channel margins in a pennsylvanian braided fluvial deposit the morien group near sydney nova scotia canada abstract braided fluvial deposits in the pennsylvanian morien group contain an unusual association of erosional features at contacts between sandstone and mudstone units which represent flat lying to vertical channel margins mudstone intraclasts up to 2 m in diameter form lensoid lags at channel bases and are interpreted as bank collapse rubble flutes on vertical channel walls channel floors and intraclasts indicate active flow whereas rills on steep surfaces resulted from downslope drainage over the edges of banks or mudclasts delicate plumose patterns on vertical fracture surfaces modified by flow formed during cracking of the muds by desiccation and bank collapse scoured desiccation cracks are common on flat lying surfaces where flow parallel linear scours 50 cm deep may have expl ited orthogonal desiccation cracks the channel margin features described here require deposition and subsequent reworking of cohesive fines on high topographic levels of a fluvial system due to alternating periods of flooding and subaerial exposure braided and ephemeral river systems with variable discharge are likely to provide the most suitable setting for these features

halokinetic sequence stratigraphy fluvial sedimentology and structural geometry of the eocene carroza formation along la popa salt weld la popa basin mexico

seasonal heat and freshwater budgets of the upper ocean in the north east atlantic heat and freshwater content changes were calculated from two repeated sections at 48 n 18 w and 48 n 26 w surveyed during the vivaldi cruise of the research ship rrs charles darwin in may 1991 best estimates of the air sea heat fluxes agreed within error with the observed heat content changes suggesting that diabatic forcing dominated the heat budget this was confirmed by a numerical model which showed that ekman and geostrophic advection and eddy diffusion together contributed less than 20 w m 2 to the heat budget however the model also showed that near the oceanic polar front under westerly winds ekman advection of cold fresh water southwards over the front can cause 40 w m 2 and 4 mm d 1 heat and freshwater content changes in the upper 53 m compared to air sea fluxes of typically 67 w m 2 and less than 1 mm d 1 the ekman advection contributed little to the model s density budget as the advective cooling and freshening had opposing effects however an air sea interaction model showed that the advective surface cooling may be reduced because it triggers an extra air sea heat flux and the remaining advective freshening then makes an important contribution to the density budget

floodplain construction of the rio grande at el paso texas usa response to holocene climate change abstract the rio grande is one of the larger rivers in north america and the development of its floodplain is related to holocene climate and climate change the late pleistocene through early holocene channel is characterized by a meander or braided system with lateral cutting and backfilling resulting in the valley wide deposition of massive to cross bedded fine to medium textured sand the late pleistocene early holocene floodplain is also the sand source for the adjacent bolson sand sheet the sand sheet stopped accumulating new sand 5000 yrs ago an event directly related to the shutting off of the sand supply caused by the deposition of overbank muds that covered and sealed the floodplain surface during the middle holocene the river may have dried intermittently with the floodplain becoming deflated and local sand dunes forming on the floodplain after 5000 yrs the climate was less arid and the river shifted to a regime of increased flooding and overbank deposition of silt and clay by 2500 yrs a late holocene period of wet climate resulted in further overbank deposition and the formation of a cumulic mollisol across the floodplain the socorro paleosol the period of wet climate corresponds to the audubon neoglacial and active rock glaciers in the southern rocky mountains speleothem growth in nearby caves and other evidence for wet cool conditions in the region after 1000 yrs the climate became drier and the deposition and accumulation of overbank muds by the flooding rio grande came to a halt even though the river has flooded often in historic times and presumably during late prehistoric times as well there is little evidence for deposition of overbank sediments on the floodplain since a d 1000 accordingly the present day surface of the lower valley is ten centuries old three channels occur on the us side of the lower valley floodplain and during the past 2500 yrs stream flow has shifted from one to the other by the avulsion process of channel reoccupation although most flow has been in the rio grande channel the largest of the three

patterns and drivers of meiofaunal assemblages in the canyons polcevera and bisagno of the ligurian sea nw mediterranean sea abstract meiofaunal abundance assemblage structure and richness of higher taxa were investigated for the first time in two submarine canyons polcevera and bisagno of the ligurian sea and along the adjacent open slope in relation with the quantity and quality of sedimentary organic matter and other environmental variables including grain size meiofaunal abundance and richness of higher taxa decreased with increasing water depth from ca 200 down to ca 2000 m depth in the open slope and polcevera canyon whereas the highest values were observed at 500 m depth in the bisagno canyon the comparison between canyons and the adjacent open slope showed the lack of significant differences in meiofaunal abundance at the same depth except for samples collected at 200 and 2000 m depth overall the biodiversity was higher in canyons than in the open slope phytopigments utilised as a proxy of the input of primary organic matter were up to 3 times higher in canyon than in slope sediments and along with grain size explained a large portion of the variability in all meiofaunal variables canyon and slope showed a high beta diversity 83 mostly due to the presence of a high portion of rare taxa in the canyons some taxa such as cladocera cumacea gastrotricha nemertina were exclusively encountered in canyon sediments whereas tardigrada were encountered only in the adjacent slope results reported here indicated that differences in meiofaunal assemblages between canyons and slopes are primarily driven by quantity and quality of the available food resources and by the presence of specific topographic features

climatic and tectonic controls on alluvial fan and axial fluvial sedimentation in the plio pleistocene palomas half graben southern rio grande rift abstract six steep 0 6 4 3 short radial length 1 5 5 km deeply incised pliocene to early pleistocene paleofans and associated axial fluvial strata are preserved adjacent to the footwall of the palomas half graben in the southern rio grande rift two different scales of interbedding of lithofacies are evident in the exposed basin fill sediment the footwall derived alluvial fan strata are arranged into 3 10 m thick cyclothems representing three events 1 development of calcic paleosols that were contemporaneously or subsequently truncated by channels up to 4 m deep 2 infilling of channels by turbulent flow horizontally bedded and cross bedded conglomerates and 3 deposition of hyperconcentrated flow pebbly sandstones these cyclothems probably resulted from paleoclimatic changes on the scale of 150 kyr on a larger geographic and temporal scale the axial river ancestral rio grande which primarily deposited cross bedded pebbly sand experienced kilometer scale lateral movement toward the footwall block resulting in one thick 80 m axial fluvial lithosome in the northern part of the basin and two or three thinner 8 25 m axial fluvial lithosomes in the south a protracted period of fault movement and consequent basin tilting was the probable driving force behind lateral movement of the river and toe cutting of the fans by the river was the dominant process

bar development in a fluvial sandstone westphalian a scotland the fluvial sandstone beneath the mill coal in the westphalian a of scotland erosively overlies a lake mudstone slightly erosive surfaces within the sandstone traceable for over 200 m are used to divide it into two types of major sedimentary units termed type a and type b type a sand units are approximately 200 m wide up to 7 m thick convex upward and lenticular in all directions the constituent cosets overlap to the ene and dip mainly at 1 2 downcurrent nnw but locally at 10 15 where thickest type a sand units display a vertical facies sequence commencing with trough cross bedded and massive sandstone overlain by a thick zone of ripple cross lamination a thin zone of trough cross beds and a variably eroded silt drape up to 0 4 m thick attenuated lateral margins are dominated by flat bedded sandstone with primary current lineation type a sand units are interpreted as deposits which were accreted on to a large fluvial bar during successive flood events the bar is thought to have had a similar topographic significance to sand waves described from the brahmaputra and slip face bounded bars observed in the south saskatchewan river palaeocurrents measured from trough cross bed sets 0 3 1 0 m thick within type b sand units indicate flow to the wsw perpendicular to the palaeoflow direction measured from type a units in sections perpendicular to the wsw flow direction type b units are lenticular and in ene wsw trending sections they can be traced for over 80 m at a constant thickness type b sand units are interpreted as the product of low stage channels which flowed across bar fronts and tops the sandstone described herein is interpreted as a braided type river deposit but is atypical because it is fine grained and has an internal structure dominated by ripple cross lamination and upper phase plane beds the palaeoriver is thought to have been of low sinuosity 7 10 m deep with a high suspended load and large rapidly fluctuating discharge at low stage a braided type flow pattern developed around submerged bars the regime of the palaeoriver was probably controlled by the fine sediment grain size and humid tropical climate

pliocene and quaternary history of the rio grande the axial river of the southern rio grande rift new mexico usa abstract the history of the rio grande the axial river of the southern rio grande rift new mexico may be divided into an aggradational phase 5 to 0 8 ma during which time about 100 m of fluvial sediment was deposited in eight basins and a degradational phase 0 8 ma to present when the river alternately incised and partially backfilled its basins reversal magnetostratigraphy dated volcanic rocks and vertebrate biostratigraphy allow correlation of sediment of the aggradational phase with the gilbert gauss and matuyama chrons while the degradational phase primarily encompasses the brunhes chron tectonics was the primary control on river behaviour during the aggradational phase in half grabens multistorey channel sands were deposited in narrow belts near the footwall uplifts in response to tilt of the basin floor towards the border fault and smaller footwall catchments and their alluvial fans compared to those of the hanging wall mountains in contrast the river traversed almost the entire width of full grabens depositing interbedded channel and floodplain sediment with moderately mature palaeosols condensed sections dominated by floodplain sediment with very mature palaeosols developed in basins largely abandoned by the river due to preferential tilting of the basin floor lateral growth or renewal of fault activity or alternating flow of the river between adjacent basins the degradational phase was dominated by net basin erosion related to glacial climate cycles despite continued activity on many of the basin bounding faults

deconvolving signals of tectonic and climatic controls from continental basins an example from the late paleozoic cumberland basin atlantic canada abstract the internal architecture and external form of fluvial channel bodies is governed by both intrinsic and extrinsic controls extrinsic controls such as climate eustasy and tectonism are believed to have modest effects on channel body types and geometries in high subsidence settings the effects of climate are particularly cryptic in high accommodation settings and have proven extremely difficult to separate from other extrinsic controls such as tectonics and eustasy the thick successions preserved in such basins have the potential to be relatively stratigraphically complete and are therefore valuable for interpreting basin evolution this study documents the external geometry and internal architectural styles of fluvial channel bodies in a spectacularly exposed 7 km thick mississippian permian section from the cumberland basin atlantic canada four fluvial styles are recognized perennial strongly seasonal ephemeral and fixed fluvial styles are not randomly distributed throughout the stratigraphic succession instead discrete stratigraphic intervals consist of predominantly one type of fluvial style four stratigraphic intervals e1 e4 in which strongly seasonal fluvial styles are predominant are recognized and alternate with intervals that are characterized by either perennial or ephemeral deposits this suggests that a coherent record of climate change as manifested by changes in precipitation and runoff regime is recorded in the internal architecture of sandbodies

calcic paleosols of the plio pleistocene camp rice and palomas formations southern rio grande rift usa abstract seventy four separate paleosols are recognized in the plio pleistocene camp rice and palomas formations of the southern rio grande rift seven types of profiles are present a bw bk c a bt bk c bw bk c bt bk c bt k c bk c and ak calcic and petrocalcic horizons bk and k commonly overlain by argillic horizons bt dominate most paleosol profiles greater pore size and enhanced permeability typical of sandy and silty parent material favored the development of argillic horizons however micrite is the dominant form of calcium carbonate in bk and k horizons regardless of parent material grain size non calcified a horizons are typically lighter in color than adjacent subsurface pedogenic intervals due to their oxidized nature or lower clay content they are only rarely preserved probably due to erosion prior to final burial calcified root mats ak are not directly associated with other pedogenic horizons abundant horizontal roots suggest root mats formed under high water table conditions restriction of ak horizons to the distal piedmont lithofacies supports their development as spring or pond deposits near the toes of alluvial fans individual pedogenic horizons can often be traced hundreds of meters to kilometers normal and parallel to a basin s axis paleosol maturity and preservation potential are greatest for symmetrical basins especially where pedogenesis was far removed from active channels within the axial fluvial system or within distal piedmont settings of asymmetrical basins

inferring the subduction rate and period over the north atlantic abstract the annual rate at which mixed layer fluid is transferred into the permanent thermocline that is the annual subduction rate sann and the effective subduction period x1d4af eff is inferred from climatological data in the north atlantic from its kinematic definition sann is obtained by summing the vertical velocity at the base of the winter mixed layer with the lateral induction of fluid through the sloping base of the winter mixed layer geostrophic velocity fields computed from the levitus climatology assuming a level of no motion at 2 5 km are used the vertical velocity at the base of the mixed layer is deduced from observed surface ekman pumping velocities and linear vorticity balance a plausible pattern of sann is obtained with subduction rates over the subtropical gyre approaching 100 m yr twice the maximum rate of ekman pumping the subduction period x1d4af eff is found by viewing subduction as a transformation process converting mixed layer fluid into stratified thermocline fluid the effective

late tertiary and quaternary fluvial deposits in the mesilla and hueco bolsons el paso area texas abstract the late tertiary to quaternary fort hancock and camp rice formations fill several extensional basins of the southern rio grande rift interior drainage and central playa lakes characterize most of these rift basins however sedimentation in two basins located in the central part of the southern rift the mesilla and hueco bolsons was also greatly influenced by a northern segment of the ancestral rio grande river system during the late pliocene a large scale stream system entered the north end of the mesilla bolson and deposited a south sloping fluvial plain that overwhelmed playa lake and bolson margin areas the fluvial plain subsequently advanced across the eastern or southeastern margins of the mesilla bolson then inundated a playa lake in the adjacent hueco bolson the fort hancock formation was deposited during fluvial inundation of the bolsons four lithofacies of the fort hancock formation are recognized claystone mudstone and sandstone channelized sandstone and conglomerate the conglomerate and claystone facies were deposited in bolson margin and playa depositional environments respectively the channelized sandstone facies formed the proximal fluvial plain of the ancestral rio grande system the mudstone and sandstone facies formed in both playa margin and distal fluvial plain environments by the middle pleistocene a major drainage basin south of the hueco bolson which formed the southern segment of the ancestral rio grande system extended northward into the hueco and mesilla bolsons at this time the rio grande system was entirely integrated from southern colorado to the gulf of mexico pebbly coarse sand transported through this channel system formed the middle pleistocene camp rice formation

sedimentology and palaeogeography of the regressive transgressive kurnub group early cretaceous of jordan abstract the early cretaceous kurnub group of jordan consists of three regressive transgressive fluvial marine depositional sequences in northern jordan recorded here for the first time whereas continental clastics dominated central and southern jordan deposition of the kurnub group started in the late neocomian above a regional angular unconformity by basal conglomerate and sandstone facies association of an alluvial braidplain origin during this time the tethys seaway was located to the north and northwest of jordan which afterwards during the barremian advanced in a south and southeastward direction flooding north jordan and giving rise to a tidal flat coastal swamp sequence following a subsequent regression of the sea unconfined braidplain deposits covered the area the most extensive transgression of the tethys inundated the region during the late aptian and early albian where a mixed siliciclastic carbonate sequence with interbedded inner shelf carbonates and tidal marsh coastal swamp black shales and lignites was deposited the next and last regression took place in the middle albian where a thin meandering river clastic sequence was deposited finally shallow marine sedimentation resumed over the region during the remaining time of the kurnub group which at the same time prepared for the subsequent regional cenomanian transgression upon comparison with global eustatic curves these three incursions of the tethys sea in jordan are to a great extent in accordance with the global sea level fluctuations the various formations of the kurnub group and their informal units that are established here for the first time can readily be correlated with equivalent deposits in adjacent countries the distribution of the shorelines of the barremian aptian and albian on both sides of the dead sea transform offers new evidence for 100 km northward displacement of the arabian plate against the sinai palestine plate

the heavy minerals of the kurnub sandstone early cretaceous of jordan abstract a study of the heavy mineral distribution in the kumub sandstone early cretaceous in jordan was carried out in vertical and lateral sections the heavy mineral suites of the kurnub sandstone in north and south jordan are identical and comparable to those in south israel and southwest sinai the suites are mainly opaques zircon tourmaline and rutile garnet staurolite epidot anatase barite and hornblende are less frequent staurolite and hornblende are confined to the south whereas garnet is confined to a few horizons in the north selective chemical decomposition played a significant role in the modification of the unstable heavy mineral variations in the kirnub sandstone the ultrastable heavy minerals indicate a source area predominantly composed of granitic and metamorphic rocks the association of zircon tourmaline and rutile in a pure quartz arenite indicates that the main source of the kurnub sandstone of jordan must be weathered paleozoic sediments

mixed geothermal and shallow meteoric origin of opal and calcite beds in pliocene lower pleistocene axial fluvial strata southern rio grande rift rincon hills new mexico u s a abstract exposed in upper pliocene fluvial strata in the eastern rincon hills and adjacent jornada del muerto basin southern rio grande rift new mexico usa are five laterally continuous beds 0 2 to 1 0 m thick of opal ct which straddle the east rincon hills normal fault four of these opal beds change basinward over 1 km or less to white friable lithofeldspathic sand with opal glaebules and then to microcrystalline calcite the opal and calcite generally replaced fine sand at shallow depths although two beds locally precipitated from standing water 87sr 86sr values 0 71301 to 0 71724 of the opal beds are consistent with precipitation from an advecting high temperature geothermal fluid that flowed through bedrock and or from a high temperature geothermal fluid derived from a deep crustal source carbon and oxygen isotopic values 13cpdb 7 1 to 0 6 18opdb 9 1 to 5 6 of the calcite beds lie between and overlap those of paleozoic carbonate and pliocene paleosol calcite suggesting precipitation from a mixture of a high temperature geothermal fluid that interacted with paleozoic carbonates and shallow meteoric groundwater for which paleosol calcite is a proxy the geothermal fluids are interpreted to have upwelled along the east rincon hills fault flowed laterally at or just below the surface and precipitated opal in response to rapid cooling and evaporation downflow precipitation of opal glaebules occurred as a result of decreasing silica concentrations and perhaps by mixing with shallow meteoric groundwater from which calcite precipitated probably by co2 degassing

a magnetostratigraphic record of landscape development in the eastern ordos plateau china transition from late miocene and early pliocene stacked sedimentation to late pliocene and quaternary uplift and incision by the yellow river abstract a continuous fluviolacustrine record provides the geochronological framework to reconstruct the fluvial landscape evolution of the middle reach of the huanghe yellow river magnetostratigraphic records from six sections at the north of the jinshaan gorge indicate that an isolated fluviolacustrine system occupied this gorge from 8 3 to 3 7 ma local fluvial incision initiated at the lake margin around 5 3 4 9 ma and concomitant fluvial deposits intruded laterally into fine lacustrine strata increasing the sedimentation rate ca 3 1 cm ky within the isolated lake the temporal coincidence of the onset of uplift driven valley incision at 3 7 ma along the yellow river and the onset of basin excavation suggest that uplift possibly played an important role in the late pliocene quaternary drainage evolution consequently incision of the yellow river upstream in the jinshaan gorge initiated at 3 7 ma

evaluation of cold water carbonates as a possible paleoclimatic indicator abstract the common belief currently shared by many geoscientists concerning the climatic interpretation of limestones is that a warm water environment is essential this concept is not necessarily true because the rate and extent of terrigenous sediment dilution rather than water temperature is the primary factor determining whether or not a limestone forms at nearshore or continental shelf depths because carbonate productivity is lowest in cold climates however caco3 abundance and the thickness of carbonate accumulations tend to be least at high latitudes in this regard present day continental shelves and beaches offer a poor model for comparing cold water and warm water carbonates because of the generally emergent continental tectonic framework recent eustatic sea level changes and the presence of ice caps at the modern poles typically the influence of climate on non reef continental shelf and beach environments cannot be clearly distinguished by the presence or absence of major taxonomic groups faunal diversity and equitability are more sensitive in this regard the absence of shelf depth inorganic carbonate precipitates micrite envelopes and peloids may also point to the cold water origin of a rock skeletal mineralogy and oxygen isotopes of certain unrecrystallized carbonates may be good paleoclimatic indicators however trace elements and physical textural attributes of the carbonate fraction are probably temperature insensitive previous studies of high latitude continental shelves have concentrated merely on the abundance of calcareous material and there is seemingly a disproportionate amount of information with respect to low latitude carbonate studies further research on cold water carbonates may open up new avenues for alternative paleoenvironmental and paleoclimatic interpretations

structure and circulation of the upper atlantic ocean northeast of the azores historical data primarily from the igy but spanning the years 1914 1983 have been re examined in an attempt to define the structure and circulation of the upper ocean 0 800 m in the eastern north atlantic 30 50 n 10 40 w the saline greater than 35 7 anticyclonic surface gyre shallows to the north like a wedge being 300 500 m deep at 36 n east of 30 w and outcropping at about 45 n it lies above the mediterranean water separated from it by a salinity minimum and by a pycnostad of subpolar mode water mccartney and talley 1982 eastward flow between 36 n and 46 n is primarily confined to the saline wedge with speeds of 2 4 cm s 1 the flow converges gradually towards the east resulting in fronts and strong meridional property gradients e g mixed layer depth robinson bauer and schroeder 1979 east of 15 w the majority of the supolar mode water is formed by deep winter convection north of the saline wedge and subducts to the south under it southward advection and ventilation rates in the northeast atlantic the main ventilation region for the north atlantic sarmiento rooth and roether 1982 are similar estimated to be 0 2 cm s 1 the freshening of the surface layer between 1967 and 1976 that has been found in widely separated regions of the north atlantic rockall trough sargasso sea labrador sea is also present northeast of the azores salinities down to 500 m have decreased by 0 1 equivalent to an addition of a 1 4 m column of fresh water at the surface the freshening on t 27 1 decreases to negligible values southwards of 40 n it is suggested that changes in the balance of evaporation and precipitation must have occured

3he surface exposure dating and its implications for magma evolution in the potrillo volcanic field rio grande rift new mexico usa dating of very young igneous activity has been hampered by lack of suitable chronometers we report here the results of 3he surface exposure dating kurz 1986a b craig and poreda 1986 for lavas from the potrillo volcanic field this field is particularly suited to the technique because it has well preserved young 700 ka surfaces the study applies 3he dating in a systematic manner to a well characterized volcanic field and shows the power of the technique in deciphering both relative and absolute chronologies dates are reproducible to within 14 for different samples from the same surface and are similar to within 8 for samples which based on field relations represent synchronous events cosmogenic 3he21ne confirms that 3he is retained by the samples comparison of the relative chronology with compositional trends of the lavas suggests that eruptive centers within the volcanic field are fed by individual magma chambers ages range from 80 ka to 17 ka consistent with estimates from geomorphology soil profile development and some k ar determinations

sedimentary labile organic carbon and pore water redox control on species distribution of benthic foraminifera a case study from lisbon setubal canyon southern portugal abstract rose bengal stained benthic foraminifera were studied from 11 cores collected along two depth transects off southern portugal one in the lisbon setubal canyon and the other along the canyon edge the total standing stocks and distribution of foraminifera were investigated in relation to sediment and pore water geochemistry nitrate was used as a redox indicator sedimentary chlorophyll a and cpe chloroplastic pigment equivalents contents as a measure of labile organic matter and total organic carbon as a measure of bulk organic matter availability the canyon sediments were enriched in organic carbon and phytopigments at all water depths in comparison with the canyon edge water depth seemed to control sedimentary phytopigment content but not total organic carbon no significant correlation was seen between pigment and total organic carbon content the abundance of calcareous foraminifera correlated with the phytodetritus content whereas a weaker correlation was observed for the agglutinated taxa therefore calcareous foraminifera appear to require a fresher food input than agglutinated taxa the foraminiferal species composition also varied with pigment content and nitrate penetration depth in the sediment in line with the trox concept phytopigment rich surficial cpe content 20 g cm3 sediments with a shallow nitrate penetration depth 1 cm depth were inhabited by generally infaunal species such as chilostomella oolina melonis barleeanus and globobulimina spp as the nitrate penetration increased to 2 cm depth in sediment and the pigment content remained relatively high 15 g cm3 uvigerina mediterranea and uvigerina elongatastriata became dominant species with declining cpe content and increasing nitrate penetration depth the foraminiferal assemblages changed from the mesotrophic cibicides kullenbergi uvigerina peregrina assemblage to the oligotrophic abyssal assemblage mainly consisting of agglutinated taxa

the whittard canyon a case study of submarine canyon processes submarine canyons are large geomorphological features that incise continental shelves and slopes around the world they are often suggested to be biodiversity and biomass hotspots although there is no consensus about this in the literature nevertheless many canyons do host diverse faunal communities but owing to our lack of understanding of the processes shaping and driving this diversity appropriate management strategies have yet to be developed here we integrate all the current knowledge of one single system the whittard canyon celtic margin ne atlantic including the latest research on its geology sedimentology geomorphology oceanography ecology and biodiversity in order to address this issue the whittard canyon is an active system in terms of sediment transport the net suspended sediment transport is mainly up canyon causing sedimentary overflow in some upper canyon areas occasionally sediment gravity flow events do occur some possibly the result of anthropogenic activity however the role of these intermittent gravity flows in transferring labile organic matter to the deeper regions of the canyon appears to be limited more likely any labile organic matter flushed downslope in this way becomes strongly diluted with bulk material and is therefore of little food value for benthic fauna instead the fresh organic matter found in the whittard channel mainly arrives through vertical deposition and lateral transport of phytoplankton blooms that occur in the area during spring and summer the response of the whittard canyon fauna to these processes is different in different groups foraminiferal abundances are higher in the upper parts of the canyon and on the slope than in the lower canyon meiofaunal abundances in the upper and middle part of the canyon are higher than on adjacent slopes but lower in the deepest part mega and macrofauna abundances are higher in the canyon compared with the adjacent slope and are higher in the eastern than the western branch these faunal patterns reflect the fact that the whittard canyon encompasses considerable environmental heterogeneity related to a combination of organic matter trapping current regimes due to focused internal tides and different substrates we conclude that coordinated observations of processes driving faunal patterns are needed at a fine scale in order to understand the functioning of communities in this and other submarine canyons

modification of ocean eddies by air sea interaction a mixed layer model is developed for seasonal time scales and used to investigate the modification of ocean eddies by air sea interaction an eddy is modified by the air sea interaction for the local envionment and the feedback from its surface temperature signal which alters the surface heat and water fluxes this buoyancy forcing tends to decrease the eddy temperature anomaly and seasonal changes in mixed layer depth lead to the surface signal being removed in summer and reappearing in winter the dynamical adjustment of the eddy is assessed by coupling the mixed layer model to a quasi geostrophic model the buoyancy forcing alters the eddy velocity profile and over several seasons may lead to the formation of a subsurface velocity maximum after the spring decrease in mixed layer depth the eddy potential vorticity anomaly is reduced and lateral mixing may subsequently play a role in further eroding the eddy these modelling predictions are supported by the observations of a cold core eddy in the seasonal boundary layer of the northeast atlantic

sedimentology and mineral composition of the kurnub sandstone in wadi qsieb sw jordan abstract the kurnub sandstone of early cretaceous age crops out in wadi qsieb in the southwest of jordan with a thickness of 130 m moderately developed fining upward cycles with irregular erosive bases together with the presence of plant fragments and the absence of body or trace fossils point to a fluviatile depositional environment probably a river of intermediate sinuosity results of grain size analysis confirm this interpretation the sandstones are compositionally and texturally supermature quartz arenites formed mainly by recycling from early palaeozoc sandstones and less commonly by direct supply from the arabian nubian shield the absence of feldspars and unstable heavy minerals is attributed to intense chemical weathering attacking sands that were deposited with a low rate on a craton bordering the tethys sea the thickness recorded here and the absolute absence of hornblende are in contradiction with what has been published by nasir and sadeddin 1989

reappraisal of the sequence boundary in time and space case and considerations for an su subaerial unconformity that is not a sediment bypass surface a time barrier or an unconformity abstract the sequence bounding unconformity bears the key defining traits of being a surface separating younger from older strata along which there is evidence of subaerial erosional truncation or subaerial exposure with a significant hiatus indicated van wagoner et al 1988 this subaerial component of sequence boundaries subaerial unconformity su is also broadly considered to form as a topographic surface of sediment bypass carved during relative sea level fall and buried by backfilling during relative sea level rise accordingly the su is commonly presumed to record an approximate time barrier which separates older from younger strata along its full length in this paper we show that regional composite scour rcs surfaces that are traditionally mapped as an integral component of the su were never a single subaerial topographic surface characterized by sediment bypass are not unconformities do not record an effective time barrier and form diachronously at the channel belt scale over the entire fall to rise of a base level cycle these rcs surfaces and by inference the su surfaces they comprise thus do not fully fit key defining characteristics embodied in the conceptual sequence boundary flume observations and field data show that the rcs is buried by fluvial sediment simultaneously as it is scoured accordingly the rcs is perennially covered with stored sediment during formation is only exposed as a subaerial topographic surface at the local place and time where it is undergoing active growth and forms over the duration of local marine drainage during a relative sea level cycle this cut and cover model differs greatly from more established bypass models which assume that the rcs was roughly sediment free and subaerially exposed for long durations of incision during regression and thus preserves a significant depositional hiatus upon later burial instead the rcs may commonly and locally record a hiatus more typical of a facies bounding diastem without a lacuna significantly greater than that of surfaces within the strata it binds fragments of fluvial strata may commonly and sporadically be preserved above the rcs that are older than underlying marine units overrun by this surface consequently the rcs is not an effective time barrier lateral planation by migrating and avulsing channels as the rcs expands laterally after nucleation can place younger fluvial strata over much older units which means that this surface is also composite and highly diachronous laterally at the scale of channel belts the cut and cover model has additional implications not captured by the bypass model first significant sediments may be stored within fluvial strata above the rcs during regression that are not available for contemporary falling stage and lowstand marine shorelines this can result in marine sediment starvation particularly of the sand fraction and in extreme cases can result in sand autodetachment and an absence of regressive marine reservoir sandstones second cutting of the rcs co generates a suprafluvial surface above the covering fluvial strata during regression that may be used as a mappable proxy for the conceptual maximum regressive surface mrs the mrs may be raised above this surface locally by low accommodation aggradation during lowstand normal regression but in either case preserves an approximate time line where not reworked during later transgression third valley development across the rcs does not exclusively form by landward knickpoint growth and may include complexly formed and potentially cross cutting buffer valleys su valley incision can be divided into four modes which include denudation structural buttress and buffer valley components which may work together locally and tend to have variable importance along the shore to hinterland profile although the rcs is not a good rock proxy for the conceptual sequence boundary it remains a very mappable surface which may separate facies of potentially very different origin and reservoir quality the rcs is also inseparable from the su and typically the only terrestrial erosional surface of extent in most short duration sequences its nullification as a sequence boundary would mean abandonment of depositional sequence stratigraphy as a correlation and interpretive tool within these sections an alternative to abandonment of the su as a sequence boundary is to loosen the definition of a sequence boundary to a discrete surface of erosional truncation carved landward of contemporary shorelines that is traceable beyond the scale of a single valley or comparable local system and its correlative surfaces of conformity and or non deposition and continue its use as before

the non analogue nature of pliocene temperature gradients abstract the strong warming of the north atlantic and high latitudes in the pliocene 5 3 2 6 million years ago continually fails to be simulated in climate model simulations being the last period of earth history with higher global temperatures and carbon dioxide levels similar to today it is an important target period for palaeoclimate models one of the key features of the pliocene climate is the reduced meridional gradients particularly in the high latitudes of the northern hemisphere here we show that previously unconsidered palaeogeographic changes river routing ocean bathymetry and additional landmass in the modern barents sea in the north atlantic region can produce significant temperature responses at high latitudes along with orbital forcing this can significantly decrease equator to pole temperature gradients in the atlantic ocean these additional forcings show that the large arctic warming and significantly reduced temperature gradients in the pliocene are not analogous to future warming and that careful consideration of all the possible climatic forcings is required to accurately simulate pliocene climate

sedimentation and tectonic geomorphology adjacent to major active and inactive normal faults southern greece the active psatha skinos normal fault is uplifting a contrasting variety of lithologies in its footwall including mesozoic limestones ophiolitic peridotites and poorly consolidated plio pleistocene sediments of the inactive megara basin in the latter basin linear marginal uplands border the sedimentary fill and are interpreted as degraded and segmented scarp lines which exhibit features such as facetted spurs drainage domains are defined as groups of drainage basins sharing a common tectono geological substrate contrasting domains in the footwall of the active fault have given rise to spectacular differences in drainage basin growth and form in the uplifting footwall raised coastal terrace levels are present at about 10 and 40 m the latter have yielded corals dated at between 90 126 ka and have enabled us to calculate uplift and erosional rates extrapolation of these rates indicate that some 350 m of footwall relief has been produced over approximately 1 ma most of the sediment eroded from the uplifting footwall is presumed to have been re sedimented into the alkyonides gulf basin plain during this time the prominent footwall unconformity so produced forms a fine modern analogue to features seen in ancient syn rift tilt blocks such as the viking graben footwall uplift has also backtilted the former depositional surface of the megara basin and caused reversal of flow in its axial drainage domain a variety of depositional environments are documented in the subsiding hangingwall to the coastal fault including syn quake talus cones alluvial fans intra fan marshes and swamps truncated fans transgressive barriers and spits

mammalian biochronology of the late cenozoic basins of new mexico late cenozoic mammalian remains have been collected from new mexico for more than a century the most important nineteenth century collections came from the espanola basin work in this century has continued to focus mainly on the miocene faunas in that basin and the northern part of the adjoining albuquerque basin the lithostratigraphy of these basins has recently been reviewed and revised but the description of the large collections of fossil remains from the basinal deposits is largely incomplete pliocene and early pleistocene faunas have been found in deposits that mark the development of external drainage of the major rivers of the state study of these assemblages has been cursory although the lithostratigraphy of these deposits has received considerable attention in recent years the miocene basinal deposits accumulated under conditions of internal drainage in local structural environments that led to the development of partly synchronous depositional records biostratigraphies worked out in each basin overlap sufficiently so that the composite succession forms an important biochronological standard for southwestern north america the espanola and albuquerque belen basins contain the only miocene faunas of importance presently known in new mexico their fossil records complement one another in that the northern albuquerque basin has the only adequate representation of the early miocene and the espanola basin a more complete record of the medial and late miocene synchronous faunas in these basins show a high degree of taxonomic resemblance extending to elements that represent endemic taxa or forms rare elsewhere compared with coevel assemblages in the great plains there is considerable generic and specific similarity this allows easy reference of the new mexican faunal succession to the sequence of north american mammal ages that are essentially typified by the great plains biochronology in addition to these taxonomic relationships the new mexican faunas retain throughout the miocene characters that may typify a southwestern faunal province the general features of the latter would include diverse and abundant artiodactyls especially camelidae including a late occurrence of endemic stenomyline genera and less diverse and abundant perissodactyls especially horses when compared with the great plains the fossil vertebrate record of pliocene and early pleistocene time in new mexico is largely confined to the basins of the rio grande and the gila river and is derived from deposits of the axial rivers that were the percursors of the modern streams and from the piedmont slope facies of the basin margins sites scattered along the length of the rio grande rift from the santo domingo basin near santa fe south to the international border have yielded blancan and early irvington faunas these assemblages can be arranged in temporal order from their position in local stratigraphic columns from their biological affinities and with respect to dated basalts and ashes interbedded in the sediments containing the fossil remains important reference sequences are available in adjacent arizona and texas where mammalian faunas and calibrated biochronologies compare closely with those in new mexico the new mexican record supports the southwestern biochronology for pliocene and early pleistocene time including the following events and their calibration the last appearance of hipparionine horses nannippus and the first appearance of the south american immigrants the glyptodont glyptotherium and probably the mylodontid sloth genus glossotherium were nearly synchronous events close to the gauss matuyama boundary 2 5 m y b p at least three species equus were present in the southwest by the time of the nannippus extinction the first appearance of the asiatic immigrant mammuthus in the southwest between 1 2 and 1 4 m y postdating the olduvai event and by definition indicating that the blancan irvingtonian boundary at least as determined for the southwest lies close to the beginning of medial pleistocene time

late neogene rift basin evolution and its relation to normal fault history and climate change along the southwestern margin of the gerania range central greece abstractthe south to southwest dipping north and south saros normal faults occupy the southeastern margin of the gerania range a major massif of mesozoic limestone and o phi o lite in the eastern gulf of corinth rift cen tral greece the history of the saros faults is constrained by adjacent basin ll sediments and modern drainage patterns older basin ll pliocene lower pleistocene which consists of terrestrial ne sands carbona ceous muds marls and micrite limestones is uplifted on the south saros fault block and onlaps the north saros fault footwall block on its northern side to near its crest suggest ing that it predates major fault activity in contrast younger basin ll middle pleisto cene was deposited and locally deformed during fault activity in a main basin south of the faults and in a perched basin on the south saros fault block main basin deposits consist of alluvial fan fan delta and shallow marine sediments up to 50 m thick whereas perched basin fanglomerates are 5 15 m thick fault scarp retreat and sediment onlap indicate that the faults became inactive late in the history of deposition of the younger basin ll the perched and main basins are currently undergoing incision allowing mod ern sediment to bypass the basins and to be deposited on modern fan deltas and beaches along the gulf of megara coast the absence of knickpoints and upstream deepening of the canyons suggest that a climatically driven increase in catchment runoff was responsible for basin incision although uplift and sea level change may have contributed as well the north and south saros faults each consist of three segments characterized by different strikes the major drainages cross the saros faults at or near segment boundar ies suggesting that the drainages may have initially owed between the tips of isolated fault segments as the segments became linked the antecedent drainages maintained their course and cut deep gorges at the scale of the entire eastern gulf of corinth region however older unlinked faults were aban doned and new faults were created in a gen eral northward and basinward direction the origin of this process remains controversial introduction

classification of paleosols despite increased interest in paleosols during the past decade no satisfactory classification is in current use presented here is a largely descriptive classification system that utilizes those pedogenic features that have the highest preservation potential in the rock record emphasized in the classification are morphological and mineralogical features that are easily recognizable in the field and through the petrographic microscope the classification is based on evaluation of the relative prominence in a paleosol of six pedogenic features or processes organic matter content horizonation redox conditions in situ mineral alteration illuviation of insoluble minerals compounds and accumulation of soluble minerals the most prominent of these six features processes provides the key to classifying a paleosol into one of nine orders four of the order names are borrowed from soil taxonomy histosol spodosol oxisol vertisol whereas the other five order names are presented here for the first time calcisol gypsisol gleysol argillisol protosol the orders may be preceded by one or more subordinate modifiers that describe other important features of the paleosol the classification is relatively easy to apply to the rock record and should enhance communication and aid in the standardization of terminology

interaction of a river with an alluvial basin aquifer stable isotopes salinity and water budgets summary detailed sets of tracer data isotopes salinity and the results of modflow modeling of water budgets provide an unprecedented opportunity for comparing modeling with field data in the area where the rio grande enters the hueco bolson basin of texas and chihuahua water from the rio grande has recharged the hueco bolson aquifer to a depth of 300 m below the surface in the el paso ciudad juarez area the depth of infiltration corresponding to the depth of ancestral rio grande fluvial sediments groundwater beneath the river exhibits complex isotope and salinity stratification post dam post 1916 type a river water has infiltrated to depths up to 80 m pre dam type b river water has infiltrated to 300 m depth near downtown el paso and has mixed with or been displaced further downstream by high salinity native hueco bolson groundwater type c present in the basin north of the river salinity and isotope boundaries do not correspond precisely isotope stratification corresponds to water residence time and for type c to degree of evaporation the highest salinities are associated with the most evaporated water modeling of water budgets in the basin fill beneath the river predicts present day mixing of water types b and c where changing rates of pumping have caused a reversal of groundwater flow direction between el paso and ciudad juarez and deep recharge of type b water under conditions prevailing in the 1960s

tectonic control on facies distribution of the camp rice and palomas formations pliocene pleistocene in the southern rio grande rift the pliocene pleistocene camp rice and palomas formations in the rio grande rift of southern new mexico provide an excellent test of the role of basin symmetry in the distribution of piedmont and axial fluvial facies in the asymmetrical palomas and northern mesilla basins the axial fluvial facies is characterized by multistory channel sands and sandstones and is concentrated near the locus of maximum subsidence within a few kilometers of the footwall scarp fanglomerate derived from the footwall uplift extends only a few kilometers or less from the footwall scarp whereas alluvial fan and alluvial flat conglomerate sand and mudstone deposited on the hanging wall dip slope occupy a much wider outcrop belt in the symmetrical hatch rincon basin the axial fluvial facies extends to within a few kilometers of both the northern and southern basin margins and has a much higher percentage of fine grained overbank deposits some of which contain calcareous paleosols in all three basins a tongue of fanglomerate as much as 30 m thick prograded over the axial fluvial facies near the end of camp rice and palomas deposition the distribution of facies of the camp rice and palomas formations supports previously published models that predict a two stage history of asymmetrically subsiding basins during tectonically active periods axial river channels preferentially avulse into the topographically lowest area of the alluvial plain which is directly above the axis of maximum subsidence during the postorogenic stage when erosion rate exceeds subsidence rate coarse transverse dispersed sediment progrades toward the center of the basin

spatial and temporal variability of meiobenthic density in the blanes submarine canyon nw mediterranean abstract meiofaunal density distribution was studied from 400 m to 1500 m depth inside blanes submarine canyon nw mediterranean and on the eastern open slope in autumn 2003 and spring 2004 our multidisciplinary approach allowed to study the hydrodynamics and sedimentary processes in the blanes canyon that characterize it as highly heterogeneous environment inside the canyon area particle fluxes were higher than on the slope area increased from autumn to spring and mostly consisted of lithogenic material moreover the canyon s locations experienced more intense bottoms currents and sediment disturbance being reflected in a greater variability of meiobenthic densities both between stations and sampling times than on the open slope no clear trends e g declining densities associated with increasing depths were observed contrary in the open slope current velocities were relatively lower compared with the canyon area and showed lower temporal variability at the same time the nutritional quality of the particle fluxes at deeper grounds were higher probably allowing the meiofaunal densities not to change over time in conclusion the meiobenthos in our system apparently showed a higher temporal variability inside the canyon area strongly affected by particle fluxes or erosive and sediment mixing processes linked to current modifications induced by the canyon topography

lateral erosion toe cutting of alluvial fans by axial rivers implications for basin analysis and architecture abstract we document the neglected phenomenon of lateral erosion toe cutting of alluvial fans by non incising axial river channels field examples from the holocene of the big lost river basin idaho and the plio pleistocene of the rio grande rift new mexico help to establish architectural models with more general application to basin analysis the process of toe cutting can lead to complete fan destruction and may be a response to climate change tectonic tilting fault propagation or a combination of these variables it gives rise to near horizontal erosion surfaces cut in fan sediment steep fan margin scarps progressive up fan incision from the scarp by a network of channels soil formation up fan away from the incised channel network a deposit of axial alluvium that overlies the erosion surface and onlaps the scarp once avulsion occurs to take the axial channel away from the bajada margin distinctive healing wedges of fan alluvium prograde across abandoned axial river channel and floodplain deposits gradually onlapping the eroded scarp and its upstream network of incised channels toe cutting has important stratigraphic basin analysis and economic consequences bajada deposits subject to the process exhibit appreciable extra groundwater and petroleum reservoir potential in the intercalations of more porous and permeable axial fluvial sediments

spillover models for axial rivers in regions of continental extension the rio mimbres and rio grande in the southern rio grande rift usa the pliocene early pleistocene history of the ancestral rio grande and quaternary history of the rio mimbres in the southern rio grande rift new mexico illustrate how axial rivers may alternately spill into and subsequently abandon extensional basins three types of spillover basins are recognized based on the angle at which the axial river enters the basin and whether it descends the hanging wall dip slope or footwall scarp to reach the basin floor in the mimbres basin type the axial river enters and flows through the spillover basin nearly parallel to the footwall scarp resulting in a narrow belt of basin axis parallel channel sand bodies located near the footwall scarp in contrast an axial river may enter a spillover basin at a high angle to its axis either descending the hanging wall dip slope columbus basin type or footwall scarp tularosa basin type and construct a fluvial fan consisting of radiating distributary channels orientated nearly perpendicular to the basin axis faulting exerts significant control on river spillover by creating the topographic gaps through which the axial river moves and by terminating spillover by subsequently uplifting or tilting the gap spillover may also be autocyclic in origin as a result of aggradation to the level of a pre existing gap headward erosion creating and or intersecting a gap or simple river avulsion upstream of a gap predicting facies architecture in the three types of spillover basins is critical to successful subsurface exploration for hydrocarbon reservoirs groundwater aquifers or placer mineral deposits

the distribution and discrimination of shallow authigenic carbonate in the pliocene pleistocene palomas basin southern rio grande rift nine types of authigenic carbonate are present in the pliocene pleistocene alluvial fan and axial fluvial sediment of the palomas half graben in the southern rio grande rift pedogenic and other vadose carbonate includes 1 pedogenic carbonate of stage ii and stage iii morphology underlying bw and bt horizons 2 mudstones in which the carbonate nodules may be pedogenic or the result of shallow groundwater invasion of the vadose zone 3 pedogenic calcic nodules and tubules in eolian sand and 4 gully bed cement of proximal fan conglomerates formed by infiltration and evaporation of surface runoff shallow groundwater carbonate exists as 5 thin 30 50 cm massive beds with an upper fringe of nodules and tubules precipitated at the water table and in the capillary fringe 6 thick 1 5 3 m massive beds deposited by lateral flow of groundwater or at springs and 7 thin 30 cm calcified root mats associated with near surface water saturated sediment or springs phreatic spar cements 8 occupy the interstices of conglomerates and sandstones and locally exist as 9 oriented concretions groundwater carbonates are best developed near the toes of the large hanging wall derived alluvial fans whereas phreatic cement preferentially exists in footwall derived alluvial fan conglomerates pedogenic carbonate is distinguished from groundwater carbonate by the association with other diagnostic paleosol horizons a predominantly vertical arrangement of root traces peds desiccation cracks and calcic tubules and by gradational contacts the 13 c and 18 o values are similar among pedogenic and shallow groundwater carbonate although locally nodules in eolian sand and gully bed cement have higher 18 o values perhaps due to the effects of evaporation some phreatic cements may be distinguished from pedogenic and shallow groundwater carbonate by lower values of 13 c and 18 o authigenic carbonate in footwall derived alluvial fan sediment has consistently higher values of 13 c than that in hanging wall derived sediment which may reflect differences in vegetative type and or density on either side of the basin

stratigraphic architecture of an experimental basin with interacting drainages abstract the stratigraphic architecture of intracontinental rift basins is defined by a dynamic relationship between depositional processes associated with the basin floor and flanking tributary streams the resulting depositional belts are sensitive to a variety of factors including basin geometry subsidence rate and sediment discharge the experimental earthscape run in 2006 xes06 examined the development of fluvial morphology and alluvial architecture as a function of subsidence and sediment flux in an experimental basin based on the form of a simple half graben sediments from tributary drainages were introduced into the axial stream through toe cutting and realignment of transverse drainage courses to parallel the prevailing axial flow direction transverse sediment contributions to the axial stream were almost equally apportioned over a wide range of sediment discharges tested in the experiments sediment tracers showed a larger contribution of footwall derived sediment into the axial belt probably due to more frequent and aggressive toe cutting by axial streams changes in the axial transverse deposit boundary to external forcing by subsidence and sediment discharge and relatively rapid intrastage stabilization of the depositional belts resembles the large scale self organization observed in moving boundaries that define the morphology of fluviodeltaic systems basin sedimentation was matched to subsidence in order to maintain a constant base level which made the location and width of the axial belt sensitive to the relative sediment fluxes from the transverse systems rather than the axis of maximum subsidence the asymmetrical subsidence pattern and the transverse fan morphology influenced the preservation of sedimentary sequences stage bounding stratigraphic lacunae were well preserved in the hanging wall succession providing a reliable record of basin development

the first north american mammoths taxonomy and chronology of early irvingtonian early pleistocene mammuthus from new mexico in north america some of the most complete and well dated records of primitive mammoths are from lower pleistocene deposits in the rio grande rift of central and southern new mexico the oldest of these mammoths are early irvingtonian in age 1 3 1 4 ma and are assigned to mammuthus meridionalis based on their primitive jaw morphology and relatively broad low crowned molars with low plate ratios and thick enamel the somewhat younger primitive new mexican mammoths are also early irvingtonian 0 8 1 3 ma but are more advanced morphologically so we refer them to m imperator the primitive mammoths from the early irvingtonian leisey shell pit in florida are morphologically similar and we refer them to m imperator the recent suggestions that north american mammuthus is derived from eurasian m trogontherii and that all north american mammoths except the late arriving m primigenius belong to one species m columbi are rejected because they are based on internal inconsistency incorrect data and inadequate analysis of the north american mammoth record the new mexican mammoths confirm the presence of m meridionalis grade mammuthus in north america before 1 3 ma and the rapid evolution of an m imperator grade mammoth by 1 2 ma

a test of models of fluvial architecture and palaeosol development camp rice formation upper pliocene lower pleistocene southern rio grande rift new mexico usa numerical experimental and theoretical models of fluvial architecture and palaeosol development are tested with outcrops of upper pliocene lower pleistocene sediment in the southern rio grande rift new mexico the sediment was deposited and subsequently exhumed in the jornada del muerto basin a westward tilted half graben whose footwall corresponds to the rincon hills and san diego mountain fault blocks the axial river the ancestral rio grande shared time between the jornada del muerto basin and the adjacent corralitos basin the ancestral rio grande entered the jornada del muerto basin via a gap between the footwall blocks periodically flowing southward towards san diego mountain or making a broad northward sweep into the northern fluvial salient towards the rincon hills fault block and unfaulted northern edge of the basin ten logged sections up to 35 m thick are correlated using the top of the formation la mesa surface a 1 59 ma pumice conglomerate and a ground water carbonate opal bed additionally one of the sections is dated by reversal magnetostratigraphy consistent with the model of bridge leeder 1979 and bridge mackey 1993a differential tilting of the jornada del muerto half graben resulted in sections directly adjacent to the faults that consist almost exclusively of multistorey channel sands sandstones whereas more distal sections contain a greater proportion of crevasse splay fine sand and overbank mudstone and calcic palaeosols along the axis of the northern fluvial salient a northward decrease in channel floodplain ratio a decrease in channel recurrence interval from 171 kyr to 685 kyr and an increase in the maturity of calcic palaeosols are consistent with southward tilt of the unfaulted northern edge of the basin an upsection decrease in sediment accumulation rate in the northern fluvial salient from 0 036 mm yr to 0 017 mm yr corresponds to an increase in the ratio of channel floodplain facies and in the number of multistorey channel sands sandstones and is consistent with the model of bridge leeder 1979 in which avulsion frequency is independent of sediment accumulation rate stage ii and iii calcic palaeosols indicate 103 105 year of landscape stability and soil formation between periods of floodplain deposition in response not only to basin tilting but also because the ancestral rio grande had multiple paths within the jornada del muerto basin and shared time between the corralitos and jornada del muerto basins

weathering recycling hydraulic sorting and metamorphism metasomatism implications of the ne gondwana lower cambrian lower cretaceous siliciclastic succession of jordan abstract whole rock major elements detrital and authigenic light heavy and clay minerals and neoformed zeolite minerals of the ne gondwana lower cambrian lower cretaceous siliciclastic succession of jordan were investigated to evaluate the factors controlling the chemical composition of the sandstone the provenance source rocks controlled by the tectonic setting at the time of deposition of the subarkosic arenites and the quartzarenites were the principal mineral and chemical governing factor followed by an interplay of chemical weathering recycling hydraulic sorting diagenesis and very low grade metamorphism hydrothermal metasomatism the sandstone provenance was mainly granitoids of the arabian shield formed during the neoproterozoic gondwana amalgamation and minor paleozoic and mesozoic siliciclastic strata high cia and low wip weathering index values indicate an intensive chemical weathering event that affected the provenance during the early cambrian middle ordovician and gave rise to mature first cycle quartzarenites high cia wip and sio2 al2o3 ratios indicate a pronounced recycling in the early cretaceous responsible for super mature second poly cycled quartzarenites the subarkosic arenites were formed either under a thorough chemical weathering coupled with a high rate of erosion and a rapid deposition in adjacent braidplains or an arid glacial climate devoid of chemical weathering hydraulic sorting caused enrichment of al and k in the detrital clay minerals ti in the silt sized ti bearing minerals and si in the sand sized quartz the very low grade metamorphism hydrothermal metasomatism recorded here for the first time is indicated by illite crystallinity ic 0 36 2 illite sericite muscovite transformation zeolites apatite authigenesis and alteration of monazite and titanite ilmenite into thorite and leucoxene hematite

10be exposure ages of ancient desert pavements reveal quaternary evolution of the dead sea drainage basin and rift margin tilting abstract early to late pleistocene 10 be exposure ages of abandoned surfaces in the negev desert reveal the regional drainage evolution history and its relationship with the subsidence of the western margin of the dead sea rift the dated desert paved surfaces have developed over originally westward flowing rivers which were abandoned by early pleistocene and whose relicts are now progressively tilted towards the rift axis the slow and non destructive subsidence coupled with extreme hyperaridity enabled the preservation of these ancient surfaces along some of the main water divides in the negev nearly irrespective of their distance from the rift axis constraints on the tilting history are obtained from analyzing the spatial pattern of the exposure ages suggesting subsidence rates as low as 120 300 m ma 1 in the southern arava valley since the late pliocene it is shown that the transition from the pliocene to current drainage pattern occurred over a short period during the early pleistocene and that the governing fluvial response that followed the delineation of current basins is represented by a continuous spectrum of ages of inset terraces

fluvial morphology and sediment flux steering of axial transverse boundaries in an experimental basin abstract the distinction between depositional belts associated with the basin axis and flanking piedmont streams is a fundamental attribute of the stratigraphic architecture of intracontinental rift basins spatiotemporal distributions of these lithofacies associations are sensitive to a combination of factors including basin geometry subsidence rate and sediment discharge however most studies have focused on one or two controls and one depositional component axial or tributary of the basin fill succession a new perspective on how these depositional belts develop under simple but precisely controlled boundary conditions of steady subsidence sediment flux and water discharge is achieved through the creation of an experimental stratigraphic succession the experimental earthscape run in 2006 xes06 focused on the geomorphic evolution of sedimentary successions within an asymmetrically subsiding basin analogous to a simple half graben containing four interacting supply points of sediment and water under the imposed conditions the experimental system self organized into an axial stream flanked by transverse fans imposition of various combinations of longitudinal and lateral sediment flux showed that the locations and widths of the axial and transverse systems were strongly controlled by relative sediment fluxes flux steering and less influenced by the location of the subsidence maximum and subsidence rate the axial drainage was dominated by transversely sourced sediment through toe cutting of the transverse fans except during the highest axial sediment discharges footwall fans persisted even under conditions of very large axial sediment discharge aided by topographic inheritance of the steeper transverse depositional slopes

provenance of triassic feldspathic sandstones in the iberian range spain significance of quartz types abstract the base of the triassic in the iberian range is represented by detrital sediments buntsandstein facies deposited initially in a continental environment finally evolving into a marine environment that is represented at the top of the sequence the lithology of this facies is dominated by arkosic sandstones the aim of this study is to reconstruct the nature and position of the source areas of these sandstones provenance research was carried out by quartz grain typology eleven stratigraphic sections were sampled the amount of interstitital matrix has been considered in selecting samples because mechanical compaction suffered by sandstones with little matrix may give rise to a significant increase in the undulosity of monocrystalline quartz the ollo de sapo gneissic formation located in the hesperian massif has been mentioned as source rocks of feldspathic sandstones in previous works in order to verify the provenance of feldspathic sandstones in artificial sands derived by grinding gneisses and sand samples collected at stream heads that drain the gneiss outcrops we followed the methodology of basu et al 1975 analytical results indicate that two different areas within the triassic basin were notably influenced by different source areas a a western zone the nearest to the gneissic source rocks where monocrystalline nonundulatory quartz grains predominate qm 5 increase sediment evolution during transport processes is markedly reflected by the increase in qm 5 ratios in the westernmost zone away from the source area low values in the above mentioned ratios in the eastern zone are interpreted as results of local influence by low ranking metamorphic source areas finally this ethod also allows for the monitoring of the evolution of sediment maturity throughout the basin

first quantitative test of alluvial stratigraphic models southern rio grande rift new mexico since 1978 the results of computational architectural models have been widely used to aid interpretation of ancient alluvial successions here we present the first quantitative test of such models we parameterize variables from field and magnetostratigraphic data collected from the well exposed pliocene pleistocene camp rice and palomas formations of the rio grande rift in south central new mexico computational runs establish that the lab leeder allen and bridge model correctly predicts the gross architectural patterns of ancestral axial rio grande half grabens and full grabens convergence of tectonic subsidence rate and mean sedimentation rate over the studied interval suggests that the dynamic basis of the models is correct i e it is the tectonic drawdown of axially supplied sediment that controls the net preservation potential of alluvial successions

fluvial conglomerates in continental red beds of the buntsandstein lower triassic in the eifel f r g and their palaeoenvironmental palaeogeographical and palaeotectonic significance abstract fluvial conglomerates occur in a variety of facies within the continental red bed sequence of the buntsandstein lower triassic in the eifel at the western margin of the mid european triassic basin the alluvial rudites are classified into channel floor lag channel bar channel top lag crevasse splay and floodplain lag conglomerates the conglomerates were predominantly deposited in scott type and in subordinate amounts also in donjek type and south sasketchewan type braided rivers the vertical distribution of clast size and frequency within the megacycles reflects the palaeotectonic sequence of uplift events in the source area resulting in supply of large amounts of coarse detritus which cause recurrences in fluvial style gradually upwards diminishing size and abundance of gravel indicate continuous lowering of source area relief during weakening endogenic activity or even tectonic quiescence after final peneplanation the palaeoenvironmental interpretation of the individual members and the palaeotectonic analysis of the conglomerate successions are combined with a reconstruction of the depositional history of the eifel buntsandstein which comprises an evolution of fluvial deposition the terminal stage of the palaeoenvironmental evolution is highlighted by a climax of regional diversification of conglomerate sedimentary milieu the horizontal distribution of clast size and abundance delineates the palaeogeographical evolution of the elongated eifel basin giving evidence of a progressive sidewards extension of the depositional area with time lateral supply from parts of the western margin and mixing of proximally derived coarse clasts with distantly delivered fine detritus result in highly inhomogeneous gravel distributions within the sedimentary region often not being characterized by gradually decreasing size and abundance of gravel in downstream direction the stepwise southwestwards shift of the marginal centre of supply of coarse gravel with time during the course of the lateral extension of the basin results in ascension of the fluvial conglomerate wedges into successively younger formations comprising consecutively middle buntsandstein upper buntsandstein lower muschelkalk middle muschelkalk and finally middle keuper the extraformational conglomerates mainly delineate the palaeogeographical framework whereas the intraclastic rudites primarily give evidence of processes operating within the depositional area reflecting erosion and reworking of overbank sequences with floodplain fines palaeosols and aeolian dune sands during lateral channel shift the brockelbank intraformational carbonate breccias to conglomerates originating from reworking of calcrete palaeosols are a peculiar facies element with particularly high palaeoenvironmental significance they document the frequency spatial extension and temporal persistence of pedogenesis within the alluvial plain the size of the extraformational clasts gives evidence of the range of current velocities during aggradation of the channels the distribution of conglomerate type and clast characteristics within cyclothems indicates the presence of stage fluctuations and variations in discharge in parts of the sequence the preservation of complete cyclothems or the multistoreying of channel bar conglomerates reflects the differential importance of the two main mechanisms controlling accumulation of sediments in the alluvial plain primary depositional restriction to suppression of formation and secondary erosional removal to destruction of finer grained channel sediments floodplain deposits and aeolian dune sands or palaeosols condensation of a series of depositional events within monotonous stacked conglomerate sequences obliterates the full range of sedimentary processes and mimics periods of long term stability of conglomerate formation waning flow mud drapes are particularly significant instruments to split up the individual genetical units of formation of fluvial conglomerates often comprising discrete flood phases separated by stage fluctuations of different magnitude the homogeneous or microcyclic composition of the coarse member reflects uniphase or multiphase aggradation of watercourses with gradually declining or abruptly waning individual flood periods the fluvial rudites thus are of high significance in the reconstruction of the depositional milieu in the eifel buntsandstein and provide a key to detailed interpretation of palaeoenvironmental processes palaeogeographical constellations and palaeotectonic events which could not have been identified to such an extent in exclusively sandy sequences

combined use of tracer approach and numerical simulation to estimate groundwater recharge in an alluvial aquifer system a case study of nasunogahara area central japan summary in this study we simulate the spatial and temporal distribution of groundwater recharge in an alluvial aquifer system in the nasunogahara area of japan natural stable isotopes 18 o d were considered as additional calibration targets in a numerical model the reliability of the model outputs was further validated by comparing the results from the numerical simulation and an independent tracer approach the results indicated that the calibrated model can effectively simulate the spatial and temporal characteristics of the contribution ratios of recharge sources to groundwater in the nasunogahara area however the tracer approach i e end member mixing analysis provided more reliable results at point scale particularly for the estimated contribution ratios of paddy field water the precipitation in the nasunogahara area is the major recharge source its mean contribution ratio is 58 for a one year period over the entire alluvial fan river seepage is significant in the upstream area of the alluvial fan and the contribution ratio of river waters along the river channels in the upstream area increases during the wet season paddy field water is a highly important recharge source in the midstream and downstream areas of the alluvial fan and the contribution ratio of paddy field water obviously increases from dry season to wet season because of irrigation this study demonstrates that combined use of the tracer approach and numerical simulation with stable isotopes as additional calibration targets can eliminate their respective limitations and can assist in better understanding the groundwater recharge mechanism in alluvial aquifer systems

organic geochemistry of submarine canyons the portuguese margin abstract the organic geochemistry of the portuguese margin of the north eastern atlantic ocean reveals a highly heterogeneous environment that is strongly influenced by canyons that incise the continental margin suspended particulate organic matter spom is funnelled through the canyons to the deep sea particularly in the nazare canyon where there are high concentrations of spom even at 2000 m water depth the nature of the spom through the water column varies with that transported through the canyons having higher contributions of terrestrial organic matter higher c n and larger contribution of land plant derived lipids than spom in overlying waters and close to the seafloor on the adjacent slope zooplankton derived lipids dominate spom associated with the upper and lower boundaries of the mediterranean overflow water mow 600 and 1500 m respectively canyon sediments are enriched in organic carbon when compared to slope sediments but sedimentary organic matter also appears to derive from multiple sources and undergoes significant alteration prior to deposition on the open slope low sedimentation rates and long oxygen exposure times lead to intensive oxidation of organic matter

development of the temperature and salinity structure of the upper ocean over two months in an area 150 times 150 km and discussion during the two months of the jasin experiment a regular conductivity temperature depth station pattern was worked by hr neth ms tydeman giving a total of eight surveys of temperature and salinity structure in an area 100 km times 150 km the data are averaged to obtain hourly and spatial mean profiles it is shown that this averaging conserves heat and salt content the spatial mean profiles are compared with heat budget computations and it is found that on average surface heat fluxes dominate the time history of the oceanic heat content on the scale of the whole survey area on smaller scales advection due to mesoscale structures dominates masking any differences in heating in different water masses comparison with results from a one dimensional mixed layer model indicates that this type of model satisfactorily simulates the development of the temperature profile as a spatial average for the survey area in this paper we have shown that it is possible to obtain average profiles of temperature and salinity that can be considered representative for an ocean area of about 100 km times 150 km covering several meoscale features total removal of the eddy signal from temperature profiles is found to be impossible owing to the eddy signal s varying with depth we have shown that on average the surface heat fluxes 50 w m 2 balance the changes in the oceanic heat budget advective terms being generally smaller by an order of magnitude 10 w m 2 during most of the jasin field experiment though measured currents were high up to 26 cm s 1 most of the flow was associated with the eddies and was contained within the 100 km times 150 km area and did not lead to large transport of heat in or out of the area on scales less than an eddy diameter 90 km eddy advection 400 300 w m 2 dominated local changes in heat content a one dimensional model is presented capable of simulating the observed changes in the temperature profile

reconstructing the ancestral plio pleistocene rio grande in its active tectonic setting southern rio grande rift new mexico usa deposits of the ancestral rio grande arg belonging to the camp rice formation are preserved and exposed in the uplifted southern portion of the robledo mountains horst of the southern rio grande rift the sediments are dated palaeomagnetically to the gauss chron upper pliocene the lower part of the succession lies in a newly discovered palaeocanyon cut into underlying eocene rocks whose margins are progressively onlapped by the upper part detailed sedimentological studies reveal the presence of numerous river channel and floodplain lithofacies indicative of varied deposition in channel bar complexes of low sinuosity pebbly sandbed channels that traversed generally dryland floodplains and shifted in and out of the study area five times over the 1 myr or so recorded by the succession notable discoveries in the deposits are 1 complexes of initial avulsion breakout channels at the base of major sandstone storeys 2 common low angle bedsets ascribed to deposition over low angle dunes in active channels 3 palaeocanyon floodplain environments with evidence of fluctuating near surface water tables sandbody architecture is generally multistorey with palaeocurrents indicative of funnelling of initial avulsive and main fluvial discharge from the neighbouring mesilla basin through a narrow topographic gap into the palaeocanyon and out over the study area an avulsion node was evidently located at the stationary southern tip to the east robledo fault during gauss times with arg channels to the north flowing close to the fault and preventing fan progradation subsequent matuyama growth of the fault caused 1 deposition to cease as the whole succession was uplifted in its footwall 2 development of a thick petrocalcic horizon and 3 fan progradation into the mesilla basin parameters for the whole arg fluvial system are estimated as active single channels 2 m deep and 25 m wide valley slope 0 24 0 065 maximum mean aggradation rate 0 05 mm year 1 major channel belt avulsion interval 200 ky individual channel recurrence interval 100 ky minimum bankfull mean flow velocity 1 54 m s 1 minimum single channel discharge 77 m3 s 1 bed shear stress 22 3 n m 2 and stream power 34 3 w m 2

pleistocene incision rates in the western united states calibrated using lava creek b tephra the lava creek b ash bed erupted from the yellowstone caldera ca 0 64 ma provides a datum for measuring long term fluvial incision west of the mississippi river the ash is widely preserved due to its substantial volume broad initial dispersal and the aggrading environment into which the ash fell drainages incised soon after lava creek b deposition isolating the ash from fluvial erosion and preserving it in fill terraces calculated rates of incision since ca 0 60 ma range from 2 to 30 cm k y 1 rates are high in most areas near the rocky mountains and downstream along rivers draining mountainous terrain and are lowest east of the high plains and along the snake river incision rates along many rivers decrease downstream rates of downcutting increased in the late pleistocene along several major rivers indicating that climate change altered sediment budgets regional and temporal data suggest that fluvial incision records increased middle and late pleistocene runoff from the southern rocky mountains rather than epeirogenic uplift but regional rock uplift cannot be excluded as a significant factor

aggradation incision and interfluve flooding in the ganga valley over the past 100 000 years testing the influence of monsoonal precipitation abstract in order to investigate fluvial responses to climate forcing stratigraphic data from seven cores in the ganga valley of india and a valley margin cliff section 1 3 km long are compared with proxy records for the intensity of the southwest indian monsoon luminescence dates indicate that the strata cover the past 100 ka five aggradational periods separated by incisional episodes are apparent in the valley fill some of which have correlative strata along the valley margin during marine isotope stages mis 4 and 5 the valley experienced fluvial activity with thin floodplain successions and probable discontinuities along the interfluve margin modest fluvial activity characterised the mid part of mis 3 at about 37 ka aggradation of channel sands preceded by incision is documented for late mis 3 23 to 30 ka as well as for late mis 2 to early mis 1 11 16 ka with fluvial dates focused around the younger dryas period of monsoon reduction the most recent aggradational period took place in the latest holocene

modern flood deposition erosion and fan channel avulsion on the semiarid red canyon and palomas canyon alluvial fans in the southern rio grande rift new mexico u s a abstract in the summer of 2006 large floods occurred on the red canyon footwall derived and palomas canyon hanging wall derived alluvial fans which are located on opposite sides of the rio grande floodplain in the palomas half graben of the southern rio grande rift the initial phase of the red canyon flood took place on the active central fan lobe but subsequent avulsion of the main channel shifted the flood to the south where it eroded all but two small relicts of the former inactive toe cut lobe before depositing up to 2 m of coarse gravel deposition of 0 5 m of gravel size detritus by the palomas canyon flood was largely confined to the active incised channel and to gravel bars that built into the river although floodwater spilled over the southern bank of the channel near its mouth depositing a thin 15 cm veneer of fine sand on the floodplain measurements of mean and maximum grain size of the flood deposits channel bed slopes and flood depth based on vegetative high water marks allow estimates of mean flood velocity red canyon 8 6 m s 1 palomas canyon 7 4 m s 1 floodwater discharge red canyon 971 m3 s 1 palomas canyon 179 m3 s 1 and volume of flood deposits red canyon 3 19 105 m3 palomas canyon 1 72 104 m3 mapping of the modern floodplain and outcrop analysis of the palomas formation pliocene lower pleistocene in the palomas basin provide insight into facies architecture in half grabens footwall derived alluvial fan detritus consists principally of shallow multistory gravel conglomerate channels produced by channel avulsion across the surface of the small fans asymmetrical basin tilting causes toe cutting of the footwall derived fans by the axial river and incision of hanging wall derived alluvial fan channels the latter resulting in ribbon shaped gravel conglomerate channels interbedded with finer grained distal fan sediment the red canyon and palomas canyon floods changed the location width and depth of the rio grande causing flooding of the western floodplain for 1 km upstream of the constriction because the rio grande has been dammed since 1916 it no longer has the stream power to effectively redistribute large volumes of fan detritus and must be dredged in order to avoid upstream flooding by the river

tectonic and climatic controls on holocene channel migration incision and terrace formation by the rio grande in the palomas half graben southern rio grande rift usa in order to evaluate potential effects of tectonics and climate change on the behaviour of the axial rio grande in the rio grande rift a 16 5 km stretch of modern floodplain and holocene terraces were mapped in the tectonically active palomas half graben south central new mexico usa in addition 51 cores and natural exposures were logged and 20 radiocarbon dates were obtained from charcoal bulk organic matter mollusc shells and pedogenic calcite the holocene alluvium comprises four terraces above the modern floodplain each of which formed by a period of river incision followed by stability and renewed floodplain construction to a level below that of the previous terraces estimated times of incision between terraces i and ii ii and iii and iii and iv are after 12 400 8040 to 5310 and 760 to 550 yr bp respectively whereas the incision between terrace iv and the modern floodplain occurred within the last 260 years although there is some evidence for tectonic control on river behaviour in the southern part of the basin terrace formation is interpreted as being related to climate change with periods of incision corresponding to times of increased aridity and low sediment water discharge ratio in the rio grande this process may have resulted from a reduction in intensity and magnitude of summer storms which supply sediment to the axial river coupled with an increase in spring discharge peak caused by snowmelt in upstream mountain catchments

detrital and authigenic feldspars in permian and early triassic sandstones eastern alps austria abstract detrital and authigenic feldspars of permian and early triassic scythian sandstones of the eastern alps austria have been investigated using thin section microscopy cathodoluminenscence cl x ray diffraction and electron microprobe sandstones of permian alluvial sequences are low in detrital feldspars due to strong weathering and diagenetic alteration within early permian sandstones detrital feldspar type is strongly dependent on the source rock late permian sandstones of all sections investigated are very low in detrital feldspars most of which are alkali varieties early triassic sandstones are characterized by a better degree of sorting and rounding and higher feldspar contents especially in the marine environment subarkoses to arkoses alkali feldspar dominates by far in all sections of the alpine buntsandstein formation drau range gurktal nappe and northern calcareous alps in the werfen formation of the drau range and gurktal nappe alkali feldspars also dominate whereas albites are the most common detrital feldspars in the northern calcareous alps due to different source rocks despite the fact that late permian groden formation and early triassic sandstones alpine buntsandstein and werfen formations are derived from reworking of intra permian rhyolitic volcanics to a great extent containing sanidines it is evident from x ray diffraction and cl investigations that detrital alkali feldspars within these units are not of volcanic but of metamorphic origin being microclines with bright blue cl sanidines of intra permian volcanics as being very unstable due to their structural state appear to have been completely destroyed during weathering and diagenesis authigenic feldspar overgrowths almost pure potassium feldspars frequently occur in scythian sandstones of the drau range and gurktal nappe particularly in the marine environment compared to the detrital cores authigenic feldspar overgrowths are characterized by different optical orientation chemical differences in minor and trace elements and absence of cl dissolution of volcanic sanidine volcanic rock fragments plagioclases and other unstable silicate minerals increased the concentration of pore waters for al si and k leading to the precipitation of diagenetically formed k feldspar overgrowths in sandstones of marine origin

proximal braidplain deposits in the middle devonian malbaie formation of eastern gaspe quebec canada the middle devonian malbaie formation of eastern gaspe canada comprises sharply alternating conglomerate and sandstone units their petrography suggests derivation from the same source but palaeocurrents indicate different dispersal systems for the sand and gravel the principal conglomerate facies is horizontally stratified with well developed imbrication characteristic of deposition on a high energy proximal braidplain minor cross stratified conglomerate shows well defined size sorting attributed to avalanching down foresets and sorting within minor bedforms on bar tops the sandstone units mainly comprise erosion surfaces overlain by mudstone intraclasts alternating with lineated low angle to horizontally stratified sandstone or trough cross stratified sandstone the sandstone units were deposited on a proximal braidplain with highly variable discharge but the absence of calcrete indicates that dry periods were not prolonged the malbaie is the coarsest uppermost formation of a devonian clastic wedge formed during the acadian orogeny the uniformity of facies association and palaeocurrents particularly in conglomerate units indicates derivation from a broad upwarp to the south this implies that the acadian uplands resulted from straight compression in contrast to the localized uplifts formed by strike slip faulting during the carboniferous

upper ocean eddy transports of heat potential vorticity and volume in the northeastern north atlantic vivaldi 1991 abstract mesoscale eddies in the northeast north atlantic were investigated using the seasoar towed ctd and adcp data from the 1991 vivaldi cruise these data cover an area of 1700 km 1500 km between 39 and 54 n and between 35 and 10 w to maximize statistical significance but retain the possibility of determining north south gradients statistics of eddy quantities were calculated separately for the northern and southern halves of the cruise area the mean flow in the south is essentially zero in the north the flow is dominated by the north atlantic current nac with a mean speed of 6 5 cm s 1 the eddy kinetic energy in the south 205 cm2 s 2 is however only slightly less than in the north 272 cm2 s 2 the eddy momentum transports or reynolds stresses u show a poleward decrease corresponding to an acceleration of the mean eastward flow associated with the nac of 0 03 cm s 1 day 1 the eddy heat transports u t are not significantly different from zero in the south but show a clear po

lateral advection of organic matter in cascading dominated submarine canyons in the gulf of lions gol dense water overflowing off the shelf occurs seasonally and represents the main mechanism affecting the shelf slope exchange of particulate organic matter om most of the dense water export takes place in the south western gol and in particular through cap de creus cdc submarine canyon here benthic instruments were deployed to collect down canyon particulate fluxes whereas surface sediments were taken after the cascading event along the sediment dispersal system on the shelf in cdc canyon and in the nearby lacaze duthiers ld canyon the chemical composition of the suspended material and surface sediments were investigated using several proxies including organic and inorganic carbon total nitrogen biogenic silica 13c 14c and alkaline cuo oxidation products thermohaline anomalies and high current speed events were measured in cdc canyon since december 2004 until mid april 2005 indicating a marked off shelf export of dense water trough the canyon during the cascading mud and relatively coarse shelf and upper canyon sediments were the major component of the mass flux conversely advection of fine material via nepheloid layers dominated down slope fluxes during pre and post cascading the resulting change in grain size affected the flux of mineral bound terrigenous oc indicating that the down canyon transport of land derived om did not occur as bulk but rather its composition is driven by sediment sorting associated with different transport mechanisms both surface sediments and sediment trap samples indicated that cdc canyon is well connected to the gol terrigenous dispersal system conversely our results suggest an overall limited influence of land derived om in ld canyon in spite of the reduced fluvial nutrient supply a significant pulsed input of modern marine om was observed in april 2005 at the end of the cascading period both intense mixing and lack of strong water column stratification likely played a key role allowing for both diffusion of nutrients rich waters into the euphotic zone and efficient vertical sink of marine oc on its way toward the seafloor this fresh pool of oc interacted with the dense plume overflowing off the shelf becoming part of the material laterally advected to the slope

depositional environments of the early cretaceous kurnub hathira sandstones north jordan abstract the kurnub hathira sandstones in north jordan which are most probably of early cretaceous age are about 300 m thick varicoloured friable quartz arenitic sandstones based on grain size analysis sedimentary structures palaeocurrent fossil content and petrography these sandstones are postulated to be dominantly of fluvial origin with a few interfingering shallow marine horizons a southward displacement of jordan by at least 100 km would bring these sandstones opposite to similar rocks west of the jordan araba rift with jordan being higher during the early cretaceous

a three dimensional ocean mesoscale simulation using data from the semaphore experiment mixed layer heat budget a primitive equation model is used to simulate the mesoscale circulation associated with a portion of the azores front investigated during the intensive observation period iop of the structure des echanges mer atmosphere proprietes des heterogeneites oceaniques recherche experimentale semaphore experiment in fall 1993 the model is a mesoscale version of the ocean general circulation model ogcm developed at the laboratoire d oceanographie dynamique et de climatologie lodyc in paris and includes open lateral boundaries a 1 5 level order turbulence closure scheme and fine mesh resolution 0 11 for latitude and 0 09 for longitude the atmospheric forcing is provided by satellite data for the solar and infrared fluxes and by analyzed or reanalyzed for the wind atmospheric data from the european centre for medium range weather forecasts ecmwf forecast model the extended data set collected during the iop of semaphore enables a detailed initialization of the model a coupling with the rest of the basin through time dependent open boundaries and a model data comparison for validation the analysis of model outputs indicates that most features are in good agreement with independent available observations the surface front evolution is subject to an intense deformation different from that of the deep front system which evolves only weakly an estimate of the upper layer heat budget is performed during the 22 days of the integration of the model each term of this budget is analyzed according to various atmospheric events that occurred during the experiment such as the passage of a strong storm this facilitates extended estimates of mixed layer or relevant surface processes beyond those which are obtainable directly from observations surface fluxes represent 54 of the heat loss in the mixed layer and 70 in the top 100 m layer while vertical transport at the mixed layer bottom accounts for 31 and three dimensional processes account for 14

depositional environment and diagenesis of the lower part of the kurnub sandstone formation lower cretaceous mahis area jordan abstract the lowest part of the kurnub sandstone formation lower cretaceous in the mahis area was deposited in a fluvial environment kaolinite is the major clay mineral associated with quartz the transformation of feldspars and mica to sericite and finally to kaolinite was a major degradation process and was the result of intensive action of acidic circulating water most of the kaolinite flakes however are believed to be detritally deposited under freshwater conditions

grain size analysis of the lower cambrian lower cretaceous clastic sequence of jordan sedimentological and paleo hydrodynamical implications abstract 356 sand sized samples ranging in age from early cambrian epoch to late cretaceous epoch of known depositional environments were analyzed mechanically to obtain the grain size parameters of mode median mean and sorting the constructed grain size distribution curves for the various paleozoic and mesozoic formations were interpreted in terms of the paleo hydrodynamic processes prevailing through transportation and deposition the study proved that the grain size parameters of sand sized sediments most sensitive to paleo depositional environmental recognition were the graphic mean grain size and the inclusive graphic sorting mean grain size values below 1 77 of a sand sized sample could indicate a fluvial channel paleo depositional environment whereas the mean grain size values above 2 8 are indicative to a shallow marine paleo depositional environment sorting values above 1 1 may indicate a fluvial channel paleo depositional environment a bivariate discriminatory plot of mean grain size versus sorting yields two fields that can successfully discriminate between the fluvial channel paleo depositional environment and the shallow marine paleo depositional environment a new grain size parameter termed the mean sorting index was introduced in this study and calculated by dividing the mean grain size value over the sorting value it is recorded here that the mean sorting index is more sensitive to paleo depositional environment recognition than the individual mean grain size and sorting parameters

icebergs in the nordic seas throughout the late pliocene the arctic cryosphere is changing and making a significant contribution to sea level rise the late pliocene had similar co2 levels to the present and a warming comparable to model predictions for the end of this century however the state of the arctic cryosphere during the pliocene remains poorly constrained for the first time we combine outputs from a climate model with a thermodynamic iceberg model to simulate likely source regions for ice rafted debris ird found in the nordic seas from marine isotope stage m2 to the mid piacenzian warm period and what this implies about the nature of the arctic cryosphere at this time we compare the fraction of melt given by the model scenarios with ird data from four ocean drilling program sites in the nordic seas sites 911a 909c and 907a show a persistent occurrence of ird that model results suggest is consistent with permanent ice on svalbard our results indicate that icebergs sourced from the east coast of greenland do not reach the nordic seas sites during the warm late pliocene but instead travel south into the north atlantic in conclusion we suggest a continuous occurrence of marine terminating glaciers on svalbard and on east greenland due to the elevation of the east greenland mountains during the late pliocene the study has highlighted the usefulness of coupled climate model iceberg trajectory modeling for understanding ice sheet behavior when proximal geological records for pliocene ice presence or absence are absent or are inconclusive

tectonic sedimentology sediment systems deciphering global to local tectonics tectonic sedimentology has broad appeal because it can be applied at many time and length scales such as sedimentary consequences of changing rates of plate creation at mid ocean ridges continent continent collisions plateaux uplift active plate margins extensional rift tectonics and the birth growth and death of individual folds and faults tectonic sedimentology deals with the direct influence of neotectonics on sedimentation and basin development and with the inverse problem of reconstructing the order and development of palaeotectonic structures this review attempts to show how the scope and importance of the subject has developed over the last decade and is divided into five themes i at the largest tectonic scale constraints on mid ocean ridge activity and continent continent collisions come from a precise chemical analyses of fluid inclusions in marine halite deposits dating back to ca 550 ma b sr isotopic ratios of marine phanerozoic calcitic fossils and c chemical composition of archaean and proterozoic banded iron formations ii at regional scales constraints on the timing and extent of continental plateau uplift incision and cratonic tilting are given by a palaeoaltimetry estimates from oxygen isotope depletion in carbonate palaeosols b radiometric dating of palaeowater table speleothems and c preferential river migration iii at basin scales catchment processes are emphasized as key controls on sediment flux from tectonic uplands to sedimentary basins the inadequacy of sediment transport algorithms based on tractive stress and flow power to describe erosion incision and sediment transport during the most formative catchment hydrological events is emphasized iv rates of basin scale fault and fold growth displacement death and basement uplift are provided by application of facies analysis and sequence stratigraphy to accurately dated sediments in sedimentary basins v the effects of changing climate and varying basin base level in modifying tectonic influences on erosion and sedimentation are examined in such cases experimental and numerical modelling using multi variate parameters of subsidence rate sediment supply and sea level change can shed light on the problem future developments will undoubtedly improve such models hopefully establishing full linkage and feedback between sediment water supply and changing climate within an overall tectonic framework that may itself be changing

plio pleistocene pumice floods in the ancestral rio grande southern rio grande rift usa abstract at least four times during the late pliocene and early pleistocene pyroclastic eruptions in the jemez volcanic field northern rio grande rift flooded the ancestral rio grande with gravel sized pumice following as much as 400 km of fluvial transport the pumice was deposited in beds 0 2 to 2 0 m thick in the camp rice formation of the southern rio grande rift a combination of reversal magnetostratigraphy and single crystal sanidine 40 ar 39 ar dating constrains the ages of pumice clast conglomerates at 3 1 2 0 1 6 and 1 3 ma the coarsest pumice beds cobbles boulders were deposited as antidune like bedforms in a fluvial channel and as a crevasse splay sheet granule and pebble sized pumice was deposited as dune bedforms in fluvial channels and as ripple bedforms on the floodplain the abundance of pumice clasts in the gravel fraction 60 100 suggests very rapid transport downriver probably in a few days or weeks the two older pumice clast conglomerates correlate with the puye formation in the jemez volcanic field whereas the younger two are coeval to the lower bandelier tuff and cerro toledo rhyolite

channel shifting of the rio grande southern rio grande rift implications for alluvial stratigraphic models abstract presented here is the history of channel course changes of the rio grande based on bureau of reclamation and other maps from prior to 1844 exact date unknown to 1912 over an 80 km stretch of the semi arid mesilla and upper hueco half grabens of the southern rio grande rift the historical rio grande was a pebbly sand bedload stream occupying a relatively narrow 8 km floodplain incised about 100 m into pliocene and early pleistocene alluvium prior to completion of elephant butte dam in 1916 the river experienced late spring floods due to snowmelt near its headwaters throughout the 68 year history recorded here the river channel had variable width 1300 100 m and sinuosity 1 9 1 2 and displayed kilometres of lateral migration of both straight and sinuous stretches neck cutoff of meander loops and large and small scale avulsions three major avulsions occurred in different parts of the mesilla basin 1 between 1844 and 1852 in the north central part of the basin 2 in 1865 in the northern part of the basin and 3 between 1903 and 1912 in the southern part of the basin the length scale of the avulsions distance from node to reoccupation of previous channel ranged from 17 to 30 km and the 1865 avulsion is documented to have occurred in one flood season the historical rio grande is unique among other rivers described in the literature because of the high frequency of channel migration and avulsion it sheds doubt on the applicability of sedimentary models requiring time dependant levee growth avulsion functions

unraveling rift margin evolution and escarpment development ages along the dead sea fault using cosmogenic burial ages abstract the dead sea fault dsf is one of the most active plate boundaries in the world understanding the quaternary history and sediments of the dsf requires investigation into the neogene development of this plate boundary dsf lateral motion preceded significant extension and rift morphology by 10 ma sediments of the sedom formation dated here between 5 0 0 5 ma and 6 2 2 1 inf ma yielded extremely low 10be concentrations and 26al is absent these reflect the antiquity of the sediments deposited in the sedom lagoon which evolved in a subdued landscape and was connected to the mediterranean sea the base of the overlying amora formation deposited in the terminal amora lake which developed under increasing relief that promoted escarpment incision was dated at 3 3 0 8 0 9 ma burial ages of fluvial sediments within caves 3 4 0 2 ma and 3 6 0 4 ma represent the timing of initial incision initial dsf topography coincides with the earliest red sea morb s and the east anatolian fault initiation these suggest a change in the relative arabian african plate motion this change introduced the rifting component to the dsf followed by a significant subsidence margin uplift and a reorganization of relief and drainage pattern in the region resulting in the topographic framework observed today