Sediment Drift Research Articles

Impact of Tectonic, Glacial and Contour Current Processes on the Late Cenozoic Sedimentary Development of the Southeast Greenland Margin

To understand the geomorphological contrast between the northern and southern parts of the Southeast Greenland margin with its marked differences in sedimentary regime, bathymetric and seismic reflection, data have been compiled and analysed. While previous studies focused on selected parts of this margin, the present study provides an intergraded overview of the entire margin from Cap Farewell to Denmark Strait. The prominent north–south contrast shows a wide northern shelf and a narrow southern shelf. The origin of this width disparity can be traced back to the initial formation stage of the Irminger Sea due to regional differences in uplift versus oceanic subsidence. This regional tectonic discrepancy also created a difference in sediment accommodation space that, in combination with a weak ocean circulation regime, favoured formation of Oligocene–Miocene turbidite fan complexes along the lower southern slope. These fan complexes became the core of sediment drift ridges that strike perpendicular to the slope. Strong bottom currents, which gradually increase in strength towards the south, were mainly prevalent during warmer climate stages. During glacial periods, downslope transport of glacigenic sediments and hyperpycnal meltwater flow further shaped the large drift ridges and formed several relatively narrow, V-shaped turbidite channels extending towards the deep Irminger Sea basin. These V-shaped channels are still active today when cascading dense winter water from the shelf flows downwards along the shelf to the Irminger Sea basin.

Compositional variation in modern estuarine sands: Predicting major controls on sandstone reservoir quality

Primary depositional mineralogy has a major impact on sandstone reservoir quality. The spatial distribution of primary depositional mineralogy in sandstones is poorly-understood and consequently empirical models typically fail to accurately predict reservoir quality. To address this challenge, we have determined the spatial distribution of detrital minerals (quartz, feldspar, carbonates and clay minerals) in surface sediment throughout the Ravenglass Estuary, UK. We have produced, for the first time, high resolution maps of detrital mineral quantities over an area that is similar to many oil and gas reservoirs. Spatial mineralogy patterns (based on x-ray diffraction data) and statistical analyses revealed that estuarine sediment composition is primarily controlled by provenance, i.e. the character of bedrock and sediment drift in the source area. The distributions of quartz, feldspar, carbonates and clay minerals are primarily controlled by the grain size of specific minerals (e.g. rigid versus brittle grains) and estuarine hydrodynamics. The abundance of quartz, feldspar, carbonates and clay minerals is predictable as a function of depositional environment and critical grain-size thresholds. This study may be used, by analogy, to better predict the spatial distribution of sandstone composition, and thus reservoir quality in ancient and deeply-buried estuarine sandstones.

Geomorphological evidence of carbonate build-up demise on equatorial margins: A case study from offshore northwest Australia

The demise of Miocene carbonate build-ups in the Browse Basin, Northwest Australia, has been explained as relating to geological and oceanographic processes. These include accelerated tectonic subsidence driven by subduction, ocean cooling following the mid-Miocene climate optimum, nutrient excess, poisoning by sediment drifts and local erosion driven by current winnowing, occurring discretely or simultaneously. Here, we critically assess the evidence for these different mechanisms using a combination of high-resolution 3-D seismic data, regional 2-D seismic profiles, and numerical stratigraphic forward modelling. Seismic interpretation and numerical modelling found that the proposed uniform subsidence rate of 125 m/Ma between 16.5 Ma and 5.33 Ma for the northern Browse Basin (Belde et al., 2017), when combined with the published estimate of eustatic sea level in Miller et al. (2005), was insufficient to drown the Miocene carbonate sequence and generate the geomorphological changes (barrier reef to isolated carbonate build-ups) observed on seismic data. Instead, a subsidence profile comprising pulses of rapid and slow subsidence is required. Significantly, our results suggest that subsidence rates exceeded 400 m/Ma in the northern Browse Basin, and that parts of the basin record the accumulation of sediment drifts. These sediment drifts are interpreted to have buried some carbonate build-ups, while suspended sediment reduced light transmissivity, inhibiting carbonate production. Thus, we postulate that current activity and excess nutrient supply are key, but often overlooked, oceanographic processes that lead to the demise of carbonate build-ups.

Modeling Procedure of Coastal Protection Shaped Blocks with High Wave Suppressing and Interlocking Capacity

A groyne is a shore protection structure built perpendicular to the shoreline of the coast (or river), over the beach and into the shoreface (the area between the nearshore region and the inner continental shelf), to reduce longshore drift and trap sediments. A groyne field or system is a series of groynes acting together to protect a beach. Concret is often used as construction material. On the basis of analysis of wave suppression efficiency and stability on the slope of more than one hundred existing shaped massives the new type of coast protecting reinforced concrete blocks – so called “Hexablock” (“Hexablock” was called because of its 6 facets) characterized with higher wave suppression properties, interlocking capacity, stability on the slope and longer life time is proposed.

A New Seismic Stratigraphy in the Indian‐Atlantic Ocean Gateway Resembles Major Paleo‐Oceanographic Changes of the Last 7 Ma

AbstractThe exchange of water masses between the Indian Ocean and the Atlantic constitutes an integral interocean link in the global thermohaline circulation. Long‐term changes in deep water flow have been studied using seismic reflection profiles but the seismic stratigraphy was poorly constrained and not resolved for the time period from the late Miocene onward. Here we present results from International Ocean Discovery Program Site U1475 (Agulhas Plateau) located over a sediment drift proximal to the entrance of North Atlantic Deep Water into the Southern Ocean and South Indian Ocean. Site U1475 comprises a complete carbonate‐rich stratigraphic section of the last ~7 Ma that provides an archive of climate‐induced variations in ocean circulation. Six marker reflectors occurring in the upper 300 m of the drift are identified here for the first time. The formation of these reflectors is mainly due to density changes that are mostly caused by changes in biogenic versus terrigenous sediment deposition. Synthetic seismograms allow age assignments for the horizons based on biostratigraphy and magnetostratigraphy. Prominent reflectors are related to late Pleistocene glacial/interglacial variability, the middle and early Pleistocene transitions, and the onset of the northern hemisphere glaciation. A peculiar early Pliocene interval (~5.3–4.0 Ma) bounded by two reflectors is characterized by fourfold elevated sedimentation rates (>10 cm/kyr) and the occurrence of sediment waves. We argue that this enhanced sediment transport to the Agulhas Plateau was caused by a reorganization of the bottom current circulation pattern due to maximized inflow of North Atlantic Deep Water.

The evolution of a Middle Miocene deep-water sedimentary system in northwestern New Zealand (Taranaki Basin): Depositional controls and mechanisms

Abstract Through the Oligocene and Miocene, New Zealand basins underwent widespread subsidence, related to the evolution of the convergent plate boundary between the Pacific and Australian plates. In Taranaki Basin on the western margin of the North Island, a deep water siliciclastic sedimentary system developed in response to basin subsidence and hinterland uplift. Basinward of the evolving shelf, basin floor sandstones and mudstones were deposited, some of which constitute important petroleum reservoirs and seals. Extensive 3D reflection seismic coverage has enabled us to map the character and distribution of basin floor sedimentary units and to develop a comprehensive sequence stratigraphic model. The stacking patterns of depositional sequences reflect an overall progradation of basin floor sedimentary facies and change in geometries through time, while associated elements such as fan lobes and channel systems increased in dimension. Structural change and southward progressing tectonic uplift most likely controlled increasing sediment input into the basin. In addition, an intensification of bottom current activity led to the development of sediment drifts, which we suggest was related to oceanographic changes at the end of the Middle Miocene Climatic Optimum. While turbidite depositional systems were dominant during lowstands, sediment reworking by shore parallel currents is interpreted to have been a dominant process during highstands. We document a change from sand-dominated to more mud-dominated deposits through the Middle Miocene and propose that this change in sediment character may be related to a higher degree of chemical weathering on land, possibly related to the northward migration and intensification of westerly winds.

In search of sediment deposits from the Limpopo (Delagoa Bight, southern Africa): Deciphering the catchment provenance of coastal sediments

The discrimination of sediment provenance from specific source regions is a crucial prerequisite for the paleoclimatic interpretation of terrigenous sediment archives. The terrigenous material in sediments on the Delagoa Bight near Maputo, Mozambique, has several potential source areas including the Limpopo, Incomati, Matola, and Lusutfu river catchments. While the last three represent a coastal region bordered to the west by the Drakensberg mountains, the Limpopo catchment is much larger and reaches farther into the center of the continent. Due to local current patterns, the sedimentation in the Delagoa Bight is very complex. This may be the reason why previous studies in this area interpreted the origin of sediment bodies only on the basis of seismic profiles. Analytical investigations to the question where which material was/is deposited in the Delagoa Bight, especially the suspension load from the Limpopo River, do not exist. In this study, end-members for the four river catchments were determined based on a selection of aluminium-normalized trace element concentrations in river sediment samples. Relative end-member contribution to core top samples from the shelf, partitioned using a constrained least squares model, and age data of marine surface sediments, indicate a very effective eastward sediment drift, caused by local cyclonic circulation. This strong lee circulation (the Delagoa Bight Eddy) may have meant that hardly any material has been deposited in the eastern and central parts of the bight for ~1000 years. In addition, our results confirm previous studies showing that the majority of Limpopo sediments are dumped onto the eastern flank of the Inharrime Terrace from where material is probably drifted further south under the influence of the Agulhas Current.

New interpretation for the main sediment source of the rapidly deposited sediment drifts on the northern slope of the South China Sea

The slope of the northern South China Sea (SCS) is one of the world’s most active areas of modern marine sedimentary processes. A rapidly deposited sediment drift (RDSD) was identified on the slope near Dongsha Island. The sources of this body have been studied and discussed by several authors, but no consensus has been achieved. Based on multi-channel seismic profiles interpretation and data analysis of long-term observation of bottom currents, we identified that although the amounts of sediments input from the Pearl and Hanjing Rivers, and from Kao-ping and Tseng-Wen Rivers are large, considering the current situation of northern SCS, none of the Pearl River, the Hanjiang River, the Kao-ping River and the Tseng-Wen River can maintain the deposition pattern of the northern SCS margin as the single source, especially to maintain the supper high sedimentation rate at the RDSD area. The Miocene drape formation (MDF) calmly draped over an unconformity after rifting stage resulting in a relatively constant thickness of about 2000 m throughout the overall northern SCS continental margin, and followed by a standard configuration of a clinoform, the Pliocene formation and another clinoform of about another 700 m in total thickness. Due to Dongsha uplift since 3 Ma, roughly 1/2 of MDF and the N2 formation in the Dongsha area measures 150 km by 200 km were denudated resulting in an average annual denudation rate of 60 × 106 t/y. If these sediments were deposited on a slope region within an area measuring 100 km by 100 km, the sedimentation rate could reach 250 cm/ky. This is clearly an impressive new sediment source that has never been discussed before. Moreover, the RDSD is near the Dongsha Uplift and on the adjacent slope. We believe that this new sediment source should be the main contributor for the RDSD development.

Assessing the shoreline trend changes in Southern tip of India

Variations in shoreline trend was examined for 21 stations between Manuvai (in the west) and Vijayapathi (in the east), along the southern tip of India. Multispectral satellite data of Landsat MSS (9th Feb, 1973), Landsat TM 5 (4th Sep 2001) and Landsat ETM+ (21st Jan 2006) were used to assess the temporal dynamics of shoreline trend present in the region. The images were pretreated by radiometric calibration in order to avoid the temporal deviation of spatial and spectral information. The exact shorelines were estimated by two steps of image processing techniques: Normalized Difference Water Index (NDWI) is used to classify the land and sea water by and Sobal edge detection techniques are used to extract boundary line between land and water body. The rate of changes between the period 1973 and 2006 has shown that, the average shoreline rate is accelerated in the study area at 1.78 m/year. However, unusual shoreline changes ranging from 3.60 m/year to 15.60 m/year has been observed between the period 2001 and 2006 due to the impact of Tsunami. The station-wise shoreline data endorsed that Chinna muttom to Visvanarayanapuram and Lipuram are under continuous depositional process whereas other stations are under erosional process. This result shows that littoral sediment movement, with respect to the wave climate and anthropogenic activities are the predominant factors that affect the shoreline trend and sediment drift prevailing in the coast.

The last big marine transgression of the Western Interior Seaway: Almond Formation development from barrier spits across south Wyoming

Abstract The stratigraphic response to marine shoreline transgressions have been debated for the last six decades. A particularly interesting aspect is that transgressive ravinement often removes evidence of the shoreline itself, until there is turnaround to regression. To elucidate this topic, we present a high-resolution chronostratigraphic study of an overall transgressive coastline, documented with evidence from over 1450 wells covering an area of 6200 km2 to define the fundamental sandbodies and relevant stratigraphic surfaces. The mapping of 15 elongate sandstone units stacked into 6 reservoirs shows that there was a spectacular westward rising of back-stepping barrier spits, sourced by long-shore currents mobilizing sand from a delta to the north. Each fundamental barrier spit unit (BSU) is a 6–12 metres thick, regressive, southward elongate and narrowing sandbody generated by longshore drift of sandy sediment. Each barrier sand body and its related overlying transgression is estimated to represent some 20 Ky. Strong transgressive ravinement events periodically flooded the barrier spits and shifted the deposition westward in four to 35 km steps. Westward transgressive-stepping across and into a structurally-generated embayment progressively dampened wave energy with each backstep. Morphologically, there were two endmember sandbody types: 1) narrow, drum stick-like sandbodies built mostly by longshore accretion, i.e. true barrier bars, and 2) broader and more extensive regressive belts of sandstone that resemble strandplains. The former display typically longer backsteps across lagoonal areas whereas the latter show a more aggradational stacking arrangement which evidences a quasi-balance between accommodation and sediment supply. There is no evidence of a smooth and continuous transgression controlling sandstone deposition and preservation. A hybrid punctuated transgression model, that considers the alternation of long-term coastal retrogradation and short-lived barrier spit development by longshore accretion and seaward progradation, is the most appropriate model for creating and preserving Upper Almond sandbodies.

Tidal inlet sediment bypassing at mixed-energy barrier islands

The large-scale littoral sediment drift along barrier island coasts involves alongshore sand transport at the islands’ surf zone and across tidal inlets. Mechanisms of sediment bypassing at non-migrating, mixed-energy tidal inlets are discussed based on process-based numerical modeling of sediment dynamics at an exemplary barrier island system in the southern North Sea. Residual transport pathways of distinct sediment grain-size fractions and morphological changes reveal the complexity of processes at tidal inlets driven by the non-linear interaction of competing tidal and wave forces. Sediment bypassing from the updrift to the downdrift shoreline of a tidal inlet is evaluated and the ratio of bypassed to recirculated sand volumes is estimated. Common inlet bypassing schemes are discussed and verified. It is shown that the different bypassing mechanisms can happen simultaneously and are related to the transport behavior of particular sediment grain-size fractions: Very fine to fine sand bypasses the inlet along the entire ebb-tidal delta periphery by wave-induced transport processes. Fine to medium sand is transported by the ebb-directed tidal currents in the inlet throat to the ebb-tidal delta where wave-driven transport processes and bar welding bypasses the sediments to the downdrift shore. For fine to medium and medium sands, a sediment recirculation cell at the downdrift ebb-tidal delta and reversal to the main inlet throat is identified.

Erosional features identification along a recently prograding coastal barrier by ground penetrating radar facies analysis: Paradeep, Odisha, India

Coastal barrier dynamics is a complicated system which mainly involves shoreline changes due to accretion and erosion of the coast. Erosional activity in the coastal area of Paradeep, Odisha is risking the lives of the people and the community/factory infrastructures of this major port city, adjoining to the Bay of Bengal. So, understanding of the complex barrier dynamics is more important in this study area. The purpose of this study was to identify several erosional features within sedimentary beddings by Ground Penetrating Radar (GPR) survey and to understand the processes involved in this microtidal barrier from obtained GPR facies/radar facies. GPR reflection survey, with 200 MHz antenna, along (17 profiles) and across (21 profiles) the barrier was done to delineate shapes and sizes of the sedimentary features, erosional surfaces, channels, scour-and-fill structures, progradational beddings and internal geometry of the beach ridge deposits. GPR facies analyses of the beach ridge have established the longshore drift of sediments from nearby river mouths e.g. Mahanadi and Devi river mouths. This interpretation technique has also characterized the palaeo-tidal channels of the study area into two types – (a) larger channels which are perpendicular to the shoreline having channel width of about 400 m with maximum depth of 3.4 m from the surface and (b) smaller channels (width up to 60 m) flow parallel to the shoreline. Here, seaward-dipping beach progradational facies is positioned within oblique erosional surfaces below the facies boundary. This describes the cyclicity of erosion and accretion activity at Paradeep coastal barrier.

Late Quaternary infilling of the Assu River embayment and related sea level changes in NE Brazil

A detailed geomorphological survey using Light Detection and Ranging (LiDAR) was carried out along the western part of the Assu River valley, NE, Brazil. The study was complemented by the investigation of sedimentological, mineralogical, and sediment benthic foraminifera indicators within the 14C geochronological framework. The integration of data sets permitted the reconstruction of the main phases in the evolution of this area during the Holocene. The shallow embayment, which is now completely infilled, acquired its present form within the limits of antecedent morphology developed since the last interglacial period. The main forcing factors responsible for repositioning the shoreline, which ran along the strike-slip Afonso Bezerra fault at an angle of approximately 35° to the present coast in the Early/Mid Holocene, were as follows: (1) tectonic activity along the strike-slip Afonso Bezerra fault, (2) fast inundation of the shallow paleo-valley embayment during the last pulse of Holocene transgression ca. 8000 cal yr BP, (3) advance of the Assu river mouth through accretion of fluvial bay head delta and costal drift sediments and (4) sheltering of embayment by barrier islands which permitted a widespread development of mangrove forest during the last 3 millennia. The estimated rate of progradation of the Assu estuary that led to the present stage of terminal infilling is in the order of 3–4 m/yr.

Ocean and climate response to North Atlantic seaway changes at the onset of long-term Eocene cooling

Around the early–middle Eocene boundary, the first occurrence of contourite drift sediments and widespread deep ocean erosion indicate changes in the North Atlantic ocean circulation. Interestingly, these changes coincide with the first steps of Cenozoic cooling from the Paleogene greenhouse climate towards the modern icehouse. The cause for this ocean circulation reorganization is poorly understood since modern water mass tracers may have worked fundamentally different in the past and the paleoceanographic proxy record is limited in both time and space. As a result, it is challenging to reliably reconstruct the climatic and tectonic boundary conditions e.g. atmospheric greenhouse gas concentration and the depth and geometry of developing and closing passages between ocean basins. In this study, we attempt to identify thresholds in tectonic gateway passages and atmospheric CO2 concentration, using the fully coupled Earth System Model COSMOS. Indeed, the simulation of Earth's past climates can unravel the physical processes driving deep-water formation in a greenhouse world. Specifically, we use COSMOS to evaluate the impact of changes in the North Atlantic gateways at the early–middle Eocene boundary on the North Atlantic Deep Western Boundary Currents under low obliquity configuration. We find that Northern Component Waters start to form when the Greenland Scotland Ridge reaches a threshold depth of deeper than 200 m, while the Arctic Ocean is still shut off from the North Atlantic. In this scenario, the relatively deep Greenland Scotland Ridge allows for sufficient inflow of warm, salty Atlantic surface waters into the Nordic Seas to initiate convection during winter cooling. Opening the seaway towards the Arctic leads to a cessation of Northern Component Water formation as it allows for inflow of brackish surface waters into the northern Nordic Seas, hindering Northern Component Water formation.

Sedimentary proxies for Pacific water inflow through the Herald Canyon, western Arctic Ocean

Pacific water inflow to the Arctic Ocean occurs through the shallow Bering Strait. With a present sill depth of only 53 m, this gateway has been frequently closed during glacial sea-level low stands of the Pleistocene. Here, we investigate the sedimentological and mineralogical response to sea-level rise and the opening of the Bering Strait during the last deglaciation in a 6.1 m-long marine sediment core (SWERUS-L2-4-PC1) from the Herald Canyon. Grain size data indicate an abrupt erosional contact at 412 cm down core that likely formed when Pacific waters first started to flow into the Arctic Ocean around 11 cal ka BP, and was topographically steered into the Herald Canyon. A transitional unit between 412 and 390 cm appears to be a condensed interval with minimal local sedimentation. The underlying sediments, deposited in a shallow, river-proximal setting, exhibit a rather uniform bulk and clay mineral composition similar to mineral assemblages from surface sediment samples of the Chukchi Sea. Enhanced contributions from Pacific waters above 390 cm (< 8.5 cal ka BP) are reflected by elevated chlorite/illite and (chlorite + kaolinite)/illite ratios, and are anti-correlated with intervals of higher illite/smectite ratios, interpreted as periods of enhanced advection of shelf transformed waters originating from the East Siberian Sea. Clay mineral changes in the Holocene drift sediments are best explained by the interplay between two origins for bottom waters in the Herald Canyon and are consistent with modern oceanographic observations.

Carbonate delta drift: A new sediment drift type

Based on high-resolution reflection seismic and core data from IODP Expedition 359 we present a new channel-related drift type attached to a carbonate platform slope, which we termed delta drift. Like a river delta, it is comprised of several stacked lobes and connected to a point source. The delta drifts were deposited at the exit of two gateways that connect the Inner Sea of the Maldives carbonate platform with the open ocean. The channels served as conduits focusing and accelerating the water flow; Entrained material was deposited at their mouth where the flows relaxed. The lobe-shaped calcareous sediment drifts must have formed under persistent water through flow. Sediment supply was relatively high and continuous, resulting in an average sedimentation rate of 17 cm ka−1. The two delta drifts occupy 342 and 384 km2, respectively; with a depositional relief of approximately 500 m. They have a sigmoidal clinoform reflection pattern with a particular convex upward bending of the foresets. In the Maldives the drift onset marks the transition from a sea-level controlled to a progressively current dominated depositional regime. This major event occurred in the Serravallian about 13 Ma ago, leading to the partial drowning of the carbonate platform and the creation of shallow seaways. The initial bank-enclosed topography resembles an “empty bucket” geometry which is rapidly filled by the drift sediments that aggrade and prograde into the basin. Thereby the depositional environment of the delta drifts changes from deep water (>500) to shallow-water conditions at their topsets, indicated by the overall coarsening upward trend in grain size and the presence of shallow water large benthic foraminifers at their top.

Late Holocene oceanographic and climatic variability recorded by the Perseverance Drift, northwestern Weddell Sea, based on benthic foraminifera and diatoms

Abstract The Perseverance Drift, located in the Joinville-D' Urville Trough, northwestern Weddell Sea, records changes in ocean and sea ice conditions throughout the middle to late Holocene, with a record extending back to ca. 3400 yr BP. The 2562-cm composite record collected from a water depth of 806 m, documents the uppermost section of the 90-m thick sediment drift. Spring-blooming diatoms (Chaetoceros subg. Hyalochaete) are abundant through the sedimentary record. The greater proportion of Chaetoceros vegetative valves compared to resting spores indicates that the marine environment is highly productive, and nutrients generally are not limiting. Epiphytic diatoms, dominated by Cocconeis spp., are observed throughout JKC36, suggesting transport of algal detritus from shallower regions to the benthos. Three foraminiferal assemblages (FAs): Miliammina spp., Globocassidulina spp., and Paratrochammina bartami/Paratrochammina lepida/Portatrochammina antarctica characterize the benthic foraminiferal fauna and reflect affinities with water masses circulating across the Perseverance Drift and tolerance to corrosive bottom waters. The interval 3400–1800 yr BP is marked by high abundances of Globocassidulina spp., indicating incursions of Weddell Sea Transitional Water over the drift site. This interval implies a period of “freshening” of the water column, coinciding with an open-marine or seasonally open-marine environment during the middle-to-late Holocene Climatic Optimum. The interval 1800 yr BP to the present displays characteristics of slightly colder conditions, as indicated by the absence of the calcareous Globocassidulina spp. FA, and the pronounced presence of agglutinated P. bartami/P. lepida/P. antarctica FA, along with other agglutinated species that are indicative of the presence of sea ice. Therefore, this interval is interpreted to represent the onset of Neoglaciation at the northeastern tip of the Antarctic Peninsula. The consistent presence of Miliammina spp. FA corroborates that the sedimentary record represents a productive, open-marine setting with seasonally variable sea ice extent. The Drift is a unique geologic archive that provides an excellent target for future coring based on the preservation of abundant carbonate material for radiocarbon dating and the potential to develop a multi-proxy data set that could offer a robust understanding of the Holocene depositional and paleoclimatic conditions of the northwestern Weddell Sea.

Genesis and morphological evolution of coastal talus-platforms (fajãs) with lagoons: The case study of the newly-formed Fajã dos Milagres (Corvo Island, Azores)

Supratidal talus-platforms are low-relief subaerial accumulations of debris produced by mass wasting along high coastal cliffs, being particularly abundant at reefless volcanic islands subjected to high wave energy. Known as “fajãs” across the Portuguese-speaking Atlantic archipelagos, these coastal features, on rare occasions, may exhibit lagoons, constituting sites of high geological, biological, landscape, and social value. Whilst the origin of fajãs is firmly established as being the product of coastal landslides, little is known about the processes that shape fajãs with lagoons. In particular, doubts still remain concerning whether fajãs featuring lagoons are a fortuitous product of mass wasting, or result from marine reworking (by waves and currents) after emplacement. On October 30, 2012, a coastal landslide (~0.001 km3) occurred on Corvo Island, Azores Archipelago, forming a nearshore gravel islet that later migrated to the island's coast, resulting in a fajã with an ephemeral lagoon (Fajã dos Milagres). This event provided a unique opportunity to study the generation and development of fajãs with lagoons, and therefore a 3-year survey was carried out to record its evolution. This GIS-based study used aerial oblique photography and satellite optical imagery, complemented with a land survey for a more precise topographic reconstruction. Analysis of data concerning bathymetry, precipitation, and wave regime was also employed to investigate the driving forces behind the morphodynamic evolution of the deposit. “Fajã dos Milagres” evolved very rapidly, through an evolutionary pattern with five main stages: 1) “islet stage”; 2) “gravel spit stage”; 3) “early lagoon stage”; 4) “mature lagoon stage”; and 5) “fajã (without lagoon) stage”. Our reconstructions show that, for fajãs with lagoons to be formed, several factors should converge: a) presence of high coastal cliffs, made up of composite volcanic sequences, capable of producing large landslides that supply sufficient mobile sediment to the shelf; b) presence of a shallow, wide insular shelf where the sediments can be transported without significant loss to the submarine slopes; and c) a wave-dominated, high-energy regime, capable of significant cross-shore and longshore sediment drift. These observations allowed us to propose a preliminary conceptual evolutionary model for the generation of fajãs with lagoons, where marine reworking plays a fundamental role. Finally, this study documents the generation and very rapid subsequent evolution of a clastic coastal morphology solely driven by the action of waves and currents, and without interference from relative sea level and/or external sediment replenishment, with possible implications to other settings.

The influence of submarine currents associated with the Subtropical Front upon seafloor depression morphologies on the eastern passive margin of South Island, New Zealand

ABSTRACTSubmarine currents are a principal factor in controlling seafloor geomorphology. Herein, we investigate the role of dynamic current systems associated with the Subtropical Front in the formation and modification of seafloor depressions off the east coast of New Zealand’s South Island. Seafloor depressions are widespread in this region, with a diverse range of morphologies and sizes. We focus on two ‘end-member’ classes of depressions; densely spaced decametre-scale structures and more isolated ‘giant’ depressions of up to 12 km in diameter. Our results reveal a direct correlation between the dominant current flow direction, and the modification and alignment of depressions. We present a model to illustrate the role of submarine currents in shaping the morphology of these enigmatic seafloor depressions. This model demonstrates how contour currents, and potentially eddy currents, have extensively modified seafloor structures, resulting in elongate, asymmetrical depressions, partially infilled by sediment drift deposits.

Drift potential of UAV with adjuvants in aerial applications

The reduction of pesticide aerial spraying drift is still one of the major challenges in modern agriculture. The aim of this study was to evaluate the drift potential of different types of unmanned aerial vehicle (UAV) and adjuvant products for reducing spray drift in aerial applications. Three types of UAV (3WQF120-12 and 3CD-15 fuel oil powered single-rotor UAV and HY-B-15L battery powered single-rotor UAV) were selected in this study with regular application parameters to compare each spray drift, and 3WQF120-12 fuel oil powered UAV was selected to quantify spray drift of 6 adjuvants dissolved in water under field conditions. Solutions were marked with brillant sulfoflavin dye (BSF) at 0.1%. Petri dishes and rotary impactors were used to collect airborne and sediment drift, respectively. Drift deposits were evaluated by spectrophotometry in order to quantify deposits. The results showed that when the flight height was 1.5-2.0 m above the crop at the flight speed of 4-5 m/s and the average wind speed of 1.63-1.73 m/s, 3WQF120-12 fuel oil powered UAV had lower drift potential than the other two types; DV0.5 and percentage of droplets with diameter ≤75 μm had very significant effects on spray drift percentage (p=0.01); the risk of drift in agricultural spraying could be significantly decreased not only by reducing the percentage of fine droplets but also by changing droplet spectra. Compared to water, Silwet DRS-60, ASFA+B, T1602, Break-thru Vibrant, QF-LY and Tmax could reduce by 65%, 62%, 59%, 46%, 42%, and 19% spray drift, respectively. when water without adjuvants were sprayed, 90% of drift droplets were located within a range of 10.1 m of the target area while with 0.8% Silwet DRS-60 adjuvant in water, the distance was shortened to 6.4 m. Keywords: spray drift, UAV, adjuvant, aerial application, drift potential evaluation, droplet size DOI: 10.25165/j.ijabe.20181105.3185 Citation: Wang X N, He X K, Song J L, Wang Z C, Wang C L, Wang S L, et al. Drift potential of UAV with adjuvants in aerial applications. Int J Agric & Biol Eng, 2018; 11(5): 54–58.