early diageneitc isotopic signal at the cretaceous tertiary boundary israel abstract carbon and oxygen isotope records from carbonate fractions in marls overlying the k t boundary in southern israel are used to interpret paleoenvironmental changes and the history of early diagenetic events in the earliest tertiary the 13c record of the whole rock does not significantly depart from the original values and reflects the global productivity drop shortly after the k t boundary and the subsequent recovery fine fraction oxygen isotope values reflect the addition of carbonate cement highly depleted in 18o throughout the profile the 18o record demonstrates two main episodes in which contact with fresh water affected the sediments one is below a short hiatus at planktic foraminiferal subzone transition po p1a guembelitria cretacea parvularugoglobigerina eugubina and the other at an pyrite rich clay layer near the top to planktic foraminiferal subzone p1b globigerina taurica the latter event suggests introduction of sapropelic bottom conditions in the oceanic paleoenvironment

biogeography of terminal cretaceous deep sea benthic foraminifera from the atlantic and pacific oceans abstract most species of late cretaceous deep sea benthic foraminifera are believed to be cosmopolitan and therefore to exhibit only minor biogeographical differences in this preliminary report six deep sea drilling project dspd sites from different oceans paleolatitudes and paleodepths were analyzed for terminal cretaceous abyssal bathyal benthic foraminifera in order to investigate their assumed cosmopolitan distribution and the question of whether different faunal compositions are related to time different paleolatitudes and or different paleodepths the material studied was obtained from the low latitude site 465 pacific ocean and the intermediate latitude sites 384 north atlantic and 356 516 525 and 527 south atlantic the material analyzed represents a time slice encompassing the last 20 50 k y of the cretaceous the faunas contain numerous velasco type species such as gavelinella beccariiformis white cibicidoides velascoensis cushman nuttallides truempyi nuttall gaudryina pyramidata cushman and various gyroidinoids and buliminids the results contradict the general assumption of the cosmopolitan nature of late cretaceous deep sea benthic foraminifera advocated in the literature only about 9 of the taxa identified were found to be truly cosmopolitan through their occurrence at all the sites analyzed on the basis of correspondence analysis and relative abundance data three assemblages and three subassemblages were recognized 1 a bathyal abyssal assemblage nuttallinella sp a cibicidoides hyphalus fisher valvalabamina sp evolute form and gyroidinoides spp at the south atlantic sites 356 516 525 and 527 divided into three subassemblages namely a a middle bathyal subassemblage eouvigerina subsculptura mcneil and caldwell tritaxia aspera cushman and g pyramidata at sites 516 and 525 b a lower bathyal subassemblage osangularia sp pyramidina rudita cushman and parker and quadrimorphina camerata brotzen at site 356 and c an abyssal subassemblage gyroidinoides sp c hyperammina bathysiphon gyroidinoides beisseli white and globorotalites sp b at site 527 2 an abyssal assemblage buliminella cf plana cushman and parker and bulimina incisa cushman at the north atlantic site 384 and 3 a middle bathyal assemblage vulvulina sp a osangularia navarroana cushman alabamina sp bulimina velascoensis cushman spiroplectammina spp calcereous forms and bulimina trinitatensis cushman and jarvis at the pacific site 465

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

giant ooids in a neoproterozoic carbonate shelf simla group lesser himalaya india an analogue related to neoproterozoic glacial deposits abstract this study is the first comprehensive documentation of giant ooids and related facies associations in the kunihar formation proterozoic simla group lesser himalaya himachal pradesh analysing the understanding of processes and controls on development of giant ooids based on field observations supplemented by outcrop based facies analysis petrography and delineation of environmental variations four facies associations have been delineated i peritidal siliciclastic carbonate fa1 ii shelf lagoon fa2 iii reef complex fa3 iv fore reef slope fa4 deposition of giant ooids and associated facies associations of kunihar formation occurred in a carbonate rimmed shelf with high tidal influence size of giant ooids from kunihar formation is the largest as compared to giant ooids from other geological formations kunihar giant ooids developed when normal ooids were washed from ooid shoals intertidal into slightly deeper regions shallow subtidal resulting in the increased dimension of ooids in suspension due to higher hydrodynamics scanning electron microscopy sem studies support microbial origin of ooids giant ooids and stromatolites of kunihar formation increased microbial activity in kunihar formation is attributed to increase in nutrients by virtue of weathering of underlying darla volcanics abundant carbonate and microbially induced sedimentary structures miss deposition in lower part of simla group points to increased microbial activity which likely increased the volume of oxygen in neoproterozoic atmosphere ushering in ice house conditions during the subsequent deposition of blaini group giant ooids associated with neoproterozoic glacial deposits throughout the world occupy stratigraphic positions below above or between glaciations simla group is another example where giant ooids lie stratigraphically below marinoan blaini tillites increased magmatic activity and weathering before and during the neoproterozoic glaciations increased nutrients in marine waters which increased algal growth thus giant ooids were deposited due to such phases of increased microbial activity before after glaciation and during interglacial periods

the cretaceous tertiary boundary transition in the antarctic ocean and its global implications abstract three antarctic ocean k t boundary sequences from odp site 738c on the kerguelen plateau odp site 752b on broken ridge and odp site 690c on maud rise weddell sea have been analyzed for stratigraphic completeness and faunal turnover based on quantitative planktic foraminiferal studies results show that site 738c which has a laminated clay layer spanning the k t boundary is biostratigraphically complete with the earliest tertiary zones p0 and p1a present but with short intrazonal hiatuses site 752b may be biostratigraphically complete and site 690c has a hiatus at the k t boundary with zones p0 and p1a missing latest cretaceous to earliest tertiary planktic foraminiferal faunas from the antarctic ocean are cosmopolitan and similar to coeval faunas dominating in low middle and northern high latitudes although a few endemic species are present this allows application of the current low and middle latitude zonation to antarctic k t boundary sequences the most abundant endemic species is chiloguembelina waiparaensis which was believed to have evolved in the early tertiary but which apparently evolved as early as chron 30n at site 738c since this species is only rare in sediments of site 690c in the weddell sea this suggests that a watermass oceanographic barrier may have existed between the indian and atlantic antarctic oceans the cosmopolitan nature of the dominant fauna began during the last 200 000 to 300 000 years of the cretaceous and continued at least 300 000 years into the tertiary this indicates a long term environmental crisis that led to gradual elimination of specialized forms and takeover by generalists tolerant of wide ranging temperature oxygen salinity and nutrient conditions a few thousand years before the k t boundary these generalists gradually declined in abundance and species became generally dwarfed due to increased environmental stress there is no evidence of a sudden mass killing of the cretaceous fauna associated with a bolide impact at the k t boundary instead the already declining cretaceous taxa gradually disappear in the early danian and the opportunistic survivor taxa ch waiparaensis and guembelitria cretacea increase in relative abundance coincident with the evolution of the first new tertiary species

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

ecology and paleoecology of triserial planktic foraminifera guembelitrinidae are a group of small sized planktic foraminifera that ranges from the middle cretaceous to the present in this paper we discuss the morphology and stratigraphic distribution of triserial planktic foraminifera and establish the ecology of the living ones to draw parallels with fossil counterparts in surface water plankton pump samples 0 5 m from the north indian ocean the modern representativegallitellia vivans cushman has its highest relative frequencies south of india where upwelling waters cause highly variable conditions on the outer shelf oxygen isotope analysis on specimens from a core taken in the banda sea indonesia indicates thatg vivans belongs to the planktic community and that in open marine circumstances it lives inbetween the surface dwellersglobigerinoides trilobus reuss andglobigerina bulloides d orbigny and the deep dwellinggloborotalia menardii d orbigny similar habitats can be deduced for fossil guembelitrinidae the triserials can live in environments with variable or extreme conditions as exemplified byguembelitria cretacea cushman which is one of the few cretaceous planktic foraminiferal species that survived the cretaceous tertiary boundary event for the most part open ocean sediments contain few specimens but triserials may be common to abundant in assemblages from sediments that represent unstable marine conditions e g el kef tunisia presumed gaps in the stratigraphic range of triserial planktics appear to be a sampling artifact caused by their patchy geographic distribution and their small size only very rare specimens are present in the 63 m fraction we foundguembelitria cretacea to be present in the 45 63 m fraction of coniacian santonian and campanian sediments of a section near el kef tunisia an extensive search of the small sized fractions 63 125 m of samples from various localities and ages showed that the range ofgallitellia vivans can be extended into the late pliocene as a part of this stratigraphic study a new species guembelitria turrita kroon and nederbragt is described from upper campanian lower maastrichtian sediments

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

multiple deep water sources and trophic regimes in the latest cretaceous deep sea evidence from benthic foraminifera benthic foraminifera from 24 dsdp odp sites were investigated to assess their global horizontal and vertical distribution in the deep sea environment at the end of the cretaceous period the samples analyzed are from the late maastrichtian and within the planktic forammiferal abathomphalus mayaroensis zone from a wide range of oceans and paleolatitudes including the low latitude sites 10 and 384 atlantic ocean 47 171 305 and 465 pacific ocean the mid latitude sites 20 111 356 363 516 525 527 548 and 605 atlantic ocean 216 217 and 758 indian ocean and the high latitude sites 208 pacific ocean 689 698 700 738 and 750 southern ocean correspondence analysis based on the 75 most common taxa shows a clear biogeographic trend along the first correspondence axis by arranging the sites in paleolatitudinal order the assemblages from the tethyan realm i e low latitudes are marked by abundant heavily calcified buliminids such as bulimina incisa b trinitatensis b velascoensis and reussella szajnochae and aragonia spp whereas high latitude faunas are characterized by abundant alabamina creta gyroidinoides quadratus and pullenia coryelli the results indicate that the faunas at low and high latitudes respectively were influenced by quite different environmental conditions this is based on the much higher abundance of infaunal morphotypes at low and mid latitudes compared to high latitudes suggesting that the biogeographic trend found in the data set coincides with the trophic regime at the various sites the results also provide support for the hypothesis that postulates two simultaneous sources and mechanisms for deep water formation during the late cretaceous including warm saline deep water produced by evaporation at low equatorial latitudes in contrast to the formation of cold deep waters at high southern latitudes

latest cretaceous to late paleocene radiolarian biostratigraphy a new zonation from the new zealand region the scarcity of records of early paleocene radiolarians has meant that while radiolarian biostratigraphy is firmly established as an important tool for correlation there has been a long standing gap between established zonations for the cretaceous and from latest paleocene to recent it has also led to considerable speculation over the level of faunal change across the cretaceous tertiary k t boundary consequently the discovery of rich and diverse radiolarian assemblages in well delineated k t boundary sections within siliceous limestones of the amuri limestone group in eastern marlborough new zealand is of great significance for biostratigraphy and k t boundary research this initial report is restricted to introducing a new latest cretaceous to mid late paleocene zonation based on the radiolarian succession at four of these sections and a re examination of faunas from coeval sediments at dsdp site 208 lord howe rise three new paleocene species are described amphisphaera aotea amphisphaera kina andstichomitra wero six new interval zones are defined by the first appearances of the nominate species in ascending order these are lithomelissa hoplites foreman zone rk9 cretaceous amphisphaera aotea n sp zone rp1 paleocene amphisphaera kina n sp rp2 stichomitra granulata petrushevskaya rp3 buryella foremanae petrushevskaya rp4 andburyella tetradica rp5 good age control from foraminifera and calcareous nannofossils permits close correlation with established microfossil zonations where age control is less reliable radiolarian events are used to substantially improve correlation between the sections no evidence is found for mass extinction of radiolarians at the end of the cretaceous however the k t boundary does mark a change from nassellarian to spumellarian dominance due to a sudden influx of actinommids which effectively reduces the relative abundance of many cretaceous survivors an accompanying influx of diatoms in the basal paleocene of marlborough together with evidence for an increase of total radiolarian abundance suggests siliceous plankton productivity increased across the k t boundary possible causes for this apparently localised phenomenon are briefly discussed

trace element and stable c o and radiogenic sr isotope geochemistry of stromatolitic carbonate rocks of the mesoarchaean pongola supergroup implications for seawater composition abstract the mesoarchaean pongola supergroup hosts one of the oldest well preserved stromatolitic carbonate successions major and trace element geochemistry along with c o and sr isotopic analyses of three stratigraphic sections of stromatolitic carbonate rocks were undertaken in order to infer the depositional environment and to unravel the chemical characteristics of contemporaneous seawater the carbonate rocks consist mainly of dolomite and to a lesser extent ankerite their variable sr concentrations of 95 to 450 mg kg are interpreted as resulting from early to late dolomitization of metastable carbonates aragonite and or high mg calcite facies control and calcitization during meteoric diagenesis 18o values range from 19 6 to 12 0 vpdb and reflect recrystallization of carbonates caused by high water rock interactions during diagenesis and metamorphism a 13c value of 2 5 vpdb was measured in carbonate samples least affected by alteration and we suggest that it approximates the composition of dissolved inorganic carbon in coeval seawater the samples display variable 87sr 86sr isotopic ratios from as low as 0 708 to 0 777 these ratios are considerably higher than those expected in archaean open ocean water masses buffered by hydrothermal interaction with the mantle we interpret the highly radiogenic sr isotopic ratios in some carbonate samples to reflect isotopic exchange with radiogenic sr from siliciclastic volcaniclastic components in the samples and fluids from clay rich layers intercalated with the carbonates the least radiogenic sr isotopic ratio may approximate the mixed isotopic composition of seawater in the epicontinental basin and of riverine freshwater draining the kaapvaal craton the dolomitic carbonate samples show shale normalized rare earth element and yttrium distribution patterns that resemble those of modern ocean water with positive lasn gdsn and ysn anomalies superchondritic y ho ratios a small negative cesn anomaly and depleted light rare earth elements relative to the heavy rare earth elements these anomalies are not as pronounced as expected for an open marine setting which together with the sr isotopic results support a more restricted setting with riverine input and fluctuations in marine ingressions a convex upward shale normalized rare earth element and yttrium pattern is probably a result of several factors including organic matter complexation and element fractionation during estuarine mixing the small negative cesn anomaly may suggest small amounts of free oxygen in shallow waters due to local oxygenic microbial activity

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

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

recent benthic foraminifera from the continental margin of northwest africa community structure and distribution abstract sediment grab samples were collected at 107 locations along the continental margin of northwest africa these samples form a series of depth transects between the straits of gibraltar and dakar senegal the greater than 250 m size fraction was retained for a census of both the live and dead foraminifera after deleting trace occurrences jaccard and correlation coefficient based cluster analyses were performed to decipher the community structure for this margin the geographic distribution of the four major faunal provinces recognized is conventional in that for both the live and dead assemblages three are related to depth upper slope and shelf middle slope and lower slope and continental rise the biotopes and thanatotopes within these provinces are strongly restricted along vertical or latitudinal boundaries when the data are analysed using jaccard coefficients dendrograms constructed from correlation coefficients emphasize depth related faunal communities dominant species such as cibicides lobatulus trifarina fornasinii planulina ariminensis uvigerina finisterrensis and c wuellerstorfi are generally distributed within a definite depth range along this margin and strongly influence the correlation coefficient based dendrograms other distributions are clearly not depth related but correspond to various environmental variables for example cancris auriculus coarse substrate bolivina subaenariensis oxygen minimum cibicidoides kullenbergi and hoeglundina elegans low organic carbon uvigerina peregrina is also a notable exception to depth dependence in that this dominant species and the province it represents are generally confined to the continental slope south of cape blanc its preference for that region may arise from the high organic carbon and fine grain size of the sediment there from low salinity of the bottom water or from other unknown variables the most important vertical faunal boundary occurs between cape barbas and cape blanc between 22 and 21 n latitude in contrast the canary island ridge intersects the continental margin at a saddle depth of about 1500 m but that physiographic barrier has little effect on provincialism of the deep water benthic foraminifera

a low extinction rate of intermediate water benthic foraminifera at the cretaceous tertiary boundary the contrast between the high extinction rates of calcareous marine plankton and low extinction rates of deep water calcareous benthic foraminifera across the cretaceous tertiary k t boundary is now recognized however the water depth at which the vertical change in extinction rates of marine organisms occurred at the k t boundary is not yet known because of the lack of data on the extinction rates of intermediate water organisms the extinction rate of intermediate water benthic foraminiferal species from kawaruppu hokkaido japan was determined by distinguishing locally extinct species a distinctly low extinction rate 10 for calcareous benthic foraminiferal fauna from the upper part of the intermediate water is documented for the first time this rate is almost equal to the extinction rate of deep water benthic foraminifera 10 and is much smaller than the planktic foraminiferal extinction rate 81 the extinction rate curve for calcareous foraminifera in a vertical water column indicates that a rapid change from a high extinction rate 80 to a low extinction rate 10 took place at a water depth of about 150 m this depth of change is equivalent to the boundary depth between the surface and intermediate waters and between the euphotic and aphotic zones furthermore this coincidence is consistent with the hypothesis that acid rain and a darkness induced breakdown of the marine food chain produced by a cometary or asteroidal impact at the k t boundary were the main causes of the mass extinction of calcareous planktic organisms in surface waters

paleocology of late maastrichtian heterohelicidae planktic foraminifera from the atlantic region abstract late maastrichtian planktic foraminiferal heterohelicidae from deep sea drilling project sites in the northwestern atlantic 111 and 605 the south atlantic 356 and 357 and from mediterranean land sections near e1 kef tunisia and caravaca spain show two bioprovinces site 111 has transitional heterohelicid faunas in which a few heterohelix species dominate while the other localities have diverse tethyan faunas a quantitative analysis allows for a more detailed subdivision within the tethyan faunas heterohelicid species occur in different relative frequencies at the south atlantic the north atlantic and the mediterranean localities the south atlantic dsdp sites contain heterohelix rajagopalani govindan in addition to all other tethyan species the faunas from the two mediterranean sections are comparable however the overall diversity at el kef is the lowest of all tethyan sections and the area is interpreted as representing paleo upwelling the otherwise diverse faunas from the north atlantic site 605 contain some transitional elements which suggests mixing with cooler surface waters possibly derived from a proto labrador current

latest paleocene lithologic and biotic events in neritic deposits of southwestern new jersey in the southwestern new jersey coastal plain four drill holes contain continuous neritic sedimentation across the paleocene eocene boundary calcareous nannofossil zone np 9 np 10 boundary significant lithologic and biotic changes occur in these strata near the top of the paleocene global warming increased precipitation and other oceanographic and climatic events that have been recognized in high latitude deep oceanic deposits of the latest paleocene also influenced mid latitude shallow marine and terrestrial environments of the western north atlantic the diverse well preserved calcareous nannofossil flora that is present throughout the entire new jersey boundary section accurately places these events within the uppermost part of the upper paleocene zone np 9 several rapid but gradational changes occur within a 1 1 m interval near the top of zone np 9 the changes include 1 a change in lithology from glauconitic quartz sand to clay 2 a change in clay mineral suites from illite smectite dominated to kaolinite dominated 3 a change in benthic foraminiferal assemblages to a lower diversity fauna suggestive of low oxygen environments 4 a significant increase in planktonic foraminiferal abundance and 5 an increased species turnover rate in marine calcareous nannofossils pollen was sparse in the new jersey drill holes but terrestrial sporomorph species in virginia exhibit increased turnover rates at a correlative level foraminiferal assemblages and lithology indicate that relative sea level rose in new jersey at the same time as these late paleocene events occurred in late biochron np 9 the higher sea levels influenced sediment type and absolute abundance of planktonic foraminifers in the deposits above the initial increase of kaolinite in the upper part of zone np 9 the kaolinite percentage continues to increase and the maximum kaolinite value occurs in the uppermost part of zone np 9 there are few changes in either the sediments or the biota precisely at the zone np 9 np 10 boundary in new jersey the clay rich deposits with a high kaolinite clay mineral suite the lowered diversity benthic foraminiferal assemblages the abundant planktonic foraminiferal specimens and the calcareous nannofossil assemblages continued essentially unchanged into the earliest eocene zone np 10 within the lower part of zone np 10 the kaolinite percentage decreased to very low values

the ecology of living stained deep sea benthic foraminifera from the sulu sea the distribution of living rose bengal stained deep sea benthic foraminifera was determined in the upper 20 cm of sediments of eight soutar box cores taken from two depth transects 510 4515 m in the thermospheric 10 c sulu sea despite the uniformity of bottom water temperatures salinities and dissolved oxygen levels below 1000 m significant faunal differences exist at different depths in the low oxygen 1 25 ml l below 1000 m basin the shallowest site 510 m is dominated 10 of the calcareous fauna by cibicidoides uvigerina 150 m and bolivina 63 m while siphonina is codominant with cibicidoides and uvigerina in the 1005 m core the 2000 m cores are dominated by cibicidoides gyroidinoides and oridorsalis while cibicidoides bradyi and oridorsalis umbonatus dominate the 3000 and 4000 m cores infaunal assemblages of valvulineria mexicana are found in the sediments of the 4515 m core relatively low bottom water oxygen values do not necessarily yield typical low oxygen taxa such as bolivina uvigerina chilostomella bulimina and globobulimina changes in the abundances of these taxa in fossil assemblages have been used as indicators of changes in ancient bottom water oxygen levels but may instead reflect organic carbon contents of the sediments an examination of the vertical distributions of foraminiferal assemblages from the 63 m and 150 m fractions reveals that taxa have microhabitat preferences similar to those observed in other regions taxa found in the upper 0 to 1 cm interval epifaunal include cibicidoides wuellerstorfi and hoeglundina elegans while taxa such as chilostomella and globobulimina reach maximum abundances in subsurface sediments and have infaunal microhabitat preferences cibicidoides bradyi and o umbonatus live in sediment depths from 0 to 4 cm and have transitional preferences with both epifaunal and infaunal occurrences intrageneric differences in test morphologies including pore distribution rounded peripheries and variable spire height are observed in cibicidoides and gyroidinoides and are suggested to be related to microhabitat preferences vertical distributions of a number of taxa found in both the 63 to 150 m and 150 m fractions are similar suggesting that juveniles and adults live under similar microhabitat conditions ontogenetic changes in microhabitat preferences of most species are not observed in this study and therefore would not be expected to account for isotopic vital effects reported for some taxa in previous studies

high resolution profile of stable isotopes and iridium across a k t boundary section from koshak hill mangyshlak kazakhstan oxygen and carbon isotopes were measured to a high depth resolution in a nannoplankton carbonate sequence spanning the cretaceous tertiary boundary at koshak hill mangyshlak peninsula kazakhstan the boundary is characterized by the presence of a 1 cm thick clay layer having a sharp peak in iridium concentration with a maximum value of 3 7 ng g 1 the 18 o data reveal rapid 10 3 years excursion of sea surface temperature at the boundary where an initial cold pulse is followed by a persistent warm period the 13 c data in contrast indicate only a gradual change in productivity across the boundary the observations suggest a biogeochemical scenario for the boundary event pertaining to shallow epicontinental seas

atmospheric circulation upwelling and organic rich rocks in the mesozoic and cenozoic eras abstract by using the basic principles of atmospheric circulation and analogies from present circulation patterns it is possible to construct qualitative atmospheric circulation models on paleogeographic maps the wind patterns predicted by these models then serve as the basis for predicting the locations of ancient upwelling zones atmospheric circulation and upwelling models for seven geologic stages in the mesozoic and cenozoic were constructed and the distribution of the upwelling zones compared with the distribution of organic rich rocks for all time periods together the correlation was statistically significant when the individual time periods were analyzed separately the following pattern emerged significant correspondence between upwelling zones and organic rich rocks in the triassic middle early cretaceous to late cretaceous and middle paleogene to neogene no significant correspondence was found for the intervening times upwelling does not account for all organic rich rocks so called anoxic oceanic events and transgressions play an important role in their deposition it is suggested that upwelling contributes significantly to the pattern of organic rich rock distribution and is important in determining organic facies

late proterozoic aragonitic cement crusts bambui group minas gerais brazil the late proterozoic pedro leopoldo facies bambui group in the vicinity of belo horizonte brazil comprises alternating laminated microsparitic limestones 10 35 mm thick beds and fibrous limestones 10 55 mm thick the latter are composed of a mosaic of sparry calcite crystals these irregularly crosscut rays and fans are composed of feathery precursor crystal bundles with squared off growth zones ghosts of an original fibrous mineral hexagonal in cross section are visible the petrographic characteristics very high strontium content and low magnesium content of the fibrous beds as well as microspar beds strongly argue for an original aragonitic mineralogy the rays are interpreted as having formed by precipitation at the sediment water interface whereas the micrite was precipitated from the water column prior to deposition on the sea floor the lack of emergence features suggests widespread aragonite precipitation under persistently subtidal conditions

k t boundary extinction geologically instantaneous or gradual event evidence from deep sea benthic foraminifera a stepped pattern of benthic foraminiferal decimation survival and recovery identified across the cretaceous tertiary k t boundary at caravaca southeast spain suggests that an exceptionally large influx of nutrients reached the sea floor suddenly at the time of the k t extinction event rapid reestablishment of pre k t boundary environmental conditions followed our data demonstrate a close coupling between the collapse of the ecologic system in the upper water column at caravaca and a correspondent decimation of bottom dwellers on the sea floor the dramatic environmental collapse of deep water benthic foraminiferal communities at the end of the cretaceous at caravaca suggests that the k t boundary event was geologically instantaneous and catastrophic

synsedimentary diagenesis in a cryogenian reef complex ubiquitous marine dolomite precipitation abstract analysis of the synsedimentary diagenetic phases from a pervasively dolomitised cryogenian 650 ma reef complex south australia reveals a fundamentally different style of marine diagenesis to that of phanerozoic carbonates textural evidence from dolomitised and undolomitised lithologies of the oodnaminta reef complex indicates that depositional components were precipitated initially as calcium carbonate aragonite and calcite dissolution textures and preserved fabrics in ooids indicate an originally aragonitic mineralogy early fibrous marine cements that have well preserved fibrous crystallographic fabrics with a length fast optical character are likely to have precipitated as high magnesium calcite however following this very early phase of diagenesis the dominant marine process occurring in these reefs was dolomite precipitation this involved the dolomitisation of earlier depositional and diagenetic phases as well as the precipitation of fibrous dolomite cements these fibrous marine cements include the newly described radial slow fascicular slow radiaxial slow and rhombic dolomite cements the cements have optical properties chemical zonation and cathodoluminescent characteristics indicating that they were direct marine precipitates dolomite precipitation during marine diagenesis in this reef complex suggests that the oceans of the cryogenian were chemically different to those of the phanerozoic abundant dolomite formation appears to be linked to anoxic magnesium rich seawater during this time marine dolomite precipitation under these conditions may explain the abundance of dolomite in the precambrian sedimentary record

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

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

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

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

secular variation of calcium carbonate mineralogy an evaluation of ooid and micrite chemistries three ooid types are recognized from the lower tournaisian kohlenkalk shelf facies at velbert germany ooids from this unit have a predominantly concentric laminae fabric radial concentric and small radial fibrous ooids are minor components to this oolite the diagenetic response of kohlenkalk ooid chemistry is significantly different from that observed in contemporaneous crinoid and brachiopod material fabric evidence suggests that radial concentric and radial fibrous ooids were probably originally aragonite high mg calcite and high mg calcite respectively fabric and trace elemental chemistries of the concentric fabric ooids suggests that they were originally precipitated as aragonite and subsequently altered to low mg calcite

how complete are cretaceous tertiary boundary sections a chronostratigraphic estimate based on graphic correlation cogent interpretations of data bearing on the cretaceous tertiary k t extinction controversy depend on the existence of accurate chronostratigraphic models for the various k t boundary sections we have employed the graphic correlation technique to summarize biostratigraphic and lithostratigraphic data from 15 intensively sampled k t boundary sections within a common chronostratigraphic model our results indicate that almost all of these sections along with 13 additional boundary sections not used to construct the model contain prolonged and in many cases multiple hiatuses of these 28 boundary sections only six were found to contain a continuous record of sediment accumulation across the k t boundary itself these six k t complete sections are el kef tunisia agost spain caravaca spain and three sections along the brazos river texas a comparative analysis of hiatus distributions among these 28 k t boundary sections also reveals the presence of systematic differences between continental shelf and deep sea depositional environments the lower danian interval immediately following the k t boundary and extending into biochronozones p0 and p1a is typically missing from the deep sea whereas boundary sections deposited in shallower middle neritic to upper slope environments are in most cases complete across the k t boundary these shallow neritic boundary sections however are in many instances disrupted by hiatuses at the p0 p1a boundary and again in the upper part of zone p1a these differential patterns of hiatus distribution between deep sea and continental shelf depositional settings appear to be linked to sea level fluctuations our data suggest that the apparently sudden mass extinction of planktonic foraminifera and anomalies in the occurrence of geochemical tracers that are characteristic of the k t boundary in deep sea sections may be artifacts of a temporally incomplete deep sea stratigraphic record

sr and nd isotopic and trace element compositions of quaternary volcanic centers of the southern andes isotopic compositions of samples from six quaternary volcanoes located in the northern and southern extremities of the southern volcanic zone svz 33 46 s of the andes and from four centers in the austral volcanic zone avz 49 54 s range for 87sr 86sr from 0 70280 to 0 70591 and for 143nd 144nd from 0 51314 to 0 51255 the ranges are significantly greater than previously reported from the southern andes but are different from the isotopic compositions of volcanoes in the central and northern andes basalts and basaltic andesites from three centers just north of the chile rise trench triple junction have 87sr 86sr 143nd 144nd la yb ba la and hf lu that lie within the relatively restricted ranges of the basic magmas erupted from the volcanic centers as far north as 35 s in the svz of the andes the trace element and sr and nd isotopic characteristics of these magmas may be explained by source region contamination of subarc asthenosphere with contaminants derived from subducted pelagic sediments and seawater altered basalts by dehydration of subducted oceanic lithosphere in the northern extremity of the svz between 33 and 34 s basaltic andesites and andesites have higher 87sr 86sr rb cs and hf lu and lower 143nd 144nd than basalts and basaltic andesites erupted farther south in the svz which suggests involvement of components derived from the continental crust in the avz the most primitive sample high mg andesite from the southernmost volcanic center in the andes 54 s has sr and nd isotopic compositions and kr b and ba la similar to morb the high la yb of this sample suggests formation by small degrees of partial melting of subducted morb with garnet as a residue samples from centers farther north in the avz show a regionally regular northward increase in sio2 k2o rb ba ba la and 87sr 86sr and decrease in mgo sr kr b rb cs and 143nd 144nd suggesting increasingly greater degrees of fractional crystallization and associated intra crustal contamination

dynamics of anoxia abstract a simple steady state one dimensional advective diffusive model of the ocean s coupled carbon oxygen and phosphorous system is developed the model is an extension of wyrtki s 1962 model of the oxygen distribution the occurrence of anoxia requires two conditions 1 sufficiently high productivity and 2 sufficiently low oxygen concentration in the bottom water it is shown that anoxic layers are most likely to occur fairly high in the water column anoxic events may be associated with timesof vigorous thermohaline circulation in contrast to stagnation arguments often invoked the model results are used to interpret both modern and ancient oceanic anoxic events

ooids and cements from the late precambrian of the flinders ranges south australia abstract both fabric and geochemical evidence suggest that the oolite units of the late precambrian trezona formation had both aragonitic and calcitic precursors ooids inferred to be originally aragonitic occur as ooid molds filled by blocky ferroan calcite and as calcitized ooids of neomorphic spar the former are occassionally deformed forming irregular shapes and the calcitized ooids have elevated sr concentration of between 3 000 ppm to 5 000 ppm some of the interparticle cements associated with these ooids have high sr concentrations of between 2 000 ppm 5 000 ppm the fabrics of these cements include clear calcite mosaics and poikilotopic spar the precursor mineralogy and genesis of these cements remain uncertain and various possibilities are evaluated the majority of ooids have micritic and microsparitic fabrics with clear sparry calcite replacing the central cortical parts of the ooids the precursor mineralogy of these ooids is not interpretable with the confidence of the aragonitic ooids in some of the micritic ooids the replacing spar has microdolomite inclusions this might indicate a high mg calcite precursor but the process responsible for the retention and concentration of the mg is not known the sr content of these micritic ooids is between 600 and 1 500 ppm the micritic ooids invariably have cloudy bladed to subgranular isopachous cements with sr content of 800 1 200 ppm

extended period of extinctions across the cretaceous tertiary boundary in planktonic foraminifera of continental shelf sections implications for impact and volcanism theories discussion and reply

geochemical evidence for suppression of pelagic marine productivity at the cretaceous tertiary boundary the normal biologically productive ocean is characterized by a gradient of the 13c 12c ratio from surface to deep waters here we present stable isotope data from planktonic and benthic micro fossils across the cretaceous tertiary boundary in the north pacific which reveal a rapid and complete breakdown in this biologically mediated gradient the fluxes of barium a proxy for organic carbon and caco3 also decrease significantly at the time of the major marine plankton extinctions the implied substantial reduction in oceanic primary productivity persisted for 0 5 myr before the carbon isotope gradient was gradually re established in addition the stable isotope and preservational data indicate that environmental change including cooling began at least 200 kyr before the cretaceous tertiary boundary and a peak warming of 3 c occurred 600 kyr after the boundary event

calcareous nannofossils at the k t boundary el kef no evidence for stepwise gradual or sequential extinctions a detailed quantitative study of well preserved nannofossil assemblages in closely spaced samples across the cretaceous tertiary k t boundary at el kef tunisia reveals no extinctions of nannoplankton in the uppermost 4 m of maastrichtian marls as has been reported for planktonic foraminifers from the same samples nannofossil assemblages below the boundary show no trends to indicate that ecologic stresses such as temperature change foreshadowed the k t event in the tethyan region on the other hand the disappearance of several species of the more depth sensitive planktonic foraminifers below the boundary at el kef is probably the result of sea level regression or sampling effects rather than preboundary climate change or other environmental stresses cretaceous nannofossil specimens present above the k t boundary at el kef are interpreted to have been reworked rather than having survived the k t event this interpretation is suggested by abundance patterns of common cretaceous species and a correlation with short term sea level lowstands

the precambrian cambrian boundary seawater chemistry ocean circulation and nutrient supply in metazoan evolution extinction and biomineralization this paper reviews the evidence for changes in the global environment from the late precambrian into the cambrian against which the evolution of many metazoan groups and the development of biomineralization should be seen with higher carbon dioxide levels precambrian seawater was more supersaturated with respect to caco 3 than phanerozoic seawater and carbonates were precipitated easily from the late precambrian to the early cambrian there was a decrease in the mg ca ratio and an increase in the a co 2 of seawater changes in global climate icehouse to greenhouse and increased plate tectonic activity resulted in major changes in ocean circulation and nutrient levels a rise in global temperature and the formation of extensive shallow seas the vendian cambrian radiation events and onset of biomineralization must have been strongly influenced if not driven by these global environmental changes

paleoproductivity from benthic foraminifera abundance glacial to postglacial change in the west equatorial pacific surface productivity is correlated with the rate of accumulation of benthic foraminifera on the deep sea floor as a rule of thumb for each 1 mg of organic carbon arriving at the sea floor one benthic foram shell 150 m is deposited the correlation can be used to reconstruct organic flux to the sea floor in the past and hence the productivity of past oceans applying the appropriate equations to box core data from the ontong java plateau in the western equatorial pacific we found that productivity during the last glacial maximum exceeded present productivity by a factor of between 1 5 and 2 0 with intermediate values for the mid transition period accumulation of benthic foraminifera was depressed on top of the plateau during the glacial and transitional period presumably because increased winnowing removed part of the food supply

neoproterozoic aragonite dolomite seas widespread marine dolomite precipitation in cryogenian reef complexes the extraordinary abundance of dolomite in the proterozoic challenges our understanding of precambrian marine environments here we show that synsedimentary marine dolomite precipitation was pervasive within cryogenian reef complexes from the adelaide fold belt south australia although these reefs are composed of dolomite textural evidence indicates an originally aragonitic mineralogy for depositional components in common with many other neoproterozoic carbonates allochthonous slope debris from the reefs invariably contains both limestone and dolomite clasts indicating synsedimentary dolomitization in the reefs we describe several new forms of fibrous marine dolomite cement from the reefs that have a length slow optical character these fascicular slow radial slow and rhombic dolomite cements have finely preserved cathodoluminescent growth zones and optical characteristics that indicate they originally precipitated as dolomite rather than replacing calcite or aragonite cements abundant early marine dolomite precipitation implies a radically different seawater chemistry for the cryogenian perhaps these aragonite dolomite seas are associated with extreme neoproterozoic glacial events and or ocean anoxia

the impact of paleocene eocene boundary events on middle neritic benthic foraminiferal assemblages from egypt abstract a 25 m upper paleocene to lower eocene marly sequence exposed at gebel duwi quseir red sea coast of egypt provides a good opportunity for studying paleocene eocene p e boundary stratigraphy and events various bio eco and isotope stratigraphic correlations accurately delineate the position of the p e boundary i e the level of stable isotopic excursions and deep sea benthic extinctions in the middle part of this section within zones p5 and np9 in this paper the impact of p e boundary environmental perturbations on benthic foraminiferal communities of the shallow tethyan shelf is examined benthic foraminiferal assemblages from gebel duwi characterized by large frondicularia phosphatica and f nakkadyi in addition to a number of other neritic taxa but without any typical outer neritic bathyal taxa suggest middle neritic 75 100 m deposition throughout the studied interval and only minor relative sea level variations perhaps some 10 20 m across the boundary sea level appears to have been stable yet a distinct faunal turnover marks the p e boundary of this shallow site which in contrast to deep sea records is less abrupt being preceded by a gradual diversity decrease starting some four meters below the boundary moreover most exits are either local or just temporary and thus not true extinctions many lazarus taxa reappear at some point above the boundary while all but one of the disappearing taxa are known from other lower eocene neritic deposits in egypt in general benthic foraminiferal assemblages display low diversities and high dominance values notably anomalinoides aegyptiacus up to 74 suggesting high levels of environmental stress at the sea floor in combination with occasionally very high p b ratio s up to 98 p and generally laminated sediments the character of the benthic assemblage points to a strong influence of recurrent dysoxia and or anoxia we suggest that these resulted from surface eutrophication by intermittent coastal upwelling and reduced ventilation of the bottom environment although these conditions prevailed during most of the time interval studied they were most severe during the latest paleocene and early eocene when eutrophication intensified and the organic carbon flux to the sea floor increased enhanced atmospheric contrasts between the tethys seaway and the african continent resulting in intensified longshore tradewinds may have controlled these changes at the p e boundary the bottom environment became minimally ventilated perhaps due to reduced oxygen advection from deeper waters three meters above the boundary a succession of increasingly diverse assemblages indicate a gradual decrease of environmental stress and a return to more normal conditions although the organic carbon flux to the sea floor remained high

paleoproductivity the benthic planktonic ratio in foraminifera as a productivity index abstract when the effects of differential dissolution are excluded the benthic to planktonic ratio in deep sea foraminifera can be read as a productivity index for pelagic conditions we use the bz index which is the product of the benthic planktonic ratio in percent and the depth of deposition which controls supply of organic matter for hemipelagic conditions we use bz d which is the product of the bz value and a factor for proximity to the shore square root of distance from land which controls coastal productivity anomalous values readily stand out from the normal populations which cluster around typical values of bz or bz d off northwest africa wherever calcite dissolution can be excluded as a factor because of presence of aragonite these anomalies are due to lateral supply of redeposited organic matter

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

carbon isotopes and precambrian cambrian boundary geology south australia ocean basin formation seawater chemistry and organic evolution a carbon isotope stratigraphy from the lowest cambrian strata in the adelaide fold belt of south australia is interpreted in terms of the geological context of the sequence major transgression developing circulation patterns and upwelling resulting from an adjacent opening ocean and biomass increases stemming from the cambrian radiation event there is also evidence from the textures of ooids and cements in late precambrian cambrian strata for subtle variations in seawater chemistry across the boundary and these may well have been instrumental in the development of calcareous skeletons in the early metazoans

sedimentology diagenesis and stratigraphic occurrence of giant ooids in the ediacaran rainstorm member johnnie formation death valley region california the rainstorm member of the late neoproterozoic johnnie formation contains several distinctive features of possibly regional to global significance the johnnie oolite an incised valley with a carbonate breccia fill and an enigmatic bed of giant ooids the rainstorm giant ooids although the johnnie oolite and the incised valley occur in most johnnie formation outcrops scattered throughout the death valley region the giant ooids have only been observed in one area restricted to the southern nopah range if these giant ooids were deposited as part of the rainstorm member they would represent the youngest known occurrence of neoproterozoic giant ooids and the only such unit deposited after the last precambrian glaciation the gaskiers however since the giant ooid bed is associated with the incised valley fill it could simply be a large block of oolite derived from the stratigraphically lower beck spring dolomite known to contain giant ooids this study uses mapping petrography and isotope geochemistry to compare giant ooids from the rainstorm member and the beck spring dolomite with the goal of determining the provenance of the rainstorm giant ooids all lines of evidence suggest that the rainstorm giant ooids form a unit distinctly different from those of the beck spring dolomite carbon isotope values from the ooid bed indicate that it was probably deposited after the shuram 13 c excursion making this the youngest known precambrian giant ooid unit the most plausible explanation for this bed is that it is a raft derived from a so far unobserved pre incision rainstorm member giant ooid bed which would also have been the source of many of the giant ooid clasts in the incision breccia

the depth dependency of planktonic benthic foraminiferal ratios constraints and applications abstract study of the ratio between planktonic and benthic foraminifera in a great number of areas shows that variation of this ratio with depth can be described using organic matter flux equations essentially the share of benthic foraminifera in the total association is inversely proportional to depth as is the amount of organic matter resulting from primary productivity reaching the sea bottom variation in the p b ratio from area to area appears to be strongly dependent on the amount of inbenthic living foraminifera if the ratios are corrected for this the regressions between the proportion of planktonic foraminifera p and depth appear to be near identical in the gulf of mexico the gulf of california the west coast of the usa and the adriatic sea this regression can be described by depth e 3 58718 0 03534 p a study of the behaviour of this function in nine cores from the adriatic upper quaternary reveals that the palaeodepth reconstructions are not influenced by fluctuations in productivity and temperature but that they are significantly influenced by redeposition of fine grained deposits

petrology and diagenetic evolution of neoproterozoic ooids libby formation western montana u s a abstract radial concentric and twinned sparry ooids from the upper belt supergroup originally formed as mixed mg calcite and aragonite and aragonite textural evidence suggests that mg calcite ooids may have formed along with the ooids having an original aragonite mineralogy strontium concentrations of 2400 to 2900 ppm support an aragonitic precursor to the twinned sparry ooids and sr values of 2500 ppm strongly suggest that the radial concentric ooids had an aragonitic component in addition to the mg calcite suggested by the preserved fabric trace element mn mg fe and sr values of ooids and early carbonate cements suggest that diagenetic trends for these proterozoic carbonates are similar to those established for their phanerozoic and archean counterparts mg fe and mn increase and sr decreases with successively later carbonate phases

selective extinction and survival across the cretaceous tertiary boundary in the northern atlantic coastal plain the inner atlantic coastal plain in new jersey and the delmarva peninsula is underlain by an upper cretaceous lower tertiary sequence of marine and paralic sand clay and glauconitic beds campanian maastrichtian danian and thanetian deposits are especially fossiliferous and yield a succession of marine faunas that reveal a pattern of selective extinction and survival across the cretaceous tertiary k t boundary in this area cretaceous benthic invertebrate communities are dominated by oysters and other semi infaunal and infaunal molluscs with planktotrophic larval stages these are replaced in the danian by brachiopod dominated communities that are composed of epifaunal benthos with a variety of nonplanktotrophic reproductive strategies a similar pattern is observable in the nektonic cephalopod populations in this sequence the typical ammonites of the cretaceous became extinct at the k t boundary whereas the nautilids survived ammonites are thought to have had a planktotrophic larval stage whereas nautilids are known to lay large lecithotrophic eggs this pattern of differential survival is attributed to the planktonic population crash at the k t boundary which placed planktotrophically reproducing species at a disadvantage while favoring the varied groups that practiced alternative reproductive strategies

gradual mass extinction species survivorship and long term environmental changes across the cretaceous tertiary boundary in high latitudes stable isotope and planktic foraminiferal analyses across the cretaceous tertiary k t boundary transition at nye klov indicate longterm oceanic instability associated with global sea level fluctuations a gradual mass extinction and decreased magnitude of the 13 c shift in high latitudes oceanic instability which began at least 100 kyr before the k t boundary and continued for about 300 kyr into the tertiary was accompanied by a gradual faunal turnover the maximum sea level lowstand during latest maastrichtian is recorded about 75 cm below the k t boundary a sea level rise first in evidence at 20 cm to 40 cm below the boundary continued into zone p0 boundary clay this sea level rise was accompanied by 2 c of cooling in surface and bottom waters prior to the k t boundary 13 c values remained relatively stable up to 10 cm below the k t boundary a negative shift of 0 5 to 1 0 per mil occurred in the boundary clay in both planktic and benthic foraminifera the surface to deep 13 c gradient remained nearly unchanged in contrast to low latitudes where this gradient is virtually eliminated no sudden mass extinction occurred in this cosmopolitan high latitude fauna and nearly all cretaceous taxa thrived well into the tertiary when they gradually disappeared shallow seas dominated by cretaceous survivor taxa and a well developed oxygen minimum zone prevailed during the earliest tertiary short term sea level lowstands are marked by hiatuses at the top of zones p0 and p1a about 50 kyr and 230 kyr after the k t boundary respectively rising sea level reestablished normal marine conditions about 300 kyr to 350 kyr after the k t boundary coincident with the first post k t boundary recovery of the tertiary fauna and extinction of cretaceous survivors during this time high latitude regions temporarily acted as centers of origin and dispersal for planktic foraminifera long term oceanic instability gradual faunal turnover absence of a sudden mass extinction and greatly diminished 13 c shift in high latitudes suggest that a k t boundary bolide impact was not the primary cause for the k t boundary faunal transition moreover these data strongly imply that the destructive effects of the bolide impact would have been greatest in low latitudes and negligible in high latitudes

oceanic anoxia at the cretaceous tertiary boundary supported by the sulfur isotopic record abstract a temporary and drastic increase in 34s 32s ratio of whole rock sulfide has been recognized just at the cretaceous tertiary boundary within the continuous marine sedimentary sequence of the kawaruppu section in eastern hokkaido japan the apparent extent of fractionation with respect to inferred contemporaneous seawater sulfate in the anomaly zone which includes the boundary claystone at the bottom lies in the range of 25 10 whereas that in the lower and upper siltstone strata is roughly twice as much giving the values in the range of 49 10 the former is quantitatively equivalent in magnitude with the range of kinetic isotope effect in bacterial dissimilatory sulfate reduction and the latter with the typical variation range as observed in sedimentary diagenetic sulfides in ordinary oxic marine basins the present data would strongly support the temporary occurrence of an aerobe free anoxic oceanic sedimentary environment beginning just at the cretaceous tertiary boundary and continuing for approximately 70 000 years probably as a consequence of a certain catastrophic event responsible for the terminal cretaceous mass extinction

new constraints on early tertiary palaeoproductivity from carbon isotopes in foraminifera one of the most pronounced features of marine sections at the cretaceous tertiary k t boundary is the negative excursion in biogenic carbonate 13c in the early tertiary carbon isotope record1 9 the coincidence of this excursion with the elimination of many marine plankton species supports predictions that large scale reduction of primary productivity in the oceans would disrupt the biological carbon pump resulting in a diminished surf ace to deep 13c gradient10 13c carbonate accumulation rates and other geochemical indices support the idea that the oceans were less productive in the early palaeocene9 here we present carbon isotope analyses of individual species of benthic and planktonic foraminifera spanning the k t boundary in oop hole 690c weddell sea antarctica which demonstrate that primary productivity following the k t extinctions may not have diminished to the extent or for the duration indicated by previous isotope studies the magnitude of the 13c gradient change is dependent on the species analysed reflecting differing depths of calcification seasonal contrasts and or disequilibrium effects the lack of any change in benthic 13c at the k t boundary indicates that the antarctic may not have been a significant source of deep water during the early palaeocene contrary to previous suggestion11 13

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

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

a paleoslope model of campanian to lower maestrichtian foraminifera in the north american basin and adjacent continental margin campanian to early maestrichtian benthic foraminiferal assemblages of the new jersey and delaware coastal plain and the baltimore canyon trough contain distinct bathymetric biofacies each occurring in adjacent settings to one another in a profile downdip toward the north american basin the assemblages are interpreted as representing inner shelf to uppermost middle bathyal environments of deposition 10 to 500 m water depth a unique biofacies which consists of predominantly arenaceous foraminifera in a lithology of dark lignitic shales is present in restricted intervals within the baltimore canyon region this biofacies probably developed under oxygen deficient conditions in middle shelf to upper bathyal paleodepths within the north american basin benthic foraminifers from campanian to lower maestrichtian sections at various dsdp sites indicate that deposition took place in middle bathyal to abyssal environments 500 m to more than 3000 m paleodepth a complete paleoslope profile shelf to abyssal is identified within the north american basin and adjacent continental margin the foraminiferal composition of this paleoslope is as follows gavelinella nelsoni g pinguis lenticulina pseudosecans cibicides harperi andpullenia americana characterize shore face to inner shelf regions of 10 to 50 m water depth species that show maximum development in middle shelf environments 50 to 100 m water depth includeclavulina trilatera hoeglundina supracretacea and nodosariids in the outer shelf 100 200 m water depth praebulimina carseyae gavelinella compressa g spissocostata coryphostoma plaitum andpullenia jarvisi predominate the upper bathyal environment of 200 500 m water depth is characterized by species such asarenobulimina subspherica dorothia oxycona verneuilina dickinsonensis n sp stensioina exculpta gracilis andgyroidinoides globosus pullenia cretacea gavelinella ammonoides g whitei g intermedia praebulimina reussi p cushmani pleurostomella subnodosa andstilostomella pseudoscripta are species common to the middle bathyal environment of 500 to 1500 m water depth species that characterize lower bathyal environments 1500 to 2500 m water depth includearagonia velascoensis reussella szajnochae osangularia utaturensis clavulina gabonica tritaxia aspera andspiroplectammina dentata many of the middle and lower bathyal indicator species extend into the abyssal realm 2500 m water depth where they are associated with more abundant species such asaragonia ouezzanensis reussella pseudospinulosa hyperammina elongata rhizammina indivisa andsaccammina complanata the resulting paleoslope model allows a more critical evaluation of the role played by benthic foraminiferal species in shelf slope and abyssal environments it also enhances the accuracy of estimating paleobathymetry especially in shelf regions of the campanian to early maestrichtian

productivity across the cretaceous tertiary boundary in high latitudes in low and middle latitudes the cretaceous tertiary boundary is marked by a sudden and pronounced decrease in 13c values of near surface water carbonates and a reduction in the surface to bottom 13c gradient these isotopic data have been interpreted as evidence of a decline in surface water productivity that was responsible for the extinction of many planktic foraminiferal species and other marine organisms at or near the k t boundary we present planktic and benthic foraminiferal isotopic data from two almost biostratigraphically complete sections at ocean drilling program site 738 in the antarctic indian ocean and at nye klov in denmark these data suggest that planktic carbonate 13c values in high latitudes may not have decreased dramatically at the k t boundary thus surface water productivity may not have been reduced as much as in low and middle latitudes comparison of the records of site 738 with those of odp sites 690 and 750 indicates a pronounced decline in 13c values of planktic and benthic foraminifera and fine fraction bulk carbonate 200 000 yr after the k t boundary this reflects a regional shift in the carbon isotopic composition of oceanic total dissolved carbon tdc and correlates with a similar change in benthic foraminiferal 13c values at mid and low latitude deep sea drilling project sites 527 and 577 this oceanographic event was followed by the ecosystem s global recovery 500 000 yr after the k t boundary these data suggest that the environmental effects of the k t boundary may have been less severe in the high latitude oceans than in tropical and subtropical regions