sedimentation at manop site h eastern equatorial pacific over the past 400 000 years climatically induced redox variations and their effects on transition metal cycling gravity cores recovered from manganese nodule project site h 6 33 n 92 49 w show marked downcore variations in the abundance of calcium carbonate organic carbon opal manganese and other components deposited over the past 400 000 years variations in the downcore abundance of organic carbon which ranges from 0 2 to 1 0 can be used to hindcast redox conditions in the surface sediments over this time the results indicate that the depth to the manganese redox boundary varied from about 5 to 25 cm below the seafloor during four major cycles downcore variations in solid phase mn ni and cu can be produced by such changes in redox conditions a model which predicts that solid phase mn can be trapped and buried when the mn redox boundary migrates rapidly upward is consistent with the observed organic carbon and mn records and supports the reconstructed redox variations the history of redox variations at site h can be explained by changes with time in surface water productivity major productivity variations at the site occur over 100 kyr cycles with relatively higher productivity occurring during glacial stages thus quaternary climate changes influence surface water productivity redox conditions in sediments and the cycling of transition metals

interaction between normal faults and pre existing thrust systems in analogue models the influence of pre existing thrusts on the development of later normal faults was investigated using scaled laboratory analogue models experiments consisted of a phase of shortening followed by extension at variable angles of obliquity a to the shortening direction results suggest that the angle a has a major influence on the surface fault pattern and on the interaction between shortening related structures and later extensional structures three different modes of interactions were identified depending upon the extension kinematics 1 for orthogonal extension a 1 4 08 shortening related fold and thrust structures strongly influence the development of normal faults graben structures nucleate within anticlines and the normal faults reactivate thrusts at depth branching at depth mode of interaction 2 for highly oblique extension a 458 shortening related structures exert no influence on normal faults as extension related steeply dipping faults characterized by an oblique component of movement displace early thrusts no interaction mode 3 for intermediate obliquity angles a 1 4 158 308 an intermediate mode of interaction characterizes the experiments where the no interaction and branching at depth modes coexist in different regions of models modelling results can be used to infer regional extension directions as is shown for the northern appenines italy it has been shown that in many cases pre existing thrust systems play an important role in controlling the architecture of superimposed normal faults mechanical theory suggests that the probability of reactivation of pre existing thrust faults depends on their orientation with respect to the superimposed extensional stress field e g sibson 1985 the process was investigated in previous analogue models krantz 1991 faccenna et al 1995 and references therein suggesting that the initial dip of thrust faults has a major control on the development of successive normal faults both studies started with a phase of shortening that resulted in progressively steeper thrust faults prior to extension model results suggested that three different types of interactions between pre existing thrusts and successive normal faults may arise e g faccenna et al 1995 1 no interaction occurs in case of low dip thrusts 328 18 and normal faults form independently displacing pre existing thrusts 2 branching at depth of normal faults with thrusts is observed for intermediate dip angles 328 182 418 18 3 total reactivation occurs on thrusts dipping at angles higher than 418 18 these three basic mode of interaction between normal faults and thrust systems have been recognized and described in natural systems such as the central apennines italy and the north sea region faccenna et al 1995 active extensional structures interacting with early thrust systems have been also recognized in the northern apennines e g finetti et al 2001 in this fold and thrust belt the early compressive structures show a prominent curvature along strike and the successive normal faults display strong variations in terms of trend arrangement and kinematics in different sectors of the chain fig 1 in particular where thrusts are orthogonal to the regional ne sw extension direction e g mugello basin fig 1 normal faults are long and linear display a mainly pure dip slip kinematics and from buiter s j h schreurs g eds 2006 analogue and numerical modelling of crustal scale processes geological society london special publications 253 65 78 0305 8719 06 15 00 the geological society of london 2006 are subparallel to the early compressive structures delle donne et al 2003 conversely where thrusts are slightly oblique to the extension garfagnana lunigiana area fig 1 normal faults are arranged en echelon are characterized by an oblique slip kinematics and display a mean peak in distribution oriented at about 108 with respect to the earlier thrusts piccardi et al 1999 in case of high obliquity e g martani mounts terni basin area fig 1 normal faults are linear are characterized by an important locally dominant strike slip component of movement and form at an angle of 208 to the pre existing structures bonini et al 2003 these features suggest that the different orientation of thrusts with respect to the direction of extension may have exerted an important control on the pattern of successive extensional structures this influence is investigated in this study by means of analogue models we present a series of experiments on polyphase deformation consisting of orthogonal shortening followed by extension at variable angles of obliquity

changes in deep ocean water δ18o and temperature from the last glacial maximum to the present estimates are made of changes of the oxygen isotope anomaly of deep ocean water and of deep ocean temperature for the atlantic indian and pacific oceans from the time of the last glacial maximum to the present several independent sources of data including oxygen isotope records of planktic and benthic foraminifera at selected core sites primarily in the equatorial oceans climate long range investigation mapping and prediction sea surface temperatures estimates and geosecs 18o data for the present ocean water are utilized together with the paleotemperature equation of epstein et al 1953 glacial to interglacial change in oxygen isotope composition of the global deep ocean water is found to be 1 41 per mil compared with a global average change of 1 75 per mil for benthic foraminifera the former value implies a sea level change between 128 and 141 m depending on the choice of the isotope sea level conversion constant a global deep ocean warming of 1 4 c from glacial maximum to the present is found from the above isotopic difference of 0 34 per mil the consistency of the results in this paper with those of chappell and shackleton 1986 suggest that there is no significant contribution from isotopically light floating ice shelves surrounding antarctica as proposed by johnson and andrews 1986 at least for the change from glacial maximum to the present the ocean transition from glacial to interglacial episodes was accompanied by an estimated warming of 2 0 c in the atlantic 1 4 c in the indian and 1 1 c in the pacific oceans the glacial pacific was colder than the atlantic ocean but the difference between the two oceans was smaller than today

alkenone molecular stratigraphy in an oceanic environment affected by glacial freshwater events the sedimentary record of a ratio uk37 of long chain c37 unsaturated alkenones is a useful indicator of glacial interglacial climatic change in the late quaternary northern gulf of mexico where a planktonic foraminiferal 18o caco3 record is complicated by meltwater and or fluvial events williams and kohl 1986 application of a laboratory temperature calibration of the uk37 ratio prahl and wakeham 1987 to a pigmy basin hydraulic piston core record deep sea drilling project core 619 suggested that the minimum glacial surface mixed layer sml temperature was 8 1 c colder than the holocene high sml temperature of 25 6 0 5 c this predicted glacial interglacial temperature difference was significantly larger than the differences predicted by either the foraminiferal 18o or foraminiferal assemblage temperature methods 0 8 2 0 c this large difference may be caused by local prymnesiophyte assemblage changes in response to climatically induced hydrographic changes interglacial periods may be dominated by pelagic prymnesiophyte assemblages while glacial periods may be dominated by neritic assemblages a combined mechanism of both climatically varying prymnesiophyte species assemblage and depth of alkenone biosynthesis may account for the large difference between the temperature methods

modelling hanging wall accommodation above rigid thrust ramps abstract experimental models are used to study the role of material rheology in hanging wall accommodation above rigid flat ramp flat thrust footwalls the deformation in the hanging wall was accomplished by forwards sliding along a rigid basal staircase trajectory with a variable ramp angle ranging from 15 to 60 we model different ramp angles to examine hanging wall accommodation styles above thrust ramps of overthrust faults ranging from 15 to 30 as well as above pre existing normal faults ranging from 45 to 60 for the hanging walls we used stratified frictional sand and viscous silicone putty materials in this paper we study three types of models type 1 models represent purely frictional hanging walls where accommodation above thrust ramps was by layer parallel thickening and by generating a series of back thrusts type 2 and 3 models represent stratified frictional viscous hanging walls in these models accommodation was by a complex association of reverse and normal faults mainly controlled by the rheological anisotropy as well as by the ramp inclination angle in type 2 models the silicone covered only the lower flat while in type 3 models it also covered the rigid ramp for 30 in type 2 models and 45 in type 3 models the viscous layer inhibited the development of back thrusts in the frictional hanging wall instead the silicone thickened to develop a ductile ramp for values higher than 30 in type 2 models and 45 in type 3 models back thrusts develop in response to the bulk compression the experiments simulate many structures observed above natural thrust ramps with 30 and pre existing normal faults with 45 the models emphasise the importance of a basal ductile layer which allows the hanging wall to step up over the rigid ramp by building up its own ductile ramp the models also emphasise that foreland directed normal faulting can develop at a thrust front in the case that the vertical stress due to gravity exceeds the horizontal stress due to end loading within a thrust wedge

forward modeling of the southern apennines forward kinematic modeling has been developed to reconstruct the successive geometries of geological sections the method is tested here on a geological section across the southern apeninnes where syntectonic neogene deposits are of help in determining the timing of the deformation that progressively affected more eastern parts of the apulian margin well known triassic and paleogene decollement levels induced thin skinned tectonics in the mesozoic and cenozoic sedimentary cover but the basement geometry is only poorly revealed by subsurface data two distinct hypotheses have been tested 1 thin skinned tectonics and 2 basement involved tectonics the shortening of the prism is estimated to be between 170 and 210 km whether or not the basement is involved in the imbricated stack of thrust sheets the results are discussed in the light of regional constraints i e regional flexure uplifts etc which favor basement involved structures at depth in addition to the effects of compression other phenomena affected the geometry of the prism and have to be taken into account because of the recent uplift of the belt the inner parts of the apenninic wedge have emerged and undergone erosion part of this eroded material has been simultaneously trapped in piggyback basins which record both the geometric and temporal evolution of the prism normal faulting also affected the western part of the southern apennines reactivating older thrust as detachment surfaces along which block rotation occurred

fluid pressure and effective stress in sandbox models abstract we have done a series of simple tests on sandpacks involving upward flow of compressed air through the pores and its effect on the yield strength the ultimate objective is to model deformation coupled with fluid flow in sedimentary basins for all tests we used a single batch of fontainebleau sand sieved to a grain size between 0 200 and 0 315 mm poured into a cylindrical container and then fluidized the density of this sand was 1 585 g cm3 irrespective of sand thickness the lithostatic pressure was proportional to the thickness of the sandpack a yield envelope was obtained by shearing the sandpack horizontally compressed air entered the base of the sandpack and flowed upwards through the pore spaces for 69 measurements on air flow without shearing a plot of discharge velocity versus gradient of fluid pressure is close to a straight line verifying darcy s law and yielding an intrinsic permeability of about 1 7 darcy for the sand for 72 tests on simultaneous shearing and fluid flow the estimated effective stress lithostatic stress minus estimated pore fluid pressure ranged from 0 to 1600 pa and the pore fluid ratio between air pressure and lithostatic pressure from 0 0 to 1 0 a plot of shear stress versus effective stress at failure is almost linear verifying terzaghi s principle of effective stress the best fit slope coefficient of internal friction is about 0 55 and the intercept on the shear stress axis cohesion is less than 85 pa the tests show that it is feasible to use compressed air within sandpacks as a means of modelling deformation coupled with fluid flow the next step will be to build sandbox models of layered sequences and to investigate detachments caused by abnormal fluid pressures

the permian to cretaceous structural evolution of the western approaches basin melville sub basin uk summary the tectonic sedimentary evolution of the western part of the western approaches basin melville sub basin was initiated during early permian times when synrift clastic sedimentation and volcanism commenced within an ene trending half graben this sequence thickened to the south and onlapped a high to the north during the permian an early nnw sse basin extension was accommodated on an array of ene wsw trending normal faults linked by nnw sse orientated transfer faults this was followed by a period of ene wsw extension along the basin axis when the normal and transfer faults of the previous faulting episode swapped roles this was possibly related to early rifting in the bay of biscay both sets of faults appear to be controlled to some extent by variscan thrusts and strike slip faults within the basement during the upper triassic the ridge in the north subsided allowing a thick sequence of salt to be deposited where there had previously been a topographic high during jurassic times sedimentation extended across the permian triassic half graben into the french sector this was followed by an episode of rifting and wrench deformation and inversion during which the permian to jurassic basin was domed and uplifted the cretaceous to tertiary sedimentation which followed probably resulted from postrift thermal subsidence related to cooling of the continental platform adjacent to the opening atlantic ocean steep normal and or strike slip faults data from the earliest part of this postrifting stage

the record of late pleistocene biogenic sedimentation in the eastern tropical pacific ocean we have generated 300 kyr records of biogenic opal calcite and organic carbon corg for three cores in the eastern and central equatorial pacific ocean and have compared the records to determine whether common periods of biogenic sedimentation have occurred throughout the region we find that corg has been deposited in common pulses throughout the area while opal has a much more local pattern of variation calcite varies regionally but the record is shaped by superimposed dissolution and productivity processes the most intense corg peak occurs at 18 ka and can have greater than 2 times the holocene corg content other major corg peaks occur 150 ka and perhaps at 280 ka we have compared the corg record in one of the cores v19 28 to a model deepwater oxygen record developed from 13c data in the nearby v19 30 to test whether the corg record has been mostly shaped by degradation or by the rain of organic matter from the euphotic zone we found no coherence between the two records implying that the corg record is primarily a measure of productivity by comparing the opal calcite and corg records in v19 28 a core which is at or above the lysocline we found that both increased calcite and opal deposition matches high corg accumulation we also found however that the calcite and opal records were uncorrelated so that episodes of high opal deposition do not necessarily accumulate calcite rapidly we hypothesize that at least two different plankton communities have been dominant in the waters above this site one rich in opal secreting plankton and one more dominated by calcite producers the opal rich plankton community was dominant during the intervals 10 15 ka and 35 60 ka supplement data table 2 is available with entire articleon microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document p88001 2 50 payment must accompany order

on the reactivation of extensional fault systems in terranes that have undergone substantial extension three sets of faults dominate a shallow to steep dipping commonly rotational normal faults b a really extensive shallow dipping normal detachment faults and c steep dipping transfer faults that strike at high angles to the normal faults these fault systems may extend through a large fraction of the crust reactivation of these fault systems will depend primarily on the relative strengths of the faults shear zones and their host rock and their orientation in the prevailing stress field it is concluded that reactivation is generally mechanically favoured but that it will probably only take place when the fault shear zones are in near ideal orientations consideration of the tectonic setting of extended terranes and of the limited number of well described examples suggests that reverse thrust reactivation of the normal and detachment faults and wrench reactivation of transfer faults are the most likely styles examples of these styles are described from the bass strait basins of southeastern australia because extended terranes commonly underlie sedimentary basins for example on passive continental margins reactivation of extensional faults may be a key control on the tectonic evolution of such basins i e basin inversion

oxygen isotope analyses and deep sea temperature changes implications for rates of oceanic mixing since the first measurements were made more than thirty years ago1 analysis of oxygen isotopes in foraminifera from deep sea sediments has gained widespread use as a palaeoclimatic and stratigraphic indicator isotopes stages are commonly used to define the ice ages2 but controversy still remains regarding the relative contributions of temperature and ice volume change to the down core 18o record for the past decade temperature has commonly been considered a trivial portion of the signal3 recent reports however suggest that as much as one third of the measured 18o variations can be ascribed to cooler glacial maximum temperatures4 5 this interpretation requires mean deep ocean temperatures 0 c through much of late quaternary time here we explore some of the consequences of this hypothesis for the heat budget of the deep sea and conclude that either thermohaline overturn must have been faster than at present or that cooling of the deep ocean at the glacial maximum may have been overestimated

an automatic method for determining three dimensional normal fault geometries we describe a general kinematic method for automatically determining the three dimensional 3 d geometry of normal faults at depth from the 3 d geometry of deformed hanging wall horizons the method should be applicable to normal faults which do not change shape as deformation proceeds it is a generalization of two dimensional models and assumes that the hanging wall deforms by arbitrarily inclined bulk simple shear deformation in three dimensions is parameterized by the three euler angles which describe the horizontal slip vector the rake angle and the inclination of shear planes as in two dimensions differential compaction can be included by assuming that the axis of shortening is parallel to the direction of shear three dimensional fault geometry and the three euler angles can all be automatically determined provided the geometries of two or more hanging wall horizons are known here the method is tested on both synthetic data and on 3 d sand box models synthetic modeling shows that unique solutions can be found and more importantly that the horizontal slip vector can be constrained solutions obtained from sand box models are also encouraging in most cases the method can predict automatically the correct direction of extension and a 3 d fault geometry close to the fault geometry used hence arbitrarily inclined bulk simple shear appears to be a good approximation of hanging wall deformation in three dimensions this general method will allow 3 d palinspastic analysis to be undertaken on 3 d seismic reflection data sets

the oceanic salt pump does it contribute to the glacial interglacial difference in atmospheric co2 content sea ice formation drives salt from the surface to the deep sea in so doing it lowers the salinity of polar surface waters we show here that this reduction in turn lowers the co2 partial pressure of polar surface waters and hence also of the atmosphere we propose that during glacial time when more sea ice existed this pumping action may have been stronger if so part of the glacial to interglacial atmospheric co2 content change observed in ice cores may have been driven by the ocean s salt pump

on the late pleistocene ocean geochemistry and circulation a box model of the atmosphere and ocean was developed to investigate how geochemical distributions extant during the late pleistocene may have come about the model simulates the regional distribution of calcium carbonate dissolution as well as the chemical oceanography and atmospheric co2 13c and radiocarbon if the downward biological flux of particulate carbon increases by a factor of 2 to 3 in the antarctic and if this increase is combined with a relative increase of the atlantic sector antarctic bottom water aabw versus north atlantic deep water nadw source ratio from 1 3 to about 2 1 then the model predicts several changes that seem to be recorded in the sedimentary record as follows 1 a global redistribution of nutrients and 12c from the intermediate to deep water takes place with the atlantic intermediate water phosphate decreasing 0 6 mole kg 1 and the 13c increasing 0 3 to 0 5 2 the dissolved oxygen level of the deep sea is reduced from an average of about 180 to 70 mole kg 1 but the intermediate water oxygen declines only a small amount 3 the decrease in intermediate water nutrient concentration results in lower average organic carbon and calcium carbonate production in the warm surface ocean 4 the atmospheric co2 decreases by 90 to 110 ppm 5 initially a global increase in calcium carbonate dissolution occurs which is followed by a relaxation toward better preservation than exists for the present ocean in the model in this paper the reduction of nadw by itself does not produce these effects rather the nutrient decrease that does occur is found mostly in north pacific intermediate water and the model atmospheric co2 decrease is only 10 to 30 ppm it is observed that 92 of the atmospheric co2 change takes place according to a 200 year time constant in the model this corresponds to the response time of the upper ocean and atmosphere to a change in the stationary state atmospheric pco2 thus according to this model the time lag between the nutrient based cause and the atmospheric co2 response is not expected to be particularly large

glacial interglacial co2 change the iron hypothesis several explanations for the 200 to 280 ppm glacial interglacial change in atmospheric co2 concentrations deal with variations in southern ocean phytoplankton productivity and the related use or nonuse of major plant nutrients an hypothesis is presented herein in which arguments are made that new productivity in today s southern ocean 7 4 1013g yr 1 is limited by iron deficiency and hence the phytoplankton are unable to take advantage of the excess surface nitrate phosphate that if used could result in total southern ocean new production of 2 3 1015 g c yr 1 as a consequence of fe limited new productivity holocene interglacial co2 levels preindustrial are as high as they were during the last interglacial 280 ppm in contrast atmospheric dust fe supplies were 50 times higher during the last glacial maximum lgm because of this fe enrichment phytoplankton growth may have been greatly enhanced larger amounts of upwelled nutrients may have been used and the resulting stimulation of new productivity may have contributed to the lgm drawdown of atmospheric co2 to levels of less than 200 ppm background information and arguments in support of this hypothesis are presented

germanium silicon fractionation during biogenic opal formation model results and empirical data show that germanium is fractionated from silica during biogenic opal formation in a two box model of the ocean particulate ge si can vary between the average ocean ge si and the average ocean ratio times the ge fractionation coefficient the two box model requires a ge fractionation coefficient near 0 48 to reproduce si and ge concentrations similar to the ocean analysis of paired water and opal samples yields a ge fractionation coefficient of 0 51 as a consequence of this fractionation the ge si of opal can be an upwelling indicator small shifts of opal ge si in adjacent centimeter scale lighter and darker layers in the miocene monterey formation are consistent with other sedimentologic indicators of productivity and upwelling variations opal ge si are lower in lighter layers and are consistent with interpretations that the lighter layers were formed by increased productivity in overlying waters

climatically forced organic carbon burial in equatorial atlantic and pacific oceans over the past ten years sedimentary geochemists have noted that climate changes associated with pleistocene glaciations have had a pronounced effect on the rate of organic carbon burial found in the tropical oceans1 4 in particular two to five times higher organic carbon accumulation rates have been observed for the 18 kyr bp glacial maximum than for the holocene in several short sediment cores from both oceans see fig 1 here i present 300 kyr time series for organic carbon mass accumulation rate from four sediment cores two each from the equatorial pacific and atlantic and show that orbital forcing of global climate has strongly affected the rate of organic carbon burial in the equatorial oceans

carbon isotope composition of tropical surface water during the past 22 000 years carbon isotope values of many species of planktonic foraminifera are size dependant values of 13c of individual size fractions are therefore an integration of low 13c values of calcite precipitated in the juvenile growth stage and high values precipitated in later stages in general the selection of a particular size fraction for downcore studies has been subjective analysis of different size fractions of planktonic foraminifera however yields different time series in downcore studies by measuring the 13c of many size fractions the 13c precipitated throughout the growth of the foraminifera can be calculated time series of the 13c of calcite precipitated in the late growth stages of planktonic foraminifera from two nearby cores from the caribbean sea result in a better correlation than time series of constant size fractions these 13c records indicate similar 13c values during the last glaciation and the late holocene and a broad deglacial minimum approximately synchronous with a minimum in the 13c records of benthic foraminifera from intermediate depth atlantic cores the deglacial minimum may be a reflection of the isotopic composition of the underlying intermediate water which may be affected by circulation changes or changes in preformed 13c values and or of the flux of water upwelled into the surface layer the small 0 2 to 0 0 glacial interglacial 13c difference in tropical surface water is also believed to be affected by the chemistry of the underlying source water

detachment folding related miocene submarine slope instability in the romagna apennines italy 1 the relationships between slope failure and growing thrust related structures have been explored in the miocene marnoso arenacea foredeep basin romagna apennines impressive fossil slump layers are distributed along the footwall of the regional mount nero thrust which evolved from detachment fold to breakthrough thrust during the detachment fold stage development of growth strata on the rotating forelimb was preceded by the emplacement of slump layers that are currently part of the mount nero thrust footwall in this process sliding is assumed to nucleate along the contacts between different lithologies in the semiconsolidated rock mass the conditions of sliding specifically the critical angle of sliding crit are quantified by adding the influence of cohesion of sediments to the equilibrium analysis reported in hubbert and rubey s 1959 classical work the resulting angles crit are discussed with respect to the depth of the basal surface of sliding and pore fluid pressure states on the basis of such an analysis and field work results an evolutionary model is proposed in which slide sheets come from the crest and upper forelimb of growing detachment folds and attain a deeper detachment depth as the forelimb rotates and steepens pore fluid pressure is found to play a major role by radically decreasing the critical angle of sliding likewise localization of overpressures may also control the depth of sliding during progressive forelimb rotation to allow sliding along gently dipping bedding surfaces slope failure is interpreted as being related to the reactivation of anisotropies represented by lithological discontinuities

stable isotopic fractionation among particles in quaternary coccolith sized deep sea sediments oxygen and carbon isotopic ratios of individual grain size splits of the 38 m fraction of deep sea carbonate particles vary systematically with size over a range of 1 25 4 0 most splits are dominated by just a few coccolith taxa and other types of particles the 18o and 13c values of individual splits are linearly related to each other with a slope of 1 5 13c 18o in all holocene and glacial samples analyzed although the observed variability is less than predicted from culture experiments of individual components compositional variations can significantly influence the stable isotopic stratigraphies measured on the nannofossil fraction

reconstructing past particle fluxes in the tropical atlantic ocean using a research strategy analogous to modern sediment trap studies sediment accumulation patterns on submarine rises can be interpreted in terms of past ocean chemistry and circulation we have followed this research strategy to reconstruct the history of surface water productivity and deep water chemistry and circulation in the eastern equatorial atlantic sierra leone rise and western equatorial atlantic ceara rise during the last glacial maximum 18 000 b p on shallow sections of these rises at depths with little carbonate particle degradation we assume that the accumulation of skeletal carbonate approximates the carbonate production rate in surface water during the last glacial maximum the rate of carbonate productivity was lower in the eastern atlantic than it is today while the western atlantic exhibited no glacial interglacial difference in carbonate productivity based on the difference in carbonate accumulation rates between shallow and deep cores on the rises we observed greater dissolution in both basins during the last glaciation the eastern atlantic always had a lower rate of dissolution than the western atlantic despite having deep water with a lower 13c during the last glacial maximum organic carbon accumulation in the eastern atlantic increased with depth in the water column during the last glaciation suggesting that there was a bathymetric decrease in dissolved oxygen concentration at that time these observations are consistent with a glacial decrease in the production rate of northern source deep water during the last glaciation at that time the mixing zone between northern source and southern source deep water migrated to the north in the atlantic resulting in a greater proportion of corrosive southern source deep water in the western atlantic and entering the eastern atlantic through low latitude fracture zones today the ratio of northern and southern components entering the eastern atlantic is about 4 1 based on 13c and carbonate accumulation our best estimate of this ratio during the last glaciation is 1 1

the δ13c of equatorial atlantic surface waters implications for ice age pco2 levels carbon isotopic records of nutrient depleted surface water place constraints on the past fertility of the oceans and on past atmospheric pco2 levels the best records of nutrient depleted 13c are obtained from planktonic foraminifera living in the thick mixed layers of the western equatorial and tropical atlantic ocean we have produced a composite stacked globigerinoides sacculifer 13c record from the equatorial atlantic which exhibits significant spectral power at the 100 000 and 41 000 year milankovitch periods but no power at the 23 000 year period similar to the record presented by shackleton and pisias 1985 surface deep ocean 13c produced with the g sacculifer record leads the 18o ice volume record however the glacial interglacial amplitudes of 13c differ between our record and shackleton and pisias 1985 record although large changes in 13c occur in the equatorial atlantic during early stages of the last three glacial cycles surface deep 13c at glacial maxima 18o stage 2 late stage 6 and late stage 8 was only about 0 2 greater than during the subsequent interglacial our results imply that nutrient driven pco2 changes account for about one third of the pco2 decrease observed in ice cores and consequently 13c should not be used as a proxy pco2 index enough variance in the ice core pco2 records remains to be explained that conclusions about pco2 and ice volume phase relationships should also be reexamined as much as 40 ppm pco2 change still has not been accounted for by models of past physics and chemistry of the ocean

tectonics of nisyros island greece by field and offshore data and analogue modelling abstract we use new on land and offshore structural data and scaled analogue models to analyse the fault tectonic pattern at nisyros island greece which has an active caldera that shows a complicated network of faults fractures and volcano tectonic structures we measured 157 faults that show dominant dip slip normal motions along planes mainly striking ne sw nne ssw and nnw sse inside the caldera dykes necks and morphometric parameters of volcanic domes explosion craters and fumarole pits indicate the control by ne striking discontinuities on magma and gas paths the nnw and ne striking faults bound a major block that underwent repeated downthrow and uplift movements during the late pleistocene holocene experiments with scaled models of caldera resurgence and two magma chambers indicate the formation of an hourglass shaped fault pattern as seen in plan view with an asymmetric increase in the fault offset and a widening of the fault divergence towards the volcano flank all these data suggest that regional fault tectonics and stress state strongly guided magma upwelling and the emplacement of volcanic centres whereas periodical bulging due to the overpressure of a second magma chamber located northwest of the caldera combined with faulting due to tectonic stresses can account for the overall deformation field

experiments on basin inversion above reactivated domino faults abstract results are presented from scaled sand box experiments which investigate the structural inversion of half graben basins generated by the contractional reactivation of extensional domino fault systems the overburden was deformed above a series of rigid basement fault blocks that were extended in a domino manner the models were constructed from either 1 sand with mica interlayers anisotropic behaviour 2 pure sand isotropic behaviour or 3 a sand clay mixture behaviour with increased competence during the extensional phase of deformation sand or alternating sand mica layers were deposited in teh half grabens associated with individual domino faults to simulate a syn extensional stratigraphic sequence together with a component of overall subsidence after termination of the extensional phase sand layers were added to represent a post rift passive subsidence stratigraphy subsequent contraction of the experimental configuration resulted in progressive reactivation of the domino fault system which was accompanied by back rotation of both the footwall and hanging wall in each of the individual fault blocks this produced null points along the profile section of the fault planes which separated net contraction above from net extension below continued shortening of the system led to further contraction being accommodated along footwall shortcut faults it is suggested that these shortcuts developed in response to 1 the accommodation of space problems generated by increased bed length in the graben acquired during extension and 2 by more efficient low angle fault trajectories in keeping with coulomb failure during horizontal to subhorizontal compression during inversion in the anisotropic model folding in the footwall partially suppressed the initiation of footwall shortcut faults footwall shortcut faulting did not occur in experiments where the dips of the original extensional faults were decreased before the inversion in all inversion experiments the contractional deformation associated with the shortening of the half graben was concentrated in the footwall to each domino basin bounding fault a control experiment in which an undeformed sand pack was deposited above an extended series of basement fault blocks revealed that the early extensional architecture formed in the other experiments had a profound influence on the resultant inversion geometries the results show clear similarities to interpreted examples of natural basin inversion structures associated with reactivated domino fault systems as well as to inferred strike slip induced flower structures

the salinity contrast between the atlantic and pacific oceans during glacial time in today s ocean the salinity of low latitude surface waters in the pacific is on the average 1 per mil lower than in the atlantic oxygen isotope records for planktonic foraminifera suggest that an even larger salinity deficit may have existed for pacific surface water during glacial time if so the transport of water vapor from the atlantic to the pacific must have been as strong as or even stronger to balance the tendency toward salt buildup the atlantic would have had to export during glacial time waters saltier than it received from the other oceans

using preexisting cleavage to define extensional fault geometries an example from glacier national park montana the geometry of the rocky mountain trench extensional fault system in northwest montana can be defined by using as reference features pervasive asymmetric cleavages associated with the preexisting lewis thrust these laramide fabrics act as preextensional markers of regional dip and elevation and thus deformation of these passive markers can be used to determine the specific hanging wall geometry of each extensional fault two types of extensional fault are distinguished 1 planar faults with tilt block geometries that cut through the lewis thrust and 2 curved faults with rollover geometries that reactivate the existing lewis thrust the deformed laramide markers indicated that the rocky mountain trench system is dominated by a series of tilt blocks upon with the preexisting thrust had only a localized effect

sandbox model studies of inversion tectonics abstract scaled plane strain sandbox models have been used to simulate basement controlled structural inversion in a sedimentary overburden two basement configurations were tested in the first one reversal of movement along vertical and normal faults that controlled a graben relief induced only a partial recovery of displacement along the pre existing overburden faults the inversion produced new reverse faults in the footwall of the pre existing overburden faults the reactivated normal faults and the new reverse faults defined wedge shaped fault blocks at the edges of the inverted structure in the second configuration the relationship between inversion and tilted fault blocks was tested when a tilting basement block does not move parallel to its bounding fault a compression is induced in the overburden which generates an inverted structure bounded by new reverse faults both experiments show that structural inversion not only reactivates pre existing faults but also generates new faults in the overburden faults related to inversion are the result of horizontal compression either associated with rotation of one of the fault blocks or with vertical uplift of basement blocks

sandbox experiments on basin inversion testing the influence of basin orientation and basin fill analogue modelling experiments using brittle materials are performed to study the inversion of extensional structures asymmetric grabens of two different orientations are first created during a phase of extension and progressively filled they are subsequently shortened in the same direction the aim of our experiments is to determine factors affecting the style of deformation during inversion we specifically investigate variations in thickness and distribution of strong and weak layers constituting the graben fill and in initial basin orientation the main advantage of our experimental set up is that we have a complete control on graben location width infill and orientation before inversion the experiments show that shortening results only in limited reactivation of pre existing normal faults in general forward thrusts and backthrusts cut across normal faults into the footwall of the graben the forward thrusts either propagate parallel to the enveloping surface of faulted blocks or they cut across basin limiting normal faults at various angles the graben fill is mechanically extruded by displacement along forward thrusts that accommodate most of the shortening both pre existing faults and weak graben fill act as zones of weakness during inversion and determine the orientation and location of both backthrusts and forward thrusts the results of our experiments conform well to natural examples of inverted graben structures

opening the carbon isotope vital effect black box 1 seasonal temperatures in the euphotic zone recent laboratory experiments with orbulina universa show that the carbon and oxygen isotope signals from this symbiont bearing planktonic foraminifera record distinct environmental parameters irradiance and temperature since light levels are correlated with depth in the marine environment the carbon isotopic composition of o universa can be utilized to differentiate individuals from different depth habitats by combining 18o and 13c data from individuals in an assemblage estimates of seasonal temperature ranges are possible for the upper and lower euphotic zone of the ocean reconstruction of seasonal temperatures using individual holocene o universa from western equatorial pacific ocean boxcore erdc 83 yields ranges of 23 5 to 29 9 c and 20 1 to 24 5 c for the shallow and deep euphotic zone respectively these values are in excellent agreement with recent temperature measurements from this region analyses of individual late glacial 12 000 13 000 years b p o universa from this site suggest the seasonal upper euphotic zone temperature range was approximately 2 5 c lower than it is today a function of cooler summers

mechanical behaviour of granular materials used in analogue modelling insights from grain characterisation ring shear tests and analogue experiments abstract the mechanical behaviour of several dry granular materials is investigated through ring shear tests grain characterisation and simple analogue experiments analysed by x ray computed tomography an improved knowledge of granular materials is essential to determine their suitability as analogues for upper crustal rocks in experimental models and to compare analogue and numerical experiments the ring shear tests show that the granular materials have an elastic frictional plastic behaviour with strain hardening preceding failure at peak strength followed by strain softening until a dynamic stable value is reached this is similar to the behaviour exhibited by experimentally deformed rocks the physical characteristics of the grains determine the amount of diffuse deformation before failure the percentage of strain softening and act on the thickness of the shear zones before broadening initial shear zone width in extensional and contractional experiments is between 11 and 16 times the mean grain size the angle of internal friction defining one of the mechanical properties of granular materials and thus fault dip is not only related to physical characteristics of the grains and to the handling technique used e g sieving or pouring but also to the overburden and to the experimental setup used

precise timing of the last interglacial period from mass spectrometric determination of thorium 230 in corals the development of mass spectrometric techniques for determination of 230 th abundance has made it possible to reduce analytical errors in 238 u 234 u 230 th dating of corals even with very small samples samples of 6 x 10 8 atoms of 230 th can be measured to an accuracy of 3 percent 2 and 3 x 10 10 atoms of 230 th can be measured to an accuracy of 0 2 percent the time range over which useful age data on corals can be obtained now ranges from about 50 to about 500 000 years for young corals this approach may be preferable to 14 c dating the precision with which the age of a coral can now be determined should make it possible to critically test the milankovitch hypothesis concerning pleistocene climate fluctuations analyses of a number of corals that grew during the last interglacial period yield ages of 122 000 to 130 000 years the ages coincide with or slightly postdate the summer solar insolation high at 65 n latitude which occurred 128 000 years ago this supports the idea that changes in pleistocene climate can be the result of variations in the distribution of solar insolation caused by changes in the geometry of the earth s orbit and rotation axis

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

formation of caldera periphery faults an experimental study changing stresses in multi stage caldera volcanoes were simulated in scaled analogue experiments aiming to reconstruct the mechanism s associated with caldera formation and the corresponding zones of structural weakness we evaluate characteristic structures resulting from doming chamber inflation evacuation collapse chamber deflation and cyclic resurgence inflation and deflation and we analyse the consequential fault patterns and their statistical relationship to morphology and geometry doming results in radial fractures and subordinate concentric reverse faults which propagate divergently from the chamber upwards with increasing dilation the structural dome so produced is characterised bysteepening in the periphery whereas the broadening apex subsides pure evacuation causes the chamber roof to collapse along adjacent bell shaped reverse faults the distribution of concentric faults is influenced by the initial edifice morphology steep and irregular initial flanks result in a tilted or chaotic caldera floor the third set of experiments focused on the structural interaction of cyclic inflation and subsequent moderate deflation following doming caldera subsidence produces concentric faults that characteristically crosscut radial cracks of the dome the flanks of the edifice relax resulting in discontinuous circumferential faults that outline a structural network of radial and concentric faults the latter form locally uplifted and tiltedwedges half grabens that grade into horst and graben structures this superimposed fault pattern also extends inside the caldera we suggest that major pressure deviations in magma chamber s are reflected in the fault arrangement dissecting the volcanoflanks and may be used as a first order indication of the processes and mechanisms involved in caldera formation

measurements of friction coefficients and cohesion for faulting and fault reactivation in laboratory models using sand and sand mixtures abstract simple laboratory tests have been made on dry quartz sand and on mixtures of sand and clay and sand and cement tests were made on both low and high density specimens of each mixture as determined by physical handling techniques the tests included measurements of density estimates of the coefficient of internal friction based on fault orientation and estimates of the friction coefficients and cohesion values for fault initiation and reactivation in a shear frame apparatus which was also used to test artificial fault zones made from pure clay glass microspheres and wheat flour the results suggest that density is determined more by handling technique than by composition and that friction coefficients and perhaps cohesion both increase with increasing density the shear testing revealed a consistent drop in cohesion for fault reactivation in all densely packed mixtures tested although small this drop may be significant for some types of laboratory models

the tectonic evolution of the southern dutch north sea during the palaeogene basin inversion in distinct pulses abstract in this paper we discuss the response of a sedimentary basin to compressional reactivation of extensional faults in distinct pulses the inversion of the broad fourteens basin in the southern dutch north sea is used as a case study the first pulse of inversion occurred during the late mesozoic as a result of the sub hercynean phase a second pulse occurred during the mid palaeocene laramide phase a final inversion pulse occurred around the eocene oligocene boundary coinciding with the pyrenean tectonic event we reconstructed the stratigraphic and structural development of the area during the palaeogene in detail basic data are two 2d seismic surveys supported by 74 geophysical wireline logs on which newly constructed depth and thickness maps are based the reconstruction is aided by a quantitative subsidence analysis cessation of compression resulted in relaxation and tensional reactivation of faults caused differential subsidence inheritance of geological structures is a key element in the tectonic activity in the broad fourteens basin during the palaeogene tectonic movement during the palaeogene was always accommodated by reactivation of palaeozoic mesozoic faults the intensity of inversion in the southern north sea basin during the pyrenean phase appears much larger than previously noticed moreover the area affected by the inversion is much wider than during previous phases minor differences in the direction of the local stress field between the tectonic phases and by the deposition of a thick sedimentary succession during the periods of tectonic quiescence between the inversion phases can account for this

the influence of pre existing thrust faults on normal fault geometry in nature and in experiments relations between normal faults and pre existing thrust faults are classically described in terms of three basic situations normal faults can cross cut thrust faults they can branch out from thrust faults at depth on a de collement level or they can entirely reactivate thrust planes the mechanical aspects of these types of interaction were studied by analogue modelling in which sand simulates the brittle rocks and silicone putty an interlayered de collement the models underwent compression producing thrust faults with variable dips followed by extension three possible ways of interaction are described here a no interaction occurs in the case of low dip thrust faults 32 1 and normal faults are developed independently displaying a listric geometry b branching at depth on the de collement level occurs when dip of the thrust faults reaches 32 1 in this case the dip of the normal faults whose geometry becomes planar decreases with increasing thrust dip we suggest that this change in dip of normal faults depends upon the rotation of stress tensor axes along the pre existing fault zone where a drop in the friction coefficient is likely to occur c reactivation occurs in brittle material when dip of the pre existing fault exceeds 41 1

pleistocene sea level fluctuations and human evolution on the southern coastal plain of south africa abstract humans evolved in africa but where and how remain unclear here it is proposed that the southern coastal plain scp of south africa may have served as a geographical point of origin through periodic expansion and contraction isolation in response to glacial interglacial changes in sea level and climate during pleistocene interglacial highstands when sea level was above 75 m human populations were isolated for periods of 360 3400 25 yr generations on the scp by the rugged mountains of the cape fold belt climate and vegetation barriers the scp expands five fold as sea level falls from 75 to 120 m during glacial maxima to form a continuous unobstructed coastal plain accessible to the interior an expanded and wet glacial scp may have served as a refuge to humans and large migratory herds and resulted in the mixing of previously isolated groups the expansive glacial scp habitat abruptly contracts by as much as one third in 300 yr during the rapid rise in sea level associated with glacial terminations rapid flooding may have increased population density and competition on the scp to select for humans who expanded their diet to include marine resources or hunted large animals successful adaptations developed on an isolated scp are predicted to widely disperse during glacial terminations when the scp rapidly contracts or during the initial opening of the scp in the transition to glacial maxima the hypothesis that periodic expansion and contraction of the scp as well as the coastal plain of north africa contributed to the stepwise origin of our species over the last 800 thousand years kyr is evaluated by comparing the archeological dna and sea level records these records generally support the hypothesis but more complete and well dated records are required to resolve the extent to which sea level fluctuations influenced the complex history of human evolution

co 2 record in the byrd ice core 50 000 5 000 years bp the analysis of air in polar ice cores revealed 30 lower co2 values during glacial periods than during interglacial periods at present this is confirmed by results from six different ice cores two from greenland and four from antarctica1 5 in all cores the co2 change coincides with the change in the isotopic composition of the ice expressed as either the 18o or d ratio both are indicators for the mean annual surface temperature6 to investigate the relationship between atmospheric co2 concentration changes with changes in climate the atmospheric co2 concentration during and at the end of the last glaciation has to be known in detail to achieve this we have studied a great number of samples from the deep ice core from byrd station westantarctica drilled in 1968 these measurements allow us to reconstruct the atmospheric co02 concentration in the time period 50 000 15 000 yr bp in great detail

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

a 210 000 year record of barium variability in the deep northwest atlantic ocean the deep ocean is the storehouse for most of the carbon and nutrients in the ocean atmosphere system together with its out crops at high latitudes the deep ocean is of great importance in driving glacial interglacial changes in the carbon dioxide content of the atmosphere1 3 the chemical and physical structure of the deep glacial oceans can be reconstructed by means of palaeochemical tracers for example the cadmium and carbon isotope contents of benthic foraminifera have been used to reconstruct the phosphate or labile nutrient compositions of deep waters4 14 recently it was proposed15 that barium in benthic foraminifera could be used to reconstruct the distribution of refractory deep regenerated chemical properties in the water masses of the glacial oceans a reconstruction of barium concentra tions in the oceans at the time of the last glacial maximum revealed the greatest changes in the north atlantic where barium concentrations in deep water were up to 50 higher than at present16 here we present a record of the benthic ba ca ratio in the deep northwest atlantic stretching back to interglacial stage 7 210 kyr ago encompassing two full glacial cycles a comparison of the barium record with that of the other nutrient like tracers lends confidence in the general agreement between these tracers while showing some spectral variability unique to barium thus underscoring its utility as an additional palaeoceanographic tracer

normal faulting block tilting and decollement in a stretched crust extensional tectonics cover a wide range of crustal structures from narrow continental rifts to large continental areas if we except continental and oceanic rifts stretched portions of the crust exhibit complex faulting patterns at upper levels with high angle and low angle normal faults very little is known concerning the geometry of structures and physical processes at depth it is therefore difficult to extrapolate surface observations to the crustal scale five general models are proposed that combine continuous and discontinuous deformation and geometrical and geological tests are proposed two natural examples the west armorican atlantic margin and eldorado mountains basin and range province are presented they are characterized by an association of high angle normal faults tilted blocks and low angle normal faults field and geometrical arguments are given to demonstrate that low angle faults are controlled by decollement surfaces along preexisting interfaces geometrical implications of the tilted block pattern are presented and the gravity gliding hypothesis is proposed as a possible explanation of block tilting when associated with low angle normal faults in such cases the amount of stretching cannot be related to bulk thinning of the crust

deep structure of the foreland to the caledonian orogen nw scotland results of the birps winch profile the winch marine deep seismic reflection profile crosses the hebridean shelf the proterozoic foreland to the caledonian orogen west of scotland the data quality is very good the upper crust is largely devoid of coherent seismic reflections although this may in part be due to acquisition techniques being inappropriate for this problem in contrast the middle and lower crust 10 25 km depth exhibits good reflections the mid crust contains reflectors which may be relics of early palaeozoic caledonian or earlier grenvillian eastward dipping thrust zones which pass into an acoustically strongly layered lower crust the outer isles thrust is mapped from the surface to the mid crust and tied into its land outcrop on north lewis reactivation of this thrust offshore in a normal sense in mesozoic times caused the formation of the minch and north lewis basins the mono is defined by a strong band of reflections at about 27 km depth which correlates well with results from the hmse explosion seismic survey moho depth is apparently rather uniform in the area of the foreland crossed by winch winch and hmse results together suggest a mean crustal velocity for the hebridean shelf of 6 4 0 1 km s 1 the eastward dipping flannan thrust can be mapped into the upper mantle on three lines from about 15 to 45 km depth well into the upper mantle neither the flannan thrust nor the outer isles thrust appear to pass straight through the reflective lower crust suggesting that the lower crust is a region of high strain the outer hebrides is a positive block probably formed as an isostatic response to mesozoic normal faulting which reactivated the outer isles thrust

can the greenland climatic jumps be identified in records from ocean and land sharp jumps in climate punctuate the records from borings in the greenland ice cap during the time interval 60 000 to about 20 000 yr ago rapid fluctuations are also seen in foraminifera records for cores from the northern atlantic and in a pollen record from a core from a bog in the vosges mountains in france in this paper we present a new radiocarbon chronology for northern atlantic deep sea core v23 81 which permits comparison with the radiocarbon dated vosges mountains pollen record because of the lack of a 14c chronology for the greenland ice record and of distortions peculiar to each of the three records it is not yet possible to say whether or not the events are genetically related

moist and the continuity of crustal reflector geometry along the caledonian appalachian orogen new aspects of the deep structure of the scottish caledonides are revealed by the moine and outer isles deep seismic reflection traverse moist the caledonian foreland is underlain by an easterly dipping strongly reflecting surface cutting through the moho and traceable to more than 45 km depth thrusts within the foreland basement and caledonian orogen have been reactivated as normal faults bounding half grabens filled with sediments of late palaeozoic to mesozoic age the moine thrust which carries rocks of the orogen over lewisian foreland dips at 20 25 to the e on moist and is either a the westernmost of a series of easterly dipping reflections thrusts which flatten or terminate at 17 20 km depth or b a thrust lying further e which structurally overlies these easterly dipping reflectors by comparison with easterly dipping reflections on cocorp lines in the northern and southern appalachians the latter interpretation is preferred implying that many of the easterly dipping reflections on moist correspond to off shelf metasedimentary rocks with slivers of basement stacked and imbricated against the lewisian basement edge regional seismic refraction and conductivity data from northern scotland suggest that regions of the caledonian orogen have lower mid crustal velocity gradients and higher conductivities than the foreland which might be explained by this interpretation of the easterly dipping reflections despite similarities in crustal reflector geometries there are important differences between the moist and cocorp lines including 1 a remarkably continuous relatively horizontal moho seen on moist data at about 25 km depth and 2 the sedimentary basins offshore from northern scotland which have formed by reactivation under crustal extension of the easterly dipping thrusts furthermore it is probable that the easterly dipping reflectors in these areas of the moist and cocorp lines were formed at different times in the early palaeozoic

a note on fault reactivation reactivation of existing faults whose normal lies in the 1 3 plane of a stress field with effective principal compressive stresses 1 2 3 is considered for the simplest frictional failure criterion n n p where and n are respectively the shear and normal stresses to the existing fault p is the fluid pressure and is the static friction for a plane oriented at to 1 the stress ratio for reactivation is 1 3 1 cot 1 tan this ratio has a minimum positive value at the optimum angle for reactivation given by 12tan 1 1 but reaches infinity when 2 beyond which 3 0 is a necessary condition for reactivation an important consequence is that for typical rock friction coefficients it is unlikely that normal faults will be reactivated as high angle reverse faults or thrusts as low angle normal faults unless the effective least principal stress is tensile

cyclic caldera collapse piston or piecemeal subsidence field and experimental evidence many multicycle caldera volcanoes display a complex extracaldera fault system genetically linked to caldera evolution on gran canaria canary islands the miocene tejeda caldera was filled by ignimbrites and epiclastic sediments and intruded by syenites and a major cone sheet swarm obscuring intracaldera structural relations extracaldera radial and circumferential faults and dikes are well exposed we used field data and experiments scaled to the island of gran canaria to clarify the poorly understood structural temporal and genetic relationship of peripheral faults to the central caldera the experimental setup comprises a cone of medium grained sand in which a rubber balloon was repeatedly inflated and deflated balloon inflation resulted in updoming and a dominantly radial fault pattern whereas balloon deflation caused piecemeal caldera collapse and a concentric peripheral fault arrangement on the edifice flanks a complex interplay of repeated inflation and deflation cycles of the experimental magma chamber is found to explain the peripheral fault system of the tejeda caldera on gran canaria and offers insight into the structure of the caldera floor and the mechanisms acting in multicycle caldera volcanoes