global dinoflagellate event associated with the late paleocene thermal maximum the late paleocene thermal maximum or lptm ca 55 ma represents a geologically brief time interval 220 k y characterized by profound global warming and associated environmental change the lptm is marked by a prominent negative carbon isotope excursion cie interpreted to reflect a massive and abrupt input of 12 c enriched carbon to the ocean atmosphere reservoir possibly as a result of catastrophic gas hydrate release on time scales equivalent to present day rates of anthropogenic carbon input the lptm corresponds to important changes in the global distribution of biota including mass extinction of marine benthic organisms the dinoflagellate cyst record indicates that surface dwelling marine plankton in marginal seas also underwent significant perturbations during the lptm we report on the dramatic response of representatives of the genus apectodinium from two upper paleocene lower eocene sections in the southern new zealand and northern austria hemispheres where the dinoflagellate records are directly correlated with the cie benthic foraminifera extinction event and calcareous nannofossil zonation the results indicate that the inception of apectodinium dominated assemblages appears to be synchronous on a global scale and that the event is precisely coincident with the beginning of the lptm apectodinium markedly declined in abundance near the end of the lptm this apectodinium event may be associated with 1 exceptionally high global sea surface temperatures and or 2 a significant increase in marginal marine surface water productivity such a globally synchronous acme of dinoflagellate cysts is unprecedented within the dinoflagellate cyst fossil record

enhanced terrestrial weathering runoff and surface ocean carbonate production during the recovery stages of the paleocene eocene thermal maximum 1 the carbonate saturation profile of the oceans shoaled markedly during a transient global warming event known as the paleocene eocene thermal maximum petm circa 55 ma the rapid release of large quantities of carbon into the ocean atmosphere system is believed to have triggered this intense episode of dissolution along with a negative carbon isotope excursion cie the brevity 120 220 kyr of the petm reflects the rapid enhancement of negative feedback mechanisms within earth s exogenic carbon cycle that served the dual function of buffering ocean ph and reducing atmospheric greenhouse gas levels detailed study of the petm stratigraphy from ocean drilling program site 690 weddell sea reveals that the cie recovery period which postdates the cie onset by 80 kyr is represented by an expanded 2 5 m thick interval containing a unique planktic foraminiferal assemblage strongly diluted by coccolithophore carbonate collectively the micropaleontological and sedimentological changes preserved within the cie recovery interval reflect a transient state when ocean atmosphere chemistry fostered prolific coccolithophore blooms that suppressed the local lysocline to relatively deeper depths a prominent peak in the abundance of the clay mineral kaolinite is associated with the cie recovery interval indicating that continental weathering runoff intensified at this time as well robert and kennett 1994 such parallel stratigraphic changes are generally consonant with the hypothesis that enhanced continental weathering runoff and carbonate precipitation helped sequester carbon during the petm recovery period e g dickens et al 1997 zachos et al 2005

rapid stepwise onset of antarctic glaciation and deeper calcite compensation in the pacific ocean the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution is termed the calcite compensation depth at present this depth is 4 500 m with some variation between and within ocean basins the calcite compensation depth is linked to ocean acidity which is in turn linked to atmospheric carbon dioxide concentrations and hence global climate1 geological records of changes in the calcite compensation depth show a prominent deepening of more than 1 km near the eocene oligocene boundary 34 million years ago 2 when significant permanent ice sheets first appeared on antarctica3 4 5 6 but the relationship between these two events is poorly understood here we present ocean sediment records of calcium carbonate content as well as carbon and oxygen isotopic compositions from the tropical pacific ocean that cover the eocene oligocene boundary we find that the deepening of the calcite compensation depth was more rapid than previously documented and occurred in two jumps of about 40 000 years each synchronous with the stepwise onset of antarctic ice sheet growth the glaciation was initiated after climatic preconditioning7 by an interval when the earth s orbit of the sun favoured cool summers the changes in oxygen isotope composition across the eocene oligocene boundary are too large to be explained by antarctic ice sheet growth alone and must therefore also indicate contemporaneous global cooling and or northern hemisphere glaciation

geochemistry of oolitic iron ores an electron microprobe study oolitic iron ores are made up of silicate oxide and carbonate minerals that are part of solid solution series the compositions of the minerals can depart from pure end members and show variation among deposits this variability can be quantified using electron microprobe techniques iron silicates are represented by chamositic clays both berthierine and chamosite glauconite was not seen in any of these samples berthierine predominates in younger deposits whereas the paleozoic ores studied contained only chamosite compositions of the chamositic clays however were independent of age iron oxides are mostly goethite in younger deposits or hematite in older deposits both minerals lack appreciable al in solid solution most analyses show small amounts of al but usually balanced by si in the same proportion as in chamosite indicating a slight admixture of clay iron carbonates are siderite with appreciable substitution of ca and mg but not of mn apatite is common but no iron phosphates were found the compositions of the silicates and carbonates are close to those reported for early diagenetic minerals from other types of sedimentary rocks indicating that ironstone formation does not require unusual chemical conditions other than a large supply of iron the analytical results can be used to argue against several hypotheses of ironstone genesis the lack of al in the goethitic and hematitic ooliths is inconsistent with an origin either by redeposition of soil ooliths or by oxidation and leaching of earlier chamositic ooliths the presence of high al contents in the chamositic ooliths shows that they cannot have formed from earlier aragonitic ooliths and the presence of small amounts of chamositic clay and apatite as discrete laminae in goethitic and hematitic ooliths suggests that this type of oolith could also not have formed by replacement of aragonite times of ironstone deposition show a correlation with climate and sea level stands that suggests a mechanism for generating locally high iron concentrations in seawater a combination of a warm humid climate and low average continental relief would intensify lateritic weathering and the formation of iron enriched detritus coincidence of this increased detrital iron supply with intensification and shallowing of the oxygen minimum layer in the ocean could lead to mobilization of iron from offshore shelf clastics to be redeposited near the shoreline in intertidal to shallow subtidal environments

facies analysis and palaeoclimatic significance of ironstones formed during the eocene greenhouse lower and middle eocene ironstone sequences of the naqb and qazzun formations from the north east bahariya depression western desert egypt represent a proxy for early palaeogene climate and sea level changes these sequences represent the only palaeogene economic ooidal ironstone record of the southern tethys these ironstone sequences rest unconformably on three structurally controlled cenomanian palaeohighs for example the gedida harra and ghorabi mines and formed on the inner ramp of a carbonate platform these palaeohighs were exposed and subjected to subaerial lateritic weathering from the cenomanian to early eocene the lower and middle eocene ironstone sequences consist of quiet water ironstone facies overlain by higher energy ironstone facies the distribution of low energy ironstone facies is controlled by depositional relief these deposits consist of lagoonal burrow mottled mud ironstone and laterally equivalent tidal flat stromatolitic ironstones the agitated water ironstone facies consist of shallow subtidal intertidal nummulitic ooidal oncoidal and back barrier storm generated fossiliferous ironstones the formation of these marginal marine sequences was associated with major marine transgressive regressive megacycles that separated by subaerial exposure and lateritic weathering the formation of lateritic palaeosols with their characteristic dissolution and reprecipitation features such as colloform texture and alveolar voids implies periods of humid and warm climate followed major marine regressions the formation of the lower to middle eocene ironstone succession and the associated lateritic palaeosols can be linked to the early palaeogene global warming and eustatic sea level changes the reworking of the middle eocene palaeosol and the deposition of the upper eocene phosphate rich glauconitic sandstones of the overlying hamra formation may record the initial stages of the palaeoclimatic transition from greenhouse to icehouse conditions

fluvial lacustrine interaction on skeiðararsandur iceland implications for sandur evolution abstract a complex assemblage of fluvial and lacustrine sediments is identified in a major section through proglacial sediments on skei ararsandur south iceland high magnitude low frequency events are identified in both the fluvial and lacustrine sediments however much of the sedimentary succession is composed of normal low magnitude high frequency sediments retreat of skei ararjokull following a surge event created a topographic basin occupied at various times by both fluvial and lacustrine depositional systems and also subjected to a high magnitude jokulhlaup previous studies have examined the processes and events occurring on skei ararjokull in isolation this paper improves the understanding of the way in which processes with varying magnitude and frequency regimes interact and contribute to the sedimentary record of proglacial environments

significant southern ocean warming event in the late middle eocene a prominent middle eocene warming event is identified in southern ocean deep sea cores indicating that long term cooling through the middle and late eocene was not monotonic at sites on maud rise and the kerguelen plateau a distinct negative shift in 1 8 o values 1 0 is observed ca 41 5 ma this excursion is interpreted as primarily a temperature signal with a transient warming of 4 c over 600 k y affecting both surface and middle bathyal deep waters in the indian atlantic region of the southern ocean this isotopic event is designated as the middle eocene climatic optimum and is interpreted to represent a significant climatic reversal in the midst of middle to late eocene deep sea cooling the lack of a significant negative carbon isotope excursion as observed during the paleocene eocene thermal maximum and the gradual rate of high latitude warming suggest that this event was not triggered by methane hydrate dissociation rather a transient rise in pco 2 levels is suspected possibly as a result of metamorphic decarbonation in the himalayan orogen or increased ridge arc volcanism during the late middle eocene

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

paleogene stable isotope events the oxygen isotope record in paleogene benthic foraminifera shows that at the base of the paleogene the ocean deep waters had a temperature of about 10 c rising to about 12 c at the base of the eocene and cooling between 51 ma and 49 ma to about 9 c the most dramatic event occurred just after the eocene oligocene boundary at about 35 8 ma when ocean deep waters cooled by several degrees within 104 105 yr probably in association with temporary glaciation in the antarctic region another more intense glacial event in antarctica may have occurred later in the oligocene at about 31 ma and a third near the top of the oligocene at 24 ma in the marine carbon isotope record a very rapid negative excursion occurred precisely at the cretaceous tertiary boundary a recovery to unusually positive values in the late paleocene was followed by a second negative excursion close to the paleocene eocene boundary that was even more extreme in magnitude although it was not as rapid these major carbon isotope events permit very accurate stratigraphic correlation there are many other smaller features in the carbon isotope record that will also prove useful for this purpose

mammalian generic diversity and turnover in the late paleocene and early eocene of the bighorn and crazy mountains basins wyoming and montana usa abstract patterns of mammalian generic turnover richness and faunal composition were investigated for faunas from 17 biostratigraphic zones in middle paleocene through early eocene deposits of the bighorn and clarks fork basins of northern wyoming and the crazy mountains basin of south central montana significance of turnover was evaluated 1 by comparison of observed turnover to expected turnover calculated from the multiple regression of turnover on zone duration and generic richness and 2 by comparison of observed turnover to a bootstrapped turnover distribution patterns of turnover and richness also were assessed in light of relative sampling quality of each faunal zone the analysis identified four intervals of significant faunal change the torrejonian tiffanian transition the late tiffanian the earliest wasatchian and the middle to late wasatchian the first interval was characterized by a high number of last occurrences in the latest torrejonian resulting in a decrease in standing generic richness in the earliest tiffanian but no major changes in ordinal composition during the next interval of significant turnover the late tiffanian higher than expected first occurrences resulted in an increase in standing richness and a change in faunal composition most probably reflecting the immigration of taxa from outside north america the third and most dramatic interval of significant generic turnover took place in the earliest wasatchian and was distinguished by a high number of first occurrences but relatively few last occurrences this led to a marked increase in generic richness a pattern similar to that for the early wasatchian of north america as a whole the major change in faunal composition as in the late tiffanian was largely composed of immigrants from other continents the pattern of faunal change during the early wasatchian of the bighorn basin along with evidence for global warming at the paleocene eocene boundary supports previous interpretations associating this episode in mammalian evolution with the opening of high latitude intercontinental dispersal routes during the fourth interval of interest the middle to late wasatchian the bighorn basin fossil record shows a drop in generic richness this differs from the overall north american pattern and may be in part an artifact of still inadequate sampling for the latest part of the stratigraphic sequence in the bighorn basin

basaltic explosive volcanism but no comet impact at the paleocene eocene boundary high resolution chemical and isotopic records from egypt spain and denmark in the search for a triggering mechanism for the paleocene eocene p e boundary event 55 ma centimeter resolution chemical e g ir os pt and isotope e g os o 187 os 188 he 3 he 4 sr 87 sr 86 records across this boundary have been established for six uplifted marine sections in egypt spain and denmark the sections studied represent some of the stratigraphically most complete records across the onset of the carbon isotopic excursion cie and associated benthic foraminifera extinctions that mark the paleocene eocene boundary high sensitivity analyses failed to uncover evidence of extraterrestrial element or isotope enrichments in the six sections refuting the hypothesis of a major comet impact at the boundary preliminary searches for other impact indicative features such as spherules or shocked quartz also gave negative results in the danish section studied three basaltic ir rich ash layers occur at the paleocene eocene boundary but no similar ashes were found in egypt or spain the three ashes represent the earliest known manifestation of an unusual i to 2 million year long phase of explosive basaltic volcanism in the faero greenland region this volcanism is synchronous with major flood basalt effusions in east greenland and is associated with prominent paleogeographic changes in the high latitude north atlantic region discharge of mantle derived os to seawater during this volcanism may explain a small decrease in os o 187 os o 188 ratio at the paleocene eocene boundary in the zumaya section in spain the environmental perturbations at the paleocene eocene boundary appear to have been triggered by basaltic volcanism but any model for the detailed causal relation remains speculative c 2004 elsevier b v all rights reserved less

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

stable warm tropical climate through the eocene epoch earth s climate cooled from a period of extreme warmth in the early eocene epoch ca 50 ma to the early oligocene ca 33 ma when a large ice cap first appeared on antarctica evidence from the planktonic foraminifer oxygen isotope record in deep sea cores has suggested that tropical sea surface temperatures declined by 5 10 degrees over this interval eventually becoming much cooler than modern temperatures here we present paleotemperature estimates from foraminifer isotopes and the membrane lipids of marine crenarcheota from new drill cores in tanzania that indicate a warm and generally stable tropical climate over this period we reinterpret the previously published isotope records in the light of comparative textural analysis of the deep sea foraminifer shells which shows that in contrast to the tanzanian material they have been diagenetically recrystallized we suggest that increasingly severe alteration of the deep sea plankton shells through the eocene produced a diagenetic overprint on their oxygen isotope ratios that imparts the false appearance of a tropical sea surface cooling trend this implies that the long term eocene climatic cooling trend occurred mainly at the poles and had little effect at lower latitudes

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

high resolution 104 years deep sea foraminiferal stable isotope records of the eocene oligocene climate transition we have constructed high resolution 104 105 years benthic foraminiferal 13c and 18o records for the upper eocene through lower oligocene of two pelagic sequences deep sea drilling project dsdp site 522 in the angola basin south atlantic ocean and ocean drilling program odp site 744 in the southern indian ocean these records provide improved constraints on both the timing and magnitude of marine oxygen and carbon isotope events from 30 to 35 ma the oxygen isotope records indicate that the ubiquitous 18o increase oi 1 which marks the rapid expansion of continental ice sheets and a minimum of 3 to 4 c of cooling of bottom waters in the earliest oligocene 33 6 ma occurred in 350 kyr more than half the transition occurred over the final 40 50 kyr this period of lower temperatures and widespread continental glaciation persisted for roughly 400 kyr i e the duration of magnetochron c13n these records also indicate that this interval was characterized by at least two 100 kyr waxing and waning cycles oi 1a and oi 1b and possibly several higher frequency events the benthic foraminiferal 13c records show a positive 0 8 excursion that is nearly isochronous with the oi 1 oxygen isotope increase similar magnitude 13c increases at other sites indicate this was a global phenomenon suggestive of an unusually large perturbation to the carbon cycle this excursion was followed by smaller amplitude 13c oscillations with periods of roughly 400 kyr we suspect that the ubiquitous oi 1 13c excursion resulted from a brief but substantial increase in export production and carbon burial

depositional environments and iron ooid formation in condensed sections callovian oxfordian south eastern paris basin france carbonate platforms across western europe were superseded at the middle upper jurassic callovian oxfordian boundary either by alternating marl limestone and widespread marl deposits or by condensed sections containing iron ooids the characteristics of marine condensed sections in the south eastern part of the paris basin france and their distribution pattern are examined here and a model of iron ooid formation is developed iron ooids are found from the shoreface to the offshore zone they are most abundant in the median to distal offshore transition zone where they originally formed they also occur commonly albeit often as reworked grains in the proximal offshore zone to which they were transported the contemporaneous thick predominantly marl sections that occur laterally are devoid of iron ooids and were deposited in deeper settings distal offshore zone the iron ooids are composed of goethite typically they have a nucleus made up of a clump of goethite crystals and a laminated cortex three distinctive nanostructures are identified in the cortex laminae i a nanograined crystalline structure typical of primary goethite ii a secondary nanoflaked structure thought to have formed mechanically by reorientation of the goethite crystals and iii a coalesced structure acquired by subsequent diagenetic recrystallization the iron ooids formed successively i by lamina growth when goethite precipitated in the surface layer of the sediment nanograined structure and ii by interruption of growth when the ooids were remobilized by hydrodynamic agents as reflected by the flaked nanostructure iii these two nanostructures were sometimes transformed into a coalesced structure by recrystallization when ooids were buried

turnover of larger foraminifera during the paleocene eocene thermal maximum and paleoclimatic control on the evolution of platform ecosystems the larger foraminifera turnover lft during the paleocene eocene transition constitutes an important step in paleogene larger foraminifera evolution involving a rapid increase in species diversity shell size and adult dimorphism a platform to basin transect in egypt provides new data on timing and causal mechanisms through correlation with planktic biozonations and through integration with regional paleoenvironmental data the lft coincides with the boundary between shallow benthic biozones sbz4 and sbz5 and closely correlates with the paleocene eocene thermal maximum petm enhanced oligotrophy from the late paleocene onward favored the diversification of k strategist larger foraminifera we suggest that a short term eutrophication during the petm led to a temporary decline of extreme k strategist larger foraminifera species providing opportunities for new taxa with different ecological strategies to develop during post petm oligotrophic conditions these new taxa were able to evolve rapidly and soon dominated early eocene larger foraminifera assemblages whereas many paleocene taxa gradually disappeared the success of larger foraminifera during the early paleogene appears climatically controlled because of the vulnerability of corals to high surface water temperatures the late paleocene to early eocene global warming may have favored larger foraminifera at the expense of corals as the main carbonate producing component on carbonate platforms at lower latitudes

structural diversity of biogenic carbonate particles in microbial mats non skeletal carbonate particles in microbial mats were studied using thin sections and scanning electron microscopy the microbial mats form biolaminated units so called potential stromatolites in salterns this study emphasizes the coexistence of different particle forms and makes a genetic connection between the heterogeneity of the organic substrate built by bacteria and diatoms and their extracellular polymeric substances eps whereas allochthonous particles are scarce lanzarote microbial mats provide various autochthonous surfaces for the attachment of cells and eps including sheaths and capsules of cyanobacteria frustules of diatoms metabolic products such as gas bubbles liquid globules and faecal pellets as well as the carbonate precipitates themselves morphologically different carbonate precipitates are i calcified organic clumps peloids ii particles composed of concentric aragonite and biofilm laminae ooids and oncoids hi isolated particles floating in gel supported mats and coated by rims of fibrous cement cortoids iv particles bound by cryptocrystalline matrices or cement resulting in aggregate grains and v lobate cement which fills out spaces and pores and fixes the particles peloids are suggested to represent faecal pellets although microbial systems also generate cell clumps by non faecal processes ooid and oncoid constructions clearly record alternating processes of biofilm accumulation and aragonite encrustation further characteristic features of carbonate particles generated within a microbial mat are i an irregular distribution ranging from isolated particles floating within the gel like matrix to closely packed particles ii the amalgamation of different particle types e g peloids and ooids in aggregate grains iii the heterogeneous nature of nuclei comprising bacterial clumps intraclasts individual cells cell colonies and bubbles iv the enrichment of remains casts and imprints of cells within precipitates and v deformation e g truncated cortices of particles

climate change and the formation of nickel laterite deposits one of the major controls on nickel laterite deposit formation is climate a comparison of climatic data for regions where ultramafic rocks are exposed shows that areas currently conducive to nickel laterite formation receive 1000 mm yr precipitation have cold month mean cmm temperatures between 15 and 27 c and warm month mean wmm temperatures between 22 and 31 c using a compilation of paleoclimatic data and the defined climatic window of nickel laterite deposit formation allows an assessment of the timing and duration of paleo nickel laterite formation in ancient terrains to illustrate the potential of this technique we show that the formation of the caldag nickel laterite deposit of western turkey most likely initiated when the ultramafic protolith of cretaceous age was exposed in the early eocene and that the majority of the deposit formed during the eocene in contrast the formation of the bitincke deposit south albania was mostly complete by the early eocene after which cmm temperatures dropped below the optimum for laterite formation

eocene continental climates and latitudinal temperature gradients global climate during the mesozoic and early cenozoic is thought to have been warmer than at present but there is debate about winter temperatures paleontological data indicate mild temperatures even at high latitudes and in mid latitude continental interiors whereas computer simulations of continental paleoclimates produce winter temperatures closer to modern levels foliar physiognomy and floristic composition of 23 eocene floras from the interior of north america and australia indicate cold month means generally 2 c even where the mean annual temperature mat was

tectonic and eustatic control on deposition and preservation of upper cretaceous ooidal ironstone and associated facies peace river arch area nw alberta canada the late coniacian shallow marine bad heart formation of the western canada foreland basin is very unusual in that it contains economically significant ooidal ironstone deposition of shallow water and iron rich facies appears to have been localized over the crest and flanks of a subtle intrabasinal arch in part interpreted as a forebulge and partly attributed to reactivation of the long lived peace river arch the formation comprises two upward shoaling allomembers typically 5 10 m thick that are bounded by regionally mappable ravinement surfaces the lower unit allomember 1 grades up from laminated mudstone to bioturbated silty sandstone which is abruptly overlain by bioturbated ooidal silty sandstone grading into an almost clastic free ooidal ironstone up to 7 m thick ooidal ironstone was concentrated into nw to se trending ridges kilometres wide and tens of kilometres long ironstone formation appears to have been promoted by a drowning of the arch which progressively curtailed sediment supply and b enhanced reworking over the shallowly submerged arch and over a fault bounded block that underwent episodic vertical movement of 10 20 m during bad heart deposition allomember 2 also shoals upwards from mudstone to bioturbated and laminated silty sandstone but lacks ooids apparently reflecting a rejuvenated supply of detrital sediment from the arch the marine ravinement surface above allomember 2 is a skolithos firmground above which is developed a regional blanket of ooidal sediment in the east ooids are dispersed in a bioturbated silty sandstone with abundant evidence of repeated reworking and early siderite and phosphate cements westwards this facies grades over about 40 km into almost clastic free ooidal ironstone about 5 m thick the lateral facies change may reflect progressive clastic starvation distal to a low relief source area the two allomembers are interpreted to reflect eustatic oscillations of about 10 m superimposed on episodic tectonic warping and block faulting events the development of ooidal ironstone immediately above initial marine flooding surfaces indicates a close relationship to marine transgression reflecting sediment starved conditions ironstone does not appear to be related to either sequence boundaries or maximum flooding surfaces the bad heart formation is blanketed by marine mudstone deposited in response to major flexural subsidence and rejuvenation of clastic sources in the cordillera to the sw

stability and facies association of early diagenetic mineral assemblages an example from a jurassic ironstone mudstone succession u k abstract sedimentological and petrographic data from two lower liassic ooidal ironstones the frodingham and pecten ironstones and associated mudstones from eastern england have been collected within these ironstones early diagenetic berthierine siderite and minor glauconite have a limited lateral extent associated with an intrabasinal high the market weighton swell this mineral assemblage passes laterally and vertically into mudstones and silty mudstones within which pyrite is the dominant early diagenetic iron mineral the ironstones are stratigraphically condensed having experienced low net sediment accumulation rates and shallow high energy conditions thermodynamic considerations indicate that berthierine and siderite should be stable in anoxic environments where sulfide activity is negligible pyrite is rare within the ironstones suggesting that sulfate reduction was a negligible process during ironstone formation where pyrite is present it postdates berthierine and siderite indicating that sulfate reduction may have been a later process in some beds we propose that berthierine and siderite were precipitated during suboxic diagenesis where sulfate reduction was inhibited and iron reduction was the dominant process of organic matter oxidation suboxic diagenesis resulted from the extended periods of physical and biological sediment reworking during ironstone deposition which favored the oxidation of iron minerals and aerobic egradation and loss of organic matter berthierine formed during early suboxic diagenesis at the expense of detrital clays and iron oxides during later suboxic diagenesis pore water bicarbonate activities increased leading to siderite precipitation early glauconite also formed in places and it seems likely that it formed close to the oxic suboxic interface the predominance of pyrite in the mudstones indicates that sulfate reduction was the major process of organic matter oxidation during early diagenesis

fluvial and lacustrine palaeoenvironments of the miocene siwalik group khaur area northern pakistan the miocene siwalik group upsection the chinji nagri and dhok pathan formations in northern pakistan records fluvial and lacustrine environments within the himalayan foreland basin thick 5 m to tens of metres sandstones are composed of channel bar and fill deposits of low sinuousity 1 08 1 19 single channel meandering and braided rivers which formed large low gradient sediment fans or megafans river flow was dominantly toward the south east and likely perennial palaeohydraulic reconstructions indicate that chinji and dhok pathan rivers were small relative to nagri rivers bankfull channel depths of chinji and dhok pathan rivers were generally 15 m and up to 33 m for nagri rivers widths of channel segments including single channels of meandering rivers and individual channels around braid bars were 320 710 m for chinji rivers 320 1050 m for nagri rivers and 270 340 m for dhok pathan rivers mean channel bed slopes were on the order of 0 000056 0 00011 bankfull discharges of channel segments for chinji and dhok pathan rivers were generally 700 800 m3s 1 with full river discharges possibly up to 2400 m3s 1 bankfull discharges of channel segments for nagri rivers were generally 1800 3500 m3s 1 with discharges of some larger channel segments possibly on the order of 9000 32 000 m3s 1 full river discharges of some of the largest nagri braided rivers may have been twice these values thin decimetres to a few metres sandstones represent deposits of levees crevasse channels and splays floodplain channels and large sheet floods laminated mudstones represent floodplain and lacustrine deposits lakes were both perennial and short lived and likely less than 10 m deep with maximum fetches on the order of a few tens of kilometres trace fossils and body fossils within all facies indicate the former existence of terrestrial vertebrates molluscs bivalves and gastropods arthropods including insects worms aquatic fauna e g fish turtles crocodiles trees bushes grasses and aquatic flora palaeoenvironmental reconstructions are consistent with previous palaeoclimatic interpretations of monsoonal conditions

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

climatic evolution on the southeastern margin of the tethys negev israel from the palaeocene to the early eocene focus on the late palaeocene thermal maximum during the early palaeocene zones p1 to p2 the southeastern tethyan margin experienced a warm and humid climate with high rainfall as indicated by the abundance of kaolinite within marine sedimentary rocks subsequently in zone p2 arid climatic conditions evolved in the coastal basins of the southern tethys margin as indicated by the gradual disappearance of kaolinite and the increased abundance of palygorskite and sepiolite arid climatic conditions persisted during the selandian and thanetian late palaeocene and reached a maximum in the ypresian early eocene during the late palaeocene thermal maximum warm climatic conditions were associated with increased aridity and led to sea surface warming though not bottom water warming as suggested by the planktic 18 o excursion observed at the zomet telalim basin negev israel strongly reduced surface productivity accompanied by unusually light 13 c are associated with the late palaeocene thermal maximum in the negev as well as globally

beyond methane towards a theory for the paleocene eocene thermal maximum abstract extreme global warmth and an abrupt negative carbon isotope excursion during the paleocene eocene thermal maximum petm have been attributed to a massive release of methane hydrate from sediments on the continental slope 1 however the magnitude of the warming 5 to 6 c 2 3 and rise in the depth of the ccd 2 km 4 indicate that the size of the carbon addition was larger than can be accounted for by the methane hydrate hypothesis additional carbon sources associated with methane hydrate release e g pore water venting and turbidite oxidation are also insufficient we find that the oxidation of at least 5000 gt c of organic carbon is the most likely explanation for the observed geochemical and climatic changes during the petm for which there are several potential mechanisms production of thermogenic ch4 and co2 during contact metamorphism associated with the intrusion of a large igneous province into organic rich sediments 5 is capable of supplying large amounts of carbon but is inconsistent with the lack of extensive carbon loss in metamorphosed sediments as well as the abrupt onset and termination of carbon release during the petm a global conflagration of paleocene peatlands 6 highlights a large terrestrial carbon source but massive carbon release by fire seems unlikely as it would require that all peatlands burn at once and then for only 10 to 30 ky in addition this hypothesis requires an order of magnitude increase in the amount of carbon stored in peat the isolation of a large epicontinental seaway by tectonic uplift associated with volcanism or continental collision followed by desiccation and bacterial respiration of the aerated organic matter is another potential mechanism for the rapid release of large amounts of co2 in addition to the oxidation of the underlying marine sediments the desiccation of a major epicontinental seaway would remove a large source of moisture for the continental interior resulting in the desiccation and bacterial oxidation of adjacent terrestrial wetlands

abrupt climate change and transient climates during the paleogene a marine perspective detailed investigations of high latitude sequences recently collected by the ocean drilling program odp indicate that periods of rapid climate change often culminated in brief transient climates with more extreme conditions than subsequent long term climates two examples of such events have been identified in the paleogene the first in latest paleocene time in the middle of a warming trend that began several million years earlier the second in earliest oligocene time near the end of a middle eocene to late oligocene global cooling trend superimposed on the earlier event was a sudden and extreme warming of both high latitude sea surface and deep ocean waters imbedded in the latter transition was an abrupt decline in high latitude temperatures and the brief appearance of a full size continental ice sheet on antarctica in both cases the climate extremes were not stable lasting for less than a few hundred thousand years indicating a temporary or transient climate state geochemical and sedimentolog

iron bacterial and fungal mats bajocian stratotype mid jurassic northern normandy france abstract the oolithe ferrugineuse de bayeux formation is located at the historical bajocian stratotype of sainte honorine des pertes north of bayeux normandy the condensed formation ranges from the base of the humphriesianum zone to the parkinsoni zone and is divided into four beds of decimetric scale three main microfacies are present 1 oncoid rudstones 2 ooid bioclastic packstones and 3 silty burrowed wackestones packstones sedimentation took place in a very quiet environment below the photic zone and below or near the storm wave base the general setting is a distal carbonate ramp its lower part characterized by hemipelagic sedimentation indicated by the presence of planktonic foraminifers the inferred depth is around 100 m free oxygen concentration was low dysaerobic conditions are indicated by a scarcity of benthic macrofauna ferruginous structures are numerous in the first two microfacies and absent in the last hematite staining is not uniform and follows many sedimentary patterns among the more widespread fe structures are perforation infillings with endolithic micro organisms microstromatolites oncoids ooids blisters coatings and hardgrounds these structures can be associated and none are mutually exclusive hematite coated filaments of different sizes and shapes are observed in the micrite matrix the walls of various organisms the calcite crystals associated with the fe cortical laminations the perforations and burrow the hardgrounds and microstromatolites petrographical and sem examinations suggest that the laminated crusts oncoids and hardgrounds are formed by microbial iron mats dominated by filamentous bacteria and fungi seven types of microbes are recognized filaments five morphotypes spheroidal bodies and stalked bodies filamentous microfossils of type 1 to 4 resemble the present day filamentous bacteria beggiatoales and cytophagaceae because of their large diameter and their branching nature filaments of type 5 are possibly filamentous fungi another argument in favor of fungi is the presence of stalked and spheroidal bodies that resemble zoosporangia and oogonia of some oomycota in deep calm and dysaerobic waters many interfaces e g between aerobic and dysaerobic waters are present in the sediments the stability of the soluble reduced state of iron fe 2 is higher at such interfaces and many ferric iron encrusted microbial fossils are observed iron could thus serve as an electron donor for microbial iron oxidation processes other microbial iron deposition pathways are also possible it appears that regardless of geological age paleozoic mesozoic and geographical location the same microbiological mechanisms are probably responsible for the red color in calcareous stratified or unstratified bodies the presence of fossilized iron encrusted bacteria and fungi at interfaces may therefore serve as an indicator of anoxic to dysaerobic conditions in various paleo micro environments

review of cenozoic ooidal ironstones abstract cenozoic tertiary ooidal ironstones coi in 20 districts 39 deposits developed between the equatorial zone and 60 n except for one eocene district in mid southern latitude stratigraphic distribution paleocene oi occur in northern pakistan western siberia southern germany northwestern venezuela and northeastern colombia eocene oi in western siberia southern germany northwestern romania central north africa central west saudi arabia southwestern central africa northwestern venezuela northeastern colombia south central usa and northwestern australia oligocene oi in northwest and west central kazakhstan central denmark and north central iran miocene oi in northwestern venezuela northeastern colombia and southeastern malaysia pliocene oi in southeastern ukraine geotectonic framework ten districts developed in an interior or fractured craton five along the south trending uralian seaway and one along the east trending northern european seaway the south trending trans saharan seaway in or near an early red sea embayment in southeastern malaysia and in northwestern australia ten districts lay near a eratonic margin one along divergent margin and nine along the broad east trending caribbean and tethyan seaways almost all coi accumulated during the paleogene relatively high stand of sea level especially in early and middle eocene time as sea level fell gradually in neogene time coi developed in only three marginal districts including the giant pliocene kerch taman deposit in southeastern ukraine sedimentary environment almost all of the coi developed in deltaic to shallow marine facies these are commonly associated with shoaling upward siliciclastic sequences a few are in mixed siliciclastic carbonate sequences a few coi apparently occurred in fluvial and lacustrine facies some of these may have been reworked from laterite or from marine ironstones sedimentary petrology many coi are less than a few tens of centimeters thick and sporadic the ooids are entirely or predominantly ferric oxide a few contain a minor amount of berthierine 7a only the oldest one northern pakistan contains chamosite 14a more than half of the coi are associated directly or more remotely with glauconite nearly all the coi need much more rigorous examination for both their individual composition and their comparison with older ooidal ironstones

mineralogical and geochemical investigations of the middle eocene ironstones el bahariya depression western desert egypt abstract the middle eocene ironstone succession is located in the northeastern part of el bahariya depression western desert egypt this succession is subdivided into lower and upper sequences and consists of two main shallow marine ironstone facies associations the first is a lagoonal manganiferous mud and fossiliferous ironstone facies association and consists mainly of goethite and hematite detrital minerals quartz rutile and feldspars manganese minerals todorokite psilomelane pyrolusite birnessite aurorite and manjiroite and authigenic clay minerals kaolinite and illite the second is a peritidal microbially mediated stromatolitic and nummulitic ooidal oncoidal ironstone facies association consists of goethite apatite and secondary minerals that include quartz jarosite psilomelane and pyrolusite organic materials such as proteinaceous compounds lipids cellulose and carotenoids were detected in the cortices of the ferruginous ooids and oncoids the marine ironstone facies were exposed to subaerial weathering and subsurface alteration processes the weathering resulted in the formation of lateritic iron ores and paleosols during humid climatic periods the lateritic iron ores consist mainly of colloform goethite hematite and psilomelane the identification of cavity filling sulfate nitrate carbonate and silicate minerals in the marine ironstones and the lateritic iron ore may indicate more recent alteration under arid climatic conditions the subsurface alteration is attributed to the oxidation of sulfides primarily pyrite and weathering of glauconitic clastic rocks in the underlying cenomanian bahariya formation during the interaction with acidic heated groundwater the formation of ferrous and ferric sulfate and silicate minerals and mobilization of trace metals are the products of the alteration process enrichments in ba co k pb and sr are correlated with manganese oxides whereas anomalous p v cr ni zn as mo and u are correlated with iron oxyhydroxides

lower palaeozoic iron oolites and volcanism from a baltoscandian perspective the ordovician iron oolites in baltoscandia are generally geographically extensive but lean 30 ooids sensu bhattacharyya d p 1989 concentrated and lean oolites examples from nubia formation at aswan egypt and significance of the oolite types in ironstone genesis in young t p taylor w e g eds phaneorozoic ironstones geological society special publication 46 93 103 and have undergone minimal reworking and diagenetic alteration the ooids were formed in a normal shallow marine environment around a nucleus of a calcite skeletal grain the oolites were formed during the period of the highest global iron oolite production ever most of the major oolites from this period have been altered in various ways which has obscured their origin the presence of volcanic matter in the baltoscandian and some other european oolites points to a volcanic origin a conclusion further supported by the ree distributions in iron ooids which are close to those in associated volcanic tuffs the global 87sr 86sr curve for phanerozoic seawater in general and for the palaeozoic in particular shows that negative excursions in the sr isotope ratio often coincide with periods of high global iron oolite productivity this temporal coincidence points to a possible causal link iron ooids volcanic ashes and bentonite beds occur in the ordovician of baltoscandia during a negative excursion in the 87sr 86sr curve the variation in the 87sr 86sr ratio in seawater mirrors the balance between the two major sources of sr mid ocean ridge volcanism and continental weathering and indicate that volcanism could be the general cause of most palaeozoic iron oolites two cambrian iron oolites occur in baltoscandia and at least one of them is suggested to be of volcanic origin

john joly 1857 1933 and his determinations of the age of the earth abstract john joly 1857 1933 was one of ireland s most eminent scientists of the late nineteenth and early twentieth centuries who made important discoveries in physics geology and photography he was also a respected and influential diplomat for trinity college dublin and various irish organizations including the royal dublin society measuring the age of the earth occupied his mind for some considerable time a problem he was to address using a diverse range of methods his sodium method of 1899 for which he is best known was hailed by many as revolutionary but it was later superseded by other techniques including the utilization of radiometric dating methodologies although joly himself carried out much research in this area he never fully accepted the large age estimates that radioactivity yielded nevertheless joly s work in geochronology was innovative and important for it challenged earlier methods of arriving at the earth s age particularly those of lord kelvin although his findings and conclusions were later discredited he should be remembered for his valuable contribution to this important and fundamental debate in the geological sciences

the blast in the past the rapidity and amount of carbon being released through human agency have been thought to be unprecedented not so it emerges from the evidence of anomalies in the ratios of carbon isotopes in an ocean core it seems that around 55 million years ago there was an equivalently swift and massive blast of carbon into the ocean and atmosphere the source was probably methane hydrates that are usually locked up in huge deposits on continental shelves

lower ordovician iron ooids and associated oolitic clays in russia and estonia a clue to the origin of iron oolites abstract on the baltic platform a lower llanvirn ordovician iron oolite can be traced for a distance of 1200 km from norway to the east of lake ladoga in russia this oolite is usually thin seldom exceeding 0 5 m and is dominated by goethite limonite type ooids the easternmost part of the oolite from tallinn to ladoga is examined here the oolitic limestone is intercalated with oolitic clay beds the mineralogical chemical and isotopic composition and other indicators point to volcanic ash being the source for the clay similarities in ree distribution patterns and immobile element contents between ooids and the oolitic clay suggest that the ooids were also formed from volcanic ash

sedimentology of a sandur formed by multiple jokulhlaups kverkfjoll iceland abstract the kverkfjoll sandur in north iceland is the furthest upstream of a suite of fluvial landforms extending for 200 km along the jokulsa a fjollum river incision of the sandur exposes over 3 km of sedimentary sections up to 15 m in height a sandur wide well bedded succession of matrix rich cobble gravel and pebble granule gravel with individual beds 0 2 to 0 5 m thick indicates that the sandur is primarily the product of sandur wide sheet floods with sediment rich hyperconcentrated flows and also some debris flows and channelised turbulent flows this interpretation is evidenced by bedded hyperconcentrated flow deposits occurring as laterally extensive tabular depositional units that dominate the entire sandur reflecting the unconfined nature of the flow clast supported boulder gravel units interpreted as the product of macroturbulent flow occur in relatively narrow but deep channels the sedimentary succession is interpreted as the product of at least six volcanically generated catastrophic outburst floods jokulhlaups during the little ice age the sedimentology of these little ice age flood deposits on a small high gradient sandur contrasts strongly with the deposits of volcanically generated jokulhlaups on large low gradient coastal sandar and sandar associated with retreating glaciers which have been the basis for most previous models of jokulhlaup sedimentation

a depositional model for the liassic minette ironstones luxemburg and france in comparison with other phanerozoic oolitic ironstones

a transient rise in tropical sea surface temperature during the paleocene eocene thermal maximum the paleocene eocene thermal maximum petm has been attributed to a rapid rise in greenhouse gas levels if so warming should have occurred at all latitudes although amplified toward the poles existing records reveal an increase in high latitude sea surface temperatures ssts 8 to 10 c and in bottom water temperatures 4 to 5 c to date however the character of the tropical sst response during this event remains unconstrained here we address this deficiency by using paired oxygen isotope and minor element magnesium calcium ratios of planktonic foraminifera from a tropical pacific core to estimate changes in sst using mixed layer foraminifera we found that the combined proxies imply a 4 to 5 c rise in pacific sst during the petm these results would necessitate a rise in atmospheric pco 2 to levels three to four times as high as those estimated for the late paleocene

the significance of incision and fluvial sedimentation in the basal white river group eocene oligocene badlands of south dakota u s a abstract a newly defined lithostratigraphic unit the chamberlain pass formation cpf records the initial episode of incision fluvial sedimentation and pedogenesis in sw south dakota following the retreat of the cretaceous interior seaway the cpf is middle to late eocene in age and consists of fluvial sandstone and mudstone pedogenic modification of the unit has created a distinctive pedostratigraphic unit the interior paleosol series the cpf thickens from west to east achieving a maximum channel belt thickness of 11 m paleoflow data indicate that deposition of the cpf was restricted to a fault controlled basin southeast of the black hills uplift sandstones in the cpf were derived from a recycled sedimentary rock source area to the west in contrast sandstones in the overlying chadron formation late eocene had a variety of sources including the precambrian core rocks of the black hills uplift deposition of the cpf brackets four significant paleogene changes in baselevel that occurred in this region these events were 1 late cretaceous to middle eocene relative baselevel fall weathering and erosion of the cretaceous pierre shale to form the yellow mounds paleosol and fluvial incision 2 middle to late eocene relative baselevel rise and deposition of the cpf 3 late eocene relative baselevel fall weathering and erosion of the cpf to form the interior paleosol and fluvial incision and 4 late eocene to oligocene relative baselevel rise and deposition of the chadron formation the first event was probably eustatic the second was controlled primarily by local subsidence in a fault bounded basin the third records the tectonic uplift and unroofing of the black hills and the fourth event was probably primarily controlled by eustasy but other factors may have been important

environmental perturbation in the southern tethys across the paleocene eocene boundary dababiya egypt foraminiferal and clay mineral records foraminiferal and clay mineral records were studied in the upper paleocene to lower eocene dababiya section egypt this section hosts the gssp for the paleocene eocene boundary and as such provides an expanded and relatively continuous record across the paleocene eocene thermal maximum petm deposition of illite smectite clay minerals is interpreted as a result of warm and arid conditions in the southern tethys during the latest paleocene benthic foraminiferal assemblages are indicative of seasonal variation of oxygen and food levels at the seafloor a sea level fall occurred in the latest paleocene followed by a rise in the earliest eocene foraminiferal diversity and densities decreased strongly at the p e boundary coinciding with the level of global extinction of benthic foraminifera bee and start of the carbon isotope excursion cie and petm in the lower cie the seafloor of the stratified basin remained nearly permanently anoxic and azoic a sudden increase in mixed clay minerals kaolinite and others suggests that warm and perennial humid conditions prevailed on the continent high levels of toc and phosphathic concretions in the middle cie are evidence for increased organic fluxes to the sea floor related to upwelling and to augmented continental runoff low densities of opportunistic taxa appeared indicating occasional ephemeral oxygenation and repopulation of the benthic environment the planktic community diversified although conditions remained poor for deep dwelling taxa an increase in illite smectite dominated clay association is considered to mark the return of a seasonal signature on climatic conditions during the late cie environmental conditions changed to seasonally fluctuating mesotrophic conditions and diverse and rich benthic and planktic foraminiferal communities developed post cie planktic faunas consisted of both deep and shallow dwelling taxa and buliminid dominated benthic assemblages reflect fluctuating mesotrophic conditions the frequent environmental perturbations during the cie petm at dababiya provided a rather specialized group of foraminiferal taxa i e anomalinoides aegyptiacus the opportunity to repopulate survive and subsequently dominate by a hypothesized capacity to switch to an alternative life strategy population dynamics habitat shift or different metabolic pathway the faunal record of dababiya provides insight into the cause and development of the bee various severe global changes during the petm e g ocean circulation caco3 dissolution productivity and temperature changes disturbed a wide range of environments on a geologically brief timescale explaining together the geographically and temporally variable character of the bee this allowed a number of specific but different foraminiferal assemblages composed of stress tolerant and opportunistic taxa to be successful during and after the periods of environmental perturbations associated with the petm

coupled greenhouse warming and deep sea acidification in the middle eocene 1 the middle eocene climatic optimum meco is an enigmatic warming event that represents an abrupt reversal in long term cooling through the eocene in order to further assess the timing and nature of this event we have assembled stable isotope and calcium carbonate concentration records from multiple deep sea drilling project and ocean drilling program sites for the time interval between 43 and 38 ma revised stratigraphy at several sites and compilation of 18o records place peak warming during the meco event at 40 0 ma chron c18n 2n the identification of the 18o excursion at sites in different geographic regions indicates that the climatic effects of this event were globally extensive the total duration of the meco event is estimated at 500 ka with peak warming lasting 100 ka assuming minimal glaciation in the late middle eocene 4 6 c total warming of both surface and deep waters is estimated during the meco at the study sites the interval of peak warming at 40 0 ma also coincided with a worldwide decline in carbonate accumulation at sites below 3000 m depth reflecting a temporary shoaling of the calcite compensation depth the synchroneity of deep water acidification and globally extensive warming makes a persuasive argument that the meco event was linked to a transient increase in atmospheric pco2 the results of this study confirm previous reports of significant climatic instability during the middle eocene furthermore the direct link between warming and changes in the carbonate chemistry of the deep ocean provides strong evidence that changes in greenhouse gas concentrations exerted a primary control on short term climate variability during this critical period of eocene climate evolution

modern and palaeozoic iron ooids a similar volcanic origin abstract the discovery of an unconsolidated deposit of iron ooids of a kind not previously described and in the vicinity of a volcanic island in indonesia has shed new light on the genesis of many ancient iron oolites the discovery shows that iron ooid formation is geologically a rapid process the ooids form by chemical precipitation of cryptocrystalline iron oxyhydroxides on available grains on the seafloor from seawater enriched with fe al and si the enrichment can be a result of hydrothermal fluids volcanic ash falls into shallow basins or rapid weathering of fresh volcanic rocks ordovician iron ooids from northern europe are strikingly similar to the modern ooids in chemical composition ree distributions and internal structures the differences in mineralogy can be explained as diagenetic transformation reactions under different environments a model for the formation of the ordovician iron ooids in northern europe from volcaniclastic material is presented which could be applicable to other ancient oolites in the world

short paper a standardized model for tethyan tertiary carbonate ramps low latitude carbonates in massive and clinoform bedded sheets termed ramps occur throughout the tertiary tethyan realm and are characterized by recurring biofacies usually including large foraminifera rhodolithic algae coralgal patch reef and gastropod dominated sequences all can be interpreted broadly within a standardized tertiary carbonate ramp model biota can be used to define precise palaeobathymetric zones which have a predictive utility in palaeoenvironmental modelling especially where data are limited the carbonate ramp model of earlier authors has been elaborated by read 1982 and ramp formation occurs mostly in passive margin and extensional tectonic settings ramps are characterized by slope gradients of less than 1 degree and once established are conservative to change much use has been made of the ramp model for palaeozoic and mesozoic lithofacies modelling in contrast published work on cenozoic ramps is limited however tethyan ramps are particularly widespread and extend tens to hundreds of kilometres along strike and occupy tens of kilometres of slope many studies have dealt with cenozoic ramp associations and sequences e g pedley 1983 reiss hottinger 1984 purser 1973 and have demonstrated the diversity of biotal and sediment detail but without ascribing them to a ramp model biota were quick to adapt to the tertiary environments left vacant after the k t boundary extinction events new genera of foraminifera mollusca bryozoa and echinoder mata rapidly replaced the extinct forms in bursts of innovative opportunism codiacean algae rhodophyta and marine angiosperms were equally adaptive colonizers of the carbonate platforms novel biofacies associations were derived from

cool climate or warm spike lateritic bauxites at high latitudes abstractlaterites and bauxites and their associated ultisols and oxisols are widespread in warm wet climates today and their spread to high latitudes has been attributed to episodes of past global warming bauxitic paleosols from the early eocene monaro volcanics of southeastern australia have been claimed as exceptions formed in a cool wet climate reexamination and chemical analysis of a sequence of intrabasaltic paleosols in the bega no 7 core of radiometrically dated monaro volcanics now show highly variable paleotemperature and precipitation the core includes 53 successive paleosols mostly nonbauxitic but bauxitic paleosols reveal local spikes in warmth and precipitation coincident with early eocene 55 52 51 and 48 ma global spikes of warmth precipitation and high atmospheric co2 these bauxitic paleosols thus formed in warm wet not cool dry climates and their poleward spread coincided with global greenhouse spikes

microbial structures in oolitic iron formations ferriferous ooids and microoncoids occur in many sedimentary iron formations these ferriferous coated grains are found in fine grained carbonate rich groundmasses iron mineral encrusted microbiota are observed in both the coated grains and the groundmass the branching nature and other morphological features of the microorganisms suggest fungal origins for the oolitic iron ores particularly of the lower jurassic lorraine minette the similarity of the microbial structures in coated grains and their groundmasses suggests that both had developed within microbial mats growing under calm environmental conditions the contribution of stromatolitic marine fungal mats to the fast extraction and immobilization of iron and thus to the genesis of iron ores is demonstrated observations on well preserved freshwater derived fungal stromatolites of the tertiary and laboratory experiments with organotrophic fungal mats confirm the findings on the jurassic and imply a general role of microorganisms in the formation of such deposits

uranium isotopic evidence for the origin of the bahariya iron deposits egypt abstract the economic iron ore deposits of egypt are located at bahariya oasis in the lower middle eocene limestone the main iron minerals are goethite hematite siderite pyrite and jarosite manganese minerals are pyrolusite and manganite gangue minerals are barite glauconite gibbsite alunite quartz halite kaolinite illite smectite palygorskite and halloysite geochemical comparison between the ore and the nubia sandstone showed that the ore is depleted in the residual elements al ti v and ni and enriched in the mobile elements fe mn zn ba and u which indicates that the bahariya iron ore is not a lateritic deposit despite the deep weathering in this area on the other hand the nubia sandstone showed depletion in the mobile elements which demonstrates the leaching process in the nubia aquifer the presence of such indicator minerals as jarosite alunite glauconite gibbsite palygorskite and halloysite indicate that the ore was deposited under strong acidic conditions in fresh water isotopic analyses of the uranium in the amorphous and crystalline phases of the ore in the country rocks and dissolved in the nubia aquifer water all support the conclusion that u and fe were precipitated together from warm ascending groundwater u and fe display strong co variation in the ore and the 234u 238u activity ratio of the newly precipitated u in the country rock and the leached component of u in the groundwater are identical there is only slightly more uranium in the amorphous phase than in the crystalline and only a slightly lower 234u 238u activity ratio suggesting that the iron in the two phases have a similar origin comparison of the excess 234u in the water and in the total ore leads to the conclusion that the precipitation of the u and by inference the iron occurred within the last million years however that both precipitation and leaching of u have occurred over the last 300 000 years is evidenced by the extreme 230th 234u disequilibria observed in some of the samples some of the amorphous depositional events have been very recent perhaps within the last 10 000 years

sequence stratigraphy and marine to nonmarine facies architecture of foreland basin strata book cliffs utah u s a the desert member of the blackhawk formation and the castlegate sandstone in the book cliffs of utah and colorado were analyzed to develop a model of sequence stratigraphy and facies architecture in foreland basins stratal architecture of these rocks is controlled by two regionally extensive surfaces of incision and subaerial exposure interpreted as major sequence boundaries and at least six surfaces of incision and subaerial exposure with more limited lateral extent interpreted as minor sequence boundaries each sequence boundary is a regionally correlatable single surface major sequence boundaries can be traced from marine into proximal alluvial plain environments sequence boundaries have different physical expressions depending upon where in the basin they are observed strata beneath sequence boundaries are unrelated to strata above and time lines cannot be carried across these boundaries flooding surfaces called parasequence or parasequence set boundaries also exert an important control on facies architecture based on parasequence stacking patterns position of sequence boundaries and facies associations the desert member and castlegate sandstone have been divided into sequences with durations of 200 000 to 300 000 yr there are an order of magnitude more sequences in this interval than are predicted by the global sea level chart of haq et al 1988 the major sequences have been divided into the following systems tracts or sequence sets 1 grassy highstand sequence set below the desert sequence boundary named for the grassy member of the blackhawk formation 2 desert lowstand transgressive and highstand systems tracts between the desert and castlegate sequence boundaries 3 castlegate lowstand sequence set resting on the castlegate sequence boundary and 4 castlegate transgressive systems tract parasequence stacking patterns suggest that the grassy highstand sequence set and the desert highstand systems tract were deposited during a relative rise in baselevel the grassy highstand sequence set is punctuated by minor relative falls in baselevel both of these stratal units contain thick

oolitic ironstone of the cretaceous western interior seaway east central utah abstract a thin but distinctive red weathered oolitic ironstone occurs 7272within the upper cretaceous mancos shale of east central utah it is characterized by a grain supported ooid rich lithology containing iron clay berthierine muscovite hematite goethite and carbonate minerals around clastic nuclei associated grains of phosphatic material bone and fish teeth are common admixed with fossil hash and wood pieces internal structures within the mappable oolitic ironstone bodies include channel scours cross bedding contorted bedding load structures mud rip up clasts and marine trace fossils the oolitic ironstone is encased within the mancos shale and cannot be traced laterally however four additional facies occur in vertical succession with the ironstone inoceramus mounds siltstone shale fine grained channel sandstone and coarse grained lithic sandstone the sedimentologic features of the oolitic ironstone and its associated facies indicate a prodelta environment influenced by river dominated flooding in the delta front environment providing sand fed through small channels and by fluctuating or alternating sea floor bottom conditions due to periodic storm or current action the oolitic ironstone is inferred to have formed as shoals within the inner shelf like setting a key factor in formation of the oolitic ironstones is eustatic control in the western interior seaway the ironstone was deposited during a relative sea level low and then winnowed during a transgressive rise to create a condensed section thus the interval is an important stratigraphic marker in an otherwise monotonous section of shale and it represents a parasequence boundary expression in offshore deposits where eustatic influences are commonly difficult to recognize

modern iron ooids from a shallow marine volcanic setting mahengetang indonesia an unconsolidated submarine deposit of iron ooids and pisoids located offshore the volcanic island mahengetang indonesia is described herein the deposit occurs in a shallow marine setting in an area characterized by venting of hydrothermal fluids and expulsion of gas across the sediment water interface the ooid deposit is essentially pure to a minimum depth of 0 5 m and covers an area of at least 1000 m 2 ooids are composed of concentric accretionary layers of limonite admixed with amorphous silica precipitated around andesitic rock fragments the smallest layers forming the ooids are about 10 min thickness the iron rich precipitate is 50 iron by weight ooid formation is likely promoted by precipitation of iron and silica from exhalative fluids rising up through the substrate concentric layering is thought to result from constant agitation of ooids associated with currents and expulsion of gas from the sediment

depositional history of the eocene chumstick formation implications of tectonic partitioning for the history of the leavenworth and entiat eagle creek fault systems washington the chumstick basin opened as an extensional half graben prior to 51 ma and was subsequently modified by two episodes of tectonic partitioning of drainage prior to basin deformation initially westward flowing fluvial systems formed a unified depositional system with the swauk basin tectonic partitioning of drainage at 51 49 ma and at 44 42 ma was controlled by localized uplift on the leavenworth lfz eagle creek ecfz and entiat efz fault zones and led in each instance to the truncation of regional depositional systems modification and reversal of paleoflow and internal drainage relief on the lfz at 51 49 ma may be the result of isostatic uplift of the extensional footwall producing the swauk and chumstick basins as a pair of west facing half grabens the earliest convincing evidence for the onset of oblique slip in the region is at about 48 ma folding in the swauk basin or about 44 42 ma probable transpressive uplift at left stepping bends of the lfz development of a transtensional step over basin between the ecfz and efz horsetail splays in the ecfz and possible flower structures in the lfz and ecfz in the chumstick basin each episode of tectonic partitioning was followed by proximal onlap and overtopping of fault zones to reestablish regional flow systems the chumstick formation was deformed by dextral transpression between 37 34 ma and is unconformably overlain by the oligocene wenatchee formation the chumstick basin is an example of an extensional basin modified by subsequent strike slip tectonics thus caution should be used in applying idealized basin models