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The northwestern part of Indian plate consists of a number of sedimentary basins such as the Jaisalmer basin with Early Jurassic to Quaternary deposits. The NW-SE trending Kanoi fault and Ramgarh fault with Mari-Jaisalmer Arch in the basin are tectonically active. We delineate the tectonically active areas of the basin by considering watersheds, micro-scale basins and spot locations. Analytic Hierarchy Process (AHP) is applied to calculate the Index of Active Tectonics (IAT) for the watersheds. Basin asymmetry (AF), valley floor width to height ratio (Vf) and hypsometric curve are calculated/generated. Computed R2 values and the IAT identify watershed-4, Miajlai depression, to be tectonically most active. Three individual spots along the NW-trending Mari highland have tectonic control on drainage patters. The hydrocarbon fields are located in the Shahgarh and the Miajlar depression zones within watersheds 3 and 4, which are under tectonically moderate and high activities, respectively. [ABSTRACT FROM AUTHOR]

Three-dimensional coordinate systems define the location of zero-dimensional points. Higher dimensional spatial objects such as lines and planes become apparent from sets of adjacent points. Any point defined in three-dimensional space within a sedimentary basin could be simultaneously located on the surface of a sand grain and a bedding plane in a kilometer-scale fold, and structure at any other scale. Therefore, like many other aspects of geology and geophysics, structural geology is multiscale which is why filtering, smoothing, scale bars and the like are prerequisites for any kind of geological mapping and outcrop imagery. It is argued here that the association of points with higher-dimensional objects that form the spatial building blocks of geology singles out length scale as a geometrical parameter that is fundamental to the definition of an object. Properties such as curvature, porosity, color and so on can only be attributed after location and scale are defined. It is proposed that length scale be treated as a fourth spatial dimension in geological and geophysical applications, on an equal footing to the three spatial coordinate dimensions. The utility of adopting a four spatial dimension approach in geoscience is that it forces length scale to be explicitly specified in descriptions where it is routinely omitted, for example, measurements of structural orientation where a scale parameter greatly simplifies later mapmaking and model building. Taken together with geological time, it is convenient to define geological and geophysical structure in five spacetime dimensions. [ABSTRACT FROM AUTHOR]

This paper summarizes and analyzes the results of long-term field and analytical studies, as well as petroleum-field data (measurements of temperatures and productivity of wells, analyses of the physicochemical properties of hydrocarbons (HCs) and the hydrochemical composition of waters, etc.) for onshore and offshore fields and mud volcanoes in the South Caspian Basin (SCB). In the last 30 years, research has been carried out using the most modern methods: 3D seismic exploration, rock pyrolysis, isotope-geochemical and biomarker studies of organic matter (OM) and HCs, a reconstruction of the thermal history of the basin, basin modeling, etc. The resulting data, taking into account global experience in studying oil and gas systems of other sedimentary basins, formed the basis for the sedimentary-condensation model of the formation of HC fields in the SCB developed by the author. The model uses predictive estimates of the temperatures and phase state of HCs at the base of various stratigraphic complexes. It is shown that, under severe temperature conditions in the basal layers of the sedimentary strata (temperatures of 250–500°С), a gas consisting mainly of methane and water vapor is formed as a result of cracking of liquid HCs. The dominant role of vapor-gas solutions (having an increased ability to dissolve high-molecular OM) in the mass transfer of liquid HCs to traps, accompanied by phase differentiation of the fluid during ascending migration, has been substantiated. Under conditions of a high degree of closure of deeply buried sediments, the main pathways of pulse-injection focused migration of fluids are deep faults, and systems of crevices and channels of mud volcanoes. [ABSTRACT FROM AUTHOR]

The seismic hazard in the İzmit basin, located in Marmara region of western Turkey, is high due to the northern branch of the North Anatolian Fault (NAF) and the potential ground motion amplification that may be caused by local site conditions, sedimentary basin effect as well as fault zone (FZ) induced site effect resulting from the generation of guided waves. In this study, we elaborate the relevance of the FZ-induced site effect in the İzmit basin along a 16.5-km-long N-S profile across the basin and perpendicular to the NAF by time and frequency domain analysis of waveforms obtained from two-dimensional (2D) simulations of viscoelastic wave propagation for a double-couple source at 14 km depth using a reference (basin-only) model and three basin-with-fault models: shallow (6 km), intermediate (12 km) and deep (19 km) FZ models. Our results show that the FZ-induced site effect within and near the northern branch of NAF in the İzmit basin can be very prominent with amplifications of about 5–10 in the frequency range of 0.05–4 Hz and about 20 at frequencies above 2 Hz, respectively. We obtain the most dramatic results for the deep FZ model causing shear- and surface-wave amplifications of about 15 at frequencies higher than 2.5 Hz for the distances between 6 and 13 km. [ABSTRACT FROM AUTHOR]

Rapid urban growth has led to large population densities in foreland basin regions, and therefore a rapid increase in the number of people exposed to hazard from earthquakes in the adjacent mountain ranges. It is well known that earthquake-induced ground shaking is amplified in sedimentary basins. However, questions remain regarding the main controls on this effect. It is, therefore, crucial to identify the main controls on earthquake shaking in foreland basins as a step towards mitigating the earthquake risk posed to these regions. We model seismic-wave propagation from range-front thrust-faulting earthquakes in a foreland-basin setting. The basin geometry (depth and width) and source characteristics (fault dip and source-to-basin distance) were varied, and the resultant ground motion was calculated. We find that the source depth determines the amount of near-source ground shaking and the basin structure controls the propagation of this energy into the foreland basin. Of particular importance is the relative length scales of the basin depth and dominant seismic wavelength (controlled by the source characteristics), as this controls the amount of dispersion of surface-wave energy, and so the amplitude and duration of ground motion. The maximum ground motions occur when the basin depth matches the dominant wavelength set by the source. Basins that are shallow compared with the dominant wavelength result in low-amplitude and long-duration dispersed waveforms. However, the basin structure has a smaller effect on the ground shaking than the source depth and geometry, highlighting the need for understanding the depth distribution and dip angles of earthquakes when assessing earthquake hazard in foreland-basin settings. [ABSTRACT FROM AUTHOR]

The continental shelf adjacent to the municipality of Salvador (CSS), state of Bahia, Brazil, is one of the narrowest in the world (8 km) although it is located in a passive margin. This shelf is also shallow, with low accommodation space and sediment input. During the Quaternary, the area was exposed most of the time to subaerial conditions. This long period of erosion, controlled by the structural and lithological framework of the Cretaceous Northern Camamu Sedimentary Basin, was highly influential on shelf physiography. The paleo relief that was generated, in turn, controlled sedimentation during the sea-level rise since the Last Glacial Maximum (LGM). The present study used high-resolution shallow seismic surveys to investigate the influence of the structural framework of the Northern Camamu Sedimentary Basin on the erosion of CSS during lowstands and on sediment accumulation during highstands. Five seismic units were identified, representing the Crystalline Basement, the Northern Camamu Sedimentary Basin, and the Quaternary Sediments. Bathymetric highs and lows on the shelf are associated, respectively, with antiforms and synforms present in the syn-rift strata of the sedimentary basin. Normal and transfer faults related to the installation of the sedimentary basin controlled the incision of valleys during periods of subaerial exposure. This structural framework still presents a morphological expression on the shelf due to an immensely reduced sediment input, which precluded the burial of these structures. [ABSTRACT FROM AUTHOR]

Many volcanoes are buried within Te Riu-a-Māui/Zealandia sedimentary basins. Based on a large collection of seismic reflection and drillhole data, this paper outlines the morphology, location and age of over 400 volcanoes buried and preserved in offshore New Zealand basins. We discuss the relationships of these volcanoes to the timing and locations of the main tectonic events that shaped Zealandia in the last 105 Myr. Late Cretaceous volcanism mainly formed large (>20 km3) composite cones and volcanic complexes that erupted along rift faults related to the break-up of Zealandia from south-eastern Gondwana. Cenozoic intraplate volcanic activity was widespread, typically forming clusters of scattered small-volume (<1 km3) craters and cones. In contrast, large Cenozoic volcanic complexes, composite cones and shield volcanoes erupted along linear arcs associated with subduction along the Pacific-Australian plate boundary. In detail, the presence of pre-existing structures and types of host rocks also influence the passage of magma in the shallow (<5 km) crust and the location of eruptive centres, regardless the tectonic setting of eruption. Insights from this work demonstrate the value of characterising volcanoes buried in sedimentary basins for improved understanding of the interplay between volcanism and plate tectonics in Zealandia and further afield. [ABSTRACT FROM AUTHOR]

Structures rooted in the crystalline basement frequently control the deformation of the host bedrock and the overlying sedimentary sequences. Here, we elucidate the structure of the c. 2‐km deep Precambrian granitic basement in the Anadarko Shelf, Oklahoma, and how the propagation of basement faults deformed the sedimentary cover. Although the basin is foreland in origin, the gently dipping shelf sequences experienced transpressional deformation in the Late Palaeozoic. We analyse a 3‐D seismic reflection data set and basement penetrating well data in an area of 824 km2. We observe: (a) pervasive deformation of the basement by basement‐bounded interconnected mafic sills, and a system of subvertical discontinuity planes (interpreted as faults) of which some penetrate the overlying sedimentary cover; (b) three large (>10 km‐long) through‐going faults, with relatively small (<100 m) vertical separation (Vsep) of the deformed stratigraphic surfaces; (c) upward propagation of the large faults characterized by faulted‐blocks near the basement, and faulted‐monoclines in the deeper sedimentary units that transition into open monoclinal flexures up‐section; (d) cumulative along‐fault deformation of the stratigraphy exhibits systematic trends that varies with offset accrual; (e) two styles of Vsep—Depth distribution which include a unidirectional decrease of Vsep from the basement through the cover rocks (Style‐1) and a bidirectional decrease of Vsep from a deep sedimentary unit towards the basement and shallower sequences (Style‐2). We find that the basement‐driven propagation (Style‐1) shows greater efficiency of driving the fault deformation to shallower depths compared to the intrasedimentary‐driven fault nucleation and propagation (Style‐2). Our study demonstrates an evolution of cumulative Vsep trends with offset accrual on the faults, and the partial inheritance of the heterogeneous intra‐basement deformation by the sedimentary cover. This contribution provides important insight into the upward propagation of basement‐driven faulting associated with structural inheritance in contractional sedimentary basins. [ABSTRACT FROM AUTHOR]

The Saronikos Gulf hosts the northwestern end of the South Aegean Active Volcanic Arc. It is affected by extensional back-arc tectonism in a prominent N-S direction, while older E-W rifting is also manifested. Recently acquired swath bathymetry and high-resolution seismic profiles led to the precise morphological mapping of five Quaternary continental shelf basins, along with their neotectonic delineations and their cross-correlation to the onshore active fault zones. Aegina and Methana basins, in the southeast Saronikos Gulf, display subsidence along ENE-WSW and NW-SE axes, and continuous marine sedimentation throughout the Upper Quaternary. Salamina basin in the northeast Saronikos Gulf is a shallow, relatively stable sedimentary basin, intermittently connected to the SE and NW Saronikos Gulf through the Aegina-Fleves and the Aegina-Salamina plateau respectively. In the western and most active region of Saronikos Gulf, the onshore E-W–trending faults of Kechrees and Agios Vassileios extend eastwards until the Salamina-Aegina plateau. The Megara basin is WNW-ESE oriented, possibly affected by the N-S Korfos fault valley, which connects the Megara and Epidavros basins. E-W–trending faults tilt the Quaternary sedimentary blocks, in compatibility to the N-S extensional tectonic regime of the adjacent Gulf of Corinth. Prograding clinoforms in the Megara and Epidavros basins reveal an Upper Quaternary-age intermittent connection to the open sea. Mass transport deposits and volcanic flows in-between the Upper Quaternary sediments of the Epidavros basin manifest the 500–400 ka tectonic phase that affected both the NE Peloponnese coast and the active N-S and NW-SE to WNW-ESE striking faults of the Epidavros basin margin. [ABSTRACT FROM AUTHOR]

The seismic structure of the complex underlying the stratified sedimentary cover in the Amundsen Basin in Siberia indicates that the formation of a large-scale rift-related basin lying on a hyper-extended continental crust preceded the spreading process in the Eurasian Basin. [ABSTRACT FROM AUTHOR]

Descriptions of exposed salt structures help improve the ability to interpret the geometry and evolution of similar structures imaged in seismic reflection data from salt‐bearing sedimentary basins. This study uses detailed geologic mapping combined with well and seismic data from the southeastern end of the Gypsum Valley diapir (Paradox Basin, Colorado), to investigate the three‐dimensional geometry of the terminations of both the salt wall and its associated megaflap. The salt wall trends NW‐SE and is characterized by highly asymmetric stratal architecture on its northeastern and southwestern flanks, with thicker, deeper, gently dipping strata in the depositionally proximal (NE) minibasin and thinned older strata rotated to near‐vertical in a megaflap on the distal (SW) side. The megaflap terminates to the SE through a decrease in maximum dip and ultimately truncation by a pair of radial faults bounding a down‐dropped block with lower dips. East of these faults, the salt wall termination is a moderately plunging nose of salt overlain by gently southeast‐dipping strata, separated from the down‐dropped NE minibasin by a counterregional fault. From this analysis, and by comparison with analogue structures located elsewhere in the Paradox Basin and in the northern Gulf of Mexico, we propose a series of simple end‐member models in which salt walls and megaflaps may terminate abruptly or gradually. We suggest that controlling factors in determining these geometries include the original thickness and spatial distribution of the deep salt, the presence of nearby diapirs (which determines the fetch area for salt flow into the diapir), spatial patterns of depositional loading, and variations in the nature and location of salt breakout through the roof of the initial salt structure. [ABSTRACT FROM AUTHOR]

Abstract Tectonic processes from the breakup of Rodinia to Gondwana assembly have been studied on large continents. However, the role of micro-continental blocks in Neoproterozoic supercontinental cycle is barely known. Geochronological and geochemical studies on a combination of 57 (meta-) sedimentary and (meta-) igneous rocks (one igneous rock and four meta-sedimentary samples are from this study) in the Indochina block (including its north part, i.e. the Simao terrane) reveal the paleoposition and tectonic processes during Precambrian supercontinental cycle. A mylonitized monzogranite from the NW part of the Indochina block (the Chongshan area) shows zircon U Pb ages of 867 ± 19 Ma. Precambrian and Early Paleozoic strata share similar zircon U Pb age peaks at ca. 2.5 Ga and ca. 0.95 Ga. The ca. 1.75 Ga age peak in the Precambrian strata is absent in those Early Paleozoic strata. The newly discovered 867 ± 19 Ma felsic intrusion in the Chongshan Metamorphic Belt and the shift of detrital zircon age patterns from the Neoproterozoic to Early Paleozoic confirm the presence of Precambrian magmatic activities in the Indochina block. Paleoposition and magmatic records show the Indochina block should be part of an Andean-type orogeny along the NW margin of the Rodinia during the Neoproterozoic. During the Neoproterozoic to Early Paleozoic, the role of Indochina as a continental block coherent with the Indian Craton at least during the breakup of Rodinia and Gondwana assembly. After Gondwana assembly, the Indochina block, as a section of an Andean-type continental arc along the eastern margin, blocked the exotic inputs and changed the age distribution patterns dramatically. Highlights • Neoproterozoic monzogranite was discovered in the Chongshan Metamorphic Belt in the Indochina block. • Indochina block should be part of an Andean-type orogeny along the NW margin of the Rodinia. • Indochina was coherent with the Indian Craton at least during breakup of Rodinia and Gondwana assembly. • A continental arc blocked the 1.75 Ga exotic inputs in the Early Paleozoic sediments. [ABSTRACT FROM AUTHOR]

Abstract As an important stage in continental rift basin evolution, late syn-rift stage is characterized by the combination of broad crustal subsidence and episodic pulses of extension. Sequence architecture and sedimentary filling process during this period present a certain particularity due to distinctive tectonic subsidence and variable influencing factors. This paper analyzes sequence stratigraphy and sedimentary facies development and their evolution in the Fulongquan Depression, a continental rift basin of the Songliao Basin, and discusses the determinants influencing the sequence architecture and depositional systems evolution. During late syn-rift stage, a major transition in the depositional systems, from predominantly lacustrine and correlated depositional systems to fluvial-floodplain settings, was recorded in the evolution of basin fill. This gradual and slow peneplanation is the final response to the decrease of differential subsidence. The spatial and temporal variability of sedimentary evolution are mainly associated with specific growth history of the major boundary faults. Sequence stratigraphic units recognized in the Fulongquan Depression are likely corresponded to different episodic pulses of extension respectively. Each sequence can be further divided into a lowstand systems tract (LST), transgressive systems tract (TST) and highstand systems tract (HST). Maximum differential subsidence and water deepening mainly occur in the LST. The expanded TST and HST of each sequence tend to be developed in a broader thermal subsidence regime. The depositional systems transition and detrital provenance changes usually occur in the HST. Throughout the late syn-rift stage, in addition to major changes of provenance systems, tectonic movement is likely to be the main factor in controlling the variations of sediment supply. With the decrease of tectonic activity, the impact of climate changes and lake level fluctuations on basin filling tends to be increased. Highlights • Evolution process of the peneplanation in Fulongquan Depression has been rebuilt. • Two types of late syn-rift sequences have been identified. • Different controls and their interactions on sequence architecture and sedimentary evolution were discussed. [ABSTRACT FROM AUTHOR]

Highlights • New bathymetric and seismic data in Skyros Basin, North Aegean Sea • Oblique opening of the Skyros Basin similar to the North Aegean Basin • 19 major active faults that can generate M > 6.0 have been mapped for the first time. • Seismic hazard underestimated, only 3 active faults within the seismic catalogues • Subsidence of the North Aegean Sea is accelerated since Middle Pleistocene. [ABSTRACT FROM AUTHOR]

Abstract In this study, the development of the north-eastern Tibetan Plateau is investigated via an integrated study of the sedimentology, magnetostratigraphy, palaeogeography, and cross-section comparisons of the Neogene sedimentary basins of the Tibetan Plateau. From 23 to 17 Ma, this region was characterized by widespread angular unconformities and a sedimentary hiatus, indicating the comprehensive uplift of the plateau. The tectonic event that created the Tibetan Plateau triggered the evolution of sedimentary basins. During the Middle Miocene climatic optimum event, the growing Qilian Shan formed a barrier, leading to cooler and drier conditions on the western side of the mountain. However, humid and warm conditions persisted on the eastern side of the range. After this event, this region was influenced by a global cooling trend and enhanced tectonic activity in the north-eastern Tibetan Plateau. At approximately 10–8 Ma, sedimentary data, which were consistent with low-temperature thermochronological records, indicated the inversion of the surrounding mountains and rapid exhumation of the Laji Shan. Since 5.0–3.6 Ma, these intermontane basins gradually shrank and disappeared due to the overall uplift of the Tibetan Plateau and the accelerated global cooling trend and were associated with unconformities and growth strata that formed during stepwise-north-eastward thrusting tectonism. Highlights • During 23–17 Ma, the northeastern Tibetan Plateau was covered by widespread angular unconformities. • The tectonic event creating the Tibetan Plateau triggered the evolution of the sedimentary basins. • Growing Qilian blocking the eastern Asian moisture during the Middle Miocene climatic optimum, lead to westward aridification. • Among 10–8 Ma, the granularity and sedimentary rates of sedimentary basins increased abruptly. • Scince 5.0–3.6 Ma, these basins gradually withered away controlled by the overall uplift of the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Multi-scale reflection seismic data, from deep-penetration to high-resolution, have been analyzed and integrated with near-surface geophysical and geochemical data to investigate the structures and gas hydrate system of the Formosa Ridge offshore of southwestern Taiwan. In 2007, dense and large chemosynthetic communities were discovered on top of the Formosa Ridge at water depth of 1125 m by the ROV Hyper-Dolphin. A continuous and strong BSR has been observed on seismic profiles from 300 to 500 ms two-way-travel-time below the seafloor of this ridge. Sedimentary strata of the Formosa Ridge are generally flat lying which suggests that this ridge was formed by submarine erosion processes of down-slope canyon development. In addition, some sediment waves and mass wasting features are present on the ridge. Beneath the cold seep site, a vertical blanking zone, or seismic chimney, is clearly observed on seismic profiles, and it is interpreted to be a fluid conduit. A thick low velocity zone beneath BSR suggests the presence of a gas reservoir there. This “gas reservoir” is shallower than the surrounding canyon floors along the ridge; therefore as warm methane-rich fluids inside the ridge migrate upward, sulfate carried by cold sea water can flow into the fluid system from both flanks of the ridge. This process may drive a fluid circulation system and the active cold seep site which emits both hydrogen sulfide and methane to feed the chemosynthetic communities. [ABSTRACT FROM AUTHOR]

The Yanshan movement/orogeny has been proposed for 90 years, which is of special significance in the history of geological research in China. This study conducted a review by synthesizing major achievements regarding episodic deformation features, sedimentary and magmatic records of the Yanshan orogeny in China, and clarified the episodic tectono-magmatism and its geodynamic origins. The tectonic implications of the Yanshan orogeny are discussed in the context of global plate tectonics and supercontinent reconstruction. Lines of evidence from structural, sedimentary and magmatic data suggest that the Yanshan orogeny represents a regional-scale tectonic event that affected the entire China continent in late Mesozoic period. Numerous age and structural constraints consistently indicate that the Yanshan orogeny was initiated in the Jurassic (at ∼170±5 Ma). and was characterized by alternating stages of crustal shortening at ∼170-136 Ma, crustal extension at ∼135-90 Ma, and weak shortening at ∼80 Ma. The 170-136 Ma crustal shortening was reflected in the generation of two regional stratigraphic unconformities (the Tiaojishan and Zhangjiakou unconformities), which were initially named the A and B episodes of "the Yanshan Orogeny" by Mr. Wong Wenhao in 1928. Geodynamically, the Yanshan orogeny in East Asia was associated with nearly coeval oceanic subduction and continental convergence in the Paleo-Pacific, Neo-Tethys, and Mongol-Okhotsk tectonic domains. As a consequence, three giant accretionary-collisional tectonic systems were formed along the continental margins of East Asia, i.e., the Mongol-Okhotsk, Bangonghu-Nujiang, and SE China subduction- and collision-related accretionary systems. The Yanshan orogeny induced widespread crustal-scale folding and thrusting, tectonic reactivation of long-lived zones of crustal weakness, and extensive magmatism and mineralization in intraplate regions. Based on the time principle of supercontinent assembly and break-up, we propose that the mid-Late Jurassic multi-plate convergence in East Asia might represent the initiation of the assembly of the Amasia supercontinent, and the Yanshan orogeny might be the first "stirrings" that is a prerequisite for the birth of the Amasia supercontinent. [ABSTRACT FROM AUTHOR]

Abstract Piggyback basins often display asymmetric sedimentary successions influenced by both regional and local syn -depositional tectonic structures. There are few examples where a complete exhumed piggyback basin fill can be analyzed, from proximal, close to source areas, to the distal deep-water sinks. The study of these basins is a key to extract the stratigraphic signal of intrabasinal tectonics, which often competes and can even overprint other controlling factors such as eustasy, climate, or autogenic processes. The purpose of this paper is to propose a more detailed model of the evolution of piggyback basin fills, which recognizes the influence of intrabasinal tectonic activity, specific to the piggyback context and the resulting stratigraphic architecture. We investigate the Tremp-Graus-Ainsa piggyback basin, located in the southern Pyrenees, during early Eocene, which was influenced by the development of the Montsec frontal thrust. Twenty four stratigraphic sections, totaling 14 km of logged thickness, are analyzed, covering 60 km of the basin. The stratigraphic surfaces have been correlated in order to define large-scale stratigraphic units and a new sequence stratigraphic framework. The influence of local tectonics in the basin record is identified by abrupt lateral sediment thickness variations, abrupt changes of depositional environments, local erosion surfaces, and changes in dominant sedimentary process regimes and paleocurrent directions through space and time. As a result, we propose a new tectono-stratigraphic model for the development of the Tremp-Graus-Ainsa Basin. Specifically, we identify (1) an underfilled stage with initial high flexural subsidence and a frontal subaqueous blind anticline thrust propagation that controls a dominantly carbonate environment, followed by a progressive increase in siliciclastic sediment supply, and (2) an overfilled stage with an increase in frontal thrust propagation causing new emergent sediment sources. This second stage evolves from an active emerged blind anticline thrust to a migrating thrust that moved along lateral ramps, and which caused the decoupling of the Tremp-Graus uplifted wedge-top sub-basin from the Ainsa subsiding foredeep domain. Finally, we provide a new model intrinsic to the piggyback basin development with four main stages, controlled by changes in intrabasinal tectonic activity, flexural subsidence and orogeny axial zone evolution, which ultimately modulate sediment supply and creation and distribution of accommodation space. [ABSTRACT FROM AUTHOR]

Thrust zones in a deep-water fold-thrust belt, offshore northwestern Borneo, display prominent reflections that can be mapped through a three-dimensional seismic volume. Unlike faultplane reflections obtained from thrusts in other systems, these have positive polarity. Well data show that the reflections in the Borneo data set originate from fault-bound sandstone slices, with porosity-occluding calcite cement, entrained along the thrust zone. The thrust zone can support elevated fluid pressures beneath the fault with the cemented sandstones. Multiple sandstone slices indicate complex patterns of thrust zone localization, perhaps a common feature for deformation in sedimentary multilayers typical of many deep-water depositional successions. [ABSTRACT FROM AUTHOR]

The Cao Bang Basin is the northernmost of the basins related to the Cao Bang-Tien Yen Fault Zone in northern Vietnam. The basin is filled with a thick series of continental deposits. However, the exact age of the sedimentary basin infill has been under discussion for a long time. Because of new published data, the authors have decided to revisit this basin. Palynological data has allowed us to assign the Cao Bang Basin infill to the Lower Oligocene PC1 complex of the Shangcun Fm. (southern China). Among the saccate grains of gymnosperms, the domination of Cathaya and Pinus was observed, whereas angiosperms are represented by Carya, Celtis, Hammamelidaceae, Ulmus and also Pterocarya, Quercus, the Castanea-Castanopsis-Lithocarpus group, and the Loranthaceae. Among pteridophytes occur Laevigatosporites, Osmundaceae, and Pteris. The sedimentological features of the Cao Bang Basin are distinct from those of other basins from the Cao Bang-Tien Yen Fault Zone. The basin is filled with a wide variety of clastic deposits, from some of coarse-grained, alluvial-fan origin, through sandy beds of fluvial origin up to fine, organic-rich lacustrine deposits. The coarse-grained lithofacies are built of clasts derived mainly from local sources. The sandstones from the basin equally are submature or immature. They contain a lot of lithoclasts, the composition of which depends on the sample location within the basin. The potential source area is composed of older sedimentary units and of granitic rocks. The geochemical samples studied reflect the geochemical composition of silicic source rocks with only a minor contribution of basic components. The succession that fills the basin is interpreted as a typical fill for relatively long-lasting evolving half-graben or strike-slip basins. Moreover, the basin is partly occupied by a subsequent present-day sedimentary basin of Quaternary age. [ABSTRACT FROM AUTHOR]

To investigate the timing of deposition and provenance of early Mesozoic strata in the northeastern North China Craton (NCC) and to understand the early Mesozoic paleotectonic evolution of the region, we combine stratigraphy, U–Pb zircon geochronology, and Hf isotopic analyses. Early Mesozoic strata include the Early Triassic Heisonggou, Late Triassic Changbai and Xiaoyingzi, and Early Jurassic Yihe formations. Detrital zircons in the Heisonggou Formation yield ∼58 % Neoarchean to Paleoproterozoic ages and ∼42 % Phanerozoic ages and were sourced from areas to the south and north of the basins within the NCC, respectively. This indicates that Early Triassic deposition was controlled primarily by the southward subduction of the Paleo-Asian oceanic plate beneath the NCC and collision between the NCC and the Yangtze Craton (YC). Approximately 88 % of the sediments within the Late Triassic Xiaoyingzi Formation were sourced from the NCC to the south, with the remaining ∼12 % from the Xing'an–Mongolia Orogenic Belt (XMOB) to the north. This implies that Late Triassic deposition was related to the final closure of the Paleo-Asian Ocean during the Middle Triassic and the rapid exhumation of the Su–Lu Orogenic Belt between the NCC and YC. In contrast, ∼88 % of sediments within the Early Jurassic Yihe Formation were sourced from the XMOB to the north, with the remaining ∼12 % from the NCC to the south. We therefore infer that rapid uplift of the XMOB and the onset of the subduction of the Paleo-Pacific Plate beneath Eurasia occurred in the Early Jurassic. [ABSTRACT FROM AUTHOR]

Abstract Borehole electrical image log with core-like presentation is an efficient way to conduct sedimentary description in the subsurface. The key is to set up a series of geological diagnostic criteria. The subsurface Lower Cretaceous Bashijiqike Formation in the Kelasu belt, Kuqa Depression, described as a sedimentary facies of braided river-delta front, has measured a mass of borehole image logs and open-hole logs at depths more than 6000 m. Combined with comparative outcrops, limited cores and thin sections, high-quality borehole images were fine calibrated to reveal their sedimentary details, with the aim of subtle sedimentary interpretation in the uncored intervals. The image elements all have corresponding geological indications. The lithologies are interpreted including mudstones, siltstones, fine- and medium sandstones and conglomerates, and the sedimentary structures are interpreted in terms of various bedding types, scoured surface and stacking modes. Thus, interdistributary bay, sandy or conglomerate subaqueous distributary channel and channel mouth bar are interpreted based on the lithologies, sedimentary structures and textures, basal and top contacts and succession variations. Furthermore, determination of paleo-current direction using borehole image logs is proposed for some time, but is far from mature and need to consider tectonic deformation settings of studied stratigraphy. Based on this, the paleo-current in the Kelasu belt is interpreted to flow southward from the Southern Tianshan to the depression during the Early Cretaceous which is consistent with the results derived from the heavy mineral analysis. However, the subaqueous distributary channels could frequently migrate locally and the paleo-current direction changed at localities with an offset angle varied between 30° and 150°. Regionally, the scale of single sand-body decreases lakeward and the sand-body may stretch at a maximum distance of 685.1 m along the flow direction. The diagnostic criteria and the workflow for borehole image interpretation in this study will have potential application to subsurface sedimentary description and guide sedimentary architecture where cores are not available. Highlights • A river-delta was characterized by imaging log with comparative outcrop and core. • Structural dip removal must take into account deformation setting. • Borehole images can fine determine depositional evolution over a depth interval. • The workflow can guide quantitative sedimentary characterization in the subsurface. [ABSTRACT FROM AUTHOR]

The results of studying the deep structure of the Earth’s crust and upper mantle in the central part of the Russian platform from receiver functions are presented. The records of teleseismic waves by the Monakovo small-aperture seismic array in the region of the northwestern slope of the Tokmovskii Arch of the Volga-Kama anteclise are used. The modification of the P-receiver function method (Vinnik, 1977) suggested in (Sanina et al., 2014) for analyzing the receiver functions in the regions with a complexly structured upper part of the section and the presence of a thick sedimentary cover is applied. The method is based on separating the high- and low-frequency components of the seismic record and successive reconstruction of the V-s velocity section in the upper part of the crust, which is performed first and, next, the entire deep section of the crust and the mantle down to a depth of ~300 km. The positions of the seismic conversion boundaries in the crust and upper mantle beneath the Monakovo array are determined. The upper mantle velocity section constructed based on the observations at the Mikhnevo array (Sanina et al., 2014) is compared with the world data on the ancient Precambrian platform. [ABSTRACT FROM AUTHOR]

Based on analysis and interpretation of seismic and other geological-geophysical data, duplex rifting is identified in the Paleozoic evolution of the South Barents Basin. Its first, pre-Late Devonian, phase was manifested on the southeastern side zone that limited the Pechora Plate structures. After a certain pause, a second, pre-Late Carboniferous phase involved the western Barents Sea region, including the slope of the Central Barents Rise and the western South Barents Basin. Thus, Late Paleozoic riftogenic structures in the western and southeastern South Barents Basin formed at different times. All this caused an asymmetric structure profile and asynchronicity of evolution of the rift system sides. In the Mesozoic, under the effect of formation of the Novaya Zemlya fold-and-thrust structure, the asymmetry of the riftogenic trough became even more contrasting. [ABSTRACT FROM AUTHOR]

Three‐dimensional seismic data from an oilfield in the Campos Basin, SE Brazil, was used to characterize a karstified unconformity surface at the top of the Albian – Cenomanian Macaé Group. Macaé Group carbonates underwent intense karstification associated with subaerial exposure during a period of some 10 to 15 Ma resulting in the development of canyons, valleys, sinkholes and cave systems. The carbonates host commercial oil accumulations at a number of important oil fields. Understanding how the karstification process has affected the carbonates' reservoir properties is essential for future exploration, not only to improve recovery rates but also to avoid drilling‐related issues such as thief zones. In this context, this study aims to characterize the top‐Macaé Group paleokarst system by investigating the morphology of the associated reflectors recorded on seismic data, together with endokarst features in the underlying carbonate succession such as cave systems and collapse structures. The top‐Macaé Group seismic horizon can be divided into two principal geomorphological domains: highlands, characterized by abrupt relief with well‐developed erosional features; and lowlands, marked by a smoother topography. Collapse sinkholes occur in both domains and take the form of closed circular depressions. The study of endokarst features from an analysis of amplitude anomalies (bright spots) indicates the presence of heterogeneous cave systems. The interpreted data contributes to a better understanding of the spatial distribution of the paleokarst system in the Macaé Group carbonates and may assist with future hydrocarbon exploration in the Campos Basin. [ABSTRACT FROM AUTHOR]

Abstract: Focal mechanisms of induced earthquakes reflect anthropogenic contributions to preexisting geological features and fault slippages. In this paper, we examine fault‐related (double‐couple (DC)) and possibly fluid‐related (non‐double‐couple (non‐DC)) mechanisms of induced earthquakes (M2–6) at regional scales. We systematically compare well‐resolved focal mechanisms of 33 events in the Western Canada Sedimentary Basin, among which 12 were induced by hydraulic fracturing and one by secondary recovery. Most of the seismicity is dominated by strike‐slip/thrust faulting regimes, whereas limited (but consistent) non‐DC components are obtained from injection‐induced seismicity in central Alberta. We interpret the persistent compensated‐linear‐vector‐dipole components (M2.1–3.8) as reflecting fracture growth and/or noncoplanar faults slippages during hydraulic‐fracturing stimulations. We further expand the moment tensor decomposition analysis to four representative classes of induced seismicity globally and find that the overall contribution of non‐DC components is comparable between induced and tectonic earthquakes. [ABSTRACT FROM AUTHOR]

The complex geomorphic and sedimentary evolution of the central Po Plain (northern Italy) during the last 30 ky was reconstructed through the integration of stratigraphic, geomorphological, geochemical and radiocarbon data. A key element of the Late Pleistocene stratigraphy is a 20 km-wide channel-belt sand body, with its top at a depth of ~13 m, fed by the Po River. Whereas the southern boundary of the Po fluvial channel belt coincides with a sharp lithological contact with floodplain muds, its northern boundary is an erosional (sand-on-sand) surface that was traced tentatively in the subsurface with the aid of sediment provenance (Po versus Alpine) proxies and radiocarbon data. Stratigraphic and geomorphological features testify to a decoupled sedimentary and geomorphic response of the Alpine and Po River systems to climate change in the last 30 ky. Contemporaneous Po River incision and Alpine rivers aggradation occurred at the onset of the Last Glacial Maximum (LGM). In contrast, Po River aggradation and Alpine rivers entrenchment took place during early deglaciation. The Holocene stratigraphy records the overall aggradation and northward migration of the Po River, with the consequent erosion of distal Alpine LGM deposits and formation of a fluvial scarp parallel to the Po River course. Late Pleistocene and Holocene climate change influenced river dynamics controlling (i) the balance between sediment supply and water discharge, through glacier and vegetation dynamics, and (ii) the rate of sea-level fall/rise. Apennine, Alpine and Po river systems responded in distinct ways to climate forcing due to the influence of local factors. Lithology, drainage area and mean elevation of river catchments, as well as river and valley gradients, determined the type of sedimentary response (e.g., aggradation versus degradation). This study shows that a combined geomorphic and stratigraphic approach focusing on the geometric relations between exposed and buried features can provide valuable information about the evolution of a fluvial system and its controlling factors. [ABSTRACT FROM AUTHOR]

Recent oil discoveries in the L13-L15 sub-sag area in the Pearl River Mouth basin have inspired interest in Paleogene hydrocarbon targets. However, the structures and their control on reservoirs have not been completely studied. The aim of this paper is to address the tectonics and Eocene sedimentation based on 3D seismic data. We documented characteristics from four aspects of the faults in the study area: (a) fault arrangement; (b) fault segmentation; (c) flower structures; and (d) distribution of the depocenters along the faults. Based on the above data, we propose that the structures in the studied area were formed by a right-handed wrench. The principal shear for this model was caused by NNE- to NE-ward motion of the eastern part of the Eurasia plate due to the collision of the Indian-Australian and Eurasian plates starting approximately 49 Ma ago. The L13-L15 sub-sag area underwent early Eocene rifting, a late Eocene rifting-depression transition and an Oligocene-Quaternary thermal depression. The rift phase included three stages: the initial rifting, intensive rifting and late rifting. The deep lake mudstone deposited during the intensive rifting stage is the source rock with the most potential for oil generation. Shallow lake source rocks formed in the late rifting and transition stages are the secondary source rocks. Reservoir sweet spots were formed in the early period of the intensive rifting and late rifting stages. The junction sites between the front of the meandering river delta plain and fault steps are favorable places for good reservoirs. The sediments in the transition stage are rich in sandstone, making them perfect sites for prospecting reservoirs. [ABSTRACT FROM AUTHOR]

The Nanyang Sag in the Nanxiang Basin, eastern China, has a large petroleum resource, although the genetic potential of source rocks and oil–rock correlation in the Paleogene Hetaoyuan Formation is unclear. Organic geochemistry and molecular geochemistry analyses of mudstone and oil samples were performed to evaluate source rock potential, classify oil groups, and establish accurate oil–source rock correlation. The results suggest that the second member (Eh2) and the third member (Eh3) of the Hetaoyuan Formation are good source rocks, contain abundant organic matter and oil‐prone kerogen, and are thermally mature. Oil samples from Eh2 and Eh3 were separated into 3 groups derived from different source rocks. Group I oils are mainly distributed in the Eh2 and Eh3 members around the Dongzhuang (Dongz) structure belt and are characterized by a low saturated hydrocarbon content (SAT, 39.07–49.54%), high total resin (RE) and asphaltene (ASP) content (17.22–22.80%), low gammacerane index (gammacerane/C3017α(H)‐hopane < 0.60), and low Pr/Ph (<0.7). The organic matter is in an early mature stage and is mainly sourced from algae and land plants. The oils of this group are derived from the Eh2 and Eh3 source rocks around the Dongz secondary sag. Group II oils occur in the Eh2 around the Weigang–Beimazhuang (Weig–Beimz) structure belt and north of the Zhangdian–Heilongmiao (Zhangd–Heilm) structure belt and have intermediate SAT, RE, and ASP contents, a low gammacerane index (<0.47), and high Pr/Ph (0.72–1.25). The organic matter includes mainly algae and land plants. The source rocks should be the Eh2 and Eh3 in the Dongz and Niusanmen (Niusm) secondary sags. Group III oils are located in the Eh3 just north of the Weig–Beimz and Zhangd–Heilm structure belts, with a high SAT (55.62–78.42%), low RE and ASP proportion (3.60–6.16%), high gammacerane index (>0.88), and low Pr/Ph (<0.72). This organic matter is composed of mostly land plants. The oils in this group are mainly derived from the Eh3 near Baiqiu (Baiq). [ABSTRACT FROM AUTHOR]

Seismic reflection and refraction data acquired from both onshore and offshore in the South China area and on the continental shelf of the northern South China Sea passive margin provide new constraints on the P‐wave velocity structure beneath the continental shelf and contribute to constructing a continental rift evolution model. Based on the crustal thicknesses and P‐wave velocities derived from the velocity structure of the seismic profile OBS2010‐2 across the continental shelf, two distinct domains are identified: (a) the thinned/extended continental crust and (b) the transitional crust. The thinned continental crust has a thickness of 25–27 km across the Hainan Rise, decreasing to 21–23 km further south in the rift and faulted depression zone. The transitional crust is characterized by a thickness of 20–21 km. High‐velocity values (>7.0 km/s) in the lower crust of the transitional domain may indicate possible magmatic underplating during rifting. Our results show that the Cathaysia Block extends from onshore South China to offshore into the South China Sea and is bounded by the transitional crust of the continental shelf. The initial rifting of the continental margin occurred in the rift and faulted depression zone and might be explained by the upwelling of the lithosphere based on a depth‐dependent extension mechanism during the late Cretaceous or Paleocene rifting. [ABSTRACT FROM AUTHOR]

Six distinct alluvial fans have developed in the western Ganga basin's piedmont zone between the Ganga (aka Ganges) River in the west and the Sarda River in the east. The basin margin is demarked by the active Himalayan Frontal Thrust along which the Siwalik ranges are uplifted and placed over the alluvia of the Ganga basin. The 6 alluvial fans show marked morphological variances, but their morphometric parameters exhibit proportionality relationships with the “mountain‐front sinuosity index (Smf),” “stream‐gradient index (SL),” and “valley‐floor width to height ratio (Vf)” of the adjoining mountain‐front segments. Correlation and regression analyses reveal that these relationships are statistically significant. The size of the fan is directly proportional to the magnitude of Smf and inversely proportional to the magnitude of SL, whereas the fan gradient is inversely proportional to Smf. The higher the Smf and the lower the SL values, the larger and gentler is the alluvial fan. Given that the studied alluvial fans have developed in the same climatic zone and their drainage basins have similar physiographic, geologic, and climatic conditions, the morphological diversities among the alluvial fans are attributed to the tectonics of the basin margin. Moreover, statistical analyses further rule out any significant relationships of the fan size with area, or drainage density of the drainage basin. The lower values of Smf and Vf and higher values of SL indicate a more active nature and, thus, greater/faster uplift of the mountain‐front and expected deepening of the accommodation space in the adjoining basin, which favoured vertical aggradation and development of smaller and steeper alluvial fans. Conversely, the higher values of Smf and Vf and lower values of SL indicate a less active nature and, thus, relatively lower/slower uplift of the mountain‐front and thus creation of shallower accommodation space in the adjoining basin, favouring the development of larger and gentler alluvial fans. [ABSTRACT FROM AUTHOR]

Shell beds represent a useful source of information on various physical processes that cause the depositional condition. We present an automated method to calculate the 3D orientations of a large number of elongate and platy objects (fossilized oyster shells) on a sedimentary bedding plane, developed to support the interpretation of possible depositional patterns, imbrications, or impact of local faults. The study focusses on more than 1900 fossil oyster shells exposed in a densely packed Miocene shell bed. 3D data were acquired by terrestrial laser scanning on an area of 459 m2 with a resolution of 1 mm. Bivalve shells were manually defined as 3D-point clouds of a digital surface model and stored in an ArcGIS database. An individual shell coordinate system (ISCS) was virtually embedded into each shell and its orientation was determined relative to the coordinate system of the entire, tectonically tilted shell bed. Orientation is described by the rotation angles roll, pitch, and yaw in a Cartesian coordinate system. This method allows an efficient measurement and analysis of the orientation of thousands of specimens and is a major advantage compared to the traditional 2D approach, which measures only the azimuth (yaw) angles. The resulting data can variously be utilized for taphonomic analyses and the reconstruction of prevailing hydrodynamic regimes and depositional environments. For the first time, the influence of possible post-sedimentary vertical displacements can be quantified with high accuracy. Here, the effect of nearby fault lines—present in the reef—was tested on strongly tilted oyster shells, but it was found out that the fault lines did not have a statistically significant effect on the large tilt angles. Aside from the high reproducibility, a further advantage of the method is its non-destructive nature, which is especially suitable for geoparks and protected sites such as the studied shell bed. [ABSTRACT FROM AUTHOR]

The Central Metasedimentary Belt boundary zone (CMBbz) is a crustal-scale shear zone that juxtaposes the Central Gneiss Belt and the Central Metasedimentary Belt of the Grenville Province. Geochronological work on the timing of deformation and metamorphism in the CMBbz is ambiguous, and the questions that motivate our study are: how many episodes of shear zone activity did the CMBbz experience, and what is the tectonic significance of each episode? We present electron microprobe data from monazite (the U–Th–Pb chemical method) to directly date deformation and metamorphism recorded in five garnet–biotite gneiss samples collected from three localities of the CMBbz of Ontario (West Guilford, Fishtail Lake, and Killaloe). All three localities yield youngest monazite dates ca. 1045 Ma; most of the monazite domains that yield these dates are high-Y rims. In comparison with this common late Ottawan history, the earlier history of the three CMBbz localities is less clearly shared. The West Guilford samples have monazite grain cores that show older high-Y domains and younger low-Y domains; these cores yield a prograde early Ottawan (1100–1075 Ma) history. The Killaloe samples yield a well-defined prograde, pre- to early Shawinigan history (i.e., 1220–1160 Ma) in addition to some evidence for a second early Ottawan event. In other words, the answers to our research questions are: three events; a Shawinigan event possibly associated with crustal thickening, an Ottawan event possibly associated with another round of crustal thickening, and a late Ottawan event that resists simple interpretation in terms of metamorphic history but that coincides chronologically with crustal thinning at the base of an orogenic lid. [ABSTRACT FROM AUTHOR]

The West African region embraces a number of coastal sedimentary basins, which continued in deep-water areas of the Atlantic Ocean. It includes the following oil-and-gas-bearing basins: the Gulf of Guinea, the Kwanza-Cameroonian, and the Namibian. The sedimentary cover of the basins of this passive margin is represented by Mesozoic-Cenozoic deposits. The composition of sediments accumulated in them is quite specific and surprisingly units over the vast areas. The tectonic structure of the majority of the continental margins of West Africa makes possible to refer them to the margins of epiplatform orogenic belts. The existence of two systems of linear troughs—internal and external—on the passive margins at the early stages of continent-ocean transition zones relates deep-water hydrocarbon deposits to internal troughs filled by younger sediments: the alluvial fans of submarine rivers and landslide fronts with prograde formations (turbidites, debris flows, etc.). Late Cretaceous and Middle Paleogene clay formations played the role of source beds in the region, so-called “black clays.” An analysis of over 200 hydrocarbon fields, mainly petroleum, discovered in the past 10-15 years in the region revealed a clear tendency of these fields occurring in a productive zone of oil pools extending in a sea depth interval of 400-3000 m on the continental slope and possibly to 4000 m at the continental rise. Moreover, all discovered fields have been estimated in terms of reserves from large to giant. It is also noteworthy that within the shallow of this region, which includes the shelf and the coastal plain, only a number of small, insignificant oil and gas pays have been discovered. The main of oil and gas bearing potential prospects are related to deposits in the middle and lower parts of the continental slope and possibly adjacent areas of the continental rise. In the long term, the drilling objectives will be both postsalt and presalt deep-water oil-and-gas fields. [ABSTRACT FROM AUTHOR]

Integrated processing and interpretation of high-resolution aeromagnetic and two-dimensional (2-D) seismic-reflection data in the Athabasca region, near Buffalo Creek, northeastern Alberta (368500 Easting and 6252380 Northing, North American Datum of 1927, Zone 12), reveal the existence of a set of buried southwest-northeast-striking (N59°E ± 11°) magnetic lineaments. The anomaly signature of these features on the aeromagnetic data appears to range between 5 and 20 nT in amplitude. These anomalies are recognized by narrow vertical disturbance zones on the 2-D seismic profiles. We believe these lineaments are dike-like igneous bodies and refer to them as the Buffalo Creek dike field. Forward magnetic modeling indicates the depth of the dikes to be more than 200 m, and they are intruded into Western Canadian sedimentary basin strata. The magnetic model and seismic evidence suggest that the intrusion could have been produced at any time in the interval from the Frasnian to the Aptian. The proximity of the Buffalo Creek dike field to the Birch Mountain field may suggest that they could have identical origin and be related to subduction of the Farallon plate under the west coast of the North American plate. [ABSTRACT FROM AUTHOR]

The South Yellow Sea is a superimposed basin overlying Mesozoic-Cenozoic continental sediments, which in turn overlie Paleozoic-Mesozoic marine deposits that are now the target of hydrocarbon exploration. Strongly modified by multiple tectonic events, the marine sediments feature a large tectonic relief, with obvious horizontal anisotropy in seismic velocity, which significantly affects the seismic image quality. In this study, the sedimentary velocity anisotropy and its influence on image quality were analyzed using an analytical theory method, assuming transversely isotropic medium with vertical axis of symmetry (VTI), and using seismic and well-log data. Additionally, an anisotropic prestack time migration was used for the imaging of the field data. The results showed that the anisotropic pre-stack time migration processing could be used to significantly improve the accuracy of the seismic images in areas with distinct faults, offering clear images of accurately located fault planes and fault edges, thereby improving the lateral resolution of the seismic data and its signal-to-noise ratio. [ABSTRACT FROM AUTHOR]

The 492 km-diameter Apollo impact basin post-dates, and is located at the inner edge of, the ∼2240 km-diameter South Pole–Aitken (SPA) basin, providing an opportunity to assess the SPA substructure and lateral heterogeneity. Gravity Recovery and Interior Laboratory gravity data suggest an average crustal thickness on the floor of SPA of ∼20 km and within the Apollo basin of ∼5 km, yet remote sensing data reveal no conclusive evidence for the presence of exposed mantle material. We use the iSALE shock physics code to model the formation of the Apollo basin and find that the observational data are best fit by the impact of a 40 km diameter body traveling at 15 km/s into 20–40 km thick crustal material. These results strongly suggest that the Apollo impact occurred on ejecta deposits and collapsed crustal material of the SPA basin and could help place constraints on the location, size and geometry of the SPA transient cavity. The peak ring in the interior of Apollo basin is plausibly interpreted to be composed of inwardly collapsed lower crustal material that experienced peak shock pressures in excess of 35 GPa, consistent with remote sensing observations that suggest shocked plagioclase. Proposed robotic and/or human missions to SPA and Apollo would present an excellent opportunity to test the predictions of this work and address many scientific questions about SPA basin evolution and structure. [ABSTRACT FROM AUTHOR]

The occurrence of km-scale exhumations during syn- and post-rift stages has been documented along Atlantic continental margins, which are also characterised by basins undergoing substantial subsidence. The relationship between the exhuming and subsiding domains is poorly understood. In this study, we reconstruct the evolution of a 50 km long transect across the Moroccan rifted margin from the western Anti-Atlas to the Atlantic basin offshore the city of Sidi Ifni. Low-temperature thermochronology data from the Sidi Ifni area document a ca. 8 km exhumation between the Permian and the Early/Middle Jurassic. The related erosion fed sediments to the subsiding Mesozoic basin to the NW. Basement rocks along the transect were subsequently buried by 1–2 km between the Late Jurassic and the Early Cretaceous. From late Early/Late Cretaceous onwards, rocks present along the transect were exhumed to their present-day position. [ABSTRACT FROM AUTHOR]

The tectonic evolution of the transition zone from the Pacific Ocean to the Atlantic Ocean is closely linked with the destruction of the American-Antarctic continental bridge in the Scotia Sea. The western segment of the bridge combines the Terror, Pirie, and Bruce banks, as well as the Protector and Dove basins between them. Modeling—primarily based on original geological and geophysical materials—of linear magnetic anomalies and calculation of the floor kinematics in these basins have made it possible for the first time to reveal that the collapse of the western segment of the American-Antarctic continental bridge occurred 18-25 Ma ago via a two-stage separation of the Pirie Rise from the Bruce Rise with the formation of the Dove Basin and a two stage separation of the Terror Rise from the Pirie Rise with the formation of the Protector Basin. [ABSTRACT FROM AUTHOR]

We investigate episodic soft-sediment deformation structures cross-cut by normal faults preserved in unlithified finely laminated calcite rich sediments in the Hirlatz cave in the Northern Calcareous Alps (Austria). These sediments comprise varve-like alternations of brighter carbonate/quartz rich layers, and darker clay mineral rich layers. The deformed sediments contain abundant millimeter to centimeter-scale soft-sediment structures (load casts, ball-and-pillow structures), sheet slumps (thrust faults and folds), erosive channels filled with slides and chaotic slumps. After deposition and soft-sediment deformation normal faults developed within the entire sedimentary succession, an event that probably correlates with an offset of c. 10 cm of the passage wall above the outcrop. Our major conclusions are: (i) The sediments have a glacial origin and were deposited in the Hirlatz cave under phreatic fluvio-lacustrine conditions. The deposition and the soft-sediment deformation occurred most likely during the last glaciation (i.e. around 25 ka ago); (ii) The liquefaction and formation of the soft-sediment structures in water-saturated stratified layers was triggered by episodic seismic events; (iii) The internally deformed sediments were later displaced by normal faults; (iv) A possible source for the seismic events is the active sinistral Salzach-Ennstal-Mariazeller-Puchberger (SEMP) strike-slip fault which is located about 10 km south of the outcrop and plays a major role in accommodating the extrusion of the Eastern Alps towards the Pannonian Basin. To our knowledge, the described structures are the first report of liquefaction and seismically induced soft-sediment deformations in Quaternary sediments in the Eastern Alps. [ABSTRACT FROM AUTHOR]

The provenance of Chinese loess is fundamental for understanding its origin, transportation and climatic significance. In this paper, eight samples were collected for detrital zircon age analysis, five from different deserts, and three from the Jingbian Section in the northern Chinese Loess Plateau, covering an age range of 2.6–0.03 Ma. The new results, integrated with knowledge of relevant topography and wind patterns, demonstrate that the age spectra of the detrital zircons in the loess are different from those of the sands from the Tarim, Junggar and Qaidam basins, implying that these basins were not the sources of the silts of the Loess Plateau. Further analysis suggests that the three sources for the loess are: (1) clastic materials eroded from the mountains of the Central Asian Orogenic Belt (especially the Gobi Altai and Hangay), (2) clastic loess-sized materials generated by erosion of the Qilian Mountains in the NE Tibetan Plateau, and (3) minor clastic debris derived from the mountains of the North China Craton. Thus, silts of the Loess Plateau have a complex origin, although inland basins, long believed to be important sources, have only a minor role at most. [ABSTRACT FROM AUTHOR]

Major structures considered important for controlling mineralisation in the Halls Creek Orogen, east Kimberley are identified via integrated interpretation of geophysical and geological data combined with geodynamic numerical modelling. In the numerical geodynamic models, the second invariant of strain rate ( ε ̇ II ) is used to investigate the shearing processes that led to the development of major faults or shear zones and assessing their role as lithospheric-scale conduits and pathways for the movement of magmatic and hydrothermal fluids into the upper crust. The influence of these deep structures interpreted from the geodynamic models is evaluated through structural interpretation of geophysical, remotely-sensed and geological data. When compared to the location of Ni and Au mineral deposits the deep-crustal scale structures delineated in the models and compared to those mapped in the region contain a close spatial relationship with mineral deposits. It is apparent that 1st order crustal-scale structures acted as fluid conduits in the deep crust resulting in the formation of Ni-Cu-PGE deposits and are associated with Au mineralisation. However, 2nd and 3rd order structures manifesting in the upper crust as deformation focused mineralising fluids and magma resulting in the formation of gold deposits. Large-scale structures developed early in the genesis of the Halls Creek Orogen, appear to be long-lived and have been reactivated. These form the margins of Kimberley Craton domains and influence the location of Ni-Cu-PGE mineralisation, whereas the lower-order structures acted as structural traps for the subsequent deposition of Au mineralisation. [ABSTRACT FROM AUTHOR]

Subsurface basement topography in the Nigerian portion of the Benin Basin has been studied using borehole data of wells drilled to the basement and one strike line of seismic section. Two areas of a sharp drop in topography with a horst in between were observed in the study area. These features were projected to a seismic section in the offshore area of the Benin basin. The result depicts the structural features as horst and grabens coinciding with the Avon platform bounded on the right side by Ise graben, and the Orimedu graben to the left. The observed relationship of the grabens with the present day location of Avon Canyon on the seismic section also suggests an active subsidence along fractured zones. The subsidence, which probably is occurring along similar fracture zones in the Gulf of Guinea, could be responsible for the occasionally reported seismicity on the margin of West Africa. A detailed seismographic study of the fracture zones is recommended. [ABSTRACT FROM AUTHOR]

The Northern Apennine prowedge exposes two adjacent sectors showing a marked along-strike change in erosion intensity, namely the Emilia Apennine to the northwest and the Romagna Apennine to the southeast. This setting has resulted from Pliocene erosion (≤5 Ma) and exhumation, which have affected the whole Romagna sector and mostly the watershed ridge in Emilia. Such an evolution has conceivably influenced the equilibrium of this fold-and-thrust belt, which can be evaluated in terms of critical Coulomb wedge theory. The present state of the thrust wedge has been assessed by crosschecking wedge tapers measured along transverse profiles with fluid pressure values inferred from deep wellbores. The interpretation of available data suggests that both Emilia and Romagna are currently overcritical. This condition is compatible with the presence in both sectors of active NE-dipping normal faults, which would work to decrease the surface slope of the orogenic wedge. However, the presence of Late Miocene-Pliocene passive-roof and out-of-sequence thrusts in Romagna may reveal a past undercritical wedge state ensuing during the regional erosion phase, thereby implying that the current overcritical condition would be a recent feature. The setting of the Emilia Apennine (i.e., strong axial exhumation and limited erosion of the prowedge) suggests instead a long lasting overcritical wedge, which was probably contemporaneous with the Pliocene undercritical wedge in Romagna. The reasons for this evolution are still unclear, although they may be linked to lithosphere-scale processes that have promoted the uplift of Romagna relative to Emilia. The lessons from the Northern Apennine thus suggest that erosion and exhumation have the ability to produce marked along-strike changes in the equilibrium of a fold-and-thrust belt. [ABSTRACT FROM AUTHOR]

The Geita Greenstone Belt is a late Archean greenstone belt located in the Tanzania Craton, trending approximately E-W and can be subdivided into three NW-SE trending terrains: the Kukuluma Terrain to the east, the Central Terrain in the middle and the Nyamullilima Terrain in the west. The Kukuluma Terrain, forms a NW-SE trending zone of complexly deformed sediments, intruded by the Kukuluma Intrusive Complex which, contains an early-syntectonic diorite-monzonite suite and a late-syntectonic granodiorite suite. Three gold deposits (Matandani, Kukuluma and Area 3W) are found along the contact between the Kukuluma Intrusive Complex and the sediments. A crystal tuff layer from the Kukuluma deposits returned an age of 2717 ± 12 Ma which can be used to constrain maximum sedimentation age in the area. Two granodiorite dykes from the same deposit and a small granodiorite intrusion found along a road cut yielded zircon ages of 2667 ± 17 Ma, 2661 ± 16 Ma and 2663 ± 11 Ma respectively. One mineralized granodiorite dyke from the Matandani deposit has an age of 2651 ± 14 Ma which can be used to constrain the maximum age of the gold mineralization in the area. The 2717 Ma crystal tuff has zircon grains with suprachondritic 176 Hf/ 177 Hf ratios (0.28108–0.28111 at 2717 Ma) and positive (+1.6 to +2.6) εHf values indicating derivation from juvenile mafic crust. Two of the granodiorite samples have suprachondritic 176 Hf/ 177 Hf ratios (avg. 0.28106 and 0.28107 at 2663 and 2651 Ma respectively) and nearly chondritic εHf values (avg. −0.5 and −0.3 respectively). The other two granodiorite samples have chondritic 176 Hf/ 177 Hf ratios (avg. 0.28104 and 0.28103 at 2667 and 2661 Ma respectively) and slightly negative εHf values (avg. −1.1 and −1.5 respectively). The new zircon age and isotope data suggest that the igneous activity in the Kukuluma Terrain involves a significant juvenile component and occurred within the 2720 to 2620 Ma period which, is the main period of crustal growth in the northern half of the Tanzania Craton. [ABSTRACT FROM AUTHOR]

A land gravity survey was carried out in the Kinigi geothermal field, Northwest Rwanda using 184 gravity stations during August and September, 2015. The aim of the gravity survey was to understand the subsurface structure and its relation to the observed surface manifestations in the study area. The complete Bouguer Gravity anomaly was produced with a reduction density of 2.4 g/cm 3 . Bouguer anomalies ranging from −52 to −35 mGals were observed in the study area with relatively high anomalies in the east and northwest zones while low anomalies are observed in the southwest side of the studied area. A decrease of 17 mGals is observed in the southwestern part of the study area and caused by the low-density of the Tertiary rocks. Horizontal gradient, tilt angle and analytical signal methods were applied to the observed gravity data and showed that Mubona, Mpenge and Cyabararika surface springs are structurally controlled while Rubindi spring is not. The integrated results of gravity gradient interpretation methods delineated a dominant geological structure trending in the NW-SE, which is in agreement with the regional geological trend. The results of this gravity study will help aid future geothermal exploration and development in the Kinigi geothermal field. [ABSTRACT FROM AUTHOR]

The Anambra basin constitutes the southeastern lower portion of the Benue Trough, which is a large structural depression that is divided into lower, middle and upper parts; and is one of the least studied inland sedimentary basins in Nigeria. Sequence stratigraphic interpretation had been carried out in parts of the Anambra Basin using data from three wells (Alo-1 Igbariam-1 and Ajire-1). Geophysical well logs and biostratigraphic data were integrated in order to identify key bounding surfaces, subdivide the sediment packages, correlate sand continuity and interpret the environment of deposition in the fields. Biostratigraphic interpretation, using foraminifera and plankton population and diversity, reveals five maximum flooding surfaces (MFS) in the fields. Five sequence boundaries (SB) were also identified using the well log analysis. Four 3rd order genetic sequences bounded by maximum flooding surfaces (MFS-1 to MFS-6) were identified in the areas; four complete sequences and one incomplete sequence were identified in both Alo-1 and Igbariam-1 wells while Ajire-1 has an no complete sequence. The identified system tracts delineated comprises Lowstand Systems Tracts (progradational to aggradational to retrogradational packages), Transgressive Systems Tracts (retrogradational packages) and Highstand Systems Tracts (aggradational to progradational packages) in each well. The sand continuity across the fields reveal sands S1 to S5 where S1 is present in Ajire-1 well and Igbariam-1 well but not in Alo-1 well. The sands S4 to S5 run across the three fields at different depths. The formations penetrated by the wells starting from the base are; Nkporo Formation (Campanian), Mamu Formation (Late Campanian to Early Maastrichtian), Ajali Sandstone (Maastrichtian), Nsukka Formation (Late Maastrichtian to Early Palaeocene), Imo Formation (Palaeocene) and Nanka Sand (Eocene). The environments of deposition revealed are from coastal to bathyal. The sands of lowstand system tract and highstand system tract found in Ajali, Nsukka, Nkporo and Imo (Ebenebe Sandstone) Formations show good continuity and as such good reservoir qualities while the shales of the transgressive system tracts which includes the Imo Formation, Mamu, and Nkporo Formations where most of the maximum flooding surfaces were delineated, can serve as seals to the numerous reservoir units. Combinations of the reservoir sands of the lowstand system tract and highstand system tract and the shale units of the transgressive system tract can form good stratigraphic traps for hydrocarbon and hence should be hydrocarbon exploration targets. [ABSTRACT FROM AUTHOR]