geometric and kinematic models for detachment folds with fixed and variable detachment depths abstract detachment folds are defined by competent rock units and are cored by incompetent units deformed internally above a detachment horizon we have developed two geometric models to constrain possible geometries and kinematic paths for ideal detachment folds the models each independently relate fold geometry to shortening and to detachment depth model assumptions include plane strain constant competent bedlength constant cross sectional area chevron fold geometry and no bed parallel shear outside the fold detachment depth is constant in one model but may vary in the other thus allowing evaluation of the implications for fold geometry and kinematics of fixed vs variable detachment depth detachment folds formed above a detachment unit of constant thickness constant detachment depth must be initially symmetrical and cannot grow with fixed hinges fixed arc length or a self similar geometry detachment folds formed above a detachment unit of variable thickness variable detachment depth must also be initially symmetrical but any one fold geometry can have a range of possible initial and final detachment depths kinematic paths for folds with fixed hinges fixed arc lengths migrating hinges variable arc lengths and selfsimilar geometries are all possible if detachment depth varies the change in detachment depth during deformation can be determined using the variable detachment depth model if either initial or final detachment depth is known the models demonstrate a wider range of variability in the geometry and kinematics of ideal detachment folds particularly for the variable depth model than is the case for ideal fault bend and fault propagation folds this variability limits the usefulness of simple geometric models for reconstructing the geometry of natural detachment folds balancing cross sections over a sufficient area and evaluating strain may compensate for these limitations

variability of the arctic front during the last climatic cycle application of a novel molecular proxy in the nordic seas the arctic front af marks the boundary between the waters of the north atlantic drift norwegian current and those of the arctic domain long or short term shifts in the position of the af may affect climate conditions in the northern hemisphere arctic water masses are also the loci of modern open ocean convection hence defining these areas in the past is important for reconstructing and modelling ocean circulation and its variability c37 alkenones are biomarkers for some algae of the class prymnesiophyceae e g coccolitho phorids such as emiliania huxleyi these alga occur in most parts of the oceans in ice free conditions and are found nowadays throughout the nordic seas we have related the sedimentary abundance of the tetraunsaturated c37 alkenone c37 4 to two types of water masses in the nordic seas in locations affected by atlantic water masses percentages of c37 4 are less than 5 whereas in arctic type water masses these increase to more than 5 we propose that this observation can be used as a modern analogue to reconstruct the position of the af in north atlantic quaternary sediments using this novel molecular proxy we can infer that the southward migration of the af in the ne atlantic reached 50 n during the last glacial maximum lgm but perhaps only 60 n during the younger dryas and that ocean conditions free of sea ice prevailed throughout the northern north atlantic in summer

origin of the northern atlantic s heinrich events as first noted by heinrich 1988 glacial age sediments in the eastern part of the northern atlantic contain layers with unusually high ratios of ice rafted lithic fragments to foraminifera shells he estimated that these layers are spaced at intervals of roughly 10 000 years in this paper we present detailed information documenting the existence of the upper five of these layers in odp core 609 from 50 n and 24 w their ages are respectively 15 000 radiocarbon years 20 000 radiocarbon years 27 000 radiocarbon years about 40 000 years and about 50 000 years we also note that the high lithic fragment to foram ratio is the result of a near absence of shells in these layers although we are not of one mind regarding the origin of these layers we lean toward an explanation that the heinrich layers are debris released during the melting of massive influxes of icebergs into the northern atlantic these sudden inputs may be the result of surges along the eastern margin of the laurentide ice sheet

warming of surface waters in the mid latitude north atlantic during heinrich events 1 during the six heinrich events of the last 70 kyr episodic calving from the circum atlantic ice sheets released large numbers of icebergs into the north atlantic these icebergs and associated meltwater flux are hypothesized to have led to a shutdown of atlantic meridional overturning circulation and severe cooling in large parts of the northern hemisphere however due to the limited availability of high resolution records the magnitude of sea surface temperature sst changes related to the impact of heinrich events on the midlatitude north atlantic is poorly constrained here we present a record of u37k based ssts derived from sediments of integrated ocean drilling project site u1313 located at the southern end of the ice rafted debris ird belt in the midlatitude north atlantic 41 n we demonstrate that all six heinrich events are associated with a rapid warming of surface waters by 2 4 c in a few thousand years the presence of ird leaves no doubt about the simultaneous timing and correlation between rapid surface water warming and heinrich events we argue that this warming in the midlatitude north atlantic is related to a northward expansion of the subtropical gyre during heinrich events as a wide range of studies demonstrated that in the central ird belt heinrich events are associated with low ssts these results thus identify an antiphased seesaw pattern in ssts during heinrich events between the midlatitude warm and northern north atlantic cold this highlights the complex response of surface water characteristics in the north atlantic to heinrich events that is poorly reproduced by freshwater hosing experiments and challenges the widely accepted view that within the ird belt of the north atlantic heinrich events coincide with periods of low ssts

diagenetically enhanced bedding in argillaceous platform limestones stratified cementation and selective compaction a field and petrographic study has been made of 34 massive beds in argillaceous limestones of open marine platform facies in the u k lithologies include grainstones packstones wackestones and lime mudstones the rocks are of silurian carboniferous and jurassic ages additional information was obtained from other limestones in the u k the u s a canada and continental europe the beds are parts of sequences composed of couplets of strata fissile limestones alternating with hard limestones in the fissile limestones the effects of mechanical compaction and pressure dissolution have been concentrated whereas in the hard limestones they are minimal or absent bedding planes visible in outcrop are diagenetic in origin and lie in the middle parts of the fissile limestones where compaction has been most severe the features produced by pressure dissolution are dissolution seams and fitted fabric there are no stylolites the original carbonate sediments were bioturbated and any structures produced by flowing water were destroyed the vertical distribution of the bedding planes bears no relation to primary depositional bedding planes which are rare or absent it is inferred that the strata which were to become the hard limestones were selectively cemented before mechanical compaction had been completed thenceforth mechanical compaction and then pressure dissolution were concentrated in the less cemented strata these became the fissile limestones pressure dissolution acted late in the diagenetic history and provided only an insignificant part if any of the carbonate for cementation it is concluded that the orientation of beds couplets is parallel to successive sea floors and that the sediments that eventually became single beds accumulated synchronously similar couplets in platform limestones of the mississippian and pennsylvanian of the u s a extend over thousands of square kilometres the signal that controlled the initial selective cementation must have been widespread and synchronous and also syndepositional in its timing but otherwise cannot be further defined on the basis of the data so far collected the presumed order of events was 1 accumulation of carbonate sediment terrigenous clay and organic matter 2 hydrodynamic reworking and bioturbation the latter finally overprinting the former 3 selective cementation of the more carbonate rich strata yielding couplets each consisting of a relatively well cemented stratum and a poorly cemented stratum 4 mechanical compaction concentrated in the less cemented strata 5 pressure dissolution concentrated in the same strata

surface water temperature salinity and density changes in the northeast atlantic during the last 45 000 years heinrich events deep water formation and climatic rebounds we developed a new method to calculate sea surface salinities sss and densities ssd from planktonic foraminiferal 18o and sea surface temperatures sst as determined from planktonic foraminiferal species abundances sst sss and ssd records were calculated for the last 45 000 years for biogeochemical oceanic flux study bofs cores 5k and 8k recovered from the northeast atlantic the strongest feature is the dramatic drop in all three parameters during the heinrich ice rafting events we modelled the possibility of deepwater formation in die northeast atlantic from the ssd records by assuming that the surface waters at our sites cooled as they flowed further north comparison with modelled north atlantic deepwater densities indicates that there could have been periods of deepwater formation between 45 000 and 30 000 14c years b p interrupted by iceberg meltwater input of heinrich event 3 and 4 at 27 000 and 38 000 14c years b p and during the holocene no amount of cooling in the northeast atlantic between 30 000 and 13 000 years could cause deep water to form because of the low salinities resulting from the high meltwater inputs from icebergs our records indicate that after each heinrich event there were periods of climatic rebound with milder conditions persisting for up to 2000 years as indicated by the presence of warmer and more saline water masses after these warm periods conditions returned to average glacial levels these short term cold and warm episodes in the northeast atlantic are superimposed on the general trend towards colder conditions of the last glacial maximum lgm heinrich event 1 appears to be unique as it occurs as insolation rose and was coeval with the initial melting of the fennoscandian ice sheet we propose that meltwater input of heinrich event 1 significantly reduced north atlantic deep water formation reducing the heat exchange between the low and high latitudes thus delaying deglaciation by about 1500 radiocarbon years 2000 calendar years

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

isotope stratigraphy sedimentation rates deep circulation and carbonate events in the labrador sea during the last 200 ka high resolution stable isotope and accelerator mass spectrometry 14c measurements in 25 box and piston cores from the labrador sea allow the reconstruction of major paleoceanographical changes during the last 200 ka in this basin and also document the links between the interior of the laurentide ice sheet and the north atlantic ocean during this interval two deep circulation regimes are indicated by contrasting sedimentation rates on the slopes i the modern situation is characterized by a gyre of the north atlantic deep water nadw components into the basin which is responsible for the high energy western boundary undercurrent this regime also prevailed during the former true interglacials and possibly during shorter warm intervals e g bolling allerod ii a more frequent nadw free situation during glacial and interstadial intervals is marked by the presence of a vertically homogeneous water mass in the basin sedimentological records also indicate that carbonate events i e pulses of

vertical strain variations in the osen roa thrust sheet north western oslo fjord norway abstract vertical variations in deformation style and shortening within the osen roa thrust sheet are examined on the north western side of the oslo fjord using thrust distribution diagrams and graphs of throw against height in the stratigraphy particular formations are identified in which thrusts are either created or destroyed many thrusts are killed by a combination of 1 dissipation of slip by splaying of thrusts in shales and 2 the presence of a thick competent unit that requires a thrust to attain a specific displacement value in order to propagate through the unit in one jerk the upper didymograptus shales and ampyx limestone make an effective combination that kills thrusts with less than 50 m of throw within the thrust sheet deformation styles change vertically from imbricate slices pop up and triangle zones with tip line folds in the cambro ordovician shales and limestones to buckle folds in the silurian limestones sandstones and shales this change is accompanied by a decrease in shortening from 34 in the former to 17 in the latter hence one or several higher bedding parallel detachment horizons need to be invoked to separate areas of varying deformation character

rapid changes of glacial climate simulated in a coupled climate model abrupt changes in climate termed dansgaard oeschger and heinrich events have punctuated the last glacial period approximately 100 10 kyr ago but not the holocene the past 10 kyr here we use an intermediate complexity climate model to investigate the stability of glacial climate and we find that only one mode of atlantic ocean circulation is stable a cold mode with deep water formation in the atlantic ocean south of iceland however a warm circulation mode similar to the present day atlantic ocean is only marginally unstable and temporary transitions to this warm mode can easily be triggered this leads to abrupt warm events in the model which share many characteristics of the observed dansgaard oeschger events for a large freshwater input such as a large release of icebergs the model s deep water formation is temporarily switched off causing no strong cooling in greenland but warming in antarctica as is observed for heinrich events our stability analysis provides an explanation why glacial climate is much more variable than holocene climate

experimental and field study of the effects of lithological contrasts on thrust related deformation 1 the influence of mechanical contrasts related to stratigraphy on thrust related deformation are investigated by sandbox modeling using combinations of granular materials possessing different mechanical properties and by structural analysis of a natural example from the spanish pyrenees the models used in this study consist of loose sand and glass microbeads in varied stratigraphic thicknesses and sequences and the natural example consists of a weakening upward sequence of sandstones and carbonates in both cases layers of different composition had a mechanical significance and accommodated shortening differently model sand and natural sandstone exhibited most shortening by thrust imbrication irrespective of stratigraphic position whereas glass microbeads and carbonates exhibited wider deformation zones and enhanced folding accompanied by displacement reduction along thrust surfaces cutting them transitions of structural style were guided by the stratigraphy rather than by a simple unidirectional propagation from a step up layer parallel shortening was accommodated by diverse mechanisms but did not vary significantly in layers which had different properties the magnitude with which mechanical contrasts were expressed in the models was influenced by the strength at the decollement zone the effect of mechanical contrast was more profound in models shortened above a low friction decollement

sea surface temperatures did not control the first occurrence of hudson strait heinrich events during mis 16 1 hudson strait hs heinrich events ice rafting events in the north atlantic originating from the laurentide ice sheet lis are among the most dramatic examples of millennial scale climate variability and have a large influence on global climate however it is debated as to whether the occurrence of hs heinrich events in the eastern north atlantic in the geological record depends on greater ice discharge or simply from the longer survival of icebergs in cold waters using sediments from integrated ocean drilling program iodp site u1313 in the north atlantic spanning the period between 960 and 320 ka we show that sea surface temperatures ssts did not control the first occurrence of hs heinrich like events in the sedimentary record using mineralogy and organic geochemistry to determine the characteristics of ice rafting debris ird we detect the first hs heinrich like event in our record around 643 ka marine isotope stage mis 16 which is similar as previously reported for site u1308 however the accompanying high resolution alkenone based sst record demonstrates that the first hs heinrich like event did not coincide with low ssts thus the hs heinrich like events do indicate enhanced ice discharge from the lis at the end of the mid pleistocene transition not simply the survivability of icebergs due to cold conditions in the north atlantic

centrifuge modelling of fold thrust structures in a tripartite stratigraphic succession abstract analog models measuring 127 76 mm in plan were deformed at 2500 4000 g in a centrifuge scaled stratigraphic sequences were constructed of anisotropic multilayers with individual layers of plasticine and silicone putty as thin as 40 m the plasticine silicone putty multilayers are analogs for interbedded competent carbonates and clastics and incompetent pelites given the model ratios of acceleration 2500 g length 5 10 6 specific gravity 0 6 time 10 10 modelling of fold thrust tectonics emphasizes the influence of stratigraphic succession on structural evolution the models are constructed with a tripartite stratigraphic succession comprising basal and upper well laminated and incompetent units and a middle somewhat more isotropic and competent unit the models deform by three mechanisms layer parallel shortening folding and thrust faulting they reproduce a number of fold thrust relationships that have been observed in nature folds are typically periclinal in en echelon arrays folds and thrusts are arcuate in plan reflecting differential shortening fold attitudes grade from upright at high levels to overturned at deeper levels within a structural panel reflecting drag against the basal decollement fold axial surfaces and thrust faults are listric while competent units may be offset by localized displacement on thrust faults the discrete faults may die out both upwards and downwards into regions of ductile strain in less competent units thrust faults appear to follow staircase trajectories through the strata transecting incompetent units at shallow angles to bedding and competent units at steeper angles however the apparent staircase pattern results from propagation of a fault along a relatively straight trajectory through previously folded strata foreland verging thrusts are more common than back thrusts the latter have steeper dips the models suggest a mechanism of thrust ramp nucleation following detachment folding long wavelength buckling of a competent unit can initiate localized strain folding and layer parallel shear in an underlying incompetent unit beneath the anticlines of the competent unit thrust faults propagate up section from these high strain zones through the foreland dipping limbs of buckle folds in the competent unit this mechanism may explain the commonly observed spatial periodicity of thrust ramps the model results bear similarities to natural fold thrust belts in which the stratigraphic succession consists of three mechanical units for example the asiak foreland and bear creek hills fold thrust belts of the slave province northwest territories canada

secondary detachments within carbonates of the saraburi group triassic khao khwang fold and thrust belt thailand abstract permian limestones of the saraburi group in central thailand deformed during the triassic indosinian orogeny exhibit detachments formed in response to the following variations in lithology thin shale beds within a limestone sequence massive limestone overlaying well bedded limestone massive limestone overlying interbedded limestones and shales within well bedded limestones thin shales interbedded with limestones overlying limestones where shales are present the decoupling of layers is similar to examples previously described in the literature from outcrop and analogue models however more unusually detachments are also present within limestone units while detachment folds are typically developed above a basal weak unit usually salt or shale in the study area is an example developed entirely within well bedded limestones instead of flow of the weak unit into the core of the fold room problems in the core of the fold are accommodated by pressure solution parallel to bedding thrusts small fault propagation folds and intense folding variations in structural style are largely influenced by the spacing intensity of bedding limestone clay content and the efficiency of pressure solution during deformation and the presence absence and thickness of interbedded shales a ductile detachment zone is developed between well bedded limestones and overlying massive limestones the detachment zone separates highly folded sequence dominated by steep dips from a weakly folded sequence dominated by gentle dips pressure solution processes and variability in pressure solution intensity related to clay content play a very strong role in accommodating the difference in deformation styles across the detachment

the thermal threshold of the atlantic meridional overturning circulation and its control by wind stress forcing during glacial climate 1 paleo proxy data suggest that the atlantic meridional overturning circulation amoc was shallower and weaker at the last glacial maximum lgm than at present in this study we have identified the existence of a thermal threshold of the amoc which may explain why many coupled climate models fail to simulate the weaker amoc during the lgm by using results obtained from a coupled climate model and conducting sensitivity simulations with an ocean general circulation model we found that the sudden transition from the present day amoc to the weaker glacial amoc occurs when we gradually change the degree of surface cooling from present day to glacial conditions this result is related to response of deep convection in the northern north atlantic ocean moderate cooling enhances deep convection whereas sufficient cooling results in total covering of sea ice there and suppression of deep convection the findings indicate the existence of a thermal threshold controlling the amoc where the present day type amoc suddenly shifts to the weaker glacial amoc once the surface cooling exceeds this threshold we also demonstrate that wind stress forcing plays a critical role in controlling the value of the thermal threshold our study suggests that slight differences in the degree of surface cooling or wind stress forcing for lgm simulations could lead to the very different response of the amoc during the lgm as reported in previous lgm simulations

determination of the tectonic evolution from fractures faults and calcite twins on the southwestern margin of the indochina block in polyphase tectonic zones integrating a study of fault and fracture with calcite twin analysis can determine the evolving paleostress magnitudes and principle stress directions that affected the area this paper presents the results of the analyses of fractures striated faults and calcite twins collected within the khao khwang fold thrust belt in central thailand se asia here we attempt to reconstruct the orientation of the principal stresses that developed during the tectonic evolution of this highly deformed polyphase orogen tectonic data were collected in the permian carbonates of the khao khad formation of the saraburi group and five successive tectonic stages are determined that are interpreted to have developed before during and after the triassic indosinian orogeny the first three stages predate the main deformation event the first stage is interpreted as a pre indosinian n s extensional stage the second stage described a n s strike slip and compressional regime largely perpendicular to the fold axes of the main structures while the third stage is associated with an e w compressional strike slip phase a further two stages took place after or during the main folding event and correspond to n s compression and to an e w composite strike slip contractional stage the latter which is interpreted to represent cenozoic deformation related to the india asia collision

understanding sibumasu in the context of ribbon continents abstract well described ribbon continent collision belts and modern examples with 2d seismic coverage particularly zealandia provide analogues for the permo triassic development of sibumasu two key parameters for the ribbon continents are their width and how rifting developed which in turn impact the structural metamorphic igneous and stratigraphic development of ribbon continents in ways that make them significantly different from the collisional development of major continents key characteristics of the tectonics of sibumasu are 1 a tendency towards basin inversion during the late triassic and possibly early jurassic and mixed thick skinned and thin skinned style deformation 2 extensional collapse around 215 ma is an important feature of sibumasu particularly in northern thailand and probably other areas too 3 slab delamination and extension related decompression melting were probably important mechanisms for generating granites in addition to crustal thickening 4 metamorphism is relatively high temperature lower pressure

on the role of incompetent strata in the structural evolution of the zagros fold thrust belt dezful embayment iran abstract the dezful embayment is the most important fertile oil province of the zagros fold thrust belt it includes several incompetent strata as basal and intermediate decollement levels that play a significant role on the structural styles and hydrocarbon preservation based on the interpretation of seismic profiles the influence of the gachsaran formation and the evaporitic kalhur member of the asmari formation on the geometry of deformation was investigated in different parts of the dezful embayment obtained results revealed that the thickness of the incompetent strata plays a crucial role in the formation and geometry of different types of fold structures e g rounded box chevron detachment fold in the dezful embayment there is a sharp difference between the geometry of surface and deep seated structures due to the existence of thick intermediate decollements e g gachsaran and kalhur in the dezful embayment therefore fault geometry and fold styles in upper and lower parts of these decollements are totally different in addition these incompetent strata act as a barrier level against the propagation of deep seated faults into the overlying layers therefore it seems that most of the faults exposed on the surface have originated from the upper decollement levels in the study area

abrupt wind regime changes in the north atlantic ocean during the past 30 000 60 000 years 1 the inputs of higher plants in blake outer ridge subtropical western north atlantic during marine isotope stage 3 mis3 have been recorded at high resolution by quantification of c23 c33 odd carbon numbered n alkanes and c20 c30 even carbon numbered n alkan 1 ols in sediment sections of ocean drilling program site 1060 the changes of these proxies at this open marine site are mainly related to eolian inputs their concentrations and fluxes exhibit major abrupt variations that are correlated with dansgaard oeschger d o patterns in greenland ice cores the ratios between interstadials and stadials range between 2 and 9 times the intense flux increases in the d o stadials are linked to strong enhancements of the westerly wind regime at these subtropical latitudes during stadials the observed variation was paralleled by changes in wind blown dust and the polar circulation index in greenland ice which is in agreement with previously hypothesized atmospheric teleconnections between northern and middle low latitudes of the northern hemisphere the close correspondence between sedimentary and ice core proxies is evidence that crossings of the glacial climate thresholds involved major reorganizations of the troposphere the observed large rise in higher plant biomarkers indicates that climate stabilization in the d o stadial conditions led to main increases in wind intensity

experimental modelling of orogenic wedges a review abstract experimental modelling applied to the study of orogenic wedge dynamics has been a subject of fruitful research for more than 30 years although the technique dates back as far as the early xix th century on one hand several first order parameters controlling the structural evolution of mountain belts have been intensively investigated using the classic tectonic sandbox models the main parameters are the properties of the basal decollement the deforming material the backstop and fluxes kinematics and surface processes on the other hand the morphological evolution of a mountain relief subjected to changing tectonic or climatic forcing has been addressed using another kind of approach called geomorphic models nowadays the literature is extremely rich particularly for the sandbox technique so that it becomes difficult to have an exhaustive view of the effects of the above parameters on mountain evolution in this article we propose a detailed review of the main results obtained using both tectonic and geomorphic approaches our goal is to provide an almost complete state of the art in the experimental study of relief dynamics to guide present and future researchers in their understanding of mountain belt evolution

chert geochemistry depositional setting stratigraphic and structural significance for the permian nong pong formation khao khwang fold and thrust belt saraburi thailand abstract the deepwater chert shale limestone tuff permian nong pong formation npf of the saraburi group is a major unit within the triassic indosinian orogeny khao khwang fold and thrust belt kkftb whether the npf was deposited in a continental margin or ocean basin remains uncertain and impacts structural sedimentary and stratigraphic interpretations of the kkftb this study investigates chert geochemistry from a 60 m section of the formation near muak lek town to determine its depositional environment radiolarian fauna from the chert beds includes follicucullus porrectus rudenko probable late guadalupian late middle permian indicating the npf is time equivalent to adjacent carbonate platform deposition khao khwang and khao khad formations high ratios of sio2 sio2 al2o3 fe2o3 and fe al mn plots indicate a biogenic origin radiolarians sponge spicules for the cherts far from a hydrothermal source trace element ratios for u th sc th and sr ba and ce anomalies in the nasc normalized ree distribution are ambiguous and range between shallow to deep ocean basin and continental margin settings major elements analysis of cherts show 1 high ratios of sio2 sio2 al2o3 fe2o3 range 0 60 0 82 0 76 average 2 al al fe mn range 0 67 0 82 and 3 average mno tio2 0 14 the mno tio2 and al2o3 al2o3 fe2o3 ratio 100 fe2o3 sio2 vs 100 al2o3 sio2 and fe2o3 100 sio2 vs al2o3 100 sio2 diagrams indicate deposition on a continental margin the lan cen versus al2o3 al2o3 fe2o3 discrimination diagram indicates a pelagic continental margin setting combined geochemical structural and sedimentary facies analyses suggests the npf was deposited in a deep marine normal fault bounded basin on a rifted ribbon continent margin where carbonate platforms grew on structural highs

simulated resumption of the north atlantic meridional overturning circulation slow basin wide advection and abrupt local convection abstract the resumption process of the north atlantic meridional overturning circulation moc is investigated in a series of freshwater hosing experiments using a comprehensive coupled climate model four different freshwater perturbations are applied to the north atlantic between 50 n and 70 n leading to a substantial weakening of moc and an expansion of winter sea ice cover over the greenland iceland norwegian gin seas deactivating the freshwater forcing leads to a two phase recovery of the moc the first phase is a slow basin wide advection process whereas the second phase is an abrupt decadal scale transition located in the north atlantic the slow basin wide advection process to an intermediate state of the moc is characterized by a restart of the deep water production in the area of the subpolar gyre and the irminger basin however the ice cover over the gin seas remains whereas the surface density gradually increases in the gin seas on a century time scale the length of this intermediate state depends on the strength of freshwater perturbation which determines the magnitude of the meridional density gradient in the north atlantic the second transition phase is triggered by a model specific density threshold reached in the gin seas when passed the moc abruptly intensifies by 60 within 60 80 years the analysis shows that this abrupt intensification only depends on surface salinity in the gin seas the model results reveal that the simulated sea ice retreat in the gin seas and a rapid increase of the greenland air temperature of the second phase of the resumption of the moc are similar in amplitude to temperature proxies observed during dansgaard oeschger events of the last ice age

variability of surface water characteristics and heinrich like events in the pleistocene midlatitude north atlantic ocean biomarker and xrd records from iodp site u1313 mis 16 9 1 a reconstruction of milankovitch to millennial scale variability of sea surface temperature sst and sea surface productivity in the pleistocene midlatitude north atlantic ocean marine isotope stage mis 16 9 and its relationship to ice sheet instability was carried out on sediments from integrated ocean drilling program iodp site u1313 this reconstruction is based on alkenone and n alkane concentrations u37k index total organic carbon toc and carbonate contents x ray diffraction data magnetic susceptibility and accumulation rates increased input of ice rafted debris occurred during mis 16 12 and 10 characterized by high concentrations of dolomite quartz and feldspars and elevated accumulation rates of terrigenous matter minimum input values of terrigenous matter on the other hand were determined for mis 13 and 11 peak values of dolomite coinciding with quartz plagioclase and kalifeldspar peaks and maxima in long chain n alkanes indicative for land plants are interpreted as heinrich like events related to sudden instability of the laurentide ice sheet during early and late deglacial phases of the glacials the coincidence of increased toc values with elevated absolute concentrations of alkenones suggests increased glacial productivity probably due to a more southern position of the polar front alkenone based sst reached absolute maxima of about 19 c during mis 11 3 and absolute minima of 10 c during mis 12 and 10 within mis 11 prominent cooling events mis 11 22 and 11 24 occurred the absolute sst minima recorded directly before and after the glacial maxima mis 10 2 and 12 2 are related to heinrich like event meltwater pulses as supported by the coincidence of sst minima and maxima in c37 4 alkenones and dolomite these sudden meltwater pulses especially during terminations iv and v probably caused a collapse of phytoplankton productivity as indicated by the distinct drop in alkenone concentrations ice sheet disintegration and subsequent surges and outbursts of icebergs and meltwater discharge may have been triggered by increased insolation in the northern high latitudes

patterns of ice rafted detritus in the glacial north atlantic 40 55 n the observation by heinrich 1988 that during the last glacial period much of the input of ice rafted detritus to the north atlantic sediments may have occurred as a succession of catastrophic events rekindled interest on the history of the northern ice sheets over the last glacial period in this paper we present a rapid method to study the distribution of these events both in space and time using whole core low field magnetic susceptibility we report on approximately 20 cores covering the last 150 to 250 kyr well defined patterns of ice rafted detritus appear during periods of large continental ice sheet extent although these are not always associated within their maxima most of the events may be traced across the north atlantic ocean for the six most recent heinrich layers hl two distinct patterns exist hl1 hl2 hl4 hl5 are distributed along the northern boundary of the glacial polar front over most of the north atlantic between 40 and 50 n hl3 is more restricted to the central and eastern part of the northern atlantic the nd sr isotopic composition of the material constituting different heinrich events indicates the different provenance of the two patterns hl3 has a typical scandinavia arctic icelandic young crust signature and the others have a large component of northern quebec and northern west greenland old crust material these isotopic results obtained on core su 9008 from the north american basin are in agreement with the study by jantschik and huon 1992 who used k ar dating of silt and clay size fractions of an eastern basin core me 68 89 these data confirm the large spatial scale of these events and the enormous amount of ice rafted detritus they represent

millennial scale changes in north atlantic deep water circulation during marine isotope stages 11 and 12 linkage to antarctic climate the time interval represented by marine isotope stages mis 11 and 12 ca 360 470 ka may contain the most extreme glacial and interglacial climate conditions of the late pleistocene sediments from the bermuda rise western north atlantic provide clues to the nature of climate variability during this period our geochemical records indicate that millennial scale climate instability and associated changes in north atlantic deep water nadw production occurred during both interglacial mis 11 and glacial mis 12 stage 12 is punctuated by a series of interstadial events that occurred at a 5 6 k y periodicity and the occurrence of ice rafted debris at various times during stage 12 indicates that icebergs were present at least as far south as 34 n during this glacial period within the limits of our correlation the atmospheric temperature changes recently reported for the vostok ice core for the stage 11 time period appear to be represented by coeval changes in nadw flow specifically warming in antarctica is associated with increased production of nadw

structure of the sibumasu indochina collision central thailand a section through the khao khwang fold and thrust belt abstract mainland se asia is composed of a number of continental fragments and volcanic arcs separated by oceanic suture zones which were accreted to the growing asian continent during the triassic indosinian orogeny the evolution of this orogeny has always been quite controversial indeed the effects of this orogeny in thailand have often been interpreted without considering the detailed tectonic evolution of the portion of the indochina block s margin formed by khao khwang platform area of the saraburi group in central thailand this area is unusual because 1 an extensive area representing a thin skinned fold and thrust belt is well exposed due to quarrying and 2 the fold and thrust belt displays a series of e w and wnw ese striking thrusts and associated folds that are not easily explained in the context of the traditional interpretation where the terranes have been accreted broadly along n s striking collisional zones detailed structural observations in numerous quarries around highway 21 in a 13 km long dip direction traverse have revealed that overall the thrust belt is composed of several large thrusts with an approximately northwards transport direction in the southern part of the area south verging structures are present although the dominant structural trend is northwards verging interference structures and late strike slip faults indicate there is more than one phase of structural development present

geometry and evolution of fold thrust structures at the boundaries between frictional and ductile detachments abstract fold thrust belts formed above a ductile detachment typically contain detachment folds whereas those formed above frictional detachments contain fault related fold complexes such as imbricate thrust systems analog models using silica sand to represent sediments and silicone gel to represent salt were conducted to study the fold geometry fold fault relations and sequential development of structures formed in each setting and at the boundaries between the two settings the results showed a relatively thinner wedge above a ductile detachment so that the deformation front propagated farther forward than that above a frictional detachment the thrust front connects across the two settings with a significant change in position and a resulting change in orientation the geometry of the deformation front is strongly controlled by that of the detachment boundary so that an oblique detachment boundary results in an oblique thrust front in the transition zone modifications in the taper geometry also result from the presence of a frictional belt behind a ductile belt the width of the ductile detachment which limits the location of the deformation front and the lateral propagation of thrust faults between the two regimes the experimental models can be used to explain observed geometries in natural examples of fold thrust belts marked by transitions between frictional and ductile detachments

development of the khao khwang fold and thrust belt implications for the geodynamic setting of thailand and cambodia during the indosinian orogeny abstract the indosinian orogeny in thailand is often viewed as having developed between strongly linear terranes which today trend approximately n s the terranes were subsequently disrupted by later tectonics particularly nw se trending cenozoic strike slip faults the ene wsw to ne sw striking thrusts and folds in the khao khwang platform area of the saraburi group on the sw margin of the indochina terrane are not easily explained in the context of this traditional view reversal of the clockwise rotation shown to have affected the block north of the mae ping fault zone only enhances the e w orientation of structures in the fold and thrust belt and moves the belt further east towards cambodia one solution for the trend that fits better with regional understanding from hydrocarbon exploration of the khorat plateau is that the indochina terrane was actually a series of continental blocks separated by permian rifting during the early triassic the early stages of collision south china cathaysian terrane collision with vietnam indochina resulted in the amalgamation of disparate blocks that now form the indochina terrane by closure along the rifts at the same time or following on from the collision there was closure of the back arc area between indochina and the sukhothai zone the rift basins were thrusted and inverted during the early stages of the indosinian orogeny and only underwent minor reactivated when later sibumasu collided with sukhothai zone indochina terrane margin during the late triassic the scenario described above requires the presence of a minor e w trending suture in nw cambodia evidence for this suture is suggested by the presence of permo triassic calc alkaline volcanism

variability of unusual distributions of alkenones in the surface waters of the nordic seas 1 samples of filtered particulate organic matter pom were obtained during the summers of 1999 and 2000 from the surface waters of the nordic seas to monitor the spatial distribution of long chain alkenones the aim of the study was to appraise existing alkenone based climatic proxies in northern high latitudes unusually high percentages of the tetraunsaturated alkenone were measured in the polar waters of the east greenland current with c37 4 of up to 77 in 80 of sea ice cover values of percent c37 4 across the nordic seas showed a strong association with water mass type analysis of coccoliths in filters indicated that calcified emiliania huxleyi could not be discounted as the biological precursor of alkenones in all the water masses a combined data set of 69 samples of pom revealed a stronger correlation of percent c37 4 to sea surface salinity sss r2 0 72 than to sea surface temperature sst r2 0 50 values of percent c37 4 in sea surface pom were much higher than those in surficial sediments of the northern north atlantic to explain the discrepancy in sedimentary and surface water column percent c37 4 we propose that the alkenone contents in surface sediments underlying arctic and polar waters are a combination of autochthonous and allochthonous inputs of alkenones our results show that percent c37 4 can be used to reconstruct the relative extension of arctic polar water masses in the north atlantic however the results prevent confirmation of percent c37 4 as a paleo sss proxy in the nordic seas given its multivariate nature in our data set and the decoupling between its range of values in surface waters and sediments

distinguishing coeval patterns of contraction and collapse around flow lobes in mass transport deposits abstract gravity driven mass transport deposits mtds form by the downslope directed movement of sediment associated with slope failure simple models suggest that extension forms at the upslope head area contraction is focussed in the downslope toe of the slump while differential shear associated with strike slip is restricted to the lateral margins of the slump although the head and toe are considered to be dominated by layer parallel shear lps differential layer normal shear lns may be generated around the lateral margins of slumps and potentially also within mtds where flow has been separated into different lobes despite this realisation that lns must form there has been little work into the geometries and spatial relationships of resulting structures using the late pleistocene lisan formation exposed around the dead sea basin as our case study we examine detailed

structural models of faulted detachment folds faulted detachment folds represent a common structural style in several hydrocarbon producing fold and thrust belts including the zagros idaho wyoming utah carpathian and albanide belts and several deep water fold belts including the mississippi fan and per dido belts these structures form in units with high competency contrasts and display a transition in deformational behavior from detachment folding to progressive fault propagation with increasing shortening the structures first form by symmetric or asymmetric detachment folding with the fold wavelength controlled by the thickness of the dominant units volumetric constraints require the movement of material from the synclines to the anticlines contin ued shortening results in tighter folds with limb rotation by hinge migration limb segment rotation and internal shear rotation of limb segments between locked hinges results in thrust faults which propagate through deformation zones on the frontlimb and possibly the backlimb the faults may terminate both up and down section within brittle or ductile deformation zones eventually a through going fault connects one of the major faults with the basal detach ment variations in the structural geometry are related to the rela tive thickness and competency of the units and the mechanisms of deformation because faulted detachment folds superficially resem ble fault propagation folds their geometry can be misinterpreted in areas of poor data quality characteristic features for distinguish ing these structures include 1 smaller variations in anticlinal length during fold evolution 2 a more open and rounded fold geometry 3 complex and nonuniform variations in fault slip 4 a significant variation in deformational behavior among different units and 5 fold fault relationships indicating transition from folding to faulting such as footwall synclines and decapitated fold geometries

macrostructures vs microstructures in evaporite detachments an example from the salt range pakistan abstract the salt range pakistan is the surface expression of an evaporite detachment over which the potwar plateau fold thrust belt has moved whilst previous publications regarding this region have focused on the petroleum prospectivity deformation and large scale processes this paper characterises the salt range detachment at the meso 10 cm to 10s of metres and micro scale cm to m and examines correlations to the macro scale 10s of metres to kms two detailed scaled cross sections are analysed alongside structural measurements to characterise the detachment at the meso scale with optical analysis of microstructures that formed during deformation characterising the micro scale both ductile and brittle features observed in cross section indicate composite deformation processes acting simultaneously this contrasts with models of salt detachments behaving homogeneously microstructural analysis indicates processes of grain boundary migration and crystal lattice distortions the microstructurally revealed competition between intra crystalline deformation and recrystallization at shallow depths and low temperatures links passes up scale to mesoscale evaporite mylonites and progressively in the weaker units whereas more brittle processes operate in the stronger lithologies in this near unique outcrop of a the emergent toe of a major salt bearing detachment fault

review of major shale dominated detachment and thrust characteristics in the diagenetic zone part ii rock mechanics and microscopic scale abstract characterising large shale thrust zone behaviour down to the diagenetic metamorphic boundary is both simple and complex the task in critical taper analogue and numerical models has been successfully approximated using simple material parameters yet the weakness of shales thrusts on a case by case basis show great variability in key factors across a wide range of scales understanding of these variables and their relationships to different tectonic settings is patchy due to the different objectives of workers studying the various systems e g seismic hazards hydrocarbon exploration structural geology research and the types of available geological and geophysical data early research recognized that megathrusts feature creeping and locked patches which may be described using the rate and state formalism in addition to temperature differential stress and strain rate key controlling factors on thrust weakness are mineralogy amount of weak phase present structure localization mechanisms grain size and shapes porosity permeability and pore fluid pressure the smectite illite transition has been a focus of seismic hazard research due to its coincidence with the top of the seismogenic zone while there may be a relationship other factors such as pore fluid pressure variations or structure localization are also important the critical taper model is a simple means of determining whether basic rock mechanics data e g frictional strength pore fluid pressure is appropriate for natural wedges for example aseismic basal detachments of gravity driven systems smaller critical taper wedges appear to retain higher pore fluid pressures along the basal detachment than seismogenic basal detachments higher critical taper wedges in many continental and deltaic fold and thrust belts high organic carbon content is a very important factor in shale weakness due to 1 the overall more ductile and well cleaved nature of the shale when organic content is high 2 the presence of high overpressures due to maturation of organic material and 3 metamorphism of carbon to low friction graphite this multifaceted influence of organic carbon content is just one example of the diversity of potential influences on shale thrust zone weakness which enable shales to be weak despite considerable lateral deposition related and vertical burial related changes in composition some key variations between different types of fold and thrust belt gravity driven accretionary prism andean himalayan type lie in systematic variations in clay mineralogy magnitudes and origins of overpressures seismic versus aseismic detachments and different structural localization mechanisms further research is required to explore the viability of such distinctions and their impact on structural styles

formation and inversion of salt detached ramp syncline basins results from analog modeling and application to the columbrets basin western mediterranean abstract the widespread extensional deformation that took place during jurassic to cretaceous times in western europe and the north atlantic margin resulted in the formation of several rift systems some of the resulting basins associated with these rifts show broad synclines detached on pre or syn kinematic permian or triassic salts and are filled by thick sedimentary successions the development of these salt detached ramp syncline basins has been associated to the extensional motion of ramp flat extensional sub salt faults the shape and kinematics of such faults have usually been established using the architecture of syn kinematic units and by assuming complete coupling of the hanging wall rocks therefore there are fault interpretations that do not consider the role played by the deep salt layers which clearly act as an effective detachment decoupling sub and supra salt deformations moreover the complexity of these scenarios further increases due to some of these basins which during latest cretaceous and cenozoic times were partially inverted and were often incorporated into fold and thrust belts based on analog models and using the mesozoic columbrets basin western mediterranean as a case study the aim of this research is to decipher the influence of the ramp flat extensional fault during the syncline development and the interaction with a pre kinematic salt and to infer how salt detached ramp syncline basins are subsequently inverted to achieve this goal we carried out an experimental program consisting of eight different sandbox models our results show that the main structure formed at the end of the extension is a salt detached ramp syncline and that its geometry not only depends on the dip and length of the fault panels but also on the fault displacement and salt thickness the inversion of these salt detached ramp synclines resulted in a major thick skinned fault bend anticline with minor thin skinned contractional structures

molecular stratigraphy of cores off northwest africa sea surface temperature history over the last 80 ka the molecular stratigraphy of biogeochemical oceanic flux study core 31k 19 n 20 10 w and ocean drilling program hole 658c 20 45 n 18 35 w has been studied for c37 alkenone abundances over the past 80 ka at high resolution circa 200 500 years the derived uk37 sea surface temperature record for both cores shows a range of temperatures from about 18 c during the last glacial to 21 5 c during the early holocene both records also reveal changes in sea surface temperature as much as 2 4 c over a few hundred years which correlate well with similar abrupt climatic changes observed in cores from elsewhere in the ne atlantic associated with heinrich events our results indicate that meltwater produced by these ice rafting events was transmitted southward by the canary current where it had considerable impact on sea surface temperatures in the subtropical eastern atlantic

impact of an interbedded viscous decollement on the structural and kinematic coupling in fold and thrust belts insights from analogue modeling abstract fold and thrust belts ftbs can be segmented both across and along strike because of various factors including tectonic and stratigraphic inheritance in this study we investigated along across strike structural interactions in a ftb propagating toward a foreland which displays contrasted lithological sequences a set of analogue models was performed in a compressional box where a single viscous level of varying width was interbedded within a frictional series the tectonic interaction between the viscous and the frictional provinces was tested both along and across strike results indicate that a frictional province influences the along strike tectonic evolution of an adjacent viscous province this influence decreases when the width of the viscous province increases the frictional provinces control the taper structural style obliquity of the structures trend and kinematics of the shallow deformation front of the viscous province results evidence how far a frictional province can impact the deformation of an adjacent viscous province for frictional viscous wedges it appears that the critical taper theory which is generally applied in 2 d should be likely considered in terms of 3 d moreover the kinematics of the deep deformation front shows mutual influences between the adjacent viscous and frictional provinces experimental results are compared to natural examples in the kuqa basin southern tian shan china and the salt range pakistan and give an insight to a better understanding of the dynamics of fold and thrust belts bearing a viscous decollement such as salt

review of major shale dominated detachment and thrust characteristics in the diagenetic zone part i meso and macro scopic scale there is considerable variability in the thickness structure and macroscopic deformation style within shale prone major thrust zones which also impacts the structural style in the overlying and sometimes the underlying section the properties and percentages of clay minerals and percentages of organic material quartz and calcite affect fault zone weakness and behaviour the distribution of competent units within a shale prone zone can also significantly affect fault zone architecture even over short strike distance of 10s to 100s of metres other influences include high pore fluid pressures and associated veins deformation of the fault zone may disrupt the original principal displacement zones and force them to relocate including switching lithologies calcite veins can become concentrated locally in the fault zone and become a focus of fault zone weakness we still need many more descriptions of shale prone fault zones to understand the potential variations in thrust sheet structural style caused by differences in shale detachment characteristics the variations in structural style in the hanging walls of shale detachments are broad and range between the sledge runner style in many appalachian examples and the extensive closely spaced imbricate style of the osen roa detachment southern norway such contrasts are related to several factors including thrust sheet mechanical stratigraphy thickness of the overburden lateral continuity of the detachment detachment mechanical properties composition pore fluid pressures presence absence of higher level detachments and strain rate in many structural locations and at many scales shale prone sequences will pile up to produce over thickened masses cleavage duplexes s c fabrics duplexes imbricates pseudo duplexes and vein formation can all contribute to the thickening at nested scales a mixture of brittle and solution diffusion processes overall cause the affected unit to exhibit flow like characteristics while the broad principles are now well established considerable work remains to be done understanding the full range of structural geometries associated with shale detachments what factors regarding the nature of the detachments affect overlying structural styles rates of deformation and the controls on deformation mechanisms within the thrust zones

complex structure of an upper level shale detachment zone khao khwang fold and thrust belt central thailand abstract shale detachment zones have been previously described as largely mobile in character however increasing resolution of seismic images and understanding of these zones suggest brittle deformation may have a significant role in their deformational behaviour and in the deformation of overlying fold and thrust belts dependence on seismic imaging and other indirect and low resolution study methods has resulted from the lack of outcropping shale detachment zones both active and ancient for detailed study however a newly described upper level detachment zone in a shale unit in the khao khwang fold and thrust belt in central thailand is exceptionally well exposed we use detailed structural analysis to investigate deformational mechanisms of this ancient exhumed detachment zone as an analogue to active modern day examples through detailed field mapping we were able to construct multiple cross sections through the detachment zone these cross sections were subdivided into structural domains which display an increase in density and complexity of deformational structures folds faults and heterogeneity of their orientations toward the thrust at the base of the detachment zone contrasting strain rates in zones of continuous discontinuous deformation result from contrasting rock competencies through the sections we conclude that the fault damage zone in this study constitutes an upper level detachment and is potentially analogous to those in active collisional fold and thrust belts it displays mixed brittle ductile deformation and a complex three dimensional anastomosing fault system

bipolar seesaw in the northeastern tropical atlantic during heinrich stadials two sst records based on mg ca of g ruber pink from the continental slope off west africa at 15 n and 12 n shed new light on the thermal bipolar seesaw pattern in the northeastern tropical atlantic during periods of reduced atlantic meridional overturning circulation amoc associated with heinrich stadials h1 to h6 the two records indicate that the latitudinal position of the bipolar seesaw s zero anomaly line between cooling in the north and warming in the south gradually shifted southward from h6 to h1 a conceptual model is presented that aims to provide a physically consistent mechanism for the southward migration of the seesaw s fulcrum the conceptual model suggests latitudinal movements of the intertropical convergence zone driven by a combination of orbital forced changes in the meridional temperature gradient within the realm of the hadley cell and the expansion of the northern hemisphere cryosphere as a major factor

syn deformation temperature and fossil fluid pathways along an exhumed detachment zone khao khwang fold thrust belt thailand abstract shale detachment zones their influence on deformational style and their internal mechanisms of deformation are an understudied aspect of fold thrust belts properties such as deformational temperature lithology and mineralogy are often recognized as having a key influence on the rheology and deformational style of detachment zones and overlying fold thrust belts however little work has been conducted on rock properties of known detachment zones a recently described upper level detachment zone in the exhumed khao khwang fold thrust belt of central thailand provides an ideal natural laboratory for investigation of the deformation conditions of the detachment zone and association with its complex deformational style the low grade metamorphic indicator illite crystallinty is used to broadly constrain deformational temperatures while oxygen and carbon stable isotope analysis provides insight into fluid flow history and fluid rock interaction illite crystallinity data indicate deep diagenetic to low anchizonal conditions and temperatures of 160 210 c in the shale detachment interpreted as reflecting peak metamorphic conditions during the triassic indosinian orogeny no trend between the intensity spacing complexity of structures and illite crystallinty is observed however shale shear zones of continuous style deformation and inferred higher finite strain display uniformly higher illite crystallinty than surrounding packages of discontinuously faulted shales we also note a positive association between total organic carbon content in the shales and the spacing and complexity of deformational structures data from limestones and syn tectonic vein fills detail the history of fluid rock interaction during early mesogenesis through to orogenesis the early covariant trend of increasingly negative 13 c and 18 o values is attributed to increasing burial while a divergent orogenic trend of increasingly negative 18 o values is interpreted as the result of a loss of matrix permeability and interruption of fluid rock re equilibration these hottest fluids were concentrated along large thrusts which facilitated fluid movement during orogenesis

distributions of uk37 and uk37 in the surface waters and sediments of the nordic seas implications for paleoceanography in this paper we revise the application of the u and u indices as sea surface temperature sst proxies in the nordic seas in the summer of 1999 and 2000 we obtained samples of filtered particulate organic matter pom from surface waters 6 m depth of the nordic seas a number of samples were collected from polar waters with up to 80 of sea ice cover alkenones were detected in all of the major water masses of the nordic seas across a spectrum of sst values from 0 5 to 13 c and sss values from 29 6 to 35 6 psu concentrations of alkenones were similar in magnitude to those reported previously for the north atlantic and the southern ocean values of u from the new nordic seas pom data show no correlation with sst below 8 c in contrast below this temperature a linear correlation exists between u and regional sst supporting previous suggestions that overall u may be a more appropriate sst index for the region it must be noted however that u is calculated using the tetraunsaturated alkenone and the dominant control on this compound is not yet fully understood the new data highlight major differences between distributions of u and u in the water column pom and surficial sediments of the nordic seas we also examine the geographical dependence of the u versus sst relationship in the region s surficial sediments some areas are associated with unreliable sst estimates whereas in others the u versus sst relationship falls within the range of a global core top calibration it is suggested that the breakdown of the u sst relationship in some regions is due to ecological and sedimentological factors the latter relates to the extension of the habitats of alkenone producers in polar waters the former to the resuspension of sediments and laterally transported alkenone inputs this suggests that accurate alkenone derived sst estimates in the nordic seas are geographically constrained

contrasting paleoceanographic conditions off morocco during heinrich events 1 and 2 and the last glacial maximum abstract past hydrological and primary productivity regimes on the basis of dinocyst and foraminiferal fossil assemblages as well as on stable isotopes o c and alkenones were investigated over the last 30 ka at upwelling site md04 2805 cq off morocco the results show highest upwelling intensity during heinrich event he 1 time coeval with a distinct plateau of heavy planktonic 13 c values high concentrations of pinus pollen and heterotrophic dinocysts caused by an increased northern wind regime in addition we also present regional reconstructions of paleo sea surface temperatures ssts using three different proxy tools dinocyst and foraminiferal transfer functions as well as alkenones u k 37 sst the reconstructed ssts depict coherent scenarios as modulated by the typical northern hemisphere climatic fluctuations furthermore specific occurrences of the dinocyst spiniferites lazus and of the foraminifer turborotalita quinqueloba are noted for he 2 he 1 and the younger dryas whereas in the alboran sea and in peri iberian waters these cold events were accompanied by the dinocyst bitectatodinium tepikiense and the subpolar foraminifer neogloboquadrina pachyderma s both implying a marked southward shift in the planktonic population in response to the migration of polar water masses this very pronounced demarcation between the planktonic communities better seems to attest the presence of a distinct hydrological structure in proximity of the strait of gibraltar which separated at that time african north of morocco from european southern iberia water masses

new insights into the glacial latitudinal temperature gradients in the north atlantic results from uk 37 sea surface temperatures and terrigenous inputs abstract sea surface temperatures sst and input of continental materials have been reconstructed from the study of the long chain alkenones and n alkanes respectively in a core located in the western side of the mid atlantic ridge md952037 37 05 n 32 02 w 2630 m depth both the long and short term variability recorded by the temperatures and the planktonic 18o are basically the same over the last 280 kyr showing a clear glacial interglacial evolution comparison with core su90 08 located only 6 north and directly influenced by the cold polar waters associated with the polar front during glacial times revealed different climatic conditions during glacial periods at both locations whereas core md952037 recorded similar sst values during the last two glacial periods ca 14 15 c the northern core displayed colder conditions during isotopic stage 2 8 10 c than in stage 6 13 15 c these results indicate the existence of a well developed steep north south gradient between 37 and 43 n during the last glacial period but not during stage 6 which suggests a southern expansion of the polar front during the last glacial maximum

stratigraphy of deformed permian carbonate reefs in saraburi province thailand kilometre scale thrusts affect the stratigraphic order of the sedimentary rocks that form the khao khwang platform in central thailand the effect of these thrusts requires detailed analysis to unravel the original distribution of the sedimentary units and their associated facies the khao khwang platform comprises three carbonate dominated units identified previously as the phu phe khao khad and khao khwang formations these carbonates are intercalated with clastic mixed siliciclastic and carbonate sequences the sap bon pang asok and nong pong formations the palaeogeography of the area prior to the indosinian orogeny is poorly known and has herein been investigated by combining structural reconstructions microfacies and biostratigraphy in the saraburi area a stratigraphic model for the yakhtashian midian carbonate platform palaeogeography using the well developed exposed sections of the khao khwang platform located in the saraburi province of thailand is presented this has revealed the presence of several separate carbonate platforms dominated by four major middle permian facies peritidal platform interior algal reef and basin slope which are dated using foraminifera and algae this model integrates recent structural studies and considers their impact on the present day distribution of the facies in terms of platform development using biostratigraphy and detailed microfacies analysis supplementary material characteristic images of the six facies high resolution stratigraphic logs a timescale correlation chart and a table detailing the common fossils identified in this study are available at https doi org 10 6084 m9 figshare c 3861796

decollement in the alpine system an overview decollement in the alpine system is implied in the nappe concept jura decollement originally proposed bybuxtorf 1907 is the latest addition north of the alps the rheology of evaporites shows easy feasibility of jura decollement which is required by material balance in eastern switzerland the front of the alpine foreland thrust belt in the molasse is a typical triangle structure tectonic wedge an important decollement structure also in other places and scales the helvetic nappes are flat and ramp structures similar to the jura but translated by greater amounts and deformed under larger overburden corresponding basement deformation was largely ductile basement lobes and lagged behind the penninic nappes are usually metamorphosed in various degrees except some cover nappes transported far into the foreland coordination between basement and displaced cover is uncertain the austroalpine cover nappes of switzerland and adjacent austria as a rule are only weakly metamorphosed and resemble the southern alps in both stratigraphy and its expression in tectonics the basement part of both are essentially upright slivers not more than five kilometers thick with a frontal ramp fold splitting apart of the sedimentary sequence particularly in the carnian with tectonic wedging is frequent in both domains extensional decollement occasionally accompanied by tectonic denudation and high cooling rates occurred during several episodes most notably during early jurassic rifting and between the compressional phases gosau oligocene early miocene episodes the main strike slip elements of the transpressive neoalps are the insubric fault system with its dextral riedel shears and the dextrally arranged brachyanticlines of the late alpine windows which again imply decollement

structural and fluid evolution of saraburi group sedimentary carbonates central thailand a tectonically driven fluid system abstract a stable isotopic study focused on calcite cements vein fill calcite and various bioclasts was conducted on variably deformed and thrusted lower and middle permian carbonates of the saraburi group samples were collected in quarry faces across 3 areas in the saraburi lopburi region of central thailand stable isotope crossplots carbon and oxygen using texture aware isotope samples defined variable but related fluid cement histories which are tied to regional burial and then orogenic overprints driven by the indosinian triassic orogeny this was followed by telogenetic overprints driven by late cenozoic uplift the studied carbonates were deposited along the western margin of the indochina block where they were deposited as isolated calcareous algal sponge and fusilinid rimmed platforms on highs bound by extensional faults the platform areas passed laterally and vertically into more siliciclastic dominated sequences deposited in somewhat deeper waters within probable fault bound lows regional post depositional mesogenetic fluid rock re equilibration of the isotope values in ongoing calcite precipitates occurred until the matrix permeability was occluded via compaction and pressure solution this regional burial regime was followed by collision of the indochina and sibumasu blocks during the indosinian triassic blocks which drove a set of structurally focused thrust plane related increasingly warmer set of fluids through the studied sequences the final diagenetic overprint seen in the isotopic values of the latest calcite cements occurs in a telogenetic uplift setting driven by cenozoic tectonics and isostatic uplift integration of isotope data with its structural setting establishes a clear separation in fluid events related to two time separate tectonic episodes its fluid chemistry defines the permo triassic closure of the paleotethys and its subsequent reactivation during the tertiary collision of india and asia the c o covariant plot fields in the permian carbonates of central thailand are so distinct that it is possible to use their signatures to separate burial from meteoric cements in drill cuttings and hence recognise equivalent subsurface unconformities and likely zone of porosity development in possible buried hill plays in thailand

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

empirical green s functions calculated from the inversion of earthquake radiation patterns in this paper the empirical green s function is calculated based on a method that inverts the radiation patterns of earthquakes the method utilizes several close lying earthquakes with known foca

late quaternary high resolution biomarker and other sedimentary climate proxies in a northeast atlantic core we studied variations in terrigenous input and sea surface temperature over the last 208 ka using a multiproxy approach involving direct comparison of terrigenous and marine molecular biomarker foraminiferal abundance and other sedimentological data for the same horizons in a single northeast atlantic core core t88 9p 48 23 n 25 05 w 3193 m water depth 790 cm core length with a well resolved 18o stratigraphy the abundances of three land derived long chain compound classes the n alkanes c27 c29 and c31 the n alkanoic acids c24 c26 and c28 and the n alkanols c24 c26 and c28 show glacial interglacial related changes in the past 208 ka which generally parallel the weight percent noncarbonate the abundances of these three compound classes are higher in glacial than in interglacial sediments such changes are consistent with the expected higher dust inputs during glaciations as well as enhanced advection of particulate matter in current systems ice rafted debris heinrich events may also contribute to the terrigenous biomarker record the sea surface temperature sst signals derived from the alkenone unsaturation index uk 37 give an average sst during interglacial periods of 13 c which is about 3 4 c higher than the average glacial sst estimate the uk 37 derived sst values dropped markedly in some heinrich layers while sometimes leading the onset of the layer the percent neogloboquadrina pachyderma s which is another frequently used qualitative temperature proxy generally shows maxima coinciding with the layers our results show that most heinrich layers were produced during times of intensely cold waters in the eastern north atlantic they demonstrate that sufficient alkenones are present in the sediments for alkenone stratigraphy to be used as a tool for the assessment of short term variations in sea surface temperatures even in these oligotrophic north atlantic waters

hydrological impact of heinrich events in the subtropical northeast atlantic reconstructing the impact of heinrich events outside the main belt of ice rafting is crucial to understanding the underlying causes of these abrupt climatic events a high resolution study of a marine sediment core from the iberian margin demonstrates that this midlatitude area was strongly affected both by cooling and advection of low salinity arctic water masses during the last three heinrich events these paleoclimatic time series reveal the internal complexity of each of the last three heinrich events and illustrate the value of parallel studies of the organic and inorganic fractions of the sediments

palaeostress magnitudes in the khao khwang fold thrust belt new insights into the tectonic evolution of the indosinian orogeny in central thailand using the khao khwang fold thrust belt in central thailand as case study we handled data from calcite twinning analysis in order to propose the quantification of the effective principal palaeostresses magnitudes since the onset of the early stages of the indosinian orogeny we also combined the differential stress estimates from mechanically induced calcite twins with geochronological data in order to constrain the timing of the palaeoburial depth and subsequent uplift by folding within the khao khwang fold thrust belt the proposed mechanical scenario is based on the time constrained kinematic sequence of fracturing faulting and folding in the strata of the carbonate formations of the saraburi group cross checking the data on the palaeostress orientations regimes and differential stress magnitudes with rock mechanics analysis we provided data on the principal stress magnitudes for each tectonic stage that developed during the indosinian orogeny further 40ar 39ar and u pb geochronological data allowed to place reliable constraints on the amount and rate of vertical uplift of the carbonate formations of the saraburi group

assessment of sea surface temperature variations in the central north atlantic using the alkenone unsaturation index u37k abstract a high resolution record of u37k derived sst estimations has been obtained in a core from the central north atlantic ocean su90 08 43 30 n 30 24 w spanning a time period of 280 ky the general trend of the u37k profile parallels closely the 180 signal and represent an independent confirmation that the sst variations in the glacial interglacial time scales are correlated with the northern ice sheets evolution in contrast to the climap 1984 conclusions based on the foraminiferal transfer function technique the sst during the last interglacial period lip isotopic stage 5 5 are 2 3 c warmer than during the holocene this result is in good agreement with many studies based in coastal and continental records that strongly suggest warmer climatic conditions over north america and europe finally the sst estimates during the last glacial maximum lgm 18 ky bp where 4 5 c cooler than during the previous glacial period pgp stage 6 we argue that this difference is caused by a northward position of the polar front during the pgp in the central north atlantic

changes in sea surface hydrology associated with heinrich event 4 in the north atlantic ocean between 40 and 60 n abstract the changes in distribution of sea surface temperature and salinity in the north atlantic between 40 and 60 n were reconstructed for the time interval between 40 and 30 kyr bp which includes the large iceberg discharge event associated with the deposition of heinrich layer 4 we found that the meltwater input during deposition of heinrich layer 4 resulted in a 1 2 kyr temperature decrease of about 2 c and a salinity decrease in the range of 1 5 3 5 between 40 and 50 n sites above 50 n did not experience significant salinity variations a much larger area was affected by the reduction in sea surface temperature the amplitude of the sea surface temperature shift was however much smaller than the atmospheric temperature changes over greenland at gisp and grip sites

analogue modeling of the role of multi level decollement layers on the geometry of orogenic wedge an application to the zagros fold thrust belt sw iran the presence of evaporate and incompetent formations i e decollement horizons within the sedimentary sequence of fold thrust belts can control their structural style and deformation evolution in the present study the influence of the decollement layers e g basal and internal decollement layers on the deformation style of several segments of the zagros fold thrust belt zftb sw iran e g fars arc dezful embayment and izeh zone was investigated using a series of analogue models of accretionary wedges the study of seismic profiles to understand the structural evolution of these segments of the belt where several decollement intervals acted as basal and internal decollements is complemented by the analogue model results the experimental results reveal that the thickness of the internal decollement layers influences the creation of fold dominated or thrust dominated deformations respectively experimental models and seismic data highlight that incompetent layers act as barrier units against fault propagation in sequence and or out of sequence faults into overlying strata towards southwest by fore deformation and control the rate of deformation propagation in the zftb the presence of both the basal and internal decollement layers located at different stratigraphic levels is required to form disharmonic decollement folds in the foreland of the zftb in addition the geometry spacing activity and propagation of faults as well as the topographic height of the critical wedges are directly controlled by low frictional decollements geophys j int 165 1 336 356 2006 geochem geophys geosyst 14 1131 1155 2013 the seismic profiles of the zftb showed that in addition to lithological contrasts the existence and activity of deep seated and basement faults had a big impact on the structural styles of the region

detecting the source of heinrich layers an organic geochemical study 1 there are controversies regarding the origin of heinrich layer 3 h3 the massive ice rafting and meltwater event in the north atlantic during the last glacial cycle spanning a time window between 29 and 30 kyr b p some argue in favor of a laurentide ice sheet source similar to other heinrich layers while a contending view argues for the european ice sheet source existing geochemical proxies such as 40ar 39ar 206pb 204pb or nd etc could not be used to distinguish among various sources of ice rafted debris in h3 because of their low abundances suggesting a background glacial sediment signal in order to circumvent this problem a biomarker based approach is used to characterize the provenance of h layers 2 3 and 4 and other non heinrich layers the presence of hopanes and steranes and their aromatic counterparts in the h layers is incompatible with recent sediments and is attributed to the transportation of organic matter because of the glacial erosion of source rocks the most diagnostic and useful signatures of this ancient organic matter in the h layers are the dominance of c34 hopanoids over c33 and the occurrence of isorenieratane along with palaerenieratane biomarkers signatures in h layers 2 and 3 of the labrador sea suggest no difference in their source hydrocarbon distributions suggest that these sediments were derived from the middle to late ordovician and silurian source rocks of the hudson bay of eastern canada biomarker data of the h layer 4 from the northwest atlantic reveal that the sediments of this layer have a similar source to the h layers in the labrador sea

zooming in on heinrich layers theories explaining the origin of the abrupt massive discharges of ice rafted detritus ird into the glacial north atlantic the heinrich layers hls generally point to the laurentide ice sheet as the sole source of these events until it was found that the irds also originated from icelandic and european ice sheets bond and lotti 1995 snoeckx et al 1999 grousset et al 2000 this apparent contradiction must be reconciled as it raises fundamental questions about the mechanism s of hl origin we have analyzed two 12 cm thick hls in an ultrahigh resolution mode 1 2 century intervals in a mid atlantic ridge piston core the 18o record n pachyderma left coiling reveals strong excursions induced by the melting of the icebergs these excursions are associated with a strong decrease in the amount of planktic foraminafersand with a 3 c cooling of the surface waters counts of coarse detrital grains reveal that ird are deposited according to a typical sequence 1 volcanic glass 2 quartz and feldspars 3 detrital carbonate that implies a chronology in the melting of the differentpan atlantic ice sheets sr and nd isotopic composition confirm that in both heinrich layers h1 and h2 precursor ird came from first europe iceland followed then by laurentide derived ird an internal cyclicity can be identified during h1 and h2 about four to six major abrupt discharges occurred roughly on a century timescale the 13c and 15n records reveal that dominant inputs of continent derived organic matter are associated with ird within the hls hiding the plankton productivity signal