the great extinction that never happened the demise of the dinosaurs considered the concept of a sudden extinction of the dinosaurs consequent upon the impact of some extraterrestrial object is so dramatic that it has taken hold upon the imaginations of many scientists as w

records of post cretaceous tertiary boundary millennial scale cooling from the western tethys a smoking gun for the impact winter hypothesis the record of both dinoflagellate cysts and benthic foraminifera across the cretaceous tertiary boundary at el kef tunisia reveals a brief expansion of the boreal bioprovince into the western tethys suggesting that an 2 k y cooling occurred during the earliest danian we show that this prolonged cooling phase is consistent with the oceanographic response to an impact winter

paleocene sea level and productivity changes at the southern tethyan margin el kef tunisia integrated analysis of quantitative distribution patterns of organic walled dinoflagellate cysts dinocysts and benthic foraminifera from the paleocene el kef section nw tunisia allows the reconstruction of sea level and productivity fluctuations our records indicate that the environment evolved from an initially oligotrophic open marine outer neritic to upper bathyal setting towards a more eutrophic inner neritic setting influenced by coastal upwelling by the end of the paleocene an overall second order change in paleodepth is reflected by both microfossil groups from the base of planktic foraminifera zone p4 onwards the main phase of shallowing is evidenced by an increase of inner neritic dinocysts of the areoligera group disappearance of deeper water benthic foraminifera and increasing dominance of shallow marine taxa several buliminids haplophragmoides spp trochammina spp the total magnitude of this shallowing is obscured by interaction with a signal of eutrophication but estimated to be around 150 m from 200 to 50 m superimposed on the overall trend third order sea level fluctuations have been identified and correlated to sequences in other regions paleoproductivity indicators notably protoperidinioid dinocysts and buliminids show a trend from an oligotrophic to a eutrophic setting d 2005 elsevier b v all rights reserved

arsenic enrichment in groundwater of west bengal india geochemical evidence for mobilization of as under reducing conditions abstract the mechanism of as release and source s of as has been investigated in a small part of a watershed in the murshidabad district of west bengal analyses include major ion and trace element concentrations as well as o h and s isotope ratios of groundwater surface water and a thermal spring the results indicate that all water samples belong to the ca hco 3 type except for the thermal spring which is of the na hco 3 type shallow and deeper groundwaters have distinct hydrochemical features high as contents were registered only in the deeper groundwater horizon factor analysis and the distribution pattern of major and trace elements indicate that as is present in the aquifer as a scavenged phase by fe iii and to a lesser extent by mn iv phases the release of as into the groundwater occurs gradually in successive stages corresponding to the actual redox state in the aquifer the main stage of as release is related to the bacterial reduction of fe iii to fe ii i e to the simultaneous dissolution of fe oxyhydroxides low redox conditions in highly polluted areas are indicated by low so 4 concentration and high 34 s values during bacterial so 4 reduction residual so 4 in groundwater is depleted in the lighter s isotope 32 s however the cause of the gradual decrease of the redox state in the groundwater is still not well understood

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

contamination and mobilization of arsenic in the soil and groundwater and its influence on the irrigated crops manipur valley india the arsenic concentration in groundwater used for irrigating the rice crops varies from 10 to 475 ppb the disang shales deposited under marine environment appear to be the main source of arsenic contaminating the groundwater the arsenic content in the rice roots vary from 32 to 52 ppm while the arsenic in the grains is far above the limit prescribed by who sequential extraction process results indicate that a large part of arsenic is present in the residual phases high concentration of arsenic at root depth is present in crystalline fe oxides and is available for the rice plants sequential extraction experiment on soils indicate low arsenic content in organic matter compared to the above phases

global comparisons of organic matter in sediments across the cretaceous tertiary boundary a tract the cretaceous tertiary k t boundary is marked by extensive changes in the sedimentary fossil record of continental and marine life organic matter in sediments from above and below the k t boundary has been studied to identify consequences of the biotic extinctions and of the changes in biological productivity which occurred at this time data from locations encompassing a variety of marine paleoenvironments were examined to assess the global extent and local expressions of these biological changes characterizations of organic matter included rock eval pyrolysis stable carbon isotope ratios and distributions of extractable biomarkers in general organic carbon concentrations are a few tenths of a percent in the chalks and marls above and below the k t boundary in some boundary clay samples concentrations up to 5 are found the elevated amounts near the boundary result from oxidation of marine organic matter consequent dissolution of carbonates and concentration of the surviving organic matter at all locations the organic matter has been microbially reworked and evidently was deposited in oxidizing environments carbon isotope shifts in open marine sediments suggest biological productivity was depressed following the k t boundary repetition of these changes at different locations verifies the global extent of the boundary event yet local variations in its expression are evident

paleooceanography of the mesogean sea based on ostracods of the northern tunisian continental shelf between the late cretaceous and early paleogene a new method analysis used in the study of the el kef section north western tunisia led to the paleooceanographic reconstruction of the mesogean between late cretaceous and early paleogene several changes observed are in fact worthy of particular mention paleobathymetrically the area changed from an upper bathyal environment of about 400 m deep to an outer shelf domain of 100 50 m furthermore the oxygen minimum zone o m z became highly intense at a the cretaceous tertiary transition catastrophic event b the p1 p2 boundary intense thermic stratification and c between p4 and p6 very active paleoproductivity in this last episode the continental shelf environment was subjected to intense upwelling responsible for the formation of a prephosphatic environment at water sediment interface the paleooceanographic history of phosphates in the gafsa metlaoui basin is in fact in perfect stratigraphic and paleoenvironmental agreement with the paleobathymetric evolution of the kef region finally paleooceanographic communication between the mesogean and the north atlantic was at this period highly free because of lack of hydrologic relations between the north atlantic and the norwegian sea

benthic foraminiferal turnover across the cretaceous paleogene boundary at agost southeastern spain paleoenvironmental inferences abstract we studied upper cretaceous and lower paleogene benthic foraminifera from the agost section southeastern spain to infer paleobathymetrical changes and paleoenvironmental turnover across the cretaceous paleogene k p transition benthic foraminifera indicate uppermost bathyal depths at agost during the abathomphalus mayaroensis biochron from about 400 kyr before the k p boundary through the early plummerita hantkeninoides biochron about 120 150 kyr before that boundary the depth increased to middle bathyal for the remainder of the cretaceous and remained so for the danian part of the studied section parasubbotina pseudobulloides biochron at least 200 kyr after the k p boundary there were no perceivable bathymetrical changes at the k p boundary where 5 of the species became extinct and the species composition of the benthic foraminiferal fauna changed considerably below the boundary infaunal morphogroups constitute up to 65 73 of the faunas directly above the boundary in the black clays of the lower guembelitria cretacea biozone benthic foraminifera are rare several opportunistic taxa e g the agglutinant haplophragmoides sp have short peaks in relative abundance possibly reflecting low oxygen conditions as well as environmental instability with benthos receiving food from short lived local blooms of primary producers above the clays through the end of the studied interval epifaunal morphogroups dominate up to 70 of the assemblages or there is an even mixture or epifaunal and infaunal morphogroups infaunal groups do not recover to pre extinction relative abundances indicating that the food supply to the benthos did not recover fully over the studied interval about 200 kyr after the k p boundary the benthic foraminiferal faunal changes are compatible with the direct and indirect effects of an asteroid impact which severely destabilized primary producers and the oceanic food web that was dependent upon them

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

is the transition impact to post impact rock complete some remarks based on xrf scanning electron microprobe and thin section analyses of the yaxcopoil 1 core in the chicxulub crater the transition from impact to post impact rocks in the yaxcopoil 1 core is marked by a 2 cm thick clay layer characterized by dissolution features the clay overlies a 9 cm thick hardground overlying a 66 cm thick crossbedded unit consisting of dolomite sandstone alternating with thin micro conglomerate layers with litho and bioclasts and the altered remains of impact glass now smectite the micro conglomerates mark erosion surfaces microprobe and backscatter sem analysis of the dolomite rhombs show an early diagenetic complex zoned idiomorphic overgrowth with mn rich zones possibly formed by hot fluids related to cooling melt sheet in the crater the pore spaces are filled with several generations of coelestite barite k feldpar and sparry calcite xrf core scanning analysis detected high mn values in the crossbedded sediments but no anomalous enrichment of the siderophile elements cr co fe and ni in the clay layer shocked quartz occurs in the crossbedded unit but is absent in the clay layer the basal paleocene marls are strongly dissolved and do not contain a basal paleocene fauna the presence of a hardground the lack of siderophile elements shocked quartz or ni rich spinels in the clay layer and the absence of basal paleocene biozones p0 and pa all suggest that the top of the ejecta sequence and a significant part of the lower paleocene is missing due to the high energy sedimentation infill a hiatus at the top of the impactite is not unexpected but there is nothing in the biostratigraphy geochemistry and petrology of the yaxcopoil 1 core that can be used to argue against the synchroneity of the end cretaceous mass extinctions and the chicxulub crater

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

stress induced changes in plate density vail sequences epeirogeny and short lived global sea level fluctuations the stratigraphic record contains clear evidence that broad regions have experienced rapid changes in sea level unrelated to changes in glacial ice volume e g third and higher order vail sea level variations continental foundering we propose that many of these changes can be caused by stress induced changes in plate density stress changes produce significant changes in the density of the crust and lithosphere a point missed in previous investigations and propagate across even the largest plates in less than 30 000 years lithospheric plates interacting at existing boundaries can produce stress related density changes sufficient to cause several meters change in plate elevation these may account for many of the regressions and transgressions seen in the stratigraphic record the creation of new rifts could increase plate compression enough to cause 50 m of plate subsidence plate elevation changes of up to 200 m could result from increased plate compression during continental collisions a particularly enigmatic kind of rapid nonglacial global ngg sea level change is a coupled 50 m sea level fall regression and roughly equal rise transgression occurring in less than 106 years these couplets associated with black shales and marine extinctions can be explained by the elastic snapback attending the rapid formation of a new rift isostatic disequilibria along the new rift depresses the seafloor sufficiently to cause a 50 m fall in sea level mantle flow restores isostatic equilibrium along the rift axis and erases the fall in 60 000 years unusually intense hydrothermal circulation along the new rift during the snapback promotes anoxic bottom water conditions and deposition of black shales a rapid drop in global sea levels reduces the area of ocean bottom within the photic zone causing overpopulation food exhaustion and extinctions the connections between changes in plate stress and density have many implications perhaps the most far reaching is that tectonic events on the 3 4 of the globe that is covered by oceans as well as the 1 4 that is subaerial are recorded in sedimentary strata

impact of irrigation with as rich groundwater on soil and crops a geochemical case study in west bengal delta plain india abstract the distribution of as was explored in soils and crops in order to investigate the influence of irrigation with as rich groundwater on the soil plant system and to determine its impact on the environment and human health the study was carried out in an intensively cultivated agricultural area of the bengal delta plain west bengal india soils plants and irrigation water from adjacent rice and wheat fields were analysed for as and other elements irrigation water has concentrations of up to 780 g l 1 as in the study area rice and wheat grains are not contaminated by as about 0 3 and 0 7 mg kg 1 respectively but concentrations in rice roots were found to be 169 178 mg kg 1 as which is more than 20 times higher than value of 7 7 mg kg 1 measured at the uncontaminated reference site this high content is due to an fe rich plaque which coats the rice roots a significant increase of as concentration was registered also in the stems of the rice plants irrigated with as rich groundwater 6 55 7 06 relative to 0 36 mg kg 1 as in the reference plant arsenic concentration in the uppermost soil layers of the rice paddy field 38 mg kg 1 was found to be roughly twice as high as in the soil of the less intensively watered wheat field 18 mg kg 1 and more than 5 times higher than in the soil of a rice paddy irrigated with uncontaminated water 7 mg kg 1 in both soil sections as contents decreased downwards to 11 mg kg 1 at 100 110 cm depth approaching the background value of 5 10 mg kg 1 measured in an unaffected reference area sequential extraction experiments show that most of the mobile as in soils is bound to fe oxides though no tight correlation was found between fe and as in the bulk soil samples these experiments coupled with synchrotron radiation xrf analysis of single soil particles from the rice paddy also indicates that additional to the mobile fraction a substantial part of as is immobilized in chiefly fe bearing silicates in rice soil some as was also found in the sulphide bearing phase of the extraction

review of arsenic geochemical characteristics and its significance on arsenic pollution studies in karst groundwater southwest china abstract as a metalloid element arsenic as is widely distributed in the natural environment its ingestion can cause cancer deformities and mutations therefore it has become an important environmental problem in recent years there are large amounts of arsenic ore and coal with high arsenic content in southwest china a karst area there arsenic occurs in wastewater from mines contaminate soil vegetation and surface water karst underground aquifers are also contaminated through pipes cracks scuttles and sinkholes leading to a more serious arsenic pollution problem than in non karst areas due to the unique karst hydrogeological conditions to prevent and curb karst underground water contamination and guarantee water resource security and public health a review on the arsenic contamination in the karst area is necessary this paper discusses the progress of geochemical studies on arsenic through an analysis of the hydrogeology of karst areas this paper proposes that studies on arsenic pollution in karst regions should be combined with the spatial distribution and redox characteristics of groundwater more attention should be paid to chemical compositions of water soil and rocks as well as adsorption desorption processes between water and sediment when conducting arsenic geochemical research in karst groundwater

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

late cretaceous to early paleocene climate and sea level fluctuations the tunisian record abstract climate and sea level fluctuations across the cretaceous tertiary k t transition in tunisia were examined based on bulk rock and clay mineralogies biostratigraphy and lithology in five sections el melah el kef elles ain settara and seldja spanning from open marine to shallow inner neritic environments late campanian to early danian trends examined at el kef and elles indicate an increasingly more humid climate associated with sea level fluctuations and increased detrital influx that culminates at the k t transition this long term trend in increasing humidity and runoff in the tethys region is associated with middle and high latitude cooling results of short term changes across the k t transition indicate a sea level lowstand in the latest maastrichtian about 25 100 ka below the k t boundary with the regression marked by increased detrital influx at el kef and elles and a short hiatus at ain settara a rising sea level at the end of the maastrichtian is expressed at elles and el kef by deposition of a foraminiferal packstone a flooding surface and condensed sedimentation mark the k t boundary clay which is rich in terrestrial organic matter the p0 p1a transition is marked by a sea level lowstand corresponding to a short hiatus at ain settara where most of p0 is missing and a period of non deposition and erosion in the lower part of p1a 64 95 ma at seldja p0 and possibly the topmost part of cf1 are missing these sea level fluctuations are associated with maximum humidity these data suggest that in tunisia long term environmental stresses during the last 500 ka before the k t boundary and continuing into the early danian are primarily related to climate and sea level fluctuations within this long term climatic trend the pronounced warm and humid event within the latest maastrichtian zone cf1 may be linked to greenhouse conditions induced by deccan volcanism the absence of any significant clay mineral variations at or near the k t boundary and ir anomaly suggests that the bolide impact had a relatively incidental short term effect on climate in the tethys region

a review of the source behaviour and distribution of arsenic in natural waters the range of as concentrations found in natural waters is large ranging from less than 0 5 g l 1 to more than 5000 g l 1 typical concentrations in freshwater are less than 10 g l 1 and frequently less than 1 g l 1 rarely much higher concentrations are found particularly in groundwater in such areas more than 10 of wells may be affected defined as those exceeding 50 g l 1 and in the worst cases this figure may exceed 90 well known high as groundwater areas have been found in argentina chile mexico china and hungary and more recently in west bengal india bangladesh and vietnam the scale of the problem in terms of population exposed to high as concentrations is greatest in the bengal basin with more than 40 million people drinking water containing excessive as these large scale natural as groundwater problem areas tend to be found in two types of environment firstly inland or closed basins in arid or semi arid areas and secondly strongly reducing aquifers often derived from alluvium both environments tend to contain geologically young sediments and to be in flat low lying areas where groundwater flow is sluggish historically these are poorly flushed aquifers and any as released from the sediments following burial has been able to accumulate in the groundwater arsenic rich groundwaters are also found in geothermal areas and on a more localised scale in areas of mining activity and where oxidation of sulphide minerals has occurred the as content of the aquifer materials in major problem aquifers does not appear to be exceptionally high being normally in the range 1 20 mg kg 1 there appear to be two distinct triggers that can lead to the release of as on a large scale the first is the development of high ph 8 5 conditions in semi arid or arid environments usually as a result of the combined effects of mineral weathering and high evaporation rates this ph change leads either to the desorption of adsorbed as especially as v species and a range of other anion forming elements v b f mo se and u from mineral oxides especially fe oxides or it prevents them from being adsorbed the second trigger is the development of strongly reducing conditions at near neutral ph values leading to the desorption of as from mineral oxides and to the reductive dissolution of fe and mn oxides also leading to as release iron ii and as iii are relatively abundant in these groundwaters and so4 concentrations are small typically 1 mg l 1 or less large concentrations of phosphate bicarbonate silicate and possibly organic matter can enhance the desorption of as because of competition for adsorption sites a characteristic feature of high groundwater as areas is the large degree of spatial variability in as concentrations in the groundwaters this means that it may be difficult or impossible to predict reliably the likely concentration of as in a particular well from the results of neighbouring wells and means that there is little alternative but to analyse each well arsenic affected aquifers are restricted to certain environments and appear to be the exception rather than the rule in most aquifers the majority of wells are likely to be unaffected even when for example they contain high concentrations of dissolved fe

a terrestrial scenario for the cretaceous tertiary boundary collapse of the marine pelagic ecosystem in this paper we present an expansion of the model for marine ecosystem collapse at the cretaceous tertiary boundary presented by brinkhuis and zachariasse 1988 a long term sea level drop at the end of the cretaceous culminated in a short term regressive pulse at k t time deep water production was curtailed minimizing the vertical advection of nutrients and oxygen in the oceans consequently a productivity crisis developed which could only be survived by cosmopolitan shallow dwellers and the oxygen minimum zone omz expanded no sustained oceanic anoxic event followed the k t boundary event since productivity had dropped to extremely low values at k t time however the short term expansion of the omz invoked by the combination of minimized oxygen advection and abrupt mass mortality caused dysoxic conditions even to reach up to the shelves as can be deduced from sedimentological chemical and faunistic observations

influence of irrigation practices on arsenic mobilization evidence from isotope composition and cl br ratios in groundwater from datong basin northern china environment isotopes 18o and 2h and cl br ratios in groundwater have been used to trace groundwater recharge and geochemical processes for arsenic contamination in datong basin the arsenic concentrations of groundwater samples ranged from 0 4 to 434 9 g l with the average of 51 2 g l which exceeded china s drinking water standard 10 g l all the groundwater samples are plotted on or close to the meteoric water line of the 18o vs 2h plot indicating their meteoric origin the relationship between 18o values and cl br ratios and cl concentrations demonstrate that leaching and mixing are the dominant processes affecting the distribution of high arsenic groundwater in this area the observed non linearity in the trend between 18o and arsenic concentration is due to combined effects of mixing and leaching the similarity of the trend in cl br ratios and 18o values for high arsenic groundwater demonstrate that extensive leaching of irrigation return and salt flushing water flow could be the dominant process driving arsenic mobilization in the groundwater system moreover the long term irrigation practice can cause the drastic change of the biogeochemical and redox condition of in the aquifer system which in turn promotes the mobilization of arsenic therefore groundwater pumping for irrigation in this area of waterborne endemic arsenic poisoning should be under strict control to protect groundwater quality in this area

late cretaceous deep water agglutinated foraminiferal assemblages from the north atlantic and its marginal seas the stratigraphic and biogeographic distribution of more than 170 species of deep water agglutinated benthic foraminifers dwaf from the north atlantic and adjacent marginal seas has been compared with paleoenvironmental data e g paleobathymetry oxygenation of the bottom waters amount of terrigenous input and substrate disturbance six general types of assemblages in which deep water agglutinated taxa occur are defined from the turonian to maastrichtian times 1 high latitude slope assemblages 2 low to mid latitude slope assemblages 3 flysch type assemblages 4 deep water limestone assemblages scaglia type 5 abyssal mixed calcareous agglutinated assemblages 6 abyssal purely agglutinated assemblages latitudinal differences in faunal composition are observed the most important of which is the lack or extreme paucity of calcareous forms in high latitude assemblages east to west differences appear to be of comparatively minor importance most dwaf species occur in all studied regions and are thus considered as cosmopolitan biostratigraphic turnovers in the taxonomic content of assemblages are observed in the lowermost turonian mid campanian and in the upper maastrichtian to lowermost paleocene these datum levels correspond to inter regional and time constant paleooceanographic events which probably also affected the deep water benthic biota this allows us to use deep water agglutinated foraminifers for biostratigraphy in the north atlantic sequences deposited below ccd and to geographically extend the currently used zonal schemes which have been established in the carpathian and alpine areas

changes in coiling direction of cibicidoides pseudoacutus nakkady across the cretaceous tertiary boundary of tunisia palaeoecological and biostratigraphic implications abstract the analysis of coiling direction preference in the benthic foraminifera cibicidoides pseudoacutus nakkady has been carried out across the cretaceous tertiary boundary k t boundary from four tunisian sections representing a palaeobathymetric transect from a middle outer neritic to lower upper bathyal depositional setting our study reveals that c pseudoacutus developed a preference for sinistral coiling in a short time period during the lowermost danian the comparison of the coiling ratio number of sinistral vs dextral individuals record with isotope data and dinoflagellate cyst assemblage distribution suggests that the development of sinistrally coiled populations of cibicidoides pseudoacutus might be related to a short term cooling of both surface and bottom waters which occurred at the k t boundary and lasted for some 7 kyr the continuous occurrence and the high abundance of cibicidoides pseudoacutus through the k t boundary in neritic to upper bathyal depositional environments around southern tethys make identification of the shift in its coiling ratio relatively easy the development of a sinistrally coiled population in this benthic foraminiferal species is regarded as a potential marker for the base of planktonic foraminiferal zone p0 in tethyan shallow water settings

danian faunal succession planktonic foraminiferal response to a changing marine environment planktonic foraminiferal evolution following the cretaceous tertiary boundary extinction event is marked by a series of events in which one assemblage is rapidly replaced by another this pattern is characteristic of a highly changing pelagic environment the observed changes in the planktonic foraminifera may be related to long term changes in oceanic productivity that persisted for about the first 2 m y of the danian

sedimentology and ichnology of the cretaceous tertiary boundary in denmark implications for the causes of the terminal cretaceous extinction abstract trace fossils and other sedimentologic evidence of bioturbation in latest cretaceous and earliest tertiary marine deposits in denmark provide important clues to understanding the ecology of the sea bottom immediately before during and after the terminal cretaceous boundary event trace fossil associations at all the onshore danish boundary sites indicate a general upward shoaling of the late maastrichtian chalk sea which was accompanied by an abrupt shift from a carbonate ooze sea floor to a marly clay rich unstable substrate at the boundary although the substrate condition may have become more stable in the early danian water depths never did return to their former deep level there is evidence of localized anoxia during the deposition of some boundary sediments in the fish clay in shallow parts of the danish maastrichtian sea but no clear evidence of anaerobic conditions occurring at the era boundary was observed in boundary strata deposited in deeper water near the center of the basin in fact earliest danian marl there is totally bioturbated a pulse of calcite dissolution in shallow water coincided precisely with the era boundary and this event played a major role in the formation of the fish clay in eastern denmark which is a condensed series of smectitic clay rich layers from which much calcite has dissolved the effects of this dissolution episode however were not so extreme in the marl that was deposited at the same time in slightly deeper water in northwestern denmark evidence from cretaceous tertiary boundary sequences in denmark and elsewhere suggests that no single catastrophe can account for the major biotic extinctions that occurred at the end of the cretaceous period the primary causal factors of the terminal cretaceous extinction event appear to be drastic global sea level regression occurring simultaneously with extensive volcanism on land and a strong pulse of calcite dissolution in ocean surface waters

stable isotope and foraminiferal changes across the cretaceous tertiary boundary at stevns klint denmark arguments for long term oceanic instability before and after bolide impact event abstract stable isotope and planktic and benthic foraminiferal analyses of the k t boundary transition at stevens klint denmark indicate a 100 500 kyr long period of instability in oceanic bottom water temperature and sea level during the latest maastrichtian from 2 7 m below and up to the k t boundary bottom water temperatures gradually cooled about 1 5 c as surface water temperatures remained constant at the k t boundary bottom water temperatures decreased additionally 3 c and then returned to pre boundary values just above the boundary interval coincident with the onset of the first temperature decrease there was a prominent sea level fall estimated between 50 100 m as observed in benthic and planktic foraminiferal assemblages as well as in a decreasing surface to bottom 13 c gradient about 40 cm below the iridium rich k t boundary clay sea level began to rise poor preservation of foraminifera above the k t boundary allows only tentative interpretation of danian events at stevns klint however sea level generally continued to rise interrupted by short sea level falls associated with the observed sea level changes are three important hiatuses at the contact between the white chalk and overlying grey white bryozoan chalk about 2 7 m below the k t boundary at or near the top of the fish clay zone pla parvularugoglobigerina eugubina missing and at the contact of the cerithium limestone and overlying bryozoan limestone about 60 cm above the k t boundary part of zone plc missing these unconformities are coeval with hiatuses observed in many continental shelf sections and indicate a global eustatic rather than regional isostatic response notable is that at stevns klint the episode of oceanic instability is registered over approximately the same stratigraphic interval in which supposed extraterrestrial amino acids occur a circumstance that may indicate a connection a gradual positive shift in 13 c is registered in both benthic and planktic foraminiferal assemblages in the upper maastrichtian at stevns klint the positive shift is followed by a prominent negative 13 c shift 1 3 at the k t boundary an upper maastrichtian positive 13 c excursion followed by a negative 13 c anomaly at or near the k t boundary has previously been observed in deep sea cores from the pacific ocean and the weddell sea antarctica implying a global event previous suggestions of a relation between the uppermost maastrichtian positive 13 c excursion and sea level variation are not supported by the data for stevns klint

delineation of groundwater flow paths using hydrochemical and strontium isotope composition a case study in high arsenic aquifer systems of the datong basin northern china summary strontium isotopic compositions and major ion chemistry were used to delineate flow paths in an arsenic affected groundwater flow system in the datong basin china total of 28 samples including one spring and one river water were collected for major ions and strontium isotopic compositions and concentration analysis the ion ratios indicate that dissolution of silicates and carbonates is the dominant geochemical process controlling the hydrochemistry of groundwater from two recharge areas at the basin margins while the water chemistry in the center of the basin is affected by the dissolution of evaporites including gypsum and halite groundwater from eastern and western margin areas have relatively high 87 sr 86 sr values ranging from 0 72114 to 0 72604 and from 0 71119 to 0 71151 which are consistent with expected values for groundwater dominantly affected by dissolution of silicates however in the discharge area the groundwater samples had lower 87 sr 86 sr values and varied between 0 71016 and 0 71753 the contour map of 87 sr in groundwater shows the general tendency of decrease from the western and eastern margin areas to the discharge area the plot of 87 sr 86 sr vs sr na indicates that interactions between quaternary aquifer sediment and groundwater in the recharge areas along the flow paths control the hydrochemistry and strontium isotopic compositions of groundwater by contrast groundwater samples from the discharge area are plotted on the mixing line indicating that mixing of groundwater from recharge area with low 87 sr 86 sr values groundwater could be the controlling factor on their hydrochemistry and strontium isotopic compositions four main flow paths of groundwater were inferred from hydrochemical and isotopic data the results of phreeqc inverse modeling matched quite well with the results of strontium isotopic and ion compositions along the flow paths the distribution of high arsenic groundwater in this area could be attributed to the combined effect of the vertical flow and local groundwater flow on the redox conditions of the groundwater system

trace elements stable isotopes and clay mineralogy of the elles ii k t boundary section in tunisia indications for sea level fluctuations and primary productivity abstract trace elements and stable isotopes in bulk rocks and foraminifera bulk rock and clay mineral compositions are used as palaeoproxies to evaluate sea level fluctuations climatic changes and variations in primary productivity across the k t transition at elles ii in tunisia from 1 m 33 kyr below to 1 m 70 kyr above the k t boundary results on clay minerals major and trace elements stable isotopes in bulk rock samples e g ca cu zn rb sr zr ba 13c and 18o and in foraminifera sr ca 13c 18o indicate that the latest maastrichtian last 33 kyr in tunisia was marked by a relatively warm but humid climate and a rising sea level the transgressive surface is marked by deposition of a foraminiferal packstone just below the k t boundary followed by maximum flooding across the k t boundary red layer and black clay layer humid warm conditions accompanied the maximum flooding along with increased total organic carbon values and rapidly decreasing primary productivity at the k t boundary an impact event ir anomaly ni rich spinels spherules exacerbated already stressed environmental conditions leading to the mass extinction of tropical planktic foraminifera increasingly more humid conditions prevailed within the lowermost danian zone p0 50 kyr culminating in a sea level lowstand near the top of p0 a slow recovery of the ecosystem in zone p1a coincided with a rising sea level and gradually less humid climatic conditions

experimental evidence for mobility of zr and other trace elements in soils a soxhlet extraction was carried out over a period of 27 d on a column comprising 3 cm of quartz overlain by 4 cm of soil from the b horizon and then 1 cm of soil from the a horizon of a granitic podzol major and trace elements were leached from the column and accumulated in a reservoir at the base of the column total loss of elements from the soil over the course of the experiment ranged from 0 002 to 1 wt with major elements and the light and heavy rare earth elements ree showing the largest percentage losses zirconium 0 002 and then al 0 008 showed the lowest percentage loss the light ree were leached out of the soil preferentially to the mid ree all elements showed accumulation by a factor of 2 to 11 in the quartz layers at the base of the column particularly in the upper first 1 cm of the quartz major elements were leached from the column at a rate of 0 02 to 0 59 mol h 1 whereas zr nd sm gd dy rb and sr were leached at the rate of 0 5 to 30 10 6 mol h 1 concentrations of other ree in the reservoir increased over the duration of the experiment but they were poorly correlated with time so leaching rates were not calculated normalization of the major element leaching rates to take into account the constant flushing of water through the column the average annual rainfall in the allt a mharcaidh catchment in scotland from where the soil was sampled and the cross sectional area of the soil in the column together with the temperature of the soil in the column 70 c compared with the average annual temperature of the allt a mharcaidh catchment 5 7 c gave major element release rates from the soil of 0 002 to 0 97 meq m 2 yr 1 depending on the choice of ea the dissolution activation energy which are generally less than those measured in the field of 0 1 to 40 9 meq m 2 yr 1 calculations showed that despite the redistribution and loss of zr from the column assumptions of zr mobility would have had a negligible effect on calculated element release rates of na ca fe and mg however significant underestimates of the release of k 5 ti 57 al 5 and si 10 as well as some trace elements e g nd 23 rb 54 sr 24 would have occurred concentrations of ca and sr leached from the column correlated well rsq 0 93 p 0 01 supporting the idea of the use of sr release as a proxy for ca release in weathering rate calculations the release rates and percentage loss of ree from the soil varied between elements indicating that ree distribution patterns of rocks and soils may not be preserved in drainage waters

the cretaceous tertiary transition the fossil sequences from cores across the cretaceous tertiary boundary show a range of transition times and transition time intervals depending on the fossil indicators and the location of the site these variations together with the pattern of iridium distribution with depth at some sites differences in total amounts of iridium variations in noble metal abundances normalized to extraterrestrial concentrations the depositional effects that might be expected in a reducing environment and the clay mineralogy of the boundary layer clays put into question the interpretation that an extraterrestrial event was the cause of the faunal changes and the iridium anomaly in the vicinity of the cretaceous tertiary transition it seems more likely that an explanation for the changes during the transition will come from continued examination of the great variety of terrestrial events that took place at that time including extensive volcanism major regression of the sea from the land geochemical changes and paleoclimatic and paleoceanographic changes

planktonic and benthic foraminiferal extinction events during the last 100 m y abstract five major planktonic and benthic foraminiferal extinction events occurred during the past 100 m y at the cenomanian turonian c t boundary at the cretaceous tertiary k t boundary in the latest paleocene in the late eocene and in the early middle miocene to clarify the character of the five events i estimated 1 paleo waterdepths and paleoenvironments where foraminifera were affected 2 the duration of each extinction event and 3 evaluated possible causes for each extinction event on the basis of recent literature these extinction events can be classified into three fundamentally different types 1 the mass extinction event at the k t boundary was abrupt and concentrated among surface dwelling species 2 extinctions at the c t boundary and during the latest paleocene were abrupt and mainly affected intermediate and deep water taxa over short periods 3 the late eocene and early middle miocene events affected surface and deep water species and involved stepwise or gradual extinctions over a long period 4 m y i attributed the extinction events to 1 a bolide impact for the k t event 2 a decrease in dissolved oxygen in intermediate and deep waters due to climatic warming for the c t and latest paleocene events and 3 long term global cooling for the late eocene and early middle miocene events the following relationships exist between the causes and types of extinction events 1 large extraterrestrial impacts strongly affected surface dwelling organisms in short term extinction events 2 intermediate and deep water low oxygen conditions induced by climatic warming have severely affected intermediate and deep water organisms over medium and short terms

the cretaceous tertiary transition in guatemala limestone breccia deposits from the south peten basin limestone breccia deposits in southern mexico guatemala and belize have recently been interpreted as proximal to distal ballistic fallout deposits generated by a bolide impact that struck yucatan at k t boundary time we review the age lithology and the depositional environment of five k t boundary sections in the south peten area of guatemala caribe aserradero chisec actela chemal in order to evaluate the nature and origin of k t limestone breccia deposition the sections are located 500 km south of the proposed impact site at chicxulub and trend in an east west direction from the guatemala mexico border to southern belize in four of the five sections examined a breccia unit up to 50 m thick overlies reef bearing shallow water limestones of late cretaceous campanian maastrichtian age rhythmically bedded limestones marls and siltstones of early danian age overlie the breccia and were deposited under middle to outer neritic conditions the breccia consists of differently coloured layers of shallow water limestones clast size generally decreases upsection to thin layers of predominantly rounded clasts and these fine grained rudstones grade into grainstones at the top in at least one section ei caribe diagenetically altered glass spherules are present in the uppermost layers of the grainstone these glass spherules are of stratigraphic position and chemical composition similar to black and yellow glass from beloc haiti and mimbral mexico which some workers have chemically linked to melt glass within the breccia of the chicxulub cores we suggest that breccia deposition in guatemala may have been multi event over an extended time period and related to the collision of the yucatan and chortis plates as well as related to a major impact or volcanic event at the end of the cretaceous

refractory element mobility in volcanic soils refractory trace element concentrations in strongly weathered hawaiian soils ranging in age from 20 to 4100 ka are highly elevated over parent rock values due to extensive mass loss of more soluble major elements during pedogenesis nb and ta exhibit virtually no mobility soil nb ta ratios are within the range of fresh bedrock even when soil nb concentrations are residually enriched by a factor of 10 in contrast al zr and hf are depleted relative to nb in surface soil horizons but are enriched at depth clearly indicating mobility of these elements variations in th nb ratios in soil profiles indicate significant th mobility within the soil column however mass balance calculations require that accretion of th enriched asian dust has resulted in a net increase in th in some soils soils developed on a 150 ka rainfall gradient show that the mobility and loss of zr increase with mean annual precipitation

benthic foraminiferal assemblages between two major extinction events the paleocene el kef section tunisia abstract the development of benthic foraminiferal assemblages from the paleocene outcrops of the el haria formation near el kef tunisia is discussed qualitatively and quantitatively the aim of the study is to reconstruct the paleoenvironmental evolution between the k pg boundary interval and the late paleocene event and to compare this evolution with results from other sites along the southern tethyan margin eighty four samples covering virtually the entire paleocene provide a dataset that allows detailed qualitative and multivariate analysis the benthic foraminiferal faunas indicate a complex pattern of environmental changes during the paleocene marked by the succession of different benthic associations following the k pg boundary event community restoration was characterized by the gradual build up of faunal diversity decreasing dominance and the entry of taxa common to normal marine outer neritic to upper bathyal environments indicate the completion of the ecosystem restoration in zone plb a highly diverse benthic foraminiferal assemblage persisted throughout the remainder of the early paleocene into the earliest late paleocene at the p3a p3b zonal transition relative sea level lowering is evidenced by the sudden disappearance or decreasing abundance of deeper water taxa e g anomalinoides affinis a susanaensis gavelinella beccariiformis neritic deposition continued into zone p4 when trophic levels at the seafloor increased as indicated by the entry and increasing dominance of species such as anomalinoides cf aegyptiacus bulimina midwayensis and b strobila which we consider to be sensitive to eutrophication the combined effect of shallowing and the subsequent eutrophication led to the establishment of assemblages similar to late paleocene benthic foraminiferal assemblages from egyptian sections some of which record the latest paleocene extinction event these assemblages were interpreted to be indicative of a middle neritic highly eutrophic environment enhanced vertical fluxes of organic matter along the southern tethyan margin may have resulted from intensified upwelling this eventually led to oxygen deficiency at the seafloor it appears that oxygen deficient high productivity shelves were a common feature of the southern tethyan margin during the latest paleocene

arsenic associations in sediments from shallow aquifers of northwestern hetao basin inner mongolia understanding the mechanism of arsenic mobilization from sediments to groundwater is important for water quality management in areas of endemic arsenic poisoning such as the hetao basin in inner mongolia northern china aquifer geochemistry was characterized at three field sites sh hf tys in hangjinhouqi county of northwestern hetao basin the results of bulk geochemistry analysis of sediment samples indicated that total as concentrations have a range of 6 8 58 5 mg kg with a median of 14 4 mg kg the highest as concentrations were found at 15 25 m depth in the meanwhile the range of as concentration in the sediments from background borehole is 3 21 8 mg kg with a median value of 9 mg kg the as sediments concentrations with depth from the sh borehole were correlated with the contents of fe sb b v total c and total s generally the abundance of elements varied with grain size with higher concentrations in finer fractions of the sediments distinct lithology profile and different geochemical characteristics of aquifer sediments indicate the sediments are associated with different sources and diverse sedimentary environments up to one third of arsenic in the sediments could be extracted by ammonium oxalate suggesting that fe oxyhydroxides may be the major sink of as in the aquifer sequential extraction results indicate that arsenic occurs as strongly adsorbed on and or co precipitated with amorphous fe oxyhydroxides in sediments accounting for 35 and 20 respectively of the total contents of arsenic the release of as into groundwater may occur by desorption from the mineral surface driven by reductive dissolution of the fe oxide minerals furthermore small proportions of as associated with iron sulfides occur in the reductive sediments

warm saline bottom water in the ancient ocean considerable isotopic evidence indicates that oceanic bottom water was much warmer in the geological past a simple convection model driven by multiple turbulent buoyant plumes and observations of present deep water formation have led to the development of a theory for the formation of warm saline bottom water it is suggested that changes in the size and configuration of marginal seas in net evaporation zones due to lithospheric plate motions and eustatic sea level change caused these seas to become sources of warm saline bottom water evidence from the palaeotemperature record and palaeogeography during the late cretaceous is used to reinforce the hypothesis climatic and chemical consequences of the formation of warm saline bottom water are discussed

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

the cretaceous palaeogene k p boundary at ain settara tunisia restructuring of benthic foraminiferal assemblages benthic foraminiferal assemblages in contrast to planktic foraminifera generally did not suffer mass extinctions at the cretaceous palaeogene k p boundary extinctions were fewer in deeper water however the outer shelf upper bathyal section at ain settara tunisia records a dramatic change in the structure of benthic foraminiferal assemblages across the k p boundary at the level of extinction of planktic assemblages and enrichment in ir and other geochemical anomalies highly diversified low dominance upper maastrichtian assemblages with infaunal and epifaunal morphogroups were suddenly replaced by taxonomically impoverished assemblages strongly dominated by epifaunal morphogroups this extinction or temporary emigration of most infaunal morphogroups is interpreted to be the result of a sudden breakdown in food supply this in turn is the consequence of a sudden collapse in primary productivity probably resulting from the impact of the k p asteroid

sedimentogenesis and hydrobiogeochemistry of high arsenic late pleistocene holocene aquifer systems geogenic enrichment of arsenic as in groundwater has been a topic of worldwide concern over the past several decades due to the severe health threat to an estimated over one hundred million people despite the genetic diversity and the spatial variability of as concentrations the most common geogenic as enriched groundwater occurs in flat low lying river floodplains and fluvial lacustrine plains within river systems draining the himalaya tectonic movement sedimentological processes and palaeoclimatic optima after the last glacial maximum have created favorable conditions for the formation of high as aquifer systems mainly within the late pleistocene holocene deposits the co deposition of as bearing fe oxides and reactive organic matter within sediments of deltas floodplains or fluvial lacustrine plains forms the premise for as release under reducing geochemical environments however depending on the reactivity of organic matter and as bearing fe oxides as well as the availability of aqueous sulfate geochemical mechanisms controlling as enrichment in the groundwater differ between the coastal floodplains of south and southeast asia and the fluvial lacustrine plains of north and central china the indigenous geomicrobes thriving to adapt to specific aquifer environments may mediate fe s as biogeochemical cycling responsible for as speciation transformation dissolution desorption and hence mobilization hydrologic processes regulated by the local and regional groundwater flow regimes control as transport as well as its spatial distribution special attention must be paid to anthropogenic perturbation from intensive groundwater pumping and land use changes that affect the aquifer hydrological conditions and the biogeochemical processes thus altering groundwater as levels to decipher the patterns of as variation within the aquifers an integrated approach characterizing the major sedimentological hydrobiogeochemical and anthropogenic processes influencing as release and transport needs to be applied to ensure sustainable water supply for domestic and agricultural needs

tsunamis and submarine landslides in suruga bay central japan caused by nankai suruga trough megathrust earthquakes during the last 5000 years abstract magnitude 8 megathrust earthquakes that have generated large tsunamis with wave heights of 5 m in coastal areas of southwestern japan have occurred every 100 150 years along the nankai suruga trough which marks the convergent boundary between the eurasian and philippine sea plates using sedimentological geochemical and paleontological analyses as well as 14c dating we examined tsunami deposits in 12 sediment cores collected from the hamatome lowland yaizu plain shizuoka which faces the suruga trough four sandy tsunami deposits sands 1 4 are identified in sediments deposited during the last 5000 years sand 1 was deposited between 805 and 405 bc suggesting that only one tsunami left a sedimentological imprint in the hamatome lowland lagoon during the period of 4000 years between 3090 and 2913 bc and the ad 1096 eicho tokai earthquake this very low frequency of tsunami inundation may suggest that this tsunami was larger than those typically associated with megathrust earthquakes sands 2 4 are correlated with tsunamis associated with the eicho tokai ad 1361 shohei koan and ad 1498 meio tokai earthquakes respectively our data indicate that a sand spit which had previously protected the lagoon from oceanic waves was abruptly destroyed following the ad 1096 eicho tokai earthquake and did not re form at the same location this disappearance of the sand spit is inferred to have involved an earthquake induced submarine landslide the data presented in this paper together with information obtained from historical documents indicates that m8 megathrust earthquakes in ad 1096 and ad 1498 caused submarine landslides in the study area resulting in coastal subsidence and damage to coastal areas additional to that caused by the tsunamis

arsenic in groundwater testing pollution mechanisms for sedimentary aquifers in bangladesh in the deltaic plain of the ganges meghna brahmaputra rivers arsenic concentrations in groundwater commonly exceed regulatory limits 50 m gl 21 because feooh is microbially reduced and releases its sorbed load of arsenic to groundwater neither pyrite oxidation nor competitive exchange with fertilizer phosphate contribute to arsenic pollution the most intense reduction and so severest pollution is driven by microbial degradation of buried deposits of peat concentrations of ammonium up to 23 mg l 21 come from microbial fermentation of buried peat and organic waste in latrines concentrations of phosphorus of up to 5 mg l 21 come from the release of sorbed phosphorus when feooh is reductively dissolved and from degradation of peat and organic waste from latrines calcium and barium in groundwater come from dissolution of detrital and possibly pedogenic carbonate while magnesium is supplied by both carbonate dissolution and weathering of mica the 87 sr 86 sr values of dissolved strontium define a two component mixing trend between monsoonal rainfall 0 711 6 0 001 and detrital carbonate 0 735

biotic geochemical and paleomagnetic changes across the cretaceous tertiary boundary at braggs alabama exposed near braggs alabama is one of the few well studied nearly continuous shallow marine cretaceous tertiary boundary sections it allows a glimpse of the biotic and environmental changes that occurred in the latest cretaceous to earliest paleocene paleomagnetic strontium isotopic and biostratigraphic data closely constrain the age of a series of lithologic geochemical and biotic variations and suggest that no more than 100 200 ka could be missing at the boundary a major reduction in macrofaunal diversity associated with lithofacies changes occurs prior to but within 300 ka of the nannofossil defined boundary approximately 40 of the apparent faunal reduction is attributed to the lazarus effect faunal and floral assemblages trends in carbon isotopic composition of benthic invertebrates and lithologic characteristics indicate that a latest maestrichtian regression culminated near the boundary chron c29r micula murus zone significantly later than recent estimates water depths at this site remained shallow during the subsequent early paleocene zone np1 transgression and did not reach depths equivalent to those of the late maestrichtian until zone np2 relatively minor climatic changes across the boundary are suggested by a 4 c cooling trend seen in the oxygen isotope paleotemperatures a high resolution 87 sr 86 sr record from well preserved macrofossil calcite shows a pattern of smooth variation and elevated values near the boundary however the early paleocene spike of other workers was not found

biotic turnover in benthic foraminifera across the cretaceous tertiary boundary at el kef tunisia abstract the cretaceous tertiary boundary section exposed near el kef tunisia is the most complete boundary sequence known to date it contains nearly 1 m of black and gray boundary clay containing planktic foraminiferal zone poa b 2 m of clayey shales of p1a globigerina eugubina zone and 4 m of shales and marls of p1b g taurica zone quantitative analysis of the benthic foraminiferal fauna suggests that deposition during the latest cretaceous occurred in an upper slope to outer shelf environment which shallowed at the k t boundary to an outer to middle shelf depth and shallowed further by p1b time to mid shelf depth a major reduction in benthic diversity occurred near the k t boundary with about 50 of the fauna disappearing diversity remained an average of 37 lower during deposition of the first 3 m of sediment above the boundary poa b p1a and productivity was very low surviving and thriving foraminifers during this interval were primarily low oxygen tolerant epifaunal and infaunal species a sharp decrease in the low oxygen tolerant fauna and appearance of a shallow mid shelf fauna at about 4 m above the boundary p1b zone signals a second regression return to higher oxygen levels and higher productivity although the environmental effects of the k t boundary event can be inferred from benthic faunas the ultimate cause remains elusive faunal changes prior to and the long recovery period after the k t boundary are difficult to explain by a single impact hypothesis

high resolution planktonic foraminiferal analysis from the cretaceous tertiary boundary at ain settara tunisia evidence of an extended mass extinction the ain settara section located in the kalaat senan area of north central tunisia spans the cretaceous tertiary k t boundary which is characterized by a red layer and a thin non bioturbated boundary clay sediment accumulation across the k t boundary at ain settara was probably interrupted by three short hiatuses and or condensed sedimentation the first hiatus occurs at the top of the cf1 zone the second hiatus condensation occurred just below the boundary clay and the third hiatus at the p0 p1a boundary in the earliest danian these hiatuses are marked by weak unconformities bioturbation and sudden disappearances appearances of species which are known to disappear evolve sequentially in continuous sections quantitative high resolution planktonic foraminiferal analysis across zones cf1 upper p0 and p1a 1 reveals an extended and selective mass extinction all 41 of the species which disappeared at or below the k t boundary are rare to very rare and primarily ecologically specialized keeled deeper dwelling tropical subtropical forms globotruncana globotruncanita gublerina planoglobulina rosita contusotruncana racemiguembelina their combined relative abundance varies between 10 and 15 of the total population at the end of the maastrichtian the k t crisis thus appears more catastrophic when viewed in tropical subtropical assemblages and based on analysis of larger species 200 m which preferentially includes the more specialized forms though in fact the k t mass extinction actually involved a relatively small part of the foraminiferal population in terms of relative abundance the pattern of extinction and changes in dominant population at ain settara appear to be very similar to the planktonic foraminiferal turnover of the other north central tunisian sections el kef elles the selective mass extinction pattern suggests that the catastrophic effects of the bolide impact superimposed those related to long term environmental changes such as variations in temperature sea level and associated water mass changes