deposition and modification of a flood layer on the northern california shelf lessons from and about the fate of terrestrial particulate organic carbon the 1995 flood of the eel river in northern california provided an opportunity to follow the short term history of riverine particulate matter on a continental shelf particulate organic carbon including both vascular plant debris and soil carbon was utilized as a tracer of the distribution and modification of the shelf flood deposit these components were sorted during initial emplacement of the deposit both in the river plume and in the benthic boundary layer during the 8 months following the flood lateral transport shallow burial and bioturbation contributed to spatial changes in the amount and character of carbon in the flood deposit study of the deposit suggests that this and previous flood layers may be preserved in the shelf and upper slope stratigraphic record as clay rich beds with relatively high carbon to nitrogen ratios and more negative 13c values than background non flood sediment concentrations of vascular plant debris are locally characteristic of such layers and may serve as distinctive stratigraphic markers investigation of organic carbon in the 1995 flood layer on the eel river shelf provides insight into the fate of terrestrial particulate carbon on continental margins in general flooding of the eel river and of similar river systems draining mountainous terrains introduces large quantities of terrestrial carbon to the marine environment and may favor the preservation of both terrestrial and marine carbon the abundant woody vascular plant debris discharged during floods is especially likely to survive oxidation and sulfate reduction in the shallower zones of the seabed this study reveals the dominant role that physical and biological processes may play in attenuating the terrestrial organic carbon signal on shelves over monthly to yearly time scales

moho topography in the central andes and its geodynamic implications p to s converted waves at the continental moho together with waves multiply reflected between the earth s surface and the moho have been used to estimate the moho depth and average crustal vp vs variations in the central andes our analysis confirms and significantly complements the moho depth estimates previously obtained from wide angle seismic studies and receiver functions the resulting crustal thickness varies from about 35 km in the forearc region to more than 70 km beneath the plateau and thins 30 km further to the east in the chaco plains beneath the andean plateau the moho is deeper in the north altiplano and shallower in the south puna where the plateau attains its maximum elevation a non linear relation exists between crustal thickness and elevation and bouguer gravity suggesting that the crust shallower than 50 55 km is predominately felsic in contrast to a predominately mafic crust below such a relation also implies a 100 km thick thermal lithosphere beneath the altiplano and with a lithospheric thinning of a few tens of kilometers beneath the puna absence of expected increase in lithospheric thickness in regions of almost doubled crust strongly suggests partial removal of the mantle lithosphere beneath the entire plateau in the subandean ranges at 19 20 s the relation between altitude and crustal thickness indicates a thick lithosphere up to 130 150 km and lithospheric flexure beneath a relative topographic low at the salar de atacama a thick crust 67 km suggests that the lithosphere in this region is abnormally cold and dynamically subsided possibly due to coupling with the subducting plate this may be related to the strongest ms 8 0 known intra slab earthquake in the central andes that happened very close to this region in 1950 the average crustal vp vs ratio is about 1 77 for the altiplano puna and it reaches the highest values 1 80 1 85 beneath the volcanic arc indicating high ambient crustal temperatures and wide spread intra crustal melting 2002 elsevier science b v all rights reserved

geochemistry and isotope systematics of small to medium volume neogene quaternary ignimbrites in the southern central andes evidence for derivation from andesitic magma sources the geochemical and isotopic compositions of small to medium volume 10 km3 50 km3 neogene quaternary ignimbrite sheets of the southern central andes 25 00 26 45 s 67 30 69 30 w have been analysed in order to assess the petrogenesis of this type of calc alkaline magma the ignimbrites are derived from the active volcanic zone around salar de la isla sis in chile and from behind the active arc in the area of the salar de antofalla saf argentina the ignimbrites in both areas are characterized by 87sr 86sr t ratios 0 7066 0 7090 that are lower and end t values 2 4 to 5 1 that are higher than in the large volume caldera sourced ignimbrites of cerro galan 100 km further east and those of ignimbrites from other megacalderas of the central andes this difference reflects smaller amounts of crustal material in the sis and saf ignimbrites rather than a change in basement composition as indicated by pb provinciality the isotope signature of the sis and saf ignimbrites is similar to that of late to post miocene composite calc alkalic andesite dacite stratovolcanoes of the frontal arc in this region this finding combined with major and trace element modelling lends support to a petrogenetic model for the sis and saf ignimbrites involving fractional crystallization from a lil depleted andesitic parental magma which was beforehand modified by crustal contamination

puzzling out a palimpsest testing an interdisciplinary study in level o of abric romani abstract cultural deposits especially those accumulated in caves and rock shelters are usually the results of several occupational events in the same space forming palimpsests in addition the materials of these occupational events tend to be deposited along with remains of natural origin and may be altered partially destroyed or reworked due to the process of superimposition the work presented here focuses on dissecting the palimpsest of level o at abric romani through an interdisciplinary analysis we analyzed a particular area located in the northeastern corner of the site this work is based on the study of the lithic and faunal remains recovered in this area with the aim of dissecting the palimpsest into the smallest possible units to do this we used different methods and techniques including archaeostratigraphy intra site spatial archaeology zooarchaeology tooth microwear taphonomy lithic technology and faunal and lithic refits these methods allowed us to identify two archaeolevels in this area oa and ob oa comprises a maximum of three accumulations and ob holds two accumulations of archaeological remains these accumulations are generally related to combustion structures based on the results obtained from zooarchaeological taphonomic and lithic technology analyses we characterized each accumulation the analysis of the lithic and faunal refits helped to identify synchronic and diachronic links after having processed all of the results we were able to interpret the intra area organization and its role in relation to the rest of the site our results have shown that it is possible to obtain high resolution data for dissecting a palimpsest using different methodologies it is however important to remember that although we were able to distinguish these finer units we were still working with palimpsests nevertheless the study of these finer units makes it possible to work with time scales that are closer to ethnographic time thereby facilitating further ethno archaeological interpretation

seismicity and shape of the subducted nazca plate an updated compilation of earthquake locations and focal mechanism solutions from the international seismological centre and preliminary determination of earthquakes is the basis of a comprehensive study of the geometry of the wadati benioff zone beneath western south america the new data support previous mapping of a sharp flexure rather than a tear in the subducted nazca plate beneath southern peru and provide evidence for a similar flexure in the southward transition from nearly horizontal subduction to a slab with 30 dip at latitude 33 s in contrast the transition from 30 slab dip beneath bolivia to a nearly horizontal dip in the region between 28 s 32 s is more gradual occurring over several hundred kilometers of along strike distance between 20 s and 32 s this southward flattening corresponds to a broadening of a horizontal benchlike part of the subducted plate formed between 100 and 125 km depth the transition in continental tectonic style near 27 s 28 s from a wide volcanically active plateau to a narrow nonvolcanic cordillera appears not to be associated with the main slab flattening which begins to the north of these latitudes but with a more abrupt change in curvature of the subducted slab from convex upward to concave upward immediately below the plate boundary interface the concept of gaussian curvature is applied to slab bending to explain how subduction geometry is affected by the shape of the south american plate we hypothesize that the polarity of vertical curvature in the subducting slab is governed by the orientation of lateral curvature of the plate margin focal mechanism solutions for intermediate and deep earthquakes are grouped by geographic region and inverted for the orientation and relative magnitudes of the principal stresses results of the inversion indicate that downdip extension dominates in the slab above 350 km while downdip compression dominates at greater depths

crustal thickness in the central andes from teleseismically recorded depth phase precursors summary although crustal thickness is a critical constraint for geodynamic models of andean orogenesis relatively few measurements exist from local seismic studies in this study we use reflections from the underside of the moho as illuminated by intermediate depth earthquakes to provide new estimates of crustal thickness for the central andes 16 34 s these reflected signals pmp are identified as precursors to the depth phase pp when recorded at teleseismic distances 35 85 although relatively small in amplitude the pmp phase is often clear even on single seismograms less obvious pmp phases were enhanced by stacking traces from arrays this method was most effective for events of m w 6 and depth 100 km crustal thickness determined in this study ranges from 59 to 70 km in southern peru from 49 to 80 km across the puna altiplano and from 50 to 60 km above the pampean flat slab the lack of such phases for certain events may be evidence of heterogeneity at the moho and some precursors appear to correspond to intracrustal magma and lithospheric mantle discontinuities the results obtained using the pmp technique combined with those from other studies show the crustal thicknesses under the central andes are more variable than expected from purely isostatic considerations we infer that one or a combination of geodynamic processes involving lower crustal flow lower crustal delamination and mantle crustal lithospheric coupling can explain the highly variable topography on the moho beneath the central andes

spatial variability in sedimentary processes on the eel continental slope the northern california continental margin receives episodically large quantities of sediment from the eel river which seasonally discharges to the shelf regional circulation broadcasts this sediment widely not only affecting sedimentation on the shelf but on the slope as well a suite of 60 cores has been collected to examine the processes of sediment accumulation and sediment delivery to the eel continental slope in waters 800 m deep spatial surveys of accumulation rate 0 2 1 3 g cm 2 year 1 and surficial sediment grain size 4 8 5 demonstrate that sediment is accumulating throughout the eel margin reflecting a rapid and widespread redistribution of the fluvial discharge downcore grain size profiles of heterogeneous sediments suggest that hemipelagic and other episodic sediment delivery processes may be important for the slope in areas proximal to the river in more distal areas downcore profiles reveal relatively homogeneous sediments delivered dominantly by hemipelagic processes a budget for fine grained sediment shows that this upper portion of the slope contains at a maximum 20 of the river s annual discharge a combined budget for the shelf and upper slope suggests that at least 60 of the annual sediment load is not accounted for in these areas the eel continental slope because of the large terrigenous sediment input the narrow width of the adjacent shelf and its energetic environment is a good analogue for slopes during transitional stands of sea level and for modern tectonically active settings processes typically associated with these geological settings i e supply of sediment to the slope and downslope mass movement are actively occurring 1999 elsevier science b v all rights reserved

shallowing and steepening subduction zones continental lithospheric loss magmatism and crustal flow under the central andean altiplano puna plateau

modern accumulation rates and a sediment budget for the eel shelf a flood dominated depositional environment the northern california continental margin is periodically impacted by geologically significant storms which have a marked influence on terrigenous sediment supply flood deposition and long term accumulation of fine grained sediment on the eel shelf accumulation of eel river muds on the adjacent shelf was investigated using 210pb and 137cs geochronologies in order to understand the fate of sediment discharged by the eel river and to relate patterns of net sediment accumulation 100 yr time scale to sediment dynamics 210pb data demonstrate that modern accumulation of river mud occurs from the 50 m isobath seaward across shelf accumulation rates decrease from maximum mid shelf values of 0 6 1 7 g cm 2 yr 1 to values of 0 2 0 4 g cm 2 yr 1 at the shelf break with a spatially weighted mean of 0 5 g cm 2 yr 1 0 4 cm yr for the entire shelf 210pbxs sediment depth profiles from the region of highest accumulation rate are characterized by subsurface intervals of low and uniform activity which are produced by flood deposition in some cores particular 210pbxs activity intervals may be associated with major eel river floods of 1955 1964 and 1974 it is postulated that because of the coincidence of high river flow events and southerly winds during cyclonic winter storms net northward transport allows for preferential deposition of fine grained sediment north of the river mouth over the past 100 years fluvial sediment input combined with marine dispersal processes have produced a mid shelf depocenter evident by both the spatial distribution of 210pb accumulation rates and by clay rich flood layers partially preserved in shelf deposits a fine grained sediment budget for the dispersal system based on hydrological data and 210pb geochronologies demonstrates that a maximum of 20 3 109 kg yr of the mean annual supply of fluvial mud 14 109 kg yr is trapped on the shelf the results of this study demonstrate that 1 short term sedimentation processes associated with floods can influence sediment accumulation on longer time scales and 2 a major fraction of fine grained sediment supplied to tectonically active margins by flood prone mountainous rivers bypasses narrow continental shelves

seismotectonics of thin and thick skinned deformation in the andean foreland from local network data evidence for a seismogenic lower crust local network data from san juan argentina provides new information about crustal seismicity in the andean foreland above a horizontal segment of the subducted nazca plate the authors find two areas of foreland seismicity one associated with the sierras pampeanas basement uplifts and the other beneath but not within the precordillera foreland fold thrust belt the precordillera seismicity provides direct evidence for basement deformation beneath the sediments of the thrust belt and supports the idea that its eastern part is significantly modified by underlying basement deformation in both areas events are concentrated between 15 and 35 km depth and have volumetric rather than planar fault like distributions the depth distribution is usually deep for intraplate earthquakes and suggests a brittle ductile transition near 30 35 km it also suggests the upper plate may have a geotherm similar to stable cratonic regions rather than a steeper one that may be expected due to a lithospheric thinning implied by the location of the subducted plate this can be understood as a transient effect of a neogene flattening of the dip of the subducted plate where a rapid thinning of the upper plate was followed with underplating by the cool subducted plate leaving the upper plate geothermmore unchanged while producing a thinned mechanically weaker lithosphere finally a spatial correlation of upper plate seismicity and structures with subducted plate seismicity raises the possibility that a major lithospheric structure cutting across the strike of the foreland near 31 degree s may be related to subduction of the juan fernandez ridge less

patterns of ice rafted detritus in the glacial north atlantic 40 55 n the observation by heinrich 1988 that during the last glacial period much of the input of ice rafted detritus to the north atlantic sediments may have occurred as a succession of catastrophic events rekindled interest on the history of the northern ice sheets over the last glacial period in this paper we present a rapid method to study the distribution of these events both in space and time using whole core low field magnetic susceptibility we report on approximately 20 cores covering the last 150 to 250 kyr well defined patterns of ice rafted detritus appear during periods of large continental ice sheet extent although these are not always associated within their maxima most of the events may be traced across the north atlantic ocean for the six most recent heinrich layers hl two distinct patterns exist hl1 hl2 hl4 hl5 are distributed along the northern boundary of the glacial polar front over most of the north atlantic between 40 and 50 n hl3 is more restricted to the central and eastern part of the northern atlantic the nd sr isotopic composition of the material constituting different heinrich events indicates the different provenance of the two patterns hl3 has a typical scandinavia arctic icelandic young crust signature and the others have a large component of northern quebec and northern west greenland old crust material these isotopic results obtained on core su 9008 from the north american basin are in agreement with the study by jantschik and huon 1992 who used k ar dating of silt and clay size fractions of an eastern basin core me 68 89 these data confirm the large spatial scale of these events and the enormous amount of ice rafted detritus they represent

40ar 39ar and k ar chronology of pleistocene glaciations in patagonia during the pleistocene east of lago buenos aires argentina at 46 5 s at least 19 terminal moraines were deposited as piedmont glaciers from the patagonian ice cap advanced onto the semi arid high plains adjacent to the southern andes exceptional preservation of these deposits offers a rare opportunity to document ice cap fluctuations during the last 1 2 m y 4 0 ar 3 9 ar incremental heating and unspiked k ar experiments on four basaltic lava flows interbedded with the moraines provide a chronologic framework for the entire glacial sequence the 4 0 ar 3 9 ar isochron ages of three lavas that overlie till 90 km east of the cordillera at lago buenos aires and another 120 km from the andes along rio gallegos at 51 8 s that underlies till strongly suggest that the ice cap reached its greatest eastward extent ca 1100 ka at least six moraines were deposited within the 256 k y period bracketed by basaltic eruptions at 1016 10 ka and 760 14 ka similarly six younger more proximal moraines were deposited during an 651 k y period bracketed by an underlying 760 14 ka basalt and the 109 3 ka cerro volcan basalt flow that buried all six moraines coupled with in situ cosmogenic surface exposure ages of moraine boulders the 109 ka age of cerro volcan implies that moraines deposited during the penultimate local glaciation correspond to marine oxygen isotope stage 6 further westward toward lago buenos aires six additional moraines younger than the cerro volcan basalt flow occur surface exposure dating of boulders on these moraines combined with the 1 4 c age of overlying varved lacustrine sediment indicates deposition during the last glacial maximum lgm 23 16 ka although antarctic dust records signal an important patagonian glaciation at 60 40 ka moraines corresponding to marine oxygen isotope stage 4 are not preserved at lago buenos aires apparently these were overrun and obliterated by the younger ice advance at 23 ka notwithstanding the overall pattern of glaciation in patagonia is one of diminishing eastward extent of ice during successive glacial advances over the past 1 m y we hypothesize that tectonically driven uplift of the patagonian andes which began in the pliocene yet continued into the quaternary in part due to subduction of the chile rise spreading center during the past 2 m y maximized the ice accumulation area and ice extent by 1 1 ma subsequent deep glacial erosion has reduced the accumulation area resulting in less extensive glaciers over time

vegetation and environmental conditions in the donana natural park coastal area sw iberia at the beginning of the last glacial cycle detailed reconstructions of the vegetation of iberia during the last glacial inception are rare due to the limited number of terrestrial sites recording this period active retreat of el asperillo cliff located on the atlantic coast of southwestern iberia has exposed a fossil organic level dating back to one of the early stades of the last glacial cycle pollen and macrofossil analyses from this site show that the donana area was covered mainly by steppic vegetation temperate trees survived the coldest periods albeit in reduced numbers mediterranean taxa are extremely reduced in contrast with other dry areas of southern iberia over this time span this vegetation suggests cold and arid climatic conditions in accordance with paleoclimatic reconstructions based on several atlantic marine cores

the geochemistry of a dying continental arc the incapillo caldera and dome complex of the southernmost central andean volcanic zone 28 s the pleistocene incapillo caldera and dome complex 5 570 m marks the southernmost siliceous center of the andean central volcanic zone 28 s where the steeply dipping 30 segment of the subducting nazca plate transitions into the chilean flatslab to the south the eruption of the incapillo caldera and dome complex began with a 3 1 ma effusive phase characterized by 40 rhyodacitic dome eruptions this effusive phase was terminated by an explosive caldera forming event at 0 51 ma that produced the 14 km3 incapillo ignimbrite distinctive and virtually identical chemical signatures of the domes and ignimbrites sio2 67 72 wt la yb 37 56 ba la 16 28 la ta 30 50 87sr 86sr 0 70638 0 70669 e nd 4 2 to 4 6 indicate that all erupted lavas originated from the same magma chamber and that differentiation effects between units were minor the strong hree depletion sm yb 6 8 that distinguishes incapillo magmas from most of the large ignimbrites of the altiplano puna plateau can be explained by the extent and degree of partial melting at lower crustal depths 40 km in the presence of garnet at upper crustal depths this high pressure residual geochemical signature also common to adjacent late miocene pliocene pircas negras andesites was partially overprinted by shallow level assimilation and fractional crystallization processes energy constrained afc modeling suggests that incorporation of anatectic upper crustal melts into a fractionated adakite like dacitic host best explains the petrogenesis of incapillo magmas the diminution of the sub arc asthenospheric wedge during nazca plate shallowing left the incapillo magma chamber unreplenished by both mafic mantle derived and lower crustal melts and thus stranded at shallow depths within the andean crust based on its small size and distinctive high pressure chemical signature the incapillo caldera and dome complex provides an endmember model for an andean caldera erupting within a waning magmatic arc over a shallowing subduction zone

detailed investigation of continental shelf morphology using a high resolution swath sonar survey the eel margin northern california abstract the eel shelf northern california lies within an active compressional tectonic margin subject to abundant terrigenous sediment input from the eel river a recent high resolution swath sonar survey provides us with the opportunity to investigate seafloor morphology and acoustic backscatter patterns within this dynamic region our analysis of the statistical character of bathymetry demonstrates a clear separation into large and small scale morphologies at a 3 10 km scale with smaller scale morphology heavily damped relative to large scale morphology the eel shelf bathymetry is subtle but several structures can be readily discerned in a residual bathymetry formed by removal of the downslope gradient some shelf structures are evidently related to depositional processes as evidenced by correlation with 100 yr sediment accumulation rates whereas others appear related to tectonic processes as evidenced by correlation with subsurface synclines and anticlines the sidescan structure of the shelf is dominated by the low backscatter over the eel and mad river subaqueous deltas evidently associated with the sand to mud transition however contrary to usual correlations between backscatter and grain size in this situation higher backscatter is associated with the muddy sediments in addition we observe a series of shore perpendicular striations or ribbons spaced 0 2 1 0 km apart which extend northward from the eel river subaqueous delta and lie at or near the sand to mud transition some aspects of ribbon morphology suggest that they may be associated with down slope flows

geology of the eel river basin and adjacent region implications for late cenozoic tectonics of the southern cascadia subduction zone and mendocino triple junction two upper cenozoic depositional sequences of principally marine strata about 4000 m thick overlie accreted basement terranes of the central and coastal belts of the franciscan complex in the onshore offshore eel river basin of northwestern california the older depositional sequence is early to middle miocene in age and represents slope basin and slope blanket deposition whereas the younger sequence late miocene to middle pleistocene in age consists largely of forearc basin deposits youthful tectonic activity related to gorda north american plate convergence indicates an active cascadia subduction zone and strong partial coupling between these plates structures of the northeastern margin of the eel river basin are principally north northwest trending east northeast dipping thrust and reverse faults that form imbricate thrust fans many faults merge downward into sole thrusts that extend to or near the gorda north american plate interface in the southern part of the region these structures have been modified by northward encroachment of the pacific plate the coastal belt fault the early tertiary accretionary suture between the franciscan central and coastal belts can be traced from arcata bay northward offshore to the southern oregon border it is tentatively extended farther northward based on aeromagnetic data to an offshore position west of cape blanco thereafter it may coincide with the offshore fulmar fault if so the franciscan coastal belt in california is correlative with the offshore fulmar terrane in oregon the cascadia subduction zone csz does not join the mendocino transform fault at the commonly depicted offshore location of the mendocino triple junction mtj instead the csz extends southeastward around the southern eel river basin and shoreward along mendocino canyon to join the petrolia shear zone similarly the mendocino fault may extend shoreward via mattole canyon and join the cooskie shear zone these two shear zones intersect onshore north of the king range and the area of their intersection is the probable location of the mtj

crustal thickness beneath the andes and sierras pampeanas at 30 s inferred from pn apparent phase velocities 1 we obtained a 2d crustal model beneath central chile and western argentina using apparent pn phase velocities recorded along an ew trending transect at 30 s this model is characterized by a thick 65 km crustal root beneath the high cordillera a 60 km thick crust beneath the precordillera and a gradual shallowing of moho depths beneath the sierras pampeanas from 55 km in the west to 40 km in the east beneath the sierras pampeanas where very little crustal shortening is observed the thick crust must be explained by means other than simple tectonic shortening isostatically balanced crustal thickness is consistently shallower than our model shows suggesting the existence of dynamic forces possibly linked to the flat slab

the nature of orogenic crust in the central andes 1 the central andes 16 22 s are part of an active continental margin mountain belt and the result of shortening of the weak western edge of south america between the strong lithospheres of the subducting nazca plate and the underthrusting brazilian shield we have combined receiver function and surface wave dispersion results from the banjo seda project with other geophysical studies to characterize the nature of the continental crust and mantle lithospheric structure the major results are as follows 1 the crust supporting the high elevations is thick and has a felsic to intermediate bulk composition 2 the relatively strong brazilian lithosphere is underthrusting as far west 65 5 w as the high elevations of the western part of the eastern cordillera ec but does not underthrust the entire altiplano 3 the subcrustal lithosphere is delaminating piecemeal under the altiplano ec boundary but is not completely removed beneath the central altiplano the altiplano crust is characterized by a brittle upper crust decoupled from a very weak lower crust that is dominated by ductile deformation leading to lower crustal flow and flat topography in contrast in the high relief inland sloping regions of the ec and sub andean zone the upper crust is still strongly coupled across the basal thrust of the fold thrust belt to the underthrusting brazilian shield lithosphere subcrustal shortening between the altiplano and brazilian lithosphere appears to be accommodated by delamination near the altiplano ec boundary our study suggests that orogenic reworking may be an important part of the felsification of continental crust

crossing forest thresholds inertia and collapse in a holocene sequence from south central spain a holocene palaeoecological sequence from villaverde south central spain is presented the pollen stratigraphy is used to infer past vegetation changes within a catchment area that represents the boundary between semi arid plateau and mountain vegetation from c 9700 7530 cal yr bp pinus is dominant probably as a result of a combination of a relatively dry climate and natural fire disturbance from c 7530 5900 cal yr bp moderate invasion by quercus appears to be a migrational response following increased moisture and temperature but in part shaped by competitive adjustments from c 5900 5000 cal yr bp the pine forests are replaced by deciduous quercus forests with an important contribution from corylus betula fraxinus and alnus mediterranean type forests spread from c 5000 to 1920 cal yr bp coincident with expansions of artemisia juniperus and other xerophytes from c 1920 1160 cal yr bp pinus becomes dominant after a disturbance mediated invasion of the oak forests human impact u

retreat velocity of the north atlantic polar front during the last deglaciation determined by 14 c accelerator mass spectrometry the glacial oscillations which dominate the quaternary global climate are closely related to changes in incoming solar radiation but the details of palaeoclimatic spectra suggest that other parameters usually referred to as feedback have significantly increased the climatic response to extraterrestrial forcing1 the last deglaciation appears to be one of the more characteristic examples of nonlinearity because its abruptness strongly contrasts with the smooth shape of the associated solar radiation maximum dated at 11 000 yr bp in addition the presence of the younger dryas cold event concomitant with the solar radiation maximum could be interpreted as a transitory phenomenon caused by the rapid meltwater influx linked to the first phase of the ice sheet s disintegration2 3 here using accelerator mass spectrometry we date precisely the movements of the polar front during the whole period of glacial retreat 15 000 8 000 yr bp our results show that the polar front has moved between 35 n and 55 n in 1 000 yr for the earliest retreat 12 500 12 000 bp and moved almost instantaneously that is 400 yr during the two abrupt climatic changes associated with the younger dry as cold event

climate instability during the last interglacial period recorded in the grip ice core isotope and chemical analyses of the grip ice core from summit central greenland reveal that climate in greenland during the last interglacial period was characterized by a series of severe cold periods which began extremely rapidly and lasted from decades to centuries as the last interglacial seems to have been slightly warmer than the present one its unstable climate raises questions about the effects of future global warming

eruptive processes and caldera formation in a nested downsagcollapse caldera cerro panizos central andes mountains abstract the cerro panizos ignimbrite center in the central andes mountains produced two ignimbrite sheets and many lava flows the ignimbrite of quebrada cienago was erupted at 7 9 ma and effusive eruptions continued until the two cooling units of the crystal rich dacitic cerro panizos ignimbrite were emplaced at 6 7 ma the lower unit has no laterally continuous flow breaks and was erupted from a single vent or small cluster of vents with limited fluctuation in discharge lithic fragments reach significant concentrations 5 only in the uppermost two meters of this cooling unit where they document vent wall collapse or the opening of a new vent the upper cooling unit contains many flow units with variations in welding thicknesses and lithic fragment concentrations implying an unsteady eruption column the opening of many vents and probable caldera collapse triangulation of anisotropy of magnetic susceptibility flow direction measurements locate a single vent for the lower cooling unit whereas the upper cooling unit had many vents within the present dome cluster a 15 km diameter topographic depression marked by inward dips of 4 8 at the cooling unit contact is centered on the vent area of the lower cooling unit the depression is interpreted as a downsag caldera formed during emplacement of the lower cooling unit collapse began late in the eruption of the lower cooling unit and continued through the emplacement of the upper cooling unit resurgent magmatism occurred as lava flows that mundated the caldera area a ring of dacite domes erupted until at least 6 1 ma in the northern half of the downsag caldera traces the margin of a collapse caldera associated with the upper cooling unit maximum caldera subsidence 353 km 3 is not enough to account for the erupted volume 652 km 3 dre minimum the ash poor crystal rich nature up to 50 crystals in the pumice 75 in the matrix of the cerro panizos pyroclastic flows resulted in poor retention of gases and there is little evidence of fluidization the high crystal content however favored modified grain flow processes in which several particle support mechanisms combine with grain dispersive forces it is postulated that the flows were initially partially fluidized but rapidly lost their gases and grain flow processes grew in relative importance grain flow processes destroyed evidence of fluidization before deposition

northern iberian abrupt climate change dynamics during the last glacial cycle a view from lacustrine sediments abstract we present a palaeoclimatic reconstruction of the last glacial cycle in iberia ca 120 000 11 600 cal yrs bp based on multi proxy reconstructions from lake sediments with robust chronologies and with a particular focus on abrupt climate changes the selected lake sequences provide an integrated approach from northern iberia exploring temperature conditions humidity variations and land sea comparisons during the most relevant climate transitions of the last glacial period thus we present evidence that demonstrates i cold but relatively humid conditions during the transition from mis 5 to mis 4 which prevailed until ca 60 000 cal yrs bp in northern iberia ii a general tendency towards greater aridity during mis 4 and mis 3 ca 60 000 to 23 500 cal yrs bp punctuated by abrupt climate changes related to heinrich events he iii a complex highly variable climate during mis 2 23 500 to 14 600 cal yrs bp with the mystery interval mi 18 500 to 14 600 cal yrs bp and not the global last glacial maximum lgm 23 000 to 19 000 cal yrs bp as the coldest and most arid period the last glacial transition starts in synchrony with greenland ice records at 14 600 cal yrs bp but the temperature increase was not so abrupt in the iberian records and the highest humidity was attained during the allerod gi 1a to gi 1c and not during the bolling gi 1e period the younger dryas event gs 1 is discernible in northern iberian lake records as a cold and dry interval although iberian vegetation records present a geographically variable signal for this interval perhaps related to vegetation resilience

palaeoecology of neanderthals during dansgaard oeschger cycles in northeastern iberia abric romani from regional to global scale abstract the sequence from abric romani has provided several palaeoecological studies this paper presents a synthesis of the results yielded by palynology including the data from the entire non excavated deposits and the data obtained through the study of large mammals micromammals herpetofauna and anthracology from the excavated layers the palaeobotanical studies show that the sequence is mainly related to pine forests and near or within these dominant forests there were smaller plant formations and or secondary species with a mediterranean and or atlantic character nevertheless continuous forest did not dominate the entire region the fauna occupying the territory indicate open spaces in which seasonal grasslands proliferated dry assemblages in sunny areas and humid ones in mountain shadows the non excavated archaeological layers correspond to mis 4 initially characterized by temperate and humid conditions and thereafter cool and humid until hs 6 and mis 3 afterwards at the beginning of the mis 3 the dansgaard oeschger cycles 1500 yr rapid and abrupt climatic changes occurred during the deposition of the archaeological levels o n m l k and j later these events were interrupted by a cold and dry phase between ca 49 and 47 ka bp which affected levels ja i and h culminating with hs 5 finally this cold episode was followed by the hengelo interstadial or do 12 characterized by a temperate and humid climate identified in levels e and d

inversion of sonobuoy data from shallow water sites with simulated annealing an enhanced simulated annealing algorithm is used to invert sparsely sampled seismic data collected with sonobuoys to obtain seafloor geoacoustic properties at two littoral marine environments as well as for a synthetic data set inversion of field data from a 750 m water depth site using a water gun sound source found a good solution which included a pronounced subbottom reflector after 6483 iterations over seven variables field data from a 250 m water depth site using an air gun source required 35 421 iterations for a good inversion solution because 30 variables had to be solved for including the shot to receiver offsets the sonobuoy derived compressional wave velocity depth vp z models compare favorably with vp z models derived from nearby high quality multichannel seismic data there are however substantial differences between seafloor reflection coefficients calculated from field models and seafloor reflection coefficients based on commonly used vp regression curves gradients reflection l

paleoenvironment and stratigraphy during the last glacial in the belgian dutch border region the weichselian deposits of the flat dutch belgian coversand area are characterized by highly varying facies types the geomorphological location and the role of water during the deposition and the transportation of the original eolian sediments may fully explain the texture and sedimentary structures of the lithostratigraphic units directly deposited eolian loams and sands on the dry interfluves contrast with the same but reworked sediments in wet valleys and depressions the formation of periglacial phenomena is also dependent on the geomorphologic lithologic and hydrologic conditions the occurrence of peaty beds is restricted to wet environments without precise climatic significance the pleniglacial sequence is subdivided into early and late pleniglacial stades both characterized by partial permafrost conditions interrupted by a middle pleniglacial interstadial complex with clearly milder conditions

neandertal extinction and the millennial scale climatic variability of ois 3 population models seeking climate as a triggering factor for the extinction of neandertals and the colonisation of europe by anatomically modern humans are contradictory due to uncertainties in the dating methods in the cultural attribution of archaeological layers and to the lack of terrestrial continuous and well dated palaeoclimatic sequences this is particularly the case for the iberian peninsula where neandertal populations seem to have survived later than in other regions of europe a review of the available palaeoclimatic evidence for ois3 of iberia reveals that this mainly consists of low resolution fragmentary ill dated and often ill interpreted records correlation between palaeoenvironmental sequences from two images pollen rich deep sea cores and archaeological data from western europe the electronic archive of the radiocarbon dates is available at qsr website http www elsevier nl locate quascirev indicates that aurignacian moderns colonised france and the north of iberia at the onset of the h4 event during this cold episode a probable contraction of neandertal populations is recorded in southern iberia where no aurignacian settlements are detected such a decline in population density is correlated with the particular desert steppe like environments made up of artemisia chenopodiaceae and ephedra characterising the h4 of this area while reducing the size of neandertal populations this inhospitable environment may have favoured their persistence in this region mainly exploiting herds of herbivores adapted to graminees rich grasslands the aurignacian moderns were probably not interested in colonising these arid mediterranean biotopes and did that only after the h4 event

geochronological position of badlands and geomorphological patterns in the guadix baza basin se spain abstract the guadix baza basin is one of a number of intramontane depressions located within the betic cordillera se spain where the geological and geomorphological evolution is controlled by tectonic activity the basin ceased to be closed after capture by the atlantic network when five main land systems developed late pleistocene geological evolution basically consisted of erosional modelling when badlands were deeply incised in highly erodible materials marls and silts three travertine platforms and several palaeolithic sites were used to determine that this main incision period fell within a 115 000 48 000 yr range there are few signs of geomorphological evolution of this basin in the last 48 000 yr based on these geomorphological data and soil development tectonic uplift of the basin probably played a secondary role in its evolution and climatic conditions in southern iberia in the 144 000 48 000 yr period were more humid and variable than later

magma evolution in the purico ignimbrite complex northern chile evidence for zoning of a dacitic magma by injection of rhyolitic melts following mafic recharge the 1 3 ma purico complex is part of an extensive neogene pleistocene ignimbrite province in the central andes like most other silicic complexes in the province purico is dominated by monotonous intermediate ash flow sheets and has volumetrically minor lava domes the purico ignimbrites total volume 80 100 km3 are divided into a lower purico ignimbrite lpi with two extensive flow units lpi i and lpi ii and a smaller upper purico ignimbrite upi unit crystal rich dacite is the dominant lithology in all the purico ignimbrites and in the lava domes it is essentially the only lithology present in the first lpi flow unit lpi i and in the upper purico ignimbrite but the lpi ii flow unit is unusual for its compositional diversity it constitutes a stratigraphic sequence with a basal fall out deposit containing rhyolitic pumice 68 74 wt sio2 overlain by ignimbrite with dominant crystal rich dacitic pumice 64 66 wt sio2 rare andesitic and banded pumice 60 61 wt sio2 are also present in the uppermost part of the flow unit the different compositional groups of pumice in lpi ii flow unit rhyolite andesite dacite have initial nd and sr isotopic compositions that are indistinguishable from each other and from the dominant dacitic pumice end 6 7 to 7 2 and 87sr 86sr 0 7085 0 7090 however two lines of evidence show that the andesite dacite and rhyolite pumices do not represent a simple fractionation series first melt inclusions trapped in sequential growth zones of zoned plagioclase grains in the rhyolite record fractionation trends in the melt that diverge from those shown by dacite samples second mineral equilibrium geothermometry reveals that dacites from all ignimbrite flow units and from the domes had relatively uniform and moderate pre eruptive temperatures 780 800 c whereas the rhyolites and andesites yield consistently higher temperatures 850 950 c hornblende geobarometry and pressure constraints from h2o and co2 contents in melt inclusions indicate upper crustal 4 8 km magma storage conditions the petrologic evidence from the lpi ii system thus indicates an anomalously zoned magma chamber with a rhyolitic cap that was hotter than and chemically unrelated to the underlying dacite we suggest that the hotter rhyolite and andesite magmas are both related to an episode of replenishment in the dacitic purico magma chamber rapid and effective crystal fractionation of the fresh andesite produced a hot rhyolitic melt whose low density and viscosity permitted ascent through the chamber without significant thermal and chemical equilibration with the resident dacite isotopic and compositional variations in the purico system are typical of those seen throughout the neogene ignimbrite complexes of the central andes these characteristics were generated at moderate crustal depths 30 km by crustal melting mixing and homogenization involving mantle derived basalts for the purico system assimilation of at least 30 mantle derived material is required

la pacana caldera and the atana ignimbrite a major ash flow and resurgent caldera complex in the andes of northern chile the recently discovered la pacana caldera 60 35 km is the largest caldera yet described in south america this resurgent caldera of pliocene age developed in a continental platemargin environment in a major province of ignimbrite volcanism in the central andes of northern chile at about 23 s latitude collapse of la pacana caldera was initiated by the eruption of about 900 km3 of the rhyodacitic atana ignimbrite the atana ignimbrite was erupted from a composite ring fracture system and formed at least four major ash flow tuff units that are separated locally by thin air fall and surge deposits all four sheets were emplaced in rapid succession about 4 1 0 4 ma ago caldera collapse was followed closely by resurgent doming of the caldera floor accompanied by early postcaldera eruptions of dacitic to rhyolitic lava domes along the ring fractures the resurgent dome is an elongated asymmetrical uplift 48 5 12 km which is broken by a complex system of normal faults locally forming a narrow discontinuous apical graben later postcaldera eruptions produced large andesitic and dacitic stratocones along the caldera margins and dacitic domes on the resurgent dome beginning about 3 5 ma ago and persisting into the quaternary hydrothermally altered rocks occur in the eroded cores of precaldera and postcaldera stratovolcanoes and along fractures in the resurgent dome but no ore deposits are known a few warm springs located in salars within the caldera moat appear to be vestiges of the caldera geothermal system

tectonics sedimentation and erosion in northern california submarine geomorphology and sediment preservation potential as a result of three competing processes abstract on the continental margin of northern california north of the mendocino triple junction the geomorphic grain varies dramatically between the coast and the toe of the accretionary wedge this grain represents the composite signature of three competing processes tectonics sedimentation and erosion all three are active across the region but their rates and orientations vary spatially and temporally affecting the resultant grain and preservation potential in this rapid sedimentation environment at the toe of the accretionary wedge the relative rate of tectonic deformation exceeds the rate of sediment accumulation and erosion is largely limited to areally restricted but at times large mass wasting features in this region isobaths representing the geomorphic grain are parallel to structural highs and lows as in most forearcs and sediment accumulation is restricted to small basins located between anticlinal ridges the slope between the shelf break and the accretionary complex shows the competing effects of sediment accumulation erosion and tectonism slope perpendicular gullies are the prominent erosional features in this area especially in the region surrounding the trinity submarine canyon anticlinal ridges crop out on the seafloor although the ridge crests decrease in bathymetric expression both up and down slope on the shelf the rate of sediment accumulation 6 12 mm yr exceeds the relative rate of tectonic deformation with 1 3 mm yr of active uplift on land in this region the geomorphic grain is controlled by sediment accumulation with compressed but continuous stratigraphic sections above anticlinal highs and expanded sections in actively subsiding regions

the last climatic cycle at la grande pile vosges france a new pollen profile a new pollen diagram has been made from an old unanalyzed core from la grande pile gp xx correlations with the previous work of woillard 1975 1978 leads to the following conclusions the end of the eemian was marked by a minor climatic change prior to the melisey i stadial the ognon ii and ognon iii interstadials are not consistent and correspond to the level of reworking of mesophilous taxa during the last pleniglacial the limitations of the botanical interpretation of pollen spectra from the last pleniglacial are underlined lastly bruckenthalia and larix are identified for the first time at la grande pile the respective roles of these taxa following the eemian are additional arguments for correlating the st germain i and ii with the early weichsel interstadials in the north of middle europe

probing the evolving andean lithosphere mid late tertiary magmatism in chile 29 30 30 s over the modern zone of subhorizontal subduction in the mid late tertiary 27 6 m y ago volcanism diminished then ceased in the main andean cordillera in chile between 29 and 30 30 s over the same time span the subduction angle shallowed under this region which today lies in the modern shallowly dipping nonvolcanic segment of the south central andes 28 33 s the trace and major element chemistry and mineralogy of the volcanic rocks in this region record the detailed pattern of lithospheric cooling and crustal thickening that accompany this major tectonic transition volcanic changes include in addition to a decreased rate of volcanism a decrease in the range of compositions from basaltic andesites to rhyolites in the oldest rocks to only rhyolite in the youngest rocks a change in source and fractionating mineralogy with an increased role for amphibole and garnet in the younger rocks and an increase in crustal assimilation these volcanic changes also correlate in time with deformational events that help to account for crustal thickening and the space time pattern of deformation and volcanism in the foreland region although the model stands alone support for the tectonic setting and magmatic source region of these tertiary volcanic rocks can be found in comparisons with recent volcanic rocks erupting over more steeply dipping modern andean segments the older dona ana formation 27 18 m y is similar to volcanic rocks in the southern volcanic zone while the younger cerro de las tortolas 14 10 m y and vallecito 6 m y formations are similar to volcanic rocks over regions of thicker crust in the central volcanic zone and the northern part of the southern volcanic zone

gas hydrates on the northern california continental margin the inner continental margin of northern california is underlain by a well defined and extensive acoustic reflector that crosses other reflectors and mimics the surface of the sea floor this bottom simulating reflector bsr lies at a typical subsurface depth of about 250 m and has been mapped continuously beneath the klamath plateau and upper slope water depths of 800 to 1200 m for a distance of more than 130 km it covers an area of at least 3000 km 2 limited data show that the bsr extends northward into oregon and seaward at least to the base of the slope 3000 m the water depths subsurface depths and pervasive nature of the bsr all suggest that it represents the base of a natural gas hydrate using standard phase boundary diagrams for hydrate stability we estimate the local geothermal gradient within the gas hydrate to be about 55 c km this value is higher than that of most subduction margins and may be a result of the youthfulness of the subducting oceanic crust this acoustically inferred gas hydrate is the first to be mapped on the western conterminous united states continental margin

pleistocene calcareous tufa from the ellera basin umbria central italy as a key for an integrated paleoenvironmental and tectonic reconstruction abstract continental carbonates calcareous tufa and associated deposits represent a natural archive of paleoenvironmental and tectonic information that can be fully disclosed only by the application of a multidisciplinary approach the aim of this paper is to describe the geological features of the ellera basin umbria central italy by integrating physical stratigraphy sedimentology geochemistry tectonics and biological paleontology palynology data the study of the ellera basin represents a starting point for the improvement of a methodology that could be applied to similar sedimentary systems regardless of their actual location extension and age two stratigraphic units were recognized in the ellera basin both characterized by multiple events of calcareous tufa deposition during the pleistocene in the lower san biagio unit the concurrent finding of hippopotamus h antiquus and leptobos remains associated with late villafranchian molluscs suggests an attribution to the early pleistocene tasso or farneta faunal unit about 1 8 1 5 ma both sedimentological and paleontological data indicate a periodically flooded alluvial plain depositional environment and isotopic values of 13c and 18o register the establishment of a wet paleoclimate the overlying santa sabina unit lies with an angular unconformity on the san biagio unit and was dated to 115 000 8000 years by the application of the u th method the age of the santa sabina unit falls within a period of warm and humid climate mis 5d e and paleoclimatic inferences are supported by the isotopic record 13c and 18o the unit deposited in a well vegetated fluvio lacustrine and fluvio palustrine environment locally dominated by herbaceous taxa as revealed by palynological analysis despite the 1 5 ma time lag between the two units their depositional evolution shared the presence of calcareous tufa whose deposition was controlled by similar paleoenvironmental and paleoclimatic conditions hot and humid interglacial conditions with high rainfalls characterized both periods as well as by the local tectonic setting and activity in both units the maximum thickness abundance of the calcareous tufa occurs at the intersection between two regional tectonic lineaments controlling both the basin subsidence and the ascent of co2 rich water

undrowning a lost world the marine isotope stage 3 landscape of gibraltar abstract the rock of gibraltar at the south western extreme of the iberian peninsula and 21 km from the north african coast is a 6 km long limestone peninsula which was inhabited by neanderthals from mis 5e until the end of mis 3 a total of 8 sites either with neanderthal fossils or their mousterian lithic technology have been discovered on the rock two gorham s and vanguard caves are the subject of ongoing research these caves are currently at sea level but during mis 3 faced an emerged coastal shelf with the shoreline as far as 5 km away at times they hold a unique archive of fauna and flora in the form of fossils charcoal and pollen helping environmental reconstruction of now submerged shelf landscapes in addition geological and geomorphological features a 300 metre dune complex elevated aeolian deposits raised beaches scree speleothems complement the biotic picture the work is further complemented by a study of the ecology of the species recorded at the site using present day observations the species composition in this fossil record closely matches the present day fauna and vegetation of the donana national park sw spain a mosaic of pine groves coastal dunes shrubland and seasonal wetlands and currently the richest reserve in terms of biodiversity in the iberian peninsula located only 100 km to the northwest from gibraltar all this information permits for the first time the quantification of the vegetation structure of the ancient coastal plain and the modelling of the spatio temporal dynamics of the mis 3 coastal shelf off gibraltar

subsurface gas offshore of northern california and its link to submarine geomorphology abstract the northern california continental margin contains evidence of abundant subsurface gas and numerous seafloor features that suggest a causative link between gas expulsion and geomorphology analyses of seismic reflection sidescan sonar and high resolution multibeam bathymetric data show that the occurrence of subbottom gas and the migration processes beneath the shelf differ from those beneath the slope subsurface gas inferred from enhanced reflectors and other geophysical indicators is spatially variable and related more to total depth and stratigraphy than to underlying structure with the exception of one band of gas that follows the regional structural trend shallow depressions on the seafloor pockmarks are used to infer expulsion sites the largest zone of acoustically impenetrable subsurface gas occurs between water depths of 100 m and 300 m where expulsion features are rare the upper slope water depths 400 600 m has a high concentration of pockmarks diameter 10 20 m in contrast to a near absence of pockmarks at water depths shallower than 400 m of nearly 4000 pockmarks observed on sidescan sonar records more than 95 are located in water depths deeper than 400 m bottom simulating reflectors bsrs on some seismic reflection profiles indicate the possible presence of gas hydrate we find that gas and pore fluid migration in the offshore eel river basin is 1 correlated to surface morphology 2 a contributor to seabed roughness 3 a significant mode of sediment redistribution on the upper slope and 4 potentially a factor in large slope failures

late quaternary fluvial dynamics of the jarama river in central spain the jarama river and its catchment provide a valuable natural archive to study and reconstruct past environmental conditions in central spain this region is highly prone to changes in the hydrological cycle under predicted climate warming in particular with respect to aridity periods rainfall variability and the occurrence of extreme flood events this paper presents 15 exposures covering a time span of the last 44 ka which were documented in the field and of which seven exposures were soil chemical analyzed regarding soil texture organic matter as well as carbonate and iron content ages are based on radiocarbon dating on 32 samples latest holocene sediments were found within the channel belt where permanent remobilization of sediments takes place due to the migration of the meandering river course in more distal floodplain positions sediment sequences show a complex fluvial architecture referring to periods of varying character and intensity of alluviation as well as periods of geomorphic stability indicated by soil formation furthermore sedimentation patterns vary along different river sections aggradations of coarse gravels took place between 40 and 18 ka cal bp over the entire valley floor alluviation of fine material was documented between 17 and 16 at 7 5 between 5 1 and 3 3 at 2 8 between 2 1 and 1 5 at 1 0 and around 0 4 ka cal bp until recent times astonishingly in late holocene times between 4 2 and 3 1 ka cal bp aggradations of coarse gravels even in distal floodplain areas overlap with sedimentation of fine material in adjacent river sections pointing to a complex constellation of parameters involved periods of soil formation were detected around 43 at 31 between 16 and 12 6 after 7 5 until 5 1 between 2 8 and 2 1 and at times after 1 5 ka cal bp phases of geomorphic stagnation were found at 38 ka cal bp and for a duration of 200 years at 3 0 ka cal bp and refer to absent geomorphic or pedogenic processes all these patterns are an expression of the interaction between climatic variations tectonic impulses and human influences a comparison with other terrestrial archives enabled us to reconstruct late pleistocene and holocene palaeoenvironmental conditions on a regional scale and furthermore to link specific stages of floodplain development to prevalent influencing variables thus with emphasis on the fluvial system response a model of a cause and effect relationship is presented that concentrates on rapid climate changes long lasting climatic deteriorations and the role of human interventions

estimating river sediment discharge to the ocean application to the eel margin northern california abstract hydrotrend a synthetic river discharge numerical model can simulate the natural variability daily annually and longer in the flux of water and sediment delivered to the coastal ocean the numerical model is designed to make discharge predictions based on climate even though field measurements of river flow are not available provided that appropriate assumptions are made regarding past climate the model can predict how a river may have behaved in the geological past sediment load is determined from a river s rating coefficients when applied to the flood dominated eel river northern california hydrotrend captures the intermonthly and interannual variability of discharge and loads over a century or more hydrotrend is applied to the ice age paleo eel river when sea level was lower and climate much cooler and wetter the paleo eel river at 18 000 year bp would see its hinterland runoff increase but not the magnitude of the peak discharges the post dicted sediment load of the paleo eel river was 25 greater than today s although basin precipitation was 45 greater and the hinterland area 4 greater through sea level lowering a method is provided to obtain sediment discharge rating coefficients for unmonitored modern rivers and paleo rivers the relationship q s g 1 2 h 3 2 a 1 2 provides for an estimate of a river s sediment load q s to within a factor of 3 over 7 orders of magnitude from knowledge of basin relief h and basin area a rating coefficients are determined from this estimate of q s and the power law rating curve q s aq b 1 where q is discharge

abrupt climatic changes during the last glaciation based on pollen analysis of the abric romani catalonia spain the abric romani continental pollen record provides evidence of abrupt climate variations during the last glaciation the pollen record reveals a pattern of high frequency variations similar to that in ice cores as shown by oxygen isotopes or dust content analyses of 14 travertine samples yield coherent u series ages in correct stratigraphic order ranging from 40 000 to 70 000 yr according to changes in the composition and structure of the vegetation five paleoclimatic phases have been differentiated the oldest ranging from 70 200 to 65 500 yr ago records thermophilous taxa which correspond to the last warm events of isotopic stage 5 the next phase from 65 500 to 56 800 yr records a cold humid climate that correlates with isotope stage 4 during the third phase from 56 800 to 49 500 yr relatively warm and cold events alternate the fourth phase from 49 500 to 46 200 yr records a cold dry climate the fifth phase ranging from 46 200 to 40 800 yr records a milder phase that is similar in appearance to the beginning of the holocene

lake banyoles northeastern spain a last glacial to holocene multi proxy study with regard to environmental variability and human occupation analyses of a 67 m long sediment core from lake banyoles northeastern spain have revealed evidence for the palaeoclimate history of the northern iberian peninsula investigations have included hi

the nature and distribution of upper cenozoic ignimbrite centres in the central andes abstract a wide variety of upper cenozoic ignimbrite centres have been identified and studied on landsat imagery of the central andes some have been investigated in the field lower miocene ignimbrite centres are distributed along an arc which in north chile diverges markedly from the line of the present trench and parallels an arc of lower miocene plutons in the eastern cordillera of bolivia much of the ignimbrite erupted since the late miocene has been erupted around the faulted margins of the altiplano basin of western bolivia particularly where the western and eastern cordilleras converge typical examples of ignimbrite centres are described some centres take the form of ignimbrite shield volcanoes other ignimbrite sheets are more widely dispersed the degree of dispersal probably relates to the height of the eruption column partial or total caldera formation sometimes took place and a few of these calderas have resurgent centres late stage lava extrusions are common and some of these are located on caldera ring fractures

upper pleistocene palaeoenvironmental change in eastern spain new pollen analytical data from cova beneito alicante abstract the results of a palynological investigation of the upper palaeolithic interval from the beneito cave southeastern spain are herewith considered in the context of results from a previous report on the underlying deposits two new percentage and concentration pollen diagrams with good correspondence are presented the upper palaeolithic sequence is dominated by poaceae chenopodiaceae and artemisia whereas arboreal pollen are less important mesophilous trees and mediterranean taxa show a constant presence but in low proportions the new data add support to the view that interpleniglacial development of mediterranean taxa was important in eastern spain while they were considerably reduced during upper pleniglacial times emphasis is placed on aridity as a limiting factor in influencing major vegetation changes in the area two additional topics are also presented they deal with the extrapolation of north european interstadials to mediterranean spain and the palaeoecological value of archaeopalynological records

formation of high grade ignimbrites part ii a pyroclastic suspension current model with implications also for low grade ignimbrites analogue experiments in part i led to the conclusion that pyroclastic flows depositing very high grade ignimbrite move as dilute suspension currents in the thermo fluid dynamical model developed the degree of cooling of expanded turbulent pyroclastic flows dynamically evolves in response to entrainment of air and mass loss to sedimentation initial conditions of the currents are derived from column collapse modeling for magmas with an initial h2o content of 1 3 wt erupting through circular vents and caldera ring fissures the flows spread either longitudinally or radially from source up to a runout distance that increases with higher mass flux but decreases with higher gas content temperature bottom slope and coarser initial grain size progressive dilution by entrainment and sedimentation causes pyroclastic currents to transform into buoyant ash plumes at the runout distance the ash plumes reach stratospheric heights and distribute 30 80 of the erupted material as widespread co ignimbrite ash pyroclastic suspension currents with initial mass fluxes of 107 1012 kg s can spread for tens of kilometers with only limited cooling although they move as supercritical strongly entraining currents for the eruption conditions considered here with increasing eruption mass flux cooling during passage through the fountain diminishes while cooling during flow transport increases the net effect is that eruption temperature exerts the prime control on emplacement temperature pyroclastic suspension currents can form welded ignimbrite across their entire extent if eruption temperature is to 1 3 tmw the minimum welding temperature high eruption rates a large fraction of fine ash and a ring fissure vent favor the formation of extensive high grade ignimbrite for very hot eruptions producing sticky partially molten pyroclasts analysis of particle aggregation systematics shows that factors favoring longer runout also favor more efficient aggregation which reduces runout as a result very high grade ignimbrites cannot spread more than a few tens of kilometers from their source in cooler pyroclastic currents particles do not aggregate and the sedimentation process may involve re entrainment of particles which potentially leads to more extensive cooling and longer runout such effects however are only significant when net erosion of substrate occurs model results can be employed to estimate mass flux and duration of ignimbrite eruptions from measured ignimbrite masses and aspect ratios the model also provides an alternative explanation of the observed decrease in h lratios with ignimbrite mass

role of plate kinematics and plate slip vector partitioning in continental magmatic arcs evidence from the cordillera blanca peru new structural and geochronological data from the cordillera blanca batholith in the peruvian andes coupled with nazca south american plate slip vector data indicate that oblique convergence and associated strike slip partitioning strongly influenced continental magmatic arc evolution both the strain field and mode of magmatism plutonism vs volcanism in the late miocene peruvian andes were controlled by the degree to which the arc parallel component of the plate slip vector was partitioned into the arc strong strike slip partitioning at ca 8 ma produced arc parallel sinistral shear strike slip intercordilleran basins and east west oriented tension fractures that facilitated emplacement of the cordillera blanca batholith ca 8 2 0 2 ma periods during which the strike slip component was not partitioned into the arc ca 10 and ca 7 ma were associated with roughly arc normal contraction and ignimbrite volcanism the data thus support the contention that contraction within continental magmatic arcs favors volcanism whereas transcurrent shear favors plutonism the tie between oblique convergence and batholith emplacement in late miocene peruvian andes provides a modern analogue for batholiths emplaced as the result of transcurrent shear in ancient arcs

evidence for holocene sea level and climate change from almenara marsh western mediterranean in the almenara marsh western mediterranean four cores were analyzed to establish the relationship between the marsh record of the almenara marshlands and the environmental factors responsible for its evolution during the holocene one hundred and eighty six samples were collected for sedimentologic and paleontological study 63 for biomarker analysis 5 for amino acid racemization aar dating and 5 for 14 c dating litho and biofacies analyses identified distinct paleoenvironments with the presence of a marsh environment alternating with inputs of alluvial material and marine sediments biomarkers indicated the constant presence of terrestrial herbaceous plants together with a variable development of aquatic macrophytes during the holocene transgression the almenara marsh was occupied by oligohaline marsh facies with an oscillating water level and peat formation which was established at the bottom of the record at 7570 cal yr bp and persisted until 3100 780 yr aar maximum surface flooding occurred at 5480 cal yr bp registered 450m from the current coastline at least three peat beds dated with 14 c dating and aar correlated with bond episode 5900 cal yr bp and wanner episodes 4800 4500 and 3300 3500 cal yr bp cycles and thus correspond to a regional model that affected the northern hemisphere

palynological approach in upper quaternary terrestrial carbonates of central italy anything but a mission impossible a palynological survey has been carried out on two late quaternary travertine s l deposits of central italy at serre di rapolano and bagnoli tuscany region the principal aim was to improve the understanding of factors that affect the accumulation and preservation of pollen grains in thermal i e travertine and ambient temperature i e calcareous tufa terrestrial carbonates for this purpose 52 526 pollen grains belonging to 118 pollen taxa from local to extra regional sources were analysed in 200 samples from different travertine and calcareous tufa lithofacies of these 97 samples generally from thermal travertines were barren in palynomorphs by contrast pollen grains in the remaining samples were well preserved and did not show differential preservation features these observations suggest that the ph of the solutions from which travertine or tufa precipitate is not a limiting factor in causing corrosion and or destruction of pollen grains rather the barrenness recorded in many samples appears to reflect a paucity of pollen rather than post depositional destruction results suggest that the depositional energy of the environment during the deposition of travertine plays an important role in controlling pollen concentration as verified in both depressions lower energy to higher pollen concentration and slopes higher energy to lower pollen concentration respectively analysis of pollen data suggests that relatively high depositional temperatures and rates of carbonate deposition are also major limiting factors for efficient accumulation of pollen grains results of this study reveal that understanding pollen taphonomy processes in travertine and calcareous tufa is critical to developing accurate palaeoenvironmental and palaeoclimatic reconstructions

late quaternary western mediterranean pollen records and african winds abstract late quaternary vegetation changes of regional and global significance in the mediterranean region are generally interpreted as being controlled by changes in the circulation patterns of north atlantic air masses however the possibility cannot be excluded that they may also be related to winds blowing from africa long pollen records from southwest europe show that cedrus pollen of northwest african provenance is found during the glacial periods and occasionally during abrupt deforestation events in the forest dominated periods of the interglacials a pollen concentration record from central italy shows that during the holocene the presence of cedrus pollen coincides with two abrupt deforestation events around 8 1 and 4 2 cal kyr bp these observations raise the question of a possible influence of eolian activity on arboreal vegetation during phases of climatic stress towards aridity and suggest the use of modern pollen monitoring as a strategy for revealing tendencies towards aridification in southwestern europe

delamination of southern puna lithosphere revealed by body wave attenuation tomography the southern puna plateau has been proposed to result from a major pliocene delamination event that has previously been inferred from geochemical geological and some preliminary geophysical data seventy five seismic stations were deployed across the southern puna plateau in 2007 2009 by scientists from the u s germany chile and argentina to test the delamination model for the region the puna passive seismic stations were located between 25 and 28 s using the seismic waveform data collected from the puna experiment we employ attenuation tomography methods to resolve both compressional and shear quality factors qp and qs respectively in the crust and uppermost mantle the images clearly show a high q nazca slab subducting eastward beneath the puna plateau and another high q block with a westward dip beneath the eastern cordillera we suggest that the latter is a piece of delaminated south american lithosphere a significant low q zone lies between the nazca slab and the south american lithosphere and extends southward from the northern margin of the seismic array at 25 s before vanishing around 27 5 s this low q zone extends farther west in the crust and uppermost mantle at the southern end of the seismic array the low q zone reaches 100 km depth beneath the northern part of the array but only 50 km depth in the south lateral variations of the low q zone reflect the possible mechanism conversion between mantle upwelling related to delamination and dehydration the depth of the nazca slab as defined by q images decreases from north to south beneath the plateau which is consistent with the steep flat transition of the angle of the subducting slab as defined by previous earthquake studies

a coastal reservoir of terrestrial resources for neanderthal populations in north eastern iberia palaeoenvironmental data inferred from the small vertebrate assemblage of cova del gegant sitges barcelona coastal areas as reservoirs of resources for hominid groups have been widely studied in recent years these areas combine marine with terrestrial and wetland resources and would have been optimum sites for hominids including neanderthals this is the case with the cova del gegant a cave that today opens directly onto the mediterranean sea and is located in the north eastern iberian peninsula the geomorphological evolution of the massis del garraf has provided evidence that during the late pleistocene there was a littoral platform between 8 and 13 km wide in front of the cova del gegant within this framework the data derived from analysis of the small vertebrates and large mammals recovered from cova del gegant including taxa currently absent from the massis del garraf suggest that the landscape surrounding the cave provided a richer terrestrial ecosystem for neanderthals than is available in this zone today analysis of the small vertebrate association from the cave reveals that the landscape surrounding the cave was dominated by woodland edge and open environments and that the climate was mediterranean the results have been compared with the only iberian site with similar characteristics to the cova del gegant gorham s cave southern iberia gibraltar revealing differences and similarities in the landscape and climate on the basis of the small mammal assemblages as well as the differences in the accessibility to terrestrial mammalian resources for the neanderthal groups the landscape and the climate were reasonably similar at the two sites but the differences in the accessibility of resources for the neanderthals are directly related to the location of the sites and the coastal position whereas the cova del gegant was on a route of mammal migration between the ebro valley and france suited for securing terrestrial resources gorham s cave is located on a small peninsula with a lower abundance of terrestrial mammal resources this is probably why the neanderthal groups at gorham s cave exploited marine resources whereas there is no evidence of marine resources having been exploited at cova del gegant even though the seashore was nearby copyright 2011 john wiley sons ltd

the timing of caldera collapse at mount katmai in response to magma withdrawal toward novarupta several thin layers of nonjuvenile lithic rich tephra from mount katmai are intercalated with 1912 plinian pumice fall deposits that originated at novarupta 10 km away demonstrating that caldera collapse at katmai and eruption at novarupta were synchronous emplaced by phreatic explosions and avalanche generated dustclouds each katmai derived layer is thickest and coarsest at the caldera rim and pinches out within 5 8 km in contrast thicknesses and clast sizes of plinian layers a g decrease radially away from novarupta the first katmai derived layer lies between novarupta derived layers b2 and b3 indicating that collapse began after release of 6 9 km of magma at novarupta the first major earthquake ms 6 5 at 2356 h on 6 june 11 hours after the eruption began may have marked the onset of collapse the katmai river landslide and several debris flow deposits are also sandwiched within the plinian deposits indicating that they too were emplaced during the eruption

pollen analysis of a long upper pleistocene continental sequence in a velay maar massif central france abstract a new 20 m sequence is presented which is based on 279 spectra derived from a coring at le bouchet lake massif central france the vegetational history of this region is described back to the end of the last interglacial ribains interglacial the two preglacial early glacial forested interstadials st geneys 1 and st geneys 2 are evidence for the first time in the massif central in spite of the altitude of the site 1200 m they suggest a quite temperate vegetation with the same mesophilous character as during the holocene the pleniglacial appears to be threefold with two cold episodes lower and upper pleniglacial divided by a long complex period of moderate climatic improvement the vegetation history of this mountain region is compared with that evidenced for the same period on the basis of the sequence of les echets at a lower altitude 267 m botanical and climatic inferences are discussed

terrasses de la riera dels canyars gava barcelona the landscape of heinrich stadial 4 north of the ebro frontier and implications for modern human dispersal into iberia abstract terrasses de la riera dels canyars is an upper pleistocene fluvial deposit containing the remains of large mammals principally accumulated in the framework of hyena denning in the area as well as a few artifacts radiocarbon dated to 39 6 ka cal bp the time of heinrich stadial hs 4 this site enables us to reconstruct the environmental conditions then prevalent in the ne of the iberian peninsula the concentration in a single locus of finds generated by different agents relates to a flash flood event the rapidity of which combined with the absence of archaeological ecological or paleontological incongruities in the composition of the assemblage warrants an assumption of broad contemporaneity for its contents the ecofactual evidence fauna pollen charcoal phytoliths indicates a steppe dominated environment for the coastal areas between the pyrenees and the ebro delta the dominant elements are cold and dry adapted species but a mediterranean component is present implying a less rigorous climate than farther north in europe the artifacts are clearly upper paleolithic and assignment to the modern human associated aurignacian technocomplex is supported by the radiocarbon dates and the typology of a bilaterally retouched blade this evidence is consistent with the notion that anatomical modernity spread across europe over open landscape niches available pollen data from deep sea cores indicate that during some of the interstadials of marine isotope stage mis 3 a significant vegetation gradient existed at 40 n broadly coincident with the ebro frontier temperate and warm temperate trees expanded significantly to the south while steppe tundra landscapes remained dominant to the north a contrast best seen during greenland interstadial gi 8 such an environmental boundary must have implied a durable barrier to diffusion and migration during interstadials under the cold and arid conditions of hs4 the site of canyars shows that the eurasian steppe tundra extended as far south as the llobregat delta however the environmental reconstructions available for the lower ebro valley and adjacent mountains of the iberian range farther south suggest that they formed at this time a belt of semi desert or steppe desert landscapes thus maintaining the boundary effect despite the climatic reversal the persistence of such a boundary through hs4 and the interstadials that bracket it must have played a role in the delayed arrival of the aurignacian and modern humans to southern and western iberia which continued to be settled by middle paleolithic neanderthals well beyond 40 ka cal bp

the generation of overpressure in felsic magma chambers by replenishment abstract evidence of magma mixing is common in the products of explosive felsic eruptions and it is generally accepted as a common mechanism for triggering such events in order to quantify the potential for magma mixing to trigger explosive eruptions we have developed a simple analytical model based on previous models of magma chamber replenishment which considers the injection of volatile rich mafic magma into a chamber occupied by a homogeneous volatile rich felsic magma we assume that the overpressure caused by the injection of new magma is not sufficient to trigger an eruption for which additional overpressure is required two mixing related mechanisms have traditionally been considered to have the potential to generate the additional overpressure 1 exsolution of volatiles from the felsic magma during forced convection and 2 exsolution of volatiles from the mafic magma by oversaturation during cooling and subsequent crystallization our calculations suggest that exsolution of volatiles from the felsic magma is not an effective mechanism to generate additional overpressure however significant overpressure can be achieved by volatile exsolution from the mafic magma during its cooling and crystallization the time scale between intrusion and eruption considered in our model is of the order of a few days to a few months which coincides with petrological and geophysical evidence obtained from magma mixing related eruptions we also suggest that replenishment of shallow felsic magma chambers by mafic magma in most cases does not lead to large scale mixing as eruption will occur before thermal equilibrium between the two magmas is reached so that density and viscosity contrasts between the two magmas will remain significant

the last interglacial ocean the final effort of the climap project was a study of the last interglaciation a time of minimum ice volume some 122 000 yr ago coincident with the substage 5e oxygen isotopic minimum based on detailed oxygen isotope analyses and biotic census counts in 52 cores across the world ocean last interglacial sea surface temperatures sst were compared with those today there are small sst departures in the mid latitude north atlantic warmer and the gulf of mexico cooler the eastern boundary currents of the south atlantic and pacific oceans are marked by large sst anomalies in individual cores but their interpretations are precluded by no analog problems and by discordancies among estimates from different biotic groups in general the last interglacial ocean was not significantly different from the modern ocean the relative sequencing of ice decay versus oceanic warming on the stage 6 5 oxygen isotopic transition and of ice growth versus oceanic cooling on the stage 5e 5d transition was also studied in most of the southern hemisphere the oceanic response marked by the biotic census counts preceded led the global ice volume response marked by the oxygen isotope signal by several thousand years the reverse pattern is evident in the north atlantic ocean and the gulf of mexico where the oceanic response lagged that of global ice volume by several thousand years as a result the very warm temperatures associated with the last interglaciation were regionally diachronous by several thousand years these regional lead lag relationships agree with those observed on other transitions and in long term phase relationships they cannot be explained simply as artifacts of bioturbational translations of the original signals

palaeoenvironmental and palaeoclimatic reconstruction of the latest pleistocene of l arbreda cave serinya girona northeastern iberia inferred from the small mammal insectivore and rodent assemblages abstract l arbreda cave is one of the southernmost of the reclau caves serinya girona northeastern iberian peninsula located between the west margin of the pla d usall and the serinyadell river at an altitude of about 211 m a s l the pla d usall forms part of the banyoles besalu basin which is bounded by eocene and neogene reliefs it is filled with sediments of plio pleistocene age the cave is a shelter formed by travertine cascades with a degree of karstification and contains sedimentary deposits ranging from the end of the middle pleistocene to the early holocene thus constituting an important archaeo palaeontological record for an understanding of the prehistoric occupation of northeastern iberia it is one of the most complete and best dated terrestrial sequences in iberia from the mousterian to the early holocene period in this paper we present a palaeoenvironmental and palaeoclimatic reconstruction of the sequence based on non flying small mammals insectivores and rodents and pollen analyses the environmental and climatic results together with the absolute dating of the sequence and direct comparison with northgrip 18 o and the sea surface temperatures sst of the alboran sea allow us to identify various climatic periods within our sequence a cold period between interstadials 12 and 10 in level i probably interstadial 10 in level h the last glacial maximum lgm in levels c and b the bolling allerod interstadial b a in level a and the preboreal boreal pr b in the terra rossa level

crustal thickness variations in the central andes we estimated the crustal thickness along an east west transect across the andes at lat 20 s and along a north south transect along the eastern edge of the altiplano from data recorded on two arrays of portable broadband seismic stations banjo and seda waveforms of deep regional events in the downgoing nazca slab and teleseismic earthquakes were processed to isolate the p to s converted phases from the moho in order to compute the crustal thickness we found crustal thickness variations of nearly 40 km across the andes maximum crustal thicknesses of 70 74 km under the western cordillera and the eastern cordillera thin to 32 38 km 200 km east of the andes in the chaco plain the central altiplano at 20 s has crustal thicknesses of 60 to 65 km the crust also appears to thicken from north 16 s 55 60 km to south 20 s 70 74 km along the eastern cordillera the subandean zone crust has intermediate thicknesses of 43 to 47 km crustal thickness predictions for the andes based on airy type isostatic behavior show remarkable overall correlation with observed crustal thickness in the regions of high elevation in contrast at the boundary between the eastern cordillera and the subandean zone and in the chaco plain the crust is thinner than predicted suggesting that the crust in these regions is supported in part by the flexural rigidity of a strong lithosphere with additional constraints we conclude that the observation of airy type isostasy is consistent with thickening associated with compressional shortening of a weak lithosphere squeezed between the stronger lithosphere of the subducting nazca plate and the cratonic lithosphere of the brazilian craton

vegetation dynamics during the last interglacial glacial cycle in the arno coastal plain tuscany western italy location of a new tree refuge abstract pollen analysis of the pre last glacial maximum succession of a 105 m long continuous core from tirrenia tuscany provides evidence for the existence of an area of relatively high ecological stability where the effects of climate change were mitigated the chronological framework of the vegetation record spanning the last interglacial glacial cycle was established by i ams 14c dating ii correlation with well dated pollen sequences and iii local stratigraphical constraints a high lithological and sedimentological variability with facies associations changing from fluvial to alluvial and coastal plain enhances the palaeoenvironmental control on pollen distribution thus helping to discriminate the impact of local factors on vegetation history the most remarkable evidence however is represented by the continuous record of temperate trees throughout the whole glacial period which provides useful indications on the location and nature of cold stage refugia most of the vegetation changes recorded in the core can be compared to the vegetation history of the last interglacial glacial cycle from southern europe as a whole in addition local geographic and environmental features account for a more complex and varied floristic composition only the last phase of the penultimate glacial mis6 which was characterized by the diffusion of an arid steppe tundra is recorded at the base of the core the subsequent last interglacial mis5e interval shows a poor and scattered pollen content due to the instability of the sedimentary environment nevertheless it provides evidence of both global and local controls on vegetation dynamics as indicated by the initial expansion of thermophilous forests and the remarkably late diffusion of conifers pinus abies picea forests respectively similarly the transition to the last glacial mis5b and 5a in the core is characterized by a reduced vegetation response to the typical stadial interstadial climate variability this is because the diffusion of a characteristic pioneer vegetation mainly represented by hippophae cf rhamnoides helped to confer to the local environment a high ecological stability buffering vegetation changes finally during the last glacial mixed broad leaved deciduous and pinus forests widely occupied the arno coastal plain demonstrating that this area acted as an important tree refuge local ecological conditions favourable to tree survival were determined mainly by i high precipitation as a function of orographic uplift of air charged with moisture from the nearby tyrrhenian sea ii mild temperatures which were also influenced by proximity to the sea and iii high topographic variability providing a series of suitable microenvironments

the age and origin of the younger dryas climate event in greenland ice cores 230th 234u and 14c dating of barbados corals has extended the calibration of 14c years b p to calendar years b p beyond the 9200 year tree ring series bard et al 1990 this now permits the conversion of 14c chronozones which delimit major climate shifts in western europe to calendar years the younger dryas chronozone defined as 11 000 to 10 000 14c years b p corresponds to 13 000 to 11 700 calendar years b p this calibration affects the interpretation of an intensely studied example of the younger dryas climate event the 18o anomaly between 1785 and 1793 m in dye 3 ice core the end of the 18o anomaly in dye 3 ice core has been dated by measurements of 14c in air bubbles andree et al 1984 1986 and by annual layer counting hammer et al 1986 the older 14c dates fall out of the range of the tree ring calibration series but can now be calibrated to calendar years using the barbados 230th 234u calibration the 14ccorrected age for the end of the 18o event is 10 300 400 calendar years b p compared to the annual layer counting age of 10 720 150 years b p thus the younger dryas event in the dye 3 ice core ends in the preboreal chronozone 11 700 to 10 000 calendar years b p and is not correlative with the end of the younger dryas event identified in pollen records marking european vegetation changes the end of the dye 3 18o event is however correlative with the end of meltwater pulse ib fairbanks 1989 marking a period of intense deglaciation with meltwater discharge rates exceeding 13 000 km yr

andean tectonics related to geometry of subducted nazca plate seismological and geological data show that tectonic segmentation of the andes coincides with segmentation of the subducted nazca plate which has nearly horizontal segments and 30 east dipping segments andean tectonics above a flat subducting segment between 28 s to 33 s are characterized by from west to east 1 a steady topographic rise from the coast to the crest of the andes 2 no significant quaternary and possibly neogene magmatism 3 a narrow belt of eastward migrating apparently thin skinned neogene to quaternary shortening of the andes and 4 plio pleistocene uplift of the crystalline basement on reverse faults in the pampeanas ranges from about 15 to 24 s over a 30 dipping subducted plate a west to east andes cross section includes 1 a longitudinal valley east of coastal mountains 2 an active neogene and holocene andesitic volcanic axis 3 the altiplano puna high plateau 4 a high neogene but inactive thrust belt eastern cordillera and 5 an active eastward migrating subandean thin skinned thrust belt tectonics above a steeply subducting segment south of 33 s are similar west of the volcanic axis but quite different to the east early cenozoic tectonics of western north america were quite similar to the neogene andes however duration of segmentation was longer and the width of deformation was greater in the western united states patterns of crustal seismicity are systematically related to plio quaternary structural provinces implying that current deformational processes have persisted since at least the pliocene horizontal compression parallel to the plate convergence direction is indicated to a distance of 800 km from the trench above flat subducting segments crustal seismicity occurs over a broad region whereas over steep segments it is confined to the narrow thrust belt strain patterns in the forearc region are complex and perhaps extensional and a broad region of the altiplano puna and eastern cordillera appears to be aseismic

the high sensitivity of the palynological record in the vico maar lacustrine sequence latium italy highlights the climatic gradient through europe for the last 90 ka the palynological study of the vice maar lacustrine sequence italy is realized from the correlation of three drillholes the time span covers a period from the end of oxygen isotope substage 5b till the beginning of stage 1 from ca 90 to ca 10 ka bp at the base of the pollen diagram pollen zone 0 a younger dryas like fluctuation is observed after pollen zone 1 which is a well developed forest period substage 5a the forests of pollen zones 3 and 5 correspond to extensive climate improvements these last two zones are correlated to the ognon complex of the grande pile france and to interstadial periods 20 and 19 defined in the grip ice core greenland 72 6 66 2 ka before the stage 5 4 transition these two interstadial periods are global events found in the greenland and antarctica ice sheets as well as in north atlantic marine cores in other pollen records from north of the alps changes have been recorded but they are less pronounced than in vico pollen zone 7 stage 3 shows ca 7 warm humid fluctuations that might have a link to the dansgaard oeschger events greenland during zone 9 the lateglacial interstadial is recorded as well as the younger dryas event the localization of vice near plant refugia and far from the ice cap enables its pollen diagram to record abrupt and intense response to climate changes possibly through a link to the atlantic ocean via westerly winds c 1996 elsevier science ltd

the incapillo caldera and dome complex 28 s central andes a stranded magma chamber over a dying arc abstract the plio pleistocene incapillo caldera and dome complex 5570 m is situated at the southernmost termination of the andean central volcanic zone 28 s where the more steeply dipping segment of the subducting nazca plate transitions into the chilean pampean flat slab to the south the 250 m high walls of the elliptical caldera 6 5 km are composed of a homogeneous pumice rich rhyodacitic ignimbrite that radiates 15 km from the caldera rim new biotite 40 ar 39 ar ages along with previous k ar ages reveal that the final eruption of the incapillo caldera occurred at 0 51 0 04 ma flanking the caldera are 40 steep sided rhyodacitic domes that predate the main caldera forming ignimbrite the morphology of these domes reflects the non explosive effusive eruption of a crystal rich gas poor rhyodacitic magma a volumetrically minor debris flow composed of abundant pumice dacites and lithic clasts is topographically confined to a glacial valley south of the caldera and unconformably overlies the ignimbrite mixed pumices at the distal end of the ignimbrite reflect the convective physical condition within the magma chamber immediately prior to the pyroclastic eruption including the domes and ignimbrite the total estimated volume of erupted incapillo magma is 37 km 3 based on its age small size and effusive eruptive style the incapillo caldera and dome complex provides an endmember model for an andean caldera erupting within a waning magmatic arc over a shallowing subduction zone

a 50 000 year record of climate oscillations from florida and its temporal correlation with the heinrich events oscillations of pinus pine pollen in a 50 000 year sequence from lake tulane florida indicate that there were major vegetation shifts during the last glacial cycle episodes of abundant pinus populations indicate a climate that was more wet than intervening phases dominated by quercus oak and ambrosia type ragweed and marsh elder the pinus episodes seem to be temporally correlated with the north atlantic heinrich events which were massive periodic advances of ice streams from the eastern margin of the laurentide ice sheet possible links between the tulane pinus and heinrich events include hemispheric cooling the influences of mississippi meltwater on sea surface temperatures in the gulf of mexico and the effects of north atlantic thermohaline circulation on currents in the gulf

paleoenvironmental context of neanderthal occupations in northeastern iberia the small mammal assemblage from abric romani capellades barcelona spain the abric romani site capellades barcelona spain constitutes a key site for understanding the latest neanderthal occupations in western europe here we present a comprehensive systematic and taphonomic analysis of a small mammal assemblage from level o of the abric romani site with the aim of reconstructing the paleoecological context in which the neanderthals lived the assemblage which probably dates from a stadial episode between interstadial 15 and interstadial 14 contains fifteen small mammal species including species uncommon for the northeast of iberia such as sciurus vulgaris nyctalus lasiopterus and pipistrellus pipistrellus taphonomic studies suggest a predatory origin for the assemblage probably related to strix aluco and paleoecological inferences suggest lower temperatures 3 4 c and higher rainfall 70 170 mm than at present and a landscape dominated by an open forest with watercourses the new data improve our knowledge of trends associated with marine isotope stage 3 that affected neanderthal populations in the iberian peninsula showing that the neanderthals were well adapted to cooler and wetter conditions across iberia

biostratigraphy of the last glacial period in europe the european early weichselian early wurmian is characterized by two long and relatively warm interstadials brorup and odderade which can be traced and correlated with certainty across large parts of europe the amersfoort interstadial described earlier from the netherlands has been included in the brorup and represents the older part of it both great interstadials were forested in north west central and southern europe in the north conifer forests prevailed giving way towards the south to deciduous forests the climatic gradient was distinctly steeper mainly due to southward displacement of the gulf stream the two great interstadials are synchronous with the isotopic stages 5a and 5c in the deep sea cores subsequent to eemian brorup and odderade and from within the context of a continuous series two additional and clearly delimited interstadials have been recorded in a new standard profile from oerel nw germany these are now described as the oerel and glinde interstadials they were not forested and belong to the early pleni weichselian the lower one oerel can probably be correlated with the 3rd weichselian wurmian interstadial in southern central europe ognon ii durnten samerberg 3 while the upper one glinde has so far no known counterpart for the younger pleni glacial it is assumed that there was a long phase during which it was not too cold the formation of humic layers during this phase took place at different times partly due to local edaphic factors so that the relevant 14c dates show a wide scatter the hengelo and denekamp interstadials represent only slight ameliorations which facilitated the formation of shrub tundra and can be recorded in certain regions only

the holocene and upper pleistocene pollen record from padul granada spain a new study two borings were made at the site of padul granada pollen analysis of 200 spectra from two successive sequences 14 8 and 8 m deep enables a description of the vegetational and climatic history of this region the most southern one in europe from early wurmian times the chronology is supported by twenty one 14c dates original equivalents are found for the great european prewurm interstadials a markedly arid though thermically not extreme episode exactly equivalent to stage 4 of the marine isotopic stratigraphy closes this relatively temperate period the middle part of the last glacial shows climatic fluctuations that are poorly characterized as is often the case in europe for this period a long section very probably corresponding to the complete last pleniglacial does not show any climatic amelioration towards 15 000 yr b p a change in the diagram is noted that can only be interpreted as reflecting a larger expansion of a regional steppe cover this event also reported on three occasions in southeast france marks the beginning of the oldest dryas the climatic amelioration of ca 13 000 yr b p is far more pronounced here than anywhere else in europe whereas that at 10 000 yr b p is not so clearly marked this unexpected result may be accounted for by the fact that padul is the first continental site so far south and so near pleniglacial refuges to be known on the other hand this result is consistent with what is known from oceanic isotopic stratigraphy a quite new late glacial and holocene vegetational history is revealed characterized by the early appearance and dominance of quercus ilex oak forests of a southern type and the early occurrence of quercus suber and olea it is the first account of a complete history of the postglacial reafforestation in a region with a modern semi arid mediterranean climate from the palaeoclimatic point of view it shows that the hot and humid holocene optimum was attained slightly before 8000 yr b p and that the holocene climatic fluctuations were of but small amplitude

strataform overview of its design and synthesis of its results abstract the strata formed on continental margins record the history of both marine and terrestrial events occurring on earth the strataform program was created to develop a better understanding of relationships between these events and margin stratigraphy in order to obtain the maximum information from strata they are being examined simultaneously on various temporal and spatial scales and their formation is being studied where events and accumulation are known to be active the general objectives of strataform are to add geological perspective to studies of sedimentary processes to constrain stratigraphic interpretations better and to develop numerical models relating processes and stratigraphy this research is being undertaken on margins off northern california and new jersey which provide unique opportunities for investigation of short term and long term stratigraphy respectively this volume and paper focus upon studies undertaken off northern california north of cape mendocino this area is tectonically active with a coastal mountain range narrow shelf and input of sediment primarily from the eel river recent estimates indicate that 1 to 3 10 7 t yr of mud silt and clay are supplied to the continental shelf sand accumulates on the inner shelf 70 reaches the continental slope or deeper during the previous lowstand of sea level sediment discharge was 25 greater and probably led to hyperpycnal debris and other flows transporting sediment down the slope on the eel shelf flood and storm events combine to create normally stratified fine grained layers with basal sand and much terrestrial organic debris these layers are modified through time but some can be buried and preserved subsurface flood layers seem to impact observations of acoustic backscatter on the middle shelf and subsurface fluids gas freshwater affect electromagnetic measurements on the inner shelf budgets of eel river mud accumulation for the past century indicate 20 trapped on the adjacent shelf and 20 on the upper slope 150 600 m the remaining 60 is dispersed to more distal locations over holocene time scales eel river sediment has built a small sandy subaqueous delta and a subtle bulge of muddy sediment on the middle shelf north of the river gullies have been eroded on the open slope during lowstands of sea level and have accreted upward during highstands a massive failure has formed the humboldt slide due to earthquake activity and unstable substrates possibly from excess pore pressures and gas the tectonic setting has impacted margin stratigraphy from small scales fluid expulsion pockmarks to large scales spatial variation of late cenozoic sedimentation the broad dispersal of eel sediment demonstrates the three dimensional character of the resulting stratigraphy including the large scale clinoform structure developed on the shelf upper slope the rollover point topset foreset boundary for this feature is the shelf break i e below sea level which is important information for stratigraphic interpretations of sea level change

recent contributions to the climatology of the last glacial interglacial cycle based on french pollen sequences abstract new pollen data derived from three long french sequences and methodological improvements in the methods used to reconstruct past climates are summarized here after a short presentation of the study sites and pollen diagrams estimated climate parameters during the major episodes of the last 140 000 years are shown to be coherent between sites analysis of the seasonality variations provides much additional information in particular it is shown that the advection from the ocean has governed the last climatic cycle on the european continent

river response to high frequency climate oscillations in southern europe over the past 200 k y a 200 k y chronology of river response to climate related environmental change has been established for northeast spain using newly developed luminescence dating techniques this constitutes the best documented record of late quaternary river behavior currently available for the north atlantic region and enables fluvial stratigraphies to be compared with high resolution ice core and marine oxygen isotope climate series pleistocene and holocene river aggradational episodes coincide with stadial or neoglacial events while phases of river incision occur during interstadial or interglacial periods alluviation and erosion cycles would appear to track variations in sediment supply controlled by vegetation cover and winter storm frequency

identification of arid phases during the last 50 cal ka bp from the fuentillejo maar lacustrine record campo de calatrava volcanic field spain geochemical element analysis molecular analysis of organic compounds physical palynological mineralogical and sedimentary facies analysis were performed to characterise the sedimentary record in fuentillejo maar lake in the central spanish volcanic field of campo de calatrava in order to reconstruct the palaeoenvironmental and palaeoclimatic processes which controlled vegetation patterns and deposition of different sedimentary facies the upper 20 m of core fuent 1 show variations in clastic input water chemistry vegetation and organic fraction sources in the lake throughout the late pleistocene and holocene the temporal framework provided by 14c accelerator mass spectrometry dating allows assigning the sequence to the last 50 cal ka bp arid phases identified in the fuent 1 sequence are correlated to heinrich events he and to stadials of the dansgaard oeschger d o cycles siliciclastic facies with high magnetic susceptibility values high juniperus pollen content a low paq index aquatic macrophysics proxy index a decrease in the relative percentage of the n c27 and an increase in the n c31 alkanes are indicative of arid and colder climatic events related to he 2 he 1 and the younger dryas yd similar short cold and arid phases during the holocene were identified at 9 2 8 6 7 5 7 and 5 5 5 cal ka bp in dolomite mud facies the pollen data show an increase in the herbs component mainly chenopodiaceae artemisia and ephedra steppe taxa a low paq index a decrease in the relative percentage of the n c27 alkane and an increase in the n c31 alkane are also observed this facies was probably the result of lower lake levels and more saline alkaline conditions which can be interpreted as linked to arid warm periods these warm and arid phases were more frequent during marine isotope stage mis 3 and the interstadials of mis 2 he 4 he 2 he 1 and the yd in core fuent 1 were immediately followed by increases of warm steppe pollen assemblages that document rapid warming similar to the d o cycles but do not imply increasing humidity in the area fuentillejo hydrology is controlled by changes in the atmospheric and oceanic systems that operated on the north atlantic region at millennial scale during the last 50 cal ka bp copyright 2009 john wiley sons ltd

central andean mantle and crustal seismicity beneath the southern puna plateau and the northern margin of the chilean pampean flat slab earthquake hypocenters recorded in the andean southern puna seismic array 25 28 s 70 65 w provide new constraints on the shape of the subducting nazca plate beneath the puna plateau the transition into the chilean pampean flat slab and the thermal state of the mantle and crust some 270 new mantle hypocenters suggest that the subducting slab under the puna shoals into the flat slab segment more abruptly and farther to the north than previously indicated the revised geometry is consistent with the central volcanic zone incapillo caldera being the southernmost center with pleistocene activity until reaching the southern side of the flat slab region evidence for the revised slab geometry includes three well defined hypocenter clusters in the pipanaco nest 27 5 29 s 68 66 w which are interpreted to reflect slab bending stresses a few low magnitude earthquakes with strongly attenuated s waves in the long recognized antofalla teleseismic gap 25 5 27 5 s support a continuous slab under the southern puna the paucity of gap earthquakes and the presence of mafic magmas are consistent with a hot mantle wedge reflecting recent lithospheric delamination evidence for a hot overlaying puna crust comes from new crustal earthquake hypocenters concentrated at depths shallower than 5 km two notable short duration swarms were recorded under the resurgent dome of the 2 ma back arc cerro galan caldera and the near arc cerro torta dome new crustal earthquake focal mechanisms from 17 events in the array along with two existing mechanisms have strike slip oblique reverse and oblique normal solutions fitting with regional e w compression and n s extension

tyrrhenian sea tephrochronology of the oxygen isotope record for the past 60 000 years abstract a chronology of the marine oxygen isotope record of the past 60 ka is proposed by correlating eight marine ash layers with terrestrial volcanic deposits dated by the 14c and or k ar methods detailed oxygen isotope analyses were made on the planktonic foraminifera of three cores collected in the central tyrrhenian sea the origin of the ash layers was determined by major and trace elements analyses then the major pyroclastic terrestrial deposits were sampled and analysed in order to provide land sea correlations two ash layers occurred during the warm event that followed the first step of the deglaciation and which was dated at 12 6 0 5 ka b p another ash layer is present near the last glacial maximum that we have dated at 17 5 0 3 ka b p during isotopic stage 3 five ash layers were recognized and dated which allowed us to assign ages to the isotopically light oxygen peaks warmer interstadials at 31 1 5 ka and 33 4 1 6 ka denekamp at 37 5 2 ka hengelo and successively at 49 2 ka 52 4 2 2 ka 57 2 2 ka and 60 5 2 2 ka moershoofd complex

thermogenic hydrocarbons in unconsolidated sediment of eel river basin offshore northern california thermally produced hydrocarbons were recovered from unconsolidated sediment ponded within a bathymetric depression on the surface of a shale diapir in the offshore eel river basin of northern california evidence that the hydrocarbons are thermogenic consists of the following 1 very high concentrations of hydrocarbon gases particularly ethane through butanes c2 c4 2 methane having a carbon isotopic composition relative to the pdb standard of 43 and 44 per mil 3 presence of gasoline range c5 hydrocarbons and 4 presence of a complex mixture of heavy hydrocarbons c15 with n alkanes having a petroleumlike distribution this mixture of gaseous and liquid hydrocarbons likely originated deep within the basin an migrated to the surface through fractures and faults developed during the emplacement of the diapir the presence of thermogenic hydrocarbons in unconsolidated surface sediment indicates that conditions for petroleum generation have existed within this offshore basin

observations of gas hydrates in marine sediments offshore northern california biogenic gas hydrates were recovered in shallow cores 6 m deep from the eel river basin in offshore northern california between 40 38 and 40 56 n the gas hydrates contained primarily methane 13c 57 6 to 69 1 and occurred as dispersed crystals small 2 20 mm nodules and layered bands within the sediment these hydrates recovered in sediment at water depths between 510 and 642 m coincide nearly but not exactly with areas showing bottom simulating reflectors bsrs on seismic reflection records this study confirms indirect geophysical and geologic observations that gas hydrates are present north of the mendocino fracture zone in sediment of the eel river basin but probably are absent to the south in the point arena basin this discovery extends the confirmed sites of gas hydrates in the eastern pacific region beyond the peruvian and central american margins to the northern california margin

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

the formation of high grade ignimbrites i experiments on high and low concentration transport systems containing sticky particles high grade ignimbrites are thought to be deposited by pyroclastic flows at temperatures exceeding minimum welding temperature or even solidus temperature corresponding pyroclastic flow particles range from plastic to partially liquid and are able to aggregate or coalesce this contrasts with particles in pyroclastic flows producing unwelded ignimbrite which are capable of elastic grain interactions the low aspect ratio and great areal extent of high grade ignimbrites requires transport in a particulate state either by a high concentration mass flow facilitated by fluidizing gas reducing internal friction or by b expanded turbulent flow of low but downward increasing concentration this paper presents experiments designed to investigate the effects of plastic to liquid particles on these two contrasting transport mechanisms gas fluidization experiments using polyethyleneglycole peg powders heated above minimum sintering tms and melting tm temperatures cover a wide range of fluidization velocities umf ua 0 6 ut but are always in the bubbly fluidization regime similar to fluidized ignimbrite ash where particle volume concentration outside the bubbles is high 10 1 when the powders reach a critical temperature tm t tms defluidization by catastrophic particle aggregation immediately commences in both stationary and laterally moving fluidized beds as well as in experiments using mixtures of high and low tm 30 wt peg powders when t tms of the lower tm powder this indicates that extended particulate transport at t tms is not possible at such high particle concentrations in the turbulent flow experiments liquid sprays of molten peg or water vertically injected into a high re 104 horizontal air flow form a low concentration 10 5 to 10 4 turbulent suspension current proximal formation of partially coalesced aggregates which settle faster than individual particles causes the measured downstream decay of sedimentation rate to be steeper than predicted by theory of single solid particle sedimentation from turbulent suspensions as particles become finer downstream and coalescence efficiency decreases in response to cooling more distally formed aggregates become too small and rare to modify sedimentation rate decay from that of suspension flows containing solid particles the key difference between the two transport systems is particle concentration c since particle collision rate rcoll c2 collision rates in fluidized beds are so high that all particles immediately aggregate when coalescence efficiency 1 ecoal 0 is larger than 10 3 low concentration suspensions on the other hand require much higher values of ecoal for significant aggregation to occur dilute pyroclastic flows will have higher particle volume fractions 10 3 than the experimental currents but then viscous pyroclasts should have lower coalescence efficiencies than peg droplets experimental results thus support an expanded turbulent transport mechanism of pyroclastic flows generating extensive high grade ignimbrite sheets

magma sources and tectonic setting of central andean andesites 25 5 28 s related to crustal thickening forearc subduction erosion and delamination