Subaerial Zones Research Articles

The Ore-Forming Process of Washan Porphyrite Iron Deposits in the Ningwu District Associated with Iron Oxide Apatite (IOA) Deposits and Iron Oxide Copper Gold (IOCG) Deposits

The Washan iron deposits in Ningwu district contain different magma-related genetic natures, including magmatic, magmatic–hydrothermal and hydrothermal types, and their ore-forming processes remain a subject of debate. To elucidate the ore-forming processes of iron ores from Washan, we present textural, major element analytical, and thermal data of magnetites from various ore bodies in Washan, probing the crystallization conditions and subsequent formation sequence of magnetites. SEM analysis with back-scattered electron (BSE) imaging reveals diverse magnetite textures, including mineral inclusions, exsolution lamellae, and recrystallization features, reflecting the transitional environment from magmatic to hydrothermal. Based on Ti, V, and Cr compositions of magnetite from different ore bodies, two distinct evolution trends of genetic processes are identified, including evolution paths from porphyry-type to IOA- and IOCG-type magnetite. High-resolution WDS mapping highlights the intensifying alterations during this process. Calculated magnetite crystallization temperatures among different types of magnetite range from 597 °C to 378 °C, suggesting a cooling trend from porphyry-type magnetite (~558 °C) to IOA-type magnetite (~515–439 °C) and IOCG-type magnetite (~378 °C). These results underscore the significant role of magma-derived hydrosaline liquids and vapors in the formation of iron ores from Washan, where variations in the salinity of ore-forming fluids lead to different evolutionary paths for subsequent generations of magnetite. The metallogenic model of the Washan iron deposit suggests that highly saline, iron-rich fluids connect the varying geneses of magnetite, transitioning from deeply formed porphyry-type magnetite to IOA- or IOCG-type magnetite generated in the subaerial zone.

A critical review of soil algae as a crucial soil biological component of high ecological and economic significance.

Aero-terrestrial algae are ecologically and economically valuable bioresources contributing to carbon sequestration, sustenance of soil health, and fertility. Compared to aquatic algae, the literature on subaerial algae is minimal, including studies of distinctive habitats such as forest soils, agricultural fields, deserts, polar regions, specific subaerial zones, artificial structures, and tropical soils. The primary goal here was to identify the gaps and scope of research on such algae. Accordingly, the literature was analyzed per sub-themes, such as the "nature of current research data on terrestrial algae," "methodological approaches," "diversity," "environmental relationships," "ecological roles," and "economic significance." The review showed there is a high diversity of algae in soils, especially members belonging to the Cyanophyta (Cyanobacteria) and Chlorophyta. Algal distributions in terrestrial environments depend on the microhabitat conditions, and many species of soil algae are sensitive to specific soil conditions. The ecological significance of soil algae includes primary production, the release of biochemical stimulants and plant growth promoters into soils, nitrogen fixation, solubilization of minerals, and the enhancement and maintenance of soil fertility. Since aero-terrestrial habitats are generally stressed environments, algae of such environments can be rich in rare metabolites and natural products. For example, epilithic soil algae use wet adhesive molecules to fix them firmly on the substratum. Exploring the ecological roles and economic utility of soil and other subaerial algae could be helpful for the development of algae-based industries and for achieving sustainable soil management.

Mineralogical and geochemical characterization of the Old Tailings Dam, Australia: Evaluating the effectiveness of a water cover for long-term AMD control

Establishing a shallow water cover over tailings deposited in a designated storage facility is one option to limit oxygen diffusion and retard oxidation of sulfides which have the potential to form acid mine drainage (AMD). The Old Tailings Dam (OTD) located at the Savage River mine, western Tasmania contains 38 million tonnes of pyritic tailings deposited from 1967 to 1982, and is actively generating AMD. The OTD was constructed on a natural gradient, resulting in sub-aerial exposure of the southern area, with the northern area under a natural water cover. This physical contrast allowed for the examination of tailings mineralogy and geochemistry as a function of water cover depth across the OTD. Tailings samples (n = 144, depth: ≤ 1.5 m) were collected and subjected to a range of geochemical and mineralogical evaluations. Tailings from the southern and northern extents of the OTD showed similar AMD potential based on geochemical (NAG pH range: 2.1 to 4.2) and bulk mineralogical parameters, particularly at depth. However, sulfide alteration index (SAI) assessments highlighted the microscale contrast in oxidation. In the sub-aerial zone pyrite grains are moderately oxidized to a depth of 0.3 m (maximum SAI of 6/10), under both gravel fill and oxidized covers, with secondary minerals (e.g., ferrihydrite and goethite) developed along rims and fractures. Beneath this, mildly oxidized pyrite is seen in fresh tailings (SAI = 2.9/10 to 5.8/10). In the sub-aqueous zone, the degree of pyrite oxidation demonstrates a direct relationship with cover depth, with unoxidized, potentially reactive tailings identified from 2.5 m, directly beneath an organic-rich sediment layer (SAI = 0 to 1/10). These findings are broadly similar to other tailings storage facilities e.g., Fox Lake, Sherritt-Gordon ZnCu mine, Canada and Stekenjokk mine, Sweden where water covers up to 2 m have successfully reduced AMD. Whilst geotechnical properties of the OTD restrict the extension of the water cover, pyrite is enriched in cobalt (up to 2.6 wt%) indicating reprocessing of tailings as an alternative management option. Through adoption of an integrated mineralogical and geochemical characterization approach for tailings assessment robust management strategies after mine closure can be developed.

Mesoscale Morphological Change, Beach Rotation and Storm Climate Influences along a Macrotidal Embayed Beach

Cross-shore profiles and environmental forcing were used to analyse morphological change of a headland bay beach: Tenby, West Wales (51.66 N; −4.71 W) over a mesoscale timeframe (1996–2013). Beach profile variations were attuned with longer term shoreline change identified by previous research showing southern erosion and northern accretion within the subaerial zone and were statistically significant in both sectors although centrally there was little or no significance. Conversely a statistically significant volume loss was shown at all profile locations within the intertidal zone. There were negative phase relationships between volume changes at the beach extremities, indicative of beach rotation and results were statistically significant (p < 0.01) within both subaerial (R2 = 0.59) and intertidal (R2 = 0.70) zones. This was confirmed qualitatively by time-series analysis and further cross correlation analysis showed trend reversal time-lagged associations between sediment exchanges at either end of the beach. Wave height and storm events displayed summer/winter trends which explained longer term one directional rotation at this location. In line with previous regional research, environmental forcing suggests that imposed changes are influenced by variations in southwesterly wind regimes. Winter storms are generated by Atlantic southwesterly winds and cause a south toward north sediment exchange, while southeasterly conditions that cause a trend reversal are generally limited to the summer period when waves are less energetic. Natural and man-made embayed beaches are a common coastal feature and many experience shoreline changes, jeopardising protective and recreational beach functions. In order to facilitate effective and sustainable coastal zone management strategies, an understanding of the morphological variability of these systems is needed. Therefore, this macrotidal research dealing with rotational processes across the entire intertidal has significance for other macrotidal coastlines, especially with predicted climate change and sea level rise scenarios, to inform local, regional and national shoreline risk management strategies.

An analysis of subaerial beach rotation and influences of environmental forcing adjacent to the proposed Swansea Bay Tidal Lagoon

Beach Profiles surveys and gale climate data were utilised to assess medium timescale beach rotation at four beaches located along the shores of a crenulated embayment within Swansea Bay, Southwest Wales. The proposed Tidal Lagoon is located within this Bay. Results identified a 7 year (1998–2005) record of cyclic summer/winter rotation and a 14 year (1999–2013) record of annual rotation within the subaerial zone on all four assessed beaches. In the absence of headlands to trap sediment it is asserted that the driving force for beach rotation is the presence of Swansea Dockland/Tawe dredged channel complex, Port Talbot Harbour and the Neath dredged channel which form surrogate headlands essentially creating four separate beach systems through restricting sediment by-pass. Seasonal averaged wind and wave variables showed differing correlation with volume changes and cross-correlation results showed that volume variation lagged behind forcing variables by up to six months (i.e. the resolution of the data). This was confirmed by the annually averaged results which showed only subtle correlation. Here volume change in most cases lagged forcing variables by less than one year. Based on correlations, wind direction variability follows closely with volume changes but wind speed, wave period and height are generally opposite. Initial results suggest that the proposed Swansea Bay Tidal Lagoon, located between sediment cells and surrogate headlands, would have little negative effect on subaerial coastal processes. These datasets will be used as a benchmark for monitoring prior to, during and post construction, with results being used to update and inform subsequent strategies.

鹿島灘沿岸の大規模侵食の回復過程

Strong low-pressure systems traveled along Japanese Main Island in October 2006. High waves and storm surge attacked Kashima Coast resulting huge and historical erosion. This study analyzes sand loss and gain in sub-aerial zone of northern part, a stretch of approximately 38 km from Ooarai Port to Kashima Port, and of southern part, a stretch of approximately 15 km from Kashima Port to Tone River, using airborne laser data measured in October 2005, November 2006 and May 2011. Eroded volumes of sub-aerial zone from year 2005 to 2006 were estimated 620,000 m3 for the northern part, and 600,000 m3 for the southern part. Recovery from year 2006 to 2011 was prominent for the southern part which was 1,000,000 m3, whereas it was small for the northern part.

Medium timescale beach rotation; gale climate and offshore island influences

Beach profile surveys, gale climate and atmospheric variations were utilized to assess medium timescale morphological change at South Sands, Tenby, West Wales. Due to beach aspect in relation to offshore islands, gale wave height decreased as wave direction rotated eastwards (r = 0.83) and westwards (r = 0.88). Similarly, wave heights were in attuned to variations in positive (r = 0.68) and negative (r = − 0.72) NAO Index, showing a wave height reduction occurred during weakly negative/positive or transitory phases; morphological change was attuned to atmospheric variation at a 2-year timelag. Shelter from offshore islands is given to waves from the predominant southwesterly direction and was confirmed by negligible correlation with South Sands morphology. However, outside the shelter of these offshore islands, correlation was found between south-eastward rotating wave directions (135°–180°) and morphological change, which resulted in southern and central beach erosion and accretion to the north. With a southwesterly rotation (243°–256°) the opposite was true. Beach rotation expressed by volume change within the sub-aerial zone had a negative phased relationship between beach extremities (r = − 0.94) and a timelagged association within the intertidal zone (r = 0.55). Analyses resulted in the development of two medium timescale rotation models based on incident wave direction and climatic variability. Results have global implications for headland bays in the lee of offshore islands, as well as macro-tidal beach areas; and consequently similar models could inform local, regional and national beach management strategies

SEDIMENT EXCHANGE BETWEEN THE SUB-AQUEOUS AND SUB-AERIAL COASTAL ZONES.

The coastal system consists of a sub-aqueous and a sub-aerial zone which can be separated by a border. At this border sediment exchange takes place from one zone to the other. This paper hypothesizes that conditions and therefore sediment exchange at this border are dependent on active profile characteristics. To analyze morphological developments due to combined marine and aeolian processes data acquired at a measurement site located along the southwest Holland coast is exploited. Based on the monthly morphological profile measurements the border between the marine and aeolian zone is determined. It is found that during accretive conditions the vertical location of this border, and with that the conditions near the border, is dependent not on the foreshore slope of the surf/swash zone as expected but on the slope of the entire active profile.

The influence of alongshore and cross‐shore wave energy flux on large‐ and small‐scale coastal erosion patterns

ABSTRACTA strong low‐pressure system traveled along the Japanese main island Honshu in October 2006. High waves and storm surge attacked the Kashima Coast resulting in huge erosion over the area. Airborne laser data measured in October 2005 and November 2006 were analyzed to estimate cross‐sectional changes within the subaerial zone. The results of the alongshore distribution of the changes of cross‐sectional area indicate that the amount of erosion of the 38 km‐long northern and 15 km‐long southern parts decreased toward the south in each part and that the amount of erosion was smaller in protected areas with artificial headlands than in unprotected areas. The local alongshore variation of the erosion and accretion patterns showed wavy fluctuations of several hundreds of meters. The total amounts of the estimated eroded volume of the subaerial zone over the northern and southern parts were 620 000 m3 and 600 000 m3, respectively. The Simulating Waves Nearshore (SWAN) wave model was applied to estimate wave conditions along the coast during the storm. The computational results were verified, and then the alongshore distribution of wave energies, expressed as the alongshore and cross‐shore components of the wave energy flux, was compared with the alongshore distribution of cross‐sectional change. The results show that the distribution of energy flux explains the distribution of erosion well: The alongshore variability in the cross‐shore energy flux is responsible for the large‐scale variability in erosion, and shorter‐scale variability is due to gradients in the alongshore energy fluxes, especially for the areas without coastal works. Copyright © 2011 John Wiley & Sons, Ltd.

Analyses on Erosion of Kashima Coast due to 2006 Autumn Storm Event

A strong low-pressure system traveled along Japanese Main Island in October 2006. High waves and storm surge attacked Kashima Coast resulting huge erosion over the area. This study analyzes sand loss in sub-aerial zone of southern part of the coast, a stretch of 16 km from Kashima Port to Tone River, using airborne laser data measured in October 2005 and November 2006, and X-band radar images captured during the storm. Longshore distribution of cross sectional change has been estimated from the laser data. Eroded volume of sub-aerial zone was estimated as 600, 000 m3. Pattern of erosion was controlled by headlands in the southern section, and by drainages in the northern section. Shoreline position during the storm has been digitized from radar images with locations of scarps read from aerial imagery.

Relationship between Spring and Geyser Activity and the Deposition and Morphology of High Temperature (> 73 C) Siliceous Sinter, Yellowstone National Park, Wyoming, U.S.A.

ABSTRACT Six classes of alkaline hot springs and geysers are here distinguished in Yellowstone National Park based on activity and eruptive style: (1) non-surging, non-boiling springs, (2) gently surging, non-boiling springs, (3) non-surging to gently surging, boiling springs; (4) strongly surging springs, (5) fountain geysers, and (6) cone geysers. Each displays morphologically distinctive siliceous sinter deposits in the high-temperature (> 73°C) parts of the vent and outflow systems. Non-surging and gently surging, non-boiling springs that do not overflow their rims develop thin digitate to lilypad-like sinter rims that grow horizontally over the pool surfaces. Similar springs with rim overflow have rims that accrete vertically. Boiling springs often have nearly circular, steep-sided pools and rims dominated by splash and rim-overflow and composed mainly of spicular and columnar sinter. Fountain geysers, characterized by broad fountain-like eruption bursts, have a central vent surrounded by a zone of spicular sinter beyond which is a broad, flat-bottomed moat, but lack steep sinter cones. Cone geysers have narrow vents, jet-like discharges that cool rapidly and fall close to the vent, and steep-sided spicule-dominated sinter cones. Sinter deposition takes place within three main zones: (1) fully subaqueous sides and bottoms of vent pools, outflow basins, and outflow channels; (2) periodically wetted splash zones surrounding hot springs and geysers; and (3) largely subaerial parts of the rim and outflow areas wetted mainly by overflow and surging and that dry quickly. Fully subaqueous surfaces are covered by fine earthy particulate siliceous sediment (PSS) composed largely of amorphous silica spherules and spherule aggregates that appear to have precipitated around heterogeneous nuclei, including microbes. Splash zones of hot springs and geysers are characterized by spicular sinter. Largely subaerial zones, wetted mainly by rim overflow and surging with little or no splash, show complex varieties of terraced, columnar, and knobby sinter. The highest silica deposition rates occur where surfaces are wetted frequently and evaporate to dryness, such as the tops of spicules, columns, and knobs. Associated lower areas and crevices that remain wet or moist show slow accumulation of PSS. Most continuously wet surfaces in high-temperature (> 73°C) hot spring and geyser vent and outflow systems are probably covered by microbial biofilms. Although microbes may locally influence rates of silica deposition and sinter microstructure, the results of this study suggest that the depositional sites, morphology, and macrostructuring of high-temperature sinter are controlled largely by the processes of surface wetting, evaporation, and drying.

A study of the monsoonal beach processes around Alleppey, Kerala

The responses of a sandy beach to the southwest monsoonal waves are studied based on biweekly observations. The onslaught of the first spell of monsoonal breakers causes maximum erosion in the sub-aerial section of the beach. However, further spells of high breakers do not affect this zone significantly. The erosion in the sub-aerial zone is followed by accretion in the nearshore zone and vice versa. Whereas the sub-aerial zone has a net erosion the total section of the beach including the nearshore zone shows near equilibrium condition. It is concluded that in spite of erosion or accretion of the sub-aerial zone, equilibrium conditions may be found in the total section of the beach.