petrified wood of southwestern oregon implications for cenozoic climate change abstract over 1900 petrified wood specimens were collected from six localities spanning the eocene to miocene along a northeast transect parallel to the dip of the payne cliffs formation and western cascades group in southwestern oregon this study also presents new 40ar 39ar plateau age data for cenozoic deposits in southern oregon lower to middle eocene deposits yielded 305 specimens of petrified wood from sandstones and conglomerates of the basal part of the payne cliffs formation with only 6 of dicotyledons exhibiting distinct growth rings and none having ring porous or semi ring porous wood middle eocene exposures just stratigraphically above the first locality produced 278 specimens from the lower to the middle part of the payne cliffs formation with 66 of the dicotyledons exhibiting distinct growth rings two specimens of palmoxylon were also collected from sediments at this locality an upper eocene exposure produced 792 petrified wood specimens from volcaniclastic sediments with 88 of the dicotyledons exhibiting distinct growth rings sediments at this locality also produced one specimen of cibotium oregonensis oregon tree fern and several specimens of palmoxylon middle oligocene deposits yielded 218 petrified wood specimens from volcaniclastic sediments of the middle part of the western cascades group with 97 of the dicotyledons exhibiting distinct growth rings an upper oligocene exposure yielded 254 specimens from volcaniclastic sediments of the upper part of the western cascades group with all dicotyledons exhibiting distinct growth rings and 59 having ring porous or semi ring porous wood further this study establishes a 40ar 39ar plateau age date of 24 09 0 24 ma from plagioclase crystals in a tuffaceous sandy to pebbly siltstone at this locality finally lower miocene rocks yielded 101 specimens including 20 dicotyledons of which 70 were ring porous or semi ring porous with most specimens consisting of gymnosperms the increase over time in the percentages of dicotyledon specimens with distinct growth rings and with ring porous and semi ring porous wood from this study suggests an overall climatic shift from tropical early eocene to cool temperate early miocene in southwestern oregon these results are consistent with a similar climatic shift evidenced by paleoecological reconstructions for the eocene to miocene of the john day fossil beds in central oregon

simulation of groundwater exchange between an unconfined aquifer and a discrete fracture network with laminar and turbulent flows abstract in this study a new approach is developed to simulate groundwater flow through both an overlying unconfined aquifer and an underlying discrete fracture network the groundwater exchange between the aquifer and the fracture network including magnitude and direction is explicitly simulated based on the mass conservation which depends on a variety of parameters related to flow and network characteristics in the overlying unconfined aquifer we approximate the flow using the dupuit assumptions in the underlying fracture network we use the cubic law and forchheimer s law to iteratively simulate laminar or turbulent flow in individual fractures depending on the reynolds number explicitly separating laminar and turbulent flows in the fractures results in a system of nonlinear equations which is iteratively solved while the flow from the overlying unconfined aquifer is a small portion of the overall flow in the underlying fracture network incorrect use of the laminar or turbulent flow equation in the fractures can lead to significant errors in simulating the flow exchange as apertures increase both the portion of the total flowrate in the aquifer and the portion of the flow in the fractures coming from the aquifer decrease as the overall hydraulic gradient increases both the portion of the total flow in the aquifer and the portion of the fracture flow that comes from the aquifer increase the portion of the total flow in the aquifer increases with the aquifer thickness while the portion of fracture flow coming from the overlying aquifer decreases

analytical solution for groundwater flow in an anisotropic sloping aquifer with arbitrarily located multiwells this paper presents a new analytical solution to describe the hydraulic head distribution and flow system in an anisotropic unconfined aquifer with a sloping bed and arbitrarily located multiwells under transient recharge unlike the existing analytical solutions for delineating the capture zones the solution presented in this study is easy and convenient to calculate flow field in some complicated systems and it can provide useful information for the pump and treat design in addition the presented solution may have the possible application in evaluating the sensitivity of hydrogeological parameters or estimating the hydraulic parameters when coupled with an optimization approach to analyze the aquifer data

alluvial and volcanic pathways to silicified plant stems upper carboniferous triassic and their taphonomic and palaeoenvironmental meaning petrographic imaging in combination with qualitative and quantitative instrumental analyses of mineral mass allow us to obtain material signatures of silicified plant stems that are relatively common in sediments of continental basins since the late palaeozoic these fossils can be found in their original strata but commonly have been removed from their environmental and stratigraphic context redeposited and scattered on the recent land surface after erosion of the parent rocks analytical data gathered from x ray diffraction analysis hot cathodoluminescence cl imaging and spectroscopy electron microprobe analysis raman spectrometry and polarised light microscopy serve to characterise material signatures of samples from basins in brazil germany the czech republic sultanate of oman mongolia antarctica france and the usa this collection includes silicified pennsylvanian and permian plant taxa and a few from the triassic found in fluvial environments and sites influenced by volcanism with the purpose to discern fundamental material characteristics formed under particular environmental circumstances late pennsylvanian and permian silicified stems in fluvial rocks include the presence of well crystalline quartz alpha sio2 sometimes with a trace of kaolinite showing weak cl mostly blue or dark reddish occasional mosaic or patchy preservation of anatomical details and other signs of pressure distortion of wet trunks in fluvial deposits and subsequent diagenetic recrystallisation the presumed silica source for the initial stage of silicification was weathering of labile minerals mostly feldspars in the alluvium in wood from aeolian deposits moganite in combination with goethite was detected based on our results we propose that the stems were silicified in sandy or gravelly fluvial deposits most frequently in arkoses and arkosic sands indicators of relatively warns climate with pronounced seasonal distribution of precipitation excluded from this interpretation are steins silicified primarily by volcanic material these are distinguished by a higher species diversity silicification close to the site of growth miscellaneous mineralogy usually with very colourful cl shades and the presence of metastable forms of sio2 opal ct or moganite this volcanic influence on silicification mode is less clearly controlled by seasonality of precipitation or palaeoclimate

palaeoclimatic interpretation of the wood structures of the trees in the chinle formation upper triassic petrified forest national park arizona usa abstract typically the fossil woods in the upper triassic chinle formation in petrified forest national park arizona usa do not show annual growth rings but contain irregular growth interruptions similar to those found in trees now growing in the humid tropics these interruptions could be due to endogenous hormonal effects or to occasional local variations in water supply therefore it is conclucded that the late triassic fossil forests in the park lived in conditions that permitted continuous tree growth limited data from areas outside of the park suggests that similar conditions prevailed in adjacent areas in the southwestern united states during the late triassic although this region is reported to have been under the influence of a monsoonal circulation pattern during the late triassic the growth of the trees does not appear to have been greatly affected

pennsylvanian fossil forests in growth position t0 assemblages origin taphonomic bias and palaeoecological insights abstract fossil forests buried in growth position in a geological instant t 0 assemblages are far more abundant in pennsylvanian successions than in any other part of the geological record in this review paper we evaluate the fundamental controls on the origin of these phenomena investigate the taphonomic biases that influence their composition and summarize their palaeoecological significance following earlier workers we highlight that high rates of burial and accommodation are essential for the formation and preservation of t 0 assemblages contexts especially favourable for their origin include ashfalls proximal to volcanic centres coastal plains drowned by relative sea level rise and fluvial environments such as channel bars crevasse splays and distributary lobes long term preservation requires high rates of subsidence consequently the vast majority of palaeozoic t 0 assemblages are confined to wetland settings at or close to sea level whereas drylands are poorly represented and uplands rarely sampled if ever however this is not the only major bias in the fossil record taphonomic processes selectively preserve plants dependent on their anatomy and stature and on groundwater chemistry thus although t 0 assemblages offer unrivalled insights into the nature of ancient forests whole plant reconstructions tree density canopy height productivity plant hydraulics cohort dynamics spatial heterogeneity ecological gradients tree sediment interactions and animal plant interactions to name but a few it is naive to believe they provide photographic snapshots9 of palaeoecosystems none the less careful taphonomic analysis of t 0 assemblages offers the potential for a nuanced understanding of these evocative phenomena and much remains to be learned from these important palaeoecological resources

late eemian warming in the nordic seas as seen in proxy data and climate models 1 we analyze a transient simulation of the last glacial inception in a climate model of intermediate complexity focusing on sea ice ocean circulation dynamics in the north atlantic and nordic seas as northern high latitude summer insolation decreases toward the end of the eemian interglacial arctic sea ice export to the north atlantic increases this surface fresh water transport weakens deep water formation in the north atlantic and the near surface circulation of the subpolar gyre as a consequence the relative contribution of subpolar gyre waters to the atlantic inflow into the nordic seas is reduced giving way to more warm and saline subtropical waters from the north atlantic current we thus find an episode of relatively high heat and salt transport into the nordic seas during the last glacial inception between 119 000 and 115 000 years before present this stabilizes deep ocean convection in the region and warms scandinavia during a phase of low insolation these findings are in good agreement with proxy data from the nordic seas and north atlantic at the end of the warm interval sea surface temperature drops by about 3 c marking the onset of large scale glacier growth over scandinavia

a paleoecological analysis of the petrified trees in the specimen creek area of yellowstone national park montana u s a abstract petrified trees from specific stratigraphic units of the specimen creek locality in yellowstone national park have previously been identified at the genera level the identified woods were plotted on modern climatic ranges specific units exhibit the following climatic ranges unit 1 subtropical to boreal mostly warm temperate to cool temperate unit 5 tropical to boreal mostly subtropical to cool temperate unit 9 warm temperate to boreal mostly cool temperate and boreal several features have emerged which suggest that this sequence of layers containing petrified trees does not represent natural communities buried in situ these are 1 the presence of uncommon mixture of tree types within a level 2 the absence of correlation in numerous cases between the vertical fossil trees and the associated microfossils and 3 the change in composition of tree types from one level to the next the model proposed by fritz 1980 permitting some transport of wood and plant remains from different habitats appears at present to offer the best explanation for the observed data

holocene sea surface conditions in the western north atlantic spatial and temporal heterogeneities 1 holocene records of sea surface conditions in the western nordic seas were obtained from quantitative reconstructions based on dinoflagellate cyst assemblages two sediment cores from the east greenland and the north iceland shelves provide a detailed account of the long and short term dynamics of the opposing flows of arctic versus atlantic waters both marker species and quantitative reconstructions depict an overall trend toward warmer winter temperatures saltier surface waters and decreased sea ice extent the latter is supported by a close relationship between relative abundances of an atlantic dinocyst species nematosphaeropsis labyrinthus and ice rafted debris ird records we propose that the late holocene increased ird delivery in the denmark strait region was primarily induced by a combination of less extensive sea ice cover under increased atlantic water inflow and sustained iceberg calving tied to the readvance of the greenland ice sheet our records thus suggest diminishing polar water supplies throughout the holocene although the timing of regime changes differs between the western and eastern sides of the denmark strait finally comparison of our records with a core from southern greenland points to very heterogeneous sea surface conditions in the western north atlantic which could be explained by the decoupled dynamics of the two irminger current branches similarities between the southern greenland marine record and a continental record nearby suggest a close coupling with atmospheric processes reminiscent of a north atlantic oscillation like climate pattern

stream depletion rate and volume from groundwater pumping in wedge shape aquifers in river basins with several tributaries wells in alluvial valleys are often located near the wedge shaped confluence of two tributaries therefore stream depletion characteristics namely stream depletion rate sdr and stream depletion volume sdv induced by the pumping wells are distributed between two tributaries upstream from the confluence existing methods for the evaluation of stream depletion characteristics are applicable only for a wedge shaped aquifer with special or uncommon wedge angles or for steady state conditions in water resources management temporal stream depletion characteristics are important for the adjudication of water rights a new and practically important method for analytical evaluation of transient sdr and sdv is developed for a wedge shaped aquifer with arbitrary wedge angles results are obtained for each of two tributaries or the tributary segment lengths a simple expression for the sdr fraction that originates from each tributary is presented for long period of pumping after which 100 of the pumping rate is supplied by stream depletion the sensitivity analyses for different parameters are performed to examine their affects on the influence period of the total sdr and the results indicated that the sdr is sensitive to the angles of wedge shaped aquifer and the pumping well the results and sensitivity analysis presented in this study may provide useful information in the assessment of water balance or exploitation of river basins

burial of trees by eruptions of mount st helens washington implications for the interpretation of fossil forests lahars and fluvial sediments which buried trees following the 18 may 1980 eruption of mount st helens were investigated during august of 1982 trees buried in older mudflows dated at a d 1885 a d 1450 1550 and 36000 years b p also were examined although many logs clearly were transported large numbers of trees were buried in growth position burial by lahars generally resulted in the death of trees whereas some trees survived burial by fluvial sediments scanning electron microscope studies show that trees buried in lahars are well preserved pre 1885 buried woods show incipient silicification and woods buried 36000 years b p show silica impregnation of cell walls features of in situ and allochthonous burial very similar to those seen in southern washington are found also in eocene silicified forests in yellowstone national park wyoming u s a and in cretaceous fossil forests in southeastern alexander island antarctica observations of recent wood from volcaniclastic deposits of mount st helens provide valuable insights into processes of burial and silicification of fossil forests of various ages around the world

modelling of aquifer response to time varying recharge and pumping from multiple basins and wells this paper deals with the development of an analytical solution of two dimensional linearized boussinesq equation to predict water table variation in response to time varying recharge and pumping from any number of basins and wells the rates of time varying recharge and pumping are approximated by series of line elements of different lengths and slopes depending on the nature of variation of the recharge and or pumping rates advantage of this approach is that any complex nature of recharge and pumping rates for any number of basins and wells and for any number of these operations can be approximated with more accuracy application of the solution in the prediction of water table variation is demonstrated with the help of an example problem also the results of the analytical solution are compared with those obtained from modflow both results are found to be in good agreement

the salinity contrast between the atlantic and pacific oceans during glacial time in today s ocean the salinity of low latitude surface waters in the pacific is on the average 1 per mil lower than in the atlantic oxygen isotope records for planktonic foraminifera suggest that an even larger salinity deficit may have existed for pacific surface water during glacial time if so the transport of water vapor from the atlantic to the pacific must have been as strong as or even stronger to balance the tendency toward salt buildup the atlantic would have had to export during glacial time waters saltier than it received from the other oceans

late quaternary deep sea ostracodes in the polar and subpolar north atlantic paleoecological and paleoenvironmental implications two sediment cores from the northern north atlantic one from the iceland plateau and one from the rockall plateau were investigated in order to examine the response of deep sea benthic ostracodes to climate related environmental changes since marine isotope stage mis 7 ostracode fauna was divided into three factor assemblages by using q mode factor analyses and diversity was calculated using the shannon wiener index the iceland plateau revealed an interglacial assemblage dominated by henryhowella a transitional assemblage dominated by eucythere and a background assemblage that consists of the common taxa krithe and cytheropteron the presence of henryhowella is linked to conditions that prevailed during the peak interglacial periods mis 5e and 1 characterized by increased food supply well oxygenated bottom water and lateral advection the presence of eucythere mainly during the interstadial periods appears to be related to slightly increased food supply whereas the background assemblage is considered to be opportunistic and able to cope with decreased food supply as interpreted for glacial times on the rockall plateau the opportunistic background assemblage consisting mainly of krithe argilloecia and cytheropteron shows no obvious relation to climate changes the interglacial assemblage consists of several taxa dominated by pelecocythere but as on the iceland plateau it also contains henryhowella the third assemblage is the glacial assemblage that consists of a variety of taxa several of which are known from the modern arctic ocean and the greenland sea shelf thus this assemblage indicates glacial conditions on the rockall plateau that are comparable to those found in the present day arctic ocean diversity calculations revealed higher ostracode diversities in glacial than in interglacial episodes in both cores and particularly high diversities during periods of increased input of iceberg rafted debris ird in the rockall plateau core both cores reveal lower surface water productivity during the glacial compared to the interglacial periods and particularly low productivity during the ird events as inferred from carbonate contents we assume therefore that ostracode diversity in the study areas is negatively correlated with food flux

water table fluctuation owing to time varying recharge pumping and leakage this paper presents an analytical solution of a 2 d linearized boussinesq equation to predict water table variation in a horizontal aquifer induced by time varying recharge and or withdrawal from any number of recharge basins pumping wells and leakage sites of different dimensions the rate of time varying recharge or withdrawal is approximated by series of line elements of different lengths and slopes depending on the nature of variation of recharge or withdrawal rate advantage of this approximation scheme is that any complex nature of recharge and or withdrawal rates for any number of recharge basins pumping wells and leakage sites and for any number of these operations can be approximated with more accuracy application of the solution in the prediction of water table variation in the presence of time varying recharging pumping and leakage is demonstrated with the help of an example problem the present analytical solution is validated by comparing its results with the corresponding numerical results obtained from modflow for the same example problem

late quaternary calcareous nannofossil biozonation chronology and palaeo oceanography in areas north of the faeroe iceland ridge abstract the stratigraphic distribution of late quaternary calcareous nannofossils from the european arctic ocean the fram strait and the norwegian and greenland seas are summarised in a biozonation scheme the nannofossil events are directly correlated to oxygen isotope stratigraphy leading to an absolute chronology comprising approximately the last 500 ka the zones are defined by the qualitative and quantitative content of calcareous nannofossils zones n g 2 4 6 8 and 10 comprise intervals mainly barren of nannofossils zone n g 1 is characterised by high abundances of coccolithus pelagicus and emiliania huxleyi zone n g 3 is recognised by dominant gephyrocapsa muellerae and common e huxleyi zone n g 5 is characterised by dominant g aperta n g 7 by dominant g muellerae n g 9 by common g muellerae g aperta and g caribbeanica and zone n g 11 is recognised by dominant g caribbeanica and rare pseudoemiliania lacunosa intervals in which nannofossils occur in high abundances reflect comparatively warmer periods and influences of north atlantic surface water strong inflows of north atlantic water have occurred several times during the last 500 ka in oxygen isotope stage 1 the last 8 ka and in oxygen isotope stages 5 11 12 and 13 north atlantic surface water penetrated into the central parts of the norwegian and greenland seas also during oxygen isotope stage 9 nannofossil barren intervals are mainly formed during time periods with a year round ice cover

comparison of glacial and interglacial conditions between the polar and subpolar north atlantic region over the last five climatic cycles a multiparameter based interpretation of sediment records from the northeast atlantic and the western nordic seas suggests that during the last 500 000 years only in marine isotopes stage mis 11 5e and 1 were there somewhat comparable interglacial boundary conditions in both regions i e strongly reduced occurrence of iceberg rafted debris ird and high carbonate bioproductivity although the northeast atlantic experienced such conditions during all peak interglaciations with the exception of mis 7 planktic foraminiferal 18o from this region would still indicate that significantly colder sea surface temperatures sst prevailed during mis 11 than during mis 9 5e and 1 this assumption is corroborated by a continuous input of ird into the western nordic seas during mis 11 implying a much steeper sst gradient between the polar and subpolar region and an overall reduced thermohaline activity in the polar latitudes the iceberg proxy also reveals that maximum ird discharge always happened during the final phase of glaciation and into early deglaciation terminations as these ird records from the two regions are characterized by a high time coherency it is concluded that short term variability is a persistent feature of the glacial climate system

modelling of water table variation in response to time varying recharge from multiple basins using the linearised boussinesq equation a mathematical model is presented to describe the variations of the water table in an unconfined aquifer due to time varying recharge applied from four rectangular basins the model is developed by solving the linearised boussinesq equation using the extended finite fourier cosine transform the time varying recharge rate is approximated by a number of piecewise linear elements of different lengths and slopes depending on the nature of the variation in recharge rate application of this model for the prediction of water table fluctuations and in the sensitivity analysis of various controlling parameters on the aquifer response is demonstrated in an example

steady state response of annular wedge shaped aquifers to arbitrarily located multiwells with regional flow abstract wedge shaped aquifers are sometimes cut by crossing streams so that the areal geometry can be delineated by an annular wedge of infinite radial extent despite their worldwide spread the problem of groundwater flow in such geometrical entities has not received much attention in analytical studies this paper presents a closed form analytical solution for the aquifer head distribution in response to a system of multiwells superimposed on a background regional flow the aquifer is isotropic homogeneous and in prefect hydraulic connection with the surrounding streams a steady state green s function is constructed for this laterally bounded aquifer system the formulation is general in the sense that the aquifer vertex angle as well as number of wells and their positions can be arbitrary chosen closed form expression for the stream function is obtained by integration of the cauchy riemann equations three types of hydrogeological boundary conditions are considered combining streams of constant and linearly varying head and no flow barrier the results are applicable to both confined and unconfined flows extremely simple expressions are derived to quantify the amount of water exchange across stream aquifer interfaces flow nets are given for a number of hypothetical test cases demonstrating different aspects of the generated flow field sensitivity maps are prepared for the stream depletion rates due to a single pumping well and the role of aquifer vertex angle on the model response is investigated multiple stagnation points in the flow field are identified on a semi analytical basis this helps to assess how the position of a single stagnation point is affected by changes in the gradient of regional flow for relatively high gradients it is observed that the radial position of the stagnation point coincides with that of the well itself finally the formulation is extended to account for rainfall recharge over an unconfined aquifer having the same areal extent the aquifer response is found to agree well with other analytical and numerical results

atlantic water advection versus sea ice advances in the eastern fram strait during the last 9 ka multiproxy evidence for a two phase holocene a sediment core from the west spitsbergen continental margin was studied to reconstruct climate and paleoceanographic variability during the last 9 ka in the eastern fram strait our multiproxy evidence suggests that the establishment of the modern oceanographic configuration in the eastern fram strait occurred stepwise in response to the postglacial sea level rise and the related onset of modern sea ice production on the shallow siberian shelves the late early and mid holocene interval 9 to 5 ka was generally characterized by relatively unstable conditions high abundance of the subpolar planktic foraminifer species turborotalita quinqueloba implies strong intensity of atlantic water aw inflow with high productivity and or high aw temperatures resulting in a strong heat flux to the arctic a series of short lived cooling events 8 2 6 9 and 6 1 ka occurred superimposed on the warm late early and mid holocene conditions our proxy data imply that simultaneous to the complete postglacial flooding of arctic shallow shelves and the initiation of modern sea ice production strong advance of polar waters initiated modern oceanographic conditions in the eastern fram strait at 5 2 ka the late holocene was marked by the dominance of the polar planktic foraminifer species neogloboquadrina pachyderma a significant expansion of sea ice icebergs and strong stratification of the water column although planktic foraminiferal assemblages as well as sea surface and subsurface temperatures suggest a return of slightly strengthened advection of subsurface atlantic water after 3 ka a relatively stable cold water layer prevailed at the sea surface and the study site was probably located within the seasonally fluctuating marginal ice zone during the neoglacial period

early holocene temperature variability in the nordic seas the role of oceanic heat advection versus changes in orbital forcing received 7 january 2011 revised 15 july 2011 accepted 21 july 2011 published 22 october 2011 1 the separate roles of oceanic heat advection and orbital forcing on influencing early holocene temperature variability in the eastern nordic seas is investigated the effect of changing orbital forcing on the ocean temperatures is tested using the 1dice model and the 1dice results are compared with new and previously published temperature reconstructions from a transect of five cores located underneath the pathway of atlantic water from the faroe shetland channel in the south to the barents sea in the north the stronger early holocene summer insolation at high northern latitudes increased the summer mixed layer temperatures however ocean temperatures underneath the summer mixed layer did not increase significantly the absolute maximum in summer mixed layer temperatures occurred between 9 and 6 ka bp representing the holocene thermal maximum in the eastern nordic seas in contrast maximum in northward oceanic heat transport through the norwegian atlantic current occurred approximately 10 ka bp the maximum in oceanic heat transport at 10 ka bp occurred due to a major reorganization of the atlantic ocean circulation entailing strong and deep rejuvenation of the atlantic meridional overturning circulation combined with changes in the north atlantic gyre dynamic causing enhanced transport of heat and salt into the nordic seas

charcoal reflectance as a proxy for the emplacement temperature of pyroclastic flow deposits hot pyroclastic flow deposits often entomb and preserve vegetation as charcoal when studied in polished section this charcoal is highly reflective novel data from experimentally charred woods demonstrate that reflectance increases with both temperature and time at temperatures above 250 c reflectance rises rapidly for the first hour effectively stabilizing after 4 h for temperatures below 400 c however for higher temperatures reflectance only stabilizes after 24 h charcoalified woods from block and ash flow deposits generated by the soufriere hills volcano in montserrat have yielded interpreted deposit temperatures based on reflectance data of 325 525 c these temperatures compare favorably with directly measured data 365 640 c from the same deposits indicating that charcoal reflectance is useful as a temperature proxy for ancient pyroclastic flow deposits particularly where magnetic or mineral data are absent for this purpose however caution should be exercised as only a minimum temperature can be inferred where the heating duration of the deposit is unknown unlike magnetic or mineral data temperature data from charcoalified woods can be obtained from reworked deposits providing a valuable means of validating observations made about the style of eruption of volcanoes in ancient settings

contrasting ocean changes between the subpolar and polar north atlantic during the past 135 ka variations in the poleward directed atlantic heat transfer was investigated over the past 135 ka with special emphasis on the last and present interglacial climate development eemian and holocene both interglacials exhibited very similar climatic oscillations during each preceding glacial terminations deglacial ti and tii like ti also tii has pronounced cold warm cold changes akin to events such as h1 bolling allerod and the younger dryas but unlike ti the cold events in tii were associated with intermittent southerly invasions of an atlantic faunal component which underscores quite a different water mass evolution in the nordic seas within the eemian interglaciation proper peak warming intervals were antiphased between the nordic seas and north atlantic moreover inferred temperatures for the nordic seas were generally colder in the eemian than in the holocene and vice versa for the north atlantic a reduced intensity of atlantic ocean heat transfer to the arctic therefore characterized the eemian requiring a reassessment of the actual role of the ocean atmosphere system behind interglacial but also glacial climate changes key points reduced amoc during the eemian ba yd type warming cooling in termination 1 and 2 comparison of glacial inceptions reveals present climate status

petrifaction of wood by silica minerals abstract seventy five woods of australian origin have been examined by means of x ray diffraction optical and scanning electron microscopy and differential thermal analysis the silica is in one or other of the following forms opal a opal ct chalcedony quartz quartz chalcedony opal chalcedony more than half of them consist of opal ct or chalcedony the results indicate that petrifaction by silica involves penetration of the wood via splits or checks permeation of cell walls via a reticulated system of micropores enlargement of the micropore system as cell wall components break down and continuing deposition of silica ata rate and in a manner consistent with maintaining the dimensional stability of the wood deposition of silica in cell lumina and intercellular voids may be sometimes but not always a separate and later event the final stages of lithification involve loss of water and perhaps transformation of one form of silica into another

a neogene structural dome in the klamath mountains california and oregon regional structural doming of neogene age has affected rocks of the klamath and cascade mountains near the california oregon border evidence for this is seen in 1 subannular outcrop patterns of pre cretaceous lithotectonic units 2 a crude pattern of radially oriented high angle faults 3 tilted jurassic plutons 4 tilted cretaceous to miocene strata and 5 various geomorphological features the age of doming is constrained by a major middle miocene to earliest pliocene angular unconformity within the cascade mountains and uplifted upper miocene marine beds on the western edge of the klamath mountains uplift and doming may be the result of shortening in the cascade fore arc region or more speculatively the recent accretion of subducted material to the north american plate beneath the klamath mountains

the silicification of trees in volcanic ash an experimental study abstract the permineralization of trees by pervasive silicification that is when forests are buried by volcanic pyroclastics is simulated with closed system experiments at 100 c the silica source was a ground rhyolitic obsidian glass the wood samples were coniferous pseudotsuga menziesii douglas fir from the family pinaceae and the medium transporting silica from the lithic matrix into the wood tissue was water reaction of wood with silica enriched water shows that wood has a marked affinity to scavenge silica complexes from an aqueous solution and precipitate them on organic surfaces inside the wood cells in the form of opal diffusion and advection models are used to estimate how long it may take to permineralize wood logs as massive as those found in petrified forests worldwide the time scales are on the order of thousands of years

implications of stratigraphic and paleoclimatic records of the last interglaciation from the nordic seas climatic reconstruction of glacial to interglacial episodes from oxygen isotopes in sediment cores from the nordic seas is complicated by strong local meltwater contributions to the oxygen isotope changes combination of benthic and planktic foraminiferal isotope data with foraminiferal abundances and ice rafted debris ird allows separation of local and global effects and subdivision of the marine oxygen isotope events 6 2 5 4 which include the last interglaciation into 1 a meltwater phase after glacial stage 6 recorded by large amounts of ird and low foraminiferal abundance indicating surface water warming 2 an ird free period with high deposition rates of subpolar foraminifera and other caco3pelagic components recognized here as the full interglaciation and 3 a phase with the recurrence of ird and the demise of subpolar species comparison of ice core records and marine data implies that the global climate during the last full interglaciation and that during the postdeglacial holocene were similar the records show no significantly different variations in the proxy data in contrast the oxygen isotopes of planktic foraminifera and ice cores indicate significant differences during each of the deglacial transitions terminations i and ii that preceded these two interglaciations these suggest that during termination ii the climatic evolution in the nordic seas was less affected by abrupt changes in ocean atmosphere circulation than during the last glacial to interglacial transition

cretaceous and early tertiary climates of antarctica evidence from fossil wood abstract fossil wood is abundant in cretaceous and early tertiary sediments of the northern antarctic peninsula region the wood represents the remains of vegetation that once grew in high palaeolatitudes when the polar regions were warmer during former greenhouse climates fossil wood is a unique data store of palaeoclimate information analyses of growth rings and anatomical characters in fossil wood provide important information about temperature rainfall seasonality and climate trends for this time period in antarctica climate signals from fossil wood supported by sedimentary and geochemical evidence indicate a trend of cool climates during the early cretaceous followed by peak warmth during the coniacian to early campanian narrower growth rings suggest that the climate cooled during the maastrichtian and palaeocene cool wet and possibly seasonal climates prevailed at this time with tentatively estimated mean annual temperatures mats falling from 7 c to 4 8 c respectively determined from dicotyledonous dicot wood anatomy the late palaeocene early eocene was once again warm with estimated mats of 7 15 c from dicot wood analysis but conditions subsequently deteriorated through the latter part of the eocene when cold seasonal climates developed ultimately leading to the onset of cenozoic ice sheets and the elimination of vegetation from most of antarctica

a new analytical method for groundwater recharge and discharge estimation summary a new analytical method was proposed for groundwater recharge and discharge estimation in an unconfined aquifer the method is based on an analytical solution to the boussinesq equation linearized in terms of h2 where h is the water table elevation with a time dependent source term the solution derived was validated with numerical simulation and was shown to be a better approximation than an existing solution to the boussinesq equation linearized in terms of h by calibrating against the observed water levels in a monitoring well during a period of 100 days we shown that the method proposed in this study can be used to estimate daily recharge r and evapotranspiration et as well as the lateral drainage it was shown that the total r was reasonably estimated with a water table fluctuation wtf method if the water table measurements away from a fixed head boundary were used but the total et was overestimated and the total net recharge was underestimated because of the lack of consideration of lateral drainage and aquifer storage in the wtf method

transient solution for stream unconfined aquifer interaction due to time varying stream head and in the presence of leakage summary this paper presents new analytical solutions of a linearized boussinesq equation characterizing groundwater flow in a stream unconfined aquifer system due to transient seepage the aquifer is underlain by a horizontal leaky bed and interacts with an adjoining stream of varying water level through a semipervious vertical stream bank close form analytical expressions are derived to predict water head distribution flow rate and volumetric exchange of water in response to time dependent rise or drop in the stream water level comparison between analytical and numerical results shows satisfactory agreement the effects of the finite and semi infinite lengths of the domain are considered in detail certain asymptotic situations such as sudden rise or drop in the stream water level no flow condition at the aquifer s base and absence of vertical stream bank can be dealt with as limiting cases of main results an illustration of the new analytical approach is used to quantify the accretion recession of the bank storage due to variation in various aquifer parameters

eocene oligocene extinction and paleoclimatic change near eugene oregon thick ash fl ow tuffs provide marker beds through fossiliferous eocene and oligocene marine and non marine sedimentary rocks near eugene oregon new mapping radiometric dating and paleomagnetic stratigraphy of these tuffs and rocks now allow dating of local fossil fl oras the comstock goshen rujada and willamette fl oras have been widely used as evidence for eocene oligocene climatic cooling and drying eocene leaves from comstock and hobart butte included such thermophilic taxa as liquidambar the early oligocene goshen fl ora lacked liquidambar but retained many thermophilic species with large leaves that have entire margins and acuminate apices drip tips in contrast fossil leaves from later oligocene rujada and willamette fl oras are small and serrate and most lack drip tips marine faunas also indicate climatic cooling and local disappearance of thermophilic molluscs such as anadara ficus and conus our dating and compilation of plant and molluscan fossil occurrences indicate a steady rise in species diversity from 46 ma to maximal diversity of thermophilic taxa at 35 34 ma then extinctions of 60 of plant species after 33 4 ma and 32 of marine invertebrates after 33 2 ma both signifi cantly postdating the eocene oligocene boundary at 33 7 ma plant diversity rebounds during the early oligocene but marine invertebrates continue to decline into the oligocene in part due to the retreat of fully marine environments from the eugene area neither these data nor evidence from coeval fossil plants and soils in central oregon support the notion of a terminal eocene event nor any other single abrupt paleoclimatic shift or extinction the eocene oligocene biotic and climatic transition was drawn out over some 6 m y abrupt forcings such as meteorite impacts or volcanic eruptions are less likely explanations for cooling and diversity decline than long term processes such as mountain building changing ocean currents or reorganization of the carbon cycle by coevolution of grasses and grazers

multiproxy fossil comparison reveals contrasting surface ocean conditions in the western iceland sea for the last two interglacials abstract dinoflagellate cyst dinocyst coccolith and planktic foraminiferal assemblages from a core in the western iceland sea were used to reconstruct and compare the surface ocean developments of the holocene and the last interglacial marine isotopic stage or mis 5e while increasing subpolar planktic foraminifers from 10 ka indicate subsurface warming peaking around 7 5 ka the dinocyst data suggest that the uppermost ocean remained dominated by cold waters until 6 5 ka a reduced advection of cold polar waters through the east greenland east icelandic current thereafter entailed warmest and most saline holocene conditions between 6 5 and 5 ka in turn followed by a general cooling trend by contrast both planktic foraminifers and dinocysts show an increased presence of atlantic type waters from 122 ka onward resulting in a mis 5e thermal optimum around 120 5 ka nonetheless occasional freshwater input from melting drift ice created stratified but also seasonally variable conditions during this first half of mis 5e this stratification signature disappeared at 120 ka when a marked repositioning of the oceanographic fronts occurred slightly colder conditions are indicated by both phyto and zooplankton from there on until the end of mis 5e around 117 ka a late mis 5e cooling at the iceland plateau is opposite to a late mis 5e optimum observed in the eastern nordic seas this regional difference is likely explained by various feedback mechanisms following the major reorganisation of the oceanic fronts at 120 ka the holocene and mis 5e interglacial variability is not reflected in the quasi monospecific coccolith assemblages and illustrates the low sensitivity of living coccolithophore communities to subtle temperature changes in the low temperature regions of the nordic seas overall quite different surface water properties appear to have characterised both interglacial intervals with a higher share of warm atlantic elements in the planktic communities during mis 5e this suggests a higher contribution of atlantic waters in the southwestern nordic seas probably due to a more northward expansion of the irminger current under weakened polar east greenland east icelandic currents such a reduced influence of polar waters in the southwestern nordic seas may thus explain other evidence for relatively warm conditions in mis 5e all around southern greenland

an analytical solution for groundwater flow to a vertical well in a triangle shaped aquifer the problem of drawdown and determination of velocity field near a fully penetrating pumping well which is located in a confined aquifer is investigated an isosceles triangular domain defining the geometry of the aquifer is considered in this paper the combination of streams with without impervious layer forms the boundaries of the domain of interest the concept of image well is employed to formulate the problem the method of green s function together with two dimensional fourier series expansion is used to obtain the closed form solution for the problem the isopotential lines and corresponding velocity field are presented for a particular position of pumping well also the water depletion from interfacing streams is analytically calculated for different positions of pumping well and the results are plotted the plots can be effectively used in water resources management and environmental engineering

silica diagenesis origin of inorganic and replacement cherts abstract silicification of originally non siliceous sediments affects a wide variety of rock types and materials and ranges from minor to pervasive partial and minor chertification occur mostly in phanerozoic carbonates carbonate bearing sandstones evaporites and fossil wood the source of the silica is predominantly biogenic in petrified wood the silicification mechanism is a permeation or void filling process not a replacement in this example the sequence of silica phase transformation is the same as that in deep sea siliceous sediments in many silicified rocks particularly in certain carbonates the transformation sequence is different from that in radiolarites or diatomites the chemical environment and conditions of early diagenetic chert formation in shallow water carbonates are delineated by the general mixing model of knauth 1979 but remain unknown for most other types an exception are the flint nodules and bands of the english chalk a detailed geochemical study of the paramoudra flint structures by clayton 1986 provided remarkable insight into the replacement process seven different recurring silica fabrics have been recognized in chert replaced carbonates including equigranular microcrystalline quartz or microquartz and megaquartz and fibrous types chalcedony quartzine or length slow chalcedony lutecite zebraic chalcedony and microflamboyant quartz among the latter quartzine and microflamboyant quartz are common in but by no means restricted to chert replaced evaporites for which milliken 1979 recognized a sequence of seven quartz fabrics as a single criterion only anhydrite inclusions in megaquartz quartzine or microflamboyant quartz provide unequivocal evidence for an evaporite precursor the relative timing between silicification and well established diagenetic carbonate reactions shows that virtually all theoretically possible sequences occur chertification of carbonate host sediment thus may take place during early intermediate or late diagenesis and even during anchimetamorphism pervasive to complete silicification has been described in lacustrine pedogenic and hydrothermal volcanogenic rocks and occurs on the scale of individual beds members or entire formations it may affect some of the aforementioned rock types too for example carbonates the source of the silica is predominantly inorganic chert formation in these environments includes direct chemical silica precipitation from solution through a gel stage magadi type cherts result from the conversion of the hydrous sodium silicate magadiite into microcrystalline quartz which has occurred in east african rift valley lakes such as lake magadi in late pleistocene time they are closely related to directly precipitated inorganic cherts which have been observed in alkaline environments of playa lakes silcretes originate from weathering and soil forming processes under climatic and environmental conditions conducive to the formation of duricrusts and laterites in more humid climates however non weathering profile silcretes occur which have been distinguished from weathering profile silcretes four to five different silcrete fabric types have been established including the 1 grain supported or quartzitic 2 floating terrazzo 3 matrix albertinia and opaline and 4 conglomeratic types in volcanic edifices silicification related to hydrothermal activity occurs 1 along the ascent routes of the fluids vents within the volcanic complexes 2 in isolated ponds and depressions on the sea floor where the fluids discharge mostly in the median rift valley of mid ocean ridges and 3 in geothermal areas on land associated with spreading lineaments volcanic islands arcs transform faults or continental hot spots attention has focussed on the associated base metal concentrations and less on the silicification and accompanying iron enrichment processes the precambrian banded iron formations may be indirectly or directly related to hydrothermal volcanic processes the origin of these cherty iron formations certainly requires more than one genetic model and at present remains a major unresolved problem despite massive efforts to tackle it

a high resolution study of holocene paleoclimatic and paleoceanographic changes in the nordic seas 1 high resolution records from images core md95 2011 in the eastern norwegian sea provide evidence for relatively large and small scale high latitude climate variability throughout the holocene during the early and mid holocene a situation possibly driven by consistent stronger westerlies increased the eastward influence of arctic intermediate and near surface waters for the late holocene a relaxation of the atmospheric forcing resulted in increased influence of atlantic water the main changes in holocene climate show no obvious connection to changing solar irradiance and spectral analysis reveals no consistent signature for any periodic behavior of holocene climate at millennial or centennial timescales there are however indications of consistent multidecadal variability

steady state groundwater recharge in trapezoidal shaped aquifers a semi analytical approach based on variational calculus summary this study presents a semi analytical solution for steady groundwater flow in trapezoidal shaped aquifers in response to an areal diffusive recharge the aquifer is homogeneous anisotropic and interacts with four surrounding streams of constant head flow field in this laterally bounded aquifer system is efficiently constructed by means of variational calculus this is accomplished by minimizing a properly defined penalty function for the associated boundary value problem simple yet demonstrative scenarios are defined to investigate anisotropy effects on the water table variation qualitative examination of the resulting equipotential contour maps and velocity vector field illustrates the validity of the method especially in the vicinity of boundary lines extension to the case of triangular shaped aquifer with or without an impervious boundary line is also demonstrated through a hypothetical example problem the present solution benefits from an extremely simple mathematical expression and exhibits strictly close agreement with the numerical results obtained from modflow overall the solution may be used to conduct sensitivity analysis on various hydrogeological parameters that affect water table variation in aquifers defined in trapezoidal or triangular shaped domains

three growth in the mesozoic and early tertiary and the reconstruction of palaeoclimates abstract evidence from the distribution and characteristics of fossil wood in the mesozoic and early tertiary indicates that a much warmer global climate prevailed in those times there appears to have been a broad zone of largely non seasonal climate stretching from about 32 n to 32 s palaeolatitudes in addition to this low latitude zone forest growth extended into very high palaeolatitudes where trees cannot grow at the present day a number of theories have been proposed to account for the palaeoclimate responsible for this distribution of forests most notable have been those involving changes in the amount of carbon dioxide in the atmosphere in the positions of the continents or in the obliquity of the earth s axis of rotation evidence from fossil forests indicates that a combination of the effects of an increased quantity of carbon dioxide in the atmosphere and the palaeopositions of the continents in the mesozoic and early tertiary appears at the moment to be the simplest explanation for the climate of those geological times without the need to invoke axial movement

paleoceanographic reconstructions of surface ocean conditions in the greenland iceland and norwegian seas through the last 14 ka based on diatoms prior reconstructions of the last glacial maximum and the holocene did not include detailed paleoclimate data from the greenland iceland and norwegian gin seas which cover sensitive areas for oceanographic boundaries sea ice distribution and deep water formation in order to fill this gap we studied nine well dated sediment cores from this area and reconstructed the paleoceanographic conditions of the surface gin seas at 2000 year intervals since 13 400 bp based on the diatom record results show that a n s extending sea ice free corridor had opened along norway already at 13 400 bp indicating a northward flow of a branch of the north atlantic drift possibly caused by a change in the jet stream flow due to the decreased height of the north american ice sheet a major change of climatic conditions occurred over the gin seas as the insolation anomaly reached its maximum around 9000 bp when the sea ice cover and the oceanic fronts retreated to a northwesterly position along greenland and the ocean temperatures rose the first half of the holocene is recorded as the warmest period during the last 13 400 bp in the gin seas the duration of this climatic optimum decreased both toward the north and toward the margins of the area the second half of the holocene is characterized by a cooling trend in step with the decreasing insolation these results support the proposal of imbrie et al 1992 that the gin seas region acts as an initial responder to insolation changes

variations in surface water mass conditions in the norwegian sea evidence from holocene coccolith and dinoflagellate cyst assemblages coccolith and dinoflagellate cyst assemblages have been investigated in five sediment cores from the norwegian sea and fram strait both fossil groups are characterized by similar patterns of composition the assemblages contain high proportions of single species the coccolith flora is of low diversity and consists almost entirely of coccolithus pelagicus and emiliania huxleyi the dinoflagellate cysts are generally dominated by operculodinium centrocarpum and nematosphaeropsis labyrinthus other species especially bitectatodinium tepikiense peridinium faeroense and impagidinium pallidum sometimes contribute considerably to the assemblages based on the abundance of the assemblages and the ratio change between the dominating species it has been possible to establish three intervals of distinct major changes in surface water mass conditions sparse occurrences of coccoliths and dinoflagellate cysts have been observed before 10 000 yrs b p indicating harsh environmental conditions with a distinct influence of meltwater and temporarily very slight inflow of atlantic water the modern surface water circulation pattern was reinitiated during termination ib the assemblages suggest slightly cooler and probably less saline surface water conditions than are present today until 7500 yrs b p solar insolation may have caused a first temperature peak which is responsible for the early holocene productivity maximum a considerable change in the composition of dinocyst and coccolith assemblages occurs corresponding approximately to the onset of the holocene climatic optimum this change was most probably linked to an almost synchronous reorganization of the hydrographic properties in the entire north atlantic realm after the ice sheets had vanished since 6000 yrs b p the norwegian current with its modern oceanographic and ecological properties has been fully established

biochronology and paleoceanography of late pleistocene and holocene calcareous nannofossil abundances across the arctic basin biochronology and paleoceanography of late pleistocene and holocene calcareous nannofossils across the arctic basin