Sea Level Elevation Research Articles

Terrigenous sediment input responding to sea level change and East Asian monsoon evolution since the last deglaciation in the southern South China Sea

Abstract Siliciclastic grain size, clay mineralogy, and major element geochemistry of Core MD05–2893 from the lower continental slope off the Sunda Shelf in the southern South China Sea were investigated to assess the response of terrigenous sediment input to sea-level and climatic changes since the last deglaciation. The chronology is based on foraminiferal AMS 14C dates and oxygen isotope records combined with carbonate stratigraphy. In this study, we reconstruct variations in terrigenous sediment input using clay/silt, TiO2/CaO, SiO2/Al2O3, Al2O3/K2O, and smectite/(illite + chlorite) proxies. Clay/silt, TiO2/CaO, and SiO2/Al2O3 ratios are clearly correlated to sea-level change, showing high values during the early phase of deglacial sea-level rise (17.2–14.5 cal ka BP, Stage I) and rapidly decreasing values during the meltwater pulse 1A and further sea-level rise (14.5–11.1 cal ka BP, Stage II). Meanwhile, variations in Al2O3/K2O and smectite/(illite + chlorite) correspond well to monsoon rainfall variability during the late phase of deglacial sea-level rise and Holocene sea-level highstand (11.1–1.5 cal ka BP, Stage III). Based on these records, we recognize three stages of evolution of terrigenous sediment input to the southern South China Sea continental slope. Dominance of terrigenous sediment input occurred during Stage I, when most part of the Sunda Shelf was still exposed and drained by several rivers. The stepwise elevated sea level by meltwater pulse 1A and subsequent rising sea-level after 14.5 cal ka BP could have led to a drop in terrigenous sediment input to this area due to regression of the paleo-Sunda river systems (Stage II). Thereafter during last phase of sea-level rise and sea-level highstand with the evolution of the modern coast, sediments have a clear fingerprint of chemical weathering induced by a strengthening of the East Asian summer monsoon (Stage III). Our findings highlight that the variability of terrigenous sediment input to the lower continental slope in the southern South China Sea was first in the late Pleistocene mainly driven by sea-level change and later in the Holocene by a strengthened East Asian summer monsoon.

Effect of the Planting Location (Elevation) on the Composition of Fatty Acids in Olive Oil

In Jordan there are different environments and altitudes that have an effect on olive oil properties and fatty acid composition, which therefore affect its quality. Taking into account that there are no previous similar studies in this field, this study investigates the ratios and composition of the main fatty acids in mixed olive oil from different areas in Jordan (above and below the sea level); namely the Jordan Valley, Subaihi, Kufranja and Madaba areas where the elevation ranges between (-230 m) below sea level and (+785 m) above sea level. The study measures the impact of the location of olive orchards on the fatty acid composition of olive oil and of its quality. Three olive oil samples were collected from the “Nabali Muhasan” and “Baladi” varieties from each area. They were analyzed in the National Agriculture Research Center (NARC) laboratories using GAS Chromatography. The results showed that the ratios of fatty acids are significantly affected by the degree of above elevation of the olive trees sea level. This confirms the impact of the geographical and climatic environment, which is reflected on the olive oil quality due to differences in the ratios of fatty acids in the four planting areas. This shows that the mean concentration of the fatty acids in the olive oil in these four planting areas is not equal. In general, there is a significant difference in the fatty acid concentrations compared to the standard concentration because of the planting location of olive trees, given that olive oil fatty acids in each location work together in a balanced integrative relationship.

Landscape Evolution of a Fluvial Sediment-Rich Avicennia marina Mangrove Forest: Insights from Seasonal and Inter-annual Surface-Elevation Dynamics

Mangrove forests are vulnerable to accelerated sea-level rise associated with climate warming because they occupy a relatively narrow zone on the mid-to-upper-intertidal flats. The fate of these ecosystems largely depends on their capacity to accrete sediment at a rate sufficient to maintain their elevation relative to sea level. We investigated the role of biophysical processes and feedbacks controlling surface-elevation dynamics in a fluvial sediment-rich Avicennia marina mangrove forest (New Zealand) at seasonal-to-inter-annual timescales (over 9 years) using the Rod Surface Elevation Table method. We found that sediment accretion in the forest was not measurably enhanced by episodic and short-lived storm discharges from rivers nor by elevated sea levels during storms. Critically, the coupling of frequent onshore winds and resulting resuspension of intertidal muds, with the fortnightly cycle of spring tide inundation, controlled sediment delivery and resulting accretion rates of 13 to 47 mm y−1. In turn, net surface-elevation trends of 0 to 28 mm y−1 were dominated by the physical processes of sediment accretion and shallow subsidence due to seasonal desiccation and resulting compaction of the infrequently inundated forest platform (4 to 16 mm y−1). Our data suggest that monthly and seasonal variation in tidally controlled hydroperiod and sediment delivery rather than episodic storm events are important for the maintenance of mangrove elevation within the intertidal zone.

Anatomy of a late Quaternary carbonate island: Constraints on timing and magnitude of sea-level fluctuations, West Caicos, Turks and Caicos Islands, BWI

The data set of the island of West Caicos consists of a combination of high-resolution lidar and digital imagery, radiometric data, and amino acid racemization (AAR) D/L values as well as extraordinary preservation of sedimentary and bio-constructed deposits on the island. Together with a well-established regional stratigraphic framework from the neighboring Bahamian island chain and detailed field mapping, the West Caicos data set provides an opportunity to advance our understanding of the link between carbonate stratigraphy and the controlling parameters of sea level, sediment supply, tectonics, and climate. The exceptionally well-preserved stratigraphic record of the mid–late Pleistocene from West Caicos allows recognition of marine isotope stages (MIS) 9/11, 5e, and Holocene. The west coast of the island provides a continuous 8.4 km exposure of the MIS 5e record that enhances our understanding of the intra-MIS 5e bipartite succession in this region and supports a sea-level lowering that occurred during the last interglacial (LIG).West Caicos accreted as a series of eolian, foreshore–shoreface, barrier-reef, and fringing-reef facies. Shoreline positions for all but the MIS 7 and MIS 5a/c deposits are now captured in the sub-meter geodetic-quality topobathy lidar survey. The Star Town unit of MIS 9/11 age forms the southern margin of the island as well as the central karst-modified spine, with uranium–thorium (UTh) coral ages of between 368 and 365 thousand years ago (ka) and a D/L Glu average of >0.60. Early MIS 5e strata include the Railroad Ridge unit in the center of the island, which was previously identified as one of the older units. The Railroad Ridge unit is a north–south linear dune ridge that has a D/L Glu average of 0.52 and indicates the onset of sediment sources from the east associated with a flooded central Caicos Platform. Approximately synchronously, the early MIS 5e South Reef unit (+3.75–4 m sea-level elevation) nucleated on the western coast of West Caicos, attached to the middle Pleistocene Star Town unit. The South Reef corals yield an average coral UTh age of 126.5 ka, with an average D/L Glu from skeletal matrix of 0.46. This transitional barrier/fringing reef is unconformably overlain by the late MIS 5e Boat Cove unit. Corals in the basal transgressive phase of this upper MIS 5e Boat Cove unit yield an average 120.6 ka UTh and average D/L Glu of 0.45. Shallow-marine, foreshore, and eolian facies of the late MIS 5e rest on a wave-cut terrace that cuts the early MIS 5e South Reef unit by as much as 3 m down to a +0.5 m above present sea-level elevation. The upper MIS 5e Boat Cove unit displays a maximum of +4.5 m elevation above present-day sea level, measured from the middle of the foreshore. This estimate may be a minimum value as the exposures on the west coast are part of a forced regressive foreshore sequence. Last stages of the upper MIS 5e deposition are seen in a series of regressive dune-beach ridge deposits referred to as the Northeast Ridges unit, with sea-level positions ranging from +4.5 m early in the central part of West Caicos, to +0.5 m on the far northeast coast, eventually building down below present-day sea level. This sea-level history fits well with previously documented records in the Bahamas and globally, and the extensive erosion supports a short-lived (between 126 and 120 ka) intra-MIS 5e relative-sea-level fall. Holocene deposition on West Caicos is restricted to northern and eastern margins of the island as a combination of strandplain and dune ridge mixed skeletal–oolitic units.Using the high-resolution digital elevation model (DEM) and linked digital geologic map makes it possible to compare areas of the different Pleistocene and Holocene units quantitatively and to constrain volumetric assessments and accumulation rates on the island for different units. The peak sediment volume production/accumulation rate—between 6.5 and 8 × 106 m3 or between 2.2 and 2.7 × 106 m3 per ka—is observed in the upper MIS 5e unit. This rate is 5 times greater than the 0.5 × 106 m3 per ka estimated for the Holocene ooid dune-ridge/strandplain complex, suggesting that the combination of higher sea level, greater wave and wind energy, and warmer ocean temperatures may have fostered the higher rate of chemically precipitated sediment supply.

Shoreline morphology changes along the Eastern Coast of India, Andhra Pradesh by using geospatial technology

Shoreline changes on account of global climate change and sea level rise is one of the major problems along the coastlines in different continents of the world. This study was carried out along the coastlines of Andhra Pradesh state in India using multi-temporal satellite images from 1973 to 2015 period. Long-term coastal erosion and accretion rate over a period of 42 years has calculated using Digital Shoreline Analysis System and prepared shoreline maps by using GIS-Software. End point rate (EPR) statistical method is applied to estimate the shoreline change rate. Various coastal parameters like sea level rise, geomorphology, elevation and coastal slope were used to find out the interactive relationship between the physical parameters and shoreline changes in the area. The study revealed that the coastal changes are more dominant in Krishna and Godavari Deltaic plain. The average erosion and accretion rate observed in the Krishna Godavari delta was 10.63 and 17.29 m per year respectively. The study indicated that, climatic changes and fluvial process are playing key role in changing shoreline positions. The study exhibited that elevation and slope are played intense role in the shoreline positional change. The present study demonstrates that combined use of satellite imagery and EPR statistical method as an accurate and reliable method for shoreline change analysis.

A Copula-Based Bayesian Network for Modeling Compound Flood Hazard from Riverine and Coastal Interactions at the Catchment Scale: An Application to the Houston Ship Channel, Texas

Traditional flood hazard analyses often rely on univariate probability distributions; however, in many coastal catchments, flooding is the result of complex hydrodynamic interactions between multiple drivers. For example, synoptic meteorological conditions can produce considerable rainfall-runoff, while also generating wind-driven elevated sea-levels. When these drivers interact in space and time, they can exacerbate flood impacts, a phenomenon known as compound flooding. In this paper, we build a Bayesian Network based on Gaussian copulas to generate the equivalent of 500 years of daily stochastic boundary conditions for a coastal watershed in Southeast Texas. In doing so, we overcome many of the limitations of conventional univariate approaches and are able to probabilistically represent compound floods caused by riverine and coastal interactions. We model the resulting water levels using a one-dimensional (1D) steady-state hydraulic model and find that flood stages in the catchment are strongly affected by backwater effects from tributary inflows and downstream water levels. By comparing our results against a bathtub modeling approach, we show that simplifying the multivariate dependence between flood drivers can lead to an underestimation of flood impacts, highlighting that accounting for multivariate dependence is critical for the accurate representation of flood risk in coastal catchments prone to compound events.

Extreme Sea Level Rise off the Northwest Coast of the South China Sea in 2012

Tide gauge data are used to investigate sea level variability off the northwest coast of the South China Sea (SCS) in 2012, and a significant sea level elevation with a magnitude approaching 79 mm is observed. Analysis suggests that an abnormal sea surface heat flux and freshwater flux may have contributed to this abnormal rise in sea level, together with the remote influence of an ENSO event. Further investigation shows that the event was dominated by the positive freshwater flux, where large volumes of water entered the ocean, and a maximum is centered to the south of Guangdong province, China. Simultaneously, a positive anomalous heat flux occurred in the northwestern part of the SCS, which is considered to have made a positive contribution to the high local sea level elevation. In addition to the heat flux, the ENSO event also had a significant effect on the event, where the La Nina-induced northwest Pacific cyclone contributed to sea level rise over the northwestern SCS through dynamic and thermodynamic interactions.

Effect of coastal-trapped waves on the synoptic variations of the Yellow Sea Warm Current during winter

Significant short-term fluctuations of the Yellow Sea Warm Current (YSWC) at several days' time scale were observed in the Yellow Sea (YS) during winter of 2006–2007. Observations indicated that the synoptic fluctuations of the YSWC appear to be associated with low-frequency sea level variations. By analyzing direct current measurements, sea level elevations and results from a regional ocean model, this study characterizes the variation of the YSWC at synoptic time scale and examines its connection with propagation of coastal-trapped waves during winter. The model captures the observed short-term fluctuations of the YSWC at several days’ periods and suggests a close relation between coastal-trapped waves and the YSWC variability. The YSWC is intensified (weakened) when the westward sea level-related barotropic pressure gradient is enhanced (diminished) due to the propagation of coastal-trapped waves. Model experiments with idealized periodic surface forcing further identify the important role of the coastal-trapped waves on adjusting the strength of the YSWC. The model results also suggest that the propagation of coastal-trapped waves contribute to the intermittent northwestward intrusion of Cheju Warm Current (CWC) in the frontal region northwest of Cheju. Generation and propagation of the coastal-trapped waves give rise to the westward barotropic pressure gradient in the YS entrance, which periodically pumps the CWC water into the YS interior west of Cheju.

Vineyard site suitability analysis by use of multicriteria approach applied on geo-spatial data

In this research, multicriteria decision analysis with pairwise comparison weighting method was utilized to determine the suitable locations for vineyard plantation in Sarkoy region of Turkey. Soil maps, meteorological measurements, slope, aspect and elevation maps were used as input to conduct spatial analysis. Different methods were compared and pairwise comparison method was identified as the most appropriate method of weighting for this spatial analysis. Current vineyard areas were determined using Worldview-2 imagery and their spatial distribution compared with the resulting suitability map to determine the current suitability. Comparisons showed current vineyards were mostly established in locations where suitability map expresses low capability. Further inspection unveiled that, these low capability lands are closer to the transportation networks and city/county centres that tend to be in sea level elevations as opposed to vine grapes thriving in higher altitudes. Results also enabled providing suggestions on alternative sites for new vineyard plantation.

SEDIMENT TRANSPORT IN THE BASIN OF PULAU BAAI PORT, BENGKULU

The 2D horizontal model has been simulated to investigate a sedimentation and erosion pattern in the basin of Pulau Baai port — Bengkulu Sumatera. The model was verified with observed data from the Indonesian Research Center for Marine Geology (Arifin et al., 2001). The simulation results of the hydrodynamic model shows a good agreement with the observed data. In -regard to the elevation of sea level, the difference between simulation and the observed data is about 4.6 cm, giving averaged error of about 2.93 %, and the difference in velocity is 6.8 cm/s or in the order of error of about 20.1 %. The results of the model on sediment transport qualitatively show comparable values to the observed ones, although in some parts of the area, the model is still to be adjusted. Simulation results show that the strong current occurs in the harbor channel during the time of spring flood tide with a speed of about 95.4 cm/s, while the ebb current is 54.1 cm/s. The results of the model on sediment transport show that the erosion area occurs in the northeastern part of the basin and sedimentation takes place in the southwestern to southeastern of the channel. The channel port is generally eroded, and sedimentation occurs in the mouth and the western part of offshoreward of the channel, and erosion is identified in the eastern part of the offshoreward of the channel.

Geospatial Risk Assessment of Marine Terminal Infrastructure to Storm Surge Inundation and Sea Level Rise

Planning resiliency and sustainability of port operations and critical infrastructure requires risk assessment of storm surge exposure and potential sea level rise. An approach for rapid, screening-level assessment is developed to estimate the current and future risk of exposure to severe storm surges posed to marine terminal facilities in Norfolk, Virginia. The approach estimates the vertical elevation of local mean sea level fifty years into the future and attendant increases in potential storm surge heights. Inundation models are designed for baseline water levels and storm surges for category 1–3 hurricanes across five precautionary future sea level rise scenarios. In addition, tidal flooding poses an emerging threat because sea level rise will also force tides to higher elevations, suggesting that today’s extreme high tides may be the future mean high tide and today’s “nuisance” tidal flooding may in the future recur with chronic regularity. Potential tidal flooding levels are also modeled for each sea level scenario. This approach allows a port to assess relative risk tolerance across the range from lesser to more severe flooding events. Maps and tabular information in linked scenarios are used to summarize the extent, pattern, and depth of potential flooding. The methodology and data developed in this study may be applied to inform the timing and placement of planned assets and can be leveraged in the broader pursuit of optimization in support of long-term master planning at marine terminals.

Enhanced land subsidence in Galveston Bay, Texas: Interaction between sediment accumulation rates and relative sea level rise

Galveston Bay is the second largest estuary along the northern Gulf of Mexico coast, with a watershed containing one of largest concentrations of petroleum and chemical industries globally, as well as Houston, the fifth largest metropolitan area in the USA. Throughout the last century, extensive groundwater extraction to support these industries and an expanding population has resulted in significantly enhanced land subsidence (0.6–3.0 cm yr−1). The highest subsidence rates observed in the bay are within the lower 15 km of the San Jacinto River/Houston Ship Channel region (SJR/HSC), with distal areas in East and West Galveston Bays having subsidence rates on the order of 0.2 cm yr−1. In order to investigate the impacts of subsidence on sedimentation, a series of 22 vibracores were collected throughout the bay, and 210Pb and 137Cs radioisotope geochronologies and grain size distributions were determined. Sediment accumulation rates are highest (1.9 ± 0.5 cm yr−1) in the SJR/HSC, and decrease (<0.6 cm yr−1) both seaward and towards low subsidence regions. These results indicate sedimentation rates are significantly (p < 0.01) higher in areas with elevated Relative Sea Level Rise (RSLR). However, throughout most of Galveston Bay sedimentation rates are lower (as much as 50%) than estimated RSLR, indicating a sediment accretionary deficit. In areas (e.g., Scott Bay) within the SJR/HSC, the bay has deepened by more than 1.5 m, suggesting that sediment accumulation cannot keep pace with RSLR. Ultimately, this has resulted in a loss of coastal wetlands and a conversion of marine habitats from relatively shallow to deeper water settings.

Biophysical Factors and Canopy Coupling Control Ecosystem Water and Carbon Fluxes of Semiarid Sagebrush Ecosystems

The sagebrush-steppe ecosystem covers much of western North America, and its productivity is sensitive to warming and increasingly variable precipitation. Interannual variation in precipitation has been shown to be the most significant factor controlling biogeochemical cycling while both soil and atmospheric drought are dominant factors of ecosystem fluxes. We show that plant canopies can also act to limit water losses through stomatal and aerodynamic control. We use 4 data-yr from 2 sites (2 069 and 2 469 m above sea level elevation, respectively) to evaluate control of carbon and water fluxes and to calculate the degree to which the ecosystem canopy and atmosphere are decoupled. Environmental conditions were similar between the two sites, although the lower elevation site was slightly warmer (1.8°C higher temperature) and drier (0.2 kPa higher vapor pressure deficit). Ecosystem responses of net ecosystem exchange (NEE) and evapotranspiration (ET) to environmental drivers were similar between sites and years, with the wet site-yr 2009 having the largest ET and NEE fluxes. Canopy leaf area led to divergent behavior of the canopy-atmosphere decoupling parameter under high (> 11% by volume) soil moisture conditions. During low (< 11%) soil moisture periods, both sites had tight ecosystem stomatal control on ET with little NEE activity. This study highlights how semiarid ecosystems can alter their canopy leaf area in order to control how decoupled semi-arid canopies are to the atmosphere, potentially moderating impacts of climate change.

Analyzing the Long-Term Phenological Trends of Salt Marsh Ecosystem across Coastal LOUISIANA

In this study, we examined the phenology of the salt marsh ecosystem across coastal Louisiana (LA) for a 16-year time period (2000–2015) using NASA’s Moderate Resolution Imaging Spectroradiometer’s (MODIS) eight-day average surface reflectance images (500 m). We compared the performances of least squares fitted asymmetric Gaussian (AG) and double logistic (DL) smoothing functions in terms of increasing the signal-to-noise ratio from the raw phenology derived from the time-series composites. We performed derivative analysis to determine the appropriate start of season (SOS) and end of season (EOS) thresholds. After that, we extracted the seasonality parameters in TIMESAT, and studied the effect of environmental disturbances/anomalies on the seasonality parameters. Finally, we performed trend analysis using the derived seasonality parameters such as base green biomass (GBM) value, maximum GBM value, seasonal amplitude, and small seasonal integral. Based on root mean square error (RMSE) values and residual plots, we selected the best thresholds for SOS (5% of amplitude) and EOS (20% of amplitude), along with the best smoothing function. The selected SOS and EOS thresholds were able to capture the environmental disturbances that have affected the salt marsh ecosystem during the 16-year time period. Our trend analysis results indicate positive trends in the base GBM values in the salt marshes of LA. However, we did not notice as much of a positive trend in the maximum GBM levels. Hence, we observed mostly negative changes in the GBM amplitude and small seasonal integral values. These negative changes indicated the overall progressive decline in the rates of photosynthesis and biomass allocation in the LA salt marsh ecosystem, which is most likely due to elevated atmospheric carbon dioxide levels and sea level rise. The results illustrate both the relative efficiency of MODIS-based biophysical models for analyzing salt marsh phenology, and performances of the smoothing techniques in terms of improving the signal-to-noise ratio of the MODIS-derived phenology.

Short communication: Massive erosion in monsoonal central India linked to late Holocene land cover degradation

Abstract. Soil erosion plays a crucial role in transferring sediment and carbon from land to sea, yet little is known about the rhythm and rates of soil erosion prior to the most recent few centuries. Here we reconstruct a Holocene erosional history from central India, as integrated by the Godavari River in a sediment core from the Bay of Bengal. We quantify terrigenous fluxes, fingerprint sources for the lithogenic fraction and assess the age of the exported terrigenous carbon. Taken together, our data show that the monsoon decline in the late Holocene significantly increased soil erosion and the age of exported organic carbon. This acceleration of natural erosion was later exacerbated by the Neolithic adoption and Iron Age extensification of agriculture on the Deccan Plateau. Despite a constantly elevated sea level since the middle Holocene, this erosion acceleration led to a rapid growth of the continental margin. We conclude that in monsoon conditions aridity boosts rather than suppresses sediment and carbon export, acting as a monsoon erosional pump modulated by land cover conditions.

Gravity, magnetic and resistivity investigations of the Okauia Low Temperature Geothermal System in alluvial sediments of the Hauraki Depression, New Zealand

Gravity, ground magnetics, DC resistivity traversing, and time domain electromagnetic soundings (fixed-loop and in-loop) were conducted to investigate the Okauia Low Temperature Geothermal System near the eastern boundary of the Hauraki Depression in North Island of New Zealand. The gravity study revealed a hidden extension of the Tertiary-age Waiteariki Ignimbrite, underlying plio-Pleistocene alluvium deposits of the Hinuera Formation, which locally host an aquifer of warm geothermal fluids. A 3D magnetic model derived from the ground magnetic measurements helped identify probable paleo-channels within the sedimentary sequence of the Hinuera Formation. These paleo-channels could represent higher permeability at shallow (<50 m) depth, although the exact relationship between the locations of the surface thermal manifestations and identified paleo-channels is still unclear. The results of the resistivity surveys suggest that values less than 25 Ωm are indicative of the presence of warm waters at Okauia. Most warm water occurrences at Okauia take place near the Okauia Fault, particularly at 0 m RL (sea level) elevation. The near-surface extent of the Okauia Low Temperature Geothermal System can be approximated from the results of this study.

Assessing tectonic subsidence from estimates of Holocene relative sea-level change: An example from the NW Mediterranean (Magra Plain, Italy)

New sedimentological sea-level indicators are presented from the River Magra coastal plain, in NW Italy. Chronologically well-constrained paralic peats and organic sediments which had been deposited in a defined relationship with sea level were recovered in four of the seven boreholes considered in this work. Their evolution scatters in the time span of the past 6000 years. Since the cores are located within a single sedimentary basin, it was possible to correct the elevation of marker horizons for the effect of sediment compaction by means of both a field and a geotechnical method. Thus, seven reliable index points for the mid- to late-Holocene sea-level rise were obtained. The age–depth model derived from them was compared with that of sea-level predictions from two different Glacial Isostatic Adjustment (GIA) models available for the area. In both cases, the modelled sea-level estimates overlie the index points, suggesting lower relative sea-level elevation than the one predicted considering the combined eustatic and hydro-isostatic components. Based on the general tectonic setting of the area, this finding was interpreted as the effect of a tectonic subsidence of the basin, the rate of which can be quantified on average as 0.5 mm/yr since the middle Holocene, with a sharp increase after 2500 yr BP. By providing a reliable estimate of the rate of tectonic subsidence in a coastal area of NW Italy, this research contributes to refining the geodynamic model of this part of the Mediterranean basin.

Sea-level variations during Marine Isotope Stage 7 and coastal tectonics in the eastern Seto Inland Sea area, western Japan

Relative sea-level (RSL) observations for Marine Isotope Stage (MIS) 7 were obtained from three sites (Higashinada, Kakogawa and Mitsu) of the eastern Seto Inland Sea area, western Japan. We evaluated the magnitude of sea-level highstands during MIS 7 and the local tectonics based on RSL records of this coastal area. For this purpose, we analyzed diatom assemblages and sedimentary sulfur, and carried out tephra analysis. We also constructed a linear age model to determine the depositional ages of the sediments using altitudes of astronomical age control points obtained mainly from the present diatom data. At the Mitsu site, RSLs were estimated to be −22.87 ± 0.50 m at the MIS 7.5 highstand peak (234.6 ka), below −20.17 m at 211.2 ka, and below −20.00 m at 209.9 ka. With a tectonic subsidence rate of 0.11 ± 0.02 m/ka since the Last Interglacial Maximum at the Mitsu site, the elevation of the tectonically corrected MIS 7.5 highstand peak may have been +2.94 ± 5.19 m. The tectonically corrected sea-level elevations during MIS 7.3 are inferred to have been below +3.06 ± 4.72 m at 211.2 ka and below +3.09 ± 4.70 m at 209.9 ka. Comparisons between the diatom-inferred RSLs and the isotopically derived sea-level curve indicate that the MIS 7.3 highstand peak was above −18 m and may have been lower than the MIS 7.5 and 7.1 highstands. Based on the isotopically derived sea-level curve and the RSL data from Higashinada and Kakogawa, a tectonic subsidence rate of 0.26–0.32 m/ka was derived for Higashinada and a tectonic uplift rate of >0.17 m/ka and <0.29 m/ka was derived for Kakogawa. A relative uplift rate of >0.43 m/ka and <0.61 m/ka was derived along the traverse from Higashinada to Kakogawa. The uplift rate derived for Kakogawa relative to Mitsu is > 0.26 m/ka and <0.42 m/ka. These values indicate the intensity of crustal movements associated with active faulting of the Rokko–Awaji fault system along this tectonically active coast.

Landslide susceptibility mapping in Bijar city, Kurdistan Province, Iran: a comparative study by logistic regression and AHP models

Landslides and instability slopes are major risks for human activities which often lead to losing economic resources and damaging properties and structures. The main aims of this study are identifying the underlying effective factors of landslide occurrence in Bijar, Kurdistan Province, and evaluating the regions prone to landslide to prepare the susceptibility map using the logistic regression (LR) and analytical hierarchy process (AHP). At first, using field surveys, questionnaires, geological and topographic maps and reviewing the related studies, ten effective factors including the elevation of sea level, slope inclination, slope aspect, geology, distance from the linear elements (fault, road, and river), precipitation and land use were recognized. Then, they were processed using ARC GIS 10 and ILWIS 33. The dependent variable included 144 of slopes prone to landslide selected across the region as the landslide data (code 1), and also 144 stable landslide slopes were randomly selected as landslide free data (code 0). The results of the evaluation showed that LR model with PCPT index equals to 83.4; −2LL index equals to 229.226; and ROC index equals to 98.5% and landslide susceptibility map based on SCAI index had high verification in the case study. Therefore, 75.489% of the area had very low susceptibility, 10.037% low susceptibility, 3.628% moderate susceptibility, 4.062% high susceptibility and 6.784% very high susceptibility. Based on the preferences of the AHP method, the weighting of selected parameters was logically performed so that the parameters could be arranged according to their priorities. The results of the AHP model showed that 3.4% of the area had very low susceptibility, 30.43% low susceptibility, 46.68% moderate susceptibility, 18.14% high susceptibility, and 1.33% very high susceptibility.

Carbon isotope gradient of the Ediacaran cap carbonate in the Shennongjia area and its implications for ocean stratification and palaeogeography

The geochemistry and paleogeography of the Doushantuo succession in the Shennongjia area have been insufficiently studied. Here, we report on the carbon and oxygen isotope compositions of Ediacaran Doushantuo cap carbonates from four sections (Longxi, Muyu, Yazikou and Songluo) in the Shennongjia area. A large C-isotopic gradient (~5‰) between the Longxi and Songluo sections, here identified for the first time, is inferred to have been dynamically maintained by photosynthesis in surface waters and anaerobic oxidation of dissolved organic carbon (DOC) in deep waters. Spatial variation in C-isotope chemostratigraphy among the four sections was related to Marinoan post-glacial sea-level elevation changes. At Longxi, a positive δ 13Ccarb shift below the horizon containing tepee-like structure resulted from intense photosynthesis during early regression. A negative δ 13Ccarb shift within the tepee-horizon was triggered by sulfate reduction and freshwater mixing with 13C-depleted dissolved inorganic carbon (DIC) during late regression. A positive δ 13Ccarb excursion in the uppermost part of the cap carbonate was related to enhance primary productivity and organic matter burial during early transgression. At Muyu, the carbon isotopic variation tendency, which is similar to that at Longxi, may have been mildly influenced by the surface water environment. At Songluo, the positive δ 13Ccarb excursion, up to -4‰ in the lower part of the cap carbonate, was probably associated with methanogenesis in deep waters during late transgression to early regression and subsequently disappeared due to decomposition of methane hydrate during late regression. At Yazikou, the consistently stable δ 13Ccarb values around -4‰ indicate that the cap carbonate may have deposited at intermediate water depths. As evidenced by diagnostic sedimentary characteristics of the study sections, the palaeogeographic framework of the Shennongjia area exhibited deepening from SE to NW during the Early Ediacaran Period in the aftermath of Snowball Earth.