an isotopic study of soils in chronological sequences of alluvial deposits providence mountains california the carbon sup 14 c and sup 13 c and oxygen isotopic composition of pedogenic carbonate was determined for two soil chronosequences on limestone and granitic alluvium in the providence mountains area in the mojave desert california the measured sup 14 c ages of pedogenic carbonate coating on clasts were interpreted in the light of a diffusion reaction model developed in our recent studies model ages of soil formation calculated from the measured sup 14 c ages of pedogenic carbonate are in correct relative order as determined by geomorphic evidence and are also consistent with model ages from the measured sup 14 c ages of soil organic matter sup 14 c model ages suggest that the order geomorphic surfaces we studied are of late pleistocene age ca 47 17 ka and the younger surfaces formed during the holocene ca 11 4 ka these age estimates of the geomorphic surfaces are older than the previously assigned ages based on a combination of soil development geomorphic relationships and several infrared stimulated luminescence dates but they are within a few thousand years of these other age estimates stable carbon isotopic composition of the soil carbonate indicates either a slight increase in c sub 4 or cam crassulacean acid metabolism plants or a decrease inmore plant density in this area during the holocene both the carbon and oxygen isotopic composition of soil carbonates suggests that the climate in the eastern mojave desert has in general become warmer and drier during the holocene 57 refs 9 figs 5 tabs less

rates of late quaternary normal faulting in central tibet from u series dating of pedogenic carbonate in displaced fluvial gravel deposits along the main boundary fault of the central tibetan shuang hu graben two well preserved fluvial terrace surfaces are vertically offset by 1 3 m terrace i and 14 8 m terrace ii using thermal ionization mass spectrometry tims we have determined 48 230th 234u 238u ages of small 10 40 mg samples from pedogenic carbonate rinds on clasts in the terrace deposits based on textural microstratigraphic and geochemical criteria we conclude that the u series ages of innermost rind samples provide reliable ages of 16 4 1 9 ka for terrace i and 233 1 9 3 ka for terrace ii this constrains the average rate of vertical displacement along the normal fault to be 0 079 0 011 mm yr during the past 16 kyr and 0 064 0 007 mm yr during the past 233 kyr combining these results with slip rate estimates for other normal faults along the graben margins indicates that the cumulative vertical displacement on all normal faults did not exceed 0 3 mm yr during the late quaternary this new rate from central tibet is distinctly lower than the rate of 1 9 0 6 mm yr inferred for normal faults bounding the yadong gulu graben system in southern tibet consistent with more pronounced and common graben development in southern tibet we therefore suggest that normal faulting in southern tibet is largely controlled by local processes and that the age of its initiation is not a valid proxy for uplift of the tibetan plateau as has been widely assumed our data also place chronologic constraints on the termination of periglacial conditions in central tibet during the last three interglaciations rind formation appears to have been relatively continuous on clasts in terrace i from 16 ka clast rinds from terrace ii in contrast are characterized by three main episodes of rind growth that are widely separated in time the earliest and least well preserved episode started at 233 1 9 3 ka a second episode occurred at 131 8 7 8 ka and a third episode was approximately coeval with rind formation in terrace i after 16 4 1 9 ka in each case the age of onset of carbonate rind accumulation coincides with independently estimated ages of global deglaciation accordingly we conclude that periglacial conditions in the central tibetan plateau terminated synchronously with early stages of global warming following the last three glacial maxima and that fluvial aggradation terrace formation and pedogenic carbonate accumulation in terrace soils ensued rapidly

the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

stable carbon and oxygen isotopes of terra rossa in guizhou province of china and their relationship to climate and ecology this paper analyzed stable carbon and oxygen isotopic changes in organic matter 13csom and disseminated carbonate 13csc and 18osc in four terra rossa profiles in gouzhou southwestern china the objectives were to understand more information about climate change in this area and to determine whether the isotope values of disseminated carbonate in terra rossa preserved a record of environmental change and to distinguish environmental sources that may have influenced the isotopic chemistry results suggested that carbonate in terra rossa is mainly pedogenic carbonate and its formation is closely associated with root activities the 13csom variations indicate a climate change into warmer and drier conditions at about 6000 8000 a bp 12000 14000 a bp and 28000 a bp plants were more depleted in 13c when carbonate precipitated compared with the 13csom the 13csc tends to reflect more average climate change information most large variations of the 13csc and 13csom between adjacent sampling layers are accompanied with the change in soil color and texture suggesting a certain connection between the 13c and the soil properties this study found a positive linearity between 13csc and 18osc a striking different value and correlation coefficient in different sites may provide a meaningful signal of regional climate change

pedogenic carbonates forms and formation processes abstract soils comprise the largest terrestrial carbon c pool containing both organic and inorganic c soil inorganic carbon sic was frequently disregarded because 1 it is partly heritage from soil parent material 2 it undergoes slow formation processes and 3 has very slow exchange with atmospheric co2 the global importance of sic however is reflected by the fact that sic links the long term geological c cycle with the fast biotic c cycle and this linkage is ongoing in soils furthermore the importance of sic is at least as high as that of soil organic carbon soc especially in semiarid and arid climates where sic comprises the largest c pool considering the origin formation processes and morphology carbonates in soils are categorized into three groups geogenic carbonates gc biogenic carbonates bc and pedogenic carbonates pc in this review we summarize the available data and theories on forms and formation processes of pc and relate them to environmental factors after describing the general formation principles of pc we present the specific forms and formation processes for pc features and the possibilities to use them to reconstruct soil forming factors and processes the following pc are described in detail earthworm biospheroliths rhizoliths and calcified roots hypocoatings nodules clast coatings calcretes and laminar caps the second part of the review focuses on the isotopic composition of pc 13c 14c and 18o as well as clumped 13c and 18o isotopes known as 47 the isotopic signature of pc enables reconstructing the formation environment the dominating vegetation 13c temperature 18o and 47 and the age of pc formation 14c the uncertainties in reconstructional and dating studies due to pc recrystallization after formation are discussed and simple approaches to consider recrystallization are summarized finally we suggest the most important future research directions on pc including the anthropogenic effects of fertilization and soil management in conclusion pc are an important part of sic that reflect the time periods and formation processes in soils a mechanistic understanding of pc formation is a prerequisite to predict terrestrial c stocks and changes in the global c cycle and to link the long term geological with short term biological c cycles

kinematic model of active deformation in central asia the velocity field of present day deformation in central asia is modelled using a set of four rotating blocks siberia tarim tibet india on a spherical earth a best fit is inverted on the basis of estimated shortening rates across the main thrust zones himalayas tien shan and measured slip rates along the principal strike slip faults altyn tagh and karakorum separating those blocks the fit to the data implies that nearly all the present convergence between india and asia can be accounted for by slip partitioning on these four zones with as much as 50 absorbed by northeastwards extrusion of tibet this suggests that localised deformation governs the present mechanical behaviour of the central asian lithosphere

assessing the origin of carbonates in a complex soil with a suite of analytical methods abstract stable isotope c analysis is the most reliable method used for the distinction and understanding of soil carbonates origin however in soils with a complex geological setting the carbonate 13 c signature could lead to incorrect interpretations if used alone thus coupling this technique to other methods may be necessary in this work we evaluated advantages and disadvantages of several methods some of which are well known while others are still unused to distinguish among carbonates of different origins in a soil developed on valle versa chaotic complex a marly geological formation in north western italy for a better evaluation of their potentialities the methods were also applied to simpler situations used as a reference for carbonate of pedogenic and lithogenic origins thin sections analysis revealed the presence of three kinds of carbonates in the investigated complex soil one was pedogenic while two showed clear lithogenic origin the lithogenic carbonate that showed a low 13 c about 9 was interpreted as freshwater while isotopic signature increased up to 4 with the presence of marls thus no evidence of pedogenic precipitations could be obtained with isotopic analysis the mean crystallite domain l 104 was highly variable and related to the amounts of co precipitated impurities in the carbonates thus these methods provided important information about the formation environment these rarely used techniques permitted to distinguish between pedogenic and lithogenic material in simple systems but did not adequately support the presence of pedogenic carbonates in the complex soil surface areas and porosity evaluated by n 2 adsorption are particularly influenced by the processes occurring during calcification such as the development of coatings and pore infillings the comparison between additive models and measured specific surface area indeed allowed us to observe the effect of pedogenic carbonate on the physical properties although it did not permit any quantification these results indicated that although all the methods were able to distinguish between pedogenic and lithogenic origins in simple systems only micromorphology and n 2 adsorption techniques allowed for the identification of pedogenic carbonate in a more complex soil system

radiocarbon age discrepancies between the carbonate cement and the root relics of rhizoliths from the badain jaran and the tengeri deserts northwest china abstract carbonate rhizolith is one of mineral encrustations of plant roots the radiocarbon 14c dates and stable carbon isotopes of rhizoliths are widely used to study geochronology paleoclimate paleoecology and paleoenvironment changes however due to a few available comparisons of 14c dates of the carbonate cement and the plant root relics within the same rhizoliths the carbon sources that form rhizolith cements are largely unknown here we present accelerator mass spectrometry ams 14c dates of carbonate cement and the plant root relics within the same rhizoliths from dune surface soils in the badain jaran and the tengeri deserts northwestern china the modern dead plant roots and bulk soil carbonates nearby were also dated it is found that the root relics range from 1825 ce to 1983 while the carbonate cements of the rhizoliths have ages from 6 900 to 4 700 calibrated years before present calbp the ages of the bulk soil carbonates vary from 18 700 to 35 300 and 39 300 calbp revealing complicated soil carbonate matrix the results suggested that the carbon sources for the carbonate cements of the rhizoliths were derived mainly from ancient soil carbonates with a small contribution from dead plant roots and a minor contribution from lithogenic carbonates mass balance of stable carbon isotopes was used to calculate the proportional contribution of the carbon from ancient soil carbonates and plant roots relics after subtracting the modern carbon contribution from the decomposed plant roots in fraction of modern carbon f14c the mass balance estimated that the ancient soil carbonates were formed within 7 750 5 000 calbp about 850 300 years older than obtained rhizolith cement ages it is proposed that dead roots decay triggered the rhizoliths formation by releasing co2 to form acid media with free hco31 co32 ions which caused dissolution of the old soil and lithogenic carbonates in soil matrix carbonate recrystallization took place to form rhizoliths tubes around the dead roots detailed age discrepancies between rhizolith cements and dead root relics provide new insight for better understanding the dynamics of the rhizolith formation and associated implications for paleoenvironment reconstructions

systematic variations in the carbon and oxygen isotopic composition of pedogenic carbonate along elevation transects in the southern great basin united states stable carbon and oxygen isotope variations in holocene soil carbonates that formed in the unsaturated zone were examined along several elevation transects in the southern great basin united states a region with a semi arid climate our intent was to study the relationship between the stable isotopic composition of pedogenic carbonates and climate ecological variations differences in parent material and soil depth 13 c of pedogenic carbonate in three different soil profiles from different elevations decreases with soil depth indicating a decrease in the ratio of atmospheric to plantderived co 2 downprofile pedogenic carbonate at the soil air interface approaches a 13 c value in equilibrium with atmospheric co 2 in all three soils observed 13 c profiles for pedogenic carbonate can be described using a one dimensional model for 12 co 2 and 13 co 2 assuming isotopic equilibrium between soil co 2 and soil carbonate the modeled best fit to observed isotopic profiles suggests that the profile differences in part result from differing soil respiration rates at each site 13 c in deep pedogenic carbonate 50 cm varies by about 12 per mil over a 2 440 m elevation range being enriched in 13 c at the lowest elevations the slope of 13 c for these carbonates versus elevation is very similar for soils developed on carbonate and on noncarbonate parent materials depletion by 4 6 to 4 7 per mil per 1 000 m increase in altitude between 300 to 2 740 m above mean sea level for the localities studied this concordance makes it likely that there has been complete isotopic exchange between hco 3 in solution and soil co 2 prior to carbonate precipitation soil co 2 and soil respiration rates increase systematically with elevation the plantderived component of soil co 2 indicates that c 3 plants dominate the biomass at most measured sites in agreement with plant surveys calculated equilibrium fractionation factors between soil co 2 and soil carbonate are very similar to those observed again indicating complete isotopic exchange between carbon species in all the soil co 2 and soil carbonate data suggest that the 13 c variation with elevation observed in the soil carbonates results from differing soil respiration rates at each site as well as from variations in the proportion of c 3 to c 4 and cam plants in each site9s surface biomass 18 o values in pedogenic carbonates are higher at lower elevations due in part to the more positive 18 o values for meteoric waters at lower elevations the average 18 o value of deep 50 cm pedogenic carbonate at all sites however is enriched 2 4 to 3 7 per mil with respect to values we predict should be in equilibrium with the isotopic composition of local meteoric waters this suggests that evaporative isotopic enrichment of soil waters may have occurred at all elevations prior to precipitation of carbonate or that seasonal differences in the isotopic composition of meteoric waters coupled with differential infiltration may be taking place one or both of these processes also may explain the 18 o decrease in soil carbonate with depth observed in two of three soil profiles

new u th pb constraints on timing of shearing and long term slip rate on the karakorum fault 1 zircons and monazites from 6 samples of the north ayilari dextral shear zone nasz part of the karakorum fault zone kfz have been dated with the u th pb method using both id tims and sims techniques the ages reveal 1 inheritance from several events spanning a long period between the late archean and the jurassic 2 an eocene oligocene magmatic event similar to 35 32 ma 3 an oligo miocene magmatic event similar to 25 22 ma at least partly synkinematic to the right lateral deformation and 4 a period of metamorphism metasomatism similar to 22 14 ma interpreted as thermal and fluid advection in the shear zone the labhar kangri granite located similar to 375 km farther southeast along the kfz is dated at 21 1 0 3 ma such occurrence of several oligo miocene granites along the kfz some of which show evidence for synkinematic emplacement suggests that the fault zone played an important role in the genesis and or collection of crustal melts we discuss several scenarios for the onset and propagation of the kfz and offset estimates based on the main sutures zones our preferred scenario is an oligo miocene initiation of the fault close to the na range and propagation along most of its length prior to similar to 19 ma in its southern half the averaged long term fault rate of the kfz is greater than 8 to 10 mm a in good agreement with some shorter term estimates based on the indus river course or quaternary moraines and geodesy our results show the kfz cannot be considered as a small transient fault but played a major role in the collision history

reply to comment on interplay of deformation and magmatism in the pangong transpressional zone eastern ladakh india implications for remobilization of the trans himalayan magmatic arc and initiation of the karakoram fault abstract in the eastern part of ladakh the right lateral karakoram fault zone kfz bifurcates into two strands called the pangong strand and the tangtse strand these two strands bound a region called the pangong transpression zone ptz which consists of migmatitic dioritic gneiss calc silicates and the durbuk pluton a pluton of two mica leucogranite outcrop scale observations suggest pervasive migration of leucogranitic melt through the existing tectonic structures of the gneiss magnetic fabric from both the tectonized and undeformed parts of the durbuk pluton show parallelism with the tectonic fabric of the host gneiss which along with pervasive melt migration indicates syn kinematic relationship between deformation along the kfz leucogranite magmatism and emplacement of the durbuk pluton u pb geochronology of zircons from the dioritic gneiss yields a crystallization age of 63 6 1 5 ma and also shows younger zircon growth down to 13 ma which suggest arc magmatism at 65 ma followed by partial melting and leucogranite magmatism in the kfz till 13 ma one two mica leucogranite sample from the durbuk pluton gives a crystallization age of 22 7 0 5 ma as the durbuk pluton is syn tectonic with deformation along kfz it is inferred that the kfz initiated at least 23 ma ago

structure and composition of calcified roots and their identification in calcareous soils abstract fine white branching structures isolated from calcareous soils in southern france were shown by microscopy and by chemical and mineralogical analysis to be calcified roots these structures occur mainly in rendzinas calcic xerosols and cambisols that are dense or rich in fines and where drainage is slow visible to the naked eye they can locally represent up to a quarter of the soil mass calcified roots consist of calcite elements whose mean size varies from 60 to 80 m and which retain the structure of the original cells of the root cortex each calcified cell has a central nucleus composed of two crystals on average and is coated with a thin mineral layer that seems to be poorly crystallized some retain organic remnants and the structure of cell walls calcified cells contain tubes less than 1 m in diameter which appear to have formed by weathering although they have generally not been recognized as calcified roots similar microstructures have been indicated in some calcareous soils and calcretes both present day and ancient ones that suggests that calcified roots are widespread and that their occurrence contributes to the genesis of some calcareous soils

quantifying pedogenic carbonate accumulations using stable carbon isotopes abstract four pedons from a late quaternary chronosequence developed in calcareous alluvium in central texas were investigated to assess the ability of the stable c isotope method to partition and quantify pedogenic carbonate accumulations to quantify pedogenic carbonate accumulations with this method 13 c values of bulk pedogenic and parent carbonate must be known for each pedon 13 c values of bulk carbonate were measured on a horizon by horizon basis the parent carbonate end member for all pedons was approximated by averaging the bulk 13 c values for all horizons from the weakly developed floodplain soil the diffusion model of cerling 1984 and quade et al 1989 was used to estimate the pedogenic carbonate end member quantification of pedogenic carbonate accumulations by the isotopic method was compared to quantitative estimates conducted by field morphology binocular light microscope point counts and thin section point counts results suggest that the isotopic method is superior to other methods of quantifying pedogenic carbonate accumulations whole soil pedogenic carbonate accumulations as calculated by the isotopic method for the chronosequence were 1 1 to 4 vol by 2000 years 2 4 to 15 vol by 5000 years and 3 1 to 12 vol after 15 000 years these results reveal net soil carbonate loss through time for central texas climates this corroborates similar conclusions drawn for the same chronosequence using mass balance analysis to calculate the flux of carbonate net carbonate loss through time also indicates that these soils do not serve as long term carbonate c sequesters

southward propagation of the karakoram fault system southwest tibet timing and magnitude of slip the net slip on the southern portion of the karakoram fault system in southwest tibet is estimated by restoring a piercing line defined by two key surfaces in the south kailas thrust system a regional counter thrust along the indus yalu suture assuming that the thrust system is planar across the karakoram fault we calculate 66 5 5 km of normal right slip documentation of the south kailas thrust active at 13 ma implies that the karakoram fault in southwest tibet did not initiate until after the cessation of motion on the thrust however field investigations of the central portion of the karakoram fault system document the fault to have been active at 17 ma and to have accumulated a maximum of 150 km of right slip we suggest that these along strike variations in the magnitude of slip and timing constraints are best explained by southward propagation of the karakoram fault system this is inconsistent with major right lateral slip on the fault system which was used in support of extrusion models for tibet

a comment on large scale geometry offset and kinematic evolution of the karakoram fault tibet by r lacassin et al earth planet sci lett 219 2004 255 69

large scale geometry offset and kinematic evolution of the karakorum fault tibet the total offset lifespan and slip rate of the karakorum fault zone kfz western tibet are debated along the southern fault half ongoing oblique slip has exhumed dextrally sheared gneisses intruded by synkinematic leucogranites whose age v23 ma u pb on zircon indicates that right lateral motion was already in progress in the late oligocene ar ar k feldspar thermochronology confirms that rapid cooling started around 12 ma likely at the onset of the present dextral normal slip regime correlation of suture zones across the fault requires a total offset greater than 250 km along the active northern fault branch an average long term slip rate of 1 0 3 cm yr is inferred assuming that this offset accrued in a time span of 23 34 ma southwest of the ladakh karakorum range the large scale boudinage of ophiolitic units suggests that an offset of several hundreds of kilometers exists along another southern branch of the kfz towards the southeast in the mount kailas region the fault zone does not end at gurla mandatha but continues eastwards as a transpressive flower structure along the indus tsangpo suture our new data thus suggest that the kfz contributed to absorb hundreds of kilometers of india asia convergence

the precession phase of the boreal summer monsoon as viewed from the eastern mediterranean odp site 968 the astronomical timescale of the eastern mediterranean plio pleistocene builds on tuning of sapropel layers to northern hemisphere summer insolation maxima a 3000 year precession lag has become instrumental in the tuning procedure as radiocarbon dating revealed that the midpoint of the youngest sapropel s1 in the early holocene occurred approximately 3000 years after the insolation maximum the origin of the time lag remains elusive however because sapropels are generally linked to maximum african monsoon intensities and transient climate modeling results indicate an in phase behavior of the african monsoon relative to precession forcing here we present new high resolution records of bulk sediment geochemistry and benthic foraminiferal oxygen isotopes from odp site 968 in the eastern mediterranean we show that the 3000 year precession time lag of the sapropel midpoints is consistent with 1 the global marine isotope chronology 2 maximum monsoonal precipitation conditions in the mediterranean region and china derived from radiometrically dated speleothem records and 3 maximum atmospheric methane concentrations in antarctica ice cores we show that the time lag relates to the occurrence of precession paced north atlantic cold events which systematically delayed the onset of strong boreal summer monsoon intensity our findings may also explain a non stationary behavior of the african monsoon over the past 3 million years due to more frequent and intensive cold events in the late pleistocene

formation and evolution of strike slip faults rifts and basins during the india asia collision an experimental approach the processes which have governed the formation and evolution of large tertiary strike slip faults during the penetration of india into eastern asia are investigated by means of plane strain indentation experiments on layered plasticine models the steady state deformation of plasticine obeys a power creep flow law e c t n the stress exponent n is between 6 and 9 at 25 c uniaxial plane strain tests on cubic specimens show that the growth of faults in layered plasticine results from strain softening a process observed for strain rates ranging from 3 5 10 5 to 3 6 10 3 s 1 fault or shear zones form after only 7 10 bulk strain subsequent deformation is controlled by the geometry of the fault pattern rather than the physical properties of the plasticine a series of nine plane strain indentation experiments shows the influence of boundary conditions as well as that of the internal structure of the plasticine model on the faulting sequence the ubiquity of strain softening in experimental deformation of a variety of rocks as well as the widespread occurrence of shear zones in nature suggest that long term deformation of the continental lithosphere may also be primarily influenced by the geometry of large faults which rapidly develop with increasing strain the deformation and faulting sequence observed in the plasticine indentation experiments may thus be compared to collision induced strikeslip faulting in asia particularly to total offsets and rates of movements on the faults the experiments simulate the evolution of the western ends of the strike slip faults which have probably been analogous to trench fault fault triple junctions the experiments also illustrate mechanisms for the formation of extensional basins such as the south china sea north china basin and andaman sea near active continental margins the basins which appear to absorb terminal offsets along major strike slip faults near such margins may result from mismatch between the sharply angular shape of the deformed continental edge and the more regularly curved trench along which the smoothly flexed oceanic lithosphere subducts the existence of distinct phases of strike slip extrusion corroborates the idea that the discontinuities in time which typify intracontinental tectonics and orogenic cycles may often result from strain localization and the ensuing discontinuous non steady state deformation of the continental lithosphere

transtensional deformation in the central himalaya and its role in accommodating growth of the himalayan orogen 1 field mapping structural analysis and geochronologic data from northwestern nepal reveal major normal right slip motion along a previously unrecognized west northwest striking system of shear zones that we term the gurla mandhata humla fault system gmh the gmh obliquely cuts across the greater himalayan crystalline sequence and into the lesser himalayan imbricate thrust belt via two right step over structures the average slip direction on the gmh parallels the strike of the himalayan orogen motion along this fault system has resulted in an apparent left separation of the south tibet detachment main central thrust zone and lesser himalayan imbricate thrust belt along a north striking segment of the fault system we estimate a minimum of 21 km of net slip on the southern branch of the gmh by restoring the trace of the main central thrust zone parallel to the average slip direction on the fault taking into account slip estimates from the northern branch of the gmh yields a minimum net slip estimate of 24 4 to 32 4 km for the gmh the 232th 208pb ion microprobe monazite ages from leucogranite bodies indicate that motion on the gmh occurred after 15 ma its initiation immediately followed crustal thickening between the main central thrust zone and indus yalu suture zone motion on the gmh is contemporaneous with arc normal contraction in the southernmost himalayan orogen these observations can be explained by a model that involves foreland propagating structural systems facilitating arc normal contraction in the foreland and arc parallel extension in the hinterland that work together to maintain the arcuate shape of the himalayan orogen

reply to comment by m p searle and r j phillips 2009 and r r parrish 2009 on does the karakoram fault interrupt mid crustal channel flow in the western himalaya by mary l leech earth and planetary science letters 276 2008 314 322

human induced calcretisation in anthropogenic soils and sediments field observations and micromorphology in a mediterranean climatic zone israel abstract for over a century the study of pedogenic calcrete and its formation focuses on natural processes disregarding the possible role of humans in its formation here we present field and micromorphological evidence from archaeological and modern sites in the eastern mediterranean region israel that indicate that some specific calcretes are human induced we demonstrate that anthropogenic affected calcrete differs from natural non human induced calcrete we show that the occurrence of the human induced calcrete is spatially limited and is associated with both macro and micro scale remnants and occasionally high content of organic material we propose an operative definition for anthropogenic calcretisation as the interference of humans with a component s that influence the formation of calcrete we assume that if present day calcretised environments will retain their calcretisation prone conditions for the next 5 10 millennia a distinct calcretic morphology could become a significant terrestrial formation this discovery can be particularly useful for evaluating past human impact on the environment adding a new archaeological set of research tools that should further be developed

geological evidence against large scale pre holocene offsets along the karakoram fault implications for the limited extrusion of the tibetan plateau two end member models proposed to accommodate the convergence between india and asia north of the himalaya are 1 homogeneous crustal thickening of the tibetan plateau and 2 continental escape or extrusion of tibet and southeast asia away from the indenting indian plate foremost among the arguments supporting the latter would be large scale 1000 km offsets and high present day slip rates along the major strike slip faults bounding the postulated extruding crust notably the altyn tagh fault along the northern margin of tibet and the karakoram fault along the sw margin satellite photographic interpretation and field mapping in the karakoram mountains in pakistan the nubra siachen area of north ladakh and the pamirs in xinjiang show that although the karakoram fault is extremely active today geological offsets along the right lateral fault are probably less than 120 km the 21 0 5 ma baltoro monzogranite leucogranite batholith has been rotated clockwise about a vertical axis 35 40 into nw se alignment parallel with the karakoram fault east of the siachen glacier with a maximum offset of 90 km across the fault the bangong shyok suture zone similarly has a dextral offset of 85 km the course of the indus river which was antecedent to the rise of the ladakh karakoram and himalayan ranges has been offset dextrally by 120 km south of pangong lake if present day slip rates approximately 32 mm yr avouac and tapponnier 1993 are correct only 4 ma are required to obtain a 120 km offset there is no geological evidence for any larger scale pre holocene offsets and it is suggested that the karakoram fault cannot have accommodated major eastward lateral motion of tibetan crust the fault has also exerted little or no influence on surface topographic uplift cutting obliquely across the highest peaks of the karakoram dextral motion along the central part of the karakoram fault has been transferred in the north to the rangkul murghab and karasu transpressional faults in the central pamir north of tashkurgan the karakoram fault shows mainly normal motion around the kongur and mustagh ata gneiss domes metamorphic core complexes and the extensional muji graben minor dextral displacement has occurred along the shiquanhe fault but this motion cannot be linked to the jiale fault of east tibet the southern end of the karakoram fault merges with the indus yarlung suture zone near mount kailas and does not cut across the himalaya the lack of large scale geological offsets along the karakoram fault together with its very recent initiation 5 or 4 ma suggests that it is related to the pliocene quaternary northward indentation of the pamir and not to any long term extrusion of tibetan crust following the indian collision

crustal lithospheric structure and continental extrusion of tibet crustal shortening and thickening to c 70 85 km in the tibetan plateau occurred both before and mainly after the c 50 ma india asia collision potassic ultrapotassic shoshonitic and adakitic lavas erupted across the qiangtang c 50 29 ma and lhasa blocks c 30 10 ma indicate a hot mantle thick crust and eclogitic root during that period the progressive northward underthrusting of cold indian mantle lithosphere since collision shut off the source in the lhasa block at c 10 ma late miocene pleistocene shoshonitic volcanic rocks in northern tibet require hot mantle we review the major tectonic processes proposed for tibet including rigid block continuum and crustal flow as well as the geological history of the major strike slip faults we examine controversies concerning the cumulative geological offsets and the discrepancies between geological quaternary and geodetic slip rates low present day slip rates measured from global positioning system and insar along the karakoram and altyn tagh faults in addition to slow long term geological rates can only account for limited eastward extrusion of tibet since mid miocene time we conclude that despite being prominent geomorphological features sometimes with wide mylonite zones the faults cut earlier formed metamorphic and igneous rocks and show limited offsets concentrated strain at the surface is dissipated deeper into wide ductile shear zones

stable carbon and oxygen isotopes in quaternary soil carbonates as indicators of ecogeomorphic changes in the northern chihuahuan desert usa stable carbon and oxygen isotopes in soil carbonates provide an additional technique for investigating quaternary ecogeomorphic changes in arid and semiarid regions this study presents 13c and 18o values in surface and buried soils in a basin and range region of southern new mexico and west texas three landform categories were investigated for their isotopic content 1 middle piedmont slopes 2 a lower piedmont slope and adjacent playa depressions and 3 an intermontane basin floor soils of the middle piedmont slopes had greatest 13c variability ranging from 0 6 in buried soils to 11 1 pdb in surface soils soils of the basin floor had greatest variability in 18o values ranging from 0 6 to 7 6 pdb fossil pollen patterns roughly paralleled 13c shifts with cheno am pollen exhibiting greatest changes both isotope and pollen data across stratigraphic discontinuities suggest that a conversion from c4 grasses to c3 desert shrubs accompanied holocene erosion

mesozoic and cenozoic tectonic evolution of the shiquanhe area of western tibet 1 in the shiquanhe area of far western tibet mid cretaceous strata lie unconformable on ophiolitic melange and jurassic flysch associated with the bangong nujiang suture zone on the basis of our mapping and geochronologic studies we suggest that these cretaceous strata were shortened by 57 over a north south distance of 50 km during late cretaceous early tertiary time the late cretaceous narangjiapo thrust placed permian strata 20 km over ophiolitic melange and cretaceous strata north of the narangjiapo thrust 40 km of shortening was accommodated by the late cretaceous early tertiary south directed jaggang thrust system that involves jurassic flysch and cretaceous strata and roots into a decollement within ophiolitic melange the most recent shortening was accommodated to the south of the narangjiapo thrust along the north dipping shiquanhe thrust the shiquanhe thrust cuts flat lying 22 6 0 3 ma volcanic rocks and underlying folded tertiary nonmarine strata in its footwall and was likely active during slip along the oligocene gangdese thrust system of southern tibet ophiolitic melange and structurally overlying jurassic flysch near shiquanhe are interpreted to represent remnants of a subduction accretion complex and forearc basin respectively that were obducted southward onto the margin of the lhasa terrane during late jurassic early cretaceous closure of the bangong nujiang ocean subsequent imbrication of the obducted sheet could have produced the two east west trending belts of ophiolitic melanges separated by 100 km in western tibet late cretaceous early tertiary thin skinned shortening may have been accommodated in the deeper crust by northward underthrusting and duplexing of lhasa terrane rocks beneath the obducted ophiolitic melange and the qiangtang terrane to the north

pedogenic carbonate cutans on clasts in soils as a record of history of grassland ecosystems pedogenic carbonate cutans coatings pendants rinds on coarse clasts are common in stony soils of arid and semiarid regions dominated by open vegetation this paper gives an overview of the potential of the carbonate cutans for paleograssland research using data from literature and personal observations carbonate coatings are stratified into distinct microlamina which can provide a record of local environmental changes lamina made of a rather pure calcium carbonate with better formed and parallel oriented crystals seem to be indicative of relatively dry phases that were less favorable for biological activity a high content of admixtures poorer formed and randomly oriented calcite crystals presumably mark wetter periods characterized by climatic amelioration at a most general level n 13 c of the cutan carbonate can provide information on the type of photosynthesis of local vegetation whereas n 18 o in carbonate material of the coatings correlates with oxygen isotopic composition of precipitation water at the site and is sensitive to fluctuations in temperature to obtain chronological evidence on cutan formation the 14 c and th u methods can be applied with certain limitations additionally cutan growth rates can be used to evaluate the age of these features fl 2002 elsevier science b v all rights reserved

circulation changes and nutrient concentrations in the late quaternary aegean sea a nonsteady state concept for sapropel formation sapropel forming conditions we identify the start of seasonal stratification and highlight a lag in d 18 o response of the planktonic foraminifer n pachyderma to termination t1b as identified in the d 18 o record of g ruber by use of a simple model we determine that this offset cannot be a function of bioturbation effects the lag is of the order of 1 kyr and suggests that isolation of intermediate deep water preceded the start of sapropel formation by up to 1 5 kyr using this discovery we propose an explanation for the major unresolved problem in sapropel studies namely the source of nutrient supply required for export productivity to reach levels needed for sustained sapropel deposition we suggest that nutrients had been accumulating in astagnant basin for 1 1 5 kyr and that these accumulated resources wereutilized duringthe deposition of s1 in addition we provide a first quantitative estimate of the diffusive 1 e mixing timescale for the eastern mediterranean in its stratified sapropel mode which is of the order of 450 years index terms 1050 geochemistry marine geochemistry 4835 4850 3030 marine geology and geophysics micropaleontology 3339 meteorology and atmospheric dynamics ocean atmosphere interactions 0312 4504 4267 oceanography general paleoceanography 4870 oceanography biological and chemical stable isotopes keywords sapropel mediterranean holocene foraminifera climate variability

quantitative analysis of quaternary nannoplankton in the subtropical northwestern pacific ocean abstract time progressive changes of nannoflora and biometry of coccoliths for the last 1 3 m y were investigated for a piston core recovered from the west mariana ridge the species compositions were quantitatively investigated under an electron microscope and six assemblages assemblages a through f were identified significant changes in relative abundances of various types of genus gephyrocapsa are the main cause for the stratigraphic change of the flora a dominant occurrence of gephyrocapsa protohuxleyi var a which can be identified only under an electron microscope was observed for the first time in a thin sequence which corresponds to the lowest part of the brunhes epoch 0 75 0 62 ma because of this characteristic occurrence assemblage d was further subdivided into three subassemblages the dominant occurrence of small gephyrocapsa which is well known in the small gephyrocapsa zone of the equatorial pacific ocean was not observed but the almost complete absence of medium to large gephyrocapsa during approximately 200k years of the middle pleistocene was confirmed a stratigraphically restricted occurrence of a large form of reticulogenestra was also confirmed by the biostratigraphic study under a light microscope and the last and first occurrences of the largest form reticulofenestra sp a 6 5 m were identified at 0 81 and 0 98 ma respectively in addition to these four events precise ages for another five well known evolutionary events were also calibrated these ages are generally in good agreement with previously reported ages from other world oceans and diachronism was not evident for most of these evolutionary events

needle fiber calcite a critical review and a proposed classification abstract from a review of the recent literature and our own observations the different morphologies of needle fiber calcite are classified they can be characterized as monocrystalline rods with or without serrated edges or as polycrystalline chains the simplest monocrystalline habit of needle fiber calcite is the individual micro rod m larger monocrystalline rods ma exist in multiples of two more complex forms are found as paired monocrystalline rods with serrated plates along their length mb this group includes three habits which can be distinguished by the number of plates and their orientation relative to the rod finally there is a monocrystalline form mab intermediate between the categories ma and mb which shows the transition from the simple coupled rods to rods with errated plates although polycrystalline needles p have rarely been reported in the literature three types of morphologies have been identified each type of crystal has a specific origin the m micro rods are physicochemical nuclei or calcified bacteria they do not seem to evolve towards larger or more complex morphologies the ma rods are related to biomineralization inside the fungal sheaths the mb rods postdate liberation of ma rods from mycelian bundles the serrated plates are secondary syntactic crystallizations of physicochemical origin whose growth can be inhibited for various reasons the origin of p chains is less well understood but they seem to be physicochemical crystallizations related to evaporation and desiccation therefore these three groups m ma mb and p have similar morphologies but do not seem to be related genetically the only known link is between the ma and mb rods there is no evolutionary s quence of needle fiber calcite habits but a convergence of forms between crystals whose origins are different and independent structures described in the literature as convoluted random cutane and nest like are the result of either evolution of the mycelian bundles or movement of material and organisms in the soil in the case of m micro rods the microfabric is related to the random precipitation around nuclei in pores filled with a highly supersaturated solution initially the p chains also precipitate without preferential organization and later on the growth seems to preferentially constitute chains although the mechanisms are still not understood moreover needle fiber calcites do not indicate a particular climatic environment

syn kinematic emplacement of the pangong metamorphic and magmatic complex along the karakorum fault n ladakh this paper investigates the age p t conditions and kinematics of karakorum fault kf zone rocks in the nw part of the himalaya karakorum belt granulite to greenschist facies assemblages were developed within the kf zone during strike slip shearing the granulites were formed at high temperature 800 c 5 5 kbar were subsequently retromorphosed into the amphibolite facies 700 750 c 4 5 kbar and the greenschist facies 350 400 c 3 4 kbar the tangtse granite emplaced syn kinematically at the contact between a lt and the ht granulite facies intrusion occurred during the juxtaposition of the two units under amphibolite conditions microstructures observed within the tangtse granite exhibit a syn magmatic dextral s c fabric compiled u pb and ar ar data show that in the central kf segment granulite facies metamorphism occurred at a minimum age of 32 ma subsequent amphibolite facies metamorphism at 20 18 ma further shearing under amphibolite facies 650 500 c was recorded at 13 6 0 9 ma and greenschist facies mica growth at 11 ma these data give further constrains to the age of initiation and depth of the karakorum fault the granulite facies conditions suggest that the kf accommodating the lateral extrusion of tibet could be at least a crustal or even a lithosphere scale shear zone comparable to other peri himalayan faults

tertiary deformation history of southeastern and southwestern tibet during the indo asian collision geologic mapping and geochronological analysis in southwest kailas area and southeast zedong area tibet reveal two major episodes of tertiary crustal shortening along the classic indus tsangpo suture in the yalu river valley the older event occurred between ca 30 and 24 ma during movement along the north dipping gangdese thrust the development of this thrust caused extensive denudation of the gangdese batholith in its hanging wall and underthrusting of the xigaze forearc strata in its footwall examination of timing of major tectonic events in central asia suggests that the initiation of the gangdese thrust was approximately coeval with the late oligocene initiation and development of north south shortening in the eastern kunlun shan of northern tibet the nan shan at the northeastern end of the altyn tagh fault the western kunlun shan at the southwestern end of the altyn tagh fault and finally the tian shan north of the tarim basin such regionally synchronous initiation of crustal shortening in and around the plateau may have been related to changes in convergence rate and direction between the eurasian plate and the indian and pacific plates the younger thrusting event along the yalu river valley occurred between 19 and 10 ma along the south dipping great counter thrust system equivalent to the locally named renbu zedong thrust in southeastern tibet the backthrust system in south central tibet and the south kailas thrust in southwest tibet the coeval development of the great counter thrust and the north himalayan granite gneiss dome belt is consistent with their development being related to thermal weakening of the north himalayan and south tibetan crust due perhaps to thermal relaxation of an already thickened crust created by the early phase of collision between india and asia or frictional heating along major thrusts such as the main central thrust beneath the himalaya

stable isotope geochemistry of vertisols formed on marine limestone and implications for deep time paleoenvironmental reconstructions abstract carbon and oxygen isotope compositions of pedogenic carbonate preserved in paleosols have been used extensively to reconstruct ancient environmental conditions one concern is that pedogenic carbonate precipitated in association with a limestone parent material may include a contribution from inherited detrital lithogenic marine calcite thus compromising interpretations of stable isotope compositions to investigate the impact of lithogenic calcite on environmental interpretations using paleosols we measured stable isotope ratios in pedogenic carbonates and coexisting soil organic matter som in modern vertisols fine smectitic thermic udic haplusterts from riesel texas heiden series and zabcikville texas houston black series forming on cretaceous chalk deposits the pedogenic and lithogenic components in the heiden series soil at riesel were identified using micromorphology and cathodoluminescence cl which showed incorporation of luminescent marine allochems i e foraminifera mollusks into hard nodules and soft powdery pedogenic masses additionally micromorphology showed evidence of meteoric recrystallization of the allochems despite the presence of these inherited carbonates into hard nodules and soft powdery masses the stable isotope compositions recorded a partial pedogenic signal recrystallization of the marine allochems resulted in overprinting of primary marine isotope ratios with ratios that are more similar to those expected for pedogenic carbonates in these soils this study demonstrates that incorporation of parent material into pedogenic carbonates does not necessarily compromise the pedogenic signal that is useful for paleoenvironmental reconstructions however overprinting of marine allochems if present can be important and needs to be identified using micromorphology and cathodoluminescence before using stable isotope ratios of pedogenic carbonates for paleoenvironmental reconstructions

massive middle miocene gypsic paleosols in the atacama desert and the formation of the central andean rain shadow abstract the central andes of south america are one of the highest and broadest mountain ranges on earth and have a profound influence on climate in the southern hemisphere yet the timing of andean uplift and its subsequent impact on atmospheric circulation is not well known here we use fossil soils from along an 800 km transect 19 25 s in the atacama desert of northern chile to identify the initiation of extreme aridity along the west coast of south america and infer a minimum age for the development of the central andean rain shadow paleosols record the onset of extreme aridity at the boundary between the middle and late miocene 12 10 ma lower miocene 24 20 ma soils are chemically weathered and contain soil carbonate indicative of a vegetated landscape and semi arid climate in contrast gypsum dominates massive 2 5 m thick upper middle miocene soils that formed on a hyperarid landscape devoid of vegetation the development of extreme hyperaridity is linked to the formation of the central andean rain shadow through the divergence of oxygen isotope values oxygen isotope values of lower miocene soil carbonates in the atacama desert 5 0 1 1 vpdb and central andes 7 8 1 are similar indicating no or a limited rain shadow by 15 mya however 18 o values of soil carbonate differ by 8 with values of soil carbonate in altiplano paleosols getting lower due to uplift while soil carbonate values in the atacama desert get higher due to aridity therefore by 15 mya there is clear evidence for a rain shadow from the central andes by the latest middle miocene ca 12 10 ma paleosols in the altiplano decreased to 11 8 1 0 while soils in the atacama desert increase to 1 5 4 5 this almost 14 divergence in the 18 o values of soil carbonate for soils only 250 km apart is evidence of a strong central andes rain shadow effect in place during the late middle miocene 12 10 ma

structural complexity resulting from pervasive ductile deformation in the karakoram shear zone ladakh nw india 1 the nw se trending 800 km long dextral karakoram shear zone bounds southwest tibet we investigate an area immediately nw of the pangong lake where midcrustal rocks sections of the shear zone are exposed here the dominant shear zone is characterized by dextral mylonitic rocks sheared at amphibolite facies and partly retrogressed to greenschist facies these rocks define a kilometric se plunging inclined to recumbent fold in the footwall of a north directed oblique dextral thrust that exhumed anatectic rocks of the pangong range argon cooling ages reveal that the pangong range cooled from 700 c to 300 c between 18 15 and 10 ma contemporaneously with overthrusting toward the se closer to the pangong lake this kilometric fold is rotated from its nw se trend to an e w trend and the sense of shear changes to sinistral with a broadly north directed thrusting component the documented structures contradict predictions of normal movement in this area derived from considerations of rigid block behavior of the crust and support the interpretation that the system records dextral transpression thrusting and exhumation of the deeper and hot rocks exposed in the pangong range folding of the thrust footwall and the development of a sinistral e w trending shear zone are all compatible with transpression caused by a northward push by a rigid indenter such as the ladakh batholith

u pb age of the baltoro granite northwest himalaya and implications for monazite u pb systematics the baltoro granite is a major late to post tectonic plutonic phase of the karakoram batholith of the northwest himalaya in northern pakistan u pb zircon analyses indicate both emplacement at 21 0 0 5 ma and significant precambrian zircon inheritance dates on monazite are 17 19 ma and are interpreted to have remained near their closure temperature of about 700 c for several million years after emplacement resulting in pb loss by diffusion we suggest that the granite was emplaced into rocks which were at high temperature and that they remained so until late miocene northeast tilting rapid uplift and or tectonic denudation and cooling

the formation of caliche in soils of the mojave desert california abstract radiocarbon and 230th 234u dates of calcic horizons from calciorthid soil profiles in the mojave desert were used to calculate the rate of deposition of pedogenic caco3 a major period of caco3 deposition appears to have occurred about 20000 ybp forming calcic horizons below 100 cm depth during a climatic regime with greater effective rainfall than in the present the overall rate of deposition has been 1 0 to 3 5 g caco3 m2 yr during soil formation this rate is consistent with present day rates assuming that the atmospheric deposition of ca limits the process stable isotope ratios in calcic horizons indicate that caco3 precipitated from a soil environment with co2 of 15 5 13 c 12 c vs pdb and h2o of 2 0 18 o 16 o vs smow these values suggest that caco3 precipitates when seasonal drought simultaneously lowers soil pore pco2 and enriches soil water 18o by evaporation the role of soil calcic horizons in the global geochemical cycle of carbon is discussed

abrupt shoaling of the nutricline in response to massive freshwater flooding at the onset of the last interglacial sapropel event a detailed assessment of the respective roles of production export and subsequent preservation of organic carbon corg in the eastern mediterranean emed sediments during the formation of sapropels remains elusive here we present new micropaleontological results for both surface samples taken at several locations in the emed and last interglacial sapropel s5 from core lc21 in the southeastern aegean sea a strong exponential anticorrelation between relative abundances of the lower photic zone coccolithophore florisphaera profunda in the surface sediments and modern concentrations of chlorophyll a chl a at the sea surface suggests that f profunda percentages can be used to track past productivity changes in the emed prior to s5 deposition an abrupt and large increase of f profunda percentages in lc21 coincided within the multidecadal resolution of the records with the marked freshening of emed surface waters this suggests a strong coupling between freshwater bound surface to intermediate water density stratification and enhanced upward advection of nutrients to the base of the photic zone fuelling a productive deep chlorophyll maximum dcm underneath a nutrient starved surface layer our findings imply that at least at the onset of sapropel formation physical and biogeochemical processes likely operated in tandem enabling high corg accumulation at the seafloor

comment on does the karakoram fault interrupt mid crustal channel flow in the western himalaya by mary l leech earth and planetary science letters 276 2008 314 322 abstract leech leech m l 2008 does the karakoram fault interrupt mid crustal channel flow in the western himalaya earth planet sci lett 276 314 322 proposed that 1 himalayan granites are significantly more abundant east of the karakoram fault termination around mount kailas in sw tibet than west of it in the zanskar kumaon region that 2 the fault may have created a barrier to southward flow of mid crustal channel flow and that 3 the fault acted as a vertical conduit for these melts these inferences are based upon new u pb shrimp data from the leo pargil dome nw india and the analysis of published u pb ages from additional himalayan domes here we point out the flaws in all these hypotheses and suggest a much closer comparison of granites along the karakoram shear zone to the widespread miocene crustal melt granites of the baltoro karakoram range in north pakistan field relationships combined with u th pb dating of granites and metamorphic rocks clearly shows that the leucogranites exhumed along the karakoram fault are related to regional metamorphic and melting events along the baltoro karakoram range of the asian plate and not to indian plate himalayan leucogranites at all we discuss individually the points raised

paleoclimatic controls on stable oxygen and carbon isotopes in caliche of the abo formation permian south central new mexico u s a abstract the stable oxygen and carbon isotopic composition of caliche in fluvial and supratidal rocks of the abo formation permian south central new mexico is controlled by paleoclimate and depositional environment fluvial caliche consists of low mg calcite nodules and vertically oriented tubules that display stage ii texture micrite matrix support brecciation ooids pisoliths aveolar septal texture and peloids are common in the fluvial caliche and along with red color and slickensides in the host shale indicate pedogenesis in a well oxidized vadose zone in contrast periodic waterlogging of the supratidal paleosols probably due to high water table is indicated by drab colors carbonaceous flecks horizontal rhizoliths and the paucity of vadose textures in the stage ii caliche n dules stable oxygen isotopes are similar in the fluvial and supratidal caliches and range from 21 6 to 30 5 smow the data exhibit a crude bimodality and 18o enrichment with a decrease in age higher in the section consideration of these data in the context or temperature relations suggests that 1 surface waters responsible for caliche formation increased in 18o from roughly 8 to 1 over the 18 m y time interval that separated the lowest stratigraphic nodule horizon from the highest 2 the inc easing 18o values also reflect a warming trend approximately 15 to nearly 3 c in the mean monthly temperature over this same time period with perhaps an associated increase in permian ocean temperatures and 3 the significant variation in 18o from oldest to youngest caliche was probably enhanced by the amount effect such that as the temperature increased the amount of precipitation decreased resulting in high 18o values caliches in the abo are enriched in heavy carbon 7 2 to 1 5 pdb compared to that of soil carbonate derived exclusively from c plants 12 pdb and the supratidal caliches contain somewhat heavier carbon compared to the fluvial caliche the 13c values for both environments increase with a decrease in caliche age these results indicate that as the temperature increased and rainfall decreased with time the level of c3 plant productivity apparently declined allowing a greater influx of atmospheric co2 into the soil this can only occur when soil respiration rates are quite low or at very sha low depths less than 10 cm or both atmospheric co2 seems to have invaded the supratidal soils to a somewhat greater extent than the fluvial soils

seasonal bias in the formation and stable isotopic composition of pedogenic carbonate in modern soils from central new mexico usa in order to better calibrate pedogenic carbonate as a proxy for past environments we compared the stable isotopic composition of soil co 2 soil water and pedogenic carbonate in young soils from central new mexico usa seasonal changes in the 13 c value of soil co 2 the 18 o value of soil water and the soil temperature were monitored to establish the timing of isotopic equilibrium with the carbonate calcite solubility was calculated from measured temperatures and co 2 concentrations in the soil this approach allowed us to determine the conditions associated with pedogenic carbonate formation carbon isotope equilibrium oxygen isotope equilibrium and minimum calcite solubility all occurred simultaneously during warm dry conditions in may 2008 when soil co 2 concentrations were low it is therefore concluded that pedogenic carbonate forms during warm dry periods and does not record mean growing season conditions as typically assumed the seasonal bias in pedogenic carbonate formation may explain the occurrence of pedogenic carbonate in monsoon climates and its absence in regions where annual precipitation is more uniformly distributed the implications of the seasonal bias for stable isotope based paleoenvironmental reconstructions are that paleoelevations may have been previously over or underestimated paleoatmospheric co 2 concentrations likely have been signifi cantly overestimated and pedogenic carbonate provides a c 4 biased record of paleovegetation especially in dry soils

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

differentiation of pedogenic and lithogenic carbonate forms in texas abstract sixteen pedons representing soils developed from limestone and fluvial deltaic sediments were sampled in central and western texas 300 800 mm annual precipitation to differentiate pedogenic secondary and lithogenic inherited carbonate forms by field and laboratory techniques lithogenic carbonate forms identified in the field included indurated limestone bedrock and coarse limestone fragments lithorelicts field identified pedogenic forms included petrocalcic horizons thin laminar cappings on indurated limestone carbonate joint seams pendants on pebbles and carbonate films and threads on ped faces small

karakoram fault zone rocks cool in two phases the karakoram fault zone of ladakh india is a major strike slip boundary along which the tectonic evolution of tibet has been accommodated in this paper 40 ar 39 ar isotopic age data are integrated with structural and metamorphic data to infer an exhumation history for granites and low to intermediate grade metamorphic rocks exposed adjacent to two strands of the fault zone near tangtse leucogranites which crystallized c 17 ma ago are cut by the karakoram fault zone indicating that fault movement was initiated subsequent to 17 ma the 40 ar 39 ar data give temperature time histories which indicate that the two phases of rapid cooling of karakoram fault zone rocks are evident one at c 17 ma to c 13 ma and another following an intervening period of relatively slow cooling starting at c 8 ma and continuing until at least 7 ma uplift since c 17 ma via dextral oblique thrusting has resulted in exhumation from amphibolite facies metamorphic conditions possibly with a larger thrust component from 17 to 13 ma followed by a change to dominant strike slip motion at about 13 ma rapid cooling starting at c 8 ma at greenschist facies temperatures is probably the result of renewed oblique thrusting it is notable that the two episodes of rapid cooling recorded in karakoram fault zone rocks coincide with episodes of exhumation in the pakistani karakoram and also in southern tibet

carbon isotopic subsets of soil carbonate a particle size comparison of limestone and igneous parent materials abstract the c isotopic analysis of pedogenic carbonate is an important method for investigating paleoclimatic conditions and carbon sequestration however a calcic soil sample may contain multiple types of carbonate especially in soils formed in limestone parent material to evaluate isotopic values of the different soil carbonate types stable c isotopic analysis was applied to an array of particle size classes in bulk soil that was collected from soils formed in limestone parent material and neighboring soils formed in igneous parent material a pronounced trend of decreasing 13 c with progressively decreasing soil particle size was revealed in soils of both parent materials ranging from about 2 to 6 for limestone soils and 1 to 5 for igneous soils thin section microscopy and radiocarbon dating also indicated multiple subsets of calcium carbonate types in soils thin section analysis disclosed the presence of limestone detritus calcitans aggregates of carbonate crystals and calcified root hairs radiocarbon dating revealed different 13 c values of carbonate crystals of different ages ranging from about 2620 to 40 290 years for limestone soils and 1660 to 5830 years for igneous soils these results indicate 1 limestone particles in soil may contribute to a complex mixture of 13 c values that is absent from soils formed in igneous parent material and 2 it is necessary to recognize that isotopic values of bulk soil represent a mixture of different 13 c values from different size fractions and ages in both limestone and igneous soils

micromorphological fabrics and developmental stages of carbonate nodular forms related to soil characteristics abstract carbonate nodules often constitute the first stage of calcrete formation micromorphological analysis of carbonate nodules and nodular fabrics in different soil materials shows that their development is a function of several factors nature of the host matrix texture porosity carbonate and non carbonate clay distribution bulk density and the interactions among them different micromorphological stages therefore exist in different soil materials in calcareous medium textured soil materials the stages of nodule formation are related to the increase of the density of the nodule caused by the accumulation of microcalcites in such a soil material the following stages occur 1 microcalcites within the low to moderate density matrix 2 microcalcites of moderate to high density and moderately dense diffuse nodules parallel calcans may occur 3 microcalcites of high density with dense microcalcitic nodules during these stages the amount of non carbonate clay decreases but is homogeneously dispersed and disseminated with the microcalcites in general the size of microcalcites 1 8 m is inversely related to the clay content in non calcareous medium to fine textured soil materials secondary carbonate precipitates in intrapedal and or interpedal voids as large sparry crystals due to pedoturbation processes the nodules thus formed are subjected to recrystallization resulting in a microsparry pattern the development stages are 1 few calcans and crystal chambers 2 crystic nodules mainly of sparry crystals and an increase of calcans and crystic chambers 3 recrystallized nodules composed mainly of microspars in coarse grained materials secondary carbonates precipitate directly in voids as sparry crystals and the resulting nodules are of the crystic type the large crystals are often subjected to recrystallization in partly calcareous coarse grained materials with additions of calcareous dust particular micromorphological carbonate forms occur in the c horizon cutanic calciasepic fabric forms besides zones of crystic fabric which gradually become calciasepic in the b horizon and include the typical nodular forms of the calcareous medium textured soil material together with appreciable amounts of glaebular halos the processes leading to the formation of these stages occur essentially without a significant biogenic influence where carbonate segregation occurs as rhizomorphs surrounding active roots the fabric is always micritic even in coarse textural soil material

role of calcium oxalate biomineralization by fungi in the formation of calcretes a case study from nazareth israel abstract biomineralized fungal filaments often referred to as calcified filaments are of interest because of their role in the calcium cycle in calcretes the mineralogy of the crystals associated with these filaments and the evolution of their numerous crystal habits in a calcrete from nazareth israel are the subject of this study removing the be window from an energy dispersive spectrometry eds microprobe coupled with a scanning electron microscope sem permitted the measurement of the light elements c and o us well as ca comparison of crystal spectra to those of known standards demonstrated that the great majority of needles associated with the fungal filaments are calcium oxalate based on these results a model of fungal filament mineralization is proposed that describes the e olution of weddellite polyhydrate calcium oxalate into whewellite monohydrate calcium oxalate in a sequence that includes all of the crystal morphologies observed by sem followed by a less well understood diagenetic transformation of monohydrate calcium oxalate into calcium carbonate

caco3 recrystallization in saline and alkaline soils abstract are desert ecosystems a stable sink for atmospheric co 2 although the uptake of atmospheric co 2 by soil during the nighttime is detected in deserts and some semi deserts the underlying mechanisms remain elusive in order to determine the factors affecting the co 2 fluxes into soil and to reveal the relationship between co 2 fluxes and carbonate formation and recrystallization in saline and alkaline soils four soils with contrasting salinity from two sites aksu and yingbazar along the tarim river were analysed soils were incubated in 14 co 2 labelled atmosphere for 90 days at three co 2 concentrations 0 04 0 4 and 4 the 14 c activity was measured in soil water and air as well as in carbonates after 2 14 and 90 days the 14 c incorporation in caco 3 increased with corresponding 14 c decrease remaining in the co 2 the highest 14 c incorporation into caco 3 54 was observed in the yingbazar saline soil the carbonate recrystallization rates increased logarithmically r 2 0 97 with the co 2 concentration the average carbonate recrystallization rate from three sampling times was highest in the yingbazar saline soil under 4 co 2 8 45 10 6 day 1 and lowest in the aksu alkaline soil under 0 04 co 2 0 03 10 6 day 1 the average carbonate recrystallization rate increased with electric conductivity corresponding to soil salinity but decreased with ph r 2 0 99 for 4 co 2 the alkaline soils incorporated less 14 c into caco 3 than the saline soils at the highest co 2 concentration of 4 the full recrystallization period of the remaining primary carbonates was 10 to 100 fold shorter than at the lower co 2 concentrations therefore besides soil chemical parameters e g ph caco 3 content co 2 concentration respiration of microorganisms and roots is an important factor for caco 3 recrystallization and formation of pedogenic carbonates in desert soils it is the most important factor for caco 3 recrystallization and so for the formation of pedogenic carbonates

dating fluvial terraces by 230th u on pedogenic carbonate wind river basin wyoming abstract reliable and precise ages of quaternary pedogenic carbonate can be obtained with 230th u dating by thermal ionization mass spectrometry applied to carefully selected milligram size samples datable carbonate can form within a few thousand years of surface stabilization allowing ages of quaternary deposits and surfaces to be closely estimated pedogenic carbonate clast rinds from gravels of glacio fluvial terraces in the wind river basin have median concentrations of 14 ppm u and 0 07 ppm 232th with median 230th 232th 270 making them well suited for 230th u dating horizons as thin as 0 5 mm were sampled from polished slabs to reduce averaging of long 105 yr and sometimes visibly discontinuous depositional histories dense translucent samples with finite 230th u ages preserve within rind stratigraphic order in all cases ages for terraces wr4 167 000 6 400 yr and wr2 55 000 8600 yr indicate a mean incision rate of 0 26 0 05 m per thousand years for the wind river over the past glacial cycle slower than inferred from cosmogenic nuclide dating terrace wr3 which formed penecontemporaneously with the final maximum glacial advance of the penultimate rocky mountain bull lake glaciation has an age of 150 000 8300 yr indicating that it is broadly synchronous with the penultimate global ice volume maximum

a review of criteria for the identification of magmatic and tectonic foliations in granitoids abstract foliations in granitoids can form by magmatic flow submagmatic flow high temperature solid state deformation and moderate to low temperature solid state deformation a review of previous work suggests that no single criterion can consistently distinguish foliations in granitoids formed by flow during ascent diapiric emplacement and expansion emplacement during regional deformation or regional deformation post dating emplacement however a magmatic origin is favoured for foliations defined by the alignment of igneous commonly euhedral minerals particularly where the foliation is parallel to internal or external pluton contacts foliations formed during expansion or ballooning of diapirs may be strictly magmatic in origin although some studies suggest that solid state deformation also may occur if so we would hope to find evidence of deformation of crystal melt systems and that the solid state deformation occurred at high temperatures the inference of syntectonic foliations is most convincing where magmatic and high temperature solid state foliations are subparallel these foliations are continuous with regionally developed foliations in the wall rocks synkinematic porphyroblasts are present in the wallrocks and igneous minerals have the same age as metamorphic minerals associated with the regional cleavage a strictly tectonic origin for foliations in granitoids is favoured when the foliation is defined by metamorphic minerals no alignment of igneous minerals occurs the foliation is locally at high angles to pluton wallrock contacts and the foliation is continuous with a regionally developed cleavage

phanerozoic organic carbon rich marine sediments overview and future research challenges one of the major obsessions of many early workers to the mid 1900s was the application of uniformitarian principles to deposi tional models for black shales arthur and sageman 1994 the purpose of this overview of organic carbon oc rich marinesediments is to provide a brief but current summary of the historicaldevelopments principle concepts and remaining challenges in inte grated sapropel and black shale research as such it provides asubstantive introduction to the special issue of palaeogeography palaeoclimatology palaeoecology on organic carbon rich sedimentsthrough the phanerozoic processes progress and perspectives giventhis focused scope the overview does not aim to be comprehensive orcomplete but to provide a solid setting for the fourteen individualresearch papers that constitute this special issue and two previousspecial issues meyers and negri 2003 negri et al 2006 thatcoverresearch aspects complementary to this one like the individualcontributions this introduction and overview is organized intocenozoic mesozoic and palaeozoic units the cenozoic and palaeozoicunitsaredeliberatelylargerthanthemesozoicunit acknowledgingthatmuch ground on mesozoic black shale is already covered in the twoprevious special issues because the late cenozoic sapropels of themediterraneanbasinhavebeenextensivelystudied understandinghowthese near modern analogs of ancient black shales were depositedprovidesagoodfoundationforunderstandinghowtheoldersequencesmayhaveevolved incontrast becausefarlessisgenerallyknownabouttheblackshalesofthepalaeozoicthancomparableoc richsequencesofeither the cenozoic or the mesozoic a more comprehensive summaryand comparison of the more ancient sequences is particularly appro priate to the theme of this special issue 1 introductionsediments rich in organic carbon are restricted to small areas alongcontinental margins in the modern ocean and have rarely accumulatedduringthecenozoic yetorganic rich sediments werewidely depositedduring multiple intervals of mesozoic palaeozoic time and even earlierduringtheproterozoic archean globalmarinedepositsdocumentthatepisodes of accumulation of oc rich sediments occurred in differentregions and at different times these episodes were linked to climaticandpalaeoceanographicperturbationsthat resulted inmassive uctua tions in hydrologic and nutrient cycles and in oceanchemistryand thatrecurred throughout geologic time however the paucity of survivingpalaeozoic and earlier black shale sections makes it dif cult toimpossible to recognize the internal structure of global events that arecommon inyounger oc rich sedimentary sequences asunderlinedbelow themarinesectionsinmanylocalitiesconsistof intercalated carbonates and shales that may grade into purecarbonate or black shale sedimentation often re ecting shallowing

age constraints on ductile deformation and long term slip rates along the karakoram fault zone ladakh the dextral karakoram fault zone that bounds the southwestern margin of tibet is widely regarded as one of the major strike slip faults that accommodates the eastward extrusion of the thickened crust of tibet in northern ladakh the karakoram fault bounds the pangong transpressional zone with the active fault trace following the eastern margin of the range exhumation within this zone reveals mylonites that have absorbed much of the deformation along the fault two sets of dikes are evident within the main fault strand that bounds the transpressional zone whilst one dike set is concordant with the dominant foliation and shows mylonitic fabric the youngest dike set are less deformed and cross cut the shear zone fabric using u pb id tims data from five shear zone samples deformed by differing degrees we infer that fault initiation occurred between 15 68f0 52 and 13 73f0 28 ma since absolute offset is difficult to determine we couple these age constraints with suggested minimum and maximum offsets of the baltoro type granites the offset range of 40 150 km reveals that the karakoram fault has a longterm average slip rate in the range 2 7 10 2 mm year the lower rate being compatible with gps insar and cosmogenic data for the fault the small range of offset and low slip rates do not support rapid large scale extrusion of tibet along lithosphericscale faults and strengthens the argument that tibet does not behave in a rigid plate like manner d 2004 elsevier b v all rights reserved

slip rates of the karakorum fault ladakh india determined using cosmic ray exposure dating of debris flows and moraines most recent major glacial advance occurred at 90 15 ka this is consistent with the inference of others that alpine glaciers in this region have not necessarily expanded in concert with northern hemisphere continental ice sheets if features including lateral moraines that liu inferred to have been offset 300 350 m by the karakorum fault date from the same period they too imply a slip rate of 3 4 mm yr 1 this slip rate is comparable to rates of extension across grabens within tibet with recent evidence that slip along the altyn tagh fault occurs at 10 mm yr 1 our rate suggests that slip along the boundaries of tibet is not significantly more rapid than extension within the plateau hence plate tectonics in the strictest sense ought not be applied to tibet because tibet does not behave as a rigid plate index terms 1824 hydrology geomorphology 1625 1035 geochemistry geochronology 9320 information related to geographic region asia 8107 tectonophysics continental neotectonics keywords karakorum fault slip rate cosmic ray exposure age beryllium 10

new radiometric dating constrains the time for initiation of the karakorum fault zone kfz sw tibet abstract the karakorum fault zone kfz composed of strike slip faults has played an important role in intra continental deformation during the cenozoic convergence between the indian and eurasian plates however the spatial and temporal evolution of the kfz remains under debate this paper reports new zircon u pb sensitive high resolution ion microprobe shrimp and biotite 40ar 39ar ages for samples from the fault zone to clarify the timing of events the ages of zircon u pb fall mainly around 47 50 ma which corresponds to a period of important magmatic activity of the gangdese granitic belt also known as the trans himalayan magmatic belt a metamorphic event followed in the period around 32 ma and that was then followed by a medium temperature cooling event between about 12 and 7 7 ma biotite 40ar 39ar ages provide evidence that the 12 7 7 ma cooling event coincides with the initiation of the kfz cutting through the ayilari granite the ayilari granite pluton does not seem to have experienced the separate 25 23 ma cooling event as shown in previous studies 60 80 km west of the current study area lacassin r valli f arnaud n leloup p h paquette j l li h tapponnier p chevalier m l guillot s maheo g xu z 2004 large scale geometry offset and kinematic evolution of the karakorum fault tibet earth and planetary science letters 219 3 4 255 269 valli f arnaud n leloup h p sobel e r maheo g lacassin r guillot s li h tapponnier p xu z 2007 twenty million years of continuous deformation along the karakorum fault western tibet a thermochronological analysis tectonics 26 doi 10 1029 2005tc001913 valli f leloup p paquette j arnaud n li h tapponnier p lacassin r guillot s liu d deloule e xu z mahe o g 2008 new u th pb constraints on timing of shearing and long term slip rate on the karakorum fault tectonics 27 doi 10 1029 2007tc002184 we conclude that the 25 23 ma cooling event bears no relationship to the activity of the kfz but resulted from a local metamorphic event caused either by a regional tectonic event such as activity of the south kailas thrust fault or by magmatism around shiquanhe also known as gar the study of the kfz around namru supports the opinion that the kfz propagated along the fault strike to the gar menshi area around 12 ma

review and new aspects concerning the formation of eastern mediterranean sapropels abstract in this paper it is proposed that the formation of eastern mediterranean sapropels occurred in an anti estuarine type of circulation which was to some degree weakened relative to the present in response to reduction of the eastern mediterranean excess of evaporation over freshwater input this reduction of excess evaporation would have been imposed by intensifications of 1 the indian ocean summer sw monsoon influencing the eastern mediterranean via increased nile discharge and 2 the system of mediterranean depressions an element of the westerly atlantic system causing increased precipitation and decreased evaporation both the indian ocean summer monsoon and the westerly atlantic system would be intensified in response to the occurrence of distinct minima in the cycle of precession it is demonstrated that reduced excess evaporation whether or not coinciding with global phases of deglaciation would lead to reduction of surface water salinities in the eastern mediterranean causing isolation of previously formed high salinity cooler deep water thus mixing was severely reduced possibly even restricted to eddy diffusion with only occasional convective events that because of the existing density gradient hardly ever would reach the deepest parts of the basin the consequently diminished oxygen advection down from a few hundred meters in the water column favoured preservation of the sinking organic matter this would however suffice only to enable the formation of sapropels with low organic carbon contents the high organic carbon contents observed in various sapropels are argued to reflect superimposed increases of export production the described scenario accounts for previously reported 1 increases of organic carbon content with increasing depth of deposition within individual sapropels and 2 asymmetrical sequences of sapropel deposition characterized by gradual build up and rather abrupt ending it is furthermore in agreement with 3 isotopic and faunal reconstructions of the history of exchange transports through both the strait of sicily and the strait of gibraltar and 4 faunal and floral reflections of the presence or absence of a distinct deep chlorophyll maximum with its associated increases in export production indicating the presence or absence of a shallow pycnocline within the euphotic layer moreover the described scenario 5 is in no way conflicting with the reports of sapropels in the western mediterranean and 6 seems to be endorsed by occasionally intercalated intervals suggestive of somewhat improved oxygenation amidst anoxic benthic desert levels a situation that has been observed in a few quaternary and pliocene sapropels

sulphidic mediterranean surface waters during pliocene sapropel formation sapropels organic matter rich layers are common in neogene sediments of the eastern mediterranean sea the formation of these layers has been attributed to climate related increases in organic matter production1 2 3 and increased organic matter preservation due to oxygen depletion in more stagnant bottom waters2 3 here we report that eastern mediterranean pliocene sapropels4 contain molecular fossils of a compound isorenieratene known to be synthesized by photosynthetic green sulphur bacteria suggesting that sulphidic euxinic and therefore anoxic conditions prevailed in the photic zone of the water column these sapropels also have a high trace metal content which is probably due to the efficient scavenging of these metals by precipitating sulphides in a euxinic water column the abundance and sulphur isotope composition of pyrite are consistent with iron sulphide formation in the water column we conclude that basin wide water column euxinia occurred over substantial periods during pliocene sapropel formation in the eastern mediterranean sea and that the ultimate degradation of the increased organic matter production was strongly influential in generating and sustaining the euxinic conditions