magnitude of post middle jurassic bajocian displacement on the central altyn tagh fault system northwest china the altyn tagh fault system a key structural feature in the tectonic collage of central asia is an active left lateral strike slip fault system however its age of initiation kinematic history and total magnitude of displacement are not well known middle jurassic nonmarine sedimentary rocks that crop out along the central segment of the altyn tagh fault were deposited in a contiguous tarim qaidam foreland style basin that was geodynamically linked to mesozoic contraction in the tian shan bei shan qilian shan and kunlun shan this study documents the best evidence of a piercing point to date consisting of an offset lacustrine shoreline demarcated by aalenian bajocian open lacustrine strata to the west and fluvial and alluvial strata of comparable age to the east detrital compositions palynology paleocurrents and lithostratigraphy support correlation of these sections restoration of this jurassic facies boundary indicates 400 60 km of post bajocian left lateral separation on the altyn tagh fault consistent with this result restoration of the jurassic shoreline aligns felsic plutons across the western segment of the altyn tagh fault system that may have been left laterally offset by 360 km these two pairs of offset features suggest that the current best estimate for net magnitude of post bajocian left lateral separation on the altyn tagh fault is about 360 km

flexural subsidence by 29 ma on the ne edge of tibet from the magnetostratigraphy of linxia basin china abstract this study provides a detailed magnetostratigraphic record of subsidence in the linxia basin documenting a 27 myr long sedimentary record from the northeastern edge of the tibetan plateau deposition in the linxia basin began at 29 ma and continued nearly uninterruptedly until 1 7 ma increasing rates of subsidence between 29 and 6 ma in the linxia basin suggest deposition in the foredeep portion of a flexural basin and constrain the timing of shortening in the northeastern margin of the plateau to late oligocene late miocene time by late miocene early pliocene time a decrease in subsidence rates in the linxia basin associated with thrust faulting and a 10 clockwise rotation in the basin indicates that the deformation front of the tibetan plateau had propagated into the currently deforming region northeast of the plateau

significant late neogene east west extension in northern tibet field mapping in northern tibet reveals that the normal slip along late cenozoic northsouth trending faults is comparable to that estimated for equivalent structures in southern tibet the orientation of fault striations in two north south trending rifts suggests an eastnortheast west northwest direction of extension in northern tibet which in turn implies that northeast striking active faults in northern tibet have significant left slip components initiation of rifting in northern tibet postdates the early oligocene and possibly occurred after 4 ma the broad similarities in the magnitude of slip and the direction of extension for normal faults in both northern and southern tibet imply that the entire plateau has been extending this precludes significant eastward extrusion of north tibet relative to south tibet and requires a regional boundary condition as the cause of east west extension for the entire tibet plateau

present day deformation of the qaidam basin with implications for intra continental tectonics abstract the qaidam basin is a plateau of low relief about 3 km in elevation and covering a large area of 1 2 105 km2 physiographically the basin marks a transitional region between the northeastern tibetan plateau 5 0 5 km in elevation and the surrounding low lying areas the northeastern and southwestern edges of the basin are bounded by the qilian shan nan shan and qimantag eastern kunlun shan mountain belts respectively at present the entire region is under northeast southwest compression based on a synthesis of recent geological and geophysical results we propose that each flanking mountain belt consists of a sequence of crustal nappes originating from ramp thrusts at mid crustal levels 15 km deep over a distance range of 700 km these two broad fold and thrust belts operating in tandem and with some uniform shortening in the intervening qaidam basin successively raised the surface elevation from below 2 km to 5 km at depth the crust is correspondingly thickened from 40 km beneath the foreland of the qilian shan to approximately 55 km under the interior of the qaidam basin and then to nearly 70 km beneath tibet in contrast to the himalayan front where earthquake faulting occurs down to a depth of 50 km in the foreland but the zone of active thrust faulting is less than 200 km in width plateau building in the qaidam region illustrates how a wide orogen is developing along northeastern tibet in the interior of eurasia

cenozoic crustal shortening between the pamir and tien shan and a reconstruction of the pamir tien shan transition zone for the cretaceous and palaeogene the magnitude of the late cenozoic crustal shortening during convergence of the pamir and tien shan was determined using a contemporary pattern consisting of facies zones palaeomagnetic data regarding the rotation of tectonic units and data on the structure of the tadjik depression by late cenozoic cretaceous and palaeogene facies zones were cut by the vakhsh trans alay overthrust and darvaz strike slip faults and a significant part of the cretaceous palaeogene tadjik basin was overthrust by the pamir massif the sediments of easternmost part of the basin are preserved in the tarim depression the facies zones of the southern slope of the afghan tadjik basin were deformed and moved northward a pattern of facies zones indicates a convergence between the pamir and tien shan over a distance of 300 400 km a number of cross sections through the tadjik depression were used to establish the structure before folding a rotation of tectonic units indicated by structural data conforms to the angles of rotation as determined in palaeomagnetic studies the data suggest 300 km of convergence between the pamir and tien shan stratigraphic lithological structural and palaeomagnetic data formed the basis for the construction of the palinspastically restored palaeogeographic and sedimentologic environments for the tadjik shallow sea basin which was situated between the pamir and tien shan before their convergence in the late cenozoic the maps were constructed for the eight stratigraphic levels of the cretaceous and palaeogene the tadjik sea was a bay in the enormous turan sea in the early aptian this bay was located in what is now the afghan tadjik basin in late cretaceous the eastern shore of the bay lay 600 700 km further eastward and in the eocene marine environments extended even further eastward but after the rupelian continental environments occupied all of this region 2000 elsevier science b v all rights reserved

magnitude of late quaternary left lateral displacements along the north edge of tibet images taken by the earth observation satellite spot of the quaternary morphology at 18 sites on the 2000 kilometer long altyn tagh fault at the north edge of tibet demonstrate that it is outstandingly active long term left lateral strike slip offsets of stream channels alluvial terrace edges and glacial moraines along the fault cluster between 100 and 400 meters the high elevation of the sites mostly above 4000 meters in the periglacial zone suggests that most offsets resulted from slip on the fault since the beginning of the holocene these data imply that slip rates are 2 to 3 centimeters per year along much of the fault length and support the hypothesis that the continuing penetration of india into asia forces tibet rapidly toward the east

a first palaeomagnetic study of jurassic formations from the qaidam basin northeastern tibet china tectonic implications summary we present a new palaeomagnetic study on upper jurassic red beds collected at nine sites near huatugou 38 46 n 90 75 e in the qaidam basin thermal demagnetization up to 690 c shows both low and high temperature components ltc and htc respectively ltc seems to be a recent overprint htc carried principally by haematite and presenting a sole reverse polarity passes the fold test at the 95 per cent confidence level the palaeomagnetic pole calculated from the tilt corrected overall mean direction ds 220 4 i s 34 8 95 7 5 is situated at 50 1 n 198 0 e dp dm 5 0 8 6 the comparison of this result with coeval palaeomagnetic poles from tarim the north china block ncb and the apparent polar wander path of eurasia reveals a large scale tectonic evolution of the asian continent since the late jurassic this study suggests that the northward convergence of the qaidam block is statistically negligible with respect to tarim 4 5 8 2 since late jurassic times however a significant relative clockwise rotation of the studied area with respect to tarim seems to have occurred 16 2 11 2 whether this rotation is representative of the whole qaidam basin or is of a local character is yet to be confirmed the important feature of this study resides in the difference of northward displacement of the qaidam block with respect to eurasia on one hand and with respect to the ncb on the other hand the overall ns convergence absorbed between qaidam and eurasia is 19 3 9 2 whereas that absorbed between the qaidam and the ncb is 8 0 6 2 we suggest that the latter value is the result of the india asia collision while its difference with respect to the former would be absorbed during the mongol okhotsk ocean closure at the end of the jurassic or at the jurassic cretaceous boundary at the latest

miocene range growth along the altyn tagh fault insights from apatite fission track and u th he thermochronometry in the western danghenan shan china the left lateral strike slip altyn tagh fault that defines the northern margin of the tibetan plateau plays a crucial role in accommodating the cenozoic deformation related to the growth of plateau however the slip history along the fault remains highly debated here we report new 14 16 ma apatite fission track aft and 9 11 ma apatite u th he ahe data in the western danghenan shan north tibet age elevation relationships and aft ahe age differences suggest a period of rapid exhumation with an average rate of 0 1 0 3 km ma from 16 to 9 ma for this area thermal history modeling indicates that this was preceded by accelerated exhumation between the late oligocene and middle miocene 15 ma a northward increase in aft ages and asymmetric topography across the western danghenan shan indicate that the uplift and exhumation are mainly controlled by the thrust fault along the southern flank of the western danghenan shan as the thrust fault is a branch of the altyn tagh fault the rapid exhumation probably represents onset of the transition along the altyn tagh fault from left slip motion to crustal shortening in the dangnenan shan region our findings show that the middle miocene deformation is not only recorded in the middle and northern qilian shan but also in the southwestern portion of the qilian shan which favors a synchronous middle miocene deformation model for the entire qilian shan

formation of internally drained contractional basins by aridity limited bedrock incision 1 low internal relief aridity and internal drainage characterize the puna altiplano plateau and the tibetan plateau and the tarim basin structurally these areas are reverse fault bounded terrains with intervening wedge top basins that store thick accumulations of sediment for millions of years orographic barriers along the margins of these basins are oriented normal to moisture bearing winds resulting in regional aridity the combination of this aridity rapid shortening and uplift rates and resistant exposed lithologies coincides with the location of these internally drained basins we hypothesize that these large internally drained areas persist indefinitely when uplift overwhelms the fluvial systems and defeats the channel network to test this hypothesis we developed models of channel defeat to examine the threshold conditions required to fragment the channel network the results of these models suggest that low erodibility rocks moderate to high uplift rates and low precipitation favor defeat of orogen traversing channels most coupled tectonic landscape development models prevent the development of internal drainage and so may overestimate the voracity of erosion in regimes that favor internal drainage profoundly influencing predicted orogenic growth patterns

neogene evolution of the north eastern tibetan plateau based on sedimentary paleoclimatic and tectonic evidence abstract in this study the development of the north eastern tibetan plateau is investigated via an integrated study of the sedimentology magnetostratigraphy palaeogeography and cross section comparisons of the neogene sedimentary basins of the tibetan plateau from 23 to 17 ma this region was characterized by widespread angular unconformities and a sedimentary hiatus indicating the comprehensive uplift of the plateau the tectonic event that created the tibetan plateau triggered the evolution of sedimentary basins during the middle miocene climatic optimum event the growing qilian shan formed a barrier leading to cooler and drier conditions on the western side of the mountain however humid and warm conditions persisted on the eastern side of the range after this event this region was influenced by a global cooling trend and enhanced tectonic activity in the north eastern tibetan plateau at approximately 10 8 ma sedimentary data which were consistent with low temperature thermochronological records indicated the inversion of the surrounding mountains and rapid exhumation of the laji shan since 5 0 3 6 ma these intermontane basins gradually shrank and disappeared due to the overall uplift of the tibetan plateau and the accelerated global cooling trend and were associated with unconformities and growth strata that formed during stepwise north eastward thrusting tectonism

how to find high quality petroleum source rocks in saline lacustrine basins a case study from the cenozoic qaidam basin nw china abstract despite having made significant contributions to global hydrocarbon occurrences source rocks in saline lacustrine basins show great mineralogical and organic geochemical heterogeneity and the controlling mechanism is weakly studied here we use the cenozoic qaidam basin as an example to compare the organic and inorganic parameters of fine grained sediments in different lacustrine facies and to figure out the characterization and distribution of effective petroleum source rocks in saline lacustrine systems organic inorganic database of six selected boreholes show that in the bench margin high gradient lacustrine system fine grained sediments in sublittoral brackish mesosaline zones containing low chlorides

cenozoic structural inversion from transtension to transpression in yingxiong range western qaidam basin new insights into strike slip superimposition controlled by altyn tagh and eastern kunlun faults abstract a cenozoic structural inversion event from transtension to transpression involving salt tectonics has been uncovered in the yingxiong range the western qaidam basin seismic reflection data show that there are two common structural styles in the yingxiong range 1 the positive flower structure 2 the thrust controlled fold at shallow depth and the positive inverted flower structure at deep levels which are separated by a salt layer in the upper xiaganchaigou formation the yingxiong range experienced a first stage of transtension in the eocene induced by the altyn tagh fault and a second stage of transpression from the early miocene to present jointly controlled by the altyn tagh and eastern kunlun faults the eocene transtension produced numerous nw striking right stepping en echelon transtensional normal faults or fractures in the yingxiong range at the same time evaporites and mudstone were deposited in the vicinity of these faults in the early miocene the eocene transtensional normal faults were reactivated in a reverse sense and the thrust controlled folds at shallow depth started to form simultaneously with transpression enhanced in the late cenozoic positive flower structures directly formed in places without evaporites the cenozoic transtension to transpression inversion of the yingxiong range is the result of strike slip superimposition controlled by the altyn tagh and eastern kunlun faults in time and space

progressive evolution of a fault related fold pair from growth strata geometries sant llorenc de morunys se pyrenees abstract new structural stratigraphical mapping constrains the three dimensional kinematics and mechanisms of eocene oligocene growth folding at sant llorenc de morunys ne ebro basin spain a 1 km wide sub vertical panel of syntectonic alluvial gravels passes southwards via a highly asymmetrical growth fold pair to shallowlydipping strata the axial surface of the anticline comprises either continuous or en echelon segments while that of the syncline is concave and usually continuous while converging upwards the axial surfaces do not define growth triangles principal and subsidiary growth unconformities and thickness changes occur across both axial surfaces and the common limb dips within the common limb decrease up stratigraphy and up dip mesostructures indicate that internal deformation was ongoing during folding at all stratigraphical levels and concentration of cleavage in the syncline indicates that this hinge was essentially fixed sequential restoration of three profiles shows that folds amplified principally by limb rotation but incorporated minor passive hinge migration particle movement vectors generated by section restoration are arcuate about a hinterland pinpoint a new trishear model of fault propagation folding involving non rigid limb rotation reproduces the rounded hinge forms thickening geometries and limb dip variations observed simple kink band migration models fixed axis and constant thickness theories do not replicate these features

late plio pleistocene humidity fluctuations in the western qaidam basin ne tibetan plateau revealed by an integrated magnetic palynological record from lacustrine sediments abstract deciphering the climatic evolution of the tibetan plateau region during the plio pleistocene is hampered by the lack of continuous archives and proxy datasets indicative of moisture availability here we assess the suitability of magnetic susceptibility measured on lacustrine sediments as a paleohydrological proxy based on material from drill core sg 1 2 69 0 08 ma from the western qaidam basin our assessment is based on directly comparing with the artemisia chenopodiaceae a c pollen ratio which represents a sensitive well established proxy for moisture changes in arid environments we find that higher and lower values represent drier and less dry conditions respectively for the late plio pleistocene less dry phases were likely caused by transiently increased influence of the westerlies and or decreased influence of the asian winter monsoon on glacial interglacial time scales an exception from this relationship is the interval between 1 9 and 1 3 ma when the sg 1 record exhibits a 54 ka cyclicity which may indicate summer monsoon influence on the qaidam basin during that time after 1 3 ma the summer monsoon influence may have ceased due to global cooling with the consequence that the asian winter monsoon and the westerlies exerted a stronger control on the hydrology of the qaidam basin

evaporite minerals and geochemistry of the upper 400 m sediments in a core from the western qaidam basin tibet qaidam basin is a tectonically controlled depression on the northern margin of the tibetan plateau in 2008 a long core was drilled in the qahansilatu sub basin in the western qaidam basin the sediment layers in the upper 400 m alternate between evaporite mineral layers and carbonaceous clay layers the detailed mineralogical investigation focused on evaporite minerals including halite gypsum mirabilite thenardite glauberite eugsterite and bloedite gypsum and halite make up the majority of the evaporate minerals environmentally induced variations in the mineralogy and crystal habit of the sulfates have been extensively investigated gypsum has prismatic and pyramid habits such as disc pyramid stubby prismatic slender prismatic visible isolated gypsum and aggregates rosette radial and twins are mostly scattered in carbonaceous clay layers suggesting that secondary gypsum is well developed gypsum may be a precursor mineral of glauberite and thenardite is the precursor of bloedite as a metastable and rare mineral eugsterite does not appear in other tibetan areas it forms at the expense of pre existing gypsum or thenardite in the core at an experimental temperature of higher than room temperature the presence of eugsterite indicates a warm and or hot climate at its deposition time

aridification recorded by lithofacies and grain size in a continuous pliocene quaternary lacustrine sediment record in the western qaidam basin ne tibetan plateau abstract the pliocene quaternary aridification of the asian interior is key to understanding the impacts of global cooling and tibetan plateau uplift and the potential linkage to north pacific ocean biochemical processes and global changes however there is a lack of detailed continuous pliocene quaternary paleoclimatic records from the asian interior because most climatic records have been obtained from discontinuous coarse sediment outcrops around the rims of inland basins here we provide a continuous high resolution 3 1 myr record of grain size from the well dated sg 3 borehole in the western qaidam basin on the northeastern tibetan plateau nw china the results reveal a long term upward coarsening trend in grain size that can be divided into three phases i 3 1 1 1 ma laminated fine sediments fine to medium silts containing scattered gypsum crystals and interbedded by thin beds of marl ii 1 1 0 15 ma massive medium to coarse silts interbedded by beds of mirabilite iii 0 15 0 ma coarse silts containing thin layers of mirabilite halite bloedite and polyhalite this pattern reflects the upward shallowing and shrinking of the lake from a brackish lake to a salt lake and then to a playa suggesting a long term stepwise drying of the asian interior since the late pliocene probably forced by global cooling and uplift of the tibetan plateau

cenozoic deformation history of the qaidam basin nw china results from cross section restoration and implications for qinghai tibet plateau tectonics abstract the deformation and uplifting history of the qinghai tibet plateau is a controversial issue and so far there has been insufficient evidence for interpretation investigations of the cenozoic deformation in the northeastern edge of this plateau may provide some relevant information in this paper the cenozoic deformation history of the qaidam basin has been studied based on results from the balanced cross section restoration of six geological sections they indicate that 1 the qaidam basin has been undergoing continuous shortening since the beginning of cenozoic with two relatively fast shortening phases the first during 42 8 40 5 ma and the second during 2 8 ma present 2 the shortening rate of the qaidam basin reached its maximum value since 2 8 ma and approximately 32 of the average total cenozoic shortening took place in this period and 3 the shortening of all sections reached approximately 50 of their respective total shortening by miocene the cenozoic deformation history of the qaidam basin shows good synchroneity with uplifting history of the qinghai tibet plateau it is therefore proposed that the deformation and uplifting in the south and north edges of the qinghai tibet plateau was almost synchronous with the altyn tagh fault formed at the beginning of india asia collision accordingly it is postulated that since the india asia collision at the beginning of cenozoic the indian plate moved northward continuously with two relatively fast phases the first during 42 8 40 5 ma and the second during 2 8 ma present approximately 50 of the total cenozoic northward displacement of the indian plate of the total amount of crustal shortening and uplifting of the qinghai tibet plateau and of the total cenozoic strike slip displacement of the altyn tagh fault were probably reached by the early miocene moreover another 30 40 might have taken place during 2 8 ma present the periods during 42 8 40 5 ma and during 2 8 ma present may also be the two fast phases for crustal shortening and uplifting of the qinghai tibet plateau and strike slip displacement of the altyn tagh fault

northeastward growth of the tibet plateau deduced from balanced reconstruction of two depositional areas the qaidam and hexi corridor basins china we address the problem of late cenozoic uplift erosion and growth of northeastern tibet by reconstructing from isopach maps and drill holes the volumes and masses of sediments deposited in the qaidam and hexi corridor basins since 35 myr ago the mass budget is based on simple geometrical assumptions such as regional similarity of the thickness ratios between strata of different ages in the qaidam where our record extends back to the oligocene the budget shows a huge rise of the accumulation rates after the beginning of the pliocene 5 3 ma the early pliocene seems to be the period of maximum deposition with accumulation rates in excess of 1 mm yr 1 2 7 kg m 2 yr 1 of compacted rocks throughout the basin there also seems to be a southeastward shift of the largest depocenters between the upper pliocene 3 4 1 6 ma and the quaternary in the hexi corridor sedimentation is confined to small foreland flexural depressions associated with the frontal thrusts of the qilian shan and occurs at an average rate one order of magnitude smaller than in the qaidam basin the accumulation rate is maximum in the quaternary the sedimentation history appears to support a plateau building mechanism resulting from the combination of two geologicallly common processes crustal scale thrusting and sedimentary basin infilling the time needed to completely fill the qaidam basin and make its catchment a plateau closely resembling that of the highest part of tibet qangtang is of the order of 9 myr the mechanism now at work north of the kunlun which involves rapid infilling of broad flat areas separated by relatively narrow mountain ranges has thus probably been important in producing the high smooth topography that characterizes much of central tibet

cenozoic tectonic evolution of the qaidam basin and its surrounding regions part 3 structural geology sedimentation and regional tectonic reconstruction the qaidam basin is the largest topographic depression inside the tibetan plateau because of its central position understanding the tectonic origin of the qaidam basin has important implications for unraveling the formation mechanism and growth history of the tibetan plateau in order to achieve this goal we analyzed regional seismic reflection profiles across the basin and a series of thickness distribution patterns of cenozoic strata at different time slices the first order structure of the basin is a broad cenozoic synclinorium which has an amplitude ranging from 16 km in the west to 48 in the west to 15 s 1 to 1 3 10 17 s 1 the eastward decrease in upper crustal shortening requires a progressive shift in crustal thickening mechanisms across qaidam basin from dominantly upper crustal shortening in the west to dominantly lower crustal shortening in the east although sedimentation began synchronously at 65 50 ma across the entire basin the initiation ages of the southern and northern basin bounding structures are significantly different deformation started at 65 50 ma in the north and at 29 24 ma in the south this information and the existing inference that the uplift of the eastern kunlun range south of qaidam basin began after 30 20 ma imply that the paleogene 65 24 ma qaidam and hoh xil basins on both sides of the eastern kunlun range may have been parts of a single topographic depression 500 km wide in the north south direction between the qilian shan and fenghuo shan thrust belts in the north and south the development of this large paleogene basin in central tibet and its subsequent destruction and partitioning by the neogene uplift of the eastern kunlun range requires a highly irregular sequence of deformation possibly controlled by preexist ing weakness in the tibetan lithosphere

evidence for a change in the periodicity of tropical climate cycles at 2 4 myr from whole core magnetic susceptibility measurements the earth s orbit about the sun is influenced by gravitational interactions with the moon and other planets the resulting orbital perturbations give rise to cyclical variations in orbital eccentricity obliquity and precession with periods of 100 41 19 and 23 kyr respectively1 these variations are climatically important because they affect the seasonal and latitudinal distribution of solar radiation magnetic susceptibility measurements in deep sea sediment cores can be used as a sensitive indicator of temporal variations in the concentration of terrigenous material supplied to the sea bed here we use this approach to study the evolution of cycles of terrigenous sedimentation at ocean drilling program sites in the arabian sea and the eastern tropical atlantic we show from spectral analyses of the two susceptibility time series spanning the past 3 2 3 5 myr that the records are driven strongly by orbital forcing before 2 4 myr before present bp both records are strongly influenced by the 23 and 19 kyr periodicities but after 2 4 myr they are both significantly influenced by the 41 kyr periodicity this shift coincides with the beginning of major northern hemisphere glaciation which indicates for the indian ocean site that the supply of terrigenous sediment carried by monsoonal winds has responded to the rapid increase in ice cover at this time we cannot however exclude possible effects of changes in bottom water circulation on the susceptibility record of the atlantic site

magnetostratigraphy and sedimentologically derived geochronology of the quaternary lacustrine deposits of a 3000 m thick sequence in the central qaidam basin western china the qaidam basin is a large basin in western china where the thickness of quaternary deposits has a range of 2000 3000 m at its subsiding depocentre this study investigated the chronology of the quaternary deposits including palaeomagnetics biostratigraphic correlation rates of sediment accumulation seismic reflection surveys and electrical property correlations the results give a full interpretation of ages for the sequence from bottom to top the oldest sequence age was defined by the first appearance of microlimnocythere sinensis huang and was placed in the gauss epoch estimated at approximately 3 ma by extrapolation of accumulation rates the m g boundary occurs at the base of the third fossil zone of ostracoda the first appearance of qinghaicypris crassa huang or at the marker layer k 10 of the electrical log in the sebei anticline area considered here to be 2 48 ma the olduvai event in the fifth fossil zone spanning electrical layers k 4 and k 3 in the sebei area occurs at reflection layer t 0 1 of seismic stratigraphy which could be stratigraphically correlated in the whole basin the boundary of early middle pleistocene such as the brunhes and matsuyama b m boundary falls within the eighth fossil zone and coincides with electrical marker k 0 1 two boundaries corresponding to middle late pleistocene and pleistocene holocene occur at the bases of the 11th and 12th biozones respectively neither of which can be correlated with seismic stratigraphy and electrical logs in the basin due to the lack of widely distributed lacustrine deposits since the middle pleistocene the ages of the boundaries can be tested by deposition rates of different facies derived from the varves and synchronous deposits as a result geochronological sequences of subsurface stratigraphy could be established within a basin wide area on the synchronology of seismic reflectors and correlations of electrical logs as well as biozones c 1998 elsevier science b v all rights reserved

stratigraphic and paleomagnetic evidence of mid pleistocene rapid deformation and uplift of the ne tibetan plateau abstract the ne tibetan plateau has become an important region for deciphering the cenozoic uplift of the plateau previous studies have verified that the quaternary uplift in this region had a multi stage character however geologists have not established which event constituted the main tectonic phase fortunately stratigraphic and paleomagnetic evidence from the jiuquan basin gansu province china now confirm that the laojunmiao movement represented as an angular unconformity occurred between 0 9 and 0 8 ma and an almost synchronous tectonic event has been well recorded within and around the plateau moreover many proxies indicate that the global climate changed more rapidly after 0 9 ma these proxies include eolian loess and vermiculated red soils caused by the asian monsoon the eolian sedimentation rate the stilostomella extinction changes in the global thermohaline circulation and the increased 13 c values recorded in the marine sediments based on the uplift driven climate change the mid pleistocene transition mpt could be the result of the laojunmiao movement certainly the laojunmiao movement and mpt had the significant impact on the quaternary earth we conclude that the laojunmiao movement was likely the main tectonic phase of the quaternary plateau uplift

a late neogene framework and transpressional system within the yingxiongling range western qaidam basin northeast tibetan plateau insights from seismic reflection profiles and active tectonics abstract the yingxiongling range is a topographically unique and active tectonic belt in the western qaidam basin that has recorded the structural evolution and interactions between itself and surrounding ranges throughout the late cenozoic although a large scale fault fold system within this region accommodates transpressive deformation the overall kinematic pattern remains highly debated regional seismic reflection profiles earthquake distributions focal mechanisms and displacement vector results are used in this study to rebuild a northern verging thrust and wedge tectonic system in a perpendicular direction interpretations of newly acquired three dimensional seismic data the timing of growth strata and the kinematics of active structures strongly support lateral structural deformation propagation and evolution of the southern yingxiongling range in the late neogene a novel analysis of active tectonic and seismic profiles enables us to rebuild the framework kinematics and evolutionary pattern of the yingxiongling range we also provide a new interpretation of lateral differentia along the yingxiongling range based on critical taper theory and suggest that this overall structure is an integrated part of the qimen tagh wedge since the late neogene rapid uplift in this area occurred in response to northward propagation of the qimen tagh wedge

jurassic to cenozoic exhumation history of the altyn tagh range northwest china constrained by 40ar 39ar and apatite fission track thermochronology

high resolution magnetostratigraphy of the neogene huaitoutala section in the eastern qaidam basin on the ne tibetan plateau qinghai province china and its implication on tectonic uplift of the ne tibetan plateau abstract the closed inland qaidam basin in the ne tibetan plateau contains possibly the world s thickest 12 000 m continuous sequence of cenozoic fluviolacustrine sedimentary rocks this sequence contains considerable information on the history of tibetan uplift and associated climatic change however work within qaidam basin has been held back by a paucity of precise time constraints on this sequence here we report on a detailed paleomagnetic study of the well exposed 4570 m huaitoutala section along the keluke anticline in the northeastern qaidam basin where three distinct faunas were recovered and identified from the middle miocene through pliocene constrained by these faunal ages the observed thirty three pairs of normal and reversed polarity zones can be readily correlated with chrons 2n 5br of the gpts this study assigns the age of the section to the interval between ca 15 7 ma to 1 8 ma in addition the widely used stratigraphic units the xia youshashan shang youshashan the shizigou and qigequan formations were formed at 15 3 ma 15 3 8 1 ma 8 1 2 5 ma and

tectonic history of the altyn tagh fault system in northern tibet inferred from cenozoic sedimentation the active left slip altyn tagh fault defines the northern edge of the tibetan plateau to determine its deformation history we conducted integrated research on cenozoic stratigraphic sections in the southern part of the tarim basin fission track ages of detrital apatites existing biostratigraphic data and magnetostratigraphic analysis were used to establish chronostratigraphy whereas composition of sandstone and coarse clastic sedimentary rocks was used to determine the unroofing history of the source region much of the detrital grains in our measured sections can be correlated with uplifted sides of major thrusts or transpressional faults implying a temporal link between sedimentation and deformation the results of our studies together with existing stratigraphic data from the qaidam basin and the hexi corridor suggest that crustal thickening in northern tibet began prior to 46 ma for the western kunlun shan thrust belt at ca 49 ma for the qimen tagh and north qaidam thrust systems bounding the north and south margins of the qaidam basin and prior to ca 33 ma for the nan shan thrust belt these ages suggest that deformation front reached northern tibet only 10 5 m y after the initial collision of india with asia at 65 55 ma because the aforementioned thrust systems are either termination structures or branching faults of the altyn tagh left slip system the altyn tagh fault must have been active since ca 49 ma the altyn tagh range between the tarim basin and the altyn tagh fault has been a long lived topographic high since at least the early oligocene or possibly late eocene this range has shed sediments into both the tarim and qaidam basins while being offset by the altyn tagh fault its continuous motion has made the range act as a sliding door which eventually closed the outlets of westward flowing drainages in the qaidam basin this process has caused large amounts of oligocene miocene sediments to be trapped in the qaidam basin the estimated total slip of 470 70 km and the initiation age of 49 ma yield an average slip rate along the altyn tagh fault of 9 2 mm yr remarkably similar to the rates determined by gps global positioning system surveys this result implies that geologic deformation rates are steady state over millions of years during continental collision

timing and magnitude of displacement on the altyn tagh fault constraints from stratigraphic correlation of adjoining tarim and qaidam basins nw china the altyn tagh fault plays an important role in growth of the north western tibetan plateau but the timing of its inception and magnitude of left lateral displacement are not well constrained this study provides new independent constraints by correlating stratigraphic development and spatial distribution of the neighbouring tarim and qaidam basins it is shown that the tarim and qaidam basins experienced quite similar stratigraphic and sedimentary evolution from late sinian to early palaeogene times this fact indicates that the tarim and qaidam basins were a single block at least until oligocene time which was then offset by the altyn tagh fault early palaeozoic and late triassic suture zones within the east and west kunlun and pinch outs of mesozoic strata are chosen as piercing lines restoration of these lines gives total offset estimates of 350 400 km across the south western and central segments of the altyn tagh fault

new early and late carboniferous paleomagnetic results from the qaidam block nw china implications for the paleogeography of central asia abstract there is an ongoing debate regarding the paleogeographic evolution of the qaidam block 37 3 n 96 4 e in northwest china during the late paleozoic to provide a reliable constraint on the paleogeographic reconstruction and to determine the relationship with the adjacent area we performed a paleomagnetic investigation of early and late carboniferous sediments from the qaidam block stepwise thermal demagnetization successfully isolated high unblocking temperature characteristic directions from the samples the tilt corrected mean direction of the early carboniferous sediments is ds is 298 6 46 4 with 95 4 7 and n 15 sites corresponding to a paleopole at 3 2 n 147 5 e with a95 4 8 the late carboniferous paleomagnetic direction is ds is 320 1 46 1 with 95 5 3 and n 8 sites corresponding to a paleopole at 15 1 n 132 2 e with a95 5 4 a positive fold test for the early carboniferous paleomagnetic directions and consistency with the kiaman reversed superchron for the late carboniferous paleomagnetic directions indicates the primary origin of the characteristic remanence of the studied section the new paleomagnetic results suggest that the qaidam block was located at about 27 n and did not undergo significant n s movement during the carboniferous however the qaidam block experienced a counter clockwise rotation of about 21 during this period comparisons of the paleomagnetic results from the major blocks of central asia suggest that the qaidam block may have experienced a relatively rapid northward movement and collided with the tarim block after the late permian based on the paleomagnetic poles of the qaidam block and adjacent blocks we present a tentative paleogeographic reconstruction for central asia during the early and late carboniferous

late cenozoic deformation and uplift of the ne tibetan plateau evidence from high resolution magnetostratigraphy of the guide basin qinghai province china the cenozoic intramontane gonghe guide basin in qinghai province china is tectonically controlled by the sinistral strike slip framework of the kunlun and altyn tagh south qilian faults in the northeastern tibetan plateau the basin is filled with thick cenozoic clastic sedimentary formations which provide important evidence of the deformation of this part of the plateau although they have long lacked good age constraints detailed magnetostratigraphic and paleontologic investigations of five sections in the guide basin and their lithologic and sedimentary characteristics allow us to divide a formerly undifferentiated unit the guide group into six formations where ages are now magnetostratigraphically well established they are given in parentheses the amigang 1 8 2 6 ma ganjia 2 6 3 6 ma and herjia formations 3 6 to ca 7 0 7 8 ma and the older miocene ashigong garang and guidemen formations these rocks document a generally upward coarsening sequence characterized by increasing accumulation rates increasing gravel content and sizes of its components changes of bedding dips and source rock types and marginal growth faults collectively reflect accelerated deformation and uplift of the ne tibetan plateau after 8 ma punctuated by a sharp increase in sedimentation rate at ca 3 2 ma that reflects the boulder conglomerates of the ganjia formation interestingly much of the vergence of the compressional deformation in the basin is to the south accommodated by a sequence of six thrusts f1 f6 which become active one by one progressively later toward the south undoubtedly contributing to the uplift of this part of the plateau f1 likely initiated the guide basin due to crustal flexure in the oligocene f2 was active in the early miocene f4 and f5 at ca 3 6 ma and f6 was active in the early pleistocene the detailed late miocene and younger magnetostratigraphy allows us to place much improved time constraints on the deformation and hence uplift of northeastern tibet which when compared with ages for events on other parts of the plateau provides important boundary conditions for the geodynamical evolution of tibet

magnetostratigraphy of deep drilling core sg 1 in the western qaidam basin ne tibetan plateau and its tectonic implications abstract the qaidam basin is the largest intermontane basin of the northeastern tibetan plateau and contains a continuous cenozoic sequence of lacustrine sediments a 1000 m deep drilling sg 1 with an average core recovery of 95 was carried out in the depocenter of the chahansilatu playa sub depression in the western qaidam basin aimed to obtain a high resolution record of the paleoenvironmental evolution and the erosion history stepwise alternating field and thermal demagnetization together with rock magnetic results revealed a stable remanent magnetization for most samples carried by magnetite the polarity sequence consisted of 16 normal and 15 reverse zones which can be correlated with chrons 1n to 2an of the global geomagnetic polarity time scale magnetostratigraphic results date the entire core sg 1 at 2 77 ma to 0 1 ma and yielded sediment accumulation rate sar ranging from 26 1 cm ka to 51 5 cm ka maximum sars occurred within the intervals of 2 6 2 2 ma and after 0 8 ma indicating two episodes of erosion which we relate to pulse tectonic uplift of the ne tibetan plateau with subsequent global cooling

new paleomagnetic constraints on central asian kinematics displacement along the altyn tagh fault and rotation of the qaidam basin received 23 july 2001 revised 9 january 2002 accepted 26 february 2002 published 5 october 2002 1 in order to better understand the tectonic evolution of central asia under the influence of the india asia collision we carried out a paleomagnetic study of 1500 cores from 106 sites along the altyn tagh fault in the qaidam and tarim basins and on the tibetan plateau samples were mainly collected from jurassic to neogene siltstones and sandstones in most cases stepwise thermal demagnetization unblocks low and high temperature components carried by magnetite and hematite low temperature components are north and down directed and lie close to the recent geomagnetic field high temperature components from 10 of 13 age locality groups pass fold and or reversal tests and likely represent primary remanent magnetizations the ten overall mean directions display a complex pattern of vertical axis block rotations that are compatible with a tectonic model of clockwise rotation of the qaidam basin and concomitant left lateral slip on the altyn tagh fault two of the ten localities are rotated significantly counterclockwise they lie adjacent to the altyn tagh fault zone consistent with the idea that left lateral strike slip motion occurred along it the age of counterclockwise rotation near the eastern extremity of the fault was dated as younger than 19 ma three widely spread areas within the qaidam basin exhibit similar and significant clockwise rotations on the order of 20 with respect to the north china block tarim and eurasia the mean of the three values is thought to represent the total rotation of qaidam because the youngest rocks displaying clockwise rotations are oligocene the main phase of qaidam basin rotation and hence shear on the altyn tagh fault took place after or near the end of the oligocene 24 ma upper neogene strata located on the qaidam basin are not significantly rotated thus tectonic deformation acting since the upper neogene 5 ma is not resolvable by paleomagnetic methods given a 20 5 clockwise rotation of the qaidam basin with respect to the tarim basin the maximum left lateral displacement on the altyn tagh fault since 24 ma is 500 130 km index terms 1525 geomagnetism and paleomagnetism paleomagnetism applied to tectonics regional global 1527 geomagnetism and paleomagnetism paleomagnetism applied to geologic processes 8105 tectonophysics continental margins and sedimentary basins

new early cretaceous paleomagnetic data from volcanic and red beds of the eastern qaidam block and its implications for tectonics of central asia abstract in order to better understand anomalously low paleomagnetic inclinations in the cretaceous rocks of central asia a combined geochronologic and paleomagnetic investigation has been performed on cretaceous basalt sequences intercalated with red beds from zeku area in the eastern qaidam block northeastern tibetan plateau potassium argon k ar dating indicates that the basalt sequences are of early cretaceous age 89 9 2 8 to 112 1 2 4 ma isothermal remanent magnetization irm thermal demagnetization of a three component irm and curie point experiment suggest that magnetite and hematite dominate in red beds magnetite in basalt flows stepwise thermal demagnetization successfully isolated stable characteristic remanent magnetization chrm from 7 lava flows and 12 red beds sites the chrms of red bed and basalt sites pass fold test and likely represent primary remanent magnetization the tilt corrected mean direction from red bed sites basalts plus baked red bed site is d s 18 4 i s 55 3 s 69 1 95 5 5 n 11 sites d s 16 1 i s 52 0 s 42 6 95 8 6 n 8 corresponding to a pole at 75 2 n 182 3 e with a 95 7 07 76 9 n 194 9 e with a 95 10 0 respectively the consistent inclination recorded in red beds and basalts implies no significant inclination shallowing caused by deposition compaction in red beds from the studied area compared with the early cretaceous poles from the north china block ncb or eurasia insignificant post early cretaceous northward motion may have occurred between the qaidam block and the ncb on the basis of the existing regional paleomagnetic data the qaidam block has not experienced wholescale vertical axis rotation since the early cretaceous with respect to ncb

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

the topographic controls on the decadal scale erosion rates in qilian shan mountains n w china abstract the relationships between climate topography and erosion are significant in understanding landscape evolution in order to study this relationship in a tectonically active landscape the details of 11 drainage basins were collected from qilian shan mountains decadal scale erosion rates including the mechanical load and solute load contributions are estimated in natural conditions the calculated erosion rates show that the average erosion rate of qilian shan mountains is about 0 08 mm yr while the variation of annual erosion rates within each basin is significant the changes of topography and climate which potentially control erosion rates are also employed in this paper for correlating analyses correlation analyses indicate that erosion rates are more closely correlated with topographic variables such as mean local relief and mean slope than all of the climatic variables and mean local relief and decadal scale erosion rates show a linear relationship in these tectonically active mountains however some topographic variables like basin area and elongation ratio exert limited influence on erosion rates while others such as basin elevation basin relief and basin roughness show poor correlation the results indicate that topographic control like aspects of the local terrain steepness plays the most important role in spatial distribution of decadal scale erosion rates throughout qilian shan mountains under topographic control some climatic variables like discharge and runoff however could account for the significant variation of annual erosion rates in individual basin when comparing erosion rates on different timescales we found that the decadal scale erosion rates are lower than the long term river incision rates as well as the exhumation rates during early and middle miocene the change to more arid climatic condition since the middle miocene combining with tectonic uplift should attribute to the inconsistent erosion rates over different timescales in qilian shan mountains

paleocene eocene syncontractional sedimentation in narrow lacustrine dominated basins of east central tibet sedimentologic stratigraphic compositional and structural data from four elongate basins 30 km long in the nangqian yushu region of east central tibet near the headwaters of the mekong and yangtze rivers indicate nonmarine sedimentation synchronous with paleocene eocene northeast southwest shortening sedimentation in the nangqian niuguoda xialaxiu and shanglaxiu basins involved 1 mud and carbonate accumulation in offshore to nearshore lacustrine environments and 2 gravel and sand deposition in fan delta to alluvial fan environments localized near basin margins growth strata in both fine and coarse grained deposits primarily in upper levels of basin fill provide evidence for sedimentation contemporaneous with motion on fold thrust structures provenance data collected from 25 measured stratigraphic sections including 1500 paleocurrent measurements and 150 conglomerate compositional analyses show that each basin was fed sediment from several directions by proximal source areas composed of carboniferous triassic rocks the source area proximity and a stratigraphic variability among the basins suggest that each basin evolved independently and was filled by sediment derived from relatively small drainage networks 103 km2 age control for basin fill is based on paleogene fossils 38 37 ma 40ar 39ar ages from volcanic rocks interbedded with uppermost strata of the nangqian basin and 51 49 ma 40ar 39ar ages from igneous rocks that intrude and unconformably overlie strata of the shanglaxiu basin strata containing middle cretaceous palynomorph and ostracod assemblages are present only locally in the lowermost part of the nangqian basin although the tectonic setting for cretaceous sedimentation is unclear early tertiary basin development was controlled by thin skinned fold thrust deformation we interpret the narrow widths of paleocene eocene basins to be a result of thrust spacing which in turn may have been controlled by the depth to the decollement 5 km deep according to our balanced cross section from which imbricate thrusts ramped up through the carboniferous triassic section sedimentologic and provenance evidence for internal drainage limited unroofing and relatively low average sediment accumulation rates in these syncontractional plateau interior basins indicates generally small drainage systems short main stem rivers shallow regional slopes and limited denudation in east central tibet during early tertiary time such geomorphic conditions which are similar to the modern low relief interior of the tibetan plateau suggest that the deeply incised mekong and yangtze rivers of eastern tibet were not established until after the termination of paleogene basin development in the region

paleocene early eocene uplift of the altyn tagh mountain evidence from detrital zircon fission track analysis and seismic sections in the northwestern qaidam basin

preliminary magnetostratigraphy of dabusan lake qaidam basin central asia abstract sediment samples from a 528 m deep borehole located about 60 km north of golmud on the northern side of dabusan lake have been used to determine the change in magnetic inclination with depth normal polarity brunhes inclination values are present throughout the section but there are six departures from this value five with negative inclinations and one shallow inclination an attempt has been made to date the core using the magnetic inclination departures together with a limited number of 14c dates

eastward migration of the qaidam basin and its implications for cenozoic evolution of the altyn tagh fault and associated river systems the qaidam basin is the largest cenozoic intermontane basin within the tibetan plateau bounded by the qilian shan range to the north the east kunlun range to the south the altyn tagh range to the west and the ela shan range to the east its deposits consist of nonmarine sedimentary rocks with a maximum thickness exceeding 13 400 m modern sedimentation mainly takes place along the marginal areas of the basin where alluvial fans are formed along a series of rivers that originate from the surrounding mountains nevertheless drilling sedimentary and seismic data reveal that the depocenter of the basin during much of cenozoic time was not developed as foreland basins of the qilian shan belt to the north and the east kunlun belt to the south but instead the depocenter was in the center of the western part of the basin and had a northwest southeast trend that shifted eastward 380 km during oligocene to quaternary time this indicates that most of the basin sediments were not derived from the surrounding mountain ranges the results of the fi ssion track age dating reveal that the rapid uplift of the yousha shan anticline bounding the depocenter to the southwest initiated at ca 31 ma indicating that the southeastward shift of the depocenter began at that time yielding a migration rate for the depocenter of 10 2 mm yr the northwestern margin of the depocenter of the qaidam basin lies to the east of the westward prolongation of the qaidam basin the tula trough a 300 km long narrow trough fl anked by the altyn tagh range along the altyn tagh strikeslip fault on the north and the east kunlun thrust belt on the south the sedimentary and deformational evidence from this region indicates that the tula trough was formed as a syncline along which a paleoriver fl owed to the east into the qaidam basin to the southwest this river valley merges with the trace of the altyn tagh fault the latter and its westward continuation are interpreted to have extended to the northern margin of the pamir folded belt north of the western syntaxis of the himalaya we propose that most of the sediments within the depocenter of the qaidam basin were transported from the northern margin of the pamir folded belt along a progressively lengthening 2000 kmlong longitudinal river that developed along the left lateral altyn tagh fault and its western continuation as the eastward extrusion of the tibetan plateau took place in oligocene time both the crustal uplift and continuous southeastward aggradations of the sediments carried by the paleo kunlun river are interpreted to be the cause for southeastward migration of the depocenter of the qaidam basin the longitudinal river disappeared in late cenozoic time 2 4 ma due to stream capture and climate change

impact of wind erosion on detecting active tectonics from geomorphic indexes in extremely arid areas a case study from the hero range qaidam basin nw china abstract geomorphologic analysis has been used widely to detect active tectonics in regions where fluvial incision is the major erosional process in this paper however we assess the feasibility of utilizing these frequently used geomorphic indexes e g hypsometric curves longitudinal channel profiles normalized stream length gradient slk index to determine active tectonics in extremely arid areas where wind erosion also plays an important role the case study is developed on the hero range in the western qaidam basin one of the driest regions on earth with severe wind erosion since late pliocene the result shows that in the west and south sectors as well as the western part of the east sector of the hero range where fluvial incision prevails these geomorphic indexes are good indicators of active faulting and consistent with the geological result based on study of fault traces scarps faulted holocene fans and historical seismicity within the past four decades in contrast along the northeastern margin the ne and the se parts of the east sector of the range where wind erosion is also important the results from the geomorphic indexes show quite active tectonics contrary with the geological evidence favoring weakly active tectonics moreover the positive slk anomaly lies oblique to the fault trace and the anticline axis but parallel to the wind direction to reconcile the contradiction we propose that wind erosion caused by northwestern winds has a tendency to make geomorphic indexes exhibit anomalous values that indicate higher activities by way of 1 lowering the base level to generate knickpoints on the longitudinal channel profiles and therefore positive slk anomalies and 2 lateral erosion of the mountain front making the hypsometric curves and even the longitudinal channel profiles more convex and producing obvious slope breaks

paleomagnetic rotation constraints on the deformation of the northern qaidam marginal thrust belt and implications for strike slip faulting along the altyn tagh fault discordant cenozoic paleomagnetic rotation results obtained throughout the northeastern tibetan plateau have yielded different tectonic models for the evolution of the altyn tagh fault and the northeastern tibetan plateau here based on detailed existing magnetostratigraphic age constraints we carried out an in depth paleomagnetic study along the hongliugou section in the middle northern qaidam marginal thrust belt to address the cenozoic rotations of this region a total of 1 342 jurassic neogene siltstone sandstone core samples were collected from 128 sites across 18 time intervals rock magnetic analysis suggested that magnetite and hematite are the dominant magnetic carriers detailed thermal demagnetization analyses were performed and the characteristic remanent magnetizations of 90 sites 743 samples were obtained which yielded positive fold and reversals tests indicating that they likely represent primary magnetizations detailed paleomagnetic declination versus age analyses revealed three periods of rotations 12 515 7 degrees statistically insignificant counterclockwise rotations during 45 33ma successive clockwise rotations of 32 215 4 degrees during 33 14ma and subsequent statistically insignificant counterclockwise rotations of 8 79 4 degrees after 14ma these three periods of rotations are similar to those calculated based on previously available magnetostratigraphic data from the nearby dahonggou section based on the integration of these data with other lines of geological evidence we attributed the latter two periods of rotations to fast strike slip faulting along the altyn tagh fault

a jackknife for magnetostratigraphy we investigate the problem of evaluating the reliability of a magnetostratigraphic section using a jackknife resampling scheme we define a parameter j as the slope relating the percentage of polarity zones of a sampled section remaining after random deletion of sites increasing in proportion to a total of 20 of the initial collection so defined j quantifies the dependence of a magnetostratigraphic record on the distribution of sampling sites based on simulated magnetostratigraphic sections j was found to be an indicator of the approximate percentage of polarity zones present in the original reference sections that were recovered in the sampled section j will perhaps be most helpful as a guide to investigators as to whether further sampling would provide useful information as well as to the non paleomagnetist user of black and white interpretive polarity logs as an estimate of the reliability of a given section

cenozoic qaidam basin china a stronger tectonic inversed extensional rifted basin qaidam basin is a composite sedimentary basin developed on typical continental crust it comprises a jurassic foreland basin and a cenozoic extensional basin the geologic history of the cenozoic qaidam basin can be divided into two megastages on the basis of stratigraphy and structure the first megastage from latest cretaceous to oligocene consisted of two periods of rifting due to upwelling of the hot upper mantle this is demonstrated by two tectono sequences formed by the rifting the synrifting magmatic thermal activity and the control of protobasin development by syndepositional faults the second megastage comprises three tectono sequences that developed in the miocene and pliocene and was a period of structural inversion that consisted of compressive downwarping and reverse faulting this tectonic inversion may be ascribed to the long distance propagation of compressive stress caused by the collisions of the indian and eurasian plates the thick sequence of primary oil source rocks was deposited in the major rifted depression and the restricted drainage graben of the rifted protobasin during the tectonic inversion megastage they were subject to deep burial and prolonged heating a major and a minor oil generating basin have developed the tectonic inversion processes produced several structural features that may contain potential hydrocarbon reservoirs and traps

a new terrestrial analogue site for mars research the qaidam basin tibetan plateau nw china abstract remote sensing observations and rover missions have documented the presence of playas salts and wind erosion landforms of lacustrine sediments on mars all of these observations suggest mars was aqueous in its early history however abundant questions remain how wet was the environment what were the properties of the liquids and the possibility of ancient habitability and what kinds of geological processes shaped the present landforms to explore these unknowns analogue studies can play a key role in this contribution we introduce the qaidam basin tibetan plateau northwestern china as a new and unique analogue site for studying the past aqueous and present arid environments of mars the qaidam basin the highest and one of the largest and driest deserts on earth is located in a dry cold and high uv environment similar to the surface of mars we demonstrate a variety of landforms and also their counterparts on mars which include aeolian dunes and yardangs polygons gullies valleys and fluvial fans in the qaidam basin various environmental regimes for the formation of linear and asymmetric barchans have been described saline lakes and playas representing different stages of lake evolution in arid environment are also present in the qaidam basin and provide promising cases for studying the habitability in mars like environments results for microorganism isolation suggest that halophiles are the most important fraction in the hypersaline sediments and this may shed light on studying present martian habitability moreover the remote but ready accessibility of the qaidam basin make it a potential site for engineering testing in regards to future martin exploration missions we propose that the variety of exogenic and endogenic geomorphic types lacustrine sediments evaporite mineral assemblages and mars like extreme environments collectively point to the qaidam basin as an optimal

paleomagnetism indicates no neogene rotation of the qaidam basin in northern tibet during indo asian collision paleomagnetic data were obtained from tertiary red sedimentary rocks at two locations separated by several hundred kilometers within the qaidam basin in the east central part of the basin 30 sites from the lower pliocene youshashan formation yielded characteristic remanent magnetization chrm directions with intermediate unblocking temperatures 100 600 8c chrm with high unblocking temperatures to 680 8c was isolated from 14 sites in the same area chrm directions were obtained from six sites within the oligocene lower gancaigou formation characteristic magnetization was also determined from 16 sites within the lower gancaigou formation exposed in the e bo liang range of the north central qaidam basin when compared with equivalentage expected directions for eurasia the mean paleomagnetic directions indicate no neogene vertical axis rotation of the qaidam basin or the altyn tagh fault the qaidam basin may act as an indentor translating without rotation toward the north china block and driving clockwise vertical axis rotations by differential shortening within the nan shan fold and thrust belt

early cenozoic faulting of the northern tibetan plateau margin from apatite u th he ages models to explain the distributed nature of continental deformation predict the propagation of strain and high topography away from the plate boundary yet a growing body of evidence in the tibetan orogen suggests that deformation occurred at the far northern extent of the modern plateau early in the orogen s history and thus our current mechanical understanding of orogenic plateau development is incomplete new apatite u th he ages from four elevation transects document periods of rapid exhumation related to erosion pulses in hanging wall rocks of major thrust structures accelerated erosion is used as a proxy of fault timing and is interpreted in a larger context of structural data and sediment accumulation in adjacent foreland basins helium results are synthesized with published geologic thermochronometric and sedimentologic data from which a growing picture of regional compressional deformation in middle to late eocene time in northern tibet emerges we relate the early cenozoic period of deformation to the initiation of collision between india and eurasia despite the fact that the plate boundary was located 3000 km to the south regardless of whether or not high topography was built simultaneously as a result of this deformation early cenozoic strain signifies that the modern limit of the orogen has been relatively stationary since continental collision began and that deformation has not significantly propagated farther away from the plate boundary in time

vertebrate paleontology biostratigraphy geochronology and paleoenvironment of qaidam basin in northern tibetan plateau abstract qaidam basin is the largest terrestrial basin of the tibetan plateau and has the most continuous sedimentary record in the cenozoic although constituting the first known fossil vertebrates of the tibetan plateau and discovered in early scientific expeditions in the 1930s mammalian fossils from qaidam basin have not played a significant role in studying the basin stratigraphy our explorations in the qaidam basin during the past 8 years have resulted in the first well documented collection of fossil vertebrates from there in addition to being the best organisms for terrestrial biostratigraphy in the cenozoic the new fossil vertebrates offer a unique window into the ancient biotas that chronicle the late cenozoic uplift of the plateau and associated environmental changes here we establish for the first time a faunal sequence of early oligocene to early pliocene age four mammalian faunas are recognized olongbuluk mammal fauna middle miocene tuosu mammal fauna early late miocene shengou mammal fauna early late miocene and huaitoutala mammal fauna early pliocene all four mammal faunas can be directly or indirectly tied to a paleomagnetic section in the olongbuluk huaitoutala area permitting robust calibration of the chronology of these faunas at least four fish faunas are also found lulehe fish fauna late early to early late oligocene shengou fish fauna early late miocene eboliang fish fauna late late miocene to early pliocene and yahu fish fauna early pliocene the fish faunas represent the only records of their respective times in the tibetan plateau and thus by themselves cannot be used for age determination however these fish faunas are either integrated into paleomagnetic sections or directly tied to mammal faunas of known ages permitting independent assessment of their chronology zoogeographically qaidam mammal faunas show increasing endemism through time presumably related to topographic barriers formed by the growth and uplift of the tibetan plateau and to climatic changes triggered by the same tectonic process fishes that were trapped in internally drained basins developed pachyostotic morphologies caused by hypersaline environments which are associated with the increasing aridity of the tibetan plateau since early pliocene

high resolution magnetostratigraphic study of the paleogene neogene strata in the northern qaidam basin implications for the growth of the northeastern tibetan plateau abstract the cenozoic terrestrial intermontane qaidam basin on the northeastern edge of the tibetan plateau contains 12 km of sedimentary rocks that potentially document the accommodation of india asia convergence and the growth of the plateau the chronology remains incomplete hindering cross basin correlation between lithostratigraphic units and their further interpretation here we present a high resolution magnetostratigraphy spanning 5 km of paleogene neogene sequence at dahonggou in the northern qaidam basin based on correlation with the geomagnetic polarity time scale gpts we have dated the section to being between 52 and 7 ma the bottom conglomeratic unit ranging from 52 ma to 44 ma was deposited in high energy environments e g alluvial fan or braided river reflecting the earliest deformation and uplift of the basin bounding qilian shan fold thrust belt in response to india asia collision in addition we identified two major increases in sedimentation rate at 25 16 ma and after 9 5 ma and three phases of lesser increases at 52 44 ma 38 33 ma and 14 6 12 0 ma these increases in sedimentation rate are consistent with regional thermochronology and basin analysis studies which revealed enhanced motion on basin bounding thrust faults we argue that these accelerated sedimentation rates indicate pulsed tectonism in the northeastern tibetan plateau the pulse at 25 16 ma may further relate to phases of strong rainfall linked to an intense monsoon at that time

formation and re orientation of the suerkuli basin within the altyn tagh in northeastern tibetan plateau since late miocene abstract the altyn tagh fault atf had formed in eocene time however the temporal evolution of slip along the fault remains elusive despite its important role in governing growth of the tibetan plateau tp and evaluating models of continental lithosphere deformation here we perform a high resolution magnetostratigraphic study on neogene sediments from the suerkuli basin a small basin located between two active strands of the atf results show that both depositional environment and the sedimentation rate changed at about 5 4 and 6 ma respectively lithofacies shift from conglomerates and sandstones with parallel and cross beddings to mudstones with horizontal bedding suggesting a sedimentary fluvial to lacustrine depositional environment shift even aridification increased over northern china from the tarim basin to the qaidam basin during late miocene to early pliocene times lacustrine deposition had started in the suerkuli basin still we argue that an increase in slip rate along the atf triggered concurrently forming of the intermontane basin the inferred timing of increased slip rate on the atf coincides with a variation in movement of the indian plate relative to eurasian plate since late miocene early pliocene time our work suggests that a re orientation of crustal shortening and deformation in the northern tp began since late miocene and supports the idea that the modern boundary of the tp orogen had rejuvenated to adjust deformation in plate boundary conditions

intermontane basin development in the past 4 myr in the north west himalaya the through the combined use of magnetic polarity stratigraphy with fission track dating of volcanic ashes a new chronology spanning 4 myr has been developed for the intermontane basin of kashmir in the northwestern himalaya

lidar strip adjustment application to volcanic areas dems derived from lidar data are nowadays largely used for quantitative analyses and modelling in geology and geomorphology high quality dems are required for the accurate morphometric and volumetric measurement of land features we propose a rigorous automatic algorithm for correcting systematic errors in lidar data in order to assess sub metric variations in surface morphology over wide areas such as those associated with landslide slump and volcanic deposits our procedure does not require a priori knowledge of the surface such as the presence of known ground control points systematic errors are detected on the basis of distortions in the areas of overlap among different strips discrepancies between overlapping strips are assessed at a number of chosen computational tie points at each tie point a local surface is constructed for each strip containing the point displacements between different strips are then calculated at each tie point and minimization of these discrepancies allows the identification of major systematic errors these errors are identified as a function of the variables that describe the data acquisition system significant errors mainly caused by a non constant misestimation of the roll angle are highlighted and corrected comparison of dems constructed using first uncorrected and then corrected lidar data from different mt etna surveys shows a meaningful improvement in quality most of the systematic errors are removed and the accuracy of morphometric and volumetric measurements of volcanic features increases these corrections are particularly important for the following studies of mt etna calculation of lava flow volume calculation of erosion and deposition volume of pyroclastic cones mapping of areas newly covered by volcanic ash and morphological evolution of a portion of an active lava field over a short time span

pliocene uplift of the northern tibetan plateau neogene redbeds passing upward into upward coarsening conglomerate and debris flow deposits at the foot of the kunlun mountains record the change in paleoslope related to uplift of the surface of the northern tibetan plateau detailed magnetostratigraphy of a 4 5 km section near yecheng in the western kunlun mountains shows that the change from deposition on distal alluvial plains to proximal alluvial fans occurred during the gilbert reversed chron 4 5 3 5 ma the change in depositional facies was accompanied by an increase in sedimentation rate from an average 0 15 mm yr between the earliest oligocene and the earliest pliocene to 1 4 mm yr in the gauss normal chron 3 6 2 6 ma we interpret the change in depositional facies and increase in sedimentation rate as indicating that the main uplift of the northwestern tibetan plateau began ca 4 5 ma

reverse modelling of detachment folds application to the pico del aguila anticline in the south central pyrenees spain abstract a simple method to estimate fold amplification and thrust movement rates for detachment folds is documented and illustrated by its application to a symmetrical detachment fold in the southern pyrenees spain the technique provides a complete record of the kinematic evolution of detachment folds and is based on the application of equations for detachment folds involving limb rotation the method uses the stratal pattern of the syntectonic sediments and assumes that these growth strata were deposited horizontally that the folds involve a homogeneous competent unit detached over a ductile horizon and that the folds can be represented by chevronkink bands the procedure is applicable to any detachment fold with associated growth strata that display wedge geometries progressive unconformities indicating limb rotation through time this method can be used for both detachment folds formed with constant limb length or variable limb length and it can also accommodate undecompacted or decompacted growth strata

tibetan plateau aridification linked to global cooling at the eocene oligocene transition the eocene oligocene transition about 33 5 million years ago was a major global climate event the end of the eocene was unusually warm with no significant ice on antarctica but the oligocene saw the arrival of a permanent antarctic ice sheet two papers this week relate to the continental effects of this global change dupont nivet et al examined sedimentary records from the tibetan plateau and find a drop in atmospheric water which caused cooling and aridification coincident with antarctic cooling previous studies attributed this phenomenon to the rapid uplift of the tibetan plateau but this new work suggests that regional tibetan climate was influenced by global events in an unrelated paper on the same climate transition zanazzi et al explore the cooling in north america at the time using stable isotope measurements from fossil teeth and bones to create a proxy temperature record they find a large drop in mean annual temperature of 8 2 c a greater fall than seen in the oceans this continental transition may explain why many cold blooded reptiles and amphibians became extinct whereas mammals able to regulate their body temperature escaped relatively unscathed precisely dated evidence details that aridification on the tibetan plateau occurred at the time of the eocene oligocene transition in the marine records this suggests a direct link between the palaeontological and palaeoenvironmental changes recorded in continental asia at the time and global climate cooling continental aridification and the intensification of the monsoons in asia are generally attributed to uplift of the tibetan plateau and to the land sea redistributions associated with the continental collision of india and asia1 2 3 whereas some studies suggest that past changes in asian environments are mainly governed by global climate4 5 6 the most dramatic climate event since the onset of the collision of india and asia is the eocene oligocene transition an abrupt cooling step associated with the onset of glaciation in antarctica 34 million years ago7 8 9 however the influence of this global event on asian environments is poorly understood here we use magnetostratigraphy and cyclostratigraphy to show that aridification which is indicated by the disappearance of playa lake deposits in the northeastern tibetan plateau occurred precisely at the time of the eocene oligocene transition our findings suggest that this global transition is linked to significant aridification and cooling in continental asia recorded by palaeontological and palaeoenvironmental changes10 11 12 and thus support the idea that global cooling is associated with the eocene oligocene transition13 14 15 we show that with sufficient age control on the sedimentary records global climate can be distinguished from tectonism and recognized as a major contributor to continental asian environments

geochronology of the baye mn oxide deposit southern yunnan plateau implications for the late miocene to pleistocene paleoclimatic conditions and topographic evolution 40ar 39ar laser incremental heating analyses of supergene k mn oxides from weathering profiles at the baye mn deposit southern yunnan plateau sw china were carried out to place constraints on the timing of weathering and derive insights into local paleoclimatic and landscape evolution weathering profiles in the baye mn mine are dominated by 20 30 m thick saprolites which are locally covered by unconsolidated alluvial deposits we analyzed 70 grains from 35 hand samples collected from four sites located at distinct elevations in most cases different grains from the same hand sample and different samples from the same site have reproducible 40ar 39ar plateau ages the plateau ages of individual grains are also consistent with the respective isochron integrated and ideogram ages this age consistency attests to the reliability of the geochronological results as numerical constraints on the formation and evolution of these weathering profiles sixty four grains from 32 hand samples collected from weathering profiles at four sites a to d yield well defined plateau or pseudoplateau ages ranging from 2 98 0 07 to 0 16 ma 2 the age results show that mn oxides become progressively younger towards lower elevations samples collected from the highest elevation site 1855 m a s l have the oldest ages at 2 98 0 07 to 2 83 0 13 ma samples from intermediate elevations 1821 to 1815 m a s l yield ages ranging from 2 91 0 10 to 2 08 0 11 ma and those from the lowest sites 1768 to 1753 m a s l are younger than 1 25 0 08 ma the age versus elevation relationship indicates fast downward propagation of weathering front since the late pliocene and permits estimating the weathering rates at 3 3 3 8 6 6 1 2 and 11 1 1 9 m myr 1 during the time periods of 2 98 2 83 2 91 2 08 and 1 25 to 0 16 ma respectively the average river incision rates estimated from the surface exposed ages range from 235 10 to 416 19 m myr 1 during the past 3 million years the incision rate calculated from minimum exposed ages at sites b d is 33 2 m myr 1 for the time period of 2 91 1 25 ma which is consistent with the slow incision of streams on the ridges over the yunnan plateau since the early pleistocene three mn oxide pebbles contained in the alluvial deposits overlying the saprolite dominated weathering profiles at the two highest sites provided additional information on the timing of weathering four grains from two pebbles yield plateau ages of 6 32 0 19 to 5 27 0 10 ma whereas the other two grains from the third pebble indicate the minimum formation ages of 8 2 0 4 and 9 3 0 3 ma these ages confirm the existence of older weathering profiles now dismantled in the region manganese oxide 40ar 39ar ages of the baye deposit when combined with results from other localities indicate that lateritic weathering and supergene mn enrichment and by inference warm and humid climates conducive to intense weathering have prevailed over the plateau since the middle to late miocene the climatic conditions inferred from the weathering geochronology are consistent with multiple independent marine and terrestrial sedimentary and paleontological records confirming that supergene mn oxides can be used as a useful proxy for past climate age clusters of mn oxides at 2 9 2 4 1 2 0 8 and 0 6 0 4 ma are broadly coincident with and thus likely reflect intensification events of the indian summer monsoon that brings moisture and abundant precipitation to the yunnan plateau these clusters also coincide with the periods of significant surface uplift in the yunnan plateau demonstrating a causal link between topographic evolution plateau uplift and intensification of the monsoonal climate

late neogene magnetostratigraphy in the western qaidam basin ne tibetan plateau and its constraints on active tectonic uplift and progressive evolution of growth strata abstract the qaidam basin as the largest intermontane basin of the ne tibetan plateau is the ideal place to provide constraints on depositional and tectonic patters to determine its tectonic deformation history and progressive evolution of growth strata we conducted paleomagnetic study on the late neogene stratigraphic section in the western qaidam basin a magnetostratigraphic study of the well exposed 805 m qigequan section at the qigequan anticline in the western qaidam basin reveals twelve pairs of normal and reversed polarity zones which can be readily correlated with chrons c1n 3ar of the geomagnetic polarity time scale gpts from this correlation we can conclude that the shizigou and the qigequan formations were formed at 6 9 ma 2 5 ma and 2 5 0 4 ma respectively accumulation rates determined from our chronology together with the occurrence of unconformities suggest four phases of tectonic uplift which began at about 3 6 ma 2 5 ma 1 1 ma and 0 8 ma the results also suggest that offlap growth strata according to the limb rotation model on the anticlinorium started to occur at 8 2 ma they progressively become younger from the frontal region of the altyn tagh mts 8 2 ma to the southwestern basin 2 5 ma and to further east of the qaidam basin

magnetostratigraphy of the dahonggou section northern qaidam basin and its bearing on cenozoic tectonic evolution of the qilian shan and altyn tagh fault article i nfo the timing of uplift of the tibet plateau has a central role in the development of tectonic models for the tibet plateau and cenozoic global climate change a detailed magnetostratigraphic study of the dahonggou section northern qaidam basin reveal that the section spans from 34 to 8 5 ma and the ages of the shang ganchaigou xia youshashan and shang youshashan formations are from 34 to 22 20 ma 22 20 to 13 ma and 13 to 8 5 ma respectively variations in lithofacies sedimentation rate and magnetic susceptibility k suggest that the southern qilian shan was tectonically inactive and didn t respond to the rapid slip on the altyn tagh fault at 30 ma in contrast the similar sedimentary records in the dahonggou section the xishuigou section along the altyn tagh fault and even more localities along much of the qilian range front imply that the qilian shan and the altyn tagh fault were synchronously tectonically active at about 12 ma the lower k between 12 ma and 8 5 ma in the sediments of the dahonggou section is interpreted to be due to long distanced oxidation and sorting which cause not only that magnetite was oxidated to hematite but also that magnetic minerals are enriched in fine grained sediments and coarse grained sediments bear few magnetic mineral

cenozoic tectonic evolution of qaidam basin and its surrounding regions part 1 the southern qilian shan nan shan thrust belt and northern qaidam basin cenozoic qaidam basin the largest active intermountain basin inside tibet figures importantly in the debates on the history and mechanism of tibetan plateau formation during the cenozoic indo asian collision to determine when and how the basin was developed we conducted detailed geologic mapping and analyses of a dense network of seismic reflection profiles from the southern qilian shan nan shan thrust belt and northern qaidam basin our geologic observations provide new constraints on the timing and magnitude of cenozoic crustal thickening in northern tibet specifically our work shows that the southernmost part of the qilian shan nan shan thrust belt and contractional structures along the northern margin of qaidam basin were initiated in the paleocene early eocene 65 50 ma during or immediately after the onset of the indo asian collision this finding implies that stress was transferred rapidly through tibetan lithosphere to northern tibet from the indo asian convergent front located 1000 km to the south the development of the thrust system in northern qaidam basin was driven by motion on the altyn tagh fault as indicated by its eastward propagation away from the altyn tagh fault the eastward lengthening of the thrust system was spatially and temporally associated with eastward expansion of qaidam basin suggesting thrust loading was the main control on the basin formation and evolution the dominant structure in northern qaidam basin is a southwest tapering triangle zone which started to develop since the paleocene and early eocene 65 50 ma and was associated with deposition of an overlying southwest thickening growth strata sequence recognition of the triangle zone and its longevity in northern qaidam basin explains a long puzzling observation that cenozoic depocenters have been located consistently along the central axis of the basin this basin configuration is opposite to the prediction of classic foreland basin models that require the thickest part of foreland sediments deposited along basin edges against basin bounding thrusts restoration of balanced cross sections across the southern qilian shan nan shan thrust belt and northern qaidam basin suggests that cenozoic shortening strain is highly inhomogeneous varying from 20 to 60 both vertically in a single section and from section to section across the thrust belt the spatially variable strain helps explain the conflicting paleomagnetic results indicating different amounts of cenozoic rotations in different parts of qaidam basin the observed crustal shortening strain also implies that no lower crustal injection or thermal events in the mantle are needed to explain the current elevation 3000 3500 m and crustal thickness 45 50 km of northern qaidam basin and the southern qilian shan nan shan thrust belt instead thrusting involving continental crystalline basement has been the main mechanism of plateau construction across northern qaidam basin and the southern qilian shan nan shan region