the rock elm meteorite impact structure wisconsin geology and shock metamorphic effects in quartz the rock elm structure in southwest wisconsin is an anomalous circular area of highly deformed rocks 6 5 km in diameter located in a region of virtually horizontal undeformed sedimentary rocks shock produced planar microstructures pms have been identified in quartz grains in several lithologies associated with the structure sandstones quartzite pebbles and breccia two distinct types of pms are pres ent p1 features which appear identical to planar fractures pfs or cleavage and p2 features which are interpreted as possible incipient planar deformation features pdfs the latter are uniquely produced by the shock waves associated with meteorite impact events both types of pms are oriented parallel to specific crystallographic planes in the quartz most commonly to c 0001 11 batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document overline 2 end document 2 and r z 10 batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document overline 1 end document 1 the association of unusual structurally deformed strata with distinct shock produced microdeformation features in their quartz bearing rocks establishes rock elm as a meteorite impact structure and supports the view that the presence of multiple parallel cleavages in quartz may be used independently as a criterion for meteorite impact preliminary paleontological studies indicate a minimum age of middle ordovician for the rock elm structure a similar age estimate 450 400 ma is obtained independently by combining the results of studies of the general morphology of complex impact structures with estimated rates of sedimentation for the region such methods may be applicable to dating other old and deeply eroded impact structures formed in sedimentary target rocks

saqqar a 34 km diameter impact structure in saudi arabia here we present the first proof of an impact origin for the saqqar circular structure in northwestern saudi arabia neville et al 2014 with an apparent diameter of 34 km centered at 29 35 n 38 42 e the structure is formed in cambrian devonian siliciclastics and is unconformably overlain by undeformed cretaceous and paleogene sediments the age of impact is not well constrained and lies somewhere between 410 and 70 ma the subsurface structure is constrained by 2 d reflection seismic profiles and six drilled wells first order structural features are a central uplift that rises approximately 2 km above regional datums surrounded by a ring syncline the crater rim is defined by circumferential normal faults the central uplift and ring syncline correspond to a bouguer gravity high and an annular ring like low respectively the wells were drilled within the central uplift the deepest among them exceed 2 km depth sandstone core samples from these wells show abundant indicators of a shock metamorphic overprint planar deformation features pdfs were measured with orientations along 0001 103 and less frequently along 101 and 104 planar fractures pfs predominantly occur along 0001 and 101 and are locally associated with feather features ffs in addition some shocked feldspar grains and strongly deformed mica flakes were found the recorded shock pressure ranges between 5 and 15 gpa the preserved level of shock and the absence of an allochthonous crater fill suggest that saqqar was eroded by 1 2 km between the devonian and maastrichtian the documentation of unequivocal shock features proves the formation of the saqqar structure by a hypervelocity impact event

mechanics of kink bands during torsion deformation of muscovite aggregate abstract the growth geometry and bulk mechanical behavior of grain scale kink bands were investigated during layer parallel non coaxial deformation torsion of synthetic polycrystalline aggregates of muscovite at constant displacement rate 3 10 4 s 1 and various confining pressures cp 50 300 mpa temperatures t 300 800 c and finite shear strains 0 2 5 0 the kink instabilities were observed during elastic to plastic transition yield at finite shear strain of ca 0 2 the shear stress required to form the kinks is a function of pressure and temperature and range from ca 20 to 90 mpa within the experimental conditions the kink bands formed in non coaxial torsion tests are asymmetric involve strain partitioning show complex microstructures with increased deformation and have a limited lifetime as the structure is destroyed at ca 5 these results suggest a domain of pressure and temperature conditions where kink band structures should be common results obtained from torsion experiments are compared to those of layer parallel axial compression conducted with the same displacement rate at 600 c and 300 mpa for 5 10 and 17 bulk shortening combining microstructures viewed on surfaces parallel and perpendicular to the torsion plane a 3d geometrical model is constructed to discuss the kink mechanism the microstructural evolution and the mechanical behavior

a strain based porosity model for use in hydrocode simulations of impacts and implications for transient crater growth in porous targets numerical modelling of impact cratering has reached a high degree of sophistication however the treatment of porous materials still poses a large problem in hydrocode calculations we present a novel approach for dealing with porous compaction in numerical modelling of impact crater formation in contrast to previous attempts e g p alpha model snowplow model our model accounts for the collapse of pore space by assuming that the compaction function depends upon volumetric strain rather than pressure our new e alpha model requires only four input parameters and each has a physical meaning the model is simple and intuitive and shows good agreement with a wide variety of experimental data ranging from static compaction tests to highly dynamic impact experiments our major objective in developing the model is to investigate the effect of porosity and internal friction on transient crater formation we present preliminary numerical model results that suggest that both porosity and internal friction play an important role in limiting crater growth over a large range in gravity scaled source size

nonlinear principal component analysis tropical indo pacific sea surface temperature and sea level pressure abstract nonlinear principal component analysis nlpca is a generalization of traditional principal component analysis pca that allows for the detection and characterization of low dimensional nonlinear structure in multivariate datasets the authors consider the application of nlpca to two datasets tropical pacific sea surface temperature sst and tropical indo pacific sea level pressure slp it is found that for the sst data the low dimensional nlpca approximations characterize the data better than do pca approximations of the same dimensionality in particular the one dimensional nlpca approximation characterizes the asymmetry between spatial patterns characteristic of average el nino and la nina events which the 1d pca approximation cannot the differences between nlpca and pca results are more modest for the slp data indicating that the lower dimensional structures of this dataset are nearly linear

a late miocene early pleistocene palynological record and its climatic and tectonic implications for the yunnan plateau china abstract in this paper we provide a late miocene tortonian to early pleistocene gelasian palynological record from the eryuan basin yunnan plateau china to investigate plant diversity over this time between 7 6 and 4 3 ma the palynological assemblage was dominated by coniferous trees 70 2 on average with subordinate amounts of broadleaved trees 8 8 on average this suggests that the vegetation mainly comprised mixed forests and that the climate was relatively warm and humid after 4 3 ma the proportion of conifer pollen increased overall and amount of cold temperate coniferous forest picea and abies pollen in particular increased significantly from 19 1 to 41 9 concurrent with decreases in the pollen of broadleaved trees shrubs herbs and other plant taxa we suggest that these plant variations and overall reduced diversity may be responses to the tectonic uplift of the yunnan plateau and global cooling

interannual and decadal variability of the subsurface thermal structure in the pacific ocean 1961 90 heat content anomalies are analyzed to understand subsurface variability on both aparticular focus on the evolving basinwide patterns and oceanic connections between the extratropics and tropics various analyses indicate two distinct modes one interannual and the other decadal that involve the tropics and the north pacific subtropical gyre respectively interannual variability is associated with el nino in the tropics with a prominent see saw pattern alternately on and off the equator and in the east and west respectively the interannual cycle features a coherent propagation of subsurface signals around the tropical pacific eastward along the equator but westward off the equator at 10 15 n decadal signals are dominant in the subtropics and midlatitudes but also have a tropical component that appears to be independent of interannual variations an oceanic connection can be seen between subsurface anomalies in the midlatitudes in the subtropics and tropics on decadal time scales subsurface thermal anomalies associated with midlatitude decadal variability can propagate through the subtropics into the tropics which may modulate the intensity of interannual variability in the tropics for example in the middle and late 1970s a significant warm temperature anomaly appeared to penetrate into the western and central tropics at depth warming the tropical upper ocean and depressing the thermocline during the development of el nino therefore an extratropically preconditioned subsurface state e g an enhanced positive heat content anomaly in the western and central tropical pacific would favor a warmer sea surface temperature anomaly in the eastern equatorial pacific potentially increasing the intensity of ocean atmosphere coupling these changes in the thermocline structure and possibly in the coupling strength can further alter the very character of tropical air sea interactions this may help to explain decadal variability of el nino evolution in the tropical pacific as observed in the 1980s our subsurface variability analysis presents observational evidence for the detailed space time structure of decadal oceanic links between the extratropics and the tropics

an evaluation of enso asymmetry in the community climate system models a view from the subsurface abstract the asymmetry between el nino and la nina is a key aspect of enso that needs to be simulated well by models in order to fully capture the role of enso in the climate system here the asymmetry between the two phases of enso in five successive versions of the community climate system model ccsm1 ccsm2 ccsm3 at t42 resolution ccsm3 at t85 resolution and the latest ccsm3 nr with the neale and richter convection scheme is evaluated different from the previous studies not only is the surface signature of enso asymmetry examined but so too is its subsurface signature by comparing the differences among these models as well as the differences between the models and the observations an understanding of the causes of the enso asymmetry is sought an underestimate of the enso asymmetry is noted in all of the models but the latest version with the neale and richter scheme ccsm3 nr is getting closer to the observations than the earlier versions the net surface heat flux is found to damp th

north pacific thermocline variations on enso timescales abstract the north pacific thermocline 250 to 400 m is studied using xbt observations acquired during the 1970s and 1980s interannual variations 3 5 yr timescales in thermocline temperature with o 0 1 c amplitude at 400 m are found to exhibit westward propagation throughout the extratropical north pacific up to 45 n southward of 30 n the features propagate intact across the basin from the eastern boundary to the western boundary northward of 30 n the features can be observed to propagate only as far as the date line the observed midlatitude thermocline anomalies are often related to tropical enso events in that they occur most strongly after the development of tropical el nino or la nina conditions and propagate westward from near the eastern boundary in the midlatitudes but it is found that the observed midlatitude thermocline anomalies have larger phase speeds than theoretically predicted free baroclinic rossby waves also the observed anomalies have larger wavelength and faster propagati

sedimentary facies analysis mineralogy and diagenesis of the mesozoic aquifers of the central perth basin western australia abstract assessment and successful exploration for and exploitation of aquifers in the perth basin require knowledge of their petrophysical and sedimentological characteristics and geometries this study provides a sedimentological and lithofacies analysis of core from the mesozoic yarragadee formation cadda formation cattamarra coal measures eneabba formation and lesueur sandstone of western australia recovered from pinjarra 1 cockburn 1 gingin 1 and gingin 2 wells provide insights into changes in depositional environment over time and space in the central perth basin in studied sections nine different fluvial dominated lithofacies have been identified in the yarragadee formation cadda formation and cattamarra coal measures that occur in similar proportions whereas the lesueur sandstone is dominated by coarse grained deposits of high energy fluvial systems vertical variation in lithofacies on the order of 10 cm to approximately 2 m vertical scale is observed in all formations and wells changes in the lithofacies linked to local depositional environments are probably associated with fluvial alluvial to fluvio deltaic systems that have complex 3d architecture including braided and to probably meandering systems and are affected by channel avulsion point counting and automated mineral analysis of thin sections of core showed detrital mineralogy dominated by monocrystalline quartz with rare polycrystalline quartz a moderate amount of alkali feldspar and very minor amounts of garnet organic fragments muscovite and biotite these data show a lithofacies dependence of the proportion of minerals with little variation between equivalent lithofacies from different depths formations or wells grain size and sorting that have a first order control on porosity are strongly lithofacies dependent individual lithofacies types show a trend of decreasing porosity with depth due to the increasing effects of compaction quartz overgrowth cementation and authigenic clay mineral development lithofacies and depth are the main controls on permeability and so lithofacies distribution exerts a key control on hydraulic behaviour

the marine lockne impact structure jamtland sweden a review the lockne impact structure in jamtland 63 00 20 n 14 49 30 e formed in the middle ordovician at approximately 455 ma the structure is a concentric crater with a total diameter of 13 5 km the impact took place in a marine environment seawater played an important role in the cratering process and in crater morphology and the amount of melt remaining in the structure seawater rushed back into the crater in a resurge eroding and redepositing the ejecta among the resurge deposit seawater furthermore facilitated the hydrothermal system which was driven by the residual heat in the structure the lockne structure hosts shocked quartz and an iridium anomaly the rim wall round the crater collapsed in the modification stage of the crater and was annihilated by the resurge the fractured basement and the impact breccia were initially rich in open cavities these became partly filled with dominantly calcite the filling contributed to a low density contrast generating a negative gravity anomaly of 22 gu the gravity model indicates a central uplift and a nw directed tilt of the structure this tilt is also seen in the magnetic models the apparent absence of any impact melt is probably real and related to the environment of impact

quantitative climate reconstructions of the late miocene xiaolongtan megaflora from yunnan southwest china the late miocene xiaolongtan megaflora from kaiyuan in southeast yunnan 23 degrees 48 45 n 103 degrees 11 52 e 1050 m a s l was chosen for palaeoclimatic reconstruction using three quantitative techniques i e the coexistence approach ca leaf margin analysis lma and the climate leaf analysis multivariate program clamp the reconstructed climatic parameters are also compared with those of the two adjacent miocene floras currently available in yunnan i e the early to middle miocene carpological mangdan flora 24 degrees 24 n 97 degrees 49 e 1620 m a s l and the late miocene luhe palynoflora 25 degrees 10 n 101 degrees 22 e 1930 m a s l quantitative analyses of the xiaolongtan flora supports the previous qualitative results of a southern humid subtropical climate being more humid and having a slightly higher mean annual temperature mat than today the mats calculated by ca lma and clamp overlap 16 7 19 2 degrees c 22 3 2 05 degrees c 18 1 1 2 degrees c respectively and are close to the present day value 19 7 degrees c the overlapping of temperatures derived using the three techniques is unusual and probably related to the low latitude of the xiaolongtan area and the southern subtropical nature of its vegetation both the mean temperatures of the warmest month wmt and of the coldest month cmt reconstructed by ca wmt 25 4 26 0 degrees c cmt 7 7 8 7 degrees c and clamp wmt 25 9 1 6 degrees c cmt 10 8 1 9 degrees c are similar to those of today wmt 24 3 degrees c cmt 12 8 degrees c but great changes appear in the mean annual precipitation map the clamp results suggest a higher precipitation 1964 335 9 mm than ca 1215 1639 mm but they are much higher than the present map 820 5 mm this is consistent with results from the luhe palynoflora which also developed under a warmer subtropical climate with higher precipitation 803 6 1254 7 mm than that of today 815 9 mm in contrast the mangdan flora situated in a more complicated topographic region to the west of xiaolongtan and near the sino myanmar border implies a slightly lower precipitation 1170 1300 mm than that of today 1300 1400 mm overall the wetter climate during the late miocene around the xiaolongtan area suggests that the himalayas had not yet uplifted to its present altitudes at that time c 2009 elsevier b v all rights reserved

nonlinear modes of decadal and interannual variability of the subsurface thermal structure in the pacific ocean 1 the nonlinear principal component analysis a neural network technique is applied to the observed upper ocean heat content anomalies hca in the pacific basin from 1961 to 2000 by applying the analysis to high passed and low passed data nonlinear interannual and decadal modes are extracted separately the first nonlinear interannual mode is mainly characterized by the el nino southern oscillation enso structure in the tropical pacific with considerable asymmetry between warm el nino and cool la nina episodes for example during strong el nino the negative hca in the western tropical pacific is much stronger than the corresponding positive hca during strong la nina the first nonlinear decadal mode goes through several notable phases two of the phases are related to decadal changes in the la nina and el nino characteristics revealing that the decadal changes for la nina episodes are much weaker than the changes for el nino episodes other phases of the decadal mode show a possible anomaly link from the middle latitudes to the western tropical pacific via the subtropical gyre the decadal changes in the hca around 1980 and around 1990 were compared and contrasted

experimental constraints on shock induced microstructures in naturally deformed silicates abstract planar deformation features pdfs in various minerals have long been accepted as evidence of impact induced deformation the uniqueness of this association was challenged in the context of the k t boundary extinction debate after mosaicism and microstructures similar to pdfs were reported from the products of explosive volcanism as a result of this debate a significant volume of new experimental and observational data on the development of shock induced microstructures has become available over the last ten years the results reveal that factors such as pre shock temperature pulse duration and crystallographic orientation of target minerals to the shock wave have a primary influence on how these microstructures develop data from diamond anvil cell and high pressure friction experiments reveal that the same solid state amorphization process that produces shock induced pdfs at low temperatures also occurs at much lower strain rates in static experiments the experimental data indicate that the amorphization process is thermally activated and that the character of the resulting pdfs is a function of the applied strain rate shock induced amorphization occurs along those crystallographic planes that are most readily transformed to the high pressure phase during very short pulse durations and produces pdfs that are visible at the optical scale lower strain rate deformation produces tem scale amorphization with orientations that are more homogeneously distributed throughout the target mineral and produces no optically visible pdfs the data confirm the uniqueness of multiple intersecting sets of optically visible pdfs as a diagnostic indicator of hypervelocity impact the data also support the hypothesis that the amorphization process can occur at a wide range of strain rates and that the limiting pressure for the process is controlled by the phase stability of the target mineral under the applied loading conditions not by the hel the data also suggest that the onset pressure the maximum pressure and the pressure range for producing optically visible pdfs decrease with increasing temperature and decreasing strain rate as the pressure range for optically visible pdf formation decreases it is replaced by homogeneous amorphization as observed in the anvil cell experiments thus the uniqueness of multiple intersecting sets of optically visible pdfs to hypervelocity impact is not due to a unique process but rather to a specific set of loading conditions that produce an optically visible microstructure likewise single sets of microdeformations observed in volcanic rocks are produced by the same process but at different loading conditions that preclude the development of multiple intersecting sets of pdfs the data also indicate that shock mosaicism which occurs above the hel represents a plastic response of the target mineral to loading rates that are too large to be accommodated by crystal plastic mechanisms observational data for some naturally deformed samples from the k t boundary the vredefort dome and volcanic rocks along with the experimental observations are used to constrain the range of conditions under which the natural microstructures form and to understand the differences between microstructures produced by impact volcanic and other natural processes finally some possible mechanisms for producing the microstructures observed in volcanic rocks are proposed

mechanical twinning in quartz shock experiments impact pseudotachylites and fault breccias abstract increasing use of diffraction methods to study preferred orientation of minerals has established that quartz in deformed rocks not only displays characteristic c axis orientation patterns but that there is also generally a distinct difference in the orientation of positive and negative rhombs in the trigonal quartz crystal structure positive and negative rhombs are structurally different and particularly negative rhombs e g 01 1 1 are much stiffer than positive rhombs e g 10 1 1 here we focus on the role of mechanical dauphine twinning under stress as a cause of this difference and illustrate with ebsd measurements ubiquitous twinning in quartz bearing rocks subjected to high stresses characteristic twinning is observed in experimentally shocked sandstones and stishovite bearing quartzites from the vredefort meteorite impact site in south africa similar twinning is documented for quartz associated with pseudotachylites from the santa rosa mylonite zone in southern california whereas quartz in underlying ductile mylonites are more or less twin free it suggests that twinning was produced by local seismic stresses that caused fracture and frictional melting on fault surfaces quartz bearing breccias from the safod san andreas fault observatory at depth drilling project also show evidence of twinning and suggest high seismic stresses in the currently creeping segment of the san andreas fault at parkfield from these observations it appears that dauphine twin microstructures can be diagnostic of high local and transient stresses

preservation of detrital shocked minerals derived from the 1 85 ga sudbury impact structure in modern alluvium and holocene glacial deposits detrital shocked minerals can provide valuable residual records of eroded impact structures recent studies have reported shocked minerals in modern alluvium in a subtropical climate from the deeply eroded 2 02 ga vredefort dome impact basin in south africa to evaluate the detrital shocked mineral record at a large impact structure in a temperate setting with a holocene glacial erosional history we investigated 4000 detrital zircons and 20 000 quartz grains at the less eroded 1 85 ga sudbury basin in ontario canada for the presence of shocked sand grains modern alluvium from rivers within and outside the basin and holocene glaciofluvial sands eskers and outwash deltas across the basin were investigated for shocked minerals shocked zircon and or quartz were found in all modern rivers and most holocene glacial deposits within but not outside the basin petrography and scanning electron microscopy sem backscattered electron bse cathodoluminescence cl imaging and analysis energy dispersive x ray spectroscopy eds electron backscatter diffraction ebsd were used to document shock microstructures of the total detrital zircons surveyed 3 118 3978 were identified as shocked holocene samples contained higher average percentages of shocked zircon 63 1361 or 4 6 with a high of 29 compared to modern alluvium 55 2617 or 2 1 with a high of 6 ebsd analysis revealed a range of shock microstructures including planar fractures deformation microtwins and crystal plastic deformation at sudbury detrital shocked quartz is rare compared to zircon only 15 grains 0 08 were identified all with decorated planar deformation features pdfs these results demonstrate that a detrital shocked mineral record exists at a large impact basin that is in a youthful stage of erosion despite its age in addition to modern alluvium our results also identify glaciofluvial eskers and deltas as reservoirs for detrital shocked minerals glacial episodes thus enhance the dispersal and preservation of shocked detritus in sedimentary systems despite physical differences the observation that the two largest precambrian impact basins continue to contribute detrital shocked minerals 2 b y after impact suggests that a shocked mineral record of impacts on early earth should reside in precambrian siliciclastic rocks

feather features a low shock pressure indicator in quartz 1 feather features are a recently discovered type of microstructure in shocked quartz they occur as short parallel to subparallel lamellae with spacing similar to that of planar deformation features pdfs these lamellae are always found in combination with a planar fracture pf feather features are crystallographically controlled 0001 101 and 112 orientations are common while 103 and 102 orientations are lacking samples from the nordlinger ries and the matt wilson impact structures are compared with plane wave shock recovery experiments 16 gpa microscopic analysis of quartz grains with feather features show that their formation is linked to shearing along the associated pfs during shock deformation the generation of shear fractures with feather features in plane wave shock recovery experiments suggests a pressure range of 7 10 gpa although further constraints are needed for an upper and lower pressure limit the orientation of feather features in rock samples is suggested to be controlled by the direction of the principal axis of stress with sheared pfs at 45 angles to the axis and most feather feature lamellae aligned parallel to the axis 20 the majority of feather feature lamellae emanate from the pfs in the same direction and in experiments point in the direction from which the shock wave came on the basis of their appearance in shocked quartz grains from 26 impact craters and the current lack of reports of these features in endogenically deformed crustal rocks their uniqueness as a new type of impact induced planar microstructure alongside pdfs and pfs is proposed

neogene evolution of the himalayan tibetan region constraints from odp site 758 northern ninetyeast ridge bearing on climatic change abstract magnetic susceptibility remanence and lithostratigraphic profiles for the neogene quaternary sequence at site 758 odp leg 121 on the northern ninetyeast ridge show distinct changes dated from biostratigraphy and detailed magnetostratigraphy at 17 5 10 4 10 0 8 8 6 5 5 4 5 1 2 7 2 5 1 9 and 1 2 1 1 ma these magnetic and lithologic changes appear to reflect changes in the supply and character of terrigenous material from the himalayan tibetan region resulting from changes in gradient of the ganges brahmaputra and probably the ancient indus drainage systems the sedimentary changes can be correlated with changes in uplift sensitive markers such as the oceanic 87 sr 86 sr ratio and monsoonal induced upwelling but not clearly so with sealevel variations we interpret these sedimentary changes therefore to primarily reflect changes in the tectonic evolution of the himalayan tibetan region the changes in the distal marine sedimentary record of the northern ninetyeast ridge are compared with isotopic control on the timing of himalayan tibetan tectonic phases and magnetostratigraphic control on their reflection in the proximal siwalik molasse record this comparison indicates that the distal ninetyeast ridge record can be used to detail and to place minimal age constraints on tectonic phases in the wider himalayan region and on evolution of the proximal molasse sequence with a time lag determined for the four earliest changes at less than 1 m y the changes at 17 5 ma and 5 4 5 1 ma can be interpreted in terms of the causative chain enhanced plate motion uplift and sedimentation change climatic change supporting arguments that the late cainozoic global climatic deterioration is driven by uplift of large plateaus such as the himalayan tibetan region and the western cordillera

latest miocene benthic δ 18 o changes global ice volume sea level and the messinian salinity crisis oxygen isotope evidence indicates high but variable 18o values in benthic foraminiferal calcite during the latest miocene and earliest pliocene these high values may represent increases in global ice volume and associated sea level fall the 18o record resembles glacial interglacial cycles but with only one third the amplitude of the late pleistocene signal this variability may reflect instability in the antarctic ice sheet and palaeomagnetic correlation points to an isotopic event coinciding with the isolation and desiccation of the mediterranean basin during the latest messinian

the keurusselka impact structure finland impact origin confirmed by characterization of planar deformation features in quartz grains although the meteorite impact origin of the keurusselkaimpact structure central finland has been established on the basis of the occurrence of shatter cones no detailed microscopic examination of the impactites from this structure has so far been made previous microscope investigations of in situ rocks did not yield any firm evidence of shock features raiskila et al 2008 kinnunen and hietala 2009 we have carried out microscopic observations on petrographic thin sections from seven in situ shatter cone samples and report here the discovery of planar fractures pfs and planar deformation features pdfs in quartz and feldspar grains the detection and characterization of microscopic shock metamorphic features in the investigated samples substantiates a meteorite impact origin for the keurusselkastructure the crystallographic orientations of 372 pdf sets in 276 quartz grains were measured using a universal stage u stage microscope for five of the seven distinct shatter cone samples based on our u stage results we estimate that investigated shatter cone samples from the keurusselkastructure have experienced peak shock pressures from approximately 2 gpa to slightly less than 20 gpa for the more heavily shocked samples the decoration of most of the pdfs with fluid inclusions also indicates that these originally amorphous shock features were altered by postimpact processes finally our field observations indicate that the exposed surface corresponds to the crater floor it is however difficult to estimate the exact diameter of the structure and the precise amount of material that has been eroded since its formation

reconstruction of neogene zonal vegetation in south china using the integrated plant record ipr analysis abstract reconstructions of past vegetation are crucial for our understanding of palaeoenvironments however we still lack good quantitative reconstructions for the neogene vegetation of china this geological time is key for the development of the modern vegetations in china because it corresponds to the establishment and evolution of the south east asian monsoon system the present study uses integrated plant record ipr vegetation analysis for the first time on the chinese neogene data including 71 palaeobotanical sites from five time intervals early early miocene aquitanian early burdigalian late early to early middle miocene late burdigalian early langhian late middle miocene late langhian serravalian late miocene to earliest pliocene tortonian messinian early zanclean and pliocene late zanclean piacenzian based on the ecophenological type of the nearest living relative to the fossils ipr analysis reconstructs six types of vegetation broad leaved deciduous forests mixed mesophytic forests broad leaved evergreen forests subhumid sclerophyllous forests xeric open woodlands and xeric grasslands or steppe the geographic distribution of reconstructed palaeovegetation shows a distinct latitudinal gradient which is congruent with the latitudinal temperature gradient recognised from previous studies throughout the neogene the broad leaved deciduous bld component is greater in the more northern regions whereas the broad leaved evergreen ble component is greater in the more southern areas during the pliocene there was a further rise of the ble component in the southern areas indicating an increasingly warm and moist climate an episodic longitudinal aridity gradient was also recorded during the neogene the more western areas were drier than the eastern ones in the early miocene but this gradient vanished in the late miocene with all areas having a balanced supply of moisture a second episode of aridification of the western regions occurred in the pliocene

late cenozoic genus fupingopollenites development and its implications for the asian summer monsoon evolution an extinct palynomorph fupingopollenites was used as the basis for a discussion of the late cenozoic asian summer monsoon asm evolution and its possible driving forces based on the spatial and temporal variations in its percentages across inner and east asia we found that fupingopollenites mainly occurred in east asia with boundaries to the ne of ca 42 degrees n 135 degrees e and nw of ca 36 degrees n 103 degrees e during the early miocene ca 23 17 ma this region enlarged westwards reaching the eastern qaidam basin ca 36 degrees n 97 5 degrees e during the middle miocene ca 17 11 ma before noticeably retreating to a region bounded to the nw at ca 33 degrees n 105 degrees e during ca 11 5 3 ma the region then shrank further in the pliocene with the ne boundary shrinking southwards to about 35 degrees n 120 degrees e the area then almost disappeared during the pleistocene 2 6 0 ma the flourishing and subsequent extinction of fupingopollenites is indicative of a narrow ecological amplitude with a critical dependence on habitat humidity and temperature most likely mean annual precipitation map 1000 mm and mean annual temperature mat 10 degrees c therefore the fupingopollenites geographic distribution can indicate the humid asm evolution during the late cenozoic revealing that the strongest asm period occurred during the middle miocene climate optimum mmco similar to 17 14 ma after which the asm weakened coincident with global cooling we argue that the global cooling played a critical role in the asm evolution while the tibetan plateau uplifts made a relatively small contribution c 2015 international association for gondwana research published by elsevier b v all rights reserved

shocked quartz grains from the malingen structure sweden evidence for a twin crater of the lockne impact structure the malingen structure in sweden has for a long time been suspected to be the result of an impact however no hard evidence i e shock metamorphic features or traces of the impactor has so far been presented here we show that quartz grains displaying planar deformation features pdfs oriented along crystallographic planes typical for shock metamorphism are present in drill core samples from the structure the shocked material was recovered from basement breccias below the sediment infill and the distribution of the orientation of the shock produced pdfs indicates that the studied material experienced low shock pressures based on our findings we can exclude that the material is transported from the nearby lockne impact structure which means that the malingen structure is a separate impact structure the seventh confirmed impact structure in sweden furthermore sedimentological and biostratigraphic aspects of the deposits that fill the depression at malingen are very similar to features at the lockne impact structure this implies a coeval formation age and thus also the confirmation of the first known marine target doublet impact craters on earth i e the lockne malingen pair

the preferred structure of variability of the northern hemisphere atmospheric circulation a nonlinear generalisation of principal component analysis pca is applied to the 500mb geopotential height field of the northern hemisphere extratropical atmosphere it is found that the low frequency variability of the mid troposphere is characterised by three distinct quasi stationary states the states are described and compared to those obtained from applications of cluster analyses and linear pca to the height field evidence is provided that modes obtained through pca notably the arctic oscillation ao are not independent dynamical modes of variability of the northern hemisphere extratropics rather they arise as the optimal linear compromise between the preferred quasi stationary states of the circulation

subduction of decadal north pacific temperature anomalies observations and dynamics abstract observations of oceanic temperature in the upper 400 m reveal decadal signals that propagate in the thermocline along lines of constant potential vorticity from the ventilation region in the central north pacific to approximately 18 n in the western pacific the propagation path and speed are well described by the geostrophic mean circulation and by a model of the ventilated thermocline the approximate southward speed of the thermal signal of 7 mm s 1 yields a transit time of approximately eight years the thermal anomalies appear to be forced by perturbations of the mixed layer heat budget in the subduction region of the central north pacific east of the date line a warm pulse was generated in the central north pacific by a series of mild winters from 1973 to 1976 and reached 18 n around 1982 after 1978 a succession of colder winters initiated a cold anomaly in the central north pacific that propagated along a similar path and with a similar speed as the warm anomaly then arrived in the west

enso like interdecadal variability 1900 93 a number of recent studies have reported an enso like eof mode in the global sea surface temperature sst field whose time variability is marked by an abrupt change toward a warmer tropical eastern pacific and a colder extratropical central north pacific in 1976 77 the present study compares this pattern with the structure of the interannual variability associated with the enso cycle and documents its time history back to 1900 the analysis is primarily based on the leading eofs of the sst anomaly and anomaly deviation fields in various domains and the associated expansion coefficient or principal component time series which are used to construct global regression maps of sst sea level pressure slp and a number of related variables the use of anomaly deviations i e departures of local sst anomalies from the concurrent global mean sst anomaly reduces the influence of global mean sst trends upon the structure of the eofs and their expansion coefficient time series an important auxiliary time series used in this study is a southern oscillation index based on marine surface observations by means of several different analysis techniques the time variability of the leading eof of the global sst field is separated into two components one identified with the enso cycle related variability on the interannual timescale and the other a linearly independent residual comprising all the interdecadal variability in the record the two components exhibit rather similar spatial signatures in the global sst slp and wind stress fields the sst signature in the residual variability is less equatorially confined in the eastern pacific and it is relatively more prominent over the extratropical north pacific the corresponding slp signature is also stronger over the extratropical north pacific and its counterpart in the cold season 500 mb height field more closely resembles the pna pattern the amplitude time series of the enso like pattern in the residual variability reflects the above mentioned shift in 1976 77 as well as a number of other prominent features including a shift of opposite polarity during the 1940s

sedimentary indicators of atmospheric activity in the northern hemisphere during the cenozoic abstract the concentrations and accumulation rates of eolian phases and the mineralogy of sediments from a north pacific core ll44 gpc3 have been used to evaluate changes in eolian sedimentation and atmospheric activity during the cenozoic the quartz content and clay mineralogy of the sediments reflect changing source areas for eolian material whereas the accumulation rates of eolian phases reflect climatic variation and wind intensity eolian sedimentation decreased from 70 to 50 m y ago at the site as it moved north out of the equatorial pacific where it was supplied with eolian debris from north america and africa low rates of eolian sediment accumulation 50 to 25 m y ago reflect the temperate humid environment of the early tertiary and the lack of vigorous atmospheric circulation at that time from 25 to 7 m y ago eolian accumulation increased as the site moved into the influence of the westerlies from 7 to 3 m y ago there was a more rapid increase in accumulation of eolian material at the site which was not accompanied by changes in mineralogy or quartz content and was therefore related to climatic change and more vigorous atmospheric circulation about 2 5 m y ago a dramatic increase in eolian sedimentation accompanied the onset of dry northern hemisphere glaciation

reconstructing neogene vegetation and climates to infer tectonic uplift in western yunnan china neogene climates and vegetation history of western yunnan are reconstructed on the basis of known fossil plants using the coexistence approach ca and leaf margin analysis lma four neogene leaf floras from tengchong jianchuan and eryuan in southwestern china are analyzed by the ca and the paleoclimatic data of one miocene carpoflora from longling and three pliocene palynofloras from longling yangyi and eryuan are used for comparison the miocene vegetation of the whole of west yunnan is subtropical evergreen broad leaved forest and a similar mean annual precipitation is inferred for tengchong longling and jianchuan however by the late pliocene a large difference in vegetation occurred between the two slopes of gaoligong mountain western yunnan the region of tengchong retained a subtropical evergreen broad leaved forest vegetation whereas in yangyi and eryuan a vertical vegetation zonation had developed which consists in ascending order of humid evergreen broad leaved needle and broad leaved mixed evergreen and coniferous forests distinctively the late pliocene vegetational patterns of west yunnan were already very similar to those of the present and the pliocene mean annual precipitation in tengchong was markedly higher than that of yangyi and eryuan considering that the overall vegetation of west yunnan and the precipitation at yangyi and eryuan have undergone no distinct change since the late pliocene we conclude that the hengduan mountains on the northern boundary of west yunnan must have arisen after the miocene and approached their highest elevation before the late pliocene furthermore the fact of the eastern portion of the tibetan plateau underwent a slight uplift after the late pliocene is also supported c 2010 elsevier b v all rights reserved

clay mineral assemblages in the zhaotong basin of southwestern china implications for the late miocene and pliocene evolution of the south asian monsoon abstract the characteristics of the evolution of the south asian monsoon during the late miocene through the pliocene are highly debated to obtain a better understanding we studied the clay mineral assemblages and the clay fraction content of a high quality sedimentary sequence borehole core zk1 spanning the interval of 8 8 2 62 ma in the zhaotong basin southwestern yunnan province on the southeastern margin of the tibetan plateau smectite kaolinite illite and vermiculite were the four main clay minerals identified and changes in their relative abundance reveal a distinct pattern of climate change during the study interval until the very late miocene kaolinite and smectite with a small amount of illite were dominant suggesting a relatively warm and humid climate from 6 2 to 2 8 ma smectite was dominant with a minor amount of kaolinite and illite indicating a relatively cool and humid climate and from 2 8 to 2 62 ma vermiculite hiv and illite were dominant with a minor amount of kaolinite indicating a relatively cold and humid climate the variation in clay mineral assemblages indicate substantial changes in the south asian monsoon in the zhaotong basin that promoted a change from a warm and humid climate in the late micoene to cool and humid climate in the very late miocene through pliocene followed by a gradual trend towards a cold and humid climate in the very late pliocene comparison with records from elsewhere indicates that the observed variations in the south asian monsoon were mainly controlled by global cooling rather than by tibetan plateau uplift

impact origin for the hummeln structure sweden and its link to the ordovician disruption of the l chondrite parent body several studies of meteorites show that a large disruption of an asteroid occurred ca 470 ma in our solar system s asteroid belt as a consequence a large number of meteorite impacts occurred on earth during the following few million years the finding and characterization for the first time of planar deformation features in quartz grains from rocks collected at the middle ordovician hummeln structure sweden prove the hypervelocity impact origin of the structure the unambiguous shock features allow us to close an similar to 200 yr old discussion about its origin and further the hypothesis of enhanced asteroid bombardment during the middle ordovician adding an impact crater to the increasing number confirmed and properly dated from this period despite its relatively small size similar to 1 2 km in diameter similar to the young meteor crater arizona usa and its old age the hummeln structure is remarkably well preserved contradicting the general assumption that small craters are not preserved on earth for more than a few tens of thousands to a couple of million years less

understanding oblique impacts from experiments observations and modeling natural impacts in which the projectile strikes the target vertically are virtually nonexistent nevertheless our inherent drive to simplify nature often causes us to suppose most impacts are nearly vertical recent theoretical observational and experimental work is improving this situation but even with the current wealth of studies on impact cratering the effect of impact angle on the final crater is not well understood although craters rims may appear circular down to low impact angles the distribution of ejecta around the crater is more sensitive to the angle of impact and currently serves as the best guide to obliquity of impacts experimental studies established that crater dimensions depend only on the vertical component of the impact velocity the shock wave generated by the impact weakens with decreasing impact angle as a result melting and vaporization depend on impact angle however these processes do not seem to depend on the vertical component of the velocity alone finally obliquity influences the fate of the projectile in particular the amount and velocity of ricochet are a strong function of impact angle

evidence for a wind driven intensification of the kuroshio current extension from the 1970s to the 1980s the spatial and temporal characteristics of oceanic thermal variations in the mixed layer and main thermocline of the midlatitude north pacific are distinctive suggesting different physical origins within the main thermocline 400 m depth the variability is dominated by a westward intensified pattern of decadal scale indicative of enhanced eastward geostrophic flow along the southern flank of the kuroshio current extension during the 1980s relative to the 1970s the authors argue that the decadal scale change in the strength of the kuroshio extension was a result of the dynamical adjustment of the oceanic circulation to a decadal variation in wind stress curl according to sverdrup theory four times daily wind stress fields from the national center for atmospheric research national centers for environmental prediction reanalysis project are used to compute the decadal change in sverdrup transport associated with the 1976 77 climate transition it is shown that the decadal changes in sverdrup transport inferred from the wind stress curl field and in observed geostrophic flow inferred from the upper ocean thermal field are consistent both in terms of spatial pattern and magnitude the decadal change in depth averaged geostrophic transport along the kuroshio extension referenced to 1 km is 11 6 sv similar to the sverdrup transport change 11 5 13 9 sv the decadal scale thermocline variation along the western boundary between 308 and 408n exhibits a lag of approximately 4 5 yr relative to the decadal variation in the basin wide wind stress curl pattern this delay may be indicative of the transient adjustment of the gyre scale circulation to a change in wind stress curl via long baroclinic rossby waves

estimating average shock pressures recorded by impactite samples based on universal stage investigations of planar deformation features in quartz sources of error and recommendations planar deformation features pdfs in quartz are the most widely used indicator of shock metamorphism in terrestrial rocks they can also be used for estimating average shock pressures that quartz bearing rocks have been subjected to here we report on a number of observations and problems that we have encountered when performing universal stage measurements and crystallographically indexing of pdf orientations in quartz these include a comparison between manual and automated methods of indexing pdfs an evaluation of the new stereographic projection template and observations regarding the pdf statistics related to the c axis position and rhombohedral plane symmetry we further discuss the implications that our findings have for shock barometry studies our study shows that the currently used stereographic projection template for indexing pdfs in quartz might induce an overestimation of rhombohedral planes with low miller bravais indices we suggest based on a comparison of different shock barometry methods that a unified method of assigning shock pressures to samples based on pdfs in quartz is necessary to allow comparison of data sets this method needs to take into account not only the average number of pdf sets grain but also the number of high miller bravais index planes both of which are important factors according to our study finally we present a suggestion for such a method which is valid for nonporous quartz bearing rock types which consists of assigning quartz grains into types a e based on the pdf orientation pattern and then calculation of a mean shock pressure for each sample less

a record of ancient cataclysm in modern sand shock microstructures in detrital minerals from the vaal river vredefort dome south africa the record of terrestrial meteorite impacts is fragmentary because most impact structures and ejecta are removed by erosion or buried discovery of the missing impact record from hadean to present may be advanced through identifi cation of residual shocked detritus to evaluate which shocked minerals survive erosion and sedimentary transport we investigated modern sands from the vaal river in south africa where it crosses the 2 02 ga vredefort dome the largest terrestrial impact structure known to date shocked minerals were identifi ed in all sediment samples including from the vaal channel and tributaries within the structure in transmitted light detrital quartz preserves discontinuous decorated planar features previously identifi ed as brazil twins which are readily visible as bright continuous features in cathodoluminescence images detrital zircons preserve fi ve orientations of planar fractures pfs which can produce dramatically offset growth zoning and apparent rotation of subgrains other zircons contain fi lled fractures that may represent a new shock microstructure detrital monazite preserves four orientations of pfs and many grains contain oscillatoryzoned shocked zircon inclusions which thus represent shocked inclusions within shocked accessory grains zircon and monazite with granular texture were also identifi ed this study is proof of the concept that shocked minerals can be identifi ed in sediments up to 2 billion years after an impact event and it demonstrates their potential for preserving evidence of ancient impacts the recognition of a new geological repository for impact evi dence provides a means for identifying distal shocked detritus from eroded structures of any age and may be particularly relevant to early earth studies

nanoscale records of ancient shock deformation reidite zrsio4 in sandstone at the ordovician rock elm impact crater the terrestrial record of meteorite impacts is difficult to decipher because unequivocal evidence of impact is increasingly destroyed with time by erosion burial and tectonics zircon survives these processes as a shocked mineral and above 20 gpa transforms to reidite a high pressure zrsio 4 polymorph diagnostic of impact however the utility of reidite has been limited by its occurrence it has only been reported from three relatively young 36 ma impact craters globally here we report a new occurrence of reidite in brecciated sandstone from the ordovician rock elm impact crater in wisconsin united states electron backscatter diffraction mapping was used to identify reidite and microtwins within shocked zircons smaller than 50 m in diameter reidite occurs both as 200 500 nm wide lamellar intergrowths and as nanoparticulate grains and not only provides the first diagnostic evidence for ultrahigh pressure shock metamorphism at rock elm but is also the oldest reported occurrence of reidite considering its small size and the ubiquitous presence of detrital zircon in siliciclastic rocks reidite may be more common in the rock record than has been reported but has potentially gone undetected the recognition that nanoscale reidite can be preserved over deep time within zircon in shock metamorphosed sandstone presents new opportunities for investigating earth9s impact record as it could potentially preserve nanoscopic evidence of impact events much older than the one that formed rock elm given that shocked zircons have been shown to survive sedimentary cycling the identification of reidite within zircons in siliciclastic rocks could facilitate investigating the impact chronology over much of the geological time scale as the oldest terrestrial minerals known are detrital zircons

stable isotopic and elemental characteristics of pale and dark layers in a late pliocene lignite deposit basin in yunnan province southwestern china implications for paleoenvironmental changes abstract the carbon and nitrogen stable isotopic compositions and elemental characteristics of pliocene pale and dark lignites in the jinsuo basin yunnan province southwestern china were investigated these data were used to develop paleoenvironmental models and to discuss possible geological driving forces for the formation of pale and dark layers the 13c values of fossil wood av 24 79 and fusain samples av 24 19 are generally higher than the values obtained from bulk pale av 27 01 and dark av 26 38 lignite samples in contrast the 15n values of fossil wood av 0 63 and fusain samples av 1 29 are lower than the average values of bulk pale lignites av 2 17 and dark lignites av 1 79 the difference in the carbon isotopic values between pale and dark lignites can be explained by the very high amount of liptinite and strong degradation of woody material by bacterial activity in pale lignites which resulted in depletion of 13c in pale lignites and the wet humid depositional conditions contributed to the relatively heavy stable carbon isotope compositions of dark layers the higher 13c values in the fossil wood and fusain samples can be explained by the general enrichment of 13c in woody material compared to leaves the weakly negative correlation between the 15n and 13c values indicates that besides bacterial degradation the liptinite content could also influence the carbon and nitrogen compositions of lignites the influence of the original plant community gymnosperms angiosperms on the carbon and nitrogen isotopic compositions of bulk lignites is insignificant in the jinsuo basin the paleoenvironmental model suggests deposition of pale layers under relatively dry cold conditions supporting the expansion of gymnosperms such as pinus yunnanensis the slight stepwise uplift of the tibetan plateau and the approximate co occurrence of the more intense asian monsoon might have supported short periods of a locally dry cold climate resulting in the lowering of water table which was favorable for the formation of pale layers the low 13c values in pale layers further support this the relatively high sio2 al2o3 ratios higher values of the average detrital authigenic index and high levels of tio2 and zr in pale layers suggest an increased detrital input relative to dark layers the dark layers however formed in a tropical subtropical warm humid climate that favored angiosperm dominance of the vegetation the long term geologically stable conditions together with the regionally warm humid climate resulted in a rise in the water table in the basin which led to the formation of dark layers until the subsequent slight uplift of the tibetan plateau this conclusion is also supported by the high 13c values in dark layers and the thickness differences between pale thin and dark thick layers and the changes in major elements and minerals changes between the two types of layer

modeling damage and deformation in impact simulations numerical modeling is a powerful tool for investigating the formation of large impact craters but is one that must be validated with observational evidence quantitative analysis of damage and deformation in the target surrounding an impact event provides a promising means of validation for numerical models of terrestrial impact craters particularly in cases where the final pristine crater morphology is ambiguous or unknown in this paper we discuss the aspects of the behavior of brittle materials important for the accurate simulation of damage and deformation surrounding an impact event and the care required to interpret the results we demonstrate this with an example simulation of an impact into a terrestrial granite target that produces a 10 km diameter transient crater the results of the simulation are shown in terms of damage a scalar quantity that reflects the totality of fragmentation and plastic strain both total plastic strain the accumulated amount of permanent shear deformation regardless of the sense of shear and net plastic strain the amount of permanent shear deformation where the sense of shear is accounted for damage and plastic strain are both greatest close to the impact site and decline with radial distance however the reversal in flow patterns from the downward and outward excavation flow to the inward and upward collapse flow implies that net plastic strains may be significantly lower than total plastic strains plastic strain in brittle rocks is very heterogeneous however continuum modeling requires that the deformation of the target during an impact event be described in terms of an average strain that applies over a large volume of rock large compared to the spacing between individual zones of sliding this paper demonstrates that model predictions of smooth average strain are entirely consistent with an actual strain concentrated along very narrow zones furthermore we suggest that model predictions of total accumulated strain should correlate with observable variations in bulk density and seismic velocity

yallalie a buried structure of possible impact origin in the perth basin western australia an enigmatic buried structure located in mesozoic sedimentary rocks in the perth basin western australia was discovered in 1990 by ampol exploration the basin like yallalie structure centred on 30 26 40 3 s 115 46 16 4 e is circular in plan view and about 12 km in diameter high resolution seismic reflection profiles across the structure show a basin shaped area of chaotic reflec tions that extend to a depth of approximately 2 km below the surface the structure has sharp boundaries with surrounding faulted but otherwise relatively undisturbed rocks in the centre of the structure there is an uplifted area approximately 3 4 km across similar to those described from com plex meteorite impact structures the seismically defined structure coincides with a circular topo graphic depression and image processing of digital elevation data has allowed recognition of concentric and radial structures extending as far as 40 km from the centre of the depression gravity surveys show the structure to be associated with a positive gravity anomaly of about 30 gu aeromagnetic surveys have defined annular anomalies associated with the central uplifted section and possibly margins of the structure a search for siderophile element enrichments by neutron activation analysis in the rocks of the structure which would indicate the presence of a meteorite component proved negative quartz grains in cores that penetrate the structure show the development of prismatic cleavage fractures and irregular slightly curved planes formed by brittle fracture an allochthonous breccia of late cretaceous rocks occurs a few kilometres west of the western margin of the structure quartz grains from a thin veneer of tertiary sediments that drape the structure are essentially unde formed however multiple sets of closely spaced planar deformation features in quartz characteristic of highly shocked rocks have yet to be observed in the rocks of the yallalie structure and the allochthonous breccia the morphology of the yallalie structure determined from topographic and geophysical data suggests strongly that it is of impact origin geological and geochemical evidence is equivocal but is not inconsistent with this interpretation

climatic and ecological implications of late pliocene palynoflora from longling yunnan china abstract the longling coal mine w yunnan is situated in an area of substantial geotectonic activity its late pliocene palynoflora is of considerable interest since the area represents a centre of biodiversity eighty two palynomorphs belonging to 61 families were recovered from the lignite the palynoflora is dominated by angiosperms 68 3 with ferns 24 4 gymnosperms 4 9 and algae 2 4 comparisons indicate that most of the palynoflora was derived from the montane humid evergreen broad leaved forest with lesser contributions from the tsuga dumosa forest and evergreen coniferous broad leaved mixed forest as well as the montane mossy evergreen broad leaved forest this indicates that the late pliocene climate was cooler than that of the present in the course of the accumulation of the lignite the climate underwent five major phases of warming and cooling

paleoclimatic estimation reveals a weak winter monsoon in southwestern china during the late miocene evidence from plant macrofossils the late miocene xianfeng flora of yunnan province southwestern china was chosen to reconstruct the paleoclimate and the intensity of the asian monsoon three available quantitative climate reconstruction methods from fossil plants i e leaf margin analysis lma the climate leaf analysis multivariate program clamp and the coexistence approach ca were used in this study mats mean annual temperatures resulting from these three approaches i e lma 17 2 2 38 degrees c clamp 15 43 1 25 degrees c ca 17 2 21 7 degrees c appear to have been higher than the present 14 9 degrees c suggesting a much warmer climate in the late miocene both the growing season precipitation gsp from clamp 1908 7 217 7 mm and mean annual precipitation map from ca 1206 0 1613 0 mm estimates are higher than modern values 1003 2 mm gsp and 1038 mm map respectively indicating a more humid climate during the late miocene by comparing these with climates reconstructed from neighboring late miocene floras we conclude that the general late miocene climate appears warmer and more humid than present conditions in southwestern china furthermore the evident differences in estimated monthly temperatures between the summer and winter and precipitations between the humid and dry seasons indicate the existence of seasonality though not as strong as that of today difference in precipitation of dry season indicates a marked strengthening in the winter monsoon since the late miocene a new monsoon intensity index has also been defined based on precipitation seasonality to investigate the intensity of the asian monsoon c 2012 elsevier b v all rights reserved

pollen and macrofossils attributable to fagopyrum in western eurasia prior to the late medieval an intercontinental mystery abstract the widespread perception that buckwheat fagopyrum esculentum and f tataricum did not occur in western eurasia prior to the late medieval is challenged by numerous pollen finds we traced some 240 localities from the area with pollen or macrofossils attributed to fagopyrum in often much earlier time slices this paper evaluates various explanations for these finds within the context of palaecological methods vegetation history and cultural development the clear morphological characteristics make large scale misidentification of the pollen unlikely although some records are suspect contamination is improbable for the vast majority of the pollen diagrams also long distance transport of pollen of fagopyrum snowdenii or oxygonum from africa seems unlikely as the pollen rain of that continent hardly contains that pollen the option that fagopyrum was present in western eurasia already much earlier than the late medieval must therefore be seriously considered cultivated species may have reached the area by trade between the mediterranean and eastern chinese realms which was regular since 2000 bce as the low pollen values argue against large scale cultivation the taxon may merely have occurred as a weed or its pollen was transported with other products and subsequently re emitted the pervasive notion that buckwheat was cultivated on large scale by the scythians in the ukrainian realm since 800 bce is highly ambiguous and probably wrong there are some indications that wild fagopyrum or a related taxon may have occurred widespread in eurasia during the pleistocene glaciations and the early middle holocene i e predating 2000 bce

structural styles in the perth basin associated with the mesozoic break up of greater india and australia abstract the perth basin constitutes one of the principal tectonic features along the western continental margin of australia and formed through permo cretaceous rifting of greater india and australia it is composed of northerly striking sub basins troughs and ridges bounded by faults which display evidence for normal dip slip and possibly dextral strike slip movement transfer faults divide the basin into compartmentalised regions of similar structural style extension and transtension occurred during the jurassic early cretaceous associated with continental break up stretching was accommodated mainly by the reactivation of pre existing northerly oriented faults which display both planar and listric geometries the darling fault system along the eastern margin of the basin has a planar profile the hanging wall succession in the adjoining perth basin has undergone block rotation and tilting with syn sedimentary depositional thickening of rock units towards the fault listric normal faults occur in both the onshore and offshore portions of the basin and influence geometry of the sub basins dip on these faults decreases through the basin sequence and probably soles out in the upper level of basement rollover anticlines develop within the hangingwall of these structures extension oblique to the main structural trends of the basin in the late jurassic the earliest cretaceous resulted in dextral strike slip movement along major north striking faults and the development of en echelon folds in the basin compressive deformation developed during this event at constraining bends of the major fault systems two orientations of transfer zones are recognised and significantly influence basin structures the first are east west trending transfer faults which formed in the permian and were reactivated during jurassic extension but can only be recognised in the northernmost perth basin these transfer faults link basin segments of different characteristics and transfer dip displacement among the northerly striking faults the transfer zones striking nw only influence late jurassic early cretaceous age deformation features they are characterised by either a swing in a left lateral sense in the orientation of northerly striking fractures as they cross the transfer zones or a termination of the fracture at the transfer zone the transfer zones are parallel to and may be related to transform belts in the indian oceanic crust basin wide uplift occurred during the break up and resulted in basin inversion and erosion of up to thousands of metres of the sedimentary succession folding by dextral strike slip motion along the darling urella fault system also inverted the pre break up sequences in major onshore depocentres

late pliocene temperatures and their spatial variation at the southeastern border of the qinghai tibet plateau it is widely accepted that the late pliocene spans a time with globally warmer conditions compared to today regional specifics in temperature patterns from this period however remain poorly known in this study we reconstruct quantitatively late pliocene climates for eight sites at the southeastern border of the qinghai tibet plateau sbtp based on palaeobotanical data compiled from published sources using the coexistence approach coa and analyze anomalies with respect to modern climates the reconstructed temperatures indicate that in the late pliocene the northwestern part of the study area was cooler than its southern part this spatial differentiation in temperature was largely due to differences in altitude the northwest of the sbtp probably had higher altitudes than the south at that time mean annual temperatures mats were around 1 degrees c higher than today suggesting a cooling trend since the late pliocene our data show that summer temperatures have declined significantly since the late pliocene while winter temperatures have remained similar to those of the present different from observations in other territories the unexpected summer and winter temperature changes can be explained by the regional orogenic uplift plus the global cooling the eastward extrusion of the qinghai tibet plateau might have blocked the southward cold high pressure of the winter monsoon and forced it to circumvent the eastern flank of the plateau weakening its impact on the sbtp the post pliocene mountain uplift increased the overall altitude of the region which caused the temperature decline for both summer and winter the reconstructed summer precipitation was lower while the winter precipitation was higher than today suggesting a weaker monsoon climate during the late pliocene c 2015 elsevier ltd all rights reserved