direct correlation of millennial scale changes in western north american vegetation and climate with changes in the california current system over the past 60 kyr terrestrial pollen and marine climate proxies from seven sediment cores taken on the continental margin of western north america between 32 and 43 n show systematically related short term changes superposed on milankovitch scale oscillations of the past 60 kyr during oxygen isotope stage 3 brief warming events in california and oregon appear correlative with interstadial events in waters offshore as do the rapid climate oscillations of the last glacial transition 14 10 ka estimated temperature depression of the coastal lowlands ranges from 10 c in southern california to 5 c in oregon during the last glacial the absence of long distance migration of pacific coastal plant assemblages concurs with marine evidence that southward movement of the polar front during the last glacial maximum was limited correlative changes in terrestrial and marine ecosystems imply that broad reorganizations of circulation in the northeast pacific ocean were synchronous with reorganizations of atmospheric circulation over western north america

late quaternary movement of aspy fault nova scotia an emerged sangamonian 125 ka intertidal rock platform at 7 m asl is apparently upthrown to 22 m asl along aspy fault on cape breton island the 15 m displacement may be an isostatic response to rapid ice retreat or erosional unloading or it may be a tectonic effect due to release of crustal stress stored during wisconsinan glacier cover

late quaternary pollen record from the central california continental margin abstract a pollen record obtained from a deep sea core from the continental margin off central california contains evidence of the terrestrial floral adaptation to changing climatic conditions over the last ca 20 000 cal bp the pollen record is divided into three pollen zones two of which are late pleistocene in age glacial and transitional and the third is holocene interglacial the glacial pollen zone ca 20 000 17 000 cal bp is characterized by pinus and abies pollen reflecting environmental conditions during the last glacial maximum overlying this ca 17 000 11 600 cal bp is the transitional pollen zone containing a pollen assemblage indicative of a transitional climatic regime with species that reflect more arid environmental conditions pinus and artemisia decreasing in abundance and those reflecting moister conditions sequoia and alnus rising in abundance pediastrum and dinoflagellates are common and are attributable to increased nutrient rich coastal runoff the bolling allerod 295 256 cm ca 14 600 12 900 bp and younger dryas 256 243 cm ca 12 900 11 600 bp events occur within the transitional pollen zone as well the interglacial pollen zone ca 11 600 cal bp to present is characterized by decreasing pinus and increasing sequoia quercus and asteraceae reflecting changes in vegetation during the climatic warming of the holocene two brief dry periods are represented in this pollen zone one from 150 to 125 cm ca 8000 6400 cal bp and the other at 22 20 cm ca 800 700 cal bp they are correlated with the middle holocene dry period and the medieval climate anomaly respectively

stress directions in eastern north america determined to 4 5 km from borehole elongation measurements stress directions have been determined to depths of 4 5 km in eastern north america from borehole elongation measured by dipmeter calipers in 47 wells the average maximum horizontal stress directions are eastern canada n54 e 7 appalachian basin n58 e 8 and the illinois basin n89 w 5 stress directions determined for the illinois and appalachian basins are in agreement with published interpretations from hydraulic fractures and earthquake fault plane solutions new results from eastern canada and the appalachian basin show that stress directions are everywhere consistent with the midcontinent stress province these data suggest that the maximum horizontal stress does not rotate from the ene midcontinent trend to nw near the atlantic coast a directional analysis of hydraulic fractures petal centerline fractures and natural fractures from the appalachian basin shows that borehole elongation is systematically aligned perpendicular to the directions of hydraulic fractures centerline fractures and northeast striking natural fractures but is not systematically aligned with northwest striking natural fractures these observations indicate that borehole elongations provide reliable stress orientations

moored wind temperature and current observations made during coastal ocean dynamics experiments 1 and 2 over the northern california continental shelf and upper slope moored observations of winds currents and temperature made over the northern california shelf and upper slope during the 1981 and 1982 upwelling seasons as part of the coastal ocean dynamics experiment code are described in both field experiments code 1 and code 2 the onset of the upwelling season is triggered by the strengthening of the north pacific high off northern california and signalled by the presence of water colder than 9 c near the bottom over the shelf vertical temperature stratification over the shelf is reduced during active upwelling local winds and subtidal currents over the shelf are strongly polarized in the alongshelf direction and the mean wind stress is directed equatorward response of alongshelf currents to wind forcing is similar at all depths over the shelf the response of the cross shelf current is more complex in the surface layer offshelf flow is significantly and positively correlated with the upwelling favorable alongshelf wind stress beneath this layer a weak return flow exists the thickness of the upper mixed layer varies greatly reaching 60 m during upwelling events thus direct wind forcing affects a substantial fraction of the water over the shelf low frequency wind stress current and temperature fields are adequately described by a few energetic empirical orthogonal functions with simple spatial structure the most energetic mode typically accounts for 75 or more of the variance of wind stress and temperature over the middle and inner shelf the most energetic current mode accounts for 90 or more of the variance is dominated by he alongshelf component and veers to the left with depth the low frequency alongshelf flow fluctuations are quasi barotropic with some vertical shear but no reversal with depth vertical shear in alongshelf current and the cross shelf density gradient obey the thermal wind relation the simple structure of the subdiurnal currents allow estimation of the alongshelf volume transport between the 60 and 130 m isobaths through three cross shelf transects in code 2 volume transport over the shelf is often nearly two dimensional but occasional large differences indicate significant mass exchange between the shelf and the adjacent upper slope correlation of low frequency currents and alongshelf wind stress shows the response of alongshelf current to be maximum near the surface and near midshelf where a 15 cm 1 alongshelf flow lags a 1 dyn cm 2 alongshelf wind stress by the order of 10 hours currents over the upper slope are not significantly correlated with local wind alongshelf transport over the shelf is highly correlated with local wind stress explaining 80 of the variance in the low frequency transport during code 2 volume transport is best correlated with wind stress approximately 30 km to the south winds in the code area during spring and summer are characterized by strong and persistent upwelling favorable winds interrupted by shorter periods of weak winds regression analysis indicates that in the absence of wind a poleward barotropic current jet exists over the shelf with a maximum amplitude over the inner shelf in the code area an upwelling favorable wind counters this jet over the shelf so that the alongshore flow is everywhere equator ward during strong wind events since the maximum response to wind forcing is found at midshelf and near surface the mean current over the upwelling season is strongly sheared in both the vertical and cross shelf directions mean flow over the outer shelf is surface intensified and is directed offshelf and equatorward while the deeper flow at midshelf and through most of the water column over the inner shelf is directed poleward

half graben filling processes in the early phase of continental rifting the miocene namurungule formation of the kenya rift abstract the miocene namurungule formation crops out on the eastern flank of the kenya rift representing basin fill that developed in association with miocene rifting the formation is characterized by large volumes of volcaniclastics supplied passively by pyroclastic fall facies analysis reveals that this formation consists mostly of lacustrine delta deposits with minor alluvial fan deposits at its base the conspicuous occurrence of a flood plain facies with infrequent channel fill deposits in the lower part of this formation suggest that the drainage area was limited in the early stage of deposition pyroclastic fall would therefore have been an important source of sediment during the early stages of rift development the delta deposits are divided into two distinct successions based on lithological characteristics separated by a thick pyroclastic layer in the middle part of the formation the stacking pattern of the lower succession is retrogradational whereas the upper succession is characterized by a pile of prograding bodies both delta successions are interpreted to have accumulated in an underfilled basin the change in depositional mode from the lower to upper is considered to be due to a change in the balance between the sedimentation rate and the rate of lake level rise assuming constant sediment supply the apparent difference in flooding scale between the lower and upper successions is attributed to the topographical widening of the basin flat similar successions also occur in another basin in the east african rift ngorora formation central kenya in which pyroclastic sediments are dominant and upward decrease in sedimentation rate is recognized the differing in the stacking patterns between the namurungule formation and the ngorora formation is probably induced by basin width the narrow namurungule basin seems to have been sensitive to increased sediment supply owing to the expansion of the catchment area

analyses of fault mechanisms and expansion of southwestern anatolia since the late miocene abstract neotectonic field studies and detailed analyses of neogene and quaternary fault mechanisms in southwestern anatolia enable us to recognize a succession of compressional and extensional events and to characterize the direction of corresponding regional stresses the three most important compressive phases occurred during the miocene and a much smaller one near the plio quaternary boundary the last one or two interrupted a widespread extension of much greater duration and amplitude the whole tectonic evolution resembles that of the aegean the large extension by normal faulting is consistent with a minimum stress along a nne ssw average direction it appears that this direction was n s during the pliocene and changed to ne sw sometime during the quaternary this dominant nne ssw extension which began during late miocene or earliest pliocene was related to the development of the southwestern anatolian graben system

an example of an accretionary forearc basin from northern central anatolia and its implications for the history of subduction of neo tethys in turkey deformed sedimentary sequences of late cretaceous middle eocene age located between the sakarya continent and the anatolian complex have been interpreted as the fill of a forearc basin the history and structure of this basin are critical for understanding the evolution of the neo tethyan subduction in the middle east i test and elaborate upon this interpretation on the basis of three basic outcrop areas of upper cretaceous lower tertiary sedimentary sequences confined to a northeast southwest trending belt in north west ankara these are the alci kinik and orhaniye areas they expose two different sedimentary sequences called alci and orhaniye in the alci area the sequence starts at the base with the continental red clastic rocks on the erosional surface of an underlying ophiolitic melange and continues upward into the shallow marine reefal buildup of the late maastrichtian age the upper half of the alci sequence is separated from its lower half by a local disconformity and dominated by the continental debris flow deposits composed mostly of volcanic material by contrast both the kinik and orhaniye areas are characterized by a thick continuous and coarsening upward sequence overlying conformably the underlying ophiolitic melange the lower half of the orhaniye sequence is dominated by a deep marine flysch its middle part by continental clastic material and the topmost part by the shallow marine reefal buildup lower contact relationships lithologic composition facies distribution internal structures and the regional tectonic settings of both sequences strongly suggest that the above mentioned three outcrops preserve the remnants of a peripheral accretionary forearc basin forming the north northwestern margin of the haymana polath accretionary forearc basin during middle campanian middle eocene time this peripheral basin is here named orhaniye accretionary forearc basin

initiation of the neomagmatism in east anatolia abstract in eastern anatolia the neotectonic episode commenced with the complete elemination of the neo tethyan ocean floor as a result of collision between arabia and eurasia during early miocene time after the collision continuing convergence initiated a new tectonic regime and coeval magmatic activity the post collisional convergence caused crustal shortening and thickening as evidenced by regionwide development of e w trending folds and thrusts and conjugate strike slip faults the related volcanic activity has progressed in three cycles in the initial cycle weakly alkaline volcanic rocks were produced that are known as the solhan volcanics they outcrop at the western end of an e w striking neotectonic depression called the mus basin which constitutes the western prolongation of the lake van basin the basin is a thrust bounded depression that developed out of an original syncline by the disruption of its limbs the lavas of the first cycle reached the surface along n s aligned extensional structures in the second volcanic cycle a widespread k type ca volcanism occurred through crustal contribution during the late miocene early pliocene time when the continuing north south convergence caused substantial shortening and thickening of the continental crust the last volcanic cycle produced a thick volcanic cover consisting of rocks of alkaline affinity during the pleistocene and the quaternary when the thickened crust began to accommodate the ongoing north south shortening by east west extension after the formation of the east and north anatolian transform faults

millennial scale climate variability of the northeast pacific ocean and northwest north america based on radiolaria and pollen abstract radiolaria and pollen abundances in marine sediment cores from the northeast pacific are used to reconstruct oceanographic and continental climate change during the past glacial cycle 0 150 kyr these data allow direct comparison of the climate response of continental and oceanic systems detailed 18 o and ams 14 c measurements provide a link into global stratigraphic frameworks canonical correlation analysis extracts two modes of variation common to both the radiolaria and pollen records the first mode of variation correlates an assemblage of radiolaria associated with coastal upwelling with increased redwood western hemlock and alder pollen this association is consistent with the modern relationship between coastal upwelling coastal fog and redwood forests a second canonical mode relates an oceanic fauna now found in highest abundance in the far north pacific with reduced pine and western hemlock pollen abundance comparison of these records to an ice core 18 o record suggests that at wavelengths 3000 years warm events in greenland are correlated to intervals of increased coastal upwelling off oregon decreases in importance of very cold north pacific fauna suggesting warming and increases in pollen associated with wetter coastal environments radiolarian based sea surface temperature estimates suggest that the variability of the northeast pacific on this time scale is about 2 c warming in the coastal regions reflects reduced advection of the california current but is moderated by increases in cool coastal upwelling we infer that the response of the northeast pacific to millennial scale climate changes is related to changes in atmospheric circulation at mid to high latitudes preliminary analysis suggests that oceanic variability off oregon at wavelengths 18 o records this variability is associated with changes in subtropical faunal elements without similar changes in other faunal elements this finding suggests that unlike longer period millennial scale events the propagation of the shorter wavelength events to the northeast pacific is through subtropical or tropical teleconnections

postglacial vegetation and fire history eastern klamath mountains california usa pollen and high resolution charcoal data from bluff lake and crater lake california indicate simi lar changes in climate vegetation and fire history during the last 15 500 years pollen data at bluff lake suggest that the vegetation between c 15 500 and 13 100 cal bp consisted of subalpine parkland with scattered pinus and abies after 13 100 cal bp a relatively closed forest of p monticola p contorta and abies developed and fire event frequency was low the inferred climate then was cooler and wetter than present pinus and quercus vaccinifoliadominated at both sites during the early holocene when conditions were warm and dry as climate became wetter and cooler in the late holocene abies spp at both sites and tsuga mertensi ana at crater lake increased in importance displacing pinus and quercus the two lake records have similar trends in fire history with high event frequencies at c 8400 4000 and 1000 cal bp and low values at c 4800 cal bp the fire and vegetation history at both sites suggests a similar response to large scale changes in climate during the holocene

palynostratigraphy and vegetation characteristics of neogene continental deposits interbedded with the cappadocia ignimbrites central anatolia turkey a palynological analysis of the late miocene and early pliocene successions of the cappadocian volcanic province central anatolia turkey has been carried out with the aim of reconstructing the palaeovegetation and palaeoclimatic conditions the samples are collected from outcrop sections from three different localities a akdag b bayramhacili and g guzeloz the pollen spectra reveals the existence of a steppe vegetation dominated by amaranthaceae chenopodiaceae and artemisia typical of present day arid and semi arid continental areas i e middle east and asteraceae asteroideae in the a section late miocene developed in arid climatic conditions the flora of the g early pliocene and lower part of the b late miocene sections reflects steppes on which asteraceae asteroideae was dominant this flora also indicates arid conditions the development of trees in the upper part of the b section was possibly related to local paleoenvironmental conditions rather than a climatic change this study provides the first palynological data to reveal the presence of an amaranthaceae chenopodiaceae and artemisia steppe already during the late miocene in turkey

comparison of young volcanic associations of western and eastern anatolia formed under a compressional regime a review abstract turkey is characterised by widespread post oligocene volcanism in western anatolia volcanic activity began during the late oligocene early miocene in a compressional regime a widespread suite of andesitic and dacitic calc alkaline rocks was erupted in this period they were accompanied by locally developed high level granitic intrusions the abrupt change from n s compression to n s stretching in the middle miocene was accompanied by a gradual transition to alkali basaltic volcanism in eastern anatolia the collision related compressional tectonics and associated volcanic activity began in the late miocene to pliocene and continued almost without interruption into historical times one minor and two major volcanic phases may be distinguished an initial minor eruptive phase of basic and intermediate alkaline rocks was followed by widespread eruptions of andesitic and dacitic calc alkaline rocks during the pliocene partly penecontemporaneous with this a second more important major phase of volcanism involving alkaline and transitional lavas began and continued during the quaternary the calc alkaline lavas of both regions were erupted at a time when the compressional regime led to crustal thickening these lavas display many geochemical and isotopic signatures that may be interpreted in terms of contamination of magma involving continental crustal materials the alkaline lavas in both regions began during the final stage of the compressional regime and form two groups one group is geochemically and isotopically similar to the calc alkaline rocks and the other is more typically alkaline the volcanic evolution of these two regions of turkey followed a somewhat similar pattern producing highly contaminated calc alkaline lavas at the beginning and evolving towards uncontaminated alkaline lavas at the end

segmented african lithosphere beneath the anatolian region inferred from teleseismic p wave tomography summary lithospheric deformation throughout anatolia a part of the alpine himalayan orogenic belt is controlled mainly by collision related tectonic escape of the anatolian plate and subduction roll back along the aegean subduction zone we study the deeper lithosphere and mantle structure of anatolia using teleseismic finite frequency p wave traveltime tomography we use data from several temporary and permanent seismic networks deployed in the region approximately 34 000 p wave relative traveltime residuals measured in multiple frequency bands are inverted using approximate finite frequency sensitivity kernels our tomograms reveal segmented fast seismic anomalies beneath anatolia that corresponds to the subducted portion of the african lithosphere along the cyprean and the aegean trenches we identify these anomalies as the subducted aegean and the cyprus slabs that are separated from each other by a gap as wide as 300 km beneath western anatolia this gap is occupied by slow velocity perturbations that we interpret as hot upwelling asthenosphere the eastern termination of the subducting african lithosphere is located near the transition from central anatolia to the eastern anatolian plateau or arabian eurasian collision front that is underlain by large volumes of hot underplating asthenosphere marked by slow velocity perturbations our tomograms also show fast velocity perturbations at shallow depths beneath northwestern anatolia that sharply terminates towards the south at the north anatolian fault zone nafz the associated velocity contrast across the nafz persists down to a depth of 100 150 km hence our study is the first to investigate and interpret the vertical extent of deformation along this nascent transform plate boundary overall the resolved upper mantle structure of anatolia is directly related with the geology and tectonic features observed at the surface of the anatolian plate and suggest that the segmented nature of the subducted african lithosphere plays an important role in the evolution of anatolia and distribution of its tectonic provinces

petrological and geochemical characteristics of cenozoic high k calc alkaline volcanism in konya central anatolia turkey abstract late miocene to pliocene volcanic rocks outcrop west northwest and southwest of the konya area in central anatolia turkey volcanic products are lava domes nuee ardentes and ignimbrite deposits predominantly andesitic to dasitic in composition together with rare basalt basaltic andesite basaltic trachyandesite and trachyandesite 50 35 69 39 sio2 the serie exhibits high k calc alkaline affinities fractional crystallization of pyroxene plagioclase and fe ti oxides is the main process in the magmatic evolution of konya volcanic rocks volcanic units exhibit typical high k calc alkaline character their geochemical characteristics e g enrichments in lil elements such as k rb ba sr depletion in hfse such as ti nb and high ba nb and low nb y ratios are consistent with those of active continental margin regions high 87 sr 86 sr 0 704841 0 707340 and low 143 nd 144 nd 0 512390 0 512618 ratios suggest crustal involvement in their petrogenesis correlations between 86 sr 87 sr isotope with rb rb nb rb ba and rb sr also emphasize the effect of crustal contamination on the andesitic and dacitic magmas as a consequence konya volcanic rocks are products of assimilation and fractional crystallization afc processes of a magma which seems to be linked to the subduction of the african plate underneath the anatolian plate during miocene

exhumation with a twist paleomagnetic constraints on the evolution of the menderes metamorphic core complex western turkey 1 much remains to be understood about the links between regional vertical axis rotations continental extension and shortening in western turkey miocene vertical axis rotations have been reported that occur simultaneously with the extensional exhumation of the menderes metamorphic core complex which has been related to back arc extension in the eastern part of the aegean back arc in this paper we explore the spatial and temporal relationships between vertical axis rotations in southwestern turkey and extensional unroofing of the menderes massif to this end we provide a large set of new paleomagnetic data from western turkey and integrate these with the regional structural evolution to test the causes and consequences of oroclinal bending in the aegean region the lycian nappes and bey daglari are shown to rotate 20 between 16 and 5 ma defining the eastern limb of the aegean orocline this occurred contemporaneously with the exhumation of the central menderes massif along extensional detachments and after the latest oligocene to early miocene exhumation of the northern and southern menderes massifs exhumation of the latter two was not associated with vertical axis rotations the lower miocene volcanics in the region from lesbos to usak to the north of the central menderes massif underwent a small clockwise rotation insignificant with respect to eurasia this shows that exhumation of the central menderes massif was associated with a vertical axis rotation difference between the northern and southern menderes massifs of 25 30 this result is in excellent agreement with the angle defined by the trends of buyuk menderes and alasehir detachments as well as the angle defined by the regionally curving stretching lineation pattern across the central menderes massif these structures define a pivot point rotation pole for the west anatolian rotations the rotation of the southern domain including the southern menderes massif the lycian nappes and bey daglari must have led to n s contraction east of this pole the eastern limit of the rotating domain is formed by the transpressional couple of the aksu thrust and kirkkavak fault in the center of the isparta angle previously reported clockwise rotations in the volcanic fields near afyon may be the result of distributed n s shortening east of the pivot point the precise accommodation of this shortening history remains open for investigation late oligocene to early miocene extension in the eastern part of the aegean back arc was ne sw oriented and likely bounded by a discrete transform this transform may be associated with an early evolution of the eastern aegean subduction transform edge propagator fault oroclinal bending in the west anatolian region is likely related to a reconnection of the eastern part of the aegean orocline with the african northward moving plate in tandem with roll back in the aegean back arc comparable to a recently postulated scenario for western greece

neotectonic deformation in the western sector of tectonic escape in anatolia palaeomagnetic study of the afyon region central turkey abstract following final closure of the neotethyan ocean during the late miocene deformation in central turkey has led to crustal thickening and uplift to produce the anatolian plateau followed by westward extrusion of terranes by strike slip widespread volcanism has accompanied this latter neotectonic phase and palaeomagnetic study of the volcanism shows a coherent record of differential block rotations indicating that the anatolian region is not a plate or platelet sensu stricto but is undergoing distributed internal deformation to evaluate the scale of neotectonic rotations in the transition zone near the western limit of tectonic escape and the border of the extensional domain in central west turkey we have studied the palaeomagnetism at 82 sites in volcanic suites distributed along a 140 km lineament with north south trend and ranging in age from 18 to 8 ma comparable deflection of magnetic remanence from the present field direction is identified along the full length of the lineament a mean clockwise rotation of 12 3 4 2 is determined for this western sector of the anatolian strike slip province since similar rotations are observed in the youngest and oldest units this cumulative rotation occurred after the late miocene when interpreted together with results elsewhere in anatolia it is inferred that the rotation is later than crustal thickening and uplift of the anatolian plateau and entirely a facet of the tectonic escape inclinations are mostly 10 shallower than the predicted miocene field and are considered to reflect the presence of a persistent inclination anomaly in the mediterranean region larger rotations departing from the regional trend are also observed within the study region but are confined to the vicinity of major faults notably those bounding the afyon aksehir graben the pattern of neotectonic declinations across anatolia identifies strong anticlockwise rotation in the east near the arabian pincer with progressive reduction in the amount of rotation towards the west it becomes zero or slightly clockwise at the western extremity of the accreted terrane collage rotations also appear to become generally younger towards the south crustal deformation has therefore been distributed and the net effect of terrane extrusion to the west and south has been to expand the curvature of the tauride arc the westward radial expansion of the extruded terranes is inferred to combine with backroll on the hellenic arc to produce the contemporary extensional province in western turkey

evidence for a younger dryas like cooling event on the british columbia coast two independent paleoclimatic records from the pacific coast of canada indicate that a late glacial warming trend was interrupted by a return to colder conditions between about 11 000 and 10 200 radiocarbon yr b p correlative with the classical younger dryas chronozone of the north atlantic region fossil benthic foramnifera from three cores from the continental shelf dated by accelerator mass spectrometry show peak abundances of the cold water indicator species cassidulina reniforme at this time fossil pollen spectra from two sites on the queen charlotte islands record a shift from forest to open herb rich vegetation after 11 100 yr b p probably in response to colder and wetter conditions identified by pollen climate transfer functions these preliminary data for a cold oscillation between ca 11000 and 10000 yr ago in the northeast pacific argue that this deglacial phenomenon was not restricted to the north atlantic but was a hemispheric and possibly global event

late glacial to holocene changes in winds upwelling and seasonal production of the northern california current system abstract a core 120 km off the coast of southern oregon was examined for changes in lithology diatoms and pollen over the past 30 000 yr primary production during the late pleistocene was about half that of the holocene evidence from diatoms and pollen indicates that summer upwelling was much weaker implying an absence of strong northerly winds early pliocene diatoms found throughout the late pleistocene section were probably derived from diatomites east of the cascades and provide evidence for strong easterly winds over a dry continental interior the findings verify predictions of a climate model based on glacial maximum conditions there is no compelling evidence for a climatic reversal corresponding to the european younger dryas chron during the early holocene 9000 7000 yr b p there may have been years when winds were insufficiently strong to support upwelling so that warm stratified waters lay closer to the coast

vegetation response to southern california drought during the medieval climate anomaly and early little ice age ad 800 1600 abstract high resolution studies of pollen in laminated sediments deposited in santa barbara basin sbb core spr0901 02kc reflect decadal scale fluctuations in precipitation spanning the interval from ad 800 1600 from ad 800 1090 during the medieval climate anomaly mca sbb sediments were dominated by xeric vegetation types drought resistant coastal sagebrush and chaparral implying reduced precipitation in the southern california region drought adapted vegetation abruptly decreased at ad 1090 and was rapidly replaced by mesic oak quercus woodlands associated with an increased pollen flux into the basin after a mesic interval lasting 100 years pollen flux and the relative abundance of quercus pollen dropped abruptly at ad 1200 when the rapid rise of chaparral suggests a significant drought similar to that of the mca ad 800 1090 this brief resurgence of drought adapted vegetation between ad 1200 1270 marked the end of the mca droughts a gradual increase in mesic vegetation followed characterizing cool hydroclimates of the little ice age lia in coastal southern california the presence of xeric vegetation in sbb coincides with major drought events recorded in tree rings and low lake levels elsewhere in california except for the brief drought between ad 1130 1160 correlative diatom and terrigenous sediment input proxy records from sbb are largely supportive of the pollen record predominantly linking the mca with drought and la nina like conditions and the lia with wetter more el nino like conditions differences between paleoclimate proxies pollen diatoms and terrigenous sediment in sbb exist however possibly reflecting the temporal and spatial differences in the generation of each proxy record as well as their individual sensitivity to climate change

the large scale coastal wind field along the west coast of north america 1981 1982 we study the statistical properties of the coastal wind field along the west coast of north america for two summers 1981 and 1982 coastal ocean dynamics experiments 1 and 2 respectively and the intervening winter using measured winds and geostrophic winds calculated from fleet numerical oceanography center atmospheric pressure analyses summer wind fluctuations are driven primarily by the interaction between two relatively stationary pressure systems the north pacific subtropical high and southwest u s thermal low and by their interactions with propagating atmospheric systems to the north in particular propagating cyclones and associated fronts are often followed by a northeastward intensification of the high producing strong upwelling events along the california coast this summer event sequence occurs more frequently and is displaced farther to the south on average during summer 1981 winter wind fluctuations are primarily driven by propagating cyclones and anticyclones and they tend to have larger variance and space scales than in summer a preference for poleward equatorward propagation exists in summer winter and the largest time scales are observed in summer 1982 coastal atmospheric boundary layer processes substantially modify winds within 100 200 km of the coast consequently measured wind fluctuations are strongly polarized in the alongshore direction and have means and rms amplitudes that can vary considerably between nearby stations along the coast calculated wind fluctuations are less polarized in the alongshore direction and have alongshore correlation scales about 60 larger than those for measured winds they represent fluctuations with alongshore wavelengths of 900 km rather well but represent poorly those with smaller wavelengths and those due to coastal atmospheric boundary layer effects

duration and severity of medieval drought in the lake tahoe basin droughts in the western u s in the past 200 years are small compared to several megadroughts that occurred during medieval times we reconstruct duration and magnitude of extreme droughts in the northern sierra nevada from hydroclimatic conditions in fallen leaf lake california stands of submerged trees rooted in situ below the lake surface were imaged with sidescan sonar and radiocarbon analysis yields an age estimate of w1250 ad tree ring records and submerged paleoshoreline geomorphology suggest a medieval low stand of fallen leaf lake lasted more than 220 years over eighty more trees were found lying on the lake floor at various elevations above the paleoshoreline water balance calculations suggest annual precipitation was less than 60 normal from late 10th century to early 13th century ad hence the lake s shoreline dropped 40e60 m below its modern elevation stands of pre medieval trees in this lake and in lake tahoe suggest the region experienced severe drought at least every 650e1150 years during the mid and late holocene these observations quantify paleo precipitation and recurrence of prolonged drought in the northern sierra nevada published by elsevier ltd

palynostratigraphy and th u ages of upper pleistocene interglacial and interstadial deposits on cape breton island eastern canada on cape breton island nova scotia near the margin of the wisconsinan ice sheet karst depressions in mississippian gypsum bearing rocks contain interglacial and interstadial organic rich deposits three palynostratigraphic units have been observed and tentatively dated by th u measurements on embedded fossil wood the first dated at ca 125 ka may be assigned to the oceanic sup 18 o substage 5e thermophilous forests quercus ostrya pinus strobus developed in response to a climate warmer than the present the second unit rich in abies balsamea pollen and dated at ca 87 ka may relate to the sup 18 o substage 5a it reflects a cool and wet climate not unlike that of today the third unit probably spans part of the mid wisconsinan sup 18 o stage 3 it shows alternating boreal forest tundra forest assemblages indicative of climatic oscillations during a generally cold interval

high resolution climatic evolution of coastal northern california during the past 16 000 years holocene and latest pleistocene oceanographic conditions and the coastal climate of northern california have varied greatly based upon high resolution studies ca every 100 years of diatoms alkenones pollen caco 3 and total organic carbon at ocean drilling program odp site 1019 41 682 n 124 930 w 980 m water depth marine climate proxies alkenone sea surface temperatures ssts and caco 3 behaved remarkably like the greenland ice sheet project gisp 2 oxygen isotope record during the balling allerod younger dryas yd and early part of the holocene during the yd alkenone ssts decreased by 3 c below mean bolling allerod and holocene ssts the early holocene ca 11 6 to 8 2 ka was a time of generally warm conditions and moderate caco 3 content generally 4 the middle part of the holocene ca 8 2 to 3 2 ka was marked by alkenone ssts that were consistently 1 2 c cooler than either the earlier or later parts of the holocene by greatly reduced numbers of the gyre diatom pseudoeunotia doliolus 10 and by a permanent drop in caco 3 to 3 starting at ca 5 2 ka coastal redwood and alder began a steady rise arguing for increasing effective moisture and the development of the north coast temperate rain forest at ca 3 2 ka a permanent ca 1 c increase in alkenone sst and a threefold increase in p doliolus signaled a warming of fall and winter ssts intensified higher amplitude and more frequent cycles of pine pollen alternating with increased alder and redwood pollen are evidence that rapid changes in effective moisture and seasonal temperature enhanced el nino southern oscillation enso cycles have characterized the site 1019 record since about 3 5 ka

abrupt increase in greenland snow accumulation at the end of the younger dryas event the warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate the best known of which is the younger dryas event1 despite much study of the causes of this event and the mechanisms by which it ended many questions remain unresolved1 oxygen isotope data from greenland ice cores2 4 suggest that the younger dryas ended abruptly over a period of about 50 years dust concentrations2 4 in these cores show an even more rapid transition 20 years this extremely short timescale places severe constraints on the mechanisms underlying the transition but dust concentrations can reflect subtle changes in atmospheric circulation which need not be associated with a large change in climate here we present results from a new greenland ice core gisp2 showing that snow accumulation doubled rapidly from the younger dryas event to the subsequent preboreal interval possibly in one to three years we also find that the accumulation rate change from the oldest dryas to the bo11ing allerod warm period was large and abrupt the extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the north atlantic climate system

the younger dryas cold interval as viewed from central greenland abstract greenland ice core records provide an exceptionally clear picture of many aspects of abrupt climate changes and particularly of those associated with the younger dryas event as reviewed here well preserved annual layers can be counted confidently with only 1 errors for the age of the end of the younger dryas 11 500 years before present ice flow corrections allow reconstruction of snow accumulation rates over tens of thousands of years with little additional uncertainty glaciochemical and particulate data record atmospheric loading changes with little uncertainty introduced by changes in snow accumulation confident paleothermometry is provided by site specific calibrations using ice isotopic ratios borehole temperatures and gas isotopic ratios near simultaneous changes in ice core paleoclimatic indicators of local regional and more widespread climate conditions demonstrate that much of the earth experienced abrupt climate changes synchronous with greenland within thirty years or less post younger dryas changes have not duplicated the size extent and rapidity of these paleoclimatic changes

sediment distribution and transport along a rocky embayed coast monterey peninsula and carmel bay california abstract field measurements of beach morphology and sedimentology were made along the monterey peninsula and carmel bay california in the spring and summer of 1997 these data were combined with low altitude aerial imagery high resolution bathymetry and local geology to understand how coastal geomorphology lithology and tectonics influence the distribution and transport of littoral sediment in the nearshore and inner shelf along a rocky shoreline over the course of decades three primary modes of sediment distribution in the nearshore and on the inner shelf off the monterey peninsula and in carmel bay were observed along stretches of the study area that were exposed to the dominant wave direction sediment has accumulated in shore normal bathymetric lows interpreted to be paleo stream channels where the coastline is oriented parallel to the dominant wave direction and streams channels trend perpendicular to the coast sediment filled paleo stream channels occur in the nearshore as well but here they are connected to one another by shore parallel ribbons of sediment at depths between 2 and 6 m where the coastline is oriented parallel to the dominant wave direction and onshore stream channels are not present only shore parallel patches of sediment at depths greater than 15 m are present we interpret the distribution and interaction or transport of littoral sediment between pocket beaches along this coastline to be primarily controlled by the northwest trending structure of the region and the dominant oceanographic regime because of the structural barriers to littoral transport peaks in wave energy appear to be the dominant factor controlling the timing and magnitude of sediment transport between pocket beaches more so than along long linear coasts accordingly the magnitude and timing of sediment transport is dictated by the episodic nature of storm activity

early miocene to quaternary evolution of volcanism and the basin formation in western anatolia a review abstract western anatolia largely affected by extensional tectonics witnessed widespread volcanic activity since the early miocene the volcanic vents of the region are represented by epicontinental calderas stratovolcanoes and monogenetic vents which are associated with small scale intrusions as sills and dykes the volcanic activity began with an explosive character producing a large ignimbritic plateau all over the region indicating the initiation of the crustal extension event these rhyolitic magmas are nearly contemporaneous with granitic intrusions in western anatolia the ignimbrites emplaced approximately contemporaneous with alluvial fan and braided river deposits flowed over the basement rocks prior to extensional basin formation the lacustrine deposits overlie the ignimbrites the potassic and ultrapotassic lavas with lamprophyric affinities were emplaced during the late miocene pliocene the volcanic activities have continued with alkali basalts during the quaternary

a review of evidence of glacially induced faulting and seismic shaking in eastern canada abstract evidence of early postglacial glacially induced seismic activity should be abundant in eastern canada which was formerly covered by the laurentide ice sheet during the late wisconsinan glaciation this review identified only two probable and at most nine possible examples of glacially induced faulting over an area of 4 million km2 a far lower number than that expected from a long term rate of background seismicity the probable sites are the holy grail scarp manitoba and the series of faults buried in the sub bottom of round lake ontario the possible nine glacially induced faults include the aspy fault nova scotia and timiskaming east shore fault ontario but there is little published information on the other seven features despite this low number the common occurrence of subaqueous mass transport deposits interbedded within or immediately overlying glaciolacustrine glaciomarine deposits in many modern lake basins strongly hints at an elevated period of glacially induced seismicity over widespread areas of eastern canada in southern quebec the age of these mass transport deposits suggests that glacially induced earthquake activity began as early as about 13 5 ka cal bp which corresponds to the time of local ice melt back this indicates that glacially induced seismicity began at the time of local deglaciation in southern quebec rather then being delayed as existing fault instability models imply it is anticipated that new candidate glacially induced or younger faults will be identified in eastern canada over the next decade or so because of the increasing availability of new high resolution data imagery sources

living neogloboquadrina pachyderma sin and its distribution in the sediments from oman and somalia upwelling areas abstract microfaunal analysis of plankton nets collected offshore oman yemen and sediment traps offshore somalia shows that neogloboquadrina pachyderma sin is abundant during the sw monsoon upwelling the sediment traps recorded the highest flux 136 specimens m 2 day 1 and the highest relative frequency 3 55 of the total foraminifera assemblage of the species during this period during the intermonsoon it became less abundant and decreased in size and only very few n pachyderma sin were found in the water column during the ne monsoon sediment trap and recent sediment data collected along a downslope transect off somalia show that the species frequency decreases offshore the highest concentrations of n pachyderma sin in plankton nets off oman yemen were found at a depth of 300 500 m however the oxygen isotope compositions of n pachyderma sin at the depth of 300 500 m and from the surface 8 m are identical and also similar to that of globigerina bulloides which reflects properties of the upper 25 m of the water column the carbon isotope values are relatively consistent within the studied samples from both areas except for the specimens from the surface water samples offshore oman yemen the data show that the 18o ratio of n pachyderma sin is in equilibrium with the ambient water while the 13c values are at least 0 8 lower we infer that n pachyderma sin in the arabian sea reproduces grows and calcifies in the upper 25 m of the water column but possibly descends into deeper waters later during its life cycle

stable isotope record of late holocene salinity and river discharge in san francisco bay california abstract oxygen and carbon isotopic measurements of fossil mollusks from san francisco bay are used to derive a record of paleosalinity and paleostreamflow for the past 5 900 years the 18 o and 13 c values of river water 12 and 9 are markedly different than seawater 0 and 1 and vary systematically as a function of salinity in the estuary the data show that annually averaged salinity in the south central part of the bay was very close to the modern diversion corrected value of 26 8 over the past 2 700 years and 4 lower than modern between 3 800 and 5 100 yr b p based on those salinities the average annual river inflow to san francisco bay is calculated to have been 1290 m 3 s over the past 2 400 years and 1990 m 3 s between 3 800 and 5 100 yr b p 1 8 times greater than the modern diversion corrected value of 1100 m 3 s assuming a constant bay volume the inferred river discharge record generally corroborates independent paleohydrologic records in california including tree ring treeline and lake level records

carbon isotope diatom and pollen evidence for late holocene salinity change in a brackish marsh in the san francisco estuary analysis of diatoms pollen and the carbon isotopic composition of a sediment core from a brackish marsh in the northern part of the san francisco estuary has provided a paleosalinity record that covers the past 3000 yr changes in marsh composition and diatom frequencies are assumed to represent variations in freshwater inflow to the estuary three periods of relatively high salinity low freshwater inflow are indicated 3000 to 2500 cal yr b p 1700 to 730 cal yr b p and ca a d 1930 to the present the most recent period of high salinity is primarily due to upstream storage and water diversion within the sacramento san joaquin watershed although drought may also have been a factor the two earlier high salinity periods are likely the result of reduced precipitation low salinity high freshwater flow is indicated for the period 750 cal yr b p to a d 1930 c 2001 university of washington

composite volcanoes in the south eastern part of izmir balikesir transfer zone western anatolia turkey abstract during the early middle miocene western anatolia several volcanic fields occur along a ne sw trending shear zone known as izmir balikesir transfer zone this is a deformed crustal scale sinistral strike slip fault zone crossing the bornova flysch and extending along the nw boundary of the menderes massif by accommodating the differential deformation between the cycladic and menderes core complexes within the aegean extensional system here we discuss the volcanic activity in yamanlar and yuntdagi fields that is closely related to the extensional tectonics of the izmir balikesir transfer zone and in the same time with the episodic core complex denudation of the menderes massif this study documents two composite volcanoes yamanlar and yuntdagi whose present vent area is strongly eroded and cut by a variety of strike slip and normal fault systems the transcurrent nw se being the dominant one the erosional remnants of the vent areas resembling a shallow crater intrusive complex illustrate the presence of numerous dykes or variably sized neck like intrusions and lava flows typically associated with hydrothermal alteration processes propylitic and argillic such vent areas were observed in both the examined volcanic fields having 6 km in diameter and being much more eroded toward the south along the nw se fault system lava flows and lava domes are sometimes associated with proximal block and ash flow deposits in the cone building association part besides lava flows and remnants of lava domes rare block and ash and pumice rich pyroclastic flow deposits as well as a series of debris flow deposits have been observed the rocks display a porphyritic texture and contain various proportions of plagioclase clinopyroxene orthopyroxene amphibole rare biotite and corroded quartz the examined rocks fall at the limit between calc alkaline to alkaline field and plot predominantly in high k andesite and dacite fields and one is rhyolite the trace element distribution suggests fractional crystallization processes and mixing in upper crustal magma chambers and suggests a metasomatized lithospheric mantle lower crust source this preliminary volcanological petrological and geochronological base study allowed documenting the yamanlar and yuntdagi as composite volcanoes generated during post collisional early middle miocene transtensional tectonic movements

coeval plutonism and metamorphism in a latest oligocene metamorphic core complex in northwest turkey a metamorphic core complex of latest oligocene age crops out in the kazdag mountain range in northwest turkey the footwall of the core complex consists of gneiss amphibolite and marble metamorphosed at 5 1 kbar and 640 50 c the average muscovite and biotite rb sr ages from the gneisses are 19 ma and 22 ma respectively and imply high temperature metamorphism during latest oligocene times the hangingwall is made up of an unmetamorphosed lower tertiary oceanic accretionary melange with upper cretaceous eclogite lenses the hangingwall and footwall are separated by an extensional ductile shear zone two kilometres thick mylonites and underlying high grade metamorphic rocks show a n trending mineral lineation with the structural fabrics indicat ing down dip top to the north shear sense the shear zone the accretionary melange and the high grade metamorphic rocks are cut by an undeformed granitoid with a 21 ma rb sr biotite age analytically indistinguishable from the rb sr biotite ages in the surrounding footwall gneisses the estimated pressure of the metamorphism and that of the granitoid emplacement indicate that the high grade metamorphic rocks were rapidly exhumed at 24 ma from a depth of 14 km to 7 km by activity along the shear zone the subsequent exhumation of the metamorphic rocks to the surface occurred during pliocene quaternary times in a transpressive ridge between two overstepping fault segments of the north anatolian fault zone the high grade metamorphic rocks of the kazdag range are surrounded by voluminous calc alkaline volcanic and plutonic rocks of late oligocene early miocene age which formed above the northward dipping hellenic subduction zone the magmatic arc setting of the core complex and stratigraphic evidence for subdued topography in northwest turkey prior to the onset of extension suggest that the latest oligocene regional extension was primarily related to the roll back of the subduction zone rather than to the gravitational collapse

the mount kozak magmatic complex western anatolia abstract the mount kozak igneous complex is located close to the towns of ayvalik bergama and burhaniye in the western anatolia turkey magmatic activity occurred during the late oligocene early miocene beginning with the emplacement of the kozak pluton sheet intrusive rocks formed around it coevally they are surrounded by the volcanic rocks partly contemporaneously with the emplacement of the granitic rocks during the early miocene the upper oligocene lower miocene magmatic rocks of the kozak region are represented by a high k calc alkaline suite of predominantly intermediate and acidic composition their geochemical characteristics suggest that the magmas are hybrid and were formed from a similar source representing mantle derived magmas contaminated by crustal materials the cogenetic plutonic rocks the hypabyssal rocks and the overlying volcanic associations are related to one another in space and time and appear to have been connected to a shallow level granitic intrusion in a caldera collapse setting the calc alkaline magmatic activity waned during the middle miocene when the volcanism was rejuvenated during the late miocene pliocene alkaline basalt lavas were formed as fissure eruptions

evidence for a stronger oxygen minimum zone off central california during late pleistocene to early holocene of 31 deep sea cores collected along the central california continental slope 18 have distinctly laminated sediment at depth but none have laminations in the top few centimetres the cores with laminated facies are restricted to water depths between 508 and 1508 m but not all cores taken from this depth interval have laminated facies 14 c dates yield an extrapolated age of 4700 b p for the top of the uppermost laminated unit comparisons of the diatom flora in the laminated couplets with diatom floras in a 13 month sediment trap record suggest that the laminations are varvelike couplets of seasonal sedimentation the laminated facies represent a period from the last global deglaciation to early holocene when the oxygen minimum zone along the northeastern pacific ocean was stronger than at present a stronger oxygen minimum zone during this time is inferred to be the result of intensified upwelling

glacio seismotectonics ice sheets crustal deformation and seismicity abstract the last decade has witnessed a significant growth in our understanding of the past and continuing effects of ice sheets and glaciers on contemporary crustal deformation and seismicity this growth has been driven largely by the emergence of postglacial rebound models pgm constrained by new field observations that incorporate increasingly realistic rheological mechanical and glacial parameters in this paper we highlight some of these recent field based investigations and new pgms and examine their implications for understanding crustal deformation and seismicity during glaciation and following deglaciation the emerging glacial rebound models outlined in the paper support the view that both tectonic stresses and glacial rebound stresses are needed to explain the distribution and style of contemporary earthquake activity in former glaciated shields of eastern canada and fennoscandia however many of these models neglect important parameters such as topography lateral variations in lithospheric strength and tectonic strain built up during glaciation in glaciated mountainous terrains glacial erosion may directly modulate tectonic deformation by resetting the orogenic topography and thereby providing an additional compensatory uplift mechanism such effects are likely to be important both in tectonically active orogens and in the mountainous regions of glaciated shields in general the short term response to ice fluctuations is similar to the earth s response to fluctuations in water reservoirs with the subsequent increase or decrease in seismicity which depends on the pre existing stress state when the ice fluctuations occur on the spatial scale and magnitude of the late pleistocene glaciation and deglaciation however the viscoelastic response of the earth especially the mantle causes significant changes in crustal deformation and earthquake activity that is spatially extensive and temporally complex the regions of greatest ice thickness and the regions marginal to the late pleistocene ice sheets indicate the most dramatic evidence of earthquake faulting the mantle response to these large ice mass fluctuations and the change in mass between the oceans and land caused and continues to cause measureable crustal deformation at hundreds of kilometres from the ice margins for both tectonically active and cratonic regions palaeoseismic investigations of late pleistocene and holocene faults are an important tool in evaluating earthquake hazard the predicted response of the earth over this time however is very dependent on the model assumed for most regions far more carefully designed field observations are needed to constrain the existing rheological and ice models

tectono stratigraphic terranes in cape breton island nova scotia implications for the configuration of the northern appalachian orogen cape breton island is divided into four terranes on the basis of contrasts in pre carboniferous geology the blair river complex in the north is an exposure of north american grenvillian basement analogous to the humber zone basement in newfoundland ordovician to devonian metavolcanic metasedimentary gneissic and granitic rocks of the aspy terrane are correlative with parts of the gander terrane of newfoundland and new brunswick the bras d9or terrane characterized by low pressure gneisses a carbonate clastic platform sequence and late precambrian early cambrian plutons may be correlative with units previously included in the gander terrane in southern newfoundland and the avalon terrane in southern new brunswick the mira terrane in southeastern cape breton island including late precambrian to early cambrian volcanic and sedimentary sequences and fossiliferous cambrian ordovician units is clearly part of the avalon terrane therefore with the exception of the dunnage terrane which is not represented in cape breton island the terranes of newfoundland continue through cape breton island they are offset to the northwest to the mainland part of the appalachian orogen in new brunswick

alluvial geoarchaeology of a small drainage basin in western anatolia late holocene landscape development and the question of the mouth of the paleo bakircay abstract late holocene landscape evolution in the geyikli basin a sub catchment of the bakircay basin on the west anatolian coast and its implications for the plaeogeography of the environs of ancient pergamon modern bergama were studied by a combination of archaeological and geographical investigations the study aims to investigate whether the dorpfeld scenario of the paleogeographical situation in the lower bakircay valley is true or not the scenario postulates that during the late holocene an alluvial fan fed from the geyikli valley progressively closed a topographical constriction between the aegean sea and a supposed paleo gulf that occupied the lower bakircay valley initially this caused the development of an inland lake and finally the shift of the mouth of the paleo bakircay from a northern position to its modern southern position the lithostratigraphy of four sediment outcrops in the lower geyikli basin and in the topographical constriction between the aegean coastal plain and the bakircay valley shows that during the past ca 1950 years the lower geyikli valley was inhabited by a braided river with a highly dynamic depositional system sedimentation totalled about 4 6 m in the past 1950 years indicating a drowning of the landscape in terrestrial sediments in recent times gravel mining has led to a deformation of the valley floor and the geyikli s fluvial terrace has become inactive the lack of any sediment related to a paleo gulf or a paleo lake inside the bakircay basin as well as the lack of any sediments of a northern paleo bakircay documents that the dorpfeld scenario does not apply for the past 1950 years archaeological findings show that the geyikli basin was intensively settled in historic times but there is no evidence that the geyikli basin was anthropogenically deformed in a way that could have contributed to the dorpfeld scenario

paleoceanographic changes on the farallon escarpment off central california during the last 16 000 years abstract new benthic and planktic foraminiferal assemblage census data and benthic foraminiferal oxygen index bfoi values previously published marine climate proxy data stable isotopes and ca cd and unpublished results of total carbon organic carbon and calcium carbonate analyses of sediments recovered off central california on the farallon escarpment 1605 m water depth 37 13 4 n 123 14 6 w core f 8 90 g21 document paleoceanographic changes during the latest quaternary which reflect the intensity and source of north pacific intermediate water npiw and surface productivity accelerator mass spectrometry radiocarbon dates of both benthic and planktic species provide an excellent age depth model for the last 16 000 years covering the latest glacial bolling allerod younger dryas and early middle and late holocene intervals a q mode cluster analysis separated the benthic fauna into three clusters one pleistocene and two holocene whereas the planktic fauna was divided only into pleistocene and holocene clusters stable oxygen isotope values show an increase in water temperature of 1 c from the late glacial to late holocene and a change in faunal composition of the planktic assemblage implies surface waters warmed as well a general trend of decreasing dissolved oxygen concentration from the pleistocene high oxic 3 0 6 0 ml l o2 to the holocene low oxic 1 5 3 0 ml l o2 suggested by the bfoi and cd ca data reflect decreased ventilation as the source of the npiw shifted from the sea of okhotsk to the tropical east pacific at 11 000 cal bp the middle holocene cooling reported in other central and northern california margin studies is not apparent in f 8 90 g21 which compares more favorably with studies from southern california and british columbia total carbon and organic carbon values are highest in the bolling allerod early holocene and late holocene similarly calcium carbonate values are high in the bolling allerod and peak in the early holocene but decrease significantly in the latest middle and late holocene which coincides with a depauparate planktic foraminiferal fauna in the upper 60 cm 70000 0 cal bp of the core and poor preservation of the benthic foraminiferal fauna at 40 cm 3000 cal bp decoupling is evident between the planktic and benthic faunal response to changing climatic conditions with the surface dwelling assemblage often leading the bottom dwelling assemblage by several millennia

timing of tectonic events in the menderes massif western turkey implications for tectonic evolution and evidence for pan african basement in turkey the menderes massif forms the western of the two large metamorphic culminations within the turkish alpide orogen it has three major lithologic units with a gneissic core at the base and a schist and a marble envelope overlying it successively although relations between them have been largely obscured by the polymetamorphic and structurally complex history of the massif we present a review of the available stratigraphic evidence and combine it with new isotopic ages from the central and southern parts of the massif to constrain the timing of major tectonic events that shaped the massif since the late proterozoic pt3 in the southern part of the massif sensu stricto three episodes of deformation and metamorphism are distinguished whereas in its northern part there are four the first episode occurred at 500 10 ma with intense deformation and metamorphism at high grade amphibolite facies with local anatexis in the central part of the massif the 470 9 ma old now highly deformed tonalitic and granitic intrusions mark the end of this episode on a cambrian reconstruction of continents around the eastern mediterranean the menderes massif forms the southern end of the pan african orogenic collage of northeastern africa and arabia the area of earliest palaeozoic deformation in the menderes may connect with the northwest african orogenic collage along the strike via the bozburun and saricicek diabases arkoses and schists in the center of the karacahisar dome interpreted herein as fragments of a pan african suture the earliest palaeozoic deformations to affect the rocks were probably related to the last pan african collisions and associated postcollisional convergence the southern part of the massif was undeformed from early ordovician to the early later eocene whereas the northern part was deformed metamorphosed and intruded possibly during the late triassic related to the closure of the karakaya marginal basin of palaeo tethys the next major event affecting the whole of the massif was the intense deformation and widespread metamorphism that reached high amphibolite grade in the structurally lower parts and only greenschist grade in the outermost envelope this metamorphism here called the main menderes metamorphism mmm is biostratigraphically constrained between early eocene and early oligocene time rb sr isotopic data show a spread of ages between 60 ma and 25 ma with the greatest number of determinations around 35 5 ma this number is in excellent agreement with the stratigraphic evidence and shows that mmm took place during latest eocene time or at the transition from eocene to oligocene time along the northern border of the massif deformation and metamorphism had already taken place during the late cretaceous in a high pressure low temperature hp lt metamorphic belt northernmost part of menderes massif sensu lato which was then covered by palaeocene molasse the evolution of the hp lt belt was probably related to the obduction of the bozkir ophiolites from the izmir ankara branch of the neo tethys ocean and preceded terminal collision in the evolution of the massif the mmm was a product of the latest palaeocene collision across neo tethys and the consequent internal imbrication of the menderes taurus block that resulted in the burial of the menderes massif area beneath the lycian nappe complex a low grade metamorphic event dated at 10 to 5 ma is interpreted to be related to the extensional deformation in the aegean and western turkey which has been dated stratigraphically to have begun during the tortonian 11 5 ma

late quaternary environments in ruby valley nevada abstract palynological data from sediment cores from the ruby marshes provide a record of environmental and climatic changes over the last 40 000 yr the modern marsh waters are fresh but no deeper than 3 m a shallow saline lake occupied this basin during the middle wisconsin followed by fresh and perhaps deep waters by 18 000 to 15 000 yr b p no sediments were recovered for the period between 15 000 and 11 000 yr b p possibly due to lake desiccation by 10 800 yr b p a fresh water lake was again present and deeper than modern conditions lasted until 6800 yr b p the middle holocene was characterized by very shallow water and perhaps complete desiccation the marsh system deepened after 4700 yr b p and fresh water conditions persisted until modern times vegetation changes in ruby valley were more gradual than those seen in the paleolimno logical record sagebrush steppe was more widespread than at present through the late pleistocene and early holocene giving way somewhat to expanded shadscale vegetation between 8500 and 6800 yr b p shadscale steppe contracted by 4000 yr b p but had greater than modern coverage until 1000 to 500 yr ago pinyon juniper woodland was established in the southern ruby mountains by 4700 yr b p

tertiary and quaternary volcanism of the erzurumkars area eastern turkey geochronological data and geodynamic evolution abstract this paper presents new geochemical and geochronological data on the neogene and quaternary volcanic products from the area of erzurum and kars eastern turkey the affinity of most of the volcanic rocks concerned is calc alkaline with the exception of minor quaternary alkaline rocks that outcrop in the kars sector ages range from 8 m y to 1 3 m y the time space distribution of the calc alkaline volcanism in eastern turkey nw iran is characterized by a sudden northward jump that occurred around 6 m y ago from the van erzurum southern belt to the kars northern belt available data indicate that this northward migration of volcanism was due to changes in the subduction geometry of the arabian plate under eurasia

paleodeviations of radiocarbon marine reservoir values for the northeast pacific differences in the radiocarbon ages of coeval marine shells and wood from emergent glaciomarine sediments in the fraser lowland of southwestern british columbia and northwest washington indicate that a total marine radiocarbon reservoir value of 1 1 1 k y is applicable in the region this is 40 greater 300 yr than the 800 yr value currently used to correct the ages of both modern and late pleistocene marine shells from this area the glaciomarine sediments were deposited rapidly between ca 12 5 and 11 5 1 4 c k y b p paleodeviations of the marine reservoir value may illustrate that rapid environmental changes occurred during the last glacial to interglacial transition these variations are thought to have been caused by changes in both deep and surface ocean circulation and by variations in the production of atmospheric radiocarbon 1 4 c these findings may indicate a rapid reordering of oceanic atmospheric circulation in the region

late glacial vegetation and climate change in western oregon abstract pollen records from two sites in western oregon provide information on late glacial variations in vegetation and climate and on the extent and character of younger dryas cooling in the pacific northwest a subalpine forest was present at little lake central coast range between 15 700 and 14 850 cal yr b p a warm period between 14 850 and 14 500 cal yr b p is suggested by an increase inpseudotsugapollen and charcoal the recurrence of subalpine forest at 14 500 cal yr b p implies a return to cool conditions another warming trend is evidenced by the reestablishment ofpseudotsugaforest at 14 250 cal yr b p increased haploxylonpinuspollen between 12 400 and 11 000 cal yr b p indicates cooler winters than before after 11 000 cal yr b p warm dry conditions are implied by the expansion ofpseudotsuga a subalpine parkland occupied gordon lake western cascade range until 14 500 cal yr b p when it was replaced during a warming trend by a montane forest a rise inpinuspollen from 12 800 to 11 000 cal yr b p suggests increased summer aridity pseudotsugadominated the vegetation after 11 000 cal yr b p other records from the pacific northwest show an expansion ofpinusfrom ca 13 000 to 11 000 cal yr b p this expansion may be a response either to submillennial climate changes of younger dryas age or to millennial scale climatic variations

the distribution and relationship between palynomorphs in aerosols and deep sea sediments off the coast of northwest africa abstract palynomorphs in eolian dust and bottom sediments from the northeastern atlantic off the coast of northwest africa were studied primary examination was for terrestrial plant detritus pollen spores opal phytoliths and freshwater diatoms but observations about marine entities were also made three distinct geographic palynofloras were detected a northern palynoflora consisting of pollen derived primarily from the mediterranean basin a central or saharan palynoflora characterized by pollen derived from desert plants and a southern tropical equatorial palynoflora composed of pollen derived from tropical plants but including up to 50 allochthonous pollen from the drier interior of west africa palynomorph distributions are related closely to both source vegetation and to atmospheric and oceanic transport mechanisms and in many cases distribution patterns in bottom sediments and aerosols are complementary the quantity of pollen and spores per gram of bottom sediment ranges from greater than 2000 off the saharan coast in mauritania to less than 50 in deep ocean basins pollen and spores in mediterranean aerosols may exceed 40 per cubic meter of air during the summer and range between 4 to 6 for tropical aerosols during the winter tropical aerosols and bottom sediments contained the greatest abundance of fungal spores the distribution of opal phytoliths and freshwater diatoms in both aerosols and bottom sediments indicates that dust storms are a major transporting agent for these entities from the interior of west africa to the gulf of guinea these storms are also an important agent for the transport of pollen to the tropical atmosphere distances of transport may exceed 5000 km for mediterranean pollen and even greater distances for palynomorphs in eolian dust from interior west africa the abundance of dinoflagellates and microforaminifera in bottom sediments is directly related to the area of upwelling off the west african coast

active tectonics of the alpine himalayan belt between western turkey and pakistan summary over 80 new fault plane solutions combined with satellite imagery as well as both modern and historical observations of earthquake faulting are used to investigate the active tectonics of the middle east between western turkey and pakistan the deformation of the western part of this region is dominated by the movement of continental material laterally away from the lake van region in eastern turkey this movement helps to avoid crustal thickening in the van region and allows some of the shortening between arabia and eurasia to be taken up by the thrusting of continental material over oceanic type basement in the southern caspian mediterranean makran and black sea thus central turkey bounded by the north and east anatolian strike slip faults is moving west from the van region and overrides the eastern mediterranean at two intermediate depth seismic zones one extending between antalya bay and southern cyprus and the other further west in the hellenic trench the motion of northern iran eastwards from the van region is achieved mainly by a conjugate system of strike slip faults and leads to the low angle thrusting of iran over the southern caspian sea the seismicity of the caucasus shows predominantly shortening perpendicular to the regional strike but there is also some minor elongation along the strike of the belt as the causcasus overrides the caspian and black seas the deformation of the eastern part of this region is dominated by the shortening of iran against the stable borders of turkmenistan and afghanistan the north east direction of compression seen in zagros is also seen in north east iran and the kopet dag where the shortening is taken up by a combination of strike slip and thrust faulting large structural as well as palaeomagnetic rotations are likely to have occurred in ne iran as a result of this style of deformation north south strike slip faults in southern iran allow some movement of material away from the collision zone in ne iran towards the makran subduction zone where genuinely intermediate depth seismicity is seen within this broad deforming belt large areas such as central turkey nw iran azerbaijan central iran and the southern caspian appear to be almost aseismic and therefore to behave as relatively rigid blocks surrounded by active belts 200 300 km wide the motion of these blocks can usefully be described by poles of rotation the poles presented in this paper predict motions consistent with those observed and also predict the opening of the gulf of iskenderun ne of cyprus the change within the zagros mountains from strike slip faulting in the nw to intense thrusting in the se and the relatively feeble seismicity in se iran baluchistan this description also explains why the north south structures along the iran afghanistan border do not cut the east west ranges of the makran within the active belts surrounding the relatively aseismic blocks a continuum approach is needed for a description of the deformation even though motions at the surface may be concentrated on faults the evolution of fault systems within the active zones is controlled by geometric constraints such as the requirement that simultaneously active faults do not in general intersect many of the active processes discussed in this paper particularly large scale rotations and lateral movement along the regional strike are likely to have caused substantial complexities in older mountain belts and should be accounted for in any reconstructions of them

biostratigraphic implications for the turbidite depositional processes on the monterey deep sea fan central california abstract recognition of the pleistocene holocene boundary and biohorizons on the continental margin of california is complicated by turbidite deposition the coiling ratio of neogloboquadrina pachyderma ehrenberg the relative frequencies of subarctic and transitional planktonic foraminifers radiolarian number and the radiolarian foraminiferal ratio all show variability in upper quaternary sections that appear related to downslope transport processes in addition to the environment of surface waters and carbonate dissolution we examined the distribution of microfossils in ten turbidites from the western levee of the monterey fan to determine 1 how turbidite microfossil assemblages differ from those of hemipelagic intervals 2 if turbiditic muds can be distinguished from hemipelagic muds based on fossil content and 3 if microfossils used to define biostratigraphic zones are significantly affected by turbiditic processes using cluster analysis samples were successfully divided into hemipelagic and turbiditic groups based on the relationship among five of 16 variables cluster a sand content the relative frequency of shallow water benthonic foraminifera benthonic foraminiferal number adjusted benthonic foraminiferal number and the relative frequency of dextral neogloboquadrina pachyderma ehrenberg the variables jointly characterize a transitional assemblage transported from a bathyal or neritic source both radiolaria and planktonic foraminifera are used to mark biohorizons on the california continental margin in this study it was found that both fossil groups vary significantly in concentration and relative frequency between turbiditic and hemipelagic muds of the monterey fan and microfossil assemblages are measurably different between tops and bases of turbidites the coiling ratio of neogloboquadrina pachyderma ehrenberg varies the least and may be most resistant to bias by hydraulic sorting and differential carbonate preservation related to transport processes

timing of cenozoic extensional tectonics in west turkey the timing of the transition from compressional to extensional tectonics in the late cenozoic evolution of west turkey has been constrained by k ar geochronology from acidic volcanic rocks and tourmaline leucogranite dykes in the central and east margin respectively of the gordes basin dacites and rhyolites in the centre of the gordes neogene sedimentary basin cut both the basement ophiolites of the izmir ankara suture zone and the neogene sediments on the basin s eastern margin the leucogranites cut metamorphic basement along a major ne sw trending normal fault that controls the regional structure of the basin pebbles of these leucogranites occur in adjacent neogene turfites and conglomerates k ar dates on biotites from the central volcanic rocks vary from 18 4 0 8 ma to 16 3 0 5 ma early miocene whilst muscovite from a leucogranite on the eastern margin of the basin provides ages of 24 2 0 8 ma and 21 1 1 1 ma latest oligocene to early miocene geochronological data and field relationships demonstrate that the earlier compressional regime had been replaced by extensional tectonics by latest oligocene early miocene

california current system response to late holocene climate cooling in southern california 1 new holocene high resolution planktonic foraminiferal assemblage data from santa barbara basin california documents variability in ocean circulation as the california current system responded to millennial scale climate change during late holocene climatic cooling climatic variability increased at 4 ka when a series of extreme cool events notably at 2 2 1 5 and 0 8 ka associated with glacial advance in the pacific northwest punctuated the predominantly warm holocene simultaneously high subtropical species abundance suggests increased interannual variability el nino frequency severity or greater seasonality during the late holocene planktonic foraminiferal assemblages indicate that the magnitudes of climatic shifts were greatest after 1 5 ka during an interval of extreme terrestrial hydrological variability in western north america and that the coolest interval of the holocene in santa barbara basin was coincident with the little ice age

holocene multidecadal and multicentennial droughts affecting northern california and nevada abstract continuous high resolution 18 o records from cored sediments of pyramid lake nevada indicate that oscillations in the hydrologic balance occurred on average about every 150 years yr during the past 7630 calendar years cal yr the records are not stationary during the past 2740 yr drought durations ranged from 20 to 100 yr and intervals between droughts ranged from 80 to 230 yr comparison of tree ring based reconstructions of climate change for the past 1200 yr from the sierra nevada and the el malpais region of northwest new mexico indicates that severe droughts associated with anasazi withdrawal from chaco canyon at 820 cal yr bp calendar years before present and final abandonment of chaco canyon mesa verde and the kayenta area at 650 cal yr bp may have impacted much of the western united states during the middle holocene informally defined in this paper as extending from 8000 to 3000 cal yr bp magnetic susceptibility values of sediments deposited in pyramid lake s deep basin were much larger than late holocene 3000 0 cal yr bp values indicating the presence of a shallow lake in addition the mean 18 o value of caco 3 precipitated between 6500 and 3430 cal yr bp was 1 6 less than the mean value of caco 3 precipitated after 2740 cal yr bp numerical calculations indicate that the shift in the 18 o baseline probably resulted from a transition to a wetter 30 and cooler 3 5 c climate the existence of a relatively dry and warm middle holocene climate in the truckee river pyramid lake system is generally consistent with archeological sedimentological chemical physical and biological records from various sites within the great basin of the western united states two high resolution holocene climate records are now available from the pyramid and owens lake basins which suggest that the holocene was characterized by five climatic intervals tic and 18 o records from owens lake indicate that the first interval in the early holocene 11 600 10 000 cal yr bp was characterized by a drying trend that was interrupted by a brief 200 yr wet oscillation centered at 10 300 cal yr bp this was followed by a second early holocene interval 10 000 8000 cal yr bp during which relatively wet conditions prevailed during the early part of the middle holocene 8000 6500 cal yr bp high amplitude oscillations in tic in owens lake and 18 o in pyramid lake indicate the presence of shallow lakes in both basins during the latter part of the middle holocene 6500 3800 cal yr bp drought conditions dominated owens lake desiccated and lake tahoe ceased spilling to the truckee river causing pyramid lake to decline at the beginning of the late holocene 3000 cal yr bp lake tahoe rose to its sill level and pyramid lake increased in volume

quaternary climates and sea levels of the u s atlantic coastal plain uranium series dating of corals from marine deposits of the u s atlantic coastal plain coupled with paleoclimatic reconstructions based on ostracode marine and pollen continent data document at least five relatively warm intervals during the last 500 000 years on the basis of multiple paleoenvironmental criteria we determined relative sea level positions during the warm intervals relative to present mean sea level were 7 5 meters at 188 000 years ago 7 5 1 5 meters at 120 000 years ago 6 5 3 5 meters at 94 000 years ago and 7 3 meters at 72 000 years ago the composite sea level chronology for the atlantic coastal plain is inconsistent with independent estimates of eustatic sea level positions during interglacial intervals of the last 200 000 years hydroisostatic adjustment from glacial interglacial sea level fluctuations lithospheric flexure and isostatic uplift from sediment unloading due to erosion provide possible mechanisms to account for the discrepancies alternatively current eustatic sea level estimates for the middle and late quaternary may require revision

the late holocene dry period multiproxy evidence for an extended drought between 2800 and 1850 cal yr bp across the central great basin usa abstract evidence of a multi centennial scale dry period between 2800 and 1850 cal yr bp is documented by pollen mollusks diatoms and sediment in spring sediments from stonehouse meadow in spring valley eastern central nevada u s we refer to this period as the late holocene dry period based on sediment recovered stonehouse meadow was either absent or severely restricted in size at 8000 cal yr bp beginning 7500 cal yr bp the meadow became established and persisted to 3000 cal yr bp when it began to dry comparison of the timing of this late holocene drought record to multiple records extending from the eastern sierra nevada across the central great basin to the great salt lake support the interpretation that this dry period was regional the beginning and ending dates vary among sites but all sites record multiple centuries of dry climate between 2500 and 1900 cal yr bp this duration makes it the longest persistent dry period within the late holocene in contrast sites in the northern great basin record either no clear evidence of drought or have wetter than average climate during this period suggesting that the northern boundary between wet and dry climates may have been between about 40 and 42 n latitude this dry in the southwest and wet in the northwest precipitation pattern across the great basin is supported by large scale spatial climate pattern hypotheses involving enso pdo amo and the position of the aleutian low and north pacific high particularly during winter

selective transport of palynomorphs in marine turbiditic deposits an example from the ascension monterey canyon system offshore central california abstract the pollen assemblage of a deep sea core 15g collected at lower bathyal depths 3491 m on a levee of monterey canyon off central california was investigated to gain insights into the delivery processes of terrigenous material to submarine fans and the effect this transport has on the palynological record thirty two samples were obtained down the length of the core 19 from hemipelagic and mixed mud deposits considered to be the background record and 13 others from displaced flow deposits the pollen record obtained from the background samples documents variations in the terrestrial flora as it adapted to changing climatic conditions over the last 19 000 cal yrs bp a q mode cluster analysis defined three pollen zones a glacial pollen zone ca 20 000 17 000 cal yr bp an overlying transitional pollen zone ca 17 000 11 500 cal yr bp and an interglacial pollen zone ca 11 500 cal yr bp to present another q mode cluster analysis of both the background mud and flow deposits also defined these three pollen zones but four of the 13 turbiditic deposits were assigned to pollen zones older than expected by their stratigraphic position this was due to these samples containing statistically significant fewer palynomorphs than the background muds as well as being enriched 10 35 in some cases in hydraulically efficient pinus pollen a selective bias in the pollen assemblage such as demonstrated here may result in incorrect interpretations e g climatic shifts or environmental perturbations based on the floral record indicating turbiditic deposits should be avoided in marine palynological studies particularly in the case of fine grained flow deposits that may not be visually distinct granulometry and grain size frequency distribution curves may not be enough to identify these biased deposits determining the relative abundance and source of displaced shallow water benthic foraminifera entrained in these sediments serves as an excellent additional tool to do so

sea surface temperatures in the subarctic northeast pacific reflect millennial scale climate oscillations during the last 16 kyrs changes of sea surface temperature sst in the subarctic ne pacific over the last 16 000 calendar years before present 16 kyr bp have been inferred from the study of c 37 alkenone unsaturation in a sediment core from the western canadian continental slope between 16 0 and 11 0 kyr three distinct cold phases 6 7 c interrupt two warmer periods 9 10 c within the 2 range of the radiocarbon based time control the observed sst oscillations correspond to the oldest dryas the bolling the older dryas the allerod and the younger dryas periods in the gisp2 18 o record these results represent the first high resolution marine paleotemperature estimates off the northern west coast of north america and imply that the climate of this region may be very strongly coupled to that of the north atlantic given the fast rates of sst change 1 c 40 80 yr such coupling must be controlled by atmospheric transmission of the climate signal

oxygen 18 16 variability in greenland snow and ice with 10 3 to 105 year time resolution the 3 km long greenland ice sheet project 2 gisp2 ice core presents a 100 000 year detailed oxygen isotope profile covering almost a full glacial interglacial cycle measuranents of isotopic fluctuations in snow frost and atmospheric water vapor samples collected during summer field seasons up to 20 0 are compatible with the large and abrupt 80 160 changes observed in accumulated tim snow pit 15 80 profiles from the gisp2 summit area however show rapid smoothing of the 180 160 signal near the surface beyond about 2 m depth the smoothedi5180 signal is fairly well preserved and can be interpreted in terms of average local weather conditions and climate the longer climate fluctuations also have regional and often global significance in the older part of the record corresponding to marine isotope stages mis 5a to 5d the effect of orbital climate forcing via the 19 and 23 kyr precession cycles and the 41 kyr obliquity cycle is obvious from the end ofmis 5a at about 75 000 years b p till the end of the glacial at the younger dryas preboreal transition at 11 650 years b p the o180 160 record shows frequent rapid switches between intermediate interstadial and low stadial values fourier spectra of the oscillations that are superimposed on the orbitally induced changes contain a strong periodicity at 1 5 kyr a broad peak at 4 0 kyr and additional shorter periods detailed comparison of the gisp2 180 160 record with the vostok antarctica 15d record pacific ocean foraminiferal 180 160 grande pile france tree pollen and insolation indicates that a counterpart to many of the rapid 180 160 fluctuations of gisp2 can be found in the other records and that the gisp2 isotopic changes clearly are the local expression of climate changes of worldwide extent correlation of events on the independent gisp2 and specmap time scales for the interval 10 000 50 000 years b p shows excellent chronometric agreement except possibly for the event labeled 3 1 the glacial to interglacial transition evidently started simultaneously in the arctic and the antarctic but its development and its expression in greenland isotopes was later suppressed by the influence of meltwater especially from the barents sea ice sheet on deep water formation and ocean circulation meltwaters from different ice sheets bordering the north atlantic also influenced ocean circulation during the bolling allerod interstadial complex and the younger dryas and led to a distinct development of european climate and greenland 180 160 values the holocene interval with long term stable mean isotopic values contains several fluauations with periods from years to millennia dominant is a 6 3 year oscillation with amplitude up to 3 to 4 0 periodicities of 11 and 210 years also found in the solar modulated records of the cosmogenic isotopes 1obe and 14c suggest solar processes as the cause of these cycles depression of180 160 values cooling by volcanic eruptions is observed in stacked gisp215 80 records but the effect is small and not likely to trigger major climate changes

evolution of the bayramic magmatic complex northwestern anatolia abstract during the oligocene middle miocene period widespread magmatic activity developed in western anatolia following the continental collision between the sakarya continent and the tauride anatolide platform this produced both intrusive and extrusive rocks which appear to be associated in space and time as exemplified from the bayramic area in the bayramic area the magmatic activity started with the intrusion of the evciler granite and the coeval lower volcanic association this was followed by the development of the upper volcanic association these rock groups form collectively the bayramic magmatic complex which was generated under an on going north south compressional regime the bayramic magmatic complex has a subalkaline composition displaying a calcalkaline trend trace elements and ree contents resemble to island arc and collision related magmas according to the isotope values the bayramic magmatic complex was derived from the magmas of lithospheric mantle origin which were later contaminated while passing through the thick continental crust in a post collisional tectonic setting during the oligocene early miocene period the latest product of the magmatism is the late miocene pliocene basalt lavas their geochemical properties are clearly different from the oligocene early miocene magmatic rocks the basalts were generated when the north south compression gave way to the north south extensional regime

paleoseismology in canada a dozen years of progress canadian studies in paleoseismology have led to the publication of over 40 papers in the last 12 years 80 of which have appeared since 1989 considerable progress has been achieved by confirming that the last great earthquake on the cascadia subduction zone happened about 300 years ago and by working toward a chronology of prior earthquakes from their tsunami and turbidite records as yet sparse evidence suggests that the geological effects of large crustal earthquakes are also recorded in southwestern british columbia but there is as yet no chronology in the stable craton of eastern canada studies of silt layers in lakes that are floored by organic sediments have shown considerable potential to provide local earthquake chronologies that can be tested against the more sporadically preserved evidence from liquefaction landslides and other possible indicators of paleoshaking by contrast research using more traditional techniques involving direct examination of faults through geomorphological studies or trenching has been hampered by the difficulty of identifying active faults in the first place on the basis of the past dozen years an accelerating pace of discovery should be expected in the next decade

le volcanisme quaternaire d anatolie centrale turquie association de magmatismes calco alcalin et alcalin en domaine de convergence collision volcanism in central anatolia cappadocia began at least in the late miocene because of the north south arabian eurasian convergence since this period the anatolian block is displaced towards the west along the north and east anatolian strike slip faults kinematic reconstructions show that the east anatolian fault is both sinistral and convergent as a consequence the anatolian block is currently being deformed quaternary volcanism in central anatolia is represented by several hundreds of monogenetic scoria cones lava flows maars and domes as well as two strato volcanoes hasan dag and erciyes dag the monogenetic volcanism is bimodal basalts and rhyolites whereas the stratovolcanoes exhibit a complete calc alkaline suite from basalts to rhyolites most of the igneous products are calc alkaline basalts erupted mainly from the monogenetic cones lava flows and maars andesites are encountered in the strato volcanoes as lava flows domes and nuees ardentes deposits dacites and rhy

correlation of marine and coastal terrestrial records of central california response to paleoceanographic and paleoclimatic change during the past 19 000 years new benthic foraminiferal census data combined with previously published planktic foraminiferal and pollen data from the continental margin off central california provide a unique opportunity to document concurrent paleoceanographic and paleoclimatic changes in the region during the late quaternary all three datasets were evaluated in gravity core s3 15g collected at a depth of 3491 on the western levy of the monterey fan 36 23 53 n 123 20 52 w accelerator mass spectrometry radiocarbon dates and the ratio of the planktic foraminiferal species neogloboquardrina pachyderma ehrenberg to neogloboquadrina incompta cifelli provide a good age depth model for the last 19 000 years covering the last glacial bolling allerod younger dryas and holocene intervals separate q mode cluster analyses of the hemipelagic as well as mixed combined hemipelagic and turbiditic mud samples grouped the benthic foraminiferal fauna into two clusters reflecting faunal adaptation to changing climatic conditions during the pleistocene and holocene r mode cluster analysis also differentiated glacial uvigerina senticosa and globobulimina auriculata and interglacial melonis pompilioides and gyroidina planulata faunas a general trend of slightly increasing oxygen in the deep sea is suggested from the pleistocene to holocene based on the reduction in abundance of g auriculata and increased frequency of m pompilioides q mode cluster analysis of the planktic foraminifera illustrates a change in the surface water from a glacial subpolar fauna in the pleistocene to a transitional fauna in the holocene whereas the pollen record separated into three clusters two of pleistocene age glacial and transitional and one in the holocene interglacial reflecting the terrestrial floral adaptation in the california coast ranges of central california to the warmer climate in the holocene decoupling is evident between the benthic and planktic foraminiferal and terrestrial floral responses to changing oceanographic and climatic conditions the floral response leads the surface dwelling fauna by several millennia and is followed by the deep dwelling benthic foraminiferal fauna a millennium later

genesis of collision volcanism in eastern anatolia turkey late cenozoic volcanism in eastern anatolia extends in a broad sw ne trending belt across the arabia eurasia collision zone from the arabian foreland basin in the southwest and to the kars plateau and lesser caucasus in the northeast foreland volcanism is dominated by basaltic shield and fissure eruptions of transitional tholeiitic alkaline composition volcanism on the thickened crust north of the bitlis thrust zone varies from the mildly alkaline volcano nemrut and older mus volcanics in the south through the transitional calc alkaline alkaline volcanoes bingol and suphan and the alkaline volcano tendurek to the calc alkaline volcano ararat and older kars plateau volcanics in the north isotope sr nd and trace element systematics indicate that the lavas from the foreland were derived from the mantle lithosphere of the arabian continent which had been enriched by small volumes of asthenospheric melts over a period of time and that lavas from the alkaline volcanic area around mus and the volcanoes nemrut and tendurek north of the bitlis thrust zone were derived from a lithospheric source of similar composition either from the same underthrust arabian continent or from the bitlis massif microcontinent by contrast the transitional lavas from bingol and suphan and the calc alkaline lavas from ararat and kars were derived from lithosphere carrying a distinct subduction signature inherited from pre collision subduction events positive correlations between 87sr 86sr and sio2 and rb nb and sio2 in the alkaline and transitional lavas suggest that combined assimilation and fractional crystallization was an important process within at least part of the thickened crust of the collision zone trace element covariation diagrams such as y rb indicate the importance of hornblende crystallization at depth and orthopyroxene at shallow levels within the calc alkaline provinces in contrast to the consistently anhydrous crystallization sequences of the alkaline lavas trace element diagrams based on the covariation of compatible and incompatible elements point to moderate low degrees of partial melting with residual clinopyroxene throughout and residual garnet in the foreland province consideration of mineral stabilities mantle solidi and geothermal gradients before and after collision suggest that lithospheric thickening should both increase the thickness of metasomatized lithosphere and depress the metasomatized zone to greater depths probably beneath the amphibole and dolomite breakdown curves perturbation of the thickened lithosphere by delamination of the thermal boundary layer perhaps coupled with local stretching associated with pull apart basins on strike slip fault systems is then sufficient to generate melt the composition of that melt being largely dependent on the enrichment history of the lithosphere in question in eastern anatolia volcanism appears to have started between about 8 and 6 ma ago some 5 ma after the start of rapid uplift of the east anatolian plateau

a record of past ocean atmosphere radiocarbon differences from the northeast pacific a record of the 14c age differences between atmosphere and the mixed layer of the northeast pacific ocean was obtained from 58 radiocarbon measurements on shells and associated wood from coastal sediments in british columbia this series of mixed layer reservoir ages spans the holocene and extends into the period of the younger dryas cold event in the north atlantic and surrounding regions the data reflect the extent of upwelling in the northeast pacific and thus constrain models of carbon cycling and ocean circulation most of the reservoir ages are only slightly less than than the present preindustrial value of about 800 years and may be identical when probable sampling errors are taken into account either the north pacific reached a state close to its present mode of circulation at or before the end of the younger dryas or a different circulation fortuitously produced a similar reservoir age our results support the hypothesis that slow changes in atmospheric radiocarbon concentrations over the holocene arose from 14c production rate changes data corresponding to a radiocarbon age of around 6400 years b p give a reservoir age of 1200 years if this result is confirmed it indicates a much greater variability for the holocene ocean circulation than was previously believed possible

late quaternary climatic change on the american north pacific coast temporal changes in solar radiation caused by variations in the earth s orbit figure prominently in current quaternary climate theory1 4 experimental design of atmospheric circulation models emphasizes the importance of solar radiation in the heating of interglacial land and ocean surfaces at different seasons of the year whereby monsoon type circulation seasonal shifting of regional cyclonic and anticyclonic centres develops while during glacial ages seasonality is greatly modified by the influence of ice sheets5 7 we investigated the late quaternary climate of the north pacific where according to modelling solar radiation in the early holocene at the time of the summer solstice is high and in the late holocene is relatively low we compared quantitative temperature and precipitation estimates from southern alaska obtained by application of transfer functions to fossil pollen records with estimates from western washington8 and southern british columbia9 data extending over 10 000 years show a broadly consistent pattern of climatic change in general agreement with predicted variations in solar radiation and their effect on atmospheric circulation and seasonal duration of pressure systems over the north pacific ocean in the early holocene as monsoon type circulation became established with melting of glaciers the subtropical north pacific anticyclone annually regulated climate for a longer period at higher latitudes than at present so that warmth and dryness high summer radiation increased in southern alaska the aleutian low pressure centre locus of cyclonic storm activity intensified during the late holocene resulting in colder and more humid coastal climate low summer radiation over much of the year and increased frequency of glacier growth in the cordillera

postglacial faulting in eastern canada nature origin and seismic hazard implications abstract at more than 70 locations in southeastern canada and the adjacent united states tiny bedrock faults displace glacial striations that are about 10 000 years old these reverse faults mostly of small displacement occur in a broad arc from western ontario to newfoundland the faults lie near the margin of the laurentian ice sheet strike generally tangential to it and imply compression nearly normal to the ene directed contemporary regional stress these observations and some age relationships suggest that the faults formed very soon after deglaciation perhaps in the first few thousand years after ice melting in each place and probably represent the release of stresses caused by flexural deformation of the upper crust although the individual offsets are small the faults are believed to be pervasive and individual outcrops reflect amounts of stress relief consistent with stresses implied by the postglacial tilt of nearby lake shorelines

late quaternary vegetation and climate history near little lake central coast range oregon pollen and plant macrofossils recovered from little lake oregon provide the first record of late quaternary climate and vegetation changes in oregon9s central coast range the pollen data suggest that the period from ca 42 000 to 24 770 yr b p featured an open forest of western white pine western hemlock and fir the inferred climate was cooler and wetter than today the full glacial period was characterized by a parkland of spruce lodgepole pine and mountain hemlock which suggests that the climate was colder and possibly drier than today the oregon coast range was not a glacial refugium for temperate conifers as has been proposed by 16 000 yr b p the pollen and plant macrofossil data suggest the development of a montane forest composed of pine fir western hemlock and mountain hemlock temperate taxa were present in the vegetation at 13 500 yr b p during a period of climatic amelioration a reversal in this warming trend may have occurred between 11 000 and 10 500 yr b p when pine western and mountain hemlock and spruce were slightly more abundant early holocene forests featured douglas fir red alder and bracken fern implying more severe summer drought and more frequent fires after 5600 yr b p douglas fir western hemlock and western red cedar dominated the record marking the introduction of the present day cool moist climate however during the past 2800 yr increased douglas fir and decreased cedar suggest the possibility of reduced effective moisture at little lake

a 14 300 year long record of fire vegetation climate linkages at battle ground lake southwestern washington high resolution macroscopic charcoal analysis was used to reconstruct a 14 300 year long fire history record from the lower columbia river valley in southwestern washington which was compared to a previous vegetation reconstruction for the site in the late glacial period ca 14 300 13 100 cal yr bp pinus picea dominated parkland supported little to no fire activity from the late glacial to the early holocene ca 13 100 10 800 cal yr bp pseudotsuga abies dominated forest featured more frequent fire episodes that burned mostly woody vegetation in the early to middle holocene ca 10 800 5200 cal yr bp quercus dominated savanna was associated with frequent fire episodes of low to moderate severity with an increased herbaceous i e grass charcoal content from the middle to late holocene ca 5200 cal yr bp to present forest dominated by pseudotsuga thuja type and tsuga heterophylla supported less frequent but mostly large or high severity fire episodes fire episodes were least frequent but were largest or most severe after ca 2500 cal yr bp the fire history at battle ground lake was apparently driven by climate directly through the length and severity of the fire season and indirectly through climate driven vegetation shifts which affected available fuel biomass

integration of bed characteristics geochemical tracers current measurements and numerical modeling for assessing the provenance of beach sand in the san francisco bay coastal system abstract over 150 million m3 of sand sized sediment has disappeared from the central region of the san francisco bay coastal system during the last half century this enormous loss may reflect numerous anthropogenic influences such as watershed damming bay fill development aggregate mining and dredging the reduction in bay sediment also appears to be linked to a reduction in sediment supply and recent widespread erosion of adjacent beaches wetlands and submarine environments a unique multi faceted provenance study was performed to definitively establish the primary sources sinks and transport pathways of beach sized sand in the region thereby identifying the activities and processes that directly limit supply to the outer coast this integrative program is based on comprehensive surficial sediment sampling of the san francisco bay coastal system including the seabed bay floor area beaches adjacent rock units and major drainages analyses of sample morphometrics and biological composition e g foraminifera were then integrated with a suite of tracers including 87sr 86sr and 143nd 144nd isotopes rare earth elements semi quantitative x ray diffraction mineralogy and heavy minerals and with process based numerical modeling in situ current measurements and bedform asymmetry to robustly determine the provenance of beach sized sand in the region

regional and local controls on postglacial vegetation and fire in the siskiyou mountains northern california usa article i nfo the siskiyou mountains of northwestern california and southwestern oregon are a floristic hotspot and the high diversity of conifers there likely results from a combination of geological ecological climatological and historical factors to evaluate how past climate variability has influenced the composition structure and fire regime of the siskiyou forests pollen charcoal and lithological evidence was examined from two lakes along a moisture gradient to reconstruct the vegetation fire and climate history the late glacial period was characterized by subalpine parkland and infrequent fire at both sites during the late glacial early holocene transition period subalpine parkland was replaced by a closed forest of pinus cupressaceae abies and pseudotsuga and more frequent fires a 1000 years earlier at the wetter site and it is likely that reduced pacific ocean upwelling created warmer drier conditions at the coast in the early holocene pinus cupressaceae were less abundant and fire less frequent at the coastal site during a period of increased coastal upwelling and fog production in the late holocene abies pseudotsuga pinus and quercus vaccinifolia increased in the forest at both sites suggesting a widespread response to cooling fewer fires at the wetter site may account for the abundance of picea breweriana within the last 1000 years the comparison of the two records implies that large scale controls in climate during the last 14 000 cal yr bp have resulted in major changes in vegetation and fire regime asynchrony in the ecosystem response of wetter and drier sites arises from small scale spatial variations in effective moisture and temperature resulting from topographically influenced microclimates and coastal to inland climate gradients

late cenozoic tectonics and volcanism along the north anatolian fault new structural and geochemical data abstract different types of volcanic activity have developed along the north anatolian fault zone naf in turkey detailed analysis of satellite images and digital elevation models dems and field observations have been made in order to understand the tectonics and the distribution of volcanic vents in the anatolian block some faults are oblique to the naf and delimit extensional escape wedges vents rooted on open tension fractures show that emplacement of the volcanism is related to tensional fracturing of the anatolian continental block which we attribute to the onset of free borders in the south and west along the naf earliest extension 1 is directed s to ssw and the latest 2 towards w to wsw parallel to the sinistral slip along the naf major and trace element geochemical data indicate that the dominant calc alkaline rocks are associated with various alkaline lavas k ar ages of the volcanics range from 22 to 8 5 ma in galatia massif 900 to 100 ka in niksar and 3 to 12 ka in erzincan isotopic and trace element data are interpreted as reflecting a dominantly lithospheric mantle source slightly mixed with asthenospheric liquids most magmas were fractionated and contaminated by continental crust during their ascent 1 and 2 tectono volcanic events have propagated through time and space from west to east the 1 extension is late oligocene in the galatia massif late miocene in niksar and late pliocene in erzincan the 2 extension and strike slip event along the naf began in the late miocene in the galatia massif early pliocene in niksar and quaternary in erzincan signature from an asthenospheric source in the second event in the three regions suggests that an ancient suture zone galatia massif and or the lithospheric naf transform niksar and erzincan have served to channel small quantities of asthenospheric melts existing at the base of the lithosphere

the influence of the water saturation on the strength of volcanic tuffs used as building stones moisture content is one of the most important factors influencing the strength of building stones ayazini and seydiler afyonkarahisar turkey tuffs were investigated with the goal to determine the influence of the water on their strength mercury porosimetry was used to determine the pore size distribution ayazini tuffs have pore sizes ranging from about 200 000 to 10 nm and seydiler tuffs ranging from about 7000 to 10 nm the tuff samples are immersed in water with different time periods of 1 6 24 and 48 h the following physico mechanical properties were measured for all the samples both in dry and saturated condition compressive strength and flexural strength test results were indicated by simple regression analysis good correlations were found between physico mechanical properties with dry and saturated tuff samples the results had shown their mechanical strength decreases in wet conditions for dry samples tested had 22 21 mpa uniaxial compression strength while 1 h immersed samples had 15 11 mpa which indicates a decrease of 31 96 after the 48 h water immersion time period the value of compression strength decreases by 43 99 and becomes 12 44 mpa

palaeomagnetism and magnetic properties of the cappadocian ignimbrite succession central turkey and neogene tectonics of the anatolian collage abstract the cappadocian ignimbrite succession of central southern anatolia comprises at least nine major and two minor calc alkaline rhyolitic sheets emplaced at 1 2 ma intervals between 11 2 and 1 1 ma it records the last phase of neotethyan subduction during final emplacement of the tauride orogen in southern turkey this study reports magnetostratigraphy and describes associated rock magnetic properties remanence resides in ti poor titanomagnetites haematisation is locally produced by post emplacement oxidation but does not contribute significantly to the palaeomagnetic signature although secondary processes within the ignimbrite sheets have produced composite isothermal remanent magnetisation spectra and variable intensities of magnetisation weak anisotropy of magnetic susceptibility describes tensors with maximum axes close to bedding and minimum axes perpendicular to this plane directions of kmax with weak imbrication mostly suggest flow away from centres of eruption located by gravity and remote sensing older ignimbrites upper and lower goreme akdag zelve from the cardak centre are all of normal polarity later ignimbrites partly erupted from the derinkuyu centre comprise the sarimaden r cemilkoy r tahar r kizilkaya r incesu n and valibaba sofular r ignimbrites the overall reversed group mean is d i 174 51 n 10 units r 9 84 95 6 6 k 55 and all magnetisation directions from the upper goreme 9 0 ma onwards are rotated anticlockwise with respect to eurasian and african palaeofields this sense of rotation characterises most of central anatolia and averages 9 5 in this sector the rotation rate from 8 to 1 ma bp was 1 25 ma but it appears to have accelerated during the latter part of the quaternary to about an order higher than rates determined from gps rotation has resulted from extrusion of fault blocks during tectonic escape of the anatolian collage to the southwest and followed crustal thickening as the afro arabia plate has continued to impinge differentially into eurasia cenozoic magnetic inclinations are systematically shallower across anatolia than inclinations expected from the geocentric dipole model and the apparent polar wander of bordering major plates only part of this difference 400 km can be accommodated by northward movement and crustal thickening in central anatolia since mid miocene times shallow inclinations observed in the aegean region extend into turkey they are observed in young volcanics and appear to reflect a regional geomagnetic anomaly the pattern of neotectonic declinations across anatolia shows rotations that are strongly anticlockwise rotated in the east near the arabian pincer but diminish towards the west to become zero or slightly clockwise at the western extremity of the collage rotations also seem to become generally younger towards the south crustal deformation has therefore been distributed and the net effect of terrane extrusion to the west and south has been to expand the curvature of the tauride arc and by inference the cyprus arc

a magnetite rich cyprus type vms deposit in ortaklar a unique vms style in the tethyan metallogenic belt gaziantep turkey abstract the ortaklar vms deposit is hosted in the kocali complex consisting of basalts and deep sea pelagic sediments which formed by rifting and continental break up of the southern neotethyan in late triassic the basalts are of nmorb type without notable crustal contamination from the surface to depth the ortaklar deposit consists of a gossan zone a thick massive ore zone and a poorly developed stockwork zone primary mineralisation is characterised by distinctive facies including sulphide breccias proximal graded beds distal stockworks and chimney fragments ore mineral abundances decrease in the order of pyrite magnetite chalcopyrite and sphalerite two distinct phases of mineralisation massive magnetite and massive sulphide are present in the ortaklar deposit textural evidence e g magnetite replacing sulphides and the spatial relationships with the host rocks indicate that magnetite and sulphide minerals were generated in different stages the transition from sulphide to magnetite mineralisation is interpreted to relate to variation in h2s content of ore fluids the 1st stage massive sulphide ore might have formed by early hydrothermal fluids rich in fe and h2s the 2nd stage massive magnetite might have formed by later neutral hydrothermal fluids rich in fe but poor in h2s replacing the pre existing sulphide ore the alteration patterns mineral paragenesis lithological features massive ore stockwork ore gossan of the ortaklar deposit together with its trace elements cu pb zn au ag and ree signatures are all consistent with a cyprus type vms system the 34s values in pyrite and chalcopyrite samples range from 2 6 to 5 7 indicating that the hydrothermal fluids were associated with sub seafloor igneous activity typical of cyprus type vms deposits however magnetite formed later than sulphide minerals in the ortaklar deposit contrasting with typical cyprus type vms deposits where magnetite generally occurs in lower sections consequently although the ortaklar deposit generally conforms to cyprus type deposits it is distinguished from them by its late stage and high magnetite concentration thus the ortaklar deposit is thought to be an exceptional and perhaps unique cyprus type vms deposit

geology and petrology of the simav magmatic complex nw anatolia and its comparison with the oligo miocene granitoids in nw anatolia implications on tertiary tectonic evolution of the region the oligo miocene granitic plutons and their related volcanic subvolcanic successions form a nw se trending magmatic belt along the northern border of the menderes massif this belt evolved within a nappe package consisting of the menderes metamorphics sakarya continent afyon zone and tavsanli zone and also intruded this nappe package the ezine evciler eybek kozak alacam koyunoba egrigoz and the baklan plutons emplaced along this belt and show similarities in their internal structures emplacement mechanisms and petrological characteristics these different granitic plutons cut and stitch various combinations of the nappe package of the above mentioned tectonic belts and evolved during and following the alpine collision they all show characteristic map patterns of shallow seated plutons and range from granite to monzogranite the granitic plutons display calc alkaline i type and post collisional geochemical characteristics the egrigoz koyunoba plutons and their subvolcanic volcanic phases simav magmatic complex were studied in detail the geochemical characteristics and field occurences of the simav magmatic complex were compared to the other magmatic associations in western anatolia and it was determined that it is of collisional origin and not related to an extensional tectonic regime as suggested in some recent studies

black mats spring fed streams and late glacial age recharge in the southern great basin black mats are prominent features of the late pleistocene and holocene stratigraphic record in the southern great basin faunal geochemical and sedimentological evidence shows that the black mats formed in several microenvironments related to spring discharge ranging from wet meadows to shallow ponds small land snails such asgastrocopta tappanianaandvertigo berryiare the most common mollusk taxa present semiaquatic and aquatic taxa are less abundant and include catinellids fossaria parva gyraulus parvus and others living today in and around perennial seeps and ponds the ostracodescypridopsis okeechobiandscottia tumida typical of seeps and low discharge springs today as well as other taxa typical of springs and wetlands are common in the black mats several new species that lived in the saturated subsurface also are present but lacustrine ostracodes are absent the 13c values of organic matter in the black mats range from 12 to 26 reflecting contributions of tissue from both c3 sedges most shrubs and trees and c4 saltbush saltgrass plants carbon 14 dates on the humate fraction of 55 black mats fall between 11 800 to 6300 and 230014c yr b p to modern the total absence of mats in our sample between 6300 and 230014c yr b p likely reflects increased aridity associated with the mid holocene altithermal the oldest black mats date to 11 800 11 60014c yr b p and the peak in the14c black mat distribution falls at 10 00014c yr b p as the formation of black mats is spring related their abundance reflects refilling of valley aquifers starting no later than 11 800 and peaking after 11 00014c yr b p reactivation of spring fed channels shortly before 11 20014c yr b p is also apparent in the stratigraphic records from the las vegas and pahrump valleys this age distribution suggests that black mats and related spring fed channels in part may have formed in response to younger dryas yd age recharge in the region however the inception of black mat formation precedes that of the yd by at least 40014c yr and hydrological change is gradual not rapid

palynologic and geomorphic evidence for environmental change during the pleistocene holocene transition at point reyes peninsula central coastal california abstract three sites on the point reyes peninsula california provide evidence of major environmental change during the pleistocene holocene transition a 12 300 yr long pollen record from coast trail pond reveals a change from closed canopy pseudotsuga abies forest to coastal scrub and grassland about 10 000 yr b p the same change is also evident in pollen records from two sea cliff exposures that contain a series of buried soils interstratified with fluvial and debris flow deposits eight radiocarbon dates from these exposures indicate that aggradation at both sites began ca 12 000 yr b p and that the change from forest to scrub and grassland occurred between 10 300 and 9400 yr b p high percentages of alder pollen and bracken fern spores reflect repeated geomorphic disturbance at ca 10 400 yr b p the occurrence of major aggradation accompanied by recurrent debris flows between ca 12 000 and 10 000 yr b p suggests that this was a period of more frequent high intensity storms