rock conductivity and fractal nature of porosity while the d c electrical properties of a rock through the volume conductivity provide information on pore space structure formation factor and pore fluid the frequency dependence of the electrical parameters allows the characterization of the pore matrix interfaces to illustrate these properties we present here some results of measurements performed on sedimentary rocks vosges and fontainebleau sandstones these samples have a classical electrical response i e a cole and cole frequency behaviour near a certain relaxation frequency and a low frequency dispersion we discuss some of the models that have been proposed in the past to explain this behaviour it appears that most of them are valid near and above the relaxation frequency but only dissado and hill s model seems to be satisfactory over the whole frequency range the fractal nature of the interfaces assumed in two of these models but appropriate only for one of them could also be a convenient explanation for the frequency dependence

thermal genesis of dissolution caves in the black hills south dakota jewel cave 118 km of mapped passages beneath an area of 2 7 km 2 and wind cave 70 km beneath 1 8 km 2 are respectively the fourth and tenth longest known cave systems and the world9s foremost examples of three dimensional rectilinear networks of solutional passages other caves in the black hills are similar they occur in 90 140 m of well bedded mississippian limestone and dolomite walls throughout jewel cave are lined with euhedral calcite spar as much as 15 cm thick wind cave displays lesser encrustations and remarkable calcite boxwork since 1938 opinion has favored cave excavation by slowly circulating meteoric waters in artesian confinement similar to that surrounding the black hills we believe that the caves were developed by regional thermal waters focusing on paleospring outlets in outlying sandstones four sets of criteria are evaluated 1 morphological the three dimensional one phase maze form having convectional features is similar to known and supposed thermal caves in europe 2 petrographic and mineralogical study of the chief precipitates shows a record of carbonate solution calcite precipitation consonant with a model of cooling then degassing waters 3 a thermal anomaly at regional hot springs is shown to extend beneath wind cave where basal lake water samples show chemical and isotopic affinities with the thermal waters and 4 13 c and 18 o measurements place all suspected paleothermal water precipitates in the domain of thermal calcites reported by others and being deposited at the modern hot springs finally u series dates show that the wind cave deposits are quaternary and that the cave is still draining jewel cave is truly relict and divorced from the modern thermal ground water system its great calcite spar sheets are probably older than 1 25 1 50 ma

spring related carbonate rocks mg clays and associated minerals in pliocene deposits of the amargosa desert nevada and california the amargosa desert of nevada california is a spring fed structural basin containing large amounts of pliocene carbonate rocks and mg clays deposited in playas marshland ponds and flood plains pliocene basin fill deposits dated at 2 4 to 3 2 ma are subdivided into three lithofacies designated tpa tld and tpl tpa is chiefly limestone and was deposited in marshland and ponds tld consists chiefly of limestone and montmorillonite claystone that were deposited in varied environments including ponds and flood plains tpl is almost entirely mg clays limestone and dolomite which were deposited in playas and associated marshland the largest area of playa sediments termed east playa is in the east central part of the basin limestone and dolomite seepage mounds and caliche breccia musses were formed along zones of ground water leakage within east playa chemically precipitated mg smectite and sepiolite form large deposits in tpl sepiolite was formed in water of low salinity whereas mg smectite was formed in water of higher salinity authigenic celadonitic illite and k feldspar are commonly associated with mg smectite and are very likely reaction products of montmorillonite in saline alkaline water silicic vitric ash layers were locally altered to phillipsite and k feldspar in saline alkaline water and to montmorillonite as a result of leaching by water of low salinity carbonate rocks are locally silicified along seepage zones carbonate minerals of the pliocene deposits have stable isotopic compositions that vary with their lithofacies tpa limestones deposited in or near areas of spring discharge have low 18o values averaging 16 6 tld limestones recrystallized in the vadose zone have higher 18o values averaging 18 1 carbonate minerals of tpl are the most 18o rich with calcite averaging 20 3 and dolomite 24 3 reflecting evaporative concentration in playas much of the dolomite is of replacement origin yet is in approximate isotopic equilibrium with the calcite it replaces relatively pure sepiolite has lower 18o values than do mg smectite clays which fits with the lower salinity inferred for sepiolite precipitation sepiolite and mg smectite disseminated in limestone fall outside the oxygen isotopic limits of the relatively pure clays possibly because of diagenetic recrystallization the pliocene climate was wetter than that of the present and springs were more widespread in the amargosa basin this dolomite may have formed in water isotopically and chemically about the same as that of the calcite and dolomitization may have been chiefly a result of the differing crystallization kinetics of calcite and dolomite and of fluctuating water chemistry in a playa environment the saline alkaline water of east playa resulted from evaporation of a mixture of alkali bicarbonate runoff from the volcanic terrane to the north with ca mg bicarbonate water discharged in springs from the ash meadows ground water system whose recharge area is principally in paleozoic carbonate rocks to the east and northeast seepage along fault zones in east playa was initially of ash meadows type low in silica and changed to siliceous water derived from volcanic rocks resulting in silicification of carbonate deposits caliche breccias along the western margin of the basin record a similar change in the composition of ground water seepage which may be attributed to a period of decreased precipitation about 2 5 ma which reduced recharge from nearby carbonate rocks relative to that from more distant volcanic rocks to the north and northwest

calibration of the calcite water oxygen isotope geothermometer at devils hole nevada a natural laboratory abstract the 18 o of ground water 13 54 0 05 and inorganically precipitated holocene vein calcite 14 56 0 03 from devils hole cave 2 in southcentral nevada yield an oxygen isotopic fractionation factor between calcite and water at 33 7 c of 1 02849 0 00013 1000 ln calcite water 28 09 0 13 using the commonly accepted value of calcite water t of 0 00020 k 1 this corresponds to a 1000 ln calcite water value at 25 c of 29 80 which differs substantially from the current accepted value of 28 3 use of previously published oxygen isotopic fractionation factors would yield a calcite precipitation temperature in devils hole that is 8 c lower than the measured ground water temperature alternatively previously published fractionation factors would yield a 18 o of water from which the calcite precipitated that is too negative by 1 5 using a temperature of 33 7 c several lines of evidence indicate that the geochemical environment of devils hole has been remarkably constant for at least 10 ka accordingly a re evaluation of calcite water oxygen isotopic fractionation factor may be in order assuming the devils hole oxygen isotopic value of calcite water represents thermodynamic equilibrium many marine carbonates are precipitated with a 18 o value that is too low apparently due to a kinetic isotopic fractionation that preferentially enriches 16 o in the solid carbonate over 18 o feigning oxygen isotopic equilibrium

devils hole nevada δ18o record extended to the mid holocene abstract the mid to late pleistocene devils hole 18 o record has been extended from 60 000 to 4500 yr ago the new 18 o time series in conjunction with the one previously published is shown to be a proxy of pacific ocean sea surface temperature sst off the coast of california during marine oxygen isotope stages mis 2 and 6 the devil hole and sst time series exhibit a steady warming that began 5000 to 10 000 yr prior to the last and penultimate deglaciations several possible proximate causes for this early warming are evaluated the magnitude of the peak 18 o or sst during the last interglacial lig is significantly greater 1 per mill and 2 to 3 c respectively than the peak value of these parameters for the holocene in contrast benthic 18 o records of ice volume show only a few tenths per mill difference in the peak value for these interglacials statistical analysis provides an estimate of the large shared information variation between the devils hole and eastern pacific sst time series from 41 to 2 n and enforces the concept of a common forcing among all of these records the extended devils hole record adds to evidence of the importance of uplands bordering the eastern pacific as a source of archives for reconstructing pacific climate variability

tectonomagnetism and tectonoelectricity the last four years has seen a considerable waning of efforts in the u s to use the inherent stress sensitivity of the magnetization of rocks in tectonically active regions as a tool for understanding and perhaps predicting earthquake activity and volcanic eruptions the primary reasons for this decreased interest derive from accumulating evidence that the mean deviatoric stress release during earthquakes and the ambient shear stress near active faults is lower than than had been previously assumed and secondly the observational limits of magnetometers separated by about 10 km after application of a variety of noise reduction techniques appear to be no better than about 0 1 nt lower estimates of the average change in deviatoric stress associated with earthquake rupture correspondingly reduce the fields calculated from tectonomagnetic models at the same time some unexpected and exciting results have been obtained which indicate many aspects of magnetic field changes near active faults and volcanoes are still not completely understood the more important of these results are 1 the observation of correlated magnetic strain uplift and gravity changes during the latter stages of a remarkable deformation episode near the san andreas fault in southern california 2 indications of anomalous change in magnetic fields along the san andreas fault to the southeast of palm springs 3 an unambiguous observation of a volcanomagnetic effect at mt st helens prior to an extrusive eruption and 4 the first observations of coseismic seismomagnetic effects on two independent magnetometers during the july 8 1986 ml 5 9 north palm springs earthquake a resurgence of interest has occurred during the quadrennium in a related area concerning electrical phenomena and electromagnetic effects related to earthquakes and volcanoes mechanisms have been proposed to explain the occurrence of earthquakes lights and the possibility of electromagnetic emission prior to the 1960 chilean earthquake has been proposed self potential anomalies have been observed before and during several eruptions on kilauea volcano in hawaii

boxwork and ferromanganese coatings in hypogenic caves an example from sima de la higuera cave murcia se spain abstract this paper examines the greyish blue deposits that were recently discovered in the lower levels of the sima de la higuera cave murcia se spain which occur as patinas over the walls and ceilings as well as coating boxwork formations their mineralogy was determined using xrd and micro raman spectroscopy while edx microanalysis was used to determine their elemental composition the mineralogical analyses revealed the presence of mn oxides todorokite and pyrolusite and fe with a low degree of crystallinity whereas edx microprobe showed elevated concentrations of mn 38 2 wt fe 15 2 wt and pb 8 1 wt the ferromanganese oxyhydroxides occur as botryoidal aggregates overlying blades of calcite that have a visibly sugary texture the speleogenetic model proposed describes 1 an initial phase of precipitation of hydrothermal calcite veins of hypogenic origin within the fissures of the host rock under phreatic conditions and 2 a subsequent vadose phase involving preferential corrosion of the carbonate host rock caused by lowering of the ph resulting from co 2 diffusion in condensed water and oxidation of fe and mn under aerobic conditions probably mediated by microorganisms it is this later phase that gave rise to the boxwork the boxwork of the sima de la higuera cave is a singular example of a formation that is generated by dissolution corrosion of the rock due to acidification caused by oxidation of iron and manganese

corrosion morphology and cave wall alteration in an alpine sulfuric acid cave kraushohle austria abstract whereas most karstic caves worldwide are formed by carbonic acid a small but significant number of sub surface cavities are the product of sulfuric acid speleogenesis sas in the eastern alps no cave has so far been attributed to this type in this multidisciplinary study we demonstrate that kraushohle in northern styria was indeed formed by sas the cave pattern shows individual chambers 3d mazes and blind galleries as well as typical sas morphologies such as cupolas gypsum replacement pockets corrosion notches and convection niches ceiling pendant drip holes are described here for the first time and these corrosion features are fully consistent with the sas model other features of kraushohle include thick gypsum deposits with strongly depleted 34 s values and other minerals mostly sulfates indicating highly acidic conditions we also studied acid rock interaction processes giving rise to widespread corrosion and concomitant replacement by gypsum petrographic and geochemical analyses reveal the presence of a distinctive alteration layer of highly increased porosity at the interface between the host limestone and the secondary gypsum dissolution and replacement of the limestone was fast enough to prevent the development of c and o isotopic alteration halos but resulted in selective leaching of elements this stable isotope signal is thus different from the pronounced isotope gradient commonly observed in co 2 dominated hypogenic caves petrographic observations reveal that the limestone gypsum replacement was a nearly constant volume process

borehole guided avo analysis of p p and p s reflections quantifying uncertainty on density estimates seismic properties of isotropic elastic formations are characterized by the three parameters acoustic impedance poisson s ratio and density whilst the first two are usually well estimated by analysing the amplitude variation with angle ava of reflected p p waves density is known to be poorly resolved however density estimates would be useful in many situations encountered in oil and gas exploration in particular for minimizing risks in looking ahead while drilling we design a borehole seismic experiment to investigate the reliability of ava extracted density receivers are located downhole near the targeted reflectors and record reflected p p and converted p s waves a non linear wide angle based bayesian inversion is then used to access the a posteriori probability distributions associated with the estimation of the three isotropic elastic parameters the analysis of these distributions suggests that the angular variation of reflected p s amplitudes provides additional substantial information for estimating density thus reducing the estimate uncertainty variance by more than one order of magnitude compared to using only reflected p waves

speleogenetic history of the hungarian hydrothermal karst the hydrothermal karst of hungary displays at least two principal stages of development in two differing environments caves of an early stage were formed within a deep zone of low thermal gradient these caves vugs are small tens of centimeters and lined with scalenohedral crystals of calcite that are often in association with barite calcite yields fluid inclusion temperatures of 55 95 c and is depleted in18o 11 2 to 17 6 per mil pdb the caves were formed by ascending thermal waters charged with co2 solubility of caco3 in such a system gradually increases with the ascent of the fluid solutional zone but drops sharply at a depth of 250 m to 500 m below the water surface depositional zone caves formed in the solutional zone may be shifted into the depositional zone due to tectonic uplift and calcite lines their walls large caves tens to thousands of cubic meters of a late stage were formed within a shallow zone of high thermal gradient immediately below and above the thermal water table the calcite of the phreatic crusts has a rhombohedral habit displays lower fluid inclusion temperatures 35 55 c and less and a depletion in18o of 9 5 to 14 6 per mil pdb several powerful cave forming processes may operate there including convection mixing cooling corrosion and condensation corrosion due to differences in the rate of tectonic uplift rate of hydrothermal system decay and hydrogeologic pattern these caves were either filled with water for a long period of time phreatic calcite crusts are formed or partly dewatered early in their history waterline and subaerial speleothems are formed the zones of thermal cave formation recognized in hungary may have a universal character very similar features are found in other hydrothermal karst areas of the world kirghizia algeria south dakota

severity and speed of northern hemisphere glaciation pulses the limiting case a brief pulse of ice sheet growth of enormous amplitude predicted by the theory of milankovitch is confirmed by oxygen isotopic and other evidence in pacific and north atlantic cores this glaciation bisected interglacial isotopic stage 7 lasted no more than 23 000 yr from inception to end and resulted in a very large ice volume buildup and a full glacial climatic response of the north atlantic ocean this pulse along with other episodes of rapid and large scale ice growth does not conform to the conventional sawtooth model of slow ice accumulation and rapid ice decay ice growth rates on such pulses can approach the mean ice decay rates on isotopic glacial terminations

complex resistivity measurements of confined rock complex resistivity was measured for samples of westerly granite and berea sandstone saturated with 0 01 m kclaq a four electrode technique was employed to make measurements over a frequency range of 10 3 to 106 hz and a confining pressure range of 0 2 to 200 mpa when the electrical response was analyzed in terms of equivalent conductivity and relative permittivity k both of these quantities varied more with confining pressure for the granite samples than they did for the sandstone in addition both rock types exhibited large low frequency dispersion of permittivity while previous studies have measured the response of near dc conductivity to changes in pressure measurements of pressure dependence of the full complex resistivity provide greater insight into earthquake related phenomena as well as induced polarization measurements and other remote sensing techniques

mass spectrometric 230th 234u 238u dating of the devils hole calcite vein the devils hole calcite vein contains a long term climatic record but requires accurate chronologic control for its interpretation mass spectrometric u series ages for samples from core dh 11 yielded 230 th ages with precisions ranging from less than 1 000 years 2 for samples younger than 140 ka thousands of years ago to less than 50 000 years for the oldest samples 566 ka the 234 u 238 u ages could be determined to a precision of 20 000 years for all ages calcite accumulated continuously from 566 ka until 60 ka at an average rate of 0 7 millimeter per 10 3 years the precise agreement between replicte analyses and the concordance of the 230 th 238 u 234 u 238 u ages for the oldest samples indicate that the dh 11 samples were closed systems and validate the dating technique in general

hypogene speleogenesis in dolomite host rock by co2 rich fluids kozak cave southern austria a growing number of studies suggest that cave formation by deep seated groundwater hypogene is a more common process of subsurface water rock interaction than previously thought fossil hypogene caves are identified by a characteristic suite of morphological features on different spatial scales in addition mineral deposits speleothems may provide clues about the chemical composition of the paleowater which range from co2 rich to sulfuric acid bearing waters this is one of the first studies to examine hypogene cave formation in dolomite kozak cave is a fossil cave near the periadriatic lineament an area known for its abundance of co2 rich springs the cave displays a number of macro meso and micromorphological elements found also in other hypogene caves hosted in limestone marble or gypsum including cupolas cusps laughohle type chambers and notches the existance of cupolas and cusps suggests a thermal gradient capable of sustaining free convection during a first phase of speleogenesis while triangular cross sections laughohle morphology indicate subsequent density driven convection close to the paleowater table notches mark the final emergence of the cave due to continued rock uplift and valley incision very narrow shafts near the end of the cave may be part of the initial feeder system but an epigene vadose overprint cannot be ruled out vadose speleothems indicate that the phreatic phase ended at least about half a million years ago drill cores show no evidence of carbon or oxygen isotope alteration of the wall rock this is in contrast to similar studies in limestone caves and highlights the need for further wall rock studies of caves hosted in limestone and dolomite

a 250 000 year climatic record from great basin vein calcite implications for milankovitch theory a continuous record of oxygen 18 18o variations in the continental hydrosphere during the middle to late pleistocene has been obtained from a uranium series dated calcitic vein in the southern great basin the vein was deposited from ground water that moved through devils hole an open fault zone at ash meadows nevada between 50 and 310 ka thousand years ago the configuration of the 18o versus time curve closely resembles the marine and antarctic ice core vostok 18o curves however the u th dates indicate that the last interglacial stage marine oxygen isotope stage 5 began before 147 3 ka at least 17 000 years earlier than indicated by the marine 18o record and 7 000 years earlier than indicated by the less well dated antarctic 18o record this discrepancy and other differences in the timing of key climatic events suggest that the indirectly dated marine 18o chronology may need revision and that orbital forcing may not be the principal cause of the pleistocene ice ages

a mechanism to explain the generation of earthquake lights explanations of how earthquake lights might arise have failed to show how large charge densities can be concentrated and sustained in a conductive earth a physical model is proposed based on frictional heating of the fault that solves this and related problems

looking ahead with vertical seismic profiles several operations enhance our ability to predict the subsurface below the bottom total depth td of the well when applied to zero offset vertical seismic profiling vsp data other key issues regarding the use of vsp data in this fashion are resolution and look ahead distance an impedance log is the most useful form for presenting vsp data to look ahead of the drill bit the vsp composite trace must first tie reliably to the surface seismic section and to the well log synthetic seismogram the impedance log is obtained by inverting this vsp composite trace however before performing the inversion we need to 1 correct the composite trace for attenuation effects below td and 2 input velocities to provide low frequency information an exponential gain function applied to the vsp data below td adequately compensates for the loss of amplitude caused by attenuation a calibration of the seismically derived velocities with vsp velocities yields the necessary low frequency information these concepts ar

solution conduits as indicators of late quaternary sea level position abstract solution conduits or caves can provide a measure of glacio eustatic sea level position for the quaternary in high latitudes cave deposits contain artifacts fossils and sediments that reflect surface conditions with respect to climate secondary calcite deposits most notably stalagmites record growth episodes during ice minima and non growth during ice maxima they provide an indirect estimate of areal ice cover at high latitudes and are an indirect measure of sea level in low latitudes stable carbonate platforms contain caves that provide a direct measure of past sea level position solution conduits developing in a fresh water lens will record the position of the lens and therefore sea level as sea level fluctuates fresh water lens horizons and conduit development horizons will shift preserving a record of past sea level position cave wall rock and cave deposits can produce a chronology for given conduit positions secondary calcite deposits notably stalagmites record growth periods during sea level low stands or ice maxima and record growth hiatuses during flooding by sea level high stands or ice minima the inverse of high latitude stalagmites lighthouse cave san salvador island bahamas records a sea level high stand at 1 to 6 m for some time period between 85 000 and 70 000 years ago based on position and timing of conduit development and records sea level at present elevation for some time period between 49 000 and 37 000 years ago based on a stalagmite with a marine overgrowth

condensation corrosion speleogenesis above a carbonate saturated aquifer devils hole ridge nevada abstract the devils hole ridge a small block of paleozoic carbonate rocks surrounded by the amargosa desert in southern nevada is located at the discharge end of the ash meadows regional carbonate groundwater flow system the massif hosts the famous devils hole a near vertical extensional fracture which intersects slightly thermal groundwater 33 6 c and whose walls are coated below the water table by thick mammillary calcite the latter was deposited continuously over the last ca 600 kyr indicating that the water underneath devils hole ridge was supersaturated with respect to calcite during this time span rocks located more than 9 m above the present day water table remained in the unsaturated vadose zone continuous long term presence of thermal water and the extensional tectonic setting creating underground thermal lakes in open fractures is associated with intense dissolution above the water table condensation corrosion is responsible for modifications of the morphology of the subaerial parts of the tectonic caves we also describe for the first time the devils hole prospect cave which was created almost entirely by condensation corrosion caves and cavities in the devils hole ridge are an interesting example of hypogene speleogenesis by condensation corrosion operating above an aquifer which was demonstrably supersaturated with respect to calcite for hundreds of thousands of years

tectonic speleogenesis of devils hole nevada and implications for hydrogeology and the development of long continuous paleoenvironmental records devils hole in southern nevada is a surface collapse into a deep planar steeply dipping fault controlled fissure in cambrian limestone and dolostone the collapse intersects the water table about 15 m below land surface and the fissure extends at least 130 m deeper below water most of the fissure is lined with a 30 cm thick layer of dense maxillary calcite that precipitated continuously from groundwater for 500 000 yr the thick mammillary calcite coat implies a long history of calcite supersaturated groundwaters which combined with the absence of dissolutional morphologies suggests that devils hole was not formed by karst processes devils hole is located in a region of active extension its tectonic origin is shown by evidence of spreading of its planar opening along a fault and by the orientation of its opening and others nearby perpendicular to the northwest southeast minimum principal stress direction of the region most quaternary tectonic activity in the area including seismicity and quaternary faults and fractures occurs on or parallel to northeast striking structures the hydrogeologic implications of this primarily structural origin are that fracture networks and caves opened by extensional tectonism can act as groundwater flowpaths functionally similar to those developed by karst processes and that during active extension transmissivity can be maintained despite infilling by mineral precipitation such extensional environments can provide conditions favorable for accumulation of deposits preserving long continuous paleoenvironmental records the precipitates in devils hole store chronologies of flow system water level fluctuations hydrochemistry a half million yr proxy paleoclimate record evidence of devils hole s tectonic origin and probably atmospheric circulation

complex resistivity of fault gouge and its significance for earthquake lights and induced polarization we have measured complex resistivity of 2 water saturated san andreas fault gouges from 10 3 to 106 hz and confining pressures of 0 2 to 200 mpa consistent with earlier observations of clays and common rocks large low frequency permittivities were observed in all cases comparisons were made to induced polarization ip measurements by inversion of the data into the time domain where we found that principal features of the ip response curves were due to these large low frequency permittivities the results also suggest that following large earthquakes significant electrical charge could remain for many seconds and could result in a variety of reported electromagnetic effects

monte carlo bayesian look ahead inversion of walkaway vertical seismic profiles we describe a method to invert a walkaway vertical seismic profile vsp and predict elastic properties p wave velocity s wave velocity and density in a layered model looking ahead of the deepest receiver starting from bayes s rule we define a posterior distribution of layered models that combines prior information on the overall variability of and correlations among the elastic properties observed in well logs with information provided by the vsp data this posterior distribution of layered models is sampled by a monte carlo method the sampled layered models agree with prior information and fit the vsp data and their overall variability defines the uncertainty in the predicted elastic properties we apply this technique first to a zero offset vsp data set and show that uncertainty in the long wavelength p wave velocity structure results in a sizable uncertainty in the predicted elastic properties we then use walkaway vsp data which contain information on the long wavelength p wave velocity in the reflection moveout and on s wave velocity and density contrasts in the change of reflectivity with offset the uncertainty of the look ahead prediction is considerably decreased compared with the zero offset vsp and the predicted elastic properties are in good agreement with well log measurements

oxygen isotopes sea level changes and the temperature history of a coral reef environment in new guinea over the last 105 years abstract coral reef terraces consisting of an upward succession of fringing and barrier reef types are preserved on land along the raising coast of huon peninsula new guinea seven coral reef units i vii from the coast landwards spaced at about 20 kyr interval provide a rather complete record of sea levels oxygen isotopes and temperature of teh surface tropical ocean over the duration of the high sea level events of the last glacial cycle the systematic sampling of the coral reefs was restricted to the massive tridacna gigas species the giant clam which are about 0 7 0 enriched in 18o relative to calcite equilibrium value and the presence of symbionts seems to have no effect on the 18o of their aragonitic skeleton sea levels rose rapidly to 5 6 5 m above present during the last interglacial which on stratigraphic grounds and 18o compositions can be separated into an early phase whose 18o is similar to modern reef viia dated at 138 kyr and a late phase that is 0 6 0 heavier reef viib dated at 118 kyr fringing reefs vi v iv iii and ii record short lived high sea levels stands at 107 85 60 45 to 40 and 31 kyr respectively that stopped short of the present sea level 12 19 28 32 to 42 m the general decline of the high sea level stands corresponds to an average 18o enrichment of 1 7 0 measured between the early interstadials of isotope stage 5 vi and v and the late interstadials of isotope stage 3 iv iiia iiib and ii the maximum 18o enrichment of 1 7 0 relative to present was registered during a regressive phase of reef iiia stratigraphic evidence indicates that sea level lows in the range of 37 to 55 m below present have occurred in between the high sea level stands but those are unlikely to represent the lowest sea levels of the last glacial cycle sea levels and 18o ddta pair offer important clues regarding the partitioning of ice volume and temperature in 18o records the results suggest that the ice volume effect accounts for the observed 18o changes during the early interstadial culminations but only for 29 46 during the late interstadial culminations sea water cooling beyond the threshold limit of coral reef growth 18 c did not occur during the last glacial cycle the temperature of the surface tropical ocean was similar to present during the early interstadials of isotope stage 5 and cooler by 3 c below present during the later interstadials of isotope stage 3

experimental studies in natural groundwater recharge dynamics the analysis of observed recharge events abstract the amounts and time distribution of groundwater recharge from precipitation over an approximately 19 month period were investigated at two instrumented sites in south central kansas precipitation and evapotranspiration sequences soil moisture profiles and storage changes water fluxes in the unsaturated zone and hydraulic gradients in the saturated zone at various depths soil temperatures water table hydrographs and water level changes in nearby wells clearly depict the recharge process antecedent moisture conditions and the thickness and nature of the unsaturated zone were found to be the major factors affecting recharge although the two instrumented sites are located in sand dune environments in areas characterized by shallow water table and subhumid continental climate a significant difference was observed in the estimated effective recharge the estimates ranged from less than 2 5 to approximately 154 mm at the two sites from february to june 1983 the main reasons for this large difference in recharge estimates were the greater thickness of the unsaturated zone and the lower moisture content in that zone resulting from lower precipitation and higher potential evapotranspiration for one of the sites effective recharge took place only during late winter and spring no summer or fall recharge was observed at either site during the observation period of this study

cainozoic evolution of the state of stress and style of tectonism of the basin and range province of the western united states cainozoic evolution of the modern plate boundary along the western united states from subduction to a predominantly transform boundary coincided with a change from compressional to extensional deformation in the western united states extensions tectonism responsible for the modern basin and range province appears to represent a unique late stage episode of a much longer period of extension initiated in an in tra arc setting contemporaneously with calc alkaline magmatism basin range extension is distinguished from early extension on the basis of angular unconformities differences in fault trends and spacing and associated magmatism basaltic prebasin range extension i e extension preceding the break up of the region into ranges resembling the modern ones was under way locally by at least 30 ma and is now recognized by faulted and highly tilted strata exposed in uplifted range blocks by large regions of the crust underlain by passively emplaced subvolcanic batholiths and by the thickness and distribution of stratigraphic units locally high strain rates that accompanied early extensions of as much as 50 100 are implied data on preferentially orientated dyke swarms and fault slip vectors indicate a strikingly uniform wsw ene least principal stress orientation in the period ca 20 10 ma during this early extension the change from early extension to basin range style faulting of the upper 15 km of crust which resulted in broadly spaced ranges 25 35 km crest crest spacing was time transgressive and probably not abrupt locally both types occurred concurrently southern basin and range block faulting occurred largely in the period 13 10 ma in response to a stress field orientated similarly to that responsible for the early extension in contrast northern basin and range block faulting developed after 10 ma and continues to the present in response to a stress field orientated approximately 45 clockwise to the earlier stress field this modern stress field with a wnw ese to e w directed least principal stress characterizes the entire modern basin and range province and rio grande rift region the 45 change in least principal stress orientation is consistent with superposition of dextral shear associated with the development of the san andreas transform fault inclusion of pre basin range extension may help resolve the discrepancy between estimates of 15 30 for basin range block faulting and total extension estimates of 100 300 for the basin and range province

duration and structure of the past four interglaciations reanalysis and additional dating of the devils hole 18o paleotemperature record confirm that the last interglaciation in the great basin the continental analog of marine isotopic substage 5e lasted 22 000 yr consistent with the vostok paleotemperature record which suggests a duration of 19 000 yr for this event in antarctica the three preceding interglaciations in the devils hole record analogs of marine isotopic substages 7e 9c and 11c range from 20 000 to 26 000 yr in duration a 20 000 yr duration for the last interglaciation is consistent with tims uranium series dated sea level high stands thus the widely held view that interglaciations were of 11 000 to 13 000 yr duration and constituted only about 10 of mid to late pleistocene climatic cycles needs reexamination the warmest portion of each interglaciation in the devils hole time series is marked by a 18o plateau signifying apparent climatic stability for periods of 10 000 to 15 000 yr duration

the distribution of 230th234u ages in corals and the number of last interglacial high sea stands abstract the 104 available 230 th 234 u analyses of unrecrystallized corals from stable emerged terraces indicate that the last interglacial period occurred approximately 125 000 yr ago an estimate is made of the exact duration of this period by accounting for the surprisingly small distribution width observed among the 80 most reliable analyses this distribution width is compared with those obtained for model populations generated by assuming various characteristic analytical errors and various lengths of the last interglacial period the results show that 1 if there was only a single rise in sea level it probably lasted no more than 12 000 yr in agreement with previous estimates and 2 if there were two separate rises of sea level the gap between them must have been less than 7500 yr and not 12 200 as proposed by some authors

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

changes in complex resistivity during creep in granite a sample of westerly granite was deformed under constant stress conditions a pore pressure of 5 mpa a confining pressure of 10 mpa and an axial load of 170 mpa pore volume changes were determined by measuring the volume of pore fluid 0 01m kclaq injected into the sample after 6 days of creep characterized by accelerating volumetric stain the sample failed along a macroscopic fault measurements of complex resistivity over the frequency range 0 001 300 hz taken at various times during creep showed a gradual increase in both conductivity and permittivity when analysed in terms of standard induced polarization ip techniques the changing complex resistivity resulted in systematic changes in such parameters as percent frequency effect and chargeability these results suggest that it may be possible to monitor the development of dilatancy in the source region of an impending earthquake through standard ip techniques

electromagnetic precursors to earthquakes in the ulf band a review of observations and mechanisms despite over 2 decades of international and national monitoring of electrical signals with the hope of detecting precursors to earthquakes the scientific community is no closer to understanding why precursors are observed only in some cases laboratory measurements have demonstrated conclusively that self potentials develop owing to fluid flow and that both resistivity and magnetization change when rocks are stressed however field experiments have had much less success many purported observations of low frequency electrical precursors are much larger than expectations based on laboratory results in some cases no precursors occurred prior to earthquakes or precursory signals were reported with no corresponding coseismic signals nonetheless the field experiments are in approximate agreement with laboratory measurements maximum resistivity changes of a few percent have been observed prior to some earthquakes in china but the mechanism causing those changes is still unknown anomalous electric and magnetic fields associated with fluid flow prior to earthquakes may have been observed finally piezomagnetic signals associated with stress release in earthquakes have been documented in measurements of magnetic fields

computer processing of vertical seismic profile data vertical seismic profiles vsp are a powerful tool in a variety of seismic exploration situations only after extensive computer processing of the raw field data however can the full value of this tool be realized with the help of processing relations between important rock parameters and acoustic properties can sometimes be established and highly reliable ties from well logs to surface seismic profiles can usually be obtained the basic theory of the processing techniques is well known however the techniques used in processing standard surface seismic profiles usually must be modified to adapt them to the unique conditions associated with vsps processing procedures and their relevance to the interpretation of vsp and surface seismic profile data are described

the last pluvial climatic episodes in the deserts of southwestern north america long term variations in the effective moisture of deserts are linked both to glacial interglacial climatic cycles and through the milankovitch theory to orbitally induced changes in solar radiation intensity1 4 for southwestern north america comparison of palaeobotanical data with model predictions of palaeoclimate reveals two distinct pluvial regimes during the late wisconsin and early holocene 23 8 kyr bp southward displacement of the aleutian low pressure centre and strengthened westerlies from 40 to 30 n were important features of the full glacial 18 kyr bp pluvial maximum increased cyclonic storms and weakened monsoons led to a winter precipitation regime a feature seen both in the fossil record5 6 and climate models7 8 dominantly zonal flow during this period contrasts with the latest wisconsin and early holocene 12 8 kyr bp when meridional circulation transported maritime tropical air into the desert interior we now show that plant macrofossil assemblages from packrat neotoma spp middens9 in the mojave desert provide evidence for increased temperatures and summer rainfall during this period10 12 the anomalously late persistence to 8 kyr bp of woodland in low latitude low elevation deserts of the south west13 is attributed to enhanced monsoonal circulation3

the last interglacial ocean the final effort of the climap project was a study of the last interglaciation a time of minimum ice volume some 122 000 yr ago coincident with the substage 5e oxygen isotopic minimum based on detailed oxygen isotope analyses and biotic census counts in 52 cores across the world ocean last interglacial sea surface temperatures sst were compared with those today there are small sst departures in the mid latitude north atlantic warmer and the gulf of mexico cooler the eastern boundary currents of the south atlantic and pacific oceans are marked by large sst anomalies in individual cores but their interpretations are precluded by no analog problems and by discordancies among estimates from different biotic groups in general the last interglacial ocean was not significantly different from the modern ocean the relative sequencing of ice decay versus oceanic warming on the stage 6 5 oxygen isotopic transition and of ice growth versus oceanic cooling on the stage 5e 5d transition was also studied in most of the southern hemisphere the oceanic response marked by the biotic census counts preceded led the global ice volume response marked by the oxygen isotope signal by several thousand years the reverse pattern is evident in the north atlantic ocean and the gulf of mexico where the oceanic response lagged that of global ice volume by several thousand years as a result the very warm temperatures associated with the last interglaciation were regionally diachronous by several thousand years these regional lead lag relationships agree with those observed on other transitions and in long term phase relationships they cannot be explained simply as artifacts of bioturbational translations of the original signals

two million year record of deuterium depletion in great basin ground waters fluid inclusions in uranium series dated calcitic veins from the southern great basin record a reduction of 40 per mil in the deuterium content of ground water recharge during the pleistocene this variation is tentatively attributed to major uplift of the sierra nevada range and the transverse ranges during this epoch with attendant increasing orographic depletion of deuterium from inland bound pacific storms

stick slip charge separation and decay measurements of charge separation in rock during stable and unstable deformation give unexpectedly large decay times of 50 sec time domain induced polarization experiments on wet and dry rocks give similar decay times and suggest that the same decay mechanisms operate in the induced polarization response as in the relaxation of charge generated by mechanical deformation these large decay times are attributed to electrochemical processes in the rocks and they require low frequency relative permittivity to be very large in excess of 105 one consequence of large permittivity and therefore long decay times is that a significant portion of any electrical charge generated during an earthquake can persist for tens or hundreds of seconds as a result electrical disturbances associated with earthquakes should be observable for these lengths of time rather than for the milliseconds previously suggested

late quaternary u series speleothem growth record from southeastern minnesota southeastern minnesota contains an extensive karst developed in limestones and dolomites ranging in age from early ordovician to middle devonian preliminary results from u series dated speleothems from caves within the karst show cyclic deposition of secondary calcium carbonate that coincides with cycles of late pleistocene glaciation peak intervals of deposition which broadly correlate with interglacial or interstadial climates occur from the present to 13 000 yr b p from 35 000 to 70 000 yr b p from 90 000 to 170 000 yr b p and an undivided interval from 170 000 to 350 000 yr b p intervals of little or no deposition are thought to reflect glacial climates the youngest growth intervals can be interpreted in terms of known glacial records in the midwest but for the older intervals where the glacial record is not well defined and beyond the range of radioactive dating it becomes more difficult to correlate speleothem deposition to glacial cycles although the groups of ages are in general agreement with sea level curves the correlation is not exact local climatic conditions seem to have had as much importance in determining when deposition occurred as did the major climatic cycles recorded in the marine record

earthquake prediction by animals evolution and sensory perception animals living within seismically active regions are subjected episod ically to intense ground shaking that can kill individuals through burrow collapse egg destruction and tsunami action although anecdotal and retrospective reports of animal behavior suggest that although many organisms may be able to detect an impending seismic event no plausible scenario has been presented yet through which accounts for the evolution of such behaviors the evolutionary mechanism of ex aptation can do this in a two step process the first step is to evolve a vibration triggered early warning response which would act in the short time interval between the arrival of p and s waves anecdotal evidence suggests this response already exists then if precursory stimuli also exist similar evolutionary processes can link an animal s perception of these stimuli to its p wave triggered response yielding an earthquake predictive behavior a population genetic model indicates that such a seismic escape response system can be maintained against random mutations as a result of episodic selection that operates with time scales comparable to that of strong seismic events hence additional understanding of possible earthquake precursors that are presently outside the realm of seismology might be gleaned from the study of animal behavior sensory physiology and genetics a brief review of possible seismic precursors suggests that tilt hygroreception humidity electric and mag netic sensory systems in animals could be linked into a seismic escape behavioral system several testable predictions of this analysis are discussed and it is recom mended that additional magnetic electrical tilt and hygro sensors be incorporated into dense monitoring networks in seismically active regions

devils hole paleotemperatures and implications for oxygen isotope equilibrium fractionation subaqueous calcite in devils hole nevada was growing continuously from slightly super saturated groundwater providing a 570 kyr long o18 paleoclimate record due to its very slow growth it has been assumed to have grown under conditions of isotopic equilibrium however its holocene o18 value is 1 5 higher than predicted by laboratory precipitation based oxygen isotope thermometer calibrations the suggestion that devils hole calcite anchors the isotope thermometer to more 18o enriched values has stirred a debate as to which paleothermometer calibration is relevant for paleoclimate and casts doubt on the validity of o18 based paleotemperatures we used clumped isotopes to test the assumptions of the devils hole alternative 18o thermometer carbonate clumped isotopes are a temperature proxy that measures the abundance of 13c18o bonds in caco3 this proxy is independent of the water composition and therefore gives independent estimates of temperatures when calcite forms at thermodynamic and isotopic equilibrium we find that devils hole water paleotemperatures were constant at 30 6 2 6 c between 27 and 180 ka similarly to the modern groundwater temperature of 32 8 34 3 c the proximity of the devils hole clumped isotope data to values expected based on modern groundwater temperatures supports the notion that devils hole calcite grew under equilibrium conditions therefore the commonly used laboratory based o18 temperature calibrations should be reconsidered the constant water temperature over the glacial interglacial cycles indicates that the long devils hole o18 record reflects only variations in the groundwater o18 values and as such represents a valuable archive of paleoclimate and isotope paleohydrology

relationship between karstification and burial dolomitization in permian platform carbonates lower khuff oman large breccia fabrics associated with karst constitute an important structure in massive limestone successions the dimensions and shapes of breccia structures are controlled by the initial fracture pattern of the limestone and preferential pathways of the karstifying fluids but subsequently breccia fabrics can also govern the migration of later fluids therefore breccias are highly relevant features to capture for reservoir characterisation outcrop analogues for lower khuff units in the middle east present in the central oman mountains reveal brecciated fabrics up to 10 s of meters in diameter these brecciated units are closely associated with dolomite bodies of late diagenetic origin based on an integrated set of data the breccias are interpreted as collapsed karst cavities either formed by meteoric or hypogenic fluids the exact origin of the fluids could not be constrained due to an overprint by later dolomitizing fluids based on the composition of the clasts and matrix in the breccias two dolomitization events are interpreted to have affected the succession one prior to early diagenetic ed dolomite and one after brecciation late diagenetic dt2 dolomite dolomite of shallow burial origin ed dolomite was only observed as clasts within breccia and is much more frequent than late diagenetic medium to deep burial dolomite clasts thus the timing of the brecciation and collapse is assumed to postdate shallow burial early diagenetic dolomitization late diagenetic replacive dolomite dt2 dolomite forms 90 of the matrix in the breccia fabrics with the exception of a small area that was not affected by dolomitization but is rarely present as clasts stable isotope measurements 18o 2 5 to 6 vpdb and 13c 2 9 to 4 8 vpdb suggest a burial origin for the late diagenetic dolomite potentially with the participation of hydrothermal fluids the dolomitized matrix indicates a migration of late dolomitizing fluids subsequent to or postdating the collapse of the karstic cavities thus early karstification processes seem to have played a big role in controlling subsequent loci of late dolomitization in the oman mountains and potentially in other similar settings elsewhere

uranium series dating of sediments from searles lake differences between continental and marine climate records one of the major unresolved questions in pleistocene paleoclimatology has been whether continental climatic transitions are consistent with the glacial 18 o marine record searles lake in california now a dry salt pan is underlain by sediment layers deposited in a succession of lakes whose levels and salinities have fluctuated in response to changes in climate over the last 3 x 10 6 years uraniumseries dates on the salt beds range from 35 x 10 3 to 231x 10 3 years this range of dates allows identification of lake sediment horizons that are time correlatives of the boundaries of marine isotope stages from the recent 3 4 boundary back to the 8 9 boundary the 5 6 boundary coincided with a deepening of the lake but the analogous 1 2 boundary coincided with desiccation the 3 4 4 5 6 7 7 8 and 8 9 boundaries correspond in age to horizons that record little or no change in sedimentation or climate these hydrologic results demonstrate that the continental paleoclimate record at this mid latitude site does not mimic the marine record

hypogenic origin geologic controls and functional organization of a giant cave system in precambrian carbonates brazil abstract this study is focused on speleogenesis of the toca da boa vista tbv and toca da barriguda tbr the longest caves in south america occurring in the neoproterozoic salitre formation in the sao francisco craton ne brazil we employ a multidisciplinary approach integrating detailed speleomorphogenetic lithostratigraphic and geological structure studies in order to reveal the origin of the caves their functional organization and geologic controls on their development the caves developed in deep seated confined conditions by rising flow the overall fields of passages of tbv and tbr caves represent a speleogenetically exploited large ne sw trending fracture corridor associated with a major thrust this corridor vertically extends across the salitre formation allowing the rise of deep fluids in the overall ascending flow system the formation of the cave pattern was controlled by a system of sub parallel anticlines and troughs with nne ssw dominant orientation and by vertical and lateral heterogeneities in fracture distribution three cave stratigraphic stories reflect the actual hydrostratigraphy during the main phase of speleogenesis cavities at different stories are distinct in morphology and functioning the gross tree dimensional pattern of the system is effectively organized to conduct rising flow in deep seated confined conditions cavities in the lower story developed as recharge components to the system a laterally extensive conduit network in the middle story formed because the vertical flow from numerous recharge points has been redirected laterally along the highly conductive unit occurring below the major seal a scarcely fractured unit rift like and shaft like conduits in the upper story developed along fracture controlled outflow paths breaching the integrity of the major seal and served as outlets for the cave system the cave system represents a series of vertically organized functionally largely independent clusters of cavities developed within individual ascending flow cells lateral integration of clusters occurred due to hydrodynamic interaction between the flow cells in course of speleogenetic evolution and change of boundary conditions the main speleogenetic phase during which the gross cave pattern has been established and the caves acquired most of their volume was likely related to rise of deep fluids at about 520 ma or associated with rifting and the pangea break up in triassic cretaceous this study highlights the importance of speleogenetic studies for interpreting porosity and permeability features in carbonate reservoirs

vertical seismic profiling vertical seismic profiling is one of the rapidly developing areas of geophysical technology for exploring in mature basins the measurement basically involves recording the total upgoing and downgoing seismic wave fields propagating through a stratigraphic section by means of geophones clamped to the wall of a drilled well

vertical seismic profile reflectivity ups over downs the idea of designing a deconvolution operator for the vertical seismic profile vsp based on its downgoing waves is well known anstey 1976 gaiser et al 1984 hubbard 1979 lee and balch 1983 kennett et al 1980 many variations of the scheme exist anstey 1976 recommends the average of the downgoing wave from all levels as the basis for designing an inverse operator lee and balch 1983 use the downgoing wave from a single level to deconvolve all the vsp traces gaiser et al 1984 and hubbard 1979 recommend doing the deconvolution independently at each depth level as observed by hubbard there are similar disparities in the literature about whether all or only part of the downgoing wave train should be used in the design of an inverse operator although all of the above approaches are identical if multiples are generated in a limited zone near the sea bottom they differ for more complex media we recommend and in this note we explore the theoretical properties of the level by level deconvolution based on the entire downgoing wave train the expressions we develop apply to the general case of the vertical vsp response to any number of horizontal layers with any degree of complexity in the process that generates multiples

deep water formation and quaternary glaciations a large fraction of climatic varability on the quaternary time scale can be explained by nonlinear interactions between the radiation balance of the global atmosphere ocean system and the mass balance of northern hemisphere ice sheets recent analyses of paleoclimatic proxy data indicate a further important contribution to this variability from changes in deep water formation occurring in the north atlantic subpolar sea we study the effects of these changes on variations in global temperature and ice volume characteristic of the late quaternary the novel framework of boolean delay equations bdes is used to formulate a conceptual model of the climatic system under study and to analyze this formal model selfsustained oscillations in the intensity of the atlantic ocean s thermohaline circulation result from the interaction of sea ice formation with the waxing and waning of continental ice sheets the comparison of model results with paleoclimatic records suggests a considerable slowing down of the abyssal circulation during glacial episodes