did a katian large igneous province trigger the late ordovician glaciation a hypothesis tested with a carbon cycle model abstract the ordovician is known as a period with high temperatures and high sea levels and a cooling event at the end of the period leading to the hirnantian glaciation and the first of the big five mass extinctions of marine life the cause of this cooling event remains unclear several authors correlate it with a drop in atmospheric p co 2 to a threshold permitting the ice accumulation on the gondwana supercontinent however what are the reasons of the atmospheric p co 2 decrease here we follow the hypothesis initiated by barnes 2004 that an ordovician superplume event occurred during the middle to late ordovician such an event would not only have a large impact on the ordovician biodiversification barnes 2004 but it would also be responsible for the climatic upheaval during the late ordovician by the emplacement of a low latitudinal continental basaltic province that had an impact on the atmospheric p co 2 there is no direct evidence of a superplume event or of basaltic traps and the present study is therefore a hypothetical modelling approach where we demonstrate with a numerical box model including carbon alkalinity and phosphorus cycles coupled with a 1d climate model energy balance model ebm francois and walker 1992 that such a scenario allows to explain both the mid ashgill katian global warming event known as the boda event fortey and cocks 2005 and the subsequent late ordovician hirnantian glaciation because silicate weathering is enhanced upon warm and wet climate we try to constrain the size and the latitudinal emplacement of the basaltic province leading to a sufficient consumption of atmospheric p co 2 to the threshold proposed by herrmann et al 2004 a b to initiate a glaciation on gondwana

paired carbon isotopic analysis of ordovician bulk carbonate δ 13 c carb and organic matter δ 13 c org spanning the great ordovician biodiversification event abstract paired measurements of bulk carbonate 13ccarb organic matter 13corg and their difference 13c can be used to estimate changes in isotopic fractionation through time as a function of o2 co2 in the atmosphere however because local scale processes can also affect 13c it is essential to compare sections from widely separated water masses here we present new 13corg data from ordovician carbonate rocks from the great basin oklahoma and appalachian basin and compare with published 13ccarb records from these sections and paired 13c values from other carbonate successions around north america these new data complement previous studies that focused on upper ordovician 13ccarb excursions and now provide a composite ordovician 13corg record new lower ordovician tremadocian stage 13corg data range from ca 26 to 28 decreasing throughout the lower middle ordovician floian dapingian stages to ca 29 to 31 13corg values remain at their lowest throughout the sandbian and are similar to other published upper ordovician sandbian katian 13corg data from north america 13c values from well preserved intervals generally vary between 26 to 28 throughout the lower to middle ordovician tremadocian to early darriwilian but increase to 31 during the mid late darriwilian and mid sandbian similar to published data from younger late ordovician positive 13c excursions known as the guttenberg gice and hirnantian hice events the overall 13c trend shows a 3 increase throughout the early middle ordovician and coincides with a previously interpreted period of ocean cooling and some of the earliest pulses of global biodiversity of marine invertebrates and planktonic organisms modeling studies predict that pco2 decreased during this time suggesting that the effect of pco2 on 13c may have been overwhelmed by other controls such as an in increase in po2 or a higher o2 co2 ratio during this biodiversification event

carbon isotopes and event stratigraphy near the ordovician silurian boundary yichang south china abstract the organic carbon isotope data through the unweathered ordovician silurian boundary strata at the wangjiawan riverside section which is c 180 m southeast of the wangjiawan north section the gssp for the base of the hirnantian stage upper ordovician show that a positive 13 c org excursion begins just below the base of the hirnantian stage and peaks in the lower part of the n extraordinarius biozone this is followed by an interval of slightly reduced 13 c values and a second peak of 2 above pre hirnantian values which occurs in the lower part of the n persculptus biozone upper hirnantian the peaks in 13 c org values can be correlated well with episodes of glacial expansion described from africa and peri gondwanan europe evidence from sedimentological faunal and geochemical data from south china as well as the evidence of glacial sediments in north africa all suggests a short lived glaciation of 1 ma in the ordovician south pole region consisting of at least two major pulses the first phase of gradual glacial expansion began just before the hirnantian epoch and the second phase ended with rapid melting in the late hirnantian early n persculptus biozone

carbon and oxygen isotope stratigraphy of the lower mississippian kinderhookian lower osagean western united states implications for seawater chemistry and glaciation a positive carbon isotope 1 3 c excursion has been recognized in upper kinderhookian and early osagean carbonates in three sections in southeast idaho and nevada the oldest 1 3 c peak 7 is dated to the isostichaconodont zone and a younger peak occurs in the typicus zone the shifts are recorded in a range of carbonate lithofacies representing various water depths along the shelf lithofacies sampled for 1 3 c and 1 8 o at the samaria mountain section in southeast idaho record the shallowest water conditions indicated by cross bedded skeletal and peloidal grainstones the deepest water conditions are present in the pahranagat range section in eastern nevada which consists mainly of bioturbated lime mudstone and skeletal wackestone the 1 3 c values from these widely separated sedimentary basins show a consistent trend that correlates with early mississippian curves generated from brachiopod calcite in western europe and the midcontinent of north america as well as dolomites in utah and wyoming 1 8 o values become more positive up section generally paralleling the positive trend in 1 3 c during the late kinderhookian no subaerial exposure surfaces are recognized in the sections examined in southeast idaho and nevada and at least the 1 3 c trends are interpreted as primary seawater fluctuations sea level changes occurred near the beginning of the late kinderhookian 1 3 c shift early to middle parts of the isosticha zone and within the peak of the 1 3 c excursion kinderhookian osagean boundary although tectonic changes associated with the antler orogeny have likely modified the eustatic signature

raw material quality and oldowan hominin toolstone preferences evidence from kanjera south kenya the role of raw material quality in oldowan technology has not been fully explored there are numerous studies suggesting oldowan hominins preferred certain types of stone for artifact manufacture previous studies of the artifact assemblage from the early pliocene oldowan locality of kanjera south south rachuonyo district kenya show that raw material selection and transport was an important aspect of late pliocene hominin adaptations yet the exact properties of stones that hominins were selecting remain enigmatic two potentially important features of artifact raw material are durability and fracture predictability we investigate fracture predictability through mechanical tests of stone and investigations of the affect of stone properties on fracture patterns in archaeological collections we investigate stone durability with actualistic studies of edge attrition combined with further mechanical tests of various lithologies oldowan hominins at kanjera appear to have selected raw materials based on their durability the ability for a stone to fracture consistently does not appear to be as important in hominin toolstone preference as previously assumed hominins that produced the assemblages at kanjera south appear to have incorporated an extensive understanding of various attributes of raw material in the transport and production of stone artifacts when combined with previous research on the transport patterns at kanjera the results of this study provide evidence for a more complex raw material acquisition strategy than has previously been suggested for late pliocene oldowan hominins

is the dingcun lithic assembly a chopper chopping tool industry or late acheulian abstract the famous palaeolithic site of dingcun ting ts un in north china is located on the third terrace of the fenhe river which is one of the main tributaries of the yellow river after it was discovered a series of localities with similar stratigraphic profiles was excavated in 1954 since then the artifacts from dingcun have been classified as a chopper chopping tool industry assigned to the late pleistocene the authors re examined the lithic assemblage and carried out an additional field survey at these localities the local geomorphologic background and especially the chinese loess paleosol sequence re define the chronology of the site uranium series dates on mammal teeth are 160 ka 210 ka hence the site is re assigned to the late middle pleistocene the dingcun lithic assemblage is also re classified as late acheulian characterized by classic acheulian tools such as handaxes cleavers and picks with the addition of some light duty tools including scrapers notches borers and denticulates this paper aims to present a new interpretation of the chronology and the cultural characteristics of the dingcun site

middle palaeolithic raw material gathering territories and human mobility in the southern massif central france first results from a petro archaeological study on flint during the middle palaeolithic in the south eastern massif central and the bordering rhone valley humans collected almost all their raw materials from various secondary outcrop which can be distinguished by the inherent characteristics of the materials similar lithic facies are unlikely to be encountered on two or more different natural outcrops and every artefact shows a surface that is well enough preserved to be studied according to a morphoscopic analysis at various magnifications for all sites some more remote sources were also exploited however most of the supposed exogenous materials such as some cretaceous flints identified in the velay assemblages of sainte anne i and baume vallee for example come from the heart of the massif where they occur in secondary alluvial deposits nevertheless the extent of the foraging territories as revealed by raw materials sourcing covers a large band of various relief between the western and southern causses the rhone corridor and the northern limagne and forez plains and animal species hunted by these groups express an environmental mosaic which fits with the image of landscape given by the raw materials

geochemical differentiation and prehistoric procurement of obsidian in the mount taylor volcanic field northwest new mexico abstract recently due to an increasing number of analyses of archaeological obsidian worldwide the reporting of chemically differentiated and compositionally zoned obsidian producing rhyolite domes has increased while these studies have been important and furthered our knowledge of the potential chemical variability of rhyolite magmas as they relate to archaeological obsidians they are rarely made relevant to archaeological issues in northwestern new mexico the grants ridge source in the mount taylor volcanic field exhibits two compositionally differing glasses derived from the same magma source that also exhibit significant megascopic variability correlating with raw material quality while grants ridge was previously seen as a single source this study suggests that one of the localities was considered a more viable raw material in prehistory at least in the local area the grants ridge study indicates the value of more intensive investigations of archaeological obsidian sources in the southwest including systematic geoprospection and chemical analysis the wavelength and energy dispersive x ray fluorescence analysis reported here provides the first systematic study of this high silica archaeological obsidian source in the mount taylor volcanic field

lithofacies and depositional mechanisms of the ordovician silurian wufeng longmaxi organic rich shales in the upper yangtze area southern china the ordovician silurian organic rich shales in the wufeng and longmaxi formations are widespread in southern china and are the most important shale gas producers in china the shales display varying total organic carbon content ranging from 0 2 to 6 and are composed of black siliceous mudstone shelly limestone siliceous clay rich mudstone gray silty shaly interlaminated mudstone gray argillaceous mudstone and calcareous or dolomitic mudstone detailed stratigraphic correlation of these formations was achieved and a high resolution sequence stratigraphy was constructed based on the integration of well log data mineralogical geochemical and petrophysical analyses the wufeng formation and the guanyinqiao bed were interpreted to be a condensed section with four cycles of sea level fluctuation the longmaxi formation consists of three members the long 1 member was interpreted to be a third order depositional sequence that can be subdivided into a transgressive systems tract an early highstand systems tract and a late highstand systems tract within the constructed isochronal stratigraphic framework the characteristics and genetic mechanism of different shale lithofacies were studied the deposition of black siliceous mudstone of high total organic carbon in the wufeng formation and the long 1 transgressive systems tract was likely influenced by volcanic activity the guanyinqiao shelly limestone or calcareous mudstone was associated with the ordovician silurian transition when glaciation and mass extinction took place the gray silty shaly interlaminated mudstone of moderate total organic carbon in the long 1 early highstand systems tract was the product of bottom flow intrusion the deposition of gray argillaceous mudstone and calcareous or dolomitic mudstone with low total organic carbon in the long 1 late highstand systems tract resulted from enhanced terrigenous input from peripheral uplifts the distribution pattern of different lithofacies varies greatly in the upper yangtze area and this difference is a result of dissimilar sediment provenances and variable hydraulic restriction levels that were controlled by basin geometry a better understanding of the distribution pattern and depositional history of the wufeng and longmaxi formations might provide guidance for future profitable shale gas exploration

oldowan behavior and raw material transport perspectives from the kanjera formation the archaeological record of oldowan hominins represents a diverse behavioral system it has been suggested that exploitation of lithic resources by oldowan hominins was simplistic and represented mostly use of local sources of stone here we investigate the raw material selection and transport behaviors of oldowan hominins reflected in the stone artifact assemblages from the kanjera south formation south rachuonyo district kenya using geochemical methods ed xrf artifacts are linked to primary and secondary source outcrops throughout southwestern kenya these data show that hominins selected raw materials for transport at frequencies that are significantly different from their availability on ancient landscapes furthermore a substantial proportion of the assemblage represents transport over relatively long distances 10 km our study further suggests that in the early stages of stone tool use hominins used a wide variety of raw materials and selected these materials at some distance from their eventual discard locations early hominin behavior may have incorporated an understanding of raw material source distributions across a more extensive landscape than has been previously documented this supports the growing perspective that oldowan technology represents a more complex behavioral pattern than is usually associated with the beginnings of hominin tool use

hominin migration in south asia and raw material sources in the banas berach basin abstract previous research conducted by v n misra in the berach river basin and its tributaries identified dozens of early and middle paleolithic sites although southeastern rajasthan is non coastal and outside of the purana gondwana basin zones described by korisettar sufficient resources in the form of water food and stone made the region habitable in the pleistocene misra s groundbreaking survey indicated that several non riverine raw materials were used by hominins but no evidence had been produced outside of the immediate vicinity of the rivers to demonstrate pursuit of stone material mobility restricted to riverine zones would present a challenge to migration between various ecological zones and ultimately to populating the subcontinent this paper presents the results of a recent survey conducted directly to the south of misra s study and identifies an open air site situated on a raw material source this find upholds the claim for non riverine pleistocene habitation by hominins in southeastern rajasthan and the ability of hominins to migrate between multiple ecological zones

calibrating the late ordovician glaciation and mass extinction by the eccentricity cycles of earth s orbit a process based sedimentological analysis of upper ordovician glacial marine rocks in africa suggests that full glaciation of the continental shelf started in the late extraordinarius zone of the hirnantian two cycles of ice sheet growth are represented during full glaciation initial terrestrial ice sheet growth in the early extraordinarius zone influenced the first event of the late ordovician mass extinction retreat of the ice sheet from the shelf ended by the persculptus zone when the second event of the late ordovician mass extinction began eccentricity controlled ice sheet growth is assumed periodicity 0 1 m y hence two cycles of full glaciation lasted 0 2 m y the duration of the extraordinarius zone is estimated as 0 5 m y therefore the minimum duration of the first extinction event was 0 3 m y

carbon isotope δ13ccarb stratigraphy of the lower middle ordovician tremadocian darriwilian in the great basin western united states implications for global correlation abstract new stable carbon isotope data 13ccarb from lower middle ordovician tremadocian to darriwilian carbonate mudstone and wackestone rocks of the pogonip group are presented from two sections in the great basin region usa shingle pass east central nevada and the ibex area western utah the pogonip group is a succession of mixed carbonate and siliciclastic rocks that accumulated on a carbonate ramp under normal marine conditions during the late cambrian furongian to middle ordovician darriwilian the shingle pass and ibex area sections have been previously studied for their conodont biostratigraphy and contain a north american midcontinent conodont fauna that range from the cordylodus intermedius zone uppermost cambrian to the phragmodus polonicus zone darriwilian the 13c trend has four distinct characteristics recognized in both great basin sections 1 a drop in 13c from 1 at the base of the ordovician tremadocian to 0 7 2 a 1 to 2 positive 13c shift in the uppermost rossodus manitouensis zone during the late tremadocian 3 a gradual 13c increase from 2 to ca 0 during the end of the early ordovician floian and 4 a steady 13c decrease from 0 to 4 to 5 during middle ordovician dapingian darriwilian in the lower ordovician 13c trends reported here from the great basin are not consistent with a causal mechanism involving sea level change and the migration of isotopically distinct water bodies instead these lower ordovician isotope data most likely reflect primary seawater chemistry and changes in 13c on a global scale this interpretation is supported by the excellent correlation of 13c in the lower ordovician to other 13c trends reported from the sections in the argentine precordillera la silla and san juan formations and in western newfoundland st george and table head groups these correlations using 13c are consistent with published biostratigraphic data and provide an integrated and high resolution chemo biostratigraphic framework for the lower ordovician sedimentary record of the laurentian margin the middle ordovician portion of the 13c curves in the great basin represented by the kanosh and lehman formations shows significant isotopic depletion relative to the section in argentina thus although there is some indication that minima and maxima in the middle ordovician curves can be correlated the great basin sections show clear evidence of overprinting by local variables related to both diagenesis dolomitization and platform restriction

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 climatic significance of late ordovician early silurian black shales the ordovician silurian transition approximate to 455 430ma is characterized by repeated climatic perturbations concomitant with major changes in the global oceanic redox state best exemplified by the periodic deposition of black shales the relationship between the climatic evolution and the oceanic redox cycles however remains largely debated here using an ocean atmosphere general circulation model accounting for ocean biogeochemistry mitgcm we investigate the mechanisms responsible for the burial of organic carbon immediately before during and right after the latest ordovician hirnantian 445 444ma glacial peak our results are compared with recent sedimentological and geochemical data we show that the late katian time slice approximate to 445ma typified by the deposition of black shales at tropical latitudes represents an unperturbed oceanic state with regional organic carbon burial driven by the surface primary productivity during the hirnantian our experiments predict a global oxygenation event in agreement with the disappearance of the black shales in the sedimentary record this suggests that deep water burial of organic matter may not be a tenable triggering factor for the positive carbon excursion reported at that time our simulations indicate that the perturbation of the ocean circulation induced by the release of freshwater in the context of the post hirnantian deglaciation does not sustain over sufficiently long geological periods to cause the rhuddanian approximate to 444ma oceanic anoxic event input of nutrients to the ocean through increased continental weathering and the leaching of newly exposed glaciogenic sediments may instead constitute the dominant control on the spread of anoxia in the early silurian

environmental change and raw material selection strategies at taoshan a terminal late pleistocene to holocene site in north eastern china the lesser khingan mountains of north eastern china are heavily forested making archaeological site identification difficult owing to poor ground surface visibility nevertheless several prehistoric archaeological site discoveries have been made in recent years and a limited number of excavations have been initiated one of the most important sites to emerge is taoshan which has yielded stratified stone tool assemblages dating from the last glacial maximum lgm to the mid holocene pollen profiles indicate significant changes in vegetation fluctuating from steppe conditions during the lgm to forested conditions in the bolling allerod interstadial b a and the mid holocene the stone tool assemblages from taoshan were primarily produced from varieties of volcanic tuff rhyolite hornfels and agate geological prospecting and petrological analyses were performed to document procurement sources and changes in raw material exploitation strategies during the lgm the predominant raw material was vitric tuff available from a source ca 5 10 km from taoshan in the b a and mid holocene layers emphasis was on the exploitation of raw materials in gravel bars although stone tool reduction techniques and raw material preferences changed considerably during this time interval diachronic changes in raw materials and exploitation strategies correspond to changes in vegetation and human adaptations

first record of the hirnantian upper ordovician δ13c excursion in the north american midcontinent and its regional implications the most prominent of the two major global delta c 13 excursions in the ordovician the hirnantian delta c 13 excursion hice which is previously recorded from the uppermost ordovician in a few sections in nevada quebec arctic canada baltoscandia scotland and china is documented for the first time from the north american midcontinent samples through the girardeau limestone and leemon formation in missouri and illinois show elevated delta c 13 values of 4 parts per thousand to 5 parts per thousand although not determined precisely the beginning of the hice is likely to be in the upper part of the orchard creek shale and it ends in the upper leemon formation being extraordinarily useful chronostratigraphically the presence of the hice makes it possible to provide a firm dating of the study interval whose age has long been controversial comparison between the study sections and coeval hice sequences in north america and europe show striking similarities especially in sea level history indicating that major local lowstands reflect eustatic sea level changes a comparison with hirnantian diamictite successions in north and south africa and argentina suggests that these lowstands correspond to two major gondwanan glacial episodes less

sponge dominated offshore benthic ecosystems across south china in the aftermath of the end ordovician mass extinction abstract offshore benthic communities were sparse after the end ordovician mass extinction the recent discovery of diverse abundant sponges in south eastern china anhui and zhejiang provinces that flourished during the hirnantian late ordovician post extinction interval raises questions over the extent and ecological significance of the sponge community at that time this paper dramatically expands the scale of the hirnantian sponge fauna within south china with seven new occurrences across 2000 km these occurrences cross the ordovician silurian boundary interval in the marginal and submerged platform areas of the yangtze sea in jiangsu hubei hunan chongqing and sichuan provinces in condensed sections platform margin facies the occurrences are normally represented by extensive spiculite layers but several sites yield entire exceptionally preserved body fossils at ganggangshan near nanjing jiangsu province such preservation is abundant the new occurrences are combined with palaeogeographic and tectonic reconstructions to produce a model for the distribution and preservation of the sponge fauna we argue that the exceptional preservation was due largely to nepheloid layers that were generated during rapid post glacial transgression that flooded the weathered land surface of the uplifted cathaysia block nepheloid layer collapse led to rapid deposition of suspended sediment within the deeper parts of the intra plate restricted basin and on adjacent platform margins and slopes the suspended sediment influx also introduced abundant nutrients to the water column as indicated by a significant 13c excursion during the sponge bearing mudstone interval at ganggangshan the combined sponge assemblage was dominant over large areas of the hirnantian offshore sea floor across south china we predict that similar occurrences with exceptional preservation will also be found in other continental blocks abundant articulated sponges may be encountered particularly in restricted basin successions containing rapidly deposited graptolitic mudstones near the ordovician silurian boundary

provenancing hornfels in the dingcun industry the exploitation of the vicinity source in this paper we attempt to determine the source of the hornfels used to make the famous late middle pleistocene lithic industry from dingcun in north china by combining geological mapping and geochemical fingerprinting xrf we demonstrate that the source of the hornfels was around the dagudui mountain 7 km east of dingcun taking into consideration the gujiao site which is also located along the fenhe river the palaeolithic inhabitants of the fenhe river drainage basin had a good knowledge of the local rock sources and used them over a very long period from the middle pleistocene to the neolithic our geochemical data not only helps us to establish the source of the dingcun industry but also provides a reliable basis for the sub classification of the hornfels that is more accurate than that resulting from visual inspection in addition our research initiates a new method for studying raw material sources of chinese paleolithic sites

paired isotope records of carbonate and organic matter from the middle ordovician of argentina intrabasinal variation and effects of the marine chemocline abstract we investigate the expression of the middle darriwilian isotope carbon excursion mdice across marine shelf environments in the argentine precordillera previous work identified the mdice in the las chacritas formation in argentina but did not recognize the expression of the mdice in time equivalent strata of the deeper water las aguaditas formation albanesi et al 2013 palaeogeography palaeoclimatology palaeoecology v 398 p 48 66 recent biostratigraphic investigations of these units have for the first time provided the opportunity for high resolution correlation which suggest that the mdice or at least the initiation of the mdice should be observed in both the las chacritas and las aguaditas formations here we present new paired carbon isotope data of carbonate and organic carbon from the las chacritas and las aguaditas formations we identify a 2 positive shift in the isotopic composition of marine carbonate in the las chacritas formation whereas values abruptly fall to

the impact of raw material on acheulian large flake production raw material properties and availability have always been considered as having a definitive impact on the morphology size and production technology of acheulian large cutting tools shape and size of the naturally available raw material blocks have been cited as key factors in determining acheulian biface blank production technology as well as tool morphological variability in other words where large blocks of raw material were available africa large flakes were produced and where only smaller cobbles and nodules were to be found europe they become the primary type of blank used in this paper i explore a large body of data collected from acheulian sites from india to morocco and from south africa to england to test this common premise different raw material exploitation patterns as reflected in the bifacial tools in the various assemblages are described and analyzed the results indicate that in large flake based acheulian assemblages raw material constraints did not significantly affect either the blank production process or large cutting tool shape and size variability the acheulian large cutting toolmakers used the rock types available in the vicinity of their site in a sophisticated reduction sequence aimed to produce large cutting tools that are surprisingly similar regardless of the original shape size and type of raw material from which they were produced

sequestration of 12c in the deep ocean during the early wenlock silurian positive carbon isotope excursion abstract marine carbonates from three biostratigraphically well dated silurian sections from the mid continent of north america were analyzed for carbon isotopic 13 c carb study the early wenlock positive carbon isotope excursion ireviken excursion is recorded in three sections from tennessee iowa and ohio with values of 4 5 this global shift in the carbon isotopic ratio of marine waters began during a protracted extinction event ireviken event that spanned the llandovery wenlock boundary although several oceanographic models have been developed to account for the coincident changes in lithology biology and carbon isotope stratigraphy during this interval of the silurian their proposed causal connections among glaciation oceanography primary productivity and the global carbon cycle remain a matter of debate this investigation provides carbon isotopic and lithologic evidence that the ireviken excursion occurred during a time of relatively oligotrophic conditions a third order transgressive regressive cycle and increased carbonate production throughout the mid continent of north america the ireviken excursion is recorded in relatively pure carbonate sequences and is immediately preceded by a significant unconformity in each of the measured sections it is proposed that the ireviken excursion was the product of sequestration and burial of 12 c in deep water as a result of altered deep ocean circulation

hirnantian strata identified in major intracratonic basins of central north america implications for uppermost ordovician stratigraphy carbon isotopes are analyzed for the first time from the ordovician silurian boundary interval in the williston and hudson bay basins of manitoba revealing a prominent positive excursion the nature of this excursion and its co occurrence with the appearance of the ozarkodina hassi conodont zone and a distinctive coral dominated macrofauna indicate that this is the upper portion metabolograptus persculptus graptolite zone of the globally recognized hirnantian isotopic carbon excursion hice as a result the ordovician silurian boundary is placed at a higher position than previously thought at the disconformable stonewall fisher branch formational boundary in the williston basin and probably the port nelson severn river formational boundary in the hudson bay basin disconformities within sections suggest periods of nondeposition due to subaerial exposure as sea level fluctuated during the late ordovician glaciation latest ordovician hirnantian deposition was far more widespread on the laurent

the late ordovician mass extinction abstract near the end of the late ordovician in the first of five mass extinctions in the phanerozoic about 85 of marine species died the cause was a brief glacial interval that produced two pulses of extinction the first pulse was at the beginning of the glaciation when sea level decline drained epicontinental seaways produced a harsh climate in low and mid latitudes and initiated active deep oceanic currents that aerated the deep oceans and brought nutrients and possibly toxic material up from oceanic depths following that initial pulse of extinction surviving faunas adapted to the new ecologic setting the glaciation ended suddenly and as sea level rose the climate moderated and oceanic circulation stagnated another pulse of extinction occurred the second extinction marked the end of a long interval of ecologic stasis an ecologic evolutionary unit recovery from the event took several million years but the resulting fauna had ecologic patterns similar to the fauna that had become e

macroevolutionary transition in crinoids following the late ordovician extinction event ordovician to early silurian abstract the end katian late ordovician crinoid mass extinction triggered the change from the early to the middle paleozoic crinoid evolutionary faunas cefs this was a change from diplobathrid camerate disparid hybocrinid dominated faunas to faunas dominated by monobathrid camerate cladid and flexible crinoids all clades suffered extinctions at the end katian event but diplobathrid camerates disparids and hybocrinids suffered higher rates of extinction the primary amount of diversification occurred in clades that would become dominant during the silurian however the formation of the characteristic middle paleozoic cef was protracted beyond the late ordovician extinction event monobathrid camerates and flexibles diversified through the llandovery but both dendrocrinid and cyathocrinid cladids did not diversify until later monobathrid camerate genera and families diversified the flexible diversification was largely at the genus level cyathocrine diversification was largely among families and dendrocrinids did not diversify significantly until after the llandovery overall disparity decreased during the end katian extinction by reducing the disparity within each clade disparity remained fairly constant during the hirnantian but increased significantly during the llandovery by both increasing disparity within clades and expanding the morphospace of the disparids due to the radiation of families with new morphologies north america was the biogeographic center of origination for the families that survived to become dominant silurian clades

the end ordovician glaciation and the hirnantian stage a global review and questions about late ordovician event stratigraphy abstract this paper proposes a global review of hirnantian event stratigraphy the hirnantian gssp in south china is tentatively correlated with latest ordovician strata from the peri gondwanan glacial regions problems of biostratigraphical correlation are highlighted at a worldwide scale the major biostratigraphically useful fossil groups graptolites chitinozoans brachiopods conodonts acritarchs are analysed and their limits for global correlation of the uppermost ordovician are discussed palaeobiogeographical disparities are invoked as the primary cause of the difficulty in establishing an effective late ordovician global biostratigraphical scheme as an alternative correlative tool the hice hirnantian isotopic curve excursion event is often put forward in the literature however carbon isotope chemostratigraphy shows like biostratigraphy some limits to the present state of knowledge no good independent biostratigraphical control of the hice exists in both shallow carbonate deposits and deeper shaly ones recent studies have also demonstrated inconsistencies between carbon isotopic signals obtained from organic 13corg and inorganic 13ccarb carbon species further complicating the use of the hice as an isochronous benchmark all of these difficulties for hirnantian event stratigraphy are discussed in detail in order to enable them to be overcome in the future precise late ordovician and early silurian event stratigraphies are essential for the understanding of the mechanisms linked to the first of the big five extinctions

toolstone constraints on knapping skill levallois reduction with two different raw materials lithic raw material constraints are widely assumed to be a determining factor of flaked stone tool morphology but this assumption remains largely untested we conducted a controlled experiment to determine whether a knapper s growing replication skills would be hindered if the toolstone used was switched from large flakes of an easily worked chert to nodules of less tractable one two batches of preferential levallois cores were knapped an earlier series made from standardised large flakes of sediments dominated by chalcedonic quartz followed by a more challenging one using variably shaped cortical nodules of microcrystaline quartz that varies in the completeness of quartz replacement of calcite and dolomite skill level markers were designed to measure the knapper s ability to achieve a series of set goals these were quantified and subjected to statistical testing in all but one test significant increases in skill could be detected from the earlier to the later batch of reductions despite the drop in toolstone quality significant improvements in the consistency of the knapper s output could also be detected however the switch to a more challenging nodular chert did require extra shaping which resulted in more waste this masked visible progress towards producing a less costly core overall our results do not support the assumed primacy of toolstone constraints over other factors in influencing the morphology of flaked stone tools

high resolution carbon isotopic records from the ordovician of south china links to climatic cooling and the great ordovician biodiversification event gobe abstract the great ordovician biodiversification event gobe represented the largest increase in diversity in the marine biosphere during the phanerozoic eon yet its causes and consequences remain poorly understood patterns of isotopic variation in high resolution 13ccarb and 13corg records from a well exposed section at honghuayuan in south china may provide important insights regarding the gobe the honghuayuan isotopic profiles which can be correlated with c isotopic records from contemporaneous sections globally reveal large perturbations to the global carbon cycle during the ordovician a 8 increase in 13corg values in the floian implies a large albeit transient increase in the burial rate of organic matter during the mid early ordovician that may have contributed to climatic cooling and played an important role in triggering the gobe a 4 increase in 13ccarb and high frequency variation in 13corg in the darriwilian to sandbian suggest a second episode of elevated organic carbon burial rates accompanied by substantial instability in the global carbon cycle during the late middle and early late ordovician this pattern may mark the onset of climate changes culminating in the end ordovician hirnantian glaciation and mass extinction event that terminated the gobe

towards an orbital time scale for chinese loess deposits abstract in this study we analyzed the grain size of the baoji loess soil sequence at 10 cm intervals results show that grain size variations are very sensitive to loess soil alternations with loess units being much coarser than soils such a change in loess soil grains is interpreted as the result of the glacial interglacial cyclic variations in the intensity of the winter monsoon winds out of siberia the grain size record is thus employed as a proxy indicator of the winter monsoon circulation and tuned to the orbital records calculated recently by berger and loutre 1991 under the control of major magnetic reversals the tuning is independent of any correlation with 18o signals in the deep sea sediments the resulting grain size time scale is tightly constrained as suggested by the following facts 1 the filtered obliquity and precession components from the grain size data on the orbital time scale closely match the theoretical orbital records 2 ages of the major magnetic reversals estimated from the grain size time scale are in good agreement with the k ar dated ages 3 there is close coherence between the baoji grain size time series and the orbital variations at the orbital frequency bands over the entire 0 2 5 ma period and 4 the grain size record on the orbital time scale shows a close similarity to the orbitally tuned dsdp site 607 and odp site 677 18o records examination of time dependent characteristics of the grain size record suggests that there are two major shifts of dominant periodicities in the long term monsoonal cycles one occurring at about 0 8 ma bp and the other around 1 7 ma bp

high resolution stable isotope stratigraphy of the upper cambrian and ordovician in the argentine precordillera carbon isotope excursions and correlations abstract we report the occurrence of important carbon isotope excursions in early paleozoic formations of the eastern and central argentine precordillera the steptoean positive isotope carbon excursion spice is known from north america kazakhstan south china australia and south america and the negative isotope carbon excursion snice has been described for the first time in south america we report here the record of the spice and snice in a single section in the eastern precordillera in the central precordillera a minor middle darriwilian positive carbon isotope excursion mdice and a late sandbian positive isotope carbon excursion the gice 3 c bicornis biozone are reported from two sections one pre gice positive carbon isotope excursion sandbian sa1 n gracilis biozone in the central precordillera with a 13c peak of 2 is perhaps equivalent to the positive spechts ferry 13c excursion of north america a positive 13c excursion 6 n persculptus biozone recorded at the base of the late hirnantian la chilca formation probably corresponds to hice these carbon isotope excursions resulted from more than one factor where paleoceanographic events probably played a major role a sea level fall and vigorous fluctuations in the steptoean spice b sea level rise in the sunwaptan snice c important transgression in the sandbian pre gice and gice and d sea level fall in the late hirnantian hice in the darriwilian and sandbian stages organic burial has led to a large 12c sequestration in the deep anoxic ocean with saline bottom water recorded by the graptoliferous black shales of the gualcamayo and los azules formations in central precordillera helped the building of the mdice and gice anomalies 18o values for the upper cambrian carbonates are likely near primary isotope signals that point to progressive cooling from the spice to the snice whereas for sandbian carbonates they suggest strong temperature fluctuations the 13c peak of the gice coincides with a cooler period with temperatures warming up towards the late hirnantian to rhuddanian the upper cambrian to the middle ordovician of the precordillera recorded a decrease of seawater 87sr 86sr ratios in accordance to the global picture this decrease probably reflects the influence of widespread volcanic activity from arc terranes in low latitude settings along eastern margins of laurentia and in the argentine precordillera in the early to middle ordovician five carbonate samples from san juan gualcamayo and los azules formations yielded end values that along seven already published values seem to plot along the nd isotopic evolution trend of the iapetus ocean together the record of global upper cambrian and ordovician carbon isotope excursions in the argentine precordillera is a valuable proxy in refining early paleozoic stratigraphy establishing of regional global high resolution correlations and sea level change history in south america

millennial scale paleoclimate cycles recorded in widespread palaeozoic deeper water rhythmites of north america rhythmically interbedded limestone and shale or limestone and chert rhythmites are a common feature of many deep water phanerozoic carbonate marine deposits seventeen different palaeozoic rhythmite successions from across north america 8 studied in detail 9 studied in reconnaissance are described and summarized individual rhythmite couplets 4 20 cm thick are composed of fine grained laminated to massive detrital limestone alternating with shale or marl or laminated spiculitic chert stratigraphic and primary depositional features within rhythmites and associated facies indicates that the carbonate rich and carbonate poor interbedding is the result of repetitive changes in sediment input primary rather than due to diagenetic redistribution of calcareous material secondary the average duration of individual rhythmite couplets is calculated using spectral analysis to determine couplet thickness combined with biostratigraphically calibrated undecompacted average sediment accumulation rates the duration of rhythmite couplets from the eight well studied successions ranges between 150 and 4900 yrs with the majority lying between 1000 and 3000 yrs i e millennial scale the paucity and low diversity of skeletal and trace fossils preserved suspension laminae lack of sediment reworking and facies associations indicate rhythmite accumulation was favored by 1 deposition below storm wave base which limited reworking by currents 2 dysaerobic bottom waters which restricted bioturbation and intermixing of interbedded lithologies and 3 proximity to nearshore carbonates supplying abundant fine grained detrital carbonate these combined conditions were best met along flooded subtropical continental shelves or epeiric seas during my scale 3rd order sealevel rises the rhythmic alternation between carbonate rich and carbonate poor layers is interpreted to represent millennial scale paleoclimatic changes related to 1 wet dry climate cycles which influenced the amount of continent derived eolian and or fluvial sediment input 2 variations in offshore transport via storm generated or density currents of nearshore derived terrigenous or carbonate sediments and or 3 changes in wind driven upwelling and availability of recycled biogenic silica the various rhythmite successions accumulated under dramatically different paleoenvironment and paleogeographic conditions including active to passive tectonic settings equatorial to subtropical latitudes long term icehouse through greenhouse climatic conditions calcite versus aragonitic seas variable atmospheric co2 concentrations before and after land plant and animal evolution and across widely varying ocean basin configurations if our short term paleoclimatic interpretations for the rhythmites are correct then it is apparent that millennial scale climate changes occurred over a very wide spectrum of paleoceanographic paleogeographic paleoclimatic tectonic and biologic conditions and over time periods from the cambrian to the quaternary given this it is difficult to invoke models of internally driven thermohaline oceanic oscillations or continental ice sheet instabilities to explain their origin instead we suggest that

improved efficiency of the biological pump as a trigger for the late ordovician glaciation the first of the big five phanerozoic mass extinctions occurred in tandem with an episode of glaciation during the hirnantian age of the late ordovician the mechanism or change in the carbon cycle that promoted this glaciation thereby resulting in the extinction is still debated here we report new coupled nitrogen isotope analyses of bulk sediments and chlorophyll degradation products porphyrins from the vinini creek section vinini formation nevada usa to show that eukaryotes increasingly dominated marine export production in the lead up to the hirnantian extinction we then use these findings to evaluate changes in the carbon cycle by incorporating them into a biogeochemical model in which production is increased in response to an elevated phosphorus inventory potentially caused by enhanced continental weathering in response to the activity of land plants and or an episode of volcanism the results suggest that expanded eukaryotic algal production may have increased the community average cell size leading to higher export efficiency during the late katian the coincidence of this community shift with a large scale marine transgression increased organic carbon burial drawing down co2 and triggering the hirnantian glaciation this episode may mark an early palaeozoic strengthening of the biological pump which for a short while may have made eukaryotic algae indirect killers enhanced algal productivity during the late ordovician may have led to carbon drawdown and the inception of the hirnantian glaciation according to sediment geochemistry and carbon cycle modelling

nd isotope records of late ordovician sea level change implications for glaciation frequency and global stratigraphic correlation abstract detailed records of ice sheet advances and retreats are reconstructed for the hirnantian and katian ages of the late ordovician using nd isotopes e nd as a sea level proxy in three study sections from the western margin of laurentia two shallow water platform sections located south and north of the paleo equator and one deep water section located in a continental slope rise setting when sea level was high and paleo shorelines had migrated eastward the e nd value of seawater in the vicinity of each of the study sections shifted toward the e nd value of the eastern panthalassa ocean 4 0 by contrast when sea level was low and paleo shorelines had migrated westward the e nd value of seawater shifted toward the e nd value of the continental weathering flux from laurentia 8 5 0 2 2 mean these stratigraphic patterns of changing e nd values are interpreted to reflect the eustatic sea level fluctuations that previous studies have documented in response to gondwanan ice sheet advances and retreats thus linking the e nd sea level proxy to late ordovician global scale climate changes the e nd profiles for the two platform sections yielded similar proxy sea level curves with five cycles of oscillation recorded during the latest katian and hirnantian three additional cycles of late katian sea level change are recognized in the e nd profile of the deep water continental slope rise section the combination of e nd 13 c and graptolite biostratigraphic data facilitates a precise interregional correlation of the hirnantian age and the paleoclimate changes that took place during this interval the new correlations support previous findings that the hirnantian ice age comprised two major glacial periods separated by a minor interglacial during the early part of the metabolograptus persculptus biozone the younger glacial confined to mid m persculptus biozone time led to more extensive sea surface cooling than did the earlier one and resulted in extensive eustatic sea level drawdown and c cycle changes it records the strata most often recognized as hice the hirnantian carbon isotope excursion in sedimentary successions worldwide such as anticosti island scotland estonia siberia and south china the results of this study support and strengthen the view that glaciation predated the hirnantian age in the late ordovician and that the records of small positive 13 c excursions in katian successions from baltica and eastern north america are themselves proxy indicators of glaciation frequency and eustatic sea level changes

graptoloid evolutionary rates track ordovician silurian global climate change graptoloid evolutionary dynamics show a marked contrast from the ordovician to the silurian subdued extinction and origination rates during the ordovician give way during the late katian to rates that were highly volatile and of higher mean value through the silurian reflecting the significantly shorter lifespan of silurian species these patterns are revealed in high resolution rate curves derived from the conop constrained optimization scaled and calibrated global composite sequence of 2094 graptoloid species the end ordovician mass depletion was driven primarily by an elevated extinction rate which lasted for c 1 2 ma with two main spikes during the hirnantian the early silurian recovery although initiated by a peak in origination rate was maintained by a complex interplay of origination and extinction rates with both rates rising and falling sharply the global 13 c curve echoes the graptoloid evolutionary rates pattern the prominent and well known positive isotope excursions during the late ordovician and silurian lie on or close to times of sharp decline in graptoloid species richness commonly associated with extinction rate spikes the graptoloid and isotope data point to a relatively steady marine environment in the ordovician with mainly background extinction rates changing during the katian to a more volatile climatic regime that prevailed through the silurian with several sharp extinction episodes triggered by environmental crises the correlation of graptoloid species diversity with isotopic ratios was positive in the ordovician and negative in the silurian suggesting different causal linkages throughout the history of the graptoloid clade all major depletions in species richness except for one were caused by elevated extinction rate rather than decreased origination rate

stratigraphic variation in marine carbonate carbon isotope ratios stratigraphic variation in the carbon isotopic 13c value of marine carbonate and organic matter preserved within it has become a popular tool for supporting paleoclimatic hypotheses and refining stratigraphic correlation virtually every important biostratigraphic and sequence stratigraphic event of the last 800 million years has had a 13c dataset collected to aid in interpreting the causal environmental factors that contributed to the event the stratigraphic resolution obtainable using 13c has yielded critical temporal constraints on the interplay between carbon cycle variation and environmental events such as mass extinction and eustasy although the non uniqueness of the carbon isotopic response to different environmental stimuli has frustrated the identification of a unified mechanism linking marine 13c variation with distinct environmental forcing functions the interpretation of 13c variation can nonetheless provide important insights into processes that influence major global climatic and surficial systems early studies of marine carbonate minerals suggested that the 13c value of ancient oceans was essentially 0 versus the peedee belemnite standard pdb clayton and degens 1959 schidlowski et al 1975 see also keith and weber 1964 it was later recognized however that departures from the pdb standard represented secular variation in the 13c values of the marine environment rather than analytical noise that the record was potentially rich with stratigraphic and paleoenvironmental information scholle and arthur 1980 veizer et al 1980 wadleigh and veizer 1982 arthur et al 1985 holser et al 1986 zachos and arthur 1986 and that variation was intimately linked to the global carbon oxygen and sulfur cycles kump and garrels 1986 holser et al 1988 it is now well established that carbonate 13c values vary within 3 from the pdb standard for

a major drop in seawater 87sr 86sr during the middle ordovician darriwilian links to volcanism and climate a large drop in seawater 87 sr 86 sr during the middle ordovician was among the most rapid in the entire phanerozoic new 87 sr 86 sr measurements from nevada indicate that the rapid shift began in the pygodus serra conodont zone of the upper darriwilian stage we use a numerical model to explore the hypothesis that volcanic weathering provided the flux of nonradiogenic sr to the oceans a close balance between volcanic outgassing and co 2 consumption from weathering produced steady p co 2 levels and climate through the middle katian consistent with recent ordovician paleotemperature estimates in the late katian outgassing was reduced while volcanic weathering continued and resulted in a cooling episode leading into the well known end ordovician glaciation

large perturbations of the carbon and sulfur cycle associated with the late ordovician mass extinction in south china high resolution 13 c data of organic carbon from a continuous section of the late ordovician early silurian reveal two positive 13 c excursions that are associated with the mass extinction in south china the fi rst stratigraphic 34 s measurements on pyrite tied to well established biostratigraphy indicate a large perturbation of the sulfur cycle consistent with major sea level changes related to the glaciation the elevated 34 s values of pyrites and a large short lived negative 34 s excursion of 20 associated with the decay of the glaciation suggest deep water anoxia during the hirnantian stage in contrast to the conventional view that the global oceans were oxygenated we suggest that deep water anoxia may have contributed to the late ordovician mass extinction in south china and possibly elsewhere

scarcity of the c30 sterane biomarker 24 n propylcholestane in lower paleozoic marine paleoenvironments abstract 24 n propylcholestane 24 npc a c30 sterane compound derived from sterol precursors which are the major sterol constituents of modern pelagophyte microalgae occurs in certain neoproterozoic rocks and oils and throughout the phanerozoic rock record this broad distribution leads 24 npc to be widely considered a reliable indicator of open to partially restricted marine depositional conditions for source rocks and oils here we report two significant hiatuses in the occurrences of 24 npc in the lower paleozoic marine rock record the first in the middle late cambrian and the second in the late ordovician early silurian transition for a range of lithofacies carbonates and siliciclastic rocks organic carbon contents both organic lean and organic rich and paleoceanographic environments shelf and deeper water marine settings and observed offshore of two paleocontinents laurentia and baltica the ordovician silurian gap is at least 9 million years and possibly up to 20 million years in duration robust older occurrences of 24 npc steranes in some neoproterozoic rocks and oils suggest that oceanographic conditions in our intervals of lower paleozoic time were unfavorable for the proliferation of pelagophyte algae as phytoplankton caution should therefore be applied when interpreting a lacustrine versus marine depositional environmental setting for source rocks and oils in these intervals of early paleozoic time using lipid biomarker assemblages

late ordovician mass extinction a new perspective from stratigraphic sections in central nevada integrated sequence stratigraphic biostratigraphic and chemostratigraphic analyses of three stratigraphic sections in central nevada indicate that late ordovician glaciation induced sea level fall produced diachronous stepwise faunal turnover in graptolites conodonts chitinozoans and radiolarians and also triggered a strong but transient positive 13c excursion this pattern is very different from that described for most mass extinction events

stable isotope evidence for gradual environmental changes and species survivorship across the cretaceous tertiary boundary high resolution 13c and 18o records have been generated from analyses of the planktonic foraminiferal species heterohelix globulosa and the benthonic foraminiferal taxon lenticulina spp from 3 m of a cored section spanning the cretaceous tertiary k t boundary at brazos river texas these are the first stable isotope records across the k t boundary based on monospecific and monogeneric foraminiferal samples they show a gradual decrease in 13c values of about 2 5 permil beginning at the k t boundary as defined by the first appearance of tertiary planktonic foraminifera and continuing 17 20 cm above the boundary approximately 40 000 years later gradual 13c depletion contrasts with the sudden 13c drop at the k t boundary observed in many deep sea sections the surface to bottom 13c gradient decreased to less than zero approximately 25 000 30 000 years after the k t boundary and remained negative for at least the next 140 000 years concomitant with change in 13c values is a gradual decrease of about 2 5 permil in 18c values which has not been observed at other localities this 18o depletion suggests changes in temperature and or salinity in the earliest paleocene gulf of mexico no extinction of foraminiferal species is associated with the k t boundary or the onset of 18o and 13c depletions instead two phases of cretaceous species extinctions occur one extinction phase is below the k t boundary and below the tsunami bed of bourgeois et al 1988 and may be linked to sea level regression and environmental perturbations the second extinction phase coincides with the minimum in 13c and 18o values in the early danian zone p0 pla and appears directly related to environmental changes reflected in the isotopic record h globulosa which is commonly present in maastrichtian and danian sediments exhibits significantly lower 18o 16o and 13c 12c ratios in tertiary sediments relative to specimens from maastrichtian sediments demonstrating the survival of this important cretaceous taxon after the k t boundary event

raw material quality and prepared core technologies in northeast asia the design and assembly of lithic toolkits is mediated by a number of factors including the abundance and quality of raw materials available in general low raw material abundance and high raw material quality are thought to lead to formal tool designs whereas high raw material abundance and low raw material quality lead to informal designs low raw material quality is seen as the overriding factor producing informal tool designs even where low raw material abundance would favour formal designs in north china the predominance of simple flake and core technologies based on relatively poor quality raw materials and the near absence of sophisticated prepared core technologies seems to corroborate the importance of raw material quality in toolkit design recent studies of a late pleistocene lithic assemblage from the lower grotto at tsagaan agui cave mongolia suggest however that raw material quality is not an absolute constraint on the development of sophisticated core reduction strategies levallois like and other prepared core forms based on large flake blanks are conspicuous in the lower grotto assemblage despite the poor quality of raw material available at the site contrary to expectations these core forms appear to have developed directly in response to poor raw material quality the implication is that raw material quality alone cannot explain the apparent technological simplicity of the north chinese middle and upper paleolithic

environmental controls on marine ecosystem recovery following mass extinctions with an example from the early triassic abstract the recovery of marine ecosystems following a mass extinction event involves an extended interval of increasing biotic diversity and ecosystem complexity the pace of recovery may be controlled by intrinsic ecosystem or extrinsic environmental factors here we present an analysis of changes in marine conditions following the end permian mass extinction with the objective of evaluating the role of environmental factors in the protracted 5 myr long recovery of marine ecosystems during the early triassic specifically our study examines changes in weathering productivity and redox proxies in three sections in south china chaohu daxiakou and zuodeng and one in northern india mud our results reveal 1 recurrent environmental perturbations during the early triassic 2 a general pattern of high terrestrial weathering rates and more intensely reducing marine redox conditions during the early griesbachian late griesbachian mid smithian and more weakly the mid spathian 3 increases in marine productivity during the aforementioned intervals except for the early griesbachian and 4 stronger and more temporally discrete intervals of environmental change in deepwater sections chaohu and daxiakou relative to shallow and intermediate sections zuodeng and mud our analysis reveals a close relationship between episodes of marine environmental deterioration and a slowing or reversal of ecosystem recovery based on metrics of biodiversity within community alpha diversity infaunal burrowing and ecosystem tiering we infer that the pattern and pace of marine ecosystem recovery was strongly modulated by recurrent environmental perturbations during the early triassic these perturbations were associated with elevated weathering and productivity fluxes implying that nutrient and energy flows were key influences on recovery more regular secular variation in deepwater relative to shallow water environmental conditions implies that perturbations originated at depth i e within the oceanic thermocline and influenced the ocean surface layer irregularly finally we compared patterns of environmental disturbance and ecosystem recovery following the other four big five phanerozoic mass extinctions to evaluate whether commonalities exist in general the pace of ecosystem recovery depends on the degree of stability of the post crisis marine environment

did changes in atmospheric co2 coincide with latest ordovician glacial interglacial cycles article i nfo the late ordovician hirnantian stage 444 million years ago was one of three time periods during the past half billion years in which large continental glaciers formed over earth s polar regions the effects of this glaciation were far reaching and coincided with one of the largest marine mass extinction events in earth history the cause of this ice age is uncertain and a paradoxical association with evidence for high atmospheric co2 levels has been debated precise linkages between sea level ice volume and carbon isotope 13 ccarb and 13 corg proxy records of pco2 have been poorly understood due in part to uncertainties in stratigraphic correlation and the interpretation of globally important sections although correlation difficulties remain recent hirnantian biostratigraphic studies now allow for improved correlations here we show that consistent trends in both 13 ccarb and 13 corg from two well dated stratigraphic sequences in estonia and anticosti island canada coincide with changes in late ordovician hirnantian climate as inferred from sea level and the extent of ice sheets the integrated datasets are consistent with increasing pco2 levels in response to ice sheet expansion that reduced silicate weathering ultimately the time period of elevated pco2 levels is followed by geologic evidence of deglaciation

local and global perspectives on carbon and nitrogen cycling during the hirnantian glaciation abstract the impact of climate and ocean circulation changes on marine carbon and nitrogen cycling was investigated for a period covering the late ordovician hirnantian glaciation three sections were studied two from nevada one proximal and one distal and one from the yukon the opportunity to compare 13 c carb 13 c org and 13 c grap profiles between ocean and epeiric platform settings enabled a more thorough assessment of environmental and diagenetic factors influencing the preservation of seawater 13 c values at each stratigraphic section using the best preserved sedimentary components from the two nevada sections a lowstand sedimentary gradient of 4 was found between platform and ocean settings during the hirnantian glaciation gradients of similar magnitude have been reported from hirnantian platforms in the canadian arctic and baltic basins taking the outboard sections as the most representative of the ocean carbon pool a mean positive 13 c shift of just 2 7 0 4 is calculated which is significantly smaller than the 5 7 positive shifts recorded in epeiric platform settings the discrepancy is attributed to the effects of local carbon cycling in tropical and subtropical epeiric seas it is hypothesized that increased carbonate weathering caused 13 c values of local carbon weathering fluxes to increase which in turn caused seawater 13 c values to increase in basin proximal settings in addition nutrient dust fluxes may have contributed to increased levels of photosynthetic activity in proximal settings driving sedimentary 13 c values even higher much higher than sediment deposited in outboard settings where carbon exchanges with the surface ocean were less restrictive a 15 n profile reconstructed from deposits of the distal vinini creek section records a 1 5 positive shift through the hirnantian glacial interval interpreted as a major late ordovician upwelling zone high organic carbon 1 wt and high hydrogen indices 400 600 make the vinini creek section a suitable candidate for the preservation of original sedimentary 15 n records to explain the results a conceptual model of ocean nitrogen cycling under greenhouse climate conditions is presented that highlights the role of cyanobacteria as both primary producers and nitrogen fixers it is hypothesized that in greenhouse climates the fixed nitrogen inventory of the abyssal ocean was low due to efficient denitrification in the ocean s expansive oxygen minimum zones this caused algal productivity to become strongly dependent on continuous supplies of fixed nitrogen from cyanobacteria in the photic zone yielding sedimentary 15 n values between 0 and 2 by contrast the cooler icehouse climate of the hirnantian led to increased ocean ventilation greater partitioning of atmospheric oxygen into downwelling surface waters and oxygen minimum zone shrinkage as a result fixed nitrogen levels climbed in the ocean s abyssal depths due to the lower denitrification rates this in turn allowed nitrogen with high 15 n values to recycle back into the photic zone driving sedimentary 15 n values higher during the hirnantian glaciation

late ordovician carbon isotope trend in estonia its significance in stratigraphy and environmental analysis abstract carbon isotope changes during most of late ordovician time from the mid caradoc kinnekulle k bentonite until the beginning of the silurian were investigated as the corresponding sequence of rocks is stratigraphically nearly complete in estonia an attempt was made to use it to elaborate the general pattern of carbon isotope changes in the late ordovician complications were caused by several local or regional hiatuses in the middle and late caradoc and hirnantian a total of 385 whole rock samples were studied from eight drill cores in northern and central estonia the following positive carbon isotope events were observed 1 the mid caradoc excursion peak 13c value 2 2 in the uppermost part of the keila stage also known in sweden 2 the first late caradoc excursion 1 9 in the lower part of the rakvere stage 3 the second late caradoc excursion 2 4 in the upper part of the nabala stage 4 the early ashgill excursion 2 5 in the lowermost part of the pirgu stage 5 the widely known large hirnantian excursion in estonia the peak value reaches 6 7 in the porkuni stage the study interval comprises a long 10 ma period characterized by low magnitude carbon isotope changes and a following brief 2 ma interval with large changes no obvious lithological preference for hosting the positive shifts was recorded in principle the 13c values exceeding the background values may occur in all types of rocks present in a sedimentary basin several 13c positive excursions values 1 5 to 3 in the mohawkian of north america are evidence that the minor caradoc and early ashgill 13c positive shifts in baltoscandia may have counterparts in laurentia if correctly correlated these shifts may have global significance the hirnantian excursion is usually linked to a major glacial event even if some carbon cycling mechanisms are not completely understood the environmental causes suggested for the earlier minor shifts range from global climatic and glacial events to very local changes in basin regime and sea level our study supports the primary role of climatic or climatically triggered oceanic processes

are obsidian subsources meaningful units of analysis temporal and spatial patterning of subsources in the coso volcanic field southeastern california archaeologists frequently assign artifacts to chemically discrete subsignatures of major obsidian sources while the technical ability to do so has been demonstrated it remains to be shown that such information is behaviorally meaningful indeed some analysts choose not to make such determinations under the presumption that the data are not anthropologically relevant using a case study from the coso volcanic field which has at least four distinct subsignatures we examine this problem and conclude that subsource identification can be useful and quite interesting this is particularly so when large datasets encompassing spatially expansive areas can be assembled and statistically analyzed

the late aeronian graptolite sedgwickii event associated positive carbon isotope excursion and facies changes in the prague synform barrandian area bohemia study of the lower silurian black shale succession of the prague synform has enabled detailed insight into graptolite faunal dynamics and diversity trends from the mid aeronian diversity maximum through to the late aeronian crisis graptolite diversity decreased from 33 taxa in the lituigraptus convolutus biozone to 17 taxa in the upper part of the stimulograptus sedgwickii biozone and newly erected lituigraptus rastrum biozone the graptolite assemblages of the latter biozones exhibit low species richness along with high dominance many graptolite species that became extinct in the early part of the sedgwickii zone were promptly replaced by new forms in the later part of the sedgwickii zone however replacement of extinct species by new forms considerably decelerated the increased rate of graptolite extinction recorded in the convolutus sedgwickii biozone boundary beds coincided with subtle changes in black shale lithologies and a positive shift in 13 c org of 2 2 compared to baseline values sea level drawdown can be inferred from siltstones and or temporary nondeposition in the middle sedgwickii zone this level also sees total organic carbon toc fluctuations and a strong positive 13 c org excursion with a peak shift of at least 7 the sedgwickii event exhibits substantial reorganization of the graptolite fauna its taxonomic impoverishment and concomitant increase in species dominance rather than a sudden collapse of the pre extinction assemblage associated changes in lithology toc and the pronounced 13 c org excursion suggest a relatively extended and probably multi phase period of stressed conditions that affected the pelagic realm inhabited by graptolites in the course of the late aeronian interval

late ordovician to earliest silurian graptolite and brachiopod biozonation from the yangtze region south china with a global correlation late ordovician to earliest silurian is an important geological period marked by large geological and biological events however the strata and fossils of this interval are not complete in many parts of the world based on studies of 43 sites in south china in particular the continuous sections on the yangtze platform we recognize a complete succession including seven graptolite zones and two shelly faunas in ascending order the graptolite zones are the dicellograptus complanatus dicellograptus complexus paraorthograptus pacificus including lower subzone tangyagraptus typicus subzone and diceratograptus mirus subzone normalograptus extraordinarius normalograptus ojsuensis normalograptus persculptus akidograptus ascensus and parakidograptus acuminatus zones the shelly faunas are the foliomena nankinolithus and hirnantia faunas which may be correlated with d complanatus zone and n extraordinarius n ojsuensis to part of n persculptus zones respectively the biozonation through this interval from the yangtze region can be correlated with that of other parts of the world such as dob s linn in scotland spain and portugal thuringia saxonia bavaria bohemia poland kazakhstan kolyma malaya peninsula yukon canadian arctic islands nevada argentina niger and victoria australia the hirnantian substage which has been proposed by us recently includes the n extraordinarius n ojsuensis zone hirnantia fauna and n persculptus zone the base of the hirnantian substage is marked by the first appearance data fads of n extraordinarius and n ojsuensis which have been determined to be synchronous on a global scale

a useful measure of the desirability of different raw materials for retouch within and between assemblages the raw material retouch index rmri abstract due to their predictable fracture and the quality of the edge that can be produced on them fine grained raw materials such as chert have long been favoured by prehistoric toolmakers for the production of relatively small retouched artefacts it is common to find far higher frequencies of retouch in such materials than is the case in all other rock types in order to quantify the desirability of different materials for retouch i propose a simple index relating the frequency of retouched tools in a raw material to the frequency of that material in the entire assemblage using the raw material retouch index rmri one can compare relative raw material desirability both within and between assemblages

a late acheulean culture on the chinese loess plateau the techno economic behavior of the dingcun lithic industry abstract the chinese loess plateau is the largest loess area in the world and covers 400 000 km2 with a loess palaeosol sequence that is comparable with marine isotope stages mis as a quaternary terrestrial timescale of climatostratigraphy and chronology the dingcun lithic industry was recovered in 1954 in the loess plateau and has been known for its large flake acheulean tools technological analysis based on the concept of chaine operatoire was applied in this paper to update our knowledge of the techno economic behaviours at this site and in the loess plateau area the results show that there are two chaine operatoires 1 one focused on the production of large flake blanks faconnage for making large cutting tools lcts and 2 a small to medium debitage to obtain flakes for light duty tools experiments were applied to check the knapping technique the results confirmed the probability that hard hammers were used to produce large flakes on hornfels blanks and soft hammer techniques were not used when compared with the acheulian lcts of other sites in china dingcun is different from the acheulian culture of south china danjiangkou reservoir region drr and the bose basin and more similar to the luonan acheulian industry therefore it seems that a large flake acheulean was developed the loess plateau area in the late middle pleistocene

the ireviken event in the lower silurian of gotland sweden relation to similar palaeozoic and proterozoic events abstract for a long time the silurian was thought to represent a time of stable environmental conditions in the greenhouse period that followed the late ordovician glaciation during the past decade knowledge about the silurian has increased markedly and today it is known that the conditions in the silurian were much more variable than previously assumed detailed isotopic investigations have revealed several distinct positive excursions in both carbon and oxygen isotope values in low latitudes these periods of high c and o isotope values are in many cases characterised by the growth of reefs and the formation of extended carbonate platforms the sediments deposited during these excursions contain impoverished fossil assemblages especially with respect to conodonts graptolites and trilobites a conspicuous isotope excursion coincident with facies changes and a marked mass extinction is observed near the llandovery wenlock boundary this event is called the ireviken event after its type locality on the island of gotland sweden jeppsson l 1987 in palaeobiology of conodonts ellis horwood ltd chichester pp 129 145 here isotope data from nine sections at the nw coast of gotland are presented that cover the time interval of the ireviken event the 13c mean values rise from 1 4 to 4 5 and the 18o values increase from 5 6 to 5 0 the relative timing of stable isotope development extinctions and facies development is discussed it is shown that first extinctions precede the isotope excursion this indicates that extinction events and stable isotope development are only indirectly connected but might reflect the same causes other events characterised by similar relationships between positive isotope excursions mass extinctions and facies development are found in younger parts of the silurian late wenlock and ludlow in the late ordovician the late cambrian and with some reservations in the proterozoic the similarities between these events indicate analogous controlling mechanisms for the silurian climatic changes between humid and arid conditions in low latitudes were postulated in an earlier study of the authors a palaeoceanographic climatic model was postulated which is consistent with most of the sedimentological palaeontological and geochemical data here we demonstrate that this model may be applicable also for the older events

graptolite biozone correlation charts charts are presented showing the correlation of graptolite biozonations for the lower ordovician to lower devonian i e for the entire stratigraphical range of the planktonic graptoloid graptolites regions chosen are those for which the most detailed biostratigraphical studies have been undertaken for baltica average graptolite zone chron duration appears to vary from c 300000 years ludlow epoch to 2 4 ma lochkovian epoch