Increase In Subsidence Research Articles

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.

A globally robust relationship between water table decline, subsidence rate, and carbon release from peatlands

Peatland ecosystems are globally important carbon stores. Disturbances, such as drainage and climate drying, act to lower peatland water table depths, consequently enhancing soil carbon release and subsidence rates. Here, we conduct a global meta-analysis to quantify the relationship among water table depth, carbon release and subsidence. We find that the water table decline stimulated heterotrophic, rather than autotrophic, soil respiration, which was associated with an increase in subsidence rate. This relationship held across different climate zones and land uses. We find that 81% of the total annual soil respiration for all drained peatlands was attributable to tropical peatlands drained for agriculture and forestry and temperate peatlands drained for agriculture. Globally, we estimate that, drained peatlands release 645 Mt C yr–1 (401–1025 Mt C yr–1) through soil respiration, equivalent to approximately 5% of global annual anthropogenic carbon emissions. Our findings highlight the importance of conserving pristine peatlands to help mitigate climate change.

Understanding along-strike variability in controlling mechanisms of paleoenvironmental conditions and stratigraphic architecture: Ordovician successions in the Alborz Mountains of Iran at the northern Gondwana margin

Changes in stacking patterns of facies, stratal architecture and shoreline trajectory along depositional strike are mainly dependent on along-strike differences in factors such as physical processes (rivers, waves, tides), tectonics, eustatic changes, sediment supply, and local physiography. The lower-upper Ordovician successions (Lashkerak Formation) deposited in a Peri-Gondwana shallow continental shelf have been interpreted using the sequence stratigraphic concepts. This approach allowed to highlight main differences along-strike in the co-existing depositional systems (coastal plains, estuaries, deltas, and shoreline to shelf systems) in the Alborz basin along the northern edge of Gondwana. On the basis of sedimentary and ichnological characteristics, the siliciclastic successions are divided into four facies associations: (i) Wave-dominated estuarine, (ii) Wave-dominated shoreface-offshore complex, (iii) Mixed fluvial (F)- and wave (W)-influenced delta (Fw and Wf), and (iv) Tide-dominated, fluvial-influenced delta (Tf). Six third-order depositional sequences (DS1-DS6) were recognized, each of them are bounded by unconformities and pronounced shifts in the facies. Along depositional strike (NE/SW- a distance of c. 150 km), significant intrabasinal changes in sediment supply produced evident lateral changes in the shoreline trajectory and stratal architecture, of the DS1-DS3 (Tremadocian-Floian), may be attributed to differences in physical processes (rivers, waves, tides activity) and topographic irregularities derive probably by different rates of subsidence in the basin. During the deposition of the DS1-DS3, a significant along-strike differences in the composition of ichnological suites and the lifestyle of benthonic organisms, dependent on the relative supremacy of wave, storm, river, and tidal processes. Sedimentary supply and processes are the main controlling factors for the stratigraphic architecture rather than the tectonic activity between Tremadocian and Floian. While during the Darriwilian-Katian interval (DS4-DS6), the tectonic activity predominates with the beginning of extensional phases related to the rifting in the Alborz basin causing the activation of syn-depositional normal faults and the development of block-faulted craton-ward margin. Typically, differential subsidence due to extensional tectonic activity causes the uplift of tectonic blocks west of the Alborz Basin into the emerging areas, on one hand, and simultaneous deepening-upward stacking patterns (i.e., increased subsidence rates) in the hanging-wall depocenters of east of the Alborz Basin, on the other hand. This outcrop-based study suggests that the identification of genetically related depositional units in a larger paleogeographic context is fundamental for understanding along-strike variability in controlling mechanisms of the spatial distribution and stratigraphic architecture of coexisting and linked depositional systems.

Anatomy of Anthropically Controlled Natural Lagoons through Geophysical, Geological, and Remote Sensing Observations: The Valli Di Comacchio (NE Italy) Case Study

Newly collected morphobathymetric and seismic reflection data from the Valli di Comacchio coastal lagoons, south of the Po River delta (Northeast Italy), combined with historical, remote sensing, and geodetic data highlight a complex geological evolution during the Holocene, strongly affected by anthropic control. All data allowed us to define the present-day depositional environment of the lagoons and reconstruct their recent (late Pleistocene/Holocene) geo-history. We focused on the effects of the anthropic impacts in modifying the pristine environments created by the Holocene transgression along the Adriatic Sea coast, at the mouth of a major river. They include land reclamation works, artificial damming, channel excavations, fluvial diversions, and a recent (last decades) increase in subsidence rate due to gas and water withdrawals. Despite the development of economic activities, which promoted occupation and exploitation of this area in the last millennia, the post-Glacial evolution of the lagoons shows the important role of inherited morphological features, such as sand ridges and barriers. This complex and relatively well-documented evolution makes the Comacchio lagoons a unique example of deep connections between natural processes and long-term human controls, offering insights into the management policies of these important and delicate environments challenged by global changes.

Assessing the efficiency of mitigation measures to reduce groundwater depletion and related land subsidence in Querétaro (Central Mexico) from decadal InSAR observations

Groundwater overexploitation occurs throughout Central Mexico and is a major threat to the sustainable development of the region. The two most direct impacts are on groundwater/surface water interactions and uneven land subsidence causing ground fracturing. The latter implies frequent and costly repairs to linear urban infrastructure such as roads or water/gas distribution conduits. In 2011, the state of Querétaro drastically changed the water management scheme to solve the groundwater depletion and ground fracturing issues in the Querétaro Valley. Groundwater extraction was decreased by half and the missing portion was replaced by water imports transported through a major 123 km-long aqueduct infrastructure. In this paper, we evaluate if this change in the water sourcing strategy has helped reducing groundwater overexploitation and the related ground fissuring. We present four consecutive radar interferometry-derived ground deformation time-series covering ∼75% of the period 2004–2020. We observed that maximum ground deformation has drastically decreased by a factor of ∼5 after 2011, from −25 to −50 mm/yr to ∼−10 mm/yr, suggesting the effectiveness of the drastic water management change. However, while groundwater static pressure has recovered in the range [4, 10] m in the six years following the change, extraction has been constantly increasing. Interferometric observations based on Radarsat-2 and Sentinel-1 data, in 2013–2014 and 2017–2020 respectively, detect increasing subsidence rates up to ∼−15 mm/yr. This suggests that the water management change only reduced the problem, and that a longer-term strategy will have to be implemented to fulfill the ever-increasing water demand in the region.

Large-scale vertical movements in Cenomanian to Santonian carbonate platform in Iberia: indicators of a Coniacian pre-orogenic compressive stress

The Cenomanian to early Santonian interval is usually considered a time of postrifting tectonic quiescence around the northern margins of Iberia that preceded the onset of the Pyrenean convergence by crustal thrusting in the latest Santonian. However, plate kinematic models of the Mesozoic evolution of Iberia poorly constrain the Turonian-Santonian position of Iberia relative to Eurasia. This study reconstructs changes in the sedimentary facies and architecture of the Iberian carbonate platform throughout the Late Cretaceous and sheds new light on the geodynamic evolution of the Iberia-Eurasia relationship at that time. Sixteen outcrop sections were described and 24 sedimentary facies identified that define 5 depositional environments ranging from the deep marine basin to the continental setting. From these and previously published field data we reconstruct the evolution of the Pyrenean carbonate platform, on an east-west transect nearly 400 km long, on the basis of 11 short-term depositional sequences and 5 long-term hemicycles. In our interpretation, the Cenomanian and Turonian correspond to a postrift stage during which the European and Iberian margins, together with the deep basin between them, subside gently, as shown by accommodation rates varying from ∼15 to 30 m/My in the margins and ∼100 to 150 m/My in the basin. The Coniacian and early Santonian are characterized by a large-scale flexural response consisting of (1) uplift of the southern Iberian margin, with negative accommodation rates, karstified surfaces and paleosols, and (2) increasing subsidence rates in the basin and its edges (the northern Iberian margin and eastern Aquitaine platform), with accommodation rates several times greater than during the Turonian. We propose that far-field stress possibly related to the northeastward motion of Africa, and/or onset of shortening at the Iberia-Europe boundary in the central and eastern Pyrenees led to the incipient large-scale flexural deformation in the Pyrenean domain. The late Santonian and Campanian are an early orogenic stage marked by rapid subsidence throughout the Pyrenean domain, except at its western end. We evidence for the first time a pre-orogenic flexure at the Iberia-Europe plate boundary induced by regional plate reorganisation between Africa and Europe during the Coniacian and the early Santonian.

Evaluation of Soil Ameliorants on Immature and Mature Oil Palms in Acidic Peat

Although peat soil has a low pH range of 3.2 to 3.8 units, it remains unclear whether this is a major constraint to oil palm cultivation, as the cultivar is known to tolerate fairly high levels of acidity without any serious adverse effects. Earlier work on liming and acidity correction has often given conflicting and sometimes, even negative results. In view of the latter, two trials were established to evaluate a number of soil ameliorants and their impact if any, on the growth and yield of newly planted and young mature palms in deep acidic peat. This paper summarises results over a 7- year evaluation period. Of the four ameliorants evaluated on newly planted seedlings in trial no.1, limestone dust (LSD) was the most effective in correcting acidity, raising the soil pH from 3.6 to 5.4 - 6.1 units in the top 30 cm of soil. Despite the significant improvement in soil pH, no advantage in nutrient uptake, palm growth and fresh fruit bunch (FFB) yield was recorded over unlimed control plots. In contrast, oil palm bunch ash (BA), eucalyptus fly ash (EFA) and paddy husk ash (PHA) had a smaller impact on soil acidity, but increased FFB yield from 2 per cent to 9 per cent, of which BA was the most effective, especially at the higher rate of application (9.0 kg/palm/year). One negative aspect of acidity amelioration is its impact on peat subsidence. Being highly caustic, application of LSD and BA accelerated decomposition and mineralisation of the peat, increasing subsidence rates by as much as 1.0 cm per annum. In trial no.2 which evaluated two potash sources [muriate of potash (MOP) and BA] on young mature palms, only annual applications of BA significantly improved soil pH, requiring up to 9.0 kg per palm per year to improve and maintain top soil pH above 5.0 units. BA was also superior to MOP in improving soil fertility, particularly the levels of exchangeable potassium, calcium and magnesium and also significantly reduced the concentration of free aluminium ions and aluminium saturation to low or negligible levels. Although BA ameliorated soil acidity and significantly improved soil fertility, no significant differences in FFB yield were recorded between BA and MOP. With MOP, response to fertiliser inputs was linear, highest yield being achieved with 6.0 kg per palm per year. In contrast, no significant differences were recorded between the different BA rates applied, with 4.50 kg per palm per year producing the same yield response as the highest rate of 11.25 kg per palm per year. For peat soil, BA appeared to be the more efficient K source, as it could attain the same yield as MOP, but at lower K inputs. As peat is reported to be very deficient in silica, it is suspected that any positive responses elicited by application of ash products (which have high silica content) could be a response to silica rather than correction in soil acidity. However, as no soil, foliar and product analysis was carried out for silica content in both trials, the latter will remain a hypothesis until proven otherwise. Trials are currently underway to evaluate the impact of silica on oil palm growth and yield in peat soils. Keywords: Acidity, bunch ash, oil palm, peat, soil amelioration.

Combined Study of a Significant Mine Collapse Based on Seismological and Geodetic Data—29 January 2019, Rudna Mine, Poland

On 29 January 2019, the collapse of a mine roof resulted in a significant surface deformation and generated a tremor with a magnitude of 4.6 in Rudna Mine, Poland. This study combines the seismological and geodetic monitoring of the event. Data from local and regional seismological networks were used to estimate the mechanism of the source and the ground motion caused by the earthquake. Global Navigation Satellite System data, collected at 10 Hz, and processed as a long-term time-series of daily coordinates solutions and short-term high frequency oscillations, are in good agreement with the seismological outputs, having detected several more tremors. The range and dynamics of the deformed surface area were monitored using satellite radar techniques for slow and fast motion detection. The radar data revealed that a 2-km2 area was affected in the six days after the collapse and that there was an increase in the post-event rate of subsidence.

Dating of mining-induced subsidence based on a combination of dendrogeomorphic methods and in situ monitoring

Mining-induced subsidence is a worldwide environmental problem that leads to damage to infrastructure and property; thus, knowledge of its past–recent development is critically needed during land-use planning. Moreover, the temporal occurrence of subsidence is greatly variable, with tendencies for gradual to abrupt movements. Subsidence rates can currently be achieved via radar interferometry, but these data usually cover short time periods and are less accurate in forested areas. In such cases, dendrogeomorphic dating can provide chronologies of past subsidence activity. In addition, comparisons of tree-ring-based data with in situ monitoring may answer the sensitivity and reliability of dating methods in these specific conditions of continuous ground movement. Geomorphic mapping and dendrogeomorphic dating were performed at two forested landslide sites affected by coal mining subsidence in the Upper Silesian Basin (Czech Republic), and the resulting chronology from one site was compared with levelling campaigns occurring from 1998 to 2015. Based on 284 increment cores from 71 trees, we were able to identify 7 subsidence events at the site dominated by a pioneering forest and 19 subsidence events at the site overgrown by a mature forest, with the most frequent responses occurring from 1956 to 1971 and 2005–2011. The occurrence of multiple compression wood growth intervals, some occurring in different directions of tree stems (more than 30% of sampled trees) indicated complex deformations presented by the flow-like mechanism of waterlogged surfaces, ongoing subsidence spreading, and fragmentation of larger blocks and grabens. A comparison of tree-ring-based chronology with in situ monitoring revealed good synchronicity with the periods of increased subsidence rates (between 1 and 3 m.year−1), thus indicating the high relevance of dendrogeomorphic methods for the determination of the most intense periods of ground subsidence. Our results show the first comparison of dendrogeomorphic methods with in situ monitoring of human-induced subsidence areas and provide an alternative option for reconstructing decadal to centennial development of the affected areas.

Change from rimmed to ramp platform forced by regional and global events in the Cretaceous of the Friuli-Adriatic Platform (Southern Alps, Italy)

Carbonate platforms are sedimentary archives recording the evolution of the global carbon cycle. Their stratigraphic architecture depends on the regional tectonics, controlling subsidence rates and geometries, as well as the paleoceanography and evolutionary trends, controlling the different organisms thriving at their margins, such as frame-building corals or mound-building microbes. We present an integrated bio- and chemostratigraphic study of the Aptian to Santonian interval of a base-of-slope section located in the Southern Alps of northeastern Italy that we correlate with the classic section representing the Friuli-Adriatic Carbonate Platform, one of the largest isolated platforms of the low latitude Tethys. We show the effects of the end of the passive-margin stage and the interaction between foreland flexuring due to the growing Alps, to which the study area represented the retroforeland, and the approaching prowedge of the Dinarides. The Friuli-Adriatic platform margin shows an abrupt change from reef rimmed to ramp, where abundant microbial mounds provided the habitat for the rudists to thrive. This change occurred around the late Albian and likely correlates with the Oceanic Anoxic Event (OAE) 1d. The previous OAE's did not change the structure of this platform, whose margins were mostly rigid and colonized by corals and calcareous sponges. Late Albian was a time of important changes in paleoceanography in Tethys and North Atlantic Oceans. We propose that the paleooceanographic changes related to the OAE- 1d had more profound impacts on the Friuli-Adriatic Platform than the previous Cretaceous OAE's since they co-occurred with the tectonic transition from passive margin to foreland ramp. The increased subsidence rates, in conjuction with the important late Albian paleoceanographic changes, created favourable conditions for a dramatic change in the platform margin physiography and ecology.

Geological parameters affected land subsidence in Mashhad plain, north-east of Iran

Mashhad plain is an area with a dry-to-semi-dry climate in Razavi Khorasan Province, Iran. About 60% of 6 million population of the province live in this plain, and mainly in Mashhad city. Overexploitation of ground water during the past decades has led to a severe drop in groundwater table and land subsidence. In this respect, some parts of the plain show an annual groundwater-level decline of 1.5 m. The surface subsidence features such as rising of the well casing, well collapse, and tension cracks observed in different parts of the area. Studying of ENVISAT ASAR images in a period of 2003/06/30 to 2010/05/24 shows the maximum subsidence rate of 32 cm/year in the north-west of the Mashhad city, but there was a mismatch between groundwater drop and ground subsidence in some parts of the plain. The evaluation of geological characteristics of subsidence area reveals, in addition to the groundwater decline, tectonic condition and active faults which change the bedrock depth have a key role in the pattern and rate of subsidence. Also, consolidation of the Pleistocene marl bedrock located in the central part of the plain is effective in the increased subsidence rate of the study area.

Multi-Sensor SAR Geodetic Imaging and Modelling of Santorini Volcano Post-Unrest Response

Volcanic history of Santorini over recent years records a seismo-volcanic unrest in 2011–12 with a non-eruptive behavior. The volcano deformation state following the unrest was investigated through multi-sensor Synthetic Aperture Radar Interferometry (InSAR) time series. We focused on the analysis of Copernicus Sentinel-1, Radarsat-2 and TerraSAR-X Multi-temporal SAR Interferometric (MT-InSAR) results, for the post-unrest period 2012–17. Data from multiple Sentinel-1 tracks and acquisition geometries were used to constrain the E-W and vertical components of the deformation field along with their evolution in time. The interpretation of the InSAR observations and modelling provided insights on the post-unrest deformation pattern of the volcano, allowing the further re-evaluation of the unrest event. The increase of subsidence rates on Nea Kameni, in accordance with the observed change of the spatial deformation pattern, compared to the pre-unrest period, suggests the superimposition of various deformation sources. Best-fitting inversion results indicate two deflation sources located at southwestern Nea Kameni at 1 km depth, and in the northern intra-caldera area at 2 km depth. A northern sill-like source interprets the post-unrest deflation attributed to the passive degassing of the magma intruded at 4 km during the unrest, while an isotropic source at Nea Kameni simulates a prevailing subsidence occurring since the pre-unrest period (1992–2010).

The role of subsidence in shelf widening around ocean island volcanoes: Insights from observed morphology and modeling

On reefless volcanic islands, insular shelves are thought to have formed essentially by the combined effects of wave erosion and glacio-eustatic sea-level oscillations. Subsidence, however, has also been recognized as having an important role in the development of these morphologies. Yet, few studies have quantified the relative contribution of subsidence to shelf generation and development, particularly to shelf width. A better understanding of this contribution, however, is key to understand the long-term evolution of coasts at volcanic islands, particularly given that subsidence may exacerbate the effects of marine erosion. In this study we assess quantitatively the role of subsidence in shelf development by comparing real cross-shore shelf profiles with modeled profiles using varied rates of subsidence. To achieve this, we used shelf bathymetric profiles from Faial and São Jorge islands in the Azores, which we compared with predictions of a numerical model of coastal erosion that has been calibrated previously against other field data. The first set of model runs was made to calibrate the model by determining the values that produced shelves with break depths, widths, and profile shapes that were similar to those observed. The second set of runs, which served to evaluate the contribution of subsidence to shelf widening, revealed that subsidence may have been responsible for increasing shelf widths by almost 2.5 times relative to shelves formed only by the combined effects of wave erosion and glacio-eustatic oscillations. Modeling shelf formation on the same islands but with increased subsidence rates up to 2.2 mm/yr resulted in shelf profiles up to 19 km wide, a value 3 to 6 times greater than observed on these islands. Our study therefore reinforces the idea that subsidence is a key contributor to the generation of broad insular shelves, given its role in enhancing coastal retreat. Our shelf evolution modeling also suggests that, notwithstanding the crucial role subsidence plays in increasing the width of shelves, on islands subjected to energetic wave regimes (as it happens in the Azores and Hawaii), modification by erosion is important enough to result in shelf morphologies that are not constructional in essence, but rather dominantly erosive surfaces. This study therefore contributes to a better understanding of how insular shelves and submarine terraces form and develop by proving important new quantitative insights of the role of subsidence on the generation of these morphologies.

Ediacaran-Paleozoic subsidence history of the Volyn-Podillya-Moldavia Basin (W and SW Ukraine, Moldova, NE Romania)

Tectonic subsidence history was analysed for the Ediacaran-Paleozoic Volyn-Podillya-Moldavia Basin, by performing 1D backstripping for 21 boreholes located in western and SW Ukraine, Moldova and NE Romania. Tectonic subsidence history is coherent across the area studied. Development of the basin commenced with an Ediacaran phase of extension, initiated with the emplacement of rift-related volcanic rocks and associated with rapid syn-rift tectonic subsidence. During this event, tectonic subsidence increased towards the SW, i.e. towards the edge of the East European Craton, where the Ediacaran rift zone was located. At that time, a rift developed along the whole SW margin of the East European Craton from Scandinavia to the Black Sea. Development of this large extensional basin was related to the latest stages of break-up of the Precambrian supercontinent Rodinia/Pannotia and ultimately the formation of the Tornquist Ocean. The latest Ediacaran to Late Ordovician tectonic subsidence pattern was characteristic of the post-rift thermal sag stage of extensional basins. The SW margin of the newly formed Baltica, including the area studied, became a passive continental margin. The late Cambrian uplift and erosion was presumably related to a far-field effect of contractional events or intra-plate stresses. Since the Late Ordovician, a gradual change to a collisional tectonic setting is observed across the SW margin of Baltica. In the study area, this is indicated by a systematic increase in subsidence rate from Wenlock to Early Devonian time, creating subsidence curves with convex shapes typical of foreland basin development. The Silurian to Early Devonian Volyn-Podillya-Moldavia Basin is interpreted here as a flexural foredeep related to a Caledonian collision zone located further to the SW. The prominent diachroneity in the initiation of the foredeep basin development at a scale of the whole SW margin of Baltica is coherent with a model of oblique collision of Avalonia and Baltica. During the Pragian-Emsian, the basin was part of a system of post-collisional Old Red basins, with subsidence driven presumably by lithospheric isostatic imbalance resulting from the Caledonian collision and development of an accretionary wedge. Middle to Late Devonian short-term phases of rapid subsidence in small depocentres might be regarded as an indication of a transtensional tectonic regime

Spatial and temporal patterns of deformation at the Tendaho geothermal prospect, Ethiopia

Observations of ground deformation in East Africa have been fundamental for unveiling the tectonics of continental rifting, assessing the seismic and volcanic hazard to development, and identifying geothermal resources. Here we investigate the active natural and anthropogenic processes in the Tendaho Graben, Afar using Interferometric Synthetic Aperture Radar (InSAR) collected by the Envisat satellite in 2004–2010. We used the Poly-Interferometric Rate And time series Estimation (π-RATE) method to calculate displacement in satellite line-of-sight, and a least-square inversion to decompose the line-of-sight displacement into vertical and rift perpendicular components. We observe two zones of deformation: a 20 km wide circular region of subsidence located 10 km northeast of the town of Semera with a maximum displacement rate of ∼5 cm/yr; and elongated zone (50 km) of subsidence in the area of the geothermal prospect, maximum rate of ∼4 cm/yr. The temporal characteristics of subsidence varies between these zones, with an increase in subsidence rate observed in the circular region in August 2008. We used a Bayesian inversion to find the best fitting source models and compared this to locations of seismicity and other geophysical observations. The pattern of deformation is consistent with a combination of magmatic and geothermal processes, but there does not appear to be a direct link to a sequence of dyke intrusions during 2005–2010 at Manda Hararo graben ∼60 km away, but dynamic stress changes or deep crustal flow could account for the observations.

Linking the Qinling Orogeny with the Chang 7 shale (Triassic Yanchang Formation) deposition: Evidence from major, trace, and rare earth element geochemistry

The lacustrine organic‐rich shale of Triassic Chang 7 Member is an unconventional shale oil reservoir that is a major hydrocarbon target in the Ordos Basin, northern China. This study uses major, trace, and rare earth element (REE) abundance documented through a 115‐m‐thick core obtained from the western part of the Ordos Basin to assess dominant controls on temporal variations in total organic carbon in the Chang 7 shale. Our results suggest that total organic carbon trends in the Chang 7 can be directly linked with the tectonic and magmatic evolution of Qinling orogen. The Chang 73 and Chang 72 submembers of the lower part of the Chang 7 were likely deposited in association with heighted tectonic and magmatic activity of the Qinling Orogeny. Sediments derived from these submembers display light REE and trace element compositions similar to the Tianshui rhyolites suggesting deposition contemporaneous with magmatic and/or volcanic activity of the Qinling Orogeny. Higher nutrient concentrations introduced by volcanic eruptions would have stimulated primary productivity in the surface water enhancing the organic carbon flux to the lake bottom. In addition, higher rates of mountain building in the Qinling Orogeny may have been responsible for increasing subsidence rate of the southern Ordos Basin, also favourable for the establishment of anoxic bottom‐water conditions. In contrast, lower light REE and trace element abundances of the Chang 71 submember at the top of the Chang 7 suggest deposition during a tectonically and magmatic quiescent period of the Qinling Orogeny. The diminished volcanic flux could have lowered the rate of primary productivity. Moreover, a reduced rate of mountain building would have decreased the rate of foredeep subsidence favouring shallower water and oxic/suboxic bottom‐water conditions. Thus, the hydrography of the lake during accumulation of the Chang 71 was not conducive for organic carbon accumulation. Together, the correlation of the Qinling mountain building and magmatism and deposition of the Chang 7 shale provide evidence for the role of tectonism in the accumulation of organic carbon enriched sediment.

Subsidence in the Kathmandu Basin, before and after the 2015 Mw 7.8 Gorkha Earthquake, Nepal Revealed from Small Baseline Subset-DInSAR Analysis

Land subsidence in densely urbanized areas is a global problem that is primarily caused by excessive groundwater withdrawal. The Kathmandu Basin is one such area where subsidence due to groundwater depletion has been a major problem in recent years. Moreover, on 25 April 2015, this basin experienced large crustal movements caused by the Gorkha earthquake (Mw 7.8). Consequently, the effects of earthquake-induced deformation could affect the temporal and spatial nature of anthropogenic subsidence in the basin. However, this effect has not yet been fully studied. In this paper, we applied the SBAS-DInSAR technique to estimate the spatiotemporal displacement of land subsidence in the Kathmandu Basin before and after the Gorkha earthquake, using 16 ALOS-1 Phased Array L-band Synthetic Aperture Radar (PALSAR) images during the pre-seismic period and 26 Sentinel-1 A/B SAR images during the pre- and post-seismic periods. The results showed that the mean subsidence rate in the central part of the basin was about −8.2 cm/year before the earthquake. The spatial extents of the subsiding areas were well-correlated with the spatial distributions of the compressible clay layers in the basin. We infer from time-series InSAR analysis that subsidence in the Kathmandu basin could be associated with fluvio-lacustrine (clay) deposits and local hydrogeological conditions. However, after the mainshock, the subsidence rate significantly increased to −15 and −12 cm/year during early post-seismic (108 days) and post-seismic (2015–2016) period, respectively. Based on a spatial analysis of the subsidence rate map, the entire basin uplifted during the co-seismic period has started to subside and become stable during the early-post-seismic period. This is because of the elastic rebound of co-seismic deformation. However, interestingly, the localized areas show increased subsidence rates during both the early-post- and post-seismic periods. Therefore, we believe that the large co-seismic deformation experienced in this basin might induce the local subsidence to increase in rate, caused by oscillations of the water table level in the clay layer.

Detrital zircon microtextures and U‐PB geochronology of Upper Jurassic to Paleocene strata in the distal North American Cordillera foreland basin

AbstractDetrital zircon surface microtextures, geochronologic U‐Pb data, and tectonic subsidence analysis from Upper Jurassic to Paleocene strata in the Black Hills of South Dakota reveal provenance variations in the distal portion of the Cordillera foreland basin in response to tectonic events along the outboard margin of western North America. During Late Jurassic to Early Cretaceous time, nonmarine strata record initially low rates of tectonic subsidence that facilitated widespread recycling of older foreland basin strata in eolian and fluvial systems that dispersed sediment to the northeast, with minimal sediment derived from the thrust belt. By middle Cretaceous time, marine inundation reflects increased subsidence rates coincident with a change to eastern sediment sources. Lowstand Albian fluvial systems in the Black Hills may have been linked to fluvial systems upstream in the midcontinent and downstream in the Bighorn Basin in Wyoming. During latest Cretaceous time, tectonic uplift in the study area reflects dynamic processes related to Laramide low‐angle subduction that, relative to other basins to the west, was more influential due to the greater distance from the thrust load. Provenance data from Maastrichtian and lower Paleocene strata indicate a change back to western sources that included the Idaho‐Montana batholith and exhumed Belt Supergroup. This study provides a significant contribution to the growing database that is refining the tectonics and continental‐scale sediment dispersal patterns in North America during Late Jurassic‐early Paleocene time. In addition, it demonstrates the merit of using detrital zircon grain shape and surface microtextures to aid in provenance interpretations.

High-resolution InSAR constraints on flood-related subsidence and evaporite dissolution along the Dead Sea shores: Interplay between hydrology and rheology

Sinkhole generation and land subsidence are commonly attributed to dissolution of subsurface layers by under-saturated groundwater and formation of cavities. Along the Dead Sea (DS) shorelines, this process also involves seasonal flash floods that are drained into the subsurface by existing and newly formed sinkholes. We quantify the contribution of flash-floods to salt dissolution and land subsidence using high-resolution interferometric synthetic aperture radar (InSAR). Subsidence rates during a 3-year period (2012–2015) were calculated from 57 COSMO SkyMed X-band interferograms bracketing major flood events and intra-flood periods in 21 sinkhole sites. The sites are located within channels and alluvial fans along the western shores of the Dead Sea, Israel. The observed subsidence reaches maximum rates of ~2.5mm/day, accumulating in specific sites to 500mm/year. In most of the sinkhole sites a gradual increase in the annual subsidence rate is observed during the 3-year study period. Three different modes of response to floods were observed: (1) sites where floodwater is not directly channeled into sinkholes do not respond to floods; (2) sites adjacent to active channels with sinkholes are unaffected by specific floods but their subsidence rates increase gradually from early winter to mid-summer, and decay gradually until the following winter; and (3) sites in active channels with sinkholes are characterized by an abrupt increase in subsidence rates immediately after each flood (by a factor of up to 20) and by a subsequent quasi-exponential subsidence decay over periods of several months. In these latter sites, subsidence rates after each flood are temporally correlated with alternating groundwater levels in adjacent boreholes. The rapid rise in groundwater head following floods increases the hydraulic gradient of the under-saturated groundwater and hence also the groundwater discharge and the dissolution rate of the subsurface salt layer. A subsequent quasi-exponential water level drop results in similar deceleration in dissolution and subsidence rates, with a similar characteristic decay time of about 150days. The observed subsidence decay pattern may also be explained by viscoelastic relaxation of the overburden in response to instantaneously-formed dissolution cavities. Utilizing a Kelvin viscoelastic model, we show that the contribution of this process is most probably <30% of the total observed subsidence and is sensitive to the sediment mechanical properties. On a broader scale, this study demonstrates how high-resolution InSAR measurements can improve our understanding of subsurface dissolution and subsidence processes and provide independent constraints on the mechanical properties of heterogeneous alluvial sediments.

How much subsidence is enough to change the morphology of river deltas?

AbstractUnderstanding the effect of subsidence on fluviodeltaic morphology is important not only to maintain sustainable coastal cities and habitats but also to interpret the information contained in the stratigraphic record. While tectonic steering in alluvial environments has been investigated, similar studies in fluviodeltaic environments are limited to physical experiments and field observations. We perform numerical experiments with a parcel‐based cellular model to analyze the deltaic surface and subsurface responses to regional subsidence. We quantify model results using robust metrics and show that while sediment partitioning and shoreline pattern vary gradually with increasing subsidence rate, channel mobility and stratigraphic connectivity of channel deposits show a threshold transition. Conditions for this transition are captured with a dimensionless filling index β, defined as the ratio between the rates of accommodation creation and sediment supply. A channel‐locking mechanism activates when β exceeds 0.6 and is responsible for the threshold transition.