orbital scale evolution of the indian summer monsoon since 1 2 ma evidence from clay mineral records at iodp expedition 355 site u1456 in the eastern arabian sea abstract clay mineral assemblages at international ocean discovery program expedition 355 site u1456 drilled in the eastern arabian sea have been investigated to reveal the sediment provenances and reconstruct the erosion weathering patterns in the western himalaya and indian subcontinent thus constraining the evolution of the indian summer monsoon and its forcing mechanism since 1 2 ma the clay mineral assemblages at site u1456 mainly comprise smectite with an average value of 59 and illite with an average value of 33 with chlorite with an average value of 5 and kaolinite with an average value of 3 as minor constituents in terms of sediment provenance our results indicate that illite and chlorite are predominantly derived from the indus river which originates from the western himalaya and karakoram while smectite is primarily sourced from the narmada river and tapti river in the deccan traps with a non negligible contribution from the indus river in some cases variations in smectite illite chlorite ratio are ultimately controlled by the indian summer monsoon which is characterized by approximate glacial interglacial cyclicity showing higher values i e enhanced chemical weathering during interglacial periods in addition a major shift in smectite illite chlorite ratio at 0 9 ma is correlated to the mid pleistocene transition 1 2 0 9 ma both the marine isotope stage 13 event 533 478 ka and the mid brunhes event 430 ka are also recorded in the clay mineral proxies based on the spectral analysis smectite illite chlorite ratio displays a transition from nonprimary periodicity 29 kyr to strong eccentricity 100 kyr and precession 22 kyr periodicities at approximately 0 9 ma which corresponds to the mid pleistocene transition our study indicates that the variability of the indian summer monsoon at orbital timescales is controlled by high latitude i e ice volume and low latitude i e summer insolation processes

magnetic parameter variations in the chaona loess paleosol sequences in the central chinese loess plateau and their significance for the middle pleistocene climate transition abstract a high resolution rock magnetic investigation was performed on the chaona quaternary loess paleosol sequences in the central chinese loess plateau based on a newly developed independent unturned time scale and magnetic records we reconstructed the history of the east asia monsoons during the last 3 ma and explored the middle pleistocene climate transition mpt rock magnetic results show that the loess layers are characterized by relatively high coercivity and remanent coercivity lower magnetic susceptibility ms and that the paleosol layers are characterized by relatively high ms saturation magnetization and remanent saturation magnetization spectrum analyses indicate that there are various periods in addition to orbital periodicities according to the onset and stable appearance of 100 kyr period we consider that the mpt recorded in this section began at 1 26 ma and was completed by 0 53 ma which differs from previous investigations based on orbitally tuned time scales the forcing mechanism for the mpt was more complicated than just the orbital forcing we conclude that the rapid uplift of the tibetan plateau may have played an important role in the shift of periodicities during the middle pleistocene

paleomagnetic evidence for the miocene counter clockwise rotation of northeast japan rifting process of the japan arc paleomagnetic results have been obtained from more than 700 oriented samples in igneous rocks of cretaceous to miocene age from northeast japan the remanent magnetizations of welded tuffs with age between 32 ma and 21 ma old from 17 widely distributed sampling sites in northeast japan are fairly well grouped with a mean ofd 41 2 i 56 5 95 7 2 the remanent magnetization of welded tuffs of 14 ma and 11 ma from 4 sites shows a northerly direction d 11 7 i 60 5 95 15 3 these data imply that northeast japan was apparently subjected to a counter clockwise rotation through 47 14 about a vertical axis on the representative point of northeast japan 141 e 39 n during the past 21 ma comparing with the period of the clockwise rotation of southwest japan the differential rotation between northeast japan and southwest japan is concluded to have occurred concurrently during the period between 21 ma and 12 ma a rifting model of the japan arc is proposed northeast japan rotated counter clockwise through 50 about a northern pivot at 146 e 44 n while southwest japan rotated clockwise through 54 about a southern pivot at 129 e 34 n the differential rotation about different rotation pivots gives rise to the opening of a diamond shaped back arc basin the japan sea

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

mountains and arid climates of middle latitudes simulations from a global climate model with and without orography have been used to investigate the role of mountains in maintaining extensive arid climates in middle latitudes of the northern hemisphere dry climates similar to those observed were simulated over central asia and western interior north america in the experiment with mountains whereas relatively moist climates were simulated in these areas in the absence of orography the experiments suggest that these interior regions are dry because general subsidence and relatively infrequent storm development occur upstream of orographically induced stationary wave troughs downstream of these troughs precipitation bearing storms develop frequently in association with strong jet streams in contrast both atmospheric circulation and precipitation were more zonally symmetric in the experiment without mountains in addition orography reduces the moisture transport into the continental interiors from nearby oceanic sources the relative soil wetness of these regions in the experiment without mountains is consistent with paleoclimatic evidence of less aridity during the late tertiary before substantial uplift of the rocky mountains and tibetan plateau is believed to have occurred

chronology and paleoenvironmental records of a drill core in the central tengger desert of china abstract the desertification history of inland asia provides most direct evidence for asian drying history but the formation ages of the most asian deserts are not clear due to the lack of outcrops the tengger desert one of the main proximal deserts of the chinese loess plateau clp is of special paleoclimatic significances for its dust emission and environmental affection here we report lithofacies paleomagnetic ages and paleoenvironmental proxy indexes of the first drill core wedp01 from the central tengger desert paleomagnetism measurements reveal that the core spans from 3 55 ma to present consistent with the electron spin resonance esr dating results the strata of the central desert consist of alluvial fluvial deposits lacustrine fluvial deposits mixed with dust and eolian sand from bottom to top sedimentary analysis reveals that continuous eolian sand started by 0 9 ma marking the initial formation of the tengger desert and the domination of eolian sand in the strata with similar characters of the modern desert appeared by 0 68 ma indicating expansion of the tengger desert the proximal deserts formation and simultaneous increase of dust accumulation in the clp and the north pacific ocean in mid pleistocene demonstrate the role of proximal deserts for the dust loading of northern china and even northern hemisphere our analysis suggests the uplift of tibetan plateau in the mid pleistocene probably played the main role for this drying event and desert formation while global cooling may strength the arid environment of the proximal deserts

an early unroofing in northeastern tibet constraints from 40ar 39ar thermochronology on granitoids from the eastern kunlun range qianghai nw china abstract in order to better constrain the mechanisms accommodating the india asia collision along the whole kunlun range northern tibet which is essential to better understand the evolution of the entire deformations area a 40 ar 39 ar thermochronological study has been carried out on a suite of granitoids collected in the vicinity of golmud eastern kunlun range biotite and k feldspar have been analysed and the cooling histories of the latter have been modelled the ranges of 40 ar 39 ar data bt 128 257 ma kf 102 228 ma are similar to previous rb sr and k ar data indicating both a middle paleozoic unit and a mesozoic unit including a triassic series and a jurassic cretaceous series this suggests that the two geological units previously reported in the western kunlun are also present in the eastern part of the range suggesting that eastern and western kunlun ranges might have been left laterally offset by as much as 500 km along a strike slip fault presently parallel to the altyn tagh fault the cooling histories based upon k feldspar modelling show that samples from the southern part of the range recorded an important cooling event 9 15 myr around 30 ma which is thought to reflect an increasing rate of denudation related to the tectonic activity in this area minimum denudation rates of 0 2 0 3 km ma have been estimated in contrast samples from the northern part of the range did not record any variation in their cooling history this heterogeneous denudation across the range is thought to be related to ramp stacking and normal faulting with associated uplift mainly affecting the southern part of the range suggesting that the eastern kunlun underwent an important crustal thickening period 30 ma ago this crustal thickening event is suggested to be related to the motion along the great asian strike slip faults in a way which remains problematic but possibly associated to the cenozoic propagation of the altyn tagh fault finally unroofing in the eastern kunlun range appears to predate that in the western kunlun range where it is suggested to have started around 20 ma ago this diachronous denudation could be related to a higher denudation rate in western kunlun range and it is thus highly probable that the important unroofing event outlined around 20 ma ago in the western kunlun has also affected the eastern part of the range even though the signature is not available at the moment

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

mesozoic and cenozoic tectonics of the northern edge of the tibetan plateau fission track constraints abstract fission track analysis on zircons and apatites yields new information about the timing of deformation of the northern tibetan plateau ages on zircons ranging from 221 22 to 96 4 ma are indicative of a general late triassic early jurassic cooling probably driven by the collision between the qiantang and kunlun blocks mid jurassic slow cooling is recorded also in the apatites in regions not affected by later cenozoic deformation this jurassic denudation was followed by a period of sedimentation during the cretaceous except along the altyn tagh fault atf zone and in some restricted areas of the western and eastern qilian shan this long and relatively quiet period ended at about 40 10 ma along the major altyn tagh and kunlun strike slip fault zones which were activated by the india asia collision this first movement along lithospheric faults resulted in the eastward extrusion of the tibet plateau which was followed in late oligocene miocene times by a major compression event initiating the formation of the high relief of north tibet a final compressional event took place at 9 5 ma and is well correlated with high sedimentation rates in the basins of this region this compression induced continental subduction in the kunlun ranges the altun shan belt and possibly the qilian shan belt

intensified deep pacific inflow and ventilation in pleistocene glacial times the production of cold deep waters in the southern ocean is an important factor in the earth s heat budget1 the supply of deep water to the pacific ocean is presently dominated by a single source the deep western boundary current east of new zealand here we use sediment records deposited under the influence of this deep western boundary current to reconstruct deep water properties and speed changes during the pleistocene epoch in physical and isotope proxies we find evidence for intensified deep pacific ocean inflow and ventilation during the glacial periods of the past 1 2 million years the changes in throughflow may be directly related to an increased production of antarctic bottom water during glacial times possible causes for such an increased bottom water production include increasing wind strengths in the southern ocean or an increase in annual sea ice formation leaving dense water after brine rejection and thereby enhancing deep convection we infer also that the global thermohaline circulation was perturbed significantly during the mid pleistocene climate transition between 0 86 and 0 45 million years ago

late cenozoic tectonic evolution of the southern chinese tian shan structural sedimentological magnetostratigraphic and 40ar 39ar thermochronological investigations were conducted in the southern chinese tian shan on the basis of our own mapping and earlier investigations in the area the late cenozoic southern tian shan thrust belt may be divided into four segments based on their style of deformation from west to east they are 1 kashi aksu imbricate thrust system 2 the baicheng kuche fold and thrust system 3 the korla right slip transfer system and 4 the lop nor thrust system the westernmost kashi aksu system is characterized by the occurrence of evenly spaced 12 15 km imbricate thrusts the baicheng kuche and korla systems are expressed by a major north dipping thrust the kuche thrust that changes its strike eastward to become a nw striking oblique thrust ramp the korla transfer zone the lop nor system in the eastern most part of the southern chinese tian shan consists of widely spaced thrusts all involved with basement rocks geologic mapping and cross section construction suggest that at least 20 40 km of crustal shortening with a horizontal shortening strain of 20 30 has occurred in the southern chinese tian shan during the late cenozoic these estimates are minimum because of both conservative extrapolation of the thrust geometries and partial coverage of the thrust belt by the cross sections the timing of initial thrusting is best constrained in the kuche basin where crustal shortening may have occurred at 21 24 ma the time of a major facies transition between lacustrine and braided fluvial sequences constrained in general by biostratigraphy and in detail by magnetostratigraphy this estimate represents only a minimum age as development of thrusts in the southern chinese tian shan may have propagated southward toward the foreland thus the sedimentary record only represents the southernmost and therefore youngest phase of thrusting if our estimate of timing for the thrust initiation 21 24 ma is correct using the estimated magnitude of shortening 20 40 km and shortening strain 20 30 the averaged rates of late cenozoic horizontal slip and shortening strain are 1 1 9 mm yr 1 and 2 9 4 5 10 16 s 1 respectively our reconnaissance 40ar 39ar thermochronological analysis in conjunction with earlier published results of apatite fission track analysis by other workers in the chinese tian shan suggests that the magnitude of cenozoic denudation is no more than 10 km most likely less than 5 km we demonstrate via a simple airy isostasy model that when the thermal effect on changes in surface elevation is negligible determination of the spatial distribution and temporal variation of both horizontal shortening strain and denudation becomes a key to reconstructing the elevation history of the tian shan using this simple model the loosely constrained magnitude of crustal shortening strain and denudation in the southern chinese tian shan implies that it may have been elevated 1 0 2 0 km since the onset of cenozoic thrusting

paleoclimatic record from the clay mineralogy of quaternary sediments of drill core dwj from jiudong subbasin western hexi corridor nw china the thick sedimentary deposits of the jiudong subbasin in the western hexi corridor of nw china can potentially provide important records of climate change in arid and semiarid areas subject to the interaction of the east asian summer monsoon easm and the westerlies here we present the results of a study of the clay mineralogy of the sediments of drill core dwj from the jiudong subbasin the clay minerals consist mainly of illite followed by chlorite kaolinite and smectite the clay mineral assemblages are used to define four paleoclimatic stages since 1 8 ma 1 during 1 8 1 2 ma the climate was relatively cold and arid 2 during 1 2 0 9 ma it was relatively warm and wet with strongly seasonal precipitation 3 during 0 9 0 3 ma there was a long term trend of cooling and drying and 4 during 0 3 0 1 ma the climate was warmer and wetter than during the previous period with strongly seasonal precipitation the paleoclimatic record of the jiudong subbasin since 1 8 ma is consistent with records from the tengger desert and typical monsoonal areas this suggests that the easm penetrated into the central regions of the north qilian shan and zhangye jiudong subbasin during 1 2 0 9 and 0 3 0 1 ma

early pleistocene uplift of the northeastern tibetan plateau evidence from the dunhuang basin nw china abstract the cenozoic uplift of the tibetan plateau plays an important role in global climate change basin mountain geomorphology formation and desertification in western china as an important component the early pleistocene uplift process and its influence on the northeastern tibetan plateau has been controversial for many years quaternary synorogenic sediments within the dunhuang basin on the northeastern tibetan plateau record the details of plateau uplift detailed grain size analysis rock magnetic properties mudstone 36cl dating and 40ar 39ar detrital mica dating were conducted on the quaternary alluvial fluvial lacustrine aeolian sediments of the dunhuang basin the aksay section in the southern dunhuang basin is dominated by conglomerate sandstone siltstone and mudstone detrital mica 40ar 39ar ages show major age populations of 200 160 ma 400 200 ma and 510 430 ma from the northeastern altyn mountains the results of 36cl ages and rock magnetic properties show that the altyn mountains rapidly uplifted at 1 16 ma from 1 16 to 0 80 ma the sedimentary environment was stable with two small scale uplift pulses at ca 1 03 ma and 0 98 ma after 0 80 ma the climate became arid and the kumtag desert formed in the dunhuang basin these multistage uplifts are also widely found in the northeastern tibetan plateau the early pleistocene uplift of the altyn mountains corresponding to the kunhuang movement resulted in the northeastern margin of the tibetan plateau reaching its present height and climate changeing towards drought in this region

magnetic proxy for the deep pacific western boundary current variability across the mid pleistocene climate transition the deep western boundary current dwbc inflow to the sw pacific is one of the largest transporting 40 of the total input of deep water to the world s oceans here we use a sedimentary record from the giant piston core md97 2114 collected on the northern flank of the chatham rise located at 1935 m water depth east of new zealand to investigate dwbc variability during the pleistocene epoch when the period of glacial cycles changed progressively from a 41 kyr to 100 kyr rhythm magnetic grain size may be directly related to orbitally forced fluctuations in the strength of the upper circumpolar deep water ucdw through its interaction with terrigenous sediments supplied from the south and west the long term trends in magnetic properties are characterized by two main perturbations centered at 870 ka marine isotope stage mis 22 450 ka mis 12 which is broadly consistent with the inferred perturbation during the mid pleistocene climate transition based on sedimentological paleocurrent reconstruction from ocean drilling program site 1123 located at 3290 m water depth in the main core of the dwbc flow on the north chatham drift this similarity suggests that both the upper and middle cdw are modulated by similar processes and fluctuations of antarctic bottom water production could be directly responsible for this deep pacific ocean inflow variability over the past 1 2 ma

miocene cooling in the northern qilian shan northeastern margin of the tibetan plateau revealed by apatite fission track and vitrinite reflectance analysis apatite fission track and vitrinite reflectance data from phanerozoic rocks of the northern qilian shan and jiuxi basin at the northeastern margin of the tibetan plateau show a complex thermal history with multiple paleothermal events peak paleotemperatures reached in the middle cretaceous suggest that hydrocarbon generation occurred in the basin at that time paleozoic mesozoic samples show evidence of a middle tertiary cooling episode between 20 and 10 ma this thermal fingerprint is significant because stratigraphic evidence for miocene exhumation is overwhelmed by spectacular pliocene pleistocene deformation and erosion we interpret the miocene cooling as recording initial exhumation of the northern qilian shan earlier than other models have proposed i e after 6 5 ma miocene cooling is broadly coincident with cenozoic uplift and exhumation recorded elsewhere in the tibetan tarim region

two episodes of volcanism in the wudalianchi volcanic belt ne china evidence for tectonic controls on volcanic activities abstract the nnw striking wudalianchi cenozoic volcanic belt wvb in ne china is mainly composed of volcanoes in menlu river area keluo wudalianchi and erkeshan k ar radiometric dating suggests two episodes of volcanism in the wvb specifically the pliocene to early pleistocene volcanism is distributed only in the northern part of wvb whereas middle pleistocene to holocene volcanism occurred over the entire wvb geomorphological analyses further delineate four northeast striking linear alignments of cones in the wudalianchi and keluo volcanic fields probably related to magma feeding fractures with en echelon arrangement no age progression is observed along these alignments we propose that a nnw trending rift may have controlled the eruption from pliocene to early pleistocene and a dextral transpression stress field may have influenced the volcanism from middle pleistocene to holocene we suggest that the pliocene and early pleistocene volcanism is associated with far effect of the india eurasia collision while the middle pleistocene to holocene volcanism in wvb may have resulted from interaction between the india eurasia collision and the subduction of the pacific plate

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

magnetostratigraphy of sediments from the yumu shan hexi corridor and its implications regarding the late cenozoic uplift of the ne tibetan plateau abstract the yumu shan located on the northernmost margin of the north qilian shan contributes key information for deciphering the deformation and uplift of the ne tibetan plateau this paper presents magnetostratigraphic results from late cenozoic sediments in the yumu section of the northwestern yumu shan the upper shulehe fm yumen conglomerates fm and jiuquan gravels fm were deposited before 5 23 ma during the periods 3 58 to perhaps 1 77 ma and after 0 8 ma respectively four significant tectonic episodes occurred at 5 89 ma 3 58 ma during 2 88 2 58 ma and 0 9 0 8 ma based on sedimentation magnetic susceptibility and angular unconformities being synchronous with tectonic activity throughout the ne tibetan plateau these tectonic ages do not support the northward growth model for the ne tibetan plateau during the late cenozoic

tibetan uplift prior to the eocene oligocene climate transition evidence from pollen analysis of the xining basin uplift of the tibetan plateau and the himalayas since the onset of the indo asia collision is held responsible for asian aridifi cation and monsoon intensifi cation but may also have gradually cooled global climate leading to the 34 ma eocene oligocene transition to unravel the interplay between tibetan uplift and global climate proxy records of asian paleoenvironments constrained by accurate age models are needed for the paleogene period here we report the 38 ma appearance of high altitude vegetation recovered from palynological assemblages in precisely dated lacustrine sediments from the xining basin of the northeastern tibetan plateau region this result confi rms previous evidence for important regional uplift in the central and northern tibetan plateau regions during the early stage of the indo asia collision this is consistent with the idea that the associated increase in rock weathering and erosion contributed to lowering of atmospheric co 2 leading to the eocene oligocene transition

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

geology of the haiyuan fault zone ningxia hui autonomous region china and its relation to the evolution of the northeastern margin of the tibetan plateau the haiyuan area located along the northeastern margin of the tibetan plateau in north central china provides a laboratory for studying how the plateau has grown in late cenozoic time rocks in the area range from pre silurian precambrian to recent the pre silurian and cenozoic rocks form the most extensive outcrops the pre silurian rocks consist of amphibolite and greenschist grade metasedimentary and metaigneous rocks unconformably overlain by silurian and devonian red beds all of these rocks are intruded by granodiorite of unknown age cenozoic rocks consist of 2 6 3 0 km of eocene to miocene red beds that were deposited over an extensive area in this part of china pliocene conglomerate contains clasts from all older formations and is interpreted to have been derived from highlands developed during the beginning of cenozoic deformation in the haiyuan area except for the widespread loess deposits quaternary rocks reflect deposition in local tectonic environments the oldest cenozoic structures in the haiyuan area are folds and small thrust faults that generally strike n30 45 w and involve mostly pre quaternary rocks these structures and all the quaternary rocks are cut by the haiyuan left lateral strike slip left slip fault zone that generally trends n60 65 w and is nearly vertical at the western end of the mapped area a fault zone which strikes n75 90 w forms a left stepping transfer zone that connects with another segment of the haiyuan fault zone which continues n60 65 w west into gansu province a small basin the salt lake basin is marked by active faults in the area of the transfer zone and is interpreted as a pull apart basin along the left slip haiyuan fault zone at its eastern end the haiyuan fault zone has an irregular surface trace east of luzigou an active fault striking n35 45 w branches to the south this southern branch appears to be a younger fault and now accommodates most of the left slip deformation that formerly occurred on the easternmost part of the haiyuan fault zone this younger fault connects through a left stepping transfer zone to a parallel fault the xiaokou fault that can be traced into the liupan shan about 60 km to the southeast the laohuyaoxian basin is interpreted as a very young pull apart basin in the area of the transfer zone matching different geological features across the haiyuan fault zone yields a total left slip offset of between 10 5 and 15 5 km and the best constrained offsets yield 12 9 14 8 km if left slip began near the end of the pliocene time or earliest pleistocene time it indicates an average slip rate between 5 and 10 mm yr progressively smaller offsets can be determined on progressively younger geological features but dates for these younger features are too imprecise to constrain slip rates through time surface ruptures that formed during the 1920 haiyuan earthquake m 8 7 show mostly left slip displacement with magnitudes of more than 10 m in some places active faulting in the region suggests the tibetan plateau may be extending to the northeast in time in the haiyuan area deformation probably began in pliocene time compared with a likely earlier initiation to the southwest thus deformation began about 40 45 m y after collision between india and asia formation of the low ranges to the northeast of the haiyuan area however may have developed at different times and deformation may not have propagated regularly to the northeast a total displacement of 10 5 15 5 km on the haiyuan fault zone indicates that this fault zone does not accommodate large scale eastward lateral transfer of continental fragments in the northern tibetan plateau

mid pleistocene extinction of deep sea foraminifera in the north atlantic gateway odp sites 980 and 982 abstract the pulsed decline and eventual extinction of 51 species of elongate cylindrical deep sea benthic foraminifera stilostomellidae pleurostomellidae and some nodosariidae occurred at intermediate water depths 1145 2168 m sites 980 and 982 in the northern north atlantic during the mid pleistocene transition mpt 1 2 0 6 ma in the early pleistocene prior to their disappearance these species comprised up to 20 of the total abundance of the benthic foraminiferal assemblage at 2168 m but up to only 2 at 1145 m the mpt extinction of 51 species represents 20 of the total benthic foraminiferal diversity at bathyal depths in the north atlantic excluding the myriad of small unilocular forms the extinction rate during the mpt was approximately 10 species per 0 1 myr being one or two orders of magnitude greater than normal background turnover rates of deep sea benthic foraminifera comparison of the precise timings of declines and disappearances highest occurrences of each species shows that they were often diachronous between the two depths the last of these species to disappear in the north atlantic was pleurostomella alternans at 0 679 and 0 694 ma in sites 980 and 982 respectively which is in good agreement with the previously documented global stilostomella extinction datum within the period 0 7 0 58 ma comparison with similar studies in intermediate depth waters in the southwest pacific gateway indicates that 61 of the extinct species were common to both regions and that although the pattern of pulsed decline was similar the precise order and timing of the extinction of individual species were mostly different on opposite sides of the world previous studies have indicated that this extinct group of elongate cylindrical foraminifera lived infaunally and had their greatest abundances in poorly ventilated lower oxygen environments this is supported by our study where there is a strong positive correlation r 0 8 between the flux of the extinction group and low oxygen high organic input species such as uvigerina bulimina and bolivina during the mpt suggesting a close relationship with lower oxygen levels and high food supply to the sea floor the absolute abundance flux and number of the extinction group of species show a progressive withdrawal pattern with major decreases occurring in cold periods with high 13c values this might be related to increasing chemical ventilation of glacial intermediate water

underlying causes for long term global ocean δ13c fluctuations over the last 1 20 myr pleistocene stable carbon isotope 13c records from surface and deep dwelling foraminifera in all major ocean basins show two distinct long term carbon isotope fluctuations since 1 00 ma the first started around 1 00 ma and was characterised by a 0 35 decrease in 13c values until 0 90 ma followed by an increase of 0 60 lasting until 0 50 ma the subsequent fluctuation started with a 0 40 decrease between 0 50 and 0 25 ma followed by an increase of 0 30 between 0 25 and 0 10 ma here we evaluate existing evidence and various hypotheses for these global pleistocene 13c fluctuations and present an interpretation where the fluctuations most likely resulted from concomitant changes in the burial fluxes of organic and inorganic carbon due to ventilation changes and or changes in the production and export ratio our model indicates that to satisfy the long term stability of the pleistocene lysocline the ratio between the amounts of change in the organic and inorganic carbon burial fluxes would have to be close to a 1 1 ratio as deviations from this ratio would lead to sizable variations in the depth of the lysocline it is then apparent that the mid pleistocene climate transition which apart from the glacial cycles represents the most fundamental change in the pleistocene climate was likely not associated with a fundamental change in atmospheric pco2 while recognising that high frequency glacial interglacial cycles are associated with relatively large 100 ppmv changes in pco2 our model scenario with burial changes close to a 1 1 ratio produces a maximum long term variability of only 20 ppmv over the fluctuation between 1 00 and 0 50 ma

tectonic and sedimentary evolution of basins in the northeast of qinghai tibet plateau and their implication for the northward growth of the plateau the northeast of the qinghai tibet plateau from the hoh xil basin to the hexi corridor basin demonstrates a basin ridge geomorphy that is the result of the long term uplift of the qinghai tibet plateau the geological evolution of the qinghai tibet plateau is recorded in its associated basins from the cenozoic sedimentary filling pattern in the hoh xil qaidam and jiuquan basins we find that the evolution of these basins is similar they began as strike slip basins evolved into foreland basins and then to intermontane basins foreland basins are the direct result of orogenic activity in the northeast of qinghai tibet plateau and can be documented to have formed over the following time periods 49 23 ma for the hoh xil foreland basin 46 2 45 ma for the qaidam foreland basin and 29 5 0 ma for the jiuquan foreland basin this northward migration in the timing of foreland basin development suggests that the northeastern part of tibet grew at least in part by accretion of cenozoic sedimentary basins to its northern margin

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

quaternary time scale for the ontong java plateau milankovitch template for ocean drilling program site 806 a 2 m y oxygen isotope record of globigerinoides sacculifer from the ontong java plateau based on cores from ocean drilling program leg 130 is dated by matching variations to an orbital template the procedure allows us to present the most complete quaternary record available for the western equatorial pacific the template generating algorithm describes a balance between growth and melting of ice following basic milankovitch theory ice growth is taken as constant while melting is taken to depend on summer insolation current ice mass and average past ice mass template settings must be changed once between 1 and 1 2 ma to reflect a major shift in climate template fits are strikingly good over much of the record and can be used to detect and fill gaps from core breaks and other disturbances one result of template dating is an exact age for the brunhes matuyama magnetic reversal boundary at 790 5 ka as well as several other precise dates 900 ka for the middle pleistocene climate shift 1070 1240 and 1450 ka for isotope stages 31 37 and 47 respectively sedi mentation rates fluctuate between 18 and 28 m m y a ca 400 ka cycle being the most prominent major anomalies arise within the transitional regime 1 2 to 1 ma the origin of the cycles is unknown we propose productivity variations in the western equatorial pacific

forcing of late cenozoic northern hemisphere climate by plateau uplift in southern asia and the american west geologic evidence indicates that net vertical uplift occurred on a large kilometer scale and at accelerating rates during the middle and late cenozoic in plateaus of southern asia and the american west based on this evidence general circulation model sensitivity tests were run to isolate the unique effects of plateau uplift on climate the experiments simulated significant climatic changes in many places some far from the uplifted regions the basic direction of most of these simulated responses to progressive uplift is borne out by changes found in the geologic record winter cooling of north america northern europe northern asia and the arctic ocean summer drying of the north american west coast the eurasian interior and the mediterranean winter drying of the north american northern plains and the interior of asia and changes over the north atlantic ocean conducive to increased formation of deep water the modeled changes result from increased orographic diversion of westerly winds from cyclonic and anticyclonic surface flow induced by summer heating and winter cooling of the uplifted plateaus and from the intensification of vertical circulation cells in the atmosphere caused by exchanges of mass between the summer heated and winter cooled plateaus and the mid latitude oceans disagreements between the geologic record and the model simulations in alaska and the southern rockies and plains may be related mainly to the lack of narrow mountain barriers in the model orography taken together the observed regional trends comprise much of the pattern of late cenozoic climatic deterioration in the northern hemisphere that culminated in the plio pleistocene ice ages the success of the uplift sensitivity experiment in simulating the correct pattern and sign of most of the observed regional climatic trends points to uplift as an important forcing function of late cenozoic climatic change in the northern hemisphere at time scales longer than orbital variations however the modest amplitude of the uplift induced cooling simulated at high latitudes indicates a probable need for additional climatic forcing

pliocene pleistocene magneto cyclostratigraphy of iodp site u1499 and implications for climate driven sedimentation in the northern south china sea abstract a high resolution astronomical tuned magnetostratigraphy was obtained from a continuous 333 m succession recovered at international ocean discovery program iodp hole u1499a in the north margin of the south china sea scs during joint legs 367 368 a total of 12 magnetic reversals are identified through the pliocene and pleistocene the cycle analysis of natural gamma ray ngr data shows an average suite of ca 33 m and 8 m wavelengths with lesser 1 5 m cycles which are consistent with the ratios of milankovitch orbital climate oscillations caused by long eccentricity 405 kyr short eccentricity 100 kyr and precession 20 kyr the astronomical tuned magnetostratigraphy correlates with nearly all features of the pliocene pleistocene geomagnetic polarity time scale there was a significant shift to 100 kyr dominated cyclicity at ca 1 3 ma which marks the onset of the mid pleistocene transition during which the influx of the clay component decreased a general enrichment in silt sand influx during the past 0 4 myr was punctuated by surges in coarser grained components lowest ngr during or at the end of each major global glacial event comparison to a high resolution sediment record spanning the pliocene pleistocene on the southern margin of the scs odp site 1143 indicates common intervals of changing rates of sediment accumulation in both regions there are relatively lower rates of sediment accumulation during the late zanclean mid pliocene ca 4 1 to 3 6 ma early gelasian ca 2 5 to 2 0 ma early calabrian ca 1 6 to 1 4 ma and the earliest middle pleistocene ca 0 6 ma the merger of magnetostratigraphy cyclostratigraphy and the ngr record to produce a high resolution profile of bulk sediment accumulation rates and relative clay to sand silt components is a powerful tool and climate proxy to reconstruct the general history of sediment input into the scs and its relationships to east asia monsoon and tectonic evolution

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

cenozoic multiple phase tectonic evolution of the northern tibetan plateau constraints from sedimentary records from qaidam basin hexi corridor and subei basin northwest china an integrated research of sedimentology stratigraphy and provenance analysis on eleven sedimentary sections from the qaidam basin hexi corridor and subei basin representing 36 km cenozoic strata provides a detailed record of the northern tibetan plateau growth since the early eocene sections are divided into three groups based on age geological similarities and geographical locations group one includes three early eocene late miocene sections from the northern qaidam basin group two contains four sections along the altyn tagh fault atf which preserve a complete stratigraphic record from the oligocene to late miocene group three contains the four youngest sections investigated from the northeastern qaidam basin and hexi corridor which preserve a record since the middle miocene to quaternary together the sections reveal a multiple phase tectonic history of the northern tibetan plateau the punctuated history can be divided into four phases 1 the eocene lulehe formation from the northern qaidam basin is interpreted as a synorogenic conglomerate deposited by high gradient depositional systems strong unimodal paleocurrent towards the southwest coarse lithology and distinct recognizable clast types constrain the sediment source within the north qaidam and south qilian terranes indicating activity on inferred thrust faults within the north qaidam and south qilian terranes in response to the initial india eurasia collision the activity on these thrust faults continued through the late eocene 2 the early oligocene conglomerate from group two formed in response to the sinistral transpression related to motion on the atf suggesting inception of substantial slip on the atf in the early oligocene in order to accommodate the continuing indentation of india into eurasia 3 oligocene early miocene fine grained fluvio lacustrine sediments from groups one and two formed as the result of development of internal drainage systems in the qaidam basin in response to the large amplitude slip motion on the atf paleocurrents collected from the oligocene early miocene strata of group one are northwest directed pointing towards the atf consistent with the pre existing subsurface data showing the shift of depocenter from along north qaidam and south qilian terranes toward the atf 4 all eleven sections preserve a post early miocene upward coarsening sequence consistent with the extensive crustal shortening and topographic growth across the northern tibetan plateau

benthic foraminiferal extinctions linked to late pliocene pleistocene deep sea circulation changes in the northern indian ocean odp sites 722 and 758 during the late pliocene middle pleistocene 63 species of elongate bathyal upper abyssal benthic foraminifera extinction group stilostomellidae pleurostomellidae some nodosariidae declined in abundance and finally disappeared in the northern indian ocean odp sites 722 758 as part of the global extinction of at least 88 related species at this time the detailed record of withdrawal of these species differs by depth and geography in the indian ocean in northwest indian ocean site 722 2045 m the extinction group of 54 species comprised 2 15 of the benthic foraminiferal fauna in the earliest pleistocene but declined dramatically during the onset of the mid pleistocene transition mpt at 1 2 1 1 ma with all but three species disappearing by the end of the mpt 0 6 ma in northeast indian ocean site 758 2925 m the extinction group of 44 species comprised 1 5 of the benthic foraminiferal fauna at 3 3 2 6 ma but declined in abundance and diversity in three steps at 2 5 1 7 and 1 2 ma with all but one species disappearing by the end of the mpt at both sites there are strong positive correlations between the accumulation rate of the extinction group and proxies indicating low oxygen conditions with a high organic carbon input in both sites there was a pulsed decline in extinction group abundance and species richness especially in glacial periods with some partial recoveries in interglacials we infer that the glacial declines at the deeper site 758 were a result of increased production of colder well ventilated antarctic bottom water aabw particularly in the late pliocene and during the mpt the extinction group at shallower water depths site 722 were not impacted by the deeper water mass changes until the onset of the mpt when cold well ventilated glacial north atlantic intermediate water gnaiw production increased and may have spread into the indian ocean increased chemical ventilation at various water depths since late pliocene particularly in glacial periods possibly in association with decreased or more fluctuating organic carbon flux might be responsible for the pulsed global decline and extinction of this rather specialised group of benthic foraminifera d 2005 elsevier b v all rights reserved

the mid pleistocene climate transition as documented in the deep south atlantic ocean initiation interim state and terminal event abstract the mid pleistocene transition mpt of the global climate system initiated by a shift towards much larger northern hemisphere ice shields at around 920 ka and ending with predominance of 100 kyr ice age cyclicity since about 640 ka is one of the fundamental enigmas in quaternary climate evolution climate proxy records not exclusively linked to global ice volume are necessary to advance understanding of the mpt here we present a high resolution pleistocene magnetic susceptibility time series of 12 sediment cores from the subtropical south atlantic essentially reflecting dissolution driven variations in carbonate accumulation controlled by changes in deep water circulation in addition to characteristics known from 18o records the data sets reveal three remarkable features intimately related to the mpt 1 an all pleistocene minimum of carbonate accumulation in the south atlantic at 920 ka 2 a mpt interim state of reduced carbonate deposition indicating that the mpt period may have been a discrete state of the pleistocene deep water circulation and climate system and 3 a terminal mpt event at around 540 530 ka documented in several peculiarities such as thick laminated layers of the giant diatom ethmodiscus rex

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

intact seismic scale platforms and ramps in the lower to middle jurassic of morocco implications for stratal anatomy and lithofacies partitioning the jurassic carbonate platforms of the central high atlas in morocco are well known for several high quality outcrops in the central high atlas there are two complementary locations that offer critical lessons for our understanding of jurassic carbonate system evolution in extensional basins a lower jurassic high relief carbonate platform with steep slopes that developed on the footwall of a rotating fault block in an active half graben djebel bou dahar dbd and an upper lower to middle jurassic low angle prograding carbonate ramp rich in ooids amellago ramp ar the dbd and ar outcrops provide superbly exposed structurally intact and fully accessible platform to basin transects they provide valuable analogs for depositional geometries at reservoir and seismic scales that are highly relevant for hydrocarbon exploration and production the dbd serves as an analog for isolated carbonate platforms developed in rift basins particularly synrift carbonate platforms with a coral calcareous sponge and microbial boundstone facies belt in the upper slope and margin the ar provides one of the rare examples whereby a large scale oolitic ramp can be examined in great detail providing an analog for a range of oolitic reservoirs mostly mesozoic

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

the himalaya bengal fan denudation accumulation system during the past 20 ma mass balances for both denudation in the himalayas and sediment accumulation in the subhimalayan basins including the bengal deep sea fan but excluding the indus fan yield 7 1 106 km3 and 7 4 106 km3 s 20 rock of 2 75 g cm3 density respectively for the past 20 million years coarsening and increased sediment accumulation rates in the foreland basin and in the bengal foredeep indicate accentuated tectonic activity and unroofing in the himalayas since that time the sediment volume includes 1 106 km3 of neogene bengal fan sediment that was lost via the nicobar fan to the sunda accretionary wedge in addition the indian peninsular rivers contributed about c 0 6 106 km3 of solid load to the basins average denudation during the past 20 m y as derived from geothermobarometric data and restored cross sections occurred most rapidly along the high himalayan crystalline chain vertical unroofing c 1000 m m y northward lateral retreat of southern himalayan slope exposed to monsoonal rain

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

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

late quaternary slip rates and holocene paleoearthquakes of the eastern yumu shan fault northeast tibet implications for kinematic mechanism and seismic hazard abstract the yumu shan yms fault zone at the northeastern margin of the tibetan plateau is characterized by actively growing fault related folds and northeast vergent thrusts or buried faults this fault zone is expressed by an arc shaped fault line and can be divided into two segments the northern and eastern yms faults numerous studies indicated that the northern yms fault is marked by reverse faulting with a left lateral component and has undertaken two surface rupturing events in the holocene but previous studies on the eastern yms fault were conducted in the 1990s and the limitations of dating and survey techniques led to a large uncertainty in fault slip rates and paleoseismological results in addition the kinematic mechanism of the arc shaped yms fault zone remains unknown in this study combining with the interpretation of high resolution satellite imagery real time kinematic rtk gps survey optically stimulated luminescence osl and accelerator mass spectrometry ams radiocarbon dating of deformed landforms and trenching we study slip rates and paleoseismology along the eastern yms fault our results show that its late quaternary vertical and horizontal slip rates are 0 3 0 4 mm yr and 1 1 0 1 mm yr respectively at its northwest tip the fault consists of several sub parallel branches and becomes dominantly reverse or thrusting with a vertical rate of 1 1 mm yr trenching data indicate that two events ruptured the eastern yms fault occurring at 7 37 5 24 ka and 5 17 4 01 ka respectively the eastern yms fault may behave synchronously or interact with the northern yms fault we propose that the arcuate structure under the perpendicular compression to the arch apex might illustrate the kinematic mechanism of the yms fault zone

northeastward growth and uplift of the tibetan plateau magnetostratigraphic insights from the guide basin 1 most of the evidence for the uplift of the tibetan plateau comes from its southern and central parts although the northern rim has been less studied it may greatly contribute to the understanding of the mechanism and timing of the uplift recent studies on the northeastern part of the plateau suggest that the uplift can largely be explained by cenozoic thrusting and folding linked to the movement of the altyn tagh and kunlun faults and that diffuse shortening might be a realistic way to explain the thickening of the continental interior nevertheless the age of sediments that record the tectonic processes is poorly known the terrigenous formations in the guide gonghe basin ne tibet show several phases of deformation and include thick deposits of conglomerates interbedded with sandstones and siltstones that are thought to be the result of an increased sediment flux dating of these gravel deposits with magnetostratigraphic and faunal studies has permitted the precise timing of the basin infilling and its tectonic evolution to be established our results indicate that the onset of conglomerate accumulation occurs in the pliocene an observation that is in agreement with those of the linxia basin just east of the plateau if the high sedimentation rates 22 cm kyr in the guide basin are mostly due to tectonism then significant uplift occurred as late as pliocene

active thrusting and folding in the qilian shan and decoupling between upper crust and mantle in northeastern tibet fieldwork south of the city of gaotai gansu province china shows that active shortening of surface sediments in the foothills of the yumu shan a large fore mountain of the qilian shan at the northeastern edge of tibet involves both overthrusting and flexural slip folding north of this mountain we found and mapped a prominent north facing thrust scarp that offsets a holocene fan sloping gently 3 4 to the north part of this scarp appears to be related to the m 7 5 180 a d earthquake that may have led to the demise of the han dynasty city of luo tuo chen in the hexi corridor a set of 10 100 150 m long profiles measured across this scarp 3 2 m high on the average can be made to fit the diffusion degraded morphology of a surface break related to the 180 a d event using a value of about 3 3 m 2 10 3 yr for the mass diffusivity of fanglomerates in this part of gansu province smaller mountain facing scarps on a terrace capped foothill result from bedding slip concurrent with active folding of underlying steeply northdipping plioquaternary sandstone and conglomerate beds holocene uplift rates along the yumu shan which is only one of the qilian shan ranges are estimated to be between 0 4 and 1 9 mm yr which implies that much of the mountain formed in the quaternary the periclinal structure of the plioquaternary envelope under which the paleozoic core of the yumu shan plunges towards the west suggests that the whole 3200 m high mountain is a basement ramp anticline mountains striking parallel to the yumu shan with similar structure and comparable or greater sizes north and south of the hexi corridor probably also correspond to recent crustal ramp anticlines this implies that the wide mountainous upper crustal wedge making the northeastern edge of the tibet qinghai plateau is detached from the underlying lower crust and upper mantle

aeolian origin of the red earth in southeast china a clay like deposit known as red earth is widely distributed over the terraces and high lands of the yangtze river valley in southeast china its typical pedo stratigraphical features have attracted the interest of pedologists and geologists for many years although its origin is still debated here we report an analyses of the grain size distributions rare earth element bee patterns and upper continental crust ucc normalised major elemental composition of the red earth and compare them with those of the loess and other aeolian deposits in northern china the results show that the red earth in southeast china has two or three end member grain size distributions similar to the sedimentary characteristics and geochemical composition of aeolian deposits found in northern china together with other evidence from field observations these results suggest that the red earth is probably of acolian origin on the basis of these data we suggest that thick aeolian dusts were also deposited in the wet subtropics and that the effect of the winter monsoonal winds upon the dust transport in eastern china was more important than previously believed copyright c 2002 john wiley sons ltd

magnetostratigraphy of drill core sg 1b in the western qaidam basin ne tibetan plateau and tectonic implications the qaidam basin is an ideal archive to study long term climate and erosion histories at the ne tibetan plateau we present a magnetostratigraphic study of the 723 m deep drill core sg 1b of lacustrine sediments at the jianshan anticline in the western qaidam basin the polarity sequence shows 18 normal and 19 reverse polarity zones which can be readily correlated with chrons c1n c3br of the geomagnetic polarity time scale 2004 gpts 2004 dating the core at about 7 3 1 6 ma the resulting mean sediment accumulation rate sar between polarity boundaries ranges from 6 5 to 30 4 cm ka 1 high sars occur within the intervals of 7 3 6 0 5 2 4 2 and 3 6 2 6 ma indicating three episodic phases of higher erosion from the derived variation of sars and previous results we conclude that growth strata at the jianshan anticline started to develop at similar to 1 6 ma by limb rotation all this we relate to pulse tectonic uplift of the ne tibetan plateau and fault propagation folding in the qaidam basin

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

late cenozoic increase in accumulation rates of terrestrial sediment how might climate change have affected erosion rates abstract accumulation rates of terrestrial sediment have increased in the past few million years both on and adjacent to continents although not everywhere apparently erosion has increased in elevated terrain regardless of when last tectonically active or what the present day climate in many regions sediment coarsened abruptly in late pliocene time sparser data suggest increased sedimentation rates at 15 ma approximately when oxygen isotopes in benthic foraminifera imply high latitude cooling if climate change effected accelerated erosion understanding how it did so remains the challenge some obvious candidates such as lowered sea level leading to erosion of continental shelves or increased glaciation account for increased sedimentation in some but not all areas perhaps stable climates that varied slowly allowed geomorphic processes to maintain a state of equilibrium with little erosion until 3 4 ma when large oscillations in climate with periods of 20 000 40 000 years developed and de

a millennial scale planktonic foraminifer record of the mid pleistocene climate transition from the northern south china sea a high resolution record similar to 1100 yr of planktonic foraminifers from odp site 1144 in the northern south china sea reveals rapid and strongly variable climatic changes during the mid pleistocene transition period the abundance of warm water species decreased from an average of 60 in marine isotope stage mis 29 to 40 at mis 22 followed by a steady increase in cool water species toward younger intervals many deep dwelling warm water species decreased to a minimum during mis 22 and remained extremely rare or even became absent in younger glacial intervals indicating stepwise sea surface cooling in the region estimated ssts show large fluctuations mostly at glacial interglacial transitions a maximum winter temperature difference of 11 degrees c 17 28 degrees c across mis 23 22 boundary likely corresponded to a major growth of boreal ice sheets across the mpt center at 0 9 myr coupled with a strengthened winter monsoon over east asia the mpt event not only led to a better correlation between changes in species abundances and glacial interglacial cycles but also a more constrained thermocline that shoaled considerably during subsequent glacial periods the oxygen isotope record and the abundance of shallow water species display power spectra closely in pace with the 41 000 and 100 000 years cyclicities a lower coherence over these cyclicities between deep water dwelling species and the planktonic delta 18 o a shoaled thermocline and more pisitive glacial delta 18 o together suggest disturbances of surface and subsurface waters by intensified winter monsoons over the last 1 1 0 5 myr in the south china sea c 2005 elsevier b v all rights reserved

formation and evolution of the badain jaran desert north china as revealed by a drill core from the desert centre and by geological survey abstract the deserts in north china are regarded as direct records of the process of inland asian aridification amongst these deserts those proximal to the chinese loess plateau clp are especially important because of their role as sediment source areas in order to investigate the formation history of the badain jaran desert the largest desert proximal to the clp a 310 m long drill core was obtained from the desert centre which reached the underlying basement rock the lithology of the core consists of an upper layer of aeolian sand with three intercalated layers of lacustrine sediments overlying alluvial fluvial deposits which are developed unconformably over red coloured basement rock a geological survey indicates that the lower red coloured basement rock is of late cretaceous age and is cut by a mesozoic erosion surface widely developed over the badain jaran area on the basis of optically stimulated luminescence and electron spin resonance dating and stratigraphic correlation a preliminary chronological framework was established which was improved by tuning the aeolian sand proportion of the drill core to earth orbital obliquity and precession this final chronology suggests that 1 the basal age of the desert strata is at least 1100 ka corresponding to the formation of the badain jaran desert and 2 that the formation of the erosion surface terminated and the surface had begun to subside by at least 1200 ka the formation of the desert can be summarized as follows the alluvial fluvial fan formed by the heihe river draining the qilian mountains provided sufficient sedimentary material to form the desert under an arid climate while the asian winter monsoon and the westerlies entrained the clastic sediments from the fan area which finally accumulated downwind more distant sediment transport was prevented by the intervening mountainous terrain these coupled processes were driven by tibetan plateau uplift and ongoing global climatic cooling after initial formation of the desert three humid phases occurred in mis 13 15 mis 5 and the holocene during which extensive lakes developed the sequential drying out of the lakes may reflect inter relationships between global climate and the intensity of the asian summer monsoon and the westerlies

oligo miocene magnetostratigraphy and rock magnetism of the xishuigou section subei gansu province western china and implications for shallow inclinations in central asia magnetostratigraphy of 222 remanent directions together with late oligocene to early miocene mammal and charophyte paleontology suggest that 2179 m of the xishuigou section subei gansu province china were deposited from 26 to 19 ma stratigraphic patterns of bulk susceptibility anisotropy of magnetic susceptibility parameters and natural and anhysteretic remanent magnetization intensities demonstrate that 1 faulting does not significantly affect the record 2 sediment deposition was relatively continuous 3 sediment source changed around 23 ma and 4 rapid uplift near subei occurred at 21 ma subei rotated 27 5 counterclockwise with respect to the 20 ma pole from the eurasian synthetic apparent polar wander path folding and rotation of the section took place after 19 ma the paleolatitude of subei is 14 less than at present and 19 3 less than predicted from the reference pole both rock magnetic and paleomagnetic data sets suggest that the unusually low paleolatitude is the result of synsedimentary inclination shallowing a phenomenon which has likely affected other paleomagnetic data from central asia

the mid pleistocene climate transition a deep sea carbon isotopic perspective five 13c records from the deep ocean extending back to 1 3 ma were examined in order to constrain changes in mean ocean carbon isotope composition and thermohaline circulation over the 41 to 100 ka climate transition these data show that significant perturbations in mean ocean carbon chemistry were associated with the mid pleistocene climate transition notable features of the last 1 3 myr are 1 a pronounced 0 3 decrease in mean ocean 13c between 0 9 and 1 0 myr followed by a return to pre 1 0 ma values by 400 ka b p which we propose was due to the onetime addition of isotopically depleted terrestrial carbon to the ocean possibly associated with an increase in global aridity and decrease in the size of the biosphere across the 41 to 100 ka transition 2 no change in the atlantic pacific a p 13c gradient over the last 1 3 myr suggesting no change in mean ocean nutrient content accompanied the addition of light carbon and 3 stronger vertical nutrient fractionation in the north atlantic in the middle pleistocene between sites 607 and 552 suggesting weaker north atlantic deep water formation at this time relative to the early and late pleistocene we also find evidence for a more pronounced deep recirculation gyre in the western north atlantic basin in the early brunhes as evidenced by aging of deep northern basin water site 607 relative to deep water in the equatorial atlantic site 664

evolution of the arid climate in high asia since 1 ma evidence from loess deposits on the surface and rims of the tibetan plateau the formation and development of the arid climate in high asia remain controversial this is largely because of the scarcity of continuous high resolution geological records from the asian interior region thick loess sequences deposited on the surface of the tibetan plateau and its rims provide great potential to reconstruct a high resolution history of the formation and evolution of high asia arid climate based on detailed investigations of the grain size and carbonate content of representative loess sequences in high asia a persistent drying of high asia occurred in the past 1 ma and two major rapid drying events occurred at about 0 9 0 8 ma and 0 5 ma persistent and rapid stepwise uplifts of the tibetan plateau since the mid pleistocene might play a dominant role in the drying of high asia although the mid pleistocene global cooling may partially contribute to the event

sensitivity of climate to late cenozoic uplift in southern asia and the american west numerical experiments experiments with general circulation models with no mountains half mountains and full modern mountains show the sensitivity of atmospheric circulation patterns to progressive amounts of uplift the experiments were motivated by geologic evidence for large kilometer scale uplift in the late cenozoic in southern asia and the american west particularly within the last 10 m y in january the amplitude of the mid latitude upper tropospheric planetary waves increased with uplift and the low level winds were progressively blocked or diverted around the topographic features in july the progressive uplift caused monsoonlike circulations to develop in the vicinity of the colorado and tibetan plateaus atmospheric heating rates midtroposphere vertical motion and upper tropospheric planetary wave amplitudes varied approximately linearly with progressive uplift these results suggest that geologically recent kilometer scale uplift may have had climatic consequences comparable in magnitude and pattern to those of earlier stages of uplift comparison of the simulated climatic effects of uplift with the geologic evidence for late cenozoic climatic change especially for the last 10 m y is given in accompanying papers

timing of the tianshan mountains uplift constrained by magnetostratigraphic analysis of molasse deposits abstract the tianshan mountains lie in the actively deforming part of the india asia collision zone the thrust faulting and folding of the neogene and quaternary sediments forming linear roughly east west anticlines at the northern and southern borders of the orogenic belts indicate crustal shortening and thickening in late cenozoic time detailed magnetostratigraphic studies of the molasse deposits of the folded neogene and quaternary strata in the northern edge of the tianshan mountains indicate that the onset of uplift occurred at 7 ma deposition of the thick conglomerates between 7 and 2 58 ma in the studied region was mainly in response to the tectonic uplift while the accumulation of the early pleistocene conglomerates xiyu formation was mostly controlled by both tectonics and climatic cooling our results indicate that the present high relief of the tianshan mountains is the result of two dominant phases of uplift occurring at about 7 2 58 ma and the early pleistocene

stratigraphic evidence for the uplift of the tibetan plateau between 1 1 and 0 9 myr ago uplift of the tibetan plateau is manifest not only in widespread denudation but also by an increased deposition rate of sediment near or far from the exhumed regions our results indicate that the mass accumulation rate mar of eolian dust increased between 1 1 and 0 9 myr ago we associate this increase in mar and median grain size with uplift of the tibetan plateau and its adjacent regions during this period this middle pleistocene uplift can also be evidenced by the age of volcanism in the marginal region the existence of thick conglomerate deposits surrounding the uplifted plateau and the increased sedimentation rate of lacustrine deposits in the qaidam basin northeastern tibetan plateau between 1 1 and 0 9 myr ago the correlation between the loess and marine records indicates that after 0 9 myr ago these two records correlate well this good correlation probably suggest that the middle pleistocene upheaval event not only brought the plateau into the cryosphere but also enhanced the coupling of regional scale chinese loess transportation and deposition to the global ice volume variations through its effects on glacial grinding rock denudation and east asian monsoonal circulation

exploring the structure of the mid pleistocene revolution with advanced methods of time series analysis the mid pleistocene climate transition is a complex global change leading to late pleistocene ice ages with increased mean ice volume and dominant 100 ka cycle a thorough understanding of this transition demands quantitative investigations in the time and frequency domains and in the stochastic domain three methods of time series analysis are presented which have been adapted for this purpose they are tested by means of predefined artificial time series and applied to benthic oxygen isotope d18o records which serve as ice volume indicator results are as follows a the time dependent mean shows an increase of 0 35 vs pdb from 942 to 892 ka b evolutionary spectral analysis reveals an abrupt in crease of 100 ka cycle amplitude at approximately 650 ka c probability density function exhibits a bifur cation behavior at approximately 725 ka these find ings point to a multiple transition from a more linear climate system to a strong nonlinear system the signif icant lead of the transition in mean in relation to the 100 ka amplitude change and bifurcation is left open for explanation

a fluvial record of fault propagation folding along the northern qilian shan front ne tibetan plateau abstract the kinematics of thrust fault is key to understand the deformation and uplift of mountain ranges along the northern front of the central qilian shan mountain range the ne tibet plateau a flight of terraces developed along the red sand river were deformed above a growing fault propagation fold via luminescence and 10be exposure dating abandonment ages of the terrace surfaces were determined to be 100 9 5 8 ka bp for t9 88 7 7 0 ka bp for t8 and 68 8 7 6 ka bp for t7 terrace profiles measured by differential gps across the monocline were used to constrain the recent fold deformation and the trishear model was applied to estimate the fault slip rate and thrust history we thus derived an average slip rate of 1 3 0 1 mm a for the heihekou hhk fault since 90 ka bp in addition our results imply that the onset of the hhk fault occurred at 0 8 1 4 ma indicating a recent northeastward propagation of the active thrust faulting of the north qilian shan fault nqf our results also indicate uniformly distributed slip along the western central and eastern segments of the north qilian shan due to the different thrust kinematics along the nqf the uplift rate is not uniformly distributed along the hanging wall of the thrust

rock magnetic and grain size evidence for intensified asian atmospheric circulation since 800 000 years b p related to tibetan uplift abstract paleomagnetic rock magnetic and grain size studies of a thick loess sequence in the west qin ling mountain range show that loess deposition there began about 800 ka the data reveal a progressively increasing coarse grain size fraction upwards into the holocene the averages of these coarse size fractions are higher than in the central loess plateau which was apparently farther from the source area and slightly lower than those of the western loess plateau and the eastern tibetan plateau which were therefore closer to the source area the coarsening and source area location suggest 1 that asian air circulation may have changed and intensified at about 800 ka resulting in dust deposition in west qin ling 2 that dust carrying winds were driven not only by the asian winter monsoon but included also the westerlies and a winter monsoon caused by the tibetan plateau high and 3 that intensification of all these air circulation systems continues to the present increased elevation of the tibetan plateau so that it reached into the cryosphere by about 800 ka and a subsequent persistent uplift of the plateau may have been the mechanisms to trigger a change and intensify the air circulation system moreover this circulation shift and intensification simultaneous with a shift in milankovitch periodicity may have contributed to large global climate changes such as the 15 increase in global ice volume at ca 800 ka

geochemical characteristics of lake clay drilled in well qz 4 its implication for geochemical response to climate change in the central tibetan plateau in the middle late pleistocene a colour sequence which is composed of a yellow subsequence in the lower unit and a grey subsequence in the upper unit is an important climate archive for the central tibetan plateau in the middle late pleistocene however little study has been done on it in well qz 4 this colour sequence is thicker than 116 m which is an important climate archive for the central tibetan plateau in the middle late pleistocene in this work the esr dating and geochemistry analysis have been carried out to provide a preliminary insight into the paleo climate change in the central tibetan plateau it can be concluded that the 23 56 ka 125 96 149 52 ka bp time interval which is marked by the angular unconformity surface at 272 48 m in depth proves that the deposition of this colour sequence is dominated by gonghe movement after this movement chemical weathering is reduced however the sedimentation rate is increased from 0 18 to 3 5 m ka in the central tibetan plateau the climate became colder and drier in the middle late pleistocene which is roughly consistent with global paleo climate change at that time all these changes are correlated with the change of elevation and atmospheric circulation in the tibetan plateau and its surrounding area which are driven by the tectonic uplift of gonghe movement the gonghe movement is likely a driving force for the short lived spike at about 120 ka

danghe area western gansu china biostratigraphy and implications for depositional history and tectonics of northern tibetan plateau the danghe area in western gansu province is at the focal point of interaction of the northeastern end of the left lateral altyn tagh fault and growing ramp thrusts of the danghe nanshan mountains along the northern rim of the qinghai tibetan plateau with a thick sequence of tertiary sediments and associated fossil records the danghe area is one of few places on the tibetan plateau that can offer integrated studies of its tectonic history depositional environment and biological records including vertebrate and plant fossils past studies however have not been able to capitalize on the paleontological data or were often misguided by an outdated notion of regional chronology incorrect age estimates in these studies often have profound effects on tectonic interpretations we present new stratigraphic and paleontologic evidence from the danghe area and demonstrate a new chronologic scheme that indicates a much younger age for the majority of the sediments we recognize three packages of sediments in the danghe area 1 oligocene paoniuquan new name formation basal predominantly fine grained dark purple mudstones and siltstones that include the classic yindirte fauna which forms the basis of the tabenbulukian mammal age 2 early miocene to early late miocene tiejianggou new name formation that contains a new platybelodont proboscidean in a coarsening upward sequence terminating in a massive conglomerate and 3 an unnamed late neogene formation that contains another coarsening upward sequence in light of our new stratigraphic framework we reinterpret a previously published magnetic column for the middle sequence in xishuigou as representing chrons c6n through c4ar corresponding to a span of about 20 9 3 ma much younger than has been realized so far this new chronological framework suggests a depositional history of the danghe nanshan that spans at least the early oligocene through late miocene to possibly pliocene early depositions during the oligocene through middle miocene are dominated by fine grained sediments indicating a distant source of sedimentation paleontological data suggest a relatively dry environment as is typical of northern china today by late miocene around 9 12 ma the danghe area began to receive coarse sediments and was much closer to the mountain front the new stratigraphic framework indicates an earlier onset of sedimentation than has generally been assumed but also suggests the presence of sediments much younger than many have realized c 2003 elsevier science b v all rights reserved

the mid pleistocene climate transition onset of 100 ka cycle lags ice volume build up by 280 ka the mid pleistocene climate transition mpt is the complex climatic change which brought the late pleistocene ice ages we explore the mpt in the time and frequency domains by new methods of time series analysis high resolution oxygen isotope records reveal that the ice volume related increase in 18o mean amplitude 0 29 0 05 1 transition midpoint 922 12 ka duration 40 9 ka significantly preceded the abrupt increase in the amplitude of the 100 ka cycle at 641 9 ka this finding can be quantitatively simulated using a simple ice bedrock model in which due to the additional ice the calving threshold is exceeded the simulated calving events prior to 650 ka are separated by 77 ka whereas after 650 ka they occur pseudo periodically with a mean period of nearly 100 ka the cause for the delay of the 100 ka calving cycle was not a slow bedrock relaxation rather the coincidental combination of insolation existing ice mass and bedrock depression