internal geometry and origin of the hubat structural culmination oman mountains abstract the hubat structure is a doubly plunging antiform affecting an allochthonous succession of mesozoic sedimentary rocks the hawasina complex overlain by the haybi complex and the semail ophiolite it is cored by a well exposed imbricated nappe of the hamrat duru group detailed investigations of the hamrat duru group led to the recognition of a main phase of imbrication followed by a phase of meso and macroscopic folding with axes at a high angle to the strike of the imbricates parallel to their assumed transport direction thrust relationships displayed in this area indicate that the floor thrust of the semail ophiolite is younger than the emplacement of the lower units and therefore out of sequence this culmination may have originated either as a result of a post emplacement regional compressive event of tertiary age or during the emplacement of allochthons above an oblique ramp during the late cretaceous orogeny

geometric analysis of fold development in overthrust terranes abstract fault bend folding fault propagation folding and detachment or decollement folding are three distinct scenarios for fold thrust interaction in overthrust terranes simple kink hinge models are used to determine the geometric associations implicit in each scenario bedding maintains constant thickness in the models except in the forelimb of the fold the forelimb is allowed to thicken or thin without limit the models address individual folds and the calculated fold geometries are balanced structures each mode of fold thrust interaction has a distinct set of geometric relationships final fold geometry is adequate in itself to discern many fault bend folds this is not the case for fault propagation and detachment folds these two fold forms have very similar geometric relationships some knowledge of the nature of the underlying thrust or decollement zone is usually needed to distinguish between them the geometry of a fold is altered in a predictable fashion by transport through an upper ramp hinge and by fault parallel shearing of the structure the shearing results in a tighter fold whereas transport through the ramp hinge produces a broader fold the viability of the geometric analysis technique is demonstrated through its application to a pair of detachment folds from the canadian cordillera the geometric analysis is also used to evaluate cross sections through subsurface structures in an example from the turner valley oil field the analysis indicates how the interpretation should be altered so as to balance the cross section the analysis reveals hidden assumptions and specific inconsistencies in structural interpretations

the calculation of bulk strain in oblique and inclined balanced sections abstract the calculation of bulk strain from balanced sections is a technique commonly used in the study of orogenic belts the validity of a balanced section is often enhanced by controls such as seismic and or borehole data the construction of a conventional vertical section perpendicular to orogenic strike i e in the transport direction may not allow control data to be directly incorporated into the section the control data can be projected into the plane of the section or alternatively the section may be constructed in an orientation such that it contains the available control data in the case of a vertical section constructed at an oblique angle to the transport direction the bulk strain value obtained is a minimum and can be corrected to the true value of bulk strain in the perpendicular vertical section by a simple trigonometric calculation if the section is perpendicular to strike but inclined at an angle to the vertical the correction of the bulk strain values is mathematically unique to the section this problem can be overcome by using a digitizing table in conjunction with a simple computer program the general case of a section both oblique to the strike direction and inclined to the vertical can be resolved by removing the effects of the inclination to produce a vertical oblique section from which the bulk strain can be obtained and corrected in realistic geological problems the oblique section will be a more common problem than the inclined section in both cases deviations of 10 and less introduce such small errors in the estimates of bulk strain that their effects can be ignored

co2 record between 40 and 8 kyr b p from the greenland ice core project ice core co2 ice core records show an increase in the atmospheric concentration of 80 100 parts per million by volume ppmv from the last glacial maximum lgm to the early holocene we present co2 measurements performed on an ice core from central greenland drilled during the greenland ice core project grip this co2 profile from grip confirms the most prominent co2 increase from the lgm with a mean concentration of 200 ppmv to the early holocene with concentrations between 290 and 310 ppmv some structures of the new co2 record are similar to those previously obtained from the dye 3 ice core greenland which indicated a dilemma between greenland and antarctic co2 records oeschger et al 1988 both greenland cores show high co2 values for rather mild climatic periods during the last glaciation whereas co2 records from antarctica do not show such high co2 variations during the glaciation and furthermore the co2 values in the early holocene are about 20 30 ppmv higher in the grip record than in antarctic records there is some evidence that the difference could be due to chemical reactions between impurities in the ice leading to an increase of the co2 concentration under certain conditions if in situ processes can change the co2 concentration in the air bubbles the question arises about how reliably do co2 records from ice cores reflect the atmospheric composition at the time of ice formation the discrepancies between the co2 profiles from greenland and antarctica can be explained by in situ production of excess co2 due to interactions between carbonate and acidic species since the carbonate concentration in antarctic ice is much lower than in greenland ice co2 records from antarctica are much less affected by such in situ produced co2

eight glacial cycles from an antarctic ice core the antarctic vostok ice core provided compelling evidence of the nature of climate and of climate feedbacks over the past 420 000 years marine records suggest that the amplitude of climate variability was smaller before that time but such records are often poorly resolved moreover it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records here we report the recovery of a deep ice core from dome c antarctica that provides a climate record for the past 740 000 years for the four most recent glacial cycles the data agree well with the record from vostok the earlier period between 740 000 and 430 000 years ago was characterized by less pronounced warmth in interglacial periods in antarctica but a higher proportion of each cycle was spent in the warm mode the transition from glacial to interglacial conditions about 430 000 years ago termination v resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases but there are significant differences in the patterns of change the interglacial stage following termination v was exceptionally long 28 000 years compared to for example the 12 000 years recorded so far in the present interglacial period given the similarities between this earlier warm period and today our results may imply that without human intervention a climate similar to the present one would extend well into the future

geometrical modeling of fault related folds a pseudo three dimensional approach abstract area balanced cross sections of ramp anticlines and tip line folds in thin skinned fold thrust belts can be quantitatively constructed using plane strain fault bend and fault propagation fold models cross sections alone however are somewhat inadequate for interpreting along strike changes in thrust related fold geometry complex interplay between along strike changes in fault slip and fault shape determines a range of geometric configurations which are difficult to visualize without the aid of quantitative three dimensional models we extend conventional two dimensional folding theories into the third dimension by allowing for continuous variations in fault slip and fault shape along strike geometric equations relating map view angles between fold axial surface traces are derived for a case assuming a uniform fault geometry and an along strike displacement gradient the resulting folds possess no unique fold axis but rather are characterized by multiple fold hingelines each corresponding to bends in the fault for typical displacement gradients observed in the field analysis of the models suggests that discernible differences exist between map patterns of fault bend folds and fault propagation folds whereas little difference exists between map patterns of similar and parallel fault bend folds map view angles between axial surface traces for parallel fault bend folds and fault propagation folds are a function of both ramp cutoff angle and fault slip whereas these same angles for similar fault bend folds are solely a manifestation of fault slip examples assuming uniform shortening and continuously varying fault geometry along strike are also presented fault geometry is varied along strike to simulate oblique and lateral ramps depending upon model type and fault shape parameter modified resulting folds exhibit either cylindrical or non cylindrical fold geometries closure is generated by a decrease in fold amplitude where there is a decrease in ramp cutoff angle along strike or where a fault laterally cuts up section in either instance closure develops without varying shortening along strike model map patterns resemble actual thrust related fold geometries and can be compared to maps of real structures to help predict subsurface geology

quaternary stratigraphy and ice cores abstract ice cores contain highly detailed continuous stratigraphic records extending from the present to 800 ka bp a large variety of climate proxies related to atmospheric and climate changes can be analysed and dated with an accuracy ranging from a few years for recent centuries to a few millennia for older records over the past two decades the contribution of ice core studies to the reconstruction and interpretation of past climate changes became fundamental they allowed the direct measurement of greenhouse gas changes in the past and the detection of rapid climatic changes this paper presents a short summary of ice core results restricted only to those relevant for the stratigraphy of the quaternary at the base of the epica dome c dc ice core the matuyama bruhnes m b magnetic reversal has been indirectly identified at the end of marine isotopic stage mis 19 and dated 764 776 6 ka bp allowing the correlation with the m b boundary observed in the deep sea sediments the details of the m b transition observed in the epica dc ice core are of interest for an improved characterization of this time marker which is crucial for the identification of the lower middle pleistocene boundary a clear increase in the amplitude of the glacial interglacial cycles is observed at 430 ka bp at the mis 12 11 transition in the epica dc climatic curves this mid bruhnes event marks a change in the pattern of climatic changes the middle upper pleistocene boundary at the base of the eemian stage is clearly detectable in the antarctic ice cores as a sharp increase in the methane signal coinciding with the initial peak of temperature derived from stable isotope profile around 128 ka bp in good agreement with vegetation changes on land in the northern hemisphere in greenland ice cores the last climatic cycle is marked by high amplitude millennial scale climatic variations bounded by abrupt limits that appear to correlate with stadial interstadial stages these climatic events are also present in the antarctic ice cores but smoothed smaller in amplitude and out of phase with respect to their northern counterparts therefore the stratigraphy of the deglaciation and of the transition from the upper pleistocene to the holocene differs in the two opposite hemispheres the holocene in ice cores is different from previous interglacials and it deserves a specific identification in the geological history despite its short duration compared to other epochs the formal definition of the pleistocene holocene boundary has been recently proposed and ratified on the ngrip ice core and fixed at 11 7 ka before ad 2000 about 200 years before present the sharp increase of co 2 and methane above the natural interglacial level as well as the sudden increase of atmospheric pollutants are a clear stratigraphic evidence for a recent global event caused by the human impact

thin skinned tectonics in the ponga region cantabrian zone nw spain the variscan thrust and associated fold structures of the ponga region cantabrian zone nw spain are interpreted in terms of thin skinned tectonics with a dominant eastward transport direction

three dimensional geometry and interference of fault bend folds examples from the ponga unit variscan belt nw spain abstract examples of the three dimensional geometry and interference patterns between fault bend folds occur in the ponga unit of the variscan cantabrian foreland thrust and fold belt of nw spain the ponga unit consists of several e directed thrust sheets with a cumulative displacement of 93 km which were emplaced during upper westphalian stephanian time two major lateral ramps developed in the basal thrust of the ponga unit reaching 15 and 20 km in length respectively and some 3 km in height lateral structures are also common within the hangingwall thrust sheets the three dimensional staircase trajectories of thrust faults together with the tectonic superposition of thrust sheets has produced a complex interference pattern of fault related folds most map scale folds formed as fault bend folds related to interference between frontal and lateral ramps fold geometry and size varies depending on the geometry and size of the associated thrust ramp and flat the axial traces are grouped into lateral and frontal sets which are sub parallel or sub perpendicular to the tectonic transport direction respectively corner folds form with plunging axes at the intersections of frontal and lateral ramps and generally link pairs of frontal lateral folds they have relatively short axial traces that are oblique to the tectonic transport direction fold plunge varies due to the superposition of lateral and frontal structures of a thrust fault and also depends on the geometry of subsequent thrusts in the footwall the final geometry of frontal folds in the ponga unit are not only the result of the bending mechanism but have been modified by simple shear parallel to the emplacement direction major lateral structures have been reactivated as reverse faults and are locally overturned due to post emplacement north south compression

gas records from the west greenland ice margin covering the last glacial termination a horizontal ice core abstract certain sites along ice sheet margins provide an easily accessible and almost unlimited supply of ancient ice at the surface measurements of gases in trapped air from ice outcropping at pakitsoq west greenland demonstrate that ancient air is mostly well preserved no alterations in 18 o atm and 15 n of n 2 are apparent and alterations in methane are found in only a few ice sections using measurements of these gases we have unambiguously identified a stratigraphic section containing ice from the end of last glacial period as well as bolling allerod younger dryas and preboreal intervals extensive sections of ice from the holocene and most ages within the last glacial period are probably also present very accurate dating has been possible in the ice section containing the younger dryas preboreal abrupt climate transition signal the ice at pakitsoq is folded and non uniformly thinned with many cross cutting bands of bubble free ice and dust the cross cutting features are associated with anomalies in both the gas and the ice records with careful sampling to avoid these the ice at pakitsoq is suitable for recovery of large volume samples of the ancient atmosphere for analysis of trace constituents such as 14 ch 4

fold interference structures in thrust systems abstract the accommodation problems associated with the generation of interference folds in thrust belts are examined there are several ways in which interference folds may grow in thrust systems such as moulding on to non planar ramps or via the interaction of non coaxial structures the geometries of interference folds from thrust belts in spain and pakistan are described and form the basis of an analog model the model is used to quantify the volume of rock which must be accommodated during the growth of these structures mechanisms which might solve the inherent space problem are discussed the simplest geometrical solution would involve a mechanism which caused thickening in the fold hinges but this was not observed in the field field evidence is used to construct a linked fold and fault model which reconciles the absence of thickening in the interference fold hinge with the volume of material which must be accounted for

a tentative reconstruction of the last interglacial and glacial inception in greenland based on new gas measurements in the greenland ice core project grip ice core parameters the grip d 18 oice chronological sequence is obtained by comparing a new set of d 18 o of atmospheric o2 and ch4 measurements from the bottom section of the grip core with their counterpart in the vostok antarctic profiles this comparison clearly identifies ice from the penultimate glacial maximum mis 6 190 130 kyr b p in the grip core further it allows rough reconstruction of the last interglacial period and of the last glacial inception in greenland which appears to lay its antarctic counterpart our data suggest that while antarctica is already entering into a glaciation greenland is still experiencing a warm maximum during mis 5e index terms 1040 geochemistry isotopic composition chemistry 1827 hydrology glaciology 1863 3344 meteorology and atmospheric dynamics paleoclimatology keywords interglacial ice cap firn

the terminology of structures in thrust belts abstract a review of structures and geometric relationships recognized in thrust belts is presented a thrust is defined as any contractional fault a corollary being that thrusts must cut up section in their transport direction flats are those portions of a thrust surface which were parallel to an arbitrary datum surface at the time of displacement and ramps are those portions of thrusts which cut across datum surfaces ramps are classified on the basis of their orientation relative to the thrust transport direction and whether they are cut offs in the hangingwall or footwall of the thrust lateral variations in the form of staircase trajectories are joined by oblique or lateral ramps which have a component of strike slip movement an array of thrusts which diverge in their transport direction may form by either of two propagation models these are termed piggy back propagation which is foreland directed and overstep propagation which is opposed to the thrust transport direction an array of thrust surfaces is termed an imbricate stack and should these surfaces anastamose upwards a duplex will result the fault bounded blocks are termed horses a duplex is bounded by a higher roof thrust and a lower floor thrust the intersection of any two thrust planes is termed a branch line thrusts can be classified on the basis of their relationship to asymmetric fold limbs which they cut a further classification arises from whether a particular thrust lies in the hangingwall or footwall of another one the movement of thrust sheets over corrugated surfaces or the local development of thrust structures beneath will fold higher thrust sheets these folds are termed culminations and their limbs are termed culmination walls accommodation of this folding may require movement on surfaces within the hangingwall of the active thrust these accommodation surfaces are termed hangingwall detachments and they need not root down into the active thrust this category of detachment includes dip slip hangingwall drop faults which are developed by differential uplift of duplex roofs and out of the syncline thrusts which develop from overtightened fold hinges back thrusts as well as forming as hangingwall detachments may also form due to layer parallel shortening above a sticking thrust or by rotation of the hangingwall above a ramp

fold interference structures and coaptation folds abstract coaptation folds are bends in rock layers formed at the junctions of intersecting folds in a manner analogous to the line of junction between two intersecting cylinders they form purely as a geometric consequence of the fitting together of the fold forms and have no tectonic significance however the presence of unidentified coaptation folds may lead to misinterpretation of fold geometry and structural history interference patterns affected by coaptation folds are modified versions of ramsay s 1962 type 1 basin and dome patterns but form where the three dimensional shape of the interference structure is a convoluted conical shape rather than a simple conical shape

chronology reconstruction for the disturbed bottom section of the gisp2 and the grip ice cores implications for termination ii in greenland and d 18 oatm in the trapped gases our reconstructed ages for basal ice samples are based on comparison of published measurements of ch4 and d 18 oatm from the disturbed section of the grip and gisp2 cores with the same properties in the vostok ice core ngrip d 18 oice values are also used to constrain the chronology during the end of marine isotope stage 5e for each sample we assign an age that represents the unique or most probable time of gas trapping given its gas composition of 157 samples with ch4 and d 18 oatm data 10 give unique ages twenty five newly measured values of the triple isotope composition of o2 from the disturbed section of the gisp2 core add a third time dependent gas property that agrees with our reconstruction our reconstruction supports earlier conclusions of landais et al 2003 that the disturbed section primarily includes ice from the last interglacial mis 5e and the penultimate glacial period mis 6 the oldest ice in the basal layer of gisp2 and grip has an age 237 ka the climate history we derive suggests that the last interglacial at summit greenland around 127 ka was slightly warmer than the current interglacial period reduction of various ion concentrations in ice and thickening of the ice sheet during termination ii was similar to that in termination i

complex strain patterns developed at the frontal and lateral tips to shear zones and thrust zones abstract many of the complex strain patterns seen in shear zones and thrust zones such as variable fabric orientations refolded folds and fabrics together with folds with hinges almost parallel to the main transport direction can be explained in terms of differential movement within the shear zones these strains are developed at the frontal and lateral tips of the zones as they propagate examples are taken from the moine thrust zone of scotland which show variations in strains particularly at the lateral tips the form of differential movement described here may lead to complex strain paths and non plane strain ellipsoids and the spatial variations in finite strain may be used to delineate zones of extensional and compressional flow and differential movement in the shear zones or thrusts

fold interference structures the influence of layer competence contrast using the geometrical properties of curved surfaces it can be predicted that the geometries of natural refolded folds should differ from the well known forms resulting from superposed shear folds if the sequence undergoing folding contains competent horizons the simple dome and basin patterns expected from kinematic considerations are incompatible with constant bed length folding isometric deformation isometric deformation requires that a flat sheet folds to give a surface consisting of points of zero gaussian curvature like for example the surfaces of cylindrical and conical folds we suggest that the coaptation folds recently recognized by stauffer 1988 are topologically necessary crumples on the flanks of domes and basins rather than bends at the intersection of two oblique intersecting folds and should be known as curvature accommodation folds

three dimensional geometry and kinematic evolution of the pine mountain thrust system southern appalachians the pine mountain thrust system is the westernmost major structure in the southern appalachian valley and ridge in virginia tennessee and kentucky surface subsurface and seismic reflection data have been integrated to construct a series of balanced cross sections and interpret the three dimensional geometry and kinematic evolution of the structure the structure is subdivided into three main areas on the basis of structural style in the southwestern and northeastern areas the structure consists of a simple ramp related anticline the powell valley anticline related to a ramp in the pine mountain thrust from the cambrian rome to the devonian chattanooga formation in the central oil producing area the pine mountain thrust is exposed in several erosional fensters as a result of folding by one or more subthrust imbricates here the pine mountain thrust develops a double ramp geometry with an intermediate flat in the cambrian maynardville formation the structure varies from a system of overlapping anticlines in the brooks and martin creek fenster sections to two anticlines separated by an intermediate syncline in the bethel and sulphur springs fenster sections to a partially overlapping duplex imbricate system in the big stone gap section the total shortening associated with the pine mountain thrust system decreases from about 70 000 ft 21 3 km at the southwest end to less than 10 000 ft 3 0 km at the northeast end in the central fenster area the total shortening is distributed between the pine mountain thrust and its subthrust imbricates the structural elevations in both the pine mountain and bales i sheets are greatest in the central fenster area the greatest structural elevations in the bales i sheet are in the rose hill and ben hur oil fields palinspastic restorations of the thrust system and the construction of detailed fault maps indicate that variations in structural geometry and shortening along strike are accommodated by interactions between thrust faults and oblique ramps or tear faults the variations in three dimensional geometry can be explained in terms of combinations of three main mechanisms unequal hanging wall displacements over a single footwall ramp equal displacements over a footwall ramp displaced along an oblique ramp and displacement of part of a footwall ramp due to movement on one or more frontal thrusts

hangingwall strain a function of duplex shape and footwall topography abstract the concept of piggy back thrust tectonics implies that foreland is progressively accreted onto a developing thrust sheet during duplex formation lateral shape changes in duplexes in the hangingwall of a thrust and corrugations in the footwall will fold higher thrust sheets to give culminations and depressions balancing of parts of high level thrust sheets with lower sheets and foreland requires a sequence of extensional and compressional strains orientated normal to the thrust transport direction culmination walls will be sites of strike parallel extension subsequent adjacent culminations will compress early culmination walls which will result in a sequence of irrotational strains examples of this geometry are given from the moine thrust zone of northwest scotland the model allows a re examination of strains and hangingwall evolution in some thrust sheets in the helvetic and external zones of the alps

stable carbon cycle climate relationship during the late pleistocene a record of atmospheric carbon dioxide co2 concentrations measured on the epica european project for ice coring in antarctica dome concordia ice core extends the vostok co2 record back to 650 000 years before the present yr b p before 430 000 yr b p partial pressure of atmospheric co2 lies within the range of 260 and 180 parts per million by volume this range is almost 30 smaller than that of the last four glacial cycles however the apparent sensitivity between deuterium and co2 remains stable throughout the six glacial cycles suggesting that the relationship between co2 and antarctic climate remained rather constant over this interval

biosedimentological zonation of boundary bay tidal flats fraser river delta british columbia boundary bay tidal flats on the inactive southern flank of the fraser delta have surface sediments consisting almost entirely of very fine to fine well to very well sorted sands which show a gradual fining shorewards trend five floral sedimentological zones form distinct biofacies these are from the shoreline seaward the saltmarsh algal mat upper sand wave eelgrass and lower sand wave zones the lower limit of the saltmarsh lies at a constant level above which the maximum duration of continuous exposure rises abruptly from 12 to 40 days similarly at the lower limit of the algal mat zone the maximum duration of continuous exposure jumps from 1 to 2 days and at the upper limit of the eelgrass zone from 0 5 to 0 8 days these correlations between exposure and zonation are suggested to be causal in the algal mat and eelgrass zones microtopography of biogenic origin only a few centimetres high creates lateral heterogeneity within the zonal biofacies in the upper sand wave zone very low amplitude a 0 1 m symmetrical sand waves 30 m of probable storm wave origin have a similar effect in the lower sand wave zone sand waves a 0 5 m 60 m are formed by tidal currents or wave action and physical sedimentary structures dominate over biogenic ones the densities of the following macrofaunal organisms which produce distinctive biogenic sedimentary structures were determined on two surveyed transects callianassa californiensis and upogebia pugettensis both thalassinidean shrimps three polychaete worms abarenicola sp spio sp and clymenella sp the bivalve mya arenaria and the gastropods batillaria attramentaria and nassarius mendicus callianassa excavate unlined temporary feeding burrows whereas upogebia build mud lined permanent dwelling burrows upogebia are restricted to below mean sea level where continuous exposure is 0 5 days whereas callianassa extend up to a level just below mean higher high water where maximum continuous exposure rises abruptly from 4 to 9 days this difference in range is probably due to the latter s greater anoxia tolerance a necessary adaptation for life in an unlined feeding burrow

role of shear in development of the helvetic fold thrust belt of switzerland the geometric features of the helvetic nappes of the alps show intense internal deformation set up predominantly by simple shear during nappe transport the nappes are bounded by thrusts that parallel incompetent layers and ramp upward stratigraphically across competent units in the direction of tectonic transport stratal layering is oblique to nappe boundaries thrust surfaces formed after ductile shear zones developed in underlying pre triassic gneissic basement the broad zone of shearing narrowed down as deformation increased to form zones of intense shear and ultimately to form thrust faults contraction along competent layers obliquely inclined to shear surfaces produced buckle folds the geometry of these folds was modified by further shearing as their normal limbs became aligned in the extension field of the strain ellipse for simple shear producing normal faults

ch4 and δ18o of o2 records from antarctic and greenland ice a clue for stratigraphic disturbance in the bottom part of the greenland ice core project and the greenland ice sheet project 2 ice cores the suggestion of climatic instability during the last interglacial period eem based on the bottom 10 of the greenland ice core project grip isotopic profile has been questioned because the bottom record from the neighboring greenland ice sheet project 2 gisp2 core 28 km away is strikingly different over the same interval and because records of the 18o of atmospheric o2 from both cores showed unexpected rapid fluctuations here we present detailed methane records from the vostok antarctica grip and gisp2 cores over the relevant intervals the grip and gisp2 data show rapid and large changes in methane concentration which are correlative with variations of the 18o of the ice while the vostok record shows no such variations this discrepancy reinforces the suggestion that the bottom sections of the greenland records are disturbed by combining the methane data with measurements of 18o of o2 in the same samples we attempt to constrain the nature of the stratigraphic disturbance and the age of the analyzed ice samples our results suggest that ice layers from part of the last interglacial period exist in the lower section of both ice cores and that some of the apparent climate instabilities in the grip core would be the result of a mixture of ice from the last interglacial with ice from the beginning of the last glaciation or from the penultimate glaciation

sequences of thrusts and displacement transfer in the superposed duplexes of the esla nappe region cantabrian zone nw spain abstract in a cross section through the southern arm of the cantabrian zone several duplexes have been identified below the esla nappe which is the uppermost and main thrust sheet of the area the folds deforming the esla nappe are culmination walls linked to frontal and lateral ramps belonging to the lower thrust sheets the thrust sequence can be established on the basis of quantitative analysis of displacement transfer and out of sequence thrusting the primitive footwall ramps of the esla nappe region were often subsequently broken by decollements developed in successively lower stratigraphic levels of these footwalls the kinematics of the lowest duplex are more complicated than those of typical duplexes described elsewhere some thrusts transfer only part of their displacement to the roof thrust while the remaining part is accommodated along the higher thrusts of previously emplaced duplexes cutting out of sequence one or more floor or roof thrusts cumulative displacement of the thrusts in this region is about 90 km giving a present thickness 3 times that of the original pre orogenic sequence together with a translation of at least 60 km for the synorogenic basin

termination v in the vostok antarctica ice core the age depth relationship of the vostok antarctica ice core has been reconstructed in the depth interval 3300 3347 m by comparing three gas properties in ice co 2 ch 4 and 18 o atm with those in the epica dome c antarctica core fourteen vostok depths were examined in this interval and it was found that nine samples are uniquely dated if candidate ages are restricted to the interval between 400 and 650 kyr one of these samples is uniquely dated without restriction the analysis supports previous reports that this section contains ice from termination v but that the stratigraphic order of ice is reversed the top of the overturned layer lies between 3316 and 3319 m at least one other stratigraphic disturbance was found between 3340 and 3343 m as indicated by another reversal of the age depth relationship finally the oldest ice in this section is dated at 440 kyr confirming the existence of ice from the cold marine isotope stage mis 12 interval

geometric and kinematic evolution of basement cored structures intraplate orogenesis within the yanshan orogen northern china abstract detailed surface mapping lithology facies analysis drillcore data and aeromagnetic interpretation reveal the geometries of the basement involved structures of laowopu nantan liudaohe xinglong and malanyu to have been generated by folding and thrusting the resulting basement cored anticlines are asymmetric with a shallowly dipping top and backlimb and a steep to overturned forelimb and or frontal fault linked with a gently dipping synclinal limb both the fold axes and frontal faults trend roughly east west suggesting north south shortening north to northeast trending faults behave as tear lateral or oblique ramp structures and formed coevally with their frontal faults their trends may have been inherited from proterozoic synsedimentary faults and archaean basement ductile shear zones foliations and mafic dikes thin skinned thrusts and their three dimensional geometry are locally controlled by detachment within mechanically incompetent layers four types of interrelationships between the thick and thin skinned structures occur including 1 lateral changes along the length of a fault 2 displacement transfer between thick and thin skinned structures 3 buttressing of thin skinned thrusts against the basement involved structures and 4 generation of an out of the syncline thrust under thick skinned shortening most of the deformation within the study area involved brittle behaviour but ductile shear zones developed where fluid access was possible both the basement involved structures and the thin skinned structures formed in the early mesozoic as constrained by cross cutting relationships isotopic ages of igneous rock and syntectonic basins the model of geometric and kinematic evolution of the basement involved structures and their relationship with the thin skinned structures defined in this paper provides an alternative to the current metamorphic core complex model used for the yanshan intraplate orogen

the co2 concentration of air trapped in gisp2 ice from the last glacial maximum holocene transition measurements of the co2 concentration of air trapped in greenland ice sheet project two ice show an increase from approximately 190 ppm to 270 ppm during the 8000 years between the end of the last glacial maximum and the beginning of the holocene this increase is in agreement with other parallel records from both greenland and antarctica although the gisp2 data exhibit considerable variability over periods as small as 50 100 years and show that co2 can be affected by processes occurring within the ice after bubble formation the in situ reactions which contribute to the modification of the concentrations of paleoatmospheric co2 may include both co2 uptake as well as co2 production the existence of two major episodes of co2 enrichment in addition to the variability of the data prevents a precise determination of the progression of the increase in atmospheric co2 although the 80 ppm rise between 18 0 kybp and 10 4 kybp is evident these results strongly suggest that some intervals of the gisp2 co2 record must be interpreted in the context of the chemical composition of the ice and that records of atmospheric co2 in polar ice can be considered accurate only if the ice is either essentially carbonate free or contains abundant carbonate