reconstructing the avalon continent marginal to inner platform transition in the cambrian of southern new brunswick a west to east marginal to inner avalonian platform transition comparable to that in southeast newfoundland and southern britain is present in the cambrian of southern new brunswick the saint john caton s island hanford brook area lay on the marginal platform and its thick uppermost precambrian lower lower cambrian is unconformably overlain by trilobite bearing upper lower cambrian an inner platform remnant is preserved in the cradle brook outlier 60 km northeast of saint john in contrast to the marginal platform sequences the cradle brook outlier has a very thin lower lower cambrian and has middle lower cambrian strata bonavista group not present on the marginal platform the cradle brook lower cambrian closely resembles inner platform successions in eastern massachusetts and trinity and placentia bays southeast newfoundland a limestone with camenella baltica zone fossils on cradle brook seems to be the peritidal limestone cap of the subtrilobitic lower cambrian known in avalonian north ame

chemical sedimentology and paleoenvironmental history of lake olduvai a pliocene lake in northern tanzania lake olduvai was a saline highly alkaline closed basin lake in which lacustrine sediments of bed i and lower bed ii of olduvai gorge were deposited between ca 1 92 and 1 70 ma the lake consisted of a lacustrine area the central basin cb surrounded by lake margin terrain that was alternately flooded and dried the lacustrine deposits consist largely of authigenic clay and carbonate minerals zeolites k feldspar chert and pyrite claystones of the cb and most of the eastern lake margin elm terrain consist chiefly of mg rich authigenic illite smectite and interlayered illite smectite i s these clays were formed penecontemporaneously with detrital clay deposition by interaction of the detrital clays with the saline highly alkaline water the lake olduvai clays average 65 70 mg 2 sio 2 and alkali ions from lake water and the remaining 30 35 is detrital clay lacustrine clays of the elm indicate that this area was flooded by saline water for substantial periods of time hominids occupied the elm at times of lower lake levels when the clays were dried calcite is the most abundant carbonate mineral and occurs chiefly as sand size euhedral crystals dispersed in claystone and less commonly as calcite crystal limestones and nodules the sand size calcite crystals were formed diagenetically at shallow depths possibly from a gaylussite and or micritic calcium carbonate precursor dolomite occurs chiefly in the form of dolostones some of which are probably of replacement origin the oxygen isotope composition of lake water and pore fluid of the cb varied over 11 as determined from calculated delta 18 o h 2 o values of authigenic minerals clay minerals were formed chiefly in the more saline waters sand size calcite crystals were generated mostly from less saline pore fluids and limestone nodules were formed chiefly from dilute pore fluid dolostones were formed from fluids of varying salinity hydrogeology of the central basin was complex and postdepositional fluid movements are documented by differing delta 18 o h 2 o values for different authigenic minerals of the same samples pore fluids moved within the lake deposits for a considerable period of time after deposition as shown by 18 o values of quartz and k feldspar formed at different times downward flow of lacustrine fluids is indicated by zeolitic alteration of the underlying tuffaceous alluvial deposits lake olduvai became overall shallower during the deposition of bed i and the subaerial exposure increased leading to occasional playa conditions these changes very likely resulted from increasing aridity and tectonic activity the lake that deposited lower bed ii was larger than that responsible for upper bed i and episodes of wetter climate alternated with drier periods in which salinity and probably temperatures were higher than in the bed i lake

reconstructing the avalonia palaeocontinent in the cambrian a 519 ma caliche in south wales and transcontinental middle terreneuvian sandstones an early cambrian caliche on the st non9s formation emended is the base of the caerfai bay formation unit term changed at caerfai bay south wales subaerial exposure and the caliche mean the two formations were not genetically related units the st non9s is an older sand sheet likely tidalitic not delta related referred to avalonian depositional sequence ads 2 and the caerfai bay is a shallow mud basin unit refered to ads 4a the similar random formation upper ads 2 in north american avalonia has a basal age of c 528 ma and is unconformably overlain by red mudstones or sandstones in fault bounded basins on the avalonian inner platform coeval british sandstones lower hartshill wrekin st non9s brand hills are unconformably overlain by latest terreneuvian ads 3 or epoch 2 ads 4a units dates of 519 ma on caerfai bay ashes give an upper bracket on the late appearance of avalonian trilobites and suggest an ads 2 4a hiatus of several million years post st non9s and post random basin reorganization led to abundant caerfai bay formation volcanic ashes and sparse brigus formation ashes in newfoundland the broad extent of erosional sequence boundaries that bracket lithologically similar to identical units emphasize that east and west avalonia formed one palaeocontinent the inner platform in southern britain was larger than the midlands craton a tectonically defined later palaeozoic area unrelated to terminal ediacaran early palaeozoic depositional belts the cool water successions of early palaeozoic avalonia were distant from coeval west gondwanan carbonate platforms

palynological dating arenig of the sedimentary sequence overlying the ishkarwaz granite upper yarkhun valley chitral pakistan a sedimentary sequence overlying a granite pluton near ishkarwaz upper yarkhun valley chitral pakistan karakorum microplate contains abundant but poorly preserved acritarchs probably referable to the late early arenig early late arenig interval the palynological assemblages of karakorum show a marked similarity to the cold water peri gondwana assemblages i e to those of li jun s arbusculidium coryphidium striatotheca mediterranean bioprovince biogeographical and geological comparisons suggest that before the accretion of cimmerian microplates to the eurasian continent the karakorum microplate was located along the northern margin of gondwana in a latitude intermediate between the mediterranean region and south china yangtze platform

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

mixed siliciclastic carbonate deposition in an early cambrian oxygen stratified basin chapel island formation southeastern newfoundland abstract the upper portion of member 3 and member 4 of the uppermost precambrian vendian lower cambrian chapel island formation represents a large scale shoaling up deposit dominated by shelf siliciclastic mudstone medium scale higher order shoaling up cycles at the top of member 3 and in member 4 are capped by peritidal limestones that contain a wide variety of stromatolitic buildups and algal mud mounds sedimentation took place in an oxygen stratified basin with accumulation of gray dysaerobic mudstone offshore and green and red mudstone in shallower more oxygenated waters biofacies models for dysaerobic basins can be applied to this sequence and help in understanding the distribution of trace fossils skeletal fossils shells and pyritic steinkerns and diagenetic features these da a are important for the understanding of the stratigraphic distribution of shelly fossils within this lowest cambrian unit a mixed carbonate siliciclastic facies model is presented in which carbonate sediments formed in intertidal areas along the shoreline of a siliciclastic muddy shelf the carbonate shoreline prograded during periods of increasing rate of relative sea level fall or decreasing rate of relative sea level rise restriction of carbonate sediments to the peritidal environment may have been due to a combination of higher rates of carbonate sediment production and accumulation in the peritidal zone seaward dilution by siliciclastic mud and a paleogeographic position near the latitudinal climatic extreme for carbonate production

metamorphic evolution of the kamuikotan high pressure and low temperature metamorphic rocks in central hokkaido japan the kamuikotan complex in the sorachi yezo belt located in central hokkaido japan has been extensively subjected to subduction related high pressure and low temperature metamorphism on the basis of geological petrological and geochronological data the coherent metamorphic rocks are divided into six units as follows susunai horokanai harushinai biei pankehoronai and shizunai based on their metamorphic mineral sequences the six units can be classified into the following three baric types high pressure 1 hp1 high pressure 2 hp2 and high pressure intermediate hi the horokanai and shizunai units belong to the hp1 type the harushinai and biei units belong to the hp2 type and the susunai and pankehoronai units belong to the hi type metabasites of the hp1 type are defined by the association of lawsonite na amphibole or epidote na amphibole glaucophane or crossite the hp2 type is characterized by the assemblage of pumpellyite na pyroxene chlorite and the representative low variance asssemblages are lawsonite pumpellyite na pyroxene chlorite and pumpellyite na pyroxene na amphibole chlorite in the hi type the most common low variance assemblage is pumpellyite epidote actinolite chlorite these results together with the previously published k ar and 40ar 39ar ages suggest that the kamuikotan metamorphic rocks gradually decreased in pressure during the cretaceous this tendency indicates an increase in the kamuikotan subduction geotherm during early cretaceous to early eocene time the increase in the paleogeotherm may result from the change of subduction rates and subducting slab ages

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

properties and development of channel calcretes in a mountain catchment tabernas basin southeast spain nonpedogenic channel calcretes of up to 3 5 m thick occur in a number of locations across the tabernas basin in almeria province southeast spain they represent the last major phase of late quaternary calcium carbonate cementation to affect this semiarid drainage basin channel calcretes are situated within the basal parts of sequences of 12 m thick poorly sorted coarse grained and schist dominated fluvial gravels that were deposited within confined bedrock channels channel calcretes occupy the full basal width of the bedrock channels within which they occur and mostly crop out near the mouths of tributary valleys to the main rambla de tabernas drainage system six profiles from five separate channel calcrete outcrops were logged and sampled all samples were analysed in thin section and under scanning electron microscope sem from these analyses the macro and micromorphological properties were identified and the mode of origin of channel calcrete profiles was assessed results indicate that all channel calcretes are massively cemented by calcite and appear uniform at the field profile scale microscale analyses reveal that detrital grains within the calcretes are initially coated by micrite which is overlain by grain coating and pore filling sparite a series of broad trends in cement type and micromorphology are recognised within individual field profiles all profiles exhibit an increasing degree of calcite crystal size in a down profile direction most field profiles predominantly contain micrite in upper parts with an increasing percentage of sparite towards the base some profiles are however dominated by sparite and show increasing crystal size and occurrence of euhedral crystals towards the profile base many profiles also contain evidence of postcalcite cementation diagenesis in the form of dissolution of calcite crystal faces or replacement of the calcite cement by amorphous silica with alteration mostly occurring in the lower parts of profiles the trends within the calcrete fabric appear to have developed in conjunction with a fluctuating water table with the increased crystal size and occurrence of euhedral crystals towards the base of profiles arising from greater duration of wetting in basal zones cementation in some field profiles occurred at depths of up to 12 m within the host sediment well below the zone of capillary rise and pedogenesis and in the absence of significant organic activity as such channel calcretes in the tabernas basin may represent an ideal opportunity to observe the influence of groundwater upon cementation of coarse grained sediments by carbonate

microcodium an extensive review and a proposed non rhizogenic biologically induced origin for its formation abstract microcodium has been previously described as a mainly cenozoic calcification pattern ascribed to various organisms a review of the available literature and our data reveal two peaks in microcodium abundance the moscovian early permian and the latest cretaceous paleogene a detailed analysis of late paleozoic and cenozoic examples leads to the following new conclusions typical microcodium forming unilayered corn cob aggregates of elongated grains and thick multilayered palisade replacing structures cannot be linked to smaller grained intracellular root calcifications as became widely accepted after the work of klappa klappa c f 1979 calcified filaments in quaternary calcretes organo mineral interactions in the subaerial vadose environment j sediment petrol 49 955 968 typical microcodium is recognized from the early carboniferous with doubtful devonian reports to quaternary as a biologically induced mineralization formed via dissolution precipitation processes in various aerobic ca rich soil and subsoil terrestrial environments morphology and 13c signatures of microcodium suggest that neither plants algae or roots and root associated mycorrhiza regulate the formation of these fossil structures non recrystallized microcodium grains basically consist of slender 1 5 4 m curved radiating monocrystalline prisms with occasionally preserved hyphae like morphology thin 0 5 3 m hypha like canals can also be observed these supposed hyphae may belong to actinobacteria however thin fungal mycelia cannot be excluded we propose a model of microcodium formation involving a mycelial saprotrophic organism responsible for substrate corrosion and associated bacteria capable of consuming acidic metabolites and caco3 reprecipitation into the microcodium structures

carbonate deposition and hydrocarbon reservoir development at the precambrian cambrian boundary the ara group in south oman abstract the ediacaran early cambrian ara group in the south oman salt basin consists of six evaporite carbonate cycles a0 a1 to a6 that record tectono eustatic sea level changes the a4 cycle developed at the precambrian cambrian boundary 542 ma it forms a single depositional sequence with evaporites deposited in a lowstand systems tract lst overlying carbonates represent an open marine shallowing upward ramp succession that developed in transgressive tst and highstand systems tracts hst the low energy carbonate ramp occupied a relatively protected site between a large shelf and an exposed paleogeographical high the tst facies include sulfates evaporite carbonate laminites and organic rich carbonate laminites that record initial flooding deepening of the basin and establishment of an outer ramp depositional environment carbonate sediment flux was low and the environment was partly subject to cyclically elevated salinity subsequent hst facies comprise mostly fine grained clastic carbonates and stromatolites that formed in middle and inner ramp settings these facies show evidence of shoaling and establishment of a carbonate factory that probably operated over most of the middle and inner ramp sediment was redistributed in suspension by muddy turbidity currents muddy debris flows storm and shallow water currents during the late hst carbonate facies were affected by elevated salinity and recorded the gradual transition to the overlying lst evaporite unit a combination of strong tectonic subsidence and transient flooding caused significant shallow water evaporite deposition to occur not only down dip but also on top of the former carbonate platform where several hundreds of meters of evaporites accumulated the transgressive carbonate laminites are the main reservoir facies and thus represent a relatively unusual reservoir unit the presence of organic material and the relative scarcity of carbonate mud influenced diagenesis and reservoir properties distribution of organic material and carbonate mud can be linked to specific environmental conditions low physical and biogenic disturbance of sediment and stratified water mass and the sequence stratigraphic position low flux of fine grained carbonate during tst in contrast diagenetic evaporite formation has largely degraded reservoir quality in porous shallow water facies near the top of the a4c

chemostratigraphy of the cerro victoria formation lower cambrian uruguay evidence for progressive climate stabilization across the precambrian cambrian boundary abstract petrographic isotopic and geochemical data are reported for the cerro victoria formation of the arroyo del soldado group uruguay it is divided into four informal lithostratigraphic units a to d which are mainly composed of an alternation of stromatolitic oolitic and clastic dolostones the genesis of dolomite as a primary or penecontemporaneous precipitate is discussed considering excellent preservation of textural details whereas 87 sr 86 sr ratios in the least altered samples are too high 0 7106 0 7109 to represent seawater values 13 c determinations are interpreted as reflecting near seawater composition the curve obtained for the cerro victoria formation is characterized by negative values at its base 3 5 pdb passing into a slightly positive plateau up section peak values of 0 64 pdb are encountered in the upper unit c the upper cerro victoria formation is characterized by a return to moderately negative values the shape of the 13 c curve is consistent with the data reported for the nemakit daldyn stage of the lower cambrian we suggest that the precambrian cambrian boundary is located at the cerros san francisco cerro victoria transition or slightly lower in the succession thalassinoides bearing dolostones of the upper cerro victoria formation might reach the tommotian or atdabanian in the arroyo del soldado group 13 c excursions parallel sea level oscillations transgressive events being characterized by positive 13 c values falling amplitudes of coupled 13 c sea level fluctuations recorded in these carbonates are in accordance with the trend observed in ediacaran lower cambrian successions worldwide covariance of 13 c and sea level might be explained by bioproductivity fluctuations affecting the carbon cycle atmospheric co 2 concentrations climate ice volume and ultimately sea level while these oscillations were of large magnitude in the late neoproterozoic they progressively faded away in the cambrian giving place to a more stable environment the cause of the amplitude decrease in biogeochemical climatic and sea level perturbations might be the decreasing rates of nutrient input at mid ocean ridges as reflected by rising 87 sr 86 sr values between 800 and 500 ma punctuated by at least three events roughly coincident with rifting episodes of rodinia

early palaeozoic peri gondwana terranes new insights from tectonics and biogeography following the late neoproterozoic early cambrian breakup of the supercontinent rodinia gondwana evolved as one of the principal continental masses on earth embracing most of south america africa australasia antarctica much of western europe and parts of asia around its margins were various other terranes that had varying tectonic and biogeographical affinities with the main continental block this book incorporates a series of reviews and multidisciplinary research papers that together explore the tectonic palaeogeographical and palaeobiogeographical evolution of the elements that made up the peri gondwanan collage the stratigraphical scope of the coverage embraces the late precambrian through early devonian providing a comprehensive overview of structural stratigraphical and biological evolution through this significant interval of earth history integration of these various processes throughout the volume will be of broad based interest to a wide range of geoscientists

integrated correlation of the vendian to cambrian arroyo del soldado and corumba groups uruguay and brazil palaeogeographic palaeoclimatic and palaeobiologic implications abstract the corumba group of sw brazil and the arroyo del soldado group asg of uruguay are correlated on the basis of litho bio and chemostratigraphy both units represent marine sedimentation with alternating siliciclastics and carbonates developed on a stable continental shelf in the corumba basin sedimentation began in the varangerian represented by the glaciomarine puga formation a series of sea level fluctuations coupled with climatic changes are recorded up section while uppermost deposits of the asg are of lowermost cambrian age sedimentation ceased in the latest vendian in the corumba basin an assemblage of six species of organic walled microfossils dominated by bavlinella faveolata and soldadophycus bossii three species of vendotaenids and two species of skeletal fossils cloudina and titanotheca is described from the corumba group the vendotaenid eoholynia corumbensis sp nov is described from siltstones of the guaicurus formation an important diversity of skeletal fossils in the corumba arroyo del soldado and nama groups points to favourable vendian palaeoclimatic conditions in sw gondwana preliminary carbon isotopic data show a series of alternating positive and negative excursions corroborating the upper vendian age indicated by fossils for both units previously reported strontium isotopic data are also consistent with this age it is postulated that the corumba and asgs were deposited onto the same shelf which opened to the east the rio de la plata superterrane craton extends farther to the north than previously expected or it was already amalgamated with the amazonian craton by vendian times collision of the platform with the parana block caused closure of the basin during the cambrian early ordovician finally models of neoproterozoic glaciations based on enhanced bioproductivity driven by high nutrient availability are discussed

early cambrian continental reconstructions climatically related sedimentary facies and faunal distributions have been combined with palaeomagnetic data to make provisional reconstructions of the early cambrian world laurentia baltica and siberia appear to have formed a continental group which rifted apart from each other prior to 600 ma the consolidation of much of gondwana probably occurred in the pan african orogeny well before the cambrian though the assembly of several east asian terranes is still speculative the archaeocyathan reefs of siberia southern europe and morocco with their bigotinid trilobite fauna suggest that these areas were adjacent to each other and at low latitudes avalonia had close faunal links with western gondwana but lacked bigotinids and archaeocyathans and may have been situated off west africa and florida during the early cambrian there was a northward migration of laurentia towards the equator as its separation from baltica and siberia increased and a southward movement of gondwana

the proterozoic cambrian transition within the charnian supergroup of central england and the antiquity of the ediacara fauna a revised interpretation for the charnian supergroup is suggested from ichnological and lithological comparisons with the cambrian of nuneaton and other parts of the avalonian superterrane late neoproterozoic volcaniclastic sediments contain an ediacara fauna in the maplewell group these are succeeded by one or more inferred erosional breaks and overlain by passive margin sediments quartzarenites glauconitic greywackes pelites of the brand group which yield cambrian trace fossils including abundant large teichichnus this transformation is compared with that between the neoproterozoic caldecote volcanic formation and the cambrian hartshill formation at nuneaton the hanging rocks formation of the brand group lies above a major erosional break but shares a volcanogenic island arc petrology with the underlying maplewell group conglomeratic sandstones at the base of the brand hills formation contain purple pelite clasts comparable with underlying lithologies plus clasts of weathered diorite showing granophyric textures identical to those seen in the enigmatic south charnwood diorites nd sm isotope studies confirm the geochemical similarity between these diorites and those that intruded the caldecote volcanics at nuneaton previously u pb zircon dated at 603 2 ma these strong similarities with the nuneaton succession suggest that deposition of the brand hills formation in the cambrian was preceded by the local unroofing of diorite and erosion of underlying mudrocks much as seen in other parts of avalonia a date of 603 2 ma for the south charnwood diorites provides a minimum age for the local ediacara fauna but this is in need of substantiation

further shrimp geochronology on the early cambrian of south china zircon 206pb 238u ages are reported for bentonites from two cambrian sections in south china the meishucun and the fandian the analyzed zircons vary widely in age because of the presence of detrital and altered grains spot ages were corrected for calibration drift during analysis and the age of reference zircon sl13 was calibrated as 580 ma against other standards using sims use of mixture modeling was essential to resolve the different age components and to identify the volcanic ages two age groups occur within the meishucun bed 5 bentonite of which the larger at 518 7 2 5 ma is interpreted as a post depositional zircon growth event and the other at 539 4 2 9 ma as the volcanic age bentonites from the meishucun bed 9 and its fandian equivalent have two age groups 526 5 1 1 ma and 540 2 1 0 ma we interpret the younger of these as the tuff magmatic age and the older as detrital small shelly fossils indicate meischucunian bed 5 is an equivalent of the late nemakit daldynian and its 539 4 2 9 ma age both closely times the base of the cambrian and is a maximum for the basal tommotian the 526 5 1 1 ma for bed 9 and its equivalents approximates the close of the tommotian

first evidence for cambrian glaciation provided by sections in avalonian new brunswick and ireland additional data for avalon gondwana separation by the earliest palaeozoic abstract the first evidence for cambrian glaciation is provided by two successions on the avalon microcontinent the middle lowest cambrian middle terreneuvian series and fortunian stage stage 2 boundary interval has an incised sequence boundary overlain by a fluvial lowstand facies and higher olive green marine mudstone on hanford brook southern new brunswick this succession in the lower mystery lake member of the chapel island formation may be related to melting of an ice sheet in avalon the evidence for this interpretation is a muddy diamictite with outsized up to 10 cm in diameter proterozoic marble and basalt clasts that penetrated overlying laminae in the marine mudstone that eustatic rise was associated with the mudstone deposition is suggested by an approximately coeval rise that deposited sediments with watsonella crosbyi zone fossils 650 km away in avalonian eastern newfoundland a sea level rise within the watsonella crosbyi chron at ca 535 ma may correspond to a unnamed negative 13 c excursion younger than the basal cambrian excursion bace and the zhuce excursion in stage 2 of the upper terreneuvian series cambrian dropstones are now also recognized on the northern gander margin of avalon in continental slope rise sedimentary rocks in southeast ireland although their age early middle cambrian is poorly constrained dropstones in the booley bay formation provide additional evidence for cambrian glaciation on the avalon microcontinent besides providing the first evidence of cambrian glaciation these dropstone deposits emphasize that avalon was not part of or even latitudinally close to the terminal ediacaran cambrian tropical carbonate platform successions of west gondwana

suspect terranes and accretionary history of the appalachian orogen the north american connection or the grenvillian continental crust that separated from eastern north america during the initiation of the appalachian orogenic cycle is poorly defined within the present orogen a variety of terranes occur outboard of the north american miogeocline all structurally uncoupled and therefore suspect stratigraphic analysis indicates that appalachian accretion progressed from the miogeocline outward the boundaries of the earliest accreted western terranes are marked by melange and ophiolite complexes later boundaries between eastern terranes are steep mylonitic zones and brittle faults accretionary events defined by stratigraphic analysis correspond to times of major deformation plutonism and metamorphism in the history of the orogen