neogene rotations in the jiuquan basin hexi corridor china vertical axis rotations of blocks in around the tibetan plateau can be attributed to the india asia collision study of the vertical axis rotations of these blocks will increase our understanding of the mechanisms and kinematics of continent continent collisions we report here a new palaeomagnetic study of rotations using data from four localities five magnetostratigraphy sections in the jiuquan basin our study indicates that the mean declinations of each section are different from each other similar to what has been observed in the other localities in the ne tibetan plateau however using the mean directions of every 100 m of section we observe that the four localities have similar sequential patterns of rotations during the last 13 ma significant continuous counterclockwise before c 8 0 ma insignificant rotations between 8 0 4 0 ma and slight clockwise rotation after 4 0 ma this indicates that rather than being a record of spatially varying declinations it is a temporal variation in the occurrence of regional rotations combined with other geological evidence the rotation patterns may suggest two major tectonic activity phases of the northeastern tibetan plateau during the last 13 ma an eastward extrusion and strike slip dominant phase before 8 0 ma a significant shortening and a rapid uplift dominant phase after 8 0 ma

the greenland earthquake of 11 july 1987 and postglacial fault reactivation along a passive margin abstract intraplate earthquakes in many cases occur near continental margins this observation applies very well to the case of greenland a stable continental region with low seismicity the seismicity of greenland is nearly totally concentrated along the coastlines of the island where it is relatively free of ice cover on 11 july 1987 the largest greenland earthquake of instrumental record m b 5 5 m w 5 4 occurred in continental crust off the northeastern coast in the wandel sea waveforms of long and short period teleseismic p and long period teleseismic sh waves have been modeled to estimate the source parameters for this earthquake the focal mechanism determined is a normal faulting with a strike slip component strike 148 dip 59 and rake 131 the strike direction of one of the nodal planes was found to be consistent with the direction of the dominant structural trend observed in the area a previous normal faulting mechanism with very different strike directions for this event was found to have inferior waveform fit and is not consistent with the fault strike directions from the local geological setting the seismic moment of the july 1987 earthquake is 1 75 10 24 dyne cm the focal depth and stress drop are 5 km and 389 bars respectively the high stress drop may relate to the relatively long earthquake repeat time in the region the observed normal faulting of this earthquake can be interpreted as a rupture due to an extensional stress field at the forebulge outside of the ice sheet because of deglaciation flexure in the region another major earthquake 26 november 1971 m b 5 1 311 km to the south of the 11 july 1987 event was likewise determined to be normal faulting and can be explained as another event triggered by deglaciation in addition we find that the sparse general seismicity of greenland can also be related to postglacial rebound

evidence for northeastern tibetan plateau uplift between 25 and 20 ma in the sedimentary archive of the xining basin northwestern china the growth history of the tibetan plateau provides a valuable natural laboratory to understand tectonic processes of the india asia collision and their impact on and interactions with asian and global climate change however both tibetan plateau growth and asian paleoenvironments are generally poorly documented in pre pliocene times and reflect limited temporal coverage for different parts of the plateau here we present magnetostratigraphic results from the xining basin at the ne margin of the tibetan plateau precisely dating the record between the earliest oligocene 33 ma to the middle miocene 16 ma the pattern of observed paleomagnetic polarity zones is unequivocally correlated to the geomagnetic polarity time scale gpts indicating relatively constant and low sediment accumulation rates 32 m myr except for a peculiar period of unstable accumulation between 25 3 and 19 7ma at the beginning of this interval a marked permanent increase in magnetite content of the sediments is observed and likely relates to a change in provenance we directly relate this unstable period of sediment accumulation and provenance change to the coeval exhumation recently reported by low temperature thermochronology from the laji shan range which subsequently formed the southernmargin of the xining basin evidence for ne tibet tectonismat 25 20 ma can be associated with widespread deformation over the entire himalayan tibetan orogen at this time which may be linked to the coeval appearance of monsoon climate in eastern asia and the onset of central asian desertification

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

late quaternary paleoclimatic and geomorphological evolution at the interface between the menyuan basin and the qilian mountains northeastern tibetan plateau abstract the tibetan plateau is regarded as an amplifier and driver of environmental change in adjacent regions because of its extent and high altitude however reliable age control for paleoenvironmental information on the plateau is limited osl appears to be a valid method to constrain the age of deposits of glacial and fluvial origin soils and periglacial structures in the menyuan basin on the northeastern tibetan plateau dating results show glaciers advanced extensively to the foot of the qilian mountains at 21 ka in agreement with the timing of the global last glacial maximum lgm recorded in northern hemisphere ice cores comparison with results from the eastern tibetan plateau suggests that the factor controlling glacial advance in both regions was decreased temperature not monsoon related precipitation increase the areas of the menyuan basin occupied by glacio fluvial deposits experienced continuous permafrost during the lgm indicated by large cryoturbation features interpreted to indicate that the mean annual temperature was 7 c lower than at present glacio fluvial systems in the menyuan basin aggraded and terraces formed during cold periods penultimate glaciation lgm and possibly the younger dryas as a response to increased glacial sediment production and meltwater runoff then

the environmental effects of the uplift of the qinghai xizang plateau the intense upheaval of the qinghai xizang plateau took place 2 ma bp the terraces of the yellow river in the lanzhou region and its upper sections provide a record of the uplift of the plateau the interaction of glaciation cycles resulting from climatic changes and pulsating tectonic upheavals are both involved in the record of environmental change across the plateau three tectonic climatic events which are termed respectively the qinghai xizang movement the huanghe yellow river movement and the gonghe movement occurred 2 1 5 1 0 and 0 15 ma bp the upheaval of the qinghai xizang plateau was the trigger mechanism of the asian monsoon the loess plateau was formed in the monsoon triangle of east asia human origins and human evolution may have been stimulated by the uplift of the qinghai xizang plateau

cenozoic tectonic evolution of the elashan range and its surroundings northern tibetan plateau as constrained by paleomagnetism and apatite fission track analyses abstract magnetostratigraphic studies of sediments in the western gonghe and eastern qaidam basins together with apatite fission track aft analyses in the elashan range suggest that the elashan range and its surroundings experienced a two stage evolution a protracted uplift from the cretaceous to the early tertiary which explains the absence of the paleogene strata in the region and an accelerated growth of the elashan range since the latest oligocene caused by extensively distributed thrust faults in the region this later phase of uplift resulted in the subsequent thick sediments within the both easternmost qaidam and gonghe basins basal ages of 21 22 ma in the wulan section of 20 ma in the southern gonghe section and of l2 ma in the chaka section the two phases of thrust motion and range growth mean that the qaidam and gonghe basins were never united during cenozoic times the strike slip is likely to have occurred at l0 ma as shown by the paleomagnetic declination data which show a rapid transition in rotation sense from counterclockwise to clockwise at that time this time is also similar to the 9 ma age of initiation of the wenquan fault determined by backward calculation based on its late quaternary slip rate eventually the qinghai nan shan thrust belt began to develop at 6 ma

cosmogenic burial ages reveal sediment reservoir dynamics along the yellow river china burial dating using cosmogenic al 26 and be 10 is an emerging technique for establishing chronologies of fluvial deposits ranging in age from ca 0 5 ma to 5 ma the determination of burial age however requires an assumption that sediment is buried with a known initial al 26 be 10 ratio using a sequence of well dated fluvial terraces along the yellow river in lanzhou china we demonstrate that this assumption may be violated when upstream sediment sources include neogene sedimentary basins samples of fluvial gravel from six terraces yield burial ages ranging from ca 0 83 ma to 2 81 ma comparison of these results to independent ages determined from magneto stratigraphic and loess paleosol studies demonstrates a high degree of correspondence between ages in the lower three terraces in the higher terraces however burial ages are systematically too old implying a previous burial history these results can be exploited to place quantitative constraints on the provenance of sediment in the terrace deposits our results reveal that rapid incision and excavation of late neogene sedimentary basins ca 1 7 ma led to injection of fluvial sediment with low initial al 26 be 10 ratios dilution of this source through time occurred as incision progressed into upstream bedrock ranges our results suggest that cosmogenic nuclides can illuminate the timing of long term storage and remobilization of sediment in continental scale river systems

magnetostratigraphic dating of river terraces rapid and intermittent incision by the yellow river of the northeastern margin of the tibetan plateau during the quaternary up to 23 paleosols have been identified in loess sequences that overlie fluviatile sediments on seven terraces of huang he the yellow river and daxia he in the linxia basin at the northeastern margin of the tibetan plateau the magnetostratigraphic record in the oldest sequence appears to be fairly complete and spans the entire quaternary it includes evidence for the jaramillo and olduvai normal polarity subchrons within the matuyama chron as well as the cobb mountain and stage 54 formerly gilsa events age constraints within the brunhes are provided by 14c and thermoluminescence optical stimulated luminescence dating the magnetostratigraphic chronology of the quaternary sediments indicates that terraces were formed at about 1 66 1 4 1 1 0 6 0 12 0 055 and 0 01 ma the terraces may represent climatically induced pauses in long term tectonically induced incision by the rivers on the basis of terrace heights and ages incision rates were highest from 1 66 to 1 4 ma 1 m kyr decreased from 1 4 to 0 12 ma 0 1 m kyr and increased from 0 12 ma to present 0 75 m kyr if river incision is attributed solely to uplift of the tibetan plateau then this uplift appears to have been rapid as well as intermittent following the first evidence of the existence of huang he in this area at about 1 75 ma however the effects of uplift cannot be fully separated from incision caused by changes in climate copyright 1997 by the american geophysical union

mesozoic cenozoic evolution of the xining minhe and dangchang basins northeastern tibetan plateau magnetostratigraphic and biostratigraphic results 1 accurate stratigraphic ages are crucial to understanding the deformation history of the tibetan plateau prior to and during the indo asian collision efforts to quantify mesozoiccenozoic ages are hindered by limited fossils and a paucity of volcanic horizons and regionally correlative strata magnetostratigraphic and biostratigraphic results from the xining minhe longzhong basin complex and dangchang basin provide an improved chronology of nonmarine basin development over a large region of the northeastern tibetan plateau 34 37 n 101 105 e analyses of 171 magnetostratigraphic levels and 24 palynological assemblages 120 species indicate late jurassic early cretaceous to mid tertiary deposition although magnetic polarity zonation is incomplete independent palynological age control partially restricts possible correlations to the geomagnetic polarity timescale the sediment accumulation record basin provenance structural geology and published thermochronological data support a history of jurassic exhumation late jurassic early cretaceous fault related basin initiation and cretaceous paleogene reduced accumulation these patterns which are compatible with late jurassic early cretaceous extension and cretaceous paleogene postrift thermal subsidence were disrupted at about 40 30 ma when shortening related to the indo asian collision induced localized range uplift vertical axis rotation and amplified subsidence indexterms 1520 geomagnetism and paleomagnetism magnetostratigraphy 8102 tectonophysics continental contractional orogenic belts 9320 information related to geographic region asia 9604 information related to geologic time cenozoic 9609 information related to geologic time mesozoic keywords tectonics magnetostratigraphy tibetan plateau cenozoic mesozoic sedimentary basins

the physics of explosive volcanic eruptions edited by j s gilbert and r s j sparks geological society special publication no 145 geological society london 1998 186 pp isbn 1862390207 us 98 59 00 members us 48 29

magnetostratigraphy of cenozoic sediments from the xining basin tectonic implications for the northeastern tibetan plateau 1 the xining subbasin of the longzhong basin holds the longest continuous cenozoic stratigraphic record at the margin of the northeastern tibetan plateau despite a rich biostratigraphic content including the xiejia mammal fauna the tectonic evolution of the basin is largely unconstrained in this study we present stratigraphic biostratigraphic and magnetostratigraphic results that provide a basis for reconstructing the cenozoic tectonic evolution of the xining basin with respect to adjacent regions of the northeastern tibetan plateau magnetostratigraphic analysis from three red bed sections in the xining basin indicates continuous deposition at low and nearly constant accumulation rates average 2 2 cm kyr from 52 0 to 17 0 ma we interpret this result to indicate that no major regional tectonic event implying large sediment accumulation variations has affected the xining basin deposition during this considerable time window in detail accumulation rate variations outline a three stage evolution with 1 8 cm kyr from 52 0 ma to 34 5 ma 4 1 cm kyr from 34 5 to 31 0 ma and 2 3 cm kyr from 31 0 to 17 0 ma the second order increase between 34 5 and 31 0 ma can be interpreted to result from either a distal tectonic event or to be of climatic origin although the region was tectonically quiescent for much of the cenozoic tectonic activity occurred during basin initiation or reactivation at circa 55 0 52 5 ma and during intense basin deformation after 17 0 ma

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

rapid fluvial incision along the yellow river during headward basin integration the onset of fluvial erosion in an area of tectonic uplift is thought to reflect the timing of the uplift geomorphological data from the yellow river in tibet indicate that the rapid incision of this river channel occurred as a result of climate change at least six million years after the onset of plateau uplift

age and palaeoclimatic significance of the loess of lanzhou north china extending in a broad arc that abuts the sandy non gobi deserts the loess plateau of northern china1 3 is one of the most massive accumulations of loess in the world the loess sequence is typically characterized by an alternation of silty or sandy loess with more clay rich palaeosols these alternations in conjunction with their enclosed faunas and distinctive mineralogies have been interpreted as reflecting pleistocene glacial interglacial cycles3 8 because it holds implications for the climatic and anthropological history of china9 10 the definition of a reliable chronological framework for loess deposition is of great interest recent palaeomagnetic studies4 5 have indicated that loess deposition in shaanxi province commenced 2 4 myr ago to assess the synchrony of loess accumulation across the loess plateau we have dated a 330 m thick loess sequence near lanzhou gansu province the magnetostrati graphical results reported here indicate that the base of this loess succession dates from 1 3 my r ago this young age in comparison to the shaanxi sequence is attributed to uplift along the northern fringe of the tibetan plateau11 that precluded early pleistocene loess preservation in this mountainous region palaeosols in the basal loess occur on average once every 25 kyr suggesting that climates conducive to soil forming events may have been modulated by orbital precession in the early pleistocene

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

plio pleistocene drainage development in an inverted sedimentary basin vera basin betic cordillera se spain abstract the vera basin is one of a series of interconnected neogene quaternary sedimentary basins located within the internal zone of the betic cordillera southeast spain since the pliocene the vera basin has been subjected to low uplift rates 11 21 m ma 1 and inverted via compressive tectonics that are related to the ongoing oblique collision between the african and iberian plates within this paper the sedimentary and geomorphic response to basin inversion is explored sedimentary processes and environments are established for key stratigraphic units of the pliocene plio pleistocene basin fill and pleistocene dissectional landscape these data are subsequently utilised to reconstruct an evolving basin palaeogeography fault and uplift data are employed to discuss the role of tectonically driven basin inversion for controlling the resultant palaeogeographic changes and associated patterns of drainage development during the early mid pliocene the vera basin was characterised by shallow marine shelf conditions cuevas formation a major palaeogeographic reorganisation occurred during the mid late pliocene strike slip movement along the eastern basin margin coupled with uplift and basin emergence created a protected partially enclosed marine embayment that was conducive for gilbert type fan delta sedimentation from fluvial inputs along the northern and eastern basin margins espiritu santo formation the vera basin then became fully continental and internally drained through the development of a consequent drainage network that formed following the withdrawal of marine conditions during the late pliocene to early pleistocene alluvial fans developed along the northern and western basin margins grading to a bajada and terminating in a playa lake in central basin areas salmeron formation during the early mid pleistocene a switch from basin infilling to dissection took place recorded by alluvial fan incision a switch to braided river sedimentation and fluvial incision into the underlying basin fill sediments and basin margin mountainous topography fluvial incision headwards erosion expansion and modification of the consequent drainage network is documented within a series of up to four major inset river terrace levels and associated landforms fluvial incision and drainage network expansion are attributed to differential uplift and the creation of regional gradients between adjacent basins the relatively low plio pleistocene uplift rate of the vera basin 11 21 m ma 1 in comparison to adjacent basins sorbas 80 160 m ma 1 huercal overa 50 m ma 1 resulted in a switch from internal to external basin drainage ancestral forms of the principal drainage systems within the vera basin the rios almanzora aguas and antas captured basins and mountain catchment areas to the north huercal overa basin southwest sorbas basin and west sierra de los filabres range the switch from basin infilling to fluvial dissection is coincident with a phase of early mid pleistocene compressional tectonics expressed by extensional faulting this deformation is probably linked to accelerated strike slip movement along the palomares fault zone the faulting is superimposed onto the longer term pattern of plio pleistocene uplift and basin inversion

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

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

differential impact of small scaled tectonic movements on fluvial morphology and sedimentology the huang shui catchment ne tibet plateau abstract the aim of this paper is to investigate the morphological implications of the interplay between tectonic movements at different rates timescales and spatial extent in a catchment of intermediate size the huang shui river a main tributary of the yellow river in the ne tibet plateau river incision started from a peneplain like surface that developed in post miocene pliocene times at the end of the tertiary a general tectonic uplift of the tibetan plateau initiated river incision this general uplift also caused local fragmentation of the huang shui catchment into blocks kilometers or maximally a few tens of kilometers of local extent that have subsided and or uplifted relative to one another fluvial deposition of 30 m in the subsiding blocks contrasts with erosion and formation of gorges in the uplifted blocks incision into the former peneplain was not continuous but a staircase of terraces developed under climatic influences terrace deposits are sometimes capped by interglacial soils or soil derived material apparently terrace incision occurred at the transition to the next cold period the different rates of uplift and subsidence of the individual blocks resulted in the simultaneous development of erosion and accumulation terraces of different sizes within the same catchment even within the same tectonic block this makes it impossible to connect the terraces of the different blocks except for the three youngest terraces representing the last 300 000 years thus illustrating the uniform tectonic history of the catchment since that time

tectonic controls for transverse drainage and timing of the xin ding paleolake breach in the upper reach of the hutuo river north china abstract the upper reach of the hutuo river flows along the xin ding basin and cuts a transverse drainage through the xizhou mountain and the taihang range into the north china plain previous studies showed that the xin ding basin was occupied by a lake during the early middle pleistocene however the timing of the paleolake breach and the mechanism for the creation of the transverse drainage are unknown we constructed the fluvial terrace sequence in the upper reach of the hutuo drainage combined with thermoluminescence tl and optically stimulated luminescence osl dating as well as the timescale of the overlying loess paleosol sequence our results reveal that 1 five terraces t5 t1 developed along the upper reach of the hutuo river amongst which terraces t4 t1 were formed synchronously at 600 120 130 20 26 and 6 7 ka respectively 2 the creation of the transverse drainage and breach of the xin ding paleolake occurred between 600 and 130 ka and 3 the mechanism for the creation of the transverse drainage is via river piracy of paleostreams on both sides of the drainage divide localized differential uplift and associated tilting of the xizhou mountain block during the middle pleistocene result in the formation of the transverse drainage and breach of the xin ding paleolake

the fluvial cycle at cold warm cold transitions in lowland regions a refinement of theory abstract a previously established non linear theory of river cyclicity as a response to climate change states that short phases of fluvial instability occur both at the transition from relatively warm temperate to cold periglacial and from relatively cold to warm periods such instability typically starts with vertical erosion successively followed by sedimentary fill of the erosive scar in spite of frequent confirmation of this theory by geomorphological reconstructions a few problems arise first there are fewer incision phases than climatic transitions secondly remnants of erosion at cold warm transitions are scarce in contrast to obvious erosion relics at warm cold transitions furthermore it appears that the incision style is strikingly different at both kinds of climatic transitions similarly the long stable phases are also expressed in terms of different floodplain development in cold and warm periods these arguments require a modification of the general non linear theory at the transition from relatively temperate to colder conditions rivers transformed gradually from a regular low energy single channel course to a periodically high energy multi channel type the latter braided type is characterized by intense lateral movement rather than by deep vertical erosion this results in a well expressed morphology of wide extensive floodplains and terraces in contrast the linear and constrained meandering channels incise with small width depth ratio and build floodplains of limited lateral extent consequences are twofold 1 the spatial limitation of the deeply incised meandering valleys at the beginning of warm periods counts against their recognition 2 relatively strong lateral migration of the braided rivers removes most traces of previous meandering systems which contrasts with the limited lateral activity of confined meandering channels it means that in a warm cold warm alternation generally only one phase of vertical erosion is preserved the one that is caused by the high energy braided river at the start of the cold period

chronological sequence and subdivision of chinese neogene mammalian faunas six land mammal ages are recognized for the neogene of east asia the ages are based upon updated large and small mammal faunas and replace or redefine the land mammal stages erected by li et al 1984 comparisons and correlations are made to faunas in europe northern and southern asia and north america in addition methods of utilizing mammalian faunal data to define and recognize geochronologic ages are discussed

the growth of northeastern tibet and its relevance to large scale continental geodynamics a review of recent studies recent studies of the northeastern part of the tibetan plateau have called attention to two emerging views of how the tibetan plateau has grown first deformation in northern tibet began essentially at the time of collision with india not 10 20 myr later as might be expected if the locus of activity migrated northward as india penetrated the rest of eurasia thus the north south dimensions of the tibetan plateau were set mainly by differences in lithospheric strength with strong lithosphere beneath india and the tarim and qaidam basins steadily encroaching on one another as the region between them the present day tibetan plateau deformed and its north south dimension became narrower second abundant evidence calls for acceleration of deformation including the formation of new faults in northeastern tibet since 15 ma and a less precisely dated change in orientation of crustal shortening since 20 ma this reorientation of crustal shortening and roughly concurrent outward growth of high terrain which swings from nne ssw in northern tibet to more ne sw and even ene wsw in the easternmost part of northeastern tibet are likely to be in part a consequence of crustal thickening within the high tibetan plateau reaching a limit and the locus of continued shortening then migrating to the northeastern and eastern flanks these changes in rates and orientation also could result from removal of some or all mantle lithosphere and increased gravitational potential energy per unit area and from a weakening of crustal material so that it could flow in response to pressure gradients set by evolving differences in elevation

lithologic and rock magnetic evidence for the mid miocene climatic optimum recorded in the sedimentary archive of the xining basin ne tibetan plateau abstract thick cenozoic deposits in the xining basin provide great potential for understanding the tectonic and climatic evolution of the ne tibetan plateau however the middle miocene climatic optimum mmco in this basin has not been reported up until now due to the poor exposure of the uppermost strata covering this interval in this study a 194 m deep core of flood plain to channel flood deposits was obtained from the tashan flats above the xiejia section in the xining basin magnetostratigraphic dating of the core determines its age at ca 18 5 13 5 ma lithological and rock magnetic analyses demonstrate that the most prominent changes recorded in the present study occurred between 17 and 14 ma during this period the sedimentary sequence mostly consists of gray white or bluish gray claystone and muddy siltstone intercalated with some thin red claystone the rock magnetic parameters show a large variability with higher values in thin red claystone beds and lower values in gray white or bluish gray layers these features demonstrate that due to a warm and wet climate extensive rivers had developed in the mid miocene and that a reducing sedimentary environment prevailed these favorable climatic conditions coincide with the mmco as based on global deep sea deposit records indicating that this warm event exerted a major impact on regional climate change in the ne tibetan plateau during the mid miocene

paleocurrent and fabric analyses of the imbricated fluvial gravel deposits in huangshui valley the northeastern tibetan plateau china abstract gravel deposits on fluvial terraces contain a wealth of information about the paleofluvial system in this study flow direction and provenance were determined by systematic counts of more than 2000 clasts of imbricated gravel deposits in the xining region northeastern tibetan plateau china these gravel deposits range in age from the modern huangshui riverbed to miocene aged deposits overlain by eolian sediments our major objectives were not only to collect first hand field data on the fluvial gravel sediments of the xining region but also to the reconstruct the evolution of the fluvial system these data may offer valuable information about uplift of the northeastern tibetan plateau during the late cenozoic era reconstructed flow directions of the higher and lower gravel deposits imply that the river underwent a flow reversal of approximately 130 180 in addition the lithological compositions in the higher gravel deposits differ significantly from the lower terraces suggesting that the source areas changed at the same time eolian stratigraphy overlying the gravel deposits and paleomagnetic age determination indicate that this change occurred sometime between 1 55 ma and 1 2 ma we suggest that tectonic activity could explain the dramatic changes in flow direction and lithological composition during this time period therefore this study provides a new scenario of fluvial response to tectonic uplift a reversal of flow direction in addition field observation and statistical analyses reveal a strong relationship between rock type size and roundness of clasts

late miocene quaternary rapid stepwise uplift of the ne tibetan plateau and its effects on climatic and environmental changes abstract the way in which the ne tibetan plateau uplifted and its impact on climatic change are crucial to understanding the evolution of the tibetan plateau and the development of the present geomorphology and climate of central and east asia this paper is not a comprehensive review of current thinking but instead synthesises our past decades of work together with a number of new findings the dating of late cenozoic basin sediments and the tectonic geomorphology of the ne tibetan plateau demonstrates that the rapid persistent rise of this plateau began 8 1 ma followed by stepwise accelerated rise at 3 6 ma 2 6 ma 1 8 1 7 ma 1 2 0 6 ma and 0 15 ma the yellow river basin developed at 1 7 ma and evolved to its present pattern through stepwise backward expansion toward its source area in response to the stepwise uplift of the plateau high resolution multi climatic proxy records from the basins and terrace sediments indicate a persistent stepwise accelerated enhancement of the east asian winter monsoon and drying of the asian interior coupled with the episodic tectonic uplift since 8 ma and later also with the global cooling since 3 2 ma suggesting a major role for tectonic forcing of the cooling

stable isotope evidence for topographic growth and basin segmentation implications for the evolution of the ne tibetan plateau lithologic magnetostratigraphic and stable isotope records from the neogene xunhua and linxia basins along the tibetan plateau9s northeastern margin suggest that topography in the intervening jishi shan mountain range began to develop between 16 and 11 ma perturbations to local climate patterns resulting from the evolution of local topography are tracked through comparison of stable isotope compositions of calcareous basin fill materials across the jishi shan similarity of isotopic compositions is interpreted to reflect the presence of integrated basins whereas distinct isotopic compositions reflect unique basin hydrologies divergent isotope trends develop between ca 16 and 11 ma and are indicative of hydrologic separation in the adjacent xunhua and linxia basins and increased aridity in the leeward xunhua basin the development of aridity in the lee of the growing topography along the plateau9s northeast margin highlights the importance of evaporative enrichment in this extremely continental setting and explains the presence of anomalously positive 18 o values in modern rainfall our findings add to a growing body of evidence for deformation along the plateau9s north and northeastern margins in the middle to late miocene

termination of fluvial alluvial sedimentation in the xining basin ne tibetan plateau and its subsequent geomorphic evolution the xining basin in northern china lies topographically in the transitional zone between the tibetan plateau and the loess plateau and climatically in the transitional zone between humid east asia and the arid asian interior during the cenozoic the basin accumulated a thick continuous sequence of fluviolacustrine dominated red beds and subsequent eolian loess the termination of sediment deposition in the xining basin is the key to understanding its subsequent evolution the development of the modern yellow river and the history of dust deposition here we present the results of a detailed paleomagnetic study of the upper sedimentary sequence of the xining basin below the river terraces and in addition we review previous studies of river evolution development our results indicate that the age of the uppermost part of the continuous sequence of fluviolacustrine dominated red beds in the xining basin ranges from ca 20 ma to 4 8 ma suggesting that basin sedimentation ended at the earliest at 4 8 ma and they also provide an earliest age constraint for the subsequent river terrace development and eolian dust deposition in addition these results demonstrate that the termination of sedimentation in the xining basin and the nearby linxia basin was approximately coeval suggesting the rapid regional tectonic uplift of the ne tibetan plateau and resulting reorganization of the landforms and development of the paleo yellow river in the late pliocene c 2017 elsevier b v all rights reserved

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