monsoon fluctuations in two 20 000 yr b p oxygen isotope pollen records off southwest india abstract two marine pollen diagrams for sediments off the southwest coast of india provide a 20 000 yr history of the nearby continental vegetation determined by the monsoon climate within the framework of the isotopic stratigraphy two important phases of the evolution of the monsoon climate are a very arid period about 22 000 18 000 yr b p and a very humid period culminating at 11 000 yr b p the very arid period corresponds to the lowest pollen representation of mangrove vegetation which is used here as an indirect indicator of monsoonal runoff this aridity is due to a very weak southwest airflow a great reduction of summer monsoonal rainfall and reduced runoff of the western ghats rivers the extension of the monsoon over india after the last glacial maximum has been a gradual process following the northward progression of the intertropical convergene zone the very humid period corresponding to the highest pollen representation of mangrove vegetation and the heaviest summer rainfall is a climatic response to the maximum summer insolation of the northern hemisphere at 11 000 yr b p

reply to l v dimieri and m m turienzo 2012 comment on fault inversion vs new thrust generation a case study in the malargue fold and thrust belt andes of argentina by j f mescua and l b giambiagi journal of structural geology 35 2012 51 63

kinematic models of basement cover interaction insights from the malargue fold and thrust belt mendoza argentina abstract we investigate through natural examples from the malargue fold and thrust belt the manner in which the basement structures interact with the cover in a thick skinned fold and thrust belt our work suggests that there is a broad spectrum of basement cover interaction mechanisms with two end members coupled and uncoupled interactions the kind of bonding between basement and cover is related to the propagation to slip ratio p s because high values of this ratio indicate rapid forward propagation of shortening into the cover while low values favour welding between basement and cover structures we analyse the factors controlling the kinematics of basement cover deformation and find that not only the strength of the cover its thickness and its mechanical anisotropy control the p s and basement cover bonding but also the strain rate the thickness of synorogenic strata and the presence of pre existing faults

the role of the subcutaneous zone in karst hydrology abstract the subcutaneous zone is the upper weathered layer of rock beneath the soil but above the permanently saturated phreatic zone it is of particular hydrological importance in karst because of its high secondary permeability arising from the considerable chemical solution in this zone however corrosional enlargement of fissures diminishes with depth thus permeability decreases in the same direction with the result that percolation is inhibited except down widened master joints and faults storage of water consequently occurs in this zone particularly after storms the upper surface of this suspended saturated layer in the subcutaneous zone is defined by a perched water table which slopes towards points of rapid vertical percolation the potential induces lateral water movement converging on the most permeable areas such as beneath dolines leakage from the subcutaneous store sustains slow percolation in the vadose zone cross correlation of rainfall with percolation rates in caves in new mexico u s a and new zealand reveal response lags of 2 14 weeks with no apparent relationship to depth below the surface other percolation sites show no correlation with rainfall interpreted as being a consequence of considerable friction in tight fissure networks the recognition of storage and rapid as well as very slow percolation from the subcutaneous zone requires re interpretation of the components of hydrographs from karst springs and of some conceptual models of karst aquifers the importance of subcutaneous storage in sustaining baseflow discharge at some sites must be recognised as must the contribution of subcutaneous water to flood hydrographs methods of estimating the volumes of subcutaneous and phreatic components of karst spring flood hydrographs are presented the paper concludes with a discussion of the significance of subcutaneous hydrologic processes for an understanding of karst geomorphology the desirability of explaining karst landform evolution in terms of hydrologic processes is stressed

temporal and spatial relationships of thick and thin skinned deformation a case study from the malargue fold and thrust belt southern central andes abstract in this paper we analyse two end member models of temporal and spatial interactions between thick and thin skinned structures in a thrust front with pre existing rift structures in the most commonly accepted model a hinterland to foreland sequence of inversion of pre existing normal faults is proposed as a result the emplacement of shallow thrust sheets in the sedimentary cover occurs before the basement inversion in the foreland in the other model basin inversion occurs early in the deformation history of the external part of a fold and thrust belt as the result of a foreland to hinterland sequence of inversion the malargue fold and thrust belt 34 36 s formed in response to compression of the mesozoic neuquen basin during neogene to pleistocene times integrating detailed structural data from the northern part of this belt with new ar ar dating we propose a revised kinematic model of thick and thin skinned interaction and define the temporal spatial evolution of the belt comparison of the timing of deformation in the thick and thin skinned areas strongly supports the hypothesis that the reactivation of normal faults was coeval with the insertion of shallow detachments and low angle thrusting along the migrating front of the thrust belt and occurred from the foreland to the hinterland detachments occur at several stratigraphic horizons including a deep basement decollement related to the basement involved thrusting and shallow detachments located within the jurassic and cretaceous beds these shallow and deep detachments were coeval producing simultaneous development of thrusts during the complex deformation of the thrust front between 15 and 8 ma

a 50 000 year record of late pleistocene tropical vegetation and human impact in lowland borneo abstract there has been considerable uncertainty about the nature of pleistocene environments colonised by the first modern humans in island se asia and about the vegetation of the last glacial maximum lgm in the region here the palynology from a series of exposures in the great cave of niah sarawak malaysian borneo spanning a period from ca 52 000 to 5000 bp is described vegetation during this period was climate driven and often highly unstable interstadials are marked by lowland forest sometimes rather dry and at times by mangroves stadials are indicated by taxa characteristic of open environments or as at the lgm by highly disturbed rather open forest stadials are also characterised by taxa now restricted to 1000 1600 m above sea level suggesting temperature declines of ca 7 9 c relative to present by comparison with modern lapse rates the practice of biomass burning appears associated with the earliest human activity in the cave

cenozoic deformation and tectonic style of the andes between 33 and 34 south latitude 1 the andes of argentina and chile between latitudes 33 and 34 s are composed from west to east of an oligocene to miocene volcanic arcs and the neogene east vergent aconcagua fold and thrust belt of the cordillera principal and the basement block faulted cordillera frontal a regional cross section suggests that shortening across the andes was achieved by thrusting along detachments at several levels in the crust while thin skinned deformation along newly formed thrusts occurred in mesozoic sequences of the eastern cordillera principal reactivation of preexisting jurassic and oligocene normal faults has resulted in additional hybrid thick and thin skinned structures in the western cordillera principal five major thrusting events are recognized in this part of the andes 1 early to middle miocene tectonic inversion of the extensional faults in the western cordillera principal 2 middle to late miocene development of the aconcagua fold and thrust belt 3 late miocene uplift of cordillera frontal 4 late miocene early pliocene out of sequence thrusting in the cordillera principal and 5 pliocene to present deformation of the foreland

effects of glaciations upon karst aquifers in canada abstract in canada there are 5 7 10 5 km 2 of limestone and marble outcrop 6 10 5 km 2 of dolomite and 8 10 4 km 2 of sulfate rocks in addition halite subscrops beneath 5 10 5 km 2 of the central prairie region and interacts with modern groundwater circulation to a varying extent more than 90 of the total outcrop subcrop has been repeatedly glaciated the most recent glaciation late wisconsin terminated 13 000 5000 yrs b p in different areas carbonate terrains still partly buried by glacier ice may be inspected in the rocky mountains nine distinct effects of glacial action upon the propagation and efficiency of karst aquifers are recognized destructive effects include erasure dissection infilling and injection bedrock solution may be inhibited during non glacial periods by a cover of glacial drift rich in carbonate clasts glacial burial may also preserve an aquifer and enhance its storage characteristics aquifer expansion may be stimulated by raising the hydrostatic head or steepening hydraulic gradients or by crustal flexure during deglacial isostatic rebound the differing effects make general prediction of the state of an aquifer in glaciated terrains difficult

the goose arm karst newfoundland canada abstract goose arm karst comprises 200 km2 of deformed carbonates with relief of 60 350 m blanketed with carbonate rich till of the last glaciation principal karst landforms are 50 large bedrock depressions implying mature well integrated karst development modern groundwater systems are short young non integrated the anomaly is explained by injection of glacial till into a paleo aquifer clogging it buffering by till also yields a remarkably uniform bicarbonate water chemistry but groundwater temperatures are anomalous

palynology of eastern indonesian marine piston cores a late quaternary vegetational and climatic record for australasia abstract pollen analyses of late quaternary sediments from nine marine piston cores reveal a continuous vegetation and environmental record for eastern indonesia and northern australia on the island of halmahera a montane oak forest largely replaced the tropical lowland vegetation during the last glacial period while fern cover was strongly reduced during its maximum 18 000 yr b p climate was cooler and slightly drier than today around 10 000 yr b p mangrove vegetation expanded following the rising sea level in our western new guinea record at 14 000 yr b p climate grew warmer and slightly wetter until it stabilised around 10 000 yr b p at that time the mid to upper montane forests expanded to their full altitudinal range and fern cover increased while montane oak forest grassland and woodland areas had contracted in our marine pollen records during the last glacial the climate of northern australia was distinctly drier than today grassland vegetation with sedges increased considerably at 38 000 and 24 000 yr b p replacing eucalypt forest and culminating in a maximum grassland cover at the height of the last glaciation 18 000 yr b p the rapid sea level rise allowed the expansion of mangrove forests and salt bush marshes which had become established on the large tidal flats of the drowning sahul shelf around 12 000 yr b p one piston core g6 4 extends to 300 000 yr b p and shows that glacial periods are characterized by high pollen concentrations in marine sediments recording expanding grassland vegetation during interglacial woodland and fern cover increased while pollen concentrations in the sediments were low after 190 000 yr b p a more open vegetation suggests that conditions were in general much more arid than before repeated mangrove vegetation expansions suggest major rises in sea level at around 244 000 220 000 and 130 000 yr b p

effects of glaciations and permafrost upon the development of karst in canada canadian examples suggest that karst landforms may be divided into eight types in terms of their temporal relationships to the record of repeated quaternary glaciations two types are postglacial two are subglacial one type occurs where glacial features are adapted to karstic drainage and three types display sequences of karstic and glacial action glacier effects upon karst landforms and their underlying aquifers display the gamut of possibilities they may destroy inhibit preserve or stimulate karst development where continuous permafrost is maintained when covered by glacier ice postglacial karst is limited to the active layer epikarst where permafrost is thawed beneath ice or during deglaciation there are a variety of postglacial karst developments depending in part upon climate and in part upon local lithologic and relief conditions

reply to the comments of faulkner on wilson et al 2012 surface lowering of limestone pavement as determined by cosmogenic 36cl analysis earth surface processes and landforms 37 1518 1526

dips of normal faults in british coal measures and other sedimentary sequences fault dip measurements n 3291 from 122 faults in british coalfields are presented two classes of normal fault are recognized a gently dipping 55 post coalification tectonic faults formed at depths of about 2 5 km which comprise 90 of the faults analysed dip data from the steeply dipping faults are variable standard deviation 9 both on single faults and between faults and 70 is a better approximation of fault dip than the commonly accepted value of 60 data on tectonic normal faults with comparable depths of formation using the modified griffith fracture criterion the dips of faults at varying depths up to 4 km are calculated for both unsaturated dry and saturated rocks the dips of normal faults are expected to vary from 90 at the surface to 60 at 3 4 km and this variation is consistent with the limited field data available the coalfield data are consistent with fault formation at standard hydrostatic pore fluid pressures at depths of about 2 5 km below depths of a few kilometres normal faults are expected to flatten out gradually to a dip of 45 but such flattening is not necessarily an indication of an underlying detachment

episode of strengthened summer monsoon climate of younger dryas age on the loess plateau of central china abstract the baxie loess section just east of the tibetan plateau contains evidence showing that the asian monsoon climate experienced an abrupt reversal near the end of the last glacial age rapid deposition of dust under cool dry full glacial conditions gave way to an interval of soil development and reduced dust influx attributed to a strengthening of the warm moist summer monsoon a subsequent abrupt increase in dust deposition a response to a weakening of the summer monsoon was later followed by renewed soil formation as summer monsoon circulation again intensified during the early holocene by one interpretation the thin upper loess is a manifestation of the european younger dryas oscillation however in this case the available 14c ages require either that 1 onset of loess deposition lagged the beginning of the younger dryas event in europe by as much as 2000 calibrated 14c years or 2 all the 14c ages are too young possibly due to contamination alternatively the late glacial paleosol the top of which is synchronous with the abrupt end of the late glacial 18o anomaly in the dye 3 greenland ice core records the younger dryas event such an interpretation is consistent with general circulation model simulations of younger dryas climate that show strong seasonality and a strengthened summer monsoon and with marine cores from the western pacific ocean that contain evidence of pronounced cooling of surface waters during younger dryas time

new constraints on the age of the last ice sheet glaciation in nw england using optically stimulated luminescence dating optically stimulated luminescence osl has been used to date silts interpreted as either primary or colluviated loess deposited in karstic depressions at three sites on the carboniferous limestone of nw england two of the ages presented here constrain the onset of the last late devensian ice in this region to later than ca 27 2 ka and the other two date initial deglaciation prior to ca 19 2 ka in the morecambe bay area and ca 17 2 ka in the karst of the yorkshire dales while these ages are broadly consistent with existing estimates from lacustrine and speleothem evidence they offer the tightest constraints yet published on the presence of the last ice sheet from northern england copyright 2009 john wiley sons ltd

comment on fault inversion vs new thrust generation a case study in the malargue fold and thrust belt andes of argentina by j f mescua and l b giambiagi journal of structural geology 35 2012 51 63 fil dimieri luis vicente consejo nacional de investigaciones cientificas y tecnicas centro cientifico tecnologico conicet bahia blanca instituto geologico del sur universidad nacional del sur departamento de geologia instituto geologico del sur argentina

geometry and kinematics of the fuegian thrust fold belt southernmost andes fil torres carbonell pablo juan consejo nacional de investigaciones cientificas y tecnicas centro austral de investigaciones cientificas argentina

evidence for the younger dryas climatic event in southeast asia abstract this article reviews evidence for the younger dryas climatic event from the limited data available from mainland and island southeast asia and from deep sea cores from the region data from highland indonesia and regional deep sea cores suggest a climatic reversal at the time of the younger dryas may be more widely detectable with finer resolution pollen analysis and additional radiocarbon dating but it should be remembered that dates of this age cannot be calibrated locations are suggested in the region where more sites and finer resolution analysis is needed before definite statements on the younger dryas can be made at present the best evidence for its occurrence comes from one sumatran pollen diagram but even that is very tentative

thick skinned and thin skinned thrusting in the la ramada fold and thrust belt crustal evolution of the high andes of san juan argentina 32 sl abstract the cenozoic structural evolution of the la ramada fold and thrust belt in the high andes of argentina between 32 00 s and 32 30 s shows in time and space the interaction of thin skinned and thick skinned deformations based on geometric and kinematic constraints three different deformation stages have been recognized the first began with thin skinned nnw trending structures detached in upper jurassic gypsum in the second stage the basement was involved by tectonic inversion of triassic normal faults producing a thick skinned fold and thrust belt this inversion combined with the ductile rheology of the jurassic gypsum resulted in refolding of older structures the uplift of the basement by high angle reverse faults at the ramada espinacito massif produced a sticking point in the foreland propagation of the thrust belt this was responsible for the third stage of deformation characterized by thin skinned nnw out of sequence thrusts developed in the westernmost sector the total andean shortening calculated in the area was 21 24 km near 30 the structure of the la ramada fold and thrust belt was integrated into a crustal scale cross section at 32 s latitude based on gravimetric models and surface geology a crustal model is proposed for the andes of chile and argentina a shortening of 180 km was calculated between the chile trench and the sierra de pie de palo this implies a mean deformation rate of 2 8 mm year 1 during cenozoic times an initial crustal thickness of ca 33 km was computed a two layer model with a middle detachment level is proposed to explain the spatial decoupling between maximum shortening at the surface and maximum crustal thickening the upper layer was balanced based on surface structural information the lower layer is interpreted to have been constructed by an imbricate thrust system controlled by the mercedario rift master shear and the precordillera chilenia suture

people and large carnivores as biostratinomic agents in lateglacial cave assemblages biostratinomic analysis processes acting between death and burial of lateglacial mammal bone assemblages from three caves in northern england demonstrates the value of re examining archived assemblages with ams radiocarbon dating of key specimens these assemblages shed light on the ecology of a region at the northern limit of lateglacial human activity in britain during the lateglacial interstadial bears wolves and humans expanded into the region bears by around 12 500 14c yr bp and the earliest evidence for human presence is around 12 300 14c yr bp at victoria cave wolf activity included predation and scavenging of large ungulates and scavenging bear carcasses apparently resulting from hibernation deaths the scavenging of bear carcasses is possibly confined to the first part of the lateglacial interstadial whereas evidence for wolf scavenging large ungulates increases later in the interstadial after about 11 800 14c yr bp perhaps reflecting changes in the productivity of the lateglacial ecosystem and in human subsistence patterns the assemblage from sewell s cave is wolf den debris from the very end of the lateglacial interstadial around 10 800 14c yr bp whilst that from kinsey cave is dominated by large bodied carnivores and is argued to have a quite different taphonomic history copyright 2007 john wiley sons ltd

influence of mechanical stratigraphy and initial stress state on the formation of two fault propagation folds abstract kinematic and mechanical modeling of the rip van winkle se new york usa and la zeta sw mendoza argentina anticlines illustrate the influence of mechanical stratigraphy and initial stress state on the kinematics of fault propagation folding in both anticlines faults nucleating at distinct stratigraphic levels open upward into triangular zones of folding folding intensity and finite strain attenuates with distance from the fault tip trishear reproduces the bulk geometry and finite strain of the relatively homogeneous limestone sequence of the rip van winkle anticline and predicts an initial location of the fault tip consistent with the field observations folding of the heterogeneous sedimentary section of la zeta anticline however cannot be simulated by the trishear model alone an additional mode of deformation involving transport of material from the backlimb into the hinge area and extension parallel to the direction of fault propagation is necessary to reproduce the geometry and finite strain of the anticline mechanical distinct element modeling dem of the anticlines indicates that their contrasting kinematics could have resulted from differences in mechanical stratigraphy and initial stress state folding of a homogenous normally consolidated assemblage initial horizontal to vertical stress ratio k o 1 is trishear like and resembles the rip van winkle anticline folding of a heterogenous layered such as la zeta over consolidated assemblage k o 1 departs from the trishear model and resembles la zeta anticline based on the dem simulations we postulate that the rip van winkle anticline formed at high depths high overburden loads and lithostatic stress conditions and that la zeta anticline formed at shallow depths after substantial uplift and erosion of the andean mountain front which induced over consolidation and high k o

variations of the monsoon regime during the upper quaternary evidence from carbon isotopic record of organic matter in north indian ocean sediment cores abstract the 13 c 12 c ratios and contents of organic carbon in deep sea sediment cores of the north indian ocean have been compared for the different climatic stages as determined by oxygen isotope stratigraphy using the differences in the 13 c values between marine and terrestrial organic matter the terrestrial contribution to the eastern gulf of bengal and the andaman sea has been determined for modern and glacial times the geographical distribution of the terrestrial organic carbon linked to sea surface circulation shows that during the last glacial period the ne monsoon circulation was the dominant feature the organic carbon abundance within the sediment which is related to local productivity was greater during glacial times in the areas where production depends on the ne monsoon strength coast of north india in the arabian sea and andaman sea suggesting its reinforcement

a 400 000 year record of vegetational and climatic changes from a volcanic basin leizhou peninsula southern china abstract the tianyang lake in leizhou peninsula is an enclosed crater formed during the early to middle pleistocene over 200 m of diatomaceous mud and clay were deposited in the last 400 000 years providing a continuous middle and late quaternary lacustrine sequence for paleoenvironmental studies the pollen record spans the last four glacial interglacial cycles equivalent to oxygen isotope stages ois 10 to 1 during most of the glacial phases fagaceous monsoon forest was replaced by altitudinal vegetation indicating a regional landscape transformation on the peninsula the montane forest reached down to the lowland by at least 600 m during the ois 6 and 8 in a cool and relatively wet condition with temperature estimated to be more than 4 c lower than present a further lowering of the montane forest belts by about 800 1000 m occurred in the ois 4 2 as implied by the appearance of many temperate elements during the last glacial maximum this mixed forest subsequently gave way to the poaceae grassland a savanna vegetation type favored by drier and cooler climatic conditions this drastic change implies a more significant drop in temperature and precipitation than the previous three glacial periods ois 10 8 and 6 it is thus inferred that the weakening of summer monsoon was more significant towards the end of the late pleistocene particularly during the last glacial maximum lgm

late quaternary environmental changes and the alluvial record in humid tropical environments abstract ice core and ocean drilling records now confirm the evidence from lakes rivers and mires concerning temperature depression in the humid tropics during the lgm by at least 5 c on land and this accords with the recent ccm1 model output there is less agreement about fluctuation in precipitation amount intensity and seasonality during the late quaternary pollen records remain indeterminate because of the absence of sites in lowland rainforest locations and a widespread hiatus in sedimentation spanning the lgm alluvial sediments have often been ignored by specialists from other disciplines but they also provide a valuable source of palaeoenvironmental information that reflects catchment wide conditions current evidence shows that prolonged sedimentation took place in stage 3 at sites in s america and se asia and this was followed by incision for up to 9 ka spanning the lgm streams either produced little sediment or were characterised by braided channels and sometimes fan deposits until the transition towards an interglacial mode took place after 12 700 bp 14 c in many places this transition was marked by large floods incision and deposition of coarse sediment but as the holocene climates stabilised and fluctuations of runoff reduced in amplitude so meandering rivers developed floodplains with thick overbank silts and clays these changes have regional and intercontinental patterns not everywhere identical in bracketing dates but demonstrating major changes to the fluvial systems as a result of profound changes to the hydrology of forested tropics during the last 60 ka

structure and function of a conduit aquifer the hydrological function of a karst aquifer is strongly controlled by its physical structure observations of physical hydrology and water chemistry along with artificial tracing allow aquifer behaviour to be identified so that hypothetical aquifer structures can be envisaged such structures can be evaluated in terms of the geology and geomorphology of the area in question and explained in terms of the geomorphological evolution of the aquifer a study of the castleguard meadows karst aquifer rocky mountains alberta is used to demonstrate this four karst springs one perennial the remainder intermittent in one group are considered to be the outlets to a number of conduits the oldest and largest of these is possibly choked by sediment and acts as a reservoir rather than a conduit while others convey overflow floods from the upper saskatchewan glacier the aquifer is of great antiquity but has been disrupted by glaciation the aquifer model developed is a simple hypothesis but provides a valuable

pollen evidence of changing holocene monsoon climate in sichuan province china pollen evidence from lake shayema mianning county was obtained to examine postglacial vegetation and climatic change in southwestern sichuan china the sclerophyllous character of the region s warm temperate vegetation today is a reflection of extreme drought in spring before the onset of the asian monsoons the pollen record displays several changes in the vegetation over the last 11 000 yr from 11 000 to 9100 yr b p cold tolerant species such as abies betula and deciduous oaks dominated the vegetation between 9100 and 7800 yr b p the abundance of deciduous oaks decreased and evergreen oaks increased as did tsuga and mesic deciduous species this change suggests a warming climate with increased precipitation from 7800 to 4000 yr b p sclerophyllous species increased at the expense of mesic deciduous species an indication that precipitation was becoming more seasonal except for increased disturbance starting ca 1000 yr b p the predominance of sclerophyllous vegetation continued until today the pollen results are compatible with proposed global circulation hypotheses of a strengthened monsoon system during the early to mid holocene

late pleistocene monsoon variability in northwest thailand an oxygen isotope sequence from the bivalve margaritanopsis laosensis excavated in mae hong son province abstract long continuous records of late quaternary environmental change are rare in southeast asia yet they are crucial for understanding the nature of early human dispersal and occupation in the australasian region we present a new record of palaeomonsoon activity extending back to 35 000 bp years before the present based on the analysis of oxygen isotope ratios 18 o in the freshwater bivalve margaritanopsis laosensis excavated from the tham lod and ban rai rockshelters in mae hong son province northwest thailand long term changes in the m laosensis 18 o record reflect changes in the 18 o of the river water in which these organisms grew and correlate well with changes in speleothem 18 o records of east asian monsoon rainfall from hulu cave and dongge cave in china the new northwest thailand 18 o sequence indicates wetter and relatively unstable climatic conditions from 35 000 to 20 000 bp followed by drier conditions from 20 000 to 11 500 bp a period of peak aridity occurred around 15 600 bp during heinrich event 1 suggesting that the intertropical convergence zone shifted southward when the north atlantic region cooled however there is little evidence for the younger dryas event at 12 800 11 500 bp after 9 800 bp precipitation increased substantially and climatic variability declined our findings provide an improved baseline against which to gauge interactions between early humans and climate change in southeast asia for example there was no significant change in the prehistoric flake stone technology used at tham lod and ban rai despite the bivalve 18 o evidence for substantial climate change in the region also the climatic impact of the younger dryas event appears to have been less intense in northwest thailand compared to the cooling and drying observed in china and may explain why agriculture made a relatively late appearance in thailand possibly involving migrants from china

a high resolution sea surface temperature record from the tropical south china sea 16 500 3000 yr b p the timing and magnitude of sea surface temperature sst changes in the tropical southern south china sea scs during the last 16 500 years have been reconstructed on a high resolution c 14 dated sediment core using three different foraminiferal transfer functions simmax28 ram fp 12e and geochemical u 37 k sst estimates in agreement with climap reconstructions both the fp 12e and the u 37 k sst estimates show an average late glacial interglacial sst difference of 2 0 degreesc whereas the ram and simmax28 foraminiferal transfer functions show only a minor 0 6 degreesc or no consistent late glacial interglacial sst change respectively both the u 37 k and the fp 12e sst estimates as well as the planktonic foraminiferal delta o 18 values indicate an abrupt warming ca 1 degreesc in 200 yr at the end of the last glaciation synchronous within dating uncertainties with the bolling transition as recorded in the greenland ice sheet project 2 gisp2 ice core whereas the ram derived deglacial sst increase appears to lag during this event by ca 500 yr the similarity in abruptness and timing of the warming associated with the bolling transition in greenland and the southern scs suggest a true synchrony of the northern hemisphere warming at the end of the last glaciation in contrast to the foraminiferal transfer function estimates that do not indicate any consistent cooling associated with the younger dryas yd climate event in the tropical scs the u 37 k sst estimates show a cooling of ca 0 2 0 6 degreesc compared to the bolling allerod period these u 37 k sst estimates from the southern scs argue in favor of a northern hemisphere wide synchronous cooling during the yd period c 2001 university of washington

vegetation climate and sea level in the past 55 000 years hanjiang delta southeastern china abstract pollen in quaternary deposits from the subtropical hanjiang delta records three major phases in the local vegetation and climate history during the last 55 000 yr 1 a prevalent cool to temperate and humid climate at ca 24 000 14c yr b p is indicated by abundant pollen of temperate trees including conifers 2 between 20 000 and 15 000 14c yr b p a cold dry environment was associated with low sea level during the last glaciation leading to subaerial exposure weathering and interruption of sedimentation as well as departure from the region of dacrydium and sonneratia 3 a short term expansion of grassland at ca 10 300 14c yr b p reduced the predominant lauraceae fagaceae evergreen forest possibly corresponding to the younger dryas cooling the combined data indicate a maximum sea level rise in the mid holocene 7500 4000 14c yr b p and a marine influence in the late pleistocene at 45 000 20 000 14c yr b p the holocene warming however did not bring back moisture sensitive taxa indicating high seasonal aridity probably caused by renewed monsoon conditions

tectonic wedge geometry at bardas blancas southern andes 36 s argentina abstract a tectonic wedge at the mountain front of the cordillera principal mendoza province argentina shows some geometrical features that depart from examples described elsewhere this wedge underthrusts the roof sequence beneath a blind thrust the wedge is deformed by imbricate backthrusting that branches into the hangingwall ramp of the leading horse this backthrust system contributed to the uplift and shortening of the mountain front

late pleistocene and holocene development of the interior peat accumulating basin of tropical tasek bera peninsular malaysia the stratigraphy of holocene peat deposits from an interior lowland basin of tropical peninsular malaysia provides insight into the hydrological ecological and climatic controls on tropical peatland development interpretations about vegetation and climate dynamics including storm intensity over the past 5000 years are integrated with regional and global climatic and eustatic changes to serve as a proxy for past ecology and climate tasek bera basin tbb is a lowland dendritic basin in tropical peninsular malaysia accumulation of organic matter occurred in local lakes during the last glacial maximum lgm but widespread peat deposition did not start until 5300 bp when climatic changes led to the evolution of a wetland system peat accumulation progressively expanded with terrestrialisation of channels and subbasins to paludification of the riparian part of the lowland forest zone lithofacies can be distinguished despite the highly diverse peat and organic rich sediment composition as a result of the climatic and hydrologic changes over the past 5300 years peat accumulation rates ranging from 0 7 to 2 5 mm year are highest in pandanaceae environments and lowest in high ash swamp forests and environments dominated by cyperaceae transects of peat cores across the mire system show the stratigraphic complexities of the peat is the result of hydrological variations and thus plant successional changes ash yield shows that periods of high mineral matter input into the drainage system occurred since the mid holocene indicating rapid and cyclic changes in frequency and magnitude of runoff events and by inference storms stratigraphic analysis of peat and ash yield are tools that provide a proxy for development of holocene hydrologic events in topogenous peat deposits

oblique half graben inversion of the mesozoic neuquen rift in the malargue fold and thrust belt mendoza argentina new insights from analogue models abstract the malargue fold and thrust belt located in the andean mountains between 34 s and 36 30 s formed in response to contraction during cenozoic times its structural style and geometry was controlled by the mesozoic rift system that formed the neuquen basin in west central argentina the rift architecture in the southern sector of this belt was previously interpreted in terms of the present n s compressive structural trends assuming the inversion of pre existing normal faults with the same orientation here we propose that the nw se trending el manzano liu cullin lineament located in the northern termination of the sierra azul reflects the presence of a half graben master fault in the subsurface this hypothesis is supported by subsurface data a balanced cross section and it is tested using a series of scaled sandbox analogue models we suggest that the lineament responds to a reactivated nw trending half graben fault hidden by the mainly n s trending andean structures the proposed orientation is in agreement with the ne sw extension developed in the neuquen basin during the triassic early jurassic the modeling of the inverted oblique half graben reveals that the strikes of the main structures of inversion related belts may often be independent of the orientation of the previously developed extensional system providing a new perspective for their interpretation

fault inversion vs new thrust generation a case study in the malargue fold and thrust belt andes of argentina abstract the reverse reactivation of pre existing normal faults has been documented in many orogens in other cases the lack of sub surface information has allowed the construction of both inversion and non inversion structural models we will analyze the possibility of fault inversion in one such case in the malargue fold and thrust belt in the andes of argentina in order to address this issue we modeled fault inversion vs new thrust generation using the reactiva 2 4 software and varying the physical parameters for the pre existing fault and the host rock the results of modeling are compared to the possible sub surface characteristics of faults in the malargue fold and thrust belt we show that the orientation of these structures in the andean stress field makes them likely to reactivate if the pre existing fault planes present a low coefficient of friction and or fluid overpressure both are expectable in the geological setting in which the structures are found we conclude that fault inversion cannot be dismissed and should be taken into account for structural models of the malargue fold and thrust belt our results can be extended to other orogens with similar characteristics

cenozoic tectonics of the high andes of west central argentina 30 36 s latitude abstract the structure of the central andes shows three distinctive segments characterized by different geometries these geometries are superimposed on the present large scale plate tectonic setting characterized by distinct subduction segments the northern la ramada segment is a thick skinned fold and thrust belt formed by tectonic inversion of a late triassic rift the central aconcagua segment consists of a thin skinned fold and thrust belt while the southern malargue segment like the first one is a thick skinned fold and thrust belt developed by tectonic inversion of a late triassic early jurassic rift system during late cenozoic times the amount of shortening gradually decreases from north to south as indicated by the crustal roots of the central andes the different geometries along the principal cordillera controlled the abrupt changes in the shortening among segments the structure of precordillera and sierras pampeanas has also been considered in order to account for the total shortening in the la ramada segment the main shortening occurred in the precordillera in the aconcagua segment in the principal cordillera while in the malargue segment the shortening is widely distributed in a broader principal cordillera because south of the flat slab subduction segment the precordillera and sierras pampeanas are missing

the control of pre existing extensional structures on the evolution of the southern sector of the aconcagua fold and thrust belt southern andes abstract the aconcagua fold and thrust belt located in the andean mountains at 32 30 to 34 s has been described as a classic model of a thin skinned thrust belt however new structural data from its southern sector have shown that it has a complex structural framework reflected in multiple mesozoic extensional phases overprinted by structural inversion as well as thin and thick skinned tectonics two major superimposed extensional structural styles have been identified for the mesozoic characterized by distinctly oriented stress fields a key role in the evolution of this part of the fold and thrust belt was played by a late triassic to early jurassic depocentre and by late jurassic block faulting shortening was accommodated by a combination of inversion of pre existing normal faults development of footwall short cuts and both thin and thick skinned thrusting synrift and postrift sedimentary rocks were uplifted by reactivation of normal faults with further shortening along newly formed thin skinned thrust faults the geometry of thin skinned fault systems is controlled by the architecture of the rift basin competent footwalls forming barriers to the lateral propagation of detachments

mechanisms of basin contraction and reactivation in the basement involved malargue fold and thrust belt central andes 34 36 s we have conducted a structural study of both the basement involved malargue fold and thrust belt mftb and the active san rafael block srb which are located in the central andes at latitude 34 36 s based on several field examples located both in the inner and frontal part of belt and from the distal foreland zone we focus on the relationships between basement and cover deformation with respect to the known palaeogeography and structural inheritance in several zones we point out similarities in the structural and sedimentary responses to andean shortening the recent morphologic response has also been investigated through the analysis of active deformation along the eastern border of the srb we show that these structural and sedimentary processes are continuous in time and space since they can be applied in the various parts of the fold belt and also at different stages of fold and thrust belt building as well finally we propose the illustration of those mechanisms by complete cross section along the rio grande valley and a possible kinematic scenario of deformation propagation

biomass burning in indonesia and papua new guinea natural and human induced fire events in the fossil record abstract microscopic charcoal preserved in sediments from ten wetlands in the indonesian and papua new guinea region provide a proxy record of regional fire events during the last 20 000 years two periods of high regional charcoal frequency are encountered during the last glacial transition 17 000 9000 years b p and the middle to late holocene 5000 years b p to the present despite the presence of humans in the region throughout the last 20 000 years there is no suggestion that on a regional spatial scale fire frequencies were solely related to changing subsistence patterns of the human population pollen data from these same sites suggest that during times of high charcoal the rate at which vegetation changes represented by the fossil pollen spectra also increases high climate variability may promote a greater community turnover rate and in turn a more fire susceptible forest community rapid climate change and high variability during the last glacial transition and intensification of el nino related climate variability during the middle to late holocene may have been important mechanisms for promoting fire in rainforest environments and maintaining diversity of tropical rain forests

kinematic analysis of a transtensional fault system the atuel depocenter of the neuquen basin southern central andes argentina abstract the atuel depocenter of the neuquen basin originated as an upper triassic to lower jurassic rift system later inverted during the andean contractional deformation in order to study the extensional architecture and the kinematic evolution of this depocenter we collected a large amount of field and sub surface data consisting of slip data from outcrop scale normal faults thickness and facies distribution within the synrift deposits and structural data from angular and progressive unconformities the atuel depocenter has a nnw trend showing a bimodal distribution of nnw and wnw major faults first and second order faults on the other hand from kinematic indicators measured on outcrop scale faults third and fourth order faults we found a mean ne internal extension direction which is oblique to the general trend of the sub basin taking these particular characteristics into account we interpreted the atuel depocenter as an oblique rift system we evaluated two mechanisms in order to explain the development of this transtensional system 1 reactivation of upper crustal nnw oriented paleozoic shear zones and 2 oblique stretching of a previous nnw oriented lithospheric weakness zone