iron control of past productivity in the coastal upwelling system off the atacama desert chile 1 biogenic opal and organic carbon vertical rain rates in sediment cores reveal a strong cyclicity in the productivity of the upwelling system off presently arid northern chile during the last 100 000 years changes in productivity are found to be in phase with the precessional cycle 20 000 years and with inputs of iron from the continent during austral summer insolation maxima increased precipitation and river runoff in the region appear to have brought high inputs of iron mainly from the andes to the coastal ocean enhancing primary productivity there we interpret our results as providing evidence for iron control of past productivity in this upwelling system and for a tight link between productivity and orbital forcing at midlatitudes

on the in situ aqueous alteration of soils on mars abstract early 3 gy wetter climate conditions on mars have been proposed and it is thus likely that pedogenic processes have occurred there at some point in the past soil and rock chemistry of the martian landing sites were evaluated to test the hypothesis that in situ aqueous alteration and downward movement of solutes have been among the processes that have transformed these portions of the mars regolith a geochemical mass balance shows that martian soils at three landing sites have lost significant quantities of major rock forming elements and have gained elements that are likely present as soluble ions the loss of elements is interpreted to have occurred during an earlier stage s of weathering that may have been accompanied by the downward transport of weathering products and the salts are interpreted to be emplaced later in a drier mars history chemical differences exist among the sites indicating regional differences in soil composition shallow soil profile excavations at gusev crater are consistent with late stage downward migration of salts implying the presence of small amounts of liquid water even in relatively recent martian history while the mechanisms for chemical weathering and salt additions on mars remain unclear the soil chemistry appears to record a decline in leaching efficiency a deep sedimentary exposure at endurance crater contains complex depth profiles of so4 cl and br trends generally consistent with downward aqueous transport accompanied by drying while no model for the origin of martian soils can be fully constrained with the currently available data a pedogenic origin is consistent with observed martian geology and geochemistry and provides a testable hypothesis that can be evaluated with present and future data from the mars surface

complex multiple cosmogenic nuclide concentration and histories in the arid rio lluta catchment northern chile terrestrial cosmogenic nuclide tcn concentrations measured in river sediments can be used to estimate catchment wide denudation rates by investigating multiple tcn the steadiness of sediment generation transport and depositional processes can be tested measurements of 10be 21ne and 26al from the hyper to semi arid rio lluta catchment northern chile yield average single denudation rates ranging from 12 to 75 m myr 1 throughout the catchment paired nuclide analysis reveals complex exposure histories for most of the samples and thus the single nuclide estimates do not exclusively represent catchment wide denudation rates the lower range of single nuclide denudation rates 12 17 m myr 1 established with the noble gas 21ne is in accordance with palaeodenudation rates derived from 21ne 10be and 26al 10be ratio analysis since this denudation rate range is measured throughout the system it is suggested that a headwater signal is transported downstream but modulated by a complex admixture of sediment that has been stored and buried at proximal hillslope or terrace deposits which are released during high discharge events that is best evidenced by the stable nuclide 21ne which preserves the nuclide concentration even during storage intervals the catchment wide single 21ne denudation rates and the palaeodenuation rates contrast with previous tcn derived erosion rates from bedrock exposures at hillslope interfluves by being at least one order of magnitude higher especially in the lower river course these results support earlier studies that identified a coupling of erosional processes in the western cordillera contrasting with decoupled processes in the western escarpment and in the coastal cordillera copyright 2008 john wiley sons ltd

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

sequential extraction of iron in marine sediments from the chilean continental margin iron content of the bulk marine sediment from the chilean continental margin has been used to infer millenial scale climate changes in southeast pacific lamy f klump j hebbeln d wefer g 2000 rapid climate change in northern chile over the last 80 ka recorded in a marine sediment core terra nova 12 8 13 changes of iron contents have been related to a varying contribution of andean fe rich versus coastal range fe poor source rocks ultimately controlled by continental rainfall changes however variations observed could also be produced by changes in the proportions of two components in the sediment a detrital component with low and constant fe content and an authigenic phase fe oxide pyrite apatite etc with high fe content a sequential extraction has been used to partition the total iron content in the sediment of core geob 7101 at the continental margin of chile the extraction steps included five fractions exchangeable bound to carbonates bound to fe mn oxides bound to organic matter and residual iron appeared to be mainly present in the residual fraction i e in the detrital component our study indicates that total fe or fe al may be used to infer millenial scales climate changes in the southeastern pacific

prediction of coal seam details and mining safety using multicomponent seismic data a case history from china abstractwith the increasing mining depth of coal mines geologic hazards have become the main source of accidents for this reason coal seam prediction requires more assessment parameters such as the degree of anisotropy vp vs value and elastic modulus these parameters are difficult to determine using only the pp wave we have inverted and interpreted multicomponent seismic data acquired from a 2 56 km2 area in the guqiao mine located on the southern margin of the north china plate under the constraints of drill log and rock physics test data the production coal seam 11 2 of the mine located in the permian formation was our focus of this study and our objective was to determine the structure fracture development thickness surrounding rock lithology roof stability and mining safety of the seam to achieve this we first performed an analysis of s wave splitting and joint pp and ps wave inversions the inversion results were then combined to derive additional parameters such as the vp vs

a 130 ka reconstruction of rainfall on the bolivian altiplano new efforts to link climate reconstructions from shoreline deposits and sediment cores yield an improved and more detailed lake history from the bolivian altiplano on the southern altiplano 10 lake oscillations have been identified from this new unified chronology each coincident with north atlantic cold events such as heinrich events h5 h2 h1 and the younger dryas by coupling this new lake history to a hydrologic budget model we are able to evaluate precipitation variability on the southern bolivian altiplano over the last 130 ka these modeling efforts underscore the relative aridity of the altiplano during the rare and small lake cycles occurring between 80 and 20 ka when colder temperatures combined with little or no change in rainfall produced smaller paleolakes relative aridity between 80 and 20 ka contrasts with the immense tauca lake cycle 18 1 14 1 ka which was six times larger than modern lake titicaca and coincided with heinrich event 1 this improved paleolake record from the southern altiplano reveals a strong link between central andean climate and atlantic sea surface temperature gradients during the late pleistocene even though today rainfall variability is driven mostly by pacific sea surface temperature anomalies associated with el nino southern oscillation however not all heinrich events appear to result in lake expansions most conspicuously during the global cold interval between 80 and 20 ka when the altiplano and amazon basin were relatively arid

late quaternary coastal evolution and aeolian sedimentation in the tectonically active southern atacama desert chile abstract analyses of aeolianites and associated dune surficial carbonate and marine terrace sediments from north central chile 27 54 s yield a record of environmental change for the coastal southern atacama desert spanning at least the last glacial interglacial cycle optically stimulated luminescence dating indicates phases of aeolian dune construction at around 130 111 98 77 69 and 41 28 ka thin section and stable carbon and oxygen isotope analyses suggest a predominantly marine sediment source for the three oldest dune phases aeolianites appear to have accumulated mainly from tectonically uplifted interglacial marine sediments that were deflated during windier and or stormier intervals bedding orientations indicate that sand transporting winds varied in direction from s ese during mis 5e and wnw ese during mis 5c 5a winds from the southeast quadrant are unusual today in this region of the atacama suggesting either major shifts in atmospheric circulation or topographic airflow modification thin section evidence indicates that the aeolianites were cemented by two phases of vadose carbonate tentatively linked to wetter periods around 70 and 45 ka tectonic uplift in the area has proceeded at an average rate of 305 542 mm kyr 1 the study illustrates the complexity of understanding onshore offshore sediment fluxes in the context of late quaternary sea level fluctuations for an area undergoing rapid tectonic uplift

paleomagnetic study of the ordovician table head group port au port peninsula newfoundland a paleomagnetic study of the ordovician table head group in the port au port peninsula of western newfoundland reveals a simple two component magnetization history comprising a reversely magnetized stable southeasterly remanence with a shallow to moderate inclination and an unstable present day overprint pole positions for the stable component both with and without tectonic tilt correction correspond with the early to middle ordovician pole positions for north america suggesting this remanence is early although the nature of the geomagnetic field in the ordovician is not well known the polarity observed is consistent with that reported from other mid ordovician studies and appears to reflect a predominance of reverse polarity for this time interval evidence of significant rotation of any of the sites studied is absent indicating that the continental margin in this region acted in an integral rather than a fragmented fashion during deformation previously published and new but preliminary resul

changes in biological productivity and ocean climatic fluctuations during the last 1 5 kyr in the humboldt ecosystem off northern chile 27 s a multiproxy approach abstract a sedimentary box core biac072014 collected in a coastal environment in the humboldt current ecosystem hce inglesa bay 27 s northern chile was used to reconstruct the changes in biological productivity and ocean climate fluctuations during the last 1 5 kyr via geochemical mineralogical and micropaleontological analyses from 510 ce to 930 ce el nino like conditions prevailed while during the medieval climate anomaly mca 950 ce to 1450 ce la nina like conditions predominated this pattern might have resulted from weakening strengthening of the walker cell contraction expansion of the south pacific sub tropical high spsh and a predominance of warm cold phases of the pacific decadal oscillation pdo between 1820 ce and the present inglesa bay experienced a reduction in the oxygen minimum zone omz intensity and biological productivity an increase in the detritic input and a decrease in sea surface temperature sst despite the regional intensification and secular cooling 14 s and 27 s of coastal upwelling the similarity between the reduction in biological productivity and omz intensity in this region and that in the central zone of chile 36 s suggests that inglesa bay acts a transition zone in relation to the oceanographic behaviour of the hce the reduction in the omz intensity and biological productivity during the last 200 years could be explained by greater subsurface ventilation in intermediate depths due to more northward displacement of the subduction region of the eastern south pacific intermediate water espiw near 30 s in response to the strengthening of the circulation of the subtropical gyre the coastal cooling observed in the northern section of hce during the current warm period suggests that it is not possible to demonstrate that el nino like conditions promoted the reduction in biological productivity and omz intensity in inglesa bay

glacial millennial scale fluctuations in central african precipitation recorded in terrigenous sediment supply and freshwater signals offshore cameroon abstract evidence of rapid climatic oscillations like those observed in the greenland ice cores and sediments from high latitudes of the northern atlantic have been recognized in the pulses of terrigenous material to continental margin sediments off cameroon fe ca ratios used as a parameter to quantify the relative proportions of terrigenous fluxes versus marine carbonate monitor the variability of the west african monsoon they reveal the history of abrupt changes in precipitation over western and central africa during the past 52 kyr these rapid changes are particularly pronounced during the last glacial period and occur at timescales of a few thousand years stable oxygen isotope 18o records of globigerinoides ruber pink show high negative values reflecting periods of high monsoon precipitation the fe ca pattern is very similar to the dansgaard oeschger cycles from the greenland ice cores the good correspondence between the warm interstadials of the dansgaard oeschger cycles from the gisp2 ice core records and the high pulses of fe ca sedimentation in our core suggest a strong teleconnection between the low latitude african climate and the high latitude northern hemisphere climate oscillations during the last glacial this climatic link is probably vested in the west african monsoonal fluctuation that alters tropical sea surface temperatures thermohaline circulations and in turn net export of heat from the south to the north atlantic coupled with the variability of the low latitude southeast trade winds

ordovician paleomagnetic results from the st george and table head carbonates of western newfoundland we have studied 85 limestone and dolostone samples from 21 sites of the st george and table head groups lower and middle ordovician on port au port peninsula humber zone their gentle 15 tilt is probably devonian a steep viscous component dominant in the natural remanence is removed by thermal and less efficiently alternating field demagnetization in about 60 of all samples the thermal treatment yielded a southeasterly reverse component a which typically remained blocked to 450 500 c and then decayed to noise mean a component directions calculated from zijderveld plots and referred to bedding are d i 148 5 33 6 for n 9 st george sites and d i 150 0 i 40 7 for n 5 table head sites corresponding antipoles are 17 5 n 152 3 e dp dm 2 8 4 9 and 13 4 n 149 2 e dp dm 2 9 4 7 respectively we interpret these results as representative of the geomagnetic field in the early and mid ordovician in 14 samples mainly from the older st george strata thermal

palaeomagnetism of the early carboniferous deer lake group western newfoundland no evidence for mid carboniferous displacement of acadia early carboniferous visean to possibly earliest namurian sedimentary rocks of the deer lake group of western newfoundland rest unconformably on grenvillian basement rocks of the canadian shield which form the western border of the early palaeozoic appalachian orogen in addition to magnetically soft magnetizations directed along the present field three families of magnetization directions are found two of them referred to as n north and s south are antiparallel and prefolding and were probably acquired during the depositional process n and s are roughly of equal frequency they have a mean direction irrespective of sign of 0 7 35 2 k 40 95 8 9 and a palaeopole 21 5 n 121 8 e 10 3 6 0 corresponding to a palaeolatitude of 20 6 s this agrees with the palaeolatitude 17 5 s determined from the somewhat older early carboniferous tournaisian terenceville formation of the avalon platform on the eastern side of the appalachian orogen in newfoundland the third magnetization referred to as h roughly horizontal has a mean direction 156 8 13 3 k 37 95 10 1 and a palaeopole 45 4 n 140 3 e 10 3 5 3 corresponding to a palaeolatitude of 7 4 n we interpret this to be an early kiaman latest carboniferous to early permian overprint probably acquired chemically the palaeolatitude determined from the h overprint agrees with that determined from early carboniferous rocks of cratonic north america west of the appalachians therefore we argue early carboniferous palaeofield determinations for cratonic north america have been strongly biased by unremoved kiaman overprints because of this and because of the good agreement between early carboniferous palaeolatitudes obtained from opposite margins of the appalachian orogen we suggest that there is at present no palaeomagnetic evidence for the previously proposed 1500 km displacement from the south of an eastern portion of the appalachians acadia relative to cratonic north america during the carboniferous

a threshold in soil formation at earth s arid hyperarid transition the soils of the atacama desert in northern chile have long been known to contain large quantities of unusual salts yet the processes that form these soils are not yet fully understood we examined the morphology and geochemistry of soils on post miocene fans and stream terraces along a south to north 27 to 24 s rainfall transect that spans the arid to hyperarid transition 21 to 2 mm rain y 1 landform ages are 2 my based on cosmogenic radionuclide concentrations in surface boulders and ar isotopes in interbedded volcanic ash deposits near the driest site indicate a maximum age of 2 1 my a chemical mass balance analysis that explicitly accounts for atmospheric additions was used to quantify net changes in mass and volume as a function of rainfall in the arid 21 mm rain y 1 soil total mass loss to weathering of silicate alluvium and dust 1030 kg m 2 is offset by net addition of salts 170 kg m 2 the most hyperarid soil has accumulated 830 kg m 2 of atmospheric salts including 260 kg sulfate m 2 and 90 kg chloride m 2 resulting in unusually high volumetric expansion 120 for a soil of this age the composition of both airborne particles and atmospheric deposition in passive traps indicates that the geochemistry of the driest soil reflects accumulated atmospheric influxes coupled with limited in soil chemical transformation and loss long term rates of atmospheric solute addition were derived from the ion inventories in the driest soil divided by the landform age and compared to measured contemporary rates with decreasing rainfall the soil salt inventories increase and the retained salts are both more soluble and present at shallower depths all soils generally exhibit vertical variation in their chemistry suggesting slow and stochastic downward water movement and greater climate variability over the past 2 my than is reflected in recent 100 y rainfall averages the geochemistry of these soils shows that the transition from arid to hyperarid rainfall levels marks a fundamental geochemical threshold in wetter soils the rate and character of chemical weathering results in net mass loss and associated volumetric collapse after 105 to 106 years while continuous accumulation of atmospheric solutes in hyperarid soils over similar timescales results in dramatic volumetric expansion the specific geochemistry of hyperarid soils is a function of atmospheric sources and is expected to vary accordingly at other hyperarid sites this work identifies key processes in hyperarid soil formation that are likely to be independent of location and suggests that analogous processes may occur on mars

application of a high resolution seismic investigation in a greek coal mine high resolution seismic methods were applied to map the detailed structure and thickness of the domeniko coal basin central greece and to search for lateral discontinuities such as pinch outs and faults extensive tests were performed to optimize recording parameters and equipment reflection events which can be attributed to coal layers can be interpreted from depths of approximately 30 to 150 m on cdp stacked and inverted sections several low throw faults have been interpreted from the sections results obtained from the high resolution seismic reflection survey combined with drillhole information clearly revealed the 3 d model of the coal field using geostatistical methods the results of the high resolution reflection seismic survey were combined with the information from the borehole program to clearly reveal the 3 d model of the basin

development of a pleistocene calcrete over a sequence of marine terraces at tongoy north central chile and its paleoenvironmental implications abstract the importance of the norte chico region in north central chile has long been recognized for the paleoclimates recorded in its soils this area lies in an extreme climate gradient between the hyper arid atacama desert in the north and a mediterranean climate in the south which has made it very sensitive to past climate changes nevertheless few paleoclimate studies have been undertaken in the region and these were mostly concentrated on the holocene we studied pleistocene climate changes recorded in soils that formed over a series of marine terraces near tongoy about 60 km south of la serena the calcrete and soil development took place on four marine terraces associated with marine isotope stages mis 11 mis 7e mis 5e and mis 1 the different types of calcretes that developed on the three oldest terraces containing calcareous material indicate that they developed during different periods and that climatic conditions favorable for the development of these soils existed in the area at least from mis 11 412 ka until post mis 5e 125 ka the calcrete horizons show well defined development stages recording cyclic climate changes varying between arid and more humid during the late pleistocene these climate changes recorded in the tongoy soils are reflected by sedimentological geomorphological and pedogenic processes climate cycles have only been recorded previously for the post mis 5e stage in the area this study being the first to include climate variations reaching mis 11

holocene evolution and geochronology of a semiarid fluvial system in the western slope of the central andes ams 14 c data in el transito river valley northern chile abstract in this paper we discriminate the contribution of the different sediment sources into a river situated in the semiarid region of northern chile differentiating the ones driven by the paraglacial response from the ones yielded to the tributary junction alluvial fans or the ones coming from the hillslopes the sedimentary infilling is accurately described in the main landforms such as alluvial fans alluvial terraces and landslides in the current valley floor where twenty six 14c ams samples were picked up the 14c age data indicate that the aggradation in the uppermost part of the valley immediately postdates the glacial retreat at 15 000 14c years cal b p and spans the whole holocene starting at 11 ka b p and finishing about 2 ka b p the main sources for lateral inputs are debris flows from tributary catchments in the portion where the river is embedded in between 1000 and 2000 m a s l as well as catastrophic landslides additionally an extensive detailed geomorphological mapping is provided to discuss the meaning of the ages together with an assessment of where the samples came from finally the dataset and field criteria provided in this work contribute to better perform paleoclimatological interpretations for the semiarid fluvial systems of northern chile these interpretations usually consider the increased influence of the westerlies during the holocene and the span of time that the paraglacial response delivers glacigenic sediments into the system

coastal tectonics on the eastern margin of the pacific rim late quaternary sea level history and uplift rates channel islands national park california usa abstract the pacific rim is a region where tectonic processes play a significant role in coastal landscape evolution coastal california on the eastern margin of the pacific rim is very active tectonically and geomorphic expressions of this include uplifted marine terraces there have been however conflicting estimates of the rate of late quaternary uplift of marine terraces in coastal california particularly for the northern channel islands in the present study the terraces on san miguel island and santa rosa island were mapped and new age estimates were generated using uranium series dating of fossil corals and amino acid geochronology of fossil mollusks results indicate that the 2nd terrace on both islands is 120 ka and the 1st terrace on santa rosa island is 80 ka these ages correspond to two global high sea stands of the last interglacial complex marine isotope stages mis 5 5 and 5 1 respectively the age estimates indicate that san miguel island and santa rosa island have been tectonically uplifted at rates of 0 12 0 20 m ka in the late quaternary similar to uplift rates inferred from previous studies on neighboring santa cruz island the newly estimated uplift rates for the northern channel islands are however an order of magnitude lower than a recent study that generated uplift rates from an offshore terrace dating to the last glacial period the differences between the estimated uplift rates in the present study and the offshore study are explained by the magnitude of glacial isostatic adjustment gia effects that were not known at the time of the earlier study set in the larger context of northeastern pacific rim tectonics channel islands uplift rates are higher than those coastal localities on the margin of the east pacific rise spreading center but slightly lower than those of most localities adjacent to the cascadia subduction zone the uplift rates reported here for the northern channel islands are similar to those reported for most other localities where strike slip tectonics are dominant but lower than localities where restraining bends such as the big bend of the san andreas fault result in crustal shortening

a review of paleomagnetic results from the carboniferous of north america the concept of carboniferous geomagnetic field horizon markers results from the east coast carboniferous basin contain an important time stratigraphic horizon of possible global significance late carboniferous units are found to have mostly reversed magnetizations while older carboniferous units may have normal reverse or most frequently dual polarity magnetizations this feature records the change in geomagnetic field from a period of common polarity changes to a period of mainly reversed polarity the kiaman magnetic interval recognition of the stratigraphic position of this polarity feature provides a time line for correlation of units within and among carboniferous basins in the east coast carboniferous basin of atlantic canada this horizon has now been located at the riversdale group level early pennsylvanian namurian westphalian boundary since remanence acquisition of red sediments is often a lengthy process possibly spanning field reversal time scales red bed units pre dating and post dating this time line can in most instances be readily distinguished the former generally recording both polarities and the latter just one reverse polarity a polar displacement of at least 16 is recorded in the results from the east coast carboniferous basin paleolatitude maps show that the area was located near the equator and was displaced northwards by about 8 during the pennsylvanian it cannot be ascertained if those observations are representative of the whole of north america or merely the atlantic seaboard poles derived from other areas of north america do not all fit the regular pattern observed on the atlantic coast using the horizon marker as a tool it is suggested that those poles are post time line in age so that none of them is representative of the position of north america prior to the time line

climate variability at the southern boundaries of the namib southwestern africa and atacama northern chile coastal deserts during the last 120 000 yr abstract in this study we present grain size distributions of the terrigenous fraction of two deep sea sediment cores from the se atlantic offshore namibia and from the se pacific offshore northern chile which we unmix into subpopulations and which are interpreted as coarse eolian dust fine eolian dust and fluvial mud the downcore ratios of the proportions of eolian dust and fluvial mud subsequently represent paleocontinental aridity records of southwestern africa and northern chile for the last 120 000 yr the two records show a relatively wet last glacial maximum lgm compared to a relatively dry holocene but different orbital variability on longer time scales generally the northern chilean aridity record shows higher frequency changes which are closely related to precessional variation in solar insolation compared to the southwestern african aridity record which shows a remarkable resemblance to the global ice volume record we relate the changes in continental aridity in southwestern africa and northern chile to changes in the latitudinal position of the moisture bearing southern westerlies potentially driven by the sea ice extent around antarctica and overprinted by tropical forcing in the equatorial pacific ocean

early paleozoic paleogeography and accretionary history of the newfoundland appalachians new paleomagnetic results were obtained from several units in the central mobile belt of the north central newfoundland appalachians combined with recently published data the results place important limits on interpretations of early paleozoic paleogeography and evolution of the appalachian caledonian orogen the ordovician appalachian margin of north america located at low paleolatitudes and facing roughly south was separated from the southern margin of iapetus avalon armorica by 3500 km primary directions in pillowed volcanic rocks of the moreton9s harbour group that are part of an early ordovician island arc show that these rocks were formed near the north american margin at a paleolatitude of 12 s early to middle ordovician volcanic rocks of the roberts arm chanceport and summerford groups on the other hand were extruded at paleolatitudes of 30 40 s unconformably overlying volcanics of the silurian botwood group were extruded subaerially at a paleolatitude of 24 s combined with tectonostratigraphic data these results suggest the following tectonic history in early ordovician time northerly subduction of the main iapetus basin was accompanied by the formation of a volcanic arc and a back arc basin near the north american margin middle ordovician emplacement of ophiolites on the north american margin reflects the closure of this back arc basin iapetus i and continued northerly subduction in silurian time closed the main basin iapetus ii

association between wave and current aided hyperpycnites and flooding surfaces in shelfal mudstones an integrated sedimentologic sequence stratigraphic and geochemical approach

coupled c s fe geochemistry in a rapidly accumulating marine sedimentary system diagenetic and depositional implications in the present study we have investigated the c s fe systematics in a sediment core md161 13 from the krishna godavari k g basin bay of bengal the core covers the late holocene period with high overall sedimentation rate of 573 cm kyr 1 pore fluid chemical analyses indicate that the depth of the present sulfate methane transition zone smtz is at 6 mbsf the ta ca mg so42 ratios suggest that both organoclastic degradation and anaerobic oxidation of methane aom drive sulfate reduction at the study site the positive correlation between total organic carbon content toc and chromium reducible sulfur crs content indicates marked influence of organoclastic sulfate reduction on sulfidization coupled occurrence of 34s enriched iron sulfide pyrite with 12c enriched authigenic carbonate zones is the possible records of paleo sulfate methane transition zones where aom driven focused sulfate reduction was likely fueled by sustained high methane flux from underlying gas rich zone aluminum normalized poorly reactive iron fepr al and la yb ratios suggest increasing contribution from deccan basalts relative to that of archean proterozoic granitic complex in sediment flux of krishna godavari basin during the last 4 kyr

the sensitivity of hillslope bedrock erosion to precipitation decoupling the impacts of climate and tectonics on hillslope erosion rates is a challenging problem hillslope erosion rates are well known to respond to changes in hillslope boundary conditions e g channel incision rates through their dependence on soil thickness and precipitation is an important control on soil formation surprisingly though compilations of hillslope denudation rates suggest little precipitation sensitivity to isolate the effects of precipitation and boundary condition we measured rates of soil production from bedrock and described soils on hillslopes along a semi arid to hyperarid precipitation gradient in northern chile in each climate zone hillslopes with contrasting boundary conditions actively incising channels versus non eroding landforms were studied channel incision rates which ultimately drive hillslope erosion varied with precipitation rather than tectonic setting throughout the study area these precipitation dependent incision rates are mirrored on the hillslopes where erosion shifts from relatively fast and biologically driven to extremely slow and salt driven as precipitation decreases contrary to studies in humid regions bedrock erosion rates increase with precipitation following a power law from 1 m ma 1 in the hyperarid region to 40 m ma 1 in the semi arid region the effect of boundary condition on soil thickness was observed in all climate zones thicker soils on hillslopes with stable boundaries compared to hillslopes bounded by active channels but the difference in bedrock erosion rates between the hillslopes within a climate region slower erosion rates on hillslopes with stable boundaries decreased as precipitation decreased the biotic abiotic threshold also marks the precipitation rate below which bedrock erosion rates are no longer a function of soil thickness our work shows that hillslope processes become sensitive to precipitation as life disappears and the ability of the landscape to respond to tectonics decreases copyright 2010 john wiley sons ltd

an advance of soler glacier north patagonian icefield at c ad 1222 1342 soler glacier is a temperate outlet glacier on the eastern side of the north patagonian icee eld in chile the glacier is currently receding from its little ice age maximum position attained sometime between ad 1600 and 1900 across the snout and foree eld of the glacier is an arcuate belt of well sorted granule gravel and coarse sand containing tree remains these sediments are interpreted as reworked glaciolacustrine material elevated to the glacier surface by thrusting and folding radiocarbon dating of samples of tree remains in these reworked glaciolacustrine sediments demonstrates that the glacier overrode this lake bed sometime between ad 904 and ad 1334 in situ tree remains plastered onto a large boulder in front of the glacier constrain this advance to the period between ad 1222 and ad 1342 this advance precedes by several hundred years the maximum little ice age extent of other north patagonian icee eld outlet glaciers suggesting either an early age for the onset of little ice age conditions or a previously unrecognized period of glacier advance prior to the advance at c ad 1222 to ad 1342 soler glacier was more recessed than at present cone rming the dynamic response of patagonian glaciers to holocene climatic e uctuations

enhancing the detection of small coal structures by seismic diffraction imaging abstract faults are the most important geological structures that need to be detected in any modern underground coal mining project even a fault with a throw of a few metres can create safety issues and lead to costly delays in mine production while seismic surveys are usually successful at locating faults with throws greater than 5 10 m reliable techniques for resolving more subtle faults dykes and other minor features are yet to be developed in seismic data there are two types of seismic energy signatures that can be used for subsurface imaging specular reflections and diffractions specular reflections are created by relatively smooth surfaces between layers of differing impedance contrasts such as at coal rock interfaces specular reflections are used in conventional seismic reflection surveys diffractions are generated by local discontinuities caused by surface roughness faults dykes and fractures in this paper we describe the use of a moving average error filter which along with a process of reflection event flattening for accommodation of dips and undulations of coal seam reflections can be used to effectively extract diffraction signals from post stack reflection seismic data by identifying diffractions small faults and other minor features that are elusive using conventional seismic reflection processing can be detected suggesting that diffraction imaging may be a superior method to seismic reflection imaging both synthetic and real 2d and 3d coal seismic data are used to illustrate the feasibility of diffraction imaging for small fault detection it is demonstrated from synthetic examples that the extracted diffractions can be used to detect faults with a throw of 1 m while a real data example shows that it is possible to detect igneous dykes with widths of just 4 m

multi millennial scale climate variability during mis 3 and mis 2 inferred from luminescence dating of coastal sand dunes and buried paleosol sequences in central chile 32 s

sedimentary facies and high resolution primary production inferences from laminated diatomacous sediments off northern chile 23 s the oceanographic conditions at the mejillones bay 23 s are strongly influenced by an important wind driven upwelling cell of the humboldt current system hcs as well as by the presence of the oxygen minimum zone omz in this region laminated diatomaceous sediments in this bay were analysed using different qualitative and quantitative techniques on the sediment cores 33c and 32b to interpret the main physical ocean climate factors driving sedimentation processes the composition of these sediments is dominated by the high concentration of resting spores of the genus chaetoceros sp which denotes the strong influence of the upwelling events and primary production on hemipelagic sedimentation processes within the basin the laminae characterized by thickness ranging from 1 mm to several cm are associated with changes in density porosity due to the different concentration and composition of phytoplankton remains and organic matter dark laminae are generally characterized by higher concentration of chaetoceros r s toc organic matter carbonates and lithic minerals with respect to the adjacent lighter laminae representing periods of strong upwelling events high primary production rates and intensified hypoxia contrarily relatively lighter laminae are characterized by diminished concentration of chaetoceros r s and relative increases of the concentration of centric and pennate diatoms producing a more porous sediment some of these light laminae could be associated with short lived major oceanographic enso like events the variability of the sedimentary fluxes observed in both cores represents mostly ocean climate trends at decadal interdecadal and secular time periods the secular trends of the sedimentary fluxes suggest an intensification of the upwelling events and primary production from the second half of the 19th century as well as intensified processes during the 20th century these changes seem to occur contemporaneously with ocean climate variations in the southwestern tropical pacific ocean suggesting a major basin scale climate change during this period

late quaternary precessional cycles of terrigenous sediment input off the norte chico chile 27 5 s and palaeoclimatic implications abstract the palaeoclimatic conditions during the last glacial maximum lgm of southern south america and especially latitudinal shifts of the southern westerly wind belt are still discussed controversially longer palaeoclimatic records covering the late quaternary are rare a particularly sensitive area to late quaternary climatic changes is the norte chico northern chile because of its extreme climatic gradients small shifts of the present climatic zonation could cause significant variations of the terrestrial sedimentary environment which would be recorded in marine terrigenous sediments to unveil the history of shifting climatic zones in northern chile we present a sedimentological study of a marine sediment core geob 3375 1 from the continental slope off the norte chico 27 5 s sedimentological investigations include bulk and silt grain size determinations by sieving atterberg separation and detailed sedigraph analyses additionally clay mineralogical parameters were obtained by x ray diffraction methods the 14c dated core covering the time span from approximately 10 000 to 120 000 cal yr b p consists of hemipelagic sediments terrigenous sedimentological parameters reveal a strong cyclicity which is interpreted in terms of variations of sediment provenance modifications of the terrestrial weathering regimes and modes of sediment input to the ocean these interpretations imply cyclic variations between comparatively arid climates and more humid conditions with seasonal precipitation for northern chile 27 5 s through the late quaternary the cyclicity of the terrigenous sediment parameters is strongly dominated by precessional cycles for the palaeoclimatic signal this means that more humid conditions coincide with maxima of the precession index as e g during the lgm higher seasonal precipitation for this part of chile is most likely derived from frontal winter rain of the southern westerlies thus the data presented here favour not only an equatorward shift of this atmospheric circulation system during the lgm but also precession controlled latitudinal movements throughout the late quaternary precessional forcing of latitudinal movements of the westerly atmospheric circulation system may be conceivable through teleconnections to the northern hemisphere monsoonal system in the atlantic ocean region

late quaternary rapid climate change in northern chile analyses of terrigenous sediments from the chilean continental slope off the southern border of the atacama desert 27 5 s focusing on illite crystallinity and the fe al ratio of the sediments reveal a high frequency variability of the position of the southern westerlies which is very similar to the coeval short term climatic events known from greenland ice cores and from north atlantic sediments besides showing dominantly precession driven variability in precipitation over the andes these analyses also reveal rapid changes in weathering intensity along the chilean coastal range during the last 80 000 years these rapid changes occur at much shorter timescales than the 19 100 kyr orbital forcing of the milankovitch cycles

statistical significance of the fold test in palaeomagnetism summary the significance of the change in direction dispersion on applying the fold test in palaeomagnetism is used as the criterion for deciding whether or not the fold test has statistical significance a set of tables is compiled which can be used for quick application of the test

the vibroseis system a high frequency tool exploration methods are extended to their limits as we continue the search for energy resources successful application of high frequency seismic method requires evaluating each element in the seismic acquisition system and ensuring that each part of the system contributes to the success of the method this extends from seismic signal generation through data processing where good equipment performance and correct parameter selections are required the vibroseis system depends upon the ability of vibrators to generate synchronous repeatable sweeps over the frequency range of interest to support our high frequency seismic efforts conoco inc has developed and built a new high frequency vibrator this paper includes some of the consideration used in building the vibrator along with typical baseplate responses showing excellent drive levels to the design goal of 200 hz with an excellent source available correct application is essential to assure retention of high frequency data recording offsets ar

active erosion deposition cycles in the hyperarid atacama desert of northern chile 10be 21 ne abstract there is significant debate over the rates and types of fluvial activity at the plio pleistocene boundary in the hyperarid atacama desert of chile to quantify fluvial processes and help resolve this debate we measure terrestrial cosmogenic nuclide tcn 10 be and 21 ne concentration depth profiles in three settings representing a chronosequence 1 a late pliocene alluvial fan representative of major regional deposits 2 a modern active channel and 3 an adjacent low terrace inset into the pliocene alluvium late pliocene deposits that are widely preserved in the region contain tcn profiles consistent with relatively rapid stripping of upland sediment at the plio pleistocene boundary deposits inset into these late pliocene features record cut and fill cycles that rework sediment throughout the quaternary the tcn profile in the modern channel is best explained by sediment aggradation at 2 1 m myr 1 during the last 250 000 yr similarly the adjacent low terrace sediments contain tcn concentration profiles consistent with aggradation of 2 0 m myr 1 over a period of 250 000 750 000 yr prior to the last 250 000 yr of stability in summary depth profiles of two tcns provide constraints on the rates of sediment deposition sources of sediment and transport history as well as the subsequent exposure conditions of the sediment following deposition our results are consistent with early quaternary initiation of hyperaridity for the region during the quaternary winter precipitation events experienced at our sites latitude 241s drive active erosion deposition cycles the northward migration of the subtropical front during quaternary glacial cycles may have enhanced precipitation at 241s leading to more active fluvial processes during cooler periods

chronology of quaternary coastal aeolianite deposition and the drowned shorelines of southwestern western australia a reappraisal abstract aeolianite successions of low gradient continental margins commonly show complex records of coastal dune deposition linked to a wide range of sea level positions and climatic periods of the middle and late pleistocene recording both regional and broader scale drivers of sediment production coastal dune development and landform preservation to better characterise the general pattern of sedimentation that occurs over quaternary glacial interglacial cycles on low gradient temperate carbonate continental shelves we examine the morphology stratigraphy and age of aeolianite deposits in the perth region western australia this includes an analysis of well defined drowned coastal landforms preserved on the adjacent shelf new and previously published optical ages provide a preliminary timeframe for the deposition of aeolianite in the perth region and on rottnest island 17 km offshore an extensive aeolianite ridge near perth representing a former barrier has optically stimulated luminesence osl ages that range from 120 12 to 103 10 ka mis 5e 5a in the context of associated age uncertainties osl ages for an exposure in the same ridge 2 5 km inland record the onlap of much older aeolianite osl age 415 70 ka by shell rich estuarine beds osl age 290 30 ka a further 5 5 km inland from the coast two thick aeolianite units separated by a well developed palaeosol have stratigraphically consistent osl ages of 310 30 and 155 20 ka in contrast aeolianite units that form the northern coast of rottnest island have osl ages of 77 12 ka and 27 5 ka the new osl ages and previously reported tl and u th ages indicate that the bulk of the island comprises dunes deposited around the end of the last interglacial sensu lato mis 5a 4 and during the last glacial mis 4 2 accumulating over a last interglacial coral reef and basal calcarenite drowned barrier and dune landforms preserved on the adjacent continental shelf reveal that barriers were formed during periods of intermediate sea level e g mis 3 and significant dune mobility occurred when the shelf was subaerially exposed the pattern of shelf sedimentation discernible in the perth region large scale coastal carbonate dune deposition during periods of high and intermediate sea level and reactivation during glacial lowstands is largely consistent with published stratigraphic and age data for large scale aeolianite deposits on other low gradient carbonate shelves based on these data a general model is proposed for the cycle of quaternary sedimentation and landform evolution that occurs on these shelves which are dynamic sedimentary environments with coastal landforms and sedimentary successions that are very sensitive to erosion and sediment reworking

enso tropical extratropical climate teleconnections and mechanisms for holocene debris flows along the hyperarid coast of western south america 17 24 s abstract el nino the warm phase of the enso cycle involves ocean climate anomalies in the tropical pacific ocean and in the extratropics which frequently result in heavy rainfall episodes along the equatorial and subtropical regions of western south america here we investigate meteorological mechanisms producing heavy rains floods and debris flows along the less known hyperarid coasts of southern peru and northern chile to evaluate the paleoclimate significance of holocene debris flow deposits our results reveal that heavy rainfall over the coast of southernmost peru occurs either during austral summer at the mature stage of el nino in connection with warmer sea surface temperatures and anomalous jet streams off northern chile or during the previous austral winter spring associated with equatorward shifted pacific south america psa atmospheric teleconnection patterns at antofagasta in northern chile such events occur almost exclusively in the latter season when deeper psa related anomaly poles extend their influence equatorwards beyond central chile during non el nino conditions short lived heavy rainfall episodes in southernmost peru can be associated with similar albeit weaker or less persistent circulation anomalies in addition to that a seasonally enhanced low level southerly flow provides orographic uplift rainfall favourable conditions by the andes at the 18 s coastal bend ultimately the trigger for rainfall events in all seasons and phases of the enso cycle was invariably connected with mid troposphere wave disturbances from mid latitudes the chronostratigraphy of debris flow deposits from both areas and its comparison with other paleoclimate records at the western side of the andes suggests that the enso related teleconnection patterns operated only during the second half of the holocene supporting an onset of modern el nino manifestations at 5300 5500 cal bp and increased frequency of major events during recent times we suggest that several debris flows dated between 12 900 and 8400 cal bp in southernmost peru previously interpreted as an indication of strong el nino events were associated with short and intense heavy rainfall episodes similar to those described here during the late winter spring season in non el nino conditions concomitant with stronger low level southerlies strengthened south eastern pacific subtropical anticyclone and intensified coastal upwelling

variability in erosion rates related to the state of landscape transience in the semi arid chilean andes we quantify erosion rates in the higher sectors of the huasco valley in the main cordillera of the semi arid andes of chile using elevation differences between three successive geomorphic markers pediments and paleo valleys and the present day valley available ar ar ages of neogene pediments are used to estimate mean erosion rates for the three periods 16 to 13 my 13 to 8 my and following 8 my the landscape of the huasco valley is in a transient state as indicated by well preserved pediment surfaces in interfluves valleys deeply incised by fluvial and glacial erosion and scarped head valleys that represent the current knickzones higher erosion rates 45 75 m my are calculated for the more recent period 8 my during which deep incision developed compared to previous periods 6 31 m my quantitative data indicate that glaciers had a much higher erosional capability than fluvial activity in the higher sectors of the main cordillera comparison with erosion rates calculated in other drainage basins of the chilean andes suggests that the variability of erosion rates depends on the landscape s transient erosive state the landscape s geomorphologic response to the uplift of the main cordillera results in the retreat of a knickzone for which retreat velocity depends on precipitation rate pattern and glacial erosion intensity copyright 2011 john wiley sons ltd

using remote sensing to quantify aeolian transport and estimate the age of the terminal dune field dunas pampa blanca in southern peru abstract aeolian dunes are widely used to reconstruct paleoenvironmental conditions however terminal dune fields ergs in the coastal desert of southern peru where information regarding quaternary paleoenvironmental conditions is very limited have until now not been used for paleoenvironmental reconstructions and the time depth of their accumulation is unknown here different estimates are derived to constrain the time depth recorded in the dunas pampa blanca a terminal dune field in coastal southern peru dune field age is calculated using the volume of the dunas pampa blanca and i recent aeolian transport rate in migrating transverse dunes feeding the dunas pampa blanca derived from digital processing of sequential landsat and quickbird images and ii limitations posed by recent fluvial sediment supply to the source of aeolian transport the resulting maximum age estimate of 70 8 ka from aeolian transport compares with a minimum age estimate of 4 75 ka from sediment supply however a minimum age estimate of 110 450 ka is deduced from the tectonic and topographic evolution of the region this discrepancy contradicts the hypothesis of late quaternary stability in the peruvian coastal desert and indicates that recent conditions of aeolian sediment supply and transport are not representative for the late quaternary

late quaternary changes in biogenic opal fluxes in the southern indian ocean abstract late quaternary sedimentary and paleoenvironmental conditions in the southern indian ocean have been reconstructed from radioisotope and proxy element profiles biogenic opal and organic carbon measured on five sediment cores taken along a transect across the indian sector of the antarctic circumpolar current dissolution corrected opal rain rates were used to reconstruct past changes of opal productivity for this region records from these five cores indicate that opal productivity during glacial periods was lower than presently recorded south of the antarctic polar front apf probably due to increased ice cover north of apf opal productivity was slightly greater during glacial periods than during the holocene probably in response to 1 the northward migration of the apf by approximately 5 latitude 2 a northward transport of si from the antarctic zone and 3 an increase of fe necessary for opal producing organisms via upwelling and the erosion of the kerguelen plateau we also invoke a decoupling between opal burial and organic carbon flux to the seabed to explain the variation in buried si c ratio between glacial and interglacial sediment this decoupling is principally explained by better organic carbon preservation in the glacial sediments due to strong sediment focussing an increase in glacial export paleoproductivity is not supported by the data implying that bioproductivity variations in the southern indian ocean are unlikely to have contributed to the glacial drawdown of atmospheric co 2 inferred from ice core data

premine study of shallow coal seams using high resolution seismic reflection methods geological investigations in the illinois basin coalfields have shown that significant differences in safe and economical exploitation of coal depends directly on accurate mapping of the roof rock overlying the seam as well as on geological structures in the coal measures in roof rock transition zones above the herrin no 6 coal where the nonmarine energy shale changes to the anna shale a change often occurs from low to high sulfur coal and from low to high stability roof rocks in many instances use of borehole data alone is inadequate to locate these features in advance of mining high resolution seismic reflection data collected near harco illinois were used as part of premine planning to help predict roof instability areas of low sulfur coal and geologic disturbances several faults channels and facies changes affecting the herrin no 6 and the springfield no 5 coal seams at depths of 137 m and 167 m respectively were interpreted and modeled one and two dimensional synthetic seismo

dynamics of the low level jet off the west coast of subtropical south america the subtropical west coast of south america is under the influence of the southeast pacific anticyclone year round which induces persistent southerly winds along the coast of north central chile these winds often take the form of a low level coastal jet in many aspects similar to the coastal jet existing off the california coast extensive diagnostics of mesoscale model results for a case in october 2000 are used here to describe the mean momentum budget supporting the coastal jet the jet appears to occur when midlatitude synoptic conditions induce a northerly directed pressure gradient force along the coast of northcentral chile the very steep coastal terrain precludes the development of a significant easterly low level wind that would geostrophically balance the pressure gradient instead the meridional flow accelerates until turbulent friction in the marine boundary layer balances the meridional pressure gradient the resulting force balance is semigeostrophic with geostrophy valid only in the zonal cross shore direction at higher levels the topographic inhibition of the easterlies relaxes and a small easterly flow ensues which turns out to be very important in the temperature and stability budgets of the layer capping the marine boundary layer

high resolution 3 d seismic survey over a coal mine reserve area in the u s a case study a high resolution three dimensional 3 d seismic survey was conducted in advance of coal mine development in the illinois basin in may 1989 to better define a geologic structure with the potential to adversely affect longwall mining conditions the 3 d seismic data indicate that an abrupt change in seam elevation or roll encountered near the northern property line trends south into the reserve area and then turns southeast a personal computer based workstation was used to integrate borehole and seismic data for modeling in which 3 d block diagrams of the calculated seam elevations were generated the block diagrams show a steep slope on the west flank of the roll that gradually decreases as the roll turns to the southeast the survey also reveals a geologic structure beneath the roll at an estimated depth of 46 62 m horizontal time slice sections of this feature suggest the presence of a paleochannel that meanders on a similar course as the roll which apparently was connected to a larger paleochannel system a conoco high frequency vibroseis unit was successfully used as the seismic source to generate the high frequencies necessary to detect and resolve the thin coal beds

glacial to holocene changes in sea surface temperature and coastal vegetation in north central chile high versus low latitude forcing abstract north central chile is located at an important climatic transition zone between humid conditions under the influence of the southern hemisphere westerly winds in the south and the extremely dry climate of the atacama desert in the north offshore equatorward flowing cold waters of the peru chile current converge with relatively warmer waters coming from the low latitudes based on terrestrial and marine proxies from the same archive geob 7139 2 30 12 s 71 59 w we show that during the glacial between 33 and 19 kyr cold sea surface temperatures paralleled enhanced humidity with high terrestrial input and abundant vegetation on the adjacent land suggesting a stronger influence of cold waters from the antarctic circumpolar current and the westerly winds while the deglacial sea surface temperature warming started at 19 kyr the humidity decrease occurred around 17 16 kyr bp the early to mid holocene is characterized by extremely warm and dry conditions we suggest that climate changes were driven by fluctuations in antarctic sea ice extent and the circulation of the hadley cell both ultimately linked to insolation changes our records further imply warm and dry conditions in north central chile during the northern hemisphere heinrich events

relationship between antarctic sea ice and southwest african climate during the late quaternary here we compare late quaternary southwest african climate records from the west coast of southern africa published winter rainfall and trade wind intensity records from a core off the coast of namibia to records of antarctic sea ice extent this comparison reveals coherent changes between antarctic sea ice extent and the southwest african winter rain region since 45 k y b p with enhanced winter rainfall and trade wind vigor during periods of increased sea ice presence we propose an oceanic and atmospheric coupling between antarctic sea ice and the winter rainfall zone of southwest africa that may lead to increased desertification in the region if global warming persists

paleoproductivity in the southern peru chile current through the last 33 000 yr abstract based on a multiparameter approach including organic carbon biogenic opal carbonate and the species composition of planktic foraminifera this paper provides the first qualitative assessment of the history of paleoproductivity on glacial interglacial time scales in the southern peru chile current pcc off chile which belongs to the least studied parts of the world ocean during the last glacial maximum lgm highest relative paleoproductivity of the last 33 kyr indicated by high accumulation rates of organic carbon biogenic opal and carbonate has been found contrasted by lowest values during the early and middle holocene this shift from high to low productivity is accompanied by a major change in the species composition of planktic foraminifera from a dominance of neogloboquadrina pachyderma sin to the dominance of n pachyderma dex the temporal pattern of paleoproductivity off chile is very similar to the history of the continental paleoclimate in the region which is supposed to be driven by the position of the southern westerlies this observation points to a functional relationship between the position of the southern westerlies and the history of paleoproductivity off chile assuming that atmospheric and oceanographic circulation are closely linked a northward displacement of the antarctic circumpolar current during the lgm in line with the northward movement of the southern westerlies would bring the main nutrient source closer to our core sites resulting in increased productivity however based on the available data it is not clear if the higher productivity in the southern pcc during the lgm reflects generally higher productivity during this time or only a regional displacement of the main productivity centers

monsoon rainfall and contrasting source rocks influenced sediment composition of peninsular basins along the east coast of india western bay of bengal abstract the peninsular india is characterized by remarkable variation in lithological composition as well as contrasting rainfall distribution patterns the erosional and weathering history of these source rocks along with monsoonal changes are archived in sediments deposited in the basins along the east of coast of india here we present a 60 ky record of sr nd isotope ratios coupled with major elemental compositions of a sediment core off krishna godavari k g basin western bay of bengal the marked temporal variation in 87sr 86sr end and mg al ratios are attributed to the changes in relative contribution of sediments from the deccan basalts dcb and archean proterozoic gneissic complexes apgc the enhanced contribution of apgc associated with an increase in monsoon precipitation may be attributed to heightened erosion of the granitic gneissic rocks on the other hand a close correlation of 87sr 86sr ratios with rb sr ratio 18og ruber and cia profiles indicate the possible influence of weathering intensity on the sediment composition

the impact of sediment provenance on barium based productivity estimates abstract biogenic barium in marine sediments has been suggested to be a reliable proxy of export productivity from the surface ocean and algorithms have been developed to link these properties however problems arise when the proposed algorithms are applied to predominantly terrigenous sediments a major source of error is incorrect estimates of the terrigenous ba al ratio in normative calculations of the amount of biogenic barium in the sediment compared to an often used global average ba al ratio much better results can be obtained by estimating the terrigenous ba al ratio from exponential regression of the ba al ratios of surface sediments obtained from continental slope transects this method has been applied to surface sediments from the chilean continental slope the calculated regional terrigenous ba al ratios could be verified with purely terrigenous samples from chilean rivers the resulting accumulation rates of biogenic barium on the chilean continental slope reliably reproduce the regional pattern of primary productivity in the southern peru chile current indicating the potential of biogenic barium as a useful paleo productivity proxy

paleomagnetism of certain constituents of the bay st george sub basin western newfoundland abstract paleomagnetic studies have been made of certain constituents of the bay st george sub basin specifically results are reported from the spout falls formation tournaisian the jeffreys village member of the robinsons river formation visean and the searston formation namurian westphalian the following magnetizations have been isolated spout falls a tournaisian with d 343 5 i 22 7 k 61 2 95 7 1 and the corresponding pole at 28 6 n 139 5 e 4 5 8 5 spout falls b kiaman with d 166 7 i 12 2 k 51 7 95 10 7 and the corresponding pole at 34 5 s 42 7 w 5 5 10 9 jeffreys village a visean with d 351 2 i 27 3 k 54 0 95 7 6 and the corresponding pole at 26 5 n 130 7 e 4 5 8 3 searston a namurian with d 161 7 i 11 7 k 107 95 7 4 and the corresponding pole at 33 9 s 37 2 w 3 8 7 5 and searston c with d 111 6 i 13 8 k 28 8 95 14 5 and the corresponding pole at 19 6 s 19 0 e 7 6 14 8 after comparison with paleopoles of similar ages derived from eastern and western newfoundland rocks from constituents of the east coast basin and for interior north america it is concluded that 1 it is unlikely that any large scale relative motion took place since the early carboniferous between eastern and western newfoundland 2 it is unlikely that any north south relative motion took place between the east coast basin and the bay st george sub basin and 3 the bay st george sub basin results do not support the earlier proposed displaced terrane hypothesis of the northern appalachians in as much as the motions during the carboniferous are not supported there is evidence of the northward motion of the appalachians and north america as a whole during the carboniferous the magnetostratigraphic horizon marker in the carboniferous separating a dominant normal and reversed magnetization on the older side and an entirely reversed kiaman magnetization on the younger side may be placed in the bay st george sub basin at the base of the searston formation

a 70 kyr sea surface temperature record off southern chile ocean drilling program site 1233 1 we present the first high resolution alkenone derived sea surface temperature sst reconstruction in the southeast pacific ocean drilling program site 1233 covering the major part of the last glacial period and the holocene the record shows a clear millennial scale pattern that is very similar to climate fluctuations observed in antarctic ice cores suggesting that the southern hemisphere high latitude climate changes extended into the midlatitudes involving simultaneous changes in air temperatures over antarctica sea ice extent extension of the antarctic circumpolar current and westerly atmospheric circulation a comparison to other midlatitude surface ocean records suggests that this antarctic millennial scale pattern was probably a hemisphere wide phenomenon in addition we performed sst gradient reconstructions over the complete latitudinal range of the pacific eastern boundary current system for different time intervals during the last 70 kyr the main results suggest an equatorward displaced subtropical gyre circulation during marine isotope stages 2 and 4

paleomagnetism of the lawrenceton formation volcanic rocks silurian botwood group change islands newfoundland paleomagnetic sampling of the lawrenceton formation of the silurian botwood group in northeastern newfoundland was combined with detailed structural mapping of the area in order to determine the deformation history and make adequate structural corrections to the paleomagnetic data structural analysis indicates that the lawrenceton formation experienced at least two folding events i a regional northeast southwest trending siluro devonian folding episode that produced a well developed axial plane cleavage and ii an episode of local north trending folding bedding regional cleavage relationships indicate that the latter event is older than the regional folding thermal demagnetization of the lawrenceton formation yielded univectorial southerly and shallow directions in situ a fold test on an early mesoscale fold indicates that the magnetization of the botwood postdates this folding event however our results combined with an earlier paleomagnetic study of nearby lawrenceton formation rocks demo

modelling the joint variability of grain size and chemical composition in sediments abstract the geochemical composition of siliciclastic sediments correlates strongly with grain size hence geochemical composition may serve as a grain size proxy in the absence of grain size variations geochemical data of siliciclastic sediments may be used to characterise size independent processes i e sediment provenance weathering mixing shape density sorting and diagenesis in general however geochemical data sets contain both types of information in order to formalise interpretation of geochemical data we propose a mathematical method to decompose the total geochemical variability of a series of genetically related specimens into a grain size dependent the shared signal and a grain size independent part the residual signal the former may serve as a proxy for grain size whereas the latter represents geochemical variability that would have been observed if all sediments would have had the same grain size distribution the two data sets are jointly decomposed by means of partial least squares pls and orthogonal projection subsequently the presence of significant grain size independent geochemical variability in the residual signal is determined in a statistically rigorous manner using a 2 test using a synthetic example we show that the residual record effectively reveals an imposed provenance signal which could not have been resolved from the geochemical or grain size data sets individually we analysed the relation between grain size and geochemical composition in three quaternary marine sediment cores located offshore west africa and south america geob7920 2 geob9508 5 and geob7139 2 both sites are characterised by biogenic sediment input in addition to fluvial and aeolian sediment input from the continent it was found that all cores show a strong but different correlation between the mean grain size and the bulk geochemical composition these results demonstrate that geochemical grain size proxies are empirical and site specific it was also found that the geochemical and grain size data in cores geob7920 2 and geob7139 2 do not contain unique information whereas in core geob9508 5 ti varies independently from the grain size this residual ti signal correlates with the transport mechanism as demonstrated by statistically different values of aeolian and fluvial dominated sediments however a unique interpretation of this residual signal in terms of the postulated grain size independent mechanisms could not be provided without additional information we conclude that the proposed model facilitates identification and validation of different element ratios as grain size proxies and more importantly as proxies for size independent processes for this reason the model paves the way for rigorous analysis of multi proxy data which are widely used in palaeoceanographic and palaeoclimatic research

paleomagnetism of the clam bank formation and paleolatitude estimates for western newfoundland n 16 sites k 25 3 a 7 5 with a corresponding paleopole at 23 2 n 145 0 e dp dm 4 s0 8 2 component b with d 172 9 i 5 7 n 35 specimens k 10 2 a 6 4 with a corresponding paleopole at 38 2 n 130 1 e dp dm 3 2 6 4 component c with d 350 4 i 69 8 n 33 specimens k 8 9 a9 8 9 a pre mesozoic origin of the a and b components is indicated by the presence of normal and reversed components in specific sites by the lack of correspondence between the a and b paleopoles and the mesozoic and later pole positions from the appalachians and the north american craton and by agreement with paleozoic poles from the region the a component was probably acquired immediately after deformation during the acadian orogeny the b component is probably a chemical remanence that was acquired during permo carboniferous kiaman time the c component is of recent origin probably acquired in the present earth s field paleomagnetic data from western newfoundland are used in a localized setting to construct a paleopole sequence and to estimate paleolatitudes for western newfoundland during the paleozoic keeping in mind the paucity of data for siluro devonian age from this region western newfoundland seems to have been at its southernmost position at the end of the ordovician and to have occupied equatorial latitudes during the permo carboniferous the paleolatitude trend suggests that this block which is part of the north american craton moved in a southerly direction during the early paleozoic and in a northerly direction during the middle and late paleozoic

advances in seismic reflection profiling for us coal exploration the utilization of seismic reflection methods in us coal exploration increased during the last decade as evidenced by the number of publications and papers presented at technical meetings the increased application of innovative techniques adapted from the petroleum industry has resulted in improvements in seismic data acquisition processing and interpretation the objective of this paper is to present some advances in the application of high resolution seismic reflection methods to us coal exploration since they were adopted in the mid 1970s

tomographic imaging of rock conditions ahead of mining using the shearer as a seismic source a feasibility study roof falls due to poor rock conditions in a coal longwall panel may threaten miner s life and cause significant interruption to mine production there has been a requirement for technologies that are capable of imaging the rock conditions in longwall coal mining ahead of the working face and without any interruption to production a feasibility study was carried out to investigate the characteristics of seismic signals generated by the continuous coal cutter shearer and recorded by geophone arrays deployed ahead of the working face for the purpose of seismic tomographic imaging of roof strata condition before mining two experiments were conducted at a coal mine using two arrays of geophones the experiments have demonstrated that the longwall shearer generates strong and low frequency 40 hz seismic energy that can be adequately detected by geophones deployed in shallow boreholes along the roadways as far as 300 m from the face using noise filtering and signal cross correlation techniques the seismic arrival times associated with the shearer cutting can be reliably determined it has proved the concept that velocity variations ahead of the face can be mapped out using tomographic techniques while mining is in progress

precession modulation of the south pacific westerly wind belt over the past million years the southern westerly wind belt sww interacts with the antarctic circumpolar current and strongly impacts the southern ocean carbon budget and antarctic ice sheet dynamics across glacial interglacial cycles we investigated precipitation driven sediment input changes to the southeast pacific off the southern margin of the atacama desert over the past one million years revealing strong precession 19 23 ka cycles our simulations with 2 ocean atmosphere general circulation models suggest that observed cyclic rainfall changes are linked to meridional shifts in water vapor transport from the tropical pacific toward the southern atacama desert these changes reflect a precessional modulation of the split in the austral winter south pacific jet stream for precession maxima we infer significantly enhanced rainfall in the southern atacama desert due to a stronger south pacific split jet with enhanced subtropical subpolar jets and a weaker midlatitude jet conversely we derive dry conditions in northern chile related to reduced subtropical subpolar jets and an enhanced midlatitude jet for precession minima the presence of precessional cycles in the pacific sww and lack thereof in other basins indicate that orbital scale changes of the sww were not zonally homogeneous across the southern hemisphere in contrast to the hemispherewide shifts of the sww suggested for glacial terminations the strengthening of the jet is unique to the south pacific realm and might have affected winter controlled changes in the mixed layer depth the formation of intermediate water and the buildup of sea ice around antarctica with implications for the global overturning circulation and the oceanic storage of atmospheric co2

limestones of western newfoundland that magnetized before devonian folding but after middle ordovician lithification a positive fold test and a negative conglomerate test help determine when and how stable remanence was acquired in the middle ordovician table head group limestones of the port au port peninsula of newfoundland the limestones magnetized after lithification and incorporation as clasts into a middle ordovician breccia hence the limestones do not carry a detrital or other primary remanence despite their very low conodont colour alteration index of 1 the remanence may be thermoviscous or diagenetic and was acquired before devonian folding this suggests the need for caution in interpreting paleomagnetic results from other early paleozoic limestones whose remanence resides in magnetite of blocking temperature lower than 400 c

optically stimulated luminescence osl dating of loessic sediments and cemented scree in northwest england optically stimulated luminescence osl dates are reported for silts and very fine sands believed to be loessic sediments from northwest england at three sites loessic sediments were initially interpreted as primary aeolian deposits and at two other sites as loess incorporated into the matrix of cemented scree however the results of osl dating indicate a more complex pattern of accumulation than originally hypothesized and have prompted reconsideration of these materials whatever the process es and underlying cause s it is evident that significant amounts of soil erosion occurred on the limestone uplands earlier than previously thought all but one of the ages fall entirely within the holocene period and suggest that these deposits contain reworked rather than primary loess four of the five sites are characterized by non gaussian dose distributions and consequently equivalent doses have been estimated using a range of appropriate age models the implications of differences in the ages derived f

development of a cliff top dune indicated by particle size and geochemical characteristics rubjerg knude denmark particle size and geochemical data have been used to investigate the development of a large cliff top dune at rubjerg knude located on the western coast of jutland denmark textural parameters and geochemical ratios provided useful indicators of the dune sediment provenance and mode of evolution of the dune the dune sediments themselves showed no significant spatial particle size trends and reflect a number of processes including grainfall wind ripple migration and avalanching grainflow which formed a high proportion of the deposits on both the stoss and lee sides of the present dune fine grainfall sediments which have accumulated to form a sandplain in the lee of the dune show fining and improved sorting with distance and extend more than 2 km downwind of the dune crest comparison of the textural and geochemical data from rubjerg knude and other locations on the jutland coast indicates that although there is a contribution of sand to the dune from local marine sources the main source of sand to the cliff top dune and sand plain sediments has been provided by the wind erosion of the underlying cliffs which are composed of weichselian age sandy glaciofluvial and glaciolacustrine deposits optically stimulated luminescence dating indicated an apparent age for the sand at the base of 274 14 years if this date is reliable it suggests that accumulation of the aeolian sand in this area began within approximately the last 300 years map and photographic evidence indicate that the modern high dune only began to form after 1885 apparently associated with an acceleration in the rate of coastal cliff retreat

fe speciation and fe al ratio in the sediments of southeastern arabian sea as an indicator of climate change aluminum titanium and iron are the major lithogeneous contributors to the marine sediment and their abundance varies strikingly with the intensity of monsoonal precipitation al and ti concentration in a sediment core sk 129 gc 05 from southeastern arabian sea exhibit very strong positive correlation r 0 92 n 140 suggesting their lithogenous association whereas ti and fe does not correlate so strongly r 0 44 this suggests that part of fe is present as structurally unsupported and is evident by two fold increased fe al ratio 0 87 average compared to upper continental crust 0 44 the presence of structurally unsupported fe is confirmed by the sequential leaching of fe which is associated with different fractions such as exchangeable 0 98 carbonate 1 98 fe mn oxide 30 8 organic carbon 4 7 and biogenic opal 11 4 which together constitutes nearly 50 of the bulk fe content there is a good correlation between time series fe al and differential solar insolation suggesting warmer and humid climatic condition resulting intense weathering of hinterland rocks associated with increased monsoonal precipitation probably decoupled soluble fe and its transportation to southeastern arabian sea

shallow seismic reflection investigations of coal in the sydney basin surface reflection profiling with the mini sosie technique successfully mapped shallow coal seam structure in the western sydney basin new south wales several minor faults and zones of fracturing were detected in regions of thick triassic sandstone cover data quality was poor and unsuitable for geologic interpretation synthetic seismograms based on nearby borehole and petrophysical control show excellent agreement with the mini sosie sections and illustrate the deleterious filtering effects of coal seams and sequences to establish a phenomenological basis for seismic wave propagation in shallow coal measures two vertical seismic profiles vsps which used small explosive charges were recorded with high spatial and temporal sampling numerous multiple reflections were observed in the downgoing wave display the isolated upgoing waves were migrated to yield blurred images of the main coal seams the subsurface velocity function also deduced from the vsp shows broad correlation with the geologic log

the topographic imprint of a transient climate episode the western andean flank between 15 5 and 41 5 s mountain range topography is determined by the complex interplay between tectonics and climate however often it is not clear to what extent climate forces topographic evolution and how past climatic episodes are reflected in present day relief the andes are a tectonically active mountain belt encompassing various climatic zones with pronounced differences in rainfall erosion and glacier extent under similar plate boundary conditions in the central to south western andes climatic zones range from hyperarid desert with mean annual rainfall of 5 mm a 22 5 s to year round humidity with 2500 mm a 40 s the andes thus provide a unique setting for investigating the relationship between tectonics climate and topography we present an analysis of 120 catchments along the western andean watersheds between 15 5 and 41 5 s which is based on srtmv3 90m data and new medium resolution rainfall tropical rainfall measurement mission trmm dataset for each basin we extracted geometry relief and climate parameters to test whether andean topography shows a climatic imprint and to analyze how climate influences relief our data document that elevation and relief decrease with increasing rainfall and descending snowline elevation furthermore we show that local relief reaches high values of 750 m in a zone between 28 s to 35 s during pleistocene glacial stages this region was affected by the northward shifting southern hemisphere westerlies which provided moisture for valley glacier formation and extended glacial coverage as well as glacial erosion in contrast the southern regions between 35 s to 40 s receive higher rainfall and have a lower local relief of 200 m probably related to an increased drainage density we distinguish two different climatically controlled mechanisms shaping topography 1 fluvial erosion by prolonged channel hillslope coupling which smoothes relief and 2 erosion by valley glaciers that generates relief finally our results suggests that the catchment scale relief of the andes between 28 s to 35 s is characterized by a pronounced transient component reflecting past climatic conditions copyright 2010 john wiley sons ltd

biogenic silica and diatom thanatocoenosis in surface sediments below the peru chile current controlling mechanisms and relationship with productivity of surface waters abstract based on 76 surface sediment samples collected between ca 22 and 44 s along the chilean coast in the southeast pacific ocean we report on the north south distribution of opal content and diatom concentration and the quantitative and qualitative composition of the preserved diatom community latitudinal differences in the siliceous signal reflect the influence of two main mechanisms of surface water production coastal upwelling off northern and central chile till ca 38 s and nutrient enrichment by the input of cold southern non upwelling associated waters south of ca 38 s the poleward increase in biogenic opal and diatom values parallels well the north south increase of pigment concentration in surface waters as recorded by satellites between 22 and 33 s where low pigment concentrations are measured opal content and diatom concentration are mostly low except at 22 23 s in contrast both higher opal and diatom values at 34 38 s and 41 42 s correspond well with higher pigment estimations preserved diatom populations document the present day dominant hydrographical conditions nutrient enrichment of surface waters due to coastal upwelling results in intensive production of diatoms off northern and central chile reflected by the predominance of the richly composed association of chaetoceros spores north of ca 38 s the diatom association shows that the area between 35 and 38 s is transitional the abrupt decrease of chaetoceros spores south of 38 s off chile coupled with the enhanced contribution of thalassiosira spp representatives of high productivity low temperature waters points to the presumed high nutrient supply by the iron limited nutrient rich antarctic circumpolar water the contribution of benthic diatoms reflects some lateral transport from the near shore area into deeper positions south of 38 s

late pleistocene human occupation of the hyperarid core in the atacama desert northern chile abstract few archeological sites in south america contain uncontroversial evidence for when the first peopling of the continent occurred largely ignored in this debate extreme environments are assumed either as barriers to this early wave of migration or without potential for past habitability here we report on a rare 12 13 ka human occupation from quebrada mani site qm12 a plantless near rainless landscape 1240 m asl and 85 km from the pacific ocean located in the hyperarid core of the atacama desert this location harbored wetlands and riparian woodlands that were fed by increased rainfall further east in the central andes during the latest pleistocene excavations at qm12 yielded a diverse cultural assemblage of lithics burned and cut bones marine gastropods pigments plant fibers and wooden artifacts alongside a prepared fireplace sixteen radiocarbon dates from site qm12 on charcoal marine shells animal dung plant remains and wood reveal that the occupation took place between 12 8 and 11 7 ka these results demonstrate that the atacama desert was not a barrier to early american settlement and dispersal and provide new clues for understanding the cultural complexity and diversity of the peopling of south america during the last glacial interglacial transition

an absolute chronology for the raised beach and associated deposits at sewerby east yorkshire england the raised beach sediments revealed in the cliffs at sewerby east yorkshire are widely regarded as ipswichian in age previously reported evidence for this dating is reviewed and new results from a range of luminescence dating techniques applied to the blown sand deposit overlying the raised beach are reported these provide the first absolute date for the sewerby site of 120 84 11 82 ka which places the blown sand at the boundary between oxygen isotope stages ois 5e and 5d as the underlying raised beach is little older than the blown sand it probably formed during ois stage 5e as suggested by the faunal evidence

paleomagnetism of the moreton s harbour group northeastern newfoundland appalachians evidence for an early ordovician island arc near the laurentian margin of iapetus paleomagnetic results have been obtained from mafic volcanic units in the upper part of the moreton s harbour group which is part of an accreted island arc terrane that is preserved in the notre dame bay subzone of the central mobile belt of the newfoundland appalachians detailed thermal and alternating field demagnetization reveals a stable characteristic component of magnetization carried by magnetite at a large number of sites in pillow basalts and coeval basaltic dikes the intrusives contain both polarities and a primary age for the characteristic magnetization is indicated by a positive contact test for one of the dikes and by a positive structural test involving a correction for block rotations strike correction the overall mean direction for the characteristic component after tectonic tilt and strike correction flows and intrusives d 171 i 22 k 22 6 95 6 5 pole 29 n 135 e flows d 166 i 22 k 33 2 95 6 5 corresponds to an early ordovician paleolatitude for the arc of 11 s which is indistinguishable from the expected paleolatitude of the north american margin this implies that the arc formed at or near the margin of the craton in contrast the avalon block which formed the other margin of iapetus was widely separated from the arc and the craton at this time the early ordovician paleolatitude of the arc terrane supports a tectonic model in which coeval ophiolitic sequences inboard of the arc were formed in a narrow ocean basin between the arc and the craton subsequent convergence between the arc and laurentia in middle ordovician time resulted in closure of this narrow ocean basin and obduction of the back arc basin oceanic crust onto the ancient margin of the craton thus giving rise to the taconic orogenic pulse in the newfoundland appalachians

modeling studies of interference reflections in thin layered media bounded by coal seams high resolution seismic data collected over a major u s coal basin indicated potential complex problems associated with interference reflections these problems differed from those normally encountered in the exploration of oil and gas because of differences in the geologic boundary conditions modeling studies were conducted to investigate the effects of overlapping primary reflections and the composite reflection that result from stacking individual wavelets a modified empirical formula of lindseth s linear relationship between acoustic impedance and velocity is used to extrapolate velocity information from density logs to provide appropriate geophysical properties for modeling the synthetic seismograms generated from density and synthetic sonic logs correlated well with the processed seismic data a 150 hz ricker wavelet is used to convolve with the computer models and the models showed that certain anomalous composite reflections result from the superposition of overlapping primary reflections de

locating faults in underground coal mines using high resolution seismic reflection techniques a high resolution seismic reflection technique was used to locate faults in coal seams that were not visible on the surface and could only be observed in underground coal mines an 8 gauge buffalo gun built by the research and development department of consolidation coal company was used as the seismic source the coal seam at a depth of 700 ft produces a reflection with a predominant frequency of about 125 hz the high resolution seismic data permitted faults with vertical displacements of the same magnitude as the seam thickness to be detected at depths of several hundred feet beneath the surface several faults were detected and interpreted from the seismic sections and the magnitudes of their displacement were estimated by matching the recorded seismic data to synthetic seismic data subsequent underground mine development in the study area confirmed two interpreted faults and their estimated displacements mining engineers were able to use the information provided by the seismic survey to plan an

turbidite paleoseismology along the active continental margin of chile feasible or not abstract much progress has been made in estimating recurrence intervals of great and giant subduction earthquakes using terrestrial lacustrine and marine paleoseismic archives recent detailed records suggest these earthquakes may have variable recurrence periods and magnitudes forming supercycles understanding seismic supercycles requires long paleoseismic archives that record timing and magnitude of such events turbidite paleoseismic archives may potentially extend past earthquake records to the pleistocene and can thus complement commonly shorter term terrestrial archives however in order to unambiguously establish recurring seismicity as a trigger mechanism for turbidity currents synchronous deposition of turbidites in widely spaced isolated depocenters has to be ascertained furthermore characteristics that predispose a seismically active continental margin to turbidite paleoseismology and the correct sample site selection have to be taken into account here we analyze 8 marine sediment cores along 950 km of the chile margin to test for the feasibility of compiling detailed and continuous paleoseismic records based on turbidites our results suggest that the deposition of areally widespread synchronous turbidites triggered by seismicity is largely controlled by sediment supply and hence the climatic and geomorphic conditions of the adjacent subaerial setting the feasibility of compiling a turbidite paleoseismic record depends on the delicate balance between sufficient sediment supply providing material to fail frequently during seismic shaking and sufficiently low sedimentation rates to allow for coeval accumulation of planktonic foraminifera for high resolution radiocarbon dating we conclude that offshore northern central chile 29 32 5 s holocene turbidite paleoseismology is not feasible because sediment supply from the semi arid mainland is low and almost no holocene turbidity current deposits are found in the cores in contrast in the humid region between 36 and 38 s frequent holocene turbidite deposition may generally correspond to paleoseismic events however high terrigenous sedimentation rates prevent high resolution radiocarbon dating the climatic transition region between 32 5 and 36 s appears to be best suited for turbidite paleoseismology

marine radiocarbon reservoir effect along the northern chile southern peru coast 14 24 s throughout the holocene abstract through an extensive sampling and dating of pairs of associated shells and charcoal fragments combined with reanalysis of all the available previous data we reconstruct the evolution throughout the holocene of the regional marine radiocarbon reservoir effect r values along the northern chile southern peru area 14 24 s after elimination of the cases in which the terrestrial component yielded older ages than the marine shells to which they were associated the study is based upon data from 47 pairs of associated marine and terrestrial material our results suggest major changes in both the magnitude and variability range of r during the whole holocene period 1 between 10 400 and 6840 cal yr bp high values 511 278 yr probably result from a strengthened se pacific subtropical anticyclone and shoaling of equatorial subsurface waters during intensified upwelling events 2 between 5180 and 1160 cal yr bp lower values 226 98 yr may reflect a major influence of subtropical water and diminished coastal upwelling processes 3 during the last thousand years high values between 355 105 and 253 207 yr indicate an increased influence of 14 c depleted water masses and of enso for the early twentieth century a r value of 253 207 yr was calculated

early silurian paleopole for redbeds and volcanics of the king george iv lake area newfoundland redbeds and felsic and mafic volcanics of the king george iv lake area of the dunnage zone in southwestern newfoundland have been studied paleomagnetically after unfolding both hematite and magnetite carry a consistent direction of magnetization d 29 6 i 1 0 k 19 3 95 11 3 corresponding to a near equitorial paleolatitude 0 5 n 6 and yielding a paleopole at 84 6 e 35 9 n dm 11 3 dp 5 6 a positive fold test shows that the remanence was acquired before devonian deformation a positive conglomerate test and a reversal of the magnetization in a continuous redbed sequence demonstrates that the remanence was acquired at the time of formation which has been assigned to the early silurian on the basis of a u pb zircon date of 431 5 ma no other undisputed primary or pre fold remanence has been reported from atlantic canada for the late ordovician silurian period therefore from paleomagnetic data it is not yet possible to estimate the amount of post silurian movement within