Aeolian Facies Research Articles

Are aeolian ichnofacies distinctive and useful? An analysis of trace fossil assemblages from Cretaceous aeolian facies in northern Patagonia, Argentina

In this paper, Cretaceous trace fossil assemblages are reported from aeolian facies within four units from Patagonia, Argentina, to evaluate the usefulness of the aeolian ichnofacies concept. From oldest to youngest, studied units comprise the Agrio (Valanginian-Hauterivian), Cerro Barcino (Aptian-Cenomanian), Candeleros (Cenomanian), and Allen (Campanian-Maastrichtian) formations. Twenty one ichnotaxa were recorded, including ten of invertebrate origin (Archaeonassa fossulata, Arenicolites tenuis, Beaconites isp., Digitichnus laminatus, Edaphichnium lumbricatum, cf. Octopodichnus isp., Palaeophycus tubularis, Skolithos linearis, Taenidium barretti, and an unidentified arthropod trackway), seven tetrapod footprints and burrows (Avipeda isp., Brasilichnium isp., cf. Chelonipus isp., Reniformichnus katikatii, two types of indeterminate footprints, and burrow fills) and four rhizolith types. Entradichnus meniscus (formerly used as eponym of an aeolian ichnofacies) is considered a junior synonym of Taenidium barretti. Common ichnotaxa in aeolian and fluvial sequences like Taenidium barretti, Skolithos linearis and Palaeophycus tubularis are facies-crossing ichnotaxa and should not be used to distinguish ichnofacies. Trace fossil assemblages and ichnofabrics from aeolian dune, dry interdune and wet interdune facies are interpreted in terms of the potential producers and their palaeoecological and palaeoenvironmental constraints. This procedure is more informative than the ichnofacies approach in aeolian deposits. Based on a literature review of 32 examples of trace fossil assemblages from Cretaceous aeolian sequences worldwide, we conclude that the most distinctive ichnotaxa occur in aeolian dunes, including Brasilichnium, Farlowichnus, lacertoid footprints, Octopodichnus and Paleohelcura. It is recommended to abandon the usage of the Chelichnus, Entradichnus and Entradichnus-Octopodichnus ichnofacies, which are poorly defined in terms of recurrence and environmental significance or based on uncharacteristic or unavailable ichnotaxa. We propose a new definition of the Octopodichnus ichnofacies, diagnosed by the presence of subequant tetrapod footprints in quadrupedal trackways and/or selected arachnid /insect trackways. This ichnofacies is a taphofacies recorded from the Permian to the Cretaceous, and probably extends to the Cenozoic.

Quartz grain microtextures of Holocene sebkhas sediments in southeast Tunisia: Implications for sedimentary processes and depositional environments

Detrital quartz grains extracted from sebkha sediments in southeastern Tunisia underwent scanning electron microscopy analysis to identify sediment sources and assess the influence of the saline environment on the grains. Core sediments collected from Sebkha el Melah and Sebkha Mhabeul cover the last 5000 and 2000 BP, respectively. The uppermost Unit III, present in both cores, exhibits two distinct facies based on the mechanical microtextures of its quartz grains. The aeolian facies sediments are characterized by quartz grains with rounded outlines, upturned plates, and crescentic percussion marks. In contrast, the fluvial facies sediments are associated with quartz grains featuring subangular outlines, v-shaped percussion cracks, conchoidal fractures. Observations on the quartz grains of the sebkhas suggest multiple transportation and processing events, indicating long-distance transport and rapid deposition rates. The majority of quartz grains appear to originate from the surrounding terrain, reflecting the dynamic geological history of the region. This study delves into the connection between microtexture variations on quartz grain surfaces and specific historical climatic conditions in the sebkhas. By examining geochemical variations along the cores, facies with elevated salt concentrations corresponding to warmer periods reveal extensively weathered quartz grains. This substantial chemical alteration is evident through microtextures such as oriented etch pits, anastomosed dissolution networks and solution crevasses. The profound dissolution has significantly impacted the quartz lattice, resulting in the decomposition of the grains and the formation of "cauliflower" or "spongy" shapes, erasing prior microtextures. Conversely, during less warm periods, quartz dissolution was less severe, thereby preserving microtextures.Sand grain surfaces are notably sensitive to both transport processes and variations in the physicochemical environment. In the hypersaline and confined environments of sebkhas in southeastern Tunisia, potent post-sedimentary processes can obliterate and obscure the original microtextures recorded on grains from previous environments due to highly fluctuating physicochemical conditions.

Stratigraphy and evolution of the late Pleistocene (MIS 5) coastal Barrier III in southern Brazil

Abstract The structure and origin of the Pleistocene (Marine Isotope Stage [MIS] 5) coastal Barrier III in southern Brazil were investigated through analysis of lithofacies, numerical ages, and ground-penetrating radar (GPR) data obtained in outcrops and subsurface deposits. The stratigraphic succession is characteristic of transgressive barriers, with muddy lagoon bottom facies unconformably overlying an older unit (Barrier II) and overlain by landward-dipping lagoon margin and aeolian facies. The back-barrier lagoon was filled with sediments and shells transferred from the foreshore through overwash and/or inlets during the MIS 5e transgressive-high-stand phase, with a higher sea level that reached about +6 to +7 m relative to the present. Marine sediments and shells on the seaward side of the barrier dated to ~100–106 ka indicate another high stand at +4 to +5.1 m during MIS 5c. One shell dated to ~87 ka and aeolian deposits dated to ~82 and ~85 ka suggest a third high stand during MIS 5a that reached at least −2 m relative to the present. The two (possibly three) juxtaposed marine deposits show that Barrier III is a more complex unit than previously recognized, built by successive orbitally forced eustatic sea-level oscillations also recorded in other deposits along the Brazilian coast and worldwide.

Westerly aridity in the western Tarim Basin driven by global cooling since the mid-Pleistocene transition

To explore the relationship between the global cooling, westerlies, and central Asian aridity, we report ∼1.1 Ma local sedimentary environment changes according to physical-chemical parameters from an 800-m core (KT11) from the Kashgar region in the western Tarim Basin, China. Grain size end-member (EM) modelling is employed to quantify the processes of sediment transport and deposition. Four end members with modal values of 272 μm, 144 μm, 45.6 μm and 12.7 μm were extracted and explained 97.9% of the variance in the grain size data, corresponding aeolian dynamics, river energies, delta development and pedogenesis/long-term suspension components transported by wind or water, respectively. Four dominant sedimentation types, including lacustrine facies, delta facies, fluvial facies, and aeolian dunes, were identified through lithology and grain size frequency curves. The 1.1 Ma sedimentary successions experienced delta deposits interbedded with fluvial and aeolian deposits and lacustrines (1.1–0.6 Ma), alternating fluvial and aeolian facies with the occurrence of deltas and lacustrines (0.6–0.15 Ma), and aeolian facies interbedded with deltas and fluvial facies (0.15 Ma-present). Stepwise drying sedimentary conditions and enhanced desertification indicated by increasing rubidium/strontium ratios and proportion of aeolian sands, and decreasing total organic carbon since the past 1.1 Ma, implied intensified westerlies, likely resulted from ice volume expansion and ongoing global cooling according to geological record comparison and simulations during the Last Glacial Maximum compared to preindustrial conditions, which may have controlled the expansion of the permanent deserts in inland Asia. These persistent drying trends and intensified westerly circulation in arid regions during glacial periods after the mid-Pleistocene Transition indicated by larger amplitudes of aeolian sand proportion than prior to 0.6 Ma are similar to those in the interior monsoonal Asia, where the larger-amplitude of median grain size indicated enhanced Asian winter monsoon intensity and drier glacials.

The edge of a Permian erg: Eolian facies and provenance of the Lyons Sandstone in northern Colorado

ABSTRACT Facies of the Permian Lyons Sandstone are described and interpreted based on analyses of 23 cores from Larimer and Weld counties, Colorado. Here, the Lyons Sandstone consists of very fine- to medium-grained sandstone with minor silt and mudstone interbeds. The unit has five recurrent siliciclastic facies that can be grouped into two facies associations (FA). FA1 consists of (1) high-angle, cross-laminated sandstone (Facies 1; interpreted as eolian dune remnants); (2) low-angle, cross-laminated and horizontally laminated sandstone (Facies 2; interdune); and (3) chaotically bedded to folded sandstone (Facies 3; lower dune flanks). FA2, in contrast, is mainly (4) wavy- to irregularly laminated silty sandstone (Facies 4; wet to damp interdune); and (5) massive to wavy-laminated silt-rich mudstone (Facies 5; ponded water areas between dunes) with minor amounts of high-angle, cross-laminated sandstone (Facies 1) and low-angle, cross-laminated and horizontally laminated sandstone (Facies 2). FA1 is hypothesized to have been produced in an eolian system akin to those that might exist in the dune-dominated portion of an erg, whereas FA2 was deposited in the intermittently wet portion of this eolian system, perhaps along erg margins or in flat dune-adjacent settings that were impacted by the water table. Isopach data suggests that the study area is on the fringe of a larger Lyons system that spans > 100,000 km2, and was deposited close to the Ancestral Rockies—a paleogeography consistent with deposition in erg to erg-margin paleoenvironments. Detrital zircon populations from nearby Colorado Front Range outcrops and from 12 correlative eolian units are dominated by small, well-rounded Paleoproterozoic and Mesoproterozoic grain populations that are remarkably similar between units, signaling a well-mixed system that also received an influx of distally sourced sediment from the Appalachian orogen. Detrital zircon-based maximum depositional ages of the Lyons Sandstone and its equivalents are internally consistent with deposition of the unit during the latest Artinskian to Kungurian.

Facies and architectural element analysis of the Upper Bokabil Sandstone in the Bengal Basin

The Upper Bokabil Sandstone is a geologically significant unit in the Bengal basin, hosting the most prolific hydrocarbon reservoirs and serving as a source of groundwater. Despite its economic importance, the depositional setting of this unit has not yet been thoroughly studied, largely due to the limited accessibility to the outcrops. This research aims to provide the first modern sedimentological interpretation of the Upper Bokabil Sandstone in the Bengal basin utilizing data from outcrops and well logs. A generic model of the depositional environment is proposed based on sedimentary facies and architectural elements. The sedimentary facies of the Upper Bokabil Sandstone were examined at outcrops in the Sari River section of Jaintiapur (northern Bengal basin) and Paglir Bill in Ukhiya (southern Bengal basin). A total of 12 fluvial lithofacies and multiple high and low order erosional surfaces were identified. Facies associations and their relationship with their bounding erosional surfaces have been utilized to identify the architectural elements. The unit is characterized by laterally and vertically amalgamated channels and bar complexes, with downstream and lateral accreted barforms being the dominant architectural elements. Lateral Accretion (LA) is more prevalent in the southern part of the basin. The presence of the fluvial facies, distinct architectural elements associated with typical braided river and lack of aeolian facies lead to the interpretation of a low sinuosity braided river with seasonal fluctuation in discharge as the depositional environment of the Upper Bokabil Sandstone.

Three‐dimensional bounding surface architecture and lateral facies heterogeneity of a wet aeolian system: Entrada Sandstone, Utah

ABSTRACTAeolian deposits form noteworthy reservoirs (for example, Norphlet Formation and Rotliegend Group) in hydrocarbon extraction and carbon capture and storage contexts, but stratigraphic architecture imparts significant heterogeneity. Bounding surfaces result from autogenic and allogenic controls and can represent important changes in dune‐field dynamics. To further evaluate the impacts of facies heterogeneity and flow‐inhibiting bounding surfaces on reservoir performance and reconstruct ancient erg evolution, the stratigraphic architecture of aeolian systems must continue to be studied at multiple scales. This study pairs traditional methods (for example, measured stratigraphic sections) with advanced technologies (for example, drone‐derived outcrop models) to precisely resolve the metre to kilometre‐scale three‐dimensional stratigraphic architecture of wet aeolian Middle Jurassic Entrada Sandstone outcrops located at Rone Bailey Mesa near Moab, Utah, USA. Five facies are identified, primarily based on sedimentary fabrics, and are grouped into three associations named dune, sabkha and sand sheet. Statistical analyses of gamma‐ray spectrometer and automated mineralogy data indicate a distinct mineralogical difference between dune (quartz‐rich) and sabkha (more feldspathic) packages, suggesting that gamma‐ray logs may be used to better predict facies distribution in the subsurface. Seven modelled super bounding surfaces are planar to undulatory, with no perceived spatial trends. Five modelled interdune migration surfaces are undulatory but exhibit an average 0.09° angle of climb roughly parallel to the palaeocurrent direction. Two modelled superposition surfaces are linear to sinuous in plan‐view. Laterally discontinuous sabkha packages observed are interpreted to be remnants of closed, damp, interdune flats located between ca 8.5 to 17.0 m tall, sinuous, transverse bedforms or patches of such bedforms. Based on stratigraphic architecture interpretations, the Entrada Sandstone preserves signals of allogenic forcing and localized autogenic bedform cannibalization of the substrate. The findings of this study, some of which are not commonly recognized in wet aeolian facies models, enhance the understanding of erg evolution and can parameterize static models of aeolian reservoirs.

Late Pennsylvanian aridification in Gondwana mid-latitudes contemporaneous to high-latitudes ice cap expansion, upper Piauí Formation, Brazil

The Pennsylvanian Epoch was marked by a well-known glaciation period documented in several basins across the Gondwana. However, stratigraphic data from the Parnaíba Basin suggest that drier climate conditions dominated mid-paleolatitudes simultaneously to the glaciation. To investigate the possible time equivalence and the causes of aridification in mid-paleolatitudes, high-resolution stratigraphic analysis of the upper Piauí Formation were conducted in the eastern margin of the Parnaíba Basin. As a result, three stratigraphic intervals separated by key stratigraphic surfaces were identified: The first stratigraphic interval is dominantly composed of fluvial deposits progressively overlain by eolian facies; the second stratigraphic unit is essentially composed of lacustrine deposits and represent a regional flooding related to a period of lake expansion and finally, the third stratigraphic unit is characterized by three eolian genetic units and depicts cyclic expansion and contraction of a dune field. The overall vertical stratigraphic succession represents a progressive change from original fluvial sedimentation to essentially eolian accumulation and constitutes a drying upward trend that reflects an increasing aridification in the Parnaíba Basin during the Late Pennsylvanian age. The detailed analysis of the paleoclimatic conditions and the atmospheric circulation during the Late Pennsylvanian Epoch evidenced that the waning and waxing of the ice sheets controlled the development, expansion and contraction of the upper Piauí Formation dune-field.

Sedimentology of the latest Permian to Early Triassic in the terrestrial settings of the North China Basin: Low-latitude climate change during a warming-driven crisis

Abstract In terrestrial settings, the Permo-Triassic mass extinction is commonly linked to major changes in sedimentological and climatic conditions that include a switch from meandering to braided fluvial systems and increased aridity. We examined the predominantly terrestrial strata of North China to reveal that, on the contrary, there was little substantial sedimentological change during the Permo-Triassic mass extinction. The crisis level occurs in the upper Sunjiagou Formation, where a range of environments, including low-sinuosity rivers, distally terminating alluvial fans, and mud-dominated coastal plains are recorded. A major sedimentological change occurred slightly higher, within the lowest Triassic, and involved a switch to braided fluvial and shallow lacustrine/fluviodeltaic conditions of the Liujiagou Formation. Later in the Early Triassic, fine-grained, playa lake, and alluvial plain facies became widespread (Heshanggou Formation). Paleosols are present throughout the basin fill and record a transition from Aridisols and Vertisols in the Late Permian to Inceptisols in the Early Triassic followed by gleyed Aridisols, Vertisols, and Inceptisols later in the Early Triassic. Previously reported aeolian facies from Lower Triassic strata were not encountered in this study and were unlikely to have occurred given the prevalence of lacustrine and fluvial conditions at this time. Overall, the North China Basin experienced an increase in seasonal rainfall in the latest Permian and a base-level rise that introduced marine conditions into the southwest of the basin. During the Early Triassic, seasonal or interannual rainfall was frequent, with strong evaporation in a hot climate. Overall, substantial sedimentological changes occurred in the terrestrial Permo-Triassic environments of North China, but despite earlier claims from studies in North China and elsewhere, there was no abrupt transition in fluvial styles around the Permo-Triassic mass extinction.

Ground-Penetrating Radar Prospections to Image the Inner Structure of Coastal Dunes at Sites Characterized by Erosion and Accretion (Northern Tuscany, Italy)

In this study we aimed to gain insights into dune formation and evolution from select coastal tracts of Northern Tuscany by inspecting their internal sedimentary architecture with Ground-Penetrating Radar (GPR) analysis. Erosion, equilibrium and accretion characterize the selected coastal tracts, and this analysis remarks on some GPR features consistently associated with specific coastal evolution states. A standard sequence of data processing made it possible to trace several radar surfaces and reflectors in the GPR profile, eventually interpreted in terms of depositional processes and erosive events. The stable or currently accreting coastal sectors show radar features compatible with a general beach progradation process, punctuated by berm formation in the general context of a positive sedimentary budget. Additionally, the radar facies distribution locally supports a mechanism of dune nucleation on an abandoned berm. Conversely, the GPR profile of the coastal sector today affected by erosion shows how a negative sedimentary budget inhibited coastal progradation and favored destructive events. These events interacted also with the active dunes, as demonstrated by the overlapping of wave run-up and aeolian radar facies. GPR prospections were effective at delineating the recent/ongoing coastal sedimentary budget by identifying radar features linked to construction/destruction phenomena in the backshore, and to dune nucleation/evolution.

The Paleoproterozoic Kombolgie Subgroup (1.8 Ga), McArthur Basin, Australia: Sequence stratigraphy, basin evolution, and unconformity-related uranium deposits following the Great Oxidation Event

ABSTRACTProterozoic continental sedimentary basins contain a unique record of the evolving Earth in their sedimentology and stratigraphy and in the large-scale, redox-sensitive mineral deposits they host. The Paleoproterozoic (Stratherian) Kombolgie Basin, located on the Arnhem Land Plateau, Northern Territory, is an exceptionally well preserved, early part of the larger McArthur Basin in northern Australia. This intracratonic basin is filled with 1 to 2 km-thick, relatively undeformed, nearly flat-lying, siliciclastic rocks of the Kombolgie Subgroup. Numerous drill cores and outcrop exposures from across the basin allow sedimentary fabrics, structures, and stratigraphic relationships to be studied in great detail, providing an extensive stratigraphic framework and record of basin development and evolution.Tectonic events controlled the internal stratigraphic architecture of the basin and led to the formation of three unconformity-bounded sequences that are punctuated by volcanic events. The first sequence records the onset of basin formation and is comprised of coarse-grained sandstone and polymict lithic conglomerate deposited in proximal braided rivers that transported sediment away from basin margins and intra-basin paleohighs associated with major uranium mineralization. Paleo-currents in the upper half of this lower sequence, as well as those of overlying sequences, are directed southward and indicate that the major intra-basin topographic highs no longer existed. The middle sequence has a similar pattern of coarse-grained fluvial facies, followed by distal fluvial facies, and finally interbedded marine and eolian facies. An interval marked by mud-rich, fine-grained sandstones and mud-cracked siltstones representing tidal deposition tops this sequence. The uppermost sequence is dominated by distal fluvial and marine facies that contain halite casts, gypsum nodules, stromatolites, phosphate, and “glauconite” (a blue-green mica group mineral), indicating a marine transgression. The repeating pattern of stratigraphic sequences initiated by regional tectonic events produced well-defined coarse-grained diagenetic aquifers capped by intensely cemented distal fluvial, shoreface, eolian, and even volcanic units, and led to a well-defined heterogenous hydrostratigraphy. Basinal brines migrated within this hydrostratigraphy and, combined with paleotopography, dolerite intrusion, faulting, and intense burial diagenesis, led to the economically important uranium deposits the Kombolgie Basin hosts.Proterozoic sedimentary basins host many of Earth's largest high-grade iron and uranium deposits that formed in response to the initial oxygenation of the hydrosphere and atmosphere following the Great Oxygenation Event. Unconformity-related uranium mineralization like that found in the Kombolgie Basin highlights the interconnected role that oxygenation of the Earth, sedimentology, stratigraphy, and diagenesis played in creating these deposits.

Evolution of Storm Surges over the Little Ice Age Indicated by Aeolian Sand Records on the Coast of the Beibu Gulf, China

The Wutou section, hereinafter referred to as “WTS”, lies in Jiangping, Guangxi Province, China (21°32′8.25″ N, 108°06′59.9″ E; thickness of 246 cm) and consists of fluvial-lacustrine facies and dune sands of the Late Holocene. This study reconstructed the evolution of storm surges along the coast of the Beibu Gulf, Guangxi over the Little Ice Age, based on three accelerator mass spectrometry (AMS)-14C, optically stimulated luminescence (OSL) dating ages, and the analyses of grain size and heavy minerals. The analysis results indicated that the storm sediments interspersed among aeolian sands, lagoon facies, and weak soil display a coarse mean grain size and poor sorting. The storm sediments also show high maturity of heavy minerals and low stability resulting from rapid accumulation due to storm surges originating from the land-facing side of the coastal dunes. Records of seven peak storm surge periods were recorded in the WTS over the past millennium and mainly occurred after 1400 AD, i.e., during the Little Ice Age. The peaks in storm surges, including the 14Paleostrom deposit (hereinafter referred to as “Pd”) (1425–1470AD), 10Pd (1655–1690AD), 6Pd (1790–1820AD), and 4Pd (1850–1885AD) approximately corresponded with the periods of minimum sunspot activity, suggesting that the periods of storm surge peaks revealed by the WTS were probably regulated to a great extent by solar activity.

CPT Parameters of Loess Subsoil in Lublin Area

Loess soils were created by the wind transporting particles with later or in parallel occurred protogenetic, syngenetic and epigenetic processes. As a result, various genetic processes affected loesses strength and deformability characteristics. The aim of the study is to estimate the main CPT parameters of loess subsoil in Lublin area according to divided facies. The subsoil in the area of the Nałęczowski Plateau, where Lublin is located, consists mainly of loess from aeolian and aeolian–diluvial facies, and in the deeper parts—from aeolian–alluvial facies. Most of the results obtained for the aeolian facies at the level of qc in the range from 4.5 to 8.0 MPa indicate that these soils are a good load-bearing substrate for building structures. Cone resistances mostly at the level of 1.5–4.0 MPa for the diluvial and alluvial facies confirm that these facies constitute less favorable foundation conditions. The reduced resistance results mainly from the increased water content in ground pores. It is especially the soils of the diluvial facies that provide unfavorable foundation conditions, as they occur near the surface. Genetic processes are a very important element that should be taken into account in engineering research.

Dinosaurs and rivers on the edge of a desert: A first recognition of fluvial deposits associated to the Botucatu Formation (Jurassic/Cretaceous), Brazil

This work aimed to investigate the ichnofossiliferous sites in Nioaque and surrounding region, Mato Grosso do Sul state, Brazil, analyzing their paleontological, stratigraphic and paleoenvironmental context, because dinosaur tracks were found in an area previously mapped as Permo–Carboniferous age. Some sedimentary facies previously assigned to the glacial Aquidauana Formation were herein reinterpreted as part of the basal section of the Botucatu Formation (Late Jurassic/Early Cretaceous) and include floodplain and residual channel deposits, possibly representing the lower half of this formation's sequence in the studied area. The ichnofossils that have been found include both isolated tracks of Theropoda and Ornithopoda, a trackway of Eubrontes isp., a vertebrate burrow and invertebrate traces (Palaeophycus) possibly related to the Entradichnus ichnofacies. Sedimentological interpretation suggests the existence of a river system just before the deposition of the typical Botucatu eolian facies in this region. This is the first documented record of fluvial deposits transitionally to the traditional eolian Botucatu Formation. Noteworthy, the dinosaur tracks have played a key role for the interpretation of these rocks as Botucatu Formation and for better understanding the whole system due to the impossible Paleozoic age (dinosaur tracks).

Andean orogenic signature in the Quaternary sandy barriers of Southernmost Brazilian Passive Margin – Paradigm as a source area

Multiple source provenance of sediments and submarine fan formation are herein investigated based on Quaternary sandy barriers of the Brazilian Southernmost Coastal Plain. LA-ICP-MS dating on 1625 detrital zircons from marine and aeolian facies sands of four successive lagoon-barrier systems are analyzed. The characterization of Archean to Pleistocene zircons into a younger Andean (22 ± 4 Ma to 1 ± 1 Ma, 48 from 1625), Mesozoic to Paleozoic, and Mesoproterozoic (479 from 1622) populations suggest that the main feeding of sediments to the coastal plain occurred through the La Plata River drainage system. The significant contribution of sediments is transported from the mouth of La Plata River northward by longshore circulation (littoral drift). Minor contributions are also recognized as. a farther source associated with the Patagonia drainage and nearby source related to the Uruguay/Rio Grande do Sul Shield and the Paraná Basin, drained by the Camaquã and Jacuí rivers. The latter one is recognized by the contribution from Neoproterozoic to Early Paleozoic, and some Paleoproterozoic and Archean zircon grains. The definition of the sources of clastic sediments allows inferences about the origination of Rio Grande Fan where both the cold Falkland and the warm Brazil currents played a major role.

Quaternary sequence stratigraphy of onshore Abu Dhabi Emirate

Glacially driven eustatic sea-level fluctuations have left a clear signature only along the coastal regions and barrier islands of the Abu Dhabi Emirate. Four marine sequences are identifiable although others are known to exist offshore. The stratigraphy is complicated by aeolian processes associated especially with the Shamal winds which have blown from the northwest to create dune fields that dominate the Quaternary sedimentation. Whilst aeolian facies can clearly be identified separating marine incursions along the coastal regions, aeolian deflation has complicated the stratigraphy by recycling sediment partly in response to loss of windward sediment sources during marine transgressions and partly in response to glacially driven climatic changes. Unravelling the sequence stratigraphy of the desert dunes inland, especially beyond the coastal sabkhas, is therefore extremely difficult. The late Quaternary aeolian dunes and their veneer of mobile aeolian sands are grouped into a single poorly defined formation which spans the entire timescale of the sequences identified along the coast.

Formation age of Jiudong Sandy Land, in the western Hexi Corridor, NW China

Jiudong Sandy Land in the western Hexi Corridor is one of the dust source regions of the Chinese Loess Plateau and is highly sensitive to climate change. Determination of when this sandy land formed would help resolve major questions about the desertification history of inland Asia; however, until now, this has been hindered by the lack of depositional records. Here, we report the results of optically stimulated luminescence (OSL) dating, grain size and grain surface analyses from a new drill core obtained from Jiudong Sandy Land. Our aims are to constrain its age of formation. Analysis of sedimentary facies reveals that the sediments in the lower part of the core (35.2–16.7 m) were deposited by fluvial processes, but that the sediments in the upper part consist primarily of aeolian sand. The OSL dating results indicate that the transition from fluvial to aeolian facies occurred at ∼89.8 ± 7.6 ka. Combined with various loess-based environmental proxies from Jiudong Basin, the new litho- and chronostratigraphic evidence reported in this study indicates that the age of ∼89.8 ± 7.6 ka represents the formation age of the Jiudong Sandy Land.

Facies distribution as a response to early rift tectonic activity in the Sergipe-Alagoas Basin, northeastern Brazil

Accommodation rates in rift basins are mainly controlled by tectonics. However, during early rift stages, normal fault activity is dispersed and incipient, which makes it difficult to recognize the effects of early crustal extension. The sedimentary stacking pattern of rift-related depositional environments can be decisive to address this question. This paper aimed to evaluate the stratigraphic record of the Tithonian-Berriasian (?) Serraria Formation (Sergipe-Alagoas Basin, Brazil), which was deposited in the Afro-Brazilian Depression, as a result of the early extension of West Gondwana. In total, 14 lithofacies were described, interpreted and arranged into 7 facies associations. At the base of the formation, bars and sand sheets were deposited by low discharge braided channels, which were deposited on top of lacustrine mudstones of the Bananeiras Formation. There is a change in stratigraphic architecture in the middle of the section, where fluvial channels become deeper due to increasing discharge, promoting an increase in grain size of the transported bedload and greater rates of coarse sand and gravel bar stacking. Rare crevasse channels and restricted aeolian dune fields occur adjacent to braided channel belts. Upwards, the Serraria Formation becomes dominated by delta front and delta plain deposits. The fluvial and aeolian facies associations represent a progressive decrease in accommodation, while the upper fluvio-deltaic interval means an increase in accommodation, pointing to the early rift stage climax. The fluvial “Caioba” sandstone on top of the Serraria Formation indicates reestablishment of fluvial drainage either due to decreasing tectonism or due to low accommodation at the time of deposition. Thus, the sedimentary stacking pattern of Serraria Formation represents higher frequency cycles within an early rift tectonic system tract.

Anatomy of a late Quaternary carbonate island: Constraints on timing and magnitude of sea-level fluctuations, West Caicos, Turks and Caicos Islands, BWI

The data set of the island of West Caicos consists of a combination of high-resolution lidar and digital imagery, radiometric data, and amino acid racemization (AAR) D/L values as well as extraordinary preservation of sedimentary and bio-constructed deposits on the island. Together with a well-established regional stratigraphic framework from the neighboring Bahamian island chain and detailed field mapping, the West Caicos data set provides an opportunity to advance our understanding of the link between carbonate stratigraphy and the controlling parameters of sea level, sediment supply, tectonics, and climate. The exceptionally well-preserved stratigraphic record of the mid–late Pleistocene from West Caicos allows recognition of marine isotope stages (MIS) 9/11, 5e, and Holocene. The west coast of the island provides a continuous 8.4 km exposure of the MIS 5e record that enhances our understanding of the intra-MIS 5e bipartite succession in this region and supports a sea-level lowering that occurred during the last interglacial (LIG).West Caicos accreted as a series of eolian, foreshore–shoreface, barrier-reef, and fringing-reef facies. Shoreline positions for all but the MIS 7 and MIS 5a/c deposits are now captured in the sub-meter geodetic-quality topobathy lidar survey. The Star Town unit of MIS 9/11 age forms the southern margin of the island as well as the central karst-modified spine, with uranium–thorium (UTh) coral ages of between 368 and 365 thousand years ago (ka) and a D/L Glu average of >0.60. Early MIS 5e strata include the Railroad Ridge unit in the center of the island, which was previously identified as one of the older units. The Railroad Ridge unit is a north–south linear dune ridge that has a D/L Glu average of 0.52 and indicates the onset of sediment sources from the east associated with a flooded central Caicos Platform. Approximately synchronously, the early MIS 5e South Reef unit (+3.75–4 m sea-level elevation) nucleated on the western coast of West Caicos, attached to the middle Pleistocene Star Town unit. The South Reef corals yield an average coral UTh age of 126.5 ka, with an average D/L Glu from skeletal matrix of 0.46. This transitional barrier/fringing reef is unconformably overlain by the late MIS 5e Boat Cove unit. Corals in the basal transgressive phase of this upper MIS 5e Boat Cove unit yield an average 120.6 ka UTh and average D/L Glu of 0.45. Shallow-marine, foreshore, and eolian facies of the late MIS 5e rest on a wave-cut terrace that cuts the early MIS 5e South Reef unit by as much as 3 m down to a +0.5 m above present sea-level elevation. The upper MIS 5e Boat Cove unit displays a maximum of +4.5 m elevation above present-day sea level, measured from the middle of the foreshore. This estimate may be a minimum value as the exposures on the west coast are part of a forced regressive foreshore sequence. Last stages of the upper MIS 5e deposition are seen in a series of regressive dune-beach ridge deposits referred to as the Northeast Ridges unit, with sea-level positions ranging from +4.5 m early in the central part of West Caicos, to +0.5 m on the far northeast coast, eventually building down below present-day sea level. This sea-level history fits well with previously documented records in the Bahamas and globally, and the extensive erosion supports a short-lived (between 126 and 120 ka) intra-MIS 5e relative-sea-level fall. Holocene deposition on West Caicos is restricted to northern and eastern margins of the island as a combination of strandplain and dune ridge mixed skeletal–oolitic units.Using the high-resolution digital elevation model (DEM) and linked digital geologic map makes it possible to compare areas of the different Pleistocene and Holocene units quantitatively and to constrain volumetric assessments and accumulation rates on the island for different units. The peak sediment volume production/accumulation rate—between 6.5 and 8 × 106 m3 or between 2.2 and 2.7 × 106 m3 per ka—is observed in the upper MIS 5e unit. This rate is 5 times greater than the 0.5 × 106 m3 per ka estimated for the Holocene ooid dune-ridge/strandplain complex, suggesting that the combination of higher sea level, greater wave and wind energy, and warmer ocean temperatures may have fostered the higher rate of chemically precipitated sediment supply.

Genetic units and facies architecture of a Lower Cretaceous fluvial-aeolian succession, São Sebastião Formation, Jatobá Basin, Brazil

The Lower Cretaceous São Sebastião Formation of Jatobá Basin consists of continental strata accumulated in an arid environment dominated by aeolian deposits. The best outcrops are located in the county of Ibimirim, in the Pernambuco State. Through the description of several stratigraphic sections, three aeolian and two fluvial facies associations characterize this formation. The aeolian facies represent (a) aeolian crescentic dunes, (b) aeolian sand sheets, and (c) blowouts; the fluvial facies record (d) sheet floods and (e) channelized ephemeral rivers. These facies associations are organized into three genetic units that are bounded by supersurfaces. The unit 1 is formed by the intercalation of sheet flood, aeolian dry sand sheets, and aeolian dunes facies associations, often with soft sediment structures. The cross-bedded strata ascribed to aeolian dunes become larger and more frequent towards the top of the unit, as the soft sediment deformation structures become scarcer. The Unit 2 comprises aeolian sand sheets facies scoured by fluvial channels, with erosive concave bases, and by blowouts, which are subsequently filled by aeolian dunes deposits. Unit 3 consists of cross-bedded strata related to medium-to-large, either simple or compound aeolian dunes (draas). Supersurfaces bound the genetic units recording depositional gaps, thus defining different episodes of accumulation.