a palynofacies study of past fluvio deltaic and shelf environments the oligocene miocene succession north sea basin a reference data set for similar cenozoic systems abstract correct interpretations of depositional environments are fundamental for evaluating the geological history of a sedimentary basin palynofacies analyses are a valuable supplement to sedimentological and seismic studies in order to develop a palynofacies reference dataset for fluvio deltaic and shelfal successions a study of the assemblages of sedimentary organic particles from seven different well defined depositional environments within the uppermost oligocene lower miocene succession onshore denmark eastern north sea basin has been performed the study deals with the following environments floodplain lagoon washover fan flat prodelta shoreface offshore transition and shelf the sedimentary organic particles were grouped into four major categories 1 structured wood particles 2 amorphous organic matter aom in the present study mainly consisting of partly degraded vitrinite 3 cuticle and membranes and 4 palynomorphs the palynomorphs were grouped into eight subcategories 1 microspores 2 non saccate pollen 3 bisaccate pollen 4 botryococcus 5 other freshwater algae 6 fungal hyphae and spores 7 acritarchs and 8 organic walled dinoflagellate cysts a combination of a univariate box plots and a multivariate principal component analysis pca of the palynofacies data clear revealed the quantitative characteristics and variations within each discrete environment as well as their principal similarities and differences in spite of some natural overlaps for example between the lagoon and offshore transition environments the data revealed distinct characteristics e g a strong dominance of wood particles in the shoreface environment a strong dominance of bisaccate pollen in the washover fan flat environment and a near absence of dinocysts in the floodplain environment an overall increase in relative abundances of dinocysts and a decrease in abundances of non saccate pollen in the proximal distal trend were also outlined this study outlines a palynofacies reference dataset that can be used as a tool for interpreting depositional environments in equivalent settings preferentially combined with other information such as seismic data well logs and or lithology

palynological analyses of eocene to oligocene sediments from dsdp site 338 outer voring plateau article i nfo against the background of the profound global climatic shift from greenhouse to icehouse conditions during the eocene oligocene transition major geographic and oceanographic changes were taking place in the norwegian greenland sea region the voring plateau was a prominent structural feature which influenced the evolution of water mass circulation in the nordic seas and we present detailed palaeoenvironmental reconstructions of this structure new palynological results suggest that shallow water inner neritic environments were developed across parts of the voring plateau during early eocene times with terrestrial and brackish water palynomorphs indicating that both basement highs to the north and the crestal part of the voring escarpment may have been emergent a transition from marginal marine to open marine conditions occurred around 44 ma ago with the complete subsidence of the voring plateau below sea level facilitating inter basinal surface water circulation and promoted a significant increase in photic zone fertility carbon sequestration associated with such enhanced productivity in the late eocene nordic seas may have contributed to declining cenozoic atmospheric carbon dioxide levels thence to declining global temperatures and the development of limited northern hemisphere continental ice on greenland in the latest eocene

revised calendar date for the taupo eruption derived by 14c wiggle matching using a new zealand kauri 14c calibration data set taupo volcano in central north island new zealand is the most frequently active and productive rhyolite volcano on earth its latest explosive activity about 1800 years ago generated the spectacu

strong climate coupling of terrestrial and marine environments in the miocene of northwest europe a palynological and organic geochemical record from a shallow marine paleoenvironmental setting in se netherlands documents the coupled marine and terrestrial climate evolution from the late burdigalian 17 ma through the early zanclean 4 5 ma proxy climate records show several coeval variations in both relative sea surface deduced from percent cool dinocysts and terrestrial subtropical vs cool temperate pollen temperature indices the terrestrial climatic trend is confirmed by a quantitative reconstruction of annual mean air temperature based on the distribution of fossil branched glycerol dialkyl glycerol tetraethers showing a cooling from 27 c to 14 c between 17 and 5 ma punctuated by short term variations decreases in sea surface temperature broadly correlate to inferred third order sea level variations and correspond to isotope glacial events mi 3 through mi 7 an additional strong sst decrease occurs around 8 4 ma coincident with a strong reduction and regional disappearance of subtropical pollen types this cooling phase seems associated with lowered sea levels but it has not yet been described from the deep sea 18o record 2009 elsevier b v

late eocene to early oligocene dinoflagellate cysts from the priabonian type area northeast italy biostratigraphy and paleoenvironmental interpretation abstract marginal marine late eocene through early oligocene dinoflagellate cyst successions have been studied from the type area of the priabonian stage northeast italy the results allow the recognition of dinoflagellate zones previously defined in bio and magnetostratigraphically well calibrated pelagic sequences from central italy thus providing a first order correlation of the priabonian stage to the standard chronostratigraphic scale with unprecedented precision within this detailed biostratigraphic framework successive shifts in the composition of the dinoflagellate cyst assemblages are interpreted in terms of sea level and sea surface temperature sst fluctuations the evaluation of ecologically and sedimentary controlled changes in the composition of dinoflagellate cyst assemblages in combination with sequence stratigraphic analysis allows the reconstruction of third and fourth order sea level fluctuations the third order sea level fluctuations appear to correspond to exxon cycles ta4 1 4 5 the stratigraphically and palaeoenvironmentally important late eocene dinoflagellate cyst species glaphyrocysta priabonensis sp nov is formally described

evidence for a mazama like tephra deposited ca 10 000 bp at copper lake banff national park alberta mazama tephra is a widespread mid holocene stratigraphic marker dating to ca 6845 bp and is considered useful for the correlation of holocene events in western north america we present evidence from copper lake alberta for a tephra layer that underlies mazama tephra and appears to be a discrete tephra layer but that is indistinguishable from the conventional mazama tephra by microprobe analysis of glass shards three alternative hypotheses are considered to explain this tephra underlying mazama in situ position of an earlier mazama like tephra recycling of tephras and settling of tephra slabs through the gyttja the size distributions of birch pollen grains indicate that the mazama like tephra is in primary stratigraphic position in the early holocene gyttja and that sediment recycling has not destroyed the integrity of copper lake sediment stratigraphy it is concluded that most probably a mazama like tephra was deposited between 9700 and 10 500 bp if this in situ hypothesis is correct the id

sequence stratigraphy of the upper oligocene lower miocene of eastern jylland denmark role of structural relief and variable sediment supply in controlling sequence development the upper oligocene lower miocene succession in eastern jylland can be subdivided into three sequences a c from older to younger deposited on and around the ringkobing fyn high the development of the sequences reflects a complex interaction between eustatic sea level changes physiography and variable sediment supply superimposed on this frequent storms promoted longshore sediment transport and the development of spit systems adjacent to structural highs as a consequence sequence boundaries and flooding surfaces are not always expressed as portrayed in conventional sequence models sequence boundaries or flooding surfaces may only be marked by subtle changes in depositional environment that can only be revealed by careful integration of sedimentological observations with palynological data the influence of the topography resulted in the development of brackish water basins that were sufficiently large to permit the deposition of hummocky cross stratified sands with muds these deposits are overlain by clean hummocky and swaley cross stratified sands that were deposited in a fully marine high energy environment this evolution from mud rich storm influenced sediments to sand dominated shoreface sediments resulted from a rise in sea level and was not the result of shoreface progradation and downstepping during a sea level fall in addition to the topographic control on sequence development sediment supply to the study area changed significantly during the deposition of the three sequences initially the basin was sediment starved favouring the formation of glaucony rich sediments the sediment input gradually increased and the influence of structural highs and lows became less significant with time consequently both sequence boundaries and flooding surfaces are characterized by more conventional features in the younger part of the succession where a basinward displacement of the shoreline resulted in thick lowstand delta deposits

source and depositional processes of the surface sediments and their implications on productivity in recent past off mahanadi to pennar river mouths western bay of bengal abstract spatial distribution and depositional processes of surface sediments along 4 transects from 27 to 2825 m water depth off mahanadi godavari krishna and pennar river mouths from western part of bay of bengal were studied using grain size clay minerals organic carbon nitrogen phosphorus calcium carbonate and metal concentration grain size distribution of surface sediments has revealed that overall the sediment size decreased with increasing water depth away from the coast which indicates a transport direction from west to east and also north to south in the study area high sand content and tio 2 values at shallow water depth indicate their terrigenous source and relatively high energy conditions prevailed near the shore off mahanadi river mouth illite was the dominant clay mineral while off godavari krishna pennar river mouths smectite was the dominant clay mineral indicating input from felsic and mafic rocks respectively slightly higher ti off godavari krishna rivers as compared to mahanadi also suggested mafic source for the sediments large illite concentration in the northern part of study area supports its major supply from himalayas furthermore the decreased illite concentration southwards indicates dilution of ganges borne clays from river inputs of peninsular region possible loss of energy of ganges waters during transport inhibits the southward movement of sediments along transect off mahanadi the c n ratio varied from 6 53 to 9 43 indicating a mixed source for organic matter derived from terrestrial as well as marine along godavari krishna and pennar river mouth regions the c n ratio varied between 8 19 and 13 54 indicating increased terrestrial organic matter input supplied through the rivers all transects showed higher c n values in shallower regions c n ratio in most of the sediments was higher than redfield ratio except in deeper areas off mahanadi where they are closer to redfield ratio however n p and c p ratios were lower than the redfield ratio indicating significant limitation of p in the area calcium carbonate concentration in this region was low due to increased clay loads which cause dilution of carbonates the turbidity occurring near river mouths due to suspension of fine particles creates oxidizing conditions under such oxygenated waters preservation of organic carbon and phosphorus is less possible thereby estimating reduced productivity than actual mn excess values observed in this region may also represent oxic waters prevalent in the region high fe excess values off mahanadi godavari and pennar indicate additional iron input from terrigenous source in addition ferric hydroxide minerals from the red beds off visakhapatnam must have contributed to fe excess the al ti ratios were distinctly different off the mouth of mahanadi godavari and krishna at 9 06 6 35 and 3 97 respectively suggesting that they are possibly provenance signatures of these three rivers and could be useful as typical end members

age and impacts of the caldera forming aniakchak ii eruption in western alaska the mid holocene eruption of aniakchak volcano aniakchak ii in southwest alaska was among the largest eruptions globally in the last 10 000 years vei 6 despite evidence for possible impacts on global climate the precise age of the eruption is not well constrained and little is known about regional environmental impacts a closely spaced sequence of radiocarbon dates at a peatland site over 1000 km from the volcano show that peat accumulation was greatly reduced with a hiatus of approximately 90 120 yr following tephra deposition during this inferred hiatus no paleoenvironmental data are available but once vegetation returned the flora changed from a cyperaceae dominated assemblage to a poaceae dominated vegetation cover suggesting a drier and or more nutrient rich ecosystem oribatid mites are extremely abundant in the peat at the depth of the ash and show a longer term increasingly wet peat surface across the tephra layer the radiocarbon sample immediately below the tephra gave a date of 1636 1446 cal yr bc suggesting that the eruption might be younger than previously thought our findings suggest that the eruption may have led to a widespread reduction in peatland carbon sequestration and that the impacts on ecosystem functioning were profound and long lasting

holocene tephra stratigraphy in four lakes in southeastern oregon and northwestern nevada usa abstract to better understand the regional tephra stratigraphy and chronology of northern nevada and southern oregon tephras in archived cores taken as part of the steens mountain prehistory project from four lakes diamond pond fish and wildhorse lakes in southeastern oregon and blue lake in northwestern nevada were reexamined using more advanced electron microprobe analytical technology the best preserved and most complete core from fish lake along with wildhorse lake hosted two tephras from mt mazama llao rock and the climactic mazama a mid holocene basaltic tephra from diamond craters oregon two medicine lake tephras and an unexpected late holocene chaos crags mt lassen volcanic center tephra which was also found in the other lakes blue lake was the only lake that hosted a devils hill tephra from the three sisters volcano in west central oregon another tephra from the three sisters volcano previously reported in sediments of twin lakes in ne oregon has now been confirmed as rock mesa tephra the chaos crags devils hill and rock mesa tephras are important late holocene stratigraphic markers for central and eastern oregon and northwestern nevada

out of tune the dangers of aligning proxy archives abstract tuning is a widespread technique to combine date and interpret multiple fossil proxy archives through aligning supposedly synchronous events between the archives the approach will be reviewed by discussing a number of literature examples ranging from peat and tephra layers to orbital tuning and 18o series from marine and ice deposits potential problems will be highlighted such as the dangers of circular reasoning and unrecognised chronological uncertainties and some solutions suggested fossil proxy research could become enhanced if tuning were approached in a more quantitative reliable and objective way and especially if individual proxy archives were non tuned and kept on independent time scales

identification and correlation of visible tephras in the lake suigetsu sg06 sedimentary archive japan chronostratigraphic markers for synchronising of east asian west pacific palaeoclimatic records across the last 150 ka abstract the lake suigetsu sg06 sedimentary archive from honshu island central japan provides a high resolution palaeoenvironmental record including a detailed record of explosive volcanism from japan and south korea thirty visible tephra are recorded within the 73 m long sg06 core which spans the last 150 ka here we describe and characterise these tephras based on major element glass composition which is useful for the identification and correlation of these tephras and the age models of the records in which they are found utilising the large number of radiocarbon measurements n 600 from terrestrial plant macrofossils in the lake suigetsu sg06 record we are able to provide precise and accurate ages for the tephras from eruptions within the last 50 ka glass compositional data of some of the largest eruptions from japan k ah at aso 4 aso a aso d and ata sampled at proximal outcrops are also presented these data show that the major element glass chemistry is distinctive for many of the visible sg06 tephra units and allows some of the layers to be correlated to known eruptions from volcanoes in japan and south korea namely k ah sg06 0967 u oki sg06 1288 at sg06 2650 aso 4 sg06 4963 sg06 4979 k tz sg06 5181 aso abcd sg06 5287 and ata sg06 5181 the following ages were obtained for the sg06 tephra units 3 966 4 064 cal ka bp 95 4 probability range for the sg06 0588 tephra 10 242 10 329 cal ka bp 95 4 probability range for sg06 1293 19 487 112 sg06 2012 ka bp 2 for sg06 1965 28 425 194 sg06 2012 ka bp 2 for sg06 2504 28 848 196 sg06 2012 ka bp 2 for sg06 2534 29 765 190 sg06 2012 ka bp 2 for sg06 2601 29 775 191 sg06 2012 ka bp 2 for sg06 2602 43 713 156 sg06 2012 ka bp 2 for sg06 3485 46 364 202 sg06 2012 ka bp 2 for sg06 3668 49 974 337 sg06 2012 ka bp 2 for sg06 3912 50 929 378 sg06 2012 ka bp 2 for sg06 3974 and improved ages for two of the most important tephra markers across japan the k ah 7 165 7 303 cal ka bp at 95 4 probability range sg06 0967 and at tephra 30 009 189 sg06 2012 ka bp at 2 sg06 2650

age and duration of volcanic activity at diamond craters southeastern oregon abstract diamond craters one of several young basalt lava fields dotted across southeastern oregon was active in the time between about 7320 and 7790 years ago calibrated ages this timing is determined by a two step analysis first new radiocarbon ages from samples that underlie the lava field and existing ages from overlying deposits constrain the volcanic activity to between 6130 and 7790 years ago second paleomagnetic directions specifically a steep inclination of about 71 further constrain the age of emplacement to the older part of that interval the time before 7320 years ago paleomagnetic directions for lava emplaced early and late in the eruptive activity are essentially the same the duration of diamond craters eruptive activity must have been at least 1 2 decades in order to account for the extrusion of 1 6 km 3 of dense rock equivalent magma at rates typical of long lived basaltic eruptions whether the duration was only that brief or persisted to a century or more is irresolvable from paleomagnetic directions although the coincidence of directions from beginning to end is evidence that the eruption certainly was not protracted over many centuries

bayesian tools for tephrochronology it is suggested that bayesian statistical methods for radiocarbon data interpretation already widely used in archaeology also have potential to improve the dating of tephra layers and hence enhance their use for tephrochronology by re analysing data from a recently published paper in which the authors sought to identify the calendar date of the eruption of fourteenth century ad kaharoa tephra a key marker in new zealand prehistory it is shown that bayesian methods can be used to draw together a coherent collection of radiocarbon data undertake formal outlier detection and include prior information regardless of the calibration curve adopted the distribution of likely dates for the kaharoa eruption is multimodal by including prior information from wiggle matched dendrochronology the uncertainty on the estimate of the calendar date is reduced from a range of about 100 years to about 25 years i e 648 623 cal bp with modes at 638 and 632 cal bp using sensitivity analysis however it is shown that such estimates are affected by the quality and nature of the prior information available as a result we urge tephrochronologists to seek fastidiously both high quality radiocarbon data and reliable stratigraphic sequences that might inform future geochronological model building

major and trace element characterization expanded distribution and a new chronology for the latest pleistocene glacier peak tephras in western north america keuhn s c froese d g carrara p e foit jr f f pearce n j g rotheisler p 2009 major and trace element characterization expanded distribution and a new chronology for the latest pleistocene glacier peak tephras in western north america quaternary research 71 2 201 216 sponsorship nserc discovery grant alberta ingenuity new faculty award to duane froese

distribution and geochemical association of clay minerals on the inner shelf of central kerala india abstract the clay mineral suite of the inner shelf sediments of central kerala consists of substantial proportions of kaolinite and montmorillonite with gibbsite in minor quantities kaolinite and montmorillonite exhibit an inverse relationship in spatial distribution which has been attributed to the differential settling velocities of the minerals the geochemical association suggests a terrestrial origin for all the clay minerals the aluminous laterites of the coast seem to be the source for the kaolinite and gibbsite the absence of a relationship between trace elements and detrital clay minerals could be attributed to desorption mechanisms in the marine environment

the tephra stratigraphy of two lakes in south central british columbia canada and its implications for mid late holocene volcanic activity at glacier peak and mount st helens washington usa several mid late holocene glacier peak tephras along with mazama and mount st helens wn and p tephras were found in cores from cooley and rockslide lakes in southeastern british columbia 300 km northeast of glacier peak the sediments in cooley lake host the late holocene glacier peak a tephra 2010 calibrated cal years bp four separate glacier peak dusty creek gpdc tephras 5780 5830 cal years bp and a glacier peak set d tephra 6060 cal years bp this is the first report of glacier peak a and d tephras in british columbia the a tephra has been correlated on the basis of glass composition and age to a late holocene glacier peak tephra in the sediments of big twin lake 75 km northeast of glacier peak the glasses in the four gpdc tephra layers from cooley lake are compositionally indistinguishable from those in mount barr cirque and frozen lakes in southwestern british columbia the layers likely represent four eruptions taking place over 50 years although set d tephra has not been correlat

the intav intercomparison of electron beam microanalysis of glass by tephrochronology laboratories results and recommendations abstract the international focus group on tephrochronology and volcanism intav of the international union for quaternary research inqua has conducted an intercomparison of tephrochronology laboratories with electron beam microanalytical data on volcanic glasses submitted from 27 instruments at 24 institutions in 9 countries this assessment includes most active tephrochronology laboratories and represents the largest intercomparison exercise yet conducted by the tephrochronology community the intercomparison was motivated by the desire to assess the quality of data currently being produced and to stimulate improvements in analytical protocols and data reporting that will increase the efficacy of tephra fingerprinting and correlation participating laboratories were each supplied with a mount containing three samples for analysis 1 rhyolitic lipari obsidian id3506 2 phonolitic sheep track tephra from mt edziza british columbia canada and 3 basaltic laki 1783 a d tephra a fourth sample rhyolitic old crow tephra was also distributed most laboratories submitted extensive details of their analytical procedures in addition to their analytical results most used some combination of defocused or rastered beam and modest beam current to reduce alkali element migration approximately two thirds reported that they routinely analyze one or more secondary standards to evaluate data quality and instrument performance despite substantial variety in procedures and calibration standards most mean concentrations compare favorably between laboratories and with other data typically four or fewer data contributions had means for a given element on a given sample that differed by more than 2 standard deviations from the overall means obtaining accurate na 2 o concentrations for the phonolitic tephra proved to be a challenge for many laboratories only one half of the data sets had means within 1 standard deviation of the 8 2 wt na 2 o value obtained by other methods one mean is higher and 14 are lower three of the data set means fall below 7 wt na 2 o most submissions had relative precision better than 1 5 for the major elements for low abundance elements the precision varied substantially with relative standard deviations as small as 10 and as large as 110 because of the strong response to this project the tephrochronology community now has a large comparative data set derived from common reference materials that will facilitate improvements in accuracy and precision and which can enable improved use of published data produced by the participating laboratories finally recommendations are provided for improving accuracy precision and reporting of electron beam microanalytical data from glasses

clay minerals and trace metal association in the gangolli estuarine sediments west coast of india x ray diffraction analysis of the clay fraction of surficial sediments of gangolli estuary reveals that smectite is the dominant clay mineral followed by kaolinitechlorite and illite the distribution of clay minerals is almost uniform throughout the estuary most of the trace elements except cu pb zn and ti do not show any association with clay minerals this may be due to the desorption of trace elements which normally takes place in high saline estuarine environment organic matter and calcium do not show any significant effect on the abundance and distribution of clay minerals it appears that the detrital source is the dominating factor in influencing the relative abundance of clay minerals in the estuary

correlation of widespread holocene and pleistocene tephra layers from newberry volcano oregon usa using glass compositions and numerical analysis abstract during the last ca 500 000 years newberry volcano in oregon has produced at least 50 rhyolitic and dacitic tephras ranging from locally distributed pumice rings and cones to ignimbrites to widely dispersed plinian fallout deposits to date 13 tephra units with ages ranging from about 1525 14c years bp to 200 000 years bp have been traced to 20 sites across five western states of the usa correlations have been established by applying similarity coefficient and discriminant function analysis to major element compositions of tephra derived glasses determined by electron microprobe analysis newberry pumice correlates to four locations in oregon and idaho east lake or central pumice cone tephra correlates to two locations in oregon paulina creek ice quarry 9912d 9920c 984f 984g5 9917c and 9881c tephras correlate to ash beds at summer lake oregon paulina creek tephra also correlates to several locations in northern california and is equivalent to the olema ash bed tephra 9917c is very similar to tephras k and d at pringle falls oregon lava pass or a related tephra correlates to an unnamed tephra in the bonneville basin utah

discovery of mount mazama cryptotephra in lake superior north america implications and potential applications this research was supported by a regents professor grant by the university of minnesota to johnson

mount mazama eruption calendrical age verified and atmospheric impact assessed geochemical identification of mount mazama ash in the greenland ice sheet project 2 gisp2 ice core gives a calendrical age of 7627 150 cal yr b p 5677 150 b c for the eruption thus providing a more accurate early holocene stratigraphic time line than previously available the gisp2 record of volcanically derived sulfate suggests a total stratospheric aerosol loading between 88 and 224 mt spread over an 6 yr period following the eruption of mount mazama taking into account the likelihood of some tropospheric aerosol transport to greenland realistic estimates of the resulting atmospheric optical depth range from 0 6 to 1 5 these values may have produced a temperature depression of 0 6 to 0 7 c at mid to high northern latitudes for 1 3 yr after the eruption these results indicate that the 5677 b c eruption of mount mazama was one of the most climatically significant volcanic events of the holocene in the northern hemisphere we also calculate a maximum stratospheric cl release of 8 1 mt by the eruption which may have led to substantial stratospheric ozone depletion

pollen distribution in recent marine sediments eastern canada analysis of 90 samples from coastal and continental shelf areas off eastern canada between 42 and 69 n shows that quaternary pollen and spores are present in recent marine muds throughout this region pollen and spore concentrations range from 50 000 to 100 grains per cm3 and they decrease both offshore as a function of distance from vegetation sources and northwards as a function of lower vegetation density north of the summer arctic frontal zone isopercentage contours show that maximum relative abundances of most palynomorphs occur in marine sediments adjacent to their regions of highest vegetation representation onshore however pinus and picea pollen tend to increase in percentage abundance with distance offshore presence of these tree pollen in marine sediments off baffin island implies that wind transport is an important pathway by which bisaccate pollen types enter the ocean in addition to fluvial transport q mode factor analysis shows that four major factors account for 89 of the variance amo

vegetation and climate development of the new jersey hinterland during the late middle miocene iodp expedition 313 site m0027 abstract we investigated the palynology of sediment cores from site m0027 iodp exp 313 45 km off the present day coast of new jersey to infer palaeoenvironmental conditions during the second half of the mid miocene climatic optimum and the transition to global cooler conditions in sum 79 taxa were identified via light microscopy 13 gymnosperms 63 angiosperms 3 pteridophytes among them diospyros and reevesia which until now have not been identified from the eastern coast of north america most of the identified taxa belong to the extended multi layered broadleaved mesophytic forest that occupied the lowlands of the new jersey hinterland and reflects the zonal vegetation during time of deposition in higher altitudes or on edaphically drier slopes the mesophytic forest was replaced by conifer forest landscape changes probably induced the spread and diminution of several vegetation units during the late middle miocene an expansion of a conifer forest from 15 8 to 15 6 ma is probably connected to the appalachian uplift and a subsequent spreading of cupressaceae between 15 0 and 14 8 ma probably reflects a period of enhanced inundation of coastal lowlands the modern representatives of the main climatic elements among the encountered taxa are characterized by a typical temperate distribution climatic parameters mat cmmt wmmt map were calculated using bioclimatic analysis in light of the ongoing discussion concerning identifications of cupressaceae pollen grains two different variations of the bioclimatic analysis were performed both variations indicate humid warm temperate climatic conditions with mean annual temperatures of 13 c 5 c coldest month temperatures of 4 3 c 5 3 c and warmest month temperatures of 21 9 c 4 5 c annual precipitation values exceed 1000 mm for all samples both zonal vegetation and the calculated regional lowland palaeoclimate show no significant changes one factor creating generally climatically stable conditions between 15 8 and 12 7 ma was likely the buffering effect of the gulf current loop

paleoclimatic and paleoenvironmental records of the oligocene miocene transition central jylland denmark a multidisciplinary study of the oligocene miocene o m transition was carried in two boreholes harre 1 and horn 1 from the danish land area in order to improve the understanding of the paleodimatological and environmental changes across the mi 1 the earliest miocene cooling event dinoflagellate cyst dinocyst biostratigraphy supported by re evaluation of the foraminiferid biostratigraphy a new set of magnetic data and stable carbon isotope delta c 13 records were applied to improve the age model for the studied succession as well as the positioning of the o m boundary these data further enabled a correlation of the two investigated profiles with the well established stratigraphical framework for the danish area the bit index an organic proxy indicating the relative input of soil derived organic matter dinocyst assemblages and palynofacies have been applied for establishing the paleoenvironmental changes across the oligocene miocene o m boundary our data indicate a shallowing upward trend in the latest oligocene resulting in the establishment of a very restricted marine setting in the earliest miocene our study confirms that the o m boundary is located at a sequence boundary the local sequence boundary b sb b and corresponds to an increase in terrestrial organic matter input a mean air temperature record based on the mbt cbt proxy reveals an similar to 2 degrees c drop in temperature at the o m and the sequence boundary our findings confirm previous suggestions that this sequence boundary is a result of the glacio eustatic sea level fall related with the mi 1 cooling event the unconformity at the sequence boundary probably correlates with the coldest part of mi 1 and thus no deposits from this period have been preserved this suggests that the temperature drop might have been greater than 2 degrees c

distribution and dispersal of clay minerals on the western continental shelf of india abstract sediment samples distributed over a distance of 1700 km from the inner continental shelf of western india were analysed for their clay mineral content by x ray diffraction the clay minerals present in the sediments in order of abundance are montmorillonite kaolinite illite chlorite and gibbsite based on the abundance of montmorillonite and kaolinite four clay mineral provinces on the continental shelf have been demarcated these are 1 the montmorillonite kaolinite illite chlorite province off the gulf of kutch 2 the montmorillonite rich zone off the gulf of cambay 3 a transition zone on the central parts of the shelf and 4 a relatively montmorillonite poor gibbsite province on the southwestern part of the shelf source rock influence on clay mineral composition appears to be more important than physical transport the southwest monsoon drift in the present case in the northwestern part of the study area the high velocity tidal streams of the macrotidal gulf of kutch act as dynamic barriers to longshore sediment dispersal leading to distinct clay mineral assemblages on the shelf north and south of the gulf mouth

new dates for first millennium bc tephra isochrones in ireland three distinct first millennium bc tephras bmr 190 omh 185 gb4 150 have been recognized in irish peat deposits including a previously undated ash bmr 190 we present the results of a programme of high precision 14c wiggle matching on a peat profile containing all three tephras from glen west county fermanagh northern ireland the wiggle match provides highly refined dates of 705 585cal bc for bmr 190 755 680cal bc for omh 185 and 800 758cal bc for gb4 150 the tephras constitute valuable widespread isochrones for palaeoecological research across the first millennium bc when a prolonged 14c calibration plateau between 750 and 400 cal bc presents a major problem to dating and correlating palaeoenvironmental events from multisite multiproxy studies of the period

middle miocene palaeoenvironments of the niger delta abstract in order to recognize the palaeoenvironments of the deltaic sequence of the middle miocene oil bearing e2 0 reservoir in the kolo creek field investigations of sediment grain size textures structures trace fossils mineralogical composition diagenetic imprints palynodebris types palynomorphs and foraminifera have been carried out on materials from two boreholes using this multidisciplinary approach the following have been identified in the reservoir ten lithofacies two palynofacies associations a total of 103 palynomorph taxa and a low diversity assemblage of benthic foraminifera these criteria have provided information on the positions of the deposits relative to the palaeocoastline as well as the physical and ecological conditions within the delta the overall depositional conditions were found to be broadly similar to those in the present day niger delta although the climatic conditions were somewhat drier in the middle miocene as reflected in the abundance of the grass pollen graminidites seven or possibly eight deltaic sub environments of deposition have been recognized based on an interpretation of gamma ray and resistivity log profiles as well as sedimentological and microfossil data from cores of two boreholes in the field these depositional settings are the distributary channel fill tidal channel fill lagoon tidal flat lagoonal delta flood tidal delta in the lower delta plain the coastal barrier and the delta fringe and prodelta in the outer delta the two palynofacies associations a c and b d which emerged from average linkage cluster analysis of the palynodebris are environmentally significant

depositional settings and palynofacies assemblages of the upper triassic fluviodeltaic mungaroo formation northern carnarvon basin western australia

miocene climate evolution of northern europe a palynological investigation from denmark a palynological investigation has been conducted on lower upper miocene sediments from jylland denmark corresponding to the time interval of about 19 to 8 ma the sediments derived from the sdr vium drill core were deposited in marine to marginal marine environments as shown by the relatively high abundance of dinoflagellate cysts in all samples nevertheless rich and diverse pollen assemblages occur throughout the succession and the palynological analysis reveals that coastal areas of the study area were during the miocene dominated by taxodium swamp forests that also hosted terrestrial angiosperms such as nyssa betula alms and elements of the myricaceae further inland a mixed deciduous evergreen forest prevailed in areas with better drained soils or on elevated areas gymnospermous conifer forests prevailed including taxa such as pinus sequoia and sciadopitys overall the climate in the study area was warm temperate during major parts of the miocene with mean annual temperatures between 15 5 and 20 degrees c by employing the coexistence approach combined with the method of allocating taxa into standardized climatic groups four different climatic miocene events are detected within the studied succession correlated to the coeval climate record of northwestern europe the oldest event is a cooling during the earlier burdigalian at approximately 19 ma coinciding with the mbi 1 oxygen isotope excursion at ca 18 5 ma in mid burdigalian a warming phase is reconstructed characterized by the highest precipitation rates observed in the sedimentary succession a warming trend starting in the latest burdigalian corresponds to the globally recognized middle miocene climatic optimum mmco while a longer term late neogene cooling was initiated in the mid serravallian about 13 ma c 2011 elsevier b v all rights reserved less

neogene inversion of the central graben and ringkobing fyn high denmark abstract inversion in the north sea area and onshore denmark is a well known phenomenon and the main phase is interpreted to have occurred in the cretaceous and early cenozoic this study demonstrates an important early neogene inversion phase that resulted in the most distinct flexuring of the southern danish central graben during the cenozoic reactivation of structures on the ringkobing fyn high also took place during this inversion phase apatite fission track data confirm marked uplift of the marginal areas of the fennoscandian shield the recognition of the inversion of the ringkobing fyn high is based on new high resolution seismic data and has not been reported previously minor inversion pulses continued throughout the early and middle miocene and ceased in the early late miocene the early neogene inversion was the last major influence of the alpine orogeny in the danish area as a consequence of the early neogene inversion clastic sediments were flushed into the norwegian danish basin due to increased relief in the hinterland the high sediment supply continued throughout the early miocene despite changing climatic conditions from an overall cold temperate climate to a subtropical climate at the transition from the early miocene to the middle miocene the high sediment yield however ceased due to marked subsidence in the middle late miocene following the last inversion pulse in the middle miocene

a high precision age estimate of the holocene plinian eruption of mount mazama oregon usa the climactic eruption of mount mazama in oregon north america resulted in the deposition of the most widespread holocene tephra deposit in the conterminous united states and south western canada the tephra forms an isochronous marker horizon for palaeoenvironmental sedimentary and archaeological reconstructions despite the current lack of a precise age estimate for the source eruption previous radiocarbon age estimates for the eruption have varied and greenland ice core ages are in disagreement for the mazama tephra to be fully utilised in tephrochronology and palaeoenvironmental research a refined precise and accurate age for the eruption is required here we apply a meta analysis of all previously published radiocarbon age estimations n 81 and perform bayesian statistical modelling to this data set to provide a refined age of 7682 7584 cal yr bp 95 4 probability range although the depositional histories of the published ages vary this estimate is consistent with that estimated from the gisp2 ice core of 7627 150 yr bp zdanowicz et al 1999

palynofacies classification of submarine fan depositional environments outcrop examples from the marnoso arenacea formation italy abstract basin floor fans contain some of the largest deep water hydrocarbon accumulations discovered however they also demonstrate extremely complex stratigraphic architecture understanding of which is crucial for maximum recovery here we develop a new method based upon palynofacies analysis for the distinction of the different depositional environments that are commonly associated with basin floor fans previous studies and our sedimentological analysis allow good confidence in the discrimination of the different depositional environments of the outcropping marnoso arenacea formation fan system one hundred and thirty five samples were collected from mudstones in conjunction with sedimentary logging of 871 m of outcrops six lithofacies associations are described and interpreted to represent lobe axis lobe fringe fan fringe contained interlobe basin plain and starved high depositional sub environments palynofacies of these elements demonstrate turbidites to be rich in terrestrial organic matter with sixteen categories of matter recognised the abundances and proportions of particles varies between sub environments with lobe axis deposits containing the largest densest particles with a transition to ever smaller and lighter particles moving toward the basin plain fuzzy c means statistical analysis was used to explore this trend distribution of organic matter is not random but is dominated by hydrodynamic sorting and sequential fall out of particles as turbidity currents passed across the basin this allows a palynofacies classification scheme to be constructed to assist the identification of depositional environments of submarine fans which may be combined with subsurface data to assist reservoir characterisation

were there two borrobol tephras during the early lateglacial period implications for tephrochronology abstract a series of ams radiocarbon measurements of terrestrial plant macrofossil remains are presented from a lake sequence in southernmost sweden in an attempt to constrain the age of the borrobol tephra this recently identified ash layer has been frequently suggested as a potentially significant marker horizon for assessing the precise timing of the initial warming in different parts of europe at the start of greenland interstadial 1 gi 1 two different methods are adopted in order to derive a calendar age estimate for this event an age of ca 13 900 cariaco varve yrs bp is derived from a visual wiggle match of the age series to the cariaco basin data set the second approach is based on bayesian probability analysis and constrains the age of the borrobol tephra in southern sweden to between 13 800 14 450 and 13 667 14 331 cal yrs bp 95 confidence using the cariaco and lake suigetsu records as calibration data sets respectively these new age depth models together with the pollen stratigraphy suggest that the borrobol tephra as found in southern sweden falls within the late older dryas gi 1d or the early allerod gi 1c whereas other european sequences indicate that this tephra falls close to the gs 2 gi 1 transition whether or not this indicates that the different occurrences of the bt in northern europe are coeval is discussed and the implications that arise for the application of tephrochronology during this period are outlined

new accelerator mass spectrometry radiocarbon ages for the mazama tephra layer from kootenay national park british columbia canada charcoal fragments recovered from the mazama air fall tephra layer in cores from dog and cobb lakes kootenay national park british columbia yielded accelerator mass spectrometry ages of 6720 70 and 6760 70 14c years bp respectively these two new ages together with other previously published radiocarbon ages on charcoal and twig fragments from mazama air fall deposits indicate that the climactic eruption of mount mazama occurred 6730 40 14c years bp

cenozoic structures in the eastern north sea basin a case for salt tectonics discussion abstract clausen et al 2012 rule out that regional tectonism was important in the development of the eastern north sea basin during the miocene however detailed study of outcrops boreholes and high resolution seismic data across the eastern north sea reveals that regional tectonism was important in the development of the basin regional tectonism both resulted in inversion of former basins and in the triggering of salt movements reactivation of older fault system may also have occurred the morphology of the basin created by these processes strongly controlled major displacements of the shoreline in routing the fluvial systems in shaping valleys and in transporting very coarse grained sediments far into the basin the role of salt tectonism as indicated by clausen et al 2012 is in agreement with earlier studies but the significant salt movements during the quaternary onshore denmark must be clearly separated from only minor movements in the miocene

a revised age for the kawakawa oruanui tephra a key marker for the last glacial maximum in new zealand abstract the kawakawa oruanui tephra kot is a key chronostratigraphic marker in terrestrial and marine deposits of the new zealand nz sector of the southwest pacific erupted early during the last glacial maximum lgm the wide distribution of the kot enables inter regional alignment of proxy records and facilitates comparison between nz climatic variations and those from well dated records elsewhere we present 22 new radiocarbon ages for the kot from sites and materials considered optimal for dating and apply bayesian statistical methods via oxcal4 1 7 that incorporate stratigraphic information to develop a new age probability model for kot the revised calibrated age 2 standard deviations for the eruption of the kot is 25 360 160 cal yr bp the age revision provides a basis for refining marine reservoir ages for the lgm in the southwest pacific

laacher see tephra a widespread isochronous late quaternary tephra layer in central and northern europe a late quaternary tephra layer widespread in central and northern europe resulted from explosive plinian and phreatomagmatic eruptions of the laacher see volcano 11 000 yr b p the tephra is distinguished from other late quaternary andesitic rhyolitic airfall tuff layers in northern europe and from basaltic or trachytic tuff deposits in southern europe by its phonolitic composition and abundance of sanidine plagioclase clinopyroxene amphibole and sphene the proximal tephia sequence at laacher see is divided into three main deposits the predominantly plinian deposits of lower and middle laacher see tephra llst and mlst and phreatomagmatic deposits of the upper laacher see tephra ulst the mlst member is further subdivided into beds a b and c1 c2 and c3 the chemical composition of the magma is highly differentiated phonolite in the llst to mlst b sections but mafic phonolite in the mlst c1 to ulst sections all deposits are considered to be isochronous the frequency maximum of 16 radiocarbon datings indicating an eruption about 11 000 50 yr b p distal ash was deposited in three main fans directed to the northeast lst traced up to 1 100 km distance south lst traced up to 600 km and southwest lst traced up to 100 km tephrostratigraphic correlation of the distal ash deposits is based on a the major element composition of glass shards b lithology and c heavy mineral analyses the northeastern fan consists of deposits from llst mlst b and mlst c1 eruptive phases the southern fan comprises mlst a mlst c2 and ulst deposits and the southwestern fan consists exclusively of ash from the ulst eruptive phase northeastern transport of ash during eruptive phases with high plinian eruption columns but southern and southwestern transport of ash along phases of relatively low eruption columns are interpreted in terms of prevailing southwesterly paleowinds at high altitudes tropopause level but northerly winds dominating in the lower atmosphere the laacher see eruption columns were emplaced into an atmosphere vertically zoned with respect to paleowind directions which also explains the near vent shifting of llst mlst b and mlst c1 iso pach axes from east southeast to northeast within the first 20 km of transport

latest caledonian to present tectonomorphological development of southern norway abstract the regional resultant stress field of the northeastern north atlantic has shifted significantly throughout the phanerozoic in fennoscandian parts of the caledonian orogen mountain building which was characterized by nw se contraction reference to present north was followed by a collapse with transport both parallel and transverse to the mountain chain the late palaeozoic mesozoic saw several stages of e w to nw se extension varying in time and position local episodes of inversion are traceable in some cases particularly in connection with deep seated and long lived zones of weakness the cenozoic has to a larger degree been affected by compression including folding and basin inversion again some of the more pronounced effects of local inversion are related to pre existing fault systems neogene uplift of the western mountainous area in scandinavia can be unravelled by potential field study aft data and reflection seismic sections assuming that the region is close to isostatic equilibrium the uplifted areas must be supported at depth by substantial volumes of low density material within the crust or the mantle close to the crust mantle interface or close to the lithosphere asthenosphere interfaces a series of nw se oriented cross sections representing successive stages of development from the late caledonian to present were prepared and used to analyse the tectonomorphological development as related to the shifting stress configurations three stages are inferred stage 1 devonian late permian denudation of the caledonian mountain chain during the latest stage of closing of the iapetus ocean in early to mid devonian times the caledonian mountain chain reached its maximum elevation of perhaps as much as 8 9 km including the foreland basins to the east the average topographic gradient of the eastern flank may have been in the order of 1 3 the denudation of the caledonian mountains continued into the permian and by the end of the permian the mountain system was more or less obliterated with a gradient of the eastern flank probably continued to fall to less than 0 1 stage 2 triassic late cretaceous tectono thermal uplift of central south norway uplift of central south norway was rejuvenated in triassic times and continued throughout the jurassic and early cretaceous the gradient of the eastern flank increased to a maximum of approximately 0 15 and master structural elements like the laerdal gjende olestol fault complex again played important roles in the development stage 3 tertiary present renewed tectono thermal activity and post glacial rebound a second phase of post caledonian tectono thermal uplift of south central norway started in oligocene time again increasing the gradient of the eastern flank of south norway around 0 2

a record of late quaternary vegetation from davis lake southern puget lowland washington abstract pollen and macrofossil analyses of a core spanning 26 000 yr from davis lake reveal late pleistocene and holocene vegetational patterns in the puget lowland the core ranges lithologically from a basal inorganic clay to a detritus gyttja to an upper fibrous peat and includes eight tephra units the late pleistocene pollen sequence records two intervals of tundra parkland vegetation the earlier of these has high percentages of picea gramineae and artemisia pollen and represents the vegetation during the evans creek stade fraser glaciation ca 25 000 17 000 yr b p the later parkland interval is dominated by picea tsuga mertensiana and gramineae it corresponds to the maximum ice advance in the puget lowland during the vashon stade fraser glaciation ca 14 000 yr b p an increase in pinus ontorta pollen between the two tundra parkland intervals suggests a temporary rise in treeline during an unnamed interstade after 13 500 yr b p a mixed woodland of subalpine and lowland conifers grew at davis lake during a period of rapid climatic amelioration in the early holocene the prolonged expansion of pseudotsuga and alnus woodland suggests dry temperate conditions similar to those of present rainshadow sites in the puget lowland more mesic forests of tsuga eterophylla thuja plicata and pseudotsuga similar to present lowland vegetation appeared in the late holocene ca 5500 yr b p

correlation of distal tephra layers in loess in the channeled scabland and palouse of washington state abstract thirty two distal tephra layers that are interbedded in quaternary loess at 13 sites in the channeled scabland and palouse were sampled as part of a regional study of the stratigraphy and chronology of dominantly windblown sediments on the columbia plateau an electron microprobe was used to determine the elemental composition of volcanic glass in all of the samples and also to determine the composition of ilmenite in 14 of them two of the distal tephra layers correlate with glacier peak eruptions 11 200 yr b p five with mount st helens tephra set s 13 000 yr b p and nine with mount st helens tephra set c ca 36 000 yr b p based on analysis of glass and ilmenite in reference pumices from glacier peak mount st helens mount mazama mount rainier and mount jefferson on the calculation of similarity coefficients for comparisons of both glass and ilmenite reference compositions with those of distal tephras and on considerations of stratigraphic position the composition of glass and ilmenite and the stratigraphic position of one distal tephra layer in the loess suggests that it is from an eruption of mount st helens at least several thousand years older than the set c eruptions glass composition and stratigraphic position of a distal tephra at another site in loess suggested a possible correlation with some layers of the pumice castle eruptive sequence at mount mazama ca 70 000 yr b p but similarity coefficients on ilmenite of only 45 and 48 fail to support the correlation and show why multiple correlation methods should be used similarity coefficients higher than 96 for both glass and ilmenite establish a correlation with mount st helens layer cw for distal layers in two widely separated sites these layers are in sedimentary successions that are closely associated with giant floods in the channeled scabland the 36 000 yr b p radiocarbon age of the mount st helens set c establishes a minimum limiting date for an episode of flooding that predates the widespread late wisconsin floods a correlation of distal tephra layers at two other sites in the scabland and palouse establishes a chronostratigraphic link to a still older episode of flooding within the brunhes normal polarity chron six distal tephra layers in pre late quaternary loess that are not correlated with known or dated eruptions have compositions and distinctive stratigraphic positions relative to magnetic reversal boundaries that make them key markers for future work

unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on antarctica since the earliest oligocene circa 35 ma the growth and decay of ice sheets during the oligocene to modern ice house world caused glacioeustatic sea level changes the early eocene was an ice free greenhouse world but it is not clear if ice sheets existed during the middle to late eocene doubt house world benthic foraminiferal 18o records place limits on the history of glaciation suggesting the presence of ice sheets at least intermittently since the earliest oligocene the best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic 18o records although planktonic isotope records from the western equatorial regions are limited subtropical planktonic foraminifera may also record such ice volume changes it is difficult to apply these established principles to the cenozoic 18o record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events we improved oligocene to miocene correlations of 18o records and erected eight oxygen isotope zones oi1 oi2 mi1 mi6 benthic foraminiferal 18o increases which are associated with the bases of zones oil circa 35 8 ma oi2 circa 32 5 ma and mil circa 23 5 ma can be linked with 18o increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near antarctica our new correlations of middle miocene benthic and western equatorial planktonic 18o records show remarkable agreement in timing and amplitude we interpret benthic planktonic covariance to reflect substantial ice volume increases near the bases of zones mi2 circa 16 1 ma mi3 circa 13 6 ma and possibly mi5 circa 11 3 ma possible glacioeustatic lowerings are associated with the 18o increases which culminated with the bases of zone mi4 circa 12 6 ma and mi6 circa 9 6 ma although low latitude planktonic 18o records are required to test this these inferred glacioeustatic lowerings can be linked to seismic and rock disconformities for example we link 12 oligocene early late miocene inferred glacioeustatic lowerings with 12 of the sequence boundaries inferred eustatic lowerings of haq et al 1987

revised 14c age for st helens y tephra at tonquin pass british columbia the age of a mount st helens set y tephra at tonquin pass british columbia previously assumed to be 4300 years bp is revised to ca 3400 years bp based on bracketing 14c dates of 3140 70 beta 13558 and 3680 80 years bp beta 13559 the implications of this revision for tephrostratigraphy of this area are discussed

the application of ichnology to palaeoenvironmental and stratigraphic analysis it has been increasingly realized by sedimentologists in the petroleum industry and academia that integration of ichnological information into sedimentological models and vice versa is one of the main means by which we can improve our understanding of ancient depositional environments this volume aims to provide an analytical review of the ichnology of all major depositional environments and the use of ichnology in biostratigraphic and sequence stratigraphic analysis as well as highly refined palaeoenvironmental studies the remit of the book is achieved through a combination of review articles and novel research papers that outline methodologies and protocols for improving our understanding of ancient palaeoenvironments trace fossils from microscopic borings to dinosaur footprints are considered the comprehensive coverage of ancient depositional environments means that the book will be of use as a course text for undergraduates as well as an invaluable reference text for all students of ichnology whether they are ichnologists sedimentologists or petroleum geologists by trade

insights from a synthesis of old and new climate proxy data from the pyramid and winnemucca lake basins for the period 48 to 11 5 cal ka abstract a synthesis of old and new paleoclimatic data from the pyramid and winnemucca lake basins indicates that between 48 0 and 11 5 103 calibrated years bp hereafter ka the climate of the western great basin was to a degree linked with the climate of the north atlantic paleomagnetic secular variation psv records from pyramid lake core plc08 1 were tied to the gisp2 ice core record via psv matches to north atlantic sediment cores whose isotopic and or carbonate records could be linked to the gisp2 18o record relatively dry intervals in the western great basin were associated with cold heinrich events and relatively wet intervals were associated with warm dansgaard oeschger do oscillations the association of western great basin dry events with north atlantic cold events and vice versa switched sometime after the laurentide ice sheet lis reached its maximum extent for example the lahontan highstand which culminated at 15 5 ka and a period of elevated lake level between 13 1 and 11 7 ka were associated with cold north atlantic conditions the latter period with the youngest dryas event relatively dry periods were associated with the bolling and allerod warm events a large percentage of the lis may have been lost to the north atlantic during heinrich events 1 and 2 and may have resulted in the repositioning of the polar jet stream over north america the trego hot springs wono carson sink and marble bluff tephras found in core plc08 1 have been assigned gisp2 calendar ages of respectively 29 9 33 7 34 1 and 43 2 ka given its unique trace element chemistry the carson sink bed is the same as wilson creek ash 15 in the mono lake basin this implies that the mono lake magnetic excursion occurred at approximately 34 ka and it is not the laschamp magnetic excursion the entrance of the first americans into the northern great basin is dated to approximately 14 4 ka a time when the climate was relatively dry evidence for human occupation of the great basin is lacking for the next 1100 years y i e the oldest western stemmed point site in the great basin dates to 13 3 ka two hypotheses are suggested for this cultural hiatus 1 the climate had deteriorated to the point that people vacated the great basin or 2 people moved to basin bottom wetlands that persisted during the dry period and then the subsequent younger dryas wet event erased the archaeological evidence deposited around the low elevation wetland sites

paleomagnetic and tephra evidence for tens of missoula floods in southern washington paleomagnetic secular variation and a hiatus defined by two tephra layers confirm that tens of floods from glacial lake missoula montana entered washington s yakima and walla walla valleys during the last glaciation in these valleys the field evidence for hiatuses between floods is commonly subtle however paleomagnetic remanence directions from waterlaid silt beds in three sections of rhythmically bedded flood deposits at zillah touchet and burlingame canyon display consistent secular variation that correlates serially both within and between sections the secular variation may further correlate with paleomagnetic data from fish lake oregon and mono lake california for the interval 12 000 17 000 14 c yr b p deposits of two successive floods are separated by two tephras derived from mount st helens washington the tephras differ in age by decades indicating that a period at least this long separated two successive floods the beds produced by these two floods are similar to all of the 40 beds in the slack water sediment sequence suggesting that the sequence is a product of tens of floods spanning a period of perhaps a few thousand years

eruptive history and geochronology of mount mazama and the crater lake region oregon geologic mapping k ar and 40 ar 39 ar age determinations supplemented by paleomagnetic measurements and geochemical data are used to quantify the quaternary volcanic history of the crater lake region in order to define processes and conditions that led to voluminous explosive eruptions the cascade arc volcano known as mount mazama collapsed during its climactic eruption of 50 km 3 of mainly rhyodacitic magma 7700 yr ago to form crater lake caldera the mazama edifice was constructed on a pleistocene silicic lava field amidst monogenetic and shield volcanoes ranging from basalt to andesite similar to parental magmas for mount mazama between 420 ka and 35 ka mazama produced medium k andesite and dacite in 2 1 proportion the edifice was built in many episodes some of the more voluminous occurred approximately coeval with volcanic pulses in the surrounding region and some were possibly related to deglaciation following marine oxygen isotope stages mis 12 10 8 6 5 2 and 2 magmas as evolved as dacite erupted many times commonly associated with or following voluminous andesite effusion establishment of the climactic magma chamber was under way when the first preclimactic rhyodacites vented ca 27 ka the silicic melt volume then grew incrementally at an average rate of 2 5 km 3 k y 1 for nearly 20 k y the climactic eruption exhausted the rhyodacitic magma and brought up crystal rich andesitic magma mafic cumulate mush and wall rock granodiorite postcaldera volcanism produced 4 km 3 of andesite during the first 200 500 yr after collapse followed at ca 4800 yr b p by 0 07 km 3 of rhyodacite the average eruption rate for all mazama products was 0 4 km 3 k y 1 but major edifice construction episodes had rates of 0 8 km 3 k y 1 the long term eruption rate for regional monogenetic and shield volcanoes was d 0 07 km 3 k y 1 but only 0 02 km 3 k y 1 when the two major shields are excluded plutonic xenoliths and evidence for crystallization differentiation imply that the amount of magma intruded beneath mount mazama is several times that which has been erupted the eruptive and intrusive history reflects competition between 1 crystallization driven by degassing and hydrothermal cooling and 2 thermal input from a regional magma flux focused at mazama before ca 30 ka relatively small volumes of nonerupted derivative magma crystallized to form a composite pluton because the upper crust had not been heated sufficiently to sustain voluminous convecting crystal poor melt subsequently and perhaps not coincidentally during mis 2 a large volume of eruptible silicic magma accumulated in the climactic chamber probably because of heating associated with mantle input to the roots of the system as suggested by eruption of unusually primitive magnesian basaltic andesite and tholeiite west of mazama

radiocarbon dating of pollen by accelerator mass spectrometry radiocarbon dating of bulk sediments has been the standard method for establishing chronologies in the studies of lake sediment cores which have contributed significantly to our knowledge of late quaternary paleo environments these bulk sediment dates are presumed to be direct ageindicators for the speciments e g pollen or macrofossils which are actually being studied however several recent studies have reinforced long standing apprehensions concerning this presumption in this study we demonstrate for the first time the radiocarbon dating of pollen concentrate samples by accelerator mass spectrometry the dates obtained by this method should provide more reliable radiocarbon chronologies for paleo environmental studies than have been obtainable by bulk sediment dating

deposition models for chronological records abstract long term sedimentary sequences provide a wealth of useful information for research into the palaeo environment especially in relation to past climate change shorter records provide similar information in many archaeological contexts however if such records are to be used to provide precise timing of events and more critically the relative timing between different records methods are needed to provide accurate and precise age depth models for these sequences given the imprecision of individual calibrated radiocarbon determinations it is necessary to use the information we have about the deposition process to refine our chronologies and also to provide interpolation between dated levels in any sequence even with layer counted chronologies the uncertainties are sometimes hard to quantify this paper outlines a range of bayesian models for deposition which have been implemented in the computer programme oxcal these models can be used to combine information from the sediments themselves with radiocarbon or other direct dating information such models have the potential to integrate information between different records and provide a coherent chronology on which to base environmental or archaeological research