Historical tsunamis and storms recorded in a coastal lowland,Shizuoka Prefecture,along the Pacific Coast of Japan

Four sand units deposited by tsunamis and one sand unit deposited by storm surge(s) were identified in a muddy marsh succession in a narrow coastal lowland along the Pacific coast of central Japan. Tsunamis in ad 1498, 1605, 1707 and 1854 that were related to large subduction‐zone earthquakes along the Nankai Trough, and storm surges in 1680 and/or 1699 were responsible for the deposition of these sand units. These sand units are distinguished by lithofacies, sedimentary structures, grain‐size and mineral composition, and radiocarbon ages; their ages are supported by events in local historical records. The tsunami deposits in the study area are massive or parallel‐laminated sands, with associated intraclasts, gravels, draping mud layers and, rarely, a return‐flow subunit. The storm surge deposits are devoid of these characteristics, and are composed of groups of thin, current ripple‐laminated sand layers. The differences in sedimentary structures between the tsunami and storm surge deposits are attributed to the different characteristics of tsunami and storm waves.     

An iron-bearing wave-dominated siliciclastic shelf: Facies analysis and palaeogeographic implications (Silurian-Lower Devonian Sierra Grande Formation,Southern Argentina)

The Sierra Grande Formation (Silurian-Early Devonian) consists of quartz arenites associated with clast supported conglomerates, mudstones, shales and ironstones. Eight sedimentary facies are recognized: cross-stratified and massive sandstone, plane bedded sandstone, ripple laminated sandstone, interstratified sandstone and mudstone, laminated mudstone and shale, oolitic ironstone, massive conglomerate and sheet conglomerate lags. These facies are interpreted as shallow marine deposits, ranging from foreshore to inner platform environments. Facies associations, based on vertical relationships among lithofacies, suggest several depositional zones: (a) beach to upper shoreface, with abundant plane bedded and massive bioturbated sandstones; (b) upper shoreface to breaker zone, characterized by multistorey cross-stratified and massive sandstone bodies interpreted as subtidal longshore-flow induced sand bars; (c) subtidal, nearshore tidal sand bars, consisting of upward fining sandstone sequences; (d) lower shoreface zone, dominated by ripple laminated sandstone, associated with cross-stratified and horizontal laminated sandstone, formed by translatory and oscillatory flows; and (e) transitional nearshore-offshore and inner platform zones, with heterolithic and pelitic successions, and oolitic ironstone horizons. Tidal currents, fair weather waves and storm events interacted during the deposition of the Sierra Grande Formation. However, the relevant features of the siliciclastics suggest that fair weather and storm waves were the most important mechanisms in sediment accumulation. The Silurian-Lower Devonian platform was part of a continental interior sag located between southern South America and southern Africa. The Sierra Grande Formation was deposited during a second order sea level rise, in which a shallow epeiric sea flooded a deeply weathered low relief continent.     

Karst subsidence as a control on the accumulation and preservation of aeolian deposits: A Pleistocene example from a proglacial outwash setting,Ebro Basin,Spain

Meltwater flows emanating from the Pyrenees during the Pleistocene constructed a braided outwash plain in the Ebro Basin and led to the karstification of the Neogene gypsum bedrock. Synsedimentary evaporite dissolution locally increased subsidence rates and generated dolines and collapses that enabled the accumulation and preservation of outwash gravels and associated windblown deposits that were protected from erosion by later meltwater flows. In these localized depocentres, maximum rates of wind deceleration resulted from airflow expansion, enabling the accumulation of cross‐stratified sets of aeolian strata climbing at steep angles and thereby preserving up to 5 m thick sets. The outwash plain was characterized by longitudinal and transverse fluvial gravel bars, channels and windblown facies organized into aeolian sand sheets, transverse and complex aeolian dunes, and loess accumulations. Flat‐lying aeolian deposits merge laterally to partly deformed aeolian deposits encased in dolines and collapses. Synsedimentary evaporite dissolution caused gravels and aeolian sand deposits to subside, such that formerly near‐horizontal strata became inclined and generated multiple internal angular unconformities. During episodes when the wind was undersaturated with respect to its potential sand transporting capacity, deflation occurred over the outwash plain and coarse‐grained lags with ventifacts developed. Subsequent high‐energy flows episodically reached the aeolian dune field, leading to dune destruction and the generation of hyperconcentrated flow deposits composed in part of reworked aeolian sands. Lacustrine deposits in the distal part of the outwash plain preserve rhythmically laminated lutites and associated Gilbert‐type gravel deltas, which developed when fluvial streams reached proglacial lakes. This study documents the first evidence of an extensive Pleistocene proglacial aeolian dune field located in the Ebro Basin (41˙50° N), south of what has hitherto been considered to be the southern boundary of Pleistocene aeolian deposits in Europe. A non‐conventional mechanism (evaporite karst‐related subsidence) for the preservation of aeolian sands in the stratigraphic record is proposed.     

A Younger Dryas (Loch Lomond Stadial) jökulhlaup deposit, Fort Augustus, Scotland

This study provides an insight into the impact of probably the largest flood ever to have been identified in mainland Britain by examining new sedimentary evidence from the Auchteraw terrace, Fort Augustus, Scotland. Study of three sections reveals a succession consisting of: (1) sheet gravels; (2) large trough-shaped depressions infilled with cross-stratified sands and gravels; (3) smaller-scale, finer-grained cross-strata; and (4) sheet-like, occasionally channelized, bimodal sand and gravel beds. This study shows that both the sedimentology and morphology of the Auchteraw terrace are consistent with jökulhlaup deposition and reveal a greater variety of lithofacies types than identified in previous studies of jökulhlaups from ice-dammed lakes. The fine-grained nature of the sediment discussed in this study emphasizes the importance of sediment supply for the formation of distinctive jökulhlaup successions. The sedimentary evidence recorded here provides a valuable tool for the interpretation of the magnitude and frequency of proglacial meltwater flows associated with Pleistocene ice sheets worldwide.     

Facies and ground-penetrating radar characteristics of coarse-grained beach deposits of the uppermost Pleistocene glacial Lake Algonquin, Ontario, Canada

The lithofacies of the uppermost Pleistocene ( ca 11 800 to 10 400 ¹⁴C yr  bp ), cold-temperate, coarse-grained beach deposits of Lake Algonquin, the precursor of the present Lake Huron of North America, have been studied and interpreted based on analogous features of modern beaches from the same region. Ice foot and ice-cementation develop during winter but, unlike Arctic beaches, ice-related sedimentary features are seldom, if ever, preserved in the Pleistocene and recent deposits of the Great Lakes. Instead, the deposits retain the typical characteristics of wave-dominated, pure gravel and mixed sand and gravel beaches, there including the classical subdivision of infill zone, swash zone/sand run, imbricated zone, coarse flat-clast zone and coastal dunes. These zones form a regular succession on the surface of many modern beaches; however, they seldom occur as quasi-complete vertical successions in older deposits. In the studied uppermost Pleistocene deposits, the various components are separated vertically by erosional contacts (bounding surfaces) readily recognizable on working faces of large sand and gravel pits and mappable in the subsurface by ground-penetrating radar. The lithofacies are sufficiently diagnostic to allow recognition of depositional settings, and the lithofacies architecture allows the deciphering of important geological events, such as: (i) local input of fluvial material onto the shoreface, where it was partially reworked by waves and moved onto the beachface; (ii) occurrence of major storm events; and (iii) repeated rapid transgressions and regressions typical of the glacial-lake precursors of the modern Great Lakes.     

Wavy lamination in a mixed sand and gravel foreshore facies of the Pleistocene Hosoya Sandstone, Aichi, central Japan

Although sandy foreshore facies are generally characterized by parallel lamination, wavy lamination is predominant in the mixed sand and gravel foreshore facies of the Pleistocene Hosoya Sandstone, which crops out along the Pacific coast of the Atsumi Peninsula, Aichi, central Japan. The foreshore facies consists of three sedimentary subfacies; interbeds of gravel and parallel laminated sand of the lower foreshore facies, parallel laminated fine to medium sand beds containing scattered pebbles and cobbles of the middle foreshore facies, and wavy laminated fine to medium sand beds containing scattered pebbles and cobbles of the upper foreshore facies. A lack of erosional surfaces in the middle foreshore facies indicates the continuous accumulation of sand in flat beds under upper plane bed flow. The wavy laminated sands of the upper foreshore facies exhibit erosional surfaces indicative of repeated deposition and erosion. The erosional surfaces are undulatory, with depressions (10 cm wide and 3 cm deep) that contain scattered pebbles and cobbles. These depressions reflect backwash erosion of sand around and below the pebbles and cobbles. Sand draping over the undulating erosional surfaces forms the wavy lamination. The wavy laminated sand with scattered pebbles and cobbles is a key facies of an upper foreshore or swash zone, and is a good sea-level marker.     

Ancient and modern cold-climate aeolian sand deposition: A review

Although partly active aeolian sand sheets and dunes cover large areas in the zones of (dis)continuous permafrost, little precise information is available about the influence of cold-climate conditions on modern aeolian processes. This means that palaeoenvironmental reconstructions in the stabilised, mainly Late Pleistocene dune fields and cover sand regions in the ‘sand belts’ of the European Lowlands and the Northern Great Plains of the USA and Canada, are necessarily still based on ancient evidence. Cold-climate wind deposits are typically derived from areas of abundant sediment supply like unvegetated flood plains, glacial outwash plains, till plains and lake shores. The common parabolic and transverse dune forms resemble those observed in temperate regions. Although a variety of periglacial features has been identified in Late Pleistocene dune and cover sands none of them indicate that permafrost is crucial to aeolian activity. Specific structures in aeolian strata permit tentative interpretation of the moisture content of depositional sand surfaces, the nature of annual sedimentation cycles and the processes by which strata were deposited and/or contorted. But surprisingly little is known about the role of vegetation in the process of sand accumulation. Dunes are most informative with respect to reconstructions of past wind regimes, which offer important data for verification of palaeoclimatic simulations.     

Palaeoenvironmental interpretation of a Pleistocene alluvial succession in central Poland: sedimentary facies analysis as a tool for palaeoclimatic inferences

A Pleistocene valley-fill alluvial succession deposited in the Kleszczów Graben, central Poland, has been studied in the Belchatów openpit mine. The succession, palynologically documented to represent the Drenthe/Warthe interstadial, consists of three alluvial complexes whose component lithofacies associations indicate a fluvial system evolving from temperate-climate meandering river to transitional-type shallow braided network, to periglacial well-developed braided river influenced by aeolian sand supply. The study suggests that the abundance of fine-grained overbank deposits, occurrence of peats/palaeosols and fining-upward cyclothems are diagnostic attributes of perennial meandering river alluvium, which may indicate temperate climatic conditions. Periglacial braided river alluvium is recognizable by an admixture of wind-derived sand grains with aeolian surface textures and by the occurrence of ice-wedge features, indicative of cold climatic conditions. The distinction between the two basic types of alluvium is aided by the analysis of architectural elements and palaeocurrent directional data. The study demonstrates that sedimentological facies analysis can be a useful tool for the recognition of palaeoclimatic changes in Pleistocene alluvial successions.     

Quaternary fluvial, pedogenic and mass-movement processes at St George's Down, Newport, Isle of Wight

Recent geological mapping on the Isle of Wight by the British Geological Survey has shown the ‘Plateau Gravel’ to be a mixture of fluvial, solifluction, pedogenic and marine deposits ranging from pre-Anglian to Holocene age. As part of the resurvey of the island, several new exposures of the ‘Plateau Gravel’ between Newport and Downend were examined. A working gravel pit on St George's Down, near Newport, revealed a succession of flint gravels with an inter-bedded sequence of laminated silts. An upper in situ succession of pre-Anglian fluvial gravels caps the plateau, but a second, probably younger suite of gravel-rich sediments is exposed in a quarry on a topographically lower spur. These overlie in situ Clay-with-flints resting on Upper Cretaceous Chalk. These lower sediments are well exposed and display a complex stratigraphy. They consist predominantly of flint gravel, but include a dipping succession of laminated silts and palaeosols preserved in a hollow or small channel feature, intercalated between two distinct soliflucted cold-stage gravel sheets. Palynological and pedological evidence analysis suggests that these laminated silts and sands were deposited under a temperate climate but with frequent episodes of disruption caused by mass-movement and possibly freeze-thaw. The age of these laminated sediments are not known with any certainty but are likely to date to a temperate interval within the Late Pleistocene. The top of the laminated unit is cut by a heavily cryoturbated horizon presumed to be of Devensian age.     

Sedimentology of gravelly Lake Lahontan highstand shoreline deposits,Churchill Butte,Nevada, USA

Gravelly shoreline deposits of the latest Pleistocene highstand of Lake Lahontan occur in pristine depositional morphology, and are exposed in gravel pits along Churchill Butte in west-central Nevada. Four environments differentiated at this site are alluvial fan/colluvium, lakeshore barrier spit, lake lower-shoreface spit platform, and lake bottom. Lakeshore deposits abut, along erosional wave headcuts, either unsorted muddy to bouldery colluvium fringing Churchill Butte bedrock, or matrix-supported, cobbly and pebbly debris-flow deposits of the Silver Springs fan. The lakeshore barrier spit is dominated by granule pebble gravel concentrated by wave erosion of the colluvial and alluvial-fan facies. The lakeward side of the barrier consists of beachface deposits of well-sorted granules or pebbles in broad, planar beds 1–10 cm thick and sloping 10–15°. They interfinger downslope with thicker (10–25 cm) and less steep (5–10°) lakeward-dipping beds of fine to medium pebble gravel of the lake upper shoreface. Interstratified with the latter are 10–40-cm-thick sets of high-angle cross-beds that dip southward, alongshore. Higher-angle (15–20°), landward-dipping foresets of similar texture but poorer sorting comprise the proximal backshore on the landward side of the barrier. They were deposited during storm surges that overtopped the barrier berm. Gastropod-rich sand and mud, also deposited by storm-induced washover, are found landward of the gravel foresets in a 15-m-wide backshore pond. Algal stromatolites, ostracodes, and diatoms accumulated in this pond between storm events. The lake lower shoreface, extending from water depths of 2 to 8 m, consists of a southward-prograding spit platform built by longshore drift. The key component of this platform is large-scale sandy pebble gravel in 16° southward-dipping `Gilbert' foresets that grade at a water depth of about 6–7 m to 4°-dipping sandy toesets. A shift from bioturbated lower-shoreface sand and silt, to flat and laminated lake-bottom silt and mud, occurs between water depths of 10–40 m and over a shore-normal distance of ≥250 m. This lake-bottom mud facies, unlike the others, is areally expansive.     

Development of sediment–landform associations at cold glacier margins,Dry Valleys,Antarctica

The impact of modern cold glaciers on arid periglacial landscapes has received little attention compared with other glacial regimes, and there is a widely held assumption that cold glaciers are not effective geomorphological agents, despite recent studies to the contrary. This paper focuses on the processes operating at the margins of a number of glaciers in the Dry Valleys of Victoria Land, notably the Wright Lower Glacier. The glaciers are entraining primarily older drift deposits and highly weathered regolith which texturally are sandy gravels, as well as well‐sorted sands of fluvial origin. Despite basal temperatures of the order of ?16°C, frozen layers and blocks of sand and gravel are being incorporated into the base of the glaciers by folding and thrusting. The sedimentary products are ridges and aprons several metres high within which the principal lithofacies are sand, gravel, foliated glacier ice, lake ice and snow. These facies are glaciotectonized strongly. Draped over these landforms is a veneer of well‐sorted aeolian sand up to half a metre thick. Supraglacial streams flowing off the glaciers incise these landforms and the sediment is redeposited as alluvial fans, lake deltas and lake‐bottomset deposits. Overall the sediment/landform association differs markedly from those of other glacial regimes, with sand and gravel being the dominant facies, while the usual indicators of glacier working (such as facets and striations on clasts) are lacking. The preservation potential for these landforms on a thousand‐year time scale is high, as modification in this arid regime by slope processes and running water is limited. Sublimation of buried ice is so slow that ridge features are likely to remain ice‐cored almost indefinitely, modified only by wind transport and weathering.     

Pleistocene evolution of the Nile Valley in northern Upper Egypt

In the El Minia district of northern Upper Egypt, the Pleistocene deposits of the Nile Valley include (?)Early Pleistocene conglomerates of the Armant Formation and (?)Middle Pleistocene sands of the Qena Formation. These sediments are exposed along both sides of the valley in terraces at different heights, unconformably overlying Eocene limestones. Field observations suggest that the conglomerate facies of the Armant Formation was deposited in proximal and mid-alluvial fans. The sands of the Qena Formation are differentiated into two facies: a cross-bedded sandstone, representative of alluvial fan—braided stream environments, and a facies of sand interbedded with mud that may have been deposited by a meandering river. The heavy minerals of the Armant Formation are markedly different from those of the Qena Formation, suggesting derivation from different sources. Surface textures of quartz grains from the Qena sands, observed by SEM, exhibit chemical features, attributed to a fluviatile origin. Sand from the Armant Formation is characterized by mechanical and chemical surface textural features that suggest original aeolian derivation followed by later fluvial sedimentation.     

Origin of yellow sand from Tamala Limestone on the Swan Coastal Plain,Western Australia

There has been considerable debate concerning the origin of the Spearwood Dunes on the Swan Coastal Plain in Western Australia. In general, it is believed that the Spearwood Dunes are a complex of calcareous coastal dunes deposited during the Quaternary and now consist of an aeolianite core (the Tamala Limestone) plus tracts of surficial residual sand from dissolution thereof. However, in the mid‐seventies a counter view was presented suggesting that the sand was not residual but was transported by aeolian processes from inland sources. At 11 sites on the Swan Coastal Plain a combination of grainsize analysis and heavy‐mineral analysis was used to demonstrate that the sand of the Spearwood Dunes has evolved as a result of in situ weathering of the underlying Tamala Limestone. This supports previous work on the Swan Coastal Plain and other sandplains in Western Australia, suggesting that there has been very little long‐range aeolian transport of sands during the Late Pleistocene.     

Amalgamated accumulations resulting from climatic and eustatic changes, Akchar Erg, Mauritania

The Akchar Erg of the Sahara of western Mauritania shows a morphology and stratigraphy that can be recognized as the amalgamation of late Pleistocene and Holocene deposits that reflect eustatic and climatic events. Mapping, trenching, and dating by ¹⁴C methods and artefacts show that the prominent complex linear dunes (draas) of the Akchar Erg are actually composite features showing at least three constructional and two destructional phases. The constructional phases are represented by three convex-up layers: (i) a modern veneer moulded into superimposed crescentic dunes, which partially mantle the larger linear bedforms; (ii) a middle, partly root-turbated sand deposited sometime during the last 4000 years; and (iii) a core of linear dune sand formed during the last glacial period (13 000–20 000 yr BP), which today shows relict relief, intense root-turbation, and pedogenesis. These constructional phases are separated by super bounding surfaces that coincide with erg destructional phases. Surface 2 bounds the middle aeolian sand, and is marked by a lag surface of small granules. Surface 1 is a very prominent surface with an abundance of Neolithic artefacts, and represents stabilization of the linear dunes during the humid, interglacial period (4000–11 000 yr BP). Interdraa deposits originated during the interglacial period, and consist of continental lacustrine limestones and sandstones, humic sands deposited in marshes, and sabkhas on the coast. The sabkhas originated during interglacial highstand of sea-level when interdraa areas were marine embayments, and subsequently dried during regression. The draa and interdraa sequences, therefore, in spite of being adjacent facies, actually represent different events and were not formed simultaneously. The upwind sand-sheet margin of the Akchar Erg shows exposures of the middle and core aeolian sands (which were previously protected from deflation by vegetation) being progressively cannibilized in the current phase of erg construction, and revealing a crystalline basement rock. In this proximal area, conditions are not favourable for the incorporation of these aeolian accumulations into the stratigraphic record.     

Sedimentology and morphology of a low-sinuosity river: Calamus River, Nebraska Sand Hills

A study reach of the Calamus River, Nebraska Sand Hills, has a low sinuosity (less than 1.3) and braiding parameter (less than 1). Depending on sinuosity, the channel is occupied by alternate bars and point bars, the emergent parts of which form nuclei for midstream bars (islands). Channel migration occurs by bend expansion and translation, downstream and lateral growth of islands, and by chute cutoff. Channel-bed sediment is mainly medium-grained sand, but gravel and coarser sand sizes occur in thalweg areas adjacent to cutbanks and upstream parts of bars and islands, and finer sands occur on the downstream parts of bars and filling channels. Curved-crested dunes cover most of the channel bed at most flow stages, with ripples restricted to shallow areas near banks. Bed material is mostly large-scale cross-stratified, with small-scale cross-strata interbedded with plant debris occurring in topographically high areas near banks. Vibracores through channel bars show a basal erosion surface overlain by large-scale cross-stratified sands, in turn overlain by small-scale cross-stratified sand interbedded with plant debris. The overall sequence generally fines upwards, but the large-scale cross-stratified portion either fines upwards, coarsens upwards, or shows little grain size variation. Lithofacies distributions vary spatially within and between bars depending on position in the bar and local channel curvature/width, in a similar way to unbraided rivers elsewhere. Lithofacies of bar deposits are similar to those in the active channel, and the elevations of the basal erosion surface and adjacent channel thalweg correspond closely. Channels abandoned by chute cutoff are filled progressively from the upstream end, and comprise deposits similar to the downstream parts of bars (i.e. fining upwards). The downstream extremities of channel fills may contain large proportions of peat relative to sand, but little mud due to the paucity of such fine suspended load in the Calamus.     

Lower Pleistocene deltaic and marine sediments in boreholes from the central North Sea

Lower Pleistocene sediments recovered in boreholes from the Aberdeen Ground Formation in the central North Sea indicate that the unit was deposited in a delta front to prodelta/shallow, open shelf marine setting. Possible estuarine and clastic nearshore marine deposits have been identified on the western margin of the basin. The delta front sediments consist of interbedded, structureless to laminated sands and muds with organic debris, ferruginous nodules and common soft sediment deformation structures. Sporadic rippled and graded beds, basal scours to beds and starved ripples suggest periodic wave–current reworking. Prodelta/shelf marine sediments are predominantly argillaceous with only occasional thin sand beds and rare phosphatic bands. One exceptionally thick sand body or submarine channel-fill although this remains uncertain. The estuarine/clastic nearshore marine sediments include coarse channel-lag deposits and rippled and laminated subtidal sands. A rich microfossil assemblage recovered from the prodelta/shelf marine sequence indicates that deposition occurred under fluctuating climatic conditions.     

Jet-efflux deposits of a subaqueous ice-contact fan,glacial Lake Rinteln,northwestern Germany

The coarse-grained, ice-contact, Porta Subaqueous Fan/Delta Complex was deposited in glacial Lake Rinteln at the margin of the Saalian ice sheet that advanced south of the Weser Chains, NW Germany. The ice-proximal depositional system was up to 15 km long and 10 km wide. The present study deals with ice-proximal subaqueous fan deposits, which are interpreted as products of a subcritical plane-wall outflow jet that periodically passed into a supercritical jet with hydraulic jump. The proximal facies assemblage consists of the coarse, clast-supported gravelly deposits of a hyperconcentrated (high-density) effluent and of related cohesionless debris flows attributed to the conduit or immediate proximal jet outflow zone of flow establishment. The intermediate facies assemblage, attributed to the outflow jet proximal zone of flow transition, is dominated by normally graded and cross-stratified gravels with scour structures at their bases; these gravels were deposited by a high-density effluent capable of forming mouthbar-like features. These deposits pass downcurrent into an assemblage of planar parallel-stratified and planar and trough cross-stratified sands and pebbly sands (partially interpreted as antidunes), with abundant scour structures and intercalated layers of fine sand/silt and silty mud, attributed to the jet distal zone of flow transition. The distal facies assemblage consists of trough cross-stratified sands and pebbly sands, and is attributed to the outflow jet proximal zone of established flow. The sedimentary succession as a whole has wedge-shape geometry, with a gentle fan-shaped inclination of the bedding from the southeast to the southwest. Repeated vertical alternations of supercritical and subcritical deposits and muddy interlayers can be attributed to temporary fluctuations in the meltwater outflow, whereas the overall upward fining of the succession indicates a net decline of meltwater discharges.     

Tectonic setting and sedimentology of Ganga River sediments, India

The Ganga basin provides a present-day example of a peripheral foreland basin. The course of the river is controlled by Himalayan tectonics. Three main types of architectural elements, such as channels (CH), sandy bedforms (SB) and overbank fines (OF) have been developed in Ganga River sediments. The channels (CH) include gravelly (Gs) and sandy channel (Ss) lithofacies. The sandy bedforms (SB) include trough cross-stratified (St), planar cross-stratified (Sp), horizontal stratified (Sh), sandy massive (Sm) and climbing ripple cross-laminated (Sr) lithofacies, all of which are active channel deposits. The overbank fines (OF) include massive silt and clay (Fm), parallel laminated silt and clay (FI) and climbing ripple cross-laminated (Sr) lithofacies. Mega units have been developed in the lower part of the active channel deposits, while small units have been developed in the upper part of active channel deposits, in inactive channel deposits and overbank fines. This study illustrates the seasonal and tectonic control on sedimentation. Petrofacies studies of the sediments indicate a recycled orogen provenance. The sediments are derived from rapidly uplifted fault blocks comprising granite, gneiss and basic and ultrabasic rocks. Lack of textural and compositional maturity suggests a local source of derivation. The principal control on sand composition is source lithology. The hot and humid climate may slightly increase the content of quartz in sand derived from reworked foreland basin sediments. but the effect is neither sufficient to shift the sand compositions out of the recycled orogen field nor does it obscure composition mixing patterns.     

Facies analysis of a Toarcian–Bajocian shallow marine/coastal succession (Bardas Blancas Formation) in northern Neuquén Basin,Mendoza province,Argentina

Strata of the Bardas Blancas Formation (lower Toarcian–lower Bajocian) are exposed in northern Neuquén Basin. Five sections have been studied in this work. Shoreface/delta front to offshore deposits predominate in four of the sections studied exhibiting a high abundance of hummocky cross-stratified, horizontally bedded and massive sandstones, as well as massive and laminated mudstones. Shell beds and trace fossils of the mixed Skolithos-Cruziana ichnofacies appear in sandstone beds, being related with storm event deposition. Gravel deposits are frequent in only one of these sections, with planar cross-stratified, normal graded and massive orthoconglomerates characterizing fan deltas interstratified with shoreface facies. A fifth outcrop exhibiting planar cross-stratified orthoconglomerates, pebbly sandstones with low-angle stratification and laminated mudstones have been interpreted as fluvial channel deposits and overbank facies. The analysis of the vertical distribution of facies and the recognition of stratigraphic surfaces in two sections in Río Potimalal area let recognized four transgressive–regressive sequences. Forced regressive events are recognized in the regressive intervals. Comparison of vertical distribution of facies also shows differences in thickness in the lower interval among the sections studied. This would be related to variations in accommodation space by previous half-graben structures. The succession shows a retrogradational arrangement of facies related with a widespread transgressive period. Lateral variation of facies let recognize the deepening of the basin through the southwest.