architecture of miocene overbank deposits in northern pakistan abstract understanding the geometry of sediment bodies and patterns of sediment disruption in ancient fluvial overbank successions is fundamental to interpretations of overbank deposition overbank deposits of the fluvial chinji formation siwalik group can be divided into sequences 1 20 m thick defined by the alternation of stratified sediments and paleosols preservation of stratified sequences does not support a gradual vertical aggradation of overbank sediments over the extent of the floodplain but instead indicates periods of rapid sediment deposition followed by long hiatuses and soil development rapid deposition of overbank sequences is predicted by models that hypothesize 1 episodic vertical aggradation of the entire floodplain 2 deposition controlled by the growth of alluvial ridges 3 incision and filling of local valleys 4 rapid filling of localized low areas or 5 rapid deposition associated with river channel avulsion these models also have important implications for understanding fossil preservation and floodplain paleoecology paleosol bounded sequences in the chinji formation can pinch out laterally over kilometers indicating that episodes of rapid deposition were restricted to local areas on the floodplain there is no evidence that bases of sequences are erosional and they do not appear to record valley incision and filling sequences generally do not thin and fine systematically away from the terminating margins of major channel deposits suggesting they are not related to the growth of alluvial ridges along active channels lithologic variations and patterns of sediment disruption within sequences appear to reflect the rapid tilling of low areas on the floodplain both adjacent to and distal from the major river channel this infilling of floodplain topography may reflect a continuous process whereby local areas were always being filled somewhere on the floodplain by sediments from minor tributary or crevasse channels alternatively the filling of local flood plain topography may have been caused by widespread but short lived events associated with river channel avulsion

control of relative sea level and climate on coal character in the westphalian c atokan four corners formation central appalachian basin u s a abstract peat successions preserved as coal seams preserve high resolution records of ancient terrestrial water table base level fluctuations that are driven by changes in relative sea level and or paleoclimatic change the aim of this study is to establish the roles of relative sea level and climate in controlling water table fluctuations within coal seams from the fluviodeltaic westphalian c bolsovian atokan four corners formation of the central appalachian basin usa comparison of the characteristics of 10 coals in the four corners formation with accommodation trends identified from analysis of intra coal clastic strata indicates that their thickness and vitrinite inertinite ratio correlate readily with the accommodation setting of the depositional sequence in which they occur coals that accumulated in relatively high accommodation fourth order sequences are high in vitrinite thin and overlain by or intercalated with marine and lacustrine sediments the coals have simple internal organization suggesting that they span parts of single high resolution accommodation cycles coals that accumulated in lower accommodation fourth order sequences are high in inertinite thick and overlain by or intercalated with terrestrial sediments the coals have composite internal organizations typified by multiple high resolution accommodation cycles and characteristic abrupt discontinuities of coal facies representing periods of depositional hiatus the correlations between the composition and thickness of the coals and the magnitude of associated marine transgression imply that relative sea level change was the principal control governing bulk accommodation in these mires landward of the paleoshoreline high frequency accommodation cycles within the coals reflect water table fluctuations in the original mires and were driven by high frequency sea level and or climate change the results of this study provide considerable insight into the manner in which coal composition and stratigraphy at a single locality vary over time in response to changing accommodation and provide a means to predict coal seam quality in an established sequence stratigraphic framework

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

effect of moisture and temperature conditions on the decay rate of a purple mudstone in southwestern china soil formation and geomorphology are primarily influenced by the rock decay which in turn is strongly determined by moisture and temperature conditions however it remains unclear whether rock decay is dominated by thermal stresses or by hydration disintegration and there is little information on mudstone decay rate in southwestern china this study hypothesized that rock decay is dominated by hydration mechanism and focused on the physical decay characteristics of typical purple mudstones using a combination of field and laboratory based experiments the bedrock of a penglaizhen group j 3 p in yanting county sichuan province southwestern china was exposed and covered with nylon fabric in situ soil depths of 10 20 40 and 60 cm were laid on this nylon fabric in 2003 and the decay rate the quantity of clastic particles 2 mm that were decayed from the bedrock in t km 2 yr 1 under the nylon fabric was measured both in 2005 and 2009 in addition fresh mudstones sampled from the matoushan group k 2 m the tuodian group j 3 t and the lufeng group j 1 l in yuanmou county shuangbai county and lufeng county of yunnan province southwestern china respectively were subjected to alternating applications of moisture temperature and their interaction seven treatments in the laboratory and their decay ratios the mass of decayed rock of 2 mm clastic particles to sampled rock mass in percent were measured in 2010 in the field the decay rate of the bedrock showed a significant p 0 05 positive relationship with both the daily moisture and temperature variation at the interface between the soil and bedrock in the laboratory results showed that the effect of moisture variation but not temperature alternation on rock decay was apparent suggesting that purple rock decay is dominated by hydration mechanism freezing thawing in particular affects the sampled rocks because it causes more spalling and fracturing the j 3 t rock had the highest decay ratio because it had the highest clay mineral content and porosity of the three rock types hierarchical clustering analysis suggested that the variation of moisture content and h2o phase solid or liquid within rock plays a key role in rock decay processes both field and laboratory studies consistently showed that the alteration of wetting drying and freezing thawing as well as moisture content substantially influenced rock decay c 2012 elsevier b v all rights reserved

structure degradation and changes in the mechanical behaviour of a stiff clay due to weathering the paper discusses the results of research into the causes of weathering of stiff pleistocene clays located in the montemesola basin ta italy and on the effects of weathering on the clay s mechanical behaviour the weathered clays are yellow brown and overlie the original grey clays in the whole basin the liquidity indexes of both the yellow and the grey clays their fabric as observed by means of scanning electron microscopy as well as the yellow clay oxidation features suggest that drying has been the main weathering process in the basin this is confirmed by the results of drying wetting cycle tests carried out in the laboratory on undisturbed clay samples which show the drying wetting cycles to produce changes in the grey clay similar to those present in situ due to weathering results of oedometer stress path and triaxial tests show that weathering has caused a degradation of the clay bonding and an associated reduction in the size of the clay state boundary surface both one dimensional an

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

the role of subduction induced subsidence in the evolution of the karoo basin abstract the stratigraphic record indicates that during the late carboniferous to early triassic south africa experienced an episode of large scale subsidence that resulted in the development of the karoo basin the southern margin of the region was contemporaneously dominated by an episode of compressional tectonics and there is evidence for subduction of the paleo pacific plate beneath the karoo basin we propose that the long wavelength component of the basin subsidence resulted from the deflection of the lithosphere due to mantle flow coupled to the adjacent subduction this was followed by a recovery phase during which the entire region was uplifted on cessation of subduction and subsequent loss of dynamic support for subsidence contributing to the present day high elevation topography of south africa numerical models of mantle convection are presented and show that a shallow dipping slab is able to reconcile the observed long wavelength subsidence of the basin a significant component of the n

decalcification and residual shear strength reduction in fuller s earth clay analyses of borehole samples at 1 m intervals through the fuller s earth succession at bath reveal an inverse correlation between calcite content and atterberg limits the calcareous component of t

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

coalbed gas systems resources and production and a review of contrasting cases from the san juan and powder river basins coalbed gas has been produced commercially from the northern appalachian basin since the 1930s and from the san juan basin since the early 1950s however the magnitude and economic sig nificance of coalbed gas resources were realized only in the 1970s and early 1980s when the u s bureau of mines u s department of energy the gas research institute and oil and gas operators made a concerted effort to demonstrate commercial production of coalbed gas from vertical wells exploration and development ex panded in the late 1980s and early 1990s due partly to an uncon ventional fuels tax credit by 2000 coalbed gas accounted for 8 8 of the reserves 15 7 tcf 0 44 tm3 and 9 2 of the annual pro duction 1 38 tcf 40 gm3 of dry gas in the united states from 1989 through 2000 cumulative united states coalbed gas produc tion was 9 63 tcf 272 gm3 today coalbed gas development has spread to about a dozen basins in the united states and exploration is progressing worldwide coal beds are self sourcing reservoirs that can contain ther mogenic migrated thermogenic biogenic or mixed gas coalbed gas is stored primarily within micropores of the coal matrix in an adsorbed state and secondarily in micropores and fractures as free gas or solution gas in water the key parameters that control gas resources and producibility are thermal maturity maceral compo sition gas content coal thickness fracture density in situ stress permeability burial history and hydrologic setting these param eters vary greatly in the producing fields of the united states and the world in 2000 the san juan basin accounted for more than 80 of the united states coalbed gas production this basin contains a gi ant coalbed gas play the fruitland fairway which has produced more than 7 tcf 0 2 tm3 of gas the fruitland coalbed gas system and its key elements contrast with the fort union coalbed gas play in the powder river basin the fort union coalbed play is one of the fastest developing gas plays in the united states its production escalated from 14 bcf 0 4 gm3 in 1997 to 147 3 bcf 4 1 gm3 in 2000 when it accounted for 10 7 of the united states coalbed gas production by 2001 annual production was 244 7 bcf 6 9 gm3 differences between the fruitland and fort union petroleum systems make them ideal for elucidating the key elements of contrasting coalbed gas petroleum systems

a second order bulk boundary layer model abstract bulk mass flux models represent the large eddies that are primarily responsible for the turbulent fluxes in the planetary boundary layer as convective circulations with an associated convective mass flux in order for such models to be useful it is necessary to determine the fractional area covered by rising motion in the convective circulations this fraction can be used as an estimate of the cloud amount under certain conditions matching conditions have been developed that relate the convective mass flux to the ventilation and entrainment mass fluxes these are based on conservation equations for the scalar means and variances in the entrainment and ventilation layers methods are presented to determine both the fractional area covered by rising motion and the convective mass flux the requirement of variance balance is used to relax the well mixed assumption the vertical structures of the mean state and the turbulent fluxes are determined analytically several aspects of this simple m

stratigraphy and structure of coalbed methane reservoirs in the united states an overview stratigraphy and geologic structure determine the shape continuity and permeability of coal and are therefore critical considerations for designing exploration and production strategies for coalbed methane coal in the united states is dominantly of pennsylvanian cretaceous and tertiary age and to date more than 90 of the coalbed methane produced is from pennsylvanian and cretaceous strata of the black warrior and san juan basins investigations of these basins establish that sequence stratigraphy is a promising approach for regional characterization of coalbed methane reservoirs local stratigraphic variation within these strata is the product of sedimentologic and tectonic processes and is a consideration for selecting completion zones coalbed methane production in the united states is mainly from foreland and intermontane basins containing diverse compressional and extensional structures balanced structural models can be used to construct and validate cross sections as well as to quantify layer parallel strain and predict the distribution of fractures folds and faults influence gas and water production in diverse ways however interwell heterogeneity related to fractures and shear structures makes the performance of individual wells difficult to predict

geologic factors controlling co2 storage capacity and permanence case studies based on experience with heterogeneity in oil and gas reservoirs applied to co2 storage a variety of structural and stratigraphic factors control geological heterogeneity inferred to influence both sequestration capacity and effectiveness as well as seal capacity structural heterogeneity factors include faults folds and fracture intensity stratigraphic heterogeneity is primarily controlled by the geometry of depositional facies and sandbody continuity which controls permeability structure the permeability structure in turn has implications for co2 injectivity and near term migration pathways whereas the long term sequestration capacity can be inferred from the production history examples of gulf coast oil and gas reservoirs with differing styles of stratigraphic heterogeneity demonstrate the impact of facies variability on fluid flow and co2 sequestration potential beach and barrier island deposits in west ranch field in southeast texas are homogeneous and continuous in contrast seeligson and stratton fields in south texas examples of major heterogeneity in fluvial systems are composed of discontinuous channel fill sandstones confined to narrow sinuous belts these heterogeneous deposits contain limited compartments for potential co2 storage although co2 sequestration effectiveness may be enhanced by the high number of intraformational shale beds these field examples demonstrate that areas for co2 storage can be optimized by assessing sites for enhanced oil and gas recovery in mature hydrocarbon provinces

extratropical low frequency variability as a low dimensional problem ii stationarity and stability of large scale equilibria stationarity and stability properties of large scale persistent anomalies in the northern hemisphere are addressed the low order model developed in part i is used for this purpose it was obtained as the projection of a three level quasi geostrophic system on the ten leading empirical orthogonal functions three global quasi stationary states are identified which represent the arctic high and the positive and negative phases of the main teleconnections pacific north american and north atlantic oscillation the quasi stationary solutions have only a partial correspondence to the weather regimes found in part i stability analysis shows a growing mode that describes an oscillation between the two phases of the teleconnections the negative teleconnection state is also shown to be much more stable than the other two possible decay mechanisms are also discussed copyright 2002 royal meteorological society

large scale facies sequences in alluvial overbank environments abstract gradational coarsening upwards or fining upwards sequences order of meters thick in overbank environments can be produced by progressive crevasse splay levee progradation or abandonment while the channel belt remains unchanged in position in contrast meter scale facies sequences related to periodic channel bell avulsion may show relatively abrupt changes in facies and paleocurrent direction simulation models suggest that the number of such avulsion related facies changes in any overbank sequence bounded above and below by channel belt deposits is on the order of 1 to 10 this is confirmed using an ancient example in this example the average thickness of each avulsion bounded overbank facies sequence was 3 m assuming an average recurrence interval for avulsions of about 1 000 ye rs the mean overbank deposition rate was about 3 mm per year

explicit filtering and reconstruction to reduce grid dependence in convective boundary layer simulations using wrf les abstractas model grid resolutions move from the mesoscale to the microscale turbulent structures represented in atmospheric boundary layer simulations change dramatically at intermediate resoluti

multiple scale simulations of stratocumulus clouds 1 this study introduces a flexible multiple nested modeling framework developed from the weather research and forecasting wrf model for boundary layer cloud research it features a nested large eddy simulation in a hindcasting mode that allows a direct comparison between simulations and observations using this approach we simulated two stratocumulus cases observed at the southern great plains observing site the simulation observation comparisons demonstrate that the multiple nested wrf well reproduces the cloud properties and vertical velocity fields detected by cloud radar and other remote sensing instruments the simulations show that 1 the cloud fields can be strongly modulated by mesoscale organizations 2 the vertical velocity variance and skewness in the boundary layer have well defined diurnal variations and are strongly dependent on external forcings but the in cloud turbulent statistics appears to be more controlled by the internal turbulent processes 3 the organized structures of stratocumulus are only slightly skewed which is consistent with the cloud radar observations that the updraft fraction is close to 50 and 4 the vertical distribution of cloud water and the associated high order moments of continental stratocumulus can be substantially different from its marine counterpart due to different ambient thermodynamic structures this study suggests that the multiple scale wrf modeling system provides a great numerical framework that can be used to address various issues regarding the parameterization of boundary layer clouds

on the relationship among cloud turbulence droplet formation and drizzle as viewed by doppler radar microwave radiometer and lidar cloud radar microwave radiometer and lidar remote sensing data acquired during the atlantic stratocumulus transition experiment astex are analyzed to address the relationship between 1 drop number concentration and cloud turbulence as represented by vertical velocity and vertical velocity variance and 2 drizzle formation and cloud turbulence six cases each of about 12 hours duration are examined three of these cases are characteristic of nondrizzling boundary layers and three of drizzling boundary layers in all cases microphysical retrievals are only performed when drizzle is negligible radar reflectivity 0 5 between radar reflectivity and in cloud vertical velocity variance although one of the boundary layers that experienced drizzle exhibited a negative correlation between these parameters however in the subcloud region all boundary layers that experienced drizzle exhibit a negative correlation between radar reflectivity and vertical velocity variance

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

mechanism and effect of chemical weathering of sedimentary rocks the mineralogy geochemistry and physical and mechanical properties of rocks from four weathering profiles of miocene to pleistocene mudstones and sandstones in japan showed that chemical weathering of sedimentary rocks is characterized by sequential reaction between percolating groundwater and rock forming minerals pyrite a common mineral contained in sedimentary rocks is especially important in these sequential reactions pyrite is oxidized by oxygen coming from the ground surface and sulfuric acid is generated at the base of the oxidized zone the sulfuric acid in turn dissolves rock forming materials to make a dissolved zone if the fluxes of oxygen and water are in the same direction sulfuric acid generated at the oxidation front migrates farther and forms a dissolved zone if these fluxes are in opposite directions the oxidized and dissolved zones are not differentiated rocks in the dissolved zone are caused to deteriorate by the acid leaching and are acidic if buffering minerals such as calcite and zeolite are absent in the oxidized zone sandstone is strengthened because of cementation by iron oxide or hydroxide while mudstone is weakened because it has greater clay fractions and larger specific surface areas than sandstone

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

plinian activity during the early eruptive history of the sabatini volcanic district central italy abstract the early activity of the sabatini volcanic district svd central italy was characterised by highly explosive eruptions that produced widespread subplinian and plinian fall deposits in this study four major eruptive units informally named as units a b c and d were recognised in the 514 449 ka age interval in particular unit d was emplaced during the early phase of the 449 ka tufo rosso a scorie nere pyroclastic flow forming eruption the most important event in the whole svd activity history estimates of relevant eruptive parameters indicate tephra fall volumes up to 4 km3 for individual units peak eruption column heights in the range of 14 29 km and corresponding mass eruption rates of 7 8 106 1 3 108 kg s isopach and isopleth maps of fallout deposits as well as the distribution of the proximal lag breccia of the tufo rosso a scorie nere consistently indicate a common vent area which does not correspond to any volcanic centre identified up to now in the svd this was located along ne sw trending tectonic lineaments that also controlled the location of the other major volcanic centres of the svd the characterisation by means of field aspects grain size componentry and density and chemical composition of juvenile clasts renders the studied fall deposits as valuable stratigraphic markers for the svd and well beyond it in fact their wide areal dispersals toward the e and se may allow correlations on a regional scale for the quaternary successions of intermountain basins of the central apennine and the adriatic sea basin successions finally the correct identification of distal tephra from plinian and co ignimbrite plumes and their attribution to specific explosive eruptions of the svd and the other volcanic districts of the roman province rather than to local intra apennine centres provides crucial implications for geodynamic reconstructions

prediction of channel connectivity and fluvial style in the flood basin successions of the upper permian rangal coal measures queensland predicting the presence and connectivity of reservoir quality facies in otherwise mud prone fluvial overbank successions is important because such sand bodies can potentially provide connectivity between larger neighboring sand bodies this article addresses minor channelized fluvial elements crevasse splay and distributary channels and attempts to predict the connectivity between such sand bodies in two interseam packages of the upper permian rangal coal measures of northeastern australia channel body percent as measured in well logs was 2 in the upper aries castor interseam and 17 in the lower castor pollux interseam well spacing were too great to allow accurate correlation of channel bodies the ob river siberia was used as a modern analog to supply planform geometric measurements of splay and distributary channels so that stochastic modeling of channel bodies was possible the resulting models demonstrated that 1 channel body connectivity is more uniform between minor distributary channels than between crevasse splay channels 2 relatively good connectivity is seen in proximal positions in splays but decreases distally from the source as channel elements diverge and 3 connectivity tends to be greater down the axis of splays with more isolated channel bodies occurring at the margins

architecture of vertically stacked fluvial deposits atane formation cretaceous nuussuaq central west greenland excellent exposures of thick multistorey fluvial deposits from the deltaic atane formation on south east nuussuaq central west greenland show the architecture of up to 100 m thick continuously aggrading fluvial depositional complexes the succession comprises vertically stacked channel belt sandstones separated by thin floodplain deposits with little to no incision between storeys architectural elements and palaeocurrent patterns of channel deposits indicate deposition in large relatively stable low sinuosity rivers probably located within an incised valley gradual transitions from channel to floodplain deposits accompanied by a gradual change from floodplain to spillover sand suggest avulsion on the floodplain as a possible mechanism for the vertically alternating channel and floodplain deposits despite its relative proximity to contemporaneous sea level ca 35 km upstream from the palaeo shoreline the depositional complex is entirely non marine the aggrading nature of the deposits suggests a continuously rising base level coupled with a high and steady sediment supply vertical alternations between floodplain and channel deposits may be forced by subtle interruptions in this balance or autocyclic mechanisms on the floodplain this study provides an example of aggrading lowstand non marine transgressive systems tract deposits

reddish metagranites from the gennargentu igneous complex sardinia italy insight into metasomatism induced by magma mingling the recrystallization of quartz and plagioclase to higher calcium concentrations the progressive increase in the mgo mgo feo of chlorite closer to the contact indicates that this phase also recrystallized the iron released during chlorite recrystallization was buffered by hematite formation in the pores of metasomatic k feldspar the gennargentu metagranites provide evidence that metasomatic fluids can play a major role in driving metamorphic reactions in contact aureoles for instance the expected increase of ca in plagioclase owing to thermal equilibration was not achieved in the high t zone of the aureole because of fluid assisted removal of cations we conclude that caution should be taken when interpreting the processes that underpin contact metamorphism in terms of thermally driven ionic diffusion alone because the role of fluids may be significant if not overwhelming in the domains closest to the magmatic source

implications of weathering on the engineering properties of the fuller s earth formation the fuller s earth formation is an overcon solidated jointed randomly assured calcareous mudstone with some thin to medium jointed argillaceous limestone bands south of bath the formation contains the commercial montmorillonite rich fuller s earth bed this paper reviews the effect of the proportion of calcite present on the moisture content atterberg limits particle size and residual shear strength attention is drawn to the importance of appreciating that the calcite percentage and the clay mineralogy are both likely to change with time as a result of weathering processes this will affect the stability of natural slopes and man made cuttings excavations etc la formation de terre a foulon est un limon compact calcaire surconsolide jointe et fissure au hasard qui contient des bandes de chaux argillacee jointees d epaisseur faible ou moderee au sud de bath la formation comprend la couche de terre a foulon commerciale qui est riche en montmorillonite l article examine l influence de la prop

formation and development of nocturnal boundary layer clouds over the southern great plains abstract the formation and evolution of nocturnal boundary layer clouds over land are studied using a simple well mixed boundary layer theory by analyzing the deepening rate of the mixed layer depth based on the turbulent kinetic energy budget of the whole boundary layer the authors studied how the formation of idealized nocturnal boundary layer clouds is related to the physical processes associated with the land surface and the boundary layer preliminary analysis indicates that for a range of surface moisture and heat fluxes wind shear can be an important factor in triggering the formation of nocturnal stratus the relative importance of different physical processes responsible for cloud formation can be evaluated by the ratio between the lifting condensation level and a critical level which is proportional to the monin obukhov length scale in this study data collected from the atmospheric radiation measurement site in the southern great plains are used to examine the results of the theoretical an

static and dynamic characterization of alluvial deposits in the tiber river valley new data for assessing potential ground motion in the city of rome 1 the paper presents the results of a case study conducted on the holocene alluvial deposits of the tiber river valley in the city of rome the main test site selected for the study valco s paolo is located about 2 km south of rome s historical centre the alluvial deposits were dynamically characterized in a comprehensive way via site investigations and geotechnical laboratory tests normalized shear modulus decay and damping curves g g0 and d d0 vs were obtained for the dominantly fine grained levels the curves demonstrate that these levels have a more marked shear stiffness decay if compared with the underlying pliocene bedrock decay curves from laboratory tests for the tiber alluvia correlated well with the trend of the function proposed by hardin and drnevich making it possible to derive their specific interpolation function coefficients use was made of the extrapolation of the findings from the valco s paolo test site to a large part of rome s historical centre by means of two other test sites supported by an engineering geology model of the complex spatial distribution of the tiber alluvia the experimental valco s paolo vs profile was extrapolated to the other test sites on the basis of a stratigraphic criterion the analysis of seismic noise measurements obtained for the three test sites validated the engineering geology based extrapolation and showed that the main rigidity contrast occurs inside the alluvial body at the contact with the underlying basal gravel level g and not between the alluvia and the plio pleistocene bedrock composed of highly consistent clay marne vaticane the 1d modeling of local seismic response to the maximum expected earthquakes in the city of rome confirms that the deposits have one principal mode of vibration at about 1 hz however the simulation also evidenced that the silty clay deposits level c making up the most part of the tiber alluvial body play a key role in characterizing the soil column deformation profile since it can be affected by non linear effects induced by the maximum expected earthquake when some stratigraphic conditions are satisfied

looking into a volcanic area an overview on the 350 m scientific drilling at colli albani rome italy abstract a 350 m deep borehole was drilled in the colli albani volcanic district central italy in order to understand the shallow crust structure beneath the volcanic complex characterize the rock physical properties especially through in situ measurements and afterward laboratory experiments assess the local present day stress field install a broad band seismometer at depth the borehole is located adjacent to the western rim of the tuscolano artemisio caldera where several phenomena of unrest recently occurred in 1989 90 a seismic swarm affected this area and a related uplift was recognized in addition high gas concentrations mainly co 2 and h 2 s in aquifers and soils caused illnesses and casualties among inhabitants and animals in the past we describe the investigations carried out at the drill site and the results achieved from data analysis wire line drilling produced a complete stratigraphic record of the quaternary volcanic units down to the plio pleistocene sedimentary sequence and geophysical logs allowed a characterization of the rock physical properties from a tectonic point of view data provided by dipmeter and borehole televiewer were used for investigations on the recent and present day stress field and the results are compared to those available in the literature in the volcanic units we recognized two main fracture systems sw and nw dipping several faults intersecting the borehole show planes with oblique striae indicating a prevalent strike slip component of the movement finally borehole breakout analysis defined an active stress field with a e w oriented minimum horizontal component at the end of the drilling a blow out occurred due to pressurized fluids trapped into the sandy unit drilled in the last few meters of the hole sampling these fluids gave an additional value to the borehole providing information about the deep volcanic circulation and its possible connection to a deep seated magma chamber the main results show water with a na hco 3 chemistry and the highest salinity ever recognised in the area electrical conductivity 10 12 ms cm stable o and h isotopes reveal a meteoric origin of water and the absence of tritium points out a long residence time in the aquifer emitted gas is co 2 dominated with n 2 as second most important component helium isotopic composition of the gas allows us to estimate a magmatic component ranging in the interval 40 50 one of the highest in the colli albani carbon isotopes of co 2 0 53 vs pdb suggest that it could derive partly from a magmatic source and partly by the thermal decarbonation of the carbonatic basement

the spatial variability of overbank sedimentation on river floodplains abstract river floodplains are important landforms and information on rates and patterns of overbank sediment deposition is essential for understanding their development such information is also needed for validating existing overbank floodplain flow and sediment transport and deposition models the use of bomb derived 137cs for documenting rates of overbank sediment deposition on river floodplains offers the potential for assembling data for a large number of points on a floodplain and therefore for investigating the spatial patterns involved this approach also overcomes some of the operational and sampling problems encountered in traditional monitoring techniques the study reported uses 137cs measurements on sediment cores to investigate the spatial variability of sediment deposition on selected floodplain reaches of five british lowland rivers attention is given both to the overall reach and to more detailed investigations of small areas the observed spatial patterns of sediment deposition are interpreted in terms of the major controls involved which include the floodplain microtopography and morphology the relationship between the grain size composition of deposited sediment and sedimentation rate is also considered

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

vertical velocity structure of nonprecipitating continental boundary layer stratocumulus clouds 1 continental boundary layer bl stratocumulus clouds affect the local weather by modulating the surface energy and moisture budgets and are also intimately tied to the diurnal cycle of the turbulence in the bl vertical velocity structure of these clouds is studied using data from the atmospheric radiation measurement program s southern great plains observing facility located near lamont oklahoma data from vertically pointing cloud radar from eleven cases of nonprecipitating bl stratocumulus clouds are used to obtain half hourly values of in cloud vertical velocity variance skewness updraft fraction downdraft fraction and mass flux the variance showed a general decrease with height while the skewness was weakly positive in the cloud layer and negative near cloud top on half hourly time scales vertically coherent structures spanning through the entire cloud layer were responsible for 40 of the observed vertical velocity variance while horizontally temporally coherent structures lasting at least 20 s were responsible for 77 of the vertical velocity variance the half hour periods were then classified on the basis of the surface buoyancy flux b as small b periods b 60wm 2 small b periods exhibited lower variance near cloud base compared to large b periods with the differences being reversed near cloud top the skewness was positive in the cloud layer during large b periods and negative during small b periods while the skewness was negative near cloud top in both scenarios the small b periods had about ten times more updrafts greater than 1 m s 1 near cloud top compared to large b periods

geological discontinuities main flow path and chemical alteration in a marly hill prone to slope instability assessment from petrophysical measurements and borehole image analysis clay shale landscapes are sensitive to landslide erosion and re sedimentation processes in this context tectonized clay shales have peculiar hydrological and mechanical behaviours in order to improve our understanding of the processes involved in such systems an experimental site has been settled in the draix observatory ore draix on a black marl hill slope of the southern alps france in the framework of the ecou pref project the site is a natural laboratory to study the evolution of clay shale landscapes at several scales regional to m in this study we aim to characterize the internal structure and fissure patterns of a stable interfluve in order to locate preferential water flows within the system and anticipate its evolution this work is based on a series of mutli disciplinary approaches including petrophysical analyses well pulse injection tests and downhole geophysical measurements borehole geophysical results were combined with laboratory measurements on core plugs permeability density porosity and acoustic velocity optical and acoustical images have been used as an original tool for internal discontinuities characterisation and potential active flow path detection they allowed the identification of three main lithological units interpreted as several stages of shale alteration in addition several main structural plane discontinuities open fractures schistosity planes and fractures infilled with calcite or clays were identified from the images and their potential transmissivity discussed with regard to piezometric and tracer measurements in all the integration of measurements leads to propose a simple scenario of fluid circulation and chemical alteration of the interfluve copyright 2011 john wiley sons ltd

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

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

a quantitative determination of the effect of moisture on purple mudstone decay in southwestern china aims the moisture condition is well known to be a key factor that apparently influences rock decay but little is known about the quantitative correlations between a rock s decay rate and its moisture content which makes it difficult to quantitatively predict the rate of rock decay under varied moisture conditions thus in this paper our aim is to observe the decay rates of various purple mudstones with different moisture contents and to develop an equation to calculate the decay rate

weathering of valle ricca stiff and jointed clay abstract the study proposes a weathering model of pliocene pleistocene stiff and jointed blue grey clay transforming into yellow clay physical mineralogical chemical and textural changes as well as the weathering profile were investigated in a quarry of central italy based on geological records and inferences these changes are likely to have occurred within a time span of about 50 000 years bp upon overburden stress unloading and in a stress regime that is locally controlled by suction weathering propagated into the clay at a rate of about 0 3 mm year and was enhanced by the enlargement of the pre existing tectonic discontinuities and by the formation of new joints a mass loss of about 22 25 wt was calculated considering fe and p as immobile elements the individual oxides contribute to mass loss in the following order sio2 cao co2 al2o3 mgo k2o s na2o tio2 mno the fe2o3 fe2o3 feo ratio varies from 9 29 in the blue grey clay to 75 82 in the yellow one oxidation and or dissolution of 7 a fe2 bearing clay minerals mica like minerals and calcite and parallel increase of smectite and fe hydroxides play a critical role in the chemical changes and explain the higher plasticity of the yellow clay with respect to the blue grey one the role of water during the weathering process was inferred to occur in cyclical steps 1 seepage of meteoric water 2 dissemination of highly oxidizing meteoric water 3 triggering of oxidation and dissolution of minerals 4 water evaporation 5 partial migration of the elements contained in the aqueous solution and consequent deposition of minerals in the joints

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

palaeomagnetism and rock magnetism in the upper pliocene valle ricca rome italy section summary a revision of the magnetostratigraphy in the valle ricca monterotondo rome pliopleistocene section was carried out this section consisting mainly of blue grey marly clays was previously investigated for palaeomagnetic effects by arias et al 1980 1990 who detected a normal polarity interval close to a volcanic ash layer which was correlated to the reunion subchron this interpretation conflicts however with new biostratigraphic data and palaeomagnetic observations in order to investigate the possible origin of these discrepancies we performed a detailed sampling for palaeomagnetic and rock magnetic analyses in the controversial interval around the volcanic ash layer the present results show strong variations in the rock magnetic parameters and suggest significant changes in the magnetic mineralogy two levels with a high intensity low temperature normal component of magnetization were distinguished at these two levels the rock magnetic parameters are typical of greigite and a widespread occurrence of framboids of micron sized iron sulphide grains was found by mineralogical analyses a high temperature reversed component of magnetization carried by magnetite was isolated for the whole interval investigated we demonstrate that the previously recognized normal polarity interval is the effect of changes in the magnetic mineralogy and it does not represent a true reversal of the earth s magnetic field the origin of the low temperature normal component of magnetization is discussed in light of the present knowledge about greigite formation and remanence acquisition

precession scale cyclicity in the fluvial lower eocene willwood formation of the bighorn basin wyoming usa little is known about controls on river avulsion at geological time scales longer than 104 years primarily because it is difficult to link observed changes in alluvial architecture to well defined allogenic mechanisms and to disentangle allogenic from autogenic processes recognition of milankovitch sale orbital forcing in alluvial stratigraphy would provide unprecedented age control in terrestrial deposits and also exploit models of allogenic forcing enabling more rigorous testing of allocyclic and autocyclic controls the willwood formation of the bighorn basin is a lower eocene fluvial unit distinctive for its thick sequence of laterally extensive lithological cycles on a scale of 4 to 10 m intervals of red palaeosols that formed on overbank mudstones are related to periods of relative channel stability when gradients between channel belts and floodplains were low the intervening drab heterolithic intervals with weak palaeosol development are attributed to episodes of channel avulsion that occurred when channels became super elevated above the floodplain in the deer creek amphitheater section in the mccullough peaks area these overbank and avulsion deposits alternate with a dominant cycle thickness of ca 7 1 m using integrated stratigraphic age constraints this cyclicity has an estimated period of ca 21 6 kyr which is in the range of the period of precession climate cycles in the early eocene previous analyses of three older and younger sections in the bighorn basin showed a similar 7 to 8 m spacing of red palaeosol clusters with an estimated duration close to the precession period intervals of floodplain stability alternating with episodes of large scale reorganization of the fluvial system could be entirely autogenic however the remarkable regularity and the match in time scales documented here indicate that these alternations were probably paced by allogenic astronomically forced climate change

simulation and parameterization of the turbulent transport in the hurricane boundary layer by large eddies 1 hurricane boundary layer hbl processes especially the structure of the coherent large eddy circulations lecs and their induced vertical transport are not well understood this paper introduces a large eddy simulation les framework in a weather hindcasting mode developed from a multiple scale nested weather research and forecasting wrf model using the wrf les this study investigated the structure of the hbl lecs and the associated vertical transport during the landfall of hurricane ivan 2004 the simulation shows that the hbl lecs exist in a mean stable environment and consist of well defined updraft and downdraft statistically the hbl lecs are only slightly skewed with the updrafts and downdrafts relatively evenly distributed spatially the inversion base basically envelopes the upper boundary of lecs the trough in between two adjacent lecs is where most entrainment takes place whereas the crest of the lecs is where boundary layer air detrains out of the hbl in such a way lecs directly connect the surface the hbl and the main body of a hurricane vortex and enhance the exchange of energy moisture and momentum between them it is found that the current boundary layer schemes significantly underestimate the resolved turbulent fluxes due to the fact that the effects of lecs have not been included in the parameterizations on the basis of the statistical structure of lecs simulated by the wrf les this paper proposes a conceptual updraft downdraft model that can potentially be implemented in weather forecasting models to parameterize the fluxes induced by the hbl lec transport

chemical weathering mechanisms and their effects on engineering properties of soft sandstone and conglomerate cemented by zeolite in a mountainous area abstract sandstone and conglomerate cemented by zeolite crystals in a humid mountainous area in japan are weathered and also weakened or strengthened by chemical interaction with percolating water that was originally in equilibrium with the atmosphere near the ground surface carbonic acid generated by the dissolution of carbon dioxide from the atmosphere and biological activity in the soil dissolves zeolite and thereby weakens the rocks at the oxidation front the base of the oxidized zone oxygen from the atmosphere reacts with pyrite in the rock to form sulfuric acid and iron oxide and or hydroxide the iron oxide and or hydroxide precipitates on zeolite surfaces and strengthens the rocks by cementing the grains to each other beneath the oxidation front and extending to the dissolution front sulfuric acid migrates downward dissolves zeolite and thus weakens the rocks this weathering mechanism and the resulting changes in mechanical properties of rocks generally are to be expected in marine sandstone and conglomerate with small amounts of clay in the matrix because the most common cementing mineral is carbonate which is also easily dissolved by acid and further because pyrite is a common rock forming mineral in marine sedimentary rocks the effects of chemical weathering on the mechanical properties of sandstone and conglomerate are different from those of mudstone because the latter contains much larger amounts of clay minerals the cementation of constituent grains by iron oxide and or hydroxide is inhibited by clay minerals because clay minerals have high specific surface areas and also because large amounts of iron can be incorporated in the minerals

large eddy simulation of the diurnal cycle of shallow cumulus convection over land summary large eddy simulations of the development of shallow cumulus convection over land are presented many characteristics of the cumulus layer previously found in simulations of quasi steady convection over the sea are found to be reproduced in this more strongly forced unsteady case furthermore the results are shown to be encouragingly robust with similar results obtained with eight independent models and also across a range of numerical resolutions the datasets produced are already being used in the development and evaluation of parametrizations used in numerical weather prediction and climate models

a laboratory study of post rupture strength stiff intact clays exhibit rapid loss of strength after failure with the formation of slip surfaces and the development of a well defined post rupture strength envelope this paper describes an experimental study of the influence of a number of factors on the post rupture strength of initially intact samples of vallericca clay these include changes in confining pressure after the formation of a slip surface the magnitude of the relative displacement across the surface comparison between the post rupture strength envelopes in triaxial compression and extension and the influence of existing slip surfaces on the formation and strength of subsequent rupture planes formed by rotation of the principal stresses the results show that the post rupture strength envelope is well defined repeatable and not very sensitive to stress history or the rotation of the principal stresses little reduction in shearing resistance takes place for relative displacements up to about 10 mm the results are believed to be

integration of channel and floodplain suites ii vertical relations of alluvial paleosols abstract extrachannel sediments of the lower eocene willwood formation which were subdivided into different pedofacies or developmental stages exhibit two well developed orders of pedofacies sequences over which a grosser scale cyclicity is superposed simple sequences with thicknesses measured in meters are comprised of one or more soil profiles that are bounded above and below by pedogenically unmodified crevasse splay deposits on a larger scale compound pedofacies sequences are tens of meters thick and consist of several simple sequences sandwiched between channel sandstones between these sandbodies pedogenic maturity of the multistorey paleosols progressively increases and then decreases upwards in response to episodic avulsion formation of both compound and simple pedofacies seq ences was largely controlled by local patterns of deposition and erosion that produced vertical variability in both rate of sediment accumulation and parent material because paleosol maturity also reflects the effects of extrabasinal factors a pedofacies megasequence which is hundreds of meters thick developed in response to changes in tectonic activity through willwood time comparison between willwood deposits in the northern and central parts of the bighorn basin also reveals that areally differing sediment accumulation rates and thereby basin subsidence rates can be interpreted from large scale pedofacies sequences consequently paleosols are useful in determining changes in relative rates of sediment accumulation that are controlled by both intrabasinal and extrabasinal factors

the sequence stratigraphy of fluvial depositional systems the role of floodplain sediment storage abstract the currently used model for alluvial sequence stratigraphy has been criticised miall 1991 and an alternative model is offered here in this model alluviation mainly takes place during transgressive and not highstand phases when accommodation space allows sediment storage the high capacity for some river systems to store floodplain sediments is a critical consideration the effects of climatic and intrinsic geomorphic changes during fluvial deposition are likely to greatly complicate simple base level controlled sequence models and recognising higher order fourth and fifth order cycles will be particularly difficult

a hierarchical approach for evaluating fluvial systems architectural analysis and sequential evolution of the high net sand content middle wasatch formation uinta basin utah well exposed three dimensional fluvial outcrops of the high net sand content middle wasatch formation in three canyon uinta basin utah were used to create and develop a new methodology for describing the architecture of fluvial systems the methodology builds on the works of campbell jackson allen and miall and addresses sedimentary processes scale and temporal context for reservoir and non reservoir bodies the methodology developed herein is a three level hierarchical framework that classifies meso and macroscale architecture of fluvial systems the three level hierarchy contains from smallest to largest stories elements and archetypes eight story types provide the foundational building blocks of this framework and account for sedimentation in both channel belt and floodplain belt elements including 1 downstream accreting 2 laterally accreting 3 erosionally based fine grained fill 4 fine grained fill associated with laterally accreting 5 levee 6 splay 7 crevasse or overbank channels and 8 floodplain fines two types of elements are recognized 1 channel belt and 2 floodplain belt an archetype consists of a channel belt element and its genetically related floodplain belt elements two distinct upward stacking patterns differentiate braided and meandering archetypes in deconstructing the evolution of archetypes three distinct associations between channel belt elements and their adjacent splays are documented 1 unassociated splays 2 associated coeval splays and 3 associated non coeval splays width and thickness for stories channel belt elements and archetypes are documented providing dimensional constraints for analog high net sand content fluvial systems additionally this methodology provides object based models with shape defined reservoir and nonreservoir geobodies that realistically compare to fluvial systems

the turbulence structure in a continental stratocumulus cloud from millimeter wavelength radar observations abstract the turbulent scale vertical velocity structure in a continental stratocumulus cloud is studied using a 3 mm wavelength doppler radar operating in a vertically pointing mode the radar observations provided 30 m sampling in the vertical with 2 s averages of 10 000 samples vertical velocity measurements were made continuously for an 8 h period and were further supported by measurements of cloud base height from a laser ceilometer and liquid water path from a microwave radiometer during the beginning of the observational period the cloud layer extended between 200 and 800 m the vertical velocity variance profiles evolved systematically over the period from a well defined peak in the upper part of the cloud layer of 0 7 m2 s 2 to a peak in the lower part of the cloud layer of 0 2 m2 s 2 as the layer became decoupled later in the observing period the vertical velocity skewness during the well coupled conditions was negative through most of the cloud consistent with the presence of relatively n

sedimentary products of avulsions in the holocene rhine meuse delta the netherlands abstract the main objective of this study was to describe the characteristics of deposits related to avulsion to determine if avulsion locations can be recognized by characteristic sediment architecture in the rhine meuse delta the majority of avulsion sites is accompanied by crevasse splay deposits with a relatively large areal extent these crevasse splay complexes occur near the base of the overbank deposits of the newly formed channel belt and are similar to avulsion belt deposits described by smith et al sedimentology 36 1989 1 can j earth sci 35 1998 453 the lithology of all investigated crevasse splay deposits ranges from coarse sand to silty clay sand is concentrated in crevasse splay channels and silty and sandy clay occurs as distal deposits and as levee deposits between the channels the total volume of sand is small relative to clay and silt of a total of 91 avulsion sites three sites were studied in detail one each representing the sedimentary architecture of a full nodal avulsion a failed avulsion and a crevasse splay complex that did not lead to avulsion it is concluded that dating evidence of the abandoned and newly formed paleo channel is always required to verify if avulsion really occurred although the presence of large scale sandy crevasse splay deposits in combination with two main meandering channels often indicates avulsion based on a 2 d outcrop or just one cross section it is impossible to determine whether a splay complex was associated with an avulsion or not because the architecture and lithology in both cases can be identical not all avulsion locations are characterized by crevasse splay deposits there are two possible explanations for this 1 splay deposits were eroded by the newly formed channel or 2 splay deposits were never formed this may be a result of reoccupation of an old channel in this case avulsive flow is immediately appropriated by the pre existing channel and no large scale splay formation occurs alternatively splay deposits were not formed because avulsion resulted from headward erosion

surface based observations of mesoscale cumulus stratocumulus interaction during astex abstract data obtained from the island of santa maria in the azores during the atlantic stratocumulus transition experiment astex are used to describe cloud and boundary layer structure for a 24 h period on 15 june 1992 over the east central atlantic 37 n 25 10 w the evolution of the mesoscale cloud structure during a 24 h period in the vertical column above the surface site was characterized using a 94 ghz radar a laser ceilometer 3 h radiosonde ascents and surface micrometeorological instrumentation mesoscale circulations and drizzle were found to be key elements of the boundary layer clouds observed in this region during the late night and predawn hours of the study period a single layer of stratocumulus that averaged 200 m in thickness topped a well mixed marine boundary layer mesoscale cellular convection mcc which had ascending regions with horizontal dimensions of 7 km was observed during this period at sunrise decoupling was imposed on this mcc and extreme mesoscale variatio

geochemical discrimination of clastic sedimentary rock sources abstract factors controlling the geochemistry of a clastic sedimentary rock can include 1 composition of source terrain 2 chemical weathering 3 hydraulic sorting 4 diagenesis 5 metamorphism and 6 hydrothermal alteration a linear solution inferring source terrain composition from geochemistry of the sediment is impossible in this multivariate system as several unknowns will commonly be present the use of graphical analysis of element pairs circumvents the problem chemically immobile elements will maintain invariant ratios during rock mass change caused by either addition or depletion of mobile elements this results in chemically immobile element scattergrams exhibiting linear trends along radians extending from the origin if the major mineral phases of the immobile elements have behaved in a hydrodynamically similar manner as chemically mobile element plots will produce a scatter of points this relationship can be used to test chemical immobility and similarity in hydrodynamic sorting history the constraint on analysis is that the source area must be compositionally uniform or the sediment well mixed prior to delivery to the basin a second technique using sio2 plots has also been developed to investigate element mobility and hydrodynamic behaviour of the mineral phases containing the elements sio2 immobile element plots result in a linear arrangement of points extending towards either 0 or 100 sio2 the 0 intercept position occurs for elements with major mineral phases concentrated in sand the 100 intercept for those concentrated in clays plotting chemically mobile elements produces different patterns and this can be used to gain information on alteration and sorting history elemental ratios for chemically immobile elements with similar hydrodynamic behaviour will be the same as those for the weighted average composition of the source material this provides a powerful tool for deducing source terrain from sediment geochemistry techniques outlined above were tested on archaean metasandstones from superior province canada immobile element ratio diagrams for nb al ti and zr al ti indicate that a calc alkaline extrusive intrusive suite lying to the north of the study area was the source and not five other volcanic suites in the region this conclusion agrees with previous clast lithology studies and accentuates the applicability of the geochemical techniques

holocene avulsion styles and sedimentation patterns of the saskatchewan river cumberland marshes canada abstract this paper describes the styles and sedimentation patterns of holocene avulsions of the saskatchewan river at the cumberland marshes predating the most recent 1870 s avulsion holocene avulsions involved two major styles 1 progradation of lacustrine deltas and splay complexes and 2 local reoccupation or appropriation of preavulsive channels most avulsions were progradational and occurred in floodplain lakes occupying floodbasin areas between elevated alluvial ridges the two most recent avulsions old channel and 1870 s diverted mainly into inundated peatland progradational avulsions were accompanied by deposition of avulsion belt sediments associated with multiple channel networks the characteristics of avulsion belt deposits include 1 sediments dominated by poorly sorted silt and very fine sand 2 lateral continuity in transverse and longitudinal directions with subhorizontal upper and lower boundaries 3 predominantly nonerosional contacts with underlying sediments 4 coarsening upward successions 5 consistent radiocarbon dates for the tops of preavulsive substrates and 6 occurrence beneath levee and overbank deposits of the associated major channel belt indicating that avulsion belt deposition occurs prior to the development of a new master channel the width of ancient avulsion belts reaches 18 km with typical thicknesses of 2 3 m avulsion belt deposition accompanied by many small channels was followed by flow reversion to a few larger channels and eventually to one single channel accompanied by deposition of levee and channel deposits reoccupational avulsions were not accompanied by deposition of widespread avulsion belt sediments and led mainly to the modification of pre existing channel belts the sedimentation patterns of holocene avulsions of the saskatchewan river reveal that avulsion belt sediments represent major components of the floodplain deposits supporting the model developed from observations of the 1870 s avulsion

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

bio and magneto stratigraphy in the tiber valley revised abstract the stratigraphy of three sections of marine deposits in the tiber valley north of rome was investigated in detail biostratigraphic investigation covered the valle ricca tini quarry fosso liano and lugnano sections the valle ricca and lugnano sections show continuity in sedimentation from the latest pliocene to early pleistocene in the fosso liano section upper pliocene sediments are missing as in other outcrops in central italy and the lower pleistocene deposits lie unconformably on the middle pliocene ones possible causes of these features are discussed magnetostratigraphy and rock magnetism analyses were performed only in the valle ricca section the data shows that the previously recognised reversal around a volcanic level is the effect of strong changes in the magnetic mineralogy and it is not representative of true geomagnetic changes

facies model for fluvial systems in the seasonal tropics and subtropics facies models that summarize the deposits of fluvial systems are well established for humid climate settings and for desert environments but the deposits of rivers in the sub humid and semiarid seasonal tropics have been largely ignored our observations and data from modern streams and recent deposits in northeastern australia show how such rivers with extremely variable discharge have distinctive deposit characteristics that are substantially different from conventional fluvial facies models these properties include 1 erosionally based channel fill lithosomes that exhibit complex lateral facies changes with 2 abundant pedogenically modified mud partings 3 complex internal architecture that may lack the macroform elements typical of other fluvial sediment bodies 4 an abundance of sedimentary structures formed under high flow stage and 5 an abundance of in situ trees that colonize channel floors and are adapted to inundation by fast flowing water we illustrate examples of this fluvial style from the rock record and set out a new facies model the recognition of such a distinctive fluvial character and of changes in character through vertical successions will aid paleoclimate and reservoir analysis

tributary distributary and other fluvial patterns what really represents the norm in the continental rock record abstract this paper evaluates the recent claim made by weissmann et al 2010 that deposits of distributive fluvial systems dfs may form the bulk of the continental fluvial record weissmann et al 2010 define dfs as a pattern of channel and floodplain deposits that radiate outward from an apex that is located where the river enters the sedimentary basin as such dfs are fan like systems on which multiple channels coexist and distribute water and sediment across the fan published criteria for the recognition of dfs weissmann et al 2010 are 1 a radial pattern of channels from the dfs apex 2 downslope decreases in channel size 3 down dfs grain size decreases and 4 a lack of lateral channel confinement however in weissmann et al 2010 and subsequent papers only the first of these criteria is applied rigorously thus allowing a variety of types of fluvial system including avulsive incised anabranching and coastal plain distributary systems to potentially be classified uncritically as dfs an ancient succession formed by dfs should preserve mostly small channel bodies with a limited range of dimensions and no outsized channel bodies channel bodies in dfs dominated successions should also decrease in size in a down palaeoslope direction and show palaeocurrent relationships indicative of radial dispersal in order for the term dfs to be applied these characteristics should also be established within stratigraphic bodies that formed coevally however very few examples have yet been published that satisfy these criteria if the claim that dfs dominate the alluvial stratigraphic record is valid then few if any sedimentary bodies formed by large channels should be preserved a review of published research demonstrates however that the alluvial stratigraphic record contains a broad diversity of fluvial network styles including abundant representatives of tributary avulsive anabranching and incised in addition to distributary types it is also clear that the deposits of large main stem rivers that are comparable to the big rivers of the modern world are abundantly preserved in the stratigraphic record an analysis of the planimetric area of modern tributary and distributary fluvial systems is presented demonstrating that tributary systems are also likely to represent a far larger proportion of the ancient sedimentary record than dfs the body of evidence presented herein from modern and ancient alluvial systems thus suggests that the hypothesis of weissmann et al 2010 should be wholly rejected dfs do not dominate the continental stratigraphic record

significance of different modes of rhizolith preservation to interpreting paleoenvironmental and paleohydrologic settings examples from paleogene paleosols bighorn basin wyoming u s a abstract different modes of preservation of root traces rhizoliths provide information on soil moisture regimes in alluvial paleosols in the paleogene fort union and willwood formations of the bighorn basin wyoming u s a this paper links different styles of rhizolith preservation to paleosols whose other pedogenic attributes provide information on ancient soil drainage consequently the paleodrainage significance of different rhizolith preservation patterns is established more confidently rhizoliths consisting of elongate gray mottles rhizohaloes with red rims are common in relatively well drained red paleosols the gray zones are depleted of iron fe whereas the color of the rims indicates hematite accumulation these features are typical of surface water gley processes that caused fe and manganese mn to move from the root channel outward to the soil matrix calcareous rhizocretions either calcareous tubular concretions or micro accumulations of carbonate within gray rhizotubules are also common in moderately well drained red paleosols more poorly drained purple paleosols also have rhizoliths consisting of fe depletion zones however the rhizohaloes are surrounded by yellow brown goethite rims rather than red hematitic rims in many paleosols the red and yellow brown accumulation rims were partly removed by continued depletion producing abundant irregular shaped mottles the nature of the rhizohalo and the color of the fe oxide rim provide information about the intensity of gleying that a paleosol underwent the poorly drained paleosols also show rhizoliths preserved as goethite accumulations contained within gray depletion zones indicating movement of reduced fe from the matrix towards the root channel probably as a result of groundwater gley processes the goethite accumulations are intermingled locally with lignite representing preservation of the root organic material some rhizoliths are preserved as tube shaped concentrations of small 0 1 0 2 mm diameter black spheres whose color indicates a mix of mn and fe oxides these are most common in paleosols with low chroma gray matrix colors indicating very poor drainage the very poorly drained paleosols also show rhizoliths preserved in jarosite which is an oxidation product of pyrite careful observational and geochemical analysis of rhizoliths which are common in continental deposits can help produce a clearer and more thorough interpretation of ancient drainage conditions information about degree of ancient soil wetness or moisture is important for understanding past climatic conditions and for reconstructing terrestrial paleolandscapes

numerical study of convection observed during the winter monsoon experiment using a mesoscale two dimensional model abstract a two dimensional version of the pennsylvania state university mesoscale model has been applied to winter monsoon experiment data in order to simulate the diurnally occurring convection observed over the south china sea the domain includes a representation of part of borneo as well as the sea so that the model can simulate the initiation of convection also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle this allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck which typically occupies several hundred kilometers of the domain frank and cohen s cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area the major conclusions are ice phase processes are important in determining the level of maximum large scale heating and vertical motion because there is a strong anvil componen

a mechanism of chemical weathering of mudstone in a mountainous area abstract the chemical weathering of marine mudstone in humid mountainous areas of japan is dominated by the oxidation of pyrite a common mineral in marine sedimentary rocks this process occurs at the oxidation front that is the base of the oxidized zone and sulfuric acid is formed chlorite is transformed into smectite due to the oxidizing and acidic conditions as sulfuric acid migrates downward from the oxidation front minerals are dissolved and components are leached out from the underlying dissolved zone whose lower boundary is the dissolution front the oxidation and dissolution fronts migrate downward as weathering progresses in mountainous areas

conduction phenomena from theory to geotechnical practice virtually all geotechnical problems involve the flow of fluids chemicals and energy a current review of the types of direct and coupled flow through soil is given and assessment of their significance in geotechnical practice is made darcy s fourier s ohm s and fick s laws provide a suitable practical basis for the analysis of water heat electrical and chemical flows due to gradients of the same type prolonged application of gradients of the different types can cause significant changes in the state and properties of a soil and flows through it the quantification of coupled flows is most easily done by direct measurement of coupling coefficients when only two types of flow are important the application of irreversible thermodynamics is useful for quantification of flows in more complex systems relationships are provided for the expression of coupling coefficients in terms of directly measurable soil parameters such as hydraulic conductivity coupled fluid flows due to electrical and chemical gr

the influence of weathering on the geotechnical properties and slope angles of mudstone in the mineoka earth slide area japan three active earth slide slopes of tertiary mudstone were investigated slope 1 has an angle of 17 4 slope 2 of 12 9 and slope 3 of 11 6 infinite slope analysis indicated that the instability of these three slopes can be well explained by using the residual strength parameters of earth slide soils near the sliding surface in conjunction with the highest ground water table the residual angle of shearing resistance o r plays an important role in the determination of slope angle because it differs greatly among slopes mineralogical studies and x ray diffraction analyses were performed for the clay minerals included in the slope material the results showed that illite and chlorite were found in slope 1 and also in slopes 2 and 3 together with interstratified illite montmorillonite and montmorillonite the degree of weathering is progressive in order of slopes 1 2 and 3 the alteration of clay minerals by weathering causes the reduction in o r values i e 19 4 in slope 1 steep less weathered and 12 1 9 2 in slopes 2 and 3 gentle much more weathered this result indicates that the degree of weathering has a great influence on the value of o r which in turn determines the slope angle

genesis of coffinite and the u ti association in lower old red sandstone sediments ousdale caithness scotland the mineralogy of a fault related uranium occurrence in clastic rocks overlying granite is described from borehole material coffinite is the only important uranium mineral other notable minerals are sulphides fluorite calcite and hydrocarbon coffinite is epigenetic and paragenetically late rimming sulphides and hycrocarbon it occurs partly in spatial association with a tio2 mineral probably anatase this u ti association is attributed to adsorption of u by altered ti minerals prior to growth of the u mineral thus is has similarities with many diagenetic occurrences though their mineralogy is usually different the u ti association being represented by uranotitanates the latter are attributed to local supersaturation of tio2 which did not occur at ousdale because ti was relatively mobile in the fluids coffinite tio2 quartz is interpreted as a stable low temperature assemblage the mineralogy thus indicates a hydrothermal uranium mineralization of an unusual type without prominent uraninte formed from relatively low temperature fluids containing complexing agents which mobilized ti

axial river evolution in response to half graben faulting carson river nevada u s a abstract the holocene history of faulting and river channel movement for the carson valley nevada allows the tectonic alluvial interactions of an active half graben to be studied topographic surveys maps cores radiocarbon dates and paleohydrology are used to study the temporal and spatial patterns of carson river channel change the influence of faulting and associated ground tilting on channel movement is determined by comparing the pattern and timing of river movements with the published event history of the basin bounding fault inverse modeling of the fault history assuming rigid block motion suggests that surface gradients perpendicular to the channel and basin axis have progressively increased through the holocene from an initially horizontal surface the greater part of this movement occurred during and immediately after faulting channel avulsion in response to this increased tectonic ground tilting appears to be the most important factor controlling alluvial architecture although intrinsic fluvial processes and regional climate change may have triggered individual avulsions channel belts avulsed towards the fault onlap after each tectonic event during periods of tectonic quiescence they migrated away from the fault offlap taking the path of maximum overall gradient lag times between faulting and channel avulsion are very short instantaneous to hundreds of years the observed holocene history of the carson river is consistent with positions of channel belts predicted by half graben stratigraphic models and therefore this study provides the first confirmation that the underlying alluvial tectonic assumptions of these models are broadly correct

characterizing avulsion stratigraphy in ancient alluvial deposits guidelines for identifying ancient avulsion deposits were set forth by kraus and wells kraus m j wells t m 1999 recognizing avulsion deposits in the ancient stratigraphical record in smith n d rogers j eds fluvial sedimentology vi special publication of the international association of sedimentologists vol 28 pp 251 268 building on the study by smith et al smith n d cross t a dufficy j p clough s r 1989 anatomy of an avulsion sedimentology 36 1 23 of the modern saskatchewan river system cumberland marshes central canada and serve to characterize avulsion depositional sequences in the ancient willwood and fort union formations paleogene bighorn basin nw wyoming usa we recognize however that the model is not universally applicable to avulsion dominated successions specifically systems which lack defining heterolithic avulsion deposits set forth by kraus and wells kraus m j wells t m 1999 recognizing avulsion deposits in the ancient stratigraphical record in smith n d rogers j eds fluvial sedimentology vi special publication of the international association of sedimentologists vol 28 pp 251 268 observations in several fluvial intervals suggest that the avulsion stratigraphy outlined by kraus and wells kraus m j wells t m 1999 recognizing avulsion deposits in the ancient stratigraphical record in smith n d rogers j eds fluvial sedimentology vi special publication of the international association of sedimentologists vol 28 pp 251 268 represents one category of avulsion stratigraphy found in the rock record but does not capture the nature of avulsion deposits everywhere based on observations using measured sections outcrop photo panels and aerial photographs in the willwood formation eocene wyoming and ferris formation cretaceous paleogene wyoming we present two end member categories of avulsion stratigraphy in ancient deposits stratigraphically abrupt when a main paleochannel is stratigraphically juxtaposed directly atop floodplain overbank deposits and stratigraphically transitional where crevasse splays and other non floodplain overbank deposits stratigraphically precede a main paleochannel this characterization provides a broader more inclusive way to recognize and describe avulsion stratigraphy in ancient deposits and may be an important factor to consider when modeling connectivity in fluvial reservoirs furthermore our observations show that one type of avulsion channel stratigraphy may prevail over another within an ancient basin suggesting that system wide factors such as splay proneness or avulsion style i e aggradational incisional etc slingerland r smith n d 2004 river avulsions and their deposits annual review of earth and planetary sciences 32 257 285 may be primary controls on the type of avulsion stratigraphy deposited and preserved in ancient basin fills

variability of channel belt dimensions and the consequences for alluvial architecture observations from the holocene rhine meuse delta the netherlands and lower mississippi valley u s a abstract over the past decades many studies have focused on the dimensions of channel belt sand bodies referred to as channel belts in fluvial deposits because of their relevance for hydrocarbon exploration and production some field studies have revealed a significant downstream decrease of channel belt width and width thickness ratio along the length of the channel belt to verify whether this is a common feature in fluviodeltaic settings eight holocene channel belts in the rhine meuse delta the netherlands were selected and one in the lower mississippi valley u s a we determined channel belt geometry width or width thickness ratio using geological geomorphological maps and detailed cross sections based on borings it was found that the width of channel belts encased in cohesive deposits decreases by a factor of 4 to 6 5 in a downstream direction along the length of the channel belts the width thickness ratio decreases by a factor of 2 5 to 5 on the other hand the width of a channel belt incised in a noncohesive substrate remains constant along its entire course these observations are related to longitudinal changes in bank erodibility and stream power it is suggested that bank erodibility is the dominating factor determining the geometric properties of channel belts and the variability therein at least in the rhine meuse delta the currently available alluvial architecture models most likely overestimate sand quantities and connectedness in alluvial successions because channel belt dimensions are held constant in all models we therefore propose that the factors bank erodibility and stream power which influence width and width thickness ratio of channel belts should be incorporated in future alluvial architecture models in order to make more realistic estimates of sand quantities in river deltas

sedimentology and architecture of the douglas creek terminal splay lake eyre central australia douglas creek terminal splay sited on the western shoreline of lake eyre north central australia covers a surface area of approximately 4 km2 with a down system length of 2 5 km from the distributary channels terminus to the splay fringe two distributary channels feed two sediment lobes which have amalgamated to form the terminal splay three primary facies associations have been identified sub dividing the creek terminus into distributary channel proximal and distal splay sections proximal splay sediments are characterized by erosionally based relatively thick 100 mm stacked sheets of coarse to medium sand which commonly display trough and planar cross bedding whereas the distal splay is characterized by thin generally 50 mm massive beds of very fine sand silt and clay the change in splay sedimentology is interpreted as reflecting the transition from bedload dominated deposition to suspended load dominated deposition from decelerating sheetfloods as they spread out from the channel onto the dry lake bed a proximal to distal splay transition zone is also noted where deposits of both facies associations interfinger laterally and vertically in scale geometry and facies associations the douglas creek terminal splay is very different to the often cited neales terminal splay complex located 70 km to the north it is suggested that these architectural differences reflect variations in discharge volume input sediment distribution and the degree of vegetation cover understanding the variation in terminal splay architecture has very significant implications for the modelling of analogous subsurface petroleum systems which at present relies on few modern day analogues

weathering rate of mudstone and tuff on old unlined tunnel walls abstract the mechanisms and rate of weathering of soft sedimentary rocks exposed along unlined tunnel walls were investigated using mineralogical chemical and physical methods tunneling occurred several decades ago within the kakinokidai formation middle pleistocene and the kiwada formation lower pleistocene of the kazusa group of chiba prefecture as well as within the fukuda formation miocene of saitama prefecture in japan since then the walls of the tunnels have been desiccated by ventilation sulfuric acid has been generated by pyrite oxidation calcite and glass have been dissolved by sulfuric acid and gypsum has crystallized on the surface of the tunnel walls the oxidized zone was formed on the surface of the walls by the weathering the formation of this zone and weathering rates determined as rates of movement of the oxidation fronts in the vadose zone are explained by the diffusion of oxygen from the surface of the tunnel walls the relationship between the depth of the oxidation front lcm and the number of years since excavation tyear was expressed by l r oxi t the roxi values from the tunnels ranged among 5 for the middle pleistocene sandy mudstone 2 4 for the middle pleistocene mudstone 0 3 for the lower pleistocene mudstone and 1 3 for the miocene tuff roxi depends on the diffusion coefficients of oxygen and the chemical composition of rocks the diffusion coefficients of oxygen de calculated using the roxi and chemical compositions of the four kinds of rock above were 10 5 cm2 s 10 7 10 5 cm2 s 5 10 8 cm2 s and 4 10 7 3 10 6 cm2 s respectively depending on the air permeabilities of the rocks that correlate closely with the coefficient of water permeabilities k the relationship for the mudstone was log de cm2 s 0 91 log k cm s 0 71 the values of de for the tuff were smaller than for the mudstone due to the smaller air porosities of 0 01 0 04