new age constraints for the salamanca formation and lower rio chico group in the western san jorge basin patagonia argentina implications for cretaceous paleogene extinction recovery and land mammal age correlations the salamanca formation of the san jorge basin patagonia argentina preserves critical records of southern hemisphere paleocene biotas but its age remains poorly resolved with estimates ranging from late cretaceous to middle paleocene we report a multi disciplinary geochronologic study of the salamanca formation and overlying rio chico group in the western part of the basin new constraints include 1 an 40ar 39ar age determination of 67 31 0 55 ma from a basalt flow underlying the salamanca formation 2 micropaleontological results indicating an early danian age for the base of the salamanca formation 3 laser ablation hr mc icp ms high resolution multi collector inductively coupled plasma mass spectrometry u pb ages and a high resolution tims thermal ionization mass spectrometry age of 61 984 0 041 0 074 0 100 ma for zircons from volcanic ash beds in the penas coloradas formation rio chico group and 4 paleomagnetic results indicating that the salamanca formation in this area is entirely of normal polarity with reversals occurring in the rio chico group placing these new age constraints in the context of a sequence stratigraphic model for the basin we correlate the salamanca formation in the study area to chrons c29n and c28n with the banco negro inferior bni a mature widespread fossiliferous paleosol unit at the top of the salamanca formation corresponding to the top of chron c28n the diverse paleobotanical assemblages from this area are here assigned to c28n 64 67 63 49 ma 2 3 million years older than previously thought adding to growing evidence for rapid southern hemisphere floral recovery after the cretaceous paleogene extinction important peligran and carodnia zone vertebrate fossil assemblages from coastal bni and penas coloradas exposures are likely older than previously thought and correlate to the early torrejonian and early tiffanian north american land mammal ages respectively

abyssal circulation and benthic foraminiferal changes near the paleocene eocene boundary a major change in cenozoic deep sea benthic foraminifera occurred in the atlantic indian and pacific oceans near the paleocene eocene boundary benthic foraminiferal abundance changes began at about 61 5 ma at pacific deep sea drilling project dsdp site 577 a major extinction event followed at 58 57 ma between zones p6a and p6b and a series of first appearances continued until circa 55 5 ma zone p6c these faunal changes occurred during a 6 c warming of pacific bottom water and may indicate that the primary cause was changing temperature other potential causes of the faunal turnover include global changes in surface ocean productivity and changing bottom water source regions comparison of benthic and planktonic 13c records requires no change in the ratio of oceanic phosphorous to carbon during the late paleocene to early eocene which weakens the case for but does not disprove a change in surface ocean productivity at this time interbasinal comparisons of benthic foraminiferal 13c records document that water with high 13c values filled the cape basin during the late paleocene and possibly the early eocene circa 61 57 ma but apparently did not extend into the western basins of the atlantic this pattern suggests a supply of antarctic source water for the cape basin and possible tectonic isolation of the western atlantic basins during at least part of the late paleocene carbon isotope comparisons show that bottom water supply to the cape basin was reduced in the early eocene eolian grain size data suggest that a decrease in zonal wind intensity occurred at the end of the paleocene these late paleocene climatic changes bottom water warming and decreased wind intensity correspond with evidence for an important global tectonic reorganization and extensive subaerial volcanism which may have contributed to climatic warming through increased supply of co2

dissociation of oceanic methane hydrate as a cause of the carbon isotope excursion at the end of the paleocene isotopic records across the latest paleocene thermal maximum lptm indicate that bottom water temperature increased by more than 4 c during a brief time interval 104 years of the latest paleocene 55 6 ma there also was a coeval 2 to 3 excursion in the 13c of the ocean atmosphere inorganic carbon reservoir given the large mass of this reservoir a rapid 13c shift of this magnitude is difficult to explain within the context of conventional hypotheses for changing the mean carbon isotope composition of the ocean and atmosphere however a direct consequence of warming bottom water temperature from 11 to 15 c over 104 years would be a significant change in sediment thermal gradients and dissociation of oceanic ch4 hydrate at locations with intermediate water depths in terms of the present day oceanic ch4 hydrate reservoir thermal dissociation of oceanic ch4 hydrate during the lptm could have released greater than 1 1 to 2 1 1018 g of carbon with a 13c of approximately 60 the release and subsequent oxidation of this amount of carbon is sufficient to explain a 2 to 3 excursion in 13c across the lptm fate of ch4 in oceanic hydrates must be considered in developing models of the climatic and paleoceanographic regimes that operated during the lptm

paleoceanography a review for the gsa centennial the central problem of paleoceanography is the history of the circulation of the ocean although speculation about ancient oceanic circulation goes back to the past century the field of paleoceanography was founded in the 1950s as oxygen isotope studies suggested that oceanic deep waters were warmer in the past than they are today extensive coring of deep sea sediments by numerous expeditions after world war ii was followed by the ocean drilling programs providing a rich data base paleoceanographic interpretations have tried to explain the most obvious changes in sea floor sediments and their contained fossils changing paleotemperatures indicated by oxygen isotopes fluctuations in the calcium carbonate compensation depth accumulations of organic carbon rich sediments and the unexpected abundance of hiatuses in a setting which had been thought to be the ultimate sedimentary sink the result has been the intriguing discovery that although the positions and circulation of the major surface gyres is generally stable the deep circulation of the ocean may reverse on a variety of time scales it has been suggested that formation of north atlantic deep water which causes the uneven distribution of nutrients alkalinity and oxygen in the deep sea today may have been replaced by formation of north pacific deep water during the last deglaciation reversing the concentration gradients of nutrients alkalinity and oxygen on a longer time scale the present general circulation which is dominated by production of oxygen rich cold deep water in the subpolar regions today may have replaced a pre oligocene general circulation in which warm saline oxygen poor deep waters were formed in warm seas in the arid zones paleoceanography is still in its infancy many new clues to the history of the ocean are being discovered and many new ideas about conditions in the past are being developed the beginning of the next century should see continuing rapid growth and maturation in this exciting new field

tree ring δ18o from southeast china reveals monsoon precipitation and enso variability abstract considerable advances have been made in use of tree ring 18o for climate reconstructions in southeast china the east asian summer monsoon region however the relationships among tree ring cellulose 18o 18ocell local hydroclimate precipitation 18o 18opre and el nino southern oscillation enso have not yet been fully resolved the usual interpretation has been that local hydroclimate influences 18ocell through both the amount effect on 18opre and evaporative enrichment but it cannot fully explain the high inter site correlation of 18ocell chronologies or their response pattern to enso in this study we use a newly developed 18ocell chronology of pinus massoniana from a water stressed site in zhejiang province in combination with another three 18ocell chronologies in southeast china to investigate their climatic implications from a regional perspective the results show that besides local hydroclimate 18opre is also significantly correlated with 18ocell but with different effects spatially homogeneous 18opre variation causes high spatial correlations among 18ocell from different sites analyses show that enso variations are responsible for the large scale common signals in 18ocell by modulating 18opre therefore combining 18ocell chronologies from different locations can enhance enso signals which provides us new opportunities to reconstruct paleo enso activities furthermore eliminating the part of enso signal that is not related to the growing season hydroclimate from 18ocell can increase the explained variance of observed values these findings provide a guide for future optimized enso and local paleoclimate reconstructions using 18ocell

cool kaolins in finland we use d h and 18o 16o ratios to explore the age of kaolins on the fennoscandian shield sub cretaceous kaolins in southern scandinavia have isotopic compositions indicative of weathering under warm mean annual temperatures mats of 15 c deep kaolins on the shield surface in finland previously also have been regarded as products of humid tropical weathering of mesoproterozoic to eocene age new oxygen and hydrogen isotope ratios indicate however weathering by cool groundwater under mats of 13 15 c isotope ratios are also not consistent with deep 1 km burial by cover rocks indicating that a very old age for the weathering is unlikely palaeotemperatures are below cretaceous mats yet substantially above plio pleistocene mats comparisons with palaeotemperatures in n europe and around the arctic ocean indicate that the finnish kaolins developed on the shield surface in the palaeogene or alternatively miocene deep weathering was selectively developed in highly fractured shield rocks and took place in response to latest cretaceous and palaeogene uplift and after stripping of palaeozoic cover rocks the cool kaolins in finland indicate that previous routine attributions of kaolinitic weathering products in the geological record to humid tropical environments should be closely scrutinised

coupled and decoupled responses of continental and marine organic sedimentary systems through the paleocene eocene thermal maximum new jersey margin usa 1 the flux of sediment and organic carbon from continents to the coastal ocean is an important factor governing organic burial in coastal sediments and these systems preserve important records of environmental and biogeochemical conditions during past global change events burial of organic materials in coastal systems can be promoted by chemical resilience or through protection by association with mineral surfaces but the role and influence of these processes on organic records from ancient sediments is poorly known we studied sediment and organic matter burial as particulate organic matter pom and mineral bound organic matter mom in near shore marine sediments from the wilson lake core new jersey usa that span the paleocene eocene thermal maximum petm a climatic perturbation 55 9 myr ago our results show that distinct pom and mom fractions can be isolated from sediments both fractions appear to be dominated by terrestrial material but pom consisted primarily of recently synthesized material whereas mom included a significant fraction of pre aged organic matter from soils or ancient sediments variation in organic burial through the petm is associated with changes in inorganic nitrogen burial clay mineralogy and clastic grain size that we associate with enhanced continental weathering erosion and redeposition of ancient kaolinites and eustatic sea level variation respectively these results provide a new perspective on factors governing carbon burial and carbon isotope records in ancient marine margin settings and offer information on rate and phasing of late paleocene early eocene earth system changes that may constrain interpretations of the cause of the petm climate change event

shallow marine response to global climate change during the paleocene eocene thermal maximum salisbury embayment usa the paleocene eocene thermal maximum petm was an interval of extreme warmth that caused disruption of marine and terrestrial ecosystems on a global scale here we examine the sediments flora and fauna from an expanded section at mattawoman creek billingsley road mcbr in maryland and explore the impact of warming at a nearshore shallow marine 30 100 m water depth site in the salisbury embayment observations indicate that at the onset of the petm the site abruptly shifted from an open marine to prodelta setting with increased terrestrial and fresh water input changes in microfossil biota suggest stratification of the water column and low oxygen bottom water conditions in the earliest eocene formation of authigenic carbonate through microbial diagenesis produced an unusually large bulk carbon isotope shift while the magnitude of the corresponding signal from benthic foraminifera is similar to that at other marine sites this proves that the landward increase in the magnitude of the carbon isotope excursion measured in bulk sediment is not due to a near instantaneous release of 12c enriched co2 we conclude that the mcbr site records nearshore marine response to global climate change that can be used as an analog for modern coastal response to global warming

investigating high zircon concentrations in the fine fraction of stream sediments draining the pan african dahomeyan terrane in nigeria sixteen hundred stream sediments 150 m fraction collected during regional geochemical surveys in central and sw nigeria have high median and maximum concentrations of zr that exceed corresponding zr concentrations found in stream sediments collected from elsewhere in the world with similar bedrock geology x ray diffraction studies on a sub set of the analysed stream sediments showed that zr is predominantly found in detrital zircon grains however the main proximal source rocks pan african older granites of nigeria and their proterozoic migmatitic gneiss country rocks are not enriched in zircon or zr nevertheless u pb la icp ms dating with cathodoluminescence imaging on detrital zircons both from stream sediment samples and underlying pan african older granites confirms a local bedrock source for the stream sediment zircons a combination of tropical chemical weathering and continuous physical weathering both by wet season flash flooding and dry season unidirectional winds are interpreted to have effectively broken down bedrock silicate minerals and removed much of the resultant clay phases thereby increasing the zr contents in stream sediments the strong correlation between winnowing index th al and zr concentration across the study area support this interpretation therefore anomalous high values of zr as well as other elements concentrated in resistant heavy minerals in nigeria s streams may not reflect proximal bedrock concentrations of these elements this conclusion has important implications for using stream sediment chemistry as an exploration tool in nigeria for primary metal deposits associated with heavy minerals

abrupt increase in seasonal extreme precipitation at the paleocene eocene boundary a prominent increase in atmospheric co at the paleocene eocene boundary ca 55 ma led to the warmest earth of the cenozoic for similar to 100 k y high resolution studies of continental flood plain sediment records across this boundary can provide crucial information on how the hydrological cycle responds to rapidly changing co2 here we show from continental records across the paleocene eocene boundary in the spanish pyrenees a subtropical paleosetting that during the early most intense phase of co2 rise normal semiarid coastal plains with few river channels of 10 200 m width were abruptly replaced by a vast conglomeratic braid plain covering at least 500 km 2 and most likely more than 2000 km 2 this braid plain is interpreted as the proximal parts of a megafan carbonate nodules in the megafan deposits attest to seasonally dry periods and together with megafan development imply a dramatic increase in seasonal rain and an increased intra annual humidity gradient the megafan formed over a few thousand years to similar to 10 k y directly after the paleocene eocene boundary only repeated severe floods and rainstorms could have contributed the water energy required to transport the enormous amounts of large boulders and gravel of the megafan during this short time span the findings represent evidence for considerable changes in regional hydrological cycles following greenhouse gas emissions less

oxygen isotope evidence of climate change from pedogenic clay minerals in the himalayan molasse abstract in this study we examine the oxygen isotope ratios of smectite and kaolinite in a stratigraphic sequence of paleosols in the siwalik himalayan molasse on the potwar plateau northern pakistan there is a 3 4 o increase in the smectite 18 o values synchronous with a 3 5 o increase in 18 o values of pedogenic calcite at 8 5 6 5 ma previously observed by quade et al 1989 the covariation of the 18 o values of smectite with calcite gd 18 o values through time strongly suggests a pedogenic origin of smectite and that its 18 o values reflect the oxygen isotope ratio of the soil water present during pedogenesis these data show that the 18 o values of clay minerals in paleosols in aggrading sedimentary sequences are viable paleoclimate indicators kaolinite 18 o values are similar to smectite 18 o values as would be expected for pedogenic kaolinite but there is greater variation in these data which we attribute to incomplete mineral separation the measured permil oxygen isotope fractionation between calcite and smectite within individual paleosols is on average 3 o higher than the equilibrium fractionation this isotopic disequilibrium can be explained by the calcite forming predominantly during the dry winter season and the smectite forming predominantly during the wet summer season the synchronous 3 5 o increase in oxygen isotope ratios of smectite and calcite at 8 5 6 5 ma indicates that this 18 o 16 o increase is not due to diagenesis but rather results from a climate change the most likely causes of the 18 o 16 o increase in smectite and calcite are either increased aridity resulting in increased soil water evaporation thus 18 o enrichment and or a change from more continental to more marine sourced precipitation the tibetan plateau which is suggested to have undergone rapid uplift around 8 ma e g harrison et al 1992 may have acted as an effective orographic barrier to low 18 o precipitation originating from central asia causing higher 18 o values of the precipitation falling on the potwar plateau currently it is impossible to distinguish between these two potential causes of the 18 o 16 o increase at 8 5 6 5 ma but these clay mineral 18 o values support that there was a significant climate change in this region

palaeoclimatic interpretation of clay minerals in marine deposits an outlook from the continental origin abstract as distribution of clay minerals in modern oceans seems to be controlled by contemporary climates marine clays in ancient deposits have been widely used to reconstruct palaeoclimates in this review we examine this question mainly from the continental origin of the clay minerals and show the difficulties of retrospective analysis of the influence of climate on common marine deposits we examine successively how soils develop and behave are reworked and palaeoweatherings are preserved focusing the review on kaolinitic soils indicative of tropical wet climates several stages intervene between the time of clay mineral development in soils and their final deposition in the basin 1 the persistence over geological times of huge amounts of kaolinitic palaeoweathering materials in the landscapes may seriously alter the palaeoclimatic signal of kaolinite in the sedimentary record although the kaolinite deposited in recent sediments of the world oceans is consistent with wet climatic zones this is mainly because the major kaolinitic and bauxitic palaeosurfaces coincide with the tropical areas where kaolinite is still developing at present 2 possible development of deep kaolinitic profiles at high latitudes and cold conditions under co 2 enriched palaeoatmospheres or even by unusual acidic weathering linked with dry climates is misleading palaeoenvironments for palaeoclimatic reconstruction 3 erosion and transport processes always cloud the signal to some extent because frequently erosion products from the bedrock and different soil horizons will be mixed and major drainage systems may include soils of different climatic zones 4 the arrival of the soil clay assemblages in the basin inevitably lags against their formation on the continent and may occur several million years after formation of the soils on the continent and climate may have considerably changed at that time it is pointed out that sedimentologists and palaeoclimatologists should consider the complexity of the relations between soil and sedimentary clay minerals soil formation rates are slow and therefore the resolution of the palaeoclimatic record in marine clay may not be closer than 1 or 2 ma at present the palaeoclimatic interpretations of marine clay assemblages are yielding at best nothing more than rather broad palaeoclimatic information this approach cannot achieve the same degree of resolution as other techniques such as isotope or microfossil studies clay mineral assemblages may provide integrated records of overall climatic impacts whereas other techniques are more likely to reveal local or temporary climates

mineralogical evidence for warm and dry climatic conditions in the neo tethys eastern turkey during the middle eocene abstract minerals in stratigraphic sections are valuable tools for reconstructing past environmental conditions given the state of preservation of clay minerals it is possible to determine under what conditions they formed which provides clues about continental weathering inherited minerals and geochemical conditions in the water column or pore waters neoformed or transformed of the sedimentary environment this study presents new mineralogical and chemical data from the baskil section a well preserved middle eocene neo tethys sequence from eastern turkey greater terrigenous input is marked by the increase of silicate minerals e g phyllosilicates quartz and albite in the section from 40 5 to 40 ma which diluted the marine carbonate content this period is correlative with the global middle eocene climatic optimum meco event authigenic palygorskite increased from the middle to the uppermost portion 40 to 37 3 ma of the section indicating dryer conditions in the continent and availability of si and mg in the water column and pore waters favorable for its formation additionally we suggest a stratified water column with warmer and more saline conditions at greater depths e g 200 m after 40 ma favoring palygorskite and possibly authigenic dolomite precipitation the mineralogical variations and element chemistry of rocks in the baskil section reflect how detrital sources and weathering regimes changed in this area during the middle eocene and how these changes can be related to global regional and local processes

paleogene geochronology an integrated approach geochronology is the conceptual division of continuous time as measured geochronometry by the progression in an ordinal series of events this is best achieved by an approach which integrates four independent data sets magnetostratigraphy seafloor spreading magnetic lineation patterns biostratigraphy and isotopic ages this integrated approach results in an ordinal framework which can measure time with greater resolution though perhaps less accuracy than a radiometric approach alone a comparative analysis of two recently proposed paleogene geochronologic time scales is presented

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

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

transient drying during the paleocene eocene thermal maximum petm analysis of paleosols in the bighorn basin wyoming abstract the paleocene eocene thermal maximum petm was a transient episode of global warming that occurred at the paleocene eocene boundary the event is marked by a sharp decline in carbon isotope values that is globally recognized from marine and continental sections the negative isotope excursion has been attributed to the release of methane hydrates from oceanic sediments although studies concur that temperatures rose during the petm changes in precipitation are not well understood alluvial paleosols in the bighorn basin that span the petm interval contain a continuous and highly resolved record of climate including information on precipitation they show a significant but transient decrease in precipitation at the onset of the petm but a gradual return to pre petm levels by the end of the interval the paleosols also show additional although less dramatic wet dry cycles within the petm interval that may correspond to precessional cycles that have been identified in the marine record of the petm this study counters interpretations of increased precipitation for wyoming at this time and shows the importance of detailed case studies of continental strata to test climatic generalizations and models that have been developed for petm precipitation patterns

drought reconstructions for the continental united states abstract the development of a 2 lat 3 long grid of summer drought reconstructions for the continental united states estimated from a dense network of annual tree ring chronologies is described the drought metric used is the palmer drought severity index pdsi the number of grid points is 154 and the reconstructions cover the common period 1700 1978 in producing this grid an automated gridpoint regression method called point by point regression was developed and tested in so doing a near optimal global solution was found for its implementation the reconstructions have been thoroughly tested for validity using pdsi data not used in regression modeling in general most of the gridpoint estimates of drought pass the verification tests used in addition the spatial features of drought in the united states have been faithfully recorded in the reconstructions even though the method of reconstruction is not explicitly spatial in its design the drought reconstructions show that the 1930s dust bow

the potassic granites of the igbeti area further evidence of the polycyclic evolution of the pan african belt in southwestern nigeria abstract field geochemical and isotopic studies on granitic rocks in the igbeti area of southwestern nigeria indicate that this pan african belt was affected by two episodes of granite plutonism represented by an older augen gneiss and a younger relatively undeformed coarse grained porphyritic granite these rocks have similar major element characteristics but their trace element compositions are sufficiently different to warrant a suggestion that they are probably of different origin rb sr whole rock isotopic analysis give an eburnean age of 1904 18 ma for the augen gneisses and a pan african age of 617 37 ma for the coarse grained porphyritic granite a low initial 87 sr 86 sr ratio 0 7005 0 0025 for the augen gneiss suggests derivation from the mantle or a low rb sr source whereas a value of 0 7120 0 0016 for the coarse grained porphyritic granite indicates a significantly older crustal component in the magma alkaline magmatism may have been an important component of orogenic magmatism during the eburnean event

tree ring reconstructed summer temperature anomalies for temperate east asia since 800 c e we develop a summer temperature reconstruction for temperate east asia based on a network of annual tree ring chronologies covering the period 800 1989 c e the east asia reconstruction is the regional average of 585 individual grid point summer temperature reconstructions produced using an ensemble version of point by point regression statistical calibration and validation tests indicate that the regional average possesses sufficient overall skill to allow it to be used to study the causes of temperature variability and change over the region the reconstruction suggests a moderately warm early medieval epoch ca 850 1050 c e followed by generally cooler little ice age conditions ca 1350 1880 c e and 20th century warming up to the present time since 1990 average temperature has exceeded past warm epochs of comparable duration but it is not statistically unprecedented superposed epoch analysis reveals a volcanic forcing signal in the east asia summer temperature reconstruction resulting in pulses of cooler summer conditions that may persist for several years substantial uncertainties remain however particularly at lower frequencies thus requiring caution and scientific prudence in the interpretation of this record

structural orientations and precambrian deformational episodes of uwet area oban massif se nigeria abstract orientations of planar linear and micro structures are consistent with the results of isotopic data from the uwet area of southeastern nigeria which indicate that the area was subjected to polyphase deformation and polymetamorphism during the precambrian the dominant trends of the mesoscopic structures are n s to ne sw 0 50 with dips or plunges varying from 8 to 90 structures showing these attitudes represent imprints of penetrative pan african deformation and regional metamorphism that occurred in the uwet area 676 26 ma and 527 16 ma ago foliation trends of nw se 100 140 with dips of 25 60 towards 40 and fold axes plunging steeply 70 80 towards 70 are interpreted as representing relicts of a pre pan african deformation and metamorphism that also occurred in the uwet area 784 31 ma ago and possibly earlier during the kibaran orogeny

south pacific intermediate water oxygen depletion at the onset of the paleocene eocene thermal maximum as depicted in new zealand margin sections 1 extreme global warming and massive input of 13c depleted carbon into the exogenic carbon cycle characterize the paleocene eocene thermal maximum petm circa 55 5 ma previous work indicates that dissolved o2 concentrations dropped in some regions of the ocean during this event but spatial temporal and causal relationships between warming carbon input and o2 deficiency remain elusive we present lithologic carbon isotopic and trace fossil results from outcrops in new zealand that clarify this issue sections exposed at mead and dee streams in eastern marlborough south island contain expanded sedimentary intervals that were deposited before during and after the petm on an upper continental slope the petm in these intervals is characterized by enhanced siliciclastic deposition a hallmark negative carbon isotope excursion and a loss of bioturbation importantly however the latter only occurs during the prominent drop in 13c and not during its recovery our results suggest that south pacific intermediate waters became hypoxic coincident to carbon injection at the start of the petm while higher sea surface temperatures throughout the petm would have decreased the dissolved oxygen content of sinking surface waters we argue here that oxygen depletion was driven by some combination of elevated temperature water column stratification and intermediate water methane oxidation

u pb dating of precambrian rocks from northern cameroon orogenic evolution and chronology of the pan african belt of central africa abstract northern cameroon has been classically divided into an old basement complex a middle proterozoic cover series intermediaires and granites emplaced during the pan african orogeny new u pb geochronological data on different rock units from this region are presented a rhyolite from the poli schists series intermediaires gives an age close to 800 ma migmatitic gneisses of the basement complex seem to derive from different detrital or magmatic sources the metadiorites and foliated granites of the basement complex give ages around 630 ma the 800 ma age is interpreted as dating volcanic activity probably related to the initial stage of the pan african evolution ages around 630 ma date a syn tectonic plutonism dominated by a regional scale basic to intermediate plutonic suite bip zircons of the bip suite are almost concordant and show no evidence of inheritance the suite shows calc alkaline affinity and relatively low 87 sr 86 sr initial ratios thus the bip suite represents material newly added to the crust during the panafrican orogeny these data are at variance with previous interpretations of this part of the mobile belt as old precambrian crust reactivated during the pan african orogeny the previous distinction between the series intermediaires and a regional basement complex must be reappraised similar ages being found in both units a chronological succession of the pan african evolution is established and tentatively compared with that of the trans saharan belt in nigeria and hoggar

antarctic subtropical humid episode at the paleocene eocene boundary clay mineral evidence clay mineral assemblages from east antarctica have been analyzed at high stratigraphic resolution 20 to 1 ka throughout the interval from 55 6 to 55 0 ma which includes the terminal paleocene isotopic excursion in ocean drilling program site 690b on maud rise lat 65 s in the weddell sea region changes in the clay associations reflect a major increase in chemical weathering caused by increased temperature and or rainfall in at least this sector of east antarctica for a brief 270 ka interval in the latest paleocene this represents the most intense warming known for the cenozoic this high latitude climatic episode is recorded synchronously by stable isotopes and clay minerals a progression is evident in the clay assemblages during the latest paleocene that apparently reflects changing relations between temperature and precipitation this sequence began with the interval of rapid temperature increase that marks the beginning of the oxygen isotopic excursion a brief increase in kaolinite at the inception of the excursion suggests a temporary increase in year round precipitation in antarctica in response to an increased continent to ocean temperature gradient this kaolinite spike was followed by almost total dominance by smectite for the remainder of the isotopic excursion 120 ka suggesting that warmer southern ocean surface temperatures of 18 to 22 c were associated with seasonal precipitation alternating wet and dry seasons claymineral variations on antarctica during the isotopic excursion reflect a tight coupling between oceanic and continental climate change immediately following the excursion at 55 22 ma kaolinite percentages increased to values similar to modern subtropical tropical areas for 150 ka a remarkable event for the antarctic abundant kaolinite suggests perennial rainfall and minimum soil temperatures of 15 c during at least part of the year the kaolinite increased during a time of lower southern ocean surface water temperatures suggesting increased atmospheric heat transport toward the poles a temporary change in atmospheric circulation is suggested from dominantly zonal to meridional

paleocene eocene thermal maximum environmental change in the new jersey coastal plain benthic foraminiferal biotic events abstract the environmental impact of the paleocene eocene thermal maximum petm has been intensively studied in the new jersey coastal plain but the benthic foraminiferal response reflecting bottom water conditions has not been documented at high resolution we use benthic foraminiferal data across the paleocene eocene boundary in cores from wilson lake wl and bass river br to recognize 5 foraminiferal associations based on species clusters their varying abundances allow the identification of a stratigraphic succession of 8 distinct biofacies across the studied interval uppermost paleocene biofacies 1 corresponds to the glauconitic sands of the vincentown formation and contains rare small planktic foraminifera and a diverse benthic fauna sediments accumulated slowly in a sufficiently oxygenated outer neritic setting depth 100 110 m at wl 140 150 m at br under fairly oligotrophic conditions the embayment was storm dominated and influenced by strong currents inhibiting deposition of suspended fine particles e g planktic foraminifera clay and enhancing re suspension no significant pre petm environmental changes are detected in the benthic foraminiferal assemblages deposition of the fine grained silty clays of the marlboro clay started at the onset of the petm with transitional lithology present at wilson lake gavelinella beccariiformis common at deep shelfal to bathyal abyssal depths is the only taxon to become extinct at this level water depth increased during the petm to a maximum of 130 150 m at wl planktic foraminifera increased strongly in abundance while the benthic foraminiferal assemblage changed to a more opportunistic less diverse assemblage dominated by stress tolerant taxa tappanina selmensis pulsiphonina prima and anomalinoides acutus biofacies 2 increased riverine influence may have reduced vertical mixing initiating stratification of the water column and establishment of a continuously dysoxic mud belt benthic diversity then gradually increased indicating environmental recovery biofacies 3 and 4 40 95 kyr post petm onset riverine influence probably became more variable generating peak abundances of specialized taxa in a mud belt system with increased accumulation rates the latest petm biofacies 5 95 kyr post onset contains a poorly diverse bulimina callahani assemblage indicative of reoxygenated but still eutrophic bottom water conditions with renewed vertical mixing the lower eocene glauconitic sandy clays of the manasquan formation contain an outer neritic benthic fauna biofacies 6 8 depth 100 135 m at wl indicative of persistent high primary production with return of more vigorous currents higher abundances of buliminids may have been triggered by upwelling along frontal zones our environmental interpretations indicate relatively stable benthic foraminiferal ecosystems at persistently outer neritic water depths 100 150 m despite distinct temporary changes during the petm including eustatic sea level rise of up to 30 m and widespread establishment of dysoxic conditions

rare metal pegmatites of wamba central nigeria their formation in relationship to late pan african granites he sn nb ta mineralization of the wamba field central nigeria occurs in muscovite quartz microcline pegmatites which are related to the late orogenic pan african f 550 ma older granites the emplacement of granites and pegmatites was controlled by late pan african shear tectonics the granitoid magmatism was multiphase and has produced peraluminous biotite granite biotite muscovite granite and muscovite granite plutons sodic metasomatism has altered highly evolved granite cupolas and many of the pegmatite dikes the pegmatitic mineralization of predominantly cassiterite is closely associated with albitization chemical data of granites and granitic and pegmatitic muscovites show that rb cs sn nb and ta are enriched during both magmatic and postmagmatic evolution with highest contents of these elements in early muscovites of the albitized and mineralized pegmatites trace element chemistry of the pegmatitic muscovites reveals a chemical zonation of the pegmatite field related to the late orogenic shear system

where are the eburnian transamazonian collisional belts the reconstruction of early proterozoic crustal evolution and geodynamic environments in africa and south america is incomplete if cratonic areas alone are studied if the presence of high grade

persistent environmental change after the paleocene eocene thermal maximum in the eastern north atlantic the paleocene eocene thermal maximum petm 56 ma is associated with abrupt climate change carbon cycle perturbation ocean acidification as well as biogeographic shifts in marine and terrestrial biota that were largely reversed as the climatic transient waned we report a clear exception to the behavior of the petm as a reversing climatic transient in the eastern north atlantic deep sea drilling project site 401 bay of biscay where the petm initiates a greatly prolonged environmental change compared to other places on earth where records exist the observed environmental perturbation extended well past the 13 c recovery phase and up to 650 kyr after the petm onset according to our extraterrestrial 3he based age model we observe a strong decoupling of planktic foraminiferal 18 o and mg ca values during the petm 13 c recovery phase which in combination with results from helium isotopes and clay mineralogy suggests that the petm triggered a hydrologic change in western europe that increased freshwater flux and the delivery of weathering products to the eastern north atlantic this state change persisted long after the carbon cycle perturbation had stopped we hypothesize that either long lived continental drainage patterns were altered by enhanced hydrological cycling induced by the petm or alternatively that the climate system in the hinterland area of site 401 was forced into a new climate state that was not easily reversed in the aftermath of the petm

crust forming ages and proterozoic crustal evoluton in nigeria a reappraisal of current interpretations abstract radiometric ages in the nigerian basement cluster around 3 5 3 1 3 0 2 7 2 5 2 1 1 8 and 0 6 ga however not all these ages correspond to times of crust formation there are significant discrepancies between u pb and rb sr ages and nd and sr model ages with a definite trend for the orthogneisses and granitoids analysed results show good agreement between model ages tnd tsr and emplacement ages for early archaean and imply that these model ages date the time of crust mantle differentiation the archaean early proterozoic boundary was most probably a major crust forming period in sw nigeria as indicated by u pb zircon ages that are in agreement with nd model ages in that segment of the nigerian basement on the other hand late proterozoic and younger rocks which include migmatized gneisses pan african granitoids and jurassic younger granites have model ages in excess of their crystallization ages such model ages that lie between pan african or jurassic and well known older geologic ages do not correspond to any specific crust forming event rather they are mean crust residence ages reflecting contributions from juvenile material and remelted older archaean crustal components the overall scenario is consistent with widespread archaean crust and its involvement in the genesis of late proterozoic and younger crust in the nigerian basement this is in agreement with an intra cratonic setting far removed from the suture to the west

terrestrial records of a regional weathering profile at the paleocene eocene boundary in the williston basin of north dakota the orange zone within the bear den member of the golden valley formation williston basin north dakota represents a terrestrial weathering profile formed by intense pedogenesis during an ancient ca 55 ma global warming event referred to as the paleocene eocene thermal maximum distinctive features of the orange zone include 1 high abundances of kaolinite 2 a strongly leached character with a bright orange iron enriched horizon 3 poor organic carbon preservation and 4 ferric pans pisoliths at its basal contact equivalent to modern lateritic materials though conclusive evidence such as a distinctive paleocene eocene thermal maximum flora and or definitive carbon isotope excursion is lacking the stratigraphic succession of palynofloral datums preserved within the upper part of the bear den orange zone is similar to that associated with the later stages of other terrestrial paleocene eocene thermal maximum records from the u s western interior bulk 13 c org ratios decrease through the orange zone as well but the magnitude of this isotopic decrease is less than that of the carbon isotope excursion thus the collective evidence indicates that the early initial stages of the paleocene eocene thermal maximum are either preserved within the barren condensed interval of the lower orange zone or are missing altogether from the williston basin stratigraphy and that the orange zone likely developed during the later recovery stages of the paleocene eocene thermal maximum the williston basin records generally agree with the tenet that continental weathering intensified during the paleocene eocene thermal maximum moreover these records indicate that the paleohydrology of the basin varied markedly and that sequestration of terrestrial organic carbon was greatly reduced as this transient global warming event unfolded

structure and u pb geochronology of central hoggar algeria a reappraisal of its pan african evolution discovery of large scale deep seated thrusts in central hoggar with a plurifacial evolution ranging from lower amphibolite facies to upper greenschist facies conditions and linked to a regional refoliation has led us to reconsider the pan african tectonic and metamorphic history in that region two areas are described and a review of other thrusts leads to an interpretative cross section of a large portion of reactivated continental crust the age and kinematics of this structural reworking have been approached using u pb zircon dating in the tamanrasset region despite the difficulty of estimating the age of the initiation of the assumed intracontinental a type subduction the results provide a time span of 30 40 m y between the climax of granitoid emplacement and a late retrogressive offset along the thrust planes some key ages were determined 1 2075 30 ma is the age given by granulite facies remnants which escaped from the refoliation the corresponding lower intercept at 530 70 ma confirms the pan african imprint 2 615 5 ma reflecting the age of syntectonic to late tectonic granitoids emplaced in reworked gneisses and in preserved granulites 3 580 ma the concordant age of sphenes and monazites from the same granitoids which is interpreted as corresponding to the end of medium grade conditions no evidence has been found of a 1000 ma age a kibaran event does not appear to exist in central hoggar the age similarity between the observed deep intracontinental evolution of central hoggar and the collision related tectonics of western hoggar and iforas suggests a common origin for both phenomena

stratigraphic and climatic implications of clay mineral changes around the paleocene eocene boundary of the northeastern us margin abstract kaolinite usually is present in relatively small amounts in most upper paleocene and lower eocene neritic deposits of the northern us atlantic coastal plain however there is a short period less than 200 000 k y in the latest paleocene upper part of calcareous nannoplankton zone np 9 when kaolinite dominated clay mineral suites replaced the usual illite smectite dominated suites during this time of global biotic and lithologic changes kaolinite increased from less than 5 of the clay mineral suite to peak proportions of 50 60 of the suite and then returned to less than 5 in uppermost paleocene lowermost eocene strata this kaolinite pulse is present at numerous localities from southern virginia to new jersey these sites represent both inner and middle neritic depositional environments and reflect input from several river drainage systems thus it is inferred that kaolinite rich source areas were widespread in the northeastern us during the latest paleocene erosion of these source areas contributed the kaolinite that was transported and widely dispersed into shelf environments of the salisbury embayment the kaolinite increase which occurred during a time of relatively high sea level probably is the result of intensified weathering due to increased temperature and precipitation the southern extent of the kaolinite pulse is uncertain in that uppermost paleocene beds have not been identified in the southern atlantic coastal plain the late paleocene kaolinite pulse that consists of an increase to peak kaolinite levels followed by a decrease can be used for detailed correlation between more upbasin and more downbasin sections in the salisbury embayment correlations show that more upbasin paleocene eocene boundary sections are erosionally truncated they have varying portions of the kaolinite increase and if present at all discontinuous portions of the subsequent kaolinite decrease as these truncated sections are disconformably overlain by lower eocene strata rapid erosional removal of large parts of the most kaolinite rich p e boundary clay deposits occurred by early eocene time erosion of the kaolinite rich p e boundary beds was enhanced during times of sea level fall when kaolinite rich sediments were redeposited to produce kaolinite spikes in basal beds of lower and middle eocene sequences that have little or no kaolinite elsewhere in the sequence in contrast more downbasin sites document only the upper decreasing part of the kaolinite pulse the absence of strata documenting the earlier kaolinite increase is attributed to slow sedimentation condensed interval as a result of a significant sea level rise that ponded most sediments in shallower waters combined with the probable subsequent erosional removal of these thin downbasin deposits by oceanic currents

clay assemblage and oxygen isotopic constraints on the weathering response to the paleocene eocene thermal maximum east coast of north america the paleocene eocene thermal maximum a transient global warming event is character ized by extensive evidence of a more active hydrological cycle this includes a widespread pulse of kaolinite accumulation on continental margins viewed as the by product of either enhanced chemical weathering consistent with much more humid conditions and or increased erosion of previously deposited laterites the former would be more consistent with year round humid conditions whereas the latter might be indicative of extreme seasonal precipi tation patterns to assess these hypotheses we present a new high resolution clay mineral assemblage and oxygen isotope record from bass river a site on the new jersey margin east coast of north america which shows a sharp rise in the abundance of kaolinite beginning a few thousand years before the onset of the carbon isotope excursion cie the 18 o of the 2 m size fraction exhibits a shift toward lower values during the event on the basis of a coeval shift in clay assemblages the shift in 18 o clays can be explained by a shift in the relative percent of the primary clay phases rather than a change in the isotopic composition of kaolinite as would be expected if the kaolinite had been produced primarily during the paleocene eocene thermal maximum this fi nding points to accelerated exhumation and ero sion of kaolinitic soils most likely cretaceous laterites

proterozoic history of the borborema province ne brazil correlations with neighboring cratons and pan african belts and implications for the evolution of western gondwana 1 geological and geochronological correlations between borborema province ne brazil and neighboring cratons and brasiliano pan african belts indicate that the amazonian west african and sao francisco congo cratons and the basement of the araguaia borborema nigerian and cameroon provinces were part of the atlantica supercontinent this continent was established at the end of the transamazonian eburnean cycle 2 0 ga and apart from ubiquitous taphrogenesis in the 1 8 1 7 ga interval remained largely unaffected for the following 1 ga around 1 ga an important magmatic event in borborema province correlates with rifting episodes and anorogenic magmatism in the sao francisco congo and amazonian cratons these events are interpreted as failed attempts to break up atlantica which at this time may have been part of the larger rodinia supercontinent renewed extensional conditions in borborema province during the middle and late neoproterozoic are attributed to far field stresses transmitted to the interior of atlantica by outwardly dipping subduction zones that encircled its northern present day coordinates portion the rarity of petrotectonic assemblages typical of subduction zone environments indicates that extension did not evolve enough to form large oceans basins and thus that the borborema province essentially includes reworked intracontinental domains regional deformation and metamorphism starting at 650 640 ma and shear zone development beginning at 590 595 ma were continuously developed through time and were synchronous throughout most of the borborema araguaia cameroon and nigerian provinces postorogenic conditions were reached 540 530 myr ago while active deformation was still occurring in other belts that accreted around atlantica to form western gondwana

paleoweathering and paleoenvironmental change recorded in lacustrine sediments of the early to middle eocene in fushun basin northeast china deciphering the long term interaction among continental silicate weathering global climate and atmospheric co2 concentrations is helpful in understanding the mechanisms of the cenozoic climate change and accessing the future climatic and environmental response to anthropogenic carbon emissions the eocene which is characterized by the early eocene climatic optimum eeco and the following global cooling represents an ideal test case here we generate geochemical data of the eocene lacustrine sediments from the fushun basin northeast china to explore the regional climatic response to the global climate change the chemical index of alteration cia and plagioclase index of alteration pia consistently show a gradual long term decrease indicating a climatic transition from warm and humid to relatively cold and arid during the eocene in the fushun basin this climatic trend is broadly coincident with the global cooling and decreasing co2 concentration implying that the regional climate is closely correlated with the global climate change over geological time scales additionally the extreme silicate weathering and high lake productivity as reflected by relatively positive 13c values of lacustrine organic matter are associated with the eeco this consistency may demonstrate that enhanced continental weathering and lake productivity had served as effective sinks to lower atmospheric co2 across the eeco collectively our new geochemical data add supporting evidence for a long term close coupling among continental silicate weathering climate and global carbon cycle during the eocene

global change at the paleocene eocene boundary climatic and evolutionary consequences of tectonic events rea d k zachos j c owen r m and gingerich p d 1990 global change at the paleocene eocene boundary climatic and evolutionary consequences of tectonic events palaeogeogr palaeoclimatol palaeoecol 79 117 128 events of the paleocene eocene boundary provide the clearest example to date of how a tectonic event may have global climatic consequences recent advances permit well constrained stratigraphic determination of several events that occurred at that boundary in chron c24r a many fold increase in sea floor hydrothermal activity a global warming a reduction in the intensity of atmospheric circulation a conversion to salinity driven deep ocean circulation a marked lightening of oceanic 313c values extinction and evolution of both benthic foraminifera and land mammals and important plate boundary reorganizations including the outpouring of the east greenland volcanics and the initiation of the oceanic rift between norway and greenland we hypothesize that enhanced sea floor hydrothermal activity occasioned by global tectonism resulted in a flooding of the atmosphere with coz causing a reduced pole to equator temperature gradient and increased evaporation at low latitudes increased formation of warm salty probably low nutrient waters coupled with the warm temperatures at high latitudes occasioned a salinity driven rather than temperature driven deep water circulation this newly evolved ocean circulation pattern changed the apportionment of global heat transport from the atmosphere to the ocean with concomitant changes in the circulation intensity of both reduced intensity of atmospheric circulation resulted in lower oceanic biological productivity and enhanced seasonality of climate on the continents a major extinction event among benthic foraminifera was probably a response to the new low nutrient and chemically changed bottom waters and endemism following rapid evolution and dispersal of mammalian orders may have been in response to the new continental climate regime

geochemical evidence for volcanic activity prior to and enhanced terrestrial weathering during the paleocene eocene thermal maximum abstract the re os and major element geochemistry of an expanded gray shale sequence from the central basin in spitsbergen svalbard archipelago norway over the paleocene eocene thermal maximum petm is presented the data suggest that a significant volcanic episode as indicated primarily by a large drop in 187 os 188 os occurred just prior to or coincident with the onset of the petm the distinct geochemistry of the inferred ash component is consistent with the geochemistry of contemporaneous ashes previously sampled in denmark and persists in the sedimentary record for 8 ka based on the substantial size of the 187 os 188 os decrease 187 os 188 os 0 23 the volcanic event must have involved widespread ash deposition in the local catchment the terrestrially deposited ash weathered rapidly shifting the 187 os 188 os of the basin water column to 187 os 188 os to more radiogenic values and depositing clastic materials with higher chemical index of alteration and lower na ti persistently anoxic sedimentary pore fluids interpreted to reflect bottom water anoxia initiated close to the onset of the petm anoxic mainly euxinic conditions persisted for 50 ka ending abruptly 55 77 ma anoxia appears related to enhanced high latitude hydrological cycling and consequent basinal stratification during the petm

paleohydrological and paleoenvironmental changes recorded in terrestrial sediments of the paleocene eocene boundary normandy france the paleocene eocene boundary 55 8 ma is associated with the paleocene eocene thermal maximum petm which is characterized by a negative carbon isotope excursion cie reflecting a major perturbation of the carbon cycle and by an extreme and rapid global warming the cap d ailly area upper normandy france in which previous studies have revealed the paleocene eocene transition is a reference locality for organic rich terrestrial and lagoonal deposits of the sparnacian stage widespread in northwestern europe in this study we focus on the organic matter content of the vasterival section organic data rock eval palynofacies biomarker analyses and compound specific isotope analyses were acquired in order to constrain the paleoenvironmental and paleohydrological changes that occurred at the paleocene eocene boundary stable carbon isotope compositions of higher plant leaf wax n alkanes reveal a cie of 4 5 extending throughout the second half of the studied section palynofacies observations reveal i an abrupt shift from a closed quiescent marsh pond to an open eutrophic swamp subjected to algal blooms concomitant with the onset of the cie and ii the evolution from a swamp to a tidal flat due to the marine transgression that occurred during the petm higher plant biomarkers and their hydrogen isotopic composition compared to nitrogen analyses suggest i dry episodes just before the petm that may help to understand the triggering of this hyperthermal event ii a moister climate associated with a stronger seasonality during the early petm

gold potential of the pan african trans sahara belt and prospect for further exploration abstract the trans sahara belt is one of the mobile belts formed during the pan african orogeny that spans between 870 and 550 ma the trans sahara belt was formed as result of the collision between the converging west african craton congo craton and the sahara metacraton continental blocks the belt with major exposure in the tuareg and dahomeyan consists of pre neoproterozoic basement which were thoroughly reworked during the pan african orogeny neoproterozoic metasedimentary and metavolcanics and syn tectonic pan african granitoids which intrude archean and paleoproterozoic rocks the trans sahara belt though less endowed when compared to older archean orogenic greenstone belts in terms of gold mineralization displays reasonable gold mineralization in both the tuareg shield and dahomeyan shield with about 160 tons of gold reported so far across the belt mineralization is associated with varying lithologies across the belt and appears to have been regionally controlled by n s trending pan african shear zones in the tuareg shield mineralized quartz veins are associated with syntectonic granitoids mylonitic and meta volcanosedimentary rocks conversely gold mineralization is only associated with metasediments and migmatite gneisses in the dahomeyan shield with occurrences largely confined to metasedimentary sequence in benin and nigeria the prevailing tropical climate in the dahomeyan shield has also facilitated secondary concentration of gold in alluvial bed of river draining supracrustal rocks hosting primary gold mineralizations the occurrence of primary mineralization in variety of rocks across the tuareg and dahomeyan shield and widespread occurrence of placer gold deposits in the dahomeyan shield justifies the need for further exploration and evaluation of mineralization potential the emplacement of gold which occur between 535 and 500 ma is controlled by n s trending pan african mega shear zones however at the district scale it is evident that the pan african mega shear zones are not the only important structures lower order faults and shear zones are important structures to consider in exploration targeting exploration particularly at district scale might benefit from gis based prospectivity mapping considering the mineralizations are generally structural controlled gis based prospectivity mapping which integrates multifaceted digital data sets can provide a foundation for vectoring towards explorations targets in many mineralized districts within the trans sahara belt

surface water freshening and high latitude river discharge in the eocene north sea abstract a shark tooth apatite 18 o record of the early palaeogene north sea reflects changes in regional hydrography by showing variable temperatures and salinities a 2 4 ma period in the early eocene was particularly influenced by substantial surface water freshening indicated by a 3 4 reduction of 18 o values the magnitude of the 18 o decrease indicates a depletion in 18 o of surface waters by 2 3 relative to eocene mean ocean water this value is lower than that of coeval lakes reconstructed from freshwater gastropod 18 o values from the paris basin suggesting that large rivers with high latitude catchment areas drained into the north sea the period of surface water freshening began close to the palaeocene eocene thermal maximum when relative sea level fall tectonic uplift and basaltic volcanism caused a temporary isolation of the north sea north atlantic and north sea surface waters became reconnected during a series of early eocene transgressions

tectonometamorphic evolution of ghana togo and benin in the light of the pan african brasiliano orogeny abstract the south pan african belt of west africa ghana togo and benin province can be divided into three domains 1 1 the external nappes thrust over the west african craton derived from passive margin sedimentary deposits middle to late proterozoic and displaying middle to high pressure metamorphism such as the kante and atacora nappes 2 2 the intermediate nappes including the suture zone rocks with eclogitic assemblages protoliths ca 800 ma and mainly monocyclic metasedimentary rock and orthogneiss that are found in central togo and northwest benin 3 3 the internal nappes composed of high grade commonly anatectic gneiss anatexis ca 600 ma including orthogneiss eburnian plutons elongated granulite belts reworked archean basement and an intrusive granite and charnockite association ca 600 ma which are exposed in benin and nigeria the p t t d paths calculated from rocks in these three domains show a prograde retrograde evolution 1 1 an initial clockwise evolution related to an early burial stage hp ht in the intermediate nappes followed by oblique thrusting in a sw direction that caused nappe stacking and subsequent uplift 2 2 a second anti clockwise evolution with late temperature and pressure increases only recorded in the more internal units this temperature increase was a consequence of the previous crustal thickening with subsequent doming extension and anatexis the pressure increase was related to movement along the kandi fault working as a dextral strike slip fault with a transpressional component under late e w shortening the retrograde trend corresponds to the final uplift the evolution of the belt can thus be divided into three successive stages 1 1 a first stage was characterized by an oblique collision inducing sw oblique thrusting with associated syn foliation reverse metamorphism 2 2 during a second stage anatectic doming took place followed by 3 3 a third stage at still high temperature with dextral wrench faulting and associated n s post foliation folding under late e w shortening comparison between the west african north brasiliano and central african late proterozoic belts shows very strong similarities between their lithology kinematics and metamorphism and indicates that the pan african brasiliano chain resulted from collision between three major continental domains the west african and sao francisco congo cratons and a late proterozoic mobile domain

a new model for atmospheric oxygen over phanerozoic time a mathematical model has been constructed that enables calculation of the level of atmospheric o2 over the past 570 my from rates of burial and weathering of organic carbon c and pyrite sulfur s burial rates as a function of time are calculated from an assumed constant worldwide clastic sedimentation rate and the relative abundance and c and s contents of the three rock types marine sandstones and shales coal basin sediments and other non marine clastics red beds arkoses by our model values of o2 versus time using a constant total sedimentation rate agree with those for variable sedimentation derived from present day rock abundances and estimates of erosional losses since deposition this agreement is the result of our reliance on the idea that any increase in total worldwide sediment burial with consequently faster burial of c and s and greater o2 production must be accompanied by a corresponding increase in erosion and increased exposure of c and s on the continents to o2 consumption via weathering it is the redistribution of sediment between the three different rock types and not total sedimentation rate that is important in o2 control to add stability to the system negative feedback against excessive o2 fluctuation was provided in the modeling by the geologically reasonable assignment of higher weathering rates to younger rocks resulting in rapid recycling of c and s we did not use direct o2 negative feedback on either weathering of c and s or burial of c because weathering rates are assumed to be limited by uplift and erosion and the burial rate of c limited by the rate of sediment deposition the latter assumption is the result of modern sediment studies which show that marine organic matter burial occurs mainly in oxygenated shallow water and is limited by the rate of supply of nutrients to the oceans by rivers results of the modeling indicate that atmospheric o2 probably has varied appreciably over phanerozoic time during the late carboniferous and permian periods o2 was higher than previously because of the rise of vascular land plants and the widespread burial of organic matter in vast coal swamps a large decrease in o2 during the late permian was due probably to the drying up of the coal swamps and deposition of a large proportion of total sediment in c and s free continental red beds sensitivity study shows that major parameters affecting results are the mean c concentration in coal basins and the relative sizes of the reservoirs of young rapidly recycled versus old rocks less sensitivity was found for changes over time in total land area undergoing weathering and the use of direct o2 negative feedback on marine carbon burial good agreement for rates of c burial calculated via our model and via independent models which are based on the use of stable carbon isotopes indicates that the dominant factor that has brought about changes in atmospheric o2 level and the isotopic composition of dissolved inorganic carbon in seawater over phanerozoic time is sedimentation and not weathering or higher temperature phenomena such as basalt seawater reaction

ocean nutrient distribution and oxygenation limits on the formation of warm saline bottom water over the past 91 m y it has been proposed that deep water formation in the oceans would be quite different during geologic intervals with reduced equator to pole temperature gradients salinity rather than temperature differences might drive the deep ocean circulation saline water would tend to form at subtropical latitudes where evaporation exceeds precipitation we point out a likely consequence of warm saline bottom water formation on ocean chemistry the tendency to drive the ocean toward anoxia this effect is not due to the previously noted lower oxygen solubility with increasing ocean temperature but rather to the increased efficiency with which plankton will extract nutrients from convecting waters at low latitudes the present ocean nutrient content is sufficient to induce deep water anoxia if circulation were to change yet anoxia is rare in the paleoceanographic record a simple ocean chemical model makes explicit the tradeoffs between mean ocean nutrient content and circulation parameters that will satisfy the geologic observations of an oxygenated ocean since the mid cretaceous barring decreases of ocean phosphate on the order of 30 50 deep water formation at high latitudes was a major source of ocean ventilation in the warmer past

warm saline bottom water in the ancient ocean considerable isotopic evidence indicates that oceanic bottom water was much warmer in the geological past a simple convection model driven by multiple turbulent buoyant plumes and observations of present deep water formation have led to the development of a theory for the formation of warm saline bottom water it is suggested that changes in the size and configuration of marginal seas in net evaporation zones due to lithospheric plate motions and eustatic sea level change caused these seas to become sources of warm saline bottom water evidence from the palaeotemperature record and palaeogeography during the late cretaceous is used to reinforce the hypothesis climatic and chemical consequences of the formation of warm saline bottom water are discussed

clay mineralogical constraints on weathering in response to early eocene hyperthermal events in the bighorn basin wyoming western interior usa series of transient greenhouse warming intervals in the early eocene provide an opportunity to study the response of rock weathering and erosion to changes in temperature and precipitation during greenhouse warming chemical weathering is thought to increase the uptake of carbon from the atmosphere while physical weathering and erosion control sediment supply a large ancient greenhouse warming event is the paleocene eocene thermal maximum at 56 ma in many coastal sites an increase in the abundance of kaolinite clay during the paleocene eocene thermal maximum is interpreted as the result of reworking from terrestrial strata due to enhanced runoff caused by increased seasonal precipitation and storminess during a time of decreased vegetation cover in the continental interior of north america paleocene eocene thermal maximum paleosols show more intense pedogenesis and drying which are indicated by deeply weathered and strongly oxidized soil profiles the weathering and oxidation could be related to temperature and precipitation changes but also to increased time available for weathering and increased soil permeability in coarser sediment here we provide evidence for enhanced climate seasonality increased erosion of proximal laterites and intrabasinal floodplain soils and a potential slight increase in chemical weathering during the smaller early eocene hyperthermals eocene thermal maximum 2 including h1 and h2 postdating the paleocene eocene thermal maximum for which no previous clay mineral data were available hyperthermal soil formation at the site of floodplain deposition causes a similar insignificant clay mineralogical change as occurred during the background climates of the early eocene by showing small increases in smectite and decreases in illite smectite and illite remarkably the detrital sediments during the hyperthermals show a similar pedogenic like increase of smectite and decreases of mixed layer illite smectite and illite while the kaolinite and chlorite proportions remained low and unchanged since sedimentation rates and provenance were similar during the events enhanced smectite neoformation during soil formation in more proximal settings and associated reworking is the likely process causing this clay mineralogical change the hundreds to thousands of year time scales at which individual paleosols were formed were probably too short for significant alteration of the rocks by in situ chemical weathering despite changing climates during the two post paleocene eocene thermal maximum greenhouse warming episodes the relatively small signal however raises the question of whether increased chemical weathering can indeed be a strong negative feedback mechanism to enhanced greenhouse gas warming over the time scales at which these processes act

the dynamics of global change at the paleocene eocene thermal maximum a data model comparison we integrate published stable isotopic chemical mineralogical and biotic data from the onset of the paleocene eocene thermal maximum petm at site 690 maud rise in the southern ocean the integrated data set documents a sequence of environmental steps including warming of the ocean from the surface downward and modification of its thermal and nutrient structure acidification of the deep ocean and the onset of continental weathering the age of the events with respect to the onset of the petm is calibrated with three different age models the relative and absolute timing of the steps are compared with simulated temperature salinity calcite saturation and dissolved po4 and o2 at different depths in the ocean generated with the uvic earth system climate model of intermediate complexity the simulation supports the top to bottom transfer of heat and carbon and generally agrees with age models in terms of the durations of leads and lags in temperature c isotope and biotic responses moreover the simulation shows that stratification increased and the nutricline strengthened at the onset of the petm these environmental changes explain the abundance of deep dwelling nannoplankton and foraminifera during the early part of the event the modeled calcite saturation is consistent with a harsh deep sea habitat at the time of the benthic foraminiferal extinction

thermo tectonic evolution of the basement complex around okene nigeria with special reference to deformation mechanism abstract at least three successive thermo tectonic episodes the last of which involved a largescale heterogeneous simple shear deformation can be structurally distinguished in the okene area of the basement complex of nigeria evidence for the first episode is only observed in a suite of banded gneisses early gneiss the earliest metamorphic fabric in the banded gneisses predates the fabric in a swarm of minor metamorphosed intermediate basic dykes the second episode is distinguished by the earliest fabric in a suite of metasediments and meta intrusives main phase gneiss which is co eval with the fabric of the intermediate basic dykes the early gneiss occurs as competent relics interleaved between the foliation planes of the main phase gneiss both suites constituting a large scale sheeted rock body the gneiss complex sigmoidal gently plunging asymmetric folds of the gneiss complex and intrusives of pan african age late intrusive suite which cross cut the gneiss complex distinguish the third episode because a sub horizontal stretching lineation superimposed on the gneiss complex is sub parallel to the axes of the folds and the late intrusive suite is tectonised only in the steep limb and tight hinge regions of the folds the last episode is inferred to have involved a lateral heterogeneous simple shear of an originally flat lying gneiss complex

effects of rapid global warming at the paleocene eocene boundary on neotropical vegetation temperatures in tropical regions are estimated to have increased by 3 to 5 c compared with late paleocene values during the paleocene eocene thermal maximum petm 56 3 million years ago event we investigated the tropical forest response to this rapid warming by evaluating the palynological record of three stratigraphic sections in eastern colombia and western venezuela we observed a rapid and distinct increase in plant diversity and origination rates with a set of new taxa mostly angiosperms added to the existing stock of low diversity paleocene flora there is no evidence for enhanced aridity in the northern neotropics the tropical rainforest was able to persist under elevated temperatures and high levels of atmospheric carbon dioxide in contrast to speculations that tropical ecosystems were severely compromised by heat stress

carbonate to biosilica transition at the norian rhaetian boundary controlled by rift related subsidence in the western tethyan lagonegro basin southern italy abstract the lagonegro basin located in the southern apennines italy records a transition from carbonate sediments of the calcari con selce fm cherty limestone to biosiliceous sediments of the scisti silicei fm siliceous shale around the norian rhaetian boundary nrb upper triassic sedimentologic and chemostratigraphic analysis of three sections pignola abriola monte volturino and madonna del sirino representing a proximal to distal transect across the basin document marine productivity redox and chemical weathering conditions the basin was characterized by low to moderate productivity and mainly oxic deep waters with no systematic secular variation throughout the 10 myr long study interval a weathering proxy the chemical index of alteration cia shifts toward higher values from 0 70 to 0 80 in all three study sections suggesting development of warmer and or more humid conditions just before the nrb the lack of evidence for changes in marine productivity or redox conditions and the time transgressive nature of the carbonate biosilica transition suggests that the latter was caused not by changes in planktonic communities but rather by a rise in the ccd the most likely cause of which was seafloor subsidence within the actively rifting ionian ocean i e the westernmost branch of the tethys ocean the tectonically active character of the lagonegro basin is also reflected in evidence of synsedimentary paleoseismic activity e g numerous debris flows around the basin margins the present study thus documents sedimentologic changes within a marginal basin in a geologically young ocean

d h evidence for the timing of kaolinization in northeast bavaria germany the dsmow values of sedimentary kaolins from the western border of the bohemian massif northeast bavaria that did not suffer a deep burial less than 1000 m nor a hydrothermal overprint change systematically from late triassic 50 to mid jurassic and late cretaceous 56 to 66 to upper oligocene mid miocene 77 to 90 all analyzed clays are far from hydrogen isotope equilibrium with present day meteoric waters combined oxygen and hydrogen isotope data of selected samples indicate low temperatures of formation 30 c and no evidence for preferential d h exchange with younger waters the hydrogen isotopic evolution of kaolins is interpreted as reflecting a systematic isotopic change of paleo meteoric waters in that region this can be related mainly to the northward drift of stable europe after the break up of gondwana increasing continentality surface uplift and global cooling are additional factors responsible for decreasing dsmow values since the mid cretaceous kaolinite hydrogen isotope ratios of two large residual economic deposits tirschenreuth dsmow 80 to 76 hirschau schaittenbach dsmow 70 to 63 can be used in combination with additional geological evidence to constrain the timing of weathering in these areas a late early cretaceous kaolinization age is suggested for the early triassic sandstone hosted deposits near hirschau schnaittenbach whereas a late oligocene to mid miocene age is indicated for the carboniferous granite hosted tirschenreuth deposits

extreme warming of mid latitude coastal ocean during the paleocene eocene thermal maximum inferences from tex86 and isotope data changes in sea surface temperature sst during the paleocene eocene thermal max imum petm have been estimated primarily from oxygen isotope and mg ca records generated from deep sea cores here we present a record of sea surface temperature change across the paleocene eocene boundary for a nearshore shallow marine section located on the eastern margin of north america the sst record as inferred from tex86 data indicates a minimum of 8 c of warming with peak temperatures in excess of 33 c similar ssts are estimated from planktonic foraminifer oxygen isotope records al though the excursion is slightly larger the slight offset in the oxygen isotope record may reflect on seasonally higher runoff and lower salinity

unprecedented january july warming recorded in a 178 year tree ring width chronology in the dabie mountains southeastern china abstract previous tree ring studies indicate that tree growth at high elevations is strongly limited by temperatures in the southeastern china where the climate is dominated by the east asian monsoon based on this result we built a highly replicated 202 year tree ring width chronology from high elevation sites in the dabie mountains southeastern china the most reliable period of the chronology is from 1834 to 2011 according to a subsample signal strength cutoff of 0 85 based on this chronology january july minimum temperature was reconstructed for the last 178 years with an explained variance of 57 6 during the instrumental period 1956 2010 the reconstructed temperature series matches reasonably well with three other tree ring based temperature reconstructions at decadal time scales in the region the coldest periods are 1891 1898 and 1904 1914 however the longest cold period is from 1948 to 1973 the warmest period is 1990 2010 both the recent 1990 2010 warming and recent 1948 2010 temperature increase rates are unprecedented compared with any same long period during the past 178 years in the study region