faulting of rocks in three dimensional strain fields i failure of rocks in polyaxial servo control experiments abstract the dependence of the number of sets of faults and their orientation on the intermediate strain axis is investigated through polyaxial tests reported here and theoretical analysis reported in an accompanying paper in the experiments cubic samples of berea sandstone sierra white and westerly granites and candoro and solnhofen limestones were loaded on their three pairs of faces by three independent mutually perpendicular presses at room temperature two of the presses were servo controlled and applied constant displacement rates throughout the experiment most samples display three or four sets of faults in orthorhombic symmetry these faults form in several yielding events that follow a stage of elastic deformation in many experiments the maximum and the intermediate compressive stresses interchange orientations during the yielding events where the corresponding strains are constant the final stage of most experiments is characterized by slip along the faults

rapid stepwise onset of antarctic glaciation and deeper calcite compensation in the pacific ocean the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution is termed the calcite compensation depth at present this depth is 4 500 m with some variation between and within ocean basins the calcite compensation depth is linked to ocean acidity which is in turn linked to atmospheric carbon dioxide concentrations and hence global climate1 geological records of changes in the calcite compensation depth show a prominent deepening of more than 1 km near the eocene oligocene boundary 34 million years ago 2 when significant permanent ice sheets first appeared on antarctica3 4 5 6 but the relationship between these two events is poorly understood here we present ocean sediment records of calcium carbonate content as well as carbon and oxygen isotopic compositions from the tropical pacific ocean that cover the eocene oligocene boundary we find that the deepening of the calcite compensation depth was more rapid than previously documented and occurred in two jumps of about 40 000 years each synchronous with the stepwise onset of antarctic ice sheet growth the glaciation was initiated after climatic preconditioning7 by an interval when the earth s orbit of the sun favoured cool summers the changes in oxygen isotope composition across the eocene oligocene boundary are too large to be explained by antarctic ice sheet growth alone and must therefore also indicate contemporaneous global cooling and or northern hemisphere glaciation

the paleoclimatic record provided by eolian deposition in the deep sea the geologic history of wind the mineral component of pelagic sediment is brought to the deep sea by transport in the wind extraction and analysis of this dust allows estimation of the past aridity of the eolian source region via flux determinations and of the intensity of the transporting winds from grain size data these two parameters the grain size and mass flux of dust vary independently there are three significant sources of modern dust eastern and central asia northwest africa and arabia all in the northern hemisphere as the rainfall associated with the intertropical convergence zone is an effective barrier to southerly transport of dust the northern hemisphere is an order of magnitude more dusty than is the southern an asymmetry that has characterized most of the cenozoic eolian flux data show that most of the northern hemisphere was more arid during glacial maxima with 3 to 5 times as much dust transported during glacial stages than during interglacials only northwestern south america varied in the opposite sense the periodicity of quaternary variation in both eolian flux and eolian grain size data is strongly influenced by the milankovitch cycles of orbital variability wind intensities vary on a shorter time scale than the general 100 kyr cycles of glaciation and general aridity eolian grain sizes display forcing at precessional 19 and 23 kyr tilt 41 kyr and at approximately 30 kyr periodicities as a result the generalization that winds are uniformly stronger during glacial times is not valid whole cenozoic records show that the largest change in dust flux an order of magnitude increase occurred in the northern hemisphere and reflects continental drying associated with the late pliocene onset of northern hemisphere glaciation southern hemisphere eolian records show no sign of paleoclimatic changes in the late pliocene the most important change in cenozoic atmospheric circulation was a severalfold reduction in wind intensity that occurred at the time of the paleocene eocene boundary before then latest cretaceous and paleocene winds were essentially as strong as those of the late cenozoic this shift appears to be one of several climatic responses to a change in the nature and amount of global heat transport at about 55 ma

correcting the cenozoic δ18o deep sea temperature record for antarctic ice volume abstract the oxygen isotope signal in benthic foraminifera from deep sea cores is mainly determined by deep ocean temperature and land ice volume separating the temperature and ice volume signals is a key step in understanding the evolution of cenozoic climate except for the last few million years fluctuations in land ice volume were determined mainly by the size of the antarctic ice sheet here a simplified antarctic ice sheet model and composite deep sea oxygen isotope records are used to derive a deep sea temperature history for the cenozoic the ice sheet model is forced with the oxygen isotope record which is instantaneously corrected for the calculated ice volume therefore the resulting deep sea temperature and antarctic ice volume curves are mutually consistent the temperature record of lear et al science 287 2000 269 derived from the mg ca ratio in benthic calcite is also used to force the ice sheet model the resulting ice volume does not agree well with the ice volume history inferred by lear et al from a comparison of mg ca and 18 o records the most important points emerging from this study are the cenozoic 18 o record from benthic forams is a truly mixed signal ice volume and deep sea temperature contribute equally to the variance for the period of 45 to 30 ma ago 18 o temperatures are significantly lower than mg ca temperatures rapid nonlinear build up of a continental scale ice sheet on the antarctic continent can easily occur for a linear cooling rate it is unlikely that the method of lear et al provides a reliable measure of ice volume the cooling rate at the beginning of the pliocene is much larger in the 18 o temperature curves than in the mg ca temperature curve

structural controls on the base metal vein deposits of the northampton complex western australia abstract the northampton complex is a proterozoic inlier near the west coast of western australia 450 km north of perth the copper lead and zinc vein type deposits occupy dilational sites along brittle ductile shear zones there are four types of structural settings of the ore deposits 1 lens structures 2 shear breccia link shear structures extensional strike slip duplexes 3 intersecting brittle ductile shears and 4 curved brittle ductile shears a model involving n s dextral wrenching along the darling mobile belt best explains the various features of the deposits in this model proterozoic granulite facies paragneisses of the northampton complex were fractured with the development of predominantly extensional fractures and normal faults and to a lesser extent riedel both r and r restraint and principal displacement shears since previous isotopic dating has not resolved the age of mineralisation crosscutting relationships between mineralisation the older dolerite dykes 650 800 ma and younger 330 trending sinistral shears 500 650 ma are used to constrain the timing to between 650 ma and 800 ma ne sw shortening across the paterson and king leopold mobile belts between 650 ma and 800 ma may also have been associated with the dextral movements along the darling mobile belt

catastrophic ice shelf breakup as the source of heinrich event icebergs 1 heinrich layers of the glacial north atlantic record abrupt widespread iceberg rafting of detrital carbonate and other lithic material at the extreme cold culminations of bond climate cycles both internal glaciologic and external climate forcings have been proposed here we suggest an explanation for the iceberg release that encompasses external climate forcing on the basis of a new glaciological process recently witnessed along the antarctic peninsula rapid disintegrations of fringing ice shelves induced by climate controlled meltwater infilling of surface crevasses we postulate that peripheral ice shelves formed along the eastern canadian seaboard during extreme cold conditions would be vulnerable to sudden climate driven disintegration during any climate amelioration ice shelf disintegration then would be the source of heinrich event icebergs

calibration between eustatic estimates from backstripping and oxygen isotopic records for the oligocene eustatic estimates from the backstripping of oligocene sections are compared quantitatively with d 18 o data each of the nine oligocene d 18 o events maxima identified in previous studies correlates with a stratigraphically determined sea level lowstand oxygen isotopic records from planktonic foraminifers from western equatorial atlantic ocean drilling program odp site 929 indicate an isotopic increase of 0 16 per 10 m decrease in the depth of the ocean apparent sea level asl amplitudes of asl change also correlate with moderate and high resolution benthic foraminiferal d 18 o records from odp sites 803 western tropical pacific and 929 and from deep sea drilling project dsdp site 522 south atlantic ocean with an isotopic change of 0 22 per 10 m of asl change r 2 5 0 807 and 0 960 respectively and with records from odp site 689 southern ocean 0 13 per 10 m of asl change r 2 5 0 704 this correlation suggests that southern ocean deep water temperature changes were smaller than tropical sea surface temperature changes between million year scale glacials and interglacials it also suggests that the deep sea southern ocean records may provide the best means to calibrate sea level to oxygen isotopes

paleogene calcite compensation depth in the eastern subtropical pacific answers and questions 1 ocean drilling program leg 199 drilled a north south transect across the eocene paleoequator in the eastern pacific permitting reconstruction the calcite compensation depth ccd since earliest eocene time the ccd was relatively shallow near the early eocene pacific equator 3200 m and unlike modern latitudinal ccd gradients deepened to the north to 3600 m paleolatitude 10 n at 41 ma the ccd underwent a brief sharp transient deepening of 700 m then remained shallow until the eocene oligocene boundary at the e o boundary the ccd deepened by 1200 m in less than 300 kyr this rapid deepening served to more than double the area of seafloor subject to caco3 deposition sea level fall associated with ice volume buildup and ensuing shelf basin fractionation is unlikely to be the sole cause of the increased deep ocean caco3 burial rather a sudden rapid increase in the amount of ca entering the ocean appears necessary to explain the observations

strike slip duplexes abstract strike slip fault systems often contain zones of steep imbricate faults geometrically similar to imbricate fans and duplexes in dip slip thrust and normal fault systems they are evident in map view rather than in vertical sections examples of duplexes are cited from both active and ancient systems and from theoretical and physical models duplexes may form at bends on strike slip faults by a process kinematically analogous to the sequential imbrication of ramps on dip slip faults however some may form and many may initiate as non sequential riedel fractures at fault offsets or on straight fault segments this process is more marked than in dip slip systems where primary anisotropy such as bedding exerts more control on fault geometry strike slip duplexes may be shunted along the fault system parallel to the regional slip vector however duplexes or individual horses will usually also move up or down perpendicular to the slip vector because of the unconstrained upper surface to the fault system these factors mean that no section through a strike slip system should be expected to area balance the faults of strike slip duplexes and imbricate fans may root in kinematically necessary low dip faults or may converge downwards and appear in vertical sections as flower structures

neogene history of the calcite compensation depth and lysocline in the south pacific ocean the depth time pattern of calcite accumulation recorded at deep sea drilling project dsdp sites beneath the oligotrophic subtropical gyre in the south east pacific ocean allows us to define here both the calcite compensation depth ccd and the lysocline the neogene ccd history is one of shoaling before 15 or 20 myr and subsequent deepening to the present level of 4 100 m a broad zone of increased calcite dissolution 600 m thick formed during early to middle miocene time and has remained this zone the lysocline denotes an important change in ocean chemistry and may reflect either an increase in the volume of more corrosive deep water beginning about 18 myr and reaching steady state by 14 myr the time of rapid ice build up in antarctica or an increase in calcite rain rate caused by an increase in surface water productivity

application of benthic foraminiferal mg ca ratios to questions of cenozoic climate change abstract we investigate the evolution of cenozoic climate and ice volume as evidenced by the oxygen isotopic composition of seawater 18osw derived from benthic foraminiferal mg ca ratios to constrain the temperature effect contained in foraminiferal 18o values we have constructed two benthic foraminiferal mg ca records from intermediate water depth sites ocean drilling program sites 757 and 689 from the subtropical indian ocean and the weddell sea respectively together with the previously published composite record of lear et al science 287 2002 269 272 and the neogene record from the southern ocean of billups and schrag paleoceanography 17 2002 10 1029 2000pa000567 we obtain three almost complete representations of the 18osw for the past 52 myr we discuss the sensitivity of early cenozoic mg ca derived paleotemperatures and hence the 18osw to assumptions about seawater mg ca ratios we find that during the middle eocene 49 40 ma modern seawater ratios yield mg ca derived temperatures that are in good agreement with the oxygen isotope paleothermometer assuming ice free conditions intermediate waters cooled during the middle eocene reaching minimum temperatures by 40 ma the corresponding 18osw reconstructions support ice growth on antarctica beginning by at least 40 ma at the eocene oligocene boundary mg ca ratios and hence temperatures from weddell sea site 689 display a well defined maximum we caution against a paleoclimatic significance of this result and put forth that the partitioning coefficient of mg in benthic foraminifera may be sensitive to factors other than temperature throughout the remainder of the cenozoic the temporal variability among 18osw records is similar and similar to longer term trends in the benthic foraminiferal 18o record an exception occurs during the pliocene when 18osw minima in two of the three records suggest reductions in global ice volume that are not apparent in foraminiferal 18o records which provides a new perspective to the ongoing debate about the stability of the antarctic ice sheet maximum 18osw values recorded during the pleistocene at southern ocean site 747 agree well with values derived from the geochemistry of pore waters schrag et al science 272 1996 1930 1932 further highlighting the value of the new mg ca calibrations of martin et al earth planet sci lett 198 2002 193 209 and lear et al geochim cosmochim acta 66 2002 3375 3387 applied in this study we conclude that the application of foraminiferal mg ca ratios allows a refined view of cenozoic ice volume history despite uncertainties related to the geochemical cycling of mg and ca on long time scales

seismic interpretation of pelagic sedimentation regimes in the 18 53 ma eastern equatorial pacific basin scale sedimentation and infilling of abyssal valleys understanding how pelagic sediment has been eroded transported and deposited is critical to evaluating pelagic sediment records for paleoceanography we use digital seismic reflection data from an integrated ocean drilling program site survey amat03 to investigate pelagic sedimentation across the eastern central equatorial pacific which represents the first comprehensive record published covering the 18 53 ma eastern equatorial pacific our goals are to quantify 1 basin hill scale primary deposition regimes and 2 the extent to which seafloor topography has been subdued by abyssal valley filling sediments the eastern pacific seafloor consists of a series of abyssal hills and basins with minor late stage faulting in the basement ocean crust rarely outcrops at the seafloor away from the rise crest both hills and basins are sediment covered the carbonate compensation depth is identified at 4440 m by the appearance of acoustically transparent clay intervals in the seismic data overall we recognized three different sedimentation regimes depositional high sedimentation rate transitional and minimal sedimentation low sedimentation rate regimes in all areas the sedimented seafloor mimics the underlying basement topography although the degree to which topography becomes subdued varies depositional regimes result in symmetric sedimentation within basins and subdued topography whereas minimal sedimentation regimes have more asymmetric distribution of sediments within topographic lows and higher seafloor relief regardless of sedimentation regime enhanced sediment deposition occurs within basins however we observe that basin infill is rarely more than twice as thick as sediment cover over abyssal hills if this variation is due to sediment focusing the focusing factor in the basins as measured by 230th is no more than a factor of 1 3 of the total vertical particulate rain

current plate velocities relative to the hotspots incorporating the nuvel 1 global plate motion model nuvel 1 is a new global model of current relative plate velocities demets et al 1990 which differ significantly from those of prior models here we incorporate nuvel 1 into hs2 nuvel1 a new global model of plate velocities relative to the hotspots hs2 nuvel1 was determined from the hotspot data and errors used by minster and jordan 1978 to determine am1 2 which is their model of plate velocities relative to the hotspots am1 2 is consistent with minster and jordan s relative plate velocity model rm2 here we compare hs2 nuvel1 with am1 2 and examine how their differences relate to differences between nuvel 1 and rm2 hs2 nuvel1 plate velocities relative to the hotspots are mainly similar to those of am1 2 minor differences between the two models include the following 1 in hs2 nuvel1 the speed of the partly continental apparently non subducting indian plate is greater than that of the purely oceanic subducting nazca plate 2 in places the direction of motion of the african antarctic arabian australian caribbean cocos eurasian north american and south american plates differs between models by more than 10 3 in places the speed of the australian caribbean cocos indian and nazca plates differs between models by more than 8 mm yr although 27 of the 30 rm2 euler vectors differ with 95 confidence from those of nuvel 1 only the am1 2 arabia hotspot and india hotspot euler vectors differ with 95 confidence from those of hs2 nuvel1 thus substituting nuvel 1 for rm2 in the inversion for plate velocities relative to the hotspots changes few euler vectors significantly presumably because the uncertainty in the velocity of a plate relative to the hotspots is much greater than the uncertainty in its velocity relative to other plates

estimating the hydrologic induced signal in geodetic measurements with predictive filtering methods the high precision achieved with continuous geodetic instruments makes it necessary to take ambient factors into account among these one of the most disturbing is the hydrologic agent after giving a characterization of the induced signals in the specific case of subsurface tilt and extensometric measurements the techniques of predictive filtering are shown to solve the problem of modeling the induced signals the results obtained here may be applied also to other continuous geodetic and gravity measurements

collection and three dimensional modeling of gps and tilt data at merapi volcano java we study here the deformations associated with the november 1996 to march 1997 eruption period at mount merapi central java one of the most active volcanoes in indonesia this activity period includes a vertical explosion on january 17 and an increase of the lava dome volume by about 3 106 m3 two global positioning system gps campaigns have been carried out on a six benchmark network at the beginning and at the end of the period relative displacements with respect to the reference point show an average subsidence of 6 5 cm a multicomponent tilt station installed on the southeast flank 3 km from the summit recorded a tilt of 11 1 0 7 rad in the tangential direction and 0 9 0 4 rad in the radial direction these data are interpreted using a three dimensional 3 d elastic model based on the mixed boundary element method and a near neighbor monte carlo inversion interpretation of tilt data requires an accurate mesh for discretizing the 3 d topography the final result supports a horizontal elliptic magma source located 8 5 0 4 km below the summit and 2 0 4 km to the east of it in particular the data cannot be consistent with the location of a magma chamber determined from seismic activity analysis i e 2 km below the summit the computed depth depends strongly on the source shape and cannot be constrained properly because of the small amount of data the computed deflation of 11 2 106 m3 is about 3 times larger than the observed increase in the lava dome volume this difference is attributed to rock avalanches and pyroclastic flows on the flanks of the volcano

neogene carbonate burial in the pacific ocean 1 i have compiled caco3 mass accumulation rates mars for the period 0 25 ma for 144 deep sea drilling project and ocean drilling program drill sites in the pacific in order to investigate the history of caco3 burial in the world s largest ocean basin this is the first synthesis of data since the beginning of the ocean drilling program sedimentation rates caco3 contents and bulk density were estimated for 0 5 myr time intervals from 0 to 14 ma and for 1 myr time intervals from 14 to 25 ma using mostly data from initial reports volumes there is surprisingly little coherence between caco3 mar time series from different pacific regions although regional patterns exist a transition from high to low caco3 mar from 23 20 ma is the only event common to the entire pacific ocean this event is found worldwide the most likely cause of lowered pelagic carbonate burial is a rising sea level trend in the early miocene the central and eastern equatorial pacific is the only region with adequate drill site coverage to study carbonate compensation depth ccd changes in detail for the entire neogene the latitude dependent decrease in caco3 production away from the equator is an important defining factor of the regional ccd which shallows away from the equatorial region examination of latitudinal transects across the equatorial region is a useful way to separate the effects of changes in carbonate production productivity from changes in bottom water chemistry dissolution upon carbonate burial

cooler winters as a possible cause of mass extinctions at the eocene oligocene boundary the eocene oligocene boundary at about 33 7 myr ago marks one of the largest extinctions of marine invertebrates in the cenozoic period1 for example turnover of mollusc species in the us gulf coastal plain was over 90 at this time2 3 a temperature change across this boundary from warm eocene climates to cooler conditions in the oligocene has been suggested as a cause of this extinction event4 but climate reconstructions have not provided support for this hypothesis here we report stable oxygen isotope measurements of aragonite in fish otoliths ear stones collected across the eocene oligocene boundary palaeotemperatures reconstructed from mean otolith oxygen isotope values show little change through this interval in agreement with previous studies5 6 from incremental microsampling of otoliths however we can resolve the seasonal variation in temperature recorded as the otoliths continue to accrete new material over the life of the fish these seasonal data suggest that winters became about 4 c colder across the eocene oligocene boundary we suggest that temperature variability rather than change in mean annual temperature helped to cause faunal turnover during this transition

rapid cenozoic glaciation of antarctica induced by declining atmospheric co2 the sudden widespread glaciation of antarctica and the associated shift towards colder temperatures at the eocene oligocene boundary 34 million years ago refs 1 4 is one of the most fundamental reorganizations of global climate known in the geologic record the glaciation of antarctica has hitherto been thought to result from the tectonic opening of southern ocean gateways which enabled the formation of the antarctic circumpolar current and the subsequent thermal isolation of the antarctic continent5 here we simulate the glacial inception and early growth of the east antarctic ice sheet using a general circulation model with coupled components for atmosphere ocean ice sheet and sediment and which incorporates palaeogeography greenhouse gas changing orbital parameters and varying ocean heat transport in our model declining cenozoic co2 first leads to the formation of small highly dynamic ice caps on high antarctic plateaux at a later time a co2 threshold is crossed initiating ice sheet height mass balance feedbacks that cause the ice caps to expand rapidly with large orbital variations eventually coalescing into a continental scale east antarctic ice sheet according to our simulation the opening of southern ocean gateways plays a secondary role in this transition relative to co2 concentration

tilt and strain deformation induced by hydrologically active natural fractures application to the tiltmeters installed in sainte croix aux mines observatory france we investigate the deformation induced by water pressure variations in hydrologically active natural fractures and recorded by tiltmeters and strainmeters the deformation associated with a single fracture is derived using finite element modelling fem a range in fracture geometries is explored first to highlight the sensitivity of each geometrical parameter to the deformation and secondly to allow transfer to observation sites water level variations in the fracture are then derived from a hydrological model driven by observed rainfall and calibrated on fracture water flow measurements the modelling results are explicitly applied to constrain the local hydrological contribution to observations with the 100 m long hydrostatic tiltmeter installed at sainte croix aux mines france our study shows that well founded physical modelling of local hydrological effect allows a substantial correction of records in observatories

paleogene tropical pacific clues to circulation productivity and plate motion 1 stratigraphic data from 63 deep sea drilling project and ocean drilling program odp sites that sample the lower neogene and paleogene sediments of the tropical pacific have been compiled and put on the biostratigraphic and paleomagnetic timescale refined by odp leg 199 scientists sediment accumulation rates have been calculated for ten intervals ranging in age from 10 to 56 ma and have been plotted for the midpoint of each interval at the associated paleoposition for each site used a fixed hot spot model was used for reconstruction of the pacific lithospheric plate all such reconstructed intervals show the development of a tongue of high accumulation rates associated with the oceanographic divergence at the geographic equator the development of this equatorial band is weakest between 46 and 56 ma the time of the peak warmth in paleogene climate possible motion of the hawaiian hot spot or true polar wander between 46 and 56 ma appears to have had little effect on the plate rotation estimate of the position of the equator in addition to temporal changes in the calcite compensation depth and in productivity the biggest change in the patterns of sediment accumulation rates in the eastern tropical pacific was the development of a relatively strong divergence between 6 and 10 n near the region of divergence between the modern north equatorial current and the north equatorial counter current changes in the equatorial circulation appear to be associated in time with the opening and closing of oceanic gateways particularly the complex closing of the caribbean pacific gateway

sedimentological evidence for the formation of an east antarctic ice sheet in eocene oligocene time middle eocene to late oligocene sediments recovered at ocean drilling program sites 689 and 690 on maud rise in the southernmost atlantic ocean and at sites 738 and 744 on kerguellen plateau in the southernmost indian ocean were analysed in order to study the depositional environment and the palaeoclimate special emphasis was placed on the reconstruction of the formation of a cryosphere on the antarctic continent the investigations include quantifications of carbonate and opal contents grain size analyses and studies of clay mineral assemblages the sedimentary sequence at all sites under investigation is highly pelagic with nannofossil oozes and chalks dominant the first indication of probable glacierization at sea level is in the form of isolated gravel and terrigenous sand grains which indicate ice rafting from middle eocene time at c 45 5 ma this is supported by enhanced concentrations of detrital chlorite and reworked kaolinite probably some glaciers reached the sea while most of the continent remained under the influence of a humid and warm to temperate climate the growth of the inland ice resulted in enhanced physical weathering and in increased contents of detrital chlorite and kaolinite from about 40 ma a strengthening of the glacial conditions and the onset of continental east antarctic glaciation is recorded in early oligocene sediments with an age of 36 ma all major sediment parameters document this event the clay mineralogy changed between c 36 3 ma and c 35 5 ma from smectite dominated assemblages to illite and chlorite dominated assemblages the latter being indicative of physical weathering under cooler climates large quantities of ice rafted gravel and sand accumulated on the kerguelen plateau between 36 0 ma and 35 8 ma at the same time an increase in opal content occurred as well as a decrease in carbonate the sediment parameters imply that the east antarctic continent was more or less totally buried beneath the ice during oligocene time the ice sheet however probably did not have a polar but a temperate character as indicated by the occurrence of nothofagus and relatively warm surface water temperatures prohibiting the long distance transport of debris by icebergs

equatorial ocean circulation in an extremely warm climate 1 the warm climates of the early paleogene and the associated diminished near surface winds should have resulted in a reduction in near surface ocean circulation one check on this deduction is the delineation of biogenic sediments associated with an equatorial current system of the early eocene pacific a latitudinal seismic reflection transect across the tropical pacific along early paleogene ocean crust reveals a basal high amplitude reflection package that we take to be the lower eocene section this unit varies in thickness by a factor of about two with the thickest portion forming a low mound some 3 4 north of the 56 ma paleoequator this mound may represent the position of a divergence generated in the frontal region between two currents flowing in opposite directions and its position suggests that the wind driven equatorial circulation of the early eocene was one without a pronounced equatorial divergence

measurements and interpretations of tilt strain gauges in seismically active areas abstract an overview of different aspects of deformation measurements is given an introduction to the general theory of point crustal deformations with an application to the stress strain relations at the earth surface is made the instrumentation used in crustal deformation measurements is briefly explained emphasizing different constructions of tilt and strainmeters the problems connected with the housing of the instruments i e the cavity and topography effects and with the ambient noise factors as the hydrological and pressure effects are discussed the last part of the paper is concerned with the relation between deformation measurements and seismic events both from a theoretical and observational standpoint a number of examples are shown that report on pre co and post seismic and the secular term deformation in different areas of the world

the change in strain comes mainly from the rain kipapa oahu strain data from the benioff type gauge installed in the kipapa tunnel on oahu hawaii are analyzed for the period february 1964 to may 1978 the predominant response is due to temperature variations and rainfall a rainfallstrain transfer function is obtained using rain water infiltration and groundwater recession models developed by hydrologists numerical values obtained range from 0 27 to 0 53 10 7 strain inch of rain at a nearby rain gauge subtracting expansion of the quartz rod due to temperature variation the linear expansion coefficient of in situ tholeiitic basalt of 32 10 7 c is obtained

cockade breccia product of mineralisation along dilational faults cockade breccias are fault fills in which individual clasts are completely surrounded by concentric layers of cement they occur particularly in low temperature near surface hydrothermal veins at least six mechanisms have been proposed for the formation of cockade breccia like textures but only two repeated rotation accretion and partial metasomatic replacement of clast minerals have been supported by detailed evidence a typical example of cockade breccia from the gower peninsula south wales shows clear evidence for the rotation accretion mechanism in particular overgrown breakage points in cement layers where cockades were previously touching each other and rotated geopetal infills of haematitic sediment based on the available evidence it is proposed that cockade textures result from low rates of cement growth compared to high rates of dilational fault slip seven criteria are given for the correct identification of cockade breccias

tertiary climatic changes at middle latitudes of western north america abstract a new multivariate analysis of leaf physiognomy provides the basis for estimating various climatic parameters for angiosperm leaf assemblages estimates from this climate leaf analysis multivariate program clamp are both accurate valid and precise repeatable application of clamp to fossil leaf assemblages from western north america confirms that eocene mean annual temperature mat was generally high early eocene mat 19 c at paleolat 70 n and 27 c at paleolat 45 n significant fluctuations 5 8 in mat occurred during the eocene each successive warm period was cooler than the preceding warm period mean annual range of temperature mart was generally low during the eocene especially at middle latitudes but then markedly increased by 12 13 c at 33 ma as mat decreased by 7 8 c these changes at 33 ma largely involved a decrease in cold month mean temperature which continued to decline into the early miocene but then increased significantly into the mid miocene thermal optimum warm month mean temperature changed little from the eocene through the early miocene this parameter however markedly decreased at 13 ma which coincides with the growth of the east antarctic ice sheet clamp also indicates that the coastal region of western north america had significantly higher mat than interior regions such as the great basin and rocky mountains these differences in mat appeared by or during the eocene and indicate that much of the interior had high altitudes in the paleogene these inferences have a significant bearing on global circulation models proposed for tertiary climates

neoproterozoic sinistral displacement along the darling mobile belt western australia during gondwanaland assembly evidence is provided for neoproterozoic sinistral displacement along the darling mobile belt between greater india and precambrian terranes of western australia a dilatational bend in the shear zone is thought to have controlled emplacement of alkali granites anorthosite and mafic intrusives of the leeuwin complex which was deformed during progressive deformation faults formed in this event extend across the albany mobile belt and control the formation of the stirling basin on the southern margin of the yilgarn craton the regional extent of this event and the rotation of mesoproterozoic trends in the albany mobile belt through 90 suggests that the darling mobile belt may be part of a shear system of regional importance during assembly of proto east gondwanaland much attention is being focused on the assembly of gondwanaland and the relative displacements between archaean cratons along proterozoic mobile belts e g powell 1993 unrug 1994 yoshida 1994 southwestern australia is a key area within proto east gondwanaland as in reconstructions such as de witt et al 1988 and powell et al 1988 it constitutes the junction between the archaean yilgarn craton of western australia india greater india and the east antarctic shield fig 1 this paper examines the timing and nature of displacements along the darling mobile belt glikson lambert 1973 mathur shaw 1982 on the western margin of the yilgarn craton and contemporaneous structures within the albany mobile belt and southern yilgarn craton fig 2 the darling mobile belt the darling mobile belt referred to by myers 1990 as the

the structure of shear related vein type gold deposits a review abstract the structure of vein type gold deposits is defined by the shapes and geometrical relationships of mineralized bodies the form of the mineralization making up these bodies and the sequence of vein forming events most mineralized zones occur within or are spatially associated with shear zones especially shear zones in larger systems of intersecting shear zone sets they range in shape from tabular to linear and in form from disseminated to breccia to stockwork or sheeted veinlet zones to single veins there typically is a complex history of mineral deposition which overlaps and is genetically related to the deformation that generated the host structural zone the purpose of this paper is to consider the structural features of vein type deposits in relation to the geometrical properties and evolution of veinhosting fractures particularly shear zones the evidence indicates that veins are localized by tectonically generated dilatancy in an environment of low mean stress caused by high fluid pressure it is proposed that a major cause of tectonic dilation of shear zones is the interference between intersecting shears during bulk inhomogeneous flattening by movement on systems of intersecting shear zone sets

early oligocene ice sheet expansion on antarctica stable isotope and sedimentological evidence from kerguelen plateau southern indian ocean sedimentological and stable isotope data from a pelagic sequence recovered from the southern indian ocean provide the most convincing evidence to date for short term expansion of a large ice sheet on antarctica during the earliest oligocene 36 ma terrigenous debris identified as ice rafted in origin on the basis of textural compositional and size criteria is present at the same stratigraphic level as the ubiquitous early oligocene oxygen isotope shift the highest benthic foraminiferal 18o values 3 0 of the paleogene occur in samples from within the ice rafted debris interval these values are similar to those recorded by holocene benthic foraminifera implying that the ice sheet may have attained a volume similar to that of the present day ice sheet on antarctica the stratigraphic distribution of ice rafted debris and high oxygen isotope values indicate that these conditions persisted for roughly 100 ka

extensional duplexing in the york cliffs strike slip fault system southern coastal maine abstract a 150 m long sinistral strike slip fault system consisting of left stepping en echelon fault segments cuts deformed paleozoic metasediments and early mesozoic dike intrusions in coastal terrace outcrops in southern maine the longer fault segments follow the vertical bedding in the metasediments and accommodate approximately 1 m of displacement detailed mapping at scales down to 1 6 indicates that overlap zones between offset layer parallel fault segments consist of high dilation angular breccias rounded attrition breccias and extensional duplexes where the offset segments straddle upright quartzite layers in one 10 m long duplex r and r shears cut the layering in the quartzite at 28 and 69 respectively relative to the dominant layer parallel fault segments creating a doubly tapered imbricate r shear lens segmentation structure individual imbricate lenses accommodate additional layer parallel extension through conjugate x x shear fractures with average orientations of 109 and 60 respectively relative to the dominant fault segments extensional fractures oblique to the dominant fault segments are rare within this duplex but commonly form distinctive horsetail arrays at fault terminations that average 44 to the layer parallel faults strain analysis shows that approximately 60 80 cm of measured strike slip displacement is accommodated internally within this duplex as layer parallel extensional strain using the r shear and x x shear fracture mechanisms the strain distribution and observed cross cutting relations suggest an outward symmetric growth of the duplex structure from left stepping sinistral fault segments that developed sequences of tip to plane r shear overlap linkages during continued displacements cyclic r r to x x shear fracturing may relate to stress reorientation following r shear ruptures during episodic growth of the duplex and incremental slip of the fault system

the marine 187 os 188 os record of the eocene oligocene transition the interplay of weathering and glaciation abstract osmium os isotope analyses of bulk sediments from the south atlantic equatorial pacific and the italian apennines yield a well dated and coherent pattern of 187os 188os variation from the late eocene to the early oligocene the resulting composite record demonstrates the global character of two prominent features of the low resolution ll44 gpc3 os isotope record pegram and turekian geochim cosmochim acta 63 1999 4053 4058 these are 1 a pronounced minimum in 187os 188os 0 22 0 27 in the late eocene between 34 and 34 5 ma and 2 a subsequent rapid increase in 187os 188os to approximately 0 6 by 32 ma an ultramafic weathering event and an increased influx of extraterrestrial particles to the earth are discussed as alternative explanations for the late eocene 187os 188os minimum comparison of the 187os 188os to benthic foraminiferal oxygen isotope records demonstrates that the nearly three fold increase in 187os 188os from the late eocene minimum coincides with the growth and decay of the first large ice sheet of the oligocene oi1 miller et al j geophys res 96 1991 6829 6848 the fine structure of the os isotope record indicates that enhanced release of radiogenic os unrelated to the recovery from late eocene minimum lagged the initiation of the oi1 event by roughly 0 5 myr this record in conjunction with weathering studies in modern glacial soils blum in w f ruddiman ed tectonic uplift and climate change plenum press new york 1997 pp 259 288 peucker ehrenbrink and blum geochim cosmochim acta 62 1998 3193 3203 suggests that exposure of freshly eroded material during deglaciation following oi1 enhanced chemical weathering rates and may have contributed to ice sheet stabilization by drawing down atmospheric carbon dioxide the improved temporal resolution and age control of the refined eocene oligocene os isotope record also makes it possible to illustrate the late eocene os isotope excursion as a tool for global correlation of marine sediments

transient deformation of karst aquifers due to seasonal and multiyear groundwater variations observed by gps in southern apennines italy we present gps hydrological and grace gravity recovery and climate experiment observations in southern apennines italy pointing to a previously unnoticed response of the solid earth to hydrological processes transient patterns in gps horizontal time series near to large karst aquifers are controlled by seasonal and interannual phases of groundwater recharge discharge of karst aquifers modulating the extensional 3 mm yr strain within the tectonically active apennines we suggest that transient signals are produced below the saturation level of the aquifers and above a poorly constrained depth in the shallow crust by time dependent opening of sub vertical fluid filled conductive fractures we ascribe this process to the immature karstification and intense tectonic fracturing favouring slow groundwater circulation and to multi year variations of the water table elevation influenced by variable seasonal recharge the vertical component displays seasonal and multi year signals more homogeneously distributed in space and closely correlated with estimates of total water storage from grace reflecting the elastic response of the lithosphere to variations of surface water loads the different sensitivities of vertical and horizontal components to the hydrologically induced deformation processes allow us to spatially and temporally resolve the different phases of the water cycle from maximum hydrological loading at the surface to maximum hydrostatic pressure beneath karst aquifers finally we suggest that transient deformation signals in the geodetic series of the apennines are correlated to large scale climatic patterns northern atlantic oscillation through their influence on precipitation variability and trends at the regional scale

structure of the western albany mobile belt southwestern australia evidence for overprinting by neoproterozoic shear zones of the darling mobile belt abstract the albany mobile belt is dominated by ductile fabrics and regional structures formed during progressive dextral transpression at 1190 ma d1 resulting from nw se to nnw sse shortening and represents the oblique convergence between the west australian and east antarctic shields deformation was accompanied by metamorphism up to granulite facies and granitoid intrusion neoproterozoic extension and progressive deformation within a sinistral transcurrent to transtensional shear zone in the leeuwin complex of the southern darling mobile belt may be contemporaneous with transpressional shearing along the donnybrook nannup shear zone on the western yilgarn craton margin during this neoproterozoic event e w mesoproterozoic trends in the western albany mobile belt have been rotated into a n s orientation ductile reactivation and overprinting of mesoproterozoic structures is accompanied by retrogression of granulite facies assemblages to amphibolite facies migmatisation and pegmatite and granitoid intrusion in demonstrating that the n s orientation of the western albany mobile belt results from a younger event a continuation of this mobile belt is expected in northeast india whilst a continuation of the darling mobile belt may exist in the mirnyy area of east antarctica folding and the formation of conjugate brittle ductile shear zones during ne sw shortening and early cambrian conjugate faulting and jointing resulting from ese wnw shortening is common to both the western albany mobile belt and leeuwin complex

early oligocene glaciation and productivity in the eastern equatorial pacific insights into global carbon cycling the onset of sustained antarctic glaciation across the eocene oligocene transition eot marks a pivotal change in earth s climate but our understanding of this event particularly the role of the

structural control of greenstone hosted gold mineralization by transcurrent shearing a new interpretation of the kalgoorlie mining district western australia abstract the kalgoorlie mining district encloses the golden mile and mt charlotte mining areas and has produced 1200 metric tons of gold it is classed as one of the largest archaean gold deposits in the world the district is located in the norseman wiluna greenstone belt of the yilgarn craton western australia this greenstone belt is characterized by nnw trending transcurrent shear zones some of which are traceable over more than 500 km strike length mineralization in the district is controlled by second third and fourth order structures located between principal shear zones of regional extent an early deformation phase of regional folding d1 associated with prograde regional metamorphism of low grade preceded two phases of wrenching the geometry of mineralized shear zones in both mining areas as well as field and microstructural studies allow us to distinguish an early phase of transpressional sinistral shearing d2 from a later phase of transcurrent dextral shearing d3 the earlier sinistral shear system in the golden mile area was in part reactivated but its gross original geometry was preserved these observations are consistent with clay model experiments carried out by the authors hydrothermal carbonate sericite alteration and gold mineralization commenced during the sinistral shear event and continued into the dextral event mineralization within individual shear zones forms tabular orebodies whereas pipe shaped ore shoots occur at the intersection of shear zones the ore shoots contain high grade telluride mineralization locally relative timing relationships show that mineralization postdates the peak of regional metamorphism hydrothermal activity in the district was preceded by the intrusion of calc alkaline porphyry dykes of granodioritic to tonalitic composition and accompanied by the intrusion of lamprophyre dykes

earthquakes and lineament infrastructure a further result attending to the disturbances of the surface of the earth has been to produce rents or fissures in the rocks which have been subject to their violent movements and to convert them into receptacles of metallic ores accessible by the labours of men reverend william buckland geology and mineralogy with reference to natural theology london william pickering 1836 analyses of the nucleation propagation and stopping of moderate to large earthquake ruptures coupled with high precision studies of background and aftershock microearthquake activity are yielding insights into the infrastructure of major transcurrent fault zones within the seismogenic regime curvature and echelon segmentation of a principal slip surface within a ca 1 km wide main fault zone appear to exert major controls on the starting and stopping of ruptures geometrical irregularities of this kind transverse to the direction of rupture propagation may be usefully classified into dilational and antidilational jogs referring to the area change in the plane defined by the slip vector and the pole to planar segments of the fault extensional fracture systems linking echelon fault segments across dilational jogs allow long term transfer of fault slip but appear to play an especially important role as kinetic barriers impeding or arresting rapid rupture propagation in fluid saturated crust the rapid transfer of slip is opposed by suctions arising from rupture induced differential fluid pressures delayed slip transfer delineated by intense aftershock activity may then occur as fluid pressures re equilibrate fossil examples of such linking extensional fracture systems are characterized by multi episode hydraulic implosion breccias dilational zones of this kind may migrate along faults or remain fixed for relatively long time periods they serve as particularly favourable sites for hydrothermal mineralization and may also localize magmatic activity along major lineaments

the influence of topographic and lithologic features on horizontal deformations summary a number of studies have been carried out in order to determine the magnitude of effects originating from the surroundings of an observation site which influence seismometer records or deformation observations with tilt or strainmeters the investigations generally comprise thermal atmospheric topographic and cavity effects as well as ocean loading recently these studies have been continued and extended using finite element fe modeling the effects are investigated exemplarily using air pressure variations as loading signal the observatory sites differ in their local surroundings based on this the influence on topographic and lithologic features is investigated with respect to air pressure changes the models developed reflect different topographies around stations wide and narrow valleys hill flanks and flat areas at the foot of the hill flank galleries are integrated into the models the topographic and the gallery geometry influence are systematically investigated with regard to e g rock coverage above an observation site changes in the hill slope width of a valley and lithology the deformations are only caused by air pressure changes and not associated with gravity changes due to an advancing pressure front for loading different air pressure scenarios are simulated with an uniform load and a pressure front which moves over the model in different directions as an elastic rheology is considered the effects can be scaled to actual occurring air pressure variations initial studies focus on the cavity effect to estimate the order of magnitude to separate the pure cavity effect from other influences studies of topographic effects e g an increasing slope angle yield a non linear increase in the strain component with amplitudes up to 2 nstrain and tilt changes up to 2 nrad for a uniform air pressure load of 1 hpa for prem parameterized models different lithologies can result in five times larger deformations for moving high pressure areas changes emerge in strain of up to 2 nstrain and in tilt of up to 4 2 nrad the results obtained improve the interpretation of deformations observed with regard to fundamental geodynamic processes and contribute to the selection of future observation sites

a comparison of spatially resolved and global mean reconstructions of continental denudation under ice free and present conditions we assess the impact of continental scale processes on global denudation through the use of spatially resolved information for both an ice free paleoclimate and the present climate runoff from general circulation modeling cases representing the early eocene is superimposed upon an eocene paleogeologic reconstruction and this information is combined with chemical denudation rates for silica dissolved moles si and bicarbonate dissolved moles hco3 global fluxes of silica and bicarbonate to the global ocean are then calculated a parallel procedure is carried out with present day distributions of lithology and model derived runoff this work demonstrates that fluxes produced by a simple model such as the one used here are significantly different when calculated with spatially uniform runoff values versus those calculated with a spatially varying runoff distribution having the same global mean value use of a uniform runoff distribution produces denudation rates that are significantly higher than the global results derived from a spatially varying runoff distribution we show that present day fluxes of silica calculated by our model containing spatially varying runoff and lithology are similar to observations of current fluxes suggesting that our model captures the first order relationship accurately however the bicarbonate value compares less well to observations comparison of eocene and present day flux results shows that present day fluxes of si are greater than eocene values while calculated present day hco3 fluxes are greater than or equal to eocene values this result occurs despite the existence of greater global mean annual runoff for the eocene cases and despite the existence of ice covered areas by definition not contributing to chemical weathering in our model in the present case the increase in si global denudation fluxes from the eocene to the present are caused primarily by the large increase in exposed granitic basaltic and shale lithologies and a decrease in exposed sandstone areas between the eocene and present

cenozoic deep sea temperatures and global ice volumes from mg ca in benthic foraminiferal calcite a deep sea temperature record for the past 50 million years has been produced from the magnesium calcium ratio mg ca in benthic foraminiferal calcite the record is strikingly similar in form to the corresponding benthic oxygen isotope 18o record and defines an overall cooling of about 12 c in the deep oceans with four main cooling periods used in conjunction with the benthic 18o record the magnesium temperature record indicates that the first major accumulation of antarctic ice occurred rapidly in the earliest oligocene 34 million years ago and was not accompanied by a decrease in deep sea temperatures

strainmeters and tiltmeters despite steady effort over the last century continuously recording tiltmeters and strainmeters have not yet been successful except for earth tide measurements this article reviews the techniques and instrument designs that have been developed in this field the continuous measurement of true tectonic motions which have rates of 10 14 s 1 requires extremely high instrument stability but more rapid motions tides and seismic waves apart are even smaller and not much more easily detectable much past effort has been spent improving the transducers used in these instruments which usually measure small displacements the commonest choices are optical the most accurate capacitive the most sensitive and inductive the most rugged nowadays building a transducer is the easiest part a much harder task equally important to a good design is attaching the instrument to the ground so that it can detect the signal wanted this part of the design includes choosing a location a large underground opening is thermally stable but distorting a surface installation is easy to build but noisy because of soil weathering and a borehole is inaccessible to weather but also to the operator all such installations and indeed the whole field of strain and tilt measurement of course rely on the assumption that the deformations of interest can be measured over baselengths of a few hundred meters or less this is true for tides and seismic waves but unproven for tectonic motions appropriate attachment techniques differ for each location and many mundane details such as cementing techniques for borehole instruments remain to be worked out the goal of measuring tectonic and tidal tilt has created many tiltmeter designs most are relatively small instruments that use some form of pendulum or bubble level a few use a liquid surface to measure tilts over a long baseline repeated experience has shown the latter type when well built to be superior to the former proving end monument motions to be a dominant source of noise the same appears to hold true for strainmeters the best results coming from long base laser instruments though strainmeters using rigid or flexible material length standards are useful for special purposes and borehole instruments show promise because achieving a good design has been so difficult it is important to select the goals an instrument must meet and be prepared to compromise on others the difficulty of validating results from this type of instrument makes comparison tests essential such tests as have been made so far show that good results cannot be gotten at low cost or without careful attention to details

early cenozoic glaciation antarctic weathering and seawater 87sr 86sr is there a link abstract stable and radiogenic isotopic and sedimentological data from sub antarctic deep sea sediment cores reveal a temporal link between changes in seawater 87 sr 86 sr ratios and major episodes of late eocene early oligocene climate change the 87 sr 86 sr records show two major inflections one at 38 39 ma near the middle late eocene boundary followed by another at 33 4 ma similarly the oxygen isotope ice rafted debris and clay assemblage records indicate two important climatic events the appearance of alpine glaciers and or small ice sheets on antarctica in the late eocene at 38 39 ma followed by a rapid transition to larger and more permanent temperate ice sheets in the early oligocene at 33 4 ma moreover during the early oligocene 30 33 ma three to four inferred peaks in glacial activity appear to coincide with subtle steps in the 87 sr 86 sr record the coupled variations in climate and seawater sr isotope ratios during the eocene oligocene imply a strong causal link between the two either changes in climate directly influenced patterns of continental weathering and hence seawater chemistry and or a tectonic event e g uplift as reflected in weathering and seawater chemistry triggered relatively abrupt changes in global climate