Aeolian Systems Research Articles

Provenance and formation mechanism of aeolian sands on the eastern bank of Co Nag Lake on the Qinghai-Tibet Plateau

Studies of the provenance of aeolian dunes are crucial for providing knowledge of landscape evolution and developing management strategies to control aeolian desertification. The lakeshore dune is a typical aeolian landform that is widely distributed around the world. However, there has been little work on the provenance and formation mechanism of lakeshore dunes. By comparing the elemental and grain-size compositions of lakeshore dunes and potential sources around Co Nag Lake, this paper combines sediment fingerprinting analysis and end-member modeling. The results identify the provenance of aeolian sands on the eastern bank of Co Nag Lake and draw the following conclusions. (1) The combined use of fingerprinting analysis and grain-size analysis can yield a comprehensive and reliable provenance assessment. (2) The lakeshore dunes on the eastern bank of the lake are primarily derived from lacustrine deposits and fluvial deposits on the eastern bank. The coupling of fluvial and aeolian systems promotes the development of eastern sandy land. (3) Sand-control projects in the Co Nag Lake region should be carried out according to the sources of aeolian sands. It is necessary to strengthen efforts to control lacustrine deposits and sands in gullies.

Hybrid dry-wet interdune deposition in Precambrian aeolian systems: Galho do Miguel Formation, SE Brazil

It is currently not known whether the construction and accumulation of Precambrian aeolian interdunes occurred in the same way as for their Phanerozoic counterparts. To investigate this, a Mesoproterozoic aeolian succession, the Galho do Miguel Formation (SE Brazil), was studied using facies and architectural-element analyses. The sedimentary succession comprises deposits of simple dunes, draas (megadunes), and dry and wet interdunes. Dry and wet aeolian sub-environments were coeval and their development was likely controlled by local topographic relief that governed a hybrid dry-wet aeolian system. The dry sub-environment was composed of interconnected interdune corridors between large and well-developed bedforms (simple dunes and draas). The water table did not influence the construction of climbing dunes and dry interdunes, but this was fundamental for long-term aeolian accumulation. Due to the proximity of the water table to the depositional surface, the dry interdune flats were eroded only up to the groundwater level, where the wetness inhibited sand removal during dune migration. This condition enabled the accumulation of thick packages of dry interdune deposits (up to 3 m thick). The wet sub-environment is represented by extensive interdune flats, non-climbing dunes, and a continuously near-surface water table. In this context, the interdune deposits underwent only minimal reworking associated with dune migration. This setting allowed the progressive rise of the interdune substrate and the amalgamation of interdune deposits of different generations, thereby producing thick wet-interdune stratal packages (up to 8 m thick). The accumulation of thick packages of interdune strata in both sub-environments was generated by: (i) high rates of vertical accumulation of the interdune substrate due to high rates of sediment input for aeolian construction in Precambrian systems, and (ii) progressive relative rise of the water table. These conditions enabled the long-term accumulation and successive preservation of Precambrian aeolian systems, in which the stabilising effects of vegetation did not operate. Therefore, the aeolian architecture of the Galho do Miguel Formation suggests that: (i) Precambrian aeolian systems probably produced thicker dry and wet interdune deposits than their Phanerozoic counterparts, and (ii) hybrid dry-wet aeolian systems likely provided the most favourable conditions for long-term accumulation and successive preservation of these types of deposit in the Proterozoic.

Revised map of European aeolian deposits derived from soil texture data

European aeolian deposits have been mapped using the LUCAS topsoil texture database and the location, thickness and grain size mode of loess sections described in the literature have been compiled. The map, in fairly good agreement with those based on a classical geological approach, has the advantage of being of equal precision for the whole study area and makes it possible to highlight grain size gradients. It shows three main types of aeolian systems, i.e. systems associated with ice sheets (FIS, BIIS, AIS) and the rivers they feed, continental systems related to the erosion of sedimentary rocks, and coastal systems. Each aeolian system is comprised of a band of coversands of varying extent close to the sources and bands of sandy loess and loess away from the sources. The thickness of loess is highly variable throughout Europe. The areas of greatest accumulation are associated with the rivers draining the AIS (Rhine, Danube, Rhône). The Middle Danube, which combines sources of glacial origin (AIS) and local sources, constitutes the main accumulation area in Europe. Conversely, continental and coastal systems generated only limited loess cover. The latitudinal gradient of vegetation probably played an important role in loess sedimentation during the LGM. Weak interference between particle transport and vegetation (periglacial desert in the sand belt, cryptogamic crusts and steppe in the north European loess belt) allowed for particle sorting through aeolian transport to develop. The loess band is extensive in low-relief areas and is typified by a low sand content. In southern Europe, on the other hand, the capture of saltating and suspended particles by the shrubby steppe vegetation led to the dominant accumulation of sandy loess near sources.

Residual dune ridges: Sedimentary architecture, genesis, and implications for palaeo‐climate reconstructions

AbstractSedimentary architecture and genesis of residual dune ridges in a temperate climate are presented and implications for their use as archive of changes in long‐term precipitation and wind climate are discussed. Residual dunes are common features of wet aeolian systems, where they form sets of shallow ridges, oriented perpendicular to the prevailing wind direction. Residual dune ridges of the study area are vegetated and typically elevate 0.6 to 2.5 m above the surrounding interdune flats. They develop on the lower stoss side of active transgressive dunes, triggered by periods of elevated groundwater table and hence colonization of the foot of the dune by rapid growing pioneer vegetation. Stabilized by plants, the growing ridge detaches from the active transgressive dune and gets abandoned within years in the course of the downwind‐migration of the transgressive dune. Grain‐size data suggest a main sediment supply from the transgressive dune and only minor input from other sources. Ground‐penetrating radar reveals that the residual dune ridges are composed of windward‐dipping as well as leeward‐dipping sedimentary beds. Leeward‐dipping strata reflect sediment supply from the parental dune, whereas windward‐dipping beds are seen to result from sediment redistribution along the ridge and sediment supply from the adjacent swales during the ridge growth period. Multi‐annual to multi‐decadal variability in precipitation leads to the development of sequences composed of tens of ridges, spanning time periods of several centuries. Spacing of individual ridges in these sequences is controlled not by long‐term variability in precipitation alone, but probably also reflects variable wind intensity which affects the migration rate of the parental dune. The important role of vegetation in ridge construction makes these landforms a demonstrative example of landscape development by geo‐biosphere interacting processes.

Texture and mineralogy as proxies of late Holocene tsunami deposits from the Doñana National Park (SW Spain)

The multidisciplinary analysis (dating, texture, total mineralogy) of two deep cores collected in the Donana National Park (SW Spain) allows to distinguish the main features of three tsunami deposits found in three different paleoenvironmental scenarios (TSU-1: inner area of an open lagoon; TSU-2: inner area of a restricted lagoon; TSU- 3: outer area of a restricted lagoon). The main textural feature of the inner lagoonal tsunami deposits is the increase in bioclastic sands, while the outer TSU-3 is composed almost entirely of medium and fine sands without bioclasts. The mineralogical analysis of TSU-1 and TSU-2 reveals a decrease in phyllosilicates in the basal layers of these tsunami deposits and a parallel increase of quartz, feldspars, dolomite and sometimes calcite. Silica is the main component of TSU-3, whose mineralogical composition changes progressively due to the action of tidal currents in the inlet lagoon on which it is deposited. This rich- SiO2 outer tsunami deposit is derived from the erosion of the adjacent aeolian systems, while the inner TSU-1 and TSU-2 were generated by the transport of bioclastic sands from the outermost parts through the lagoon (TSU-1), or through a nearby tidal channel (TSU-2).

Spatial variation in the sedimentary architecture of a dryland fluvial system

AbstractAncient dryland terminal fluvial systems are often recognized within the rock record for having a progressive downstream decrease in the size and amalgamation of channel elements and systematic downstream increase in sheet and overbank elements, alongside the downstream decrease in grain size that is displayed by most fluvial systems. The spatial distribution and downstream trends displayed by the fluvial sediments of the Lower Jurassic Kayenta Formation of south‐western USA, have been examined quantitatively. The results indicate many trends that are similar to those of a dryland terminal fluvial system, including; a lack of confinement of the fluvial system, a downstream decrease in channel and sheet element amalgamation and width‐to‐thickness ratios, a downstream decrease in grain size, albeit very small, and an increase in the percentage of overbank elements downstream. However, the study highlights several downstream relationships that are atypical. While some of these relationships may be the result of external factors inherent in this study, others, including the thicknesses of channel‐fill and sheet elements that display no significant relationships to distance downstream, and channel‐fill elements that display no significant variation in average grain size with distance downstream, may be a consequence of fluvial interaction with a competing and coeval aeolian system. This work demonstrates the inherent complexity in arid dryland fluvial systems and the downstream architectural and compositional relationships that they depict. Consequently, models for fluvial style may provide only a first‐order approximation for downstream trends in dryland systems, because the controlling factors upon these systems are inherently difficult to unravel, and the sedimentary detail is strongly dependent upon external setting and internal complexity. Consequently, a generalized model may not always be applicable to these systems.

Distinct Aeolian-fluvial Interbedded Landscapes in Three Watersheds of the Northern China

Due to the complex dynamic of aeolian and fluvial interacted processes behind the landform development, most of previous works started from classifying the types of landscape characterized by various aeolian and fluvial features. Such classifications are usually generalized based on large geomorphic data set abstracted from satellite images without field verification and dynamic field data. In this study, we identified river banks in deserts as a unique geographical unit dominated by aeolian-fluvial processes. Three distinct locations have been identified as representative study cases, which are in the Keriya River Basin in the west, the Mu Bulag River Basin in the middle and the Xar Moron River Basin in the east of the northern China. The aeolian-fluvial interaction types were quantified based on site observation and measurement, topographic mapping and remote-sensing image analysis. Dimensional morphological relationship between river channel and adjacent sand dunes areas were explored. We concluded that different channels are often associated with different distributions of riparian dunes. The quantitative data enabled us to distinguish statistically four different types of landscape in aeolian-fluvial dominant environment, namely riverside dunes-straight channel, symmetrical interleaving dunes-meandering channel, river-island dunes- braiding channel, and grid-like dunes-anastomosing channel, aiming to provide compensational information to current aeolian-fluvial interaction studies. The angle of interaction between aeolian and fluvial systems, the windward and leeward sites of the bank, vegetation coverage and underlying landform determines the distribution, morphology, scale and direction of extension of the riparian dunes. The results of the work study can provide a reference for study of aeolian-fluvial interactions at different spatial scales in arid region.

A Mesoproterozoic hybrid dry-wet aeolian system: Galho do Miguel Formation, SE Brazil

Based on Phanerozoic and present-day cases, aeolian systems are categorised into dry, wet and stabilising types. It is questioned here whether these models are applicable to Proterozoic systems when environmental conditions on the Earth's surface were markedly different. Facies and architectural-element analyses have been applied to the Mesoproterozoic aeolian succession of the Galho do Miguel Formation, SE Brazil. The aim is to identify and discuss what controlling factors govern the construction and preservation of Proterozoic aeolian systems, and to explain how these differ from Phanerozoic models. In the metaquartzarenites of the Galho do Miguel Formation four aeolian subenvironments - megadunes (draas), large-scale isolated dunes with dry interdunes, small-scale isolated dunes with damp or wet interdunes and salt flats - coexisted and alternated temporally and spatially. The construction of megadunes, large-scale dunes and dry interdunes occurred in topographically elevated areas, usually above the water table, but that were occasionally flooded; isolated dunes with damp and wet interdunes, and salt flats formed in low-lying areas with water table at or close to the surface.A long-lived sediment supply combined with ongoing tectonic subsidence enabled the accumulation of a thick aeolian succession (1000–1500 m) that covered a large area (4000 km2). The water table controlled the accumulation of this unit. Where it was close to the accumulation surface, it acted to limit the availability of the wind-blown sand, hampering the construction of large and compound bedforms and allowing the deposition of damp and wet interdunes and salt flats as a wet aeolian system. Where large and compound bedforms with dry interdunes developed as a dry aeolian system, slow but progressive subsidence-driven water-table rise provided accumulation space that enabled system preservation. The Galho do Miguel Formation constitutes a hybrid aeolian system, in which both dry and wet environmental conditions were coeval.In the Mesoproterozoic, the absence of rooted-vegetation capable of acting as a sand stabilising agent allowed the widespread generation of aeolian systems in humid as well as arid environments. In humid environmental settings, water played a significant role in the accumulation and preservation of aeolian deposits, preventing their reworking by the wind or other exogenous agents.

Quantitative analysis of the sedimentary architecture of eolian successions developed under icehouse and greenhouse climatic conditions

AbstractThe continental terrestrial record preserves an archive of how ancient sedimentary systems respond to and record changes in global climate. A database-driven quantitative assessment reveals differences in the preserved sedimentary architectures of siliciclastic eolian systems with broad geographic and stratigraphic distribution that developed under icehouse versus greenhouse climatic conditions. Over 5600 geological entities, including architectural elements, facies, sediment textures, and bounding surfaces, have been analyzed from 34 eolian systems of Paleoproterozoic to Cenozoic ages. Statistical analyses have been performed on the abundance, composition, preserved thickness, and arrangement of different eolian lithofacies, architectural elements, and bounding surfaces. Results demonstrate that preserved sedimentary architectures of icehouse and greenhouse systems differ markedly. Eolian dune, sand sheet, and interdune architectural elements that accumulated under icehouse conditions are significantly thinner relative to their greenhouse counterparts; this is observed across all basin settings, supercontinents, geological ages, and dune field physiographic settings. However, this difference between icehouse and greenhouse eolian systems is exclusively observed for paleolatitudes <30°, which suggests that climate-induced changes in the strength and circulation patterns of trade winds may have partly controlled eolian sand accumulation. These changes acted in combination with variations in water table levels, sand supply, and sand transport, ultimately influencing the nature of long-term sediment preservation. During icehouse episodes, Milankovitch cyclicity resulted in deposits typified by glacial accumulation and interglacial deflation. Greenhouse conditions promoted the accumulation of eolian elements into the geological record due to elevated water tables and biogenic- and chemical-stabilizing agents, which could protect deposits from wind-driven deflation. In the context of a rapidly changing climate, the results presented here can help predict the impact of climate change on Earth surface processes.

The Silurian inception of inland desert ecosystems: trace fossil evidence from the Mereenie Sandstone, Northern Territory, Australia

The Silurian was an interval of profound change in terrestrial ecosystems as the earliest non-marine animal communities began to become established on the continents. Whilst much is known about the transition of pioneering animals from shallow-marine to coastal and alluvial habitats, evidence for animal activity in contemporaneous aeolian strata is rare. Here, we present trace fossil evidence that closes this knowledge gap, indicating that Silurian desert environments, dominated by aeolian processes, were occupied by resident invertebrate communities. The evidence comes from the Mereenie Sandstone, Northern Territory, Australia, which is demonstrated to have been deposited in a wet inland aeolian system, typified by small crescentic sand dunes and extensive interdune flats. The invertebrate trace fossil associations from the Mereenie Sandstone ( Arenicolites isp., ‘burrow entrance with radial feeding traces', Didymaulichnus lyelli, Diplichnites gouldi, Helminthopsis isp., Laevicyclus isp., Palaeophycus isp., Polarichnus garnierensis , Skolithos isp.) are restricted to damp interdune deposits, whereas dune strata are barren. The ichnofauna are described and compared to those from other Palaeozoic aeolian systems, in order to re-evaluate the timing of the early stages of arthropod terrestrialization.

Hunter-gatherer mobility and territories in the dunefields of center Argentina

The distribution of certain rocks in the landscape allows us to reconstruct diverse aspects of past hunter-gatherer behavior. In this work, we evaluate the mobility patterns employed by these groups and the presence or absence of boundaries in the Aeolian system of the center of Argentina. To accomplish this objective, we consider two types of evidence: 1) raw material frequencies and distributions in three areas of this Aeolian System and 2) presence and frequency of knapping stones from Tandilia sources. We construct a fall-off curve that is based on the relationship between the frequency of an item and the distance to the source of supply. The characteristics of each area yielded the human groups that inhabited delineate different modes of exploitation of the rocks. The fall-off curve documents a steep drop-off between 300 and 350 km from the Tandilia source and the spatial analysis indicates that within this distance the source probably represents the threshold of direct access to the quarries. Tandilia stone-tools seem to systematically supply a relatively wide area of the Central Pampean Dunefields of the Pampa grasslands, through varied processes, but they arrive at very low frequencies over great distances. The presence of Tandilia rocks in the Western Pampean Dunefields and Western Pampas Sand Mantles and Dunefields indicates social interaction between human groups that shared some common technological knowledge. The presence of stones in the Central Pampean Dunefields coming from the xerophytic woodland of the Dry Pampas can be related with contacts and exchanges among the hunter-gatherer group that occupied different territories.

Determining sediment provenance history in a Gondwanan erg: Botucatu formation, Northern Paraná Basin, Brazil

The Lower Cretaceous Botucatu Formation comprises a dry-aeolian system developed in western Gondwana and preserved within the Paraná Basin of central South America. Multiproxy provenance analysis (detrital zircon UPb dating, heavy mineral, petrographic and granulometric analysis) was undertaken along two 500 km transects of the northern Paraná Basin (NW and NE transects). To assess the provenance variation within the aeolian stratigraphy, samples were taken from the base and top of the Botucatu Formation and from sandstones interbedded with volcanics in the overlying Serra Geral Formation. Granulometric analysis shows a mean fine- to very fine-grained sand. The bulk petrography yields an average composition of Q91F6L2, and heavy mineral analysis gives a mean of 86% of zircon-tourmaline-rutile, demonstrating the overall polycyclic nature of the sediment. The discrete occurrence of garnet, apatite and epidote indicates local sediment input points, providing indirect evidence for point-sourced fluvial input into an overall dry aeolian system. Detrital zircon UPb LA-ICP-MS dating demonstrates a dominant Cambrian to Late Neoproterozoic (520–750 Ma) population with subsidiary Tonian-Stenian (0.9–1.2 Ga) and Orosirian-Rhyacian (1.9–2.3 Ga) contributions. The Botucatu Formation along the northern basin margin displays similar provenance to the southern part of the basin, pointing to a predominance of recycling processes within the basin. Statistical plots illustrate the detrital zircon age variability - recording an upward decrease in the age proportion of Permian and Tonian-Stenian populations and an increase in Cambrian-Late Neoproterozoic dates towards the top. Such variability can be related to the recycling of distinct Paraná Basin strata. The proportion of Cambrian-Late Neoproterozoic dates increases in the NE, indicating a possible input from the Ribeira Belt granitoids. Similar to major-scale dune-fields, Botucatu erg register variable sand sources there are possibly linked with coexisting depositional systems. In summary, the northern Botucatu erg is mostly fed by local sources reworked from underlying Paraná Basin units, with little direct input from basement sources and limited impact of regional wind-pattern variability.

Measuring Ripple and Dune Migration in Coprates Chasma, Valles Marineris: A Source to Sink Aeolian System on Mars?

AbstractActive aeolian systems are present across the martian surface, with active dune fields commonly found in depressions such as craters and valleys. There are many dune fields within the equatorial region of Mars, including Valles Marineris, but the effects of topography on wind regimes and consequently dune migration in Valles Marineris is poorly understood. We investigated both the ripple and dune migration in a dune field in Coprates Chasma using High Resolution Science Experiment Images (HiRISE) and Context Camera (CTX) images. Migration rates of dune brinks and ripples were measured over varying time scales, between Earth years 2007–2014. The dunes here are some of the tallest on Mars, with heights of up to 182 m. The dune brinks are migrating eastwards at a rate of 0.1–0.3 m/EY through the valley due to topographical influences on the local winds. Potential sediment sources for the dune field were identified and investigated by studying thermal inertia and mineralogy. The topographic slope‐related katabatic winds travel down the valley walls and converge with the dominant winds traveling through the center of the valley, causing overall eastwards dune migration. Topography is likely the dominant control on the local wind regime; slope winds travel down the sides of the valley walls and are funneled through the center of the valley. These local winds subsequently facilitate the migration of the large dunes in Coprates Chasma, thus expanding our understanding of local winds in the Martian environment.

A database of Aeolian Sedimentary Architecture for the characterization of modern and ancient sedimentary systems

The Database of Aeolian Sedimentary Architecture (DASA) records the architecture and spatio-temporal evolution of a broad range of modern and recently active aeolian systems, and of their preserved deposits in ancient successions. DASA currently stores data on >14,000 geologic and geomorphic entities (including bounding surfaces and transition relationships) extracted from >60 case-study examples documented in the published literature. DASA stores data on a variety of aeolian and associated non-aeolian entities of multiple scales, including attributes that characterize their type, geometry, spatial relations, hierarchical relations, temporal significance, and textural and petrophysical properties; associated metadata are also stored.Database output describes (1) stratigraphic relationships between aeolian and associated fluvial, lacustrine and paralic depositional systems; (2) the geometry of aeolian architectural elements, and hierarchical and spatial relationships between them; (3) the probabilities of vertical and lateral transition from one type of deposit or landform to another; (4) the presence and nature of aeolian bounding surfaces at different scales, and their nested, hierarchical relationships; (5) aeolian lithofacies types, proportions and distributions, and (6) grain-scale textural parameters.DASA is applied to quantitatively characterize and compare modern and ancient aeolian sedimentary systems. Examples of database outputs demonstrate how DASA outputs can be tailored for numerous applications, including: (1) the development of bespoke quantitative facies models, specifically tailored for particular sets of boundary conditions; (2) the empirical assessment of how aeolian systems, and associated preserved sedimentary architectures, represent a response to allogenic and autogenic forcings; and (3) the instruction of forward stratigraphic models and 3D geocellular subsurface models. DASA is a valuable tool for the characterization of subsurface aeolian successions, such that output can help to (1) predict three-dimensional lithological heterogeneity in subsurface successions that are resource targets, (2) constrain geocellular stochastic models, and (3) facilitate borehole correlations of aeolian dune sets or associated non-aeolian elements.

Late Cretaceous aeolian desert system within the Mesozoic fold belt of South China: Palaeoclimatic changes and tectonic forcing of East Asian erg development and preservation

This study recognises and identifies the Late Cretaceous aeolian desert system from the Jianshi Basin, located in the intra-continental orogen within the Yangtze Block, South China. Erg deposits comprise aeolian dunes and dry aeolian sandsheets with alluvial facies associations at the margin and show an alluvial-aeolian depositional system. Palaeowind reconstruction of aeolian dune foresets showed that the dominant prevailing winds were westerlies, followed by northeasterlies and subordinate northwesterlies and southeasterlies. It is possible that monsoon rains recharged the water inflow system and caused the development of fluvial sand bodies at the margin of the Jianshi desert during the early deposition stage. The alluvial deposits in the study area were related to regional tectonism, while the dry aeolian system was dominated by mid- and low-latitudinal subtropical highs and the monsoonal climate. Orogenic topography, combined with planetary-scale subtropical high-pressure systems, blocked the transport of moisture, enclosed the low-lying land, and led to the aridification and development of desert depositional systems in the East Asian interior. Moreover, fault-controlled subsidence provided accommodation space in desert basins for alluvial and aeolian deposits. Based on the results obtained from palaeowind reconstructions, the divergent axis of subtropical highs during the Late Cretaceous was located in mid- and low-latitude areas of the Jianshi, Jianghan, Xinjiang, and Hengyang basins in South China. The relatively scattered nature of palaeowinds in the Jianshi Basin and adjacent deserts may indicate a seasonal drift in the divergent axis under the influence of a monsoonal climate.

Aeolian dunes morphodynamics and wind regime reconstruction in mid-latitudes of the Gondwana during Early Permian, Aracaré Formation, Sergipe-Alagoas Basin, Brazil

Aeolian systems play an important role in palaeoclimatic studies, allowing the inference of arid regions in different geological periods, in addition to being the best records for acquiring palaeowind data. Morphodynamic reconstruction of ancient aeolian dunes is extremely important for understanding the local wind regime. This study aims to contribute to the morphodynamic reconstruction of aeolian deposits of the Aracaré Formation in response to Gondwana's palaeoclimatic variations and to indicate the prevailing wind regime. Permian Aracaré Formation is located in the Sergipe-Alagoas Basin, northeast region of Brazil, and exhibits sand accumulation of successive sets of aeolian cross-strata which are interpreted as dry aeolian system. Aracaré Formation is characterized by smaller cross-bedded sets of barchanoid dunes at the base that are overlaid by larger cross-bedded sets of transverse dunes. Aeolian cross-strata show a repetitive alternation of grainflow and wind-ripple packages, separated by reactivation surfaces indicating seasonal variations in wind direction. Cross-strata mean vectors dip consistently towards ESE when corrected for the palaeogeographic position of the Lower Permian. Cyclic stratification pattern suggests an alternation of westerly transverse winds responsible for dune migration, followed by reverse winds that caused dune reworking and led to the formation of reactivation surfaces and the related deposition of wind-ripple. Sometimes, reverse winds are more intense (storms?), strongly eroding the lee face of the aeolian dunes, generating master reactivation surfaces. The comparison between the wind patterns of Aracaré Formation and Sakmarian climate models showed good correlation with disposition of westerlies wind regime in mid-latitude in Gondwana landmass.

Interpreting pre-vegetation landscape dynamics: The Cambrian Lower Mount Simon Sandstone, Illinois, U.S.A.

ABSTRACTThe Cambrian Mount Simon Sandstone has been the subject of extensive study and multiple industrial-scale carbon storage demonstrations at Decatur, Illinois, USA. The development of a reliable paleoenvironmental model is critical to successful large-scale carbon dioxide (CO2) storage, but is complicated by the need to interpret pre-vegetation sedimentation processes. The present study presents a paleoenvironmental model of the Lower Mount Simon Sandstone, based on analysis of primary sedimentary structures in two cores and four complete high-resolution resistivity logs (FMI).The Lower Mount Simon Sandstone represents a vertical “drying-up” sequence composed of three associated depositional units: a north–south oriented coastal system at the base, an eastward-directed fluvial unit in the middle, and a westward-directed eolian system at the top that recycled medium- and fine-grained sand in the basin. Quantitative analysis of fluvial cross-strata indicates that the perennial river system was shallow (c. 1 m deep) with relatively narrow channel belts (c. 1 km). Adjacent sandy eolian-floodplain deposits contain abundant thin, crinkly planar laminae that are enriched in fines and are interpreted as cementation surfaces, likely of biological origin. Deflation lags and wind-ripple strata are commonly interbedded with the crinkly strata, suggesting that the recurrence of erosion and deposition that controlled sedimentary preservation on the floodplain were dominated by eolian transport, re-wetting, and (bio-) cementation. Such a prominent role of exposure to the wind, basin-scale sediment recycling, and eolian removal of fine-grained sediment would have ceased to exist for most climates after the development of vegetation on land, yet, may well be key to understanding the environmental context for early life on Earth.

Morphology, accumulation and preservation of draa systems in a Precambrian erg (Galho do Miguel Formation, SE Brazil)

Proterozoic aeolian successions tend to exhibit a low complexity in the architectural organisation, generally related to simple dunes with low morphological diversity. Although most palaeoenvironmental reconstructions of ancient ergs confirm this scenario, the general conditions in the Precambrian landmass should have allowed the construction of larger and more complex sedimentary aeolian systems than those recorded in the Phanerozoic successions. To address this paradigm, the present work proposes to discuss the development and morphodynamics of ancient draa-scale bedforms and to understand which controlling factors produced the apparent absence of draa architecture in the Precambrian sedimentary record. For this purpose, this study examines an interval of c. 80 m of the Galho do Miguel Formation, which is a Mesoproterozoic aeolian succession composed of metasandstones showing well-preserved primary sedimentary structures and geometries with excellent vertical and horizontal exposures. A detailed sedimentological analysis allowed the recognition of six main architectural elements: (i) simple transverse dune, (ii) simple linear dune; (iii) compound transverse draa; (iv) complex linear draa, (v) dry interdune and (vi) sand sheet. The lateral and vertical relationships between these architectural elements support the evidence of coeval spatial coexistence of distinct aeolian morphologies (transverse and linear bedforms), probably controlled by lateral variations in sand saturation and in circulation pattern of the palaeowind. The stratigraphic organisation indicates different intervals of draa construction and destruction, which appear to be associated with different sedimentary pulses. The intervals of draa construction represent the vertical succession between simple and compound dunes of similar morphologies, representing temporal variation in sedimentary availability and changes in angle of dune climbing. The erosional and irregular surface at the bottom of compound sets of cross-strata can represent periods of irregular accumulation, associated with partial draa destruction (dune cannibalisation), probably due to seasonal variations in sedimentary availability throughout construction stages. Evidence of a near-surface water table level, as small wave ripples, indicates that the position of the water table was directly linked to the sedimentation pattern throughout these intervals. This relationship implies that ground water was the main controlling factor on sand availability and wind saturation during aeolian morphodynamics, as well as on accumulation and preservation processes. Moreover, in conditions of high rates of subsidence, the thickness accumulated and preserved via water table fluctuation is incorporated in the sedimentary record; otherwise, these deposits would have eroded due to aeolian deflation or fluvial reworking. Apparently, the absence of large and complex aeolian systems in the Precambrian record can be related to the absence of continuous near-surface water table during the draa development, directly decreasing their preservation potential.

Mapping and chronology of coversands and dunes from the Aquitaine basin, southwest France

New stratigraphic (including GPR profiles) and chronological data provide a detailed understanding of the emplacement of aeolian sands in the Aquitaine basin (SW France). The main phase of coversand deposition ranges from 25 ka to 14 ka. The ages cluster around two periods that match Heinrich events (He-2 and He-1) and reflect increased sedimentation in response to aridification and high mean wind speeds. The age distribution is skewed toward recent phases, which likely results from continuous sand recycling. The dunes currently visible in the landscape were formed during the Younger Dryas/very early Holocene and the historical period. The Younger Dryas dunes are inland low parabolic dunes that have been strongly degraded. Only the last phases of the progression of the coastal dunefield are preserved because of coastal erosion. Two depositional phases have been identified, the Dark Ages Cold Period and the Little Ice Age, which correspond to phases of increased storminess already known from the coastal record in Europe. The Dark Ages Cold Period dunes are high parabolic dunes, whereas the Little Ice Age dunes are predominantly barchanoid. The impact of trampling of the dunes by cattle during the latter period, resulting in reduced vegetation cover, and their artificial stabilization by pine forests seems to be the plausible causes of this morphological difference. Overall, the Aquitaine aeolian system is a good example of a mid-latitude coastal to inland system that was intermittently active during the Quaternary, and where the reconfiguration of the coast following sea level fluctuations played an important role in the chronological distribution of sediments.

Hierarchical scales of soft-sediment deformation in erg deposits, Lower Jurassic Navajo Sandstone, Moab area, Utah, U.S.A.

ABSTRACTExtensive soft-sediment deformation (SSD) of multiple expressions and scales record active and dynamic events and processes in erg deposits of the Lower Jurassic Navajo Sandstone near Moab, Utah. The erg deposits preserve depositional environments of eolian dune, interdune, fluvial, playa, lake, and spring. A large range of SSD features, from intact beds showing little deformation to pervasively disturbed beds, exist in many of these deposits. A simplified classification index captures the different scales of SSD in ascending order of deformation intensity: 1) mostly intact bedding with small-scale wavy or undulatory deformation structures within single beds; 2) dish and flame structures; 3) meter-scale, kinked, slumped, rolled, overturned, vertical, and detached contorted crossbedding, and associated centimeter- to meter-scale pipes; and 4) disruptive diapirs and laterally extensive massive sandstone. The SSD features of deformed crossbed sets, diapirs, and massive sandstone beds, are consistently juxtaposed, and are thus genetically linked.Although the Navajo Sandstone has been considered a classic example of an extensive dry eolian system, both individual and combinations of strata bounded SSD features exemplify dynamic deformation, liquefaction, and fluidization that took place at various times after deposition. The lowest degree of deformation, SSD 1, is largely attributed to autogenic––inherent to the eolian system––or local allogenic processes. Larger degrees of deformation, SSD 2–4, were more likely produced by allogenic, external-forcing processes from regional changes in climate and/or near-surface groundwater conditions originating from the Uncompahgre uplift, with the deformation triggered by some event(s). Possible significant ground motion could have led to large-scale disruption in the Navajo sand sea across kilometer-scale intervals. The Navajo example establishes valuable hierarchical relationships of processes and products for recognizing and interpreting SSD in other ancient and modern eolian systems. This has particular relevance to sedimentary discoveries on Mars, where SSD features are visible from remote sensing imagery and rover exploration.