Progradation Processes Research Articles

Agroecological assessments of arable and post-arable soils and trends of the post-agrogenic evolution of soils over a 30-year-long period under conditions of changing climate in the northern part of the Upper Volga Region, Russia

A potential level of agricultural productivity of formerly arable soils was assessed in a case study within the Poshekhonsky District of the Yaroslavl Oblast, Russia, with the use of an actualized soil-ecological index (SEI). This index showed low and medium fertility levels in most of the studied arable soils during the period of 1988–1990, which was followed by agricultural abandonment of many arable lands. The re-assessment of post-arable varieties of the same soils in 2019 allowed us to identify multidirectional trends of evolutionary changes in soil properties over the three decades. Post-arable soils on loamy parent materials were characterized by the development of stable hydromorphic features, dehumification, a sharp decline in the supply of available nutrients and occasionally an acidification of humus horizons, which was reflected in the reduction of SEI values by 1.1–1.9 times over the study period. Post-arable sandy soils, on the contrary, were characterized by a predominance of progradation processes associated with increasing humus contents and decreasing acidity levels. The post-agrogenic evolution of soils including the development of new soil properties should be taken into account in agroecological assessments and prognoses of the agricultural production potential of soils under conditions of changing climate.

Multi proxy analysis for reconstructing the late Holocene evolution of a Mediterranean Coastal Lagoon: Environmental variables within foraminiferal assemblages

This study reconstructs the evolution of foraminiferal assemblages and the environmental variables (type of substrate, content in calcium carbonate and content in organic matter) in the Valencia lagoon (western Mediterranean) in response to changes in the late Holocene. In this area of low tidal range, several multiproxy analyses were carried out to determine which environmental variables influence the distribution of the fossil assemblage, and its association with global, regional or local climatic phenomena. The statistical results show that in environments with higher exposure to marine conditions, the calcium carbonate content is the dominant factor, whereas in more restricted environments the type of substrate (grain size) is determinant. The micropaleontological content reveals the evolution from a saline paleoenvironment with a clear marine influence towards the hyposaline or freshwater conditions, recorded at the top.Three phases were identified in the evolution of this area from 2800 cal yr BP to the present. A brackish lagoon with marine connection at the base, followed by a deposit of brackish lagoon (1232 ± 74 cal yr BP − 791 ± 104 cal yr BP), culminating in a brackish marsh (791 ± 104 cal yr BP to present), interpreted as the definitive closure process of the lagoon, favored by the coastal progradation processes related with an extraordinary input of sediments. These findings reflect the climatic variability of the Medieval Climate Optimum (MCO) (1.05 and 0.65 kcal BP) and the migration of the river Turia mouth, which favored the coastal progradation processes. The flood events registered at this phase, may have coincided with changes in the landscape and greater anthropic influence at the end of the LIA, 150 cal yr BP. Coastal processes are mainly responsible for the evolution of this area during phase I, while the influence of fluvial processes is significant towards the top, especially in phase III.

Changes in the Ratio of Aggregate Fractions in Humus Horizons of Chernozems in Response to the Type of Their Use

Data on the aggregate-size distribution (dry sifting method) in humus horizons of chernozems were processed by principal components analysis (PCA) with the centered logratio transformation of the initial data set. The analysis of the positions of treatments in the space of principal components coupled with the analysis of eigenvector magnitudes made it possible to identify several size fractions of aggregates, whose contents in the soils reflect soil degradation or progradation processes. These groups fitted well to the partial lognormal curves of aggregate sizes. In addition, the distribution of water-stable aggregates in coarse aggregate fractions (>10, 10–7, 7–5, and 5–3 mm) was analyzed. The integral analysis of the obtained data made it possible to propose the following conceptual model of the recovery of the structure of tilled chernozems. In the course of tillage, soil particles 10 mm) water-unstable aggregates (clods). With the removal of tillage loads, large aggregates interact with fresh organic matter, and the water stability of aggregates increases. At the same time, the largest aggregates (mainly >10 mm) tend to transform into aggregates of smaller sizes.

An outcrop analogue for deepwater salt withdrawal mini-basins: lateral and vertical variations in basin-fill

Mini-basins are well known targets for petroleum exploration as they can contain significant hydrocarbon reserves, such as in the Gulf of Mexico. Though mini-basins have been studied before, their reservoir rock distributions remain poorly predictable. This is especially the case where mini-basins are near salt-diapirs. The Donkey Bore Syncline in the Flinders Ranges, South Australia, presents an excellently exposed deepwater mini-basin reservoir analogue. Detailed outcrop study, including vertical and lateral logged sections presented here, shed considerable light on the depositional system, especially with regards to depositional style and stages of basin-fill. Based on the observed facies and deposit geometries, the authors have been able to detect the change from a carbonate to a siliciclastic deposition system and interpret mini-basin-fill initiation and progradation processes. Sandy gravity-flow deposit lobe areas are identified, enclosed within shales. Along with paleocurrent data, these enable the description and interpretation of basin-fill stages and the lateral character of reservoir-analogue depositional tracts. This will be useful for better interpretation of mini-basin turbidite sequences and will help reduce uncertainties in subsurface exploration. This may also improve prediction of basin-fill where well spacing is inadequate.

Palaeogeography and dynamics of the deltaic wetland of Save River, Mozambique

Many mangrove wetland systems in deltaic environments are negatively affected by massive sedimentation from river inflows. In this paper we use the example of the Save River delta to assess the palaeogeographic distribution of mangrove wetlands and to analyze their dynamics. To track past occurrences of mangrove wetlands in the study area we have integrated sedimentological data with siliceous microfossil analysis combined with AMS radiocarbon and OSL dating. The results show a fine-grained deposit with an approximate thickness of 2m, present at different sampling sites. In the upper deltaic plain, the deposit is interbedded between sand layers, while in the lower deltaic plain the deposit occupies the uppermost stratigraphic position. In most of the sampling sites the deposit shows a succession with brackish-marine diatoms at the bottom of the sequence while the upper part shows only scattered occurrences. Based on sedimentological and microfossil characteristics we have interpreted the layer to represent a mangrove wetland deposit. The development of the deposit in the study area is suggested to have been initiated around 3100cal. yr BP, induced by sea-level rise. Thereafter, the development followed the combined effect of a sea-level fall and delta progradation processes. In some areas, particularly in the proximal part of the delta, the mangrove deposit has developed progressively on top of the delta-front. From around 1300years ago (OSL) onwards, massive alluvial sedimentation impacted the mangrove ecosystem. However, the retreat of mangrove wetland coincided with a regional fall of sea level. At the edges of the alluvial deposit, the current mangrove ecosystem has reclaimed the habitat in some sectors where gully erosion has exposed the once extinct mangrove habitat.

Effects of basin bottom slope on jet hydrodynamics and river mouth bar formation

River mouth bars are strategic morphological units primarily responsible for the development of entire deltaic systems. This paper addresses the role of receiving basin slope in the hydrodynamics of an exiting sediment-laden turbulent jet and in resulting mouth bar morphodynamics. We use Delft3D, a coupled hydrodynamic and morphodynamic numerical model, along with a theoretical formulation to reproduce the physics of the problem, characterized by a fluvially dominated inlet free of waves and tides. We propose an updated theoretical model with a slope-dependent entrainment coefficient, showing that the rate at which ambient fluid is incorporated into a jet increases with higher basin slopes. Transient results reveal that the magnitude of a basin slope can alter the stability of a jet, favoring the formation of an unstable meandering jet. While a stable jet gives rise to “middle-ground” bars accompanied by diverging channels, a “lunate” mouth bar results from unstable jets. Additional morphodynamic simulations demonstrate that the time required for mouth bar stagnation in its final position increases linearly with the basin slope. In contrast, the distance at which the mouth bar eventually forms decreases until reaching an asymptotic value for slopes higher than 2%. Moreover, the basin slope highly influences sedimentary processes responsible for bar formation: for milder slopes, progradation processes prevail, while in steeper basins aggradation is more relevant. Finally, the minimum relative water depth over a bar crest that forces the flow to bifurcate around a fully developed bar decreases with the basin slope.

Агрогенная и постагрогенная трансформация почв Льговского района Курской области

In this work we consider the processes of degradation and changes of properties of gray forest soils and migration-mycellar chernozems as a result of agrogenesis and erosion. We also consider progradation processes, which lead to forming of anthropogenic deeply transformed soils, and post-agrogenic processes, which are characterized by reclamation of the natural parameters of soils. The most dramatic changes occur in the composition of profiles, and also in morphological, physical and agrochemical properties. The results of investigations allowed us to determine four trends of the development: agrogenically-degradational and also agrogenically progradational, which is familiar for large areas of arable lands, and also postagrogenic nature-like, which is typical for laylands. The most of the soils, involved in agricultural activivities, are affected by degradation as a result of agrogenesis. This is manifested in the developments of processes of surface and linear erosion, in the decrease of humus content and the thickness of humus layer of the soil mass. There are also observed such processes as forming of compaction under the arable layer, the changes in structure and the decrease of water resistance of aggregates. In the agro-gray soils of agrogenically-degradational trend we observe the significant decrease of the thickness arable layer and humus content, and as contrary, the increase of silt and physical clay content, and also the increase of solidity values in comparison to the gray soils. In the same agrogray soils of agrogenically-erosional trend, we observed the increased density and solidity, the increase of non-agregated material content, the decrease of humus content, the decrease of melkozem content and the decrease of fine fraction content, which are valuable for plants. The results obtained are the additional information base for the convertion of Uniformed State Register of the soil resources of Russia on a regional and local level.

Sedimentation patterns on a cold-water coral mound off Mauritania

An unconformity-bound glacial sequence (135cm thick) of a coral-bearing sediment core collected from the flank of a cold-water coral mound in the Banda Mound Province off Mauritania was analysed. In order to study the relation between coral framework growth and its filling by hemipelagic sediments, U-series dates obtained from the cold-water coral species Lophelia pertusa were compared to 14C dates of planktonic foraminifera of the surrounding matrix sediments. The coral ages, ranging from 45.1 to 32.3kaBP, exhibit no clear depositional trend, while on the other hand the 14C dates of the matrix sediment provide ages within a much narrower time window of <3000yrs (34.6–31.8calkaBP), corresponding to the latest phase of the coral growth period. In addition, high-resolution computer tomography data revealed a subdivision of the investigated sediment package into three distinct parts, defined by the portion and fragmentation of corals and associated macrofauna as well as in the density of the matrix sediments. Grain size spectra obtained on the matrix sediments show a homogeneous pattern throughout the core sediment package, with minor variations. These features are interpreted as indicators of redeposition. Based on the observed structures and the dating results, the sediments were interpreted as deposits of a mass wasting event, namely a debris flow. During this event, the sediment unit must have been entirely mixed; resulting in averaging of the foraminifera ages from the whole unit and giving randomly distributed coral ages. In this context, for the first time mass wasting is proposed to be a substantial process of mound progradation by exporting material from the mound top to the flanks. Hence, it may not only be an erosional feature but also widening the base of the mound, thus allowing further vertical mound growth.

Tidal channel meander formation by depositional rather than erosional processes: examples from the prograding Skagit River Delta (Washington, USA)

AbstractChannel meander dynamics in fluvial systems and many tidal systems result from erosion of concave banks coupled with sediment deposition on convex bars. However, geographic information system (GIS) analysis of historical aerial photographs of the Skagit Delta marshes provides examples of an alternative meander forming process in a rapidly prograding river delta: deposition‐dominated tidal channel meander formation through a developmental sequence beginning with sandbar formation at the confluence of a blind tidal channel and delta distributary, proceeding to sandbar colonization and stabilization by marsh vegetation to form a marsh island opposite the blind tidal channel outlet, followed by narrowing of the gap between the island and mainland marsh, closure of one half of the gap to join the marsh island to the mainland, and formation of an approximately right‐angle blind tidal channel meander bend in the remaining half of the gap. Topographic signatures analogous to fluvial meander scroll bars accompany these planform changes. Parallel sequences of marsh ridges and swales indicate locations of historical distributary shoreline levees adjacent to filled former island/mainland gaps. Additionally, the location of marsh islands within delta distributaries is not random; islands are disproportionately associated with blind tidal channel/distributary confluences. Furthermore, blind tidal channel outlet width is positively correlated with the size of the marsh island that forms at the outlet, and the time until island fusion with mainland marsh. These observations suggest confluence hydrodynamics favor sandbar/marsh island development. The transition from confluence sandbar to tidal channel meander can take as little as 10 years, but more typically occurs over several decades. This depositional blind tidal channel meander formation process is part of a larger scale systemic depositional process of delta progradation that includes distributary elongation, gradient reduction, flow‐switching, shoaling, and narrowing. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Architecture and evolution of the tide-dominated Changjiang (Yangtze) River delta, China

The Changjiang (Yangtze) River, China, has formed a large tide-dominated delta on the western coast of the East China Sea. This paper presents the architecture and Holocene evolution of the delta, based on analyses of three borehole samples taken from the present delta plain. The deltaic sediments are 25–30 m thick and composed largely of subaqueous deposits, which can be divided into three facies: prodelta, delta front and delta plain, in ascending order. Tide-influenced sedimentary structures such as sand–mud couplets and bi-directional crosslaminations characterize the delta plain and delta front deposits. An upward-coarsening facies succession from prodelta to delta front is overlain by an upward-fining facies succession from the uppermost delta front to the delta plain. The deposits at the boundary between delta plain and delta front are composed of well-sorted, coarse deposits because it is in the zone of highest energy. The depth from the top of the intertidal facies of the delta plain to this boundary is almost the same, 9–11 m, among the three cores. Sediment accumulation rates are highest in the delta front facies (ca. 10 m/kyr maximum) and decrease toward both delta plain and prodelta facies (ca. 1 m/kyr). The evolution of the Changjiang delta, which began in a bay approximately 8 kyr bp, can be divided into two stages by its stacking pattern: aggradational and progradational. The aggradational system developed during the slow rise of sea level from 8 to 6 kyr bp, and the progradational system developed after sea level reached or approached its present position. The evolution of distributary channels and related river-mouth sand bars was an important process of delta migration or progradation.

Partial melting in crustal xenoliths and anatectic migmatites: a comparison

Abstract Anatectic xenoliths from the volcanic fields of the Eifel (Germany) and the Chaine des Puys (Massif Central, France) contain a glass phase (quenched in-situ melt) along mineral grain boundaries. Microanalytical studies show that on a mm- to cm-scale melt chemistry is strongly controlled by the mineral phases involved in anatexis. Domains rich in mafic phases (biotite, orthopyroxene, spinel, garnet) contain brown glass with much higher abundances of FeO, MgO and TiO 2 than colourless glass in quartzofeldspathic layers. By contrast, K 2 O abundances are similar. Differences in melt composition in turn strongly control the crystallization of minerals from the melt as well as minor reactions between the melt and the xenolith phase assemblage. In comparison, textural features of anatectic HT-LP migmatites from SW Finland provide evidence of both prograde and retrograde reactions between minerals and melt. They reveal, that the modal and also the chemical composition of migmatites is more strongly affected by retrograde processes than in xenoliths. Hence, microanalytical and textural studies of partially melted crustal xenoliths can provide important insights in prograde processes operating in migmatitic terranes.

Cannibalisation of Holocene gravel beach-ridge plains,northern Tierra del Fuego, Argentina

Gravel beach-ridge plains form where there is sufficient availability of gravels and wave energy competent to transport the gravel. Even though beach-ridge plains are formed on coasts where sea level has risen during the Holocene, they occur extensively on stable or emergent coasts. Unfortunately, the Holocene evolution of these plains is hard to decipher because of the lack of datable material and their reworked character (minimum age). The rollover of barriers is expected on submerging coasts. On falling sea-level coasts, the beach-ridge plains are in a punctuated process of progradation. Cannibalisation is common in both settings; that is, sediment is eroded to maintain longshore growth. We present morphological and sedimentological data from three gravel beach-ridge plains (San Sebastián, Rı́o Chico and Cabo Peñas) of the northern coast of Tierra del Fuego. These beach complexes occupy embayments that were infilled during the last 5000 yr under different environmental conditions (depth, flooded area, local oceanographic processes and sediment availability). In the evolution of Bahı́a San Sebastián, a strong control was imposed by high waves originating within the bay (due to the strong westerlies). The Rı́o Chico beach-ridge plain evolved during different stages of beach progradation, cannibalisation, spit growth and saltmarsh development. The Cabo Peñas beach-ridge plain evolved in opposite directions due to wave refraction caused by rocky reefs and cannibalisation also took place.

Shoreline forms and deposits in Gallocanta Lake (NE Spain)

The Quaternary evolution of Gallocanta Lake (central Iberian Chain, Spain) is deduced from comparison between ancient deposits and present shoreline sedimentary forms. Present shoreline dynamics in the lake are controlled by persistent winds, parallel to the long-axis of the lake, creating wave fronts at the shore and net longshore currents. Present lake level fluctuations lead to a shoreline progradation during periods of lowering and to a partial erosion of ancient deposits during periods of rising level. Quaternary deposits in the region are represented by stepped lacustrine terraces which reflect a greater extension of the lake in the past. The sedimentological analysis of such deposits shows that their origin is linked to past lake-level fluctuations. Short-term (e.g. seasonal to multi-annual) fluctuations would have led to the building of a single terrace level by shoreline progradation processes. Long-term fluctuations, related to regional climatic changes, would have led to the present landscape of stepped terraces, reflecting a progressive aridification of the area.

Paleosols in shallow marine carbonate sequences

Shallow water carbonate sequences in the geological record commonly exhibit numerous exposure surfaces reflecting emersion of sediment due to progradation processes and sealevel oscillations. Some ancient platform sequences contain hundreds of such surfaces, associated with paleosols (fossil soils), typically calcretes. A wide range of macro- and microstructures are associated with these calcretes which are reviewed. Profile types and stages in profile development can be defined. The nature of the exposure surface and associated paleosols can be used to identify the nature of the prevailing climate, although hydromorphic effects related to marine flooding of the platforms can modify the paleosols. A potentially important use of paleosols is to define the nature of sequence boundaries; several studies have identified sets of paleosols with varying maturities reflecting changes in rates of accommodation space creation during sealevel rises and falls.

Internal structure and environmental reconstruction of eocene transitional fan-delta deposits, monllobat-castigaleu formations, Southern Pyrenees, Spain

A detailed study has been made of a part (500 × 200 × 15 m) of the Eocene Monllobat Formation. The conglomeratic bottomset—foreset—topset build up of a small fan-delta passes into sand- and mudstone layers. Ultimately the sandstone layers wedge into the mudstone due to concave-upwards basal surfaces and convex top surfaces or due to thickening of intercalated mud layers. Sequences vary accordingly from coarsening upwards in the proximal parts to fining upwards distally. Both sequences are topped by a thin layer fining upwards. The proximal fan-deltaic part consists of interconnected lobes. Crescentic, transverse bars deposited gravel on a slightly inclined top. Conglomerates of the moderately inclined foreset show some imbrication. The bottomset consists of tabular cross-bedded and cross-laminated sandstone. Parallel-laminated and tabular cross-bedded sandstone layers drape rises of fine sediment in front of the fan-delta face. Continued progradation brought about truncation of these backset sediments. Sandstone lobes of the distal part are not connected. Tabular croos-bedding and parallel lamination are the main sedimentary structures. Climbing, large-scale bedforms are prominent on top surfaces. Most of the lobes are enveloped by blue-grey mud. Layers covered by mottled mud terminate in foreset faces. Highly energetic inflow took place from a shallow, braided stream with longitudinal bars. The low sedimentary relief caused jetflow. The high flow energy, the large grain-size range and the large quantities of sediment caused great differences from inflow models for the deltaic environment. Sedimentation was effected by flow deceleration. Expansion, inertial forces, friction or a combination of these phenomena were responsible for the deceleration. Expansion and inertial forces caused development of moderately inclined foreset faces. Due to expansion, steeply inclined foresets were formed. Sand was deposited in shallow marine water and in scour pits in continental deposits during flow deceleration caused by frictional and inertial forces. Parallel-laminated backsets connected with flat, tabular sets developed due to flow deceleration by expansion and frictional forces. The deposits were formed in the transition zone of a fan-delta under a tropical climate with marked dry and wet periods. Wide, braided streams entered a restricted, shallow marine basin at right angles to the basin axis. Aggradation exceeded water depth. Progradation processes were influenced by large- and small-scale tectonic activity.

Deltaic Environment Reservoir Types and Their Characteristics

Processes responsible for creating end members of a continuum of deltaic Processes responsible for creating end members of a continuum of deltaic sedimentation and the characteristics of reservoirs resulting from these processes are presented. Deltas tend to be either high-energy sand deltas processes are presented. Deltas tend to be either high-energy sand deltas or low-energy mud deltas. In either case, reservoirs generally are confined to the bar-fringe sands and/or to distributary channel sands. Frequently, reservoir quality is discontinuous. Introduction The need to increase ultimate recovery requires that the engineer and earth scientist work together to depict accurately the character and geometry of a reservoir. This synergistic relationship results in a better understanding of the quality, distribution, and continuity of the reservoir and its contained fluids. As most known accumulations of oil and gas trapped in terriginous (land-derived) sediments are contained in sandstones deposited in deltas, there is an increasing need to understand these reservoir types better. Knowledge ofthe type of reservoir potentially available,the distribution and quality of pore space in terms of porosity, permeability, and capillary pressure properties, and porosity, permeability, and capillary pressure properties, andthe location of barriers to flow, both internal and external, should enhance greatly the ultimate recovery from this important source of oil and gas. The need for information about these reservoirs prompted this summary paper, which is based solely on prompted this summary paper, which is based solely on and distilled from information available in published sources. In view of the spectrum of environments in which deltas, both ancient and modern, are known to exist, it would be foolhardy in this summary to attempt a review of the myriad types available. Therefore, only the processes responsible for creating the end members of a processes responsible for creating the end members of a continuum of deltaic sedimentation and the characteristics of reservoirs created by these processes are presented. With this information and enough data, the presented. With this information and enough data, the inquiring geological/engineering team should be able to build on this foundation and depict accurately any specific reservoir in the deltaic environment. Principles of Deltaic Sedimentation Principles of Deltaic Sedimentation Deltas are abundant in the geologic record and are known to exist in ancient, recent, and modern settings. For example, 32 large deltas are forming at this time (Fig. 1). Countless others are in various stages of growth throughout the world. In 1912, Joseph Barrell described a delta as "a deposit partly subaerial (above sea level) built by a river into or partly subaerial (above sea level) built by a river into or against a body of permanent water." Three prerequisites for deltaic sedimentation are apparent from this apt description (Fig. 2):drainage basin, a source of sediment,river, to move the material, andreceiving basin, to store and rework it. As a delta forms, the outer and lower parts are constructed below water, and the upper and inner surfaces become land "reclaimed" from the sea. Therefore, even though deltas are visualized commonly as subaerial, their subaqueous portions are truly significant. A delta is created by an iterative process of progradation (built outward) in which sediment literally builds on progradation (built outward) in which sediment literally builds on itself until a particular pathway is no longer available, and another delta forms in a different location. Thus, any given delta is a composite reflecting conditions at hand from the time of inception until ultimate abandonment of a particular deposition center. JPT P. 1538