the permian triassic transition and the onset of mesozoic sedimentation at the northwestern peri tethyan domain scale palaeogeographic maps and geodynamic implications the main aim of this paper is to review middle permian through middle triassic continental successions in european secondly areas of middle late permian sedimentation the permian triassic boundary ptb and the onset of triassic sedimentation at the scale of the westernmost peri tethyan domain are defined in order to construct palaeogeographic maps of the area and to discuss the impact of tectonics climate and sediment supply on the preservation of continental sediment at the scale of the western european peri tethyan basins the upper permian is characterised by a general progradational pattern from playa lake or floodplain to fluvial environments in the northern variscan belt domain areas of sedimentation were either isolated or connected to the large basin which was occupied by the zechstein sea in the southern variscan belt during the late permian either isolated endoreic basins occurred with palaeocurrent directions indicating local sources or basins underwent erosion and or there was no deposition these basins were not connected with the tethys ocean which could be explained by a high border formed by corsica sardinia palaeorelief and even parts of the kabilia microplate the palaeoflora and sedimentary environments suggest warm and semi arid climatic conditions at the scale of the whole study area an unconformity more or less angular is observed almost everywhere between deposits of the upper permian and triassic except in the central part of the germanic basin the sedimentation gap is more developed in the southern area where in some basins upper permian sediment does not occur the large sedimentary supply erosion and or lack of deposition during the late permian as well as the variable palaeocurrent direction pattern between themiddle late permian and the early triassic indicate a period of relief rejuvenation during the late permian during the induan all the intra belt basins were under erosion and sediment was only preserved in the extra belt domains the northern and extreme southern domains in the northern domain the central part of the germanic basin sediment was preserved under the same climatic conditions as during the latest permian whereas in the extreme southern domain it was probably preserved in the tethys ocean implying a large amount of detrital components entering themarinewaters mesozoic sedimentation began in the early olenekian the ephemeral fluvial systems indicate arid climatic conditions during this period three distinct areas of sedimentation occur a northern and southern domain separated by an intra belt domain the latter accumulated sediments during the early middle permian and experienced erosion and or no deposition conditions between the middle late permian and the beginning of mesozoic sedimentation dated as anisian to hettangian at the top of the lower triassic another tectonically induced more or less angular unconformity is observed the hardegsen unconformity which is dated as intra spathian and is especially found in the north european basins this tectonic activity created new source areas and a new fluvial style with marine influences at the distal part of the systems during the anisian and ladinian continental sedimentation was characterised by a retrogradational trend in other words the fluvial system evolved into fluvio marine environments attesting to a direct influence of the tethys ocean in the southern and northern domains both at the end of the olenekian spathian and during the anisian the presence of palaeosols micro andmacrofloras indicate less arid conditions throughout this domain

aeolian sand sea development along the mid cretaceous western tethyan margin spain erg sedimentology and palaeoclimate implications the existence of a mid cretaceous erg system along the western tethyan margin iberian basin spain was recently demonstrated based on the occurrence of wind blown desert sands in coeval shallow marine deposits here the first direct evidence of this mid cretaceous erg in europe is presented and the palaeoclimate and palaeoceanographic implications are discussed the aeolian sand sea extended over an area of 4600 km2 compound crescentic dunes linear draa and complex aeolian dunes sand sheets wet dry and evaporitic interdunes sabkha deposits and coeval extradune lagoonal deposits form the main architectural elements of this desert system that was located in a sub tropical arid belt along the western tethyan margin sub critically climbing translatent strata grain flow and grain fall deposits pin stripe lamination lee side dune wind ripples soft sediment deformations vertebrate tracks biogenic traces tubes and wood fragments are some of the small scale structures and components observed in the aeolian dune sandstones at the boundary between the aeolian sand sea and the marine realm intertonguing of aeolian deposits and marine facies occurs massive sandstone units were laid down by mass flow events that reworked aeolian dune sands during flooding events the cyclic occurrence of soft sediment deformation is ascribed to intermittent marine flooding of aeolian dunes and associated rise in the water table the aeolian erg system developed in an active extensional tectonic setting that favoured its preservation because of the close proximity of the marine realm the water table was high and contributed to the preservation of the aeolian facies a sand drift surface marks the onset of aeolian dune construction and accumulation whereby aeolian deposits cover an earlier succession of coastal coal deposits formed in a more humid period a prominent aeolian super surface forms an angular unconformity that divides the aeolian succession into two erg sequences this super surface formed in response to a major tectonic reactivation in the basin and also marks the change in style of aeolian sedimentation from compound climbing crescentic dunes to aeolian draas the location of the mid cretaceous palaeoerg fits well to both the global distribution of other known cretaceous erg systems and with current palaeoclimate data that suggest a global cooling period and a sea level lowstand during early mid cretaceous times the occurrence of a sub tropical coastal erg in the mid cretaceous of spain correlates with the exposure of carbonate platforms on the arabian platform during much of the late aptian to middle albian and is related to this eustatic sea level lowstand

climate control on erosion distribution over the himalaya during the past 100 ka sediment samples from a 50 m long core representing 100 ka of deposition taken from the ganga plain on the campus of the indian institute of technology kanpur were analyzed for sr and nd isotope compositions both 87 sr 86 sr and nd vary significantly with depth in the core 0 72701 0 76708 and 14 4 to 16 6 respectively within the range for silicate rocks of the higher and the lesser himalaya the variations in the isotope compositions reflect variations in the mixing proportion of sediments from the higher and lesser himalaya the two major sediment sources to the ganga the opposite trends in 87 sr 86 sr and nd depth profiles further confirm this hypothesis the isotope profiles exhibit two major excursions ca 20 ka and ca 70 ka ago coinciding with periods of precipitation minima and larger glacial cover these excursions are the result of a decrease in the proportion of sediment from the higher himalaya due to a decrease in monsoon precipitation and an increase in glacial cover that are in turn caused by lower solar insolation this study highlights the significant influence of climate on erosion in the himalaya

stratigraphy and facies architecture of the fluvial aeolian lacustrine sergi formation upper jurassic reconcavo basin brazil abstract the sergi formation encompasses an upper jurassic fluvial eolian lacustrine succession deposited within a wide intracratonic basin its sand bodies represent the largest and more important reservoirs in the reconcavo basin hosting 362 million m 3 of oil in place the main goal of this paper is to provide a detailed stratigraphic analysis of the sergi formation based on core and outcrop data it was achieved through the recognition and correlation of regional surfaces that have allowed the subdivision of this unit into distinct depositional sequences and the reconstruction of its depositional history the studied succession can be subdivided into three unconformity bounded sequences sequence i is composed of lacustrine mudstone at its base which is overlain by fine to medium grained sandstone related to aeolian dune and sand sheet and ephemeral fluvial stream deposits fluvial strata indicate northeastward flowing streams whereas aeolian dune deposits suggest the action of southwestward blowing winds the regional unconformity bounding sequences i and ii denotes both a climate change and tectonic rearrangement of the basin this surface delineates a change in the depositional style from fluvial aeolian lacustrine sequence i to entirely fluvial sequence ii the latter includes coarse grained to conglomeratic sandstone deposited within northwestward flowing braided channel belts changes in fluvial palaeocurrent from sequence i to ii indicate rearrangement of the drainage system related to basin tectonism furthermore a change in the fluvial discharge regime took place as a result of a change from a drier to a wetter climate fluvial deposition in sequence i was related to ephemeral streams whereas fluvial facies architecture of the sequence ii deposits indicates perennial braided streams with significant discharge variation another regional unconformity this time related to a stratigraphic base level fall and consequent widespread basinwide aeolian deflation separates the braided fluvial facies of sequence ii from the fine to medium grained sandstones ascribed to sheet floods aeolian dunes and aeolian sand sheets of sequence iii the resumption of aeolian sedimentation indicates a return to drier conditions in the basin the abrupt change from fluvial aeolian deposits to the lacustrine deposits of the overlying itaparica formation suggest a rapid rise of the water table and consequent basinwide flooding

sequential architecture and cyclicity in permian desert deposits brodick beds arran scotland this study of ancient desert deposits permian brodick beds tests the possibility that cyclicityin these interbedded aeolian fluvial and lacustrine deposits was orbitally controlled the 740 m thicksuccession of desert deposits forms one sequence which can be divided into three genetic units a majordeflation surface forms the basal sequence boundary and represents a drop in base level groundwatertable on top of the sequence boundary are rather uniform aeolian dune and sand sheet sediments unit1 formed in an erg during low base level with increasing rates of base level rise they are followed byinterbedded aeolian dune aeolian sand sheet and flood reworked aeolian sediments unit 2 representingerg margin deposits formed during increasing rates of base level rise the uppermost part of the sequenceis composed of gravel sheets unit 3 representing alluvial fan deposition during a high base level withdecreasing rates of base level rise the succession is cyclic and spectral analysis of sedimentary andgeochemical parameters reveal cycles with a thickness of 25 7 29 3 m 34 5 m and 64 5 m and fieldworkreveals cycles of 155 m and 675 m these sedimentary cycles are thought to reflect climatic oscillations the lack of detailed time control makes it diffcult to link these climatic fluctuations to orbital cycles although the detected cyclicity matches well with milankovitch theory

sedimentary architecture of an ancient linear megadune barremian neuquen basin insights into the long term development and evolution of aeolian linear bedforms linear aeolian bedforms are the most abundant bedform type in modern earth sand seas and are very common in our solar system despite their abundance the long term development of these bedforms and its impact upon the resulting sedimentary architecture in the geological record is still poorly understood the aims of this paper are to study the exposed record of an ancient linear megadune in order to discuss the factors that impact the development and sedimentary architecture of aeolian linear bedforms the outcrops of the ancient troncoso sand sea barremian neuquen basin argentina provide a unique opportunity to access a preserved megadune record with an external body geometry that unequivocally confirms its linear morphology architectural analysis of the bedform record reveals significant differences for several aspects of cross stratified set bodies and bounding surfaces and allows for the identification of three architectural complexes insights from deterministic models analysis of set body relative chronology and distribution suggest that complexes result from distinctive phases in bedform development it also clearly shows that the megadune s construction was achieved by expansion from a core where the oldest deposits are located and that its development was characterized by sustained growth and strong longitudinal dynamics factors that impact the development and architecture of linear bedforms are identified discussed and compared to bedforms of transverse dynamics finally a scheme of expected styles of sedimentary architecture for linear bedforms is presented this case study shows how growth can be a critical factor conditioning linear bedform architecture and indicates how the preservation of certain styles of sedimentary architecture in the geological record may not be as unusual as previously thought

intensifying aeolian activity following the end permian mass extinction evidence from the late permian early triassic terrestrial sedimentary record of the ordos basin north china

controls on marine erg margin cycle variability aeolian marine interaction in the mid cretaceous iberian desert system spain the interaction between aeolian dunes of the iberian erg and tethys waters during the mid cretaceous led to a variety of sedimentary facies associations such as subtidal deposits aeolian dunes playa lakes coastal lakes with tidal creeks and marshes and lagoonal embayments with tide influenced delta deposits facies associations are organized in several stacked cycles every cycle is defined by a sand drift surface separating playa lake deposits below from aeolian dune deposits above followed by a transgressive surface separating aeolian deposits below from shallow marine deposits above the latter are covered by playa lake deposits and finally topped by the next sand drift surface similar marine erg margin cycles have been explained previously in terms of high order relative sea level variations normally controlled by glacioeustasy the studied erg margin developed during the mid cretaceous which is considered to be the archetypal example of a polar ice free greenhouse period this manuscript presents an alternative explanation for the cycles as caused by climate induced variations in the aeolian sediment supply in this scenario orbitally induced latitudinal shifts of the boundary between climate belts led to alternating periods of increased and decreased precipitation in the highland catchments of the back erg system variscan iberian massif when climate belts shifted to lower latitudes back erg highlands were under the influence of the northern warm humid belt while arid conditions prevailed in the lowland central erg increased precipitation in the highlands and the consequent recharge of ground water led to a rise of the phreatic level in the erg system that diminished wind erosion and windblown sediment input to the fore erg so that the desert margin contracted with ongoing basin subsidence this favoured the transgression the increased desert ground water flux favoured permanent coastal lakes in the fore erg margin and the local development of vegetation in places where such lakes lagoons were connected to the sea tidal channels were active as seen nowadays along the desert coast of qatar persian gulf when climate belts moved to higher latitudes the catchment areas in the back erg iberian massif were under the influence of the northern hot arid belt and a decrease of precipitation led to a drop of the phreatic level allowing deflation of dunes and exposed wadi channel floors and the formation of desert pavements and deflation lags in the back erg area this favoured the import of large volumes of windblown sand and dust forcing progradation of the erg and consequently a retreat of the coastline the sand fraction accumulated in climbing aeolian dunes and dust was trapped in extensive playa lake systems another long term allocyclic control is formed by active extensional tectonics that enhanced the creation of accommodation space especially in the first cycle a high ground water table sustained by subsurface water supply from the variscan iberian massif generated coastal fresh brackish lakes in which tide influenced meandering channels and salt marshes developed erg margin cycles thin upward in response to a decrease of the rate of basin subsidence suggesting that transgressions led to deep erosion of the underlying aeolian dune sands

paleomagnetism and 40ar 39ar ages from volcanics extruded during the matuyama and brunhes chrons near mcmurdo sound antarctica maps of virtual geomagnetic poles derived from international geomagnetic reference field models show large lobes with significant departures from the spin axis these lobes persist in field models for the last few millenia the anomalous lobes are associated with observation sites at extreme southerly latitudes to determine whether these features persist for millions of years paleomagnetic vector data from the continent of antarctica are essential we present here new paleomagnetic vector data and ar 40 ar 39 ages from lava flows spanning the brunhes and matuyama chrons from the vicinity of mcmurdo sound antarctica oriented paleomagnetic samples were collected from 50 lava flows by e mankinen and a cox in the 1965 1966 austral summer season preliminary data based largely on the natural remanent magnetization nrm directions were published by mankinen and cox 1988 we have performed detailed paleomagnetic investigations of 37 sites with multiple fully oriented core samples to investigate the reliability of results from this unique sample collection of these only one site fails to meet our acceptance criteria for directional data seven sites are reversely magnetized the mean normal and reverse directions are antipodal the combined mean direction has d over bar 12 i over bar 86 alpha 4 kappa 37 and is indistinguishable from that expected from a gad field we obtained reproducible absolute paleointensity estimates from 15 lava flows with a mean dipole moment of 49 zam 2 and a standard deviation of 28 zam 2 ar 40 ar 39 age determinations were successfully carried out on samples from 18 of the flows our new isotopic ages and paleomagnetic polarities are consistent with the currently accepted geomagnetic reversal timescales

complex sedimentology and palaeohabitats of holocene coastal deserts their topographic controls and analogues for the mid cretaceous of northern iberia abstract desert coasts in plate margins contain one of the most variable sedimentary records in terms of facies and stacking patterns reliefs in these basins together with massif palaeogeography and palaeotopography strongly control the spatial distribution of facies belts and complex lateral facies changes between very different coeval sub environments leading to mixtures of sedimentary particles with variable composition palaeotopography and palaeogeography also control the distribution of flora palaeohabitats in the desert basins depending on the spatial distribution of fresh water the basin geometry the topographic variability and associated phreatic level as well as the effective distance from highlands to the coast the albian desert basin that developed in northern iberia presents similarities with the geomorphology of modern oman uae and eritrea desert coasts in both systems cretaceous and holocene the distance between highlands and arid coastline determines the occurrence of extensive aeolian sand seas e g wide desert basin where distance between the highlands and the coastline increases or the development of wadi fed alluvial fans that reach directly the desert coast e g narrow desert basin leading to a variety of clastic and mixed carbonate facies due to prevailing arid conditions vegetation is mainly restricted to highlands and water conditioned lowland environments such as wadis tidal coastal marshes and lagoons depending on sea influence and water availability cretaceous vegetation in iberia were characterized by montane communities including arboreal shrubby gymnosperms mainly conifers and lowland communities composed by a patchy mixture of ferns cupressaceae cypress family cheirolepidiaceae and early angiosperms and or costal woodlands incorporating araucariaceae monkey puzzle tree family this distribution presents similarities with the ecosystems observed today in eritrea mountains and other holocene desert coasts

braided rivers within an arid alluvial plain example from the lower triassic western german basin recognition criteria and expression of stratigraphic cycles based on a detailed sedimentological analysis of lower triassic continental deposits in the western germanic sag basin i e the eastern part of the present day paris basin the conglomerat basal gres vosgien and conglomerat principal formations three main depositional environments were identified i braided rivers in an arid alluvial plain with some preserved aeolian dunes and very few floodplain deposits ii marginal erg i e braided rivers aeolian dunes and aeolian sand sheets and iii playa lake an ephemeral lake environment with fluvial and aeolian sediments most of the time aeolian deposits in arid environments that are dominated by fluvial systems are poorly preserved and particular attention should be paid to any sedimentological marker of aridity such as wind worn pebbles ventifacts sand drift surfaces and aeolian sand sheets in such arid continental environments stratigraphic surfaces of allocyclic origin correspond to bounding surfaces of regional extension elementary stratigraphic cycles i e the genetic units have been identified for the three main continental environments the fluvial type fluvial aeolian type and fluvial playa lake type at the time scale of tens to hundreds of thousands of years these high frequency cycles of climatic origin are controlled either by the groundwater level in the basin or by the fluvial siliciclastic sediment input supplied from the highland lower triassic deposits from the germanic basin are preserved mostly in endoreic basins the central part of the basin is arid but the rivers are supplied with water by precipitation falling on the remnants of the hercynian variscan appalachian mountains consequently a detailed study of alluvial plain facies provides indications of local climatic conditions in the place of deposition whereas fluvial systems only reflect climatic conditions of the upstream erosional catchments

preservation of pre vegetational mixed fluvio aeolian deposits in a humid climatic setting an example from the middle proterozoic eriksfjord formation southwest greenland abstract sedimentological studies of a 30 m thick coastal cliff section within the middle proterozoic eriksfjord formation in western south greenland reveals three distinct types of fluvial sand sheet deposits that reflect perennial streams type i semi perennial streams type ii and ephemeral flash floods type iii perennial river sand sheets are characterised by co sets of medium scale trough cross beds interbedded with isolated medium and large scale high angle tabular cross beds indications of desiccation or subaerial exposure are absent semi perennial fluvial sand sheets consist predominantly of low angle cross beds interbedded with isolated sets of high angle tabular cross beds with common reactivation surfaces horizontal lamination and climbing ripple lamination form subordinate structures associated with the sand sheets are adhesion structures and 0 05 0 4 m thick sets of wind ripple lamination indicating periods of subaerial exposure and aeolian reworking high energy ephemeral flash flood sand sheets consist almost exclusively of planar parallel lamination and climbing ripple lamination with some isolated sets of low angle cross bedding scouring and internal truncation surfaces are common the three types of sand sheets are considered to reflect deposition under changing climatic conditions varying from humid to arid or semi arid aeolian deposits are preserved within the sand sheets showing characteristics of dominantly perennial flow punctuated by shorter periods of desiccation type ii while sand sheets showing features typical of arid and or semi arid flow conditions type iii contain no preserved aeolian deposits this selective preservation is interpreted to be a result of the combined effect of groundwater table level and fluvial style which in turn are inferred to have been controlled by the climatic regime the deposits show that during pre vegetational times the preservation of aeolian deposits under certain conditions may be more optimal in fluvial systems formed in a humid climate than in fluvial systems formed under semi arid or arid circumstances the occurrence of aeolian deposits within a precambrian succession of fluvial deposits therefore need not be an indication of the most arid environmental conditions

aeolian sediments in lower to middle triassic rocks of central wyoming abstract the lower to middle triassic red peak and crow mountain formations of central wyoming have commonly been interpreted as being of shallow marine or shelf origin this paper presents conclusive evidence of an aeolian origin for parts of the two formations the interpretation is based on highly indicative sedimentary structures including wind ripple grainfall and grainflow strata lag deposits and granule ripples in the sediments of these formations facies in the upper red peak and lower crow mountain formations represent aeolian dune sandsheet wet interdune and sabkha environments emphasis is placed on the recognition and interpretation of correlative surfaces of regional extent which not only allow subdivision of the aeolian sediments into different genetic sequences but also aid in the reconstruction of the depositional history the recognition of an aeolian deposystem and of regional bounding surfaces adds valuable information to the efforts of reconstructing the triassic paleogeography of the western interior

high resolution stratigraphic architecture and lithological heterogeneity within marginal aeolian reservoir analogues marginal aeolian successions contain different lithological units with variable geometries dimensions and spatial distributions such variations may result in considerable heterogeneity within hydrocarbon reservoirs developed in successions of this type which poses a high risk to their efficient development here such heterogeneity is described and characterized at inter well 1 km scales using two well exposed outcrop analogues of end member marginal aeolian deposits from the permian cedar mesa sandstone and jurassic page sandstone of south central utah usa the sedimentology and stratigraphic architecture of the cedar mesa sandstone was studied in a 1 2 km2 area in the indian creek region of southern utah where the interval consists of interbedded fluvial and aeolian deposits representative of a fluvial dominated erg margin the page sandstone was studied in a 4 3 km2 area near escalante close to the utah arizona border where it consists of interbedded sabkha and aeolian deposits representative of a transitional marine erg margin the three dimensional stratigraphic architectures of both reservoir analogues have been characterized in order to establish the dimensions geometries and connectivity of high permeability aeolian sandstones facies architecture of the aeolian sabkha deposits is characterized by laterally continuous aeolian sandstone layers of relatively uniform thickness that alternate with layers of heterolithic sabkha deposits aeolian sandstones are thus likely to form vertically unconnected but laterally widespread flow units in analogous reservoirs facies architecture in the aeolian fluvial deposits is more complex because it contains alternating intervals of aeolian sandstone and fluvial heterolithic strata both of which may be laterally discontinuous at the studied length scales aeolian sandstones encased by fluvial heterolithic strata may form small isolated flow units in analogous reservoirs although the limited continuity of fluvial heterolithic strata results in vertical connectivity between successive aeolian sandstones in other locations these architectural templates may be used to condition zonation schemes in models of marginal aeolian reservoirs

sedimentary cycles and facies architecture of aeolian fluvial strata of the upper jurassic guara formation southern brazil the upper jurassic guara formation comprises an 80 200 m thick continental succession exposed in the western portion of the rio grande do sul state brazil it comprises four distinct facies associations i simple to locally composite crescentic aeolian dune sets ii aeolian sand sheets iii distal floodflows and iv fluvial channels the vertical stacking of the facies associations defines several 5 14 m thick wetting upward cycles each cycle starts with aeolian dune sets followed by aeolian sand sheets deposits and culminating in either fluvial channels or distal flood strata within some cycles aeolian sand sheets are absent and fluvial deposits rest directly above aeolian dune facies the transitions from one facies association to another are abrupt and marked by erosive surfaces that delineate distinct episodes of sediment accumulation the origin of both the wetting upward cycles and the erosive surfaces was controlled by the ground water table level dry sand availability and aeolian and fluvial sediment transport capacity variations related to climatic fluctuations between relatively arid and humid conditions preservation of the fluvial aeolian deposits reflects an overall relative water table rise driven by subsidence

sand drift surfaces a neglected type of bounding surface sand drift surfaces are sharp generally erosional surfaces separating waterlaid deposits from overlying eolian sand sheet deposits they form in many modern playa lake ephemeral stream and alluvial fan environments but have rarely been reported from ancient sequences sand drift surfaces are an important type of bounding surface one which marks the transition from subaqueous to eolian depositional processes thereby providing valuable information for environmental reconstructions architectural element analysis and short and long term climate changes because of their nature sand drift surfaces cannot be described by existing bounding surface classifications to overcome some of the classification problems we suggest a simple nonhierarchical terminology

evidence for 2 0 ga continental microbial mats in a paleodesert setting abstract early evolved microbial communities characterized the initial biological invasion of precambrian continental landscapes in modern arid settings microbial mats and biological soil crusts are well developed and stabilize sediment the paleoproterozoic makgabeng formation in south africa is one of the oldest and best preserved dryland systems on earth six types of microbial mat related structures are now recognized within these depositional systems this paper presents three newly discovered structures that include tufted microbial mat biological soil crusts and gas escape features in addition to three previously documented structures that include roll up features sand cracks and wrinkled features these discoveries demonstrate that microbial communities were well established and inhabited diverse continental settings by 2 0 ga approximately 200 million years after the onset of the great oxidation event

facies distribution as a response to early rift tectonic activity in the sergipe alagoas basin northeastern brazil abstract 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

lower triassic sequence stratigraphy of the western part of the germanic basin west of black forest fluvial system evolution through time and space abstract the aim of this paper is to analyse the fluvial evolution of the lower triassic in the western part of the germanic basin through time and space as well as the impact of the geodynamic and climatic setting on the preservation of fluvial deposits the lower triassic crops out only in the vosges massif and the black forest so well log studies are required to realise sequence stratigraphy correlations and establish comparisons with others parts of the germanic basin in a first step we use well log data analyses to characterise the electrofacies associations in the triassic and then define the well log signatures of each formation in a second step the characterisation and recognition of genetic sequences and their stacking pattern allow us to define seven minor cycles integrated into two major cycles finally the quantification of the lithologies at different stages of basin evolution leads to the reconstruction of paleoenvironmental maps to illustrate facies evolution through space and time a comparison with cycles defined in the germanic basin allows us to propose correlations of the lower triassic on either side of the rhine graben and leads to a discussion of the evolution of fluvial systems through time and space during the scythian the fluvial style is characterised by braided fluvial systems evolving laterally into lake deposits towards the central part of the germanic basin during this stage the basin was a huge depression with very few marine connections in its extreme eastern part the stratigraphic cycles represent rhythmic fluctuations in relative lake level that could be attributed to sediment supply and or lake level variations in an arid setting four minor stratigraphic cycles are observed that are integrated within a single major stratigraphic cycle during the period of the stratigraphic base level rise of the major cycle a maximum of 233 m of sediment would represent a duration of sedimentation in the paris basin of at least 1 8 m y during the period of the stratigraphic base level fall of the major cycle a maximum of 65 m of sediment would have accumulated over 2 5 m y on the western edge of the germanic basin the top of the scythian is marked by a major sedimentary break characterised by a planation surface with preservation of the first paleosols followed by the hardegsen unconformity this unconformity is tectonically deformed leading to the development of a new sedimentation area in the west of the basin the fluvial sedimentation above this discontinuity shows a trend towards enhanced development of floodplain or lacustrine type environments at its western margin with the formation of paleosols the fluvial systems are linked with sabkhas and then with a shallow sea connected to the tethys ocean in this context the stratigraphic cycles are caused by variations in relative sea level and or sediment supply the fluvial deposits are preserved in an exoreic basin

the interaction of aeolian and fluvial processes during deposition of the upper cretaceous capping sandstone member wahweap formation kaiparowits basin utah u s a abstract detailed examination of the upper cretaceous capping sandstone member of the wahweap formation in the kaiparowits basin utah reveals the presence of aeolian stratification deposition by aeolian processes is recognized and distinguished from subaqueous deposition by the presence of centimeter scale inversely graded wind ripple stratification the aeolian stratification in the wahweap formation is the first occurrence reported from upper cretaceous strata on the colorado plateau of the western u s a aeolian stratification occurs as thin wind reworked caps of fluvial bar sandstones deposited within low sinuosity braided streams and as more extensive deposits of small scale dunes that developed in geographically restricted dune fields aeolian reworking of bars took place during low stage flow and was possibly controlled by intermittent seasonal discharge variations prolonged aridity led to increased sand supply entering the aeolian system dunes nucleated and grew rapidly between the braided stream systems these small scale dunes rarely developed extensive or tall slip faces as evidenced by the rare preservation of grain flow strata and the dominance of wind ripple stratification the dune field was characterized by sinuous crested dunes probably barchans amid and linked to the extensive braided stream systems based on modern analogs the resulting change in sand storage supply probably is related to a short term shift to a more semi arid arid climate possibly seasonally however a longer term climate change to semi arid arid may be indicated for the dune complex near the boundary with the overlying kaiparowits formation