accumulation patterns of tertiary calcareous nannofossils around extinctions quantitative analysis of accumulation of tertiary calcareous nannofossil species allows a precise evaluation of their extinction patterns and thus of their biostratigraphic value accumulation of species commonly shows marked variability indicating that short sample intervals are necessary for estimating the true ranges the stratigraphic resolution which can be achieved is primarily determined by the sediment accumulation rate and the depth of homogeneous sediment mixing caused by bioturbation at about the time of extinction the accumulation usually shows a final sharp decline which often is followed by a tail of strongly reduced accumulation having a duration in the range of 2 3 103 to 4 5 105 years it is shown that this tail represents accumulation caused either by true production or postdepositional sediment mixing because of the difficulties involved in distinguishing these two casual mechanisms from each other biostratigraphic indications defined by the final sharp decline are generally superior in terms of synchroniety and ease of identification to those defined by the absolutely last occurrence

the late maastrichtian nannofossil record of climate change in the south atlantic dsdp hole 525a abstract the phytoplankton response calcareous nannofossils to the late maastrichtian climate evolution is investigated in the south atlantic dsdp hole 525a and compared to published geochemical and micropaleontological data the results point to a succession of dramatic climatic fluctuations cool water indicators ahmuellerella octoradiata kamptnerius magnificus and nephrolithus frequens suggest cool surface water conditions prevailed during chron c30n at the top of c30n their sudden drop in abundance the last occurrence of b constans and the concomitant increase in the tropical species micula murus suggest warming and lower surface water productivity an m murus acme within chron c29r reflects maximum warming during the last 100 kyr of the maastrichtian the decrease in m murus and increase in cool water indicators reflect rapid cooling with the cool climate persisting over the calcareous nannoplankton response to climate change correlate with similar findings in the equatorial atlantic hole 1258a and parallels the stable isotope record of planktic and benthic foraminifera of dsdp hole 525a as well as the decline in 187os 188os comparison of this marine record and the continental climate record in north america suggests a link between deccan volcanism and the late maastrichtian warm event

forcing mechanisms for mid cretaceous black shale formation evidence from the upper aptian and lower albian of the vocontian basin se france calcareous nannoplankton palynomorph benthic foraminifera and oxygen isotope records from the supraregionally distributed niveau paquier early albian age oceanic anoxic event 1b and regionally distributed niveau kilian late aptian age black shales in the vocontian basin se france exhibit variations that reflect paleoclimatic and paleoceanographic changes in the mid cretaceous low latitudes to quantify surface water productivity and temperature changes nutrient and temperature indices based on calcareous nannofossils were developed the nutrient index strongly varies in the precessional band whereas variations of the temperature index reflect eccentricity since polar ice caps were not present during the mid cretaceous these variations probably result from feedback mechanisms within a monsoonal climate system of the mid cretaceous low latitudes involving warm humid and cool dry cycles a model is proposed that explains the formation of mid cretaceous black shales through monsoonally driven changes in temperature and evaporation precipitation patterns the lower albian niveau paquier which has a supraregional distribution formed under extremely warm and humid conditions when monsoonal intensity was strongest bottom water ventilation in the vocontian basin was diminished probably due to increased precipitation and reduced evaporation in regions of deep water formation at low latitudes surface water productivity in the vocontian basin was controlled by the strength of monsoonal winds the upper aptian niveau kilian which has a regional distribution only formed under a less warm and humid climate than the niveau paquier low latitude deep water formation was reduced to a lesser extent and or on regional scale only the threshold for the formation of a supraregional black shale was not reached the intensity of increases in temperature and humidity controlled whether black shales developed on a regional or supraregional scale at least in the vocontian basin the increased preservation of organic matter at the sea floor was more significant in black shale formation than the role of enhanced productivity

mineralogy of mafic xenoliths and their reaction zones in the olivine lamproite from prairie creek arkansas and the paragenesis of haggertyite ba fe6ti5mg o19 the recently discovered mineral haggertyite which belongs to the magnetoplumbite family occurs in the prairie creek lamproite exclusively in a reaction zone at the contact between the olivine lamproite and serpentized xenoliths compositional characteristics of the lamproite are an extreme enrichment in elements such as k ba and ti associated with very low al2o3 based on textural evidence it appears that the xenoliths represent a quenched very mafic magma possibly komatiitic an absence of perovskite in the reaction zone is the consequence of si diffusion from the xenolith iron available in the xenolith may be the controlling factor for the crystallization of haggertyite and other fe and ti oxides involved in the reaction other elements k ti and ba diffused from the lamproite toward the xenolith zone but only the outermost edge of the xenoliths reacted the crystallization of haggertyite appears to have resulted from a local chemical environment created by element diffusion between the two significantly contrasting lithologies

mesozoic igneous activity in the maranha o province northern brazil 40ar 39ar evidence for separate episodes of basaltic magmatism low and high ti basaltic rocks of the maranha o province in northern brazil appear to be related to the opening of the atlantic ocean 40ar 39ar dating was carried out on powdered whole rock basalts both washed and unwashed in dilute nitric acid to document this relationship acid treatment does not alter the argon retention properties of retentive phases but is effective in removing alteration phases high ca k degassed at low laboratory temperatures our results identify that at least two periods of volcanic activity formed the maranha o province low ti basalts from the western sector are 200 190 ma and are related to the opening of the north atlantic high ti basalts from the eastern sector are 129 124 ma slightly younger than compositionally similar rocks in the serra geral flood basalt province of southern brazil and are related to the opening of the south atlantic other flood basalts such as the columbia river deccan rajmahal ferrar and siberian provinces were each predominantly formed in 1 2 ma the maranha o basalts remnants of separate igneous events spanning 70 ma should not be classed as a single flood basalt province the temporal complexities noted in the maranha o basaltic rocks appear to be related to the tracks of hotspots that led to the rifting of the atlantic ocean two sets of mesozoic basaltic rocks occur in southern africa india and south america resulting from events leading to the fragmentation and dispersal of sections of gondwanaland in each sub continent the two provinces were formed by events separated by 50 70 ma of these pairs only the maranha o and serra geral show geochemical similarities indicating compositionally distinct upper mantle source regions under sections of brazil separated by 3000 km

trends and evolution of contamination in a well dated water reservoir sedimentary archive the brno dam moravia czech republic the sedimentary record from dams can provide important information about stratigraphy and pollution history of densely populated river basins the brno dam is a small reservoir within the morava river catchment czech republic accumulating lacustrine sediments since 1940 dam filling the stratigraphy of the dam sediments was studied using multiproxy stratigraphic analysis x ray densitometry bulk magnetic susceptibility diffuse spectral reflectance and cation exchange capacity of five sediment cores supported by ground penetration radar sections concentrations of heavy metals were studied by x ray fluorescence analysis the thickness of the dam sediments decreases from 220 cm in the proximal part near the feeder to only 10 cm in the distal part near the dyke sediments consist predominantly of finely laminated silty sands silts and clays the sedimentation rate for the last 22 years inferred from 137cs dating decreases from 4 2 cm per year in the proximal part of the dam to 0 29 cm per year in its distal part distinct long term trends were found in the depth profiles of heavy metal concentrations the heavy metal contents increase significantly after 1940 in all cores with peak concentrations confined to layers deposited in the 1960s and 1980s a decreasing trend occurred after 1989 the decline in czech heavy industry the results also show that heavy metal contamination is dependent on lithology hyperpycnal flow layers related to floods increased concentrations of phosphorus in the sediments indicate long term eutrophication of the dam despite the recent decreasing trends in heavy metal concentrations the phosphorus contents remain high in recent years and have caused persisting problems with algal growth in the dam mentioned by previous authors

middle cretaceous calcareous nannofossil biogeography and preservation in the atlantic and indian oceans implications for paleoceanography abstract the quantitative study of calcareous nannofossil preservation and biogeographic distribution puts constraints on paleoceanographic models for the atlantic and indian oceans during the middle cretaceous we establish a dissolution ranking of middle cretaceous calcareous nannofossils based on susceptibility to dissolution a positive correlation of organic carbon content of the sediments and the relative abundance of watznaueria indicates that much of the carbonate dissolution was caused by the release of carbon dioxide during oxidation of organic matter the depth distribution of the most dissolution resistant species watznaueria barnesae shows relative abundance maxima at the deepest sites and a maximum where intermediate waters impinge on slopes this reflects stagnant oxygen poor bottom waters and possibly a mid water oxygen minimum zone with increased deposition and catabolic breakdown of organic matter factor analyses are performed on various data sets for three different time slices ranging in age from late aptian to early albian middle albian and late albian to cenomanian the resulting factors can be related to paleoceanographic conditions such as colder water at high latitudes high fertility upwelling conditions and neritic conditions for all three time intervals a wide tropical to subtropical zone was flanked by boreal and austral zones upwelling conditions probably existed along the north african margin and over the falkland plateau zonal upwelling is tentatively postulated for the northwestern and northeastern margin of the north atlantic in the middle albian and for the eastern margin of the north atlantic off western europe for the late albian to cenomanian we speculate on surface water current patterns location of upwelling regions and haline driven deep circulation for the middle cretaceous

revision of the early middle pleistocene calcareous nannofossil biochronology 1 75 0 85 ma the extant nannofossil biostratigraphic and biochronologic framework for the early middle pleistocene time interval has been tested through the micropaleontological analysis of globally distributed high quality low to mid latitude deep sea successions the quantitative temporal distribution patterns of relative abundances of selected taxa were reconstructed in critical intervals and the following biohorizons were defined first occurrence of medium sized gephyrocapsa spp last occurrence of calcidiscus macintyrei first occurrence of large gephyrocapsa spp last occurrence of large gephyrocapsa spp first occurrence of reticulofenestra asanoi re entrance of medium sized gephyrocapsa spp and last occurrence of reticulofenestra asanoi the detailed patterns of abundance change at these biohorizons were used to generate a detailed biostratigraphy and the biostratigraphic data were transformed into a precise biochronology by means of correlation to isotope stratigraphies and astronomical timescales the degree of isochrony or diachrony of the biohorizons was evaluated biohorizons and are isochronous occurring close to marine isotope stages mis 55 and mis 22 respectively and and are slightly diachronous on the order of 30 40 kyr whereas biohorizons and are confirmed as diachronous on the order of 100 80 and 60 kyr respectively some of the events are clearly controlled by environmental conditions e g the last occurrence of r asanoi related to significant environmental changes associated with the first large amplitude glaciation of the late quaternary mis 22

the timing of late cretaceous alkalic igneous activity in the northern gulf of mexico basin southeastern usa upper cretaceous igneous rocks in the northern gulf of mexico basin are poorly understood due both to the paucity of material recovered from drillholes in the sedimentary basins and lack of geochronological data rocks from the alkalic igneous complexes at magnet cove and granite mountain arkansas the monroe uplift and the jackson dome louisiana and mississippi yielded 40ar 39ar ages ranging from 94 ma to 65 ma high precision plateau ages reveal that the magnet cove complex 94 ma predates granite mountain by 4 myr igneous activity in the monroe uplift may have been contemporaneous with that at magnet cove and continued sporadically for 30 myr a single specimen from the jackson dome indicates volcanism at 65 ma coincident with waning igneous activity at the monroe uplift based on geochemical and geochronological data the source for volcanoclastic material in the woodbine formation arkansas are rocks belonging to the magnet cove phase of magmatism cretaceous alkalic rocks of central ark

tectonic history and setting of a seismogenic intraplate fault system that lacks microseismicity the saline river fault system southern united states abstract although the northwest striking saline river fault system of southeastern arkansas is not defined by microseismicity it is associated with sand blows and shows evidence of pleistocene and holocene surface ruptures suggesting a significant seismogenic potential this fault system is within the northern gulf of mexico interior coastal plain a region only recently recognized as containing seismogenic faults to better characterize this active fault system we reconstructed its post paleozoic history using petroleum and coal industry wire line well log and seismic reflection subsurface data the saline river fault system initiated as a series of northwest striking grabens during triassic jurassic uplift and incipient gulf of mexico rifting along the basement alabama oklahoma transform margin of the north american proterozoic craton during post rift subsidence these grabens were buried by gulf sediments until mid cretaceous uplift and igneous activity resulted in minor extensional reactivation of graben faults faulting style changed from extension to transpression during the late cretaceous due to compression of eastern north america as the north atlantic rapidly widened and due to thermal weakening of the alabama oklahoma transform lithospheric discontinuity as it obliquely crossed a mantle hot spot in the late cretaceous graben faults experienced contractional reactivation and steep deeply rooted transpressional faults developed within and parallel to the graben system these transpressional faults locally displace eocene pleistocene and holocene sediments fault activity continues on the saline river fault system due to thin crust along the alabama oklahoma transform and to high heat flow which act together to weaken the crust and promote seismogenic tectonism the fault system may lack appreciable microseismicity because the aftershock sequence of the last large earthquake has had time to dissipate

identifying and quantifying natural co2 sequestration processes over geological timescales the jackson dome co2 deposit usa co2 sources sinks and migration mechanisms in natural co2 gas fields provide critical analogues for developing the safe application of anthropogenic co2 sequestration technologies here we use noble gas and carbon isotopes together with other gases to identify and quantify the origin transport and trapping mechanisms of co2 in the late cretaceous jackson dome co2 gas deposit 98 75 to 99 38 co2 located in central mississippi usa and producing from 5000 m it is one of the deepest commercial co2 gas fields in the world 10 gas samples from producing wells were determined for their noble gas chemical and stable carbon isotope composition he 3 he 4 ratios range between 4 27r a and 5 01r a where r a is the atmospheric value of 1 4 x 10 6 indicating a strong mantle signature similar to co2 deposits worldwide co2 he 3 decreases with increasing groundwater derived ne 20 and he 4 we model several different processes that could account for the jackson dome data and conclude that similar to other co2 dominated deposits a groundwater gas stripping and re dissolution ggs r process best accounts for observed ne 20 ar 36 kr 84 ar 36 co2 he 3 delta c 13 co2 he 4 ne 20 and ar 36 in this context crustal and magmatic co2 components contribute 57 and 43 respectively changes in co2 he 3 across the field show that groundwater contact is responsible for up to 75 loss of original emplaced co2 delta c 13 co2 variance limits the degree of precipitation to be less than 27 with the remaining co2 loss being accounted for by dissolution only a higher degree of dissolution gas loss and evidence for water contact at the reservoir crest compared to the reservoir flanks is used to argue that co2 in this system has not undergone subsequent loss to either dissolution or precipitation since shortly after reservoir filling at over 60 ma c 2012 elsevier ltd all rights reserved

the cretaceous peri atlantic alkaline pulse paap deep mantle plume origin or shallow lithospheric break up abstract although the early jurassic initial phases of atlantic rifting were marked by the tholeiitic basalt flows and dikes of the central atlantic magmatic province camp the cretaceous era was characterised by widespread alkaline igneous activity on widely separated peri atlantic continental margins nearly half the peri atlantic alkaline rocks dated between 250 to 50 ma fall within the 125 80 ma range this period of intense alkaline activity during the mid cretaceous formed the peri atlantic alkaline pulse paap the mechanisms for the opening of the atlantic ocean as well as for the camp and later paap magmatic events have been attributed either to deep mantle plumes or to a combination of tensional forces lithospheric rifting and structural controls we describe the paap event for the first time and test the plume and structural models the paap displays evidence of strong structural control and appears to be related to reactivation of pre existing lithospheric structures throughout the peri atlantic zone early stages of continental separation and abrupt changes in plate motion were the most likely mechanisms for the reactivation of favourably oriented pre existing structures mid cretaceous pulses in alkaline magmatic activity were closely associated with major atlantic tectonic events the opening of the south atlantic the change in intensity and direction of both seafloor spreading and plate motion and the consequent fluctuation in intra plate stresses were responsible for two spikes in peri atlantic alkaline magmatism at 125 ma and 85 80 ma the general lack of evidence for a deep hotspot associated with the peri atlantic zone seems incompatible with a mantle plume origin on the other hand the spatial distribution of the paap along passive continental margins suggests an ideal setting for the development of edge driven convection we propose that the periodic reactivation of deep seated pre existing zones of weakness during the major stages of atlantic tectonic evolution combined with coeval asthenospheric upwelling due to edge driven convection and continental insulation flow enhanced the ascent of alkaline magmas this mechanism of shallow small scale upwelling during periodic structural reactivation provides a more likely explanation for the paap than the commonly proposed deep mantle plume scenario

calcareous nannofossils and milankovitch cycles the example of the albian gault clay formation southern england a quantitative study of calcareous nannofossil assemblages was carried out on the albian gault clay formation england this unit consists of grey marly claystones and marlstones with phosphatic nodules and glauconitic layers as minor lithologies two cores were analyzed in detail to focus on changes in nannofloral assemblages and consider their significance preservation of calcareous nannofossils is excellent and therefore diagenesis cannot be invoked to explain not even partially the changes registered in assemblages fast fourier spectral analysis was performed on percentages of selected nannofossil species fluctuations in abundance of both biscutum constans and watznaueria barnesae regarded as fertility and non fertility indices respectively appear to be orbitally driven because spectral analysis showed periodicities of approximately 41 kyr obliquity cycle and 100 kyr short eccentricity cycle in all the spectra the axial obliquityc cycle is a strong signal as expected at these high latitude sites from the boreal realm the same pattern was observed in another fertility controlled taxon zygodiscus cf erectus but cross correlation shows that its abundance plot is displaced with respect to that of b constans orbital perturbations induce variations in climate and ocean circulation because they influence the earth s insolation and seasonality during times of high seasonality strong gradients cause vigorous oceanic circulation a better cycling of nutrients and higher fertility whereas during times of low seasonality low gradients induce more sluggish circulation and lower fertility the carbonate content of the gault clay cores is not correlatable to the higher fertility indices as the abundance curves of b constans w barnesae and z cf erectus are displaced with respect to caco3 content variations this also means that cyclicity in nannofossil assemblages is not a result of diagenesis but an original signal abundance fluctuations of repagulum parvidentatum and combined parhabdolithus asper p splendens colder and warmer water indicators respectively provide evidence for orbital periodicities suggesting that also cyclic variations of surface water temperature might have influenced the nannofossil assemblage patterns within the gault clay

calcareous nannofossil biostratigraphy and paleoecology of the cretaceous tertiary transition in the central eastern desert of egypt abstract the gebel qreiya and nearby wadi hamama sections of the central eastern desert are among the most complete k t boundary sequences known from egypt the two sections were analyzed spanning an interval from l 83 myr below to about 3 myr above the k t boundary a 1 cm thick red clay layer at the k t boundary at gebel qreiya contains an ir anomaly of 5 4 ppb the high resolution study and well preserved nannoflora provide good age control and the first quantitative records of calcareous nannofossil assemblages for paleoecological interpretations across the k t transition in egypt four zones micula murus micula prinsii np1 and np2 were distinguished and correlated with other nannofossil and planktonic foraminiferal zonations that are broadly applicable for the eastern tethys region latest maastrichtian assemblages are abundant and diverse though cretaceous species richness progressively decreased across the k t boundary dominant species include arkhangelskiella cymbiformis micula decussata and watznaueria barnesae with high abundance of dissolution resistant m decussata reflecting periods of high environmental stress thoracosphaera blooms mark the k t boundary and are followed by an acme of the opportunistic survivor braarudosphaera bigelowii the first appearance of the new tertiary species cruciplacolithus primus and an acme of coccolithus cavus pelagicus these successive abundance peaks provide the basis for subdivision of the early danian zones np1 and np2 into five subzones correlation of selected nannofossil taxa from the egyptian sections with those from various onshore marine and deep sea sections provides insights into their paleoenvironmental and paleoecological affinities

calcareous nannofossil evidence for the existence of the gulf stream during the late maastrichtian 1 upper maastrichtian calcareous nannofossil assemblages from eight cores on the south carolina coastal plain onshore set and three deep sea drilling sites from the continental slope and abyssal hills offshore set were analyzed by correlation and principal component analysis to examine the ancient surface water thermal structure in addition a temperature index derived from independently published paleobiogeographic information was applied to the sample data all three methods indicate a strong separation of the samples into onshore and offshore sets with the offshore data set exhibiting significantly warmer paleotemperatures the great disparity between these two sample sets indicates that there was a strong thermal contrast between the onshore and offshore surface water masses that persisted throughout the late maastrichtian despite evident short term changes in fertility productivity and community structure this suggests the gulf stream was present as a major oceanographic feature during the late maastrichtian

the calcareous nannofossil biostratigraphic framework of the late maastrichtian danian north sea chalk abstract the calcareous nannofossil biostratigraphy of cored maastrichtian tor formation and danian ekofisk fm chalk sections from 10 selected wells of the greater ekofisk area central north sea was studied wells come from the edda tor se tor ekofisk and eldfisk fields among others more than 1000 m of cores were examined and about 500 samples were selected and analysed most of them quantitatively the main emphasis was placed on the danian sequence and on the k t boundary biostratigraphy provided detailed subdivision for the danian sediments intra danian hiatuses were detected and consistently recorded at the regional scale extensive mass movement was observed highlighting the complex depositional history during this time interval intervals of cretaceous chalk were found embedded in the danian sequence well 2 5 7 redeposited by slides as discrete chalk packages similarly lower danian intervals were recognised as transported into younger danian sediments well 2 4 b19a an attempt to reconstruct a regional stratigraphic picture for the area north of edda field including ekofisk se tor and tor fields has been made this suggests the following salient features the k t boundary of three wells of the northern sector of the studied area tor field is preceded by a prediscosphaera stoveri acme suggesting the presence of a rather complete maastrichtian sequence below the boundary above the k t boundary a few tens of centimetres of generally clay enriched pelagic chalk of the basal danian d1 biantholithus sparsus zone are present in most of the studied wells above this a condensed section often marked by hard ground levels or clay rich intervals was detected in almost all the wells the sedimentary expression of upper d1 above cruciplacolithus primus fad d2 and d3 time interval is lacking or extremely reduced in some cases sediments whose age is near the early late paleocene boundary were found unconformably overlying pelagic chalk referred to d5 d6 biozones

terminal cretaceous warming event in the mid latitude south atlantic ocean evidence from poleward migration of contusotruncana contusa planktonic foraminifera morphotypes abstract spatial and temporal patterns in test size and shape test conicity and spiral roundness and absolute abundance accumulation rate of the planktonic foraminifer contusotruncana contusa were studied in the south atlantic ocean dsdp sites 356 516 525 and 527 during an interval corresponding to the last 800 kyr of the cretaceous the variation in absolute abundance of c contusa was characterised by alternating periods of high and low abundance some of these periods were traceable across the entire mid latitude south atlantic ocean while the mean spiral roundness did not show any interpretable patterns a sudden increase of the mean test size and mean test conicity occurred between 65 3 and 65 2 ma based on linear interpolation within the cretaceous part of subchron c29r at all sites studied indicating a poleward migration followed by rapid withdrawal of the low latitude c contusa morphotypes from the mid latitude south atlantic ocean we suggest that this event was caused by a short period of surface water warming in the southern mid latitudes corresponding to the brief high latitude warming event and associated faunal migrations in the boreal and austral realms

foraminiferal dissolution at shallow depths of the walvis ridge and rio grande rise during the latest cretaceous inferences for deep water circulation in the south atlantic abstract a high resolution 10 20 kyr record of variations in caco3 content and dissolution was established for latest cretaceous last 0 7 myr deep sea sediments from the south atlantic ocean dsdp site 516 from the rio grande rise and sites 525 and 527 from the walvis ridge the degree of fragmentation of planktonic foraminifera dfp was used as a measure of calcite dissolution high negative correlations between dfp and other independent measures of carbonate dissolution percentage of sand fraction absolute abundance of planktonic foraminifera and planktonic benthic foraminiferal ratio validate its use as a sensitive index of calcite dissolution in upper maastrichtian deep sea sediments very high dfp and a significant negative correlation between dfp and caco3 content suggest that site 516 was located below the foraminiferal lysocline during the entire interval studied such a shallow position of the lysocline paleodepth of site 516 was 1 2 km may be explained by upwelling of corrosive deep waters along the southern margin of the rio grande rise sites 525 and 527 were located above the foraminiferal lysocline however three short periods of enhanced dissolution were recognised at site 525 paleodepth 1 km and one interval of strong dissolution was identified at site 527 paleodepth 2 7 km the lack of correspondence between the dissolution regimes at sites from the walvis ridge suggests limited deep water communication across this physiographic barrier two of the dissolution maxima recognised at site 525 correspond to carbonate maxima at site 527 variations in upwelling intensity along the walvis ridge resulting in fluctuations in primary productivity in this area may be the proximal cause of both carbonate cycles at site 527 and dissolution cycles at site 525 we suggest that development of the bottom ekman layer between a hypothetical westward geostrophic current and the topographical height of the rio grande rise walvis ridge system may be a plausible hydrodynamical explanation for the proposed upwelling along the southern margin of this topographical structure

short term environmental changes in the cretaceous tethyan ocean micropalaeontological evidence from the early albian oceanic anoxic event 1b to better understand the linkage between climate and ocean circulation under greenhouse conditions we have studied calcareous nannofossils palynomorphs and benthic foraminifera from the early albian oceanic anoxic event 1b black shale oae 1b in the vocontian basin se france we propose that monsoonal activity resulting from precessional forcing and modulated by eccentricity driven temperature changes represents the driving factor of oae 1b formation in low latitudes with the onset of oae 1b increasingly warm and humid conditions stronger winds and enhanced terrestrial input led to higher surface water productivity therefore increased productivity is an important factor for oae 1b formation in the vocontian basin however monsoonally forced productivity changes are a regional climate signal only the supraregional occurrence of the oae 1b is probably due to a reduction of deep water formation in the low latitudes under extremely warm and humid conditions leading to enhanced preservation of organic matter

diamond economics of the prairie creek lamproite murfreesboro ar usa abstract the prairie creek lamproite is the largest of seven ultramafic vents that make up the prairie creek lamproite province diamonds were first discovered in 1906 and commercial mining continued intermittently until about 1931 the evaluation program undertaken by the arkansas state parks commission in the 1990s resulted in the mapping and evaluation of four major vent facies rock types olivine lamproite epiclastic sediments phlogopite rich tuff and olivine rich tuff significant diamond contents were found only within the phlogopite rich tuff 0 11 carat 100 tonnes and olivine rich tuff 1 1 carats 100 tonnes stratigraphic relationships indicate that the diamondiferous tuffs have undergone

geochronology of the arkansas alkaline province southeastern united states abstract the arkansas alkaline province aap consists of intrusive bodies ranging in lithology from carbonatite and lamproite through nepheline syenite apatite and titanite fission track ages fall into two groups 101 94 ma and 88 ma new 40ar 39ar ages and those reported in the literature define a third age group of 106 ma apatite and titanite fission track ages are concordant indicating rapid cooling due to the emplacement of these intrusions at high levels during a time of regional uplift there is a relationship between age and petrology 1 lamproites are emplaced at 106 ma 2 carbonatites and associated silica undersaturated rocks are emplaced between 101 and 94 ma and 3 large nepheline syenite bodies are emplaced at 88 ma chemical and isotopic data support the inference that the lamproites are derived from subcontinental lithosphere while the other sequences are derived from the asthenosphere the ages for the aap and other conflicting information do not support the hypothesis that t

calcareous nannofossil and dinoflagellate stratigraphy across the cretaceous tertiary boundary at hor hahar israel in israel the cretaceous tertiary k t boundary at hor hahar occurs within the interval from the top of the ghareb formation maastrichtian to just below the horizon of dark marl and clay within the overlying taqiye formation paleocene the studied interval contains all the calcareous nannofossil zones micula prinsii latest maastrichtian markalius inversus np1 earliest paleocene andcruciplacolithus tenuis np2 early paleocene they correlate in sequence with theabathomphalus mayaroensis p0 p1a p1b and p1c planktic foraminiferal zones the palynological assemblages consist mainly of dinocysts with only few pollen grains and spores these assemblages are used to interpret five stratigraphic phases of environmental change across the k t boundary in the hor hahar section in the latest maastrichtian there is an overwhelming dominance of the nannofossilmicula decussata which probably reflects environmental stress preceding the terminal cretaceous mass extinction a nearshore marine environment at the boundary is suggested by the increase in number of specimens of the dinocystcyclonephelium and by the predominance of terrigenous organic matter sediment there followed two episodes of transgression and regression the calcareous cyst producing dinoflagellatethoracosphaera futterer 1976 becomes dominant in two episodes at the boundary and approximately one meter above it it alternates in abundance with the organic walled dinoflagellates which suggests that different environmental parameters were operating for each group maastrichtian dinocysts decline in abundance toward the k t boundary they reach greatest abundance and species diversity at the same strata where foraminiferids recover after their mass extinction at the boundary calcareous nannofossils recover only later in the early paleocene changes in 13c and total organic carbon as as well as dinocyst and nannofossil composition indicate an episode of strong ecological stress about one meter above the boundary

reconstructing nutricline dynamics of mid cretaceous oceans evidence from calcareous nannofossils from the niveau paquier black shale se france abstract a high resolution calcareous nannofossil record is presented from the lower albian niveau paquier black shale from the vocontian basin se france the niveau paquier black shale represents the regional equivalent of the supraregionally distributed oceanic anoxic event 1b oae 1b to reconstruct surface water fertility a nutrient index based on zeugrhabdotus erectus discorhabdus rotatorius high fertility indicators and watznaueria barnesae low fertility indicator was established using principal component analysis in addition the distribution of nannoconus spp and absolute abundances of coccoliths coccoliths per gram were used for reconstructing nutricline dynamics of the surface waters high surface water fertility coincides with low percentages of nannoconids and vice versa moreover high percentages of nannoconids correlate with low absolute abundances of all other coccoliths based on the observed nannoplankton distribution pattern and a suggested similarity in ecological requirements between nannoconids and the modern taxon florisphaera profunda a model is proposed that couples nannoconid abundances with dynamics of the nutricline time series analyses of the nutrient index show fluctuations within the precessional band the precession controlled fluctuations of the surface water fertility may represent a monsoonal signal with the nutrient supply in the surface waters depending on the strength of monsoonal activity during periods of enhanced monsoonal activity which were characterized by humid conditions and stronger winds mixing of the upper water column was enhanced during that time the abundance of nannoconids decreased as a consequence of enhanced wind stress that improved vertical mixing and led to an entrainment of nutrients into the surface waters this resulted in an increase of primary production during periods of reduced monsoonal activity marked by drier conditions and reduced wind stress the surface waters were depleted in nutrients as a result of a deep nutricline and a reduced nutrient supply to the upper photic zone in a stratified water column percentages of nannoconids increased according to the mechanisms outlined above fluctuations of the nutrient index and nannoconid percentages have been used as a proxy for reconstructing the physical structure of mid cretaceous oceans steered by precession forced monsoonal activity the results of the study show that the formation of the lower albian oae 1b from the vocontian basin occurred under strongly fluctuating surface waters fertility

a valanginian early cretaceous boreal nannoplankton excursion in sections from romania abstract in order to resolve both sea level and palaeoclimatic signals for the earliest cretaceous 161 calcareous nannofossil samples of berriasian to valanginian age have been studied from romania these samples are derived from three biostratigraphically well dated sections of tethyan litho and biofacies the nannofossil assemblages recorded are of high diversity reflecting stable warm water conditions typical for the earliest cretaceous of the tethys the floras are characterised by abundant watznaueria spp and nannoconus spp whereas other taxa are less common long term trends on the scale of 1 4 my are reflected by shifts from watznaueria spp dominated assemblages in the lower berriasian to nannoconus spp assemblages in the middle upper berriasian back to watznaueria spp in the upper berriasian lower valanginian and again to nannoconus spp in the upper valanginian these changes are thought to be caused by palaeoclimatic shifts periods with a dominance of cosmopolitan eurytopic watznaueria are thought to reflect cooler humid conditions and well mixed surface waters those with a dominance of nannoconus warmer conditions and a rather stabile surface water stratification crucibiscutum salebrosum very common at high latitudes is extremely rare in the romanian samples it occurs only at one specific interval of early late valanginian age saynoceras verrucosum ammonite zone associated with other rare boreal taxa also restricted to this particular level this boreal nannoplankton excursion is believed to be controlled by sea level rather than by climate since simultaneously tethyan ammonites found their way into the boreal realm

new geochemical evidence for the onset of volcanism in the central atlantic magmatic province and environmental change at the triassic jurassic boundary the late triassic early jurassic was a time of major global change however the fundamental processes driving these changes are less than clear we have determined the re and os abundances and os isotope compositions of marine mudrock samples that span the triassic jurassic boundary in the uk and have established that major isotopic and geochemical shifts in the composition of seawater took place in the latest triassic we argue that these shifts were caused by the sudden initiation of widespread igneous activity within the central atlantic magmatic province associated with rifting of the supercontinent pangea the os isotope composition of seawater responded rapidly to these events demonstrating that the seawater os isotope system has great potential in identifying the nature and precise timing of major environmental change