patterns of fault displacement and strain at yucca mountain nevada abstract yucca mountain nevada is the sole candidate site for underground disposal of high level radioactive waste in the united states the mountain is composed of tertiary 12 8 11 6 ma volcanic tuff cut by west dipping normal faults that divide the mountain into north trending east dipping cuestas geologic characterization of yucca mountain by the u s department of energy doe has focused on mapping lithostratigraphic units faults including single plane small displacement surfaces of discontinuity and large displacement fault zones and fractures quasi planar zones that have experienced loss of cohesion including joints partially mineralized joints veins and small displacement faults faults and fractures are important to repository design because they affect seismic hazard rockfall and fluid transmissivity in the surrounding rock mass geologic maps and detailed studies of rock pavements and tunnel walls reveal that faults and fractures within yucca mountain are not uniform in orientation or intensity we investigate two aspects of distributed deformation arising from fault displacement patterns at yucca mountain first fault parallel strains elongation parallel to cutoff lines where stratigraphic horizons intersect fault planes develop as a result of lateral fault displacement gradients using existing data we analyze the likely state of strain in fault blocks at yucca mountain second fault strike perpendicular strains can develop where two normal faults propagate past each other a component of the total strain is distributed into the surrounding rock to produce synthetic layer dip or a network of smaller faults and fractures we find that small scale faulting and fracturing at yucca mountain is variable and is strongly controlled by larger scale fault system architecture

relief inversion in the geomorphological evolution of sub saharan west africa abstract the geomorphology of much of sub saharan west africa is dominated by the presence of plateaux and plains with ferruginous and locally aluminous bauxitic duricrusts the plateaux occur at different elevations and have been correlated as two or more palaeosurfaces across much of the region the duricrusts have generally been considered to be residual formed by conformable erosion and chemical wasting of immediately underlying bedrock this concept has been central to interpretations as diverse as the formation and evolution of the landscape and the development of geochemical exploration models recent regolith landform mapping field observations and experience from mineral exploration in southern mali and burkina faso however demonstrate that the duricrusts are mainly ferricretes i e fe oxide cemented sediments these observations require a re interpretation of the geomorphological evolution of the region during the cenozoic the landscape has evolved by several cycles of weathering and erosion deposition triggered by climatic tectonic or other environmental changes it is proposed that an initial bauxitic lateritic regolith was partly eroded following uplift and or a change to a more arid climate and that the detritus rather than being removed was deposited on slopes and valleys during a subsequent humid period of lateritic weathering fe oxide cementation of this detritus formed ferricrete dehydration and hardening of the ferricrete after further uplift or aridity increased its resistance to erosion resulting in relief inversion with the detritus in turn being deposited downslope this too has been weathered and cemented to form a younger ferricrete the occurrence of ferricrete landforms in adjacent countries noted by field observation and inferred from satellite imagery demonstrates that relief inversion is a very widespread and important phenomenon in southern mali burkina faso and adjacent countries in semi arid west africa

magnetostratigraphic constraints on the age of the lower beaufort group western karoo basin south africa and a critical analysis of existing u pb geochronological data we studied three partially overlapping sections with a composite thickness of 600 m in the upper permian fluvial siltstones and fine grained sandstones of the abrahamskraal formation the basal unit of the beaufort group in the karoo basin of western cape province south africa paleomagnetic analysis reveals three components of natural remanent magnetization nrm heating to 180 c removes a remanent magnetization parallel to the present day field which is interpreted as a viscous overprint an intermediate unblocking temperature component is removed by heating to 450 c this direction is always of normal polarity and is identical to a regional overprint imparted during the early jurassic emplacement of the karoo large igneous province a high temperature component isolated above 450 c is of dual polarity and is interpreted as primary on the basis of a positive reversals test the virtual geomagnetic pole position for the abrahamskraal formation computed from the average high temperature characteristic remanent magnetization direction is in agreement with the late permian directions for stable gondwana and with previous results from the lowermost abrahamskraal formation and waterford formation at the ouberg pass section the predominantly normal polarity of this magnetization is in agreement with either a middle late lopingian age ca 254 256 ma or a late guadalupian age ca 262 ma according to the global geomagnetic polarity time scale we integrate these new results with existing magnetostratigraphic biostratigraphic and geochronological results from the karoo basin with particular emphasis on the controversy over zircon age data reported from the underlying ecca group

interpreting avulsion process from ancient alluvial sequences guadalope matarranya system northern spain and wasatch formation western colorado alluvial deposits of the guadalope matarranya system oligocene ebro basin spain and the wasatch formation eocene western colorado provide time integrated records of the process of river channel avulsion these sequences consist of isolated channel belt sandstones incised into and abruptly overlain by flood plain siltstones indicating deposition by avulsive river systems the geometry and distribution of channel incisions suggest that avulsion was not controlled by tectonics climate or base level changes but formed by autocyclic processes measurements from 221 channel fills in the guadalope matarranya system and 38 from the wasatch formation allow us to statistically characterize channel geometries we infer to be associated with establishment and abandonment of individual river avulsions paleoflow depths in both systems average 1 4 to 1 6 m aggradation height superelevation of channel margin levees are on average 0 6 and 1 1 times paleoflow depth in the guadalope matarranya and wasatch systems respectively these results are consistent with values from recently avulsed modern rivers and suggest that 1 flow depth is the appropriate parameter against which to scale the critical superelevation necessary for channel avulsion and 2 the increase in potential energy due to channel perching drives the lateral instability that is needed for avulsion to be successful numerous stacked channel fills indicate repeated reoccupation of the same site by avulsing channels these reoccupation channels indicate that inherited flood plain topography here abandoned channel forms was an important control on the arrival site of newly avulsed channels comparison of our results to others suggests two end member types of avulsion can take place incisional avulsion seen here is characterized by an early incision phase followed by infilling by migrating bar forms aggradational avulsion begins with aggradation followed in time by stream integration into a single downcutting channel we suggest that the type of avulsion is strongly influenced by whether or not the adjacent flood plain is well or poorly drained in both cases subsequent aggradation and channel perching increase the chances that some triggering event will lead to avulsion

tectonic implications of a dense continuous gps velocity field at yucca mountain nevada 1 a dense continuous gps network was established in the yucca mountain area in 1999 to provide the most reliable measurements possible of geodetic strain patterns across the nation s only proposed permanent repository for high level radioactive waste the network lies astride a boundary between the geodetically stable central great basin and the active western great basin which at the latitude of yucca mountain is undergoing distributed right lateral shear at a rate of 60 nstrain yr monitoring from 1999 to 2003 3 75 years yields a velocity field characterized by nearly homogenous n20 w rightlateral shear of 20 2 nstrain yr net velocity contrast of 1 2 mm yr across a 60 km aperture in the vicinity of the proposed repository site comparison of time series of continuous results with earlier campaign surveys indicating 50 nstrain yr of westnorthwest extension from 1991 to 1997 suggests that the more rapid rates were in part transient motions associated with the 1992 ms 5 4 little skull mountain earthquake postseismic motions do not appear to affect the 1999 2003 velocity field in either campaign or continuous data the magnitude of the velocity contrast across the area the overall linearity of the gradient and the large area of undeforming crust to the east of yucca mountain are difficult to explain by elastic bending of the crust associated with the death valley fault zone a major right lateral strike slip fault about 50 km west of the repository site these observations along with apparent local variations in the velocity gradient suggest that significant right lateral strain accumulation with displacement rate in the 1 mm yr range may be associated with structures in the yucca mountain area the absence of structures in the area with equivalent late quaternary displacement rates underscores the problem of reconciling discrepancies between geologic and geodetic estimates of deformation rates index terms 1208 geodesy and gravity crustal movements intraplate 8110 1243 geodesy and gravity space geodetic surveys 8107 tectonophysics continental neotectonics 8109 tectonophysics continental tectonics extensional 0905 keywords geodesy tectonics yucca mountain

abnormal monsoon years and their control on erosion and sediment flux in the high arid northwest himalaya abstract the interplay between topography and indian summer monsoon circulation profoundly controls precipitation distribution sediment transport and river discharge along the southern himalayan mountain front shf the higher himalayas form a major orographic barrier that separates humid sectors to the south and arid regions to the north during the indian summer monsoon vortices transport moisture from the bay of bengal swirl along the shf to the northwest and cause heavy rainfall when colliding with the mountain front in the eastern and central parts of the himalaya precipitation measurements derived from passive microwave analysis ssm i show a strong gradient with high values at medium elevations and extensive penetration of moisture along major river valleys into the orogen the end of the monsoonal conveyer belt is near the sutlej valley in the nw himalaya where precipitation is lower and rainfall maxima move to lower elevations this region thus comprises a climatic transition zone that is very sensitive to changes in indian summer monsoon strength to constrain magnitude temporal and spatial distribution of precipitation we analyzed high resolution passive microwave data from the last decade and identified an abnormal monsoon year amy in 2002 during the 2002 amy violent rainstorms conquered orographic barriers and penetrated far into otherwise arid regions in the northwest himalaya at elevations in excess of 3 km asl while precipitation in these regions was significantly increased and triggered extensive erosional processes i e debris flows on sparsely vegetated steep hillslopes mean rainfall along the low to medium elevations was not significantly greater in magnitude this shift may thus play an important role in the overall sediment flux toward the himalayan foreland using extended precipitation and sediment flux records for the last century we show that these events have a decadal recurrence interval during the present day monsoon circulation hence episodically occurring amys control geomorphic processes primarily in the high elevation arid sectors of the orogen while annual recurring monsoonal rainfall distribution dominates erosion in the low to medium elevation parts along the shf

changing fluvial environments across the permian triassic boundary in the karoo basin south africa and possible causes of tetrapod extinctions abstract the karoo supergroup is a 12 km thick succession of sedimentary rocks that accumulated in a large intracratonic retroarc foreland basin in southwestern gondwana the strata record 100 million years of almost continuous sediment accumulation from the permo carboniferous 300 ma through to the early jurassic 190 ma under a range of climatic regimes and within several tectonically controlled sub basins alluvial sediments dominate the succession from the late permian onwards fossils of synapsid reptiles and early dinosaurs are sufficiently common to be used in a ten fold biostratigraphic subdivision of these strata the permian triassic boundary in the karoo succession is marked by a major extinction of the herbivorous dicynodonts which co incides with a rapid change in fluvial facies this study uses field observations of the sedimentary facies palaeosols and in situ fossils of well exposed p tr boundary sequences in the southern karoo basin to provide evidence of environmental changes that may have caused the tetrapod extinctions in the main karoo basin below the p tr boundary sequence the sediments comprise drab greenish grey mudrocks with a few thick 3 12 m multistoried laterally accreted fine grained sandstone bodies the mudrocks host hydromorphic palaeosols with palustrine carbonate horizons and mostly disarticulated skeletal remains of dicynodon assemblage zone fauna above a transition zone of approximately 20 m thickness these strata change into reddish brown mudrocks with numerous thin 0 5 5 m ribbon sandstone bodies and more continuous sheet sandstones calcic palaeosols with rhizocretions nodular horizons and pervasive calcareous encrustation of articulated skeletons of lystrosaurus and associated fauna of the lystrosaurus assemblage zone within a 20 m thick interval of the transitional strata fossils of dicynodon and lystrosaurus occur together the facies transition that co incides with the latest permian dicynodont extinction is interpreted as a change in fluvial style from meandering to low sinuosity channels with general drying of the floodplain habitats and redistribution of vegetation belts the horsetails in particular became significantly reduced in areal distribution the changes in fluvial style in the karoo basin at the end of the permian were triggered by a pulse of thrusting in the southerly source area dated at 247 ma 2 ma which brought about rapid progradation of a large sandy braided fan system the katberg sandstone fm into the central parts of the basin a concomitant basinward migration of depositional environments allowed the lystrosaurus communities that were adapted to dry floodplains to colonise the entire basin to the detriment of most of the wet floodplain dicynodon fauna that lived there

fluvial form in modern continental sedimentary basins distributive fluvial systems comment weissmann et al 2010 1 discuss what they term distributary fluvial systems dfs to address a key question in the earth sciences what modern systems are appropriate analogues to the rock record they conclude since dfss dominate depositional patterns in all continental sedimentary

facies analysis of the kosi megafan deposits abstract the kosi river shows distinct changes in its channel pattern from chatra where the river enters the indogangetic plains to kursela where it joins the ganga river i e gravelly sandy braided zone 1 sandy braided zone 2 and straight zone 3 to meandering zone 4 facies analysis of the kosi channel deposits suggests that in zones 1 and 2 mid channel bars islands side bars 3 d dunes and various types of linguoid dunes are the most common features large linguoid dunes with lengths of up to 1 km and with superimposed smaller 3 d dunes are also common the deeper parts of the channel are probably characterized by longitudinal bars in zone 1 and sandwaves in zone 2 lateral accretion of sandy bars is a significant process in these zones zone 3 is characterized by side bars with deposition by lateral accretion as on point bars linguoid dunes may migrate up a side bar or move across it subparallel to the main channel thalweg the uppermost sedimentary sequence 8 10 m thick of the kosi megafan consists of mainly sands and minor gravels in the proximal northern half and sand and mud 45 vol in the distal southern half of the megafan this downfan trend reflects the change from braided to straight channel pattern numerous spring fed streams rework the surficial sediments of the megafan and produce a fining upward sequence up to 4 7 m thick on top of braided straight channel deposits of the megafan

ephemeral fluvial deposits integrated outcrop and simulation studies reveal complexity ephemeral fluvial sandstones form the main reservoirs in many oil and gas fields production histories and development difficulties suggest these deposits are more complex than is commonly supposed in the petroleum industry there is inadequate published information to account for this observation relevant sedimentological literature on such deposits is qualitative and unsuitable for detailed reservoir characterization studies therefore integrated sedimentological petrophysical and fluid flow simulation studies have been conducted on outcrop analogs in the southwestern united states our key objectives were to define flow units and to find areas of sensitivity inherent both in the sediments and in the analytical and statistical procedures used to describe and model s ch systems we report results of integrated studies on the lower jurassic kayenta formation in southeastern utah the kayenta formation is a relatively proximal sand rich succession dominated by channel fill sandstones sedimentological analysis identified eight main genetic units in contrast reservoir simulations based on probe permeameter data collected at outcrop show that six of the main genetic units have uniform flow behavior intraformational mudclast conglomerates are the dominant permeability barriers both because of the clasts themselves and because they act as sites of preferential cementation stochastic permeability models conditioned to the outcrop data produce results little different from models based on averaged values for each facies the most sensitive feature of the mode s concerns the assumptions made about the mudclast conglomerates the model results show that only by integrating analytical approaches can we understand the full character of an outcrop analog in such a way that we can use it predictively

a mechanistic model for river incision into bedrock by saltating bed load 1 abrasion by bed load is a ubiquitous and sometimes dominant erosional mechanism for fluvial incision into bedrock here we develop a model for bedrock abrasion by saltating bed load wherein the wear rate depends linearly on the flux of impact kinetic energy normal to the bed and on the fraction of the bed that is not armored by transient deposits of alluvium we assume that the extent of alluvial bed cover depends on the ratio of coarse sediment supply to bed load transport capacity particle impact velocity and impact frequency depend on saltation trajectories which can be predicted using empirical functions of excess shear stress the model predicts a nonlinear dependence of bedrock abrasion rate on both sediment supply and transport capacity maximum wear rates occur at moderate relative supply rates due to the tradeoff between the availability of abrasive tools and the partial alluviation of the bedrock bed maximum wear rates also occur at intermediate levels of excess shear stress due to the reduction in impact frequency as grain motion approaches the threshold of suspension measurements of bedrock wear in a laboratory abrasion mill agree well with model predictions and allow calibration of the one free model parameter which relates rock strength to rock resistance to abrasive wear the model results suggest that grain size and sediment supply are fundamental controls on bedrock incision rates not only by bed load abrasion but also by all other mechanisms that require bedrock to be exposed in the channel bed

inversion of relief a component of landscape evolution inversion of relief occurs when materials on valley floors are or become more resistant to erosion than the adjacent valley slopes as erosion proceeds the valley floor becomes a ridge bounded by newly formed valleys on each side areas of lava flows contain many examples of inversion of relief but it is also common in areas of duricrusts inversion of relief is so widespread in some areas that it should be regarded as a general component in a model of landscape evolution inversion of relief has some important implications drainage lines will shift significantly over time slope soil relationships catenas have to be reassessed because the regolith on the upper part of a hill slope may have developed under very different conditions from those existing at present the resulting catena is not a simple expression of soils and response to landscape position this also has important implications for geochemistry where present day ridge tops were once valley floors geochemical signatures will reflect lateral water movement in the old landscape rather than simple in situ weathering and vertical redistribution in the present landscape finally inversion of relief can produce erosion surfaces of very low relief that cannot be termed peneplains pediplains or etchplains because they have a very different genesis this underlines the importance of determining the complexities of landscape evolution before such genetic terms are applied to any landscape

the role of vegetation in the formation of anabranching channels in an ephemeral river northern plains arid central australia as the distribution and abundance of vegetation in drylands is often controlled by the greater availability of water along river channels riparian vegetation has the potential to influence significantly dryland river form process and behaviour this paper demonstrates how a small indigenous shrub the inland teatree melaleuca glomerata influences the formation and maintenance of anabranching channels in a reach of the ephemeral marshall river northern plains arid central australia here the marshall is characterized by ridge form anabranching where water and sediment are routed through subparallel multiple channels of variable size which occur within a typically straight channel train channels are separated by channel train ridges narrow flow aligned vegetated features or by wider islands by providing a substantial element of boundary roughness dense stands of teatrees growing on channel beds or atop the ridges and islands influence flow velocities flow depths and sediment transport resulting in flow diversion bank and floodplain erosion and especially sediment deposition ridges and islands represent a continuum of forms and their formation and development can be divided into a three stage sequence involving teatree growth and alluvial sedimentation 1 teatrees colonize a flat sandy channel bed initiating the formation of ridges by lee side accretion individual ridges grow laterally vertically and longitudinally and maintain a geometrically similar streamlined lemniscate form that presents minimum drag 2 individual ridges grow in size and interact with neighbouring ridges causing the lemniscate forms to become distorted ridges in the lee of other ridges tend to be protected from the erosive effects of floods and survive whereas individual teatrees or small ridges exposed to flow concentrated between larger ridges tend to be removed 3 ridges lengthen and coalesce with downstream ridges eventually subdividing the channel train into well defined anabranches this sequence turns a channel initially obstructed with dense and chaotic stands of teatrees into a well organized system of ridge form anabranches in the moderate to low gradient marshall river which is colonized by an abundance of within channel vegetation and subject to declining downstream discharges this helps to minimize flow resistance thereby maintaining an efficient water and sediment flux copyright 2000 john wiley sons ltd

classification of large scale subaqueous bedforms a new look at an old problem sepm bedforms and bedding structures abstract a symposium entitled classification of large scale flow transverse bedforms was convened at the 1987 mid year meeting of sepm in austin texas with the purpose of examining the problems involved in classifying large subaqueous flow transverse bedforms developed in fluvial intertidal and marine environments and recommending changes in nomenclature the consensus of the participants is that despite the wide spectrum of morphologies of large scale flow transverse bedforms excluding antidunes they all occupy a similar position in the lower flow regime sequence between ripples and upper plane bed the wide variety of forms is a reflection of secondary effects such as channelization fluctuating water levels and unsteady and reversing flows the bedforms appear not to fall into size classes with naturally occurring boundaries but rather form a continuum with spacing from just under 1 m to over 1 000 m the symposium panel proposes therefore that they should have only one name dune dune is preferred as it has historical precedence over other terms in use such as megaripple and sand wave the term dune should be modified by rimary descriptors of shape i e 2 d or 3 d and size based on spacing small 0 6 5 m medium 5 10 m large 10 100 m or very large 100 m and the adjective subaqueous when it is important to distinguish them from eolian dunes the panel recommends a morphologically based classification that is descriptive with an underlying genetic rationale second order descriptors such a sediment size and bedform superposition may be used to describe more thoroughly the variety of subaqueous dunes in nature

pattern of vertebrate extinctions across an event bed at the permian triassic boundary in the karoo basin of south africa the extinction of vertebrates around the time of the permian triassic boundary has long been regarded as a gradual event occurring over millions of years our new field investigations of fluvial strata in the central and southern karoo basin of south africa have revealed the presence of an event bed coinciding with a mass extinction of terrestrial fauna and flora the bed is in a sedimentary sequence that is marked by a reddening of flood plain mud rocks and a change from high to low sinuosity river channel systems here we show that the pattern of vertebrate taxa disappearing below this boundary and the subsequent appearance of new taxa above the boundary are consistent with a relatively sudden possibly catastrophic event perhaps of 50 000 yr duration or less

significance of channel belt clustering in alluvial basins the distribution of channel deposits in alluvial basins is commonly used to interpret past changes in climate tectonics and sea level here we present preliminary evidence that longtime scale 10 3 10 5 yr self organization in fl uvial systems may generate structured stratigraphic patterns spontaneously in the absence of or independent from changing basin boundary conditions a physical experiment and an ancient alluvial succession ferris formation latest cretaceous paleogene south central wyoming both show stratigraphy where clusters of many closely spaced channel deposits are separated from each other by extensive intervals of overbank mudstones analysis using spatial point process methods shows that channel deposits in both basins are statistically clustered over intermediate basin length scales in the experiment external controls base level subsidence rate and sediment water supplies were not varied and therefore not factors in cluster formation likewise the ancient system lacks stratigraphic and sedimentologic evidence of external controls on channel clustering we propose that channel clusters as seen in this study refl ect a scale of flself organization that is not usually recognized in ancient deposits this type of internally generated stratigraphy should be considered when reconstructing tectonic climate and sea level changes from

the okavango fan and the classification of subaerial fan systems abstract controversy exists over the classification of fluvially formed subaerial fans authors either restrict alluvial fans to debris flow dominated types or extend the spectrum to fans dominated by braided rivers the okavango fan provides an end member which extends this spectrum to fans dominated by meandering and low sinuosity rivers the fan is a large 150 km radial axis shallowly sloping 0 00036 highly vegetated subaerial fan which can be subdivided into four subenvironments these are 1 the entry corridor or panhandle characterized by single and anastomosing meander belts 2 the upper fan characterized by meander belts diverging from the fan apex comprising peat confined meandering channels with interchannel swamps forming thick peats 3 the middle fan with highly confined single and anastomosing low sinuosity rivers and less common prograding meander belts whose channels are confined by thick peats with however little chance of peat preservation and 4 the lower fan in which annual floods from relatively unconfined channels spread over the fan surface and interact with pre existing aeolian and lacustrine deposits with the recognition of this new fan type the spectrum of subaerial fan types can be expressed in terms of 1 debris flow dominated fans of which the death valley fans are a member 2 braided river dominated fans of which the kosi fan is a member and 3 low sinuosity meandering losimean river dominated fans of which the okavango fan is a member this spectrum can be expressed in terms of variation in slope maximum size and percentage of surface vegetation but crucial to the evolution of the various fan types is variation in the flashy to continuous nature of the discharge and the degree of channel confinement evident on the fan surface comparable ancient examples of the three fan types are recognizable many of which provide intermediates between the ideal end members debris flow dominated and braid dominated fan types are known from throughout earth history however the losimean fan type because of its reliance on confining vegetation may only have developed after the devonian period the spectrum of subaerial fan types can be expressed on a triangular field of variation with the vertices defined by the relative importance of the processes which shaped a particular fan system be they debris flows processes associated with braided rivers or processes associated with meandering and low sinuosity rivers

upper permian magnetic stratigraphy of the lower beaufort group karoo basin abstract we carried out a magnetostratigraphic and geochronological study of late permian sediments in the karoo basin of the western cape province south africa a continuous 700 m thick section of deltaic sediments of the upper waterford formation uppermost ecca group and the fluvial sediments of the abrahamskraal formation lowermost beaufort group were sampled at the meter scale u pb dating of zircons from interbedded volcanic ash beds by ion microprobe shrimp provided absolute age constraints on the age of the sedimentary rocks paleomagnetic analysis reveals a partial overprint of the natural remanent magnetization nrm that is tentatively ascribed to the emplacement of the karoo large igneous province in the western cape region during the middle jurassic a stable component of the nrm was found at temperatures higher than 450 c and was interpreted as a characteristic remanent magnetization chrm acquired during deposition supported by a positive reversals test for this dual polarity chrm the virtual geomagnetic pole position for the waterford and abrahamskraal formations computed from the average chrm direction is in general agreement with the late permian directions for stable gondwana a significantly different average inclination and thus paleomagnetic pole position is obtained by correcting the inclination shallowing error by the elongation inclination method tauxe and kent 2004 the presence of both normal and reversed polarity zones indicate deposition after the end of the kiaman superchron moreover the polarity sequence is in good agreement with the illawarra sequence of steiner 2006 our results indicate a capitanian late guadalupian age for the abrahamskraal fm in agreement with the late permian age based on presence of glossopteris flora and dicynodont fauna traditionally assigned to the fluvial lacustrine sediments of the beaufort group however the u pb zircon ages of ca 264 268 ma suggest an age of 269 ma for the top of the kiaman superchron

diagnosing the annual cycle of the equatorial undercurrent in the atlantic ocean from a general circulation model abstract ten year long output series from a general circulation model forced by daily realistic winds are used to analyze the annual cycle of the equatorial undercurrent euc in the atlantic ocean two well defined transport maxima are found one present during boreal summer and autumn in the central part of the basin is generally recognized and regarded as a near equilibrium response to the equatorial easterly trades that culminate in this period another one most pronounced near the western boundary occurs in april may when the trades relax this second maximum is less patent in the observations but concomitant signals in previously published analyses of the north brazil current and surface velocity seasonal variations might be indirect manifestations of its reality because this intensification appears at periods when the boundary between the tropical and equatorial gyres nears the equator the authors relate its existence to wind stress curl variations at subequatorial latitudes a link between

crevasse splays from the rapidly aggrading sand bed braided niobrara river nebraska effect of base level rise base level rise of 2 35 m on the niobrara river has resulted in aggradation of the channel belt and a recent avulsion overbank areas have become flooded by rising groundwaters and more than eight crevasse splays have formed between 1993 and 1997 two crevasse splays situated on the west and east sides of the niobrara have been studied using ground penetrating radar gpr shallow boreholes and topographic surveys the vibracores and gpr profiles provide a nearly three dimensional view of the architecture of crevasse splay deposits the east splay was initiated in the winter of 1993 94 and has expanded to cover an area 200 m by 1000 m with sediment up to 2 5 m thick the west splay which was initiated by the opening of a crevasse channel through a levee in the autumn of 1995 covers an area 150 m by 250 m with up to 1 2 m of sand deposited in a single year the niobrara splays are sand dominated and characterized by bedload deposition within channels 5 30 m wide and 0 5 2 m deep with the development of slipfaces where splays prograde into standing bodies of water sedimentary structures in cores include horizontal lamination ripple lamination and sets of cross stratification there is a slight tendency for splays to coarsen up but individual beds within the splays often fine up the abundance of crevasse splays on the niobrara river contrasts with other braided river floodplains in the niobrara crevasse splay formation followed aggradation within the channel belt which occurred in response to base level rise the link between crevasse splays channel aggradation and base level rise has important implications for the interpretation of ancient braided river and floodplain sequences it is suggested that crevasse splay deposits should be an important component of aggrading fluvial sediments and hence should be preserved within the rock record in this case the aggradation and crevassing have been tied to a rise in base level elevation and it is suggested that similar deposits should be preserved where braided rivers are affected by base level rise for instance during transgression and filling of palaeovalleys

testing for fault activity at yucca mountain nevada using independent gps results from the bargen network 1 data from bargen gps stations around yucca mountain ym have been independently processed using gipsy oasis and gamit globk the rms velocity differences between these solutions is 0 06 mm yr east component and 0 10 mm yr north indicating an ability to resolve tectonic signals 0 3 mm yr with high confidence inversion of gps station velocities for eastern california shear zone ecsz fault parameters produces an unreasonably deep locking depth of 30 km for the death valley furnace creek fault system contradicting seismological evidence the gps cluster locally west of ym observes a strain rate of 17 0 1 8 ns yr marginally higher than our ecsz model predicts 13 9 0 7 ns yr significantly the cluster to the east observes 22 3 2 1 ns yr which is 6 2 higher than the model 8 6 0 7 ns yr suggesting that additional sources of strain more local to ym 0 7 mm yr

heartbeat of a mountain diagnosing the age of depositional events in the karoo gondwana basin from the pulse of the cape orogen careful consideration of the effects of the cape orogeny on sedimentation in the carboniferous jurassic karoo basin provides an indirect tool for accurately dating these rocks fossil and radiometric data especially when combined with sedimentological and structural information yield partly overlapping age brackets which can be used to correlate the successive tectonic pulses with specific depositional events application of these principles to associated basins in gondwanaland can provide a firm foundation for more dependable stratigraphic correlation on a global scale the exercise also suggests that a number of widely held opinions on the age of certain stratigraphic units in the karoo supergroup may be incorrect

episodic caldera volcanism in the miocene southwestern nevada volcanic field revised stratigraphic framework 40ar 39ar geochronology and implications for magmatism and extension the middle miocene southwestern nevada volcanic field swnvf is a classic example of a silicic multicaldera volcanic field in the great basin more than six major calderas formed between 15 and 7 5 ma the central swnvf caldera cluster consists of the overlapping silent canyon caldera complex the claim canyon caldera and the timber mountain caldera complex active from 14 to 11 5 ma and centered on topographic timber mountain locations of calderas older than the claim canyon caldera source of the tiva canyon tuff are uncertain except where verified by drilling younger peralkaline calderas black mountain and stonewall mountain formed northwest of the central swnvf caldera cluster we summarize major revisions of the swnvf stratigraphy that provide for correlation of lava flows and small volume tuffs with the widespread outflow sheets of the swnvf new laser fusion 40 ar 39 ar isotopic ages are used to refine and revise the timing of eruptive activity in the swnvf the use of high sensitivity mass spectrometry allowed analysis of submilligram sized samples with analytical uncertainties of 0 3 1 permitting resolution of age differences as small as 0 07 ma these results confirm the revised stratigraphic succession and document a pattern of episodic volcanism in the swnvf major caldera episodes belted range crater flat paintbrush timber mountain and thirsty canyon groups erupted widespread ash flow sheets within 100 300 k y time spans and pre and post caldera lavas erupted within 100 300 k y of the associated ash flows peak volcanism in the swnvf occurred during eruption of the paintbrush and timber mountain groups when over 4500 km 3 of metaluminous magma was erupted in two episodes within 1 35 m y separated by a 750 k y magmatic gap peralkaline and metaluminous magmatism in the swnvf overlapped in time and space the peralkaline tub spring and grouse canyon tuffs erupted early and the peralkaline thirsty canyon group tuffs and stonewall flat tuff erupted late in the history of the swnvf flanking the central volumetrically dominant peak of metaluminous volcanism magma chemistry transitional between peralkaline and metaluminous magmas is indicated by petrographic and chemical data particularly in the overlapping grouse canyon and area 20 calderas of the silent canyon caldera complex volcanism in the swnvf coincided with the miocene peak of extensional deformation in adjoining parts of the great basin although regional extension was concurrent with volcanism it was at a minimum in the central area of the swnvf where synvolcanic faulting was dominated by intra caldera deformation significant stratal tilting and paleomagnetically determined dextral shear affected the southwestern margin of the swnvf between the paint brush and timber mountain caldera episodes larger magnitude detachment faulting in the bullfrog hills southwest of the central swnvf caldera cluster followed the climactic timber mountain caldera episode postvolcanic normal faulting was substantial to the north east and south of the central swnvf caldera cluster but the central area of peak volcanic activity remained relatively unextended in postvolcanic time volcanism and extension in the swnvf area were broadly concurrent but swnvf area were broadly concurrent but in detail they were episodic in time and not coincident in space

spatial and temporal evolution of an avulsion on the taquari river distributive fluvial system from satellite image analysis avulsion processes have been observed and analyzed using field based studies however they have rarely been analyzed through use of satellite imagery even though such an approach allows documentation of spatial and temporal variations of the resulting deposits in order to document changes that are occurring at the caronal avulsion on the taquari river brazil a time series of landsat imagery from 1985 to present 2010 was compiled as of july 2010 the imagery shows that the avulsion is not yet complete with discharge being routed to both the parent channel and the avulsion channel in the floodbasin the avulsion was initiated as flow was diverted from the parent channel to the floodbasin through two small crevasses allowing the development and evolution of splays with a single splay stabilizing only since 1999 the avulsion area is marked by the growth of new splays the formation of an avulsion belt and progradation of avulsion deposits into the floodbasin the parent channel downstream of the avulsion site has experienced decreasing width through time associated with the higher volumes of water and sediment being captured by the avulsion channel because this avulsion is not yet complete we expect more morphological changes to occur as the avulsion belt evolves into the primary channel rapid sedimentation caused by this avulsion and the 24 year time series of imagery that captured this change allowed us to construct a 3d block representing the evolution of depositional environments associated with avulsion using time in the vertical dimension thus we could represent the evolution of geomorphological patterns including floodbasin proximal levee distal levee and channel deposits and project their distributions through time this block of evolving sedimentary settings can be used as a guide for future sedimentologic studies by offering visual clues regarding the way which depositional systems track avulsion initiated changes

historical geomorphology and pedology of the gandak megafan middle gangetic plains india the gandak megafan of eastern uttar pradesh and northwestern bihar lies in the middle gangetic plains the gandak river has shifted about 80 km to the east due to tilting in the last 5000 years this has created a soil chronoassociation similar to the chronosequences found on some flights of river terraces this chronoassociation has five members qgd1 5 they are distinguished on the basis of profile development clay mineralogy and calcium carbonate content chlorite transforms to vermiculite on a large scale from qgd1 to qgd3 and decreases drastically in member qgd4 kaolinite and interstratified kaolinite smectite are abundant in the older members of the chronoassociation the youngest soils qgd1 500 b p while qgd3 soils like those on the older gandak plain and old rapti plains date back to 2500 b p qgd4 soils like those on the oldest gandak plain are dated as 5000 years b p whilst the oldest qgd5 soils as on the old ghaghra plain and ganga ghaghra interfluve date back to 10000 b p these soils which include pedogenic calcite and a saline epipedon indicate a dry climatic spell during the period 9000 11000 b p faults developed on the megafan are not related to the basement structures

architectural styles and sedimentology of the fluvial lower beaufort group karoo basin south africa abstract the permo triassic beaufort group comprises in excess of 3000 m of sandstone and mudstone rich fluvial deposits that vary both laterally and vertically in abundance architecture and clustering styles the lower 1370 m has been studied in detail detailed stratigraphic logging and photographic interpretation have been carried out on river cliffs and hillside sections and sedimentary structures have been mapped by close inspection of clean outcrops seven fluvial architectural styles have been identified encompassing sand body and sand body cluster scales 1 flat topped sheets dominated by lateral accretion 2 concave up topped sheets dominated by lateral accretion 3 heterolithic ribbons dominated by lateral accretion 4 flat topped ribbons with attached splays dominated by downstream accretion 5 unconfined moderately amalgamated concave up topped complexes 6 unconfined strongly amalgamated sheet complexes and 7 valley confined strongly amalgamated ribbon complexes the internal architecture of each indicates mixed lateral and downstream accretion modes on several scales with local variability lateral accretion deposits differ from typically published facies models in that trough cross bedding is rare possibly the result of an inability to generate dunes due to the dominant very fine sandstone grain size the observed architecture and sedimentary structures are the product of 1 a semiarid climate producing fluvial and debris flows and cementation of sediment packages at the surface which exerts a strong control on the magnitude of channel scour the nature of channel fill and compaction history 2 local variability in subsidence rate causing variation in the vertical spacing of channel belts channel slope and plan form and variation in preservation of topographically higher features e g levees 3 relative position in a fluvial megafan influencing suspended load to bedload partitioning from proximal to distal locations and formation of channel belt complexes and 4 relative sea level changes causing incised valley formation and fill only in the most distal parts of the system

alluvial paleosols and pedofacies sequences in the permian lower beaufort of the southwestern karoo basin south africa abstract three types of paleosol profiles are described as representative of the range of soil types that developed on the ancient alluvial plains of the southwestern karoo basin during the late permian continuous 3 dimensional exposures of the lower beaufort adelaide subgroup strata allow detailed sedimentological taphonomic and paleopedological observation of thick floodplain sequences that contain numerous stacked paleosol profiles various floodplain strata contain characteristic paleosol profiles that are regulated by the periodicity and competence of overbank flooding both of which decrease with increasing distance from the contributing channel paleosols developed in levee or channel bank deposits are immature calcic entisols displaying evidence of early carbonate translocation but without well developed horizonation proximal floodbasin paleosols at the foot of the meanderbelt slope are mature calcic vertisols with more fully developed profiles containing zones of both carbonate and clay illuviation as well as some groundwater calcretes slickensided stress argillans in the b horizons are indicative of multiple cycles of wetting and drying distal floodbasin paleosols are dominated by hydromorphic and evaporitic processes as a result of their axial position in the floodbasin sheet like networks of mudcrack casts composed of calcretized aeolian sand and silt suggest that dust was a major source of calcium carbonate to the e soils the paleosols are interpreted as having formed under warm to hot semi arid climatic conditions with a strongly seasonal rainfall of 500 to 800 mm per annum and a mean annual moisture deficiency the geomorphic setting was similar to the holocene indo gangetic alluvial plain vertebrate burrow casts in the proximal floodbasin facies indicate a minimum depth to watertable of 150 cm the distribution of rooted horizons reflects dense vegetation flanking major drainage channels and sparse cover in the distal floodbasin a simple stratigraphic sequence of once laterally continuous paleosols is termed a pedofacies stacked sequences of pedofacies within approximately 20 50 m thick and 100 250 m thick stratigraphic successions reflect second and first order sedimentary cycles respectively both scales of cyclicity are attributed to autocyclically controlled avulsions of differentially aggrading channels in the first instance and of complete drainage networks in the second

crevasse splay processes and deposits in an ancient distributive fluvial system the lower beaufort group south africa abstract up to 12 of the mud prone ephemeral distributive fluvial system stratigraphy in the permo triassic lower beaufort group south africa comprises tabular fine grained sandstone to coarse grained siltstone bodies which are interpreted as proximal to distal crevasse splay deposits crevasse splay sandstones predominantly exhibit ripple to climbing ripple cross lamination with some structureless and planar laminated beds a hierarchical architectural scheme is adopted in which 1 m thick crevasse splay elements extend for tens to several hundreds of meters laterally and stack with other splay elements to form crevasse splay sets up to 4 m thick and several kilometers in width and length paleosols and nodular horizons developed during periods or in areas of reduced overbank flooding are used to subdivide the stratigraphy separating crevasse splay sets deposits from crevasse splays differ from frontal splays as their proximal deposits are much thinner and narrower with paleocurrents oblique to the main paleochannel in order for crevasse splay sets to develop the parent channel belt and the location where crevasse splays form must stay relatively fixed during a period of multiple flood events beaufort group splays have similar geometries to those of contemporary perennial rivers but exhibit more lateral variability in facies which is interpreted to be the result of more extreme fluctuations in discharge regime sharp based crevasse splay packages are associated with channel avulsion but most are characterized by a gradual coarsening upward interpreted to represent progradation the dominance of progradational splays beneath channel belt deposits may be more characteristic of progradational stratigraphy in a distributive fluvial system rather than dominated by avulsion processes in a trunk river system this stratigraphic motif may therefore be an additional criterion for recognition of distributive fluvial systems in the ancient record

erosional decay of the yucca mountain crest nevada abstract a simple numerical landscape evolution model is used to investigate the rate of erosional decay of the yucca mountain crest in nevada usa a location proposed as a permanent repository for high level radioactive waste the model is based on a stream power approach in which we assume that the rate of erosion is proportional to the size of the catchment as a proxy for water flux and to the square of the topographic gradient the proportionality constants in the model are determined using the structural history of the region extensional tectonics has dissected the region into a series of well defined tilt blocks in the last 11 my and the ratio of fault displacement and gully incision during this time is used to scale the model forward predictions of our model into the future show that the crest will denude to the level of the proposed site between 500 000 years and 5 my this prediction is based on conservative estimates for all involved parameters erosion may be more rapid if other processes are involved for example our model does not consider continuing uplift or catastrophic surface processes as they have been recorded in the region we conclude that any total system performance analysis tspa as has been performed for the yucca mountain region to predict geological events inside the ridge must consider erosion as an integral part of its predictions

modeling the influence of horizontal advection deformation and late uplift on the drainage development in the india asia collision zone 1 we present results of a new model in which we couple a mechanical model to describe continental indentation in plan view with a landscape evolution model to describe drainage development we apply the model to investigate aspects of the development of drainage systems erosion and exhumation in the india asia collision zone it is shown that the orogen scale distribution of erosion and exhumation can be well matched by the model however the elevation of the tibetan plateau and the steep topographic gradients at its margins are difficult to reproduce they appear to require an additional cause of uplift we show that some of the major observed river capture events can be reproduced by invoking such a late uplift in much of the orogen except the region of the sichuan basin this includes the inferred capture of the yarlong tsangpo by the brahmaputra and that of the upper yangtze by the lower yangtze thereby deserting the red river

altered river morphology in south africa related to the permian triassic extinction the permian triassic transition in the karoo basin of south africa was characterized by a rapid and apparently basin wide change from meandering to braided river systems as evidenced by preserved sedimentary facies this radical changeover in river morphology is consistent with geomorphic consequences stemming from a rapid and major die off of rooted plant life in the basin evidence from correlative nonmarine strata elsewhere in the world containing fluvial permian triassic boundary sections suggests that a catastrophic terrestrial die off of vegetation was a global event producing a marked increase in sediment yield as well as contributing to the global 13 c excursion across the permian triassic boundary

a simple model of the mass exchange between the subtropical and tropical ocean abstract a simple ventilated thermocline model is used to study the subtropical tropical mass exchange it is found that the water subducted in the western subtropical gyre recirculating window tends to recirculate within the subtropical gyre while the water subducted in the eastern part exchange window tends to penetrate equatorward the exchange window expands with an increased easterly wind or basin width on the southern boundary of the subtropical gyre but shrinks with an increased wind curl within the subtropical gyre furthermore the total exchange transport increases with the easterly wind or the width of the basin on the southern boundary of the subtropical gyre but it is independent of subtropical wind the ventilation mechanism is important in supporting the exchange transport for wind with realistic strength at the southern boundary the reduction of the exchange transport is about 15 30 of the ekman transport finally relative to the exchange transport in the interior of the ocean

processes facies and architecture of fluvial distributary system deposits abstract there is evidence from the stratigraphic record of examples of fluvial deposits that were the products of deposition from river systems which had decreasing discharge down flow and transitions from proximal channelised to distal unconfined flow these deposits form fan shaped bodies several tens of kilometres in radius and their stratigraphic architecture is aggradational with no evidence of deep incision driven by base level fall the fluvial systems that generated these deposits formed under conditions for which there is no complete analogue today an endorheic basin with a relatively arid climate adjacent to an uplifted area with higher precipitation a conceptual model for fluvial systems of this type has therefore been built on the basis of outcrop examples and a consideration of the controls on sedimentation proximal areas are characterised by amalgamated coarse pebbly and sandy channel deposits with little preservation of overbank facies channel dimensions are generally smaller in the medial areas but sizes are variable deposits are of braided meandering and simple channels which show varying degrees of lateral migration the channel fills may be mud or sand with overbank flow processes playing an important role in filling channels abandoned on the floodplain after avulsion the proportion of overbank deposits increases distally with sheets of sand deposited as lateral and terminal splays by unconfined flow interconnection of sandstone bodies is poor in the distal areas because channel fill bodies are sparse small and are not deeply incised the radial pattern of the sediment body forms by the repeated avulsion of channels active channels build up lobes on the alluvial plain and rivers switch position to follow courses on lower lying areas the term fluvial distributary system is here used to describe a river system which has a downstream decrease in discharge and has a distal zone which is characterised either by terminal splays on to a dry alluvial plain or a lake delta during periods of lake highstand

influence of el nino on the upper ocean circulation in the tropical atlantic ocean abstract this study investigates the influence of el nino on the upper ocean circulation in the tropical atlantic ocean via changes in the atlantic trade winds by analyzing observed sea surface temperature sst together with an ocean general circulation model integration forced by the ncep ncar reanalysis during periods with anomalously warm cold eastern equatorial pacific sst the southern atlantic tropical cell is strengthened weakened the difference of the cell strength between el nino and la nina years is about 20 of the mean cell strength however the variability of the cell is not dominated by the remote forcing from the eastern equatorial pacific but seems to be caused by intrinsic tropical atlantic variability a strengthening weakening for periods with anomalously warm cold eastern equatorial pacific sst is also found for the zonal surface and subsurface currents topex poseidon altimetry data are used to validate the results based on the ogcm integration

facies analysis of the balta formation evidence for a large late miocene fluvio deltaic system in the east carpathian foreland abstract deposits of the balta fm are preserved in a large arcuate sediment body that covers about 60 000 km 2 and is up to 350 m thick the balta fm spans ca 5 ma as constrained by underlying tortonian bessarabian and overlying messinian early pontian paratethys strata it contains frequent terrestrial mammal fossils and fresh as well as brackish water paratethys molluscs and ostracods over the past 140 years our understanding of the sedimentary architecture of the formation and its origins has remained in its infancy which has limited insight into the evolution of the east carpathian foreland here we provide the first modern sedimentary facies analysis of the balta fm which is integrated with an extensive review of previously published local literature it is supported with micropalaeontological results and a wealth of historical borehole information we show that the balta fm has a tripartite vertical division its lowermost part is clay dominated and consists of subordinate delta front sand bodies interspersed between muds the middle unit contains separate delta plain channels or channel belts encased in thick muds these are overlain by a unit with amalgamated delta plain channel deposits with only minor amounts of associated mud the abundance of upper flow regime sedimentary structures in channel sands the absence of peats or coals and the presence of calcareous nodules suggest a strongly seasonal and relatively dry climate with a flashy discharge regime deposition of the balta fm in an area previously characterized by distal shelf and prodelta environments indicates large scale progradation triggered by high sediment volume from the uplifting carpathian orogen and enhanced by a general lowering of paratethys sea level the tripartite internal architecture of the balta fm indicates that progradation continued during deposition its wedge shaped geometry suggests that tectonic activity in the carpathians generated a 300 km wide foreland basin that allowed for significant delta plain aggradation despite of the generally regressive trend in paratethys sea level

structural geology of the proposed site area for a high level radioactive waste repository yucca mountain nevada geologic mapping and fracture studies have documented the fundamental patterns of joints and faults in the thick sequence of rhyolite tuffs at yucca mountain nevada the proposed site of an underground repository for high level radioactive waste the largest structures are north striking block bounding normal faults with a subordinate left lateral component that divide the mountain into numerous 1 4 km wide panels of gently east dipping strata block bounding faults which underwent quaternary movement as well as earlier neogene movement are linked by dominantly northwest striking relay faults especially in the more extended southern part of yucca mountain intrablock faults are commonly short and discontinuous except those on the more intensely deformed margins of the blocks lithologic properties of the local tuff stratigraphy strongly control the mesoscale fracture network and locally the fracture network has a strong influence on the nature of intrablock faulting the least faulted part of yucca mountain is the north central part the site of the proposed repository although bounded by complex normal fault systems the 4 km wide central block contains only sparse intrablock faults locally intense jointing appears to be strata bound the complexity of deformation and the magnitude of extension increase in all directions away from the proposed repository volume especially in the southern part of the mountain where the intensity of deformation and the amount of vertical axis rotation increase markedly block bounding faults were active at yucca mountain during and after eruption of the 12 8 12 7 ma paintbrush group and significant motion on these faults postdated the 11 6 ma rainier mesa tuff diminished fault activity continued into quaternary time roughly half of the stratal tilting in the site area occurred after 11 6 ma probably synchronous with the main pulse of vertical axis rotation which occurred between 11 6 and 11 45 ma studies of sequential formation of tectonic joints in the context of regional paleo stress studies indicate that north and northwest striking joint sets formed coevally with the main faulting episode during regional east northeast west southwest extension and that a prominent northeast striking joint set formed later probably after 9 ma these structural analyses contribute to the understanding of several important issues at yucca mountain including potential hydrologic pathways seismic hazards and fault displacement hazards

the neglected early history of geology the copernican revolution as a major advance in understanding the earth many geologists think of geology as a young science that originated about 1800 two centuries after the copernican revolution in astronomy and physics gave rise to modern science we suggest that this view ignores the early history of what is now geology and we argue that the copernican revolution represented not only a revolution in astronomy and physics but also a radical change in understanding the earth prior to the copernican revolution the concepts of earth and planet had nothing whatsoever to do with each other but after that revolution scientists recognized that earth itself is one of the planets and they rejected the aristotelian view that earth is made of fundamentally different material than are the sun stars and planets this was an essential step in the development of a valid science of geology and the copernican revolution should therefore be considered not only an episode in the history of astronomy and physics but as a central part of the history of geology as well

western united states extension how the west was widened abstract cenozoic extension in the western united states presents a complex interrelation of extension volcanism and plate boundary tectonics that defeats simple notions of active or passive rifting forces driving extension can originate at plate boundaries through basal traction basal normal forces or from buoyancy forces internal to the crust and lithospheric mantle the latter two are most responsible for driving extension where it is observed in the basin and range the complex evolution of the northern basin and range probably represents removal or alteration of mantle lithosphere interacting with buoyancy stored in the crust in contrast crustal buoyancy forces combined with a divergent plate boundary between about 28 and 16 ma to drive extension in the southern basin and range the central basin and range most likely extended as a result of boundary forces external to itself but arising from buoyancy forces elsewhere in the western united states

assessment of recession flow variability and the surficial lithology impact a case study of buffalo river catchment eastern cape south africa the recession identity is an essential indicator of river performance health and diminution status this study therefore presents an assessment of streamflow recession characteristics in relation to the hydrostratigraphy property of watershed the streamflow recession assessment was carried out by computing the flow duration curve fdc and baseflow index bfi analyses of 28 year streamflow records at six distinct streamflow gauging stations digital processed aeromagnetic map was hybridized with geological survey and map review for the construction and characterization of concise watershed surficial lithology the fdc plot of low flow slopes and q reported the flow per station as thus buffalo 0 0113 0 0026 tshoxa 0 0029 0 0016 yellowwoods 0 0022 0 0008 mgqakwebe 0 0017 0 0007 quencwe 0 0009 0 0002 and ngqokweni 0 0005 0 0001 similarly bfi results show the following rank buffalo 0 541 yellowwoods 0 488 tshoxa 0 450 mgqakwebe 0 443 quencwe 0 415 and ngqokweni 0 332 the recession analysis revealed that the q slope of the stochastic fdc approach is a more reliable recession estimate for environmental flow the assessment of the recession lithology relationship suggests that the porosity network of the contact zone and fracture system of dolerite may produce a weightier impact of baseflow discharge in support of environmental flow over the hydraulic conductivity of sandstone the physiographic trends of streamflow response suggest the influence of the high relief on streamflow flux the overall results suggest that the hybrid approach of fdc and bfi analyses are highly effective for replicating the streamflow recession at the catchment stage and could be adopted for investigation of river sustainability

decadal variability of pycnocline flows from the subtropical to the equatorial pacific abstract a method based on isopycnal trajectory analysis is proposed to quantify the pathways from the subtropics to the tropics for a continuous stratified ocean a virtual streamfunction is defined which can be used to characterize these pathways this method is applied to the climatological dataset produced from a data assimilated model analysis indicates that in each layer contours of the virtual streamfunction are a good approximation for streamlines even if there is a cross isopycnal mass flux the zonal integrated meridional transport per unit layer thickness through each pathway varies in proportion to 1 sin where is latitude the vertical integrated total transport through pathways behaves similarly transport through pathways has a prominent decadal variability results suggest that in decadal time scales the interior pathway transport ipt anomaly may be mainly caused by the wind stress anomaly at low latitude the western boundary pathway transport wbpt anomaly often has a sign oppos

mechanisms controlling the clustering of fluvial channels and the compensational stacking of cluster belts abstract analysis of sand body distribution reveals that fluvial channel sands in the upper cretaceous lower williams fork formation in the central piceance basin colorado usa are not randomly distributed but are predictable in their spatial and stratigraphic position sand bodies are organized in channel belt clusters that are compensationally stacked on different temporal scales while channel clustering occurred over a shorter period channel and channel belt scale 10s ky to 100s ky compensational stacking occurred over a much longer time scale channel cluster belts 400 ky the lower williams fork formation consists of three distinct intervals of clustered channel belts each 400 ft 122 m thick topped by a thin coal layer the primary control on the cluster formation is autogenic channel avulsion during an overall aggradational phase short lived changes in in basin accommodation caused by either changes in tectonic subsidence or high frequency eustatic changes due to milankovitch band orbital forcing at the end of each cluster interval result in a distinct increase in channel thickness and coal formation towards the end of each cycle coals at the end of each sub cluster span the entire study area but their overall thickness is greater in the inter cluster floodplain prone areas the resulting differential early coal compaction is greatest in the inter cluster areas and has a significant control on the subsequent cluster belt position overlying the coal channel sands overlying the coals are concentrated in the previously low net gross floodplain prone inter cluster areas resulting in compensationally stacked cluster belts on the longest time scale 1 to 1 5 my which encompasses the entire lower williams fork changes in channel geometries and sand body thickness seem to be controlled mainly by long term changes in eustasy and autogenic processes are of lesser importance

rivers turned to rock late quaternary alluvial induration influencing the behaviour and morphology of an anabranching river in the australian monsoon tropics abstract late quaternary alluvial induration has greatly influenced contemporary channel morphology on the anabranching gilbert river in the monsoon tropics of the gulf of carpentaria the gilbert one of a number of rivers in this region has contributed to an extensive system of coalescing low gradient and partly indurated riverine plains extensive channel sands were deposited by enhanced flow conditions during marine oxygen isotope oi stage 5 subsequent flow declined probably associated with increased aridity however enhanced runoff recurred again in oi stages 4 3 65 50 ka aridity then capped these plains with 4 7 m of mud a widespread network of sandy distributary channels was incised into this muddy surface from sometime after the last glacial maximum lgm to the mid holocene during a fluvial episode more active than the present but less so than those of oi stages 5 and 3 this network is still partly active but with channel avulsion and abandonment now occurring largely proximal to the main gilbert flow path a tropical climate and reactive catchment lithology have enhanced chemical weathering and lithification of alluvium along the river resulting in the formation of small rapids waterfalls and inset gorges features characteristic more of bedrock than alluvial systems thermoluminescence tl and comparative optically stimulated luminescence osl ages of the sediments are presented along with u th ages of pedogenic calcrete and fe mn oxyhydroxide oxide accumulations they show that calcrete precipitated during the late quaternary at times similar to those that favoured ferricrete formation possibly because of an alternating wet dry climate intense chemical alteration of the alluvium leading to induration appears to have prevailed for much of the late quaternary but probably due to exceptional dryness not during the lgm the result has been restricted channel migration and a reduced capacity for the channel to adjust and accommodate sudden changes in bedload consequent avulsions have caused local stream powers to increase by an order of magnitude inducing knickpoint erosion local incision and the sudden influx of additional bedload that has triggered further avulsions the gilbert river while less energetic than its pleistocene ancestors is clearly an avulsive system and emphasizes the importance in some tropical rivers of alluvial induration for reinforcing the banks generating nickpoints reworking sediment and thereby developing and maintaining an indurated and anabranching river style

onshore to offshore anatomy of a late quaternary source to sink system po plain adriatic sea italy abstract in understanding the evolution of siliciclastic systems late quaternary analogs may enable reliable predictive models of facies tract architecture the po plain adriatic sea system where a wealth of research has been conducted during the last 20 years represents one of the most intensively investigated late quaternary successions with the aid of a chronologically well constrained stratigraphy paleoenvironmental evolution is tracked for the first time from fluvial to deep marine realms over 1000 km in length vertical stacking trends onshore and stratal terminations offshore are the key observations that allow identification of surfaces with sequence stratigraphic significance systems tract boundaries in the distinct segments of the system recurring motifs in stratigraphic architecture showing tight coupling of sedimentary responses among source area catchment basin and coastal and marine depocenters reveal a cyclicity driven by glacio eustatic fluctuations in the milankovitch band due to high rates of subsidence middle pleistocene forced regressive systems tracts are exceptionally expanded and the mis5e mis2 interval late pleistocene preserves a nearly continuous record of fourth order 100 kyr stepwise sea level fall the stratigraphic architecture of last glacial maximum deposits highlights the genetic relations between channel belt development pedogenesis and sediment delivery to the lowstand delta through narrow incised valley conduits the late glacial holocene succession records the last episode of sea level rise and stabilization through well developed patterns of shoreline transgression regression tst hst that can be readily traced updip from offshore to onshore locations architectural styles across the whole system reflect a dominance of allogenic forcing in the tst as opposed to a predominantly autogenic control on stratigraphic development in the hst external drivers of facies architecture were also effective on millennial timescales the younger dryas cold reversal which marks the transgressive surface on land records a short lived episode of subaqueous progradation that is correlative onshore with widespread immature paleosol development and small sized channel belt formation quantitative assessment of sediment budgets over different time intervals requires precise positioning of the key bounding surfaces based on this approach we outline for the first time over the entire po adriatic basin an estimate of the sediment volumes stored in each systems tract

comparison of the bedform distribution and dynamics of modern and ancient sandy ephemeral flood deposits in the southwestern karoo region south africa abstract during january 1981 unusually high rainfall patterns in the semi arid southwestern karoo region of south africa gave rise to catastrophic floods in the area the most devastating of which was the ephemeral flash flood that partially destroyed the town of laingsburg flood waters at laingsburg spread from a dry river bed rising to a depth of 12 m within 7 h washing away houses and burying the town with up to 3 5 m of sand and silt facies sequences and bedforms in the laingsburg flood deposits are related to specific subenvironments and flow conditions during the flood event two large scale sedimentary units in erosive contact with each other were deposited by two major discharge pulses within the same flood event vertical and lateral variations in the bedform distributions reflect fluctuations in flow velocity and turbulence comparison is drawn between the laingsburg flood deposits and fluvial sandstones of the permian lower beaufort in the southwestern karoo the multistoried sandstone bodies composed mainly of a horizontally laminated lithofacies are interpreted as the products of a complex series of ephemeral flooding events individual storey units in the palaeochannel sequences are generally envisaged as the deposits of different floods however evidence from the modern flood shows that separate pulses of a single flooding episode can also produce a sequence of storey units bounded by erosive scours spectacular palaeosurfaces in the lower beaufort also have modern analogues in the laingsburg overbank deposits discussion on the preservation potential of delicate sedimentary structures and biogenic traces on these surfaces emphasizes the necessity for pulsatory deposition of bedload and suspended load material over short intervals of time by comparing facies profiles and surface bedforms the ephemeral fluvial facies model for the lower beaufort is critically appraised

fluvial incision and tectonic uplift across the himalayas of central nepal the pattern of fluvial incision across the himalayas of central nepal is estimated from the distribution of holocene and pleistocene terraces and from the geometry of modern channels along major rivers draining across the range the terraces provide good constraints on incision rates across the himalayan frontal folds sub himalaya or siwaliks hills where rivers are forced to cut down into rising anticlines and have abandoned numerous strath terraces farther north and upstream in the lesser himalaya prominent fill terraces were deposited probably during the late pleistocene and were subsequently incised the amount of bedrock incision beneath the fill deposits is generally small suggesting a slow rate of fluvial incision in the lesser himalaya the terrace record is lost in the high range where the rivers are cutting steep gorges to complement the terrace study fluvial incision was also estimated from the modern channel geometries using an estimate of the shear stress exerted by the flowing water at the bottom of the channel as a proxy for river incision rate this approach allows quantification of the effect of variations in channel slope width and discharge on the incision rate of a river the determination of incision rates requires an additional lithological calibration the two approaches are shown to yield consistent results when applied to the same reach or if incision profiles along nearby parallel reaches are compared in the sub himalaya river incision is rapid with values up to 10 15 mm yr it does not exceed a few millimeters per year in the lesser himalaya and rises abruptly at the front of the high range to reach values of 4 8 mm yr within a 50 km wide zone that coincides with the position of the highest himalayan peaks sediment yield derived from the measurement of suspended load in himalayan rivers suggests that fluvial incision drives hillslope denudation of the landscape at the scale of the whole range the observed pattern of erosion is found to closely mimic uplift as predicted by a mechanical model taking into account erosion and slip along the flat ramp flat geometry of the main himalayan thrust fault the morphology of the range reflects a dynamic equilibrium between present day tectonics and surface processes the sharp relief together with the high uplift rates in the higher himalaya reflects thrusting over the midcrustal ramp rather than the isostatic response to reincision of the tibetan plateau driven by late cenozoic climate change or late miocene reactivation of the main central thrust

architectural elements and bounding surfaces in fluvial deposits anatomy of the kayenta formation lower jurassic southwest colorado abstract three well exposed outcrops in the kayenta formation lower jurassic near dove creek in southwestern colorado were studied using lateral profiles in order to test recent regarding architectural element analysis and the classification and interpretation of internal bounding surfaces examination of bounding surfaces within and between elements in the kayenta outcrops raises problems in applying the three fold classification of allen 1983 enlarging this classification to a six fold hierarchy permits the discrimination of surfaces intermediate between allen s second and third order types corresponding to the upper bounding surfaces of macroforms and internal erosional reactivation surfaces within the macroforms examples of the first five types of surface occur in the kayenta outcrops at dove creek the new classifications is offered as a general solution to the problem of description of complex three dimensional fluvial sandstone bodies the kayenta formation at dove creek consists of a multistorey sandstone body including the deposits of lateral and downstream accreted macroforms the storeys show no internal cyclicity neither within individual elements nor through the overall vertical thickness of the formation low paleocurrent variance indicates low sinuosity flow whereas macroform geometry and orientation suggest low to moderate sinuosity the many internal minor erosion surfaces draped with mud and followed by intraclast breccias imply frequent rapid stage fluctuation consistent with variable seasonal monsonal ephemmeral flow the results suggest a fluvial architecture similar to that of the south saskatchewan river through with a three dimensional geometry unlike that interpreted from surface studies of that river

helical burrow casts of therapsid origin from the beaufort group permian of south africa abstract large helical burrow casts of vertebrate origin have been discovered at several localities in the lowermost strata of the teekloof formation of the beaufort group permian in the southwestern karoo basin south africa they are not only the oldest but also the first vertebrate burrows of helical geometry to be found in rocks of pre mammalian age the burrow casts are vertically disposed spiralling tubes filled with fine grained sandstone or siltstone often with a calcareous cement tube diameters gradually increase from 60 mm in the upper entrance decline through two non contacting dextral coils to about 160 mm at the base of the spiral whereupon the tube straightens and widens into a horizontal terminal chamber burrow depths range from 0 5 0 75 m and the ramp angle ranges from 10 to 32 although within any single spiral it is constant articulated skeletons of the small dicynodont diictodon have been found within the terminal chambers and spirals of three sand filled burrows linear ridges preserved on the outer walls and floor of some of the terminal chambers resemble scratch marks possibly made by the claws and beak of diictodon during burrow excavation the sedimentary sequences at two separate localities are interpreted as having been deposited by episodic sheet floods and distributary splay fans in the proximal floodbasin areas flanking an aggrading meanderbelt rise comparison is drawn between helical burrow casts in the lower beaufort and other recorded occurrences in particular daimonelix a beaver burrow from the miocene of nebraska fundamental similarities far outweigh differences to the extent that the beaufort helical burrows may be grouped with the daimonelices it is concluded that the excavation of large helical burrows an activity usually attributed to rodents was pre empted by mammal like reptiles some 50 million years before the first anatomical mammals evolved

recognition of the sedimentary architecture of dryland anabranching anastomosing rivers abstract the application of rigorous criteria for identifying fluvial style from sedimentary deposits is crucial if environmental reconstructions from stratigraphy are to be reliable from modern observations it appears that anabranching anastomosing rivers can be divided into separate humid and dryland classes each class has dissimilar characteristics to the other necessitating different criteria for their recognition in the rock record the criteria being used by sedimentologists to recognize deposits of anabranching rivers are derived solely from modern examples in humid regions heavily biased to a few specific cases in canada these criteria are dominated by the concept of ribbon sandstone bodies encased in fine grained floodplain sediment with an overall low sand to mud ratio in the succession there has been a general failure to appreciate that dryland anabranching rivers have characteristics significantly different from these and almost certainly leave a sedimentary record quite dissimilar to that previously expected avulsion or obtrusion the gradual formation of an alternative channel are the characteristic dynamic of anabranching rivers forming and maintaining coexisting multiple anabranch channels avulsion or obtrusion require stream banks to have a high resistance to erosion usually achieved by cohesive bank sediments or the reinforcement of banks by vegetative root mats in some drylands riparian vegetation can be sparse and bank resistance may depend in large part on a high clay content here channel fills are mud dominated and floodplains have a uniform fine grained character which is usually structureless because of intense pedoturbation and some bioturbation the evidence from such present day dryland anabranching rivers suggests that their sedimentary record is likely to be one of laterally extensive mud rich beds with weak or enigmatic fluvial indicators elsewhere dryland anabranching systems are sand dominated their banks reinforced with riparian gallery forests sustained by infrequent flow and a shallow water table though the stratigraphy of these has barely been investigated they are clearly different from humid region anabranching systems for their channels and islands are predominantly sandy anabranching rivers with prominent channel sandbodies separated by muddy islands have never been described from contemporary drylands the interpretation of a dryland origin for ancient stratigraphic successions with this form is made therefore without evidence that they can actually exist in the light of this such interpretations should be reevaluated

ion probe u pb dating of authigenic and detrital opal from neogene quaternary alluvium abstract knowing depositional ages of alluvial fans is essential for many tectonic paleoclimatic and geomorphic studies in arid environments the use of u pb dating on secondary silica to establish the age of neogene quaternary clastic sediments was tested on samples of authigenic and detrital opal and chalcedony from depths of 25 to 53 m in boreholes at midway valley nevada dating of authigenic opal present as rinds on rock clasts and in calcite silica cements establishes minimum ages of alluvium deposition dating of detrital opal or chalcedony derived from the source volcanic rocks gives the maximum age of sediment deposition materials analyzed included 12 samples of authigenic opal one sample of fracture coating opal from bedrock one sample of detrital opal and two samples of detrital chalcedony uranium lead isotope data were obtained by both thermal ionization mass spectrometry and ion microprobe uranium concentrations ranged from tens to hundreds of g g relatively large u pb allowed calculation of 206 pb 238 u ages that ranged from 1 64 0 36 2 to 6 16 0 50 ma for authigenic opal and from 8 34 0 28 to 11 2 1 3 ma for detrital opal chalcedony three samples with the most radiogenic pb isotope compositions also allowed calculation of 207 pb 235 u ages which were concordant with 206 pb 238 u ages from the same samples these results indicate that basin development at midway valley was initiated between about 8 and 6 ma and that the basin was filled at long term average deposition rates of less than 1 cm ka because alluvium in midway valley was derived from adjacent highlands at yucca mountain the low rates of deposition determined in this study may imply a slow rate of erosion of yucca mountain volcanic strata underlying the basin are offset by a number of buried faults to a greater degree than the relatively smooth sloping bedrock alluvium contact these geologic relations indicate that movement on most faults ceased prior to erosional planation and burial therefore ages of the authigenic opal from basal alluvium indicate that the last movement on buried faults was older than about 6 ma

escarpment evolution on high elevation rifted margins insights derived from a surface processes model that combines diffusion advection and reaction experiments with a surface processes model of large scale 1 1000 km long term 1 100 m y erosional denudation are used to establish the controls on the evolution of a model escarpment that is related to the rifting of a continent the model describes changes in topographic form as a result of simultaneous short and long range mass transport representing hillslope diffusive processes and fluvial transport advection respectively fluvial entrainment is modeled as a first order kinetic reaction which reflects the credibility of the substrate and therefore the fluvial system is not necessarily carrying at capacity one dimensional and planform models demonstrate that the principal controls on the evolution of an initially steep model escarpment are 1 antecedent topography drainage 2 the timescale or equivalently a length scale in the fluvial entrainment reaction 3 the flexural response of the lithosphere to denudation and 4 the relative efficiencies of the short and long range transport processes when rainfall and substrate lithology are uniform a significant amount of discharge draining over the escarpment top causes it to degrade only when the top of the model escarpment coincides with a drainage divide can escarpment retreat occur for these conditions an additional requirement for retreat of a model escarpment without decline is a long reaction time scale for fluvial entrainment this corresponds to a substrate that is hard to detach by fluvial erosion and therefore to fluvial erosion that is not transport limited continuous backtilting of an escarpment due to flexural isostatic uplift in response to denudational unloading helps maintain the scarp top as a divide it is essential if the escarpment gradient is to be preserved during retreat in a uniform lithology low flexural rigidities promote steep and slowly retreating escarpments for given rainfall and substrate conditions the morphology of a retreating model escarpment is determined by the ratio of the short range diffusive and long range advective transport efficiencies a low ratio which is interpreted to correspond to a relatively arid climate and weathering limited conditions promotes steep sharp topped escarpments with straight main slopes and escarpment retreat occurs over a wide range of height scales a high ratio interpreted to correspond to a more humid temperate climate produces a convex upper slope and concave lower slope morphology and only major escarpments are predicted to preserve a high scarp gradient lithological contrasts in the model produce more complex morphologies and predict the formation of scarps crowned by an erosionally resistant caprock however resistant caprocks are not an essential requirement for model scarps to retreat we conclude that the inferred controls and model behavior are both consistent with the present day morphology of rifted continental margins and with modern conceptual models of landscape evolution

pedogenic slickensides indicators of strain and deformation processes in redbed sequences of the appalachian foreland pedogenic slickensides are convex concave slip surfaces that form during expansion contraction in expansive clay soils such as vertisols in the central appalachians they occur near the tops of fining upward cycles in paleozoic redbeds such as the bloomsburg catskill and mauch chunk formations pedogenic slickensides are found in association with other pedogenic or paleosol features such as clay skinned peds in situ calcareous nodules and root impressions repeated movements along these shear planes during pedogenesis produce strongly aligned clay particles adjacent to pedogenic slickensides as a result they are preserved as discrete fractures throughout diagenesis compaction and superimposed tectonic deformation during whole rock deformation pedogenic slickensides segregate penetratively deformed rocks into independent foliated packets and serve as discontinuities that are followed by later structural features because the original morphology of pedogenic slickensides is known they can be used as crude strain markers

volumetric analysis and hydrologic characterization of a modern debris flow near yucca mountain nevada abstract on july 21 or 22 1984 debris flows triggered by rainfall occurred on the southern hillslope of jake ridge about 6 km east of the crest of yucca mountain nevada rain gages near jake ridge recorded 65 mm and 69 mm on july 21 and 20 mm and 17 mm on july 22 rates of rainfall intensity ranged up to 73 mm h on the twenty first and 15 mm h on the twenty second digital elevation models with 2 0 m grid node spacing measured from pre storm and post storm aerial stereo photographs were used to map hillslope erosion and the downslope distribution of debris volumetric calculations indicate that about 7040 m 3 of debris was redistributed on the 49 132 m 2 hillslope study area during the two day storm period about 4580 m 3 65 of the eroded sediment was deposited within the study area and the remaining 35 was deposited outside the study area in a short tributary to fortymile wash and in the wash itself the maximum and mean depths of erosion in the study area were about 1 8 m and 5 cm respectively the mean depths of erosion on the upper and middle hillslope were 27 cm and 4 cm respectively the mean depth of deposition on the lower hillslope was 16 cm analysis of the values of cumulative precipitation in the context of the precipitation frequency atlas of the national oceanic and atmospheric administration indicates that precipitation from the main storm on july 21 was more than double that expected on average once during a 100 year period the relations of precipitation intensity duration developed from data recorded at a nearby precipitation gage indicate a storm interval of 500 years or greater the amount of erosion caused by such a storm is primarily dependent on three variables storm intensity development of the drainage network on the hillslope and the amount of available colluvium additionally the erosive ability of successive storms of equal intensity will decrease because such storms would tend to progressively isolate and reduce the amount of colluvium available the preservation of pleistocene deposits on hillslopes of yucca mountain in general indicates that erosional events that strip 5 of the available hillslope colluvium must be quite rare we conclude that the recurrence interval of an erosional event comparable to the july 1984 event is probably much longer than 500 years

ichnology and sedimentology of the trace fossil bearing fluvial red beds from the lowermost member of the paleocene funing formation in the jinhu depression subei basin east china abstract the lowermost member of the paleocene funing formation which is composed of bioturbated fluvial red beds is extensively distributed throughout the jinhu depression subei basin east china despite its economic value as one of the most important oil bearing reservoirs in the subei basin the sedimentology ichnology and paleoenvironment of this formation in the jinhu depression remain poorly understood in this work we investigated the ichnofossils and sedimentary facies analyzed the ichnofacies and potential tracemakers and reconstructed the paleoenvironment of the jinhu depression based on cores from the lowermost member of the paleocene funing formation this formation contains a moderately diverse ichnofauna 9 ichnotaxa of the scoyenia ichnofacies that includes meniscate burrows taenidium barretti taenidium satanassi and beaconites coronus simple horizontal cylindrical burrows palaeophycus tubularis palaeophycus heberti and planolites isp simple vertical or subvertical burrows skolithos linearis and skolithos isp and plant root traces the other complex branched and chambered burrows are left in open nomenclature these ichnofossils are widespread throughout the three facies associations identified in this study 1 ephemeral fluvial channel 2 crevasse splay and 3 distal floodplain facies associations multiple lines of sedimentological and ichnological evidence namely the predominance of massive and upper flow regime structures the occurrence of invertebrate burrows e g skolithos and taenidium in the lower and middle parts of the channel deposits and the dramatic changes in the color and mottling in channel and overbank sediments indicate that the river discharge was short lived and that the water table was highly variable the variations in the discharge and water level are attributed to the influence of seasonal rainfall the cyclic nature of intense rainfall events and dry periods suggests that the subei basin was likely located in a semiarid region with a seasonal rainfall pattern during the early paleocene this study also reveals that the ephemeral fluvial channel is the facies association with the highest potential to yield oil bearing reservoirs in the paleocene red beds of the jinhu depression additionally the influence of bioturbation on the reservoir quality in this region should be considered in future research

ground truthing chemostratigraphic correlations in fluvial systems changes in elemental chemistry have been used to define stratigraphic correlations between wellbores in petroleum basins few publications however relate defined chemical stratigraphy to physical correlations and none have been found that do so in fluvial systems here chemostratigraphy is applied to permian fluvial sediments within the beaufort group of the karoo basin in south africa and a correlation between three logged sections is defined this correlation is tested against physically determined chronostratigraphic correlations achieved using heli lidar data to provide a high resolution correlation between two sections 7 km 4 4 mi apart and mapping of strata using google earth to produce a correlation between sections 25 5 km 15 8 mi apart the chemostratigraphic characterization that is defined using data from fine grained lithologies resulted in the recognition of eight chemostratigraphic packages with thicknesses between 50 and 250 m 164 and 820 ft over a stratigraphic interval of approximately 900 m 2953 ft two distinctive changes in geochemical composition of the coarser lithologies fluvial channel belts were seen over this interval in the two sections that are 7 km 4 4 mi apart higher resolution subdivision of chemostratigraphic packages was achieved to produce four correlative geochemical units 30 60 m 98 197 ft in thickness that provide a high resolution correlation the chemostratigraphic and chronostratigraphic correlations are in close agreement in both the 7 km 4 4 mi and the 25 5 km 15 8 mi spaced sections the thickness of the study interval and spacing of sections is analogous to published chemostratigraphy studies on subsurface sequences thereby ground truthing the use of chemostratigraphy for correlation in subsurface fluvial systems that are to some degree analogous to the beaufort group sediments of this paper

meridional extent and interannual variability of the pacific ocean tropical subtropical warm water exchange altimetric observations of sea surface height anomaly ssha from the topex poseidon and ers satellites hydrography and the ecmwf and florida state university wind products are used to track warm water 20 c as it is exchanged between the equatorial pacific ocean and the higher latitudes during 1993 2003 the large el nino event of 1997 98 resulted in a significant discharge of warm water toward the higher latitudes within the interior of the pacific ocean the exchange of anomalous warm water volume with the northern hemisphere appears to be blocked under the intertropical convergence zone consistent with most current ideas on the time mean tropical subtropical exchange little of the warm water discharged northward across 5 and 8 n during the 1997 98 el nino event could be traced as far as 10 n to the south however these anomalous volumes of warm water were visible at least as far as 20 s primarily in the longitudes around 130 160 w in both hemispheres most of the warm water appeared to flow westward before returning to the tropics during the recharge phase of the el nino la nina cycle the buildup of warm water in the tropics before the 1997 98 el nino is shown to be fed primarily by warm water drawn from the region in the western pacific within 5 s 15 n the exchange cycle between the equatorial band and the higher latitudes north of the equator leads the cycle in the south by 6 8 months these results are found in all three datasets used herein hydrography altimetric observations of ssha and sverdrup transports calculated from multiple wind products which demonstrates the robustness of the results