interdune areas of the back island dune field north padre island texas abstract the small young about 100 yrs back island dune field on north padre island south texas consists of fairly persistant oblique dunes up to 6 m high with well developed interdune areas that grade northwestward to small ephemeral transverse and barchan dunes with interconnected interdune areas thence sheet sand areas the subhumid climate is marked by rain associated with frontal systems and tropical storms winds are seasonally bimodal prevailing southeasterly are punctuated by northerly and northwesterly winds with the passage of frontal systems in winter the entire dune field and individual oblique dunes show a net migration of about 15 m yr 1 to the northwest the dunes however are on a seasonally reversing track changing their slipface direction and migration direction with frontal systems one year of monitoring shows sand transport in the dune interdune system to be complex and cyclic during the wind reversals of winter dunes are very ineffecfive sand traps owing to loss of flow separation and much sand is lost to the interdune areas interdune areas store sand during these wet winter months as a result of the wind reversals and higher moisture content during the summer the interdune areas deflate and the dunes build in size the overall dune field deposit appears to consist of three laterally contiguous zones from southeast to northwest 1 continuous climbing oblique dune and interdune deposits 2 discontinuous lenses of dune sand in overall interdune layers and 3 a chaotic mixture of dune and horizontal deposits of the sheet sand areas one year s mapping and trenching documents that interdune sedimentary structures are extremely variable laterally and vertically reflecting specific microenvironments within the interdune flat wet surface features consist of current and wave ripples channel fill miniature deltas wrinkle marks mini ripples rills algae and sand volcanoes abundant adhesion structures rain impacted ripples brecciated surfaces and microtopography reflect damp surface deposits dry surface features are predominately wind ripples others include small isolated barchan and shadow dunes organic debris lag surfaces deflation scours beetle bioturbation plant root structures associated with shadow dunes and grainfall from the adjacent dunes interdune deposits account for about 40 of the total dune field deposits which seems reasonable compared to some ancient examples by virtue of occupying a relative basin interdune deposits are selectively preserved compared to dune deposits in general interdune sedimentation is enhanced by non eolian depositional mechanisms a high water table early evaporatic cements and a variable wind regime the actual thicknesses of individual dune and interdune deposits are less on padre than ancient examples reflecting the relative scale of the bedforms in many respects sequences of sedimentary structure in padre island interdune deposits are typical of ancient coastal interdune strata but some marked departures occur adhesion structures relatively rare in some ancient examples but abundant within padre interdune deposits seem favored by the small size of dune and interdune area the climate and a variable wind regime penecontemporaneous deformation absent in padre interdune deposits but pronounced in some ancient examples probably reflects dune size and the nature of the deposits wavy laminae in ancient interdune deposits probably result from many causes but seem best represented by modern examples of evaporitic algal bacterial formed structures

eolian fluvial and pan playa facies of the tertiary tsondab sandstone formation in the central namib desert namibia abstract the pliocene to recent sand sea in the central part of the 2000 km long namib desert is underlain widely by sediments comprising the tsondab sandstone formation tsf of early to middle tertiary age this formation is the earliest record of terrestrial sedimentation in the central namib desert and formerly was thought to consist of only eolian dune and sand sheet deposits of a desert origin however recent field investigations indicate that the tsf also includes deposits of ephemeral watercourses and pans playas these fluvial and playa sediments are associated intimately with the eolian dune and sand sheet deposits as is likewise the case in the present extreme arid namib desert sedimentary structures and trace fossils in the tsf eolianites resemble those found in the modern sand sea furthermore these eolianites were deposited under a dominant southerly and a subordinate easterly quadrant wind regime which is similar to the present day circulation pattern in the namib since the cold benguela current was established only in the late tertiary the tsf represents a major ancestral arid phase in the namib tract that was controlled by an early anticyclonic wind regime and a geographic location on the rainshadow side of southern africa

reanalysis of s to p amplitude ratios for gross attenuation structure long valley caldera california because of the strong interest in the magmatism and volcanism at long valley caldera eastern california and because of recent significant improvements in our knowledge of the caldera velocity structure and earthquake locations i have reanalyzed the local earthquake s to p amplitude ratio data of sanders 1984 for the gross three dimensional attenuation structure of the upper 10 km of long valley caldera the primary goals of the analysis are to provide more accurate constraints on the depths of the attenuation anomalies using improved knowledge of the ray locations and an objective inversion procedure the new image of the high s wave attenuation anomaly in the west central caldera suggests that the top of the principal anomaly is at 7 km depth which is 2 km deeper than previously determined because of poor resolution in much of the region some of the data remain unsatisfied by the final attenuation model this unmodeled data may imply unresolved attenuation anomalies perhaps small anomalies in the kilometer or two just above the central caldera anomaly and perhaps a larger anomaly at about 7 km depth in the northwest caldera or somewhere beneath the mono craters the central caldera s wave attenuation anomaly has a location similar to mapped regions of low teleseismic p wave velocity crustal inflation reduced density and aseismicity strongly suggesting magmatic association

interaction between aeolian fluvial and playa environments in the permian upper rotliegend group uk southern north sea the permian upper rotliegend group in offshore uk quadrants 42 43 47 and 48 comprises a sequence of mixed aeolian fluvial playa deposits these deposits are up to 300 m thick and contain a record of the interaction between desert fluvial systems and adjacent aeolian and playa environments the relative dominance of water vs wind transport and deposition in this stratigraphic package was a function of fluctuations in the discharge of ephemeral fluvial systems and changes in water table playa level driven by a combination of climatic change and syndepositional tectonics the rotliegend sedimentary record is punctuated by numerous surfaces recording erosion by wind and water the origin of these surfaces is mostly climatic with periods of increased runoff resulting in fluvial incision especially near active faults during periods of reduced runoff wind erosion of fluvial deposits occurred with fluvially derived sand being reworked into expanding aeolian dune fields wind erosion also occurred as a rising water table isolated dunes from their sediment supply resulting in deflation of dunes down to the water table these surfaces formed in a basin that was subsiding thus even in a background of overall increasing accommodation space climatically driven falls in the water table allowed for periods of erosion the occurrence of significant erosion especially near syndepositional fault zones resulted in a sedimentary record that shows pronounced lateral as well as vertical facies variations

primary magmatic calcite reveals origin from crustal carbonate abstract we have investigated lava flows representative of the whole eruptive history of the colli albani ultrapotassic volcanic district central italy one of the most intriguing features concerning some of these lava flows is the occurrence of primary magmatic calcite in the groundmass the primary magmatic nature of calcite has been inferred by microtextural investigations showing that it typically occurs i interstitially associated with clinopyroxene nepheline and phlogopite ii in spherical ocelli associated with nepheline fluorite and tangentially arranged clinopyroxene and iii in corona like reaction zones around k feldspar xenocrysts these microtextural features distinctly indicate that calcite crystallized from a carbonate melt in a partially molten groundmass implying that the temperature of the system was above the solidus of the hosted lava flow 850 c geochemical features of calcite crystals i e stable isotope values and trace element patterns corroborate their primary nature and give insights into the origin of the parental carbonate melt the trace element patterns testify to a high temperature crystallization process not hydrothermal involving a carbonate melt coexisting with a silicate melt the high 18o around 27 smow and wide 13c 18 to 5 pdb values measured in the calcites preclude a mantle origin but are consistent with an origin in the crust in this framework the crystallization of calcite can be linked to the interaction between magmas and carbonate bearing wall rocks and in particular to the entrapment of solid and or molten carbonate in the silicate magma the stability of carbonate melt at low pressure and the consequent crystallization of calcite in the lava flow groundmass are ensured by the documented high activity of fluorine in the studied system and by the limited ability of silicate and carbonate melts to mix at syn eruptive time scales

the geophysics of a restless caldera long valley california at 9 33 pdt on the morning of may 25 1980 a strong earthquake of local magnitude ml 6 1 heralded the onset of an earthquake sequence that focused worldwide attention on the major geologic and tectonic fea ture nearest its epicenter the long valley caldera of eastern california this sequence included two additional ml 6 events on may 25 and a fourth ml 6 event on may 27 accompanied by more than 300 ml 3 aftershocks over the next several weeks all of which were located either within or to the south of the caldera uhrhammer ferguson 1980 cramer toppozada 1980 these were not the first major events to occur regionally within the last decade the october 4 1978 bishop event m l 5 7 located some 20 km to the southeast of long valley initiated a sequence of swarm like activity that migrated generally toward the caldera over the next two years ryall ryall 1980 van wormer ryall 1980 in fact van wormer ryall 1980 in a manuscript written prior to the may 1980 earthquakes identified this sequence of events as a

high energy ephemeral stream deltas an example from the upper silurian holmestrand formation of the oslo region norway abstract the late orogenic deposits of the upper silurian holmestrand formation of the oslo region norway comprises sharply alternating ephemeral stream and sandy beach face deposits the formation is divided into three units reflecting the down slope change on an extensive ephemeral stream delta system the lower unit of the formation comprises ephemeral stream sediments as stacked sheet sandstone bodies deposited on a broad coastal floodplain each sheet is bounded by a lower intraclast strewn scoured surface overlain by massive horizontally stratified low angle and trough cross bedded sandstones in the medial and upper units of the formation the ephemeral stream sediments alternate with beach face deposits forming ephemeral stream deltas the ephemeral stream deltas are marked by intraclast strewn scoured surfaces and dominated by trough cross bedded sandstones they may contain escapement burrows marine bioturbation and wave working of the delta surfaces the beach face deposits are composed of alternating irregular horizontally stratified sandstones with current and wave ripple cross lamination and tabular cross bedded sandstones deposition took place in a coastal non to micro tidal shallow water environment influenced by longshore currents and low palaeo wave energy seven ichnotaxa are recognized and support the sedimentary record of a transitional environment between a broad coastal floodplain and a shallow marine environment the presence of calcretes indicate an arid to semi arid palaeo climate

early permian rotliegendes palaeowinds of the north sea abstract the classical desert sediments of the early permian upper rotliegendes were deposited in a post variscan basin that extends from eastern england to the russo polish border which has been referred to as the southern permian basin these sediments comprise four main depositional facies fluvial wadi aeolian sabkha and lacustrine the lacustrine facies includes important bedded halites the southern permian basin is separated from the smaller northern permian basin by the fragmented mid north sea ringkobing fyn system of highs and beyond the grampian spur lies the even smaller moray firth basin these latter basins contain rock sequences similar to those of the southern basin with the exception that bedded halite has not been recognised in the lacustrine facies the rotliegendes of the southern basin apparently conforms to deposition in a northern hemisphere tradewind desert similar to the modern southern sahara apart from regional palaeomagnetic considerations and the occurrence of sediments of a non arid nature south of the variscan highlands the strongest evidence supporting this interpretation is the pattern of palaeowind directions deduced from the orientations of dune bedding this is seen in both outcrop and core and derived from the continuous dip meter logs of many north sea wells by plotting the poles to the bedding attitudes on polar nets palaeowind directions have also been deduced from the dip meter logs of wells drilled in the northern and moray firth basins in general they indicate winds that blew in a direction opposed to those of the southern basin thus an area of high barometric pressure seems to have been located over the mid north sea high when the bedding attitudes in a well are roughly unidirectional an origin on a transverse dune is normally indicated with some wells the indicated palaeowind direction is regionally anomalous in many cases this can be rectified if the well is presumed to have drilled down through one flank of a seif dune the indicated palaeowind is thus changed by up to 90 and then commonly fits the regional pattern these early permian desert basins were smaller and closer to the equator than the modern sahara their location in the centre of a continent between the caledonian and variscan mountain ranges suggests the analogy of a more tropical equivalent of the central asian takla makan desert

trace fossils as paleoenvironmental indicators in the taylor group devonian of antarctica abstract the taylor group of southern victoria land antarctica contains varied and abundant trace fossils which have been interpreted by palaeontologists as indicating marine deposition however sedimentologists have largely favoured non marine deposition on the basis of desiccation polygons fining upward cycles unidirectional paleocurrents small channels red beds and paleosols the debate is reconciled by a reinterpretation of the trace fossil assemblage it is shown that widespread and well preserved cruziana diplichnites rusophycus and skolithos which have previously been used as marine indicators comprise an ichnofacies scoyenia which is entirely typical of fresh water

multiple ruptures for long valley microearthquakes a link to volcanic tremor despite several episodes of ground deformation and intense seismic activity starting in 1978 the long valley california volcanic area has not produced clearly recognized volcanic tremor instead a variety of atypical microearthquakes have been recorded during these episodes including events dominated by low frequency long period or mixed high and low frequency hybrid signals during a 1997 episode a number of unusual microearthquakes occurred within a temporary 40 station seismic network surrounding the casa diablo area allowing the events to be precisely located and analyzed as a function of azimuth offset and source characteristics eight prime examples lie within two 7 km deep clusters of seismicity separated by about 1 km with four events in each cluster empirical green s function deconvolution shows that these events are composed of two to three sub events the sub events consisting of ordinary single rupture double couple microearthquakes the delay times between the sub events are constant within each cluster equaling 0 092 s in one and 0 06 s in the other events from other clusters show similar delays the signal interference produced by the closely spaced sub events gives rise to modulated delay dependent source spectra the regularity of the delays suggests that the sub events are being triggered by a fixed length and or time scale process an example being the length inflation rate of a magmatic or hydrothermal flow structure with continued action of the triggering process the sub events could proliferate and evolve into observable volcanic tremors at mammoth

major bounding surfaces in aeolian sandstones a climatic model large areas of fixed vegetated dunes occur in the sahel and southern margin of the sahara these dunes were active during late pleistocene times and have been stabilized as a result of a change to more humid less windy conditions in the holocene the stabilized surfaces which are in part of erosional origin are of regional extent within aeolian sand sequences such surfaces form the highest order bounding surfaces since regional bounding surfaces of this type occur in all the world s major deserts it is suggested that they should also be present in some ancient aeolian sandstone sequences

significance of interdune deposits and bounding surfaces in aeolian dune sands bounding surfaces and interdune deposits provide keys for detailed interpretations of the development shape type wavelength and angle of climb of aeolian bedforms as well as overall sand sea conditions current alternate interpretations of bounding surfaces require very different but testable models for sand sea deposition two perpendicular traverses of jurassic entrada sandstone utah reveal relations among cross strata first order bounding surfaces and horizontal strata these field relations seem explicable only as the deposits of downwind migrating climbing enclosed interdune basins horizontal strata and dune bodies consisting of superimposed smaller crescentic dunes cross stratified deposits a 1 7 km traverse parallel to the palaeowind direction provides a time transgressive view showing continuous cosets of cross strata first order bounding surfaces and interdune deposits climbing downwind at an angle of a few tenths of a degree changes occur in the angle of climb cross strata structure and interdune deposits these reflect changes in depositional conditions through time a 1 5 km traverse perpendicular to the palaeowind direction provides a view at an instant in geological time showing first order bounding surfaces and interdune deposits forming flat laterally discontinuous lenticular bodies the distribution of interdune sedimentary structures in this traverse is very similar to that of some modern interdune basins such as those on padre island texas hierarchies of bounding surfaces in an aeolian deposit reflect the bedform development on an erg the presence of three orders of bounding surfaces indicates dune bodies consisting of smaller super imposed dunes the geometry of first order bounding surfaces is a reflection of the shape of the inter dune basins second order bounding surfaces originate by the migration of the superimposed dunes over the larger dune body and reflect individual dune shape and type third order bounding surfaces are reactivation surfaces showing stages in the advance of individual dunes the presence of only two orders of bounding surfaces indicates simple dunes modern and entrada interdune deposits show a wide variety of sediment types and structures reflecting deposition under wet damp and dry conditions interdune deposits are probably the best indicators of overall erg conditions and commonly show complex vertical sequences reflecting changes in specific depositional conditions

morphology and genesis of asymmetric adhesion warts a new adhesion surface structure abstract adhesion surface structures have been studied during their formation on a fluvial bar in east greenland two main types occurred adhesion ripples and asymmetric adhesion warts adhesion ripples formed on moist surfaces their crests lay transverse to the wind direction and they migrated by trapping dry wind blown sand on their steep fronts asymmetric adhesion warts new structure formed because of falling moisture content by preferred upwind migration of small protuberances on the adhesion ripples the protuberances were apparently inherited from an initial rain sculpturing of the bar surface the asymmetric adhesion warts here described for the first time were elongate parallel to the wind associated with steep upwind facing fronts and commonly displayed sand shadow tails tapering in a downwind direction a study of devonian flood basin deposits hornelen basin norway revealed the existence of adhesion surface structures very similar to their modern analogues the devonian examples were associated with rain sculptured surfaces which are believed to have controlled the morphology of the adhesion surface structures as in the modern example the orientation of the ancient adhesion surface structures is here used for determination of the palaeowind which blew from the ene

high level triggers for explosive mafic volcanism albano maar italy abstract colli albani is a quiescent caldera complex located within the roman magmatic province rmp italy the recent via dei laghi phreatomagmatic eruptions led to the formation of nested maars albano maar is the largest and has erupted seven times between ca 69 33 ka the highly explosive nature of the albano maar eruptions is at odds with the predominant relatively mafic sio 2 48 52 wt foiditic k 2 o 9 wt composition of the magma the deposits have been previously interpreted as phreatomagmatic however they contain large amounts up to 30 vol of deep seated xenoliths skarns and all pre volcanic subsurface units all of the xenoliths have been excavated from depths of up to 6 km rather than being limited to the depth at which magma and water interaction is likely to have occurred suggesting an alternative trigger for eruption high precision geochemical glass and mineral data of fresh juvenile magmatic clasts from the small volume explosive deposits indicate that the magmas have evolved along one of two evolutionary paths towards foidite or phonolite the foiditic melts record ca 50 mixing between the most primitive magma and ca rich melt late stage prior to eruption a major result of our study is finding that the generation of ca rich melts via assimilation of limestone may provide storage for significant amounts of co 2 that can be released during a mixing event with silicate magma differences in melt evolution are inferred as having been controlled by variations in storage conditions residence time and magma volume

fluvial aeolian interactions part i modern systems two modern fluvial aeolian depositional systems great sand dunes national monument colorado and the mojave river wash california are remarkably similar in spite of different climates sizes fluvial sediment textures and relative directions of aeolian and fluvial transport dune growth and migration and deflation of blowouts create 8 10 m of local relief in unflooded aeolian landscapes there are six prominent fluvial aeolian interactions 1 fluvial flow extends into the aeolian system until it is dammed by aeolian landforms 2 interdune areas overbank interdunes upstream of aeolian dams and alongside channels are flooded 3 water erodes dunes alongside channels and interdunes 4 flood waters deposit sediment in interdune areas 5 fluvially derived groundwater floods interdunes interdune playas 6 wind erodes fluvial sediment and redeposits it in the aeolian system unique and characteristic sediments are deposited in overbank interdunes and in interdune playas reflecting alternate fluvial and aeolian processes and rapidly changing flow and salinity conditions these fluvial aeolian interdune deposits are characterized by irregular concave up bases and flat upper surfaces containing mudcracks or evaporite cement characteristic low relief surfaces form in aeolian systems as an effect of flooding fluvial deposits are resistant to aeolian deflation aeolian sand is preserved when flood sediments are deposited around the bases of the dunes thus repetitive fluvial and aeolian aggradation tends to be stepwise as interdune floors are suddenly raised during floods the effects of flooding should be easy to recognize in ancient aeolianites even beyond the area covered with overbank muds

oxygen isotope geochemistry of pyroclastic clinopyroxene monitors carbonate contributions to roman type ultrapotassic magmas the oxygen isotope geochemistry and chemical composition of clinopyroxene crystals from alban hills pyroclastic deposits constrain the petrological evolution of ultrapotassic roman type rocks volcanic eruptions in the 560 35 ka time interval produced thick pyroclastic deposits bearing clinopyroxene phenocrysts with recurrent chemical characteristics clinopyroxenes vary from si mg rich to al fe rich with no compositional break indicating that they were derived from a continuous process of crystal fractionation based on the 18o and trace element data no primitive samples were recovered monomineralic clinopyroxene cumulates set the oxygen isotope composition of primary magmas in the range of uncontaminated mantle rocks 5 5 but their ree composition resulted from extensive crystal fractionation departing from these mantle like 18ocpx values the effects of crustal contamination of clinopyroxene o isotope composition were identified and used to monitor chemical variations in the parental magma 18o values in si mg rich clinopyroxene are slightly higher than typical mantle values 5 9 6 2 and the low ree contents are representative of early stages of magmatic differentiation 18o values as high as 8 2 are associated with al fe3 rich clinopyroxene showing high ree contents these 18o values are characteristic of crystals formed during the late magmatic stages of each main eruptive phase geochemical modelling of 18o values vs trace element contents indicates that these ultrapotassic magmas were derived from fractional crystallization plus assimilation of limited amounts of carbonate wall rocks starting from a primary melt and from interaction with co2 derived from country rocks during crystal fractionation

subsurface valleys and geoarcheology of the eastern sahara revealed by shuttle radar the shuttle imaging radar sir a carried on the space shuttle columbia in november 1981 penetrated the extremely dry selima sand sheet dunes and drift sand of the eastern sahara revealing previously unknown buried valleys geologic structures and possible stone age occupation sites radar responses from bedrock and gravel surfaces beneath windblown sand several centimeters to possibly meters thick delineate sand and alluvium filled valleys some nearly as wide as the nile valley and perhaps as old as middle tertiary the now vanished major river systems that carved these large valleys probably accomplished most of the erosional stripping of this extraordinarily flat hyperarid region underfit and incised dry wadis many superimposed on the large valleys represent erosion by intermittent running water probably during quaternary pluvials stone age artifacts associated with soils in the alluvium suggest that areas near the wadis may have been sites of early human occupation the presence of old drainage networks beneath the sand sheet provides a geologic explanation for the locations of many playas and present day oases which have been centers of episodic human habitation radar penetration of dry sand and soils varies with the wavelength of the incident signals 24 centimeters for the sir a system incidence angle and the electrical properties of the materials which are largely determined by moisture content the calculated depth of radar penetration of dry sand and granules based on laboratory measurements of the electrical properties of samples from the selima sand sheet is at least 5 meters recent september 1982 field studies in egypt verified sir a signal penetration depths of at least 1 meter in the selima sand sheet and in drift sand and 2 or more meters in sand dunes

nonlinear teleseismic tomography at long valley caldera using three dimensional minimum travel time ray tracing the authors explore the impact of three dimensional minimum travel time ray tracing on nonlinear teleseismic inversion this problem has particular significance when trying to image strongly contrasting low velocity bodies such as magma chambers because strongly refracted and or diffracted rays may precede the direct p wave arrival traditionally used in straight ray seismic tomography they use a simplex based ray tracer to compute the three dimensional minimum travel time ray paths and employ an interative technique to cope with nonlinearity results from synthetic data show that their algorithm results in better model reconstructions compared with traditional straight ray inversions the authors reexamine the teleseismic data collected at long valley caldera by the u s geological survey the most prominent feature of their result is a 25 30 low velocity zone centered at 11 5 km depth beneath the northwestern quandrant of the caldera beneath this at a depth of 24 5 km is a more diffuse 15 low velocity zone in general the low velocities tend to deepen to the south and east the authors interpret the shallow feature to be the residual long valley caldera magma chamber while the deeper feature may represent basaltic magmas ponded in the midcrust the deeper position of the prominent low velocity region in comparison to earliermore tomographic images is a result of using three dimensional rays rather than straight rays in the ray tracing the magnitude of the low velocity anomaly is a factor of approximately 3 times larger than earlier models from linear arrival time inversions and is consistent with models based on observations of ray bending at sites within the caldera these results imply the presence of anywhere from 7 to 100 partial melt beneath the caldera 40 refs 1 fig 1 tab less

mineralogy and petrogenesis of a ba ti zr rich peralkaline dyke from sebkovice czech republic recognition of the most lamproitic variscan intrusion abstract a peralkaline ultrapotassic dyke found at sebkovice t ebic district western moravia is a mineralogically extreme member of a dyke swarm occurring along the south eastern border of the moldanubian region of the bohemian massif the dyke shows a simple zoning with a very fine grained marginal zone grading into a medium grained central zone it has a primary mineral assemblage of microcline and potassic amphiboles with accessory apatite and altered phlogopite the microcline exhibits an unusual red luminescence colour and pronounced substitution of fe3 for al with measured contents of fe2o3 up to 8 5 wt 0 31 apfu fe3 amphiboles have very high k up to 0 99 apfu and si contents their compositions follow an alkaline fractionation trend from potassic richterite to potassic magnesio arfvedsonite characterized by an increase of na k and a decrease of ca mg fe2 and ti via heterovalent substitutions b ca c mg fe2 b na c fe3 and ti mg 2fe3 the most evolved apatite is significantly enriched in sro up to 9 7 wt 0 49 apfu sr the core of the dyke and late veinlets contain unique late to post magmatic ba ti zr bearing mineral assemblages of baotite henrymeyerite titanite rutile benitoite and bazirite anhedral baotite fills interstices distributed inhomogeneously in the dyke centre it is locally replaced by a ba bearing titanite henrymeyerite rutile quartz assemblage henrymeyerite the second record in a lamproite shows variable fe ti ratios and represents a solid solution of the hepta and hexatitanate components euhedral crystals of benitoite and bazirite are enclosed in the late stage quartz titanite apatite veinlets in the fine grained margin of the intrusion in terms of a mineralogical genetic classification the sebkovice dyke can be considered as a new high silica 57 wt sio2 variety of lamproite variety sebkovice and represents a unique expression of post collisional potassic magmatism on the south eastern border of the bohemian massif the peralkaline dykes from this area show mineralogical and geochemical features similar to those of silica rich orogenic lamproites emplaced at destructive plate margins in terms of the modern classification of lamproites the sebkovice dyke is the first lamproite recognised in the variscan orogenic belt

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

seismic reflection investigations of the mount cayley bright spot a midcrustal reflector beneath the coast mountains british columbia an unusually high amplitude midcrustal reflector was discovered by a lithoprobe seismic reflection survey crossing a predominantly plutonic region in southwestern british columbia canada the bright spot was observed adjacent to mount cayley a large quaternary volcanic center associated with the cascadia subduction zone magmatic arc characterization of the bright spot may advance our understanding of either the midcrustal structure of magmatic supply systems or the presence and storage of saline fluids in the midcrust the location and three dimensional geometry of the reflector were determined using travel time inversion the resulting suite of models consistently describe a northwest dipping reflector that lies 12 5 to 13 km beneath the mount cayley volcanic complex the areal extent of the reflective surface is 3 km by 1 km and the structure is less than 1 6 km thick the transition between the body and the country rock must be rapid 200 m and exhibit a large impedance contrast in order to generate reflections of such high frequencies 30 hz and relative amplitudes 8 0 db our preferred interpretation for the reflector is a fossil sill complex associated with the volcanic development of mount cayley however the data do not rule out the possibility that the reflective structure represents melt lenses or saline fluid produced by the dewatering of the subducted slab the mount cayley bright spot lies just below the brittle upper crust as do the midcrustal reflectors detected beneath japanese subduction arc volcanoes this correlation suggests that thermal and rheological properties just below the brittle ductile crustal transition may be favorable for reflector formation

sand sheet dynamics and quaternary landscape evolution of the selima sand sheet southern egypt abstract the selima sand sheet occupies more than 120 000 km 2 of the hyperarid uninhabited darb el arba in desert centered at the border of egypt and sudan at latitude 22 n and is characterized by a featureless surface of lag granules and fine sand broken only by widely separated dune fields and giant ripples of varying height and wavelength monitoring of the largest of these chevron shaped ripples using repeat orbital images and field surveys indicates migration rates of 500 1000 m yr accompanied by 0 2 0 cm erosion or deposition of the youngest sand sheet stratigraphic units beneath this active surface several developmental stages of sand sheet sediments have undulatory upper contacts and varying degrees of pedogenic alteration the younger stages retain their horizontal lamination and have cracking patterns indicative of past wetter conditions while older stages have lost their laminar structure through pedogenesis historical remains in the desert as well as 14 c and uranium series dating indicate that the younger strata of the sand sheet have a very low accumulation rate despite the active movement of the surface the lower strata were extensively modified during mid and late pleistocene pluvials resulting in an initial undulatory surface that set the stage for later accumulation of sand sheet below these quaternary sediments lies irregular topography dissected by channels of mid tertiary drainage the selima sand sheet is neither the result of net aggradation nor degradation but results from inheritance of an initial fluvial landscape increasingly modified during climatic cycles wet periods led to local drainage and deposition while the increasingly severe arid periods of the late pleistocene and holocene resulted in deposition of the blanketing bimodal sediments of the sand sheet

paleoenvironmental implications of fixed dune systems in southern africa extensive systems of fixed linear dunes occur in the kalahari region of southern africa from 28 s to 16 30 s they provide evidence for large scale expansion of arid climates in the subcontinent during the quaternary on the basis of differing dune morphologies and alignments three periods of upper pleistocene aridity are recognised patterns of dune alignments reflect paleosand flow regimes and permit deduction of past winds and circulation patterns leading to the conclusion that arid episodes were associated with and probably caused by greater strength and persistence of the south african anticyclone a tentative chronology of the arid periods tends to support the hypothesis that subtropical aridity was contemporaneous with glacial conditions in high latitudes

coda wave imaging of the long valley caldera using a spatial stacking technique numerous geological and seismological studies of the long valley caldera eastern california suggest that it is at present an active magmatic system tomographic measurements utilising local and regional earthquake data have traditionally been made on the principle direct arrivals this paper presents the results from a technique developed to image the s wave attenuation structure we measure the attenuation value of the s wave coda from almost 17 000 vertical component seismograms a more stable estimate of q is determined from coda waves which are less sensitive to local path effects than direct waves as they sample a volume we find that the resultant tomograms produced from spatial stacking show a high attenuation anomaly qs 125 centred within the caldera compared with qs 220 outside the caldera

constraints on the upper crustal structure of the long valley mono craters volcanic complex eastern california from seismic refraction measurements during the summers of 1982 and 1983 field work was completed on 10 new seismic refraction profiles in the long valley mono craters region located within the technically active zone between the eastern sierra nevada and the basin and range province the four profiles presented here sample the upper 7 10 km of the crust within the western half of long valley cladera the mono craters ring fracture system and the normal crust north and northeast of long valley the entire area shares a common crystalline basement consisting primarily of mesozoic granitic rocks at a depth of 2 km beneath the topographic surface the p wave velocity is uniformly 5 6 km s beneath which the velocity increases with a gradient of about 0 1 s 1 clear secondary arrivals observed on a profile crossing the west part of the caldera support evidence from 1972 seismic refraction profiles for a reflecting boundary at a depth of 7 8 km beneath the west margin of the resurgent dome which may represent the top of a magma chamber structural details resolved in the upper 2 km of the crust lead to the following conclusions 1 p wave velocities in the crystalline basement at depths shallower than 2 km vary from 3 6 to 5 0 km s this variation reflects differences in the degree of fracturing of the upper portion of the basement 2 an apparently homogeneous basement in the upper 7 10 km beneath the mono craters ring fracture system indicates that any extensive magma chamber must be at least 10 km deep there 3 the downdropped crystalline basement beneath the western half of long valley caldera dips genty 5 10 to the northeast apparent offsets along steeply dipping caldera bounding faults are 1 0 1 7 km along the northern western and southern sides of the caldera with largest offsets in the north 4 rocks forming the caldera fill fall into essentially three p wave velocity groups from the surface downward these velocity groups are 100 400 of 1 2 1 8 km s material corresponding to unconsolidated fluvial or lacustrine deposits or highly fractured rhyolite flows 200 400 m of 2 8 3 1 km s material corresponding to sparsely jointed postcaldera rhyolite rhyodacite and basalt flows and approximately 1000 m of 3 9 4 4 km s material corresponding to deposits of bishop tuff

the origin of k feldspar megacrysts hosted in alkaline potassic rocks from central italy a track for low pressure processes in mafic magmas abstract in situ sr isotope and microchemical studies were used to determine the provenance of k feldspar megacrysts hosted in mafic alkaline potassic ultrapotassic rocks and in differentiated rocks from two nearby volcanic apparatus in central italy at monte cimino volcanic complex mafic leucite free ultrapotassic megacryst bearing rocks of olivine latitic composition are associated with evolved latite and trachyte here latites and trachytes straddle the sub alkaline field age corrected 87sr 86sr values sri of the analysed cimino olivine latites vary from 0 71330 and 0 71578 and strongly increase at constant mg value latite and trachyte have lower sri than olivine latites ranging between 0 71331 and 0 71361 sri of k feldspar megacrysts from olivine latites are between 0 71352 and 0 71397 but core and rim 87sr 86sr ratios within individual megacryst are indistinguishable in all the mafic rocks the megacrysts are not in isotopic equilibrium with the hosts k feldspar megacrysts from both the latite and trachyte have similar sr isotope compositions sri 0 71357 0 71401 to those in the olivine latites however sri of megacryst in the trachyte vary significantly from core to rim sri from 0 71401 to 0 71383 as with the olivine latites the k feldspar megacrysts are not in isotopic equilibrium with bulk rock compositions of the latite or trachyte at vico volcano megacryst bearing rocks are mafic leucite free potassic rocks mafic leucite bearing ultrapotassic rocks and old trachytic rocks the mafic leucite bearing and leucite free rocks are a tephri phonolite and an olivine latite respectively a megacryst in vico trachyte is isotopically homogeneous sri core 0 71129 rim 0 71128 and in equilibrium with the host rock sri bulk rock 0 71125 sri of megacryst from tephri phonolite is clearly not in isotopic equilibrium with its host sri bulk rock 0 71158 and it increases from core sri 0 71063 to rim sri 0 71077 a megacryst in vico olivine latite is isotopically homogeneous sri core 0 71066 rim 0 71065 but not in equilibrium with the host rock sri bulk rock 0 71013 the sr isotope microdrilling technique reveals that cimino megacrysts were crystallised in a cimino trachytic magma and were subsequently incorporated by mixing mingling processes in the latitic and olivine latitic melts a model invoking the presence of a mafic sub alkaline magma which was mixed with the olivine latite is proposed to justify the lack of simple geochemical mixing relation between cimino trachytes and olivine latites this magmatological model is able to explain the geochemical characteristics of cimino olivine latites otherwise ascribed to mantle heterogeneity the similarity of core sri of megacrysts hosted in vico tephri phonolite and olivine latite suggests that the k feldspar megacrysts are co genetic isotopic equilibrium between megacryst and vico host trachyte indicates that the trachyte is the parent of this megacryst on the contrary the megacrysts hosted in tephri phonolite and olivine latite do not derive from the old trachytic magma because no diffusion process may explain the core to rim sr isotope increase of the xenocryst hosted in the tephri phonolite the megacrysts hosted in the vico mafic rocks might derive from a trachytic melt similar in composition to the old vico trachytes

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

the palaeoenvironmental significance of dune size hierarchies the size of a dune is a function of many factors one of which is the length of the period of consistent wind regime under which it grew ephemeral dunes are defined as those that are adjusted to diurnal wind regimes meso dunes to annual wind regimes and mega dunes to wind regimes that persist for longer periods these longer periods could be major climatic cycles but there seem to be no dunes whose size reaches that allowed by the length of some of these periods there may therefore be a maximum size beyond which mega dunes cannot grow dictated by sand supply aerodynamic processes such as speed up or by the scale of the atmospheric boundary layer these concepts are tested on dunes in the wahiba sands in oman analysed from a landsat image it is hypothesised that a large set of megadunes here formed in the lgm that a smaller set of mega dunes may be of younger dryas age and that there is a meso dune series of holocene age

a stratigraphic model to account for complexity in aeolian dune and interdune successions wet aeolian systems in which the water table or its capillary fringe are in contact with the accumulation surface such that moisture influences sedimentation are well known from modern aeolian systems and several ancient preserved successions are recognized from outcrop one common mechanism by which accumulation of wet aeolian system deposits occurs is via a progressive rise in the relative water table level that is coincident with ongoing dune and interdune migration the angle of dune climb being determined by the ratio between the rate of relative water table rise and the rate of downwind migration of the bedforms accumulations of wet aeolian system deposits tend to be characterized by units of climbing dune strata separated by units of damp or wet interdune strata for simple geometric configurations where the size of the dune and interdune units the rate of bedform migration and the rate of aggradation all remain constant over space and time the resulting accumulation has a simple architecture characterized by sets of uniform thickness inclined at a constant angle however the dynamic nature of most aeolian dune systems means that such simple configurations are unlikely in nature the complexity inherent in these systems is accounted for here by a numerical model in which key controlling parameters including dune and interdune wavelength and spacing migration rate and aggradation rate are allowed to vary systematically both spatially from a dune field centre to its margin and temporally in response to changes in sediment availability or water table level the range of synthetic stratigraphic architectures generated by the model accounts for all the best known examples of aeolian dune and interdune stratigraphic configurations documented from the stratigraphic record modelling results have enabled the erection of a scheme for the classification of dune system type whereby the many elaborate stratal architectures known to exist in nature can effectively be accounted for by only four parameters that are allowed to vary over space and time dune and interdune wavelength and spacing rate of bedform migration and rate of accumulation results have applied implications including the modelling of reservoir heterogeneity and the prediction of fluid flow pathways of hydrocarbons water co2 and contaminants in subsurface reservoirs and aquifers in which low permeability interdune units might act as baffles or barriers

alluvial facies evolution during the palaeozoic greening of the continents case studies conceptual models and modern analogues the palaeozoic greening of the continents the appearance and expansion of embryophytes land plants in terrestrial environments was arguably the most fundamental phanerozoic change to the earth system thirteen case studies of cambrian to devonian fluvial deposits from north america and europe are documented here to illustrate the evolution of fluvial style during this period during the cambro ordovician prior to the advent of terrestrial vegetation fluvial systems laid down relatively coarse sands with little mud resulting in self formed channels and an architecture dominated by broad sheets of trough cross beds sheet braided style similar deposits formed across a wide range of latitudes and passed basinward into sandy coastal deposits from the mid ordovician onwards an increase in floodplain mudstone corresponds broadly with the appearance of embryophytes which would have progressively enhanced upland weathering mud production and floodplain storage of fines during the late silurian small heterolithic channel bodies with lateral accretion sets provide the first evidence of meandering channels and floodplain mudstones contain more varied palaeosols especially calcretes which appear abundantly for the first time by the early devonian channel deposits comprise sandstone lenses channelled braided style probably due to the increased bank strength and cohesion and reduced potential for sediment sorting imparted by sand mud mixtures muddy coastal deposits are prominent by the upper devonian fluvial deposits commonly contain fossil trees and large mainstem meandering channels with lateral accretion sets indicating that rooted vegetation stabilized channels the advent of stable floodplains with levees crevasse splays and organic litter would have encouraged the diversification of terrestrial invertebrates which left alluvial ichnological signatures from the late silurian onwards

attenuation of short period seismic waves at mt vesuvius italy we analysed short period seismograms from about 250 very local events recorded by a network of high dynamic range short period seismic stations deployed on mt vesuvius to estimate the site corrected short period seismic attenuation we calculated qc 1 the inverse of the quality factor for coda waves for short lapse times 12 s and qp 1 and qs 1 the inverse of the direct body wave quality factors for p and s waves follow ing shallow ray paths we used the single scattering assumption to fit the amplitude envelopes of the coda at different frequency bands obtaining a qc 1 slowly varying with frequency similar to values measured for other volcanoes at the same lapse time site corrected qp 1 and qs 1 were estimated using the frequency decay method for both p and s waves in two frequency bands 1 6 hz and 15 24 hz results show that qp 1 is 0 028 in both frequency bands and qs 1 is 0 015 and 0 017 at low and high frequencies respectively almost independent of the frequency and that the value of qp 1 is about twice that of qs 1 as measured worldwide a check was made by measuring the broadening of the first p wave pulse with station source distance finding qp 1 0 024 using the independent estimates of qc 1 and qs 1 we separated the intrinsic from the scattering quality factor at mt vesuvius obtaining a high scattering and a low intrinsi c q 1 as already observed for other volcanoes this result confirms the hypothesis of the predominant role of the scattering phenomena with respect to the intrinsic dissipation in the seismogram formation for volcanic earthquakes

three dimensional gravity modeling of the geologic structure of long valley caldera a 48 mgal gravity low coincides with long valley caldera and is mainly attributed to low density caldera fill gravity measurements by unocal geothermal have been integrated with u s geological survey data vastly improving gravity station coverage throughout the caldera a strong regional gravity trend is mainly attributed to isostasy a best fitting based on regional control of basement densities airy heiskanen isostatic model was used for the regional correction a three dimensional multiple unit gravity modeling program with iterative capabilities was developed to model the residual gravity the density structure of long valley caldera and vicinity was modeled with 22 discrete density units most of which were based on geologic units information from drill hole lithologies surface geology and structural geology interpretations constrain the model some important points revealed by the three dimensional gravity modeling are that 1 the volume of ejected magma associated with the bishop tuff eruption is greater than previously thought 2 the caldera structure is strongly influenced by precaldera topography and the extensions of major active faults 3 the main west ring fracture is coincident with the inyo domes mono craters fracture system 4 a relatively low density region probably underlies the caldera and 5 a silicic magma chamber may underlie devils postpile

volcano seismology hazards assessment the last few years have seen several impressive examples of seismic monitoring at volcanoes to provide warnings that have saved lives and property changes in the rates and character of volcanic earthquakes provided precursory signs to explosive eruptions of moderate size at redoubt volcano alaska mount unzen japan mount spurr alaska and rabaul caldera papua new guinea as well as the large eruption at mount pinatubo philippines in all these cases information was successfully communicated and put to practical use through broadcasts of public warnings prior to the eruptions and evacuations were initiated for the volcanoes located in populated areas at mount pinatubo probably thousands and possibly tens of thousands of lives were saved

palaeoclimatic evidence from sand seas abstract sand seas can be an important source of information on the quaternary history of many deserts because sand seas appear to react sensitivity to climatic changes the quality of palaeoenvironmental information obtained from them is frequently much better than that from adjacent rocky desert areas patterns of dune alignments may be used to reconstruct the wind directions that formed currently inactive or fixed dunes and thus can provide information on palaeocirculation patterns the climatic conditions under which these dunes formed can be examined using palaeoclimatic models to explore the combinations of wind velocity rainfall and evaporation rates required to reactivate them choice of appropriate values for these parameters may be hampered by the problems of dating episodes of dune activity in many sand seas the best palaeoclimatic information comes from studies of interdune lacustrine or playa deposits which may reflect increased local rainfall or higher groundwater discharge or greater penetration of the sand sea by rivers with headwaters outside the desert caution should be taken in the interpretation of such deposits for juxtaposition of aquatic and aeolian environments can occur even in modern hyperarid and seas the record of climatic changes preserved in the deposits of modern sand seas suggests that periods of dune formation may have been interrupted by long periods of stability which may also have included deposition of interdune lacustrine deposits for example within the past 40 000 years active dune formation in many sand seas appears to have been restricted to the interval between about 20 000 and 12 000 yr b p and to the late holocene approximately 1 4 to 1 3 rd of the time

s wave attenuation structure in long valley caldera california from three component s to p amplitude ratio data using s to p amplitude ratios measured from three component seismograms we tomographically imaged spatial variations in s wave attenuation in parts of long valley caldera data from seismograms of local earthquakes in the long valley caldera region that occurred during 1984 were employed with the s to p amplitude ratio technique with corrections for source radiation pattern to determine q s resolution is limited throughout most of the model however significant resolution and acceptable error in parts of the model allow meaningful interpretation of the results the primary result is the image of a low q s anomaly at 7 8 km depth beneath the resurgent dome this is independent evidence for high temperatures and possible magma accumulation at this location other regions of anomalously low q s are marginally significant or poorly resolved of these low q s at 4 5 km depth beneath the inyo domes has the most potential significance the similarity of the results from the three component data and from the vertical component data implies that vertical component data which are generally more abundant can be used with confidence

crustal structure beneath long valley caldera from modeling of teleseismic p wave polarizations and ps converted waves in this study the authors present new constraints on the nature of the low velocity zone beneath long valley caldera based on the measured propagation directions of teleseismic p waves and on modeling of p to s converted waves the low velocity body is a large asymmetrical volume which deepens to the east extending from depths of 7 to 30 km it contains lower velocities than originally proposed by earlier teleseismic studies in particular there is a tabular feature between 7 and 11 km depth that has a reduction in velocity of about 30 these low velocities imply a much greater percentage of melt in the crust beneath long valley caldera than previously estimated array analysis of large delayed arrivals identifies them to be ps converted waves from the shoulders and roof of this tabular zone these conversions bound the depth to the magma chamber roof to be within about 10 km of the surface these results are consistent with elements from several other studies and the authors present an integrated and improved model of crustal structure at long valley the concordance of the deeper low velocity zones with regional structural trends implies that the shallow low velocity feature is a cupola on topmore of an asymmetric diapiric ridge rising up from the migmatized lower crust of the basin and range the authors present two contrasting interpretations of the geometry of low velocity zones in the crust one implies a time invariant magma chamber and conduit system for long valley caldera the other implies an evolution of that system from a simple vertical regime to its current asymmetrical geometry 37 refs 19 figs 1 tab less

the depositional environments and tectonic development of a mesozoic intra arc basin atacama region chile a thick succession of continental redbeds was deposited in a 50 km wide intra arc basin on the andean active continental margin in the atacama region of northern chile during early cretaceous times upper jurassic to early cretaceous marine limestones were buried by the seaward progradation of a succession of coastal dunes saline lakes and sandflats aeolian dune fields migrating towards the east across these coastal plains became stabilized by the growth of vegetation interdune alluvial areas between the sand dunes and dune fields developed into extensive alluvial braid plains which were in turn superimposed by alluvial fans these fans were inundated by a regionally extensive saline lake produced by tectonic or volcanic damming of the sedimentary basin this lake dried up leaving a large area of playa lake mudflats the climate was warm and semi arid with a low and seasonal rainfall parts of the area supported a substantial vegetation of woody plants together with a vertebrate fauna of dinosaurs pterosaurs and crocodiles the continental redbeds were derived from a volcanic source and were deposited on continental crust in a deep but narrow north south elongated fault bounded graben this extensional basin formed in an intra arc setting within an active andesitic volcanic chain upwards coarsening sedimentary successions were the product of uplift of the fault bounded margins of the basin

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

cross stratification parallel protosols west bengal india an eolian signature abstract the periodic occurrence of paleosols along cross stratifications are widely known in pleistocene eolian dunes particularly in coastal ones and these are believed to have formed during pauses in the migration of the dunes over thousands of years protosols with the same relationship have been observed in subrecent dunes at bakkhali beach west bengal india calculation of the annual rate of migration of the dunes reveals that the protosols formed during a seasonal decline in wind velocity because comparable seasonal aerodynamic variability exists in many parts of the world such annual protosols in eolian dunes are likely to be widespread particularly in warm and humid areas cross stratification parallel paleosols being unknown in aqueous bedforms provide potential tools for recognizing eolian dune deposits in the rock record mature paleosols apparently require long term climatic cycles such as those witnessed in glacial ages and thus are not likely to be very common in the stratigraphic record whereas the seasonal protosols are extreme subtleness of most other eolian features makes these paleosol marked reactivation surfaces especially significant in recognition of ancient eolian dune deposits

controls on fluvial deposition in mixed fluvial and aeolian facies within the tumblagooda sandstone late silurian of western australia abstract the tumblagooda sandstone late silurian of western australia was deposited dominantly by fluvial processes on a palaeoslope to the northwest interbedded fluvial and aeolian sandsheet deposits occur within the formation in which winds blowing obliquely up the palaeoslope to the southeast reworked the sandy unvegetated and unconsolidated surface into aeolian sandsheets and small parallel crested aeolian dunes with ne sw crest lines the water table was generally high but flashy river discharge resulted in deposition of thin up to 3 m laterally extensive hundreds to thousands of metres sheets of medium coarse sandstone with dominant trough cross bedding and subordinate planar cross bedding and parallel laminated beds in the absence of vegetation and levees floods were virtually unconfined and current directions are locally unimodal with narrow variation flood waters were sometimes diverted by aeolian surface morphology similar mixed fluvial and aeolian environments are considered to have been frequent in a wide range of climatic regimes prior to the advent of abundant land plants

p wave velocity variations in the coso region california derived from local earthquake travel times inversion of 4036 p wave travel time residuals from 429 local earthquakes using a tomographic scheme provides information about three dimensional upper crustal velocity variations in the indian wells valley coso region of southeastern california the residuals are calculated relative to a coso specific velocity model corrected for station elevation weighted and back projected along their ray paths through models defined with layers of blocks slowness variations in the surface layer reflect local geology including slow velocities for the sedimentary basins of indian wells and rose valleys and relatively fast velocities for the sierra nevada and argus mountains in the depth range of 3 5 km the inversion images an area of reduced compressional velocity in western and northern indian wells valley but finds no major velocity variations beneath the coso volcanic field to the north these results are consistent with a recent study of anomalous shear wave attenuation in the coso region between 5 and 10 km depth low velocity areas 7 slow appear at the southern end of the coso volcanics reaching east to the coso basin numerical tests of the inversion s resolution and sensitivity to noise indicate that these major anomalies are significant and well resolved while other apparent velocity variations in poorly sampled areas are probably artifacts the seismic data alone are not sufficient to uniquely characterize the physical state of these low velocity regions because of the coso region s history of pleistocene bimodal volcanism high heat flow geothermal activity geodetic deformation and seismic activity one possibility is to link the zones of decreased p velocity to contemporary magmatic activity

controls on spatial and temporal distribution of precambrian eolianites abstract inversely graded stratification generated by the migration of wind ripples and adhesion structures permit unequivocal identification of precambrian eolianites these criteria in combination with scale of cross beds angle of inclination of foresets geometry of depositional units and associated non eolian facies are used to discriminate between precambrian dune draa dune plinth sand sheet and interdune deposits that formed in inland and coastal settings based on an analysis of published literature fundamental conclusions can be drawn on the spatial and temporal distribution of precambrian eolianites the oldest reported eolianites are from the ca 2 1 ga deweras group in zimbabwe and hurwitz group in canada and numerous examples of eolianites are reported from the 1 8 ga and younger rock record lack of archean and early paleoproterozoic eolianites and their widespread development after 1 8 ga are examined with respect to absence of vegetation crustal growth and tectonic setting relative sea level fluctuations unfavorable atmospheric and or climatic change and non recognition the lack of pre 2 2 ga eolianites may be related to reworking by braided rivers combing across non vegetated floodplains reworking of coastal eolianites during transgression or their non recognition in the early precambrian record the temporal concentration of eolianites at 1 8 ga may best be related to the early stages of breakup and the assembly phases of supercontinents

geophysical and petrological modelling of the structure and composition of the crust and upper mantle in complex geodynamic settings the tyrrhenian sea and surroundings abstract information on the physical and chemical properties of the lithosphere asthenosphere system las can be obtained by geophysical investigation and by studies of petrology geochemistry of magmatic rocks and entrained xenoliths integration of petrological and geophysical studies is particularly useful in geodynamically complex areas characterised by abundant and compositionally variable young magmatism such as in the tyrrhenian sea and surroundings a thin crust less than 10 km overlying a soft mantle where partial melting can reach about 10 is observed for magnaghi vavilov and marsili which belong to the central tyrrhenian sea backarc volcanism where subalkaline rocks dominate similar characteristics are seen for the uppermost crust of ischia a crust about 20 km thick is observed for the majority of the continental volcanoes including amiata vulsini roccamonfina phlegraean fields vesuvius vulture stromboli vulcano lipari etna and ustica a thicker crust is present at albani about 25 km and at cimino vico sabatini about 30 km the structure of the upper mantle in contrast shows striking differences among various volcanic provinces volcanoes of the roman region vulsini sabatini alban hills sit over an upper mantle characterised by vs mostly ranging from about 4 2 to 4 4 km s at the alban hills however slightly lower vs values of about 4 1 km s are detected between 60 and 120 km of depth this parallels the similar and rather homogeneous compositional features of the roman volcanoes whereas the lower vs values detected at the alban hills may reflect the occurrence of small amounts of melts within the mantle in agreement with the younger age of this volcano the axial zone of the apennines where ultrapotassic kamafugitic volcanoes are present has a mantle structure with high velocity lid vs 4 5 km s occurring at the base of a 40 km thick crust beneath the campanian volcanoes of vesuvius and phlegraean fields the mantle structure shows a rigid body dipping westward a feature that continues southward up to the eastern aeolian arc in contrast at ischia the upper mantle contains a shallow low velocity layer vs 3 5 4 0 km s just beneath a thin but complex crust the western aeolian arc and ustica sit over an upper mantle with vs 4 2 4 4 km s although a rigid layer vs 4 55 km s from about 80 to 150 km occurs beneath the western aeolian arc in sardinia no significant differences in the las structure are detected from north to south the petrological geochemical signatures of italian volcanoes show strong variations that allow us to distinguish several magmatic provinces these often coincide with mantle sectors identified by vs tomography for instance the roman volcanoes show remarkable similar petrological and geochemical characteristics mirroring similar structure of the las the structure and geochemical isotopic composition of the upper mantle change significantly when we move to the stromboli campanian volcanoes the geochemical signatures of ischia and procida volcanoes are similar to other campanian centres but sr pb isotopic ratios are lower marking a transition to the backarc mantle of the central tyrrhenian sea the structural variations from stromboli to the central vulcano and lipari and western aeolian arc are accompanied by strong variations of geochemical signatures such as a decrease of sr isotope ratios and an increase of nd pb isotope and lile hfse ratios the dominance of mafic subalkaline magmatism in the tyrrhenian sea basin denotes large degrees of partial melting well in agreement with the soft characteristics of the uppermost mantle in this area in contrast striking isotopic differences of plio quaternary volcanic rocks from southern to northern sardinia does not find a match in the las geophysical characteristics the combination of petrological and geophysical constraints allows us to propose a 3d schematic geodynamic model of the tyrrhenian basin and bordering volcanic areas including the subduction of the ionian adria lithosphere in the southern tyrrhenian sea and to place constraints on the geodynamic evolution of the whole region

holocene lake deposits and palaeoenvironments in central sahara northeastern mali abstract extensive and fossiliferous lacustrine deposits have been found in a now hyperarid area south of the tanezrouft 20 30 21 n 1 w between the erg ine sakane and the djebel takabart the assemblage of fish molluscs ostracods and charophytes among which lychnothamnus is observed in africa for the first time testify to fresh water conditions however stable carbon and oxygen isotopic values provide evidence for phases of strong evaporation the presence of limicolaria sp a terrestrial pulmonate first observed in the sahara indicate permanent soil humidity around the palaeolake s the remains of large steppe type mammals elephant antelopes buffalo as well as neolithic sites and burials in brown soils also contribute to evidence a northward shift of the sahel belt 3 4 in latitude this period is radiocarbon dated from 6130 180 b p to 7520 70 b p on molluscan shells the human material could be younger 3750 100 b p on charcoal

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

absence of evidence for a shallow magma chamber beneath long valley caldera california in downhole and surface seismograms a downhole seismometer at 900 m depth and a temporary network of surface stations were deployed to use rays from local microearthquakes to study the upper and middle crust beneath the long valley caldera the downhole seismograms show s waves with high apparent amplitudes from earthquakes located 2 20 km to the south of the downhole seismometer in contrast s waves from earthquakes located in the distance range 20 30 km to the south have low apparent amplitudes if p and s amplitudes are normalized relative to the respective coda amplitudes the s to coda amplitude ratios appear to remain constant but the p to coda amplitude ratios vary significantly with takeoff angle a comparison of the calculated radiation patterns for a double couple in a uniform halfspace and focal mechanisms of the recorded earthquakes suggest that the observed variations in p and s amplitudes are caused by radiation pattern effects reanalysis of possible travel time delays found by elbring and rundle 1986 who used a subset of the borehole data analyzed in this study shows that they underestimated the epicentral distances to three of the earthquakes and hence generated an artificial kink in the reduced travel time versus depth curve synthetic calculations of reduced travel time versus depth suggest that an apparent velocity of 5 7 km s gives less scatter than 6 0 km s used by elbring and rundle 1986 plots of ts tp versus depth show that contrary to the findings of elbring and rundle 1986 the vp vs ratio stays fairly constant with depth and a small 3 km diameter magma chamber cannot easily be resolved furthermore combined analysis of downhole and surface data shows that neither data set requires a low velocity zone or a zone of anomalously high vp vs at depth below the casa diablo area

seismic attenuation at rabaul volcano papua new guinea abstract the attenuation structure around rabaul volcano new britain papua new guinea is studied using broadband records from a pair of sites inside and outside of the rabaul caldera complex using regional earthquakes estimates of attenuation for p and s waves between 0 5 and 5 hz indicate that near surface rocks within the caldera complex are significantly more attenuative than outside the caldera the average strength of this anomaly is defined in terms of t s 0 2 s over and above the region outside the caldera t s is the time integral of the inverse quality factor of attenuation in this case along the path of a shear wave this attenuation anomaly appears to be strongest at depth and to the south of the kaivuna site in the northern part of the caldera complex the ratio of attenuation estimates for p and s waves is t s t p 2 7 indicating that intrinsic attenuation contributes significantly to the process of attenuation no frequency dependence of the quality factor is resolved within this frequency band path averaged lithospheric attenuation is estimated from s p spectral ratios at both stations yielding quality factors on average q 180 but possibly significantly lower around and below the volcano shear waves are observed along paths passing underneath the central southern caldera at depths greater than about 5 km although they are strongly attenuated this indicates that they have not passed through a large extensively molten body

the pennsylvanian pewamo formation and associated haybridge strata toward the resolution of the jurassic ionia red bed problem in the michigan basin u s a abstract two distinct and newly recognized formation scale stratigraphic units predominantly red bed sandstones and shales are found on the surface and in the shallow subsurface of the central michigan region here we use core field and laboratory observations to document these strata which we propose as one new formation the pewamo formation the pewamo formation consists of eolian quartz sandstones with red coloration due to iron oxide diagenesis and interbedded interdune lacustrine siliciclastic mudstones we also describe for the first time the haybridge strata which contains red sandstones red and gray shales and coal and has plant fossils and paleosol features macroscopic plant fossils and palynomorphs suggest a pennsylvanian age for both units these newly described continental deposits provide data about past environments life and climate for the late carboniferous of michigan in addition this study is an evaluation of michigan s controversial jurassic red beds and ionia sandstone

phase relations and fractionation sequences in potassic magma series modelled in the system camgsi 2 o 6 kalsio 4 mg 2 sio 4 sio 2 f 2 o 1 at 1 bar to 18 kbar liquidus phase relations in the system diopside kalsilite forsterite quartz with 3 wt f were examined at 1 bar and the locations of important invariant points were determined at 18 kbar at all pressures within this range a large liquidus field for fluorphlogopite phl exists and has a large influence on both melting and fractionation processes one eutectic point was found to the silica rich side of the plane lc fo di at di1ks30fo2qz67 where a melt coexists with san qz phl and di at 840 c and 1 bar another eutectic point must exist in the silica poor part of the system because the phase topology determines that thermal barriers must exist at this point a feldspathoid either lc or ks must coexist with fo phl and a ca bearing phase such as di the exact location and phase assemblage were not determined but the equilibrium melt must have a composition rich in di 29 wt and extremely poor in qz 8 wt the composition of the first eutectic moves towards lower sio2 contents with increasing pressure di3ks40fo1qz56 at 18 kbar whereas the second does not exist at 18 kbar due to the disappearance of lc as a stable liquidus phase liquids which coexist with mafic minerals such as en fo phl and di are important for the genesis of potassium rich mafic rocks by partial melting in the mantle and for the early stages of fractional crystallisation the equilibrium melt at the invariant point fo en phl di l at 1125 c is very poor in fo and di components at atmospheric pressure di5ks37fo5qz53 whereas at 18 kbar the melt contains large amounts of fo and di di19ks31 fo28qz21 and has a composition close to that of natural lamproites kamafugites do not correspond to melts in this system under any of the studied conditions and appear to require co2 in the source fractionation processes from primitive potassic basanite melts are controlled principally by the size and not the mere presence of the liquidus phase field for phlogopite at high pressures where the phl field is large olivine is eliminated early from the fractionating assemblage and cpx phl fractionation may lead to relatively silica rich rock differentiates such as trachytes at low pressures extensive olivine and restricted phl crystallisation prevents silica enrichment in the melt resulting in phonolitic differentiates later crystallisation of alkali feldspar accentuates the trends laid down in the early stages of fractionation

runoff induced sediment yield over dune slopes in the negev desert 1 quantity and variability although extensive data exist on runoff erosion and rates for non sandy hillslopes data for arid dune slopes are scarce owing to the widespread perception that the high infiltrability of sand will reduce runoff however runoff is generated on sandy dunes in the hallamish dune field western negev desert israel p 95 mm due to the presence of a thin usually 1 3 mm microbiotic crust the runoff in turn produces erosion sediment yield was measured on ten plots 140 1640 m2 on the north and south facing slopes of longitudinal dunes two plots facing north and two facing south were subdivided into three subplots the subplots represented the crest of the active dune devoid of crust the extensively crusted footslope of the dune and the midslope section characterized by a patchy crust the remaining plots extended the full length of the dune slope no runoff and consequently no water eroded sediments were obtained from the crest subplots devoid of crust however runoff and sediment were obtained from the mid and footslope crusted subplots sediment yield from the footslope subplots was much higher than from the midslopes despite the higher sediment concentration that characterized the midslope subplots the mean annual sediment yield at the hallamish dune field was 432 g per metre width and was associated with high average annual concentrations of 32 g l 1 the data indicate that owing to the presence of a thin microbiotic crust runoff and water erosion may occur even within arid sandy dune fields copyright 2001 john wiley sons ltd

conditions favourable for the formation of warm climate aeolian sand sheets aeolian sand sheets are areas of aeolian sand where dunes with slipfaces are generally absent sand sheets are ubiquitous to modern warm climate sand seas generally occurring marginal to dune fields although they may exist within the interior of a sand sea or independent of a dune field sand sheet deposits are recognized in ancient aeolian sequences where they may account for significant accumulations of low angle aeolian stratification we suggest that the occurrence of sand sheets instead of dunes indicates that conditions are outside the range within which dunes form or that one or more factors interfere with dune development while also favouring the accumulation of sand sheets a study of six modern sand sheets in north america located at great sand dunes gran desierto dumont algodones padre island and colorado river delta indicates that the factors favourable for sand sheet development are 1 a high water table 2 surface cementation or binding 3 periodic flooding 4 a significant coarse grained sediment population and 5 vegetation these factors are reflected in the nature of stratification and the accessory features of sand sheet accumulations within the areas of modern sand sheets as well as in their ancient counterparts in the triassic dolores and pennsylvanian permian rico formations

seismic velocity structure and earthquake relocation for the magmatic system beneath long valley caldera eastern california abstract a new three dimensional 3 d seismic velocity model and high precision location catalog for earthquakes between 1984 and 2014 are presented for long valley caldera and its adjacent fault zones in eastern california the simul2000 tomography algorithm is applied to derive the 3 d vp and vp vs models using first arrivals of 1004 composite earthquakes obtained from the original seismic data at the northern california earthquake data center the resulting vp model reflects geological structures and agrees with previous local tomographic studies the simultaneously resolved vp vs model is a major contribution of this study providing an important complement to the vp model for the interpretation of structural heterogeneities and physical properties in the study area the caldera is dominated by low vp anomalies at shallow depths due to postcaldera fill high vp and low vp vs values are resolved from the surface to 3 4 km depth beneath the center of the caldera corresponding to the structural uplift of the resurgent dome an aseismic body with low vp and high vp vs anomalies at 4 2 6 2 km depth below the surface is consistent with the location of partial melt suggested by previous studies based on vp models only and the inflation source locations based on geodetic modeling the sierran crystalline rocks outside the caldera are generally characterized with high vp and low vp vs values the newly resolved velocity model improves absolute location accuracy for the seismicity in the study area and ultimately provides the basis for a high precision earthquake catalog based on similar event cluster analysis and waveform cross correlation data the fine scale velocity structure and precise earthquake relocations are useful for investigating magma sources seismicity and stress interaction and other seismological studies in long valley

attenuation of p and s waves in a magma chamber in long valley caldera california shallow earthquakes around the southwest boundary of long valley caldera west of the hilton creek fault are characterized by lack of s waves at regional seismic network stations to the northwest north and northeast and p waves for these same station event combinations are deficient in frequencies higher than about 2 3 hz earthquakes east of the hilton creek fault and southeast of the caldera have normal p and s wave signatures at the same stations these effects are explained by propagation through a magma chamber in the south central part of long valley caldera at depth greater than 7 8 km

anomalous shear wave attenuation in the shallow crust beneath the coso volcanic region california we use seismograms of local earthquakes to image relative shear wave attenuation structure in the shallow crust beneath the region containing the coso volcanic geothermal area of eastern california sv and p wave amplitudes were measured from vertical component seismograms of earthquakes that occurred in the cososouthem sierra nevada region from july 1983 to august 1985 seismograms of 16 small earthquakes show sv amplitudes which are greatly diminished at some azimuths and takeoff angles indicating strong lateral variations in s wave attenuation in the area three dimensional images of the relative s wave attenuation structure are obtained from forward modeling and a back projection inversion of the amplitude data the results indicate regions within a 20 by 30 by 10 km volume of the shallow crust one shallower than 5 km that severely attenuate sv waves passing through them these anomalies lie beneath the indian wells valley 30 km south of the coso volcanic field and are coincident with the epicentral locations of recent earthquake swarms no anomalous attenuation is seen beneath the coso volcanic field above about 5 km depth geologic relations and the coincidence of anomalously slow p wave velocities suggest that the attenuation anomalies may be related to magmatism along the eastern sierra front

aeolian beach ridges and their significance for climate and sea level concept and insight from the levant coast east mediterranean abstract relict beach ridges of aeolian origin and associated soils are often used for inferring relative sea level and climate with contrasting results most studies link the aeolian coastal deposits to regressive phases some to high sea level stands and a few to intermediate relative sea level positions we interpret the apparent contradictions as indicating the lack of an over arching concept and the inconsistent usage of sea level related terms in this paper we present an integrated morpho sedimentological concept for a microtidal mid latitudinal coast and review existing data from the levant east mediterranean coast to evaluate the concept and to eliminate nomenclatural confusion a coastal depositional environment in a semi arid environment consists of shallow marine aeolian and alluvial facies which together form an aeolian beach ridge complex as a package of strata which respond simultaneously to sea level change a transgressive complex forms through reworking or overstepping of the coastal foredune and a regressive complex forms by downstepping under transgression the aeolian beach ridge represents the highstand deposit and its adjacent shallow marine sediment is the transgressive deposit under regression the complex represents the falling stage and the associated downdip surface marks the lowstand on the levant coast we find chronologically well constrained offlapping aeolian beach ridges as parts of six downstepping beach ridge complexes formed between 200 ka and 10 ka the complexes represent the falling stage systems tract fsst of a short lived 5th order depositional sequence when the shoreline shifted from a position close to the modern coastline to the shelf or below the shelf edge three of these fssts and their up dip and down dip super bounding surface together form the 4th order 100 ka sequence of the last interglacial glacial cycle the absence of transgressive highstand and lowstand systems tract is explained by the poor preservation potential due to the small sediment budget of the complex the falling stage complex has a high preservation potential because sediment source area increases while the sand drift potential remains above the local threshold on the levant coast sand delivery to the backshore continued during relative sea level falls for distances of up to 10 km between dune and coastline which is unprecedented in most modern analogues the significance of the dune soil succession for climate is limited because the dunes are governed by relative sea level change the vegetation response to changes in precipitation is non linear and the dune dynamics are characterised by low resilience and hysteresis

time dependent geochemistry of clinopyroxene from the alban hills central italy clues to the source and evolution of ultrapotassic magmas abstract we investigated chemical and isotopic compositions of clinopyroxene crystals from well age constrained juvenile scoria clasts lava flows and hypoabyssal magmatic ejecta representative of the whole eruptive history of the alban hills volcanic district the alban hills is a quaternary ultra potassic district that was emplaced into thick limestone units along the tyrrhenian margin of italy alban hills volcanic products even the most differentiated are characterised by low sio2 content we suggest that the low silica activity in evolving magmas can be ultimately due to a decarbonation process occurring at the magma limestone interface according to the liquid line of descent we propose the differentiation process is driven by crystallisation of clinopyroxene leucite apatite magnetite coupled with assimilation of a small amount of calcite and or with interaction with crustal co2 by combining age chemical data strontium and oxygen isotopic compositions and ree content of clinopyroxene we give insights into the evolution of primitive ultrapotassic magmas of the alban hills volcanic district over an elapsed period of about 600 kyr geochemical features of clinopyroxene crystals consistent with data coming from other italian ultrapotassic magmas indicate that alban hills primary magmas were generated from a metasomatized lithospheric mantle source in addition our study shows that the 87sr 86sr and lree hree of alban hills magmas continuously diminished during the 600 35 ka time interval of the alban hills eruptive history possibly reflecting the progressive depletion of the metasomatized mantle source of magmas

characterization of fluvial deposits interbedded with flood basalts neoproterozoic catoctin formation central appalachians usa abstract the catoctin formation infills a neoproterozoic age rift basin associated with the development of the laurentian continental margin one of several similar basins that are distributed along the length of the southern to central appalachian basin the catoctin formation consists of a flood basalt sequence with intercalated sedimentary deposits two types of architectural elements channel element ce and sheet element se are recognized within these sedimentary deposits massive structureless sandstones and conglomerates are the dominant facies within the ce and se and are interpreted to record deposition from hyperconcentrated flows lack of vegetative binding of sediment coupled with a relatively high stream gradient and possibly a high water table enhanced the probability of developing hyperconcentrated flows by the process of bulking addition of sediment to a flow additional facies present are the products of normal stream flow that developed from waning hyperconcentrated flows basaltic effusive rate sediment supply and extension subsidence controlled the generation of ce and se all ce reflect deposition in isolated fluvial channels incised into lava flows and are present within the lower member of the catoctin formation the presence of ce most likely indicates a high rate of lava extrusion low sediment supply and possible high subsidence rates the se composing the sedimentary member of the catoctin formation reflects a decrease in effusive and subsidence rates and a increase in sediment supply from the hinterland overlying the se is the last phase of basin infill characterized by basalts with minor interbedded clastic rocks the final phase of infilling was effected by an increase of effusive and subsidence rates and a potential cutoff of sediment supply the catoctin formation basin displays a more complex infill history than generally associated with the rift deposits of the laurentian margin

geometry of magma bodies beneath long valley california determined from anomalous earthquake signals one hundred and ninety two small earthquakes which occurred recently near the southern edge of long valley caldera at depths from 1 to 13 km are used to map the subsurface geometry of magma bodies in the caldera seismograms of these events recorded northwest north northeast and east of long valley with ray paths through the caldera are often anomalous in that s wave arrivals are absent and high frequency p wave energy is missing these anomalous ray paths intersect in an area of the south central caldera which we interpret to be a region of molten or partially molten rock this magma body lies between about 4 1 2 and at least 13 km depth and is 10 km long by 5 km wide beneath 7 km the magma appears to be relatively contiguous below 7 km and more dispersed above another magma body may be present in the northwest caldera coincident with an interpreted 7 8 km deep reflection from the top of a magma chamber

radiocarbon chronology of holocene hydrologic changes in northeastern mali abstract a detailed chronology of hydrological changes that occurred in northeastern mali during the holocene is based on approximately 30 14 c dates of molluscs which were collected from the lacustrine and paludal deposits of the ine sakane sand sea the presence of cemented paleodunes indicates that the end of the pleistocene was and arid period this was followed by an early holocene lacustrine episode ca 9500 6500 yr b p during which numerous lakes occupied depressions formed in the cretaceous limestones and between the sand ridges these lakes reflect a significant rise in the water table between ca 6500 and 5500 yr b p the lakes dried up although the water table remained close to the ground surface in several areas calcareous concretions formed at the water table fringe during this time thereby fossilizing some of the middle holocene dunes a second lacustrine episode is dated between ca 5500 and 4500 yr b p it corresponds to the establishment of numerous neolithic settlements in the area arid conditions have developed since about 4500 yr b p to attain the conditions of the present day the isotopic composition 18 o and 13 c of the fauna reflects highly variable hydrological conditions groundwaters were recharged by precipitation which was occasionally very depleted in heavy oxygen 18 o 13 evaporation induced an enrichment in 18 o high concentrations characterize some lakes the 13 c content of fossil shells reflect 1 species ecological requirements 2 isotopic composition of the total inorganic dissolved carbon tidc in groundwaters and 3 the lake metabolism

seismic tomography of compressional wave attenuation structure for kilauea volcano hawai i we present a frequency independent three dimensional 3 d compressional wave attenuation model indicated by the reciprocal of quality factor qp for kilauea volcano in hawai i we apply the simul2000 tomographic algorithm to the attenuation operator t values for the inversion of qp perturbations through a recent 3 d seismic velocity model and earthquake location catalog the t values are measured from amplitude spectra of 26708 p wave arrivals of 1036 events recorded by 61 seismic stations at the hawaiian volcanology observatory the 3 d qp model has a uniform horizontal grid spacing of 3 km and the vertical node intervals range between 2 and 10 km down to 35 km depth in general the resolved qp values increase with depth and there is a correlation between seismic activity and low qp values the area beneath the summit caldera is dominated by low qp anomalies throughout the entire resolved depth range the southwest rift zone and the east rift zone exhibit very high qp values at about 9 km depth whereas the shallow depths are characterized with low qp anomalies comparable with those in the summit area the seismic zones and fault systems generally display relatively high qp values relative to the summit the newly developed qp model provides an important complement to the existing velocity models for exploring the magmatic system and evaluating and interpreting intrinsic physical properties of the rocks in the study area

applications of attenuation tomography to imperial valley and coso indian wells region southern california spatial variations in seismic wave attenuation were tomographically imaged from observed s to p wave amplitude ratios in the imperial valley and coso indian wells regions of southern california in the coso indian wells region a highly attenuating body s wave quality factor q 30 coincides with a slow p wave anomaly mapped by walck and clayton 1987 this coincidence suggests the presence of a 3 to 5 km depth magmatic or hydrothermal body in the indian wells region in the imperial alley slow p wave travel time anomalies and highly attenuating s wave anomalies were found in the brawicy seismic zone at a depth of 8 12 kin the effective s wave quality factor is very low q 20 and the p wave velocity is 10 slower than the surrounding area these results suggest either magmatic or hydrothermal intrusions or fractures at depth possibly related to active shear in the brawley seismic zone this attenuation tomographic technique is shown to be useful in delineating the spatial variations in seismic wave attenuation and in estimating the effective seismic quality factor of attenuation anomalies

great sand sea and selima sand sheet eastern sahara geochronology of desertification the relation of playa sediments and associated archeological sites with longitudinal dunes allows estimation of ages for the two uppermost strata of the great sand sea active dune formation corresponds with interpluvial periods of hyperaridity dune stability corresponds with semiarid pluvial periods archeological sites associated with truncated paleosols in the selima sand sheet suggest a similar climatic relation and indicate that the isohyets of central sudan shifted at least 400 kilometers northward during the peak of pluvials

sedimentary cycles in a mesoproterozoic aeolian erg margin succession mangabeira formation espinhaco supergroup brazil aeolian systems were abundant and widespread in the early proterozoic post 2 2 ga however the majority of aeolian successions of such great age are intensely deformed and are preserved only in a fragmentary state meaning that hitherto few attempts have been made to apply a sequence stratigraphic approach to determine mechanisms of aeolian construction accumulation and preservation in such systems the mangabeira formation is a well preserved mesoproterozoic erg successions covering part of the sao francisco craton northeastern brazil the lower unit of the mangabeira formation 500 m thick comprises aeolian deposits of dune interdune and sand sheet origin as well as some of waterlain origin these deposits are organized into vertically stacked depositional cycles each 6 to 20 m thick and characterized by aeolian sandsheet and waterlain deposits succeeded by aeolian dune and interdune deposits indicative of a drying upward trend aeolian cross strata exhibit a mean dip direction to the north each of these cycles likely arose in response to climatic oscillation from relatively humid to arid conditions possibly related to orbital forcing the lower unit of the mangabeira formation comprises up to 14 erg sequences the accumulation and preservation of each was determined by the relative rate of water table rise and the availability of sand for aeolian transport both of which changed through time resulting in the preservation of a succession of repeated drying upward cycles

seismological evidence for magmatic and hydrothermal structure in long valley caldera from local earthquake attenuation and velocity tomography we compare the results of six different tomographic inversions for the three dimensional seismic attenuation and velocity structure in long valley caldera california in order to constrain interpretations on the location and character of magmatic and geothermal structure in the caldera crust p and s wave amplitudes and arrival times obtained in previous studies from seismograms of local earthquakes recorded on vertical and three component seismographis were inverted for q sv 1 q sh 1 q s 1 q p 1 and v p v s in the upper 9 km of teh caldera crust detailed comparisons of the results of the inversions suggest significant locations of high temperatures and perhaps magma and hydrothermal zones in the caldera a region of low q s with locally variable q p and v p v s is imaged in the 7 9 km depth range beneath the resurgent dome overlying and adjacent to this anomaly are significant low q p and low v p v s anomalies as well as smaller zones of low q s and high v p v s together these suggest zones of high temperature magma below and adjacent to zones of supercritical hydrothermal fluids at 4 5 km depth along the southern rim of the caldera just east of mammoth mountain a significant anomaly with relatively low q p and relatively low v p v s is imaged and is interpreted as a supercritical hydrothermal zone poorly resolved relatively low q p and relatively high v p v s are seen at 4 5 km depth beneath the inyo craters suggesting possible high temperatures and perhaps magma because of lack of data in the individual inversions the resultant images have spatially variable error and resolution however by comparing multiple images of different seismic parameters we have improved our ability to determine the significance of an constrain interpretation of seismic structure anomalies

location and configuration of magma bodies beneath long valley california determined from anomalous earthquake signals recordings of 281 small earthquakes which occurred recently near the southern edge of long valley caldera at depths from 1 to 15 km are used to map the subsurface geometry of shear wave attenuating bodies in the caldera signatures of these events recorded northwest north northeast and east of long valley with ray paths through the caldera are often anomalous in that s wave arrivals have very low amplitudes and high frequency p and s wave energy is missing for the same station event combinations the volcanic and geothermal history of the region suggests that ray paths for these anomalous signals have passed through magma which absorbed much of the s wave energy and also attenuated the higher frequencies with over 1200 normal and anomalous ray paths through the caldera we have located two apparently massive magma bodies in the central and northwest caldera as well as two more dispersed magma areas in the southern caldera and beneath crowley lake the central magma body extends from 4 5 to at least 13 km beneath the surface and the northwest body is as shallow as 5 5 km these two magma bodies are probably connected below about 8 km secondary arrivals seen on select seismograms are tentatively interpreted as reverberations inside the central magma chamber and are consistent with the interpreted lateral extent of the magma the northwest and central magma bodies lie beneath the northwest and southeast corners of the caldera s resurgent dome and probably connect beneath the dome s center also the shallower parts of these magma bodies and the southern anomalous area lie beneath the surface expression of the medial graben faults suggesting that structural features seen at the surface of the valley may be related to magma location at depth

amalgamated interdune deposits white sands new mexico abstract cores taken by mckee and moiola 1975 from white sands dune field indicate that interdune areas are underlain by 7 0 10 4 m of clastic gypsum deposits clean sand bodies as much as 4 5 m thick are separated by thin beds of silly sand mckee and moiola interpreted the sequence to be the product of climbing bed forms interdune silty sands were interpreted to be deposited upon truncated dune sands and to be soon buried by the next wave of advancing dunes if the dunes are climbing in such a manner a pinchout of interdune sediments downwind across interdune surfaces is required the thickness of the silly sands should be related to the size of the interdune area and the rate of dune migration we tested this autocyclic hypothesis by trenching the length of the interdune areas in both t e barchanoid and transverse dunes trenches revealed that interdune deposits form flat lying sheets which extend uninterrupted to positions directly beneath the windward slopes of dunes at the downwind end of each interdune area this relationship precludes the possibility that under present conditions thick dune sands are being preserved because there is little or no net accumulation of dune sand interdune deposits are being amalgamated thin lenses of dune sediment exposed on the wall of one trench show that a minimum of three interdune deposits have been fused to form the uppermost 30 cm of the interdune deposit clean sand in the cores may have accumulated during periods when sediment supply was greater than at present silly sediments accumulated during periods when as in the p esent sand supply was limited and dunes did not climb appreciably future studies of modern and ancient eolian sediments should attempt to document whether the interdune deposits represent deposition within single interdune areas or amalgamation of several discrete deposits