kinematic models of fluvial terraces over active detachment folds constraints on the growth mechanism of the kashi atushi fold system chinese tian shan during detachment folding the relationship between differential uplift and shortening depends on the mechanism of fold growth such as limb rotation or hinge migration and may vary over the lifetime of a fold thus neither long term shortening rates nor the present fold geometry unambiguously constrain the kinematics of fold growth where rivers cut through growing anticlines flights of abandoned fluvial terraces act as passive kinematic markers as shortening progresses the terraces become deformed and thereby preserve critical information about the kinematics and evolution of active fold growth to constrain recent fold growth across three detachment folds in the kashi atushi fold system in the sw tian shan china we surveyed flights of deformed terraces and compared them with geometric models of successively emplaced horizontal unconformities terraces across pregrowth strata deformed by hinge migration limb rotation and a combination of the two migration of angular hinges and curved hinge zones were also compared each kinematic model predicts both a distinct geometry for the deformed terraces and contrasting angular relationships between the terraces and the pregrowth strata notably limb rotation and migration of curved hinge zones result in progressively rotated terraces that cut across pregrowth strata whereas all limb lengthening models result in parallelism between pregrowth strata and terrace straths across much of the fold the kashi atushi terraces show clear evidence of abandoned axial surfaces concentrated deformation near the core of the folds and progressive tilting with age when compared to the model predictions the folds are likely growing by a combination of limb rotation in the tight cores of the folds and hinge zone migration of pregrowth strata across the flanks of the folds

geomorphic constraints on listric thrust faulting implications for active deformation in the mackenzie basin south island new zealand 1 deformed fluvial terraces preserved over active thrust related folds record the kinematics of folding as fault slip accumulates on the underlying thrust in the mackenzie basin of southern new zealand the kinematics revealed by folded fluvial terraces along the active ostler and irishman creek fault zones are inconsistent with traditional models for thrust related folding in which spatially uniform rock uplift typically occurs over planar fault ramps instead warped and tilted terraces in the mackenzie are characterized by broad continuous backlimbs and abrupt forelimbs and suggest folding through progressive limb rotation by relating this pattern of surface deformation to the underlying thrust with a newly developed simple geometric and kinematic model we interpret both faults as listric thrusts rooted at depth into gently dipping planar fault ramps constraints on the model from detailed topographic surveying of deformed terraces ground penetrating radar over active fault scarps and luminescence dating of terrace surfaces suggest slip rates for the ostler and irishman creek faults of 1 1 1 7 mm yr and 0 5 0 7 mm yr respectively the predicted depth of listric faulting for the ostler fault 0 7 0 2 0 1 km and the irishman creek fault 1 3 0 5 0 1 km generally agrees with geophysical estimates of basin depth in the mackenzie and suggests control of preexisting basin architecture on the geometry of active thrusting despite the potential effects of changes in fault curvature and hanging wall internal deformation the methodology presented here provides a simple tool for approximating the kinematics of surface deformation associated with slip along listric or curviplanar thrust faults

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

active thrusting and folding along the northern tien shan and late cenozoic rotation of the tarim relative to dzungaria and kazakhstan we have studied geometries and rates of late cenozoic thrust faulting and folding along the northern piedmont of the tien shan mountain belt west of urumqi where the m 8 3 manas earthquake occurred on december 23 1906 the northern range of the tien shan rising above 5000 m overthrusts a flexural foredeep filled with up to 11 000 m of sediment of the dzungarian basement our fieldwork reveals that the active thrust reaches the surface 30 km north of the range front within a 200 km long zone of neogene quaternary anticlines fault scarps are clearest across inset terraces within narrow valleys incised through the anticlines by large rivers flowing down from the range in all the valleys the scarps offset vertically the highest terrace surface by the same amount 10 2 0 7 m inferring an early holocene age 10 2 kyr for this terrace which is continuous with the largest recent fans of the piedmont yields a rate of vertical throw of 1 0 0 3mm yr on the main active thrust at the surface a quantitative morphological analysis of the degradation of terrace edges that are offset by the thrust corroborates such a rate and yields a mass diffusivity of 5 5 2 5 m 2 kyr a rather fresh surface scarp 0 8 0 15 m high that is unlikely to result from shallow earthquakes with 6 m 7 in the last 230 years is visible at the extremities of the main fold zone we associate this scarp with the 1906 manas earthquake and infer that a structure comprising a deep basement ramp under the range gently dipping flats in the foreland and shallow ramps responsible for the formation of the active fault propagation anticlines could have been activated by that earthquake if so the return period of a 1906 type event would be 850 380 years the small size of the scarp for an earthquake of this magnitude suggests that a large fraction of the slip at depth 2 3 is taken up by incremental folding near the surface comparable earthquakes might activate flat detachments and ramp anticlines at a distance from the front of other rising quaternary ranges such as the san gabriel mountains in california or the mont blanc aar massifs in the alps we estimate the finite cenozoic shortening of the folded dzungarian sediments to be of the order of 30 km and the cenozoic shortening rate to have been 3 1 5 mm yr assuming comparable shortening along the tarim piedmont and minor additional active thrusting within the mountain belt we infer the rate of shortening across the tien shan to be at least 6 3 mm yr at the longitude of manas 85 5 e a total shortening of 125 30 km is estimated from crustal thickening assuming local airy isostatic equilibrium under the same assumption serial n s sections imply that cenozoic shortening across the belt increases westwards to 203 50 km at the longitude of kashgar 76 e as reflected by the westward increase of the width of the belt this strain gradient implies a clockwise rotation of tarim relative to dzungaria and kazakhstan of 7 2 5 around a pole located near the eastern extremity of the tien shan west of hami 96 e 43 5 n comparable to that revealed by paleomagnetism between tarim and dzungaria 8 6 8 7 a 6 mm yr rate of shortening at the longitude of manas would imply a rate of rotation of 0 45 m y and would be consistent with a shortening rate of 12 mm yr north of kashgar taking such values to be representative of late cenozoic rates would place the onset of reactivation of the tien shan by the india asia collision in the early to middle miocene 16 22 9 m y in accord with the existence of particularly thick late neogene and quaternary deposits such reactivation would thus have started much later than the collision roughly at the time of the great mid miocene changes in tectonic regimes denudation and sedimentation rates observed in southeast asia the himalayas and the bay of bengal and of the correlative rapid change in seawater sr isotopic ratio 20 to 15 ma like these other changes the rise of the tien shan might be a distant consequence of the end of indochina s escape

climatic versus tectonic control on river incision at the margin of ne tibet 10be exposure dating of river terraces at the mountain front of the qilian shan 1 we document late pleistocene holocene aggradation and incision processes at the mountain front of the qilian shan an active intracontinental fold and thrust belt accommodating a significant portion of the india asia convergence the shiyou river cuts through a nne vergent fault propagation fold with miocene red beds in the core and pliocene quaternary growth strata on the northern forelimb south of the anticline miocene strata dip 20 ssw suggesting a similar orientation for the basal decollement after aggradation of an 150 m thick late pleistocene valley fill the shiyou river formed three terraces the highest terrace located 170 m above the river constitutes the top of the fill the other terraces are fill cut terraces their treads are located 130 105 m and 37 m above the river respectively the 10be exposure dating of the terraces suggests that river incision accelerated from 0 8 0 2 mm yr 1 to 10 mm yr 1 at 10 15 kyr we interpret fast holocene river incision as largely unrelated to tectonic forcing the late pleistocene incision rate of 0 8 0 2 mm yr 1 places an upper limit of 2 2 0 5 mm yr 1 on the horizontal shortening rate assuming that incision is solely caused by rock uplift above a decollement dipping 20 however the actual shortening rate may lie between 2 2 mm yr 1 and zero because deformation of the terraces and the valley fill cannot be unequivocally demonstrated our estimate is consistent with the bulk shortening rate of 5 10 mm yr 1 across several faults in ne tibet derived from neotectonic and gps data although in case of the shiyou river holocene deformation is barely discernible owing to intense climate induced river incision

stable isotopic biogeochemistry of carbon and nitrogen in a perennially ice covered antarctic lake lake hoare 77 degrees 38 s 162 degrees 53 e is an amictic oligotrophic 34 m deep closed basin lake in taylor valley antarctica its perennial ice cover minimizes wind generated currents and reduces light penetration as well as restricts sediment deposition into the lake and the exchange of atmospheric gases between the water column and the atmosphere the biological community of lake hoare consists solely of microorganisms both planktonic populations and benthic microbial mats lake hoare is one of several perennially ice covered lakes in the mcmurdo dry valleys that represent the end member conditions of cold desert and saline lakes the dry valley lakes provide a unique opportunity to examine lacustrine processes that operate at all latitudes but under an extreme set of environmental conditions the dry valley lakes may also offer a valuable record of catchment and global changes in the past and present furthermore these lakes are modern day equivalents of periglacial lakes that are likely to have been common during periods of glacial maxima at temperate latitudes we have analyzed the dissolved inorganic carbon dic of lake hoare for delta 13c and the organic matter of the sediments and sediment trap material for delta 13c and delta 15n the delta 13c of the dic indicates that 12c is differentially removed in the shallow oxic portions of the lake via photosynthesis in the anoxic portions of the lake 27 34 m a net addition of 12c to the dic pool occurs via organic matter decomposition the dissolution of caco3 at depth also contributes to the dic pool except near the canada glacier where a substantial amount of allochthonous organic matter enters the lake the organic carbon being deposited on the lake bottom at different sites is isotopically similar suggesting an autochthonous source for the organic carbon preliminary inorganic carbon flux calculations suggest that a high percentage of the organic carbon fixed in the water column is remineralized as it falls through the water column at nearby lake fryxell the substantial relative to lake hoare glacial meltstream input overprints fryxell s shallow water biological delta 13c signal with delta 13c depleted dic in contrast lake hoare is not significantly affected by surface water input and mixing and therefore the delta 13c patterns observed arise primarily from biological dynamics within the lake organic matter in lake hoare is depleted in 15n which we suggest is partially the result of the addition of relatively light inorganic nitrogen into the lake system from terrestrial sources

tsunami deposits refine great earthquake rupture extent and recurrence over the past 1300 years along the nankai and tokai fault segments of the nankai trough japan abstract study of prehistoric to medieval age tsunami deposits along a riverbank site near the eastern nankai trough central japan show that not only did tokai earthquakes occur with a higher frequency than previously thought but that contemporaneous ruptures of the tokai and nankai fault segments were also more common the site revealed a 1 km long coast normal cross section of the strand plain and exposed four sandy tsunami deposits each of which indicates inundation over 2 km inland of the coast radiocarbon dating of previously studied and newly discovered deposits in the region indicates a shorter recurrence time for tokai earthquakes and clarifies their linkage with nankai earthquakes we attribute the younger two tsunami deposits to the 1498 and 1096 ce tokai earthquakes the older two deposits confirm the occurrence of the tokai earthquakes in 887 ce and in the latest 7th century these events are not reliably recorded in historical documents in the tokai region but were noted in the nankai area the 887 ce earthquake likely represents a full length rupture of the tokai and nankai segments as was the case for the 1707 ce earthquake integrated with the previous studies these new results show that nine tokai earthquakes occurred over the last 1300 years the oldest in the latest 7th century and in 887 1096 1361 1498 1614 1707 1854 and 1944 ce recalculated recurrence intervals range from 90 to 265 years except for the 1498 meio tokai earthquake the tokai earthquakes occurred simultaneously with nankai earthquakes

cenozoic tectonics in the urumgi korla region of the chinese tien shan cenozoic deformation within the tien shan of central asia has accommodated part of the post collisional indentation of the indian plate into asia within the urumgi korla region of the chinese tien shan this occurred dominantly on thrusts with secondary strike slip faulting the gross pattern of deformation is of moderate to steeply dipping thrusts that have overthrust foreland basins to the north and south of the range the junggar and tarim basins respectively smaller foreland basins lie within the margins of the range itself turfan chai wo pu korla and qumishi basins these lie in the footwalls of local thrust systems both the turfan and the korla basins contain major thrusts within them they are complex foreland basins deformation has progressively affected regions further into the interior of the junggar basin and propagated into the interiors of the intermontane basins no unidirectional deformation front has passed across the tien shan in the neogene and quaternary an oligocene unconformity may indicate the time of the onset of the cenozoic deformation but most of the cenozoic molasse has been deposited after the palaeogene the rate of deposition in basins next to the uplifted ranges has increased since the onset of deformation there has been at least about 80 km of cenozoic shortening across this part of the tien shan cenozoic shortening is greater in sections of the range further west these are nearer to the northern margin of the indian indenter cenozoic compression has reactivated structures created by the two late palaeozoic collisions that created the ancestral tien shan these palaeozoic structures have exerted a strong control over the style and location of the cenozoic deformation

active deformation of the pacific northwest continental margin tilted and uplifted marine terraces in southern oregon show progressive landward tilting of the coastal ranges at about 5 16 10 8 rad yr 1 for the last 0 25 m y tide gauges in washington and british columbia and ten resurveyed leveling lines running inland from the coast indicate contemporary landward down to the east tilt rates of about 1 12 10 8 rad yr 1 averaged over periods of from 10 to 50 years the leveling lines traverse and the terraces cut across dipping cenozoic strata pleistocene dips to 3 mio pliocene dips to 30 and eocene dips to 60 southern oregon from cape blanco to the siletz river shows geodetic or terrace tilting in the same direction as the underlying stratal dips hence present day deformation continues past deformation of the coastal ranges and is most likely related to active subduction of the juan de fuca plate the steep stratal dips lack of major active faults and historic earthquakes and presence of very young bedding plane faults suggest that much of the onshore deformation and shortening within the overlying north american plate is taken up by folding rather than thrust faulting present shortening rates across north trending folds near the coast are between 0 02 and 1 9 10 7 yr 1 the rate of shortening decreases rapidly eastwards from the juan de fuca north american plate boundary a total of about 25 mm yr 1 of permanent shortening could be occurring within the north american plate most of it in the westernmost 40 km the landward tilt and shortening rates are similar to those above many other subduction zones that have experienced great thrust earthquakes while a high strain rate measured near seattle washington has been interpreted as elastic strain accumulation before a thrust earthquake the low level of historic seismicity and the similarity of short and long term deformation rates suggest alternatively that the subduction beneath washington is aseismic the issue has considerable implications for seismic hazard evaluation in the pacific northwest and could be resolved by a search for the effects or lack of effects of prehistoric great earthquakes

jellyfish lake palau early diagenesis of organic matter in sediments of an anoxic marine lake jellyfish lake a meromictic marine lake in the palau islands western pacific ocean is accumulating organic matter rich sediments 46 wt wt below anoxic highly sulfidic bottom water elemental and stable isotope 13c data indicate that the sedimentary organic matter is primarily derived from vascular plant remains 65 90 and would form a type 2 kerogen a bacterial layer at the oxic anoxic interface in the water column may play an important role in the rapid recycling of algal derived organic matter from the highly productive surface waters the major postdepositional change in the sedimentary organic matter is carbohydrate biodegradation as shown by 13c nmr lignin and aliphatic substances are preserved in the sediments dissolved organic matter in pore waters is primarily composed of carbohydrates reflecting the degradation of sedimentary carbohydrates rate constants for organic carbon degradation and sulfate reduction in sediments of the lake are about 10 lower than in other anoxic sediments this may reflect the vascular plant source and partly degraded nature of the organic matter reaching the sediments of the lake elemental results from sediment cores and stable isotope 18o 13c studies of shells from the sediments indicate probable climatic or ecological fluctuations affecting the depositional environment of the lake between 80 and 110 yr ago the high sedimentation rate and stable environment of jellyfish lake make it a possible environment for studies of climatic fluctuations during the holocene

occurrences of dendritic gold at the mclaughlin mine hot spring gold deposit two styles of gold dendrites are variably developed at the mclaughlin mine the most abundant occurrence is hosted by amber coloured hydrocarbon rich opal silica likely precipitated from a boiling hydrothermal fluid and complexed with immiscible hydrocarbons forming an amorphous hydrocarbon silica phase this phase likely scavenged particulate gold by electrostatic attraction to the hydrocarbon silica phase the dendritic nature of the gold is secondary and is the result of dewatering of the amorphous hydrocarbon silica phase and crystallization of gold into syneresis fractures the second style of dendritic gold is hosted within vein swarms that focused large volumes of fluid flow the dendrites occur along with hydrocarbon rich silica at the upper contact of the vein margins which isolated the dendrites allowing sufficient time for them to grow in a manner similar to the amber coloured opal the dendrites may have formed by scavenging particulate gold by electrostatic attraction to the hydrocarbon silica phase

a newly dated cretaceous hydrothermal event in the iberian ranges eastern spain and its significance within the mesozoic thermal history in the iberian peninsula abstract the iberian peninsula hosts the world class hg mining district of almaden besides pre hercynian ore bodies alpine cycle hg bearing veins are also present in the eastern iberian ranges espadan deposits we present both the first absolute ages 84 4 and 85 3 ma for a post hercynian hg deposit in spain obtained from primary muscovites and a complete compilation of published mesozoic radiometric absolute ages of the iberian peninsula we deduce that there are three main thermal episodes that affected the iberian peninsula which have been revealed after the comparison among the magmatic metamorphic and hydrothermal ages moreover the espadan hydrothermal system was active when both the cretaceous alkalic magmatism took place in southern portugal and in the pyrenees and during the opening of the bay of biscay

a geologically constrained monte carlo approach to modeling exposure ages from profiles of cosmogenic nuclides an example from lees ferry arizona we present a user friendly and versatile monte carlo simulator for modeling profiles of in situ terrestrial cosmogenic nuclides tcns our program available online at http geochronology earthsciences dal ca downloads models html permits the incorporation of site specific geologic knowledge to calculate most probable values for exposure age erosion rate and inherited nuclide concentration while providing a rigorous treatment of their uncertainties the simulator is demonstrated with 10be data from a fluvial terrace at lees ferry arizona interpreted constraints on erosion based on local soil properties and terrace morphology yield a most probable exposure age and inheritance of 83 9 14 1 19 1 ka and 9 49 2 52 1 21 104 atoms g 1 respectively 2 without the ability to apply some constraint to either erosion rate or age shallow depth profiles of any cosmogenic nuclide except for nuclides produced via thermal and epithermal neutron capture e g 36cl cannot be optimized to resolve either parameter contrasting simulations of 10be data from both sand and pebble sized clasts within the same deposit indicate grain size can significantly affect the ability to model ages with tcn depth profiles and when possible sand not pebbles should be used for depth profile exposure dating

river response to an active fold and thrust belt in a convergent margin setting north island new zealand high resolution digital elevation data topsar 10 m grid are used to reconstruct late quaternary growth histories of subtle folding in the wairarapa fold and thrust belt north island new zealand outcrop data of deformed latest miocene and younger strata are combined with observations of warped and faulted late quaternary terrace surfaces to unravel the geomorphic and structural history of the huangarua river valley optically stimulated luminescence osl dating of loess that accumulated on these strath terraces and paleosol stratigraphy allow temporal correlation among the terraces and with glacial climate cycles since the last interglaciation these data indicate that five intervals of strath cutting occurred at 125 60 70 30 15 and 10 ka strath beveling is largely independent of local folding or regional base level change we hypothesize that straths are cut when an increase in sediment supply during cool climatic periods brings river sediment load and river transport capacity into balance in the wairarapa strath cutting events appear to occur near the end of cool climatic cycles this study shows that the identification of subtle departures from regional topographic trends becomes practical when a high resolution dem is available after subtraction of an average valley gradient from the digital topography the residual topography on the terrace treads reveals cross valley and longitudinal tilting although rates of folding are slow and the magnitude of deformation is commonly limited to less than a few tens of meters these topographic anomalies define fold axes that coincide with subsurface structures when combined with time control these anomalies serve to define the patterns and rates of fold growth over the past 125 kyears

crustal deformation styles along the reprocessed deep seismic reflection transect of the central iberian zone iberian peninsula abstract the multichannel normal incidence 230 km long deep seismic reflection profile alcudia was acquired in summer 2007 this transect samples an intracontinental variscan orogenic crust going across from north to south the major crustal domain the central iberian zone and its suture zone with the ossa morena zone the central unit both build up most of the southwestern part of the iberian peninsula basement this high resolution 60 90 fold profile images about 70 km depth 20 s twtt of the continental lithosphere a new data processing flow provides better structural constraints on the shallow and deep structures resulting in an image that reveals indentation features which strongly suggest horizontal tectonics the alcudia seismic image shows an upper crust c 13 km thick decoupled from the comparatively reflective lower crust the shallow reflectivity of the upper crust can be correlated with surface geological features mapped in the field whereas the deep reflectivity represents inferred imbricate thrust systems and listric extensional faults the reflectivity of the mid lower crust is continuous high amplitude and horizontal to arcuate though evidences of deformation are present as ductile boudinage structures thrusting and an upper mantle wedge suggesting a transpressional flower structure the image reveals a laminated c 1 5 km thick subhorizontal to flat moho indicating an average crustal thickness of 31 33 km the moho shows laterally variable signature being highly reflective beneath the central iberian zone but discontinuous and diffuse below the ossa morena zone the gravity response suggests relatively high density bodies in the mid lower crust of the southern half of the transect the seismic results suggest two major horizontal limits a horizontal discontinuity at c 13 15 km corresponding to the brittle ductile transition and the moho boundary both suggested to act as decoupling surfaces

reconstruction of the 2 4 million km2 late pleistocene ice sheet on the tibetan plateau and its impact on the global climate during 20 expeditions new data were obtained on the maximum extent of glaciation in tibet and the surrounding mountains evidence was found of moraines at altitudes as low as 460 m on the southern flank of the himalayas and 2300 m on the northern slope of the tibetan plateau in the qilian shan on the northern slopes of the karakorum aghil and kuen lun moraines occurred as far down as 1900 m in southern tibet radiographic analyses of erratics document former ice thicknesses of at least 1200 m glacial polishing and knobs in the himalayas and karakorum are proof of glaciers as thick as 1200 2000 m on the basis of this evidence a 1100 1600 m lower equilibrium ela line was reconstructed for the ice age which would mean 2 2 4 million km2 of ice covering almost all of tibet since the equilibrium ela line was far below the average altitude of tibet on mount everest and k2 radiation was measured up to 6650 m yielding values of 1200 1300 w m2 because of the subtropical latitude and the high altitude solar radiation in tibet is 3 4 times greater than the energy intercepted between 60 and 70 n or s with an area of 2 2 4 million km2 and an albedo of 90 the tibetan ice sheet caused the same heat loss on the earth as a 6 9 6 million km2 sized ice sheet at 60 70 n because of its proximity to the present day equilibrium ela line tibet must have undergone large scale glaciation earlier than other areas being subject to intensive radiation the tibetan ice must have performed an amplifying function during the onset of the ice age

local erosion rates versus active tectonics cosmic ray exposure modelling in provence south east france over the past decade in situ produced cosmogenic nuclides have revolutionised the study of landscape evolution in particular numerous studies have demonstrated that in active tectonic settings cosmic ray exposure dating of deformed or displaced geomorphic features makes it possible to quantify long term deformation rates in western european countries erosion due to climatically driven processes and human activities is probably the factor that most limits the accuracy of exposure ages and landscape modification rates in this study we present the results of a depth profiling technique applied to alluvial terraces located along the rhone and the moyenne durance rivers the expected decrease with depth of the measured 10be concentrations has been modelled using a 2 inversion method in order to constrain the exposure history of the alluvial sediments the results suggest that 1 over the quaternary the local surface erosion rates including both regional uplift and climatically driven processes acting on landforms are on the order of 30 m myr in southeastern france and 2 providing a fairly good bracketing of the exposure age the modelled abandonment age of alluvial terraces affected by the moyenne durance fault allows estimating incision rates comparing the alluvial terrace elevations with topographic river profiles and a minimum vertical slip rate value of roughly 0 02 mm yr for the southern segment of the moyenne durance fault

holocene environmental variations recorded by organic related and carbonate related proxies of the lacustrine sediments from bosten lake northwestern china we reconstructed a multiproxy record of the holocene climate changes from a 9 53 m core from bosten lake in the southern xinjiang of northwestern china based on a chronology supported by nine ams 1

evidence for a tropical freshwater spike during the last glacial interglacial transition in the venezuela basin δ18o and δ13c of calcareous plankton abstract oxygen and carbon isotope analysis of planktonic foraminifera and calcareous nannofossils from five box cores from the venezuela basin collected at depths between 3500 and 4800 m has revealed a detailed paleoglacial and paleoceanographic history for the last 18 000 yrs several climatic events have been recorded in these cores such as shift towards 18 o enriched values at about 13 000 yrs b p in planktic foraminifera which may be related to a sudden re advance of the northern hemisphere ice sheet and a tropical fluvial spike at about 8000 yrs b p during the completion of deglaciation comparison of carbon isotopes of nannofossils and globigerinoides sacculifer have revealed cyclical variations which has been correlated with changes in surface water circulation and productivity in the present day oceans cycles in surface water productivity have been found in the more northerly shallower cores analyzed these cycles are believed to be related to variations in intensity of upwelling during the last 18 000 yrs in the northern part of the basin the southern part of the basin had increased upwelling and productivity which resulted in increased carbonate deposition during glacial times during the present interglacial foraminifera show increased dissolution with depth but during the glacial period foraminifera are well preserved throughout the basin indicating increased watercolumn turnover rates nannofossils are well preserved during the glacial and interglacial periods analysis of the relationship of water depth to the preserved isotopic record of these two major calcareous plankton groups indicates that in this region nannofossils preserve a better record of surface water isotopic variations than planktonic foraminifera

a late pleistocene holocene lacustrine record from lake manas zunggar northern xinjiang western china information on the late quaternary palaeoclimate in the zunggar desert northern xinjiang is deduced from the study of three 5 m long cores taken from lake manas analyses including the mineralogical composition of bulk sediments stable isotope contents of carbonates organic matter pollen and diatoms were performed to help reconstruct the environmental evolution of the area the chronology is provided by 9 ams 14c dates done on carbonates or organic matter the record suggests a late pleistocene humid episode radiocarbon dated at 37 000 32 000 yr b p this episode is followed by a period of extreme aridity attributed to the last glacial maximum the early mid holocene record indicates conditions generally wetter than today as previously established for western china however our results show that the holocene period is rather complex after a minor wet warm pulse estimated to be around 12 000 yr b p the most important environmental change is recorded at 10 000 yr b p it led to the establishment of a steppic vegetation cover in the catchment and of a permanent lake which lasted 4000 years fluvial sedimentation took place between about 6000 and 4500 yr b p and it coincided with a decrease in moisture availability for vegetation growth a second lacustrine episode is recorded from about 4500 to 2500 yr b p although the pollen record and a sudden influx in detrital organic matter suggest a short term dry event around 3800 3500 yr b p the last 2500 years show climate unstability and the step wise establishment of hypersaline conditions in lake manas the major post glacial environmental changes appear to be roughly in phase with those observed in tibet

fluid inclusion gas compositions from an active magmatic hydrothermal system a case study of the geysers geothermal field usa abstract hydrothermal alteration and the active vapor dominated geothermal system at the geysers ca are related to a composite hypabyssal granitic pluton emplaced beneath the field 1 1 to 1 2 million years ago deep drill holes provide a complete transect across the thermal system and samples of the modern day steam the hydrothermal system was liquid dominated prior to formation of the modern vapor dominated regime at 0 25 to 0 28 ma maximum temperatures and salinities ranged from 440 c and 44 wt nacl equivalent in the biotite hornfels adjacent to the pluton to 305 c and 5 wt nacl equivalent at distances of 1730 m from the intrusive contact the major minor and noble gas compositions of fluid inclusions in the hydrothermally altered rocks were integrated with microthermometric and mineralogic data to determine their sources and the effects of mixing and boiling major and minor gaseous species were released from the inclusions by crushing or thermal decrepitation noble gases were released by crushing the samples were analyzed by mass spectrometry the analyses document the presence of magmatic crustal and meteoric components in the trapped fluids hydrothermal fluids present during the liquid dominated phase of the system contained gaseous species derived mainly from crustal and magmatic sources at the geysers n 2 ar ratios greater than 525 and 3 he 4 he ratios of 6 10 7 ra are diagnostic of a magmatic component crustal gas has co 2 ch 4 ratios less than 4 n 2 ar ratios between 45 and 525 and low 3 he 4 he ratios 0 5 ra meteoric fluids have co 2 ch 4 ratios greater than 4 and n 2 ar ratios between 38 air saturated water and 84 air however n 2 ar ratios between 15 and 110 can result from boiling ratios less than 15 reflect the incorporation of n 2 into nh 3 bearing clay minerals in the central geysers the incursion of meteoric fluids occurred during the transition from the liquid to vapor dominated regime variations in the relative ch 4 co 2 and h 2 contents of the gas analyses demonstrate that boiling took place under open system conditions the gas data indicate that the inclusions have remained closed to the diffusion of he and h 2 since their formation

estimation of slip rates in the southern tien shan using cosmic ray exposure dates of abandoned alluvial fans cosmic ray exposure dates based on in situ produced 10 be in combination with measured heights of fault scarps that cut three abandoned fans imply a slip rate of less than 2 mm yr on the bounding thrust fault along a segment of the southern flank of the tien shan of central asia this rate somewhat lower than those for the segment farther west and for the northern margin of the belt implies that the distribution of shortening across the tien shan must change markedly along the belt the date of abandonment of the smallest of the three fans is consistent with fan formation since the last glacial maximum but the other two fans appear to have been formed and abandoned prior to that time these and other results suggest that advances and retreats of alpine glaciers may not be synchronized with continental ice sheets and that not all prominent geomorphological features in arid asian regions have formed since the last glacial maximum in this study we have assessed the relationship between cosmogenic nuclide content of individual clasts and the time since their deposition on a surface cosmogenic nuclide accumulation represents the integrated total surface exposure of rocks in source regions during transport and since deposition postdepositional processes erosion burial bioturbation and cryoturbation all of which decrease the quantity of cosmogenic nuclides produced in a rock in a given time and hence the apparent exposure age also cause significant scatter among apparent ages of samples from the surfaces very low 10 be concentrations in material from active streambeds and at depth below one of the fan surfaces indicate that exposure prior to deposition onto fan surfaces was minimal

geochemistry of modern carbonaceous sediments overlain by a water mass showing photic zone anoxia in the saline meromictic lake kai ike southwest japan i early diagenesis of organic carbon nitrogen and phosphorus abstract the early diagenetic effects of organic matter om decomposition in carbonaceous sediments overlain by an anoxic water body were investigated using a sediment core kai4 from the saline meromictic lake kai ike in southwest japan lake kai ike a current model for past anoxic ocean environments is characterized by development of photic zone anoxia and a bacterial plate which create permanent density stratification in the water over the last 40 years rapid decreases in organic carbon corg 55 nitrogen 60 and reactive phosphorus p 85 contents accompanied by 1 increase positive shift in the stable isotope compositions of corg 13corg which is attributed to a preferential loss of low 13corg components during early diagenesis are reflected with increasing depth of the sediments the molar corg p and n p ratios increase with depth from initial values that are very close to those of the redfield ratio during the early diagenesis of om degradation the decomposition rate of p is much faster than that of corg and n in contrast the molar corg n ratios are rather insensitive to various biogeochemical reactions confirming their utility as a proxy for source om although the stable isotope compositions of nitrogen 15n in sedimentary om are useful indicators of om sources correlations to the above mentioned parameters for the kai4 core remain unclear we emphasize that the om present in ancient carbonaceous sediments or sedimentary rocks was most likely subject to very rapid

elemental mercury at submarine hydrothermal vents in the bay of plenty taupo volcanic zone new zealand hot springs in active geothermal areas such as yellowstone national park the geysers geothermal field in california and the taupo volcanic zone in new zealand are notably enriched in the trace metals au ag as sb and hg such near surface hot springs have formed many of the world s important deposits of gold and silver and some of the largest deposits of mercury the majority of these are associated with continental geothermal systems in subaerial environments here we report the discovery of active mercury depositing hot springs in a submarine setting at nearly 200 m water depth within the offshore extension of the taupo volcanic zone of new zealand these vents contain the first documented occurrence of elemental mercury on the sea floor and provide an important link between offshore hydrothermal activity and mercury depositing geothermal systems on land the discovery has implications for mercury transport in sea floor hydrothermal systems and underscores the importance of submarine volcanic and geothermal activity as a source of mercury in the oceans

jellyfish lake palau regeneration of c n si and p in anoxic marine lake sediments sediment cores from jellyfish lake were processed under an inert atmos phcre and the pore waters extracted and analyzed for the following parameters ph titration alkalinity ta cl h4si04 pod3 nh4 ca2 mg2 sod2 and h2s additionally in one set of pore water samples core lo the 613c of the x0 was also determined the ta h4si04 pod3 nh and h s increased with depth in the pore waters above anoxic bottom water values h s values increased to 3 8 pm in one case both h sio and pod3 concentrations increased to a maximum value and then decreased with depth suggesting removal into solid phases the h sio concentrations are equal to or greater than pore water values observed in sediments underlying upwelling areas pod3 concentrations are in general lower than pore water values from terrigenous nearshore areas but higher than nearshore carbonate pore water values from florida bay or bermuda the ca2 cl and mg2 cl ratios show slight decreases in the top 15 20 cm suggesting that authigenic carbonate may be forming this suggestion is supported by the fact that the pore waters are saturated with respect to caco due to the very high tas the 613c measurements of the pore water x0 are from a shorter core these measurements reach their most negative concentration at 72 cm and tilen become slightly heavier this change is accompanied by a decrease in ta suggesting the onset of methanogenesis at this location in this core

use of in situ produced 10be in carbonate rich environments a first attempt we have determined the production rate of in situ produced 10be in calcite through measurements of 10be and 36cl concentrations in the same calcite samples and of 10be concentrations in depth profiles of flint from the same erosional surface this yields a 10be production rate in calcite of 37 9 6 0 at g yr at sea level and high latitude approximately sixfold higher than production in the coexisting flint we propose that this higher rate of production may be due to high production cross sections for c spallation by cosmic rays with energies below 50 mev these results also open the possibility of dating burial events in carbonate rich environments by differential radioactive decay of 10be and 36cl

active alluvial systems in the korla basin tien shan northwest china sedimentation in a complex foreland basin the tien shan is a cenozoic orogenic belt in central asia caused by the post collisional convergence of india with asia that reactivated palaeozoic faults the korla basin is a complex foreland basin within the chinese tien shan elongate sub basins within it have received sediment from both the hangingwall and footwall blocks above and below reverse faults on their northern margins the footwall blocks are themselves uplifted by the next fault to the south the greater part of the sediment supply measured by area comes from the footwall block this sediment supply pattern is analogous to that of extensional half graben

biogeochemical cycling in an organic rich coastal marine basin 7 sulfur mass balance oxygen uptake and sulfide retention sulfur and oxygen fluxes were quantified in the seasonally varying anoxic marine sedimentary system of cape lookout bight n c u s a over the three year study period 1981 1983 the mean annual sulfate reduction rate was determined to be 18 2 1 6 moles m 2 y 1 this value added to the estimate of the detrital sulfur input of 1 2 4 4 gave a total sulfur input of 19 4 4 7 moles m 2 y 1 the sulfide flux to the sediment water interface measured in anaerobic benthic chambers was 4 6 0 5 moles m 2 y 1 and represented 37 of the annual oxygen uptake rate of 25 2 2 8 moles m 2 y 1 the sulfide burial rate determined to be 15 5 3 1 moles m 2 y 1 was within 5 of the value predicted by summing the fluxes at the sediment water interface the cs weight ratio of sediment below the depth of diagenetic reaction was determined to be 2 75 the sulfide retention rate in these rapidly accumulating sediments 10 cm yr was 77 19 comparison of this result with previous studies shows that rapid sediment accumulation and the lack of bioturbation control this unusually high degree of sulfide retention

quaternary climate change and the formation of river terraces across growing anticlines on the north flank of the tien shan china nested stream terraces warped upward over actively growing anticlines along the north flank of the tien shan in western china appear to record alternating phases of valley widening and incision differences of relative heights between remnants of four separate strath terraces along one river and between two such terraces along another reach 100 to 120 m over the crests of the anticlines we infer that this spacing is due to alternating stages of valley widening and rapid incision associated with climate changes with a periodicity of 100 kyr the crests of the anticlines appear to emerge from the aggrading flanks of the anticlines at an average rate of about 1 mm a the maximum heights of 25 and 35 10 m for the lowest terraces above their projected initial profiles imply ages of roughly 25 kyr and 35 kyr 10 kyr hence they suggest that flood plains which were abandoned to form the terraces developed adjacent to active stream beds during the last glacial period when climates were relatively

hydrocarbon and ore bearing basinal fluids a possible link between gold mineralization and hydrocarbon accumulation in the youjiang basin south china the youjiang basin which flanks the southwest edge of the yangtze craton in south china contains many carlin type gold deposits and abundant paleo oil reservoirs the gold deposits and paleo oil reservoirs are restricted to the same tectonic units commonly at the basinal margins and within the intrabasinal isolated platforms and or bioherms the gold deposits are hosted by permian to triassic carbonate and siliciclastic rocks that typically contain high contents of organic carbon paragenetic relationships indicate that most of the deposits exhibit an early stage of barren quartz pyrite stage i a main stage of auriferous quartz arsenian pyrite arsenopyrite marcasite stage ii and a late stage of quartz calcite realgar orpiment native arsenic stibnite cinnabar dolomite stage iii bitumen in the gold deposits is commonly present as a migrated hydrocarbon product in mineralized host rocks particularly close to high grade ores but is absent in barren sedimentary rocks bitumen dispersed in the mineralized rocks is closely associated and or intergrown with the main stage jasperoidal quartz arsenian pyrite and arsenopyrite bitumen occurring in hydrothermal veins and veinlets is paragenetically associated with stages ii and iii mineral assemblages these observations suggest an intimate relationship between bitumen precipitation and gold mineralization in the paleo petroleum reservoirs that typically occur in permian reef limestones bitumen is most commonly observed in open spaces either alone or associated with calcite where bitumen occurs with calcite it is typically concentrated along pore vein centers as well as along the wall of pores and fractures indicating approximately coeval precipitation in the gold deposits aqueous fluid inclusions are dominant in the early stage barren quartz veins stage i with a homogenization temperature range typically of 230 c to 270 c and a salinity range of 2 6 to 7 2 wt nacl eq fluid inclusions in the main and late stage quartz and calcite are dominated by aqueous inclusions as well as hydrocarbon and co2 rich inclusions the presence of abundant hydrocarbon fluid inclusions in the gold deposits provides evidence that at least during main periods of the hydrothermal activity responsible for gold mineralization the ore fluids consisted of an aqueous solution and an immiscible hydrocarbon phase aqueous inclusions in the main stage quartz associated with gold mineralization stage ii typically have a homogenization temperature range of 200 230 c and a modal salinity around 5 3 wt nacl eq homogenization temperatures and salinities of aqueous inclusions in the late stage drusy quartz and calcite stage iii typically range from 120 c to 160 c and from 2 0 to 5 6 wt nacl eq respectively in the paleo oil reservoirs aqueous fluid inclusions with an average homogenization temperature of 80 c are dominant in early diagenetic calcite fluid inclusions in late diagenetic pore and fissure filling calcite associated with bitumen are dominated by liquid c2h6 vapor ch4 ch4 h2o and aqueous inclusions with a typical homogenization temperature range of 90 c to 180 c and a salinity range of 2 8 wt nacl eq it is suggested that the hydrocarbons may have been trapped at relatively low temperatures while the formation of gold deposits could have occurred under a wider and higher range of temperatures the timing of gold mineralization in the youjiang basin is still in dispute and a wide range of ages has been reported for individual deposits among the limited isotopic data the rb sr date of 206 12 ma for au bearing hydrothermal sericite at jinya as well as the re os date of 193 13 ma on auriferous arsenian pyrite and 40ar 39ar date of 194 6 2 ma on vein filling sericite at lannigou may provide the most reliable age constraints on gold mineralization this age range is comparable with the estimated petroleum charging age range of 238 185 ma and the sm nd date of 182 21 ma for the pore and fissure filling calcite associated with bitumen at the shitouzhai paleo oil reservoir corresponding to the late indosinian to early yanshanian orogenies in south china the close association of carlin type gold deposits and paleo oil reservoirs the paragenetic coexistence of bitumens with ore stage minerals the presence of abundant hydrocarbons in the ore fluids and the temporal coincidence of gold mineralization and hydrocarbon accumulation all support a coeval model in which the gold originated migrated and precipitated along with the hydrocarbons in an immiscible gold and hydrocarbon bearing basinal fluid system

alluvial sequence in the north piedmont of the chinese tian shan over the past 550 kyr and its relationship to climate change abstract a new division of middle and late pleistocene alluvial sequence in the north piedmont of the chinese tian shan based on geomorphologic stratigraphic and chronologic criteria provides a framework for examining their relationship to climate change during glacial interglacial transitions over the past 550 kyr at least four major alluviation episodes occurred within the piedmont along the major river valleys in this region each episode of alluvial fan deposition morphologically correlates with a major river terrace these correlations create a regionally applicable framework for subdivision of the quaternary alluvial sequence in the study area where seven stepped river terraces are defined our new chronology of this fluvial sequence suggests that following intervals of aggradation three highest river terraces and equivalent alluvial fans were abandoned at 530 ka 300 ka and 10 ka respectively paleosols at the base of the loess sequences that directly overlie the older terraces and fans suggest that episodes of aggradation occurred late in the glacial cycles the subsequent incision that caused abandonment stabilization of these terraces and fans occurred near to glacial interglacial transitions a relatively high degree of synchrony in major river incision events across the piedmont despite disruption by several discrete structure zones with asychronous tectonic activities supports the dominant control exerted by climatic conditions on alluvial deposition and terrace creation during the quaternary across the north piedmont of the chinese tian shan

vegetation and climate during the last 30 000 years in ladakh abstract pollen analysis was carried out from a 23 m core dating from about 30 000 to 9000 yr b p from the alpine tsokar lake about 4572 m above sea level in ladakh trans himalayan region this study reveals the continuation of the alpine steppe with four periods of expansion of juniperus communities during 28 000 30 000 yr b p 21 000 18 375 yr b p slightly before 15 800 yr b p and at 10 000 yr b p these phases of juniperus expansion were interpreted as events of amelioration of climate within the alpine steppe during the later part of the last weichselian glaciation in the alpine trans himalayan region

irregular earthquake cycle along the southern tianshan front aksu area china 1 a long deformation record 16 5 ka showing nonsteady earthquake recurrence is established for the aksu thrust tianshan china on the basis of cosmogenic 10be dating of faulted surfaces topographic leveling across the aksu fault scarp indicates up to 10 m uplift across a moraine abandoned 16 5 ka and similar uplift of 6 m across two inset surfaces yielding ages of 12 5 and 5 ka successively smaller uplifts of terraces younger than 5 ka indicate that three or more major earthquakes occurred during this period these data show that the aksu thrust fault was quiet for at least 7500 years and active in the last 5000 years and probably in the interval 16 5 12 5 ka the seismic cycle along the aksu thrust fault over the last 16 500 years was thus strongly irregular showing long quiescence and clustering which is a challenge for paleoseismology and hazard assessment this irregularity also makes it more difficult to estimate long term shortening rates nevertheless we are able to constrain a minimum total shortening rate 7 mm yr across the southern tianshan front for the last 12 500 years that is about a third of the total geodetic rate for the western tianshan 20 mm yr

dating of alteration episodes related to mercury mineralization in the almaden district spain the almadin mercury deposits represent one of the largest geochemical anomalies on earth but the mode and timing of their formation remains a matter of controversy there are two main possibilities hydrothermal solutions associated with alkali basalt volcanism in the silurian and devonian or regional hydrothermal activity during later hercynian metamorphism although these models can be distinguished by determining the age of ore deposition no suitable isotopic method had been applied to the problem prior to this study we report here on vacuum encapsulated and more traditional laser ar ar dating performed on illite concentrates and cr rich micas that are intimately associated with mercury mineraiization in both devonian and silurian host rocks illite is associated with a later stage of hg mineralization cinnabar kaolinite pyrophyllite chlorite which locally replaces an earlier episode associated with carbonates and cr mica the dating results from illite separates suggest that the later stages of hg mineralization or remobilization occurred about 360 ma which is about 20 ma younger than any mercury hosting rocks in the district and coincides with the onset of regional deformation during the hercynian orogeny cr mica ages are variable and range from 365 ma to 427 ma this age range spans the period between the deposition of the criadero quartzite the oldest sedimentary unit hosting mercury and the later episode of mineralization this suggests that mineralization started at least by the mid to lower silurian and the younger argon ages for cr mica could represent partial to nearly total argon loss caused by the hercynian metamorphic event it appears that both postulated styles of mercury mineralization occurred separated in time by up to 80 million years

a 900 k y record of strath terrace formation during glacial interglacial transitions in northwest china the timing of the development of strath terraces with respect to climatic variability remains equivocal previous studies attribute strath terrace formation to glacial or interglacial climates or to variations in sediment and water fluxes that cause lateral erosion followed by vertical incision a chronology of strath terrace formation spanning similar to900 k y has been generated on the basis of loess paleosol couplets and paleomagnetic thermoluminescence and radiocarbon dating of strath terraces in the qilian shan of northeastern tibet repetitive stratigraphic and geomorphic patterns on each terrace indicate that they formed during glacial interglacial transitions long term bedrock incision rates and inferred rock uplift rates appear steady and unrelated to strath formation over the past 900 k y

quaternary rate of folding of the ventura avenue anticline western transverse ranges southern california upper quaternary terraces of the ventura river california are uplifted tilted and folded over the ventura avenue anticline rates of uplift and tilting have decreased since inception of the structure over the past 200 ka assuming that the chronology based on amino acid racemization 14c dates and soils correlation is approximately correct then the minimum possible average rate of uplift in the axial region of the fold has decreased from 14 mm yr to 2 mm yr during the past 200 ka interval rates of uplift for the periods 200 ka to 80 or 105 ka 80 or 105 ka to 30 ka and 30 ka to present are respectively about 20 mm yr 9 mm yr and 5 mm yr the rate of tilting shows a similar trend decreasing from 5 8 urad yr 2 5 urad yr and 1 2 urad yr for the same time intervals respectively based on the mechanics of flexural slip folds in stratified sedimentary rocks these data suggest that the rootless ventura avenue anticline is a fold that has been shortening at a relatively constant rate of about 9 mm yr since its inception

examination of surface exposure ages of antarctic moraines using in situ produced 10be and 26al concentrations of 10be t12 1 5 106 y and 26a1 t12 0 72 106 y have been determined by accelerator mass spectrometry ams in a suite of quartz samples taken from sandstone boulders in several moraines in arena valley a dry valley adjacent to the taylor glacier in the quatermain mountains southern victoria land east antarctica these isotopes are produced in surficial quartz by cosmic ray spallation of o and si the concentrations in these samples ranged from 6 1 105 to 3 0 107 at g 1 for 10be and from 9 4 106 to 1 2 108 at g 1 for 26a1 depending upon the extent of exposure at the surface analyses of 10be in several samples from a single moraine at altitudes ranging from 1300 to 1650 m permitted an estimation of the air attenuation pathlength of cosmic ray neutrons the value of 142 96 41 g cm 2 is consistent with other published values production rates of 17 6 4 at g 1 y 1 for 10be and 113 54 16 at g 1 y 1 for 26a1 at 1300 m and 87 s and a 26al 10be production ratio of 6 5 1 3 1 3 were calculated from the data these values correspond to sea level production rates at high geomagnetic latitude of 6 4 at g 1 y 1 and 41 7 at g 1 y 1 for 10be and 26a1 respectively consistent with determinations based on 11 ky glacially polished surfaces in the sierra nevada in california these production rates imply exposure ages for the various moraines ranging from 50 ky to 2 5 my in accordance with other geological evidence the 10be and 26al ages of these rocks compare favorably with those found using a similar dating method based on in situ production of 3he examination of the 3he concentrations in conjunction with the present data set yields an estimate of 3he production of 230 8540 at g 1 y 1 corresponding to 85 31 15 at g 1 y 1 at sea level this is lower than previously reported values of 240 60 at g 1 y 1 and 190 at g 1 y 1 scaled to sea level and high geomagnetic latitude based respectively on volcanic flows less than 2000 years old at low latitude and samples collected from 14 400 year old volcanic flows this discrepancy is likely due to diffusive losses which may become significant up to 50 for surface exposure ages on the order of 2 0 my nevertheless the general correlations among the three isotopes suggest that 3he does not suffer gross losses through diffusion

uplift and active tectonics of southern albania inferred from incision of alluvial terraces abstract in albania the osum and vjoje rivers cross the active graben system and the active frontal thrust system of the albanides the effects of climatic and geodynamic forcing on the development of these two rivers were investigated by the means of field mapping topographic surveying and absolute exposure age dating we established the chronology of terraces abandonment from the compilation of new dating 14c and in situ produced 10be and previously published data we identified nine fluvial terraces units developed since marine isotope stage 6 up to historic times from this reconstituted history we quantified the vertical uplift on a time scale shorter than the glacial climatic cycle regional bulging produces an overall increase of the incision rate from the west to the east that reaches a maximum value of 2 8 m ka in the hinterland local pulses of incision are generated by activation of normal faults the most active faults have a sw ne trend and a vertical slip rate ranging from 1 8 to 2 2 m ka this study outlines the geodynamic control in the development of rivers flowing through the albanides on the scale of 103 105ka

early pleistocene incision of the san juan river utah dated with 26al and 10be cosmogenic 26al and 10be in alluvial gravel on a strath 150 m above the san juan river utah reveal a depositional age of batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document 1 36 0 20 0 15 end document ma this gravel is correlative with a series of terraces that grade to glen canyon on the colorado river indicating a similar age for incision there the calculated incision rate 110 14 m m y is somewhat slower than that of the colorado river in the eastern grand canyon and suggests active steepening of the colorado river the cosmogenic nuclides also indicate rapid erosion in the sediment source area and are consistent with alluviation due to enhanced pleistocene erosion in the san juan mountains

speciation and isotopic composition of sulfur in sediments from jellyfish lake palau abstract jellyfish lake palau is a meromictic marine lake with high organic productivity low reactive fe content and anoxic bottom waters sediment samples from jellyfish lake were examined for the distribution of sulfur species and their isotopic signatures in order to gain a better understanding of sedimentary sulfur incorporation in fe poor environments surface samples were taken along a transect from a near shore site to the center of the lake and include a sample below oxic water a sample below the chemocline layer and samples below anoxic waters three additional samples were taken from a core 2 m long collected near the lake center sulfur to organic carbon weight ratios in all samples were lower than the expected value of 0 36 for normal marine sediment probably because the lake water is deficient in reactive fe to form iron sulfides total sulfur contents in the surface sediments indicated no changes with distance from shore however the sulfur content of the surface sample at the chemocline layer may be slightly higher total sulfur content increased with depth in the core and is inversely related to organic carbon content organic sulfur is the major sulfur species in the samples followed in descending order by sulfate disulfides and monosulfides sulfate sulfur isotope 34 s values are positive from 20 56 to 12 04 reflecting the marine source of sulfate in jellyfish lake disulfide and monosulfide 34 s values are negative from 25 07 to 7 60 because of fractionation during bacterial reduction of sulfate monosulfide 34 s values are somewhat higher than those of disulfides and they are close to the 34 s values of organic sulfur these results indicate that most of the organic sulfur is formed by reaction of bacteriogenic monosulfides or possibly monosulfide derived polysulfides with organic matter in the sediment

low slip rates and long term preservation of geomorphic features in central asia in order to understand the dynamics of the india asia collision zone it is important to know the strain distribution in central asia whose determination relies on the slip rates for active faults1 2 3 4 5 many previous slip rate estimates of faults in central asia were based on the assumption that offset landforms are younger than the last glacial maximum 20 kyr ago 6 7 8 9 10 11 in contrast here we present surface exposure ages of 40 to 170 kyr obtained using cosmogenic nuclide dating for a series of terraces near a thrust at the northern margin of the tibetan plateau combined with the tectonic offset the ages imply a long term slip rate of only about 0 35 mm yr 1 for the active thrust an order of magnitude lower than rates obtained from the assumption that the terraces formed after the last glacial maximum our data demonstrate that the preservation potential of geomorphic features in central asia is higher than commonly assumed

use of a new 10be and 26al inventory method to date marine terraces santa cruz california usa marine terraces along active continental margins reflect the interplay between sea level oscillations and rock uplift well dated marine terraces record the timing of sea level highstands and delimit both uplift and geomorphic rates cosmogenic radionuclides provide a new tool for dating previously undatable terraces because the five marine terraces north of santa cruz california are capped by well developed soils formed in regressive marine sands both predepositional cosmogenic radionuclide inheritance and bioturbation of the profile must be accounted for we present a new cosmogenic radionuclide inventory method that uses the depth integrated cosmogenic radionuclide concentration to determine the terrace age this method yields terrace ages that correlate well with sea level highstands of marine oxygen isotope stages 3 5a 5c 5e and 7 the implied uplift rate is steady at 1 1 mm yr and is two to three times higher than rates suggested by earlier studies

origin of petroleum and mercury in the culver baer cinnabar deposit mayacmas district california the culver baer mercury deposit mayacmas district is located within the strike slip mercuryville fault zone at the margin of the geysers geothermal area where serpentine magnetite protolith is altered to silica carbonate rock silica carbonate rock is silica rich at the center of the deposit and consists of the assemblage quartz magnesite pyrite this assemblage is cut by numerous quartz chalcedony veins and breccia veins composed of quartz chalcedony or cinnabar or petroleum or millerite or barite the cinnabar which is chemically pure and the petroleum which consists predominantly of polycyclic aromatic hydrocarbons occur preferentially along the hanging walls of the breccia veins outward from the deposit center there is a zonation to carbonate rich silica carbonate rock which consists of magnesite or quartz or pyrite at the deposit margin itself magnesite or magnetite is the dominant stable assemblage all rock samples reveal a consistent temporal evolution from magnesite veinlets to silica veinlets geochemical modeling indicates that the mineralogical zonation from serpentinite to silica rich silica carbonate rock in the center of the deposit can arise from the interaction of serpentinite with a co 2 rich h 2 o co 2 fluid pco 2 or 30 bars at 200 degrees c petrographic and analytical data suggest that other than co 2 the only components added to the system during alteration and mineralization were h 2 s hg and petroleum isotopic and biological marker data support the hypothesis that all of these components may have been derived from local sedimentary rocks in response to heating and transported to the site of deposition in a gas phase the association of petroleum and cinnabar particularly along the hanging walls of breccias is most likely due to a common source and transport in a relatively buoyant fluid rather than due to a direct chemical link because there is no evidence for the introduction of any other components these data suggest that the culver baer deposit may be a fossil condensate zone akin to the model of white et al 1971

late oligocene early miocene initiation of shortening in the southwestern chinese tian shan implications for neogene shortening rate variations abstract the cenozoic tian shan is one of the preeminent examples of an intracontinental orogen however there remains a significant controversy over when deformation related to the india asia collision commenced and therefore how shortening within the mountains has been partitioned over time one approach has been to look at the modern shortening rate as measured by geodetic studies combined with estimates of the total shortening across the range and extrapolate backwards this approach suggests that the onset of range construction was ca 10 ma k y abdrakhmatov s a aldazhanov b h hager m w hamburger t a herring k b kalabaev k b kalabayev v i makarov p molnar s v panasyuk m t prilepin r e reilinger i s sadybakasov b j souter y a trapeznikov v y tsurkov a v zubovich relatively recent construction of the tien shan inferred from gps measurements of present day crustal deformation rates nature 384 6608 1996 450 453 an alternate method is to determine the age of the onset of exhumation using thermochronology we present 19 new apatite fission track aft results from the southwestern chinese portion of the belt this region represents the first area exhumed during the late tertiary along a transect at ca 76 e exhumation commenced at the oligocene miocene boundary 24 ma along the maidan and muziduke thrusts which bound the southern side of the kokshaal range subsequently deformation propagated ca 20 km south to the kashi basin bounding thrust kbt which was exhumed by no earlier than 18 9 3 3 ma three detrital aft samples from plio pleistocene strata deposited ca 20 km farther south contain fission track grain age peaks that young monotonically upwards from 20 9 7 0 5 3 ma to 15 9 5 4 4 0 ma with a fairly constant lag time of 16 to 18 ma these ages combined with structural data suggest that both the hanging wall and the footwall of the kbt experienced a renewed episode of exhumation during the latest cenozoic the discrepancy between the late oligocene miocene initiation of significant exhumation shown herein and the 10 ma initiation estimate from geodesy suggests that the tian shan has undergone a complex late cenozoic shortening history assuming that the present shortening rate could account for the total amount of cenozoic shortening in 10 ma and realizing that shortening initiated at least 15 myr earlier we conclude that the shortening rate must have varied over time possibly in pulsed southward migrating events and that the present rate may not reflect the average rate since initiation of range uplift

nutrient cycling and the biogeochemistry of manganese iron and zinc in jellyfish lake palau the oxic waters in jellyfish lake a stagnant marine lake in palau are depleted in n03 pod3 dissolved si mn fe and zn while the underlying anoxic waters are significantly enriched in these species and nh nh and pod3 regeneration and dissolved sulfide production in the anoxic zone yield a stoichiometry of c n p for organic matter undergoing recycling in the anoxic waters in the anoxic zone dissolved mn fe and zn reach maximum concentrations of 30 22 and 2 5 nm the fe concentrations are consistent with mackinawite or greigite solubility control mn approaches saturation with respect to haurite zn may be controlled by the solubility of zns coprecipitate the sediments are enriched in fe and depleted in zn relative to asian dust at enewetak a twobox model is used to calculate an eddy diffusion coefficient of 0 00 15 cm2 s l across the chemocline the upward diffusive loss of nh added to the sedimentation rate of n and multiplied by the stoichiometric c n ratio yields an organic carbon flux into the anoxic waters of 1 200 pmol c cm 2 yr i which is 13 of the total primary productivity

geomorphic evidence of active deformation and uplift in a modern continental wedge top foredeep transition example of the eastern ecuadorian andes abstract the eastern ecuadorian andes appear as a fold and thrust belt adjacent to a continental foredeep represented by one of the world s largest tropical alluvial megafans the pastaza megafan debouching into the amazonian lowland the apex of the pliocene pleistocene megafan situated in the present day wedge top subandean zone has been cut by an erosion surface the western part of which has been uplifted of 500 m along the frontal thrust forming a poorly dissected plateau the mera plateau this erosion surface erased most of the previous fluvial landscape but preserved a large thrust related anticlinal hinge deforming less erodible underlying strata the mirador fold and smaller sized anticlines this surface has been then incised by two antecedent major rivers the pastaza and the napo and few tributaries the plateau edge is marked by a series of large scale gently sloping landslides clustered along a 70 km long concave eastward line associated with the frontal thrust fault the newly formed immature rivers issued from the landslides or sourced within east dipping remnants of the erosion surface downstream of the landslide line constitute the greatest part of the streams feeding the ecuadorian amazonian basin at 70 to 100 km from the landslide line the drainage abruptly changes from highly immature to mature with a well defined hinge line representing the outer limit of landslide and tectonic control the diversions of the pastaza river indicate ongoing fold growth since at least the late pleistocene in the eastern cordillera and the early holocene in the mera plateau the preserved terraces of the pastaza valley are all degradational and are ascribed to periods of tectonic seismic activity alternating with periods of tectonic quiescence or decreased seismic activity rather than to climatic events 14c dating of the plateau erosion surface and of the upper pastaza terraces indicates that the minimum average incision rate since 18 000 years bp varies locally in the upper pastaza valley from 0 5 to 0 67 cm year 1 increasing from 18 000 years bp to now a comparison of these incision rates with fold and thrust fault uplift rates indicates that incision in the upper pastaza valley was a result of rapid uplift up to 1 cm year 1 along the mirador fold and thrust which caused a restoration of the local equilibrium profile of the upper reach combined with smaller local fault uplift along the westernmost thrust faults the uplift of the whole mera plateau with respect to the upper amazonian basin gives a minimum average uplift rate of 2 8 cm year 1 since 18 000 years bp the overall uplift of the mera plateau and the eastern cordillera is likely to have been caused by a regional scale low angle thrust ramp emerging as the frontal thrust fault

mechanisms of active folding of the landscape southern tian shan china 1 we explore the kinematic mechanisms of active large scale folding based on analysis of two adjacent major anticlines in tian shan central asia that share an acceleration of shortening rate leading to topographic emergence and folded geomorphic surfaces their folding mechanisms are fundamentally different yakeng anticline is a gentle pure shear detachment fold with 1200 m of shortening and a well constrained history of growth beginning at 5 5 ma with an order of magnitude increase in shortening rate from 0 16 to 1 2 1 6 mm yr at 0 16 0 21 ma the shape of the deformed topographic surface and of subsurface horizons deposited during deformation is a linearly proportional image at reduced amplitude of the deeper structure which shows that instantaneous uplift rates have been pointwise linearly proportional to the current finite fold amplitude in contrast quilitak anticline is a complex fault bend fold with uplift rates proportional to the sine of the fault dip showing discontinuities in uplift rate across active axial surfaces the 10 to 20 km wide anticline is topographically emergent only in a central 5 to 7 km wide mountainous uplift the abrupt southern edge of which is marked by 600 to 700 m high triangular facets that result from active folding of a pediment across an active axial surface the giant facets are shown to form by kink band migration and record postemergence deformation since an order of magnitude acceleration in shortening rate from 0 6 to 4 5 mm yr apparently contemporaneous with yakeng sections logged across the active 115 m wide hinge zone show that recent strata provide a bed by bed record of fold scarp growth which is quantitatively deciphered by fitting bed shapes to a finite width kink band migration model

quantifying passive margin denudation and landscape development using a combined fission track thermochronology and cosmogenic isotope analysis approach abstract a new approach to empirically constraining numerical models of denudation and landscape development across passive continental margins is presented involving a combination of apatite fission track thermochronology and cosmogenic isotope analysis this integrated strategy is applied to the namibian sector of the south west african margin where the conventional landscape evolution model of inland retreat of an escarpment initiated at the coast at break up implies a mean rate of retreat of 1 km ma 1 the thermochronological and cosmogenic isotope data are incompatible with a simple escarpment retreat model since they show that denudation rates oceanward of the present escarpment position have been low 1 since the end of the eocene and the estimated rate of escarpment retreat has been only 10 m ma 1 this low rate of retreat is however consistent with numerical landscape evolution models where the escarpment is pinned at an inland drainage divide

uplift driven valley incision and river terrace formation in southern england outside the limits of middle pleistocene glaciation the river basins of southern england contain long cenozoic terrestrial sedimentary records of greatest importance are the river terrace sequences which contain biostratigraphical and sedimentary evidence that testifies to the high amplitude climatic changes of the quaternary however trends in valley development cannot easily be accommodated within the framework of quaternary climatic change it is argued in this paper that episodic incision and terrace development result from uplift a consequence of the interplay between continuing alpine orogenic movements and erosion driven isostasy using a simple linear model height age an uplift rate of ca 7 cm ka 1 is estimated for the terrace sequence in the upper thames valley this preliminary model is evaluated using the records of adjacent basins 1997 john wiley sons ltd

geometric and numerical model of progressive limb rotation in detachment folds a simple area balanced geometric model of progressive limb rotation in detachment folds allows the quantification of displacement uplift and rotation and the assessment of their effect upon growth strata geometries translation of this geometric model into a velocity model of deformation allows the modeling of associated growth strata resulting from background sedimentation and local erosion transport and deposition we show that with constant displacement and sedimentation rate this model predicts a progressive unconformity indicating the onlap and eventual overlap of the fold limb caused by a decreasing uplift rate this decrease is a consequence of the kinematics of progressive limb rotation increases in displacement rate with sedimentation rate kept constant can lead to offlap and angular unconformities although subsequent onlap does not necessarily reflect a return to a lower displacement rate modeled growth strata geometries exhibit many of the features reported from the literature

the fluid inclusion and mineralogic record of the transition from liquid to vapor dominated conditions in the geysers geothermal system california the geysers an active vapor dominated geothermal system related to a hypabyssal granitic pluton was liquid dominated from its inception at 1 2 to 0 3 ma when the modern vapor dominated regime formed as the hydrothermal liquids boiled off a vapor dominated heat pipe developed in which the flow of steam was balanced by downward percolation of condensate a record of the transition from liquid to vapor dominated conditions is contained within late stage quartz and calcite crystals that are common in the upper part of the steam reservoir and overlying cap rock samples from three localities were examined in detail quartz from these veins is characterized by corroded crystal faces solid inclusions of contemporaneous calcite that are generally etched coeval high and low salinity fluid inclusions primary low salinity liquid rich inclusions and abundant vapor rich inclusions primary vapor rich inclusions up to 2 mm across were trapped mainly on rhombic and prism faces of skeletal quartz crystals during periods of rapid growth these inclusions nucleate crystals of co2 that disappear by sublimation rather than melting at temperatures ranging from 92 9 to 56 7 c liquid rich fluid inclusions from veins near the top of the modern steam reservoir yield homogenization temperatures ranging from 304 to 188 c these temperatures commonly exceed boiling point to depth relationships based on the paleoground surface suggesting that pressures were initially greater than hydrostatic temperature salinity relationships indicate that the early shallow liquids had salinities of 1 5 to 2 wt percent nacl equiv and that boiling began by 300 c as the fluids boiled off salinities of the residual liquid increased to 3 to 4 wt percent nacl equiv trapping of low salinity fluids 0 0 0 5 wt nacl equiv interpreted as condensate in primary liquid rich inclusions suggest vapor dominated conditions had begun to develop by the time temperatures had dropped to 290 c the primary origin of these inclusion fluids indicates that they were capable of depositing quartz and calcite during the evolution of the vapor dominated system the hydrothermal fluids were at different times but at the same location undersaturated in equilibrium or oversaturated with respect to quartz and calcite the hydrothermal fluids initially deposited quartz and calcite as they boiled off dissolution of these minerals occurred as the condensate which was initially undersaturated with respect to quartz and calcite percolated down subsequent deposition of these minerals occurred as the condensate or mixtures of condensate and boiled liquid that leaked back into the fractures vaporized during periods of intermittent pressure reduction the top of the vapor dominated system migrated downward with time as the overlying fractures were progressively sealed off today pressures within the steam reservoir are vaporstatic and temperatures range from 240 to at least 342 c

explicit treatment of inheritance in dating depositional surfaces using in situ 10be and 26al we describe a new strategy for dating depositional landscape surfaces using in situ produced cosmogenic radionuclides crns that removes the complication of nuclide inheritance by clasts prior to depositon two amalgamated samples each consisting of 30 clasts one from the surface and one from a fixed depth in the subsurface constrain this crn inheritance and date the surface the inheritance may be used to estimate minimum exhumation rates and maximum transport times within the geomorphic system we test the technique using sup 10 be and sup 26 al to date the third fr3 of five terraces along the fremont river utah and the third wr3 of 15 along the wind river wyoming whereas effective ages based solely upon the surface samples yield 118 138 ka fr3 and 93 ka wr3 the subsurface samples reveal that inheritance accounts for 22 wr3 to 43 fr3 of the total crn concentration taking this into account yeilds terrace ages of nearly 61 81 ka for fr3 and nearly 67 76 ka for wr3 we explore the dependence of age estimates on the accumulation history of the terrace silt caps 22 refs 3 figs 1 tab

diagenetic changes in lake superior sediments as seen from ftir and 2d correlation spectroscopy abstract isotopic and elemental analysis fourier transform infrared spectroscopy ftir principal components analysis pca and two dimensional 2d correlation analysis where core depth was used as perturbation were used to study the diagenesis of organic matter om in lake superior sediments changes in om composition were examined at five lake stations over a depth range of 0 10 cm pca results show that depth related changes among sites are similar leading to an increased contribution from inorganic and possibly refractory aromatic organic components at each site and a loss of contribution from other organic components synchronous spectra reveal that aliphatic esters and carbohydrates are degraded significantly with increasing depth leading to an increased contribution from clay biogenic silica inactive carbohydrates asynchronous spectra show that in general carboxyl groups including aliphatic ester and amide in protein are degraded first followed by a group of carbohydrates and then aromatic compounds and or the si o framework in clay and biogenic silica site dependent compositional variation occurs and appears to be influenced by topography and geology e g the delivery of a larger load of terrestrial inorganic silicate minerals to certain sites and re suspension re deposition leading to less intensive down core variation at mid lake central and eastern basin sites the study demonstrates the usefulness of ftir coupled with pca and 2d correlation approaches for exploring structural changes in sedimentary material during diagenesis

phosphorus pathways in atolls interstitial nutrient pool cyanobacterial accumulation and carbonate fluoro apatite cfa precipitation significant dissolved phosphate concentrations were measured in reef interstitial waters and in small brackish ponds free water and underlying interstitial water occupying the emerged rim of the tuamotu atolls french polynesia these ponds are the sites of accumulation of organic matter of pure microbial origin in the form of thick stromatolitic cyanobacterial mats called kupara by tuamotu natives the profiles of dissolved phosphate interstitial waters seem to show a positive trend with depth within kopara the phosphorus pathway after biological uptake is studied by measuring the c and p concentrations in raw material and in humic substances humin fulvic and humic acids in order to examine the liberation of p from organic matter for comparison the same analysis is led on the residual organic matter of phosphate samples from mataiva deposit tuamotu the results show a relative enrichment in phosphorus with age of kopara and a similar distribution of humic substances in kopara and phosphate samples other work on hydrocarbons from kopara and phosphate samples demonstrates the strong relationship of these materials if such evolution of organic matter can be observed in kopara ponds it should be possible to generalize to closed atoll lagoons which function as mega kopara ponds and where phosphorus rich layers are present e g the niau atoll the different steps leading to atoll phosphogenesis viewed as phosphorus sink in cyanobacterial mats to final massive cfa accumulation could then be rationally explained the interstitial nutrient pool can be a necessary and sufficient factor to provide phosphorus for the kopara growth and accumulation o elsevier science b v all rights reserved keyvords interstitial nutrients cyanobacterial mats apatite precipitation

distribution of forms of sulfur in peats from saline environments in the florida everglades abstract although there is published information on the mechanism of sedimentary pyrite formation resulting from bacterial reduction of sulfate little is known about the distribution of forms of sulfur including organic in peats in order to increase understanding of the geochemistry of sulfur in coals we have determined distributions of forms of sulfur in five cores of saline peat and one of brackish peat all from areas near the shark river and whitewater bay in the coastal swamps of south florida all concentrations vary widely with depth total sulfur concentrations range up to 6 of dry solids minor amounts of sulfur are present as h2s s0 so42 and acid soluble sulfide but the principal forms are usually pyritic and organic the ratio organic pyritic is highly variable but at a majority of levels in a profile is considerably greater than unity it is inferred that topochemical factors are important in determining the distribution of sulfur forms in any element of volume

climatically controlled formation of river terraces in a tectonically active region along the southern piedmont of the tian shan nw china abstract combined tectonic uplift and quaternary climate variability control the deposition and abandonment of terraces along the southern tian shan in northwest china several preserved terraces have been deformed by an actively growing anticline within the uplifted frontal thrust system of the southern tian shan we combine geomorphic mapping topographic surveys of the deformed terrace surfaces 10be terrestrial cosmogenic nuclide tcn depth profile dating and optically stimulated luminescence osl dating to develop a new chronology for the terraces along the huangshui he since 550 ka our in situ 10be dating of fluvial gravels capping strath terraces suggests a relationship between the formation and abandonment of the terraces and glacial climate cycles since the middle late pleistocene these data indicate that the formation of the four terraces occurred at 550 430 350 and 60 ka we suggest that episodes of aggradation were facilitated by high sediment supply during glacial periods followed by subsequent incision that led to abandonment of these terraces during deglaciation we also estimate that tectonically induced river incision may account for about 60 70 of the total incision however during the intervening time between 350 ka and present only one terrace was formed and preserved we suggest that this record might be caused by a gradually decreasing uplift rate of the anticline through time and thus has influenced the preservation of terraces therefore our results demonstrate the utility of chronologic records from southern tian shan for deconvolving the effects of tectonics and climate on fluvial incision

uplift driven valley incision and climate controlled river terrace development in the thames valley uk abstract the sequence of terraces of the river thames in southeast england has previously been shown to span the period from the earliest pleistocene to the present this terrace sequence contains biostratigraphical and sedimentary evidence that testifies to the high amplitude climatic changes of the quaternary large scale fluvial incision resulting in basin wide terrace formation appears to have been concentrated at the warming limbs of the major climatic glacial interglacial cycles when sediment supply was greatly reduced this incision and subsequent valley floor widening created the accommodation space for the later aggradation of the terrace sediments during the following warm cold transitions and during the cold stages when high sediment supply conditions prevailed although the timing of terrace aggradation may be controlled by climate change the progressive valley incision recorded by terrace staircases cannot easily be explained in terms of quaternary climatic change alone and recently developed models suggest that long term incision by the thames has been driven by uplift this paper presents an overview of the available terrace data and tabulates incision amounts and rates between key stratigraphic horizons superimposed upon these broad changes revealed by the complex internal sedimentary architecture of many terrace sediments are the geomorphological system responses to both higher frequency climate driven changes and more localized intrinsic fluvial system adjustments

paleozoic accretion and cenozoic redeformation of the chinese tien shan range central asia the tien shan range in central asia contains two late paleozoic sutures the older southern suture marks the collision of a passive margin at the north of the tarim block and an active continental margin subduction under the latter was to the north the younger northern suture separates a northern carboniferous island arc from an active continental margin developed over a south dipping subduction zone the subduction direction under the island arc is unknown mesozoic elastics were deposited over the doubly sutured orogen rate and energy of sedimentation waned until deposition of oligocene conglomerates above a regional unconformity interpreted as marking the onset of deformation induced by the india asia collision molasse deposition accelerated in pliocene and quaternary time and deposition continues today as active thrusts generate relief paleozoic structures control the gross divergence of cenozoic thrusts across the orogen

late paleozoic tectonic amalgamation of northwestern china sedimentary record of the northern tarim northwestern turpan and southern junggar basins sedimentary rocks contained in basins adjacent to the tian shan provide a long and complex record of the late paleozoic continental amalgamation of northwestern china complementing that provided by rocks preserved within the range this record which comprises dramatic changes in sedimentary facies sediment dispersal patterns sandstone provenance and basin subsidence rates broadly supports previous interpretations of a two part evolution of the tian shan late devonian to early carboniferous collision of the tarim continental block with the central tian shan followed by collision of this combined block with island arcs in the north tian shan and bogda shan in late carboniferous early permian times the first collision resulted in widespread angular unconformities within the tarim basin continued convergence following the collision created a long lived flexural foredeep along the northern margin of the tarim block which received at least 2000 m of lower carboniferous through lower permian fluvial and marine sediment derived from the interior of tarim subsequent early permian continental extension of the northern tarim basin resulted in the deposition of interbedded nonmarine siliciclastic sedimentary rocks and mafic to felsicvolcanic rocks sandstone within this interval was derived from the paleo tian shan and is composed predominantly of lithic volcanic grains similar to the rhyolite in contrast to the tarim basin calc alkaline volcanic rocks and volcanogenic sedimentary rocks dominated carboniferous and permian sedimentation in the northern turpan and northwestern junggar basins volcanic arcs remained active in the north tian shan and bogda shan through the early late carboniferous depositing a kilometers thick interval of deep marine sediment gravity flows in the northwestern junggar basin major arc magmatism ceased in the late carboniferous in response to closure of the oceanic basin between the combined tarim central tian shan block and the north tian shan bogda shan arcs upper carboniferous through lower permian rocks in the northwestern junggar basin compose the sedimentary fill of a bathymetric basin of oceanic depth on the northern side of the volcanic arcs culminating in a 1000 m thick marine regressive sequence middle to upper permian sandstones were derived from the uplifted paleo tian shan and bear the distinctive provenance imprint of granitic rocks presently exposed within the range late permian subsidence of the junggar basin accommodated 5 km of nonmarine sediments however the cause of this subsidence and its relationship to regional tectonic events remain controversial

william river an outstanding example of channel widening and braiding caused by bed load addition the lower william river in northwestern saskatchewan canada presents an excellent and unambiguous example of rapid channel adjustment to abrupt additions of sandy bed load a relatively narrow and deep single channel stream as it flows northward to lake athabasca the river picks up a 40 fold increase of bed load over a 27 km reach as it encounters a large dune field just south of the lake as a result of the large infusion of eolian sand the channel develops a thoroughly braided pattern while undergoing a 5 fold increase in width and a 10 fold increase in width depth ratio

isotope geochemistry of mercury in source rocks mineral deposits and spring deposits of the california coast ranges usa abstract we present here the first study of the isotopic composition of mercury in rocks ore deposits and active spring deposits from the california coast ranges a part of earth s crust with unusually extensive evidence of mercury mobility and enrichment the franciscan complex and great valley sequence which form the bedrock in the california coast ranges are intruded and overlain by tertiary volcanic rocks including the clear lake volcanic sequence these rocks contain two types of mercury deposits hot spring deposits that form at shallow depths the franciscan complex and great valley sequence contain clastic sedimentary rocks with higher concentrations of mercury than volcanic rocks of the clear lake volcanic field mean mercury isotopic compositions 202hg for all three rock units are similar although the range of values in franciscan complex rocks is greater than in either great valley or clear lake rocks hot spring and silica carbonate mercury deposits have similar average mercury isotopic compositions that are indistinguishable from averages for the three rock units although 202hg values for the mercury deposits have a greater variance than the country rocks precipitates from spring and geothermal waters in the area have similarly large variance and a mean 202hg value that is significantly lower than the ore deposits and rocks these observations indicate that there is little or no isotopic fractionation

evaluating the role of climate and tectonics during non steady incision of the yellow river evidence from a 1 24 ma terrace record near lanzhou china abstract the competing roles of bedrock uplift and climatic change in the formation of fluvial terraces remain uncertain most of recent studies have attributed terrace formation to climatic changes and held that even in tectonically active settings climate variations control cycles of terrace planation and abandonment based on field investigations of loess paleosol sequences magnetostratigraphy and optically stimulated luminescence osl dating we develop a new chronology for a spectacular flight of terraces along the yellow river near lanzhou china over past 1 24 ma all the terraces are strikingly similar in that they have several meters of paleosol developed directly above fluvial deposits on the terrace treads suggesting that the abandonment of each terrace due to river incision occurs during the transition from glacial to interglacial climates however the ages of terraces cluster in two relatively short time periods 1 24 0 86 ma and 0 13 ma present during the intervening time between 0 86 ma and 0 13 ma terraces either did not form or were not preserved we suggest that this record indicates that rock uplift rates varied through time and influenced terrace formation preservation thus our results demonstrate the utility of deep chronologic records from fluvial terraces for deconvolving the effects of tectonics and climate on fluvial incision

pleistocene alluvial deposits dating along frontal thrust of changhua fault in western taiwan the cosmic ray exposure point of view abstract to tackle the history of active thrusts it is necessary to open the observation window on time scales on the order of 104 105 years by studying the surface morphologies resulting from their activities because fluvial systems are particularly sensitive to recent environmental changes geomorphic features such as alluvial terraces are frequently used as markers to gauge tectonic deformation together with the measurement of cumulative displacements the chronological framework of emplacement and abandonment of these geomorphic markers is thus fundamental to determine long term fault slip rates in taiwan the geomorphic features associated with fault activity have been studied in detail with a high level of resolution however the use of deformed and partially preserved alluvial terraces is often hampered by the absence of well documented ages the purpose of this paper is two fold first we take the opportunity to review the chronological constraints that have been published in taiwan so far second we present how the cosmogenic dating method in situ produced 10be can be used to constraint the chronological framework of alluvial deposits over a pleistocene time scale thanks to a comparison of our cosmogenic derived ages with existing data we present a consistent regional chronological framework for the pakua tadu area along the changhua fault one of the most active frontal thrusts in the western foothills of the taiwan mountain belt we also discuss its relationships with global eustatism and its tectonic implications for the timing of propagation of the deformation front during the last 450 kyr