Tectonic Subsidence Research Articles

Location, extent, and magnitude of dynamic topography in the Late Cretaceous Cordilleran Foreland Basin, USA: New insights from 3D flexural backstripping

AbstractMantle‐induced dynamic topography (i.e., subsidence and uplift) has been increasingly recognized as an important process in foreland basin development. However, characterizing and distinguishing the effects (i.e., location, extent and magnitude) of dynamic topography in ancient foreland basins remains challenging because the spatio‐temporal footprint of dynamic topography and flexural topography (i.e., generated by topographic loading) can overlap. This study employs 3D flexural backstripping of Upper Cretaceous strata in the central part of the North American Cordilleran foreland basin (CFB) to better quantify the effects of dynamic topography. The extensive stratigraphic database and good age control of the CFB permit the regional application of 3D flexural backstripping in this basin for the first time. Dynamic topography started to influence the development of the CFB during the late Turonian to middle Campanian (90.2–80.2 Ma) and became the dominant subsidence mechanism during the middle to late Campanian (80.2–74.6 Ma). The area influenced by >100 m dynamic subsidence is approximately 400 by 500 km, within which significant (>200 m) dynamic subsidence occurs in an irregular‐shaped (i.e., lunate) subregion. The maximum magnitude of dynamic subsidence is 300 ± 100 m based on the 80.2–74.6 Ma tectonic subsidence maps. With the maximum magnitude of dynamic uplift being constrained to be 200–300 m, the gross amount of dynamic topography in the Late Cretaceous CFB is 500–600 m. Although the location of dynamic subsidence revealed by tectonic subsidence maps is generally consistent with isopach map trends, tectonic subsidence maps developed through 3D flexural backstripping provide more accurate constraints of the areal extent, magnitude and rate of dynamic topography (as well as flexural topography) in the CFB through the Late Cretaceous. This improved understanding of dynamic topography in the CFB is critical for refining current geodynamic models of foreland basins and understanding the surface expression of mantle processes.

Post‐collisional sedimentation of the Early Mesozoic Munamdong Formation in South Korea

Post‐collisional processes cause uplift and exhumation of the overthickened crust together with the formation of sedimentary basins. To determine the influence of post‐collisional processes on sedimentation, we investigated the Early Mesozoic Munamdong Formation of the Yuljeon Basin in the Korean Peninsula, deposited immediately after the orogenic events caused by the collision of the North China Block and South China Block. Facies analysis shows that the Munamdong Formation was deposited in a streamflow‐dominated alluvial fan under tropical/subtropical climatic conditions. Vertically, the Munamdong Formation exhibits a fining‐upward trend with changes in stacking patterns, from highly amalgamated channel conglomerates to floodplain fines, indicating a progressive increase in the creation of accommodation space exceeding sediment supply. Moreover, the types of gravels in the conglomerate beds and the petrographic characteristics of the sandstones suggest that the sediments were supplied rapidly from nearby Precambrian high‐grade metamorphic rocks and Triassic post‐collisional plutons. These results indicate the supply of sediment from restricted sources, implying that the drainage basins did not widen even during intermittent quiescence of basin subsidence. We interpret the fining‐upward trend and uniform composition of sediments to have resulted from rapid uplift and exhumation of the orogenic crust, together with rapid tectonic subsidence, possibly aided by post‐collisional magmatism. This study shows that the Munamdong Formation reflects a close connection between surficial sedimentation and post‐collisional tectonic processes. This study will help to fill the gap of understanding between deep crustal processes and post‐collision sedimentation with insight into the Early Mesozoic tectonic environment of the East Asian continental margins.

Tectonic subsidence of the southeast China coast: New evidence from Late Pleistocene transgression in Ningde bay

Subsidence of the ancient Zhejiang-Fujian Uplift (ZFU) is important to understand opening of the Chinese marginal seas and geomorphology of the east China coast. However, little was known about its subsidence history during the Quaternary. In this study we clarify three marine sedimentary layers constrained by luminescence (OSL) chronology in Ningde area of the southeast China coast, to reveal the regional subsidence evolution related to the ancient ZFU. The results show that three marine sedimentary layers above bedrock in Ningde area are formed during global sea-level highstands of MIS1, MIS3 and MIS5e, constrained by OSL datings of the three representative cores. Limited marine influence of MIS5e highstand indicated both by microfacies of the representative cores and by the paleo-shoreline outlined from 120 cores, implies that tectonic subsidence occurs here during the Late Quaternary. The offsets between the peak global sea level and the corrected paleo-shoreline elevations of MIS5e and MIS3 reveal that the average subsidence rate is ∼0.5 m/kyr since MIS5e and ∼ 0.8 m/kyr between MIS5e and MIS3 in Ningde area. This evidence suggests that the ancient ZFU possibly subsided rapidly since MIS5e and stabilized since MIS3. This study provides new insights into the subsidence history of the ancient ZFU and land-sea interaction in the tectonic subsidence region.

Depositional evolution, sequence stratigraphic framework and its response to relative sea-level change, the Middle and Lower Ordovician carbonate system on outcrops, north-western margin of Tarim Basin

Middle and Lower Ordovician series carbonate platform deposits develop well in the north-western Tarim Basin, Kalpin and Bachu outcrop. An integrated analysis of the outcrop, hand specimen, thin slice and geochemical data allows for interpreting the sequence framework, depositional architecture and the response to sea-level changes. The Middle and Lower Ordovician Yingshan and Yijianfang Formations comprise 2 composite sequences (CS1 and CS2) bounded by regional or major unconformities, 5 third-order sequences (Sq1–Sq5) defined by subaerial exposure unconformities or facies changing and 13–15 fourth-order sequences classified by the outcrop depositional cycle change. Twelve microfacies and seven microfacies associations are identified using hand specimens and thin sections. The primary depositional facies include platform margin reef–bank complexes, open platform intraclast or bioclast shoal, intra-shoal and restricted platforms shoal-dolomitic or intra-clastic tidal flats. The research indicates that the carbonate platform evolved from arid and semiarid ramps, restricted platform and dolomitic tidal flat (CS1) to the open and rimmed platform margins (CS2) and eventually was drowned at the end of the Middle Ordovician. The sea-level changes have been studied using the Fischer plot method, showing two sets of long-term shallow–deep–shallow trends. Large-scale transgressions occurred at the lower parts of Sq4, with a significant negative shift of δ13C and low-energy mudstone or wackestone depositional architectures. The Fischer plot, lithofacies cycle and the geochemical indicators correlate well and are comparable with Haq's global sea-level changes. Sea-level changes dominate the sequence framework and depositional evolution, and dual factors of sea-level change and tectonic subsidence constrain local Sq3-HST. The high-frequent fluctuation of sea-level changes has a noticeable control effect on the development of fourth-order depositional cycles of carbonate deposits.

Crustal Thickness Variations in the Central Midcontinent, USA, and Their Tectonic Implications: New Constraints Obtained Using the H‐κ‐c Method

AbstractThe central midcontinent of the USA's cratonic platform is a region of low elevation and relief underlain by tectonic basins, domes, faults, and monoclines. To investigate potential correlations among shallow crustal structure and crustal thickness, we produced a high‐resolution Moho‐depth map of the region by applying the recently developed H‐κ‐c receiver‐function method to data from EarthScope Transportable‐Array and Flexible‐Array stations. Results indicate that Moho depth varies from 38 to 57 km. Changes of Moho depth and of Vp/Vs ratios do not correlate with Precambrian tectonic boundaries, suggesting that they reflect post‐accretion tectonics. Deeper Moho underlies sedimentary basins, implying a relationship between crustal thickness and lithospheric subsidence. Thicker crust may be due to rift‐related underplating, and thinner crust may have undergone delamination. Some depth changes underlie known faults and fold zones. Since short‐wavelength undulations were detected only under high‐density seismic arrays, they may occur more widely but have yet to be resolved.

An allostratigraphic framework for the Late Albian to Early Cenomanian upper Fort St. John Group across the foredeep of the Western Canada Foreland Basin, NE British Columbia

Abstract The Upper Albian to Lower Cenomanian Hasler and Cruiser shales and intervening Goodrich Sandstone are up to about 800 m thick and constitute most of the upper Fort St. John Group in the foredeep of NE British Columbia. These rocks exhibit pronounced lateral changes in lithology and thickness from west to east, making their lithostratigraphic boundaries highly diachronous. An allostratigraphic approach to correlation, based primarily on discontinuity surfaces represented in wireline well logs, allows subdivision of these broad lithostratigraphic units, and permits correlation of genetic stratal packages across facies transitions, and from subsurface to outcrop. Upper Fort St. John strata spanning the foredeep in British Columbia are shown to be correlative with Viking allomember VD, and with the overlying Westgate and Fish Scales alloformations, previously defined in Alberta on the basis of outcrop, core and wireline log data. Bounding surfaces have also been correlated northward to connect with successions described from the Sikanni and Liard river areas of British Columbia. In the British Columbia study area, pyritic, largely unbioturbated mudstone of allomember VD thickens from 20 to 200 m, indicating syn-depositional flexural subsidence, greatest in the north-western part of the study area. The Westgate alloformation is also dominated by weakly bioturbated mudstone, but includes more common, thin, fine-grained sandstone beds, many with wave- and combined-flow ripples, organized in parasequences up to approximately 20 m thick. Westgate allomembers WA through WD take on a progressively more tabular geometry upward, reflecting diminishing flexural subsidence with time. Allomember WD includes shoreface/delta front sandstones (‘Goodrich Formation’) that extend eastward from the Foothills outcrop for up to 70 km. The Fish Scales alloformation, the base of which is defined by surface FE1, marks an abrupt introduction of sand across a muddy sea floor in response to sea-level fall. The upper boundary of the Fish Scales is the condensed section/downlap surface ‘Fish Scales Upper’ (FSU) beneath the Dunvegan alloformation. The Fish Scales alloformation is a pronounced wedge, thickening westward from approximately 100 to approximately 400 m. It consists mainly of pyritic, unbioturbated mudstone to claystone with a variable content of fish debris, indicative of dysaerobic to anaerobic bottom-water conditions. Ammonites do, however, indicate oxic surface waters. The Fish Scales alloformation comprises allomembers FA and FB, separated by an erosion surface termed the Base Fish Scales Marker (BFSM) which, throughout the Peace River region, has a veneer of chert pebbles that mark a major sea-level lowstand; pebbles were subsequently reworked by marine transgression. A 15 m thick conglomerate-filled channel (or paleovalley?), exposed in Hasler Creek, directly underlies the BFSM surface and is interpreted to be the deposit of a large river that supplied sediment to the lowstand shoreline. In the far west, close to the Foothills, the Fish Scales alloformation becomes sandy and bioturbated, and includes stacked ‘Goodrich’ shoreface sandstone bodies that prograded a few tens of km eastward. Mapped to the SE, allomember FA pinches out close to the Alberta-British Columbia border, whereas allomember FB persists as a thin and highly radioactive phosphatic mudstone, the base of which comprises the merged FE1 and BFSM erosion surfaces. Despite up to about 800 m of subsidence, sedimentary structures throughout the succession show that the sea floor, which formed a homoclinal ramp, remained above storm wave base, attesting to a very high sedimentation rate and effective offshore dispersal of sediment, primarily by storm-driven combined flows. Bivalves of the genus Posidonioceramus have recently been proposed as a marker for the base of the Cenomanian Stage. These fossils are found in the study area as low as the base of Viking allomember VD, which implies that the Albian-Cenomanian boundary may lie at a level significantly lower than the long-accepted ‘Base of Fish Scales’ erosion surface.

Experimental study of the parametric impact on size growth of maltodextrin particles in counter-current spray dryer

Spray drying is closely related to the final product quality as it is mostly the last unit operation in the processing line. Counter-current spray drying experiments are relatively difficult to perform and due to this reason limited data is available. In this study, extensive experimental data is analyzed and results are presented. To better understand and optimize the performance of the spray dryer, an analysis of the final product received from 45 experimental runs of counter-current drying of maltodextrin solution was performed to check for the dependency of product properties on operating conditions. Effects of varying degrees of drying air swirl, atomizing nozzle gas-to-liquid ratios (GLR), the position of the nozzle with respect to drying air inlet, and power input for drying were analyzed. An optical measurement technique was used to measure the particle size distribution, velocity, and direction of motion. Samples were collected and scanning electron microscope (SEM) images were taken to analyze the particle morphology. Hollow spherical particles with thin crust were generated. Puffing and agglomeration were observed to be the phenomena that contributed to the increase in particle size, however the impact of puffing was found to be marginal. The results proved a strong dependency of the counter-current spray drying process on nozzle spray parameters and its position in the tower. The moisture content of the product showed a strong negative correlation with the temperature of the drying medium. • 45 experiments carried out in semi-industrial scale counter-current spray dryers using maltodextrin. • Impact of each operational parameter on product properties was calculated using the Pearson correlation factor. • Gas-to-Liquid ratio of the slurry at the nozzle had the highest impact on the final product. • Smaller droplets dry quicker and do not agglomerate as often as larger droplets. • Larger particles obtained had lower sphericity, indicating the formation of agglomerates.

Petrogenesis of Jurassic granitic plutons in Liaodong Peninsula, NE China: Insights into the subduction of Paleo − Pacific plate

• Jurassic granites in Liaodong Peninsula formed at 184–179 and 162–151 Ma. • Granite geochemistry reveals the thinning of continental crust from Early to Late Jurassic . • The granites constrain the subduction history of the Paleo–Pacific plate. There is a debate about the subduction of Paleo − Pacific plate in the Jurassic tectonic evolution of the northeastern North China Craton. Here we present new geochronological and geochemical investigations for Early and Late Jurassic granites on Liaodong Peninsula. The Early Jurassic granites (184–179 Ma) show high SiO 2 and low MgO contents, and are classified as I − type granites, with enrichment in large − ion lithophile elements (LILEs) and light rare earth elements (LREEs) and depletion in high − field − strength elements (HFSEs) and heavy REEs (HREEs), and enriched Sr − Nd − Hf − O isotopic compositions. Combined with their typical adakitic properties as high Sr, low Y and Yb contents, and high Sr/Y ratios, we conclude that they originated from thickened lower crust. The spatio − temporal distribution of Early Jurassic intrusive and volcanic rocks and large scale of compressive deformation suggest the onset of flat subduction of Paleo − Pacific plate. In contrast, the Late Jurassic granites (162–151 Ma) are classified as I − type granites, with enrichment in LILEs and LREEs and depletion in HFSEs and HREEs and more enriched Sr − Nd − Hf − O isotopic compositions. Based on Sr and Y contents and Sr/Y ratios, we divided them into two groups. Group 1 show high SiO 2 and low MgO contents and typical adakitic properties, indicating an origin of thickened lower crust. In contrast, group 2 show relatively higher SiO 2 and lower MgO contents, with low Sr and high Y contents and high Nb/U ratios, suggesting an origin of lower crust in normal thickness. The spatio − temporal distribution of Late Jurassic bimodal igneous rocks and continuous volcanic and sedimentary deposition as well as the shifted accretionary complexes, indicate the oblique subduction of Paleo − Pacific plate.

Tectono‐Stratigraphic Evolution of the Foreland Fold‐and‐Thrust Belt of the United Arab Emirates

AbstractThe subsurface and surface structural geometries of the United Arab Emirates (UAE) fold‐and‐thrust belt (FTB) and foreland basins are interpreted from seismic, well data, and surface geology. Twelve horizons ranging in age from Miocene to Lower Jurassic were interpreted and mapped. Additionally, we outlined subsurface extent of Sumeini and Hawasina allochthonous nappes. The tectonic subsidence curves suggest that the final major passive margin rifting event occurred in the early Aalenian and lasted till Oxfordian. Loading of the Semail ophiolite thrust sheet and accompanying allochthonous thrust sheets resulted in uplift at ca. 95 Ma and rapid subsidence at ca. 83 Ma, indicating the transition of the Arabian margin from a rifted passive margin to a foreland basin. The region witnessed an accelerated subsidence during the late Oligocene‐Miocene, attributed to the initial collision of the Central Iran and Arabian plates. The Permian‐Jurassic NW‐SE oriented rift faults were reactivated as thrust faults during the Late Cretaceous ophiolite obduction and late Oligocene‐Miocene continental collision. Two different tectonic regimes are identified in the FTB. The northern regime is characterized by major inversion of the rift faults with up to 3,700 m throw, whereas the southern regime has a major pop‐up structure with possible basement origin. Four major west‐verging and east‐dipping thrusts, which cross the northern area, form fault‐propagation folds and dissect the entire stratigraphy. Moreover, the Hawasina décollement, together with the inverted basement structures formed the Jabal Hafit anticline as a backthrust structure.

Critical metal enrichment in crustal melts: The role of metamorphic mica

Abstract Metals such as Li, Be, V, Co, Nb, In, Cs, Sn, Ta, and W are considered resources that are critical for modern economies. They can be significantly enriched in granites and pegmatites, but the mechanisms of enrichment remain poorly understood. Many metal-enriched granitic magmas form through mica dehydration reactions during high-grade metamorphism. The preferential incorporation of these metals into micas provides a mechanism for concentration and mobilization during crustal melting. Comprehensive data sets of these elements and their partitioning in metamorphic micas across different metamorphic grades are currently lacking. We present the first extensive in situ laser ablation–inductively coupled plasma–mass spectrometry element data set collected from metasediment-hosted muscovite and biotite from three different metamorphic cross sections traversing sub-greenschist- (~400 °C) to granulite-facies conditions (>900 °C). Within the same sample, Li, V, Co, Cs, and Ta concentrations are higher in biotite, whereas Be, In, Sn, and W concentrations are higher in muscovite. Subsolidus micas record only nonsystematic compositional variations between samples. Suprasolidus biotites show systematic depletion in Li, Be, Sn, and Cs and enrichment in V and Co with increasing temperature in the highest-grade (muscovite-absent) samples. Indium and W reach peak concentrations in biotite at 750 °C and 850 °C, respectively. Muscovites record systematic enrichment in In and W and depletion in Be, Sn, and Cs with increasing metamorphic grade. These distinctive trends appear to be independent of tectonic setting (i.e., continental collision and crustal thinning). Our data set highlights the importance of higher-temperature melting (>750 °C), in particular, biotite breakdown reactions, for the release of Li, Be, Sn, Cs, and W into crustal melts.

Evidence of secular variation in Archean crust formation in the Eastern Indian Shield

Understanding the dominant crustal accretion model in any Archean craton is the key to understanding the dominant geodynamic process responsible for early crust formation during the Hadean (> 4.0 Ga) and Archaean (4.0–2.5 Ga). The continental crust has been proposed to have formed through either horizontal/vertical accretion related to subduction or mantle plume tectonic processes. Here, the Moho depths and average crustal Vp/Vs ratios are modelled at 16 broadband stations in the Eastern Indian Shield (EIS) through HK stacking of radial P-receiver functions (PRFs). These modelled parameters are used to test both plume and subduction models, which might have played a key role in the crustal accretion of the EIS throughout the Archean. We observe a correlation between crustal age and composition within the ellipsoidal Paleoarchean cratonic domain in the Singhbhum-Odisha-Craton (SOC), which reveals an increase in age from the younger granitoid core of the SOC (with thinning of felsic crust) to the surrounding older greenstone belts (with thickening of felsic crust). A thinner mafic crust resulting from multiple magmatic events characterizes the neighbouring Meso-Proterozoic Chotanagpur Granitic Gneissic terrain (CGGT). The Common Conversion Point (CCP) image of radial PRFs reveals northward subduction of the Paleoarchean SOC below the Meso-Proterozoic CGGT.

Depositional environment and sequence stratigraphy architecture of continuous Upper Permian and Lowermost Triassic deep marine deposits in NW and SW Iran

The end-Permian mass extinction, the greatest biotic crisis through the Phanerozoic, caused a severe loss of marine organisms in terms of abundance and diversity. Knowing sea level fluctuations, environmental conditions and the sequence stratigraphic architecture of the Upper Permian deposits will enable us to reconstruct events before the mass extinction and across the Permian/Triassic boundary in a regional and global context. The Upper Permian deposits are examined in well-known sections in Julfa, NW Iran and Abadeh in SW Iran using microfacies analyses, depositional environment interpretation and sequence stratigraphic framework. Detailed petrographic examination and microfacies analyses show third- and fourth-order cycles both in Wuchiapingian and Changhsingian deep-water distally deposited strata of Julfa and Abadeh sections. Considering Iranian tectonics during Permian through Triassic time, there was rifting accompanied by drift and subsequent subsidence. Tectonics was a main factor that influenced the depositional environment and sequence stratigraphic framework in the study areas. According to previous studies, since subsidence increased in a North to SW direction during Middle Permian through Triassic time, this effect is seen in lithologic characteristics of the Wuchiapingian with more mid-ramp settings in Julfa Beds in Julfa area, compared to the more outer-ramp settings of the Unit 6 of the Hambast Formation in Abadeh area. Tectonic subsidence influence was also responsible for creating the fourth-order cycles within third-order cycles despite the absence of common glacial events to create high-frequency cycles in Iran during the Lopingian. The Lopingian successive deepening in Iran caused the faunal changes which is evident in decreasing trend of body size and biodiversity in brachiopods and ammonoids and also marks the beginning of the transgressive system tracts during this time interval.

The Tucano Basin (Cretaceous, Brazil) – a world-class example of an aborted rift system with anomalous depth

The structural and stratigraphic characteristics of the central portion of the Tucano Basin, a Cretaceous continental rift basin in northeast Brazil, was investigated, using post-stack 2-D reflection seismic, gravity and well data. Methodology was steered by the principles of seismic stratigraphy, targeting at an adequate identification of stratal terminations and on the mapping of structural features, where a negative flower structure was interpreted. The identification of erosional truncations led to a stratigraphic framework of seven intra-rift unconformities, forming eight third-order rift sequences, while the literature on the Tucano basin recognizes only two depositional sequences forming the rift sedimentary infill. In order to study the abnormal depth of Central Tucano depocenter, gravity data were processed and a spectral analysis was performed, which located the depocenter at approximately 16.8 km, a rare configuration for a rift basin. Gravity models were created in order to verify the seismic interpretation and the depth found by the spectral analysis; and to provide a view of the basin in a regional scale, analysing its crustal architecture. The modelling confirmed the abnormal depth and also indicated a severe crustal thinning under Central Tucano Basin, where the Moho was interpreted around 24 km and a major crustal necking was observed. The models introduced the geometry of the lower continental crust and indicated the presence of a high-density layer (3000 kg/m3) at its base, which this work suggests to be a result of magmatic underplating. The paper closes discussing the role of tectonics and basement inheritance over the Central Tucano Basin structural framework and commenting on the mode of extension for the Recôncavo-Tucano-Jatobá rift system.

Resolving the Tectonic Setting of South China in the Late Paleozoic

AbstractThe tectonic setting of South China during the late Paleozoic is essential to understanding the geodynamics off the eastern margin of Pangea supercontinent due to its unique paleo‐position at the confluence of the Paleo‐Tethys and Panthalassic oceans. Limited late Paleozoic magmatic and matemorphic records in South China have hampered resolution of this tectonic setting. Here, we present integrated biostratigraphic, geochronological, and isotope geochemical data on the late Carboniferous siliciclastic rocks from southeast South China in order to decipher the tectonic evolution of the South China Block. The sandstones were predominantly sourced from the Wuyi Terrane via short‐distance transportation. Rapid exhumation of ca. 318 Ma plutonic rocks in the source region, evolution of source of magmatism, and continuous crustal thinning demonstrate that southeast South China underwent episodic lithospheric delamination triggered by thermal perturbation as a result of subduction of the paleo‐Pacific plate beneath the South China Block in the late Paleozoic.

Characterization and evolution of a carbonate basin floor fan on a leeward side of an isolated carbonate platform, Sirte Basin, Libya

The recognition of carbonate basin floor fans and the interpretation of their formation and evolution are extremely crucial to the hydrocarbon exploration since they form important oil and gas reservoirs. There has been little research on the geometries and controlling factors of the carbonate basin floor fans from subsurface three-dimensional (3D) seismic and wireline log data. Most studies have been conducted on siliciclastic basin floor fans. Thus, this study characterizes the internal configuration and processes controlling the deposition of a lower Eocene carbonate basin floor fan system in the Sirte Basin in a sequence stratigraphic context through integrated 3D seismic and wireline log interpretations. The carbonate fan complex shows hummocky to undulated seismic geometries on vertical seismic sections and bounded by an unconformable sequence boundary at the base and a downlap surface at the top. It has an aerial extension of around 9 km from south to north along depositional dip and at least 8 km from east to west along strike. In well data, the fan system predominantly comprises limestone units intercalated with thin shale intervals. Log curves display an overall funnel-shaped trend, suggesting progradational stacking pattern. The vertical thickness of the fan complex varies from 120 to 165 m. The evolution of the carbonate fan was influenced by the interplay of accommodation space and sediment supply. A pre-existing topography, tectonic subsidence, and sea-level rise generated accommodation space for the deposition of the fan system, whereas sediment-gravity flows transported the fan sediments from the platform interior and margin to the basin floor. This study provides sedimentological and stratigraphic criteria to recognize and interpret the evolution of basin floor fans along isolated carbonate platforms from 3D seismic and wireline log data and may serve as an analog for ongoing and future studies on carbonate basin floor fans elsewhere.

Causes of Variable Shortening and Tectonic Subsidence During Changes in Subduction: Insights From Flexural Thermokinematic Modeling of the Neogene Southern Central Andes (28–30°S)

AbstractThe Andes of western Argentina record spatiotemporal variations in morphology, basin geometry, and structural style that correspond with changes in crustal inheritance and convergent margin dynamics. Above the modern Pampean flat‐slab subduction segment (27–33°S), retroarc shortening generated a fold‐thrust belt and intraforeland basement uplifts that converge north of ∼29°S, providing opportunities to explore the effects of varied deformation and subduction regimes on synorogenic sedimentation. We integrate new detrital zircon U‐Pb and apatite (U‐Th)/He analyses with sequentially restored, flexurally balanced cross sections and thermokinematic models at ∼28.5–30°S to link deformation with resulting uplift, erosion, and basin accumulation histories. Tectonic subsidence, topographic evolution, and thermochronometric cooling records point to (a) shortening and distal foreland basin accumulation at ∼18–16 Ma, (b) thrust belt migration, changes in sediment provenance, and enhanced flexural subsidence from ∼16 to 9 Ma, (c) intraforeland basement deformation, local flexure, and drainage reorganization at ∼12–7 Ma, and (d) out‐of‐sequence shortening and exhumation of foreland basin fill by ∼8–2 Ma. Thrust belt kinematics and the reactivation of basement heterogeneities strongly controlled tectonic load configurations and subsidence patterns. Geo/thermochronological data and model results resolve increased shortening and combined thrust belt and intraforeland basement loading in response to ridge collision and Neogene shallowing of the subducted oceanic slab. Finally, this study demonstrates the utility of integrated flexural thermokinematic and erosion modeling for evaluating the geometries, rates, and potential drivers of retroarc deformation and foreland basin evolution during changes in subduction.

Land Subsidence Due to Creep of the Gulf Coast Aquifer System in the Houston-Galveston Region

ABSTRACT The compaction measurements of Quaternary and Tertiary Gulf Coast aquifer system sediments in the Houston-Galveston region (TX) show spatially variable compression of 0.08 to 8.49 mm/yr because of geohistorical overburden pressure when groundwater levels in the aquifer system were stable after about the year 2000. An aquifer-system creep equation is developed for evaluating this variable compression, with a thickness-weighted average creep coefficient based on Taylor's (1942) secondary consolidation theory. The temporal variation of aquifer system creep can be neglected in a short-term observation period (such as a decade) after a long-term creep period (such as over 1,000 years) in geohistory. The creep coefficient of the Gulf Coast aquifer system is found to be in a range of 8.74 × 10−5 to 3.94 × 10−3 (dimensionless), with an average of 1.38 × 10−3. Moreover, for silty clay or clay-dominant aquitards in the Gulf Coast aquifer system the creep coefficient value varies in the range of 2.21 × 10−4 to 3.94 × 10−3, which is consistent with values found by Mesri (1973) for most soils, which vary in the range of creep coefficient, 1 × 10−4 to 5 × 10−3. Land subsidence due to secondary consolidation of the Gulf Coast aquifer system is estimated to be 0.04 to 4.33 m in the 20th century and is projected to be 0.01 to 0.64 m in the 21st century at the 13 borehole extensometer locations in the Houston-Galveston region. The significant creep should be considered in the relative sea level rise, in addition to tectonic subsidence and primary consolidation.

Sedimentary characteristics and main controlling factors of the Middle-Upper Permian and Middle-Upper Triassic around Bogda Mountain of Xinjiang, NW China

Based on field geological survey, interpretation of seismic data and analysis of drilling and logging data, the evolution of geological structures, stratigraphic sedimentary filling sequence and sedimentary system around the Bogda Mountain were analyzed according to the idea of “structure controlling basin, basin controlling facies and facies controlling assemblages”. The tectonic evolution of the basin around the Bogda Mountain can be divided into nine stages. The Middle-Late Permian–Middle-Late Triassic was the development stage of intracontinental rift, foreland basin and inland depression basin when lake, fan delta and braided river delta sedimentary facies developed. Early intracontinental rifting, late Permian tectonic uplift, and middle-late Triassic tectonic subsidence controlled the shape, type, subsidence rate and sedimentary system evolution of the basin. The Bogda Mountain area was the subsidence center and deposition center of the deep water lake basin in the Middle Permian with mainly deep-water deposition and local gravity flow deposition. This area had tectonic inversion in the Late Permian, when the Bogda Mountain uplifted to form a low bulge and a series of fan delta sand bodies. In the Middle-Late Triassic, subsidence occurred in the Bogda low uplift, characterized by extensive development of braided river delta deposits.

Thicknesses of Mare Basalts in the Chang’E‐5 Landing Region: Implications for the Late‐Stage Volcanism on the Moon

AbstractChina's Chang’E‐5 mission has collected lunar samples from a young mare plain with elevated thorium contents in the northeastern Oceanus Procellarum of the Moon. In this study, we first established a local stratigraphic column of the landing region based on the radial variation of the titanium content in the ejecta of large penetrating craters, and we found that the landing region was flooded by at least four layers of mare basalts. By using the latest imagery, spectral, topographic, and gravity data, we then estimated the basalt thickness of each layer based on the excavation depth of penetrating craters, the morphology of partially buried craters, and the effective density spectrum technique, which can help to better understand the late‐stage volcanism on the Moon. Our results show that the four layers of basaltic lava flows in the landing region have accumulated thicknesses of 9–175, 11–167, 19–478, and 0–800 m. Combined with surface areas and ages of the basaltic units, we then calculated the eruption rate of mare basalts in the landing region, which shows an uptick at about 2 Ga. This result indicates a rejuvenated volcanic activity on the Moon, most likely due to the presence of heat‐producing elements in the KREEP layer. Alternatively, the long‐standing volcanism in this region could be also sustained by extra heating induced by the tidal force and/or a thin crust layer that favors the magma ascent.

Quaternary subsidence history of Xisha Islands (northern South China Sea): Evidences from the reef-bank system

Subsidence is a potentially important factor influencing the evolution of carbonate platforms. Yet, few studies have been carried out on the quantitative reconstruction of subsidence history of carbonate platforms in the South China Sea. Using paleo-water depth constraints from core XK-1, drilled in the Xisha Islands, northern South China Sea, the tectonic and total subsidence history of Xisha Islands during the Quaternary is quantitatively reconstructed in this study. Slow tectonic subsidence between 1.945 and 0.988 Ma was related with magmatic intrusion beneath the Xisha Islands, while the relatively high tectonic subsidence rate between 0.988 and 0.781 Ma and the subsequent gradual decline in tectonic subsidence rate between 0.781 and 0.07 Ma were linked to the thermal cooling process. A rapid tectonic uplifting process after 0.07 Ma occurred as a result of compression and volcano eruption. Total subsidence rate showed an increase from the stage of 1.945–0.988 Ma to the stage of 0.988–0.781 Ma, and a gradual decline during the stage of 0.781–0.07 Ma. After 0.07 Ma, there was a rapid uplifting in response to the tectonic movement. The high eustatic sea level and intermediate total subsidence rate from 1.945 to 1.0 Ma caused the domination of bank deposits on the Xisha carbonate platform. From 0.988 to 0.65 Ma, the long-term eustatic sea-level lowering and the relatively high total subsidence rate favored the production of thick reef units. By contrast, the low eustatic sea level and the slow total subsidence between 0.65 and 0.42 Ma forced the accommodation space to be limited, resulting in formation of thin reef-bank deposits and occurrence of exposure horizons. During the stage of slow subsidence, the high eustatic sea level around 0.4 Ma allowed the last presence of thick reef unit in the Quaternary section, after which the lower eustatic sea level reduced the accommodation space again and only thin bioclastic bank deposits and iron-stained exposure horizon occurred. Around 0.07 Ma, the Xisha Islands were continuously exposed due to the uplifting and low eustatic sea level. The strong winter monsoon caused a heterozoan factory nearby the Xisha Islands, and blew the carbonate sediments onshore forming aeolianites. Our results proves that the total subsidence has indeed greatly influenced the evolution of Quaternary carbonate system in the Xisha area. The long-term (at scale of Myr) sea-level lowering could facilitate the flourishment of corals, and a moderate total subsidence in the context of secular sea-level lowering would provide more effective accommodation space for the continuous reef accretion, favoring the formation of thick reef units in the tropical areas.