carbon isotopes stratigraphy and environmental change the middle upper cambrian positive excursion spice in port au port group western newfoundland canada in many basins upper cambrian carbonate successions display intervals with a positive carbon isotope excursion cie of up to 5 in north america this marks the boundary between the sauk ii iii super sequences a steptoean positive carbon isotope excursion spice locality previously identified in the port au port peninsula western newfoundland has been revisited and an additional potential spice locality found in both locations a cie is found to be associated with a prominent bioherm and sandstone layer within a sequence of carbonate rocks at march point columnar stromatolites occur whereas at felix cove thrombolites can be seen in the latter the sandstone immediately overlies the thrombolites coincident with the cie whereas at march point a dolomitized grainstone occurs above the stromatolites the sandstone at this locality post dates the cie although lower than the spice in some localities a positive cie is present in both sections march point 1 1 and felix cove 1 8 additional

cambrian grand cycles a northern appalachian perspective large scale sedimentary cycles or grand cycles are the most obvious features of the port au port group in southwestern newfoundland each cycle is interpreted to represent deposition in outer platform muddy tidal flats lower shaly half cycle and ooid shoal complexes upper carbonate half cycle unpredictable metre scale assemblages of oolite and carbonate laminite constituting the carbonate half cycles are attributed to frequent migration of the shoal complexes in response to hydrographic factors such as tidal fluctuations and storms predictable metre scale shallowing upward cycles of parted limestone and shale in the shaly half cycles were probably controlled mainly by variable rates of carbonate sedimentation a eustatic mechanism however cannot be discounted comparison with other north american grand cycles suggests a eustatic mechanism for grand cycle formation possibly involving variations in the rate of sea level rise the interpreted sequence of formation established on the basis of the port au port group involves 1 a rapid sea level rise which flooded the platform with shoreward derived siliciclastic muds and resulted in the development of muddy tidal flats and 2 the gradual development of ooid shoal complexes which encroached onto the tidal flats with decreasing rates of sea level rise in contrast to western north american examples newfoundland grand cycles are composed almost entirely of peritidal sediments they are also thinner and have a smaller areal extent than do those in the west these differences may be due to such factors as narrower shelves slower rates of sedimentation and lower amplitudes of sea level rise on the present northeastern margin of the north american craton than on the western margin

effects of grand cycle cessation on the diagenesis of upper cambrian carbonate deposits in the southern appalachians u s a abstract the vertical transition from the mainly subtidal alternating shale and carbonate units or grand cycles of the conasauga group middle to upper cambrian to the peritidal dolostone of the knox group upper cambrian to lower ordovician marks a major change in the early paleozoic passive margin sedimentation of the southern appalachians the grand cycles represent an interplay between intrashelf shale basin and carbonate platform deposition the end of grand cycle deposition occurred in response to carbonate platform progradation over the infilled intrashelf basin and is associated with a prominent change in diagenetic patterns observed in the uppermost conasauga group strata the maynardville formation the maynardville records upward shallowing from subtidal shale and limestone into peritidal dolostone this change from a subtidal into a peritidal depositional regime influenced the early diagenesis of the maynardville and in conjunction with the changes in the regional facies distribution at the end of grand cycle deposition extended its influence upon the burial diagenesis of these deposits the subtidal deposits of the maynardville contain a variety of calcite cements dolomite is not abundant in these deposits where it occurs mainly as a fine crystalline ferroan phase associated with argillaceous layers and pressure dissolution features the local source for this dolomite during burial was provided by expulsion of pore fluids from interbedded shale deposits diagenesis of clay minerals and pressure dissolution of carbonates ferruginous coatings on hardgrounds in the subtidal deposits provided an additional local source of iron for the formation of replacement saddle dolomite the subtidal deposits also contain saddle dolomite cement associated with mississippi valley type mvt minerals which indicate the involvement of externally derived fluids during late burial diagenesis of these strata the peritidal deposits on the other hand are extensively dolomitized fine crystalline dolomite most likely represents early diagenetic replacement of tidal flat carbonate sediment coarse crystalline replacement dolomite formed during burial by recrystallization of early dolomite and dolomitization by warm burial brines fenestrae desiccation cracks and evaporite dissolution voids are occluded with dolomite cement which is commonly complexly zoned zoned dolomite precipitated during shallow to intermediate burial and is postdated by saddle dolomite cement saddle dolomite in pore centers dissolutional voids and tectonic fractures formed during late burial from warm fluids associated with the migration of mvt brines the effects of changes in the depositional setting on diagenesis are reflected in similar early diagenesis between the subtidal maynardville and the underlying conasauga group carbonate deposits and between the peritidal deposits of the upper maynardville and the rest of the overlying knox group the depositional environments and early diagenesis also affected the burial diagenesis the changes in regional facies distribution caused by carbonate platform progradation at the end of grand cycle deposition resulted in a decrease in the proportion of siliciclastic components this decrease was accompanied by a decline in the amount of ferroan carbonate in the peritidal deposits the maynardville is conformably overlain by carbonate deposits of the knox group this allowed the maynardville knox succession to behave as a single hydrologic unit for the migration of burial fluids in response to the formation of the ordovician foreland sevier basin to the southeast during the conversion from a passive into a convergent continental margin the nolichucky shale separates the maynardville knox succession from the carbonate deposits of the underlying conasauga group which were in contrast affected by the migration of burial fluids from the cambrian intrashelf shale basin to the west

tectonics and foreland basin development at the leading edge of the humber arm allochthon western newfoundland canadian appalachians the thrust front of the northern appalachians involves ediacaran rift related structures of the laurentian margin that were re worked in taconic ordovician salinic mainly silurian and acadian mainly devonian deformation events much of the thrust front is concealed under the gulf of st lawrence but port au port peninsula in western newfoundland provides a cross section through the laurentian passive margin overlying foreland basins and the humber arm allochthon a large area of foreland basin strata is present in areas formerly mapped as humber arm allochthon abrupt thickness changes and an abundance of fault scarp derived limestone conglomerate indicate that deposition was influenced by block faulting and differential subsidence in a basin undergoing active flexural extension a coarsening upward trend in the goose tickle group represents a transition from a distal to a proximal sediment source as the humber arm allochthon was emplaced westwards goose tickle group separates two packages of allochthonous rocks the west bay thrust sheet the lower package represents the leading edge of the taconic allochthon its timing of emplacement is constrained by darriwilian 3 graptolites both above and below the thrust sheet its present day configuration results from a combination of processes including thrusting extension by gravity spreading gravity gliding and subsequent erosion of material that was deposited in the goose tickle group the structurally higher lourdes thrust sheet is an out of sequence structure associated with acadian devonian orogenesis high angle faults show a protracted history of movement that includes early taconic flexural extension acadian inversion and later carboniferous or mesozoic strike slip motion the leading edge of the humber arm allochthon was influenced by both thin skinned and thick skinned tectonics throughout the development of the appalachian orogen

diastasis cracks mechanically generated synaeresis like cracks in upper cambrian shallow water oolite and ribbon carbonates upper cambrian limestones and dolostones of western newfoundland canada display conspicuous synsedimentary mud cracks cracks occur in carbonate mudstone interbedded with ooid and peloid grainstone unwashed oolite and ribbon rock lithofacies the traditional interpretation is that these are desiccation cracks the weight of evidence supports an alternative e explanation cracks resulted from the differential mechanical behaviour under stress of stiff mud interlayered with loose ooid peloid sand the processes envisaged to cause such diastasis cracks may be applicabl e to a wide variety of both carbonate and terrigenous clastic deposits composed of interlayered sediments of contrasting material properties and may be a viable alternative to synaeresis

the red island road formation early devonian terrestrial fill in the anticosti foreland basin western newfoundland more than 100 m of nearly flat lying fluvially derived thick bedded and lensoid clast supported conglomerate and sandstone are found on red island off the coast of the port au port peninsula western newfoundland formally described herein and named red island road formation the strata represent a unique lithologic formation not exposed or known anywhere else in the region characteristic features include abundant rounded highly weathered and varnished cobbles and boulders derived from an unknown mixed volcanic and very low to low grade metamorphic terrane although the unit is largely unfossiliferous a thin sandstone bed near the top of the type section contains primitive dichotomously branched plant remains and biostratigraphically significant palynomorphs among more than 25 species of spores it is the diversity of emphanisporites dictyotriletes and dibolisporites and in particular dibolisporites echinaceus dictyotriletes canadensis emphanisporites annulatus e erraticus and e schultzi

duration of the early cambrian u pb ages of volcanic ashes from avalon and gondwana volcanic zircons from three ashes give a u pb date of 511 1 ma on trilobite bearing upper lower cambrian upper branchian series strata of southern new brunswick that correlate into the siberian middle botomian toyonian stage interval this very young age on the late but not latest early cambrian of avalon is consistent both with a 519 1 ma age on the older caerfai bay shales of south wales that are tentatively correlated into strata with the oldest avalonian trilobites lower branchian and with a 517 1 5 ma age on the antatlasia gutta pluviae zone trilobites of morocco determination of a 522 2 ma zircon age on the moroccan subtrilobitic lower cambrian lie de vin formation is consistent with an earlier reported 521 7 ma age from the lie de vin but suggests that a 526 4 ma age on australian trilobite bearing lower cambrian rocks may be too old a 33 ma duration of the avalonian early cambrian and an 8 ma length of the avalonian trilobite bearing lower cambrian support proposals that

stratigraphie framework for the cambrian ordovician rift and passive margin successions from southern quebec to western newfoundland the taconian humber zone stretches from western newfoundland to southern quebec the early cambrian slope succession in newfoundland is found in the curling group whereas in quebec various units were deposited during that first time slice biostratigraphic data allow correlation of the curling group with the labrador group in newfoundland and with the newly time constrained slope succession in quebec the end of the rift drift transition is marked by a sea level lowstand at the end of the early cambrian the middle cambrian to latest early ordovician passive margin history recorded five cyclic sea level fluctuations three of these cycles are recorded in the shallow marine middle to late cambrian platform port au port group and slope sediments preserved in the cow head and northern head groups in newfoundland the biostratigraphic information assists correlation with cambrian passive margin units in quebec major sea level lowstands are recognized along the continental margin in early middle late camb

the middle late cambrian reef transition and related geological events a review and new view abstract the reefs of the middle late cambrian cambrian epoch 3 furongian have long been simply considered as microbialites that flourished in the aftermath of the archaeocyath extinction thorough review of the reefs in these periods shows however that the cambrian epoch 3 and the furongian actually yield different types of reefs the cambrian epoch 3 reefs are dominated by thrombolites and dendrolites largely constructed by the calcified microbes epiphyton and renalcis on the other hand the furongian reefs consist mainly of maze like maceriate reefs and columnar stromatolites the maceriate reefs most likely formed by siliceous sponges and calcified microbes including girvanella and tarthinia whereas the columnar stromatolites were mainly constructed by girvanella tarthinia and minor siliceous sponges other microbial reefs e g non columnar stromatolites persisted during the cambrian epoch 3 and the furongian mainly as small patch reefs or reefal crusts lithistid sponge microbial reefs initially formed in the cambrian epoch 3 and occurred throughout the furongian but occupied only a minor portion during these periods several geological events occurred across the boundary between the cambrian epoch 3 and the furongian including positive carbon and sulfur isotope excursions a eustatic sea level drop major faunal turnover of trilobites and diversification of new organisms the coincidence of these events and the transition in reefal fabrics suggest that reef ecosystems were significantly influenced by at least some of these events among the events it is likely that sea level change would have affected reefs although further studies are required in order to test whether and how the other events influenced the reef transition epiphyton and renalcis and thrombolites and dendrolites formed by them declined greatly most likely due to sea level fall and thus decreased in shallow marine habitat at the end of cambrian epoch 3 the cambrian epoch 3 thrombolites and dendrolites were gradually replaced by a sponge microbial association of the maze like maceriate reefs and the columnar stromatolites in the furongian coincident with a sea level rise

sabkha facies and the preservation of a falling stage systems tract at the sauk ii iii supersequence boundary in the late cambrian eilean dubh formation nw scotland the durness group of northwest scotland represents a nearly one kilometer thick succession of mid cambrian to lower middle ordovician carbonates these rocks crop out in a narrow belt along the foreland of the caledonian orogen and in the moine thrust zone stretching some 170 km from loch eriboll southwestwards to the isle of skye the cambrian parts of the succession represent deposition on a paleo southeast facing low latitude passively subsiding continental margin situated at around 20 s carbonate deposition in scotland formed part of the extensive great american carbonate bank the sauk ii iii supersequence boundary occurs above an interval of thin meter scale shallowing upward peritidal cycles containing intraclast dolorudstones stromatolites tepees siliciclastic sand and surface karst evidence of former evaporites in the succession comprises pseudomorphs of nodular and bedded anhydrite crystal shaped calcite filled vugs representing growth of sulfate dissolution breccias and local halite casts these features represent sabkha facies arranged into cycles that constitute a preserved falling stage systems tract fsst the top of the fsst is marked by a pronounced karst surface of sandstone filled fissures the section preserves a rare snapshot of a seldom preserved environment on the cambrian laurentian margin its preservation during a time of falling relative sea level under slow tectonic subsidence is discussed

relative sea level changes and the development of a cambrian transgression the lower cambrian in northwest scotland is one example of a lower palaeozoic orthoquartzite carbonate succession deposited on a slowly subsiding peneplained precambrian basement during a period of relative sea level rise this particular setting led to the development of a very wide low gradient shelf which was extremely sensitive to minor sea level changes the basal quartz arenite section lower member pipe rock is a transgressive tide dominated systems tract but lacks a systematic parasequence architecture because of three factors a fluvial sediment flux was insufficient to induce shoreline progradation accommodation space was limited during sea level falls which are commonly expressed by widespread erosional surfaces and sediment yield to the shelf by transgressive reworking was a major contributor towards the preserved stratigraphy the storm dominated fucoid beds represent a condensed section and also show the effects of rapid and widespread facies belt oscillations because of the low shelf gradient an overlying highstand systems tract is also lacking partly due to the absence of a large fluvial sediment yield and also due to lowstand and transgressive reworking an erosively based tidal sandsheet at the top of the fucoid beds interpreted to be a lowstand systems tract therefore rests directly on the condensed section of the underlying sequence this was in turn reworked into linear tidal sandbanks salterella grit during slow sea level rise prior to the next major transgression the limited accommodation space therefore introduced a preservational bias towards deepening upward trends on a parasequence and sequence scale the oscillations in facies belts episodic subareal exposure and the potential to remove substantial portions of systems tracts suggests that lower palaeozoic orthoquartzite successions may exhibit regular and abrupt vertical shifts in depositional environment which given their subtle lithological character may require detailed analysis to identify such successions may also display incomplete development of several components of transgressive regressive sequence architecture

reappraisal of the cambrian glauconite bearing anse maranda formation quebec appalachians from deep sea turbidites to clastic shelf deposits the cambrian anse maranda formation is a glauconite bearing clastic succession within the quebec reentrant it is part of the appalachians humber zone particularly of the shale feldspathic sandstone assemblage which represents the rift to drift deposits of the laurentian margin the massive sandstones of the anse maranda were originally interpreted as the proximal turbidites of a deep sea fan the occurrence of glauconite and the high degree of bioturbation which give the sandstones a massive aspect suggest a different depositional environment detailed ichnology and lithofacies descriptions indicate that the anse maranda predominantly represents shelf sediments deposited in storm influenced environment and that intense bioturbation destroyed most of the sedimentary structures the paleo geographic reconstruction suggests that the anse maranda was deposited seaward of a headland identified as the montmorency promontory along a narrow shelf with an irregular topography some coeval turbidites of sim

mesoscale subduction at the antarctic polar front driven by baroclinic instability abstract a study of mesoscale subduction at the antarctic polar front pf is conducted by use of hydrographic data from a high resolution quasi synoptic survey of the front the geostrophic velocity and isopycnal potential vorticity pv fields are computed and the ageostrophic flow diagnosed from the semigeostrophic omega equation it is found that the ageostrophic circulation induced by baroclinic instability counteracts the frontogenesis and frontolysis effected by the confluence and difluence respectively of the geostrophic velocity field though the sense of the ageostrophic circulation is reversed repeatedly along the front the existence of pv gradients along isopycnals leads to a net cross front bolus transport in response to a reversal of this gradient with depth a necessary condition for the onset of baroclinic instability the bolus transport is northward at the protruding temperature minimum layer that characterizes the pf and southward above this net cross front overturning circul

deep water stratigraphic cyclicity and carbonate mud mound development in the middle cambrian marjum formation house range utah usa in mid middle cambrian time shallow water sedimentation along the cordilleran passive margin was abruptly interrupted by the development of the deep water house range embayment across nevada and utah the marjum formation 330 m in the central house range represents deposition in the deepest part of the embayment and is composed of five deep water facies limestone argillaceous limestone rhythmites shale thin carbonate mud mounds bioturbated limestone and cross bedded limestone these facies are cyclically arranged into 1 5 to 30 m thick parasequences that include rhythmite mound rhythmite shale rhythmite bioturbated limestone and rhythmite cross bedded limestone parasequences using biostratigraphically constrained sediment accumulation rates the parasequences range in duration from 14 to 270 kyr the mud mounds are thin 2 m closely spaced laterally linked symmetrical domes composed of massive fenestral peloidal to clotted microspar with sparse unoriented poorly sorted skeletal material calcitized bacterial filaments tubes and abundant fenestrae and stroma tactoid structures these petrographic and sedimentological features suggest that the microspar peloids clots and syndepositional micritic cement were precipitated in situ from the activity of benthic microbial communities concentrated growth of the microbial communities occurred during periods of decreased input of fine detrital carbonate transported offshore from the adjacent shallow water carbonate platform in the neighbouring wah wah range and throughout the southern great basin coeval mid middle cambrian shallow water carbonates are composed of abundant metre scale upward shallowing parasequences that record high frequency 104 105 years eustatic sea level changes given this regional stratigraphic relationship the marjum formation parasequences probably formed in response to high frequency sea level fluctuations that controlled the amount of detrital carbonate input into the deeper water embayment during high frequency sea level rise and early highstand detrital carbonate input into the embayment decreased as a result of carbonate factory retrogradation resulting in the deposition of shale base of rhythmite shale parasequences or thin nodular rhythmites followed by in situ precipitated mud mounds lower portion of rhythmite mound parasequences during the ensuing high frequency sea level fall lowstand detrital carbonate influx into the embayment increased on account of carbonate factory pro gradation towards the embayment resulting in deposition of rhythmites upper part of rhythmite mound parasequences reworking of rhythmites by a lowered storm wave base cross bedded limestone deposition or bioturbation of rhythmites by a weakened lowered o2 minimum zone bioturbated lime stone deposition this interpreted sea level control on offshore carbonate sedimentation patterns is unique to palaeozoic and earliest mesozoic deep water sediments after the evolution of calcareous plankton in the jurassic the presence or absence of deeper water carbonates was influenced by a variety of chemical and physical oceanographic factors rather than just physical transport of carbonate muds

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

primary aragonite and high mg calcite in the late cambrian furongian potential evidence from marine carbonates in oman acknowledgements fieldwork and sampling was funded by petroleum development oman during s al marjibis s ph d their help is gratefully acknowledged we also thank colleagues at the university of aberdeen julie dougans suerc for assisting with stable isotope analysis and dr richard hinton eimf for assistance with ion microprobe analysis profs kiessling tucker bosence coleman dr dickson and an anonymous reviewer are thanked for their helpful and encouraging comments

carbonate platform dominated by peloidal sands lower ordovician la silla formation of the eastern precordillera san juan argentina the lower ordovician la silla formation of the precordillera of west central argentina is part of the west facing early palaeozoic tropical carbonate platform succession that comprises the core of the cuyania terrane up to 360 m thick it is exposed in several thrust sheets over a distance of some 250 km along and across depositional strike over a palinspastically unrestored distance of about 35 km la silla formation is a strikingly pure limestone with subordinate finely crystalline dolomite and rare chert it accumulated on a more or less uniformly subsiding passive margin copious precipitation of microcrystalline calcite probably influenced by microbial activity to varying degrees led to the generation of peloids ooids and aggregates of these grains as well as small amounts of lime mud intraclasts stromatolites and thrombolites rare bioclasts are limited mostly to scattered gastropods and trilobite sclerites bioturbation is present locally the array of carbonate rock types is grouped into eight recurring lithofacies in order of decreasing abundance i peloidal grainstone ii laminated dolostone iii intraclastic rudstone iv microbial laminite v peloidal packstone vi ooidal grainstone vii thrombolite boundstone and viii mudstone these facies represent sediments that formed solely in a shallow subtidal marine environment with no evidence of restricted conditions hypersalinity or subaerial exposure no events of eustatic sea level change are recorded by far the dominant facies is grainstone composed of well sorted fine sand sized peloids and peloidal aggregates in homogeneous tabular to gently undulating medium to thick beds cross lamination is scarce clusters of sub metre sized microbial patch reefs developed sporadically the shallow platform is envisaged to have been covered by extensive peloidal sand flats and low relief banks and little lime mud was generated the setting was probably microtidal and may not have been affected by strong trade winds it was washed by frequent relatively gentle wave action but without experiencing powerful storms in the middle member anomalous lenses of intraclastic rudstone and laminated dolostone occur as graded beds overlying sharply downcut scoured surfaces up to 20 cm deep these are interpreted to indicate a phase when accretion was punctuated occasionally by tsunamis generated from rift faulting seaward of the platform margin the remarkably uniform peloidal grainstone composition over a broad area shows that given the appropriate combination of climate environmental and ecological factors large portions of some early palaeozoic platforms were dominated by grainy sediment and remained under well agitated conditions within fair weather wave base without distinct lateral facies differentiation or tidal flat aggradation

flat pebble conglomerate its multiple origins and relationship to metre scale depositional cycles carbonate flat pebble conglomerate is an important component of precambrian to lower palaeozoic strata but its origins remain enigmatic the upper cambrian to lower ordovician strata of the snowy range formation in northern wyoming and southern montana contain abundant flat pebble conglomerate beds in shallow water cyclic and non cyclic strata several origins of flat pebble conglomerate are inferred for these strata in one case all stages of development of flat pebble conglomerate are captured within stormdominated shoreface deposits of hummocky cross stratified hcs fine carbonate grainstone a variety of synsedimentary deformation structures records the transition from mildly deformed in situ stratification to buckled beds of partially disarticulated bedding to fully developed flat pebble conglomerate these features resulted from failure of a shoreface and subsequent brittle and ductile deformation of compacted to early cemented deposits failure was induced by either storm or seismic waves and many beds failed along discrete slide scar surfaces centimetre scale laminae within thick amalgamated hcs beds were planes of weakness that led to the development of platy clasts within partly disarticulated and rotated bedding of the buckled beds in some cases buckled masses accelerated downslope until they exceeded their internal friction completely disarticulated into clasts and transformed into a mass flow of individual cm to dm scale clasts this transition was accompanied by the addition of sand sized echinoderm rich debris from local sources which slightly lowered friction by reducing clast clast interactions the resulting dominantly horizontal clast orientations suggest transport by dense viscous flow dominated by laminar shear these flows generally came to rest on the lower shoreface although in some cases they continued a limited distance beyond fairweather wave base and were interbedded with shale and grainstone beds the clasts in these beds show no evidence of extensive reworking i e not well rounded or condensation i e no rinds or coatings a second type of flat pebble conglomerate bed occurs at the top of upward coarsening metre scale cycles the flat pebble conglomerate beds cap these shoaling cycles and represent either lowstand deposits or in some cases may represent transgressive lags the clasts are well rounded display borings and have iron rich coatings the matrix to these beds locally includes glauconite these beds were considerably reworked and represent condensed deposits thrombolites occur above the flat pebble beds and record microbial growth before initial transgression at the cycle boundaries a third

lithostratigraphic and allostratigraphic framework of the cambrian ordovician potsdam group and correlations across early paleozoic southern laurentia the potsdam group is a cambrian to lower ordovician siliciclastic unit that crops out along the southeastern margins of the ottawa graben from its base upward the potsdam consists of the ausable hannawa falls and keeseville formations in addition the potsdam is subdivided into three allounits allounit 1 comprises the ausable and hannawa falls and allounits 2 and 3 respectively the lower and upper parts of the keeseville allounit 1 records early to middle cambrian syn rift arkosic fluvial sedimentation ausable formation with interfingering mudstone arkose and dolostone of the marine altona member recording transgression of the easternmost part of the ottawa graben rift sedimentation was followed by a middle cambrian climate change resulting in local quartzose aeolian sedimentation hannawa falls formation allounit 1 sedimentation termination coincided with latest middle cambrian tectonic reactivation of parts of the ottawa graben allounit 2 lower keeseville records mainly upper cambrian quartzose fluvial sedimentation with transgression of the northern ottawa graben resulting in deposition of mixed carbonate siliciclastic strata of the marine riviere aux outardes member sedimentation was then terminated by an earliest ordovician regression and unconformity development allounit 3 upper keeseville records diachronous transgression across the ottawa graben that by the arenigian culminated in mixed carbonate siliciclastic shallow marine sedimentation theresa formation the contact separating the potsdam group and theresa formation is conformable except locally in parts of the northern ottawa graben where the presence of localized islands and or coastal salients resulted in subaerial exposure and erosion of the uppermost potsdam strata and accordingly unconformity development

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

carbon isotope δ13ccarb heterogeneity in deep water cambro ordovician carbonates western newfoundland abstract carbonates of western newfoundland span the cambro ordovician interval and preserve a record of slope basinal deposition in the cow head group near cow head this unit consists of conglomerates and ribbon and laminated limestone interbedded with shale that is well exposed in sea cliffs at cow head peninsula these conglomerates although prevalent throughout the section vary in thickness and abundance stratigraphically and record both local disruption and large scale episodic sedimentation events microfacies drilled for carbon isotope 13 c carb analysis of conglomerates reveal isotopic heterogeneity within individual samples in some cases more than 1 while this might be an expected outcome of drilling multiple areas of a heterogeneous conglomerate hand sample permil level variability was observed both between individual clasts in a sample between different parts of the same matrix and between a clast and its surrounding matrix no associated variation in 18 o carb or trace element distributions exists to suggest that this 13 c carb variability is the result of later stage meteoric diagenesis the 13 c carb variability suggests multiple sources of dissolved inorganic carbon dic associated with carbonate precipitation for phases within these individual samples these data indicate that processes such as local organic matter remineralization and early authigenic carbonate precipitation during lithification at the sediment water interface swi are either contributing to or controlling 13 c carb values in cambrian carbonates perhaps more so than at other intervals in earth history

elastic wave attenuation in fluid saturated berea sandstone in a previous publication o hara 1985 i presented detailed measurements on the attenuation of elastic waves in fluid saturated berea sandstone these measurements were used in a systematic empirical study of the frequency dependence of attenuation as a function of external pressure applied to the sandstone pore fluid pressure and the saturated sandstone temperature two pore fluids were used in the study a brine solution and n heptane i measured the attenuation of the extensional and torsional rod modes of cylindrical specimens of the sandstone at identical conditions of pressure and temperature for each of the two fluids

sequence sequence stratigraphy sea level changes and depositional systems in the cambro ordovician of the north china carbonate platform abstract the cambro ordovician strata in north china were deposited over a very extensive craton extending some 1500 km east west and 1000 km north south the dominantly shallow water carbonate succession reaches up to 2000 m in thickness and two megasequences transgressive regressive cycles can be distinguished lower cambrian through lower ordovician strata and middle through upper ordovician strata separated by a major palaeokarst the first megasequence consists of nine sequences which are generally 50 150 m in thickness the lower cambrian sediments consist of phosphorites and phosphatic sandstones deposited during the flooding of the craton carbonates mudrocks and evaporites were deposited in the early cambrian under an arid climate laying the foundation for the subsequent long period of shallow water carbonate deposition which lasted some 70 m y the middle and lower upper cambrian sequences consist predominantly of mudrocks and storm deposits tempestites in the lower part and oolitic grainstones and tidal flat lime mudstones in the upper part these represent outer mid and mid inner ramp depositional systems respectively of the transgressive and highstand systems tracts these sequences have strong similarities with the grand cycles in the cambro ordovician successions of north america in the upper cambrian there is a distinctive unit of glauconitic purple red mudstone several metres thick which is interpreted as the deposits of the maximum flooding of the first megasequence in the upper cambrian there was a phase of tilting of the north china carbonate platform to the north and storm deposits especially intraclastic conglomerates and hummocky cross stratified grainstones packstones were very common at this time also common in upper middle and lower upper cambrian strata are stromatolitic thrombolitic bioherms several metres in diameter the upper upper cambrian through lower ordovician strata are dominantly fine grained limestones and dolomites deposited in shallow subtidal and inter to supra tidal environments on a low energy epeiric sea platform this part of the succession is the regressive part of the first megasequence so that overall the platform shows an evolution from platform initiation to platform foundation to a ramp depositional system and then an extensive epeiric platform on a small scale the succession is composed of metre scale shallowing upward cycles parasequences arranged into cycle sets of 10 30 m thick the middle upper ordovician megasequence consists mostly of shallow water carbonates with several thick evaporite units minor palaeokarsts and palaeosoils separate the sequences which are composed of metre scale cycles regional uplift affected the north china platform in the ordovician and sedimentation did not resume until the carboniferous there is a good correlation of the two transgressive regressive megasequences described here with the global 2nd order relative sea level curve for the cambro ordovician

upper cambrian carbonate platform evolution elvinia and taenicephalus zones pterocephaliid ptychaspid biomere boundary northwestern wyoming abstract the pterocephaliid ptychaspid biomere boundary is an upper cambrian extinction horizon that can be used to correlate mixed carbonate siliciclastic strata in northwestern wyoming the biomere boundary is defined by the change between the elvinia and taenicephalus zones of the standard north american trilobite zonation it is also signaled chemostratigraphically by a positive trend in carbon isotope ratios thus both biostratigraphic horizons and carbon isotope data are used to constrain the position of the biomere boundary in northwestern wyoming study of 21 stratigraphic sections reveals the presence of distinct facies belts for the middle and upper elvinia zone and lower taenicephalus zone these are interpreted to reflect deposition in three distinct paleoenvironments 1 oolitic shoal 2 intrashelf basin and 3 inner platform margin following a major hiatus in sedimentation in wyoming during much of pterocephaliid biomere time a healthy shallow water carbonate factory was reestablished during elvinia zone time this produced abundant deposits of oolitic and skeletal packstone in the shoal environment and an areally extensive thrombolite boundstone facies in the intrashelf basin setting approximately coincident with the biomere boundary extinction event irvingella major time ooid production was terminated and the thrombolites were drowned the correlation of this major change in the pattern of sedimentation allows for the recognition of parts of two depositional sequences in the study area this drowning event sequence boundary may also be coeval with the accumulation of transported shallow water carbonate deposits in an inner platform margin environment during early taenicephalus zone time sedimentation rates were apparently reduced and the entire study area is marked by thin concentrations of trilobite and brachiopod shells the nonskeletal carbonate factory was never reestablished in the former shoal environment where thick successions of homogeneous lime mud accumulated during the rest of taenicephalus zone time flat pebble conglomerate and shale accumulated in the storm influenced intrashelf basin during this time sea level change and changes in seawater chemistry likely both played roles in the drowning event across the elvinia taenicephalus boundary a positive trend in carbon isotope values across the pterocephaliid ptychaspid biomere boundary is observed in the six sections analyzed this is consistent with previous studies that indicated that the mass extinction occurs within a regional shift towards positive values and this may reflect the development of low oxygen conditions on the shelf the global significance of these isotopic trends changes in relative sea level and the mass extinction has not been confirmed although recent study of the extinction event at the base of the pterocephaliid biomere has revealed a similar trend towards positive carbon isotope values that is worldwide

facies anatomy of an upper cambrian grand cycle bison creek and mistaya formations southern alberta the bison creek and mistaya formations form the youngest cambrian sedimentary grand cycle exposed in banff and jasper national parks the shaly half cycle of the bison creek formation records the displacement of a carbonate bank during a major rise in sea level that can be identified in other parts of north america lithofacies of the bison creek formation fall into three recurrent associations that represent sedimentation in shallow subtidal storm dominated shelf settings the mistaya formation records the reestablishment of carbonate bank deposition probably due to a decrease in the rate of sea level rise and includes two facies associations that represent a mosaic of shallow subtidal to supratidal environments the grand cycle was terminated by a sea level rise possibly eustatic in nature that drowned the carbonate platform the overlying shales mudstones packstones grainstones and rudstones of the survey peak formation mark a return to subtidal storm dominated shelf conditions

source rock characterization and oil to source rock correlation of a cambrian ordovician fold and thrust belt petroleum system western newfoundland abstract in this study we use biomarker and isotope data to address the complexities of petroleum system analysis in fold thrust systems specifically related to hydrocarbon generation and migration such as variable thermal maturities of source rocks complex migration pathways and mixing source rocks extracts and oil samples are taken from paleozoic rocks along the appalachian structural front in western newfoundland oil seeps along this fold and thrust belt have motivated episodic exploration efforts over the last 150 years however economic development has been unsuccessful to date in part because of the complex nature of oil to source relationships pyrolysis analyses identify promising source intervals in lower ordovician floian formations with an excellent source potential containing type i ii organic matter toc up to 9 35 hi up to 840 a second good source interval identified within the late cambrian furongian continental slope and rise sediments contains type ii iii organic matter toc up to 2 34 hi 380 source rock samples from outcrops are marginally mature to mature with tmax values between 436 and 447 geochemical analyses of source rock extract imply a clastic shale dominated source rock with a minor contribution from carbonate source rocks chemometric analyses yield 3 extract groups groups 1 and 2 contain lower ordovician samples with organic matter derived from oxidized micro plankton with varying amounts of gleocapsomorpha prisca extract group 3 originates from cambrian samples and shows evidence of a bacterial derived organic matter similar genetic relationships among 10 oil samples from natural oil seeps and abandoned well sites are indicated by high resolution biomarker analyses seven oil samples originated from ordovician source rocks that produced high api oils with low bisnorhopane hopane tricyclic hopane ratios and high sterane concentrations supporting interpretation of a source containing algal derived organic matter three oils originated from cambrian shales these high api oils show high bisnorhopane hopane and tricyclic hopane ratios low sterane concentrations and low carbon isotope values all indicative of organic matter derived from bacteria generated over a wide range of maturities 0 98 1 26 ro thermal maturity sensitive biomarkers and naphthalene ratios show that source rocks generated oils with a wide range of maturities related to their dipping character in the imbricated thrust stack the cambrian source generated oils that locally experienced secondary cracking during acadian inversion whereas the ordovician source generated oil with low maturities after the acadian inversion oil operaters exploring fold and thrust belt petroleum systems may expect extreme changes of oil properties for example api gravity in spacially restricted areas

the late cambrian spice δ13c event and the sauk ii sauk iii regression new evidence from laurentian basins in utah iowa and newfoundland carbon isotope data from upper cambrian sections in three laurentian basins in northern utah central iowa and western newfoundland record a large positive d 13 c excursion spice event of up to 1 5 peak d 13 c ratios are well dated by trilobite collections to the middle of the steptoean stage dunderbergia zone and occur during maximum regression associated with formation of the sauk ii sauk iii subsequence boundary on the north american craton max imum regression was marked by an influx of quartz sand into carbon ate platform settings in all three widely separated basins in northern utah this quartz sand formed a thick sequence known as the worm creek quartzite which marks a conspicuous interruption of carbonate deposition during the middle to late cambrian in the region in west ern newfoundland the thickness of the quartz sand unit is much re duced but still marks a brief shutdown of the carbonate factory that is unique to the cambrian shelf succession of the area in the central iowa area of the cratonic interior an upward shallowing carbonate succession culminates in cross stratified trilobite grainstones at the peak of the spice in dunderbergia zone time and the lowest point on the relative sea level curve is associated with the occurrence of coarse quartz sand derived from the encroaching shoreface although it is difficult to determine precisely the departure from baseline d 13 c that marks the beginning of the spice excursion in the stratigraphic successions analyzed our results are consistent with a rise and subsequent fall in d 13 c tracking a major regressive transgressive event recorded across northern laurentia the correlation of a major d 13 c excursion with regression is similar to that described for the late ordovician for which the pattern has been attributed to either in creased carbonate relative to terrigenous weathering rates as ice sheets covered up organic matter containing silicates at high latitudes or high productivity and organic carbon burial driven by oceanic overturn the lack of known steptoean age ice sheets that could have affected the ratio of carbonate to silicate weathering rates suggests that organic carbon burial was the likely cause of the spice event we suggest that increased weathering and erosion rates during relative sea level fall sauk ii iii increased the burial fraction of organic carbon in an expanded region of fine grained siliciclastic deposits in shelf and upper slope environments during the steptoean

carbonate deposition and sequence stratigraphy of the terminal cambrian grand cycle in the southern appalachians u s a abstract the cessation of shale and carbonate deposition of the conasauga group grand cycles middle to upper cambrian and the establishment of the widespread peritidal carbonate deposition of the knox group upper cambrian to lower ordovician represent a prominent change in sedimentation along the early paleozoic passive continental margin in the southern appalachians to evaluate the causes for this change this study focuses on the maynardville formation which is the uppermost carbonate unit of the conasauga group the maynardville consists of 1 a lower subtidal facies succession which is underlain by the nolichucky shale and resembles the rest of the conasauga group carbonate deposits and 2 an upper peritidal facies succession which is conformably overlain by similar peritidal deposits of the copper ridge dolomite knox group deposition of shale and subtidal carbonate took place in deep ramp nolichucky to shallow ramp subtidal shoal and lagoonal settings lower maynardville the carbonate ramp was westward sloping toward the conasauga intrashelf shale basin to the east the ramp was linked to a broad semiarid carbonate tidal flat encompassing a variety of peritidal environments upper maynardville and copper ridge the maynardville is a shallowing upward succession that formed by carbonate platform aggradation and basinward progradation the transition between the maynardville and the copper ridge dolomite is within a conformable peritidal carbonate succession that contains common siliciclastic sand size detritus this interval is interpreted as a sequence boundary correlative with the craton wide late steptoean dresbachian franconian or sauk ii sauk iii unconformity the change from a conasauga to a knox depositional style may be related to distinct stages in passive margin evolution the end of grand cycle deposition in the early late cambrian is coincident with the cessation of tectonic activity along extensional features an intracratonic graben and other fault systems and marks the transition into a mature passive margin setting the mature margin was characterized by decreased rates of thermal subsidence which coupled with the infilling of the conasauga intrashelf basin favored shallow water carbonate deposition the final stabilization of the margin is reflected in the deposition of the thick peritidal carbonate strata of the knox group

a basin wide record of the late cambrian steptoean positive carbon isotope excursion spice in the amadeus basin australia abstract the cambrian paibian sedimentary succession of the central australian amadeus basin contains a sequence of supratidal to subtidal shallow marine siliciclastic and oolitic stromatolitic limestones and dolostones basin wide sequence stratigraphy in combination with biostratigraphy revealed the g stolidotus zone within a 3rd order transgressive systems tract tst the westward transgression caused changes from a fluvial dominated depositional environment towards a shallow marine oolitic carbonate shoal environment the eastern succession is dominated by stromatolitic oolitic carbonate rocks with 2 to 5 m 5th order shoaling upward cycles with several 4th order cycles the change from tst to hst highstand systems tract is marked by a maximum flooding surface within the goyder formation which coincides with the peak of the steptoean positive carbon isotope excursion spice the spice shows a facies independent synchronous positive 13c excursion of 5 in a 130 m interval in 8 sections across a 460 km transect the spice peak is lowest in the nearshore successions 0 4 13c and highest in the platform succession 4 9 13c and is interpreted to be related to the chemical gradient of seawater and mixing of the dic with atmospheric co2 derived i e terrestrial bicarbonate the recovery from spice is recorded by 4th order shoaling upward cycles that compose the 3rd order hst this is the first time that sequence stratigraphy and biostratigraphy has been combined with carbon isotope chemostratigraphy across the nearshore to subtidal cambrian basin succession in australia

mesoscale instability and upwelling part 1 observations at the north atlantic intergyre front abstract mesoscale instabilities have been found with a wavelength of about 85 km growing along the meandering jet of the north atlantic intergyre front at about 52 n 33 w they show the signature of baroclinic instabilities and are typified by vertical motions of up to 5 m d 1 which have been diagnosed using the equation the effect of the earth s curvature on motion on these scales is shown to be negligible

melanges and disrupted rocks at the leading edge of the humber arm allochthon w newfoundland appalachians deformation under high fluid pressure abstract the humber arm allochthon was structurally emplaced onto the laurentian margin in western newfoundland during taconian ordovician and acadian devonian deformation on port au port peninsula disrupted allochthonous rocks previously mapped as melange and scaly shale include three mappable variably disrupted stratigraphic units in addition mixed rocks constitute melange with much smaller area than previously mapped at outcrop scale a qualitative assessment of disruption distinguishes broken but coherent stratigraphy from a more disrupted and mixed melange unit within coherent regions three generations of folds are probably related to taconian acadian and carboniferous deformation events more disrupted regions show an average of 24 blocks to 76 matrix with block sizes 0 5 158 cm a new sampling technique allowed recovery of oriented melange samples for thin section multiple orientations of extensional fractures suggest approximately coaxial extension abundant carbonate and less common bitumen filled veins suggest that high fluid pressure played a role in the emplacement of the allochthon high fluid pressure was probably also responsible for dewatering structures sandstone dykes and partially brecciated carbonate beds map relationships outcrop and thin section scale observations lead to a reinterpreted structural history for western newfoundland in which an early taconian west bay thrust sheet was rapidly emplaced onto the laurentian margin during emplacement debris flows initially contributed igneous blocks to the allochthon but the majority of fragmentation took place in an environment of horizontal tectonic extension promoted by high fluid pressure that encouraged brittle fracture the west bay thrust sheet was subsequently overridden by the out of sequence lourdes thrust parts of the allochthon were probably re imbricated in later events but because of previous disruption an organized imbricated thrust belt was not developed at the tip of an advancing thrust wedge a clear distinction between tectonic and surficial processes of melange formation may not be possible

transient upwelling hot spots in the oligotrophic north pacific 1 vertical exchange between deep nutrient rich and nutrient depleted surface waters controls the physical supply of nutrients into the euphotic zone in the oligotrophic waters of the subtropical north pacific ocean sea surface temperature and ocean color satellite images are used in this study to show that submesoscale chlorophyll patches are locally intensified these patches are associated with surface temperature fronts and regions of strong stretching of the eddying flow the latter are identified by calculating the finite size lyapunov exponents of the geostrophic flow derived from the sea surface height field from altimetry surface frontogenesis and nonlinear ekman pumping nlep arise as natural candidates for the sporadic generation of large vertical velocities that could favor the formation of these features a high resolution regional numerical model simulation confirms that large vertical velocities are indeed associated with strong density fronts and gradients of relative vorticity using the q vector divergence as a proxy for frontogenetically generated vertical velocities yields good agreement with the model vertical velocities particularly in regions where they are large the pattern and magnitude of nlep suggests that it is also contributing to the strong vertical motions although nlep and model vertical velocities are not necessarily in phase surface frontogenesis and nlep provide a possible explanation for the episodic injection of nutrients at the submesoscale which are then horizontally stirred and modulated by the unstable manifolds of the flow field given that these surface intensified processes would be biogeochemically more effective when the pycnocline is shallow they could also serve as one possible explanation for the late summer chlorophyll blooms that are known to occur in the region

a subaerial arthropod trackway from the upper silurian clam bank formation of newfoundland trackways are reported for the first time from silurian rocks in newfoundland they occur in the clam bank formation of the port au port peninsula at least one of the trackways represents one of the earliest known occurrences of a large subaerial arthropod trace fossil it is preserved in hyporelief in a red fine grained sandstone the trackway diplichnites dawson 1873 consists of two parallel series of clearly defined imprints it is attributed to a myriapod similar to the lower devonian eoarthropleura the sandstone contains halite pseudomorphs that indicate that the sediment horizon had been subject to desiccation immediately prior to the formation of the trackway the arthropod walked on a red siltstone deposited in an alluvial flats environment analysis of the trackway suggests that the arthropod was approximately 23 cm long and had 17 pairs of walking appendages it appears that a high geared gait with a ratio of forestroke backstroke of 8 2 was used in walking across the substrate that is ap