intercontinental trilobite based correlation of the moroccan early middle cambrian refined correlations of lower middle cambrian boundary strata and middle cambrian strata between cambrian paleocontinents require an improved understanding of local stratigraphic ranges of well defined trilobite genera and species the conventional definition of the base of the middle cambrian in spain base of acadoparadoxides mureroensis zone has led to problems even when correlations into other west gondwanan regions i e moroccan are attempted because paradoxides acadoparadoxides mureroensis and protolenid species from immediately underlying strata have been regularly misidentified the a mureroensis zone is shown to correlate into strata above the base of the moroccan middle cambrian and paradoxidid trilobites a guide to the middle cambrian have a lower occurrence in morocco these correlations are strengthened by a reevaluation of higher middle cambrian trilobite genera and species in morocco and their use in correlation into spain and baltica two new genera and eight new species of middl

marine oxygenation lithistid sponges and the early history of paleozoic skeletal reefs abstract microbial carbonates were major components of early paleozoic reefs until coral stromatoporoid bryozoan reefs appeared in the mid ordovician microbial reefs were augmented by archaeocyath sponges for 15 myr in the early cambrian by lithistid sponges for the remaining 25 myr of the cambrian and then by lithistid calathiid and pulchrilaminid sponges for the first 25 myr of the ordovician the factors responsible for mid late cambrian microbial lithistid sponge reef dominance remain unclear although oxygen increase appears to have significantly contributed to the early cambrian explosion of marine animal life it was followed by a prolonged period dominated by greenhouse conditions as sea level rose and co2 increased the mid late cambrian was unusually warm and these elevated temperatures can be expected to have lowered oxygen solubility and to have promoted widespread thermal stratification resulting in marine dysoxia and hypoxia greenhouse conditions would also have stimulated carbonate platform development locally further limiting shallow water circulation low marine oxygenation has been linked to episodic extinctions of phytoplankton trilobites and other metazoans during the mid late cambrian we propose that this tendency to dysoxia hypoxia in shallow marine environments also limited many metazoan reef builders in contrast during the mid late cambrian the ability of lithistid sponges to withstand low oxygen levels allowed them to create a benthic association with microbial carbonates that dominated global reefs these conditions ameliorated during the ordovician as temperature decline promoted ocean ventilation the prolonged time gap occupied by low diversity reefs between the cambrian explosion and the great ordovician biodiversification event reflects elevated temperatures and reduced marine oxygenation that limited metazoan diversification in shallow marine environments

archaeocyathan zonation of the yangtze platform implications for regional and global correlation of lower cambrian stages detailed analysis of the distribution of archaeocyaths in five lower cambrian sections in south china has resulted in the erection of four new archaeocyathan zones and one new archaeocyathan bed listed in order of ascending age these are the dailycyathus xiuqiensis zone the dictyocyathus shaanxiensis zone the spirillicyathus duplex range zone the sibirecyathus meitanensis range zone and the archaeocyathus yanjiaoensis beds these new subdivisions permit a correlation of lower cambrian strata both within the area of the yangtze platform south china as well as between this region and siberia australia western europe and north america within the yangtze platform area archaeocyaths of the dailycyathus xiuqiensis and dictyocyathus shaanxiensis zones co occur with trilobites of the middle and upper eoredlichia trilobite zone of the qiongzhusian stage the spirillicyathus duplex and the sibirecyathus meitanensis range zone correspond to the malungia yiliangella yunnanaspis and drepanuroides trilobite zones of the basal and middle canglangpuan stage respectively finally the archaeocyathus yanjiaoensis beds belong to the palaeolenus fengyangensis trilobite zone of the upper canglangpuan stage global correlations based on archaeocyath assemblage zones suggest that 1 the middle upper qiongzhusian of south china correlates with the middle atdabanian stage of the siberian platform the warriootacyathus wilkawillinensis archaeocyath zone in south australia the middle issendalenian stage of morocco and the lower ovetian stage in spain 2 the lowermost canglangpuan stage of south china correlates with the uppermost atdabanian of the siberian platform the spirillicyathus tenuis jugalicyathus tardus archaeocyath zones in south australia the uppermost issendalenian lower banian stages of morocco the middle ovetian stage of spain and the middle montezuman stage of north america 3 the middle canglangpuan stage approximates the lowermost botoman stage of the siberian platform middle banian stage of morocco the uppermost ovetian lowermost marianian stages of spain and the upper montezuman stage of north america 4 the uppermost canglangpuan stage is equivalent of the middle toyonian stage of the siberian platform archaeocyathus abacus beds in australia the middle bilbilian stage in spain and the middle dyeran stage bolbolenellus euryparia trilobite zone in north america

gradient array profiles over thin resistive veins f urness p 1993 gradient array profiles over thin resistive veins geophysical prospecting 41 113 130 gradient array geoelectric surveys are commonly used to explore for buried sheet like targets it is demonstrated that under certain circumstances the responses of such features can become practically equivalent for a range of models differing considerably in resistivity and thickness this is the dual of the familiar equivalence phenomenon associated with thin beds in geoelectric sounding operations hence the geoelectric response profiles over thin dipping resistive veins are conveniently studied by considering equivalent forms with vanishing thickness and infinite resistivity but with the same resistivity thickness product the effects of varying the dip depth of burial depth extent and resistivity thickness product of such features on the gradient array response profiles are investigated by means of a series of numerical experiments these demonstrate several effects of significance to survey design and data interpretation in particular it is found that while the resistivity thickness product influences the amplitude of the response profiles it has little effect on their form a similar behaviour is found to be exhibited by veins with extended depth extent when the dip is varied a complete quantitative interpretation of gradient array profiles over thin dipping resistive veins is thus only possible for veins of limited depth extent for veins with an extended depth dimension the data is ambiguous in a practical sense in terms of the dip and the resistivity thickness product here the interpretation can only be expected to deduce the horizontal and vertical locations of the vein apex

coupled oceanic oxygenation and metazoan diversification during the early middle cambrian the early middle cambrian fortunian to age 4 is characterized by a significant increase in metazoan diversification furthermore this interval is marked by a prominent environmental and ecological expansion of arthropod and echinoderm rich biotas recent redox work has suggested that this shift occurred during stable or decreasing marine oxygen levels suggesting that these paleobiological and paleoecological transformations were decoupled from a redox control we tested this idea by conducting new paleoredox analyses on age 2 age 4 cambrian outer shelf jiuqunao wangjiaping slope wuhe geyi and basinal zhalagou sections of the south china craton multiple sections indicate that mid depth waters transitioned from anoxic conditions during cambrian age 2 to stable oxic conditions during cambrian age 4 these findings suggest a stepwise expansion of oxic waters from shallow to deep settings during the early middle cambrian consistent with a redox control of metazoan diversification and ecological expansion more broadly despite the surge in redox work over the past decade this study highlights the need for continued coupled redox and paleontological studies to directly test models about the links between the evolution of animals ecosystems and marine redox conditions

geoelectrical investigations by means of resistivity methods in karst areas in romania the applicability of resistivity methods to ground water investigations is well recognized as water saturated rock formations have a lower electrical resistivity than dry ones an electrical resistivity survey should result in low resistivity anomalies normally such anomalies are interpreted to indicate areas of potentially significant ground water flows in karst areas however interpretation may not be as straightforward for example large electrically conductive domains can represent water bearing zones whose fluid permeability may be poor alternatively fast flow conduits which may be unsaturated occur as slender objects and not as clear anomalous features in order to deal with such extreme heterogeneities resistivity investigations require some specific adjustments one example is the so called mise a la masse method in romania it was used to trace the cold karst water inflows that detrimentally affected the commercial exploitation of a thermal spring hercules at baile herculane conventional geoelectrical approaches such as using resistivity highs to detect air filled cave passages are proved to be less efficient in the considered karst investigations

zoisite and clinozoisite segregations in metabasites tauern window austria as evidence for high pressure fluid rock interaction high pressure zoisite and clinozoisite bearing segregations are common in garnet and albite bearing amphibolites of the palaeozoic part of the lower schieferhulle south central tauern window austria the zoisite segregations primary assemblage zo qtz cal formed during an early to pre hercynian high pressure event p 0 6 gpa t 500 550 c by hydrofracturing as a result of protolith dehydration zoisite is growth zoned from fe3 poor cores al 2 fe 9 mol to fe3 rich rims 17 mol and has high sr pb and ga contents and lree enriched ree patterns controlling the trace element budget of the segregations hercynian deformation at c 0 7 gpa 600 c kinked and cracked primary zoisite and enhanced breakdown into secondary zoisite 13 mol al 2 fe clinozoisite 40 55 mol al 2 fe albite an 20 calcite and white mica during an eoalpine high pressure event at 0 9 1 2 gpa 400 500 c the clinozoisite segregations primary assemblage czo qtz omp ttn chl cal are mm to cm wide vein like bodies cross cutting fabric elements of the host garnet amphibolite they formed during the eoalpine high pressure event at 0 9 1 2 gpa 400 500 c during alpine exhumation omphacite was pseudomorphed by amphibole albite quartz and clinozoisite oxygen isotope data suggest equilibrium between host metabasite and zoisite segregations and indicate an internal fluid source and fluid buvering by the protolith mobility of p nb and lree changed the protolith s trace element composition in the vicinity of the zoisite segregations mobilization of lree is evidenced by decreasing modal amounts of lree rich epidote and decreasing lree contents in lree rich epidote towards the segregations chang ing the ree patterns of the host metabasite from lree enriched to lree depleted tectonic discrimi nation diagrams based on the trace element content of metabasites should be applied with extreme caution

nd and sr isotopic ratios and trace element geochemistry of epidote from the swiss molasse basin as provenance indicators implications for the reconstruction of the exhumation history of the central alps abstract epidote is a common heavy mineral in sandstones its use as a provenance indicator however is limited because it appears in a wide range of lithologies and geological settings in order to discriminate between mantle and crust derived source rocks we measured isotopic and trace element compositions of detrital epidote from sandstones of the swiss molasse basin the compositions of the detrital epidotes were compared to epidotes from penninic metabasites and austroalpine metagranites from the present day exposures and to epidote from ophiolitic and metagranitic pebbles from the molasse basin we found that nd isotopic ratios of epidote allow a good discrimination between different types of source rocks with end values ranging between 6 1 and 8 6 for metabasic lithologies and between 9 7 and 2 8 for metagranitic lithologies sr isotope ratios reveal similar trends but do not allow such a clear discrimination ba u rb nb and th contents of epidote correlate well with the end values yielding the same provenance signal according to isotopic and trace element compositions three types of epidote bearing sandstones can be distinguished one received epidote from lower austroalpine metagranites another from penninic ophiolites and a third type of sandstone received epidote from both sources the provenance of the detrital epidote has important bearing on the exhumation history of the central alps elucidating the transition between the erosion of lower austroalpine felsic lithologies and the onset of erosion of the penninic lower plate according to our data the penninic lower plate became exposed simultaneously in the hinterland of all molasse fans at 21 20 ma at the same time the relief collapsed as reflected by a drastic decrease of sediment accumulation rates in the foreland basin the combination of both events fits well to the geodynamic scenario of large scale lateral extension processes affecting the central alps in post collisional times

the use of vertical line sources in electrical prospecting for hydrocarbon conventional electrical prospecting can be extended to the search for deep seated hydrocarbon deposits by using the steel casings of drill holes as vertical line sources these sources produce at depth a density of current higher than the density created by point sources located at the ground surface several tests have shown that the contrast of conductivity between resistive hydrocarbon deposits and the surrounding salt water produces relevant anomalies on a resistivity map obtained with vertical line sources especially where there exists a superficial masking effect caused by a highly resistive layer in a survey carried out in the ussr combined measurements were performed both with line source and with surface point sources the detected residual resistivity anomaly roughly delineates the contours of the known hydrocarbon deposit

palaeogeographical controls on the cambrian trilobite immigration and evolutionary patterns reported in the western gondwana margin abstract southward drifting of the western gondwanan margin during the cambrian has been demonstrated by means of both palaeomagnetic methods and lithological indicators of climate such as carbonates and evaporites recent improvements in biostratigraphical correlations permit an enhanced understanding of the climatic and palaeobiogeographical constraints that controlled the distribution of cambrian benthic communities palaeogeographical and biogeographical reconstructions based on trilobites are reported in this paper in order to test interaction between migration speciation and extinction rates the variability of the documented biogeographical patterns is directly related to species diversity in which wider distribution coincides with transgressive trends and subsequent connection of neighbouring platforms early cambrian trilobite faunas show a high degree of both substrate control and endemicity although transgressions led to parallel shifts in faunal compositions by contrast mid cambrian trilobite faunas are relatively uniform across western gondwana and latest mid and late cambrian associations document influence of an increased similarity with asian trilobite faunas

early cambrian microbial reefs archaeocyathan inter reef communities and associated facies of the yangtze platform abstract a sedimentological and paleoecological study of part of the northern yangtze platform of china was conducted three sections of the early cambrian atdabanian botomian stage xiannudong formation where studied and reveal that stromatolite and thrombolite reefs flourished in close association with an inter reef community of archaeocyaths and other organisms adjacent to the reef environment were migrating ooid shoals oncoids peloids and silty sandy lime mud no archaeocyathan reefs were observed in any of the measured sections but irregular archaeocyaths were found in some microbial reefs and archaeocyaths form the bulk of the debris in float rudstone that was deposited between microbial reefs we interpret the archaeocyath rich float rudstone to represent a storm churned inter reef deposit typically regular type archaeocyaths dominated the float rudstone while irregular type archaeocyaths were found in abundance dwelling within the microbial reefs this trend changed upsection as irregular type archaeocyaths dominated both the float rudstone and in the microbial reefs the oncolite and peloidal mudstone are interpreted as representing a quiet water lagoonal environment created by the presence of the microbial reefs and ooid shoals during large storms material from the ooid shoals or microbial reefs would wash into the lagoon the silty sandy micrite represents a quiet water setting which could either be a deep subtidal environment or a restricted lagoonal environment the facies associations of these three sections along with other published data indicate that the yangtze platform at least during the early and middle cambrian was a carbonate platform and equatorially located

allanite and other ree rich epidote group minerals epidote group minerals rich in rare earth elements ree in particular allanite are common accessory phases in igneous metamorphic metasomatic and sedimentary rocks small amounts of ree are present in most epidote group minerals but in allanite and the related minerals dissakisite ferriallanite dollaseite khristovite and androsite the ree are essential structural constituents an important characteristic of ree rich epidote group minerals is that their octahedrally coordinated m sites contain major amounts of divalent cations this paper summarizes literature data for these minerals and discusses their chemistry occurrence phase relations and petrologic and geologic significance the chapter emphasizes allanite because it is the most common and best studied of the ree rich epidote group minerals epidote group minerals contain isolated silicon tetrahedra and corner sharing groups of two tetrahedra and are thus assigned to the disilicate or sorosilicate structural family for a detailed description of the structure see franz and liebscher 2004 the epidote group structural formula is a2m3 sio4 si2o7 o f oh or in a simplified form a2m3si3o11 o f oh in which a ca sr pb2 mn2 th ree3 and u and m al fe3 fe2 mn3 mn2 mg cr3 and v3 deer et al 1986 there are two structurally different a sites a 1 and a 2 with different coordination numbers and there are three different m sites m 1 m 2 and m 3 which are all octahedrally coordinated ueda 1955 dollase 1971 in epidote group minerals trivalent ree are accommodated in the a sites which in endmember epidote both contain ca the incorporation of ree3 is commonly charge balanced by a divalent cation fe2 mn2 mg substituted for a trivalent one in the m sites table 1

simple data processing of tripotential apparent resistivity measurements as an aid to the interpretation of subsurface structure the advantages of the wenner tripotential method carpenter 1955 for apparent resistivity profiling are described and two new data processing techniques introduced as an aid to the interpretation of apparent resistivity sections pseudo sections these techniques were developed from model data computed using a two dimensional finite difference method oscillatory components present in anomalies on tripotential profiles and related to electrode spacing are shown to be effectively removed by linear filtering that also simplifies their form and aids recognition furthermore it is shown that the ratio of the beta and gamma apparent resistivities is a good indicator of resistivity variation and is particularly sensitive to lateral change model data indicates that over a wide range of conditions enough subsurface information can be obtained by inspection of tripotential resistivity and ratio profiles and from space sections to make possible a useful and sometimes semi quantitative interpretation a rationale for the general interpretation of tripotential data is developed field data are described from an area of weathered granite basement in nigeria a model of the subsurface is developed using parameters derived from the processed observations the observed and calculated apparent resistivity space sections are very similar

a silurian sphinctozoan sponge from east central cornwallis island canadian arctic the first silurian sphinctozoan ever recorded is reported from the canadian arctic the polysiphonate sphinctozoan rigbyspongia catenula n gen n sp is found associated with numerous anthaspidellid sponges diagnostic features of the new genus are its numerous axial siphons and vertical pillars within each chamber although it is structurally complex for a sphinctozoan of this age and is the only silurian representative of the order this new genus provides few clues to the still enigmatic problem of paleozoic sphinctozoan phylogeny

potential contributions of ancient oceanic islands to evolutionary theory before much was known about the geology of continental margins and the occurrence of oceanic islands in suspect terranes tests of theories related to island biogeography were undertaken mostly by ecologists and in paleontological investigations of non insular biota a significant new source of paleontological data with which to test models for species equilibrium over evolutionary versus ecological time scales and other important problems in evolutionary theory exists within circum oceanic belts where ancient oceanic islands are preserved as allochthonous terranes research on faunas from these areas simplifies attempts to apply the theory of island biogeography to the fossil record and to trace the history of island populations over evolutionary time scales paleontologic data from a paleozoic island arc alexander terrane show significant fluctuations in the taxonomic diversity of brachiopods and thus question one of the main assertions of the dynamic equilibrium model these data also support the con

skeletal faunas of the lower cambrian yu anshan formation eastern yunnan china metazoan diversity and community structure during the cambrian age 3 abstract the lower cambrian stage 3 yu anshan formation in yunnan province south china hosts the chengjiang lagerstatte an exceptional window on the cambrian explosion however skeletal microfossils from this formation have long been neglected owing to the dominance of siliciclastics over carbonates here we characterize a new assemblage of small shelly fossils from the maotianshan shale member of the yu anshan formation the assemblage consists of univalved mollusc hyolith and brachiopod shells trilobite and bradoriid carapaces chancelloriid sclerites sponge spicules and echinoderm ossicles combining this information with taxonomic data previously tabulated for fossil assemblages from three other facies we performed quantitative comparisons of the genus level taxonomic diversity and modes of life and nutrition of four mutually equivalent early cambrian age 3 paleocommunities 1 skeletal faunas of the inner shelf 2 predominantly soft bodied faunas of the intra shelf basin 3 archaeocyathan faunas of the carbonate shelf and 4 sponge dominated faunas of the slope to basin areas the taxonomic and paleoecological distinctness of these four paleocommunities indicate possible low levels of competition within the communities and rapid expansion of habitat ecospace ranges though with similarities in the taxonomic composition of poriferans and arthropods reflecting the rapid migration of these two groups into new habitats the present integrative study provides a more comprehensive portrait of metazoan diversification and paleocommunity evolution during the peak phase of the cambrian explosion than do investigations based on single communities

detection of lateral variations in geological structures using electrical resistivity gradient profiling1 hydrogeological problems which involve the determination of lateral variations in structures or physical properties may be solved with electrical resistivity gradient profiling if there are significant variations in electrical resistivity spatially or temporally the method is explained evaluated for sensitivity compared with other methods and applied to the location of volcanic dike zones that are impounding an anomalous water body near schofield oahu hawaii from the electrical soundings and other independent data the lateral positions of the boundaries have been refined and their nature estimated

interpretation of resistivity measurements over 2d structures1 resistivity measurements were carried out in a survey area in the south of germany this area is characterized by complicated subsurface geology schlumberger full arrays and their respective half arrays were recorded simultaneously the results obtained by the one dimensional 1d interpretation of the full array measurements were incorrect because of a resistivity discontinuity this discontinuity under a relatively thick overburden could only be located by the half array soundings its exact location and the resistivity distribution in the subsurface were ascertained by comparing the sounding curves with 2d model curves which are calculated by a finite difference method

a new gorstian radiolarian fauna from the upper silurian of the cape phillips formation cornwallis and bathurst islands canadian arctic this study provides a taxonomic treatment and comparison of lower gorstian silurian radiolarians recovered from two sections of the cape phillips formation in the canadian arctic that accumulated in two different paleoenvironmental settings twilight creek is more basinal located 100 km from the paleo shelf margin whereas snowblind creek is located within 1 km of the paleo shelf break on cornwallis island the fauna like other material from the cape phillips formation is extremely well preserved and was recovered from four samples at two localities all from the lobograptus progenitor graptolite zone an interval that has few published studies regarding radiolarians a total of 28 species are recognized of which two are new and described herein fusalfanus bilateralis n sp and pseudospongoprunum parvispina n sp belonging to the haplotaeniatidae inaniguttidae sponguridae ceratoikiscidae entactiniidae palaeoscenidiidae and secuicollactidae based on these new data the stratigraphic r

geochronology and geochemistry of precambrian gneisses metabasites and pegmatite from the tobacco root mountains northwestern wyoming craton montanathis article is one of a series of papers published in this special issue on the theme of geochronology in honour of tom krogh t e krogh deceased april 2008 the middle mountain metamorphic domain of the montana metasedimentary terrane northwestern wyoming craton within the northwestern tobacco root mountains mainly comprises migmatized tonalitic gneiss interlayered with amphibolitic hornblende gneiss both of which are cut by metamorphosed mafic rocks together these gneisses are defined as middle mountain gneiss archean tonalitic gneiss from west of and amphibolitic gneiss from east of the bismark fault give from chemically and air abraded zircon grains u pb id tims ages of 3325 5 1 7 and 3340 ma respectively these results reflect primary magmatic ages and show that the middle mountain gneiss extends into the northern area of the central fault block between the bismark and mammoth faults older crustal processes in the tonalitic gneiss are evidenced by inherited grains the oldest of which is 3460 ma a metabasite hosted in tonalitic gneiss in the bismark fault selvage zone yields a zircon age of 2468 ma which is interpreted as the time of

resistivity profiling with different electrode arrays over a graphite deposit motivated by several papers by indian colleagues suggesting that a single pole array is the most favorable one for locating electrically conductive targets in the underground detailed measurements were carried out with different electrode arrays over a well known graphite deposit near pfaffenreuth germany the following arrays were used 1 wenner array 2 single pole array 3 half wenner array 4 half schlumberger array each of the arrays established the location of the main graphite deposit the half schlumberger array turned out to be the most reliable one since it showed details which were only very poorly indicated by the other arrays or not at all mathematical modeling of three dimensional bodies simulating the geological situation for this deposit were carried out these results show an unexpectedly good correlation with the measured effects

island arc carbonates characterization and recognition in the ancient geologic record abstract carbonates of island arc origin that are preserved in paleozoic mesozoic terranes of the north american cordillera exhibit a distinctive suite of paleontologic and lithologic features and share a fundamental similarity with limestones forming in modern volcanic arcs this study provides the first detailed synthesis of carbonate depositional systems in island arcs and documents primary sedimentary constituents based on facies relationships and faunal communities models are developed that show patterns in the long term evolution of shallow marine organisms and the construction evolution and demise of carbonate platforms in island arcs a suite of criteria is identified that may be used to differentiate island arc carbonates from limestones that accumulated in other platform settings biogeographic isolation prolonged subsidence steep submarine slopes and tectonic instability of volcanic edifices contribute to the development of relatively high levels of species endemism impoverished normal marine faunas complex provincial affinities and relict biotas in limestones that are characterized by exceptionally thick platform and periplatform sequences fringing and barrier reefs at the shelf margin extensive lagoonal deposits and rapid lateral and vertical facies changes although destructive tectonic and geologic processes in island arcs may hinder determining the original size and extent of the carbonate platform and particular facies types may not be represented e g fringing and barrier reefs may be replaced by sand shoals at the platform margin many characteristics have potential value for identifying carbonates of island arc origin in the ancient rock record apart from being associated with calc alkaline volcanic and volcaniclastic assemblages the most valuable suite of features for recognizing island arc carbonates is marine biotas that exhibit elevated levels of endemism and mixed paleobiogeographic affinities extraordinary thicknesses of platform shallow marine and periplatform carbonates and rapid facies changes between volcanic and carbonate rocks and between shallow and deep water limestones recognizing that an ensemble of features is distinctive within island arc carbonates considerably enhances identification of volcanic arcs in the ancient geologic record and thus improves the likelihood of successfully unraveling the complex geologic history of ocean basins

a numerical comparison of 2d resistivity imaging with 10 electrode arrays numerical simulations are used to compare the resolution and efficiency of 2d resistivity imaging surveys for 10 electrode arrays the arrays analysed include polepole pp pole dipole pd half wenner hw wenner wn schlumberger sc dipole dipole dd wenner wb array gm multiple or moving gradient array gd and midpoint potential referred measurement mpr arrays five synthetic geological models simulating a buried channel a narrow conductive dike a narrow resistive dike dipping blocks and covered waste ponds were used to examine the surveying efficiency anomaly effects signal to noise ratios and the imaging capabilities of these arrays the responses to variations in the data density and noise sensitivities of these electrode configurations were also investigated using robust l1 norm inversion and smoothness constrained least squares l2 norm inversion for the five synthetic models the results show the following i gm and wn are less contaminated by noise than the other electrode arrays ii the relative anomaly effects for the different arrays vary with the geological models however the relatively high anomaly effects of pp gm and wb surveys do not always give a high resolution image pd dd and gd can yield better resolution images than gm pp wn and wb although they are more susceptible to noise contamination sc is also a strong candidate but is expected to give more edge effects iii the imaging quality of these arrays is relatively robust with respect to reductions in the data density of a multi electrode layout within the tested ranges iv the robust inversion generally gives better imaging results than the l2 norm inversion especially with noisy data except for the dipping block structure presented here v gd and mpr are well suited to multichannel surveying and gd may produce images that are comparable to those obtained with dd and pd accordingly the gd pd dd and sc arrays are strongly recommended for 2d resistivity imaging where the final choice will be determined by the expected geology the purpose of the survey and logistical considerations

upper cambrian archaeocyatha from antarctica geological mapping in the ellsworth mountains of west antarctica have established the existence of extensive middle and late cambrian strata forms tentatively referred to archaeocyatha have been examined by f d and a r who concluded that despite the commonly held opinion that the phylum became extinct at the boundary of the lower and middle cambrian the ellsworth mountains forms represented irregularian archaeocyatha which survived in protected niches into the late cambrian the age of the fauna containing the archaeocyaths is firmly dated by abundant trilobites including species of homagnostus pseudagnostus kormagnostella erixanium and onchopeltis modified journal abstract

a new cambrian sphinctozoan sponge from north america its relationship to archaeocyaths and the nature of early sphinctozoans a new early cambrian sponge of sphinctozoan organization named polythalamia americana nov gen et sp is described from nevada and alaska u s a p americana nov gen et sp shows little resemblance to other cambrian reported sphinctozoans but is similar to late palaeozoic to early mesozoic forms from europe and asia e g stylothalamia and amblysiphonella the polyphyletic origin of sphinctozoans based upon spicule criteria from younger examples is therefore corroborated by the varied morphology and clearly widespread palaeogeographic distribution of cambrian forms which were hitherto recognized only from australia p americana nov gen et sp possesses a relatively small globular multi chambered calcareous skeleton with thin but densely perforate walls and a central retrosiphonate perforate spongocoel the skeleton is composed of an irregular microstructure of unknown but probable calcitic original mineralogy there are no spicules or primary internal structures but secondary vesicular filling tissue is present the pore organization however it directly comparable to archaeocyaths e g coscinocyathines and this character is taken to be the only synapomorphy available for taxonomic and phylogenetic purposes indeed p americana nov gen et sp is closely associated with a diverse archaeocyath assemblage and draws attention to morphological similarities between some archaeocyaths and sphinctozoans thus questioning the criteria at present used to distinguish between these groups accordingly a list of nomenclatural synonymies is given to aid comparison coscinocyathine archaeocyaths possess chambered juvenile stages and p americana nov gen et sp is suggested to represent an aspiculate lineage of sphinctozoan grade which may be derived from forms such as clathricoscinus by neoteny it appears that at least three clades of sphinctozoan grade calcified sponges were present by end of early cambrian time and their occurrence in association with island arcs of the palaeopacific rim is confirmed

sequence stratigraphy chemostratigraphy and facies analysis of cambrian series 2 series 3 boundary strata in northwestern scotland globally the series 2 series 3 boundary of the cambrian system coincides with a major carbon isotope excursion sea level changes and trilobite extinctions here we examine the sedimentology sequence stratigraphy and carbon isotope record of this interval in the cambrian strata durness group of nw scotland carbonate carbon isotope data from the lower part of the durness group ghrudaidh formation show that the shallow marine laurentian margin carbonates record two linked sea level and carbon isotopic events whilst the carbon isotope excursions are not as pronounced as those expressed elsewhere correlation with global records sauk i sauk ii boundary and olenellus biostratigraphic constraint identifies them as representing the local expression of the roece and dice the upper part of the roece is recorded in the basal ghrudaidh formation whilst the dice is seen around 30m above the base of this unit both carbon isotope excursions co occur with surfaces interpreted to record regressive transgressive events that produced amalgamated sequence boundaries and ravinement flooding surfaces overlain by conglomerates of reworked intraclasts the roece has been linked with redlichiid and olenellid trilobite extinctions but in nw scotland olenellus is found after the negative peak of the carbon isotope excursion but before sequence boundary formation

upper silurian lithistid sponge reefs on somerset island arctic canada the upper ludlow douro formation contains the first reported silurian sponge reefs these relatively small 5 35 m diameter mound shaped structures contain on average 35 lithistid demosponges reefs are surrounded by irregular haloes of crinoid debris abundance and diversity of all fossil groups decreases away from the reefs each reef is underlain by a lens of crinoid wackestone to grainstone rich in crinoid holdfasts trepostomate bryozoans solenoporacean algae and rhynchonellid brachiopods are locally common the bulk of each reef consists of lime mudstone with abundant lithistid sponges this is capped by a thin layer of wackestone with abundant tabulate and rugose corals and fewer lithistid sponges calcareous algae trepostomate bryozoans and stromatoporoids this zonation in which a sponge colonization community was replaced by a coral diversification community is similar to that reported from some middle ordovician upper jurassic and holocene sponge reefs the douro sponge reefs were relatively low structures with about 3 m maximum topographic relief they grew on a broad carbonate platform probably in warm tranquil turbid waters of normal or near normal marine salinity periodic influxes of terrigenous mud adversely affected reef size and caused biotic changes some of the reef lime mud was derived from non reef sources but significant quantities were also produced on the reefs reefs underwent synsedimentary lithification bioerosion and minor storm erosion fabrics and compositions of sparry calcite in cavities record three generations of meteoric cementation originally siliceous spicules of the lithistid sponges were dissolved and the moulds later filled with sparry calcite early dissolution of siliceous spicules is common in reef environments and may have caused fossil sponges to be under represented in ancient reefs

resistivity measurements on the sea bottom to map fracture zones in the bedrock underneath sediments1 refraction seismics with the shotpoints and the hydrophone cable on the sea bottom have become the standard geophysical method for investigating rock quality before constructing offshore tunnels in norway in connection with the construction of a sub sea tunnel by the norwegian public roads administration research work was carried out to compare two low velocity zones indicated by refraction seismics with other methods a special resistivity cable for pole dipole measurements on the sea floor with 10 m between the electrodes was constructed a 200 m long profile crossing the two low velocity zones was measured with all combinations of electrode distances the two zones were detected as low resistivity zones a special data processing technique to enhance the anomalies is described resistivity soundings in a seawater environment to detect fracture zones in the bedrock underneath the bottom sediments are discussed it is concluded that severely fractured zones which may cause difficulties for the tunnel construction can be detected both with sea surface and sea floor arrays using long electrode spacings

epidote group minerals in low medium pressure metamorphic terranes epidote group minerals are common in metamorphosed mafic to intermediate igneous rocks quartzofeldspathic sediments and calc alumina silicate marl rocks of higher grade zeolite to medium grade amphibolite facies of low medium pressure contact and regional metamorphic terranes i e pressure and temperature conditions below the calcite to aragonite transition within any one rock epidote composition in terms of fe3 fe3 al can be variable but in general is limited by whole rock composition such that epidote group minerals in metabasite lithologies are more fe rich than those in marls that tend to be more al rich and typically include zoisite because of their wide range of p t stability epidote group minerals of variable composition may form in a single rock during several stages of metamorphic re equilibration slow rates of intra crystalline fe3 al exchange especially at low temperatures preserve complex zonation patterns in individual grains that can serve as a tape recorder providing evidence for continuous or discontinuous prograde and retrograde reactions and the p t fluid redox conditions of metamorphism thus relic lower grade epidote typically fe rich often form cores over which new typically less fe rich higher grade epidote rims form in such a case the boundary between the two generations of epidote may be sharp or gradational depending on the temperature history of the rock and fe3 al diffusivity often compositional differences are blurred across the boundary in addition to zoning is the spread of individual epidote grain compositions within a rock even on a thin section scale this is related to variation in the composition of coexisting phases or reactants e g quartz ca al silicates such as plagioclase margarite lawsonite mafic silicates such as chlorite pumpellyite amphiboles other ca fe3 silicates such as prehnite andraditic garnet carbonates fe oxides relict volcanic glass which serve as compositional micro domains in which epidote may form

development of microboudinage an estimate of changing differential stress with increasing strain microboudin structure has so far been used in structural analysis as a reliable measure of plastic strain and recently it has been proposed to use it as a measure of relative differential stress this paper demonstrates that stress and strain can be simultaneously deduced if the stress and strain analyses are carried out in combination the analysed samples are quartz schists from four localities of different high p low t type metamorphic belts in japan the samples include microboudinaged competent piedmontite grains within a ductile quartz matrix the analyses strongly suggest that the estimated differential stresses tend to increase with increasing strain and that at the final stage of the microboudinage they reach a maximum

deep shelf biostrome of late permian in south china and its implications for the adaptability of calcisponges to water depth abstract the yangtze platform of south china was an area of extensive carbonate accumulation during the late permian with abundant benthic fossils and reef buildups its northern margin has long been considered to be bordered by deep shelf sediments rich in radiolarians and ammonoids however recent investigations found a sponge biostrome in deeper shelf settings in the uppermost permian the biostrome is about 0 45 m thick with an organic framework formed by autochthonous calcisponges in contrast to more diverse shallow marine reef communities at this time the biostrome was almost entirely constructed by the sponge genus peronidella as the only frame building organism this low biodiversity reflects a relatively deep water environment peronidella individuals in the biostrome are apparently larger than the same genus in shallow platform settings including the diameters of both the sponge bodies and the central tubular spongocoel as well as the thicknesses of the body walls this increased size may be related to the low biodiversity and therefore to reduced competition with sponge individuals having increased space in which to develop biostrome development was terminated by volcanic clay deposition

use of the resistivity method in geological mapping case histories from raniganj coalfield india the effectiveness of the electrical resistivity method has been studied using various configurations with different spacings over the southern boundary fault in the northwestern part and across a dolerite dyke named salma dyke in the central part of the raniganj coalfield india it has been observed that the delineation of the fault and the dyke was made possible under differential tropical weathering conditions geoelectric sections across the fault and the dyke have been prepared on the basis of schlumberger sounding results in profiling wenner two electrode half schlumberger and part of al chalabi s configurations were applied over the southern boundary fault across the dyke alpha beta and gamma wenner schlumberger half schlumberger and two electrode configurations were employed azi muthal two electrode sounding was also studied over the fault the interpretation of the results of apparent resistivity profiles across the southern boundary fault suggests that the wenner and two electrode configurations possess certain diagnostic features which help in mapping a single lithological contact provided sufficient resistivity contrast exists although schlumberger configuration seems to be quite suitable other configurations may also be usefully employed over the dyke

transient electromagnetic finite difference time domain earth modeling over steel infrastructure including highly conductive steel infrastructure into electromagnetic em earth modeling is motivated by the fact that long metal cased boreholes have the potential to be used as boosting antennas that enable larger source dipole moments and greater signal penetration depths unfortunately geophysical algorithms designed to simulate em responses over rather regional scales are complicated by material property contrasts and structure geometries that are more typical for em engineering applications hence the great majority of earth modeling algorithms that consider em responses from steel cased boreholes use integral equation methods to be able to model complex casing scenarios we revisited the finite difference time domain fdtd method to advance the modeling of transient em field responses from steel cased boreholes a time dependent function that allows for larger fdtd time steps in the dufort frankel method was developed alleviating the generally large computational overhead we compared our method against three different kinds of benchmark solutions to demonstrate the reliability of the fdtd field solutions these test cases were carried out to check the feasibility of a final hydraulic fracturing study images of the electric current distribution in a sheetlike rock fracture were calculated for the cases with and without the presence of a connecting borehole casing demonstrating the casing s potential of illuminating deep target zones

synthesis of fe pumpellyite and its stability relations with epidote hydrothermal synthesis of fe pum pellyites was conducted using high pressure cold seal apparatus and solid oxygen buffering techniques at temperatures between 250 c and 550 c and 2 0 9 1 kbar pfluid fe pumpellyites were synthesized from partially crystalline gel mixtures of compositions 4cao 2 1al2o3 1 5feo 0 3mgo 6sio2 ii and 3cao 1 5 al2o3 2 7feo 0 3mgo 6sio2 iii in the presence of excess h2o at pfluid of 5 9 1 kbar temperatures between 275 c and 325 c and fo2 defined by the qfm and hm buffers for both of these compositions ii and iii the condensed synthetic run products included minor 7a chlorite garnet fe oxide the cell dimensions and aggregate refractive index a 19 13 2 a b 5 940 4 a c 8 847 5 a 97 37 6 and n 1 702 2 of the pum pellyite synthesized from the bulk composition ii mix are compatible with those of natural pumpellyites containing similar total fe contents attempts at synthesizing fe pumpellyites from a mg free bulk composition were not successful these results are consistent with the total absence of natural mg free pumpellyites the higher temperature higher oxygen fugacity assemblages of the equivalent bulk compositions ii and iii consist of epidote minor amounts of chlorite garnet quartz hematite and magnetite the results of these synthesis experiments accord with the mineral parageneses observed in low grade metabasites which imply that fe pumpellyites are replaced by epidote with increasing temperature and or fo2 and that fe3 is preferentially partitioned into epidote with respect to coexisting pum pellyite in addition these synthesis experiments indicate that fe bearing pumpellyites crystallize at and are stable to lower temperatures than more aluminous pumpellyites a result also consistent with natural systems

chemical variations in assemblages including epidote and or chlorite in the fossil hydrothermal system of saint martin lesser antilles abstract epidote and or chlorite are common minerals in the roots of the fossil geothermal system of saint martin lesser antilles they appear in four distinct assemblages 1 epidote actinolite quartz magnetite near the contact between the tuffaceous host rocks andesitic modal composition and the quartz diorite intrusion of philipsburg 2 epidote chlorite quartz in host rocks as far as a lateral distance of about 3 km from the intrusion 3 epidote chlorite haematite quartz locally in iron and manganese rich host rocks 4 chlorite phengite magnetite appearing as late sealing of porosity in fracture controlled quartz veins with strongly phengitized wall rocks all these assemblages constitute a large alteration grading from propylitic alteration to thermal metamorphism actinolite bearing assemblage detailed microprobe studies of epidotes replacing plagioclases and of chlorites replacing glass and mafic minerals reveal notable compositional variations which have been studied with respect to temperature paleogradients estimated from fluid inclusions study distance from the thermal source and fo2 conditions the mean ps pm 100 fe3 mn3 al3 fe3 mn3 of epidotes vary from 21 in the presence of magnetite near the intrusion to 32 in haematite bearing iron and or manganese volcanic and sedimentary formations the intra grain chemical scattering of epidotes increases with increasing distance of the pluton and decreasing temperature of crystallization all the chlorites coexisting with epidote are mg rich xfe

deformation of granitoids at low metamorphic grade i reactions and grain size reduction abstract deformation and chemical reaction in granitoids at greenschist facies conditions were investigated in samples from three shear zones two from the alps corvatsch granodiorite and aiguilles rouges granite switzerland and one from eastern australia wyangala granite when examined by light and electron microscopy all show similar features of deformation that progressed from coarse parent rock through to fine grained mylonite quartz deformed plastically while both k feldspar and plagioclase fractured and recrystallized in conjunction with chemical change which had as its end point an assemblage albite quartz white mica caal silicates k feldspar and calcic plagioclase depending on fluid chemistry from the parent rock were unstable at low metamorphic grades in the presence of aqueous fluid since ca bearing plagioclase was not stable in these environments myrmekite did not replace k feldspar in any of the rocks examined recrystallization of feldspar which should perhaps be termed neocrystallization was initiated predominantly at clast margins or along microfractures that are marked by fluid inclusions and twin offsets in old feldspar grains particularly in plagioclases dislocations exist in wall like structures that are commonly associated with voids suggesting origins in microfractures these dislocations had severely limited mobility and subgrain rotation does not appear to have contributed to recrystallization we conclude that recrystallization mainly occurred via a classical nucleation mechanism with minor contributions from twin boundary migration we argue that the 450 550 c lower limit for recrystallization of feldspar referenced throughout the literature is not applicable to the rock systems under investigation and should be discarded as a universal limit microfracturing microboudinage and reaction are seen as the prerequisites for mylonite formation from coarse grained granitic rocks at low metamorphic grades see part ii of this paper neocrystallization fluid access and nucleation appear to have accompanied or immediately followed the first deformation increments and were primarily responsible for continued grain size reduction transgranular fracture was comparatively important only at the onset of deformation since the formation of shear zones in granitoids commonly takes place under conditions of low metamorphic grade in the presence of aqueous fluids in the earth s crust breakdown reactions and nucleation recrystallization in feldspars may be important influences upon localization of deformation in granitoids

biosedimentological features of major microbe metazoan transitions mmts from precambrian to cenozoic abstract biotic activities are involved in almost all sedimentation processes throughout the evolutionary history of life on our planet however deep time organism induced sedimentation and biosedimentary records remain unclear in terms of lithologic types strata stacking patterns and possible controlling factors we document biosedimentary features of major transitions from microbe dominated switching to metazoan dominated biosedimentary systems based on the global distributions of both microbial and metazoan carbonates through precambrian to phanerozoic times with emphasis on sedimentary records from china the compilation of 150 and 180 well documented metazoan and microbial reefs respectively from china reveals that metazoan reefs proliferated during the middle ordovician middle devonian and middle permian whereas microbial reefs were well developed during the cambrian late devonian and early middle triassic plus a moderate development during the early silurian these stratigraphic abundances of metazoan and microbial carbonates of china generally match the global patterns the updated variation trends of microbial and metazoan carbonates throughout the late precambrian and phanerozoic reveal that there were five major microbe metazoan transitions mmts the late ediacaran the cambrian and the aftermaths of the mass extinctions of the end ordovician late devonian and end permian the late ediacaran mmt began with microbe dominated oceans with occasional occurrences of metazoans the presence of cloudina dominated reefs in the latest ediacaran marks the completion of the switching of this microbe dominated depositional system into a metazoan dominated system the cambrian saw the expansion of skeletal microbes i e epiphyton renalcis in the oceans and the stratigraphic successions yield the most diverse biosedimentary deposits and or structures of the entire phanerozoic the cambrian mmt was the longest microbial metazoan alternation period and is marked by two metazoan occurrence peaks marked by dominance of abundant archaeocyath buildups during its epoch 2 and by maceriate and lithistid sponge reefs during the late furongian epoch the early silurian in china saw the deposition of a thick suite of organic rich black shales followed by alternations of microbe rich sediments oil shales and metazoan bearing deposits which are replaced by microbial and metazoan reefs during the late early silurian the late devonian mmt started during the late frasnian and persisted into the early mississippian and thus extended slightly longer than the aftermath of the frasnian famennian extinction interval alternating occurrences of microbial and metazoan reefs characterize this late devonian mmt almost all microbe mediated sediments structures observed in the cambrian mmt reoccurred in the aftermath of the end permian mass extinction during the early middle triassic mmt suggesting high similarities between those two mmts cambrian and early middle triassic mmts also share comparable carbon and sulfur isotopic perturbations warming regimes and generally oxygen deficient seawaters some of these environmental and climatic extremes may also occur during other mmts but they usually did not occur synchronously most mmts seem to have undergone four developmental stages they initiated as microbe dominated successions stage a and then were characterized by alternations of microbe dominated and of metazoan bearing or bioturbated successions stage b both microbial and metazoan reefs co occurred during stage c and a dominance of metazoan reefs marks the development of stage d ediacaran and cambrian mmts seem to have undergone the first three development stages whereas the three post extinction mmts experienced the full set of stages a d corresponding to metazoan survival initial recovery and full recovery the majority of volatile rich large igneous provinces lips coupled with intensive acidification events anoxia and global warming regimes took place during the mesozoic cenozoic however microbe dominated sediments were only widely deposited during the early triassic and greatly declined after that time therefore it seems that microbial abundance in mmts may not be directly related to these extreme lip events this is probably because a primary source of food for the metazoans might have shifted to phytoplankton e g coccoliths dinoflagellates and radiolarians in the marine waters since the triassic certainly the pre mesozoic oceans were not dominated by phytoplankton perturbations in the carbon isotope record characterize all mmts and thus may be reliable proxies indicating mmt biosedimentary systems

p t evolution of metasediments from the eclogite zone south central tauern window austria abstract petrologic data on the paragenesis of i kyanite zoisite marbles and ii garnet chloritoid quartz mica schists are presented with the goal of providing constraints on the pressure temperature evolution of the eclogite zone tauern window austria the peak metamorphic assemblages in the two rock types are i kyanite zoisite dolomite quartz zoisite muscovite dolomite calcite quartz and ii garnet chloritoid kyanite muscovite quartz epidote dolomite zn staurolite the estimated peak metamorphic conditions are 19 2 kbar 590 20 c secondary alteration of the kyanite zoisite marbles was accomplished in two stages the early stage resulted in the production of margarite paragonite secondary muscovite and chlorite and the later stage resulted in the formation of sudoite a di trioctahedral mg al layer silicate and kaolinite the early alteration is bracketed at conditions between 3 and 10 kbar 450 550 c and the later alteration between 200 and 350 c p 3 kbar the p t path is characterized by maximum burial to approximately 19 kbar 60 70 km at 590 c followed by nearly isothermal decompression to approximately 10 kbar 30 km and then more gradual decompression with cooling to approximately 3 kbar 10 km alteration was apparently accomplished by the influx of h 2 o rich fluids with the composition of the fluid locally buffered by the mineral assemblage

geochronological constraint on the cambrian chengjiang biota south china the cambrian chengjiang biota of south china provides compelling fossil evidence for the rapid appearance of metazoan phyla in earth history the cambrian explosion however the timing of the chengjiang biota is poorly constrained owing to lack of datable rock materials within the maotianshan shale that yields the fossils here we integrate secondary ion mass spectrometry sims and chemical ablation isotope dilution thermal ionization mass spectrometry ca id tims u pb analyses of detrital zircons from the maotianshan shale to provide high precision geochronological constraint on the chengjiang biota the youngest group of sims u pb detrital zircon dates yields an age peak at 520 ma six zircons from this group are further dated by the ca id tims u pb technique but suggesting that they were not formed from a single zircon growth event thereby neither the age peak nor the weighted mean age defined by the youngest sims u pb dates could represent the maximum depositional age of the maotianshan shale instead the youngest ca id tims u pb date 518 03 0 69 0 71 ma 2 analytical uncertainty incorporates u pb tracer calibration uncertainty provides the first robust maximum age of the chengjiang biota this new geochronological constraint on the chengjiang biota indicates that the cambrian explosion reached its major phase around 518 03 0 69 0 71 ma demonstrating a protracted process 22 myr for the cambrian explosion supplementary material sims and ca id tims zircon u pb data are available at https doi org 10 6084 m9 figshare c 4024849

the late early cambrian microbial reefs immediately after the demise of archaeocyathan reefs hunan province south china abstract the archaeocyath bearing reefs that first appeared in south china in the atdabanian were last seen in the lower toyonian e g in the tianheban and jindingshan formations the upper toyonian lower amgan qingxudong formation of hunan province examined in this study includes large sized reefs formed solely by calcimicrobes of epiphyton kordephyton girvanella hedstroemia and renalcis during the middle and upper cambrian small scale stromatolite reefs were formed the qingxudong reefs are therefore interpreted to be the most well developed microbial reefs of the post archaeocyath bearing reefs in the late early cambrian the transition from archaeocyath bearing to purely microbial reefs was caused by a decline in the diversity of metazoans and was accompanied by a reduction in the abundance of reefs possibly related in part to late early cambrian regression the late early cambrian reefs of south china contain a well preserved record of reef succession and provide important insights into the factors that led to the demise of archaeocyath bearing reefs and the subsequent long lasting hindrances to the development of skeletal dominated reefs during the middle and late cambrian

cambrian chronostratigraphy current state and future plans abstract important steps have been made by the international subcommission on cambrian stratigraphy iscs toward global chronostratigraphic subdivision of the cambrian the consensus of opinion is that the system should be subdivided into four series representing subequal spans of time the lower two series will correspond approximately to the traditional lower cambrian the third series will correspond approximately to the traditional middle cambrian and the fourth series corresponds approximately to the traditional upper cambrian the fourth series called the furongian series was ratified by the international commission on stratigraphy ics and the international union of geological sciences iugs in 2003 selection of horizons representing evolutionary events that can be correlated on a global scale and which can be used as stage or series boundaries is much more difficult for the lower two series intervals of the cambrian than it is for the upper two series intervals of the cambrian the most practical concept for subdividing the system into stages involves the establishment of two stages each for the first and second series and the establishment of three stages each for the third and fourth series the lowermost stage of the furongian called the paibian stage has been ratified by the ics and the iugs

discovery of triassic phylloid algae possible links with the paleozoic triassic phylloid algae have recently been discovered in a reef in the southern yukon these plate like algae are the primary frame builders in a few small patches in the upper section of the reef where they are associated with fossils and sedimentary structures suggesting deposition in very shallow water a vague porous microstructure in some of the algae suggests affinities with paleozoic codiacean phylloid algae but preservation is too poor to permit definite classification nevertheless the indication that phylloid algae did not become extinct at the end of the paleozoic as formerly supposed increases the possibility of finding missing evolutionary links between paleozoic phylloid algae and their modern counterparts

fluid inclusions in epidote minerals and fluid development in epidote bearing rocks the widespread occurrence of epidote minerals in metamorphic and igneous rocks as well as in many ore deposit types makes it a promising candidate for fluid inclusion studies apart from high to very high temperature and low to intermediate pressure conditions epidote minerals are stable over a wide range of pressure and temperature in the continental and oceanic crust e g poli and schmidt 1998 yet fluid inclusion studies on epidote minerals are surprisingly scarce even in fluid saturated environments like certain vein type deposits or hydrothermal volcanic vugs and druses for example epidote minerals are not mentioned in the subject index of roedder s 1984 outstanding summary and review of fluid inclusion studies and occurrences which lists more than sixty different host minerals for fluid inclusions nonetheless more recent studies showed fluid inclusions in epidote minerals to be the only direct witness of the physiochemical and compositional fluid evolution during certain geodynamic processes mainly found in fossil geothermal systems ore deposits and high pressure to ultra high pressure rocks the aim of this review is to outline and summarize some aspects and interpretations of geodynamic processes which are based on temperature t pressure p molar volume v and composition x data from fluid inclusions in epidote minerals as well as associated host minerals from various geological environments the review starts with a chapter on some typical mixed volatile solid fluid equilibria involving epidote minerals which are relevant for the here discussed environments this is followed by a short introduction into the basic concepts of fluid inclusion research and the role of epidote minerals the next section covers fluid inclusion studies on epidote minerals from active and fossil geothermal systems as well as low grade metamorphic rocks and constraints on the p t x properties of the fluids present in these systems this is followed by a short introduction

lower cambrian shelf and shelf margin buildups flinders ranges south australia1 carbonate buildups in the flinders ranges of mid early cambrian age grew during a period of high archaeocyath diversity and are of two types 1 low energy archaeocyath sponge spicule mud mounds and 2 high energy archaeocyath calcimicrobe calcified microbial microfossil bioherms mud mounds are composed of red carbonate mudstone and sparse to abundant archaeocyath floatstone have a fenestral fabric display distinct stromatactis contain abundant sponge spicules and form structures up to 150m wide and 80 m thick bioherms are either red or dark grey limestone and occur as isolated small structures 2 20 m in size surrounded by cross bedded calcarenites and calcirudites or as complexes of mounds and carbonate sands several hundreds of metres across red bioherms comprise masses of white epiphyton with scattered archaeocyaths and intervening areas of archaeocyath rich lime mudstone grey bioherms are complex intergrowths of archaeocyaths encrusting dark grey renalcis and thick rinds of fibrous calcite cement the bioherms were prone to synsedimentary fracturing and exhibit large irregular cavities up to 1 5 m across lined with fibrous calcite the buildups are isolated or in contiguous vertical succession mud mounds occur alone in low energy frequently nodular limestone facies individual bioherms and bioherm complexes occur in high energy on shelf and shelf margin facies the two types also form large scale shallowing upward sequences composed of basal deep water mud mounds grading upward into archaeocyath calcimicrobe bioherm complexes and bioherms in cross bedded carbonate sands the uppermost sequence is capped by ooid grainstone and or fenestral to stromatolitic mudstone the calcimicrobe and metazoan associations form the two major biotic elements which were to dominate reefs throughout much of subsequent phanerozoic time

comparative rheological behaviour of albite and quartz in siliceous schists revealed by the microboudinage of piedmontite abstract this paper presents a detailed comparison of the microboudinage of piedmontite in two different mineralogical hosts a quartz matrix and albite porphyroblasts in a siliceous schist with the aim of clarifying the rheological properties of albite in relation to those of quartz stress and strain analyses of the microboudinage confirm that the boudinage took place in the retrograde stage of metamorphism during decreasing temperature and reveal that albite deformed at the same strain rate as quartz above the plastic brittle transition temperature of albite

weakening and strain localization produced by syn deformational reaction of plagioclase there are many observations in naturally deformed rocks on the effects of mineral reactions on deformation but few experimental data in order to study the effects of chemical disequilibrium on deformation we have investigated the hydration reaction plagioclase h2o more albitic plagioclase zoisite kyanite quartz we utilized fine grained 2 6 m plagioclase aggregates of two compositions an54 and an60 both dried and with 0 1 0 4 wt h2o present in shear deformation experiments at two sets of conditions 900 c 1 0 gpa in the plagioclase stability field and 750 c 1 5 gpa in the zoisite stability field dry samples and those deformed in the plagioclase stability field underwent homogeneous shearing by dislocation creep but samples with 0 1 to 0 4 wt water deformed in the zoisite stability field showed extreme strain localization into very narrow 1 3 m shear bands after low shear strain in these samples the microstructures of reaction products in the matrix differ from those in the shear bands in the matrix large up to 400 m zoisite crystals grew in the direction of finite extension and relict plagioclase grains are surrounded by rims of recrystallized grains that are more albitic in the shear bands the reaction products albitic plagioclase zoisite white mica and traces of kyanite form polyphase aggregates of very fine grained 0 1 m dislocation free grains most of the sample strain after 2 has occurred within the shear bands within which the dominant deformation mechanism is inferred to be diffusion accommodated grain boundary sliding dagbs the switch from dislocation creep in dry samples deformed without reaction to dagbs in reacted samples is associated with a decrease in flow stress from 800 to 200 mpa these experiments demonstrate that heterogeneous nucleation driven in part by chemical disequilibrium can produce an extremely fine grained polyphase assemblage leading to a switch in deformation mechanism and significant weakening thus localization of deformation in polyphase rocks may occur on any pressure p temperature t path where the equilibrium composition of the constituent minerals changes

combined sounding profiling resistivity measurements with the three electrode arrays a combination of dc resistivity sounding and profiling measurements can be used to obtain the maximum information about distribution of resistivities in the earth combined sounding profiling measurements with the amn mnb arrays are considered the resistivity data from such measurements can be presented as a normal sounding curves b combined sounding profiling curves c profiling curves d pseudo sections or as transformations obtained by the so called gradient processing to emphasize the influence of the target objects the examples chosen from numerical modeling and field tests show the efficiency of measurements with three electrode arrays to accurately locate thin conductors and contacts of lithological units of different resistivities an interpreted cross section is compared with the results of other geophysical measurements vlf r dipole em ip showing good correlation

mass rock creep and landsliding on the huangtupo slope in the reservoir area of the three gorges project yangtze river china the huangtupo slope is one of the most noted large scale slopes with geologic hazards that cause problems related to the residential safety of immigrants in the reservoir area of the three gorges project yangtze river china the gravitational process blended with tectonic deformation large scale covering of loose debris and long term surficial mass movement complicates the huangtupo slope and gives rise to a lack of consensus on the slope nature and stability characterization of the structural geometry of the slope deformation and reconstruction of its development history are believed to be pivotal in understanding what has happened and what will happen to the slope based on a thorough field investigation combined with an electrical resistivity survey a three stage model involving mass rock creep primary landsliding partial reactivation is proposed the first stage follows the incision of the yangtze river along the axes of the guandukou syncline when huangtupo experienced long term gravitational deformation referred to as mass rock creep mass rock creep in the huangtupo slope can be classified as two basic processes toppling and deep seated creep toppling mainly occurs on the exterior part of the slope and is characterized by inclination sliding and segmentation of brittle deformation of cleavage rocks deep seated creep occurs predominantly in the interior part of the slope and brittle ductile flow folding accompanying low angle shearing is its representative deformation a primary large scale landslide occurred in the second stage as a subsequence of previous mass rock creep the landslide was ca 4 107 m3 in volume with elevations of 640 m a s l at the head and of 80 m a s l at the foot significant evidence for the landslide is the variation of attitudes of structural foliation and lineation among outcrops in the slope the last stage began subsequent to the original sliding surficial and partial reactivation on the huangtupo landslide plays a leading role in this stage two sliding events in this area in 1995 were ascribed to the partial reactivation mainly due to rainfall water level fluctuation of the yangtze river as well as human activity it was suggested that analogous failures in 1995 would continue on the huangtupo landslide and become even more frequent under the combined effect of human activity and reservoir filling

physical and chemical properties of the epidote minerals an introduction epidote minerals are known since the 18th century but at that time the greenish to dark colored varieties were termed actinolite or schorl and not distinguished from the minerals to which these names apply today hauy defined the mineral species and introduced the name epidote in 1801 whereas werner in 1805 used the term pistacite quoted from hintze 1897 epidote is derived from greek epidosis to increase because the base of the rhombohedral prism has one side larger than the other and pistacite refers to its green color all references for names after luschen 1979 blackburn and dennen 1997 weinschenk 1896 proposed the name clinozoisite from its monoclinic symmetry and zoisite like composition for those monoclinic members of the epidote family that are fe poor optically positive and have low refractive indices and birefringence zoisite was probably confused with tremolite until the beginning of the 19th century in 1804 siegmund zois baron von edelstein 1747 1819 an austrian sponsor of mineral collections found and described a new mineral in a handspecimen from the saualpe mountains in carinthia that was named zoisite by werner hauy 1822 interpreted zoisite as a variety of epidote and included it in his epidote spezies weiss 1820 presented a theory of the epidote system and also discussed crystal morphological features of the epidote minerals weiss 1828 rammelsberg 1856 studied the relationship between epidote and zoisite and presented a compilation of chemical analyses of zoisite he already noticed that the relative concentrations of di tri and tetravalent cations are identical in zoisite and epidote but that the fe content in zoisite about 2 3 5 wt fe2o3 is generally less than in epidote about 9 12 wt fe2o3 piemontite see bonazzi and menchetti 2004 was probably first described in 1758 by cronstedt

constraints on rates of granitic magma transport from epidote dissolution kinetics epidote is stable only at high pressure in granitic magmas but is found in magmas crystallized at shallow crustal levels this observation suggests qualitatively that magma transport is sufficiently rapid to prevent complete epidote resorption experimental measurements of epidote dissolution showed that the presence of epidote implies that magma transport from the deep crust in these systems was rapid and that the transport was by dikes rather than diapirs

detecting small scale targets by the 2d inversion of two sided three electrode data application to an archaeological survey abstractthe detecting capabilities of some electrical arrays for the estimation of position sizeand depth of small scale targets were examined in view of the results obtained from2d inversions of apparent resistivity data the two sided three electrode apparent resistivity data are obtained by the application of left and right hand pole dipolearrays that also permit the computation of four electrode and dipole dipoleapparent resistivity values without actually measuring them synthetic apparent resistivity data sets of the dipole dipole four electrode and two sided three electrodearrays are calculated for models that simulate buried tombs the results of two dimensional inversions are compared with regard to the resolution in detecting theexact location size and depth of the target showing some advantage for the two sided three electrode array a field application was carried out in the archaeologicalsite known as alaca hoyuk a religious temple area of the hittite period the two dimensional inversion of the two sided three electrode apparent resistivity data hasled to locating a part of the city wall and a buried small room the validity of theinterpretation has been checked against the results of subsequent archaeologicalexcavations introductionthe two dimensional 2d inversion of direct current dc sounding data has become a standard tool for the investiga tion of targets buried at shallow and intermediate depths theapplications include archaeology environmental and hydro geological works mining exploration and engineeringstudies when using the traditional electrode arrays thedata acquisition is usually carried out by expanding electro des along a measurement profile the apparent resistivitydata obtained from all soundings are then used as the input ofa 2d inversion algorithm pelton rijo and swift 1978 andsasaki 1981 first introduced inversion algorithms applied tothe dipole dipole and schlumberger arrays respectively later loke and barker 1996 introduced a fast 2d inversionmethod for the wenner and dipole dipole electrode arrays this algorithm is based on a quasi newton method whichcalculates an approximate value of partial derivatives of theapparent resistivity data with respect to model parameters the finite difference technique is used for the computation ofthe model response one of the remarkable developments in dc methods is theuse of modern measuring systems with multicore cableswhich allows automatic switching between electrodes forpractical field operations the electrodes are located at equallyspaced measurement stations for example morris ronningand lile 1997 described a data acquisition system thatsimultaneously collects schlumberger and two dipole dipoledata however they did not indicate a quantitative inter pretation tool acworth and griffiths 1985 and griffithsand turnbull 1985 described wenner tripotential apparent resistivity measurements to reduce the number of ambiguitiesarising in the qualitative interpretation of apparent resistivitypseudosections the tripotential method produces threeapparent resistivity measurements for each position of acollinear equispaced quadripole of electrodes they used the

a new post early cambrian archaeocyath from antarctica a new species of archaeocyath sponge dictyocyathus neptunensis is described from the lower third of the nelson limestone of the neptune range antarctica based on the presence of the trilobites nelsonia schesis and amphoton oatesi these strata are interpreted to be mid to late middle cambrian in age d neptunensis shows a branching low integration modular form and a very simple skeletal type such an organization is predicted from known morphological trends within the early cambrian archaeocyatha specimens are not in life position and probably form part of a storm deposit the absence of dictyocyathus from latest early cambrian toyonian strata worldwide suggests a convergent nature for this highly simplified skeletal type in archaeocyaths

a new lower cambrian shelly fossil biostratigraphy for south australia abstract definition of early cambrian chronostratigraphic boundaries is problematic with many subdivisions still awaiting ratification integrated multi proxy data from well resolved regional scale schemes are ultimately the key to resolving broader issues of global correlation within the cambrian in australia early cambrian biostratigraphy has been based predominantly on trilobites phosphatic shelly fauna have great potential as biostratigraphic tools especially in pre trilobitic strata because they are widespread and readily preserved but they have remained underutilised here we demonstrate their value in a new biostratigraphic scheme for the early cambrian of south australia using a diverse shelly fauna including tommotiids brachiopods molluscs and bradoriids biostratigraphic data are derived from ten measured stratigraphic sections across the arrowie basin targeting hawker group carbonates including the wilkawillina wirrapowie and ajax limestones and the mernmerna formation the stratigraphic ranges of shelly fossils are predictable and repeatable across the arrowie basin allowing three discrete shelly biozones to be identified spanning terreneuvian stage 2 to series 2 stages 3 4 the kulparina rostrata zone new and part of the overlying micrina etheridgei zone new are pre trilobitic predominantly terreneuvian the cambrian series 2 stage 3 dailyatia odyssei zone new features a very diverse shelly fauna and will be described in detail in a separate publication these zones provide robust means to correlate terreneuvian series 2 successions in neighbouring coeval basins in australia particularly the stansbury basin wider correlation is possible throughout east gondwana and especially with south china

eve of biomineralization controls on skeletal mineralogy carbonate mineralogies have oscillated between aragonite and calcite seas through geological time proposed to be due mainly to secular variation in the magnesium calcium ratio driven by changing rates of ocean crust production a quantitative compilation of inorganic and biominerals from the onset of biomineralization late ediacaran middle ordovician reveals a correspondence between seawater chemistry and the first adopted mineralogy of skeletal clades ediacaran tommotian skeletons and inorganic precipitates were composed exclusively of aragonite or high mg calcite but these were replaced by low mg calcite mineralogies during the early atdabanian implying the onset of a calcite sea this transition is empirically constrained by fluid inclusion data late atbadanian botoman inorganic precipitates returned to aragonite with high mg calcite echinoderms and solitary tabulaconids and massive aragonitic tabulaconids originating during this interval middle cambrian ordovician inorganic precipitates were low mg calcite and the ordovician radiation in skeletal expression was due mostly to groups with low mg calcite mineralogies these short lived transitions can be most parsimoniously explained by minor oscillations of mmg ca around 2 during this period possibly combined with the progressive onset of greenhouse conditions during the mid late cambrian

controlled source electromagnetic monitoring of reservoir oil saturation using a novel borehole to surface configuration to advance and optimize secondary and tertiary oil recovery techniques it is essential to know the areal propagation and distribution of the injected fluids in the subsurface we investigate the applicability of controlled source electromagnetic methods to monitor fluid movements in a german oilfield bockstedt onshore northwest germany as injected brines highly saline formation water have much lower electrical resistivity than the oil within the reservoir the main focus of this study is on controlled source electromagnetic simulations to test the sensitivity of various source receiver configurations the background model for the simulations is based on two dimensional inversion of magnetotelluric data gathered across the oil field and calibrated with resistivity logs three dimensional modelling results suggest that controlled source electromagnetic methods are sensitive to resistivity changes at reservoir depths but the effect is difficult to resolve with surface measurements only resolution increases significantly if sensors or transmitters can be placed in observation wells closer to the reservoir in particular observation of the vertical electric field component in shallow boreholes and or use of source configurations consisting of combinations of vertical and horizontal dipoles are promising preliminary results from a borehole to surface controlled source electromagnetic field survey carried out in spring 2014 are in good agreement with the modelling studies

solid solution between piemontite and androsite la a new mineral of the epidote group from andros island greece a new member of the epidote group androsite la was found at andros island cyclades greece as an accessory constituent of metamorphic mn rich rocks associated minerals are rhodochrosite braunite rhodonite spessartine and quartz the mineral is brown red in color transparent with vitreous luster and very strong pleochroism lattice parameters are a 8 896 1 b 5 706 1 c 10 083 1 a 3 113 88 1 v 468 0 1 a3 z 2 space group p2 m crystal structure refinement and chemical analyses yielded the ideal formula mn ca reeaimnhmnh sio si207 0 oh another mn rich sample of the epidote group was found at varenche mn mine valle di saint barthelemy western alps italy because of its chemical composition and crystallographic features it can be considered an intermediate member of the piemontite androsite la series

a triassic sponge from vancouver island possible holdover from the cambrian tiny cap shaped fossils recovered from silicified residues in upper triassic rocks of vancouver island wrangellia are identified as a calcareous sponge nucha vancouverensis n sp nov the genus nucha pickett and jell was first reported from middle cambrian rocks of australia the triassic example constitutes the first occurrence outside the cambrian system and the continent of australia the absence of representatives in rocks between triassic and cambrian age suggests that it is a long range refugium taxon the occurrence of such a wide ranging holdover organism reinforces the role of refugia in preferential survivorship over long periods of geologic time other holdover taxa are known from volcanic displaced terranes of western american cordillera and their study may help clarify neglected aspects of survival and evolution

latest middle cambrian metazoan reef from northern iran middle and late cambrian reefs were built mainly by cyanobacterial communities a few reefs with a metazoan as well as an algal component however are known from this interval a middle cambrian reef formed primarily by spicular demosponges is described here from the mila formation in the elburz mountains northern iran the reef is enclosed within calcareous grainstones which contain terminal middle cambrian late mayan trilobites the mila formation reef was constructed by sponges of the family anthaspidellidae and bacterial algal sheaths and is the earliest metazoan reef to be documented from the interval after the demise of archaeocyath sponges the reefal community is typical of subsequent reefal communities of early middle ordovician age the ordovician examples differ only by the incorporation of additional metazoan elements

cambrian evolutionary radiation context correlation and chronostratigraphy overcoming deficiencies of the first appearance datum fad concept abstract use of the first appearance datum fad of a fossil to define a global chronostratigraphic unit s base can lead to intractable correlation and stability problems fads are diachronous they reflect species evolutionary history dispersal biofacies preservation collection and taxonomy the cambrian evolutionary radiation is characterised by diachronous fads biofacies controls and provincialism of taxa and ecological communities that confound a stable lower cambrian chronostratigraphy cambrian series and stage definitions require greater attention to assemblage zone successions and non biostratigraphic particularly carbon isotope correlation techniques such as those that define the ediacaran system base a redefined basal cambrian trichophycus pedum assemblage zone lies above the highest ediacaran type biotas vendobionts putative metazoans and calcareous problematica such as cloudina and the basal asteridium tornatum comasphaeridium velvetum zone acritarchs this definition and the likely close correspondence of evolutionary origin and local fad of t pedum preserves the fortune head newfoundland gssp of the cambrian base and allows the presence of sub cambrian branched ichnofossils the sub tommotian equivalent base of stage 2 a suggested laolinian stage should be defined by the i l4 zhuce 13 c positive peak bracketed by the lower ranges of watsonella crosbyi and aldanella attleborensis molluscs and the skiagia ornata fimbrioglomerella membranacea zone acritarchs the w crosbyi and a attleborensis fads cannot define a stage 2 base as they are diachronous even in the newfoundland type w crosbyi zone the series 2 base cannot be based on a species fad owing to the provincialism of skeletalised metazoans in the terreneuvian series 2 boundary interval and global heterochrony of the oldest trilobites a series 2 and stage 3 a suggested lenaldanian series and zhurinskyan stage new gssp base is proposed at the siberian lower atdabanian 13 c iv peak which correlates into south china avalonia and morocco and assigns the oldest trilobites to the terminal terreneuvian series

regional scale hydrothermal alteration in the central blake river group western abitibi subprovince canada implications for vms prospectivity the late archean blake river group is a thick succession of predominantly mafic volcanic rocks within the southern zone of the abitibi greenstone belt it contains a number of silicic volcanic centers of different size including the large noranda volcanic complex which is host to 17 past producing volcanogenic massive sulfide deposits the noranda complex consists of a 7 to 9 km thick succession of bimodal mafic and felsic volcanic rocks erupted during five major cycles of volcanism massive sulfide formation coincided with a period of intense magmatic activity cycle iii and the formation of the noranda cauldron hydrothermal alteration in these rocks is interpreted to reflect large scale hydrothermal fluid flow associated with rapid crustal extension and rifting of the volcanic complex the alteration includes abundant albite chlorite epidote and quartz silicification which exhibit broad stratigraphic and structural control and correlate with previously mapped whole rock oxygen isotope zonation the mine sequence volcanic rocks are characterized by abundant iron rich chlorite fe fe mg 0 5 hydrothermal amphibole ferroactinolite and coarse grained epidote of clinozoisite composition 10 wt fe2o3 lacking the clinozoisite solid solution alteration in the mine sequence volcanic rocks persists along strike well beyond the limits of the main ore deposits as far as several tens of kilometers and can be readily distinguished from greenschist facies metamorphic assemblages at a regional scale the lack of similar alteration in the pre cauldron sequences is consistent with limited 18o depletion and suggests that the early history of the volcanic complex did not support large scale high temperature fluid flow in these rocks comparisons with a much smaller barren volcanic complex in nearby ben nevis township reveal important differences in the alteration mineralogy between volcanoes of different size with implications for area selection during regional scale mineral exploration the ben nevis complex consists of a 3 to 4 km thick succession of mafic intermediate and felsic volcanic rocks centered on a small subvolcanic intrusion alteration of the volcanic rocks comprises mainly low temperature assemblages of prehnite pumpellyite magnesium rich chlorite fe fe mg 10 wt fe2o3 and calcite actinolite magnetite alteration occurs proximal to the intrusive core of the complex but the limited extent of this alteration indicates only local high temperature fluid circulation adjacent to the intrusion a distal zone of carbonate alteration is located 4 6 km from the center of the volcano although iron bearing carbonates are present locally within this zone the absence of siderite argues against a high temperature origin for this alteration these observations do not offer positive encouragement for the existence of a fossil geothermal system of sufficient size or intensity to have produced a large massive sulfide deposit

phosphatized early cambrian archaeocyaths and small shelly fossils ssfs of southwestern mongolia abstract archaeocyaths are an enigmatic group of calcifying sponges prevalent in early cambrian terreneuvian to series 2 successions around the world and preserved predominantly in reefal buildups but also in adjacent reworked deposits here we report exceptionally preserved phosphatized archaeocyaths and small shelly fossils from phosphatized reef flank deposits at the top of the salaagol formation of southwestern mongolia recent chemostratigraphic age models suggest that these archaeocyaths are among the earliest reported in the terreneuvian stage 2 tommotian these fossils provide a window into the mechanisms of archaeocyath phosphatization a generally rare mode of archaeocyath preservation to assess the composition and nature of phosphatization fossil assemblages were examined in insoluble residue and thin section these archaeocyaths are preserved as phosphatic internal molds in residue and both phosphatized and unphosphatized archaeocyaths are present in thin section the occurrence of internal molds and complementary mineralogical data suggest that the decay of organic material within the archaeocyaths created the necessary redox conditions for apatite nucleation we propose that shortly after death this assemblage was transported to a deeper water environment and that the presence of organic matter in a low oxygen setting led to abundant phosphatization of archaeocyaths

comment a new lower cambrian shelly fossil biostratigraphy for south australia by marissa j betts john r paterson james b jago sarah m jacquet christian b skovsted timothy p topper glenn a brock

cyanobacterial archaeocyathan radiocyathan bioherms in the wirrealpa limestone of south australia the 140 m thick wirrealpa limestone of south australia is an open shelf marine deposit of early middle cambrian botomian or toyonian age bioherms preserved within this unit have a distinctive epiphyton thrombolitic stromatolite framestone core colonized by a low diversity archaeocyathan radiocyathan biota of ajacicyathus sp archaeocyathus abacus n sp and girphanovella gondwana n sp together with other skeletal invertebrates and macroborers the largest bioherm some 3 m in thickness and 36 m in length is enclosed within an interval of thin bedded to nodular silty bioclast limestone but rests directly on a substrate of bioclast intraclast and onkoid packstone floatstone rudstone the archaeocyathan radiocyathan biota represents the youngest known australian occurrence of these groups

archaeocyathan limestone blocks of likely antarctic origin in gondwanan tillite from the falkland islands cambrian limestone clasts containing a rich well preserved archaeocyathan fauna have been recovered from the late carboniferous fitzroy tillite formation of the falkland islands since neither cambrian strata nor limestone are present anywhere in the indigenous rock succession the clasts are regarded as exotic erratics introduced during the permo carboniferous gondwana wide glaciation most recent reconstructions of gondwana rotate the falklands into proximity with the eastern cape south africa and the ellsworth mountains antarctica in both of these areas permo carboniferous diamictites correlated with the fitzroy tillite formation also contain rare exotic clasts of archaeocyathan limestone the transantarctic mountains seem the most likely source for all of these unusual erratics this interpretation sustains the requirement for substantial rotation of the falklands microplate into gondwana reconstructions and illustrates the extent of the late carboniferous ice sheet apparent differences in the tillite clast assemblages between east and west falkland suggest variable provenance within the regional ice flow regime

hydro frac monitoring using ground time domain electromagnetics as motivation for considering new electromagnetic techniques for hydraulic fracture monitoring we develop a simple financial model for the net present value offered by geophysical characterization to reduce the error in stimulated reservoir volume calculations this model shows that even a 5 improvement in stimulated reservoir volume for a 1 billion barrel bbl field results in over 1 billion u s dollars us in net present value over 24 years for us 100 bbl oil and us 0 5 billion for us 50 bbl oil the application of conductivity upscaling often used in electromagnetic modeling to reduce mesh size and thus simulation runtimes is shown to be inaccurate for the high electrical contrasts needed to represent steel cased wells in the earth finescale finite difference modeling with 12 22 mm cells to capture the steel casing and fractures shows that the steel casing provides a direct current pathway to a created fracture that significantly enhances the response compared with neglecting the steel casing we consider conductively enhanced proppant such as coke breeze coated sand and a highly saline brine solution to produce electrically conductive fractures for a relatively small frac job at a depth of 3 km involving 5 000 bbl of slurry and a source midpoint to receiver separation of 50m the models show that the conductively enhanced proppant produces a 15 increase in the electric field strength in line with the transmitter in a 10 m background in a 100 m background the response due to the proppant increases to 213 replacing the conductive proppant by brine with a concentration of 100 000 ppm nacl the field strength is increased by 23 in the 100 m background and by 2 3 in the 10 m background all but the 100 000 ppm nacl brine in a 10 m background produce calculated fracture induced electric field increases that are significantly above 2 a value that has been demonstrated to be observable in field measurements

3d modelling of combination of array results for resistivity profiling data over a dyke for groundwater exploration and development detailed three dimensional 3d modelling of resistivity profiling data collected across the long outcropping in situ dyke with significant width 25 30 m and intruded within the granite host rock was performed to evaluate the resistivity anomaly response understand the dyke characteristics properties and its role in groundwater flow the main objective of the present research work is to develop information about the subsurface and explain the observed anomaly data confirm the resistivity anomaly response using two different electrode configurations namely wenner and schlumberger interpretation of the 3d modelling results indicate high resistivity anomaly over the in situ dyke the extent of degree of weathering of rocks here granite is quite and clearly visible from the anomaly responses in model output in terms of resistivity contrasts the results are fairly well in agreement with the field resistivity anomaly especially in terms of shape of the anomaly the 3d theoretical forward modelling approach performed using resistivity profiling data set is much helpful and significant in establishing the knowledge of true anomaly caused due to subsurface dyke in the present geological set up it resolved the shape and width of the dyke both laterally and vertically the degree of weathering of dyke near the surface is well resolved the comparison of the modelling results with the field data gives a strong correlation between resistive anomalies and the subsurface the study is very useful for groundwater exploration and development and helps us to understand precisely the role of dyke based on the 3d modelling study

application of the fast fourier transform to interpret geoelectric anomalies preliminary results archaeological structures are commonly buried at shallow depths nevertheless their geophysical signatures measured at the surface may be weak and contaminated with noise thus difficult to interpret however regional residual separation techniques commonly used in gravity and magnetics to enhance the signal of interest also can be applied to the interpretation of one dimensional resistivity profile data such a process is done based on a frequency analysis the resistivity response of synthetic models has been computed analytically by the images method for a wenner array different curves were analysed varying the observation step p the width t of two vertical layers the resistivity p of the media and the electrodes interval a the fourier transform is applied to the theoretical resistivity profiles to compute and analyse its amplitude spectrum such a function presented three regions of interest a low frequency zone was selected to design a low pass filter to calculate the regional of the resistivity curve a residual resistivity anomaly was calculated by taking the difference between that and the observed profile such an anomaly depicted highs that corresponded to the location of the resistive interfaces after assessing the technique with theoretical data an application to a real case was studied the real data are from the city of denia alicante located in the eastern coast of spain in the mediterranean sea the area of interest was covered by eight resistivity profiles two of them lay on a road under construction where remains of a roman structure were discovered during the construction works residual resistivity anomalies were computed by applying the method of regional residual separation in the wave number domain a correlation process between the computed residual and the theoretical response of the wall model was carried out to locate the position of the boundaries of the village foundations the geophysical interpretation enabled the archaeological work to discover the remains of a warehouse complex related to the ancient roman port of dianium buried close to the surface below the road so far no excavation has been undertaken in the reminder electrical profiles

compositional order disorder and stable isotope characteristics of al fe epidote state 2 14 drill hole salton sea geothermal system epidote ca2fe3si3o12 oh ca2al3si3o12 oh is a common hydrothermal mineral in metasediments and veins at depths 900 m in the state 2 14 drill hole of the salton sea geothermal system the mole fraction of ca2fe3si3o12 oh in epidotes xps from this drill hole ranges from 0 11 to 0 42 and complex compositional zoning of octahedral fe3 and al is typical within single grains with increasing depth there is an overall but irregular decrease in the fe3 content of epidotes in metasandstones in most samples vein epidotes are more fe3 rich and exhibit a wider compositional range than metasandstone epidotes from the same depth octahedral fe3 in the m 1 sites in four epidotes evaluated by 57fe mossbauer spectroscopy ranges from 7 5 1 7 to 11 4 1 5 of the total iron the most ordered epidote formed in veins at 2618 m in the biotite zone this epidote has an ordering parameter 1 2xfe3 m 1 of 0 85 0 03 which corresponds to a calculated state of equilibrium order disorder at 390 60 c in close agreement with the probable downhole temperature of 340 c two epidote samples from the chlorite calcite zone 1420 m 265 c 1867 m 300 c are more disordered corresponding to calculated states of equilibrium order disorder of 450 c these data suggest that the analyzed epidotes from the chlorite calcite zone are in a metastable state of substitutional order disorder the measured value of depidote from 1420 m is 96 which is 5 6 lighter than epidotes from 1867 m depidote 90 2227 m depidote 91 and 2618 m depidote 90 when compared to the reservoir fluid from the december 1985 flow test the derived fractionation of hydrogen isotopes between epidote and the geothermal brine is 19 at 1867 m and 340 c this value is in accord with published experimental hydrogen isotope fractionations between iron rich epidote and aqueous electrolyte solutions therefore considering the complexity of the salton sea brine the isotopic temperature is similar to the inferred downhole temperature

interpretation and depth of investigation of gradient measurements in direct current geoelectrics gradient measurements in a homogeneous electrical primary field can easily be interpreted for simple models the simplified solution conducting or resistant body in a homogeneous space in a homogeneous electrical field is often sufficiently accurate as comparisons with the exact solution body of finite resistivity in a homogeneous half space in a quasihomogeneous electrical field show the exact geometry of the body cannot be determined by gradient measurements the same anomaly of apparent resistivity can be caused by different bodies in particular the similarity between a sphere and a cube of the same volume is very high there is a distinct influence of the resistivity of the overburden the higher this resistivity is the stronger is the effect caused by a buried body if a deviation of 10 of the apparent resistivity is assumed as the lower boundary at which a buried body can be detected by gradient measurements the depth of investigation for a three dimensional body is approximately equal to its width in the two dimensional case the thickness of the overburden can be twice the width if the overburden has a resistivity which is higher than the resistivity of the substratum these depths are greater the greatest possible depth is approximately three times the width of the body

manganese in monoclinic members of the epidote group piemontite and related minerals according to mayo 1932 who provided a brief historical review of the names used for piemontite the first researcher who described this mineral has been cronstedt in 1758 who named it rod magnesia in 1790 chevalier napione analyzed the sample described by cronstedt and termed it manganese rouge on the basis of his chemical data hauy designated the substance as manganese oxide violet silicifere in 1801 later in his traite de mineralogie hauy 1822 adopted the name proposed by cordier 1803 who first recognized the mineral as an epidote manganesifere the name piedmontite was proposed in 1853 by kenngott the basis of the type locality and more recently transformed into piemontite according to the standard guidelines for mineral nomenclature the name piemontite should be reserved to members of the ternary solid solution ca2al2 mn fe al si2o7 sio4 o oh that basically contains mn3 dominant at one site nonetheless the use of this name for any monoclinic manganiferous epidote group members showing the characteristic strong red yellow violet pleochroism is very common and probably convenient with special regard to petrographic purposes indeed the color of manganian i e mn3 bearing epidote or clinozoisite ranges to red to pinkish while manganoan i e mn2 bearing members do not exhibit the characteristic reddish hue the discredited name withamite was used to describe poorly manganiferous piemontite hutton 1938 yoshimura and momoi 1964 but corresponds on the basis of the current nomenclature to a manganian clinozoisite the name thulite sometimes erroneously used for pinkish clinozoisite should be reserved to mn3 bearing orthorhombic members in this chapter we focus on piemontite sensu stricto with the ideal formula ca2al2mn3 si2o7 sio4 o oh but also include for the reasons explained above those members of the clinozoisite epidote piemontite

stable and radiogenic isotope systematics in epidote group minerals epidote minerals the epidote group together with the orthorhombic polymorph zoisite occur in a wide range of igneous metamorphic and sedimentary lithologies although often present in only small quantities epidote group minerals can nonetheless be used to generate important quantitative constraints on processes such as regional metamorphism deep seated pluton emplacement and uplift hydrothermal fluid flow and sedimentary provenance e g zen and hammarstrom 1984 brandon et al 1996 cartwright et al 1996 keane and morrison 1997 spiegel et al 2002 petrologic studies on epidote group minerals formed by these and other processes are reviewed in bird and spieler 2004 grapes and hoskin 2004 enami et al 2004 and schmidt and poli 2004 in this chapter stable and radiogenic isotope studies of epidote group minerals will be reviewed although stable and or radiogenic isotope data exist for epidote group minerals from a number of different geologic settings such data have produced particularly important insights into 1 fluid flow associated with variable grades of metamorphism particularly ultra high pressure uhp metamorphism 2 intrusion of deep seated plutonic systems 3 the nature of hydrothermal alteration in geothermal systems 4 age relations in hydrothermal systems and 5 sedimentary provenance based on the chemical composition of naturally occurring epidote minerals oxygen hydrogen and chlorine stable isotopes all have the potential to be important petrogenetic indicators in systems involving epidote minerals oxygen is present in epidote minerals bound in isolated to4 tetrahedra t2o7 groups and in the hydroxyl site as both oh and o 2 hydrogen and chlorine are present in the hydroxyl site as oh and cl respectively although cl is present in only very small quantities frei et al 2004 to date oxygen and hydrogen isotope systematics have been studied both