detection of low chloride fluids beneath a cold seep field on the nankai accretionary wedge off kumano south of japan chemical and isotopic characteristics were determined for interstitial waters extracted from surface sediments in and around dense biological communities on the seafloor of the nankai accretionary prism off kumano south of japan we found the following unique features when compared with usual interstitial water samples of normal seafloor in those of samples from bacterial mats on the oomine ridge one of the outer ridge in the nankai accretionary prism 1 significant depletion of chloride concentration maximum 10 depletion from bottom seawater 2 high concentrations of ch4 and co2 more than 660 mol kg and 60 mmol kg respectively 3 sulfate depletion more than 90 depletion compared to bottom seawater and 4 dh2o and 18oh2o depletion more than 4 and 0 7 depletion respectively compared to standard mean ocean water smow the highest ch4 value among these samples was comparable to the highest value so far reported at one of the most active seep areas in the nankai trough suggesting that these sites should also be regarded as one of the most active seep sites in the nankai trough the chemical compositions of the samples taken from the oomine ridge strongly suggest that the fluid originates not from normal sediment seawater interaction at the sediment surface of hemipelagic environments but from active seepage of fluids that are rich in ch4 and co2 depleted in cl and so42 and low in dh2o and 18oh2o compared to normal seawater values for the carbon isotopic composition 13cch4 of the dissolved methane in the interstitial fluid less than 70 peedee belemnite pdb and for the c2h6 ch4 ratio less than 10 3 suggest that the methane originates from microbial production in a relatively shallow layer of sediment not from the deep sedimentary layer of higher temperature than 60 c at the depth of more than 300 m below the seafloor the cl 0 mmol kg extrapolated end member dh2o and 18oh2o values of low chloride fluids were 46 7 and 6 3 0 7 smow respectively suggesting that land derived groundwater could be one of the possible sources for the low cl fluids depth profiles of chloride concentrations of interstitial fluids show the heterogeneity of end members and upward fluid flow velocities suggest that active fluid seepage on the oomine ridge seems to be a localized phenomenon assuming steady state emission of fluid from the cold seep vent upward fluid flow velocities from the seeping vent are estimated to be 40 200 cm year 1 comparable to the previously reported values within the bacterial mats in the nankai trough accretionary wedge development of bacterial mat might favor slower advection which might allow longer time for diagenetic reactions in the vent conduits and consequently carry more reductive compounds in the fluids

violent breaking wave impacts part 1 results from large scale regular wave tests on vertical and sloping walls abstract as part of an investigation into the detailed characteristics of wave impacts experimental data are presented for the impact pressures and forces generated by waves up to 1 7 m high breaking onto a vertical wall and a wall inclined at 27 to the vertical particular attention is given to the influence of entrained and entrapped air and by selecting regular wave conditions that produce impacts trends are identified for highly variable phenomena that could easily be missed when masked by the even greater variability associated with irregular waves the characteristics of the impacts are found to depend on the breaker conditions and four different types of impact are identified and discussed the distinctive features of low aeration and high aeration impacts are considered in some detail and it is shown that a high level of aeration does not always reduce the peak pressure although it tends to increase both the rise time and duration consequently high levels of aeration can increase both the force and impulse on the structure alternate compression and expansion of the air can also generate potentially detrimental sub atmospheric pressures the largest impact pressures tend to occur around still water level and distributions in terms of both the incident wave height and the peak pressure are presented in dimensionless terms for each type of impact although the highest pressures are associated with low and high aeration impacts the results suggest that slightly breaking and broken wave impacts should not be neglected and percentage exceedance curves are included to give an indication of the frequency of extreme values whilst nominally identical waves often produce very different spatial and temporal pressure distributions the impulse on the structure during an impact is far less variable and is shown to be broadly proportional to the peak momentum flux of the incident waves the pressures forces and impulses associated with an impact on the sloping wall tend to be lower than those on the vertical wall in the same circumstances however the total impulse caused by a whole wave event impact plus quasi hydrostatic phases is found to be independent of wall slope in accordance with basic principles the paper concludes by demonstrating that for the conditions investigated the impact can account for up to 30 of the total impulse

fresh water seepage and pore water recycling on the seafloor sagami trough subduction zone japan we collected 19 samples of bottom sea water including 8 samples of shimmering fluid using the japanese submersible shinkai 2000 in the bathyal calyptogena community area the hatsushima area along sagami trough at the northern end of the philippine sea plate in order to clarify the source of fluid seepage shimmering fluid samples showed a maximum temperature of 11 6 c which is about 9 c higher than the ambient sea water the fluid chemistry of these samples is summarized as follows 1 alkalinity h2s sio2 nh4 co2 and ch4 show enrichment and cl so4 k na mg and ca show depletion compared with ambient sea water 2 cl depletion is about 20 and 3 the content and 3he4he ratio of dissolved helium show little anomaly compared with ambient sea water the observed chemical composition and temperature of the fluid is well explained by mixing of sea water pore water and land derived groundwater with a temperature of about 40 c and a seeping flux of about 400 m3 per day a preliminary estimation of the global chemical flux implies that groundwater discharge to the ocean including pore water recycling is an important factor in controlling ocean chemistry

geomorphically driven late cenozoic rock uplift in the sierra nevada california geologists have long accepted that the sierra nevada california experienced significant late cenozoic tectonically induced uplift a flexural isostatic model presented here shows however that a large fraction of the primary evidence for uplift could be generated by the lithospheric response to coupled erosion of the sierra nevada and deposition in the adjacent central valley and therefore requires less tectonic forcing than previously believed the sum of range wide erosion and the resultant isostatic rock uplift would have lowered sierra mean elevation by 200 to 1000 meters since 10 million years ago and could also have increased summit elevations during the current period of relief production

seismic structure of the lithosphere from teleseismic converted arrivals observed at small arrays in the southern sierra nevada and vicinity california 21 well distributed teleseisms 30 to 100 distance were recorded by mixed broad band bb and short period sp seismic arrays at mineral king mk and horseshoe meadow hm in the southern sierra nevada and at darwin plateau dp between the inyo and argus ranges these arrays permit identification and separation of direct p and s arrivals reflections from topography scattered energy and arrivals from different back azimuths multipath arrivals p to s conversions can be identified from beamed bb or sp seismograms least squares time domain processing recovered single event receiver functions from these beamed seismograms converted phases attributable to the moho are clear and uncomplicated at dp ps p times of 3 9 4 2 s correspond to crustal thicknesses of 31 33 km assuming a mean p crustal velocity of 6 2 km s and a poisson s ratio of 0 255 ps p times at hm eastern sierra are 3 9 4 6 s 32 37 km excepting some unusual seismograms from events at back azimuths of 225 239 mk western sierra times for ps p show a strong e w asymmetry 3 9 4 1 s 31 33 km from the east and 4 8 5 3 s 39 42 km from the west the mk arrivals from the east are multiple and substantially weaker by comparison with hm and dp these results confirm the absence of a thick crust under the southern high sierra inferred from both a refraction experiment coincident with this experiment and some earlier studies at dp the moho event follows an intracrustal negative polarity event defining the top of an s wave low velocity zone this feature dips west under the sierran crest at hm but is absent farther west at mk this feature appears to be a manifestation of extensional strain and thus indicates that the surficially undeformed sierra overlies a tectonized lower crust sub moho energy is absent under the basin and range dp but is conspicuous under the high sierra at positive arrivals 7 3 s mk and 9 s hm after the p these arrivals might be from the base of a low velocity low density upper mantle body supporting the sierra

paleotopography in the western u s cordillera issue 2 of volume 312 of the american journal of science brings together several new papers bearing on the history of orogenesis paleotopography and paleoclimate in a region whose geologic record has been more important to the modern development of ideas about these processes than any other in

geochemical constraints on the origin and volume of gas in the new albany shale devonian mississippian eastern illinois basin this study involved analyses of kerogen petrography gas desorption geochemistry microporosity and mesoporosity of the new albany shale devonian mississippian in the eastern part of the illinois basin specifically detailed core analysis from two locations one in owen county indiana and one in pike county indiana has been conducted the gas content in the locations studied was primarily dependent on total organic carbon content and the micropore volume of the shales gas origin was assessed using stable isotope geochemistry measured and modeled vitrinite reflectance values were compared depth of burial and formation water salinity dictated different dominant origins of the gas in place in the two locations studied in detail the shallower owen county location 415 433 m 1362 1421 ft deep contained significant additions of microbial methane whereas the pike county location 832 860 m 2730 2822 ft deep was characterized exclusively by thermogenic gas despite differences in the gas origin the total gas in both locations was similar reaching up to 2 1 cm3 g 66 scf ton lower thermogenic gas content in the shallower location lower maturity and higher loss of gas related to uplift and leakage via relaxed fractures was compensated for by the additional generation of microbial methane which was stimulated by an influx of glacial melt water inducing brine dilution and microbial inoculation the characteristics of the shale of the maquoketa group ordovician in the pike county location are briefly discussed to provide a comparison to the new albany shale

geometric scale invariance genesis and self organization of polygonal fracture networks in granitic rocks abstract we documented polygonal fracture networks in the tuolumne intrusive suite sierra nevada batholith by collecting data on the size orientation and length of fractures and fracture bound polygons in nearly isotropic granitic rocks polygonal fracture networks are constrained to sheets of rock sub parallel to the underlying rock with the sheets bound above and below by fractures i e free surfaces data indicate that most geometric characteristics of the polygonal fracture networks are scale invariant large m scale networks exhibit the same geometry as small cm scale networks a linear correlation exists between sheet thickness and average polygon size polygons within the networks are anisotropic with the degree of anisotropy correlated with the degree of sheet curvature the preferred orientation of the polygons correlates with the inclination of the sheet with long axes of polygons parallel to sheet strike based on geometry we suggest that the polygonal fracture networks in granitic rocks observed in this study formed from temperature fluctuations that caused thermal expansion and contraction in the rock repeated cycles of expansion contraction led to the initiation and propagation of fractures within the network we propose that the observed fracture patterns are not a product of extrinsic conditions but rather a product of interactions between fractures implying that the polygonal fracture networks are self organizing systems

valley incision and the uplift of mountain peaks simple end member models describe the effect of isostatically compensated valley incision on the elevation of mountain peaks these models allow calculation of the maximum portion of mountain peak elevations attributable to the development of observed relief and predict general downstream patterns of ridgetop uplift in response to erosion by fluvial processes analyses of topographic profiles across major drainages of the central sierra nevada and the tibetan plateau indicate that isostatically compensated valley incision could account for at most 5 10 of the present elevation of mountain peaks in contrast analyses of topographic profiles across the himalaya show that as much as 20 30 of the present elevation of himalayan peaks could be explained by isostatically compensated valley incision the degree to which valley incision is compensated locally however depends on the flexural rigidity of the lithosphere the size of the range and its tectonic boundary conditions these results show that while a tectonic control is required for late cenozoic surface uplift of the sierra nevada a significant portion of the elevation of himalayan peaks may reflect late cenozoic valley incision on the margin of the tibetan plateau

paleovalley morphology and fluvial system evolution of eocene oligocene sediments auriferous gravels northern sierra nevada california implications for climate tectonics and topography in the northern sierra nevada california eocene oligocene fluvial sediments the auriferous gravels rest unconformably in well defined basement incised paleovalleys providing a record of paleolandscape geomorphology and drainage system evolution paleovalley surface mapping shows that local topography and bedrock lithology controlled the location of broad terraced paleovalley segments which formed in the central and eastern metamorphic bedrock belts and subsequently became areas of significant fluvial deposition high gradient high energy deposits are present near the edges of these areas suggesting that tributaries and outlets resided in steeper narrow paleovalleys multiple strath terraces are common in broad paleovalleys indicating that incision events occurred both before deposition and during paleovalley widening followed by periods of aggradation broad paleovalley deposits contain predominantly braided stream facies deposited in an energetically variable system multiple upward fining cycles bounded by erosional surfaces are composed of alternating coarse grained channel belt and fine grained floodplain packages an overall upward fining succession suggests that the locus of fluvial deposition shifted and depositional energy waned over time as the system backfilled successive broad paleovalleys paleochannel slope estimates of 0 004 0 055 were obtained based on average grain sizes of coarse channel fills anomalously thick up to 11 m laterally continuous 1 3 km floodplain units containing kaolinite rich clay and oxisol intervals record high fine grained sediment supply driven by high rates of chemical weathering in the warm eocene climate based on sedimentary characteristics combined with floral and detrital zircon data braided stream deposition within the basin occurred from the late early eocene through late eocene and aggradation primarily occurred in broad lower gradient reaches behind a major bedrock knickpoint created in the late mesozoic early cenozoic possibly due to asymmetric batholith unroofing the diachronous localized nature of paleovalley incision and braided stream aggradation within the northern sierra nevada invalidates previous estimates of the timing and amount of range uplift based on paleochannel reconstructions and gradients both internal and external drivers influenced the evolution of the fluvial system through 1 the pattern of basin filling as the locus of deposition migrated east to west 2 the warm eocene climate which increased chemical weathering and contributed a high sediment supply and 3 changes in base level due to eustasy and or laramide tectonism this record of laramide tectonics in the sierra nevada and basin and range is important for the timing of sierra nevada uplift for tectonic reconstructions of western north america and for studies of landscape evolution in tectonically active orogens

impact of complex aquifer geometry on groundwater storage in high elevation meadows of the sierra nevada mountains ca recent research has indicated that sierra nevada meadows are hydrologically more complex than previously considered improved understanding of the effects of aquifer parameters and climate change on water resources in and downstream of meadows is critically needed to effectively manage mountain meadows for ecosystem services and watershed contributions this research investigates the roles of bedrock geometry saturated hydraulic conductivity and meadow gradient in affecting groundwater storage dynamics and surface water outflows in site scale high elevation meadows under current and projected lower snowpack conditions we modeled groundwater flow in representative high elevation meadows considering two conceptual aquifer thickness models uniform and variable thickness spatially variable aquifer thicknesses interpreted from bedrock depths 0 28 m were identified from a high resolution ground penetrating radar survey conducted at tuolumne meadows ca our interpreted bedrock surface indicated several buried u shaped valleys including a buried ridge that separates two u shaped valleys groundwater flow simulations show that an increase in meadow gradient and hydraulic conductivity led to a decrease in seasonal storage and an increase in surface water outflow however models with varying bedrock geometries change the magnitude and timing of these processes uniform thickness models overestimated storage at the model edges and resulted in higher projected volumes of water being released to streams earlier than previously observed

organic geochemistry of saanich inlet bc during the holocene as revealed by ocean drilling program leg 169s abstract sites 1033 and 1034 of odp leg 169s in saanich inlet have an unusual diagenetic system that has the appearance of being depth reversed i e a bacterial methane accumulation zone underlain by a sulphate reduction zone during the late pleistocene grey undifferentiated glacio marine clays were deposited with low corg contents

submarine hydrothermal mineralization in the okinawa trough sw of japan an overview abstract the okinawa trough is a heavily sedimented rifted back arc basin formed in an intracontinental rift zone submarine hydrothermal activity is located within the six back arc rifts located in the middle and southern okinawa trough and its distribution is controlled principally by tectonic factors subduction of the daito and gagua ridges beneath the ryukyu arc has resulted in fracturing of the brittle lithosphere beneath the okinawa trough hydrothermal activity is strongest in the volcanic arc rift migration phenomenon vamp area plus the jade site and southernmost part of the okinawa trough spot area which form the prolongation of these two ridges these areas are characterized by extremely high heat flow locally submarine hydrothermal fluids from the okinawa trough tend to be strongly influenced by interaction of the hydrothermal fluids with organic matter in the sediment resulting in high alkalinity and nh 4 concentrations of the fluids the fluids also contain high concentrations of co 2 of magmatic origin submarine hydrothermal mineralization in the trough is diverse the clam site consists principally of carbonate chimneys interaction of the hydrothermal fluid with organic matter in the sediment is particularly strong at this site this is most probably a sediment hosted deposit in which sulphide minerals have deposited within the sediment column leaving spent ore fluids to emerge at the seafloor the jade site consists of active and inactive sulphide sulphate chimneys and mounds the zn pb rich sulphides at this site contain the highest concentrations of pb ag and au so far recorded in submarine hydrothermal sulphide deposits at minami ensei knoll and hatoma knoll active and inactive chimneys consist principally of anhydrite and barite as a result of phase separation of the hydrothermal fluids beneath the seafloor an intense black smoker has recently been discovered at yonaguni knoll in the spot area if it is confirmed that sulphide mineralization is dominant at this site this could be a highly prospective area the most prospective areas for economic grade minerals in the okinawa trough appear to be the jade site and the spot area

multiple origins of methane in the earth methane occurrences in the earth s crust are predominantly of biogenic origin i e their ultimate source is biologically formed organic matter methane can also form through inorganic reactions and is consequently termed abiogenic biogenic methanes can either form through bacterial or thermogenic processes bacterial processes follow a co2 reduction and or fermentation pathway the fermentation processes are quantitatively more important in recent fresh sediments and swamps methane formed by co2 reduction however is most common in older sediments and commercial gasfields temperature organic substrate and age may be the major factors controlling the relative importance of the two pathways stable isotope concentrations in thermogenic methanes seem to be controlled by the extent of conversion of organic matter the timing of gas expulsion and trapping the different character of methane in individual sedimentary basins may be a result of the geologic history geothermal methanes are most likely derived from pyrolysis of organic matter abiogenic methane occurs in hydrothermal vents and ophiolite complexes inorganic reactions either surficial or deep seated are the likely source of such methanes a uniform mantle origin of methane is not supported by the observed isotope variations in naturally occurring methanes

methane seepage along the hikurangi margin of new zealand geochemical and physical data from the water column sea surface and atmosphere the concentration and carbon isotope values of dissolved methane were measured in the water column at rock garden omakere ridge and wairarapa areas in the first dedicated cold seep investigation along the hikurangi margin of new zealand these measurements provide a high resolution impression of the methane distribution in the water column and show that these seep sites are actively venting methane with varying intensity the highest concentrations up to 3500 nm measured in water samples obtained from conductivity temperature depth ctd operations were at faure site of rock garden here seafloor bubble release was observed by rov the omakere ridge area is actively venting over almost its entire length not vert similar 25 km in particular at bear s paw a newly discovered seep site in the wairarapa area another new seep site called tui was discovered where methane measurements often exceeded 500 nm no evidence was obtained from water column or sea surface measurements along the hikurangi margin to indicate that methane from seeps is reaching the sea surface in fact a consistent upper boundary was observed at a density of 26 85 kg m3 which occurs at about 500 m below sea surface above which methane decreased to background concentrations no obvious oceanographic feature is associated with this 500 m ch4 boundary bubble dissolution calculations show that about 500 m was also the model derived maximum bubble rise height a wide range of 13cch4 values from 71 to 19 vpdb were measured with the highest ch4 concentrations having the lowest 13cch4 values of about 71 to 68 simple mixing and isotope fractionation calculations show that changes of 13cch4 values are predominantly caused by the dilution of seep fluids with the seawater with some anaerobic oxidation also occurring

earthquake refraction profiles of the root of the sierra nevada we examine the seismic structure of the sierra nevada using records of nine earthquakes and one explosion in and near the sierra recorded on stations in the sierra we first interpret travel times from these paths which are confined to a single tectonic block in terms of one dimensional structures the most nearly reversed pair of earthquakes the 1966 truckee and 1983 durrwood meadows earthquakes share refracted pn arrival times corrected to surface focus along a line t 8 75 0 25 8 0 suggesting that a nearly flat layer of 8 0 km s mantle material lies at depths of 46 48 km first arrivals from these events do not constrain velocities from 30 to 45 km depth secondary arrivals and some first arrivals from other earthquakes suggest that velocities in part of this region range between 6 9 and 7 8 km s the presence of this 7 x km s layer can help to explain previous contradictory observations the 7 x km s layer could be interpreted as either the mafic bottom of a silicic mesozoic magmatic arc or as accreted mafic underplating or rejuvenated mantle related to cenozoic arc volcanism or basin and range spreading arrivals at stations in the foothills and the crest of the sierra cannot be fit with a single longitudinal structure indicating a lateral variation of velocity structure these variations support previously inferred variations of lithospheric structure with higher velocity thinner crust to the west beneath the sierran foothills and slower velocity crust or possibly upper mantle beneath the high mountains in the eastern sierra rapid changes in arrival times between stations separated by short distances in the eastern sierra suggest that a sharp boundary exists between the sierra and the basin and range at moho depths we also present fresh evidence of the asymmetry of the root of the sierra wherein arrivals from earthquakes on the west of the sierra are delayed within the sierra and return to original values in the basin and range while arrivals from earthquakes and explosions from the sierra into the great valley we suggest that if the 7 x km s material occurs in a wedge above the moho then the asymmetry can be explained by arrivals from the west being delayed by the dipping 8 0 km s moho while those from the east may be entering the root along a 7 x km s layer that is near the depth of the basin and range moho

the late cenozoic evolution of the tuolumne river central sierra nevada california erosional remnants of volcanic rock deposited in a 10 m y old channel of the tuolumne river permit its partial reconstruction projection of the reconstructed channel west to the central valley and east to the range crest together with several assumptions about the position of the hinge line and changes in channel gradient allows estimates of the amount of uplift at the range crest during the past 10 m y at tioga pass this amounts to as much as 1 830 m as compared to the 2 150 m estimated in an earlier study for deadman pass at the san joaquin river 30 km to the south comparison of the geometry of these river systems leads to the conclusion that 10 m y ago an ancestral range of hills occupied the present site of the sierran crest and although of relatively moderate relief it was a barrier to westward drainage even before late cenozoic uplift at that time the san joaquin river was apparently the only river flowing westward across the range from well south of mount whitney north to sonora pass the tuolumne river evidently never extended east of this range comparison of the ancient channel with the modern channel of the tuolumne river permits analysis of the later evolution of the river system and the development of hetch hetchy valley and the grand canyon of the tuolumne at rancheria mountain where the volcanic dam in the ancient channel was highest the river was forced to shift laterally southward around the dam and adjacent to the volcanic infilling and start its new channel in granitic bedrock near rancheria mountain as much as 1 525 m of new channel incision has taken place in the past 10 m y and the modern channel is about 915 m lower than the abandoned channel an undetermined amount of this downcutting was from glacial erosion the tuolumne river system provides no direct evidence for timing the onset of uplift but the shape of the 10 m y old channel at rancheria mountain suggests that uplift had been underway for some time before the volcanic infilling this timing is compatible with evidence from the upper san joaquin river hetch hetchy valley on the tuolumne is a much fresher glaciated valley than is yosemite valley hetch hetchy was filled to the brim with glacial ice as recently as 15 000 20 000 yr ago tioga glaciation whereas yosemite valley probably has not been filled for 750 000 yr or more sherwin glaciation thus the upper reaches of yosemite valley cliffs have been shaped by spalling rather than by glacial scour and are much more irregular than those in hetch hetchy

fractures and drainage in the granite mountainous area a study from sierra nevada usa abstract this paper provides an analysis of relationships between drainage patterns and fractures in the part of sierra nevada california north of the yosemite valley bedrock is cretaceous granite and cut by numerous lineaments of various orientation length and geomorphic expression we have mapped fractures and drainage lines from aerial photographs 1 40 000 scale in four test areas ranging in size from 32 5 to 266 km 2 azimuths are shown on rose diagrams for fractures and drainage lines and then visually and statistically compared the coincidence of drainage and fracture patterns is strong which implies causal relationships in plan the majority of valleys follow fractures even if this locally means a different orientation in respect to the regional slope arising from tectonic tilt of the range main streams occupy deeply incised troughs coincident with master fractures of regional extent among two principal fracture directions ssw nne to sw ne and wsw ene the former exerts more control on the drainage lines the presence of a central zone of structural weakness within the major valleys provided significant constraints for the course of glacial erosion and may explain why multiple pleistocene glaciers did not succeed in transforming valley cross sections into expected u shapes

seafloor spreading obduction and triple junction tectonics of the mineoka ophiolite central japan abstract the tertiary mineoka ophiolite occurs in a fault zone at the intersection of the honshu and izu forearcs in central japan and displays structural evidence for three major phases of deformation normal and oblique slip faults and hydrothermal veins formed during the seafloor spreading evolution of the ophiolite at a ridge transform fault intersection these structures may represent repeated changes in differential stress and pore fluid pressures during their formation the second series of deformation is characterized by oblique thrust faults with riedel shears and no significant mineral veining and is interpreted to have resulted from transpressional dextral faulting during the obduction of the ophiolite through oblique convergence and tectonic accretion this deformation occurred at the nw corner of a ttt type trench trench trench triple junction in the nw pacific rim before the middle miocene the third series of deformation of the ophiolite is marked by contractional and oblique shear zones riedel shears and thrust faults that crosscut and offset earlier structures and that give the mineoka fault zone its lenticular phacoidal fabric at all scales this deformation phase was associated with the establishment and the southward migration of the ttt boso triple junction and with the kinematics of oblique subduction and forearc sliver fault development the composite mineoka ophiolite hence displays rocks and structures that evolved during its complex geodynamic history involving seafloor spreading tectonic accretion and triple junction evolution in the nw pacific rim

tectonics of pliocene removal of lithosphere of the sierra nevada california pliocene ca 3 5 ma removal of dense eclogitic material under the sierra nevada has been proposed from variations in the petrology and geochemistry of neogene volcanic rocks and their entrained xenoliths from the southern sierra the replacement of eclogite by buoyant warm asthenosphere is consistent with present day seismologic and magnetotelluric observations made in the southern sierra a necessary consequence of replacing eclogite with peridotite is that mean surface elevations and gravitational potential energy both increase an increase in potential energy should increase extensional strain rates in the area if these forces are insuffi cient to signifi cantly alter pacifi c north american plate motion then increased extensional strain rates in the vicinity of the sierra must be accompanied by changes in the rate and style of deformation elsewhere changes in deformation in california and westernmost nevada agree well with these predictions existing geologic evidence indicates that a period of rapid uplift along the sierran crest of more than 1 km occurred between 8 and 3 ma most likely as a consequence of removal of lower lithosphere about this same time extensional deformation was initiated within 50 km of the eastern side of the sierra 5 3 ma and regional shortening began to produce the california coast ranges 5 3 ma we suggest that these events were induced by the 1 2 10 12 n m increase of gravitational potential energy generated by the sierran uplift evidence for pliocene uplift adjoining crustal extension and shortening in directly opposing parts of the coast ranges is found along nearly the entire length of the sierra nevada and implies that lithosphere was removed beneath all of the presentday mountain range the uplifted area lies between two large upper mantle high pwave velocity bodies under the south end of the san joaquin valley and the north end of the sacramento valley these high velocity bodies plausibly represent the present position of material removed from the base of the crust lithospheric removal may also be responsible for shifting of the distribution of transform slip from the san andreas fault system to the eastern california shear zone a prediction that awaits better defi ned slip histories on both faults overall the late cenozoic deformational history of the sierra nevada and vicinity illustrates that locally derived forces can infl uence deformation kinematics within plate boundary zones

seasonal seismicity of northern california before the great 1906 earthquake during the late nineteenth century coastal parts of northern california experienced seismicity which was more intense than at any other time in its historical record and was concentrated in spring the seasonal character of this anomalous seismicity was statistically significant from the 1880s if not earlier until the time of the great 1906 earthquake it can be explained as a result of seasonal stress transients caused by the large seasonal sediment loads which accumulated in coastal bays that overlie active strike slip faults as a result of hydraulic mining of gold in inland areas such localised loading will increase the absolute vertical stress and reduce the absolute horizontal stress thus facilitating shear failure by unclamping vertical fault planes however rather than simply influencing the timing of earthquakes which would otherwise have occurred anyway sometime later this process appears to have affected the character of the region s seismicity causing a sequence of magnitude 5 6 earthquakes which propagated outward from these coastal depocentres these results have three important implications first the proposed physical mechanism is only feasible provided the deepest continental crust in this region has a viscosity no greater than 1017 pa s giving it a maxwell time of the order of weeks these observations of seasonal seismicity thus suggest that such low viscosities are reasonable a conclusion which has been difficult to establish using other evidence they indicate that future calculations of the stress field in this region for instance for investigating the role of earthquake triggering should incorporate this response by lower crustal flow not just the immediate elastic effect second the conclusion that seasonal stress transients caused by seasonal changes in surface processes can affect seismicity has important implications for hazard assessment it raises the possibility that surface processes may influence the seasonal timing and character of seismicity in other regions also finally it indicates that the decades of intense seismicity widely interpreted as precursory activity to the 1906 earthquake were atypical of the longer term record analogous sequences of moderate sized events cannot necessarily be expected to provide advance warning of future large earthquakes in this region

pore water geochemistry of eastern mediterranean mud volcanoes implications for fluid transport and fluid origin abstract the pore water chemistry of mud volcanoes from the olimpi mud volcano field and the anaximander mountains in the eastern mediterranean sea have been studied for three major purposes 1 modes and velocities of fluid transport were derived to assess the role of upward advection and bioirrigation for benthic fluxes 2 differences in the fluid chemistry at sites of milano mud volcano olimpi area were compiled in a map to illustrate the spatial heterogeneity reflecting differences in fluid origin and transport in discrete conduits in near proximity 3 formation water temperatures of seeping fluids were calculated from theoretical geothermometers to predict the depth of fluid origin and geochemical reactions in the deeper subsurface no indications for downward advection as required for convection cells have been found instead measured pore water profiles have been simulated successfully by accounting for upward advection and bioirrigation advective flow velocities are found to be generally moderate 3 50 cm y 1 compared to other cold seep areas depth integrated rates of bioirrigation are 1 2 orders of magnitude higher than advective flow velocities documenting the importance of bioirrigation for flux considerations in surface sediments calculated formation water temperatures from the anaximander mountains are in the range of 80 to 145 c suggesting a fluid origin from a depth zone associated with the seismic decollement it is proposed that at that depth clay mineral dehydration leads to the formation and advection of fluids reduced in salinity relative to sea water this explains the ubiquitous pore water freshening observed in surface sediments of the anaximander mountain area multiple fluid sources and formation water temperatures of 55 to 80 c were derived for expelled fluids of the olimpi area

thermal evolution of the sierra nevada tectonic implications of new heat flow data eight new heat flow measurements in the southern sierra nevada constrain models of thermal evolution and lithospheric structure low reduced heat flows 18 to 21 mw m in the southwest sierra nevada are consistent with previous results from the northwestern and central sierra nevada and extend the known region of linear heat flow heat production correlation an additional 150 km to the south isostatic residual gravity and measured rock densities are also linearly correlated in the central sierra nevada suggesting a general association between the upper crustal distribution of density and heat production the linear residual gravity density relation implies that isostatic residual gravity anomalies have upper crustal sources and therefore is evidence against a flexural model of cenozoic sierra nevada uplift new reduced heat flows measured in the southeast sierra nevada are relatively high 32 to 57 mw m and correlate spatially with a region of high seismicity that includes extensional earthquake swarms this correlation supports the view that basin and range extensional tectonics and associated magmatic processes are encroaching on the eastern sierra nevada in the stable southwest sierra nevada as in the central and northwestern sierra nevada the persistence of low reduced heat flow at the surface is consistent with a thermal origin for the cenozoic uplift of the sierra nevada provided the conductive lithosphere is at least 60 to 90 km thick simple order of magnitude calculations show that thermal uplift models combining mechanisms such as advective warming and thinning of the mantle lithosphere advection of basaltic magma and heat into the crust simple thermal expansion and eclogite to basalt phase conversion can account for the timing and amount of cenozoic sierra nevada uplift thermal models do not need the assumptions of unusual lithospheric strength and crustal buoyancy required by mechanical models for cenozoic uplift driven by a mesozoic crustal root

opening mode of the japan sea inferred from the palaeomagnetism of the japan arc the western edge of the pacific plate is marked by a chain of back arc basins stretching from the aleutians through japan and the philippines to new zealand most of the basins lie behind volcanic island arcs far from continents and are the result of extension of the oceanic lithosphere1 but the japan sea is bounded on one side by continental crust the sikhote alin and korean peninsula of the asian continent and on the other by an active arc with continental fragments it can thus be said to be associated more with continental rifting1 4 than with oceanic processes we report here palaeomagnetic data from the japan arc which indicate that since the early miocene north east japan has rotated counter clockwise through 47 around a vertical axis while south west japan has rotated clockwise through 56 refs 5 8 we attribute this differential rotation which took place concurrently between 21 and 11 myr ago to the back arc opening of the japan sea8 with a double door mode that is there are two fan shaped spreading basins facing each other such a fan shaped opening is probably peculiar to the geological phenomenon of rifting of a continental fragment from thick continental lithosphere

chemical and isotopic characterization of hydrocarbon gas traces in porewater of very low permeability rocks the example of the callovo oxfordian argillites of the eastern part of the paris basin abstract a methodology has been developed to determine chemical and carbon isotopic compositions of trace amounts of hydrocarbon gas compounds methane ethane propane iso and normal butane present as dissolved compounds in the porewater of the low permeability callovo oxfordian argillites in eastern paris basin france results indicate that the studied hydrocarbons contain significant amounts of ethane butane and propane in addition to methane carbon isotopic compositions reflect primarily thermogenic origin thermal cracking of organic matter and lack of any significant biodegradation because temperature did not exceed 50 c in the studied argillites investigated hydrocarbons must have originated in hotter deeper organic bearing formations possibly stephanian coals data supports the predominance of high maturity thermogenic gas in the upper part of the callovo oxfordian and low maturity thermogenic gas mixed with minor bacterially produced methane in the lower part of the formation a mixing between three end member gases models quite well the data one thermogenic gas with a low maturity 42 methane with a 13 c of 53 a gas with higher maturity 55 methane with a 13 c of 47 and a bacterial gas 99 45 methane with a 13 c of 80 this study illustrates that migration of hydrocarbon gases can take place in rocks with very low permeability and porosity such as compacted mudrocks given enough time it further suggests that the studied fluid migration and transfer in aquitards would help characterization and understanding of fluid movements in sedimentary basins as a complement to studies focused on water aquifers and hydrocarbon reservoirs chemical and isotopic composition of dissolved hydrocarbons in porewater can be used as natural tracers of fluid circulation in sedimentary basins in addition to more conventional tracers

thermal maturity in the shimanto accretionary prism southwest japan with the thermal change of the subducting slab fluid inclusion and vitrinite reflectance study abstract the p t path of the cretaceous shimanto accretionary complex western shikoku southwest japan was determined by a combination of vitrinite reflectance data and homogenization temperatures of fluid inclusion analysis within the complex the p t paths of the upper cretaceous yokonami melange and surrounding coherent strata were compared no p t difference was found between the yokonami melange and surrounding strata at least two types of fluids methane rich and water rich fluids migrated at different stages during metamorphism within the complex the methane rich fluid was initially trapped in vein quartz under pressures of 260 mpa and a geothermal gradient of 24 c km the water rich fluid was included in calcite at 95 125 mpa and a geothermal gradient of 50 c km the complex sequence of occurrence of the vein minerals and radiometric age data suggest that the water rich fluid was trapped during the kula pacific ridge subduction into the shimanto accretionary complex the paleoheat flow values for the two stages of subduction are consistent with the changes in the inferred slab age the metamorphism of the shimanto accretionary complex was predominantly controlled by the thermal condition of the subducting plate

diversion of the upper bear river glacial diffluence and quaternary erosion sierra nevada california abstract deep canyon erosion and diversion of more than 300 km 2 of the former upper bear river is documented with stratigraphic and morphologic evidence stratigraphic relationships constrain canyon incision to no older than late miocene in age a hypothesis is advanced that channel diversion was caused by ice spilling over a divide between the bear and south yuba drainages leading to development of glacial diffluence and deep incision the local glacial stratigraphy is mapped based on lateral moraines erratics and striae which indicate that at least two and probably three glacial advances occupied both south yuba and bear valleys stratigraphic relationships constrain most valley incision to before the last major glacial stage and probably by the end of an earlier larger glacial advance morphologic evidence supports a hypothesis of dominantly sub glacial erosion at an outlet glacier through the yuba gorge where steep valley gradients high shear stresses and large meltwater discharges led to rapid erosion and formation of a deep v shaped valley

late cenozoic uplift of the sierra nevada california a critical analysis of the geomorphic evidence from the earliest days of california geology the ramp like profile of the northern half of the sierra nevada mountains and putative signs of recent incision have been interpreted as evidence that the range was formed by the tilting of a rigid block in the late cenozoic over the years various geomorphic analyses have been used to quantify the magnitude of uplift and to establish its timing such as analyzing the gradients of ancient channels examining the tilt of sedimentary beds and reconstructing the incisional history of rivers most studies that have used these methods have supported substantial 500 m recent uplift of the sierra in contrast investigations based on other sources of paleotopographic information such as isotope records thermochronology and detrital zircon geochronology have found that the sierra have been at high elevations for much of the cenozoic this set of contradictory results motivates a re examination of the geomorphic evidence for late cenozoic uplift a critical assessment of these geomorphic studies based on new topographic analyses and field investigations reveals that their conclusions are not well supported for example several studies based their results on reconstructions of ancient channels that would have flowed up and over bedrock ridges as high as 190 m a physical impossibility other weaknesses include unjustified assumptions regarding the original tilt of fluvial deposits misinterpretations of stratigraphic relationships and inadequate recognition of the effect of lithology on channel profiles the studies supporting recent tilting in the northern sierra nevada are inconclusive and rely on observations not unique to tectonic forcing indeed much of the evidence based on the paleogradients of the tertiary channels is consistent with an early trellis drainage network formed across alternating bands of resistant and weak lithologies in addition analyses are presented to demonstrate that deep northern sierran canyons thought to have been recently incised were instead cut as early as the eocene oligocene two geomorphic studies from the southern sierra are consistent with late cenozoic tilting and uplift although ongoing tectonic activity may be insignificant finally i present a conceptual model of the evolution of the sierran landscape applicable primarily to the northern half of the range illustrating the development of three different drainage networks since the late jurassic

stable carbon isotope behaviour of natural seepage of deep underground 13c rich methane detected along a fault zone and adsorbed in mudstone tokyo bay area japan abstract gas was sampled regionally including by drilling into faults in the south kanto gas field around tokyo bay japan gas samples were collected from cores in a gas sampling container immediately after drilling a value of 13c1 44 3 was obtained for gas in the container and 13c1 36 3 for seeping gas in a fault zone however typical ch4 in this dissolved in water gas field is mainly depleted in 13c and 13c1 values range from 66 to 68 owing to microbial degradation of organic material 13c rich ch4 is so far uncommon in the south kanto gas field seepages were observed from the surface along the north south fault zone the natural gas is stored below the sandstone layer by impermeable mudstone underlying the boundary at a depth of 30 m gas seepages were not observed below a depth of 40 m gas rises along the fault zone dissolved in groundwater up to the shallow region and then separates from the groundwater 13c rich ch4 adsorbed ch4 was found to have desorbed from drilled mudstone core samples taken at depths of 1400 1900 m in the main gas production strata similarly 13c rich ch4 was found in black shale overlying the oceanic crust forming part of a sedimentary accretionary prism underling the tokyo region it also appears in the spring water of spa wells originating at a depth of 1200 1500 m along a tectonic line methane generated by microbial degradation of organic material through co2 reduction in the south kanto gas field mainly originates as biogenic gas mixed with a small amount of 13c rich ch4 derived from thermogenic gas without oil components in strata it is assumed that 12c rich ch4 is easily detached from core or pore water through gas production whereas 13c rich ch4 is strongly adsorbed on the surfaces of particles the 13c rich ch4 rises along the major tectonic line or up the 50 m wide normal fault zone from relatively deep sources in the kanto region

geochemistry of coalbed gas a review coals are both sources and reservoirs of large amounts of gas that has received increasing attention in recent years as a largely untapped potential energy resource coal mining operations such as ventilation of coalbed gas from underground mines release coalbed ch4 into the atmosphere an important greenhouse gas whose concentration in the atmosphere is increasing because of these energy and environmental issues increased research attention has been focused on the geochemistry of coalbed gas in recent years this paper presents a summary review of the main aspects of coalbed gas geochemistry and current research advances

cenozoic tectonic and topographic evolution of the northern sierra nevada california through stable isotope paleoaltimetry in volcanic glass we determine the paleoelevation of the northern sierra nevada california in the oligocene based on hydrogen stable isotope compositions of meteoric water preserved within volcanic glass from ignimbrites sampled across the range a 48 decrease in the isotopic composition of hydrated glass from ignimbrites located near paleosea level to ignimbrites 100 km to the east refl ects the effect of ancient high topography on precipitation these data show that 31 28 ma ago the northern sierra nevada had a steep western gradient and elevations similar to the present this study placed in the context of other paleoaltimetry studies suggests that the range was a high topographic feature throughout the cenozoic and that the majority of uplift occurred in the late cretaceous to early cenozoic much earlier than some studies have proposed

restoration of exotic terranes along the median tectonic line japanese islands overview abstract this paper reviews recent progress on the geotectonic evolution of exotic paleozoic terranes in southwest japan namely the paleo ryoke and kurosegawa terranes the paleo ryoke terrane is composed mainly of permian granitic rocks with hornfels mid cretaceous high grade metamorphic rocks associated with granitic rocks and upper cretaceous sedimentary cover they form nappe structures on the sambagawa metamorphic rocks the permian granitic rocks are correlative with granitic clasts in permian conglomerates in the south kitakami terrane whereas the mid cretaceous rocks are correlative with those in the abukuma terrane this correlation suggests that the elements of northeast japan to the northeast of the tanakura tectonic line were connected in between the paired metamorphic belt along the median tectonic line southwest japan the kurosegawa terrane is composed of various paleozoic rocks with serpentinite and occurs as disrupted bodies bounded by faults in the middle part of the jurassic chichibu terrane accretionary complex it is correlated with the south kitakami terrane in northeast japan the constituents of both terranes are considered to have been originally distributed more closely and overlay the jurassic accretionary terrane as nappes the current sporadic occurrence of these terranes can possibly be attributed to the difference in erosion level and later stage depression or transtension along strike slip faults the constituents of both exotic terranes especially the ordovician granite in the kurosegawa south kitakami terrane and the permian granite in the paleo ryoke terrane provide a significant key to reconstructing these exotic terranes by correlating them with paleozoic granitoids in the eastern asia continent

origin of hydrocarbons in the green tuff region of japan 129i results from oil field brines and hot springs in the akita and niigata basins abstract the akita and niigata basins are part of the green tuff region of honshu japan which hosts major occurrences of oil and gas and of hydrothermal sulfide sulfate kuroko deposits the green tuff formation is associated with the opening of the japan sea which occurred in the early miocene and was accompanied by large scale volcanic activities we measured halogen concentrations and 129i i ratios in oil and gas field brines and hot springs in order to determine the origin of iodine and indirectly of hydrocarbons in this area and their association with geological processes during the formation of the japanese island arc based on the concentration of iodine these samples fall into three categories type a i 190 m type b 150 m i 90 m and type c i

carson pass kirkwood paleocanyon system paleogeography of the ancestral cascades arc and implications for landscape evolution of the sierra nevada california tertiary strata of the central sierra nevada are dominated by widespread voluminous volcanic breccias that are largely undivided and undated the origin of which is poorly understood these dominantly andesitic strata are interpreted to be eruptive products of the ancestral cascades arc deposited and preserved within paleocanyons that crossed the present day sierra nevada before basin and range faulting began there these strata are thus important not only for understanding the paleogeography of the ancestral cascades arc but also for reconstructing the evolution of the sierra nevada landscape our regional scale mapping shows that paleocanyon fills of the central sierra nevada are dominated by intrusions and vent proximal facies along the present day sierran crest with more distal facies extending westward down the paleocanyons vent proximal facies consist of lava domes that collapsed to generate block and ash flow tuffs which in turn were remobilized down canyon to produce coarse grained volcanic mudflow and dilute flow fluvial deposits lava flows are rare instead magmas invaded wet volcaniclastic sediment to form in situ peperite piles that were partly remobilized to form debris flows or block and ash flows with peperite domains detailed mapping and dating of previously undifferentiated tertiary strata in the carson pass kirkwood area of the central sierra nevada has allowed us to identify 6 unconformity bounded sequences preserved within a paleocanyon as deep as 650 m cut into mesozoic granitic basement the carson pass kirkwood paleocanyon trends ne sw with a paleo transport direction roughly parallel to the modern mokelumne river drainage toward the sw sequence 1 consists of oligocene silicic ignimbrites sourced from nevada sequences 2 through 6 consist of dominantly andesitic rocks of the miocene ancestral cascades arc with 40 ar 39 ar ages ranging from 14 69 0 06 ma to 6 05 0 12 ma these new dates provide constraints on the ages of unconformities vertical relief on the unconformities within the paleocanyon ranges from 12 to 303 meters with paleoslope gradients range from 3 to 48 no evidence exists for widening or deepening of the paleocanyon into mesozoic basement during tertiary time so we infer that unconformity 1 the paleocanyon floor and walls was inherited from cretaceous time the deepest unconformities within the paleocanyon fill reincised into granitic basement in the early miocene unconformity 2 between 14 and 10 ma unconformity 5 and between 10 and 6 ma unconformity 6 the paleocanyon was also beheaded cut off from sources to the east by ca 10 ma we suggest that the early miocene reincision records tectonism related to the onset of arc magmatism in the sierra nevada the middle miocene reincision may record the onset of basin and range faulting in the central sierra the late miocene reincision may correspond to uplift attendant with the northward sweep of the triple junction through the latitude of the central sierra paleocanyons of the central sierra differ from those of the northern and southern sierra by showing steeper local paleorelief and the bouldery stream deposits attest to higher axial gradients than envisioned for other parts of the range this may indicate that the uplift history of the range is not uniform from segment to segment

wave impact pressure and its effect upon bodies lying on the sea bed abstract this paper is concerned with the very large sudden pressures produced by water wave impact on a vertical wall numerical and theoretical models are briefly described and we show that there are significant pressure gradients along an impermeable sea bed away from the wall this aspect of wave impact pressure has not previously been noted the effects of such transient pressure gradients on bodies lying on the bed are examined in the light of pressure impulse theory our theoretical results indicate that bodies may be displaced by these pressure gradients when ordinary fluid drag is insufficient to move them we discuss the impulse and the speed imparted to a rigid body lying within a region of pressure impulse which has constant horizontal gradient and we show that the impulse is related to the body s volume and shape analytic results are given for a hemi ellipsoidal boulder which is free to translate in a direction perpendicular to the wall the analysis for the hemi ellipsoid encompasses the special cases of a semi circular cylinder and a semi circular disc the case of a circular cylinder which touches the bed is also discussed and it is shown that there is a significant vertical impulse on the body in addition to the horizontal component of the impulse

deuterium and oxygen isotopes paleoelevations of the sierra nevada and cenozoic climate although geomorphic observations suggest that the sierra nevada has tilted so that the crest has risen 1 2 km since late miocene time deuterium and oxygen 18 isotope concentrations in cenozoic geologic materials decrease eastward across california and nevada similarly to those in modern orographically induced precipitation as if little change in sierra nevadan elevations has occurred since eocene time orographic precipitation however depends on the amount of moisture in the atmosphere which in turn can be much larger in warm air as in eocene or oligocene time and in summer than in the cooler air characteristic of present day dominantly winter precipitation moreover the integrated rainout of vapor and hence presumably in stable isotope concentrations in the remaining vapor depends largely on the difference in heights traversed by air masses not slopes of mountain ranges thus if due simply to orographically induced rainout both eocene and oligocene variations in deuterium isotopes across the sierra nevada and miocene quaternary differences in deuterium and oxygen isotopes between the great valley of california and the basin and range place only weak constraints on the slope or past elevations of the sierra nevada they do not necessarily contradict the inference that the crest of the sierra nevada has risen 1000 m or more since late miocene time

clockwise 180 rotation of slip direction in a superficial nappe pile emplaced upon a high p t type metamorphic terrane in central japan abstract understanding the exhumation process of deep seated material within subduction zones is important in comprehending the tectonic evolution of active margins the deformation and slip history of superficial nappe pile emplaced upon high p t type metamorphic rocks can reveal the intimate relationship between deformation and transitions in paleo stress that most likely arose from changes in the direction of plate convergence and exhumation of the metamorphic terrane the kinshozan atokura nappe pile emplaced upon the high p t type sanbagawa sambagawa metamorphic rocks is the remnant of a pre existing terrane located between paired metamorphic terranes along the median tectonic line mtl of central japan intra and inter nappe structures record the state of paleo stress during metamorphism and exhumation of the sanbagawa terrane the following tectonic evolution of the nappes is inferred from a combined structural analysis of the basal fault of the nappes and their internal structures the relative slip direction along the hanging wall rotated clockwise by 180 from s to n in association with a series of major tectonic changes from mtl normal contraction to mtl parallel strike slip and finally mtl normal extension this clockwise rotation of the slip direction can be attributed to changes in the plate induced regional stress state and associated exhumation of the deep seated sanbagawa terrane from the late cretaceous coniacian to the middle miocene

numerical modeling of the cenozoic geomorphic evolution of the southern sierra nevada california abstract recent geomorphic studies suggest that significant 1 5 km late cenozoic surface uplift occurred in the southern sierra nevada a conclusion that is difficult to reconcile with recent stable isotopic paleoaltimetry studies numerical modeling can play an important role in resolving this dispute in this paper i use two models of bedrock channel erosion the stream power model and a sediment flux driven model to test hypotheses for the fluvial cenozoic geomorphic evolution and surface uplift history of the southern sierra nevada cosmogenic data for upland erosion and river incision rates allow each model parameter to be uniquely constrained numerical experiments using the sediment flux driven model suggest that the modern southern sierra nevada was constructed from a 1 0 km pulse of range wide surface uplift in the latest cretaceous 60 ma and a 0 5 km pulse in the late miocene 10 ma the persistent geomorphic response to latest cretaceous uplift in this model is the result of limited cutting tools supplied from the upland low relief boreal plateau this uplift history correctly predicts the modern topography of the range including the approximate elevations and extents of the chagoopa and boreal plateaux and their associated river knickpoints numerical experiments using the stream power model are most consistent with a 1 km pulse of uplift in the late eocene 30 ma and a 0 5 km pulse in the late miocene 7 ma both models suggest that the remaining rock uplift required to produce the 4 km peak elevations of the modern southern sierra nevada was produced by flexural isostatic uplift in response to river incision the balance of evidence including the dominance of sediment flux driven erosion in granitic rocks previous paleoaltimetry studies and the timing of sediment accumulation in the great valley support the conclusions of the sediment flux driven model i e that the sierra nevada experienced range wide surface uplift events in the latest cretaceous and late miocene more broadly these results indicate that nonequilibrium landscapes can persist for long periods of geologic time and hence low relief upland landscapes do not necessarily indicate late cenozoic surface uplift