arenigian early ordovician sea level history and the response of conodont communities western newfoundland four cluster analyses were performed which recognized 17 conodont communities in the arenigian lower ordovician of western newfoundland the analyses include 69 598 identifiable conodont specimens recovered from 153 conodont bearing samples from four stratigraphical sections representing the environmental settings of the platform upper proximal slope lower proximal slope and distal slope the distribution of conodont communities along the platform to slope environmental gradient shows that sea level changes simultaneously affected the development and replacement of the conodont communities in the different facies the pattern of change in conodont communities allows an interpretation of sea level change that is correlated precisely into the detailed graptolite biozonation a gradual transgression lasted most of tetragraptus approximatus zone time which was followed by a brief regression a transgression regression cycle occurred in the t akzharensis zone time a major transgression caused a highst

paired carbon isotopic analysis of ordovician bulk carbonate δ 13 c carb and organic matter δ 13 c org spanning the great ordovician biodiversification event abstract paired measurements of bulk carbonate 13ccarb organic matter 13corg and their difference 13c can be used to estimate changes in isotopic fractionation through time as a function of o2 co2 in the atmosphere however because local scale processes can also affect 13c it is essential to compare sections from widely separated water masses here we present new 13corg data from ordovician carbonate rocks from the great basin oklahoma and appalachian basin and compare with published 13ccarb records from these sections and paired 13c values from other carbonate successions around north america these new data complement previous studies that focused on upper ordovician 13ccarb excursions and now provide a composite ordovician 13corg record new lower ordovician tremadocian stage 13corg data range from ca 26 to 28 decreasing throughout the lower middle ordovician floian dapingian stages to ca 29 to 31 13corg values remain at their lowest throughout the sandbian and are similar to other published upper ordovician sandbian katian 13corg data from north america 13c values from well preserved intervals generally vary between 26 to 28 throughout the lower to middle ordovician tremadocian to early darriwilian but increase to 31 during the mid late darriwilian and mid sandbian similar to published data from younger late ordovician positive 13c excursions known as the guttenberg gice and hirnantian hice events the overall 13c trend shows a 3 increase throughout the early middle ordovician and coincides with a previously interpreted period of ocean cooling and some of the earliest pulses of global biodiversity of marine invertebrates and planktonic organisms modeling studies predict that pco2 decreased during this time suggesting that the effect of pco2 on 13c may have been overwhelmed by other controls such as an in increase in po2 or a higher o2 co2 ratio during this biodiversification event

influence of pore pressure on the event size distribution of induced earthquakes 1 during an enhanced geothermal system egs experiment fluid is injected at high pressure into crystalline rock to enhance its permeability and thus create a reservoir from which geothermal heat can be extracted the fracturing of the basement caused by these high pore pressures is associated with microseismicity however the relationship between the magnitudes of these induced seismic events and the applied fluid injection rates and thus pore pressure is unknown here we show how pore pressure can be linked to the seismic frequency magnitude distribution described by its slope theb value we evaluate the dataset of an egs in basel switzerland and compare the observed event size distribution with the outcome of a minimalistic model of pore pressure evolution that relates event sizes to the differential stress d we observe that the decrease of b values with increasing distance of the injection point is likely caused by a decrease in pore pressure this leads to an increase of the probability of a large magnitude event with distance and time

graptolites from the lower middle ordovician st george and table head groups western newfoundland and their correlation with trilobite brachiopod and conodont zones faunal assemblages of the autochthonous shelf carbonate sequences belonging to the st george and table head groups are dominated by shelly macrofossils and conodonts rare usually monotypic graptolitic horizons enable correlation with the allochthonous cow head group which was deposited on the middle to lower slope and the shelly conodont and graptolitic zonal schemes elsewhere in north america the catoche formation of the st george group is of ibexian canadian age and yields graptolites indicative of the tetragraptus approximatus and tetragraptus akzharensis zones early arenig the basal aguathuna formation belongs to the pendeograptus fruticosus zone whereas higher parts span the ibexian whiterock boundary graptolites suggest that the table head group entirely postdates the cow head group this is supported by a whiterock early llanvirn trilobite conodont and brachiopod fauna

a revision of the stratigraphic nomenclature of the cambrian ordovician strata of the philipsburg tectonic slice southern quebec the philipsburg tectonic slice is bounded to the west by a northeast southwest trending thrust fault logan s line and preserves 10 formations of middle to late cambrian milton rock river and strites pond formations early ordovician wallace creek morgan corner hastings creek and naylor ledge formations and early middle ordovician luke hill solomons corner and corey formations age the strata were previously assigned to the philipsburg group early correlations between the philipsburg succession and coeval strata of the st lawrence platform were mainly based on sparse macrofauna and inferred stratigraphic position unconformities at the cambrian ordovician and early ordovician middle ordovician boundaries occurring in autochthonous st lawrence platform and the allochthonous philipsburg succession philipsburg tectonic slice highlight new stratigraphic interpretations between the inner shelf st lawrence platform and the outer shelf philipsburg successions the succession in the philipsburg tectonic slice is divided into three new groups the middle to upper cambrian missisquoi group new includes the milton rock river and strites pond formations the upper boundary of the missisquoi group is defined by the upper unconformable contact between the upper cambrian strites pond formation and overlying lower ordovician wallace creek formation the missisquoi group correlates with the potsdam group of the st lawrence platform the lower ordovician school house hill group new includes the wallace creek morgan corner hastings creek and naylor ledge formations the upper boundary of this group is marked by a regionally extensive unconformity at the top of the naylor ledge formation and correlates with the younger beekmantown topping unconformity the school house hill group is correlative with the lower to upper part of the beekmantown group theresa formation and the ogdensburg member of the beauharnois formation of the st lawrence platform the middle ordovician fox hill group new consists of the luke hill solomons corner and corey formations this group correlates with the uppermost part of the beekmantown group huntingdon member of the beauharnois formation and the carillon formation resume l ecaille tectonique de philipsburg est limitee a l ouest par une faille de chevauchement la ligne logan orientee nord est sud ouest et contient dix formations de strates d ge cambrien median tardif les formations de milton de rock river et de strites pond ordovicien precoce les formations de wallace creek de morgan corner

dolomitization and isotope stratigraphy of the vazante formation sao francisco basin brazil the vazante formation consists of approximately 1700 m of mainly microbial mats and stromatolitic reefal lenses that were deposited on shallow marine platform and have been entirely dolomitized samples representing different dolomite generations were taken from three boreholes covering the entire spectrum of the vazante carbonates dolomites can be classified based on petrography and geochemistry into four generations ranging in crystal size between 4 m almost micritic and 3 mm and occurring as both replacements and cements the sr ca molar ratios calculated for the dolomitizing fluid 0 0006 0 0138 suggest a contribution from a non marine possibly meteoric water component the 18 oa nd 13 c values vary from 0 1 to 14 3 pdb and 0 2 to 2 3 pdb respectively fluid inclusion study suggests that dolomitization must have commenced at a temperature lower than about 50 c a mixing zone model of dolomitization for dolomites i iii satisfies the constraints from elemental chemistry 18 o 87 sr 86 sr and fluid inclusions the petrographic and chemical criteria of the latest generation dolomite iv reflect conditions of deep burial environment at temperatures above 120 130 c the 13 c values show only small variations at the base of the formation followed by a major negative plunge 4 at the top this plunge correlated with the sturtian glacial phase in contrast to c isotopes only few samples may have retained their near primary 87 sr 86 sr values of 0 70614 0 70734 the lowest 87 sr 86 sr value 0 70614 from fibrous cement in the upper part of the formation correlates with the negative 13 c shift and is also consistent with the sr isotope signature proposed for the glacial sturtian seawater the 34 s values obtained from sulfates trapped in carbonates range between 10 8 and 16 9 with a jump to 21 3 in the overlying formation all isotope signals are within the range suggested for the early neoproterozoic seawater but the precambrian baseline is poorly known and additional work is required to confirm this tentative assignment 2001 elsevier science b v all rights reserved

propagation of slow slip leading up to the 2011 mw 9 0 tohoku oki earthquake many large earthquakes are preceded by one or more foreshocks but it is unclear how these foreshocks relate to the nucleation process of the mainshock on the basis of an earthquake catalog created using a waveform correlation technique we identified two distinct sequences of foreshocks migrating at rates of 2 to 10 kilometers per day along the trench axis toward the epicenter of the 2011 moment magnitude mw 9 0 tohoku oki earthquake in japan the time history of quasi static slip along the plate interface based on small repeating earthquakes that were part of the migrating seismicity suggests that two sequences involved slow slip transients propagating toward the initial rupture point the second sequence which involved large slip rates may have caused substantial stress loading prompting the unstable dynamic rupture of the mainshock

sulphate reduction associated with hardgrounds lithification afterburn negative excursions in 13c profiles from platform carbonates that coincide with pyritised hardgrounds are commonly linked to subaerial exposure events but we show here that they can also result from subsurface bacterially mediated early cementation in addition to the precipitation of syndepositional marine cements a non soil derived origin for 13c depleted micrites offers an alternative origin and bathymetric interpretation for these surfaces the lower cretaceous lekhwair formation platform carbonate successions from offshore abu dhabi contain abundant hardgrounds that are important for both regional correlation and control of subsurface flow the micrite from these hardgrounds have average 13c values of 0 7 1 5 lower than non hardground micrites that are similar to contemporary open ocean values hardground 13c values are due to the addition of 13c depleted carbonate generated as a by product of sulphate reduction to the normal marine calcite that caused hardground lithification pyritisation of the hardgrounds occurred before during and after normal calcite precipitation the persistence of sulphate reduction after hardground lithification is shown by the presence of pyrite and low 13c micrite in sediment up to a few mm above the hardgrounds

diachronous tectonic collapse of the ordovician continental margin eastern canada comparison between the quebec reentrant and st lawrence promontory the upper ordovician trenton group of southern quebec represents the last taconian foreland basin carbonate unit in the quebec reentrant prior to final collapse of laurentia s continental margin and its burial under synorogenic flysch the trenton group either conformably or unconformably overlies the black river group and is in turn conformably overlain by the utica shales the tripartite trenton carbonate unit records progressive deepening 1 very shallow to shallow subtidal 2 shallow to deep carbonate ramp and 3 shallow to deep outer shelf regional facies distribution lithotectonic elements and thickness variations indicate that the trenton shelf was dissected by extensional faults delineating blocks subsiding at various rates this scenario compares favourably with taconian foreland basin development in the middle ordovician table head group at the st lawrence promontory newfoundland a similar stratigraphic succession and tectono sedimentary history occurring 10 15 ma earlier at the s

nucleation process of an m2 earthquake in a deep gold mine in south africa inferred from on fault foreshock activity using a network of sensitive high frequency acoustic emission sensors we observed foreshock activity of an mw 2 2 earthquake main shock in a deep gold mine in south africa foreshock activity which selectively occurred on a part of the rupture plane of the forthcoming main shock lasted for at least 6 months until the main shock rock samples recovered from the main shock source region showed evidence of ancient hydrothermal alteration on the main shock rupture plane suggesting that the foreshock activity occurred on a preexisting weakness the foreshocks during 3 months before the main shock were concentrated in three clusters f1 f3 which we interpret as representing localized preslip at multiple sites while the location of mining area the source of stress perturbations changed with time the locations of foreshock clusters did not change suggesting that the preslip patches were controlled by strength heterogeneity rather than stress distribution activity over the entire foreshock area was generally constant but the largest cluster f2 showed accelerated activity starting at least 7 days before the main shock while mining stress did not increase in this period the main shock initiated at a point close to f1 away from f2 all the six foreshocks during the final 41 h occurred in f1 and f2 and in between these suggest that in the last stage of the preparation process of the main shock preslip patches interacted with each other through the stress concentration ahead of the expanding preslip patch f2 which should be the only driving force of the preparation process under the constant external load

effect of sliding rate on the activity of acoustic emission during stable sliding the mechanical and statistical characteristics of acoustic emission ae events during stable sliding are investigated through a laboratory experiment using a granite specimen with a pre cut fault numerous ae events are found to be generated on the pre cut fault indicating that microscopically unstable fracture occurs during macroscopically stable sliding the composite focal mechanism solution of ae events is determined from the first motion directions of p waves the determined mechanism is consistent with the double couple one expected for the slip on the pre cut fault the source radii of large ae events are estimated to be about 10 mm from the widths of the first p wave pulses these indicate that the ae events are generated by shear fracture whose faulting area is a part of the pre cut fault plane the occurrence of ae events as a stochastic process approximately obeys the poisson process if the effect of mutually dependent events consti tuting clusters is corrected the observed amplitude frequency relation of ae events approximately follows a power law for a limited amplitude range as the macroscopic sliding rate increases the number of ae events per unit sliding distance decreases this rate dependence of the ae activity is qualitatively consistent with the observation that the real area of contact between sliding surfaces decreases with an increase in the sliding rate as reported in the literature

lipid biomarker and stable isotopic profiles through early middle ordovician carbonates from spitsbergen norway abstract one of the most dramatic episodes of sustained diversification of marine ecosystems in earth history took place during the early to middle ordovician period changes in climate oceanographic conditions and trophic structure are hypothesised to have been major drivers of these biotic events but relatively little is known about the composition and stability of marine microbial communities controlling biogeochemical cycles at the base of the food chain this study examines well preserved carbonate rich strata spanning the tremadocian through upper dapingian stages from the oslobreen group in spitsbergen norway abundant bacterial lipid markers elevated hopane sterane ratios average 4 8 maximum of 13 1 detection of chlorobi markers in organic rich strata and bulk nitrogen isotopes 15ntotal averaging 0 to 1 for the open marine facies suggest episodes of water column redox stratification and that primary production was likely limited by fixed nitrogen availability in the photic zone near absence of the c30 sterane marine algal biomarker 24 n propylcholestane 24 npc in most samples supports and extends the previously observed hiatus of 24 npc in early paleozoic late cambrian to early silurian marine environments very high abundances of 3 methylhopanes average 9 9 maximum of 16 8 extends this biomarker characteristic to early ordovician strata for the first time and may reflect enhanced and sustained marine methane cycling during this interval of fluctuating climatic and low sulfate marine conditions olenid trilobite fossils are prominent in strata deposited during an interval of marine transgression with biomarker evidence for episodic euxinia anoxia extending into the photic zone of the water column

carbon isotope stratigraphy of the lower ordovician succession in northeast greenland implications for correlations with st george group in western newfoundland canada and beyond article i nfo the lower ordovician sequence on the ella o island in northeast n e greenland is a thick shallow marine platform carbonate sequence 1415 m thick and constitutes the major part of the kong oscar fjord group it consists from bottom to top of the antiklinalbugt septemberso and cape weber formations which are believed to be respectively coeval with the watts bight boat harbour and catoche formations of the st george group in western newfoundland canada samples were collected from outcrops at high resolution intervals and micritic materials were extracted by microdrilling after screening their petrographic and geochemical criteria to evaluate the degree of preservation the 13 c and 18 o values of well preserved micrite microsamples range from 5 2 to 0 5 vpdb and from 10 3 to 6 5 vpdb respectively the 13

mid pleistocene acheulean like stone technology of the bose basin south china stone artifacts from the bose basin south china are associated with tektites dated to 803 000 3000 years ago and represent the oldest known large cutting tools lcts in east asia bose toolmaking is compatible with mode 2 acheulean technologies in africa in its targeted manufacture and biased spatial distribution of lcts large scale flaking and high flake scar counts acheulean like tools in the mid pleistocene of south china imply that mode 2 technical advances were manifested in east asia contemporaneously with handaxe technology in africa and western eurasia bose lithic technology is associated with a tektite airfall and forest burning

geochemistry of modern brachiopods applications and implications for oceanography and paleoceanography abstract modern rhynchonellida terebratulida thecideida and a few inarticulated brachiopods were collected live or soon after death at 30 locations from depths of 2 3940 m from the equator to high latitudes covering the atlantic pacific indian caribbean and mediterranean oceans seas well preserved fibers of the secondary layer combined with sr 450 1928 mg kg mn 1 199 mg kg and fe 1 610 mg kg contents confirm with few exceptions the excellent preservation of the modern brachiopod material evaluation of the stable isotope compositions was conducted on 276 specimens and on 374 published samples for a total database of 650 samples from 80 locations it revealed that oxygen isotope incorporation into shell calcite secondary layer of modern articulated brachiopods in most cases occurs in equilibrium with the ambient water and as such reflects surrounding environmental conditions thecideida as a group shallow water and low latitude incorporate oxygen isotopes 3 04 to 0 35 into shell calcite in equilibrium with their ambient water a large majority of genera and species of the terebratulida shallow water and low mid latitude also incorporate oxygen 2 30 to 3 48 into shell calcite in isotopic equilibrium with their surrounding water in contrast equilibrium incorporation of oxygen isotopes into shell calcite by the rhynchonellida is uncertain but a vital effect probably applies to the craniida the question of equilibrium disequilibrium incorporation of carbon isotopes into shell calcite of modern brachiopods remains unresolved at this time isotope compositions range up to 4 5 5 6 and 1 5 for 13 c and up to 5 5 5 9 and 0 3 for 18 o for shallow water low mid and high latitude brachiopods respectively strontium isotopes of modern brachiopods as expected show no significant variation with location latitude water depth temperature salinity and general water conditions once local habitat and ecological influences of fossil brachiopods from similar latitudes are considered their isotopic elemental values should be valuable diagenetic indicators and important oceanographic chemostratigraphic proxies

post hunnebergian ordovician carbon isotope trend in baltoscandia its environmental implications and some similarities with that of nevada abstract carbon isotope changes during post hunnebergian ordovician time were investigated as the corresponding sequence of rocks is stratigraphically nearly complete in baltoscandia an attempt was made to use it to elaborate the general pattern of carbon isotope changes in most of the ordovician complications caused by several local hiatuses condensed sections and facies changes were mitigated by the study of overlapping sections a total of 326 new whole rock analyses and published data from 18 drill cores and 4 outcrops in estonia latvia and sweden were considered the following positive carbon isotope events were observed 1 the mid darriwilian excursion peak 13c value 1 9 in the aseri stage 2 the mid caradoc excursion 2 2 in the uppermost part of the keila stage 3 the first late caradoc excursion 2 3 in the lower part of the rakvere stage 4 the second late caradoc excursion 2 4 in the upper part of the nabala stage 5 the early ashgill excursion 2 5 in the lowermost part of the pirgu stage 6 the mid ashgill excursion 2 0 in the upper part of the pirgu stage 7 the widely known large hirnantian excursion in estonia the peak value reaches 6 7 in the porkuni stage the study interval comprises a long 19 ma period characterized by low magnitude carbon isotope changes and a following much briefer 12 ma interval with often medium scale shifts and a major event at the end the latter interval reflects onset in the mid caradoc of a period of variable climate alternation of arid and humid episodes which ended with a serious cooling and glaciation the baltoscandian and north american nevada 13c trends are in general lines very similar providing good prospects for global chemostratigraphical correlation and understanding of role of oceanic processes in carbon cycling

carbon isotope δ13ccarb stratigraphy of the lower middle ordovician tremadocian darriwilian in the great basin western united states implications for global correlation abstract new stable carbon isotope data 13ccarb from lower middle ordovician tremadocian to darriwilian carbonate mudstone and wackestone rocks of the pogonip group are presented from two sections in the great basin region usa shingle pass east central nevada and the ibex area western utah the pogonip group is a succession of mixed carbonate and siliciclastic rocks that accumulated on a carbonate ramp under normal marine conditions during the late cambrian furongian to middle ordovician darriwilian the shingle pass and ibex area sections have been previously studied for their conodont biostratigraphy and contain a north american midcontinent conodont fauna that range from the cordylodus intermedius zone uppermost cambrian to the phragmodus polonicus zone darriwilian the 13c trend has four distinct characteristics recognized in both great basin sections 1 a drop in 13c from 1 at the base of the ordovician tremadocian to 0 7 2 a 1 to 2 positive 13c shift in the uppermost rossodus manitouensis zone during the late tremadocian 3 a gradual 13c increase from 2 to ca 0 during the end of the early ordovician floian and 4 a steady 13c decrease from 0 to 4 to 5 during middle ordovician dapingian darriwilian in the lower ordovician 13c trends reported here from the great basin are not consistent with a causal mechanism involving sea level change and the migration of isotopically distinct water bodies instead these lower ordovician isotope data most likely reflect primary seawater chemistry and changes in 13c on a global scale this interpretation is supported by the excellent correlation of 13c in the lower ordovician to other 13c trends reported from the sections in the argentine precordillera la silla and san juan formations and in western newfoundland st george and table head groups these correlations using 13c are consistent with published biostratigraphic data and provide an integrated and high resolution chemo biostratigraphic framework for the lower ordovician sedimentary record of the laurentian margin the middle ordovician portion of the 13c curves in the great basin represented by the kanosh and lehman formations shows significant isotopic depletion relative to the section in argentina thus although there is some indication that minima and maxima in the middle ordovician curves can be correlated the great basin sections show clear evidence of overprinting by local variables related to both diagenesis dolomitization and platform restriction

delineation of large localized damage structures forming ahead of an active mining front by using advanced acoustic emission mapping techniques abstract we applied advanced mapping techniques to 291 230 acoustic emission ae events as small as around m 4 that were recorded over 50 days by an ultra high resolution network close to the active front of a tabular mining stope being advanced northward at 1 km depth in the cooke 4 gold mine in south africa we first applied joint hypocenter determination jhd to improve absolute locations and then applied the double difference relative location algorithm to the jhd output these steps resolved the seemingly continuous dense cloud of aes that extend about 20 m ahead of the stope front into several discrete steeply dipping tabular clusters a few meters thick and 10 30 m in dip extent separated by quiet intervals a few meters thick the clusters have a strike parallel to the stope face and a dip of about 65 resembling commonly observed large shear fractures along the plane of maximum shear ortlepp shears in general the activity of the clusters changed in similar ways as the stope face advanced but each cluster remained stationary and the gaps between clusters were impressively quiet this study demonstrates that high resolution ae mapping can delineate the formation of large structures of localized damage in the highly stressed intact rock mass ahead of the stope face a process that may culminate in hazardous seismic events

fluid induced swarm earthquake sequence revealed by precisely determined hypocenters and focal mechanisms in the 2009 activity at hakone volcano japan 1 a swarm earthquake sequence is often assumed to be triggered by fluid flow within a brittle fault damage zone which is assumed to be highly permeable however there is little seismological evidence of the relation between the fluid flow within the fault damage zone and the occurrence of swarm earthquakes here we precisely determine the hypocenters and focal mechanisms of swarm earthquakes that occurred in the caldera of hakone volcano central japan using data from a dense seismic network we demonstrate that the swarm earthquakes are concentrated on four thin plane like zones each of which has a thickness of approximately 100 m one of the nodal planes of the focal mechanisms agrees with the planar hypocenter distribution the swarm earthquakes that occurred during the initial stage of the activity exhibited a migration of hypocenters that appears to be represented by the diffusion equation based on the spatiotemporal distribution of the earthquakes the hydraulic diffusivity is estimated to be approximately 0 5 1 0 m2 s the observations imply that swarm earthquakes were triggered by the diffusion of highly pressured fluid within the fault damage zone a burst like occurrence of the swarm earthquakes is also observed in the later stage these swarm earthquakes are thought to have been triggered primarily by local stress changes caused by the preceding activity the complicated spatiotemporal pattern is thought to have been caused by the effect of the fluid flow within the high permeability damage zones as well as the stress perturbations generated by the swarm earthquakes themselves

emergence and disappearance of very small repeating earthquakes on a geological fault in a gold mine in south africa abstract we investigated the activities of very small 5 10 mw 2 35 repeating earthquakes that occurred during 14 months on a geological fault at a 1 km depth in the cooke 4 gold mine in south africa out of 4214 acoustic emissions occurring on the fault 1785 42 36 of the total were identified as repeaters on the basis of the waveform similarity and the proximity of hypocenters quite a few large groups having up to 57 members were recognized activities of some groups certainly continued throughout the 14 months but we also found some repeater groups that newly emerged or disappeared during this period both types often coexisted within a distance as small as 0 5 m within which background fault creep should be coherent some disappearing groups showed a decrease in the event magnitude with time these temporal changes of repeater activities may imply the formation and dissipation of topographical asperity contacts on the fault our results suggest that ultrasensitive observation of acoustic emissions can reveal the physical evolution of asperities

new 40ar 39ar stratigraphic and palaeoclimatic data on the isernia la pineta lower palaeolithic site molise italy abstract the archaeological deposits of isernia la pineta are a milestone in the european context being composed of very rich and large sized occupation layers the archaeological remains are characterised by the use of anvils in a very opportunistic and rapid way to produce a large number of flakes and residual cores usually of very small size the lithic instruments are associated with remains of large mammals which give a clear indication of the diet they are represented by bison schoetensacki freudenberg stephanorhinus hundsheimensis toula elephas palaeoloxodon namadicus falconer e cautley ursus deningeri von reichenau hippopotamus cf antiquus desmarest sus scrofa l hemitragus cf bonali harle e stehlin megaceroides solilhacus robert cervus elaphus cf acoronatus beninde dama dama cf clactoniana falconer capreolus sp and panthera leo fossilis von reichenau the rodent fauna is represented by clethrionomys sp pliomys episcopalis mehely pliomys lenki heller microtus aff arvalis pallas microtus brecciensis gieber microtus terricola gr multiplex subterraneus and arvicola cantiana hinton the insectivores are talpa sp sorex cf runtonensis hinton and crocidura sp two main archaeological layers have been identified the lower one sector i layer 3c rests on a phytoclastic travertine passing laterally to a phytohermal travertine which generated a small step in the watercourse a sandy silt layer of lacustrine environment layer 3b deposited inside travertine pools and very limited phytostromatolitic travertine sediments cover this layer the second occupation layer layer 3a rests on these sediments as well as on the travertines cross bedded fine gravelly sands cover the deposits and are interlayered with tuffs very rich in pyroxene and sanidine the latter gave 40ar 39ar ages of 610 10 and 606 2 ka 2 error this layer is covered by cross bedded gravels weathered by a thick alfisols with a well expressed bt horizon the uppermost part of the series is composed of gravels and colluvia containing another pyroclastic layer sanidines of this layer yield scattered ar ar ages with a main population at about 504 14 ka a maximum age of 474 3 ka is inferred for this layer the isernia travertines are not associated with hot water springs and indicate that the area was frequented at the end of an interglacial period the new ages demonstrate that the human frequentation occurred at the beginning of the middle pleistocene

high resolution chemostratigraphy of the cambrian ordovician gssp enhanced global correlation tool abstract the green point formation of the cow head group in western newfoundland canada represents the global stratotype section and point gssp for the cambrian ordovician boundary on laurentia the formation consists of the martin point lower and the broom point upper members which constitute a thick 170 m deep subtidal to slope marine carbonate sequence preservation of the micritic carbonates of the green point formation was evaluated by multiple petrographic and geochemical screening tools the 13 c and 18 o values of near primary micrites range from 4 7 to 1 7 vpdb and from 8 7 to 5 5 vpdb respectively with no significant correlation r 2 0 002 similarly the 13 c values show no significant correlation with mn sr ratios or total ree contents which suggest that the investigated carbonates retain their near primary 13 c signatures that can be utilized to construct a high resolution carbon isotope profile for the gssp the 13 c carb profile about the gssp trends generally positive into bed 22 of the green point formation the top of the c intermedius zone marks the onset of a negative 13 c carb shift to about 6 0 culminating in the upper part of the zone subsequently the 13 c carb profile trends positive with a double switch back about the boundary point and then continues on to the highest value in the uppermost part of bed 23 in addition the ce ce values approximately between 0 8 and 1 0 through the gssp suggest generally dysoxic waters before during and immediately after the boundary the high resolution chemostratigraphic results curve and trends covering the gssp should facilitate correlation of the cambrian ordovician boundary sections sequences from other locations

steady activity of microfractures on geological faults loaded by mining stress abstract acoustic emissions ae down to m w 4 were recorded at a site 1 km beneath the surface in the cooke 4 mine south africa several planar ae clusters with lateral extent of 10 100 m were identified most of them were located several tens of meters away from the mining front and exhibited steady activity during the analysis period of about two months some of the clusters coincided with mapped faults the planar cluster aes were sharply aggregated within a thickness of several decimeters likely delineating the fracture interface of the fault and its higher order morphology such as branches bends and stepovers the composite focal mechanism evaluated for each cluster was consistent with slip events on the fracture interface these results imply that numerous shear microfractures occur steadily on a natural fault surface subjected to a mining related stress increase the planar clusters consist of very small aes 99 7 were smaller than m w 2 exhibiting high b values much exceeding unity this contrasts with the more usual b values of the stope cluster aes which were aggregated within 20 m of the mining front and exhibited a more scattered distribution the size distribution of microfractures on a fracture interface may directly reflect fine scale irregularities of the interface on the other hand many other mapped faults near the planar ae clusters were not accompanied by ae activities despite the fact that these quiet faults were subjected to a similar stress history the presence or absence of ae activities on a fault may reflect different states of the fault including stress and strength

the ediacaran cambrian boundary in the tarim basin nw china geological data anomalies and reservoir implication abstract in this study unconformities t90 formed during the succession from the ediacaran to the cambrian were identified based on five types of data namely field outcrops c and o isotopes major and trace elements well logs and seismic data the outcrop data show notable lithological changes above and below the t90 interface the c and o isotope data show significant negative 13c and 18o excursions at the t90 interface the negative 13c excursion at the t90 interface occurred concurrently with the negative 13c excursions that occurred globally during the same period the average values of ca mg nd pr ce and la were higher below the t90 interface than that above the t90 interface and that the average mass fractions of zr sr zn ba mn s si ni fe al rb k cl and p were lower below that interface than that above it the well log data show that at the t90 interface the concentrations of u and th and the mass fraction of k increased suddenly from 97 66 to 104 308 ppm from 210 005 to 232 086 ppm and from 11 609 to 12 99 respectively and the gamma ray value increased significantly reflecting a brief land exposure of the interface onlap and truncation patterns were visible on the seismic sections above and below the t90 interface various types of unconformities have developed at the t90 interface in various areas of the tarim basin paraconformities are mainly distributed in the kuluketage and kalpin outcrop areas as well as the depressions in the northern tarim basin and a large area north of the tarim basin angular unconformities are distributed near the north wing of the central uplift belt the paleogeomorphology of the t90 unconformity interfaces limited the distribution of sedimentary facies in the overlying strata thereby affecting the distribution of the hydrocarbon source rocks of the yurtus formation and controlled the development of karst reservoirs in the underlying strata

origin of lower ordovician dolomites in eastern laurentia controls on porosity and implications from geochemistry the catoche formation of the st george group in eastern laurentia western newfoundland consists of early ordovician arenigian shallow marine platform carbonates 160 m thick which were extensively dolomitized during the course of their diagenetic history the dolomites occur as both replacement and pore filling cements and are a major control on porosity distribution in the formation the origin and diagenetic history of the catoche dolomites at daniel s harbour western newfoundland were analysed in comparison to equivalent successions at port au choix pac and port au port peninsula pap to assay the reservoir potential of these dolomites in eastern laurentia petrographic examination identified at least three generations of dolomites in the catoche formation which are 1 an early replacement sub to eu hedral micritic dolomite 4 m 30 m d1 2 eu to sub hedral dolomite 70 m 1 mm often with cloudy cores and clear rims d2 and 3 subhedral to anhedral saddle dolomite cement 200 m 3 mm d3 the micritic dolomite d1 exhibits a dull cathodoluminescence cl under cathodoluminoscope whereas dolomite d2 exhibits consistent concentric cl zonation some subhedral crystals of d3 appear zoned both in plane polarized light and cathodoluminoscope otherwise d3 exhibits a dull cl stoichiometric dolomite occurs in all three generations with d2 as the dominant dolomite by abundance the low strontium 47 25 ppm content coupled with depleted 18o value of dolomitizing fluids 10 to 11 2 vsmow and near micritic grain size suggests an early precipitation of dolomite d1 at low temperatures of near surface conditions from solutions likely formed by mixing of early ordovician sea and meteoric waters in contrast microthermometric measurements of primary two phase fluid inclusions in dolomite d2 homogenization temperatures of 102 168 c with a salinity range of 19 8 25 eq wt nacl and dolomite d3 homogenization temperatures of 158 190 c with a salinity range of 20 2 22 2 eq wt nacl suggest that both dolomite generations were generated in mid to deep burial settings from high salinity low temperature 200 c hydrothermal fluids likely under suboxic conditions this is consistent with the low sr concentrations for d2 36 4 8 ppm and d3 38 7 9 ppm 18o values of dolomitizing fluids for d2 2 1 to 8 1 vsmow and d3 6 to 8 1 vsmow coupled with fe contents of d2 1684 1096 ppm and d3 1783 7 618 ppm as well as the respective mn d2 131 2 50 and d3 197 5 55 ppm concentrations ree and shale normalized reesn values of catoche carbonates indicate enrichment in rare earth element ree composition of the earliest calcite c1 relative to those of arenig seawater whereas the reesn profiles of the dolomite generations mimic that of calcite c1 the ce ce ce sn and la la la pr pr sn anomalies of the catoche dolomites are consistent with precipitation in equilibrium with source fluids in slightly oxic to suboxic conditions whereas eu eu eu cn anomalies suggest similar source fluids for d2 and d3 results of fluid inclusion gas analysis are consistent with petrographic features and geochemical compositions and support the exclusion of magmatic fluids during dolomitization visual estimates of porosity from thin sections indicate four porous 4 12 horizons vugs and intercrystalline pores are two types of porosity associated with the dolomites with the latter being the dominant type and associated mainly with dolomite d2

a major conodont extinction event during the early ordovician within the midcontinent realm ji z and barnes c r 1993 a major conodont extinction event during the early ordovician within the midcontinent realm palaeogeogr palaeoclimatol pataeoecol 104 37 47 the major change in the lower ordovician conodont faunas of the midcontinent realm was recognized by earlier workers our recent intense study of midcontinent conodonts from the st george group port au port peninsula western newfoundland has shown that seven major conodont lineages involving some 33 multielement species completely terminate in the late tremadoc series within an interval of a few metres at a level between the lower ordovician conodont fauna c and fauna d the extinction event occurs during the peak of a regressive phase within the deposition of the st george group and at a time of apparent global eustatic fall at or slightly below the tremadoc arenig series boundary this important extinction bioevent has been recognized throughout the midcontinent realm in north america

basin evolution in western newfoundland new insights from hydrocarbon exploration the humber zone is the most external zone of the appalachian orogen in western newfoundland it records multiphase deformation of the cambrian ordovician passive margin and of the ordovician to devonian foreland basins by the taconian salinian and acadian orogenic events the recent phase of exploration drilling has provided new evidence for structural stratigraphic reservoir and source rock maturation models of western newfoundland the first well port au port 1 supported the hypothesis that the round head thrust had an earlier extensional history prior to the acadian compressional inversion that created the present day structural high of the port au port peninsula the well tested a small anticline formed in a footwall shortcut fault of the round head thrust the second well long point m 16 was drilled at the northern tip of long point to test a triangle zone identified by previous workers this well demonstrates that the frontal monocline at the western edge of the triangle zone is elevated by a stack of imbricate thrusts composed of rocks of the taconian allochthon and compressional basement involved faults that have uplifted the cambrian ordovician carbonate platform the structural model developed in the port au port area with the aid of these wells has been extended throughout the humber zone in western newfoundland changes in structural style illustrated by regional cross sections suggest that prospective trap geometries are only developed in the southern and central parts of the region the reservoir model proposed invokes exposure and karsting of the footwalls of extensional faults formed as the carbonate platform collapsed during a middle ordovician hiatus the st george unconformity structural relief became more pronounced as extensional collapse continued through the middle ordovician begin page 394 these structurally high fault footwalls became the foci for dolomitizing and mineralizing fluids that used major faults as fluid conduits during the devonian fluids deposited sulphide ores and created zebra and sparry dolomite and some sucrosic hydrothermal dolomites in the st george group and the table point formation the reservoir model maturity and source rock data and the structural models have been combined with seismic and onshore surface geology this enables the prospectivity of the western newfoundland cambrian ordovician play trend to be evaluated for further exploration

high resolution isotope stratigraphy of the lower ordovician st george group of western newfoundland canada implications for global correlation the lower ordovician st george group of western newfoundland consists mainly of shallow marine platform carbonates 500 m thick it is formed from bottom to top of the watts bight boat harbour catoche and aguathuna formations the top boundary of the group is marked by the regional st george unconformity outcrops and a few cores from western newfoundland were sampled at high resolution and the extracted micritic materials were investigated for their petrographic and geochemical criteria to evaluate their degree of preservation the d13c and d18o values of wellpreserved micrite microsamples range from 4 2 to 0 vpdb and from 11 3 to 2 9 vpdb respectively the d13ccarb profile of the st george group carbonates reveals several negative shifts which vary between 2 and 3 and are generally associated with unconformities disconformities or thin shale interbeds thus reflecting the effect of or link with significant sea level changes the st george unconformity is associated with a negative d13ccarb shift 2 on the profile and correlated with major lowstand around the end of arenig on the local sea level reconstruction and also on those from the baltic region and central australia thus suggesting that the st george group unconformity might have likely had an eustatic component that contributed to the development enhancement of the paleomargin other similar d13ccarb shifts have been recorded on the st george profile but it is hard to evaluate their global extension due to the low resolution of the documented global lower ordovician tremadoc middle arenig d13ccarb profile

evolution of a lower paleozoic continental margin carbonate platform northern canadian appalachians the western margin of the northern appalachian orogene and adjacent craton is composed of a lower paleozoic low latitude carbonate platform which originally lay along the northern margin of iapetus ocean parts of the platform interior are now exposed in quebec much lies beneath the gulf of st lawrence and the outer shelf and deep water deposits crop out in western newfoundland the shelf break and upper slope are nowhere exposed but their nature has been determined from numerous clasts in sediment gravity flows redeposited on the lower slope and now stacked in allochthonous thrust complexes four separate phases recording platform growth and demise can be differentiated reflecting the interplay between tectonics eustasy and the evolving lower paleozoic biota phase 1 preplatform shelf reflects initial siliciclastic deposition on rifted crystalline basement followed by a short phase of carbonate sedimentation dominated by archeocyathan buildups and ooid shoals that was terminated by offlap of thick quartzarenites phase 2 narrow high energy platform is characterized by mixed siliciclastic carbonate peritidal sedimentation throughout manifest as three grand cycles contemporaneous deep water sediments comprise basal welded conglomerates overlain by quartzose carbonate turbidites phase 3 wide low energy platform is an onlap package of muddy fossiliferous subtidal and peritidal carbonates arranged inmore the form of two unconformity bounded megacycles the adjacent deep water slope was a narrow belt of debris flows and wide carbonate shale apron deposited in the lower part of an oxygen minimum zone phase 4 foundered platform documents the initial uplift faulting subsidence and fragmentation of the platform in a sequence of peritidal to subtidal to deep water carbonates reflecting the initial stages of the taconic orogeny less

oxygen and carbon isotopic composition of ordovician brachiopods implications for coeval seawater one hundred and two articulate brachiopods and twenty one marine cements from ordovician strata were analyzed for oxygen and carbon isotopes these together with 200 previously published analyses of ordovician brachiopods mostly of upper ordovician age define a general trend of increasing 18o values with decreasing age from a minimum of 10 5 in the earliest ordovician to a maximum of 1 5 at the ordovician silurian boundary the 13c values show a general positive correlation with 18o and increase from 2 5 in the earliest ordovician to as high as 7 at the ordovician silurian boundary the magnitudes of ordovician excursions for both 18o and 13c are similar to those reported previously for the entire phanerozoic different genera of brachiopods from the same stratigraphie level did not yield any large differences in their isotopic compositions suggesting that vital effects did not influence decisively the isotope values of the studied skeletal parts petrographic examination and trace element analyses indicate that brachiopod shells from llandeilo to ashgill strata are well preserved and thus may have retained their primary isotopic signatures the same criteria for the tremadoc arenig and some llanvirn brachiopods suggest partial diagenetic alteration of 18o values in these samples but this does not preclude their utility as a recorder of a primary 13c signal the observed 18o trend for the well preserved portion of the record may reflect progressive cooling during ordovician perhaps complemented by a changing 18o values of seawater the latter could have been a consequence of a net increase in the rate of high temperature water rock interaction relative to its low temperature counterpart as indicated also by the large coeval decrease of marine 87sr86sr superimposed on the above long term 18o trend is a positive excursion of about 2 at the end of the ordovician probably reflecting a large expansion of polar ice caps the magnitude of this excursion indicates a degree of glaciation comparable to that at the height of the quaternary glacial episodes the secular 13c trend may reflect a progressive increase in marine organic productivity and or enhanced organic deposition in the ordovician oceans particularly noticeable at the time of the terminal ordovician glaciation

preslip and cascade processes initiating laboratory stick slip recent modeling studies have explored whether earthquakes begin with a large aseismic nucleation process or initiate dynamically from the rapid growth of a smaller instability in a cascade up process to explore such a case in the laboratory we study the initiation of dynamic rupture stick slip of a smooth saw cut fault in a 76 mm diameter cylindrical granite laboratory sample at 40 120 mpa confining pressure we use a high dynamic range recording system to directly compare the seismic waves radiated during the stick slip event to those radiated from tiny m 6 discrete seismic events commonly known as acoustic emissions aes that occur in the seconds prior to each large stick slip the seismic moments focal mechanisms locations and timing of the aes all contribute to our understanding of their mechanics and provide us with information about the stick slip nucleation process in a sequence of 10 stick slips the first few microseconds of the signals recorded from stick slip instabilities are nearly indistinguishable from those of premonitory aes in this sense it appears that each stick slip begins as an ae event that rapidly 20 s grows about 2 orders of magnitude in linear dimension and ruptures the entire 150 mm length of the simulated fault we also measure accelerating fault slip in the final seconds before stick slip we estimate that this slip is at least 98 aseismic and that it both weakens the fault and produces aes that will eventually cascade up to initiate the larger dynamic rupture

esr dating and the human evolution contribution to the chronology of the earliest humans in europe abstract in the last 20 years the electron spin resonance esr dating method has allowed the establishment of a chronological time frame over most of the history of human evolution despite many difficulties found for esr dating of bones and carbonates tooth enamel dated by esr has been proven as a reliable method in its application to fossil teeth and quartz both of the latter materials have allowed dating of early and middle pleistocene sites which are not datable using other methods such as the argon argon method in particular recent discoveries of human remains in western europe have been proposed to be sites of the earliest arrival of humans there and have been dated to the early pleistocene by esr using quartz and tooth enamel combined esr and u series dating of fossil herbivore teeth are the only means of dating layers from which such ancient remains have been recovered in western europe good examples are the sites of atapuerca gran dolina spain and visogliano italy which have been dated using tooth enamel when no bones and teeth can be found in prehistoric sites esr dating on quartz extracted from sediments has been used to date sites whose ages range over the entire quaternary period we present here two examples that occur in fluvial terraces of the river creuse france and at monte poggiolo site italy where several artefacts of an archaic pebble industry have been recovered

acoustic emissions document stress changes over many seismic cycles in stick slip experiments 1 the statistics of large earthquakes commonly involve large uncertainties due to the lack of long term robust earthquake recordings small scale seismic events are abundant and can be used to examine variations in fault structure and stress we report on the connection between stress and microseismic event statistics prior to the possibly smallest earthquakes those generated in the laboratory we investigate variations in seismic b value of acoustic emission events during the stress buildup and release on laboratory created fault zones we show that b values mirror periodic stress changes that occur during series of stick slip events and are correlated with stress over many seismic cycles moreover the amount of b value increase associated with slip events indicates the extent of the corresponding stress drop consequently b value variations can be used to approximate the stress state on a fault a possible tool for the advancement of time dependent seismic hazard assessment citation goebel t h w d schorlemmer t w becker g dresen and c g sammis 2013 acoustic emissions document stress changes over many seismic cycles in stick slip experiments geophys res lett 40 2049 2054 doi 10 1002 grl 50507

variations in earthquake size distribution across different stress regimes the earthquake size distribution follows in most instances a power law1 2 with the slope of this power law the b value commonly used to describe the relative occurrence of large and small events a high b value indicates a larger proportion of small earthquakes and vice versa statistically significant variations of b values have been measured in laboratory experiments mines and various tectonic regimes such as subducting slabs near magma chambers along fault zones and in aftershock zones3 however it has remained uncertain whether these differences are due to differing stress regimes as it was questionable that samples in small volumes such as in laboratory specimens mines and the shallow earth s crust are representative of earthquakes in general given the lack of physical understanding of these differences the observation that b values approach the constant 1 if large volumes are sampled4 was interpreted to indicate that b 1 is a universal constant for earthquakes in general5 here we show that the b value varies systematically for different styles of faulting we find that normal faulting events have the highest b values thrust events the lowest and strike slip events intermediate values given that thrust faults tend to be under higher stress than normal faults we infer that the b value acts as a stress meter that depends inversely on differential stress

determination of both chemical and stable isotope composition in milligramme size carbonate samples abstract isotopic analysis of carbonates involves dissolution of the sample in 100 phosphoric acid analysis of the acid after reaction using inductive coupled plasma source spectrometry gives the chemical composition of the same sample molar fractions of cations in carbonate minerals can be determined to about 0 1 for ca 0 04 for mg 0 06 for fe 60 ppm for mn and 90 ppm for sr even the minor carbonate component in shales can be analyzed if a correction for leaching of clay minerals is made by reference to the al content of the solution however loss in accuracy ensues because of the uncertainty in the correction

carbon isotope stratigraphy of the furongian berry head formation port au port group and tremadocian watts bight formation st george group western newfoundland and the correlative significance carbon isotope stratigraphy of the furongian stage 10 upper cambrian and tremadocian lowermost ordovician reveals distinct variations from the carbonates of the berry head and watts bight form

isotopic evidence for geochemical decoupling between ancient epeiric seas and bordering oceans implications for secular curves isotopic analysis of conodonts and their host limestones sampled between two regionally extensive altered volcanic ash layers in eastern laurentia shows that a 454 ma epeiric sea maintained large lateral differences in nd and c isotope compositions this is consistent with inferred temperature salinity defined epicontinental water masses and restricted circulation between epicontinental and oceanic environments because the majority of old marine fossils and sedimentary rocks are known from epeiric seas some isotope excursions in ancient marine strata may originate from expansion and contraction of geochemically distinct epicontinental water masses rather than global scale changes in the state of the earth ocean system

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

analysis of similar event clusters in aftershocks of the 1994 northridge california earthquake 1 we perform waveform cross correlation on over 14 000 aftershocks of the 1994 northridge mw 6 7 earthquake in southern california as recorded by short period stations of the southern california seismic network scsn approximately 10 30 of the events belong to similar event clusters depending upon the similarity criteria that are applied we relocate events within 218 of these clusters to a relative location accuracy of about 30 m using the differential times obtained from the cross correlation these relocated event clusters often show planar features suggestive of faults at depth and we apply principal parameter analysis to characterize the shape of each cluster and to compute best fitting planes in several cases these planes are parallel to the main shock fault plane however more generally the seismicity planes exhibit a wide range of orientations suggesting complexity in the aftershock faulting composite focal mechanisms can be obtained for each cluster by combining the p polarity data from individual events a comparison of polarity measurement differences within similar event clusters provides constraints on the error rate in the individual focal mechanisms for some clusters we are able to resolve the primary versus auxiliary fault plane ambiguity by comparing the computed focal mechanisms with the best fitting seismicity planes individual event focal mechanisms are in general agreement with the composite focal mechanisms for the similar event clusters events occurring along the main shock rupture plane are mainly thrust whereas events in the hanging wall are predominately strike slip

could the late permian deep ocean have been anoxic models of ocean circulation and biogeochemical cycles are used to speculate about possible mechanisms of deep sea anoxia across the permo triassic boundary two modes of likely late permian ocean thermohaline circulation are identified a vigorous thermal mode driven by cooling in southern polar latitudes and a weaker haline mode driven by evaporation from the subtropics we find that the thermal mode typical of climates such as our own is unlikely to surpport deep sea anoxia the haline mode which might exist in warm climates with enhanced hydrological cycles can lead to significant but periodic depletion of oxygen in the panthalassic deep ocean however owing to the inherent instability of the haline mode a deep sea anoxia persisting for millions of years is not clearly supported by this study though mechanisms emerge which might be consistent with the observed record the enhanced hydrological cycle or reduced oceanic diapycnal mixing required to obtain the haline mode remain unconstrained for the late permian

potential for geophysical experiments in large scale tests potential research applications for large specimen geophysical experiments include measurements of scale dependence of physical parameters and examination of interactions with heterogeneities especially flaws such as cracks in addition increased specimen size provides opportunities for improved recording resolution and greater control of experimental variables large scale experiments using a special purpose low stress 100 mpa

integration of underground mapping petrology and high resolution microseismicity analysis to characterise weak geotechnical zones in deep south african gold mines abstract a highly stressed shaft pillar is prone to large seismic events falls of ground and rockbursts which may cause injuries and loss of production especially in weak geotechnical zones it is thus important to identify weak geotechnical zones in order to mitigate risks in this study we present integrated studies underground mapping petrology rock mechanics and high resolution microseismicity analysis to understand the different geotechnical zones in the shaft pillar of cooke 4 mine in south africa the footwall of the remnant shaft pillar comprises the upper elsburg reef of the mondeor formation while the ventersdorp contact reef vcr of the venterspost formation and soft weak lavas of the westonaria formation form the hangingwall results from underground mapping and microscopic analysis show that the shaft pillar is composed of quartzites pebbly quartzites argillaceous quartzites and conglomerates underground mapping further shows that the shaft pillar is characterized by several discontinuities which vary from minor to macro scale fractures laboratory uniaxial compressive strength ucs tests indicate that quartzite has the strongest strength followed by pebbly quartzite argillaceous quartzite and lastly conglomerate analysis of high resolution acoustic emissions aes clusters indicates that the majority of aes are associated with the mining stope faces the clusters show the formation of ortlepp shears ahead of the stope which is caused by the excavation induced stress field microseismic data further reveal that the fracture turning point occurs in the soft strata weak hangingwall lavas the integration of these datasets has allowed us to develop the fracture model for different geotechnical zones which concurs with previous models developed for the similar underground environment i e weak soft lava hangingwall and quartzite conglomerate footwall this has major implications for future mining support production and safety

isotope stratigraphy of the ediacarian neoproterozoic iii of the adelaide rift complex australia and the overprint of water column stratification abstract this study establishes a high resolution 13c chemostratigraphic framework for the type ediacarian terminal proterozoic section in the adelaide rift complex a framework that contributes to the emerging global chronostratigraphic synthesis of a period that saw momentous changes in the earth s surface environment only 15 m of the 3 5 km thick type section consists of shallow water carbonates of the kind that have formed the basis of most previous studies of neoproterozoic chemostratigraphy however the organic 13corg record reveals a surprising richness of information and shows excellent utility in correlation between sections in the adelaide rift complex lateral variations in 13corg profiles correspond to expected diachronous patterns of basin fill with the addition of 87sr 86sr data correlation can also be made to the officer and amadeus basins consistent with known lithostratigraphic and sequence stratigraphic constraints sublittoral micritic carbonates of the upper nuccaleena formation cap dolostone and lower and middle wonoka formation show strong basinwide 13c depletion 13ccarb 3 to 10 despite compelling evidence for preservation of depositional 13ccarb such as good textural preservation evidence for sea floor lithification and in the wonoka formation pristine 87sr 86sr and low mn sr associated with the depleted carbonates are rare subaqueous evaporite relatively heavy 13corg and anomalously 13c depleted organic carbon of benthic microbial mat origin and a common cause salinity stratification of the water column is postulated the indicated palaeogeographic setting an evaporative mediterranean like basin tenuously connected to the world ocean is entirely consistent with previous suggestions of one or more messinian type desiccation events to explain very deep 1 km incised valleys or canyons in the adelaide rift complex and officer basin at horizons within the wonoka formation and correlates positive excursions in 13corg during basin stratification may in part be due to 12c depletion of surface waters by photosynthetic carbon fixation despite the proposed semi isolation of australian ediacarian basins from the world ocean major 13c excursions which can to some extent be differentiated by the monotonic rise in ediacarian marine 87sr 86sr appear to be correlatable to the upper windermere supergroup northwest canada

microseismic investigation of mining induced brittle fault activation in a chinese coal mine abstract the process whereby a brittle fault was activated by mining is not only significant for disaster prediction but also for earthquake prediction thus it was necessary to study their activation process in this study stress state ae acoustic emission ms microseismic activities during brittle fault activation stages of brittle fault activation and the relation between ae ms activities and brittle fault parameters were analysed and it was feasible to identify buried brittle faults determine their parameters and activation process based on ms monitoring the no 22517 working face in the dongjiahe coalmine was taken as an example firstly a buried brittle fault was identified in no 22517 working face by the ms monitoring method secondly the buried brittle fault parameters were determined its azimuth angle was 307 5 in the orbital roadway and 357 5 on the haulage roadway its dip angle was 73 and it was a reverse fault thirdly the activation process of the buried brittle fault was determined the buried brittle fault was not affected by the mining activities when the distance from mining activities to the buried brittle fault was over 300 m the disturbance stage was from 300 m to 80 m and the local activation stage from 100 m to 30 m and the whole activation stage around 30 m the b value decreased during the process of brittle fault activation and reached a minimum value at the whole activation stage it was concluded that these changes are related to the stress distribution around the brittle fault the results demonstrated that ms monitoring technology can detect small buried brittle faults ahead of the working face and is also an effective method to study the process and mechanism of brittle fault activation

carbon isotope record of late cambrian to early ordovician carbonates of the argentine precordillera a more than 2000 m thick cambrian ordovician carbonate platform succession developed on the exotic argentine precordillera terrane during rifting from laurentia and drifting towards gondwana on base of these carbonates a carbon isotope curve could be developed for the cambrian ordovician we measured 13ccarb and 13corg values on bulk rocks selected components and diagenetic cements whereas the carbon isotope signals of intertidal and supratidal rocks are altered by diagenesis most subtidal carbonates exhibit primary marine values we can report reliable curves for the middle late cambrian transition and for the latest cambrian to earliest middle ordovician the 13c curve matches well with the published data from global cambrian ordovician boundary sections excursions and shifts in the carbon isotope curve correspond to events in sequence stratigraphy this indicates the interdependence on sea level which rules the productivity and or preservation of organic carbon and therefore the partition between corg and ccarb burial

depletion of 13c in seawater σc02 on modern carbonate platforms significance for the carbon isotopic record of carbonates seawater co2 from modern carbonate platforms bahama banks and florida is depleted in 13c by as much as 4 relative to open ocean water depletion in 13c is caused by isotopically light co2 input from respiration of marine and terrestrial organic matter during water mass residence on the bank as such depletion in 13c is related to changes in water chemistry driven by evaporation freshwater discharge and caco3 withdrawal deviation of modern platform seawater 13c values away from those of surface seawater suggests that 13c values of ancient cratonic carbonate must be cautiously interpreted initial depositional environment as well as alteration during diagenesis must be considered in extracting valid secular trends for oceanic 13c variation

ocean stagnation and end permian anoxia ocean stagnation has been invoked to explain the widespread occurrence of organic carbon rich laminated sediments interpreted to have been deposited under anoxic bottom waters at the time of the end permian mass extinction however to a first approximation stagnation would severely reduce the upwelling supply of nutrients to the photic zone reducing productivity moreover it is not obvious that ocean stagnation can be achieved numerical experiments performed with a three dimensional global ocean model linked to a biogeochemical model of phosphate and oxygen cycling indicate that a low equator to pole temperature gradient could have produced weak oceanic circulation and widespread anoxia in the late permian ocean we find that polar warming and tropical cooling of sea surface temperatures cause anoxia throughout the deep ocean as a result of both lower dissolved oxygen in bottom source waters and increased nutrient utilization buildup of quantities of h2s and co2 in the late permian ocean sufficient to directly cause a mass extinction however would have required large increases in the oceanic nutrient inventory

isotope stratigraphy of the lapa formation sao francisco basin brazil implications for late neoproterozoic glacial events in south america the lapa formation is a thick carbonate sequence 900 m that constitutes the upper part of the vazante group on the s francisco craton brazil it conformably overlies a previously unrecognized glacial diamictite unit of poorly constrained age the sequence above the glacial unconformity consists predominantly of organic rich shale subtidal rhythmic dolomicrites and microbialaminites and intertidal stromatolites four boreholes spanning different depositional settings were sampled at highresolution and investigated for their petrographic and chemical criteria to evaluate their degree of preservation the 13 c and 18 o values of well preserved lapa carbonate microsamples range from 8 2 to 3 3 vpdb and from 13 6 to 0 9 vpdb respectively each of the 13 c profiles of the investigated cores reveals two strong negative excursions of up to 8 an event in post glacial dolomicrites immediately above the glaciogenic unit and a 10 m interval of organic rich shale and a second near the top of the sequence associated with a shale interval based on the observation of dropstones and sedimentary iron formation in the underlying diamictite as well as the distinguishable carbon isotope trends the lapa formation is considered as a cap carbonate lithofacies the age of the lapa formation is presently unknown but the least radiogenic 87 sr 86 sr value 0 7068 associated with a negative carbon isotope excursion matches that from the rasthof formation in namiba on the congo craton which is radiometrically constrained to be younger than ca 750 ma

characteristic small earthquake sequence off sanriku northeastern honshu japan 1 we found eight similar earthquakes of m4 8 regularly occurring from 1957 to 1995 on the plate boundary off sanriku northeastern japan the mean recurrence interval of the events is 5 35 years and its standard deviation is only 0 53 years these events have the same focal mechanisms of low angle thrust fault type and their source sizes are estimated to be around 1 km the slip of each event is comparable to the cumulative amount of relative plate motion in the inter seismic period thus these events are probably caused by repeating slip at a small but strong asperity surrounded by creeping zone on the plate boundary the next event was expected to occur by the end of november 2001 with 99 probability and actually m4 7 event occurred on november 13 2001

frequency magnitude distribution of 3 7 mw 1 mining induced earthquakes around a mining front and b value invariance with post blast time we investigated frequency magnitude distribution fmd of acoustic emissions ae occurring near an active mining front in a south african gold mine using a catalog developed from an ae network which is capable of detecting aes down to m w 5 when records of blasts were removed fmds of aes obeyed a gutenberg richter law with similar b values not depending on post blasting time from the initial 1 min interval through more than 30 h this result denies a suggestion in a previous study richardson and jordan bull seismol soc am 92 1766 1782 2002 that new fractures generated by blasting disturb the size distribution of background events which they interpreted as slip events on existing weak planes our ae catalog showed that the gr law with b 1 2 was valid between m w 3 7 and 0 for aes around the mining front further using the mine s seismic catalog which covers a longer time period of the same area we could extend the validity range of the gr law with the same b value up to m w 1

source of diagenetic fluids from fluid inclusion gas ratios abstract alteration of marine carbonates such as those from the mesoproterozoic and lower ordovician during burial history is carried out by diagenetic fluids that could potentially have different sources during precipitation diagenetic minerals may trap tiny amounts of those solutions in fluid inclusions thus providing fossil archives and aliquots that offer valuable record about the origin of fluids the analysis of various fluid inclusion gases e g ch 4 co 2 n 2 he and ar may provide reliable information which allows the discrimination among different fluid sources generally speaking the meteoric cements should have n 2 ar ratio around 38 the value for air saturated water however the gases in inclusions of the current study trapped by diagenetic carbonates cements from independent depositional basins of different ages mesoproterozoic early ordovician and modern and locations canada usa brazil and java sea have n 2 ar ratios 92 which match non magmatic modified marine or meteoric fluids also the ar he ratios 3 in the studied fluid inclusions are significantly lower than those of calc alkaline magmatic fluids 20 thus excluding magmatic fluids as a potential source on the other hand some n 2 ar and ar he ratios of the studied samples approach values reported for basinal fluids from the hansonburg mvt deposit in new mexico 68 and 1 respectively suggesting that both meteoric mixed marine meteoric evolved meteoric and basinal fluids may be involved during carbonate diagenesis

effects of physical fault properties on frictional instabilities produced on simulated faults laboratory studies of large scale simulated faults show that physical properties of the fault specifically normal stress and fault roughness significantly influence the unstable shear failure behavior of the fault in addition the experiments provide insights into important length scaling effects that are useful for assessing concepts such as critical crack length or rupture nucleation dimension stick slip shear failures have been generated along a 2 m long simulated fault in a block of sierra white granite experiments were conducted at normal stresses between 0 6 and 4 mpa with two different prepared roughnesses of the simulated fault a smooth fault with a profilometer measured roughness of 0 2 m and a rough fault with a measured roughness of 80 m high speed records of shear strains and slip velocities clearly show both the propagation of the stick slip failures and details of the local deformations and motions from which slip weakening of the fault at the onset of sliding can be resolved both the dynamic stress drops of the stick slip events and the apparent fracture energies of the events determined from the records of the fault slip weakening increase with increasing normal stress although critical slip weakening displacements are insensitive to normal stress they increase with increased fault roughness such that the apparent fracture energies are also larger on the rough fault than on the smooth fault slip velocities in these experiments are influenced by roughness and are proportional to stress drop although the onset of slip is sharply defined the termination of slip is more gradual without a clear stopping phase measured rupture velocities on the rough fault are lower than those on the smooth fault when a length scale based on rupture nucleation dimensions directly proportional to critical displacements is introduced the data suggest that at fault lengths close to the nucleation lengths rupture velocity and slip velocity increase with increasing fault length

seismological studies at parkfield vi moment release rates and estimates of source parameters for small repeating earthquakes abstract waveform data from a borehole network of broadband seismographic stations have been used to study microearthquakes along the parkfield segment of the san andreas fault saf analysis of almost 10 years of such data demonstrates that much of the seismicity in this region consists of repeating sequences quasiperiodic sequences of earthquakes that are essentially identical in terms of waveform size and location scalar seismic moments have been estimated for 53 of these repeating sequences and combined with equivalent estimates from 8 similar but larger event sequences from the stone canyon section of the fault and the main parkfield sequence these estimates show that seismic moment is being released as a function of time in a very regular manner measurements of the moment release rate combined with an assumed tectonic loading rate lead to estimates of the seismic parameters source area slip and recurrence interval such parameters exhibit a systematic dependence upon source size over a range of 10 10 in seismic moment that can be described by three simple scaling relationships several implications of these scaling relationships are explored including the repeat time of earthquakes average stress drop strength of the fault and heat generated by earthquakes what emerges from this analysis of moment release rates is a quantitative description of an earthquake process that is controlled by small strong asperities that occupy less than 1 of the fault area this means that the fault is highly heterogeneous with respect to stress strength and heat generation such heterogeneity helps to explain many of the apparent contradictions that are encountered in the study of earthquakes such as why faults appear weak why significant heat flow is not observed how significant high frequencies can be generated by large earthquakes and how various geologic features such as pseudotachylytes might form

carbonate platform to foreland basin revised stratigraphy of the table head group middle ordovician western newfoundland carbonates of the table head group and associated strata were deposited along the western margin of a foreland basin during initial stages of the taconian orogeny and record collapse and cannibalization of a long lived carbonate platform the stratigraphy of klappa opalinski and james is here revised to reflect better understanding of lithologic units within this complex tectono stratigraphic assemblage the table head group now contains only three formations the table point and table cove formations as originally defined and the cape cormorant formation redefined and restricted to western port au port peninsula black cove formation shales are removed from the table head distinctive conglomerates once placed in the cape cormorant are now recognized as separate units within the overlying flysch and called the daniel s harbour member the foreland basin developed in three stages 1 fragmentation uplift and erosion of the platform and subsequent deposition of shallow water limestones table point

dolomitization of the lower ordovician watts bight formation of the st george group western newfoundland evidence of hydrothermal fluid alterationgeological survey of canada contribution 20080544 the watts bight formation in western newfoundland consists of a lower ordovician succession of shallow water carbonates and has been extensively dolomitized these dolomites occur as both replaceme

flake modification in european early and early middle pleistocene stone tool assemblages early and early middle pleistocene archeological sites provide data about human dispersals into europe from at least 1 2 ma up to now the fragmentary archeological record indicated only sporadic hominin presence with punctated migration waves not necessarily leading to colonization we consider an alternative demographical picture in which hominin presence in europe could have been sustained from this time this paper explores the possibility that early hominin groups confronted different landscapes by adapting their technology to changing ecosystems innovative technological achievements were developed into new forms out of potential existing within the variability of early stone industries leading to the production of a more diversified toolkit among these innovations the increased secondary knapping of flakes points to conceptually more complex production sequences this paper proposes a comparative view of secondary knapped flakes from some key early middle pleistocene sites in order to explore the hypothesis of demographical stability in western europe from this time

source parameters of picoseismicity recorded at mponeng deep gold mine south africa implications for scaling relations abstract we investigate the source parameters of picoseismic and nanoseismic events m w 4 1 recorded with a high sensitivity seismic network at the mponeng gold mine in south africa to gain new insights into the scaling of small seismic events the japanese german underground acoustic emission research in south africa jaguars network composed of one three component 3c accelerometer sensitivity 50 hz to 25 khz and 8 acoustic emission ae sensors sensitivity 1 khz to 180 khz is located at a depth of 3268 m and covers the limited volume of approximately 300 300 300 m the ae sensors are calibrated with respect to the 3c accelerometer in the frequency band 400 hz 17 khz the waveform data of two datasets are analyzed 1 the aftershock sequence of an m w 1 9 event that occurred approximately 30 m from our network and 2 the postblasting activity recorded during working days located at a distance 90 m from the network at the exploitation level for the analysis we applied spectral fitting and spectral ratio methods the calculated values of m w range from 0 8 down to 4 1 with corner frequencies 0 8 khz 13 6 khz source sizes from 8 cm to 1 3 m we observe static stress drops ranging from 1 mpa to 10 0 mpa with apparent stresses of 0 01 mpa 1 00 mpa stress drops are independent of the moment suggesting self similar behavior in the analyzed magnitude range 4 1 m w

stratigraphic investigations of carbon isotope anomalies and neoproterozoic ice ages in death valley california an unusual richness of biogeochemical events is recorded in neoproterozoic cambrian strata of the death valley region california united states eight negative carbon isotope d13c excursions are found in carbonate units between 1 08 ga and the precambrian cambrian boundary four of these excursions occur in carbonates that contain textural features similar to those found globally in postglacial cap carbonates including one or more of the following laminite with rollup structures apparent tube rocks seafloor precipitates and sheet crack cements however only two of these units the sourdough limestone member of the kingston peak formation and the noonday dolomite rest directly upon glacial strata the basal beck spring dolomite and the rainstorm member of the johnnie formation each contain negative excursions and cap carbonate like lithofacies but do not rest on known glacial deposits if the negative d13c excursions are assumed to record depositional processes two equally interesting hypotheses are possible 1 the death valley succession records four glacial pulses in neoproterozoic time but glacial units are not preserved at two stratigraphic levels 2 alternatively other global oceanographic processes can cause negative excursions and cap carbonate like facies in addition to or independent of glaciation

fabric retentive non luminescent brachiopods as indicators of original delta 13 c and delta 18 o composition a test abstract fabric retentive non luminescent helderbergian brachiopods from open marine deposits analogous to brachiopods used in other studies to determine paleo oceanic stable isotopic composition exhibit depleted 13c values immediately below the erosional contact and more enriched values of 13c at greater stratigraphic distances below this surface in addition 13c values of these brachiopods display a marked shift across the erosional surface and values above it are essentially the same as those 30 m or more beneath the surface complementing these trends whole rock analyses metastable high agnesian calcite constituents echinoderms as well as early equant calcite cement also exhibit an increased depletion trend in 13c values as the helderberg oriskany contact is approached from below fabric retentive luminescent as well as obviously recrystallized brachiopods display stable isotopic values similar to those of fabric retentive non luminescent brachiopods thus best preserved fabric retentive non luminescent brachiopods exhibit values similar to obviously recrystallized brachiopods diagenetically altered metastable constituents echinoderms stable early meteoric cements and whole rock samples helderberg strata of new york state were affected by early meteoric diagenesis during a siegenian exposure event prior to deposition of the overlying marine oriskany sandstone meteoric diagenesis during this exposure gave rise to a characteristic carbon isotopic depletion trend approaching the helderberg oriskany contact all of the skeletal constituents underwent isotopic exchange during early diagenetic exposure to meteoric waters consequently the practice of using fabric retentive non luminescent brachiopods as indicators of their original chemistry and by extension paleo oceanic chemistry is questioned

sr c and o isotope geochemistry of ordovician brachiopods a major isotopic event around the middle late ordovician transition here we present sr c and o isotope curves for ordovician marine calcite based on analyses of 206 calcitic brachiopods from 10 localities worldwide these are the first ordovician wide isotope curves that can be placed within the newly emerging global biostratigraphic framework a total of 182 brachiopods were selected for c and o isotope analysis and 122 were selected for sr isotope analysis seawater 87sr 86sr decreased from 0 7090 to 0 7078 during the ordovician with a major quite rapid fall around the middle late ordovician transition most probably caused by a combination of low continental erosion rates and increased submarine hydrothermal exchange rates mean 18o values increase from 10 to 3 through the ordovician with an additional short lived increase of 2 to 3 during the latest ordovician due to glaciation although diagenetic alteration may have lowered 18o in some samples particularly those from the lower ordovician maximum 18o values which are less likely to be altered increase by more than 3 through the ordovician in both our data and literature data we consider that this long term rise in calcite 18o records the effect of decreasing tropical seawater temperatures across the middle late ordovician transition superimposed on seawater 18o that was steadily increasing from 3 standard mean ocean water smow by contrast 13c variation seems to have been relatively modest during most of the ordovician with the exception of the globally documented but short lived latest ordovician 13c excursion up to 7 nevertheless an underlying trend in mean 13c can be discerned changing from moderately negative values in the early ordovician to moderately positive values by the latest ordovician these new isotopic data confirm a major reorganization of ocean chemistry and the surface environment around 465 to 455 ma the juxtaposition of the greatest recorded swings in phanerozoic seawater 87sr 86sr and 18o at the same time as one of the largest marine transgressions in phanerozoic earth history suggests a causal link between tectonic and climatic change and emphasizes an endogenic control on the o isotope budget during the early paleozoic better isotopic and biostratigraphic constraints are still required if we are to understand the true significance of these changes we recommend that future work on ordovician isotope stratigraphy focus on this outstanding middle late ordovician event

one million years of cultural evolution in a stable environment at atapuerca burgos spain abstract the present paper analyses the evidence provided by three sites sima del elefante gran dolina and galeria located in the trinchera del ferrocarril of the sierra de atapuerca these three sites are cave infillings that contain sediments deposited from approximately 1 2 ma to 200 kyr pollen herpetofauna and small and large mammal remains are used as proxies to obtain a general picture of the environmental changes that occurred at the sierra de atapuerca throughout the one million year period represented at these sites similarly cultural changes are tracked analyzing the evidence of human behavior obtained from the study of several bone and lithic assemblages from these three sites at least three periods with different cultural features involving technology subsistence and behavior are determined from the available evidence the first two periods correspond to the mode 1 technology and homo antecessor the first is dated around 1 2 to 1 0 ma and reflects opportunistic behavior both in technology and subsistence the second period is around 800 kyr bp mode 1 technology is still maintained but subsistence strategies include systematic hunting and the use of base camps the third period is dated between 500 ka and 200 ka and corresponds to the mode 2 technology and the acquisition of directional hunting and other organizational strategies by homo heidelbergensis a transition from mode 2 to mode 3 seems to appear at the end of this time range and may reflect the early phases of a fourth cultural change with regard to the environment our main conclusion is that there was an absence of extremely harsh conditions at atapuerca throughout this time period the presence of mediterranean taxa was constant and the dominant landscape was a savannah like open environment probably with small forest patches an alternation of mediterranean and mesic species as the dominant component of the tree storey was induced by the climatic cycles and steppes spread across the landscape during the drier periods in any case it is not possible to establish clear cut off points separating entirely different environmental episodes our results show no evidence of any relationship between environmental change and cultural change at the sierra de atapuerca

earthquake nucleation on faults with rate and state dependent strength abstract dieterich j h 1992 earthquake nucleation on faults with rate and state dependent strength in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 115 134 faults with rate and state dependent constitutive properties reproduce a range of observed fault slip phenomena including spontaneous nucleation of slip instabilities at stresses above some critical stress level and recovery of strength following slip instability calculations with a plane strain fault model with spatially varying properties demonstrate that accelerating slip precedes instability and becomes localized to a fault patch the dimensions of the fault patch follow scaling relations for the minimum critical length for unstable fault slip the critical length is a function of normal stress loading conditions and constitutive parameters which include dc the characteristic slip distance if slip starts on a patch that exceeds the critical size the length of the rapidly accelerating zone tends to shrink to the characteristic size as the time of instability approaches solutions have been obtained for a uniform fixed patch model that are in good agreement with results from the plane strain model over a wide range of conditions above the steady state stress the logarithm of the time to instability linearly decreases as the initial stress increases because nucleation patch length and premonitory displacement are proportional to dc the moment of premonitory slip scales by d3c the scaling of dc is currently an open question unless dc for earthquake faults is significantly greater than that observed on laboratory faults premonitory strain arising from the nucleation process for earthquakes may by too small to detect using current observation methods excluding the possibility that dc in the nucleation zone controls the magnitude of the subsequent earthquake then the source dimensions of the smallest earthquakes in a region provide an upper limit for the size of the nucleation patch

quasi static slip patch growth to 20 m on a geological fault inferred from acoustic emissions in a south african gold mine three months of acoustic emission ae monitoring in a south african gold mine down to mw 5 revealed a newly emergent planar cluster of 7557 events 3 9 mw 1 8 typical rupture radius of 6 70 cm that expanded with time to reach a size of 20 m on a preexisting geological fault near an active mining front 1 km beneath the ground it had a sharply defined planar configuration with hypocenters aggregated within a thickness of only several decimeters we infer that the zone defines an aseismic slip patch on the fault wherein the individual aes represent failures of very small asperities being loaded by the aseismic slip additional support for the interpretation was obtained by analyzing composite focal mechanisms and repeating events the patch expansion over 2 months was likely quasistatic because all individual aes ruptured much smaller areas than the cluster size at the corresponding time the b values dropped gradually from 2 6 to 1 4 consistent with a significant increase in shear stress expected of the mining style another cluster with similar characteristics emerged later on a neighboring part of the same fault and grew to a 10 m extent in the last weeks of the study period the quasi static expansion of inferred localized slow slip patches to sizes of 10 20 m suggests that the critical crack length on natural faults can be at least as large much exceeding the decimeter range derived from laboratory stick slip experiments on saw cut rocks

foreshock sequence of the 1992 landers california earthquake and its implications for earthquake nucleation the june 28 1992 landers california earthquake mw 7 3 was preceded for about 7 hours by a foreshock sequence consisting of at least 28 events in this study we examine the geometry and temporal development of the foreshocks using high precision locations based on cross correlation of waveforms recorded at nearby stations by aligning waveforms rather than trying to obtain travel time picks for each event independently we are able to improve the timing accuracy greatly and to make very accurate travel time picks even for emergent arrivals we perform a joint relocation using the improved travel times and reduce the relative location errors to less than 100 m horizontally and less than 200 m vertically with the improved locations the geometry of the foreshock sequence becomes clear the landers foreshocks occurred at a right step of about 500 m in the mainshock fault plane the nucleation zone as defined by the foreshock sequence is southeast trending to the south and nearly north trending to the north of the right step this geometry is confirmed by the focal mechanisms of the foreshock sequence which are right lateral and follow the trend as determined by the foreshock locations on the two straight segments of the fault and are rotated clockwise for foreshocks that occur within the step the extent of the foreshock sequence is approximately 1 km both vertically and horizontally modeling of the coulomb stress changes due to all previous foreshocks indicates that the foreshocks probably did not trigger each other this result is particularly clear for the mw 4 4 immediate foreshock since stress transfer in the sequence appears not to have played a significant role in its development we infer an underlying aseismic nucleation process probably aseismic creep other studies have shown that earthquake nucleation may be controlled by fault zone irregularities this appears to be true in the case of the landers earthquake although the size of the irregularity is so small that it is not detectable by standard location techniques

scaling of the shear rupture process from nucleation to dynamic propagation implications of geometric irregularity of the rupturing surfaces a series of systematic high resolution laboratory experiments have been performed on the nucleation of propagating slip failure on preexisting faults having different surface roughnesses to demonstrate how the size scale and duration of shear rupture nucleation are affected by geometric irregularity of the rupturing surfaces on the basis of the experimental results it has been discussed theoretically how consistently scale dependent physical quantities inherent in shear rupture are scaled the experiments led to conclusive results that the nucleation process consists of two phases phase i an initial quasi static phase and phase ii a subsequent accelerating phase and that the nucleation process is greatly affected by geometric irregularities on the rupturing surfaces in phase i the rupture grows at a slow steady speed which is independent of the rupture growth length l in contrast during phase ii the rupture develops at accelerating speeds v which increase with an increase in l obeying a power law v vs l c n where vs is the shear wave velocity c is the characteristic length representing the geometric irregularity of the fault surfaces and and n are constants 8 87 10 29 and n 7 31 scale dependency of scale dependent physical quantities including the nucleation zone size and its duration is commonly ascribed to scale dependency of the slip dependent constitutive law parameter dc which is in turn governed by c it has been discussed that a unified comprehension can be provided for shear rupture of any size scale if the constitutive law for shear rupture is formulated as a slip dependent law

oxygenation as a driver of the great ordovician biodiversification event the largest radiation of phanerozoic marine animal life quadrupled genus level diversity towards the end of the ordovician period about 450 million years ago a leading hypothesis for this great ordovician biodiversification event is that cooling of the ordovician climate lowered sea surface temperatures into the thermal tolerance window of many animal groups such as corals a complementary role for oxygenation of subsurface environments has been inferred based on the increasing abundance of skeletal carbonate but direct constraints on atmospheric o2 levels remain elusive here we use high resolution paired bulk carbonate and organic carbon isotope records to determine the changes in isotopic fractionation between these phases throughout the ordovician radiation these results can be used to reconstruct atmospheric o2 levels based on the o2 dependent fractionation of carbon isotopes by photosynthesis we find a strong temporal link between the great ordovician biodiversification event and rising o2 concentrations a pattern that is corroborated by o2 models that use traditional carbon sulfur mass balance we conclude that that oxygen levels probably played an important role in regulating early palaeozoic biodiversity levels even after the cambrian explosion an increase in biodiversity 450 million years ago coincided with a rise in atmospheric oxygen concentrations suggests a geochemical analysis oxygen availability may have thus helped spur the radiation alongside climatic cooling

high resolution carbon isotope stratigraphy of the lower and middle ordovician succession of the yangtze platform china implications for global correlation the lower and middle ordovician of the yangtze platform china is characterized by a sedimentary succession dominated by carbonate rocks three sections spanning the nantsinkuan lunshan fenhsiang hunghuayuan and dawan zitai formations corresponding to the tremadocian dapingian in age have been sampled for high resolution 13c chemostratigraphy 542 samples in total our new 13c data reveal five tie points with the potential for global correlation 1 a positive 13c excursion in the lower nantsinkuan formation within the tremadocian rossodus manitouensis zone 2 an excursion with two peaks roughly within the late tremadocian paltodus deltifer zone 3 a positive 13c shift in the lower hunghuayuan formation within the early floian serratognathus diversus zone 4 a gradual positive 13c shift in the late floian ranging from the uppermost s diversus zone to the basal oepikodus evae zone 5 a minor negative shift in the lower dawan zitai formation within the early dapingian baltoniodus triangularis zone these excursions are herein used for correlation of the yangtze platform strata with successions from south china north china the argentine precordillera north america and baltica from a palaeogeographical perspective the gudongkou xiangshuidong and daling sections represent depositional environments along an inner to outer ramp profile 13c data from these sections show successively heavier higher 13c values with increasing depositional depth this is interpreted as due to remineralization of organic carbon within the carbonate rocks supplementary material carbon and oxygen isotope data are available at https doi org 10 6084 m9 figshare c 4767080

unexpectedly frequent occurrence of very small repeating earthquakes 5 1 mw 3 6 in a south african gold mine implications for monitoring intraplate faults we observed very small repeating earthquakes with 5 1 mw 3 6 on a geological fault at 1 km depth in a gold mine in south africa of the 851 acoustic emissions that occurred on the fault during the 2 month analysis period 45 were identified as repeaters on the basis of waveform similarity and relative locations they occurred steadily at the same location with similar magnitudes analogous to repeaters at plate boundaries suggesting that they are repeat ruptures of the same asperity loaded by the surrounding aseismic slip background creep application of the nadeau and johnson 1998 empirical formula nj formula which relates the amount of background creep and repeater activity and is well established for plate boundary faults to the present case yielded an impossibly large estimate of the background creep this means that the presently studied repeaters were produced more efficiently for a given amount of background creep than expected from the nj formula when combined with an independently estimated average stress drop of 16 mpa which is not particularly high it suggests that the small asperities of the presently studied repeaters had a high seismic coupling almost unity in contrast to one physical interpretation of the plate boundary repeaters the productivity of such repeaters per unit background creep is expected to increase strongly as smaller repeaters are considered mo 1 3 as opposed to mo 1 6 of the nj formula which may be usable to estimate very slow creep that may occur on intraplate faults

dolomitization of the lower ordovician aguathuna formation carbonates port au port peninsula western newfoundland canada implications for a hydrocarbon reservoir the lower ordovician aguathuna formation 100 m thick is formed of shallow marine carbonates which constitute the uppermost part of the st george group of western newfoundland sedimentation wa

interpreting carbon isotope excursions carbonates and organic matter abstract variations in the carbon isotopic compositions of marine carbonate and organic carbon provide a record of changes in the fraction of organic carbon buried through time and may provide clues to changes in rates of weathering and sources of organic carbon paired carbonate and organic carbon isotope determinations provide a possibility of interpreting not only changes in the global carbon cycle through time but changes in atmospheric pco2 as well interpretations of these types of data are typically rather qualitative a quantitative basis is required to develop a better understanding of changes in the carbon cycle for this purpose we employ a simple model of the global carbon cycle which is subjected to a number of different perturbations each lasting 500 ky i e much longer than the residence times of carbon and phosphorus in the ocean atmosphere system in addition to standard considerations of carbon mass and isotopic fluxes to the ocean atmosphere system from weathering and volcanism and fluxes of organic carbon and carbonate carbon to sediments the model incorporates sensitivity of the photosynthetic carbon isotope effect to changes in pco2 the inclusion of this parameter leads to unexpected carbon isotope responses to forcing that causes increased rates of organic carbon burial a series of simple to more complex simulations illustrates the significant effects of varying differences between the carbon isotopic composition of sedimented carbonate and organic carbon b with constant b a 50 increase in organic carbon burial produces a parallel increase in carbonate and organic carbon isotopic compositions however the same simulation with b responsive to pco2 changes produces an initial parallel 13 c increase but this is followed by an even greater 13 c enrichment in organic carbon because pco2 falls in response to increased organic carbon burial the counterintuitive overall result of the enhanced organic carbon burial event is that the carbonate carbon isotopic composition actually decreases because of the more substantial increase in 13 c org in addition we illustrate the effects on carbon isotopic compositions of the oceanic inorganic carbon reservoir and buried organic matter of a 50 increase in volcanic co2 outgassing a 50 increase in weathering rate with coupled phosphate and riverine carbon flux responses a 50 decrease in shale associated organic carbon weathering a 50 decrease in silicate weathering rate and the possible effects of the rise in abundance of c4 plants in the late miocene to recent we compare the model simulated carbon isotopic responses for some of these experiments to paired carbonate and organic carbon records to illustrate how these records might be interpreted in light of the model response

theory of time dependent rupture in the earth at a velocity x which is a well defined function of k this propagation is stable and quasi static and is referred to as subcritical crack growth we shall use the terms stable quasistatic and subcritical to mean propagation at velocities much less than the sonic velocities of the medium this behavior results from stress induced corrosion at the crack tip the principal corrodent for the present application being h20 this behavior has been firmly established in the laboratory for mode i tensile cracks in a wide variety of materials ineluding silicates and silicate glasses see cholz 1968a 1972a martin 1972 wiederhorn and bolz 1970 atkinson 1979 lawn and wilshaw 1975 knott 1973 the form of the relationship between k and x does not vary significantly with the material only the parameters in the law vary as an example we show in figure 1 data on subcritical crack growth in quartz after atkinson 1979 the empirical relationship is found to take the form