palaeomagnetism of late cretaceous sediments from southern tibet evidence for the consistent palaeolatitudes of the southern margin of eurasia prior to the collision with india abstract twenty sites were drilled in the late cretaceous shexing formation for palaeomagnetic studies in the lhasa terrane near the locality of maxiang 29 9 n 90 7 e the stepwise thermal demagnetizations successfully isolated high unblocking temperature characteristic directions the tilt corrected mean direction is d i 350 8 32 1 with 95 8 1 and n 20 sites corresponding to a paleopole at 75 0 n 306 7 e with a 95 6 8 positive fold tests indicate a primary origin for the characteristic remanence based on previous cretaceous data mainly from the takena formation and paleocene data from the linzizong volcanic rocks near the city of lhasa the latitude of the southern margin of asia is located at about 15 n and yields a stable position of the lhasa terrane during cretaceous and paleocene compared with expected paleomagnetic directions from the stable india and eurasia blocks the collision palaeolatitude further implies the total latitudinal convergence was accommodated by 1700 800 km 16 2 7 6 between southern tibet and stable eurasia and 1500 830 km 14 4 7 9 between southern tibet and stable india since the collision of india and eurasia a collision age between c 54 and 47 ma was determined using the results for the southern margin of eurasia according to our new data and the extent of greater india

anisotropy of magnetic susceptibility and paleomagnetic studies in relation to the tectonic evolution of the miocene pleistocene accretionary sequence in the boso and miura peninsulas central japan abstract anisotropy of magnetic susceptibility ams and paleomagnetic methods have been applied on the middle miocene pleistocene sedimentary sequence in the boso and miura peninsulas of central japan in order to identify the invisible regional deformation sense as well as the intensity of deformation of sediments the southern sequences of the two peninsulas were subjected to syn sedimentary deformation of folding and faulting generated in compressional tectonics a previous result of the ams experiment on the sequences shows a development of a strong magnetic lineation thus it is conceivable that the lineation had to be generated during the process of deformation and in a direction perpendicular to the shortening however the orientation of the magnetic lineations is inconsistent among the different tectonic domains in the southern sequence the paleomagnetic declination in each domain reveals a clockwise rotation in various degrees reconstructed directions of the magnetic lineations show a consistent pattern in the east west direction suggesting that the sedimentary sequence was subjected to a north southward compression in contrast the compressive direction of the sediment cover on the pliocene pleistocene sequence reveals a northwest direction our results suggest that the philippine sea plate had been subducting northward during the middle miocene pliocene and changed its direction during the pliocene

inclination variation in the late jurassic to eocene red beds from southeast asia lithological to locality scale approach summary shallowpalaeomagneticinclinationshavebeenfrequentlyreportedfromtheredbedsofcentral and southeast asia to trace the origin of this phenomenon inclination variation in southeast asia is examined on lithological to locality scale lithological aspect of this variation has been studied using the early cretaceous bailong and cangxi formations of the bazhong area 32 1 n 106 7 e the northern sichuan basin samples from 36 sites consisting 18 pairs of successive sandstones and mudstones layers were collected for this purpose from a synclinal structure stepwise thermal demagnetization of most samples revealed the presence of stable characteristic remanent magnetization which is generally unblocked by 680 c positive fold and reversal tests suggest a primary origin for this component yielding the early cretaceous palaeomagnetic direction of declination inclination 20 9 26 5 ks 37 2 95 4 4 n 30 10 pairs of sandstone and mudstone layers show almost identical inclinations isandstones 23 3 3 7 and imudstones 24 7 2 4 but 27 shallower than that expected from the eurasian apparent polar wander paths apwps indicating that no lithological variation in inclination has occurred location wise variation in inclination shallowing is examined through palaeomagnetic data from late jurassic to eocene red beds distributed around southeast asia based on these investigations no inclination shallowing is observed in the eastern part of the south china block scb whereas large degree of shallowing is observed in the sichuan and xining ninhe basins variation in inclination shallowing from one sedimentary basin to another could probably be caused by changes in the depositional environment the eastern part of the scb where no inclination shallowing have been observed is characterized by basin and range type tectono geological setting in contrast the foreland basins are bounded to the north by east west striking high altitude orogenic belt swift developmentofthesebasinsasaresultofflexuralsubsidenceisthemostlikelyreasonforinclination shallowing

optically stimulated luminescence osl dating of coastal aeolian sand accumulation in sanday orkney islands scotland optically stimulated luminescence osl dating of sand has been used to identify periods of enhanced aeolian activity at two coastal archaeological sites in orkney that coincide with periods of holocene climatic deterioration recorded elsewhere in both scotland and w europe areas of tofts ness sanday were settled from the neolithic abandoned in the late neolithic early bronze age reoccupied and permanently abandoned in the iron age sand layers above the neolithic soils have been osl dated to about 4000 bp correlating well with a period of increased aeolian activity elsewhere in w europe osl dating of aeolian sands above midden deposits and a bronze age burial at lopness on sanday suggest dune development by 3000 bp although both sites also contain sand that was deposited during the little ice age several possible mechanisms may have contributed to an increase in aeolian activity during the holocene that led to the abandonment of these sites although volcanic eruptions in iceland cannot be disc

what was the paleogene latitude of the lhasa terrane a reassessment of the geochronology and paleomagnetism of linzizong volcanic rocks linzhou basin tibet the paleogene latitude of the lhasa terrane southern tibet can constrain the age of the onset of the india asia collision estimates for this latitude however vary from 5 n to 30 n and thus here we reassess the geochronology and paleomagnetism of paleogene volcanic rocks from the linzizong group in the linzhou basin the lower and upper parts of the section previously yielded particularly conflicting ages and paleolatitudes we report consistent 40ar 39ar and u pb zircon dates of 52 ma for the upper linzizong and 40ar 39ar dates 51 ma from the lower linzizong are significantly younger than u pb zircon dates 64 63 ma suggesting that the lower linzizong was thermally and or chemically reset paleomagnetic results from 24 sites in lower linzizong confirm a low apparent paleolatitude of 5 n compared to the upper part 20 n and to underlying cretaceous strata 20 n detailed rock magnetic analyses end member modeling of magnetic components and petrography from the lower and upper linzizong indicate widespread secondary hematite in the lower linzizong whereas hematite is rare in upper linzizong volcanic rocks of the lower linzizong have been hydrothermally chemically remagnetized whereas the upper linzizong retains a primary remanence we suggest that remagnetization was induced by acquisition of chemical and thermoviscous remanent magnetizations such that the shallow inclinations are an artifact of a tilt correction applied to a secondary remanence in lower linzizong we estimate that the paleogene latitude of lhasa terrane was 20 4 n consistent with previous results suggesting that india asia collision likely took place by 52 ma at 20 n

new insights into the india asia collision process from cretaceous paleomagnetic and geochronologic results in the lhasa terrane abstract to further constrain the india asia collisional process a combined paleomagnetic and geochronologic study has been carried out on the upper cretaceous jingzhushan formation redbeds and the lower cretaceous dianzhong formation volcanic rocks dated at 121 117 ma from the cuoqin area in the central lhasa terrane stepwise thermal demagnetization successfully isolated reliable characteristic remanent magnetization chrm directions that include dual polarity and pass positive fold tests at 95 and 99 confidence levels indicating prefolding primary magnetizations the tilt corrected site mean direction for 33 redbed sites is d 316 8 i 30 2 with 95 5 4 corresponding to a paleopole at 49 0 n 344 3 e with a 95 5 3 and the other for 12 volcanic sites is d 350 5 i 25 5 with 95 7 7 corresponding to a paleopole at 70 5 n 292 9 e with a 95 7 4 our new paleomagnetic results together with reliable cretaceous paleomagnetic data obtained from the lhasa terrane demonstrate that the southern margin of asia was located at 15 1 n during the cretaceous comparison with the apparent polar wander paths apwp of india and the cretaceous paleocene paleopoles of the himalayan terrane suggests that the india asia collision was likely a complex process which consists of the collision of the lhasa and himalayan terranes at 54 0 2 1 ma the longtime subduction of an intra oceanic basin between the himalayan terrane and the indian craton from 54 0 to 40 4 ma and the collision of the himalayan terrane and the indian craton at 40 4 4 1 ma comparing with the late cretaceous average pole of the east asia apwp reveals that a latitudinal convergence of 780 240 km has taken place between the lhasa terrane and east asia the hexi corridor since the india asia collision the amount of latitudinal shortening deduced from paleomagnetic data is very consistent with the 600 1000 km accommodated by the cenozoic fold and thrust belts between the lhasa terrane and hexi corridor

quantification of magnetic coercivity components by the analysis of acquisition curves of isothermal remanent magnetisation abstract a new method of analysing isothermal remanent magnetisation irm acquisition curves based on cumulative log gaussian analysis robertson and france phys earth planet inter 82 1994 223 234 is proposed it is based on the curve fitting of the irm acquisition curve versus the logarithm of the applied field with i the acquisition curve on a linear scale ii the acquisition curve expressed as a gradient and iii the acquisition curve on a probability scale even when a sample is not saturated its magnetic properties can be defined although with less certainty the number of magnetic components required for an optimal fit to a measured irm acquisition curve is evaluated statistically the method discriminates on the basis of different mineral coercivity therefore additional rock magnetic tests are still required to separate minerals with similar coercivities

acquisition of chemical remanent magnetization during experimental ferrihydrite hematite conversion in earth like magnetic field implications for paleomagnetic studies of red beds abstract hematite bearing red beds are renowned for their chemical remanent magnetization crm if the crm was acquired substantially later than the sediment was formed this severely compromises paleomagnetic records to improve our interpretation of the natural remanent magnetization the intricacies of the crm acquisition process must be understood here we contribute to this issue by synthesizing hematite under controlled earth like field conditions 100 t crm was imparted in 90 oriented samples with varying inclinations the final synthesis product appeared to be dominated by hematite with traces of ferrimagnetic iron oxides when the magnetic field intensity is 40 t the crm records the field direction faithfully however for field intensities 40 t the crm direction may deviate considerably from that of the applied field during synthesis the crm intensity normalized by the isothermal remanent magnetization crm irm 2 5 t increases linearly with the intensity of growth field implying that crm could potentially be useful for relative paleointensity studies if hematite particles of chemical origins have consistent properties crm in hematite has a distributed unblocking temperature spectrum from 200 to 650 c while hematite with a depositional remanent magnetization drm has a more confined spectrum from 600 to 680 c because it is usually coarser grained and more stoichiometric therefore the thermal decay curves of crm with their concave shape are notably different from their drm counterparts which are convex these differences together are suggested to be a potential discriminator of crm from drm carried by hematite in natural red beds and of significance for the interpretation of paleomagnetic studies on red beds

magnetic inclination shallowing problem and the issue of eurasia s rigidity insights following a palaeomagnetic study of upper cretaceous basalts and redbeds from se china

sand drift and soil formation along an exposed north atlantic coastline 14 000 years of diverse geomorphological climatic and human impacts this paper sets out the history of aeolian deposition and soil formation over the last 14 15 000 calendar years along the exposed and gale prone atlantic coastlines of the southern isles of the outer hebrides of scotland detailed palaeoenvironmental interpretation and chronological control have been provided by field mapping soil micromorphological analyses and radiocarbon and optically stimulated luminescence osl dating programmes two dominant types of aeolian sands are described in this region quartzose sands are shown to originate mainly as periglacial wind blown sands derived from glacial and periglacial deposits of late devensian age which were formerly exposed on the present continental shelf this aeolian deposition did however continue into the early holocene with re working perhaps by slope wash taking place as recently as the 4th millenniumbp quartzose sands mantle valley floors and hillslopes by the end of the devensian and early holocene a variety of soil types with extensive horizonation had developed upon them including podzolic brown earths peaty gleys and peat soils radiocarbon and osl dating demonstrate that the carbonate sands of the machair sand sheets which characterize the present atlantic shorelines began to accumulate very early for a european shoreline from approximately 8700 calendar years ago on benbecula and north uist whereas further south deposition began later osl dating suggests that non sequences and diastems are common in greater part these machair sand sheets are best interpreted as a composite of separate slivers of sand reflecting small scale and local episodes of sand drift rather than distinct layers of region wide distribution which might reflect past major storms or significant palaeoclimatic fluctuations the new evidence presented here provides little support for the following explanatory geomorphic or stratigraphic models which have previously sought to explain the development of these coastal machair landscapes continuous development layer cake or step wise prograding coastal barrier qualified support is given for the explanations that emphasize i the long term spasmodic input and re cycling of sands and ii that the present smoothed landscapes and distinctive machair grassland vegetation are essentially recent in age and reflect the interactions of natural and human processes in a stormy environment characterized by re working widespread layers of thick organic materials within the carbonate sands in the study area which have previously been regarded as dune palaeosols dating to the bronze age and iron age are suggested by soil micromorphological analysis to be in significant part anthropogenic in origin they are organically enriched layers or midden soils the consequence of human activities notably the disposal of organic wastes and other forms of soil modification during times of significant settlement in these coastal sands these periods of relatively intense human activity are therefore shown to be associated at least locally with periods of soil formation and stability not universal instability and dune drift along these shorelines in general these extensive layers of midden soil do not necessarily imply periods of decreased storminess relatively widespread soil formation in these coastal dunes did however take place in the period between 400 and 100 years ago essentially within the period of increased storminess associated with the little ice age it is suggested that at some point s within the following periods of time broadly defined in calendar yearsbp notable sand drift affecting the quartzose sands the carbonate sands or both took place within the study area 13 700 13 000 11 000 10 500 9000 8300 7500 7000 6900 6400 5800 4200 one of the most notable episodes of drift in the outer hebrides as well as elsewhere on the coast of north west europe 3800 3300 1700 1300 600 200 with individual great storms being recorded in the 17th and 18th centuries and 100 present day limited drift associated with machair stratification

early silurian palaeolatitude of the springdale group redbeds of central newfoundland a palaeomagnetic determination with a remanence anisotropy test for inclination error we studied the palaeomagnetism of red fine grained sandstones and coarse siltstones of the early silurian springdale group of central newfoundland at 10 sites a high blocking temperature characteristic remanence carried by haematite was isolated this remanence is shown to predate probable early devonian folding anti parallel north and south directed remanences through a 100 m section of redbeds and a positive conglomerate test on haematite bearing volcanic clasts suggest absence of remagnetization inverting the south directed sites and unfolding yields a characteristic remanence with a mean declination of 23 6 and a mean inclination of 14 2 myg5 7 3 k 45 4 the inclination corresponds to a probable early silurian palaeolatitude of 7 s f 4 we find no significant difference between early silurian palaeolatitudes for central newfoundland north and south of the red indian line suture and conclude that the part of the iapetus ocean across the suture had narrowed to less than about 5 by the early silurian this is consistent with palaeomagnetic results from britain and ireland that suggest no more than a narrow iapetus at low palaeolatitude by the early silurian we also tested whether we have underestimated palaeolatitude because of sediment compaction reducing remanence inclination from that of the early silurian field we measured anisotropy of the isothermal remanence irm acquisition for one specimen from each stable site finding that a field of 200 to 800 rnt applied at 45 to bedding produced an isothermal remanence oriented on average at 42 to bedding theory then predicts that sediment compaction caused less than 2 average inclination shallowing in the springdale group redbeds and less than a 1 underestimation of palaeolatitude

the timing of india asia collision onset facts theories controversies abstract the timing of initial collision between india and asia has remained controversial for half a century this paper attempts to review this crucial and hotly debated argument describing first the different methods used to constrain the age of collision and discussing next the rationale results inferences and problems associated with each we conclude that stratigraphy represents the best direct way to unravel collision chronology other methods focusing on the magmatic metamorphic or paleomagnetic record provide additional fundamental constraints but cannot provide a robust direct estimate of collision onset initial collision in the central eastern himalaya is dated directly at the middle paleocene 59 1 ma by the abrupt change in sediment provenance recorded in trench settings the quasi synchronous unconformities documented along both tethyan passive margin of india and active margin of asia from tibet to zanskar ladakh confirm that orogeny was underway at the close of the paleocene 56 ma well before the disappearance of marine seaways in the himalaya during the early middle eocene 50 45 ma sedimentary evolution and provenance changes in marine to fluvio deltaic successions are recorded synchronously within error from the western to the central eastern himalaya failing to provide conclusive evidence for diachronous collision these coherent observations are hard to reconcile with three widely cited hypotheses invoking either paleogene arc continent collision or late cretaceous ophiolite obduction or the protracted existence of a greater india basin which are all not favored after discussing the geological evidence critically point by point a scenario no more complex than the one involving solely the passive continental margin of india and the active continental margin of asia is needed to explain the geological evolution of the nascent himalaya the collision between the tethys himalaya and the transhimalayan arc trench system does represent the collision between india and asia because the yarlung zangbo ophiolite is the forearc basement of the asian active margin its obduction onto india could not have preceded the initial closure of neo tethys ophiolite obduction began when collision began in the middle paleocene

position of the lhasa block south tibet during the late cretaceous the latitude of the lhasa block xizang south tibet during the late cretaceous early tertiary is of prime importance for understanding the collision of india and eurasia and the mechanism of the formation of the qinghai xizang plateau during the first field expedition of the french chinese collaboration several geological formations have been sampled in southern tibet between lhasa 29 40 n 91 09 e and dingri 28 35 n 86 38 e we present here the first results obtained for middle cretaceous to palaeocene red beds from the lhasa block north of the yarlung zang bo suture zone recognized as the main suture between the indian and the eurasian plates they indicate a palaeolatitude of the lhasa block of 20 n during the late cretaceous while india was situated 30 s

paleomagnetism and magnetic fabric of the deformed redbeds of the cap de la chevre formation brittany france abstract we present the results of a palaeomagnetism and magnetic fabric study in six sampling sites of the lower ordovician redbeds of the cap de la chevre formation crozon peninsula france measurement of anisotropy of magnetic susceptibility ams shows that these beds are affected by a weak but significant tectonic strain during the hercynian folding of the armorican palaeozoic cover samples containing small elliptical reduction spots allowed us to check the control of strain on ams site mean ams data were then used to provide strain estimates at each site analysis of remanent magnetization through thermal and chemical stepwise demagnetization procedures allowed us to isolate three magnetic components component a defined in the lower unblocking temperature range is a recent overprinting which clusters around the present day dipole field direction components b and c defined respectively in the intermediate and higher unblocking temperature ranges appear to be pretectonic in age the fold test however is inconclusive for both because of the significant dispersion still remaining after the simple tilt correction assuming that at least a part of this dispersion is due to strain we have applied the strain removal technique using ams derived strains at each site this results in a clustering of component c from four sites allowing recovery of the primary ordovician paleomagnetic direction d 261 i 71 95 11 in contrast unstrained component b shows a small circle distribution containing the formation mean of unstrained component c the hypothesis that component b and c distributions arise from beds being tilted during a long term magnetization acquisition in the ordovician field is discussed taking into account the extensional geodynamic context during deposition of lower palaeozoic redbeds in brittany

zircon u pb and hf isotopic constraints on the onset time of india asia collision the time of initial collision between india and asia has been extremely controversial despite the fact that it is vital to constraining the orogenesis and subsequent evolution of the himalayas and tibetan plateau here we report u pb and hf isotope analysis of detrital zircons from two principal foreland basins that is the sangdanlin and gyangze basins respectively in the western and central parts of southern tibet our data suggest that asian derived clastic sediments started contributing to sedimentation on the indian continental margin earlier than generally thought at 60 ma in both basins near the yarlung zangbo suture zone in southern tibet no evidence for the existence of an intra oceanic arc within the neotethys is observed we conclude that 60 ma can be used to constrain the onset time of the india asia collision at least in central tibet after this initial collision closure of the neotethys propagated both westward and eastward with the final closure occurring at 50 and 45 ma in northwestern and eastern himalayas respectively our conclusion differs significantly from the previous view that the india asia collision may have started in northwestern himalaya and propagated eastward with diachronous suturing

new paleomagnetic results from the lhasa block revised estimation of latitudinal shortening across tibet and implications for dating the india asia collision knowing how and when the tibetan plateau formed is of global concern as high topography modifies climate circulation patterns and alters species migration paths previous paleomagnetic work suggested that intracontinental shortening from deformation related to the india asia collision played a major role in building the tibetan plateau however these studies were derived from red bed facies which are often afflicted by inclination shallowing leading to overestimates of continental shortening we report new paleomagnetic data from the lhasa block the southern continental margin of asia before the india asia collision a high temperature characteristic remanent magnetization chrm was isolated from 43 sites of late cretaceous red beds 32 sites of late cretaceous lava flows and nine sites of eocene tuffs all the chrm directions are significantly different from the present day geomagnetic field and the mean directions of red beds lava flows and tuffs pass the fold test the distribution patterns of chrm directions derived from volcanic rocks are consistent with a secular variation model suggesting that secular variation was likely averaged out in contrast the red bed chrm directions exhibit an east west elongated distribution pattern indicative of inclination flattening the mean chrm inclination of the red beds 23 5 degrees 2 5 degrees is consistent with previous results but significantly shallower than that of 41 9 degrees 4 4 degrees carried by the coeval lava flows an elongation inclination analysis of the red bed chrm directions yielded an unflattened mean inclination of 39 7 degrees with 95 confidence limits between 37 7 degrees and 41 9 degrees the paleolatitudes of the late cretaceous volcanic rocks and inclination corrected sediments suggest about 10 degrees less shortening occurred between lhasa and siberia than previous estimates with total shortening lying between 3 3 degrees 2 6 degrees and 7 3 degrees 5 4 degrees since the late cretaceous the mean chrm inclination derived from the eocene tuffs 51 8 degrees 5 2 degrees is indistinguishable from the expected reference direction our new results imply that india asia convergence was accommodated mainly through consumption of the india plate and yield a much younger age ca 43 ma for the initial india asia collision than previously estimated by paleomagnetic data c 2010 elsevier b v all rights reserved

tectonic and sedimentary evolution of the late miocene pleistocene dali basin in the southeast margin of the tibetan plateau evidences from anisotropy of magnetic susceptibility and rock magnetic data abstract the cenozoic dali basin located at the northeast of diancang shan and south of the first bend of yangtze river is tectonically controlled by the dali fault system in the southeast margin of the tibetan plateau the basin is filled with late miocene to pleistocene fluviolacustrine sediments which provide invaluable information about the tectonic deformation and drainage network reorganization in this area in this study we discuss the anisotropy of magnetic susceptibility ams of the dasongping section in the dali basin which spans an interval from 7 6 to 1 8 ma although rock magnetic experiments indicate that magnetite and hematite are the main remanence carriers hysteresis loops low values of bulk susceptibility and low temperature susceptibility suggest that paramagnetic minerals are major contributors to low field ams the rock magnetic parameters indicate that the dali basin experienced four stages of infilling and the sediment sources may have changed at 4 2 ma the clustering of the minimum principle axes k min nearly perpendicular to the bedding plane and the pronounced n s magnetic lineation parallel to the bedding plane indicate that the ams of the dali basin is a superimposed fabric consisting of a sedimentary compaction and a mild initial deformation overprint the well defined n s magnetic lineation is likely due to the nnw and nne oblique shear caused by the heqing and red river faults

early anthropogenic soil formation at tofts ness sanday orkney abstract a buried dark coloured loam soil horizon embedded between calcareous wind blown sand deposits is identified in three areas of the tofts ness landscape the close association with early settlement sites and enhanced total phosophate levels suggests that this soil horizon is anthropogenic in origin radiocarbon dating and stratigraphic relationships with settlement sites indicate that the horizon is associated with bronze age cultural landscape activity and may have commenced formation during the late neolithic period horizon formation is interpreted through a synthesis of thin section micromorphology stable carbon isotope analysis and analysis of free soil lipids these analytical methods indicate that formation was through the application of grassy turf material together with domestic waste midden while cultivation was moderately intense as evidenced by the movement of fine material through the horizon the closest parallels to these soil horizons are the cultural plaggen soils of continental north west europe with the tofts ness soils amongst the earliest known of these soil types application of this manuring technique at tofts ness allowed arable activity in what was a highly marginal farming environment emerging evidence from other parts of the northern isles of scotland suggests that these manuring strategies were commonly used in early arable systems

cretaceous tertiary structural evolution of the north central lhasa terrane tibet 1 in the north central lhasa terrane of tibet two distinct structural levels of an east west striking thrust system are exposed along the north trending late cenozoic xiagangjiang rift upper paleozoic strata deformed by the south directed langgadong la thrust and cretaceous strata involved in variably north and south directed thrusting characterize these lower and upper structural levels respectively these two structural levels are separated by the tagua ri passive roof thrust balanced cross section restoration suggests that the thrust system accommodated 103 km 53 shortening the 40ar 39ar results together with an interpretation of synthrust deposition of upper cretaceous strata suggest that the majority of shortening occurred during the late cretaceous paleocene cretaceous strata lie unconformable on permian rocks volcanic tuffs directly above the unconformity yield u pb zircon ages of 131 ma upper cretaceous strata record a change from shallow marine to nonmarine deposition indicating uplift above sea level during this time the overall south directed vergence of the thrust belt is consistent with substantial crustal thickening in central tibet by large scale northward underthrusting of lhasa terrane basement beneath the qiantang terrane prior to the indo asian collision the documented decoupling of contractional deformation at shallow crustal levels appears to be a regional characteristic of tibet from at least the bangong suture in the north to the tethyan himalaya to the south this style of deformation explains the absence of basement exposures and major denudation in this region despite substantial crustal shortening

paleomagnetic results from the early cretaceous zenong group volcanic rocks cuoqin tibet and their paleogeographic implications article i nfo article history a paleomagnetic study has been carried out on the early cretaceous zenong group volcanic rocks ca 110 130 ma near cuoqin town in the central lhasa terrane stepwise thermal demagnetization up to 680 c isolated a stable high temperature component htc including antipodal dual polarities the htc directions passed both a fold test at 99 confidence and a reversal test at 95 confidence suggesting a primary origin the tilt corrected average direction for 18 sites is d 327 0 i 35 7 59 3 95 4 5 which corresponds to a paleopole at 58 2 n 341 9 e a95 4 6 yielding a paleolatitude of 19 8 4 6 n for the study area our results combined with previous paleomagnetic data suggest that southern tibet was at a mean paleolatitude of 20 n during the cretaceous and paleogene when compared with the apparent polar wander paths of asia the difference suggests that only ca 870 km north south crustal shortening has accumulated between the lhasa terrane and stable asia since ca 110 ma when comparing the paleolatitudes of the lhasa terrane and india the results indicate that the width of the neotethys was 6720 690 km during the early cretaceous

a quasi linear structure of the southern margin of eurasia prior to the india asia collision first paleomagnetic constraints from upper cretaceous volcanic rocks near the western syntaxis of tibet we report the first combined geochronologic and paleomagnetic study of volcanic rocks from the shiquanhe and yare basins at the westernmost lhasa terrane which aims to provide an accurate constraint on the shape and paleoposition of the southern margin of asia prior to the india asia collision three new 40ar 39ar ages of 92 5 2 9 ma 92 4 0 9 ma and 79 6 0 7 ma determined by fresh matrix or feldspar from lava flows suggest a late cretaceous age for the investigated units characteristic remanent magnetizations have been successfully isolated from 38 sites which pass positive fold and or reversal conglomerate tests and are hence interpreted as primary in origin the two paleopoles obtained from yare and shiquanhe yield consistent paleolatitudes of 13 6 n 9 6 n and 14 2 n 2 7 n respectively for a reference site of 31 5 n 80 e indicating that the southern margin of asia near the western syntaxis was located far south during the late cretaceous time a reconstruction of the lhasa terrane in the frame of eurasia with paleomagnetic data obtained from its western and eastern parts indicates that the southern margin of eurasia probably had a quasi linear orientation prior to the collision formerly trending approximately 315 e this is compatible with the shape of the neo tethys slab observed from seismic tomographic studies our findings provide a solid basis for evaluating cenozoic crustal shortening in the asian interior and the size of greater india near the western syntaxis

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

a marine isotope stage 4 age for pleistocene raised beach deposits near fethard southern ireland raised beach deposits around the irish coast have been interpreted as interglacial or last glacial in age on the south coast of ireland the courtmacsherry formation raised beach cfb near fethard county wexford was dated using optically stimulated luminescence osl this site was previously dated to marine isotope stage mis 6 5 but more recent dating of the cfb elsewhere along the south coast shows it is considerably younger mis 4 3 the osl analyses in this paper aimed to determine if new dating would support the greater age of the fethard raised beach or realign it with the cfb the new osl ages place the formation of the fethard raised beach between 57 6 and 45 6 ka with 53 5 ka the most likely age if a single depositional event is assumed this is consistent with osl dates of the cfb elsewhere an mis 4 3 age has important implications in understanding the palaeogeography and timing of glaciation in ireland and requires a reassessment of regional relative sea level history as the eustatic response to global ice volume resulted in lowered relative sea level during mis 4 2 a crustal response to glaciation is implied by the new dates

nature of remagnetization of lower triassic red beds in southwestern china summary widely distributed haematite bearing red beds are an important source of palaeomagnetic field records however unresolved issues regarding remagnetization and inclination shallowing in red beds have questioned the reliability of the palaeomagnetic results obtained from such materials in this study we investigated the remagnetization mechanism in red beds from lower triassic sandstones in yunnan province southwestern china our results indicate that the characteristic remanent magnetizations chrms of most samples 112 125 are dominated by only one component at temperatures 80 660 c with a mean direction of d i 0 9 46 6 k 440 2 95 2 1 the corresponding geomagnetic pole is 89 1 n 331 7 e k 338 2 a95 2 4 this coincides with the present geomagnetic field which is a strong indication that these chrms are remagnetized combined rock magnetic and microscope investigations reveal that the remagnetization is due to the acquisition of a chemical remanent magnetization crm carried by authigenic maghemite and haematite despite the widespread remagnetization about 7 per cent of the studied samples still record a magnetization that we consider to be primary that was isolated at high temperatures 610 660 c with a mean direction of d i 213 3 18 6 k 16 0 95 11 7 we propose that the crm overprinting is controlled by the overlapping degree of the unblocking temperature between the crm carried by the authigenic haematite and the primary remanent magnetization carried by the detrital haematite our results further suggest that microscope investigation rock magnetic proxies for the haematite concentration and susceptibility temperature curves are useful methods for pre selecting samples suitable for isolating the primary remanence at this region the linkage among the palaeomagnetic results rock magnetic proxies and crm remagnetization mechanism could be extended to other studies although the detailed proxy would be different due to specific overprint process

constraining the age and formation of stone runs in the falkland islands using optically stimulated luminescence the stone runs of the falkland islands are thought to be periglacial blockfields but their age and detailed origin remain enigmatic we examine the fine sediments that underlie two stone runs in order to establish whether optically stimulated luminescence osl dating is an appropriate technique to constrain the date of emplacement of the fine sediments and hence the stone runs six samples were collected from two accessible sections during the scotia centenary antarctic expedition in 2003 all samples were used to explore the main luminescence characteristics of the sediment followed by quartz sar dating procedures on four of the samples age estimates range from in excess of 54 ka to 16 ka suggesting that the overlying stone runs remained active until 16 ka or later saturation of luminescence from quartz limits age estimates for the oldest samples in the sequences however these are not critical to define the upper limit to the emplacement age for the overlying stone runs the sediments also contain feldspars and initial results suggest that these may be useful in extending the timescale further but require further samples to be obtained from other parts of the sequence extending the method to other stone runs in the port stanley formation may allow estimates of the age of stabilisation of the stone runs to be extended into the 1 250 ka timescale luminescence dating of the underlying sediments used in conjunction with cosmogenic isotope dating of the surface boulders from a range of locations along the stone runs appears to offer a useful route towards decoding the depositional history of these impressive deposits

cretaceous paleomagnetic results from western tibet and tectonic implications we present paleomagnetic results obtained from samples collected in the summer of 1989 along a 1000 km traverse between yecheng xinjiang and shiquanhe tibet in the western qinghai xizang plateau along 80 e longitude during this field trip 480 paleomagnetic cores in jurassic to tertiary limestones and sandstones were drilled at 49 sites 400 were measured isothermal remanent magnetization analysis indicates the existence of high coercivity minerals and thermal rather than alternating field demagnetization was found to be more efficient in isolating paleomagnetic directions the characteristic magnetization has rather low unblocking temperatures 250 560 c in most limestone samples and higher unblocking temperatures 400 c 680 c in the sandstone samples about half of the measured samples show the present geomagnetic field or aberrant directions the remainder display stable multicomponent magnetizations the stable characteristic magnetizations indicate 1 a probable jurassic remagnetization 2 a cretaceous 120 80 ma magnetization which passes a fold test yielding a mean pole at 66 2 n 245 0 e a95 5 1 n 14 sites and 3 a large scatter of tertiary directions which may be due to tectonic problems and or remagnetization in the sampling zone the cretaceous paleodirections from aksaichin and longmuco 11 sites on the qiangtang north tibet block are very similar to those from shiquanhe three sites on the lhasa south tibet block separated by 300 km this suggests that the north and south tibet blocks formed a single unit at least as early as the cretaceous comparing our results with previous paleomagnetic work on the tibetan plateau it is found that the paleolatitude of 10 6 5 1 obtained from this study for a reference at domar 33 75 n 80 4 e is close to that 9 6 2 8 obtained by achache et al 1984 and lin and watts 1988 from the takena formation 110 100 ma in the lhasa region 30 n 91 e in addition it appears that the southern margin of the tibetan blocks i e eurasia occupied an e w trending position at about 7 6 n latitude paleodeclination differences between the western and eastern tibetan blocks suggest internal deformations of the plateau at different scales from 1 to 1000 km according to differences in paleomagnetic declinations the arcuate shape of the blocks would have been partly acquired after the collision

a 7600 year sedimentary record of climatic instability in dunnet bay north scotland abstract we present a partial reconstruction of ne atlantic climatic variability the first based on stratigraphic evidence obtained from a vegetated dune system of the northern scottish coast the dune system at dunnet bay is fringed by prominent submerged peat deposits exposed only at low tide which record stable climatic periods when lower energy wind regimes prevailed allowing the formation of organic soils by contrast periods of sand influx are associated with high energy conditions the majority of sand material tested had a narrow range of particle sizes and major element composition supporting the interpretation of a common aeolian origin sand layers were dated with optically stimulated luminescence osl and peat layers were 14 c dated in four cores c1 c4 and seven sample sections s1 s7 the results from the two master sections s1 and s2 1 km apart indicate synchronous episodes of climatic stability 7650 6310 4340 4000 2690 2290 100 0 cal a bp and instability 6310 4340 4000 2690 2290 2000 170 100 cal a bp in spite of very different mean accumulation rates at the two sites 1 mm a 1 at s1 and 0 2 mm a 1 at s2 phases of sand deposition i e aeolian activity at dunnet tend to be associated with high average levels of chloride in the greenland ice sheet project 2 ice core gisp2 phases of peat development show a fairly good correspondence with low ice rafting activity in the ne atlantic and with indicators of wetness measured from a peat bog in sw sweden by contrast comparison of the dunnet depositional timeline with other regional studies e g hebrides and orkney shows little synchronicity this suggests that a local scale variables have a strong effect on regional patterns of dune instability and b the geological and geographic settings of dunnet bay mean that only large climatic regime shifts in the ne atlantic are capable of triggering instability and being preserved in the depositional record

application of luminescence dating and geomorphological analysis to the study of landscape evolution settlement and climate change on the channel island of herm abstract the optically stimulated luminescence osl dating of sands and palaeosol horizons sampled as part of an archaeological investigation and supported by geomorphological analysis has been applied to identify critical stages in the development of the landscape on herm one of the channel islands that lies off the coast of guernsey on which megalithic monuments were constructed during the neolithic period in particular there were three phases of significant aeolian activity during the prehistoric period the onsets dated by osl in this study to ca 4 3 and 2 3 ka ago where the first phase marked a significant change in the long term trend of aggradation of soils that persisted during the next two millennia osl ages were also obtained for palaeosols in which there was evidence of ploughing placing this activity in the late 2nd millennium bc and the 4th and 13th centuries ad the osl ages for basal deposits of dune sands that cover the northern part of the island indicate that they were formed by phases of intense aeolian activity during the medieval period commencing in the 13th century ad and continuing for several hundred years which can be correlated with documented high intensity storms in the north atlantic within the period 13th 15th centuries ad the phases of significant aeolian activity dated by osl to ca 4 and 2 ka ago can be linked with those detected in different regions of the north atlantic coastal areas the availability of chronologies for aeolian horizons provides a valuable tool in the study of the evolution of coastal landscape and how past coastal communities responded to climate change

statistical significance of the fold test in palaeomagnetism summary the significance of the change in direction dispersion on applying the fold test in palaeomagnetism is used as the criterion for deciding whether or not the fold test has statistical significance a set of tables is compiled which can be used for quick application of the test

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

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

paleogeographic and tectonic evolution of southern tibet since middle cretaceous time new paleomagnetic data and synthesis during the second french chinese paleomagnetic campaign in tibet in the summer of 1981 we sampled the middle cretaceous red beds of the takena formation and the cenozoic volcanics of the lingzizong formation a detailed analysis of about 400 specimens of red beds reveals a stable component of normal magnetization n in the north of the lhasa block north of the nyainqentanglha range and two stable components in the south lt ht where the red beds are more strongly folded and are unconformably overlain by the lingzizong volcanics all three components are carried by hematite blocking temperatures range from 400 to 600 c for lt and up to the neel temperature of hematite for both n and ht lt is shown to postdate part of the folding of the takena whereas n and ht both indicate a positive fold test at the 99 probability level in addition a small less than 10 of the natural remanent magnetization antiparallel component is superimposed in most samples and may be consistent with a model of long term acquisition of a chemical remanent magnetization for the red beds analysis of the volcanics reveals a single stable component with mixed polarities carried either by hematite or magnetite the paleomagnetic directions indicate that 1 the lhasa block stood at 12 5 3 n by upper cretaceous and at 13 5 6 5 n in the paleocene eocene thus confirming the limited displacement of the margin of eurasia between albian aptian deposition of the red beds and eocene onset of the india asia collision these values imply crustal shortening by as much as 1900 850 km north of the block since the upper cretaceous and by 1400 1200 km south of the block since the onset of the collision 2 southern tibet formed a single tectonic unit by middle cretaceous time and 3 differential rotations are observed within the block and are related to the collision these rotations are discussed in the frame of a recent propagating extrusion tectonics model this study confirms the close paleogeographic relationship between indochina khorat plateau and southern tibet prior to the india asia collision

reliability of magnetic fabric of weakly deformed mudrocks as a palaeostress indicator in compressive settings abstract in this work we compare the results of anisotropy of magnetic susceptibility ams with palaeostress analysis at local scale the ams data refer to 14 sites from weakly deformed mudrocks lower and middle miocene lacustrine sediments from two areas of the internal part of the ebro foreland basin the bardenas reales and monegros areas nine sites display a magnetic fabric related to a subtle tectonic overprint showing a roughly e w magnetic lineation whereas the rest of sites most of them located at the monegros area show a sedimentary fabric without a well defined magnetic lineation palaeostress data result from fault populations and joint sets exposed in the limestone beds interbedded with the mudrocks at the nearest possible outcrop from the ams site the origin of the magnetic lineation is related to a n s compression coeval with the earliest diagenesis of the studied sediments prior to consolidation the comparison between magnetic fabric and palaeostress data demonstrates the coaxiality between the ams and palaeostress ellipsoids both at local and regional scales thereby validating the reliability of ams as palaeostress indicator in compressive settings

effect of progressive deformation on remanent magnetization of permian redbeds from the alpes maritimes france abstract the relationships among the anisotropy of magnetic susceptibility the finite strain and the characteristic remanent magnetization chrm have been investigated in deformed red sediments from the alpes maritimes in southeast france the magnetic properties of these rocks are due to hematite the finite strain is known from field studies of the shapes and orientations of green reduction spots and from optical microscopy and x ray texture goniometry studies of chlorite and illite the strain data permit a classification of the magnetic results according to four main stages of progressive deformation in the compaction stage magnetic anisotropy is flattened in the bedding due to compactional loading the chrm directions approximate to a fisherian distribution about a mean value close to the known permian direction for the region as deformation proceeds pencil structure first develops and the anisotropy is characterized by a prolate pattern with maximum axis parallel to the subhorizontal azimuth of the pencil structure and fold axes with increasing deformation the magnetic susceptibility ellipsoid becomes oblate and finally triaxial at these stages of high deformation the anisotropy patterns show that the hematite grain orientations are strongly influenced by the cleavage the remanence directions in deformed rocks do not correspond to a fisher distribution and eventually deviate strongly from permian directions these results show that paleomagnetic vectors are affected by the distortional strains which accomodate shape change in the rock simple tilt correction without compensation for the strain would yield incorrect paleopole positions an attempt has been made to compensate for the effects of deformation by regarding the remanent vector as a passive marker march 1932 equations for strain removal were applied to the remanence in two ways 1 a using strain data directly obtained in the field for each site and 2 b by converting the magnetic susceptibility anisotropy of each sample to a corresponding finite strain value correcting for the finite strain by both methods improves the within site grouping of paleomagnetic vectors in strongly deformed rocks strain removal assuming the march model results in overcorrection of the remanent magnetization data in low strain regions distortion may produce mechanical rotation of the hematite particles but recrystallization may alter the deformation mechanism in regions of high strain the limits of applicability of the passive marker treatment could not be tested adequately in the deformed red sediments of the alpes maritimes

syntectonic growth strata and implications for late cenozoic tectonic uplift in the northern tian shan china abstract propagation of faults and folds in the foreland basins of tian shan is an important process accommodating cenozoic crustal shortening and mountain building but little is known about the accurate time of the cenozoic tectonic deformation based on growth strata and age determination we show that syntectonic growth strata began to develop in the middle part of tian shan since 6 ma ago geometry analysis indicates that formation of the growth strata is associated with progressive fold limb rotation formation of the growth strata is contemporaneous with the tectonic deformation in the thrusting and folding zones together with the remarkable increase of sedimentation rate as well as the accumulation of coarse molasse deposits we conclude that the late cenozoic crustal shortening and mountain building in the region initiated since about 6 ma and lasted to the early pleistocene as a consequence of intracontinental deformation within the india eurasia convergent system

paleomagnetism of the oligocene kangtuo formation red beds central tibet inclination shallowing and tectonic implications abstract a paleomagnetic study on the red beds of the oligocene kangtuo formation fm was carried out in the gerze basin of the lhasa terrane a total of 700 samples were collected from 37 sites stepwise thermal demagnetization revealed that the main magnetic carrier is hematite the natural remnant magnetization nrm consists of two components a low temperature component ltc is identified below 300 c and is interpreted to be a recent viscous overprint whereas a high temperature component htc unblocks at 665 690 c and is interpreted to be the primary magnetization the htc distributions show a clear east west elongated distribution which is considered as reflecting inclination flattening of deposited magnetic remanence carriers after inclination calibration using the e i method the htc could pass both a reversal test and a fold test at 95 confidence level showing the mean direction at ds 340 3 is 44 2 with k 63 0 and 95 3 1 corresponding to a paleopole at 71 7 n 339 3 e a95 3 1 and the paleolatitude of the sampling site at 25 9 3 1 n the paleolatitude is consistent with that expected from the coeval pole of the qiangtang terrane obtained from volcanic rocks suggesting that there has been no paleomagnetically discernable latitudinal motion between the qiantang and lhasa terranes since 30 ma comparing our new data with the apparent polar wander paths apwps of east asian blocks cogne et al 2013 europe and india besse and courtillot 2002 we have reached the following conclusions 1 there is no significant paleolatitudinal difference observed between the lhasa terrane and other central and northern asian terranes at 30 ma 2 the observed paleolatitude of the kangtuo fm is 8 0 4 9 lower than the expected paleolatitude deduced from the data of stable europe highlighting the asian inclination anomaly phenomenon but is 4 6 5 1 higher than that deduced from the data of the india plate likely presenting a 506 561 km shortening between the india and lhasa terrane since the oligocene it is inferred that this amount of shortening has been absorbed mainly by the himalaya orogenic belt

linking the late cretaceous to paleogene pacific plate and the atlantic bordering continents using plate circuits and paleomagnetic data 1 late cretaceous to paleogene paleomagnetic data from the pacific plate the emperor seamounts can be compared with data from the atlantic bordering continents through the use of plate circuit reconstructions here we summarize the uncertainties in all data sets and present formal tests we report agreement between late cretaceous pacific paleomagnetic data and predictions based on the estimates of non pacific pole positions from synthetic apparent polar wander paths this congruency points to the veracity of the plate circuits and the accuracy of the paleomagnetic estimates in contrast to the agreement seen for the late cretaceous small discrepancies are observed in the comparisons of the pacific paleogene data and predictions from synthetic apparent polar wander paths such a disparity in a younger time interval is unexpected given the agreement of the late cretaceous data the possibility that minor temporally variable nondipole field components contribute to the discrepancy cannot be completely discounted however an alternative and more straightforward explanation is suggested by further comparisons of the mean non pacific paleomagnetic data and the highest quality poles that contribute to the means in particular we note that 1 the pacific paleogene data are in full agreement with coeval poles from north america meeting strict reliability criteria and 2 the non pacific paleogene poles of synthetic apparent polar wander paths are dominated by results from the north atlantic igneous province naip but taken as a whole the naip data fail a paleomagnetic reversal test hence minor discrepancies between paleocene paleomagnetic data from the pacific and atlantic hemispheres may point to limitations of the latter which incorporate a relatively large number of older lower quality data these findings call for renewed data collections utilizing comprehensive rock magnetic and paleomagnetic demagnetization procedures to improve resolution of paleocene non pacific data the uncertainties of the pacific paleolatitude data and the non pacific reference poles are larger than the differences related to the use of the two alternative plate circuits through east to west antarctica and through australia to the lord howe rise that link the atlantic and pacific hemispheres while no preference can thus be given to either plate circuit their overall consistency with paleomagnetic data suggests that they can be used to investigate long term motion of the pacific plate since late cretaceous times

carbon isotope composition of raialo carbonates and its equivalents mesoproterozoic delhi supergroup india implications for stratigraphic correlation carbon isotopic studies are useful not only for reconstruction of palaeoenvironment but have also been used successfully for chronostratigraphic purposes the marine limestones and even dolostones faithfully record the carbon isotopic composition of the ocean water in which they formed schole and arthur 1980 gao and land 1991 wang et al 1996 saltzman et al 1998 investigated the carbon isotope stratigraphy of the welldated carbonates of the phanerozoic part of geological record and confirmed that large perturbations in the carbon isotope ratios of common carbonate rocks may be used as a precise measure of time the mesoproterozoic delhi supergroup of aravalli mountain range rajasthan india fig 1 is mainly comprised of quartz arenite conglomerate felds arenite phyllite limestone marble and calc gneiss these rocks have undergone polyphase deformation and suffered greenschist to amphibolite facies metamorphism a marginal marine depositional environment has been envisaged for the sedimentary sequences of the delhi supergroup deb 1980 singh 1982a the raialo group type area is raynahalla town of delhi supergroup is exposed on the northern extremity of the fold belt and is characterized by the frequent presence of dolomitic carbonates carbonates have also been reported on the western limits of the delhi supergroup but are significantly calcitic in composition heron 1953 the stratigraphic status of calcitic carbonates occurring on the western margin of the delhi fold belt and its correlation with carbonates from the raialo group is a matter of debate heron 1953 correlated the carbonates on the western margin of the delhi supergroup with the raialo carbonates sen 1983 on the other hand suggests that these should belong to a younger sequence roy and sharma 1999 advocated for the correlation of these carbonates with the younger sirohi group sediments to resolve the issue we have carried out sampling of carbonates from the raialo group and its equivalents occurring on the western margin of the delhi supergroup for analysis of carbon and oxygen isotope composition the whole rock carbonate samples were collected at close intervals along a stratigraphic profile in the raialo group around the rayanhalla town representative samples were however collected from the different carbonate occurrences occurring on the western margin of delhi supergroup and included in the ambit of the raialo group the preliminary isotope results are provided in table 1

paleomagnetic data bearing on the mesozoic deformation of the qiangtang block implications for the evolution of the paleo and meso tethys paleomagnetism has played an important role in quantifying the mesozoic evolution of proto tibet in this paper we present new paleomagnetic data from five middle upper jurassic sedimentary sequences quemo co buqu xiali suowa and xueshan fms of the eastern north qiangtang terrane qt at yanshiping 33 6 degrees n 92 1 degrees e the new paleomagnetic results form a large dataset 99 sites 1702 samples and reveal a paleopole at 79 1 degrees n 306 9 degrees e dp 3 9 degrees dm 6 3 degrees for the quemo co fm at 68 9 degrees n 313 8 degrees e dp 2 1 degrees dm 3 7 degrees for the buqu fm at 66 1 degrees n 332 1 degrees e dp 2 7 degrees dm 4 6 degrees for the xiali fm at 72 4 degrees n 318 6 degrees e dp 3 9 degrees dm 6 7 degrees for the suowa fm and at 76 9 degrees n 301 1 degrees e dp 7 9 degrees dm 13 2 degrees for the xueshan fm these results indicate clockwise cw rotations of similar to 19 8 9 4 degrees between similar to 171 2 and 161 7 ma and counterclockwise ccw rotations of similar to 15 4 13 4 degrees between similar to 161 7 and 157 2 ma for yanshiping we attribute the change in rotation sense at approximately similar to 161 7 ma to the initial collision of the lhasa and qiangtang terranes using this and other paleomagnetic data from the lhasa qiangtang and tarim terranes as well as other geological evidence e g tectonism related sedimentary sequences volcanism and hp metamorphism we propose a new conceptual evolution model for the mesozoic qt and tethyan oceans the longmo co shuanghu oceanic slab was subducted before 248 ma followed by continental collision of the north south qiangtang subterranes between similar to 245 and 237 ma the qiangtang terrane experienced post collisional exhumation between similar to 237 and 230 ma during subduction of the jinsha oceanic slab the collision of the qiangtang and songpan ganzi terranes occurred between similar to 230 and 225 ma the qt experienced post collisional relaxation from similar to 225 to similar to 200 ma followed by subsidence and extension related exhumation between similar to 200 and 162 ma in association with subduction of the bangong nujiang oceanic slab finally these events were followed by the scissor like diachronous collisions of the lhasa and qiangtang terranes between similar to 162 ma and the mid cretaceous c 2016 international association for gondwana research published by elsevier b v all rights reserved

magnetostratigraphic study of the kuche depression tarim basin and cenozoic uplift of the tian shan range western china abstract magnetostratigraphic and rock magnetic results from 1006 horizons in paleogene and neogene sediments between the upper kumugeliemu formation and the base of the kuche formation within the kuche depression of the tarim basin nw china are used to evaluate postcollisional uplift and deformation in the tian shan range characteristic remanences with both normal and reversed polarity were isolated by thermal demagnetization generally between 300 and 690 c and a composite magnetostratigraphy is constructed from data at 969 accepted levels correlating with polarity chrons c12n to c3r dated between 31 0 and 5 5 ma on the ck95 geomagnetic polarity time scale observed height dependent changes of rock magnetic parameters km and ams ellipsoid parameters indicate that these sediments were influenced by weak deformation with the succession accumulated before 15 ma recording the effects of compressive deformation this finding together with two substantial increases in accumulation rate at 16 17 and 7 ma define a framework for cenozoic uplift and deformation of the tian shan range we argue that thrusting in the south of the range was probably initiated at 20 ma and followed by rapid uplift at 16 17 ma on the assumption that sediment accumulation in western china was still predominately tectonically controlled at 7 ma another later pulse of rapid uplift with a much larger regional influence is also recognized in the tian shan the kuche depression was subjected to two postcollisional phases of rotational deformation with clockwise rotation prior to 12 ma 1 36 ma succeeded by counterclockwise rotation at 1 64 ma after 12 ma and possibly continuing to the present day this rotational deformation is not temporally related to the history of basin formation resolved from the magnetostratigraphy and may be linked to block interactions with adjoining terranes

paleomagnetic results from the early cretaceous lakang formation lavas constraints on the paleolatitude of the tethyan himalaya and the india asia collision abstract to better constrain the early cretaceous paleogeographic position of the tethyan himalaya and the india asia collision process a paleomagnetic study was performed on the lakang formation lava flows in the cuona area in the southeastern tethyan himalaya stepwise thermal and alternating field demagnetizations successfully isolated reliable characteristic remanent magnetization chrm directions that include antipodal dual polarities and pass positive fold tests at the 99 confidence level and reversal tests at 95 confidence level indicating prefolding primary magnetizations the distribution patterns of chrm directions from the lakang formation lava flows are consistent with young lava flows at similar latitudes suggesting that secular variation has likely been averaged out the tilt corrected site mean direction for 31 sites is d 261 6 i 68 5 with 95 3 6 which provides a paleopole at 26 8 s 315 2 e a 95 5 7 corresponding to a paleolatitude of 52 2 5 7 s for the study area comparison of the paleolatitude observed from the lakang formation lava flows with that expected from the apparent polar wander paths of india at 130 ma show a paleolatitude difference of 2 1 230 km indicating that neither a great north south continental crustal shortening occurred between the indian craton and the tethyan himalaya after 130 ma nor that a wide ocean separated them at that time comparison with reliable cretaceous paleocene paleomagnetic results observed from the tethyan himalaya and the lhasa terrane indicates that the latitudinal width of the neo tethyan ocean could have been up to 7000 km at 134 130 ma and an extension should have existed between the indian craton and the tethyan himalaya during the late cretaceous and paleocene furthermore reliable paleomagnetic results suggest that the india asia collision was a dual collision process consisting of a first collision of the tethyan himalaya with the lhasa terrane asia at 54 9 2 3 ma and a final continent continent collision of the indian craton with the tethyan himalaya at 40 0 3 3 ma

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

greater india basin hypothesis and a two stage cenozoic collision between india and asia cenozoic convergence between the indian and asian plates pro duced the archetypical continental collision zone comprising the himalaya mountain belt and the tibetan plateau how and where india asia convergence was accommodated after collision at or be fore 52 ma remains a long standing controversy since 52 ma the two plates have converged up to 3 600 35 km yet the upper crustal shortening documented from the geological record of asia and the himalaya is up to approximately 2 350 km less here we show that the discrepancy between the convergence and the shortening can be explained by subduction of highly extended continental and oceanic indian lithosphere within the himalaya be tween approximately 50 and 25 ma paleomagnetic data show that this extended continental and oceanic greater india promontory resulted from 2 675 700 km of north south extension between 120 and 70 ma accommodated between the tibetan himalaya and cratonic india we suggest that the approximately 50 ma india asia collision was a collision of a tibetan himalayan microconti nent with asia followed by subduction of the largely oceanic greater india basin along a subduction zone at the location of the greater himalaya the hard india asia collision with thicker and contiguous indian continental lithosphere occurred around 25 20 ma this hard collision is coincident with far field deforma tion in central asia and rapid exhumation of greater himalaya crys talline rocks and may be linked to intensification of the asian monsoon system this two stage collision between india and asia is also reflected in the deep mantle remnants of subduction imaged with seismic tomography

late cretaceous evolution of the coqen basin lhasa terrane and implications for early topographic growth on the tibetan plateau the tectonic evolution of the lhasa terrane southern tibetan plateau played a fundamental role in the formation of the tibetan plateau however many uncertainties remain with regard to the tectonic and paleogeographic evolution of the lhasa terrane prior to the india asia collision to determine the early tectonic processes that controlled the topographic evolution of the lhasa terrane we analyze the cretaceous strata exposed in the coqen basin northern lhasa subterrane which comprises the langshan and daxiong formations the langshan formation unconformably overlies the volcanic rocks of the lower cretaceous zelong group and consists of similar to 80 m of orbitolina bearing limestones which were deposited in a low energy shallow marine environment micropaleontological analysis indicates that the langshan formation in the coqen basin was deposited from late aptian to early cenomanian times ca 113 96 ma the overlying daxiong formation similar to 1700 m thick consists of conglomerate coarse sandstone and siltstone with interbedded mudstone and represents deposits of alluvial fans and braided rivers the daxiong formation was deposited after the early cenomanian ca 96 ma and accumulated until at least ca 91 ma indicating accumulation rates of greater than 0 3 km m y 1 by combining paleocurrent data sandstone petrology detrital zircon u pb ages and hf isotope analysis we demonstrate that the daxiong formation was derived from lower cretaceous volcanic rocks and pre cretaceous strata in the northern lhasa subterrane during late cretaceous time two thrust systems with opposite vergence were responsible for transforming the northern lhasa subterrane into an elevated mountain range this process resulted in the evolution from a shallow marine environment langshan formation into a terrestrial depositional environment daxiong formation on the southern margin of the northern lhasa subterrane given the regional paleogeographic context we conclude that the daxiong formation in the coqen basin records local crustal shortening and flexure resulting in foreland basin development on the southern margin of the northern lhasa subterrane which implies early topographic growth of the northern lhasa subterrane in southern tibet prior to the india asia collision

luminescence characterisation of quartz rich cover sands from ne thailand abstract the genesis of a several meter thick cover sand layer which is widely distributed in mainland se asia has been the subject of much debate being considered by some to be an aeolian mantle of late pleistocene early holocene origin and by others to represent a holocene biomantle samples were collected from three sites in nw thailand in 1998 to assess the potential of luminescence studies for characterisation and chronometric studies of the layer the material is a quartz rich iron stained sand with high luminescence sensitivities a pronounced 325 c tl peak and high sensitivity to phototransfer and osl a number of methods for estimating stored dose were assessed of which additive tl and regenerative osl procedures produced good laboratory results these methods have been used to produce stored dose and apparent age profiles for one of the sites the data are consistent with a late pleistocene holocene aeolian deposition process possibly modified in the upper layers by bioturbation however the possibility that the recorded profiles are the result of heterogeneous mixing of bleached and unbleached grains within the biomantle model cannot at this stage be excluded the material has excellent luminescence properties and it is likely that further luminescence studies will be able to distinguish between the formation models and contribute significantly to understanding of these regionally significant sediments

new late cretaceous paleomagnetic data from volcanic rocks and red beds from the lhasa terrane and its implications for the paleolatitude of the southern margin of asia prior to the collision with india abstract in order to improve estimation of the paleolatitude of the southern margin of asia during the late cretaceous as well as the constraints on the intracontinental convergence within asia due to the india asia collision we performed a combined geochronological and paleomagnetic investigation of late cretaceous red bed sequences and intercalated volcanic rocks from the linzhou basin in the lhasa terrane 29 9 n 91 1 e the results of potassium argon k ar dating indicated that the basalt sequences are of late cretaceous age 68 75 ma stepwise thermal demagnetization successfully isolated high unblocking temperature characteristic directions from 10 red bed sites and 11 lava flow sites positive fold and reversal tests indicate a primary origin for the characteristic remanence of the red beds and basalt sites the consistent inclination recorded in the red beds and basalt lava flows indicates that no significant compaction related inclination shallowing has occurred in the red beds from the studied section the tilt corrected mean direction is d i 0 5 20 2 with 95 6 4 and n 21 sites corresponding to a paleopole at 70 5 n 269 6 e with a 95 4 9 the paleomagnetic results yield a paleolatitude of 10 4 4 9 n for the southern margin of asia in the late cretaceous compared with expected paleomagnetic directions from the tethyan himalaya and asia significant crustal shortening of 17 7 5 5 1960 610 km and 9 4 4 7 1040 520 km respectively may have occurred between the southern margin of asia and the tethyan himalaya and within asia since the late cretaceous based on previous cretaceous and paleocene data from the lhasa terrane the latitude of the southern margin of asia was located at a stable paleolatitudinal position 10 15 n during the cretaceous and paleocene

palaeomagnetic results from the tibetan plateau palaeomagnetic measurements were carried out on 1325 oriented samples collected from 246 sites on a traverse of the tibetan plateau from lhasa to golmud in 1985 crossing the lhasa terrane qiangtang terrane and kunlun terrane high blocking temperature high coercivity statistically grouped magnetizations were isolated from the following units lhasa terrane cretaceous takena formation mid cretaceous nagqu volcanics mid cretaceous qelico volcanics qiangtang terrane norian batang group volcanics kimmeridgian yanshiping group paleocene to eocene fenghuoshan group kunlun terrane visean to namurian dagangou formation dykes of the triassic igneous province the triassic data from the kunlun terrane triassic and lower tertiary data from the qiangtang terrane and the cretaceous data from the lhasa terrane indicate palaeolatitudes ca 20 s of their present position within the eurasian frame of reference a possible interpretation is that the terranes successively accreted to eurasia and remained in the southern position until the convergence of india drove them northward via a process of tectonic shortening and or displacement of continental crust the carboniferous data from the kunlun terrane are consistent with moderate southern hemisphere latitude well separated from eurasia which was in the northern hemisphere at this time implying the existence of ocean crust between these blocks during the carboniferous

luminescence dating of aeolian sands from archaeological sites in northern britain a preliminary study luminescence dating of aeolian sands from archaeological sites has potential to contribute to regional chronologies for sediment deposition and to provide a greater understanding of climatic influences on early communities the northern and western isles of scotland provide important opportunities for sampling archaeologically intercalated sands for these purposes and to provide constrained samples for method validation a wide range of modern beaches have been sampled in the western and orkney isles of scotland to examine regional variations in luminescence sensitivity residuals and ease of bleaching these modern sands have negligible residuals for infra red stimulated luminescence irsl small optically stimulated luminescence osl residuals and significant thermoluminescence residuals the relationship between these signals and laboratory bleaching results may indicate the initial depositional environment and hence lead to a means of identifying well bleached dating samples both sensitivities and residuals show regional differences reflecting local geology preliminary ages obtained from aeolian sands associated with archaeological sites at amble northumbria and tofts ness sanday orkney using regenerative blue osl techniques on extracted quartz are broadly consistent with external age controls from the first and third millennium bc

paleomagnetism and u pb zircon geochronology of lower cretaceous lava flows from the western lhasa terrane new constraints on the india asia collision process and intracontinental deformation within asia to better understand the india asia collisional process and intracontinental deformation within asia a paleomagnetic study has been conducted on the qushenla formation lava flows dated at 132 120 ma from the yanhu area in the western lhasa terrane stepwise thermal demagnetization isolates stable characteristic remanent magnetizations which include dual polarity and pass fold tests at a 99 confidence level indicating primary magnetizations the tilt corrected site mean direction for 51 sites is d 28 2 i 34 5 and k 74 3 with 95 2 3 corresponding to a paleopole at 61 4 n 192 9 e a95 2 1 our new paleomagnetic data combined with previous cretaceous volcanic paleomagnetic data from the lhasa terrane show that the precollisional southern margin of asia was at 16 8 n with a relatively e w alignment and that the lhasa terrane did not experience significantly discrepant north south movement although local vertical axis rotations did take place after the cretaceous comparison with the apparent polar wander paths apwps of india and the cretaceous paleocene paleopoles of the tethyan himalaya shows that the india asia collision was at 54 3 ma and the greater india during the paleocene had a large northern extent of 2000 km 18 1 beyond its present northern margin comparison with the cretaceous eurasian apwp indicates that a latitudinal convergence of 1000 km has taken place between the lhasa terrane and eurasia since the india asia collision the amount of north south shortening deduced from cretaceous paleomagnetic data is consistent with that accommodated by the cenozoic fold and thrust belts between the lhasa terrane and the hexi corridor

when and where did india and asia collide timing of the collision between india and asia is the key boundary condition in all models for the evolution of the himalaya tibetan orogenic system thus it profoundly affects the interpretation of the rates of a multitude of associated geological processes ranging from tibetan plateau uplift through continental extrusion across eastern asia as well as our understanding of global climate change during the cenozoic although an abrupt slowdown in the rate of convergence between india and asia around 55 ma is widely regarded as indicating the beginning of the collision most of the effects attributed to this major tectonic episode do not occur until more than 20 ma later refined estimates of the relative positions of india and asia indicate that they were not close enough to one another to have collided at 55 ma on the basis of new field evidence from tibet and a reassessment of published data we suggest that continent continent collision began around the eocene oligocene boundary 34 ma and propose an alternative explanation for events at 55 ma

position of the lhasa terrane prior to india asia collision derived from palaeomagnetic inclinations of 53 ma old dykes of the linzhou basin constraints on the age of collision and post collisional shortening within the tibetan plateau the lhasa terrane comprises the southern eurasian margin since at least mid cretaceous therefore paleomagnetic data from the lhasa terrane are crucial to reconstruct the pre collisional southern margin of eurasia previous paleomagnetic data from the cretaceous takena formation provide a rough constraint on the pre collisional paleolatitudinal position of the southern eurasian margin however paleogene paleomagnetic data from the lhasa terrane which can provide more direct constraints are very limited in addition reliability of the existing data is ambiguous because of a possible later overprint in our new study 17 sites were drilled from mafic dykes intruded in the t1 unit of the linzizong formation of the linzhou basin near lhasa for paleomagnetic studies figure 1 the dykes were ar 40 ar 39 dated to c 53 ma by yue and ding 2006 from ten sites a higher coercivity component demagnetized between 20 and 100 mt could be isolated detailed rockmagnetic analyses reveal ti rich titanomagnetite as the remanence carrier which suggests that the rock is not much altered and the remanent magnetization is likely of primary origin this is supported by a positive fold test the occurrence of normal and reverse polarity directions within single sites the subvolcanic character of the dykes and the within site scatter as well as the scatter between site mean directions indicate that paleosecular variation is recorded within sites tilt correction was performed using the bedding of overlying fluvial lacustrine sediments and tilt angles of ignimbrite columns postdating the dyke emplacement bedding corrected directions give an overall mean direction of d i 12 3 27 2 95 10 6 k 21 7 n 10 corresponding to a paleolatitude of 13 2 5 8 n at a reference location on the suture zone 20 n 90 e comparison with previous cretaceous data mainly from the takena formation yields a stable position of the lhasa terrane during cretaceous and early eocene this indicates that no large north south crustal shortening occurred along the southern eurasian margin between late cretaceous and early eocene the difference between expected paleolatitudes determined from the apwp of eurasia and observed paleolatitudes reveals relative northward movement of the lhasa block of ca 1847 763 km since early eocene this is attributed to indentation of india into asia and implies a considerable amount of north south crustal shortening two models of greater india were used to determine the extended northern margin of india ali and aitchison 2005 proposed a greater india based on bathymetric features in the eastern indian ocean and patzelt and others 1996 determined the paleolatitude of northern india using paleomagnetic investigations on paleocene sediments of the zongpu formation at gamba and duela intersection of the pre collisional southern eurasian margin and the northern margin of india yields a collision age of the indian and eurasian continents of c 5349 ma an initial collision within this time range is in accordance with previous studies based on paleomagnetic or geologic data e g patriat and achache 1984 klootwijk and others 1992 guillot and others 2003 a significantly later collision age at the eocene oligocene boundary as proposed by aitchison and others 2007 is not in agreement with our new and previous paleomagnetic data from the lhasa block