barremian danian chemostratigraphic sequences of the cauvery basin india implications on scales of stratigraphic correlation abstract chemostratigraphic concepts postulate that distinct chemozones could be recognized from rock records to help correlate geographically separated strata many studies have upheld this view but were limited to classic boundaries such as cenomanian turonian or cretaceous tertiary only a few elements and isotopic compositions were made use in such studies an attempt to recognize chemozones of barremian danian strata of the cauvery basin south india through whole rock chemistry had revealed many complex signals and depositional events as expressed by bulk geochemical profiles the signals indicate major shift in sedimentation pattern from dynamic depocenter to stable depositional conditions during santonian varying sensitivities of different elements towards prevalent depositional conditions are also inferred trends of geochemical composition indicated domination of single depositional control all through the depositional history basinal configuration that limited terrestrial sediment source and episodic influx of detrital materials presence of distinct change in whole rock geochemistry across geochronological and lithostratigraphic boundaries is deciphered through a statistical tool anova these results demonstrate that visual delineation of chemozones in a long ranging rock record would be tenuous and has to be exercised with caution

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

the stratigraphic distribution of ni rich spinels in cretaceous tertiary boundary rocks at el kef tunisia caravaca spain and hole 761c leg 122 abstract ni rich spinels have been found throughhout the world at the cretaceous tertiary boundary these minerals have no counterparts in terrestrial rocks but have been observed in meteoroid ablation material and impact debris suggesting that the cretaceous tertiary boundary spinels result from an extraterrestrial event their stratigraphic distribution which has been observed at the cretaceous tertiary boundary sites of el kef tunisia caravaca spain and hole 761c odp leg 122 indian ocean are markedly different from site to site and are all much less extended than the ir anomalies regional differences in ni rich spinel distibution are entirely explained by a brief event recorded under different bioturbation conditions the wider stratigraphic dispersion of ir is attributed to postdepositional chemical processes at el kef the site which appears to be the least affected by bioturbation and which has the highest sedimentation rate the 1 2 mm thick ni rich spinel spike indicates that the deposition time did not exceed an upper limit of 100 years this upper limit is consistent only with the collision of an asteroid or a comet at the close of the cretaceous

dinoflagellate cysts sea level changes and planktonic foraminifers across the cretaceous tertiary boundary at el haria northwest tunisia abstract dinoflagellate cysts and planktonic foraminifers have been studied from the cretaceous tertiary k t boundary interval at el haria northwest tunisia a high resolution integrated biostratigraphy is presented the k t boundary is drawn at the level of extinction of cretaceous planktonic foraminifers and is coincident with the first occurrence of the dinoflagellate cyst species danea californica the final extinction of planktonic foraminifers is foreshadowed by a reduction in their total abundance some 5 kyr earlier at the base of the boundary clay this reduction is coeval with reported anomalies in siderophyle elements and 13 c values in the same area dinoflagellate cysts do not show accelerated rates of extinction at k t time associations of dinoflagellate cysts however change drastically and parallel changes in relative numbers of sporomorphs spores and pollen and in the quantity of land derived organic matter jointly these changes reflect a rapidly falling sea level during the final 17 kyr of the mesozoic which culminates at the level of the k t boundary this steep sea level fall at k t time represents a peak regressive pulse at the end of the well documented latest cretaceous regressive trend this short term sea level fall might show to be a wide spread phenomenon which could have caused an excess shrinking of the already reduced areal extent of marginal seas since deep waters in cretaceous oceans were primarily produced in shallow marginal seas the rate of formation of deep water might have been minimized at k t time minimum rates of formation of deep water might have curtailed the slow upward mixing of relatively cool and nutrient rich deeper water through which the thermocline weakened and surficial waters became depleted in nutrients consequently phytoplankton productivity rapidly diminished which in combination with a weakened thermal gradient pushed the highly depth stratified cretaceous planktonic foraminiferal fauna to extinction over a period of time of some 5 kyr guembelitria cretacea was the sole planktonic foraminifer which could accommodate to the low productivity conditions the oscillating rise in sea level at the beginning of the cenozoic reinforced the upward mixing of relatively cool and nutrient rich deeper water steepened the thermocline and replenished the photic layer with nutrients concomitant niche differentiation in the photic layer progressively stimulated morphological innovation amongst early cenozoic planktonic foraminifers the final return of normally sized planktonic foraminifers and of stable and well balanced dinoflagellate cyst associations at about 125 kyr after the k t boundary seems to indicate that primary productivity and niche differentiation in the photic layer begin to revert to optimum levels the earliest cenozoic planktonic foraminiferal species globoconusa minutula and parvularugoglobigerina fringa are thought to have developed from a benthic foraminiferal species rather than having a planktonic ancestry

age chemo and biostratigraphy of haiti spherule rich deposits a multi event k t scenario examination of two new expanded k t transitions and reexamination of road outcrops near beloc haiti reveals that deposition of the glass spherule rich deposit srd occurred within the early danian parvularugoglobigerina eugubina pla 1 zone followed by an ir anomaly and 50 cm above it a second pd dominated platinum group element pge anomaly the k t boundary is at an erosional unconformity between the base of the srd and underlying maastrichtian limestone where an interval representing about 100 250 thousand years appears to be missing juxtaposition of planktic foraminiferal zones pla 1 and plummerita hantkeninoides cf1 it is possible that the spherule layers are reworked from original deposits at or below the k t boundary the ir anomaly is of roughly chondritic type and compatible with an impact event whereas the pd dominated pge anomaly is a more basalt type and compatible with a magmatic origin this suggests a multi event scenario consistent with one impact followed by a major vol

paleoenvironmental changes across the cretaceous tertiary boundary at koshak kazakhstan based on planktic foraminifera and clay mineralogy abstract the koshak section of the mangyshlack peninsula kazakhstan is one of the most complete cretaceous tertiary k t transitions known from the boreal paratethys cretaceous species richness is low 11 to 13 species except for a peak of 20 species near the k t boundary in the uppermost maastrichtian top 50 cm that represents the temporary incursion of low latitude taxa this maximum species richness occurred during climatic warming associated with increased humidity as suggested by clay mineral analyses biofacies analysis suggests external platform conditions at this time followed by a more humid climate a sea level transgression and deepening basinal facies in the lower danian subzone p1a shallower platform conditions resumed in danian subzones p1b and p1c accompanied by a cooler and probably more arid climate no abrupt mass extinction occurred at the koshak k t boundary which is marked by an ir anomaly a clay layer and the first appearance of tertiary planktic foraminifera the influx of lower latitude species ends at or before the k t boundary whereas the majority of the indigenous cretaceous assemblage survived into the danian these data suggest that long term climatic changes may have been the principal factors in the progressive demise of the cretaceous planktic foraminifera in the eastern boreal paratethys

stable isotopes of carbon and sulphur as indicators of environmental change past and present stable isotopes of carbon 12 c and 13 c and sulphur 32 s and 34 s are fractionated during some of the transformations between reservoirs in the global carbon and sulphur cycles the main processes controlling the isotopic composition of earth surface reservoirs are for carbon photosynthesis respiration and equilibration between oceanic dissolved inorganic carbon and atmospheric co 2 and for sulphur bacterial sulphate reduction and sulphide reoxidation thus the different reservoirs of carbon and sulphur in the global cycles attain characteristic isotopic compositions that can be used as a fingerprint for different carbon and sulphur sources and to track changes in the balance of carbon and sulphur stored in different reservoirs these isotopic signals can be used both to examine contemporary anthropogenic impacts on the cycling of carbon and sulphur and where isotopic compositions are faithfully preserved in ancient sediments to examine historical changes in global geochemical cycles through geological time a number of case studies are discussed to illustrate how isotopic techniques represent one of the most powerful and important tools available in the study of both the causes and affects of ancient and modern global environmental change

the cretaceous tertiary boundary at gubbio revisited vertical extent of the ir anomaly abstract the classical gubbio italy cretaceous tertiary boundary section has been resampled for both magnetostratigraphy and iridium paleomagnetic samples were taken over 7 m in the maastrichtian and 6 m in the paleocene previous results obtained a decade ago are confirmed the reversal sequence is well defined and the individual reversals are somewhat more precisely located a noticeable difference is the location of the position of the 29n 29r limit which may be lowered by 20 30 cm in the stratigraphic column this would imply that the ktb occurs near the middle of chron 29r iridium measurements were made on samples from both shales and surrounding limestone beds from 2 m below to 3 m above the boundary these measurements indicate that ir is associated with clay minerals concentrations in the two types of samples are indeed compatible when reduced to a carbonate free basis iridium concentrations stand above background over almost 3 m of section corresponding to half a million years based on magnetostratigraphy this is likely to indicate a protracted duration of the external or internal source of iridium on top of which the main short lived ktb anomaly proper stands

meteoric burial diagenesis of middle pennsylvanian limestones in the orogrande basin new mexico water rock interactions and basin geothermics abstract stable isotopic compositions of cyclic middle pennsylvanian gobbler formation limestones record two stages of alteration early open system meteoric diagenesis during episodic subaerial exposure stabilized cycle top carbonate in the presence of meteoric fluid at high water rock ratios 400 4000 subsequent closed system burial diagenesis stabilized meteoric and residual marine carbonate in the presence of connate pore fluids at elevated temperatures to 150 c and low water rock ratios 1 0 10 present 18o distributions record normal to high geothermal gradients 27 86 c km during burial stabilization high basin center geothermal gradients probably resulted from elevated heat flow due to rapid crustal extens on and subsidence of the orogrande basin during the late pennsylvanian a dike injection lithospheric extension model with 40 oceanization best accounts for subsidence and geothermal patterns of the orogrande basin

deep water agglutinated foraminiferal changes and stable isotope profiles across the cretaceous paleogene boundary in the rotwandgraben section eastern alps austria abstract the studied interval extends from 2 5 m below to 1 m above the cretaceous paleogene k p boundary and encompasses the uppermost abathomphalus mayaroensis po subzones poa guembelitria cretacea and pob globoconusa conusa p or parvularugoglobigerina eugubina and lowermost p1 subzone p1a or subbotina pseudobulloides planktonic foraminiferal zones the agglutinated benthic foraminiferal assemblages of the uppermost abathomphalus mayaroensis zone are moderately diversified and composed of mixed epifaunal and infaunal morphogroups in the lower part of the guembelitria cretacea subzone benthic foraminifers are extremely rare and represented only by a few epifaunal species in the upper part of this subzone they are still not abundant but assemblages are again moderately diversified in the globoconusa conusa subzone deep water agglutinated foraminifers are abundant highly diversified and represented by mixed epifaunal and infaunal morphogroups bulk rock stable isotope analysis shows a significant drop of both 13 c and 18 o values at the k p boundary it appears that a drastic decrease in abundance and diversity of deep water agglutinated foraminifers as well as a change of the community structure from mixed epifaunal and infaunal to one dominated by epifaunal morphogroups are related to a reduction in marine primary productivity the instantaneous environmental stress and the collapse of primary productivity are compatible with a large bolide impact

extended cretaceous tertiary boundary extinctions and delayed population change in planktonic foraminifera from brazos river texas high resolution planktonic foraminiferal analysis of three brazos river sections indicates a nearly continuous cretaceous tertiary k t boundary sedimentary record second only to the world s most complete record at el kef tunisia species extinctions occur over an extended period of time and with two major extinction episodes the first extinction episode with 46 of the species extinct occurs at and just below 10 15 cm a short hiatus at the base of a sandy shell hash and clay sand unit which was interpreted by bourgeois et al 1988 to represent a tsunami bed generated by the k t boundary bolide impact the top of this tsunami bed is about 17 20 cm below the k t boundary as defined by the first appearance of tertiary planktonic foraminifera the second extinction phase with 45 of the species extinct occurs 25 cm above the k t boundary zone p0 p1a boundary of the remaining seven surviving cretaceous species six gradually disappear during planktonic foraminiferal subzones p1a and basal p1b no species extinctions or major faunal assemblage changes are directly associated with the k t boundary iridium distribution is ambiguous with one peak in the upper part of the tsunami bed and a second peak at the micropaleontologically defined k t boundary relative abundances of dominant species are stable through the late maastrichtian and only minor abundance changes coincide with the first extinction episode or the k t boundary the first major faunal change in the dominant species group coincides with the second extinction episode and leads to decline and eventual extinction of this group in subzone p1a species disappearing at the two extinction episodes 46 and 45 constitute only a small percentage 8 and 5 of the individuals of the total planktonic foraminiferal population this suggests that weakened species with low numbers of individuals and sensitive to relatively minor environmental changes were primarily affected by these extinction episodes magnetostratigraphy indicates that the first extinction phase began about 310 000 years before the k t boundary and the second extinction phase occurred 50 000 years after the k t boundary this stepped pattern of species extinctions suggests a progressively stressed ecosystem in continental shelf settings which may be related to an observed sea level regression and global cooling the hypothesis of a global catastrophic mass extinction at the k t boundary caused by a large extraterrestrial impact is not supported by the brazos river planktonic foraminiferal data

carbon and sulfur isotope geochemistry of the hirnantian late ordovician wangjiawan riverside section south china global correlation and environmental event interpretation detailed geochemical analyses 13ccarb 13corg 34ssulfide and abundance of sulfide carbonate and organic carbon were performed on samples from the wangjiawan riverside section close to the gssp global stratotype section and point for the hirnantian stage of the ordovician new data show two increases in carbonate content coincident with two glacial pulses that reduced detrital input the new 34ssulfide data show distinct changes in this section with relatively high values in the kuanyinchiao formation a pattern observed throughout the yangtze platform however there is no consensus on the cause of these changes the new 13ccarb data show a sharp rise and peak in the extraordinarius zone below the previously published 13corg peak in the persculptus zone a compilation of the new results with other sections indicates the hirnantian carbon isotope excursion starts near the pacificus extraordinarius boundary and elevated values remain until the end of the excursion in the persculptus zone for both 13corg and 13ccarb the controversy over correlating hirnantian graptolite zones with chitinozoan zones can also be addressed the new 13ccarb data also allow direct comparison with hirnantian 13ccarb data from anticosti island and the baltic region which are zoned by chitinozoan fossils this comparison favors a correlation of the taugourdeaui and scabra chitinozoan zones with the extraordinarius graptolite zone

iridium emissions from kilauea volcano during may 1983 gas and particulate samples were collected at the cooling vents of kilauea volcano in hawaii three vents on the southeast rift zone were sampled using base treated filter packs to absorb acidic gases and teflon filters for particles the samples were analyzed for 40 elements by nondestructive neutron activation analysis as with other volcanoes the chalcophilic and volatile elements were enriched by up to seven orders of magnitude relative to the erupted basalt unlike the case of other volcanoes iridium was observed to be highly enriched 105 fold at the two higher temperature vents and the degree of enrichment appears to be related to both high temperatures and high fluorine content of the gases estimates of the emission rates of ir during eruptions of kilauea based on the measurements reported here and those of the hawaiian volcano observatory yield an emission rate of about 3 g ir per 106 m3 of magma this rate amounts to only about 0 3 of the ir present in the magma that is being released by the volcano this previously unidentified ir source to the atmosphere and ocean may have a significant influence on the geochemical cycle of ir on the earth the uniqueness of kilauea in its emissions of ir is probably related to the deep source of magma which contains significant levels of ir 0 32 ppb and high levels of the halogens f and cl

fluid flow in sedimentary basins abstract the pore waters in sedimentary basins are ultimately derived from sea water meteoric water mineral bound water or from the underlying basement geochemically these waters initially have different signatures however the pore water compositions are easily altered by reactions with minerals or by mixing with other fluids meteoric water is driven downwards into sedimentary basins by the gravitational potential which approximately corresponds to the elevation of the ground water table above the sea or lake level it is difficult to model such flow however because the permeability on a large scale is almost impossible to represent realistically the continuity of confined sandstone and limestone aquifers plays an important role in determining the flux of meteoric water received by rocks in different parts of the basin but this is again difficult to predict pore water flow driven by compaction typically has velocities several orders of magnitude lower than what is commonly found in meteoric water flow regimes the average rate of upwards flow is lower than the rate of subsidence and the difference is the rate of incorporation of sea water in the topmost layer at the sea floor the salinity of formation water provides important constraints on fluid flow in sedimentary basins in the north sea basin and the gulf coast basin these types of data indicate that vertical mixing by compaction driven flow and convection is limited compaction driven flow obeys darcy s law but there are complex interdependencies between pressure permeability and compaction given the low compressibility of water the flow which can result from pressure release alone is very limited except on a local scale along permeable faults and fractures the main flow of pore water during burial is driven by compaction which is a slow process even when overpressure is released abruptly with a resulting increase in the net effective stress in the case of high permeability faults the flow into the fault from low permeability sedimentary rocks at depth may be rate limiting the displacement of pore water in adjacent sediments near the top of the faults may also slow down fluid flow on fractures that do not reach the sea floor modelling of fluid flow in sedimentary basins should be based on permeability distributions which are mostly determined by primary facies diagenesis and the tectonic history of the basin extensional tectonics produce a predominantly vertical fracture network which may serve as conduits for pore water flowing deep into the crust upward flow of hot fluids in basement fractures must have a high velocity in order to produce large thermal anomalies concentrations of dissolved components precipitate at the surface and form deposits of quartz and ore minerals if basement fractures are overlain by a thick sequence of soft sediments the rate of flow on the fractures will be reduced because of the low permeability in the sedimentary cover and conductive heat transport will dominate flow of water at high enough velocities to bring hot water to the surface and produce hot springs is most likely to occur in fractured basements rocks or well cemented sedimentary rocks concentrated precipitation of dissolved components will occur near the surface where the rate of cooling is highest also sediment hosted ores precipitated from flow of hot water on fractures are therefore likely to form before accumulation of thick overlying sedimentary sequences

the cretaceous paleogene transition at galanderud northern alborz iran a multidisciplinary approach abstract we investigated the cretaceous paleogene k pg transition at the galanderud section northern alborz iran to identify the pattern of mass extinction of planktic foraminifera and to unravel the associated paleoenvironmental changes in a little studied area of the eastern tethys we applied a high resolution quantitative and multidisciplinary study based upon benthic and planktic foraminiferal assemblages clay mineralogy rock magnetic properties stable isotopes and geochemistry in this section the k pg boundary is marked by an abrupt change in lithology from marl to a clay boundary layer a marked decrease in magnetic susceptibility a negative 2 2 13c excursion and a peak in iridium in the uppermost maastrichtian foraminifera are well preserved and diversified suggesting a stable mesotrophic environment by contrast the k pg boundary and basal danian is marked by high values of epifaunal benthic morphogroups low planktic diversity and high percentages of opportunistic species guembelitria cretacea and cervisiella operculata suggesting highly stressed and variable conditions partly due to the dramatic collapse of calcareous primary producers benthic foraminiferal assemblages indicate outer neritic uppermost bathyal depths with slight bathymetric variations the most peculiar and unique aspect of the galanderud section is the occurrence of the three thin chalk layers interbedded within clays above the k pg boundary each marked by positive shifts in 13c and 18o values and consisting of 80 carbonate we propose that the chalk clay deposits in the basal danian reflect changes in seawater chemistry and dynamic changes in circulation upwelling alternating with episodes of enhanced weathering and runoff this section on the northern margin of eastern tethys provides new clues about the pattern of the k pg mass extinction and the paleoenvironmental changes occurring during the biotic recovery phase

cretaceous tertiary boundary extinction pattern and faunal turnover at agost and caravaca s e spain abstract planktonic foraminiferal extinctions at caravaca and agost occurred over an extended time period similar to el kef and brazos river some species disappeared well below the boundary about 39 45 of the species but less than 15 of the individuals in the population became extinct at or near the k t boundary a second phase of extinction occurred at the top of the boundary clay po pla and the remaining cretaceous species except g cretacea disappeared in subzone pla species extinctions were selective eliminating geographically restricted large complex and deeper dwelling forms first and favoring survival of cosmopolitan small simple surface dwellers only surface dwellers survived the k t boundary event whereas all deeper dwelling species as well as some surface dwellers disappeared at the boundary we interprete the selective abundance decline during the latest cretaceous as a result of the seal level regression that reached a maximum just prior to the k t boundary the highly selective nature of the two phased species extinctions at and above the boundary we believe to be related to the major reduction in surface productivity and the breakdown in the water mass stratification that was associated with the rapid sea level transgression across the k t boundary a bolide impact however may have hastened the demise of an already declining cretaceous fauna

barium anomaly preceding k t boundary possible causes and implications on end cretaceous events of k t sections in cauvery basin india israel ne mexico and guatemala maastrichtian danian strata of the cauvery basin as well as selected sections of ne mexico guatemala and israel record ba anomalies away from the cretaceous tertiary boundary ktb in addition to common occurrences of geochemical and stable isotopic anomalies across the ktb ba anomalies were recorded in monotonous shallow marine sandstones of the cauvery basin south india which contain minor amounts of ba orthoclase barium anomalies were observed also in shallow marine carbonates in sections of israel ne mexico and guatemala calculation of excess ba with reference to paas post archaen average australian shale comparison of coeval geochemical anomalies depositional pattern and associated petrographic and mineralogical features of the cauvery basin revealed that while a first ba peak was related to detrital influx the second ba peak was coincident with sea level fall which in turn may have been influenced by emission of volatile hydrocarbons and resultant climatic changes in view of intrinsic involvement of ba in various geochemical processes and occurrence of ba anomalies in k t sites distributed around the world ne mexico guatemala and israel it is suggested that probable causes of such widespread ba anomalies should be taken into consideration while analyzing end cretaceous events these observations support the views espoused by many workers who have stated that the k t boundary was also accompanied by many non catastrophic events that might have contributed to environmental stress on marine fauna as a result of which selective multi stage extinctions occurred

stable isotope toc and caco3 record across the cretaceous tertiary boundary at el kef tunisia we report the results of stable oxygen and carbon isotope analysis of carbonate fine fraction and benthic and planktic foraminifers caco3 and toc determinations of sediments across the cretaceous tertiary k t boundary at el kef tunisia we used grain size analysis of the fine fraction carbonate to determine possible compositional effects and smearslide and scanning electron microscope examinations to evaluate possible diagenetic alteration and microfossil preservation the data suggests the following sequence of events upper maastrichtian oxygen and carbon isotope signals indicate relatively warm temperatures a decreasing thermal gradient possibly related to a shallowing sea and relatively high surface water productivity a sharp cooling appears to begin just below the k t boundary the k t boundary is characterized by a sudden 2 negative shift in fine fraction 13c a slight 0 6 enrichment in benthic 13c and a reduction of about 40 in caco3 sedimentation these data imply strongly reduced surface water productivity as also observed in numerous deep sea sequences worldwide the lower danian planktic foraminiferal zones p0 p1a is marked by generally low productivity and unstable environmental conditions as indicated by generally low but fluctuating fine fraction 13c values and low 5 15 carbonate deposition at the base of subzone p1b caco3 benthic and fine fraction 13c values increase gradually and reach near pre k t boundary levels in subzone p1c indicating initial recovery after the k t boundary event about 300 000 400 000 years after the k t boundary the prolonged low productivity episode after the k t crisis and the pre k t boundary cooling associated with a major reduction in planktic foraminiferal diversity are difficult to explain by a single k t boundary bolide impact

structural development of the lower paleozoic belt of south china genesis of an intracontinental orogen abstract an extensive structural study of wuyishan and surrounding areas south china brings data on the structures formed prior to the devonian unconformity building the lower paleozoic belt an ordovician tectonic event was responsible for i south directed structures in the wuyishan proper and its southern border related to both thin and thick skinned tectonics accompanied by metamorphism and crustal thickening ii north directed structures to the west of ganjiang fault and north of jiangshan shaoxing fault where only thin skinned tectonics is visible the southward deformation accommodating the shortening includes emplacement of thrust sheets involving deep crustal material and some mantle peridotite and likely repetition of continental material both responsible for crustal thickening the orogeny was due to the underthrusting of the southern part of the south china block beneath the northern part of this block closing the pre existing nanhua rift created at around 850 800 ma and involving the rift sedimentary fill in the southward thrusting the syn metamorphic tectonic piling was followed by anatexis and granite emplacement at around 440 390 ma our new u th pb epma monazite dating gives ages of 433 9 ma and 437 5 ma early silurian for the main anatectic event and a younger age of 412 5 ma late silurian early devonian for a late re heating process the lower paleozoic belt is an intracontinental orogen without oceanic suture record it shows some similarities with the cenozoic european pyrenees chain with a strong asymmetry

terminal cretaceous environmental events the geologic record of terminal cretaceous environmental events indicates that iridium and other associated elements were not deposited instantaneously but during a time interval spanning some 10 000 to 100 000 years the available geologic evidence favors a mantle rather than meteoritic origin for these elements these results are in accord with the scenario of a series of intense eruptive volcanic events occurring during a relatively short geologic time interval and not with the scenario of a single large asteroid impact event

intracontinental subduction a possible mechanism for the early palaeozoic orogen of se china the early palaeozoic orogen of se china consists of three lithotectonic elements from top to bottom a sedimentary upper unit a metamorphic lower unit and a gneissic basement the boundaries between these units are flat lying south directed ductile decollements the lower one is coeval with an amphibolite facies metamorphism m1 the belt is reworked by migmatite granite domes high temperature metamorphism m2 and granitic plutons related to post orogenic crustal melting we date here the syn m1 ductile shearing at 453 7 ma by u th pb method on monazite previous ages and our new 40 ar 39 ar ages of biotites and muscovites show that the metamorphic rocks experienced syn m2 exhumation from 440 to 400 ma the early palaeozoic orogen of se china is an intracontinental belt in which decollements accommodated the north directed subduction of the cathaysian continent this orogen is an example of intracontinental subduction that was not preceded by oceanic subduction

catastrophic mass extinction and assemblage evolution in planktic foraminifera across the cretaceous paleogene k pg boundary at bidart sw france abstract a high resolution biostratigraphic analysis of planktic foraminifers confirms that the bidart section at the eastern margin of the atlantic ocean exhibits a continuous and complete cretaceous paleogene k pg transition interval the biozones and subzones recorded in this section are less expanded than their equivalent in tunisian sections el kef global stratotype section and point gssp for the k pg boundary and elles auxiliary section but they are sufficiently thick to allow a detailed analysis of the evolution of the planktic foraminiferal assemblages across the k pg transition throughout the uppermost 4 m maastrichtian the planktic foraminiferal assemblages are highly diversified containing up to 72 species these maastrichtian assemblages are rich in cosmopolitan taxa 70 dominated by small biserial morphotypes which belong mainly to the genus heterohelix which coexist with less abundant but highly diverse tropical and subtropical species the extinction pattern at the bidart section suggests a sudden catastrophic mass extinction at the k pg boundary which affected at least 53 out of 72 species the species becoming extinct include globotruncanids e g contusotruncana spp globotruncana spp globotruncanita spp and complex heterohelicids e g racemiguembelina spp pseudotextularia spp gublerina spp at the bidart section only archaeoglobigerina cretacea disappears 2 m below the k pg boundary event specimens of 18 small and even tiny maastrichtian species are found at the lowermost danian only a few of these species belonging to the genera of guembelitria hedbergella and heterohelix are considered to be real cretaceous survivor species whereas the specimens belonging to the rest are most probably reworked because they differ in their preservation throughout lowermost danian the planktic foraminiferal assemblages are dominated by opportunistic species of the genus guembelitria these opportunists are associated to small and poorly diversified pioneer globigerinids palaeoglobigerina spp and parvularugoglobigerina spp these assemblages became progressively more diversified across the early danian containing species with cancellate walls eoglobigerina spp parasubbotina spp subbotina triloculinoides and praemurica spp and new taxa of biserial heterohelicids woodringina spp and chiloguembelina spp suggesting a paleoenvironmental recovery

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

the cretaceous tertiary boundary in the gosau basin austria the cretaceous tertiary boundary has been identified in the gosau beds elendgraben near salzburg austria the undisturbed 2 mm thick boundary clay in the palaeomagnetic g zone differs from the surrounding sediments in having significant colour no biogenic calcite and different contents of rare earth and siderophile elements carbon and magnetic minerals the clay also contains shocked quartz and plagioclase particles and indicates a dramatic change in sedimentation caused by a short lived event

an organic carbon isotope record of late ordovician to early silurian marine sedimentary rocks yangtze sea south china implications for co2 changes during the hirnantian glaciation studies of 13c of marine sedimentary organic carbon in six clastic sections with sediments deposited from the latest ordovician to earliest silurian in the yangtze sea on the south china plate show a positive 13corg excursion of up to 4 in the latest ordovician hirnantian stage corresponding in time to a major continental glaciation on gondwana various factors that might be responsible for the 13corg increase are considered including input and contribution from exogenic carbon sources secondary processes such as heterotrophy and thermal maturation and changes in yangtze sea surface water temperature productivity primary producers dissolved co2 concentrations and the isotopic composition of dissolved inorganic carbon current data are consistent with the interpretation that the observed 13corg increase may have resulted from a decrease in the surface water dissolved co2 in the yangtze sea during the hirnantian glaciation probably reflecting a significant decrease in glacial ocean atmosphere pco2 levels at that time

modern soil system constraints on reconstructing deep time atmospheric co2 abstract paleosol carbonate based estimates of paleo atmospheric co 2 play a prominent role in constraining radiative forcing and climate sensitivity in the deep time large uncertainty in paleo co 2 estimates made using the paleosol carbonate co 2 barometer however arises primarily from their sensitivity to soil respired co 2 s z this parameter is poorly constrained due to a paucity of soil co 2 measurements during carbonate formation in modern soils and a lack of widely applicable proxies of paleo soil co 2 here the 13 c values of carbonate and soil organic matter som pairs from 130 holocene soils are applied to a two component co 2 mixing equation to define soil order specific ranges of soil co 2 applicable for constraining s z in their corresponding paleosol analogs equilibrium carbonate som pairs characterized by 13 c carb som values of 12 2 15 8 define a mean effective fractionation of 14 1 and overall inferred total soil co 2 contents during calcite formation of s z during calcite formation is 1500 2000 ppmv range of 500 2500 ppmv overall higher values 2000 5000 ppmv are indicated by the subset of these soils characterized by higher moisture content and productivity near atmospheric levels 400 200 ppmv of estimated s z are indicated by immature soils recording their low soil productivity vertisols define the largest range in total soil co 2 25 000 ppmv reflecting their seasonally driven dynamic hydrochemistry a s z range of 1000 10 000 ppmv is suggested for paleo vertisols for which calcite precipitation can be constrained to have occurred in an open system with two component co 2 mixing with a best estimate of 2000 ppmv 1000 ppmv appropriate for paleo vertisols for which evidence of protracted water saturation is lacking mollisol pairs define a best estimate of s z of 2500 ppmv range of 600 4000 ppmv for late cretaceous and cenozoic analogs non equilibrium pairs with 13 c values 16 make up 51 of the dataset lending support to the hypothesis that pedogenic carbonate precipitation occurs during periods of low productivity in a soil atmosphere with a large component of atmospheric co 2 predictable scaling between estimated soil co 2 and the difference in 13 c between measured pedogenic carbonate and that predicted to have formed from soil respired co 2 inferred from measured som can be used to further constrain appropriate ranges of s z for reconstruction of paleo atmospheric p co 2 soil co 2 estimates are poorly correlated to mean annual precipitation likely reflecting that for carbonate bearing soils where moisture limits co 2 production total soil co 2 is most strongly influenced by actual evapotranspiration

changes in marine productivity and redox conditions during the late ordovician hirnantian glaciation abstract changes in marine productivity and redox conditions during the end ordovician hirnantian glaciation and ordovician silurian transition were investigated through mo isotope and major and trace element analyses of the wangjiawan hubei province and nanbazi guizhou province sections from the yangtze platform of south china katian shales of the wufeng formation which yield the graptolites dicellograptus complanatus dicellograptus complexus and paraorthograptus pacificus were deposited under euxinic conditions at both localities as shown by high mo ef u ef and 98 mo values a major sea level regression during the hirnantian glaciation resulted in shallowing and a shift toward better oxygenated conditions within the yangtze sea as well as deposition of thin bedded siliceous sediments calcirudite debris flows and limestone turbidites of the kuanyinchiao formation the base of which correlates with the first phase of the end ordovician mass extinction the termination of the hirnantian glaciation at the top of the kuanyinchiao formation was associated with a major sea level transgression a rapid expansion of euxinia in the yangtze sea as documented by a return of high mo ef u ef and 98 mo values and the second phase of the mass extinction during which the cool adapted hirnantian fauna went extinct the long term cooling trend of the middle and late ordovician which culminated in the hirnantian glaciation was driven by enhanced burial of organic carbon as documented by 13 c carb 13 c org and 34 s py records increased organic carbon burial was linked to high rates of marine productivity as shown by high toc and biogenic ba concentrations especially at the deeper less restricted wangjiawan locale producing the hice hirnantian isotopic curve excursion 13 c carb excursion the locus of organic carbon burial during the hirnantian crisis shifted to deeper water environments that were located outside the study region the relatively rapid onset and termination of the hirnantian glaciation were probably due to crossing of tipping points in the late ordovician climatic oceanic system

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

high resolution stable isotope stratigraphy of upper ordovician sequences constraints on the timing of bioevents and environmental changes associated with mass extinction and glaciation the two phases of the late ordovician mass extinction are approximately coeval with the periods of rapid climate change associated with the onset and demise of the gondwanan glaciation in this paper we argue that the distinctive late ordovician carbon isotope profile provides a chronostratigraphic ruler against which a sequence of environmental and biotic events may be located the ruler also allows regional and global high resolution correlation of successions representing very different environments cores from the upper ordovician succession of estonia and latvia record a large 1 3 c c a r b o n a t e excursion up to 6 with a similar profile shape the consistent relationship between the chemostratigraphy and biostratigraphy in the baltic region suggests that the isotope profile has a regional chronostratigraphic value the presence of similar profiles in nevada united states suggests that the excursion is a global chronostratigraphic signal this interpretation enables a detailed correlation to be made between upper ordovician shallow marine and basinal sequences that have wholly different faunas successions in the baltic area and in canada that do not display the model profile are interpreted as incomplete reinter pretation of these important successions significantly modifies the global database used to assess the pattern of diversity change during the mass extinction key levels of environmental change have been located against the carbon isotope profile new oxygen isotope data from brachiopod and ostracode calcite set tight limits on the start of the glacial events cooling and sea level fall started at the same stratigraphic level as the start of the carbon isotope excursion the later rise in sea level and fall in oxygen isotope values record the end of the glaciation these restrict the duration of the main glaciation to only 1 5 graptolite zones we propose that models of the carbon cycle should be adapted to be consistent with the temporal relationships between carbon cycling sea level fall and temperature change documented here the chronostratigraphic ruler provided by the carbon isotope profiles is used as a scale to determine the sequence of biotic changes and to allow high resolution correlation of biotic events at different locations this approach identifies regional similarities and differences in the patterns of extinction the main phase of graptolite extinction in the monitor range nevada for example is synchronous with the chitinozoan extinction in the baltic region but chitinozoan taxa survive to higher levels in nevada the benthic faunas in the baltic region demonstrate that the main extinction event corresponded with the beginning of the isotope excursion at the start of the hirnantian the level at which the marine environment started to change rapidly but that there were further extinctions of species within the early hirnantian the cold adapted hirnantia fauna did not appear immediately after the extinction in this area the relationship between the second phase of extinction and the carbon isotope excursion is less clear but the available data suggest that the extinction coincides with a time of rapid environmental change but not at the inception of environmental change as happened in the first phase

ranking of dissolution susceptibility of planktonic foraminifera at high latitudes of the south atlantic ocean surface sediment samples from the maurice ewing bank eastern falkland plateau south atlantic ocean have been analyzed to rank dissolution susceptibility of cool water planktonic foraminiferal species a dissolution index is formulated from quantitative analyses of sedimentological properties caco3 content frequency of planktonic foraminiferal fragments radiolarians mineral grains and ratio of a dissolution tolerant to a dissolution susceptible planktonic foraminiferal species this index is used to assess degrees of dissolution in the samples quantified differences in relative abundance of species between the two dissolution regimes less prominent and stronger dissolution formed the basis for differentiation the species were ranked in the following order from most resistant to least resistant sinistrally coiled variety ofneogloboquadrina pachyderma antarctic variety of this species globorotalia inflata g truncatulinoides globigerina bulloides andglobigerinita glutinata a tie dextraln pachyderma subantarctic variety globigerinita uvula andglobigerina quinqueloba fragmentation frequency of damaged tests increases with increasing dissolution in tolerant species but not in susceptible species this may be because susceptible species are completely dissolved under intense dissolution whereas tolerant species although damaged remain and increase in abundance

dynamic sulfur and carbon cycling through the end ordovician extinction revealed by paired sulfate pyrite δ34s geochemical records of the end ordovician hirnantian stage show parallel positive excursions in the stable isotope compositions of sedimentary pyrite sulfur 34spyr organic carbon 13corg and carbonate carbon 13ccarb these isotope excursions coincide with the end ordovician glaciation and mass extinction a relative increase in pyrite burial fpyr attributed to marine anoxia has been invoked to explain the sulfur isotope excursion and link oceanic redox conditions to the extinction of marine fauna an increase in fpyr would necessarily generate a parallel excursion of equal magnitude in the isotopic composition of coeval marine sulfate 34sso4 34sso4 here we present new high resolution paired sulfur isotope data from carbonate associated sulfate 34scas and pyrite from the hirnantian stage of western anticosti island quebec canada these data document a positive 20 enrichment in 34spyr comparable in magnitude to previous reports but no parallel excursion in 34scas this pattern provides new constraints on the origin of the 34spyr excursion and the nature of carbon sulfur coupling through hirnantian time specifically these observations preclude enhanced pyrite burial as the cause of the hirnantian 34spyr excursion and suggest the possible role of anoxia in the mass extinction may need to be reevaluated rather the global 34spyr excursion is best explained by a transient reduction in the isotopic fractionations expressed during microbial sulfur cycling epyr the epyr record shows a strong inverse correlation with 13c suggesting a mechanistic link between carbon cycling and processes controlling epyr during the hirnantian changes in sea level or marine redox state associated with glaciation could further impact the expression of the biological fractionation e g through syndepositional sediment reworking and or chemocline migration and resultant restricted exchange of porewater sulfate the magnitude of isotopic fractionation during microbial sulfate reduction is partially controlled by metabolic rates which are sensitive to the abundance type and lability of metabolically relevant substrates environmental change associated with the end ordovician glaciation may have elevated the flux of organic material to marine sediments or caused an increase in physical reworking of sediments leading to increased microbial sulfate reduction rates and reduced epyr as such the hirnantian 34spyr excursion may be viewed as a dynamic biological response to global climate change highlighting the connections between the carbon and sulfur biogeochemical cycles

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

marine redox conditions in the middle proterozoic ocean and isotopic constraints on authigenic carbonate formation insights from the chuanlinggou formation yanshan basin north china abstract to improve our understanding of ocean chemistry and biogeochemical cycling following the termination of large scale paleoproterozoic iron formation if deposition 1 85 billion years ago ga we conducted a fe s c mo geochemical study of the 1 65 ga chuanlinggou formation yanshan basin north china despite the cessation of if deposition our results suggest the presence of anoxic but non euxinic ferruginous conditions persisted below the surface mixed layer for the deepest portion of the continental rifting basin and that this pattern is apparently independent of the local organic carbon content however our paired s isotope data of carbonate associated sulfate and pyrite suggest presence of sulfate in pore fluids which is not consistent with insufficient sulfate for bacterial sulfate reduction in the water column despite evidence for deposition under anoxic conditions sedimentary molybdenum mo concentrations are mostly not enriched relative to average continental crust this relationship is consistent with the notion that sulfide dominated conditions in the water column and or the sediments are required for mo enrichment and validates past assertions that mo enrichment patterns in ancient shales track both the local presence and global distribution of euxinia specifically in addition we identified extensive diagenetic carbonate precipitation in the upper chuanlinggou formation with only moderately negative 13 c values 3 4 1 4 we propose with support from a numerical model that these diagenetic carbon isotope values were most likely derived from precipitation of carbonates dominantly in the methanic zone within the sediments diagenetic carbonate precipitation in the methanic zone is likely to have been more extensive in the proterozoic than the phanerozoic due to porewater oxidant limitation

a weathering hypothesis for glaciation at high atmospheric pco2 during the late ordovician new paired carbonate and organic carbon isotope analyses from nevada usa together with a consideration of the effects of mountain building and ice sheet coverage of the continents on atmospheric pco2 lead to a new hypothesis for the cause of the late ordovician glaciation we suggest that the taconic orogeny which commenced in the late middle ordovician caused a long term decline in atmospheric pco2 through increased weatherability of silicate rocks ice sheet growth was triggered when pco2 decreased to a threshold of 10 present atmospheric level and proceeded by positive ice albedo feedback in the midst of glaciation atmospheric pco2 began to rise as continental silicate weathering rates declined in response to coverage of weathering terrains by ice sheets at first this enhanced greenhouse effect was overcompensated for by ice albedo effects ultimately however atmospheric pco2 reached a level which overwhelmed the cooling effects of ice albedo and the glaciation ended the isotope results can be interpreted to indicate that atmospheric pco2 rose during the glaciation consistent with other proxy information although alternative interpretations are possible the large positive carbonate isotope excursion observed in late ordovician rocks around the world is explained as the expected response to increased carbonate platform weathering during glacioeustatic sea level lowstand rather than as a response to increased organic carbon burial

facies patterns and geography of the yangtze region south china through the ordovician and silurian transition abstract lithofacies and biofacies changes through the ordovician and silurian transition on the yangtze platform are coincident with stepwise mass extinctions recovery events global sea level changes and regional palaeogeographic configurations facies patterns through three intervals the late mid ashgill hirnantian and early rhuddanian indicate that black shale occupied most of the yangtze platform region during the late mid ashgill and early rhuddanian while the hirnantian possesses more diverse facies types the black shale was replaced by carbonate facies during the hirnantian coincident with a global sea level low stand biofacies changes from the late mid ashgill graptolitic to the hirnantian shelly facies were apparently signalled by gradual and diachronous existence of a mixed facies the manosia facies in the yangtze region however the biofacies change was abrupt from the hirnantian to the early rhuddanian when graptolitic facies occupied most areas on the yangtze platform leaving only a very narrow limited belt of shelly facies along the southern margin of the platform in northern guizhou the early rhuddanian unified biofacies pattern is a result of a global sea level rise which may be synchronized with a recovery bioevent of graptolites after hirnantian mass extinction

the cretaceous paleogene boundary and planktonic foraminifera in the flyschgosau eastern alps austria the studied interval extends from 2 5 m below to 1 m above the cretaceous paleogene k p boundary and comprises the uppermost maastrichtian marly limestone overlain by a boundary rusty layer a dark yellow orange clay 5 10 mm thick followed by a turbidite sequence of very fine sandstones and grey brown marls the following planktonic foraminiferal zones are distinguished abathompalus mayaroensis po subzones poa guembelitria cretacea and pob globoconusa conusa pa or parvularugoglobigerina eugubina and p1 subzone p1a or subbotina pseudobulloides the distribution of iridium shows a relatively sharp rise to a maximum value of 7 176 ppb about 1 2 cm above the rusty layer followed by a rapid drop to normal background levels the abathomphalus mayaroensis zone exhibits a moderately diverse planktonic foraminiferal assemblage the main extinction episode occurs within the rusty layer only a few species survived survivors are small primitive forms the first new paleocene species evolved immediately after the major cretaceous extinctions rapid extinction of planktonic foraminifers coincides with the iridium anomaly which suggests that at this site the source s of the iridium anomaly was were probably responsible for k p extinctions

late cretaceous and paroxysmal cretaceous tertiary extinctions the various geological signatures at cretaceous tertiary time including iridium and other associated elements microspherules and shock deformation features are compatible with the suggestion that the transition is marked by a period of intense volcanism the volatile emissions from this volcanism would lead to acid rain reduction in the alkalinity and ph of the surface ocean global atmospheric temperature changes and ozone layer depletion these environmental effects coupled with those related to the major sea level regression of the late cretaceous provide the framework for an explanation of the selective nature of the observed extinction record

assessing sulfate reduction and methane cycling in a high salinity pore water system in the northern gulf of mexico pore waters extracted from 18 piston cores obtained on and near a salt cored bathymetric high in keathley canyon lease block 151 in the northern gulf of mexico contain elevated concentrations of chloride up to 838 mm and have pore water chemical concentration profiles that exhibit extensive departures concavity from steady state linear diffusive equilibrium with depth minimumd 13 c dissolved inorganic carbon dic values of 55 9 to 64 8 at the sulfate methane transition smt strongly suggest active anaerobic oxidation of methane aom throughout the study region however the nonlinear pore water chemistrydepth profiles make it impossible to determine the vertical extent of active aom or the potential role of alternate sulfate reduction pathways here we utilize the conservative non reactive nature of dissolved chloride to differentiate the effects of biogeochemical activity e g aom and or organoclastic sulfate reduction relative to physical mixing in high salinity keathley canyon sediments in most cases the dic and sulfate concentrations in pore waters are consistent with a conservative mixing model that uses chloride concentrations at the seafloor and the smt as endmembers conservative mixing of pore water constituents implies that an undetermined physical process is primarily responsible for the nonlinearity of the pore water depth profiles in limited cases where the sulfate and dic concentrations deviated from conservative mixing between the seafloor and smt the d 13 c dic mixing diagrams suggest that the excess dic is produced from a 13 c depleted source that could only be accounted for by microbial methane the dominant form of methane identified during this study we conclude that aom is the most prevalent sink for sulfate

extinction survivorship and evolution of planktic foraminifera across the cretaceous tertiary boundary at el kef tunisia an expanded sediment record at el kef shows that the k t boundary extinctions of planktic foraminifera extend over an interval from 25 cm below the geochemical boundary ir anomaly to 7 cm above species extinctions appear sequential with complex large ornate forms disappearing first and smaller less ornate forms surviving longer the 14 species extinctions below the boundary appear unrelated to an impact event cretaceous species survivorship is greater than previously assumed about 10 species survive 22 into subzone p1a globigerina eugubina all cretaceous survivors are small primitive forms which are generally smaller than their ancestors in cretaceous sediments species evolution after the k t event occurs in two pulses the first new paleocene species evolve in the basal black clay zone po immediately after the major cretaceous extinctions evolving species are small and primitive similar to cretaceous survivors the second pulse in species evolution occurs in the lower part of subzone p1b with the appearance of larger more diverse species the first major increase in carbonate sedimentation and productivity occurs at this time and signals the recoveyr of the ecosystem nearly 300 000 years after the k t event the species extinctions prior to the generally assumed impact event implied by the ir anomaly and the long recovery period of the ecosystem thereafter cannot be explained by a single impact but suggest that multiple causes may be responsible such as climatic changes volcanism a sea level drop production of warm saline bottom water and the chemical consequences associated with increased salinity

terminal ordovician carbon isotope stratigraphy and glacioeustatic sea level change across anticosti island quebec canada globally documented carbon isotope excursions provide time varying signals that can be used for high resolution stratigraphic correlation we report detailed inorganic and organic carbon isotope curves from carbonate rocks of the ellis bay and becscie formations spanning the ordovician silurian boundary on anticosti island quebec canada strata of the anticosti basin record the development of a storm dominated tropical carbonate ramp these strata host the well known hirnantian positive carbon isotope excursion which attains maximum values of 4 5 in carbonate carbon of the laframboise member or the fox point member of the becscie formation the excursion also occurs in organic carbon and 13 c carb and 13 c org values covary such that no reproducible 13 c 13 c carb 13 c org excursion is observed the most complete stratigraphic section at laframboise point in the west shows the characteristic shape of the hirnantian stage excursion at the global stratotype section and point gssp for the hirnantian stage in china and the silurian system in scotland we therefore suggest that the entire hirnantian stage on anticosti island is confined to the laframboise and lower fox point members by documenting discontinuities in the architecture of the carbon isotope curve at multiple stratigraphic sections spanning a proximal to distal transect across the sedimentary basin we are able to reconstruct glacioeustatic sea level fluctuations corresponding to maximum glacial conditions associated with the end ordovician ice age the combined litho and chemostratigraphic approach provides evidence for the diachroneity of the oncolite bed and becscie limestones the former transgresses from west to east and the latter progrades from east to west the sea level curve consistent with our sequence stratigraphic model indicates that glacioeustatic sea level changes and the positive carbon isotope excursion were not perfectly coupled although the start of the isotope excursion and the initial sea level drawdown were coincident the peak of the isotope excursion did not occur until after sea level had begun to rise carbon isotope values did not return to baseline until well after the anticosti ramp was reflooded the sea level 13ccarb relationship proposed here is consistent with the weathering hypothesis for the origin of the hirnantian 13 c carb excursion

a sulfidic driver for the end ordovician mass extinction the end ordovician extinction consisted of two discrete pulses both linked in various ways to glaciation at the south pole the first phase starting just below the normalograptus extraordinarius zone particularly affected nektonic and planktonic species while the second pulse associated with the normalograptus persculptus zone was less selective glacially induced cooling and oxygenation are two of many suggested kill mechanisms for the end ordovician extinction but a general consensus is lacking we have used geochemical redox indicators such as iron speciation molybdenum concentrations pyrite framboid size distribution and sulfur isotopes to analyze the geochemistry in three key hirnantian sections these indicators reveal that reducing conditions were occasionally present at all three sites before the first pulse of the end ordovician extinction and that these conditions expanded towards the second pulse even though the n extraordinarius zone appears to have been a time of oxygenated deposition pyrite is significantly enriched in 34s in our sections as well as in sections reported from south china this suggests a widespread reduction in marine sulfate concentrations which we attribute to an increase in pyrite burial during the early hirnantian the s isotope excursion coincides with a major positive carbon isotope excursion indicating elevated rates of organic carbon burial as well we argue that euxinic conditions prevailed and intensified in the early hirnantian oceans and that a concomitant global sea level lowering pushed the chemocline deeper than the depositional setting of our sites in the n persculptus zone an interval associated with a major sea level rise our redox indicators suggests that euxinic conditions and ferruginous in some places encroached onto the continental shelves in our model the expansion of euxinic conditions during the n extraordinarius zone was generated by a reorganization of nutrient cycling during sea level fall and we argue overall that these dynamics in ocean chemistry played an important role for the end ordovician mass extinction during the first pulse of the extinction euxinia and a steepened oxygen gradient in the water column caused habitat loss for deep water benthic and nektonic organisms during the second pulse the transgression of anoxic water onto the continental shelves caused extinction in shallower habitats

predominance of stratified anoxic yangtze sea interrupted by short term oxygenation during the ordo silurian transition abstract the ordo silurian transition was a critical interval in geological history during which profound biotic climatic and oceanic changes occurred in order to explore the oceanic palaeoredox changes multiple geochemical proxies including ratios of s c fehr fet fep fehr and dop values are presented here from three sections wangjiawan western hubei sanjiaguan northern hunan and nanbazi northern guizhou across the ordo silurian boundary on the yangtze platform these palaeoredox data indicate a predominance of stratified anoxic ferruginous ocean on the yangtze block during this transition which was interrupted by a brief episode of oceanic oxygenation in the early hirnantian this oxygenation temporally coinciding with the end ordovician glaciation and global glacio eustatic sea level fall likely resulted from enhanced circulation of polar cold dense oxygen rich water onto the low latitude shelf the prior and subsequent longer term episodes of anoxic ocean particularly the later one which started in the late hirnantian occurred in parallel with the rapid climatic warming and sea level rise which could have slowed down oceanic circulation thereby enhancing oceanic stratification anoxia and organic preservation oceanic redox changes together with rapid climatic and sea level fluctuations were likely responsible for the stepwise massive demise of the ordo silurian biotic crisis

paleoecology of the cretaceous tertiary mass extinction in planktonic foraminifera abstract paleobiogeographic patterns of the cretaceous tertiary k t mass extinction in planktonic foraminifera in tunisia spanning environments from open marine upper bathyal to shelf and shallow marginal settings indicate a surprisingly selective and environmentally mediated mass extinction this selectivity is apparent in all of the environmental proxies used to evaluate the mass extinction including species richness ecological generalists ecological specialists surface and subsurface dwellers whether based on the number of species or the relative percent abundances of species the following conclusions can be reached for shallow to deep environments about three quarters of the species disappeared at or near the k t boundary and only ecological generalists able to tolerate wide variations in temperature nutrients salinity and oxygen survived among the ecological generalists heterohelicids guembelitrids hedbergellids and globigerinellids only surface dwellers survived ecological generalists which largely consisted of two morphogroups of opportunistic biserial and triserial species also suffered selectively biserials thrived during the latest maastrichtian in well stratified open marine settings and dramatically declined in relative abundances in the early danian triserials thrived only in shallow marginal marine environments or similarly stressed ecosystems during the latest maastrichtian but dominated both open marine and restricted marginal settings in the early danian this highly selective mass extinction pattern reflects dramatic changes in temperature salinity oxygen and nutrients across the k t boundary in the low latitude tethys ocean which appear to be the result of both long term environmental changes e g climate sea level volcanism and short term effects bolide impact

stable carbon isotope stratigraphy in the ordovician of south china abstract about 500 samples from 11 ordovician sections in south china have been analysed for their 13 c carb composition four sections are located in the yangtze platform region the remaining seven sections in the jiangnan slope region the sections span more or less the entire ordovician but the sample resolution in its lower part tremadocian to dapingian is lower than in its upper part darriwilian to hirnantian overall the data show a good correlation with the published global isotope curve at the cambrian ordovician boundary positive values are observed in the succeeding tremadocian the values decrease and remain negative into the early floian in the late floian the values increase to slightly positive the correlation of dapingian rocks between the yangtze and the jiangnan regions is somewhat problematic which might be due to high siliciclastic input in the yangtze section in the darriwilian a small positive excursion is observed in the yangtze platform area however it is missing in the jiangnan slope area this excursion probably correlates with the mid darriwilian excursion mdice reported from baltoscandia both chemostratigraphy and conodont biostratigraphy indicate a possible gap between the shihtzupu formation and the pagoda formation i e most of the sandbian is probably not represented in the upper yangtze region the earliest katian is characterised by a pronounced positive excursion correlating with the well known global guttenberg excursion gice in the late katian at least one additional positive excursion was determined the precise biostratigraphy however is not clear and therefore it is not known which of the known four to five remaining katian 13 c excursions identified in baltica correlate s with the one s observed in the present study and further biostratigraphic study is required the lower part of the hirnantian excursion hice is probably not preserved with only small remnants of the hice observed near the base of the kuanyinchiao bed

tracking euxinia in the ancient ocean a multiproxy perspective and proterozoic case study the evolution and extinction of life are tied intimately to the oxygen state of the ocean and particularly to the presence of anoxic and h2s containing euxinic water on a global scale anoxia and euxinia were more common in the past relative to today s 0 5 euxinic seafloor we are able to constrain the distributions of these conditions through a combination of indirect numerical modeling methods and more direct geochemical proxies with particular emphasis on fe s mo analysis of fine grained siliciclastic rocks for the latter establishing the spatiotemporal pattern of oceanic redox is more difficult with very old rocks because of the limited availability of well dated well preserved materials that span shallow and deep environments across time lines despite these difficulties the multiple approaches synthesized in our case study point to global oxygen deficiency in the deep ocean and perhaps euxinia during most if not all of the proterozoic and likely extending into the early paleozoic

some patterns of planktic foraminiferal assemblage turnover at the cretaceous tertiary boundary abstract three uppermost cretaceous through basal paleocene stratigraphic sequences are examined for planktic foraminiferal assemblage stability and temporal succession patterns these sequences are at mid latitude south atlantic dsdp site 528 then equatorial pacific dsdp site 577 and the tethyan shelf ben gurion section of the negev israel in order to better estimate biogeographic patterns and habitat preferences the results of these analyses are compared to previous cretaceous biogeographic studies and to previous analyses of cretaceous tertiary k t boundary shelf and epicontinental sections results indicate that immediately following the k t boundary the examined epicontinental and open ocean sites were exploited primarily by previously epicontinental planktic foraminiferal assemblages this pattern of k t boundary assemblage dominance suggests the geologically instantaneous break down of late cretaceous epicontinental and open ocean biogeographic provincialization this shift in open ocean foraminiferal assemblages is not consistent with models of non selective k t boundary extinctions but is consistent with models of extinction resistence and offshore expansion of near shore taxa the re establishment of stable biogeographic differences between open ocean and epicontinental planktic foraminiferal assemblages occurs by the basal parvularugoglobigerina eugubina zone at open ocean sites 528 and 577 and the outer shelf ben gurion section po and p eugubina zone faunal records are marked by a pronounced alternation between paleocene biserial and non biserial dominated assemblages this alternation appears strongly damped at shelf and epicontinental sections previously examined the first appearance and peak magnitude of abundant earliest paleocene trochospiral forms parvularugoglobigerina eoglobigerina morozovella globoconusa also vary from site to site and may depend closely on levels of primary carbonate productivity

volcanism around k t boundary time its role in an impact scenario for k t extinction events abstract a widespread debate on the cretaceous tertiary k t boundary 65 1 ma extinctions has largely revolved around an impact or a volcanic cause evidence for both events is strengthened by recent work impact triggered deccan volcanism or independent impact and mantle plume events have been suggested this review examines evidence for both events and suggests that they overlapped in time but with globally uneven effects the combined effects produced generally inhospitable k t environments leading to mass extinctions although some life forms flourished afterwards volcanic contributions to the k t boundary environment probably include increased platinum group element pge and acid rain fall out particularly from large scale mantle upwellings e g deccan cameroon and coral sea events a previously proposed post k t greenland starting plume apparently already existed in the cretaceous k t features such as the iridium ir anomaly most likely include longer term volcanic as well as sudden meteoritic impact contributions volcanic contributions were greatest from southern hemisphere sources whereas meteorite impacts featured in the northern hemisphere

calcite dissolution and the modification of planktonic foraminiferal assemblages abstract the results of an in situ experiment in the panama basin allow us to determine the way in which planktonic foraminiferal assemblages are modified by calcite dissolution pre weighed planktonic foraminiferal samples of known species composition were attached to a deep sea mooring at various water depths between 665 m and 3791 m for a period of 123 days weight loss due to dissolution during this period ranged from less than 5 for the shallowest samples to slightly over 30 for the deepest samples in terms of change in foraminiferal number this is equivalent to decreases of between 1 and 26 only in the samples placed at the two deepest levels 3769 m and 3791 m was there a significant loss in the total number of foraminifera the magnitude of change in the abundance of individual species in early related to their different susceptibilities to dissolution species such as hastigerina pelagica globigerinella aequilateralis and candeina nitida which are very susceptible to dissolution exhibited the largest decreases in frequency percentage while the more resistent species sphaeroidinella dehiscens pulleniatina obliquiloculata and globorotalia truncatulinoides had minimal changes from these results a solution susceptibility ranking for planktonic foraminifera is established that is quite similar to those derived from previous laboratory experiments and sea floor studies

end ordovician extinctions a coincidence of causes the end ordovician hirnantian extinction was the first of the five big phanerozoic extinction events and the first that involved metazoan based communities it comprised two discrete pulses both linked in different ways to an intense but short lived glaciation at the south pole the first occurring at or just below the normalograptus extraordinarius graptolite biozone mainly affected nektonic and planktonic species together with those living on the shallow shelf and in deeper water whereas the second within the n persculptus graptolite biozone was less focused eradicating faunas across a range of water depths in all about 85 of marine species were removed proposed kill mechanisms for the first phase have included glacially induced cooling falling sea level and chemical recycling in the oceans but a general consensus is lacking the second phase is more clearly linked to near global anoxia associated with a marked transgression during the late hirnantian most recently however new drivers for the extinctions have been proposed including widespread euxinia together with habitat destruction caused by plate tectonic movements suggesting that the end ordovician mass extinctions were a product of the coincidence of a number of contributing factors moreover when the deteriorating climate intensified causing widespread glaciation a tipping point was reached resulting in catastrophe

negative δ13ccarb shifts in upper ordovician hirnantian guanyinqiao bed of south china linked to diagenetic carbon fluxes abstract the late ordovician hirnantian glaciation coincided with a major perturbation of the global carbon cycle characterized by large positive excursions of 13ccarb and 13corg known as the hirnantian carbon isotopic excursion hice previous studies from south china have reported a positive shift in 13corg but ambiguous trends in carbonate carbon isotopes to better define 13ccarb variation through the ordovician silurian o s transition in south china we investigated multiple components brachiopods micritic matrix and microspar cement in five study sections representing shallow shelf to deep basin facies across the yangtze block all sections exhibit negative 13ccarb shifts near the base of the hirnantian stage with small shifts in two sections to between 2 and 1 and large shifts in three sections mostly

global fire at the cretaceous tertiary boundary cretaceous tertiary k t boundary clays from five sites in europe and new zealand are 102 104 fold enriched in elemental c mainly soot which is isotopically uniform and apparently comes from a single global fire the soot layer coincides with the ir layer suggesting that the fire was triggered by meteorite impact and began before the ejecta had settled