minimum age of initiation of collision between india and asia north of everest based on the subsidence history of the zhepure mountain section the collision of india with asia one of the most profound tectonic events to have occurred in past 100 m y is thought to have had geological geochemical and climatological consequences of global extent surprisingly the age of initiation of this collision remains poorly constrained estimates range from the late cretaceous 65 ma to latest eocene 40 ma with little consensus in between this paper reviews the stratigraphic section preserved on zhepure mountain on the north flank of everest mount qomolongma and its implied subsidence history zhepure mountain lies about 65 km south of the indus yarlung zangbo suture and contains the most complete and youngest passive margin shelf sediments in the tethyan himalayas on the basis of the subsidence history of the preserved section there is no evidence of acceleration of the subsidence up to the youngest rocks therefore collision related loading and accelerated subsidence must post date the youngest sediments preserved which date from the earl

the mass balance of soil evolution on late quaternary marine terraces northern california mass balance interpretation of a soil chronosequence provides a means of quantifying elemental addition removal and transformation that occur in soils from a flight of marine terraces in northern california six soil profiles that range in age from several to 240 000 yr are developed in unconsolidated sandy marine and eolian parent material deposited on bedrock marine platforms soil evolution is dominated by 1 open system depletion of si ca mg k and na 2 open system enrichment of p in surface soil horizons 3 relative immobility of fe and al and 4 transformation of fe si and al in the parent material to secondary clay minerals and sesquioxides net mass losses of bases and si are generally uniform with depth and substantial in some cases approaching 100 however the rate of loss of each element differs markedly causing the ranking of each by relative abundance to shift with time loss of si from the sand fraction by dissolution and particle size diminution from 100 to 80 to 90 to 10 concurrently with an increase of ai in the organic sesquioxide and clay phases to 10 and 50 respectively while only minor increases occur in the nonorganic sesquioxide phases

weathering and evolution of soils formed on granitic glacial deposits results from chronosequences of swiss alpine environments abstract two soil chronosequences of mountainous ecosystems in switzerland served as the basis to calculate the accumulation of soil organic matter transformation of pedogenic fe and al and net losses of the main elements ca mg k na fe al mn and si by means of mass balance calculations elemental losses due to deglaciation and exposure to the weathering environment were calculated these mass balance calculations indicate that extensive mineral weathering resulted in significant leaching losses of si major base cations and al particularly from the upper horizons the losses are especially pronounced in the early stages of soil formation in most cases the exponential decay model incorporating an asymptotic or logarithmic regression model seems to provide a good description of weathering the greatest changes in the soil chemistry of these alpine soils on granitic host material occurred within the first 3000 4000 years of soil development later the weathering rates decreased rapidly and the overall depletion of elements nearly reached an asymptote we also found that the mean ratio of al t fe d al d fe t of the fine earth of the a e and b horizons is closely linked to the duration of soil development a very rapid decrease of this ratio also occurred at the beginning of soil evolution in order to reach asymptotic values after about 3000 years consequently this ratio could be a good indicator of the age of alpine soils furthermore there is a close relationship between the mass of organic c or n in the whole profile and the soil age the older the soil the higher the corresponding mass per unit area the chronofunctions presented give a first attempt of the chemical soil evolution in the alps however only little data has been available up until now regarding alpine soils and this fact inhibits a more detailed observation of the changes that have occurred over a period of 2000 8000 years of soil formation under similar climatic conditions

age of initiation of the india asia collision in the east central himalaya abstract we document the stratigraphy and provenance of the lower tertiary terrigenous sections in the zhepure shan region of the tethyan himalaya southern tibet using petrographic and geochemical whole rock and single grain techniques the cretaceous early tertiary shelf deposits of shallow marine carbonates and siliciclastics of the former indian passive margin near the western end of the zhepure shan are conformably overlain by lower tertiary clastic rocks sandstones in the jidula formation paleocene mostly contain monocrystalline quartz grains of cratonic origin in contrast significant amounts of immature framework grains with a distinct ophiolitic and volcanic arc influence are present in the youxia early eocene and shenkeza post early eocene formations major trace and rare earth element concentrations in both sandstones and shales complement the petrographic data and indicate that the source of the jidula formation consisted primarily of quartzose basement rocks probably of indian con

chemical weathering of a marine terrace chronosequence santa cruz california i interpreting rates and controls based on soil concentration depth profiles abstract the spatial and temporal changes in element and mineral concentrations in regolith profiles in a chronosequence developed on marine terraces along coastal california are interpreted in terms of chemical weathering rates and processes in regoliths up to 15 m deep and 226 kyrs old quartz normalized mass transfer coefficients indicate non stoichiometric preferential release of sr ca na from plagioclase along with lesser amounts of k rb and ba derived from k feldspar smectite weathering results in the loss of mg and concurrent incorporation of al and fe into secondary kaolinite and fe oxides in shallow argillic horizons elemental losses from weathering of the santa cruz terraces fall within the range of those for other marine terraces along the pacific coast of north america residual amounts of plagioclase and k feldspar decrease with terrace depth and increasing age the gradient of the weathering profile bs is defined by the ratio of the weathering rate r to the velocity at which the profile penetrates into the protolith a spreadsheet calculator further refines profile geometries demonstrating that the non linear regions at low residual feldspar concentrations at shallow depth are dominated by exponential changes in mineral surface to volume ratios and at high residual feldspar concentrations at greater depth by the approach to thermodynamic saturation these parameters are of secondary importance to the fluid flux qh which in thermodynamically saturated pore water controls the weathering velocity and mineral losses from the profiles long term fluid fluxes required to reproduce the feldspar weathering profiles are in agreement with contemporary values based on solute cl balances qh 0 025 0 17 m yr 1 during saturation controlled and solute limited weathering the greater loss of plagioclase relative to k feldspar is dependent on the large difference in their respective solubilities instead of the small difference between their respective reaction kinetics the steady state weathering rate under such conditions is defined as r q h m sol m total 1 s v b s the product of qh and the ratio of solubilized to solid state feldspar msat mtotal define the weathering velocity the weathering gradient bs reflects the kinetic rate of reaction where sv is the volumetric surface area of the residual feldspar both this rate expression and the spreadsheet calculations produce similar plagioclase weathering rates r 5 14 10 16 mol m 2 s 1 which agree with those reported for other environments of comparable climate and age weathering dependent concentration profiles are commonly described in literature the present paper provides methods by which these data can yield a more fundamental understanding of the weathering processes involved

stratigraphy structure and tectonic evolution of the himalayan fold thrust belt in western nepal regional mapping stratigraphic study and 40ar 39ar geochronology provide the basis for an incremental restoration of the himalayan fold thrust belt in western nepal tectonostratigraphic zonation developed in other regions of the himalaya is applicable with minor modifications in western nepal from south to north the major structural features are 1 the main frontal thrust system comprising the main frontal thrust and two to three thrust sheets of neogene foreland basin deposits 2 the main boundary thrust sheet which consists of proterozoic to early miocene lesser himalayan metasedimentary rocks 3 the ramgarh thrust sheet composed of paleoproterozoic low grade metasedimentary rocks 4 the dadeldhura thrust sheet which consists of medium grade metamorphic rocks cambrian ordovician granite and granitic mylonite and early paleozoic tethyan rocks 5 the lesser himalayan duplex which is a large composite antiformal stack and hinterland dipping duplex and 6 the main central thrust zone a broad ductile shear zone the major structures formed in a general southward progression beginning with the main central thrust in late early miocene time eocene oligocene thrusting in the tibetan himalaya north of the study area is inferred from the detrital unroofing record on the basis of 40ar 39ar cooling ages and provenance data from synorogenic sediments emplacement of the dadeldhura thrust sheet took place in early miocene time the ramgarh thrust sheet was emplaced between 15 and 10 ma the lesser himalayan duplex began to grow by 10 ma simultaneously folding the north limb of the dadeldhura synform the main boundary thrust became active in latest miocene pliocene time transport of its hanging wall rocks over an 8 km high footwall ramp folded the south limb of the dadeldhura synform thrusts in the subhimalayan zone became active in pliocene time the minimum total shortening in this portion of the himalayan fold thrust belt since early miocene time excluding the tibetan zone is 418 493 km the variation depending on the actual amounts of shortening accommodated by the main central and dadeldhura thrusts the rate of shortening ranges between 19 and 22 mm yr for this period of time when previous estimates of shortening in the tibetan himalaya are included the minimum total amount of shortening in the foldthrust belt amounts to 628 667 km this estimate neglects shortening accommodated by small scale structures and internal strain and is therefore likely to fall significantly below the actual amount of total shortening

comment on biochronological continuity of the paleogene sediments of the himalayan foreland basin paleontological and other evidences bhatia s b bhargava o n 2006 jaes 26 477 487 abstract a number of studies have documented a major disconformity in the himalayan foreland basin separating marine facies extending to lutetian age from alluvial facies dated

a soil chronosequence in the semi arid environment of patagonia argentina abstract soil development with time was investigated on beach ridges with ages ranging from about 1380 to 6240 14c years bp at the eastern coast of central patagonia the main pedogenic processes are accumulation of organic matter and carbonate leaching and accumulation within the upper part of the soils soil formation is strongly influenced by incorporation of eolian sediments into the interstitial spaces between the gravel of which the beach ridges are composed different amounts of eolian material in the soils lead to differentiation into leptosols containing 10 fine earth in the upper 75 cm and regosols containing 10 fine earth soil depth functions and chronofunctions of organic carbon calcium carbonate ph ca zr mg zr k zr na zr fe zr mn zr and si al obtained from x ray fluorescence analysis were evaluated to establish soil chronofunctions mean values of the horizon data of 0 10 cm below the desert pavement were used which were weighted according to the horizon thicknesses the depth function of ph shows a decrease towards the surface indicating leaching of bases from the upper centimeters chronofunctions of ph show that within 6000 radiocarbon years of soil development ph drops from 7 0 to 6 6 in the leptosols and from 8 1 to 7 5 in the regosols the higher ph of the regosols is due to input of additional bases from the eolian sediments chronofunctions of ca zr and k zr indicate progressive leaching of ca and k in the regosols showing close relationships to time r2 0 972 and 0 995 na leaching as indicated by decreasing na zr ratios shows a strong correlation to time only in the leptosols r2 0 999 both leptosols and regosols show close relationships to time for fe zr r2 0 817 and 0 824 mn zr r2 0 940 and 0 803 and si al 0 971 and 0 977 indicating enrichment of fe and mn and leaching of si leaching of mobile elements takes place on a higher level in the regosols than in the leptosols from the beginning of soil formation hence a significant part of the eolian sediments must have been incorporated into the beach ridges very soon after their formation

late quaternary deformation of marine terraces on the cascadia subduction zone near cape blanco oregon the cape blanco region of south coastal oregon sits on the upper plate of the cascadia subduction zone about 60 70 km east of the base of the continental slope though the region has no historic coseismic deformation late quaternary deposits and landforms show abundant evidence of uplift folding and faulting a set of five late quaternary marine terraces and one uplifted holocene beach berm are preserved in the cape blanco region stratigraphic and altitudinal surveys of these physiographic features combined with several numerical and correlation age determinations permit a reconstruction of tectonic deformation near cape blanco in approximately the last 200 000 years the most cogent aspects of the neotectonics in this part of the cascadia subduction zone are that an east west trending anticline deforms the lower three terraces 80 125 ka as well as accounting for uplift of the holocene storm berm latest movement on the anticline was no more than 2 000 years ago but the anticline also deforms sediments as old as middle miocene the anticline is consistent with a north south principal contraction axis at cape blanco in about the last 100 000 years an older terrace at cape blanco approximately 200 ka is offset by two reactivated faults whose movements prior to the eocene served to suture several terranes to the north american continent tectonic tilting in the older terrace is not consistent with a north south principle axis of contraction but the axis of tilt is parallel to north northwest striking structures developed in the quaternary fold belt offshore on the continental shelf the observed deformation indicates that regional stress in the vicinity of cape blanco in the late quaternary has been accommodated by a variable pattern of strain

soil development on a beach ridge chronosequence in the gulf of mexico coastal plain and its relation to the ancient land use abstract a soil chronosequence study is presented in a beach ridge system at the mouth of the usumacinta and grijalva rivers mexico formed since a strong decrease in the rate of sea level rise some 6000 years ago four sites were selected for the chronosequence study simon sarlat ss rancho magdaleno 1 and 2 rm1 rm2 cocoteros cc and playa cocoteros pc located on beach ridges that range in age between 5000 years old to recently formed the soils show poor to moderate degree of development and the change in the pedogenic properties has been clearly evaluated the most pronounced changes are the following from the older ss rm2 to the younger soils pc cc color becoming yellowish brown in the better developed soils an increase in the amount of organic matter clay and fed iron extracted with dithionite solution a better structure with more stable aggregates a decrease in the feo proportion fe extracted with oxalate solutions and an increase in the content of fine magnetic particles formed by pedogenesis this area was densely populated and thus affected by human activities since the pre classic period 800 300 bc as many archaeological sites have been registered we evaluated soil agronomic quality in order to understand the ancient land use the results show that the soils in this area no matter their age have low agronomic quality which must have limited their use by ancient population however the strategic position near main trade routes near rich aquatic resources and a low susceptibility to flooding were favorable for human settlement on the beach ridges

4 d evolution of se asia s mantle from geological reconstructions and seismic tomography abstract how the collision between india and asia is related to processes deeper in the mantle is unclear here we compare geological reconstructions of block motions within asia since 50 ma with the tomographically imaged three dimensional 3 d morphology of subducted lithosphere to obtain insight into the spatiotemporal evolution of mantle structure past positions of the convergent margin show remarkable similarities with slab geometry at specific depths the striking change in slab geometry from a linear structure beneath 1100 km to an increasingly distorted shape at depths of less than 700 km results from collision the slab contours match the progressive deformation of asia s margin including india s indentation and sundaland s extrusion ever since the onset of collision the indian plate appears to have overridden its own sinking mantle and it does not seem at present to underthrust tibet significantly north of the zangbo suture if correct this observation would provide further evidence against models of plateau build up involving indian lithosphere the tomographic images beneath india confirm that asian deformation has absorbed at least 1500 km of convergence since collision began from the match between the southeastward motion of sundaland between 40 and 20 ma and the principal change in slab structure between 700 and 1100 km depths we infer that lateral advection in the mantle is small and that the sinking rate beneath sunda was 2 cm yr in the lower mantle and 5 cm yr above the transition zone

provenance of the lower tertiary murree redbeds hazara kashmir syntaxis pakistan and initial rising of the himalayas abstract the murree supergroup of northern pakistan is represented by an over 6 km thick succession of deltaic redbeds and intercalated impure foraminiferal limestones of latest palcocene to middle eocene ilerdian to lutetian age cropping out in the northern part of the hazara syntaxis and by redbeds of younger age early middle eocene to early miocene cropping out in the southern part of the syntaxis rawalpindi area the quartzolithic composition of the murree redbeds testifies to a collision orogen provenance detritus was derived from a suture belt including thrust sheets of metasedimentary and subordinately sedimentary rocks volcanic or volcaniclastic rocks and ophiolites phyllite rock fragments are most common in the ilerdian sandstones whereas volcanic and carbonate rock fragments are more abundant in the lutetian sandstones minor quantities of chert and serpentineschist indicating contribution from uplifted subduction complex sources as well as siltstone shale and limestone grains are invariably present detrital modes of sandstones and southwestward progradation of tertiary clastic wedges both testify to provenance from the proto himalayan chain located to the north and uplifted since the very first stages of the india asia continental collision at the end of the paleocene the coeval chulung la redbeds of the tethys himalaya instead consisting of volcanic and subordinate ophiolitic detritus testify to exclusive provenance from the obducting trans himalayan are trench system this major petrographic difference may be accounted for by the different structural setting of the chulung la piggy back and murree foreland basins these two distinct collisional basins have been separated probably since the onset of collision by a fold thrust belt beginning to rise in the position occupied today by the high and lesser himalayan structural domains throughout the murree supergroup main petrographic parameters do not vary greatly and volcanic sedimentary low grade metasedimentary and ophiolitic detritus persisted until the early miocene indicating slow progressive growth of the chain only during the middle miocene when the highly metamorphosed rocks of the high himalaya were carried southward along the main central thrust mct the mountain range began to rise to dramatic heights and huge amounts of detritus started to feed the siwalik foreland basin sandstones and the remnant ocean turbidites of the indus and bengal fans

india eurasia collision chronology has implications for crustal shortening and driving mechanism of plates the motion of the indian plate is determined in an absolute frame of reference and compared with the position of the southern margin of eurasia deduced from palaeomagnetic data in tibet the 2 600 900 km of continental crust shortening observed is shown to have occurred in three different episodes subduction of continental crust intracontinental thrusting and internal deformation and lateral extrusion the detailed chronology of the collision and plate reorganizations in the indian and pacific oceans supports the hypothesis that slab pull is a dominant driving mechanism of plate tectonics

genetic interpretations of elemental and chemical differences in a soil chronosequence california abstract soils developed on fluvial terraces in central california have similar parent materials climatic settings vegetation cover and slopes but range in age from 40 000 to 3 000 000 years the soils have chemical compositions that change systematically with increasing age such chemical differentiation is most likely the result of long term weathering and mineralogical transformations that occurred since deposition of terrace fills and stabilization of the geomorphic surfaces the changes in composition with time closely mimic other studies on mineral weathering in which alkali and alkali earth elements are lost more rapidly than transitional elements the relative rates of element loss were determined by changes in element ratios over time net losses and gains of elements in different size fractions were monitored by their concentrations relative to zr the most stable constituent both sand and finer size fractions have lost considerable amounts of ca mg na and k aluminum appears to have been lost from the sand fraction and gained in the fine fraction over a 3 million year time span although there is no evidence for losses of fe and ti from sands there is a net influx of fe and ti into finer fractions probably gained from undetectable yet significant weathering of sand grains etching of sand grains clay mineralogy and microprobe analyses also indicate that the soils have undergone these chemical transformations during their formation mineralogical analyses also mimic other studies on mineral weathering in which the pyroxenes weather more rapidly than hornblende which weathers more rapidly than sphene or zircon

the detrital record of orogenesis a review of approaches and techniques used in the himalayan sedimentary basins the sediment archive of material eroded from an active tectonic region and stored in adjacent basins can provide a valuable record of hinterland tectonism especially when information in the source region itself is obscured by later metamorphism or removed by tectonism or erosion using the sediment record to document tectonism is a well established approach but more recently there has been a burgeoning of the number of isotopic techniques which can be applied to detrital material in particular single grain analyses thus the scope for application of detrital studies to a number of different tectonic problems has widened considerably in this review the example of sediments eroded from the himalayan orogen and preserved in the suture zone basin foreland basin remnant ocean basins and deep sea fans is used to illustrate the approach techniques as diverse as petrography heavy mineral xrf and sr nd studies single grain dating by ar ar u pb and fission track methodologies and single grain sm nd and pb isotopic analyses are described the paper documents how the sediment record can be used to determine the thermal and tectonic evolution of the orogen constrain mechanisms of continental deformation exhumation rates and palaeodrainage

constitutive mass balance relations between chemical composition volume density porosity and strain in metasomatic hydrochemical systems results on weathering and pedogenesis relations characterizing the chemical physical and mechanical changes resulting from metasomatic hydrochemical processes are developed using mass balance models which formally link chemical composition to bulk density mineral density volumetric properties porosity and amount of deformation strain rigorous analysis of aqueous solute transport effects is then made possible in a variety of porous media flow environments including chemical weathering pedogenesis soil formation diagenesis ore deposition and enrichment and metamorphism application of these linear constitutive relations to chemical weathering profiles shows that immobile and locally mobile chemical elements with masses conserved on the scale of soil profiles can be accurately identified from analysis of appropriate data arrays and then used as natural geochemical tracers to infer the nature and extent of hydrochemical weathering processes and volume changes during pedogenesis assumptions commonly made in the past about the supposed immobility of certain elements e g ti and zr become unnecessary quantitative differentiation between the effects of residual and supergene fractionation is then easily made these methods are applied to ni rich laterites developed by weathering of ultramafic rocks showing that during ordinary residual enrichment ni is concentrated by as much as 4 protolith peridotite concentrations this occurs simply by silicate mineral dissolution and removal of chemical elements other than ni e g mg with a corresponding reduction in saprolite density and increase in bulk porosity without significant deformation in contrast laterites with mineable concentrations of ni which are similarly undeformed such as the nickel mountain mine in riddle oregon have experienced in addition to residual enrichment strong supergene enrichment by fractionation of ore elements between a leached zone from which ni is extracted and a complementary enriched zone positioned farther along the direction of ground water flow soil forming processes in podzol chronosequences developed on sandy beach terraces of the mendocino coast of california involved soil column collapse of 60 percent by dissolution of silicate minerals in the albic horizon of al and fe leaching and 70 percent dilation expansion in the overlying organic rich layer by root growth the amount of erosion based upon paleosurface reconstructions using the excess mass of fe al pb ga and cu in the zone of supergene enrichment spodic horizon below the ground water table indicates that subsurface erosion by dissolutional collapse is three times that of surficial erosion finally using published chemical data for ti zr and cr on major bauxite deposits in australia where erosion rates are thought to be low we infer that there may have been major amounts of dissolutional collapse to explain the upwards increase of detrital zircon and rutile in weathering profiles

reconstruction of the deformed collision zone between india and asia by backward motion of lithospheric blocks 1 on the basis of a synthesis of tectonic data available on the india asia collision we present a first attempt to reconstruct the evolution of the collision zone assuming that the deformation of the lithosphere is localized along narrow shear zones and that the interiors of mantle blocks in between remain relatively undeformed we define block contours from the fault pattern and move back the blocks along their boundary faults along convergent or extensional boundaries the crust is assumed to shorten or stretch coherently step by step we go backward in time to finally reach the collision onset for each time step we find a solution compatible with the data set available and the position of the adjacent blocks for each block the search for compatibility at the scale of the entire collision zone allows for solving the kinematics of regions with fewer data and suggests plausible scenarios for regions where data is lacking for each step we calculate large scale displacement maps and determine euler poles for each block for the most recent time step the map proposed is compared to gps motions the deformation budget implies that extrusion absorbed 30 of the convergence between india and siberia during the entire collision span but varied with time accounting for as little as 3 or as much as 60 of this convergence at different epochs

the oligocene alps domal unroofing and drainage development during early orogenic growth abstract the source of huge volumes of quartzofeldspathic detritus feeding oligo miocene foredeep turbidites of the apennines has long remained an unsolved geological enigma in this article we reinterpret the available sandstone petrography fission track stratigraphic and geomorphological evidence to demonstrate that the adriatic foredeep was dominantly sourced by a himalayan type tectonic aneurysm growing in the central alps since the late oligocene the lepontine dome the lepontine dome is the envelope of distinct subdomes that formed stepwise from east to west during northwestward indentation of adria beneath the axial alps focused erosion of domal culminations cut by antecedent drainage started suddenly in the late oligocene with unroofing of recently emplaced plutons and young amphibolite facies gneisses exhumation was tectonically driven and possibly accelerated by positive feedback between erosion and uplift of hot weak rocks from depth the huge volumes of resulting detritus gonfolite macigno clastic wedge were transported southward for hundreds of kilometers along the rapidly subsiding foredeep formed since middle eocene times in front of the alpine retrobelt and nascent apennine forebelt such massive sediment influx following 15 2 myr of starved foredeep sedimentation testifies to rapid formation of mountain relief in the central alps synchronous to dextral activity along the insubric fault the lepontine dome remains today as the only deeply dissected region in the alps where medium grade metamorphic rocks of the axial belt are extensively exposed the relationships between geological structures and drainage patterns still mirror those formed originally at oligocene times river headwaters have not been significantly displaced since then and their thalwegs constrain finite lateral displacement relative to the southalpine retrowedge to a maximum of 10 20 km our reconstruction has wide implications not only for a better understanding of the tertiary evolution of the alps apennines orogenic couple but also for general relationships among tectonic activity relief formation drainage development erosion distribution and long distance sediment transfer during continental collision and orogenic growth

subsidence history of the north indian continental margin zanskar ladakh himalaya nw india detailed geological field mapping has allowed the restoration of two full stratigraphic sections through the highly deformed mesozoic and early tertiary fold and thrust belt of the north indian continental margin the two sections which are representative of a proximal and a distal facies on the margin have been backstripped using standard techniques profiles of the tectonic subsidence and uplift through the pre collisional history of the margin have been constructed and compared with the predictions of simple thermal and mechanical models the pre collisional history can be explained by a thermal model with an initial age of rifting of 270 ma and a stretching factor of c 1 2 this model accounts for the general exponential decrease in the backstripped tectonic subsidence the model fails however to completely explain the subsidence and uplift history of the margin since the late cretaceous the history during this time is characterized by uplift at the most proximal location and an increase in subsidence at the most distal location we attribute these differential vertical movements to flexural loading of the north indian margin by obduction of the spontang ophiolite the best fit model is one in which a 70 km wide wedge shaped load tapering from 10 to 0 km thick is emplaced on rifted lithosphere with an elastic thickness t e of 5 10 km these results which are in accord with the late cretaceous timing of obduction and the structure of the spontang ophiolite provide new constraints on the t e structure of extended continental lithosphere 120 150 ma after a rifting event

age estimates and uplift rates for late pleistocene marine terraces southern oregon portion of the cascadia forearc marine terraces are prominent landforms along the southern oregon coast which forms part of the forearc region of the cascadia subduction zone interest in the cascadia subduction zone has increased because recent investigations have suggested that slip along plates at certain types of convergent margins is characteristically accompanied by large earthquakes in addition other investigations have suggested that convergent margins can be broadly classified by the magnitude of their uplift rates with these hypotheses in mind we generated new uranium series amino acid and stable isotope data for southern oregon marine terrace fossils these data along with terrace elevations and two alternative estimates of sea level at the time of terrace formation allow us to determine terrace ages and uplift rates uranium series analysis of fossil coral yields an age of 83 5 ka for the whisky run terrace at coquille point in bandon oregon a combination of amino acid and oxygen isotope data suggest ages of about 80 and 105 ka for the lowest two terraces at cape blanco these ages indicate uplift rates of 0 45 1 05 and 0 81 1 49 m kyr for coquille point and cape blanco respectively late quaternary uplift rates of marine terraces yield information about deformation in the overriding plate but it is unclear if such data vary systematically with convergent margin type in order to assess the utility of the southern oregon uplift rates for predicting the behavior of the cascadia subduction zone we compared late quaternary uplift rates derived from terrace data from subduction zones around the world on the basis of this comparison the southern oregon rates of vertical deformation are not unusually high or low furthermore late quaternary uplift rates show little relationship to the type of convergent margin these observations suggest that local structures may play a large role in uplift rate variability in addition while the type of convergent margin may place an upper limit on possible uplift rate greater upper limits serve to increase the range of possible uplift rates in the case of the southern oregon coast variability in uplift rate probably reflects local structures in the overriding plate and the rate of uplift cannot be used as a simple index of the potential for great earthquakes along the southern cascadia subduction zone

soil forming processes and rates on uplifted marine terraces in southwestern oregon usa soil chronosequences were examined on flights of tectonically uplifted marine terraces near cape blanco and cape arago southwestern oregon all of the soils contain abundant organic c and are strongly acidic ph in h2o 30 of the exchange sites saturated with al the soils in the two areas show a progression in development from spodosols to spodosols with clay enriched horizons and eventually to ultisols although the spodic and argillic horizons appear to be forming concurrently in the soils evidence is presented to support the concept that the spodic horizon is eventually masked by clay accumulation because of weathering in situ neoformation of clays and clay translocation the primary age related trends include increases in 1 the relative abundance of silt and clay 2 the ratio of quartz to feldspars in the very fine sand 100 50 m fraction and 3 the amounts of dithionite extractable fe and al and crystalline forms of fe in the profile

remnants of a cretaceous intra oceanic subduction system within the yarlung zangbo suture southern tibet extensive field investigations along the yarlung zangbo suture zone in southern tibet reveal the presence of now fragmented remnants of a south facing intra oceanic subduction system this system developed within tethys during the cretaceous the associated arc forearc ophiolite and subduction complex were emplaced onto the leading edge of india at the end of the cretaceous rapid sedimentation in oblique slip basins and disruption of water saturated sediments into melange was widespread and concomitant with ophiolite emplacement we describe the tectonic entities that developed during this previously unrecognized phase of tethys tibet evolution and present a new model for the evolution of this portion of tibet

the indus clastics forearc basin sedimentation in the ladakh himalaya india abstract the mid cretaceous to early tertiary clastic sediments of the indus group represent the forearc basin succession of the transhimalayan arc trench system in the late albian to early eocene a shallowing upward megasequence tar turbidites to nummulitic limestones and alluvial to deltaic sediments basgo and temesgam formations were deposited respectively on the southern and northern flanks of the basin clastic petrography points to provenance from the largely undissected volcanic cover of the massif with more important plutonic detritus recorded in the northern alluvial units after collision with the indian passive margin in the early eocene sedimentation in the whole basin was characterized by huge alluvial fans nurla formation and then by lacustrine deposits formed in an intermontane depression nimu formation a rapid change in petrographic and geochemical composition is recorded in post early eocene units with sharp increase in plutonic detritus and trace elements typically associated with ophiolites testifying to the uplift of both arc massif and subduction complex sources after collision with the indian passive margin the petrography of the indus basin clastics and the evolution of detrital modes compare well with volcano plutonic suites deposited in modern and ancient forearc basins the composition of sandstone units contained within the accretionary prism instead suggests provenance from an undissected magmatic arc and deposition in abyssal plain and trench settings nindam volcaniclastic turbidites reworking of arc derived sandstones took place in small basins perched on the accretionary trench slope the asian continental margin of the neotethys ocean was thus an active pacific type arc trench system until the eocene when it collided with india underwent polyphase fold thrust deformation and was finally uplifted several kilometers to form the indus suture zone of the himalayas

soil genesis along a chronosequence on marine terraces in eastern taiwan abstract soil chronosequences developed on elevated marine terraces are ideal for studying changes in soil forming processes with time the coastal range of eastern taiwan is a product of active arc continent collision vertisols mollisols and entisols are generally found on the different levels of marine terraces herein but no detailed investigations of soil chronosequence have been conducted by integrating field morphology physio chemical characterization micromorphology and mass balance interpretations five soil pedons were selected on the three marine terraces including tt 1 and tt 2 pedons typic hapluderts on the first higher level with the oldest soil age 9 10 ka tt 3 vertic hapludolls and tt 4 pedons typic hapludolls on the second intermediate level 5 6 ka and tt 5 pedon typic udipsamments on the third lower level with the youngest soil age 3 5 ka the morphological characteristics showed that strongly developed angular blocky structures pressure faces and slickensides are more common in higher terrace soils than in lower terrace soils in this study depth to c horizon solum thickness and thickness of the clay enriched zone increase with relative terrace age although only one to two profiles per terrace were characterized the following soil analytical characterizations increase with time the degree of sand grains weathering ph h2o organic carbon cec contents of fed feo and mnd based on x ray diffraction analysis of the clay size fraction soils on all terraces have a mixed mineralogy mica smectite and kaolinite have slightly increased with increasing terrace age furthermore the dominant processes identified with mass balance analysis include loss of bases ca and mg iron and clay with time the soil properties including analytical and mineralogical characterizations which do not have notable changes with time are primarily due to relatively young soil age

rates and processes of soil evolution on uplifted marine terraces northern california time dependent changes in soil development have been evaluated for two flights of uplifted marine terraces with similar site characteristics and a range in terrace ages 3 9 ka to 330 ka in northern california six pedogenic properties of soils developed in unconsolidated deposits overlying bedrock marine platforms have systematic time dependent trends but each property differs in rate of change and in the time period over which its changes are useful as relative age dating or correlation tools changes in accumulated mass of organic carbon and ph are useful properties only for the youngest soils and probably for soils less than 10 20 ka in this climatic region soils on terraces older than 29 ka have nearly similar amounts of mass of organic carbon with values of about 3 6 by weight for the upper meter of the soil profile soil reaction ph in the top 20 cm of the soil profile decreases at a rapidly declining rate reaching and maintaining a value of 5 by 39 40 ka total mass of accumulated clay is an excellent indicator of relative soil age during all stages of soil development the rate of accumulation of clay is about 0 4 g cm2 soil column per thousand years so that pedons on terraces with inferred ages of about 124 ka have accumulated at least 50 g cm2 soil column of clay systematic and linear increases in accumulated mass of several forms of pedogenic iron make them very useful for chronological purposed for at least 240 ky of soil development crystalline forms of iron enable greater distinction among young soils than amorphous forms which have negligible accumulations until at least 40 ka the rate of accumulation of crystalline forms of iron fed feo is about 0 02 g cm2 soil column per thousand years so that pedons on terraces with inferred ages of about 124 ka have accumulated about 3 g cm2 soil column of crystalline forms of pedogenic iron changes with time in accumulated mass of amorphous forms of pedogenic aluminum alo are negligible within the first 29 ka then reflect a rapid increase in rate of accumulation until at least 124 ka two pedons from the same terrace inferred age 124 ka contain strikingly different amounts of pedogenic alo however and suggest that alo may be an unreliable indicator of the degree of soil development in addition to mass values of different soil substances maximum percent values were calculated soils developed on marine terraces older than 29 ka have at least 10 maximum clay older than 100 ka at least 30 maximum clay and older than 240 ka at least 40 50 maximum clay soils on terraces younger than 29 ka have less than 1 maximum fed and soils older than 240 ka at have at least 4 maximum fed these easily obtained values provide textural and chemical boundaries for separating marine terraces younger or older than about 29 100 and 240 ka in this region but are useful only as very general tools for correlation maximum percent clay is a more reliable indicator of soil age than maximum percent fed as the latter is greatly influenced by local groundwater flux and percent values of fed have a high degree of scatter

the northern suture pakistan margin of a cretaceous island arc the northern suture is a fault separating the cretaceous kohistan island arc terrain northwest himalayas from palaeozoic sediments of the asian plate to the north the kohistan arc includes volcanic and sedimentary rocks andesitic lavas tuffs volcaniclastics slates and limestones metamorphosed to greenschist facies and intruded by the two phase kohistan batholith asian continental margin sediments are mainly of shelf type are variably metamorphosed and intruded by the karakoram batholith the northern suture is a zone of melange from 150 m to 4 km wide and contains blocks of volcanic greenstone limestone red shale conglomerate quartzite and serpentinite in a slate matrix it has a strong planar fabric but in many places bedding is preserved in blocks and matrix and depositional rather than tectonic contacts are seen between the two the melange is inferred to be an olistostrome largely derived from the kohistan arc formed in a small back arc basin between kohistan and asia limestone blocks in the melange are dated as aptian albian post tectonic intrusions yield radiometric ages from 111 to 62 ma the northern suture therefore probably formed in the early late cretaceous during closure of the back arc basin the tethys ocean lay south of kohistan where the main mantle thrust represents the westward continuation of the indus tsangpo suture

an early india asia contact paleomagnetic constraints from ninetyeast ridge odp leg 121 new paleomagnetic results from sedimentary rock and basement of the ninetyeast ridge ocean drilling program leg 121 sites 756 758 detail the northward movement of the indian plate for the past 80 m y analysis of the combined paleolatitude age profile indicates a distinct reduction in india9s northward movement rate at 55 ma interpreted as completion of suturing of greater india and asia india9s northward motion slowed from 18 19 5 cm yr to 4 5 cm yr for the location of site 758 comparison of this profile with paleomagnetic data from the wider himalayan region indicates that initial contact between northwestern greater india and southern asia was already established by cretaceous tertiary time this supports a possible causal link between the india asia convergence and the deccan traps extrusion

iron behavior in a northern estuary large pools of non sulfidized fe ii associated with organic matter the estuaries of the northern baltic sea gulf of bothnia receive an abundance of diagenetically reactivecatchment derived fe which is to a large degree complexed with organic matter or present a

provenance of eocene foreland basin sediments nepal constraints to the timing and diachroneity of early himalayan orogenesis in contrast to eocene himalayan foreland basin sedimentary deposits in india and pakistan coeval sedimentary rocks of the bhainskati formation in nepal contain scant petrographic evidence of orogenic input such data have been used as evidence to promote models of diachroneity of india asia collision in this paper we document orogenic input into the eocene foreland basin rocks of nepal from fission track analyses of detrital zircons our data provide evidence that significantly reduces the possible duration of any diachroneity of collision and brings the interpretation of the sedimentary record into better agreement with ages of early thrusting and metamorphism in the orogen we also use our detrital fission track data to bolster previous age determinations of the overlying dumri formation confirming the basin wide occurrence of a major unconformity comparison of our data set with that from coeval along strike rocks in india suggests that there is no evidence of diachroneity in early stages of the orogen s exhumation

u pb zircon ages from the spontang ophiolite ladakh himalaya the spontang ophiolite in the ladakh himalaya consist of a thrust sheet of upper mantle and oceanic crustal rocks obducted onto the northern passive continental margin of india during the late cretaceous precise isotopic ages of himalayan ophiolites are presently unavailable u pb dating of zircons from a dioritic segregation in the high level gabbros of the spontang ophiolite shows that the complex formed at 177 1 ma mid jurassic and we suggest that it represents a fragment of neo tethyan oceanic crust this jurassic age contrasts with late cretaceous ages 91 95 ma previously reported for the formation of the troodos and oman ophiolite complexes further west along the neo tethyan suture zone and also predates the early to mid cretaceous masirah ophiolite c 150 ma and its alkaline volcanic seamounts 115 125 ma an andesitic rock from an arc sequence overlying the spontang ophiolite was also dated using as 88 5 ma this late cretaceous age constrains the minimum age of initiation of subduction beneath the spontang ophiolite the complex was emplaced during the turonian maastrictian some 80 ma after its formation when the indian continental margin collided with a cretaceous arc about 25 ma before the india asia collision the lack of a sub ophiolite metamorphic sheet beneath the spontang mantle sequence may be explained by the fact that the ophiolite was old and cold at the time of obduction

late cretaceous early tertiary convergence between the indian and arabian plates recorded in ophiolites and related sediments abstract remnants of ocean floor forming the eastern ophiolite belt in oman and the western ophiolite belt in pakistan have a common plate tectonic history culminating in emplacement at the cretaceous tertiary boundary fragments of ocean floor in these two belts have ages between 150 and 65 ma and recorded tectonic events in the early indian ocean at 150 ma 130 120 ma 110 100 ma and 70 65 ma new radiometric and chronostratigraphic ages and paleomagnetic and sedimentary information are used to relocate these ophiolites in the frame of the evolving indian ocean which was characterised by the stepwise breakup of gondwana at 158 ma east and west gondwana 130 ma southern atlantic breakup of east gondwana 95 84 ma madagascar and india seychelles 65 ma india and seychelles and finally at 40 ma rifting between africa and arabia the 150 ma old oceanic rocks of masirah island in oman originally formed the extension of the basins now preserved along the eastern edge of the afro arabian plate masirah drifted together with india seychelles when a new ridge formed at approximately 130 ma separating microplates e g kabul block from the northern edge of greater india parts of this new ocean were later emplaced to form the western ophiolite belt in pakistan consumption of oceanic crust and emplacement of ophiolites during the closure of the neotethys occurred not only north of india seychelles but also along two or three subduction zones between the afro arabian plate and india seychelles documented by the formation of metamorphic soles beneath ophiolites relics of ocean floor formed approximately 65 70 ma ago now form the upper units in the western ophiolite belt of pakistan where they overlie an accretionary prism of pillow lavas of dominantly aptian albian age and sedimentary rocks the breakup of india and the seychelles at 65 ma was associated with the eruption of flood basalts deccan and seychelles and enhanced counter clockwise movement of india this breakup possibly caused the late jurassic early cretaceous fragments of ocean floor e g masirah to be thrust onto the eastern edge of oman the ophiolites which were emplaced onto the western edge of india drifted as part of this plate farther north where collision with eurasia and the accreted microplates occurred in the eocene 55 ma

quantitative geochemical approach to pedogenesis importance of parent material reduction volumetric expansion and eolian influx in lateritization abstract using mass balance techniques we test the prevalent view that laterite genesis is dominated by in situ residual enrichment during chemical weathering of bedrock through calculation of net mass fluxes through the laterite soils in mali west africa we show that residual enrichment by removal of mobile elements with a corresponding increase in bulk porosity and decrease in bulk density contributes only a very minor fraction of the enrichment of al fe si and au instead we demonstrate that the abundance of these elements is due to the influx and accumulation by selective retention of chemically mature detritus of local and foreign origin clearly evident in micromorphological infilling features at the same sample depths that accumulation reaches extreme values we show that volumetric expansion in excess of 200 has occurred locally we infer that these spatially coincidental zones of mass influx of rock forming metals fe al si and also au with dilational hyperstrains result from a mutually reinforcing mechanical interaction between material influx and the effects of subsurface deformational processes such as shrink swell cycles and root growth and decay we propose that with progressive infilling of available connected voids by illuvial microsedimentary deposits of insoluble resistate and neoformed minerals the capacity for the combined skeleton and plasma to remain isovulumetric is exceeded we speculate that the resultant space problem is relieved by upwards expansion towards the overlying free surface continued translocation and void infilling occur and are limited to the depth where the size of translocational particles is smaller than that of the connected voids consequently progressive hyperstrains accumulate above this critical depth by the long term influence of a proposed translocational wedge of chemically resistant minerals against which numerous generations of plant roots have exerted stresses eclectic surficial contaminants involved are continuously derived from above leaving no indication of a relict source region within the present soil profile from which they might have been extracted instead the source region is largely the existing regolith column itself which releases local material and in addition is supplemented by deposition of colluvial detritus shed nearby by escarpment retreat

weathering rates as a function of climate results from a climosequence of the val genova trentino italian alps a soil sequence in northern italy along an elevational gradient ranging from moderate 950 m a s l to high alpine 2440 m a s l climate zones was investigated with respect to element losses ca mg k na fe al si mn and the development of clay minerals element losses were derived from mass balance calculations that are based on enrichment depletion factors using immobile element contents ti mass balance calculations indicated that extensive mineral weathering resulted in significant leaching losses of major base cations with losses up to 80 of the initial content in the parent material al particularly from upper horizons and si element denudation was greatest in subalpine forests near the timberline weathering rates decreased with both higher and lower altitudes the pattern of smectite distribution along the climosequence has strong similarities to the al si na and k losses while an inverse trend could be detected for clay minerals with a high amount of interlayered al highest smectite contents with up to 30 of the clay fraction and also highest weathering rates were found at sites in subalpine forest near the timberline higher precipitation rates and the production of chelating compounds in the soil are believed to promote the appearance of smectites weathering rates of na and k were additionally modelled as a function of precipitation and temperature the relationship between climate and element weathering is strongly nonlinear and is thought to be overshadowed by the pronounced podzolisation effect near the timberline

paleocene eocene record of ophiolite obduction and initial india asia collision south central tibet 1 uppermost cretaceous to eocene marine sedimentary sequences occur both to the south and north of the yarlung zangbo suture in south central tibet they consist of indian margin strata of the northern tethyan himalaya and asian margin strata of the gangdese forearc both assemblages are characterized by major changes in depositional environment and sedimentary provenance at 65 ma and an appearance of detrital chromium rich spinel of ophiolite affinity tio2 generally 0 1 wt during the paleocene ophiolitic melange exposed along the suture could have provided a source for detrital spinel the melange occurs in the hanging wall of a north dipping south directed mylonitic shear zone which includes a tectonic sliver of mafic schist amphibole from the schist yields 40ar 39ar ages of 63 ma which we attribute to cooling during slip along the shear zone and southward obduction of the melange melange obduction was coeval with the development of an angular unconformity within the gangdese forearc basin to the north between late maastrichtian time and 62 ma upper paleocene to middle eocene sandstones in the northern tethyan himalaya yield 200 120 ma u pb detrital zircon ages and 190 170 ma 40ar 39ar detrital mica ages these detrital grains were most likely sourced from regions north of the yarlung zangbo suture suggesting that onset of india asia collision in south central tibet is middle eocene or older in age collectively our results support previous suggestions that oceanic rocks were obducted onto the northern margin of india during latest cretaceous earliest tertiary time coeval changes in gangdese forearc sedimentation raise the possibility that this obduction event marks onset of tectonic interaction between india and asia at 65 ma alternatively in concert with the conventional view of eocene collision initiation the obducted oceanic rocks may be of intraoceanic origin while coeval changes in gangdese forearc sedimentation may be a consequence of an increase in the rate of ocean continent convergence following the demise of the intraoceanic subduction zone

paleogeographic and paleotectonic evolution of the himalayan range as reflected by detrital modes of tertiary sandstones and modern sands indus transect india and pakistan detrital modes of sandstones derived from the himalayan suture belt record the history of the mountain range since initial collision between india and asia which began in latest paleocene time tertiary clastic wedges deposited in fore arc foreland and remnant ocean basins and exposed along the indus transect from northernmost india to the arabian sea represent the best opportunity to study sedimentary responses to successive tectonic events during continental collision quartzose continental block and feldspatholithic magmatic arc sandstones were deposited respectively on the passive indian tethys himalayan succession and active asian indus group continental margins during late cretaceous paleocene time closure of the neotethys was marked by sudden arrival of volcanic and ophiolitic detritus on the passive continental margin of the indian plate during deposition of sediments dated at foraminiferal zones p6 pakistan to p8 india starting in early eocene time deposition of chulung la formation and murree supergroup volcanic and ophiolitic to metasedimentary detritus was accumulated in rapidly subsiding piggy back and foreland basins homogeneous petrographic composition within the eocene lower miocene murree supergroup with only slight progressive increase of detrital feldspars suggests erosion of largely supracrustal rocks involved in thrusting in the north in middle miocene time marked enrichment in medium to high grade metamorphic detritus in foreland sandstones siwalik group reflects rapid uplift of a warm wedge of indian crust which was carried southward along the main central thrust this major paleogeographic change was recorded also by quartzolithic remnant ocean turbidites which were fed great distances along transverse fracture zones and later accreted in the coastal makran subduction complex panjgur association and makran group recycled orogen detritus derived from the elevated himalayan chain is still accumulating today in the indus fan enrichment in feldspars with respect to ancient sandstones reflects deep erosion levels into mid crustal rocks along the core of the growing orogen

structural evolution and sequence of thrusting in the high himalayan tibetan tethys and indus suture zones of zanskar and ladakh western himalaya reply abstract the timing of motion on major thrusts in the western himalaya shows an extremely complex sequence that spans approximately 70 ma from the latest cretaceous throughout the tertiary three major phases of thrusting can be distinguished the earliest phase t1 is associated with emplacement of tethyan basin thrust sheets lamayuru sediments and spontang ophiolite south and south westwards onto the submerged northern passive margin of india 75 60 ma collision between india and asia occurred at 50 36 ma and was followed immediately by the major phase t2 of crustal shortening involving large scale south and south westward directed thrusting of the complete palaeozoic mesozoic and late tertiary tibetan tethys zone rocks preliminary balanced cross sections show a minimum shortening of 126 km of these rocks across the zanskar range the late collision phase t3 involved re thrusting of the previously stacked pile breaching or leap frog thrusting reversing the earlier stacking order in places and widespread steepening overturning and backthrusting along the whole northern margin of the tibetan tethys zone and throughout the indus suture zone

from a black to a gray box a mass balance interpretation of pedogenesis we utilize chemical elements as tracers in a mass balance analysis that provides functional relationships among soil chemical composition bulk density and volume change in relation to parent material these analytical functions are based on the principle of conservation of mass and include a term quantifying mass flux into out of the soil and between horizons we apply the technique to the oldest member of a chronosequence developed on marine terraces in northern california it is an alfisol that evolved from beach sand to its present state nearly one third of its weight is composed of secondary clay minerals in about 240 ky aside from large increases in organic carbon desilication is the dominant factor in soil evolution 29 50 83 g cm 2 si was leached from the beach sand during pedogenesis the rate of desilication is roughly 2 1 t km 2 yr 1 0 21 g cm 2 ky 1 an order of magnitude slower than that implied by the si denudation rate calculated for the mattole river watershed weathering of primary minerals and synthesis of secondary minerals is relatively well advanced suggesting that the rate of desilication may be declining the local beach is composed of quartz and sodic plagioclase with smaller amounts of chlorite mica and kaolinite the soil has substantially different mineralogy sand is dominated by quartz and clay is dominated by kaolinite halloysite chloritic intergrades and gibbsite bases are also leached though the total mass was much less 57 2 55 g cm 2 of na in the beach sand was lost as plagioclase weathered by focusing on elemental and mineralogical gains and losses we emphasize the essential connection between the pedologic environment and the external hydrochemical environment

mass balance of soil evolution on late quaternary marine terraces in coastal oregon mass balance analysis was used to quantify elemental losses gains and transformations for a soil chronosequence developed on elevated marine terraces in south coastal oregon the four soils analyzed in the study range in age from 80 ka to greater than 250 ka and are inceptisols spodosols and ultisols dominant soil forming processes include 1 desilication and loss of base cations from the solum 2 redistribution of iron and aluminum from surface to subsurface horizons 3 transformation of iron and aluminum from sand and silt size fractions to secondary clay and crystalline sesquioxide fractions and 4 accumulation of organic matter silica represents the largest mass loss of any element from the system and varies from 6 48 g cm2 11 loss from solum compared to original amount of si in parent material to 42 99 g cm2 22 with increasing terrace age losses of silica from the sand size fraction over time 2 to 17 are accompanied by increases of silica in the clay size fraction base cations represent only a small portion of the soil mass but up to 53 0 09 g cm2 of the sodium present in the parent material is lost due to weathering and leaching iron and aluminum are redistributed within the sola of younger terraces during podzolization but are lost from the older soils due to intense weathering and leaching over time the majority of iron is transformed from the sand and silt size fractions to the crystalline sesquioxide fraction in contrast the majority of aluminum lost from the sand and silt size fractions is transformed to the clay size fraction

soil development relative dating and correlation of late quaternary marine terraces in southwestern oregon abstract flights of tectonically uplifted late quaternary marine terraces are preserved at several localities along the oregon coast intervening coastal areas without marine terraces reflect net subsidence these gaps in the coastal terrace record make it difficult to correlate terraces along the pacific coast to test the utility of soils in relative dating and correlation two flights of marine terraces near cape blanco and cape arago were investigated the terraces could be distinguished in each area from soil morphological properties and a quantitative index of soil development derived from field descriptions the soils in the two areas show a progression in development from spodosols to spodosols underlain by clayey material to ultisols the lowest two terraces at cape blanco which have reported age estimates of 80 000 and 105 000 yr are correlative with the lowest two terraces at cape arago the fifth and oldest terrace at cape blanco has no equivalent at cape arago soil development indices for the third and fourth terraces at each area allow two alternative sets of correlations

effect of north and south exposure on weathering rates and clay mineral formation in alpine soils abstract a comparison was made between two soil climosequences on north and south facing slopes in northern italy to determine the influence of slope aspect on soil processes the climosequences span an elevational gradient ranging from moderate 1200 m a s l to high alpine 2420 m a s l climate zones on surfaces having an age of about 15 000 years the soils were investigated with respect to organic c oxalate and dithionite extractable fe al and si elemental losses ca mg k na fe al si mn and clay minerals the stocks of soil org c as well as of oxalate extractable fe and al was greatest in the subalpine zone near the timberline there are no clear differences in organic c content between the soils on north and south facing sites fe oxalate and to a lesser extent alo stocks were however greater on north facing sites indicating that weathering is greater there eluviation and illuviation of al and fe within the soil profile typical for podzolisation was more distinctly expressed on the n slopes the probability of itm imogolite type material formation in the soil seemed to be greater on south facing sites on the north facing sites element leaching was most intense in the subalpine zone close to the timberline while on the south facing sites this was only the case for the base cations the n slopes exhibited higher leaching of elements which generally indicates a higher weathering intensity on south facing sites typical podzolisation processes were measurable only above 2000 m a s l the development of smectites is also a reflection of the weathering intensity smectite was discernible in the surface horizon at all sites on n slopes but the highest amount was detected in the sub alpine climate zone for the south facing sites only in the alpine climate zone could smectite be detected higher temperatures and an increased number of freeze thaw cycles on south facing slopes should theoretically enhance rates of chemical weathering this could however not be confirmed with our measurements the degree of chemical weathering increases from the south to the north facing sites that are characterised by lower temperatures lower evapotranspiration and consequently by a higher humidity although precipitation in alpine regions is abundant the availability and flux of water through the soil is the prime factor in weathering intensity

age of initiation of collision between india and asia a review of stratigraphic data abstract the collision of india with asia is perhaps the most profound tectonic event to have occurred in past 100 ma it is responsible for the uplift of the himalayas and tibetan plateau and has been argued to have been responsible for geological geochemical and climatological consequences of global extent yet the age of initiation of this collision remains poorly constrained the literature is replete with estimates that range from the late cretaceous 65 ma to latest eocene

establishment of chronofunctions for dark loessial soil on the central loess plateau based on soil chronosequences the process of soil development can be studied quantitatively by analyzing the chronofunctions of soil based on its physical and chemical characteristics which provide a basis for establishing soil development models in this paper the physical and chemical characteristics as well as the 14c age of holocene dark loessial soil profiles found in luochuan and yanchang areas on the central loess plateau were analyzed to establish soil chronosequences then linear functions logarithmic functions and third order polynomials were used to fit the soil chronosequences to establish the soil s chronofunctions which were verified both theoretically and empirically in the two soil profiles third order polynomials could best fit the age of clay 0 002 mm silt 0 002 0 02 mm and sand 0 02 2 mm and their trends reflected the characteristics of dark loessial soil layers the changes of soil organic carbon and ph in relation to soil age could be fitted by logarithmic functions lastly third order polynomials could best fit changes in the soil s caco3 content and fe zr k zr p zr na zr and mg zr ratios with soil age which represented the migration processes of caco3 and various elements in the soil

biochronological continuity of the paleogene sediments of the himalayan foreland basin paleontological and other evidences abstract the paleontological and field evidences presented in the paper demonstrate a biochronological continuity from the marine subathu late thanetian to middle lutetian through the passage beds late lutetian to middle bartonian to the dagshai and equivalent formations late bartonian to rupelian of the himalayan foreland basin east of hazara kashmir syntaxis a similar continuity has also been demonstrated in the sulaiman range based on an assignment of oligocene age to the bugti vertebrate fauna hitherto considered to be of early miocene age thus the concept of a 10 ma hiatus in the foreland basin based on 40 ar 39 ar dates of single detrital muscovite grains from the supposed basal dagshai arenite is no longer tenable while the occurrence of cr spinel and k t boundary nannoplanktons in the subathu formation and passage beds indicate a westerly northwesterly provenance that of the radiolarian chert in the dagshai and coeval formations indicates a northerly provenance from the indus suture zone coinciding with the first influx of the himalayan detritus around 40 ma

dating the indian continental subduction and collisional thickening in the northwest himalaya multichronology of the tso morari eclogites multichronometric studies of the low temperature eclogitic tso morari unit ladakh india place timing constraints on the early evolution of the northwest himalayan belt several isotopic systems have been used to date the eclogitization and the exhumation of the tso morari unit lu hf sm nd rb sr and ar ar a ca 55 ma age for the eclogitization has been obtained by lu hf on garnet omphacite and whole rock from mafic eclogite and by sm nd on garnet glaucophane and whole rock from high pressure metapelites these results agree with a previously reported u pb age on allanite and together these ages constrain the subduction of the indian continental margin at the paleocene eocene boundary during exhumation the tso morari rocks underwent thermal relaxation at about 9 3 kbar characterized by partial recrystallization under amphibolite facies conditions ca 47 ma as dated by sm nd on garnet calcic amphibole and whole rock from metabasalt rb sr on phengite apatite and whole rock and ar ar on medium si phengite from metapelites ar ar analyses of biotite and low si muscovite from metapelites which recrystallized at 5 kbar toward the end of the exhumation show that the tso morari unit was at upper crustal levels ca 30 ma these results indicate variable exhumation rates for the tso morari unit beginning with rapid exhumation while the indian margin subduction was still active and later proceeding at a slower pace during the crustal thickening associated with the himalayan collision

middle cretaceous back arc formation and arc evolution along the asian margin the shyok suture zone in northern ladakh nw himalaya abstract the shyok suture zone of the ladakh palaeovolcanic arc is made of cretaceous volcanosedimentary formations intruded by granodioritic plutons field observations show a tectonic stacking of litho units from different volcanic arc and back arc environments in the western part skardu area the shyok suture zone can be subdivided into two groups 1 the northern group which consists of olistolith basaltic blocks and tuffs the basalts are lree depleted with a lile enrichment and a slight nb depletion suggesting a back arc basin origin 2 the southern group which consists predominantly of andesites that show lree enrichment a flat hree pattern strong nb ta depletion and lile enrichment the volcanic rocks of the southern group appear to have island arc tholeiite iat to calc alkaline affinities in the eastern part of the suture zone nubra shyok area albian to cenomanian age silicoclastic sediments predominate these sediments correspond to a large detrital platform built on the northern part of the ladakh arc at the top these sediments interlayer with basaltic to andesitic lavas these lavas appear to be more differentiated and calc alkaline in nature than the skardu southern group lavas but show similar volcanic arc affinities no evidence of a back arc basin was found in this area our data from these two areas shows a northwest southeast evolution from back arc to arc formations in northern ladakh opening of this back arc basin occurred on the northwestern side of the ladakh arc this back arc was progressively closing eastward the arc itself was more mature in the east resembling the southern tibetan continental arc and was characterised by more continental sedimentation subsequent himalayan tectonometamorphic evolution closure of the back arc basin and deformation along the shyok suture reflects an early asymmetrical geometry along the asian margin and kohistan ladakh arc