calibration of the planktonic foraminiferal mg ca paleothermometer sediment trap results from the guaymas basin gulf of california 1 the mg ca ratio has been measured in two surface dwelling species of planktonic foraminifera globigerinoides ruber and globigerina bulloides from biweekly sediment trap samples collected in guaymas basin gulf of california between august 1992 and november 1997 the guaymas basin experiences significant seasonal changes in sea surface temperature sst 16 33 c and thus is an ideal location for testing the temperature dependence of mg incorporation into foraminiferal calcite the planktonic foraminiferal mg ca ratios are directly compared with concurrent temperature measurements from the study site the results from the sediment trap study reveal a strong positive correlation between sst and the mg ca ratio in both g ruber r2 0 86 and g bulloides r2 0 90 the mg ca ratio increases exponentially by 7 per 1 c change in temperature for g ruber and by 6 for g bulloides these results indicate that the mg ca ratio in g ruber and g bulloides accurately records the measured seasonal surface temperature cycle and interannual variability in the guaymas basin within 1 c the greatest deviation between mg ca estimated sst and observed sst occurs in the spring and fall for both species this variability is attributed to rapidly changing hydrographic conditions and possible offset between the time of calcification and the temperature measurements in addition g ruber and g bulloides exhibit very high mg ca ratios during the strong el nino southern oscillation years of 1992 and 1997 verifying their potential to record sst up to 33 c and 28 c respectively the trace metal data are compared with foraminiferal oxygen isotope and alkenone measurements made on the same suite of sediment trap samples to assess the internal consistency of these temperature proxies strong correlations exist between the 18o and mg ca for g ruber r2 0 86 and g bulloides r2 0 79 similarly sea surface temperature estimates from mg ca ratios are in good agreement with alkenone derived temperature estimates r2 0 89 for g ruber and r2 0 81 for g bulloides

biogenic silica fluxes and accumulation rates in the gulf of california the gulf of california though small in size plays an important role in the global silica cycle the seasonal pattern of biogenic silica flux in the gulf is closely related to that of phytoplankton biomass levels and is controlled by changes in weather and hydrographic conditions the highest opal fluxes approximately 0 35 g center dot m sup minus 2 center dot d sup minus 1 occur during winter and spring and they are comparable to those measured in some of the most productive ecosystems of the world approximately 15 25 of the biogenic silica produced in surface waters is preserved in gulf sediments a figure significantly higher than the average global ocean preservation rate however the flux of opal at 500 m water depth is less than 25 of that being produced at the surface suggesting that most of the recycling of biogenic silica in the gulf of california occurs in the upper water column 28 refs 3 figs

evaluating controls on planktonic foraminiferal geochemistry in the eastern tropical north pacific abstract to explore relationships between water column hydrography and foraminiferal geochemistry in the eastern tropical north pacific we present o 18 and mg ca records from three species of planktonic foraminifera globigerinoides ruber globigerina bulloides and globorotalia menardii collected from a sediment trap mooring maintained in the gulf of tehuantepec from 2006 2012 differences in o 18 between mixed layer species g ruber and g bulloides and thermocline dweller g menardii track seasonal changes in upwelling the records suggest an increase in upwelling during the peak positive phase of el nino and an overall reduction in stratification over the six year period for all three species mg ca ratios are higher than what has been reported in previous studies and show poor correlations to calcification temperature we suggest that low ph 7 6 8 0 and co 3 2 values 70 120 mol kg in the mixed layer contribute to an overall trend of higher mg ca ratios in this region laser ablation inductively coupled mass spectrometry analyses of g bulloides with high mg ca ratios 9 mmol mol reveal the presence of a secondary coating of inorganic calcite that has mg ca and mn ca ratios up to an order of magnitude higher than these elemental ratios in the primary calcite along with elevated sr ca and ba ca ratios some of the samples with abnormally high mg ca are found during periods of high primary productivity suggesting the alteration may be related to changes in carbonate saturation resulting from remineralization of organic matter in oxygen poor waters in the water column although similar shell layering has been observed on fossil foraminifera this is the first time such alteration has been studied in shells collected from the water column our results suggest a role for seawater carbonate chemistry in influencing foraminiferal calcite trace element calcium ratios prior to deposition on the seafloor particularly in high productivity low oxygen environments

oxygen isotopic composition of multiple species of planktonic foraminifera recorders of the modern photic zone temperature gradient abundances of 12 species of planktonic foraminifera collected in two plankton tows from the east tropical atlantic are compared to the chlorophyll content and the temperature of the sea water from which they were collected as expected from previous work in the tropics all dominant tropical species occur in greatest abundance within the photic zone many species occur in greatest abundances in the seasonal thermocline in association with the maximum chlorophyll concentration while a few algal symbiont bearing species occur in greatest abundance in the mixed layer the 18o measurements of planktonic foraminifera shells from core top sediment samples confirm the vertical stratification within the photic zone that is suggested by the relationship between hydrography and abundances found in the plankton tows and found in the statistical study by ravelo et al 1990 comparison between the measured 18o values of planktonic foraminifera with the predicted 18o profiles of the overlying water column at three core locations indicate that species abundances in the sediment record the seasonally integrated conditions of the photic zone and suggests that the abundance of a species in the sediment depends on whether the preferred ecological conditions of that species may be found within the photic zone of the overlying water column sometime during the year species which calcify below the photic zone have only trace relative abundances finally it appears that the total range of 18o values of the dominant species approximates the predicted annual 18o of calcite range in the upper 80 m of the water column

biotic and geochemical δ 18 o δ 13 c mg ca ba ca responses of globigerinoides ruber morphotypes to upper water column variations during the last deglaciation gulf of mexico abstract within the gulf of mexico gom the bryant canyon is exceptional in that rapid sedimentation sustained by high rates of terrigenous sediment delivery and surface marine productivity make this basin an excellent recorder of paleoenvironmental and paleoclimatic conditions we present a new 21 kyr record of sea surface temperature sst and local salinity changes from the nw gom core jpc 26 approximated from combined globigerinoides ruber morphotype specific 18 o and mg ca as well as ba ca which reflect the subtropical gom hydrographic dynamics and their relationship to both mississippi river discharges and climate evolution during the last deglaciation overall the reconstructed sst and sss related patterns reveal notable variations in amplitude between the analyzed morphotypes adding valuable insights to previously published g ruber w mixed gom records especially during the deglaciation bryant canyon meltwater flooding events bcdfs and associated sea surface freshening seem to be more pronounced than the sst reduction our mg ca derived sst records of both morphotypes g ruber sensu stricto s s and g ruber sensu lato s l show comparable general trends but with important sst differences t we interpret down core t as a record of changing upper water column hydrography with particular influence from the deglacial meltwater bcdfs or holocene bchfs flooding events during the warm intervals the deeper thicker and probably more seasonally persistent mixed layer led to more uniform thermal conditions for both g ruber morphotypes and therefore to a minimum t on the contrary during the cold and low salinity periods the shallower mixed layer favored more habitat divergence and caused a maximum thermal gradient in the well stratified upper water column overall this supports the notion that g ruber s s is consistently calcifying in warmer waters than g ruber s l either due to a shallower depth habitat or to a more summer weighted seasonal distribution moreover intra specific paired 13 c and ba ca differences show that g ruber s l is more sensitive to river water influence than g ruber s s due to its ability to change its depth habitat and therefore exploit optimal temperature salinity productivity stratification conditions during the low salinity events overall our observations support the current practice of treating the two g ruber morphotypes separately and further illustrate the necessity to map both their spatial and temporal distribution

periglacial cirque analogs elevation trends of cryoplanation terraces in eastern beringia abstract cryoplanation terraces are large erosional landforms common in cold unglaciated mountainous environments terrace sequences are composed of alternating slope segments with gently sloping treads and steep rubble covered risers and culminate in extensive summit flats many unglaciated upland landscapes in eastern beringia are dominated by these landforms indirect evidence indicates that they evolve through locally intensified weathering and mass movement processes associated with late lying snowcover geospatial analysis involving nearly 700 cryoplanation terraces in eastern beringia demonstrates that their elevation rises from 175 to 350 masl on bering sea islands to median values 1200 m near the alaska canada border the regional trends of cryoplanation terrace elevation are nearly identical to those of wisconsinan cirques on several transects across alaska the consistency in the elevation trends of glacial cirques and cryoplanation terraces indicates close genetic links between the two classes of feature involving topographic position continentality gradients and the mass balance of localized snow accumulations cryoplanation terraces can be considered the periglacial analogs of glacial cirques and have greater potential as sources of paleoclimatic information than smaller periglacial features more sensitive to short term climate variations process oriented studies age determinations and high resolution mapping are needed before the paleoenvironmental potential of these landforms can be realized fully

facies analysis of an ancient dismembered large caldera complex and implications for intra arc subsidence middle jurassic strata of cobre ridge southern arizona usa abstract the middle jurassic 170 ma cobre ridge caldera is an elongate caldera complex that formed during the eruption of the tuff of pajarito a crystal rich rhyodacite ignimbrite with an estimated volume 1000 km 3 the caldera subsided in two subequal blocks to the southeast caldera forming ignimbrite is as much as 3000 m thick whereas the northwest half of the caldera subsided to lesser depths during the initial eruption but was the locus of subsidence during subsequent eruptions providing a depocenter for a 1 5 km thick section of secondary and post collapse volcanic and sedimentary strata these strata record moat formation and filling and waning volcanism including 1 areally restricted ignimbrites up to several tens of meters thick that may have been ponded between caldera margins and or fault scarps 2 a 600 m thick ignimbrite whose eruption probably caused further collapse of the caldera or enlargement of the caldera margins 3 a localized debris apron deposit up to 500 m thick that represents material reworked from intra caldera pyroclastic deposits and possibly caldera walls and 4 eolian and fluvial sandstones and water lain tuffs megabreccia blocks as large as 0 5 km along strike probably demarcate approximate caldera margins suggesting that the composite caldera was approximately 50 km long by 25 km wide the preserved thickness of the strata of cobre ridge 4500 m is greater than many ancient continental volcanic sequences suggesting external i e tectonic controls on subsidence but preservation of this great thickness of strata is apparently due entirely to volcanic subsidence

reevaluation of the oxygen isotopic composition of planktonic foraminifera experimental results and revised paleotemperature equations cultured planktonic foraminifera orbulina universa symbiotic and globigerina bulloides nonsymbiotic are used to reexamine temperature 18o relationships at 15 25 c relationships for both species can be described by linear equations equations for o universa grown under low light ll and high light hl share a slope of 4 80 0 21 c 1 with a hl ll offset of 0 33 due to symbiont photosynthetic activity the effect of co32 on o universa is 0 002 mol 1 kg 1 and is insensitive to temperature for g bulloides ontogenetic effects produce size related trends in temperature 18o whereby larger shells are enriched in 18o relative to smaller specimens the o universa temperature 18o relationships are more accurate than previously published equations for describing plankton tow data our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic cibicidoides data below 10 c temperature 18o relationships for g bulloides provide good agreement with field data for this species from the northeast pacific

the physical properties of quartz micaschist and their application to freeze thaw weathering studies in the maritime antarctic as part of a study on freeze thaw weathering in the maritime antarctic an investigation was made of the physical properties of the local rock tests were made of point load compressive strength schmidt hammer in situ rock strength moisture content indentor resistance and the size range of weathering products the resulting data were used to consider the form of freeze thaw weathering operative in the field and its relationship to laboratory simulations a distinct difference between massive rock and intact rock is observed in the field it is suggested that future studies should generate a greater database pertaining to rock properties as it is an invaluable aid in the study of mechanical weathering

jurassic magmatism and sedimentation in the palen mountains southeastern california implications for regional tectonic controls on the mesozoic continental arc stratigraphic and geochronologic data from three regionally extensive mesozoic stratigraphic units exposed in the palen mountains california provide constraints on 1 the duration of supermature craton derived sedimentation within the jurassic magmatic arc 2 the timing of cessation of jurassic magmatism in southeastern california and 3 plate margin scale correlation of siliciclastic units that record the initiation of gulf of mexico rift related sedimentation these three regionally extensive units occur as a 7 5 km thick conformable succession in the palen mountains consisting dominantly of 1 eolian quartzose sandstone upper member of the palen formation 2 silicic volcaniclastic rocks and associated plugs and domes dome rock sequence and 3 terrigenous sedimentary rocks mccoy mountains formation our data constrain the age of the eolian quartz arenite upper palen formation to middle to latest early jurassic time toarcian to bathonian because its upper part is locally interbedded with the basal dome rock sequence which we have dated as 174 8 ma u pb zircon this age for the eolian quartz arenite suggests that potentially correlative middle jurassic cratonal rocks on the present day colorado plateau include the page sandstone eolian parts of the carmel formation and the temple cap sandstone all of southwestern utah and northern arizona correlation with the navajo sandstone can not be precluded although this seems unlikely because one must assume the maximum error on both the u pb zircon age and the uncertainties on the stage boundaries to obtain an overlap of only 1 m y our stratigraphic data also document a locally interfingering contact between the dome rock sequence and the overlying mccoy mountains formation the chronostratigraphic extent and tectonic significance of which are controversial we have dated three units along and below this contact 1 a green ignimbrite concordantly overlain by 2 a pink ignimbrite capped by a pink nonwelded tuff and 3 a pink plug dome complex that intrudes the pink ignimbrite and the dome talus of which interfingers with the pink tuff the dome talus also interfingers with maroon siltstone a unit that is regionally typical of the basal mccoy mountains formation the u pb zircon dates of the green ignimbrite and the pink ignimbrite overlap within error 155 8 ma and 162 3 ma respectively u pb data for zircon fractions from the plug dome complex do not further constrain the age of the upper dome rock sequence due to complex inheritance and lead loss but are consistent with the other dates taken together these data demonstrate that the lowermost mccoy mountains formation is late middle to early late jurassic bathonian to oxfordian in age a late middle to early late jurassic age for the lower unit of the mccoy mountains formation supports the previous interpretation that development of the extensional transtensional mccoy basin southeastern california and western arizona and the bisbee basin southeastern arizona was broadly coeval within the limits of sparse isotopic data in southeastern arizona and was the result of rifting during opening of the gulf of mexico we suggest that the much more abrupt volcanic to sedimentary transition in southeastern california relative to that recorded in southern arizona may reflect a greater component of strike slip faulting relative to extension in a regionally transtensional regime we speculate that this resulted from along strike variation in plate margin orientation

multiple subglacial till deposition a modern exemplar for quaternary palaeoglaciology the sedimentology of a vertical succession of alternating beds of massive and fissile diamictons on a orisjokull plateau icefield outlet foreland is employed to assess the evolution of subglacial traction tills at the margins of active temperate glaciers with deformable substrates where tills appear to form sub marginal incrementally thickened wedges that display multiple till emplacement events potentially of annual scale lodged boulders display strong a axes and surface striae alignments which parallel surface flutings indicating that fluting construction and till emplacement were related to moulding by consistent glacier flow from the ssw during the little ice age in contrast clast macrofabrics at the sub boulder size not unlike those reported from other icelandic tills are not as strong as would be expected in a subglacially sheared medium indicating shear strains too low for a steady state strain signature this separation of fabric data has isolated the strain signatures of the lodgement and deformation components of subglacial traction till whereby the orientations of the largest lodged clasts record high cumulative shear strains and those of the sub boulder sized clasts record greater susceptibility to deformation of their enclosing matrix this is likely due to the effect of clast collisions in clast rich till and the perturbations set up by the numerous large boulders consistent with observations on till fabrics in flutings and around lodged clasts a b plane macrofabric data display unusually high degrees of isotropy reflective of the more variable orientations of a b planes which are thought to reflect a b plane susceptibility to dip parallel or anastomosing shear planes a wide range of clast angularity values reflects the localized input of freshly plucked and hence relatively highly angular blocks to the deforming layer a characteristic of stepped bedrock profiles beneath the snouts of mountain glaciers finally we hypothesize that the massive and fissile units may represent a and b horizons of subglacial deforming layer couplets and that each couplet could record seasonal emplacement and partial inter couplet modification near the ice margin if the latter is the case then less than 1 m of subglacial till is advected to the glacier margin per annual deformation event

mg ca ratios of two globigerinoides ruber white morphotypes implications for reconstructing past tropical subtropical surface water conditions 1 tests of the planktonic foraminifer globigerinoides ruber white d orbigny have become a standard tool for reconstructing past oceanic environments paleoceanographers often utilize the mg ca ratios of the foraminiferal tests for reconstructing low latitude ocean glacial interglacial changes in sea surface temperatures sst we report herein a comparison of mg ca measurements on sample pairs n 20 of two g ruber white morphotypes g ruber sensu stricto s s and g ruber sensu lato s l from surface and downcore samples of the western pacific and indian oceans g ruber s s refers to specimens with spherical chambers sitting symmetrically over previous sutures with a wide high arched aperture whereas g ruber s l refers to a more compact test with a diminutive final chamber and small aperture the g ruber s s specimens generally show significantly higher mg ca ratios compared to g ruber s l our results from the mg ca ratio analysis suggest that g ruber s l specimens precipitated their shells in slightly colder surface waters than g ruber s s specimens this conclusion is supported by the differences in 18o and 13c values between the two morphotypes although it is still unclear if these two morphotypes represent phenotypic variants or sibling species our findings seem to support the hypothesis of depth and or seasonal allopatry within a single morphospecies

corroborating ecological depth preferences of planktonic foraminifera in the tropical atlantic with the stable oxygen isotope ratios of core top specimens 1 past variability in upper ocean thermocline depth is commonly estimated from the abundance of different species of planktonic organisms or the difference in oxygen isotopic composition between two species of planktonic foraminifera one that lives in the mixed layer and one that lives in or near the thermocline to test the latter relationships we measured the oxygen isotopic composition of eight species of planktonic foraminifera pink and white varieties of globigerinoides ruber globigerinoides sacculifer without the final chamber orbulina universa pulleniatina obliquiloculata globorotalia menardii neogloborotalia dutertrei and globorotalia tumida in surface sediment samples from 31 tropical atlantic deep sea sediment cores bayesian analysis was used to compare measured oxygen isotopic compositions with their predictions based on modern data sets of annual temperatures and oxygen isotopic composition of ocean water in the upper 500 m at the core sites posterior probability densities for predictive model parameters were computed probability distributions of calcification depth for analyzed species corroborated their ecological preferences inferred from net tow and sediment trap data robustness of the habitat signals in core top specimens suggests that reconstructions of the entire upper ocean temperature profiles not just their thermocline depth or temperature might be possible

core top calibration of δ18o and δ13c of g ruber white and u mediterranea along the southern adriatic coast of italy we carried out an extensive survey of the oxygen and carbon isotope composition of the planktic species g ruber white and of the benthic species u mediterranea along the southern italian coast of the adriatic sea and in the gulf of taranto comparison with seasonal satellite based sea surface temperature maps and water column profiles as well as with several sets of water samples allows estimation of the effect of salinity and different nutrient supply on the 18o and 13c of foraminifera the results indicate that g ruber white while being highly affected by different salinity and nutrient distributions related to circulation patterns of major water masses dominantly record summer temperature conditions u mediterranea reflect the recent environmental conditions such as nutrient supply and bottom water temperature characteristics along the southern italian coast and clearly show the transition from a near coastal eutrophic system to an offshore oligotrophic system

bedrock fracture by ice segregation in cold regions the volumetric expansion of freezing pore water is widely assumed to be a major cause of rock fracture in cold humid regions data from experiments simulating natural freezing regimes indicate that bedrock fracture results instead from ice segregation fracture depth and timing are also numerically simulated by coupling heat and mass transfer with a fracture model the depth and geometry of fractures match those in arctic permafrost and ice age weathering profiles this agreement supports a conceptual model in which ice segregation in near surface permafrost leads progressively to rock fracture and heave whereas permafrost degradation leads episodically to melt of segregated ice and rock settlement

the genesis and significance of hummocky moraine evidence from the isle of skye scotland abstract the range of genetic and climatic interpretations of scottish hummocky moraine is reviewed and new data are presented from the isle of skye western scotland which are used as the basis of a genetic classification hummocky moraine on skye is shown to consist of three principal sediment landform associations 1 recessional moraines 2 chaotic ice stagnation moraines and 3 drumlins and fluted moraines the recessional moraines consist of transverse moraine ridges and chains of mounds and were formed by a combination of glaciotectonics and debris accumulation at active ice margins second chaotic moraines consist of randomly distributed hummocks mounds and rim ridges and record deposition in contact with inactive ice finally drumlins and fluted moraines are longitudinally oriented subglacial bedforms formed by a combination of lodgement and sediment deformation individual occurrences of hummocky moraine may comprise one two or all of these associations the detailed study and differentiation of scottish hummocky moraine provides a valuable source of information on former glacier dynamics and landscape change

the relationship between shell size and mg ca sr ca δ18o and δ13c of species of planktonic foraminifera the relationship between shell size and mg ca sr ca 18o and 13c of planktonic foraminiferal calcite has been investigated using seventeen species in six different size fractions mg ca increases and sr ca decreases with increasing size except for two globorotaliid species which show the opposite trend the changes in mg ca broadly follow 18o calcification temperatures except that surface and near surface dwelling species show larger changes in mg ca than can be accounted for by differences in calcification temperature derived from 18o the increases in mg ca and decreases in sr ca vary linearly with the well established increase in 13c with size this is consistent with smaller individuals calcifying faster than larger individuals and larger individuals forming calcite that more closely reflects seawater temperature and composition it appears that variations in calcification rate affect mg and sr shell chemistry the observations may account for part of the temporal variability in foraminiferal sr ca within a single size fraction that has been attributed to changes in seawater sr ca

vertical thermal structure history in the western subtropical north pacific since the last glacial maximum 1 variations in sea surface temperature sst and vertical thermal structure in the western subtropical north pacific which has the largest air sea heat flux of the world s oceans provide insights into the mechanisms of climate change related to air sea interactions here we present planktonic 18o and mg ca records from the western subtropical gyre of the north pacific spanning the last 30 kyrs the results indicate that subtropical ssts were approximately 3 c lower during the last glacial than in the holocene interglacial indicating that glacial cooling occurred uniformly in the low to mid latitudes of the western north pacific a decrease in intermediate depth temperatures at the late glacial suggests that the formation and or advection of the subtropical mode water was enhanced due to a strong east asian winter monsoon the results suggest that the change in the thermal structure of the subtropical gyre was related to changes in east asian monsoon activity

the oxygen isotope composition of planktonic foraminifera from the cariaco basin venezuela seasonal and interannual variations material collected during a three year sediment trapping experiment in the cariaco basin venezuela january 1997 to december 1999 is used to examine both temporal and inter species variability in the oxygen isotope composition of planktonic foraminifera specifically this study compares the oxygen isotope composition of six species of planktonic foraminifera globigerinoides ruber pink globigerina bulloides neogloboquadrina dutertrei orbulina universa globorotalia menardii and globorotalia crassaformis with the climatology and hydrography of the region and evaluates the application of each species for use in paleoceanographic reconstructions the isotope results are consistent with known depth habitats for all six species the lowest 18 o values 1t o 2 were measured on g ruber pink and g bulloides two species that live in the surface mixed layer values for deeper dwelling species such as n dutertrei g menardii and g crassaformis are higher predominantly ranging from 0 to 0 5 temperature estimates derived using species specific paleotemperature equations indicate that g ruber pink accurately estimates sea surface temperatures ssts throughout the year while g bulloides temperature estimates are similar to measured surface temperatures only during the upwelling season january april for the remainder of the year the 18 o derived temperatures for g bulloides typically are lower than the measured sst although the maximum flux of all species occurs during upwelling the flux weighted annual mean isotopic composition of the six species indicates that only g bulloides is biased towards this season therefore we conclude that the sediment 18 o record of g ruber pink is most suitable for estimating past values of mean annual sst while g bulloides provides information on conditions during spring upwelling the depth of calcification of n dutertrei varies seasonally in response to changes in the depths of the thermocline and chlorophyll maximum as a result the 18 o difference between g ruber pink and n dutertrei provides an estimate of the annual surface to thermocline temperature gradient in the basin 2006 elsevier b v all rights reserved

extensional arc setting and ages of middle jurassic eolianites cowhole mountains eastern mojave desert block california mesozoic strata in the cowhole mountains eastern mojave block california include 200 800 m of eolian quartz arenite aztec sandstone overlain by more than 575 m of silicic ignimbrites lava flows and minor sedimentary rocks cowhole volcanics u pb zircon geochronologic data on a crystal rich dacite lava flow in the aztec sandstone indicate that the sandstone is middle jurassic and is therefore age equivalent to backarc eolianites of the temple cap and carmel formations not the lower jurassic navajo formation as previously assumed our u pb zircon data on two ignimbrites of the cowhole volcanics indicate that they are the same age within error as the lava flow in the aztec sandstone at 170 3 ma new structural and stratigraphic data together with published data indicate syndepositional normal faulting and deposition of landslide blocks throughout deposition of this section these results are consistent with our previous volcanologic studies in middle jurassic rocks of southern arizona southeastern california and the central mojave block which document ignimbrite eruptions from calderas contemporaneous with deposition of craton derived eolian sands in extensional or transtensional intra arc basins busby c j schermer e r and mattinson j m 2002 extensional arc setting and ages of middle jurassic eolianites cowhole mountains eastern mojave desert block california in glazner a f walker j d and bartley j m eds geologic evolution of the mojave desert and southwestern basin and range boulder colorado geological society of america memoir 195 p 79 9

vertical distribution and isotopic fractionation of living planktonic foraminifera from the panama basin a model1 2 which explains the vertical and seasonal distribution of planktonic foraminifera was developed using data from the western north atlantic and is comprised of three tenets 1 the conditions in the photic zone upper 80 100 m exclusively dictate planktonic foraminifera species composition and abundance throughout the water column 2 species are vertically stratified within the photic zone according to their temperature preference depth distribution according to temperature preference has been proposed by several authors3 based on isotope analyses of sediments due to seasonal temperature variations seasonal variations in the 18o composition of seawater and species specific isotope fractionation rigorous proof of this hypothesis cannot be provided from sediment analyses alone 3 the chlorophyll maximum is a major food source zone which is preferentially exploited by foraminifera our data from the panama basin which are presented here are confirmation of this model the panama basin in the eastern equatorial pacific which has a shallow and steep thermocline was sampled for living planktonic foraminifera a multiple opening closing net and environmental sensing system mocness 4 was used to collect 13 sets of eight vertically stratified oblique samples we report here the quantitative distribution and stable isotopic composition of planktonic foraminifera from four mocness tows taken over 5 days during august 1979 rv knorr cruise 73 at 5 20 n 8 50 w each tow consisted of eight samples which integrated 12 5 m intervals from 0 to 100 m for moc 126 25 m intervals from 0 to 200 m for moc 127 100 150 m intervals from 0 to 1 000 m on moc 128 and 250 m intervals from 0 to 2 000 m on moc 131

periglacial weathering and headwall erosion in cirque glacier bergschrunds glaciers produce cirques by scouring their beds and sapping their headwalls but evidence to constrain models of these processes has been elusive we report a suite of environmental measurements from three cirque glacier bergschrunds including the first temperature series recorded at depth throughout most of an annual cycle compared to the ambient air the bergschrunds were colder in summer and warmer in winter freeze thaw cycles were rare and relatively stable subfreezing temperatures persisted from november until may using a model for rock fracturing driven by ice segregation we demonstrate that favorable conditions for fracturing occur not only on the headwall above the glacier but also within the bergschrund where periglacial weathering and glacial transport can act together to drive cirque headwall retreat a small 3 c year round decrease in temperatures to conditions more typical of the pleistocene would likely intensify the weathering process though so far ignored in all glacial landscape evolution models the bergschrund likely plays an essential role in the sculpting of alpine landscapes

the source of ions for biomineralization in foraminifera and their implications for paleoceanographic proxies the global carbon cycle is strongly perturbed by fossil fuel burning leading to atmospheric co2 increase climatic warming followed by polar ice melting and global sea level rise are predicted due to the greenhouse effect of increasing co2 in the atmosphere houghton et al 1995 the ocean plays a major role in neutralizing the excess co2 because the amount of inorganic carbon available for exchange with the atmosphere in the ocean is approximately 50 60 times larger than in the atmosphere e g siegenthaler and sarmiento 1993 the bulk of the atmospheric co2 excess will eventually be neutralized by caco3 dissolution in the deep marine environment this is however is a relatively slow process that operates on the time scale of ocean circulation 1000 yrs and is therefore causing an accumulation of co2 in the atmosphere this phenomenon will result in potentially severe consequences to the well being of global ecological systems obviously the scientific attention of many biogeochemists is focused on processes controlling the response of the marine system to changes in atmospheric co2 concentrations e g archer and maier reimer 1994 broecker 1997 sigman and boyle 2000 berger 2002 foraminifera corals and coccolithophores in the global carbon cycle there are four dominant processes involved in neutralizing the excess atmospheric co2 in the ocean these are 1 gas exchange at the air sea interface and reaction with the carbonate ion to form bicarbonate 2 net primary productivity 3 caco3 production and dissolution and 4 ocean circulation most of these processes are biologically mediated and may have special importance in shallow tropical environments where the exchange with the atmosphere is more direct in this review we address the mechanism of biomineralization in one of the major groups that precipitates caco3 in the ocean the foraminifera as we will show this group

isotopic signals in two morphotypes of globigerinoides ruber white from the south china sea implications for monsoon climate change during the last glacial cycle abstract based on the study of surface and downcore sediment samples from the south china sea scs two morphotypes of globigerinoides ruber white have been differentiated by taxonomic criteria at species and or subspecies level and also by their stable isotopic compositions of oxygen and carbon the two morphotypes g ruber sensu stricto s s and g ruber sensu lato s l represent two groups with different depth habitats with g ruber s s living in the upper 30 m of the water column and g ruber s l living at depths below 30 m the different depth habitats are indicated by the comparison between the present oceanographic data and isotopic signals of the two morphotypes in the surface sediment from the scs application of this information to a hemipelagic sediment core in the northern scs shows that drastic changes existed in the morphotypes isotopic records during the last glacial cycle the isotope difference between the two morphotypes diminished during 18 o stage 2 especially during the last glacial maximum it is inferred that this is the result of intensified monsoon winds which caused mixing of the upper layer of the water column during stage 2 the proportion of g ruber s l increased which is interpreted as a result of the increased productivity due to mixing of the subsurface nutrient rich water into the surface layer

variability in vertical distributions of planktonic foraminifera in the california current relationships to vertical ocean structure 1 geochemical records from planktonic foraminifera are among the few means available to infer past changes in the upper ocean although interpretations can be confounded by variability in foraminifera habitat depths the principal environmental factors affecting foraminiferal vertical distributions were examined through 28 vertically stratified plankton tows taken off southern california in winter spring and summer each species has a dynamic range of preferred habitat depth from the mixed layer to the thermocline characterized by a unique relationship with environmental properties globigerina bulloides neogloboquadrina pachyderma dextral and neogloboquadrina dutertrei can live near the surface but frequently live deeper as stratification increases and a particular isotherm deepens globigerinoides ruber and orbulina universa vary more closely with the depth of the thermocline than the depth of a given isotherm the shifts in habitat depth are of sufficient magnitude to affect 18o records the effects of such shifts are observed for g bulloides and n pachyderma in santa barbara basin sediments geochemical signatures from multiple species of foraminifera each with a different predicted response to environmental change can permit the detection of changes in habitat depth of a given species and thus more accurately indicate past changes in hydrographic structure

the oxygen isotope composition of planktonic foraminifera from the guaymas basin gulf of california seasonal annual and interspecies variability abstract sediment trap samples collected over a seven year period february 1991 october 1997 from guaymas basin in the gulf of california were used to study the oxygen isotope composition of five species of planktonic foraminifera globigerinoides ruber white globigerina bulloides neogloboquadrina dutertrei pulleniatina obliquiloculata and globorotalia menardii the 18o data were analyzed for temporal and interspecies variability and were compared to local hydrography to evaluate the use of each species in reconstructing past oceanographic applications the two surface dwelling species g ruber and g bulloides displayed the lowest 18o values 0 0 to 5 0 while 18o values for the thermocline dwelling n dutertrei p obliquiloculata and g menardii were higher 0 0 to 2 0 the 18o of g ruber most accurately records measured sea surface temperatures ssts throughout the year g bulloides 18o tracks ssts during the winter spring upwelling period but for the remainder of the year records slightly colder subsurface temperatures the difference between the 18o of the surface dwelling species g ruber and g bulloides and that of the thermocline dwelling species n dutertrei p obliquiloculata and g menardii was used to estimate the surface to thermocline temperature gradient during the winter these 18o differences are small 0 50 reflecting a well mixed water column these interspecies 18o differences increase during the summer 1 90 in response to the strong thermal stratification that exists at this time of year

cosmogenic exposure dating of late pleistocene moraine stabilization in alaska seventy three new 1 0 be 2 6 al ages from 57 moraine boulders and 2 tors together with 43 previously published cosmogenic exposure ages from 41 moraine boulders allow us to critique the use of cosmogenic exposure ce dating of moraine boulders in alaska boulder exhumation during moraine degradation likely gives rise to the largest uncertainty in constraining the timing of initial moraine stabilization following ice retreat isotopic inheritance appears to be most important for moraines deposited close to their cirque headwalls boulder surface bedrock erosion rate can be roughly constrained and leads to a range in moraine stabilization ages snow cover history is difficult to constrain but its effect is thought to be minor for the tall boulders sampled despite these complications the ce ages provide important new information regarding the timing of the last and penultimate glaciations in alaska three penultimate moraines yielded ce ages that overlap with marine isotope stage mis 4 early mis 3 45 65 ka rather than mis 6 ca 140 ka based on a combination of our new ce chronologies and existing 1 4 c ages from six study areas glaciers retreated from their local late wisconsin maxima ca 24 27 ka kokrines hills west interior alaska ca 24 26 ka northeastern brooks range ne alaska ca 21 23 ka yukon tanana upland east interior alaska ca 22 ka ahklun mountains sw alaska ca 20 ka western alaska range central alaska ca 16 18 ka chuilnuk mountains sw alaska overall glacier retreat was concurrent with the peak of the last global glacial maximum probably in response to limited moisture availability

a theoretical model of the fracture of rock during freezing we present a mathematical model for the breakdown of porous rock by the growth of ice within cracks the model is founded upon well established principles of fracture mechanics and recent advances in soil physics ijong with the assumption that progressive crack growth results from water migrating to ice bodies in cracks much as water migrates to ice lenses in freezing soil our model predicts crack growth rates compatible with empirical data calculations for a granite and a marble indicate that sustained freezing is most effective in producing crack growth when temperatures range from 4 c to 15 c at higher temperatures thermodynamic limitations prevent ice pressure from building up sufficiently to produce significant crack growth at lower temperatures the migration of water necessary for sustaining crack growth is strongly inhibited in hydraulically open systems in which pore water pressure remains near atmospheric pressure during the freezing process crackgrowth rates during continuous cooling will generally be greatest at low rates of cooling less than 0 1 0 5 c h at higher rates of cooling the influx of water to growing cracks is significantly inhibited the model delineates clearly the role of material parameters elastic moduli fracture mechanical properties grain size and shape and crack size environmental conditions temperature temperature gradient water pressure and time in frost damage to rocks our calculations along with recent experimental work on water migration in freezing rocks fukuda 1983 lead us to question the widely accepted importance of two phenomena freezing of water in sealed cracks and freeze thaw cycling in the fracture of rock exposed to natural freezing conditions

erosion rate of a younger dryas cirque glacier at krakenes western norway an erosion rate of 0 5 to 0 6 mm a 1 is deduced for a younger dryas cirque glacier the erosion period of 700 a was determined from the laminated glaciolacustrine sediments in a small lake just outside the end moraine of the cirque and radiocarbon dates obtained below and above these sediments the volume of eroded bedrock was calculated from measurements of the deposited sediments of which the end moraine the glaciofluvial delta and the glaciolacustrine sediments are most important with a constant erosion rate the cirque could have formed in 83 to 125 000 a

debris transport by loch lomond readvance glaciers in northern scotland basin form and the within valley asymmetry of lateral moraines moraines in six cirques in northern scotland are shown to be asymmetrically developed being larger below north or east facing valley sides moraine asymmetry is strongly correlated with the distribution of free faces in the valleys a relationship that is interpreted as the result of variation in slope retreat rates analysis of clast form and roundness demonstrates that following initial release from bedrock debris entered both passive high level glacial transport and tractive transport at the ice bed interface the importance of glacier velocities and medial moraines on debris flux is discussed consideration is also given to the implications of process asymmetry to long term landform development

genesis stability and preservation potential of large lateral moraines of alpine valley glaciers towards a unifying theory based on findelengletscher switzerland abstract lateral moraines are prominent features of glaciated landscapes in high mountain environments and key landforms in glacier and palaeoclimatic reconstructions yet compared to smaller moraines they have been little studied and several aspects are not well understood we here present detailed sedimentological results from the lateral moraines of findelengletscher in sw switzerland to gain new insights into the formation of these landforms the lateral moraines studied here stand up to 140 m above the valley floor are over 3 km long and strongly asymmetrical in cross profile with distal slopes between 29 and 36 and proximal slopes that are commonly 41 64 but locally reach angles of up to 80 recorded lithofacies comprise loose clast and matrix supported stratified diamicts and intercalated sorted sediments in the distal slopes and near the crestline overconsolidated matrix supported massive and weakly stratified diamicts and streaked out sorted sediment lenses in the core and proximal slopes and partly intercalated dark brown layers overlain by loose and consolidated diamicts exposed in near vertical walls in the proximal flank these are interpreted as supraglacial debris flow units with intercalated fluvial wash horizons glaciotectonised and subglacial traction till with boudinaged and streaked out sediment lenses and palaeosoils overlain by sediment produced by overtopping of the former moraine surface during a subsequent advance of the glacier clast shape analysis and process observations reveal that the dominant mode of transport is subglacial and glaciofluvial and that the main mode of sediment delivery to the moraines is by debris flows after the material has been transferred from the bed via englacial debris bands and meltout at the surface this differs from previous studies that found that a supraglacial source was dominant sedimentary structures clast fabric and process observations during the 1979 1980 readvance of findelengletscher strongly suggest that proximal layers of reworked pre existing sediments and or basal traction zone till have been plastered onto the moraine core in several locations causing a high degree of overconsolidation and strongly clustered fabric eigenvalues s 1 0 94 with clustering parallel to the moraine crestline this suggests that a combination of basal lateral drag and lateral plastering produces the observed proximal stability and ensures a high preservation potential we develop a conceptual model that describes alpine lateral moraines as structurally complex landforms that do not just record a single event as often surmised and we discuss implications for palaeo glacier reconstruction and the application of numerical dating methods

multispecies approach to reconstructing eastern equatorial pacific thermocline hydrography during the past 360 kyr 1 stable isotope data from eastern equatorial pacific eep core tr163 19 2 15 n 90 57 w 2348 m are presented for the surface dwelling foraminifers globigerinoides ruber and g sacculifer and thermocline dwelling globorotalia menardii and neogloboquadrina dutertrei using species specific normalization factors derived from experimental and plankton tow data we reconstruct a 360 kyr record of water column hydrography across the past three glacial cycles we demonstrate that g ruber maintains a mixed layer habitat throughout the entire record while g sacculifer records a mixture of thermocline and mixed layer conditions and g menardii and n dutertrei record thermocline properties we conclude that g sacculifer is not appropriate for paleoceanographic applications in regions with steep vertical hydrographic gradients results suggest that this region of the eep had a thicker mixed layer and deeper 13cdic boundary between the surface and equatorial undercurrent during the last two glacial periods a shift in n dutertrei and g sacculifer geochemistry prior to 185 kyr suggests water column structure and chemocline gradients changed possibly due to a shift in the position of the undercurrent relative to this site the timing and magnitude of glacial interglacial 13c variations between species indicates that near surface carbon chemistry is controlled by changes in productivity atmospheric circulation and advected intermediate water sources north of the antarctic polar front these results demonstrate that when properly calibrated for species differences multispecies geochemical data sets can be invaluable for reconstructing water column structure and properties in the past

welded tuff infilling a volcanic vent at weolseong republic of korea a plug of parataxitically welded tuff with an elliptical 700 400 m cross section crops out in weolseong district republic of korea it intrudes late cretaceous granodiorite and extrusive tuffs of the chisulryoung volcanic formation and displays a steeply inclined welding foliation concordant with the intrusive contacts and a subvertical stretching lineation these fabrics are interpreted as resulting from laminar shearing in a boundary layer during deposition of the tuff by agglutination along the walls of a vent which served as a feeder for extrusive ignimbrites

stable isotopes of planktonic foraminifera from tropical atlantic caribbean core tops implications for reconstructing upper ocean stratification abstract 18o values of nine tropical subtropical planktonic foraminiferal species with different preferential habitat depths collected from 62 core top samples along an east west transect across the tropical atlantic caribbean were used to test the applicability of interspecific 18o gradients for reconstructions of tropical upper ocean stratification in general the 18o difference 18o between intermediate and shallow dwelling species decreases and 18o between deep and intermediate dwellers increases with increasing thermocline depth towards the west the statistical significance of regional differences in 18o highlights 18o between the intermediate dwellers in particular globorotalia scitula and globorotalia tumida and the shallow dweller globigerinoides ruber pink as well as 18o between the deep dwellers globorotalia crassaformis or globorotalia truncatulinoides dextral and intermediate dwellers as most sensitive to changes in tropical atlantic thermocline depth based on the observed regional variations in interspecific 18o we propose a multispecies stratification index stratrop 18ointermediate 18oshallow 18odeep 18oshallow for the tropical ocean statistically significant differences in stratrop values between the e atlantic and the caribbean suggest that this index may be a useful tool to monitor variations in tropical upper ocean stratification in the geological record

planktonic foraminifera as recorders of past surface water stratification the 18 o difference between shallow and deep living planktonic foraminifera is a proxy for the stratification of surface waters in holocene sediments from the atlantic this difference increases from about 0 in subpolar regions to 3 in the tropics the 18 o values of the shallow dwellers globigerinoides sacculifer and neogloboquadrina pachyderma mainly reflect surface water conditions the calcification depth of the deep living species globorotalia truncatulinoides right coiling is affected by the stratification of the water column in the subtropics shell formation of g truncatulinoides right coiling begins in weakly stratified surface waters in the tropics the initial shell is secreted below the mixed layer this hydrographically induced difference in calcification depth allows the use of the isotopic difference between g truncatulinoides and the shallow species as a proxy for the stratification of surface waters the 18 o between g truncatulinoides and g sacculifer from tropical gravity core geob 1523 1 was significantly lower during isotope stage 2 this suggests that the glacial temperature stratification of western equatorial atlantic surface waters was significantly reduced relative to the holocene

global calibration of ecological models for planktic foraminifera from coretop carbonate oxygen 18 abstract a global dataset of coretop planktic foraminiferal 18oc is combined with a global database of seawater 18ow observations and ocean climatologies to determine robust optimum parameters for an ecological model for six commonly measured species and varieties these parameters consist of the temperature ranges optimum temperatures depth habitat and the amount of secondary calcification for globigerinoides ruber white g ruber pink neogloboquadrina pachyderma l n pachyderma r globigerinoides sacculifer and globigerina bulloides this approach produces ecological models and temperature ranges consistent with previous work and manages to reproduce the coretop oxygen 18 carbonate values remarkably well the standard error of modelled values of coretop calcite globally and for all species is 0 53 compared to an error of 1 2 when assuming annual average mixed layer equilibrium calcite

a comparison of clast fabric and shape in late precambrian and modern glacigenic sediments abstract northeastern svalbard contains a well preserved glacigenic sequence of vendian late precambrian age in which terrestrial lacustrine intertidal and marine glacial facies are represented diamictite facies are of two main types massive and weakly to strongly bedded diamictite field appearance and relationships with other facies however provide insufficient information to allow a clear interpretation of the precise mode of glacial deposition by combining this information with data concerning the fabric of clasts in modern glacigenic sediments where the mode of glacial deposition is better known a wider understanding of the processes of glacial deposition in vendian time is obtained several diamictite samples were interpreted to be of lodgement tillite facies and material o water laid and glacigenic sediment flow origin was also recorded clast shape analyses indicate that most glacial debris was transported at least for a time at the glacier bed little angular supraglacial debris was present implying that the ice mass was of ice cap or ice sheet dimensions with few subaerial rock exposures clast shape in the late precambrian deposits was not useful in distinguishing between the variety of lithofacies derived from basally transported glacial material too few systematic studies of clast striation in modern glacigenic sediments are yet available for this criterion to be helpful in distinguishing between tillite facies lithofacies analysis together with clast fabric and shape studies provide useful and complementary lines of evidence concerning the ode of deposition of ancient diamictite sequences an understanding of the depositional processes and patterns of modern glacial sedimentation provides a fundamental framework for such studies

comparison of species specific oxygen isotope paleotemperature equations sensitivity analysis using planktonic foraminifera from the cariaco basin venezuela abstract the oxygen isotope compositions of seven species of planktonic foraminifera globigerinoides ruber pink globigerina bulloides globorotalia menardii globigerinoides sacculifer orbulina universa globorotalia crassaformis and neogloboquadrina dutertrei were measured from biweekly sediment trap samples collected in cariaco basin venezuela between 2003 and 2008 sixteen published paleotemperature equations were used to estimate calcification temperatures from this 18 o data as part of the cariaco time series routine in situ water column chemistry measurements and hydrographic monitoring has occurred since 1995 the calcification temperature estimates were compared with these monthly water column temperature measurements to ascertain species depth habitats and to determine which equations yielded the most realistic temperature estimates no single equation provided accurate temperature estimates for all species rather the equations yielded temperature estimates that varied by 2 4 c for each species overall species specific paleotemperature equations based on plankton tow samples yield the coldest temperature estimates while generic equations produce the warmest temperatures our results indicate that when using planktonic foraminiferal 18 o to make paleotemperature estimates equations must be carefully selected on a species by species basis here we provide general guidelines for selecting paleotemperature equations we also evaluated how well the 18 o difference between the surface dwelling g ruber and the deeper dwelling n dutertrei estimates the surface to thermocline temperature gradient the 18 o is small 0 61 during winter due to upwelling and increases 1 37 during summer as upwelling ceases and surface waters become thermally stratified

fluted moraine formation and till genesis below a temperate valley glacier slettmarkbreen jotunheimen southern norway clast fabric and morphological data have been used to determine the origin of fluted subglacial tills exposed by recent retreat of the slettmarkbreen glacier norway a new method for the interpretation of clast fabric data allows aspects of the strain and depositional history of the till to be reconstructed the till formed by a combination of lodgement and subsole deformation by slip along discrete shear planes lodgement was dominant for the larger size fractions 125 mm while the smaller material was more susceptible to deformation the fluted till surface reflects the tendency for the till matrix to deform into regions of low confining pressure in the lee of lodged boulders downglacier components of till flow are thought to have resulted in significant sediment transfer towards the margin

calcification depths and temperatures of planktonic foraminifera off southwest hainan island and their paleoceanographic implications abstract the east asian monsoon system influences the local oceanographic and climatic conditions of south china sea scs making the habitat depths of planktonic foraminifera pf specific for this region the previous paleo ocean reconstructions of scs have been based on calcification habitat depths derived from other oceans which may have affected the accuracy of interpretations in this study the calcification depths of globigerinoides ruber globigerinoides sacculifer and neogloboquadrina dutertrei from sediment traps deployed at 1000 m depth off southwest hainan island from july 2012 to april 2013 were analyzed with regard to the stable isotopes of oxygen 18o and carbon 13c to calculate their regional apparent calcification depths acds with the overall aim to improve the reconstruction of the upper ocean thermal structure acds and temperature estimated from foraminifera 18o ranged from 0 to 42 m and 25 c for g ruber 30 65 m and 23 3 c for g sacculifer and 75 100 m and 20 3 c for n dutertrei respectively the difference between the thermocline species n dutertrei and mixed layer species g ruber and g sacculifer 18o 18oth ml and the temperature t shows water column stratification the periods of lower and higher t and 18o were in phase with the changes in regional overlying wind speed additionally this study reveals that n dutertrei lives and calcifies its shells within the base of the mixed layer depth mld and upper thermocline depth in scs overall the results from this study provide a new insight to understand the mixed layer and thermocline depth in the northern scs

isotopic complexities and the age of the delfonte volcanic rocks eastern mescal range southeastern california stratigraphic and tectonic implications combined u pb zircon rb sr 40 ar 39 ar laser fusion and conventional k ar geochronology establish a late early cretaceous age for the delfonte volcanic rocks u pb zircon analyses define a lower intercept age of 100 5 2 ma that is interpreted as the crystallization age of the delfonte sequence argon studies document both xenocrystic contamination and postemplacement ar loss rb sr results from mafic lavas at the base of the sequence demonstrate compositionally correlated variations in initial 87 sr 86 sr ratios sr i from 0 706 for basalts to 0 716 for andesitic compositions this covariation indicates substantial mixing of subcontinental lithosphere with proterozoic upper crust correlations between rb sr and sr i may result not only in pseudoisochrons approaching the age of the crustal component but also in reasonable but incorrect apparent ages approaching the true age ages obtained in this study require that at least some of the thrust faulting in the mescal range clark mountain portion of the foreland fold and thrust belt occurred later than ca 100 ma and was broadly contemporaneous with emplacement of the keystone thrust plate in the spring mountains to the northeast comparison of the age and rb sr systematics of ash flow tuff boulders in the synorogenic lavinia wash sequence near goodsprings nevada with those of the delfonte volcanic rocks supports a delfonte source for the boulders the 99 ma age of the lavinia wash sequence is nearly identical to the delfonte age requiring rapid erosion transport and deposition following delfonte volcanism

geology of the inyo mountains volcanic complex implications for jurassic paleogeography of the sierran magmatic arc in eastern california an 3 1 km thick volcanic complex exposed in the southern inyo mountains east central california records jurassic subaerial depositional environments along the east flank of the sierran arc this complex which we name the inyo mountains volcanic complex is subdivided into lower middle and upper stratigraphic intervals the 200 580 m thick lower interval comprises predominantly epiclastic strata deposited on alluvial fans and adjacent river flood plains that were inclined northeast mafic lava flows and rare reworked tuff in this interval record the onset of jurassic volcanism in this part of the arc the 300 700 m thick middle interval is composed predominantly of intermediate to silicic lava flows and tuffs representing a major episode of volcanism ending at ca 169 ma that is contemporaneous with emplacement of numerous plutons in the region the 2260 m thick upper interval is composed of epiclastic strata with minor intercalations of volcanic rock most of this interval accumulated on low gradient flood plains that hosted evaporative lakes and that were episodically invaded by alluvial fan complexes three new u pb age determinations constrain the lower half of the upper interval to have been deposited during the interval from ca 169 ma to 150 ma the uppermost part of the complex remains undated but probably accumulated prior to 140 ma the inyo mountains volcanic complex is part of a belt of volcanic complexes that are the easternmost preserved jurassic complexes of the sierran arc these complexes share sufficient similarities to suggest that they represent a distinctive arc flank depositional province significantly different from that represented by coeval volcanic complexes preserved in roof pendants farther west closer to the magmatic axis of the arc similarities among arc flank complexes include predominantly to exclusively subaerial settings substantial 30 portions of epiclastic strata and existence at times of north to northeast inclined paleoslopes we infer on the basis of the varying types and amounts of volcanic rocks that whereas most complexes in the arc flank province were rarely if ever proximal to major eruptive centers complexes in two areas white mountains and eastern mojave desert were at times located in or adjacent to such centers these differences lead us to speculate that the east flank of the jurassic arc consisted of eastward projecting volcanic salients separated by arc recesses typified by the inyo mountains area in which epiclastic deposition was dominant

the lower atmosphere over the gulf of california automated meteorological observations at coastal and island stations instrumented aircraft flights and coastal soundings were made between july 1983 and june 1985 to define the variations of the lower atmosphere over the northern half of the gulf of california during the two important climatic seasons the mid latitude winter and the subtropical summer a marine layer is well defined over water during both seasons but dissipates within a few kilometers inland the winter large scale pressure field is dominated by the great basin high over the southwestern united states modulated by upper level synoptic activity it causes 3 to 6 days events of northwesterly winds 8 12 m s 1 directed along the gulf s axis which are coherent over basin scales and bring cool dry desert air over the gulf the vertical scale of these winds is 700 1000 m over land on the western side of the gulf close to the height of the baja california mountains but only 100 400 m over water defined by the wintertime inversion cross gulf winds related to topographic effects during upper level trough passages over baja california are particularly intense in the northwestern portion of the gulf the winter marine layer is defined by a 1 to 4 5 c temperature inversion and a dew point temperature of 6 11 c a moisture content of 6 8 g kg 1 weak subsidence reduces dew point values to 4 c above the inversion winter winds above the marine layer are coherent 0 8 across the width of the gulf the summer large scale pressure field is dominated by a thermal low over the southwestern united states and drives weak 2 5 m s 1 southeasterly winds also directed primarily along the gulf which are less spatially uniform than winter winds air temperature and moisture content are rather constant and topographic effects are absent the summer marine layer is on the order of 200 300 m thick with dew point temperatures of 26 28 c 21 24 g kg 1 and capped by a weak temperature inversion 1 2 c over water aloft the dew point temperature is 17 21 c and winds are weak and uncorrelated across the width of the gulf during june and early july 1984 four week long pulses of southeasterly winds 10 m s 1 support the existence reported previously of moisture surges from the gulf into the sonoran desert a dynamical analysis of subdiurnal motions shows that the cross gulf momentum balance is geostrophic the along gulf balance is ageostrophic with the along gulf pressure gradient opposed by friction at the surface these results are consistent with a scale analysis of the equations of motion in the marine layer over the gulf of california

miocene rhyolitic welded tuff infilling a funnel shaped eruption conduit shiotani southeast of matsue sw japan at shiotani sw japan rhyolitic welded tuff forms a steep sided funnel shaped body confined by paleogene granitic rocks to an elliptical area 1 1 5 km across the shiotani welded tuff is pervasively welded and foliated concordantly with the contact that dips inward at angles of 70 90 in contrast nearby contemporary volcaniclastic deposits are non welded and gently inclined near the contact with the granite the tuff is plastically deformed and shows lineations that plunge inward at angles of 40 65 lithic and crystal clasts in the rheomorphic outer part are rotated in a plane normal to the foliations and parallel to the lineations indicating downward flow of the welded tuff the geometry and internal structures suggest that the shiotani welded tuff was emplaced and welded in a funnel shaped eruption conduit upon collapse of a plinian or phreatoplinian eruption column the majority of the conduit filling pyroclasts probably fell back en masse into the conduit heat and steam from underlying magma and diffusion of interstitial volatiles into the glass perhaps reduced the viscosity of juvenile pyroclasts and facilitated welding in the conduit especially at deep levels the hot welded pyroclasts then flowed down the conduit wall during welding compaction and retreat of the magma these processes resulted in increased welding toward the contacts and welding foliations concordant with the steep wall emplacement of nearby correlative volcaniclastic mass flow deposits in a shelf to upper bathyal environment suggests a possibility that when active the shiotani conduit was under the sea welding compaction would occur even under the sea provided that the steam generated in the upper part of the conduit fill prevented water access

physical modelling of fault scarp degradation under freeze thaw cycles physical modelling has been developed in order to simulate the effects of periglacial erosion processes on the degradation of slopes and scarps data from 41 experimental freeze thaw cycles are presented they attest to the efficiency of periglacial processes that control both erosion and changes in scarp morphology i cryoexpulsion leads to an increase of scarp surface roughness and modifies significantly the internal structure of the active layer ii combined effects of frost creep and gelifluction lead to slow and gradual downslope displacements of the active layer 0 3 cm cycle iii debris flows are associated with the most significant changes in scarp morphology and are responsible for the highest rate of scarp erosion iv quantification of the erosion rate gives values close to 1 cm3 cm 2 for 41 freeze thaw cycles these experimental results are consistent with field data acquired along the la hague fault scarp normandy france where an erosion rate of 4 6 1 m3 m 2 per glacial stage has been computed from the volume of natural slope deposits stored during the weichselian glacial stage these results show that moist periglacial erosion processes could lead to an underestimation of plio quaternary deformation in the mid latitudes copyright 2006 john wiley sons ltd

temperature δ18o relationships of planktonic foraminifera collected from surface waters abstract most of the isotopic paleotemperature equations used for paleoceanographic reconstructions have been derived from culture experiments or inorganic precipitates of calcium carbonate to test these equations in the modern ocean we measured the oxygen isotope composition of planktonic foraminifera globigerinoides ruber globigerinoides sacculifer globigerina bulloides and neogloboquadrina pachyderma collected from atlantic and southern ocean surface waters and added published plankton tow data from the pacific indian and arctic oceans the resulting species specific regression equations of the temperature 18o relationships for g ruber g sacculifer and g bulloides are statistically indistinguishable the equations derived for g sacculifer and g bulloides agree with relationships obtained from laboratory experiments in which these species were cultured at ph values close to modern surface waters the equation derived from n pachyderma has a significantly lower slope and offset than the other three species but produces a regression equation that is nearly identical to the one for the epifaunal benthic foraminifer cibicides sp our work on plankton tow and pumped samples indicates that culture derived equations appear to be more appropriate for predicting the absolute 18o of the species examined compared to equations derived from inorganic precipitates however over the oceanic temperature range the slopes of the equations we derive for living species agree with the slopes obtained from inorganic precipitates

glaciation in the surroundings of prasilske lake bohemian forest czech republic abstract comprehensive geomorphological and sedimentological analyses confirmed three phases of wurm glaciation in the surroundings of prasilske lake and stara jimka in the bohemian forest sumava mountains glaciations were affected by a steep east facing slope by plateaus on the adjacent ridges and by local geological conditions a small valley glacier about 2 km long and 50 m thick occurred during the first phase in the second phase a glacier rock glacier developed probably based on remnants of the valley glacier during the last phase glacial activity was divided into stara jimka and the stepped cirque of prasilske lake a further shallow 3 m deep lake in stara jimka was dammed by slope movements after deglaciation 14 cal ka bp and survived until 4 cal ka bp the late pleistocene chronology of the bohemian forest seems to be related more closely to the alps than to northern europe in the mid mountains of central europe pleistocene glaciation decreases significantly eastward because of increasing continentality the presence of plateaus deflation areas around 1300 m altitude across the approach of westerly winds was important for the development of glaciers in the bohemian forest the termination of glaciation before the younger dryas is specific to the bohemian forest in comparison with the vosges and krkonose mountains

deep dwelling planktonic foraminifera of the northeastern pacific ocean reveal environmental control of oxygen and carbon isotopic disequilibria abstract we assess the utility of four species of living planktonic foraminifera as tracers of thermocline and intermediate water masses in the northern pacific ocean based on their water column distribution and shell isotopic composition assuming oxygen isotopic equilibria with the water column we infer apparent calcification depths this allows an estimate of apparent carbon isotopic disequilibria we then relax the assumption of oxygen isotopic equilibrium to examine habitat effects on kinetic disequilibrium processes in the california current left coiling neogloboquadrina pachyderma and globigerina calida calcify in the upper thermocline globorotalia scitula resides within the shallow salinity minumum potential density 25 1 26 7 while globoquadrina hexagona is associated with the deeper north pacific intermediate water 26 7 26 9 apparent carbon isotopic disequilibria corrected for oxygen isotopic disequilibria range from 1 0 1 9 in these asymbiotic species the carbon isotopic disequilibrium can be modeled as a single exponential function of temperature or a logarithmic function of potential food supply we infer that carbon isotopic disequilibrium increases with metabolic rate related to temperature and or food supply kinetic processes of oxygen and carbon isotopic disequilibria yields reasonable depth habitats if the slope of the oxygen carbon isotopic shift is about 0 35 consistent with culture data our finding of a link between environment metabolism and isotopic disequilibrium observed in oceanic settings suggests the potential to better reconstruct the structure and biological processes of the upper water column from geologic data

stable isotopes in modern planktonic foraminifera sediment trap and plankton tow results from the south china sea abstract this study reports on the stable isotopic composition of modern planktonic foraminifera tests collected from plankton tows and sediment trap moorings in the northern south china sea plankton tow samplings were conducted at water depths of 50 100 and 200 m during various seasons between december 2002 and august 2008 the sediment trap array was deployed between august 2004 and february 2005 at water depths of 121 m 619 m and 3451 m four common and widely distributed tropical subtropical planktonic foraminifer species including globigerinoides ruber white variety globigerinoides sacculifer without sac neogloboquadrina dutertrei and pulleniatina obliquiloculata were analyzed for 18o and 13c within narrow shell size ranges and compared with the concurrent sea surface temperature sst and wind stress our results show that foraminiferal 18o is primarily influenced by seawater temperature while 13c is affected by surface water nutrients which in this region can be discerned from wind stress data the 18o and 13c values from foraminifers recovered in plankton tows generally show greater variability and more depleted 18o than values of tests collected by sediment traps for foraminifer tests collected by sediment trap the 18o of the shallow dwelling g ruber shows the largest amplitude variation ca 1 6 among the four species in contrast the 13c of p obliquiloculata shows relatively constant values throughout the study period a pattern of enriched 18o values associated with marked 13c depletion is common to three species collected between late october and late december 2004 this distinct isotopic signal corresponds to a decrease in sst and increase in wind stress indicating the onset of prevailing northeast winds during the winter season

the effect of rock moisture on schmidt hammer rebound tests on rock samples from marion island and south africa in an assessment of the influence of internal rock moisture content on schmidt hammer readings rebound r values are found to decrease with increasing moisture content for samples of basalt sandstone and dolerite the maximum decrease in r values is found between oven dry values and saturated rock rebound values the magnitude of which varies from 2 to 10 points on the r scale a quartzite block has the greatest decline of 6 points at 60 per cent saturation for certain rock types under differing site to site field moisture conditions the moisture effect can be a significant factor in the interpretation of the relative state of weathering from rebound values copyright 2002 john wiley sons ltd

planktonic foraminifers as tracers of ocean currents in the eastern south atlantic the standing stock of planktonic foraminifers collected at 16 stations by multinet plankton tow has been examined in five discrete depth intervals 0 25 m 25 50 m 50 100 m 100 150 m and 150 300 m the assemblages document the status of populations in the surface and subsurface waters of the southeast atlantic during february march 1988 standing crops document hydrographic conditions in the coastal and geostrophic branch of the benguela current the angola current the tropical cyclonic gyre and the south equatorial current standing stocks are highest when primary production is intermediate very high primary production reduces foraminiferal crops significantly eleven species occur abundantly average 10 of the total standing stock a few species g glutinata g quinqueloba g clarkei are abundant at each station whereas the occurrence of other species g ruber g sacculifer g scitula g menardii g crassaformis n incompta n dutertrei is spatially restricted g ruber g rubescens and g glutinata are abundant in high salinity surface water also g ruber is abundant within the equatorial undercurrent water when this water is brought to the surface high concentrations of n incompta and g bulloides are observed in the angola benguela front when nutrient concentration is moderately elevated in surface and subsurface water upper part of the thermocline g crassaformis becomes abundant in the subsurface water of the angola benguela front this species is restricted to lower oxygenated subsurface water and traces incursions of water transported by the angola current g menardii is considered as an indicator for the equatorial undercurrent below the mixed layer whereas g scitula most probably points to an admixture of water transported by the northward flowing benguela current high abundances of g quinqueloba g clarkei in the surface and subsurface waters reflect favorable nutrient conditions like those present in the geostrophic benguela current and in the equatorial divergence zone g falconensis n dutertrei and g siphonifera appear to trace the southern equatorial current

the record of middle jurassic volcanism in the carmel and temple cap formations of southwestern utah altered volcanic ash beds in the middle jurassic temple cap and carmel formations in southwestern utah record a pulse of active arc related volcanism between 166 and 171 ma a second pulse between 148 and 155 ma has previously been documented in the upper jurassic morrison formation volcanic and volcaniclastic rocks of these same ages have also been identified closer to or within the arc in california in the inyo mountains the cowhole mountains the palen mountains and the central mojave desert the upper part of the volcaniclastic mount wrightson formation and the strata of cobre ridge in southern arizona are ca 170 ma in age and appear to be time correlative with the middle jurassic formations in southwestern utah the altered ash beds found in the temple cap and carmel formations typically contain phenocrysts of sanidine quartz biotite apatite zircon and titanite plagioclase was likely present originally in all of the ashes but was removed by alteration and is now found only in the temple cap red beds quartz and sanidine are absent in two crystal poor ash beds that contain two pyroxenes hornblende and biotite although major and trace element concentrations in the ash beds have been substantially modified compositions of relict phenocrysts reveal that the magmas were calc alkaline rhyolites to andesites two pyroxene two feldspar biotite and biotite apatite thermometers suggest that crystallization occurred at temperatures ranging from 740 to 910 8c hornblende geobarometry yields pressures of 1 2 kilobars for the two ash beds that contain the appropriate buffer assemblage the mafic silicates all have moderately high mg fe ratios this fact combined with the presence of hornblende biotite and titanite suggests that the phenocrysts crystallized at high oxygen fugacities similar to those of the granites of the batholiths of california the ash probably erupted from a low lying arc cut by strikeslip faults in what is now southern california and western nevada major jurassic unconformities occur near or within the ash bearing formations in southwestern utah laser fusion singlecrystal 40 ar 39 ar measurements have defined the ages of the unconformities and the associated volcanism the age of the j 1 unconformity found at the base of the temple cap formation in southwestern utah is older than ca 170 5 ma the j 2 unconformity which lies between the temple cap and carmel formations formed between ca 169 and 168 ma the origin of these unconformities is still unclear but may be related to the middle jurassic pulse of magmatism and the oblique plate convergence along the western margin of north america the age range of ash beds in the carmel formation between 166 3 and 168 0 6 0 5 ma is consistent with a bajocian bathonian boundary of ca 166 ma

evolution of a multi vent volcanic complex within a subsiding arc graben depression mount wrightson formation arizona the mount wrightson formation in the santa rita mountains south of tucson arizona is a homoclinally dipping section of lower jurassic volcanic subvolcanic hypabyssal and lesser sedimentary rocks that is 4 5 km thick and crops out over a strike length of 25 km the nature and distribution of volcanic lithofacies in the mount wrightson formation are interpreted to record the evolution of a multi vent volcanic complex that formed within a subsiding cratonal intra arc graben these lithofacies are grouped into the following facies assemblages 1 the near vent facies assemblage consisting of silicic to intermediate hypabyssal intrusive bodies and peperites and dacite lava flows 2 the proximal facies assemblage containing intermediate lava flows ignimbrites and debris flow deposits 3 the medial facies assemblage comprising ignimbrites debris flow deposits and reworked pyroclastic deposits and 4 the distal facies assemblage including nonwelded ignimbrites and fluvial deposits these facies assemblages are characteristic of stratovolcano complexes in the mount wrightson formation however the paucity of debris flow deposits and the burial of near vent facies assemblages by ignimbrites suggest that the formation was deposited in a low relief multi vent complex with no high standing central edifice some of the thickest most densely welded ignimbrites in the mount wrightson formation probably represent outflow from a more distant calders or calderas within the intro arc graben rather than being products of volcanism within the multi vent complex intro arc subsidence resulted in a complex juxtaposition of vent proximal medial and distal facies as vent areas were repeatedly buried by debris derived from adjacent vents in the multi vent complex and to a lesser extent by debris from calderas outside the complex this subsidence resulted in accumulation and preservation of a thick section of terrestrial volcanic and sedimentary rocks the mount wrightson complex evolved from predominantly effusive lower member to predominantly explosive middle member followed by waning volcanism upper member rapid intra arc subsidence resulted in burial of vent areas by craton derived eolian quartz arenites correlative with either the wingate or navajo sandstones on the colorado plateau this was particularly important as volcanism waned

jurassic magmatism in the central mojave desert implications for arc paleogeography and preservation of continental volcanic sequences exposures of jurassic magmatic rocks in the west central mojave desert provide insight into the changing character of volcanism throughout jurassic time and the paleogeography of the continental arc middle jurassic explosive volcanism lower sidewinder volcanic series resulted in collapse of multiple calderas this was followed by north south extension broadly coeval with batholith emplacement late jurassic effusive volcanism upper sidewinder volcanic series appears to reflect transtension over a larger region during intrusion of the independence dike swarm the lower sidewinder volcanic series consists of a subaerial nested caldera complex with an aggregate thickness of 4 km the first caldera formed during the eruption of crystal poor rhyolite ignimbrite outflow and intracaldera facies are intercalated with quartzose sandstone of probable cratonal provenance the second caldera formed during the eruption of crystal rich rhyolite to dacite ignimbrite this ignimbrite exhibits complex mineralogical zoning and contains two units of probable collapse related mesobreccia within the 1 400 m thick intracaldera sequence a third caldera nested within the second is filled with crystal rich biotite dacite ignimbrite and tuff breccia a fourth caldera largely coincident with the second formed during eruption of lithic and pumice lapilli dacite ignimbrite eruption and collapse appear to have been multistage as several units of reworked tuff and fallout tuff occur within the 1 750 m thick intracaldera sequence and caldera collapse breccias occur at the base and near the middle of the sequence the top of this sequence contains reworked tuffs and epiclastic rocks suggesting that the fourth caldera provided a posteruptive depocenter for accumulation of sediment normal faulting tilting and erosion followed explosive volcanism and was broadly contemporaneous with intrusion of middle jurassic porphyritic quartz monzonite plutons plutons and tilted lower sidewinder volcanic series are intruded and unconformably over lain by latest jurassic volcanic rocks upper sidewinder volcanic series the upper sidewinder volcanic series is characterized by alkalic basalt to basaltic andesite and rhyolite lavas hypabyssal intrusions and dikes including the 148 ma independence dike swarm regional northeast southwest extension is suggested by the presence of the northwest striking dike swarm and by bimodal volcanism the absence of debris flow deposits and epiclastic rocks suggests an intra arc region of low relief although local caldera related subsidence was the principal control on accumulation of lower sidewinder volcanic rocks preservation was likely enhanced by middle jurassic extension late jurassic extension was of broader regional extent but lesser magnitude because it did not create basins or cause significant tilting of strata the geometry timing and regional setting of middle and late jurassic extension and magmatism suggest a sinistral oblique subduction regime for the jurassic arc of the southern u s cordillera

cosmogenic 10be and 36cl geochronology of cryoplanation terraces in the alaskan yukon tanana upland cryoplanation terraces are prominent but enigmatic landforms found in present and past periglacial environments geomorphologists have debated for more than a century over processes involved in the formation of these elevated step like bedrock features presented here are the first numerical surface exposure ages and scarp retreat rates from cryoplanation terraces in the yukon tanana upland ytu in alaska part of unglaciated eastern beringia obtained from terrestrial cosmogenic nuclides tcn in surface boulders ages comprise six 10be tcn ages from two terrace treads near eagle summit and six 36 cl ages from two treads on mt fairplay based on these exposure ages scarps at both locations were last actively eroding from 49 to 22 4 ka both locations exhibit time transgressive development particularly near scarp tread junctions boulder exposure ages and distances between sampled boulder locations were used to estimate scarp retreat rates of 0 11 to 0 56 cm yr these numerical exposure ages presented here demonstrate that the cryoplanation terraces in the ytu are diachronous surfaces actively eroding during multiple cold intervals with these results hypotheses for cryoplanation terrace formation are discussed and evaluated for the ytu including those based on geologic structure nivation and the influence of permafrost

discriminating glacier thermal and dynamic regimes in the sedimentary record abstract this paper provides a description and evaluation of the sedimentary facies and environments associated with a range of glacier thermal and dynamic regimes with additional consideration given to the tectonic context new and previously published data are evaluated together and are presented from modern terrestrial and marine glacial sedimentary environments in order to identify a set of criteria that can be used to discriminate between different glacier thermal regimes and dynamic styles in the sedimentary record sedimentological data are presented from a total of 28 glaciers in 11 geographical areas that represent a wide range of contemporary thermal dynamic and topographic regimes in the context of landsystems representatives from terrestrial environments include temperate glaciers in the european alps patagonia new zealand the cordillera blanca peru cold glaciers in the dry valleys of antarctica and the antarctic peninsula region and polythermal valley glaciers in svalbard northern sweden the yukon and the khumbu himal nepal the glaciomarine environment is illustrated by data from cold and polythermal glacier margins on the east antarctic continental shelf and from a polythermal tidewater glacier in svalbard along with general observations from temperate glaciers in alaska these data show that temperate glacial systems particularly in high relief areas are dominated by rockfall and avalanche processes although sediments are largely reworked by glaciofluvial processes debris in polythermal glaciers is both thermally and topographically influenced in areas of moderate relief debris is mainly of basal glacial origin and the resulting facies association is dominated by diamicton in high relief areas such as the himalaya the debris load in polythermal glaciers is dominated by rockfall and avalanche inputs resulting in extensive accumulations of sandy boulder gravel cold glaciers are dominated by basal debris entrainment but sediments are little modified from the source materials which are typically sandy boulder gravel from older till and sand from glaciofluvial glaciolacustrine and aeolian sources similar facies associations but with different facies geometry and thickness occur in equivalent glaciomarine settings application of these concepts can aid the interpretation of glacier thermal regime and hence palaeoclimate in quaternary and ancient glacial systems

arcuate pyroclastic conduits ring faults and coherent floor at kumano caldera southwest honshu japan abstract at the 41 23 km miocene kumano caldera in southwestern japan a large arcuate pyroclastic breccia unit is interpreted as the dissected conduit for voluminous explosive eruptions the pyroclastic breccia and associated granite porphyry occur along the southern margin of the caldera these rocks collectively as much as 22 km long and 800 m wide intrude the arcuate fault bounding the southern caldera margin the breccia is interpreted as the vent facies of ash flow tuff adjacent to the caldera based on similar lithologies phenocryst modes of juvenile clasts and matrix character cataclasites along the major faults include both country rocks and pyroclastic breccia yet some cataclasite blocks are contained within the pyroclastic breccia these geometric and textural relations suggest that the faulting took place during caldera forming eruption prevolcanic sedimentary rocks enclosed by the arcuate faults are interpreted as the dissected coherent floor of the caldera which were subsided several hundreds to a thousand meters no large scale piecemeal disruption of the caldera floor is evident orientations of striations with the cataclasites and altitudes of the base of the tuff suggest the asymmetric trap door subsidence of this caldera the overall caldera geometry is the nested trap door piston cylinder subsidence each 21 15 and 25 23 km in diameter in contrast to previous interpretation of a funnel shape

reconstructing the transport history of glacigenic sediments a new approach based on the co variance of clast form indices abstract two indices are used to describe the aggregate shape and roundness characteristics of glacially transported clasts the c40 index the percentage of clasts with c a ratios 0 4 and the ra index the percentage of very angular and angular clasts in a sample analysis of the between and within sample co variance of these indices provides a powerful tool for discriminating actively and passively transported clasts in glacigenic deposits use of these indices is illustrated in an analysis of the form characteristics of clasts from lateral and frontal moraines at storbreen jotunheimen these fall between those of actively transported clasts in basal till low c40 and ra values and those of unmodified frost weathered clasts high c40 and ra values both indices decline down moraine within sample analyses of clast shape demonstrates that these aggregate clast form gradients reflect changes in the relative proportions of actively and passively transported debris on the moraines rather than progressive modification of actively transported clasts these analyses also indicate that actively transported clasts form the dominant component of the moraines particularly near the former glacier terminus further applications of the approach developed here are suggested

speculative tectonic model for the early mesozoic arc of the southwest cordilleran united states the early mesozoic continental arc of arizona california and western nevada is here interpreted to have occupied a continuous graben depression more than 1000 km long similar to the modern extensional are of central america high calculated rates of subsidence the presence of syndepositional normal faults and fault talus breccias the abundance of calderas and high level intrusions and interstratification of cale alkalic and alkalic volcanic rocks provide support for this model the arc graben depression acted as a long lived more than 40 m y trap for craton derived quartz sands which were funneled along the length and across the width of the depression

coccolithophore export production in guaymas basin gulf of california response to climate forcing abstract the flux and taxonomic composition of coccolithophores has been determined for sediment trap samples collected over a two year period from guaymas basin central gulf of california the gulf of california is a subtropical marginal sea with exceptionally high rates of primary productivity the annual biogenic sediment fluxes are largely dominated by silica with diatoms as the major contributor to the opal flux for the july 1990 through november 1992 study period the total coccolithophore export production in guaymas varied in response to the strength of el nino southern oscillation enso coccolithophore production follows the general surface primary productivity pattern with relatively high fluxes from late fall to late winter and low production in the summer when the water column is highly stratified and nutrient depleted high fluxes of up to 10 9 coccoliths m 2 day 1 and 3 10 6 coccospheres m 2 day 1 indicate that coccolithophores are an important component of the phytoplankton population in guaymas basin the intensification of enso conditions during 1992 altered the typical hydrography of the gulf of california by increasing sst and reducing the strength of spring upwelling this is reflected in reduced opal and diatom fluxes during this period conversely these more oligotrophic conditions resulted in higher total coccolithophore fluxes during spring and summer 1992 gephyrocapsa oceanica is present in the gulf throughout the study period but is dominant during weak or non enso times emiliania huxleyi and to a lesser degree florisphaera profunda are abundant during strong enso periods two major coccolithophore signals are indicative of strong enso conditions and could be used as paleo enso indicators in the gulf of california a the switch in dominance between g oceanica and e huxleyi and b high abundances of the deep dwelling species f profunda the abundance of this latter species shows a strong inverse relationship with opal fluxes a comparison of the annual coccolith flux with coccolith accumulation rates in the surface sediments indicates that only about 10 20 of the coccolith export production is preserved in the anoxic sediments of guaymas basin this very low level of preservation is probably due to bacterial processes on the sea floor which cause acidification of the bottom waters at the sediment water interface coccolith accumulation rates are higher in surface sediments from the western coast of the central gulf suggesting both higher coccolithophore production and better preservation in this region probably associated with lower diatom production tintinnids which agglutinate coccoliths are strongly selective for both coccolith size and species

sea surface temperature anomalies associated with the 1997 1998 el nino recorded in the oxygen isotope composition of planktonic foraminifera anomalously warm sea surface temperatures and associated high rainfall propagated northward from the eastern equatorial pacific along the western margin of north america during the 1997 1998 el nino we present data from the guaymas basin gulf of california and the santa barbara basin southern california borderlands that clearly demonstrate that the oxygen isotope composition of planktonic foraminifera accurately records the local sea surface temperature changes related to the el nino phenomenon on the basis of this observation the varved sediments accumulating in these basins should contain a detailed history of both the occurrence and intensity of past el nino events

assessing divergent sst behavior during the last 21 ka derived from alkenones and g ruber mg ca in the equatorial pacific equatorial pacific sst reconstructions derived from mg ca ratios in planktonic foraminifera globigerinoides ruber and from alkenone producing coccolithophorids record different trends throughout the holocene and the last deglaciation we set forth the hypothesis that their diverging behavior may be related to different seasonal sensitivities which result from the annually varying production rates of alkenone producing coccolithophorids and of g ruber using a series of transient paleoclimate model simulations forced with the time varying forcing history over the last 21 ka a good qualitative agreement is found between simulated boreal winter temperatures and alkenone sst reconstructions as well as between simulated boreal summer temperatures and reconstructed mg ca based sst variations pronounced features in the reconstructions that can be readily explained by the conjectured seasonal biases include the mismatch in middle to late holocene temperature trends and the different onsets of deglacial climate change in the eastern equatorial pacific the analysis presented here further suggests that through combinations of mg ca and alkenone sst reconstructions information can be gained on annual mean temperature changes and the amplitude of the seasonal cycle in sst our study concludes by discussing potential weaknesses of the proposed model derived seasonal bias interpretation of tropical pacific sst proxies in terms of present day core top data sediment trap studies and satellite based observations of chlorophyll

enhanced boulder weathering under late lying snowpatches a schmidt test hammer was employed to assess the aggregate surface hardness of samples of boulders dug out from under late lying snowpatches at sites in switzerland scotland and norway the results were compared with an equivalent set of readings made on boulders at nearby snow free control sites the results in every case reveal that the aggregate surface hardness of boulders buried by late lying snow is significantly less at the 0 001 level than that of boulders at the corresponding control sites this result indicates that late lying snow significantly enhances rock weathering probably because boulder and rock surfaces are exposed to prolonged wetting by percolating meltwater under late lying snowbeds

lower jurassic navajo aztec equivalent sandstones in southern arizona and their paleogeographic significance thick sequences of lower jurassic rhyolitic and andesitic volcanic rocks in several mountain ranges of southern arizona contain interbedded quartzarenites locally up to 250 m thick these sandstone lenses composed of well sorted and well rounded quartz grains commonly contain large scale cross stratification and are considered to be eolian sand deposits the eolian sands were blown up against the continental side of the early jurassic volcanic arc that trended northwest southeast across the southwestern margin of the north american continent and or plate at that time paleocurrent data suggest southerly eolian transport of the sands from the colorado plateau area correlation of these sandstones with the lower jurassic navajo and aztec sandstones is indicated by the pa eocurrent data as well as radiometric dating of the interbedded volcanics eolian sand transport southward across central arizona in the early jurassic indicates that the mogollon highlands either did not then exist or were merely low discontinuous inselbergs on a broad back arc ramp more appropriately called the mogollon slope