middle miocene ocean climate transition high resolution oxygen and carbon isotopic records from deep sea drilling project site 588a southwest pacific high resolution stable isotopic records are presented for the epi benthic foraminifer cibicidoides the inferred shallow dwelling planktonic globigerinoides quadrilobatus and the inferred deep dwelling planktonic globoquadrina dehiscens from the middle miocene 16 12 ma of deep sea drilling project site 588a lord howe rise southwest pacific high resolution multiple species oxygen and carbon isotopic data define the timing and character of the well known middle miocene climatic oceanographic transition with a resolution comparable to quaternary records the benthic foraminiferal 18o record is marked by several large fluctuations from 16 to 14 8 ma followed by a series of rapid 50 kyr 18o increases that suggest a new state of the ocean climate system after 14 8 ma the total middle miocene benthic oxygen isotopic increase of 1 2 is largely incorporated in two steps an increase of 0 8 from 14 5 to 14 0 ma and a second increase of 0 7 from 13 45 to 12 45 ma each step is comprised of a series of marked 18o increases indicative of rapid east antarctic ice sheet growth and contemporaneous deepwater cooling a strong covariance of 0 7 between the benthic and deep dwelling planktonic species from 14 5 to 14 0 ma including a rapid increase from 14 1 to 14 05 ma suggests a 0 7 increase in the 18o composition of seawater 18osw because of east antarctic ice sheet growth comparison of the 18o record of gs quadrilobatus suggests that surface waters warmed at this site by 3 c from 14 1 to 13 6 ma carbon isotopic time series for each species generally covary throughout the early to middle miocene interval 16 12 ma confirming that 13c variations in this interval largely represent reservoir changes high resolution 13c data allow improved resolution of the latter five of six 13c maxima within the well known early to middle miocene carbon isotopic excursion the monterey carbon isotopic excursion from 17 0 to 13 5 ma this is useful for global correlation the last of these maxima ends with a 1 decrease centered from 13 9 to 13 7 ma 300 kyr after the 18o increase considered to reflect east antarctic ice growth covariance between benthic 18o and 13c from 16 to 13 8 ma suggests a sensitive relation between global carbon cycling and the ocean climate system prior to 13 8 ma episodic increases in organic carbon burial may have contributed to deep sea benthic 13c maxima and synchronous global cooling the positive relationship ended at 13 8 ma indicative of changing relations between global carbon cycling and the ocean climate system brought on by the increased stability of the east antarctic ice sheet after a major growth phase from 14 5 to 14 0 ma

factors influencing recent benthic foraminifera distribution on the guadiana shelf southwestern iberia abstract benthic foraminiferal assemblages in 24 sediment surface samples collected at water depths ranging from 9 to 103 m on the continental shelf off guadiana river were analysed leading to the identification of a total of 270 species cluster analyses performed on species with a relative abundance higher than 5 led to the identification of four assemblages the shallowest assemblage down to 12 m water depth is represented by ammonia beccarii asterigerinata mamila eggerelloides scaber mississipina concentrica planorbulina mediterranensis elphidium crispum and quinqueloculina laevigata a second assemblage between 12 and 40 m water depth is characterised by bulimina elongata cribrononion gerthi and nonion fabum the assemblage between 40 and 95 m water depth is characterised by bolivina dilatata epistominella vitrea bulimina aculeata bolivina ordinaria spiroloxostoma croarae and nonionella iridea finally below a depth of 95 m on the upper outer shelf an assemblage exists characterised by brizalina spathulata bulimina marginata cassidulina minuta brizalina subaenariensis cassidulina laevigata and uvigerina peregrina the spatial distribution of assemblages is closely associated with sea bottom sedimentary environments and bathymetry the number of benthic foraminiferal tests and the distribution of several nearshore species within the two shallowest assemblages are clearly influenced by the outflow of the guadiana estuary and by local hydrodynamic conditions the deeper water assemblages on the other hand were found to be more related to low levels of tidal energy low oxygen environments associated to fine grained sediments and cold water filaments related to seasonal upwelling

uplift history of the central and northern andes a review the elevation of the andean cordillera is a crucial boundary condition for both climatic and tectonic studies the andes affect climate because they form the only barrier to atmospheric circulation in the southern hemisphere and they intrigue geologists because they have the highest plateau on earth formed at a noncollisional plate margin the altiplano puna yet until recently few quantitative studies of their uplift history existed this study presents both 1 a review of the quantitative paleoelevation estimates that have been made for the central and colombian andes and 2 an examination of the source and magnitude of error for each estimate in the central andes paleobotanical evidence suggests that the altiplano puna had attained no more than a third of its modern elevation of 3700 m by 20 ma and no more than half its modern elevation by 10 7 ma these data imply surface uplift on the order of 2300 3400 m since the late miocene at uplift rates of 0 2 0 3 mm yr paleobotanical and geomorphological data suggest a similar uplift history for the eastern cordillera namely no more than half the modern elevation present by 10 ma no evidence exists for an exponential increase in uplift rate as has been interpreted from fissiontrack data these uplift rates mostly reflect mean surface uplift rather than rock uplift that is uplift of material points because little dissection of the western eastern cordillera has occurred south of lat 19 s and of the altiplano puna thus the central andean plateau appears to be young in the colombian andes paleobotanical data imply rapid uplift of the eastern cordillera between 2 and 5 ma at rates on the order of 0 6 3 mm yr however some of this uplift is likely rock uplift due to erosion driven isostatic rebound rather than mean surface uplift

sedimentological processes in a scarp controlled rocky shoreline to upper continental slope environment as revealed by unusual sedimentary features in the neogene coquimbo formation north central chile abstract exceptionally good outcrops of miocene to pliocene deposits in the vicinity of submarine paleozoic basement scarps at carrizalillo north of la serena reveal a wealth of sedimentary features not commonly observed the most proximal facies consist of rock fall and coarse grained debris flow deposits directly abutting the basement wall from which they originated angular basement clasts are mixed with well rounded cobbles which probably formed as a basal gravel on a wave cut platform at the beginning of marine flooding subsequently accumulated at the scarp edge and were incorporated into the debris when the latter collapsed the poor sorting inverse grading and protruding cobbles and boulders are classical debris flow features with good clast imbrication indicating a laminar shearing action a medial facies is represented by secondary channels running parallel to the major scarp about 1 km downslope of the first locality in the largest channel megaflutes at the base indicate the passage of highly turbulent nondepositing flows eroding the soft silty substrate in the deepest central part of the channel a pebbly coquina shows horizontal and trough cross stratification with most of the bivalves oriented convex side up meter scale rip up clasts of the underlying siltstone are also present indicating turbulent flow with a density sufficiently high to retard settling the coquina is interpreted as a detachment deposit resulting from a hydroplaning debris flow along the central part of the channel where the velocity and rate of pore pressure decay were highest this deposit is overlain by fining upward massive to horizontally stratified sandstone very similar in texture and composition to the matrix of the debris flow suggesting its formation by surface transformation and elutriation of the latter along the channel margin a basal centimeter scale sandstone layer is virtually unaffected by the megaflute topography and clearly represents a subsequent event it is interpreted as a basal shear carpet driven by the overlying debris flow within the shear carpet a basal friction zone and an overlying collision zone containing a higher concentration of shell hash can be distinguished the overlying debris flow deposit is represented by massive coquina with scattered angular to rounded basement clasts it contains disarticulated bivalves oriented with their concave side up indicating large scale upward fluid escape during deposition a smaller secondary channel shows large rip up rafts of the underlying substrate some rafts appear to have been plucked from the substrate by a process of sand injection from an overriding high density sandy debris flow which probably originated during a tsunami such clasts can climb upward into a laminar flow by down current tilting and tumbling the most distal facies occurs below a second scarp oriented more or less parallel to the present coastline where finer grained turbidites onlap and backlap onto the stoss and lee sides of an obstacle formed by eroded boulder conglomerates the onlap deposits resemble inclined sandy macroforms recently described in submarine canyon settings they are interbedded with diatom containing volcanic ash beds with cross stratification dipping eastwards and containing deepwater microflora typical of continental upwelling zones

a giant late archean lake system the meentheena member tumbiana formation fortescue group western australia abstract the 2720 ma old meentheena member of the tumbiana formation fortescue group is a 30 50 m thick succession of alternating siliciclastic and limestone beds that crop out intermittently over a distance of 680 km across the pilbara craton western australia limestones of the member consist of flat pebble intraformational conglomerate oolite grainstone calcisiltite and calcilutite siliciclastics consist of shale siltstone and sandstone and many of these are tuffaceous sedimentary structures include abundant symmetrical ripples ripple cross stratification desiccation cracks teepee structures and planar to wavy lamination the member is superficially similar in appearance wherever it crops out however the correlation of individual beds and units over distances greater than 15 km is problematic there are no regional marker beds radiometric ages from tuffaceous units young to the west by a few million years four lithofacies are defined a flat pebble conglomerate b ripple cross laminated oolite grainstone c planar to wavy laminated calcilutite calcisiltite and d shale siltstone stromatolites are found in all three of the limestone facies evaporites are rare and include halite pseudomorphs the four lithofacies are generally found in a vertical succession that characterizes a lithofacies association and reflects a deepening upward succession associations may not have all four lithofacies but do reflect the same deepening upward pattern the uppermost portions of shale siltstone facies commonly contain symmetrical ripples and desiccation cracks indicating subaerial exposure measured sections contain as many as 25 of these parasequences indicating fluctuating water levels limestone lithology and facies commonly change abruptly laterally at the meter and greater scale and vertically centimeter to meter scale the sedimentary structures differences and abrupt changes in lithofacies patterns the inability to correlate confidently between regions and the differences in age from east to west suggest a complex diachronous depositional system of fluctuating water levels in separate bodies of water the limestone is dominated by sedimentary structures indicative of shallow water within wave base however it is devoid of evidence of any tidal influence possibilities for depositional environments include a tideless sea or a lacustrine system 87sr 86sr values from limestone differ from known archean marine carbonates ree patterns are decidedly non marine as well a lacustrine system is favored for the meentheena member based on sedimentary structures the abruptness of lithologic and facies changes the facies association lateral gradation into fluvial deposits the inability to correlate many units and beds for more than a few to several kilometers geochemical data stromatolites and comparisons with younger lacustrine basins as well as marine successions there is no single line of evidence that unequivocally establishes a lacustrine origin however multiple lines of evidence are collectively consistent with a lacustrine origin the meentheena member would therefore represent the oldest known carbonate rich lacustrine system which we call the meentheena lakes system

structure and depositional processes of a gravelly tsunami deposit in a shallow marine setting lower cretaceous miyako group japan discussion tsunamis are unexpected violent events and can rarely be studied by direct observation so that much of their hydrodynamic behaviour is uncertain careful examination of their deposits can therefore assist in determining flow conditions and depositional processes le roux and vargas 2005 but a prerequisite is that such deposits be identified correctly in our opinion the paper by fujino et al 2006 does not meet this criterion the authors mention five features that according to them can only co exist if they were formed by a tsunami although they admit that each of these features individually may be attributed to other processes here we contend that all five features can occur together in a wave dominated shallow marine environment affected by storms imbrication reflecting current reversals from seawardto landward directed is attributed byfujino et al 2006 to the onrush and backwash of successive waves during a single event because the environment was wavedominated as shown by an abundance of hummocky cross stratified hcs sandstones they rule out tidal action as a possible cause however strong wave action

bartonaspis new genus a trilobite species complex from the base of the upper cambrian sunwaptan stage in north america despite being reported widely from basal sunwaptan strata dellea punctata palmer 1965 is known from only four figured cranidia new material from nevada utah and oklahoma including librigenae and pygidia indicate that specimens assigned previously to d punctata are best interpreted as a complex of related species that are assigned to a new genus bartonaspis this genus is diagnosed by punctate sculpture a pair of fossulae at the anterior corners of the glabella and by a subelliptical pygidium with a short convex axis composed of three segments three new species b fredericksoni b palmeri and b wilsoni are described and b punctata palmer is restricted to its holotype bartonaspis is known only from the irvingella major zone and its first appearance defines the base of the sunwaptan stage dellea wilson 1949 is related to bartonaspis and is differentiated from it primarily by pygidial morphology in contrast to bartonaspis the pygidium of dellea has an axis composed of four rather

the ordovician sebree trough an oceanic passage to the midcontinent united states the sebree trough is a relatively narrow shale filled sedimentary feature extending for several hundred kilometers across the middle and late ordovician carbonate platform of the midcontinent united states the dark graptolitic shales within the trough stand in contrast to the coeval bryozoan brachiopod echinoderm rich limestones on the flanking platforms we infer from regional stratal patterns thickness and facies trends and temporal relations established by biostratigraphy and k bentonite stratigraphy that the sebree trough initially began to develop during late turinian to early chatfieldian time mohawkian series as a linear bathymetric depression situated over the failed late precambrian early cambrian reelfoot rift rising sea level and positioning of a subtropical convergence zone along the southern margin of laurentia caused the rift depression to descend into cool oxygen poor phosphate rich oceanic waters that entered the southern reaches of the rift from the iapetus ocean the trough apparently formed in a system of epicontinental estuarine circulation marked by a density stratified water column trough formation was accompanied by cessation of carbonate sedimentation deposition of graptolitic shales development of hardground omission surfaces substrate erosion and local phosphogenesis the carbonate platforms on either side of the trough are dominated by bryozoan brachiopod echinoderm grainstones and packstones that were deposited in zones of mixing where cool nutrient rich waters encountered warmer shelf waters concurrently lime mudstone and wackestone were deposited shoreward northern illinois wisconsin iowa minnesota michigan in warmer more tropical shallow seas coeval upward growth of the flanking carbonate platforms sustained and enhanced development of the trough shale facies five widespread diachronous late mohawkian and cincinnatian omission surfaces are present in the carbonate facies of the midcontinent these surfaces include sub deicke k bentonite ds1 top of black river limestone ds2 base and top of the guttenberg limestone member of the decorah formation ds3 and ds4 and top of the trenton limestone ds5 some of the surfaces correspond to previously described depositional sequence boundaries all five surfaces which embody deepening phases on top of highstand systems tracts converge in the sebree trough indicating that the trough was a long lived feature and was the source of eutrophic waters that episodically spread across the adjacent platforms terminating carbonate production late turinian and early chatfieldian incipient drowning episodes were followed by a final drowning event that began in the sebree trough during the late chatfieldian climacograptus spiniferus zone and reached southernmost minnesota and other regions far within the platform interior by richmondian time amorphognathus ordovicicus zone

pseudocryptic species of the middle cambrian trilobite eodiscus hartt in walcott 1884 from avalonian and laurentian newfoundland two species of the middle cambrian trilobite eodiscus hartt in walcott 1884 e punctatus salter 1864 and e scanicus linnarsson 1883 have been reported from several paleocontinents however in their respective type areas of avalonian britain and baltica sweden both species are poorly documented from moulds preserved in siliciclastic mudstone that are variably compacted and distorted moreover variation in such characters as surface sculpture between putative occurrences suggests that widespread use of these names may mask species differentiation within and between paleocontinents detailed examination of eodiscus sclerites that are exquisitely preserved in full relief in limestone from the manuels river formation of avalonian newfoundland and the shallow bay formation of laurentian newfoundland demonstrates the presence of multiple species that are distinct from both e punctatus and e scanicus we interpret them as a group of pseudocryptic species that are comparable to groups that are no

post hunnebergian ordovician carbon isotope trend in baltoscandia its environmental implications and some similarities with that of nevada abstract carbon isotope changes during post hunnebergian ordovician time were investigated as the corresponding sequence of rocks is stratigraphically nearly complete in baltoscandia an attempt was made to use it to elaborate the general pattern of carbon isotope changes in most of the ordovician complications caused by several local hiatuses condensed sections and facies changes were mitigated by the study of overlapping sections a total of 326 new whole rock analyses and published data from 18 drill cores and 4 outcrops in estonia latvia and sweden were considered the following positive carbon isotope events were observed 1 the mid darriwilian excursion peak 13c value 1 9 in the aseri stage 2 the mid caradoc excursion 2 2 in the uppermost part of the keila stage 3 the first late caradoc excursion 2 3 in the lower part of the rakvere stage 4 the second late caradoc excursion 2 4 in the upper part of the nabala stage 5 the early ashgill excursion 2 5 in the lowermost part of the pirgu stage 6 the mid ashgill excursion 2 0 in the upper part of the pirgu stage 7 the widely known large hirnantian excursion in estonia the peak value reaches 6 7 in the porkuni stage the study interval comprises a long 19 ma period characterized by low magnitude carbon isotope changes and a following much briefer 12 ma interval with often medium scale shifts and a major event at the end the latter interval reflects onset in the mid caradoc of a period of variable climate alternation of arid and humid episodes which ended with a serious cooling and glaciation the baltoscandian and north american nevada 13c trends are in general lines very similar providing good prospects for global chemostratigraphical correlation and understanding of role of oceanic processes in carbon cycling

progradational sequences in miocene shoreline deposits southeastern caliente range california abstract an exceptionally well exposed marine nonmarine transition in middle miocene strata exists in the southeastern caliente range california about 50 individual progradational sequences form a succession that ranges in thickness from approximately 1000 m where predominantly nonmarine to more than 2500 m where predominantly marine paleogeographic evidence in basalt flows near the top of the succession and in overlying fluvial deposits indicates that these middle miocene strata were deposited across a north northwest trending shoreline a complete progradational sequence typically is several meters to a few tens of meters thick and includes strata that represent three intertonguing stratigraphic units individual sequences generally rest on a thin gravel deposit interpreted as a transgressive lag on an erosional surface the gravel is overlain by structureless siltstone or fine grained sandstone deposited at water depths where the rate of faunal mixing exceeded that of production of structures by physical processes these rocks grade upward into bedded fine sandstone deposited closer to shore where physical processes exceeded bioturbation crossbedded lenses of coarse sand or fine gravel in the upper part of this facies suggest the presence of fairly long period surface waves the bedded fine sandstone is sharply ove lain by a cross bedded coarse sandstone facies that is interpreted as a combined offshore bar rip channel surf zone assemblage cross strata dip dominantly offshore suggesting substantial deposition from rip currents a secondary shoreparallel mode of cross strata direction suggests longshore currents produced by surface waves from the northwest the crossbedded coarse grained sandstone grades upward into planar bedded medium grained sandstone that is interpreted as a beach foreshore this facies grades upward through structureless medium grained sandstone into nonmarine or lagoonal red and green mudstone of the caliente formation the middle miocene succession was deposited in a subsiding basin that was otherwise remarkably stable tectonically the position of the strand line differed no more than a few kilometers through a period of 1 to 3 m y the average duration of the transgressive regressive cycles a few tens of thousands of years together with their distribution in groups of three or four in the lower two thirds of the succession is consistent with the pattern of long term climatic cycles produced by periodicity of the earth s solar orbit and may be related to eustatic sea level changes attendant to the development of the antarctic ice cap changes in the pattern of progradation in the upper part of the succession and nearby basaltic eruptions may have been precursors to the onset of movement along th san andreas fault in this area 12 14 m y ago

the late cambrian steptoean furongian trilobite pseudokingstonia palmer 1965 in north america the poorly known late cambrian steptoean furongian genus pseudokingstonia palmer is revised using new material from the type area in west central utah previously undocumented features of pygidial morphology including patterns of segmentation of the axis and pleural fields and articulating flanges on the anterior margin confirm that the genus is closely related to the dameselloidean cheilocephalus berkey and that together they constitute the family cheilocephalidae shaw pseudokingstonia is diagnosed by a high degree of cranidial and especially pygidial effacement an exceedingly short anterior border on the cranidium and steeply sloping pygidial borders in addition to the great basin of nevada and utah the genus is also known from alberta arkansas and pennsylvania and all occurrences are confined to the lower half of the late steptoean elvinia zone

determination of the drainage structure of a watershed using a digital elevation model and a digital river and lake network abstract distributed hydrological models require a detailed definition of a watershed s internal drainage structure the conventional approach to obtain this drainage structure is to use an eight flow direction matrix d8 which is derived from a raster digital elevation model dem however this approach leads to a rather coarse drainage structure when monitoring or gauging stations need to be accurately located within a watershed this is largely due to limitations of the d8 approach and the lack of information over flat areas and pits the d8 approach alone is also unable to differentiate lakes from plain areas to avoid these problems a new approach using a digital river and lake network drln as input in addition to the dem has been developed this new approach allows for an accurate fit between the drln and the modelled drainage structure which is represented by a flow direction matrix and a modelled watercourse network more importantly the identification of lakes within the modelled network is now possible the proposed approach which is largely rooted in the d8 approach uses the drln to correct modelled flow directions and network calculations for dem cells overlapped by the drln flow directions are determined using drln connections only the flow directions of the other dem cells are evaluated with the d8 approach which uses a dem that has been modified as a function of distance to the drln the proposed approach has been tested on the chaudiere river watershed in southern quebec canada the modelled watershed drainage structure showed a high level of coherence with the drln a comparison between the results obtained with the d8 approach and those obtained by the proposed approach clearly demonstrated an improvement over the conventionally modelled drainage structure the proposed approach will benefit hydrological models which require data such as a flow direction matrix a river and lake network and sub watersheds for drainage structure information

upper ordovician mohawkian carbon isotope δ13c stratigraphy in eastern and central north america regional expression of a perturbation of the global carbon cycle abstract the guttenberg carbon isotope excursion gice documented from eastern north america demonstrates the effects that regional geochemically distinct water masses upwelling and ocean circulation have on the carbon isotope record from carbonate platforms late turinian chatfieldian carbonates from oklahoma kentucky virginia and west virginia record a positive carbon isotope excursion 3 0 the gice excursion the gice excursion has relations to established biostratigraphy beginning in the north american midcontinent phragmodus undatus conodont zone and continuing through the plectodina tenuis zone sequence and event stratigraphy previously established models for positive carbon isotope shifts on carbonate platforms have been tested during the gice excursion where geochemically distinct water masses are defined for the upper ordovician a major eustatic sea level rise before the gice promoted a greater exchange of open ocean waters onto the carbonate platform of laurentia however restricted or sluggish circulation and exchange between water masses within the epeiric seas and the adjacent iapetus ocean were still apparent local variations documented in the gice excursion are directly related to upwelling of nutrient rich isotopically light waters increased primary productivity and the subsequent organic carbon production and burial

the hydrology of lake bosumtwi a climate sensitive lake in ghana west africa abstract lake bosumtwi lying in a million year old meteor crater is hydrologically closed in spite of the wet humid climate in this part of ghana to understand this geographical enigma a water balance model that describes both the historical lake level record and the full range of lake levels observed in terrace deposits around the lake was developed the water balance model shows that the reception of rainfall by and evaporation from the lake surface are the dominant constituents of the water balance prior to 1969 the average rainfall of 1550 mm year 1 was generally equal to lake evaporation and the average annual rise of 30 cm year 1 was produced mostly by runoff from the small watershed around the lake since 1969 with a decreased rainfall of 1380 mm year 1 the combination of rainfall and runoff has nearly equaled lake evaporation resulting in a nearly steady lake level long term simulations show that stochastic climatic variations very similar to those observed in this century could produce the full range of lake levels observed in terrace deposits the low salinity of about 1 suggests that dissolved solutes were removed by lake overflow in the recent geological past

organic matter source variation and the expression of a late middle ordovician carbon isotope excursion the carbon isotopic composition of organic matter is a powerful tool in the study of organic carbon burial and p co 2 through the geologic record however the organic matter source can affect total organic carbon 13 c values and may complicate interpretation of environmental conditions we examined the influence of organic matter source variations on a late middle ordovician positive 13 c excursion in strata of the united states midcontinent in a core from iowa the magnitude of the excursion recorded by carbonate carbon is 2 5 whereas the excursion recorded by total organic carbon is nearly 8 although this difference could arise from a profound decrease in surface water co 2 concentrations association of the organic walled microfossil gloeocapsomorpha prisca with 13 c enriched total organic carbon toc in this interval suggests that the excursion could also record a shift from normal marine to g prisca dominated organic matter carbon isotope analyses of individual biomarkers indicate that both of these explanations are required to explain the data compounds inferred to be of g prisca origin are enriched in 13 c by 7 relative to compounds derived from other algal sources furthermore compounds exclusively from either g prisca or other sources exhibit a positive shift of only 3 5 thus the large excursion recorded by toc reflects in part a change in the proportional contribution of g prisca to toc that all compounds exhibit a positive carbon isotopic shift indicates that independent of contributions from g prisca a positive organic 13 c excursion occurred and records a change in environmental conditions such as co 2 aq concentrations the 3 5 shift is similar in magnitude to that observed for toc in correlative units from pennsylvania suggesting that this event has broad geographic significance this work illustrates that organic matter source variations as well as environmental conditions govern the toc 13 c values and shows how compound specific isotope analyses can resolve these multiple controls

reply to a comment on non steady long term uplift rates and pleistocene marine terrace development along the andean margin of chile 31 s inferred from 10be dating by m saillard s r hall l audin d l farber g herail j martinod v regard r c finkel and f bondoux earth planet sci lett 277 2009 50 63

geology and paleontology of late cenozoic marine deposits in the sacaco area peru paleontologic stratigraphic and geochronologic k ar evidence demonstrate the presence of both late miocene and pliocene marine deposits in the pisco formation in the area of sacaco peru tuffaceous sandstone siltstone and shelly sandstone comprise the greater part of the ca 350 meters sequence the fine grained sediments have accumulated in large coastal lagoons while coarser sediments were deposited in semiprotected littoral and nearshore environments a rich marine vertebrate fauna from the sacaco basin includes fossil selachians teleost fishes marine birds cetaceans marine carnivores and a single edentate species a diverse invertebrate fauna consists principally of venerid and muricid molluscs five vertebrate levels have been correlated with five provisionally defined molluscan zones the vertebrate fauna has some affinity with faunas of the miocene yorktown formation at the lee creek mine of north carolina usa distinctive miocene and pliocene molluscan assemblages of the pisco formation and pleistocene molluscan assemblages from overlying terrace deposits become progressively more similar to chilean assemblages of equivalent age and less similar to tethyan faunas of the panamic and caribbean regions

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

geochronology of pediments and marine terraces in north central chile and their implications for quaternary uplift in the western andes article in north central chile a wide shore platform is morphologically connected with a high fluvial terrace and a pediment the eastward extension of quaternary coastal uplift in the southern central andes is poorly constrained since no age correlation between marine and continental landforms has been reported we use 26 al and 10 be concentrations to constrain the geomorphic evolution of these marine and continental implies that this marker is several hundreds of thousands of years old and that the high fluvial terrace began to form at 1200 ka or after finally 10 be concentrations of the high fluvial terrace the pediment and the shore platform are of the same order of magnitude which is consistent with the clear morphologic correla tion between these three types of landforms these data suggest that the marine and continental landforms studied formed synchronously with some local differences during a long period of relative tectonic stability between 1200 800 and 500 ka and uplifted after 500 ka our results confirm recent studies showing a post 400 100 ka renewal of uplift along the pacific coast after a lower to middle pleistocene period of slow uplift moreover the extension of the surfaces suggests that a broad region of 40 km has been uplifted ca 150 m during the quaternary

a pliocene mega tsunami deposit and associated features in the ranquil formation southern chile abstract an exceptionally large tsunami affected the coastline of southern chile during the pliocene its backflow eroded coarse beach and coastal dune sediments and redistributed them over the continental shelf and slope sandstone dykes and sills injected from the base of the resulting hyperconcentrated flow into underlying cohesive muds assisted in plucking up large blocks of the latter and incorporating them into the flow locally the rip up intraclasts were fragmented further by smaller scale injections to form a distinct breccia of angular to rounded mudstone clasts within a medium to coarse sandstone matrix sandstone sills in places mimic normal sedimentary beds complete with structures resembling inverse gradation planar laminae as well as ripple and trough cross lamination these were probably formed by internal sediment flow and shear stress as the semi liquefied sand was forcefully injected into cracks in borehole cores such sills can easily be misinterpreted as normal sedimentary beds which can have important implications for hydrocarbon exploration

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

late middle ordovician environmental change and extinction harbinger of the late ordovician or continuation of cambrian patterns positive excursions in carbon isotope compositions of carbonate 3 and organic carbon 4 6 from the late middle ordovician middle caradocian of the midcontinent and the eastern united states indicate widespread increases in productivity and rates of organic carbon burial that may have drawn down atmospheric p co 2 precipitating global cooling although not necessarily ice sheet formation these climatic changes were associated with regional orogenic uplift a relative rise in sea level changes in epeiric sea circulation patterns and carbonate platform destruction that led to regional extinction of marine benthos the combination of sea level rise changing ocean circulation and extinction in the middle caradocian is similar to the suite of environmental changes described for cambrian biomere boundaries suggesting shared causes for these events in contrast middle caradocian environmental changes are markedly different from the environmental patterns associated with the late ordovician mass extinction despite the evidence for long term cooling from the middle to the late ordovician

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

oroclinal bending of the juan fernandez ridge suggested by geohistory analysis of the bahia inglesa formation north central chile abstract the stratigraphy of the bahia inglesa formation in the caldera basin west of copiapo north central chile is revised based on hitherto unpublished stratigraphic sections and 87sr 86sr dating the depositional environment varied from a rocky shoreline to the upper continental slope with sea level oscillations and tectonic movements causing numerous local unconformities as well as lateral and vertical facies changes geohistory and sedimentological analyses show that the area was close to the concurrent sea level at about 15 3 ma but at the same time being elevated about 100 m above the present sea level although the basin then subsided at least 350 m until around 6 ma marine deposition was only recorded after 10 4 ma this suggests that the sea level initially dropped faster than the rate of subsidence so that subaerial erosion occurred the period of subaerial exposure before 10 4 ma can be attributed to the presence of a ne trending branch of the juan fernandez ridge below the continental crust at this time whereas the ensuing subsidence was due to subduction erosion and crustal accommodation in its wake as it migrated south along the south american coastline the subsequent uplift of at least 250 m can be explained by an acceleration in plate expansion and isostatic rebound of the continental crust after being partially submerged in the upper mantle the uplift subsidence uplift pattern mirrors those recorded around the nazca ridge in peru as well as in similar basins to the south of caldera however a higher southward migration rate of the juan fernandez ridge against the edge of the south american plate and less intense uplift subsidence uplift cycles are recorded in the latter basins this can possibly be attributed to oroclinal bending of the ridge due to friction with the overlying continental plate which diminished the angle of incidence and the intensity of the stress field but increased the migration velocity of the ridge relative to the coastline

katian upper ordovician delta c 13 chemostratigraphy and sequence stratigraphy in the united states and baltoscandia a regional comparison delta c 13 values of numerous limestone samples from katian upper ordovician successions in oklahoma and the upper mississippi valley document the presence of at least three of the four positive excursions that have been recognized in the lower middle katian interval in the cincinnati region in ohio kentucky and indiana a comparison with estonia reveals that five out of the six positive excursions now recorded through the katian succession in the cincinnati region are present in the coeval stratigraphic intervals in estonia which suggests that these represent global perturbations in the carbon cycle a study of the relations between flooding events and delta c 13 excursions shows that only some of the excursions occur in transgressive intervals whereas other excursions are in regressive strata and hence this is in conflict with the idea that positive carbon isotope excursions are forced by rises in sea level part of a previously published attempt to use upper ordovician sequence stratigraphy for trans atlantic correlation is shown to be seriously out of phase with the biostratigraphy and chemostratigraphy several of the sequences recognized in the cincinnati region do not appear to have counterparts in estonia which suggests that they do not reflect eustatic but local conditions c 2010 elsevier b v all rights reserved less

preservation of beach ridges due to pedogenic calcrete development in the tongoy palaeobay north central chile article i nfo at the tongoy palaeobay in north central chile a series of beach ridges developed during seaward progradation that took place after the mis 11 sea level highstand 412 ka the microrelief left by this succession of beach ridges has been well preserved from erosion due to the development of a calcrete petrocalcic horizons which was resistant to the chemical and physical weathering that characterized the area during humid phases of the late pleistocene and middle holocene macro and micro morphological analysis shows that the calcrete is of pedogenic origin and formed during two stages in the first stage a massive beta calcrete developed followed during the second stage by a laminar alpha calcrete each event in the development of the calcrete was intimately related to the foregoing process mainly due to changes in the permeability of the profile horizons during the first stages of development organisms played an important role in the precipitation of calcite which made the calcrete less permeable and favored the accumulation of ponded water during the wet season as a result of this increased humidity calcium carbonate with a laminar structure was precipitated the development of the calcrete was also intimately associated with the evolution of the drainage network which is characterized by a trellis pattern of tributaries parallel to the beach ridges this study demonstrates the importance of soil genesis in the geomorphological evolution of landscapes

isotopic evidence for geochemical decoupling between ancient epeiric seas and bordering oceans implications for secular curves isotopic analysis of conodonts and their host limestones sampled between two regionally extensive altered volcanic ash layers in eastern laurentia shows that a 454 ma epeiric sea maintained large lateral differences in nd and c isotope compositions this is consistent with inferred temperature salinity defined epicontinental water masses and restricted circulation between epicontinental and oceanic environments because the majority of old marine fossils and sedimentary rocks are known from epeiric seas some isotope excursions in ancient marine strata may originate from expansion and contraction of geochemically distinct epicontinental water masses rather than global scale changes in the state of the earth ocean system

evidence for a widespread carbon isotopic event associated with late middle ordovician sedimentological and faunal changes in estonia an episode of remarkable biotic climatic sea level and facies changes took place during the late viruan caradoc epoch in the baltoscandian area we studied the carbon isotopic composition of carbonate sediments from this period data on the stable carbon isotopic composition of whole rock carbonates from three south estonian core sections together with those on ostracode distribution are presented in two core sections a positive 13 c shift of 2 was revealed in the upper part of the keila stage mid caradoc the comparison of isotope and ostracode data in the sections suggested the occurrence of a gap of late keilan age in the marginal area of the basin equivalent to the north estonian confacies belt the beginning of the excursion approximately coincided with climatic and sea level changes in the shallow shelf area the peak of the late keilan excursion preceded the biotic crises and maximum black shale accumulation in the baltoscandian palaeobasin an approximately synchronous carbon isotopic event has been reported from north america referring to a possible global oceanographic event in the caradoc epoch although the positive carbon isotopic excursion and related environmental events of the late keilan age have some unique features they show more similarities to the end ordovician and silurian events characterized by oceanic change from stratified state to thermohaline circulation state than to warm anoxic events related to eustatic sea level rise

storm and tide dominated shorelines in cretaceous moosebar lower gates interval outcrop equivalents of deep basin gas trap in western canada the moosebar and gates formations crop out in the deformed foothills belt south of fort st john british columbia they permit examination of the depositional environments of sandstones and conglomerates that are gas bearing in the equivalent wilrich falher interval of the deep basin of alberta and british columbia the moosebar gates interval consists of several upward coarsening and marine to nonmarine sequences moosebar bioturbated shales pass upward into turbidites and offshore storm deposits flow directions indicate a north dipping paleoslope a second coarsening upward sequence at the top of the moosebar and base of the gates terminates in a lenticular fluvial conglomerate up to 30 m thick which is overlain by coals carbonaceous mudstones and sandstones above the carbonaceous zone a major lateral facies change is observed fluvial conglomerates in the south grade into beach conglomerates northward the upper part of the beach conglomerate consists of exposed three dimensional storm berms at least 500 m long up to 1 5 m high with wavelengths of 12 to 24 m the berms trend east west seaward of the conglomerate beach are herringbone cross bedded tidal sandstones with a marine trace fauna graded sharp based conglomerates also are present probably washed out to sea by storms farther north at the same stratigraphic level is a series of partly overlapping conglomerate bars up to 5 m thick and 40 to 50 m across the tops of these bars are covered with storm formed symmetric conglomeratic dunes details of the orientation and geometry of these conglomerate bodies along with their internal structure and pebble fabrics suggest that four major environments fluvial beach offshore conglomerate bars and offshore graded storm conglomerates should be identifiable and predictable in the subsurface

marine climatic responses to neogene tectonics of the pacific ocean seaways abstract based upon surface marine climatic evolution on both sides of the pacific ocean recently revealed by biochronostratigraphy in japan and south america the tectonics of pacific ocean seaways and associated responses of adjacent seas and ocean currents are discussed the rapid opening of the sea of japan at about 15 ma in early middle miocene time mainly by the rotation of the southwest japan arc can be correlated with the abrupt appearance of a cold water fauna on the pacific coast of northeast japan beginning ca 15 ma and an extensive hiatus along the pacific coast of southwestern japan spanning 15 ma to 12 ma the abrupt and extensive development of biosiliceous lithofacies along the pacific coast of peru beginning about 14 ma might also represent a response to the tectonic anticlockwise rotation of the peruvian block of the andean mountain range estimated to have occurred sometime during the miocene as the tectonic closing of the indonesian seaway would have strongly intensified the warm kuroshio current in the northwest pacific it is most probable that this seaway was effectively closed just prior to 15 5 ma in the earliest middle miocene when tropical marine faunas were developed in most of the japanese islands the closing of the central american seaway is estimated to have been completed at 3 5 3 ma in pliocene time the closure of this seaway would likely have intensified the warm kuroshio current affecting the marine fauna along the pacific coast of southwestern japan it is also possible that a decrease in surface temperatures at about 3 ma along the pacific coast of ecuador was due to this pliocene tectonic event

early miocene subtropical water temperatures in the southeast pacific abstract cenozoic climate of western south america is strongly controlled by features like andean uplift and the humboldt current the first strontium isotope age data from central and southern chile provide a latest oligocene to late early miocene age for classic warm water mollusk faunas reaching as far south as 45 s comparison with the biogeography of congeneric living species indicates that sea surface temperatures off central and southern chile during that time were at least 5 c higher than today i e minimum annual mean sea surface temperatures for darwin s navidad fauna at 34 s are estimated as 20 c as expected the number of tropical taxa decreases towards the south but several are still present as far south as 45 s the ages scatter relatively broadly between 24 and 16 ma partly even within individual localities shallow water and deeper water faunas are revealed to have similar ages when considered in light of convincing micropaleontological evidence for late miocene to early pliocene depositional ages the sr isotope data support a hypothesis that the mollusk fauna is reworked

a review of wanganui basin new zealand global reference section for shallow marine plio pleistocene 2 5 0 ma cyclostratigraphy abstract wanganui basin new zealand contains one of the most complete late neogene marine stratigraphic records in the world the ca 2 km thick basin fill for the last ca 2 5 ma comprises 47 superposed cyclothems which correspond to successive 5th 100 ka and 6th 41 ka order glacio eustatic sea level fluctuations on the palaeo new zealand shelf since oxygen isotope stage 100 stages 100 to 5 are represented by marine cyclothems whereas stages 17 to 3 are represented by a suite of coeval and younger uplifted marine terrace sequences additionally a predominantly glacial loess stratigraphy exists for isotope stages 12 2 the presence of interbedded tephras and an established paleomagnetic stratigraphy allows the development of an integrated cyclostratigraphy for wanganui basin which correlates closely with the global oxygen isotope scale in all except two cases cycles 12 and 36 individual unconformity bound cyclothems sequences represent a single glacial interglacial couplet of milankovitch frequency lithologic and faunal variation within the cyclothems corresponds closely to that predicted by the sequence stratigraphic model each cyclothem generally contains a transgressive systems tract a mid cycle condensed shellbed a highstand systems tract and often a regressive systems tract six common cyclothem motifs are inferred to represent deposition in shelf locations between the highstand and lowstand shorelines viz the hawera maxwell turakina seafield castlecliff and rangitikei motifs a seventh type the nukumaru motif includes coquina limestone and represents deposition in shoreface and very shallow water marine environments

a distributed surface flow model for watersheds with large water bodies and channel loops summary large water bodies 25 and 172 km 2 and channel loops exist in the study watershed the tone river basin japan in order to overcome the difficulties in routing the two dimensional surface flows in the water bodies and channel loops the large scale unified and optimization model has been developed in the model the ordering scheme based on the freely seriate tree structure is adopted to order the stream network with channel loops the diffusive wave approximation of the two dimensional free surface flow equations are employed as the governing equations for the surface flows including both overland and channel flows both overland and channel flows are placed in the same physical domain in which a channel grid cell exchanges mass and momentum with the eight adjacent grid cells of overland channels and water bodies and consequently it is simple and easy to incorporate water bodies and channel loops into the model the finite difference method based on the staggered grid scheme is utilized to discretize the governing equations and the optimization numerical scheme simple is employed to solve the finite difference equations using a tri diagonal matrix this paper focuses primarily on the formulation of the model limited model calibration and validation using point streamflow data in the tone river basin are presented and more complete evaluation of the distributed outputs is left for future work

sea level forcing of carbon isotope excursions in epeiric seas implications for chemostratigraphy five new 13c excursions are reported from the upper ordovician galena group of iowa the 13ccarb and 13corg trends are compared to sea level trends based on conventional sedimentological and novel chemostratigraphic end methods it is found that rising 13c values occur during rising sea level peak magnitude 13c values are coincident with inferred peak flooding and declining 13c values occur with declining sea levels the relationship to sea level is explained by a simple model of episodic flooding of the galena platform by cool oxygen depleted nutrient rich bottom waters originating from the sebree trough which was itself connected to the nearby iapetus ocean flooding of the inner galena shelf during sea level transgressions caused local changes in the carbon isotope balance of inner shelf waters due to 1 locally increased primary productivity and organic carbon burial 2 locally increased exchange of 13c enriched dissolved inorganic carbon dic with surrounding epeiric sea water masse

techniques for assessing spatial heterogeneity of carbonate δ13c values implications for craton wide isotope gradients the sedimentary record of carbonate carbon isotopes 13ccarb provides one of the best methods for correlating marine strata and understanding the long term evolution of the global carbon cycle this work focuses on the late ordovician guttenberg isotopic carbon excursion a ca 2 5 positive 13ccarb excursion that is found in strata globally substantial variability in the apparent magnitude and stratigraphic morphology of the guttenberg excursion at different localities has hampered high resolution correlations and led to divergent reconstructions of ocean chemistry and the biogeochemical carbon cycle this work investigates the magnitude spatial scale and sources of isotopic variability of the guttenberg excursion in two sections from missouri usa centimetre scale isotope transects revealed variations in 13ccarb and 18ocarb greater than 2 across individual beds linear 13ccarb to 18ocarb mixing lines together with petrographic and elemental abundance data demonstrate that much of the isotopic scatter in single beds is due to mixing of isotopically distinct components these patterns facilitated objective sample screening to determine the least altered data a 18ocarb filter based on empirical 18ocarb values of well preserved carbonate mudstones allowed further sample discrimination the resulting least altered 13ccarb profile improves the understanding of regional as well as continental scale stratigraphic relations in this interval correlations with other laurentian sections strongly suggest that i small scale variability in guttenberg excursion 13ccarb values may result in part from local diagenetic overprinting ii peak guttenberg excursion 13ccarb values of the midcontinent are not distinct from their taconic equivalents and iii no primary continental scale spatial gradient in 13ccarb for example arising from chemically distinct aquafacies is required during guttenberg excursion time this study demonstrates the importance of detailed petrographic and geochemical screening of samples to be used for 13ccarb chemostratigraphy and for enhancing understanding of epeiric ocean chemistry

local controls on carbon cycling in the ordovician midcontinent region of north america with implications for carbon isotope secular curves abstract the carbon isotope record from ancient epicontinental seas may contain much more of a local scale carbon cycling signal than is generally appreciated a unique opportunity exists to examine this issue in the case of the late ordovician mohawkian sea of eastern laurentia where the millbrig k bentonite stratigraphic framework has been used to delineate a time slice at 454 ma extending over 1 500 000 km2 of the eastern united states across the time slice carbonate and organic carbon 13c vary by 4 5 and 7 5 respectively a spatial variation that is as large as temporal secular changes in epeiric sea 13c that have been reported in the past these new data are considered in the context of geographic variations in lithological biological and other geochemical sediment characteristics collectively these sediment properties distinguish regions of the mohawkian sea which likely differed in terms of the nature and relative importance of carbon cycling processes water column depth and structure and barriers to free exchange of water across the mohawkian sea may have been overarching factors in the development of these regions raising the possibility that changes in circulation patterns such as those caused by sea level change played a role in driving secular carbon isotope excursions by changing the rate of exchange of dissolved inorganic carbon between water masses if the observed effects of local carbon cycling on the distribution of mohawkian sea 13c were commonplace in ancient epicontinental marine environments it would imply that local scale carbon cycling may have left a nontrivial imprint on epeiric sea records of secular variations in 13c in addition to the imprint left by changes in the global carbon cycle this may have contributed to the broad scatter in 13c values observed in the paleozoic portion of the global carbon isotope secular curve

neogene landscape evolution in the andes of north central chile between 28 and 32 s interplay between tectonic and erosional processes

bay sedimentation as controlled by regional crustal behaviour local tectonics and eustatic sea level changes coquimbo formation miocene pliocene bay of tongoy central chile abstract the north facing bay of tongoy in central chile is flanked by topographic highs in the west and east during the miocene and pliocene the bay extended inland at least 30 km farther south than a present it was filled with muds sands coquinas and gravel during a series of transgressions and regressions related to regional and local tectonic movements combined with global sea level variations 87sr 86sr and microfossil dating indicates transgressions between 11 9 11 2 ma 10 1 9 5 ma 9 0 7 3 ma 6 3 5 3 ma 4 3 2 2 ma and 1 7 1 4 ma the regional tectonic behaviour of the crust shows general uplifting from 10 5 ma to 6 9 ma associated with subduction of the juan fernandez ridge jfr beneath this part of the continent subsidence followed between 6 9 and 2 1 ma in the wake of the southeastward migrating jfr the subsequent subduction of an oceanic plateau similar to the jfr caused rapid uplift that led to the final emergence of the bay above sea level the puerto aldea normal fault along the western limit of the study area was reactivated during the regional uplift and subsidence events with reverse faulting occurring during the latter phase sporadic fault reactivation probably triggered the rapid changes in water depth reflected in the recorded vertical succession of facies

correlation of ordovician mohawkian k bentonites in the upper mississippi valley using apatite chemistry implications for stratigraphic interpretation of the mixed carbonate siliciclastic decorah formation abstract four ordovician k bentonites have been chemically fingerprinted using trace element content of apatite phenocrysts contained within the altered ash layers trace element analysis was performed using electron microprobe on individual crystals the bentonites include the deicke millbrig elkport and dickeyville beds these beds lie within the decorah formation of the northern mississippi valley outcrop area all four k bentonite beds are believed to have a taconic source whereas volcanic ash was transported by wind and deposited in the ordovician north america epeiric sea the decorah is a marine unit shaly to the north and west and carbonate rich to the south and east thirteen k bentonite samples were collected from six localities only one locality dickeyville wi contains all four beds in succession one hundred seventy one apatite crystals were handpicked and analyzed for major minor and trace elements using an electron microprobe each crystal was analyzed at three to six separate spots to ascertain compositional variation the most discriminating and diagnostic elements were mg and mn plotting mg vs mn content produces data clusters characteristic for each k bentonite clusters show only minimal change between localities allowing individual k bentonites to be identified and used for stratigraphic correlation time slices provided by the k bentonite horizons show that the decorah formation is composed of reciprocal wedges stratigraphic sequences of shale and carbonate shale was deposited in deeper water within the hollandale embayment but pinched out southeastward onto the flank of the wisconsin dome carbonates were formed largely in shoal water on the arch prograding northwestward and shaling out downramp into the embayment

anatomy of an embayment in an ordovician epeiric sea upper mississippi valley usa the integration of stratigraphic geochemical and biostratigraphic data from middle ordovician carbonates and shales indicates that the north american epeiric sea was partitioned into shelf areas with distinct characteristics the upper mississippi valley part of the epeiric sea was appraised by using regionally traceable and geochemically fingerprinted k bentonites as well as detailed lithologic correlation in the midcontinent the decorah formation records a time of high clastic sediment influx and abundant freshwater runoff from the transcontinental arch that created a salinity stratified water column and led to episodic dysoxia later relative flooding of the clastic source areas greatly reduced both the clastic sediment and freshwater runoff as a result the salinity stratification broke down oxygenating the seafloor and permitting carbonates to form associated with this change clarity of the water improved and the photic zone expanded allowing seasonal blooms of gloeocapsomorpha prisca to occur resulting in increased burial of organic matter the increase in g prisca and total organic carbon coincided with but lagged behind a regional 13 c excursion in addition the timing of the initiation of the isotopic anomaly is different across the studied area suggesting that local environmental conditions influenced the isotopic record data presented in this study support the partitioning of distinct areas within epeiric seas and the importance of this setting in storing inorganic and organic carbon and recording environmental and biological changes

shannon sandstone in hartzog draw heldt draw fields cretaceous wyoming usa reinterpreted as lowstand shoreface deposits abstract the lower campanian shannon sandstone at hartzog draw heldt draw powder river basin wyoming is interpreted in the literature as a shelf ridge complex deposited 160 km from the contemporaneous shoreline this interpretation poses difficult problems and does not discuss the significance of bounding discontinuities preserved in the sandbodies cross sections show that the shannon sandstone is present at several stratigraphic horizons and is bounded by regionally extensive discontinuities the presence of these bounding discontinuities suggests that fluctuations in relative sea level were important in controlling geometry of sandbodies on the shannon shelf in the hartzog draw heldt draw area of wyoming the base of the shannon is a planar surface with respect to a lower bentonite marker and is characterized by the abrupt appearance of bioturbated sandstone on top of black basinal mudstone siderite pebbles 1 cm in diameter are common at this contact in hartzog draw the bioturbated sandstone interval has an average thickness of 10 m and is separated from an overlying unit of cross bedded fine to medium sandstone up to 20 m thick by a ubiquitous 50 cm thick horizon of mud clasts in a cross bedded highly glauconitic medium sandstone these three units are laterally continuous in hartzog draw except where removed by erosion the top of the shannon is marked by an abrupt change from the cross bedded sandstone or bioturbated medium sandstone to laminated black mudstone mud clasts siderite pebbles chert grains and glauconite mark this abrupt contact suggesting erosional transgression this surface can be traced westward where in many areas it is a mud on mud contact marked by a lag of shell debris this transgressive surface which terminates shannon deposition is characterized by at least one regionally extensive onlapping marker in the hartzog draw heldt draw area the presence of depositional discontinuities in the shannon sandstone is suggested by 1 the sharp basal contact 2 the lateral continuity of individual facies 3 the abrupt vertical facies changes and the association of mud clasts siderite pebbles and glauconite accompanying these abrupt juxtapositions of facies 4 the stratigraphic variability and 5 the termination of shannon deposition by erosive transgression marked by onlapping markers these depositional discontinuities are the bounding discontinuities these bounding discontinuities have asymmetrical one sided scour morphologies with steeper landward margins that flatten basinward these geometries and the linearity of the overlying sandstone and the troughs defined by these scoured surfaces suggest incised shoref ce profiles truncated by erosive transgression thus the shannon sandstone in hartzog draw heldt draw is reinterpreted as a lowstand shoreface deposit

molecular indicators of redox and marine photoautotroph composition in the late middle ordovician of iowa u s a abstract saturated and aromatic hydrocarbons were used to evaluate depositional redox conditions and marine photoautotroph contributions to middle caradocian strata of the central united states ia at the base of the spechts ferry member of the decorah formation 13c enriched aryl isoprenoids derivatives of green sulfur bacteria become abundant indicating the development of photic zone anoxia this is coincident with the disappearance of the organic walled microfossil gloeocapsomorpha prisca and a marked decrease in the relative abundances of cyanobacterial biomarkers the development of dysoxic to anoxic conditions and or associated changes in basin circulation potentially affected the distributions and abundances of these organisms in the overlying guttenberg member g prisca derived organic matter becomes dominant but relative cyanobacteria abundances remain low in addition the percentage total organic carbon is greater than 20 even though selected biomarker ratios pristane phytane ratios greater than 3 and homohopane indices less than 0 5 and the presence of bioturbation indicate that bottom waters were oxygenated it is suggested that deposition of g prisca affected both organic matter preservation and depositional redox conditions observed variations in redox indicators and marine photoautotroph contributions are associated with changes in siliciclastic deposition reported macrofauna turnover and with evidence for oceanic cooling and a change in circulation patterns documented in the eastern united states

the mid cambrian series 3 guzhangian marjuman trilobite deiracephalus resser 1935 from western newfoundland species of deiracephalus resser 1935 are rare elements in most guzhangian upper marjuman trilobite faunas of laurentian north america and are characterized by striking cephalic spinosity that includes very long genal and occipital or preoccipital glabellar spines almost all previous reports of the genus have assigned sclerites to two species deiracephalus aster walcott 1916 and deiracephalus unicornis palmer 1962 however new material from the shallow bay formation of western newfoundland and restudy of type material from the southern appalachians show that as many as eight species are present although not all of them are sufficiently well known to be formally named deiracephalus aster and d unicornis are restricted to their respective holotypes from the conasauga formation of alabama new species from the shallow bay formation are deiracephalus narwhali deiracephalus rhinocerotis deiracephalus dynastoides and deiracephalus phanaeus deiracephalus unicornis d narwhali d rhinocerotis

paralic parasequences associated with eocene sea level oscillations in an active margin setting trihueco formation of the arauco basin chile abstract the eocene trihueco formation is one of the best exposed successions of the arauco basin in chile it represents a period of marine regression and transgression of second order duration during which barrier island complexes developed on a muddy shelf the strata are arranged in classical shoaling upward parasequences of shoreface and beach facies capped by coal bearing back barrier lagoon deposits these fourth order cycles are superimposed upon third order cycles which caused landward and seaward shifts of the coastal facies belts the final punctuated rise in sea level is represented by shelf mudrocks with transgressive incised shoreface sandstones relative sea level oscillations as revealed in the stratigraphy of the trihueco formation show a reasonable correlation with published eocene eustatic curves

the influence of air and sea exchange on the carbon isotope distribution in the sea we explore here the influence of the temperature dependence of isotope fractionation between atmospheric co2and ocean co2 on the distribution of carbon isotopes in the ocean this is accomplished by an analysis of departures from the expected redfield tie between po4 and 13c we find that for the surface ocean the temperature influence largely compensates for the biologic influence in the deep ocean the temperature influence imprinted at the sites of deepwater formation reduces somewhat the biologically induced difference between the carbon isotope ratios for deep waters produced in the northern atlantic and in the antarctic these same features are reproduced in the hamburg ocean model in order to assess the impact of changes in the ratio of ocean mixing rate to wind speed we have made a model run in which co2 exchange rates between air and sea were everywhere doubled as expected the influence of the thermodynamic effect on the oceanic carbon isotope distribution is magnified

holocene history of the baltic sea as recorded in a sediment core from the gotland deep a 4 m long sediment core from the gotland deep baltic sea was investigated by means of biostratigraphical and chemical parameters and c 14 datings this multidisciplinary approach allows us to ev

refinement of the time space evolution of the giant mio pliocene rio blanco los bronces porphyry cu mo cluster central chile new u pb shrimp ii and re os geochronology and 40ar 39ar thermochronology data representing one of the largest known estimated 5 gt at 1 cu and 0 02 mo porphyry system the rio blanco los bronces deposit incorporates at least five hypabyssal intrusive and hydrothermal centres extending for about 5 km from the rio blanco and los bronces mines in the north through the don luis mine to the sur sur mine la americana and los sulfatos in the south the new geochronology data which now include data on different molybdenite vein types confirm the u pb ages of the pre mineralisation intrusions but slightly increase their age range from 8 8 to 8 2 ma the distinct magmatic pulses of the mineralisation associated porphyritic intrusives late porphyries indicate an age interval instead of the previously suggested individual ages the quartz monzonite porphyry ranges from 7 7 to 6 1 ma sur sur 5 74 0 13 ma the feldspar porphyry shows an interval from 5 8 to 5 2 ma and the don luis porphyry from 5 2 to 5 0 ma the new re os data on distinct molybdenite vein types confirm the protracted history of cu mo mineralisation inferred previously the vein development occurred at least from 5 94 to 4 50 ma indicating a time span of 1 5 ma for the hydrothermal activity hydrothermal minerals dated by the 40ar 39ar method are generally too young to record the age of early high temperature mineralisation the majority of the 40ar 39ar data in the rio blanco porphyry cluster record reheating by either the youngest member of the late porphyry suite or the post mineralisation dacite or rhyolite plug formations at around 4 9 4 7 ma

nature and regional significance of unconformities associated with the middle ordovician hagan k bentonite complex in the north american midcontinent stratal patterns of the middle ordovician hagan k bentonite complex and associated rocks show that the black river trenton unconformity in the north american midcontinent formed through the complex interplay of eustasy sediment accumulation rates siliciclastic influx bathymetry seawater chemistry and perhaps local tectonic uplift the unconformity is diachronous and is an amalgamated surface that resulted from local late turinian lowstand exposure followed by regional early chatfieldian transgressive drowning and sediment starvation the duration of the unconformity is greatest in southern wisconsin northern illinois and northern indiana where the deicke and millbrig k bentonite beds converge at the unconformity on the basis of published isotopic ages for the deicke and millbrig beds it is possible that in these regions erosion and nondeposition spanned a period of as much as 3 2 m y two broad coeval depositional settings are recognized within the north american midcontinent during early chatfieldian time 1 an inner shelf subtidal facies of fossiliferous shale spechts ferry shale member and ion shale member of the decorah formation and argillaceous lime mudstone and skeletal wackestone guttenberg and kings lake limestone members extended from the canadian shield and transcontinental arch southeastward through minnesota wisconsin iowa and missouri 2 a seaward relatively deep subtidal sediment starved middle shelf extended eastward from the mississippi valley region to the taconian foreland basins in the central and southern appalachians and southward through the pericratonic arkoma and black warrior basins in the inner shelf region the black river trenton unconformity is a composite of at least two prominent hardground omission surfaces one at the top of the castlewood and carimona limestone members and the other at the top of the guttenberg and kings lake limestone members both merging to a single surface in the middle shelf region the inner and middle shelves redeveloped later in approximately the same regions during devonian and mississippian time

sedimentologic development of a late oligocene miocene forearc embayment valdivia basin complex southern chile abstract deposition of tertiary sediments in the southeastern part of the valdivia basin commenced during the late oligocene with the rapid incision of rivers draining the palaeo coastal range alluvial fans developing along the steep valley flanks joined gravelly braided streams transporting bedload to the coast tectonic and eustatic stability lasting into the early miocene subsequently allowed lateral erosion of the valley flanks and the development of extensive fluvial and estuarine peat swamps this stable period was interrupted briefly by a volcanic eruption at 23 5 ma shortly after 23 ma rapid uplift caused by an acceleration in plate convergence resulted in renewed erosion of the landscape as reflected in the deposition of coarse river gravels basin subsidence and marine transgression proceeding up the river valleys subsequently formed still deep embayments occasionally disturbed by debris flows and turbidity currents originating on the steep wooded valley flanks at the upper limits of the inlets bayhead deltas tidal flats and beaches existed in some areas fan deltas prograded into the embayments as reflected in the interfingering relationship between conglomerates and marine mudrocks in the deeper parts of the embayments the frequency of debris flows and turbidity currents increased markedly during periods of relative sea level lowstand the landscape was eventually inundated by continued subsidence and marine transgression which lasted until a possibly eustatic sea level fall in the early tortonian

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

middle miocene climatic change in the atacama desert northern chile evidence from supergene mineralization at la escondida geochronology and paleotopographic reconstruction of the porphyry copper deposit at la escondida chile are used to calculate long term erosion rates and to deduce the timing of tertiary climatic change for a portion of the atacama desert region hypogene hydrothermal alteration and protore mineralization at la escondida took place between 33 7 1 4 and 31 0 1 4 ma based on k ar dating of hydrothermal biotite and sericite supergene weathering and copper sulfide en richment processes were active from 18 0 0 7 to 14 7 0 6 ma based on k ar dating of supergene alunite distinguished from hypogene alunite by grain size color and sulfur isotopic composition reworked lenses of volcanic ash in the vicinity of la escondida provide useful time stratigraphic markers at 8 7 0 4 6 5 0 2 and 4 2 0 2 ma within present soil profiles long term average rates of erosion are determined by these age dates and quantitative calculation of eroded leached capping thickness at la escondida using mass balance analysis of geochemical profiles coupled with an estimate of unmineralized lithocap thickness based on alteration petrology and fluid inclusion geobarometry at similar deposits the observed trend of decreasing long term average erosion rates with time is consistent with arid to semiarid conditions in the early miocene changing to hyperarid conditions during the middle miocene this climatic desiccation caused termination of significant supergene copper suffide enrichment at la escondida and elsewhere in the atacama region and preservation of surficial features including the ash horizons and the leached capping middle miocene climatic desiccation in northern chile and southern peru was probably related to a pronounced decrease in temperature of coastal waters supplied by an ancestral humboldt current and an increase in upwelling intensity as the antarctic ice cap became established at approximately 15 to 13 ma the central andes cordillera which now provides a rain shadow protecting the atacama region from precipitation from the east must have attained at least half its present elevation prior to about 15 ma to have played a similar role in the middle miocene

40ar 39ar geochronology and provenance of detrital k feldspars ordovician upper mississippi valley abstract the upper ordovician strata of the upper mississippi valley contain numerous thin shale layers eighteen of these shale layers were previously thought to be altered volcanic ash beds known as k bentonites radioisotopic geochronology of six of the multiple shale bed partings throughout the upper ordovician indicate a non volcanic origin and provide clues for clastic sediment provenance and dispersal and depositional environments on epeiric seas the shale bed partings occur throughout the tippicanoe i supersequence all but one are within carbonate units one hundred thirty six 40ar 39ar single crystal laser fusion analyses of k feldspar derived from these beds yield apparent ages that range from 754 ma to 3 1 ga the age distributions of the k feldspars show distinctive populations when the data are plotted according to their stratigraphic position samples from the glenwood shale and platteville group show an age distribution clustering around 850 ma and 1 0 ga respectively shale samples from four beds within the galena group show an age distribution expanding from 754 ma to 3 1 ga the glenwood and platteville clusters correspond with the ages of nearby basement rock and cambrian ordovician sandstones while the shale bed partings of the galena are interpreted to have been sourced from a broader region these differences suggest that the glenwood and platteville samples were sourced from local rocks whereas the galena shale samples correspond with flooding of the local region area and connection to a new and complex source region these shale bed partings can be interpreted in two ways as pulses of terreginous material entering the system and overwhelming carbonate deposition or as background sediment accumulating during pauses in carbonate deposition while the older glenwood and platteville samples can be interpreted in either way the samples from the galena are better interpreted as condensed background sediment

a review of tertiary climate changes in southern south america and the antarctic peninsula part 2 continental conditions abstract climate changes in southern south america and the antarctic peninsula during the tertiary show a strong correlation with ocean warming and cooling events which are in turn related to tectonic processes during periods of accelerated sea floor spreading and mid ocean ridge activity sea levels rose so that parts of the continents were flooded and forests were destroyed however this was balanced by the large scale release of co2 during volcanic outgassing and carbonate precipitation on the continental shelves which caused rising air temperatures and the poleward expansion of sub tropical and temperate forests cooling episodes generally caused an increase in the north south thermal gradient because of an equatorward shift in climate belts so that the westerly winds intensified and brought higher rainfall to the lower latitudes an increase in wind blown dust caused temperatures to drop further by reflecting sunlight back into space the rising andes range had a marked influence on climate patterns up to the middle miocene it was still low enough to allow summer rainfall to reach central and north central chile but after about 14 ma it rose rapidly and effectively blocked the spill over of moisture from the atlantic ocean and amazon basin at this time the cold humboldt current was also established which together with the andes helped to create the arid diagonal of southern south america stretching from the atacama desert to the dry steppes of patagonia this caused the withdrawal of subtropical forests to south central chile and the expansion of sclerophytic vegetation to central chile however at the same time it intercepted more rain from the northeast causing the effect of the south american monsoon to intensify in northwestern argentina and southern bolivia where forest communities presently occur in patagonia glaciation started as early as 10 5 ma but by 7 ma had become a prominent feature of the landscape and continued apparently uninterruptedly into the pleistocene the antarctic peninsula saw its first mountain glaciation between 45 and 41 ma with major ice sheet expansion commencing at about 34 ma isolated stands of nothofagus forests were still present in low lying areas suggesting that the glaciers were initially wet based but dry based glaciers were established at around 8 ma although temperatures rose briefly during the messinian pliocene transition causing sub antarctic flora to retreat to higher elevations of the transantarctic mountains the present cold polar conditions were finally established by about 3 ma

non steady long term uplift rates and pleistocene marine terrace development along the andean margin of chile 31 s inferred from 10be dating pleistocene uplift of the chilean coast is recorded by the formation of wave cut platforms resulting from marine erosion during sea level highstands in the altos de talinay area 31 s we have identified a sequence of 5 wave cut platforms using in situ produced 10be exposure ages we show that these platforms were formed during interglacial periods at 6 122 232 321 and 690 ka these ages correspond to marine isotopic stages mis or substages miss 1 5e 7e 9c and 17 shoreline angle elevations used in conjunction with our chronology of wave cut platform formation illustrate that surface uplift rates vary from 103 69 mm ka between 122 and 6 ka to 1158 416 mm ka between 321 and 232 ka the absence of preserved platforms related to the mis 11 13 and 15 highstands likely reflects slow uplift rates during these times we suggest that since 700 ka the altos de talinay area was predominantly uplifted during 2 short periods following mis 17 and miss 9c this episodic uplift of the chilean coast in the pleistocene may result from subduction related processes such as pulses of tectonic accretion at the base of the forearc wedge

mineral deposits and cu zn as dispersion contamination in stream sediments from the semiarid coquimbo region chile this paper presents cu zn as geochemical data from stream sediment surveys carried out in the three main watersheds of the coquimbo region of chile this mountainous semiarid realm occupies an area of 40 656 km2 between 29 and 32 s given that the area has a long historical record of mining activities important environmental disturbances were expected however despite the detection of three major geochemical anomalies for cu zn or as only one can be unmistakably linked to the development of mining metal recovery procedures andacollo panulcillo an investigation of the other two anomalies elqui and hurtado reveals three major causes that fully or partially account for them 1 the type of ore deposit and associated hydrothermal alteration 2 the regional structural setting intensity of fracturing and 3 climate landscape cu au as epithermal deposits prospects along the so called el indio belt are here regarded as the sources of both the elqui and hurtado anomalies the strong advanced argillic alteration present in some of the epithermal deposits prospects of the el indio belt may have induced the loss of the buffering capacity of rocks and therefore favoured metal dispersion during later oxidation leaching of sulphides this applies to the elqui and hurtado anomalies conversely given that the potassic propylitic and phyllic alterations do not affect the buffering capacity of rocks only minor metal dispersion is observed in relation to the los pelambres porphyry copper deposit besides the epithermal belt is located within a highly fractured andean domain 3 000 4 000 m of altitude which may have conditioned the fast unroofing of ore deposits contributed to enhanced circulation of meteoric waters and eventually to strong oxidation and leaching of metals metal dispersion is aggravated during rainy years in response to strong el nino episodes

a paired apatite and calcite clumped isotope thermometry approach to estimating cambro ordovician seawater temperatures and isotopic composition the secular increase in 18 o values of both calcitic and phosphatic marine fossils through early phanerozoic time suggests either that 1 early paleozoic surface temperatures were high in excess of 40 c tropical mat 2 the 18 o value of seawater has increased by 7 8 vsmow through paleozoic time or 3 diagenesis has altered secular trends in early paleozoic samples carbonate clumped isotope analysis in combination with petrographic and elemental analysis can deconvolve fluid composition from temperature effects and therefore determine which of these hypotheses best explain the secular 18 o increase clumped isotope measurements of a suite of calcitic and phosphatic marine fossils from late cambrian to middle late ordovician aged strata the first paired fossil study of its kind document tropical sea surface temperatures near modern temperatures 26 38 c and seawater oxygen isotope ratios similar to today s ratios

a time like our own radioisotopic calibration of the ordovician greenhouse to icehouse transition tiered interpolation a new timescale methodology was used to construct the first radioisotopically calibrated composite 13c curve for the ordovician period using sanidine 40ar 39ar age determinations and existing u pb geochronology and biostratigraphic zonation tiered interpolation intercalates and temporally scales the numerical age of lithostratigraphic horizons by conducting a series of nested projections between hierarchical temporal control points for primary control points new 40ar 39ar ages and legacy u pb geochronology were screened to avoid analyses affected by inheritance and daughter loss and calibrated to reflect modern decay constants and standard values ages for secondary tertiary etc control points are obtained via linear interpolation of between higher order control points in scaling the ordovician 13c composite the following control point order was applied 1 radioisotopic ages 2 graptolite zones 3 index taxa based on speciation events north atlantic conodont zones 4 north american mid continent conodont zones and 5 stratal thicknesses at 13c sampled sections the resulting timescale utilizes the highest resolution of each component is internally consistent and is re scalable as more precise radioisotopic ages become available it provides a robust framework for independently assessing the accuracy of biostratigraphic composite timescales because it does not rely an assumption of quasi continuous sediment accumulation and or speciation to better calibrate the late ordovician and resolve a discrepancy between u pb and 40ar 39ar ages three new 40ar 39ar ages were determined via the laser fusion of multiple single sanidine phenocrysts from three bentonitic ash beds from the late ordovician marine strata of the upper mississippi valley where the record of taconic volcanism is most complete fusions of 275 individual sanidine crystals from the millbrig dygerts and rifle hill bentonites yield largely gaussian apparent age distributions with a small number of readily identified outliers and stratigraphically consistent weighted mean ages of 454 1 1 4 ma 51 of 57 450 7 1 4 ma 39 of 74 and 450 3 1 9 ma 96 of 144 for the millbrig dygerts and rifle hill bentonites respectively 2 analytical uncertainties relative to 28 201 ma for fcs the millbrig age is consistent with the existing u pb ages for both the underlying deicke bentonite and the kinnekulle bentonite of sweden the new age model permits the assembly of the first complete radioisotopically calibrated composite 13c curve for the ordovician the first icehouse to occur subsequent to the cambrian explosion the resulting 13c composite integrates all available graptolite and conodont biostratigraphic with radioisotopic ages and indicates that previous biostratigraphic composites incorporate 2 errors up to 5 ma when viewed without temporal distortions isotopic carbon excursions ices in the ordovician appear to have occurred at a similar tempo as ices in the better resolved cenozoic greenhouse to icehouse transition although boundary conditions for oceanography biogeography and continental configuration are strikingly different the tempo of isotopic changes growth of south polar ice sheets and concurrent oceanic and geomorphic responses bears both similarities and differences with the better understood cenozoic era

late cambrian ptychaspidid trilobites from western utah implications for trilobite systematics and biostratigraphy the notch peak formation late cambrian sunwaptan of western utah yields diverse silicified trilobite faunas that provide new information on the anatomy of many taxa the family ptychaspididae raymond 1924 is represented by species of keithiella rasetti 1944 idiomesus raymond 1924 euptychaspis ulrich in bridge 1931 and macronoda lochman 1964 at least four species are new of which e lawsonensis and m notchpeakensis are named formally much previous work on late cambrian trilobites has emphasized biostratigraphic utility and the recognition of geographically widespread species data from new silicified collections indicate that this approach is difficult to justify because many putative index species actually represent a plexus of closely related species whose biostratigraphic significance has yet to be determined one such plexus is represented by e kirki kobayashi 1935 whose previously reported occurrences in texas oklahoma utah nevada and northern canada record at least four distinct species similarly macronoda can now be shown to consist of at least five late sunwaptan species in south central and western north america

pliocene mass failure deposits mistaken as submarine tsunami backwash sediments an example from hornitos northern chile abstract in this study we question the former interpretation of a shallow marine backwash tsunami origin of a conspicuous pliocene coarse clastic unit at hornitos northern chile and instead argue for a debris flow origin for this unit we exclude a relation to a tsunami in general and to the eltanin impact in particular the observed deposit at hornitos was not generated either directly impact triggered tsunami or indirectly submarine mass flow caused by seismic shaking by an impact re calculation of the alleged impact tsunami including consideration of the van dorn effect shows that an impact in the southern ocean did not cause a significant tsunami at hornitos impact related seismic shaking was not able to trigger slides several thousands of kilometers away because the eltanin event was a deep sea impact that did not create a crater additionally the biostratigraphic age of 5 1 2 8 ma of the associated la portada formation is not concurrent with the newly established age of 2 511 0 07 ma for the eltanin impact instead we argue for an origin of the conspicuous unit at hornitos as a debris flow deposit caused by an earthquake in the andean subduction zone in northern chile our re interpretation considers the local synsedimentary tectonic background a comparison to recent submarine tsunami sediments and recent examples of mass wasting deposits along the chilean margin the increased uplift during the pliocene caused oversteepening of the coastal scarp and entailed a contemporaneous higher frequency of seismic events that triggered slope failures and cliff collapses the coarse clastic unit at hornitos represents an extraordinary potentially tsunami generating mass wasting event that is intercalated with mass wasting deposits on a smaller scale

interpreting carbon isotope excursions carbonates and organic matter abstract variations in the carbon isotopic compositions of marine carbonate and organic carbon provide a record of changes in the fraction of organic carbon buried through time and may provide clues to changes in rates of weathering and sources of organic carbon paired carbonate and organic carbon isotope determinations provide a possibility of interpreting not only changes in the global carbon cycle through time but changes in atmospheric pco2 as well interpretations of these types of data are typically rather qualitative a quantitative basis is required to develop a better understanding of changes in the carbon cycle for this purpose we employ a simple model of the global carbon cycle which is subjected to a number of different perturbations each lasting 500 ky i e much longer than the residence times of carbon and phosphorus in the ocean atmosphere system in addition to standard considerations of carbon mass and isotopic fluxes to the ocean atmosphere system from weathering and volcanism and fluxes of organic carbon and carbonate carbon to sediments the model incorporates sensitivity of the photosynthetic carbon isotope effect to changes in pco2 the inclusion of this parameter leads to unexpected carbon isotope responses to forcing that causes increased rates of organic carbon burial a series of simple to more complex simulations illustrates the significant effects of varying differences between the carbon isotopic composition of sedimented carbonate and organic carbon b with constant b a 50 increase in organic carbon burial produces a parallel increase in carbonate and organic carbon isotopic compositions however the same simulation with b responsive to pco2 changes produces an initial parallel 13 c increase but this is followed by an even greater 13 c enrichment in organic carbon because pco2 falls in response to increased organic carbon burial the counterintuitive overall result of the enhanced organic carbon burial event is that the carbonate carbon isotopic composition actually decreases because of the more substantial increase in 13 c org in addition we illustrate the effects on carbon isotopic compositions of the oceanic inorganic carbon reservoir and buried organic matter of a 50 increase in volcanic co2 outgassing a 50 increase in weathering rate with coupled phosphate and riverine carbon flux responses a 50 decrease in shale associated organic carbon weathering a 50 decrease in silicate weathering rate and the possible effects of the rise in abundance of c4 plants in the late miocene to recent we compare the model simulated carbon isotopic responses for some of these experiments to paired carbonate and organic carbon records to illustrate how these records might be interpreted in light of the model response

cenozoic marine sedimentation in the sechura and pisco basins peru abstract the central and northern peruvian margin consists of a series of 8 paired forearc basins which may be separated into an inner set of shelf basins and a seaward set of slope basins we have examined the cenozoic stratigraphy of the onshore portions of the sechura basin 5 7 s and pisco basin 13 16 s two shelf basins which have accumulated marine sediment discontinuously since the mid to late eocene cenozoic sediments in the pisco basin were deposited during at least three major transgressive cycles each sequence is preserved as a similar vertical progression of facies including coarse nearshore bioclastic conglomerates and sandstones grading upwards into sandy siltstones and mudstones and capped by biogenic deposits including diatomites diatomaceous mudstones dolomitic horizons and phosphate deposits stratigraphic nomenclature for the pisco basin has recently evolved a stratigraphy presented here includes the eocene caballas fm upper eocene los choros fm upper eocene to lowermost oligocene yumaque fm uppermost oligocene to middle miocene chilcatay fm and upper miocene to pliocene pisco fm major hiatuses in the pisco basin span the late cretaceous to middle eocene early to late oligocene middle miocene and late pliocene pleistocene to recent cenozoic sediments of the sechura basin were deposited within at least 4 major transgressive cycles with hiatuses during the paleocene to middle eocene oligocene early to middle miocene and late miocene based on recent biostratigraphic studies sediments enriched in biogenic components accumulated between about 40 36 ma 24 16 ma and 11 3 ma in the pisco basin and between 40 37 ma and 8 5 4 5 ma in the sechura basin in both basins the most diatomaceous sediments are restricted to the late eocene and late miocene through pliocene the temporal distribution of biogenic sediments suggests that high productivity conditions linked to coastal upwelling have occurred episodically since at least the late eocene the occurrence of diatomites and phosphorites is diachronous between the pisco and sechura basins and between the peruvian forearc and other circum pacific monterey formation analogs a reflection of the strong influence of local tectonism on sedimentation patterns the volume of neogene sediments along the peruvian forearc is nearly twice that of the monterey fm despite basin to basin facies diachroneity these deposits very likely contributed to fluctuations of the late miocene carbon co 2 system by acting as large carbon sinks

global carbon isotopic events associated with mass extinction and glaciation in the late ordovician mass extinctions and glacioeustatic sea level changes in the lower part of the hirnantian final stage of the ashgill are accompanied by shifts in marine stable isotope compositions previously published stable isotope changes have been used to identify the onset and demise of the gondwana glaciation and to suggest relationships between biotic changes and carbon cycling within the oceans however the existing isotopic data set had limitations because it was derived from ordovician low latitude settings and from carbonates or organic carbon in separate areas we report new data from ordovician high latitude carbonates and demonstrate parallel shifts in organic and carbonate 13c from baltica brachiopod shells from a high palaeolatitude periglacial setting in argentina have elevated 13c values similar to those described previously from low latitude sites the new data demonstrate that the positive hirnantian 13c excursion previously only recognised from low palaeolatitude areas was widespread and probably global in extent the poor preservation state of the brachiopods unfortunately prevented the determination of a reliable oxygen isotopic value from the same material preliminary carbon isotopic data from thermally immature organic matter from estonia provide the first indication of a synchronous shift in organic and inorganic 13c in sediments from the same basin this work provides new data of critical importance for constraining models of end ordovician palaeoceanography and climate change

determining the neogene behavior of the nazca plate by geohistory analysis geohistory analysis was performed on neogene deposits south and north of la serena central chile to determine the behavior of the crust since the middle miocene the tectonic history of both study areas was found to be similar but the timing of uplift and downwarp events at the two localities differs by 1 3 and 0 8 m y respectively which we attribute to the approach and passing of the juan fernandez ridge from trigonometric relationships between the ridge trend the plate vector and the trend between the study areas we calculated a plate convergence rate of 6 2 cm yr between 11 8 and 10 5 ma and 10 1 cm yr between 7 7 and 6 9 ma rapid uplift commenced ca 2 3 ma with a delay of 0 3 m y between the two study areas trigonometric constraints suggest the presence of a hitherto unsuspected oceanic plateau trending 014 subducted below the present continental margin flat plate subduction may thus be better developed where it is assisted by the combined buoyancy of ridge clusters instead of single subducting plateaus

rip currents as a geological tool this paper considers the nature and sedimentary significance of rip currents rip currents are the main factor responsible for the transport of coarse sediments from the littoral zone to greater depths such sediments deposited outside the zone of wave deformation may be identified as storm rip current increments within sediments deposited during fair weather composite beds deposited during a given wave cycle by storm rip currents are closely similar to turbidites and many so called fluxo turbidites described from flysch deposits using data gathered in studies conducted on the modern baltic coast supplemented by experimental work and theoretical considerations a sedimentary model is proposed the model may be used to interpret possible rip current deposits among shallow water turbidites and both modern storm sediments and ancient tempestites language en