evidence for episodic cementation and diagenetic recording of seismic pumping events north coles levee california u s a abstract bands of calcite and dolomite cements alternating with zones of nearly carbonate free sand occur in the stevens sandston aat north coles levee san joaquin valley california temperatures calculated from o isotopes suggest that the calcite cement bands were emplaced episodically as a result of repeated injections of hot water from deeper in the section burial analysis suggests that these cements precipitated from 7 ma to the present over the temperature range of 45 to 95 c carbon isotope data suggest that the c in the cements is a mixture derived from two sources detrital shell material 13c pdb and co2 liberated from maturing kerogen 13c 24 plots of 13c vs time and depth of crystallization show that the cementation sequence was 1 dolomite cements possibly concretionary precipitated at depths a log of 13c vs calculated depth of crystallization correlates with the stratigraphic column at north coles levee if the correlation is valid the light 13 in each cement sample can be tied to its source a model based on this interpretation suggests that the early light c was derived from maturing kerogen in the kreyenhagen formation eocene as it passed through the oil window between 4 and 5 ma the subsequent passage of younger sediments with less organic material produced correspondingly smaller amounts of light co2 which was reflected in the relatively heavier c isotopes in the later cements it is suggested that the epidsodic injections of hot water carried dissolved gases and minerals principally calcite upward from rocks as deep as 2 3 km below the stevens sandstone and reprecipitated the calcite in more permeable zones in the rock degassing of co2 from rising pore waters likely triggered the precipitation and accounts for the relatively large volumes of cement the sibson model for seismic pumping of pore fluids is considered a likely explanation for the observed cementation

a comparison of past small dam removals in highly sediment impacted systems in the u s abstract the ability to predict the effects of dam removal in highly sediment filled systems is increasingly important as the number of such dam removal cases continues to grow the cost and potential impacts of dam removal are site specific and can vary substantially depending on local conditions of specific concern in sediment impacted removals is the volume and rate of reservoir deposit erosion the complexity and potential accuracy of modeling methods used to forecast the effects of such dam removals vary substantially current methods range from predictions based on simple analysis of pre dam channel geometry to sophisticated data intensive three dimensional numerical models in the work presented here we utilize data collected from past dam removals to develop an additional tool for predicting the rate and volume of sediment deposit erosion through the analysis of sediment discharge deposit removal timeline channel and watershed data in conjunction with post removal monitoring data from a wide range of dam removal projects some significant trends in the evolution of reservoir deposits following dam removal can be seen results indicate that parameters such as median grain size level of cohesion spatial variability of the deposit and removal timeline are among the most influential factors in determining the rate and volume of sediment erosion by comparing local conditions of dams and reservoirs slated for removal with those of past removals we hope that predictions of the rate and volume of sediment deposit erosion can be usefully constrained

erosion and channel changes due to extreme flooding in the fourmile creek catchment colorado abstract infrequent large magnitude geomorphic events generate quantifiable change on geologically short timescales and are crucial to understanding landscape evolution airborne lidar surveys and field measurements were used to investigate floodplain erosion and deposition along a 19 5 km reach of fourmile creek colorado that was devastated by severe flooding in 2013 that followed a 2010 wildfire 350 mm of rain fell on the fourmile catchment from september 9 15 2013 generating discharge that exceeded bankfull for 120 h at the orodell gage with local unit stream power 300 w m 2 throughout the study reach debris flows occurred on steep hillslopes and tributary channels in the most intensely burned areas lidar difference measurements and field studies highlight zones of local deposition along the study reach but demonstrate overall net erosion of 0 25 m for the 19 5 km reach of fourmile floodplain mainly by channel widening tributary junctions where debris flow sediment entered the floodplain and local decreases in unit stream power controlled some zones of deposition overall mass balance calculations show that a total sediment loss of 91 000 161 000 m3 from the fourmile creek floodplain and hillslopes which is broadly consistent with channel sediment flux estimates of 71 000 111 000 m3 measurements from the fourmile catchment demonstrate that floodplain erosion was a major source of sediment in the 2013 flood and demonstrate that infrequent events marked by long duration flooding and high total energy expenditure can account for a large fraction of total sediment transport in mountain streams

stevens and earlier miocene turbidite sandstones southern san joaquin valley california a thick marine turbidite succession dominantly coarse sandstone underlies the southern part of the san joaquin valley sands are pebbly to fine grained commonly poorly sorted quartzose to arkosic and are interbedded with dark shales bearing deep water foraminifers graded bedding is common and with the depths of 2 000 to 6 000 ft 610 to 1 830 m implied by the fauna is taken to indicate a turbidity current origin for most of the sands the upper middle and lower miocene turbidite section was revealed by extensive coring at paloma and is similar to the more widespread and oil and gas productive upper miocene stevens sandstone the central basin stevens was deposited as channel sands on deep sea fans derived from several discrete troughs or canyons on the eastern and southeastern margin of the basin prior to their burial by prograding santa margarita sand sand channels and lobes in the bakersfield arch area were controlled locally by compaction structures the rising paloma anticline deflected stevens sands for a time and the very last sands were guided also by incipient folds on the outer bakersfield arch coarse stevens conglomerates and sands shed from the emergent temblor range were deflected by the buena vista hills elk hills and other anticlinal shoals and were deposited in intervening gaps as thick oil productive channel sands they merge with sands from the east side in flowing axially into the di tal northwestern basin facies recognized in the subsurface include a meander channel facies developed in the prograded muddy slope area upstream from the massive braided sand facies

a model of channel response in disturbed alluvial channels dredging and straightening of alluvial channels between 1959 and 1978 in west tennessee caused a series of morphologic changes along modified reaches and tributary streams degradation occurred for 10 to 15 years at sites upstream of the area of maximum disturbance and lowered bed levels by as much as 6 1 m following degradation reaches upstream of the area of maximum disturbance experienced a secondary aggradation phase in response to excessive incision and gradient reduction aggradation downstream of the area of maximum disturbance reached 0 12 m per year with the greatest rates occurring near the stream mouths the adjustment of channel geometry and phases of channel evolution are characterized by six process oriented stages of morphologic development premodified constructed degradation threshold aggradation and restabilization down cutting and toe removal during the degradation stage causes bank failure by mass wasting when the critical height and angle of the bank material is exceeded threshold stage channel widening continues through the aggradation stage as the slough line develops as an initial site of lower bank stability the bank profile develops three dynamic elements 1 vertical face 70 to 90 2 upper bank 25 to 50 and 3 slough line 20 to 25 alternate channel bars form during the restabilization stage and represent incipient meandering of the channel

river channel slope flow resistance and gravel entrainment thresholds 1 river beds are traditionally assumed to become mobile at a fixed value of nondimensional shear stress but several flume and field studies have found that the critical value is higher in steep shallow flows explanations for this have been proposed in terms of the force balance on individual grains the trend can also be understood in bulk flow terms if total flow resistance has base and additional components the latter due to protruding immobile grains as well as any bedforms and the stress corresponding to additional resistance is not available for grain movement in threshold conditions a quantitative model based on these assumptions predicts that critical shields stress increases with slope critical stream power is near invariant with slope and each has a secondary dependence on bed sorting the proposed slope dependence is similar to what force balance models predict and consistent with flume data and most field data possible explanations are considered for the inability of this and other models to match the very low critical values of width averaged stress and power reported for some low gradient gravel bed rivers

immediate changes in stream channel geomorphology aquatic habitat and fish assemblages following dam removal in a small upland catchment abstract dam removal is becoming an increasingly important component of river restoration with 1100 dams having been removed nationwide over the past three decades despite this recent progression of removals the lack of pre to post removal monitoring and assessment limits our understanding of the magnitude rate and sequence of geomorphic and or ecological recovery to dam removal taking advantage of the november 2012 removal of an old 190 year old 6 m high run of river industrial dam on amethyst brook 26 km2 in central massachusetts we identify the immediate eco geomorphic responses to removal to capture the geomorphic responses to dam removal we collected baseline data at multiple scales both upstream 300 m and downstream 750 m of the dam including monumented cross sections detailed channel bed longitudinal profiles embeddedness surveys and channel bed grain size measurements which were repeated during the summer of 2013 these geomorphic assessments were combined with detailed quantitative electrofishing surveys of stream fish richness and abundance above and below the dam site and throughout the watershed and visual surveys of native anadromous sea lamprey petromyzon marinus nest sites post removal assessments were complicated by two events 1 upstream knickpoint migration exhumed an older ca late eighteenth century intact wooden crib dam 120 m upstream of the former stone dam and 2 the occurrence of a 10 20 year ri flood 6 months after removal that caused further upstream incision and downstream aggradation now that the downstream reach has been reconnected to upstream sediment supply the predominant geomorphic response was bed aggradation and associated fining 30 60 reduction at dam proximal locations aggradation ranged from 0 3 to 1 m where a large woody debris jam enhanced aggradation although less pronounced distal locations still showed aggradation with a mean depth of deposition of 0 20 m over the 750 m downstream reach post removal but pre flood bed surveys indicate 2 m of incision had migrated 25 m upstream of the former reservoir before encountering the exhumed dam which now acts as the new grade control limiting progressive headcutting approximately 1000 m3 of sediment was evacuated in the first year with 67 of the volume occurring by pre flood process driven e g changes in base level controls the combination of changes in channel bed sedimentology the occurrence of a large magnitude flood and the emergence of the new crib dam that is a likely barrier to fish movement was associated with major reductions in abundance and richness in sites downstream and immediately upstream adjacent to the former dam in post removal sampling at the same time we documented the presence of four species of fish including sea lamprey which were not present above the dam prior to removal indicating that upstream passage has been achieved and we also documented lamprey spawning activity at sites immediately below the dam which had previously been unsuitable owing to an excessively coarse and armored riverbed our results point to the importance of interactions between dam removal and flood disturbance effects with important implications for short and long term monitoring and assessment of dam impacts to river systems

monterey formation porcelanite reservoirs of the elk hills field kern county california oil and gas production from monterey formation porcelanite at the elk hills field in california s san joaquin basin occurs from intervals that have quartz phase mineralogy however characteristics differ from chert and porcelanite reservoirs of the coastal california monterey formation in that matrix porosity is more typical of the opal ct phase petroleum storage is mostly in the matrix and natural fracture patterns are dominantly small scale several elk hills reservoirs located on two large anticlines produce from porcelanite the 29r ab and 31s d are the most productive porcelanite reservoirs each having cumulative oil production of about 40 million bbl although interbedded with siliceous shale sandstone and dolomite most of the porous reservoir rock is laminated porcelanite porosity averages between 20 and 25 and is evenly distributed throughout the porcelanite as extremely small pores ranging in size from 1 to 10 m matrix permeability averages 0 8 md but flow of oil and gas is enhanced through fractures parallel with and perpendicular to bedding higher than anticipated porosity may be in part due to migration of hydrocarbons into the porcelanite reservoirs while still in opal ct phase mineralogy the dissolution of opal ct and precipitation of quartz occurs in place and the resulting quartz phase mineral structure mimicks the porous opal ct framework

radiocarbon chronology of early human settlement on the isthmus of panama 13 000 7000 bp with comments on cultural affinities environments subsistence and technological change abstract the first human migrants entering south america must have used the isthmian route convincing archaeological evidence for pre clovis groups is lacking paleoindian artifacts including clovis and fishtail fluted projectile points have been found at several localities but at only one site vampiros 1 in buried and radiocarbon dated deposits 11 500 9000 bp close similarities between clovis point reduction sequences at two panamanian quarry workshops to those of early us clovis sites vouch for temporal proximity and suggest rapid movement of clovis bands through central america 11 050 10 800 bp vampiros 1 and other rock shelters were occupied during the early holocene 10 000 7000 bp when climate became warmer and wetter un fluted bifacial projectile points were made until 7000 bp widespread grinding stones and carbonized tree fruits announce a mixed economy at the beginning of the holocene cultivated leren arrowroot squash and bottle gourd appeared by 8000 bp there are no indicators of human activities at lake la yeguada 650 m asl 14 000 11 150 bp nor at vampiros 1 16 000 11 500 bp pre clovis populations were probably bound to the now drowned pacific coast intense burning and deforestation commenced at la yeguada 11 050 bp coevally with clovis human impacts were thenceforth continuous swidden farming had largely removed forest cover by 7000 bp across seasonally arid central pacific panama lake sediment data from forested areas with less seasonal climates on the caribbean and pacific watersheds indicate moderate human interference before 7000 bp the mtdna history of modern panamanians confirms native american continuity from before 10 000 bp and provides support for the pacific route of initial dispersal into south america

neutron activation analysis of 12 900 year old stone artifacts confirms 450 510 km clovis tool stone acquisition at paleo crossing 33me274 northeast ohio u s a the archaeologically sudden appearance of clovis artifacts 13 500 12 500 calibrated years ago across pleistocene north america documents one of the broadest and most rapid expansions of any culture known from prehistory one long asserted hallmark of the clovis culture and its rapid expansion is the long distance acquisition of exotic stone used for tool manufacture given that this behavior would be consistent with geographically widespread social contact and territorial permeability among mobile hunter gatherer populations here we present geochemical evidence acquired from neutron activation analysis naa of stone flaking debris from the paleo crossing site a 12 900 year old clovis camp in northeastern ohio these data indicate that the majority stone raw material at paleo crossing originates from the wyandotte chert source area in harrison county indiana a straight line distance of 450 510 km our analyses thus geochemically confirm an extreme stone source to camp site distance of a clovis site in eastern north america and thus provide strong inferential material evidence that the fast expansion of the clovis culture across the continent occurred as a result of a geographically widespread hunter gatherer social network

increased mid twentieth century riverbank erosion rates related to the demise of mill dams south river virginia a recent hypothesis suggests that fluvial processes in areas of the eastern united states are strongly influenced by the demise of colonial mill dams rather than reflecting a quasi equilibrium adjustment to the current hydrologic and sediment regime we evaluated the control of colonial mill dams on twentieth and twenty first century bank erosion rates on the south river virginia through studies of historical aerial photographs historical documents hydrologic and climatic records and hydraulic modeling historical sources and aerial photographs document eight colonial mill dams along the study reach in the early twentieth century all but one of these dams disappeared in the 1950s and the last was breached by 1976 from initially low values between 1937 and 1957 mean bank erosion rates increased by more than a factor of 2 after 1957 remaining high through 2005 accelerated bank erosion rates cannot be explained by changes in storm intensity the frequency of freeze thaw cycles or by changes in the density of riparian trees hydraulic modeling suggests that mill dams reduced velocities of the 5 yr flood through 80 of our study reach by considering the timing of mill dam loss the spatial extent of backwater influence and the locations of our study sites we find that the loss of mill dams explains the observed trends in bank erosion rates at 9 and possibly 10 of our 14 monitoring sites these results support the hypothesis that the demise of mill dams has been an important influence on fluvial processes in the region

thermal history of rocks in southern san joaquin valley california evidence from fission track analysis the theory of the fission track method and its application to sedimentary basin analysis is illustrated by a case study in the southern san joaquin valley california fission tracks provide a powerful tool for studying the thermal history of sedimentary basins because the two minerals most commonly used in fission track studies apatite and zircon occur as detrital constituents in many sedimentary rocks and their annealing temperatures span the main temperature range for oil generation fission tracks also provide information on the sedimentation record and provenance of rocks in a basin we have used fission track analysis to study the thermal and depositional history of the subsurface tertiary sedimentary rocks on both sides of the active white wolf reverse fault in the southern san joaquin valley the distinctly different thermal histories of the rocks in the two structural blocks are clearly reflected in the apatite fission track data which suggest that rocks in the rapidly subsiding basin northwest of the fault have been near their present temperature for only about 1 m y compared with about 10 m y for rocks southeast of the fault these estimates of heating time agree with previous estimates for these rocks zircon fission track data indicate that the tertiary sediments were derived from parent rocks of more than one age however from at least the eocene to late miocene or pliocene the major sediment source was rocks related to the youngest sierra nevada mesozoic intrusive complexes which are presently exposed east and south of the southern san joaquin valley

knowledge transmission and apprentice flint knappers in the acheulo yabrudian a case study from qesem cave israel abstract we present the techno typological characteristics of a lithic assemblage earlier that 300 ka originating from the southern area of qesem cave a middle pleistocene site in central israel aspects of knapping trajectories were examined in detail including core analyses demonstrating that the southern area assemblage has some distinguishable features in comparison with lithic assemblages from other areas of the cave these features permit in our opinion to suggest that various levels of knapping skills are reflected in this particular assemblage most probably characterizing both skilled knappers and unexperienced knappers or knappers in the process of learning thus these data may permit a preliminary assessment of knowledge transmission relating to flint knapping that has taken place in the southern area of qesem cave during the late lower paleolithic in the levant

dams and geomorphology research progress and future directions dams impose changes of flow and sediment transfer that drive changes of channel form along the downstream regulated river these changes have been described for more than 50 years but process form relationships have only been advanced with the establishment of a conceptual framework during the 1970s and then the extension of monitoring data and advancement of remote sensing technologies particularly over the past 20 years this paper reviews these developments and identifies three influential themes i channel dynamics ii the role of riparian vegetation and iii channel change as the driver of ecological change changes can be rapid in semi arid regions but elsewhere relaxation periods may extend to millenia in these latter cases regime or steady state models should be replaced by models of transient states applied to the reach scale in order to respond to the needs of river managers over decadal timescales

40ar 39ar age spectrum analysis of detrital microclines from the southern san joaquin basin california an approach to determining the thermal evolution of sedimentary basins abstract detrital microcline grains from sedimentary strata preserve a record of thermal evolution in the temperature range 100 to 200 c which can be revealed by40ar 39ar age spectrum analysis microcline separates from deep drill hole intersections with eocene to miocene sediments in the basin and tejon blocks of the southern san joaquin valley california analysed by the age spectrum approach show radiogenic40ar 40ar gradients that record both the slow cooling of the uplifting sediment source 65 ma ago and a recent thermal event this information in conjunction with the observation of fission track annealing in the coexisting apatites allows estimation of the temperature time conditions of this thermal event at about 140 c for 200 ka present and paleotemperature data is in accord with heating related to several kilometers of pleistocene sediment deposition heat flow calculations suggest that this recent subsidence has depressed the thermal gradient from about 30 c km 1 to the present apparent gradient of 24 c km 1 40ar 39ar analysis of detrital microcline crystals yields thermochronological information in the temperature time range of petroleum maturation and provides this technique with potential as both a useful exploration tool and as a means of probing the fundamental geodynamic processes of basin evolution

tectonic depositional and diagenetic history of monterey formation miocene central san joaquin basin california the miocene monterey formation in the central san joaquin basin of california consists of biogenic siliceous rocks with a significant terrigenous clastic component correlation of electric logs in conjunction with analysis of outcrop sections core samples and paleontologic data suggests that deposition of the monterey was controlled by an interplay of basin geometry san andreas related tectonics fluctuations in sea level and changes in climate the basin is bounded on the east by the sierran magmatic arc complex and on the west by the san andreas fault during the late saucesian through early mohnian 20 10 ma the basin was reshaped by tectonism related to the migrating mendocino triple junction creating a broad gently sloping shelf to the east that cut off the supply of clastics to the central basin with the subsequent evolution of the san andreas fault the salinian block was emplaced along the western basin margin restricting the seaway and permitting low oxygen nutrient rich waters to occupy the basin as a result laminated organic rich fine grained pelagic to hemipelagic sediments of the monterey formation were deposited a warmer climate during saucesian through luisian time with less intensive upwelling le to more calcareous less siliceous sedimentation a cooling trend during late miocene time 10 5 ma increased upwelling activity diatom productivity in the water column and deposition of diatomaceous debris although turbidites accumulated on the basin floor and terrigenous clastics were deposited on the eastern shelf relatively undiluted diatomaceous deposits developed on outer shelves and slopes atop anticlinal banks generated by wrench tectonism and in some areas of the basin floor a mid mohnian eustatic sea level rise caused fine grained deposition to extend onto the eastern shelf slightly later a mid late mohnian period of exceptionally cool temperatures resulted in the most extensive development of upwelling related siliceous sediments throughout the basin with diagenesis these deposits formed the siliceous shales and porcelanites of the monterey formation high sedimentation rates coincident with a eustatic drop in sea level led to clastic progradation in latest miocene time as the basin filled analysis of organic matter from cores of the monterey formation shows that kerogen type reflects overall sedimentation trends samples from northern and eastern areas contain abundant terrestrial organic matter whereas samples from western areas mostly contain marine kerogens source potential is thus strongly influenced by geographic locality as well as lithology maturity of kerogen was assessed using vitrinite reflectance thermal alteration indices and pyrolysis techniques the latter two appear to be the more reliable indicators of organic matter maturity in the monterey formation of the san joaquin valley although much of the monterey formation in the study area may be thermally immature portions are probably generating hydrocarbons today in deep synclinal areas

evolution of the southern san joaquin basin and mid tertiary transitional tectonics central california a cenozoic tectonic and sedimentary history is proposed for the southern san joaquin basin ssjb and tehachapi mountains that evolved adjacent to the plate margin off central california seismic reflection borehole field biostratigraphic and paleomagnetic data are integrated into geologic and fault structure maps cross sections and geohistory plots and are analyzed with previous work in the region to develop a model relating the sequence timing and distribution of complex tectonically linked events the largely buried structures and strata in the ssjb preserve an unusually complete record of the mid tertiary transition from convergent to transform plate boundary as well as the regional transition to contraction during the pliocene significant structural relief existing across both extensional and contractile features is preserved in the subsurface and an active fold thrust belt propagates basinward along the margin of the u shaped tejon embayment the cenozoic evolution of the ssjb reflects the regional deformation of central california as different tectonic events followed each other along the adjacent north american plate margin five oligocene miocene basin phases are identified in the ssjb 1 late oligocene early miocene extensional subsidence with high and low angle normal faulting accompanied by volcanism and deposition of coarse syntectonic conglomerates 2 middle miocene uplift 3 later mid miocene transtensional subsidence to lower bathyal depths 4 alternating subsidence and uplift until the late miocene and 5 flexural subsidence due to pliocene to recent contraction reconstructions of mid tertiary california place the southern san joaquin tehachapi extensional terrane as a paleotectonic block located between the western mojave terrane then to the east and the western california terrane then to the south and west regional extension occurred during a long transition period between convergent and transform boundaries along the north american plate margin significant slip along the san andreas transform postdates this extensional event its origin apparently coincided with a regional middle miocene uplift event indicating that the san andreas fault is younger than previously supposed the tertiary ssjb has subsided due to extension transtension crustal tilting and thrust related loading the maricopa subbasin floor is likely composed of ensimatic and mafic rocks like those along the west side of the sierra nevada and locally has subsided beyond 12 km in contrast the relatively stable tejon embayment underlain by sierran crystalline crust achieved its maximum subsidence in the miocene since pliocene time the ssjb has filled and continued to deepen after the basin was tectonically shut off from the pacific ocean

a systematic analysis of eight decades of incipient motion studies with special reference to gravel bedded rivers data compiled from eight decades of incipient motion studies were used to calculate dimensionless critical shear stress values of the median grain size t c 50 calculated t c 50 values were stratified by initial motion definition median grain size type surface subsurface or laboratory mixture relative roughness and flow regime a traditional shields plot constructed from data that represent initial motion of the bed surface material reveals systematic methodological biases of incipient motion definition t c 50 values determined from reference bed load transport rates and from visual observation of grain motion define subparallel shields curves with the latter generally underlying the former values derived from competence functions define a separate but poorly developed field while theoretical values predict a wide range of generally higher stresses that likely represent instantaneous rather than time averaged critical shear stresses the available data indicate that for high critical boundary reynolds numbers and low relative roughnesses typical of gravel bedded rivers reference based and visually based studies have t c50 ranges of 0 052 0 086 and 0 030 0 073 respectively the apparent lack of a universal t 50 for gravel bedded rivers warrants great care in choosing defendable t c50 values for particular applications

tectono eustatic controls on reservoir compartmentalisation and quality an example from the upper miocene of the san joaquin basin california abstract systematic changes in stratigraphic architecture and reservoir quality of upper miocene stevens sandstones at north and south coles levee fields san joaquin basin reflect tectono eustatic controls on deposition two depositional sequences 330 500 m thick are present in the coles levee stevens the upper sequence contains sandstones deposited by sediment gravity flows in water depths of 300 500 m backstepping retrogradational reservoir compartments in this sequence overlie vertically stacked to prograding compartments although the backsteps are the better reservoirs with higher permeabilities and porosities the vertically stacked to prograding compartments are volumetrically more important curiously the upper stevens section is sand rich 60 80 ss on structural highs that were also palaeotopographic highs thicker sections with less and characterise the flanks these sand distributions are anomalous since sediment gravity flows preferentially deposit in bathymetric lows apparently the flanks of stevens palaeohighs subsided faster than the crests consequently accomodation increases were greatest on the flanks and resulted in aggradation with preservation of section less accommodation on the crests resulted in progradation with erosion and reworking through lobe switching processes some sand reached all parts of the depocenter subsequent progradation with erosion of shale interbeds and attendant reworking by density currents created sand rich sections in slowly subsiding areas crests concurrent aggradation preserved shale interbeds and created shale dominated sections in rapidly subsiding areas flanks greater compaction of thicker shale dominated flanks equalised thicknesses of flank and crest sections thus the reservoir architecture represents the integrated effects of compensation lobe switching accommodation subsidence sea level and compaction

predicting the type location and magnitude of geomorphic responses to dam removal role of hydrologic and geomorphic constraints abstract using a dam removal on the ashuelot river in southern new hampshire we test how a sudden spatially non uniform increase in river slope alters sediment transport dynamics and riparian sediment connectivity site conditions were characterized by detailed pre and post removal field surveys and high resolution aerial lidar data and locations of erosion and deposition were predicted through one dimensional hydrodynamic modeling the homestead dam was a 200 year old 4 m high 50 m wide crib dam that created a 9 5 km long relatively narrow reservoir following removal an exhumed resistant bed feature of glaciofluvial boulders located 400 m upstream and 2 5 m lower than the crest of the dam imposed a new boundary condition in the drained reservoir acting as a grade control that maintained a backwater effect upstream during the 15 months following removal non uniform erosion in the former reservoir totaled 60 000 m3 equivalent to 9 3 cm when averaged across the reservoir net deposition of 10 700 m3 was measured downstream of the dam indicating most sediment from the reservoir was carried more than 8 km downstream beyond the study area the most pronounced bed erosion occurred where modeled sediment transport increased in the downstream direction and deposition occurred both within and downstream of the former reservoir where modeled sediment transport decreased in the downstream direction we thus demonstrate that spatial gradients in sediment transport can be used to predict locations of erosion and deposition on the stream bed we further observed that bed incision was not a necessary condition for bank erosion in the former reservoir in this characteristically narrow and shallow reservoir lacking abundant dam induced sedimentation the variable resistance of the bed and banks acted as geomorphic constraints overall the response deviated from the common conceptual model of knickpoint erosion and channel widening due to dam removal with thousands of dams likely to be considered for removal or repair in the coming decades this study helps to advance predictions of the geomorphic response to dam removal and contributes to a broader understanding of the variability in both style and timing of fluvial responses to disturbances

rates and processes of channel response to dam removal with a sand filled impoundment 1 dam removal projects are playing an increasingly important role in stream restoration and offer unparalleled opportunities to study sediment dynamics following disturbance we used the removal of the 4 m high merrimack village dam mvd on the souhegan river in southern new hampshire to measure processes and rates of channel evolution in a sand filled impoundment from 2007 to 2010 we repeatedly surveyed 11 cross sections and the longitudinal profile and collected sediment samples to measure changes in channel morphology and bed texture the dam removal in august 2008 resulted in a nearly instantaneous base level drop of 3 9 m and caused a two phased channel response the initial process driven phase 2 months was characterized by rapid incision and removal of the impounded sand up to 1013 t d 1 followed by channel widening once incised to base level the rate of sediment removal slowed 30 7 t d 1 and adjustments became event driven and the former impoundment segmented into a nonalluvial section and an alluvial section with erosion and deposition influenced by vegetation on the channel banks two years after the dam removal and two high magnitude floods the river has excavated 79 of the original sediment continued response will be substantially influenced by the establishment of bank vegetation within the former impoundment and the magnitude and frequency of high discharge events initial channel development and sediment erosion occurs rapidly weeks to months in sand filled impoundments but excavation of the remaining sediment occurs more slowly depending on vegetation feedbacks and flood events

sediment transport constraints on river response to regulation abstract we demonstrate that alluvial channel response to regulation depends on the characteristic mode of sediment transport in a channel and thus for a channel in supply transport equilibrium on the caliber of sediment mantling the channel bed as well as changes in characteristic water discharge and sediment load we find that regulated coarse gravel and cobble bed alluvial rivers dominated by bedload transport are predicted and observed to preserve the value of a dimensionless ratio of characteristic water discharge channel slope width and size of sedimentary particles mantling the bed associated with the critical conditions required for the onset of significant sediment transport the covariant geomorphic adjustment of such rivers to regulation is independent of the degree of sediment impoundment although the nature and rate of changes in any specific characteristic appear to be sensitive to changes in sediment supply in contrast covariant geomorphic changes in sand and fine gravel bed alluvial rivers dominated by weak suspension transport are predicted and observed to be dependent on the degree of sediment impoundment and commensurate with the change in the sediment concentration of characteristic formative flows in both cases specific geomorphic characteristics of alluvial rivers exhibit varied responses to regulation in different rivers but across all rivers a systematic covariation in channel slope width and grain size is observed that for a given mode of sediment transport preserves a characteristic value of the shields number

a generalized exner equation for sediment mass balance 1 the advance of morphodynamics research into new areas has led to a proliferation of forms of sediment mass balance equation without a general equation it is often difficult to know what these problem specific versions of sediment mass balance leave out to address this we derive a general form of the standard exner equation for sediment mass balance that includes effects of tectonic uplift and subsidence soil formation and creep compaction and chemical precipitation and dissolution the complete equation 17 allows for independent evolution of two critical interfaces that between bedrock and sediment or soil and that between sediment and flow by eliminating terms from the general equation it is straightforward to derive mass balance equations applicable to a wide range of problems such as short term bed evolution basin evolution bedrock uplift and soil formation and carbonate precipitation and transport dropping terms makes explicit what is not being considered in a given problem and can be done by inspection or by a formal scaling analysis of the terms scaling analysis leads directly to dimensionless numbers that measure the relative importance of terms in the equation for example the relative influence of spatial versus temporal changes in sediment load on bed evolution combining scaling analysis with time averaging shows how the relative importance of terms in the equation can change with timescale for example the term representing bed evolution due to temporal change in sediment load tends to zero as timescale increases

flake scar patterns of clovis points analyzed with a new digital morphometrics approach evidence for direct transmission of technological knowledge across early north america abstract clovis points are the principal diagnostic artifacts of a clovis complex that spread across north america between ca 11 050 10 800 radiocarbon years before present clovis may be the best documented paleoamerican culture in north america but much remains to be learned about the movement and interactions of clovis peoples similarities among clovis points from geographically diverse locations have led some researchers to suggest that a uniform projectile point technology existed across north america during clovis times others have rejected this idea proposing local and independent technological adaptations to different regional environments to investigate these ideas we used digital morphometrics to analyze 50 clovis points from nine different contexts first 3d surface models of the points were created with a portable laser scanner next these models were digitally cross sectioned through both faces yielding two dimensional isoheight contours of flake scar patterns that reflect the original reduction techniques used to shape the projectile points in the final step the contours were transformed with elliptic fourier analysis into fourier coefficient series and patterns of variation and symmetry were explored with principal components analysis when compared to modern clovis point replicas made by an expert knapper the flake scar contours of the ancient clovis points showed little morphological variation and a large degree of bifacial symmetry our results support the existence of a widespread standardized clovis knapping technique most likely transmitted through direct interaction between knappers from different groups

variation in the reference shields stress for bed load transport in gravel bed streams and rivers 1 the present study examines variations in the reference shear stress for bed load transport r using coupled measurements of flow and bed load transport in 45 gravel bed streams and rivers the study streams encompass a wide range in bank full discharge 1 2600 m3 s average channel gradient 0 0003 0 05 and median surface grain size 0 027 0 21 m a bed load transport relation was formed for each site by plotting individual values of the dimensionless transport rate w versus the reach average dimensionless shear stress the reference dimensionless shear stress r was then estimated by selecting the value of corresponding to a reference transport rate of w 0 002 the results indicate that the discharge corresponding to r averages 67 of the bank full discharge with the variation independent of reach scale morphologic and sediment properties however values of r increase systematically with average channel gradient ranging from 0 025 0 035 at sites with slopes of 0 001 0 006 to values greater than 0 10 at sites with slopes greater than 0 02 a corresponding relation for the bank full dimensionless shear stress bf formulated with data from 159 sites in north america and england mirrors the relation between r and channel gradient suggesting that the bank full channel geometry of gravel and cobble bedded streams is adjusted to a relatively constant excess shear stress bf r across a wide range of slopes

diagenetic mass transport in the southern san joaquin basin california u s a implications from the strontium isotopic composition of modern pore fluids abstract three types of chemically and isotopically distinct pore fluids from the southern san joaquin basin previously recognized by j b fisher and j r boles also have distinctive 87 sr 86 sr ratios and sr concentrations meteoric fluids have stable isotopic compositions which lie on or near the meteoric water line and low chlorinities sr concentrations are between 0 01 and 2 6 mg l 1 and 87 sr 86 sr ratios range from 0 7061 to 0 7078 diagenetically modified connate marine fluids have d and 18o values more positive than 35 and 0 respectively and have chlorinities generally comparable to seawater sr concentration are much higher than the meteoric group 16 198 mg l 1 although the 87 sr 86 sr ratios 0 7070 0 7081 are not distinctive mixed meteoric modified connate fluids have d 18o and chlorinity intermediate between the meteoric and modified connate groups sr concentrations are also intermediate between 16 and 22 mg l 1 but 87 sr 86 sr ratios 0 7080 0 7087 are generally more radiogenic than either the meteoric or modified connate groups all of the fluids have 87 sr 86 sr ratios comparable to or lower than tertiary seawater alteration of detrital plagioclase is the probable origin of the low isotopic ratios mass balance calculations based on the sr data suggest that essentially no transport of sr occurred during diagenesis of sandstones containing modified connate pore fluids while large amounts of sr have been transported out of meteoric reservoirs by fluid flow the chemically anomalous mixed meteoric modified connate fluids contain the most radiogenic strontium in the basin these fluids are spatially associated with major faults and may represent clay mineral dehydration waters which have been transported upward from greater depth these results suggest that the three types of fluids identified by fisher and boles represent three distinct mass transport regimes a largely stagnant deep basin system containing modified connate pore fluids an actively recharging meteoric system along the basin flanks and a third system restricted to the southern basin which may be characterized by largescale cross formational fluid flow rather than dilution by meteoric waters

the potential impact of green agendas on historic river landscapes numerical modelling of multiple weir removal in the derwent valley mills world heritage site uk the exploitation of river systems for power and navigation has commonly been achieved through the installation of a variety of in channel obstacles of which weirs in britain are amongst the most common in the uk the historic value of many of these features is recognised by planning designations and protection more commonly associated with historic buildings and other major monuments their construction particularly in the north and west of britain has often been associated with industries such as textiles chemicals and mining which have polluted waterways with heavy metals and other contaminants the construction of weirs altered local channel gradients resulting in sedimentation upstream with the potential as well for elevated levels of contamination in sediments deposited there for centuries these weirs have remained largely undisturbed but as a result of the growth in hydropower and the drive to improve water quality under the european union s water framework directive these structures are under increasing pressure to be modified or removed altogether at present weir modifications appear to be considered largely on an individual basis with little focus on the wider impacts this might have on valley floor environments using a numerical modelling approach this paper simulates the removal of major weirs along a 24 km stretch of the river derwent derbyshire uk designated as a unesco world heritage site the results suggest that although removal would not result in significant changes to the valley morphology localised erosion would occur upstream of structures as the river readjusts its base level to new boundary conditions modelling indicates that sediment would also be evacuated away from the study area in the context of the derwent valley this raises the potential for the remobilisation of contaminants legacy sediments within the wider floodplain system which could have detrimental long term health and environmental implications for the river system worldwide rivers have a common association with industry being the focus of settlement and development since the earliest civilisations with channel engineering a common practice therefore the conceptual issues raised by this study have global resonance and are particularly important where heritage protection is less robust and structures can be removed with little consideration of the environmental consequences