sequence stratigraphy in a mixed carbonate silicilastic depositional system middle miocene styrian basin austria the mixed carbonate siliciclastic weisenegg allo formation records three depositional sequences corresponding approximately to the tb 2 3 tb 2 4 and tb 2 5 global cycles sea level fluctuations were of the order of at least 30 m siliciclastic lowstand systems tracts comprise lignite deposits reworked basement and tidal siltstones above a tectonically enhanced sequence boundary as well as coastal sand bars coastal sands of the transgressive systems tract contain distinct layers of well cemented nodules they are interpreted as the first stage in hardground formation and record superimposed minor sea level fluctuations coral patch reefs and rhodolith platforms developed during transgressive phases and were subsequently drowned and or suffocated by siliciclastics during early highstand shallowing upwards siliciclastic parasequences each terminated by a bank of rhodolith limestone form the late highstand systems tract the limestone beds record superimposed fourth order transgressive pulses occasionally a carbonate highstand wedge developed lowstand carbonate shedding occurred where the top of a platform which suffered incipient drowning during highstand was near sealevel again during the following lowstand late highstand delta progradation is common

middle miocene ocean climate transition high resolution oxygen and carbon isotopic records from deep sea drilling project site 588a southwest pacific high resolution stable isotopic records are presented for the epi benthic foraminifer cibicidoides the inferred shallow dwelling planktonic globigerinoides quadrilobatus and the inferred deep dwelling planktonic globoquadrina dehiscens from the middle miocene 16 12 ma of deep sea drilling project site 588a lord howe rise southwest pacific high resolution multiple species oxygen and carbon isotopic data define the timing and character of the well known middle miocene climatic oceanographic transition with a resolution comparable to quaternary records the benthic foraminiferal 18o record is marked by several large fluctuations from 16 to 14 8 ma followed by a series of rapid 50 kyr 18o increases that suggest a new state of the ocean climate system after 14 8 ma the total middle miocene benthic oxygen isotopic increase of 1 2 is largely incorporated in two steps an increase of 0 8 from 14 5 to 14 0 ma and a second increase of 0 7 from 13 45 to 12 45 ma each step is comprised of a series of marked 18o increases indicative of rapid east antarctic ice sheet growth and contemporaneous deepwater cooling a strong covariance of 0 7 between the benthic and deep dwelling planktonic species from 14 5 to 14 0 ma including a rapid increase from 14 1 to 14 05 ma suggests a 0 7 increase in the 18o composition of seawater 18osw because of east antarctic ice sheet growth comparison of the 18o record of gs quadrilobatus suggests that surface waters warmed at this site by 3 c from 14 1 to 13 6 ma carbon isotopic time series for each species generally covary throughout the early to middle miocene interval 16 12 ma confirming that 13c variations in this interval largely represent reservoir changes high resolution 13c data allow improved resolution of the latter five of six 13c maxima within the well known early to middle miocene carbon isotopic excursion the monterey carbon isotopic excursion from 17 0 to 13 5 ma this is useful for global correlation the last of these maxima ends with a 1 decrease centered from 13 9 to 13 7 ma 300 kyr after the 18o increase considered to reflect east antarctic ice growth covariance between benthic 18o and 13c from 16 to 13 8 ma suggests a sensitive relation between global carbon cycling and the ocean climate system prior to 13 8 ma episodic increases in organic carbon burial may have contributed to deep sea benthic 13c maxima and synchronous global cooling the positive relationship ended at 13 8 ma indicative of changing relations between global carbon cycling and the ocean climate system brought on by the increased stability of the east antarctic ice sheet after a major growth phase from 14 5 to 14 0 ma

middle miocene southern ocean cooling and antarctic cryosphere expansion magnesium calcium data from southern ocean planktonic foraminifera demonstrate that high latitude similar to55degreess southwest pacific sea surface temperatures ssts cooled 6degrees to 7degreesc during the middle miocene climate transition 14 2 to 13 8 million years ago stepwise surface cooling is paced by eccentricity forcing and precedes antarctic cryosphere expansion by similar to60 thousand years suggesting the involvement of additional feedbacks during this interval of inferred low atmospheric partial pressure of co2 pco 2 comparing ssts and global carbon cycling proxies challenges the notion that episodic pco2 drawdown drove this major cenozoic climate transition sst salinity and ice volume trends suggest instead that orbitally paced ocean circulation changes altered meridional heat vapor transport triggering ice growth and global cooling

piezornagnetic field for parkfield fault model a theoretical piezomagnetic field is calculated as a function of time and ground position for an earthquake instability model applied to moderate m 6 earthquakes on the san andreas fault near parkfield california the instability model simulates fault slip and stress for all parts of a 32 year earthquake cycle including unstable mainshock slip mainshock slip occurs when a nearly locked patch of the fault becomes sufficiently loaded by surrounding aseismic slip that it reaches a condition of rapid failure the piezomagnetic field is calculated directly from fault slip using analytic solutions based on piezomagnetic nuclei that are analogous to strain nuclei during the interseismic interval increasing stress concentration on the locked patch is accompanied by a gradual evolution of the magnetic anomaly field leading to maximum cumulative changes of about 2 nt in the vicinity of the pending epicenter mainshock slip cancels about half of the interseismically accumulated changes and rapid post seismic relaxation cancels most of the rest at certain sites near the locked patch the rate of change of the field progressively increases during the interseismic interval while at others it progressively decreases this effect is most pronounced during the last 3 4 years before the mainshock and at suitably chosen pairs of sites results in reversal of the temporal trend of the differential field such reversals if separable from geomagnetic variation due to other sources would constitute precursory indicators of approaching failure

seismomagnetic observation during the 8 july 1986 magnitude 5 9 north palm springs earthquake a differentially connected array of 24 proton magnetometers has operated along the san andreas fault since 1976 seismomagnetic offsets of 1 2 and 0 3 nanotesla were observed at epicentral distances of 3 and 9 kilometers respectively after the 8 july 1986 magnitude 5 9 north palm springs earthquake these seismomagnetic observation are the first obtained of this elusive but long anticipated effect the data are consistent with a seismomagnetic model of the earthquake for which right lateral rupture of 20 centimeters is assumed on a 16 kilometer segment of the banning fault between the depths of 3 and 10 kilometers in a region with average magnetization of 1 ampere per meter alternative explanations in terms of electrokinetic effects and earthquake generated electrostatic charge redistribution seem unlikely because the changes are permanent and complete within a 20 minute period

use of tidal circulation modeling in paleogeographical studies an example from the tertiary of the alpine perimeter tidal conditions in ancient shallow marine basins as revealed by preserved sedimentary deposits reflect the strong influence of the paleobathymetry use of a tidal circulation model can test existing paleobathymetric reconstructions meso and macrotidal conditions are believed to have existed throughout most of the miocene molasse france and switzerland seaway tidal simulations using external tidal ranges of 2 and 4 m entering from the south mediterranean fail to generate mesotidal conditions in the majority of the seaway because of a narrow constriction in the present alpes du dauphine and drome areas meso tidal conditions are simulated in the rhone alp part of the seaway only after the postulated paleobathymetry is widened in the alpes du dauphine area this change allows tidal penetration from the mediterranean despite this widening the new simulations fail to generate mesotidal conditions in the swiss part of the seaway mesotidal conditions are simulated in switzerland with the addition of a second tidal input from eastern switzerland favoring an interpretation that the swiss part of the seaway was connected with either the eastern mediterranean or the indo pacific ocean the revised paleobathymetry brackets uplift events that affected the basin margin

the parkfield prediction fallacy abstract the parkfield earthquake prediction is generally stated as a 95 probability that the next moderate earthquake there should occur before january 1993 that time limit is based on a two sided 95 confidence interval because at the time of the prediction 1985 it was already clear that the earthquake had not occurred prior to 1985 a one sided 95 confidence interval would have been more appropriate that confidence interval ended in october 1991 the parkfield prediction was based on an extrapolation of five of the six events in the 1857 to 1966 earthquake sequence the 1934 event was omitted because it did not fit the regularity exhibited by the other data the fallacy in the prediction is that it did not take account of other less contrived explanations of the parkfield seismicity e g not excluding the 1934 event even if the parkfield earthquake should occur in the near future it would be better explained by less contrived hypotheses

middle miocene seasonal temperature changes in the styrian basin austria as recorded by the isotopic composition of pectinid and brachiopod shells abstract using the isotope record on pectinid and brachiopod shells we reconstructed middle miocene palaeotemperatures for a shelf environment in the styrian basin austria bivalve shells of macrochlamys sp collected from different horizons of the lower badenian leitha limestone show 18 o values in the range of 3 to 0 peedee belemnite the large intrashell variability of 3 indicates significant seawater temperature fluctuation the results suggest that despite the high geographical latitude ca 40 n the climate in southern austria was warm subtropical with a pronounced seasonality at that time in contrast the 18 o isotopic composition of a pectinid flabellipecten sp and an indeterminate terebratulid brachiopod from the siliciclastic deposits overlying the leitha limestone ranges between 0 and 1 this indicates cooler mean annual temperatures and reduced seasonal variations a 39 ar 40 ar age on fresh volcanic biotites shows a value of 14 2 0 1 ma the tuffs containing the biotites are located below the layer containing the terebratulid and the flabellipecten sp the stable isotope and radiogenic data suggest that the drop in temperature is in direct relationship with the east antarctic ice sheet expansion which started at ca 14 ma due to the variation in temperature the subtropical fauna in the retznei quarry disappeared during the early miocene and the biogenic limestones were replaced by clastic sediments the 18 o isotopic profiles from three pectinids collected from the leitha limestone indicate that these grew within ca 1 5 years growth interruptions occurred during the warm season because during this period the pectinids very likely used their energy for the growth and maturation of gonads carbon isotopic compositions vary between 0 and 2 statistical tests show that for some of the analyzed shells the cyclicity of the 13 c profiles may be explained by the temperature dependent fractionation between air co 2 and dissolved bicarbonate

fault model for preseismic deformation at parkfield california we construct an earthquake instability model to estimate precursory faulting and ground deformation before the next moderate m 5 5 6 earthquake on the san andreas fault near parkfield california the quasi static model simulates fault slip fault shear stress and ground deformation for all stages of repeated earthquake cycles unstable slip which is the analog of a moderate parkfield mainshock is caused by overall failure of a postulated strong area or patch of the fault zone the brittle patch and surrounding weaker viscous fault are defined by the sign of a spatially varying coefficient of a slip rate dependent fault law stable failure of the patch leading up to mainshock failure causes slip rate to increase at depth amplitudes and timescales of the resulting preseismic deformation anomalies are found for the current earthquake cycle at parkfield starting just after the 1966 mainshock in two ways in the first way we vary parameter values in a sequence of simulations so as to find the simulation giving best agreement with locations moments and recurrence times of past moderate earthquakes and also with fault creep and trilateration line length changes since the 1966 mainshock in the second way we assign values of most parameters from laboratory friction experiments and a temperature depth profile inferred from heat flow data overall agreement between model results and observations is comparable for the two methods in all simulations preseismic deformation anomalies arise from slip rate increase near the model earthquake focus and start several years or less before instability preseismic anomalies in surface fault creep and line length are always too small to detect in current measurements however for some simulations constrained mainly by field data the predicted anomalies in borehole dilatation are large enough to detect

magnetic field observations in the near field the 28 june 1992 mw 7 3 landers california earthquake recent reports suggest that large magnetic field changes occur prior to and during large earthquakes two continuously operating proton magne tometers lsbm and ochm at distances of 17 3 and 24 2 km respectively from the epicenter of the 28 june 1992 mw 7 3 landers earthquake recorded data through the earthquake and its aftershocks these two stations are part of a differentially connected array of proton magnetometers that has been operated along the san andreas fault since 1976 the instruments have a sensitivity of 0 25 nt or better and transmit data every 10 min through the goes satellite to the usgs headquarters in menlo park california seismomagnetic offsets of 1 2 0 6 and 0 7 0 7 nt were observed at these sites in comparison offsets of 0 3 0 2 and 1 3 0 2 nt were observed during the 8 july 1986 mt 5 9 north palm springs earthquake which occurred directly beneath the ochm magnetometer site the observations are generally consistent with seismomagnetic models of the earthquake in which fault geometry and slip have the same form as that determined by either inversion of the seismic data or inversion of geodetically determined ground displacements produced by the earthquake in these models right lateral rupture occurs on connected fault seg ments in a homogeneous medium with average magnetization of 2 a m the fault slip distribution has roughly the same form as the observed surface rupture and the total moment release is 1 1 1020 nm there is no indication of dif fusion like character to the magnetic field offsets that might indicate these ef fects result from fluid flow phenomena it thus seems unlikely that these earth quake generated offsets and those produced by the north palm springs earthquake were generated by electrokinetic effects also there are no indications of en hanced low frequency magnetic noise before the earthquake at frequencies be low 0 001 hz

paleogeographic evolution of the late miocene lake pannon in central europe abstract the paleogeographic evolution of lake pannon within the pannonian basin is reconstructed with eight maps ranging from the middle miocene to the early pliocene the maps are based on the distribution of selected biozones and specific fossils and on complementary sedimentological and seismic information our reconstruction shows that the history of lake pannon can be divided into three distinct intervals an initial stage with low water level which resulted in isolation from the sea at about 12 ma and might have led to temporary fragmentation of the lake an interval of gradual transgression lasting until ca 9 5 ma and a long late interval of shrinkage and infilling of sediments that persisted into the early pliocene the deep subbasins of the lake formed during the transgressive interval in more basinward locations than the deep basins of the preceding sarmatian age the southern shoreline running parallel with the sava and danube rivers along the northern foot of the dinarides changed very little during the lifetime of the lake while the northern shoreline underwent profound changes

a numerical model of earthquake induced piezomagnetic anomalies a numerical model for evaluating the order of magnitude of earthquake induced piezomagnetic anomalies is proposed the stress field associated with normal or reverse faulting with a 10 mpa mean stress drop is determined by mean of displacement discontinuity method the induced piezomagnetic tensor is then used to predict the associated magnetic field variations observed at ground surface the model shows that for earthquakes occurring in homogeneous magnetic masses with piezomagnetic properties of andesite rocks the associated anomalies are of the order of 0 2 nt for faults with a 5 km dip slip and 2 nt when the dip slip is 20 km long the variation of magnetic field for the case of a piezomagnetic dyke intruding a nonmagnetic body is found to be much greater for a 4 km thick dyke parallel to the fault and located 4 km from it the observed ground surface magnetic field variation is of the order of 10 nt these results outline that induced piezomagnetic effects strongly depend on the stress drop and stress distribution along and outside the fault the location of the earthquake source with respect to the piezomagnetic body and the piezomagnetic properties of the rock

forecast model for moderate earthquakes near parkfield california earthquake instability models have possible application to earthquake forecasting because the models simulate both preseismic and coseismic changes of fault slip and ground deformation in the forecast procedure proposed here repeated measurements of preseismic fault slip and ground deformation constrain the values of model parameters the early part of the model simulation corresponds to the available field data and the subsequent part constitutes an estimate of future faulting and ground deformation in particular the time location and size of unstable faulting are estimates of the pending earthquake parameters the forecast accuracy depends on the model realism and parameter resolution the forecast procedure is applied to fault creep and trilateration data measured near parkfield california where at least five magnitude 5 5 to 6 earthquakes have occurred regularly since 1881 the last in 1966 the quasi static model consists of a flat vertical plane embedded in an elastic half space spacially variable fault slip of strike slip sense is driven by an increasing regional shear stress but is impeded by a relatively strong patch of brittle strain softening fault the field data are consistent with these approximate values of patch parameters radius of 3 km patch center 5 km deep and 8 km southeast of the 1966 epicenter and maximum brittle strength of 26 bars fluctuations in the available field data prevent estimating the earthquake time with any more precision than use of the 21 8 year recurrence interval however the model may later give a more precise estimate of the earthquake time if the fault slip rate near the inferred patch increases before the earthquake as predicted by the model

recurrence models and parkfield california earthquakes main shocks of the earthquake sequences that occurred on the parkfield section of the san andreas fault in central california in 1922 1934 and 1966 are characterized by southeast rupture expansion over the same 20 to 30 km long section of the fault whereas the seismic moments for the 1922 and 1934 events are identical to within a precision of 10 the seismic moment for 1966 is 20 greater than for the earlier events to within a precision of 20 the parkfield area seismicity in general seems well described by a recurring moderate size characteristic earthquake repeating the same epicenter magnitude seismic moment rupture area and southeast direction of rupture expansion an unexplained 10 year advance of the 1934 event is the only discrepancy in the hypothesis that the parkfield earthquakes in 1857 1881 1901 1922 1934 and 1966 represent a strictly periodic process assuming the strictly periodic model and the absence since 1966 of the perturbations hypothesized for the 1922 to 1934 period the next characteristic parkfield earthquake should occur between 1983 and 1993

secular variation crustal contributions and tectonic activity in california 1976 1984 five to ten years of data from an array of 34 total field magnetometers are used to define the temporal and spatial characteristics of secular variation throughout central and southern california for this period well determined rates of secular variation are obtained at each site these rates are temporally linear but spatially variable ranging from 45 nt a near san francisco to 54 nt a near the mexican border least squares analysis of all data indicates secular variation decreases in a general southeasterly direction according to f k1 k2 k where f is in nanoteslas per year and are the geographic latitude and longitude and k1 k2 and k are 1 66 0 13 nt a deg 0 13 0 10 nt a deg and 123 2 0 2 nt a respectively deviations of as much as 1 nt a occur on scales of a few tens of kilometers these apparent small scale secular variation anomalies result in part from differences in local induction and remanent magnetization and may be reduced by determination of a site transfer function a planar surface fit to the corrected data has the form f k1 k2 k where k1 k2 and k are now 1 50 0 08 nt a deg 0 23 0 06 nt a deg and 129 2 0 1 nt a respectively residual field variations obtained after correction of all data for secular variation are most apparent on the san andreas fault in southern california between palm springs and the salton sea and marginally so along the recent coyote ml 5 9 of august 6 1979 and morgan hill ml 5 8 of april 24 1984 aftershock zones these residuals could be explained by stress localization in these regions and particularly in the case of the southern san andreas anomaly may indicate the location of a future damaging earthquake incomplete correction for complex site effects may be an alternative explanation in the first large scale test of global secular variation models we find that the models for this region do not predict either the amplitudes or the mean isogram directions of these data to better than several tens of nanoteslas per year and several tens of degrees respectively this may result from a failure to correct for site response effects at some observatories before using the data in global spherical harmonic expansions local magnetization response can therefore bias estimates of secular variation and yield apparent impulsive behavior when external fields are perturbed

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

benchmark data of a changing sea palaeogeography palaeobiogeography and events in the central paratethys during the miocene abstract the reconstruction and interpretation of terrestrial ecosystems and vegetational patterns in the central european miocene have to take into account the influence of a vast landlocked water body namely the paratethys sea as a northern appendage of the early mediterranean sea it spanned a north south gradient of at least 4 latitude and has been suggested to represent some kind of palaeothermometer which reflected slight expansions or restrictions of climatic belts due to its vulnerable marine connections it was also highly susceptible to major global sea level fluctuations which are reflected in phases of endemism hence a fairly continuous record of marine nearshore assemblages throughout the miocene reflects an extraordinary interplay of sea level fluctuations changes in climate immigrations and blooms in autochthonous elements whilst biostratigraphic implications of these patterns were recognised early in palaeontology a biogeographic model is still lacking the intermingling of palaeogeographic terms with those restricted to biogeography is still commonly used a situation which can be overcome by integrating data from different biota into a new palaeobiogeographic scheme herein a data set of 1809 species level taxa gastropoda and foraminifera serves as the base for interpretations gastropods in particular turned out to be of greatest value for the differentiation of palaeobiogeographic units due to sensitive reactions to all environmental parameters and occupying a wide range of ecological niches based on the excellent gastropod record the proto danubian province early danubian p danubian p balatonian p and a proto caspian subprovince are defined the biogeographic reorganisations are associated with five major biotic events within the gastropod faunas these big five comprise four extinctions the late ottnangian extinction event loee the mid badenian extinction event mbee the badenian sarmatian extinction event bsee the sarmatian pannonian extinction event spee and one exceptional immigration origination event termed the early badenian build up event ebbe foraminifera are less valuable for palaeobiogeographic purposes in the area and time slice studied endemisms are generally lower and turn over rates less dramatic they are however very useful for stratigraphic correlations with the mediterranean and atlantic areas this fairly well calibrated marine biostratigraphy of the central paratethys serves as stratigraphic backbone and control for continental stratigraphy

localized geomagnetic field changes near active faults in california 1974 1980 currents in the ionosphere and magnetosphere induce changes in the difference fields due to contrasting impedances at magnetometer sites these changes are identified and removed by multichannel predictive filtering using boulder magnetic observatory component fields as inputs to the prediction operator the remaining fluctuations up to several nt are attributed to crustal magnetization changes evidence that these changes are stress related includes the variation prior to the busch fault earthquake 1974 seen at the two stations closest to within 10 km the epicenter also stations within 50 km of the 1979 coyote earthquake undergo localized field change up to a year before that event if truly precursive these variations are on a broader spatial and temporal scale than those for the busch fault event during the period 1975 1978 the geomagnetic variation is approximately uniform across the array without the development of any significant anomalies this period roughly coincides with the 1975 7 1978 7 seismic lull in nearly all of california it is followed by a marked increase in crustal secular variation long range coherence between anomalous variation at different stations is not seen other than the variation before the busch fault earthquake suggesting that localized variation occurs on a scale of less than 10 km coseismic tectonomagnetic events are not observed at the times of the busch and coyote earthquakes but model calculations suggest that observable events are not expected if the observed changes are due to stress they indicate that changes of aseismic stress are significantly larger than coseismic stress release

shifts in oxygen and carbon isotope signals in marine molluscs from the central paratethys europe around the lower middle miocene transition abstract stable isotope data of mollusc shells from two adjacent time slices karpatian badenian from the central paratethys were investigated to detect differences in environmental parameters and to depict shifts in the isotope signature of the paratethyan seawater around the early middle miocene transition altogether seventeen different gastropod species and one bivalve species from the karpatian korneuburg basin and the badenian northern alpine foreland basin were selected representatives of various ecological guilds yielded different isotope patterns especially in 13c reflecting different original habitats or nutrition although molluscs precipitate their shells in oxygen isotopic equilibrium we preferred to compare isotope data of shells of the same genus of the family turritellidae from the karpatian and badenian the badenian turritella shells from the northern alpine foreland basin yielded distinctly higher 18o and 13c values than the respective karpatian shells from the korneuburg basin as the main factors controlling 18o values in gastropod shells are temperature and 18o of the water during precipitation the differences between the oxygen isotope data of the two time slices can only be explained by these factors good independent palaeotemperature proxies exist for the early to middle miocene of central europe they do not indicate a significant temperature variation therefore different 18o values of the seawater in the different basins of the central paratethys must be responsible for the contrasting 18o values when calculated with commonly assumed 18o seawater values for the miocene badenian turritella shells indicate too cold temperatures these data clearly document the danger of palaeotemperature interpretations based solely on stable isotopes as smaller and marginal marine settings such as the paratethys sea can be seriously influenced by regional differences in the isotope composition of the seawater only a thorough consistent control by other climate proxies e g palaeoecology of molluscs as in this study allows a sensible interpretation

palaeogeographic significance of tidal deposits an example from an early miocene paratethys embayment northern hungary abstract tide influenced deposits can be used in palaeogeographic reconstructions because they are good indicators of open marine connections an example is presented from the eggenburgian late aquitanian early burdigalian of the north hungarian bay this bay was part of an inland sea the paratethys tide influenced deposits prove that tidal motions in the north hungarian bay were locally amplified this required a free propagation of tidal waves from the open ocean through the paratethys into this embayment since all seaways towards the mediterranean were closed during the early eggenburgian the only connection between the north hungarian bay and open marine waters which allowed the transmission of tidal waves was the outlet towards the east slovakian basin in the northeast the presence of tide influenced deposits in the north hungarian bay implies that tidal waves entered the eastern paratethys from the east through a wide passage other examples of lower miocene tide influenced deposits in the mediterranean and paratethian regions are reported from different periods in these cases amplification of tidal motions in various embayments and straits also occurred because of the local basin morphology it is demonstrated that significant palaeogeographic changes during the early miocene resulted in changes of current pathways and related shifts of loci of tide influenced deposition

palaeomagnetic evidence for tertiary counterclockwise rotation of adria abstract with the aim of obtaining tertiary palaeomagnetic directions for the adriatic foreland of the dinaric nappe system we carried out a palaeomagnetic study on platform carbonates from stable istria from the northwestern and the central dalmatia segment of imbricated adria despite the weak to very weak natural remanences of these rocks we obtained tectonically useful palaeomagnetic directions for 25 sites from 20 localities all exhibit westerly declinations both before and after tilt correction concerning the age of the magnetizations we conclude that five subhorizontal and magnetite bearing eocene localities from stable istria are likely to carry primary remanence whereas three tilted and hematite bearing ones were remagnetized in the northwestern segment of imbricated adria the cluster of the mean directions improved after tectonic correction indicating pre tilting magnetization in contrast maastrichtian eocene platform carbonates from central dalmatian were remagnetized in connection with the late eocene oligocene deformation or miocene hydrocarbon migration based on the appropriate site locality means we calculate mean palaeomagnetic directions for the above three areas and suggest an alternative interpretation of the data of kissel et al j geophys res 100 1995 14999 for the flysch of central dalmatia the four area mean direction define a regional palaeomagnetic direction of dec 336 inc 52 k 107 95 9 from these data we conclude that stable istria in close coordination with imbricated adria must have rotated by 30 counterclockwise in the tertiary relative to africa and stable europe we suggest that the latest miocene early pliocene counterclockwise rotations observed in northwestern croatia and northeastern slovenia were driven by that of the adriatic foreland i e the rotation of the latter took place between 6 and 4 ma

piezomagnetic fields of screw dislocation fault models an analytical solution is obtained for the piezomagnetic field generated by a single screw dislocation and its image representing an infinitely long vertical fault with uniform strike slip that cuts the upper or lower portion of a half space the solution is readily extendable to other models of strike slip faults based on vertical arrays of screw dislocations for reasonable values of the relevant physical constants the field is predicted to be generally below current levels of detectability this result is a consequence of the symmetry of piezomagnetization around a screw dislocation which inhibits regions of intense piezomagnetism near the dislocation from contributing to the external field

the muddy bottom of lake pannon a challenge for dreissenid settlement late miocene bivalvia abstract the late miocene dreissenids of lake pannon a long existing eastern central european lake bear witness to two very different modes of life which allowed these bivalves to successfully settle in what appears to be an inhospitable environment one guild is restricted to the genera mytilopsis conrad 1858 and sinucongeria lorenthey 1894 these representatives are extreme r strategists which tend to produce temporal boom and bust populations during time windows of improved ecological conditions these opportunities are interpreted here to correlate with cyclic shifts in the epilimnion hypolimnion relation and the corresponding oxygenation of bottom waters events which are probably triggered by low frequency orbital forcing the second guild is composed solely of congeria partsch 1836 the paradox of the proliferation of a single species characterised by extreme size and weight in a muddy oxygen deficient lake environment avoided by nearly all other molluscs points to a hidden mechanism not accessible to other species we tentatively link this mechanism with chemosymbiosis functional morphology in interplay with a highly sulphidic over saturated interstitial water support an interpretation of the large congeria subglobosa as a successful h2s pump model

marine faunal realms of the mesozoic review and revision under the new guidelines for biogeographic classification and nomenclature consensus among the friends of paleobiogeography produced tentative guidelines to the classification and nomenclature of marine biogeographic units i e biochores based on these loose rules the present paper is a critical review of all published mesozoic marine realms subrealms and superrealms formerly called climatic belts biochores are defined by the overall endemism within geographic and time envelopes that include choro and chrono types without consideration of facies or climate the hierarchy of ranks or tiers is superrealm realm subrealm province subprovince only ranks in italics are obligatory region is informal these ranks scale with endemism geographic range and persistence in time biochores are named geographically following nomenclatural guidelines not strict rules of synonymy and homonymy with priority beginning with uhlig s paper of 1911 uhlig s two climatic belts are tentatively accepted as optional top ranking superrealms for times of exceptional global endemism available names for them are euroboreal or panboreal new and tethys panthalassa the validity of the 29 existing names for realm group biochores realms subrealms and superrealms in the marine mesozoic is discussed 19 names are rejected for a variety of reasons including synonymy homonymy and usefulness the most important realm group biochores are arctic and boreal atlantic in the boreal euroboreal realm or superrealm and tethyan mediterran caucasian indo pacific jurassic early cretaceous and austral middle late cretaceous in the tethys panthalassa superrealm

seismomagnetic effect generated by the october 1989 ml 7 1 loma prieta california earthquake a differentially connected array of proton magnetometers operated within the epicentral region of the october 18 1989 ml 7 1 loma prieta earthquake for 12 years from 1974 to 1986 the closest magnetometer station was located 7 3 km from the epicenter of the earthquake and within 3 km of the site where anomalous ulf magnetic noise measurements were observed following the earthquake the magnetometers were reinstalled with sensors replaced in the original undisturbed sensor holders comparison of pre 1986 total intensity magnetic field data with data obtained during the months following the earthquake indicate local offsets of about 1 nt may have been generated at stations nearest the epicenter tests on other continuous differenced data from 1983 to present indicate that offsets determined could be biased by as much as 0 7 nt the offsets can be approximately fit with a simple seismomagnetic model of the earthquake for which 1 9 m of right lateral and 1 3 m of dip slip southwest side up occurred on a fault patch between 6 km and 18 km deep and 45 km long the total rock magnetization is assumed to be 1 5 a m since the offset has persisted following the earthquake an alternate explanation in terms of electokinetic effects is unlikely even though transient ground water flow occurred following the earthquake comparison of pre 1986 and similar post seismic total magnetic field noise does not indicate any change caused by aliasing of ulf 0 01 hz 10 hz magnetic noise in the vicinity of the loma prieta earthquake

new surveys of the chesapeake bay impact structure suggest melt pockets and target structure effect we present high resolution gravity and magnetic field survey results over the 85 km diameter chesapeake bay impact structure whereas a continuous melt sheet is antici pated at a crater this size shallow source magnetic field anomalies of 100 nt instead suggest that impact melt pooled in kilometer scaled pockets surrounding the base of a central peak a central anomaly of 300 nt may represent additional melt or rock that underwent shock induced remagnetization models predict that the total volume of the melt ranges from 0 4 to 10 km 3 a quantity that is several orders of magnitude smaller than expected for an impact structure this size however this volume is within predictions given a transient crater of diameter of 20 40 km for a target covered with water and sedimentary deposits such that melt fragments were widely dispersed at the time of impact gravity data delineate a gently sloping inner basin and a central peak via a contrast between crystalline and sedimentary rock both features are ovoid oriented parallel to larger preimpact basement structures conceptual models suggest how lateral differences in rock strength due to these preimpact structures helped to shape the crater s morphology during transient crater modification

computer based mollusc stratigraphy a case study from the eggenburgian lower miocene type region ne austria abstract the eggenburg group comprises the type deposits of the lower miocene central paratethys regional stage eggenburgian in ne austria these marine to estuarine deposits transgress in northwestern direction either on palaeozoic rocks of the bohemian massif or on oligocene to lower miocene fluviomarine sediments they are known from three palaeo geographic units situated on the southeastern margin of the bohemian massif these are 1 the southern marginal zone 2 the northwestern n s striking horn basin and 3 the northeastern crystalline plateau termed the eggenburg bay the present study investigates distribution patterns of the exceptionally diverse mollusc fauna composed of 321 taxa species and subspecies within and between those units hierarchical cluster analysis is employed using ward s method and squared euclidean distance calculation a comprehensive database with 1900 sets based on field museum and literature investigations allows compilation of 50 taxonomic lists samples for 30 different localities and six lithostratigraphic units four marine and two brackish formations the resulting grouping pattern implies the existence of four groups three corresponding with palaeo geography and one including low diversity taxon poor samples the analysis of the diversity distribution supports the interpretation that the lower diversity of samples from marine formations stems from secondary distortions such as diagenesis or insufficient sampling hence the samples characterised by a species richness value lower than half of the maximum species richness value of the corresponding formation were excluded from analysis the resulting grouping pattern verified the secondary distortion premise the pattern remained the same except that the low diversity cluster became restricted to samples of brackish origin among the marine samples palaeoecological differences between two fully marine formations from the eggenburg bay were of minor importance as they could not be clearly separated in contrast the individual palaeogeographic regions were shown to be taxonomically coherent but inconsistent with one other as palaeobiogeographic processes were implausible in such a small geographic area the explanation of these differences is based on the time factor including speciation extinction and faunal migration processes the relative stratigraphic position of the horn basin between the marginal zone and the eggenburg bay is implied by hierarchically ordered similarities in order to also indicate their chronological ordinance the index fossil distribution was analysed the chronological pattern is unequivocally provided by the abundant presence of the lower eggenburgian pectinid chlamys gigas schlotheim which is restricted to the marginal zone and the horn basin and by the abundant upper eggenburgian to lower ottnangian pectinids flexopecten palmatus lamarck and chlamys holgeri geinitz which are restricted to the eggenburg bay this refinement of the regional stratigraphic pattern shed light on the eggenburgian marine flooding progression early in the transgression the southern marginal zone was first marine flooded at the same time the horn basin developed an estuarine environment the next phase installed the fully marine environment in the horn basin at the same time the eggenburg bay still a mainland represented a southward pointing cape it first became flooded at the beginning of the upper eggenburgian

preseismic and coseismic magnetic field measurements near the coyote lake california earthquake of august 6 1979 quake epicenter and the location of the instrument coy is shown in figure 1 the aftershocks all occurred within the dashed area approximately 21 km long and 4 km wide all the instruments shown operate at 0 25 nt sensitivity and the digital data are telemetered to menlo park at one sample every 10 min the instrument coy was installed in september 1978 the portable instrument ciy was installed 4 days after the main shock at a point where we calculated an expected maximum coseismic field perturbation due to changes in stress resuiting from failure the simplest method of isolating local magnetic field changes and reducing the effects of ionospheric and magnetospheric disturbances and most importantly the general diurnal variation is to difference the magnetic field observations between adjacent stations no more than a few tens of kilometers apart in particular we wish to search for and isolate changes that might have occurred at coy the magnetometer nearest to the coyote lake main shock figure 2a shows the magnetic field differences in 10 min samples between station coy and the surrounding stations mth euc and qsb for the period around the time of the earthquake for comparison the differences excluding coy are also shown clearly the local magnetic field did not change significantly coincident with or immediately before the earthquake we have applied several methods for noise reduction to these data to improve discrimination of signals that may be of tectonic origin the simplest of these methods is a variation on the weighted difference technique rikitake 1966 in our application this technique focuses primarily on the short term noise in the difference data that arises from incomplete cancellation of the diurnal variation by plotting the data from other sites against those from coy during the daily interval of significant diurnal variation a mean response difference or weight factor was obtained by a least squares line fit figure 2b shows the result of applying this technique to data from coy and mth

the velocity field along the san andreas fault in central and southern california the velocity field within a 100 km broad zone centered on the san andreas fault between the mexican border and san francisco bay has been inferred from repeated surveys of trilateration networks in the 1973 1989 interval the velocity field has the appearance of a shear flow that remains parallel to the local strike of the fault even through such major deflections as the big bend of the san andreas fault in the transverse ranges of southern california across strike profiles of the fault parallel component of velocity exhibit the expected sigmoidal shape whereas across strike profiles of the fault normal component of velocity are flat and featureless no significant convergence upon the fault is observed even along the big bend sector of the fault simple dislocation models can explain most of the features of the observed velocity field but those explanations are not unique about 35 mm yr of relative plate motion is accounted for within the span of the trilateration networks geologic studies indicate that the secular slip rate on the san andreas fault is about 35 mm yr the agreement between these two estimates implies that most of the strain accumulation is elastic and will be recovered in subsequent earthquakes the relative motion observed across the san andreas fault 35 mm yr plus that observed across the eastern california shear zone 8 mm yr accounts for most 43 mm yr of the observed north america pacific relative plate motion 47 mm yr