the cretaceous paleogene transition in tunisia general overview abstract the latest cretaceous paleocene paleogeography of tunisia is characterized by two subsident troughs in the north the nw tunisian trough and the ne tunisian basin and the gafsa gulf in the southwest the gafsa gulf adjacent to the saharian platform is separated from the northern basins by the kasserine island from the three domains typical successions covering the cretaceous paleogene transition are described in the present paper in the northern basins the cretaceous paleogene or k t boundary lies within the continuously deposited marine el haria formation which attains a thickness of 700 1000 m the gssp stratotype of the k t boundary at el kef lies in the nw tunisian trough

aspects of climate variability in the north atlantic sector discussion and relation to the greenland ice sheet project 2 high resolution isotopic signal this paper reviews aspects of climate variability in the north atlantic sector that may influence the seasonal to decadal scale isotopic signal in the greenland ice sheet project 2 gisp2 ice core interpretation of the isotopic signal and its spatial applicability at the seasonal level requires investigation into synoptic scale climatology we discuss possible climatic influences of 1 likely source regions of precipitation reaching the gisp2 site 2 the characteristics of cyclone activity over the north atlantic sector and 3 changes in major atmospheric features such as the mean sea level icelandic low and azores high pressure systems the north atlantic oscillation and the baffin trough next we evaluate correlations between the gisp2 deuterium isotopic signal and coastal temperatures with atmospheric pressure patterns thereby deriving climatic interpretations of the high resolution isotopic record the gisp2 site is influenced by both the icelandic low to the southeast and davis strait baffin bay storms to the southwest and west the north atlantic oscillation influences the gisp2 isotopic signal through the seesaw in winter temperatures between west greenland and northern europe agreement in excursion directions of gisp2 isotopes and east greenland and iceland temperature records is associated with different positions of the baffin trough in winter and also with anomalous 500 mbar net geostrophic flow linkages between isotopic excursion direction and atmospheric variability need to be explored further by comparison with additional seasonal data sets from other greenland ice cores

bioerosion structures in crepidula mollusca gastropoda as indicators of latitudinal palaeoenvironmental changes example from the marine quaternary of argentina abstract late quaternary marine skeletal concentrations from argentina are rich in molluscs exhibiting a great variety of bioerosion structures the shells of crepidula a characteristic gastropod occurring along more than 2000 km of coastline between the rio de la plata margin and southern patagonia show traces of dwelling predation and anchoring activities made by porifers bryozoans annelids other gastropods and brachiopods caulostrepsis entobia maeandropolydora iramena oichnus finichnus pennatichnus pinaceocladichnus podichnus and renichnus occur on the outer shell surface finichnus and oichnus are the only traces present along the entire area and the full time span considered the most characteristic structures are produced by bryozoans polychaetes and predatory gastropods traces produced by annelids and predatory gastropods occur preferentially in the central shell sector where predators gained access to the soft parts of the prey by contrast encrusting or branching bryozoan colonies are widely distributed as they can attach to any sector regardless of shell features available no strict correlation is evident between ichnodiversity and either time or latitude but ichnodiversity is linked to local oceanographical biotic controls for patagonia with a great majority of ichnotaxa made by bryozoans the general trend of higher bioerosion degree and ichnodiversity at higher latitudes is controlled by sea surface temperature productivity for the modern and the holocene several ichnodiversity peaks match with well constrained conditions substrate salinity thermal fronts by contrast this does not hold for the pleistocene dissimilar conditions probably prevailed especially during the last interglacial colder waters richer in nutrients

paleocene sea level and productivity changes at the southern tethyan margin el kef tunisia integrated analysis of quantitative distribution patterns of organic walled dinoflagellate cysts dinocysts and benthic foraminifera from the paleocene el kef section nw tunisia allows the reconstruction of sea level and productivity fluctuations our records indicate that the environment evolved from an initially oligotrophic open marine outer neritic to upper bathyal setting towards a more eutrophic inner neritic setting influenced by coastal upwelling by the end of the paleocene an overall second order change in paleodepth is reflected by both microfossil groups from the base of planktic foraminifera zone p4 onwards the main phase of shallowing is evidenced by an increase of inner neritic dinocysts of the areoligera group disappearance of deeper water benthic foraminifera and increasing dominance of shallow marine taxa several buliminids haplophragmoides spp trochammina spp the total magnitude of this shallowing is obscured by interaction with a signal of eutrophication but estimated to be around 150 m from 200 to 50 m superimposed on the overall trend third order sea level fluctuations have been identified and correlated to sequences in other regions paleoproductivity indicators notably protoperidinioid dinocysts and buliminids show a trend from an oligotrophic to a eutrophic setting d 2005 elsevier b v all rights reserved

alleged mosasaur bite marks on late cretaceous ammonites are limpet patellogastropod home scars new data contradict the mosasaur bite hypothesis for the origin of holes seen in placenticeras ammonites from the late cretaceous pierre shale and bearpaw formation of the western interior of north america observations of a limpet infested placenticeras ammonite and of several placenticeras specimens with radular scratch marks reveal that the limpets dwelled on floating ammonites and their homing activity produced circular depressions when altered during diagenesis the depressions mimic tooth punctures crushing experiments on fresh nautilus shells using a mosasaur robot show that mosasaur bites could not have produced holes resembling those in the fossils furthermore sectioning of bitten ammonites reveals that sepia are sometimes intact under the holes an observation irreconcilable with penetration by a tooth we present an alternative interpretation that the alleged bite marks in placenticeras ammonites are really limpet home scars that were altered after burial while predation of mosasaurs on ammonites remains a possibility it would have to be demonstrated by other criteria our findings do not support mosasaur ammonoid coevolution in the late cretaceous

the ellipsactinia limestones of the marsica area central apennines a reference zonation model for upper jurassic intra tethys reef complexes abstract this study presents a new and innovative distribution model of the main reef builders that thrived on bioconstructed margins of upper jurassic intra tethys platforms the proposed model is based on the zonation of an upper jurassic reef complex presently exposed in the central apennines excellent exposures allow the reconstruction of the reef profile across the platform margin biota are mainly represented by corals and calcified demosponges distributed with different amounts and aggregating structures along the reef complex microencrusters represent a secondary but important component that actively contributes to the reef construction process reef builders are distributed in variable quantities and with variable aggregating structures along the reef complex revealing a strong reef zonation like the biota the sedimentary features grain size sorting and reworking degree bioerosion cement crusts and cavities show a distinctive distribution along the reef complex three main zones have been recognized along the studied reef complex an internal more protected and deeper zone corresponding to a relatively deep back reef lagoon is dominated by corals and chaetetids a central zone reef flat where well preserved coral bioconstructions give rise to a true but discontinuous framework and a more external zone corresponding to the reef crest characterized by the shallowest depths recorded across the reef complex and dominated by stromatopores the latter forms mound shaped structures playing a role essential for the zoned character of the reef complex these structures actively contribute to the construction of a moderately high topographic relief in the reef crest

remote sensing of the albedo and detection of the slush line on the greenland ice sheet advanced very high resolution radiometer images of a section of the greenland ice sheet western part between 64 5 and 70 5 n with a size of 667 n s by 700 w e km were processed in order to retrieve the surface albedo the images were for the summer seasons of 1990 1997 inclusive and results were compared to simultaneous mass balance measurements carried out along the transect 67 n the main findings are as follows first many images show a distinct transition from low spatial variability of the albedo at higher elevations to higher spatial variability of the albedo at lower elevations it is argued that these transitions most likely correspond to transitions at the surface slush line in short from the area that is uniformly covered by snow to a mosaic of snow patches slush and ice second 70 of the interannual variations in the mean specific mass balance can be explained by interannual variations in the maximum elevation of the slush line i e the slush limit however a higher percentage 82 can be explained by interannual variations in the sum of positive degree days third in 3 years with a relatively large amount of melt the inland migration of the slush line stopped or slowed considerably down at a fixed distance from the ice sheet margin we believe that this so called maximum slush line coincides with an abrupt change in the density profile the maximum slush line forms an important limitation for the use of satellite data to monitor interannual variations in the mass balance its position is a climate indicator and was determined for the entire section of the greenland ice sheet investigated

predatorial borings in late precambrian mineralized exoskeletons the late precambrian tube forming cloudina the earliest known animal to produce a mineralized exoskeleton shows evidence of having been attacked by shell boring organisms of more than 500 tubes from shaanxi province china 2 7 have rounded holes 40 to 400 micrometers in diameter the relation between the size of the holes and the width of the bored tubes suggests that the attacking organism was a predator selecting its prey for size if true this would be the oldest case of predation in the fossil record and would support the hypothesis that selection pressures from predation was a significant factor in the evolution of animal skeletons around the precambrian cambrian boundary

paleokarst paleosol and rocky shore deposits at the mississippian pennsylvanian unconformity northwestern arkansas the mississippian pennsylvanian unconformity in northwestern arkansas contains pedogenically altered regolith preserved in low lying areas on paleokarst on the chesterian pitkin limestone the regolith is succeeded by transgressive rocky shore deposits of the cane hill member hale formation type morrowan pitkin cements reflect extensive meteoric phreatic diagenesis prior to karstiflcation and paleokarst features include large dissolution fragmented pitkin lithoclasts with numerous solution pipes on a low relief surface the overlying pedogenically altered regolith contains calcretized lithoclasts in clay matrix suggesting a shift from ever wet conditions to more seasonal rainfall prior to the pennsylvanian transgression that shift may represent local climatic change or short term fluctuations in mid carboniferous tropical climate the latter interpretation may support global climate models that predict warmer wetter tropics during periods of high latitude cooling basal cane hill strata consist of high energy shoreface boulder cobble conglomerate containing reworked pitkin clasts the conglomerate contains an unequivocal rockyshore community consisting of encrusting bryozoans and corals trypanites acrothoracican barnacle borings and possibly the earliest occurrence of gastrochaenolites preservation of poorly indurated paleosol beneath high energy transgressive deposits suggests very rapid transgression consistent with a glacio eustatic mechanism truncated pitkin strata were removed by karstification and subaerial erosion during the hiatus and not by erosion during transgression

mystery of naticid predation history solved evidence from a living fossil species observations of living cernina fluctuata sowerby the sole extant species of the mesozoic and cenozoic prosobranch gastropod family ampullospiridae show that this species is an algal grazer and is not a shell drilling predatory naticid gastropod all jurassic and early cretaceous gastropods previously assigned to naticidae belong to ampullo spiridae and are now inferred to be herbivores not shell drillers this finding refutes the triassic origin and favors a cretaceous origin for naticid drilling predation a preliminary revision of cenozoic and cretaceous species previously assigned to naticidae suggests that naticids were absent prior to the cretaceous campanian and diversified at a modern level in eocene time this pattern of naticid diversification from the late cretaceous onward coincides roughly with the evidence of naticid predation the fossil record of naticid drill holes once of anomalously short duration now accurately reflects the geologic history of naticid predation activity

ostracode turnover and sea level changes associated with the paleocene eocene thermal maximum the ostracode response to oceanographic changes during the paleocene eocene thermal maximum petm ca 55 ma is largely unknown the gebel duwi section egypt provides a detailed ostracode record across the petm in a middle neritic setting quantitative analysis of this record reveals two significant results 1 the petm is marked by a sharp faunal turnover as indicated by abundance changes local extinctions and immigrations this turnover punctuated a gradual basin wide faunal transition 2 during the 60 k y period prior to the petm relative sea level fell rapidly by 15 m this sea level fall was followed by an 20 m sea level rise during the petm a possible eustatic control on these fluctuations suggests the presence of a cryosphere and variations in its size during this time of global warmth

carbonate concretions from the london clay ypresian eocene of southern england and the exceptional preservation of wood boring communities marine driftwood bored by teredinid bivalves shipworms is common in the london clay formation ypresian eocene of southern england the london clay of sheppey kent has yielded six genera of teredinids and is the most diverse fossil assemblage of the family known the presence of several genera that are known exclusively from mangroves at the present day demonstrates the potential value of teredinids in the recognition of ancient mangroves the rapid sea floor burial of logs containing numerous individuals resulted in the borings becoming completely or partially sealed by the plug like pallets in this exceptional mode of preservation valves pseudofaeces and pallets are found in life position and early cementation prevented compaction of the wood and borings the bored wood acted as centres of carbonate concretion formation cement compositions mineral associations and 13 c and 18 o stable isotope data indicate that most precipitation occurred in the iron reduction zone with sulphate reduction also being an important source of carbonate for the sheppey concretions fractures and their infilling cements are demonstrably contemporaneous with the cement zones in which they terminate it is likely that rapid changes in cement chemistry are a consequence of sudden release of fluid by dewatering events whilst more gradual shifts in chemistry were controlled be evolution through the oxic fe mn and s reduction zones teredinid boring linings and the cements which infill them may have recrystallized by a dissolution reprecipitation process which has preserved the chemistry of successive cements and has probably not significantly changed 18 o values

surface mass balance observations and automatic weather station data along a transect near kangerlussuaq west greenland surface mass balance data from the kangerlussuaq transect k transect located on the western part of the greenland ice sheet near 678n are presented the series covers the period 1990 2003 and is the longest series of surface mass balance measurements in greenland the surface mass balance measurements cover an altitude range of 390 1850m and show a linear increase of the specific mass balance with a mass balance gradient of 3 7 10 3 mm 1 and a mean equilibrium line altitude of 1535ma s l interannual variability shows a weak 4yearly periodicity in addition to the surface mass balance data automatic weather station data at an elevation of approximately 1010m are available for the period 1997 2002 these data are used to explain observed surface mass balance anomalies over the same 5years it is shown that variations in shortwave radiation dominate interannual variability the mean annual cycle of temperature is characterized by a maximum in summer around the melting point leading to a mean summer outgoing longwave radiation of approximately 314wm 2 the mean annual cycle in wind speed shows a maximum in winter on average around 8ms 1 and a minimum in summer on average around 5ms 1 which is characteristic for a katabatic forcing during summer the net radiation is on average about 61wm 2 which is used for ice melting at a rate of typically 2cmw e d 1 net radiation contributes 84 of the total energy used for summer melting averaged over the 5years

abrupt deep sea warming palaeoceanographic changes and benthic extinctions at the end of the palaeocene a remarkable oxygen and carbon isotope excursion occurred in antarctic waters near the end of the palaeocene 57 33 myr ago indicating rapid global warming and oceanographic changes that caused one of the largest deep sea benthic extinctions of the past 90 million years in contrast the oceanic plankton were largely unaffected implying a decoupling of the deep and shallow ecosystems the data suggest that for a few thousand years ocean circulation underwent fundamental changes producing a transient state that although brief had long term effects on environmental and biotic evolution

eustatic variations during the paleocene eocene greenhouse world we reconstruct eustatic variations during the latest paleocene and earliest eocene 58 52 ma dinoflagellate cysts grain size fractions and organic biomarkers in marine sections at four sites from three continents indicate an increased distance to the coast during the paleocene eocene thermal maximum petm the same trend is recognized in published records from other sites around the world together the data indicate a eustatic rise during the petm beginning 20 to 200 ka before the globally recorded negative carbon isotope excursion cie at 55 5 ma although correlations are tentative we recognize other global transgressions during chrons c25n and c24n the latter may be associated with eocene thermal maximum 2 53 5 ma or the x event 52 ma these results suggest a link between global sea level and hyperthermal intervals potentially because of the melting of small alpine ice sheets on antarctica thermal expansion of seawater or both however the early onset of sea level rise relative to the cie of the petm suggests contributions from other mechanisms perhaps decreasing ocean basin volume on sea level rise copyright 2008 by the american geophysical union

bioerosion in an equatorial middle jurassic coral sponge reef community callovian matmor formation southern israel abstract the matmor formation middle jurassic callovian 165 161 mya in southern israel contains abundant coral sponge patch reefs and large crinoids which have been extensively bioeroded by bivalves worms barnacles phoronids and others producing eight ichnospecies it is significant for the evolutionary history of bioerosion because this is the first equatorial middle jurassic boring ichnofauna to be documented when compared to contemporaneous ichnofaunas this assemblage is of average diversity and abundance but has only rare sponge borings and contains abundant specimens of oichnus paraboloides as shallow pits on crinoid stems the matmor formation surprisingly lacks carbonate hardgrounds which are otherwise abundant in subtropical and temperate equivalents

new example of devonian predatory boreholes and the influence of brachiopod spines on predator success three abundant devonian frasnian brachiopod species from the lime creek fm of iowa usa douvillina arcuata devonoproductus walcotti and pseudoatrypa devoniana contain boreholes pooled drilling frequency is 10 6 the boreholes are small usually 1 0 mm diameter cylindrical and drilled perpendicular to the shell surface the borings appear to be type a boreholes as described by ausich and gurrola 1979 j paleontol 53 335 344 based on multiple criteria including statistically significant stereotypy with respect to valve preference site on valve and size class of the prey the boreholes are inferred to be predatory or parasitic in origin for each species the predator preferred to attack the valve closest to the substrate regardless of whether that was the pedicle or brachial valve boreholes were concentrated over the muscle field on each of the three species the success percentage percent of complete holes was statistically lower 2 p 0 04 for the spinose devonoproductus walcotti 33 33 than for the non spinose but otherwise morphologically similar douvillina arcuata 54 22 in spite of the fact that d walcotti has a thinner shell this is the first quantitative evidence for an anti predatory function for brachiopod spines

paleooceanography of the mesogean sea based on ostracods of the northern tunisian continental shelf between the late cretaceous and early paleogene a new method analysis used in the study of the el kef section north western tunisia led to the paleooceanographic reconstruction of the mesogean between late cretaceous and early paleogene several changes observed are in fact worthy of particular mention paleobathymetrically the area changed from an upper bathyal environment of about 400 m deep to an outer shelf domain of 100 50 m furthermore the oxygen minimum zone o m z became highly intense at a the cretaceous tertiary transition catastrophic event b the p1 p2 boundary intense thermic stratification and c between p4 and p6 very active paleoproductivity in this last episode the continental shelf environment was subjected to intense upwelling responsible for the formation of a prephosphatic environment at water sediment interface the paleooceanographic history of phosphates in the gafsa metlaoui basin is in fact in perfect stratigraphic and paleoenvironmental agreement with the paleobathymetric evolution of the kef region finally paleooceanographic communication between the mesogean and the north atlantic was at this period highly free because of lack of hydrologic relations between the north atlantic and the norwegian sea

bioeroding foraminifera a review abstract twenty species of foraminifera mainly from turbulent warm shallow water environments are known to make cavities in hard substrates they range from jurassic callovian to recent in age several hypotheses feeding protection and test building have been proposed to explain this mode of life and the processes involved in boring this review indicates further studies on the biology and physiology of these foraminifera should evaluate their role in bioerosion of hard substrates and the subsequent production of grain sized sediment that may affect the biotopes of sediment dwellers

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

bioerosion in shells from the early permian rio bonito formation brazil taphonomic paleobiological and paleoecological implications abstract we report the occurrence of sponge borings in composite molds of heteropectinid shells from early permian marine siliciclastic deposits of the parana basin of southern brazil sponge borings are preserved mainly as chambers entobia and channels entobia and clionolithes three preservational variations of entobia are present morphologically equivalent to the alpha beta and gamma ontogenetic stages of clionid sponges this equivalence suggests that the ontogenetic behavior in clionid sponges remains the same since early permian times and points to a conservative evolutionary trend for this group the pattern of bioerosion and other taphonomic signatures indicate rapid shell burial due to frequent and energetic storm events that might have limited the time available for bioerosion activity the new findings improve the paleozoic record of entobia and clionolithes and indicate that sponge borings have potential to be preserved in ancient siliciclastic rocks

middle ordovician chazy group cavity dwelling boring sponges microcavities in lower middle ordovician bryozoan mounds from the laval formation chazy group near montreal quebec contain evidence that endolithic boring sponges were present ramose borings with scalloped walls and swellings resembling endolithic sponge galleries faceted carbonate grains similar to modern sponge chips and siliceous spicules both in situ on the cavity wall or roof and in the sediment all point to the activities of endolithic sponges in the hard substrate of the wall and roof coelobiontic cavity dwelling endolithic sponges therefore infested cavities in skeletal mounds and reefs in the middle ordovician and appear to have exploited the cavity habitat very soon after the appearance of metazoan skeletal reefs in the ordovician

mass balance of the greenland ice sheet at high elevations comparison of ice discharge from higher elevation areas of the entire greenland ice sheet with total snow accumulation gives estimates of ice thickening rates over the past few decades on average the region has been in balance but with thickening of 21 centimeters per year in the southwest and thinning of 30 centimeters per year in the southeast the north of the ice sheet shows less variability with average thickening of 2 centimeters per year in the northeast and thinning of about 5 centimeters per year in the northwest these results agree well with those from repeated altimeter surveys except in the extreme south where we find substantially higher rates of both thickening and thinning

a benthic foraminiferal record of paleocene sea level and trophic redox conditions at gebel aweina egypt we quantitatively analyzed benthic foraminiferal assemblages in order to reveal biotic and paleoenvironmental trends in the paleocene section of gebel aweina egypt on the southern tethyan shelf the first correspondence axis ranks taxa along an empirically derived bathymetric gradient with neritic taxa e g discorbis duwi and haplophragmoides walteri opposed to bathyal taxa e g nuttallides truempyi and gavelinella beccari ormis the estimated paleodepth as reflected by the various assemblages was mostly 200 m but varied between 50 m p3a np4 and 300 m p4 n p8 the resultant four relative sea level cycles appear to be at least of regional extent and may in part be eustatically controlled the second correspondence axis reflects trends in trophic and redox development low food high oxygen conditions prevailed during biochrons plc p3b np4 np5 and late p4 np8 when assemblages were mostly dominated by cibicidoides spp most oligotrophic conditions coincided with maximum paleodepth intermediate trophic levels were established during middle p4 np6 and early p5 np9 from the level of the latest paleocene benthic extinction event bee middle p5 and np9 onwards until biochron p6a np10 assemblages dominated by buliminids marked increased trophic levels and reduced ventilation probably resulting from enhanced surface productivity enhanced surface productivity along the southern tethyan margin started during biochron p4 and at least on some shelves intensified after the bee increasing productivity during the latest paleocene contrasts with global trends this may be expected during climatic warming and an expanding trophic resource continuum leading to regionally intensified eutrophy and oligotrophy high productivity through upwelling along the southern tethyan provides support for gcm predictions of intense wind stress in this region during the warm late to latest paleocene 1998 elsevier science b v

experimental dissolution of a fossil foraminiferal assemblage paleocene eocene thermal maximum dababiya egypt implications for paleoenvironmental reconstructions abstract dissolution experiments were carried out on a foraminiferal assemblage from the paleocene eocene thermal maximum petm at dababiya egypt in order to 1 reveal the effects of differential dissolution on the composition of the foraminiferal assemblage and 2 develop objective criteria for the evaluation of dissolution in foraminiferal assemblages used in early paleogene paleoenvironmental reconstructions particularly with respect to neritic midway type assemblages from the paleocene eocene transition our results confirm two general observations on modern foraminifera 1 planktic foraminifera are much more vulnerable to dissolution than benthic foraminifera leading to depressed p b ratios and 2 dissolution susceptibility differs between size fractions with the smaller specimens dissolving more rapidly than the bigger ones leading to a larger average size of the remaining assemblage within a size fraction wall structure and thickness are considered to be the main factors controlling differential dissolution susceptibility we propose a ranking scheme for taxa with respect to dissolution resistance among the benthic taxa lenticulina is most resistant followed by the agglutinated gaudryina cf ellisorae and alabamina midwayensis biserial and triserial hyaline taxa and the porcelaneous spiroloculina sp are most susceptible to dissolution whereas rotaliines such as cibicidoides and anomalinoides have an intermediate susceptibility this implies that mild dissolution of a midway type benthic assemblage leads to a relative enrichment in lenticulina gaudryina and rotaliines amongst planktic foraminifera the muricate taxa acarinina and morozovella are most resistant followed by the cancellate subbotina the smooth and generally small globanomalina and zeauvigerina are least resistant to dissolution our data enable to objectively evaluate various degrees of dissolution in benthic and planktic foraminiferal assemblages retrieved from the lower paleogene tethyan outcrops in this way taphonomic artifacts can be readily distinguished from paleoenvironmental signals affecting the primary composition of the assemblages more generally we propose that the combined use of foraminiferal numbers p b ratio and relative abundances of non calcareous agglutinated taxa and lenticulina may provide a powerful proxy for assessing dissolution in hemipelagic assemblages from cenozoic and upper cretaceous continental margins in order to achieve more robust pre quaternary paleoenvironmental reconstructions based on quantitative foraminiferal data application of dissolution proxies like proposed here or in slightly modified form should become a more widely used micropaleontologic procedure particularly continental margin studies dealing with major biotic events e g petm or employing p b ratios for sea level reconstructions should benefit from such an approach

predation in the paleozoic gastropod like drillholes in devonian brachiopods middle devonian articulate brachiopods ludlowville and moscow formations hamilton group new york have external tapered holes with a central boss that are indistinguishable from drillholes of naticid gastropods that are known from the triassic and later drillholes are specific to prey ribbed shells were avoided and specific to sites on prey healed drillholes suggest penetration of live prey as many as 44 percent of the preferred prey are drilled indicating a level of predation that has been reported only from post paleozoic strata

bioerosion structures in high salinity marine environments evidence from the al khafji coastline saudi arabia abstract salinity is one the major stress factors that controls the biotic activities in marine environments in general the mixture with fresh water has been mention as a great stress factor but the opposite i e high salinity conditions is less developed in the ichnological literature along the al khafji coastline saudi arabia hard substrates constituted by gastropods bivalves and coral skeletons contain diverse and abundant bioerosion traces and associated encrusters field and laboratory observations allowed the recognition of eight ichnospecies belong to the ichnogenera gastrochaenolites entobia oichnus caulostrepsis and trypanites which can be attributed to various activities produced by bivalves sponges gastropods and annelids the borings demonstrate two notable ichnological boring assemblages namely entobia dominated and gastrochaenolites dominated assemblages the highly diversified bioerosion and encrustation in the studied hard organic substrate indicate a long exposition period of organic substrate with slow to moderate rate of deposition in a restricted high salinity marine environment this bioerosion study shows that high salinity at least for the study area is not an important controlling factor for ichnology

clavate borings in a miocene cetacean skeleton from tarragona ne spain and the fossil record of marine bone bioerosion abstract clavate borings found in the tympanic bulla of a miocene cetacean from el camp de tarragona basin constitute the first evidence of the ichnogenus gastrochaenolites in bones of an autochthonous cetacean carcass previous records of similar trace fossils on marine bones were described from transported or reworked remains based on their morphology and ichnotaxonomy the borings are assigned to the activity of pholadid bivalves which would have colonized the skeletal carcass on the sea floor after removal of covering soft tissues sedimentological and paleontological data indicate a low energy depositional setting with low sedimentation rate which would have provided the temporal window for bivalve colonization this new finding contributes to widen our knowledge of bioerosion in marine vertebrate skeletons

paleoenvironmental change at the danian selandian transition in tunisia foraminifera organic walled dinoflagellate cyst and calcareous nannofossil records abstract in the present study we document paleoenvironmental change across the danian selandian transition planktic foraminiferal interval p2 p3b calcareous nannofossil zone np4 subzones ntp6 ntp8a 61 59 ma in nw tunisia diversifications of paleogene planktic foraminifera with the evolution of the muricate and photosymbiotic lineages morozovella acarinina and igorina and of the biostratigraphically important nannofossils genus fasciculithus are recorded within this interval the present study aims to understand early paleogene environmental changes in the southern tethys by analyzing the evolution of surface water and to a lesser extent seafloor conditions three localities were investigated ain settara elles and el kef all representing outer neritic deposition in the same basin the tunisian trough paleoenvironmental changes are explored by combining planktic foraminiferal organic dinocyst and calcareous nannofossils assemblages and several proxy parameters planktic benthic ratio numbers of planktic foraminifera per gram peridinioid gonyaulacoid ratio terrestrial marine palynomorph ratio in addition also some geochemical parameters calcite content and stable isotopes are examined our records indicate that the environment evolved from an initially oligotrophic open marine deep outer neritic setting in p2 p3a towards a shallower and nutrient rich setting from the base of subzone p3b this change is seen in the foraminiferal assemblages with the substitution of praemurica by morozovella among the planktic foraminifera and an upward decrease in deeper benthic taxa also the organic dinocyst assemblages show a peak of peridinioid cysts cerodinium and lejeunecysta associated to these dinocyst assemblages the lowest occurrence of apectodinium is recorded which seem to have evolved in this region possibly in response to enhanced nutrient levels on the shelf additionally a distinct change in calcareous nannofossil assemblages is also described marked by the lowest appearance of chiasmolithus edentulus the lowest consistent occurrence of fasciculithus and a slight increase in near shore taxa essentially pontosphaera this project provides an accurate understanding of paleoenvironmental change across the danian selandian transition in tunisia especially integrating different proxies demonstrates a paleobathymetric shallowing from the danian to the selandian associated to increase surface paleoproductivity furthermore the results are compared with those from other localities along the southern tethyan margin egypt and jordan and a more regional paleoclimatic paleoceanographic perturbation in the southern tethys is suggested

precambrian endoliths discovered the earliest known microborings have now been found in late precambrian ooids upper riphean1 vendian2 570 700 myr of the eleonore bay group of eastern greenland the ooids were originally carbonaceous and underwent silicification after boring occurred the finding establishes that the habit of microbial boring evolved before the appearance of skeleton bearing metazoans in the geological record

on the duration of the paleocene eocene thermal maximum petm 1 the paleocene eocene thermal maximum petm is one of the best known examples of a transient climate perturbation associated with a brief but intense interval of global warming and a massive perturbation of the global carbon cycle from injection of isotopically light carbon into the ocean atmosphere system one key to quantifying the mass of carbon released identifying the source s and understanding the ultimate fate of this carbon is to develop high resolution age models two independent strategies have been employed cycle stratigraphy and analysis of extraterrestrial helium heet both of which were first tested on ocean drilling program odp site 690 these two methods are in agreement for the onset of the petm and initial recovery or the clay layer main body but seem to differ in the final recovery phase of the event above the clay layer where the carbonate contents rise and carbon isotope values return toward background values here we present a state of the art age model for the petm derived from a new orbital chronology developed with cycle stratigraphic records from sites drilled during odp leg 208 walvis ridge southeastern atlantic integrated with published records from site 690 weddell sea southern ocean odp leg 113 during leg 208 five paleocene eocene p e boundary sections sites 1262 to 1267 were recovered in multiple holes over a depth transect of more than 2200 m at the walvis ridge yielding the first stratigraphically complete p e deep sea sequence with moderate to relatively high sedimentation rates 1 to 3 cm ka where a is years a detailed chronology was developed with nondestructive x ray fluorescence xrf core scanning records on the scale of precession cycles with a total duration of the petm now estimated to be 170 ka the revised cycle stratigraphic record confirms original estimates for the duration of the onset and initial recovery but suggests a new duration for the final recovery that is intermediate to the previous estimates by cycle stratigraphy and heet

diverse sclerozoan assemblages encrusting large bivalve shells from the callovian middle jurassic of southern poland a diverse sclerozoan assemblages consisting of both encrusting and boring biota are described from the large limid bivalves ctenostreon from the callovian hardground setting of zalas in southern poland at least 27 encrusting and seven bioerosion taxa are reported here which makes this assemblage not only one of the most diverse in the middle jurassic but the richest in encrusting taxa from the callovian the encrusters consist of cryptic biota of which sedentary polychaetes and cyclostome bryozoans dominate with respect to both species number and abundance the bioerosion traces are dominated by tiny pits referred to the ichnogenus oichnus probably made by some soft bodied biota in the present case followed by the borings of acrothoracican barnacles rogerella the first colonizers of the bivalve shells probably were borers as they only occur in the host shells the encrusting pioneers presumably were oysters and oyster like bivalves followed by opportunistic serpulid sabellid polychaetes and cyclostome bryozoans the last colonizers were calcisponges and thecideide brachiopods in comparison to the only known late callovian shallow and reef associated tropical sclerozoans of israel the assemblage from the open marine deeper setting of poland is much richer in encrusting taxa such a surprising high encruster diversity in the marine northern paleo latitude may have resulted from the deeper and calmer environment with a both reduced sedimentation rate and algal cover and without any significant salinity changes the factors that are thought to have impacted the tropical and shallow marine sclerozoans from israel

visual stratigraphic dating of the gisp2 ice core basis reproducibility and application annual layers are visible in the greenland ice sheet project 2 ice core from central greenland allowing rapid dating of the core changes in bubble and grain structure caused by near surface primarily summertime formation of hoar complexes provide the main visible annual marker in the holocene and changes in cloudiness of the ice correlated with dustiness mark wisconsinan annual cycles both markers are evident and have been intercalibrated in early holocene ice layer counts are reproducible between different workers and for one worker at different times with 1 error over century length times in the holocene reproducibility is typically 5 in wisconsinan ice age ice and decreases with increasing age and depth cumulative ages from visible stratigraphy are not significantly different from independent ages of prominent events for ice older than the historical record and younger than approximately 50 000 years visible observations are not greatly degraded by brittle ice or many other core quality problems allowing construction of long consistently sampled time series high accuracy requires careful study of the core by dedicated observers

production and cycling of calcium carbonate in a shelf edge reef system st croix u s virgin islands applications to the nature of reef systems in the fossil record abstract geologic reefs are the end products of not only constructive processes that produce calcium carbonate but also of destructive processes e g bioerosion and wave action that reduce solid substrate to sediment and of physical processes that rework the reef fabric and transport sediment a study was conducted at cane bay on the island of st croix u s virgin islands to quantify the suite of processes that have influenced holocene reef development data on carbonate production reef accretion bioerosion and sediment transport were used to construct a detailed carbonate budget and to apply the findings of this study to the character of reefs observed in the fossil record total carbonate production on the reef ranged from 0 to 5 78 kg m2 per year with a reef wide average of 1 21 kg m2 per year 1 13 by corals 0 02 by coralline algae 0 06 by primarily molluscs forams and echinoderms based on 7 cores only 0 91 kg m2 per year of this have been retained within the reef interior the remaining 0 24 kg m2 per year of sediment along with the 0 06 kg m2 per year contributed directly by molluscs etc are deposited within reef channels and are probably flushed from the reef by major storms of the material recovered in the cores 58 was either loose sediment and rubble or open void space much of the recognizable coral material was demonstrably reworked and out of place accretion rates across the shelf generally increased with water depth as a result of active slumping along the steepening reef face over the past 2 000 3 000 years the importance of detrital material in the reef fabric and the major role played by secondary processes that constantly rework the substrate have resulted in a reef whose interior is more of a garbage pile than an in place assemblage of corals cemented together into a rigid framework the physical similarities between the detrital fabric of the reef at cane bay and those found in many ancient deposits imply that the general processes operating along the cane bay shelf have persisted during much of the evolution of ancient reefs it is proposed that our modern models overemphasize the importance of in place framework as a criterion for an ecologic reef

north american continental margin records of the paleocene eocene thermal maximum implications for global carbon and hydrological cycling the impacts of the paleocene eocene thermal maximum petm 55 ma one of the most rapid and extreme warming events in earth history are well characterized in open marine and terrestrial environments but are less so on continental margins a major carbon sink here we present stable isotope carbonate content organic matter content and c n ratio records through the petm from new outcrop sections in california and from cores previously drilled on the new jersey margin foraminifer 18o data suggest that midlatitude shelves warmed by a similar magnitude as the open ocean 5 c 8 c while the carbon isotope excursion cie recorded both in carbonate and organic matter 13c records is slightly larger 3 3 4 5 than documented in open ocean records sediment accumulation rates increase dramatically during the cie in marked contrast to the open ocean sites in parallel mass accumulation rates of both organic and inorganic carbon also increased by an order of magnitude the estimated total mass of accumulated carbon in excess of pre cie rates suggests that continental margins at least along north america became carbon sinks during the cie mainly because of weathering feedbacks and rising sea level this result is significant because it implies that the negative feedback role of carbon burial on continental margins was greater than previously recognized

signal and noise in four ice core records from the agassiz ice cap ellesmere island canada details of the last millennium for stable isotopes melt and solid conductivity four ice cores and two deep pit auger sequences from the top of the agassiz ice cap have been variously analysed for o18 ecm solid conductivity and ice melt layer stratigraphy the high resolution data are presented on time scales covering about the last 1000 years the 8 time series are compared and the noise examined in terms of snow drifting and wind scouring of winter snow from the higher exposed parts of flow lines the highly scoured 8 records reflect a mixture of summer biased conditions and the amount of winter scoured snow sites away from the ridges and domes are not scoured the signal part of the scoured and unscoured sites is obtained by stacking averaging normalized series the stacked unscoured series of 8 and accumulation are compared to similar stacked series from central greenland for the last century of annual averages the comparison is surprisingly good suggesting that at these resolutions low noise 8 series have some coherence over fairly large distances the percentage melt

changes in calcareous nannofossil assemblages across the paleocene eocene transition from the paleo equatorial pacific ocean quantitative analyses of selected calcareous nannofossils in deep sea sections recovered from the paleo equatorial pacific odp leg 199 provide new information about biostratigraphy biochronology and the evolutionary history of calcareous nannofossils across the paleocene eocene transition interval the sediment cores from odp leg 199 represent the first continuous paleocene eocene boundary sections ever to be sampled in the central equatorial pacific ocean calcareous nannofossil assemblages are studied to document the distribution of biostratigraphically useful taxa such as ericsonia discoaster fasciculithus rhomboaster and tribrachiatus focus is given to the evolution of the rhomboaster tribrachiatus lineage in the lower eocene interval at site 1215 and on the stratigraphic relationship of these taxa relative to species in the genus fasciculithus critical intervals of north atlantic dsdp site 550 have also been re examined the tribrachiatus digitalis morphotype was described at site 550 from an interval affected by down hole contamination partly originating from within the tribrachiatus orthostylus range the t digitalis morphotype represents an evolutionary transitional form between t contortus and t orthostylus entering the stratigraphic record within the range of the former species and disappearing within the lower part of the range of the latter species the subzonal subdivision of zone np10 hence collapses lithological and colour variability reflecting orbital cyclicity occur in the lower eocene of site 1215 permitting a relative astronomical age calibration of the tribrachiatus taxa the distinct rhomboaster spp discoaster araneus association also occurs in the paleo equatorial pacific ocean together with a marked decrease in diversity of fasciculithus spp site 1220 reveals a short peak abundance of thoracosphaera spp just above the p e boundary interval which probably reflects a stressed surface water environment

boreholes in mississippian spiriferide brachiopods and their implications for paleozoic gastropod drilling abstract bored specimens of the spiriferide brachiopod genera brachythyris and spirifer from several localities of the mississippian fort payne formation kentucky usa represent 7 0 of the total sampled population the boreholes are typically single complete circular in plan view and with their long axes perpendicular to the valve these traits and stereotypy with respect to the pedicle valve and the fold and sulcus are consistent with a predatory parasitic origin of the holes the presence of platyceratid gastropods in the fort payne localities with bored brachiopods the previously documented drilling abilities of these gastropods and the occurrence of a platyceratid snail attached to specimen of a bored devonian brachiopod atrypa argue for platyceratids as the most probable culprits

perturbation of a tethyan coastal environment during the paleocene eocene thermal maximum in tunisia sidi nasseur and wadi mezaz abstract despite the large number of studies on the paleocene eocene thermal maximum petm the knowledge of environmental and biotic responses in shallow marine environments remains quite poor benthic foraminiferal assemblages of the sidi nasseur and wadi mezaz sections in tunisia were studied quantitatively and the paleoecologic interpretations provide new insights into the complex relationship between petm global warming and perturbations of shallow marine settings these sections expose upper paleocene to lower eocene shales and marls of the el haria formation up to the phosphate layers of the chouabine formation underlying the el garia limestones the sidi nasseur section contains a more complete and expanded paleocene eocene boundary interval compared to wadi mezaz although being truncated at the top the wadi mezaz section contains a more complete post petm interval the studied interval can be subdivided into a sequence of 4 biofacies representing respectively a latest paleocene biofacies two petm biofacies and one post petm eocene biofacies the latest paleocene biofacies 1 consists of numerous calcareous benthic foraminifera e g anomalinoides midwayensis frondicularia aff phosphatica and various bulimina and lenticulina species abundant non calcareous taxa haplophragmoides and rare planktic foraminifera indicating a slightly hypersaline eutrophic inner neritic to coastal environment regularly interrupted by oxygen deficiency moderate dysoxia during the latest paleocene this highly productive environment shallowed as indicated by the increasing abundances of a midwayensis the variable dominance of non calcareous agglutinated taxa in biofacies 1 indicates post mortem dissolution effects the toc 13 c org record reveals a sharp negative excursion marking the base of the eocene in general the absence of lithologic changes an increasing sedimentation rate and absence of reworking indicate that the initial part of the petm is complete and expanded in the sidi nasseur section a sharp faunal turnover coincides with this negative 13 c org excursion and is characterized by the disappearance or diminution of common paleocene taxa in this area during the petm benthic foraminifera are less abundant and consist of opportunistic non calcareous taxa together with deeper dwelling middle neritic lagenids and buliminids biofacies 2 and 3 planktic foraminifera dominated by flat spired acarinina mainly a multicamerata become more abundant as observed in many open marine sequences worldwide all these faunal parameters suggest more stressed probably severe dysoxic sea floor conditions within a transgressive phase during the onset of the petm an estimation of the total duration of the sidi nasseur petm interval is difficult to establish yet the lack of recovery carbon isotope values suggests that the preserved petm interval reflects only a part of the cie core the top of the petm interval is truncated due to local erosion during the early eocene the eocene recovery fauna is mainly composed of lenticulina and stainforthia species biofacies 4 indicating restricted coastal to hyposaline lagoonal eutrophic conditions distinctly different from earlier environmental conditions

high resolution nannofossil biochronology of middle paleocene to early eocene at odp site 1262 implications for calcareous nannoplankton evolution abstract over the last several decades debates on the tempo and mode of evolution have centered on the question whether morphological evolution preferentially occurs gradually or punctuated i e with long periods of stasis alternating with short periods of rapid morphological change and generation of new species another major debate is focused on the question whether long term evolution is driven by or at least strongly influenced by changes in the environment or by interaction with other life forms microfossils offer a unique opportunity to obtain the large datasets as well as the precision in dating of subsequent samples to study both these questions we present high resolution analyses of selected calcareous nannofossils from the deep sea section recovered at odp site 1262 leg 208 in the south eastern atlantic the studied section encompasses nannofossil zones np4 np12 equivalent to cp3 cp10 and chrons c27r c24n we document more than 70 biohorizons occurring over an about 10 myr time interval 62 5 ma to 52 5 ma and discuss their reliability and reproducibility with respect to previous data thus providing an improved biostratigraphic framework which we relate to magnetostratigraphic information and present for two possible options of a new paleocene stratigraphic framework based on cyclostratigraphy this new framework enabled us to tentatively reconstruct steps in the evolution of early paleogene calcareous nannoplankton through documentation of transitional morphotypes between genera and or species and of the phylogenetic relations between the genera fasciculithus heliolithus discoasteroides and discoaster as well as between rhomboaster and tribrachiatus the exceptional record provided by the continuous composite sequence recovered at walvis ridge allows us to describe the mode of evolution among calcareous nannoplankton new genera and or new species usually originated through branching of lineages via gradual but relatively rapid morphological transitions as documented by the presence of intermediate forms between the end member ancestral and descendant forms significant modifications in the calcareous nannofossil assemblages are often related to significant changes in environmental conditions but the appearance of structural innovations and radiations within a single genus also occurred during stable environmental conditions these lines of evidence suggest that nannoplankton evolution is not always directly triggered by stressed environmental conditions but could be also driven by endogenous biotic control

altitudinal gradient of mass balance sensitivity to climatic change from 18 years of observations on glacier d argentiere france assessment of the contribution of small glaciers to sea level rise or the reconstruction of past glacial mass balance requires knowledge of mass balance sensitivity to climatic variations the aim of this paper is to clarify this relation the mass balance fluctuations analyzed from measurements on glacier d argentiere mont blanc massif france between 1850 and 2700 m a s l were compared with climatic variations at a nearby meteorological station statistical study of the data shows that 1 the annual mass balance fluctuations are dependent on elevation and 2 the mass balance sensitivity to temperature decreases with altitude and diverges from current model results consequences of a temperature variation of 1 c for global volume variations are significant a simple calculation on glacier des bossons mont blanc massif france shows that the sensitivity from the model can lead to volume variations twice as high as results compatible with our observations

assessment of the surface mass balance along the k transect greenland ice sheet from satellite derived albedos this paper explores the potential of using satellite derived albedos to estimate the surface mass balance of the kangerlussuaq transect k transect greenland ice sheet we first retrieved surface albedos from advanced very high resolution radar data by using among other techniques a new cloud detection algorithm based on the relation between brightness temperature and surface elevation we then computed the satellite derived mass balance bsat from the mean albedo for the transect by taking fixed values for atmospheric transmissivity and the longwave and turbulent fluxes we found that bsat explains 71 of the variance in 13 years of stake mass balance measurements bm our method also provides good estimates of the magnitude of the interannual variability in bm the performance of the method degrades considerably without correction for anisotropic reflection at the surface and recalibration of the satellite sensors with dry snow at the top of the ice sheet sensitivity tests indicate that the method s performance is hardly sensitive to uncertainties in parameters therefore we expect that the method could be successfully applied on other glaciers and parts of ice sheets and ice caps especially where accumulation rates are relatively small we show that the investigated method performs best just below the mean equilibrium line altitude

skeletal carbonate productivity and phosphogenesis at the lower middle cambrian transition of scania southern sweden the lower middle cambrian transitional interval of scania is largely represented by condensed limestone beds lithostratigraphically grouped in the gislov formation 1 5 7 m thick and the forsemolla and exsulans limestone beds lower part of the alum shale formation up to 4 in thick the strata display a combination of skeletal carbonate productivity episodic nucleation of phosphate hardground nodules and polyphase reworking recorded on a platform bordering the nw corner of baltica the shell accumulations can be subdivided into three deepening upward parasequences separated by distinct erosive unconformities the parasequences correspond biostratigraphically to the holmia kjerulfi ornamentaspis linnarssoni and ptlychagnostus gibbus zones the latter two generally being separated by a stratigraphic gap that includes the middle cambrian acadoparadoxides oelandicus superzone except for the exsulans limestone the carbonates reflect development of a prolific epibenthic biota dominated by filter feeding nonreefal chancelloriid echinoderm sponge meadows rich in trilobites and brachiopods and which were subjected to high energy conditions the absence of microbial mats or veneers encrusting the erosive surfaces of these event concentration low relief shoal complexes may be related to long hiatal episodes resulting in microboring proliferation high levels of nutrient supply resulted in high primary productivity eutrophic conditions glauconite precipitation phosphogenesis in some case microbially mediated and rnicroendolithic infestation an early diagenetic mildly reducing environment is suggested by the presence of authigenic subsequently reworked pyrite which contrasts with the syndepositional normal oxygenated conditions reflected by macroburrowing and the abundance of benthic fossils

late jurassic coral microbial reefs from the northern paris basin facies palaeoecology and palaeobiogeography abstract during the late middle oxfordian patch reefs grew on the northern margin of the paris basin according to the facies analysis of the reef and inter reef sediments the environment was a warm clear and agitated sea with highly episodic sedimentation the bioherms were a short lived phenomenon during the third phase of regional reefal development sequence stratigraphically they are associated with a highstand system tract volumetrically and trophically dominant organisms were microbes now represented by massive clotted leiolite stalactitic hemispheroids with purely thrombolitic texture are restricted to open caves corals were of structural reef building importance due to their rapid upward growth the patch reefs are characterised by thickets of ramose corals which developed a very open framework in the vicinity of these patch reefs though in hydrodynamically higher energy environments grew thickets of more stoutly branched corals however they are rarely preserved in situ and are generally represented as abundant coral rubble the reef taxa are characterised by the notable absence of several groups e g oysters serpulids bryozoans pectinids occurring at other localities where reefs of similar age developed in similar environmental conditions the reefs also have strikingly modern aspects to them in particular the presence of cryptic elements within caves and a sponge dominated borer association dwellers belong to various life form types although encrusting taxa are exceedingly rare this may be explained by the presence of soft microbial films on most surfaces the palaeoecological analysis suggests that the major controls on faunal composition and high diversity were elevated nutrient levels highly episodic sedimentation and probably seasonal environmental disturbances structural and functional aspects of the reef community grazers trigger framebuilders borers trigger binders binders hamper borers allow ecological comparisons to be made with contemporaneous as well as recent reefs the unique combination of ecological factors resulted in a specialised previously undescribed community which differs from both tethyan and northern localities in various aspects these include cavities with cryptofauna prominence of grazing gastropods and high faunal diversity in a microbially dominated build up

benthic foraminiferal extinction and repopulation in response to latest paleocene tethyan anoxia the latest paleocene benthic foraminiferal extinction event has been studied in two marlstone successions in the tethys at wadi nukhl egypt and torangly turkmenistan both sections yield a sapropelic layer at the level of the extinction event at nukhl this layer underlies a thin calcareous bed that has also been found in other middle east upper paleocene sections with the onset of anoxia at the tethyan sea floor the aerobic and oligotrophic gavelinella beccariiformis deep sea community collapsed eutrophic to mesotrophic and low oxygen conditions most likely resulting from enhanced organic carbon fluxes to the sea floor triggered an 100 200 k y repopulation sequence marked by downslope migration of several neritic communities that were dominated by opportunistic and tolerant taxa the initial ecosystem restoration was completed when an aerobic and oligotrophic nuttallides truempyi deep sea community became established we suggest that this repopulation mode could be typical for the central tethys

a fossil record full of holes the phanerozoic history of drilling predation the evolutionary history of drilling predation despite a long and rich fossil record precambrian holocene contains a 120 m y gap late triassic early cretaceous drilled bivalve and brachiopod shells from jurassic deposits of hungary india and four localities documented in the literature indicate that drillers may have existed continuously throughout the mesozoic they may have been descendants of paleozoic predators unknown mesozoic carnivores or precursors of modern drillers a literature database suggests three major phases in the phanerozoic history of drilling predators 1 the paleozoic phase latest precambrian carboniferous dominated by rare to moderately frequent drillings in brachiopods and sessile echinoderms 2 the mesozoic phase permian early cretaceous with very rare or even facultative drillers that had little impact on marine benthic communities but nevertheless may have been present continuously and 3 the cenozoic phase late cretaceous holocene dominated by frequent gastropod drillings in mollusks

glaciological investigations in the crete area central greenland a search for a new deep drilling site the results of the 1984 85 post gisp campaigns in central greenland are presented eight ice cores were obtained some spanning up to 360 years we present i geographical positions and elevations at the drill sites

bryozoans in transition the depauperate and patchy jurassic biota bryozoans were profoundly affected by the end permian and probably also by the end triassic mass extinction events their recovery in terms of diversity and disparity during the jurassic was slow and geographically patchy critical compilation of data from the published literature reveals only 172 valid species 160 cyclostomes 10 ctenostomes and 2 cheilostomes some as yet not formally named however the rate of description of new jurassic bryozoan species during the last two hundred years implies that many more species remain to be discovered and described the jurassic is the only geological period during which cyclostomes were the dominant order and is also important in having the oldest cheilostome bryozoan the first representative of the order that dominates the modern bryozoan biota species diversity peaked in the bathonian where local assemblages may contain up to 33 species encrusters account for 124 73 of the 172 jurassic species among which small sheet like forms especially those assigned to the form genus berenicea are the most numerous the overwhelming predominance in the jurassic of weeds with runner ribbon or sheet colony forms is striking unlike the triassic and cretaceous large tree like or frondose erect colonies are uncommon and species with fenestrate articulated and free living colonies are unknown of 92 geographically categorized entries for jurassic bryozoans in the zoological record 1937 2003 80 87 are european records outside europe diversity appears to have remained low throughout the jurassic and non weedy species are particularly scarce compared with the cretaceous jurassic bryozoans show no adaptations that can be interpreted as related to the increased predation pressure associated with the mesozoic marine revolution the jurassic bryozoan biota shares characteristics with both the stenolaemate dominated palaeozoic triassic biota and the cheilostome dominated cretaceous recent biotas

sclerobionts on biogenic substrates from the monte leon formation lower miocene in santa cruz province argentina taphonomic and paleoenvironmental considerations abstract study of hard substrate communities in a paleoenvironmental and taphonomic context contributes towards increasing knowledge on the depositional environments and on the history of the substrate colonized before final burial in this work we study traces produced by sclerobionts on biogenic substrates from two shell concentrations in the monte leon formation lower miocene exposed at cabeza de leon southern patagonia argentina the aims of this study are to describe the bioerosion traces and to infer the taphonomic history of the hard substrates mollusk shells based on ichnodiversity and sclerobiont distribution together with other preservational features fifteen ichnotaxa were identified at different taxonomic ranks one ichnofamily three ichnogenera and eleven ichnospecies traces produced by bryozoans were highly predominant followed by those produced by sponges foraminifera and polychaetes the biogenic substrates on which the sclerobionts settled were gastropod and bivalve shells showing different taphonomic signatures shells with high fragmentation and surface alteration are dominant suggesting that they were reworked by wave action before deposition and final burial on the other hand well preserved shells reflect less reworking and shorter transport distance the mixture of these elements could be the result of short term high energy events such as storms yet these taphonomic signatures were modified later by biologic factors mainly bryozoan bioerosion in a quiet and shallow environment with a low sedimentation rate and abundant nutrient availability bioerosion valuation in conjunction with other taphonomic attributes allowed identifying the concentrations as of mixed origin biogenic sedimentologic and including elements that underwent different taphonomic histories the results contribute to improve the knowledge about marine hard substrate communities in middle to high latitudes of the southern hemisphere in addition they highlight the importance of conducting studies on these communities in conjunction with other taphonomic data when elucidating the history of colonized substrates

greenland ice sheet mass balance distribution a variance analysis of existing field data a large number of mass balance measurements have been carried out on the greenland ice sheet but few of the series obtained are well suited for statistical studies rather than looking at the global mass balance value this paper deals with the spatial and temporal mass balance variability on the ice sheet two sorts of analysis are possible direct comparisons of the series measured at a given site or a broader approach involving comparisons between different sites using variance analysis for glaciers in the southwest ablation area a significant interannual variability around 1 0 m w e is found this variability is spatially consistent in the accumulation area the results are more complex for example there is consistent evidence of year to year variations on the west east expeditions glaciologiques internationales au groenland egig profile but other closer sites are weakly correlated these results emphasize the need for a better coverage of measurements over the entire ice sheet as well as longer and more continuous measurement series

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

greenland ice sheet high elevation balance and peripheral thinning aircraft laser altimeter surveys over northern greenland in 1994 and 1999 have been coupled with previously reported data from southern greenland to analyze the recent mass balance of the greenland ice sheet above 2000 meters elevation the ice sheet is in balance on average but has some regions of local thickening or thinning thinning predominates at lower elevations with rates exceeding 1 meter per year close to the coast interpolation of our results between flight lines indicates a net loss of about 51 cubic kilometers of ice per year from the entire ice sheet sufficient to raise sea level by 0 13 millimeter per year approximately 7 of the observed rise

visions of ice sheets in a greenhouse world abstract backstripped eustatic estimates from new jersey and the russian platform show large 25 m and rapid 18 o record highlights the enigma this was the warmest interval of the past 200 my yet it was bracketed by two inferred eustatic falls of 25 m that were associated with two large 0 75 deep sea 18 o increases 92 93 ma mid turonian and 96 ma mid cenomanian we reconcile records of warm high latitudes with glacioeustasy by proposing that late cretaceous early eocene ice sheets generally reached maximum volumes of 8 12 10 6 km 3 20 30 m glacioeustatic equivalent but did not reach the antarctic coast hence coastal antarctica hence deep water remained relatively warm even though there were significant changes in sea level as the result of glaciation unlike the oligocene and younger icehouse world these ice sheets only existed during short intervals of peak milankovitch insolation leaving antarctica ice free during much of the greenhouse late cretaceous to middle eocene these results highlight the need to re evaluate the paradigm that polar ice sheets did not exist during times of warm high latitude climates

the paleocene eocene thermal maximum as recorded by tethyan planktonic foraminifera in the forada section northern italy abstract the forada section in the venetian pre alps of northern italy represents an expanded record of the paleocene eocene thermal maximum petm at a depositional paleodepth of about 1 km 0 5 km high resolution planktonic foraminiferal analysis of this section in a time interval of approximately 1 3 myr across the paleocene eocene boundary reveals striking faunal changes that allow the identification of eight phases a h the late paleocene was represented by stable warm and oligotrophic surface water conditions phase a unstable environmental conditions start well before the onset of petm ca 150 kyr phase b and involved a change towards eutrophy as marked by the increase of subbotina and the concomitant decrease of morozovella this step is also characterized by enhanced fragmentation and dissolution the interval corresponding to the main body of the carbon isotope excursion cie is characterized by a marked increase of acarinina though with some differences in the species composition and relative abundance both in high and low latitudes particularly in the tethyan area forada is no exception to this pattern however at forada two prominent peaks in abundance of acarininids are recorded ca 30 kyr prior to the onset of the cie thus suggesting an increase in temperature heralding the onset of the petm phase c interestingly the lower peak in abundance of acarinina just precedes the 1 carbon isotope negative shift occurring below the onset of the main cie the basalmost eocene corresponding to the lower part of cie curve is represented by intense planktonic foraminiferal dissolution implying an extraordinary rise of the ccd this interval has an estimated duration of about 16 kyr phase d the dominance of acarininids in the lower part of the cie phase e f ca 14 and 22 5 kyr is interpreted as a consequence of the extreme warmth coupled with eutrophic conditions characterizing the forada depositional environment at that time these acarininids include at forada also the temporally constrained acarinina sibaiyaensis and a africana the morphological similarity between these peculiar species with the radially elongated chambered forms characterizing the cretaceous anoxic events suggests the hypothesis that depletion of oxygen in the upper water column might have been one of the factors causing their conspicuous occurrence at the petm the recovery in abundance of the specialized morozovellids and of other planktonic foraminiferal groups e g biserials globanomalinids igorinids planorotalids and pseudohastigerinids occurring in the middle part of the cie ca 30 kyr after the onset of the petm indicates an initial environmental recovery phase g a new stable state is definitely reached in the upper part of the forada section where the relative proportions of the main component of planktonic foraminiferal assemblages move towards values similar to those of the late paleocene conditions phase h however the perturbation during the petm produced significant changes in the ocean geochemistry that endured after the petm event as testified by the prominent high carbonate dissolution characterizing the marly levels and the large variability in relative abundance among different components of the planktonic foraminiferal assemblages these striking oscillations were not present in the latest paleocene

mass balance of glaciers other than the ice sheets small glaciers appear to have been at equilibrium or shrinking very slightly during 1961 90 according to analysis of an essentially compl ete set of published measurements simple calculations give an average annual mass balance of 195 59 mm a 1 water equivalent but this is too low because of systema tic errors eglect of internal accumulation is respon sible for some tens of millime ters of under esti mate uneven spatial coverage with fewer measurements where mass balances are less negative accounts for about 50 mm a 1 of underestimate this figure derives from spatial interpolati on based on global data on ice extent and on an analysis of correlations between balance time series the eorrelogram shows exponential decay the scale length being about 600 km the largest bias is due to a newly detec ted dependence of mass balance on glacier size among the 231 measured glaciers many arc small and belong to a restricted size range in which balance is negativ e but much of the small glacier extent is accounted for by larger glac iers in a size range where balance is indisti ngui shable from zero correct ing for this size bias increases the average balance to 35 89 mm a i inspection of time series for 1940 95 251 glaciers shows that mass balance was least negative during the 1960s and has varied in broad agreementvith northern hemisphere temperature anomalies smaller small glaciers a 16 km2 appear to be more sensitive than larger small glaciers to changes in thermal forci ng the small glaci er contribution to sea level rise implied by this asse ssment is only 0 06 0 32 mm a i consistent with glaciers in general mak i ng little or no contri bution to sea level change during 1961 90

boring predation and mesozoic articulate brachiopods abstract a systematic survey of all the mesozoic brachiopods in the large collections of the sedgwick museum cambridge university has revealed more than 213 predatory boreholes from a wide range of largely british localities it seems likely that this type of predation was not infrequent at least locally as evidenced by the proportion of bored valves at some localities and the degree of stereotypy shown in borehole positioning the size of the boreholes and their neat circular cross sections suggest that they were made by large epifaunal predators using chemical attack and those of post albian age may be comfortably if not confidentally assigned to muricid gastropods although it is likely that bivalves with their greater flesh yields were the preferred prey item in most mesozoic shelly benthic communities it is apparent that boring predators may have resulted in a significant predation pressure on articulate brachiopods

annual accumulation at two sites in northwest greenland during recent centuries during summer 1995 150 m firn and ice cores were drilled to determine annual accumulation rates at two greenland sites 73 84 n 49 49 w nasa u site and 78 53 n 56 83 w humboldt glacier site annual layers were identified in the cores using multiple parameters 18 o and concentrations of dust h 2 o 2 nh 4 ca 2 and no 3 using all parameters together to define annual layers resulted in a 350 year record for the nasa u core with no dating uncertainty for the lower accumulation humboldt core the dating uncertainty is about 5 years over the 852 year period of record with no uncertainty over the past 200 years annual accumulation over the periods of record at the two sites averaged about 0 34 and 0 14 m water equivalent respectively a set of 20 m firn cores drilled near the main 150 m cores showed that interannual variability of accumulation exceeded spatial variability at nasa u the humboldt cores showed equal spatial and interannual variability the accumulation rates at both sites showed a low frequency variation of about 100 years and both sites showed 200 year cumulative fluctuations of about 2 m from mean accumulation rates compared to central greenland and to nasa u the humboldt core showed higher annual accumulation rates around 1760 1810 possibly indicating a changed circulation pattern for the more northern part of greenland in that period

marine bioerosion in rocks of the prehistoric tholos of la pastora valencina de la concepcion seville spain archaeological and palaeoenvironmental implications in this study we examined the materials used in the building of the tholos of la pastora located in the archaeological site of valencina de la concepcion seville spain which represents the largest settlement of the guadalquivir valley during the third millennium bc three different types of rock were found palaeozoic sandstone shale which forms the walls of both the corridor and the chamber palaeozoic granite which makes up part of the roof slabs and neogene calcareous sandstone which forms the remainder of the roof and floor slabs as well as the jambs lintels and some blocks of the walls of the chamber intense marine bioerosion as a result of the activity of bivalves annelids and sponges was observed in some elements of the calcareous sandstone in fact the remains of some of the tracemakers were unusually well preserved as was the case for the bivalve petricola lithophaga whose shells remain in many of their burrows we infer that these bioerosion structures were formed in a shallow coastal environment intertidal and that bioerosion was possible until the few moments before its extraction as construction material thereby the environment in which rock extraction took place was likely a coastal wave cut platform in which calcareous sandstone levels outcropped and stood out between clay layers the radiocarbon dates obtained from these bivalve shells provide a time range between 4780 and 4400 cal yr bp 2830 2450 yr bc as the highest probability for rock extraction and the subsequent building of the tholos thus the date represents a terminus post quem for the construction of the monument of la pastora

taphonomic comparison between recent and fossil sand dollars abstract the taphonomy of a recent and a fossil sand dollar are compared the recent echinodiscus auritus originates from a shallow water carbonate environment in the red sea the fossil parascutella hobarthi is found in micaceous sands of the lower miocene austrian molasse zone both species show strong similarities in constructional morphology including the flattened overall shape details of the surface morphology as well as the presence of an internal support system three taphonomic features are remarkable different 1 lethal and non lethal predation especially high in the recent e auritus 2 encrustation of the test especially by coralline algae in the fossil parascutella and 3 radial cracking on implosion of the body cavity caused by sediment loading on the fossil tests differences in taphonomic signatures can be correlated with depositional environment predation and encrustation as well as factors related to burial of the fossil specimens sediment loading and diagenesis

the macroboring ichnofossil trypanites in colonies of the middle ordovician bryozoan prasopora population behaviour and reaction to environmental influences a life assemblage population 189 specimens of hat shaped hemispherical colonies of prasopora spp from the lowermost verulam formation middle ordovician at kirkfield ontario contains macroborings referable to trypanites magdefrau scolecodonts and other fragmentary microfossils identify the organisms that made the borings as polychaete annelids fifty two percent of the bryozoan colonies are bored and some colonies contain as many as 83 macroborings the polychaetes bored into dead bryozoan colonies but it appears that the borers were selective in their choice of substrates they chose large colonies with diameter height ratios between 3 1 and 3 2 concentration of high densities of borings on the sides of the colonies indicates that current direction and probably also sedimentation related to current flow and turbulence over and around the colonies were important influences on the borers the tendency for borings to occur in some colonies and not others and when they are present to be numero

microborings in early cambrian phosphatic and phosphatized fossils abstract a small proportion of phosphatic and phosphatized fossils mostly microfossils extracted from lower cambrian qiongzhusian lime mudstones of deeper water aspect belonging to the yu anshan and shuijingtuo formations of south china is perforated by microborings these microborings are present in bradoriid and phosphatocopine arthropod carapaces lingulid brachiopod valves microdictyon plates and tommotiid sclerites their absence in co occurring phosphatized eodiscid trilobite exoskeletons and palaeoscolecid worm trunk fragments indicates a substrate specificity that suggests the boring microorganism was heterotrophic extracting particular residual organic compounds present in only certain bioclast types microborings occur as meandering tunnels and grooves on bioclast surfaces and most are 10 20 m wide and circular in cross section the euendoliths were thus able to live partly exposed as well as within the substrate tunnel and groove walls bear a distinct longitudinal sculpture of straight striae separated by cuspate ridges 1 2 m apart that parallel the microboring never twisting the microborings accord with the ichnotaxon microptychoites fuquanensis dong in dong et al dong y ji q wang s 1984 the discovery of microscopic trace fossils in the sinian doushantuo formation in southwestern china scientia geologica sinica 346 347 in chinese the fluted sculpture appears to have no modern analogue but may have arisen by localized secretions at the tip of a bundle of filaments this kind of microboring had been previously reported from phosphatic substrates of ediacaran earliest cambrian middle cambrian and probably early devonian age but appears to have no recent counterpart

lower cambrian cavity dwelling endolithic boring sponges in the lower cambrian forteau formation middle bonnia olenellus zone of southern labrador cavities in archaeocyath patch reefs contain preserved coelobiontic endolithic sponges scallops and carbonate chips produced by sponge boring spicules and preserved endolithic sponge body fossils all point to the presence of endolithic sponges in lower cambrian reef cavities the oldest previously described endolithic sponges are early ordovician in age and the oldest previously known reef interior bioerosion is middle ordovician in age the presence of endolithic sponges in reef cavities of the forteau formation therefore extends both the record of endolithic sponges and of reef interior bioerosion from the ordovician to the upper lower cambrian

the impact of paleocene eocene boundary events on middle neritic benthic foraminiferal assemblages from egypt abstract a 25 m upper paleocene to lower eocene marly sequence exposed at gebel duwi quseir red sea coast of egypt provides a good opportunity for studying paleocene eocene p e boundary stratigraphy and events various bio eco and isotope stratigraphic correlations accurately delineate the position of the p e boundary i e the level of stable isotopic excursions and deep sea benthic extinctions in the middle part of this section within zones p5 and np9 in this paper the impact of p e boundary environmental perturbations on benthic foraminiferal communities of the shallow tethyan shelf is examined benthic foraminiferal assemblages from gebel duwi characterized by large frondicularia phosphatica and f nakkadyi in addition to a number of other neritic taxa but without any typical outer neritic bathyal taxa suggest middle neritic 75 100 m deposition throughout the studied interval and only minor relative sea level variations perhaps some 10 20 m across the boundary sea level appears to have been stable yet a distinct faunal turnover marks the p e boundary of this shallow site which in contrast to deep sea records is less abrupt being preceded by a gradual diversity decrease starting some four meters below the boundary moreover most exits are either local or just temporary and thus not true extinctions many lazarus taxa reappear at some point above the boundary while all but one of the disappearing taxa are known from other lower eocene neritic deposits in egypt in general benthic foraminiferal assemblages display low diversities and high dominance values notably anomalinoides aegyptiacus up to 74 suggesting high levels of environmental stress at the sea floor in combination with occasionally very high p b ratio s up to 98 p and generally laminated sediments the character of the benthic assemblage points to a strong influence of recurrent dysoxia and or anoxia we suggest that these resulted from surface eutrophication by intermittent coastal upwelling and reduced ventilation of the bottom environment although these conditions prevailed during most of the time interval studied they were most severe during the latest paleocene and early eocene when eutrophication intensified and the organic carbon flux to the sea floor increased enhanced atmospheric contrasts between the tethys seaway and the african continent resulting in intensified longshore tradewinds may have controlled these changes at the p e boundary the bottom environment became minimally ventilated perhaps due to reduced oxygen advection from deeper waters three meters above the boundary a succession of increasingly diverse assemblages indicate a gradual decrease of environmental stress and a return to more normal conditions although the organic carbon flux to the sea floor remained high

bivalve bioerosion in cretaceous neogene amber around the globe with implications for the ichnogenera teredolites and apectoichnus abstract amber samples with bivalve borings from six localities around the world ranging in age from hauterivian to miocene have been studied the possible assignment to teredolites or gastrochaenolites is discussed considering the type of substrate as an ichnotaxobase it is proposed to regard amber or similar resins as a variant of xylic substrates and to maintain the separation between the two ichnogenera and their different paleoecological implications the amber borings are assigned to teredolites clavatus leymerie 1842 and apectoichnus longissimus kelly and bromley 1984 respectively the presence of bioglyphs in a few borings suggests a mechanical production process with pholadid bivalves such as martesia preserved inside many of the samples representing the producer in general the amber producing trees mostly grew along a forested coastline where they were occasionally flooded by seawater or even transported from rivers into the sea and later deposited

calculated variations of annual ice ablation at the margin of the greenland ice sheet west greenland 1961 90 annual ice ablation has been measured at three locations at the margin of the greenland ice sheet nordbogletscher for 6 years 1977 78 to 1982 83 qaman rssup sermia 8 years 1979 80 to 1986 87 and at paakitsup akuliarusersua 7 years 1982 83 to the present as the data sets cover different periods it is difficult to compare ablation directly between the three sites however measured series at each site can be extended over the last 30 years 1961 90 by simulations using climatic data and the extended data series can be compared

ichnotaxonomy of microbial trace fossils in volcanic glass abstract ancient microbial activity in volcanic glass creates micron sized cavities that can be regarded as trace fossils these are common in glassy rims of oceanic pillow lavas and volcanic breccias morphologically comparable mineralized traces are also found in meta volcanic glasses from ophiolites and precambrian greenstone belts multiple lines of evidence indicate microbial formation of these borings although the affinity of the trace maker s is poorly constrained two broad morphological types have been previously recognized and termed granular9 and tubular9 bioalteration textures here optical microscopy and sem observations are used to erect two new ichnogenera granulohyalichnus igen nov and tubulohyalichnus igen nov five ichnospecies are also defined granulohyalichnus vulgaris isp nov a granular species tubulohyalichnus simplus isp nov an unornamented tubular species tubulohyalichnus annularis isp nov an annulated tubular species tubulohyalichnus spiralis isp nov a helicoidal tubular species tubulohyalichnus stipes isp nov a branched tubular species this systematic taxonomy is advanced to allow reliable comparisons to be made between new and existing reports of these microbial borings moreover the adoption of a taxonomic framework will aid the development of these ichnofossils as palaeoenvironmental indicators and tracers of microbial evolution

the depth dependency of planktonic benthic foraminiferal ratios constraints and applications abstract study of the ratio between planktonic and benthic foraminifera in a great number of areas shows that variation of this ratio with depth can be described using organic matter flux equations essentially the share of benthic foraminifera in the total association is inversely proportional to depth as is the amount of organic matter resulting from primary productivity reaching the sea bottom variation in the p b ratio from area to area appears to be strongly dependent on the amount of inbenthic living foraminifera if the ratios are corrected for this the regressions between the proportion of planktonic foraminifera p and depth appear to be near identical in the gulf of mexico the gulf of california the west coast of the usa and the adriatic sea this regression can be described by depth e 3 58718 0 03534 p a study of the behaviour of this function in nine cores from the adriatic upper quaternary reveals that the palaeodepth reconstructions are not influenced by fluctuations in productivity and temperature but that they are significantly influenced by redeposition of fine grained deposits

boreholes in the middle devonian blastoid heteroschisma and their implications for gastropod drilling abstract boreholes in over 100 specimens of the devonian blastoid heteroschisma and the presence of the gastropod platyceras orthonychia sp attached to a specimen of heteroschisma subtruncatus hall 1858 suggest that platyceratid gastropods were capable of drilling their hosts at least as early as the middle devonian and thus represent the first known gastropods to have evolved this ability the presence of similar holes in numerous other devonian and mississippian blastoids and the occurrence of several additional examples of platyceratids attached to blastoids indicate that the interaction between gastropods and blastoids was not infrequent as in the case of the gastropod crinoid interaction this relationship is interpreted as having been parasitic rather than predatory the parasitic drilling platyceratids may have been a factor in the paleozoic precursor of the mesozoic marine revolution some of the anti predatory defenses of crinoids described from the late paleozoic may have been strategies of avoiding platyceratid infestation

new precipitation and accumulation maps for greenland annual total precipitation and the annual accumulation on the greenland ice sheet are evaluated and presented in two maps the maps are based on accumulation measurements of 25 1 pits and cores obtained from the upper accumulation zone and precipitation measurements made at 35 meteorological stations in the coastal region to construct the accumulation map the annual precipitation was split into solid and liquid precipitation components annual total precipitation exceeding 2500 mm w e occurs on the southeastern tip of greenland while the minimum precipitation is estimated to occur on the northeastern slope of the ice sheet the mean annual precipitation for all of greenland is 340 mm w e the largest annual accumulation of about 1500 mm w e is found on the glaciers in the southeastern corner of greenland while the smallest accumulation is found on the northeastern slope of the ice sheet west of danmarkshavn the mean accumulation on the greenland ice sheet is estimated at 310 mm w e the regional difference in accumulation is examined with respect to the 850 hpa m bar level circulation the present surface topography is found to play an important role in determining regional accumulation on the ice sheet