Aeolian Facies Research Articles

Luminescence dating of an Upper Pleistocene alluvial fan and aeolian sandsheet complex: The Senne in the Münsterland Embayment, NW Germany

An up to 15 m thick alluvial fan and aeolian sandsheet complex is exposed in the upper Senne area, on the southern slope of the Teutoburger Wald Mountains (NW Germany). The origin and age of these deposits have been controversially discussed for many years, ranging from Saalian glaciofluvial to periglacial Weichselian deposits. In order to provide a high-resolution chronological framework for the deposits, we conducted luminescence dating of 12 samples from two localities (Oerlinghausen and Augustdorf pits). Both coarse-grain potassium-rich feldspar and quartz minerals were used for luminescence dating. Feldspar was measured using an elevated temperature post-IR infrared stimulated luminescence (IRSL). Quartz was measured using optically stimulated luminescence (OSL) with a conventional single aliquot regenerative dose (SAR) protocol. Feldspar results tend to overestimate quartz ages for the lower part of the sections (alluvial plain and alluvial fan facies) but are consistent with quartz ages for the upper part of the sections (aeolian facies). Quartz ages from both central and minimum age models suggest deposition during the Late Pleistocene Pleniglacial to Late Glacial.

3.2 Ga eolian deposits from the Moodies Group, Barberton Greenstone Belt, South Africa: Implications for the origin of first-cycle quartz sandstones

The 3.2Ga Moodies Group in Barberton Greenstone Belt, South Africa, contains the oldest recognized evidence for eolian processes on Earth. These eolian facies indicate that significant wind regimes existed in the Archean atmosphere. Eolian deposits are developed in the lower Moodies Group in the central part of the belt and consist of stacked inversely graded strata ranging in thickness from 2 to 10mm.Individual strata consist of fine- to medium-grained quartz sandstone at the base that passes vertically into very coarse- to coarse-grained quartz sandstone. Strata make up cross-bed sets up to 3–5m thick. Sets of wind ripple strata are either tabular tangential or in the form of broad troughs. This type of inversely graded stratification is the product of wind-ripple migration. The coarse grain size of the sediment combined with the low-angle of inclination of the strata is best interpreted as the product of sand sheet or dune plinth preservation. Based on the geometry of eolian set boundaries, dunes were probably simple barchan form.The tens-of-meters thick eolian deposits are underlain by braided stream deposits composed of subfeldspathic, pebbly sandstones. The vertical change from braided-stream subfeldspathic sandstones to eolian quartz arenites, highlights the underappreciated capacity of eolian processes to generate first-cycle quartz sandstones on landscapes pre-dating the advent of land vegetation.

Trace fossils and palaeoenvironments of the Middle Devonian Caherbla Group, Dingle Peninsula, southwest Ireland

Trace fossils from the Middle Devonian Caherbla Group of the Dingle Peninsula, southwest Ireland, record a diverse arthropod fauna inhabiting a hot‐arid intracontinental rift setting. Aeolian dunefield and coeval fluvial interdune deposits interfinger spatially and temporally with alluvial fan sedimentary rocks. Three distinct trace fossil assemblages are recognized. The Taenidium‐Scoyenia ichnocoenosis occurs in alluvial fan and fluvial channel deposits, and includes the large backfilled burrow Taenidium, interpreted as eoarthropleurid aestivation chambers. The Rusophycus‐Protichnites ichnocoenosis, composed of arthropod trackways and surface pits, occurs in an interdune ponded area that was susceptible to ephemeral fluvial flow, with Rusophycus showing preferred orientation into the oncoming palaeocurrent. Both the Taenidium‐Scoyenia and Rusophycus‐Protichnites ichnocoenoses are assignable to the globally recurring continental Scoyenia ichnofacies. They are clearly substrate‐controlled and moisture‐related due to the ephemeral nature of the fluvial system. The Palmichnium‐Entradichnus ichnocoenosis occurs in aeolian dune deposits, and includes Palmichnium, attributed to large stylonurid eurypterids, and Diplichnites, attributed to eoarthropleurids. These trackways represent the activities of dune pioneers that left their fluvial habitat to forage for detritus. Interface burrows (Entradichnus, Palaeophycus) were also constructed by arthropods moving just under the sand surface and vertical burrows (Cylindricum, Pustulichnus) were made by arthropods digging downward. Trace preservation in the aeolian environment was probably enhanced by heavy nocturnal dew‐fall or light rain. The Palmichnium‐Entradichnus ichnocoenosis is assigned to the globally recurring aeolian Octopodichnus‐Entradichnus ichnofacies. This aeolian facies, and associated ichnofauna described herein, represents the oldest development of a unique erg system in the Old Red Sandstone (Devonian) of the southern British Isles, and one of the oldest and most diverse aeolian ichnofaunas to be reported worldwide. Copyright © 2011 John Wiley & Sons, Ltd.

The aeolian system of central Argentina

Abstract The central region of Argentina comprises three main geomorphological domains, the Pampean plain, the northern Patagonia plateau and the eastern Andean piedmont. The region characterized by a complex morphostructural setting is covered by a late Quaternary aeolian apron with subordinate alluvial deposits, grading from loess and loess-like deposits in the eastern Pampas to sandy mantles and dunefields in the central, western and southern areas of the region. Eight aeolian units have been identified on the basis of the nature of the deposits, landforms and their geological-structural settings. Loess and loess-like mantles are the dominant aeolian facies of three units extending across the eastern Pampean plain: loess and loess-like mantles, loess and loess-like mantles and blowouts, sandy loess and loessial sand mantles. Dunefields and sand mantles prevail in five other units: central Pampean dunefields, western Pampean sand mantles and dunefields, western Pampean dunefields, Andean piedmont dunefields, northern Patagonia and southern Pampean sand mantles and dunefields. At a regional scale, sandy deposits are proximal facies closer to the main source area of aeolian material corresponding to the floodplain environment of the Colorado River and its tributary Desaguadero–Salado-Curaco fluvial system. The eastern loess deposits correspond to distal aeolian facies. In addition, topography governed by the complex subsurface geology and structure of the region, play a leading role as a primary controlling factor in the distribution of aeolian facies and the resulting landforms.

Facies architecture and heterogeneity of the fluvial–aeolian reservoirs of the Sergi formation (Upper Jurassic), Recôncavo Basin, NE Brazil

The Sergi Formation (Upper Jurassic) represents the main hydrocarbon reservoir of the Recôncavo Basin, Brazil. The basal vertical facies succession of the Sergi Formation comprises reservoirs formed by a complex fluvio–aeolian–lacustrine interaction. Facies architecture and detailed petrophysical analysis of these reservoirs have enhanced the understanding of heterogeneity at a variety of scales and has allowed the development of predictive models that describes the range of styles of mixed fluvial–aeolian reservoirs. At megascopic scale, the reservoirs are predominantly composed of sand bodies deposited by fluvial channel and aeolian facies associations. Regional flooding surfaces and sequence boundaries are their main flow barriers. The regional flooding surfaces are composed of fine-grained sediments deposited by lacustrine facies associations and the sequence boundaries act as flow barriers due to mechanically infiltrated clays. Based on its geometrical relations, reservoirs linked to fluvial–aeolian–lacustrine interaction formed two types of reservoirs at macroscopic scale: (i) with good lateral continuity of aeolian packages and relatively simple stratigraphic correlation and (ii) of highly compartmentalized aeolian packages with complex stratigraphic correlation and truncation by fluvial deposits. Mesoscopic heterogeneity reflects lithofacies, sedimentary structures, and lamina-scale variability within aeolian and fluvial facies associations.

The last interglacial sea-level high stand on the southern Cape coastline of South Africa

The continental margin of southern South Africa exhibits an array of emergent marginal marine sediments permitting the reconstruction of long-term eustatic sea-level changes. We report a suite of optical luminescence ages and supplementary amino acid racemization data, which provide paleosea-level index points for three sites on this coastline. Deposits in the Swartvlei and Groot Brak estuaries display tidal inlet facies overlain by shoreface or eolian facies. Contemporary facies relations suggest a probable high stand 6.0-8.5 m above modern sea level (amsl). At Cape Agulhas, evidence of a past sea-level high stand comprises a gravel beach (ca. 3.8 m amsl) and an overlying sandy shoreface facies (up to 7.5 m amsl). OSL ages between 138±7 ka and 118±7 ka confirm a last interglacial age for all marginal marine facies. The high stand was followed by a sea-level regression that was associated with the accumulation of eolian dunes dating to between 122±7 ka and 113±6 ka. These data provide the first rigorous numerical age constraints for last interglacial sea-level fluctuations in this region, revealing the timing and elevation of the last interglacial high stand to broadly mirror a number of other far-field locations.

Styles of interaction between aeolian, fluvial and shallow marine environments in the Pennsylvanian to Permian lower Cutler beds, south-east Utah, USA

The Pennsylvanian to Permian lower Cutler beds comprise a 200 m thick mixed continental and shallow marine succession that forms part of the Paradox foreland basin fill exposed in and around the Canyonlands region of south-east Utah. Aeolian facies comprise: (i) sets and compound cosets of trough cross-bedded dune sandstone dominated by grain flow and translatent wind-ripple strata; (ii) interdune strata characterized by sandstone, siltstone and mudstone interbeds with wind-ripple, wavy and horizontal planar-laminated strata resulting from accumulation on a range of dry, damp or wet substrate-types in the flats and hollows between migrating dunes; and (iii) extensive, near-flat lying wind-rippled sandsheet strata. Fluvial facies comprise channel-fill sandstones, lag conglomerates and finer-grained overbank sheet-flood deposits. Shallow marine facies comprise carbonate ramp limestones, tidal sand ridges and bioturbated marine mudstones. During episodes of sand sea construction and accumulation, compound transverse dunes migrated primarily to the south and south-east, whereas south-westerly flowing fluvial systems periodically punctuated the dune fields from the north-east. Several vertically stacked aeolian sequences are each truncated at their top by regionally extensive surfaces that are associated with abundant calcified rhizoliths and bleaching of the underlying beds. These surfaces record the periodic shutdown and deflation of the dune fields to the level of the palaeo-water-table. During episodes of aeolian quiescence, fluvial systems became more widespread, forming unconfined braid-plains that fed sediment to a coastline that lay to the south-west and which ran approximately north-west to south-east for at least 200 km. Shallow marine systems repeatedly transgressed across the broad, low-relief coastal plain on at least 10 separate occasions, resulting in the systematic preservation of units of marine limestone and calcarenite between units of non-marine aeolian and fluvial strata, to form a series of depositional cycles. The top of the lower Cutler beds is defined by a prominent and laterally extensive marine limestone that represents the last major north-eastward directed marine transgression into the basin prior to the onset of exclusively non-marine sedimentation of the overlying Cedar Mesa Sandstone. Styles of interaction between aeolian, fluvial and marine facies associations occur on two distinct scales and represent the preserved expression of both small-scale autocyclic behaviour of competing, coeval depositional systems and larger-scale allocyclic changes that record system response to longer-term interdependent variations in climatic and eustatic controlling mechanisms. The architectural relationships and system interactions observed in the lower Cutler beds demonstrate that the succession was generated by several cyclical changes in both climate and relative sea-level, and that these two external controls probably underwent cyclical change in harmony with each other in the Paradox Basin during late Pennsylvanian and Permian times. This observation supports the hypothesis that both climate and eustasy were interdependent at this time and were probably responding to a glacio-eustatic driving mechanism.

Correlações Estratigráficas Conflitantes no Limite Permo-Triássico no Sul da Bacia do Paraná: O Contato Entre Duas Seqüências e Implicações na Configuração Espacial do Aqüífero Guarani

The stratigraphic register of the Guarani aquifer system in the Parana basin involves deposits of the Triassic to the Cretaceous. The register in the south region differs from the other areas of the basin, causing confusion in the stratigraphic conception of the Pirambóia Formation. This formation is correlated with paleozoics deposits whose register is only found in the south region of the basin. The correlation that intends for these units has implications in the space configuration and distribution of the aquifer. The space relationships of this record are reinterpreted. The Rio do Rasto Formation, of late Permian age record alluvial plain system, in a progressive semiarid environment, including dune fields; in the southern part of the basin these dune field are extensive and is represented by thick record, covered again by extensive fluvial deposits of the Sanga do Cabral Fm at the PT boundary. The unconformity above records a generalized uplift, associated to the Gondwanides orogeny and to climatic changes, accompanied by progressive supply and sin-sedimentary deformation. Above the unconformity, aeolian and fluvial deposits of the Mesozoic sequence present division organized in 3 blocks: West, Central and East. Three depositional cycles were identified. The first, unconformable over Permian rocks, occurs only in the Central Block, with fluvial and lacustrine deposits filling small rifts (Santa Maria and Caturrita fms). The second cycle extends over the whole basin with fluvial deposits and humid aeolian (formations Guará and Pirambóia); the fluvial and aeolian Guará Fm lies unconformable over Sanga do Cabral Fm in the West Block. In the East Block the aeolian and fluvial unit identified as Pirambóia Fm correlative; it occurs unconformable over the Rio do Rasto Fm, omitting the Sanga do Cabral Fm and the rocks of the first cycle. The third cycle system tract records super arid dune fields of the Botucatu Formation. The Late Permian aeolian facies of the Sanga do Cabral Fm, previously called by some authors as the Pirambóia Fm, doesn't present interfingers and doesn't constitute a hydrostratigraphic unit connected to the Guarani System.

Sedimentary evolution of a Late Pleistocene temperate red algal reef (Coralligène) on Rhodes, Greece: correlation with global sea‐level fluctuations

AbstractAutochthonous red algal structures known as coralligène de plateau occur in the modern warm‐temperate Mediterranean Sea at water depths from 20 to 120 m, but fossil counterparts are not so well‐known. This study describes, from an uplifted coastal section at Plimiri on the island of Rhodes, a 450 m long by 10 m thick Late Pleistocene red algal reef (Coralligène Facies), interpreted as being a coralligène de plateau, and its associated deposits. The Coralligène Facies, constructed mainly by Lithophyllum and Titanoderma, sits unconformably upon the Plio‐Pleistocene Rhodes Formation and is overlain by a Maerl Facies (2 m), a Mixed Siliciclastic‐Carbonate Facies (0·2 m) and an Aeolian Sand Facies (2·5 m). The three calcareous facies, of Heterozoan character, are correlated with established members in the Lindos Acropolis Formation in the north of the island, while the aeolian facies is assigned to the new Plimiri Aeolianite Formation. The palaeoenvironmental and genetic‐stratigraphic interpretations of these mixed siliciclastic‐carbonate temperate water deposits involved consideration of certain characteristics associated with siliciclastic shelf and tropical carbonate shelf models, such as vertical grain‐size trends and the stratigraphic position of zooxanthellate coral growths. Integration of these results with electron spin resonance dates of bivalve shells indicates that the Coralligène Facies was deposited during Marine Isotope Stage 6 to 5e transgressive event (ca 135 to 120 ka), in water depths of 20 to 50 m, and the overlying Maerl Facies was deposited during regression from Marine Isotope Stage 5e to 5d (ca 120 to 110 ka), at water depths of 25 to 40 m. The capping Aeolian Sand Facies, involving dual terrestrial subunits, is interpreted as having formed during each of the glacial intervals Marine Isotope Stages 4 (71 to 59 ka) and 2 (24 to 12 ka), with soil formation during the subsequent interglacial periods of Marine Isotope Stages 3 and 1, respectively. Accumulation rates of about 0·7 mm year−1 are estimated for the Coralligène Facies and minimum accumulation rates of 0·2 mm year−1 are estimated for the Maerl Facies. The existence of older red algal reefs in the Plimiri region during at least Marine Isotope Stages 7 (245 to 186 ka) and 9 (339 to 303 ka) is inferred from the occurrence of reworked coralligène‐type lithoclasts in the basal part of the section and from the electron spin resonance ages of transported bivalve shells.

Facies in the Unayzah Formation and the Basal Khuff Clastics in subsurface, northern Kuwait

ABSTRACT This is the first reporting of the Unayzah Formation from a northern Kuwait deep well where a 304 ft of core was cut in the upper part of the formation. The core consists of about 202 ft of the Unayzah Formation, 74 ft of the Basal Khuff Clastics and 28 ft of the Khuff Formation. Within the Unayzah Formation six major lithofacies were interpreted: (1) high-angle cross-bedded sandstone; (2) fine-grained sandstone; (3) normally graded coarse pebbly sandstone; (4) medium- to fine-grained sandstone and siltstone; (5) red mudstone and siltstone; and (6) black shale. In the Basal Khuff Clastics, four lithofacies were recognised: (1) fine- to medium-grained clean sandstone; (2) muddy bioturbated sandstone and siltstone; (3) dark grey to black carbonaceous shale with sand interbeds; and (4) interbedded sandstone, siltstone and dolomite. These lithofacies can be subdivided into four broad palaeoenvironments; ?eolian, braided fluvial, flood plain, and coastal plain. The possible eolian facies are represented by high-angle, cross-bedded sandstones of likely dune affinity. Braided fluvial facies consist of pebbly sandstones, which may grade normally to fine-grained sandstone and siltstone. Flood-plain environments are interpreted for the red mudstone, shale, and siltstone, which consist of prominent root casts and other subaerial exposure features. This facies is prominently repeated three times within the cored zone. Coastal plain environments are represented by tidal channels consisting of fine-grained and clean sandstone, crevasse splay and interfluve sediments consisting of bioturbated sandstone, siltstone and shale and by dark grey to black shale of coastal marsh in origin. The core did not cover the lower contact of the Unayzah Formation. The upper contact of the formation with the Basal Khuff Clastics is placed at the top of the last oxidised red zone. Due to the limited palynofloral information, the age of the cored interval is not definitive but most likely is of Kazanian to Tatarian (Wordian to mid-Wuchiapingian). The Basal Khuff Clastics and the overlying Khuff Formation is equivalent to the OSPZ6 biozone and the Unayzah Formation could be in part equivalent to the OSPZ5 biozone. The sediments belonging to the Basal Khuff Clastics mark the onset of a major transgression that developed into a platform where carbonates of the overlying Khuff Formation were deposited.

Lithology and depositional environments of the Lower Jurassic Clarens Formation in the eastern Cape, South Africa

The Lower Jurassic Clarens Formation of the main Karoo Basin, South Africa, is regarded a climatically controlled fluvioaeolian to aeolian lithostratigraphic interval. It reveals a tectonically quiet period of orogenic unloading of the Cape Fold Belt and initiation of the rifting along the Indian Ocean rift axis. In the Clarens Formation outcrop area west of 27°E its lithofacies spectrum differs significantly from that known from the major part of the basin. Abundant pyroclastic and lacustrine facies elements characterise relatively small-scale local depocenters reaching below the regional base of the Clarens Formation. Such depositories have subcircular outlines and are surrounded by massive structureless sandstones being the product of phreatomagmatic crater formation. They separate the basin-wide aeolian facies succession from one illustrating the shallowing-upward crater lakes infilled due to gravitational and aeolian sediment supply. The existence of the crater lakes evidence shallow groundwater levels and reflect increased precipitation towards the end of Clarens Formation deposition. Low-frequency severe storms are suggested by hummocky cross-stratified beds in the lake-fill sequences. The strong impact of phreatomagmatic volcanic activity on the sediment supply and facies development of parts of the Clarens Formation illustrate a new facet of increasing rifting activity prior to the Lower Jurassic Karoo flood volcanism.

Taphonomy and paleoecology inferences of vertebrate ichnofossils from Guará Formation (Upper Jurassic), southern Brazil

In southern Brazil, the eolian facies of the Guará Formation (Late Jurassic) reveal footprints and trackways of vertebrates (dinosaurs), as well as burrows made by small vertebrates. All the footprints and trackways are preserved in dunes and sand sheets. The footprints made in the sand sheets are not well preserved due to intense trampling and can be distinguished only by the deformation of the sandstone laminations. In some cases it is possible to see this deformation in plan and in section. Tracks of theropods, ornithopods and middle-sized sauropods are present. Two footprints preserved in the foreset of a paleodune permitted recognition of slide structures and identification of the trackmaker, a theropod. Burrows horizontally across the foresets were found at this same paleodune. Ribbons of massive sandstone – interpreted as the partial filling of the base of the burrows – covered by little blocks of stratified sandstone – suggest the collapse of the burrow roof inward. There are no body fossils in the Guará Formation, consequently the preservation of these tracks provides unique evidence of widespread dinosaurs activity in southern Brazil near the end of the Jurassic.

Fluvial and aeolian deposition in the Siluro-Devonian Swanshaw Sandstone Formation, SW Scotland

Synopsis The recognition of fluvial and aeolian facies within the Siluro-Devonian Swanshaw Sandstone Formation of SW Scotland allows a more detailed depositional history of the Lanark basin in the southern part of the Midland Valley of Scotland to be inferred. The formation is well exposed in Ayrshire and has four main sedimentary facies associations: Channel, Aeolian, Floodplain and Mudflat. Each combines several sedimentary facies: eight facies are recognized in the channel association, three in the aeolian, four in the floodplain and two in the mudflat. These facies associations co-existed in seven different depositional settings in the western Lanark basin. Deposition occurred on a semi-arid proximal alluvial plain with an aeolian component described for the first time in the Lanark basin. Sedimentation was pulsed, largely driven by periods of source area uplift that resulted in the deposition of coarse-grained conglomeratic and sandstone-dominated facies. The principal transport was via river channels, commonly in shallow braided systems. Periods of low sediment flux are marked by fewer channels and by the preservation of floodplain successions including aeolian deposits. Abandonment of the fluvial system towards the top of the formation in Ayrshire is marked by a progression through sandflats and mudflats to the overlying volcanic formation. The relationship of the fluvial and aeolian deposits is analysed. The palaeo-wind direction is compatible with that recorded in sandstones of similar age in the Orcadian basin.

The Moenave Formation: Sedimentologic and stratigraphic context of the Triassic–Jurassic boundary in the Four Corners area, southwestern U.S.A.

The Moenave Formation was deposited during latest Triassic to earliest Jurassic time in a mosaic of fluvial, lacustrine, and eolian subenvironments. Ephemeral streams that flowed north-northwest (relative to modern geographic position) deposited single- and multi-storeyed trough cross-bedded sands on an open floodplain. Sheet flow deposited mainly silt across broad interchannel flats. Perennial lakes, in which mud, silt and carbonate were deposited, formed on the terminal floodplain; these deposits experienced episodic desiccation. Winds that blew dominantly east to south-southeast formed migrating dunes and sand sheets that were covered by low-amplitude ripples. The facies distribution varies greatly across the outcrop belt. The lacustrine facies of the terminal floodplain are limited to the northern part of the study area. In a southward direction along the outcrop belt (along the Echo Cliffs and Ward Terrace in Arizona), dominantly fluvial–lacustrine and subordinate eolian facies grade mainly to eolian dune and interdune facies. This transition records the encroachment of the Wingate erg. Moenave outcrops expose a north–south lithofacies gradient from distal, (erg margin) to proximal (erg interior). The presence of ephemeral stream and lake deposits, abundant burrowing and vegetative activity, and the general lack of strongly developed aridisols or evaporites suggest a climate that was seasonally arid both before and during deposition of the Moenave and the laterally equivalent Wingate Sandstone. We interpret growth of the erg as a consequence of marine regression during the latest Triassic through earliest Jurassic that exposed sediments on the coast of the back-arc sea to eolian reworking. Tectonic processes that created accommodation space enhanced preservation of the erg.

The Upper Jurassic (Kimmeridgian) fluvial–aeolian systems of the southern Neuquén Basin, Argentina

The Kimmeridgian Quebrada del Sapo Formation in the southernmost Neuquén Basin in Argentina represents a succession up to 40 m thick of coarse- to fine-grained fluvial deposits overlain by aeolian deposits. These fluvial–aeolian deposits reflect a significant palaeogeographic change in the basin and are related to a major, tectonically enhanced, relative sea-level fall. The fluvial section is dominated by braided-channel, fine-grained ephemeral, and sheetflood deposits. Aeolian facies are dominated by dune deposits, with minor sandsheet and interdune units. Changes in the nature of both fluvial and aeolian sedimentation within the studied area suggest a regional variability of accommodation/sediment supply conditions. The regional changes of the aeolian succession likely reflect different relative positions within a major erg. In the upwind margin of the erg, a shallow water table promoted water-lain sedimentation in interdune areas, whereas in the central parts of the erg, dry sediment accumulation took place above the regional water-table level. The vertical transition observed in the Quebrada del Sapo Formation, from fluvial to aeolian deposits, may be the result of a local climatic change to drier conditions due to the development of a climatic barrier imposed by growth of a magmatic arc to the west. Alternatively, the vertical transition could be related to a lowering of the water table associated with the compartmentalization of the basin during a period of low sea level.

Trace Fossils in Eolian Facies of the Upper Triassic-Lower Jurassic Dinosaur Canyon Member, Moenave Formation, Northern Arizona

The Dinosaur Canyon Member of the Moenave Formation, of Late Triassic to Early Jurassic (Rhaetian-Hettangian) age, consists predominantly of sandstones and mudstones deposited by sheet and channelized flow and by eolian processes. We document several previously undescribed biogenic structures in these strata. At one location, eolian dune sandstone hosts the lined, smooth-walled burrow Palaeophycus heberti (Saporta); these may be the nesting burrows of small sand wasps, or alternatively, the burrows of sand-treader camel crickets. Eolian dune facies that host abundant rhizoliths also are typically bioturbated. Circular markings that are convex in epirelief are assigned to Pustulichnus gregarious Ekdale and Picard. Unlined, non-ornamented burrows are unassigned. We speculate that both of these also were formed by the burrowing activity of one of the many species of sand wasp. Rhizoliths are particularly prominent at the tops of eolian dune sandstone beds and locally may host termite nests. Stabilization of the landscape by plants permitted pedogenic alteration of the sediments.

Sea-Level Variation During the Holocene Deduced from the Morphologic and Stratigraphic Evolution of Morgan Peninsula, Alabama, U.S.A.

Abstract Recent Gulf of Mexico shoreline studies interpret middle to late Holocene sea level as falling from a level above present elevation or stable at present elevation; however, the architecture of Morgan Peninsula, Alabama, does not support this. Morgan Peninsula is a beach-ridge strandplain composed of two obliquely aligned Holocene beach-ridge sets. Ground-penetrating radar profiles discriminate between parallel, even to wavy reflectors of the eolian dune environment and the underlying seaward-dipping, complex sigmoidal-oblique reflectors of the foreshore and upper-shoreface environment. The contact between foreshore and eolian facies in beach ridges can be used as a sea-level indicator. The average elevation of this contact in Morgan Peninsula rises throughout shoreline accretion, which occurred throughout the last 5.4 ka, suggesting that there was continual sea-level rise during this time. Morgan Peninsula is a useful modern analog to ancient shoreface–shelf parasequences and demonstrates the significant internal complexities that can exist in these deposits. Erosional discontinuities imaged in the Holocene foreshore–upper shoreface environment are laterally continuous, extend to elevations above mean sea level, and correlate to beach ridges and the transition between beach-ridge sets. An increase in the wave regime or fluctuations in sediment supply appear to be likely mechanisms for forming erosional discontinuities below beach ridges. The erosional surface separating beach-ridge sets may have formed by increased storm activity and associated barrier breaching, or a reconfiguration of the Mobile Bay tidal-delta complex superimposed on a gradual rate of sea-level rise. This boundary is recognized by a change in beach-ridge orientation at the surface and an increase in the aggradational component of shoreline accretion.

Vallecito Formation (Miocene): The evolution of an eolian system in an Andean foreland basin (northwestern Argentina)

The Vallecito Formation, a red bed sequence deposited during the Lower Miocene in the Andean foreland basins of the Precordillera (Argentina), has been studied to enable an analysis of the characteristics and temporal evolution of its facies and the major extrinsic factors that control its development. The unit is composed mainly of eolian sandstones and thin intercalations of fine-grained conglomerates and mudstones. The lithology, eolian stratification style, bounding surface type, cross-bedded set geometry, and depositional unit scale indicate six facies associations. Facies association I represents an eolian sand sheet; facies associations II, III, IV, and VI correspond to dunes and draas; and facies association V constitutes fluvial–eolian interaction deposits. With regard to sandstone composition, the Vallecito Formation is formed of feldlithic and lithic arenites with variable proportions of quartz and abundant volcanic rock fragments. The Vallecito Formation represents a large dune field developed in arid to semiarid climates during the first stages of the Andean orogeny. Its formation and development were controlled by climatic and tectonic factors. Concepts about eolian sediment states enable the establishment of a three-phase model of eolian evolution: (1) constructional, (2) maximum development, and (3) destructional. Contemporaneous influx in the constructional phase was limited by low sand availability in the marginal eolian sand sheets and the transport capacity of the wind in the main dune field. During the maximum development phase, dunes and draas grew under contemporaneous influxes limited by the transport capacity. The destructional phase corresponds to alluvial system progradation, which in some localities formed a fluvial–eolian interaction system where contemporaneous and lagged sediment influx was limited by sand availability. Eolian successions such as the ones represented by the Vallecito Formation are interpreted as foredeep deposits of continental foreland basins. In this depozone, the eolian facies correspond to very thick deposits characterized by thick cross-bedded sets, limited fluvial intercalations, a lack of paleosols, and high subsidence rates.

A REAPPRAISAL OF THE CARBONIFEROUS STRATIGRAPHY AND THE PETROLEUM POTENTIAL OF THE SOUTHEASTERN BONAPARTE BASIN (PETREL SUB-BASIN), NORTHWESTERN AUSTRALIA

A revision of the latest Tournaisian to Namurian stratigraphy of the Petrel Sub-basin is proposed following the recognition of a series of megasequences based on seismic profiles, well logs and new palaeontological information. In late Tn3c, turbidites of the Waggon Creek facies were overlain by a seal, the Milligans Formation (redefined) during the Chadian (V1a, V1b). A basal Arundian (V2a) regression, possibly driven by tectonics, deposited the Yow Creek Formation (new name) with incised valley fills. A basal Asbian (V3a) regression, deposited coarser grained clastics and limestones, the Utting Calcarenite (V3a), forming a possible local reservoir facies overlain by a regional seal, Kingfisher Shale (new name). An intra-Asbian (V3b) regression followed, possibly glaciogenic and/or tectonically driven, with the deposition of the Tanmurra Formation, dominantly coarse clastics, during the Asbian, forming reservoir facies with some source potential. Following a basal Brigantian unconformity, the Sandbar Sandstone (new name) formed a restricted ?aeolian facies, a potential local reservoir. An intra-Brigantian unconformity was followed by deposition of the carbonate Sunbird Formation (new name), generally a tight shelf edge carbonate (V3c), near Lacrosse–1 and Sunbird–1. A major basal Pendleian sea-level fall, probably glaciogenic, with major channel incision and erosion, was followed by Arnsbergian clastics with G. maculosa, the Arco Formation (new name) with basinal shales in clinoforms. The latest Arco Formation (earliest Pennsylvanian) was followed by a Late Namurian regression, and deposition of the Aquitaine Formation (new name), consisting of fluvio-deltaic siliciclastics, with minor marine influence, large scale channelling, potentially good reservoirs, and a regional upper shaly seal. This sequence is unconformably overlain by the basal Kulshill Group, which marked the onset of major Gondwanan glaciation.

The transgression of an erg — sedimentation and reworking/soft-sediment deformation of aeolian facies: the Cretaceous Troncoso Member, Neuquén Basin, Argentina

Abstract The Cretaceous Troncoso Inferior Member of the Huitrín Formation comprises fluvial and aeolian facies that form a drying-upwards succession within the Neuquén Basin. The basal fluvial sandstones were deposited as braided river deposits and lie unconformably on top of either the deep-marine Agrio Formation or, locally, the shallow-marine Chorreado Member (Huitrín Formation.). In places, the fluvial sandstones are interbedded with remnants of aeolian deposits recording an arid environment and ephemeral flows. In the study area the upper section is predominantly aeolian and was controlled by northerly winds with both linear and transverse dune types being deposited. The depositional system was rapidly flooded and dune topography (relief ranging between 2 and 35 m) was preserved on its top surface. In addition to dune topography, the Troncoso dunes also show evidence of reworking and in situ soft-sediment deformation related to the flooding. The principal aim of this paper is to document the soft-sediment deformation and preservation of topography associated with the flooding of the dune field. Within the soft sediment deformed and reworked sediments at the top of the Troncoso Inferior Member spatial and temporal relationships indicate that they formed in a specific sequence. Initially, water-escape processes created convolutedly folded and dish structures that were concentrated in areas of slightly higher preserved dune topography. Secondly, the convolutedly folded and dish facies were eroded and reworked by wave undercutting and migrating three-dimensional dunes in a shallow-marine environment. This subaqueous reworking resulted in an interbedded massive and cross-stratified unit. With further deepening of the water, the topography became stabilized and the uppermost part of the interval (0.1–0.3 m) was reworked by waves across most of the basin. In the topographic lows between dunes, liquefaction-induced sediment gravity flows deposited massive-flatlaminated facies. The reworked and soft-sediment deformed aeolian dune topography is overlain by the evaporites of the Troncoso Superior Member. The distribution of flood-related facies and the amount of preserved dune topography (2–35 m) indicates that the transgression must have been rapid but of low energy.