gzhelian asselian palaeoaplysina microencruster reef community in the taishaku and akiyoshi limestones sw japan implications for late paleozoic reef evolution on mid panthalassan atolls abstract a palaeoaplysina microencruster reef community is recognized in the gzhelian asselian interval of the taishaku and akiyoshi limestones in sw japan which represent accreted panthalassan atoll carbonates in a reef core area of the atoll the alga palaeoaplysina acted as a framebuilder and was associated with various binders e g tubiphytes archaeolithoporella cystoporate bryozoans and microbialites and sediment bafflers such as fenestrate and cryptostomate bryozoans and phylloid algae in a subtidal environment of the back reef area palaeoaplysina and phylloid algae flourished as sediment bafflers a microbial community including tubiphytes and sessile foraminifers was predominant in a very shallow peritidal environment of the back reef area palaeoaplysina was distributed mainly along the northern margin of pangea and is regarded as a boreal element during gzhelian asselian time its distribution extended to the tropical or subtropical panthalassa ocean due to global cooling on the akiyoshi atolls the palaeoaplysina microencruster community was succeeded by a sponge microencruster community in the late early permian the timing of this biotic turnover is similar to that of a change in climate from icehouse to greenhouse conditions and coincides with superplume activity beneath the mid panthalassa ocean

variations in the age of arctic sea ice and summer sea ice extent 1 three of the past six summers have exhibited record low sea ice extent on the arctic ocean these minima may have been dynamically induced by changes in the surface winds based on results of a simple model that keeps track of the age of ice as it moves about on the arctic ocean we show that the areal coverage of thick multi year ice decreased precipitously during 1989 1990 when the arctic oscillation was in an extreme high index state and has remained low since that time under these conditions younger thinner ice anomalies recirculate back to the alaskan coast more quickly decreasing the time that new ice has to ridge and thicken before returning for another melt season during the 2002 and 2003 summers this anomalously younger thinner ice was advected into alaskan coastal waters where extensive melting was observed even though temperatures were locally colder than normal the age of sea ice explains more than half of the variance in summer sea ice extent

multiple metal sources in the glaciomarine facies of the neoproterozoic jacadigo iron formation in the santa cruz deposit corumba brazil abstract the rapitan type banded iron formation bif in the banda alta formation fm of the neoproterozoic jacadigo group in brazil was deposited in a redox stratified marine sub basin which was strongly influenced by glacial advance retraction cycles with temporary influx of continental freshwater and upwelling metal enriched seawater from deeper anoxic parts these new finding are based on new stratigraphic whole rock geochemical and stable fe and c isotope data from the santa cruz hematite deposit near corumba mato grosso do sul where a stratigraphy of lower and upper dolomite rich and intermediate chert rich bif facies with up to three intercalated diamictites is revealed the ca mg fe mn carbonate chert hematite and chert hematite bif 30 45 wt fe of the lower dolomite rich facies shows chemical signatures consistent with well oxidized seawater i e low pr yb paas strong negative cepaas and positive gdpaas and ypaas anomalies as well as negative 13c carbonate typical for neoproterozoic glaciogenic carbonates sedimentation in a rather shallow water depth during relatively warm interglacial periods was likely influenced by abundant freshwater from fluviatile runoff and melting icebergs in such conditions abundant microbial activity accommodated co2 sequestration in carbonates as spheroids and mats and fractionated 57fe 2 6 and 1 2 in primary fe hydroxides in contrast the intermediate chert rich facies characterized by chert hematite bif 35 55 wt fe and isolated hematite chert and hematite mud recorded trace element signatures of non oxidized absence of ce anomalies and variable ypaas anomalies more metal enriched fe mn si ni zn pb u seawater thus deposition was within and below the shallow level redoxcline during ice cover colder water and isolation from sunlight reduced microbial activity and thus an almost non fractionated 57fe 0 7 to 0 0 fluid signature reveals that low temperature based on almost absence of eu anomaly in bif hydrothermal mor vents or sub seafloor alteration of mafic or felsic rocks or shales fertilized seawater with metals all results lead to the model that the jacadigo group formed during one major marine transgression regression cycle and bif facies in the banda alta fm were a response to first and second order periodic variations of the depth of the redoxcline induced by the juxtaposition of glacial advance retraction cycles active graben tectonics and glacial isostatic adjustment or eustatic water level changes the chert rich bif facies marked the maximum of transgression age and tectonic setting of the jacadigo basin remains contentious it may represent a continental back arc basin of the brasiliano collision zone 590 ma in which submarine alteration was possibly related to low temperature hydrothermal fluids moving through the active graben system as an alternative to basin wide benthic pore water flux this would place the jacadigo group to the suite of ediacarian gaskier glaciations although a relationship to the marinoan glaciation 660 635 ma mainly based on the published sedimentation age bracket of 706 587 ma is also possible

structure and composition of organic reefs and carbonate mud mounds concepts and categories defined here as essentially in place calcareous deposits created by sessile organisms organic reefs are diverse and complex structures with a long geological history their classification has been the subject of fierce debate often characterized by reliance on subjective features such as wave resistance and qualitative attempts to discriminate between first and second class reefs in contrast emphasis is here placed on the objective characteristic of the type of sedimentary support which largely determines the sedimentary composition of the deposit constructional and depositional processes result in three principal sedimentary components matrix m essentially in place skeletons s and cavity cement c whose proportions can be represented on msc triangular plots separately or together these components also provide the structural support for the reef on these compositional and structural bases three main categories of organic reef are recognized 1 matrix supported reefs agglutinated microbial reefs cluster reefs segment reefs 2 skeleton supported reefs frame reefs 3 cement supported reefs cement reefs agglutinated microbial reefs possess laminated clotted or aphanitic fabrics created by microbial trapping of particulate sediment in place skeletons and large primary cavities are rare early cementation may provide added support topographic relief is limited by the need for currents to provide sediment to accreting surfaces cluster reefs skeletal reefs in which essentially in place skeletons are adjacent but not in contact resulting in matrix support characterized by relatively high matrix skeleton ratios and low volumes of extra skeletal early cement sediment trapping is an important corollary of skeletal growth and cluster reef organisms are tolerant of loose sediment absence of framework limits the topographic relief that cluster reefs can attain relative to spatial extent and may permit bedding to develop within the reef close cluster reefs have skeletons up to 1 unit distance apart spaced cluster reefs have skeletons more than 1 and up to 2 unit distances apart with increasing separation of skeletons they grade to level bottom communities segment reefs matrix supported reefs in which skeletons are adjacent and may be in contact but are mostly disarticulated and mainly parauthochtonous matrix abundance is high and early cement relatively low moderate relief can develop in response to intense on reef sediment production frame reefs skeletal reefs in which essentially in place skeletons including calcified microbes are in contact characterized by relatively high skeleton matrix ratio skeletal support enables them to raise themselves above the substrate independently of cementation and particulate sedimentation simultaneously by creating partly open shelter cavities skeletal support may facilitate early cementation both relief and early lithification promote marginal talus formation skeletal shape and orientation distinguish conical stick like dendritic domical and laminar frames each of these may be open or filled open frame reefs

changes in terrestrial floras at the triassic jurassic boundary in europe abstract one of the biggest mass extinctions took place at the triassic jurassic boundary it affected both marine and terrestrial ecosystems and caused the disappearance of many animal taxa mostly marine ones its influence on floral changes has been widely discussed with arguments offered for the sudden mass extinction of plants over vast areas or alternatively for slow less extensive changes the aim of this study was to statistically verify changes in terrestrial plant composition during the tjb in europe and to examine the type and extent of these changes data from polish localities an interesting new addition to the floristic data from the tjb were compared with those from other selected localities in europe the database contains 311 macroflora taxa from 106 localities 16 polish in 13 countries grouped into 29 regions and 571 microflora taxa from 105 localities 29 polish in 11 countries grouped into 37 regions the analysed data cover the period from the anisian to the toarcian stages range based metrics for diversity dynamics were calculated to show trends in floral changes during the studied time interval the focus being on the tjb due to strong disproportions in the number of localities and occurrences the rhaetian and the hettangian stages were overrepresented the warm and humid climate of those stages promoted plant diversity and led to the formation of numerous broad floodplains conducive to the preservation of remains e g in coal the patterns established by the raw data analyses were also assessed by applying a sampling standardisation procedure our results based on accurate data from poland and the rest of europe confirm and visualize a scenario in which there were no significant changes in terrestrial plant composition at the tjb hierarchical clustering suggests that local habitat conditions are the key factor in the grouping of localities with similar floristic composition and that differences between floras are not associated with the time dimension stages

molecular records of microbialites following the end permian mass extinction in chongyang hubei province south china abstract by using gas chromatograph gc and gc mass spectrometry a series of biomarkers were identified in the aliphatic fractions of extracts from microbialites following the end permian faunal mass extinction in chongyang section hubei province south china the dominance of lower molecular weight n alkanes in the samples from the section suggests that algae and bacteria were the dominant contributors to the organic fraction preserved in this marine section with bacteria particularly enhanced within the stromatolite the end permian biotic crisis coincided with a short term suppression of autotrophs indicated by the ratio of pristane pr and phytane ph to c 17 and c 18 n alkanes and proliferation of heterotrophs shown by the ratio of branched to normal c 17 alkanes the biotic crisis also may have been associated with a transient oxygenation event in the shallow marine indicated by elevated pr ph ratios and lowered c 27 18 h 22 29 30 trisnorneohopane ts to c 27 17 h 22 29 30 trisnorhopane tm and gammacerane to c 31 homohopane c 31 hp ratios subsequently three short term episodes of intensified anoxia or enhanced salinity at chongyang are recorded by decreases in pr ph ratios in conjunction with lithological boundaries in the section

temporal variation in calcification in marine cyanobacteria periods of widespread abundance of calcified cyanobacteria in marine environments are here termed cyanobacterial calcification episodes cces intense such episodes occurred in the cambrian early ordovician late devonian and mid late triassic mild episodes occurred during the early carboniferous and jurassic early cretaceous possible episodes during parts of the silurian and permian await confirmation cyanobacterial calcification is not obligate but is dependent upon environmental factors favouring carbonate precipitation cyanobacterial calcification episodes are therefore interpreted as reflecting periods of increased marine carbonate precipitation this is supported by the general abundance of marine carbonate cements and oolites during cyanobacterial calcification episodes cyanobacterial calcification episodes correspond with phanerozoic periods for which elevated global temperatures have been inferred they do not appear to correlate closely with inferred changes in aragonite calcite facilitation the sandberg curve and p co2 through time it is concluded that variations in the precipitation rates of abiotic and quasi abiotic marine carbonates through time have been controlled primarily by temperature the mineralogy of these precipitates appears instead to have been mainly influenced by p co2 and the mg ca ratio also linked to sea level through plate tectonic processes thus the controls on rate and mineralogy of precipitation were independent of one another

oldest scleractinian coral reefs on the north american craton upper triassic carnian northeastern british columbia canada abstract bioclastic accumulations composed of crinoids brachiopods molluscs spongiomorphs and scleractinian corals occur within upper triassic strata of the lower baldonnel formation at pardonet hill in northeastern british columbia canada these small buildups 100 to 500 m3 have planar bases and broadly convex tops these mounds are interpreted as small patch reefs composed of packstone bioclastic floatstone rudstone and carbonate breccia intercalated with mixed siliciclastic carbonate sediments deposited in a shallow subtidal setting i e above fairweather wave base amalgamated hummocky cross stratified to current ripple laminated quartz dominated sandstone beds and numerous sharp based normally graded bioclastic commonly encrinitic packstone grainstone quartz sandstone couplets characterize inter reef lithologies conodont biostratigraphy indicates that the pardonet hill patch reefs occur within strata dated as earliest upper carnian lower nodosus zone the pardonet hill patch reefs originated and developed during an interval of regional sea level lowstand strata within which these patch reefs occur represent the westernmost migration of the triassic shoreline in western canada disappearance of coral reefs in the study area may have been affected by rapid marine transgression and failure of reef faunas to recolonize the new shore zone further to the east the pardonet hill locality occurred on the western margin of the north american craton during the triassic prior to their discovery reef like structures dominated by corals in the western panthalassa were limited to allochthonous terranes now part of the cordillera the pardonet hill patch reefs occur at approximately 30 triassic paleolatitude in modern settings this is at the extreme latitudinal margin of subtropical zooxanthellate reef development the presence of benthic faunas characteristic of low paleolatitude settings on the northwestern coast of pangea has significant implications in paleotectonic and paleoenvironmental reconstructions

construction model and paleogeographic distribution of late pennsylvanian phylloid algal microbial reefs a case study in eastern inner mongolia north china abstract the gzhelian late pennsylvanian reefs of the amushan formation in eastern inner mongolia north china were formed by filamentous microbes and phylloid algae loosely accumulated prostrate phylloid algae provided substrates for growth of filamentous microbes to construct a rigid reef framework filamentous microbes grew parallel to the surfaces of phylloid algae forming micritic encrustations subsequent developed stage of the filamentous microbes growing perpendicularly to the phylloid algae surfaces produced the peloid a aggregations concentrated areas of peloids of a type the remaining spaces in the phylloid algal microbial frameworks were filled by microbes that grew perpendicularly to the phylloid algae surfaces generating peloid b aggregations concentrated areas of peloids of b type microbial sediment with various proportions of phylloid algae is a significant character of the gzhelian buildups in the subtropical north china north china buildups have similar reef building organisms to the typical tethyan buildups but have a different construction model as such the subtropical north china buildups are considered as a sub type of the tropical tethyan buildups

the late triassic extinction at the norian rhaetian boundary biotic evidence and geochemical signature abstract the latest triassic was an interval of prolonged biotic extinction culminating in the end triassic extinction ete the ete is now associated with a perturbation of the global carbon cycle just before the end of the triassic that has been attributed to the extensive volcanism of the circum atlantic magmatic province camp however we attribute the onset of declining latest triassic diversity to an older perturbation of the carbon cycle 13corg of global extent at or very close to the norian rhaetian boundary nrb the nrb appears to be the culmination of stepwise biotic turnovers that characterize the latest triassic and includes global extinctions of significant marine and terrestrial fossil groups these biotic events across the nrb have been largely under appreciated yet together with a coeval disturbance of the carbon cycle were pivotal in the history of the late triassic here we present new and published 13corg data from widespread sections italy greece odp australia new zealand usa canada these sections document a previously unknown perturbation in the carbon cycle of global extent that spanned the nrb the disturbance extended across the panthalassa ocean to both sides of the pangaean supercontinent and is recorded in both the northern and southern hemispheres the onset of stepwise late triassic extinctions coincides with carbon perturbation 13corg at the nrb indicating that a combination of climatic and environmental changes impacted the biota at a global scale the nrb event may have been triggered either by gas emissions from the eruption of a large igneous province pre dating the nrb by a bolide impact of significant size or by some alternative source of greenhouse gas emissions as yet it has not been possible to clearly determine which of these trigger scenarios was responsible the evidence is insufficient to decisively identify the causal mechanism and merits further study

assessing the record and causes of late triassic extinctions accelerated biotic turnover during the late triassic has led to the perception of an end triassic mass extinction event now regarded as one of the big five extinctions close examination of the fossil record reveals that many groups thought to be affected severely by this event such as ammonoids bivalves and conodonts instead were in decline throughout the late triassic and that other groups were relatively unaffected or subject to only regional effects explanations for the biotic turnover have included both gradualistic and catastrophic mechanisms regression during the rhaetian with consequent habitat loss is compatible with the disappearance of some marine faunal groups but may be regional not global in scale and cannot explain apparent synchronous decline in the terrestrial realm gradual widespread aridification of the pangaean supercontinent could explain a decline in terrestrial diversity during the late triassic although evidence for an impact precisely at the boundary is lacking the presence of impact structures with late triassic ages suggests the possibility of bolide impact induced environmental degradation prior to the end triassic widespread eruptions of flood basalts of the central atlantic magmatic province camp were synchronous with or slightly postdate the system boundary emissions of co2 and so2 during these eruptions were substantial but the contradictory evidence for the environmental effects of outgassing of these lavas remains to be resolved a substantial excursion in the marine carbon isotope record of both carbonate and organic matter suggests a significant disturbance of the global carbon cycle at the system boundary release of methane hydrates from seafloor sediments is a possible cause for this isotope excursion although the triggering mechanism and climatic effects of such a release remain uncertain d 2003 elsevier b v all rights reserved

late paleocene early eocene tethyan carbonate platform evolution a response to long and short term paleoclimatic change abstract the early paleogene experienced the most pronounced long term warming trend of the cenozoic superimposed by transient warming events such as the paleocene eocene thermal maximum petm the consequences of climatic perturbations and associated changes on the evolution of carbonate platforms are relatively unexplored today modern carbonate platforms especially coral reefs are highly sensitive to environmental and climatic change which raises the question how sub tropical reef systems of the early paleogene reacted to gradual and sudden global warming eutrophication of shelf areas enhanced co 2 levels in an ocean with low mg ca ratios the answer to this question may help to investigate the fate of modern coral reef systems in times of global warming and rising co 2 levels here we present a synthesis of tethyan carbonate platform evolution in the early paleogene 59 55 ma concentrating on coral reefs and larger foraminifera two important organism groups during this time interval we discuss and evaluate the importance of the intrinsic and extrinsic factors leading to the dissimilar evolution of both groups during the early paleogene detailed analyses of two carbonate platform areas at low egypt and middle spain paleolatitudes and comparison with faunal patterns of coeval platforms retrieved from the literature led to the distinction of three evolutionary stages in the late paleocene to early eocene tethys stage i late paleocene coralgal dominated platforms at low to middle paleolatitudes stage ii a transitional latest paleocene platform stage with coralgal reefs dominating at middle paleolatitudes and larger foraminifera dominated miscellanea ranikothalia assilina platforms at low paleolatitudes and stage iii early eocene larger foraminifera dominated alveolina orbitolites nummulites platforms at low to middle paleolatitudes the onset of the latter prominent larger foraminifera dominated platform correlates with the paleocene eocene thermal maximum the causes for the change from coral dominated platforms to larger foraminifera dominated platforms are multilayered the decline of coralgal reefs in low latitudes during platform stage ii is related to overall warming leading to sea surface temperatures in the tropics beyond the maximum temperature range of corals the overall low occurrence of coral reefs in the paleogene might be related to the presence of a calcite sea at the same time larger foraminifera started to flourish after their near extinction at the cretaceous paleogene boundary the demise of coralgal reefs at all studied paleolatitudes in platform stage iii can be founded on the effects of the petm resulting in short term warming eutrophic conditions on the shelves and acidification of the oceans hampering the growth of aragonitic corals while calcitic larger foraminifera flourished in the absence of other successful carbonate producing organisms larger foraminifera were able to take over the role as the dominant carbonate platform inhabitant leading to a stepwise tethyan platform stage evolution around the paleocene eocene boundary this szenario might be also effective for threatened coral reef sites

variability of sea ice cover in the chukchi sea western arctic ocean during the holocene 1 dinocysts from cores collected in the chukchi sea from the shelf edge to the lower slope were used to reconstruct changes in sea surface conditions and sea ice cover using modern analogue techniques holocene sequences have been recovered in a down slope core b15 2135 m 75 44 n sedimentation rate of 1 cm kyr 1 and in a shelf core p1 201 m 73 41 n sedimentation rate of 22 cm kyr 1 the shelf record spanning about 8000 years suggests high frequency centennial oscillations of sea surface conditions and a significant reduction of the sea ice at circa 6000 and 2500 calendar cal years b p the condensed offshore record b15 reveals an early postglacial optimum with minimum sea ice cover prior to 12 000 cal years b p which corresponds to a terrestrial climate optimum in bering sea area dinocyst data indicate extensive sea ice cover 10 months yr 1 from 12 000 to 6000 cal years b p followed by a general trend of decreasing sea ice and increasing sea surface salinity conditions superimposed on large amplitude millennial scale oscillations in contrast 18o data in mesopelagic foraminifers neogloboquadrina pachyderma and benthic foraminifers cibicides wuellerstorfi reveal maximum subsurface temperature and thus maximum inflow of the north atlantic water around 8000 cal years b p followed by a trend toward cooling of the subsurface to bottom water masses sea surface to subsurface conditions estimated from dinocysts and 18o data in foraminifers thus suggest a decoupling between the surface water layer and the intermediate north atlantic water mass with the existence of a sharp halocline and a reverse thermocline especially before 6000 years b p the overall data and sea ice reconstructions from core b15 are consistent with strong sea ice convergence in the western arctic during the early holocene as suggested on the basis of climate model experiments including sea ice dynamics matching a higher inflow rate of north atlantic water

mid triassic integrated u pb geochronology and ammonoid biochronology from the balaton highland hungary ladinian middle triassic strata of the balaton highland west central hungary comprise interbedded marine carbonate and volcaniclastic rocks the sediments are noted for their rich ammonoid faunas which allow detailed biostratigraphic subdivision and correlation for the first time isotopic dating of the tuff layers was carried out to calibrate the age of ammonoid zones and subzones four successive horizons were dated from the felsouu ors section a candidate stratotype for the base of the ladinian stage within the reitzi zone which is interpreted here as the basal ladinian unit the following biostratigraphically tightly constrained u pb zircon ages were obtained felsoeoersensis subzone 241 1 0 5 ma liepoldti subzone 241 2 0 4 ma reitzi subzone 240 5 0 5 and 240 4 0 4 ma a redeposited tuff from the gredleri zone at liter yielded an additional u pb age of 238 7 0 6 ma the new isotopic ages are in agreement with published u pb dates from the southern alps together they allow estimation of the start of the ladinian at 241 5 ma and of the end of the stage at 237 ma a duration of

response of carboniferous permian mid oceanic seamount capping buildup to global cooling and sea level change akiyoshi japan abstract we discuss the response of a carboniferous permian mid oceanic atoll type carbonate buildup to global cooling and sea level fluctuation during gondwana glaciation our examination focused upon the stratigraphic distribution of emergence indicative diagenetic features as a proxy for sea level falls and we correlated their timing with hiatuses indicated by fusuline biostratigraphic discontinuities and the demise of warm adapted metazoan reef builders we examined the pennsylvanian moscovian to lower permian asselian shallow marine limestone succession ca 500 m thick of the akiyoshi limestone group southwest japan reconstructed as a mid oceanic seamount capping buildup in the panthalassan ocean the examined succession is dominated by atoll lagoon facies with subordinate coral chaetetes patch reefs and calci microbial mounds we have recognized several stratigraphic intervals less than 60 m thick in the examined succession in which emergence indicative diagenetic facies are concentrated these facies include the microcodium structure pendant cements recrystallization and algal casts each of the intervals occurs immediately below a fusuline zone boundary and represents a sea level fall event which lasted presumably 1 ma or less possibly reflecting the sea level fluctuation of third order cycles the emergence event in late kasimovian is the most prominent in the series of moscovian through asselian emergence events and resulted in a dissolution unconformity indicated by a fusuline biostratigraphic discontinuity we infer that many intercalations of less freshwater altered limestone in these stratigraphic intervals resulted from short lived emergence resubmergence episodes possibly due to the high frequency glacio eustyaic sea level fluctuation we also showed that the demise of warm adapted metazoan reef builders of corals and chaetetes happened nearly synchronously with the culmination of gondwana glaciation we hypothesize that the demise of these warm adapted reef builders is a biotic response of the akiyoshi buildup to the severe and prolonged global cooling during the pennsylvanian to early permian icehouse period the akiyoshi metazoan reef builders were replaced by calci microbes phylloid algae and calci sponges that exhibit an increasing significance during the lower to middle permian our results reveal the distinct sedimentary and biotic responses of a panthalassan atoll to global cooling and sea level fluctuation during gondwana glaciation in the southern hemisphere we conclude that carboniferous permian mid oceanic atoll stratigraphy has significant archival potential for recognizing the global palaeoclimatic change

climatic and eustatic signals in a global compilation of shallow marine carbonate accumulation rates two of the most important factors that control the accumulation rate of material in carbonate platform environments on geological time scales are climate and eustasy accurately assessing the importance of these interrelated factors through the study of both modern and ancient carbonate facies however is problematic these difficulties arise from both the complexities inherent in carbonate depositional systems and the demonstrable incompleteness of the stratigraphic record here a new compilation of more than 19 000 global phanerozoic shallow marine carbonate accumulation rates derived from nearly 300 individual stratigraphic sections is presented these data provide the first global holistic view of changes in shallow marine carbonate production in response to climate and eustasy on geological time scales notably a clear latitudinal dependence on carbonate accumulation rates is recognized in the data moreover it can also be demonstrated that rates calculated across the last glacial maximum and holocene track changes in sea level in detail the data show that globally averaged changes in carbonate accumulation rates lagged changes in sea level by ca 3 kyr reflecting the commonly observed delay in the response of individual carbonate successions to sea level rise differences between the rates of carbonate accumulation and sea level change over the past 25 kyr ostensibly reflect changing accumulation mode with platform drowning give up mode pervasive during peak early holocene sea level rise followed by a switch to catch up mode accumulation from ca 9 ka to the present carbonate accumulation rates older than the quaternary are typically calculated over time spans much greater than 100 kyr and at these time spans rates primarily reflect long term tectonically mediated accommodation space changes rather than shorter term changes in climate eustasy this finding coupled with issues of stratigraphic incompleteness and data abundance tempers the utility of this and other compilations for assessing accurately the role of climate and eustasy in mediating carbonate accumulation rates through geological time

sea ice variations in the central canadian arctic archipelago during the holocene abstract a sea ice record for barrow strait in the canadian arctic archipelago caa is presented for the interval 10 0 0 4 cal kyr bp this holocene record is based primarily on the occurrence of a sea ice biomarker chemical ip25 isolated from a marine sediment core obtained from barrow strait in 2005 a core chronology is based on 14c ams dating of mollusc shells obtained from ten horizons within the core the primary ip25 data are compared with complementary proxy data obtained from analysis of other organic biomarkers stable isotope composition of bulk organic matter benthic foraminifera particle size distributions and ratios of inorganic elements the combined proxy data show that the palaeo sea ice record can be grouped according to four intervals and these can be contextualised further with respect to the holocene thermal maximum htm spring sea ice occurrence was lowest during the early mid holocene 10 0 6 0 cal kyr bp and this was followed by a second phase 6 0 4 0 cal kyr bp where spring sea ice occurrence showed a small increase between 4 0 and 3 0 cal kyr bp spring sea ice occurrence increased abruptly to above the median and we associate this interval with the termination of the htm elevated spring sea ice occurrences continued from 3 0 to 0 4 cal kyr bp although they were more variable on shorter timescales within this fourth interval we also provide evidence for slightly lower and subsequently higher spring sea ice occurrence during the mediaeval warm period and the little ice age respectively comparisons are made between our proxy data with those obtained from other palaeo climate and sea ice studies for the caa

sedimentary processes in the thau lagoon france from seasonal to century time scales as a part of the microbent programme an investigation of the sedimentation framework was carried out at the water sediment interface in the thau lagoon french mediterranean coast two main sites c4 in the middle of the lagoon and c5 near oyster farms were visited six times between december 2001 and may 2003 interface sediments were studied using classical sedimentology parameters radiography rx grain size distribution and analysis of selected radionuclides 234th 7be 210pb 226ra on a century time scale excess 210pb 210pbxs presents classical profiles with an upper mixed layer followed by an exponential decrease of activities to undetectable levels below 20 30 cm at the central site c4 cores seem to register episodic changes in mean grain size presenting recurrently peaks the upper 10 cm of 210pbxs profiles at site c5 exhibit a mixed layer associated with coarser sediments this could be related to biological activity sedimentation rates derived from 210pbxs varied from 0 15 cm y 1 at the edge of the basin to 0 25 cm y 1 at the central site on a seasonal time scale 234th and 7be both show significant variations in activities and in penetration within the sediment bioturbation rates derived from both radionuclides agree well and range between 1 10 cm2 y 1 at site c4 and 1 31 cm2 y 1 at site c5 234th and 7be fluxes at the water sediment interface show too seasonal variations more pronounced for site c5 this latter site presents especially a higher variability that is well marked with season probably in relation with its position near oyster farms

cyclone pumping sediment partitioning and the development of the great barrier reef shelf system a review abstract the modern great barrier reef gbr is part of the world s largest and best known mixed terrigenous carbonate continental margin the gbr shelf contains three shore parallel sedimentary belts an inner shelf zone of terrigenous sedimentation at depths of 0 22 m a middle shelf zone of sediment starvation at depths of 22 40 m and an outer shelf reef tract with its inner edge at ca 40 m depth these zones are controlled by the dynamics of northward fair weather along shelf drift driven by southeasterly trade winds and by the regular passage of tropical cyclones cyclones cause wind driven north directed middle shelf flows in excess of 130 cm s which erode the seabed concentrate the sparse mobile sediment into sand ribbons and advect suspended load onto the outer part of the nearshore terrigenous sediment prism and into inter reef depocentres within the outer shelf reef tract cyclones largely control the input of new sediment into the gbr system via river flooding seabed erosion or reef breakage they also help to control the partitioning and dispersion of the three main shore parallel belts of sediment and hence stratigraphic accumulation acting as a sediment pump especially during interglacial highstands cyclones have exerted great control on the development of the modern gbr province and its sediments by maintaining a broad shelf parallel zone of episodically mobilised sediment and scoured seabed upon which coral reefs have been unable to form cyclones may also have partly controlled the timing of initiation of the first gbr at 0 6 mybp contrary to current models gbr storm beds are most likely to be preserved intact close to the shoreline and become coarser grained away from the shoreline for the central gbr highstand shedding only applies to carbonate sediment at the scale of local reefs system wide oceanographic controls cause high rates of carbonate sedimentation on the slope during both sea level rise and highstand concomitantly terrigenous sediment accumulates fastest on the slope during sea level rise and slowest during sea level lowstand and highstand

tabulate corals across the frasnian famennian boundary architectural turnover and its possible relation to ancient photosymbiosis abstract the frasnian famennian biodiversity crisis has traditionally been considered one of the big five mass extinctions among deep changes in the biosphere it almost completely erased shallow water marine ecosystems like coral stromatoporoid reefs which were widespread on the carbonate platforms in the devonian the high biodiversity of bioconstructors during the givetian frasnian acme of palaeozoic reef development contrasts sharply with very low biodiversity levels during the famennian one of major bioconstructing groups in the palaeozoic was tabulate corals a statistical analysis of colony architecture of givetian frasnian and famennian tabulates from the holy cross mountains poland reveals that givetian and frasnian tabulate faunas had smaller corallite diameters and higher colony integration compared to the famennian faunas a similar pattern occurs in the devonian of the ardennes in the holy cross mountains the biodiversity drastically decreases in the late frasnian we interpret givetian frasnian tabulate communities as generally photosymbiotic and their famennian counterparts as generally aposymbiotic in recent corals temperatures above 32 c are generally considered as a threshold for bleaching expulsion of photosymbionts a literature review indicates that in the late frasnian sea surface temperatures exceeded this threshold this leads to a discussion of the late frasnian rise of temperature as a contributing cause of extinction of photosymbiotic bioconstructors and possibility of a late devonian bleaching event

estimating mediterranean oligocene miocene sea surface temperatures an approach based on coral taxonomic richness abstract during the oligocene and miocene shallow water carbonates of the mediterranean region were rich in scleractinian corals thriving within various depositional settings including different reef types their diversity patterns although related to a complex interplay between a suite of environmental factors and palaeobiogeography are considered to be strongly controlled by climate variability and changes in sea surface water temperature by using the quantitative relationship between present day coral taxonomic richness and prevailing sea water temperature underlined by the so called energy hypothesis we test zooxanthellate coral generic richness values from a selection of 102 oligocene miocene localities of the mediterranean region as a proxy for relative palaeotemperatures for each oligocene miocene stage generic richness values per z coral site are firstly examined together with variations of the mediterranean z coral generic pool for better testing the method and assessing its potential application patterns of generic richness and inferred palaeotemperatures are then compared with global palaeoclimatic curves based on marine oxygen stable isotopes data or other climate proxies such as palaeoclimatic records from european continental floras and from fossil coral linear extension rate results clearly show that fluctuations of coral richness derived palaeotemperatures correspond relatively well with global changes of sea water temperature especially for the entire oligocene the chattian aquitanian boundary and the late miocene the well known mid miocene climatic optimum however is not recorded suggesting that regional factors acting together with important palaeogeographical changes exerted a strong control on the generic richness of mediterranean z coral communities a remarkable decline of taxonomic richness is recorded after the burdigalian together with a gradual decrease of palaeotemperatures in the region from the middle miocene onwards to the messinian however an increase in the temperature range of z coral localities is clearly visible indicating that z coral communities were able to thrive and adapt to a wider temperature range as the mediterranean was gradually migrating northwards outside the tropical belt the energy hypothesis if used at global or regional scale can be considered a promising and reliable method for estimating cenozoic palaeotemperatures from coral or other suitable fossil assemblages of shallow water carbonates

paleoceanography of the last interglacial glacial cycle in the polar north atlantic abstract using to its position close to the sites of waxing and waning of the major northern hemisphere ice sheets during the late quaternary climatic cycles the polar north atlantic plays a key role in driving global change therefore analyzing the present day sedimentation processes and reconstructing the late quaternary paleoceanography in this region has been a focus of major scientific interest through the last fifteen years this paper aims to combine the vast amount of new results about modern sediment fluxes surface sediment distribution and the paleoceanographic record and to present a comprehensive overview of the paleoceanography in the polar north atlantic through the last 200 000 years which is based on the basinwide analysis of carbonate and ice rafted detritus records during the last fifteen years the climap paleoceanographic view of the glacial polar north atlantic as an almost permanently isolated sea covered by heavy sea ice throughout the year has been shifted to a much more dynamic view of the environmental conditions a meridional current system similar to the present day conditions secured the exchange of water ice and heat between the polar north atlantic and the alantic and arctic oceans although affected by variations in strength and intensity this meridional current pattern resulted in an almost permanent presence of at least some seasonally ice free areas with all the consequences for e g marine life and deep water formation in addition the development of the continental ice sheets namely the fennoscandian and the barents sea ice sheets is closely related to this dynamic circulation pattern during the so called nordway events the pronounced inflow of temperate waters from the south provided moisture for the growth of the ice sheets the most prominent of these events stage 6 stage 4 and substage 3 1 2 ended in major glaciations reflected in the terrestrial sequences and in the deep sea ird records

cenozoic biogenic mounds and buried miocene barrier reef on a predominantly cool water carbonate continental margin eucla basin western great australian bight the southern continental margin of australia is the largest area of cool water carbonate shelf deposition on the globe interpretation of 5495 km of airgun seismic reflection data in the western part of the great australian bight indicates that the 700 m thick cenozoic section of the offshore eucla basin was deposited largely as a prograding cool water middle to high latitude carbonate ramp characterized by widespread development of broad low relief biogenic bryozoan sponge shelf and upper slope mounds the succession also contains a spectacular and extensive 475 km long buried middle miocene barrier reef the miocene little barrier reef parallel to the modern shelf edge this rimmed carbonate platform margin represents an episode of warm water sedimentation during a global climatic optimum probably coupled with strong eastward flow of a proto leeuwin current the late miocene eustatic sea level fall produced an areally restricted debris apron sequence at the foot of the reef escarpment the carbonate platform is capped by a neogene cool water carbonate ramp succession typified by aggradational to sigmoidal sequences punctuated by periods of cold water sea floor erosion interpretation of this succession in the light of global and local tectonic and oceanographic events illustrates the dominant influence of water temperature on carbonate platform and reef growth throughout the cenozoic

reef expansion during the triassic spread of photosymbiosis balancing climatic cooling the paleoreefs database indicates that reef abundance increased profoundly during the triassic period from a pronounced low in the early triassic to a major peak in the norian this expansion is also evident when standardizing for sampling corresponding to the reef expansion is a relative increase of scleractinian corals as reef builders whereas the contribution of hypercalcifying sponges and microbes decreased during the triassic the numerical expansion of corals is paralleled by a proportional increase of morphological features that are suggestive of photosymbiosis such that the norian reef boom might be explained by the spread of photosymbiosis in corals the geographical expansion of reefs was far less pronounced especially concerning palaeolatitude late triassic reef growth was limited to more or less the same latitudinal range as modern reefs as oxygen isotope data and new modeling results indicate declining temperatures and co2 concentrations during the late triassic the lack of latitudinal expansion might be attributed to global cooling reef development during the triassic can thus be explained by the evolutionary spread of photosymbiosis balancing the effects of climatic cooling

quantifying the paleogeographic driver of cretaceous carbonate platform development using paleoecological niche modeling abstract platform carbonates are a major component of the earth system but their spatial extent through geological time is difficult to reconstruct due to the incompleteness of the geological record sampling heterogeneity and their intrinsic complexity here we use coupled ecological niche modeling and deep time general circulation models to predict the occurrence of platform carbonates at the global scale during the cretaceous specifically niche modeling uses fuzzy logic to predict probable occurrence of platform carbonates as a function of sea surface temperature sea surface salinity primary productivity and water depth the first three parameters derive from cretaceous global paleoclimatic simulations using a coupled ocean atmosphere general circulation model while bathymetry is based on paleogeographical reconstructions model predictions are validated with the well documented and abundant geological data from the aptian the methodologies developed for the aptian are subsequently extended to other cretaceous time intervals the results of the niche model accurately predict the geographic distribution of aptian carbonate platforms if a preference for low open marine productivity levels is assumed for the rudist dominated carbonate factories however if a preference for high productivity levels is assumed the modeling results do not match the reported global distribution of aptian carbonate platforms from the early cretaceous into the late cretaceous sea level rose and the continents on average moved into lower latitudes the model predicts a corresponding increase in the extent of the carbonate platforms mainly due to the increasing extent of shallow water environments available to carbonate development these results indicate that long term sea level rise may have been a major factor responsible for the increase in the area of platform carbonates during the cretaceous

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

late quaternary paleoceanography of the eurasian basin arctic ocean we reconstructed late quaternary deep 3000 4100 m and intermediate depth 1000 2500 m paleoceanographic history of the eurasian basin arctic ocean from ostracode assemblages in cores from the lomonosov ridge gakkel ridge yermak plateau morris jesup rise and amundsen and makarov basins obtained during the 1991 polarstern cruise modern assemblages on ridges and plateaus between 1000 and 1500 m are characterized by abundant relatively species rich benthic ostracode assemblages in part reflecting the influence of high organic productivity and inflowing atlantic water in contrast deep arctic eurasian basin assemblages have low abundance and low diversity and are dominated by krithe and cytheropteron reflecting faunal exchange with the greenland sea via the fram strait major faunal changes occurred in the arctic during the last glacial interglacial transition and the holocene low abundance low diversity assemblages from the lomonosov and gakkel ridges in the eurasian basin from the last glacial period have modern analogs in cold low salinity low nutrient greenland sea deep water glacial assemblages from the deep nansen and amundsen basins have modern analogs in the deep canada basin during termination 1 at intermediate depths diversity and abundance increased coincident with increased biogenic sediment reflecting increased organic productivity reduced sea ice and enhanced inflowing north atlantic water during deglaciation deep nansen basin assemblages were similar to those living today in the deep greenland sea perhaps reflecting deepwater exchange via the fram strait in the central arctic early holocene faunas indicate weaker north atlantic water inflow at middepths immediately following termination 1 about 8500 7000 year b p followed by a period of strong canada basin water overflow across the lomonosov ridge into the morris jesup rise area and central arctic ocean modern perennial sea ice cover evolved over the last 4000 5000 years late quaternary faunal changes reflect benthic habitat changes most likely caused by changes in the import of cold deepwater of greenland sea origin and warmer and middepth atlantic water to the eurasian basin through the fram strait and export of arctic ocean deepwater

evolution pattern of early permian carbonate buildups with reference to the carbonate mounds in eastern inner mongolia north china abstract the sakmarian kungurian early permian carbonate mounds of the amushan formation of the deyanqimiao section in eastern inner mongolia north china comprise phylloid algae echinoderm mound fusulinid echinoderm mound and echinoderm mound they were constructed by repeating the following steps in the mid ramp and outer ramp environments 1 skeletal grains accumulated in situ or after short distance transportation 2 tubiform microbes eroded skeletal grains induced the formation of caco3 crystallites near the cell surface and trapped and bound suspended lime mud from ambient water 3 some positive topographies slightly higher than adjacent sediments were formed data from north china as well as the tropical tethyan domain and the subtropical pangean domain show a three phase development pattern of early permian carbonate buildups the first phase asselian sakmarian is marked by carbonate buildups rich in organisms such as phylloid algae palaeoaplysina shamovella sponges and bryozoans the second phase artinskian is represented by the disappearance of phylloid algae and palaeoaplysina from carbonate buildups resulted from the paleoclimatic change from an icehouse to a greenhouse the third phase kungurian is characterized by the sharp contrast between drastic decline of carbonate buildups in the subtropical pangean domain and their successful development in north china and the tropical tethyan domain

extinction trajectories of benthic organisms across the triassic jurassic boundary abstract we analysed diversity and abundance patterns of benthic organisms across the triassic jurassic t j boundary based on the paleobiology database pbdb which compiles palaeontological collection data on a global scale while sepkoski s sepkoski j j jr 2002 a compendium of fossil marine animal genera bulletins of american paleontology 363 1 563 compendium on the stratigraphic ranges of marine animal genera suggests that the dominant macrobenthic groups of the late triassic experienced significant extinctions prior to the t j boundary a significant end triassic extinction peak is evident from pbdb s data this rhaetian extinction peak is found in both an analysis of the raw data of stratigraphic ranges and a sample standardized analysis of occurrence data 41 of all mesobenthic and macrobenthic genera crossing the norian rhaetian boundary became extinct within the rhaetian although this rate suffices to characterize the end triassic extinction as a true mass extinction against a middle triassic to middle jurassic background significantly reduced rhaetian origination rates add to the strong diversity depletion in the earliest jurassic as for other mass extinctions evidence for selective extinction is meagre when the analysis is limited to the boundary interval alone and when focused on taxonomic and ecological characteristics of individual genera when taxa are separated by environmental preferences however several determinants of extinction risk become evident suggesting that reef dwellers had a significantly higher extinction risk than level bottom dwellers taxa with an inshore preference were more strongly affected than offshore taxa taxa preferring carbonate substrates were more strongly hit than taxa preferring siliciclastic substrates and taxa preferentially inhabiting low latitudes had higher extinction rates than taxa more common at intermediate and high latitudes much of this selectivity is not independent and also seen in the intervals of background extinctions suggesting that the end triassic mass extinction represents an intensification of background extinctions but not a qualitatively different macroevolutionary regime one possible exception is related to preferences for depositional environments suggesting a selective rhaetian extinction in reefs and inshore settings

water mass distribution and polar front structure in the western barents sea the water mass distribution in the western barents sea the thermohaline structure of the western barents sea polar front and the local formation of a dense water mass are described on the basis of an analysis of historical hydrographic data this study concentrated on the frontal region between bjornoya and hopen island where arctic water is found on the spitsbergen bank and atlantic water in the bear island trough and hopen trench the distributions of atlantic and arctic waters in relation to topography were consistent with the hypothesis that the location of the polar front is fixed at about the 250 m isobath by the barotropic circulation of atlantic water within the bear island trough and hopen trench in winter vertical gradients of temperature and salinity were weak throughout the frontal region consistent with a barotropic topographically controlled front in summer vertical gradients remained weak below 100 m depth but increased in the upper layer as a result of the presence of fresh warm surface water produced by melting ice the topographic control of thermohaline properties at the surface was disrupted by the meltwater pool and the meltwater contributed to water mass modification in the frontal region the following seasonal cycle of water mass formation was hypothesized summer heating melts the sea ice on the spitsbergen bank and produces the surface meltwater pool this meltwater not only increases vertical thermohaline gradients on the bank but also crosses the front and freshens the surface layer throughout the western barents sea subsequent winter cooling which creates ice over the bank also forms dense water in the bear island trough and hopen trench by convective mixing of atlantic water and the overlying meltwater

paleoreef maps evaluation of a comprehensive database on phanerozoic reefs to get a better understanding of controls on reef development through time we created a comprehensive database on phanerozoic reefs the database currently comprises 2470 reefs and contains information about geographic position paleoposition age reef type dimensions environmental setting paleontological and petrographical features and reservoir quality of each buildup reef data were analyzed in two qualitatively different ways the first type of analysis was by visualization of paleogeographic reef distribution maps five examples late devonian early permian late triassic late jurassic middle miocene are presented to show the potential of paleoreef maps for paleogeographic and paleoclimatological reconstructions the second type of analysis was a numerical processing of coded reef characteristics to realize major trends in reef evolution and properties of reef carbonates the analysis of paleolatitudinal reef distributions through time shows pronounced asymmetries in some time slices probably related to climatic asymmetries rather than controlled by plate tectonic evolution alone the dominance of particular reef builders through time suggests that there are seven cycles of phanerozoic reef development first curves for the phanerozoic distribution of bioerosion in reefs bathymetric setting and debris potential of reefs are presented the observed pattern in the temporal and spatial distribution of reefs with reservoir quality may assist in hydrocarbon exploration statistical tests on the dependencies of reefal reservoir quality suggest that large size high debris potential low paleolatitude high amount of marine aragonite cement and a platform shelf edge setting favor reservoir quality reefal reservoirs are significantly enhanced in times of high evaporite sedimentation elevated burial of organic carbon low oceanic crust production low atmospheric co2 content and cool paleoclimate as well as when they are present in aragonite oceans

paleoclimatic control of biogeographic and sedimentary events in tethyan and peri tethyan areas during the oxfordian late jurassic abstract the paleobiogeographical distribution of oxfordian ammonites and coral reefs in northern and central europe the mediterranean area north and east africa and the middle east and central asia is compared with the distribution in time and space of the most important lithofacies interest in the oxfordian is focused on changes in facies and in biogeographical patterns that can be interpreted as the results of climatic events paleotemperature trends inferred from oxygen isotopes and paleoclimatic simulations are tested against fossil and facies data a late callovian early oxfordian crisis in carbonate production is indicated by the widespread absence of lower oxfordian reefal formations there is a gap hiatus in deposition on epicontinental platforms with middle oxfordian deposits resting paraconformably on upper callovian while shales accumulated in adjacent intracratonic basins simultaneously in mediterranean tethys radiolarites accumulated in deep troughs while rosso ammonitico facies formed on pelagic swells however deposition on swells was also discontinuous with numerous gaps hiatuses and sequences that are much reduced in thickness middle callovian deposits are generally overlain by middle oxfordian limestones the dearth of carbonates is consistent with a cooling event lasting about 1 my by the middle oxfordian a warming leading to greenhouse type conditions is suggested on the basis of both biogeographical mostly coral reef distribution and geochemical data carbonates spread onto an extensive european platform while radiolarites reached a maximum development in the mediterranean tethys two distinct latitudinal belts with seemingly different accumulation regimes are therefore inferred similar latitudinal belts were also present in the late oxfordian when carbonates were widespread the distribution of reefal facies in the late oxfordian early kimmeridgian fits relatively well with gcms simulations that imply low rainfall in the tethyan mediterranean area and slightly higher precipitation in central and northern europe local salinity variations reflecting more arid or humid conditions may bias the paleotemperature signal inferred from 18o values biogeographical and facies distributions combined with 18o values unravel the ambiguity and support a late callovian early oxfordian cooling followed by warming in the later oxfordian

paleogeographic trends in late triassic reef ecology from northeastern panthalassa the late triassic was a pivotal period in reef evolution but the majority of information about reef ecology during this time comes from buildups in the alps e g the tethys ocean recent studies of reefs in western north america have recognized unique ecologies along the eastern margin of the panthalassa ocean although there are numerous twenty five localities with putative reef builders only four buildups had syndepositional relief and a rigid framework i e true reefs the most paleo northern true reefs were microbial patch reefs with only a few large skeletal bioconstructors hypercalcified sponges and spongiomorphs built the mid latitude reefs with secondary microbial encrustation and branching phaceloid retiophyllia corals corals are the primary bioconstructors in panthalassa s most paleo equatorial reefs and calcareous microbes are sparse when all reefal deposits are analyzed the n s gradient is also present with microbial and bivalve deposits in the north sponge coral deposits in the mid latitudes and coral deposits near the equator this ecological gradient is not apparent in the tethys ocean tethyan reefs thrived in oligotrophic tropical waters without strong latitudinal gradients by contrast paleoceanographic considerations suggest that cool nutrient rich waters swept south along the western north american borderlands in the late triassic the eastern boundary current is interpreted to have created a strong north south differentiation of environments in northeastern ne panthalassa that was manifested in both the biotic and abiotic characteristics of eastern panthalassic reefs reefs from equatorial panthalassa are similar to tethyan reefs warm water photozoan coral reef structures whereas higher paleo latitude reefs from panthalassa are interpreted as cool water heterozoan buildups with abundant calcareous microbes diminutive biocalcifiers and few large framework building corals

palaeoecology and evolution of marine hard substrate communities abstract marine organisms have occupied hard substrates since the archaean shells rocks wood and sedimentary hardgrounds offer relatively stable habitats compared to unconsolidated sediments but the plants and animals which inhabit them must develop means to gain and defend this premium attachment space hard substrate communities are formed by organisms with a variety of strategies for adhering to and or excavating the substrates they inhabit while mobile grazers organically attached and even soft bodied organisms may leave evidence of their former presence in ancient hard substrate communities a superior fossil record is left by sessile encrusters with mineralised skeletons and by borers which leave trace fossils furthermore encrusters and borers are preserved in situ retaining their spatial relationships to one another and to the substrate spatial competition ecological succession oriented growth and differential utilisation of exposed vs hidden substrate surfaces can all be observed or inferred hard substrate communities are thus excellent systems with which to study community evolution over hundreds of millions of years here we review the research on modern and ancient hard substrate communities and point to some changes that have affected them over geological time scales such changes include a general increase in bioerosion of hard substrates particularly carbonate surfaces through the phanerozoic this is at least in part analogous to the infaunalisation trends seen in soft substrate communities encrusting forms show an increase in skeletalisation from the palaeozoic into the mesozoic and cenozoic which may be a response to increasing levels of predation hard substrate communities considering borers and encrusters together show a rough increase in tiering through the phanerozoic which again parallels trends seen in soft substrate communities this extensive review of the literature on living and fossil hard substrate organisms shows that many opportunities remain for large scale studies of trends through time at the community and clade levels palaeontologists will especially benefit by closer integration of their work with that of neontologists particularly in aspects of ecology such as larval recruitment competition and succession

sense and non sense of shear in flanking structures abstract the deformation of marker horizons across slip surfaces can lead to the development of several types of flanking structures the development of such structures was investigated using a numerical model to simulate the flow around a slip surface in a viscous medium the modelled structures can be classified on the basis of three criteria 1 the extensional or contractional offset of markers 2 the co or counter shearing sense along the slip surfaces and 3 the normal or reverse drag of markers relative to the shear sense along the slip surfaces as a function of the kinematic vorticity of the flow and the initial orientation of the slip surface with respect to the shear zone boundaries three main types of structures can develop 1 shear bands developed along co shearing extensional slip surfaces 2 a type flanking folds developed along counter shearing slip surfaces and 3 s type flanking folds developed along co shearing contractional slip surfaces all these structures can occur with either normal or reverse drag effects shear bands and a type flanking folds recording opposite shear senses can be geometrically very similar and consequently lead to kinematic misinterpretations however correctly identified flanking structures can provide quantitative information about the kinematic vorticity of the flow

stromatolitic biotic systems in the mid triassic of israel a product of stress on an epicontinental margin abstract phanerozoic microbialites are carbonate precipitating biotic forms that are often described in modern systems from inter or supratidal hypersaline or fresh water environments and from beds associated with a variety of ecologically stressed environments over geologic time middle to late triassic microbialitic successions from southern israel were commonly subtidal and thrived under cryptic ecological stress conditions related to the regional configuration of the levant margin at that time the ladinian and carnian sequence at the ramon outcrop contains 18 successions with 28 microbialitic horizons these microbialites form isolated patches small bioherms and biostromes interleaved with other calcareous sediments including poorly diverse molluscan accumulations three distinct microbialitic facies and two associated molluscan facies were identified most were distinctly subtidal the two associated molluscan biofacies include a subtidal bivalve boundstone forming mounds and a bedded packstone of minute gastropods the ladinian carnian microbialites were not climatically forced environmental stress was caused by partial restriction of marine circulation due to tectonic movements and biotic accumulation on the outer edge of the levant margin comparison of coeval successions from central and northern israel and the north calcareous alps and southern alps in europe indicates a tethyan or global carbonate system of microbial producers separated from the open marine environment by shelf edge barriers therefore we conclude that the ramon microbialites represent a response to ecological stress of the carbonate system within the subtidal environment rather than solely to normal stresses of the intertidal environment

development of the mozambique and ruvuma sedimentary basins offshore mozambique two major sedimentary basins have been identified on the continental margin of mozambique mozambique basin and ruvuma basin the formation of the basins is related to the break up of gondwana and opening of the western part of the indian ocean the basins are relatively young having developed discordantly to the structural plan of gondwana sedimentary basins the history of the formation of the east african continental margin sedimentary basins within mozambique has been studied on the basis of the present day concept of gondwana break up and madagascar s drift with respect to africa two stages in the history of the east african basins can be recognized late gondwana and post gondwana the late gondwana stage 303 157 ma is typified by sedimentary and volcanogenic rocks of the karoo group the post gondwana stage 157 0 ma corresponds to the period of active gondwana break up and the formation of indian ocean marginal basins the mozambique basin occupies both central and southern parts of the coastal plain of mozambique extending onto the continental shelf and slope the sedimentary fill is composed of upper jurassic cretaceous and cenozoic rocks which discordantly overly the karoo basalts the upper jurassic occurs as continental red beds mostly distributed within buried grabens cretaceous rocks occur as terrigenous sediments of continental and marine genesis cenozoic deposits are of predominantly marine and deltaic origin the ruvuma basin situated in the north of mozambique is part of an extended east african marginal basin which includes parts of the coastal plains and continental margins of tanzania and kenya the basement of the basin is composed of crystalline and metamorphic rocks of pre cambrian age the sedimentary fill is represented by continental terrigenous karoo sediments marine and lagoonal jurassic deposits and marine and deltaic rocks of cretaceous and cenozoic age the main difference between the sedimentary fill of the mozambique and ruvuma basins is related to the changing sedimentary environment in the period of gondwana break up jurassic and early cretaceous when the drift of madagascar and sea floor spreading took place and the marine basin gradually extended southwards between the east african margin and madagascar from the late cretaceous on the sedimentary environment within both basins was similar the mozambique and ruvuma basins forming a single system on the east african continental margin the main stages of the basins development are illustrated by a series of palaeogeographic reconstruction maps

a biomarker based reconstruction of sea ice conditions for the barents sea in recent centuries variations in sea ice occurrence for the barents sea since c ad 1700 have been determined by analysis of the abundance of the sea ice biomarker ip25 in three marine sediment box cores obtained from locations in the north southeast and southwest parts of the region depth age models for each core were established using excess 210pb activity profiles comparisons between these depth age models with those reported previously for the barents sea suggest that the proxy sea ice record may alternatively extend back to c ad 1500 1600 sedimentation accumulation rates and bulk densities were combined with ip 25 concentrations resulting in temporal changes to ip25 fluxes which have been interpreted in terms of sea ice variability the ip25 sea ice proxy data are also compared with other bulk organic geochemical parameters total organic carbon and c n ratios and with sediment particle size distributions the data indicate ice free conditions for the southwest barents sea for the past c 300 yr consistent

middle cretaceous reef collapse linked to ocean heat transport biologically defined fluctuations in cretaceous tropical reef boundaries of the caribbean region record a dynamic rather than stable environmental history these fluctuations may be related to major thermal changes resulting from ocean heat transport with simultaneous poleward movement of surface and subsurface waters on sea level highstands the superheated middle cretaceous tropics cooled the reef line contracted diversity decreased and reef ecosystems collapsed leading to mass extinction geologic data qualitatively test and support the hypothesis of enhanced cretaceous ocean heat transport formulated from general circulation models in these models four times the present day atmospheric concentration of co 2 and twice the present day model value of ocean heat transport cooled the superheated tropics and provided the best match to the distribution of inferred middle cretaceous temperature data these dynamic changes suggest an important role for large scale disturbance in the evolution of tropical ecosystems

a mechanism for brief glacial episodes in the mesozoic greenhouse 1 the mesozoic perhaps the longest period of warmth during the phanerozoic earth history has been repeatedly affected by short lived cold interludes lasting about one million years while the origin of these cold snaps has been classically attributed to a temporary atmospheric co2 drawdown quantified mechanisms explaining these instabilities of the carbon cycle are still lacking based on a climate carbon cycle model we show that the general demise of carbonate platforms accompanying these short lived cold interludes is a powerful mechanism capable of generating a fast atmospheric co2 decrease and a moderate sea level drop associated with ice sheet buildup the temporary nature of the carbonate production decline explains the relative short time of these cold events but makes it possible to account for ice sheet waxing and waning

an ice grounding line wedge from the ghaub glaciation 635 ma on the distal foreslope of the otavi carbonate platform namibia and its bearing on the snowball earth hypothesis our detailed examination of the ghaub formation possibly 635 ma on the distal foreslope of the otavi carbonate platform is part of a regional study of the congo paleocontinental margin in northwestern namibia detrital carbonates of the ghaub formation disconformably overlie the franni aus member of the ombaatjie formation a coarsening upward stack of carbonate turbidites and oolite clast debris flow breccias interpreted to be a glacioeustatic falling stand wedge within the main ghaub formation carbonate diamictites are interleaved with mesoscale laminated to cross laminated climbing rippled grainstones and mudstones and conglomeratic carbonates amalgamation of diamictite units is observed where interleaved facies grainstones mudstones are laterally discontinuous due to reactivation of erosion followed by renewed deposition the diamictite package is progradational overall and 80 m thick on average it is overlain by the 5 15 m thick bethanis member which is unique in its lateral continuity composite fining upward trend and distinctive interbedding of turbidite grainstones argillaceous siltstones climbing rippled mudstones and meter scale stromatolite dropstones dropstones are ubiquitous within the finer grained ghaub lithofacies and their presence along with the facies context for subglacial and near grounding line deposition indicates a glacigenic origin for the ghaub formation despite its subtropical paleolatitude and distal foreslope setting we infer a glacial maximum represented by the sub ghaub disconformity followed by the main ghaub interval when an ice grounding line on the distal foreslope experienced abrupt step backs and readvances of limited magnitude terminated by the bethanis episode of unusually widespread iceberg calving and slope instability the bethanis member is overlain conformably by the keilberg member of the maieberg formation reconstruction of the foreslope places the ghaub grounding line wedge 1 3 km vertically below the rim of the platform implying an enormous base level change upon deglaciation when the platform was drowned below wave base for a period far exceeding the time scale for isostatic adjustment the magnitude of base level change supports the pan glacial hypothesis that dynamic thick ice sheets existed simultaneously on virtually all continents the snowball hypothesis that the oceans were also covered by glacial ice sea glacier provides a simple explanation for the main ghaub to bethanis transition terminal deglaciation was triggered by collapse of the sea glacier

environmental controls on marine ecosystem recovery following mass extinctions with an example from the early triassic abstract the recovery of marine ecosystems following a mass extinction event involves an extended interval of increasing biotic diversity and ecosystem complexity the pace of recovery may be controlled by intrinsic ecosystem or extrinsic environmental factors here we present an analysis of changes in marine conditions following the end permian mass extinction with the objective of evaluating the role of environmental factors in the protracted 5 myr long recovery of marine ecosystems during the early triassic specifically our study examines changes in weathering productivity and redox proxies in three sections in south china chaohu daxiakou and zuodeng and one in northern india mud our results reveal 1 recurrent environmental perturbations during the early triassic 2 a general pattern of high terrestrial weathering rates and more intensely reducing marine redox conditions during the early griesbachian late griesbachian mid smithian and more weakly the mid spathian 3 increases in marine productivity during the aforementioned intervals except for the early griesbachian and 4 stronger and more temporally discrete intervals of environmental change in deepwater sections chaohu and daxiakou relative to shallow and intermediate sections zuodeng and mud our analysis reveals a close relationship between episodes of marine environmental deterioration and a slowing or reversal of ecosystem recovery based on metrics of biodiversity within community alpha diversity infaunal burrowing and ecosystem tiering we infer that the pattern and pace of marine ecosystem recovery was strongly modulated by recurrent environmental perturbations during the early triassic these perturbations were associated with elevated weathering and productivity fluxes implying that nutrient and energy flows were key influences on recovery more regular secular variation in deepwater relative to shallow water environmental conditions implies that perturbations originated at depth i e within the oceanic thermocline and influenced the ocean surface layer irregularly finally we compared patterns of environmental disturbance and ecosystem recovery following the other four big five phanerozoic mass extinctions to evaluate whether commonalities exist in general the pace of ecosystem recovery depends on the degree of stability of the post crisis marine environment

the jiwozhai patch reef a palaeobiodiversity hotspot in middle givetian devonian of south china abstract this study is a detailed palaeontological and palaeoecological analysis of a middle givetian middle devonian high diversity patch reef located in a platform interior setting in south china the location is jiwozhai guizhou province in the dushan formation a total of 83 species including 23 undetermined species belonging to 44 genera of reef organisms were identified based on a detailed statistical analysis from 28 quadrats on the vertical section of the patch reef the main reef builders are laminar and encrusting behaviour stromatoporoids laminar tabulate corals and laminar encrusting chaetetids forming coverstones to build the reef framework while abundant massive and branching tabulate corals and solitary rugose corals are also important for the formation of the reef by filling the spaces between the components of the coverstones reef dwellers including brachiopods bryozoans tubeworms calcified cyanobacteria and gastropods are only scarcely distributed in the jiwozhai patch reef having little impact on the distribution pattern consistent with the densely distributed species at jiwozhai complex ecological relationships including extensive encrustations spatial competition and symbiosis have also been found among different organisms the high biodiversity level of the jiwozhai patch reef in platform interior emphasizes that understanding of species richness and diversity of functional groups in different habitats is critical for givetian reef ecosystem reconstruction location of the patch reef in a platform interior may be the reason for the high diversity biota the results from the jiwozhai patch reef are evidence for a stable reef structure with evenly distributed major reef frame builders and complex ecological relationships the high level of species diversity is a common feature in south china as well localities of many other palaeocontinents during the givetian period

permian triassic boundary interval as a model for forcing marine ecosystem collapse by long term atmospheric oxygen drop ecological traits of reefs across the permian triassic boundary interval coincide with a modeled decline of atmospheric oxygen throughout the permian period selective extinction and recovery patterns within the reef system are observed both at the end of the middle permian end guadalupian and at the permian triassic boundary the end guadalupian event selectively affected corals and broke down the cool water carbonate factory sponges however were largely unaffected and bloomed in reefs toward the end of the permian the end permian total destruction of the metazoan reef system only left behind poorly diverse microbial communities the temporal reef patterns are thus similar to spatial patterns of modern benthic communities approaching oxygen minimum zones this observation suggests that a decline in oxygen concentrations was at least partly involved in the destruction of reefs even where there is no direct evidence of oceanic anoxia

paleoclimatic significance of phanerozoic reefs a database of pre quaternary phanerozoic reefs is used to test the significance of ancient reefs as paleoclimatic tracers the compilation of reef paleolatitudes through time and comparison with published paleoclimate curves shows that neither the width of the tropical reef zone nor the total latitudinal range of reefs is correlated with published estimates of paleotemperature however reefs trace paleoclimate indirectly algal reefs tend to prevail during icehouse climatic intervals and distinct high latitude reefs are only developed in cold intervals whereas during greenhouse episodes the reef zone usually ended abruptly at a particular latitudinal boundary in the subtropics additionally different biotic reef types tended to be concentrated in different latitudes the lowest latitudes have usually been occupied by coralline sponge or microbial reefs coral reefs tended to grow in intermediate latitudes and bryozoan reefs constantly occupied the highest latitudinal position

coral reefs may start dissolving when atmospheric co2 doubles 1 calcification rates in stony corals are expected to decline significantly in the near future due to ocean acidification in this study we provide a global estimate of the decline in calcification of coral reefs as a result of increase in sea surface temperature and partial pressure of co2 this estimate unlike previously reported estimates is based on an empirical rate law developed from field observations for gross community calcification as a function of aragonite degree of saturation arag sea surface temperature and live coral cover calcification rates were calculated for more than 9 000 reef locations using model values of arag and sea surface temperature at different levels of atmospheric co2 the maps we produced show that by the time atmospheric partial pressure of co2 will reach 560 ppm all coral reefs will cease to grow and start to dissolve

bryozoan carbonates through time and space the calcareous skeletons of modern bryozoans are major contributors to sediments only outside the tropics and many temperate limestones are dominated by bryozoans often in conjunction with mollusks in the so called bryomol grain association can the presence of rock forming abundances of bryozoans be used to recognize nontropical sediments in the geologic past we have addressed this question by assembling a database of 176 ordovician pleistocene bryozoan rich deposits and plotting them on paleogeographical maps to obtain their latitudes of formation the results reveal a striking difference between post paleozoic and paleozoic latitudinal distributions whereas the great majority 94 of post paleozoic bryozoan rich deposits formed outside the tropics paleozoic bryozoan rich deposits have a more variable latitudinal distribution most 68 having formed within the tropics the presence of rock forming abundances of bryozoans in paleozoic sediments should not therefore be used to infer nontropical carbonate deposition the change in latitudinal distribution between the paleozoic and post paleozoic corresponds with a major taxonomic turnover in bryozoan faunas biotic interactions especially with predators may have led to the exclusion of sediment producing bryozoans from the post paleozoic tropics these evolutionary changes have had a more profound effect on carbonate platforms than has been previously appreciated

the shifting biogeography of reef corals during the oxfordian late jurassic a climatic control until recently the jurassic was thought to have been a period characterised by a predominantly warm and equable climate during the oxfordian a time span of six million years in the late jurassic the distribution of tropical coral reefs was limited to about 35 n and near to 25 s however in middle oxfordian time coral reefs were abundant only at higher latitudes and almost entirely missing near the equator during that time the area of maximum reef development had shifted poleward to a belt lying between 20 n and 35 n leaving hardly any coral formations at the lower inner tropical latitudes after demise towards the end of middle oxfordian time the low latitude reefs recovered during the late oxfordian accompanied by a southward migration of reef corals in the northern hemisphere as suggested by stable isotope and palynological data the faunal migration can be correlated with a significant rise in seawater temperature during the middle oxfordian

history of seawater carbonate chemistry atmospheric co 2 and ocean acidification humans are continuing to add vast amounts of carbon dioxide co2 to the atmosphere through fossil fuel burning and other activities a large fraction of the co2 is taken up by the oceans in a process that lowers ocean ph and carbonate mineral saturation state this effect has potentially serious consequences for marine life which are however difficult to predict one approach to address the issue is to study the geologic record which may provide clues about what the future holds for ocean chemistry and marine organisms this article reviews basic controls on ocean carbonate chemistry on different timescales and examines past ocean chemistry changes and ocean acidification events during various geologic eras the results allow evaluation of the current anthropogenic perturbation in the context of earth s history it appears that the ocean acidification event that humans are expected to cause is unprecedented in the geologic past for which sufficiently well preserved records are available

heterozoan carbonates when where and why a synthesis on parameters controlling carbonate production and occurrences abstract in modern and phanerozoic times heterozoan carbonates group a large array of depositional environments from the poles to the tropics this global assessment reviews the critical parameters and controlling factors of heterozoan carbonates i stratigraphic and global distributional trends ii oceanographic and trophic relationships and iii biological and sedimentary processes well documented case studies n 129 have been investigated when facies and stratigraphic attributes were available and when environmental settings such as oceanography climate and paleogeography were clearly identified these case studies occur during specific periods of time in the sedimentary record e g late ordovician early carboniferous early permian and neogene while they are absent during others e g triassic and jurassic periods during greenhouse to icehouse transitions and those with active thermohaline circulation are particularly conducive for heterozoan carbonates based on global oceanographic patterns and existing ecological and hydrodynamic regime classifications hallock 2001 pedley and carannante 2006 james and jones 2015 a process based classification scheme is proposed that distinguishes two main heterozoan carbonate systems i a highly productive system characterized by suspension feeding biota and ii an oligo mesotrophic warm temperate system characterized by red algal and seagrass derived biota eight depositional models are proposed that combine i the source of energy for metabolic activities that allow the carbonate producing biota to thrive and ii hydrodynamics and physiography of the depositional system that control the sediment accumulation the local and platform scale based profiles can be used to complement the facies approach of james and jones 2015

impact of long term climate change and sea level fluctuation on mississippian to permian mid oceanic atoll sedimentation akiyoshi limestone group japan abstract to understand the impacts of long term climatic episodes and sea level changes on mid oceanic atoll sedimentation the stratigraphic changes of litho and bio facies and stratigraphic levels of freshwater diagenetic alteration and biostratigraphic discontinuity of the akiyoshi limestone group upper visean to upper capitanian were reviewed this group records approximately 70 million years of atoll sedimentation in a mid oceanic realm of the panthalassa ocean which developed nearly synchronously with the late paleozoic gondwana glaciation the entire succession of the akiyoshi limestone group was divided into four facies associations skeletal oolitic grainstone muddy limestone muddy limestone skeletal grainstone and reefal limestone associations skeletal oolitic grainstone and reefal limestone associations upper visean to bashkirian are characterized by an abundance of oolite and crinoidal grainstone and reef facies of warm adapted metazoan reef builders corals chaetetes and bryozoans respectively characteristics of skeletal oolitic grainstone and reefal limestone associations indicate their deposition in a warm climate with elevated sea level muddy limestone association moscovian to kasimovian records the demise of the warm adapted metazoan reef builders and frequent emergence events of the buildup many geochemical data support the significant drop in temperature during moscovian through kasimovian time these depositional and biotic events of muddy limestone association indicate that its sedimentation was strongly affected by cool climate and generally low sea level muddy limestone skeletal grainstone association is characterized by an upward increasing significance of calcimicrobes calcareous algae and calcisponges the succession records less frequent emergence events than that of muddy limestone association ii these characters reflect a warming climate and sea level rise in gzhelian to capitanian time the climate episodes and sea level changes interpreted from the akiyoshi limestone group generally correspond to the global trend of mississippian to permian long term climatic change and sea level fluctuation related to the major glacial events of gondwana glaciation the late visean to bashkirian warm climate and elevated sea levels moscovian to kasimovian cooling and sea level lowering and gzhelian to capitanian warming and sea level rise recorded in the akiyoshi buildup are comparable to the global climate model and sea level fluctuation which contain early to middle mississippian pre glacial warm climate and highstands middle to late pennsylvanian cooling and related glacio eustatic sea level fluctuation at the culmination of gondwana glaciation and early to middle permian global warming and sea level rise due to the retreat of gondwana ice sheets akiyoshi atoll sedimentation was most significantly affected pennsylvanian global cooling and related sea level lowering but their impact was short lived the onset of the cooling and frequent emergence events in the akiyoshi buildup occurred delayed approximately 10 millions years later than that of comparable episodes on the pangean shelves the post glacial warming in the akiyoshi buildup started at least several millions of years earlier than in epicontinental seas of the pangea this phenomenon may be due to the palaeoposition of the akiyoshi buildup in a mid oceanic realm of the panthalassa ocean

sea ice and marine climate variability for nw iceland denmark strait over the last 2000 cal yr bp md99 2263 is a 46 cm box core collected from djupall a trough that cuts across the nw iceland shelf and ends above denmark strait we provide a multiproxy record that documents changes in the regional marine climate over the last 1700 yr the depth age model is based on seven calibrated radiocarbon dates on mollusk shells and on 210pb and 137cs sediment accumulation rates were variable 0 2 0 8 mm yr but increased dramatically ad 1500 grain size magnetic properties quantitative mineral composition of the 2 mm sediment fraction benthic foraminiferal composition benthic and planktic 18o ratios and abundances fluxes of the sea ice biomarker ip25 were determined to better compare the various proxies 12 of the critical climate proxies were co ordinated into 100 yr sample time series which were examined by principal component analysis the 1st axis explained 49 of the variance and the 2nd axis explained an additional 17 the variables most strongly associated with the 1st axis were sediment pr

equatorial palaeotethys as the last sanctuary for late permian metazoan reef builders new evidence from the bellerophon formation of slovenia the rise and demise of warm temperate permian reefs and biostromes reflect the complex geologic history of this dynamic period environments suitable for reef builders were devastated by the guadalupian lopingian crisis and lopingian reefs have only been recorded at a small number of localities the uppermost permian limestones of the bellerophon formation on the vojsko plateau slovenia contain small lenticular biostromes within a bioclastic wackestone packstone lithofacies the major biostrome builders are medium sized coralline sponges demospongea and calcarea encrusted by smaller sponges tube worms sessile foraminifera calcareous algae archaeolithoporella and shamovella i e tubiphytes all of which are typically covered by microbial crusts the biostromes are characteristically composed of bafflestone and bindstone incorporating sporadic framestone narrow belts of floatstone surround the buildups and sponge debris is also present in lenses within the mud matrix between metazoan bafflestones the fossils are generally well preserved although the fine skeletal microstructure has been partially recrystallized sponges are heavily calcified and ontogenic thickening of the skeleton can be observed in some encrusters framboidal pyrite forming thin films on the inner walls of sponge chambers suggests the presence of sulphate reducing bacteria these microbial symbionts may have enabled the sponges to survive in the anoxic marine environments of the uppermost permian the changshingian sponge biostromes of the vojsko plateau represent the westernmost known occurrence of contemporary metazoan boundstones in the palaeotethys

palynological evidence of holocene climate change in the eastern arctic a possible shift in the arctic oscillation at the millennial time scalethis article is one of a series of papers published in this special issue on the theme polar climate stability network dinocyst assemblages and the physical properties of two sediment cores collected in the easternmost part of the main axis of the northwest passage canadian arctic ocean cores 2004 804 009 bc and 2004 804 009 pc 74 11 2 n 81 11 7 w were used to reconstruct changes in sea surface conditions and to characterize changes in the depositional environment core 2004 804 009 pc spans the last 12 180 calibrated cal years bp with sedimentation rates ranging from 45 to 122 cm ka quantitative estimates of sea surface parameters reveal relatively large hydrographic variability at millennial time scale before 11 000 cal years bp our records suggest terrigenous inputs related to the last deglaciation between 11 000 and 9600 cal years bp harsh conditions prevailed with august sea surface temperatures 2 c and the dominance of heterotrophic taxa this episode was followed by a gradual increase in the relative abundance of phototrophic taxa and the establishment of milder condition with sea surface temperature