the pangaea megamonsoon records evidence from the triassic mungaroo formation northwest shelf of australia abstract an integrated analysis in this study of paleogeographic paleontologic seismic and sedimentologic data has been used to explain the effect of the pangaean megamonsoon on the whole triassic especially the middle late triassic mungaroo formation in the north carnarvon basin northwest shelf of australia our results show that the three triassic formations from bottom to top locker shale mungaroo formation and brigadier formation comprise a complete depositional cycle and correspond to an undeveloped strong and weak monsoon periods respectively during the strong monsoon period of the mungaroo formation the palynological evidences exhibited mixture spore pollen characteristics of the hygrophytic assemblage spore pollen from the pteridophyte spores seed ferns and cycads pollen in humid environment of lowlands and coastal plain and the xerophytic assemblage pollen from the drought tolerant plants of the interior mountainous areas the sedimentary evidences of the mungaroo formation show low angle shingled progradational seismic reflection configuration the highly seasonal variations in precipitation during deposition of the mungaroo formation exhibited typical sandwiched depositional characteristics of coarse channels sandstone fining upward fluvial aggradational cycles facs with poor to moderately sorting and angular to subangular roundness organic mudstone and coal seam interbedded finally in contrast to today s typical examples of poyang lake delta a shallow water braided delta conceptual depositional model of the mungaroo formation is formed with a large proximal and distal delta plain and small delta front the model results serve mainly to indicate the importance of various climate forming factors climate topography eustatic whereas tectonic activity unlikely played any significant role in this process

oceanwide imprint of large tectonic and oceanic events on seawater nd isotope composition in the indian ocean from 90 to 40 ma 1 we have analyzed four sediment cores from the southern indian ocean odp sites 757 758 1135 and 762 with high carbonate content in order to reconstruct the neodymium isotopic composition end of ancient intermediate south indian seawater from late cretaceous 90 ma to early eocene 40 ma the endvariations are highly consistent and exhibit reproducible patterns over a very large geographic area confirming the seawater origin of the signal combining geochemical constraints with paleogeographic reconstructions we highlight the respective roles of 1 large scale tectonic events 2 continental weathering from surrounding precambrian terrains 90 65 ma 3 oceanic circulation changes 50 40 ma and possibly 4 local volcanism of the ultra fast spreading south east indian ridge seir 60 50 ma on the nd isotopic composition of south indian seawater between 60 ma and 50 ma the regional nd isotopic variations closely mimic changes in seir spreading rate we suggest that the nd isotopic composition of seawater could be influenced by nd of volcanic origin in the vicinity of ultra fast spreading ridges 13 cm yr the india asia collision closed the equatorial seaway between asia and india and drastically changed oceanic circulation patterns in the indian ocean warm and more radiogenic pacific equatorial seawater was diverted to the south by the east indian coast a stronger mixing of this pacific seawater with south indian seawater would explain the rapid shift ofend from 50 ma 11 to 40 ma 8

palaeoenvironmental reconstruction of the late cretaceous sânpetru formation haţeg basin romania using paleosols and implications for the disappearance of dinosaurs abstract paleosols of the late cretaceous s npetru formation ha eg basin romania are the subject of macroscopic microscopic and geochemical investigation in order to reconstruct the palaeoenvironmental and palaeoclimatic conditions in which dinosaurs lived study of overbank deposits present in an 860 m thick stratigraphic interval of the s npetru formation exposed along the sibisel valley reveals the presence of one facies and five different pedotypes 1 finely laminated gray green mudstones and siltstones interpreted as pond deposits 2 bioturbated gray green mudstones lacking macroscopic pedogenic features interpreted as very poorly developed hydromorphic paleosols 3 bioturbated gray green mudstones containing carbonate concretions interpreted as poorly developed hydromorphic paleosols 4 mottled gray green mudstones containing carbonate concretions and limited illuvial clay accumulation interpreted as moderately developed paleosols characterized by a high but fluctuating watertable 5 bioturbated brown red mudstones lacking macroscopic pedogenic features other than the occasional mottles interpreted as poorly developed paleosols that formed on the higher and better drained floodplains and 6 bioturbated brown red mudstones containing carbonate nodules interpreted as moderately developed calcareous paleosols that formed on distal floodplain settings although limited exposure prevents the documentation of lateral relationships of pedotypes the presence of paleosol profiles that display characteristics of two different pedotypes suggests that they represent a lateral continuum on the landscape related to local differences in hydrology and relief i e catena the pedotype assemblage reveals that the s npetru landscape was a mosaic of wetlands seasonal wetlands and better drained floodplain habitats similar to the present day indogangetic plains pedogenic features and paleosol geochemistry indicate that the maastrichtian climate of romania was subhumid the distribution of pedotypes through the s npetru formation reveals small and large scale palaeoenvironmental changes associated with the shifting of a complex mosaic of wet and dry habitats in response to shifts in river position on the alluvial plain however a major palaeoenvironmental change occurs in the upper s npetru formation where the region was transformed into extensive wetlands such dramatic changes coincide with river competence increase change in palaeocurrent directions and dearth of macrovertebrate remains which had been previously misinterpreted as evidence for the disappearance of dinosaurs at the cretaceous tertiary boundary these palaeoenvironmental changes induced by tectonism are responsible for the shift from preservation of macrofossils concentrated by hydraulic processes into conspicuous lenticular bonebeds in the lower s npetru formation to preservation of microfossil and more rarely macrofossil remains in hydromorphic calcareous paleosols in the upper s npetru formation the consequences of palaeoenvironmental changes on vertebrate preservation mode must be considered in the search for fossils and interpretation of the fossil record

environmental controls on calcareous nannoplankton response to the cretaceous paleogene mass extinction in the tethys realm abstract the cretaceous paleogene k pg mass extinction exhibits a remarkable geographical contrast between the northern and southern hemispheres in extinction severity and recovery response yet environmental facets of this extinction selectivity are still poorly known here we statistically analyze the calcareous nannofossil counts from six k pg boundary sections from the tethys ocean representing a northern subtropical depth transect from continental shelf to abyssal plain our analyses reveal that calcareous nannoplankton from all environments underwent an ecological crisis and responded similarly to the k pg environmental catastrophe providing a solid basis for paleoecological reconstruction with nannofossils across the world oceans most interesting is the environment dependent response pattern as demonstrated by the increasing separation between shelf and deep ocean sites that signals a deepened environmental stress gradient this environment dependent response can be attributed to the marked difference in primary production and community composition between shelf and pelagic ecosystems as well as the smaller accommodation and buffering capacity of shelves while the progressive removal of susceptible species with increasing water depth seems to be of little influence

a cratonic middle jurassic paleopole callovian oxfordian stillstand j 2 cusp rotation of the colorado plateau and jurassic north american apparent polar wander 1 paleomagnetic results have been obtained from two sequences of the upper middle jurassic upper callovian summerville formation which are located on the north american craton north central new mexico the thicker of the two sections trujillo exhibits a well defined dual polarity remanence forming a magnetostratigraphy of at least 12 relatively short polarity intervals the high reversal frequency is consistent with that recorded by the oceanic crust at this time the second section romeroville is thin gypsiferous and poorly indurated consequently only a short interval 5 m was successfully sampled the characteristic magnetization was wholly normal polarity in the rapid reversals of the thicker section that thickness of normal polarity is unique and thus forms the basis of magnetostratigraphic correlation between the two sections a cratonic late middle jurassic paleomagnetic pole at 148 2 e 57 3 n k 30 3 95 6 0 was obtained from the larger trujillo sequence despite large confidence limits the small sample population of the romeroville sequence displayed the same pole throughout the western united states the summerville formation is overlain with little or no discordance by the morrison formation although the two stratigraphic units are commonly reported to be separated by an unconformity designated j 5 the new mexico paleopoles of the summerville and overlying lower morrison formations are statistically identical at the 95 confidence level a similar situation exists between summerville and lower morrison paleopoles of the colorado plateau the presence of the same geomagnetic field direction in both the summerville and the lower morrison formations suggests that the j 5 unconformity which separates them may encompass little time perhaps representing only a minor break in deposition the two newly investigated summerville sites are located east of the rio grande rift hence representative of the north american craton their paleopoles are displaced counterclockwise relative to those of the colorado plateau and in amounts consistent with other coeval craton colorado plateau pole pairs together six coeval paleopoles indicate that the colorado plateau has rotated clockwise by about 9 0 3 since late pennsylvanian time the cratonic summerville paleopole also removes the uncertainty over the jurassic north american apparent polar wander path the statistically identical summerville and lower morrison paleopoles form a substantial data set five paleopoles which indicate that na apw traced a path roughly along 60 latitude the five paleopoles stand in stark contrast to the paleopole from the slightly older 5 8 ma moat volcanics spreading rates in the central atlantic do not allow na plate motion that would include both paleopoles positions because the weight of the data five paleopoles from widely spaced localities and different tectonic blocks the moat volcanics pole cannot be representative of north america in the middle jurassic

a drying upward aeolian system of the bohdasin formation early triassic sudetes of ne czech republic record of seasonality and long term palaeoclimate change abstract the record of aeolian processes was studied in early triassic sandstones of the upper part of the bohdasin formation ne bohemia an isolated erosional relict of a triassic fluvial aeolian succession in the sudetes block of the bohemian massif central europe the aeolian system exposed in the dev t k i quarry near cerven kostelec provides a significant addition to the generally poorly preserved record of early triassic palaeoclimate and palaeowind regime in central europe two mutually interbedded facies occur in the aeolian succession 1 dune facies comprising cross strata that show interdune reactivation and superimposition bounding surfaces and 2 interdune facies formed by horizontally stratified commonly mud draped sandstones which display a number of indicators of damp to wet conditions and fluctuations in water table the succession of the dev t k i sandstones is interpreted as a record of migration and climb of dunes with intervening interdune flats which replaced an underlying fluvial system it is likely that a coeval fluvial system existed near the dev t k i dune field providing available sand in dry periods and flooding in wet periods dominant palaeowind directions are southwestward and northward in present day coordinates repeated reversals of palaeowind direction interpreted as seasonal are recorded in changes in the internal structure of the cross strata reworking and reactivation in the dune migration direction at least some episodes of dune reworking occurred simultaneously with episodes of water table rise a drying upward trend in the aeolian succession is interpreted from evidence for increased availability of sand through time the upward transition from a braided fluvial to a wet drying upward aeolian system within the bohdasin formation represents a shift toward maximum aridity of the palaeoenvironment which marks also the peak arid conditions in the long term palaeoclimatic evolution of the carboniferous triassic succession of the sudetes region and correlates with the establishment of aeolian settings in other regions of central europe during the early triassic the record of changing palaeowind directions documented in several cases to have been coupled with episodes of rapid rise in water table is taken as evidence for pronounced climatic seasonality and brings additional support to the models predicting strong monsoonal circulation during the early triassic affecting particularly the eastern subequatorial coast of pangaea and adjoining regions

early jurassic batrachopus rich track assemblages from interdune deposits in the wingate sandstone dolores valley colorado usa abstract late triassic and early jurassic tetrapod track assemblages are abundant and quite well documented from the respective chinle and glen canyon groups of the dolores valley region of western colorado and adjacent regions especially eastern utah however gaps still exist in our knowledge of the spatial and temporal distribution of representative ichnogenera the stratigraphic distribution of track assemblages in the cliff forming wingate sandstone formation the lower unit of the glen canyon group underlying the kayenta and navajo formations is difficult to determine because almost all wingate assemblages are known only from fallen blocks originating from precipitous vertical cliffs which yield both dune and interdune ichnofaunas among the characteristic lower jurassic biochron ichnogenera grallator eubrontes otozoum anomoepus and batrachopus in the dolores valley only grallator is known abundantly while otozoum and batrachopus were previously known only from single occurrences and eubrontes and anomoepus have yet to be reported we here report two large batrachopus rich assemblages that give new insight into the interdune paleoenvironments frequented by the batrachopus trackmaker traditionally regarded as a basal crocdylomorph and the theropodan trackmaker of grallator both assemblages contain the best preserved and most abundant batrachopus currently known locally in high densities where individual trackways are clearly visible they indicate that the trackmakers had variable gaits a third new assemblage containing batrachopus from salt creek is also described as is a fourth new assemblage from the uncompahgre plateau which yields moderately large theropod tracks cf eubrontes but no batrachopus although diagnostic late triassic biochron ichnogenera like brachychirotherium occur in basal units of the wingate sandstone batrachopus which is considered an early jurassic biochron ichnotaxon occurs within the formation thus vertebrate ichnotaxa help place the triassic jurassic boundary within the wingate formation shed light on their spatio temporal distribution and underscore their utility for paleoecological interpretation in a unit devoid of tetrapod body fossils

tropical westerlies over pangaean sand seas cross equatorial westerly winds are key features of tropical circulation in monsoonal regions although prominent in numerical climate models of pangaea the supercontinent straddling earth s equator late palaeozoic to early mesozoic such flow has not been confirmed previously by migration directions of ancient dunes wind blown sandstones that span 100 million years of earth history are widely exposed in south western usa if recent palaeomagnetic data from the colorado plateau are used to correct mesozoic palaeogeographic maps the plateau is placed about 10 further south than previously assumed and the prevailing north westerly surface winds recorded by dune deposited sandstones are explicable as cross equatorial westerlies the hallmark of modern monsoon circulation permian to early jurassic dunes were driven by north westerlies produced by a steep pressure gradient spanning the supercontinent during december january february although winds are light in most modern near equatorial settings the east african jet accounts for more than half the cross equatorial flow in june july august the thicknesses of annual depositional cycles within the navajo sandstone indicate that the near equatorial north westerly winds that drove these particular dunes were stronger than the modern east african jet the early jurassic dunes that deposited the thick cycles were positioned west of the dominant southern hemisphere thermal low and against highlands to the west a setting very similar to the east african jet the mountains along the western coast of pangaea not only enhanced wind strength but also cast a rain shadow that allowed active dunes to extend very close to the palaeoequator

barremian cenomanian palaeotemperatures for australian seas based on new oxygen isotope data from belemnite rostra oxygen isotope ratio 18o data are presented for 55 belemnite rostra specimens of late aptian albian age from the great artesian basin of eastern australia and of late barremian early cenomanian age from the carnarvon basin of western australia the belemnites were carefully screened for diagenesis by means of catholuminescence and trace element geochemistry the 18o record for the carnarvon basin palaeolatitude 40 s is interpreted to show a long term warming trend from 10 c in the aptian to a maximum of 15 c in the cenomanian shorter term fluctuations in the mid albian are also apparent data from the great artesian basin palaeolatitude 40 55 s show a wider 18o range which is attributed to the epeiric sea context of this sample set the larger range in 18o is interpreted to reflect differing water mass characteristics due possibly to a combination of variable freshwater dilution seasonal temperature fluctuations and isotopic exchange between seawater and pyroclastic sediment within the epeiric sea nevertheless the aptian albian 18o trends are still comparable to those obtained for the carnarvon basin the inferred palaeotemperature trends for the australian sedimentary basins are consistent with records from other regions and demonstrate that broadly synchronous palaeotemperature variations can be recognised on a global scale during the cretaceous although our data do indeed show cool temperatures within the aptian and the albian reaching a low of 10 c these estimates are somewhat warmer than those based on glendonite genesis however the exact position of the glendonite bearing and dropstone rich parts of the bulldog shale is poorly constrained with respect to our isotope data and the warmest temperatures were of late albian and early cenomanian age however to conform to greenhouse warmth and equability and to achieve parity with other palaeotemperature records the 18oseawater estimate of 1 0 that is generally used for cretaceous oceans in an ice free world needs to be adjusted to a slightly higher value

collapse of the late triassic megamonsoon in western equatorial pangea present day american southwest during the late triassic western equatorial pangea in the present day american southwest was unusually humid as indicated by sedimentological evidence and inferred from general circulation models these studies show that once equatorial pangea was assembled cross equatorial summer air flow penetrated into western equatorial pangea bringing abundant megamonsoon rainfall and warm temperatures however many of these investigations indicate that gradual aridification began sometime during the late triassic to jurassic we show from field properties geochemical transfer functions and isotopic analysis of paleosols in the chinle formation of petrified forest national park arizona that the western equatorial pangea megamonsoon collapsed by 214 7 ma during the middle norian climate shift paleosols include entisols inceptisols vertisols aridisols and alfisols with transfer functions for mean annual precipitation chemical index of alteration minus potassium cia k and mean annual temperature nak salinization developed from analogous modern data sets the most notable shift is the appearance of carbonate enriched paleo inceptisols and paleo vertisols after 214 7 ma and paleo aridisols after 210 ma prior to the middle norian climate shift the region is classified as humid humidity province based on rainfall estimates initiation of the middle norian climate shift was characterized by an increase in paleosol carbonate content and rapidly declining rainfall as the region shifted to subhumid and eventually to semiarid and arid after 210 ma paleosol derived temperatures are indicative of warm temperate to subtropical ecozones whereas general circulation models show higher temperatures and tropical conditions perhaps because boundary conditions were set to atmospheric p co 2 4 5 present elevations of 1 5 2 km adjacent to the cordilleran magmatic arc complex located 400 km west of the study area may account for nontropical temperatures after 210 ma however temperatures began to increase possibly as a result of escalating atmospheric p co 2 from shale oxidation during marine regression and from coal and paleosol organic matter oxidation during prolonged aridification paleomagnetic studies have suggested northward continental drift of western equatorial pangea to outside of the intertropical convergence zone as the cause of monsoonal collapse during the late triassic to early jurassic the formation of a rain shadow as a result of the evolving cordilleran magmatic arc as the cause of aridification is supported by recent magnetostratigraphic work substantiating that the region remained in the tropics through the triassic according to our age model the middle norian climate shift is dated to near the same time as the manicouagan impact crater but there is no evidence of such an event in the study area either geochemically or sedimentologically at our scale of observation however a regionally defined faunal turnover may have been a response to rapidly changing climates in the region

sedimentology of cold climate aeolian sandsheet deposits in the askja region of northeast iceland active aeolian sandsheets cover an area of 270 km2 in the askja region of ne iceland the sandsheet is divided into i a deflationary upwind part that is characterised by deflation lags ventifacted boulder fields and restricted aeolian sand patches in the lee of obstacles ii an accumulating central part that is characterised by continuous aeolian sand cover up to 10 m thick where three scales of aeolian ripples are evident along with larger scale forms including longitudinal zibars and iii a downwind part that is currently subject to aeolian bypass with only localised accumulation occurring in topographic hollows between basaltic lava fields trains of aeolian granule megaripples are a characteristic landform of the downwind part of the sandsheet these sinuous crested oblique bedforms attain heights of 0 35 m and downwind spacings of 6 m they are composed principally of low density pebble grade pumice clasts and other reworked volcaniclastic detritus derived from the nearby askja volcanic centre the distribution of landforms across the sandsheet reflects a regional aeolian sediment budget that is controlled by dynamic interactions between glacial ice margin fluvial aeolian and volcaniclastic processes under the influence of a distinctive climatic regime sediment supply at the upwind sandsheet margin adjacent to the dyngjujokull glacier increases during summer periods when rates of glacial ablation are at a maximum longer term controls on sediment supply rate are determined by episodes of glacier surging and retreat and by periodic eruptions of volcaniclastic debris from the askja volcanic centre the availability of sediment for aeolian transport is controlled by the level of the groundwater table the depth and continuity of the permafrost layer in the proglacial area the degree of development of armoured pebble lags and freezing of the sandsheet surface during winter months the transport capacity of the wind varies on a seasonal basis with mean wind velocities and wind gustiness reaching a maximum during winter periods both winter and summer mean wind velocities have been steadily increasing since formal records began in 1969 the suite of aeolian landforms developed within the askja region as defined by sediment texture and composition and bedform scale morphology and spatial distribution reflects a special set of controlling circumstances which mean that the askja sandsheet deposits differ significantly from those described from elsewhere

annual monsoon rains recorded by jurassic dunes pangaea the largest landmass in the earth s history was nearly bisected by the equator during the late palaeozoic and early mesozoic eras modelling experiments and stratigraphic studies have suggested that the supercontinent generated a monsoonal atmospheric circulation that led to extreme seasonality1 2 3 but direct evidence for annual rainfall periodicity has been lacking4 in the mesozoic era about 190 million years ago thick deposits of wind blown sand accumulated in dunes of a vast low latitude desert at pangaea s western margin5 6 7 these deposits are now situated in the southwestern usa here we analyse slump masses in the annual depositional cycles within these deposits which have been described for some outcrops of the navajo sandstone8 twenty four slumps which were generated by heavy rainfall appear within one interval representing 36 years of dune migration we interpret the positions of 20 of these masses to indicate slumping during summer monsoon rains with the other four having been the result of winter storms the slumped lee faces of these jurassic dunes therefore represent a prehistoric record of yearly rain events

reply to comment by francois bourges et al on carbon uptake by karsts in the houzhai basin southwest china the objectives of the study as outlined in yan et al 2011 are to understand the temporal variations of carbonuptake from carbonate dissolution and the major driver ofthatuptake itwasnotourobjectivetoconstructafullcarbonbudget for the houzhai basin therefore gaseous emissionsfrom the land surface were not included in the study seefigure 1 this addresses point 1

greenhouse crises of the past 300 million years proxies of past co 2 and climate over the past 300 m y now reveal multiple global climate change events in unprecedented detail evidence for past co 2 spikes comes from expanded and refined data on stomatal index of fossil ginkgo and related leaves new evidence for synchronous climatic change comes from paleosols in montana utah and neighboring states each co 2 spike was coeval with unusually clayey red and decalcified paleosols which can be traced throughout the colorado plateau spikes in atmospheric co 2 also were coeval with increases in paleosol alkali depletion as an indication of high temperature and spikes in paleosol base depletion and depth to calcic horizons as indications of high precipitation in the colorado plateau times of warmer climate were also more humid perhaps due to greater moisture potential of warmer air seasonality of climate did not increase during warm wet spikes the mesozoic greenhouse was not persistently hot with cool spells but warm with hot flashes these data furnish power laws predicting the sensitivity and magnitude of change in mean annual temperature mat and mean annual precipitation map due to rising co 2 in a mid latitude mid continental region the magnitude of the coming anthropogenic greenhouse pales in comparison with past greenhouse spikes at times of global mass extinctions

synapsid burrows and associated trace fossils in the lower jurassic navajo sandstone southeastern utah u s a indicates a diverse community living in a wet desert ecosystem abstract enigmatic structures in the lower jurassic navajo sandstone near moab utah occur at three localities below carbonate beds that record interdune lake deposits these structures are interpreted as mammal and therapsid burrows based on their architectural and surficial burrow morphologies type i large diameter and type ii mega diameter burrows type i burrows include sinuous tunnels y and t branched tunnels sinuous ramps and chambers and weather into mounds averaging 33 m 22 m and extend 1m above the surface type i burrows are dorsoventrally flattened in cross section averaging 9 3 cm wide and 4 2 cm high and are sand filled and structureless type i burrows mostly have smooth walls though some have scalloped walls type ii burrows are simple inclined tunnels 35 cm wide and 20 cm high and exhibit well preserved bilobate morphology along the underside of the tunnel the walls preserve a series of 3 or 4 thin 4 8 mm inclined scratch marks from the upper part of the wall and along the floor the great complexity and high density of type i burrow systems is best explained by multiple individuals living together in social groups these burrows are more complex than early triassic therapsid burrows from south africa and are most similar to burrows of extant social e g voles and eusocial mammals e g naked mole rats type ii burrows were likely constructed by therapsids based on burrow size and comparison to permian and triassic therapsid burrows from south africa and antarctica

numerical simulation of the cretaceous tethys circumglobal current certain paleobiogeographical reconstructions of ocean currents during the cretaceous about 144 to 65 million years ago suggest that a circumglobal tropical current flowed westward through the continental configuration of that time although some numerical climate models failed in initial attempts to simulate this current simulations with a coupled atmosphere ocean model with relatively high spatial resolution and a late cretaceous continental distribution show that a circumglobal current is a robust feature even though local surface currents in the tethys seaway reverse during the south eurasian monsoon months

an example of liquefaction induced interdune sedimentation from the early jurassic navajo sandstone usa abstract extensive outcrops of navajo sandstone in the southwestern united states expose eolian dune deposits that are subdivided in a complex array of foresets and bounding surfaces in the glen canyon region and other places this architecture is frequently disrupted by large scale soft sediment deformation features these features have been attributed to episodic liquefaction events that affected saturated sand below the level of the interdune surface though erosional truncation of deformation features indicates that liquefaction often occurred in the uppermost levels of navajo dune deposits very few paleotopographic disruptions due to subsurface deformation have been documented navajo sandstone outcrops in west canyon utah provide unusually comprehensive exposure of architectural details linking large scale deformation features and associated interdune deposits enabling a well constrained appraisal of their genesis at this location a 23 m succession of sandstone mudstone carbonate and chert deposits overlies a zone of deformation that extends laterally for hundreds of meters this horizontally stratified lens occupies an abrupt synform along a bounding surface between successive crossbeds that otherwise appears as a featureless sub horizontal plane large scale foresets below this bounding surface oversteepen at the margins of the synform and grade downdip into contorted stratification and structureless expanses the authors propose that liquefaction in the jurassic erg caused localized subsidence of a minor portion of a dry interdune surface to a position several meters below the contemporary water table a succession of hyperpycnal sand flows lacustrine evaporites and eolian sheet and dune deposits filled this depression prior to the advance of large dunes across the site the process response dynamics evident in this outcrop suggest that deformation may have exercised significant non systematic control over depositional architectures in areas of the erg prone to liquefaction similar dynamics are unknown from modern desert environments and their intrinsic scale defies laboratory simulation therefore close investigation of these ancient features is essential for exploring the full range of depositional controls that may be encountered in other ancient eolianites on earth and in eolian accumulations on other planets

the late permian climate what can be inferred from climate modelling concerning pangea scenarios and hercynian range altitude abstract a major unsolved geodynamic problem is the permian pangea plate configuration at the end of paleozoic era around 255 ma while consensual geology indicates a plate arrangement close to that of the jurassic prior to the atlantic opening pangea a paleomagnetic data indicates a nearly 3000 km more eastward position of gondwana with respect to laurussia leading to major plate and relieves reorganisation during permo triassic times pangea b using an atmospheric general circulation model agcm we simulate the climatic response to both configurations we also test the fundamental role of paleo elevations through sensitivity experiments each simulated climate is then compared with the aim of constraining the best fit to a particular paleogeographic scenario main trends of simulated late permian climate in agreement with paleoclimatic indicators are 1 a warm temperate climate accompanied by a monsoon circulation over the eastern side of gondwana 2 a cold temperate climate marked by strong annual thermal amplitude at high latitudes in gondwana and in siberia 3 an arid belt in the subtropics over the western side of gondwana and laurussia and 4 strong climatic differences over both hemispheres respectively main variance is found over laurussia with a simulated tropical climate while an arid climate is suggested by paleodata simulating different paleo elevations of the appalachian and the variscan fold belts can solve this discrepancy the best model data fit is reached for a mean altitude of 4500 m in the appalachians and appears to be dependent of pangea configuration with a southern europe variscan range of some 3000 m in a pangea a configuration or only 2000 m in for pangea b taking into account the geodynamic context we argue that pangea b appears to be the more probable configuration

the action of wind and water in a mid cretaceous subtropical erg margin system close to the variscan iberian massif spain aeolian processes and ephemeral water influx from the variscan iberian massif to the mid cretaceous outer back erg margin system in eastern iberia led to deposition and erosion of aeolian dunes and the formation of desert pavements remains of aeolian dunes encased in ephemeral fluvial deposits aeolian pods demonstrate intense erosion of windblown deposits by sudden water fluxes the alternating activity of wind and water led to a variety of facies associations such as deflation lags desert pavements aeolian dunes pebbles scattered throughout dune strata aeolian sandsheets aeolian deposits with bimodal grain size distributions mud playa ephemeral floodplain pebble sand and cobble sand bedload stream pebble cobble sand sheet flood sand bedload stream debris flow and hyperconcentrated flow deposits sediment in this desert system underwent transport by wind and water and reworking in a variety of sub environments the nearby variscan iberian massif supplied quartzite pebbles as part of mass flows pebbles and cobbles were concentrated in deflation lags eroded and polished by wind driven sands facets and ventifacts and incorporated by rolling into the toesets of aeolian dunes the back erg depositional system comprises an outer back erg close to the variscan highlands and an inner back erg close to the central erg area the inner back erg developed on a structural high and is characterized by mud playa deposits interbedded with aeolian and ephemeral channel deposits in the inner back erg area ephemeral wadis desiccated after occasional floods were mud cracked and overrun episodically by aeolian dunes subsequent floods eroded the aeolian dunes and mud cracked surfaces resulting in largely structureless sandstones with boulder size mudstone intraclasts floods spread over the margins of ephemeral channels and eroded surrounding aeolian dunes the remaining dunes were colonized occasionally by plants and their roots penetrated into the flooded aeolian sands upon desiccation deflation resulted in lags of coarser grained sediments a renewed windblown supply led to aeolian sandsheet accumulation in topographic wadi depressions synsedimentary tectonics caused the outer back erg system to experience enhanced generation of accommodation space allowing the accumulation of aeolian dune sands ephemeral water flow to the outer back erg area supplied pebbles eroded aeolian dunes and produced hyperconcentrated flow deposits fluidization and liquefaction generated gravel pockets and recumbent folds dune damming after sporadic rains the case of the namib desert monsoonal water discharge thar desert and meltwater fluxes from glaciated mountains taklamakan desert are three potential non exclusive analogues for the ephemeral water influx and the generation of hyperconcentrated flows in the cretaceous desert margin system an increase in relief driven by the aptian anti clockwise rotation of iberia led to an altitude sufficient for the development of orographic rains and snowfall which fed melt water fluxes to the desert margin system quartzite conglomerates and sands dominantly consisting of quartz and well preserved feldspar grains which are also observed in older cretaceous strata indicate an arid climate and the mechanical weathering of precambrian and palaeozoic metamorphic sediments and felsic igneous rocks unroofing of much of the cover of sedimentary rocks in the variscan iberian massif must therefore have taken place in pre cretaceous times

periodic accumulation and destruction of aeolian erg sequences in the permian cedar mesa sandstone white canyon southern utah usa the permian cedar mesa sandstone represents the product of at least 12 separate aeolian erg sequences each bounded by regionally extensive deflationary supersurfaces facies analysis of strata in the white canyon area of southern utah indicates that the preserved sequences represent erg centre accumulations of mostly dry though occasionally water table influenced aeolian systems each sequence records a systematic sedimentary evolution enabling phases of aeolian sand sea construction accumulation deflation and destruction to be discerned and related to a series of underlying controls sand sea construction is signalled by a transition from damp sandsheet ephemeral lake and palaeosol deposition through a phase of dry sandsheet deposition to the development of thin chaotically arranged aeolian dune sets the onset of the main phase of sand sea accumulation is reflected by an upward transition to larger scale ordered sets which represent the preserved product of climbing trains of sinuous crested transverse dunes with original downwind wavelengths of 300 400 m regularly spaced reactivation surfaces indicate periodic shifts in wind direction which probably occurred seasonally compound co sets of cross strata record the oblique migration of superimposed slipfaced dunes over larger slipfaceless draa each aeolian sequence is capped by a regionally extensive supersurface characterized by abundant calcified rhizoliths and bioturbation and which represents the end product of a widespread deflation episode whereby the accumulation surface was lowered close to the level of the water table as the sand sea was progressively cannibalized by winds that were undersaturated with respect to their potential carrying capacity aeolian sequence generation is considered to be directly attributable to cyclical changes in climate and related changes in sea level of probable glacio eustatic origin that characterize many permo carboniferous age successions sand sea construction and accumulation occurred during phases of increased aridity and lowered sea level the main sand supply being former shallow marine shelf sediments that lay to the north west sand sea deflation and destruction would have commenced at or shortly after the time of maximum aridity as the available sand supply became exhausted restricted episodes of non aeolian accumulation would have occurred during humid interglacial phases accumulation and preservation being enabled by slow rises in the relative water table subsidence analysis within the paradox basin together with comparisons to other similar age successions suggests that the climatic cycles responsible for generating the cedar mesa erg sequences could be the product of 413 000 years so called long eccentricity cycles by contrast annual advance cycles within the aeolian dune sets indicate that the sequences themselves could have accumulated in just a few hundred years and therefore imply that the vast majority of time represented by the cedar mesa succession was reserved for supersurface development

wind directions predicted from global circulation models and wind directions determined from eolian sandstones of the western united states a comparison panfish j t and peterson f 1988 wind directions predicted from global circulation models and wind directions determined from eolian sandstones of the western united states a comparison in g kocurek editor late paleozoic and mesozoic eolian deposits of the western interior of the united states sediment geol 56 261 282 wind directions for middle pennsylvanian through jurassic time are predicted from global circulation models for the western united states these predictions are compared with paleowind directions interpreted from eofian sandstones of middle permsylvanian through jurassic age predicted regional wind directions correspond with at least three quarters of the paleowind data from the sandstones the rest of the data may indicate problems with correlation local effects of paleogeography on winds and lack of resolution of the circulation models the data and predictions suggest the following paleoclimatic developments through the time interval studied predominance of winter subtropical high pressure circulation in the late pennsylvanian predominance of summer subtropical high pressure circulation in the permian predominance of summer monsoonal circulation in the triassic and earliest jurassic and during the remainder of the jurassic influence of both summer subtropical and summer monsoonal circulation with the boundary between the two systems over the western united states this sequence of climatic changes is largely owing to paleogeographic changes which influenced the buildup and breakdown of the monsoonal circulation and possibly owing partly to a decrease in the global temperature gradient which might have lessened the influence of the subtropical high pressure circulation the atypical humidity of triassic time probably resulted from the monsoonal circulation created by the geography of pangaea this circulation is predicted to have been at a maximum in the triassic and was likely to have been powerful enough to draw moisture along the equator from the ocean to the west

inconsistencies between pangean reconstructions and basic climate controls the supercontinent pangea dominated our planet from the permian into the jurassic paleomagnetic reconstructions have been used to estimate the latitudinal position of pangea during this 100 million year period atmospheric circulation recorded by eolian sandstones in the southwestern united states shows a broad sweep of northeasterly winds over their northernmost extent curving to become northwesterly in the south this evidence is consistent with paleomagnetic reconstructions of the region straddling the equator in the early permian but is at odds with its northward movement to about 20 n by the early jurassic at least one of the following scenarios must be true the latitude based on paleomagnetism is incorrect the interpretation of how winds shaped the dunes is mistaken the basic climate controls in the jurassic were different from those of today or the paleogeographic reconstructions available are insufficient to adequately reproduce the wind fields responsible for dune formation

a comparison of general circulation model predictions to sand drift and dune orientations the growing concern over climate change and decertification stresses the importance of aeolian process prediction in this paper the use of a general circulation model to predict current aeolian features is examined a gcm developed at nasa goddard space flight center was used in conjunction with white s aeolian sand flux model to produce a global potential aeolian transport map surface wind shear stress predictions were used from the output of a gcm simulation that was performed as part of the atmospheric model intercomparison project on 1979 climate conditions the spatial resolution of this study as driven by the gcm is 4 degrees x 5 degrees instantaneous 6 hourly wind stress data were saved by the gcm and used in this report a global map showing potential sand transport was compared to drift potential directions as inferred from landsat images from the 1980s for several sand seas and a coastal dune field generally results show a good correlation between the simulated sand drift direction and the drift direction inferred for dune forms discrepancies between the drift potential and the drift inferred from images were found in the north american deserts and the arabian peninsula an attempt to predict the type of dune that would bemore formed in specific regions was not successful the model could probably be further improved by incorporating soil moisture surface roughness and vegetation information for a better assessment of sand threshold conditions the correlation may permit use of a gcm to analyze open quotes fossil close quotes dunes or to forecast aeolian processes 48 refs 8 figs less

inclination flattening and the geocentric axial dipole hypothesis abstract william gilbert first articulated what has come to be known as the geocentric axial dipole hypothesis the gad hypothesis is the principle on which paleogeographic reconstructions rely to constrain paleolatitude for decades there have been calls for permanent non dipole contributions to the time averaged field recently these have demanded large contributions of the axial octupole which if valid would call into question the general utility of the gad hypothesis in the process of geological recording of the geomagnetic field earth filters distort the directions many processes for example sedimentary inclination flattening and random tilting can lead to a net shallowing of the observed direction therefore inclinations that are shallower than expected from gad can be explained by recording biases northward transport or non dipole geomagnetic fields using paleomagnetic data from the last 5 million years from well constrained lava flow data allows the construction of a statistical geomagnetic field model such a model can predict not only the average expected direction for a given latitude but also the shape of the distribution of directions produced by secular variation the elongation of predicted directions varies as a function of latitude from significantly elongate in the up down direction at the equator to circularly symmetric at the poles sedimentary inclination flattening also works in a predictable manner producing elongations that are stretched side to side and the degree of flattening depending on the inclination of the applied field and a flattening factor f the twin tools of the predicted elongation inclination relationship characteristic of the geomagnetic field for the past 5 million years and the distortion of the directions predicted from sedimentary inclination flattening allows us to find the flattening factor that yields corrected directions with an elongation and average inclination consistent with the statistical field model the method can be tested using sediments deposited in a known field application of the elongation inclination correction method to two magnetostratigraphic data sets from red beds in asia and pakistan brings the inclinations into agreement with those predicted from modern gps measurements and from global paleomagnetic data there appears to be no compelling reason at this time to abandon the geocentric dipole hypothesis which has provided such an excellent working model for so long

simulation of abrupt climate change induced by freshwater input to the north atlantic ocean temperature records from greenland ice cores1 2 suggest that large and abrupt changes of north atlantic climate occurred frequently during both glacial and postglacial periods one example is the younger dryas cold event broecker3 speculated that these changes result from rapid changes in the thermohaline circulation of the atlantic ocean which were caused by the release of large amounts of melt water from continental ice sheets here we describe an attempt to explore this intriguing phenomenon using a coupled ocean atmosphere model in response to a massive surface flux of fresh water to the northern north atlantic of the model the thermohaline circulation weakens abruptly intensifies and weakens again followed by a gradual recovery generating episodes that resemble the abrupt changes of the ocean atmosphere system recorded in ice and deep sea cores4 the associated change of surface air temperature is particularly large in the northern north atlantic ocean and its neighbourhood but is relatively small in the rest of the world

last glacial maximum and holocene climate in ccsm3 abstract the climate sensitivity of the community climate system model version 3 ccsm3 is studied for two past climate forcings the last glacial maximum lgm and the mid holocene the lgm approximately 21 000 yr ago is a glacial period with large changes in the greenhouse gases sea level and ice sheets the mid holocene approximately 6000 yr ago occurred during the current interglacial with primary changes in the seasonal solar irradiance the lgm ccsm3 simulation has a global cooling of 4 5 c compared to preindustrial pi conditions with amplification of this cooling at high latitudes and over the continental ice sheets present at lgm tropical sea surface temperature sst cools by 1 7 c and tropical land temperature cools by 2 6 c on average simulations with the ccsm3 slab ocean model suggest that about half of the global cooling is explained by the reduced lgm concentration of atmospheric co2 50 of present day concentrations there is an increase in the antarctic circumpolar current an

mid cretaceous ocean circulation results from model sensitivity studies a series of ocean general circulation model gcm experiments for mid cretaceous continental paleogeography with atmospheric forcing prescribed from atmospheric gcm experiments are utilized to investigate the nature of the mid cretaceous ocean circulation the experiments illustrate a tethys system of clockwise currents and predominant eastward flow in marked contrast with earlier reconstructions this result is apparently robust for changes in bathymetry and in the degree of planetary warmth changes in sea level have the largest potential to produce alternative circulation characteristics two major current systems outside of tethys dominate the model simulation the site of bottom water formation is the north pacific however in a sensitivity experiment for a warmer climate the eastern tethys became a site of deep water formation

petrography and environmental interpretation of tufa mounds and carbonate beds in the jurassic navajo sandstone of southeastern utah u s a abstract carbonate deposits in the jurassic navajo sandstone of utah reflect deposition in interdune lakes and springs interdune lake deposits consist of flat lying carbonate units springs formed tufa mounds that are interpreted as subaerial ambient temperature artesian spring deposits in the first systematic study of the petrography of the carbonate deposits in the navajo sandstone eleven facies were identified in several flat lying carbonate deposits and two tufa mounds fenestral mudstone and peloidal facies dominate the lacustrine deposits whereas thrombolitic mudstone characterizes the mounds the biota consists of ostracodes charophytes fish mollusks a possible freshwater sponge trace fossils and fragments of vascular plants features resulting from penecontemporaneous weathering provide evidence of episodic exposure of the lacustrine carbonate beds during deposition and formation of the tufa mounds under subaerial conditions although carbonate deposits are not rare in eolian systems few have been studied in detail comparisons between these and the navajo sandstone carbonate deposits reveal some characteristics that may be unique to the latter

paleobiology and skeletochronology of jurassic dinosaurs implications from the histology and oxygen isotope compositions of bones fossil biogenic phosphate of fast growing primary bone tissue of dinosaurs can preserve a histologic and isotopic time series of annual seasonality in temperature variations similar to tooth enamel and other accretionary skeletal phases such as corals or wood on two bone fragments from sympatric dinosaurs with different histologic patterns of bone growth high resolution oxygen isotope profiles were analyzed along the radial direction of bone growth the investigated specimens are from the jurassic shishugou formation in the junggar basin nw china and have distinct patterns of compositional variation a fibrolamellar dinosaur bone with multiple lines of arrested growth lags and periodic growth cycles of decreasing bone laminae thickness displays a cyclic intra bone variation in 18o values of about 2 corresponding with the lags these growth cycles in fast growing fibrolamellar bone provide evidence for seasonal growth of dinosaurs in lower latitudes 45 n possibly influenced by a monsoon type paleoclimate seasonal changes in temperature and water supply are consistent with the oxygen isotope composition measured in dinosaur bone phosphate as well as with growth rings in contemporaneous fossil conifer wood from the same locality in contrast a plexiform sympatric sauropod bone displays continuous growth free of lags and has a lower intra bone variation of 0 8 differences in bone histology are also reflected in the oxygen isotopic composition and its intra bone variability indicating different physiological responses to external climatic stress between sympatric dinosaur species seasonal intra bone oxygen isotope variations combined with bone histology may thus yield new insights into species specific response to climatic stress and its influence on dinosaur growth formation of growth marks growth rates as well as dinosaur thermophysiology

was there a wind driven tethys circumglobal current in the late cretaceous abstract the problem of the existence of a tethys circumglobal current tcc in the late cretaceous continental geometry campanian is addressed within an ocean model which is expected to strongly overestimate the wind driven tcc volume transport a relatively weak tcc is found for the reconstructed campanian paleogeography used as a measure of the strength of the tcc a circumglobal flow index is introduced this index is based on volume fluxes through meridional sections within the equatorial part of the domain the impact of changes in the paleogeography on the tcc is considered by computing steady flows for different shapes of eurasia the results on the extent of eurasia such that a strong tcc appears provide support that no strong wind driven tcc has existed during the campanian

itcz controls on late cretaceous black shale sedimentation in the tropical atlantic ocean 1 this study presents high resolution organic and inorganic proxy records for coniacian to santonian black shale on the demerara rise odp site 1261 in the western tropical atlantic off south america we integrate these records with approximately time equivalent geochemical data from the eastern tropical atlantic off tropical africa odp site 959 to extract the underlying relationships of intertropical convergence zone itcz dynamics and black shale formation in the tropical cretaceous atlantic at orbital time scales the geochemical records from the demerara rise show repetitive fluctuations in productivity ocean redox conditions and clastic sediment supply consistent with a dynamic paleo upwelling regime off tropical south america upwelling intensity most likely was driven by shifts of the mean annual position of the itcz which connects the large scale precipitation and wind field patterns of the hadley cells upwelling was strongest off south america and burial of oil prone organic matter most pronounced when the itcz was in its southernmost position which maximized the impact of ne trade winds on the inner tropical part of the northern hadley cell geochemical records from the deep ivorian basin equatorial atlantic suggest that source rock formation occurred in phase with regions north of the equator off tropical africa however black shale formation was primarily driven by regional rainfall and nutrient export the results of this study provide a conceptual framework that explains the formation distribution and quality of petroleum source rocks below the tropical component of the hadley cells on orbital time scales

rainfall patterns and the distribution of coals and evaporites in the mesozoic and cenozoic abstract paleoclimatologists have adequately demonstrated over the last twenty years that the distribution of climatically sensitive sediments can be related to present day climatic zones that are roughly parallel to latitude for example coals were deposited at paleolatitudes that correspond to the present day rainy zones at the equator and at about 55 n and 55 s indicating that those zones were present in the past from this it can be concluded that atmospheric circulation has not been radically different from its present configuration despite some apparently great differences in some climatic parameters such as the equator to pole temperature gradient nevertheless the zonal model for predicting the distribution of climatically sensitive sediments is not wholly adequate although general atmospheric circulation may not have been radically altered from its present pattern it would have differed in some respects because the paleogeography was different from the present geography therefore we have constructed what we believe are more realistic maps of the distribution of rainfall through time these maps are based on maps of atmospheric circulation that have been successfully used to predict the distribution of some petroleum source beds and phosphorites we have compared the predicted distribution of rainfall to the distribution of coals and evaporites for each of seven geologic stages the circulation rainfall maps were more successful than the zonal model for predicting the distribution of evaporites and coals for times when the paleogeography would have maximized the development of a monsoonal circulation which most effectively disrupts the general zonal pattern for times when a monsoonal circulation would not have been important the zonal model adequately predicted the distribution of these rocks

the hakkari nonsulfide zn pb deposit in the context of other nonsulfide zn pb deposits in the tethyan metallogenic belt of turkey abstract the hakkari nonsulfide zinc deposit is situated close to the southeastern border of turkey here both sulfide and nonsulfide zn pb ores are hosted in carbonate rocks of the jurassic cudi group with features typical of carbonate hosted supergene nonsulfide zinc mineralization the regional strike extent of the mineralized district is at least 60 km the age of the supergene deposit has not been determined but it is probable that the main weathering happened during upper tertiary possibly between upper miocene and lower pliocene the hakkari mineralization can be compared to other carbonate hosted zn pb deposits in turkey and an interpretation made of its geological setting the zinc mineral association at hakkari typically comprises smithsonite and hemimorphite which apparently replace both sulfide minerals and carbonate host rock two generations of smithsonite are present the first is relatively massive the second occurs as concretions in cavities as a final filling of remnant porosity some zinc is also hosted within fe mn hydr oxides lead is present in cerussite but also as partially oxidized galena lead can also occur in mn hydr oxides max 30 pbo the features of the supergene mineralization suggest that the hakkari deposit belongs both to the direct replacement and the wall rock replacement types of nonsulfide ores mineralization varies in style from tabular bodies of variable thickness

cave air ventilation and co2 outgassing by radon 222 modeling how fast do caves breathe abstract in general the rate and timing of calcite precipitation is in part affected by variations in cave air co2 concentrations knowledge of cave ventilation processes is required to quantify the effect variations in co2 concentrations have on speleothem deposition rates and thus paleoclimate records in this study we use radon 222 222rn as a proxy of ventilation to estimate co2 outgassing from the cave to the atmosphere which can be used to infer relative speleothem deposition rates hollow ridge cave a wild cave preserve in marianna florida is instrumented inside and out with multiple micro meteorological sensor stations that record continuous physical and air chemistry time series data our time series datasets indicate diurnal and seasonal variations in cave air 222rn and co2 concentrations punctuated by events that provide clues to ventilation and drip water degassing mechanisms average cave air 222rn and co2 concentrations vary seasonally between winter 222rn 50 dpm l 1 where 1 dpm l 1 60 bq m 3 co2 360 ppmv and summer 222rn 1400 dpm l 1 co2 3900 ppmv large amplitude diurnal variations are observed during late summer and autumn 222rn 6 to 581 dpm l 1 co2 360 to 2500 ppmv we employ a simple first order 222rn mass balance model to estimate cave air exchange rates with the outside atmosphere ventilation occurs via density driven flow and by winds across the entrances which create a venturi effect the most rapid ventilation occurs 25 m inside the cave near the entrance 45 h 1 1 33 min turnover time farther inside 175 m exchange is slower and maximum ventilation rates are 3 h 1 22 min turnover time we estimate net co2 flux from the epikarst to the cave atmosphere using a co2 mass balance model tuned with the 222rn model net co2 flux from the epikarst is highest in summer 72 mmol m 2 day 1 and lowest in late autumn and winter 12 mmol m 2 day 1 modeled ventilation and net co2 fluxes are used to estimate net co2 outgassing from the cave to the atmosphere average net co2 outgassing is positive net loss from the cave and is highest in late summer and early autumn about 4 mol h 1 and lowest in winter about 0 5 mol h 1 modeling of ventilation net co2 flux from the epikarst and co2 outgassing to the atmosphere from cave monitoring time series can help better constrain paleoclimatic interpretations of speleothem geochemical records

cyclic cross bedding in the eolian dunes of the sergi formation upper jurassic reconcavo basin inferences about the wind regime abstract the upper jurassic sergi formation displays eolian cyclic cross bedding composed of a regular intercalation of grain flow and wind ripple packages forming 1 3 m thick cycles each cycle is bound by erosive downwind surfaces and it comprises a sequence of lower angle wind ripple laminae followed by steeper grain flow strata that built out upon the wind ripple wedges in the migration direction the cross strata mean vectors dip consistently towards sw these cycles are related to seasonal changes in wind direction the cyclic stratification pattern suggests an alternation of northeasterly transverse winds responsible for slipface evolution and dune migration followed by reverse transversal or oblique winds overall southerly winds these winds caused dune degradation and reworking and led to the formation of reactivation surfaces and the related deposition of wind ripple wedges the wind pattern inferred from the eolian cyclic cross bedding is consistent with the quantitative atmospheric circulation model that indicates that a monsoonal wind regime operated in the low latitudes of gondwana during the late jurassic

recurrent deformations of aeolian desert dunes in the cretaceous of the south china block trigger mechanisms variability and implications for aeolian reservoirs abstract deposits of aeolian dunes accumulated in cretaceous intramontane deserts in the south china block underwent recurrent deformation processes affecting their toesets and foreset sediments the mid cretaceous matoushan formation preserves examples of soft sediment deformation deformations associated with theropod tracks in aeolian dune apron sandstones the late cretaceous tangbian formation in the xinjiang basin shows i seismites associated with dry interdune laminated deposits and sand injection into the interdune laminated facies generating intraclast breccias ii mass flow deposits associated with heavy rains generating interbedding of non deformed and deformed intervals in aeolian dune foresets deformed intervals display a variety of deformation styles including thrust duplexes upturned and deformed stratification recumbent folds and microfolds and liquefied intervals covered by overlying draa mega cross bedded sets animal tracks seismites monsoon rains and earthquakes are proposed as the main trigger mechanisms of the failures that led to deformation hydroseismicity associated with monsoon rains is a probable but difficult to prove trigger mechanism this process could be an important deformation agent in the case of large scale deformation recorded in ancient erg sequences mass wasting deposits in ancient erg extensive sandy deserts characterized by aeolian dunes sequences constitute significant heterogeneities for hydrocarbon migration and its architectural variability could determine the development of effective sedimentary traps in aeolian reservoirs

atmospheric circulation during warm geologic periods is the equator to pole surface temperature gradient the controlling factor paleoclimatologists have hypothesized that the equator to pole surface temperature gradient is a dominant control on the paleocirculation of the oceans and the atmosphere atmospheric simulations using realistic cretaceous 100 m y ago geography are used to examine quantitatively the relationships between paleogeography surface temperature gradients and the nature of the atmospheric circulation these results raise questions concerning the classical theories and interpretations of warm paleoclimates and suggest that paleogeography is an important factor governing the nature of the circulation

modelling late oligocene c4 grasses and climate evidence suggests that c4 grasses adapted to conditions of low co2 high temperatures and water stressed environments expanded relatively quickly and in several geographically distinct regions during the late miocene approximately 9 7 ma using a variety of modelling tools we attempt to explain this expansion in terms of changes in global climate we use a fully coupled atmosphere ocean general circulation model aogcm hadcm3l to simulate global climate before and after the expansion the late oligocene 27 ma and pre industrial we then use the simulated climates to drive a process based global vegetation model lpj contrary to indications from palaeo data the vegetation model predicts a greater c4 distribution during the late oligocene than the pre industrial the principal reason for this is that the relatively high tropical temperatures which we predict for the late oligocene confer a competitive advantage on c4 grasses over c3 grasses which outweighs the disadvantage imposed by the higher co2 concentrations we find that this result is robust to prescription of different co2 levels in the late oligocene aogcm simulation and to the vegetation model used of the several possible explanations proposed for the model data discrepancy three seem most likely first that the vegetation models do not adequately represent certain processes under extreme climate conditions such as fire disturbance or key parameters related to the competition between c3 and c4 grasses second that there existed an evolutionary niche for c4 grasses prior to their expansion in the late miocene which for some reason was not filled third that we have not adequately modelled the late oligocene climate with the aogcm future research should concentrate on the collection and analysis of additional data for the assessment of palaeo tropical land temperatures and on further testing of the sensitivity of the aogcm results

pennsylvanian to jurassic eolian transportation systems in the western united states peterson f 1988 pennsylvanian to jurassic eolian transportation systems in the western united states in g kocurek editor late paleozoic and mesozoic eolian deposits of the western interior of the united states sediment geol 56 207 260 the direction of sediment transport in eolian sandstones of permsylvanian to jurassic age was interpreted from crossbedding resultants vector means obtained from studies of eolian rocks in the western u s supplemented by data from the few eolian units of eastern north america these were compiled from the published or unpublished theses hterature from unpublished fidd data contributed by colleagues or from measurements made for this study in addition new paleogeographic maps were compiled to evaluate the influence of geographic features on the atmospheric circulation patterns that are inferred from the crossbedding studies regionally the crossbedding indicates northeasterly northerly or northwesterly winds present coordinates from pennsylvanian through most of middle jurassic time a rather abrupt change in wind directions occurred in late middle jurassic time late part of the cauovian age when westerly wind patterns developed by the late jurassic the winds shifted to southwesterly calculations of the consistency factor vector mean strength made from region wide analyses of the resultants indicate fairly unidirectional winds from the permsylvanian through the early jurassic middle jurassic circulation was more varied judging from crossbedding studies in the lower part of the entrada sandstone crossbedding in upper jurassic eolian rocks of wyoming and south dakota yielded a random pattern but upper jurassic rocks farther south on the colorado plateau and adjoining areas show a return to a fairly unidirectional pattern comparing the resultants with their reconstructed paleogeographic setting shows surprisingly little influence of major geographic features on overall circulation patterns however the greatest amount of local variation occurred at or near highly indented shorelines where the temperature contrast between land and water produces local wind currents that may vary appreciably from regional circulation patterns although they do not cause noticeable horizontal deflections in wind patterns small and low topographic highs appear to be able to promote the development of a dune field if a source of sand is available and if streams do not enter the growing dune field

3 2ga eolian deposits from the moodies group barberton greenstone belt south africa implications for the origin of first cycle quartz sandstones abstract the 3 2 ga moodies group in barberton greenstone belt south africa contains the oldest recognized evidence for eolian processes on earth these eolian facies indicate that significant wind regimes existed in the archean atmosphere eolian deposits are developed in the lower moodies group in the central part of the belt and consist of stacked inversely graded strata ranging in thickness from 2 to 10 mm individual strata consist of fine to medium grained quartz sandstone at the base that passes vertically into very coarse to coarse grained quartz sandstone strata make up cross bed sets up to 3 5 m thick sets of wind ripple strata are either tabular tangential or in the form of broad troughs this type of inversely graded stratification is the product of wind ripple migration the coarse grain size of the sediment combined with the low angle of inclination of the strata is best interpreted as the product of sand sheet or dune plinth preservation based on the geometry of eolian set boundaries dunes were probably simple barchan form the tens of meters thick eolian deposits are underlain by braided stream deposits composed of subfeldspathic pebbly sandstones the vertical change from braided stream subfeldspathic sandstones to eolian quartz arenites highlights the underappreciated capacity of eolian processes to generate first cycle quartz sandstones on landscapes pre dating the advent of land vegetation

pangaean climates megamonsoons of the megacontinent the climate for a highly idealized geographic representation of the megacontinent of pangaea corresponding to the period 250 200 m y ago is explored using a low resolution atmospheric general circulation model that is coupled to a static mixed layer ocean of constant depth with a provision for sea ice formation and decay soil moisture is included as a predicted variable on the continent because there are large uncertainties about key factors that might influence the pangaean climate sensitivity experiments are used to examine the climate for two different mean elevations 0 and 1000 m two different snowcover prescriptions and two different levels of implied greenhouse heating and solar luminosity modern co2 concentration and modern solar luminosity fivefold increase in modern co2 concentration and a 1 decrease in modern solar luminosity in all of the experiments the large bipolar land masses of laurasia and gondwanaland joined near the equator in the west and separated by the tethys sea in the east exhibit extreme continentality with hot summers cold winters and large scale summer and winter monsoon circulations year round or seasonal aridity is simulated for all but the eastern coastal regions the tropical western coast and the regions poleward of 40 latitude the simulated climate of the idealized pangaean continent has many features that correspond qualitatively with geologic evidence for tropical warmth and aridity in the late permian and triassic however the model results serve mainly to indicate the importance of various climate forming factors geography topography heating detailed comparisons will require new experiments with better models and more accurate geologic boundary conditions

mid depth calcareous contourites in the latest cretaceous of caravaca subbetic zone se spain origin and palaeohydrological significance abstract deep marine carbonates of late campanian to early maastrichtian age that crop out in the subbetic zone near caravaca se spain contain a thick succession of dm scale levels of calcareous contourites alternating with fine grained pelagites hemipelagites these contourites characterised by an abundance and variety of traction structures internal erosive surfaces and inverse and normal grading at various scales were interpreted as having been deposited under the influence of relatively deep ocean currents based on these contourites a new facies model is proposed the subsurface currents that generated the contourites of caravaca were probably related to the broad circumglobal equatorial current system the strongest oceanic feature of cretaceous times these deposits were formed in the mid depth 200 600 m hemipelagic environments at the ancient southern margin of iberia this palaeogeographic setting was susceptible to the effects of these currents because of its position close to the narrowest oceanic passage through which the broad equatorial current system flowed in the westernmost area of the tethys seaway regional uplift related to the onset of convergence between iberia and africa probably favoured the generation of the contourites during the late campanian to the early maastrichtian

response of mediterranean circulation to miocene shoaling and closure of the indian gateway a model study abstract in this regional ocean model study we explore the effect of the early to middle miocene shoaling and closure of the indian gateway on mediterranean circulation and its exchange with the adjacent oceans for this we use the regional ocean circulation model sbpom and a collection of bathymetries created from an early burdigalian paleogeographical base map in which the depth of the indian gateway is set to 1000 450 200 or 0 m a significant improvement of this work relative to previous regional modeling studies is that we also consider the possibility that the indian and atlantic gateways accommodated net westward flow as reported in many global climate model studies to this end we superimpose net westward flows of different magnitudes to the gateways because the early middle miocene climate is uncertain we start with atmospheric conditions based on the present and subsequently explore alternative atmospheric forcings similarly we first assume a relatively shallow atlantic gateway of 500 m depth and then study the effect of a connection of 900 m the extensive set of experiments performed allows us to gain detailed physics based insight into the effect of the above mentioned factors on the thermohaline circulation and water properties and provides a solid background to interpret observational evidence by comparing our modeled exchange patterns to data we are able to propose the flow configurations consistent with observations some of them not considered until now during the different stages of closure and infer the conditions climate presence absence of net flow atlantic gateway depth under which these patterns arise

evidence for climate shifts in the 2 0ga upper makgabeng formation erg south africa abstract eolian ergs and associated environs are sensitive to short and long term climatic changes in one of the oldest erg deposits the 2 0 ga makgabeng formation vertical changes in facies associations reflect one of the earliest records of short term climatic shifts in a continental setting the makgabeng formation is separated into lower and upper erg deposits by a playa or saline pan deposit the lower erg deposit consists of dune sets with thin lenses of dry and deflationary interdune strata that transition vertically to thicker damp to wet interdune strata a laterally persistent playa deposit in the middle of the section consists of mudstone with deep and shallow penetrating mud cracks and subordinate siltstone and sandstone interbeds above this lower mudstone interval the playa strata are sandy overlying the playa deposit the upper erg deposit consists of thick eolian sets with thin lenses of dry interdune deposits grain size change near the top of the upper erg deposit corresponds with the appearance of fluvial sheet flood eolian cross beds sculpted by mass flows and thin playa deposits vertical stacking of facies associations demonstrates temporal shifts in precipitation and fluctuating water tables fluvial and playa deposits record high water tables whereas low water tables are reflected in the core erg the transition from a lower to higher water table is recorded by wet interdune interspersed within the dune strata toward the top of this interval rapid climatic amelioration occurred near the termination of the makgabeng erg resulting in impingement of ephemeral river systems development of playas and generation of massive sand flows this 2 0 ga erg demonstrates the impact of climate change on erg development resulting from shifts in monsoonal impingement through time

rain induced planar collapse of eolian dune slipfaces abstract decameter scale eolian dunes were observed following a burst of intense rainfall in the sand sea of eastern saudi arabia planar translational collapse structures developed over large areas of the dune slipfaces and were observed in pristine condition hours after their formation individual slipped blocks were approximately 10 cm deep over areas up to one hundred square meters observed geometries indicate a sequence of deformation beginning with downslope creep progressing to propagation of updip tensile fractures finally thrust ramps developed at the downdip limits movement halted in all cases after about 10 displacement a mechanical model is developed here based in part on snow avalanches and landslides to account for the observed deformation sequence rainwater loading increases differential stress in the dry internal parts of the dune rainwater infiltration also forms an impermeable wetting front below which air increases in pressure bringing the effective stress state towards the frictional sliding criterion triggering downslope creep of the cohesive wet slab above the wet slab has cohesion and tensile strength via proliferation of intergranular rainwater fluid bridges downslope creep led to updip tensile cracks releasing the slab promoting slip and leading to downdip compressional failure with thrust structures exposure of the overpressured substrate in between the opening tensile cracks enabled pressure to bleed off ensuring the mechanism is self limiting and therefore less hazardous than snow avalanches the preservation potential of these structures is reasonably high due to their scale and likelihood of rapid burial by dune migration but the distribution is patchy due to pre existing moisture content of the dunes inhibiting the process and the footprint of intense rainstorms usually being relatively small compared with the sand seas

paleomagnetism of the chinle and kayenta formations new mexico and arizona paleomagnetic data were obtained from 22 sites 6 10 samples site in the upper shale member of the chinle formation 43 sites in the owl rock member of the chinle formation and 35 sites in the kayenta formation thermal demagnetization and data analyses indicate that within site dispersion is an important criterion for selecting sites which retain a high unblocking temperature characteristic remanent magnetization chrm site mean directions define at least four antipodal polarity zones within each member formation suggesting the chrm was acquired soon after deposition fifteen site mean virtual geomagnetic poles vgps from the upper shale member of the chinle formation yield an early norian paleomagnetic pole position of 57 4 n 87 8 e k 60 a95 5 0 eighteen site mean vgps from the owl rock member of the chinle formation yield a middle norian paleomagnetic pole position of 56 5 n 66 4 e k 183 a95 2 6 twenty three site mean vgps from the kayenta formation yield a pliensbachian pole position of 59 0 n 66 6 e k 155 a95 2 4 combined with paleomagnetic poles from the moenave formation and the shinarump member of the chinle formation these data record 30 m y of north american apparent polar wander apw within a regional stratigraphic succession during the camian and norian stages of the late triassic chinle poles progress westward during the hettangian through pliensbachian stages of the early jurassic the pattern of apw changed to an eastward progression even after correction for 4 clockwise rotation of the colorado plateau a sharp comer in the apw path j1 cusp is resolved near the pole from the hettangian sinemurian 200 ma moenave formation 59 4 n 59 2 e amongst other implications the sharp change in the apw path at the j1 cusp implies an abrupt change from counterclockwise rotation of pangea prior to 200 ma to clockwise rotation thereafter

stratigraphic evolution of an aeolian erg margin system the permian cedar mesa sandstone se utah usa the permian cedar mesa sandstone of south east utah is a predominantly aeolian succession that exhibits a complex spatial variation in sedimentary architecture which in terms of palaeogeographic setting reflects a transition from a dry erg centre through a water table controlled aeolian dominated erg margin to an outer erg margin subject to periodic fluvial incursion the erg margin succession represents a wet aeolian system accumulation of which was controlled by progressive water table rise coupled with ongoing dune migration and associated changes in the supply and availability of sediment for aeolian transport variation in the level of the water table relative to the depositional surface determined the nature of interdune sedimentary processes and a range of dry damp and wet flooded interdune elements is recognized variations in the geometry of these units reflect the original morphology and the migratory behaviour of spatially isolated dry interdune hollows in the erg centre locally interconnected damp and or wet interdune ponds in the aeolian dominated erg margin and fully interconnected fluvially flooded interdune corridors in the outer erg margin relationships between aeolian dune and interdune units indicate that dry damp and wet interdune sedimentation occurred synchronously with aeolian bedform migration temporal variation in the rates of water table rise and bedform migration determined the angle of climb of the erg margin succession such that accumulation rates increased during periods of rapidly rising water table whereas sediment bypassing zero angle of climb occurred in the aftermath of flood events in response to periods of elevated but temporarily static water table during these periods in the outer erg margin the expansion of fluvially flooded interdunes in front of non climbing but migrating dunes resulted in the amalgamation of laterally adjacent interdunes and the generation of regionally extensive bypass flood supersurfaces a spectrum of genetic depositional models is envisaged that accounts for the complex spatial and temporal evolution of the cedar mesa erg margin succession

large wind shift on the great plains during the medieval warm period spring summer winds from the south move moist air from the gulf of mexico to the great plains rainfall in the growing season sustains prairie grasses that keep large dunes in the nebraska sand hills immobile longitudinal dunes built during the medieval warm period 800 to 1000 years before the present record the last major period of sand mobility these dunes are oriented nw se and are composed of cross strata with bipolar dip directions the trend and structure of the dunes record a drought that was initiated and sustained by a historically unprecedented shift of spring summer atmospheric circulation over the plains moist southerly flow was replaced by dry southwesterly flow

evolution of tropical watersheds and continental hydrology during the late cretaceous greenhouse impact on marine carbon burial and possible implications for the future abstract regional climate modelling for the late cretaceous greenhouse and high resolution marine stratigraphic records from both sides of the low latitude atlantic show that tropical south american and african hydrology and watersheds had a strong effect on freshwater transfer into the equatorial atlantic and subsequently the marine carbon record this conclusion is derived from new detailed geochemical records from demerara rise off suriname drilled at ocean drilling program odp site 1261 combined with frequency analyses and climate simulations providing evidence for mainly eccentricity driven changes in carbon burial in the western tropical atlantic shorter orbital frequencies in particular precession clearly dominating black shale cycles off tropical africa odp site 959 are far less dominant at demerara rise despite comparable time resolution of the geochemical records we suggest that these different frequency patterns in carbon burial were related to the regional evolution of cretaceous watersheds and hydrology in tropical south america and africa river discharge deduced from simulations indicates higher and less variable discharge from south america compared to western africa at that time this runoff pattern would have supported more permanent anoxic conditions off south america compared to africa at least indirectly and caused the lack of strong higher frequency geochemical cycles in the western sector of the equatorial atlantic furthermore climate simulations show a general switch of primary runoff from either side of the cretaceous equatorial atlantic every half precession cycle i e every 10 kyr similarities between the developments of cretaceous and holocene hydrology in the tropical atlantic area imply that orbital scale evolution of watersheds is a robust feature through time that is independent from the mean global climate state based upon the comparison of cretaceous and holocene trends in hydrology we infer that future hydrology in the study region may develop in a comparable direction to the one observed in the cretaceous if true this suggests that the modern amazon rain forest could shrink over the next millennium due to a 30 loss of moisture while the congo rain forest in africa is likely to expand in response to a 14 gain in moisture

evolution of tethyan phosphogenesis along the northern edges of the arabian african shield during the cretaceous eocene as deduced from temporal variations of ca and nd isotopes and rates of p accumulation abstract the evolution of tethyan phosphogenesis during the cretaceous eocene is examined to try to explain fluctuations of phosphogenesis through time and whether or not they reflect long term changes in ocean circulation or in continental weathering twenty seven time stratigraphic phosphate levels in various tethyan sites covering a time span of about 90 myr from the hauterivian to the eocene were analyzed for 44 ca 42 ca and 143 nd 144 nd in their carbonate fluorapatite cfa fraction p and ca accumulation rates and bulk sedimentation rates were quantified throughout the cretaceous eocene negev sequence to examine how changes in 44 ca 42 ca and 143 nd 144 nd are reflected in the intensity of phosphogenesis a clear cut change occurs in e nd t and 44 ca and in the rates of p and ca accumulation and bulk sedimentation through the time analyzed e nd t is much lower in the hauterivian lower cenomanian 12 8 to 10 9 than in the upper cenomanian eocene 7 8 to 5 9 much lower 44 ca values occur in the hauterivian turonian 0 22 to 0 02 than in the coniacian eocene 0 23 to 0 40 p accumulation rates in the negev steeply increase from 2 k yr 1 in the albian coniacian to 1500 mol cm 2 k yr 1 in the campanian whereas a strong decrease is concomitantly recorded in the rates of ca accumulation and bulk sedimentation in addition distinct e nd t values are shown by the phosphorites of the negev 6 7 to 6 4 and egypt 9 1 to 7 6 during the campanian and by those of the negev 7 8 to 6 3 and north africa 10 1 to 8 9 during the maastrichtian eocene the culmination of p accumulation rates in the negev during the campanian occurring with a high in e nd t and 44 ca and a low in sedimentation rates indicates that paleoceanographic and paleogeographical factors mostly governed phosphorite accumulation in this area the abrupt e nd t rise after the cenomanian is attributed to increased incursion of pacific radiogenic water masses into the tethys driven by the late cretaceous global sea level rise the connection between north and south atlantic the global post santonian cooling and the progressive widening of the caribbean threshold all acting in combination to significantly intensify the tethyan circumglobal current tcc it also reflects a weakening of the continental nd signal due to a reduction of exposed landmasses caused by increased flooding of continental shelves high 44 ca values at those times also point to a decrease in weathering ca 2 fluxes and expansion of carbonate sedimentation in shelves both enriching seawater with isotopically heavy ca 2 deep ocean circulation intensified by the post santonian cooling of high latitudes increased p inventory in the tethys basin whereas the strengthened tcc and the folded shelf likely resulted in coastal and topographically induced upwelling supplying p rich intermediate waters to southeastern tethys shelves only in the paleocene eocene following major changes in global circulation produced by narrowing of tethys and widening of the atlantic did phosphogenesis shifts its locus of high intensity to the western atlantic tethys and west african atlantic coasts this change in paleocirculation is expressed by distinctly differing e nd t in the middle east and the north and west african phosphorites suggesting different oceanic p sources and current systems for these two major groups of phosphorites our nd isotope results further suggest a weaker tcc during the mid cretaceous becoming more intense in late cretaceous times they also point to the north pacific ocean as major source of deep water formation for the intermediate deep waters in the tethys basin during the late cretaceous

arabia eurasia collision and the forcing of mid cenozoic global cooling the end of the eocene greenhouse world was the most dramatic phase in the long term cooling trend of the cenozoic era here we show that the arabia eurasia collision and the closure of the tethys ocean gateway began in the late eocene at 35 ma up to 25 million years earlier than in many reconstructions we suggest that global cooling was forced by processes associated with the initial collision that reduced atmospheric co2 these are 1 waning volcanism across southwest asia 2 increased organic carbon storage in paratethyan basins e g black sea and south caspian 3 increased silicate weathering in the collision zone and 4 a shift towards modern patterns of ocean currents associated with increased vigour in circulation and organic productivity

styles of soft sediment deformation on top of a growing fold system in the gosau group at muttekopf northern calcareous alps austria slumping versus tectonic deformation abstract styles of soft sediment deformation in a syngrowth coarse grained sediment gravity flow system are described from outcrops of the upper gosau subgroup of the northern calcareous alps the deepwater sediments were deposited along the flanks and top of growing folds beside load and fluid escape structures which are commonly found in sediment gravity flow systems soft sediment deformation is mainly related to fluidization of coarse grained beds and downslope gliding of meter thick sediment packages common structures affecting single or several beds are hydroplastic folding of fine grained beds in a coarse grained fluidized matrix symmetric or asymmetric mullions at the base of coarse grained beds and folding of heterolithic units into coarse grained beds folds have varying geometries and styles and fold axes are scattered soft sediment folds also affect thick sediment packages these folds are uniformly verging asymmetric metric to dekametric folds formed at different degrees of lithification rheology of sandstones in such folds ranges from ductile to semi brittle and brittle fold axes tightly cluster about one direction the first group of deformational structures is attributed to slump related deformation whereas the second group represents folds related to tectonic deformation a dislocation model and a shear zone model are used to interpret orientation of folds related to slump deformation this considers processes taking place on the scale of the whole slump sheet and within the shear zone at the base of gliding units both models predict rotation of fold axes toward the transport direction of the slump field data support that fold axes scatter either about the downslope transport direction or about the strike of the slope

storm controlled oblique dunes of the oregon coast the large mean height 25 m spacing 300 m relatively straight crested dunes of the central oregon coast migrate an average of 3 8 m yr toward an azimuth of 26 the dunes are transverse to the strong south southwesterly winter storm winds that are responsible for their basic form orientation and migration the dry moderate north northwesterly summer winds modify the dune form but not the dune trend comparison of the sand transport calculated from wind data and the transport measured from dune migration indicates that the actual transport by the wet southerly winds is only one third of the amount calculated assuming dry conditions the resultant vector mean transport rate as recalculated by comparison of the measured and initially calculated rates is 34 m 3 m yr toward an azimuth of 45 the dunes are thus oblique by our definition of an oblique dune angle between dune trend and resultant transport direction between 15 and 75 the internal structures of the dunes confirm northward migration during wet conditions evidence for deposition during wet conditions includes slipface deposits deformed mostly by sliding and various structures formed by the adhesion of sand grains to wet surfaces most summer deposits are not preserved but those on the basal apron the gentle north slope at the base of the winter slipface have a high preservation potential a depositional model based on dune climbing predicts that the preserved record of oblique dunes formed by an obtuse bimodal wind regime would consist of tabular sets of crossbeds in which the dip angles increase upward from the base of each set

facies architecture and stratigraphic evolution of aeolian dune and interdune deposits permian caldeirao member santa brigida formation brazil abstract the permian caldeirao member santa brigida formation located in the tucano central basin northeast region of brazil is characterized by a sandstone succession of aeolian origin that comprises the preserved deposits of dunes and interdunes grainflow and translatent wind ripple strata and frequent presence of reactivation surface compose the cross bedding of crescent aeolian dune deposits the aeolian cross strata show a mean dip toward the ene in places interlayered with dune cross beds occur interdune units composed of facies indicative of dry damp and wet condition of the substrate suggesting spatial and or temporal variations in the moisture content of the interdune accumulation surface the presence of nnw current ripple cross lamination in wet interdune areas indicates streamflows confined to interdune corridors and oriented perpendicular to aeolian transport direction lenses of damp and wet interdune strata exhibit mainly interdigitated and transitional relationships with the toe sets of overlying aeolian dune units in sections parallel to aeolian transport indicating that dune migration was contemporaneous with accumulation in adjacent interdunes lateral variations in the preserved thickness of the interdune units and the associated rare occurrence of abrupt and erosive contacts between interdune and overlying dune sets suggest temporal variations in the angle of dune and interdune climb that may be related to high frequency changes in water table position four stratigraphic intervals in the caldeirao member can be identified two intervals showing cross bedding of aeolian dunes without wet interdune areas and two intervals exhibiting aeolian dunes separated by wet interdune areas marking the transition between dry aeolian systems intervals i and iii and wet aeolian systems intervals ii and iv the temporal alternations between dry and wet aeolian systems reflect changes in the availability of dry sand and or the rate in the water table rise possibly controlled by orbitally driven climatic fluctuations

methodology for reconstructing wind direction wind speed and duration of wind events from aeolian cross strata 1 a methodology for reconstructing wind direction speed and event duration from aeolian dune cross strata was developed from analysis of crescentic dunes at white sands new mexico during wind events dune lee faces were surveyed lee face deposits mapped deposition rates measured grain size sampled by stratification type and winds characterized from meteorological and field data the spatial distribution of lee face stratification styles is a function of the incidence angle formed between the wind and the brinkline with secondary controls by wind speed and dune sinuosity and height sets of wind ripple strata form at incidence angles of 25 40 grainfall grainflow foresets over wind ripple bottomsets at 40 70 and grainflow grainfall foresets at 70 90 erosional reactivation surfaces form at incidence angles up to 15 bypass surfaces up to 25 the total sediment load is fractionated within lee face stratification types wind speed can be reconstructed from relationships between grain size transport mode shear velocity and grain settling velocity where the full range of grain transport modes occurs and grain size is limited by shear stress the shear velocity and grain size range in each transport mode can be estimated by assuming the coarse fraction in grainflow strata traveled in creep and the coarse fraction in grainfall traveled in saltation the minimum duration of a wind event can be estimated using measures of shear velocity dune height and dune forward migration method limitations arise with source area control on grain size extremes in wind events and severe truncation of sets of cross strata

pangaean climate during the early jurassic gcm simulations and the sedimentary record of paleoclimate results from new simulations of the early jurassic climate show that increased ocean heat transport may have been the primary force generating warmer climates during the past 180 m y the simulations conducted using the general circulation model gcm at the goddard institute for space studies include realistic representations of paleocontinental distribution topography epeiric seas and vegetation in order to facilitate comparisons between model results and paleoclimate data three major features of the simulated early jurassic climate include the following 1 a global warming compared to the present of 5 c to 10 c with temperature increases at high latitudes five times this global average average summer temperatures exceed 35 c in low latitude regions of western pangaea where eolian sandstones testify to the presence of vast deserts 2 simulated precipitation and evaporation patterns agree closely with the moisture distribution interpreted from evaporites and coal deposits high rainfall rates are associated primarily with monsoons that originate over the warm tethys ocean unlike the megamonsoons proposed in previous studies these systems are found to be associated with localized pressure cells whose positions are controlled by topography and coastal geography 3 decreases in planetary albedo occurring because of reductions in sea ice snow cover and low clouds and increases in atmospheric water vapor are the positive climate feed backs that amplify the global warming similar to other mesozoic climate simulations our model finds that large seasonal temperature fluctuations occurred over mid and high latitude continental interiors refuting paleoclimate evidence that suggests more equable conditions sensitivity experiments suggest that some combination of ocean heat transport increase high levels of co2 and improved modeling of ground hydrological schemes may lead to a better match with the geologic record we speculate also that the record itself is biased toward equable climatic conditions a suggestion that may be tested by comparing gcm results with more detailed phytogeographic analyses

palaeobiogeographic and tectonic significance of mid cretaceous invertebrate taxa from batavia knoll eastern indian ocean abstract a newly described fossil suite from batavia knoll eastern indian ocean adds insight to the palaeobiogeographic connections between assemblages around the nascent indian ocean during the breakup of gondwana in the mid cretaceous albian and cenomanian analyses were completed on the biotic similitude of the batavia knoll and five other suites from around the indian ocean being northern australia central and southern indian madagascar and south eastern africa employing jaccard coefficients j to determine degrees of similarity between the suites it was determined that the batavia knoll invertebrate assemblage maintains strong connections to the others included in the study j 0 18 with the exception of the central indian assemblages j 0 091 this pattern was followed by most of the other suites cementing batavia knoll s palaeobiogeographic position within the east african palaeobiogeographic province the results of the analysis also extended the eastern boundary of that province to include the northern coast of australia with fauna there exhibiting similar strong affinities with other circum indian suites

changing ocean circulation and hydrothermal inputs during ocean anoxic event 2 cenomanian turonian evidence from nd isotopes in the european shelf sea nd isotopes of fish debris collected from the english chalk at eastbourne sussex uk are used to reconstruct the history of ocean circulation in the nw european shelf sea during oceanic anoxic event 2 oae 2 cenomanian turonian the eastbourne end record exhibits a 1 unit negative excursion decreasing from 9 to 10 immediately followed by a 3 unit positive excursion reaching 7 the onset of the negative end excursion lags the global 13c rise characteristic of oae 2 suggesting stable patterns of ocean circulation in the nw european shelf sea at this time both negative and positive nd isotope excursions took place during a transient cooling episode within oae 2 the negative end excursion is interpreted as due to a change in ocean circulation with northerly sourced water masses becoming the dominant bottom waters at eastbourne the positive excursion is best explained by the transport of radiogenic nd derived from a volcanic source possibly the high arctic or caribbean large igneous province lip an input of volcanic nd may reconcile the eastbourne record with coeval end records on demerara rise in the western tropical atlantic the broad synchroneity of high end values 7 registered at both sites suggests a possible period with efficient oceanic mixing between the tropical atlantic and the nw european shelf sea during the cooling episode the eastbourne end record of oae 2 together with coeval temperature reconstructions provides evidence for the coincidence of changes in ocean circulation and transient climatic cooling implying a tight coupling between the two phenomena during this interval

long lived pluvial episodes during deposition of the navajo sandstone abstract the navajo sandstone of the american southwest was deposited at approximately 190 ma in a giant subtropical dune field near the western margin of pangea from this unit we report thick intervals of dune cross strata that were churned by insects and trampled by reptiles although dunes continued to migrate freely the distribution of trace fossils shows that plant life in wet interdune areas sustained high levels of animal activity on the dunes for many thousands of years we interpret this suite of structures as the record of a pluvial episode climatologically similar to the period of greening in the sahara 4000 10 000 yr ago a high percentage of the rainfall on the navajo erg recharged the water table and led to the development of highly dilute local groundwater flow systems that discharged into interdune areas

burrows dug by large vertebrates into rain moistened middle jurassic sand dunes abstract in south central utah eolian cross strata of the escalante member of the entrada sandstone contain inclined cylindrical burrows up to 63 cm in diameter and 305 cm long of the 14 large tunnels located during this study 12 descend from second and third order bounding surfaces that formed on the lee slopes of large dune ridges well above the water table the tunnels are inclined 15 22 one tunnel ends in an expanded chamber eolian cross strata fill proximal portions of four of the tunnels and indicate that after abandonment sand drifts migrated as much as a meter into the open shafts structureless sand and breccia blocks that were generated by roof collapse fill other tunnels animals dug the tunnels in rain moistened cohesive sand the burrows may have served as temporary shelters from severe diurnal conditions in the shadeless subtropical entrada dune field

species richness and abundance patterns of tethyan cretaceous rudist bivalves mollusca hippuritacea in the central eastern mediterranean and middle east analysed from a palaeontological database abstract data about the stratigraphical and regional distribution of cretaceous rudist bivalves in the central eastern mediterranean and middle east from the barremian to the maastrichtian have been compiled in a taxonomic databank system the investigated region comprises northern central and southern regions of the cretaceous tethys the regionally different quality of taxonomic data is critically discussed both species richness and abundance number of species records peak in the early aptian late cenomanian and early campanian temporal patterns in species richness are examined in relation to evolutionary innovations of the group crises in species richness and abundance during the early and mid cretaceous were coeval with oceanic anoxia associated with platform drowning also regional emergence affected large parts of the apulian plate and other central tethyan carbonate platforms during the mid cretaceous period of globally high sea level so that these crises can be attributed to regional environmental perturbations induced by either oceanic anoxia or tectonic movements the cenomanian turonian transition marks an important faunal turnover as indicated by the demise of taxonomic groups which are characterised by recumbent ecological morphotypes and predominantly aragonitic shells during the turonian they were replaced by associations dominated by largely calcitic radiolitidae and hippuritidae among which elevator morphotypes dominated the stratigraphy of many post turonian deposits in the studied region is too imprecise for a detailed analysis of late cretaceous distributional patterns and the demise of rudists during the maastrichtian in particular the regional pattern of species richness and abundance is similar throughout most of the investigated region a notable exception is the broad north eastern african shelf from libya to lebanon where rudists were almost completely absent after the coniacian this coincided with shallow water phosphorite and black shale formation on the extended shelf of this region indicating the upwelling of nutrient rich waters and stagnant conditions during this time campanian maastrichtian species rich associations thrived along the north eastern afro arabian margin now exposed in south eastern turkey iran the united arab emirates uae and oman this region forms the single distinct faunal province during the cretaceous in the studied region as indicated by an endemism of 40 at the genus level the low species richness and abundance of hippuritidae on turonian maastrichtian central tethyan carbonate platforms when compared with regions having mixed calcareous siliciclastic sedimentation is interpreted to argue against a widespread photosymbiosis in the group several aspects of this study highlight the importance of regional tectonic and oceanographic controls of distributional and perhaps also evolutionary patterns of rudist bivalves their delineation still suffers from the regionally different quality of stratigraphical and taxonomic data

monsoonal precipitation in the paleo tethys warm pool during the latest permian abstract simulations of the late permian 251 ma are analyzed with respect to the northern hemispheric pangean monsoon we find that the presence and spatial distribution of the warm pool and not land sea temperature differences are the primary forcing agents for the monsoon the land sea temperature gradient as a monsoonal mechanism is tested by eliminating the cathyasian peninsula and is found to have little impact on the spatial character of the monsoon furthermore the response of the monsoon to the warm pool was tested by removing all paleo tethys equatorial islands which allows the warm pool to expand and migrate westward thus shifting the pattern of monsoonal precipitation given that paleogeography changes through time these results have important implications for the migration and strength of the tropical monsoon over geologic time additionally different co2 regimes are presented in which a 10 fold change in forcing produces diverging climates and therefore different warm pool and monsoon locales tropical and equatorial ocean currents impact the seasonal progression and location of the warm pool and atmospheric mass flux for the monsoonal regime is characterized and shown to change with warm pool movement experiments were conducted using the low resolution version of community climate system model version 3 ccsm3 in both coupled and fixed sea surface temperature sst context for validation purposes a modern control is briefly presented with observations and is shown to represent both the spatial and seasonal progression of the indian monsoon