Rodriguez-lopes Et Al 2014 Sedgeol

Archean to Recent aeolian sand systems and their sedimentaryrecord: Current understanding and future prospects

JUAN PEDRO RODRIGUEZ-L OPEZ*, LARS B. CLEMMENSEN , NICK LANCASTER ,NIGEL P. MOUNTNEY and GONZALO D.VEIGA*Departamento de Estratigrafa, Facultad de Ciencias Geologicas, Universidad Complutense deMadrid, Ciudad Universitaria, 28040 Madrid, Spain (E-mail: [email protected])Department of Geosciences and Natural Resource Management, Section of Geology, University ofCopenhagen, ster Voldgade 10, 1350 Kbenhavn K, DenmarkDivision of Earth and Ecosystem Sciences, Desert Research Institute (DRI), 2215 Raggio Parkway,Reno, NV 89512, USASchool of Earth and Environment, University of Leeds, Leeds LS2 9JT, UKCentro de Investigaciones Geologicas, Universidad Nacional de La Plata-CONICET, Calle 1 # 644,B1900TAC La Plata, Argentina

Associate Editor Charlie Bristow

ABSTRACT

The sedimentary record of aeolian sand systems extends from the Archean to

the Quaternary, yet current understanding of aeolian sedimentary processes

and product remains limited. Most preserved aeolian successions represent

inland sand-sea or dunefield (erg) deposits, whereas coastal systems are pri-

marily known from the Cenozoic. The complexity of aeolian sedimentary pro-

cesses and facies variability are under-represented and excessively simplified

in current facies models, which are not sufficiently refined to reliably account

for the complexity inherent in bedform morphology and migratory behaviour,

and therefore cannot be used to consistently account for and predict the nat-

ure of the preserved sedimentary record in terms of formative processes.

Archean and Neoproterozoic aeolian successions remain poorly constrained.

Palaeozoic ergs developed and accumulated in relation to the palaeogeograph-

ical location of land masses and desert belts. During the Triassic, widespread

desert conditions prevailed across much of Europe. During the Jurassic, exten-

sive ergs developed in North America and gave rise to anomalously thick aeo-

lian successions. Cretaceous aeolian successions are widespread in South

America, Africa, Asia, and locally in Europe (Spain) and the USA. Several

Eocene to Pliocene successions represent the direct precursors to the present-

day systems. Quaternary systems include major sand seas (ergs) in low-latti-

tude and mid-latitude arid regions, Pleistocene carbonate and HoloceneMod-ern siliciclastic coastal systems. The sedimentary record of most modern

aeolian systems remains largely unknown. The majority of palaeoenvironmen-

tal reconstructions of aeolian systems envisage transverse dunes, whereas suc-

cessions representing linear and star dunes remain under-recognized.

Research questions that remain to be answered include: (i) what factors con-

trol the preservation potential of different types of aeolian bedforms and what

are the characteristics of the deposits of different bedform types that can be

used for effective reconstruction of original bedform morphology; (ii) what

specific set of controlling conditions allow for sustained bedform climb versus

episodic sequence accumulation and preservation; (iii) can sophisticated

four-dimensional models be developed for complex patterns of spatial and

1487 2014 The Authors. Sedimentology 2014 International Association of Sedimentologists

Sedimentology (2014) 61, 14871534 doi: 10.1111/sed.12123

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temporal transition between different mechanisms of accumulation and pre-

servation; and (iv) is it reasonable to assume that the deposits of preserved

aeolian successions necessarily represent an unbiased record of the condi-

tions that prevailed during episodes of Earth history when large-scale aeolian

systems were active, or has the evidence to support the existence of other

major desert basins been lost for many periods throughout Earth history?

Keywords Aeolian, Archean, dunes, ergs, Mesozoic, Neogene, Palaeogene,Palaeozoic, preservation, Proterozoic, Quaternary.

INTRODUCTION

How can geologists best account for the pre-served expression of aeolian sedimentary suc-cessions and relate such deposits to the variedset of processes responsible for their generation?The answer my friend is blowin in the wind(Dylan, 1963), and has been for at least 32 bil-lion years. The aim of this study is to present anoverview of the current state of the science relat-ing to the sedimentology of aeolian sand sys-tems and their preserved successions. Specificobjectives are as follows: (i) to demonstrate thevariability and complexity of the sedimentologyof recent and ancient aeolian sand systems; (ii)to show how the spatial and temporal distribu-tion of aeolian systems and preserved succes-sions has varied throughout Earth history; (iii)to discuss the main mechanisms for the con-struction, accumulation and preservation of aeo-lian systems; and (iv) to present some futureperspectives relating to issues that currentlyremain unresolved in aeolian sedimentology,thereby highlighting research targets and oppor-tunities for the future. This study is supportedby a suite of complementary material arrangedin a series of tables that detail many of the best-known and most representative examples ofsiliciclastic, as well as some carbonate aeoliansand seas and coastal dunefields from theArchean and Proterozoic, Palaeozoic, Mesozoicand Cenozoic eras (see also Blakey et al., 1988;Tedford et al., 2005; Veiga et al., 2011a; Simp-son et al., 2012). Although this work representsan attempt to compile an authoritative databaseof case-study examples for all periods in Earthhistory, many smaller and lesser-known aeoliansystems have been omitted due to space limita-tions. The references contained in the supple-mentary tables of case studies (together withthose references cited in the main manuscript)are contained in the supplementary file entitledReferences text and tables.

AEOLIAN SAND SYSTEMS AND THEIRSEDIMENTARY RECORD: CURRENTUNDERSTANDING

Aeolian sand systems can be divided into inlandsand sea and coastal dune systems. Inland aeo-lian sand seas (also known as ergs) and the aeo-lian dunefields present within these large-scalesediment systems comprise bedforms of diffe-rent morphological types and sizes (rangingfrom ripples to megadunes or draas), areas ofsand sheets, interdunes (including non-aeoliansediments), as well as related extradune envi-ronments of alluvial, fluvial, lacustrine andmarine affinity. Coastal dunefields likewise com-prise various aeolian bedforms; many of thesedune types such as parabolic dunes are alsoseen in inland systems, whereas others suchas coast-parallel dune ridges are unique tocoastal systems. Associated sediments includebeach, wash-over fan and lagoon facies.Following Kocurek (1999), the creation of an

aeolian stratigraphic record can be considered inthree phases (Fig. 1): (i) sand-sea (i.e. dunefield)construction; (ii) aeolian accumulation; and (iii)preservation of that accumulation. Constructionof the worlds largest modern, active sand seasoccurs in arid regions that typically experienceless than 150 mm annual precipitation, althoughsites of significant aeolian construction alsooccur in non-desert settings, especially alongsandy coastlines. Although aeolian sedimenttransport takes place under a wide range ofwind energy regimes (Fryberger, 1979), it is thedirectional variability of such regimes that playsa major role in determining dune type, thereforedictating the range of sedimentary structuresthat develop on bedforms, and the style and rateof accumulation of deposits of those bedforms(Wasson & Hyde, 1983). Many present-dayactively constructing and accumulating sandseas are located at sites of relatively lower windenergy compared with upwind areas, such that

2014 The Authors. Sedimentology 2014 International Association of Sedimentologists, Sedimentology, 61, 14871534

1488 J. P. Rodrguez-Lopez et al.

sediment transport rates tend to decrease in thedirection of transport, thereby encouraging sanddeposition and accumulation. A down-windreduction in sediment transport rate that leadsto aeolian construction and accumulation mayresult from regional changes in atmospheric cir-culation patterns and wind regimes, wherebywind speed decreases and/or directional vari-ability increases (Wilson, 1973; Lancaster, 1999,2013). Coastal dunefields typically developalong lowland coasts where plentiful sedimentsupply (often beach sand) is available for inlandtransport by persistent onshore winds (e.g. Klijn,1990). The size and morphology of coastal dunesare dependent on vegetation cover, sand supply,beach-dune interaction, wind regime and coastalorientation with regard to persistent winds.Aeolian dunefield construction (the initiation

and growth of systems of bedforms) is a functionof sediment supply, the availability of that sup-ply for aeolian transport and the transportcapacity of the wind (Kocurek & Lancaster,1999). Sediment supply is the volume of sedi-ment suitable for aeolian transport generated perunit time; supply may be contemporaneous ortime-lagged (Kocurek, 1999) and can be derivedfrom multiple sources. The proximity of a dune-field to its sediment source area is reflected inthe response of the system to changes in boun-dary conditions. Dunefields that lie close totheir sediment source (including most coastaldunefields) tend to be sensitive to variations insediment supply, whereas systems that developfar from their ultimate source tend to be more

sensitive to changes in sediment mobility oravailability. Many sand seas are the depositionalsinks of local to regional-scale sediment trans-port systems. Mineralogical and geochemicalstudies, aided in some instances by remote sens-ing data, can establish clear relations betweensource areas and sediment sinks (e.g. Scheidtet al., 2011; Garzanti et al., 2012). In manyareas, however, these relations are not clear, andthe source(s) of sand for major sand seas in theSahara and elsewhere is (are) poorly constrained(Garzanti et al., 2003; Muhs, 2004). Regionalwind patterns appear to show long-distancetransport paths in the Sahara and Australia, butrecent work also points to the importance oflocal sources in Australia (Pell et al., 2000) andelsewhere (Muhs et al., 2003). The sand incoastal dunefields is derived primarily from thebeach; textural and geochemical studies offoredune deposits can give information on sedi-ment provinces and transport pathways in thenearshore environment (Saye & Pye, 2006). Sedi-ment availability is the susceptibility of surfacegrains to entrainment by the wind (Kocurek &Lancaster, 1999); stabilizing factors such as earlyintergranular cements (for example, gypsum),vegetation cover, coarse-grained lags and ele-vated water tables all limit availability. Trans-port capacity is a measure of the potentialsediment-carrying capacity of the wind.Together these factors define the sediment sys-tem state (Kocurek & Lancaster, 1999) which canbe used as a predictor of when and where epi-sodes of aeolian construction will occur.

Fig. 1. Schematic diagram showing the three-phase creation of the aeolian rock record and main controlling fac-tors as proposed by Kocurek (1999).


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Following Kocurek & Havholm (1993), threeprincipal types of aeolian systems (Fig. 2) are rec-ognized: (i) dry aeolian systems in which thewater table and its capillary fringe are sufficientlyfar below the depositional surface that they haveno effect on dune migration, sediment transportand deposition; (ii) wet aeolian systems in whichthe water table and its capillary fringe are at ornear the depositional surface, so that changes inmoisture play an important role in the style andpattern of sediment accumulation (Kocurek &Havholm, 1993; Mountney, 2012), and in whichinterdune areas are damp or wet (flooded) andcharacterized by clastic, biogenic and/or chemi-cal sediments that are indicative of a near-surfacewater table; and (iii) stabilized aeolian systems inwhich factors such as vegetation, pedogenesis,permafrost or surface or near-surface cementationeither episodically or continually act to stabilizethe substrate while the system remains activeoverall, thereby encouraging aeolian constructionand accumulation.

Aeolian accumulation to generate a body ofstrata requires a positive net sediment budget forwhich upstream sediment influx exceeds down-stream outflux (Fig. 3). Special cases include aeo-lian accumulation in front of steep cliffs (e.g.Clemmensen et al., 1997; Andreucci et al.,2010a). By contrast, neutral budgets and negativebudgets result in bypass and deflation (erosion),respectively. The positive net sediment budgetrequired for aeolian accumulation needs either adownstream spatial decrease in the transport ratein response to airflow deceleration or a temporaldecrease in flow concentration in response to areduction in dune size over time (Rubin & Hunter,1982; Kocurek & Havholm, 1993). One commonlyrecognized mechanism for the accumulation ofmigrating dunes and draas (mega-bedforms) is viabedform climbing, whereby the angle of climb(which for large bedforms might typically be onlya few tenths of a degree) is determined by the ratiobetween the rate of downwind bedform migrationand the rate of rise of the accumulation surface(Fig. 3). Climb at low angles means that only thebasal parts of large bedforms typically accumulateto generate cross-stratified sets (Fig. 3). Neverthe-less, accumulated, vertically stacked, cross-strati-fied sets recording the passage of multiple largebedforms are commonly each in excess of 10 m inthickness and some can attain thicknesses of>30 m (e.g. Mountney & Howell, 2000). The accu-mulation of sets via climbing and their composi-tion of only the basal-most parts of the originalbedforms from which they were constructed meanthat ancient aeolian accumulations are biased rep-resentations of original aeolian systems becausethey are composed of assemblages of lithofaciesarranged into architectural elements that typicallyrecord only those processes that operated on thelowermost flanks of the original bedforms; suchprocesses typically differ from those that operatedon the higher parts of bedforms (e.g. Eastwoodet al., 2012).Interdune migration bounding surfaces separate

packages of strata that represent the accumulateddeposits of successive migrating aeolian dunesand adjoining interdunes; superimpositionbounding surfaces record the style of juxtaposi-tion of smaller dunes on larger draas, and thestyle of migration of the smaller forms over thelarger forms; reactivation surfaces record episodicchanges in dune or draa lee-slope configuration,including temporal changes in steepness or orien-tation (Rubin, 1987; Rubin & Carter, 2006). Thesebounding-surface types define and delineatearchitectural elements comprising packages of

Fig. 2. Characteristics of dry, wet and stabilizing aeo-lian systems illustrating the role of aerodynamic con-figuration, water-table level and stabilizing agent ascontrols on accumulation space. After Kocurek (1998).



aeolian dune and interdune strata that are them-selves composed internally of various arrange-ments of lithofacies (Brookfield, 1977; Kocurek,1991; Chrintz & Clemmensen, 1993; Fryberger,1993). The geometry and arrangement of thesearchitectural elements are determined by: (i) thescale and morphology of the original dunes andinterdunes; (ii) the style of migration of the dunesand interdunes over both time and space; and (iii)the style of accumulation, which in many systemsis controlled by the angle of climb (e.g. Mountney& Thompson, 2002), although in other systems itis known to be controlled by other mechanisms,including the infilling of local accommodationspace between older remnant dunes (e.g. Langfordet al., 2008).When and where the net sediment budget

switches from positive to neutral or negative, aeo-lian accumulation ceases and bypass and defla-

tion commence, respectively. Both bypass anddeflation result in the generation of supersurfaces(Kocurek, 1988) that cap underlying accumula-tions. Such accumulations define aeoliansequences and their bounding supersurfaces canbe considered sequence boundaries (Fig. 4). Defla-tion operates either until the net sediment fluxbecomes neutral or positive again, or until it pro-gresses down to the water table (Stokes, 1968),which limits further deflation. Supersurfaces ofallogenic origin tend to be regional in extent andtruncate other bounding-surface types of auto-genic origin, which themselves arise as a conse-quence of interdune migration and climb,bedform superimpositioning or bedform reactiva-tion (Brookfield, 1977, Rubin, 1987; Mountney,2006a). Some supersurfaces have been correlatedlaterally into adjoining non-aeolian environmentswhere they merge into, for example, transgressive

Ang

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Proportion of accumulationsurface covered by dunes =

Dune wavelengthDune spacing

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BYPASSING AEOLIAN SYSTEMS

WET AND STABILIZING AEOLIAN SYSTEMS DRY AEOLIAN SYSTEMS

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Generation of bypass supersurface

Fig. 3. Spectrum of preserved dune and interdune architectures resulting from temporally and spatially invariable(i.e. static) aeolian system behaviour. The angle of bedform climb defines fields of accumulation and deflation,with bypass occurring when the angle of climb is zero. Within the field of accumulation, preserved sedimentaryarchitecture is partly determined by the proportion of the accumulation surface covered by dunes. Accumulatingdry aeolian systems typically require 100% dune cover whereby dunes have been constructed to a size where in-terdunes are reduced to isolated depressions between bedforms. Accumulating wet or stabilizing systems haveless than 100% dune cover. The angle of climb is determined by the ratio of the vertical accumulation rate andbedform migration rate. The stratal configurations are scale-independent and can potentially occur in systems ofany size; after Mountney (2012). Bedform spacing is the crest to crest (or toe to toe) distance between adjacentbedforms in an orientation perpendicular to the trend of elongate bedform crestlines; dune wavelength recordsthe extent of a bedform in an orientation perpendicular to the trend of the bedform crestline and this may varyfrom a maximum dune wavelength to a minimum dune wavelength within one dune segment as a function ofbedform sinuosity (Al-Masrahy & Mountney, 2013). Bedform spacing and dune wavelength will be the same forstraight-crested dunes that lack intervening interdune flats.



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AB

C

D

E

F

Fig. 4. Spectrum of interdune geometries generated by variations in the frequency and magnitude of water-tablechange, the rate of dune migration and the net aeolian sediment budget. (A) Entrada Sandstone, Kocurek (1981a).(B) Navajo Sandstone (Herries, 1993). (C) and (D) Helsby Sandstone Formation (Mountney & Thompson, 2002). (E)Cedar Mesa Sandstone (Langford & Chan, 1988, 1989; Mountney & Jagger, 2004). (F) White Sands (Simpson &Loope, 1985; Loope & Simpson, 1992). Modified after Mountney & Thompson (2002).



marine units (Havholm et al., 1993; Blakey, 1996;Blakey et al., 1996; Rodrguez-Lopez et al., 2013).Many supersurfaces that bound episodes of aeo-lian accumulation are paraconformities (diastems)considered to represent long-lived hiatuses inaccumulation: supersurfaces with associated sedi-mentary features such as large and closely spacedtree-size rhizoliths may take 104 to 105 years toform (Loope, 1985). Several authors have pro-posed that aeolian supersurface generation mayoccur as a result of Milankovitch-style orbital forc-ing operating with periodicities of 18 to 400 kyr(Loope, 1985; Clemmensen et al., 1994; Mount-ney, 2006b; Jordan & Mountney, 2010, 2012;Rodrguez-Lopez et al., 2012a). For many systems,the amount of time represented by aeolian accu-mulations probably is significantly less than thatrepresented by intervening supersurfaces (e.g. Lo-ope, 1985); thus, many preserved aeolian succes-sions probably represent only a fraction of thegeological time over which the aeolian systemswere active, and the preserved record is thereforehighly fragmentary and potentially biased towardsa specific set of formative processes.Long-term preservation of aeolian accumula-

tions in the ancient record requires that thebody of strata is placed below some regionalbaseline, beneath which erosion does not occur(Kocurek & Havholm, 1993). Thus, the rate ofgeneration of accommodation space and the rateat which aeolian accumulations fill that space isa fundamental control on preserved architecturalstyle (e.g. Howell & Mountney, 1997).Approaches to the theoretical modelling of aeo-

lian dune and interdune successions commencedwith the development of purely qualitative depo-sitional models for aeolian systems. Many suchmodels were devised in the 1970s and commonlyrecognised packages of aeolian dune and inter-dune lithofacies occurring as elements delineatedby bounding surfaces (e.g. Brookfield, 1977).These models, which typically accounted forstratigraphic complexity in two spatial dimen-sions, are the so-called static aeolian depositional(or facies) models (Mountney, 2006a). One for-ward stratigraphic modelling approach to accountfor both spatial and temporal changes in aeolianarchitecture has led to the establishment of a con-ceptual framework for the classification of aeoliansystems and their accumulated successions(Mountney, 2012). This framework identifies sim-ple, static system architectures, that are generatedby spatially and temporally invariable controls,but additionally identifies and models dynamicsystem architectures in which spatial and tempo-

ral changes in dune morphology, scale and styleof migration and accumulation (for example,angle of climb) give rise to more complex pre-served architectures.

EVOLUTION OF AEOLIAN SANDSYSTEMS THROUGH EARTH HISTORY

Archean and Proterozoic aeolian sandsystems (Table S1)

The oldest known aeolian system is the 32 to30 Ga Lower Moodies Group of the SwazilandSupergroup in South Africa (Table S1), whichaccumulated in a series of intramontane exten-sional basins through which simple barchandunes migrated (Simpson et al., 2012). The pal-aeogeographical distribution of Archaean andProterozoic aeolian systems was dictated by theworldwide geographical distribution of Archaeanand Proterozoic cratons and, due to their extremeage, the preserved global record of aeolian sys-tems from these Eons is highly fragmentary. Pal-aeoproterozoic aeolian systems accumulated inintracratonic sag basins, intracratonic and inter-continental extensional rift basins (both duringrift and thermal phases of basin evolution) andtranstensional basins (e.g. Rainbird et al., 2003;Master et al. 2010). Mesoproterozoic aeolian sys-tems accumulated in intracratonic and intramon-tane basins, rift basins and transpressive strike-slip basins (e.g. Clemmensen, 1988; Martin &Thorne, 2002). Neoproterozoic aeolian systemsaccumulated in intracratonic rift basins (e.g. Greyet al. 2005; Sarkar et al., 2011). From this, it isclear that the majority of preserved Precambrianaeolian systems are syn-rift depositional systemsin which preservation of aeolian depositsoccurred during the rifting phases of superconti-nents because of the associated increase in accom-modation space (Eriksson & Simpson, 1998).Pre-vegetation Archean and Proterozoic peri-

ods were not subject to palaeoenvironmental con-ditions that were especially well-suited to aeoliansediment accumulation and preservation (Eriks-son & Simpson, 1998). The absence of vegetationas a stabilizing agent favoured aqueous-reworkingof pre-existing aeolian deposits, leading to theirpartial or total destruction, reworking and incor-poration into a variety of coeval sedimentaryenvironments (e.g. Tirsgaard & xnevad, 1998).Proterozoic aeolian systems developed in asso-

ciation with a variety of coeval depositional sys-tems and led to fluvialaeolian interactions, such



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as those from the Palaeoproterozoic MakgabenFormation (Waterberg Supergroup, South Africa,Eriksson et al., 2000; Simpson et al., 2002), Ama-rook Formation (Wharton Group, Canada, Rain-bird & Hadlari, 2000; Rainbird et al., 2003) andThelon Formation (Barrensland Group, Canada,Rainbird et al., 2003). Marine reworking of Pre-cambrian aeolian deposits was apparently awidely occurring process along Proterozoic coast-lines; documented examples include the Palaeo-proterozoic Quartzite Member, MchekaFormation, Zimbabwe (Master et al., 2010), theWhitworth Formation, Haslingden Group, Aus-tralia (Simpson & Eriksson, 1993) and the Neo-proterozoic Venkatpur Sandstone, India(Chakraborty, 1991).Comparison of Proterozoic and Phanerozoic erg

systems reveals a general trend towards the pres-ervation of more complex aeolian systems duringthe Proterozoic. The general atmospheric circula-tion pattern influenced by palaeogeographicalchanges, palaeoland mass distributions and asso-ciated orogenic buildups, and the particular prop-erties and characteristics of Archaean andProterozoic atmospheres could have had a diffe-rent effect on aeolian transport compared toequivalent processes that operated during thePhanerozoic. Studies by Han et al. (2014) havedemonstrated that, for a particular wind speed,the ability of the air flow to transport sanddecreases with lower air density; however, underthe same conditions, the saltation heightincreases. Taking into account that recent workslike that of Som et al. (2012) have concluded thatthe density of the 27 Ga atmosphere was lessthan twice modern levels, it is possible thatchanges in air density over geological timescalescould have influenced aeolian transport mecha-nisms, and this might be recorded by the predom-inance of different aeolian bedforms at differenttimes. For example, documented examples of co-sets of strata interpreted to represent the pre-served accumulations of draa-scale bedforms arenumerous for Precambrian successions. Further-more, the preservation of very coarse-grained (si-liciclastic) Precambrian aeolian successions (for

example, the Egalapemta Member, Mesoprotero-zoic, India; Biswas, 2005) is noteworthy. The spe-cific dynamic configuration of the Precambrianatmosphere and its interaction with sedimentgrains could explain the occurrence of simple butgiant transverse dunes with maximum preservedset thicknesses (more than 50 m thick), such asthe single aeolian dune cross-bedded set recordedfrom the Late Neoproterozoic McFadden Forma-tion (Western Australia; Grey et al., 2005).The absence of Phanerozoic cold (periglacial)

aeolian dunefields compared with their occur-rence in Precambrian times is notable. The Neo-proterozoic Bakoye 3 Formation, Bakoye Groupfrom Mali (Deynoux et al., 1989) and the Neopro-terozoic Whyalla Sandstone from Australia (Wil-liams, 1998) constitute the only two examples ofPre-Cenozoic periglacial dunefields. This scarcityof periglacial dunefields in the fossil recordcould be a result of misinterpretation of theparticular palaeoclimate setting in which somePrecambrian and Phanerozoic aeolian systemsformed. A re-evaluation of this topic is needed. Itis known that glacial latitudes have changedthrough time (see Evans, 2003). The possibilitythat cold deserts could have formed in associa-tion with glacier fronts even during the Phanero-zoic should be considered. Particular attentionshould be paid to the latitudinal variation of theequilibrium-line altitude (ELA) as a control ofglaciation through time (e.g. Isbell et al., 2012).

Palaeozoic aeolian sand systems (Table S2)

During the Cambrian, ergs were located in themain land masses in the Southern Hemisphere(Fig. 5A). The Backbone Ranges Formation(Mackenzie Mountains, Canada; MacNaughtonet al., 1997) and the Wonewoc Formation (Wis-consin and Minnesota, USA; Dott et al., 1986;Runkel et al., 1998) accumulated in southernLaurentia where interaction between ergs andcoastal systems adjacent to the Iapetus Oceanoccurred (Fig. 5A). The Amin Formation andthe Lower Haima Group in Oman (Milson et al.,1996) and the Lower Roan Formation in Zambia

Fig. 5. Palaeogeographic distribution of siliciclastic aeolian sand systems during: (A) Late Cambrian. During theCambrian, ergs were located in main land masses at the Southern Hemisphere (Laurentia and north-easterm Gond-wana), under the influence of easterly trade winds between the Equator and 30 palaeolatitude. (B) Middle Ordovician.Main ergs of Cambro-Ordovician and Ordovician age were located in Laurentia and eastern Gondwana under the activ-ity of trade winds of subtropical low pressure systems. (C) Middle Silurian. Main Silurian and Siluro-Devonian aeoliandeposits are located in western/central Australia, located at the southern palaeo-hemisphere desert zone. (D) EarlyDevonian. Palaeogeographic maps from Scotese (2001) PALEOMAP Project. For legend see Figure 6D.



AB

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(Annels, 1989) accumulated as inland sandydeserts in Gondwana (Fig. 5A). Many Cambrianergs accumulated under the influence of easterlytrade winds, between the Equator and 30 pal-aeolatitude (Fig. 5A; see Dott et al., 1986).Cambro-Ordovician and Ordovician ergs were

less widespread than those of Cambrian age(Fig. 5B). Such aeolian systems again developedunder the influence of active trade winds of sub-tropical high-pressure systems in land masses ofthe southern palaeo-hemisphere in Laurentia andGondwana (Fig. 5B) (for example, the Pedra Pin-tada Formation/Alloformation; Paim & Scherer,2007; de Almeida et al., 2009). In particular, aeo-lian dunefields developed in southern Laurentiarecord marineaeolian interactions characterizedby complex associations of facies of both aeolianand aqueous origin, as is the case for the Cambro-Ordovician Nepean Formation (Postdam Group,Canada and USA; Malhame, 2007) and the Ordo-vician St. Peter Sandstone (Minnesota and Wis-consin, USA; Dott et al., 1986). In particular, theSt. Peter erg succession records palaeowinds thatare in agreement with more general reconstruc-tions of the southern palaeo-trade wind belt (Dottet al., 1986).Silurian and Siluro-Devonian aeolian succes-

sions are few in number. The main preservedsystems accumulated in Western (Perth-Carnar-von Basin) (Trewin & Fallick, 2000) and Central(Amadeus Basins) Australia (Fig. 5C) (Shawet al., 1991). The Swanshaw Sandstone Forma-tion of Scotland constitutes a mixed aeolianflu-vial succession developed in the transtensionalLanark Basin (Smith et al., 2006). These Silurianand Siluro-Devonian systems developed in thesouthern palaeo-hemisphere desert belt.During the Devonian, the assembly of Laurussia

in response to the final stages of the plate colli-sions of the Caledonian Orogeny, and the north-ward migration of Gondwana, led to an increaseof land masses present at subtropical latitudesthat were subject to the influence of the southernpalaeo-hemisphere desert belt (Fig. 5D). This pal-aeogeographical configuration enabled the con-struction, accumulation and preservation ofseveral major aeolian dunefield systems (Fig. 5D).

The most representative Devonian aeolian sys-tems are those forming part of the Old Red Sand-stone of North West Europe (e.g. Browne et al.,2002; Morrisey et al., 2012) which accumulatedin extensional basins formed as a result of the col-lapse of the overthickened crustal belt resultingfrom Caledonian compressional tectonics(McClay et al., 1986). The Old Red Sandstoneexhibits a variety of aeolian facies, many ofwhich record windwater interaction processes(for example, the Middle Devonian YesnabySandstone Group, Lower Old Red SandstoneSupergroup, Scotland; Trewin & Thirlwall, 2002).Devonian ergs are characterized by a variety of

aeolian facies including aeolian sandsheet suc-cessions (for example, the Lower Clair Group,Clair Basin, UK; Nichols, 2005), aeolian dunefieldsuccessions composed of transverse dune depo-sits (for example, the Slieve Mish Group, Ireland;Horne, 1971), barchanoid dune deposits (forexample, the Devonian of Scotland; Allen & Mar-shall, 1981) and draa deposits (for example, theKilmurry Sandstone Formation, Ireland, Dodd,1986; the Eday Sandstone, Eday Group, Scotland,Marshall et al., 1996). Devonian aeolian dune-field successions with draa and barchanoid dunedeposits are preserved in north-east Greenlandand these demonstrate aeolian interaction withephemeral streams and terminal fans (see Olsen& Larsen, 1993). Other Devonian aeolian systemshave been recorded from Antarctica (New Moun-tain Sandstone; Gilmer, 2008) and Australia (forexample, the Langra Formation, Jones, 1972; theTandalgoo Sandstone, Thornton, 1990).The majority of Carboniferous aeolian systems

are Pennsylvanian in age, with several spanningthe PennsylvanianPermian boundary. Someexamples of early Carboniferous aeolian systemsinclude the Devonian to Mid-CarboniferousKhusayyayn Formation in Saudi Arabia (Stump& Van der Eem, 1995), the recently recognizedaeolian systems of the Late Mississippian Loyal-hanna Member, Pennsylvania, USA (the MauchChunk Formation and Appalachian Formation;Swezey et al., 2012) and the DevonianMissis-sippian Harder Bjerg Formation in Greenland(Olsen & Larsen, 1993; Fig. 6A).

Fig. 6. Palaeogeographic distribution of siliciclastic aeolian sand systems during: (A) Early Carboniferous. EarlyCarboniferous aeolian systems were located in southern Laurrusia and at the northern margin of Gondwana. (B) LateCarboniferous. Late Carboniferous-Permian aeolian systems were located in Pangea supercontinent both at Northernand Southern Hemispheres. Other aeolian systems developed in northern Gondwana (Bolivia and Argentina). (C)Late Permian. During Permian times extensive erg systems developed on Pangaea, favoured by the location of thissupercontinent in subtropical latitudes under the influence of the southern and northern palaeo-hemisphere desertzones. Palaeogeographic maps from Scotese (2001) PALEOMAP Project. (D) Legend is for Figures 58.



A C

B



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During the Variscan Orogeny, Gondwana andLaurussia collided creating the SupercontinentPangaea; Pennsylvanian to Permian aeolian sys-tems were constructed in both the Northern andSouthern Hemispheres (Fig. 6B). The main sys-tems crop out in North and South America, withwell-developed examples including the EarlyPennsylvanian Jurua Sandstone Formation (theSolim~oes Basin, Brazil; Elias et al., 2007), thePennsylvanian Tyrwhitt and Tobermory Sand-stone Formations (the Rocky Mountain Super-group, Canada; Stewart & Walker, 1980) and thePennsylvanianMiddle Permian Cangapi Forma-tion (the Cuevo Group, Tarija Basin, Bolivia andArgentina; Hernandez & Echevarra, 2009), theLate CarboniferousEarly Permian Patqua For-mation (the Paganzo Group, Paganzo Basin,Argentina; Caselli & Limarino, 2002; Geunaet al., 2010). In Saudi Arabia, the Carbonife-rousPermian Unayzah Formation constitutes aneconomically important gas reservoir succession(Melvin & Heine, 2004; Melvin et al., 2010).The best-known PennsylvanianPermian ergs

are reported from the USA. The Tensleep Com-plex (the Tensleep Sandstone, Casper Forma-tion, Quadrant Sandstone; e.g. Peterson, 1988),the Honaker Trial Formation (e.g. Williams,2009) and the Cutler Group, including the lowerCutler beds (e.g. Jordan & Mountney, 2010,2012; Wakefield & Mountney, 2013), the RicoFormation (e.g. Loope, 1985; Chan & Kocurek,1988) and the Weber Sandstone (e.g. Doe & Dott,1980; Driese, 1985) are all successions that exhi-bit well-exposed examples of central-erg anderg-margin systems (see Blakey et al., 1988, forfurther examples).During the Permian, the construction of exten-

sive erg systems across large parts of Pangaeawas favoured by the location of land masses ofthis supercontinent in subtropical latitudesunder the influence of the southern and north-ern palaeo-hemisphere desert zones (Fig. 6C).The best-known Permian aeolian systems are theRotliegend Group (Rotliegendes) of the NorthSea and North-west Europe, and the Permianaeolian systems from the USA (Fig. 6C). Majorreserves of gas (and some oil) exist in PermianRotliegend desert sandstone hydrocarbon reser-voirs of North-west Europe, in particular in theSouthern Permian Basin of the North Sea andsome localities in the Northern Permian Basin(Glennie, 1970, 1972, 1998; Glennie & Buller,1983).In the Southern Permian Basin of the North

Sea, aeolian dune deposits accumulated between

wadi channels originating from the VariscanHighlands and the extensive sabkha and desertlake located southwards of the Ringkbing-FynHigh (Glennie, 1972). Reconstructed aeoliandune types of the Rotliegend Group includetransverse-crescentic dunes, barchans, longitudi-nal/linear and star dunes (for example, the Bro-dick Beds; Clemmensen & Abrahamsen, 1983;the Leman Sandstone Formation, Sweet, 1999;the Penrith Sandstone, Turner et al., 1995; Lov-ell et al., 2006), as well as interdraa, draa-plinthand draa-centre deposits (for example, YellowSands; Clemmensen, 1989; Chrintz & Clemmen-sen, 1993). Complex wind patterns resulted inthe construction of barchanoid draa with super-imposed oblique crescentic and linear dunes(for example, the Bridgnorth Sandstone Forma-tion, UK; Steele, 1981; Benton et al., 2002).Permian sedimentary basins of the USA con-

tain extensive and complex aeolian depositionalsystems and record a variety of facies and pro-cesses (see Blakey et al., 1988, for compilation).Examples of these Permian aeolian units includethe Schnebly Sandstone Formation, which com-prises deposits of an aeolian dunefield associ-ated with evaporite and carbonate deposits(Blakey & Middleton, 1983; Blakey, 1990), andthe Lyons Sandstone Formation with deposits ofparabolic dunes and blowout-type interdunes(McKee, 1979).Several Permian units in the USA preserve

complete examples of central-erg sequences thatdemonstrate evidence for a complex merging rela-tion with marine erg-margin systems. Examplesinclude the White Rim Sandstone (e.g. Chan,1989; Tewes & Loope, 1992; Kamola & Huntoon,1994), the De Chelly Sandstone (e.g. Blakey,1990; Stanesco, 1991), the Yeso Formation (Mack& Dinterman, 2002) and the Upper MinnelusaFormation (e.g. Fryberger, 1984, 1993).The Permian Coconino Sandstone constitutes

the accumulation of an inland dry erg systemformed by climbing barchans or barchanoid-ridge and transverse dunes (e.g. Blakey & Mid-dleton, 1983; Blakey, 1990, 1996). Some Per-mian ergs display examples of fluvial systemsreworking the aeolian sands; this is the case forthe Rush Springs Sandstone (the WhitehorseGroup; Kocurek & Kirkland, 1998; Poland &Simms, 2012), the Cedar Mesa Sandstone of theParadox foreland basin (Langford & Chan, 1988,1989; Mountney & Jagger, 2004; Mountney,2006a; Langford et al., 2008) and the overlyingOrgan Rock Formation (Cain & Mountney,2009, 2011).



Permian aeolian systems developed in theSouthern Hemisphere in Pangaea (Fig. 6C)include the Piramboia Formation in Brazil(Parana Basin; Dias & Scherer, 2008), the BuenaVista Formation in Uruguay (Northern Urugua-yan Basin; Goso et al., 2001) and the Permianaeolian systems of Argentina from the retroarcPaganzo Basin (for example, the Andapaico For-mation and the De la Cuesta Formation; Spallettiet al., 2010; Correa et al., 2012).

Mesozoic aeolian sand systems (Table S3)

Throughout much of the Triassic, widespreadaeolian desert and semi-desert conditions pre-vailed across much of northern Pangaea. Themajority of Triassic ergs were located in equato-rial to mid-latitudes in the Northern Hemisphereand most of these appear to be aligned followinga northsouth trend close to the eastern marginof Northern Gondwana (Fig. 7A). Triassic ergsystems of north-eastern Pangaea include theBuntsandstein of Europe, which is characterizedby a thick accumulation of red beds that recorda variety of aeolian and mixed aeolianfluviallacustrine successions (e.g. Clemmensen, 1985;Mader, 1985, Mader & Laming, 1985; Tietzeet al., 1997). The Triassic Buntsandstein faciesin the north-eastern Iberian Chain (central east-ern Spain), previously considered to be fluvialin origin, is now known to contain an evolvingerg system (Soria et al., 2011) which comprisesa succession that records the transition from awadi belt, via an inner erg-margin, to a central-erg system.The equivalent lithostratigraphic unit to the

Buntsandstein in the UK and Ireland is theSherwood Sandstone Group (New Red Sand-stone) which is present in a series of rift basinsin both onshore and offshore settings (Fig. 7A;Brookfield, 2004, 2008; Tyrrell et al., 2009). Aeo-lian dunefields were mostly characterized bybedforms of modest size, many with damp orwet interdunes controlled by the water table, asrecorded, for example, by the Wilmslow Forma-tion (xnevad, 1991; Bloomfield et al., 2006)and the Helsby Formation (Mountney & Thomp-son, 2002; Bloomfield et al., 2006) of theCheshire Basin. In Scotland, the Hopeman Sand-stone probably straddles the PermianTriassicboundary and is characterized by deposits of thepreserved remnants of a series of star dune anddraa bedforms representing a small fragment ofwhat is inferred to have been a very extensivedry aeolian system (Clemmensen, 1987; Glennie

& Hurst, 2007; Hurst & Glennie, 2008). In thesubsurface of the East Irish Sea Basin, Triassicaeolian deposits form important reservoirs forgas (Cowan & Boycott-Brown, 2003; Meadows,2006).Triassic ergs constructed close to the palaeo-

equator (for example, the Oukaimeden Sand-stone Formation, Morocco) record small aeoliandunes developed on floodplains of ephemeralfluvial systems (Fabuel-Perez et al., 2009; Mader& Redfern, 2011). Other Triassic ergs are locatedclose to the western margin of Northern Pangaeaand examples include the Nugget Sandstone ofUtah and Wyoming (Fig. 7A) (Sprinkel et al.,2011) which may be, at least in part, of LowerJurassic age.Thick and geographically widespread Jurassic

aeolian desert erg successions of the ColoradoPlateau region are extensively documented andare arguably the most intensely studied of allaeolian successions. Many authors have consi-dered these successions collectively in terms ofthe regional palaeogeographical, palaeoclimaticand palaeotectonic setting (Fig. 7B and C; e.g.Kocurek & Dott, 1983; Blakey et al., 1988; Dick-inson & Gehrels, 2003; Loope et al., 2004). Thebest-known Jurassic aeolian successions of thesouth-western United States include the Win-gate and Navajo sandstones (and stratigraphicequivalents) of the Lower Jurassic Glen CanyonGroup, and the Page and Entrada sandstones(and equivalents) of the Middle Jurassic SanRafael Group. The Wingate Sandstone representsa largely dry aeolian system representative of anerg-centre setting (with compound-draa develop-ment) and also demonstrates styles of inter-action with fluvial deposits of the MoenaveFormation in its erg-margin setting (Clemmensen& Blakey, 1989; Clemmensen et al., 1989; Tan-ner & Lucas, 2007). The Navajo Sandstone of theGlen Canyon Group is one of the most intenselystudied sedimentary formations of any type andis well-exposed across much of the ColoradoPlateau region, where it attains a thickness ofnearly 700 m in south-western Utah. The suc-cession represents the preserved remnant of agiant erg that was present across much of thewestern part of Pangaea (Fig. 7B; Hunter & Ru-bin, 1983; Chan & Archer, 2000); this systemwas subject to seasonal wind reversals associ-ated with annual monsoons that occurred eachsummer when more humid and cooler condi-tions prevailed and wind reversal occurred (Lo-ope & Rowe, 2003; Loope et al., 2008). The PageSandstone of Arizona and southern Utah repre-



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A CDB



sents accumulation in an erg system close to themargin of an interior seaway; the system is com-posed of vertically stacked, progradational ergsequences that overlie marine deposits of theCarmel Formation such that the two units inter-tongue (Jones and Blakey, 1993; Havholm &Kocurek, 1994; Dickinson et al., 2010). TheEntrada Sandstone of the San Rafael Group isexposed extensively across much of the Colo-rado Plateau region and represents the accumu-lated deposits of a coastal to inland aeoliansystem that was characterized by a complexarrangement of aeolian dune, damp and wet in-terdune, and sabkha elements (Kocurek, 1980,1981a,b; Crabaugh & Kocurek, 1993; Crabaugh &Kocurek, 1998). Relic dune topography is pre-served in places at the top of the succession as aresult of later marine transgression (Benan &Kocurek, 2000).The Upper Jurassic Norphlet Sandstone repre-

sents the accumulated deposits of a major aeo-lian erg succession that is known principallyfrom the subsurface of Alabama, the shallow-water Gulf of Mexico around Mobile Bay, andfurther offshore in the deep-water part of theGulf of Mexico, where it forms a major oil reser-voir (Taylor et al., 2004; Mankiewicz et al.,2009; Ajdukiewicz et al., 2010). Numerous aeo-lian successions of Jurassic age are documentedfrom South America and especially from Brazil.Examples include the Pedreira Sandstone of theParana Basin in Brazil, which is characterizedby climbing aeolian dune sets with interveningdamp and wet interdune units (Nowatzki &Kern, 2000) and the Guara Formation of south-

ern Brazil, which records composite crescenticaeolian dune sets and cosets, and aeolian sand-sheet elements interbedded with distal flooddeposits and fluvial channel-fill elements(Scherer & Lavina, 2006).The backarc Neuquen basin of Argentina

records a series of Jurassic aeolian successions.The Lotena Formation preserves a record of aeo-lianfluvial interactions (Veiga et al., 2011a). Atectonic inversion during the Late Jurassic led tothe desiccation of the entire basin, giving rise toa complex array of continental facies for whichaeolian deposits form a major part (Spalletti &Veiga, 2007, Spalletti et al., 2011). In the south-ern part of the basin, an upward vertical transi-tion from fluvial-dominated to aeolian-dominated deposition, probably arising from aclimatic shift to drier conditions, is recorded aspart of the Kimmeridgian Quebrada del Sapoand Tordillo formations (Zavala et al., 2005a;Veiga & Spalletti, 2007). The Tordillo Formationrepresents migration and accumulation of trans-verse and barchan dunes in a style that gene-rated a complex hierarchy of internal boundingsurfaces within a largely dry aeolian system inwhich only thin dry interdune elements accu-mulated (Zavala et al., 2005a). To the east, aeo-lian accumulation was more significant and ledto the preservation of a ca 300 m thick sequenceof mainly aeolian deposits of the Sierras Blancasand Catriel formations, which include depositsof dune, wet and dry interdune and aeoliansandsheet elements (Maretto et al., 2002; Spal-letti et al., 2011). The Piramboia Formation ofEntre Rios Province, Argentina, is an aeolian

Fig. 7. Palaeogeographic distribution of siliciclastic aeolian sand systems during: (A) Early Triassic. Triassic ergsystems occupied a broad belt across the tropical latitudes of northern Pangea in areas now occupied by Europeand North America. Other Southern Hemisphere erg systems are recorded from Gondwana (S. Africa and India).(B) Early Jurassic. The main erg systems of the Early Jurassic include the geographically widespread accumula-tions of the Glen Canyon Group in the western USA (including the Wingate, Navajo and Page sandstones) andaccumulations in the Parana and Neuquen basins. (C) Late Jurassic. The main erg systems of the Late Jurassicinclude the geographically widespread accumulations of the San Rafael Group in the western USA (including theEntrada Sandstone) and accumulations in the Parana Basin (Brazil) and southern Africa. (D) Late Cretaceous. Cre-taceous erg systems were geographically widely distributed in tropical and mid-latitudes in both the Northernand Southern Hemispheres, with major dunefields occupying SW Africa and Central Brazil prior to and immedi-ately following the onset of break up of western Gondwana. Other major ergs were located in northern China andSpain. Palaeogeographic maps from Scotese (2001) PALEOMAP Project. For each map, the aeolian successionsshown are not all necessarily of the same age and, therefore, were not necessarily all active at the same time. Fur-thermore, the global palaeogeographies depicted in each map might not necessarily be entirely accurate for aeo-lian successions that are slightly older or younger than the age shown in the maps. For example, the earlyCretaceous Botucatu Sandstone of the Parana Basin of Brazil and the Etjo Sandstone of NW Namibia are consi-dered to represent preserved portions of the same erg system that developed prior to the onset of opening of theSouth Atlantic, yet the palaeogeographic map shown depicts an interval in the Late Cretaceous, shortly after theonset of the opening of the south Atlantic. For legend see Figure 6D.



STATEOFTHESCIENCE

unit considered to be primarily of Lower Juras-sic age (Silva & Fernandez, 2004).The Lower Jurassic Clarens Formation, which

forms a unit of the Karoo Supergroup in SouthAfrica, records a progressive upward transitionfrom the deposits of a wet aeolian system thatdeveloped alongside coeval ephemeral fluvialsystems to a dry aeolian system dominated bystacked cross-bedded aeolian dune sets (Bordy &Catuneanu, 2002; Holzforster, 2007).Cretaceous aeolian successions, together with

those that probably span the JurassicCretaceousboundary, are numerous in South America andmany have been the focus of detailed study overseveral decades (Fig. 7D). The Botucatu Forma-tion of the Parana Basin (S~ao Paulo and Paranastates, Brazil) which was originally thought tobe Triassic in age (Bigarella, 1979) has lateralequivalents in Parnaiba Basin of northern Braziland is a near-equivalent of the Bauru, Guara,Sambaiba, Sanga do Cabral and Piramboia for-mations, as well as of the Etjo Sandstone inNamibia (Mountney et al., 1999a,b), and possi-bly the Kudu Formation, offshore Namibia(Mello et al., 2011). Relic aeolian dune formsand degraded topography are preserved at thetop of the succession where it is overlain byflood basalts of the Serra Geral Formation andother flood basalts related to the Etendeka-Parana Large Igneous Province (Scherer, 2002;Waichel et al., 2008). The Serra Geral Formationrecords the exceptional preservation of relic aeo-lian dune topography of a dry aeolian system byflood basalts including various types of com-pletely preserved dunes and sand-deformationfeatures, including sand diapirs and peperite-like breccia.In the backarc Neuquen Basin of west-central

Argentina, Lower Cretaceous sandy aeolianaccumulations are numerous and mainly relatedto lowstand periods and to the possible discon-nection of the basin from the proto-PacificOcean (Howell et al., 2005). These successionsconstitute important conventional oil and gasreservoirs. Aeolian deposits have been describedfrom part of the proximal system of the Valan-ginian Mulichinco Formation in the subsurfaceof the basin (Zavala et al., 2005b) and, moremarginally, as part of environments of fluvialaeolian interaction (Schwarz et al., 2011). Oneof the best-described aeolian systems in thebasin is the Hauterivian Avile Member of theAgrio Formation (Rossi, 2001; Veiga et al.,2011b). Within this non-marine unit, aeoliandeposits are locally important and record a com-

plex vertical evolution related to high-frequencyclimatic changes and to the development ofmultiple supersurfaces associated with aeoliandeflation and fluvial flooding (Veiga et al., 2002).Finally, the Baremian Lower Troncoso Memberof the Huitrn Formation is characterized by thetransition from fluvial to aeolian deposits (Veigaet al., 2005). For both the Avile and Troncosomembers, marine inundation of the dunefieldsfollowing transgression led to the preservation ofrelic dune topography, as well as to the develop-ment of a complex set of facies related to thedeformation and reworking of the aeolian sandsduring the transgression (Stromback et al., 2005;Veiga et al., 2011b). Aeolian deposits have alsobeen described in the Upper Cretaceous recordof the Neuquen Basin as part of the NeuquenGroup (Sanchez et al., 2008).In Africa, the Lower Cretaceous Etjo Sand-

stone Formation of north-west Namibia is a pre-dominantly dry aeolian system in which relicaeolian dune bedforms with up to 100 m oftopographic relief have been preserved followinginundation by flood basalts of the EtendekaIgneous Province (Mountney et al., 1999a,b;Mountney & Howell, 2000; Howell & Mountney,2001). The lower part of the succession recordsexceptionally thick examples of simple cross-bedded sets of aeolian dune origin (individualsimple sets up to 52 m thick), with preservationprobably having been enabled by the migrationof a large dune into a pre-existing topographicdepression. Aeolian sandstone occurs inter-leaved with flood basalts at multiple levelswithin the upper part of the succession, whichforms the lower part of the overlying EtendekaGroup Large Igneous Province (Jerram et al.,1999a,b, 2000a,b).Various formations composed of Cretaceous

strata of aeolian dune origin are present in sev-eral basins of China, including many in the GobiDesert region of Inner Mongolia. Cretaceous aeo-lian dune accumulations are recorded from theSichuan, Ordos, Kuche, Tarim and the Kuqabasins, and especially in Inner Mongolia andsurrounding regions. The preserved aeoliandunefield deposits preserve evidence for thedevelopment of both dry and wet (water-tablecontrolled) aeolian systems (Xie et al., 2005;Jiang et al., 2008). The Upper Cretaceous(Campanian) Djadokhta Formation of the UlanNur Basin and the area around Tugrikiin Shireeand Ukhaa Tolgod (Nemegt Basin, Mongolia)represent dunefields that experienced heavyrainfall events resulting in the development of



perched water tables, early calcite cementationand dune collapse due to sediment gravity slid-ing (Jerzykiewicz et al., 1993; Loope et al., 1999;Seike et al., 2010).In Europe (Spain), the mid-Cretaceous Iberian

Desert System, represented by the UtrillasGroup (that includes the previously known mid-dle and upper parts of the Escucha Formationand the whole Utrillas Formation) developedfrom the early Albian to the early Cenomanianalong the western Tethyan margin (IberianBasin, eastern margin of Iberia) between theTethys Ocean (to the east) and the highlandVariscan Iberian Massif (to the west) over anarea of more than 20 000 km2 (Fig. 7D;Rodrguez-Lopez, 2008; Rodrguez-Lopez et al.,2008). The mid-Cretaceous Iberian Desert Sys-tem displays a tripartite spatial configuration: aback-erg characterized by aeolianfluvial (wadi)interactions, a central-erg characterized by thickaccumulation of linear draa, other compound-draa sandstones and desert roses, and a fore-ergin which the interaction between compoundaeolian dunes (draas) and coastal sedimentaryenvironments (lagoons, tidal creeks, tidal deltasand marshes) occurred (Rodrguez-Lopez et al.,2006, 2008, 2010, 2012a). The sedimentaryrecord of this desert basin displays differenterg sequences bounded by supersurfaces(Rodrguez-Lopez et al., 2013).

Palaeogene aeolian sand systems (Table S4)

Palaeogene erg systems have been the subject ofonly relatively modest investigation, mainly aspart of regional studies; it is therefore difficultto draw conclusions regarding their distributionand development. Only one example of aeolianaccumulation has been described for the Palaeo-gene of Europe (Fig. 8A) and this corresponds tothe Sables de Fontainebleu Formation (or Fon-tainebleau Formation) of early Oligocene age(Alimen, 1936). This unit is part of the fill of theParis Basin and is composed of a 50 to 70 mthick succession of clean, fine-grained, well-sorted sand arranged in accumulationsexpressed as elongated ridges and is thought torepresent the preserved topography of anancient coastal barrier system (Thiry et al.,1988; Cojan & Thiry, 1992).Palaeogene aeolian systems of North America

are restricted to those of the Oligocene of thewestern USA (Fig. 8A). The most importantexample corresponds to the Chuska Erg, anextensive sand sea (ca 140 000 km2) developed

in the uplifted Colorado Plateau between335 Ma and 27 Ma (Lucas & Cather, 2003;Cather et al., 2008). The accumulated record ofthis sand sea (known as the Nabora Pass Mem-ber of the Chuska Sandstone) attains a maxi-mum thickness of 535 m and records thenortherly migration of transverse dunes (Catheret al., 2008). Also in the western USA, in theGreat Plains of South Dakota, Nebraska andWyoming, volcaniclastic aeolian deposits havebeen described as part of the Brule Formation ofthe White River Group (Tedford et al., 2005).Few aeolian successions have been described

for the Palaeogene of Africa and these aremainly of Middle to Upper Eocene age (Fig. 8A).The Hadida Formation, which developed in theTindoouf-Ouarzazate Basin of Morocco, includesmedium-grained, cross-bedded sandstone thatoccurs intercalated in a >300 m thick sequencemainly composed of gypsiferous mudstones(Swezey, 2009; Teson et al., 2010); this succes-sion is regarded as the earliest record of the Sah-aran system (Swezey, 2006). Apart from theseproto-Saharan deposits, sandy aeolian succes-sions have been described as part of the Palaeo-cene fill of the Congo Basin in the West Africanmargin of Gabon in the form of deposits origi-nally described as the Gres Polymorphes (DePloey et al., 1968) that comprise a 180 m thicksuccession of cross-stratified sandstones withindividual sets several metres thick interpretedas aeolian deposits (Bateke Sands, Seranneet al., 2008). Aeolian deposits have also beendescribed in the Fayum District in Egypt as partof the Qasr El-Sagha Formation (El-Fawal et al.,2011). These include a 45 m thick succession ofMiddle to Upper Eocene age, previouslydescribed as channelized delta plain deposits(Bown & Kraus, 1988), but more recently reinter-preted as part of a desertification phase thatcaps a prograding deltaic system (El-Fawalet al., 2011).The only example of Cenozoic aeolian accu-

mulation from Oceania comes from southernAustralia. The upper portion of the Middle toUpper Eocene Ooldea Sand (Barton Sand) repre-sents a barrier dune complex developed duringthe transgression of the Eucla Basin (Hou et al.,2006).

Neogene aeolian sand systems (Table S4)

Neogene sandy aeolian systems are relativelycommon and have been described worldwide(Fig. 8B and C). Most of these systems owe their



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CB

A

Fig. 8. Palaeogeographic distribution of siliciclastic aeolian sand systems during: (A) Eocene. Palaeogene aeoliansystems are scarse. Larger accumulations are located in the Colorado Plateau in western USA. African systemsmay be the precurors of Quaternary deserts and coastal aeolian systems are described in France and Australia. (B)Miocene. Miocene ergs are more numerous and mostly located in western South America in the Andes foreland.Western North America systems are also important. In Africa and the Middle East ergs are related to similar con-ditions as in the Quaternary. (C) Last Glacial Maximum (18 ka). Pliocene ergs are related in Europe to the onset ofNorthern Hemisphere glaciation and the development of stronger westerlies. African systems indicate even dryerconditions as in present times (for example, Mega Kalahari). Palaeogeographic maps from Scotese (2001) PALEO-MAP Project. For legend see Figure 6D.



origin to local climatic and tectonic factors.However, as the position of most major conti-nental landmasses has not changed significantlysince the Miocene, many Neogene aeolian sys-tems have apparently been controlled by cli-matic conditions similar to those experienced bypresent-day desert systems, and such succes-sions therefore constitute the precursors of someof the most important Quaternary aeolian sys-tems, as in the Sahara, Kalahari and Namib sandseas.Only one example of a Miocene aeolian accu-

mulation in Europe has been identified. It corre-sponds to the Vale de Chelas Sands in theLower Tejo Basin of Western Iberia, a 10 mthick succession of cross-bedded sandstones ofaeolian origin, interpreted as a coastal system(Telles Antunes et al., 1999; Pais et al., 2012).Pliocene aeolian deposits in Europe have beendescribed in more detail and are mainly relatedto the onset of the Northern Hemisphere glacia-tion that led to stronger westerly winds (Fig.8C). In central Spain, the Middle to Upper Plio-cene Escorihuela Formation records the accumu-lation and preservation of an aeolian dunefieldrelated to synsedimentary activity of normalfaults in a syn-rift environment. This system isdominated by the interaction between construc-tive and destructive episodes related to high-frequency climatic changes (Rodrguez-Lopezet al., 2012b). Accumulation during the Middleto Upper Pliocene is also recorded in the north-ern Apennines of Italy (Fig. 8C), and is associ-ated with extensional tectonics and thealternation between relatively more humid andmore arid episodes in the Valdarno Basin (Ghi-nassi et al., 2004). Here, deposits of the RenaBlanca Sand Unit are dominated by the super-imposition of wettingdryingwetting cycles thatrecord high-frequency climatic oscillations, eachapparently of ca 40 ka duration (Ghinassi et al.,2004).In the USA, several Miocene aeolian systems

have been described and are mainly controlledby local tectonic conditions associated withwarm and dry climatic conditions. In westernand central USA, some local systems havedeveloped related to extensional basins, such asthe Zia Formation of the Santa Fe Group in theAlbuquerque Basin (Galusha & Blick, 1971) andthe Ojo Caliente Sandstone of the Tesuque For-mation in the La Espa~nola Basin (Koning et al.,2004), both related to the large structure of theRo Grande Rift. These systems give rise tolocally thick successions (up to 160 m) related

to the development of dunefields that werestrongly influenced by local conditions. Aeoliandeposits have also been described in the HighPlains of the USA, including the Early MioceneArikaree Formation (Bart, 1977) in south-eastWyoming, where large-scale, cross-bedded sand-stones have been related to the accumulation ofbarchan and transverse dunes. Finally, an aeo-lian origin has also been reported for a ca 100 mthick succession of the Comondu Group in BajaCalifornia, Mexico, related to the infill of theforearc basin developed between the Late Oligo-cene and Early Miocene (Umhoefer et al., 2001).Neogene aeolian accumulations in South

America are related to the complex evolution ofthe Andes. The compressional regime in thewestern margin of South America led to thedevelopment of a complex foreland with multi-ple basins that formed important sites of accom-modation that were themselves subject to anarid local climate regime. This resulted in theaccumulation of several aeolian units, somewith local names that record this stage of evolu-tion, especially during the Miocene. Forinstance, the Petaca Formation in southern Boli-via (Uba et al., 2005) and the Aguada Member ofthe Chacras Formation (Voss, 2002) in the Salarde Antofalla in north-west Argentina probablycommenced accumulation in the latest Oligo-cene, but underwent their most important phaseof accumulation during the Lower to MiddleMiocene. These units are between 100 m and150 m thick and record the interaction betweenaeolian and fluvial systems.One of the best-described examples of an

aeolian system developed in the Andean fore-land is the Lower Miocene Vallecito Formation(Tripaldi & Limarino, 2005). This unit attains amaximum thickness of 1200 m and comprises acomplex facies arrangement that records theinteraction of dunes, aeolian sandsheets andwet interdunes that interact with fluvial andlacustrine systems. The succession records alarge aeolian system developed as the first syn-orogenic fill of the Andean foreland in this partof north-western Argentina (Tripaldi & Limari-no, 2005). Another Lower Miocene unit withsimilar characteristics is the Pachaco Formationin the Precordillera of San Juan in westernArgentina. The middle member of this forma-tion is 700 m thick and records the accumula-tion of a large dunefield dominated by barchanand seif dunes and draas (Milana et al., 1993).The Angastaco Formation is related to an aeo-lian dunefield associated with fluvial systems



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that developed in the Lower Miocene of north-western Argentina (Do Campo et al., 2010).Both the Mari~no Formation in the Precordilleraof Mendoza (Irigoyen et al., 2000) and theSanto Domingo Member of the El Durazno For-mation in the Sierra de Famatina (Davila &Astini, 2003) also record synorogenic aeoliansystems associated with the development of theAndean foreland during the Middle Miocene.In southern Patagonia, aeolian deposits havealso been described as part of the Lower toMiddle Miocene Santa Cruz Formation (Pintu-ras Formation of Bown & Larriestra, 1990), andin distal portions of the Andean Foreland andin the passive South American margin, sandyaeolian facies have been described as part ofthe Ro Negro Formation associated with a mar-ine transgression from the Atlantic (Zavala &Freije, 2001).Most of the Neogene aeolian systems of Africa

are closely related to Quaternary systems andthey record early accumulation conditions, withsome differences due to changes in climate overthe past 10 Myr (Fig. 8B). The oldest record isthe Middle Miocene Tsondab Sandstone Forma-tion in Namibia which comprises a successionup to 220 m thick of cross-stratified and massivesandstones with the local development of pedo-genic carbonates and palaeosols (Ward, 1988;Kocurek et al., 1999; Segalen et al., 2004). Thisunit is interpreted as a proto-Namib sand seathat was influenced by winds that blew from thesouth/south-west, as today, but which devel-oped under more humid conditions than thoseexperienced today (Kocurek et al., 1999). Thesuccession comprises two sequences, each sepa-rated by a stabilization surface; deposits recordthe preservation of north-trending linear dunesthat gradually undertook a lateral component ofmigration to the east. These linear forms sup-ported superimposed dunes, similar to the largelinear bedforms of the present-day Namib Des-ert, mainly as a consequence of a sustainedwind regime that has been established since theMiocene (Segalen et al., 2004). Elsewhere in theNamib, up to four aeolian sequences are recog-nized (Senut et al., 1995), comprising the depo-sits of star, linear and transverse dunes (Segalenet al., 2004).Miocene aeolian deposits have been

described in the Chad Basin and these are asso-ciated with the early hominid specimens in theToros-Menalla site 266, in northern Chad, centralAfrica (Schuster et al., 2002; Vignaud et al.,

2002). Accumulation of these aeolian succes-sions was related to the early development ofthe Sahara (Schuster et al., 2002; Vignaudet al., 2002), although the relevance of thisfinding and its implication for pre-Quaternarydesert development has been disputed (Swezey,2006).Upper Miocene to Lower Pliocene aeolian

deposits are also present in the Western Cape ofSouth Africa. In this area, the Prospect Hill For-mation is composed of calcarenites with shellfragments that record the development of acoastal dune system overlying sandy beachdeposits (Franceschini & Compton, 2004).The Garet Uedda Formation (or Members U

and V of the Sahabi Formation) in Libya(Fig. 8C) has been described as Upper Pliocenein age and an aeolian origin has been proposedfor this 25 m thick sequence of quartzitic sandsinterbedded with sandy shales (Tawadros,2012). Some relic forms of the Kalahari Desertmight be as old as Upper Pliocene and theyrecord the aeolian reworking of fluvial sands(Lancaster, 2000; Haddon & McCarthy, 2005).These units have different formal names (Gordo-nia Formation, Kalahari Sand, Bateke Sands andZambezi Formation) and they can be correlatedfrom Zaire and south-western Angola in thenorth to Botswana, Namibia and northern SouthAfrica in the south. Deposits of these succes-sions are mainly unconsolidated sand and theirdistribution suggests a larger sand sea than theQuaternary Kalahari Desert, giving rise to thelargest sand body on Earth (the Mega Kalahari)that covered over 25 million km2 (Thomas &Shaw, 1990).Neogene aeolian activity in Asia was domi-

nated by the accumulation of thick sequences offine-grained deposits (loess) in the Loess andTibetan Plateaus and aeolian deposits interbed-ded with alluvial deposits (e.g. Zheng et al.,2003). Sandstone aeolian accumulations are notcommon and only one example has been identi-fied in the Middle East: the Shuwaihat Forma-tion, a Middle Miocene unit exposed on a 16 mhigh cliff near Abu Dhabi in the United ArabEmirates (UAE; Whybrow et al., 1999), inter-preted as the record of the interaction betweentransverse and barchanoid dunes and a conti-nental sabkha (Bristow, 1999).

Quaternary aeolian sand systems

Sand seas and dunefields occurring today deve-loped during the Quaternary Era, during which



significant changes in climate and sea-levelrelated to glacialinterglacial cyclicity affectedthe supply, availability and mobility of sediment.Their accumulation and present configurationtherefore reflect the legacy of these changes, inaddition to contemporary processes. Quaternaryaeolian sand systems occur on all continents andat all latitudes, with major systems locatedbetween 45 degrees north and south (Fig. 9), andwith other smaller systems occurring at higherlatitudes, including in the Arctic and Antarctica.Quaternary aeolian systems are here sub-dividedinto those located inland and those occurringalong the coast.

Inland sand seas and dunefields (Table S5)Inland dune systems occur widely, with a con-centration in low to mid-latitude arid regions ofthe Northern Hemisphere (3550N), especiallyin the arid regions of central Asia, on the semi-arid Great Plains of North America and in low-latitude desert areas of Africa, Arabia and Aus-tralia (1530N and 1530S). Their geologicalsetting varies, with many sand seas in Africa,Australia and Arabia occurring in cratonicbasins; central Asian and South American sandseas, by contrast, are located mostly in forelandbasins (Fig. 10). Dune types also vary, with lin-ear dunes comprising ca 50% of all dunes and

dominating in many areas of the Sahara, south-east Arabia, Australia and southern Africa (e.g.Pye & Tsoar, 1990; Lancaster, 1999). Crescenticdunes comprise 40% of dunes and dominatesand seas in the northern Sahara, many parts ofArabia, and parts of central Asia and China. Stardunes comprise ca 8% of dunes in low-latitudeinland sand seas, mainly in areas where topogra-phy creates complex wind regimes.Wet systems form inland where the deposi-

tional surface intersects local perched or regio-nal groundwater tables. Good examples of wetsystems are the White Sands dunefield in NewMexico (Fig. 11; Kocurek et al., 2007) and theLiwa area of the United Arab Emirates (Glennie,2005; Stokes & Bray, 2005). Changes in sea-level,climate and/or vertical crustal movements thataffect the groundwater table may result in a sys-tem changing over time from wet to dry or viceversa, as in the Wahiba Sands of Oman (Radieset al., 2004). Likewise, spatial changes ingroundwater levels result in some parts of thesystem being dry and others wet, as in theRubal Khali sand sea of Saudi Arabia (Glennie,1970; Al-Masrahy & Mountney, 2013).It appears that the majority of modern and

Quaternary aeolian sand systems operate as drysystems in which the water table is significantlybelow the depositional surface, such that it has

Fig. 9. Location of major low-latitude and mid-latitude inland sand seas and dunefields, as well as coastal car-bonate aeolianite deposits. After Sun & Muhs (2007).



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no effect on the dynamics of the dune system.The major controls are therefore sand supply, itsavailability for transport and mobility (magni-tude and frequency of winds capable of trans-porting sand). The Namib Sand Sea (Fig. 12) is agood and comprehensively studied example of adry system, sourced principally by sand fromthe interior of southern Africa via the OrangeRiver (Garzanti et al., 2012). Its accumulation isinterpreted as the product of regional changes inwind regime, which result in a reduction oftransport rates in the direction of transport,leading to deposition of sand by bedform climb-ing and dune growth. Estimates of angles of bed-form climb made by Lancaster (1989) range from0003 for the linear dunes to 003 to 016 forcrescentic dunes in the southern part of thesand sea. There is a clear spatial pattern of sandaccumulation in central areas of the sand sea,represented by the equivalent or spread out sandthickness of complex linear dunes that reach150 to 200 m in height (Lancaster, 1989; Bullardet al., 2011) (Fig. 12). Isotopic and sedimentbudget estimates for the age of the sand sea con-verge at around one million years (Vermeeschet al., 2010), but many of the dunes are rela-tively young, with optically stimulated lumines-cence (OSL) ages of 17 to 24 ka for compoundlinear dunes in the southern sand sea (Bubenzer

et al., 2007) and

years) (Fujioka et al., 2009). In many locations,the cores of linear dunes may exceed 380 ka inage, with multiple late Pleistocene and Holoceneaccumulation episodes (Fitzsimmons et al.,2007; Lomax et al., 2011). These episodes ofdune growth have taken place without completereworking of the dunes, in large part because ofpedogenic alteration and stabilization of thedeposits of older dune accumulation episodesby aeolian addition of clay and carbonatederived from nearby alluvial and lacustrineenvironments (Cohen et al., 2010; Hesse, 2011).Successive episodes of stabilization, reworking

and dune growth result in an accretionary struc-ture for the dunes, often associated with lateralmigration in addition to dune extension (Rubin,1990). Similar structures have been observed instabilized (vegetated) linear dunes in otherregions (e.g. Roskin et al., 2011; Telfer, 2011).

Coastal systems (Table S5)Coastal dunefields may be divided into thosecomposed of siliciclastic material and thosecomposed of carbonate (or mixed carbonate andsiliciclastic) material. The former type typicallydevelops along humid-type, mid-high latitude

A

B C

Fig. 11. Example of a wet aeolian system: White Sands, New Mexico, USA: (A) cross-section of dunefield show-ing relations between aeolian and lacustrine sediments (after Kocurek et al., 2007); (B) 3 to 5 m high crescenticridges migrating across the surface of older crescentic dune deposits shown by exposed cross-bedding; (C) trenchin an interdune area showing cross-bedded dune structures. Machete is ca 06 m long.



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coasts, whereas the carbonate-rich dunes/dune-fields form along arid to semi-arid, mid-low lati-tude, coasts bordering productive carbonateplatforms.Dune types vary and their size and morpho-

logy is dependent on a number of factors includ-ing vegetation cover, sand supply, wind regimeand coastal setting. Sand blown off of the beachtypically forms partly vegetated and fixed fore-dunes. Aeolian erosion of the foredunes canlead to the formation of blowouts and parabolic

dunes and/or transgressive dunefields (Hesp,1999). Along cliffed coasts, special dune typesincluding echo dunes and climbing dunes candevelop (e.g. Clemmensen et al., 1997).Most coastal dunefields in North-west Europe

can be classified as wet because the groundwatertable typically is close to the surface. Depth tothe groundwater table is, in many cases, linkedto sea-level, especially in subsiding coastalbasins (Kocurek et al., 2001; Mountney & Rus-sell, 2009). In other examples, especially in sys-

W E

0 20 40 km

Crescentic dunes

Simple Compound

Complex lineardunes

Dendriticlinear dunes

Tsondab SandstoneFormation

Naukluft MountainsAtlanticOcean

Basement rocks

Basementrocks

?

?

Fig. 12. Example of a dry aeolian system: Namib Sand Sea, Namibia. Cross-section of central sand sea at 242S;elevation data from ASTER GDEM; extent of Tsondab Sandstone Formation after Ward (1988). Landsat image ofthe area for comparison.



tems developed on uplifting coastal areas likethe northern part of Denmark, dune dynamicsare influenced by high precipitation rates andthe formation of perched groundwater tables(Pedersen & Clemmensen, 2005; Clemmensenet al., 2009). Dunefields develop both on retreat-ing and prograding coasts. Both types may sharemany sedimentary characteristics, but progradingsystems tend to develop successive lines of sta-bilized foredune ridges (e.g. Bristow & Pucillo,2006; Madsen et al., 2007; Reimann et al.,2011), whereas retreating systems more com-monly experience phases of transgressive duneformation in the form of inland migrating para-bolic dunes (Clemmensen et al., 2001a; Pedersen& Clemmensen 2005).The Lodbjerg and Hvidbjerg coastal dunefields

provide examples of wet-stabilized siliciclasticsystems developed on a retreating coast (Figs 14and 15). These two systems form part of analmost unbroken belt of coastal dunefields thatflank the North Sea coast of Jutland, Denmark(Pedersen & Clemmensen, 2005; Clemmensenet al., 2009). Luminescence dating of the sandunits and radiocarbon dating of the peaty pal-aeosols have made it possible to establish adetailed chronology of dunefield evolution(Fig. 16). Episodes of transgressive dune forma-tion that occurred around 2200 BC, 800 BC, 100AD, 1050 to 1200 AD, and between 1550 and 1650AD were linked to periods of increased stormi-ness (cool, wet summers), whereas stabilizationtook place during periods of decreased stormi-ness (Clemmensen et al., 2009). The series ofages obtained by Clemmensen et al. (2001a)indicate accumulation of around 10 m of aeoliansand (below the present groundwater table)since 2200 BC, at an average rate of 24 mm yr1.Swina barrier coastal dune system is another

example of a wet-stabilized siliciclastic system

developed on a prograding shoreline. The Swinabarrier is situated in north-west Poland along thesouthern part of the Baltic Sea; the dunefield isdeveloped on top of two sandy spits that haveformed between Pleistocene headlands (Reimannet al., 2011). Spit formation and shoreline progra-dation have taken place during the past 66 kyr.The coast now forms a smooth and curved shore-line segment and is still prograding. The Swinabarrier system is sourced by sand eroded fromnearby headlands. Luminescence dating of thedunes indicates six hiatuses in foredune build-ing, at 2100 BC, 900 BC, 200 BC, 200 AD, 600 AD,1000 AD and 1600 AD. It is concluded that most ofthese phases of foredune erosion and instabilitywere caused by climatic shifts to a cooler andwindier climate. The transgressive dune forma-tion ca 1600 AD was linked to increased stormi-ness during the Little Ice Age and this episodeof dune formation seems to be contemporaneouswith phases of increased aeolian activity in otherdune systems in North-west Europe (e.g. Clem-mensen & Murray, 2006; Clarke & Rendell, 2009;Clemmensen et al., 2009).Carbonate-rich aeolian systems are commonly

developed in mid-latitude and low-latitude, aridand semi-arid climate belts; these aeolian sys-tems occur in a variety of settings includinglowland and cliffed coasts (e.g. Brooke, 2001;Frebourg et al., 2008). Due to the climatic settingof these systems, they are most logicallyclassified as dry. The carbonate sand is lithifiedsoon after deposition (Guern & Davaud, 2005),thereby forming one mechanism of preservationthat is poorly known from siliciclastic systems.These lithified carbonate-rich aeolian depositsare termed aeolianites (Brooke, 2001).Particularly well-developed carbonate aeolian

systems occur in the Western Mediterraneanregion (Clemmensen et al., 1997; Fornos et al.,

Fig. 13. Example of a stabilizing aeolian system: Strzelecki Desert, Australia. Along-dune profile showing multipleepisodes of dune accumulation spanning the past 120 ka. From Cohen et al. (2010). II to VII Marine isotope stages.



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2009; Andreucci et al., 2010a). Quaternary succes-sions with carbonate-rich aeolian sand units cropout quasi-continuously along the north-west coastof Sardinia near the town of Alghero (Andreucciet al., 2010a,b, 2014). The aeolian units, whichare lithified, occur along a cliffed coast and can besubdivided into cliff-front dune accumulationsand valley-head sand ramps (Andreucci et al.,2010a; Fig. 17). Note also other major Quaternaryaeolianites in South Africa (e.g. Roberts, 2008).

AEOLIAN RESEARCH: THE WAYFORWARD AND FUTURE RESEARCHPROSPECTS

Aeolian facies and sequence stratigraphicmodels: a useful approach to capturingcomplexity in aeolian successions?

Relating preserved aeolian stratigraphy tooriginal bedform morphology and behaviourAlthough it is now possible to effectivelydescribe in detail both: (i) the morphologicalcharacteristics of modern bedforms and largerdunefields; and (ii) the geometry of architecturalelements of preserved aeolian successions, nota-bly by using the forward stratigraphic modellingtechniques developed by Rubin (1987) and Ru-bin & Carter (2006), several problems remainregarding how to relate ancient preserved sets ofaeolian strata to the morphology and migratorybehaviour of the original bedforms. In particular,

Fig. 14. Ground-penetrating radarmapping of sedimentaryarchitecture; coastal dunefield atLodbjerg, Denmark (Clemmensenet al., 2001a). The surface of themodern dunefield is situated ca15 m above sea-level, and thedunefield is truncated by a coastalcliff towards the North Sea. Partlyactive cliff-top dunes aredeveloped along the cliff. Vehiclefor scale is ca 5 m long.

Fig. 15. Coastal cliff section at Lodbjerg, Denmark. AWechselian till at the base of the section is overlainby 15 to 20 m of aeolian sand with peaty soils (darkhorizons). Terminology of aeolian events after Clem-mensen et al. (2009).



problems remain in cases where large com-pound and complex morphological dune typeshave accumulated in desert basins in which therate of accommodation generation has beenhighly variable over time or space, for examplein response to spatially and temporally variablesynsedimentary tectonic activity (e.g. Rodrguez-Lopez et al., 2013).The accumulated sedimentary record of most

modern inland dunefields remains largelyunknown, with only fragmentary glimpses ofaeolian sedimentary architectures having so far

been revealed from modern aeolian systems viatechniques such as trenching (e.g. McKee, 1966)and ground-penetrating radar (GPR) studies (e.g.Bristow et al., 2000a,b). Conversely, relativelyfew ancient aeolian successions are known thatpreserve, intact, the original morphologies of thebedforms that gave rise to the architecturallycomplex set and cosets of aeolian cross-beddingthat dominate the ancient sedimentary record(e.g. Mountney et al., 1999a,b). Thus, the devel-opment of aeolian facies models that are used torelate modern dunes and dunefields to accumu-lated deposits remains problematic in terms ofhow best to interpret the preserved sedimentaryarchitectures of ancient aeolian deposits.Despite great progress in understanding of the

geomorphology of Quaternary inland sand seas,there are few data relating to their stratigraphicand sedimentological record. In many areas,Quaternary sand seas and dunefields have notleft a significant accumulation and the bedformspresent in many modern dunefields are knownto be partially or completely legacy landformsinherited from Last Glacial Maximum (LGM)times (e.g. Lancaster et al., 2002); thus, suchforms do not necessarily reflect the currentlyprevailing climatic and sediment supply condi-tions. Elsewhere, information from the subsur-face (for example, GPR data, cores and welllogs) either does not exist or is proprietary. Thecosts and logistics of acquiring such data setsare often prohibitive but, where they have beendeveloped, the understanding of the sedimen-tary record of inland sand s

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