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

quantitative conodont based approaches for correlation of the late devonian kellwasser anoxic events we present the trends of absolute conodont abundance relative genera abundance and conodont morphometrics across the late devonian kellwasser horizons at three northern gondwanan epicontinental seaway locations at three contrasting depositional settings the kellwasser events are characterized by a decrease in conodont abundance high percentage of the conodont genus icriodus and morphological change of the conodont genus palmatolepis these changes can be identified in sections where the events are expressed as interbedded anoxic and oxic deposits as well as in settings characterized by continuous anoxic sediment accumulation hence these changes are interpreted as global and synchronous and can be thus used for event correlation the paradox of these results is that despite quite similar isotopic signals faunal change during the lower kellwasser event was less than during the upper kellwasser event we interpret that this discrepancy is due to an unconformity including topmost frasnian to earliest famennian at several f f sections which removed the record of peak paleoenvironmental change

systematic occurrences of malformed teratological acritarchs in the run up of early palaeozoic δ13c isotope excursions abstract the late ordovician and silurian are characterised by several strong global positive 13 c carb excursions some of them exceed 5 and thus belong to the strongest perturbations of the carbon cycle in the phanerozoic the onset of the excursions is characterised by extinction and or turnover events of several groups of marine invertebrates the causal mechanisms of the carbon cycle perturbations however are still unknown and currently a matter of vigorous scientific debate our own investigations in the hirnantian latest ordovician have shown that the onset of the major 13 c excursion hice is characterised by very high abundances of acritarchs showing abnormal teratological forms a critical review of published reports of abnormal acritarchs from the late ordovician to early devonian and a correlation of their occurrences with the global stable carbon isotope curve show that high abundances of teratological forms of acritarchs are often coeval to the run up of 13 c excursions high abundances of teratological forms in modern marine protists are commonly observed in environments with a high degree of environmental stress in the fossil record the challenge is to attribute abnormal forms of organisms to specific environmental circumstances our study implies that they are somehow related to the global carbon cycle i e to carbon isotopic composition of the ambient sea water and that they share a common extrinsic cause with the contemporaneous extinction and or turnover events in other fossil groups

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

the rasc method for ranking and scaling of biostratigraphic events abstract the rasc method for ranking and scaling of biostratigraphic events was developed by the authors and associates during the past 20 years the purpose of ranking is to create an optimum sequence of events observed in different wells or sections subject to stratigraphic inconsistencies in the direction of the arrow of time these inconsistencies which result in crossovers of lines of correlation between sections are due to various sampling errors and other sources of uncertainty including reworking and misclassification they can be resolved by statistical averaging combined with stratigraphic reasoning subsequent scaling of the events can be carried out by estimating intervals between successive events along a relative time scale this results in the scaled optimum sequence either the ranked optimum sequence or the scaled optimum sequence can be used for biozonation and for correlation between sections with error bars to denote precision of the correlation the observed positions in the sections of different biostratigraphic events can have different degrees of precision these differences can be evaluated by analysis of variance other types of stratigraphic events including logmarkers can be integrated and incorporated with the biostratigraphic events the purpose of this review paper is to provide a succinct description of rasc as it is today using the cretaceous microfossil example of gradstein et al gradstein f m kaminski m a agterberg f p 1999 biostratigraphy and paleoceanography of the cretaceous seaway between norway and greenland earth science reviews for illustration

dynamics of phytoplankton in relation to the upper homerian lower silurian lundgreni event an example from the eastern baltic basin western lithuania abstract the silurian period was a time of significant environmental change punctuated by a series of bioevents the mid homerian lundgreni event was one of the most severe extinction episodes of the mid paleozoic which mostly affected pelagic organisms while simultaneously sparing benthos despite the great importance of phytoplankton in determining the causal mechanisms of ecosystem collapse there are very few studies on the effects of the lundgreni event on this ecological super guild here we present a detailed quantitative paleoecological analysis of the green algae and acritarchs of the upper wenlock of the vidukl 61 section western lithuania independent high resolution graptolite biostratigraphic and 13c chemostratigraphic control ensures accurate calibration of the micro phytoplankton diversity and community compositional trends the constrained clustering and assemblage zoning revealed five distinct assemblages separated by sharp changes in genus diversity and sample taxonomic composition the statistically estimated local genus richness curves revealed similarity with previously determined 4th order sedimentary cycles interestingly though it appears that the lundgreni mid homerian biotic event had a significantly smaller effect on the studied ecological super guild than the subsequent mid upper homerian regression

geochronology of the mesoproterozoic state farm gneiss and associated neoproterozoic granitoids goochland terrane virginia the goochland terrane is an isolated block of mesoproterozoic crust in the piedmont province of central virginia we report u pb zircon dates and whole rock major and trace element data for the state farm gneiss one of the main units in the terrane and additional results for a newly recognized suite of neoproterozoic granitoids that intrude the gneiss the state farm gneiss ranges in bulk composition from quartz monzodiorite to granite and three samples yield u pb zircon dates of 1046 7 6 ma 1039 18 11 ma and 1023 10 ma we interpret these dates as igneous crystallization ages which indicate a maximum emplacement interval of ca 1057 1013 ma for these samples neoproterozoic granitoids including the fine creek mills and flat rock granites are more alkaline than the state farm gneiss and display all compositional characteristics of a type granites e g high fe mg ga ga al nb zn y zr u pb zircon analyses from five separate bodies indicate crystallization ages from ca 654 to 588 ma but all results are complicated by mesoproterozoic ca 1 ga inheritance coupled in some cases with secondary pb loss we interpret the ages and compositions of the younger rocks to reflect neoproterozoic rifting of the goochland terrane but its location during rifting is uncertain the terrane may have been separated from laurentia during the neoproterozoic breakup of rodinia and later reattached

tonian fe ti p ferronorite and alkali anorthosite in the northern appalachian orogen southern new brunswick canada amazonian basement in ganderia abstract the lower coverdale plutonic suite is located in the ganderian brookville terrane of southern new brunswick canada it does not outcrop at surface but has been intersected in 11 drill holes at depths of 100 200 m below unconformably overlying carboniferous sedimentary rocks and extends to a depth of at least 1100 m no host rocks are present in the drill core which consists entirely of plutonic and meta plutonic rocks the dominant rock types are anorthosite mela anorthosite and ferronorite with layers of ilmenite and ilmenite apatite rocks they are intruded by abundant undated mafic dykes and minor ca 390 ma felsic dykes a ferronorite sample yielded a tonian age of 975 5 2 3 ma interpreted to be the igneous crystallization age of the plutonic suite a mela anorthosite sample yielded a similar but less precise age of 979 16 ma likely also the igneous crystallization age the anorthosite has characteristics of alkali anorthosite massifs including andesine an30 35 commonly with exsolution lamellae of k feldspar the lower coverdale suite is interpreted to have been emplaced during orogen scale extension following crustal thickening associated with the grenvillian orogeny the lower coverdale anorthosite and ferronorite have more isotopically evolved signatures higher 206pb 204pb and 207pb 204pb and lower nd compared to typical laurentian grenville age plutons we infer from these data that the lower coverdale plutonic suite originated in the amazonian part of the grenville orogen during the early stages of tonian breakup of rodinia it was then incorporated into ganderia before accreting to laurentia as part of the brookville terrane during the pangean phase of supercontinent assembly

andean sponges reveal long term benthic ecosystem shifts following the end triassic mass extinction abstract thick cherts and cherty dolomites in the basal jurassic aramachay formation of peru preserve a thriving continental shelf community dominated by siliceous sponges that followed the end triassic collapse of metazoan rich carbonate accumulation similar hettangian and sineumurian deposits from nevada u s a austria and morocco suggest that an early jurassic siliceous sponge takeover was a widespread phenomenon that persisted for 2 m y until metazoan driven carbonate sedimentation recovered the post extinction dominance of siliceous sponges likely resulted from the confluence of metazoan carbonate reef collapse removal of incumbents and geochemical conditions that fostered the success of the siliceous sponge dominated ecosystem simple mass balance calculations suggest the siliceous sponge takeover was likely permitted by an increased silica flux as a consequence of weathering central atlantic magmatic province camp basalts the camp basalts alone could supply all the silica needed to sustain the sponge takeover although contributions were also likely from increased hot climate weathering of other silicates and possible reductions in dissolved silica demand by radiolarians detailed sedimentological fossil and microfacies analyses were conducted at six field sites across a shallow shelf system recorded in the central peruvian andes yauli dome focusing on the metazoan contribution to sedimentation sedimentary structures at all six sites demonstrated on shelf deposition similar to the underlying upper triassic chambara formation in contrast to the black shale rich facies of the aramachay formation in other areas of peru examination of up to 147 m of cherty dolomite from the aramachay formation revealed a siliceous sponge dominated ecosystem including sponge body fossils compressed in situ sponge materials and abundant transported spiculite sediments siliceous sponges mostly demosponges and rare hexactinellids account for the chert lithology and apparently dominated the local ecology for approximately two million years the role of metazoan biocalcifiers in sediment production and ecological structure was profoundly reduced compared to the under and overlying formations representing a clear ecological state shift from pre extinction carbonate to post extinction siliceous dominated ecosystems before the carbonate system recovered 2 m y after the extinction

ultra high resolution multivariate record and multiscale causal analysis of pridoli late silurian implications for global stratigraphy turnover events and climate biota interactions abstract the upper silurian and especially pridoli epoch is a critical interval for the understanding the evolution of earth s biota since it witnessed series of powerful extinction events global reorganizations of paleocommunities and expansion of new clades which assumed dominance in the subsequent devonian period the stratigraphic record of the eastern part of the silurian baltic basin represents an excellent candidate for the fine scale analysis of paleoecological and paleoceanographic dynamics therefore we presenting here stratigraphic record of the milaiciai 103 core south western lithuania of conodonts brachiopods 13ccarb 18ocarb and a series of various geochemical and geophysical proxies most of which were sampled at a very high resolution 11 ka spanning uppermost ludlow pridoli and the lowermost devonian the analysis revealed that the pridoli was characterized by four distinct long term dynamic states here named i normal pridoli i ii silal negative carbon isotopic excursion and extinction event iii normal pridoli ii and iv klonk positive stable carbon isotopic event and excursion the most significant change in most variables is detected approximately in the middle of the pridoli at the beginning of the delotaxis detorta zone at the recovery after silal event of conodonts and at the onset of collapse of brachiopod communities the analysis of dynamic complexity revealed the strong evidence for the presence of 405 ka metronome milankovitch cycles in the record of 13ccarb which constrains the duration of the pridoli epoch to 4 3 0 2 ma the recurrence plot analyses revealed deterministic coordination between 13ccarband conodont paleocommunity dynamics at all scales finally lead lag analysis using conditional joint recurrence revealed that conodont dynamics as a rule were driven by perturbations in the carbon cycle although silal event interval shown opposite pattern thus confirming the unusual nature of this previously unrecognized coordinated climatic and biotic event

chemical weathering in a tropical watershed luquillo mountains puerto rico ii rate and mechanism of biotite weathering abstract samples of soil saprolite bedrock and porewater from a lower montane wet forest the luquillo experimental forest lef in puerto rico were studied to investigate the rates and mechanisms of biotite weathering the soil profile at the top of a ridge in the rio icacos watershed consists of a 50 100 cm thick layer of unstructured soil above a 600 800 cm thick saprolite developed on quartz diorite the only minerals present in significant concentration within the soil and saprolite are biotite quartz kaolinite and iron oxides biotite is the only primary silicate releasing significant k and mg to porewaters although biotite in samples of the quartz diorite bedrock is extensively chloritized chlorite is almost entirely absent in the saprolite phyllosilicates phyllosilicate grains are present as 200 1000 m wide books below about 50 cm depth x ray diffraction xrd and electron microprobe analyses indicate that the phyllosilicate grains contain a core of biotite surrounded by variable amounts of kaolinite lattice fringe images under transmission electron microscope tem show single layers of biotite altering to two layers of kaolinite suggesting dissolution of biotite and precipitation of kaolinite at discrete boundaries some single 14 a layers are also observed in the biotite under tem the degree of kaolinitization of individual phyllosilicate grains as observed by tem decreases with depth in the saprolite this tem work is the first such microstructural evidence of epitaxial growth of kaolinite onto biotite during alteration in low temperature environments the rate of release of mg in the profile calculated as a flux through the soil normalized per watershed land area is approximately 500 mol hectare 1 yr 1 1 6 10 9 molmg msoil 2 s 1 this rate is similar to the flux estimated from mg discharge out the rio icacos 1000 mol hectare 1 yr 1 or 3 5 10 9 molmg msoil 2 s 1 indicating that scaling up from the soil to the watershed is possible for mg release the rate of mg release from biotite normalized to brunauer emmett teller bet surface area is calculated using a mass balance equation which includes the density and volume of phyllosilicate grains porewater chemistry and flux and soil porosity the mean rates of biotite weathering calculated from k and mg release rates are approximately 6 and 11 10 16 molbiotite mbiotite 2 s 1 respectively significantly slower than laboratory rates 10 12 to 10 11 molbiotite mbiotite 2 s 1 the discrepancy in scaling down from the soil to the laboratory is probably explained by 1 differences in weathering mechanism between the two environments 2 higher solute concentrations in soil porewaters 3 loss of reactive surface area of biotite in the saprolite due to kaolinite and iron oxide coatings and or 4 unaccounted for heterogeneities in flow path through the soil

dynamics of abundance of the mid to late pridoli conodonts from the eastern part of the silurian baltic basin multifractals state shifts and oscillations

geochemistry of the arvonia formation chopawamsic terrane virginia implications for source area weathering and provenance the metasedimentary arvonia formation in the piedmont province of central virginia ranges primarily from slates to garnet schists which unconformably overly middle ordovician metavolcanic rocks of the chopawamsic arc terrane the formation has typically been interpreted as late ordovician based on poorly preserved fossils perhaps having formed as a successor basin following accretion of the chopawamsic arc to laurentia however alternative interpretations have been proposed including deposition outboard of laurentia on chopawamsic arc crust that is prior to accretion furthermore the origin of the chopawamsic arc as peri laurentian or peri gondwanan is an unresolved issue we report whole rock major and trace element compositions as well as nd isotopic compositions of the arvonia formation and use these results to evaluate further its origin samples collected along the length of the outcrop belt show similar major element compositions which are typical of shales chemical index of alteration values 68 89 corrected for k metasomatism indicate intermediate to extreme levels of source weathering a majority of the samples show uniform rare earth element ree patterns that are light ree enriched with negative eu anomalies a few samples display anomalous ree patterns indicative of some disturbance of the light ree at approximately the time of deposition a variety of trace element values or ratios indicate that arvonia sediments are similar to shale composites thus upper continental crust nd isotopic compositions for eight samples are similar with end 5 6 to 8 9 400 ma collectively these results are consistent with derivation of arvonia sediments from a single source or well mixed sources of typical upper crustal composition the isotopic data are compatible with a laurentian provenance however they are equally compatible with a strictly chopawamsic crustal source based on available nd isotopic data

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

depositional versus ecological control on the conodont distribution in the lower frasnian fore reef facies holy cross mountains poland abstract lithofacies and conodont biofacies of reef slope deposits of the wietrznia beds lower frasnian palmatolepis transitans zone were studied in three measured sections at the wietrznia quarry holy cross mts poland the diverse reef derived grained deposits interrupted the background sedimentation that included lime mudstones deposited largely at 50 to 90 m depths in oxygen depleted middle slope to toe of slope settings the mainly storm controlled proximal gradient is laterally marked by gradual changes from coarse grained tempestites represented by flat pebble conglomerate fabric to diluted muddy tempestites the mostly sparse polygnathid and mesotaxid polygnathid biofacies characterize the hemipelagic facies whilst polygnathid ancyrodellid biofacies dominates in the event layers three step taphofacies scheme is proposed distinguishing settled parautochthonous residual winnowed and displaced settled from waning currents and or transported in sediment gravity flows conodont element accumulations the primary ecological signals are still partly preserved in most of the tempestite derived assemblages indicating scarcity of truly residual lag like taphofacies the hydraulic sorting was most effective in the middle slope setting affected by unidirectional and or oscillatory flows syndepositional mixing was strengthened upslope by an importation of off reef mesotaxid faunas due to storm surge onto the reef this reworking pattern as a key factor in biofacies interpretation may be applicable only on a local scale however similarly biased conodont signature is probably common in other hurricane affected carbonate complexes even if without a disrupting impact on major biofacies belts

asteroid breakup linked to the great ordovician biodiversification event the great ordovician biodiversification event coincides 470 million years ago with the break up of a large asteroid and the resultant frequent bombardment of earth with asteroid fragments

the use of faunal gradient analysis for intraregional correlation and assessment of changes in sea floor topography in the type cincinnatian abstract in paleobiology and stratigraphy there is a growing need to develop high resolution chronostratigraphic frameworks at regional scales which would permit unprecedented assessments of spatiotemporal variation in preserved biotas here we present an intraregional correlation for the kope and lower fairview formations of the type cincinnatian on the basis of detrended correspondence analysis dca of faunal census data we believe that the method also holds promise as a tool of correlation in other fossiliferous venues the data were collected directly in the field at closely spaced stratigraphic intervals but with relatively coarse taxonomic and quantitative data resolution this approach is independent of lithologic assessments and does not require the delineation of sequence stratigraphic architecture in the study area faunal curves were constructed for each locality on the basis of stratigraphic changes in sample scores for dca axis 1 the curves were smoothed to reveal a long term signal of

recurrence and cross recurrence plots reveal the onset of the mulde event silurian in the abundance data for baltic conodonts abstractone of the severest perturbations of the silurian marine environment is the mid homerian mulde bioevent this event proceeded in several temporal steps which according to some authors implies possible globally synchronous perturbation the dynamic pace and consequences of these perturbations as well as their effects on conodont community dynamics are largely unknown here i used so called recurrence and cross recurrence plots to test the hypothesis of common forcing of the mulde event on conodont abundance dynamics at the regional scale the results of the analysis of two lithuanian sections from the baltic basin revealed that in the uppermost part of the lundgreni graptolite biozone there was sharp transition in the recurrence patterns pre mulde homerian time was characterized by high amplitude fluctuations and a low recurrence rate on the other hand the mulde interval state was characterized by low abundance and a high recurrence rate with longer horizontal vertical and diagonal lines

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

mineralogic controls on the composition of natural waters dominated by silicate hydrolysis a detailed mineral solute mass balance spreadsheet model has been developed to improve understanding of mineralogic controls on water composition in surface waters and groundwater systems dominated by silicate lithologies the spreadsheet based approach is used to investigate mass balance solutions over a range of mineral compositions for predominant multi element phases such as plagioclase biotite chlorite amphibole and dioctahedral smectite the mass balance technique has been applied to a variety of hydrogeologic environments including calibrated watersheds springs and groundwater systems lithologic settings include plutonic metamorphic minor volcanic and sedimentary alluvial and glacial deposits materials sites investigated most of which allowed comparison with earlier work include ephemeral and perennial springs of the central sierra nevada mountains california the loch vale colorado high altitude watershed four catchments in the inyo mountains california and nevada watersheds in the catoctin mountain maryland area and ground water flow systems in vekol valley arizona and in the trout lake area wisconsin analytical mass balances were derived with a novel approach that permits graphic analysis of the functional dependency of mineral mass transfer coefficients on variations in major silicate composition a 10 x 10 matrix of mineral solute reaction equations was used to solve for the best mass balances alternative methods were developed to investigate cases where the number of mineral phases exceeds the number of solute constraints 10 that are commonly found in clastic silicate dominated systems with diverse sources and or phase mixtures of variable chemistry such as an assortment of plagioclase compositions techniques were also developed to allow for important structurally controlled compositional variation in clay minerals final mass balance choices were tempered by thermodynamic stability calculations for various minerals under near surface weathering conditions mineral mass transfer ratios were also found to be useful in restricting mass balances additional constraints were provided by establishing consistent sets of similar mineral assemblages and mineral compositions for a series of wells along a ground water flow path or through comparison of multiple nearby watersheds subject to similar climatic and vegetative conditions whereas unique analytical solutions from spreadsheet mass balances were not always possible a surprisingly limited range was obtained for mineral assemblages and compositions satisfying observed mineral occurrences and thermodynamic stability conditions our results demonstrate the importance of having well characterized mineral compositions for both reactant and product phases the mass balance results are particularly sensitive to the compositions of plagioclase dioctahedral smectite and a few primary mafic mineral groups trioctahedral mica amphibole and pyroxene in addition to mineral controls the specific examples studied demonstrate effects of dolomite and calcite overprints on silicate weathering biomass fluctuations road salt contamination and on buried evaporite salts a comparison of the mass balance results from surface and groundwater systems indicates strong similarities suggesting that similar processes dominate the mineral controls in both settings and that under soil weathering conditions ion exchange might have been overemphasized except under conditions where pre existing waters are displaced by solutions of significantly different composition

quantitative biostratigraphy achieving finer resolution in global correlation abstract the fossil record preserves a wide range of events that might be used to build timescales and correlate strata from place to place the events include the originations and extinctions of species the occurrence of distinctive faunal assemblages magnetic field reversals changes in ocean chemistry and volcanic ash falls the fundamental task is to determine the global sequence of all these events modern computer algorithms can build high resolution timescales by sequencing and calibrating thousands of such events from hundreds of localities each successful sequencing algorithm can be understood in terms of a simple two dimensional visual device graphic correlation permutable sequences permutable matrices and slotting devices are each suited to a different data problem such as contradictory evidence of sequence a lack of information about sequence or uncertain correspondence of events algorithms based upon permutable sequences and evolutionary programming heuristics have the flexibili

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

vertebrate extinctions and reorganizations during the late silurian lau event during the silurian period as shown here by data from gotland sweden and other regions of the baltoscandian paleocontinent fish faunas were struck hard by extinctions caused by the late ludlow lau event also known for being associated with the largest positive stable carbon isotope excursion of the phanerozoic this event had a profound impact on the early evolutionary history of vertebrates wiping out two thirds of the fish taxa and causing significant ecological reorganizations over an estimated time span of similar to 200 ka our data show that immediately prior to the event jawed acanthodians dominated the fish faunas whereas the event led to a diverse fauna and a brief but marked dominance of the jawless thelodonts the stepwise changes observed mimic those of conodonts suggesting a similar mode of life and response to atmospheric oceanic perturbations for these clades less

high resolution late silurian correlations between gotland sweden and the broken river region ne australia lithologies conodonts and isotopes high resolution correlations partly with a precision better than 10 ka are achieved between late ludfordian sequences on gotland sweden on baltica and a section cog through the coral gardens formation along the broken river northeastern australia on gondwana despite these sections having been on different palaeocontinents facing different oceans the interval is characterised by rapid very large faunal isotopic and lithologic changes lithologies are remarkably similar in the two areas consisting of in order from below marls with thin limestone beds flaggy limestones oncoidal crinoidal limestone oncoidal marls terrigenous clastics silty clay mudstone sandstone oolite and cliff gorge forming limestones further independent correlation dates several of the lithological changes as coeval the 813 c excursion in whole rock carbonates is one of the three largest ones known during the phanerozoic the increase in delta c 13 is very similar in the two areas from below 1 parts per thousand to c 9 parts per thousand vpdb though two gotland samples yielded 9 71 parts per thousand and 10 54 parts per thousand the corresponding cog interval included fewer carbonate layers than needed to definitely exclude that this difference is due to a lack of suitable rocks for sampling compared with the lithologies and the delta c 13 curves the conodont faunas display some divergence but key taxa permit precise correlations for much of the studied interval the conodont assemblages change stepwise from very diverse in the polygnathoides siluricus zone to a low diversity fauna dominated markedly by a single taxon upper icriodontid subzone returning abruptly to a comparatively diverse ozarkodina snajdri zone fauna a method resembling graphic correlation in some respects is used to propose a similarly high resolution correlation through a longer interval for future testing c 2006 elsevier b v all rights reserved less

a late silurian extinction event and anachronistic period resurgence of microbialites and anachronistic facies in the aftermath of phanerozoic extinction events has hitherto only been documented among the major five based on the classical silurian carbonate platform strata of gotland sweden a minor biotic event is herein for the first time related to a substantial increase in anachronistic facies strata deposited during and shortly after the lau event in the baltic paleobasin eke and burgsvik formations include evidence for reduced grazing and infaunal activity in contemporaneous shallow low latitude seas e g flat pebble conglomerates normal marine stromatolites mass occurrence of oncoids and subtidal wrinkle structures e g kinneyia and microripples the latter structures have recently been suggested to be restricted to proterozoic cambrian and early triassic time and therefore are regarded as anomalous for the phanerozoic the co occurrence of these facies and global extinctions among pentamerid brachiopods and conodonts suggests that minor extinction events also resulted in anachronistic periods less devastating but fully comparable to those in the aftermath of the end ordovician and end permian mass extinctions a global positive stable carbon isotope excursion and the last appearance datum of the conodont polygnathoides siluricus may facilitate identification of the late silurian anachronistic period elsewhere less

whole rock pb and sm nd isotopic constraints on the growth of southeastern laurentia during grenvillian orogenesis the conventional view that the basement of the southern and central appalachians represents juvenile mesoproterozoic crust the final stage of growth of laurentia prior to grenville collision has recently been challenged new whole rock pb and sm nd isotopic data are presented from mesoproterozoic basement in the southern and central appalachians and the granite rhyolite province as well as one new u pb zircon age from the granite rhyolite province these data combined with existing data from mesoproterozoic terranes throughout southeastern laurentia further substantiate recent suggestions that the southern and central appalachian basement is exotic with respect to laurentia sm nd isotopic compositions of most rocks from the southern and central appalachian basement are consistent with progressive growth through reworking of the adjacent granite rhyolite province however pb isotopic data including new analyses from important regions not sampled in previous studies do not correspond with pb isotopic compositions of any adjacent crust the most distinct ages and isotopic compositions in the southern and central appalachian basement come from the roan mountain area eastern tennessee western north carolina the data set indicates u pb zircon ages up to 1 8 ga for igneous rocks inherited and detrital zircon ages 2 0 ga sm nd depleted mantle model t dm ages 2 0 ga and the most elevated 207 pb 204 pb observed in southeastern laurentia the combined u pb geochronologic and sm nd and pb isotopic data preclude derivation of southern and central appalachian basement from any nearby crustal material and demonstrate that grenville age crust in southeastern laurentia is exotic and probably was transferred during collision and assembly of rodinia these new data better define the boundary between the exotic southern and central appalachian basement and adjacent laurentian granite rhyolite province

quantifying the community turnover of the uppermost wenlock and ludlow silurian conodonts in the baltic basin abstract the homerian to ludfordian interval of the mid to late silurian period was a time of significant changes in conodont communities global climate oceanographic patterns and biogeochemical cycles the mulde and the lau events are preeminent examples of globally recognized conodont extinction episodes from this interval in earth s history the silurian baltic basin is the most suitable locality globally for studying these perturbations to the ocean atmosphere system since there is an extensive record of conodont taxa occurrences their communities and their environments spanning across shore face to open ocean settings in this study we present new conodont and 13c data from the upper homerian to ludlow interval from two core sections g luva 99 and g luva 118 representing shelfal environments and the numerical conodont data from the vidukl 61 section from deep water settings and compare them with patterns of conodont diversity change as revealed in the data rich milaiciai 103 core section for this purpose we explored the stratigraphically tied time series of conodont diversity changes employing recurrence and cross recurrence plots the binary similarity matrices that are used for deciphering complex spatial and temporal dynamic patterns the cross recurrence plots were used as a means of synchronizing the geological sections by applying dynamic time warping and the newly described moving window median recurrence point search algorithms the results revealed that the conodont community compositional data are sufficiently temporally and spatially coherent to be reasonably used for synchronizing geological records moreover the sudden state transitions detected in the cross recurrence plots suggest that the lau event was of great importance for conodont community evolution in the studied time slice

carbonate platform evolution and conodont stratigraphy during the middle silurian mulde event gotland sweden evidence from sedimentology and conodont biostratigraphy is used to reinterpret the mid homerian late wenlock succession on gotland sweden a new conodont zonation includes from below the ozarkodina bohemica longa zone including five subzones the kockelella ortus absidata zone and the ctenognathodus murchisoni zone two taxa are named ozarkodina bohemica longa and pseudooneotodus linguicornis these new zones are integrated with facies in order to correlate strata and infer the major depositional environments and the controls on deposition during the mid homerian mulde event reef associated and skeletal carbonate deposition predominated before and after the event i e during the uppermost o s sagitta zone and again in the c murchisoni zone these periods are characterized by the expansion of reefs and shoal facies across marls in the topmost slite group on eastern gotland and in the lower parts of the klinteberg formation on western gotland respectively the intervening o b longa and k o absidata zones are initially characterized by rapid facies changes including siliciclastic deposition and later stabilisation of a carbonate depositional system the composition of sediments and depositional rates are closely related to the creation and destruction of accommodation space and reflects a classical case of depositional bias of the carbonate and siliciclastic depositional systems based on coastline migration stratal boundaries and the stratigraphic position of major reef belts several facies associations can be fitted into a sequence stratigraphic model for platform evolution a highstand systems tract hst situation prevailed prior to and during the early part of the event the upper slite group including the lower frjel formation this hst was characterized by prolific skeletal production and regional reef development except for during the latest stage when carbonate production declined at the onset of the mulde event platform growth was inhibited during a following regressive systems tract rst when regional siliciclastic deposition predominated the gannarve member the subsequent lowstand resulted in regional emersion and karstification i e a complete termination of the platform the post extinction transgressive systems tract tst is exclusively composed of non skeletal carbonates the bara member of the halla formation re occurrence of reefs and a prolific skeletal production marks platform recovery during a second hst the remaining halla and the lower klinteberg formations integration of high resolution biostratigraphy and sequence stratigraphy reveals that the major physical control on platform evolution was a 5th order eustatic sea level change during an early part of the mulde event and that the bulk of the strata accumulated when the platform aggraded and prograded during the highstand systems tracts thus silurian oceanic events and associated sea level changes had profound impact on the neritic carbonate system the gotland based middle and late homerian sea level curve shows two rapid regressions both leading to truncation of highstand systems tracts the first lowstand occurred at the very end of the c lundgreni chron and the second at the end of the co ludensis chron the intervening interval was characterized by stillstand or possibly slow transgression

high resolution early paleozoic ordovician silurian time scales for much of the geologic time scale resolving power appears to be limited by the duration of biostratigraphic zones and subzones yet these zones exploit the appearance and disappearance events of only a small fraction of the species they span computer algorithms can sequence an order of magnitude more events and make explicit the uncertainties that arise when calibrating the resulting time line an illustrative case history builds an ordovician and silurian time scale from the geologic record of the entire graptolite clade over 1900 species from more than 400 localities and sections worldwide the same approach can be applied to any stratigraphic interval with detailed biostratigraphic observations it provides the foundation for time scales and paleobiologic time lines using logic similar to graphic correlation optimizing algorithms search for a composite sequence of species first and last appearance events that minimizes the implied shortcomings of all the field observations the algorithms minimize the number of species coexistences that are implied but never observed and the net adjustments needed to bring local range charts into agreement with a single composite sequence of events after total section thicknesses have been rescaled to help normalize for variation in depositional rate mean stratigraphic thicknesses are used to scale the intervals between adjacent events in the composite sequence the resulting scaled composite sequence is converted to a relative geologic time scale by identifying stage and zone boundaries within the sequence of graptolite events this relative scale is in turn calibrated by dated volcanic ash beds that were incorporated in the search for the optimal sequence these dated events are also used to test for linearity of the scaled composite the final time scale has a potential resolving power of 0 02 0 1 m y more than ten times better than can be achieved by traditional zones graptolite zones vary widely in duration from as short as 0 1 m y to nearly 5 0 m y the mean duration of zones or zonal groupings calibrated here is 1 44 m y in the ordovician and 0 91 m y in the silurian the average uncertainty in locating zone boundaries in a single composite sequence is about one fourth of the mean zone duration the variance resulting from differences in time scales developed from differing numbers of field observations and in response to changes in the optimization criteria gives a very conservative measure of the overall robustness of the method these differences indicate an average uncertainty in the age of graptolite zone boundaries that is more nearly equal to the mean zone duration for zone duration the mean uncertainty amounts to about one half of the length of an average zone

evidence for rapid environmental changes in low latitudes during the late silurian lau event the burgen 1 drillcore gotland sweden erosional outliers are an important component of the ludlow late silurian stratigraphy of gotland sweden however due to the poor degree of exposure outcrop studies have not revealed a detailed section from any of these outliers the first complete stratigraphy of such an erosional remnant the burgen outlier is presented here based on the recently recovered burgen 1 drillcore stratigraphical units encountered are from oldest to youngest the uppermost hemse group 35 m eke formation 0 4 m burgsvik formation 3 4 m and the basal hamra formation 12 in preserved based on carbon stable isotopes and lithological correlation to nearby outcrops that are zoned by conodonts it can be concluded that the most profound late ludlow sedimentary changes took place shortly after the onset of the globally recognized lau event delta 13 c values reach 8 7 parts per thousand in the lower hamra formation sedimentary changes include development of discontinuity surfaces widespread occurrence of an intraclastic conglomerate increased microbial activity rothpletzella and wetheredella and influx of clastics to the basin these changes are linked to substantial base level changes during the event a general comparison with the prague basin suggests contemporaneous sedimentary changes on baltica and on cratonic elements from peri gondwana during the event

the lundgreni event in the silurian of the east european platform poland abstract the lundgreni event late wenlock silurian is here interpreted in terms of palaeontologic graptolites microphytoplankton benthos biostratigraphic and geochemical evidence derived from homerian deposits drilled in the bartoszyce well east european platform in poland the lundgreni event in the graptolite record of bartoszyce comprises extinction survival and recovery phases the graptolite extinction proceeded in three steps lundgreni testis and flemingii dubius the testis extinction eliminated the largest number of species only the long lasting pristiograptus dubius survived the combined extinctions and was joined during the survival phase by the opportunistic gothograptus nassa and pristiograptus parvus the graptolite recovery is expressed by the diachronous arrival of new species in association with p dubius all documented phytoplankton taxa survived the lundgreni event phytoplankton frequency and diversity patterns together with total organic carbon toc fluctuations indicate that oligotrophy productivity regime was unsteady during the testis and flemingii dubius extinctions and stable during the early graptolite survival there is no evidence for extinction within benthic fauna assemblages diversified benthos appeared in a great abundance during the early survival phase this records a redox related event of substrate colonization that took place simultaneously with local decline in primary productivity the last two phases of graptolite extinction and the onset of the survival correlate with strong positive anomalies of 18o 13corg and 13ccarb the anomalies coincide with the fall in local primary productivity and the enhanced storage of organic carbon in peri gondwanan upwelling zones sudeten thuringia the stepped graptolite extinction in bartoszyce occurred in an environment that was situated within the low latitude baltica shelf and was markedly stable in terms of bathymetry distance from land and oxic regime this local extinction was most likely caused by catastrophic fluctuations in nutrient supply breaking primary productivity the trophic perturbations on the baltica shelf were coeval with and related to eutrophication of the high latitude upwelling zones of the rheic ocean the postulated spatial fluctuations in the trophic resource continuum may reflect palaeooceanographic changes that accompanied the global late sea level highstand of that time

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

biodiversity patterns of silurian radiolaria abstract data analysis of all published and well dated silurian radiolarian localities was conducted with the goal of revealing long term patterns in silurian radiolarian biological diversity the chronostratigraphic distribution of 161 species was compiled from 25 publications each selected because of their independent age control the pattern and dynamics of changes in biodiversity are described using indices that allow for the assessment of changes in taxonomic richness through time following the hirnantian end ordivician mass extinction the rhuddanian stage records very low levels of diversity which then increase gradually throughout the llandovery series and reach a maximum by the sheinwoodian stage before decreasing during the homerian and finally rebounding during the gorstian stage the early silurian llandovery appears to be an interval during which few species went extinct although the number of last occurrences increases progressively to reach a peak in the ludfordian at the same time first occurrences progressively decrease and are relatively low during the silurian only the gorstian is marked by a sudden increase in origination the early silurian is an interval of faunal recovery from the end ordovician mass extinction event similarly the gorstian stage is characterized by a recovery following the homerian low in radiolarian diversity that may be correlated with the c lundgreni extinction event which affected a number of other pelagic groups e g graptolites acritarchs conodonts and chitinozoans and with the mulde event which coincides with a 4 6 positive excursion of the 13 c curve

gecko global events impacting conodont evolution abstract with a record that spans approximately 300 million years late cambrian through the triassic jurassic transition i e the conodontozoic conodonts witnessed all principal events in the evolution of life on earth from the invasion of the land to the exploration of the air from the explosion of biomineralization in the oceans to the rise of dinosaurs and mammals including three of the major extinction events that occurred in the phanerozoic mainly used for biostratigraphic or geochemical studies the potential of conodonts to help unravel changes perceived to be of global extent rarely has been explored while specialists have identified rapid changes in conodont element morphology throughout their history the conodont animal has often been perceived to have been a static entity in a constantly evolving world when biological equilibrium in the oceans was undergoing profound alteration and faunal recoveries took place in phases that seem to have had recurrent patterns it is now essential that we begin to further investigate how conodonts as biologic entities responded to or were impacted by palaeogeographic changes eustatic and climatic fluctuations shifting redox conditions and major faunal turnovers and reorganizations that took place during the conodontozoic

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

petrophysical record of the late silurian shallow water carbonate facies across the lau event prague synform czech republic and dynamic time warping alignment of the magnetic susceptibility logs

early triassic stromatolites as post mass extinction disaster forms aftermaths of mass extinctions have been thought to be characterized by relaxation of ecological constraints accompanied by increased prominence of opportunistic generalists such taxa termed disaster forms have been shown to increase dramatically in range and abundance after several mass extinction events the cambrian ordovician stromatolite decline in normal marine level bottom environments has been explained as a direct or indirect consequence of increases in ecological constraints such as greater levels of predation and or bioturbation of microbial communities caused by early paleozoic benthic invertebrate evolution and diversification thus one would predict that in post ordovician strata stromatolites might appear in normal marine level bottom environments as disaster forms in the aftermaths of mass extinction particularly devastating to the benthic biota such as during early triassic time mounded stromatolites are present in two beds up to 1 5 m thick of the lower triassic spathian virgin limestone member moenkopi formation in the southwestern spring mountains of nevada stromatolites from level bottom normal marine subtidal environments have also been described from other lower triassic strata in north america europe and asia these stromatolites unusual in level bottom normal marine settings may have developed locally during the long aftermath 4 5 m y of the permian triassic mass extinction because of partial relaxation of the ecological constraintsmore that typically restricted them from unstressed subtidal normal marine level bottom environments less

pacing of paleozoic macroevolutionary rates by milankovitch grand cycles periodic fluctuations in past biodiversity speciation and extinction have been proposed with extremely long periods ranging from 26 to 62 million years although forcing mechanisms remain speculative in contrast well understood periodic milankovitch climate forcing represents a viable driver for macroevolutionary fluctuations although little evidence for such fluctuation exists except during the late cenozoic the reality magnitude and drivers of periodic fluctuations in macroevolutionary rates are of interest given long standing debate surrounding the relative roles of intrinsic biotic interactions vs extrinsic environmental factors as drivers of biodiversity change here we show that over a time span of 60 million years between 9 and 16 of the variance in biological turnover i e speciation probability plus species extinction probability in a major early paleozoic zooplankton group the graptoloids can be explained by long period astronomical cycles milankovitch grand cycles associated with earth s orbital eccentricity 2 6 million years and obliquity 1 3 million years these grand cycles modulate climate variability alternating times of relative stability in the environment with times of maximum volatility we infer that these cycles influenced graptolite speciation and extinction through climate driven changes to oceanic circulation and structure our results confirm the existence of milankovitch grand cycles in the early paleozoic era and show that known processes related to the mechanics of the solar system were shaping marine macroevolutionary rates comparatively early in the history of complex life we present an application of hidden markov models to macroevolutionary time series and protocols for the evaluation of statistical significance in spectral analysis

δ13c records across the late silurian lau event new data from middle palaeo latitudes of northern peri gondwana prague basin czech republic abstract during the late silurian the prague basin was located in middle southern latitudes in contrast to palaeocontinents positioned in tropical and subtropical latitudes like baltica no reefs are developed which is in accordance with the predicted cooler water the prague basin represents a relatively restricted and shallow rift basin with a complex tectonic history sections in different palaeoenvironments have been studied to document the most prominent silurian stable carbon isotope excursion recorded during the late silurian ludfordian lau event from this part of peri gondwana deeper water deposits of the kopanina formation investigated in the present study were deposited on the slope to basin transition near the kosov volcanic centre in the western part of prague basin the sediments are developed as an alternation of dark partly laminated limestones and marls with an increase of the limestone marl ratio in the upper part of the succession a pronounced positive carbon isotope excursion starts in the neocullograptus kozlowskii graptolite and in the upper polygnathoides siluricus conodont zone the maximum of the shift is observed in the lower part of an interval characterised by the ananaspis fecunda cyrthia postera community the maximum values scatter around 8 which represent the highest values reported hitherto from the prague basin in low latitudes often a decrease of 13c values towards deeper water settings is reported in contrast in the present study the 13c values of about 8 are much higher than those recorded from the contemporaneous shallow water sections studied in the classical muslovka and po ary quarries the most reasonable explanation is the presence of stratigraphical gaps in the shallow parts of the basin as indicated by karstification these gaps were caused by a sea level drop another effect of this sea level fall was a strongly reduced sedimentation of the cephalopod limestone facies around volcanic and tectonic elevations

discussion on ludlow late silurian oceanic episodes and events journal vol 157 2000 1137 1148 scientific editing by alistair crame d k loydell writes in their recent paper jeppsson aldridge 2000 p 1137 expressed reservations about the method behind the generation of my loydell 1998 sea level curve for the early silurian llandovery to earliest ludlow as the method used was based upon decades of consistent observations of graptolite distribution i am rather surprised that jeppsson aldridge could not accept the scientific basis of the sea level curve s construction simply stated graptolite diversity increases from low usually 1 3 species in nearshore environments to a maximum in outer shelf environments thus a significant rise in relative sea level can be inferred in a section where a diverse graptolite assemblage is recovered from above an unconformity or above strata with features indicative of deposition in very shallow water where such a deepening pattern can be demonstrated to occur at the same stratigraphical level on a number of different palaeocontinents a eustatic sea level rise is the logical explanation clearly it is necessary for me to cite here some of the decades of consistent observations that i refer to above which contrast low diversity inshore graptolite assemblages with diverse outer shelf assemblages i should also state here that there are no known exceptions to this pattern the examples selected below have been chosen for their wide palaeogeographical as well as stratigraphical coverage the list is by no means exhaustive berry boucot 1972 watkins berry 1977 kaljo 1978 paskevicius 1979 chen 1990 cooper et al 1991 lenz et al 1993 finney berry 1997 storch 1998 goldman et al 1999 jeppsson aldridge also note that my sea level curve loydell 1998 differs significantly from those published previously based on other criteria this is

chemical weathering in a tropical watershed luquillo mountains puerto rico i long term versus short term weathering fluxes abstract the pristine rio icacos watershed in the luquillo mountains in eastern puerto rico has the fastest documented weathering rate of silicate rocks on the earth s surface a regolith propagation rate of 58 m ma 1 calculated from iso volumetric saprolite formation from quartz diorite is comparable to the estimated denudation rate 25 50 ma 1 but is an order of magnitude faster than the global average weathering rate 6 ma 1 weathering occurs in two distinct environments plagioclase and hornblende react at the saprock interface and biotite and quartz weather in the overlying thick saprolitic regolith these environments produce distinctly different water chemistries with k mg and si increasing linearly with depth in saprolite porewaters and with stream waters dominated by ca na and si such differences are atypical of less intense weathering in temperate watersheds porewater chemistry in the shallow regolith is controlled by closed system recycling of inorganic nutrients such as k long term elemental fluxes through the regolith e g si 1 7 10 8 moles m 2 s 1 are calculated from mass losses based on changes in porosity and chemistry between the regolith and bedrock and from the age of the regolith surface 200 ma mass losses attributed to solute fluxes are determined using a step wise infiltration model which calculates mineral inputs to the shallow and deep saprolite porewaters and to stream water pressure heads decrease with depth in the shallow regolith 2 03 m h2o m 1 indicating that both increasing capillary tension and graviometric potential control porewater infiltration interpolation of experimental hydraulic conductivities produces an infiltration rate of 1 m yr 1 at average field moisture saturation which is comparable with libr tracer tests and with base discharge from the watershed short term weathering fluxes calculated from solute chemistries and infiltration rates e g si 1 4 10 8 moles m 2 s 1 are compared to watershed flux rates e g si 2 7 10 8 moles m 2 s 1 consistency between three independently determined sets of weathering fluxes imply that possible changes in precipitation temperature and vegetation over the last several hundred thousand years have not significantly impacted weathering rates in the luquillo mountains of puerto rico this has important ramifications for tropical environments and global climate change

synchronous diversification of laurentian and baltic rhynchonelliform brachiopods implications for regional versus global triggers of the great ordovician biodiversification event the profound global impact of marine radiations during the great ordovician biodiversification event gobe is widely appreciated however diversification varied among paleocontinents and these individual trajectories are less understood here we present a new species level diversity curve for rhynchonelliform brachiopods from midcontinental laurentia based on bed by bed analysis of the simpson group of oklahoma usa diversity and abundance data span the dapingian through sandbian stages which encompass the interval of maximum global diversification a rapid statistically significant increase in brachiopod diversity was observed in the early darriwilian histiodella holodentata biozone we interpret this as a biological signal because the increase cannot be explained by sampling intensity facies types or position along depositional gradient diversifications on laurentia and baltica were temporally synchronous at the biozone level and cumulative diversity curves for the regions show similar patterns suggesting a global driver for the radiations the taxonomic composition of the brachiopod faunas however differs substantially highlighting the importance of regional controls on diversification thus both global and local factors controlled diversity increase during the gobe

integrated record of ludlow upper silurian oceanic geobioevents coordination of changes in conodont and brachiopod faunas and stable isotopes abstract the ludlow epoch silurian was marked by several globally recognized but mechanistically poorly understood biotic events the most pronounced of them was the lau event which strongly decimated conodont graptolite and brachiopod faunas additionally this event coincides with the largest positive stable carbon isotopic anomaly in the whole phanerozoic as well as the resurgence of the so called anachronistic microbial facies that were frequently encountered during survival episodes of the major mass extinction events in this contribution based on the analysis of the outer shelf facies succession milaiciai 103 core from the lithuanian part of the silurian baltic basin as integrated quantitative record of conodont brachiopod and 13 c changes across most of the ludlow is presented the succession was subdivided into four conodont zones that served as a stratigraphic framework for analyzing the 13 c and palaeoecological trends the depth constrained cluster analysis revealed successions of three statistically distinct conodont and six statistically distinct brachiopod assemblages that replace each other near the change points in the stable carbon isotopic curve the application of a newly developed mathematical technique based on the analysis of recurrence patterns of the fossil assemblages revealed that both conodonts and brachiopods are represented by highly time specific assemblages in the aftermath of the lau event o snajdri interval zone the anomalous interval is confined to the transgressive and highstand phases of the 3rd order post lau transgression the discussed interval is coeval with the extensive development of stromatolitic communities in the nearshore environments around the world the results allow for the first time to quantify the profound ecosystem wide geobiological impact of the mid ludfordian event that lasted up to the latest ludfordian

grenvillian massif type anorthosites in the sierras pampeanas we report the discovery of massif type anorthosites in the andean basement of the western sierras pampeanas of argentina u pb zircon dating by sensitive high resolution ion microprobe of a cogenetic gabbronorite dyke yields ages of 1070 41 ma for igneous emplacement and 431 40 ma for metamorphism these anorthosites are petrologically and geochemically comparable with those of the grenville province of laurentia palaeogeographical reconstructions of rodinia at 1 0 1 1 ga suggest that the sierras pampeanas anorthosites were part of a large anorthosite province in the late mesoproterozoic

resolving milankovitch consideration of signal and noise milankovitch climate theory provides a fundamental framework for the study of ancient climates although the identification and quantification of orbital rhythms are commonplace in paleoclimate research criticisms have been advanced that dispute the importance of an astronomical climate driver if these criticisms are valid major revisions in our understanding of the climate system and past climates are required resolution of this issue is hindered by numerous factors that challenge accurate quantification of orbital cyclicity in paleoclimate archives in this study we delineate sources of noise that distort the primary orbital signal in proxy climate records and utilize this template in tandem with advanced spectral methods to quantify milankovitch forced paced climate variability in a temperature proxy record from the vostok ice core vimeux and others 2002 our analysis indicates that vostok temperature variance is almost equally apportioned between three components the precession and obliquity periods 28 a periodic 100 000 year cycle 41 and the background continuum 31 a range of analyses accounting for various frequency bands of interest and potential bias introduced by the saw tooth shape of the glacial interglacial cycle establish that precession and obliquity periods account for between 25 percent to 41 percent of the variance in the 1 10 kyr 1 100 kyr band and between 39 percent to 66 percent of the variance in the 1 10 kyr 1 64 kyr band these results are approximately two to four times greater than those published by wunsch 2004 for the same vostok time series in all cases most of the remaining variance is accounted for by the 100 000 year cycle which is distinct from a background continuum that resembles autoregressive red noise our analysis high lights the importance of a comprehensive assessment of the climate signals in geologic records and underscores the significance of orbital forcing pacing as a primary agent of pleistocene climate change

inverse models to analyze the spatiotemporal variations of chemical weathering fluxes in a granito gneissic watershed mule hole south india water rock reactions are driven by the influx of water which are out of equilibrium with the mineral assemblage in the rock here a mass balance approach is adopted to quantify these reactions based on field experiments carried out in a granito gneissic small experimental watershed sew mule hole sew similar to 4 5 km 2 quartz oligoclase sericite epidote and chlorite are identified as the basic primary minerals while kaolinite goethite and smectite are identified as the secondary minerals observed groundwater chemistry is used to determine the weathering rates in terms of mass transfer coefficients mtcs of both primary and secondary minerals weathering rates for primary and secondary minerals are quantified in two steps in the first step top red soil is analyzed considering precipitation chemistry as initial phase and water chemistry of seepage flow as final phase in the second step minerals present in the saprolite layer are analyzed considering groundwater chemistry as the output phase weathering rates thus obtained are converted into weathering fluxes q weathering using the recharge quantity spatial variability in the mineralogy observed among the thirteen wells of mule hole sew is observed to be reflected in the mtc results and thus in the weathering fluxes weathering rates of the minerals in this silicate system varied from few 10 mu mol l in case of biotite to 1000 s of micromoles per liter calcite similarly fluxes of biotite are observed to be least 7 5 mol ha yr while those of calcite are highest 1265 791 mol ha yr further the fluxes determined annually for all the minerals are observed to be within the bandwidth of the standard deviation of these fluxes variations in these annual fluxes are indicating the variations in the precipitation hence the standard deviation indicated the temporal variations in the fluxes which might be due to the variations in the annual rainfall thus the methodology adopted defines an inverse way of determining weathering fluxes which mainly contribute to the groundwater concentration c 2011 elsevier b v all rights reserved

silurian conodont based correlations between gotland sweden and saaremaa estonia correlations between the silurian successions of gotland and the east baltic are based on the narrowest stratigraphic units that can be distinguished in both areas in order further to increase precision true ends of ranges in measured sections have been used instead of pooled formational faunas where outcrops and collections permit some previous correlations are confirmed in other cases there are considerable changes both in levels of correlation and in precision the major differences are found mostly when one or more of the major gaps have remained unrecognized and stratigraphic units therefore have been extended and translated upwards or downwards at least some of these gaps decrease in magnitude southwards in estonia gaps at these levels are also noted on gotland although they are small and probably do not extend across the island the patterns through time of deposition during secundo episodes and gaps during primo episodes agree very well with what can be predicted from a model of oceanic and climatic cyclicity