diagenesis and hydrocarbon accumulation brent sandstone jurassic bergen high area north sea diagenesis of brent group sandstones in the bergen high area was studied and related to the history of hydrocarbon maturation and pore fluid environment calcite and kaolinite are low temperature diagenetic precipitates that formed as meteoric pore water entered the brent at the end of brent deposition and later during late cimmerian erosion a major period of feldspar dissolution associated with quartz and illite cementation occurred at huldra field precipitation of diagenetic illite in brent sandstones was closely linked with hydrocarbon maturation in the adjacent viking graben and accumulation of generated fluids in traps at structural highs at huldra field illite k ar ages suggest onset of illite diagenesis in the latest cretaceous initial reservoiring of hydroca bons during the latest paleocene to early eocene 58 ma and filling of the reservoir by early oligocene 38 ma pore water character during illite diagenesis interpreted from oxygen isotope and quartz overgrowth fluid inclusion data was warmer than predicted by burial history analysis and one and a half to two times seawater salinity the incursion of saline isotopically evolved fluids at huldra suggests replacement of paleometeoric water by basin compaction fluid illite k ar ages from veslefrikk field indicate a minimum age of hydrocarbon accumulation at about 30 ma modern pore water chemistry in the brent at veslefrikk is unlike the suggested water chemistry at huldra and indicates that migrating compaction water did not completely displace older fresh connate water this sugge ts that hydrocarbons migrated into veslefrikk as a discrete phase without great volumes of associated compaction water

diagenesis of plio pleistocene sediments of the colorado river delta southern california abstract interbedded mudrocks and fine grained sandstones from three wells in the plio pleistocene colorado river delta in the imperial valley southern california were examined by x ray powder diffraction methods chemical analyses and scanning electron microscopy sem to determine the extent and course of low temperature metamorphic reactions this sequence was compared to tertiary rocks from the u s gulf coast in an effort to explore the kinetics of low temperature reactions in natural systems mineralogical changes observed are 1 the progressive transformation of mixed layer illite smectite to pure illite over the temperature range 70 c to 210 c 2 the apparent appearance of chlorite as a diagenetic mineral at 180 c to 194 c coincident with the onset of r symbol 3 ordering in the illite smectites 3 the loss of kaolinite above approximately 210 c and 4 a progressive decrease in the amount of detrital potassium feldspar over the same temperature interval that brackets the illitization reaction comparison of bulk chemical analyses with analyses of the comparison of tertiary sequences with this plio pleistocene sequence indicates that kinetics significantly influence the appearance of clay mineral assemblages at temperatures below approximately 175 c at temperatures above 175 c temperature rather than time appears to govern the reactions

helium radon and radiocarbon studies on a regional aquifer system of the north gujarat cambay region india abstract the study reports the age evolution of groundwater as it flows from the recharge area through a regional alluvial aquifer system in north gujarat cambay region in western india radiocarbon 14 c 4 he and 4 he 222 rn dating methods have been employed sediments from a drill core in the cambay basin were also analysed for uranium u and thorium th concentrations and the measured values have been used to estimate the 4 he and 222 rn production rate for groundwater age calculations additionally factors controlling the distribution of 222 rn 4 he and temperature anomalies in groundwater vis a vis their relation to the tectonic framework and lithology of the study area have also been examined the multi isotope study indicated a reasonable correspondence in groundwater age estimates by the three methods employed the groundwater 14 c ages increased progressively in the groundwater flow direction from the foothills of aravalli mountains in the east and reached a value of 35 ka towards the region of lowest elevation linking little rann of kachchh lrk nalsarovar ns gulf of khambhat gk in the western part of the study area in this region groundwater ages obtained for free flowing thermal wells and springs employing 4 he and 4 he 222 rn systematics are in the order of million years such anomalous ages are possibly due to enhanced mobilisation and migration of excess helium from hydrothermal circulation vents along deep seated faults excluding such anomalous cases and considering all uncertainties presently estimated 4 he and 4 he 222 rn groundwater ages are in reasonable agreement with 14 c age estimates in the cambay basin for helium release factor he value of 0 4 0 3 the 4 he method also indicated west southwards progression of groundwater ages up to 100 ka beyond the cambay basin large excess helium concentrations are also seen to be generally associated with anomalous groundwater temperatures 35 c and found to overlie some of the basement faults in the study area particularly along the east and the west flanks of the cambay basin groundwater 222 rn activities in most of the study area are 800 400 dpm l but a thermal spring at tuwa on the east flank of the cambay basin having granitic basement at shallow depth recorded the highest 222 rn activity 63 000 dpm l

coevolution of bed surface patchiness and channel morphology 2 numerical experiments in gravel bed rivers bed topography and the bed surface grain size distribution evolve simultaneously but it is not clear how feedbacks between topography and grain sorting affect channel morphology in this the second of a pair of papers examining interactions between bed topography and bed surface sorting in gravel bed rivers we use a two dimensional morphodynamic model to perform numerical experiments designed to explore the coevolution of both free and forced bars and bed surface patches model runs were carried out on a computational grid simulating a 200 m long 2 75 m wide straight rectangular channel with an initially flat bed at a slope of 0 0137 over five numerical experiments we varied a whether an obstruction was present b whether the sediment was a gravel mixture or a single size and c whether the bed surface grain size feeds back on the hydraulic roughness field experiments with channel obstructions developed a train of alternate bars that became stationary and were connected to the obstruction freely migrating alternate bars formed in the experiments without channel obstructions simulations incorporating roughness feedbacks between the bed surface and flow field produced flatter broader and longer bars than simulations using constant roughness or uniform sediment our findings suggest that patches are not simply a by product of bed topography but they interact with the evolving bed and influence morphologic evolution

surface based transport model for mixed size sediment we present a transport model for mixed sand gravel sediments fractional transport rates are referenced to the size distribution of the bed surface rather than subsurface making the model completely explicit and capable of predicting transient conditions the model is developed using a new data set of 48 coupled observations of flow transport and bed surface grain size using five different sediments the model incorporates a hiding function that resolves discrepancies observed among earlier hiding functions the model uses the full size distribution of the bed surface including sand and incorporates a nonlinear effect of sand content on gravel transport rate not included in previous models the model shares some common elements with two previous surface based transport models but differs in using the full surface size distribution and in that it is directly developed from a relatively comprehensive data set with unambiguous measurement of surface grain size over a range of flow transport rate and sediments

experimental and numerical evidence for intrinsic nonmigrating bars in alluvial channels alternate bars in straight alluvial channels are migrating or nonmigrating the currently accepted view is that they are nonmigrating if the width to depth ratio is at the value of resonance or if the bars are forced by a persistent local perturbation we carried out 2 d numerical computations and a long duration mobile bed flume experiment to investigate this view we find that nonmigrating bars can also occur in straight channels without resonant width to depth ratio or steady local perturbation they appear to be an intrinsic response of the alluvial river bed this finding bears on explanations for meandering of alluvial rivers for which nonmigrating bars are seen as a prerequisite we find however that the intrinsic tendency of a straight channel to form meanders usually has a different origin the identified intrinsic nonmigrating bars can only become the dominant mechanism for incipient meandering if the erodibility of the banks is very low

rift basins in western margin of india and their hydrocarbon prospects with special reference to kutch basin the western continental margin of india can be classed as a divergent or passive margin the western continental shelf is an extensive carbonate bank bombay offshore basin passing into clastic sediments on the north and south three craton margin embayed basins kutch cambay and narmada in the northern part of the shelf are filled predominantly with clastic sediments these basins occupy grabens bounded by faults diverging seaward the grabens were formed by three rift systems along major precambrian tectonic trends the rifting developed sequentially from north to south around the saurashtra horst kutch basin was formed in the early jurassic followed by cambay basin in early cretaceous time and the narmada in the late cretaceous it appears that these rifting ev nts occurred at successive stages during the northward migration of the indian plate after its break from gondwanaland in late triassic or early jurassic it is inferred that these rift basins opened up successively as a result of the counterclockwise drift of the indian craton bombay offshore and cambay are two major oil producing basins in the western margin these basins are characterized by high geothermal gradients attributed to the shallowness of the mantle in this region oil has not been found in kutch basin which is mainly an onshore mesozoic basin the basin depocenter shifted offshore at the northwestern part of the continental shelf where the shelf is wide

gravel bed river evolution in earthquake prone regions subject to cycled hydrographs and repeated sediment pulses sediment often enters rivers in the form of sediment pulses associated with landslides and debris flows this is particularly so in gravel bed rivers in earthquake prone mountain regions such as southwest china under such circumstances sediment pulses can rapidly change river topography and leave the river in repeated states of gradual recovery in this paper we implement a one dimensional morphodynamic model of river response to pulsed sediment supply the model is validated using data from flume experiments so demonstrating that it can successfully reproduce the overall morphodynamics of experimental pulses the model is then used to explore the evolution of a gravel bed river subject to cycled hydrographs and repeated sediment pulses these pulses are fed into the channel in a fixed region centered at a point halfway down the calculational domain the pulsed sediment supply is in addition to a constant sediment supply at the upstream end results indicate that the river can reach a mobile bed equilibrium in which two regions exist within which bed elevation and surface grain size distribution vary periodically in time one of these is at the upstream end where a periodic discharge hydrograph and constant sediment supply are imposed and the other is in a region about halfway down the channel where periodic sediment pulses are introduced outside these two regions bed elevation and surface grain size distribution reach a mobile bed equilibrium that is invariant in time the zone of fluctuation free mobile bed equilibrium upstream of the pulse region is not affected by repeated sediment pulses under the scenarios tested but downstream of the pulse region the channel reaches different fluctuation free mobile bed equilibriums under different sediment pulse scenarios the vertical bed structure predicted by the simulations indicates that the cyclic variation associated with the hydrograph and sediment pulses can affect the substrate stratigraphy to some depth copyright 2017 john wiley sons ltd

palaeogene lacustrine record in mallorca nw mediterranean spain depositional palaeogeographic and palaeoclimatic implications for the ancient southeastern iberian margin abstract middle bartonian middl1e eocene and chattian upper oligocene lacustrine and alluvial lacustrine successions exist in mallorca northwestern mediterranean they yield a significant palaeobiological record comprising fossil land plants and vertebrates and constitute the best available depositional record for a preliminary palaeogeographic and palaeoclimatic analysis of the northeastern part of the palaeogene southern iberian margin western tethys both lacustrine systems developed under similar warm and humid climatic conditions increasingly affected by seasonal and or pluriannual rhythms marked by changing precipitation patterns these climatic conditions were mainly caused by the low palaeolatitude where the lacustrine systems evolved the still probable although decreasing influence of indo pacific warm surface currents and the occurrence of very extensive marine water masses adjacent to wide emerged continental zones the palaeogene lacustrine systems were shallow and characterised by low gradient depositional conditions they were perennial open freshwater oligosaline carbonate lakes where eutrophy thermal meromixis and anoxic bottom conditions could develop allowing the accumulation and preservation of macrophytic plant remains of the circum lacustrine marginal belt and neighbouring terrestrial mesophytic zones the higher plant algal bacterial organic contribution balance favoured the generation of mineable huminitic coal seams carbominerites and of gas prone kerogene type iii and iib source rocks the hydrogen bicarbonate rich waters led to high biogenic and inorganic bio induced carbonate sediment production biogenic muds cyanobacterial incrustations and travertine and tufa precipitation constituted the major carbonate products moreover the high ph conditions in the lacustrine water bodies and in the lacustrine sediment pore waters favoured bacterial sulphate reduction contributing to organic sulphur enrichment in coals these highly alkaline conditions also resulted in some cases in the exceptionally good preservation of chlorophyllinite a rare liptinite maceral recorded in the eocene coal deposits the middle eocene lacustrine system did not evolve in a very well defined tectonic setting characterised by the generation of low uplifts and gently subsiding basins terrigenous contributions from the source areas and clastic sedimentation were restricted to river mouths high autochthonous carbonate production and accumulation characterised most of the remaining lacustrine zones a significant spring recharge of the lacustrine zones is suggested by the well developed spring related travertine deposits by contrast the oligocene lacustrine zones developed both in fluvial related floodplains and in the distal zones of a major alluvial system which was fed from tectonically active source areas located to the nw of the island a more significant water runoff contribution is suggested for this system although underground recharge could also be substantial

modelling of fine and coarse sediment interaction over alternate bars abstract flume experiments demonstrated an ability to model bed features such as pavement and the alternate bar structure that are commonly encountered in natural gravel bed streams the effect of pool and riffle topography on the infiltration of fines into and their removal from the channel bed was examined fines were deposited first and removed last from the downstream side of the bar and from the pool area when there is no bed motion the flow is capable of completely removing the fines from the pavement but not from the subpavement when the bed is active both pavement and subpavement can be cleaned

hummocky cross stratification tropical hurricanes and intense winter storms most previous workers have inferred a storm origin for hummocky cross stratification which typically occurs in shallow marine deposits on the modern earth the only storms capable of profoundly affecting shallow marine depositional environments are severe tropical cyclones hurricanes and mid latitude winter wave cyclones intense winter storms this paper examines the palaeogeographic distribution including palaeolatitude and palaeogeographic setting of 107 occurrences of hummocky cross stratification ranging in age from the proterozoic to recent in each of these stratigraphic units both palaeolatitude and palaeogeography are consistent with a direct storm influence associated with the passage of hurricanes or winter storms directly over the site of deposition this palaeogeographic evidence lends support to the inferred storm origin for hummocky cross stratification further the distribution of the structure suggests that most occurrences 73 were generated by tropical hurricanes the remaining 27 being generated by intense mid latitude winter storms the preferential generation of hummocky cross stratification by hurricanes is consistent with 1 the known differences in the nature of the bottom flows generated by the two major storm types and 2 the inferred nature of the flows which form hummocky cross stratification hurricanes couple less effectively with the water column than do intense winter storms due to this ineffective coupling hurricane generated bottom flows tend to be oscillatory or multidirectional dominant with only minor unidirectional components of motion in contrast intense winter storms generally do couple effectively with the water column generating bottom flows which possess a dominant or significant unidirectional component most previous workers have suggested that hummocky cross stratification forms under oscillatory or multidirectional dominant flow thus it is conceptually reasonable that the vast majority of ancient occurrences of hummocky cross stratification were probably hurricane generated as suggested by the aforementioned palaeogeographic distribution the proterozoic palaeozoic neogene and quaternary were times when global climate was similar to that of today the distribution of hummocky cross stratification deposited during these times suggests that both hurricanes and intense winter storms occupied latitudinal belts during these times which were essentially identical to those occupied by their modern counterparts the mesozoic and palaeogene were non glacial times when global climate was much warmer than that of today the distribution of hummocky cross stratification deposited during this interval suggests that hurricanes occurred more frequently at higher latitudes during non glacial times than they do at present the possibility of a broadened hurricane belt during the mesozoic and palaeogene is consistent with climatic considerations a limited number of mesozoic and palaeogene rock units containing hummocky cross stratification were deposited in palaeogeographic settings that preclude a direct hurricane influence these examples were deposited in the middle latitudes suggesting that intense winter storms continued to form hummocky cross stratification in the middle latitudes during these much warmer times some previous workers have suggested that tsunamis may be capable of generating hummocky cross stratification the palaeogeographic distribution of the structure does not support an origin due to tsunamis lacustrine examples of hummocky cross stratification reported herein are the first known non marine occurrences they suggest that storm effects strongly influence the sedimentary record of some lakes

numerical study of alternate bars in alluvial channels with nonuniform sediment rivers typically present heterogeneous bed material but the effects of sediment nonuniformity on river bar characteristics are still unclear this work investigates the impact of sediment size heterogeneity on alternate bars with a morphodynamic numerical model the model is first used to reproduce a laboratory experiment showing alternate bar formation with nonuniform bed material subsequently the influence of sediment size heterogeneity on alternate bars is investigated distinguishing hybrid from free bars definition based on the presence absence of morphodynamic forcing considering the results of nine scenarios in four of them a transverse obstacle is used to generate forcing the computations are carried out with the telemac mascaret system solving the two dimensional shallow water equations with a finite element approach accounting for horizontal and vertical sediment sorting processes the results show that sediment heterogeneity affects free migrating and hybrid bars in a different way the difference lies in the presence absence of a migration front so that distinct relations between bed topography bed shear stress and sediment sorting are obtained sediment sorting and associated planform redistribution of bed roughness only slightly modify free migrating bar morphodynamics whereas hybrid bars are greatly impacted with decreased amplitude and increased wavelength increased sediment size heterogeneity increases the degree of sediment sorting while the sorting pattern remains the same for both free and hybrid bars moreover it produces averagely higher longer and faster free bars while in the case of hybrid bars their wavelength is increased but no general trend can be determined for their amplitude

experiments on downstream fining of gravel ii wide and sandy runs this is the second of two papers about experiments on downstream fining of gravel here we briefly summarize the complete series of runs described in the first paper where the influence of sediment feed rate was evaluated in a narrow channel we then present results for variation in two more conditions sand content and channel width the experiments were carried out in a long flume with an effective 40 m long test section with two different widths of 0 3 and 2 7 m in addition two sediment mixtures were used with different sand contents i e 33 and 55 with the remainder being gravel the following results were obtained the increase in channel width allowed the formation of transverse topography enhanced the development of sediment patches and increased the fining rate of gravel for id d5 d0 and finer percentiles increasing sand content rendered the long profile of the bed much more concave caused marked patch development and most notably increased the fining rate for all percentiles of gravel sized bed material

structural properties of mobile armors formed at different flow strengths in gravel bed rivers differences in the structure of mobile armors formed at three different flow strengths have been investigated in a laboratory flume the temporal evolution of the bed surfaces and the properties of the final beds were compared using metrics of surface grain size microtopography and bed organization at both grain and mesoscales measurements of the bed condition were obtained on nine occasions during each experiment to describe the temporal evolution of the beds structured mobile armors formed quickly in each experiment at the grain scale 1 45 mm 9 ds50 17 mm where ds50 is the median surface particle size surface complexity decreased and bed roughness increased in response to surface coarsening and the development of the mobile armor particles comprising the armor also became flow aligned and developed imbrication at a larger scale 100 200 mm the surface developed a mesoscale topography through the development of bed patches with lower and higher elevations metrics of mobile armor structure showed remarkable consistency over prolonged periods of near constant transport demonstrating for the first time that actively transporting surfaces maintain an equilibrium bed structure bed structuring was least developed in the experiments conducted at the lowest flow strength however little difference was observed in the structural metrics of the mobile armors generated at higher flows although the range of transport rates studied was limited the results suggest that the structure of mobile armors is insensitive to the formative transport rate except when rates are low 0 03 where is the dimensionless shear stress

magnetovariational study over a seismically active area in the deccan trap province of western india this paper presents the results of a magnetovariational study undertaken over a basalt covered region of western india which has been experiencing a swarm of seismic activity since early 1986 the most striking feature of the transient variations is the anomalous enhancement of the east west y component at stations bounding the seismically active belt from the nature of the horizontal transfer functions and the anomalous induction arrows it is inferred that this behaviour is related to the presence of a resistive body embedded in a north south oriented conductive belt consistent with an evolutionary model of deccan volcanism and other geophysical data it is suggested that the central resistive block coincident with the concentrated belt of earthquake epicentres represents either a dormant volcanic plug or a plutonic body rooted in upwarped conducting mantle to account for the phase relationship between the anomalous y variations and the normal north south x variations it is proposed that the upwarped asthenosphere with its associated high geothermal anomaly acts as a conducting path to channel induced current from the region of the cambay triple junction located towards the northwest of the array the existence of the strong induced currents in the region of the triple junction conforms with the induction arrow pattern observed at the array stations

field experiment on alternate bar development in a straight sand bed stream alternate bars in rivers and streams develop as a result of differences in length scales involved in the adjustment of flow and sediment transport to irregularities of the bed the amount of field evidence supporting theoretical insights is highly limited here we present results from a large scale field experiment in a 600 m long straight reach over a period of almost 3 years the channel was allowed to evolve autogenously from initially flat bed conditions subject to discharge variation alternate bars developed within 8 months from the start of the experiment the initial stages of bar development included bar growth both in wavelength and amplitude and bar migration the latter was too limited to classify the bars as being migrating bars therefore we classify the bars as nonmigrating bars toward the end of the experiment the regular alternate bar pattern evolved into an irregular pattern and bar amplitude started to decrease from the start of the experiment we observed a declining channel slope from 1 8 m km 1 initially to 0 9 m km 1 halfway the experiment after which it stabilized we applied two bar theories to establish their predictive capacity both bar theories predicted the development of alternate bars under the constructed channel conditions in response to the declining channel slope both theories predicted a decreasing likelihood for the development of alternate bars our study shows that under field conditions the applied bar theories may predict the initial stages of bed development

luminescence chronology of river adjustment and incision of quaternary sediments in the alluvial plain of the sabarmati river north gujarat india river adjustment and incision in the sabarmati basin gujarat india have been examined at a site near mahudi towards this the morphostratigraphy and depositional chronometry of the middle alluvial plains were investigated the upper fluvial sequence along with the overlying aeolian sand and riverbed scroll plains provide clues to the evolution of the present sabarmati river sedimentological analyses of the upper fluvial sequence indicate its deposition by a meandering river system during what is believed to be a persistent wetter phase luminescence chronology bracketed this sequence to between 54 and 30 ka which corresponds to oxygen isotope stage 3 during which the sw monsoon was enhanced the overlying aeolian sand has been dated to 12 ka indicating that dune accretion occurred simultaneously with the strengthening of the sw monsoon during the early holocene adjustment of the sabarmati along a n s transect is placed around 12 ka and the incision is bracketed between 12 and 4 5 ka river adjustment could have been tectonic however the incision was facilitated by the availability of continuous flow in the river caused by the sw monsoon the basin experienced two tectonic events at about 3 and 0 3 ka as demonstrated by the morphology of the scroll plains

numerical simulation of downstream fining by selective transport in gravel bed rivers model development and illustration a numerical model has been developed for the routing of gravel sized sediment along a river channel which is free to adjust both its long profile and surface texture hydraulic calculations use a step backwater approach and sediment transport is predicted with the method of parker 1990a which uses a low degree of size selectivity exchange of sediment between the surface and subsurface is described using the modified exner equation of parker and sutherland 1990 the model is applied to an idealized channel based on the highly concave allt dubhaig scotland in which fining by particle wear is minor the rapid downstream fining observed in this river is closely matched by model predictions after a time equivalent to 102 years under the present flow regime of the river the evolution of the fining pattern during the model run and associated changes in sediment transport and bed aggradation are described it is concluded that strong profile concavity can force rapid downstream fining even though bed load transport is only slightly size selective this run of the model serves as a basis for testing of the sensitivity of downstream fining to alternative choices of parameter values and boundary conditions which are summarized here and will be described in a subsequent paper

crustal structure along mehmadabad billimora profile in the cambay basin india from deep seismic soundings abstract deep seismic sounding dss investigations were carried out along a 220 km long n s profile from mehmadabad 22 50 n 72 46 e to billimora 20 46 n 72 58 e in the cambay basin india for studying the detailed crustal structure in the region seismic refraction as well as narrow and wide angle reflection travel time data were obtained for various crustal boundaries starting from the sedimentary section down to the moho by continuous profiling analysis of reversed reflection and refraction travel time data has yielded crustal velocity depth functions for the mehmadabad broach and broach navsari sections along the profile which are significantly different from each other the average velocities at depths in the magmadabad broach section have been found to be considerably lower than those in the broach navsari section by about 25 at 5 km 17 at 10 km 7 at 20 km and 2 at the moho depth and even deeper down in the upper mantle the presence of a relatively thicker sedimentary section especially in the jambusar broach area as revealed by the reversed refraction data analysis is responsible for this gross difference in the average velocity functions for the two parts of the profile and the same have therefore been used for obtaining the detailed crustal depth along the profile the cambay basin which is well known to be bounded by step faults on the eastern and western margins is also dissected into seven major crustal blocks in the n s direction from mehmadabad to billimora the various crustal blocks identified are from the north 1 i mehmadabad block 2 ii tarapur block 3 iii petlad katana block 4 iv jambusar broach block 5 v kosamba block 6 vi surat block and 7 vii navsari billimora block these blocks are displaced up or down relative to the adjacent blocks due to movements along the faults bounding them most of the faults have been found to extend quite deep and to affect the moho boundary considerably as is quite evident from the relief of the moho found along the profile further the seismic activity observed in the region during historical as well as modern times suggests that these deep faults may even be currently active the jambusar broach block which is well known as a broad regional syncline with the maximum thickness of cenozoic sediments has been found to be a major graben revealing a maximum crustal thickness of 38 40 km the granitic basement in this graben is also the deepest at 6 0 6 5 km depth towards the north and south of this major graben the moho as well as the granitic basement are found to be at relatively shallower depths in various crustal blocks the boundary velocity at the moho has been found to be 8 1 8 2 km sec whereas at the granitic basement level there seems to be a lateral velocity variation from 5 7 to 6 3 km sec the crustal depth section obtained in the present study reveals a close relationship between the deep and shallow structural features in this region the deccan traps which form the basement of the overlying tertiary sediments over most part of the profile vary in thickness from 1 0 to 1 8 km however the trap surface rises to very shallow depths on the southern part of the profile the boundary velocity in the deccan traps has been found to vary between 4 8 and 5 2 km sec in the anklesvar kosamba area there is also evidence for the presence of a 1 2 km thick layer of mesozoic sediments with a velocity of about 4 0 km sec underlying the 1 1 km thick deccan traps layer

formation of stationary alternate bars in a steep channel with mixed size sediment a flume experiment alternate bars were formed by sediment transport in a flume with froude modelled flow and relative roughness characteristic of gravel boulder channels with steep slopes the flume 0 3 m wide 7 5 m long was filled with a sand gravel mixture which was also fed into the top of the flume at a constant rate under constant discharge channel slope was set at 0 03 initially coarse particles accumulated on incipient bar heads near one side of the flume and diverted flow and bedload transport across the flume toward a pool scoured against the opposite flume wall downstream sorting in the pool directed coarse particles onto the next bar head downstream alternate sequences of pools and coarse bar heads were thereby linked down the entire flume by interactions of sediment sorting flow and channel morphology during episodes of bar construction unsorted bedload invaded interior bar surfaces and was deposited persistent deposition of coarse particles on bar heads prevented downstream migration of bars by inhibiting bar head erosion and bedload transport over bars likely factors leading to bar head stabilization in modelled gravel bed channels are coarse mixed size sediment steep channel gradients and shallow depths

rb sr ages of glauconite recrystallization dating times of regional emergence above sea level abstract rb sr ages of glauconite pellets commonly fall short of the presumed age of deposition by 10 20 according to current estimates of the geologic time scale in part the young ages are the result of preferential loss of exchangeable radiogenic sr consequently in pellets where tightly bound nonexchangeable rb and sr have remained a closed chemical system since deposition removal of the exchangeable cations with ammonium acetate nh4oac can raise the apparent age to coincide with the expected depositional age in other cases the age of pelletal glauconite remains younger than the depositional age after chemical treatment analyses of nh4oac treated disaggregated clay size fractions invariably yield young but rather consistent apparent ages these are interpre ed as recording the time of diagenetic recrystallization of the glauconite crystallites which compose the pellets glauconite recrystallization appears to have taken place in the llano uplift of central texas at 428 350 328 and 265 280 my ago these ages do not coincide with times of elevated temperatures deep burial or tectonism instead they correlate with times of regional emergence above sea level apparently a change in pore water chemistry due to an influx of meteoric water promoted recrystallization and this inference is supported by the oxygen isotope composition of the glauconite diagenesis of glauconite by this mechanism offers an opportunity to date sea level changes by isotopic methods

hyporheic exchange in gravel bed rivers with pool riffle morphology laboratory experiments and three dimensional modeling received 7 june 2005 revised 30 june 2006 accepted 25 august 2006 published 31 january 2007 1 we report the first laboratory simulations of hyporheic exchange in gravel pool riffle channels which are characterized by coarse sediment steep slopes and three dimensional bed forms that strongly influence surface flow these channels are particularly important habitat for salmonids many of which are currently at risk worldwide and which incubate their offspring within the hyporheic zone here we perform a set of laboratory experiments examining the effects of discharge and bed form amplitude on hyporheic exchange with surface subsurface mixing measured directly from the concentration decay of a conservative tracer fluorescein injected into the surface flow near bed pressure measurements were also used to predict hyporheic exchange from a three dimensional pumping transport model comparison of the predicted and observed hyporheic exchange shows good agreement indicating that the major mechanism for exchange is bed form induced advection however the effect of bed forms is modulated by discharge and the degree of topographic submergence we also tested the performance of the hydrostatic pressure as a proxy for the observed near bed pressure in driving hyporheic exchange which would facilitate field measurement and analysis of hyporheic flow in natural rivers we found agreement with measured hyporheic exchange only for low bed form amplitudes and high flows

experiments on downstream fining of gravel i narrow channel runs we present the results of three laboratory experiments in which longitudinally sorted deposits were formed by feeding poorly sorted sediment at the upstream end of a narrow 45 m long channel the input sediment had a median size of 6 mm and included significant amounts of material up to 64 mm and down to 0 2 mm water discharge was constant at 49 l s and sediment discharge varied from 0 048 to 0 19 kg s downstream fining was produced in all three runs the variation in sediment feed rate had relatively little effect on the fining profiles in all three runs the formation of a longitudinally sorted deposit was mediated by the formation of a coarse surface layer the surface layer remained at the top of the deposit during aggradation by continually reforming itself at the deposit surface the coarse surface layer fined by approximately a factor of 2 in d90 and d50 consistently in all three experiments the deposit subsurface fined less with d90 fining more strongly than d50 the short channel length a

k ar dating of time of gas emplacement in rotliegendes sandstone netherlands the time of emplacement of gas into each of two reservoirs in the rotliegendes sandstone one in the groningen field and one in the broad fourteens basin was estimated from potassium argon k ar ages of diagenetic illitic clays and careful petrographic observations of the rocks in which the clays occurred in each reservoir the intensity of diagenetic alteration increased downward within a relatively thin 15 to 175 m or 50 to 580 ft interval apparently reflecting a longer period of alteration for deeper samples this is expected in cases where a gradually accumulating gas column expels pore water from progressively deeper parts of the reservoir rock illite is a common diagenetic phase in the rotliegendes because detrital contamination in these rocks has been infer ed to be minimal k ar ages of very fine grained illite should indicate the time the illite forming process ceases in each case reported here the age of the deeper sample is younger than that of the shallower we interpret the age of the finest illite fraction in the gas zone of each reservoir to indicate the time at which illite formation ceased as the result of gas emplacement and pore fluid displacement in the rock our results indicate that gas emplacement in the groningen field commenced prior to 150 ma and that the growth of diagenetic illite continued in the present day water zone from that time until at least 120 ma

what is the active layer we note the presence in the literature of two different concepts of the term active layer in relation to fluvial sediment transport it has been used to represent the current dynamically active streambed surface or to represent the depth of event scale scour and fill these concepts involve distinct length and time scales we propose that when the distinction is important the concepts be distinguished as either a dynamical active layer or an event active layer

lacustrine carbonates and pedogenesis sedimentology and origin of palustrine deposits from the early cretaceous rupelo formation w cameros basin n spain the berriasian rupelo formation of the w cameros basin consists of a 2 200 m thickness of marginal and open lacustrine carbonate and associated deposits open lacustrine facies contain a non marine biota with abundant charophytes both stems and gyrogonites ostracods gastropods and rare vertebrates carbonate production was mainly biogenic the associated marginal lacustrine palustrine facies show strong indications of subaerial exposure and exhibit a wide variety of pedogenic fabrics silicified evaporites found near to the top of the sequence reflect a short hypersaline phase in the lake history the succession was laid down in a low gradient shallow lake complex characterized by wide fluctuations of the shoreline carbon and oxygen stable isotope analyses from the carbonates show non marine values with ranges of 13 from 7 to 11 and 18 from 3 to 7 5 differences in the isotopic composition of open lacustrine carbonates are consistent with sedimentary evidence of variation in organic productivity within the lake analyses from the entire sample suite plot on a linear trend isotopic compositions become lighter with increasing evidence of pedogenic modification this suggests progressive vadose zone diagenesis and influence of meteoric waters rich in soil derived co2 the stable isotope data thus support evidence from petrography and facies relations that palustrine limestones form through pedogenic modification of lake carbonates

lateral and vertical variations in sedimentology and geochemistry of sub horizontal laminated travertines cakmak quarry denizli basin turkey abstract the laterally extensive sub horizontal laminated travertine deposits outcropping in the cakmak quarry denizli basin turkey allows reconstructing their three dimensional geobody architecture based on field observations detailed petrographic and geochemical analyses stable carbon and oxygen isotopes major and trace elements the most important controlling porosity permeability parameters in this lacustrine dominated facies in relation to microfacies and diagenetic modifications were constrained sedimentological analyses and the observed architectural geometries allowed to subdivide the sub horizontal carbonate succession into three main depositional units these units in turn based on macro and microscopic observations were subdivided into nine dominant lithotypes reflecting an overall shrub flat and a marsh pool depositional setting the shrub flat facies mainly comprises dendritic shrub crusts boundstone pustular grainstone and clotted micrite mudstone to boundstone in contrast the marsh pool environment is dominated by coated reed rudstone to boundstone cryptalgal silty bioclast rich bioturbated mudstone and peloidal packstones the diagenetic study revealed that the sediments were affected by dissolution cementation sparmicritization recrystallization and local formation of fe oxi hydroxides and chalcedony among the diagenetic products in particular the calcite cements were investigated applying micro analysis of stable carbon and oxygen isotopes accordingly the co variation between the obtained isotopic values and the elemental concentrations sr mg na and s point to a thermogene fluid system that likely circulated through the subsurface limestones dolomites and evaporites of the lycian nappes these findings ensure an in depth understanding of continental carbonate deposition i e sub aqueous travertines in the context of a lacustrine depositional system

aggradation history and luminescence chronology of late quaternary semi arid sequences of the sabarmati basin gujarat western india the gujarat alluvial plain in the semi arid desert margin of the thar desert contains a record of continental quaternary sequences these sequences were built by drainages originating in the aravalli hills and flowing westward into the indian ocean stratigraphic studies of a part of the late quaternary succession in the sabarmati basin have resulted in a fourfold lithostratigraphic scheme the waghpur formation conglomeratic member sand member the mahesana formation lower heterolithic member upper sand member the akhaj formation and the sabarmati formation facies analysis distribution of conglomerates and cross bed azimuths of the clastic facies of the waghpur formation were used to infer ne sw trending semi arid alluvial fans the deposition of the overlying heterolithic member took place in ephemeral streams influenced by episodic flows and aeolian reworking the upper member of the mahesana formation represents aeolian and older levee deposits feasibility studies of thermoluminescence tl and infra red stimulated luminescence irsl dating on the sabarmati succession yielded stratigraphically consistent ages ranging from 5 ka to 300 ka for two samples tl ages on quartz and irsl ages on feldspar separates were consistent these results together with the stratigraphic and petrographic data reveal the following events in the accumulation history of the sabarmati sequence 1 1 significant aggradation at 300 ka gravel sand and at 58 ka sand and 2 2 pedogenesis bracketed to 58 39 ka the sabarmati river in its middle stretches follows a regional slope deviatory course interpreted previously to be a neotectonic adjustment within the cambay graben our chronological data suggest that this adjustment occurred possibly within the past 39 ka

age of metamorphism in the lesser himalaya and the main central thrust zone garhwal india results of illite crystallinity 40 ar 39 ar fusion and k ar studies

dedolomitization and other early diagenetic processes in miocene lacustrine deposits ebro basin spain abstract a variety of meteoric diagenetic features reveal the development of a syngenetic karst on lacustrine deposits of the ebro basin diagenetic processes that operated on lacustrine laminated and stromatolitic carbonates include the following 1 a first syndepositional stage with processes such as dolomitization desiccation and related breccia formation and sulphate precipitation either as lenticular gypsum crystals or nodules this stage took place under progressive evaporation due to lake level fall when the previous carbonate deposits became exposed as a supra littoral fringe surrounding saline mud flats of adjacent sulphate depositional environments 2 a second early diagenetic stage in which processes such as sulphate dissolution and collapse brecciation dedolomitization calcite spar cementation and silicification occurred as a result of meteoric water input that caused a progressive rise in lake level light isotopic compositions 13 c and 18 o of diagenetic calcites versus heavier compositions in primary laminated and stromatolitic limestones confirm a meteoric influence the syngenetic karst is best developed at the boundary between two allostratigraphic units and coincided with one of the extensive stages of sulphate deposition at the end of the early miocene the karst facies occurred in an area that was a low relief barrier that separated two sites of sulphate deposition during low lake levels this indicates that the karst development was controlled by topographic changes within the basin and record a shift from arid to wetter climatic conditions as suggested by the overlying freshwater carbonate deposits the presence of diagenetic features such as those described in the central ebro basin affecting saline lacustrine carbonates is relevant because they can be used as indicators of subaerial exposure periods in terrestrial environments and they also reveal important palaeogeographic and palaeoclimatic events of basinal extent

isotopic hydrology and paleohydrology of the madagi kenya natron tanzania basin during the late quaternary abstract three generations of stromatolites mark the recent extension of paleolakes in the magadi natron basin on the border between tanzania and kenya the last two generations are observed some 50 m above the modern lakes level they are respectively attributed to the beginning of the last interglacial and to the pleistocene holocene transition analysis of the morphology and texture of the stromatolites reveals an ecological zonation between 0 and 10 14 m below the shoreline their relatively high 18o and 13c values reflect a long residence time for the paleolake water which would have been favorable to the establishment of an isotopic equilibrium between atmospheric co2 and the dissolved inorganic carbon despite deep carbon inputs in relation to carbonititic volcanism a study of the 18o 2h and 13c contents in the hydrothermal springs perennial rivers and lacustrine brines indicates that during the last period of significant renewal of the deep saline groundwater precipitation was depleted in heavy isotopes when compared to modern precipitation this difference corresponds to a drop of about 600 1000 m in altitudinal hydroclimatic zones finally a comparison between the modern and paleohydrological data leads us to believe that the stabilization of the paleolake shorelines at the same altitude can be attributed to control by the water table level in the aquifer of the basaltic plateaus east of the basin

origin and evolution of intracratonic thermal fluids from central western peninsular india abstract the chemical and isotopic composition of several thermal springs and associated gas phases in a large sector of central western peninsular india has been investigated such springs have meteoric isotopic signature and emerge after very well developed convective circulation at depth along important tectonic structures such as the son narmada tapti rift zone and the west coast fault chemical components in both gas and liquid phases and geothermometric estimations suggest that such springs are not related to the presence of any active hydrothermal systems at shallow depth in any of the studied areas the hottest convective water emerges at tattapani at near boiling point for water at atmospheric pressure 90 c in association with an n2 rich gas phase of clear meteoric signature since such fluids do not carry any corrosive components they could be conveniently exploited for industrial purposes such as drying processes from a tectonic point of view the presence of thermal emergences scattered in a wide area along geologically well defined structures which also generate frequent moderate earthquakes suggests that such structures are active although the isotopic composition of thermal springs points to a meteoric origin their feeding aquifers are not topographically driven as in most active alpine orogenic belts the relative high quantity of total helium in the associated gas phase suggests also that they are really deep old long circulating waters we propose for such waters the term intracratonic thermal waters since the isotopic signature of he in the gas phase does not show any release of primordial 3he in any of the areas of spring emergence based on the quite low 3he 4he ratio in the gas phase we suggest also that in spite of its morphological shape the narmada son tapti rift zone cutting the indian subcontinent in two is more related to paleo suture rather than to a mid continental rift system

stable isotope characterization of the miocene lacustrine systems of los monegros ebro basin spain palaeogeographic and palaeoclimatic implications the lacustrine carbonate facies from three allostratigraphic units n1 n2 and n3 of miocene age in the los monegros region ebro basin are characterized isotopically the dominant facies are marls laminated limestones stromatolitic limestones massive limestones and bioturbated limestones these are associated with lacustrine sulphate deposits and distal alluvial facies palaeohydrological reconstructions of the study area are supported by the isotopic and the mineralogical composition of the carbonates massive and bioturbated limestones occupy a very similar compositional domain and have the lowest isotopic compositions of all the facies 9 18opdb 4 5 and 6 4 13cpdb 0 4 reflecting a short residence time of the water and variable commonly high influence of biogenic co2 laminated limestones and stromatolites define a comparatively enriched domain with 18o values ranging from 6 to 0 and 13c values ranging from 3 5 to 0 these values indicate stronger evaporation and enhanced 12c assimilation due to intense biological activity during periods of longer water residence time marls have isotopic values intermediate between these two domains and correspond to periods of lacustrine dilution dolomite bearing samples mainly laminated and stromatolitic facies show a 18odol cal 7 5 with respect to calcite from the same facies while 13c values show very little enrichment up to 1 the positive correlation r 0 85 between 18o and dolomite contents suggests that dolomite resulted from the progressive evaporative concentration of a single water mass and not from the mixing of waters of different compositions the dolomite is thought to be primary or at most the product of very early diagenetic processes the isotopic composition of the facies and their spatial and temporal variations depend on the depositional environment and were constrained by changing regional paleogeography isotopic trends from units n1 to n3 upper agenian vallesian period display a regular depletion in heavy isotopes that indicates a climatic change towards wetter conditions

bombay gravity high and eruption of deccan flood basalts india from a shallow secondary plume abstract the western margin of india especially the area surrounding the gravity high of bombay is covered by a thick pile of deccan flood basalts the massive eruption is one of the largest continental volcanic events at the cretaceous tertiary biological mass extinction boundary 65 ma ago the area is characterized by several hidden tectonic features and their origin and evolution have remained controversial in the search for magma source structure attention was focused on an unusual oval shaped positive gravity anomaly over the bombay coastal zone the gravity analysis indicates the presence of two subsurface structures at depths of 4 5 0 5 km and 18 2 km these depths correspond to the top of the crustal basaltic layer and an upwarped moho discontinuity respectively the positive gravity anomaly in three dimensional analysis reveals a possible magma conduit structure and the near absence of the granitic layer the unusually shallow moho layer coincides with the region of a broad high heat flow anomaly average heat flow more than 80 mw m2 the geophysical signatures from the neighborhood show that the asthenosphere has welled up considerably and is located at a depth of about 40 km high heat flow and asthenospheric depth estimates suggest melting conditions at very shallow depths it is suggested that the highly differentiated magma associated with the major eruptive phase of deccan traps did not originate at the d layer it is hypothesized that magma was brought to the surface by a major secondary plume at a much shallower depth within the lithosphere and possibly at the crust mantle boundary as a consequence of subcrustal erosion and secondary melting caused by the extreme velocity of india during the late cretaceous and early tertiary substantial melting of the base of the lithosphere due to frictional heating might have resulted in the accumulation of a large quantity of magma below the thinned lithosphere at the pre existing fracture zone near the continental margin the presence of a magmatic conduit structure above the moho derived from the inversion of gravity data and other tectonic conditions suggests a possible triggering of the magma reservoir by a large bolide impact 10 km diameter at the cretaceous tertiary boundary near bombay

different approaches to handling vertical and streamwise sorting in modeling river morphodynamics this paper presents an assessment of the strengths and weaknesses of four sediment continuity models for nonuniform sediment by applying these models to an aggradational flume experiment that is dominated by nonuniform sediment and dunes the author makes simulations of the flume experiment using four numerical morphodynamic model systems to which the following sediment continuity models are applied the commonly applied active layer model a a two layer model b a sorting evolution model while assuming bed form size to be regular c1 and a sorting evolution model while taking into account the variability in bed form geometry c2 the model systems that incorporate the variability of bed form geometry i e the two layer model and the sorting evolution model with irregular dunes show an improved prediction of the adaptation timescale of the composition of both the bed surface and the transported sediment as well as the vertical sorting profile this is because including the variability of bed form geometry enables the model system to account for sediment being stored temporarily at elevations that are exposed to the flow less frequently future application of both models to field cases is difficult however as the two layer model is not sufficiently generic and may lead to ellipticity of its set of equations whereas the sorting evolution model requires a very small numerical time step

the bude formation lower westphalian sw england siliciclastic shelf sedimentation in a large equatorial lake the 1300 m thick turbiditic bude formation was deposited in a lake lake bude but disagreement persists over whether the environment was a deltaic or deep water fan the tectonic setting of the lake was the northern flank of a northerly advancing variscan foreland basin close to the westphalian palaeo equator palaeocurrents indicate sediment sourcing from all quadrants except the south there is a dm m scale cyclicity whereby sandstone bodies comprising amalgamated event beds alternate with mudstone intervals containing non amalgamated event beds the ideal cycle is a symmetrical coarsening up fining up cycle consisting of three facies i 2 and 3 arranged in 12321 order facies 3 in the middle of the cycle is an amalgamated sandstone body up to 10 m thick which interfingers laterally with thin cm mudstone layers the sandstone body comprises amalgamated beds of very fine sandstone which are largely massive and up to 0 4 m thick channels are absent except for scours up to 0 2 m deep which truncate the interfingering mudstone layers sandstone bodies are inferred to be tongue shaped in three dimensions facies 1 and 2 completing the 12321 cycle are respectively dark grey fine and light grey coarse varved mudstone containing thin 0 4 m sandstone event beds fossils and burrows indicate that facies 1 and 2 were deposited respectively in brackish rarely marine and fresh water hence the ideal cycle 12321 reflects an upward decrease then increase in salinity brackish fresh brackish this is attributed to the lake sill being periodically overtopped by the sea due to glacio euitatic sea level oscillations the resulting oscillations in lake depth produced the coarsening up fining up regressivetransgressive cyclicity the central sandstone body representing the regressive maximum event beds are interpreted as river fed turbidites deposited during catastrophic storm floods combinedflow ripples and other wave influenced structures occur in event beds throughout the ideal cycle suggesting deposition of the entire bude formation above storm wave base the proposed environment is a shelf of continental shelf dimensions but lacustrine instead of marine sandstone bodies are interpreted to be river connected tongues or lobes the absence of cycles containing nearshore or emergent facies is attributed to i the lake sill preventing the water level from falling below sill level thereby insulating the lake floor from eustatically forced emergence and ii relatively distal deposition beyond the reach of shoreline progradations the lack of palaeoflow from the south is attributed to a now eroded deep water trough lying to the south in front of the northerly advancing orogen some facies 2 laminated mudstone beds grade laterally into massive and or contorted beds interpreted as in situ seismites facies 4 consistent with an active foreland basin setting development of seismites was possibly facilitated by gas bubbles and or weak cohesion in the fresh water bottom mud the late quaternary black sea with its broad northwestern shelf is probably a good physiographical analogue of lake bude and was likewise fresh at times

prediction of central california earthquakes from soil gas helium fluctuations the observations of short term decreases in helium soil gas concentrations along the san andreas fault in central california have been correlated with subsequent earthquake activity the area of study is elliptical in shape with radii approximately 160 80 km centered near san benito and with the major axis parallel to the fault for 83 percent of them 4 earthquakes in this area a helium decrease preceded seismic activity by 1 5 to 6 5 weeks there were several earthquakes without a decrease and several decreases without a corresponding earthquake owing to complex and unresolved interaction of many geophysical and geochemical parameters no suitable model is yet developed to explain the observations

rb sr evidence for punctuated illite smectite diagenesis in the oligocene frio formation texas gulf coast the size fractions of a suite of upper oligocene frio formation shale samples taken from below 10 500 ft in a well on the texas gulf coast fall on a rb sr isochron corresponding to an age of 23 6 0 8 m y the isochron shows an initial 87 sr 86 sr ratio of 0 7088 0 0004 this suggests that regularly interstratified illite smectite simultaneously equilibrated soon after burial over a range of burial depths at 7 000 8 000 ft shallower than at present oxygen isotope values for these clays are also consistent with equilibration under shallower burial conditions such a pattern conflicts with the prevailing idea of a gradual illitization of smectite with progressive burial a new model of episodic or punctuated diagenesis is proposed whereby sudden diagenesis is initiated by a change in pore water chemistry clay reaction occurs over a range of temperature at this time such that the deeper clays are transformed completely to 80 illite and the shallow clays are transformed less completely subsequent pore water chemical changes inhibit further clay reaction and the mineralogic gradient and the isotopic signature formed at 23 6 m y b p are frozen in seven to eight thousand feet of additional post oligocene burial has not resulted in the creation of younger illite smectite consequently there is no evidence that illite smectite diagenesis is currently taking place in the frio formation

holocene dolomitization of calcium carbonate sediments from the coastal sabkhas of abu dhabi u a e a stable isotope study secondary dolomitization of holocene calcium carbonate sediments occurs beneath the coastal sabkhas of abu dhabi u a e a stable isotope study of the sabhka sediments and brines indicates that the

the last glacial maximum on spitsbergen svalbard most scientists have concluded previously that the west coast of spitsbergen svalbard remained ice free during the late weichselian between 25 000 and 10 000 yr b p we conclude that the glaciation was more extensive terraces that were postulated to have been ice free are covered by a thin late weichselian till sudden drop in the marine limit and basal radiocarbon dates of raised glaciomarine sediments demonstrates that the glaciers in the main fjords isfjorden and van mijenfjorden terminated west outside of the fjord mouths basal radiocarbon dates from glaciomarine clay above till in cores from the continental shelf west of spitsbergen yielded ages of about 12 500 yr b p from which we conclude that the ice extended to the shelf edge based on the extent of amino acid diagenesis in radiocarbon dated molluscs the duration of the maximum extension of the late weichselian glaciation was short certainly less than 10 000 years during the ice free period preceding that glaciation at least back to 40 000 yr b p the glaciers on svalbard were not significantly larger than at present as shown by marine deposits close to the glacier snouts many radiocarbon dates place deglaciation of the outer coast at about 12 500 yr b p at about 10 000 yr b p the rest of the archipelago rapidly became ice free

origin of groundwater helium and temperature anomalies in the cambay region of gujarat india abstract a survey of natural helium in soil gas and groundwater was undertaken in the cambay region of gujarat india the cambay basin known for high heat flow is a graben characterised by nnw sse trending major fault system and successive down faulting along sympathetic faults parallel to major trendline and orthogonal faults cutting across several wells indicated higher than atmospheric equilibration concentration of helium referred to as anomalous helium concentration these wells generally had high groundwater temperature and appear to be located along basement faults in the study area particularly on both eastern and western flanks of the cambay basin groundwater helium anomalies are explained through a conceptual model as originating largely from within the crystalline basement through radioactive decay in the form of plumes localised by the major faults and fractures groundwater temperature anomalies originate due to setting up of a shallow 1 2 km depth convective circulation again along major faults and fractures which facilitate both upward and downward migration of groundwater the sedimentary cover acts as a dispersive medium therefore no significant helium anomalies are seen within the cambay graben that has more than 3 km thick sedimentary cover it is thus seen that even though helium and groundwater have different origins the faults and fractures in the crust can associate anomalous concentrations of helium and groundwater temperatures along themselves in a longitudinally distributed manner by providing preferred pathways for migration of helium and by facilitating establishment of convective hydrothermal circulation of groundwater

surface heat flow and igneous intrusion in the cambay basin india abstract heat flow values from some additional locations in the cenozoic cambay basin have been determined together with the previously published data they show that the heat flow is moderate 55 67 mw m in the southern part of the basin towards broach and ankleswar and that there is a clear trend of high heat flow 75 93 mw m 2 range of average values for six different widely separated locations in a part of the basin located north of the mahisagan river between cambay and mehsana along a stretch of about 140 km conductive steady state geotherms calculated using observed high surface heat flow values and appropriate models show beneath the cambay mehsana area a large degree of melting in the lower crust and upper mantle which is not suggested by the existing geodata considering this aspect and taking into account the existence of a normal crust about 37 km thick below the cambay tarapur and ahmedabad mehsana blocks as obtained from deep seismic soundings it has been inferred that the heat flow anomaly is due to transient thermal perturbations introduced from tectonic activity in the form of magmatic intrusions a careful analysis of heat flow gravity and other related geodata point out and support the possibility of a miocene pliocene basic intrusive body at a depth of around 10 km under the cambay mehsana area further the consistent trend of the thermal and gravity fields indicates thinning of the postulated intrusive body from cambay towards mehsana

composition of inland waters with marine like fauna and inferences for a miocene lake in spain abstract knowledge of the ionic composition of athalassic non marine waters where marine like organisms currently live allows to evaluate their ionic and total dissolved solid tds tolerance ranges together with other ecological data these chemical parameters can be used to interpret hydrological and hydrochemical conditions in ancient lake basins where analogous faunas have been recorded an example of such a utilization of the biological record is presented for miocene clastic dominated lacustrine deposits of the tertiary ebro basin of ne spain which contain marine like fossils comparison of the deduced chemical parameters for the miocene lake waters with the chemical composition of recent groundwaters and saline springs in the same area allows us to infer a similar mode of solute acquisition this implies that there were important cl so 4 saline inflows to the miocene lakes

late oligocene early miocene landscape evolution of the lake mead region during the transition from sevier contraction to basin and range extension late oligocene to miocene sedimentary strata of the lake mead nevada region hold evidence that can test models of central basin and range extension and tectonic evolution and illuminate paleodrainage systems related to the carving of the grand canyon in this region sevier contraction and a period of relative tectonic quiescence predate miocene extension and magmatism the herein revised rainbow gardens formation formerly the oldest member of the horse spring formation is found throughout the lake mead area and spans the transition from quiescence to the start of extension new detailed stratigraphic work within the rainbow gardens formation including paleocurrent analyses stable isotope geochemical data new 40 ar 39 ar dates tephrochronologic data and ongoing structural studies was used to build a detailed chronostratigraphic framework and reconstruct the rainbow gardens basin through time our results show that the basin formed by a combination of inherited topography and tectonic events outside the lake mead region prior to ca 25 ma sedimentation rates sedimentary facies patterns and the lack of evidence for syndepositional faulting indicate that the basin did not form during extensional faulting although recent work suggests that this basin was modified by uplift to the south between 18 and 20 ma initially the basin recorded fluvial sedimentation within the center of an e ne trending inherited valley with two facing gravel dominated bajadas on either side as the valley filled rivers from the caliente volcanic field to the north delivered an influx of volcaniclastic material into a broad area of marshes and ephemeral lakes in the final stages of sedimentation just prior to the onset of extension at ca 17 ma the basin filled with limestone in a series of shallow lakes understanding the development and evolution of this basin is crucial for testing models of extension as recorded by the younger horse spring formation in addition the detailed sedimentology and stratigraphy place constraints on models of the formation of the grand canyon and suggest that a paleo colorado river did not deposit sediment in the lake mead area between 25 and 17 ma this work highlights the importance of detailed basin analyses which are crucial companions to structural tectonic and geomorphologic studies aimed at understanding the complex evolution of lithospheric and landscape changes across a large region

modern dolomite deposition in continental saline lakes western victoria australia microcrystalline dolomite forms a major constituent of holocene sediments of numerous continental saline playa lakes in southeastern australia the lake waters are highly supersaturated with respect to dolomite as well as other mg carbonates but undersaturated or near saturation with respect to calcite and aragonite the dolomite shows no replacement textures and most likely formed by direct precipitation conditions in these lakes that appear conducive to the precipitation of dolomite are 1 high salinity 2 high mg ca ratios and 3 high alkalinity the moderate sulfate levels of the brines do not seem to be inhibiting carbonate precipitation

experimental and numerical findings on the long term evolution of migrating alternate bars in alluvial channels migrating alternate bars form in alluvial channels as a result of morphodynamic instability extensive literature can be found on their origin and short term development but their long term evolution has been poorly studied so far in particular it is not clear whether migrating bars eventually reach a dynamic equilibrium as in previous studies bars were observed to elongate with time we studied the long term evolution of alternate bars by performing two independent long duration laboratory experiments and some numerical tests with a physics based depth averaged model in a straight flume with constant water flow and sediment recirculation migrating bars followed a cyclic variation they became gradually longer and higher for a while then quickly much shorter and lower in one case all migrating bars simultaneously vanished almost completely only to reform soon after at the same time steady bars two to three times as long progressively developed from upstream gradually suppressing the migrating bars we also observed simultaneous vanishing of migrating bars in an annular flume experiment this time at intervals of 6 8 d numerical simulations of long alluvial channels with constant flow rate and fixed banks show periodic vanishing of a few migrating bars at a time occurring at regular spacing under constant flow rates migrating bars appear as a transition phenomenon of alluvial channels having a cyclic character these observations however might hold only for certain morphodynamics conditions which should be further investigated

nonmarine evaporitic sedimentation and associated diagenetic processes of the southwestern margin of the ebro basin lower miocene spain abstract in the southwestern margin of the tertiary ebro basin northeastern spain several evaporitic units are found among distal alluvial fan deposits they are made up of bioturbated microlenticular primary gypsum secondary nodular and meganodular gypsum after anhydrite chert nodules and charophyte limestones these evaporites formed in shallow saline lakes along the basin margin during the early early miocene autol gypsum unit and the late early miocene ablitas gravalos and ribafrecha gypsum units the lakes were fed principally by deeply circulated groundwaters loaded with dissolved salts from the old evaporite formations mainly triassic rocks that make up the surrounding mountain chains shallow meteoric waters of low concentration also reached the lakes episodically concentration of these waters led to deposition of microlenticular gypsum and charophytic carbonates which were then intensely bioturbated early diagenetic chert nodules and nodular anhydrite also formed in the early stages of burial large anhydrite nodules meganodules overprinted these sedimentary and early di genetic deposits with more advanced burial the primary gypsum was profoundly anhydritized in some areas with subsequent exhumation the anhydritized zones were transformed to secondary gypsum marginal lakes acted as preconcentrators of drainage waters coming from the surrounding mountain chains causing early precipitation of low solubility salts as ca carbonates gypsum and silica the remaining dissolved salts then drained toward the basin center where gypsum anhydrite glauberite polyhalite and halite precipitated in contemporaneous high salinity lakes

depth averaged two dimensional numerical modeling of unsteady flow and nonuniform sediment transport in open channels a depth averaged two dimensional 2d numerical model for unsteady flow and nonuniform sediment transport in open channels is established using the finite volume method on a nonstaggered curvilinear grid the 2d shallow water equations are solved by the isimple c n algorithms with the rhie and chow s momentum interpolation technique the proposed sediment transport model adopts a nonequilibrium approach for nonuniform total load sediment transport the bed load and suspended load are calculated separately or jointly according to sediment transport mode the sediment transport capacity is determined by four formulas which are capable of accounting for the hiding and exposure effects among different size classes an empirical formula is proposed to consider the effects of the gravity on the sediment transport capacity and the bed load movement direction in channels with steep slopes flow and sediment transport are simulated in a decoupled manner but the sediment module adopts a coupling procedure for the computations of sediment transport bed change and bed material sorting the model has been tested against several experimental and field cases showing good agreement between the simulated results and measured data

expanding the active layer discussion of church and haschenburger 2017 what is the active layer water resources research 53 5 10 doi 10 1002 2016wr019675 church and haschenburger 2017 https doi org 10 1002 2016wr019675 make helpful distinctions around the issue of defining the active layer with which we agree we propose expanding discussion and definition of the active layer in fluvial bedload transport to include the concept of the morphological active layer this is particularly applicable to laterally unstable rivers such as braided rivers in which progressive morphological change over short time periods is the process by which much of the bedload transport occurs the morphological active layer is also distinguished by variable lateral and longitudinal extent continuity over a range of flows and transport intensity we suggest that the issue of forms of active layer raised by church and haschenburger opens up an important discussion on the nature of bedload transport in relation to river morpho dynamics over the range of river types

experiments on bar formation in a straight flume 2 graded sediment laboratory experiments have been carried out in a large laboratory flume using a strongly bimodal sediment mixture in a range of flow conditions such that the initially flat bed of the flume became unstable enhancing the development of alternate bars in order to elucidate the effect of grain sorting the present experiments are compared with a previous set of experiments performed in the same flume under similar hydraulic conditions but using a nearly uniform sand with a mean geometric grain diameter equal to that characterizing present experiments the comparison suggests that sediment heterogeneity may appreciably affect bed form characteristics the development of smallscale ripples and mesoscale dunes sediment waves tended to be inhibited thus allowing a decrease in flow resistance owing to the bimodal character of the adopted mixture at low values of the bed shear stress a condition of partial transport was attained for which only the finer grained portion of the mixture was observed to move while the coarsergrained fractions remained essentially immobile throughout the experimental run however complete mobilization of all size fractions was observed to occur in runs carried out at higher slopes i e at higher bed shear stress in order to generate an alternate bar pattern selective transport of individual grain size fractions coupled with the characteristic bar topography pattern led to an intense longitudinal sorting which accreted the coarser particles on bar crests furthermore bar migration caused through scour and fill a significant vertical sorting as a consequence of these sorting processes and in accordance with previous experimental observations bar height turns out to be invariably damped with respect to uniform sediment experiments the trend exhibited by the wavelengths is less clear and suggests that in the present experiments sorting effects do not enhance the clear shortening of bar wavelengths typically observed in other series of flume experiments carried out with weakly bimodal mixtures

global aridity during the early miocene a terrestrial paleoclimate record from the ebro basin spain abstract paleosols are an important tool in the paleoclimatic and paleoenvironmental interpretation of continental deposits and can provide a high resolution proxy for paleoclimate results from geochemical climofunctions applied to early miocene strata exposed in the ebro basin spain demonstrate that mean annual precipitation was the dominant control on paleosol type and indicate that the paleoclimate was considerably wetter during the early miocene by up to 1150 mm yr 1 in comparison to modern values placing it in a subhumid climatic regime rather than an arid semiarid regime as previously suggested by sedimentological and paleontological approaches by making comparisons with published data on paleoclimate during the early miocene this article stresses the importance of regional climatic changes in global paleoclimatic interpretation

estimating bedload transport in a large sand gravel bed river from direct sampling dune tracking and empirical formulas three methods used to estimate river bedload discharges were compared in a large sand gravel bed river the unit and total bedload transport rates estimated by sediment sampling dune tracking method and the equations of van rijn and meyer peter and muller were compared the analysis was based on a large data set obtained from field surveys that combined sediment sampling acoustic doppler profiler adp measurements and multibeam echosoundings of the middle reach of the river loire france for contrasting flow conditions ranging from low flows to 2 year floods for transport stages between 2 and 6 i e between the annual mean discharge and the discharge for a 2 year flood the tested equations predicted fairly well the unit and total bedload discharges and roughly estimated the temporal variability of the bedload during floods for these transport conditions the best agreement with the sediment sampling measurements was observed with the van rijn formula for lower flow conditions the tested formulas provide lower estimates than those sampled to improve the accuracy of the equations for low flows potential solutions include integrating near bed turbulences and non uniformity of bed particles into the models the ability of the formulas to predict the temporal variability of the bedload can be improved by using the bedform roughness to adjust the estimates the bedload transport rates calculated with dune tracking method are lower than the fluxes sampled because a substantial fraction of the bedload does not participate to the dune migration finally a first rating curve that was implemented for the river loire estimates the annual bedload discharge for 2010 to be 480 000 t

groundwater helium an indicator of active tectonic regions along narmada river central india abstract results of a survey of dissolved helium fluoride and electrical conductivity in groundwater from across the main stem of the narmada river between bharuch in the west and amarkantak in the east are reported this survey was undertaken to identify active tectonic regions based on locations of high helium concentrations interpreted as indicative of upward migration of deep fluids existence of deep fluids in this region has been hypothesised earlier based on various geophysical studies in the narmada rift basin a major tectonic feature in central india samples with high helium concentration are clustered in two broad regions with known intersecting faults indicating the possibility of plumes with high helium concentration being injected into shallower groundwater in these regions facilitated by these faults and fractures locations of groundwater samples having excess fluoride remarkably correspond to these two clusters of excess helium this suggests a possible commonality between the causal factor of excess helium and higher fluoride in groundwater which needs to be further investigated

the evolution of illite to muscovite mineralogical and isotopic data from the glarus alps switzerland thirty five illite and muscovite concentrates were extracted from triassic and permian claystones shales slates and phyllites along a cross section from the diagenetic alpine foreland tabular jura and borehole samples beneath the molasse basin to the anchi and epimetamorphic helvetic zone of the central alps concentrates and thin sections were investigated by microscopic x ray infrared mossbauer thermal dta and tg wet chemical electron microprobe k ar rb sr 40ar 39ar and stable isotope methods with increasing metamorphic grade based on illite crystallinity data xrd and ir the following continuous changes are observed i the 1md 2m1 polymorph transformation is completed in the higher grade anchizone ii k2o increases from 6 8 wt diagenetic zone to 8 5 10 anchizone to 10 11 5 epizone reflecting an increase in the total negative layer charge from 1 2 to 2 0 iii a decrease of the chemical variation of the mica population with detrital muscovite surviving up to the anchizone epizone boundary iv a shift of an endothermic peak in differential thermal curves from 500 to 750 c v k ar and rb sr apparent ages of the fraction 2 m decrease from the diagenetic zone to the epizone k ar ages being generally lower than rb sr ages the critical temperature for total ar resetting is estimated to be 260 30 c k ar and rb sr ages become concordant when the anchizone epizone boundary is approached the stable isotope data on the other hand show no change with metamorphic grade but are dependent on stratigraphic age these results suggest that the prograde evolution from 1 md illite to 2m1 muscovite involves a continuous lattice restructuration without rupture of the tetrahedral and octahedral bonds and change of the hydroxyl radicals however this is not a recrystallization process this restructuration is completed approximately at the anchizone epizone boundary the isotopic data indicate significant diffusive loss of 40ar and 87sr prior to any observable lattice reorganization the restructuration progressively introduces a consistent repartition of ar and k in the mineral lattices and is outlined by the 40ar 39ar age spectra concordant k ar and rb sr ages of around 35 30 ma with concomitant concordant 40ar 39ar release spectra are representative for the main phase of alpine metamorphism calanda phase in the glarus alps a second age group between 25 and 20 ma can probably be attributed to movements along the glarus thrust ruchi phase while values down to 9 ma in regions with higher metamorphic conditions suggest thermal conditions persisting at least until the middle tortonian

k ar dating of illitic clays in jurassic nugget sandstone and timing of petroleum migration in wyoming overthrust belt abstract authigenic illite is a prominent pore fill in the nugget sandstone the main reservoir rock of most fields in the southwest wyoming overthrust belt illite a good k ar clock was dated from several well samples all from the absaroka thrust sheet this includes a producing well in the clear creek field where seven samples traverse the gas oil and water zones the ages of the clear creek suite are virtually concordant at 110 2 m y assuming hydrocarbon emplacement would have arrested authigenesis in the oil and gas zones the similarity of ages from the hydrocarbon zones with the water zone indicates hydrocarbon emplacement was post 110 m y ago middle cretaceous ages obtained from the other absaroka sheet nugget samples fall in the narrow range of 102 to 120 y b p this indicates illite authigenesis was a relatively short lived event for the nugget in the absaroka sheet the wyoming idaho utah overthrust belt involves several thrust sheets each of which was emplaced over its foreland sequentially from west to east over a time spanning tens of millions of years we attribute the mid cretaceous illite growth in the absaroka sheet to burial conditions established when that part of the nugget was thrust upon by the crawford sheet the burial was accomplished both tectonically and by synorogenically derived sediment if true our illite dates imply a somewhat older age for the crawford sheet than previously interpreted we attribute the post illite hydrocarbon emplacement in the absaroka nugget as a result of thrusting of the absaroka sheet on top of its foreland containing middle cretaceous petroleum source bed shales these beds were thermally matured wh n buried by the emplacement of the absaroka sheet and its derived sediment in the late cretaceous end of article last page 414

an opportunity to connect the morphodynamics of alternate bars with their sedimentary products field investigations that help clarify local sedimentary processes involved in the migration of alternate bars as a consequence of flood events are lacking a simple approach combining scour chains stratigraphy and frequent bathymetric surveys is proposed to connect the dynamics of free migrating alternate bars present in disconnected channels of large sandy gravelly rivers with their sedimentary products and vice versa the results show that the spatial distribution of bars before a flood partly governs the scour and fill processes and that the sediment transport rates vary significantly on a single cross section this can be due to preferential axes of the migration of the bars determined by their location on the cross section the bank direction and the discharge the approach allows the reconstruction of local sedimentary processes involved in alternate bar migration by combining maximum scour depths reached during a flood with frequent channel bed topography surveys and post flood stratigraphy it is also possible to distinguish deposited and preserved sediments compared with sediments by passed during the flood copyright 2011 john wiley sons ltd

fluvial islands first stage of development from nonmigrating forced bars and woody vegetation interactions abstract fluvial islands can develop from the channel bed by interactions between pioneer trees and bars although vegetation recruitment and survival is possible on all bar types it is easier for trees to survive on nonmigrating bars developed from a change in channel geometry or to the presence of a steady perturbation this field study details the first stages of development of a vegetated mid channel nonmigrating or forced bar and its evolution toward an island form over six years analysis of bed topographical changes vegetation density and roughness scour and fill depths sediment grain size and architecture and excess bed shear stress highlighted a specific signature of trees on topography and grain size segregation two depositional processes combining the formation of obstacle marks and upstream shifting deposition of sediments led to the vertical accretion of the vegetated bar during the first stage of the bar accretion bedload sediment supply coming from surrounding channels during floods was identified as a key process modulated by the presence of woody vegetation and a deflection effect induced by the preexisting topography grain size segregation between vegetated and bare areas was also highlighted and interpreted as an important process affecting the development of surrounding channels and the degree of disconnection and hence the speed of development of a growing island the heterogeneity of bedload supply can explain why sediment deposition and density of trees are not strictly related a general conceptual model detailing the first stages of evolution from a bar to an established island is proposed for relatively large lowland rivers

regional tectonic framework structure and evolution of the western marginal basins of india abstract the kutch saurashtra cambay and narmada basins are pericontinental rift basins in the western margin of the indian craton these basins were formed by rifting along precambrian tectonic trends interplay of three major precambrian tectonic trends of western india dharwar nnw sse aravalli delhi ne sw and satpura ene wsw controlled the tectonic style of the basins the geological history of the basins indicates that these basins were formed by sequential reactivation of primordial faults the kutch basin opened up first in the early jurassic rifting was initiated in late triassic along the delhi trend followed by the cambay basin in the early cretaceous along the dharwar trend and the narmada basin in late cretaceous time along the satpura trend the evolution of the basins took place in four stages these stages are synchronous with the important events in the evolution of the indian sub continent its breakup from gondwanaland in the late triassic early jurassic its northward drifting during the jurassic cretaceous and collision with the asian continent in the early tertiary the most important tectonic events occurred in late cretaceous time the present style of the continental margins of india evolved during early tertiary time the saurashtra arch the extension of the aravalli range across the western continental shelf subsided along the eastern margin fault of the cambay basin during the early cretaceous it formed an extensive depositional platform continuous with the kutch shelf for the accumulation of thick deltaic sediments a part of the saurashtra arch was uplifted as a horst during the main tectonic phase in the late cretaceous the present high thermal regime of the cambay bombay high region is suggestive of a renewed rifting phase

diagenesis of late proterozoic carbonates the beck spring dolomite of eastern california abstract petrographic and compositional attributes of limestone and dolostone in the beck spring dolomite of eastern california indicate that late proterozoic mineralogies isotopic compositions and diagenetic processes were similar to those inferred for younger phanerozoic marine carbonate sequences allochems in limestones include strontium rich ooids with well preserved concentric banding and cortices of equant neomorphic calcite that commonly exhibit dissolution and compaction features cements include microdolomite rich columnar marine calcite and equant spar calcites are depleted relative to dolomites and become enriched with stratigraphic depth acicular and columnar marine cement and allochems in dolostones display fabrics identical to those in limestones but are isotopically distinct dolomite ooids columnar and acicular cement crystal silt and early luminescent spar cement from four stratigraphic sections define overlapping positive oxygen carbon covariant fields that trend toward depleted calcite compositions early luminescent dolomite spar cement is unconformably overlain by depleted ferroan dolospar fabric data suggest that marine cement and ooids were precipitated as magnesian calcite and aragonite isotopic data suggest that metastable components locally stabilized to calcite during subaerial exposure while laterally dolomitization took place in mixed marine meteoric waters early dolospar precipitation began during replacive dolomitization and late ferroan dolospar precipitated during burial lack of evidence for hypersaline conditions suggests that late proterozoic normal marine carbonate isotopic composition was 0 5 2 018o and 5 3 0 5913c

experiments on bar formation in a straight flume 1 uniform sediment laboratory experiments have been carried out in a large laboratory flume using a nearly uniform sand and under controlled steady flow conditions such as to ensure the development of alternate bars on a ripple and or dune covered bed the interaction between small scale and large scale bed forms is found to enhance a modulation in time and in space of the bar pattern moreover the flow depth decrease experienced by the flow field when approaching bar fronts leading to a progressive reduction of the dimensions of small scale bed forms may influence appreciably the overall flow resistance experimental values of bar wavelength and of bar celerity are compared with the theoretical estimates obtained from a model developed within the classical framework of linear stability analysis in particular the model accounts for the local variability of friction coefficient and water level for the secondary helical flow effects and for the influence of longitudinal slope on sediment transport quantitatively satisfactory predictions of bar wavelength appear to be possible in spite of the fact that in various runs a correct estimation of flow resistance and flow discharge appears to be relatively difficult

late jurassic biogeochemical microenvironments associated with microbialite coated unionids bivalvia asturias n spain abstract the vega formation upper jurassic asturias spain contains two kimmeridgian outcrops the abeu and huerres sections with bivalves coated with carbonate microbialites oncoids the bivalve shells in the abeu section were replaced early by calcite while those of the huerres section were dissolved and the moulds filled by late diagenetic cements for the abeu shells there was a loss of sr and a gain of mg fe and mn during the replacement process but much of the original organic matter was retained part of the s present can be linked to this organic matter and part to the sulphate that replaced the carbonate groups in the calcite the thin microbialites inside the shells of some of the huerres bivalves have allowed us to estimate the influence of the growth rate on the incorporation of trace elements in calcite with an approximately six times lower growth rate the internal microbialite incorporates less mg and s and more fe and mn than the external one while maintaining the sr content the trace element content mg s sr fe and mn of the huerres and abeu microbialites are similar these coatings may therefore have been formed in the same type of freshwater but in different microenvironments given the substantial sulphate content of the microbialites from both sections this freshwater probably came from hot springs however the high fe mn ratio of the abeu microbialites suggests a reducing environment during their formation indeed 18o and 13c data confirm that the abeu and huerres microbialites were formed in different microenvironments the positive covariance for 18o and 13c of the abeu microbialites and replaced shells r2 0 83 and the wide range of variation for 18o 2 80 together suggest that the microbialite crusts grew in isolated ponds where evaporation was dominant in the huerres microbialites the positive covariance for 18o and 13c r2 0 59 and the narrow range of variation for 18o 0 74 indicate that the huerres section was formed in a more open environmental system where degassing predominated over evaporation

alternate bars in a sandy gravel bed river generation migration and interactions with superimposed dunes a field study was carried out to investigate the development of alternate bars in a secondary channel of the loire river france as a function of discharge variations we combined frequent bathymetric surveys scour chains and stratigraphical analysis of deposits with measurements and modelling of flow dynamics the channel exhibited migrating bars non migrating bars and superimposed dunes possible mechanisms of bar initiation were found to be chutes associated with changes of bank direction and instability resulting from interactions between existing bars during the fall in water level after floods we propose that the reworking of bar sediments during low flows high width to depth ratio reinforced by high values of the shields mobility parameter can explain the formation or re generation of new alternate migrating bars during a subsequent flood the migration pattern of the bars was found to be cyclic and to depend mainly on i channel layout and ii the dynamics of superimposed dunes with heights and lengths depending on location and discharge value for instance the hysteresis affecting the steepness of dunes influences the flow resistance of the dunes as well as the celerity of migrating bars during flood events we compare the findings from the field with results from theoretical studies on alternate bars this gives insight in the phenomena occurring in the complex setting of real rivers but it also sheds light on the extent to which bar theories based on idealized cases can predict those phenomena copyright 2014 john wiley sons ltd

palustrine sedimentation and associated features grainification and pseudo microkarst in the middle miocene intermediate unit of the madrid basin spain abstract a rather thick sequence 50 75 m of lacustrine limestones forms the uppermost part of the intermediate unit middle miocene in the ne part of the madrid basin central spain a gradual change from distal alluvial to open lake facies is recorded in this area red mudstones passing vertically to strongly mottled limestones are typical of the transition from distal alluvial to marginal lake deposits a wide variety of facies occur in the marginal lacustrine facies association all of them showing pedogenic features e g root traces alveolar septal structures pseudo microkarst micrites and biomicrites are interpreted as open lacustrine deposits although not as strongly pedogenically modified as the marginal lacustrine facies they still show evidence of subaerial exposure the carbonate sequence was deposited in a low gradient shallow lake system in which slight fluctuations in the water level caused extensive emergence pedogenic processes affected most of the lake deposits but modification was more intense in the marginal facies biogenic activity and mechanical reworking at lake margins led to the formation of pedogenic diagenetic pseudo microkarst and peloidal and or intraclastic limestones

recognition of lake level changes in miocene lacustrine units madrid basin spain evidence from facies analysis isotope geochemistry and clay mineralogy abstract the miocene lacustrine sequence exposed near esquivias in the central area of the continental tertiary madrid basin is formed of two main lithostratigraphic units that represent two different stages of a palaeolake system unit i consists of five lithofacies a nodular carbonates and marls b massive dolostones c bioclastic limestones d mudstones and e chert which are characteristic of sedimentation and early diagenesis in a shallow lacustrine environment two main stages of the same general lowstand situation are reflected in mineralogy and isotope geochemistry results an initial stage is suggested by the presence of non stoichiometric dolomite and trioctahedral smectites high 18o and 13c values of the dolomites 5 5 and 2 9 respectively indicate strongly evaporative conditions a second stage is characterized by the presence of calcite fibrous clay minerals and by generally lower 18o from 1 5 to 6 5 and 13c from 1 to 9 8 values for carbonates which suggest more diluted waters during this lowstand phase of the lake unit ii comprises seven lithofacies a conglomerates b intraclastic mudstones c laminated marls d massive mudstones e diatomaceous marls f laminated bioclastic limestones and g root bioturbated limestones both conglomerates and intraclast mudstones fill sharply eroded contacts in the underlying deposits of unit i we demonstrate how the arrangement of facies supported by isotopic results from the carbonates 18o from 0 7 to 7 2 13c from 4 2 to 8 6 is clearly indicative of deeper lake conditions the basal reworked facies mark the initial phase of a lake transgression in contrast with unit i the clay mineral assemblage from unit ii is mainly detrital clay minerals thus also support the interpretation of a dilute water body consistent with a highstand of the palaeolake