Large Dune Fields Research Articles

Aeolian sediments in western Mongolia: Distribution and (paleo)climatic implications

The largest dune fields in Mongolia are mainly restricted to the Basin of Great Lakes in western Mongolia. These dune fields extend from 800 m a.s.l. in the basins for 200 to 300 km into the mountains up to about 2100 m a.s.l. Analyses of these dune fields, using an integrative mapping approach, provide evidence for different wind regimes. The dune fields result from a long-term Quaternary sediment cycle. Rivers transported the sand into the basins from where the wind carried the sand eastwards along the dune fields with a concurrent loss of silt-sized particles. Different paleolake levels and sandy plains with mobilized sand at their western ends exist in the lake basins. The largest masses of dune sand are found in the central parts of the dune fields. Towards their eastern ends, lower and more vegetated dunes and sand sheets result from both the decrease in sediment supply and increased vegetation at higher elevations. Three climatic and paleoclimatic implications are derived from the mapping approach. A: Under the modern semi-arid to semi-humid climate, wind systems from north to the north-west prevail, whereas in the southern Mongolian Els also wind from the south-east occurs. B: The highest lake levels occurred during pluvial phases in the basins, caused by increased moisture supply, also due to water supply from glacier- and permafrost retreat. C: The fundamental west-east orientation of the dune fields is a result of westerly winds which were prevalent during arid periods.

Factors controlling the development of cold-climate dune fields within the central part of the European Sand Belt – Insights from morphometry

The central part of the European Sand Belt is an area where intense aeolian processes led to the development of large dune fields in the Lateglacial. They have been studied principally in terms of their stratigraphy, with less attention given to their evolution and geomorphology. It is also uncertain whether large dune fields in cold areas arise analogously to those formed in other climatic zones. To fill this gap, we performed a morphometric analysis of 31 stabilized dune fields in Poland using high-resolution LiDAR data. We related the outcomes to the morphological zones associated with the extent of the ice sheet during the LGM, the position and basement shape of the dune fields. The results indicate that dune fields in cold areas evolve in the same way as in other climatic zones, as expressed in the preserved relation between crest length, spacing, and defect density. The study found that the investigated dune fields have simple patterns composed of single populations of transverse to parabolic dunes facing E-ESE, suggesting their simultaneous formation in the Younger Dryas. At the same time, the varying degree of dune fields pattern development indicates the different duration of aeolian processes that shaped individual dune fields. The dominance of transverse dunes transformed partially or completely into parabolic dunes reflects the increasing role of vegetation over time and the decreasing supply of sand. The development of the dune field patterns was not found to be correlated with the extent of the ice sheet during the LGM, the morphological position, and the basement shape of the dune fields.

New Model of Coastal Evolution in the Ria de Vigo (NW Spain) from MIS2 to Present Day Based on the Aeolian Sedimentary Record

Galician Rias are fluvial valleys that were flooded during the last marine transgression in the Atlantic margin. The study of fossil dunes in the Cies Islands, a small archipelago in the mouth of the one of the rias (Ria de Vigo), allowed us to reconstruct the coastal evolution from the end of the Late Pleistocene to the present day. During this period, sea-level was 100 metres below the present one and the shoreline located about 5–10 kilometres away. About 15,000 years ago, sea-level rise began, radically modifying the coastline. This started with a gradual advance of large dune fields on both sides of the valley. The aeolian accretion continued until the Late Holocene, finishing when the sea reached its present level.

Chronology of recent sedimentary infill of the Inner R\xedo de la Plata Estuary, Argentina

The Inner Río de la Plata Estuary is a sedimentary depositional system that resulted from fluvial-deltaic activity. Gentle Pliocene–Pleistocene slopes make-up the northern side of the estuary whereas small cliffs of the same age constitute the southern side. A long coastal estuarine barrier developed at about 6000 years BP when the maximum flooding surface occurred. Attached to this barrier, and at a lower elevation, is a large strandplain (covering an area of about 2400 km2) which displays more than 220 beach ridges. In different areas, the dating indicates a periodicity of 13.4–13.7 years for the development of each beach ridge. These data are like the periodicity of the ENSO effects, which could be associated with the variability of Sunspots. These ridges were formed shortly after the maximum flooding surface, which was followed by a gradual fall in sea-level that contributed significantly to the Inner Río de la Plata Estuary sedimentary infill. In addition, ENSO activities were probably instrumental in the distribution of the main geoforms in the Inner Rio de la Plata Estuary. Small deltas, which were generated by other rivers and creeks such as the Nogoyá Arroyo and the Gualeguay River, developed coevally with the coastal estuarine barrier. The Ibicuy Delta grew in the middle of the inner Río de la Plata Estuary when the former Paraná River flowed northwards during the sea-level fall. The upper part of the delta front was reworked, giving rise to a large dunefield. Thereafter, a chenier plain developed along with tidal flats. The current Paraná Delta continues to prograde at a rate of about 56–64 m/year (m year−1). The sedimentary infill of the Inner Río de la Plata Estuary occurred along the Holocene.

A New Method for Automated Measurement of Sand Dune Migration Based on Multi-Temporal LiDAR-Derived Digital Elevation Models

While remote sensing methods have long been used for coastal and desert sand dune studies, few methods have been developed for the automated measurement of dune migration in large dune fields. To overcome a major limitation of an existing method named “pairs of source and target points (PSTP)”, this paper proposes a toe line tracking (TLT) method for the automated measurement of dune migration rate and direction using multi-temporal digital elevation models (DEM) derived from light detection and ranging (LiDAR) data. Based on a few simple parameters, the TLT method automatically extracts the base level of a dune field and toe lines of individual dunes. The toe line polygons derived from two DEMs are processed using logical operators and other spatial analysis methods implemented in the Python programming language in a geographic information system. By generating thousands of random sampling points along source toe lines, dune migration distances and directions are calculated and saved with the sampling point feature class. The application of the TLT method was demonstrated using multi-temporal LiDAR-derived DEMs for a 9 km by 2.4 km area in the White Sands Dune Field in New Mexico (USA). Dune migration distances and directions for three periods (24 January 2009–26 September 2009, 26 September 2009–6 June 2010, and 24 January 2009–6 January 2010) were calculated. Sensitivity analyses were carried out using different window sizes and toe heights. The results suggest that both PSTP and TLT produce similar sand dune migration rates and directions, but TLT is a more generic method that works for dunes with or without slipfaces that reach the angle of repose.

A Rock Record of Complex Aeolian Bedforms in a Hesperian Desert Landscape: The Stimson Formation as Exposed in the Murray Buttes, Gale Crater, Mars

AbstractLithified aeolian strata encode information about ancient planetary surface processes and the climate during deposition. Decoding these strata provides insight regarding past sediment transport processes, bedform kinematics, depositional landscape, and the prevailing climate. Deciphering these signatures requires a detailed analysis of sedimentary architecture to reconstruct dune morphology, motion, and the conditions that enabled their formation. Here, we show that a distinct sandstone unit exposed in the foothills of Mount Sharp, Gale crater, Mars, records the preserved expression of compound aeolian bedforms that accumulated in a large dune field. Analysis of Mastcam images of the Stimson formation shows that it consists of cross‐stratified sandstone beds separated by a hierarchy of erosive bounding surfaces formed during dune migration. The presence of two orders of surfaces with distinct geometrical relations reveals that the Stimson‐era landscape consisted of large dunes (draas) with smaller, superimposed dunes migrating across their lee slopes. Analysis of cross‐lamination and subset bounding surface geometries indicate a complex wind regime that transported sediment toward the north, constructing oblique dunes. This dune field was a direct product of the regional climate and the surface processes active in Gale crater during the fraction of the Hesperian Period recorded by the Stimson formation. The environment was arid, supporting a large aeolian dune field; this setting contrasts with earlier humid depositional episodes, recorded by the lacustrine sediments of the Murray formation (also Hesperian). Such fine‐scale reconstruction of landscapes on the ancient surface of Mars is important to understanding the planet’s past climate and habitability.

Bioprospecting of Soil-Derived Actinobacteria Along the Alar-Hotan Desert Highway in the Taklamakan Desert.

Taklamakan desert is known as the largest dunefield in China and as the second largest shifting sand desert in the world. Although with long history and glorious culture, the Taklamakan desert remains largely unexplored and numerous microorganisms have not been harvested in culture or taxonomically identified yet. The main objective of this study is to explore the diversity, novelty, and pharmacological potential of the cultivable actinomycetes from soil samples at various sites along the Alar-Hotan desert highway in the Taklamakan desert. A total of 590 actinobacterial strains were recovered by the culture-dependent approach. Phylogenetic analysis based on 16S ribosomal RNA (rRNA) gene sequences unveiled a significant level of actinobacterial diversity with 55 genera distributed in 27 families of 12 orders. Thirty-six strains showed relatively low 16S rRNA similarities (<98.65%) with validly described species, among which four strains had already been characterized as novel taxa by our previous research. One hundred and forty-six actinobacterial isolates were selected as representatives to evaluate the antibacterial activities and mechanism of action by the paper-disk diffusion method and a double fluorescent protein reporter “pDualrep2” system, respectively. A total of 61 isolates exhibited antagonistic activity against the tested “ESKAPE” pathogens, among which seven strains could produce bioactive metabolites either to be able to block translation machinery or to induce SOS-response in the pDualrep2 system. Notably, Saccharothrix sp. 16Sb2-4, harboring a promising antibacterial potential with the mechanism of interfering with protein translation, was analyzed in detail to gain deeper insights into its bioactive metabolites. Through ultra-performance liquid chromatography (UPLC)-quadrupole time-of-flight (QToF)-MS/MS based molecular networking analysis and databases identification, four families of compounds (1–16) were putatively identified. Subsequent bioassay-guided separation resulted in purification of four 16-membered macrolide antibiotics, aldgamycin H (8), aldgamycin K (9), aldgamycin G (10), and swalpamycin B (11), and their structures were elucidated by HR-electrospray ionization source (ESI)-MS and NMR spectroscopy. All compounds 8–11 displayed antibacterial activities by inhibiting protein synthesis in the pDualrep2 system. In conclusion, this work demonstrates that Taklamakan desert is a potentially unique reservoir of versatile actinobacteria, which can be a promising source for discovery of novel species and diverse bioactive compounds.

Geomorphological dynamics and human interactions in a semiarid valley in Northwestern Argentina: The Cafayate depression (Salta Province)

The aim of this study was to record the changes in the Cafayate region, Northwestern Argentina, over the last 50 years (1969–2019), with a focus on fluvial and dune systems, together with human activity. The multi-temporal analysis of different kinds of remote sensor images and field surveys allowed us to establish that the final section of the Santa María River shows a meandering channel whose arrangement and morphology have substantially changed since 1969. The Santa María River has moved from a northern position in 1969 to the current location, giving rise to a shortening in the channel length from 11756 m to 8217 m, increasing its gradient from 0.10% (1969) to 0.14% (2019), with its sinuosity index falling from 2.85 to 2, although the lateral erosion of the channel and the meanders have remained very active. The floodplain supplies sands to feed the aeolian dynamics through a close cycle that favors the development of large dune fields, especially in the river stretches where there is transversal wind direction. Moreover, the changes in land use have negatively impacted on the fluvio-aeolian dynamics of the system.

Geoheritage of East Kazakhstan

East Kazakhstan is physiographically a diverse region of north-central Asia encompassing a broad array of geomorphic zones and geo-ecosystems from the western open steppes to the interior arid basins with wind-sculptured surfaces of the surrounding rocky highlands aligned by the high alpine mountain ranges. The complex regional geological history gave rise to a mosaic of impressive landforms located within a relatively small area. The extraordinary relief with many unique geo-sites was generated by dynamic processes associated with the late Cainozoic orogenesis in conjunction with the past climatic variations. The cyclicity of bedrock weathering and mass sediment transfer are manifested by Mesozoic fossiliferous formations, large sand dune fields, and loess-palaeosol-cryogenic series providing archives of the Quaternary evolution. Pleistocene glaciations followed by cataclysmic floods from the released ice-dammed lakes during the recessional glacier stages have produced an exceptional imprint in the mountain areas. Many archaeological localities and historic monuments, some being a part of the UNESCO World Natural and Cultural Heritage, are associated with the most prominent topographic places. Geo-tourism focusing on the most exquisite landscapes and spectacular geological settings is the new trend in the country with still minor activities that take advantage of the region’s supreme geoheritage potential. The great geo-diversity accentuates the touristic value of this still marginally explored geographic area. Reconnaissance, documentation, and publicity of the most unique geo-sites and geo-parks provide an impetus for their registration in the national and international nature heritage protection programs under proper geo-environmental conservation policies.

Complex disturbance‐driven reactivation of near‐surface sediments in the largest dunefield in North America during the last 200 years

AbstractUnderstanding the historical activity of desert dune systems is important for identifying both the palaeoenvironmental drivers of change and the likelihood of future reactivation. Dating dune sediments in the Nebraska Sandhills has identified regional‐scale dune activity over centennial and millennial timescales during the Holocene, occurring at 9.6–6.5, 3.8 and 2.5 ka, and most recently spanning the Medieval Climatic Anomaly 1050–650 years BP. These periods have been interpreted as palaeoclimatic evidence of intense aridity lasting decadal and centennial timescales. A detailed record of dune activity in the historical period, since EuroAmerican arrival, is lacking however, yet important for interpreting the role of human agency amongst the factors influencing disturbance. Without a high‐resolution record of short‐term, historical, local sediment mobilization, it is not possible to distinguish the environmental factor(s) responsible for local reactivation. In this paper, the individual drivers of vegetation disturbance are reviewed and presented alongside a luminescence‐dated reconstruction of dune sediment deposition ages. This allows an integrated assessment of the relationship between drivers and environmental response over a recorded period. We focused our investigation on the aeolian reactivations of surface dune sediments and blowout features around the Niobrara Valley Preserve in the northern limits of the Nebraska Sandhills. Results show a near‐continuous (within uncertainties) timeline of local reactivation across the sites studied, with variation between the individual features indicating that both regional (i.e. climatic) and local (i.e. land use) forcings contribute to surface disturbance. © 2019 The Authors. Earth Surface Processes and Landforms published by John Wiley &amp; Sons Ltd. © 2019 The Authors. Earth Surface Processes and Landforms published by John Wiley &amp; Sons Ltd.

Recolonization of native and invasive plants after large-scale clearance of a temperate coastal dunefield

In the management of alien invasive plants in coastal dunes, plot-based approaches have generally been adopted: researchers establish a set of experimental (often topographically homogeneous) plots of a given size where the plants are removed, and recovery patterns are monitored for a period of time. Therefore, the literature still lacks a detailed understanding of where (i.e., under what topographic circumstances) native and invasive species are likely to recolonize after clearance of a large dunefield. In this study, we report on an unprecedented case from the Sindu dunefield in western Korea in which both native and invasive plants had been thoroughly removed to bare sand over a vast area (ca. 11.0 ha), followed by in situ exhaustive mapping of regeneration patterns throughout the entire cleared zone twelve times within four years. The results showed that, after removal, natives and invaders increased to occupy larger (>50%) areas than those in the pre-removal state. Furthermore, Ecological-Niche Factor Analysis revealed that these two vegetation types exhibited markedly and significantly contrasting regeneration hotspots: invasive plants expanded primarily in low-lying sites that were close to trails. These findings indicate that the recolonization of invasive species was not a spatially random process but rather concentrated along the trails through which local employees transported removed plant material, inadvertently dropping invader propagules. We conclude that removal is often costly, and if executed without a careful plan for the movement of workers, equipment, and plant debris, these efforts may even increase the extent of invasions beyond the initial state.

Natural and human controls on dune vegetation cover and disturbance

Beaches and dunes are one of the most heavily used environments on Earth, with tourism and residential uses leading to ecosystem loss and dune degradation. Many coastal dune fields also host a range of economic activities such as farming, mining, and animal grazing, which can affect their evolution. The second half of the 20th century has seen an increase of dune vegetation cover in many dunes around the world, with climatic forcing often cited as a driver for this. However, identification of the relative contributions to landscape change due to climate vs. natural and/or artificial disturbances remains unclear. This poses a problem for managers seeking to maintain some ‘desirable’ landscape characteristics, because understanding the reasons for dune field change is essential prior to implementing interventions, as is differentiating what is natural from what is not. This study proposes a systematic approach to identifying dune disturbances and isolating them from the effect of climate. The approach assumes that it is possible to measure dune disturbances by comparing observed vegetation cover with that expected due to climate. A semi-quantitative procedure is proposed to explore the existence of disturbance, its significance, and the causes for it. The procedure can also be used in reverse to explore the effect of variables driving disturbance and the likely landscape trajectory if the driver is removed. The approach is tested with a case study of the Sefton dunes in NW England, a large dune field subject to multiple interventions and degrees of human impact. The discussion focuses on the importance of disturbance location and the range of variables involved in changes to vegetation cover at this and other locations. In natural dune fields, it is recommended as best practice to managers that artificial stressors and human-led disturbances are minimized to allow coastal dune systems to evolve naturally.

PROVENANCE OF KARAKUM DESERT SAND (TURKMENISTAN): LITHIC-RICH OROGENIC SIGNATURE OF CENTRAL ASIAN DUNE FIELDS

Major deserts do not necessarily consist of eolian dunes as quartz-rich as those of the Great Nafud, Rub’ al Khali, Sahara, and Mega-Kalahari sand seas accumulated in anorogenic settings of Arabia and Africa. The Karakum dune field of Turkmenistan is one of the several examples of central Asian deserts bound by recent or recently reactivated orogenic belts where eolian sand includes abundant sedimentary and subordinately metamorphic and volcanic lithic fragments. Feldspatho-litho-quartzose detrital modes and epidote-amphibole-garnet heavy-mineral suites of southern Karakum dune sand compare well with those in mountain branches of the Amu Darya, indicating provenance from the western Pamir mountains of Tajikistan in the east. Dunes closer to the Caspian Sea in the west contain additional carbonate or felsic volcanic grains which, together with decreasing heavy-mineral concentration and increasing ZTR indices, reveals local recycling of cover strata exposed in the Kopeh-Dagh and Balkhan zone. Our data suggest that the huge Amu Darya River, which in Plio-Pleistocene to historical times has repeatedly changed its course across Turkmenistan from westward toward the Caspian Sea to northward toward the Aral Sea, represents the major sediment source for the Karakum Desert. Together with the Taklamakan sand sea of the Tarim basin, the Ordos and adjacent deserts of northern China, and the Thal and Thar deserts of the western Himalayan foreland basin, the Karakum would thus represent another example of large dune field principally fed by one major fluvial feeder system.

Late MIS 3 stabilization of dunes in the eastern Central Great Plains, USA

Abstract Extensive luminescence and 14C dating of aeolian sand dunes and sheets in the Central Great Plains (CGP) have been biased toward the western part of the region, targeted relatively large dune fields, and produced primarily Holocene (Marine Isotope Stage (MIS) 1) and latest Pleistocene (MIS 2) ages. This research luminescence dated a small discontinuous dune field perched on the high terrace of the Kansas River valley, situated on the eastern side of the CGP. These dunes have been stable since at least 30–28 ka, indicating that they are among the oldest recognizable dunes preserved in the CGP, as well as the entire North American Great Plains. The inferred stabilization of these dunes was coeval with pedogenesis and low sediment accumulation rates in upland loess, playa lunettes, and alluvial sequences in the CGP, in a time period with maximum summer insolation and relatively warm conditions. Source of the sand is presumed to have been fluvial sediments from the adjacent Kansas River, now preserved as the Buck Creek Terrace. Sand-mobilizing winds were southerly to southwesterly given that the dunes mantle only the high-terrace remnants on the north side of the valley. Long-term dune stability after MIS 3 appears to indicate that latest-Pleistocene and Holocene megadroughts were not sufficiently severe and eastward penetrating to reactivate these eastern CGP dunes.

Aeolian stratigraphy describes ice-age paleoenvironments in unglaciated Arctic Alaska

Terrestrial paleoenvironmental records with high dating resolution extending into the last ice age are rare from the western Arctic. Such records can test the synchronicity and extent of ice-age climatic events and define how Arctic landscapes respond to rapid climate changes. Here we describe the stratigraphy and sedimentology of a yedoma deposit in Arctic Alaska (the Carter Section) dating to between 37,000 and 9000 calibrated radiocarbon years BP (37–9 ka) and containing detailed records of loess and sand-sheet sedimentation, soil development, carbon storage, and permafrost dynamics. Alternation between sand-sheet and loess deposition provides a proxy for the extent and activity of the Ikpikpuk Sand Sea (ISS), a large dune field located immediately upwind. Warm, moist interstadial times (ca. 37, 36.3–32.5, and 15–13 ka) triggered floodplain aggradation, permafrost thaw, reduced loess deposition, increased vegetation cover, and rapid soil development accompanied by enhanced carbon storage. During the Last Glacial Maximum (LGM, ca. 28–18 ka), rapid loess deposition took place on a landscape where vegetation was sparse and non-woody. The most intense aeolian activity occurred after the LGM between ca. 18 and 15 ka when sand sheets fringing the ISS expanded over the site, possibly in response to increasingly droughty conditions as summers warmed and active layers deepened. With the exception of this lagged LGM response, the record of aeolian activity at the Carter Section correlates with other paleoenvironmental records from unglaciated Siberia and Alaska. Overall, rapid shifts in geomorphology, soils, vegetation, and permafrost portray an ice-age landscape where, in contrast to the Holocene, environmental change was chronic and dominated by aeolian processes.

Uses of Sand Dunes as Building Materials

During the past forty years, and due to the global climate changes, Iraq had and still suffering from the spreading and expansion of large dune fields in which many new generations have been accumulated, and older ones have expanded leading to the desertification of huge agricultural and urban areas and causing vast environmental problems that have a drastic effect on the life style of the population. To tackle such a problem, many methods have been suggested and even more are applied to fix the dunes or at least to limit their spreading so that to lessen the environmental impact. Such efforts were tried in many dune areas in Iraq, but it was in vain due to the classical nature of remedy that deals only with temporary and limited results, and in many cases worsening the problem. This is evidenced from the increased nature of dune fields in both area and problems.In this study four major dune fields expanding along four governorates in middle and southern Iraq were studied minerallogically, texturally, and chemically to attest their suitability as fine aggregate for concrete mixtures. These sands are composed of major quartz, feldspars, and calcite minerals, and are devoid of fines (clays), organic matters, and salts. Explicit dune sands of the studied area are not suitable as fine aggregate due to their poor grading, trial on mixing these sands with well-graded river sand (Dibhdiba Formation Sand) in different proportions show that the 35% is optimal for normal load works. Al-Muthana dune sands show the highest evaluations. Missan dune sands were further tested for producing pavement interlock bricks, the results confirmed their aptness for exploitation both economically and environmentally.

The Influence Of Climate-induced Salinization On Temporary Pools In A Large Dune Field

The Influence Of Climate-induced Salinization On Temporary Pools In A Large Dune Field

Large dunes on the outer shelf off the Zambezi Delta, Mozambique: evidence for the existence of a Mozambique Current

The existence of a continuously flowing Mozambique Current, i.e. a western geostrophic boundary current flowing southwards along the shelf break of Mozambique, was until recently accepted by oceanographers studying ocean circulation in the south-western Indian Ocean. This concept was then cast into doubt based on long-term current measurements obtained from current-meter moorings deployed across the northern Mozambique Channel, which suggested that southward flow through the Mozambique Channel took place in the form of successive, southward migrating and counter-clockwise rotating eddies. Indeed, numerical modelling found that, if at all, strong currents on the outer shelf occurred for not more than 9 days per year. In the present study, the negation of the existence of a Mozambique Current is challenged by the discovery of a large (50 km long, 12 km wide) subaqueous dune field (with up to 10 m high dunes) on the outer shelf east of the modern Zambezi River delta at water depths between 50 and 100 m. Being interpreted as representing the current-modified, early Holocene Zambezi palaeo-delta, the dune field would have migrated southwards by at least 50 km from its former location since sea level recovered to its present-day position some 7 ka ago and after the former delta had been remoulded into a migrating dune field. Because a large dune field composed of actively migrating bedforms cannot be generated and maintained by currents restricted to a period of only 9 days per year, the validity of those earlier modelling results is questioned for the western margin of the flow field. Indeed, satellite images extracted from the Perpetual Ocean display of NASA, which show monthly time-integrated surface currents in the Mozambique Channel for the 5 month period from June–October 2006, support the proposition that strong flow on the outer Mozambican shelf occurs much more frequently than postulated by those modelling results. This is consistent with more recent modelling studies comparing the application of slippage and non-slippage approaches—they suggest that, when applying partial slippage, a western boundary current can exist simultaneously with the southward migrating eddies. Considering the evidence presented in this paper, it is concluded that a quasi-persistent, though seasonally variable Mozambique Current does exist.

A composite mineralogical map of Ganges Chasma and surroundings, Valles Marineris, Mars

Ganges Chasma is a mineralogically diverse canyon in the far-eastern portion of the Valles Marineris system. It exposes bedrock outcrops of olivine, large dune fields enriched in olivine, a central Interior Layered Deposit with monohydrated sulfates, and Fe/Mg-phyllosilicates on the plateaus surrounding the canyon and in the canyon walls. The co-existence of hydrated minerals with unaltered olivine makes this an excellent location to study the timing of aqueous processes in this region. Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) and the High-Resolution Imaging Science Experiment (HiRISE), synthesizing them with previous data sets to produce a composite mineralogical map of Ganges Chasma. We then produce a timeline of mineralogic deposition for the Ganges area, relating it to regional geologic events.

Interplay of tidal and fluvial processes in an early Pleistocene, delta-fed, strait margin (Calabria, Southern Italy)

The architecture and morphodynamics of modern and ancient tidal straits and in particular the deposits of strait-margin zones, have been significantly understudied compared to other marginal marine settings, even though many reservoirs in the North Sea and the Norwegian Continental Shelf are developed in narrow grabens or seaways. This paper presents a detailed sedimentological and stratigraphic analysis of an early Pleistocene marginal-marine succession deposited along the northern margin of the Siderno paleostrait (southern Italy). This area represents an excellent case study of sedimentation along a tidal strait margin, interpreted to record the interaction of fluvial and tidal processes. Here, syn-depositional tectonics produced a complex coastal morphology, significantly influencing sedimentation and hydrodynamic processes. Along the strait margin, the emplacement of an isolated tectonic high (Piano Fossati) created a ca. 3.5 km-wide local passageway. This morpho-structural element induced interplays between fluvio-deltaic processes (fed from the northern strait margin) and tidal current reworking (active within the marine strait).The field-based facies analysis reported here documents an initial stage of non-tidal shallow-marine sedimentation across the strait. A subsequent regression caused river-generated hyperpycnal flows and the transfer of large volumes of pebbly and shelly sandstones into deeper water. Tidal currents became amplified in the strait, and, in the delta-front area, they were able to rework river-derived sediments generating large dune fields. Following the local tidal transport pathway, strong tidal currents skewed the delta front (causing it to be asymmetrical) and elongated sand bodies in a direction parallel to the marine strait axis. Differently from the classical tide-influenced deltas in which onshore-offshore tidal flow predominates, coast-parallel deflection and strong asymmetry of delta-front deposits is a typical feature of deltas entering tide-dominated seaways and straits, where strong tidal currents are capable of dispersing large volumes of sand for significant distances along the coast and along the strait axis. This process became progressively enhanced during the following transgression, when tide-modulated currents reworked biocalcarenitic sands over the previous delta deposits, generating southeasterly migrating dunes. At the end of the transgression, strandplain deposits formed in this area. This last stage of sedimentation was followed by a dramatic regional-scale structural uplift, which ended any marine circulation within the strait. This work provides new insights on sedimentation in a tide-dominated strait, and helps to predict sandbody distribution along the strait margin and axis. These findings can be applied to any other setting characterized by a narrow (possibly structurally-confined) basin dominated by tidal currents.