the ordovician silurian boundary on cornwallis and truro islands arctic canada preliminary data four sections of the lower part of the cape phillips formation two outcrops on northeastern cornwallis island and one outcrop and one drill core from truro island northwest territories canada provide significant new data on the ordovician silurian boundary they show evidence of continuous sedimentation through the boundary interval and a continuous sequence of graptolite zones including the bohemicus and persculptus zones which have not been previously found in arctic canada strata yield graptolites including uncompressed specimens and conodonts through most of the sections the ordovicicus conodont zone occurs within the pacificus to lower persculptus graptolite zones the nathani conodont zone contains a transitional fauna a mixing of species typical of the preceeding ordovicicus zone and those generally regarded as silurian indicators this conodont zone ranges from the middle of the persculptus graptolite zone into the lower acuminatus graptolite zone and thus spans the ordovician silur

silurian graptolite biostratigraphy in the welsh basin silurian graptolite zones are of markedly shorter duration than those of the ordovician averaging 0 8 ma several can be sub divided and further refinement will undoubtedly follow a revision of many of the graptolite species and their stratigraphic range locally integration of palaeontological and sedimentological studies facilitates correlation a premilinary subdivision of the crispus and griestoniensis zones in central wales is made

the early rhuddanian survival interval in the lower silurian of the oslo region a third pulse of the end ordovician extinction abstract ordovician silurian boundary layers with rhuddanian strata are exposed as a long continuously fossiliferous sequence in the solvik formation in the asker area central oslo region norway brachiopods belonging to benthic assemblage 5 are preserved in the lower parts of the formation this level is investigated for the presence of a survival interval after the last end ordovician extinction event the criteria for a survival interval include taxa that are dwarfed long ranging eurytopic often opportunistic as well as assemblages that show low density and diversity four species isorthis prima leangella scissa dicoelosia osloensis and eoplectodonta duplicata were collected and measured the three former were dwarfed compared to a younger aeronian fauna belonging to the same benthic assemblage detailed investigations showed a statistically significant two step reduction in size for all but d osloensis the first interval immediately above the last end ordovician extinction event displays dwarfed brachiopods but diversity is high and the number of long ranging and eurytopic species is low due to the presence of globally and locally relict ordovician species the second interval the upper parts of lower rhuddanian shows all the characteristics of a survival interval in which the sizes are statistically significantly smaller than both those in the interval below and those in the aeronian interval above no lithological change within lower rhuddanian strata could be linked to the pronounced reduction in size the second step in size reduction may be related to global occurrence of anoxia in the deep oceans with a pulse of anoxic water pushed onto the shelf at that time it is coeval with a short negative 13 c excursion found in some locales signifying a brief period of global warming the results suggest a protracted extinction event through parts of the early rhuddanian and a third and final extinction event followed by a clear survival interval

hirnantian ordovician through wenlock silurian conodont biostratigraphy bioevents and integration with graptolite biozones cape phillips formation slope facies cornwallis island canadian arctic islands cornwallis island in the canadian arctic archipelago provides one of the world s best areas for establishing an integrated graptolite conodont biozonation for the late ordovician silurian given the well exposed interfingering relationship of the basinal shale and carbonate platform facies building on earlier graptolite work 180 samples were collected from nine sections of the cape phillips formation of which 118 yielded approximately 7600 conodont elements representing 54 species in 25 genera including one new genus and species mayrodus melchini the conodonts are well preserved with minimal thermal alteration colour alteration index cai 1 nine conodont zones are recognized and defined for this region namely the amorphognathus ordovicicus distomodus kentuckyensis aspelundia expansa as fluegeli and pterospathodus celloni interval zones pt a amorphognathoides taxon range zone pt pennatus procerus and kockelella ranuliformis highest occurrence zones and k ortus absidata taxon range zone an integration of graptolite and conodont zones is documented earlier paleontological and isotope geochemical studies have demonstrated the dynamic nature of the silurian ocean climate system and identified major faunal turnovers or events five of these are recognized in the cornwallis fauna and related to oceanographic and climate changes in part referring to recent oxygen isotope data from conodonts from the cornwallis collections hirnantian extinction event sandvika event late aeronian llandovery snipklint primo episode early telychian llandovery ireviken event late telychian llandovery sheinwoodian wenlock and mulde event early homerian wenlock

does the golden spike still glitter a modus operandi for precambrian stratigraphy is suggested which combines the geochronometrical scale and late proterozoic chronostratigraphy the development of phanerozoic stratigraphical classification is followed from the pioneering days of murchison through the growing understanding of fossils in relation to time and the later distinction of rock and time rock to the advent of the golden spike criticisms of chronostratigraphy global standard stratigraphy are assessed and its value upheld stratigraphical procedures such as those of event stratigraphy are useful in particular situations but correlative methods in the phanerozoic are dominated by biostratigraphy examples are taken of its use and potential in north american cordilleran palaeozoic stratigraphy in the triassic system as a whole and in the caledonides of britain and ireland

a preliminary radiolarian biozonation for the lower silurian of the cape phillips formation nunavut canada radiolaria from the lower silurian of the cape phillips formation nunavut canada allow the definition of four biostratigraphic assemblages the haplotaeniatum assemblage extends from the basal llandovery to topmost coronograptus cyphus graptolite biozone the base is taken as the first occurrence of haplotaeniatum nunavutensis no samples were collected below the ordovician silurian boundary the top of the assemblage is defined by the first occurrence of orbiculopylorum the orbiculopylorum assemblage is marked by the first occurrence of orbiculopylorum the boundary between this assemblage and the overlying plussatispila assemblage is unclear because of a break in stratigraphy upper spirograptus turriculatus through monograptus crispus graptolite biozones the last occurrence of orbiculopylorum defines the top of the assemblage the base of the plussatispila assemblage is defined by the last occurrence of orbiculopylorum a barren interval cyrtograptus insectus to lower monograptus instrenuus cyr

aquifer chemistry of thermal waters of the godavari valley india abstract the results of a chemical study of thermal waters from three hot springs two water discharges in a mine at 180 m depth and four wells drilled for exploration of coal and water resources in the godavari valley indicate 1 a deep flow path within the lower gondwanas upper carboniferous lower triassic for agnigundala thermal water which has been found to be in equilibrium with quartz montmorillonite and kaolinite at 150 c 2 medium depth circulation also through lower gondwana sedimentary rocks and equilibrium with quartz at 100 c for waters of buga manguru and bhuttayagudem and 3 circulation within sedimentary formations for the thermal waters of the pagdaru and bhimdole areas waters of the last areas show disequilibrium but are within the stability field of kaolinite the aquifer temperature is most likely to be about 156 c for the agnigundala around 100 c for the buga and not more than 100 c for the other systems

human impact on regional groundwater composition through intervention in natural flow patterns and changes in land use schot p p and van der wal j 1992 human impact on regional groundwater composition through intervention in natural flow patterns and changes in land use j hydrol 134 297 313 the relations between groundwater composition land use soil conditions and flow patterns on a regional scale are studied for the gooi and vechtstreek area in the netherlands this densely populated area consists of a glacier created ridge with dry sand soils bordered by the vecht and eem river plains with wet peat and clay soils r mode factor analysis and q mode cluster analysis were applied to a set of 1349 groundwater analyses to determine the factors controlling groundwater composition and the main resulting water types the results indicate that groundwater composition in the study area is affected on a regional scale by human activities through changes in land use and intervention in natural flow patterns on the ridge ground water is recharged by precipitation which dissolves carbonates from the matrix of the sandy aquifer increased solute concentrations in shallow ground water especially of nitrate sulphate and potassium indicate increased pollution resulting from urbanization and increasingly intensive agricultural activity over the past decades in the vecht river plain infiltration occurs as a result of drainage of polders and groundwater extraction on the ridge recharge occurs by precipitation and from polluted surface water to which ammonium organic complexes and carbonic acid are added through decomposition of organic matter in the peat and clay soils the carbonic acid results in enhanced dissolution of carbonates present in the soil and the underlying sandy aquifer oxygen depletion and subsequent low redox potentials result in denitrification dissolution of manganese and iron oxides and sulphate ro duction the flow of ground water from high level to low level polders causes displacement of a former stagnant brackish groundwater body under the vecht river plain accompanied by increased mixing of fresh and brackish ground water

insolitignum n gen and palaeoephippium goodbody 1986 radiolaria from the lower silurian of the cape phillips formation arctic canada radiolaria of the family palaeoscenidiidae were recovered from two bedded limestone and two limestone concretion samples from the upper llandovery of the cape phillips formation cornwallis island arctic canada the new genus insolitignum is defined by two apical rays three basal rays and a principal ray in an intermediate position the principal ray distinguishes this genus from palaeoephippium insolitignum dissimile the type species of the new genus was previously placed in palaeoephippium new species described here are insolitignum peranima insolitignum vivanima and palaeoephippium adraini

the paradox of the global standard late ordovician early silurian sea level curve evidence from conodont community analysis from both canadian arctic and appalachian margins abstract relative sea level fluctuations in the late ordovician early silurian were largely driven by gondwana deglaciation three possible short lived ice readvances and the closure of the iapetus ocean this study establishes and compares sea level events on the canadian arctic and appalachian margins of laurentia based on the pattern of conodont communities and demonstrates that sea level events were not synchronous on the two margins conodont data were compared for a the arctic margin from the cape phillips formation richmondian upper ordovician through lower sheinwoodian lower silurian cornwallis island canadian arctic islands and b the appalachian margin from the upper ellis bay becscie merrimack gun river jupiter and chicotte formations richmondian upper ordovician rhuddanian aeronian and most of telychian lower silurian anticosti island quebec the pattern of late ordovician early silurian conodont communities is established based on three cluster analyses on conodonts from cornwallis island 4967 specimens representing 54 species from 77 samples cape phillips formation and anticosti island 1980 specimens representing 21 species from 25 samples upper ellis bay formation 24 839 specimens representing 42 species from 123 samples becscie merrimack gun river jupiter and chicotte formations overall the sea level curves inferred from the distribution of the conodont communities from cornwallis and anticosti exhibit gradual and rapid oscillating patterns respectively specifically during the time interval of the latest ordovician and the early silurian rhuddanian the sea level behaved differently in these two regions 1 during the latest ordovician conodont community changes show the different patterns in the two regions which reflects a transgression on cornwallis but a regression on anticosti 2 during the earliest rhuddanian similar conodont communities arose in both regions but they indicate a regression on cornwallis and a transgression on anticosti 3 in the early rhuddanian these communities were replaced by a deeper water community on cornwallis and a shallower water community on anticosti which suggest a transgression on cornwallis and a regression on anticosti 4 a highstand drove out almost all conodonts from anticosti by the end of rhuddanian which is not seen on cornwallis 5 a deep water conodont community remained almost unchanged on cornwallis from the late rhuddanian to the early aeronian whereas a shallow water conodont community returned to anticosti in the early aeronian however the sea level dropped on both cornwallis and anticosti during the late telychian and the sea level curves show a similar pattern the difference in the sea level pattern during the late richmondian rhuddanian and aeronian on both the northern and southern margins of laurentia reflected by conodont communities is supported by the studies on quaternary glaciation deglaciation events where the melting of an ice sheet was accompanied by sea level change but with variable regional isostatic effects that do not generate a uniform global eustatic signal

behaviour of thermal waters through granite rocks based on residence time and inorganic pattern summary thermal waters are certainly a substantial asset of the galicia region of spain they can be regarded as worth developing because of their human health implications and if thermal tourism is promoted their importance to the local economy in this paper the chemistry of major and trace inorganic elements in about 45 thermal springs and wells discharging in the same hydrographical system are presented and discussed for handling the results of all measurements graphical representations of b li vs so 4 2 cl ratios hill piper diagram discriminant analysis da and principal component analysis pca were employed all this with the intention to classify based on their inorganic pattern both thermal springs and wells waters but also waters circulating through adamellite and granodiorite rocks the results of the hydrogeochemistry analysis showed three main water families sulphated chlorinated and bicarbonated waters the results show also the presence of saline materials with chloride influence in the deeper aquifer allowing its classification in deeper and younger shallow waters

middle palaeozoic extinction events faunal and isotopic data abstract at least 9 and possibly as many as 12 extinction events of global or near global impact can be discriminated in the mid palaeozoic earliest silurian to early carboniferous on the basis of brachiopod coral conodont and ammonoid data and the history of carbonate build ups isotopic data from whole rock samples are presented for three of these events based on australian carbonate sequences constrained by conodont data these data represent the initial phase of a more extensive investigation using c o s sr and nd isotopic signatures derived from conodonts articulate and inarticulate brachiopod shell and fish remains from numerous australian and european sequences the aim of the project is to identify isotopic responses to extinction events and address causes for these changes in limestone sections analysed so far variations in carbon isotope compositions on a whole rock scale are most marked at horizons that can be correlated with times of significant reduction in biomass and diversity this is despite the fact that the whole rocks are in fact multicomponent systems with respect to carbon in part arising from diagenetic rearrangements of carbon distribution within the scale of the whole rock thus the carbon isotope data do provide evidence on a whole rock scale for fundamental changes in the global carbon cycle that are correlative with extinction events it is however unlikely that the magnitude of the isotopic shift will be precisely documented from such whole rock analyses the oxygen isotope results are less obviously related to the times of carbon isotope excursion this contrast in apparent resilience to post depositional modification of pristine isotope compositions exemplifies the extreme caution needed in evaluating isotopic data from carbonates

graptolites of the genus mediograptus boucek and pfibyl from the uppermost llandovery of cornwallis island arctic canada isolated specimens of three species of mediograptus are described from latest llandovery telychian strata of the cape phillips formation cornwallis island one species is new mediograptus bicercis n sp whereas the other two mediograptus flittoni and mediograptus morleyae have previously been recorded only from the telychian of wales a possible paleolatitudinal control on mediograptid distribution is suggested with one suite of taxa characterizing higher paleolatitudes bohemia the other including the species described herein lower paleolatitudes wales arctic canada the diagnosis for the genus mediograptus is emended

graptoloid evolutionary rates track ordovician silurian global climate change graptoloid evolutionary dynamics show a marked contrast from the ordovician to the silurian subdued extinction and origination rates during the ordovician give way during the late katian to rates that were highly volatile and of higher mean value through the silurian reflecting the significantly shorter lifespan of silurian species these patterns are revealed in high resolution rate curves derived from the conop constrained optimization scaled and calibrated global composite sequence of 2094 graptoloid species the end ordovician mass depletion was driven primarily by an elevated extinction rate which lasted for c 1 2 ma with two main spikes during the hirnantian the early silurian recovery although initiated by a peak in origination rate was maintained by a complex interplay of origination and extinction rates with both rates rising and falling sharply the global 13 c curve echoes the graptoloid evolutionary rates pattern the prominent and well known positive isotope excursions during the late ordovician and silurian lie on or close to times of sharp decline in graptoloid species richness commonly associated with extinction rate spikes the graptoloid and isotope data point to a relatively steady marine environment in the ordovician with mainly background extinction rates changing during the katian to a more volatile climatic regime that prevailed through the silurian with several sharp extinction episodes triggered by environmental crises the correlation of graptoloid species diversity with isotopic ratios was positive in the ordovician and negative in the silurian suggesting different causal linkages throughout the history of the graptoloid clade all major depletions in species richness except for one were caused by elevated extinction rate rather than decreased origination rate

some late wenlock and ludlow monograptid graptolites cornwallis island arctic canada seven species of uncompressed latest wenlock and ludlow monograptid graptolites isolated from calcareous concretions are described and illustrated the biostratigraphically important species pristiograptus ludensis of latest wenlock age and saetograptus fritschi linearis and monograptus ceratus of mid ludlow age are illustrated in uncompressed form for the first time the remaining species described include bohemograptus bohemicus tenuis colonograptus colonus saetograptus ex gr chimaera and pristiograptus dalejensis all of ludlow age the last named species is the most common but is biostratigraphically long ranging

carbon and oxygen isotopic composition of silurian brachiopods gotland sweden palaeoceanographic implications abstract one hundred and seventy two non luminescent brachiopod shells from the silurian sequence of gotland were investigated for their carbon and oxygen isotopic composition diagenetic alteration of the shell calcite was excluded by means of petrographic trace element and cathodoluminescence analysis oxygen and carbon isotopic signals vary considerably within the uppermost llandovery to the ludlow average 18o and 13c values of well defined stratigraphic units range from 2 4 to 5 9 and 1 to 8 respectively we observed parallel trends in the carbon and oxygen isotope curves with the most prominent shifts occurring in the lower wenlock upper wenlock and middle ludlow average 18o values 2 4 to 2 9 recorded in the middle ludlow are among the highest 18o values reported for the early palaeozoic the recorded 18o variations cannot solely be explained by changes in sea surface temperature and salinity the variations in the isotopic signals correlate negatively with changes in sea level heavy carbon and oxygen signals coincide with sea level lowstands whereas light signals are recorded during sea level highstands sea level highstands were probably characterized by the formation of warm saline waters on subtropical epicontinental shelves inducing oxygen deficiency in the basins alumshale facies the low 18o values are attributed to 18o depletion in surface waters owing to the storage of 18o enriched saline waters in the basins low 13c values are explained by a low surface water productivity since nutrients were not supplied to the photic zone but rather stored in the deeper ocean during sea level lowstands colder waters that formed in higher latitudes may have represented the main intermediate water source a better ventilation of the basins is documented by the deposition of well aerated sediments whereas the high 18o values are explained by the change in oceanic circulation the high 13c values are attributed to an enhanced primary productivity and possibly to an enhanced burial of corg the model discussed here may provide an attractive scenario for accounting for the recorded short term variations in the isotopic signals without the necessity of introducing an isotopic correction factor for silurian sea water

extent and bathymetry of north american platform seas in the early silurian the north american craton is 25 covered by lower silurian llandovery rocks based strictly upon the geographic area of surviving marine strata preserved in outcrop and the subsurface this figure does not take into account extensive post silurian tectonics and erosion isolated structural basins in which these strata are found today were not necessarily defined as corresponding topographic basins in the silurian analysis of interbasin structural arches and outliers provides important clues as to the actual extent of early silurian seas information on the age of tectonic origin for 15 prominent arches is reviewed the placement and significance of 11 key outliers is also discussed evidence of this kind indicates early silurian platform seas were among the most extensive of the paleozoic probably more than 65 of the north american craton was then flooded nothing on so vast a scale serves as a recent guide to the past the pliocene holocene bahamian banks do provide however worthy models for the role of bathymetry and water circulation as related to the changeover from laterally monotonous blanket deposits to a more complex mosaic of facies the original bathymetry of early silurian environments may be determined correlated and mapped on the basis of widespread carbonate cycles linked to sea level fluctuations the range of fully integrated facies patterns includes 1 coral stromatoporoid stromatolite paleosol cycles williston basin 2 pentamerid brachiopod coral stromatoporoid stromatolite cycles michigan basin and 3 stricklandiid brachiopod pentamerid brachiopod coral stromatoporoid cycles east iowa basin with shallow bathymetries of 0 30 m the williston class tends to represent mosaic facies while with bathymetries of 0 60 m and 10 90 m the deeper water michigan and iowa classes typically involve blanket deposits bathymetry of other basin deposits generally fits one of these three classes maximum and minimum stands in sea level during late llandovery time are represented by bathymetric maps

ordovician and silurian sea water chemistry sea level and climate a synopsis following the cambrian explosion and the appearance in the fossil record of most animal phyla associated with a range of new body plans the ordovician and silurian periods witnessed three subsequent major biotic events the great ordovician biodiversification event the end ordovician extinction the first animal extinction and second largest of the five mass extinctions of the phanerozoic and the early silurian postextinction recovery there are currently no simple explanations for these three major events combined extrinsic geological and intrinsic biological factors probably drove the biodiversifications and radiations and the appearance and disappearance of marine habitats have to be analysed in the frame of changing palaeogeography palaeoclimate and sea water chemistry the present paper reviews the relationships of the three biotic events to chemical and physical processes occurring in the ocean and atmosphere during the ordovician and silurian including sea level changes geochemical proxies 13c 18o 87sr 86sr of the ocean waters and the evolution of the atmosphere oxygen and carbon dioxide content less

the late aeronian graptolite sedgwickii event associated positive carbon isotope excursion and facies changes in the prague synform barrandian area bohemia study of the lower silurian black shale succession of the prague synform has enabled detailed insight into graptolite faunal dynamics and diversity trends from the mid aeronian diversity maximum through to the late aeronian crisis graptolite diversity decreased from 33 taxa in the lituigraptus convolutus biozone to 17 taxa in the upper part of the stimulograptus sedgwickii biozone and newly erected lituigraptus rastrum biozone the graptolite assemblages of the latter biozones exhibit low species richness along with high dominance many graptolite species that became extinct in the early part of the sedgwickii zone were promptly replaced by new forms in the later part of the sedgwickii zone however replacement of extinct species by new forms considerably decelerated the increased rate of graptolite extinction recorded in the convolutus sedgwickii biozone boundary beds coincided with subtle changes in black shale lithologies and a positive shift in 13 c org of 2 2 compared to baseline values sea level drawdown can be inferred from siltstones and or temporary nondeposition in the middle sedgwickii zone this level also sees total organic carbon toc fluctuations and a strong positive 13 c org excursion with a peak shift of at least 7 the sedgwickii event exhibits substantial reorganization of the graptolite fauna its taxonomic impoverishment and concomitant increase in species dominance rather than a sudden collapse of the pre extinction assemblage associated changes in lithology toc and the pronounced 13 c org excursion suggest a relatively extended and probably multi phase period of stressed conditions that affected the pelagic realm inhabited by graptolites in the course of the late aeronian interval

processes controlling the distribution of boron and chlorine in natural waters in iceland abstract the concentrations of b and cl in natural waters in iceland lie in the range 0 001 10 and 1 20 000 ppm respectively lowest concentrations occur in surface and groundwaters in the central highlands highest cl concentrations are found in high temperature waters on the reykjanes peninsula and highest b concentrations in well waters from high temperature geothermal systems in the axial zones of the active volcanic belts the b and cl contents of icelandic basalts are 0 1 6 6 and 75 750 ppm respectively these large variations are considered to result from variable degassing during consolidation as well as concentration variations in the initial magma tholeftes are lowest in both elements av 1 2 ppm b and 170 ppm ci transitional basalts intermediate av 2 1 ppm b and 240 ppm ci and alkali basalts highest av 3 8 ppm b and 340 ppm cl cl b ratios in tholeiites are most often within 25 50 but somewhat lower in alkali basalts most geothermal waters contain b and cl within 0 05 1 and 10 100 ppm respectively these rather low values are attributed to the low content of b and cl in the basaltic rock the b and cl distribution in the icelandic natural waters indicate that these elements act as essentially incompatible their sources of supply include 1 the atmosphere seawater spray and aerosols 2 the rock with which the water interacts 3 seawater groundwater and 4 magma intrusions in surface water and nonthermal groundwater the dominant source of supply of cl is seawater spray and aerosols but the soil and rock contribute often significantly to the b in these waters their cl b ratio is similar to that of seawater 1330 or somewhat lower boron and cl concentrations generally increase with water temperature warm waters cl b ratios intermediate between those of seawater and basalt with increasing temperature this ratio decreases and gradually approaches that of the rock some high temperature geothermal waters have as low cl b ratios as 1 and b concentrations as high as 10 ppm the cause is either b degassing of the magmatic intrusive heat source or phase separation in the producing aquifer some low temperature waters

dynamic interactions between lahars and stream flow a case study from ruapehu volcano new zealand three lahars were sampled in the whan gaehu river on the eastern flank of ruapehu volcano new zealand at 23 5 and 42 km from the source as they were flowing on september 27 and 29 and october 6 1995 the lahars were generated by water explosively ejected from the highly mineralized crater lake we used the chemical contrast between the lahars and resident stream water in their paths to describe a four phase model of a noncohesive lahar wave in a river channel 1 ambient stream water pushed ahead of the lahar in a process of miscible displacement due to hydrodynamic dispersion 2 a zone of mixing between the stream water and the lahar that increases in length with distance from source 3 a remnant of the original lahar least diluted by stream water that decreases in length and dilutes downstream 4 the tail of the lahar surge peak discharge occurs at the end of phase 1 as water is pushed ahead of the lahar peak sediment concentration occurs at the end of phase 2 where debris entrainment by the flow is at its greatest i e in front of the lahar proper deposits record only phases 2 and 3 of the lahar wave phase 1 flow left only a tide line of organic debris and phase 4 deposits were rapidly eroded by later streamflow downstream dilution by stream water eventually caused transformation of phases 2 and 3 of the lahars from debris flow to hyperconcentrated streamflow and then to normal streamflow as the flows became progressively finer grained and more turbulent

palaeoclimate perturbations before the sheinwoodian glaciation a trigger for extinctiond during the ireviken event telychian to sheinwoodian conodonts pterospathodus eopennatus ssp n 1 zone through the ozarkodina sagitta rhenana superzone were studied in detail for their oxygen isotope composition the upper kockelella ranuliformis and ozarkodina sagitta rhenana zones represent the peak interval of the sheinwoodian positive 18oapatite excursion reflecting the coolest conditions with marine sea water temperatures decreased by more than 6 c in the subtropics the 18oapatite data cover pre through post ireviken event strata the study includes also material from younger levels up to the late wenlock ctenognathodus murchisoni zone however this record is incomplete with one major hiatus reflecting the regression associated with the middle silurian mulde event the stratigraphic levels of the analyzed conodont samples from estonia can be correlated with high precision to the datum points of the ireviken event strata in the lower and upper visby formations on gotland sweden inferred short term climatic changes in the upper telychian part of the studied interval may have been caused by phases of major volcanic activity along the caledonian front across the ireviken event we observe variations in oxygen isotope ratios which allow a direct comparison to the stepwise extinctions and faunal reorganisations in different groups our data suggest that faunal extinctions are connected to time intervals of warming before the establishment of more stable and cooler conditions during the main sheinwoodian glacial the most severe extinctions and faunal turnovers at datum points 2 and 4 occurred during the early warmer interval of the event after the shift into the sheinwoodian icehouse in the lower kockelella ranuliformis zone reflected by rapidly decreasing sea water temperatures faunas restabilized and reefal communities started to flourish sedimentary evidence for the glaciation is discussed for different palaeolatitudes less

early silurian wenlockian δ13c profiles from the cape phillips formation arctic canada and their relation to biotic events geochemical data from the cape phillips formation arctic canada are examined in association with three silurian biotic crises in the graptolite community the early wenlockian ireviken mid wenlockian cyrtograptus lundgreni and end wenlockian colonograptus ludensis extinction events positive 13corg excursions are associated with the ireviken and c lundgreni events but not the co ludensis event the ireviken and c lundgreni excursions are recognized worldwide and are herein interpreted to be the result of carbonate weathering in response to eustatic sea level drop the c lundgreni excursion is of greater magnitude in the more proximal basin margin section at abbott river cornwallis island and is explained by the amplification of a more strongly positive 13c signature in shallower parts of an epeiric basin during increased exposure and weathering of the carbonate shelf excursion c5 within the c praedeubeli c deubeli zone is also of regional significance as it occurs in both the abbott r

an oceanic model for lithological and faunal changes tested on the silurian record a model for oceanic cycles is presented the cycles are expressed as changes between more humid low latitude and cooler high latitude climates p episodes and dryer low latitude and warmer high latitude climates s episodes the cyclicity may be self regulating through changes in the co 2 storage capacity of the deep ocean due to temperature changes and through changes in the oceanic input and output of dissolved carbonate the model permits over 30 predictions regarding observable changes in both deep water and shelf lithologies and variations in the abundance diversity and extinction rate of planktic and benthic faunas sedimentary changes involve fluctuations in the rate of clay deposition and carbonate production the advance and retreat of carbonate deposition on the shelf edge the timing of oolite reef and black shale formation and changes between oxic and anoxic deep water faunal effects include both iterative evolution and intermittently widespread taxa lazarus taxa these predictions agree well with changes observed in well known sequence of wenlock and ludlow age as well as changes seen in selected older and younger sequences

early silurian glaciation along the western margin of gondwana peru bolivia and northern argentina palaeogeographic and geodynamic setting the record of the ordovician silurian transition within the southern peru bolivia palaeozoic basin extending across peru bolivia and northern argentina is characterized by a diamictite bearing unit which overlies several different ordovician units and underlies mid silurian shales we review the lithostratigraphy sedimentology and biostratigraphy of this unit revising stratigraphic relationships and several ideas and interpretations previously proposed analysis of facies and lithofacies associations allow for a reinterpretation of sedimentary processes and environments involved during its deposition turbidite and shale interbeds within the diamictites indicate a deep marine environment with interbedded mud flows debris flows slumps and large displaced slabs providing evidence for sediment instability and resedimentation chitinozoan biostratigraphy indicates a llandovery age in contrast with previous proposals of a hirnantian age and suggests the need for more detailed sedimentologic and biostratigraphic studies and a reassessment of this diamictite unit in relation to adjacent regions in south america the resedimented character of the deposit explains some of the ordovician fauna previously described which must be considered as recycled from underlying units in situ fauna needs to be reassessed as it may be endemic diachronic and or indicative of migrations within gondwana glacially faceted and striated clasts as well as large granitoid boulders within the resedimented materials provide evidence for glaciation of the source area and are interpreted as recycled from former glacigenic deposits the evidence found in the central andes indicates a glaciomarine origin for the diamictites and corroborates glaciation of a western source area prior to the late llandovery telychian the precise age of glaciation in this part of gondwana cannot be confirmed do to a lack of true tillites tectonic deformation and the resulting relief are respectively identified as the origin for sediment instability and for local glaciation along the active margin of western gondwana during the late ordovician and early silurian the new data imply that the ordovician silurian boundary was not preserved in some areas of the basin and that an erosional hiatus disconformity with variable regional significance is present between different ordovician units and the diamictite unit late ordovician late caradoc early ashgill euxinic black shales locally present in the central altiplano and eastern cordillera of bolivia may represent the youngest ordovician unit in the region and more research should be focused on them paleogeographic reconstruction of the early silurian peru bolivia basin depicts the extension of the diamictite unit southwards into northern argentina and western paraguay connecting with the parana basin through the asuncion arch to the north it continued into northern peru and ecuador connecting with the silurian record in colombia and venezuela and to the northeast into brazil solimoes and amazonas basins the sedimentary record of glaciation in the peru bolivia basin was due to the development of local ice fields to the west of the basin related with tectonism and resulting reliefs along the active margin of gondwana and probably did not coincide with the development of the north african late ashgillian ice cap

comparing oxygen isotope records of silurian calcite and phosphate δ18o compositions of brachiopods and conodonts oxygen isotope compositions of silurian calcitic brachiopod shells from gotland are compared with those of phosphatic inarticulate brachiopod shells and conodonts from identical stratigraphic horizons the 18ophosphate values of inarticulate brachiopod shells vary widely 13 0 to 17 5 v smow and are significantly lower than those of coeval conodont samples 17 5 to 19 5 v smow conodont samples from individual beds have homogenous 18ophosphate values with variations close to the analytical precision 0 2 together with a significant correlation of conodont 18ophosphate and articulate brachiopod shell 18ocarbonate values r 0 85 this observation suggests that primary marine oxygen isotope compositions are better preserved in conodont apatite than in inarticulate brachiopod shell apatite however with decreasing 18ocarbonate values the 18ophosphate values of conodonts are higher than expected for theoretical isotopic equilibrium with brachiopod calcite different habitats of conodonts and brachiopods cannot account for the observed offset in 18o because both organisms were thriving on a broad shallow marine carbonate platform whereas 18ophosphate values of silurian conodonts are close to 18ophosphate values of modern and mesozoic tropical biogenic apatites most silurian calcitic brachiopod shells from gotland are depleted in 18o when compared to modern or mesozoic brachiopods we therefore suggest that silurian conodonts from gotland record paleotemperature and 18o of silurian sea water more faithfully than coeval calcitic brachiopod shells

integrated biostratigraphy of the lower silurian of the kolka 54 core latvia integrated graptolite conodont and chitinozoan biostratigraphical data are presented from the llandovery and wenlock of the kolka 54 core latvia correlations between graptolite and chitinozoan biozones are consistent with those published from other east baltic sections and the welsh basin while most correlations between graptolite and conodont biozones agree with those presented in previous studies there are important exceptions significantly we report here the discovery of distomodus staurognathoides biozone conodonts in the lowest aeronian demirastrites triangulatus graptolite biozone the base of the d staurognathoides biozone was previously considered to lie much higher in the aeronian also it is shown that walliserodus survived the late wenlock mulde event during which it was considered previously to have become extinct

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

uncompressed specimens of monograptus turriculatus barrande 1850 from cornwallis island arctic canada isolated specimens of monograptus turriculatus barrande 1850 have been recovered from calcite concretions of the turriculatus zone late llandovery from the cape phillips formation canadian arctic islands the sicula shows ventral as well as dextral lateral curvature and the thecae show a pronounced lateral asymmetry this asymmetry is manifest as a tear shaped aperture a long laterally directed spine on the outer apertural margin and a shorter ventrally directed spine on the inner apertural margin the latter spine is totally absent on the proximal thecae monograptus sedgwickii portlock 1853 is suggested as a possible ancestor to m turriculatus

hydrogeochemistry of the thermal waters from the yenice geothermal field denizli basin southwestern anatolia turkey abstract the chemical and isotopic properties of thermal waters kamara and cizmeli and cold springs from the yenice geothermal field ygf in southwestern anatolia turkey are investigated in order to establish a conceptual hydrogeochemical hydrogeological model these thermal waters derive from menderes metamorphic rocks and emerge along normal faults they are commonly used for heating of greenhouses and bathing facilities discharge temperatures of thermal waters are 32 c to 57 c mean 51 c for kamara and 35 c to 68 c mean 47 c for cizmeli whereas deep groundwaters are 15 c to 20 1 c mean 17 c and shallow groundwaters are 12 to 16 c mean 15 c kamara and cizmeli thermal waters are mostly of na ca hco3 so4 type whereas deep groundwaters are ca mg hco3 and mg ca hco3 types and shallow groundwaters are mainly mg ca so4 hco3 and ca mg hco3 types in the reservoir of the geothermal system dissolution of host rock and ion exchange reactions changes thermal water types high correlation in some ionic ratios e g na vs cl k vs cl hco3 vs cl and high concentrations of some minor elements e g as sr b cl f in thermal waters likely derive from enhanced water rock interaction water samples from ygf have not reached complete chemical re equilibrium possibly as a result mixing with groundwater during upward flow geothermal reservoir temperatures are calculated as 89 102 c for kamara and 87 102 c for cizmeli fields based on the retrograde and prograde solubilities of anhydrite and chalcedony based on the isotope and chemical data a conceptual hydrogeochemical hydrogeological model of the ygf has been constructed very negative 18o and 2h isotopic ratios kamara mean of 8 43 and 56 9 respectively and cizmeli mean of 7 96 and 53 7 respectively and low tritium values

the generative phase and the first radiation event in the early silurian monograptid history abstract the generative phase in the monograptid history that is a period between the appearance of the uniserial colony the persculptograptus persculptus biozone and the first radiation event the cystograptus vesiculosus biozone shows neither morphological nor taxonomical variety in the rhabdosomal and thecal structure it is characterized by the speciation events in the single atavograptus linage these events coincide with the recovery phase of the early silurian diplograptids and are associated mostly with deep water environments within the marginal basins in the low latitude equatorial belt the monograptid radiation in the c vesiculosus biozone is well represented in the bornholm and south urals sections koren and bjerreskov 1997 it resulted in a significant increase in diversity of derived thecal morphologies based on a simple atavograptus primitivus morphotype some important morphological novelties that were typical for almost all early monograptids such as the position of the theca 1 bud at the metasicula were also introduced in several akidograptid and dimorphograptid lineages within the parakidograptus acuminatus and c vesiculosus biozones the vesiculosus radiation led to geographical and ecological expansion of monograptids which became globally recognizable within the epipelagic and marginal basins in the low to moderate palaeolatitudes

new upper homerian uppermost wenlock silurian monograptids from arctic canada five species of new or little known upper homerian uppermost wenlock graptolites are described from the arctic islands these are lobograptus sherrardae sherwin lobograptus aff sherrardae lobograptus claudiae koren lobograptus cf cornuatus lenz and pristiograptus schedidoneus n sp the first and last named species range through the pristiograptus praedeubeli and pristiograptus ludensis biozones that is through the entire upper homerian whereas the remaining three species appear to be confined to the older p praedeubeli biozone these species further document the rapid global evolution of the late homerian graptolites and this study records lobograptus claudiae koren from outside central asia for the first time

late ordovician early silurian ashgillian llandovery sea level curve derived from conodont community analysis anticosti island quebec abstract earlier workers have established sea level curves for the ashgillian llandovery sequence on anticosti island quebec canada based on sedimentology and on brachiopod and reef communities the complete anticosti sequence has been collected for conodonts to provide a database of over 77 600 conodonts derived from 272 samples through the 800 1100 m sequence this paper uses a statistical analysis of the database to establish the pattern of conodont communities and their interpreted water depths this allows the establishment of a eustatic sea level curve for the sequence this curve is in general agreement with those of the earlier workers but is more detailed and better constrained stratigraphically given the large sampling program the curve reflects more oscillating sea level changes for the whole sequence than those constructed earlier and different water depths for certain intervals from those established earlier the curve is valuable given that the anticosti sequence is one of the most complete in the world for this interval and its divergence from global eustatic curves for this interval is noted

paleoenvironmental changes in the silurian indicated by stable isotopes in brachiopod shells from gotland sweden ratios of stable carbon and oxygen isotopes in brachiopod shells more than 370 specimens esp atrypa reticularis from the silurian of gotland sweden have been analysed preservation of biological skeletal ultrastructures observed in sem micrographs and cathodoluminescence analyses indicate that usually no diagenetical alteration occurs the silurian of gotland consists of 440 m carbonate deposits spanning the late llandovery to late ludlow epochs 431 411 m y repeatedly uniform sequences of micritic limestones and marks are interrupted by complex structured reefs and adjacent platform sediments previously the alteration of facies is interpreted as the result of sea level fluctuations caused by a gradual regression with superimposed minor transgressive pulses the silurian sequence of gotland exhibits principally parallel carbon and oxygen isotope records corresponding closely to the topostratigraphic units lower values occur in periods dominated by deposition of marly sequences higher values are observed in periods dominated by reefs and extended carbonate platforms the isotope ratios are influenced by local as well as global factors the oxygen isotope ratios are interpreted to reflect paleosalinity changes due to varying freshwater input rather than changes in paleotemperature consequently the facies distribution of gotland is interpreted as resulting from changes in terrigenous input caused by different rates of continental weathering and freshwater runoff rather than by sea level fluctuations periods of arid climate and therefore anti estuarine downwelling of oxygenated surface water appear as short episodes of reef growing 1 5 m y in an epoche characterized by a tropic humid climate which causes an estuarine circulation and the upwelling of co2 rich deep water carbon isotope ratios are obviously connected to these changes in circulation by the advection of 13c rich surface water arid episodes or upwelling of 13c depleted deep water humid episodes of a silurian ocean which itself reveals generally euxinic deep water conditions due to the burial of organic carbon in black shales

the silurian of gotland sweden facies interpretation based on stable isotopes in brachiopod shells the silurian of gotland sweden consists of 440 m of carbonate deposits repeatedly uniform sequences of micritic limestones and marls are interrupted by complex structured reefs and by adjacent platform sediments generally the alteration of facies is interpreted as the result of sea level fluctuations caused by a gradual regression with superimposed minor transgressive pulses the purpose of this study is a facies interpretation based on both field observations and stable isotope measurements of brachiopod shells approximately 700 samples from stratigraphically arranged localities in different facies areas have been investigated the carbon and oxygen isotopes show principally parallel curves and a close relationship to the stratigraphic sequence lower values occur in periods dominated by deposition of marly sequences higher values are observed in periods dominated by reefs and extended carbonate platforms the oxygen isotope ratios are interpreted to reflect paleosalinity changes due to varying freshwater input rather than to paleotemperature carbon isotope ratios are believed to have been connected to global changes in the burial of organic carbon in black shales during periods of euxinic deep water conditions consequently the facies succession on gotland results from global paleoclimatic conditions changes in terrigenous input due to different rates of weathering and freshwater runoff rather than sea level fluctuations control the carbonate formation of the silurian on gotland

upper homerian wenlock silurian graptolites and graptolite biostratigraphy arctic archipelago canada integration of graptolite data obtained from isolated and flattened material from arctic canada permits the recognition of three upper homerian biostratigraphic zones these from oldest to youngest are the pristiograptus dubius gothograptus nassa interval biozone colonograptus praedeubeli colonograptus deubeli biozone and colonograptus ludensis biozone species of flattened graptolites described in this study include c deubeli c ludensis c praedeubeli colonograptus schedidoneus lobograptus angustus n sp lobograptus claudiae lobograptus sherrardae plectograptus macilentus agastograptus clathrospinosus and gothograptus nassa with only a few exceptions the zone by zone diversity of monograptid and plectograptine graptolites of the canadian arctic is remarkably similar to that elsewhere

palaeocope ostracods from the silurian wenlock series of arctic canada silurian wenlock series deposits of the cape phillips formation on baillie hamilton island and cornwallis island arctic canada have yielded a silicified ostracod assemblage that spans the late sheinwoodian and homerian stages sixteen palaeocope ostracod species are recorded including the new species beyrichia beyrichia marssae gabrielsella copelandi and platybolbina abruptobolbina adraini the ostracod faunas can be linked into local trilobite microvertebrate and graptolite zonal schemes and a few of the ostracod species offer potential for local and perhaps wider biostratigraphical correlation the ostracods are mostly known only from the cape phillips formation but also include two taxa found in the wenlock series of the avalanche lake area northwest territories canada other ostracod species suggest links with silurian successions in northern canada and the baltic low diversity ostracod faunas characterize the level of a marked positive carbon isotope excursion and coeval mid homerian

lower paleozoic stratigraphic and biostratigraphic correlations in the canadian cordillera implications for the tectonic evolution of the laurentian margin the ancient laurentian margin rifted in the latest neoproterozoic to early cambrian but appears not to have developed as a simple passive margin through a long post rift drift phase stratigraphic and conodont biostratigraphic information from four platform to basin transects across the margin has advanced our knowledge of the early paleozoic evolution of the margin in northeastern british columbia two northern transects span the macdonald platform to kechika trough and ospika embayment and a third transect spans the parautochthonous cassiar terrane in the southern rocky mountains new conodont biostratigraphic data for the ordovician succession of the bow platform is correlated to coeval basinal facies of the white river trough in total from 26 stratigraphic sections over 25 km of strata were measured and 1200 conodont samples were collected that yielded over 100 000 conodont elements key zonal species were used for regional correlation of uppermost cambrian to middle devonian strata along the cordillera the biostratigraphy temporally constrains at least two periods of renewed extension along the margin in the latest cambrian and late early ordovician alkalic volcanics associated with abrupt facies changes across the ancient shelf break intervals of slope debris breccia deposits and distal turbidite flows suggest the margin was characterized by intervals of volcanism basin foundering and platform flooding siliciclastics in the succession were sourced by a reactivation of tectonic highs such as the peace river arch prominent hiatuses punctuate the succession including unconformities of early late ordovician sub llandovery possibly early to middle silurian and early devonian ages

biostratigraphical correlation and the stages of the llandovery the problems of defining biozones are discussed and the definitions of holland et al 1978 are considered unsatisfactory an ideal methodology of biostratigraphical correlation is outlined and is contrasted with existing practice as exemplified by recent decisions of the subcommission on silurian stratigraphy relating to stages of the llandovery series the numbers of species in the different llandovery graptolite biozones and the proportions of zonally diagnostic species at the inter biozone boundaries are tabulated the llandovery area is considered unsuitable for the establishment of stages and the stratotypes for the aeronian and telychian are considered unsatisfactorily defined in relation to graptolite zonation

the ireviken event in the lower silurian of gotland sweden relation to similar palaeozoic and proterozoic events abstract for a long time the silurian was thought to represent a time of stable environmental conditions in the greenhouse period that followed the late ordovician glaciation during the past decade knowledge about the silurian has increased markedly and today it is known that the conditions in the silurian were much more variable than previously assumed detailed isotopic investigations have revealed several distinct positive excursions in both carbon and oxygen isotope values in low latitudes these periods of high c and o isotope values are in many cases characterised by the growth of reefs and the formation of extended carbonate platforms the sediments deposited during these excursions contain impoverished fossil assemblages especially with respect to conodonts graptolites and trilobites a conspicuous isotope excursion coincident with facies changes and a marked mass extinction is observed near the llandovery wenlock boundary this event is called the ireviken event after its type locality on the island of gotland sweden jeppsson l 1987 in palaeobiology of conodonts ellis horwood ltd chichester pp 129 145 here isotope data from nine sections at the nw coast of gotland are presented that cover the time interval of the ireviken event the 13c mean values rise from 1 4 to 4 5 and the 18o values increase from 5 6 to 5 0 the relative timing of stable isotope development extinctions and facies development is discussed it is shown that first extinctions precede the isotope excursion this indicates that extinction events and stable isotope development are only indirectly connected but might reflect the same causes other events characterised by similar relationships between positive isotope excursions mass extinctions and facies development are found in younger parts of the silurian late wenlock and ludlow in the late ordovician the late cambrian and with some reservations in the proterozoic the similarities between these events indicate analogous controlling mechanisms for the silurian climatic changes between humid and arid conditions in low latitudes were postulated in an earlier study of the authors a palaeoceanographic climatic model was postulated which is consistent with most of the sedimentological palaeontological and geochemical data here we demonstrate that this model may be applicable also for the older events

graptolite biozone correlation charts charts are presented showing the correlation of graptolite biozonations for the lower ordovician to lower devonian i e for the entire stratigraphical range of the planktonic graptoloid graptolites regions chosen are those for which the most detailed biostratigraphical studies have been undertaken for baltica average graptolite zone chron duration appears to vary from c 300000 years ludlow epoch to 2 4 ma lochkovian epoch

the 2007 eruption of kelut volcano east java indonesia phenomenology crisis management and social response we focus in this paper on the processes and consequences of an unusual volcanic eruption at kelut volcano east java in november 2007 after two months of worrying precursor signs kelut volcano erupted but neither explosions nor the usual hazards observed during the historic eruptions happened e g ash falls volcanic bombs and pyroclastic flows instead of an explosive eruption the 2007 eruption was extrusive given than such an eruption could not be predicted the authorities had to manage a new situation we conducted interviews with nine stakeholders of the crisis management team and undertook a questionnaire based survey in the settlement nearest to the crater in order to understand how the authorities managed the crisis and how people reacted inquiries and questionnaires were carried out shortly after the end of the evacuation process when the volcano was still under surveillance for fear of an explosive phase the results display a real gap in what it takes to manage a crisis or live through a crisis this suggests that the unusual eruption pattern of kelut volcano was not the only factor of the misunderstanding between the authorities and the population these problems stem from more structural causes such as the lack of communication and information when there is a need to adapt to a new scenario in such a situation the inability of the crisis management system to take decisions underscored the intrinsic vulnerability of the population despite a hierarchical and strategic top down crisis management approach

the silurian graptolite zonation of china china is divided into five silurian stratigraphic regions on the basis of biostratigraphy and lithostratigraphy these regions are zhungar xingan region northwest china region xizang tibet western yunnan region yangtze region and the south china region twenty four graptolite zones are now recognized in the silurian of china the earliest silurian graptolite zones include the persculptus acuminatus and vesiculosus zones characterized by an akidograptid dimorphograptid sub fauna these are followed by the cyphus gregarius convolutus and sedgwickii zones characterized by a rastritid subfauna the late early silurian zones include the turriculatus zone with a spirograptid subfauna and the crispus griestoniensis and spiralis grandis zones bearing a streptograptid subfauna the middle silurian is characterized by a cyrtograptid subfauna which is divided into 10 zones known in ascending order as the lapworthi sakmaricus insectus centrifugus murchisoni riccartonensis rigidus flexilis

the lichid trilobite radiolichas in the silurian of arctic canada and gotland sweden radiolichas has been a poorly known and exclusively devonian genus of very limited diversity radiolichas raydaviesi sp nov and r davedaviesi sp nov are the best known members of the genus and extend its stratigraphic and geographic range to the wenlock of the central canadian arctic a further silurian occurrence is an unnamed species from the wenlock slite beds of gotland sweden radiolichas is most similar to dicranogmus together the genera lack any of the robust trochurine apomorphies linear pygidial postaxial ridge prominent pygidial border prominent cranidial fossula and appear to fall outside the phylogenetic structure of that subfamily they are similar to members of the tetralichinae particularly in pygidial features but lack the composite cranidial lobe characteristic of that subfamily their systematic position is presently unresolved

carbon isotope excursion near the wenlock ludlow silurian boundary in the anglo welsh area oxygen and carbon isotope analyses have been performed at close sampling intervals on rocks from several exposures that show the boundary between the wenlock and ludlow series in the classic silurian areas of wales the welsh borderland and the west midlands of england our data indicate a monotonic decline in 13 c from positive to negative values across the boundary between the much wenlock limestone formation wenlock series and the lower elton formation ludlow series and correlatives in all sites investigated a slightly earlier negative excursion is also present in the upper wenlock strata of two of these localities both negative 13 c excursions appear to be contemporaneous with episodes of increased ocean ventilation and eustatic sea level lowstand postulated by kemp at least one and possibly both of the late wenlock carbon isotope depletions can also be related to the decline in pelagic graptolite diversity the distribution of the carbon isotope depletion in both carbonate platform and off shelf facies implies that this trend is unlikely to have been caused by local diagenetic alteration isotope chemostratigraphy may also provide an extra correlation tool that can be integrated with traditional biostratigraphic methods for silurian strata

two new graptolites from the early silurian llandovery aeronian of central wales an origin for monoclimacid thecal morphology

early silurian sea level changes global sea level fluctuated markedly during the early silurian probably as a result of the waxing and waning of ice sheets in the south american portion of gondwana the highest sea levels of the silurian are recorded by the telychian upper crispus lower griestoniensis and spiralis lower lapworthi biozones other highstands occurred in the early aeronian during the convolutus zone mid aeronian guerichi zone and late turriculatus zone early telychian and early sheinwoodian low sea levels characterized much of the argenteus and sedgwickii zones aeronian the utilis subzone late guerichi early turriculatus zones early telychian the late telychian commencing in the mid lapworthi zone and after a period of apparently only small amplitude sea level fluctuations in the late sheinwoodian and earliest homerian the mid late homerian in particular the early nassa zone facies and faunal changes in the lower silurian do not support the p and s model of jeppsson and others but are consistent with the sea level changes proposed herein mid telychian marine red beds appear to have been deposited during a minor sea level fall immediately after a period of very high sea levels rather than during a transgressive episode as previously suggested comparison of the sea level curve presented herein with those constructed in the past is hampered by the lack of precision currently possible in the correlation of early silurian deep water graptolitic and shallow water shelly sequences improving the precision of this correlation should be a priority for future research

revision of the position of the ordovician silurian boundary in southern ontario regional chronostratigraphic implications of δ13c chemostratigraphy of the manitoulin formation and associated strata delta c 13 values of 142 samples from the manitoulin formation and subjacent strata collected from 14 exposures and two drill cores on manitoulin island bruce peninsula and the region south of georgian bay suggest that the manitoulin formation is latest ordovician hirnantian rather than earliest silurian in age a delta c 13 excursion identified as the hirnantian isotope carbon excursion hice which has a magnitude of nearly 2 5 parts per thousand above baseline values is present in an interval from the upper queenston formation to the lower to middle part of the manitoulin formation in most of bruce peninsula and in the area south of georgian bay whereas on manitoulin island the rice appears to be absent this indicates that a significant part of the manitoulin formation is older on the bruce peninsula and in its adjacent region than on manitoulin island the chemostratigraphically based conclusions are consistent with biostratigraphic data from conodonts and brachiopods the hirnantian delta c 13 curve from anticosti island quebec is closely similar to those of southern ontario traditionally the ordovician silurian boundary has been placed at the base of the manitoulin formation but the new results suggest that it is more likely to be at or near the base of the overlying cabot head formation these new results have major implications for the interpretation of the geologic history and marine depositional patterns of the latest ordovician of a large part of the north american midcontinent

graptolite biozonation of the wenlock series silurian of the builth wells district central wales the graptolite biozonation of the wenlock series in the builth wells district is reassessed the graptolite fauna is dominated by relatively few but variable species of monograptus s s pristiograptus and monoclimacis these species are mostly long ranging and are of limited biostratigraphical use biozonation is based largely on the relatively rare cyrtograptids the lower wenlock series of the district comprises the widely recognized centrifugus murchisoni and riccartonensis biozones the middle to upper wenlock biostratigraphy differs from that previously recognized in the uk above the riccartonensis biozone dubius rigidus and lundgreni biozones are distinguished separate flexilis and ellesae biozones are not recognized monograptus flexilis appears earlier than then largely co exists with cyrtograptus rigidus s l while cyrtograptus ellesae appears later than cyrtograptus lundgreni the uppermost wenlock nassa ludensis biozone is sparsely fossiliferous its subdivision has not proved possible this revised biostratigraphical scheme for the wenlock series of the builth wells district suggests that the sheinwoodian homerian boundary as defined in the welsh borderland might occur within rather than at the base of the lundgreni biozone however difficulties in correlation with other wenlock sequences particularly overseas suggest significant biofacies control with the wenlock seas of the builth wells district appearing to have been periodically inhospitable to graptolites

worldwide correlation of telychian upper llandovery strata using graptolites the formal boundaries to the telychian stage have been stated to correlate with the bases of the monograptus turriculatus biozone at the bottom and the cyrtograptus centrt ugus biozone at the top the evidence for this however is far from conclusive the telychian has been divided mainly using monograptids into eight or more biozones although fewer have been recognized in britain due to the general paucity of recent studies of the graptolite faunas of this age and to the existence of barren beds high within most british telychian sections each biozone has a duration of only a few hundred thousand years but most are at present difficult to recognize in the absence of the index species or where this species stratigraphical range extends beyond the limits of its biozone intercontinental correlation of telychian strata using graptolites is hampered to a limited extent by provincialism and water mass specificity and considerably by taxonomic problems a thorough taxonomic revision of published species would provide a firm foundation for future biostratigraphical subdivision and correlation of the telychian stage knowledge of telychian graptolite biostratigraphy would also be enhanced by restudies of two classic sections the trannon river section in wales and the bajiaokou section ziyang china the graptoloids offer the potential for some of the finest resolution biostratigraphical subdivision and correlation of strata of any fossil group at any time in the stratigraphical column being rapidly evolving planktic in many cases particularly in the silurian cosmopolitan to a certain degree facies independent and in theory at least readily identifiable to specific level the graptoloids possess the majority of the features required of the ideal zonal fossil this paper outlines the current state of telychian upper llandovery graptolite biostratigraphy the degree of precision possible in international and intercontinental correlation and highlights those areas in which future research might profitably be focused the formal boundaries to the telychian

carbon isotope event markers through the wenlock pridoli sequence at ohesaare estonia and priekule latvia abstract the ohesaare borehole in the northern part of the silurian baltic gulf penetrates shallow and deep shelf marlstones limestones and dolostones the priekule borehole in the deep shelf belt of the basin was drilled through marlstones and graptolitic mudstones most of the successions except the upper part are characterized by a high sr ca ratio close to marine calcites suggesting good preservation of carbonate material conodont alteration indices are low 1 2 carbon isotopes were measured using whole rock samples in the ohesaare core section two distinctive 13 c positive excursions were established one in the early wenlock riccartonensis and low rigidus ellesae standard graptolite zones 4 2 and the second in the late wenlock nassa zone 4 6 before and after the latter there are also intervals with low 13 c values the first just above the lundgreni zone 1 8 and another in the ludensis perhaps reaching into nilssoni zone 3 8 in the priekule section the early wenlock 13 c peak is well represented 3 1 but in the late wenlock early ludlow 13 c values show little variation from 2 0 to 1 in this section a high peak of 13 c values 5 9 was determined in the nova beds correlated with the topmost gorstian and lowermost ludfordian ludlow the carbon isotope positive excursions show good correlation with lows of the global sea level curve and with most of the biotic and supposed climatic events glaciation ocean state

morphology and classification of some early silurian monograptids graptoloidea from the cape phillips formation canadian arctic islands exquisitely preserved early to mid llandovery monograptids have been chemically isolated from calcareous concretions sampled from the cape phillips formation central canadian arctic archipelago they provide morphological information critical in refining the definition of four of the earliest known monograptid genera and in the elucidation of their phylogenetic dispersal through the llandovery monograptid radiation these primitive monograptid genera are defined primarily on the basis of derived thecal form the specific derived thecal and thecal apertural character states used in generic diagnoses are as follows species of atavograptus possess simple geniculate to slightly sigmoidal thecae with a large dorsoventral overlap species of pribylograptus possess thecae bearing lateral apertural lappets that may occur with atavograptus style thecae proximally species of coronograptus possess flared thecal apertures at least part way along the rhabdosome species of lagarograptus have conspicuous tongue

validity and composition of the silurian trilobite genera borealarges and dicranogmus with new species from the canadian arctic new silicified material from arctic canada demonstrates that the lichid trilobite genera borealarges and dicranogmus recently claimed to be synonyms are independent groups with no close phylogenetic connection to one another dicranogmus has been known mainly from cranidia alone prior association of librigenae and pygidia with the arctic canadian species d skinneri has been queried this association is correct beyond reasonable doubt based on description of new material of both d skinneri and a new species three new species of borealarges are related to b tuckerae adrain 1994 cladistic analysis supports the monophyly of this species group pending further new information however the group is retained within the genus borealarges the stratigraphic range of the species group is extended from the lower wenlock sheinwoodian to upper ludlow ludfordian by the discovery of a rare species in the douro formation of cornwallis island arctic canada new taxa from the wenlock of the cape phillips formation arctic canada include dicranogmus wynni borealarges nicoae b warholi and b yulei resume du materiel silicifie nouvellement recolte de l arctique canadien demontre que les genres lichides borealaspis et dicranogmus sont des groupes independants sans lien phylogenetique proche a l encontre de l assertion recente qu ils etaient synonymes dicranogmus n etait connu auparavant que de cranidiums isoles l association de librigenes et pygidiums referes a l espece de l arctique canadien d skinneri a ete mise en doute cette association est exacte au dela de tout doute raisonnable en se basant sur la description de nouveau materiel de d skinneri et d une autre espece trois nouvelles especes de borealaspis sont apparentees a b tuckerae adrain 1994 l analyse cladistique supporte la monophylie de ce groupe d especes par contre dans l attente de nouvelles informations ce groupe est maintenu dans le genre borealaspis la duree stratigraphique de ce groupe d especes est prolongee du wenlock inferieur sheinwoodien au ludlow superieur ludfordien suite a la decouverte d une espece rare dans la formation de douro de l ile cornwallis de l arctique canadien des taxons nouveaux du wenlock de la formation de cape phillips arctique canadien comprennent dicranogmus wynni borealarges nicoae b warholi et b yulei traduit par la redaction adrain 763

lithium isotope geochemistry of sediments and hydrothermal fluids of the guaymas basin gulf of california abstract lithium isotopic compositions of hydrothermally altered sediments of deep sea drilling project dsdp site 477 477a as well as high temperature vent fluids of the guaymas basin have been determined to gain an understanding of lithium exchange during fluid sediment interaction at this sediment covered spreading center unaltered turbidite of the basin has a 6 li value of 10 5 7 heavier than fresh oceanic basalts contact metamorphism induced by a shallow sill intrusion results in a decrease of the lithium content of the adjacent sediments and a lighter isotopic value 8 below the sill sediments altered by a deep seated hydrothermal system show strong depletions in lithium while lithium isotopic compositions vary greatly ranging from 11 to 1 the shift to lighter composition is the result of preferential retention of the lighter isotope in recrystallized phases after destruction of the primary minerals the complexity of the isotope profile is attributed to inhomogeneity in mineral composition the tortuous pathway of fluids and the temperature effect on isotopic fractionation the range of lithium concentration and 6 li values for the vent fluids sampled in 1982 and 1985 overlaps with that of the sediment free mid ocean ridge systems the lack of a distinct expression of sediment input is explained in terms of a flow through system with continuous water recharge the observations on the natural system agree well with the results of laboratory hydrothermal experiments the experimental study demonstrates the importance of temperature pressure water rock ratio substrate composition and reaction time on the lithium isotopic composition of the reacted fluid high temperature authigenic phases do not seem to constitute an important sink for lithium and sediments of a hydrothermal system such as guaymas are a source of lithium to the ocean the ready mobility of lithium in the sediment under elevated temperature and pressure conditions also has important implications for lithium cycling in subduction zones

tsunamis generated by eruptions from mount st augustine volcano alaska during an eruption of the alaskan volcano mount st augustine in the spring of 1986 there was concern about the possibility that a tsunami might be generated by the collapse of a portion of the volcano into the shallow water of cook inlet a similar edifice collapse of the volcano and ensuing sea wave occurred during an eruption in 1883 other sea waves resulting in great loss of life and property have been generated by the eruption of coastal volcanos around the world although mount st augustine remained intact during this eruptive cycle a possible recurrence of the 1883 events spurred a numerical simulation of the 1883 sea wave this simulation which yielded a forecast of potential wave heights and travel times was based on a method that could be applied generally to other coastal volcanos

silurian δ13c stratigraphy a view from north america three positive shifts in 13 c are recognized in well dated carbonate successions in north america and can be confidently correlated with shifts in the baltic region by using conodont and graptolite zonations the 13 c excursions reach distinct peaks of 3 to 4 at the ends of the amorphognathoides and siluricus conodont zones and within the ludensis graptolite zone the three events are associated with the most significant extinction horizons in the silurian and occur near clastic carbonate transitions that mark eustatic or oceanographic changes the magnitudes of the two oldest 13 c peaks compare well with the baltic region however the end siluricus excursion reaches far greater values of as much as 11 in sweden likely reflecting local modification of the global seawater signature

wenlock silurian graptolite biostratigraphy of the cape phillips formation canadian arctic islands the canadian arctic islands wenlock is represented by a diverse assemblage of graptolites from the cape phillips formation cyrtograptids are continuously present throughout all but the uppermost wenlock species of cyrtograptus constitute the main basis for biostratigraphic zonation supported to a much lesser degree by monograptus monoclimacis and pristiograptus through most of the series the uppermost wenlock is dominated by pristiograptus in association with rare gothograptus the following biostratigraphic zones and their correlations are proposed 1 cyrtograptus centrifugus cyrtograptus insectus zone earliest wenlock 2 cyrtograptus aff rigidus monograptus aff riccartonensis zone late early wenlock 3 cyrtograptus perneri monograptus cf munchi zone in which cyrtograptus multiramis is a particularly common element mid wenlock age 4 cyrtograptus lundgreni monograptus testis zone divisible into a lower monograptus testis n ssp and an upper monograptus testis testis subzon

a new ordovician silurian boundary section in san juan province argentina and its definitive graptolite fauna bed by bed collecting of the la chilca formation at talacasto san juan argentina has revealed a sequence spanning the ordovician silurian boundary and the recognition of the following graptolite zones glyptograptus persculptus probable parakidograptus acuminatus and possible atavograptus d the talacasto section thus allows the closest definition of the ordovician silurian boundary in south america the shales of the la chilca formation are 3 65 m thick rich in graptolites and have allowed us to recognize for the first time in south america several stratigraphically important forms glyptograptus persculptus climacograptus angustus c normalis c acceptus c rectangularis and paraclimacograptus innotatus also identified for the first time are rhaphidograptus and lagarograptus the following are described talacastograptus leanzai gen et sp nov pseudoclimacograptus metaclimacograptus robustus sp nov and lagarograptus praeacinaces sp nov the closest affinity of the new biserial genus is considered to be with pseudoclimacograptus the evolutionary relationships of the three new graptolites are briefly discussed

evolution of the early paleozoic cordilleran margin of laurentia tectonic and eustatic events interpreted from sequence stratigraphy and conodont community patterns several field seasons in the canadian cordillera have allowed the measurement description and sampling of over 20 000 m of lower paleozoic strata from 26 stratigraphic sections across four platform to basin transects with the recovery of over 100 000 conodonts from more than 1200 4 5 kg samples this work was part of the lithoprobe slave northern cordillera lithospheric evolution snorcle project but is also being extended through a pan lithoprobe project to understand the tectonic and eustatic response of much of the laurentian plate through the early paleozoic based on the abundant field data the complex stratigraphic framework is interpreted in terms of sequence stratigraphy and a derived relative sea level curve using detailed conodont taxonomic and biostratigraphic results cluster analysis of conodont distributional data identified an evolving series of conodont communities through space and time these communities were partitioned across the platform to basin gradient and provide an additional sensitive indicator of relative sea level change these two independent approaches generated comparable eustatic curves for this cordilleran laurentian margin during much of the early paleozoic and identified some global eustatic events noted by earlier workers this part of laurentia was not a simple passive margin during the early paleozoic but rather was affected by four main tectonic events complicated by six principal eustatic changes some success was achieved in filtering the global and regional tectonic eustatic effects and in proposing causes for some of the events

δ18o composition of conodont apatite indicates climatic cooling during the middle pridoli phosphatic microfossils such as conodonts and fish microremains dermal scales from the upper silurian pridoli of lithuania have been studied for their oxygen isotope composition the conodont c

residence time indicators in groundwater the east midlands triassic sandstone aquifer the east midlands triassic sherwood sandstone aquifer which has been the subject of detailed radiometric age studies is used to investigate both inert and reactive constituents of groundwater as indicators of residence time detailed resampling of the aquifer in 1992 has provided a considerable body of new inorganic geochemistry data though without radiocarbon several inert indicators are defined including the isotopic ratios 18o 2h 36cl noble gas ratios as well as the halogen elements cl br f i and their element ratios these form a group of essentially unreactive tracers primarily reflecting changing rainfall inputs and palaeoclimatic conditions except at outcrop where human impacts are also seen clearly the concentrations of cl mainly from atmospheric sources remain below 25 mg l 1 cl over a distance of some 30 km from outcrop reactive indicators the result of time dependent water rock interactions include 13c mg ca sr ca na cl and show diagnostic trends along the flow lines however the concentrations of certain trace elements li rb cs mn and mo which are not limited by solubility constraints show linear trends along the present day flow gradient this water rock interaction is taking place in groundwaters with low total mineralisation and it can be demonstrated that reactions involving these elements and isotopes are occurring entirely within the aquifer since high salinity groundwaters are found below the sherwood sandstone there is good correlation between some of the elements and 14c activities in the 1977 data set and this has been used to derive a concentration age relationship for the 1992 set of data a chemical timescale for the aquifer is then established using a li and b a combination of five trace elements the age of the fresh groundwater is thus shown to be up to 100 ka bp indicating the likelihood of semi continuous recharge during the devensian glacial period preceding the glacial maximum when no recharge occurred 10 20 ka bp this approach may be of value in extending groundwater dating beyond the radiocarbon timescale as well as interpreting sites where no radiocarbon data are available the scatter from the mean age line indicates those groundwaters which are derived from either rapid or slower than average flow zones within the aquifer as well as age stratification this stratification is borne out by a depth profile of groundwater from a new borehole near to outcrop which is shown by a combination of chemical and isotopic tracers to contain holocene overlying late pleistocene water

downstream dilution of a lahar transition from debris flow to hyperconcentrated streamflow nearly instantaneous melting of snow and ice by the march 19 1982 eruption of mount st helens released a 4 106 m3 flood of water from the crater that was converted to a lahar volcanic debris flow through erosion and incorporation of sediment by the time it reached the base of the volcano over the next 81 km that it traveled down the toutle river the flood wave was progressively diluted through several mechanisms a transformation from debris flow to hyperconcentrated streamflow began to occur about 27 km downstream from the crater when the total sediment concentration had decreased to about 78 by weight 57 by volume the hyperconcentrated lahar runout flood wave transporting immense quantities of sand in suspension continued to experience progressive downstream dilution although turbulence was significantly dampened by the extremely high suspended load very large standing waves and antidune waves were observed the hyperconcentrated lahar runout flow deposited an unusual faintly stratified coarse sand which locally contained small isolated gravel lenses very similar deposits in the quaternary stratigraphy of mount st helens and other cascades volcanoes suggest that lahars may be more frequent than previously recognized

integrated biostratigraphy of the lower silurian of the aizpute 41 core latvia integrated graptolite conodont and chitinozoan biostratigraphical data is presented from the rhuddanian through to lower sheinwoodian of the aizpute 41 core latvia correlation of the biozonation schemes based upon the three groups is achieved from the cyphus through to lowermost riccartonensis graptolite biozones except for the upper aeronian and lower telychian which lack both chitinozoans and graptolites and upper lapworthi through to approximately base murchisoni graptolite biozone where there is interpreted to be an unconformity datum 2 of the ireviken event is correlated with a level at the base of or within the murchisoni biozone it is possible that the changes in conodont assemblages at datum 2 on gotland are the result of an unconformity here streptograptus kaljoi sp nov from the lower spiralis graptolite biozone is described

nd isotope evolution of archaean plutonic rocks in southeastern superior province the opatica plutonic belt abitibi greenstone belt and pontiac subprovince represent a major proportion of the southeastern superior province which was formed and accreted rapidly between approximately 2 9 and 2 8 ga plutons in these belts are grouped into four types i trondhjemite tonalite granodiorite ttg suite 2 82 2 69 ga ii monzodiorite mzd suite 2 697 2 669 ga iii late alkaline granitoid alk suite 2 68 2 67 ga and iv anatectic granite and monzonite ana suite 2 69 2 64 ga the four suites are represented in all belts and show similar petrography and geochemistry in terms of nd isotope composition the ttg mzd and alk suites are typical of destructive plate margin magmatism and have 1 4 initial end 3 7 values which are very similar to that of the abitibi mantle end 2 5 the lower values for the ana suites end 0 1 to 2 4 result from recycling of crustal components in the opatica belt the ana granitoids fall on the nd isotope evolution curve defined b

multivariate statistical analysis of geochemical data as indicative of the hydrogeochemical evolution of groundwater in a sedimentary rock aquifer system summary the study of groundwater hydrogeochemistry of the paleozoic basses laurentides sedimentary rock aquifer system in quebec produced a large geochemical dataset groundwater samples were collected at 153 sites over a 1500 km2 study area and analyzed for major and minor ions the large number of data can lead to difficulties in the integration interpretation and representation of the results two multivariate statistical methods hierarchical cluster analysis hca and principal components analysis pca were applied to a subgroup of the dataset to evaluate their usefulness to classify the groundwater samples and to identify geochemical processes controlling groundwater geochemistry this subgroup consisted of 144 samples and 14 parameters ca2 mg2 na k hco 3 cl so 4 2 fe2 mn2 br sr2 f ba2 hs seven geochemically distinct clusters c1 c7 resulted from the hca samples from clusters c3 c4 c6 and c7 are mostly located in preferential recharge areas the majority of these samples have ca mg hco3 recharge groundwater c3 c6 c7 and na hco3 evolved groundwater c4 samples from the other three clusters c1 c2 c5 are characteristic of an aquifer system under confined conditions the majority of these samples have na hco3 evolved groundwater c1 c5 and na cl ancient groundwater that exhibits elevated concentrations in br c2 in addition to recognizing the importance of hydrogeological conditions on groundwater geochemistry the distribution of clusters also showed the importance of the geological formations on minor and trace elements such as fe2 mn2 sr2 f and ba2 the first five components of the pca account for 78 3 of the total variance in the dataset component 1 is defined by highly positive loadings in na cl and br and is related to groundwater mixing with champlain sea water and solute diffusion from the marine clay aquitard the high positive loadings in ca2 and mg2 of component 2 suggest the importance of dissolution of carbonate rocks in this aquifer system from their characteristic loadings the first two components are defined as the salinity and hardness components respectively components 3 5 are related to more local and geological effects the integration of the hca and the pca with conventional classification of groundwater types as well as with the hydrogeological and geological contexts allowed the division of the region into four main geochemical areas providing an improved regional picture of the aquifer system dynamics and hydrogeochemical evolution of groundwater the following factors were recognized as influencing the evolution of groundwater identified in every geochemical area 1 geological characteristics including sedimentary rock type and till mineralogy 2 hydrogeological characteristics represented by the level of confinement and the hydraulic gradient and 3 the geological history including the latest glaciation and the champlain sea invasion with its integrated approach this hydrogeochemical study contributes to the characterization and understanding of complex groundwater flow systems and provides an example of the long term geochemical evolution of hydrogeological systems after a major perturbation in this case seawater invasion

behaviour of major elements and some trace elements li rb cs sr fe mn w f in deep hot waters from granitic areas abstract analyses of selected hot springs in more than sixty areas in granites from europe are presented concentrations of major elements and of some trace elements li rb cs sr fe mn w f in high ph waters are not significantly affected by processes during uprise from the deep reservoir to the surface re equilibrations mixing with surficial waters normalized to k or na concentrations of all other elements are related to the aquifer temperature the knowledge of aquifer temperature and total electric charge of mobile elements cl s possibly f allows us to predict both major elements within 50 and trace elements within a factor 2 or 3 concentrations in alkaline waters from granites

geochemical and isotope hydrological characterisation of geothermal resources at godavari valley india thermal waters at the godavari valley geothermal field are located in the khammam district of the telangana state india the study area consists of several thermal water manifestations having temperature in the range 36 76 c scattered over an area of 35 km2 the thermal waters are na hco3 type with moderate silica and tds concentrations in the present study detailed geochemical major and trace elements and isotope hydrological investigations are carried out to understand the hydrogeochemical evolution of these thermal waters correlation analysis and principal component analysis pca are performed to classify the thermal waters and to identify the different geochemical processes controlling the thermal water geochemistry from correlation matrix it is seen that tds and ec of the thermal springs are mainly controlled by hco3 and na ions in pca thermal waters are grouped into two distinct clusters one cluster represents thermal waters from deeper aquifer and other one from shallow aquifer lithium and boron concentrations are found to be similar followed by rubidium and caesium concentrations different ternary plots reveal rock water interaction to be the dominant mechanism for controlling trace element concentrations stable isotopes 18o 2h data indicate the meteoric origin of the thermal waters with no appreciable oxygen 18 shift the low tritium values of the samples originating from deeper aquifer reveal the long residence time 50 years of the recharging waters xrd results of the drill core samples show that quartz constitutes the major mineral phase whereas kaolinite dolomite microcline calcite mica etc are present as minor constituents quartz geothermometer suggests a reservoir temperature of 100 20 c which is in good agreement with the values obtained from k mg and mg corrected k mg ca geothermometers

llandovery graptolite biostratigraphy and paleobiogeography cape phillips formation canadian arctic islands llandovery graptolites have been collected from 11 sections in the cape phillips formation of the canadian arctic archipelago melville bathurst truro cornwallis devon and ellesmere islands the cape phillips formation appears to have been deposited in a distinct subbasin here termed the cape phillips basin under deep shelf to shallow basin conditions intermediate in position between the arctic platform to the south and east and the deeper hazen trough to the northwest a total of 170 graptolite species and a further 25 subspecies have been identified their stratigraphic distribution allows the recognition of 11 graptolite zones the acuminatus atavus acinaces cyphus curtus convolutus minor turriculatus crispus griestoniensis and sakmaricus zones the curtus zone can be subdivided into the pectinatus and orbitus subzones the zones can be correlated with graptolite sequences worldwide the canadian arctic faunas show strong affinities with those of siberia china and the northern canadian

conodont bio events cladistics and response to glacio eustasy ordovician silurian boundary through llandovery anticosti basin quebec

early silurian glaciations in brazil abstract the opening of the brazilian paleozoic basins during the late ordovician was followed by a tectonic stabilization in the silurian at the time of the early silurian glaciations deposition of continental sandstones prevailed in the basins offshore environments were present in the amazonas basin and to a smaller extent in the parana basin the ice sheets advanced over fluviatile and littoral sediments except for the south margin of the amazonas basin where the glacial diamictites immediately overlie marine facies the ice produced much meltwater even when advancing and this was probably climatically controlled the ice movements were from the northwest at the northern margin of the amazonas basin and towards the northeast at the southern margin in the parnaiba basin and its outliers the jatoba basin and cariri valley the ice came from southeast and probably also from east further to the south in the parana basin it came from the north and northeast four glaciations have been dated to the early silurian the oldest is dated as latest ashgill and or earliest llandovery in the parana basin as evidenced from tillites in the upper rio ivai and lower vila maria formations including the former iapo formation it is contemporaneous with a glaciation in the cape basin south africa the next glaciation is dated as early middle llandovery gregarius graptolite zone and is present in the amazonas basin and the andean belt and probably also in the parnaiba basin and its outliers the two youngest tillites were widespread in the northern brazilian basins amazonas parnaiba and jatoba basins and cariri valley as well as in the andean belt and are dated as early late llandovery possibly starting already in the late middle llandovery and latest llandovery to earliest wenlock the latter tillite is the most widespread one assuming these glaciations are related to polar positions the apparent migration of the south pole ice cap must have been quite rapid from central north africa in late ashgill towards central brazil in the middle late llandovery the glaciation in the parana basin took place up to 45 from the late ashgillian south pole the cool climate continued during the silurian but no new glaciations are known before latest devonian

geochemical evaluation of thermal springs in odisha india the indian state of odisha has a number of thermal springs these thermal springs are located at eight places attri tarabalo deulajhari magarmuhan bankhol badaberena taptapani and boden and belong to mahanadi geothermal province which is an archean pre cambrian geothermal province the thermal water discharging from these springs shows moderately acidic to moderately alkaline character ph 5 05 8 93 and the temperature ranges from 28 boden to 58 c tarabalo total dissolved solids tds also shows a wide variation between 16 9 bankhol and 595 mg l deulajhari a wide variation in the chemical characteristics of the thermal waters has been observed as they are located in different geological settings based on water chemistry all the thermal springs can broadly be grouped into three water types na cl ca hco3 and na hco3 the thermal spring water from attri tarabalo and deulajhari belongs to na cl water type which is due to the circulation through granitic rocks higher concentrations of cl and f in these thermal waters further suggest limited mixing and longer residence time as compared to the other areas where ca hco3 and na hco3 water types were found anion variation diagram clearly indicates that the thermal waters from attri tarabalo and deulajhari are fast ascending and fall in the mature water field thus their chemical signatures can be used to determine the reservoir temperature however in other areas water chemistry is shaped by near surface groundwater mixing processes and thus the chemical geothermometers may not be applicable to determine the reservoir temperature no appreciable temporal variations have been observed in the water chemistry of the thermal waters

late wenlock ludlow silurian graptolite extinction evolution and biostratigraphy perspectives from arctic canada late wenlock early ludlow was a period of profound change in the graptolite world and two crises are evident the most important changeover occurred within the late wenlock homerian stage during which time cyrtograptus became extinct monograptids while severely reduced introduced new thecal and and sicular types and plectograptines underwent a striking diversification the second lesser change coincided with the wenlock ludlow boundary at which time monograptids reemerged as the dominant taxon group and plectograptines declined and shortly thereafter became extinct two species pristiograptus praedeubeli jaeger and lobograptus cornuatus n sp recovered in isolated and uncompressed form are described and illustrated the presence of the former species permits the subdivision of the upper homerian of the canadian arctic into two biozones the lower pristiograptus praedeubeli biozone and the upper pristiograptus ludensis pristiograptus sherrardae biozone both species exemplif

dynamic interactions between lahars and stream flow a case study from ruapehu volcano new zealand discussion and reply reply the discussion of manville et al highlights several interesting points about interpreting observations of the 1995 whangaehu lahars at ruapehu we would like to add to some of these points and to clarify some of the issues raised by the discussion whereas the three lahars we described were part

changes in whangaehu river lahar characteristics during the 1995 eruption sequence ruapehu volcano new zealand abstract during the 1995 ruapehu eruptive sequence multiple lahars occurred in the whangaehu river which drains ruapehu s crater lake during the earlier phreatic and phreatomagmatic eruptions lahars were generated by expulsion of waters from the lake but once the lake had emptied lahars were formed by remobilisation of seasonal snowpack laden with saturated freshly erupted tephra four types of lahars occurred during the eruptive sequence 1 initial snow slurry lahars composed of granular snow and ice incorporated by eruptively expelled crater lake waters which left behind frozen deposits with 2 5 20 clastic sediment 2 large dilute lahars generated as the volumes of ejected lake water increased and removed much of the readily available snow at least one third of the pre eruption crater lake volume was expelled during one day producing the largest lahars of the series these lahars were hyperconcentrated flows for up to 84 km from source leaving extensive deposits along the channel margins 3 concentrated lahars smaller volume lahars generated as the frequency of eruptions and volumes of expelled water declined these lahars were able to maintain high sediment concentrations measured at 46 52 by volume suspended sediment at 42 km from source their high sediment concentrations were maintained by erosion and incorporation of sand from the deposits of earlier flows which were lining the channel margins 4 remobilised tephra lahars generated following the two largest tephra eruptions of the sequence seasonal snowpack was covered by water saturated tephra warmer spring temperatures and heavy rainfall events caused collapse and remobilisation of snow and tephra producing several lahars in catchments draining eastern ruapehu

tsunamis of volcanic origin summary of causes with particular reference to krakatoa 1883 known tsunamis of volcanic origin are reviewed and classified according to their causes earthquakes accompanying eruptions excluding tectonic events which apparently triggered eruptions pyroclastic flows and submarine explosions have each accounted for about 20 of cases ten causes of volcanic tsunamis are discussed from the risk point of view those due to landslides are particularly dangerous eruptions at calderas are more likely to generate tsunamis than eruptions elsewhere of those killed directly by volcanic eruptions nearly a quarter have died as a result of tsunamis by transfer of energy to sea waves a violent eruption which would be comparatively harmless on land extends greatly the radius over which destruction occurs

tracking silurian eustasy alignment of empirical evidence or pursuit of deductive reasoning abstract sea level is not static but liable to fluctuations due to addition or subtraction of water in the world s oceans as well as changes to the shape and holding capacity of ocean basins relative changes in sea level are well supported by the rock record on a regional scale whether or not global eustatic changes are evident and how frequently they occurred during any given interval of time is a matter of contention among stratigraphers opinions have evolved over the last century with arguments based on refinements in biostratigraphy chemostratigraphy radiometric dating and conceptual advances in sequence stratigraphy derived from technological advances in seismic stratigraphy the pulsation theory of a w grabau 1936 attributed to paleozoic strata a global history of 11 highstands distributed through a sequence with 21 subdivisions in 1977 peter vail and associates from the exxon production research company independently interpreted a similar paleozoic history showing 10 second order highstands but distributed over 19 subdivisions vail s approach was model based and followed a deductive path while grabau s was based on inductive reasoning recent refinements in a paleozoic sea level curve by haq and schutter 2008 are based on the same deductive approach taken by the vail group but pinned to patterns in sequence stratigraphy drawing on the silurian system as a paleozoic sample the timing frequency and magnitude of sea level highstands deduced by haq and schutter are compared with those promulgated by the author from the mid 1980s onward using empirical evidence more in line with grabau s methodology both apply the concept of geographic reference areas but haq and schutter identify 50 more silurian highstands over an interval lasting 27 7 million years eight out of 10 silurian highstands identified by this author match or overlap 8 out of 15 highstands recognized by haq and schutter at issue is which if any qualify as eustatic signals with respect to current databases for biostratigraphic correlation evaluation is based on evidence reviewed from iowa new york norway estonia and austria in the paleogeographic context of three independent silurian continents

upper llandovery and wenlock graptolites from prairie creek southern mackenzie mountains northwest territories department of geology the university of western ontario london ont canada n6a 5b7 received january 13 1988 revision accepted april 6 1988 a moderately rich fauna of graptolites comprising species dominated by monograptus sensu stricto retiolites stomato graptus and cyrtograptus is documented from prairie creek southern mackenzie mountains northwest territories grapto lites of the upper llandovery monograptus turriculatus monograptus spiralis and cyrtograptus sakmaricus zones and of the wenlock unnamed zone and cyrtograptus rigidus and monograptus testis cyrtograptus lundgreni zones are recognized the species composition of these zones is significantly different from corresponding zones elsewhere in the canadian cordillera twenty six species are described and illustrated and of these two are new stomatograptus canadensis and cyrtograptus preclarus and two species monograptus aff riccartonensis and cyrtograptus aff sakmaricus might also be new several species particularly monograptus praecedens monograptus veles and monograptus cf mutuliferus strigosus have not been prevously reported in north america une faune moyennement riche en graptolites incluant les especes dominantes monograptus s s retiolites stomato graptus et cyrfograptus a ctc trouvce a prairie creek dans la partie sud des monts mackenzie tenitoires du nod ouest les graptolites du llandovery supcrieur k zones de monograptus turriculatus monograptus spiralis et cyrtograptus sakmaricus et la

end ordovician extinctions a coincidence of causes the end ordovician hirnantian extinction was the first of the five big phanerozoic extinction events and the first that involved metazoan based communities it comprised two discrete pulses both linked in different ways to an intense but short lived glaciation at the south pole the first occurring at or just below the normalograptus extraordinarius graptolite biozone mainly affected nektonic and planktonic species together with those living on the shallow shelf and in deeper water whereas the second within the n persculptus graptolite biozone was less focused eradicating faunas across a range of water depths in all about 85 of marine species were removed proposed kill mechanisms for the first phase have included glacially induced cooling falling sea level and chemical recycling in the oceans but a general consensus is lacking the second phase is more clearly linked to near global anoxia associated with a marked transgression during the late hirnantian most recently however new drivers for the extinctions have been proposed including widespread euxinia together with habitat destruction caused by plate tectonic movements suggesting that the end ordovician mass extinctions were a product of the coincidence of a number of contributing factors moreover when the deteriorating climate intensified causing widespread glaciation a tipping point was reached resulting in catastrophe