 7.5 and 2.6 Ma can be divided into three intervals: interval I, from 7.5 to 6.9 Ma, it was cool and dry; interval II, from 6.9 to 4.1 Ma, was cool-warm oscillations; interval III, from 4.1 to 2.6 Ma, was significantly warm and humid stage of the seasonal climate conditions. The proxy records display a large amplitude transition in the later interval III, from 2.8 to 2.6 Ma, which implied an abrupt climate and environment variability. Through comparison the local and global paleoclimatic records, we found that clay minerals reflect regional paleoclimatic change superimposing global climatic records during the late Miocene–Pliocene period. We conclude that the regional tectonic activity and global cooling had affected East Asia Monsoon, which was characterized by the different temperature and precipitation in the central CLP.

Zircon U-Pb chronology and provenance of the Paleogene sandstones in the Nima basin, Tibet: implication for coeval paleogeography

Nima basin which is located in the Bangongco suture was surrounded by several thrust faults and its paleogeographical features and tectonic evolution process can be restored by the Paleogene sediments. Based on the methods of petrology, sedimentology, and zircon chronology, the features of provenance, paleogeography and tectonic activities of the Nima basin were analyzed through studying its Paleogene section. The compositional characteristics of sandstones, paleocurrent direction, and zircon U-Pb chronology indicate that the adjacent terranes and the thrust belts in the suture zone are the provenance areas for Nima basin. Qm-F-Lt, Qt-FL triangular diagram shows that the component of sandstones mainly belongs to the recycling orogenic zone, and indicates that the southern depression experienced intensive tectonic activities during the Paleogene period. Based on the characteristics of heavy minerals and sediments, the tectonic evolution of the south depression of Nima basin can be divided into four stages: the stable stage in Early Eocene, the strong active stage in Late Eocene, the highly stable stage in Early Oligocene, and the highly active stage in Late Oligocene. The collision between the Indian plate and Eurasian plate in the Early Cenozoic period led to the crustal shortening and uplifting of the Nima basin and the reactivating of the thrust fault system. The ancient river system which developed due to the uplift of the surrounding terrain and the strong tectonic orogeny provided debris deposits to the sedimentary center of the ancient lake, and therefore the coarse debris of fan delta develops on the edge of the steeper terrains of the lakes. The southern Nima basin eventually evolved into an independent sedimentary depression with multi-directional source and its paleogeography feature depended on the regional tectonic activity.

The Silurian red beds of Tarim Basin: Signals of palaeoenvironment, palaeoclimate, and sea‐level change

The Silurian red beds of the Tarim Basin were formed in a coastal tidal and fluvial delta environment. They consist of red mudstone layers of the lower Tataaiertag Formation and separate the grey‐green muddy sandstones of the Kalpintag Formation from the red sandstones of the upper Tataaiertag Formation. These mudstones are regarded as the most important regional seal for Silurian oil reservoirs. They contain a significant record of palaeoenvironmental and palaeoclimate changes which is related to global sea‐level changes. Based on a systematic and continuous sedimentary study and multiple geochemistry analyses of samples taken from the Sishichang outcrop profile in west of the Tarim Basin, the Early–Middle Silurian palaeoclimate and sea‐level curve have been reconstructed. The Early–Middle Silurian Tarim Basin encountered five intervals of climate change, from humid transitioning to semi‐humid and dry–hot climate which shows signs of generally increasing oxidation. The reconstructed sea‐level curve indicates five sea‐level cycles throughout the Early–Middle Silurian succession. The most significant sea‐level drop occurred during the early Telychian stage, which represents the onset of the red mudstone section of the Tataaiertag Formation. This new sea‐level curve shows some differences compared with the earlier proposed global sea‐level curves. The dry–hot climate occurred during the late Telychian stage and the beginning of Wenlock age. The Early–Middle Silurian sea‐level change of the Tarim Basin was mostly synchronical to the eustacy. However, regional tectonic activities during the early Telychian stage further enhanced the effect of the global sea‐level fall and lead to a dry–hot climate trend which also caused the creation of the red beds of the Silurian period.

Controlling factors on the formation and distribution of “sweet-spot areas” of marine gas shales in South China and a preliminary discussion on unconventional petroleum sedimentology

Shale gas resources in China are abundant with the marine shales accounting for the largest proportion, i.e. 13 × 1012 m3. The Wufeng-Longmaxi Shale system deposited across the Late Ordovician and Early Silurian transition in South China is currently the target for shale gas exploration and development in China. Its annual output in 2018 reached 10.8 × 109 m3, making China the largest shale gas production region outside North America. Within this shale system the sweet-spot intervals of shale gas formed vertically and sweet-spot areas of shale gas formed regionally. The sweet-spot intervals occur mainly at the bottom of the Wufeng-Longmaxi Shale and are 10–40 m in thickness. The sweet-spot interval is characterized by high total organic carbon (TOC) and gas contents, relatively high porosity, high brittle mineral content, and abundant lamination fissures and fractures. The formation of shale gas sweet-spot intervals is mainly controlled by four factors in South China. They are anoxic shelf environment, abundant nano-pores in organic matter, sealed roof and floor strata, and abundant lamination and high silica content in shale, respectively. As the regional extension of the sweet-spot intervals, the formation of the sweet-spot area requires all the controlling factors for the sweet-spot interval. It was “born” in regional anoxic shelf with stable tectonics and “preserved” in relatively stable tectonic zones. Three sweet-spot areas are identified for the Wufeng-Longmaxi Shale in South China, i.e. Fuling, Weiyuan-Fushun-Yongchuan and Changning-Zhaotong areas. The total area is about 2 × 104 km2 with technically recoverable resources of 3.3 × 1012 m3.In addition, with the rapid progresses of exploration and development of unconventional petroleum resources such as shale gas, the petroleum industry around the world extends to unconventional petroleum resources, gradually accomplishing an important change of petroleum geology research focus from conventional to unconventional. Unconventional petroleum geology research focuses on continuously or semi-continuously distributed sweet-spot areas, for which the formation would be the result of coupling sedimentology from several geological events such as global or regional tectonic activity, volcanic eruption, climate change, anoxic water, biotic mass extinction and radiation, and gravity current. It is necessary to innovatively construct new insights of unconventional petroleum sedimentology in order to enrich and improve the petroleum sedimentology research and its application. Therefore, the concept of unconventional petroleum sedimentology is proposed, and its research task, method, aim and importance are preliminarily discussed.

New paleomagnetic constraints on rift basin evolution in the northern Himalaya mountains

The late Cenozoic sediments in the rift basins in the northern Himalaya Mountains document important information about the uplift and deformation of the most active tectonic region in the Tibetan Plateau. However, these sediments have not been precisely dated, hindering our ability to address the basin development and termination associated with a series of uplifts in the southern Tibetan Plateau. Here, we report a detailed magnetostratigraphic study on the fluvio - lacustrine sedimentary sequence of the Dati Formation bearing abundant Hipparion forstenae fossils in the Dati Basin in the northern frontal region of the Himalaya Mountains. The 195 m – thick section yielded six normal and seven reversed polarity zones that correlate well with Chrons C3An.1r to C4r.2r of the geomagnetic polarity time scale, constraining the section age to ~8.6 – ~6.2 Ma. Together with the magnetostratigraphic results from other rift basins in the region, these results indicate that the horizons bearing the Hipparion fossils were deposited during the age interval of 7.1–6.5 Ma in the northern Himalaya Mountains. The regional tectonic activity and comprehensive magnetostratigraphic and sedimentologic comparisons suggest that the evolution of the rift basins in the northern Himalaya Mountains has involved three major stages since the late Cenozoic, i.e., (1) ~10.0–8.0 Ma, onset of the basins with fan delta facies; (2) ~8.0–3.0 Ma, expansion of the basins with mainly lacustrine facies; (3) ~3.0–1.7 Ma, shrinking and termination of the basins with alluvial fans. The basin evolutionary history indicates an accelerated tectonic uplift of the Himalaya Mountains at ~10.0 Ma, and two deformational events at ~3.0 Ma and at ~1.7 Ma.

The effect of tectonism on deltaic wetland migration: A case study from Bendimahi River Delta System (Lake Van-Eastern Turkey)

Coastal wetlands are in decline globally because of climatic and/or hydrological changes, and anthropogenic activities. Deltaic wetlands are complex environments formed by different water sources, particularly when ionically rich soda water and freshwater and converge and influence the presence and diversity of biological activity. Lake Van is a terminal lake, 1650 meters above the sea level, surrounded by high mountains. Because of its alkaline water, vegetation and biological activity are generally rich in the deltaic areas. In this study, geological evolution of Bendimahi River Delta System, located on northeastern part of the Lake Van, is assessed as to constructive and destructive temporal factors, determined with satellite images and field studies. Bendimahi river channel is significantly deformed by regional tectonic activity and this deformation has caused migration of deltaic wetland. That migration process has resulted in abandoned deltaic area and a new delta formation. Hydrological and biological results of the migration of the Bendimahi River Delta System clearly indicate the importance of wetlands on coastal ecology, especially alkaline lakes.

Petrogenesis of Volcanic Arc Granites from Bayah Complex, Banten, Indonesia

This research aimed to reveal the petrogenesis of granitic rocks of Bayah Complex starting from magma differentiation to exposing event, this research also intended to determine the tectonic environment. The methods carried out in this research include field observation, petrographic analysis using polarized light microscopy, and geochemical analysis using X-Ray Fluorescence (XRF) and Inductively Coupled Mass Spectrometry (ICP-MS).
 Petrographic analysis shows that Bayah granitic rocks are composed of quartz, plagioclase, and K-feldspar while the rest are amphibole, biotite, sericite, chlorite, epidote, and opaque. Based on its major oxide concentrations, Bayah granitic rocks classified as granite and diorite-quartz which have high-K calc-alkaline magma. 4 samples of granitic rocks showed the A/N+K+C > 1 molar ratios belonging to the peraluminous S-type granite index while the remaining 1 sample showed a molar ratio of A/N+ K+C < 1 and A/N+K > 1 which classified as metaluminous I-type granite. Accordingly, Bayah granitic rocks are S-type granite which crystallized from sediment-derived magma, the sediments itself estimated sourced from continental especially Malay Peninsula, Indonesian Tin Island, and Schwaner Mountains. During differentiation, the magma undergone crustal contamination reflected by the increase in both SiO2 0.51 wt% and Al2O3 1.95 wt%, and decrease in Fe2O3 + MgO 0.61 wt% from the pure composition of sediment-derived magma. Furthermore, the occurrence of crustal contamination also recognized from high concentrations of Rb and Ba which indicate the interaction of magma with the materials of continental crust.
 Regard to the exposing event, Bayah granitic rocks approximated to be exposed due to regional tectonic activity which caused Orogenesa I in the Early Oligocene to the Late Oligocene. Moreover, based on the plot of trace elements especially Rb, Y, Nb, Ta, and Yb on Harker and tectonic discriminant diagrams, Bayah granitic rocks are formed on volcanic-arc active continental margins in accordance with regional tectonic setting.

Spatial distribution pattern of channel steepness index as evidence for differential rock uplift along the eastern Altun Shan on the northern Tibetan Plateau

Abstract The eastern Altun Shan is a crucial part of the Altun orogenic belt within the Tibetan Plateau. Study of the uplift rate and the related features in this area provides important clues for understanding the uplift mechanism of the Tibetan Plateau as a whole. As an important geomorphic element in landscape development, the fluvial system can record the relationship between tectonic activity and climatic change. In recent years, studies of the Channel Steepness Index Ksn, have been conducted by many researchers, using the geomorphological model of equilibrium channel longitudinal profiles, combining bedrock uplift and river incision and thus making it possible to extract rock uplift history from river profiles. This research show that regional rock uplift rate is a major factor in affecting the Ksn index. Regional tectonic activity and intensity, therefore, can be evaluated from variation in the Ksn index, which can provide a sensitive measure of uplift rate. In this paper, the Digital Elevation Map ‘ASTER GDEM’, with a spatial resolution of 30 m, was utilized as basic data, and combined with ArcGIS and MATLAB software to extract the Ksn index from the equilibrium channel longitudinal profiles model. Meanwhile, we employed statistical methods to analyze the Ksn index. Our results suggest that averaged Ksn indices, obtained from the subrange A，B，C，D, and E of the eastern Altun Shan (from west to east), are 70.93, 139.03, 108.85, 134.44 and 165.39, respectively. Further analysis implies that the variation in this index can be correlated with the distribution pattern of uplift rates within different regions. Its value increases gradually from west to east, reflecting regional uplift rate. Along the western section of the eastern Altun Shan, the uplift rate is slower and characterized by strike-slip movements, while its eastern part has uplifted faster and is controlled by thrust fault systems. Moreover, in contrast with the southern Altun Shan, the uplift rate of the northern part is high. These variations in uplift rate seem to be linked with “the imbricated thrusting transformation-limited extrusion model” of the Tibetan Plateau. Our results can be correlated with previous work on the active characteristics along the eastern Altyn Tagh Fault (ATF).

CH4and CO2Emissions From Mud Volcanoes on the Southern Margin of the Junggar Basin, NW China: Origin, Output, and Relation to Regional Tectonics

AbstractThe concentrations, isotope ratios, and fluxes of CH4and CO2from mud volcanoes measured during a field survey on the southern margin of the Junggar Basin are reported. The origins and outputs of CH4and CO2from the four mud volcanoes are assessed, and the relationship between the characteristics of degassing and regional tectonics is discussed. The geochemical data indicate that thermogenic gases derived from the hydrocarbon reservoirs beneath anticlines could be the main source of the CH4emitted from the mud volcanoes and that hydrocarbon degradation by microbes and carbonate decomposition could be the primary contributors to CO2emissions from the soil in and around the mud volcanoes. Microseepage was the main mode of release for CH4and CO2from the mud volcanoes. The total CH4output from the mud volcanoes was 147.83 ton/year, comparable to that from mud volcanoes elsewhere. The total output of CO2from the mud volcanoes was 603.96 ton/year, which suggests that more attention should be paid to CO2from mud volcanoes. The CH4and CO2outputs from the mud volcanoes, and from the Xihu fold in the four anticlines, decreased from south to north. This observation is consistent with the intensity of regional tectonic activity, which weakens from south to north. The results suggest that regional compression is the major triggering mechanism for CH4and CO2emissions from the mud volcanoes.

Structural geology and favorable exploration prospect belts in northwestern Sichuan Basin, SW China

The northwestern Sichuan region has experienced multi-stage tectonic evolution including marine cratonic basin from the Sinian to the Middle Triassic and intra-continental basin from the Late Triassic to the Cenozoic. Several regional tectonic activities caused complicated stratigraphic distribution and structural deformations in the deep-buried layers. During the key tectonic periods, some characteristic sedimentary and deformation structures were formed, including the step-shaped marginal carbonate platform of Dengying Formation, the western paleo-high at the end of Silurian, and the passive continental margin of the Late Paleozoic–Middle Triassic. The Meso-Cenozoic intra-continental compressional tectonic processes since the Late Triassic controlled the formation of complex thrusting structures surrounding and inside the northwestern basin. The northern Longmenshan fold-thrust belt has a footwall in-situ thrust structure, which is controlled by two sets of detachments in the Lower Triassic and Lower Cambrian and presents as a multi-level deformation structure with the shallow folds, the middle thin-skin thrusts and the deeper basement-involved folds. The thrust belt in front of the Micangshan Mountain shows a double-layer deformation controlled by the Lower Triassic salt detachment, which is composed by the upper monocline and deep-buried imbricate thrust structures. The interior of the basin is characterized by several rows of large-scale basement-involved folds with NEE strike direction. From the perspective of structural geology, the favorable exploration reservoirs and belts in northwestern Sichuan have obvious zoning characteristics. The favorable exploration layers of Dengying Formation of Upper Sinian are mainly distributed in the eastern and northern areas of the northwestern Sichuan Basin, in which the Jiulongshan structural belt, Zitong syncline and Yanting slope are the most favorable. The Lower Paleozoic was transformed by Caledonian paleo-uplift and late Cenozoic folding, and the midwest area such as the Zitong syncline is a potential area for hydrocarbon exploration. The favorable part of the Upper Paleozoic is mainly distributed in the northern Longmenshan belt and its frontal area, where the deep-buried thin-skin thrust structures in the footwall are the key exploration targets.

Long-term shoreline shifts on continental blocks during the Bajocian: an updated interpretation based on synthetic stratigraphical and palaeogeographical developments on regional scales

Abstract Available reconstructions of Jurassic global sea level changes differ and are in need of an update. New stratigraphical charts and palaeogeographical developments for a number of large continental blocks or their portions of these (e.g., Germany, India, northeast Africa, northwest Australia, the Russian Platform and western Siberia) reveal regional long-term shoreline shifts (i.e., transgressions and regressions) during the Bajocian Stage (168.3–170.3 Ma). A comparison of these allows to document only a single coherent feature, namely the earliest Bajocian transgression, in the majority of the continental blocks considered. Undoubtedly, this event was triggered by a eustatic rise. However, long-term shoreline shifts were either weak to absent or differed between the blocks during almost the entire Bajocian, thus providing evidence of the apparent stability of global sea level and the importance of regional tectonic activity as a control mechanism on particular transgressions and regressions. Interestingly, it appears that the earliest Bajocian eustatic rise was a constituent of a long-term eustatic pattern; the nature of this event has yet to be fully understood. Generally, the findings presented here are in better agreement with Anthony Hallam’s view of Jurassic eustasy and question some other global sea level reconstructions.

Co- and post-seismic Deformation Mechanisms of the MW 7.3 Iran Earthquake (2017) Revealed by Sentinel-1 InSAR Observations

The extraction of high-accuracy co- and post-seismic deformation fields and inversions of seismic slip distributions is significant in the comprehension of seismogenic mechanisms. On 12 November 2017, a MW 7.3 earthquake occurred on the border between Iran and Iraq. To construct the co-seismic deformation field, Sentinel-1A synthetic aperture radar (SAR) images from three tracks were used. Based on a prior knowledge, least-squares iterative approximation was employed to construct the three-dimensional (3D) co-seismic deformation field. to derive a time series of 2D post-seismic deformation, the multidimensional small baseline subset (MSBAS) technique was use. Co-seismic deformation fields were asymmetric; the maximum relative displacement was nearly 90cm in the radar line-of-sight between two centers of co-seismic deformation. The 3D co-seismic deformation field showed southwestward horizontal motion and continuous subsidence-to-uplift variation from northeast to southwest. The two-dimensional (2D) post-seismic deformation time series showed a gradual decaying trend and good correspondence with the aftershock distribution. The main mechanism of post-seismic deformation was an afterslip of the post-seismic faults. We used the elastic half-space model to invert co-seismic deformation fields and obtain source parameters of the slip model. The maximum and average slips were 2.5 and 0.72 m, respectively. The average slip angle was 126.38° and the moment magnitude was MW 7.34. The results of this study will contribute to research on regional tectonic activities.

Late Cretaceous to early Eocene geological history of the eastern Ionian Basin, southwestern Greece: A sedimentological approach

Sedimentological studies of the Upper Cretaceous–lower Eocene limestones in the western part of the Ionian basin (Araxos area) indicate that these deposits are composed of calciturbidites interbedded with breccia-microbreccia. Breccia - microbreccia deposits are structureless, display channelized geometry with calciturbiditic blocks internally to the channels. Most of the clasts were sourced from the underlying Lower Cretaceous “Vigla limestones”. Calciturbidites include Ta to Te Bouma sub-divisions, and are organized in cycles that form channelized deposits with a high degree of amalgamation. Statistical analysis confirms the presence of order in the sub-division sequence. The thickness of event beds in the studied section shows a lognormal statistical distribution, typical of turbidite successions. Limestone microfacies suggest deep-water deposits and reworked shelf deposits.The intense extensional tectonic activity in the Ionian basin during the Early Cretaceous, with synthetic and antithetic faults, produced active platform margins and asymmetrical grabens. In this regime, large amounts of coarse-grained material became available and accumulated in the basin. High slope gradients led to slumping. During the Late Cretaceous, the uplifted margins of the grabens caused erosion of the pre-existing deposits of the Lower Cretaceous “Vigla Formation”. This event led to the accumulation of channelized microbreccia and breccia units and transport of platform deposits by turbidity currents. The Early Cretaceous to early Eocene depositional history in the Ionian Basin indicates that the regional tectonic activity, rather than the eustatic sea-level changes, was the major factor that influenced the basin evolution, suggesting a syn-rift stage being active from the Jurassic to the early Eocene.

Stratigraphy of the Lungmachi black shales from the Huaying drill core in southwestern China and its palaeogeographic implications

Core samples from the Huaying well, Sichuan Province, have been analyzed for both graptolite biostratigraphy and carbon isotope chemostratigraphy. The result shows a stratigraphic sequence of Lituigraptus convolutus, Stimulograptus sedgwickii and Spirograptus guerichi biozones, and records a strong positive shift of δ13Corg at the base of the Stimulograptus sedgwickii Biozone, which coincides with those from Cornwallis Island (Arctic Canada), Arisaig (Nova Scotia, Canada), and the Barrandian area (Bohemia). Two outcrops were also studied in the Huaying region. The Yanwanggou section shows a continuous, but complicated, stratigraphical sequence, from the upper Katian to the lower–middle Rhuddanian, then a sedimentary hiatus of ∼3.26Ma, and finally a continuous sequence from the upper Aeronian to the lower Telychian, whereas the Liziya section and the Huaying well exhibit significant hiatus, which lasted from Hirnantian to middle Rhuddanian or early Aeronian times. Therefore, the eastern boundary of the Central Sichuan Oldland during the Ordovician and Silurian transition can be precisely constrained to a narrow area between the Huaying well-Liziya section and the Yanwanggou section, which indicates that the Central Sichuan Oldland was much larger than previously considered. The present data also indicate the existing of a so far unidentified stage of the Kwangsian Orogeny, which resulted in the uplift of some portions of the Yangtze Platform region and the consequent delay of the transgression in those places. The multi-stage hiatus, spanning at least from the upper Katian to middle Aeronian in the study area, resulted from a combined effect of the Hirnantian glacio-eustatic sea-level fall and the regional tectonic activity of the Kwangsian Orogeny.