Aeolian Succession Research Articles

Architecture and dynamics of Precambrian linear megadunes: Galho do Miguel Formation, Mesoproterozoic, South-East Brazil

Recognizing the deposits of linear megadunes in ancient aeolian successions is challenging when the original bedform topography is not preserved. The present study provides a detailed analysis of the depositional architecture of an ∼ 80 m-thick interval of the Mesoproterozoic Galho do Miguel Formation (SE Brazil) to reconstruct the original morphologies of linear megadunes and to understand their dynamics. The depositional architecture reveals compound cross-bedded sets, which transition laterally into thick low-angle cross-stratified sets and planar-parallel sandstone beds. The depositional features indicate the presence of complex megadunes separated by adjoining wide dry inter-megadune areas, which were themselves flooded seasonally by a water table that rose above the depositional surface. Linear megadunes experienced two phases of development: vertical accretion and subsequent episode of lateral migration. During the vertical accretion phase, high sediment supply, typical of Precambrian aeolian systems, and the convergence of winds from two distinct directions promoted high rates of megadune growth, bedform elongation, and the formation of superimposed dunes. The lateral migration phase was characterised by a component of lateral bedform shift relative to the main along-crest sediment transport direction; this prevented preservation of a bimodal pattern of dune cross-strata azimuths. The accumulation of these deposits occurred via a combination of megadune climbing that occurred with progressive rise of the water-table level. The water-table rise hindered cannibalization of the lower parts of the migrating megadunes, allowing the accumulation and subsequent preservation of megadune sandstone packages. The rise of the water table was also responsible for the accumulation of thick dry inter-megadune strata. The unusual thickness of linear megadune and inter-megadune deposits of the Galho do Miguel Formation, as compared with Phanerozoic examples, are attributed to the interplay between the barren conditions of the early Earth, the morphodynamics of the linear megadunes, and the seasonal impact of the water table at the accumulation surface. Without a water-table control, opportunities for megadune accumulation and preservation were likely limited in Precambrian ergs.

The Precambrian continental record: A window into early Earth environments

The Precambrian was characterized by unique palaeoenvironmental conditions in the Earth’s atmosphere, biosphere and geosphere. This study presents a global quantitative analysis of Precambrian sedimentary successions of aeolian, alluvial, fluvial, lacustrine and glacigenic origins, examined in the broader context of Earth evolution. In the Precambrian, an apparent scarcity of aeolian successions is observed. This may be linked to: (1) differences in atmospheric density, which controlled wind erosion and sedimentation; (2) different astronomical configurations, which may have influenced tides and atmospheric circulation, thereby affecting sand availability and the width of subtropical zones; (3) potentially hotter and more humid climates, restricting dry-sand availability; (4) a lack of vascular vegetation that could prevent reworking of aeolian deposits; (5) poor preservation potential; (6) misinterpretation of the Precambrian record. Mixed aeolian-alluvial strata are more abundant, perhaps because their preservation in the geological record was favoured by water tables sustained by incursions of alluvial systems into otherwise aeolian dominated environments. Aeolian deposits were preferentially accumulated during phases of supercontinental breakup, where rapidly subsiding rift basins provided accommodation suitable for preservation. Other than in the Neoproterozoic record, where glacigenic deposits dominate, alluvial strata are the most common and thickest type of continental deposit in the Precambrian. Precambrian braided alluvial systems were more widespread than in the Phanerozoic. Major alluvial systems formed preferentially during phases of supercontinent assembly, whereby alluvial systems drained major orogens, and long drainage pathways developed from supercontinent interiors to coastlines. In the Paleoproterozoic, ephemeral, saline to partly arid lakes developed extensively in the desertic interior of Columbia. Glacial deposits preferentially formed in the breakup phase of supercontinental cycles; this supports theories invoking enhanced chemical weathering of uplifted rift shoulders as a driver of carbon dioxide sequestration, global cooling, and glaciation. Overall, the number of identified continental successions increases towards the Precambrian-Phanerozoic boundary. This may be an artefact of an increasingly more complete stratigraphic record as time progresses. However, the abundance of continental successions varies on a quasi-periodic cycle of 500 – 700 Myr, with peaks coinciding with the tenure and breakup of Precambrian supercontinents.

Eocene dry eolian system in the Jianchuan Basin, southeastern Tibetan Plateau: Implications for regional wind regime and paleoclimate

East Asia experienced a climatic transition from a zonal pattern (climate zones defined by latitude) to a monsoon-dominated pattern during the Cenozoic. However, hitherto little consideration has been paid to the atmospheric circulation of the planetary wind system that prevailed during the early uplift of the Tibetan Plateau, due to the lack of reliable proxies. Here, we conduct a study on the eolian successions from the Eocene Baoxiangsi Formation in the Jianchuan Basin, southeastern Tibetan Plateau to reconstruct regional atmospheric circulation and paleoclimate. Two facies associations are recognized in the eolian deposits of the Baoxiangsi Formation: a dominant eolian dune association and a subordinate interdune association. Eolian dune deposits are characterized by large-scale cross-stratified sets of strata composed internally of packages of grainflow, wind-ripple strata and pinstripe lamination. These packages of laminae and cross-stratified eolian dune sets are bounded internally by superimposition and reactivation surfaces and interdune surfaces, respectively. Interdune deposits are uncommon and composed dominantly of subcritical climbing translatent strata to form sets of strata and these are themselves bounded by interdune surfaces to form cosets of strata. The association of dominant eolian dune deposits, widely distributed interdune surfaces of great lateral extent (> 450 m) and that climb at a shallow but positive angle (< 1°) is consistent with the climbing dry eolian system. The commonly occurring superimposition surfaces indicate the presence of compound dunes (megadunes, draas). Based on the analysis of 715 dip–azimuth readings of foresets of eolian cross-beds, we reconstruct the prevailing wind directions: the paleowind in the northern basin flowed toward the northeast; in the southern basin it flowed toward the southwest. This wind regime indicates that the Jianchuan Basin was located at the zonal boundary between the westerlies and the trade winds, and the construction of the dry eolian system was controlled by the subtropical high-pressure belt during the middle–late Eocene. Following the accumulation of the dry eolian system, a monsoon climate regime gradually established itself and prevailed in the Yunnan Province; this expanded northward over time. This was closely related to the uplift of the central Tibetan Plateau and the retreat of the Paratethys ocean in the late Eocene.

Precambrian aeolian systems: A unique record?

The Precambrian is associated with a set of geologically unique palaeoenvironmental conditions arising from differences in the Earth’s atmosphere, biosphere and geosphere. The extent to which these conditions operated to generate an aeolian stratigraphic record that is geologically distinct from that of the Phanerozoic remains poorly understood. This study presents a quantitative comparison of the preserved sedimentary architectures of 87 globally distributed aeolian successions from the Precambrian (30 case studies) and the Phanerozoic (57 case studies). Compared to those of the Phanerozoic, Precambrian aeolian successions are characterised by: (1) thinner aeolian dune sets, mostly documenting the accumulation of small, rapidly migrating barchan dunes; and (2) a greater occurrence of sandsheet, zibar, and damp and wet interdune deposits, many occurring interdigitated with non-aeolian strata. The nature of the Precambrian aeolian stratigraphic record reflects in part the absence of sediment-stabilizing terrestrial vegetation: compared to Phanerozoic systems developed since the evolution of land plants, aeolian processes (erosion, transport and deposition) were more active, even under markedly more humid climates. Precambrian aeolian successions record greater evidence of fluvial and marine incursions into contiguous aeolian dune fields. Water tables were commonly elevated close to the level of the accumulation surface for protracted episodes; extensive damp and wet substrates restricted the availability of dry sand for aeolian dune construction, thereby limiting dune size. In some Precambrian aeolian systems, sediment supply was additionally restricted by the development of cryptobiotic films and crusts that preferentially developed on damp substrates in the absence of vegetation. Common fluvial and marine aqueous interactions promoted the reworking of aeolian dunes into sandsheet deposits; many such accumulations likely represent eroded remnants of larger aeolian dune fields. Given the absence of vegetation-induced sediment binding and baffling, and wind-buffering effects, coarser sand fractions were more readily transported by the wind in the Precambrian; this led to the preferential development of coarse-grained zibar deposits. This study demonstrates how the Precambrian aeolian sedimentary record is geologically distinct from that of the majority of the Phanerozoic, providing new insights into the controlling factors that governed aeolian sedimentation during the Precambrian through interactions between the geosphere, biosphere and atmosphere.

A new aeolian activity proxy based on analysis of the grain size characteristics of surface soils across the Tengger Desert, northwest China, and its application to a Quaternary aeolian succession

The arid regions of northwestern China are dominated by extensive areas of mobile sand dunes. These features cause environmental problems and exert global climatic impacts; however, due to the lack of systematically-applied indicators of aeolian activity, direct evidence of past changes in aeolian activity is unreliable, especially for aeolian sand source regions. In this paper, we analyze the end-member (EM) distributions of various types of surface soil across the Tengger Desert in northwestern China, and devise a sensitive proxy for aeolian activity using a spatio-temporal substitution approach. This proxy is then used to evaluate a Quaternary aeolian succession and to understand the response of aeolian activity to regional climate change. Our results suggest that gradual increases in the coarse-grained EM components 3–5 reflect enhanced dune mobility and reduced vegetation coverage, which are a direct function of the intensity of regional aeolian activity. In the aeolian section, coarse- and medium-grained sand layers resemble modern semi-mobile and mobile dunes, whereas fine-grained sand layers are analogous to vegetated fixed/semi-fixed or semi-mobile dunes. Combining this record with independent multi-proxy evidence from the same section leads us to conclude that strong aeolian activity coincided with a dry climate, sparse vegetation cover, and strong surface winds during the Last Glacial Maximum, and that these conditions gradually attenuated at the beginning of the Last Deglacial. These inferences are in accord with independent paleoclimate records from this region, confirming that the intensity of aeolian activity in the southeastern Tengger Desert is closely associated with large-scale climate change. Our findings show that our EM proxy can be used to infer the intensity of aeolian activity and to reliably reconstruct the evolution of deserts in northwestern China.

Preserved eolian bedforms control reservoir heterogeneity: Characterization and modeling workflow for the Avilé Member, Neuquén Basin, Argentina

Under certain conditions, most commonly abrupt flooding events, entire eolian bedforms can be incorporated into the geological record. Sediment that was essentially ‘in transport’ within these bedforms at the time of preservation has a distinct sedimentary architecture compared to that of sensu stricto accumulated intervals. Despite this, while the preservation of bedforms has been readily documented from outcrop and subsurface eolian successions, stratigraphic intervals corresponding to these bedforms have rarely been identified and separated from accumulated intervals. The impact of capturing and representing bedform intervals in reservoir models has therefore not been explored. The Avilé Member (Neuquén Basin, Argentina) is a prolific oil reservoir of eolian origin in which both bedforms and accumulated intervals are documented. The aim of this study is to use the Avilé Member record at the Puesto Hernández oilfield to develop a workflow to identify, characterize, map and model discrete eolian bedform and accumulated intervals in a subsurface scenario. Characterization of the unit's geometry, sedimentary facies, and petrophysics was carried out from seismic, wireline log and core analysis. The development of a conceptual model of the accumulation system and its evolution allowed the identification of bedform and accumulated intervals. Precise mapping of these intervals required the development of a geometrical method, based on correlating interdune lows and using a datum surface to provide for an approximation to the ancient accumulation surface. A zoning scheme conditioned by the intervals was tested against a simple, ‘one-zone’ model, to determine its effectivity in separating discrete heterogeneity zones. The model was also tested in a dynamic simulator to history match the field production and analyze its impact in dynamic reservoir simulation. This example serves as a valuable reference to illustrate how eolian bedforms and accumulated intervals may be identified, characterized, and modelled in subsurface scenarios around the world.

Eolian stratigraphic record of environmental change through geological time

Abstract The terrestrial sedimentary record provides a valuable archive of how ancient depositional systems responded to and recorded changes in Earth's atmosphere, biosphere, and geosphere. However, the record of these environmental changes in eolian sedimentary successions is poorly constrained and largely unquantified. Our study presents the first global-scale, quantitative investigation of the architecture of eolian systems through geological time via analysis of 55 case studies of eolian successions. Eolian deposits accumulating (1) under greenhouse conditions, (2) in the presence of vascular plants and grasses, and (3) in rapidly subsiding basins associated with the rifting of supercontinents are represented by significantly thicker eolian dune-set, sand-sheet, and interdune architectural elements. Pre-vegetation eolian systems are also associated with more frequent interactions with non-eolian environments. The interplay of these forcings has resulted in dune-set thicknesses that tend to be smallest and largest in Proterozoic and Mesozoic successions, respectively. In the Proterozoic, the absence of sediment-binding plant roots rendered eolian deposits susceptible to post-depositional wind deflation and reworking by fluvial systems, whereby highly mobile channels reworked contiguous eolian deposits. During the Mesozoic, humid greenhouse conditions (associated with relatively elevated water tables) and high rates of basin subsidence (associated with the breakup of Pangea) favored the rapid transfer of eolian sediment beneath the erosional baseline. The common presence of vegetation promoted accumulation of stabilizing eolian systems. These factors acted to limit post-depositional reworking. Eolian sedimentary deposits record a fingerprint of major environmental changes in Earth history: climate, continental configuration, tectonics, and land-plant evolution.

Damp- to dry aeolian systems: Sedimentology, climate forcing, and aeolian accumulation in the Late Cretaceous Liyou Basin, South China

Aeolian desert systems were widely distributed in South China during the Late Cretaceous. These systems developed under the control of subtropical highs and a monsoon climate. They reveal the evolution of palaeoclimate and palaeogeography and the regional palaeowind pattern in the South China interior during this period. Based on the analyses of sedimentology and facies architecture, this study examines and reassesses the aeolian succession of the Upper Cretaceous Daijiaping Formation in the southern Liyou Basin of southeast China. This aeolian desert succession records aeolian dune, dry and damp interdune and aeolian sandsheet sedimentation in streamflow, fluvial channel and overbank settings. Aeolian dune deposits comprise low-angle dune plinth strata and superimposed sets of cross-strata bounded by a hierarchy of bounding surfaces. The deposits record two morphological types of compound crescentic dunes and complex linear dunes. Palaeowind direction in the Liyou desert agrees with the subtropical high-pressure westerly and northeasterly wind pattern that existed in the mid to low latitudes of the Northern Hemisphere, in conjunction with possible monsoon climate conditions during the Late Cretaceous. The fault-bounded basin in which the succession accumulated experienced a high subsidence rate and a high supply and availability of windblown sand, which ensured hundreds of metres of thick accumulation of the dune field system. The occurrence of a near-surface water table and soft-sediment deformation in the aeolian dune foresets indicates that the monsoon rains could have recharged the groundwater system and resulted in episodes of relative water-table rise, which played an important role in the accumulation and preservation of aeolian systems in the Liyou desert basin. Gradual and progressive subsidence of the aeolian succession combined with water-table fluctuations allowed the preservation of the aeolian accumulation system.

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.

The role of subsidence and accommodation generation in controlling the nature of the aeolian stratigraphic record

Despite a well-documented record of preserved aeolian successions from sedimentary basins characterized by widely variable subsidence rates, the relationship between aeolian architecture and subsidence-driven accommodation generation remains poorly constrained and largely unquantified. Basin subsidence as a control on aeolian sedimentary architecture is examined through analysis of 55 ancient case-studies categorized into settings of ‘slow’ (&gt;1–≤10 m Myr −1 ), ‘moderate’ (&gt;10–≤100 m Myr −1 ) and ‘rapid’ (&gt;100 m Myr −1 ) time-averaged subsidence rates. In rapidly subsiding basins, aeolian successions are thicker and associated with (1) thicker and more laterally extensive dune-sets with increased foreset preservation, (2) greater proportions of wet-type interdunes and surface stabilization features and (3) more extensive interdune migration surfaces, bounding sets that climb more steeply. In slowly subsiding basins, aeolian successions are thinner, and associated with a greater proportion of (1) aeolian sandsheets and (2) supersurfaces indicative of deflation and bypass. Rapid subsidence promotes (1) steeper bedform climb, resulting in increased preservation of the original dune foreset deposits and (2) relatively elevated water tables, leading to sequestration of deposits beneath the erosional baseline and encouraging development of stabilizing agents; both factors promote long-term preservation. Slow subsidence results in (1) lower angles of climb, associated with increased truncation of the original dune forms, and (2) greater post-depositional reworking, where sediment is exposed above the erosional baseline for extended time-periods. Quantitative analysis of sedimentary stratal architecture in relation to rates of basin subsidence helps constrain the mechanisms by which sedimentary successions are accumulated and preserved into the long-term stratigraphic record. Supplementary material: Results of statistical analyses presented here are available at https://doi.org/10.6084/m9.figshare.c.5515695.v1

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 &amp;lt;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.

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.

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.

Early Pennsylvanian fluvial - Aeolian interplay in the Amazonas Basin (central-western Gondwana) and its relation to marine transgression

The Monte Alegre Formation corresponds to the main reservoir rock in the Amazonas Basin petroleum system in Brazil and is correlated with the Pennsylvanian rocks of the Parnaíba and Solimões basins. Previous outcrop and well-based studies are concentrated on the southern edge of the basin and show that the Monte Alegre Formation basically represents an aeolian, deltaic and transitional marine succession. However, there is no published research that demonstrates the depositional system in the northern edge of Amazonas Basin. In this sense, outcrop-based facies and stratigraphic analysis is carried-out to understand the distal influence of marine incursion into the basin and its relationship with paleogeography in the Upper Carboniferous. The data show that the aeolian Monte Alegre system is represented by a braided fluvial system formed by five architectural elements: (i) sandy bedform, (ii) downstream-accretion macroform, (iii) gravel bars and bedforms, (iv) channel and (v) laminated sand sheets, pointing to a braided depositional system. The aeolian succession overlies the fluvial system and is represented by medium-scale trough cross-bedding and large-scale planar cross-bedded sandstones resulting from the accumulation and migration of transverse dunes toward the northwest that grade upward to dry interdunes and aeolian sand sheet deposits that are interbedded, consisting basically of translatent ripple cross-lamination and low-angle cross-stratified lamination sandstones related to water table raises. The stratigraphic record defines a wetting-upward stacking pattern of Monte Alegre Formation resulting from local sea level rise as a result the advance of the marine incursion that settled in the central-western region of Gondwana during the Late Carboniferous. Thus, in addition to corroborating the paleo wind directions predicted for the region during the Late Carboniferous, these deposits help to understand the paleoenvironmental relations between the northern and southern edges of the Amazonas Basin.

Eolian deposits of the northern margin of the South China (Jianghan Basin): Reconstruction of the Late Cretaceous East Asian landscape in central China

The Late Cretaceous Honghuatao Formation includes a succession of thick clastic sedimentary sequences which are widely exposed in northwestern Jianghan Basin, central China. Here, detailed sedimentological and facies architectural analyses are performed allowing to re-interpret and identify the controversy for sedimentary environment and to investigate the paleoclimatic condition. The Honghuatao stratigraphic sequence includes eolian dunes and dry interdunes deposits with fluvial channel deposits at the bottom and top. The vertical change between fluvial and eolian systems indicates alternating wet and dry climate. At the same time, the provenance analysis combined with the paleocurrents from the W, NW, and NE indicates that Huangling Dome, South Qinling Belt and Dabie Orogen supply the main detrital source for the Honghuatao Formation. The Late Cretaceous first rifting subsidence in the Jianghan Basin provided accommodation space for the preservation of the aeolian accumulation. Moreover, the existence of the mountain belts around the basin, that is, the orographic effect, precluded the winds from transporting humidity to the interior of the Jianghan Basin, generating the desert system. This study shows that the formation of eolian deposits in the Honghuatao Formation and coeval strata in numerous adjacent basins was a sedimentary response to the prevailing desert climate in the mid-to low-latitude areas of the Northern Hemisphere during the Late Cretaceous, which was predominately controlled by the subtropical high-pressure system on a planetary scale. • Late Cretaceous aeolian succession in South China was identified and paleowind patterns were characterized. • Wind-pattern model in East Asia was proposed during the Late Cretaceous. • Late Cretaceous East Asian paleogeography in central China was reconstructed.

Lower to middle pleistocene coastal dune fields formation in the western mediterranean (Western Eivissa, Balearic archipelago): Chronology and landscape evolution

Abstract Colluvial and aeolian successions in coastal environments are useful indicators of geomorphological changes that occurred during the Quaternary. Pleistocene aeolian deposits interbedded with colluvial deposits and palaeosols in areas of Cap Negret, Punta de sa Pedrera, Cala Bassa and Cala Compte, western coast of the island of Eivissa (western Mediterranean) are studied here. These deposits span almost continuously along 14 km of the coast, covering an area of approximately 22 km2. We present a sedimentological and stratigraphical description of these Pleistocene outcrops. Five major sedimentary facies involving the succession of aeolian, colluvial and edaphic environments are described. Carbonate sandstones, breccias, conglomerates and fine-grained deposits are the main components of these sequences. Optically stimulated luminescence (OSL) dating of aeolian levels indicates that deposition took place from the Lower to Middle Pleistocene. The sedimentological and chronological analysis of these deposits allows reconstructing of the coastal Pleistocene environmental history from Marine Isotopic Stage (MIS) 22 to MIS 6. Results show that the main controls on Lower to Middle Pleistocene coastal landscape evolution on Western Eivissa are changes in the average wind direction over time, modulated by the interaction with coastal relief orientation. The main episodes of aeolian activity identified and dune formation in the Western Mediterranean can be linked to periods of low sea level.

A microfacies analysis of arid continental carbonates from the Cedar Mesa Sandstone Formation, Utah, USA

AbstractArid continental environments are typically dominated by siliciclastic aeolian, alluvial and fluvial deposits. Despite their common recognition within these environments, carbonate deposits are often overlooked, yet they can provide vital insight into the depositional history, climate and tectonic controls of a sedimentary basin. This work presents a detailed microfacies analysis of the carbonates found within the Cedar Mesa Sandstone Formation of the Western USA. The Cedar Mesa Sandstone Formation is an early Permian, predominantly aeolian succession, exposed across much of the Colorado Plateau of southern Utah and northern Arizona. The formation is dominantly clastic erg deposits, that grade into a mixed carbonate/clastic sedimentary succession interbedded with carbonate and evaporitic units, interpreted to represent sabkha or sabkha‐like deposits. While many authors have worked within the aeolian dominated facies and have proposed various facies schemes for the siliciclastic components, comparatively little attention has been paid to the mixed evaporitic/clastic/carbonate aeolian‐sabkha transition zone. In this work the microfacies of the carbonates present within the Cedar Mesa Sandstone are analysed, in order to: (a) develop a record of, and interpret carbonate components, (b) propose depositional mechanisms and (c) identify evolutionary trends that stand alongside the formation's clastic depositional story. Six microfacies are presented: (MF1) Clastic Influenced Carbonate Wackestone; (MF2) Laminated Carbonate Wackestone/Packstone; (MF3) Microbial Laminated Fenestral Bindstone; (MF4) Rounded Mudclast Wackestone; (MF5) Laminated Bioclastic‐Ostracod‐Carbonate Wackestone and (MF6) Microcrystalline Quartz. The microfacies have been interpreted to document the development of carbonate interdune, lacustrine and continental sabkha environments influenced by localized fault control juxtaposed across a wetting and drying climate cycle and provide useful comparisons for other mixed evaporite/carbonate and clastic sequences.

Genesis of poikilotopic zeolite in aeolianites: An example from the Parnaíba Basin, NE Brazil

Zeolite cement is one of the main components of the Jurassic to Lower Cretaceous fluvial-aeolian succession in the Parnaiba Basin, northeastern Brazil. Core and outcrop-based stratigraphic analyses permitted the paleo-environmental and diagenetic interpretation of aeolian sandstone and showed the influence of the volcanic substrate in the origin of the zeolite cement. The substrate is represented by an extensive volcanic plain developed in the last stages of the Central Atlantic Magmatic Province (CAMP) in West Gondwana. The siliciclastic deposits consist of dune field, sand sheet and wadi deposit facies associations. The zeolite cement of the aeolian succession forms poikilotopic crystals with anomalous up to 50% modal content. X-ray diffraction and SEM/EDS/CL analyses showed laumontite and Ca-stilbite exhibiting, respectively, massive and radial textures. During eodiagenesis, the main processes included clay infiltration linked to water table fluctuations and flash flood events, producing clay coatings and displacive stilbite cementation. Massive laumontite cementation and smectite-chlorite conversion occurred in the mesodiagenesis, while in the final stages, the zeolite was partially replaced by calcite cement. Telodiagenesis is recorded by iron exsudation and the corrosion of clay films. Several processes can be inferred to explain the origin of the zeolite cement in the Jurassic-Lower Cretaceous sandstone of the Parnaiba Basin. After the first magmatic pulse (Triassic magmatism), the zeolite-bearing basalts were submitted to chemical weathering, causing cation leaching. Afterwards, the deposition of aeolian sands related to a wet desert system occurred above this weathered substrate. Fractured basaltic substrate favored the release of ions to the surface, with fluids enriched in sodium and calcium that percolated the permeable aeolian sandstone beds during the diagenesis. Furthermore, zeolite cement is geographically associated with the volcanic substrate in the western Parnaíba Basin. However, it is absent in the eastern part, where the aeolianites overlie sedimentary rocks. We suggest that the system was thermally reactivated by the last thermal CAMP phase, with basalt emplacement in the eastern Parnaiba Basin linked to the opening of the Equatorial Atlantic Ocean (Cretaceous magmatism). The progressive heating towards the western part of the basin triggered fluids convection, and the enrichment in ions such as Ca2+, Si4+, Na+, Al3+, HCO−3 and SO42−, promoting optimal conditions for zeolite crystal growth (100 °C–300 °C). Sandstone textural aspects, as well as extensional faults and fractures allowed fluids migration resulting in the massive poikilotopic zeolite cementation, characterizing one of the most singular features of the diagenetic history of the West Gondwana record.

Late Jurassic fluvial–eolian deposits from the Tianchihe Formation, Ningwu–Jingle Basin, Shanxi Province, China

Eolian systems were widespread in China in the Cretaceous. However, the reports of pre-Cretaceous eolian and its related systems are scarce, which prohibits studying the construction, accumulation and preservation of eolian systems as well as its allogenic and autogenic controlling factors. In this paper, we report on fluvial–eolian successions from the Late Jurassic Tianchihe Formation in the Ningwu–Jingle Basin. These successions represent the oldest reported inland fluvial–eolian systems in China. Fourteen lithofacies types are recognized in the Tianchihe Formation and have been grouped into six facies associations, including meandering fluvial channel, levee and overbank in the lower part, and eolian sandsheet, eolian dune, ephemeral fluvial channel and floodplain in the upper part. The fluvial system comprises a series of wetting upward cycles, which indicate humid climate culminating in high precipitation and shallow water table level. Eolian dune deposits composed of grainflow, grainfall, wind ripple strata and pin stripe laminations currently implies that all deposits types are internally bounded by reactivation surface and superimposition surface, suggesting compound dunes or draas. Eolian sandsheet deposits consist dominantly of subcritical climbing translatent strata and pin stripe lamination. The association of eolian dune and eolian sandsheet is development of a dry eolian system. Twelve drying upward cycles mainly composed of eolian sandsheet–eolian dune successions and four wetting upward cycles consisting of eolian sandsheet/dune–ephemeral fluvial channel/floodplain successions occur in the eolian system. These repeated cycles likely reflect an evolving erg system directly controlled by sediment supply, sediment availability and relative water table. The vertical transition from fluvial to eolian systems indicate a local climatic oscillation from relatively humid to arid conditions, which may be related with the uplift of the East China Plateau in the Late Jurassic.