back arc with frontal arc component origin of triassic karmutsen basalt british columbia canada the largely basaltic 4 5 6 2 km thick middle to upper triassic karmutsen formation is a prominent part of the wrangellian sequence twelve analyses of major and minor elements of representative samples of pillowed and massive basalt flows and sills from queen charlotte and vancouver islands are ferrotholeiites that show a range of 10 2 3 8 mgo as normalized h2o and co2 free and related increases in tio2 1 0 2 5 zr 43 147 ppm and nb 5 16 ppm other elemental abundances are not related simply to mgo distinct groupings are evident in al2o3 na2o and cr but considerable scatter is present in feo feo 0 9fe2o3 and cao some of the variation is attributed to alteration during low rank metamorphism or by seawater including variation of ba rb sr and cu but high field strength elements sc ti y zr and nb as well as cr ni cu and rare earth elements ree s were relatively immobile ree s show chondrite normalized patterns ranging from light ree depleted to moderately light ree enriched on eleven discriminant plots these analyses fall largely into or across fields of within plate basalt wip normal or enriched mid ocean ridge tholeiite morb and island arc tholeiite iat karmutsen basalts are chemically identical to the stratigraphically equivalent nikolai greenstone of southern alaska and yukon territory these data and the fact that the karmutsen rests on sicker group island arc rocks of paleozoic age suggest to us that 1 1 the basal arc after minor carbonate shale deposition underwent near axial back arc rifting as e g the mariana arc rifted at different times 2 2 the karmutsen basalts were erupted along this rift or basin as arc rift tholeiitite and 3 3 after subsequent deposition of carbonates and other rocks and jurassic magmatism a large fragment of this basalt sediment covered island arc was accreted to north america as wrangellia the major and minor elemental abundances of karmutsen basalt is modeled by first mixing primitive arc magma with enriched basaltic liquid derived either from garnet peridotite or metasomatized mantle followed by fractionation of olivine pyroxenes plagioclase and spinel

isotopic evidence of holocene climatic change in the san juan mountains colorado abstract the d of cellulose from 14c dated wood collected in the san juan mountains of southwestern colorado decreased by about 45 from 9600 to 3100 yr b p and an additional 25 to the present the wood samples are from trees that grew above present day tree line and reflect a time of warmer average summer temperatures these changes in d are interpreted to indicate a major change during the holocene in the sources of moisture in the seasonality of precipitation or in both

lower timberline in central colorado during the past 15 000 yr a 15 000 yr paleoenvironmental record at the elevation of lower timberline in central colorado suggests two major paleoclimatic changes during that interval 1 at 10 000 yr b p from cool moist conditions to warm moist conditions and 2 at 4 000 yr b p to warm dry conditions this sequence can be interpreted as a shift from precipitation predominantly originating from pacific winter storms before 10 000 yr b p to a predominantly monsoonal type regime lasting until 4 000 yr b p to the present pattern contemporaneity of higher upper timberline and lower lower timberline during the 10 000 to 4 000 yr b p interval is not contradictory but a result of changes in those circulation patterns

post glacial range of variability in the conejos river valley southern colorado usa fluvial response to climate change and sediment supply effective river management strategies require an understanding of how fluvial processes vary both spatially and temporally here we examine the natural range of variability in the conejos river valley southern colorado through documentation of terrace morphostratigraphic and sedimentological characteristics as well as through investigation of sediment contributions from headwaters hillslopes and tributary streams additionally soil development and radiocarbon ages together with local and regional paleoclimate reconstructions were used to infer the range of processes acting in this system since de glaciation the conejos river has fluctuated between episodes of bedrock strath formation aggradation and vertical incision morphostratigraphic relationships soil development and radiocarbon ages enable us to propose a chronology for periods of alluvial deposition around 8 9 7 6 ka 5 5 ka and from 3 5 to 1 1 ka separated by intervals of fluvial incision we infer potential forcing mechanisms by utilizing multiple working hypotheses specifically we discuss the potential for increases in sediment supply during periods of 1 para glacial adjustment 2 climatic cooling 3 increased frequency of climate change and 4 increased fire frequency or severity we also consider the effects of changes in stream discharge and extreme storm occurrence we conclude that combinations of these processes operating at different times have contributed to sediment mobilization since de glaciation stream and landform morphology also varies longitudinally due to the influence of remnant glacial topography in particular valley bottom overdeepening at tributary junctions has resulted in incision and strath formation into unlithified glacial deposits i e fill cut terraces rather than bedrock in some reaches overall the conejos fluvial system has varied significantly both temporally and spatially since de glaciation and appears to be sensitive to changes in sediment supply related to holocene scale climate fluctuations this natural range of variability must therefore be a key consideration in any future stream management policies copyright 2012 john wiley sons ltd

rapid incision of a small coarse and steep fan delta in response to base level fall the case of nahal qedem the dead sea israel the dead sea has been continuously dropping 0 4 1 0 m yr 1 since the middle of the 20th century and thus provides a unique field laboratory for studying in real time the response of drainage systems to a non tectonic base level fall the aim of this work is to study the short term ongoing erosive response to a rapid base level drop in a small steep fronted erodible fan delta setting the work explores the controls of the steep qedem fan delta guided by its clinoform structure on its incision longitudinal profiles of the fan delta and of its entrenched channel were measured in the field sedimentary facies changes fluviatile shallow lacustrine and beach were followed along exposures the existence of large boulders provided an opportunity to examine the uncertain role of armouring and boulder flux on incision the field study was combined with digital elevation models dems that were extracted from pairs of overlapping aerial photos maps of erosion and deposition were prepared using a change detection algorithm the longitudinal profile of the entrenched channel was found to be steep and linear the outlet temporarily hangs elevated and ungraded above the retreating lake level indicating years without incision flow events which cause lags in response to the rapid lake level drop in spite of the large boulders the small drainage basin and precipitation volume over the basin of the qedem the recorded vertical incision rates in the unconsolidated sediments are as high as 0 8 m yr 1 i e similar to those of the largest wadis draining to the dead sea the steep front of the fan delta is suggested to be a main factor controlling the efficient incision a unique transport mechanism of rolling boulders following undercutting contributed to the entrenchment efficiency copyright 2010 john wiley sons ltd

cerro toledo rhyolite jemez volcanic field new mexico 40ar 39ar geochronology of eruptions between two caldera forming events the cerro toledo rhyolite comprises a group of domes and tephra which were erupted during the interval between two caldera forming ignimbrites the tshirege member and otowi member of the bandelier tuff in the jemez volcanic field new mexico to provide a chronologic framework for geochemical and isotopic studies on these rhyolites which record the evolution of the bandelier magma system during this interval a 40 ar 39 ar geochronology study was undertaken pumice from major pyroclastic fall deposits within the rhyolite tephra and samples from the rhyolite domes were dated as well as the stratigraphically bracketing bandelier tuff analyzed crystal populations range from being fairly homogeneous juvenile material to very heterogeneous mixed juvenile and xenocrystic assemblages in most cases dominant groups of juvenile sanidine crystals define 40 ar 39 ar ages which agree with stratigraphic constraints plagioclase analyses are distinctly more scattered and do not typically define reasonable ages the 40 ar 39 ar ages for the two members of the bandelier tuff yield an interval of 380 20 k y between these caldera forming eruptions during this interval nine major pyroclastic pumice units were deposited in the sections studied for which six yield isochron ages one a weighted mean age one a maximum age and one no reliable age due to lack of sanidine 40 ar 39 ar dates on pumice fall units within the cerro toledo rhyolite tephra indicate that eruptive activity occurred at 1 59 1 54 1 48 1 37 and 1 22 ma 40 ar 39 ar dating of cerro toledo rhyolite domes indicates these were erupted within the caldera at 1 54 1 45 1 38 1 34 and 1 27 ma the dates obtained indicate that eruptive activity occurred throughout the 380 k y interval between the two members of the bandelier tuff but suggest that eruptions producing both tephra and domes occurred during discrete intervals at ca 1 54 1 48 and 1 38 1 34 ma the interval from 1 34 to 1 38 ma was particularly active 7 of 18 units dated are these ages

paleoclimatic significance of δd and δ13c values in pinon pine needles from packrat middens spanning the last 40 000 years we compared two approaches to interpreting dd of cellulose nitrate in pinon pine needles pinus edulis preserved in packrat middens from central new mexico usa one approach was based on linear regression between modern dd values and climate parameters and the other on a deterministic isotope model modified from craig and gordon s terminal lake evaporation model that assumes steady state conditions and constant isotope effects one such effect the net biochemical fractionation factor was determined for a new species pinon pine regressions showed thatdd values in cellulose nitrate from annual cohorts of needles 1989 1996 were strongly correlated with growing season may august precipitation amount and d 13 c values in the same samples were correlated with june relative humidity the deterministic model reconstructed dd values of meteoric water used by plants after constraining relative humidity effects with d 13 c values growing season temperatures were estimated via modern correlations with dd values of meteoric water variations of this modeling approach have been applied to tree ring cellulose before but not to macrofossil cellulose and comparisons to empirical relationships have not been provided results from fossil pinon needles spanning the last40 000 years showed no significant trend in dd values of cellulose nitrate suggesting either no change in the amount of summer precipitation based on the transfer function or dd values of meteoric water or temperature based on the deterministic model however there were significant differences in d 13 c values and therefore relative humidity between pleistocene and holocene published by elsevier science b v

timberline fluctuations and late quaternary paleoclimates in the southern rocky mountains colorado pollen and plant macrofossils from eight sedimentary basins on the west slope of the colorado rocky mountains document fluctuations in upper and lower timberline since the latest pleistocene by tracking climatically sensitive forest boundaries the moisture controlled lower timberline and the temperature controlled upper timberline paleoclimatic estimates can be derived from modern temperature and precipitation lapse rates pollen data suggest that prior to 11 000 yr b p a subalpine forest dominated by picea spruce and pinus pine grew 300 700 m below its modern limit the inferred climate was 2 5 c cooler and had 7 16 cm greater precipitation than today abies fir increased in abundance in the subalpine forest around 11 000 yr b p probably in response to cooler conditions with increased winter snow pollen and plant macrofossil data demonstrate that from 9000 to 4000 yr b p the subalpine forest occupied a greater elevational range than it does today upper timberline was 270 m above its modern limit suggesting that mean annual and mean july temperatures were 1 2 c warmer than today intensification of the summer monsoon coupled with increased summer radiation between 9000 and 6000 yr b p raised mean annual precipitation by 8 11 cm and allowed the lower limit of the subalpine and montane forests to descend to lower elevations the lower forest border began to retreat upslope between 6000 and 4000 yr b p in response to drier conditions and the upper timberline descended after 4000 yr b p when temperatures cooled to about 1 c warmer than today the modern climatic regime was established about 2000 yr b p when the summer precipitation maxima of the early and middle holocene were balanced by increased winter precipitation

seismic attributes add a new dimension to prospect evaluation and geomorphology offshore malaysia abstract the malay basin is a mature tertiary extensional basin with a later inversion regime in the late miocene the general geology is simple layer cake seismically with some compressive anticlinal inversion structures the borneo basin on the other hand is tectonically complex with steep dips overthrust and complex faulting the rocks are unconsolidated and geophysical techniques such as amplitude and other attributes should work well in early years seismic interpretation was based mostly on mapping structures the advent of avo and inversion technologies and pioneering geophysical work brought about increased usage of seismic attributes solving various problems of geologic interpretation in southeast asia concentrated efforts since 2000 in seismic data acquisition and processing have resulted in significant improvement in data quality and hence success of attribute application seismic imaging and attributes meet challenges such as 1 inversion structural plays in the malay basin 2

discriminating lithology and pore fill in hydrocarbon prediction from seismic elastic inversion using absorption attributes abstract separation of lithology from pore fill remains a daunting task even if using elastic inversion this is one of the unsolved problems for hydrocarbon prediction in malaysian basins because of complexities coupled with lithologic trends and fluid responses which produce an ambiguity due to equivalences we address this problem and propose a unique transformation in which decoupling can be achieved from the output of a constrained elastic inversion a relationship of vp vs and new attributes sqp and sqs related to attenuation by linking through rock physics can be derived they are good proxies for gamma rays sqp and resistivity logs sqs and can clearly identify the zone of interest with hydrocarbon potential these attributes can also be used for petrophysical properties prediction with high accuracy this breakthrough would have a considerable effect on hydrocarbon prediction and lithology discrimination other than being a hydrocarbon and lithology indicator sqp and sqs can also potential

tectonic geomorphology of the sierra nacimiento traditional and new techniques in assessing long term landscape evolution in the southern rocky mountains mountain front morphology is used to assess the relative role that tectonic and or climatic processes play in shaping topography in the sierra nacimiento a laramide uplift in northern new mexico rates of fault offset 0 013 mm yr in the adjacent rio grande rift are an order of magnitude slower than locally calculated rates of fluvial incision 0 17 mm year and regional denudation 0 12 0 84 mm yr thus although quaternary fault offset may be locally important in increasing relief and driving fluvial incision it is subordinate to high rates of regional fluvial exhumation in defining the geomorphic expression of the mountain front the geomorphic youthfulness of the sierra nacimiento landscape is attributed to recent and rapid erosional exhumation facilitated by fluvial processes as streams have become increasingly well adjusted to structure and rock type repeated capture events throughout the quaternary have increased drainage basin area as stream networks have become well integrated to test the i

principles of avo crossplotting hydrocarbon related avo anomalies may show increasing or decreasing amplitude variation with offset conversely brine saturated background rocks may show increasing or decreasing avo

comparison of popular avo attributes avo inversion and calibrated avo predictions amplitude variation with offset techniques are used by exploration development and production teams to assist hydrocarbon identification in clastic depositional settings while exploration groups tend to use avo attributes for detection and risk quantification exploitation and production groups use avo attributes for reservoir characterization and even fluid front monitoring accurate geoscience and engineering reservoir charcterization parametrization improve prediction of hydrocarbon reserves and reservoir production it is therefore essential to understand which seismic attributes will best contribute to the characterization of the reservoir this paper focuses on the accuracy of avo attributes commonly used in reservoir characterization in particular the effectiveness of intercept gradient lambda mu rho and elastic impedance avo attributes and their ability to accurately predict reservoir extent are presented derivative avo attribute volumes that are caliabrated to well data are also compared it can be argued that these techniques are essentially the same because each attribute set comes from the measurement of avo across a velocity corrected cmp gather but some geoscientists prefer one attribute type to another or only have access to a certain attribute this paper examines methodology differences between the various avo attributes and more importantly compares the final reservoir description predicted by these attributes please note that looking for the best avo attribute for reservoir characterization does not mean that this attribute will be the sole seismological contribution to the reservoir parameterization for reservoir simulations rather it is a method to determine the best avo input if any to accompany other geophysical and geologic inputs to the modeling a data model with variable reservoir thicknesses was constructed using well log data from the middle miocene section on the northern continental shelf of the gulf of mexico a thin blocky sand encased by shales was selected as the reservoir this sand when gas saturated can be categorized as a class

radiocarbon dating of flood events katherine gorge northern territory australia radiocarbon analyses of organic materials provide accurate dating of flood events in the katherine gorge northern territory australia selected flood events in the period 1955 1980 can be very precisely dated essentially to the calendar year through the use of curves showing the time variation of anomalously high 14 c activity in the troposphere that was generated by nuclear testing conventional radiocarbon analysis of alluvial charcoal and organic litter is used to establish dates for the largest katherine river floods of the past several centuries the improved geochronologic techniques demonstrated here will help improve paleoflood hydrologic interpretations

the evolution of the shiwanghe river valley in response to the yellow river incision in the hukou area shaanxi china abstract tributary response to mainstream incision is an important landscape evolution process the objective of this study is to examine tributary valley evolution in response to mainstream incision the shiwanghe river a tributary of the yellow river in the hukou area was chosen for a case study the terraces and knickpoints of the shiwanghe river were investigated and correlated to those of the mainstream optically stimulated luminescence osl was applied to date fluvial terraces longitudinal profiles of river and terraces were used to analyze valley evolution the terrace sequence of the shiwanghe river near their confluence is almost identical to the yellow river terraces at the hukou area this suggests that terrace formations of the tributary and the mainstream are synchronous and influenced by similar factors but the formation age of the same tributary terrace varies from downstream to the upper reaches of the river valley for such terraces their formation should be controlled by knickpoint migration a sudden drop in base level caused by the yellow river incision would trigger the formation of a knickpoint in the tributary a new terrace would be formed as the knickpoint propagated upstream throughout the tributary valley due to the different erodibility of bedrock a set of interbedded sandstone and shale the major knickpoint would disassemble into a cluster of small ones during its propagation the age of terrace formation with various valley segments depends on knickpoint migration rate and distance from the confluence vertical incision of the yellow river results in knickpoint recession of its tributaries the migration rate of knickpoints was affected by climate lithologic variation and to some extent structural control

mapping of quaternary sediments in northeastern ontario using ground electromagnetic methods since 1985 the geological survey of canada has been evaluating the suitability of electromagnetic em methods for quaternary geologic mapping initially a variety of ground em instruments were tested at the val gagne ontario site the multifrequency horizontal loop equipment apex maxmin i was selected for transect surveys in the kapuskasing timmins area after interpretation of ground em results 70 holes were drilled in the area using rotasonic equipment a correlation of drilling logs and geophysical data shows that clay till and sand have distinct em responses a constrained inversion of the ground em data in which drilling information was used to fix the layer thicknesses yielded resistivity estimates for sediments encountered in boreholes the following average resistivities were obtained clay 47 m till 123 m sand 251 m the respective standard deviations were 7 35 and 70 m resistivities of clays and tills were also determined in the laboratory on drill core samples the r

weighted stacking for rock property estimation and detection of gas amplitude versus offset concepts can be used to generate weighted stacking schemes here called geo stack which can be used in an otherwise standard seismic data processing sequence to display information about rock properties the zoeppritz equations can be simplified and several different approximations appear in the literature they describe the variation of p wave reflection coefficients with the angle of incidence of a p wave as a function of the p wave velocities the s wave velocities and the densities above and below an interface using a smooth representative interval velocity model from boreholes or velocity analyses and assuming no dip the angle of incidence can be found as a function of time and offset by iterative ray tracing in particular the angle of incidence can be computed for each sample in a normal moveout corrected cmp gather the approximated zoeppritz equation can then be fitted to the amplitudes of all the traces at each time sample of the gather and certain rock properties can be estimated the estimation of the rock properties is achieved by the application of time and offset variant weights to the data samples before stacking the properties which can be displayed by geo stack are p wave reflectivity or true zero offset reflectivity s wave reflectivity and the reflectivity of p wave velocity divided by s wave velocity or pseudo poisson s ratio reflectivity if assumptions are made about the relation between p wave velocity and s wave velocity for water bearing clastic silicate rocks then it is possible to create a display which highlights the presence of gas

40ar 39ar age constraints for the jaramillo normal subchron and the matuyama brunhes geomagnetic boundary our mid pleistocene 4oar 39ar age recalibration of the geomagnetic polarity timescale is nearly in accord with the oxygen isotope climate record calibration of the astronomical timescale proposed by johnson 1982 and shackleton et al 1990 4oar 39ar ages of a normally magnetized rhyolite dome in the valles caldera northern mexico yielded a weighted mean age of 1 004 0 019 ma a k ar age of 0 909 0 019 ma for this rock by doell and dalrymple 1966 was the linchpin for the recognition and calibration of the jaramillo normal subchron jns other 4oar 39ar ages from the vailes caldera and 4oar 39ar ages of ivory coast tektites indicate that the jns began at about 1 11 ma and ended before 0 92 ma probably near 0 97 ma the matuyama brunhes boundary occurred between 0 79 ma and 0 76 ma on the basis of 4oar 39ar sanidine ages from 1 three reversely magnetized rhyolite domes of the valles caldera 0 793 0 018 ma 0 794 0 007 ma and 0 812 0 023 ma and pumice 0 789 0 006 ma from the reversely magnetized oldest toba tuff of sumatra and 2 pumice 0 764 0 005 ma and 0 757 0 009 ma from the lower and upper units of the normally magnetized bishop tuff the age of the boundary may be close to 0 77 ma as deduced from rates of sedimentation in ancient lake bonneville utah increasingly aware that the polarity of earth s magnetic field has changed repeatedly through geologic time and isotopic dating of these polarity reversals resulted in a geomagnetic polarity time scale gpts for the late cenozoic this combined paleomagnetic and isotopic research played a pivotal role in confirming plate tectonic theory glen 19821 which revolutionized the earth sciences continual refinement of isotopic ages which define the gpts has increased the usefulness of geomagnetic polarity reversals as marker hori zons in many types of geologic studies we present 4oar 39ar data and ages for some key volcanic units that support changes in the isotopic age chronology of the gpts using volcanic rocks erupted near the time of the geologically youngest two geomagnetic polarity reversals figure 1 the older of the two reversals originally called by doell and dalrymple 1966 the jaramillo event is now named the jaramillo normal subchron jns it is recorded in middle pleistocene rocks as a brief episode of normal polar ity within the late matuyama chron the younger of the two called the matuyama brunhes boundary mbb is regis tered in middle pleistocene rocks worldwide and consists of

dem analysis on longitudinal and transverse profiles of steep mountainous watersheds longitudinal and transverse characteristics of watersheds are fundamental to describe watershed topography only a limited number of studies however have analyzed the characteristics of transverse profiles in watersheds and almost no studies have examined longitudinal and transverse profiles at the same time how transverse profiles change within a watershed and how longitudinal and transverse characteristics of watersheds are related remain to be examined to address these issues this study employs dems gis and computer programming techniques to acquire a series of longitudinal and transverse profiles of watersheds basic morphometric parameters representing the shape of these profiles were analyzed methods to classify the profiles and to identify points where the morphometric characteristics change abruptly were also developed these methods were then applied to severely dissected steep watersheds in the japanese alps the results show that spatial change in transverse characteristics reflects two factors general topography of the watersheds and local differences in channel development the form of the transverse profiles is also affected by erosion processes that create mature v shaped valleys with a characteristic slope angle the longitudinal and transverse profiles play different roles in determining watershed topography and the overall longitudinal slope exerts a major influence on the mean watershed slope the discontinuity of the longitudinal and transverse profiles however tends to occur at the same location which may reflect the occurrence of knickzones and their influences on the development of valley side slopes

aminostratigraphic relations and age of quaternary deposits northern espanola basin new mexico abstract amino acid ratios of gastropods provide a useful basis for correlation and approximate dating of middle to late quaternary fluvial deposits from the northern espanola basin new mexico sparsely fossiliferous slackwater deposits in the rio chama rio grande floodplain were buried episodically by piedmont alluvium during periods of climatic change as the axial river system cut down 120 m during the past 620 000 yr alloisoleucine isoleucine alle ile ratios in the total hydrolysate and free fraction of amino acids in succinea and vallonia are strongly correlated with elevation ratios in succinea range from 0 01 to 0 79 in the total hydrolysate and from 0 00 to 1 15 in the free fraction for deposits that range in age from modern to 620 000 yr old amino acid ratios are tightly clustered for deposits that contain the 620 000 yr old lava creek b tephra layer demonstrating their utility for correlation and providing a calibration point for a local dating curve two 14c ages from younger deposits and limiting ages for erosion surfaces that lie above gastropod bearing units tend to support the validity of much of the curve combining the dating curve with the geologic constraints suggests that aggradation events separated by episodes of net incision occurred at about 620 000 310 000 70 000 170 000 40 000 95 000 15 000 yr ago after 19 000 yr ago and during two minor periods between 80 000 and 25 000 yr ago

a holocene climatic record for the sonoran desert from pollen analysis of montezuma well arizona usa abstract pollen and macrofossil analyses of a radiocarbon dated core 1125 cm long from montezuma well elev 1125 m yavapai county arizona provide a record of summer precipitation similar to that of other monsoonal regions of the world precipitation was least from 4000 to 5000 yr b p and generally was greater than today before 8400 yr b p during the early holocene moist period oak and grass pollen are abundant and the best modern analogs are within the arizona monsoon boundary so increased summer precipitation is indicated climatic parameters are estimated with the technique of best modern analogs for fossil samples temperature was highest ca 3400 and 5700 yr b p and generally was cooler than today before 6800 yr b p brief cold intervals in the holocene match periods of global cooling and of positive 14 c and 10 be anomalies

stream incision and terrace development in frijoles canyon bandelier national monument new mexico and the influence of lithology and climate abstract the record of stream incision and terrace development in frijoles canyon nm was investigated to examine the controls on channel evolution in this region frijoles canyon developed after deposition of the voluminous ignimbrites of the tshirege member of the bandelier tuff at ca 1 22 ma which provides excellent temporal constraints on canyon evolution base level fall along the rio grande the master drainage in the region contributed to initial incision of the stream development of a major knickpoint in basalt near the rio grande however has effectively isolated most of the stream channel from direct effects of this base level change since the early or middle pleistocene late quaternary evolution of the channel has included development of strath and fill terraces that record the effects of climatic variations and local lithologic variations within the tuff on channel processes a fill terrace underlain by up to 13 m of coarse gravelly alluvium records significant aggradation in the early to middle holocene following a major regional climate change aggradation probably resulted from large increases in sediment supply in the holocene relative to the late pleistocene which was perhaps related to variations in intense summer rains rapid incision in the middle to late holocene has stranded the underlying strath up to 21 m above the modern channel and local rates of incision of up to 4 m ka are more than 10 times the average rates since 1 22 ma holocene incision displays great spatial variability associated with local lithologic variations and results in a stream profile that has evolved rapidly in the last 10 000 years the high rates of incision occur where easily eroded nonwelded tuff is exposed in the canyon bottom whereas a more resistant vapor phase altered tuff unit upstream has impeded incision incision may also have been affected by migration of knickpoints within the tuff paired strath terraces record periods of local base level stability and lateral erosion that were terminated by episodes of downcutting the downcutting was probably controlled by rare high magnitude floods capable of stripping the pervasive gravel armor and exposing nonwelded tuff beneath the stream bed no tectonic influence on late quaternary terrace development or stream incision has been recognized despite frijoles canyon being crossed by the pajarito fault zone a major bounding structure of the rio grande rift instead climatic influences on sediment supply and flood characteristics mediated by lithologic variations in the canyon bottom have controlled late quaternary stream profile evolution

geology structure and tectonics of the pajarito fault zone in the espanola basin of the rio grande rift new mexico the pajarito fault zone forms the western border of the velarde graben the presently active central subbasin of the espanola basin section of the rio grande rift in north central new mexico the fault zone is a north northeast trending zone of predominantly down to the east faults that cut miocene to pliocene volcanic rocks along the eastern flank of the jemez mountains where the fault zone cuts the 1 1 m y old tshirege member of the bandelier tuff it has produced a steep 50 to 100 m high fault scarp the total displacement across the fault zone during its 5 m y history is between 200 and 600 m rates of displacement for the time periods 0 5 0 1 1 and 1 1 5 m y ago range from 0 02 to 0 136 mm yr abrupt facies changes between older volcanics and volcaniclastic sediments of the jemez mountains appear to have controlled the local position trend and character of the pajarito fault zone the fault zone bows and or steps eastward where two large volcanic complexes are present but is found farther west in between and at either end of the volcanic complexes one complex was sufficiently massive to interfere with the development of the velarde graben slickensides on mesoscopic faults in the tshirege member of the bandelier tuff indicate that the pajarito fault zone has undergone extension in two directions during the past 1 1 m y approximately parallel and perpendicular to the local trend of the fault zone these directions indicate that the pajarito fault zone has reoriented the regional minimum and intermediate stress directions to perpendicular and parallel respectively to the local trend of the fault zone and that both minimum and intermediate stress directions are tensional a tectonic history for the pajarito fault zone area of the espanola basin begins with relatively stable accumulation of prerift and synrift sediments from eocene to oligocene time sedimentation concomitant with faulting unrelated to the pajarito fault zone filled deep central depressions within the espanola basin this faulting ceased prior to the end of the filling of the basin around 10 m y ago in the local area jemez mountain volcanism began about this time before movement along the western margin border faults of the espanola basin caused west tilting of old volcanics and sediments about 7 5 m y ago volcanism continued under relatively stable conditions until 5 m y ago at this time the pajarito fault zone and velarde graben formed faulting has continued to the present localized along this central subbasin

differentiating pleistocene tectonically driven and climate related fluvial incision the sanggan river datong basin north china the sanggan river is an alluvial river flowing through a graben basin system of the northern shanxi rift zone north china during pleistocene times the river reach in the datong basin was affected successively by various external variables such as invasion by basaltic flow along valley faulting and climatic change therefore it provides excellent constraints for differentiating tectonically driven and climate related fluvial incision in the context of tectonic subsidence based on equilibrium profile analysis k ar dating of basalts 0 74 0 41 ma studies of the river terrace and of stream action history we present a conceptual model for differentiating fault driven and climate related fluvial incision by the river the results show that fluvial incision induced by tectonic lowering of the base level due to along valley movement on the sanggan river fault is equal to fault displacement the amount of post basalt fluvial incision of the reach upstream from the lava dam is 23 to 25 m of which the fault driven and climate related incisions are 15 m and 8 to 10 m respectively the former predominating over the latter the total amount of incision in the lava dam reach is 40 to 47 m of which the fault driven and climate related incisions are 10 m and 30 37 m respectively here the latter is predominant over the former since 0 41 0 10 ma the rate of fluvial incision of the lava dam reach of the river has reached 98 115 m ma which is 1 5 2 times as great as those of the reaches upstream and downstream from the lava dam the higher rate of fluvial incision can be attributed to high water levels supplied by the onset and maintenance of backwater conditions in the reach upstream from the lava dam due to the long period of warm and humid climate in this region plucking abrasion and knickpoint migration appear to be the primary erosional processes in the lava dam reach

flood alluviation and entrenchment holocene valley floor development and transformation in the british uplands the morphology sedimentary properties and sequence of recent coarse grained flood deposits and earlier holocene alluvial fills were investigated in thinhope burn a small 12 km2 catchment in the northern pennine uplands northern england twenty one large flood events are recorded by distinctive cobble boulder bars sheets and splays and boulder berms and lobes lichenometric analysis showed that all but one of these floods dated from the mid eighteenth century the timing of large floods between 1766 and 1960 corresponds with major hydroclimatic trends evident in northern britain and northwest europe over this period discharge estimates suggest that flood magnitudes have decreased since the mid eighteenth century channel and flood plain metamorphosis in late roman times and in the eighteenth century following major valley floor entrenchment locally as much as 8 m would appear to have been caused by increased runoff and flood magnitude this was linked to a shift to a wetter climate with flow augmented by iron age and roman woodland clearance and drainage of the catchment in more recent times results from this study suggest that current models of longer term holocene and pleistocene valley floor development in the british uplands may need to be re evaluated

observations on the role of lithology in strath terrace formation and bedrock channel width field observations from western washington and eastern tibet indicate a strong lithologic influence on strath terrace formation and highlight the response of bedrock channel width to spatial gradients in bedrock erodibility and or rock uplift rates measurements of local bedrock bed and bank erosion rates together with observations of the role of weathering processes on erosion of siltstones and sandstones illustrate a mechanism that underlies a conceptual model that predicts a strong lithological control on strath terrace formation direct measurements of bedrock erosion rates in lithologies susceptible to accelerated erosion upon sub aerial exposure show that lateral rates of bedrock bank erosion can substantially exceed vertical incision below the perennial flow level due to an asymmetry in erodibility between perennially submerged rock and rock exposed to cyclic wetting and drying on bedrock channel walls under such conditions the rapid weathering mediated lowering of bedrock exposed above baseflow promotes development of a beveled bedrock platform that could become a strath terrace upon abandonment in contrast to previous studies channel widths measured across a substantial gradient in lithology slope and long term erosion rates in eastern tibet do not follow conventional relations where channel width scales as a power law function of drainage area instead as they flow across a zone of rapid uplift these channels systematically narrow relative to the predicted width extrapolated from traditional power law relations field studies from a wide range of geological settings and lithologies support the interpretation that in general strath terraces tend to be more extensive in rivers flowing over weak sedimentary rock and tend to be poorly developed and or preserved where rivers flow over hard erosion resistant rock

bedrock incision rock uplift and threshold hillslopes in the northwestern himalayas the topography of tectonically active mountain ranges reflects a poorly understood competition between bedrock uplift and erosion dating of abandoned river cut surfaces in the northwestern himalayas reveals that the indus river incises through the bedrock at extremely high rates 2 12 mm yr 1 in the surrounding mountains the average angles of hillslopes are steep and essentially independent of erosion rate suggesting control by a common threshold process in this rapidly deforming region an equilibrium is maintained between bedrock uplift and river incision with landsliding allowing hillslopes to adjust efficiently to rapid river down cutting

a middle jurassic to early tertiary andean sierran arc model for the coast belt of british columbia regional tectonic features of the western canadian cordillera can be interpreted in terms of middle jurassic accretion of a single composite superterrane stikinia wrangellia alexander to ancestral north america closure of the intervening cache creek bridge river ocean moved the continental edge to a new position west of the accreted superterrane the coast belt is primarily a succession of superimposed middle jurassic to early tertiary magmatic arcs related to prolonged subduction of pacific ocean lithosphere beneath the new north american margin discrete magmatic pulses separated by lulls or periods of relative quiescence successively overprinted the new margin the insular and intermontane superterranes previously viewed as widely separate entities prior to mid cretaceous time were already amalgamated before an initial middle jurassic overprint produced an ancestral coast belt late jurassic to early cretaceous rift related marine basins mid to late cretaceous compressional structures and early tertiary extensional features coincident with the coast belt are subsidiary intraplate attributes that reflect external adjustments in plate motions within a primary subduction related andean magmatic arc

integrated geophysics for mineral exploration in drift covered volcanic terrains examples from northern vancouver island canada known mineral occurrences in northern vancouver island are typically hosted in volcanic units of the bonanza group at a local scale the mineralization is associated with advanced argillic bedrock alteration and is often intimately related to porphyry intrusions on a larger scale faults are thought to exert the most significant control on the distribution of mineralized host rocks poor exposures and a complex glacial history limit the use of traditional methods of geological mapping and mineral exploration in this region and to date geophysical methods have been under utilized here we present findings from four standard geophysical gravity magnetics electromagnetics and seismic refraction methods recently deployed here to elucidate the subsurface geology as well as to identify new targets for base metal exploration results at two different sites show that the integrated interpretation of geophysical data constrained by physical rock property measurements yields detailed images of the subsurface at a fraction of the cost of drilling at one site east of rupert inlet the final subsurface model shows that the bonanza group is not nearly as extensive as previously presumed an extension of the holberg fault is identified some 50 km east of the visibly mapped outcrop and an extensive zone of alteration around the fault is recognized furthermore a number of the methods provide support for the existence of a porphyry dike at this site at the second site north of rupert inlet magnetic and electromagnetic data prove effective at mapping alteration and locating shear zones beneath a relatively thin drift cover together these results help outline a strategy for exploration in drift covered terrains and show that a redirection of exploration effort is warranted in the case of northern vancouver island

late quaternary sediments and geomorphic history of northern vancouver island british columbia materials from two glacial intervals and one nonglacial interval have been identified on northern vancouver island british columbia the oldest pleistocene unit termed older drift consists of glaciomarine silt and clay 38 000 years bp in age that overlie a till that has only been recorded in well logs older drift is tentatively correlated with dashwood drift of the semiahmoo glaciation early wisconsin or older no sediments of the succeeding olympia nonglacial interval mid wisconsin have been found in the area it is thought that this interval was characterized by a period of degradation in which olympia age sediments were deposited in transient sedimentary environments and subsequently eroded in part during the fraser glaciation late wisconsin the youngest pleistocene unit termed port mcneill drift includes advance deposits till and deglacial sediments all deposited during fraser glaciation ice of this glaciation did not cover most of northern vancouver island until after 20 600

the evolution towards steady state erosion in a soil mantled drainage basin semi quantitative data from a transient landscape in the swiss alps abstract this paper presents semi quantitative data concerning the pattern of erosion under present day humid climatic conditions for a ca 10 km2 large soil mantled drainage basin located in the northern foothills of the central swiss alps the present day pattern of erosion was presumably initiated at ca 15 ka at the time when the last glacial period was terminated present day erosional processes are characterized by fluvial dissection and hillslope mass failure resulting in linear geomorphic features as fluvial dissection proceeds the rivers tend to adapt steady state longitudinal stream profiles in this case the stream profiles display power law relationships between channel gradient and upstream size of the drainage basin our study shows that establishment of steady state longitudinal stream profiles requires a balanced mass flux between processes on hillslopes and in channels this situation is interpreted for locations where the downslope flux of mass on hillslopes does not exceed the erosional potential and the transport capacity in channels consequently the development of steady state drainage systems appears to be controlled by erosional processes in channels as they dictate the elevation of the base level in contrast systems that are at transient states of longitudinal stream profile development very often display non balanced mass flux between processes in channels and on hillslopes specifically low mechanical strength of the bedrock e g glacial till marls results in a downslope flux of mass that exceeds the transport capacity and the erosional potential in the channel causing the elevation of the channel floor to increase in this case processes on hillslopes are not necessarily coupled with erosion in channels and appear to control the evolution of the drainage basin for a limited time interval besides interpretations of controls on surface erosion this paper also estimates post glacial sediment yield for the analyzed drainage basin these estimates are achieved by determination of the difference between the elevation of the glacial and the present day surface the data show that ca 30 of the analyzed drainage basin experiences present day surface erosion furthermore average post glacial sediment yield measures ca 4 6 m ka if the post glacial volume of sediment is related to the area that has experienced surface erosion or ca 1 4 m ka if it is related to the whole drainage basin interestingly the erosional efficiency appears to be significantly higher for systems that display steady state stream profiles than for transient rivers

a new seismic attribute for ambiguity reduction in hydrocarbon prediction hydrocarbon prediction from seismic amplitude and amplitude versus offset is a daunting task amplitude interpretation is ambiguous due to the effects of lithology and pore fluid in this paper we propose a new attribute j based on a gassmann biot fluid substitution to reduce ambiguity constrained by seismic and rock physics the j attribute has good ability to detect hydrocarbons from seismic data there are currently many attributes for hydrocarbon prediction among the existing attributes far minus near times far and fluid factor are commonly used in this paper the effectiveness of these two existing attributes was compared with the new attribute numerical modelling was used to test the new attribute j and to compare j with the two existing attributes the results showed that the j attribute can predict the existence of hydrocarbon in different porosity scenarios with less ambiguity than the other two attributes tests conducted with real seismic data demonstrated the effectiveness of the j attribute the j attribute has performed well in scenarios in which the other two attributes gave inaccurate predictions the proposed attribute j is fast and simple and it could be used as a first step in hydrocarbon analysis for exploration

a new fluid factor and its application using a deep learning approach abstract amplitude interpretation for hydrocarbon prediction is an important task in the oil and gas industry seismic amplitude is dominated by porosity the volume of clay pore filled fluid type and lithology a few seismic attributes are proposed to predict the existence of hydrocarbon this paper proposes a new fluid factor by adding a correct item based on the j attribute the algorithm is verified through stochastic monte carlo modelling that contains various rock physical properties of sand and shale both gas and oil responses are separated by the new fluid factor furthermore an approach based on the neural network model is trained using the deep learning method to predict the new fluid factor the confusion matrix shows that this model performs well this model allows the application of the new fluid factor in the seismic data in this study the marmousi ii data set is used to examine the performance of the new fluid factor and the result is good most hydrocarbon reservoirs are identified in the shale sandstone sequences the combination of deep learning and the new fluid factor provides a more accurate way for hydrocarbon prediction

alluvial terrace preservation in the wet tropics northeast queensland australia alluvial terraces provide a record of aggradation and incision and are studied to understand river response to changes in climate tectonic activity sea level and factors internal to the river system terraces form in all climatic regions and in a range of geomorphic settings however relatively few studies have been undertaken in tectonically stable settings in the tropics the preservation of alluvial terraces in a valley is driven by lateral channel adjustments vertical incision aggradation and channel stability processes that can be further understood through examining catchment force resistance frameworks this study maps and classifies terraces using soil type surface elevation sedimentology and optically stimulated luminescence dating across five tropical catchments in northeast queensland australia this allowed for the identification of two terraces across the study catchments t1 t2 the t1 terrace was abandoned 13 9 ka with its subsequent removal occurring until 7 4 ka abandonment of the t2 terrace occurred 4 9 ka with removal occurring until 1 2 ka differences in the spatial preservation of these terraces were described using an index of terrace preservation tpi assessments of terrace remnant configuration highlighted three main types of terraces paired unpaired and disconnected indicating the importance of different processes driving preservation regional scale variability in tpi was not strongly correlated with catchment scale surrogate variables for drivers of terrace erosion and resistance however catchment specific relationships between tpi and erosion resistance variables were evident and are used here to explain the dominant processes driving preservation in these tropical settings this study provides an important insight into terrace preservation in the tectonically stable humid tropics and provides a framework for future research linking the timing of fluvial response to palaeoclimate change

geophysical issues and challenges in malay and adjacent basins from an e p perspective malay basin a northward trending pull apart extensional rift basin formed during the late eocene early oligocene and then underwent thermal subsidence and sedimentation during the early miocene reorientation of regional stress fields during the mid miocene caused structural inversion resulting in east west anticlines and half grabens

a 35 000 year vegetation and climate history from potato lake mogollon rim arizona abstract a new record from potato lake central arizona details vegetation and climate changes since the mid wisconsin for the southern colorado plateau recovery of a longer record discrimination of pine pollen to species groups and identification of macrofossil remains extend whiteside s 1965 original study during the mid wisconsin ca 35 000 21 000 yr b p a mixed forest of engelmann spruce picea engelmannii and other conifers grew at the site suggesting a minimum elevational vegetation depression of ca 460 m summer temperatures were as much as 5 c cooler than today during the late wisconsin ca 21 000 10 400 yr b p even cooler temperatures 7 c colder than today ca 800 m depression allowed engelmann spruce alone to predominate warming by ca 10 400 yr b p led to the establishment of the modern ponderosa pine pinus ponderosa forest thus the mid wisconsin was not warm enough to support ponderosa pine forests in regions where the species predominates today climatic estimates presented here are consistent with other lines of evidence suggesting a cool and or wet mid wisconsin and a cold and or wet late wisconsin climate for much of the southwest potato lake was almost completely dry during the mid holocene but lake levels increased to near modern conditions by ca 3000 yr b p

relationships between compressional wave and shear wave velocities in clastic silicate rocks new velocity data in addition to literature data derived from sonic log seismic and laboratory measurements are analyzed for clastic silicate rocks these data demonstrate simple systematic relationships between compressional and shear wave velocities for water saturated clastic silicate rocks shear wave veloci ty is approximately linearly related to compressional wave velocity and the compressional to shear velocity ratio decreases with increasing compressional velocity laboratory data for dry sandstones indicate a nearly constant compressional to shear velocity ratio with rigidity approximately equal to bulk modulus ideal models for regular packings of spheres and cracked solids exhibit behavior similar to the observed water saturated and dry trends for dry rigidity equal to dry bulk modulus gassmann s equations predict velocities in close agreement with data from the water saturated

stream terrace genesis implications for soil development genesis of three distinct types of stream terraces can be understood through application of the concepts of tectonically induced downcutting base level of erosion complex response threshold of critical power diachronous and synchronous response times and static and dynamic equilibrium climatic and tectonic stream terraces are major terraces below which flights of minor complex response degradation terraces can form these three types of terraces can be summarized by describing a downcutting aggradation renewed downcutting sequence for streams with gravell bedload by tectonically induced downcutting streams degrade to achieve and maintain a dynamic equilibrium longitudinal profile at the base level of erosion lateral erosion bevels bedrock beneath active channels to create major straths that are the fundamental tectonic stream terrace landform aggradation events record brief reversals of long term tectonically induced downcutting because they raise active channels they may be considered as major the result of climatic perturbations or minor the result of complex response model types of perturbations climatically controlled aggradation followed by degradation leaves an aggradation surface this type of fill terrace tread is the fundamental climatic stream terrace landform aggradation surfaces may be buried by subsequent episodes of deposition unless intervening tectonically induced downcutting is sufficient for younger aggradation surfaces to form below older surfaces raising of the active channel by either tectonic uplift or by climatically induced aggradation provides the vertical space for degradation terraces to form first in alluvial fill and then in underlying bedrock along tectonically active streams these are complex response terraces because they result from interactions of dependent variables within a given fluvial system pauses in degradation to a new base level of erosion and or minor episodes of backfilling lead to formation of complex response fill cut and strath or of fill terraces fill cut terraces are formed in alluvium they are complex response terraces because they are higher than the base level of erosion good exposures and dating are needed to distinguish static equilibrium complex response minor strath terraces from dynamic equilibrium tectonic major straths strath terraces may be regarded as complex response terraces where degradation rates between times terrace tread formation exceed the long term uplift rate for the reach based on ages and positions of tectonic terraces late quaternary global climatic changes control aggradation events and even the times of cutting of major tectonic straths because the base level of erosion can not be attained during times of climatically driven aggradation degradation events most terrace soils form on treads of climatic and complex response terraces aggradation surfaces may provide an ideal flight of terraces on which to study a soils chronosequence each aggradation event is recorded by a single relict soil where tectonically induced downcutting is sufficient to provide clear altitudinal separation of the terrace treads multiple paleosols are typical of tectonically stable regions where younger aggradation events spread alluvium over treads of older climatic terraces pedons on a climatic terrace in a small fluvial system commonly are roughly synchronous variations of soil properties that can be attributed to temporal differences will be minor compared to altitudinally controlled climatic factors climatic terraces of adjacent watersheds also should be roughly synchronous correlatable variations of soil properties that can be attributed to temporal differences will be minor compared to lithologic and climatic factors between different watersheds such generalizations may not apply to basins with sufficient relief that geomorphic responses to climatic changes occur at different and overlapping times and to large rivers whose widely separated reaches are characterized by different response times to climatic perturbations soils on climatic terraces of distant watershedswill not be synchronous if their respective aggradation events occur during full glacial times and interglacial times soils on some complex response terraces may be diachronous within a given fluvial system and typically are diachronous between watersheds

late cenozoic rates of erosion in the western espanola basin new mexico evidence from geologic dating of erosion surfaces erosion surfaces in the espanola basin formed before 350 ka and between 350 and 240 240 and 130 and 130 and 80 ka probably in response to climatic change and regional uplift the surfaces are cut on miocene pliocene and pleistocene deposits and range from about 200 m to 15 m above the present rio chama rio grande system periods when the surfaces formed were dated using varnish cation ratios from exposed clasts the mass of soil carbonate and amino acid ratios in pleistocene gastropods from underlying deposits thorium uranium ages from soil carbonate were used to calibrate a local curve for varnish cation ratios the range in age determined for a given surface although derived from different dating techniques implies that parts of the surface were sites of erosion or aggradation after the surface formed from 1 1 ma to present denudation rates averaged 10 cm 1 000 yr from weakly lithified sandstone less than 7 cm 1 000 yr from indurated tuff and boulder gravel and about 4 cm 1 000 yr from tuff and basalt erosion surfaces were preserved as upland benches and terraces by stream incision during periods of pluvial climate and regional uplift but our data do not permit clear separation of the two causes

climatic influence on sedimentology and geomorphology of the rio ramis valley peru abstract fluctuations in regional precipitation and in base level the level of lake titicaca trigger changes in fluvial erosion and deposition in the largest tributary valley of lake titicaca the rio ramis peru relationships between fluvial sedimentation and terrace formation demonstrate that large scale aggradational and downcutting events are associated with specific regional climatic events that have been previously documented in the lake titicaca basin and elsewhere on the altiplano five laterally extensive terrace tracts a through e are present within the valley downcutting of the ramis valley is correlative with base level lake titicaca level fall caused by a decrease in precipitation aggradation is correlative with base level rise during increasing precipitation sedimentary facies underlying the terraces record deposition in a large paleolake followed by deposition of both meandering and braided fluvial sediments the highest terrace in the valley e is underlain by a thick sequence of lacustrine strata that was deposited during an extremely wet period in the lake titicaca region that terminated at about 40 000 cal yr bp these lacustrine strata were subsequently downcut likely at a time of large drop in lake level resulting in a deeply incised valley the main phase of fluvial aggradation in the valley sediments underlying the d through b terraces was slow spanning about 25 000 years it occurred before during and after the last glacial maximum from before 35 140 790 cal yr bp until about 10 421 181 cal yr bp a time period that was mostly characterized in the lake titicaca basin by high precipitation rates and high base levels the aggradation resulted in almost 40 m of sediment accumulation in the valley and was followed by rapid about 2 000 years but episodic incision into the underlying fluvial sediments to form the c and b terraces as well as the erosional surface beneath the modern fill terrace a this erosional phase corresponded to several periods of local base level lake titicaca lowering between 10 241 181 and 1 668 76 cal yr bp the modern fill terrace has aggraded about 2 m above modern river level likely within the last 1 500 years

the neogene alert bay volcanic belt of northern vancouver island canada descending plate edge volcanism in the arc trench gap abstract the alert bay volcanic belt trends northeasterly across northern vancouver island coincident with the trace of the subducted juan de fuca explorer plate edge volcanism began in the west at brooks peninsula about 8 ma ago but occurred in most centers 3 5 1 ma ago there is a suggestion of eastward migration of activity and shift from basalt to dacite or rhyolite with time most of the volcanism was coincident with a time of rapid changes in the geometry of subduction as inferred from offshore magnetic patterns and with a hiatus in mainland cascade volcanic arc activity geometry and chronometry suggest this is a descending plate edge volcanic belt where disruption of steady state plate consumption patterns triggered magma genesis chemically the rocks are quite variable with divergent fractionation trends one trend resembles that of mull hebrides with a plagiophyric basalt of transitional alkaline subalkaline mildly tholeiitic and aluminous character which differentiated to clinopyroxene andesite and eventually to tholeiitic rhyolite and mildly tholeiitic calc alkaline dacite both of k poor magma type the other trend is like the cascades with aluminous aphyric calc alkaline basalt hornblende and or hypersthene andesite and k poor dacite this divergent character is also evident in ba rb nb and zr fractionation trends major and trace element discriminant diagrams generally identify the basalts as within plate types the 87 sr 86 sr isotope ratio is relatively low averaging 0 70325 and shows no trend with rock type or differentiation series oxygen in the entire suite is relatively heavy 18 o averaging 7 1 even the basalts are 18 o enriched oxygen shows no trend with degree of hydration rock type or series these isotopic and chemical data are compatible with minor crustal contamination of mafic primary magmas followed by fractional crystallization under different oxidation and hydration conditions

transient electromagnetic sounding for groundwater the feasibility of using the transient electromagnetic sounding ts or tdem method for groundwater exploration can be studied by means of numerical models as examples of its applicability to groundwater exploration we study four groundwater exploration problems 1 mapping of alluvial fill and gravel zones over bedrock 2 mapping of sand and gravel lenses in till 3 detection of salt or brackish water interfaces in freshwater aquifers and 4 determination of hydrostratigraphy these groundwater problems require determination of the depth to bedrock location of resistive high porosity zones associated with fresh water determination of formation resistivity to assess water quality and determination of lithology and geometry respectively the ts method is best suited for locating conductive targets and has very good vertical resolution unlike other sounding techniques where the receiver transmitter array must be expanded to sound more deeply the depth of investigation for the ts method is a

dem based identification of fluvial knickzones and its application to japanese mountain rivers stream gradients of mountain bedrock rivers in central japan were examined using gis and 50 m digital elevation models to discuss the distribution of knickzones the gradients are classified into local and trend types based on the measurement lengths the transition rate from the local to trend gradients i e the decreasing rate of gradient with increasing measurement length is then obtained as the indicator of relative steepness of a river segment which permits the objective identification of fluvial knickzones the identified knickzones occur widely in the study area and indicate that the knickzone is one of the common landforms in japanese mountain rivers the knickzones are more abundant in steep upstream reaches of the rivers subjected to active erosion and rapid rock uplift this suggests a hydraulic origin of the knickzones which is similar to step pool morphology but on a much larger scale some knickzones in piedmont areas can be on the other hand consistent with tectonic faulting at the mountain foot although some influences of volcanic activities on the formation of knickzones are observed regional lithology seems to exert a relatively weak influence on the abundance of knickzones knickzones are more consistent with other local mechanisms of fluvial erosion including reach scale processes

fire and alluvial chronology in yellowstone national park climatic and intrinsic controls on holocene geomorphic processes we employed a systemwide approach a large and robust set of radiocarbon ages and modern process analogs to interpret the holocene history of forest fire related sedimentation and overall alluvial activity in northeastern yellowstone national park debris flow and flood events following the 1988 fires provided facies models for interpreting the stratigraphic record of fire related sedimentation within valley side alluvial fans of soda butte creek fire related deposits make up approximately 30 of the late holocene fan alluvium fifty 14 c ages on fire related events cluster within the intervals of 3300 2900 2600 2400 2200 1800 and 1400 800 yr b p and suggest earlier episodes of large fires and fan aggradation around 7500 5500 and 4600 4000 yr b p a major pulse of fire related debris flow activity between 950 and 800 yr b p coincided with the height of the widely recognized medieval warm period ca a d 1050 1200 instrumental climate records over the last 100 yr in yellowstone imply that the intensity and interannual variability of summer precipitation are greater during warmer periods enhancing the potential for severe short term drought major forest fires and storm generated fan deposition along lower soda butte creek fill cut terrace treads were created by lateral migration of channels and accumulation of overbank sediments ca 8000 yr b p terrace level t1a 7000 5600 t1b 3100 2600 t2 2000 1300 t3 and post 800 yr b p t4 these periods coincide with overbank sedimentation on slough creek and the lamar river but alternate with intervals of fire related fan deposition implying a strong climatic control local paleoclimatic data suggest cooler effectively wetter conditions during terrace tread formation in warmer drier intervals reduced average runoff in axial streams results in meander belt narrowing concurrent channel incision may be caused by infrequent large floods greater resistance to downcutting however allowed fewer terraces to be formed along slough creek and the lamar river alluvial systems in northeastern yellowstone show a clear response to millennial scale climatic cycles wherein alluvial fans aggrade and prograde over flood plains in drier periods axial streams widen their flood plains and trim back the fans during wetter periods small scale climatic fluctuations of the holocene thus had substantial impact on postglacial landscapes in northeastern yellowstone

amplitude versus offset variations in gas sands seismic reflections from gas sands exhibit a wide range of amplitude versus offset avo characteristics the two factors that most strongly determine the avo behavior of a gas sand reflection are the normal incidence reflection coefficient r0 and the contrast in poisson s ratio at the reflector of these two factors r0 is the least constrained based on their avo characteristics gas sand reflectors can be grouped into three classes defined in terms of r0 at the top of the gas sand class 1 gas sands have higher impedance than the encasing shale with relatively large positive values for r0 class 2 gas sands have nearly the same impedance as the encasing shale and are characterized by values of r0 near zero class 3 sands have lower impedance than the encasing shale with negative large magnitude values for r0 each of these sand classes has a distinct avo characteristic an example of a gas sand from each of the three classes is presented in the paper the class 1 example involves a hartshorn channel s