evaluation of the results for an intermediate term prediction of the 8 january 2006 mw 6 9 cythera earthquake in the southwestern aegean during the past few decades the critical earthquake model which is based on observations concerning accelerating seismic deformation and concepts of the critical point dynamics has been proposed by various seismologists as a useful tool for intermediate term earthquake prediction a refined approach of this model has been previously applied to search for preshock critical regions in the southern aegean using all available data until the middle of 2002 a critical region corre sponding to a large mainshock had been identified papazachos et al 2002a b in the southwestern part of the aegean near the cythera island the predicted in 2002 parameters for this ensuing earthquake are u 36 5 n k 22 7 e for the epicental geographic coordinates with a model uncertainty of 120 km focal depth 100 km moment magnitude m 6 9 0 5 and origin time tc 2006 4 2 0 the generation of the strong cythera earthquake on 8 january 2006 with m 6 9 epicenter coordinates u 36 2 n and k 23 4 e and a focal depth of h 65 km satisfies this intermediate term prediction the region where significant macroseismic effects were anticipated from the predicted mainshock cythera south peloponnesus west crete and west cyclades corresponds to the area where damage by the 8 january 2006 strong earthquake has been observed the verification of this prediction is strong evidence that the intermediate term prediction of strong earthquakes is potentially feasible but additional forward testing of the model is needed to validate this result

lithostratigraphie et datation du proterozoique de la boutonniere d ifni anti atlas maroc abstract in the ifni window in the southwestern part of the moroccan anti atlas unfolded volcanic rocks and sediments rest on a lower proterozoic basement their lithology and relations with dated magmatic rocks lead to a separation into three upper proterozoic groups the absence of the middle proterozoic could also be demonstrated as well as the progressive transition from uppermost proterozoic to lower cambrian the originality of the radiometric ages obtained in the bou azzer region is emphasized as well as the evolution of the pan african tectonics throughout the western anti atlas the intensity of which progressively decreases southwestward

upper proterozoic glaciogenic rocks and their stratigraphic significance abstract among more than 300 precambrian tillites mentioned in the literature only 25 can be identified as glacial rocks tillites are known from all continents with the exception of antarctica the uneven stratigraphic distribution of tillites cannot be explained as being due to differences in knowledge roughly synchronous glacial formations and groups form wide regional glaciohorizons they are concentrated in two stratigraphic intervals named glaciocomplexes one such the canadian glaciocomplex consisting of three or four glaciohorizons occurs in the lowermost lower proterozoic in north america and south africa the second glaciocomplex the african containing four or more glaciohorizons is known in the uppermost part of the precambrian in europe asia north and south america africa australia the glaciohorizons and glaciocomplexes reflect oscillation dynamics of glaciations and show a hierarchical structure of glacial events the glaciohorizons and glaciocomplexes were deposited during glacial periods and glacial eras on and marginal to the continents in high and middle paleolatitudes of both hemispheres by comparison with late cenozoic glacial events the duration of the ancient glacioperiods can be roughly estimated at between some millions and a few tens of millions of years within these limits each glaciohorizon can be asynchronous the glaciohorizons have great importance for regional correlations of the precambrian interregional and intercontinental glacial correlations however require radiometric and biostratigraphic controls glacial units can be used in construction of a global stratigrphic scale for the precambrian

a chemostratigraphic overview of the late cryogenian interglacial sequence in the adelaide fold thrust belt south australia within the neoproterozoic sequence of the adelaide fold thrust belt south australia two of the most severe ice ages in earth history sturtian and marinoan are recorded in the glacigenic rocks which mark the base and top of the 4 5 km thick umberatana group the focus of the present chemostratigraphic study rock units from three drillholes and ten measured outcrop sections located in the southern and central flinders ranges and on the stuart shelf were sampled for isotopic analysis of their co existing calcite 13ccal dolomite 13cdol and kerogen 13corg strontium and sulphur isotopic analyses were also run on selected samples the sample sites are in tectonic domains where regional metamorphism has been insufficient to significantly alter the isotopic composition of the kerogen the resulting data when integrated with the lithostratigraphy of the umberatana group yield one of the most complete records of secular variation in the c isotope signature of the late cryogenian ocean between 750 and 680 ma its composite 13ccarb curve begins with a sharp positive excursion 3 to 1 5 in the dolomitic tindelpina shale which caps sturtian glacial diamictites wilyerpa formation then follows a steady climb through the shoaling upward tapley hill formation reaching 4 in the brighton limestone and culminating in a plateau of 13c enrichment within the platformal carbonates of the etina formation 8 to 10 the upper part of the temporal trend shows a decline to 6 to 7 in the stromatolite reef facies of the enorama shale and a dramatic drop to 8 to 9 5 followed by a recovery to 3 in the youngest carbonate unit trezona formation beneath the marinoan glacigenic elatina formation the latter is capped by a thin dolostone the nuccaleena formation which records a consistent up section decrease in 13c 1 to 3 superimposed on this overall pattern of c isotopic variation are second and third order fluctuations attributable to eustatic sea level change pyritic sulphur in the lower tapley hill formation 34s 9 to 40 is distinctly heavier than that in the underlying wilyerpa formation 4 to 20 minimum 87sr 86sr values obtained from the brighton limestone 0 7071 and etina formation 0 7076 are consistent with their late cryogenian age this sturtian to marinoan interglacial succession is more complete than equivalent sequences elsewhere and thus provides a useful reference for global chemostratigraphic correlation notable features of its c isotope curve are the strong post wilyerpa positive excursion also seen in key sections from svalbard and western mongolia the etina plateau of 13c enrichment which is remarkably similar to maxima in the terminal proterozoic c isotope records of western mongolia north western canada and brazil and the spectacular depletion of 13c in the lower trezona relative to similar carbonate facies in the underlying etina formation and enorama shale a preglacial offset in 13ccarb values of such proportions 14 is almost unprecedented except perhaps for that recently documented in the upper ombaatjie formation beneath tillites of the ghaub formation otavi group namibia it represents a key piece of evidence in the case presented by the proponents of a neoproterozoic snowball earth

neoproterozoic stratigraphy of the centralian superbasin australia abstract the basement of central australia includes the arunta block and the 1200 1100 ma musgrave block succeeded by 1075 1000 ma bimodal volcanic rifts and dolerite dykes a regional hiatus at 1000 800 ma interpreted as reflecting a central post volcanic underplated upland was followed at 800 ma by a second swarm of dykes in the musgrave block gawler craton and stuart shelf associated with the crustal sagging that initiated the centralian superbasin the centralian superbasin is defined here to encompass the neoproterozoic fill of the amadeus georgina ngalia officer and savory basins the intra cratonic superbasin was disrupted internally 540 600 ma ago petermann ranges orogeny by a central uplift and associated thrusts and by mid carboniferous 320 ma tectonism alice springs orogeny to form the structural basins listed above the stratigraphy and sedimentology of the relatively well known areas can be used as a basis for predicting those of the poorly known regions new results from acritarch biostratigraphy and isotope chemostratigraphy in conjunction with conventional lithostratigraphy and sequence analysis allow better stratigraphic resolution than previously possible field observations in the recently discovered savory basin in western australia provide a basis for correlations with the adjacent basins

late proterozoic submarine canyons of adelaide geosyncline south australia a well exposed series of major basin slope submarine canyons of late proterozoic age occur within the mixed carbonate and siliclastic wonoka formation of the adelaide supergroup adelaide geosyncline flinders ranges south australia they were cut to depths of about 1 5 km into an underlying deltaic and basin slope progradational sequence which includes the brachina formation and the abc range quartzite the canyons occur in close association with local synclinal structures an unfolded section across one canyon patsy springs canyon shows steep almost vertical canyon walls two axial channels and a tributary canyon the canyon filling sequence includes canyon wall and axial debris flow material axial channel conglomerates ripple cross laminated sands and silts hin and thick bedded turbidite sands and a series of spectacular sand filled megachannels which markedly truncate underlying units lenticular olistostromes of micritic carbonate clast breccias of carbonate platform derivation occur throughout canyon fill and immediately overlying strata the sedimentary sequence preserved in the canyons demonstrates an episodic process of canyon backfilling by onlap of an aggrading submarine fan sequence backfilled canyons were finally buried by progradation of a complex unit comprising interdeltaic carbonate platform delta and basin and slope environments evidence from the wonoka formation canyons suggests that initial canyon incision was triggered by a significant fall in relative sea level which allowed fluvial systems to deliver their bed loa s directly to the contemporary basin slope a subsequent relative rise in sea level was required during latter stages of canyon filling to account for delta and basin slope progradation of the wonoka formation

micropaleontologie du proterozoique du massif armoricain france abstract upper proterozoic sediments brioverian of brittany and normandy france contain microfossils of algal affinities 1 1 assemblages of solitary and colonial vegetative cells and possibly sporulating cells which seem strikingly similar to sphaerocongregus variabilis reported from late precambrian sedimentary rocks in north america paleocryptidium described in brittany and reported from proterozoic rocks of bohemia is probably conspecific of sphaerocongregus in brittany and normandy these assemblages are particularly abundant in lower and middle brioverian sedimentary rocks 670 1000 ma 2 2 assemblages of solitary and colonial cells which can be compared with various species of favososphaera reported from the upper proterozoic of europe in brittany these assemblages have only been detected in upper brioverian sandstones and limestones 670 580 ma

tidal deposits of the lower cambrian random formation eastern newfoundland facies and paleoenvironments the avalon tectonostratigraphic zone occupies about 25 of the area of insular newfoundland late precambrian development of the avalon terrane is distinctly different than that of other parts of the appalachian orogen and cratonic north america late precambrian volcanism and tectonic instability gave way to deposition of about 2 km of cambrian and lower ordovician dominantly epiclastic sediments on a slowly subsiding relatively stable shelf platform the lower cambrian random formation is part of the platformal sequence and is bounded by regional disconformities over much of the newfoundland avalon zone except around fortune bay where it is underlain by older terrestrial and shallow marine sediments the random formation was deposited during a time of global sea level rise and consists of up to 250 m of shoreline nearshore and open shelf deposits that record macrotidal conditions and periodic storm activity cross bedded quartzarenites occur in units to about 50 m thick one exceptional unit is 110

precadomian relicts in the armorican massif their age and role in the evolution of the western and central european cadomian hercynian belt abstract well dated precambrian is mostly developed in the north of the armorican massif in which area voluminous cadomian magmatism is dated at between 650 and 550 ma much older relicts occur at cap de la hague in guernsey and in the tregor and are also found in the northern continental margin of the iberian peninsula in all these occurrences whole rock systems have been opened so that the true ages cannot be determined by the rb sr whole rock isochron method four u pb zircon ages are between 1 8 and 2 ga in guernsey icart orthogneisses in tregor port beni trebeurden morguignen orthogneisses there is no evidence from strontium isotopes that these isolated and scattered relicts have a wide extension or that such ancient continental crust played an important role in magma genesis from 650 ma to 270 ma ago on the contrary the evolution of initial 87sr 86sr ratios with time shows that the observed mid and west european continental crust is probably not older than 700 ma the increase of the initial 87sr 86sr ratios of the magmas with time suggests that after its formation in cadomian times this segment of continental crust evolved virtually as a closed system and hercynian magmatism arose principally from re melting of relatively young sialic components

ediacaran events boundary relationships and correlation of key sections especially in armorica the transitional interval between the adelaidean and ediacaran systems in the central flinders ranges south australia comprises mainly basinal sediments with some tuff beds bunyeroo formation and a widespread thin dolomite bed which apparently evidences a brief regressive episode base of wonoka formation body imprints of metazoans trace fossils and probable faecal pellets are present at various levels in the ediacaran succession comparable assemblages occurring in key successions in southern africa northern russia siberia newfoundland and england promise a global biostratigraphy one ediacaran body fossil occurs in the yangtze gorges section china analysis of abundant late precambrian radiometric data for the present north atlantic margins suggests that the ediacaran may be dated between about 590 ma and 545 540 ma

biotic characteristics of the sinian cambrian boundary beds in china and the boundary problems abstract there is general agreement that the first appearance of various small shelly fossils should be used to help delineate the beginning of the cambrian period the history of research on this stratigraphic topic in china is briefly outlined and leads on to a discussion of the boundary problem in the light of information available both inside and outside china the sections across the precambrian cambrian sinian cambrian boundary are described with notes on fossils in 1 tianzhushan section yichang hubei 2 maidiping section emli sichuan 3 wangjiawan section jinning county yunnan and 4 kunyang section yunnan this is followed by a consideration of the biotic characteristics of sinian cambrian period the history of research on this stratigraphic topic in china is briefly outlined and leads on to a discussion of the boundary problem in the light of information available both inside and outside china this is followed by a consideration of the biotic characteristics of sinian cambrian boundary beds with respect to stratigraphy as well as organic evolution the precambrian cambrian boundary in china is estimated to have an age of 615 20 ma it is commented that the above sections are qualified to be important candidates for the selection of the sinian cambrian boundary stratotype and are also important working reference sections for the international precambrian cambrian boundary stratotype

receiver coupling effects in seismic waveform inversions seismic waveform inversion offers opportunities for detailed characterization of the subsurface however its full potential can only be exploited when any systematic source and receiver effects are either carefully avoided or appropriately accounted for during the inversions repeated crosshole measurements in the mont terri switzerland underground laboratory have revealed that receiver coupling may significantly affect the seismic waveforms more seriously coupling conditions may vary during the course of a monitoring experiment to address this problem we have developed a novel scheme that estimates medium properties frequency dependent source functions and frequency dependent receiver coupling factors we demonstrate the efficacy of the new scheme via a synthetic 2d crosshole experiment in which realistic receiver coupling factors are incorporated because determination of medium parameters and estimation of source functions and receiver coupling factors are largely separated the method can be

precambrian cambrian boundary recent state of knowledge abstract the principle of biostratigraphic delimitation of the type lower boundary of the cambrian system has become generally accepted despite a lack of recent results which further support this approach the detection of the most ancient vendian ediacara softbodied forms and cambrian skeletal fauna in a large number of localities worldwide has been the only obvious trend in recent investigations the present agreement that the base of the tommotion stage is the most satisfactory position for the precambrian cambrian boundary is based on the idea that the best type section of the boundary is to be found in the siberian platform such a decision is based largely on the unsatisfactory nature of the arguments for alternative positions

the neoproterozoic of southwestern africa with emphasis on platform stratigraphy and paleontology abstract neoproterozoic sediments in southwestern africa occur in the pan african kaoko khomas gariep vanrhynsdorp and saldania belts they were deposited in response to rifting break up of a supercontinent formed at 1000 ma and subduction and collisions of the congo kalahari rio de la plata and malvinas plates these collisions led to the formation of a neoproterozoic cambrian supercontinent this paper deals with the geology of the platform successions of the kaoko khomas gariep and vanrhynsdorp belts deposition of the sediments occurring in these belts commenced 900 to 1000 ma ago and probably ended between 500 and 520 ma the sediments record wilson cycles that ended with the deposition of red beds palaeontological and carbon isotope studies on the damara sequence gariep complex nama group and vanrhynsdorp group make intra and inter basinal correlations possible prior to deposition of the nama group two or perhaps three glaciations took place over an extensive area in southwestern africa these being the kaigas chuos 725 700 ma numees 650 600 ma or 610 590 ma and possibly the varianto 745 725 ma glaciations the numees tillite is overlain by a stratigraphic unit containing pinkish dolomite during deposition of the nama group the minor vingerbreek 600 545 ma glaciation or cold water period occurred the major kaigas chuos and numees and minor vingerbreek glaciations correspond with low 13c isotope ratios and appear to have taken place at relatively low palaeolatitudes the riphean sediments were deposited predominantly during rifting and break up of a supercontinent during the late vendian to early cambrian deposition of the nama group in southern namibia and the penecontemporaneous vanrhynsdorp group in the republic of south africa took place in the nama foreland basin detrital micas indicate that deposition of the nama group took place between 635 and 530 ma the nama foreland basin which was connected to a major ocean to the south formed as a result of collisions between the congo kalahari and rio de la plata plates with the exception of the nama group little is known about the palaeontology of the neoproterozoic in southwestern africa the lower nama group is latest proterozoic in age it contains an ediacaran fauna a depauperate assemblage of organic walled microfossils and a relatively well diversified ichnofauna with brooksella diplocraterion and nereites which are atypical of vendian strata many trace fossils are exceptionally small the occurrence of the shelly fossil cloudina and probable calcified metaphytes in the lower nama group suggest that skeletalization in animals and metaphytes occurred almost simultaneously towards the end of the proterozoic the upper nama group is early cambrian in age as indicated by the occurrence of the trace fossil phycodes pedum the upper nama group dominated by red beds contains a low diversity ichnofauna with trace fossils of normal size bio and chemostratigraphy combined with sequence stratigraphy will probably establish how the prominent unconformities which occur in the neoproterozoic of southwestern africa are related to the periods of formation of the wonoka canyons in south australia

rb sr whole rock isochron evidence for the age of the malvern hills complex the malvernian igneous complex of the malvern hills consists mainlyof plutonic rocks and their locally deformed equivalents the igneous rocks are calc alkaline and range from ultra mafic diorite to granite in composition although diorite and tonalite are the most abundant rock types a rb sr whole rock isochron plot for representative samples yields an age of 681 53 ma with an initial 87 sr 86 sr ratio of 0 7049 0 0005 2 errors this is interpreted as the age of crystallization of the igneous complex and the relatively low initial 87 sr 86 sr ratio is considered to preclude a long crustal history for the source region the malvernian complex is thus regarded as a late precambrian addition to the crust it has been compared on geological grounds with the johnston complex and the stanner hanter complex and isotopic ages between 640 and 700 ma for all these complexes indicate that they may represent the earliest phase of igneous activity in the evolution of continental crust below england and wales

pre mesozoic paleomagnetism and plate tectonics although the arguments perhaps did not convince everyone at the time the paleomagnetic polar wander paths for europe and north america plotted by runcom 1956 certainly convinced me as a young graduate student that continental drift as we called it in those pre plate tectonic days deserved serious attention then throughout the 1960s the geoscience world seemed busy documenting and refining the models of seafloor spreading and plate tectonics that governed the opening of today s oceans as the number of publications espousing plate tectonics seemed to grow exponentially an often tacit assumption was that the continental breakup was a unique event and that pangea was a quasi primordial continental configuration ahead of his time however j tuzo wilson 1966 queried in a now classical paper did the atlantic close and then re open the 1973 penrose conference in vail colorado on pre mesozoic plate tectonics dewey spall 1975 showed that by then many earth scientists were preoccupied with proving that the tacit assumption was wrong and that wilson was right but compared to mesozoic and later plate tectonics the task of quantifying pre mesozoic continental movements is much more difficult since there are no seafloor magnetic anomalies to work with and much of the potential evidence e g ophiolites diagnostic supracrustal sequences high pressure low temperature metamorphic rocks has been destroyed by that ultimate plate tectonic process the continent continent collision and by sub sequent uplift and erosion nevertheless a multitude of observations facts interpretations reinterpretations proposals and hypotheses can now be found in the literature for virtually any pre mesozoic period and any geographic

geochronology of sedimentary and metasedimentary precambrian rocks of the west african craton abstract this contribution summarizes current knowledge of the geochronology of the upper proterozoic sedimentary rocks covering the west african craton this was done by using direct dating methods correlations between the northern edge of the tindouf basin and the northern and southern part of the taoudeni basin as well as the volta basin are proposed an important depositional lack over almost the entire craton is confirmed between 1 7 ga which represents the time of the latest eburnean activities or cooling effects and about 1 0 ga which is the start of the general upper proterozoic sedimentation this lack is remarkable as the other cratons from gondwana continent are covered by middle proterozoic sediments the upper proterozoic sedimentation on the west african craton may be divided into a basal mainly sandstone period ca 1000 900 ma a middle mainly limestone period ca 900 750 ma and an upper mainly siltstone period ca 750 650 ma tectonic volcanic and thermal activities in connection with the pan african orogeny are recorded only around the craton they induced either sedimentation lacks in morocco or sedimentation excesses in hoggar unsolved problems such as the precise stratigraphic position of the uppermost proterozoic tillitic episode and the correlation within the moroccan anti atlas are also raised

geochronology of the swift current granite and host volcanic rocks of the love cove group southwestern avalon zone newfoundland evidence of a late proterozoic volcanic subvolcanic association zircon fractions from the variably deformed and metamorphosed swift current granite and host volcanic rocks of the love cove group record individually discordant u pb ages with well defined upper c

palaeomagnetism of the ejecta bearing bunyeroo formation late neoproterozoic adelaide fold belt and the age of the acraman impact abstract a new palaeomagnetic study has been conducted on haematitic shales and siltstones of the late neoproterozoic bunyeroo formation in the adelaide fold belt geosyncline south australia which host an extensive horizon of shock deformed rock fragments and microtektite like material of probable impact origin thermal step demagnetisation of 116 samples of red shale and siltstone from six sections sites revealed a high temperature component with a bedding corrected site mean direction of remanence of d 56 6 i 29 3 95 10 7 that gives a pole at 18 1 s 16 3 e dp 6 5 dm 11 8 the high temperature component provides a positive tectonic fold test 99 level of confidence the bunyeroo high temperature remanence direction is near the remanence direction d 50 i 40 indicated by modelling the subsurface magnetic source of the central high amplitude anomaly at acraman australia s largest confirmed meteorite impact structure 220 350 km west of the adelaide fold belt and also is close to the mean direction d 48 3 i 54 7 95 5 2 determined for surface melt rock from acraman statistical tests show that the virtual geomagnetic poles indicated by the directions for the subsurface central magnetic source and surface melt rock at acraman may be regarded as subsets of the bunyeroo palaeomagnetic pole position indicating that the three pole positions are statistically indistinguishable the results imply that the subsurface magnetic source and surface melt rock acquired their remanence in the ambient geomagnetic field during cooling after the impact when structural disturbance had ceased while the bunyeroo formation was accumulating the agreement among the various remanence directions argues strongly that the ejecta horizon in the bunyeroo formation was derived from acraman the present findings confirm that the acraman impact occurred in the late neoproterozoic about 590 ma which is the age of the bunyeroo formation provided by rb sr whole rock shale dating of equivalent and contiguous strata in the adelaide fold belt region the bunyeroo palaeomagnetic data give a palaeolatitude of 15 indicating a low palaeolatitude for the acraman impact and supporting other findings that the adelaide fold belt occupied low to equatorial palaeolatitudes during the late neoproterozoic