Seismic Reflection Profiles Research Articles

Extensional structures and Cenozoic magmatism in the northwestern South China Sea

This study investigates the crustal structure and Cenozoic magmatism in the northwestern South China Sea (SCS), based on two long-cable multi-channel seismic reflection profiles, together with gravity and magnetic data, and adjacent wide-angle refraction profiles. Basins/sags are bounded by large listric-normal faults (fault throws ≥ 0.5 km) and massifs are cut off by normal faults with small offsets (fault throws < 0.5 km) in the northwestern SCS. These structures are penetrated by magmatic edifices showing positive gravity and magnetic anomalies. syn-Rift magmatic intrusions/extrusions were intense in the basins/sags and continent-ocean transition zone while post-rift magmatism was widespread from basins/sags to massifs with the most intense stage occurring from 5.5 to 2.6 Ma. Based on previous geophysical and geochemical results, we suggest that syn-rift mantle upwelling from partial melting initiated seafloor spreading magmatic activities, whereas plume-related mantle upwelling contributed to the magmatism during and after seafloor spreading in the northwestern SCS. Stretching factors show that the upper and lower crusts have experienced differential extension from basins/sags to massifs. The non-uniform crustal extension resulted from upper crustal faulting and lower crustal flow. Particularly, the lower crustal flow was probably linked with the combined action of magmatic heating, mantle flow shearing stresses, and sediment loading, resulting in crustal boudinage and reestablishment of an equilibrium state over long distances.

Migration and localization of faulting near the intersection of the Dead Sea Fault and the Carmel−Gilboa−Faria Fault System

Crustal deformation and seismicity in the Levant region are mainly related to the plate-boundary Dead Sea Fault (DSF) and the intraplate Carmel−Gilboa−Faria Fault System (CGFS). The intersection between these two major fault systems is generally treated as a ∼35-km-wide deformation belt stretched between the Faria and Gilboa Faults. Here, we present spatial and temporal analysis of faulting near this intersection. Our analysis is based on new geological mapping, new high-resolution airborne light detection and ranging (LiDAR) data, and seismic reflection profiles and indicates northward migration and localization of the intersection over time since the early Miocene. We discovered and mapped outcrops of Miocene, Pliocene, and Pleistocene rock units as well as faults and reconstructed the evolution of deformation. Three main tectonic phases were identified in this area covering the following periods: the early−middle Miocene, the late Miocene−Pliocene, and the Quaternary. During the first phase, the DSF and the CGFS developed, and the CGFS faulted along a series of subparallel grabens and elongated NW−SE, between the southernmost Faria and the northernmost Gilboa faults, over a belt width of ∼35 km. During the second phase, deformation along the CGFS migrated northward and concentrated at an ∼6-km-wide zone in the northern Faria Anticline. During the third stage, small-scale northward migration and localization of the deformation to a width zone of ∼1−2 km at the southern boundary of the Beit She’an Valley occurred. Faults from the third phase reveal both sinistral and normal faulting. We propose that the currently active intersection between the DSF and the CGFS is located east of this localized deformation zone, near a right step of the DSF and the uplifted area of Tel Al-Qarn in the eastern Jordan Valley. We suggest that the northward migration and localization of this intersection are related to regional tectonic changes, spatial variations in the Sinai-Arabia Euler pole, and the localization of deformation along the DSF.

Crustal Structure of the Camamu‐Almada Margin Along the Northeastern Rift Segment of Brazil From an Integration of Deep‐Penetration Seismic Reflection Profiles, Refraction, and Gravity Modeling

AbstractThe Camamu‐Almada segment of the northeastern Brazil rifted‐passive margin covers an area of 22,000 km2 and includes: (a) thin to ultra‐thin metamorphic continental crust; (b) a transitional zone of unknown composition; and (c) Albian and younger oceanic crust. We investigate the structural‐magmatic evolution of the region by interpreting 19,000 line km of two‐dimensional reflection seismic data, 105 offshore well logs, and 15 seismic refraction stations. Interpretation of these data suggests that the 100 km‐wide rifted zone is structurally complex and composed of at least three discrete crustal blocks: (a) 10–40 km‐wide and 4–6 km‐thick zones of hyperextended continental and possibly unroofed lower continental crust with an average density of 2.88 g/cc; (b) two 20 km‐wide sub‐circular zones of exhumed mantle with an average density of 3.1 g/cc; and (c) 40–60 km‐wide and 6–7 km‐thick proto‐oceanic crust that formed in situ. These blocks are similar in thickness and composition to rifted zones described by previous workers along its conjugate margin in Gabon, West Africa, and on the rifted‐passive margin of the western Mediterranean.

Crustal‐Scale Fault Systems in the Korean Peninsula Unraveled by Reflection Seismic Data

AbstractAn approximately 40‐km long high‐resolution reflection seismic profile (P3) was acquired in the metropolitan area of Seoul in South Korea for the purpose of fault system imaging in a highly noisy and challenging urban environment. Two 12t seismic vibrators (mini‐vibs) were used as the seismic source. Data were recorded using a dual element seismic spread; 20 m spaced 421 wireless seismic recorders connected to 10 Hz geophones and 20 micro‐electro‐mechanical‐based landstreamer sensors (2 m sensor spacing) attached to one of the vibrators. The purpose of the dual spread employed was to delineate both near‐surface and deep structures. The processing results show good quality and the processing work was complemented by different analysis to further constraints the geological interpretation. The survey results provide evidence for the 3D geometry of three fault systems, including Chugaryeong, Pocheon, and Wangsukcheon faults. A gently westerly dipping set of reflectivity underlying a dome‐shaped package of reflectivity is interpreted as a fault, and could project to the known surface position of the Pocheon fault. The dome‐shaped reflectivity is interpreted as folded and faulted dyke or sill systems. Downward continuation of the interpreted fault intersects the sub‐vertical Chugaryeong fault in a zone where the current seismicity is observed, suggesting that these two major fault systems may have jointly evolved in the form of splay faults. Reflections from the Wangsukcheon fault are also present in the data and interpreted to dip approximately 60° to the east, in an opposite direction to the two other faults.

Early to middle Miocene ice sheet dynamics in the westernmost Ross Sea (Antarctica): Regional correlations

The present-day morpho-stratigraphy of the Ross Sea is the result of Cenozoic tectonic and cryospheric events, and constitutes a key record of Antarctica's cryospheric evolution. An enduring problem in interpreting this record in a broader regional context is that the correlation between eastern and western Ross Sea stratigraphy has remained uncertain due to the limited number of drill sites. We correlate the glacial-related features observed on a dense network of seismic reflection profiles in McMurdo Sound with those identified in the Nordenskjöld and Drygalski Basins, as well as the basins farther east in the central Ross Sea. We present an improved correlation of the regional patterns of early to middle Miocene ice-sheet variance across the Ross Sea constrained by new evaluation of seismic facies and age models from one site recovered by the Antarctic Drilling Project (ANDRILL) in the southwestern most part of McMurdo Sound. We also integrate this correlation with the recently published seismic framework in the central Ross Sea. The formation of U-shaped valleys during the early Miocene in McMurdo Sound, together with prograding sedimentary wedges in the western-most basins, and the central Ross Sea, suggest two major phases of overall advance of a marine-terminating ice sheet between ~18 Ma and ~17.4 Ma. Widespread formation of turbiditic channel-levee systems in McMurdo Sound and rapid sediment deposition in Nordernskjöld Basin point to subsequent ice-sheet retreat between ~17.4 Ma and ~15.8 Ma, coinciding with the onset of the Miocene Climate Optimum (MCO; ~17–14.5 Ma). However, the carving of troughs and formation of irregular morphologic features suggest that an extensive ice sheet still remained along the western Ross margin at ~17.4 Ma and a brief episode of ice-sheet advance occurred at ~16.8 Ma in the earliest interval of the MCO. Subsequent marine-based ice sheet advance during the Middle Miocene Climate Transition (MMCT, ~14.0–13.8 Ma) is indicated by widespread erosional features. Our results reconcile the semi-continouous seismic and drill core stratigraphy of the offshore Ross Sea continental shelf with inferences of ice sheet dynamics from continuous far-field deep sea and sea level records, as well as the highly discontinous (and heavily debated) onshore records of pre-MMCT glaciation and aridification of the Transantarctic Mountains at 14 Ma. • Core-log-seismic correlation allows regional correlation of the Ross Sea record • 2 major advances of marine-terminating ice sheet occurred between 18 and 17.4 Ma • Ice sheet retreated at the onset of the Miocene Climate Optimum • Short-term ice-sheet advance occurred at ~16.8 Ma • Widespread marine-based ice sheet correlates to the Miocene Climate Transition

A new metallogenic model for the giant manganese deposits in northeastern Guizhou, China

The recently discovered multiple world-class Nanhuanian manganese (Mn) ore deposits at Datangpo of northeastern Guizhou province in southern China provides substantial amount of Mn that can be economically important for industrial usage. Studies that we previously conducted suggest that these Mn ore deposits are likely manifestations of the deposition of volatile-rich Mn-bearing ore-forming materials originating from deep reservoirs. However, ore-forming structures that transport ore-forming materials, if existed, have not yet been identified. Here, integrated with three-dimensional (3D) geological modeling, aeromagnetic △T data processing and Bouguer gravity anomaly analysis, we found that the intersections of the northwest (NW)-trending early rift basins and the near east–west (EW)-trending Nanhua rift basins overlap with the localities of the giant Mn ore deposits in northeastern Guizhou. In addition, a seismic reflection profiles passing through the Mn mining district reveals an upward-widen, funnel-shaped seismically abnormal structure with a dimension of about 3-km-wide and 45-km-deep. The seismically abnormal structure highly likely represents a deep-seated diapir channel beneath the mining district. Such a structure could contribute to the transportation of Mn-bearing materials that are responsible for the final deposition of Mn ore deposits. This study not only offers a visualization of a deep-seated channel that may be part of ore-guiding structures, but also sheds light on a new metallogenic model of Mn ore deposit.

Evolution of a single incised valley related to inherited geology, sea level rise and climate changes during the Holocene (Tirso river, Sardinia, western Mediterranean Sea)

We performed a morpho-stratigraphic study of the Tirso River incised valley (Sardinia Island, western Mediterranean Sea), an erosional feature crossing the Sinis fault, a major normal fault bordering the Campidano basin between the Gulf of Oristano and the western Sardinia shelf. High-resolution seismic reflection profiles and multibeam echosounder data, integrated by age-constrained stratigraphic logs derived from 9 sediment cores enabled us to reconstruct the valley evolution during the Holocene. We found that the Tirso valley is the result of a single event of incision and infill during the last eustatic cycle, strongly controlled by the presence of the Sinis fault. In fact, this structure represents a geological threshold that marks an abrupt change in substrate lithology and seabed slope, which controlled the valley morphology, narrow when downcutting early Pliocene formations along the steeper open shelf, and wider inside the Gulf, in the Pleistocene alluvial deposits of the flatter Gulf of Oristano. The sedimentary record starts with alluvial sediments filling the valley along the shelf during the initial phase of sea level rise, i.e., over 10 ka. During the last ~9.0 ka, a bay head delta developed, with the formation of barriers at the gulf entrance. In the mid-late Holocene, the progressive sea-level rise led to rapid drowning of the barrier system, recorded by marine and estuarine sediments filling the valley. Analysis of ecological associations in the cores, collected along a valley-normal transect, allowed for a detailed reconstruction of the paleo-environmental conditions during the latest phase of the incised valley filling controlled by global climatic variations in the Mediterranean region between ~9.0 and ~ 4.5 ka. Together with eustasy, our work reveals that the evolution and sedimentary infill of the Tirso incised valley was strongly controlled by inherited geological constraints, which influenced the morphology of the valley and the stratigraphic pattern.

High-resolution magnetostratigraphic records of the pliocene sedimentary successions in Yengisar section, NW China, and its tectonic implications

The Neogene strata upward-coarsening sandstone and conglomerate sequences at the periphery of the Northeastern Pamir record the intense uplift of the paleosurface of the building mountains. To further improve our knowledge of source-sink processes, a detailed magnetostratigraphic investigation was carried out along the Yengisar section, which is located at the southwestern margin of the Tarim Basin. The new high-resolution magnetostratigraphic data revealed that the Artux Formation was deposited from 4.9 Ma to 1.9 Ma with three sedimentation rates changes. The variations in sedimentation rate may be due to the pulsating exhumation of the Western Kunlun Mountain, caused by the northward motion of the Pamir salient. By integrating the evidences from the seismic reflection profile and other magnetostratigraphic investigations in this region, the basal age of the Xiyu Formation and the early stages of growth strata deposition were estimated at ∼1.9 and 1.45 Ma, respectively. Based on the data, we propose that the progradation of the Xiyu Formation and the migration of the deformation front are the two independent responses of the sink region to the uplift events of the source region.

Detailed shallow structure of the seismogenic fault of the 1976 Ms7.8 Tangshan earthquake, China

In 1976, an Ms7.8 strong earthquake occurred in the Tangshan region of Northeast China within an ancient craton. In this study, we conducted shallow seismic exploration, drilling-based exploration, and exploratory trench excavation of ground fissures in the Tangshan Fault Zone and obtained a high-resolution shallow seismic profile. Through analysis of its lithology and sedimentary cycle, we constructed a composite drilling profile across the faults. Coupled with the shallow fault combination patterns identified from the exploratory trenches, the profile reveals that the Guye-Nanhu Fault was the shallow response fault in the seismogenic structure of the Tangshan earthquake. This fault is a strike-slip fault with a positive flower structure; the reverse fault branches become progressively steeper with depth and converge downward toward the vertical main strike-slip fault. A high-angle thrust fault is located to the west of the main strike-slip fault, and a series of small-scale normal faults appear in front of this fault, owing to local extension. The tectonic form revealed by the deep seismic reflection profiles further supports the superficial tectonic model. The near-NEE orientation of the stress field in North China and the lower strike-slip movement component of the Tanlu Fault Zone facilitate faulting in the Tangshan–Hejian–Xingtai Fault Zone, which lies diagonally in the middle rectangular area of the North China Plain faulted basin. The detailed structural model of the seismogenic fault obtained by various detection methods is of great significance for understanding the seismogenic mechanism of the Tangshan earthquake.

Morpho-stratigraphic evolution of a tectonically controlled canyon-channel system in the Gioia Basin (Southern Tyrrhenian Sea)

The Gioia-Mesima Canyon-Channel System (GMS) incises the northern part of the Gioia Basin, a post-Tortonian intra-slope basin located along the south-eastern Tyrrhenian margin. Integration of multibeam, side scan sonar and seismic reflection data allowed to reconstruct the morpho-stratigraphic evolution of the GMS and the main factors controlling its development and maintenance. The GMS drains the entire continental margin and displays a complex morphology consisting in two main courses: the Gioia-Petrace Canyon and the Mesima Canyon-Channel. These courses run parallel to each other, changing from narrow straight to meandering geometry until they merge into a single, relatively straight lower reach, which debouches in the Stromboli Valley. Seismic reflection profiles and morphometric analysis highlight a strong tectonic control on GMS location and morphology throughout its course. At large scale, tectonic structures cross cutting the GMS caused both the formation of a mini-basin in the upper slope and a larger confined sub-basin downslope. These features promote abrupt changes in slope gradients that in turn are reflected on the plan-view morphology and stratigraphic architecture (seismic facies and sediment depocenters) of the GMS. Particularly, the progressive infilling of the confined sub-basin caused changes in the GMS base level, determining a polyphased evolution of the system encompassing repeated erosional and depositional events. The complete infill of the sub-basin promoted a by-pass of turbiditic flows in the lower slope, leading to the development of the lower reach of the GMS and its connection with the Stromboli Valley. This connection favoured a base level lowering of the GMS, causing its rejuvenation by retrogressive upslope erosion. This stage was recorded only in the shelf-indenting Gioia Canyon, characterized by a narrow and entrenched course, with irregular longitudinal profile and multiple knickpoints. Based on these results, we propose an evolutionary architectural model of the GMS to point out how erosional and depositional processes of channel/canyon system in a tectonically controlled margin can rapidly change in space and time in relation to multiple factors.

Rupture characteristics and seismic assessment of the Qinling northern piedmont fault

Research on fault rupture characteristics and behaviors, as well as the quantification of activity parameters is an important basis to evaluate the future seismic hazard. What is the upper limit of the magnitude of normal fault has received more attention in recent years, especially in the several Cenozoic grabens around the Ordos block where major earthquakes have occurred. Previous work on faults in these grabens mainly focused on paleoseismicity and tectonic activity. However, research on the rupture characteristics and behaviors of these faults is relatively weak and poorly constrained, especially where the main fault is located at the contact interface between bedrock and Late Quaternary sediments. The Qinling northern piedmont fault (QNF) is an important active fault located in the southern border of the Weihe graben, separating the Qinling Mountains from the Weihe basin. The middle section of Qinling northern piedmont fault has been intensively active since the Late Quaternary and may have a high seismic risk. Therefore, we carried out shallow seismic exploration and borehole survey, as well as paleoseismological analysis in this section. Based on the seismic reflection profile and boreholes, this work reveals that the QNF is consist of the main fault, the secondary faults and the fracture zone, together constituting a typical Y-shaped structure, with a width of ∼130.0–140.0 ​m. Combined with paleoearthquake, chronology, geology and geodesy data, the future seismic hazard of the fault is evaluated, and its maximum vertical offset and maximum seismic capacity given are 2.4–5.4 ​m and 7.0–7.8, respectively.

Opening of the South China Sea marginal basin: Insights from the tectonic evolution of the ENE-striking Littoral Fault Zone

The northern South China Sea (SCS) continental margin has a very complex geological history within a multiplate convergent setting and has experienced multiphase tectonic movements, during which the largest significant petroliferous basin, the Pearl River Mouth Basin (PRMB), developed. Along the northern boundary of the PRMB, a prominent wide ENE-striking intraplate deformation zone, the Littoral Fault Zone (LFZ), stretches from west to east and is considered to be the major fault structure that formed during the spreading of the SCS and rifting of the northern continental margin. However, a lack of direct constraints on stratigraphic records and fault intersections due to difficulties with offshore geophysical exploration has resulted in uncertainty about the nature of the LFZ, especially the location, geometry and deep–shallow structural coupling, which are still unclear. In this paper, we use newly collected enhanced images provided by 2D long-offset multichannel seismic reflection profiles across the LFZ Pearl River Mouth (PRM) segment to analyse the deep structural and stratigraphic elements along the LFZ. Combining these data with previous findings, we attempt to advance the understanding of the NE–ENE-striking LFZ nature, evolutionary history and controlling effect on the tectonic and sedimentary processes that led to the formation of the PRMB. The results of this work shed new light on the geodynamic processes surrounding the PRMB. We suggest that the LFZ acted as a northern boundary fault with a three-phase transition over time. The first phase of fault activity initiated as a low-angle basement decollement (phase 1), followed by high-angle SE-dipping normal faults, which were mostly inherited from basement faults and reactivated during the Zhuqiong movement (phase 2). Above these two structures, the faults are characterized by strike-slip faulting, which occurred in the Oligocene (phase 3). The overall geometry of the LFZ shows right-step dextral features in the PRM segment that are obviously segmented by NW–WNW-trending faults. Our results highlight the significant role of this ENE-striking fault system in the basin sub-basin (sag) formation on the northern continental margin of the SCS.

The Thinnest Crust in South China Associated With the Cretaceous Lithospheric Extension: Evidence From SINOPROBE Seismic Reflection Profiling

AbstractLong‐standing debates exist over the mechanism of continental lithospheric extension and, more specifically, over the strain distribution across the lithosphere in intraplate settings. The Cretaceous extensional system in South China extends up to ∼800 km inboard of the Paleo‐Pacific convergent margin and enables investigation of the mechanism(s) of intraplate lithospheric extension. Here we use high‐resolution seismic reflection data to image the crustal and upper‐mantle architecture of the central segment of the extensional system. We identify a compositionally stratified upper lithosphere that has undergone depth‐dependent extension, expressed by heterogeneous normal faulting in the upper crust, widely distributed ductile stretching in the lower crust, mantle influx into the crust, a broadly smooth Moho with localized uplift, and mantle shear‐zone generation. We detect, beneath the center of the Ganzhou Rift, the thinnest crust (28–30 km thick) in South China. It spatially correlates with the locus of strong lithospheric thinning and asthenospheric upwelling. We suggest that the generation of the thinnest crust was assisted by lower‐crustal ductile stretching, mantle shearing, and exhumation during depth‐dependent extension. Our study provides insights into the partitioning of depth‐dependent extensional strain into an intraplate stratified lithosphere and the feedback between crustal and mantle processes that shaped the thinnest crust at a position ∼300 km inboard of the convergent margin during continental extension.

Velocity Structure and Cu-Au Mineralization of the Duobaoshan Ore District, NE China: Constrained by First-Arrival Seismic Tomography

The genesis of deeply buried deposits in the Duobaoshan ore district, the largest porphyry-related Cu-Mo-Au ore field in northeastern China, is not well understood and their exploration is lacking because the fine velocity structure of this region is not comprehensively understood. Herein, first-arrival seismic travel times were picked along a deep seismic reflection profile and inverted using the tomographic method to obtain a detailed velocity profile of the upper 2900 m of the crust beneath this region. The profile showed that the velocity varied from 1900 to 6100 m/s and that the crust was subdivided into five parts by two low-velocity (2500–4000 m/s) blocks. Based on previous studies, the boundaries between the high-speed and low-speed bodies were interpreted as hidden fractures, and the 5000–6100 m/s parts were interpreted as concealed granite bodies in these sections. Porphyry copper deposits in the Duobaoshan ore district were related to the occulted granite bodies, and epithermal Au deposits were associated with the occulted fracture zones. Comprehensive evaluation of hydrothermal activity, regional magnetic anomalies, and deposit distribution indicated that the hidden fractures served as channels for ore-related magmas. Combining previous research on the Duobaoshan ore district with our results of the high-velocity interface, we infer that the prospecting range of the Tongshan deposit is below the depth of 1000 m.

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

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

Subsurface structure of the Mazatlán basin, southeastern Gulf of California, Mexico, from seismic reflection and well data

The structure of the southeastern Gulf of California rifted margin is only partly known because of the thick sedimentary cover of the continental shelf and coastal areas of Sinaloa and Nayarit. Here we report the subsurface structure and probable age of the Mazatlán basin, one of the largest buried basins, based on interpretation of reprocessed by multichannel 2D reflection seismic profiles and an exploratory well drilled by Petroleos Mexicanos (PEMEX) between 1979 and 1980, as well as gravimetric data. The Mazatlán basin is located just north of the active subduction zone of the Rivera plate and west of the new oceanic crust accreted since the Pliocene at the mouth of the Gulf. The basin is bounded to the west by a high of the Late Cretaceous batholiths exposed in the Tres Marias Islands and in the normal faults bounding the Nayarit Troughs, and to the east by the late Oligocene-early Miocene extensional faults bounding the Sierra Madre Occidental. Based on the characteristics of the seismic profiles, the basin can be divided into three main sectors. The transition between the northern and central sectors is defined by an abrupt deepening of the basement that corresponds to the westward prolongation of ENE-WSW trending accommodation zones separating opposite tilted domains in the Sierra Madre Occidental. The acoustic basement is clearly defined in the central sector by a set of high-amplitude reflectors suggesting an igneous origin. The deepest part of the basin is located toward the coastal plain of Nayarit and coincides with a gravimetric minimum. We identify several high amplitude reflectors interpreted as mafic sills, which become more abundant toward the south. At least part of them can be correlated with the widespread mafic volcanism emplaced at 9–12 Ma along the eastern margin of the Gulf of California rift. In the northern and central sectors we identified three main stratigraphic boundaries (L1, L2, and L3) within the basin filling, which define seismo-stratigraphic sequences. The shallower sequences, limited by the L1 and L2 boundaries and attributed to the Pleistocene and part of the Pliocene, lack evidence of significant deformation. The sequence above L3 boundary, can be assigned to the earliest Pliocene and the Miocene since they are intruded by a ~ 10 Ma basaltic sill cut by the Huichol-1 exploratory well. The lower part of the basin is characterized by high amplitude reflectors that pinches out against the acoustic basement and correspond to volcanic tuffs and sedimentary deposits correlative with the lower member of the Comondú group exposed in Baja California, which includes ~23 to ~19 Ma distal part of ignimbrites sourced from the Sierra Madre Occidental in Nayarit. Faults with the most significant displacements have a listric geometry and dip from the E to NE. The maximum sediment thickness reported in the Huichol-1 well is 2800 m, with a two-way travel time of 2.7 s, but it reaches 3.7 TWTT in some areas. Based on sedimentation rates, the minimum age for the onset of sedimentation in the basin is ~19 Ma, which is consistent with the regional tectonic evolution of the margin.

Geological Characteristics of the Mesozoic Unconformities in Eastern Heilongjiang, NE China: Implications for the Mesozoic Continental Margin Evolution of Northeast Asia

Most of the significant petroleum- and coal-bearing sedimentary basins in Northeast Asia originated via rifting and thermal subsidence during the Late Jurassic-Early Cretaceous, followed by basin inversion in the Late Cretaceous. However, the tectonic background governing these basin prototype shifts has not been fully explored. The unconformities are excellent archives of plate boundary interactions and geodynamic switches in subduction zones. The Eastern Heilongjiang Province (EHLJ), Northeast China (NE China), comprises a series of Mesozoic-Cenozoic residual basins with well-preserved successions and provides significant insights into the tectonic characteristics and background of Northeast Asia. Mesozoic unconformities and large-scale contractional structures in the basins mark a series of important tectonic transitions in Northeast Asia. Based on the synthesis information of regional Mesozoic unconformities identified in the seismic reflection profiles and field outcrops of EHLJ, the tectonic characteristics and geodynamic background of the Mesozoic continental margin basins in Northeast Asia are analysed. The Middle-Upper Jurassic/basement unconformity (U1) can only be found in some areas of the Sanjiang and Hulin basins. It was a response to the continental collision of Siberia and the northern China–Mongolia tract along the Mongolia–Okhotsk suture during the Jurassic. The Paleo-Pacific Plate rapidly subducted in the NNW direction towards the eastern margin of Eurasia in the early Lower Cretaceous resulting in a mass of strike-slip faults and the widespread absence of deposits (Valanginian) (U2) in the EHLJ. Because of the subduction slab rollback of the Paleo-Pacific Plate during the late Lower Cretaceous, the local asthenospheric material upwelled, and fault and volcanic activities intensified in Northeast Asia. The Lower Cretaceous Dongshan Formation (Fm)/Muleng Fm unconformity (U3-1) reflects a specific scale of bimodal magmatism in the Songliao Basin and the EHLJ. The Pacific Plate subducted in a transformation from NNW to WNW during the early Upper Cretaceous (Cenomanian). The Houshigou Fm (Qixinhe Fm)/Lower Cretaceous angular unconformity (U3) reflects that on the basins experienced denudation after being extensively uplifted from the subduction events. With the subduction of the Kula Plate, a compression stress field during the later Upper Cretaceous Period controlled NE China. The basins underwent a widely compressive deformation, accompanied by large-scale thrusts, denudation and deplanation, resulting in Paleogene/Cretaceous unconformity (U4) was formed.

Coupled Lithospheric Deformation in the Qinling Orogen, Central China: Insights From Seismic Reflection and Surface‐Wave Tomography

AbstractWe combine a ∼485 km‐long seismic reflection profile and a S‐wave speed transect from surface‐wave tomography, to reveal the lithospheric deformation mode of the intracontinental Qinling orogeny, central China. We observe a thick lithosphere keel in the convergence zone between the Yangtze Block and the North China Craton (NCC) and a shallow‐crustal (8–15 km depth) décollement that extends into the lower crust of the Qinling Orogen. Combining with surface structural geology and magmatism, we interpret these seismic findings as kinematically linked features formed by renewed intracontinental convergence between the NCC and the Yangtze Block in the late Mesozoic. We highlight that the ∼40 km lithospheric thickening in the convergence zone was likely balanced by &gt; 130 km thin‐skinned crustal shortening along a crustal‐scale strain‐transfer décollement, and was responsible for the occurrence of late Mesozoic magmatism (∼160–100 Ma) at the southern edge of the NCC.

Quantitative Evaluation of CO2 Storage Potential in the Offshore Atlantic Lower Cretaceous Strata, Southeastern United States

The geological storage of CO2 in the Earth’s subsurface has the potential to significantly offset greenhouse gas emissions for safe, economical, and acceptable public use. Due to legal advantages and vast resource capacity, offshore CO2 storage provides an attractive alternative to onshore options. Although offshore Lower Cretaceous reservoirs have a vast expected storage capacity, there is a limited quantitative assessment of the offshore storage resource in the southeastern United States. This work is part of the Southeast Offshore Storage Resource Assessment (SOSRA) project, which presents a high-quality potential geological repository for CO2 in the Mid- and South Atlantic Planning Areas. This is the first comprehensive investigation and quantitative assessment of CO2 storage potential for the Lower Cretaceous section of the outer continental shelf that includes the Southeast Georgia Embayment and most of the Blake Plateau. An interpretation of 200,000 km of legacy industrial 2D seismic reflection profiles and geophysical well logs (i.e., TRANSCO 1005-1-1, COST GE-1, and EXXON 564-1) were utilized to create structure and thickness maps for the potential reservoirs and seals. We identified and assessed three target reservoirs isolated by seals based on their effective porosity values. The CO2 storage capacity of these reservoirs was theoretically calculated using the DOE-NETL equation for saline formations. The prospective storage resources are estimated between 450 and 4700 Mt of CO2, with an offshore geological efficiency factor of dolomite between 2% and 3.6% at the formation scale.

Physical property studies to elucidate the source of seismic reflectivity within the ICDP DSeis seismogenic zone: Klerksdorp goldfield, South Africa

Petrophysical properties of cylindrical core specimens from three boreholes from the International Continental Scientific Drilling Program, the DSeis project, measured at ambient pressure and room temperature conditions in various laboratories are presented and compared with downhole petrophysical data (sonic and density). The measured properties are from sixty-six rock specimens constituting metasediments, metabasalts and intrusives. Seismic velocities were measured using 0.5 MHz P- and S-wave transducers. To investigate the source of seismic reflectivity observed on the 2D legacy seismic data, we computed synthetic seismograms for adjacent rock units using downhole petrophysical data and compared them with seismic reflections from the reflection seismic profile. The experimental measurements show that the metasediments exhibit lower bulk densities and seismic velocities than the metabasalts and intrusive specimens. The porosity was found to be less than 2% for all the samples. No clear trends emerge when the Poisson's ratio is plotted against the P-wave velocities and porosities of the samples. A positive relationship is observed between the bulk modulus and P-wave velocities of the rock samples. The highest calculated reflection coefficients (RC) are associated with the metasediment-intrusive interfaces in all three boreholes. The intrusive-metabasalt and the metasediment-metabasalt interfaces exhibit low RC. Synthetic seismograms reveal strong reflections that coincide with high RC calculated using the bulk density and velocity data. The synthetic seismograms also revealed additional strong reflections that were not identified using the reflection coefficients calculated from the rock specimens, due to core loss in some lithological units. Successful correlations are carried out between the synthetic seismic data and the real seismic data, enabling us to correlate the stratigraphic sequence drilled in the boreholes to the seismic reflections observed on the legacy 2D reflection seismic data.