Sand Ridges Research Articles

Sequence stratigraphy and sedimentary processes since the last glacial maximum in Nha Phu Bay and adjacent shelf, central Vietnam

Three sedimentary systems tracts (LST, TST, and HST) have been identified in Nha Phu Bay and the adjacent shelf, Khanh Hoa Province, Vietnam. These have been deposited since the Last Glacial Maximum (LGM) and interpreted in this study via the analysis of high-resolution acoustic data and sediment cores. The lowstand systems tract (LST) comprises sandy sediments exposed at seabed on the outer shelf as sand ridges, and underlying the transgressive systems tract (TST) on the middle shelf. The LST developed under shallow-marine settings during the sea-level lowstand and early sea-level rise before 14.6 cal kyr BP. The TST comprises primarily fine-grained sediments deposited during the transgression between 14.6 and 8.0 cal kyr BP in an incised trough of the outer shelf, on the middle shelf, and in Nha Phu Bay. Erosion of the seaward portion of the TST on the middle shelf might occur during the late transgression (9.0–8.0 kyr BP). The highstand systems tract (HST) comprises sediments deposited during the sea-level highstand between 8.0 and 0.0 cal kyr BP and is distributed widely in the bay, on the inner-middle shelf, and partially on the outer shelf. A paleo-coast zone, located in 100–120 m present-day water depth, is recognized through the appearance of sand ridges and sandy sediments. The seafloor sediment distribution is mapped via four major acoustic echo types, combined with seabed sediment samples. The coarse-grained sediment distribution, subaqueous outcrops, and thin deglacial sediment thickness on the inner shelf indicate erosion-dominated processes under vigorous hydrodynamic conditions. Nha Phu Bay and the middle shelf are interpreted as the depocentres. The estimated sediment load deposited in Nha Phu Bay is 0.18 Mt./yr, accounting for 15–35% of the annual sediment discharge from the Dinh River. The seabed morphology, muddy sediment distribution, and deglacial sediment thickness reveal a dominant sediment-transport pathway, across the inner shelf to the middle shelf, near the northern shoreline of Nha Phu Bay under the influence of the southwest monsoon.

Seasonal variations in suspended sediment concentration and its drivers in the radial sand ridges of China's Jiangsu coast

Most studies on seasonal variations in suspended sediment concentrations (SSCs) only performed qualitative analyses and focused on the dynamic mechanisms of instantaneous SSCs rather than background SSCs and their contributions to seasonal SSCs. To quantitatively evaluate the seasonal differences in SSCs and their drivers in radial sand ridges (RSRs), we measured water depth, current velocity, SSC, wave parameters, and suspended and surficial sediment properties during summer and winter. Small grain size (fine sand, silt, and clay) was the dominant size class and suspension was the dominant transport mechanism in areas with a significantly higher SSC during winter than during summer (up to ∼2.5 times). Settling velocity, which was sensitive to temperature, grain size, and turbulence, had 0.39–0.89-fold difference between summer and winter. The stable background SSC (minimum SSC among tidal cycles) during winter was higher, with an average contribution of ∼74% to the total SSC, than that during summer. Combined with wave statistics, the lower sediment settling velocity acted in conjunction with the higher strong wave occurrence frequency and longer wave duration to sustain high background SSCs during winter. This study reinforces the utility of background SSC when estimating instantaneous SSC in different seasons.

Late Pleistocene to Holocene facies architecture and sedimentary evolution of the Zhejiang coast, East China Sea

The Holocene mud wedge that extends from the Yangtze River mouth to the Taiwan Strait along the Zhejiang–Fujian coast, East China Sea, has attracted considerable research attention; however, the pre-Holocene sedimentary evolution of the same area has been less well documented owing to limited data. We conducted an integrated analysis of 7000 km of high-resolution shallow seismic profiles and two ∼60–80-m-long borehole cores from the Zhejiang coast of eastern China to improve our understanding of the formation of the mud wedge in the context of the post-Late Pleistocene sedimentary evolution of the coastal area. Five major seismic units (numbered SU 1 to SU 5 in descending order) and various subunits that have formed since Marine Oxygen Isotope Stage (MIS) 5 were identified in the study area. SU 5 is recognizable only in the southeastern part of the study area and is interpreted to comprise subtidal to inner-shelf deposits (SU 5b) that were formed during MIS 5 and littoral to tidal-flat deposits (SU 5a) that were formed during the overall sea-level fall of MIS 4 and early MIS 3 (∼60–40 ka). These two subunits are divided by an intervening erosional surface that was likely generated by subaerial exposure of the study area during the sea-level lowstand of MIS 4. During the period from late MIS 3 to MIS 2, the study area was gradually exposed subaerially owing to further sea-level fall, with numerous small rivers incising the underlying strata to form a subaerial unconformity surface (T4). During the early postglacial transgression between ∼15.0 and ∼ 14.0 ka, the study area was progressively flooded, and the river channels were transformed into small estuaries (tidal rivers) that then coalesced into a large-scale, wave-dominated estuary during sea-level rise from ∼14.0 to ∼10.0 ka. The sandy fluvial and/or tidal-river deposits above T4 constitute SU 4. The wave-dominated estuary included a central estuarine bay on the landward side and an estuary-mouth complex on the seaward side, corresponding to fine-grained (muddy) deposits (SU 3a) and coarse-grained (sandy) deposits (SU 3b), respectively. The estuarine deposition concluded with the formation of a transgressive ravinement surface by erosional shoreface retreat during the rising sea level in the early MIS 1 from ∼13.5 ka in the southeasternmost part of the study area to ∼10.0 ka in the area closer to the shore. During the following transgressive phase, the study area was under coastal to shelf sedimentary environments during deposition of SU 2a. Tidal sand ridges (SU 2b) in the eastern part of the study area were formed at ∼11.5 ka and have been active since then. The maximum flooding surface was formed at ∼7.6 ka, and a mud wedge (SU 1) in the study area (except in the eastern part) has been developing since that time and is interpreted to have resulted from the deposition of sediments derived predominantly from the Yangtze River under the modern current system established since the maximum flooding in the Middle Holocene. The study provides new insights into the paleoenvironmental and paleogeographic evolution and facies architecture of the Zhejiang coast since MIS 5, which were controlled by preexisting geomorphological conditions and changes in sea level, hydrodynamics, and sediment supply.

The environmental significance and low-oxygen indicator potential of benthic foraminiferal assemblages in surface sediments off the Changjiang River (Yangtze River) Estuary, China

86 surface sediment samples and a core (CDZS38) from the Changjiang River Estuary (CRE) and its adjacent area were collected to investigate the environmental significance of foraminifera, and determine a microfaunal index for coastal hypoxia to be used for paleoenvironmental studies. Benthic foraminifera and their relationship with environmental parameters including grain size composition and total organic carbon in surface sediment samples were studied. The benthic foraminiferal assemblages were dominated by littoral species in the study area. R-mode cluster analysis identified three clusters based on the percentage of benthic foraminifera. Cluster 1 covers the transitional area between the Radial Sand Ridges of the South Yellow Sea and the CRE. The dominant foraminiferal assemblage is Ammonia beccarii vars.–Ammonia compressiuscula–Quinqueloculina spp., which is a good environmental indicator of an oligotrophic near-shore condition with a strong hydrodynamic force. Cluster 2 covers the inner-shelf off the CRE. The dominant foraminiferal assemblage of Cluster 2 is Epistominella naraensis–Bolivina cochei–Bulimina marginata, which can be used to represent a eutrophic, hypoxic inner-shelf environment. Cluster 3 covers the Hangzhou Bay, which is a typical macro-tidal river mouth. The dominant foraminiferal assemblage of Cluster 3 is A. beccarii vars.–E. naraensis–Ammonia convexidorsa, which is indicative of an environment that is strongly disturbed by tidal currents and influenced by substances from the Changjiang River. The occurrence of E. naraensis, B. marginata and B. cochei is always associated with the hypoxic region. With the correlation analysis with environmental parameters, these species can be considered low-oxygen foraminiferal assemblages (LOFA). We generated a low-oxygen foraminiferal index (the ratio of LOFA to the sum of LOFA and Euryhaline species) to explore the development of hypoxia at the inner-shelf off the CRE, and applied this index to the short core CDZS38. The result indicated that high LOFI values found for CDZS38 is consistent with the recorded trends in hypoxia and harmful algae bloom (HAB) for this area over the past 59 years, and reflect an increase in the hypoxic conditions over this time period.

Evolution of the hydrocarbon migration system of the lower enping formation in the pearl river estuary basin

The Enping Formation of the Paleogene System in the Lufeng south area of the Pearl River Estuary Basin has good potential for hydrocarbon exploration. It is characterized by a vertically large distribution of a crude oil type and a widely horizontal distribution of similar crude oil. With the complex characteristics of hydrocarbon distribution and migration, studying the evolution mode of this migration system on a dynamic scale is necessary. In this study, the key accumulation period was determined using existing logging, seismic, and microscopic data combined with fluid inclusion and burial history. Then, the system's migration path and the direction of migration in the key accumulation period were analyzed, and the migration system and evolution model in the study area were established. The results show two stages of accumulation in the southern Lufeng area: 19–8 Ma and 8–0 Ma. In the first stage, the reservoir mainly followed the transport of a far-source fault–sand–ridge coupling system and the traps on the migration path were favorable for hydrocarbon accumulation. In the second accumulation period, traps that developed near the oil-source faults were favorable for hydrocarbon accumulation. The favorable traps in the first accumulation period were distributed in the whole area. The traps in the southwest wells B921 and C1211 were larger than the first stage, whereas the favorable traps in the northeast and central parts were mainly distributed in B211D and its adjacent well area, with smaller and scattered traps. Favorable traps in the second accumulation period were mainly distributed in the eastern and central regions, around wells B211D and B161, whereas the traps in the southwest were not conducive to hydrocarbon accumulation due to the lack of effective transport system connection. The results of this study have a certain guiding significance for practical exploration.

Non-native tree plantations are weak substitutes for near-natural forests regarding plant diversity and ecological value

While near-natural forest stands are dramatically diminishing, monoculture tree plantations are rapidly spreading globally, including the eastern part of Central Europe. Tree plantations are regarded as simplified and species-poor ecosystems, but their functional and phylogenetic diversity and ecological value are still mostly unknown. In the present study, we investigated near-natural poplar forests and the three most common tree plantation types (native deciduous Populus alba, non-native evergreen Pinus nigra, and non-native deciduous Robinia pseudoacacia plantations) in the Kiskunság Sand Ridge, central Hungary. Our aim was to find out how different the species composition of the studied habitats is, how taxonomic, functional, and phylogenetic diversity vary among the four habitat types (i.e., near-natural forests and three types of plantations), and what the ecological value of the studied habitats is. We found that the four habitat types had significantly different species compositions. Although each habitat contained some diagnostic species, near-natural forests had the highest number of diagnostic species. While many of the diagnostic species of near-natural forests were native shrubs, tree plantations had many weeds and non-native herbs as diagnostic species. Near-natural forests had the highest per plot richness of native species and the lowest richness of non-natives. Shannon diversity, functional diversity and phylogenetic diversity were higher in the near-natural forests and two types of plantations (Populus and Pinus) compared to Robinia plantations. Based on naturalness indicator values, near-natural forests were the least degraded and Robinia plantations were the most degraded. Near-natural forests contained the most species of high conservation importance. Overall, near-natural forests proved to be much more valuable from an ecological and conservation perspective than any of the studied plantations; conservation and restoration programs should therefore focus on this type of habitat. Among the plantations, Populus alba plantations are the best substitute option in most respects, although they harbored a relatively high number of non-native species. We suggest that the native Populus alba should be preferred to non-native tree species when plantations are established. In addition, decreasing the extent of Pinus and Robinia plantations is essential on the long run if we aim to maintain the ecological integrity of the region.

Sedimentology and evolution of the Holocene radial tidal sand ridge in the south Yellow Sea, China

The radial tidal sand ridge (RTSR) off the Jiangsu Coast in the south Yellow Sea is one of the most fantastic and unique natural landscapes in the world. A large number of investigations on geomorphology and marine geology have been implemented during the last several decades. The formation and evolution of the RTSR, however, are still under debate. To resolve this issue, 10 ∼30–60 m-long cores were retrieved from the Jiangsu coastal plain and offshore sand ridge field in 2018–2019. Stratigraphic transects chronologically constrained by abundant radiocarbon dates were built based on sedimentological and paleoecological (i.e., foraminifer) data from selected cores. Combined with well-documented core stratigraphy from earlier studies, an age–depth plot with a local sea-level change curve revealed that the RTSR initiated approximately 9,000 cal a BP in a sandy bedform shape under transgressive conditions, continued throughout the Holocene, but developed mostly after 1128 AD, when the Yellow River flowed southward into the Yellow Sea. Abundant sediment supply, thus, appears to have played a major role in the formation and evolution of the RTSR in the south Yellow Sea.

Fasies Sedimen Kuarter Kaitannya Dengan Potensi Likuefaksi Di Kawasan Das Cimanuk, Indramayu, Jawa Barat

The lower Cimanuk catchment area which will be developed as industrial area is dominated by Quaternary deposits which are susceptible againts liquefaction if large earthquakes occurred. The presence of Subang, Cirebon 1 and Cirebon 2 active fault segments will trigger earthquake which potentially liquefaction. This study aims to characterize the type of sedimentary facies induced liquefaction hazard in the lower Cimanuk catchment area, Indramayu, West Java. This research methods consist of borehole description and sedimentary facies analysis based on CPT and CPTu data with cone resistance (qt) corrected value, friction ratio (Fr), laboratory analysis and liquefaction potential based on SNI 1726:2019, which is deterministic and 2,500 years return period PGA value. Based on facies association analysis there are three facies that developed in the study area. First, delta plain facies consisting of fluvial sands, silt and clay. Second, delta front facies consisting of beach ridge sands and sandy silt. Third, silt and clay prodelta facies. Liquefaction potential analysis based on N-SPT, CPT and CPTu data shows that almost all test point are potentially liquefied, especially beach ridge sands and silty sand delta front facies. Liquefaction potential is more in the northern region of the study area, caused by the low density of sand and sandy sediments (N-SPT value < 10 or qc < 6,000 kPa).

Identifying the clay-size sediment provenance of the radial sand ridges in the southwestern Yellow Sea using geochemical and Sr[sbnd]Nd isotopic tracers

Although the sediment provenance of the Jianggang radial sand ridges (RSRs) in the southwestern Yellow Sea has attracted much attention in recent years, the provenance of the clay-size fraction is rarely known. In this paper, the residual fraction of the clay-size sediments in the Jianggang RSRs was isotopically and geochemically determined to analysis their provenance contributions and transport patterns. The clay minerals of the sediments in the Jianggang RSRs, Yangtze River Mouth, Modern Yellow River Mouth and Old Yellow River Delta were characterized by high illite and low smectite contents, differing from those of the Korean rivers. The isotopic and geochemical data showed that 87Sr/86Sr ratios and εNd(0) values of the clay-size sediments ranged from 0.719 to 0.725 and from −14.5 to −12.2, respectively for the onshore RSRs, and from 0.715 to 0.724 and from −14.6 to −10.9, respectively for the offshore RSRs. The clay-size sediments in the offshore RSRs were represented by high concentrations of Sr, Co, Zr, Nb, Hf, Ta, while in the onshore RSRs were characteristic of high concentrations of other elements (except for Ba). The clay-size sediments showed partially similar Y/Hf and Rb/Sc ratios and upper continental crust (UCC)-normalized distribution patterns of trace elements between the onshore and offshore RSRs. However, there was a clearly SrNd isotopic boundary between the two RSRs, indicating that the offshore clay-size sediments were just partly transported to the onshore area. The UCC normalized patterns of the clay-size sediments in the onshore and offshore RSRs were close to those of the Yangtze River Mouth, Modern Yellow River Mouth and Old Yellow River Delta, but different from those of the Korean rivers and Cheju Island. Based on the analyses of SrNd isotopes and trace elements through MixSIAR model, the clay-size sediments of the onshore RSRs mainly originated from the Yangtze River Mouth, but those of the offshore RSRs were predominantly mixed by the Yangtze River Mouth, the Modern Yellow River Mouth and the Old Yellow River Delta, while the contributions of other sources were tiny. Through the SrNd isotopic comparisons, it was further found that there existed a large-scale transport of the clay-size sediment from the Yangtze River Mouth within the Yellow Sea to reach the Jianggang RSRs finally under the influence of the Changjiang Diluted Freshwater and the Yellow Sea Warm Current. This study not only gives deep insight into the formation and evolution theory of the Jianggang RSRs, but also enriches the sediment migration patterns in the Yellow Sea. Meanwhile, it demonstrates the effectiveness of the SrNd isotopic and geochemical tools for provenance analyses of the clay-size sediments, although 87Sr/86Sr should be used cautiously for provenance apportionment due to its indistinguishability between the Chinese and Korean rivers.

Planktic-benthic foraminifera ratio (%P) as a tool for the reconstruction of paleobathymetry and geohazard: A case study from Taiwan

The calcite tests of foraminifera are an important biogenic component of marine sediments. The abundance of foraminiferal tests in marine sediments broadly varies with bathymetry, thus has been used to reconstruct paleobathymetry. It is also promising as a tracer for downslope transport triggered by earthquakes and typhoons, especially if the displaced material from shallow locality contrasts strongly with the background autochthonous sediments in terms of foraminiferal abundance, such as the ratio of benthic and planktic foraminifera termed %P. However, its applicability in sediments off Taiwan has not been assessed. Taiwan is located in the path of typhoons and at tectonic plate margins, where typhoons and earthquakes may trigger submarine geohazards. This, combined with the fact that its seafloor spans a large bathymetric range, render this region an ideal natural laboratory to evaluate the applicability of %P as a proxy for tracing submarine geohazards and bathymetry. Here we report foraminiferal abundance, %P, grain size and elemental data from 148 surface sediment samples off 6 sectors off Taiwan, namely Southern Okinawa Trough, Hoping-Nanao-Hateruma Basins, Taitung-Hualien, Hengchun Ridge, Gaoping, and Changyun Sand Ridge. Of all the hydrographic and sedimentological parameters assessed, seafloor bathymetry is the major driver of foraminiferal abundance and %P in these regions. Notably, several data points deviate from the regional %P-water depth relationship. Based on sedimentological parameters and previous studies, we posit that these outliers may have to do with local sedimentation setting. These processes include earthquake-induced sediment transport via submarine canyon in the Southern Okinawa Trough, typhoon-triggered sediment flushing in Gaoping Canyon, cross-shelf and northward advection of planktic foraminifera on the Gaoping shelf, and carbonate dissolution in the deep Hateruma Basin. Off Taiwan, the %P value in sediments increases exponentially with bathymetry (R2 = 0.72, n = 81), and agrees well with the global calibration obtained by combining data from several regions of the global ocean (R2 = 0.86, n = 1004). The regional %P-water depth relationship may be useful for reconstructing paleobathymetry here, albeit with an uncertainty in the range of 14–1600 m. The uncertainty increases with water depth. Our results also highlight the potential of the %P index as a tracer for downslope transport and lateral advection in the water column. In conclusion, the downcore application of %P has the potential to reconstruct past geohazard events while also identifying autochthonous sediment sequences that are suitable for paleoceanographic reconstruction.

Mapping the most heavily reclaimed shorelines of the Yangtze River delta urban agglomerations

Objectively understanding the characteristics and evolution of coastal geomorphology, and predicting the growth potential of intertidal flats are the prerequisites for the effective conservation and development of shoreline resources. However, the vulnerability of shorelines in the long term and large space scale needs to be assessed since human intervention in recent decades has intensified the double oppression of river delta system transformation and land reclamation. The Yangtze River Delta Urban Agglomerations (YRDUA) is a highly developed global economy, therefore, the YRDUA with the most intense reclamation, and their dynamic shoreline changes before and after the sharply decreasing sediment supply were detected based on 4,596 remote sensing images and corresponding hydrodynamic data. We found that the sediment replenishment from the radial sand ridges on the middle Jiangsu Coast made the shoreline expansion rate reach 4–5 times that of other Jiangsu coasts. Specifically, a close correlation between the shoreline accretion rate and the amount of sediment supply was found on the eastern Chongming Wetland. Generally, there were still sufficient sediments on the Yangtze River Estuary and Hangzhou Bay interface to support the shoreline expansion despite the upstream sediment reduction. The longshore sediment transport from the delta-front erosion and the land reclamation including vegetation ecological responses were the main factors promoting the shoreline advance. Human interventions, dominated mainly by reclamation, formed positive feedback with local hydrodynamic processes and promoted continuous shoreline accretion. This study focused on the external and internal drivers and their interactions of long-term shoreline evolution with very intensive human activities, which can provide the decision-making reference for the regional coastal zone management and conservation.

Distribution and dynamics of U.S. continental shelf ridge sediment and morphology: A brief review

The U.S. continental shelf is an important sediment source for beach nourishment and restoration efforts that mitigate erosion, increase resilience to storm impacts, provide habitat, and support the economy. The continental shelf is the preferred source for borrow sediment to closely match the native grain size distribution and composition of the site being restored. However, spatiotemporal variability of continental shelf sediment ranges in size and composition, resulting from previous sea levels and contemporary variability such as normal shelf processes, storm waves, and anthropogenic activities. Understanding the nature and distribution of continental shelf ridge sediment changes over time should reduce costs of efforts required to explore offshore sediments for coastal restoration projects. This review examines the present state of knowledge on the availability, distribution, and characteristics of continental shelf sediment under normal conditions and potential variability after storms and dredging. Under normal conditions sediment on the shelf is easily located and characterized as potential borrow areas. However, storms can induce enough sediment transport to change the boundaries of sediment borrow areas and the location of known sand ridges. Dredging can also influence sediment infilling of the dredged borrow areas, which impact benthic infauna and introduce potential onshore impacts depending on the geometry and nearshore proximity of the excavation. The results of this summary have identified gaps in the present knowledge such as a need for additional sand searches in under-investigated regions, a better understanding of storm impacts on hydrodynamic-driven ridge migration and continuing to review best management practices when new research of dredging practices and impacts are presented. A brief review of the present state of knowledge on the distribution and dynamics of continental shelf sedimentology and morphology are presented here to aid in advancing the scientific and coastal management community’s knowledge of shelf sediments and dynamics as well as highlight potential future research needs.

The soil moisture regime and groundwater recharge in aged forests in the Sand Ridge region of Hungary after a decline in the groundwater level: an experimental case study

Abstract The decline in groundwater levels is a cause of concern in many regions of the world, including the Sand Ridge of Hungary. The causes of the regional depletion range from rising air temperatures, changes in precipitation, domestic and agricultural groundwater use and past amelioration and recent afforestation, including the effects of drilling for crude oil exploration. The relations between the decline, the soil water regime and groundwater recharge under existing aged forests remained unclear thus far. Based on our monitoring of groundwater and soil moisture we aim to clarify this interplay in a new experimental site on the hilltop of the Sand Ridge. We compared three land-uses: a 41-year-old black locust (Robinia Pseudoacacia) offshoot forest, an 83-year-old first generation black pine (Pinus nigra) forest, and a grassland control site. The observed differences in the soil moisture profiles and dynamics were connected to the use of water by the given type of vegetation. We indicated a connection between the disruption of the groundwater recharge and the loss of contact of the rooting system of the forests with the deepening of the unconfined aquifer. Even if the aged forests could locally contribute to the decline, we conclude that the decline at the hilltop site that may be more strongly driven by other regional factors.

Late Holocene Morphodynamic Feedback in Can Gio Mangrove Tide-Dominated River Mouth Systems, Vietnam

Can Gio (CG), a mangrove forest with a dense network of tidal creeks, gradually grew and spread seaward on a coastal platform, which was built since about 8 ka before present (BP). Along with this development, a sand ridge began to form and moved back with the shoreline withdrawal landward in the Late Holocene. This mangrove environment is likely abandoned from the mainland but was, however, the place for settlement of ancient Vietnamese a few centuries BC. The CG mangrove forest was severely destroyed during the American War and was restored since 1980. However, the historical change of the landscape along the Saigon-Dong Nai River (SG-DNR) since the Late Holocene is not completely unraveled. By analyzing sediment cores with a multiproxy approach, we investigated the recent geological development with regard to the variation of the intensity of the East Asian palaeomonsoon and regarding the accommodation space, as both regulate the development of this coastal environment. A recently significant shift in the coastline, mainly due to a change of hydroclimatic factors, was observed. A continuous coastline retreat occurred over the last millennium, changing the depositional environment and reshaping the CG mangrove landscape. Along the present coast and tidal channels, partially strong erosion and bank failures occur, alternating with accretion at other coastal sections. This development tends to increase progressively.

Geometry of sedimentary deposits and evolution of the landforms in the Chobe Enclave, Northern Botswana

The imprint of neotectonics is frequently obscured in low-relief environments by the sedimentary cover. This is the case in the Chobe Enclave, part of a pristine region of the Middle Kalahari Basin in northern Botswana, where numerous fossil landforms, such as sand dunes, pans, sand ridges, and carbonate islands, can be observed but whose detailed origins are unclear. In this study, a combination of near-surface geophysical surveys, sedimentological analysis, and optically-stimulated luminescence (OSL) dating were used to study the relationship between landscape development and neotectonic activity in one region of the Chobe Enclave. Specifically, electrical resistivity tomography (ERT) and ground penetrating radar (GPR) surveys were used to define the lateral and vertical distribution of sedimentary deposits associated with a prominent sand ridge and its margins. Sedimentological analysis and OSL dating of soil samples from pits taken along the survey lines were then used to calibrate the geophysical results and establish a chronostratigraphical framework. Our results lead to the following hypotheses regarding the evolution of this part of the Chobe landscape: (i) during the Late Pleistocene (>~25 ka), fluvial channels were buried due to epeirogenic movements, resulting in paleo-channels; (ii) between ~25 ka and ~6 ka, a paleo-lake shoreline formed, which resulted in the linear eastern margin observed on the considered sand ridge. Erosional bounding surfaces suggest the syndepositional uplift of the sand ridge morphologies during this time; (iii) a neotectonic influence on the evolution of the landscape is revealed by the incision of the sand ridge forming fluvial watergaps since ~6 ka ago; and (iv) due to continuous aeolian and fluvial reworking, the western-most ridge became gradually isolated from the floodplain resulting in an inherited relief. In conclusion, this investigation allowed the deformation caused by epeirogenic movements acting on a low relief landscape to be characterized in terms of landforms and sedimentary body properties.

The complexity of luminescence dating of tidal sand body revealed by the discrepancy of paired quartz OSL ages

Optically stimulated luminescence (OSL) dating is becoming a useful technique to yield absolute age of organic-poor sandy deposits. The buried tidal sand body (BTSB) in the coastal zone of northern Jiangsu Province, China, has been suggested to have the same origin as the offshore radial sand ridge in the Yellow Sea. However, chronological constrain of the BSTB is still quite limited. In this study, OSL measurements were conducted using silt-sized multi-grain and coarse-grained single-grain quartz to constrain the depositional history of a 25.6 m core from the BTSB. A low luminescence sensitivity of quartz was observed, and only ∼1.04% of the grains passed the standard rejection criterion for single-grain measurement. Analysis of paired OSL ages from two grain-size fractions using different protocols showed that silt-sized quartz ages were underestimated of 0.14–1.35 ka in comparison to coarse-grained quartz in the depth interval of 5.8–22.4 m. We interpret such an age discrepancy as the effects of lateral infiltration of fine-grained sediment into the sand body due to dynamic feature of channel-ridge system on the shelf. As far as we know, it is the first time that such infiltration is demonstrated through OSL dating. Our OSL data indicated that there is a significant hiatus between the Late Pleistocene stiff clay layer (50–18 ka) and the Holocene sequence. Holocene deposits only occurred in the last 2 ka, with rapid accumulation of ∼17 m-thick sediments at ∼2–1 ka, a slower accumulation between ∼1 and 0.1 ka and rapid land emergence through an accretion of ∼4 m-thick sediment over the past ∼0.1 ka. This study highlights the complexity of OSL dating in highly dynamic sedimentary environments. Therefore, examining different grain size fractions and comparing different measurement protocols are highly deserved in carrying out OSL dating in such environments. • We compared multi-grain silt-sized quartz and single-grain coarse-grained quartz ages for a tidal sand body. • Silt-sized quartz underestimated ages due to ‘younger’ sediment infiltration into tidal sand body. • The buried tidal sand body in the northern Jiangsu Province of China was formed in the last 2 ka.

Fertility capability classification for agricultural land use planning in the beach sands area of Akwa Ibom State, Nigeria

Soil survey and fertility capability classification (FCC) were carried out in an area mostly underlain by the beach ridge sands (BRS) parent material in Akwa Ibom State, Nigeria. The study applied the FCC in agricultural land use planning for efficient land management and optimal agricultural productivity of the beach soils. Field and laboratory data were obtained from 40 pedons located across eight Local Government Areas on the BRS parent material. From the results of field and laboratory studies, 11 FCC units were identified in the area. Based on similarities in certain soil profile characteristics, the 11 FCC units were grouped into four agro-ecological units (AEUs): (i) poorly drained FCC units with sandy topsoil over sandy subsoil, grouped to form AEU-A, covered 65.00% of study area; (ii) well drained FCC units with sandy topsoil over sandy subsoil, formed AEU-B and covered 22.50% of study area; (iii) poorly drained FCC units with sandy topsoil over loamy subsoil or loamy top- and sub- soils, formed AEU-C and covered 7.50% of study area; (iv) well drained FCC units with sandy topsoil over loamy subsoil, which formed AEU-D, occupied 5.00% of study area. The result of this study has shown that FCC can be employed as a simple but efficient tool in agricultural land use planning. Major soil profile characteristics used to differentiate land units within the beach sands area of Akwa Ibom State are drainage and texture.

Application of Airborne LiDAR Measurements to the Topographic Survey of the Tidal Flats of the Northern Jiangsu Radial Sand Ridges in the Southern Yellow Sea

The northern Jiangsu radial sand ridges are typical geomorphic deposit units distributed off the Jiangsu coast. A coastal tidal flat typically develops and provides a good habitat for many migratory birds and benthic organisms. However, topographic surveys of tidal flats have always been difficult in marine surveys because of the dense tidal creek, poor accessibility, and difficulty in setting up control points. In this study, we quickly obtained the point cloud data of the tidal flat near Yangkou Port in the southern part of the radial sand ridges based on an airborne LiDAR system, an integrated 3D laser scanner and a positioning and attitude determination system. We analyzed the adaptabilities of multiple filtering algorithms to tidal flats. In addition, a digital elevation model (DEM) of the tidal flat was constructed and the accuracy was verified with synchronized beach GPS-RTK topographic elevation measurements. The results show that the following: (1) Airborne LiDAR can quickly obtain high precision, high resolution, and a large area of ground point cloud information for tidal flats, overcoming the shortcomings of traditional measurement methods. (2) The triangulated irregular network (TIN) filtering effect is better than that of mathematical morphology and the filtering effect of point cloud normal vector clustering is mediocre. (3) The DEM of the LiDAR point cloud is in good agreement with RTK and the average error of the measurement results is 0.108 m. The error accuracy of the DEM satisfies the surveying specification of a 1:500 topographic map in a flat area, which proves that the airborne LiDAR system can be suitable for tidal flat elevation measurement. Nevertheless, it is possible to provide high precision terrain detection and DEM construction of a tidal flat with the development of airborne infrared and blue-green laser detection radar.

Distinctive lithofacies architecture of sand ridges built by storm and ocean currents: An example from a Middle Pleistocene shallow‐marine succession on the Boso Peninsula, Japan

AbstractSand ridges are present in modern storm‐dominated and tide‐dominated shallow‐marine environments worldwide, but the number of published ancient examples is limited. The role of ocean currents in the formation of sand ridges is also poorly understood. This study investigated the lithofacies architecture of a lenticular sandstone body (ca 70 m thick and ca 30 km long) in the upper Mandano Formation (ca 0.6 Ma) on the Boso Peninsula, Japan, to establish criteria for identifying sand ridge deposits built by storm and ocean currents. The sandstone body is unconformably underlain by coastal and valley‐fill deposits and fines upward to outer‐shelf muddy deposits. It consists mainly of medium‐grained to very coarse‐grained sandstones and pebbly sandstones that are moderately to intensely bioturbated and are represented by three‐dimensional compound dune deposits. The body consists of six 10 to 20 m thick units (units 1 to 6 in ascending order), which are each defined by an erosional base and locally capped by storm‐induced fluid mud deposits. Each unit also contains low‐angle (ca 5°) large stratification inclined obliquely to palaeocurrents, indicating lateral accretion surfaces. Units 1 and 2 are characterized by south‐eastward migration (locally north‐westward), smaller dune deposits, storm‐induced sedimentary structures and cold‐water molluscs indicating a palaeowater depth of up to 50 m. The other units are represented by east/north‐eastward migration, larger dune deposits, warm‐water molluscs indicating a palaeowater depth of up to 200 m, and a general lack of storm‐induced sedimentary structures. Temporal changes in the migration directions and lithofacies features of the units indicate that sand ridge formation was initially controlled by storm‐induced currents that were subsequently replaced by the northward or north‐eastward intruding palaeo‐Kuroshio Current in response to the expansion of the shelf during an overall transgression. The initiation and development of the sand ridges may have been supported by the supply of clastic sediments eroded from the underlying coastal and valley‐fill deposits.

Beach ridge evolution during the Holocene Climatic Optimum at Río de la Plata estuary, Argentina: Former answers for future questions?

The Holocene shows rapid climatic changes associated with alternating intervals of glacier advances and retreats. The coastal regions, where beach ridges constitute common preserved landforms, are highly sensitive to register such changes and bring light into past littoral environments. Excellent marine Argentinean Holocene deposits associated with the last climate optimum are preserved at the Río de la Plata estuary (Argentina). In this beach ridge, fourteen detailed sedimentary logs were studied in order to generate an palaeoenvironmental model. The analysis of major hierarchy surfaces of the ridge was performed combined field work and Virtual-Outcrop analysis. The ridge presents internal clinoforms that subdivide it into eleven clinothems. The first two clinothems correspond to the development of a sand ridge as a response to the erosion and reworking of previous aeolian Late Pleistocene sediments. Subsequently, a bioclastic ridge was amalgamated with the sand ridge (clinothems III to XI). Simultaneously, in a landward position, a lagoon and washover deposits were developed. Finally, after the stabilization of the beach ridge the continuous sea level fall generated the actual coastal plain deposits. Six 14C ages were obtained at the base of selected clinothems, dated between 5,240 ± 110 cal BP and 3,900 ± 90 cal BP; meaning that in 1,340 years the beach prograded 290 m. Stable isotope analyses (δ13C and δ18O) allowed to infer that the temperature during the evolution of the ridge has two maximum values of 22.5 °C and a minimum of 18.5 °C. The salinity range between 32.53‰ and 33.16‰, showing short variability. The sudden change in the composition of the ridge, from sandy to carbonate sediments, may be interpreted as a combined result of an increase of carbonate productivity along with a decrease of siliciclastic supply at the coast. This stage would have been developed approximately around 5ka B.P., in coincidence with the Holocene Climatic Optimum (as recorded in Argentina) when propitious climatic conditions may have led to the proliferation of large communities of warm and warm temperate benthic organisms. We stress that, the strong activity of the Brazilian current during the Mid-Holocene thermal maximum enabled excellent conditions for the development of a carbonate warm beach similar to that occurring at tropical and subtropical areas nowadays. This study provides an example of the strong changes occurred in coastal environments as a result of climate change, particularly in the context of global warming episodes which characterized interglacial periods of the Late Quaternary in eastern South America.