a new study of marrella splendens arthropoda marrellomorpha from the middle cambrian burgess shale british columbia canada study of over 1000 specimens of marrella splendens walcott 1912 out of the more than 9000 collected by the royal ontario museum rom since 1975 has produced new information on the anatomy functional morphology and behaviour of this most common arthropod in the burgess shale fauna among the new features recognized is the distinction between the alimentary canal and circulatory system where the former is generally three dimensional and slightly reflective the latter never presents any relief and is very reflective a larger range of size is now known from 2 4 to 24 5 mm in length with small individuals possessing 17 body segments to large specimens with more than 26 body segments representing an almost complete ontogenetic series the second pair of antennae is now interpreted as swimming appendages since the five distal segments are dorsoventrally compressed fringed with setae and with a considerable blood supply providing a paddlelike appendage capable of producing a considerable propelli

the burgess shale and associated cambrian formations west of the fossil gully fault zone on mount stephen british columbia west of the fossil gully fault zone on mount stephen the three lowest members only of the burgess shale formation are preserved the kicking horse shale the yoho river limestone and the campsite cliff shale the formation rests unconformably upon the takakkaw tongue formation whose dark basinal limestones conformably overlie paler shelf like limestones of the mount whyte formation mapping has resolved a long standing problem and shown that the stratigraphical position of the famous mount stephen trilobite beds lies within the campsite cliff shale it has also revealed some of the complexities of the fossil gully fault zone among which different periods and directions of component fault movements are indicated faunal evidence shows that the plagiura kochaspis to albertella and albertella to glossopleura zonal boundaries lie within the takakkaw tongue sequence within the burgess shale three distinct soft bodied communities occur at different stratigraphical levels on this mountain slope the oldest

olenelloid trilobites from cambrian series 2 of devon island nunavut arctic canada four species of olenelloid trilobites characterized by advanced or robust genal spines are described from the lower cambrian rabbit point formation cambrian series 2 stage 4 of eastern devon island representing the most diverse assemblage of olenelloids yet described from arctic canada new taxa bristolia kurtzi n sp paranephrolenellus cowiei n sp siciliolenellus fritzi n gen and n sp

post cambrian closure of the deep water slope basin taphonomic window exceptional faunas konservat lagerstatten that preserve traces of volatile nonmineralized tissues are statistically overabundant in the cambrian period almost all examples preserved in continental slope and shelf basin environments are of this age the hypothesis that an increase in the amount and complexity of bioturbation was an important agent in the elimination of this deep water slope basin taphonomic window is supported post cambrian ichnofaunal assemblages contain a higher proportion of pascichnia and agrichnia ethologies produced by a mobile infauna they also illustrate the lateral partitioning of organisms into different environmental niches both opportunistic and equilibrium infaunas occur in low oxygen environments in which the preservation of nonbiomineralized tissues was favored direct consumption of carcasses by bioturbating organisms was less important than changes to sediment properties as a result of bioturbation notably enhanced microbial degradation of reactive organic matter increased permeability and the disruption of geochemical gradients necessary for mineral authigenesis

the middle cambrian burgess shale and its relationship to the stephen formation in the southern canadian rocky mountains the burgess shale has been an anomalous geologic unit ever since walcott named it in 1911 as the geographic equivalent of the ogygopsis shale in the middle cambrian stephen formation of southeastern british columbia but it has never been recognized outside of its type locality so its status relative to the stephen formation remained uncertain the geologic setting of the burgess shale was determined by aitken and fritz in 1968 when they recognized the cathedral escarpment and divided the stephen formation into a thin platformal succession on top of the escarpment and a thick basinal succession which included walcott s burgess shale in front fieldwork by royal ontario museum parties between 1982 and 1997 has now demonstrated that the thin and thick stephen successions lie within different facies belts and should be regarded as separate formations the stephen shale formation is part of the middle carbonate belt succession whereas the name burgess shale formation is applied to the thick basinal

sedimentation of the phyllopod bed within the cambrian burgess shale formation of british columbia we provide the most detailed sedimentological log to date through the phyllopod bed of the mid cambrian burgess shale formation of british columbia based on millimetre scale logging of a suite of thin sections the sedimentary facies is dominated by alternations of homogeneous mudstone and a coarser grained laminated variably sandy and shelly mudstone that is locally micronodular most boundaries between these two lithologies are gradational and discrete fining upwards turbidite units were rarely recognized such a pattern is interpreted to indicate rapid sedimentation of up to decimetre thick units at this location from pulsatory quasi continuous density currents consistent with earlier proposals of exceptional preservation through rapid burial the density currents responsible were probably largely akin to mud rich slurries helping explain the transport and entombment of the fossils the homogeneous mudstone units are characterized by numerous distinctive lenses of pyrite framboids or subeuhedral crystals previously interpreted as small ripples their 3d shape however suggests an origin as subspherical early diagenetic aggregates their present morphology is consistent with the high levels of compaction inferred from the preservation of fossils

scalloped bank margins beginning of the end for carbonate platforms bathymetric seismic reflection and satellite data have revealed the common existence of a new type of carbonate bank margin scalloped margin throughout the gulf of mexico and the caribbean region these large up to tens of kilometres across irregular convexbankward embayments are interpreted as predominantly erosional features produced by large scale failure of platform margins in tectonically active areas they may be triggered by earthquake shocks whereas in stable regions they may more likely be the result of undercutting by dissolution and or deep water currents scalloped margins are common in the south eastern bahamas this suggests that these relatively small isolated bahama banks may be erosional remnants of once larger platforms the processes that create scalloped margins may result in erosional deep water carbonate basins and potentially the demise and disintegration of carbonate platforms

zebra dolomitization as a result of focused fluid flow in the rocky mountains fold and thrust belt canada discordant zebra dolomite bodies occur locally in the middle cambrian cathedral and eldon formations of the main ranges of the canadian rocky mountains fold and thrust belt they are characterized by alternating dark grey a and white b bands forming an abba diagenetic cyclicity these bands developed parallel to both bedding and cleavage dark grey a bands consist of fine 300 m non planar crystalline impure dolomite the white b bands are composed of coarse up to several millimetres milky white pure saddle dolomites b1 which are often covered by pore lining zoned dolomite b2 the b phases often possess a saddle shaped morphology in contrast to the replacement origin of the a dolomite the zoned b2 dolomite rims are interpreted as a cement formed in open cavities the b1 dolomite is interpreted as the result of recrystallization with diagenetic leaching of non carbonate components all the zebra dolomites studied are nearly stoichiometric and are characterized by enriched na and depleted sr concentrations fe and mn concentrations in these dolomites differ depending on the sample locality fluid inclusion data indicate that the dolomites formed from relatively hot th 130 200 c saline 20 23 wt cacl2 eq fluids a diagenetic high temperature origin is also supported by depleted 18o values 20 to 14 vpdb a contribution of 87sr enriched fluids is reflected in the 87sr 86sr values 0 7091 0 7123 zebra dolomite development is explained by focused fluid flow which exploited areas of structural weaknesses e g basin platform rim areas faults etc expulsion of hot basinal brines in a tectonically active regime generated overpressures which explains the development of secondary porosity during zebra dolomitization as well as the intra zebra fracturing at decimetre to micrometre scale

greenschist facies metamorphism of the burgess shale and its implications for models of fossil formation and preservation metamorphosed silty mudstones of the burgess shale and stephen shale formations record a poly metamorphic history an early greenschist facies event associated with burial by paleozoic strata produced a nearly ubiquitous bedding parallel cleavage s1 tectonic exhumation during the formation of the southern canadian rocky mountains produced a domainal subgreenschist facies retrograde overprint in which a high angle crenulation cleavage s2 was developed whereas all rocks have experienced these two events the degree of deformation and fossil pre servation varies with position relative to the cathedral escarpment this paleosubmarine cliff resulted in a zone of reduced deformation within adjacent strata by buttressing them during burial and deflecting deformation during orogenesis fossil bearing strata are composed of a typical greenschist assemblage of muscovite chlorite quartz albite are devoid of clays and contain an average of 0 28 organic carbon this typical metamudstone assemblage is consiste

reinterpretation of middle cambrian stratigraphy of the rifted western laurentian margin burgess shale formation and contiguous units sauk ii megasequence rocky mountains canada abstract until recently research on the renowned fossil animals of the burgess shale has advanced to a greater degree than an understanding of the rocks in which they are found studies addressing lithostratigraphy and hydrothermal petrography of the so called inner carbonate belt and adjacent chancellor group however have begun to re evaluate long standing hypotheses on the middle cambrian of western canada tectonic activity along the kicking horse rim buried remnants of neoproterozoic rifting during the cambrian period had more influence on local sedimentation than previously thought notably large scale collapse of the cathedral carbonate platform margin at 509 ma bp is evidence of reactivated basement faults these failures produced listric megatruncation surfaces having near vertical escarpments 150 m in height where they terminate against the platform the majority of what have been interpreted as shed olistoliths from the cathedral platform margin is herein shown instead to be carbonate mud mounds these grew in situ along the face of the cathedral escarpment and are associated with fossiliferous intervals in overlying basinal mudstones at three distinct stratigraphic horizons two within the burgess shale during the delamaran and marjuman stages the mounds nucleated where deep seated normal faults intersected the seafloor building primarily during periods of relative sea level transgression mound growth is associated with syndepositional exhalative activity inferred from stratigraphic relations sedimentology and geochemistry the new name monarch formation is proposed for the initial post collapse beds and mounds deposited against the cathedral escarpment early glossopleura zone the variably defined term takakkaw tongue is thereby confined to pre collapse slope deposits coeval to and correlative with the cathedral formation

site effect evaluation in the basin of santiago de chile using ambient noise measurements summary we performed extensive ambient vibration measurements in the basin of santiago de chile chile and we look for testing the reliability of the horizontal to vertical amplitude spectra ratio method h v as a tool to provide qualitative and quantitative information of site effects in complex geological media the interpretation of the h v data was carried out conformably to the sesame project consensus criteria and outlines three major patterns 1 clear peaked h v curves related to sharp underground velocity contrast 2 h v peak of low amplitude and flat curve related to weak contrast and 3 broad h v peak indicating the presence of strong lateral variations of underground structure h v measurements however reveal a discrepancy between the computed soil resonance frequencies and the expected building resonance therefore not leading to a straight interpretation of the intensity distribution derived from observed damage to one storey houses in santiago after the 1985 valparaiso earthquake indeed the h v technique mostly maps the first fundamental frequency however it fails to show higher resonance modes in the case of the city of santiago this method works well for assessing the seismic hazard for high rise buildings but is questionable for smaller structures as is the case of a great percentage of constructions in the city

the subsurface structure of the chalco sub basin mexico city inferred from geophysical data the chalco sub basin the hydrogeological reserve of mexico city is located in the southern portion of mexico city s basin an intramontane valley located at 2200 m a s l in the trans mexican volcanic belt central mexico several geophysical studies dc resistivity seismic refraction gravity well logging have been conducted in this area the objectives of these independent surveys were different and of regional and local scopes this study represents the first comprehensive effort to assimilate and interpret the data available to date from the area of the chalco sub basin and to infer its main basinal characteristics according to the topography we obtained of the basement a northeast southwest structural high separates the sub basin into two portions the western portion is asymmetric and deeper than the eastern one an east west half graben like structure is located in the western portion this structure could make possible an east west fluid flow at depth and it also implies a differential su

new eocrinoids from the burgess shale southern british columbia canada and the spence shale northern utah usa the family lyracystidae n fam and genus lyracystis n gen are proposed for the holotype and one paratype of the middle cambrian eocrinoid gogia radiata sprinkle the burgess shale arms from the same unit and many additional partial and more complete specimens of this eocrinoid collected from the burgess shale since 1975 a second species lyracystis reesei n gen and n sp is described from a single partly complete specimen from the similar aged spence shale of northern utah lyracystis has three wide v shaped arms bearing numerous long straight brachioles in the notch a partly organized theca having larger and smaller ridged plates with epispires and a very long multiplated stalk made up of rounded or spiny small plates lyracystis is the longest stalked suspension feeding echinoderm known from the middle cambrian the three remaining paratypes of gogia radiata and four new specimens with possible branched brachioles from the burgess shale are renamed gogia stephenensis n sp

new burgess shale fossil sites reveal middle cambrian faunal complex soft bodied and lightly sclerotized burgess shale fossils have been found at more than a dozen new localities in an area extending for 20 kilometers along the front of the cathedral escarpment in the middle cambrian stephen formation of the canadian rockies five different fossil assemblages from four stratigraphic levels have been recognized these assemblages represent distinct penecontemporaneous marine communities that together make up a normal fore reef faunal complex

response of the lower troposphere to moisture intrusions into the arctic water vapor intrusions wvis explain a significant fraction of total moisture transport and its variability in the arctic wvis can precondition the arctic atmosphere for accelerated melting of se

melt onset over arctic sea ice controlled by atmospheric moisture transport the timing of melt onset affects the surface energy uptake throughout the melt season yet the processes triggering melt and causing its large interannual variability are not well understood here we show that melt onset over arctic sea ice is initiated by positive anomalies of water vapor clouds and air temperatures that increase the downwelling longwave radiation lwd to the surface the earlier melt onset occurs the stronger are these anomalies downwelling shortwave radiation swd is smaller than usual at melt onset indicating that melt is not triggered by swd when melt occurs early an anomalously opaque atmosphere with positive lwd anomalies preconditions the surface for weeks preceding melt in contrast when melt begins late clearer than usual conditions are evident prior to melt hence atmospheric processes are imperative for melt onset it is also found that spring lwd increased during recent decades consistent with trends toward an earlier melt onset

one dimensional seismic velocity model of the sub basin of chalco mexico abstract in this work a one dimensional 1 d seismic velocity model is proposed for the central portion of the sub basin of chalco located in the southeast se sector of the basin of mexico the seismic model was integrated from spectral analysis of the seismic ambient vibrations microtremors or seismic noise records through the methodologies of modified spatial autocorrelation mspac and h v spectral ratios the one dimensional 1 d seismic model is the result of the simultaneous inversion of the h v ratios and the phase velocity dispersion curves corresponding with rayleigh waves and contained in the vertical component of the microtremor records the scheme used in the inversion process was monte carlo which allowed us to establish a best fit model configured by four representative lithological units congruent with the amplitude and dominant periods identified in this sector of the basin of mexico

middle cambrian carbonate platform collapse southeastern canadian rocky mountains regional erosion features termed megatruncation surfaces at the seaward margin of a middle cambrian carbonate platform in southeastern british columbia are inferred to be the proximal parts of gravity slide scars comparable in scale and morphology to modern examples in the caribbean region the surfaces truncate up to 200 m of outer platform strata and have low angle to near vertical headwalls they can be traced a minimum of 56 km along depositional strike and appear to extend at least 8 km basinward of the platform edge they therefore profoundly affect regional stratigraphy

polypleuraspis arthropoda trilobita from the middle cambrian miaolingian series around kane basin nunavut and greenland polypleuraspis poulsen 1927 originally established on the basis of a single trilobite pygidium from the cape wood formation of inglefield land northwestern greenland is redescribed on the basis

a new middle cambrian burgess shale type biota bolaspidella zone chancellor basin southeastern british columbia abstract a newly discovered burgess shale type bst biota occurs in southeastern british columbia on haiduk and tangle peaks the fossiliferous rocks of the informally named vermilion sub unit and duchesnay unit occur in the bolaspidella zone one trilobite biozone younger than the burgess shale formation the younger rocks abut the eldon escarpment in a stratigraphic and depositional relationship that mirrors that of the burgess shale formation and cathedral escarpment the biota concentrated at the eldon escarpment is hosted predominantly in the duchesnay unit and includes burgess shale genera of sponges worms some arthropods and brachiopods new taxa include an arborescent benthic graptolite with preserved fuselli microbial fossils including vendotaenid bacteria are locally abundant and range up to 750 m basinward of the escarpment in both the vermilion sub unit and duchesnay unit while concentrations of animal fossils are restricted to within 100 m in the vermilion sub unit large autochthonous carbonate mud mounds previously interpreted as platform derived olistoliths originated at the base of the escarpment probably over fluid conduits and then slid downslope bulldozing and entraining sediments in their paths local magnesian and barian rich brine pool deposits occur up to 750 m distal of the escarpment fractionation of the fluids may explain the differing geochemistries at least one mgo rich brine pool deposit on haiduk peak is fringed by abundant animal fossils including concentrations of priapulid worms this assemblage together with high density low diversity assemblages on tangle peak likely represent fringing fauna facies around brine seeps a model erected for similar fossil concentrations and distributions in the burgess shale intrabasinal comparison of the vermilion sub unit and duchesnay unit with the burgess shale formation reveals an identical stratigraphic ordering of carbonates and shales brine pool deposits major debris flow deposits carbonate mud mound growth and fossiliferous deposits the eldon and cathedral platform formations are known to share complimentary brine derived characteristics as well the stratigraphic patterns signify that the depositional processes producing the suite of older lithofacies recurred during deposition of the younger units interbasinal correlation with the wheeler and marjum formations utah identifies the duchesnay unit deposit as the youngest basinal burgess shale type deposit in north america decreasing abundance of animal fossils away from the eldon and cathedral escarpments is generally attributed to increasing development of tectonic fabrics however on haiduk peak rocks hundreds of metres basinward of the escarpment contact are essentially undeformed and contain rare planolites brachiopods and trilobites as the only macrofauna locally abundant vendotaenids and morania are evidence that bst preservation occurred at these distances the concentration of animal fossils at the escarpment is therefore a primary ecological feature not due to a preservational or rheological bias communities were clustered at the face of the escarpment where brines were seeping

in situ benthos and paleo oxygenation in the middle cambrian burgess shale british columbia canada the middle cambrian burgess shale was deposited under variable levels of oxygenation during periods of oxygenation low diversity shell beds were formed and the muds were colonized by infauna under these circumstances pyrite was restricted to anoxic microenvironments and formed small 1 mm discrete aggregated masses soft bodied organisms were preserved under low oxygen conditions typified by evenly dispersed pyrite and an absence of trace fossils and shell beds

site effect evaluation using spectral ratios with only one station the spectral ratio technique is a common useful way to estimate empirical transfer function to evaluate site effects in regions of moderate to high seismicity the purpose of this paper is to show that it is possible to estimate empirical transfer function using spectral ratios between horizontal and vertical components of motion without a reference station the technique originally proposed by nakamura to analyze rayleigh waves in the microtremor records is presented briefly and it is discussed why it may be applicable to study the intense s wave part in earthquake records results are presented for three different cities in mexico oaxaca oax acapulco gro and mexico city these cities are very different by their geological and tectonic contexts and also by the very different epicentral distances to the main seismogenic zones affecting each city each time we compare the results of nakamura s technique with standard spectral ratios in all three cases the results are very encouraging we conclude that if site effects are caused by simple geology a first estimate of dominant period and local amplification level can be obtained using records of only one station

the vertical structure of the lower arctic troposphere analysed from observations and the era 40 reanalysis in situ atmospheric observations in the central arctic are few and mostly from near the surface a majorityare from coastal regions whereas soundings over the arctic ocean are rare this limits our

comment on evidence of the dominance of higher mode surface waves in the lake bed zone of the valley of mexico by shapiro et al 2001 summary the purpose of this note is to contribute to the understanding of seismic ground motion in mexico city to this end we 1 compute theoretical transfer functions for various models for the deep structure and the shallow clay layers 2 study the seismic responses of various sites within the city using spectral ratios of horizontal motion relative to the motion of nearby rock sites and relative to the vertical motion at the same site and 3 discuss some characteristics of surface waves for models of the deep structure and the shallow clay layers in the valley of mexico

palaeontology and depositional environments of ancient brine seeps in the middle cambrian burgess shale at the monarch british columbia canada abstract the monarch a mountain in southeastern british columbia exposes the cathedral escarpment which abuts the basinal burgess shale and an underlying limestone the upper takakkaw tongue at one section a dolomitized megabreccia representing an intraformational collapsed cavern forms the cathedral escarpment wall the megabreccia is cross cut by the subsequent megatruncation event marking the collapse of the cathedral margin which supports previous hypotheses that dolomitizing brines were active at the cathedral margin prior to and during deposition of the burgess shale epiphyton rich carbonate megablocks within the basinal strata previously interpreted as olistoliths spalled off the escarpment are unlike the peritidal strata comprising the cathedral margin and are more likely deep water carbonate mud mounds that grew in the basin near the escarpment face evidence for early brines in basinal environments at this locality includes lenses of dark magnesium rich clinochlore 30 wt mgo vs 2 in background shales within the burgess shale at the escarpment wall these clinochlores are interpreted as precipitates from seafloor brine seeps analogous to ones currently found at the foot of the florida escarpment and on the distal shelf and slope of the northern gulf of mexico like the gulf examples the brines formed standing pools on the cambrian seafloor and hosted abundant organisms in a narrow fringe around their peripheries but not within the pools sponges priapulid worms hyoliths linguliform brachiopods and trilobites predominate shales only a few metres basinward from the pools are nearly barren of animal fossils increased biologic productivity localized at the seeps would account for the patchy distribution of fossils in the burgess shale in a narrow zone close to the escarpment the discovery of brine seep deposits and associated fringing communities at the monarch shows that at least some assemblages in the burgess shale were preserved within their habitat and were supported by chemosynthesis