distribution of marine organisms and its geological significance in the modern reef complex of the ryukyu islands abstract extensive investigations of biota in the reef complex around the ryukyu islands have revealed ecologic specificity of many benthic organisms and have shown that characteristic assemblages are found in each of the topographic zones and sub areas the moat is divisible into a nearshore seagrass bed and an offshore sand bottom both inner reef flat and outer reef flat are characterized by abundant occurrences of hermatypic corals and nonarticulated coralline algae however the former is dominated by branching and foliaceous forms of corals and various large fleshy erect forms of algae whereas the latter is dominated by encrusting and tabular forms of corals lacking these algae corals and coralline algae are not present on the reef crest which is covered by rubble and gravel where algal turf and sargassum are spreading encrusting and tabular forms of corals flourish on the shallower part of the reef slope with high coverage while with increasing depth the coverage decreases and the dominating coral forms change with hemispherical and encrusting forms on the middle part of reef slope and foliaceous and encrusting forms on the deeper part of reef slope nonarticulated coralline algae are distributed throughout the reef slope the composition of coral and coralline algal assemblages changes dramatically with increasing depth foraminiferal algal nodules rhodoliths are the most abundant constituent on the island shelf commonly with cycloclypeus carpenteri there are likely to be two types of shelves in tropical to subtropical regions nutrient rich halimeda dominant and nutrient poor rhodolith dominant sediments abundant in bryozoan skeletons occur occasionally on the shelf

growth and high resolution paleoenvironmental signals of rhodoliths coralline red algae a new biogenic archive we investigated rhodoliths coralline red algae from a subtropical locality in the gulf of california lithothamnium crassiusculum and a subarctic locality in newfoundland lithothamnium glaciale for their potential as paleoenvironmental archives using microanalytical geochemical techniques to measure variations in 18o mg and ca rhodoliths are potentially well suited as recorders of shallow water paleoenvironmental signals because they 1 have worldwide distribution from the tropics to polar regions 2 are long lived from decades to centuries and 3 display well developed growth bands our results indicate that rhodolith growth bands preserve ultrahigh resolution records of paleoceanographic paleoclimatic change and likely constitute an important new archive for reconstructing the paleoenvironmental history of littoral neritic areas in which these algae are found the 18o content of individually sampled rhodolith growth bands ranges from 2 4 to 4 6 in l crassiusculum and from 3 2 to 0 3 in l glaciale in both cases the range of 18o values suggests a slightly lower amplitude of variation in sea surface temperature than that actually measured in the ocean at the two study sites both l crassiusculum and l glaciale show a negative offset from isotopic equilibrium electron microprobe analysis of magnesium and calcium in growth bands reveals cyclic variations with values ranging between 7 7 18 5 mol mgco3 in l glaciale and 13 2 22 5 mol mgco3 in l crassiusculum in addition electron microprobe element maps highlight individual growth bands provide a powerful approach to study rhodolith formation and indicate that the specimens we analyzed have vertical growth rates of 250 450 m yr

u th ages obtained by mass spectrometry in corals from barbados sea level during the past 130 000 years the study of the sea level record during the last glacial cycle has primarily proceeded indirectly by means of oxygen isotope measurements on foraminifera from deep sea sediments1 2 the direct approach of dating sea level indicators stagnated during the past decade mainly because the samples required to complete our knowledge of the past glaciations are below the present day sea level3 7 using the 14c ages of acropora palmata samples collected by drilling offshore the island of barbados fairbanks8 presented the first detailed chronology for the last deglaciation this radiocarbon chronology is limited to the past 30 kyr because of the short half life of 14c 5 730 yr we must therefore rely on other dating methods to obtain information for the whole last glacial cycle during the past four years 230th 234u dating of corals by thermal ionization mass spectrometry has been shown to be significantly more precise and accurate than the classical counting method9 14 we have used this technique to measure u th ages in coral samples from the barbados collection and from subaerially exposed outcrops see also ref 15 here we present results bearing on the sea level record for the past 130 000 years we conclude that the last deglaciation started 3 000 years earlier than previously thought and confirm that there were two surges in melt water8 at about 11 kyr and 14 kyr bp before present

sedimentological and palaeoecological integrated analysis of a miocene channelized carbonate margin matese mountains southern apennines italy abstract lower middle miocene temperate marine carbonates occur in the matese mountains southern apennines italy these carbonates formed in an open shelf depositional system with an uneven margin 10 km long and up to 6 km wide shelf margin morphology shows multiple submarine channelized carbonate deposits which are dominated by coralline red algae and subordinate bryozoans two main channel networks pietraroia and regia piana channels with their sedimentary bodies were analysed the studied submarine channels grew by sediment accumulation as prograding bodies on a tectonic modelled substrate shallow water rhodalgal skeletal debris from moderately re mobilized up to significantly re worked built up the complex channel system fills in which sedimentary lenses overlapped and partially amalgamated one another when they were still unlithified the early channelized succession is characterized by parautochthonous bryozoan floatstone and rhodolith bryozoan floatstone representing soft muddy substrates in a low water turbulence and high turbidity setting the rhodoliths dominated by melobesioid coralline algae are sub discoidal and sub spheroidal in shape with a characteristic loosely packed inner arrangement these sediments whose latter portion underwent submarine diagenetic processes incipient to evoluted hard grounds were eroded and successively covered by shallower water gravitative deposits constituted by rhodolith floatstone rudstone their rhodoliths constituted by melobesioids mastophoroids and subordinate lithophylloids and sporolithaceans are mainly spheroidal sub spheroidal in shape with subordinate sub discoidal specimens with massive and laminar inner arrangements the lack in early lithification can be drawn back to the physiography of the channelized shelf margin to the active tectonic as well as to the temperate type carbonate dominant biogenic components the depositional surface profile and local hydrodynamic conditions were the major factors controlling sedimentary facies which differ in their relative proportions of dominant components their internal structures and sedimentary body geometries

shredding of environmental signals by sediment transport 1 landscapes respond to climate tectonic motions and sea level but this response is mediated by sediment transport understanding transmission of environmental signals is crucial for predicting landscape response to climate change and interpreting paleo climate and tectonics from stratigraphy here we propose that sediment transport can act as a nonlinear filter that completely destroys shreds environmental signals this results from ubiquitous thresholds in sediment transport systems e g landsliding bed load transport and river avulsion this morphodynamic turbulence is analogous to turbulence in fluid flows where energy injected at one frequency is smeared across a range of scales we show with a numerical model that external signals are shredded when their time and amplitude scales fall within the ranges of morphodynamic turbulence as signal frequency increases signal preservation becomes the exception rather than the rule suggesting a critical re examination of purported sedimentary signals of external forcing citation jerolmack d j and c paola 2010 shredding of environmental signals by sediment transport geophys res lett 37 l19401 doi 10 1029 2010gl044638

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

the middle to late pleistocene geomagnetic field recorded in fine grained sediments from summer lake oregon and double hot springs nevada u s a abstract a 400 000 year record of the paleomagnetic field has been acquired from 22 meters of middle to late pleistocene fine grained sediments from summer lake in south central oregon and double hot springs in northwestern nevada the stratigraphy is based on 55 tephra layers nine of which have been correlated with tephra layers from other localities on the basis of their distinct major and trace element geochemistry and their distinct petrography the paleomagnetic samples carry a strong and stable magnetization that does not appear to have been affected by the inclination error commonly associated with the magnetization of sediments the samples have accurately recorded the declination and inclination of the geomagnetic field at or near the time of deposition except for errors arising from rotations of discrete blocks of sediment predominantly about vertical axes errors introduced by this type of rotation were corrected by using paleomagnetic directions associated with correlated tephra layers the summer lake paleomagnetic record suggests that secular variations occurred throughout the middle and late pleistocene often maintaining the same waveform through several oscillations the amplitudes of these variations were similar to those of holocene variations and the periods ranged from 15 000 years to greater than 100 000 years

the heartbeat of the oligocene climate system a 13 million year continuous record of oligocene climate from the equatorial pacific reveals a pronounced heartbeat in the global carbon cycle and periodicity of glaciations this heartbeat consists of 405 000 127 000 and 96 000 year eccentricity cycles and 1 2 million year obliquity cycles in periodically recurring glacial and carbon cycle events that climate system response to intricate orbital variations suggests a fundamental interaction of the carbon cycle solar forcing and glacial events box modeling shows that the interaction of the carbon cycle and solar forcing modulates deep ocean acidity as well as the production and burial of global biomass the pronounced 405 000 year eccentricity cycle is amplified by the long residence time of carbon in the oceans

neogene coralline algal growth forms and their palaeoenvironments in the almanzora river valley almeria s e spain abstract the almanzora river valley is an elongate e w depression containing mainly neogene sediments during the late tortonian several horizons of crustose coralline algae developed in three distinct sedimentary contexts a on coastal platforms and talus slopes b on fan deltas and c associated with corals in patch reefs growing at the furthermost extremes of coastal fan deltas in the former two cases the predominant growths are as rhodoliths associated with mobile substrates in the coastal systems an increase in depth results in a change in both the morphology and the composition of the rhodoliths with depth there is a significant increase in the diversity of algal species and a concomitant increase in the size of the algal covering compared to the nucleus and thus the morphology of the rhodolith depends less and less on the shape of the nucleus itself the massive crusts and columns which mark the limit of development of the shallow water rhodoliths in the deeper examples are covered by branching and thin leafy laminar growths in the fan deltas the development of the rhodoliths is similar to that of the deeper coastal zones in the patch reefs the specific composition of the algal associations changes somewhat and the growths developed on a stable substrate under low energy conditions are mainly vertical branches arising from thin crusts

growth rate and potential climate record from a rhodolith using 14c accelerator mass spectrometry rhodoliths free living calcareous red algae create large and diverse habitats worldwide although these plants are abundant and ecologically important little is known about their growth rate we determined the growth rate for an individual rhodolith lithothamnium crassiusculum from the southern gulf of california through 14 c analysis using accelerator mass spectrometry ams to be 0 6 mm yr 21 this growth rate suggests large l crassiusculum which have been found with radii in excess of 6 cm may live over 100 yr declines in the d 14 c record associated with the large el nino events of 1957 1982 and 1992 indicate 14 c analysis may lead to identification of important climate events in the more distant past the ability to determine changes in past ocean circulation related to changes in past climatic conditions through ams 14 c analysis of rhodoliths would increase the geographic range of available climate records from the tropical oceans to the entire global ocean and potentially allow for the determination of past climate conditions from rhodoliths in fossil beds rhodoliths red nongeniculate calcareous algae occupy large areas of the world s oceans forming the basis of di verse and ecologically important communities bosence 1983 foster et al 1997 however little is known about the rate at which these communities develop their rate of re covery after natural or anthropogenic disturbances or their effects on the global carbon budget because some rhodo liths are long lived they also have the potential to provide information on past oceanic conditions as they grow these plants deposit calcium carbonate which should contain chemical and isotopic records reflecting environmental con ditions previous isotopic studies on coral and mollusks found that the amount of 14 c deposited as a part of the total carbon in biogenic carbonate records the 14 c concentration in the ocean water surrounding the organism e g druffel and linick 1978 nozaki et al 1978 druffel and suess 1983 this type of 14 c record should also be found in the carbonate of rhodoliths and can potentially be used as a re cord of climate variation rhodoliths are found in many locations and environ ments around the world ranging from polar deep water to tropical shallows bosence 1983 in the subtropical gulf

rhodalgal bryomol assemblages in temperate type carbonate channelized depositional systems the early miocene of the sarcidano area sardinia italy

alteration and mineralization at the zhibula cu skarn deposit gangdese belt tibet abstract the zhibula cu skarn deposit contains 0 32 mt cu metal with an average grade of 1 64 and is located in the gangdese porphyry copper belt in southern tibet the deposit is a typical metasomatic skarn that is related to the interaction of magmatic hydrothermal fluids and calcareous host rock stratiform skarn orebodies occur at the contact between tuff and marble in the lower jurassic yeba formation alteration zones generally grade from a fresh tuff to a garnet bearing tuff a garnet pyroxene skarn and finally to a wollastonite marble minor endoskarn alteration zonations are also observed in the causative intrusion which grade from a fresh granodiorite to a weakly chlorite altered granodiorite a green diopside bearing granodiorite and to a dark red brown garnet bearing granodiorite prograde minerals which were identified by electron probe microanalysis include andradite grossularite of various colors e g red green and yellow and green diopside retrograde metamorphic minerals overprint the prograde skarn and are mainly composed of epidote quartz and chlorite the ore minerals consist of chalcopyrite and bornite followed by magnetite molybdenite pyrite pyrrhotite galena and sphalerite three types of fluid inclusions are recognized in the zhibula deposit including liquid rich two phase inclusions type l vapor rich two phase inclusions type v and daughter mineral bearing three phase inclusions type s as the skarn formation evolved from prograde stage i to early retrograde stage ii and later retrograde stage iii the ore forming fluids correspondingly evolved from high temperature 405 667 c high salinity up to 44 0 wt nacl equiv and high pressure 500 600 bar to low moderate temperature 194 420 c moderate high salinity 10 1 18 3 and 30 0 44 2 wt nacl equiv and low moderate pressure 250 350 bar isotopic data of 34 s 0 1 to 6 8 estimated 34 s fluids 0 7 d h2o 91 to 159 and 18 o h2o 1 5 to 9 2 suggest that the ore forming fluid and material came from magmatic hydrothermal fluids that were associated with miocene zhibula intrusions fluid immiscibility likely occurred at the stage i and stage ii during the formation of the skarn and mineralization fluid boiling occurred during the stage iii which is the most important cu deposition mechanism for the zhibula deposit

astronomical theory of the pleistocene ice ages a brief historical review abstract this paper traces the evolution of the astronomical theory of the pleistocene ice ages from its origin in the work of adhemar and croll through its quantitative transformation in the hands of milankovitch to its current renaissance emphasis is given to the interplay between climatic theory and geologic observation from 1941 when milankovitch published his final version of the theory until the early 1970s most attempts to test the theory empirically were carried out in the time domain by comparing the geologic record of climate with predicted climate curves these attempts ran into serious difficulties particularly the inaccuracy of the geologic time scale and the ambiguity of climate predictions early attempts to evaluate the theory with simple radiation balance models appeared to indicate that the climatic response to secular changes in the orbit would be too small to be observed geologically but by the mid 1970s the advent of an improved time scale for pleistocene marine deposits and the availability of long closely sampled records made it possible to arrange generalized but unambiguous tests of the theory in the frequency domain by comparing orbital and climatic spectra these results decisively confirmed the idea that orbital variations significantly influenced the earth s climate during the pleistocene but they did not tell us how this influence was exercised the emphasis of current work has therefore shifted to the identification and quantitative modeling of physical mechanisms by which the climate system responds so dramatically to the predicted rather subtle changes in radiative boundary conditions

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

influence of the changing lunar orbit on the astronomical frequencies of pre quaternary insolation patterns the sensitivity of the frequencies of the earth s orbital elements involved in the astronomical theory of paleoclimates obliquity and climatic precession to the earth moon distance and consequently to the length of the day and to the dynamical ellipticity of the earth is investigated for the last billions of years but the new frequencies have been computed for the last 440 million years only a time interval over which data and a model of the earth were available moreover we consider only the impact of the changing precessional parameter assuming that the fundamental frequencies of the planetary motion are steady at the geological time scale under such hypotheses the shortening of the earth moon distance and of the length of the day back in time induces a shortening of the fundamental astronomical periods for obliquity and precession a shortening that is larger for longer periods

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

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

displaced re worked rhodolith deposits infilling parts of a complex miocene multistorey submarine channel a case history from the sassari area sardinia italy abstract in the sassari area north western sardinia italy the miocene porto torres sub basin sequences represent the complex multistorey mixed carbonate siliciclastic submarine feature called the sassari channel during the late burdigalian early serravallian repeated terrigenous supplies from uplifted paleozoic crystalline substrata fed the sassari channel system by means of turbidity and locally hyper concentrated turbidity flows shelfal areas were the source of terrigenous clasts but open shelf rhodalgal foramol carbonate areas were very productive and largely also contributed to the channel infilling re worked sands and skeletal debris were discontinuously re sedimented offshore as pure terrigenous mixed and or carbonate deposits major sediment supply was introduced between the latest burdigalian and the start of the middle langhian during which a large amount of carbonate mixed and siliciclastic sediments reached the porto torres basin sassari channel i contributions from shallow proximal source areas typify the lower intervals unit a in marginal sectors of the channel upward these evolve into autochthonous rhodolith deposits winnowed by strong currents in relatively shallow well lit settings within a complex network of narrow tidally controlled channels unit d locally bearing coral assemblages conversely re sedimented rhodoliths from the units b and c accumulated under conditions of higher turbidity in deeper parts of the channel taxonomically diversified rhodoliths point to the mixing of re deposited skeletal components from different relatively deep bathmetric settings in the latest early langhian major re sedimentation episodes resulting in large prograding bodies unit d triggered by repeated regression pulses in a frame of persistent still stand during these episodes photophile assemblages dwelled in the elevated margin sectors of the channel a significant latest early langhian drop in relative sea level resulted in impressive mass flows involving early cemented channel margin and levee blocks and culminated in the formation of major erosional surface er e such events seemingly correlate with the long term global cooling trend of the mid miocene climatic transition episodes of middle langhian re sedimentation concluded with the channel abandon phase after which new erosive episodes followed overall this led to a shift in the sassari channel ii with phases presumably started during the earlymost serravallian subsequent to the major sea level drop at the langhian serravallian boundary

carbon isotope stratigraphy across the silurian devonian transition in podolia ukraine evidence for a global biogeochemical perturbation the carbon and oxygen isotope composition of marine carbonates 13 c and 18 o respectively are studied in the fossiliferous stratigraphically well constrained and remarkably expanded successions of podolia sw ukraine spanning the silurian devonian transition significant isotopic shifts are directly comparable to previously published global secular trends in well preserved brachiopod calcite isotopic ratios from this region and therefore may be taken as a reliable primary record of seawater 13 c changes the sections reveal a major positive 13 c excursion with an amplitude above 6 beginning in the upper pridoli and reaching peak values as heavy as 4 2 in the lowermost lochkovian this turnover in carbon cycling is followed by a general trend toward more negative 13 c values in the upper lochkovian the podolian isotopic signals provide strong support for the previously inferred global biogeochemical perturbation across the silurian devonian transition reflecting a complex combination of palaeogeographical biogeochemical and evolutionary processes in the late caledonian geodynamic setting with a likely undervalued role of the expanding vegetation in vast near coastal shallows and deltas

a low order dynamical model of global climatic variability over the full pleistocene a previously formulated dynamical model of the late pleistocene ice ages based on the hypothesis that the global co sub 2 system can provide the instability to drive a natural oscillation involving feedbacks between the cryosphere atmosphere and ocean is extended to include 1 additive earth orbital forcing summer insolation changes at 65 degree n and 2 tectonic forcing in the form of a postulated variation in the multiplicative parameters rate constants of the model system the structural e g bifurcation properties of the model are examined in detail to reveal the regions of parameter space wherein the geologically inferred features of the full pleistocene can be simulated including the observed chronology the phase relationships between ice co sub 2 and north atlantic deep water formation and the mid pleistocene transition

bathymetric distribution of ichnocoenoses from recent subtropical algal nodules off fraser island eastern australia abstract coralline algal nodules living on the subtropical shelf off fraser island eastern australia from the inner to the uppermost outer shelf from 28 to 117 m water depth are pervasively bioeroded five ichnogenera have been identifed as nodule borers comprising one ichnotaxon attributed to bivalves gastrochaenolites one to sponges entobia and three to polychaetes and barnacles trypanites maeandropolydora rogerella microtraces comparable to those produced by fungi algae bacteria and or sponges are also present two ichnocoenoses have been recognised the shallow water ichnocoenosis egtm occurs at 60 m and shallower depths and includes all identified ichnogenera the deep water ichnocoenosis from 68 to 117 m is characterised by trypanites and the trypanites maeandropolydora network tm ichnocoenosis with a generally higher boring density than in shallower nodules decreasing size of algal nodules and reduced thickness of the coralline thalli probably explain the decrease in diversity of ichnogenera with depth as the larger bioeroders are excluded from the ichnoassemblages lower growth rates favour higher density of bioerosion in deeper algal nodules

crustose algal frameworks from the eocene alpine foreland abstract upper eocene algal limestones of the eastern alpine foreland in austria contain three different types of crustose algal frameworks these reveal several similarities with the present day coralligene de plateau of the mediterranean sea but the framework types differ in the crust forming algal taxa the sedimentary regime and the environmental setting 1 the coralline coral frameworks develop from siliciclastic sediments and show a succession from coverstones to bindstone to cruststone initiation of this framework in a siliciclastic regime is only possible because of the occurrence of neogoniolithon sp a species that is able to grow on fine grained soft substrate the onset of a dense crustose framework was related to the reduced sediment input and the occurrence of lithothamnion sp which is able to form cruststones 2 pure coralline algal frameworks are restricted to cruststones dominated by both lithothamnion sp and neogoniolithon sp they formed on top of maerl megaripples during calm periods and shed crustose fragments towards depressions which allowed framework progradation 3 peyssonneliacean dominated frameworks occur with intercalations of coralline algal crusts they formed in muddy environments interpreted as protected depressions between maerl dunes we found that crustose frameworks are controlled by three factors 1 sediment input low input favors the growth of frameworks while coarser grained siliciclastics cause burial of initial algal crusts terrigenous mud influences water turbidity and thus favors the occurrence of peyssonneliacean algae 2 taxonomic composition framework formation requires the existence of crustose algal taxa which are able to grow directly on fine grained soft substrate neogoniolithon sp polystrata alba or to encrust and stabilize coarse grained particles lithothamnion sp and or to form multiple successions of dense crusts lithothamnion sp p alba phymatolithon sp characteristically encrusts corals but it does not contribute to the frameworks surprisingly algae do never form protuberances within the frameworks even if they show protuberant growth forms in maerl sediment 3 substrate stability as a function of substrate composition and hydrodynamic energy due to their occurrence on maerl bottoms and the lack of evidence for submarine hardgrounds the settlement of crustose buildups requires low tidal current activity and or wave agitation

cooler winters as a possible cause of mass extinctions at the eocene oligocene boundary the eocene oligocene boundary at about 33 7 myr ago marks one of the largest extinctions of marine invertebrates in the cenozoic period1 for example turnover of mollusc species in the us gulf coastal plain was over 90 at this time2 3 a temperature change across this boundary from warm eocene climates to cooler conditions in the oligocene has been suggested as a cause of this extinction event4 but climate reconstructions have not provided support for this hypothesis here we report stable oxygen isotope measurements of aragonite in fish otoliths ear stones collected across the eocene oligocene boundary palaeotemperatures reconstructed from mean otolith oxygen isotope values show little change through this interval in agreement with previous studies5 6 from incremental microsampling of otoliths however we can resolve the seasonal variation in temperature recorded as the otoliths continue to accrete new material over the life of the fish these seasonal data suggest that winters became about 4 c colder across the eocene oligocene boundary we suggest that temperature variability rather than change in mean annual temperature helped to cause faunal turnover during this transition

ore genesis of skarn mineralization in continental collision orogens a case study from the pusangguo co bearing cu pb zn deposit in tibet abstract the gangdese belt in southern tibet is renowned for hosting numerous collision related porphyry cu mo deposits the recent discovery of pusangguo co bearing cu pb zn skarn deposits is the first reported co bearing deposit in gangdese belt as well as in tibet researches on the geological and metallogenic characteristics of pusanguo indicate that this co bearing cu pb zn deposit was formed in a collisional setting we document mineralogy fluid inclusion studies and h o s pb isotope systematics of the skarns and ores of the pusangguo deposit intense endoskarn alteration dominated by green and pink epidote and quartz is widely disseminated throughout the host granodiorite as well as in veinlets exoskarn alteration is characterized by the presence of prograde grandite andradite32 100 and grossular0 68 with minor pyroxene diopside0 46 hedenbergite38 74 and johannsenite1 62 retrograde epidotes from both the endoskarn and exoskarn show a narrow range of fe3 fe3 al ratios 0 25 0 34 ore minerals include chalcopyrite sphalerite and galena with lesser pyrite pyrrhotite bornite co minerals and falkmanite four paragenetic stages of skarn formation and ore deposition are recognized in the pusangguo cu pb zn deposit prograde stage i retrograde stage ii early sulfide stage iii and late sulfide stage iv fluid inclusions in all stages are dominated by two phase liquid rich type l inclusions during the major phase of mineralization stage iii fluid inclusions formed at low temperatures 180 240 c and with low salinities 0 5 8 6 wt nacl equiv this is in contrast to other skarn deposits within the gangdese porphyry copper belt e g the zhibula jiama and bangpu deposits that formed from highly saline fluids at high temperatures hydrogen oxygen isotopic values obtained from garnet epidote quartz and calcite are dh2o 179 to 213 and 18oh2o 9 1 to 9 3 whereas s pb isotopic values for sphalerite chalcopyrite pyrite and galena are 34s 1 0 to 1 2 estimated 34sfluid 0 05 such data are indicative of ore forming fluids and metals that originated from a magmatic hydrothermal source related to granodiorite emplacement during the miocene post continental collision extensive mixing between the magmatic hydrothermal and meteoric fluids led to the co precipitation of cu pb and zn minerals from low salinity fluids at relatively low temperatures the pusangguo co bearing cu pb zn skarn deposit shows consistent features with other porphyry related skarn deposits in the gangdese belt except for relatively low temperature and salinity the research is of great significance for understanding cobalt as an associated mineral in the gangdese sulfide skarn deposit in tibet

rhodoliths from deep fore reef to shelf areas around okinawa jima ryukyu islands japan abstract the distribution abundance composition and growth history of rhodoliths were investigated based on 222 grab samples and 202 submarine photographs taken from 223 sites arranged at regular intervals and on 13 additional samples 5 dredge and 8 grab samples these samples were collected at water depths ranging from 15 to 970 m around okinawa jima ryukyu islands japan the rhodoliths grow in deep fore reef to shelf areas at water depths of 50 to 135 m where rhodoliths occur they cover 45 of the sea bottom the rhodoliths are primarily spheroidal to ellipsoidal in shape with mean diameters usually less than 8 cm internally they are primarily composed of nongeniculate coralline algae and an encrusting foraminifer acervulina inhaerens the rhodoliths have envelopes of well preserved concentric to irregular laminations or much more commonly are bored and display various degrees of bioerosion constructional voids primary spaces between encrusters and borings range from empty to completely filled with unlithified and lithified mixtures of micrites and bioclasts the bioerosion is more extensive with increasing water depth and is progressively much more pervasive at water depths greater than 90 m the rhodoliths are covered with nongeniculate coralline algae and a inhaerens associated with other epilithic skeletal and nonskeletal organisms the living biotic cover on rhodoliths is relatively great down to water depths 100 m below this the cover decreases rapidly with increasing water depth rhodoliths with similar size shape and composing organisms to those in the ryukyu islands are commonly found on deep fore reef to shelf areas or on the banks and seamounts of tropical reef regions likely as the combined result of ecological degradation decreased number and coverage of hermatypic corals and the relative predominance of nongeniculate coralline algae and encrusting foraminifers in such areas the slow accretion rates of rhodoliths

effects of holocene sea level changes on subtidal palaeoecosystems southeastern brazil abstract southeastern brazilian marine coastal deposits provide an excellent opportunity to investigate environmental changes such as sea level and trophic variability during the holocene period in this study we present a sediment record from arraial do cabo bay rio de janeiro state in order to improve the understanding of the upper subtidal palaeoecosystem evolutionary dynamics of this bay we provide a microfacies analysis of holocene carbonate and mixed siliciclastic carbonate deposits cropping out today from the supratidal to the subtidal zones the age depth model is based on 14 c dating and revealed a basal age of 7000 cal years bp in the six distinguished microfacies the biogenic components are dominated by vermetids and coralline algae a number of subordinate components are also present including the microfacies determining thin shelled bivalves fossil vermetids are represented by monospecific clusters of overgrowing petaloconchus varians coralline red algae are represented by lithophyllum pustulatum spongites fruticulosus spongites yendoi mesophyllum engelharti and unidentified geniculate corallines the microfacies analysis revealed that the substrate of the benthic community in the upper subtidal ecosystem of the bay changed according to the relative sea level 1 during the rapid sea transgressive trend it was coarse soft substrate 2 after the postglacial sea level maximum succeeding a slow decline to present sea level it changed into fine soft substrate at 7000 years ago the coarse soft substrate was characterised by fruticose corallines and composed of quartz grains from continental run off input after the postglacial sea level maximum the highstand elevation along with the established upwelling system brought about a predominantly carbonate deposition vermetids and corallines along with thin shelled bivalves thrived in a low sedimentation rate setting and high nutrient level environment

orbital signature of interglacials a specific orbital configuration high obliquity combined with the june perihelion marked the beginning of the past three interglacials this suggests that the primary cause of the glacial cycle may be astronomical an astronomical climate index aclin is introduced which combines the three orbital variables in the time lag bivariant model designed to predict the major climate changes in the late and middle pleistocene and in the near future aclin closely correlates with the major climatic events revealed by independently dated proxy climate indicators of the past 130 000 yr it successfully differentiates the interglacials and displays a 100 000 yr periodicity it predicts an early end of the present inter glacial and the start of a new one in 114 000 yr

reconstruction of the dynamics of the climatic system from time series data abstract the oxygen isotope record of the last million years as provided by a deep sea core sediment is analyzed by a method recently developed in the theory of dynamical systems the analysis suggests that climatic variability is the manifestation of a chaotic dynamics described by an attractor of fractal dimensionality a quantitative measure of the limited predictability of the climatic system is provided by the evaluation of the time correlation function and the largest positive lyapounov exponent of the system

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

oceanic mechanisms for amplification of the 23 000 year ice volume cycle situated adjacent to the largest northern hemispher ice sheets of the ice ages the mid latitude north atlantic ocean has an important role in the earth s climate history it provides a significant local source of moisture for the atmosphere and adjacent continents forms a corridor that guides moisture bearing storms northward from low latitudes and at times makes direct contact along its shorelines with continental ice masses evidence of major ice ocean air interactions involving the north atlantic during the last 250 000 years is summarized outflow of icebergs and meltwater initially driven by summer insolation over the ice sheets affects midlatitude ocean temperatures summer heat storage winter sea ice extent and global sea level these oceanic responses in turn influence the winter moisture flux back to the ice sheets as well as ablation of land ice by calving spectral data indicate that the oceanic moisture and sea level feedbacks in part controlled by glacial melt products amplify milankovitch insolation forcing of the volumetrically dominant mid latitude ice sheets at the 23 000 year precessional cycle

multifractal and white noise evolutionary dynamics in jurassic cretaceous ammonoidea for more than a decade there has been interdisciplinary debate on whether fossil origination and extinction time series show evidence of self organized criticality soc or some other more complex hierarchical structure analyses of a new data set of jurassic and cretaceous ammonoid genera demonstrate that these taxonomic subgroups do not reproduce the patterns seen in larger data sets that pool disparate taxa rather originations and extinctions in these ammonoids show no evidence of soc limited evidence for a hierarchical multifractal pattern and at least within the suborder ammonitina evidence consistent with a white noise signal although a white noise pattern has been identified previously in an ammonoid family diversity time series the significance of such a result for ammonoid genus originations and extinctions is discussed here for the first time this white noise pattern indicates that processes acting on short time scales less than a few million years dominate the ammonitina origination and extinction records producing a nonhierarchical diversity dynamic because origination events in one interval do not appear to trigger originations in subsequent intervals ammonite evolutionary radiations were likely to be extremely rapid and driven by physical rather than biological opportunities for diversification

geology of the post collisional porphyry copper molybdenum deposit at qulong tibet porphyry deposits are usually thought to form from subduction related calc alkaline magmas in magmatic arc settings although some porphyry deposits also occur in post collisional extensional settings the post collisional deposits remain poorly understood here we describe the igneous geology alteration mineralogy and mineralization history of qulong a newly discovered porphyry cu mo deposit in southern tibet that belongs to the post collisional class the deposit is associated with miocene monzogranite granodiorite intrusions and is hosted partly by jurassic andesitic dacitic volcanic rocks the deposit contains 7 1 mt cu and 0 5 mt mo metal the 19 5 ma granodioritic monzogranitic rongmucuola pluton with diorite enclaves is the earliest miocene intrusive unit it was intruded by a regularly shaped stock p porphyry and then thin dikes x porphyry of monzogranite at about 17 7 ma the main cu mo mineralization is associated with the p porphyry a barren diorite porphyry intruded the p and x porphyries around 15 7 ma petrologic trends of the intrusions suggest that the miocene intrusions have similar origins and probably formed by fractionation of a deeper magma chamber emplacement of miocene porphyries controlled by the qulong anticline is in direct response to the rapid uplift erosion of the gangdese arc batholiths in southern tibet miarolitic cavities and unidirectional solidification textures key evidence for volatile separation have been recognized in the p and x porphyries respectively early potassic alteration characterized by quartz k feldspar anhydrite pervades the p porphyry and rongmucuola pluton laterally this alteration grades into quartz biotite anhydrite k feldspar which affects all miocene intrusions except the latest dioritic porphyry wall rocks of rongmucuola pluton and jurassic andesitic dacitic volcanics within 1 1 5 km of the porphyries are dominated by pervasive potassic alteration an outer halo of propylitic alteration epidote chlorite calcite extends up to 2 km away from the deposit feldspar destructive alteration sericite chlorite clay minerals has overprinted most of the potassic and part of the propylitic alteration the alteration is strongly pervasive in the interior of the porphyry bodies and occurs as vein halos away from the porphyry bodies the earliest quartz k feldspar alteration and veins are barren whereas approximately 60 of the cu reserves is associated with slightly later quartz biotite anhydrite alteration barren assemblages are related to irregular quartz k feldspar anhydrite veins which are truncated by the x porphyry cu sulfide bearing assemblages are associated with discontinuous chalcopyrite biotite and continuous quartz anhydrite chalcopyrite molybdenite veins deposition of cu mo with abundant anhydrite occurred during or between emplacement of closely related porphyries from high temperature magmatically derived fluids and was probably caused by the disproportionation of so

deep burial dissolution in an oligocene miocene giant carbonate reservoir perla limestone gulf of venezuela basin implications on microporosity development abstract sedimentary rocks tend to progressively lose porosity with depth due to mechanical and chemical compaction in carbonates this trend is hard to predict since many factors can create porosity in the burial setting the oligocene miocene perla limestone a giant gas reservoir located in the gulf of venezuela basin shows a complex porosity system marked by a strong diagenetic control despite exhaustive depositional facies modelling carried out in the carbonate reservoir inconsistencies remained when distributing petrophysical properties with depositional facies these inconsistencies become more important in areas strongly affected by intense diagenetic processes after the initial investigation burial dissolution was identified as the main diagenetic process affecting porosity in this succession to understand the origin of the burial dissolution process and its distribution along the reservoir detailed petrographic mineralogical and isotopic studies were carried out on recovered cores from different exploration wells results show a series of diagenetic features which were associated with the evolution of the strata including burial dissolution dolomitization and compaction as the main processes after testing several hypotheses the results support an inorganic co2 model as responsible for the burial dissolution process in the perla limestone according to this model deep burial dissolution created pervasive microporosity with subordinated moldic and vuggy pores that enhanced the reservoir quality in localized areas of the carbonate succession these features are located where the ascent of hydrothermal co2 rich fluids funneled by discontinuity surfaces faults fractures stylolites etc reached the perla limestone

nonlinearity and multifractality of climate change in the past 420 000 years 1 evidence of past climate variations are stored in polar ice caps and indicate glacial interglacial cycles of 100 kyr using advanced scaling techniques we study the long range correlation properties of temperature proxy records of four ice cores from antarctica and greenland these series are long range correlated in the time scales of 1 100 kyr we show that these time series are nonlinear for time scales of 1 100 kyr as expressed by temporal long range correlations of magnitudes of temperature increments and by a broad multifractal spectrum our results suggest that temperature increments appear in clusters of big and small increments a big positive or negative climate change is most likely followed by a big positive or negative climate change and a small climate change is most likely followed by a small climate change

milankovitch climatic origin of mid cretaceous black shale rhythms in central italy the earth s orbital variations reflected in pleistocene ice volume were also recorded in non glacial times carbonate production in pelagic mid cretaceous sediments quantified by calcium carbonate and optical densitometry time series reflects the orbital eccentricity and precessional cycles minimal eccentricity brought deep sea anoxia most of the sedimentary variability of this 100 myr old sequence lies within the milankovitch orbital frequency band

stability of the astronomical frequencies over the earth s history for paleoclimate studies the expected changes over the past 500 million years in the principal astronomical frequencies influencing the earth s climate may be strong enough to be detectable in the geological records and such effects have been inferred in several cases calculations suggest that the shortening of the earth moon distance and of the length of the day back in time induced a shortening of the fundamental periods for the obliquity and climatic precession from 54 to 35 41 to 29 23 to 19 and 19 to 16 thousand years over the last half billion years at the same time the precessional constant increased from 50 to 61 arc seconds per year the changes in the frequencies of the planetary system due to its chaotic motion are much smaller their influence on the changes of the periods of climatic precession obliquity and eccentricity of the earth s orbit around the sun can be neglected eccentricity periods used for quaternary climate studies may therefore be considered to have been more or less constant for pre quaternary times

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

re deposited rhodoliths in the middle miocene hemipelagic deposits of vitulano southern apennines italy coralline assemblage characterization and related trace fossils article i nfo an integrated analysis of rhodolith assemblages and associated trace fossils borings found in hemipelagic middle miocene orbulina marls vitulano area taburno camposauro area southern apennines italy has revealed that both the biodiversity of the constituent components and taphonomic signatures represent important aspects which allow a detailed palaeoecological and palaeoenvironmental interpretation on the basis of shape inner arrangement growth forms and taxonomic coralline algal composition two rhodolith growth stages were distinguished 1 nucleation and growth of the rhodoliths and 2 a final growth stage before burial nucleation is characterized by melobesioids and subordinately mastophoroids with rare sporolithaceans and lithophylloids the rhodolith growth main increase in size is represented by abundant melobesioids and rare to common mastophoroids very rare sporolithaceans are also present the final growth stage is dominated by melobesioids with rare mastophoroids and very rare sporolithaceans each rhodolith growth stage is characterized by a distinct suite of inner arrangement and growth form successions well diversified ichnocoenoeses gastrochaenolites trypanites meandropolydora and or caulostrepsis ento bia uniglobites micro borings related to bivalves sponges polychaetes barnacles algae fungi and bacteria are distinguished in the inner intermediate rhodolith growth stage while mainly algal fungal and bacterial micro borings are present in the outer final growth stage rhodolith growth stages and associated ichnocoenoeses indicate significant change in the depositional setting during the rhodolith growth in the vitulano area the middle miocene rhodolith assemblages formed in a shallow water open shelf carbonate platform were susceptible to exportation from their production area and then to sedimentation down to deeper water hemipelagic settings where the rhodoliths shortly kept growth and were finally buried such re deposition of unlithified or only weakly lithified i e rhodoliths and intraclasts shallow water carbonates into deeper water settings was likely favoured by storm generated offshore return currents rather than sediment gravity flows

a simple model for 100 k year oscillations in glaciation abstract a simple model is presented where response to forcing with components at 20k 40k and 100k yr where forcing however is strongly dominated by 20k yr is primarily at 100k yr the main features of the model are a very sensitive response of the snow and sea ice line to solar input a threshold to transitions between large snow and sea ice coverage to 53 latitude and very little snow and sea ice coverage and a glaciation cycle forced by the snow and sea ice fine position

lower silurian hot shales in north africa and arabia regional distribution and depositional model abstract lowermost silurian organic rich hot shales are the origin of 80 90 of palaeozoic sourced hydrocarbons in north africa and also played a major role in petroleum generation on the arabian peninsula in most cases the shales were deposited directly above upper ordovician peri glacial sandstones during the initial early silurian transgression that was a result of the melting of the late ordovician icecap deposition of the main organic rich shale unit in the north african arabian region was restricted to the earliest silurian rhuddanian stage acuminatus atavus and probably early cyphus graptolite biozones during this short period 1 2 m y a favourable combination of factors existed which led to the development of exceptionally strong oxygen deficiency in the area in most countries of the study area the post rhuddanian silurian shales are organically lean and have not contributed to petroleum generation the distribution and thickness of the basal silurian hot shales have been mapped in detail for the whole north african region using logs from some 300 exploration wells in libya tunisia algeria and morocco in addition all relevant accessible published and unpublished surface and subsurface data of the lower silurian shales in north africa and arabia have been reviewed including sedimentological biostratigraphic and organic geochemical data the lowermost silurian hot shales of northern gondwana are laterally discontinuous and their distribution and thickness were controlled by the early silurian palaeorelief which was shaped mainly by glacial processes of the late ordovician ice age and by pan african and infracambrian compressional and extensional tectonism the thickest and areally most extensive basal silurian organic rich shales in north africa occur in algeria tunisia and western libya while on the arabian peninsula they are most prolific in saudi arabia oman jordan and iraq the hot shales were not deposited in egypt which was a large palaeohigh at that time the depositional model presented may help in better understanding the source potential of the basal silurian shales in less explored regions of north africa and arabia including morocco northern niger and the kufra basin in southeast libya

components facies and ramps redefining upper oligocene shallow water carbonates using coralline red algae and larger foraminifera venetian area northeast italy abstract chattian mixed carbonate siliciclastic deposits from two palaeogeographic units of southern alps the lessini shelf and venetian foreland basin of northeast italy are studied with respect to facies distributions and controlling ecological factors on dominant biogenic components these ramp depositional systems are located in the western southern alps on the lessini shelf and in the eastern southern alps in the venetian foreland basin the successions show an extensive geographic distribution of at least 150 km 40 km at the southern margin of the southern alps palaeoenvironments are inferred following microfacies characteristics and floral and faunal indicators especially those of coralline red algae and larger foraminifera an inner to middle homoclinal ramp morphology is reconstructed based on facies distributions and taxonomic and coralline algal growth form proxy data the distribution along depositional strike shows variation from thinner carbonate dominated sequence in the west monti berici and monti lessini to a more variable mixed carbonate siliciclastic dominated environment to the east vittorio veneto alpago facies character and occurrence are controlled by local hydrodynamic conditions and varying water turbidity of the studied ramp depositional system the general facies succession shows a transgressive sequence from the proximal inner to proximal middle ramp a shoal belt of trough cross bedded sandstones occurs in a proximal inner ramp position in all of the studied areas in a gentle dipping homoclinal ramp most benthic organisms inhabited the relatively quite environments off these shoals in a distal inner ramp setting basinward environments proximal middle ramp constitute areas of maximal carbonate production and consist primarily of larger foraminiferal facies and rhodolith pavements larger foraminifera represented by two larger foraminiferal assemblages are most diversified in the shallower settings near the fair weather wave base distal inner proximal middle ramp whereas coralline algae predominate in deeper areas proximal middle ramp constructing extensive rhodolith pavements rhodolith pavements are distinguished with respect to rhodolith shape size growth forms and coralline algal taxonomic composition larger foraminifera are interpreted with respect to shell structures shell architectures and comparable recent counterparts the analysed benthic communities thrived in a mesotrophic regime within trophic gradients constrained by fluvial influence coralline algal dominance and a moderately diverse larger foraminiferal assemblage suggest a tropical warm temperate transition the considerable stability imposed on sediments by the rhodolith pavement must also have significantly contributed to the maintenance of a middle ramp profile bulge this study will contribute to a better understanding of oligocene carbonates which have received less attention than their eocene or miocene counterparts

a model study of the role of high latitude topography in the climatic response to orbital insolation anomalies abstract the response of a combined global zonal averaged energy balance model and a continental ice sheet model to insulation anomalies produced by orbital perturbations is examined although the role of ice sheet dynamics is included in the model this paper focuses mostly on the response of the atmosphere hydrosphere to the perturbations the model developed from that of suarez and held 1979 explicitly incorporates surface topography surface energy balances snow and sea ice budgets and variable static stability the ice sheet model is based on a power law rheology it is found that the presence of a high latitude plateau significantly increases the sensitivity of the climate to the insolation perturbation the sensitivity is maximized when the elevation of the summer snowline is near the elevation of the plateau as appears to be the case with baffin island today there appears to be a rapid response of the seasonal cycle to an insolation anomaly through albedo temperature feedback and with the

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

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

palaeoenvironmental dynamics of holocene shoreface bryoliths from the southern coast of brazil beds of free living coated nodules coralline algae bryozoans acervulinid foraminifera create shallow water carbonate biogenic benthic habitats which are sensitive to human disturbance and slow

a paleoclimate model of northern hemisphere ice sheets abstract a model for predicting the growth and decay of ice sheets based on the astronomical theory of climate change is presented the purpose of the study in part is to isolate the role of the ice sheet physics and earth response under varying ice load by simplifying to the extreme the role of the hydrosphere atmosphere ice sheet physics and the response of the lithosphere asthenosphere under the ice load are modeled explicitly insolation anomalies taken at a fixed latitude directly force latitudinal displacement of the snow line accumulation rate a and ablation rate a evaluated at mean sea level are specificed as external constants a a decrease linearly with ice sheet elevation rough tuning of the model to the general shape of the ice volume record of the last two major glacials determines the external constants model predictions of the ages of several events in the last major glaciation compare well with the radiological ages the six glacial terminatios i vi over the last 600 000 yr are identified and the predicted ages compare reasonably well with the 18 o record for two deep sea cores a direct comparison of model power spectra of ice volume as a function of period with spectra of the 18 o record shows apparent underprediction of power near 100 000 yr when a quantitative but heuristic method for taking into account the red noise spectrum evident in the geological records is used a much more favorable comparison is possible the model prediction lends support to the hypothesis that the nonlinearity of the ice sheet physics is responsible for the 100 000 yr periodicity in the geological record of the late pleistocene

african monsoons an immediate climate response to orbital insolation the croll milankovitch astronomical theory of climate1 3 has received strong support from the evidence of a linear climatic forcing by obliquity and precession although nonlinearity had to be assumed for eccentricity4 5 moreover interglacials have appeared to be controlled by the orbital insolation6 although a phase shift of 6 000 5 000 yr is seen between an astronomical climate index and terrestrial climate indicators dominated by the northern ice sheet dynamics climate proxy data of low latitudes are less directly dependent on the ice sheets here it is shown that during the past 464 000 yr african monsoons signalled by the east mediterranean sapropels were heaviest always and only when a northern summer monsoon index computed from the orbital variation of insolation reached maximum values this occurred during all the interglacials but also twice during glacial periods thus tropical aridity is not the single climatic pattern of glacial periods an immediate terrestrial climate response to orbital variations of insolation is established

astronomical theory of paleoclimates and the last glacial interglacial cycle in the 19th century croll and pilgrim stressed the importance of severe winters as a cause of quaternary ice ages later on mainly during the first half of the 20th century koppen spitaler and milankovitch regarded high winter and low summer insolation as favoring glaciation after koppen and wegener related the milankovitch new radiation curve to penck and bruckner s subdivision of the quaternary there was a long lasting debate whether or not such changes in the insolation can explain the quaternary glacial interglacial cycles in the 1970s with the improvements of radiometric dating and of acquiring and interpreting the long continuous geological records with the advent of computers and with the development of more sophisticated astronomical and climate models the astronomical theory and in particular its milankovitch version were revived over the last 5 years most geological astronomical and climatological obstacles have been overcome and the causal role of the orbital variations in long term variation of climate is taken almost universally for granted models of different categories of complexity from conceptual ones to 3 d atmospheric general circulation models and 2 d time dependent models of the whole climate system have now been astronomically forced in order to test the physical reality of the astronomical theory for example experiments with both low and high resolution gcms show that the increased seasonality at 9 000 bp leads to intensified summer monsoon circulation of africa and southern asia on the other hand seasonal models for simulating the transient response of the climate system to astronomical forcing are also developed and the output of these most recent modeling efforts compares favorably with data of the past 400 000 years accordingly the model predictions for the next 100 000 years are used as a basis for forecasting how climate would evolve when forced by orbital variations in the absence of anthropogenic disturbances the long term cooling trend which began some 6 000 years ago will continue for the next 5 000 years this first temperature minimum will be followed by an amelioration around 15 000 ap after present by a cold interval centered al 23 000 ap and by a major glaciation at around 60 000 ap

geology fluid inclusion and isotope constraints on ore genesis of the post collisional dabu porphyry cu mo deposit southern tibet abstract the dabu cu mo porphyry deposit is situated in the southern part of the lhasa terrane within the post collisional gangdese porphyry copper belt gpcb it is one of several deposits that include the qulong and zhunuo porphyry deposits the processes responsible for ore formation in the dabu deposit can be divided into three stages of veining stage i quartz k feldspar biotite chalcopyrite pyrite stage ii quartz molybdenite pyrite chalcopyrite and stage iii quartz pyrite molybdenite three types of fluid inclusions fis are present liquid rich two phase l type vapor rich two phase v type and solid bearing multi phase s type inclusions the homogenization temperatures for the fis from stages i to iii are in the ranges of 272 475 c 244 486 c and 299 399 c and their salinities vary from 2 1 to 49 1 1 1 to 55 8 and 2 9 to 18 0 wt nacl equiv respectively the coexistence of s type v type and l type fis in quartz of stage i and ii with similar homogenization temperatures but contrasting salinities indicate that fluid boiling is the major factor controlling metal precipitation in the dabu deposit the ore forming fluids of this deposit are characterized by high temperature and high salinity and they belong to a h2o nacl magmatic hydrothermal system the h o s pb isotopic compositions indicate that the ore metals and fluids came primarily from a magmatic source linked to miocene intrusions characterized by high sr y ratios similar to other porphyry deposits in the gpcb the fluids forming the dabu deposit were rich in na and cl derived from metamorphic dehydration of subducted oceanic slab through which nacl brine or seawater had percolated the inheritance of ancient subduction associated arc chemistry without shallow level crustal assimilation and or input of the meteoric water was responsible for the generation of fertile magma as well as co2 poor and halite bearing fis associated with post collisional porphyry deposits the estimated mineralization depths of qulong dabu and zhunuo deposits are 1 6 4 3 km 0 5 3 4 km and 0 2 3 0 km respectively displaying a gradual decrease from eastern to western gangdese deep ore forming processes accounted for the generation of giant sized qulong deposit because the exsolution of aqueous fluids with large fraction of water and chlorine in deep or high pressure systems can extract more copper from melts than those formed in shallow systems however the formation of small sized dabu deposit can be explained by a single magmatic event without additional replenishment of s metal or thermal energy in addition the ore forming conditions of porphyry cu mo deposits in gpcb are comparable to those of porphyry cu au mo deposits formed in oceanic subduction related continental or island arcs but differ from those of porphyry mo deposit formed in the dabie qinling collisional orogens the depth of formation of the mineralization and features of primary magma source are two major controls on the metal types and ore fluid compositions of these porphyry deposits

present day and fossil rhodolith pavements compared their potential for analysing shallow water carbonate deposits abstract coralline red algae represent the main biogenic components in most shallow water carbonate successions from the eocene to the recent they contribute significantly to sediment production on open platforms carbonate sediments formed by unattached coralline algae include rhodolith pavements rps which represent dense accumulations of rhodoliths as well as maerl which is composed of rhodoliths coralline algal branches and their detritus recent rps sampled off sesoko jima okinawa jima southern japan occur at depths of 50 70 m on a submarine terrace the taxonomic coralline composition is dominated by melobesioids associated with minor amounts of mastophoroids and sporolithaceans the rhodoliths are characterised by various nuclei an encrusting inner arrangement encrusting to warty outer growth forms and sub spheroidal shapes bioerosion encrustation and abrasion are the most prevalent taphonomic features possible fossil counterparts were identified in chattian and priabonian rps from middle ramp depositional systems from the venetian area north east italy a direct comparison between recent and fossil rps is possible by contrasting the constituent rhodolith characteristics including taxonomic composition nature of the nucleus inner arrangement outer growth forms size and shape as well as taphonomic signatures this allows factors controlling rhodolith formation and growth in rps to be compared especially with respect to hydrodynamic regimes and substrate type

spit platform temperate carbonates the origin of landward downlapping beds along a basin margin lower pliocene carboneras basin se spain lower pliocene temperate carbonates exhibit landward downlapping beds at the southern margin of the carboneras basin in south eastern spain this rarely documented stratal geometry resulted from the accumulation of bedded bioclastic carbonate sand and gravel by longshore currents along a spit platform located a few hundred metres from the palaeoshoreline the top of the spit platform was covered by shoals that extended over a gently dipping ramp inclined to the north on the landward slope of the spit sediments washed over from the shoal area were deposited in parallel laminated beds with a southward dip of 8 11 these beds aggraded and retrograded after an increase in accommodation space probably related to an early pliocene eustatic sea level rise as a result the beds downlap onto the underlying unconformity surface in a shoreward direction eventually the depression between the shoreline and the spit platform was filled and a gentle ramp became established these pliocene exposures in the carboneras basin and a similar upper miocene example in southern spain suggest that landward downlapping stratal geometries can be expected in nearshore temperate carbonates along basin margins and demonstrate a similarity in sedimentary dynamics to siliciclastic sands and gravels

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

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

origin of the ore forming fluids and metals of the bangpu porphyry mo cu deposit of tibet china constraints from he ar h o s and pb isotopes abstract the bangpu porphyry mo cu deposit is a representative mo dominated deposit besides the sharang porphyry mo deposit in the gangdese metallogenic belt the mo cu mineralization has a close relationship with the monzogranite porphyry and diorite porphyrite we identify three stages during the ore formation a pre ore stage a main ore stage with mo cu deposited dominantly and a post ore stage in this study he ar h o s and pb isotopic compositions of the bangpu deposit were determined based on these determinations integrated isotope geochemistry studies were performed to constrain the possible sources of the ore forming fluids and metals the 3 he 4 he and 40 ar 36 ar ratios of fluid inclusions exhibit a range of 0 12209 0 36370 ra and 275 6 346 1 respectively the 4 he and 40 ar concentrations vary from 1 51 to 3 57 10 7 cm 3 stp g 1 and 0 49 to 9 31 10 7 cm 3 stp g 1 respectively he ar isotopic compositions suggest dominantly crustal derived fluid with minor amount of meteoric water in the main ore stage the 18 o fluid and d fluid values vary from 1 3 to 3 9 and 140 5 to 73 7 respectively indicating that magma fluids mixed with meteoric water the average 34 s value of the sulfides 0 3 in the main ore stage is close to the ore forming porphyries indicating a magmatic source the lead isotopic components of ore sulfides exhibit restricted ranges with 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios of 18 450 18 728 15 602 5 672 and 38 715 39 211 respectively and values in the range of and 9 46 9 58 indicating ore forming metals of primarily an upper crust source with a small amount of mantle materials compared to the bangpu deposit the ore metals derived from mantle are even greater in the jiama and qulong deposits which leads to cu being the dominant mineralization in the jiama and qulong deposit

characteristics and metallogenic potential of skarn copper lead zinc polymetallic deposits in central eastern gangdese the skarn copper lead zinc polymetallic deposits are distributed in an ew striking metallogenic belt some 450 km long and 90 km wide the metallogenic belt can be divided into three sub belts i e lhasa xietongmen in the western part of gandese jiama linzhou in the northeast and gongga zalang zhedang in the southern part along the brahmaputra river with most of the ore deposits located in jiama linzhou sub belt the ore deposits show apparent regional zonal distribution there exist various kinds of polymetallic deposits such as iron copper copper lead zinc gold silver copper molybdenum lead zinc copper gold deposits and independent copper lead zinc and iron deposits the ore bearing strata consist mainly of jurassic cretaceous marine carbonate strata and carbonate bearing marine volcanic detrital strata the ore controlling stocks are dominated by small granitic stocks or porphyries belonging to calcic alkaline high k calcic alkaline series orebodies mainly occur in stock contact zones and tectonic zones beside stocks the main ore controlling structures include interlaminar tectonic zones stock contact zones and fracture zones the ore formation shows notable multistage mineralization characteristics the copper lead and zinc sulfides must have been precipitated mainly at the retrograde skarn stage and the favorable temperatures for ore precipitation range from 160 to 380 sulfur hydrogen and oxygen isotope studies indicate that the ore forming fluids and materials were mainly derived from magmatic fluids the re os isochronic ages of ore deposits in jiama linzhou region are concentrated in a narrow range of 15 17ma coincident with the stretching period in the crust after the formation of the main collision belt in tibet plateau this implies that the formation of skarn deposits was related to the partial melting at depth and the fluid concentration resulting from the stretching after indian asia plate collision the skarn deposits and the porphyry copper deposits in this region have similar magmatic tectonic and metallogenic geodynamic conditions these two types of ore deposits were formed in the same period and belong to the same metallogenic series the skarn deposits are characterized by polymetallic association high grade great size and high economic value central gangdese has favorable geological and geochemical environments for the formation of skarn deposits it is concluded that jima linzhou basin along leqingla qulong jiama and bangpu might constitute a potential metallogenic area dominated by skarn type copper lead zinc polymetallic deposits

simulation of the last glacial cycle by a coupled sectorially averaged climate ice sheet model 2 response to insolation and co2 variations a two dimensional climate model which links the northern hemisphere atmosphere ocean mixed layer sea ice and continents has been asynchronously coupled to a model of the three main northern ice sheets and their underlying bedrock the coupled model has been used to test the influence of several factors including snow surface albedo over the ice sheets in producing plausible ice age simulations using astronomically derived insolation and co2 data from the vostok ice core the impact of potentially important processes such as the water vapor transport clouds and deep sea circulation was not investigated in this study after several sensitivity experiments designed to identify the main mechanism governing surface temperature and ice accumulation the model is first run with ice sheet feedback by forcing it only with the astronomical insolation over the past 122 kyr large variations of ice volume are simulated between 122 and 55 kyr b p with a rapid latitudinal extension of the north american and eurasian ice sheets starting at 120 kyr b p the simulated last glacial maximum is at 19 kyr b p the model is able to simulate deglaciation as well the simulated evolution of the three northern ice sheets is generally in phase with geological reconstructions the major discrepancy between the simulation and paleoclimate reconstructions lies in the underestimation of temperature variations linked with an underestimation of the ice sheet extent and an excess in the prescribed co2 concentration sensitivity experiments show that ablation is more important to the ice sheet response than snow precipitation variations in the model a key mechanism in the deglaciation after the last glacial maximum appears to be the aging of snow which decreases its albedo the other factors which play an important role are in decreasing level of importance the ice sheet altitude insolation taiga cover and ice sheet extent a final set of experiments addresses the effects of co2 on the simulated climate of the last glacial maximum and on a new long term experiment covering the last 122 kyr this last experiment is made by forcing the model with both insolation and co2 variations this additional forcing improves the temperature and ice volume results despite the limitations inherent to the present modeling approach the sensitivity experiments performed can provide insight into the relative importance of possible mechanism responsible for the building and melting of huge ice sheets during the last glacial interglacial cycle

monsoon climate of the early holocene climate experiment with the earth s orbital parameters for 9000 years ago values for the precession and obliquity of the earth 9000 years ago indicate that the global average solar radiation for july 9000 years ago was 7 percent greater than at present when the estimated solar radiation values are used in a low resulation climate model the model simulates an intensified continent scale monsoon circulation this result agrees with paleoclimatic evidence from africa arabia and india that monsoon rains were stronger between 10 000 and 5000 years ago than they are today

rhodolith bearing limestones as transgressive marker beds fossil and modern examples from north island new zealand rhodoliths are nodular structures composed mainly of the superimposed thalli of calcareous red algae because their development is controlled by an array of ecological parameters rhodoliths are a valuable source of palaeoenvironmental information however despite their common use in palaeoecological reconstructions the stratigraphic significance of rhodolith accumulations seldom has been addressed in detail in a study of cenozoic rhodolith bearing deposits from the north island of new zealand rhodolithic units usually of limited lateral extent typically occur above major unconformities at the base of deepening upwards successions two types of transgressive rhodolith bearing deposits may be distinguished on the basis of texture and rhodolith internal structure i type a deposits are clast supported rhodolithic rudstones containing abundant pebbles and cobbles reworked from the substrate and are characterized by rhodoliths with a compact concentric to columnar internal structure and a high nucleus to algal cover ratio ii type b deposits are rhodolithic floatstones with a matrix usually consisting of bryozoan fragments benthic foraminifera and echinoid fragments or terrigenous silty fine sand the rhodoliths of type b units usually have a loose internal framework with irregular to branched crusts the two contrasting rhodolith bearing units are interpreted as characteristic facies of transgressive systems tract deposits analogous to shell concentrations formed under conditions of low net sedimentation type a deposits are correlated with relatively high energy settings and or narrow submerged palaeotopographic lows whereas type b deposits are interpreted as forming in lower energy settings the association between transgression and development of rhodolithic facies is confirmed by observations of a modern rhodolith production site at whangaparaoa peninsula in north island where algal nodules grow above a ravinement surface cut during the holocene sea level rise and also by a review of published fossil examples many of which show stratigraphic and compositional attributes analogous to those of the new zealand occurrences the review indicates that transgressive rhodolith accumulations develop more commonly in but are not restricted to non tropical settings it is suggested that a combination of factors such as low net sedimentary input nature of the substrate sea level rise and inherited physiography contribute to determine the relationship between rhodolith bearing deposits and transgressive settings

taphofacies models for epeiric sea environments middle paleozoic examples abstract skeletonized organic remains display various modes of occurrence which may be used to better understand the sedimentary dynamics of strata within which they occur aspects of skeleton biostratinomy and early diagenesis are distributed nonrandomly within the stratigraphic record and therefore are useful in discriminating taphonomic facies for purposes of taphonomic comparisons skeletonized marine taxa are reduced to five generally defined types massive arborescent univalved bivalved and multielement different skeletal types display different attributes which reflect specific responses to physical chemical and or biological processes the taphonomic properties of disarticulation reorientation and sorting fragmentation corrosion and abrasion skeletal dissolution and early diagenesis display patterns which are predictable with respect to a variety of inter related physico chemical parameters these can be quantified through indices which evaluate relative frequencies of occurrence sedimentary events alter the temporal and spatial homogeneity of processes which generate background taphofacies and superimpose event related properties thereby generating composite taphofacies such events produce taphonomic signature which in themselves correspond to specific environmental conditions i e water depth and event intensity indeed background and event related processes interact to generate complex but nonetheless diagnostic facies attributes useful in reconstructing paleoenvironments the comparison of standard indices among beds should allow the recognition of stratigraphic patterns and facilitate the diagnosis of systematic gradients among taphonomic properties deductively derived taphofacies models corroborated by empirical data from paleozoic strata illustrate the distribution of taphonomic properties with respect to environmental energy turbulence background sedimentation rate and sediment oxygenation these parameters also indirectly influence other less obvious factors including bioturbation and sediment chemistry trends in the distribution of taphonomic properties taphonomic gradients permit us to map otherwise unrecognized trends in these environmental parameters across a hypothetical onshore offshore transect within a generalized epeiric sea setting taphofacies models provide the quantifiable basis by which evolution of taphofacies may be gauged and then related to biotic and abiotic phenomena moreover taphofacies models evaluate the preservability of skeletal remains in different environmental settings and therefore provide information important in paleoecological studies

larger foraminiferal and coralline algal facies in an upper eocene storm influenced shallow water carbonate platform colli berici north eastern italy abstract facies analysis of priabonian shallow water carbonate successions in the outcrops near mossano eastern colli berici north eastern italy and the subsequent integration of palaeoecological data have been used to produce a detailed palaeoenvironmental model the facies distribution and the processes which controlled the larger benthic foraminiferal and coralline algal assemblages in the study priabonian storm influenced carbonate ramp are discussed in detail in the middle ramp trough cross bedded small nummulites and rhodolith packstones pass laterally into coralline algal crust wackestones these rhodoliths exhibit two well differentiated growth phases the first occurring during low water energy periods followed by a second developed during high energy events during which they were reworked and partially destroyed these facies pass laterally into orthophragminid rudstones and packstones characterised by orthophragminid tests and channel structures the latter were formed by storm induced return currents which swept the middle ramp creating distal middle ramp channel structures further toward the distal part of the middle ramp the return currents decreased in energy and discharged nutrients allowing the coralline crustose pavement to develop this is characterised by rhodoliths typically discoidal in shape up to 10 cm in diameter with a loose inner arrangement consisting of encrusting to foliose growth forms the occurrence of the channel structures in orthophragminid rudstones and in the coralline crustose pavement appears to be unique in upper eocene carbonate ramp depositional systems during the erosive events associated with the return currents these shallow water carbonates were unlithified or only weakly lithified and were therefore easily transported into deeper water ramp settings the model suggests that the significant changes of the middle ramp benthic communities with depth could have formed at least in part by offshore return currents which played an important role in both controlling substrates and in supplying nutrients

vostok ice core a continuous isotope temperature record over the last climatic cycle 160 000 years a continuous deuterium profile along the 160 000 year vostok ice core antarctica is interpreted in terms of atmospheric temperature changes this climatic record is the awaited terrestrial complement of the deep sea records supporting the existence of a relation between the pleistocene climate and orbital forcing

spectral analysis of the middle triassic latemar limestone abstract the middle triassic latemar limestone in the dolomites region northern italy consists of hundreds of vertically stacked meter scale platform carbonate cycles each cycle is composed of a shallow marine subtidal carbonate unit with a thin centimeter scale vadose diagenetic dolomite cap these latemar couplets are the products of repeated episodes of submergence emergence with durations estimated at 20 000 yr the couplets are arranged in upward thinning bundles of five indicating the presence of a 100 000 year modulating component we examined this high frequency cycling in the platform buildup using a variety of classical and advanced spectral analysis techniques we found si nificant evidence for the presence of a milankovitch forcing signal in this cycling we also present evidence that the adjacent coeval basinal facies the livinallongo formation exhibits a similar bundling pattern in its cm scale hemipelagic carbonate shale alternations we conclude that milankovitch forced small amplitude sea level oscillations were the most likely cause of these middle triassic carbonate rhythms

pleistocene climatic variability at astronomical frequencies abstract spectral analysis of geological records show periodicities corresponding to those calculated for the eccentricity 400 and 100 ka the obliquity 41 ka and the climatic precession 23 and 19 ka it is precisely the geological observations of this bi partition of the precessional peak confirmed to be real in astronomical computations which was one of the most impressive of all tests for the milankovitch theory concerning the question of whether or not the observed cycles account for most of the climatic variability having periods in the range predicted by the astronomical theory substantial evidence from cross spectral analysis coherency analysis and modelling is provided that at least near frequencies of variation in obliquity and precession a considerable fraction of the climate variance is driven in some way by insolation changes accompanying changes in the earth s orbit the variance components centered near a 100 ka cycle dominate most ice volume records and seem in phase with the eccentricity cycle although the exceptional strength of this cycle needs a non linear amplification by the glacial ice sheets themselves and associated feedbacks as the insolation spectra change with latitudes and with the type of parameters considered the diversity of the spectra of different climatic proxy data recorded in different places of the world over different periods is used to better understand how the climate system responds to the insolation forcing this study of the physical mechanisms involved is also achieved through the analysis of the log log shape of the geological records and through the comparison in frequency domain between simulated climatic time series and proxy data the evidence both in the frequency and in the time domain that orbital influences are felt by the climate system implies that the astronomical theory may provide a clock with which to date quaternary sediments with a precision several times greater than is now possible

crustose coralline algae from the flower garden banks northwestern gulf of mexico controls on distribution and growth morphology abstract the east and west flower garden banks in the northwestern gulf of mexico represent the northernmost tropical coral reefs and caribbean coralline algal flora on the north american continental shelf coralline algae are the dominant framework builders and sediment contributors below 50 m on the banks on the basis of growth form and taxonomic composition coralline algae on the flower garden banks can be divided into four overlapping depth zones upper coral reefs 20 30 m madracis algal ridges 30 40 m algal nodule zone 45 80 m and deep algal reefs 50 90 m corallines on the upper coral reefs are dominated by hydrolithon lithophyllum and porolithon their growth form as thick laterally restricted crusts and knobs results from intensive grazing by parrotfish and urchins grazing is diminished on the madracis algal ridges below the upper reefs and corallines grow here as laterally extensive plates binding coral rubble dominant corallines on the ridges are lithophyllum paragoniolithon and tenarea algal nodules rhodoliths o the deeper bank slopes are the most widespread algal growth form on the flower garden banks on the basis of shape internal structure and composition rhodoliths are divided into an upper zone where they have a spherical shape with concentric laminae and a lower zone discoidal shape with irregular laminae diminishing current velocity with increasing depth controls nodule morphology the red alga peyssonnelia and the foraminifer gypsina are two non coralline components that contribute substantially to nodule growth reduced current velocity in the lower nodule zone enables corallines and peyssonnelia to develop laterally extensive pavements and 1 2 m high algal reefs taxonomic composition high framework porosity and irregular internal growth morphology f the deep algal reefs distinguish these structures from shallow algal ridges described elsewhere the 90 m isobath at the flower garden banks approximates the upward limit of a turbid nepheloid layer composed of continually resuspended sediment reefal structures within this water layer are dead and are now covered by fine sediment

rate of dissolution of carbonate sediments by microboring organisms davies reef australia abstract skeletal carbonate sediments on the lagoon floor of davies reef great barrier reef australia are subject to intense attack by microboring organisms principally algae the rate at which this microboring process dissolves carbonate was measured experimentally fresh unbored molluscan sand samples placed in the shallow lagoon 5 m water depth experienced a weight loss of about 0 9 g 30 g sample or 3 in one year due to dissolution of carbonate by microborers revealed by direct measurement of weight change and point count analysis this figure may be converted to about 350 g caco3 dissolved m2 lagoon floor year which is equivalent to between 18 and 30 of the sediment influx rate to this lagoon averaged over the past 9 000 years consideration of the exp rimental design suggests that the experiment underestimated the true rate of microboring in lagoon floor sediments we conclude that the extent of microboring in carbonate sands may provide information on the rate of sediment deposition and that dissolution of carbonate sediments by microborers is a significant factor in whole reef caco3 budgets

sedimentology and palaeoecology of a miocene coralline algal biostrome from the maltese islands abstract a large coralline algal biostrome 20 km 5 km 16 m thick is well exposed in western malta and eastern gozo the biostrome is composed of limestones largely constructed by in situ coralline algae or transported algal debris some sediments are dominated by rhodoliths and others by crustose coralline frameworks six facies are distinguished crustose algal marl crustose algal wackestone rhodolith pavement algal branch packstone crustose pavement and algal crust packstone each facies is characterised by different rhodolith morphologies and coralline crusts which are constructed mainly bymesophyllum commune the coralline morphogenesis is related to the palaeoenvironmental conditions the biostrome is thought to have developed from a series of relic sand ridges to form a low relief platform of moderate depths containing a mosaic of sedimentary facies the sequence is affected by growth faulting which divides the biostrome into eight units

modern rhodoliths from the insular shelf of pico in the azores northeast atlantic ocean abstract a seabed sediment sampling survey conducted on the pico insular shelf found abundant rhodoliths between 64 and 73 m off the south coast of the island these were small and mainly ellipsoidal in shape with a maximum diameter of 3 75 cm granules and small pebbles of eroded basalt were also a typical component of these samples thin algal crusts were secreted on basalt pebbles by the coralline red algae phymatolithon calcareum which in turn were covered by lithophyllum incrustans additional samples were collected by snorkelling at mare lajes do pico a shallow lagoon 2 4 m in depth on the south coast here rhodoliths are mostly spheroidal and bigger maximum diameter of 4 75 cm formed by thin thalli of p calcareum based on these results distribution of shapes and species and previous work on the characteristics of fossil specimens from neogene deposits on santa maria island azores and other north atlantic archipelagos an empirical depositional model is proposed for the development of rhodoliths on the pico island shelf 1 nearshore rhodoliths formed solely by p calcareum are subjected to a wide range of currents and waves resulting in their spheroidal shapes however those of mare lagoon are protected from offshore transport and tend to grow larger than deep water rhodoliths 2 although not sampled there must be middle shelf rhodoliths formed solely by p calcareum that tend to form more ellipsoidal shapes due to seafloor oscillatory movements caused by waves crossing the shelf 3 during storms these middle shelf rhodoliths are then transported to the outer shelf where l incrustans overgrows the initial cover of p calcareum shallow associations are normally larger reflecting therefore a longer life span than the deeper associations transport by storms appears to be an important factor in the formation of some deep water rhodoliths around volcanic oceanic islands subjected to high wave energy however their exposure to an energetic environment and likely frequent offshore transport does not allow them to grow as large as those from shallow water

evidence for periodicity and nonlinearity in a high resolution fossil record of long term evolution the application of new signal analysis techniques provides increased insight into the study of the fossil record and processes of evolution the fossil record of 622 planktic foraminifera contains data from 200 stratigraphic stages of the past 127 m y time series analyses wavelet and fourier transform of the planktic foraminifera fossil record were used to discern periodic components in long term evolution the correlation function analysis was used to distinguish between random and deterministic behavior of the fossil record the analyses show that stationary 30 m y periodicity and complex deterministic patterns occur in the long term planktic foraminifera evolution in particular in the extinction record our results suggest that the occurrence of intense diversity fluctuations with 3 10 m y periodicity after major extinction events may be attributed to nonlinear self organized evolutionary response to the availability of new ecospace this coupled nonlinear periodic scenario may explain the repetitive appearance of similar morphotypes in 30 m y intervals

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

pleistocene coralline algal build ups coralligene de plateau and associated bioclastic deposits in the sedimentary cover of cutro marine terrace calabria southern italy

diversity growth forms and taphonomy key factors controlling the fabric of coralline algae dominated shelf carbonates the fabric of biogenic carbonate sediments can be differentiated 1 with respect to diversity of constituent components 2 using features pertaining to their growth forms and 3 upon consideration of taphonomic aspects these not only determine limestone fabrics but also form the basis for facies differentiation and palaeoecological interpre tation this study is based on coralline algae dominated lower oligocene shelf carbonates from northern slovenia from which seven facies nummulitic bivalve foraminiferal coralline algal coralline algal coralline algal coral coral and grainstone are differentiated the role of diversity growth forms and taphonomy of coralline algae in each facies is discussed nine species from seven genera of coralline algae including geniculates and non geniculates were recognized numerous different growth forms ranging from crusts protuberances lamel lae to arborescent types are present a wide range of taphonomic features including dis articulation encrustation fragmentation and abrasion can be observed the determination of diversity is dependent on taxonomic identification using preserved diagnostic characters relevant to palaeontological and botanical systematics growth form determination in thin section is influenced by orientation and sectioning effects the taphonomy of red algae is highly dependent on initial growth form and the specific environ ment in which they are found a number of taphonomic processes described in

new perspectives on orbitally forced stratigraphy this survey of the current status of research into earth s orbitally forced paleoclimatic record summarizes recent developments in the theory of earth s orbital parameters and reviews how various techniques of data collection and analysis have fared in the search and recovery of orbital signals in ancient stratigraphy the emerging significance of the quasi periodicity of earth s orbital variations as a prin cipal tool in the analysis of orbitally forced stratigraphy is discussed in detail five case studies are presented that illustrate new directions in research a time series analysis of discontinuous strata b measurement of ultra high resolution stratigraphic signals c new perspectives on the 100 kyr pleistocene glaciation problem d strati graphic evidence for solar system resonance modes and e evaluating phanerozoic length of day from orbitally forced stratigraphy the study of how earth s orbital parameters came to be recorded in ancient stra tigraphy has recently moved into a new phase of scientific inquiry and discovery notable advances in celestial mechanics and in the analysis of stratigraphic data have given rise to new ways of solving old problems and have uncovered new problems for the first time new tools have facilitated the recovery of extended high resolution orbital signals from stratigraphy advanced analytical techniques have now been fully incorporated into the field an updated theory of earth s orbital parameters provides an accurate ephemeris for the past 16 million years for precision correlation between earth s orbital parameters and orbitally forced stratigraphy some orbital eccentricity modes can be used for orbital stratal cal ibrations to several hundred million years ago these breakthroughs have transformed the study of orbitally forced stratigra phy into an applied field that addresses long standing problems in disciplines as far ranging as geochronology geodynamics and astrodynamics orbital signals provide the framework for a high resolution orbital chronostratigraphy as far back