millennial scale sea surface temperature and patagonian ice sheet changes off southernmost chile 53 s over the past 60 kyr 1 glacial millennial scale paleoceanographic changes in the southeast pacific and the adjacent southern ocean are poorly known due to the scarcity of well dated and high resolution sediment records here we present new surface water records from sediment core md07 3128 recovered at 53 s off the pacific entrance of the strait of magellan the alkenone derived sea surface temperature sst record reveals a very strong warming of ca 8 c over the last termination and substantial millennial scale variability in the glacial section largely consistent with our planktonic foraminifera oxygen isotope 18o record of neogloboquadrina pachyderma sin the timing and structure of the termination and some of the millennial scale sst fluctuations are very similar to those observed in the well dated sst record from odp site 1233 41 s and the temperature record from drowning maud land antarctic ice core supporting the hemispheric wide antarctic timing of sst changes however differences in our new sst record are also found including a long term warming trend over marine isotope stage mis 3 followed by a cooling toward the last glacial maximum lgm we suggest that these differences reflect regional cooling related to the proximal location of the southern patagonian ice sheet and related meltwater supply at least during the lgm consistent with the fact that no longer sst cooling trend is observed in odp site 1233 or any sst chilean record this proximal ice sheet location is documented by generally higher contents of ice rafted debris ird and tetra unsaturated alkenones and a slight trend toward lighter planktonic 18o during late mis 3 and mis 2

erosional and climatic effects on long term chemical weathering rates in granitic landscapes spanning diverse climate regimes abstract we used cosmogenic nuclide and geochemical mass balance methods to measure long term rates of chemical weathering and total denudation in granitic landscapes in diverse climatic regimes our 42 study sites encompass widely varying climatic and erosional regimes with mean annual temperatures ranging from 2 to 25 c average precipitation ranging from 22 to 420 cm year 1 and denudation rates ranging from 23 to 755 t km 2 year 1 long term chemical weathering rates range from 0 to 173 t km 2 year 1 in several cases exceeding the highest granitic weathering rates on record from previous work chemical weathering rates are highest at the sites with rapid denudation rates consistent with strong coupling between rates of chemical weathering and mineral supply from breakdown of rock a simple empirical relationship based on temperature precipitation and long term denudation rates explains 89 95 of the variation in long term weathering rates across our network of sites our analysis shows that for a given precipitation and temperature chemical weathering rates increase proportionally with fresh material supply rates we refer to this as supply limited weathering in which fresh material is chemically depleted to roughly the same degree regardless of its rate of supply from breakdown of rock the temperature sensitivity of chemical weathering rates is two to four times smaller than what one would expect from laboratory measurements of activation energies for feldspar weathering and previous inter comparisons of catchment mass balance data from the field our results suggest that climate change feedbacks between temperature and silicate weathering rates may be weaker than previously thought at least in actively eroding unglaciated terrain similar to our study sites to the extent that chemical weathering rates are supply limited in mountainous landscapes factors that regulate rates of mineral supply from erosion such as tectonic uplift may lead to significant fluctuations in global climate over the long term

holocene rainfall variability in southern chile a marine record of latitudinal shifts of the southern westerlies geochemical and clay mineral parameters of a high accumulation marine sediment core from the chilean continental slope 41 s provide a 7700 yr record of rainfall variability in southern chile related to the position of the southern westerlies we especially use the iron content measured with a time resolution of ca 10 yr on average of 14 caccelerator mass spectrometry dated marine sediments as a proxy for the relative input of iron poor coastal range and iron rich andean source rocks variations in this input are most likely induced by rainfall changes in the continental hinterland of the core position based on these interpretations we find a pronounced rainfall variability on multicentennial to millennial time scales superimposed on generally more arid conditions during the middle holocene 7700 to 4000 cal yr b p compared to the late holocene 4000 to present this variability and thus changes in the position of the southern westerlies are first compared to regional terrestrial paleoclimate data sets from central and southern chile in order to derive possible wider implications and forcing mechanisms of the holocene latitudinal shifts of the southern westerlies we then compare our data to ice core records from both tropical south america and coastal antarctica these records show similar bands of variability centered at ca 900 and 1500 yr comparisons of band pass filters suggest a close connection of shifts of the southern westerlies to changes within the tropical climate system the correlation to climate conditions in coastal antarctica shows a more complicated picture with a phase shift at the beginning of the late holocene coinciding with the onset of the modern state of el nin o southern oscillation system the presented data provide further evidence that the well known millennial scale climate variability during the last glacial continued throughout the holocene fl 2001 elsevier science b v all rights reserved

denudation rates and a topography driven rainfall threshold in northern chile multiple cosmogenic nuclide data and sediment yield budgets abstract the quantification of geomorphic process rates on the outcrop and the orogen scale is important to describe accurately the interaction between the relative effects of erosion tectonics and climate on landscape evolution we report single and paired cosmogenic nuclide 10 be 26 al and 21 ne derived erosion rates and exposure ages on hillslope interfluves from the tectonically active western central andes that show a distinct spatial variation a positive correlation of erosion rates with elevation and present day rainfall rates is observed erosion rates at lower altitudes the hyperarid coastal cordillera and the western escarpment with the northern part of the atacama desert are extremely low and of the order of 10 100 cm my nominal exposure ages 1 6 my in contrast erosion rates at higher altitudes the semiarid western cordillera range up to 4600 cm my nominal exposure ages 0 02 0 1 my this latter average long term bedrock erosion rate record suggested to be coupled to an orographically controlled pattern of rainfall is also reflected in the pattern of denudation rates derived from a short term decadal record of limited sediment yield data specifically denudation rates calculated from sediment flux data are of a similar order of magnitude as erosion rates deduced from long lived cosmogenic nuclides from bedrock hillslope interfluves of the western cordillera nevertheless the production and the supply of sediment from the western andean slope are very limited analysis of multiple cosmogenic nuclides allows simultaneous determination of erosion rates and exposure ages but also reveals complex exposure histories of non bedrock samples such as boulders or amalgamated clast samples notably this study shows that saturation of nuclides usually assumed in studies where only a single nuclide is analyzed is rather the exception than the rule as revealed by erosion island plots constant erosion that started much later than the formation age of the rocks or episodic erosion by spalling can partially explain non steady state concentrations and more complicated exposure scenarios furthermore the use of multiple nuclides with different half lives allowed us to infer that no significant variations in long term erosion rates have occurred and that at the western escarpment erosion rates have been low and constant for most of the late neogene nevertheless the time intervals necessary to reach steady state concentrations for cosmogenic nuclides can be quite different from those needed for landscapes to reach steady state

the last glaciation in central magellan strait southernmost chile abstract glacial landforms and drift stratigraphy in central magellan strait southernmost chile document repeated fluctuations during the last glacial cycle of outlet lobes from an ice cap centered over the southern andes the lobes developed comparatively low gradient profiles because of low basal shear stresses over soft deformable beds and this made them sensitive to even small scale changes in the mass balance such low profiles and rapid calving in deep proglacial lakes during deglaciation may have made the magellan ice lobe particularly responsive to climatic fluctuations during the last glacial cycle and to advance and retreat over considerable distances study of the glacial landforms and drift stratigraphy has led to the identification of at least five glacier advances to limits at and south of the segunda angostura fragments of mollusc shells contained in basal till indicate marine incursions between some advances thus documenting extensive deglaciation a partial chronology based on amino acid studies and radiocarbon dating suggests that five of these advances occurred during the last glacial cycle the most extensive advances may have culminated during substages of marine isotope stage 5 substage 5b or 5d and or during stage 4 slightly less extensive advances occurred between ca 28 000 and 14 000 yr b p

a 56 million year rhythm in north american sedimentation during the phanerozoic abstract long term 10 myr fluctuations in climate sea level and sedimentation have been documented in the stratigraphic record but the lack of well constrained data series has made it difficult to rigorously evaluate cyclic periodic or quasi periodic changes at this scale here we utilize a new compilation of the coverage area of sedimentary rocks in north america to investigate the dominant modes orders of stratigraphic variability and to evaluate potential long period cyclic changes in sedimentation on the continent during the phanerozoic our analysis resolves two principal temporal modes of variability 1 a strongly sinusoidal mode with a periodicity of 56 myr 3 myr and 2 a longer term phanerozoic mode the m curve linked to the wilson cycle which is indistinguishable from a stochastic autoregressive process the newly identified 56 myr cycle in sedimentation delineates most of the cratonic sequences that have previously been identified qualitatively in north america but here we propose a quantitative redefinition that includes nine distinct units and two mega sequences the timing of the 56 myr beat in sedimentation is consistent with an orogenic oscillator source or an oscillatory dynamic in mantle convection and its tempo is statistically similar to a known rhythm in number of marine animal genera in the global fossil record thus the identification of a significant periodic signal in the sedimentary record of north america provides new evidence for an important tectonic and or mantle scale cyclic process that links both large scale biological evolution and physical environmental change

structural tectonic and glaciological controls on the evolution of fjord landscapes abstract the fjord landscape of south america stretching 1500 km between golfo corcovado 43 s and tierra del fuego 56 s is the largest continuous fjord landscape on earth this paper presents the results of new structural geological and geomorphological mapping of this landscape using optical satellite images and digital elevation models first order geological structures are represented by strike slip faults forming lineaments up to hundreds of kilometres long the strike slip faulting has been active since late cretaceous times and is responsible for the presence of a conspicuous structural cleavage visible as lineaments up to 10 km long a detailed analysis of these second order lineaments from digital image data was carried out in three sectors in sector 1 located northwest of the north patagonian icefield there are three distinct mean orientations characterized by a main nearly orogen parallel orientation az 145 and two orogen oblique secondary orientations az 20 and az 65 in sector 2 located west of the south patagonian icefield there are also three separate mean orientations with most of the lineaments concentrated between azimuths 0 and 80 mean at 36 and two other orogen oblique means at azimuth 122 and 163 in sector 3 around the cordillera darwin there is a single main orogen parallel mean at 100 115 in all three sectors mapped fjord orientations bear a striking similarity to the structural data with fjords orientated preferentially in the same direction as structural lineaments we infer that successive glaciations followed the same ice discharge routes widening and deepening pre existing geological structures at the expense of the surrounding terrain to create the fjord landscape this study has broader implications for ice sheet reconstructions and landscape evolution beneath ice sheets because we demonstrate that the primary control on fjord development in glaciated areas is geological and not glaciological

construction of the cambrian and ordovician seawater 87sr 86sr curve abstract the estimated path of seawater 87 sr 86 sr during the cambrian and ordovician is based on 172 analyses the sample suite is largely from locations in oklahoma new york tennessee and texas where rocks of this age are widely exposed and well studied the oldest reliable samples examined in this study are of middle cambrian age and yield an 87 sr 86 sr near 0 70888 sw 19 the estimated ratio rises to near 0 70915 sw 8 in the lower upper cambrian the highest value during the phanerozoic and probably for all geologic time the estimated path drifts lower to near 0 70903 sw 4 at the cambrian ordovician boundary this further declines to near 0 70875 sw 32 at the end of the ibexian and reaches a value near 0 70821 sw 86 at the whiterockian mohawkian boundary the decline in the seawater 87 sr 86 sr continues into later mohawkian time to flatten abruptly near 0 70782 sw 125 this ratio is essentially constant through the latest ordovician the curve rises near to a ordovician silurian boundary value poorly constrained from our data near 0 70784 sw 123 the early paleozoic seawater curve shows the alternating dominance of continental and oceanic sources of sr continental sr dominated seawater from the beginning of the cambrian into late cambrian from that time as the cambrian transgression proceeded and radiogenic crystalline rocks were covered oceanic sr began to dominate sr from low ratio oceanic sources dominated through early mohawkian time an abrupt balance is struck between oceanic and continental sources to end the decline in the late ordovician and maintained until near the end of the ordovician the general curve shape follows the pattern suggested by proposed sealevel changes the rise and fall of seawater 87 sr 86 sr during the cambrian and ordovician characterized seawater variation during all the paleozoic

holocene microweathering rates and processes on ice eroded bedrock roldal area hardangervidda southern norway post glacial weathering of ice eroded metamorphic bedrock was investigated in the roldal area 60 n of the hardangervidda plateau in southern norway quartz veins were used as reference surfaces to determine a mean post glacial surface lowering rate of 0 55 mm ka 1 chemical characteristics of late season runoff were determined for one catchment snoskar and a chemical erosion rate of 4 9 t km 2 a 1 was obtained a mean in situ fracture enlargement due to microweathering of 0 12 mm ka 1 was also determined these rates are low although comparable with similar environments in cold regions and suggest that microweathering has had relatively little impact on holocene landscape evolution weathering rind thickness was found to be less on fracture walls than on exposed bedrock surfaces suggesting fractures have not played a significant role in microweathering observations of weathering morphology reveal a range of forms including shallow spalling tafoni and pseudokarren indicating locally intense weathering activity analysis of interrelationships between multiple weathering indices points to the importance of bedrock microweathering as a precursor to macro breakdown and landform evolution the research reasserts the importance of chemical activity in cold environments and the importance of moisture supply for effective microweathering the geological society publishing house 2009

three late quaternary pollen diagrams from southern patagonia and their palaeoecological implications abstract diagrams of fossil pollen in three deposits postdating glacial recession of the last ice age provide an account of late glacial and holocene vegetation and palaeoclimate in southern patagonia sites are mires located along the estrecho de magallanes at punta arenas 53 09 s 70 57 w and puerto del hambre 53 36 s 70 55 w and an intermittent lake some 300 km to the north at torres del paine 50 59 s 72 40 w chronostratigraphy is controlled by 20 radiocarbon dates the oldest site puerto del hambre covering close to 16 000 years charcoal from the sites and carbonate torres del paine as well as tephra layers and an instance of marine incursion puerto del hambre supply additional data of interpretive value accompanying the fossil pollen records is a reference survey of modern pollen fallout from 43 surface sample localities late glacial vegetation during deglaciation consisted mostly of tundra dominated by communities of empetrum acaena gunnera and tubuliflorae compositae under a relatively cold dry climate nothofagus although present in numbers initially at puerto del hambre did not expand until the close of the late glacial at punta arenas expansion of nothofagus was episodic occurring during apparent warmer intervals of the last three millennia of steppe tundra holocene vegetation is depicted at first as a patchwork of nothofagus woodland and steppe subject to climate of relative warmth and limited moisture except at torres del paine where moisture levels were apparently higher than at sites to the south closed nothofagus forest communities subsequently are best developed in the late holocene under a climate with generally cooler wetter parameters fire believed to be caused mostly by palaeoindians has had an important role in shaping vegetation sequences in the holocene formidable however in the development of vegetation are the latitudinal displacements variable intensities of atmospheric conditions caused by shifting storm tracks of the southern westerlies

elevated mercury accumulation in a peat bog of the magellanic moorlands chile 53 s an anthropogenic signal from the southern hemisphere increasing mercury deposition rates in the northern hemisphere recorded in natural archives such as peat bogs or lake sediments have been documented in numerous studies however data on atmospheric hg deposition in the southern hemisphere dating back to pre industrial times are rare here we provide a continuous record of atmospheric hg deposition in the southern hemisphere recorded by an ombrotrophic peat bog of the magellanic moorlands chile 53 s extending back 3000 yr pre industrial mercury accumulation rates range between 2 5 and 3 9 wg m 2 yr in the past 100 yr hg accumulation rates increased 18 fold from about 3 wg m 2 yr to a maximum of 62 5 wg m 2 yr if hg accumulation rates were normalized to peat accumulation rates maximum rates were 7 9 wg m 2 yr which is only 2 5 times the pre industrial rates thus hg accumulation rates normalized to peat accumulation rates are more comparable to the three fold net increase in atmospheric hg concentrations estimated for the same period we suggest that the increase in hg accumulation rates in the magellanic moorlands within the past 100 yr is at least partly attributed to global dispersion of hg derived from anthropogenic sources in the northern hemisphere the finding that no increase of atmospheric deposition of pb could be observed in the bog indicates the extraordinary long range transport and ubiquitous dispersion of anthropogenic derived gaseous hg compared to other metals 2002 elsevier science b v all rights reserved

the control mechanisms of erosion and weathering at basin scale from cosmogenic nuclides in river sediment the study of a sample of river sediment enables the determination of spatially averaged denudation rates that provide an exceptional perspective on erosion and weathering processes that have taken place within a landscape these measurements are done with in situ produced cosmogenic nuclides e g 10be 26al mostly in quartz from alluvial sediment cosmogenic nuclides are produced when secondary cosmic rays interact with the very uppermost layer of the earth s surface they are produced within a characteristic depth scale of about 1 m which means that the measured concentrations record an integrated denudation history while material passed through this depth interval depending on the denudation rate the resulting integration time scales are 103 to 105 years and one obtains a robust long term estimate of natural denudation that is relatively insensitive to short term changes the last 10 years have seen significant research activity using these methods and an array of fascinating tectono geomorphologic and geochemical insights are emerging amongst these is the ability to identify the physical and chemical processes with which a landscape responds to tectonic activity or climate change a compilation of world wide denudation rates in non glaciated areas that however does not yet include some of the world s most active mountain belts has resulted in the following findings some of which have been unexpected 1 no obvious relationship between precipitation or mean annual temperature and total denudation is apparent 2 topographic relief alone does not result in high rates of denudation 3 denudation rates are high in areas of landscape rejuvenation that is triggered and controlled by tectonic activity faulting escarpment formation and retreat rifting surface uplift 4 rates of weathering using a combination of cosmogenic nuclides and zirconium normalised cation loss balances co vary primarily with physical erosion rates and much less with temperature or precipitation 5 in some areas of high land use short term rates from river load gauging exceed those from cosmogenic nuclides by several orders of magnitude which serves to highlight the severity of geomorphic change caused by human action in the future the control mechanisms over denudation will be determined on all spatial scales ranging from the single soil section to entire river basins the same analysis can be done back through time on well dated terraces lake records and marine sediment cores which is possible with 10be for the past 1 2 my the rates obtained will be used to develop a quantitative understanding of tectonic geomorphologic and geochemical landscape processes which in turn is a prerequisite to design and calibrate models of the response of landscapes to tectonic climate and anthropogenic forcing

origin of oil in the sureste basin mexico geochemical and biological marker analyses of oils and rock samples from the sureste basin of mexico were effective in identifying and geographically limiting four major oil families related by age and source rock depositional environment oxfordian tithonian early cretaceous and tertiary the source rocks giving rise to the jurassic and cretaceous oils are associated with marine carbonate environments in contrast the source rocks giving rise to the tertiary oils are associated with a marine deltaic siliciclastic depositional setting biomarker and isotope differences observed in the oils derived from marine carbonate environments can be interpreted in terms of salinity clay content and oxygen depletion variations these differences provide diagnostic criteria for recognizing and differentiating five distinct organic rich depositional regimes as the sources for these oil types an anoxic hypersaline marine carbonate environment associated with a narrow and shallow semirestricted sea oxfordian age family 1 oil an anoxic marine carbonate environment associated with a silled basin geometry tithonian age family 2 oils subtype 2a an anoxic marine carbonate environment associated with a shallow gentle broad marine carbonate ramp in a distal position tithonian age family 2 oils subtype 2b a clay rich suboxic anoxic marine carbonate environment associated with a carbonate platform in a proximal position tithonian age family 2 oils subtype 2c and an anoxic marine evaporitic environment early cretaceous age family 3 oils the tertiary oils family 4 are derived from bacterially reworked terrigenous and marine organic source materials deposited in a marine deltaic environment the tithonian related oils in the mexican southern side of the gulf of mexico accumulated both offshore and onshore and throughout the stratigraphic column from kimmeridgian to pleistocene reservoirs suggesting vertical pathways as the principal secondary migration mechanism the lateral variations of these oils can be interpreted to reflect the tithonian paleogeography in the area and could be useful in predicting differences in the oil compositions

use of hydrogen and carbon stable isotopes characterizing oils from the potiguar basin onshore northeastern brazil hydrogen and carbon isotopic abundances were measured in representative samples of marine evaporitic lacustrine and mixed oils from the onshore potiguar basin the isotopic data together with chemical compositions and geological information were used to investigate relationships among ddoil and d13coil and source thermal maturity biodegradation mixing and the distance of secondary migration of these oils the marine evaporitic oils are depleted in deuterium 135 to 114 and the lacustrine oils are enriched 101 to 88 values of dd for mixed oils are intermediate 113 to 104 between those of marine evaporitic and lacustrine oils showing that ddoil is a reliable tool to identify oils that differ genetically values of ddoil were not directly related to thermal maturation biodegradation or distance of the secondary migration hydrogen isotopic compositions of the oils can be related mainly to the ddwater in the paleoenvironments in which the primary producers lived therefore ddoil values can provide rough estimates of ddwater in the depositional environments of the source rocks and consequently may provide evidence about paleoclimatic conditions at the site marine evaporitic oils are enriched in 13c 26 5 to 25 7 and lacustrine oils are depleted 33 6 to 30 2 in 13c relative contributions of marine evaporitic and lacustrine sources to mixed oils thus can be calculated independently from carbon or hydrogen isotopic mixing models when these calculations are done independently the mixed oils separate into two families and a previously unrecognized component possibly associated with environments that formed during the lacustrine to marine transition is revealed the investigation thus demonstrates the superior resolving power of two element mixing systematics

geomorphic controls on andean denudation rates abstract to predict erosion rates throughout the andes we conducted a multiple regression analysis of the sediment discharge from 47 drainage basins in the bolivian andes and various topographic climatologic and geologic parameters these mountainous basins are typically large 17 81 000 km2 documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape mathrm mean 11 000 end document km2 often have decades of measurement data on daily water and sediment discharge and display an extraordinary range of denudation 0 01 6 9 mm yr

glacial and tectonic control on fjord morphology and sediment deposition in the magellan region 53 s chile in the patagonian andes erosion by temperate pleistocene glaciers has produced a deeply incised fjord system in which glacial and non glacial sedimentswere deposited since the late glacial glacier retreat so far fjord bathymetry and structures in the sediment infill were widely unexplored here we report the results of an investigation of morphology and sediment characteristics of a 250 km long fjord transect across the southernmost andes 53 s using multibeam and parametric echosounder data and sediment cores subaquatic morphology reveals continuity of on land tectonic lineaments mapped using field and remote sensing data our results indicate that glacial erosion and fjord orientation are strongly controlled by three major strike slip fault zones furthermore erosion is partly controlled by older and or reactivated fracture zones as well as by differential resistance of the basement units to denudation basement morphology is regionally superimposed by late glacial and holocene subaquatic moraines which are associated to known glacier advances the moraines preferentially occur on basement highs which constrained the glacier flows this suggests that the extent of glacier advances was also controlled by basement morphology subaquatic mass flows fluid vent sites as well as distinct late glacial and holocene sediment infills have furthermore modified fjord bathymetry in the western fjord system close to the strait of magellan subaquatic terraces occur in 20 to 30 m water depth providing an important tag for proglacial lake level during the late glacial

postmagmatic cooling and late cenozoic denudation of the north patagonian batholith in the los lagos region of chile 41 42 15 s zircon and apatite fission track ft thermochronology was applied to investigate the history of cooling and denudation of the southern andes between 41 and 42 15 s in relation to the late cenozoic activity of the liquine ofqui fault zone lofz and the northward migration of the chile triple junction ctj fifty six zircon and 51 apatite ft ages plus 37 apatite confined track length distributions were obtained mainly from plutonic rocks of the north patagonian batholith npb in the main andean cordillera apatite ft ages and track lengths indicate a stage of rapid cooling at 5 3 ma along both sides of the lofz whereas older miocene ages with monotonous cooling histories were obtained further away from the fault zircon ft ages range from cretaceous to pliocene with marked differences observed along and across the lofz three different types of temperature time histories characterise the post magmatic cooling of the npb in the region deep intrusions with moderate and steady cooling rates intrusions in the upper crust with very slow cooling rates following a stage of initial rapid cooling and rapidly cooled and exhumed shallow intrusions the latter with younger ages towards the fault zone the most prominent denudation episode along the lofz is late miocene to pliocene coeval with plate tectonic reconstructions for the arrival and subduction of the chile rise beneath the taitao peninsula

tracking an upper limit of the carnian crisis and or carnian stage in the western carpathians slovakia the late triassic timescale especially the carnian norian boundary is poorly constrained mainly due to a paucity of high precision radio isotopic ages that can be related accurately to contradictions between the biostratigraphic and magnetostratigraphic correlations la icp ms dating of detrital zircons from five samples of the lunz formation the upper triassic siliciclastic sediments from the western carpathians slovakia provided a wide spectrum of ages that vary from late archaean ca 2582 ma to triassic ca 216 ma these marine delta sediments represent a typical product of the carnian crisis a major climate change and biotic turnover that occurred during the carnian stage in the tethys ocean within the carbonate shelf and intrashelf basins in the northern calcareous alps and the western carpathians the supply of clastic material in the studied lunz formation was derived from several sources especially i from the recycled variscan orogen ii from the remote east european platform and iii from the contemporaneous triassic volcanic sources syn sedimentary volcanic zircons with a concordia age of 221 2 1 6 ma calculated from 12 single analyses represent the maximum age of deposition of the lunz formation and demonstrate that the upper limit of the carnian crisis and or the carnian stage in the alpine carpathians realm is younger than the current age of the carnian norian boundary at ca 227 ma listed on the international chronostratigraphic chart international commission on stratigraphy 2016 12 edition

late pleistocene detrital sediment yield of the jura glacier france abstract measures of present day glacial erosion vary widely with the technique employed this paper quantifies the glacial material trapped in a proglacial lake during the wurm glacial period the combe d ain site was occupied by a meltwater lake where all the detrital material entering it from the jura glacier accumulated sediment yield is computed from three factors 1 the size of the sediment source area 2 the length of time the system operated and 3 the volume of sediment trapped the sediment budget of the lake system suggests a detrital sediment yield of 4400 1700 metric tons per square kilometer and per calendar year this represents a denudation rate of 1 6 0 6 mm per year illustrating that mechanical erosion by the jura glacier is more intensive than other processes of erosion

millennium scale volcanic impact on a superhumid and pristine ecosystem ecosystems damaged by distal volcanic ash and sulfur deposition usually recover within decades however sediment stalagmite and pollen records from the southernmost andes indicate a 2000 yr impact on forest and aquatic ecosystems after deposition of a thin tephra layer so 2 released from altering pumice produced intense soil and lake acidification in a 150 000 km 2 area acidification led to nutrient leaching and affected soil microorganisms causing plant decay and increased soil erosion in an area larger than 8000 km 2 we conclude that weakly buffered soils in humid environments are extremely vulnerable to volcanic and anthropogenic acidification causing long lasting ecosystem damage and perturbations of paleoclimate proxy records

glaciation as a destructive and constructive control on mountain building glacial erosion is thought to have an important role in controlling mountain height a common perception is that glaciers are powerful erosive agents inhibiting the ability of active mountains to rise significantly above the elevation of permanent glaciation through a process known as the glacial buzzsaw but now a study of erosion patterns and climate data from the late cenozoic in the glaciated patagonian andes suggests that glaciation can also have the reverse effect in effect making mountains higher at these polar latitudes glaciation acts as a protective layer preserving the uplifting mountains from erosion and allowing them to reach heights well above those predicted had a glacial buzzsaw been active it has been suggested that glacial erosion has an important role in controlling mountain height here spatial and temporal patterns of erosion in the glaciated patagonian andes have been assessed with the help of a low temperature thermochronologic data set the results show that between 38 s and 49 s accelerated erosion at the onset of widespread glaciation limits mountain height but at higher latitudes glaciation protects the landscape from erosion and leads to growth in mountain height and width theoretical analysis predicts that enhanced erosion related to late cenozoic global cooling can act as a first order influence on the internal dynamics of mountain building leading to a reduction in orogen width and height1 2 3 the strongest response is predicted in orogens dominated by highly efficient alpine glacial erosion producing a characteristic pattern of enhanced erosion on the windward flank of the orogen and maximum elevation controlled by glacier equilibrium line altitude3 4 where long term glacier mass gain equals mass loss however acquiring definitive field evidence of an active tectonic response to global climate cooling has been elusive5 here we present an extensive new low temperature thermochronologic data set from the patagonian andes a high latitude active orogen with a well documented late cenozoic tectonic climatic and glacial history data from 38 s to 49 s record a marked acceleration in erosion 7 to 5 myr ago coeval with the onset of major patagonian glaciation6 and retreat of deformation from the easternmost thrust front7 the highest rates and magnitudes of erosion are restricted to the glacial equilibrium line altitude on the windward western flank of the orogen as predicted in models of glaciated critical taper orogens where erosion rate is a function of ice sliding velocity3 8 in contrast towards higher latitudes 49 s to 56 s a transition to older bedrock cooling ages signifies much reduced late cenozoic erosion despite dominantly glacial conditions here since the latest miocene6 the increased height of the orogenic divide at these latitudes well above the equilibrium line altitude leads us to conclude that the southernmost patagonian andes represent the first recognized example of regional glacial protection of an active orogen from erosion leading to constructive growth in orogen height and width

rock control on microweathering of bedrock surfaces in a periglacial environment abstract microweathering of ice smoothed bedrock surfaces was investigated in the roldal area of hardanger plateau 60 southern norway postglacial rates of weathering were determined from surface lowering using quartz veins as reference surfaces weathering processes are inferred from assessment of weathering rind formation surface hardness and the preservation of small scale glacial erosional features surface lowering rates for a range of metamorphic rocks vary from 0 05 to 2 20 mm ka 1 and are broadly comparable with those obtained from crystalline rocks in other periglacial environments the mean rate of surface lowering at 0 55 mm ka 1 is low and demonstrates the relatively small impact of microweathering on postglacial landscape evolution variations in bedrock microweathering can be explained by lithological variation amphibolite and mica rich bedrock surfaces experience greater denudation and weakening least weathering rind formation and abundant preservation of glacial striae despite greater surface lowering conversely quartz rich bedrock surfaces are most resistant to denudation and weakening but have greater weathering rind formation and fewer preserved striae postglacial microweathering is achieved primarily through granular disintegration involving detachment and removal of mineral grains and weakening from increased porosity granular decomposition is manifest in the formation of weathering rinds analysis of interactions between weathering indices indicates that rind accumulation is limited by microerosion a conceptual model is proposed that illustrates the temporal interrelationships between in situ and erosional facets of microweathering in two contrasting mineral assemblages the model proposes that cyclic processes of in situ disintegration decomposition and erosion are at work the relative balance between these processes varies with lithology so that in more resistant quartz rich rocks the net effect is minimal surface lowering and accumulation of weathering rind in weaker amphibolitic and micaceous rocks the net effect is greater surface lowering and minimal accumulation of weathering rind the results of the research demonstrate the important influence of rock properties notably mineral composition in postglacial microweathering of crystalline bedrock in a periglacial environment

relative sea level changes during the cretaceous in israel detailed lithologic microfaunal and biometric investigations using relative abundances diversity indexes and duration charts of ostracods and foraminifera allowed the recognition of sea level changes during the cretaceous of israel three major transgressive regressive sedimentation cycles occur on the northwest margins of the arabian craton these cycles are the neocomian aptian which is mostly terrigenous sediments the albian turonian which is basin marls and platform carbonates and the senonian which is uniform marly chalks the cycles are separated by two major regional unconformities the aptian albian and turonian coniacian boundaries the sedimentary cycles are related to regional tectonic and volcanic events and eustatic changes the paleodepth curve il ustrates the gradual sea level rise reaching its maximum during the late cretaceous with conspicuous advances during the late aptian late albian cenomanian early turonian early santonian and early campanian major lowstands occur at the aptian albian cenomanian turonian turonian coniacian and campanian maastrichtian boundaries this model for israel agrees well with other regional and global sea level fluctuations four anoxic events black shales accompanying transgressions correspond to the cretaceous oceanic record we hypothesize the presence of mature oil shales in the present day eastern mediterranean basin close to allochthonous reef blocks detached from the cretaceous platform

chemical weathering in granitic environments abstract factors controlling chemical weathering in granitic environments are deduced using an extensive database from the literature based on a transition state theory model we evaluated the effects on chemical weathering of runoff temperature and ph the dependence between temperature and runoff and chemical weathering is complicated by other factors such as the presence depth of soil cover soil cover favors chemical weathering when it is thin and rich in weatherable minerals in contrast it reduces chemical weathering when is thick and poor in primary minerals processes that increase the contact time and the surface of the water rock interactions such as physical denudation increase chemical weathering rates in granitic environments the effect of temperature can be quantified assuming an apparent activation energy value of 48 7 kj mol to describe chemical weathering of silica in granitic crystalline environment under high runoff conditions

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

tectonic subsidence analysis of the illinois basin tectonic subsidence curves calculated from three wells indicate that the illinois basin formed through initial fault controlled mechanical subsidence and subsequent thermal subsidence thermal subsidence involved an early stage of thermal linear 520 460 ma and subsequent thermal asymptotic subsidence 460 350 ma this thermal subsidence was in response to mantle intrusion which formed a three arm rift system a second subsidence episode of unknown origin was documented from middle mississippian through early permian time subsidence mechanisms controlled sedimentation and subsidence rate trends and also sedimentation patterns for each of the four distinct tectonic subsidence phases tectonic subsidence curves were extended across the sauk tippecanoe ordovician silurian and tippecanoe kaskaskia unconformities and fit a post rift thermal contraction model the sauk tippecanoe ordovician silurian and possibly the kaskaskia absaroka unconformities formed because rates of eustatic sea level fall exceede

quantifying denudation and sediment accumulation systems open and closed lakes basic concepts and first results abstract the quantitative aspects of denudation in the drainage areas and sediment accumulation in the corresponding closed or open lakes are approached using two methods 1 from known mean rates of mechanical and chemical denudation and the ratio of the drainage lake area average terrigenous and potential chemical biogenic and evaporites sedimentation rates in the lake are determined or 2 from known sedimentation rates the average denudation rate is found in closed systems the total mass denuded during a certain unit of time is deposited in the lake as terrigenous biogenic and evaporitic sediments whereas open lake systems lose a major part of the dissolved river input derived from chemical denudation applying elementary equations describing these relationships and using ratios between mechanical and chemical denudation weathering ratio established in other regions e g chemical weathering in the lake drainage can be estimated likewise the knowledge of the bio index ratio of biogenic sediment total dissolved mass allows the calculation of the loss of dissolved matter through the outflow from the lake etc in a first step existing data from modern lake systems are evaluated later idealized lake systems in various climatic and morphotectonic zones can be simulated and the results utilized to better understand ancient lake systems modern alpine lakes reflect increased mechanical denudation rates 100 to 300 mm ka in highly elevated drainage areas of the central alps mainly crystalline rocks and high chemical denudation up to ca 100 mm ka in carbonate rocks of the northern calcareous alps mechanical denudation is significantly enhanced by glaciation but transport of the detritus into lakes may be delayed until the time immediately after glacial retreat average rates of terrigenous lake sedimentation amount to 5 to 15 mm a crystalline rocks high relief or are 5 mm a carbonate rocks delta outbuilding was a main factor in the filling of many alpine lakes lakes draining low altitude semi arid parts along the eastern margin of the alps lake balaton in hungary have low sedimentation rates and reflect the influence of increased temperature and vegetation in east africa the transition from the late pleistocene arid to the early holocene humid and again back to somewhat drier conditions caused substantial rises in lake levels and changes from closed to open lake systems in such cases the calculation of denudation from accumulation rates is biassed as a result of intermittent sediment storage at the lake margins low sedimentation rates in the lake centre during lake highstands or redeposition of sediment during lowstands lowstand shedding the modern denudation rates of east african rift lake systems vary by a factor of 15 lake tanganyika crystalline rocks and more dense vegetation cover total denudation rate ca 4 mm ka lake turkana young volcanic rocks and tephra sparse vegetation mechanical denudation rate ca 60 mm ka

macrostratigraphy of north america abstract the geological record is a three dimensional mosaic of gap bound rock bodies that at any given scale of temporal resolution were emplaced more or less continuously at any geographic location the irregular alternation of processes responsible for the formation and destruction of rock bodies results in the preservation of hiatus bound rock packages that have a distinct time of first occurrence base or oldest portion a time of last occurrence top or youngest portion and a suite of defining characters e g lithologies thickness fossils etc many important aspects of the geologic record can be quantified by compiling the stratigraphic ranges of such gap bound rock packages these include the quantity and spatial and temporal distribution of preserved rock rates of rock formation sequence stratigraphic architecture and area weighted rates of expansion and contraction erosional truncation of rock emplacement settings this approach to characterizing the rock record is scalable per

holocene denudation rates from the superhumid southernmost chilean patagonian andes 53 s deduced from lake sediment budgets abstract holocene denudation rates and their regional variations in the superhumid and temperate climate of the southernmost patagonian andes are poorly surveyed therefore we have investigated denudation in five small lake catchments 0 11 1 62 km 2 across a precipitation gradient from 600 to 9000 mm yr 1 in southernmost chile at 53 s variations in denudation rates can be defined most precisely by using small catchments and short time spans holocene thus can be related to variable bedrock types vegetation cover elevation and climate minimum physical denudation rates were determined from sediment budgets based on sediment echosounder data and physical properties of sediment cores the holocene denudation rates vary from 0 08 mm kyr 1 in the highly elevated bare granitic rock catchments to 9 01 mm kyr 1 in the low and vegetated catchments with a basement of sedimentary rocks these values are comparable with those from similar areas in norway sweden and nw iceland the high annual precipitation in the study area has only a minor effect on denudation enhanced geomorphic activity during paraglacial conditions caused a faster denudation after the glacier retreat until either the clastic glacial detritus was removed or the catchment was covered with vegetation chemical comparisons between basement rocks and lake sediments indicate a pronounced chemical denudation in catchments with peaty soils and low soil water ph values of 3 to 5 the holocene surface lowering rates are on average 200 fold lower than cenozoic surface lowering rates calculated from fission track data for the southern andes this discrepancy can be explained by significantly higher erosion rates during glacial periods

basic magmas in the early evolution of the southernmost patagonian batholith chile basic magmas played an important role in the early evolution of a segment of the patagonian batholith 141 to 34 m y exposed south of tierra del fuego chile the basic magmatism lasted 40 m y to possibly 60 m y 141 to 84 m y it is represented by early gabbros and hornblendites 141 to 103 m y and by synplutonic dikes and some of the numerous basic inclusions in the granitoids of a cretaceous 113 to 84 m y plutonic group some of the inclusions are interpreted as the disrupted portions of synplutonic dikes

magellan strait part of a neogene rift system the magellan strait joins the atlantic and pacific oceans separating tierra del fuego from southernmost continental south america the strait cuts both the andean cordillera and the magellan foreland basin other arms of the sea intrude the axial zone of the magellan basin these depressions have long been interpreted as glacial valleys on the basis of landsat images digital topography and field data we interpret the depressions as rifts or half rifts in general active rifts developed within foreland basins are unusual but in patagonia they are consistent with regional deformation and its plate tectonic setting during the neogene

tracing the impact of glacial interglacial climate variability on erosion of the southern andes sediment accumulation rates of well dated primarily terrigenous marine sediments collected along the chilean continental margin were used to infer erosion rates of the southern andes and the adjacent coastal cordillera compared to the holocene sediment supply to the margin and thus erosion were substantially enhanced during the last glacial when continental rainfall in the region was higher major changes in precipitation forcing to the southern andes on such glacial interglacial time scales appear to be transferred to offshore sedimentation rates by a fixed relation these data show that marine archives can make it possible to trace variability in erosion at adjacent continents on time scales to 10 3 yr a much better resolution than provided by commonly used methods such as thermochronometry or seismic studies

hierarchical subdivision of the cenozoic era a venerable solution and a critique of current proposals abstract if tertiary and quaternary are to be formally defined and ranked then only one topology and two ranking options for the major subdivisions of the cenozoic era are consistent with the principles of hierarchical classification these are 1 for the tertiary and quaternary to be ranked as suberas with the paleogene and neogene ranked as periods of the tertiary or 2 for the tertiary and quaternary to be ranked as periods with the paleogene and neogene ranked as subperiods of the tertiary the first option would leave the period rank empty for quaternary time however so the second option is preferred here in neither case is an extension of the neogene to the present permitted if desired however early cenozoic and late cenozoic could be defined as formal unranked chrons with the latter term providing an unambiguous expression for the same concept as the extended neogene attempts to justify an extended neogene by reference to a statement arising from the 1948 international geological congress fail because they are based on a misinterpretation of that statement likewise an appeal to the alleged original meaning of the neogene fails because it is factually superficial and would also have unacceptable consequences if applied as a general principle to the rest of the time scale four arguments against a ranked tertiary and or quaternary involve the status of these names as parts of an obsolete classification the disparity in their durations an analogy between them and the unranked precambrian and their supposed ambiguity these arguments are readily refuted arguments in favor of a ranked tertiary and quaternary include the continuing widespread use of these names their practical relevance for geologic maps and their role in honoring the pioneers of stratigraphy a recent recommendation by the international commission on stratigraphy ics would decouple the beginning of the quaternary from the beginning of the pleistocene have the neogene and pliocene overlap the tertiary quaternary boundary and have the gelasian age belong to both the pliocene and the quaternary these results violate the existing guidelines of the ics this same proposal would also regard the quaternary as a subera within the neogene period the latter being extended to the present however this arrangement violates the most fundamental rule of hierarchical classification in that a unit of superior rank would be included entirely within a unit of inferior rank given these problems the international union of geological sciences iugs must reject the ics recommendation an improved version of the ics proposal with the quaternary ranked as a period and the paleogene and extended neogene ranked as suberas would still prohibit the tertiary from being ranked and would either violate simpson s rule or else require a new name for the traditional concept of the neogene because the classification of the cenozoic advocated here is strictly hierarchical violates none of the existing guidelines of the ics obeys simpson s rule requires no new names allows the tertiary quaternary paleogene and neogene to be formally ranked and has been in general use for more than a century it is to be preferred only two current options for defining the quaternary and pleistocene are valid namely to leave the beginnings of these units where they are now vrica gssp at 1 8 ma or to move both to the piacenzian gelasian boundary monte san nicola gssp at 2 6 ma the latter option is not prohibited by lyell s types of the older pliocene nor after 2008 by the existing guidelines of the ics but if enacted could jeopardize the stability of the rest of the standard global time scale

precipitation as meteoric sediment and scaling laws of bedrock incision assessing the sadler effect abstractalthough it has been several decades since sadler 1981 first showed that sediment accumulation rates exhibit a negative power law dependence on measurement interval i e the sadler effect only recently has a manifestation of covariance in rate with duration become more widely appreciated in degradational settings because our collective understanding of rates of deposition and erosion are widely utilized to constrain the importance of active tectonism and climate forcing in shaping the surface of our planet cognizance of the dependence of rate on duration of observation is of critical importance relations between elevation change deposition erosion and rate scaling laws have often been examined by stochastic random walk simulations but this approach is generally confounded by insufficient data on amounts of land surface change on durations of land surface change and on hiatal durations separating time intervals of change deposition or erosion rates measured over short intervals suc

isotopic evidence for hydrologic change related to the westerlies in sw patagonia chile during the last millennium abstract the southern hemisphere westerly winds influence the spatial distribution of precipitation in southern south america and play a significant role in the global carbon cycle yet little is known about how this important atmospheric circulation feature has varied in the past here we present a sediment core record of late holocene variability from lago guanaco a small closed basin lake located in torres del paine national park chilean patagonia the park is located in the core of the modern wind field and variations in the intensity of the atmospheric circulation directly influence the hydrology of this region we combine stable isotopic measurements of biogenic carbonate and bulk organic matter to identify two periods of increased evaporation between 900 550 and 400 50 calendar years before present cal yr bp the first interval is coincident with the medieval climate anomaly mca while the more recent period is broadly coincident with the timing of the little ice age lia during the lia interval we observe simultaneous monotonic increases in the 18 o of biogenic carbonate and nothofagus dombeyi type pollen which we interpret as indicative of significant changes in the intensity of the southern westerlies during the last millennium the isotopic and palynological variations in the guanaco record are coincident with geochemical variations found in an antarctic ice core record from siple dome suggesting that the signal preserved in lago guanaco is regional rather than local and that the lia intensification was accompanied by a poleward shift in the southern margin of the westerlies in addition we interpret four periods of increased lake productivity centered on 900 650 500 and 200 cal yr bp from simultaneous increases in the 13 c of bulk organic material and biogenic carbonate these increases in lake productivity are most likely tied to increases in summer temperatures

deglacial palaeoclimate at puerto del hambre subantarctic patagonia chile the primary objective of this study is to further substantiate multistep climatic forcing of late glacial vegetation in southern south america a secondary objective is to establish the age of deglaciation in estrecho de magallanes bahia inutil pollen assemblages at 2 cm intervals in a core of the mire at puerto del hambre 53 36 21 s 70 55 53 w provide the basis for reconstructing the vegetation and a detailed account of palaeoclimate in subantarctic patagonia chronology over the 262 cm length of core is regulated by 20 ams radiocarbon dates between 14 455 and 10 089 14c yr bp of 13 pollen assemblage zones the earliest representing the oldest dryas chronozone 14 455 13 000 14c yr bp records impoverished steppe with decreasing frequencies and loss of southern beech nothofagus successive 100 yr long episodes of grass herbs and of heath empetrum ericaceae before 14 000 14c yr bp infer deglacial successional communities under a climate of increased continentality prior to the establishment of grass dominated steppe the bolling allerod 13 000 11 000 14c yr bp is characterised by mesic grassland under moderating climate that with abrupt change to heath dominance after 12 000 14c yr bp was warmer and not as humid at the time of the younger dryas 11 000 10 000 14c yr bp grass steppe expanded with a return of colder more humid climate later with gradual warming communities were invaded by southern beech the puerto del hambre record parallels multistep deglacial palaeoclimatic sequences reported elsewhere in the southern andes and at taylor dome in antarctica deglaciation of estrecho de magallanes bahia inutil is dated close to 14 455 14c yr bp invalidating earlier dates of between 15 800 and 16 590 14c yr bp copyright 2000 john wiley sons ltd

the south patagonian batholith 150 my of granite magmatism on a plate margin a new database of 70 u pb zircon ages mostly determined by shrimp indicates that the south patagonian batholith resulted from the amalgamation of subduction related plutons from the late jurassic to the neogene construction of the batholith began with a voluminous previously undetected late jurassic bimodal body mainly composed of leucogranite with some gabbro emplaced along its present eastern margin within a restricted time span 157 to 145 ma this episode is at least in part coeval with voluminous rhyolitic ignimbrites of the tobifera formation deposited in the deep rocas verdes basin east of the batholith this was the last of several southwestward migrating silicic volcanic episodes in patagonia that commenced in an early jurassic extensional tectonic regime the quasi oceanic mafic floor of the basin was also contemporaneous with this late jurassic batholithic event as indicated by mutually cross cutting field relationships changes in subduction parameters then triggered the generation of earliest cretaceous plutons cretaceous 1 144 137 ma west of the late jurassic ones a westward shift that culminated at 136 127 ma cretaceous 2 along the present western margin of the batholith most mid to late cretaceous cretaceous 3 126 75 ma and paleogene 67 40 ma granitoids are represented by geographically restricted plutons mainly emplaced between the previously established margins of the batholith and mostly in the far south no associated volcanic rocks of similar age are known at present in this area during the final neogene stage of plutonism 25 15 ma a recurrence of coeval volcanism is recognized within and east of the batholith typical endt values for the granitoids vary from strongly negative 5 in the late jurassic to progressively higher values for cretaceous 1 4 cretaceous 2 0 7 cretaceous 3 2 and the paleogene 5 followed by lower and more variable ones in the neogene 1 to 5 these variations may reflect different modes of pluton emplacement large crustal magma chambers developed in the early stages late jurassic to cretaceous 1 leading to widespread emplacement of plutons with a crustal signature whereas the cretaceous 2 cretaceous 3 and palaeogene parts of the batholith resulted from incremental assembly of small plutons generated at greater depths and with higher endt this does not in itself justify the idea of a reduction in crustal character due to progressive exhaustion of fusible material in the crust through which the magmas passed

holocene changes in the position and intensity of the southern westerly wind belt the position and intensity of the southern westerly wind belt varies seasonally as a consequence of changes in sea surface temperature during the austral winter the belt expands northward and the wind intensity in the core decreases conversely during the summer the belt contracts and the intensity within the core is strengthened reconstructions of the westerly winds since the last glacial maximum however have suggested that changes at a single site reflected shifts throughout the entire southern wind belt 1 4 here we use sedimentological and pollen records to reconstruct precipitation patterns over the past 12 500 yr from sites along the windward side of the andes precipitation at the sites located in the present core and northern margin of the westerlies is driven almost entirely by the wind belt 5 and can be used to reconstruct its intensity rather than varying coherently throughout the holocene epoch we find a distinct anti phasing of wind strength between the core and northern margin over multi millennial timescales during the early holocene the core westerlies were strong whereas the northern margin westerlies were weak we observe the opposite pattern in the late holocene as this variation resembles modern seasonal variability we suggest that our observed changes in westerly wind strength can best be explained by variations in sea surface temperature in the eastern south pacific ocean chile is ideally located to reconstruct past variability of the southern westerly wind belt sww as the sww almost entirely controls precipitation on the western side of the andes in southern south america with an extreme northsouth

covariation in macrostratigraphic and macroevolutionary patterns in the marine record of north america students of earth history have long recog nized the correlation between the quantity of preserved sedimentary rock and the diversity of life recorded as fossils but paleontologists have yet to determine whether this pattern refl ects a causal relationship or a unidirec tional sampling bias in fossil data imposed by preserved rock quantity distinguishing between these two alternatives has been com plicated by the fact that many of the basic patterns of paleontologic and lithologic co variation have yet to be quantifi ed rigorously here we present the fi rst analyses of the co variation between the macrostratigraphic and macroevolutionary histories of north america based on geographically and tem porally explicit co occurrences of rocks and fossils the analyses use independent quan titative summaries of the stratigraphic and fossil records by integrating the paleobiology database paleodb and macrostrat a mac rostratigraphy database for north america which allows a more direct comparison of the stratigraphic and biological histories of the continent than has heretofore been possible within the macrostrat database the rock re cord is divided into discrete packages of sedi ment that are bound by hiatuses resolvable at the stage level using per interval per pack age rates of sediment package initiation and truncation and genus fi rst and last appear ances herein regional origination and extinc tion we fia substantially stronger positive correlation between sediments and biology for extinction like parameters than we do for origination like parameters four of the largest coincident pulses of regional extinc tion and sediment truncation occur during the widely recognized end ordovician late permian end triassic and end cretaceous mass extinction intervals a further compari son of the global ranges of north american genera to north american macrostratigra phy indicates that the regional and global extinction of genera are more likely to oc cur in the same stage than are global and regional originations together these results suggest that our general understanding of biodiversity dynamics from the fossil record may not be strongly biased by the preserva tion of sediments and leaves open the pos sibility that certain large perturbations to the earth system are responsible for major changes of state in both the sedimentary and biological systems

late pleistocene to holocene marine transgression and thermohaline control on sediment transport in the western magellanes fjord system of chile 53 s abstract in the western strait of magellan in southernmost chile marine transgression occurred between 14 500 and 13 500 cal bp this is indicated by strongly increased accumulation of biogenic carbonate and first appearance of foraminifers in sediment records from that time until 11 500 cal bp sedimentation in the western fjords became predominant autochthonous due to higher salinity and clay flocculation and late glacial glacier retreat present day thermohaline zonation pattern extensively representative for the holocene and sedimentation rates indicate that westerlies hampered westward outflow of superficial 0 30 m water depth glacial clay rich freshwater from glaciated areas during the holocene isostatic uplift of the andes overcompensated sea level rise in areas with high glacial glacier loading this led to shallowing fjord sills and restricted exchange with marine water especially since high freshwater inflow produced strong pycnoclines and preserved old saline water in fjord bottoms to the east of the climate divide the seno skyring fjord system shows a year round stable stratification despite a strong wind induced eastward superficial current in the upper 30 50 m of the water column such currents enabled significant late glacial eastward transport of glacial clay sediment cores from this area indicate that east ward sediment flux slowed down during the holocene probably due to less intense westerlies investigated present day thermohaline characteristics of the fjord system across the superhumid climate divide of the southern andes indicate details of the exchange between marine and freshwater which are fundamental for evaluation of sediment transport pathways biogenic productivity and interpretation of paleoclimate records in this area

tectonic and depositional model of the arabian and adjoining plates during the silurian devonian during the late ordovician and early silurian the western part of the arabian peninsula was covered by polar glaciers that advanced from the south pole in african gondwana during this period nondeposition erosion or marginal marine conditions prevailed in eastern and northern arabia when the glaciers melted in the early silurian sea level rose sharply and the paleo tethys ocean transgressed the arabian and adjoining plates depositing a thick organic rich shale directly over the glaciogenic and periglacial rocks and related unconformities the post glacial sequence coarsens upward reflecting the passage of a coastline prograding northward from african and arabian gondwana to northern arabia a sea level drop in the late silurian placed the study area in a terrestrial environment however as sea level recovered in the early devonian a carbonate sequence blanketed most of the area the transgression however was interrupted by regional uplift and local orogenic movements in the middle and late devonian these movements constitute the onset of hercynian tectonism which resulted in erosion of the older sequences depositional hiatuses and regional facies changes

major episodes of geologic change correlations time structure and possible causes abstract published data sets of major geologic events of the past 250myr extinction events sea level lows continental flood basalt eruptions mountain building events abrupt changes in sea floor spreading ocean anoxic and blackshale events and the largest evaporite deposits have been synthesized with estimated errors these events show evidence for a statistically significant periodic component with an underlying periodicity formally equal to 26 6 myr and a recent maximum close to the present time the cycle may not be strictly periodic but a periodicity of 30myr is robust to probable errors in dating of the geologic events the intervals of geologic change seem to involve jumps in sea floor spreading associated with episodic continental rifting volcanism enhanced orogeny global sea level changes and fluctuations in climate the period may represent a purely internal earth pulsation but evidence of planetesimal impacts at several extinction boundaries and a possible underlying cycle of 28 36 myr in crater ages suggests that highly energetic impacts may be affecting global tectonics a cyclic increase in the flux of planetesimals might result from the passage of the solar system through the central plane of the milky way galaxy an event with a periodicity and mean phasing similar to that detected in the geologic changes

erosion in the western alps dora baltea basin 2 quantifying sediment yield abstract the present work shows how sediment composition can be used to constrain bed load sediment budgets in mountain catchments a database of high resolution petrographic and dense mineral analyses of detritus carried by the dora baltea river and its tributaries allowed us to partition bed load sediment budgets obtained from data available from a public authority between two different sets of sediment sources major tributaries and major geological units relative and absolute budgets of sediment bed load thus obtained are more robust than those derived from traditional empirical methods alone total detrital flux in the dora baltea drainage basin is 1 000 000 ton year bed load 590 000 ton year suspended load 410 000 ton year with denudation rates of 0 12 mm year data from italian public authority progetto di piano stralcio per l assetto idrogeologico pai parma supplemento straordinario della gazzetta ufficiale 166 more than 75 of the dora baltea total bed load 453 000 9000 ton year is derived from tributaries dora di ferret dora di veny savara grand eyvia buthier lys sourced from the highest granitoid peaks 4000 m a s l m bianco m rosa m cervino gran paradiso massifs which drain 36 of the whole catchment the m bianco massif with its granitoid lithology extreme relief and heavily glaciated drainage basins occupies only 3 of total basin area but it produces 294 000 6000 tons of arkosic sands per year which represents 50 of total dora baltea bed load the dora di veny 2 of total dora baltea mountain catchment exhibits the highest denudation rate of the whole dora baltea mountain basin 0 73 mm year the values calculated in this study compare well with measured modern river loads of partly glaciated mid latitude mountain regions

springhill formation magellan basin chile formation water characteristics and mineralogy abstract the early cretaceous springhill formation is a transgressive sequence of quartz sandstones with intercalations of shale and represents the principal hydrocarbon producer of the magellan basin analyses of its formation waters from the chilean sector surface area approximately 20 000 km2 are classified and linked to the diagenetic alteration of the formation local 18o determinations and core leaching have been carried out to evaluate homogeneity and whole rock contribution to springhill formation fluid phases formation waters are of the chlorine calcium type with na cl 1 together with an increase in organic maturity ro between 2000 and 4000 m a change is observed from authigenic kaolinite to illite and corrensite accompanied by a loss of porosity and permeability with respect to the distribution of the authigenic pore phyllosilicates the shallowest kaolinite dominated area is limited by faults against deeper sectors where corrensite and illite smectite prevail a later influx of high salinity fluids into the kaolinite area from the basin centre or continental graben sediments has let to the present day distribution of formation waters low scatter 18o ratios of kaolinite and corrensite reflect lithological consistency on a m scale residual salt analyses shows a direct relationship between the dissolution of ca and a high cao content in the whole rock sample

holocene tephrochronology record of large explosive eruptions in the southernmost patagonian andes for regionally widespread holocene tephra layers in southernmost patagonia correlations based on both chemical and chronological data indicate their derivation from five large volume 1 km3 explosive eruptions of four different volcanoes in the southernmost andes bulk tephra and tephra glass major and trace element chemistry and sr isotopic ratios unambiguously distinguish different source volcanoes and imply that two of the regionally widespread tephra mb1 and mb2 were derived from mt burney 52 s one r1 from reclus 51 s one a1 from aguilera 50 s and one h1 from hudson volcano 46 s the h1 tephra derived from the hudson volcano which is located at the southern end of the andean southern volcanic zone svz 33 46 s contains distinctive greenish andesitic glass with feo 4 5 wt and tio2 1 2 wt in contrast rhyolitic glass in tephra derived from the eruptions of mt burney reclus and aguilera volcanoes which are located in the andean austral volcanic zone avz 49 55 s is clear and transparent and has significantly lower feo and tio2 tephra derived from these three avz volcanoes all contain plagioclase orthopyroxene minor clinopyroxene and amphibole biotite occurs only in the aguilera a1 tephra which also has the highest bulk tephra and tephra glass k2o and rb contents averages of new and published 14c ages determined on organic material in soil and sediment samples above and below these tephra constrain the uncalibrated 14c age of the r1 eruption of reclus volcano to 12 685 260 years bp the mb1 and mb2 eruptions of mt burney to 8 425 500 and 3 830 390 years bp the hudson h1 eruption to 6 850 160 years bp and the a1 eruption of aguilera volcano to 3 000 100 years bp the volume of the largest of these eruptions h1 of the hudson volcano is estimated as 18 km3 the volume of the reclus r1 eruption is estimated at 10 km3 the aguilera a1 eruption at between 4 and 9 km3 and the younger mt burney mb2 eruption at 2 8 km3 the volume of the older mb1 mt burney eruption is the least well constrained but must have been larger than the younger mb2 eruption the data indicate that the frequency of explosive activity of volcanic centers in the avz is lower than in the southern svz

the tertiary and the quaternary are here to stay in 1989 and 2000 the international commission on stratigraphy ics published geologic time scales in which the term tertiary had been eliminated in the time scales published by the ics in 2004 the term quaternary was also eliminated the cenozoic shown as composed of two systems the paleogene and the neogene the neogene extending to the present was there any logical basis for these changes a review of the geologic literature since 1980 19 journals of extensive distribution and a considerable number of geologic maps time scales and stratigraphy textbooks as well as the georef clearly indicates that the tertiary and the quaternary have long been and are now in widespread use by geologists the world over and that their use has not declined at all during the last 25 yr they are very useful terms in geologic work essential for clear communication among geologists paleogene and neogene have received increasing use during the last 10 yr because they are also useful terms quaternary is probably the stratigraphic term most frequently used in the geologic literature tertiary is used as the pre quaternary part of the cenozoic by most geologists some however prefer to use paleogene and neogene instead of tertiary but it should not be a question of either tertiary or paleogene and neogene all three are needed as are cenozoic paleocene eocene oligocene miocene and pliocene to express various degrees of precision in stratigraphic assignation and dating all should be recognized as units of a standard geologic time scale geologists should retain a choice of what they think better fits their needs the preferred time scale therefore should have the cenozoic erathem comprising the tertiary and quaternary systems and the tertiary including the paleogene and neogene subsystems past attempts to eliminate the tertiary and quaternary have been ignored recent attempts will not succeed either the tertiary and the quaternary are here to stay certainly as long as geologists continue to use them as they have and continue to oppose the ill advised efforts to discard them from the geologic time scale

water chemistry and its diversity in relation to local factors in the latnjavagge drainage basin arctic oceanic swedish lapland the chemistry of precipitation snow pack and surface water has been analysed on 205 samples collected during the 2001 field season at 25 selected sites within the latnjavagge drainage basin in arctic oceanic northern swedish lapland additionally daily discharge and yield of dissolved solids have been calculated for several subcatchments and the entire latnjavagge catchment during the years 2000 2001 and 2002 chemical water analysis included the components ca2 mg2 na k fe2 mn2 cl no3 so42 and po43 with so42 and ca2 being the dominant ones in the surface water solute concentrations and chemical denudation were low but showed significant differences within the basin in areas of shade longer snow cover frozen ground and thin regolith concentrations over the summer were perceptible but so low that solutes brought into the basin from precipitation could be detected in the surface water in one locality it was even found that lake water could reflect snowmelt to such an extent that the solute concentration was less than that of summer precipitation the highest concentrations were found at a radiation exposed w facing vegetated moderately steep slope with relatively thick regolith that was thawed at the time of snowmelt in early june in such well drained sites with continuous subsurface water flow a maximum of contact between water and mineral particles could take place the concentration values revealed differences in the rate of thawing of frozen ground between shaded areas and or areas at higher altitude on the one hand and radiation exposed areas on the other a comparison with published results from karkevagge a few kilometres to the northwest as well as from other periglacial locations indicates that the chemical denudation values from latnjavagge are more representative of periglacial oceanic environments than the values from the karkevagge catchment which shows especially high chemical denudation rates the investigation in latnjavagge stresses the importance of spatial variability within even small catchments of homogeneous lithology as it demonstrates that solute concentrations from different subbasins can differ substantially dependent on exposure to radiation duration of snow cover and frozen ground conditions regolith thickness and possibly also to vegetation cover and slope angle as factors steering water turbulence and retention of drainage

strong tectonic and weak climatic control of long term chemical weathering rates the relationships among climate physical erosion and chemical weathering have remained uncertain because long term chemical weathering rates have been difficult to measure here we show that long term chemical weathering rates can be measured by combining physical erosion rates inferred from cosmogenic nuclides with dissolution losses inferred from the rock to soil enrichment of insoluble elements we used this method to measure chemical weathering rates across 22 mountainous granitic catchments that span a wide range of erosion rates and climates chemical weathering rates correlate strongly with physical erosion rates but only weakly with climate implying that by regulating erosion rates tectonic uplift may significantly accelerate chemical weathering rates in granitic landscapes

contrasting patterns and connections of rock and biotic diversity in the marine and non marine fossil records of north america abstract macrostratigraphy uses packages of continuous sedimentation that are bound by hiatuses of non deposition erosion or alternations between environments lithologies to characterize spatiotemporal patterns of sedimentation previous work has linked the macrostratigraphy of marine shelf environments to many different macroevolutionary patterns in the marine animal fossil record here we use an improved macrostratigraphic database for north america combined with fossil occurrence data in the paleobiology database to show that macroevolutionary and macrostratigraphic patterns are correlated more strongly in marine environments than in non marine environments we also test the hypothesis that the temporal distribution of lithological diversity measured as evenness similar to ecological evenness based on the number of lithostratigraphic units with a given lithologic type within each time interval has a relationship to genus level taxonomic diversity in both the marine and non marine realms uneven sampling of lithologies and their corresponding depositional environments can bias our perception of taxonomic diversity by causing taxa from poorly sampled environments to be underrepresented in the fossil record our results show a negative correlation between lithologic evenness and marine vertebrate generic richness less even sampling of lithologies corresponds to a higher observed taxonomic richness and no correlation with lithologic evenness and non marine diversity measures this suggests a difference in the relationship between biologic and sedimentary processes at work in the marine and non marine realms and possibly differences in the magnitude of the bias imposed by the rock record on the underlying biologic patterns

organic geochemistry of mid continent middle and late ordovician oils ordovician oils in mohawkian and cincinnatian reservoirs of the united states mid continent retain the biochemical imprint of middle and upper ordovician oceanic life before the evolution of land plants and most vertebrates thus these oils have some geochemical features that distinguish them from younger oils these features include 1 a predominance of n c15 n c17 and n c19 alkanes in the saturated hydrocarbon fraction 2 relatively low amounts of longer chain n alkanes 3 low amounts of chlorophyll derived isoprenoids such as pristane and phytane and 4 abundant c29 sterane relative to c27 with rearranged forms diasteranes predominant over normal steranes ordovician oils also generally contain little sulfur and have a somewhat variable light stable carbon isotopic composition with dgr13csat and dgr13caro values of 28 to 31 pmil pdb but these features are typical of many marine oils the unusual chemistry of these ordovician oils supports the interpretation of reed illich and horsfield 1986 that prokaryotic organisms provided the organic matter for most ordovician oils although their claim for gloeocapsamorpha a problematic unicellular prokaryote possibly a blue green alga or an unusually large bacterium cannot be proven from oil chemistry alone knowing that indigenous mid continent ordovician oils were derived from prokaryotic organisms may aid in future exploration for these reservoirs

cenozoic crustal thickening wrenching and rifting in the foothills of the southernmost andes abstract the southernmost andes form an orocline between the patagonian cordillera trending n s and the fueguian cordilleras trending e w on the foreland side is the magellan basin the area has a history of paleozoic compression triassic to early cretaceous rifting and late cretaceous to quaternary compression in response to changing plate tectonics major structures of late cretaceous and cenozoic age vary along the strike in the patagonian cordillera and foothills folds and thrusts trend nnw slightly oblique to the orogen whereas strike slip faults are parallel to the orogen and right lateral in the fueguian cordilleras and foothills folds and thrusts trend ese slightly oblique to the orogen whereas strike slip faults are parallel to the orogen and left lateral in the axial zone of the magellan basin folds and thrusts are parallel to the orogen and rifts are sub perpendicular to it to a first approximation the pattern of structures has mirror symmetry about the axis of the magellan basin in detail however wrenching appears to be more prevalent in the fueguian cordillera and foothills than it is in the patagonian cordillera and foothills minor faults of cenozoic age are common in the foothills from a kinematic analysis of fault slip data 1 shortening and stretching directions are mostly sub horizontal 2 shortening directions vary in trend from ene in the patagonian foothills to ne in the fueguian foothills and 3 stretching directions are sub parallel to traces of major thrusts in the fueguian cordillera and foothills strike slip faulting is prevalent in the patagonian foothills crustal thickening is prevalent over strike slip faulting the kinematics reflect a combination of thrusting and wrenching and they are consistent with the major structures to investigate the origin of the cenozoic structures we used analogue models on a fully lithospheric scale where an oceanic plate subducted beneath a continental corner the corner was an area of transition from frontal subduction to transcurrent motion the boundary conditions may not have been fully realistic but the experiments did account for the major elements of the structural pattern in southernmost south america including rifts that are perpendicular to the orogen and counterclockwise block rotations

weathering implications of water chemistry in an arctic alpine environment northern sweden this paper reports on some of the chemical characteristics of late melt season water from karkevagge valley of the boulders above the arctic circle in northern sweden included in the analyses were temperature electrical conductivity ph so4 no3 k sio2 mg mn na fe and al these were measured in rain late lying snow and water from the major stream and lake as well as from pond tributary and seep sources in the valley a total of 71 samples was collected at 57 sites between august 6 and august 23 1996 for the purpose of characterizing the present weathering regime within this classic u shaped glacial valley evidence of chemical weathering included increases in solute concentrations over precipitation inputs and a source related wide variation in water chemistry the dominant anion measured in surface water was so4 that along with the presence of caso4 coatings on streambeds indicates that pyrite oxidation may contribute to the weathering regime high so4 concentrations were associated with gypsum coated streambeds and seeps that emerge from the bedrock low so4 concentrations were associated with tributaries flowing primarily on fresh rock and originating from melting snow estimated chemical denudation rate for the valley corrected for atmospheric inputs was 19 2 tons km2 yr although this is lower than previously reported our research supports earlier work indicating that chemical weathering is a major component of mass wasting in this arctic alpine environment

sediment yield from glacio lacustrine calcareous deposits during the postglacial period in the combe d ain jura france the middle valley of the river ain jura cuts through glacio lacustrine deposits laid down in an ice dammed lake during the most recent glacial advance the total volume eroded is about 6 21 10 8 m 3 for a surface area of 3 7 10 7 m 2 erosion occurred between 18 ka bp and 6 ka bp i e over a duration of some 12 ka sediment yield from the area was of the order of 2500 t km 2 a 1 which is comparable with modern day sediment yield from nw african badlands these high values are ascribed to the amenability of glacio lacustrine deposits to mechanical weathering and to the rapid geomorphological changes that affected glacial and paraglacial sedimentary cover after the retreat of the ice the valley slopes were destabilized by mass wasting earthflow and mudflow which was the predominant erosional process the slopes are currently stabilized or very exceptionally active 1998 john wiley sons ltd

late glacial and holocene palaeoenvironmental change in the central strait of magellan southern patagonia abstract high resolution palaeoenvironmental data for the wisconsin late glacial and early holocene is provided from two sites puerto del hambre and estancia esmeralda ii in the central section of the strait of magellan southern chile palaeoecological and lithostratigraphical evidence is correlated with other palaeoenvironmental data from the magellan region using 14 c dating and tephrochronology the oldest record from puerto del hambre commences at 14 470 14 c yr bp 17 330 cal yr bp following retreat of the magellan glacier climatic warming after that time is indicated by ice retreat from the central section of the strait of magellan and palynological evidence however mean annual temperature continued to be cooler than present until c 10 300 14 c yr bp 12 270 12 110 cal yr bp the magellan environment was relatively humid between c 14 100 and c 12 550 14 c yr bp 16 910 and 15 170 14 410 cal yr bp at c 12 550 14 c yr bp there was a sharp decrease in effective moisture levels of humidity fluctuated but remained relatively low until c 10 300 14 c yr bp this period of cool and drier climate is contemporary with a significant glacier advance dated to between c 12 700 and 10 300 14 c yr bp 15 330 and 12 270 12 110 cal yr bp which would have produced an enhanced rainshadow effect around 10 300 14 c yr bp a shift to warmer conditions occurred between c 10 300 and 8550 14 c yr bp 12 270 12 110 and 9530 cal yr bp an extreme arid phase is recorded which led to an increase in fires at c 8550 14 c yr bp an increase in available moisture allowed the eastward spread of nothofagus forest at 8265 14 c yr bp 9270 9160 cal yr bp there was a relative rise in sea level in the strait of magellan this marine incursion lasted until 3970 14 c yr bp 4420 cal yr bp reaching its maximum around c 6450 14 c yr bp 7420 7340 cal yr bp