chironomid based lateglacial climatic reconstruction for southeast scotland this paper presents the first chironomid based climatic reconstruction for the uk lateglacial obtained from a lake basin in southeast scotland whitrig bog comparison of chironomid lithological geochemical and pollen data reveals a marked vegetation lag behind the warming following deglaciation warm water chironomid taxa e g chironomus had replaced cold water chironomid taxa e g paracladius prior to the arrival of shrubs and trees and when local soils were still poorly developed in addition to clear evidence for the younger dryas stadial chironomid data also reveal two short term cold episodes that punctuate the lateglacial interstadial both of which are also reflected in pollen and lithological data as reversals from open birch scrub woodland to open herbaceous tundra coinciding with inwash of minerogenic matter into the basin 1997 john wiley sons ltd

late ordovician massive bedded thalassinoides ichnofacies along the palaeoequator of laurentia abstract massive bedded thalassinoides ichnofacies occurs pervasively in widely separated areas on the vast upper ordovician carbonate platforms along the palaeoequator of laurentia from the borglum river formation in north greenland through the red river formation and bighorn dolomite of the williston basin manitoba canada to wyoming usa to the ely springs dolomite and equivalent strata of the eastern great basin utah and nevada usa the late ordovician thalassinoides is characterised by complex three dimensional anastomosing or multi level galleries that are consistent in size pattern and density with preserved depth of 1 m or greater in addition to the similar thalassinoides burrows the ichnofacies across the palaeocontinent also contains typical taxa of the red river biota such as the soccer ball sized receptaculitid fisherites large shelled diverse and abundant nautiloids the distinctively planispiral gastropod maclurina as well as diverse tabulate and rugose corals the consistent characteristics of the red river biofacies and thalassinoides ichnofacies suggest a palaeogeographically homogeneous and temporally stable depositional environment along the palaeoequatorial belt of laurentia during the pre hirnatian late ordovician the thalassinoides ichnofacies marked the first phase of mega scale invasion of burrowers into relatively deep water platform and shelf environments by successively creating a well oxygenated deep burrow system for protection and deposit feeding such substrate tiering expansion constituted an important aspect of the great ordovician biodiversification event

response of interior north america to abrupt climate oscillations in the north atlantic region during the last deglaciation several broad scale climatic oscillations during the last deglaciation are well documented in regions around the north atlantic ocean this paper reviews empirical evidence for these deglacial climatic oscillations from non coastal north america and discusses implications for testing climatic simulations and for understanding the cause and transmittal mechanisms paleoclimatic interpretation of oxygen isotope records from several small sites in the eastern great lakes region indicates a classic deglacial climatic sequence that is comparable with records from europe and greenland the climatic events as interpreted from crawford lake oxygen isotopes include the bolling allerod boa warming at 12 700 14c bp a warm boa at 12 500 10 920 14c bp an intra allerod cold period shortly before 11 000 14c bp a cold younger dryas yd climate reversal at 10 920 10 000 14c bp the holocene warming at 10 000 14c bp a brief preboreal oscillation pb at 9650 14c bp and an early holocene cold event at 7500 14c bp 8200 cal bp some of these events were also evident from changes in upland and aquatic vegetation and sediment lithology the pronounced yd climatic reversal has been documented from pollen records along the ecotones at this time and from glacier readvances in the great lakes region along the rocky mountains from alberta to colorado the yd event is indicated by alpine glacier advance and or shift in timberline vegetation in minnesota and upper new york early holocene climatic instability is also suggested by oxygen isotope records and or varve thickness the regional variations in evidence for the yd and other events in north america suggest that climatic oscillations may have different expressions in paleo records depending on geographic location and characteristics of a particular site the extent and magnitude of these climatic oscillations across north america suggest that these oscillations are an expression of climatic change that was probably widespread rather than locally induced by a nearby glacier the location of these sites implies that climatic signals were likely carried over the northern hemisphere through the atmosphere as indicated by general circulation models we hypothesize that the lack of evidence for a cold yd in interior north america west of the great lakes region and east of the rocky mountains was caused by the trapping of cold arctic air mass north of the laurentide ice sheet and by uninterrupted northward expansion of warm caribbean air this strongly contrasted climate also produced non analogous biological assemblages

a midge based late glacial temperature reconstruction from southwestern nova scotia we present a quantitative reconstruction of the thermal regime spanning the late glacial period of nova scotia 14 700 to 11 600 bp as inferred by analyzing fossil midges from a small lake lac a magie in southwestern nova scotia the gs 1 event equivalent to the younger dryas dating from 12 700 to 11 600 bp in maritime canada was marked by a 5 c decline in inferred mean july surface water temperatures and a 15 drop in organic content previous pollen and plant macrofossil analyses of this site demonstrate a response of vegetation to gs 1 cooling these data coupled with a midge inferred temperature reconstruction from a nearby site suggest that late glacial climate change was less pronounced in southern nova scotia than in other sites in maritime canada and adjacent eastern north america

coping between crises early triassic early jurassic bivalve diversity dynamics abstract the triassic is bounded by two of the most severe biotic crises but nevertheless this time was for bivalves both a recovery and a diversification period and a moment to fully exploit some of their evolutionary novelties just how and when this was achieved is analyzed in this paper which covers induan to sinemurian bivalve diversity based on a newly compiled database taxonomic diversity and ecospace dynamics are examined separately diversity and evolutionary rates were assessed extinction selectivity was tested using a resampling algorithm and cohort analysis was used to study extinction patterns during the early triassic most bivalve genera were survivors from the permian and they were mainly cosmopolitan epifaunal and semi infaunal endobyssate taxa reclined epifaunal and semi infaunal bivalves increased in diversity during the triassic but from norian on their diversity declined and they were strongly affected by the t j crisis although the triassic jurassic extinction strongly impacted bivalve taxonomic diversity it had little impact on bivalve ecologic diversity not a single bivalve life strategy was eliminated at the end of the triassic the present study does not support previous conclusions that infaunal bivalves suffered greater extinction than epifaunal ones during the t j extinction not all life strategies were equally affected by the extinction event being the deep infaunal burrowers positively selected bivalves with major energetic requirements seem to have been more affected with negative selectivity on fast shallow burrowers the ecologic diversity changes of bivalves during the late triassic and several adaptations of durophagous predators reflect the effects of increasing predation pressure and support a late triassic origin of the mesozoic marine revolution

ecologic interpretation of deep sea trace fossil communities abstract trace fossil types and their vertical arrangement tiering are closely related to the biotope and hence can provide information on ecological conditions especially on oxygenation benthic food content sedimentation rate and substrate consistency however to use the full potential of trace fossils for environmental analyses various ichnologic criteria are necessary in addition to trace fossil taxonomy based on a taxonomically oriented ichnologic evaluation of modern deep sea environments six ichnologic aspects to ecologic changes have been found to be of major importance 1 1 penetration depth of burrows is influenced by oxygenation benthic food availability and substrate consistency 2 2 the number and vertical extension of tiers varies due to environmental changes a decrease in the vertical extension of tiers telescoping indicates a decrease in oxygenation benthic food content and or sedimentation rate if shallow penetrating traces disappear oxygen may be depleted and if the deepest tiers disappear the benthic food content may be lowered 3 3 the size diameter of specific trace fossils can indicate oxygen and benthic food availability 4 4 degree of bioturbation is related to sedimentation rate and benthic food content and the diversity of the whole ichnocoenoses or within a specific tier is affected by oxygenation benthic food content sedimentation rate and substrate consistency 5 5 the type of burrow wall unlined mucus lined pellet lined mainly refers to substrate consistency and subordinately to pore water oxygenation 6 6 the type of sediment displacement by body appendages used for excavation ingestion sideward pressing or outside pumping is related to substrate consistency and grain size

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

climatic and limnological changes associated with the younger dryas in atlantic canada pollen diatom and chironomid fossils from the sediments of a core from brier island bog lake nova scotia were studied in an attempt to relate changes in microfossil composition to a climatic cooling in atlantic canada correlative with the european younger dryas ca 10 to 11 ka our paleolimnological data were then compared to similar types of data from splan pond new brunswick to determine if there were any significant differences between a coastal and a more inland site nonarboreal pollen was dominant throughout the brier island core and the interval 10 0 11 0 ka did not show the typical decline in picea and increases in tundra like vegetation characteristic of many sites in atlantic canada however the limnological indicators did undergo marked changes in taxon composition the chironomid assemblage was initially dominated by shallow water warm adapted chironomid taxa followed by abundant sergentia a cold stenotherm during 10 11 ka sergentia disappeared in the post younger dryas interval and the warm adapted genera resumed dominance chironomid inferred paleotemperature reconstructions revealed that at both brier island bog lake and splan pond summer surface water temperatures dropped abruptly to between 13 and 17 c during the 10 11 ka interval suggesting that a cooler climate was present in atlantic canada correlative with the european younger dryas diatom assemblage changes during the same period corroborate the occurrence of limnological fluctuations

the amphi atlantic distribution of the younger dryas paleoclimatic oscillation abstract interest in significant climatic fluctuations affecting large geographic areas but having a time range that is too brief to adduce the milankovitch radiation cycles has focused on the allerod younger dryas event which is a well established phenomenon of western europe manifested by glacial and vegetational reconstructions it is also shown by the foraminiferal evidence for shifts in the polar front in the north atlantic recent pollen and lithostratigraphic investigations in the maritime provinces of eastern canada and in the till plains of west central ohio on opposite sides of the late glacial spruce forest indicate that the event also left a record in eastern north america experiments with an atmospheric general circulation model with the temperature of north atlantic surface waters depressed to full glacial levels lowered summer temperatures in upwind periglacial eastern north america by 2 c just as far inland as they did downwind in western europe where the paleoecological record of cooling is clear a leading hypothesis for the cause for the younger dryas cooling appeals to the influx of tabular icebergs released from arctic ice shelves around the wasting scandinavian and siberian ice sheets during the allerod warming the resulting cooling of the north atlantic waters during the younger dryas could be facilitated or precipitated by the abrupt influx of glacial meltwater derived from almost the entire southern margin of the laurentide ice sheet and emerging from the gulf of st lawrence as brought about by a major shift in drainage direction from the mississippi river to the st lawrence river about 10 8 ka bp a supplemental influx of fresh water may have come from the contemporaneous drainage of the baltic ice lake the diversion of laurentide meltwater to the atlantic was caused by retreat of an ice lobe in northwestern ontario north of minnesota allowing the huge glacial lake agassiz in saskatchewan and manitoba to drain into the great lakes and more than double the inflow of meltwaters in the north atlantic thereby diverting the gulf stream and permitting the influx of icebergs from the north to cool the ocean surface minor readvance of the ice lobe about 10 ka bp temporarily diverted the lake agassiz drainage to the south with the final retreat of the ice the drainage again went to the east but by this time the ice sheets were much diminished and the regional climate had warmed enough so that the effects of the meltwater flux on the gulf stream were muted and the ice sheets bordering the north atlantic had retreated onto the land and no longer delivered enough icebergs to cool the surface waters the younger dryas interval thus was terminated and the warming manifested in the allerod was renewed

a high resolution late glacial and early holocene diatom record from baffin island eastern canadian arctic an interval of late glacial to early holocene sedimentation spanning the period 12 9 8 4 ka bp 14c dated by accelerator mass spectrometry is contained within 15 cm of gyttja in a core from a small lake on southwestern cumberland peninsula baffin island this sediment was subsampled in continuous 2 5 mm increments for diatom analysis extremely low sediment accumulation rates 1 8 cm ka 1 are characteristic of the initial phase of organic sedimentation but they increase rapidly to 14 2 cm ka 1 after 9 ka bp the first 0 5 cm of gyttja contained an acidophilous diatom flora resembling that of underlying mineral sediments thereafter and throughout the late glacial and earliest holocene diatom floras were dominated by alkaliphilous and circumneutral species of fragilaria around 9 ka bp shifts to acidophilous floras dominated by brachysira brebissonii and later eunotia rhomboidea and frustulia rhomboides vars saxonica and crassinervia suggest a period of natural lake acidification high dia

the amphi atlantic oscillation a proposed late glacial climatic event a contribution to the north atlantic seaboard programme of igcp 253 termination of the pleistocene abstract numerous palaeoclimatic records from europe greenland and the north atlantic ocean provide evidence for a short term cooling event which preceded the younger dryas stadial of ca 11 10 ka bp the discovery of a similar event in eastern north america the killarney oscillation ko raised the possibility of a single pre younger dryas cooling event that affected the entire north atlantic seaboard this paper reviews evidence for the ko and other pre younger dryas events and discusses the basis for their correlation the informal name amphi atlantic oscillation is proposed as a collective term for the ko and events that correlate with it

potential effects of climate changes on aquatic systems laurentian great lakes and precambrian shield region the region studied includes the laurentian great lakes and a diversity of smaller glacial lakes streams and wetlands south of permanent permafrost and towards the southern extent of wisconsin glaciation we emphasize lakes and quantitative implications the region is warmer and wetter than it has been over most of the last 12000 years since 1911 observed air temperatures have increased by about 0 118c per decade in spring and 0 068c in winter annual precipitation has increased by about 2 1 per decade ice thaw phenologies since the 1850s indicate a late winter warming of about 2 58c in future scenarios for a doubled co2 climate air temperature increases in summer and winter and precipitation decreases summer in western ontario but increases winter in western ontario northern minnesota wisconsin and michigan such changes in climate have altered and would further alter hydrological and other physical features of lakes warmer climates i e 2 co2 climates would lower net basin water supplies stream flows and water levels owing to increased evaporation in excess of precipitation water levels have been responsive to drought and future scenarios for the great lakes simulate levels 0 2t o 2 5 m lower human adaptation to such changes is expensive warmer climates would decrease the spatial extent of ice cover on the great lakes small lakes especially to the south would no longer freeze over every year temperature simulations for stratified lakes are 1 78c warmer for surface waters and 68c cooler to 88c warmer for deep waters thermocline depth would change 4 m shallower to 3 5 m deeper with warmer climates alone deepening owing to increases in light penetration would occur with reduced input of dissolved organic carbon doc from dryer catchments dissolved oxygen would decrease below the thermocline these physical changes would in turn aaect the phytoplankton zooplankton benthos and fishes annual phytoplankton production may increase but many complex reactions of the phytoplankton community to altered temperatures thermocline depths light penetrations and nutrient inputs would be expected zooplankton biomass would increase but again many complex interactions are expected generally the thermal habitat for warm cool and even cold water fishes would increase in size in deep stratified lakes but would decrease in shallow unstratified lakes and in streams less dissolved oxygen below the thermocline of lakes would further degrade stratified lakes for cold water fishes growth and production would increase for fishes that are now in thermal environments cooler than their optimum but decrease for those that are at or above their optimum provided they cannot move to a deeper or headwater thermal refuge the zoogeographical boundary for fish species could move north by 500 600 km invasions of warmer water fishes and extirpations of colder water fishes should increase aquatic ecosystems across the region do not necessarily exhibit coherent responses to climate changes and variability even if they are in close proximity lakes wetlands and streams respond diaerently as do lakes of diaerent depth or productivity diaerences in hydrology and the position in the hydrological flow system in terrestrial vegetation and land use in base climates and in the aquatic biota can all cause diaerent responses climate change eaects interact strongly with eaects of other human caused stresses such as eutrophication acid precipitation toxic chemicals and the spread of exotic organisms aquatic ecological systems in the region are sensitive to climate change and variation

allerod younger dryas coleoptera from western cape breton island nova scotia canada studies of coleoptera remains from two late glacial sites on cape breton island nova scotia canada present a picture of the paleoenvironment and paleoclimate during the allerod younger dryas transition in the maritimes region they provide evidence for the younger dryas event in northeastern north america between 11 300 and 10 800 bp the beetle assemblages at the campbell site are typical of faunas of the modern middle to northern boreal forest the west mabou site contains beetle fossils younger than 10 900 bp possibly as young as 10 500 bp extending into the time period of the younger dryas dated from 10 800 to 10 000 bp in the maritimes a cold climate indicator recognizable in the beetle fauna olophrum boreale occurs in relative abundance and provides an interesting comparison with sites in europe where the same northern boreo montane species is evident at the beginning of the younger dryas

midge inferred holocene climate history of two subalpine lakes in southern british columbia canada to investigate postglacial environmental changes in both the coastal and interior wet belts of british columbia fossil midges were analysed from two subalpine lakes one adjacent to the lower fraser canyon frozen lake and the other in mount revelstoke national park eagle lake the midge stratigraphy for frozen lake revealed an abundance of rheophilous chironomid taxa and simuliidae larvae refecting the presence of an inflowing stream an abundance of chaoborus mandibles and microtendipes during the early holocene c 10100 7700 14c years bp c 11500 8500 cal years bp suggests warmer temperatures a subsequent decline in the warm indicators and relative increases in cold stenotherms heterotrissocladius and diamesa indicate cooling until present day this climate reconstruction is consistent with other quantitative and qualitative evidence for past climatic change in southern british columbia at eagle lake the warm indicators dicrotendipes and polypedilum are seen in the early holocene c 85

a review of multi proxy data for the younger dryas in atlantic canada abstract multi proxy data obtained from lake sediments and buried organic sequences is reviewed and discussed as evidence for the younger dryas cooling event in atlantic canada sedimentological studies indicate that lake basins were subject to increased erosion due to climate cooling while glacial and periglacial sediments overlying peats have been attributed to the effects of small younger dryas ice caps building up in highland areas of nova scotia pollen evidence from over 30 sites shows two broad patterns of lateglacial vegetation change in the region the younger dryas cooling caused the replacement of closed boreal forest by shrub tundra in southern new brunswick and central mainland nova scotia and the replacement of shrub tundra by herb tundra in central new brunswick northern nova scotia and newfoundland chironomid data indicate that the younger dryas was marked by a drop in summer lake surface water temperatures of ca 6 c while diatom data suggest that marked limnological changes also occurred based on ams 14c dates from terrestrial plant macrofossils of 8 sites the younger dryas event in atlantic canada lasted from ca 10 830 to 10 000 bp these dates match most of those from northwest and central europe suggesting that this climatic event affected the entire north atlantic region essentially simultaneously

exceptionally steep north south gradients in lake temperatures during the last deglaciation during the transition from the last glacial to the present interglacial climate late glacial period high summer insolation1 combined with the presence of the laurentide ice sheet is thought to have promoted the development of strong summer thermal gradients in north america south of the ice margin2 here we use palaeoecological methods to obtain quantitative evidence for the existence of these gradients our palaeoclimate reconstructions are based on water temperatures inferred from fossil assemblages of aquatic midge larvae in five lakes along a 240 km transect extending from central new brunswick canada to southeastern maine usa we show that the temperature gradient shifted during the killarney oscillation ko and younger dryas yd cooling events and that water temperature differences of 9 and 11 c existed over distances of 55 and 240 km respectively during parts of the late glacial period these gradients are much stronger than the current north south trends of lake summer surface water temperatures for these five lakes and for lakes across the northern tree line the rapid motion of such steep temperature gradients may have affected the progressive development of aquatic and terrestrial ecosystems in the region

a late glacial holocene palaeoecological record from pye lake on the eastern shore of nova scotia canadageological survey of canada contribution 20080395 pollen and chironomid analyses and radiocarbon dating at pye lake on the eastern shore of nova scotia are used to outline the vegetation and climatic history of the area the coast was deglaciated prior to 12 200 14c bp 14 300 cal bp and herbaceous tundra vegetation invaded the area midge inferred maximum summer surface water temperatures in the lake ranged between 9 and 11 c subsequent gradual warming to 18 c by 10 800 14c bp 12 725 cal bp favoured the migration of a variety of herbaceous and shrub taxa into the region rapid cooling to 10 c saw vegetation revert to herbaceous tundra communities this interval related to the younger dryas cold interval of the north atlantic and europe lasted until 10 000 14c bp 11 630 cal bp the climate then warmed again to conditions similar to those that prevailed immediately before onset of younger dryas cooling further warming saw successive tree species migrate into the area until by the mid holocene the forests contained most of the taxa preva

paleolimnological records of climatic change in north america lacustrine fossil records provide long time series of data on limnological and climatic conditions these data are useful for establishing natural patterns of climate variability and for generating testable hypotheses about atmospheric circulation and climate ecosystem linkages shoreline features can indicate past lake level fluctuations that may reflect changes in moisture balance but often these records are discontinuous and are evidence of only extreme conditions the organisms geochemistry and sedimentology of lake sediments may provide a more continuous sequence of direct and indirect lake climate interactions in the past the most clearly interpretable paleolirnnological records of climatic change are those that use several lines of evidence to corroborate a climatic hypothesis and are from sites near an ecotone or in regions of extreme climate in all cases hydrologic setting mediates a lake s response to climate and must be considered in interpreting sedimentary sequences discussion of the impact of recent and future climatic changes necessitates a baseline against which the magnitude of observed or predicted changes can be measured commonly we look to recent history as a reference point for comparison however the landscape of recent decades or in some cases even centuries has been altered greatly by human activities thus to determine whether recent or future climatic change is unique or unusual we need long natural preanthropogenic time series against which observed or predicted climatic states and variability can be compared paleolimnological archives are a tool for looking at environmental patterns prior to anthropogenic impact and show a range of climatic states far greater than those documented by written records former strand lines of pluvial lakes bonneville and lahontan in the western u s for example testify to moisture extremes unsurpassed in recent centuries or even millennia in addition one can us the paleolimnological record as an independent climatic proxy against which patterns and rates of terrestrial response to climatic change can be compared here i present a broad overview of paleoclimatic reconstruction in north america from lacustrine records with a focus on the late quaternary the review is limited to climatic inference from paleolirnnological records a term i use in a restrictive sense to refer to records of past lake states physical biological and geochemical as opposed to records of past stream hydrology e g ely et al 1993 knox 1993 or terrestrial conditions i summarize paleolimnological tools available for reconstruction of past climate the capabilities and limitations of these tools

phanerozoic shallow water diversity driven by changes in sea level shallow water 50 m marine diversity curves for the phanerozoic based on area changes due to sea level variation and continental movements are presented it is shown that a change in the degree of endemism can alter diversity more than the effect of sea level change or change in the number of faunal provinces the pattern produced for a constant degree of endemism shows some rapid but not periodic falls in diversity these occur in the middle cambrian at the end of the ordovician devonian permian cretaceous and eocene and in the messinian there is no recurring single cause for these falls

trace fossil model for reconstructing oxygenation histories of ancient marine bottom waters application to upper cretaceous niobrara formation colorado abstract trends of decreasing trace fossil diversity burrow size and penetration depth with diminishing oxygen availability in contemporary marine settings have been incorporated with the concept of trace fossil tiering to develop a model for reconstructing the oxygenation history of ancient basin bottom waters more sensitive than traditionally employed criteria the model permits detailed evaluation of relative degree of oxygenation through the recognition of oxygen related ichnocoenosis ori units or units of strata deposited under similar levels of bottom water oxygenation when employed in detailed vertical sequence analyses the model may also be used to construct interpreted oxygenation curves that reflect rates and magnitudes of temporal change in redox conditions the utility of the model is demonstrated by its application to rhythmically bedded calcareous strata of the niobrara formation upper cretaceous exposed in colorado non laminated strata of the niobrara are characterized by four recurring trace fossil suites referred to as the 1 chondrites 2 zoophycos teichichnus 3 planolites and 4 thalassinoides assemblages on the basis of trends in trace fossil diversity burrow diameter and penetration depth these assemblages are recognized as oxygen related ichnocoenoses interpreted oxygenation curves for the basal fort hays member reflect high magnitude redox cycles characterized by rapid deoxygenation events followed by gradual reoxygenation phases curves for the overlying smoky hill member reflect an overall lower degree of oxygenation with more irregular lower magnitude redox fluctuations significant correlation between interpreted levels of paleooxygenation and organic carbon content illustrate the model s potential for evaluating the distribution of organic rich fine grained strata co interpretation of these variables with carbonate content supports the premise that deposition was controlled by paleoceanographic perturbations modulated by milankovitch like climatic cycles comparison with traditionally emphasized macroinvertebrate body fossil criteria clearly demonstrates the greater utility of the trace fossil approach for evaluating paleo oxygenation

the great ordovician biodiversification event gobe the palaeoecological dimension abstract the great ordovician biodiversification event gobe saw a spectacular increase in marine biodiversity at all taxonomic levels largely within the phyla established much earlier during the so called cambrian explosion the diversification was probably the result of a combination of several geological and biological processes and the positive feedbacks resulting from them the present paper reviews the palaeoecological dimension of the gobe it involved major increases in s and biodiversity largely associated with the rise of the paleozoic evolutionary fauna dominated by suspension feeders and involving a greater occupation of ecospace and more complex ecological structures in the ecological evolutionary units p1 and p2 in the benthos these include more complex food webs than those of the cambrian greater tiering especially above the sediment water interface and the development of guild structures indicating increased competition between taxa for particular resources the ordovician is characterized by a profound change in reef composition with a switch from microbial dominated reefs in the early and middle ordovician to metazoan dominated reefs in the late ordovician increases in complexity of deep water trace fossil assemblages began in the early ordovician and mark the increasing exploitation in that environment and the development of hardgrounds permitted bioerosion and encrusting strategies together with the appearance of cryptic communities within the water column the gobe involved a significant increase in the diversity of the phytoplankton and the development of a diverse zooplankton including planktotrophic larvae from a range of invertebrate clades this revolution in the plankton enabled the establishment of a diverse fauna of pelagic vertebrates molluscs and arthropods and promoted the rise of suspension feeders in the benthos an escalation amongst predators and thus community evolution may also have been a major driver of biodiversification

wisconsinan late glacial environmental change in nova scotia a regional synthesis a synthesis of the interpreted vegetational and climatic history of nova scotia during the wisconsinan late glacial period 14 9 ka bp is presented and described in 500 year intervals the concomitant regional deglaciation history of the region is also described a synthesis chart is provided which includes a qualitative curve of temperature reconstructions for the late glacial period

trace fossil evidence for ediacaran bilaterian animals with complex behaviors abstract distinguishing ediacaran trace fossils from tubular body fossils can be a challenge and several ediacaran fossils previously interpreted as animal traces have been shown to be tubular body fossils nonetheless true ediacaran trace fossils are present but they are relatively few and morphologically simple dominated by horizontal trails and shallow burrows such simple morphologies have been taken as evidence for a modest behavioral complexity and limited geobiological impact of animal bioturbators before the cambrian explosion here we report three types of trace fossils horizontal tunnels surface tracks trails and vertical traces from the latest ediacaran dengying formation 551 541 ma in the yangtze gorges area of south china cross cutting tunnels and the presence of scratch marks indicate that these traces are unlikely tubular body fossils instead these three types of traces likely represent animal activities related to under mat feeding epibenthic locomotion and temporary dwelling respectively we show that these three types of traces were constructed by the same bilaterian animals that had moderately complex interactions with microbial mats to exploit nutrients and o 2 resources these animals heralded a new age in ecosystem engineering animal sediment interaction and biogeochemical cycling

tiering in suspension feeding communities on soft substrata throughout the phanerozoic tiering of benthic marine suspension feeding communities on soft substrata has varied throughout the phanerozoic epifaunal tiering was most developed during the middle and late paleozoic and the triassic to jurassic with large scale reductions in tiering occurring during the permian triassic extinctions and after the jurassic infaunal tiering reached its highest level of organization after the paleozoic

a multiproxy investigation of late glacial climate and vegetation change at pine ridge pond southwest new brunswick canada abstract pollen plant macrofossil chironomid and lithological analyses of late glacial sediment from pine ridge pond all indicate that the warming following deglaciation was punctuated on two separate occasions by a return to colder climes initially by a brief and moderate cold episode the killarney oscillation followed shortly by the younger dryas the killarney oscillation ams 14 c dated at between 11 290 and 10 960 yr b p is characterized by abrupt and simultaneous increases in betula birch pollen and betula glandulosa dwarf birch macrofossils and a decline in tree pollen the younger dryas is distinguished by the reversion of a short lived closed picea spruce forest to a prolonged forest tundra stage ca 10 820 to 9500 yr b p during which macrofossils of arctic alpine plants such as salix herbaces cassiope hypnoides armeria maritima and thalictrum alpinum make their sole late glacial appearance chironomid inferred summer surface water temperatures indicate a cooling of approximately 8 and 12 c during the killarney oscillation and younger dryas respectively and coarse sand analysis indicates increased erosion on the landscape during these same intervals

response of the marine infauna to triassic jurassic environmental change ichnological data from southern england abstract the trace fossil record through the triassic jurassic boundary interval is examined at three sites in central and southern england st audrie s bay somerset pinhay bay devon and long itchington warwickshire the lower pre planorbis beds of the blue lias formation record low ichnotaxonomic diversity low bioturbation intensity small burrow diameters and an absence of deep tier bioturbation the stepwise reappearance of ichnotaxa following this interval is similar at the three sites suggesting similar rates of recovery in the benthic marine ecosystem and highlighting the potential contribution of these trace fossils to stratigraphic correlation mass extinction in the late triassic is increasingly linked to the emplacement of the central atlantic magmatic province camp timing of the onset of camp volcanism in the uk is currently imperfectly known but potentially occurred within either the westbury formation or the lilstock formation if the onset of camp was within the lilstock formation the modestly diverse trace fossil assemblage of the langport member of the lilstock formation suggests that emplacement of camp had little lasting effect on the marine benthos in central and southern england the decline in benthic activity recorded in the pre planorbis beds appears to be unrelated to the onset of camp and any associated environmental change it is more likely related to an episode of marine anoxia an episode of marine anoxia also provides a suitable causal mechanism for the reduction of infaunal tiering

holocene temperature changes in northern fennoscandia reconstructed from chironomids using bayesian modelling the recently developed bayesian multinomial calibration model bummer was applied to the fossil chironomid assemblages of a lake situated at the present tree line in northern fennoscandia to reconstruct patterns in holocene climates the results are compared with inferences derived using non bayesian weighted averaging partial least squares regression the reconstruction exhibits both long term trends as well as a series of shorter term oscillations abrupt climatic excursions were particularly characteristic for the early holocene period with cooling episodes around 9200 8600 and 8200 cal yr bp the interval from ca 8000 to 5800 cal yr bp appeared to be warm and stable but was followed by a pronounced climatic cooling around 5800 cal yr bp leading to a relatively long lasting mid holocene temperature minimum between ca 5800 and 4000 cal yr bp the reconstruction during the latter part of the holocene is relatively featureless which may partly be due to gradual shallowing of the lake by sedimentation that may have affected chironomid compositions thereby masking the climate signal the major climatic patterns in our reconstruction agree well with inferences from greenland ice and marine sediments and are also in line with the previous reconstructions based on diatoms and pollen from the same core although the finer scale variations reflected by the three proxies do not always match the overall results provide evidence for climatic complexity during the holocene epoch and demonstrate that bayesian modelling is highly suitable for reconstruction purposes

late glacial and late holocene moraines in the cerros cuchpanga central peru abstract small ice fields on the western cordillera northeast of lima were expanded to three times their present size in the recent past and the regional snow line was probably about 100 m lower than it is today outwash from the expanded glaciers formed deltas of silt in valley bottom lakes when the ice lobes retreated the reduced outwash was trapped behind recessional moraines and the clear meltwater infiltrated into the limestone bedrock and emerged at the heads of the deltas in spring pools the delta surfaces then became covered with peat and radiocarbon dates for the base of the peat 1100 70 and 430 70 yr b p for two different deltas indicate that the maximum ice advance was older than those dates and thus older than the little ice age of many north temperate regions much older moraines date from expansion of the same local summit glaciers to even lower levels in the main valleys which had previously been inundated by the cordilleran ice field the cordilleran deglaciation and this expansion of local glaciers probably occurred between 12 000 and 10 000 yr ago on the basis of slightly contradictory radiocarbon dates

chironomid evidence for late glacial climatic reversals in maine previously published pollen studies from maine have not identified any late glacial reversals despite evidence for them from adjacent areas the distribution and abundance of midge flies are strongly correlated with summer surface water temperatures we analyzed fossils of larval midge flies from the sediments of two ponds trout and tilley from maine each site reveals a major and a minor oscillation during which inferred summer surface water temperatures fell by 7 13 c and 2 1 2 6 c respectively we tentatively correlate these events with the younger dryas cooling and killarney oscillation reported from adjacent maritime canada where they have been ams 14c dated at 10 770 10 000 and 11 160 10 910 yr b p respectively a third oscillation occurs at the northernmost site tilley pond and may represent the effects of a local ice advance in northern maine

seismic monitoring and geomechanics simulation petroleum reservoir engineering involves four disciplines geology transport thermodynamics and geomechanics the latter has suffered benign neglect for decades but large scale development of viscous oils high porosity offshore reservoirs hpht cases and fractured carbonates with severe stress sensitivity are raising awareness that geomechanics is a vital aspect of reservoir management because 60 of the world s liquid fossil fuel is in the form of viscous oil in weak sandstones iea 2005 the roles of geomechanics and seismic monitoring will increase sharply in decades to come

holocene sedimentation in glacial tasikutaaq lake baffin island tasikutaaq lake on cumberland peninsula baffin island receives inflow and fine sediment from a 448 km2 drainage basin 21 of which is glacier covered during the summer of 1983 the lake remained essentially isothermal between about 4 and 6 c the suspended sediment concentration of inflow never exceeded 100 mg l 1 with overflow and homopycnal flow dominant surface sediments are clearly laminated although varves are not apparent the sediments are very fine with less than 3 sand in all but the most proximal sites average sedimentation rates between 1976 and 1983 ranged from about 4 mm a 1 to 0 25 mm a 1 down lake from the point of inflow the absence of varves is a function of the low rates of sediment accumulation and the long residence time of the fine sediments in the water column three sediment cores up to 135 cm in length reveal marked changes in sediment characteristics and diatom assemblages through the holocene during the late foxe glaciation it is likely that glacier ice contacted the la

allerod younger dryas lake temperatures from midge fossils in atlantic canada remains of freshwater midges are abundant in lake sediments and their species distributions are closely related to the surface water temperature of lakes their distributions thus provide a powerful tool for paleoclimatology the distribution of species in a core from splan pond in atlantic canada indicates that there were abrupt transitions in late glacial temperatures between warm and cold states the transitions are correlative with the well known warm allerod and cold younger dryas events in europe these data thus confirm the inference from palynological data that these events affected regions on both sides of the atlantic

phylogenetic community paleoecology of one of the earliest complex crinoid faunas brechin lagerstatte ordovician abstract integrating phylogenetic biology with paleoecology can provide a valuable context for understanding patterns of community structure and niche partitioning in ancient ecosystems however the lack of robust phylogenies for many fossil taxa precludes studies of this nature particularly among marine invertebrates fossil crinoidea echinodermata comprise an ideal model system for phylogenetic community paleoecology for three reasons 1 they preserve anatomical features that directly relate to feeding ecology 2 assemblages of well preserved specimens represent ecological snapshots in time and 3 recent advances in resolving the crinoid tree of life have produced high resolution phylogenies for ordovician lineages here we apply multivariate and phylogenetic comparative methods to investigate patterns of paleocommunity structure niche partitioning and ecomorphospace occupation in one of the earliest known complex crinoid paleocommunities the brechin lagerstatte upper ordovician katian results indicate niche differences among species were determined primarily by characters related to filtration fan morphology filtration fan density and body size distributions support phylogenetic niche conservatism but traits related to the size of the feeding area are more labile and exhibit greater divergence than expected among closely related species finally we compare changes in the shape and phylogenetic structure of niche distributions between the brechin lagerstatte and the edwardsville crinoid fauna a well studied mississippian visean paleocommunity to examine patterns of community change across the early to middle paleozoic crinoid macroevolutionary faunas

the mode and mechanism of the last deglaciation oceanic evidence changes in ocean temperature carbonate productivity and ice rafted detritus in the north atlantic suggest that half of the northern hemisphere ice volume at the last glacial maximum had disappeared by 13 000 yr b p despite the still extensive limits of the ice sheets this early thinning of the ice sheets occurred during a time when summer insolation values were slowly rising but when pollen evidence south of the ice margins indicates cold dry air masses we infer that this rapid early ice disintegration 16 000 13 000 yr b p was caused by oceanic mechanisms 1 rising sea level causing increased calving along ice margins 2 the chilling of the sea surface by icebergs and meltwater reducing moisture extraction by the atmosphere and transport to the ice sheets and 3 winter freezing of the low salinity meltwater layer suppressing local moisture extraction and the regional influx of moisture bearing storms from lower latitudes in winter and hence starving the ice sheets these oceanic feedback mechanisms were strongest from 16 000 to 13 000 yr b p and weaker but still active from that date until the end of deglaciation at 6000 yr b p

filtration models guilds and biofacies crinoid paleoecology of the stanton formation upper pennsylvanian midcontinent north america abstract filtration models make several predictions concerning the distribution of crinoids among benthic habitats 1 generally higher energy shoreward settings should contain crinoid assemblages dominated by taxa with dense mesh filtration fans 2 generally lower energy offshore settings should be dominated by crinoids with open mesh filtration fans 3 diversity should be highest in nearshore settings which generally contain low energy microhabitats within high energy settings where both dense fan and open fan forms can co occur whereas offshore assemblages should be dominated by open fan taxa thus open fan forms should be more eurytopic than dense fan forms also previous empirical models for crinoid distribution patterns note that nearshore assemblages are dominated by large forms whereas offshore assemblages are dominated by small forms filtration fan morphology and body size interact significantly to determine how and where crinoids feed and thus are used here as criteria for distinguishing late paleozoic crinoid guilds the distribution patterns of crinoid taxa and guilds among the benthic paleoenvironments of the upper pennsylvanian missourian stanton formation were used to test the predictions of the filtration models the results of quantitative analyses show that large dense fan crinoids are significantly more abundant in shoreward assemblages than smaller open fan crinoids which are more abundant in offshore assemblages these results are consistent with the aforementioned models however diversity patterns are not consistent with the filtration models indicating that mid depth and aerobic offshore assemblages are more taxonomically and trophically diverse than nearshore and dysaerobic offshore assemblages ostensibly due to the overlapping ranges of characteristically nearshore and offshore taxa analysis of guild distribution patterns also indicates some contradictions to predicted patterns of stenotopy and eurytopy indicating additional complexities to late paleozoic crinoid paleoecology five recurrent crinoid assemblages or biofacies have been identified from the stanton formation of midcontinent north america the guild structure and diversity of these biofacies are characterized here as 1 a moderate diversity nearshore biofacies dominated by large calyx dense fan guilds 2 a high diversity midshelf biofacies characterized by equitable contributions of many taxa and guilds 3 a moderate diversity offshore biofacies dominated by non pinnulate and small calyx open fan pinnulate guilds 4 a low diversity offshore dysaerobic biofacies dominated by small calyx pinnulate guilds 5 a depauperate offshore biofacies dominated by a unique stalkless species paragassizocrinus tarri except for biofacies 5 the number of guilds appears to increase offshore however the equitability of taxa among and within the guilds generally decreases offshore this pattern indicates that the heterogeneity of resources or the recognition by taxa of different classes of resources as reflected by the variety of functional types increased from nearshore to offshore but that the abundance or accessibility of these resources and or the relaxation of competition within guilds increased from offshore to nearshore

sensitivity of compaction induced multicomponent seismic time shifts to variations in reservoir properties abstractpore pressure variations inside producing reservoirs result in excess stress and strain that influence the arrival times of reflected waves inversion of seismic data for pressure changes requires better understanding of the dependence of compaction induced time shifts on reservoir pressure reduction using geomechanical and full waveform seismic modeling we investigate pressure dependent behavior of p s and ps wave time shifts from reflectors located above and below a rectangular reservoir embedded in a homogeneous half space our geomechanical modeling algorithm generates the excess stress strain field and the stress induced stiffness tensor as linear functions of reservoir pressure analysis of time shifts obtained from full waveform synthetic data shows that they vary almost linearly with pressure for reflectors above the reservoir but become nonlinear for reflections from the reservoir or deeper interfaces time shift misfit curves computed with respect to noise contaminated data from a

wisconsinan late glacial environmental chage in new brunswick a regional synthesis a synthesis is presented of the history of deglaciation vegetation cover and climate in new brunswick canada during that part of the wisconsinan late glacial period 12 9 ka bp for which detailed records exist curves of inferred temperature variations in the region during this period are presented based upon qualitative interpretations of plant records and quantitative estimates based upon fossil chironomid assemblages

quantification of paleotemperature changes during isotopic stage 2 in the la draga continental sequence ne spain based on the mg ca ratio of freshwater ostracods past summer temperature changes are quantified from the la draga sequence banyoles ne spain during stage 2 24 10 ka bp using trace element content in lacustrine ostracod valves the high resolution results from this new method are compared to summer paleotemperature reconstructions from sequences from the north atlantic area providing a discussion about the magnitudes of some temperature changes in ne spain and offshore portugal the coldest part of stage 2 is not documented at the classical date of similar to 18 c 14 ka bp similar to 21 5 calendar ka bp but rather occurred later date of ca 17 15 ka cal bp in the north atlantic area the onset of the bolling allerod interstadials was relatively synchroneous at similar to 14 6 ka cal bp although the magnitude of the bolling allerod improvement was more important in the southern area than in the northern area the duration of the younger dryas is discussed even if different durations are reported from calendar ages it seems that the summer temperature cooling of the younger dryas was similar around the north atlantic area c 1996 elsevier science ltd

modeling and analysis of compaction induced traveltime shifts for multicomponent seismic data abstractmodeling of time shifts associated with time lapse 4d seismic surveys is helpful in evaluating reservoir depressurization and inverting for subsurface stress using coupled geomechanical and full waveform seismic modeling we study the influence of compaction induced stress and strain around a simplified reservoir on compressional p shear s and mode converted ps waves we estimate compaction induced time shifts and analyze their dependence on reflector depth and pressure drop inside the reservoir time shifts between synthetic baseline and monitor surveys are obtained by processing techniques that are potentially applicable to field data although p wave time shift lags for reflectors in the overburden are indicative of induced anisotropy they are two to three times smaller than s wave time shift leads for reflectors beneath the reservoir we also investigate the contributions of the deviatoric and volumetric stains to the time shifts for all three modes time shifts for s and ps waves

trace fossil tiering in flysch sediments examples from the guipuzcoan flysch cretaceous paleogene northern spain abstract distribution of trace fossils in flysch sediments is in great part conditioned by tiering that is the vertical partitioning of trace producing organisms below the sediment water interface ichnologic studies in the guipuzcoan flysch upper albian lower eocene northern spain show that tiering in flysch sediments is strongly controlled by sediment character mode and rate of deposition and degree of oxygenation of pore waters depending on the mode of deposition trace fossil tiering in flysch developed and was preserved in two radically different styles 1 in event layers chiefly turbidites tiering is preserved without secondary distortion owing to synchronous colonization and the lack of vertical ascent through time vertical tiering structure depends primarily on sediment composition sequence and thicknesses of structural divisions and oxygen profile variations in tiering are interpreted to reflect the particular oxygen tolerances penetration potentials and nutritional requirements of tracemakers 2 in background sediments hemipelagites and pelagites tiering resulted from successive colonizations that were influenced by background sedimentation rates sediment composition and oxygen levels of pore waters tiering of actively or passively filled burrows is reflected by complex ichnofabrics and the superposition of different tiers by ascension tiering structure was frozen upon deposition of superjacent event layers the original tiering of graphoglyptids open burrows may be reconstructed from their cross cutting relationships on turbidite soles these contrasting styles of tiering development are characteristic of flysch and other sediments composed of alternating event and background deposits

late quaternary chronology and environments of square lake torngat mountains labrador sediment pollen and diatom records from square lake a small lake dammed by a segment of saglek moraine cover the period of deposition of and deglaciation from the saglek moraine the basal radiocarbon date 18 210 1900 years bp is on sediment contaminated by reworked pollen and is thus a maximum age however the date was measured on organic carbon recovered from glaciolacustrine couplets associated with deposition of the saglek moraine and thus establishes a late wisconsinan age for the saglek moraine vegetation on the ice free upland surrounding square lake at this time was a sparse tundra vegetation dominated by grasses and herbs the absence of diatoms indicates perennial lake ice cover a major transition is recorded by pollen and diatoms at 8 5 ka vegetation probably remained sparse tundra but birch and willow may have arrived in the area by 8 ka diatoms are first dominated by alkaliphil species reflecting continued influence of glaciolacustrine sedimentation an abrupt change in depos

petroleum reservoir characterization using downhole microseismic monitoring imaging of microseismic data is the process by which we use information about the source locations timing and mechanisms of the induced seismic events to make inferences about the structure of a petroleum reservoir or the changes that accompany injections into or production from the reservoir a few key projects were instrumental in the development of downhole microseismic imaging most recent microseismic projects involve imaging hydraulic fracture stimulations which has grown into a widespread fracture diagnostic technology this growth in the application of the technology is attributed to the success of imaging the fracture complexity of the barnett shale in the fort worth basin texas and the commercial value of the information obtained to improvecompletions and ultimately production in the field the use of commercial imaging in the barnett is traced back to earlier investigations to prove the technology with the cotton valley imaging project and earlier experiments at the m site in the piceance

midges and palaeotemperature reconstruction the north american experience abstract the development of midge based palaeoclimatology in north america is reviewed with a focus on lateglacial and holocene climatic change although relatively few sites have been studied midge inferred palaeotemperatures reveal detailed records of lateglacial climate oscillations and more subtle holocene temperature changes holocene climate changes are often at or near the detection limit using current palaeotemperature inference models interference from other environmental variables including water depth and oxygen concentration changes are discussed as well as the challenges inherent to developing better models the isotopic signature of chitin preserved in midge head capsules has opened new avenues for midge palaeotemperature inference through coordinated research efforts national and international collaborations will provide opportunities to reconstruct holocene palaeoclimate at continental and hemispheric scales

aftermath of the permian triassic mass extinction event paleoecology of lower triassic carbonates in the western usa paleoecologic study of invertebrate faunas from three successive early triassic seaways reveals that biotic recovery from the end permian mass extinction event was slow and that full recovery did not occur until after the early triassic simple cosmopolitan opportunistic generalists and low diversity low complexity paleocommunities were characteristic of the entire early triassic in the western usa an increase in guild and taxonomic diversity was observed with the addition of several new higher taxa in the late early triassic spathian to the almost exclusively molluscan faunas of the earlier early triassic nammalian potential disaster forms the inarticulate brachiopod lingula and the paper pecten claraia dominated the earliest early triassic faunas griesbachian and even occurred in the late early triassic normal marine stromatolites comparison with data on faunas from the permian and triassic suggests that even the most diverse early triassic faunas in the spathian were rather low in guild diversity and species richness these characteristics of genera and paleocommunities in the early triassic may be typical of mass extinction aftermaths

late glacial allerod younger dryas coleoptera from central cape breton island nova scotia canada coleoptera from three late glacial sites on cape breton island nova scotia canada provide proxy climate data from 12 600 to 10400 bp samples older than about 11 800 bp contain tundra to tree line species between 11 800 and about 10 800 bp beetle assemblages become typical of the modern boreal forest beetles younger than 10 800 bp responded to climatic deterioration during the younger dryas although coleopteran evidence for the younger dryas is not as strong as that presented by palynological and stratigraphic studies the appearance of olophrum boreale and other species found today in the northern boreal forest and on tundra or coastal tundra corresponds with the decline of shrub birch and the rise in willow and alder pollen beetles responded just as likely to changes in vegetation and ground cover as to changes in temperature the extent to which coleoptera were affected may lie somewhere between a moderated continental response seen in the great lakes region in north america and more extreme changes recorded in europe this response is consistent with shifts in the north atlantic oceanic polar front in the ruddiman and mcintyre model resumc les colkoptkres trouvks dans trois sites glaciaires tardifs de l ile du cap breton ouvelle cosse canada