Subsidence History Research Articles

Long-Term Ground Deformation Monitoring and Quantitative Interpretation in Shanghai Using Multi-Platform TS-InSAR, PCA, and K-Means Clustering

Ground subsidence in urban areas is mainly due to natural or anthropogenic activities, and it seriously threatens the healthy and sustainable development of the city and the security of individuals’ lives and assets. Shanghai is a megacity of China, and it has a long history of ground subsidence due to the overexploitation of groundwater and urban expansion. Time Series Synthetic Aperture Radar Interferometry (TS-InSAR) is a highly effective and widely used approach for monitoring urban ground deformation. However, it is difficult to obtain long-term (such as over 10 years) deformation results using single-platform SAR satellite in general. To acquire long-term surface deformation monitoring results, it is necessary to integrate data from multi-platform SAR satellites. Furthermore, the deformations are the result of multiple factors that are superimposed, and relevant studies that quantitatively separate the contributions from different driving factors to subsidence are rare. Moreover, the time series cumulative deformation results of massive measurement points also bring difficulties to the deformation interpretation. In this study, we have proposed a long-term surface deformation monitoring and quantitative interpretation method that integrates multi-platform TS-InSAR, PCA, and K-means clustering. SAR images from three SAR datasets, i.e., 19 L-band ALOS-1 PALSAR, 22 C-band ENVISAT ASAR, and 20 C-band Sentinel-1A, were used to retrieve annual deformation rates and time series deformations in Shanghai from 2007 to 2018. The monitoring results indicate that there is serious uneven settlement in Shanghai, with a spatial pattern of stability in the northwest and settlement in the southeast of the study area. Then, we selected Pudong International Airport as the area of interest and quantitatively analyzed the driving factors of land subsidence in this area by using PCA results, combining groundwater exploitation and groundwater level change, precipitation, temperature, and engineering geological and human activities. Finally, the study area was divided into four sub-regions with similar time series deformation patterns using the K-means clustering. This study helps to understand the spatiotemporal evolution of surface deformation and its driving factors in Shanghai, and provides a scientific basis for the formulation and implementation of precise prevention and control strategies for land subsidence disasters, and it can also provide reference for monitoring in other urban areas.

West Siberian sedimentary basin. Crustal subsidence caused by rock contraction in its lower part due to prograde metamorphism

The history of the crustal subsidence in the Mesozoic and Cenozoic in the West Siberian Basin – the largest sedimentary basin in the world – is considered. Most researchers associate its formation with post-rift subsidence of the crust, which followed an episode of strong lithospheric stretching about 250 million years ago near to the Permian to the Triassic transition. A characteristic feature of post-rift subsidence is a decrease in its rate in time. During the Mesozoic-Cenozoic history, in Western Siberia the rate of crustal subsidence should have slow down by an order of magnitude. However, the analysis of long (700–900 km) seismic profiles in the north of Western Siberia and in the Southern Kara Sea shows that since the beginning of the Mesozoic in these regions, on average, there has been an acceleration of the crustal subsidence. Under such circumstances, lithospheric stretching in them could be responsible for only a small part of the total subsidence of the crust of 6–7 km. In Western Siberia, the Earth’s crust is close to the isostatic equilibrium. Then, in the absence of strong stretching, the accumulation of thick sedimentary sequences in the basin could only have been caused by rock contraction in the lower crust due to prograde metamorphic reactions. To obtain the above results, we used, for the first time, some simple methods to analyze the structure of the sedimentary cover in the West Siberian Basin. Detailed seismic profiles have been published for many other deep basins on all the continents. The methods of their interpretation implemented in this paper can be easily applied to determine the role of lithospheric stretching in the formation of deep sedimentary basins on the global scale.

Effect of clayey sediment compression on fluoride enrichment in the Quaternary groundwater system of Cangzhou Plain, China

The effect of clay layer compression on the enrichment of groundwater fluoride remains unknown. Quaternary groundwater with high fluoride levels at the Cangzhou Plain, which has a long history of land subsidence caused by clay layer compression, poses a potential health risk. The spatial distribution and enrichment mechanisms of groundwater fluoride are identified by sample collection, hydrochemical analysis, and geochemical inverse modeling. The results revealed that fluoride concentrations in 82 % of the 122 groundwater samples above the limit in drinking water as 1.0 mg/L in China. Fluoride in shallow groundwater (depth <20 m, ∼average = 2.08 mg/L) was mainly originated from fluorite dissolution and influenced by groundwater HCO3−, pH, and cation exchange levels. Below ∼200 m, the main source of groundwater fluoride (∼average = 3.12 mg/L) was the compression−release of clay pore water with high F− concentration, which was generated by complex water-rock interaction. Based on hydrochemical inverse simulation and end-member mixing models, the pore water released from clayey sediments supplied 53 %−56 % of deep groundwater (>200 m) and contributed 2.07 −2.87 mg/L to F− concentration. The findings of this study provide a theoretical basis for future research on prevention of high fluoride groundwater induced by clayey sediment compression.

Eocene exhumation of the High Andes at ~30°S differentiated by detrital multimethod U-Pb-He thermochronology

Abstract The southern Central Andes (~25–40°S) exhibit a complex tectonic history, crucial for understanding orogenic processes in subduction-related orogens, yet debate on the timing and mechanisms of early Cenozoic topographic growth persists. We present double-dated detrital zircon U-Pb and (U-Th)/He thermochronology data from the early Oligocene–Miocene Bermejo Basin at ~30°S to investigate source unroofing during development of the High Andes. (U-Th)/He results yield dates of ca. 565–16 Ma (n = 73), with distinct detrital modes that indicate a mixing of sediment sources characterized by variable cooling and exhumation histories. We employ a novel approach for modeling detrital thermochronology data that leverages the shared basin subsidence history of multiple detrital modes to resolve provenance and source unroofing histories. Results from the lower Oligocene Vallecito Formation (northwestern Argentina) reveal that detritus was sourced from Permian–Triassic Choiyoi Group rocks that underwent rapid late Eocene cooling, indicated by short lag time (2–5 m.y.) between source cooling and deposition. Our findings are consistent with bedrock studies of Eocene exhumation in the High Andes and establish source-to-basin connectivity during this time. Other detrital modes with pre-Cenozoic cooling histories were derived from Carboniferous Elqui-Colangüil and Choiyoi Group rocks or recycled from Paleozoic basins. We propose that an early Oligocene drainage divide in the High Andes was located west of the Punilla–La Plata fault, an active thrust front at ~30°S. These findings challenge Paleogene neutral stress-state models for the Andes and underscore the importance of improved knowledge of erosion and deformation histories for refining models of Andean orogenesis.

Testing Mantle Convection Simulations With Paleobiology and Other Stratigraphic Observations: Examples From Western North America

AbstractMantle convection plays a fundamental role in driving evolution of oceanic and continental lithosphere. In turn it impacts a broad suite of processes operating at or close to Earth's surface including landscape evolution, glacio‐eustasy, magmatism, and climate. A variety of theoretical approaches now exist to simulate mantle convection. Outputs from such simulations are being used to parameterize models of landscape evolution and basin formation. However, the substantial body of existing simulations has generated a variety of conflicting views on the history of dynamic topography, its evolution and key parameters for modeling mantle flow. The focus of this study is on developing strategies to use large‐scale quantitative stratigraphic observations to assess model predictions and identify simulation parameters that generate realistic predictions of Earth surface evolution. Spot measurements of uplift or subsidence provide useful target observations for models of dynamic topography, but finding areas where tectonics have not also influenced vertical motions is challenging. To address this issue, we use large inventories of stratigraphic data from across North America with contextual geophysical and geodetic data to constrain the regional uplift and subsidence history. We demonstrate that a suite of typical geodynamic simulations struggle to match the amplitude, polarity and timing of observed vertical motions. Building on recent seismological advances, we then explore strategies for understanding patterns of continental uplift and subsidence that incorporate (and test) predicted evolution of the lithosphere, asthenosphere and deep mantle. Our results demonstrate the importance of contributions from the uppermost mantle in driving vertical motions of continental interiors.

2‐D Geodynamic Modeling of the Central South Atlantic Wide Rifted Margins, Implications for Evaporite Deposition

AbstractThe thick late syn‐ to early post‐rift shallow water evaporites in the most distal part of wide rifted margins is paradoxical with the deep depression at crustal breakup time predicted by isostatically compensated lithospheric thinning. Elevation of the distal margin and water depth during deposition of the late syn‐rift evaporites in the central South Atlantic are not well constrained and remain to be quantified. We use forward 2‐D thermo‐mechanical modeling coupled with melt prediction and surface processes to assess the contribution of lithospheric and mantle processes on the distal margin topography and subsidence history during continental rifting. Models show that (a) counter‐flow of depleted lower lithospheric mantle during rifting explains the magma‐poor nature of these margins and (b) weak crust and syn‐rift sediment control the wide crustal necking and subsidence history of the distal margin. Integration of our modeling results with quantified geophysical and geological observations suggests that (a) base level was down to −600 m below present‐day global sea level (bsl) during distal margin formation in the Aptian before sag and evaporite deposition, (b) base level was about −300/−400 m bsl at the end of evaporite deposition, and (c) scenarios with a fixed shallow base level (−400 m bsl) or with an increasing base level from an initially deep position (−1,600 m bsl) during evaporite deposition can both fit the observed evaporite distribution. However, erosional features along the base of evaporites suggest a deep initial base level.

Reduction of Subsidence and Large-Scale Rebound in the Beijing Plain after Anthropogenic Water Transfer and Ecological Recharge of Groundwater: Evidence from Long Time-Series Satellites InSAR

Beijing, China’s capital city, has experienced decades of severe land subsidence due to the long-term overexploitation of groundwater. The implementation of the South-to-North Water Diversion Project (SNWDP) and artificial ecological restoration have significantly changed Beijing’s hydro-ecological and geological environment in recent years, leading to a widespread rise in groundwater levels. However, whether the related land subsidence has slowed down or reversed under these measures has not yet been effectively monitored and quantitatively analyzed in terms of time and space. Accordingly, in this study, we proposed using an improved time-series deformation method, which combines persistent scatterers and distributed scatterers, to process Sentinel-1 images from 2015 to 2022 in the Beijing Plain region. We performed a geospatial analysis to gain a better understanding of how the new hydrological conditions changed the pattern of deformation on the Beijing Plain. The results indicated that our combined PS and DS method provided more measurements both in total quantity and spatial density than conventional PSI methods. The land subsidence in the Beijing Plain area has been effectively alleviated from a subsidence region of approximately 1377 km2 in 2015 to only approximately 78 km2 in 2022. Ecological restoration areas in the northeastern part of the Plain have even rebounded over this period, at a maximum of approximately 40 mm in 2022. The overall pattern of ground deformation (subsidence and uplift) is negatively correlated with changes in the groundwater table (decline and rise). Local deformation is controlled by the thickness of the compressible layer and an active fault. The year 2015, when anthropogenic water transfers were eliminated and ecological measures to recharge groundwater were implemented, was the crucial turning point of the change in the deformation trend in the subsidence history of Beijing. Our findings carry significance, not only for China, but also for other areas where large-scale groundwater extractions are causing severe ground subsidence or rebound.

Basin analysis study of block 53 in the Masilla Basin, Yemen, using a 1D-backstripping method

Basin study of 1D-backstrripping analysis was performed on the sediments in in the four exploration wells (Bayoot S1, Bayoot Sw3, Sharyoof 2, and Sharyoof 9) from Block-53, Masilla Basin. 1D backstripping analysis resulted in many curves of the subsidence of the basement during the deposition of the stratigraphic units. The 1D basin models show that the Masilla basin exhibited a complex subsidence history over a period of about 155 Ma and includes three stages of subsidence. The first stage was occurred at 132-155 Ma and shows high subsidence rate about 6.2 cm per1000 years) and deposition rate about 6.13 cm per 1000 years in the southwest part of Block-53. This stage formed as a result of thinning in the curst during the lithospheric extension. The second stage of subsidence was occurred at 66-128Ma and shows decrease the subsidence rates in the range of 1.99- 1.11 cm/1000 years and deposition rates between 1.19 and 0.69 cm/1000 years during the post-rift deposits, which is represented by Qishn Clastic and Carbonate formations (.At the third stage, the subsidence and deposition rates are high in the southwest of block-53 and found to be about 9.3 cm/1000 years and 9.2 cm/1000 years, respectively . The rapid in the subsidence rates during this stage is primary related to the cooling of lithosphere and loading of the sediments

Late Cretaceous Sevier Versus Laramide Orogenies in Wyoming‐Utah‐Colorado, USA: New Insights From Basin Subsidence History

AbstractVariability in subsidence rates within Upper Cretaceous strata of the Western Interior Basin offers crucial insights into the response of surface sedimentation styles to Sevier‐to‐Laramide tectonics and related deep mantle processes. The formation mechanisms of the Late Cretaceous Western Interior Basin in North America have long been a subject of debate. A re‐evaluation of the basin's subsidence history reveals rapid subsidence pulses lasting ca. 2 Myr within longer‐term (average 5.7 Myr) progradational or aggradational clastic wedges. The timing of these wedges, especially the widespread marine flooding resulting from subsidence, is constrained through the calibration of ammonite zonation with absolute dates. Sevier wedges exhibit a different architecture compared to the Laramide wedges. The former recorded initial rapid and widespread marine transgressions followed by long‐term coastal progradation, whereas the latter developed by initial erosional and progradational growth followed by aggradation and long‐term coastal transgression. The Sevier clastic wedges, initially accumulated within a N‐S elongated, long‐wavelength tectonic subsidence zone close to the thrust belt, gradually migrated cratonward. Starting in the early Campanian (ca. 82 Ma), the Laramide Orogeny developed along a NW‐SE trend and then migrated northeastward, roughly consistent with coeval long‐wavelength frontal basin subsidence. The spatio‐temporal variations in long‐wavelength tectonic subsidence indicate a shift in the dynamic subsidence's migration direction from eastward to northeastward, driven by changes in Farallon subduction direction and mode. Our work shows how repeated subsidence behavior in the Sevier‐to‐Laramide transition records evolving architectural responses and the trajectory of coeval dynamic topography.

Multi-phase subsidence history of the Sarawak continental margin and its regional significance

Subsidence analysis of Sarawak Basin using stratigraphic data from a selection of exploration wells revealed a multi-phase history of crustal extension (rifting), subsidence and uplift. A relatively rapid subsidence during the early rift phase from Eocene to Oligocene (ca. 37–28 Ma) was followed by a gradual decrease in subsidence rate as the extended lithosphere underwent post-rift thermal relaxation (ca. 28–22 Ma). A second phase of extension during the Early Miocene (ca. 22–17 Ma) resulted in an increase in subsidence rate, which coincided with a major episode of compressional deformation, uplift and localised erosion. This deformation event culminated in a major unconformity dated ~16 Ma, known as the Middle Miocene Unconformity (MMU), which is recognised throughout the Bunguran Trough and North Luconia regions of Sarawak Basin as a major stratigraphic hiatus spanning the Early to Middle Miocene. Since the Late Miocene, there had been an increase in the subsidence rate, probably due to progradation of the Sarawak shelf to its present-day configuration. The complex subsidence history of Sarawak Basin is similar to those reported from other parts of the South China Sea margin. The subsidence histories indicate a common, underlying tectonic factor which is probably related to rifting and sea-floor spreading in the southwestern prong of the South China Sea oceanic basin.

Paleogene carbonate ramp development in the Kohat Basin of northwestern Pakistan

A series of well-exposed Paleogene sedimentary successions in the Kohat Basin of northwestern Pakistan (western Himalayas), are used to document the development of Paleogene sedimentary sequence deposited in a clastic–carbonate–evaporate distally steepened to a homoclinal ramp setting. Larger benthic foraminifer stratigraphy, sedimentology and microfacies were used to reconstruct the depth of deposition of the sediments and to aid in reconstructing the subsidence history of the sedimentary basin through the Paleogene. Based on the timing of the cessation of marine sedimentation and the subsidence analysis of the Paleogene rocks of the Kohat Basin, we conclude that a proto-closure of the basin occurred in the early Eocene (Ypresian) at ca 50–49.5 Ma, followed by return of marine sediments, with full closure of the Tethys seaway in the middle Eocene ca 40–41.2 Ma (Lutetian), potentially resulting in diachroneity of emergence of basins along strike of the orogen.

Formation and diagenesis of authigenic silicates in the Late Paleozoic alkaline lake deposits, Junggar Basin, NW China

Authigenic silicates are typical minerals of alkaline lake deposits. Their mineral composition and lateral distribution can be used for reconstructing paleoclimates, paleoenvironments, and diagenetic subsidence histories of hydrocarbon reservoirs. In particular the examples of pre-Mesozoic alkaline lake deposits were widely missing in the literature. To unveil this, a basin-wide high-resolution mineralogical investigation is conducted on the Late Paleozoic volcanic-related alkaline lake deposit of the Fengcheng Formation in the NW Junggar Basin, NW China. The investigated Late Paleozoic shales mainly contain stable silicates like K-feldspar, albite and reedmergnerite. Laterally, the authigenic silicates are mostly distributed in the lake-central and transitional zones and are especially abundant in organic-rich shales. Authigenic K-feldspar and albite were mainly formed by replacing detrital clay minerals and K-feldspar or directly precipitating from alkaline porewaters. Reedmergnerite was later formed by replacing acid-sensitive carbonate or feldspar minerals when organic matter was mature. Organic matter thermal maturation and hydrocarbon generation helped lower porewater pH and periodically open diagenetic systems. These processes facilitated fluid migration and element exchanges and promoted the transformation of thermodynamically unstable silicates and acid-sensitive carbonates to more stable silicates and quartz. A main result of this study is thus to emphasize the control of organic matter diagenesis and temperature on authigenic silicate evolution. This model can help revisit the genesis of the dominant felsic shales in alkaline lake deposits.

Paleoenviromental evolution of the Cenozoic foreland basin to intermontane basins in the Eastern Cordillera, North-Western Argentina

The stratigraphic and sedimentological characteristics of the Cenozoic deposits are very important aspects to investigate the tecto-sedimentary evolution of the Andean foreland basin to intermontane hinterland basins in north-western Argentina. These deposits lie in an unconformity or paraconformity relationship over the Salta Group (Cretaceous-Paleocene) or older deposits. During the middle Eocene-Pleistocene, the changes in the sedimentary paleoenvironment and its evolution are the direct result of tectonic effects, a change in base level and accommodation space. This study provides the results of the integrated analysis of the middle-upper Eocene to Plio-Pleistocene basins in the Eastern Cordillera, in north-western Argentina. These basins that have been generated in the Central Andes region in north-western Argentina during the Cenozoic tectonic convergence, we divided in four sequences in the evolution from middle to upper Eocene to Plio-Pleistocene. They present fluvial deposits of different topographic slopes, with development of ephemeral fluvial systems associated with dune fields, meandering fluvial systems in arid climates, interlaced sandy-gravelly fluvial systems, sinuous sandy-gravelly fluvial systems of intermediate to high sinuosity, with the development of lagoons and swamps of tropical climate during ∼10 to ∼5 Ma, and the change to arid - semiarid claimed condition from ∼5 to ∼2.5 Ma. The sedimentary record of the Plio-Pleistocene hinterland basin in the Eastern Cordillera and the adjacent Andean Puna Plateau in the Central Andes of NW Argentina constitutes geological archive that provide spatio-temporal insights into geological evolution and associated surface uplift.These basins, probably connected at their onset during the middle Eocene, are characterized by different subsidence histories, differences in sedimentary paleoenvironment evolution, variations in topographic slopes, changes in provenance and paleocurrents, resulting in differences in tecto-sedimentary history.

Sequence stratigraphy of a wave-dominated, tidally influenced delta in the Danian of Seymour Island, Antarctica: An integrated sedimentological–palaeoecological approach

Lower Paleocene marine siliciclastics of the Sobral Formation (Seymour Island, Antarctica) form an important component of a key southern high latitude reference section for the Maastrichtian–Eocene. The formation comprises a coarsening-upward, regressive succession (270 m thick), shallowing from prodeltaic, mud-rich to sandy nearshore sediments. Sedimentary facies analysis, integrated with macrofaunal and microfloral palaeoecological studies, indicate a wave-dominated, tidally influenced deltaic environment. Four depositional sequences (1–4) record the role of relative sea-level changes in controlling the stepwise progradation of the system. Prodeltaic and distal delta-front deposits (Sequences 1, 2), comprise coarsening-upward parasequences of mud-rich heteroliths and bioturbated fine-grained muddy sands displaying draped slump scars. The overlying erosional sequence boundary is marked by incised valleys filled with fluvio-estuarine sediments; succeeding sand-rich facies (Sequences 3, 4) represent the proximal delta front and delta platform. The macro-invertebrate and palynological datasets display contrasting responses to the regressive history of the formation. The macrofaunal record in the distal deltaic sediments reflects the marine influence, though a stratigraphic increase in diversity was controlled both by ecological factors and biotic recovery following the K–Pg event. The associated palynological assemblage also displays a strong marine signal and includes typical outer neritic – oceanic dinoflagellate cyst taxa. A sharp decline in macrofossil diversity and abundance in Sequences 3, 4 is compatible with ecological stress in shallow-water, restricted inshore settings. Though the palynological record at this level is terrestrially dominated, the marine component reflects the cosmopolitan nature of dinoflagellates, displaying the highest diversities in the formation. The regressive Sobral Formation ended a protracted c. 60 Myr history of regional subsidence and marine sedimentation; although amplified by two Danian sea-level falls of probable eustatic origin, the regressive trend heralded mid-Paleocene basin inversion potentially linked to the onset of regional tectonic reorganization that ultimately led to opening of the Scotia Sea.

Cretaceous to Recent tectono‐sedimentary history and subsidence of the Barreirinhas, Ceará and Potiguar Basins, Brazilian Equatorial Margin

AbstractStratigraphy along the Brazilian Equatorial Margin is a crucial guide to the geodynamic history of rifting of Pangea and formation of the South Atlantic Ocean. Understanding the evolution of the Brazilian Equatorial Margin, which intersects the Saint Paul and Romanche Fracture Zones on the western margin of South Atlantic Ocean, is also key for reconstructing eustatic histories and natural resource exploration. In this study, we quantify the stratigraphic and subsidence histories of three sedimentary basins—Barreirinhas, Ceará, Potiguar—that sit within the margin. Stratigraphy was mapped using ca. 900‐line‐km of two‐dimensional seismic data. Biostratigraphic and check‐shot data from 23 wells drilled on the continental shelf, slope and in the distal parts of these basins were used to date and depth‐convert stratigraphy. Check‐shot data were also used to parameterise compaction. The mapped stratigraphy was backstripped to calculate subsidence histories for the basins. Subsidence curves were decompacted, water‐loaded and corrected for palaeo‐water depths using biostratigraphic data from well reports. The mapped stratigraphy of the Barreirinhas and Ceará Basins and theoretical subsidence curves indicate that stretching factors did not exceed 1.6. These values suggest that these basins can be regarded as failed rifts. In contrast, more distal stratigraphy mapped in the Potiguar Basin to the south indicates that it stretched by a factor of 5–6. Calculated subsidence histories indicate that this basin formed primarily because of Cretaceous rifting and Cretaceous to Recent post‐rift thermal sag, with amplitudes governed by the amount of initial stretching.

Evolution of the foreland basins on either side of the Tian Shan and implications for lithospheric architecture

The previous understanding of Tian Shan's lithospheric architecture can be summarized into three models: unidirectional underthrusting, bidirectional underthrusting, and mantle upwelling. These models make distinctive predictions regarding the migration and subsidence histories of the foreland basins on either side of the range. Seismic profiles crossing both foreland basins document their migration and subsidence history. We analyze a seismic profile across the Southern Junggar foreland basin (SJFB) to the north of the range, which demonstrates that the basin migrated northward at ∼3.1 mm/yr during 22–16 Ma. Combining this with previously known migration rates of the Northern Tarim foreland basin (NTFB) to the south of the range, we constrain the migration of these two foreland basins relative to their basements. We then employ an elastic plate model to simulate the subsidence profiles across these two basins at ∼20 Ma, 13–16 Ma, ∼5 Ma, and 0 Ma constrained by back stripping well log data and seismic records of the basin onlaps. Our modelling reveals the propagation rates of the southern and northern Tian Shan thrust wedges and the evolution of their topographic loads. Our analysis and modelling demonstrate that the NTFB has the characteristics of a retro-foreland basin, whereas the SJFB resembles a pro-foreland basin during early-middle Miocene times. This suggests that the Tian Shan's growth during this period was dominated by underthrusting of the Junggar lithosphere. Furthermore, our analysis and modelling reveal a convergent pattern between the Tarim lithosphere and the Tian Shan changed from lithospheric indentation to lithospheric subduction after the middle Miocene, as the plate setting of the NTFB and SJFB changed. The Tian Shan had begun to uplift before the middle Miocene, with the orogen's height reaching half of its present elevation before the late Miocene.

Cenozoic Subsidence History of the Northern South China Sea: Examples from the Qiongdongnan and Yinggehai Basins

The Qiongdongnan and Yinggehai Basins are important petroliferous basins. To study the Cenozoic subsidence characteristics of these two basins, their controlling factors, and their implications, we studied the basins’ subsidence characteristics via one-dimensional, two-dimensional, and holistic subsidence. Then, we compared the basins’ subsidence characteristics based on the evolution of several particular geological processes that occurred in the South China Sea (SCS) and adjacent areas. The results indicated that the change in the holistic subsidence of both basins occurred episodically. In addition, the subsidence in these two basins differed, including their subsidence rates, the migration of the depocenters, and the changes in the holistic subsidence. The dynamic differences between the two basins were the main factors controlling the differences in the subsidence in the two basins. In the Qiongdongnan Basin, the subsidence characteristics were primarily controlled by the mantle material flowing under the South China Block in the Eocene and the spreading of the SCS from the Oligocene to the Miocene. In the Yinggehai Basin, the subsidence characteristics were primarily controlled by the coupling between the uplift of the Tibetan Plateau and the strike-slip motion of the Red River Fault before the Early Miocene and by only the effect of the strike-slip motion of the Red River Fault from the Middle Miocene to the Late Miocene. Since the Pliocene, the subsidence characteristics of both basins have been principally controlled by the dextral strike-slip motion of the Red River Fault. The major faults contributed to the spaciotemporal variations in the subsidence within each basin.

Recovery of the Alberta Basin Sedimentary Structures in Southern‐Central Alberta Using Nonlinear Inversions of Receiver Functions

AbstractSecondary converted waves from receiver functions are highly sensitive to physical properties below the Earth's surface. When modeled properly, the waveforms of converted waves offer direct constraints on the impedance contrast, depth, and P‐to‐S velocity ratio pertaining to sedimentary, crustal and mantle interfaces. In this study we introduce a nonlinear waveform inversion algorithm that matches the first 5 s of receiver functions recorded in the Alberta Basin within the Western Canada Sedimentary Basin (WCSB). Our algorithm searches for the optimal thickness of the sedimentary cover and shear velocities of appropriately selected layers within and below it. Combining inversions with forward simulations, we determine the supracrustal stratigraphy from 80 regional broadband seismic stations in the WCSB. The inverted models show east tapering sedimentary layers with their thicknesses ranging from ∼6 km beneath the foothills of the Canadian Rocky Mountains to 3–4 km beneath the Alberta Basin. This finding is consistent with the sedimentary strata determined from regional well‐logging data. The sedimentary layer contains low velocity zones of variable thicknesses and amplitudes that, depending on the locations, may be caused by mechanisms involving deposition, composition or deformation history. Our shear velocity models near the top of the basement complement the existing sonic‐logs or single component seismic data and offer new constraints on the subsidence history of the WCSB. The resolved range of depths (0–14 km) effectively bridges the gap between the vertical scales of well logging (0–6 km) and those of traditional broadband analysis (&gt;10 km) involving receiver functions and surface waves.

Tectono-sedimentary evolution of the Paleogene Qikou Sag, Bohai Bay Basin, NE China

The Qikou Sag is a petroliferous tectonic unit within the Bohai Bay Basin, northeast China. The depositional system evolved temporally, spatially, and episodically in five rifting stages (stages 1–5) during the Paleogene and Neogene, with sedimentation responding to regional subsidence. This study focuses on the tectono-sedimentary evolution through stages 2–4, while the main oil-bearing sedimentary rocks were deposited in the Bohai Bay Basin. The depositional system exhibited retrogradation and then progradation during the rifting stage 2 (43–36.7 Ma), retrogradation in stage 3 (36.7–32.8 Ma), and upward coarsening and progradation in stage 4 (32.8–24.6 Ma). This vertical superposition corresponded to three episodic stages of rising and falling lake levels during the Paleogene, which were equivalent to a transgressive with regressive (stage 2), transgressive (stage 3), and then regressive (stage 4) cycle. The sediment fills coincided with the tectonism and the regional subsidence history of the Qikou Sag, which is composed of uplift areas and sub-sags. In this respect, the boundary fault activity around the sub-sags decreased from stages 2–4, leading to the migration of sub-sag depocenters from near faults to the center of sub-sags, which suggests that faults released control over the sedimentation. Secondly, tectonism and the total subsidence rate decreased from SQ1 to SQ7 (stages 2–3) and then accelerated at the end of stage 4 (SQ10 to SQ11). The tectonic subsidence rates decreased quicker than the total subsidence rate; this demonstrates that major rift faulting was the dominant geological process in the early Paleogene, whereas overall subsidence was dominant in the late Paleogene.

Natural History of Metacarpal Subsidence following Trapeziectomy and Its Relationship to Clinical Outcomes.

An institutional review board-approved retrospective review of patients who underwent trapeziectomy and ligament reconstruction and tendon interposition (LRTI) was conducted. Patient demographics, visual analogue scale pain scores, grip strength, pinch strengths, and radial and palmar abduction were collected. The trapezial space ratio (TSR) was measured by the scaphometacarpal distance divided by the length of the capitate. Subsidence [(postoperative TSR - preoperative TSR)/preoperative TSR] was measured and classified as severe (≥70%) or mild to moderate (<70%). Median rate of subsidence increase was calculated. Conolly-Rath scores were used to evaluate the proportion of good outcomes in each group. A total of 141 trapeziectomies with LRTI were included. Subsidence increased 6.7% (5.4% to 23.0%) per week before 16 weeks and 0.3% (0.1% to 0.8%) per week thereafter. Visual analogue scale pain scores were not significantly different between patients with severe or mild to moderate subsidence ( P = 0.25) 16 weeks after thumb mobilization. The proportion of good outcomes was comparable between the two groups ( P = 0.12). There was no correlation between subsidence and pain (ρ = -0.20; P = 0.24), grip (ρ = -0.02; P = 0.93), key (ρ = -0.13; P = 0.62), tripod (ρ = 0.16; P = 0.71), or index tip pinch strengths (ρ = -0.28; P = 0.43) or radial (ρ = -0.03; P = 0.92) or palmar (ρ = -0.15; P = 0.61) abduction. Subsidence occurs in all patients after trapeziectomy and LRTI, stabilizing 16 weeks after mobilization. Degree of subsidence does not correlate with postoperative outcomes. Risk, II.