a novel multiproxy approach to reconstruct the paleoecology of extinct cephalopods abstract reconstructing marine paleoenvironments from the skeletal hardparts of nektic organisms is often hampered by their unknown migrational pathways involving different water masses and their corresponding physico chemical parameters despite significant progress over the last years the reconstruction of migration patterns of extinct ammonoids is difficult because both vertical and horizontal ones lead to an intricate combination of reconstructed seawater temperatures paleonvironmental data retrieved from exceptionally well preserved lower albian douvilleiceras mammillatum ammonite zone uppermost cc8a nannofossil zone 110 5 111 0 ma cephalopod shells from madagascar mahajanga basin 40 42 southern latitude are reconstructed based on a novel multi proxy approach here we combine and contrast i nacre tablet paleobathymetry ii westermann morphospace and iii shell isotope geochemistry analysis results obtained allow for a robust reconstruction of habitat depth paleo seawater temperatures and paleoecology of extinct cephalopod taxa the discocone nautiloid cymatoceras is regarded as vertical migrant with a maximum habitat depth of 250 m and a mean habitat water temperature of 20 21 c all three ammonoid taxa cleoniceras desmoceras and eogaudryceras share a platycone to planorbicone shell shape suggesting a demersal life habit at maximal water depths of 450 500 m and temperatures of 19 21 c for cleoniceras and desmoceras and the deepest 525 m and coolest 14 c habitat for eogaudryceras circumstantial evidence from benthic mollusk shells from the same stratigraphic interval as well as sedimentological and paleopathological data provide further support for habitat reconstructions reconstructed paleotemperatures shown here provide well constrained evidence for the thermal structure of past oceanic water masses and have significance for cretaceous paleoceanography in general

a seismic refraction study of the crustal structure associated with the adamawa plateau and garoua rift cameroon west africa summary recordings of quarry blasts along a 300 km profile across the adamawa plateau at the eastern end of the cameroon volcanic line permitted the determination of the crustal structure of the region to the north of the plateau in the area of the garoua rift an eastern arm of benue trough the crust is about 23 km thick and is underlain by upper mantle with a p wave velocity of 7 8 kms 1 the southern part of the plateau by comparison is associated with a more normal crustal thickness of about 33 km and underlain by upper mantle with a velocity of 8 0 kms 1 between these two areas the seismological experiment was not able to delineate how the crust changes however if the topography and gravity field reflect crustal thickness then there is a rapid change in crustal thickness at the northern edge of the adamawa plateau the study thus provides the first seismic evidence for major crustal thinning beneath the garoua arm of the west african rift system as well as providing evidence for an alternative model for the formation of the cameroon volcanic line

field evidence for flank instability basal spreading and volcano tectonic interactions at mt cameroon west africa the mt cameroon volcano is the highest and most active volcano of the cameroon volcanic line little geological information is available for improving the understanding of the structure of this large volcanic system and its relationship to regional tectonics after reviewing the tectonic evolution of the region the analysis of a digital elevation model and results from a field campaign dedicated to mapping geological structures in the summit area and at the se base of mt cameroon are presented mt cameroon is a lava dominated volcano with long steep over 30 flanks it is elongate parallel to its well defined rift zone the summit plateau is bordered by 10 m high cliffs formed by summit subsidence along normal faults geological profiles were measured along rivers cutting through a topographic step at the se base of mt cameroon this step is associated with deformed miocene sediments from the douala basin that are overlain by volcanic products weak sediments of this area are deformed by 050 060 and 020 030 trending asymmetrical folds verging toward the se and thrusts faults related to the spreading of the volcano over its mechanically weak substratum combined remote sensing and field observations suggest that spreading is accommodated by summit subsidence and flanks sliding both slow spreading movements and catastrophic collapses of the steep flanks are interpreted to result from complex interactions between the growing edifice repeated dyke intrusions the weak sedimentary substratum and tectonic structures

intracontinental movements in western gondwanaland a palaeomagnetic test abstract early cretaceous intracontinental movements within africa and or south america to account for misfit problem in the pre drift reconstruction of western gondwana have been tested using palaeomagnetic poles from both continents each continent has been considered as comprising separate subplates according to the boundaries proposed by pindell and dewey 1982 and curie 1983 i e northern africa naf southern africa saf northern south america nsa and southern south america ssa visual and statistical distribution of late permian to jurassic poles from the african subplates indicate two distinct groups before rotating saf relative to naf while after the rotation they become indistinguishable the distribution and sparsity of data from south america limit the study in this continent as the data are statistically indistinguishable before and after rotation of ssa with respect to nsa when the test is extended to the reconstruction of western gondwana the tightest grouping of the poles occurs when an intracontinental movement is assumed within africa this suggests that the misfit between the two continents is probably due to intracontinental deformation within africa and not in south america if confirmed this may have profound implications in the kinematics of the processes related to the opening of the south and central atlantic oceans and also the origin of the west african rift system

fault controlled dolomite bodies as palaeotectonic indicators and geofluid reservoirs new insights from gargano promontory outcrops the upper jurassic to lower cretaceous platform slope to basinal carbonate strata cropping out in gargano promontory southern italy are partly dolomitized fieldwork and laboratory analyses petrographic petrophysical and geochemical allowed the characterization of the dolomite bodies with respect to their distribution within the carbonate succession their dimensions geometries textural variability chemical stability age porosity genetic mechanisms and relation with tectonics the dolomite bodies range from metres to kilometres in size are fault related and fracture related and probably formed during the early cretaceous at 500 m burial depths and temperatures 50 c the proposed dolomitization model relies on mobilization of early cretaceous seawater that flowed downward and then upward along faults and fractures and was modified in its isotopic composition moving through triassic and jurassic strata that underlie the studied dolomitized succession despite the numerous cases reported in literature this study demonstrates that hydrothermal and or high temperature fluids are not necessarily required for fault controlled dolomitization distribution and geometries of dolomite bodies can be used for palaeotectonic reconstructions as they partly record the characteristics size attitude and kinematics of the palaeo faults even if not preserved that controlled dolomitization in gargano promontory dolomites record early cretaceous palaeo faults from metres to kilometres long striking north west south east to east west and characterized by normal to strike slip kinematics dolomitization increases the matrix porosity by up to 7 and therefore can improve the geofluid storage capacity of tight platform slope to basinal limestones the results have a great significance for characterization of geofluid for example hydrocarbons reservoirs hosted in similar dolomitized carbonate successions distribution size and shapes of reservoir rocks i e dolomite bodies could be broadly predictable if the characteristics of the palaeo fault system present at the time of dolomitization are known this article is protected by copyright all rights reserved

middle and late albian geography oceanography and climate and the setting of the kirchrode i and ii borehole sites abstract the paper reviews the literature on the geography oceanography and climate belts during the middle and late albian emphasis is placed on the northern hemisphere and the lower saxony basin the middle and late albian represents a time with a greenhouse climate the n s temperature gradient and the temperature gradient between the shallow and deep waters of the oceans were lower than at present meaning higher temperatures especially at middle and high latitudes a more sluggish ocean circulation than today and the absence of polar ice caps warming from the early to late albian is documented in the marine sediments by oxygen isotope studies and the poleward expansion of rudist dominated carbonate platforms in the terrigenous sediments of the northern hemisphere it is documented by northward migration of low latitude relatively arid flora the opening north atlantic was still narrow at the beginning of the albian it widened and deepened through the albian a shallow seaway between the south atlantic and the western tethys developed during the late albian wide shelf seas existed on the continental plates with rising sea level the basins of the western epicontinental seas of eurasia became increasingly connected and sedimentation gradually became more calcareous nevertheless these basins received a large clastic input from the land documenting the weathering conditions on the surrounding land masses they received also a considerable biogenic particle flux from the surface waters documenting productivity of the marine plankton because of these different origins of the sediment components as well as the connections with neighbouring seas the sediments in these shelf basins were expected to document changes in climate as well as palaeo oceanographic changes earlier interpretations based on ammonite studies that indicate changing connections between the arctic ocean and the tethys during the albian can thus be tested the lower saxony basin was a shelf sea in the southern part of the warm humid climate belt at mid latitudes in the northern hemisphere in which thick deposits of hemipelagic sediments accumulated mapping previous to our study indicated that a complete undisturbed albian basinal sequence ca 400 m thick is present below a thin quaternary cover in a sub basin between the nne ssw trending benthe and lehrte salt structures in the central part of the lower saxony basin the boreholes at the kirchrode i and ii sites 52 22 35 n 9 49 87 e and 52 22 16 n 9 49 12 e respectively in hannover were drilled into this sub basin the high sedimentation rates known for the albian of the lower saxony basin are ideal for studying climatic changes with a cyclicity of a few ten thousand to a few hundred thousand years milankovitch cyclicity

microstructural preservation and the effects of diagenesis on the carbon and oxygen isotope composition of late cretaceous aragonitic mollusks from the gulf coastal plain and the western interior seaway the carbon and oxygen isotope compositions of calcium carbonate shells are widely accepted and applied proxies for tracking changes in paleoenvironmental conditions such as temperature salinity and productivity in order to accurately interpret isotopic measurements diagenetic alteration must first be assessed the occurrence of aragonitic shells is often taken as a first order sign of unaltered material because aragonite at the earth9s surface is metastable and converts to calcite however even specimens that retain an aragonitic composition and are macroscopically well preserved often exhibit subtle to considerable signs of alteration when shell microstructure is examined using scanning electron microscopy sem to determine the textural and isotopic effects of progressive alteration on differing types of shell microstructure we undertook a comparative study of aragonitic shells from two regions frequently used in paleoenvironmental reconstructions and diagenetic studies the upper cretaceous of the gulf coastal plain gcp and the western interior seaway wis because the gcp is within a passive margin setting and the wis has experienced tectonic processes we also evaluate how diagenetic history affects isotopic composition visually well preserved ammonite bivalve and gastropod shells were collected from one locality in the gcp and examined using sem to evaluate microstructural preservation we used a previously published scale based on wis specimens for nacreous shell material and a complementary scale we developed for crossed lamellar microstructure the stable carbon and oxygen isotope compositions of specimens across the preservational scale from both regions were analyzed isotopic composition does not change systematically with degrading preservation in the gcp specimens a result that contrasts strongly with patterns in wis specimens where isotopic composition systematically decreases with decreasing microstructural preservation dissimilar tectonic regimes that led to unique post depositional conditions for each region are invoked to explain this difference the wis was a foreland basin subjected to significant meteoritic groundwater flow driven by active uplift while the gcp was a passive margin that has remained close to sea level with low hydraulic potential since the time of deposition thus during diagenesis the wis shells were exposed to fluids that differed greatly from the seawater in which the organisms grew whereas diagenetic fluids in gcp settings likely were similar to marine waters as expected shells with the best preserved microstructure provide the most consistently reliable isotopic data for paleoenvironmental reconstructions but our comparisons show that similar degrees of microstructural alteration can express very different diagenetic shifts in isotopic values

carbon isotope δ13c differences between late cretaceous ammonites and benthic mollusks from antarctica abstract ammonites are one of the most common fossils of the mesozoic but there is little consensus on their mode of life isotopic studies have been used to reconstruct their preferred water temperature from 18 o measurements but 13 c values have more ambiguous interpretations previous studies have recorded population differences in 13 c values between ammonite and benthic organisms without explaining the cause in detail here we examine a molluscan community from seymour island antarctica and find a 4 carbon isotope offset between ammonites and other benthic mollusks the most likely cause of this anomaly is an increased metabolic carbon contribution to ammonite shell material when compared with other mollusks but we cannot rule out the possibility of a methane seep contribution increased respired co 2 production could be generated by a more active lifestyle and increased energy demands which may have increased the susceptibility of ammonites to the end cretaceous mass extinction

high resolution scanning proton microprobe studies of micron scale trace element zoning in a secondary dolomite implications for studies of redox behaviour in dolomites abstract secondary rhomb shaped dolomites from the limestones of the gargano peninsula italy show fine well developed zones when viewed under cathodoluminescence in order to investigate the chemical origin of these zones this material was analyzed using the high resolution scanning proton microprobe the analyses show prominent concentric micrometre scale zones enriched in fe mn and zn at the ppm level the chemical zonations observed are however very much more complex than is shown by the cathodoluminescence image the cathodoluminescent zones correlate with variations in mn concentration but there is little negative quenching effect of fe which can be observed and there is no correlation among the zones of the different elements in contrast to the pronounced and sharp zoning of mn fe and zn observed sr is distributed homogeneously in the dolomite since the activities of fe ii mn ii and zn in solution are all controlled directly or indirectly by redox reactions whereas the behaviour of sr is uninfluenced by changes in oxidation potential these observations strongly suggest that the most important variable controlling the production of zones in these dolomites was eh we believe that the sharp zoning of mn fe and zn and the clear separation of one element from another indicate repeated influxes of pore water of differing eh and possibly ph carrying different amounts of fe ii mn ii and zn in solution

surface fitting in geomorphology examples for regular shaped volcanic landforms abstract in nature several types of landforms have simple shapes as they evolve they tend to take on an ideal simple geometric form such as a cone an ellipsoid or a paraboloid volcanic landforms are possibly the best examples of this ideal geometry since they develop as regular surface features due to the point like circular or fissure like linear manifestation of volcanic activity in this paper we present a geomorphometric method of fitting the ideal surface onto the real surface of regular shaped volcanoes through a number of case studies mt mayon mt somma mt semeru and mt cameroon volcanoes with circular as well as elliptical symmetry are addressed for the best surface fit we use the minimization library minuit which is made freely available by the cern european organization for nuclear research this library enables us to handle all the available surface data every point of the digital elevation model in a one step half automated way regardless of the size of the dataset and to consider simultaneously all the relevant parameters of the selected problem such as the position of the center of the edifice apex height and cone slope thanks to the highly performing adopted procedure fitting the geometric surface along with calculating the related error demonstrates the twofold advantage of the method firstly we can determine quantitatively to what extent a given volcanic landform is regular i e how much it follows an expected regular shape deviations from the ideal shape due to degradation e g sector collapse and normal erosion can be used in erosion rate calculations secondly if we have a degraded volcanic landform whose geometry is not clear this method of surface fitting reconstructs the original shape with the maximum precision obviously in addition to volcanic landforms this method is also capable of constraining the shapes of other regular surface features such as aeolian glacial or periglacial landforms

applications of the high resolution scanning proton microprobe in the earth sciences an overview abstract the proton microprobe uses a focused beam of high energy protons to generate x rays in a sample that is to be analyzed the major advantage of the proton microprobe as compared with the electron microprobe lies in its much lower x ray background this makes possible analyses at the 5 10 ppm concentration level with a resolution of 1 m the principles of operation of the proton microprobe are reviewed and the instrument compared with the ion probe and synchrotron x ray microprobe examples of its use in analyzing finely zoned dolomite and in investigating the late stage concentration of elements on grain boundaries in garnet lherzolite xenoliths are reviewed the proton and x ray microprobes are likely to contribute increasing amounts of high quality trace element data in the near future

in situ characterization of dolomite crystals evaluation of dolomitization process and its effect on zoning dolomitization is a dissolution re precipitation process which proceeds via micrometre scale interface reaction horizons however the effect of this fundamental local medium of replacement process on precipitated dolomite crystals is rarely investigated for this purpose dolomite samples of ordovician boat harbour formation carbonates newfoundland canada from main brook and daniel s harbour about 150 km apart were studied the investigation used high resolution approaches to carry out imaging and elemental analyses of individual dolomite crystals including scanning electron microscopy scanning electron microscopy based cathodoluminescence secondary ion mass spectrometry and electron microprobe analysis the purpose was to better understand geochemical variations across the crystal traverses and their association with dolomite replacement processes and conditions the scanning electron microscopy based cathodoluminescence zoning character reveals three major crystal facies distinctly planar boundaries zoned core and indistinctly zoned core are zoned dolomite crystal facies in burial dolomite from main brook relatively unzoned crystal facies was identified in that of daniel s harbour compositionally zoned dolomite crystals are characterized by decreasing sr na y and ree but increasing mn and fe from core to rim sections core to rim zoning was not found for major mg and ca elements the zoning exhibited by the replacive dolomite crystals is interpreted to be principally a result of limited exchange between solutes of the bulk pore fluid and those of dissolving precursor marine carbonate in tandem with petrographic features the systematic compositional zoning character demonstrates that the effectiveness of the dolomitization process grades from indistinctly zoned core to relatively unzoned crystal facies via interface reaction horizons homogenization of major elements of core and rim sections seen in distinctly zoned core crystal facies and to a much greater extent in relatively unzoned crystal facies via a secondary reaction interface is the first recognized stage of the maturation process followed by homogenization of the trace elements seen largely in relatively unzoned crystal facies

regurgitalites a window into the trophic ecology of fossil cephalopods fossil oral ejecta that exclusively contain bivalved calcitic lower jaws of ammonites aptychi from late jurassic solnhofen type deposits of southern germany are described based on the symphysis length of aptychi the ammonite shell diameters were reconstructed ranging from 5 to 170 mm to identify the potential ammonite predator published reports on stomach contents coprolites and ammonite palaeopathology were critically assessed implementation of the actualistic approach together with some functional considerations includes the identification of modern cephalopod predators with a focus on the modern nautilus and the distribution of vomiting behaviour among them stomach fluid ph is also important because species with an alkaline stomach ph are unable to dissolve calcareous hardparts and have to orally eject such material herein we regard coleoids with an opportunistic diet as the most likely producers of the aptychi bearing regurgitalites this is based on finds of aptychi in the stomachs of the two coleoids plesioteuthis and trachyteuthis they were likely fast highly manoeuvrable swimmers both share a strong triangular shaped jaw apparatus that could possibly crush ammonite shells as well as arms equipped with suckers to hold their prey circumstantial evidence for coleoids as the producers comes from the alkaline ph of the stomach fluids of modern coleoids supplementary material data for lamellaptychi are available at https doi org 10 6084 m9 figshare c 4695002

active versus passive continental rifting evidence from the west african rift system fitton j g 1983 active versus passive continental rifting evidence from the west african rift system in p morgan and b h baker processes of continental rifting tectonophysics 94 473 481 the west african rift system comprises the cretaceous benue trough and the tertiary to recent volcanic cameroon line the two features are remarkably similar in shape and size and may be superimposed perfectly by rotating one with respect to the other by 7 about a pole in sudan three stages in the geological history of the system are postulated 1 the benue trough was produced by lithosphere stretching as one arm of an rrr triple junction during the early stages of the opening of the south atlantic 2 at about 80 ma santonian a short lived period of clockwise rotation interrupted the otherwise anticlockwise rotation of africa and decoupled the lithosphere from the asthenosphere the hot zone in the asthenosphere beneath the benue trough thus became displaced relative to the lithosphere and moved to a new position beneath cameroon and the gulf of guinea 3 anticlockwise rotation and asthenosphere lithosphere coupling were restored allowing the hot zone to manifest itself as the cameroon line the cameroon line is possibly a unique example of what a rift system produced actively by a thermal anomaly in the asthenosphere would look like it is significant that despite a long history of volcanism and uplift the cameroon line has not developed a graben structure the implication is that rift systems with graben structures are produced passively by lithosphere stretching

petrologic and geochemical constraints on the origin of subsurface dolomite enewetak atoll an example of dolomitization by normal seawater dolomite is present 1 250 1 400 m below sea level in eocene strata of enewetak atoll petrographically the deep enewetak dolomite postdates brittle compaction of rigid grains in the host eocene strata the 87 sr 86 sr ratio of these dolomites 0 70865 0 70901 indicates that they formed at one or more times between the middle miocene and the present since the top of the lower miocene is more than 900 m above the deep dolomitic interval the dolomite must have formed at a minimum burial depth of 900 m stable oxygen isotope determinations suggest dolomite precipitation from cold marine water lower miocene and eocene carbonate strata on the atoll are apparently in open communication with cold modern ocean water suggesting that those same strata were in open communication with ocean water during dolomitization at a depth of about 1 000 m modern pacific ocean water becomes undersaturated with respect to calcite but is still supersaturated with respect to dolomite therefore it is proposed that the deep enewetak dolomite precipitated from cold deep ocean water undersaturated with respect to calcite at a burial depth of more than 900 m

effect of diagenesis on the sr o and c isotope composition of late cretaceous mollusks from the western interior seaway of north america evaluating the effects of diagenesis on the isotopic compositions of sr o and c in marine carbonates is critical to their use as proxies in reconstructing information on the salinity temperature and dissolved inorganic carbon of ancient oceans we have analyzed a series of samples of mollusk shells from the baculites compressus zone late campanian of the pierre shale of south dakota samples included outer shell material and septa of cephalopods collected inside and outside concretions preservation was evaluated using light microscopy scanning electron microscopy sem trace element analysis and x ray diffraction all of the material consists of aragonite based on x ray diffraction an sem preservation index pi was established based on comparison of the microstructure of the fossil material with that of modern nautilus excellent preservation pi 5 was characterized by well defined nacreous plates with discrete angular boundaries in contrast samples showing fused nacreous plates with indistinct boundaries were rated poor pi 1 87sr 86sr ratios vary with preservation and average 0 707648 000021 n 10 for excellent preservation pi 5 0 707615 000028 n 5 for good preservation pi 3 0 707404 000074 n 7 for fair preservation pi 2 and 0 707261 000053 n 8 for poor preservation pi 1 these data suggest that as the quality of the preservation declines the mean 87sr 86sr ratio decreases and the standard error of the mean increases oxygen and carbon isotope analyses of the same specimens also show decreases with preservation and 18o 13c and 87sr 86sr are well correlated suggesting that these tracers are all altered as the pi decreases the sr ca ratio increases as preservation decreases indicating that sr is added to the shell material during diagenesis in contrast mg ca shows no trend with preservation if the increasing sr concentration and decreasing 87sr 86sr of the shell material with decreasing preservation represents the addition of sr to the shell during diagenesis we calculate that the added sr had 87sr 86sr ranging from 0 707582 to 0 707032 potential sources of the added sr include older marine carbonates and weathering of volcanic ash layers present in the shale the mechanisms of alteration likely include epitaxial growth of strontianite on the original shell aragonite and isotopic exchange of c and o between alteration fluids and shell carbonate we conclude that sem preservation criteria are effective in screening shell material that records original isotopic values and that variations in sr o and c isotope composition in well preserved material can be used to assess paleoenvironmental parameters such as salinity and temperature our results also indicate that assessing preservation is a critical prerequisite to the determination of numerical ages of shell material using strontium isotope stratigraphy

nacre tablet thickness records formation temperature in modern and fossil shells nacre the iridescent outer lining of pearls and inner lining of many mollusk shells is composed of periodic parallel organic sheets alternating with aragonite caco 3 tablet layers nacre tablet thickness tt generates both nacre s iridescence and its remarkable resistance to fracture despite extensive studies on how nacre forms the mechanisms controlling tt remain unknown even though they determine the most conspicuous of nacre s characteristics visible even to the naked eye thermodynamics predicts that temperature t will affect both physical and chemical components of biomineralized skeletons the chemical composition of biominerals is well established to record environmental parameters and has therefore been extensively used in paleoclimate studies the physical structure however has been hypothesized but never directly demonstrated to depend on the environment here we observe that the physical tt in nacre from modern and fossil shallow water shells of the bivalves pinna and atrina correlates with t as measured by the carbonate clumped isotope thermometer based on the observed tt vs t correlation we anticipate that tt will be used as a paleothermometer useful to estimate paleotemperature in shallow water paleoenvironments here we successfully test the proposed new nacre tt thermometer on two jurassic pinna shells the increase of tt with t is consistent with greater aragonite growth rate at higher t and with greater metabolic rate at higher t thus it reveals a complex t dependent biophysical mechanism for nacre formation

compositional sector zoning in dolomite abstract systematic compositional differences between nonequivalent growth sectors in dolomite rhombs from the mississippian burlington fm southeastern iowa are documented using various analytical methods cathodoluminescence petrography reveals that sectors forming under 1120 faces have a different overall luminescence than adjacent sectors forming under 1014 faces indicating differences in mn and or fe contents microprobe analyses confirm such a difference with 1120 sectors enriched in fe and slightly enriched in mn relative to 1014 sectors in addition 1120 sectors are enriched with mg relative to 1014 sectors both sector types are rich in calcium however transmission electron microscopy reveals that growth microstructures differ within these different growth sectors the sectoral variations can be explained using a model that depicts atomic configurations on different growth surfaces in relation to occupancies of partially formed cation sites called protosites it is shown that sector zoning requires metastable growth since growth layers added simultaneously on nonequivalent faces are compositionally different both trace and major element distributions for these dolomites and perhaps many other carbonates are influenced by factors relating to the mechanisms and perhaps rates of growth on different faces and do not represent equilibrium in addition crystal habit may indirectly influence bulk composition

enhanced carbonate petrography using fluorescence microscopy abstract fluorescence microscopy can recognize depositional facies and delineate diagenetic fabrics and porosity relationships in certain highly dolomitized or recrystallized limestones previously uninterpretable using standard petrographic techniques this tool has other valuable applications in the study of carbonate rocks these other applications include differentiating carbonate cements from neomorphic spar enhancing depositional and diagenetic fabrics rapidly evaluating mineralogical stabilization and recrystallization in holocene and pleistocene deposits and improving delineation of porosity and pore geometries in sedimentary rocks fluorescence microscopy is a rapid easily used and nondestructive technique that can be applied to unpolished thin sections or rock slabs by itself or in conjunction with other petrographic and geochemical tools it has the potential to expand our understanding of carbonate diagenetic processes and products in particular dolomitization and neomorphism and carbonate porosity evolution we strongly encourage routine usage of fluorescence microscopy in future carbonate petrographic studies

substantial iron sequestration during green clay authigenesis in modern deep sea sediments pyrite formation has been considered a key iron sink in organic rich marine sediments analyses of sediments from the ivory coast ghana marginal ridge demonstrate that iron can be buried at greater rates during green clay formation

petrology and palaeoenvironmental significance of authigenic iron rich clays carbonates and apatite in the claiborne group middle eocene ne texas the claiborne group eocene in north east texas consists of clayey sandstones and mudrocks both with variable proportions of dark green to brown clay pellets deposited in a marginal to open marine setting on the gulf coast margin the composition of concretionary carbonate and clay pellets from 5 localities has been investigated using a wide variety of analytical techniques our palaeontological sedimentological c s and stable isotope data support an interpretation of marginal marine facies with limited freshwater input for the claiborne group dark green mature pellets are predominantly associated with transgressive bioturbated marine sediments from the weches formation through to the youngest crockett formation there is a trend from pellets composed mostly of dark green serpentine rich mixed layer clay to those of mostly brown immature nontronite rich mixed layer clay the serpentine is intermediate between odinite and berthierine and may have been originally odinite that has undergone partial transformation to berthierine pellet maturity apparently corresponds with the degree of winnowing and sedimentation rate it does not appear to correspond with global temperature fluctuations though the serpentine rich rather than glauconite rich composition may do siderite cement mostly in the form of concretions post dates the iron rich clay pellets and pre dates calcite cement carbonate and apatite concretions show a wide range of mineral cement textures reflecting variation in sedimentary environment and early diagenetic processes based on water temperatures derived from verneriacardia bivalves a precipitation temperature of 20 c is assumed for the concretionary siderite using this temperature we surmise that the siderite precipitated from marine pore waters with intermittent meteoric water mixing

detecting compositional spatial and temporal attributes of glaucony a tool for provenance research abstract a reliable interpretation of glaucony bearing units requires the characterization of compositional spatial and temporal attributes of glaucony the criteria that can readily determine the differentiation of the various types of glaucony autochthonous parautochthonous or allochthonous intrasequential and detrital or allochthonous extrasequential are discussed in detail autochthonous vs allochthonous glaucony may be often detected on the basis of detailed sedimentological investigations including facies interpretation of glaucony bearing deposits and careful examination of spatial distribution of glaucony textural and morphological features although generally not diagnostic on their own provide a significant contribution to glaucony interpretation the distinction between parautochthonous and detrital glaucony can be sometimes performed by radiometric dating more commonly it requires that compositional attributes of glaucony be matched against those of putative sources glauconies from distinct parent rocks generally have different maturity and carry unique geochemical and mineralogical fingerprints that may contribute definitive data for provenance research previous work on glaucony and examples from units formed in tectonically stable areas cretaceous eocene deposits of paris basin and hampshire basin and active tectonic basin settings miocene strata of southern alps and northern apennines provide the opportunity to discuss the validity of the proposed criteria across different structural domains and emphasize the need for an integrated approach to the study of glaucony

food for thought mathematical approaches for the conversion of high resolution sclerochronological oxygen isotope records into sub annually resolved time series abstract oxygen isotope 18 o records of incrementally banded marine calcifiers provide high resolution information about modern and past environmental conditions however given their biological origin these records are often distorted by ontogenetic and seasonal growth pattern to evaluate their reliability many studies correlate skeletal 18 o records with instrumentally measured time series of environmental conditions using a variety of methods to recalculate their temporal framework lacking consistency and a limited traceability of many temporal alignment methods underline the need for standardized and flexible method for the temporal alignment of sclerochronological records here two methods for the temporal alignment of sclerochronological data and their application on measured oxygen isotope signatures of a fish otolith and a marine bivalve shell are presented and compared the first method is a flexible approach using a linear interpolation between carefully selected temporal reference points for recalculating ontogenetic growth effects with an optional extension accounting for seasonal growth oscillations the second approach uses the seasonally oscillating von bertalanffy growth function parameterized based on the oxygen isotope record to reconstruct the underlying growth model and reconstruct thereby its temporal framework using these methods we re align 18 o based water temperature records of a carlarius heudelotii otolith and a venus crebrisulca shell with measured sea surface temperature time series and compare the resulting correlation as well as the different underlying growth models our results show that both methods represent useful tools for the temporal alignment of sclerochronological records however underlying growth models strongly differ depending on the temporal alignment method and the parameters used for the reconstruction of the temporal framework this underlines the importance of a careful selection of a particular alignment method depending on the complexity of distortion due to seasonal and ontogenetic growth trajectories moreover we show that both organisms represent reliable paleoenvironmental archives providing sub seasonally resolved water temperature records

the relationship between calc alkaline volcanism and within plate continental rift volcanism evidence from scottish palaeozoic lavas lower carboniferous lavas from the midland valley and adjacent regions of scotland are mildly alkaline and intraplate in nature the sequence is dominated by basalt and hawaiite although mugearite benmoreite trachyte and rhyolite are also present basic volcanic rocks display the lil element and lree enrichment typical of intraplate alkali basalt terrains low initial87sr 86sr 0 7029 0 7046 high end 0 4 to 5 6 and moderately radiogenic206pb 204pb 17 77 18 89 ratios are also comparable with alkali basalts from other continental rifts and oceanic islands when the carboniferous lavas are compared with subduction related lavas of old red sandstone age erupted in and around the midland valley ca 50 ma earlier at 410 ma remarkable similarities are apparent significant overlap occurs in nd and pb isotopic compositions sr isotopic compositions are however more radiogenic in the older subduction related lavas this combined with high k and rb concentrations in ors lavas may be explained by the incorporation of a sediment component derived from the subducted slab which by lower carboniferous times had been lost from the mantle source region by convection a pronounced negative nb anomaly in the ors subduction related lavas may be explained by the retention of a nb bearing phase in the mantle during hydrous melting of the mantle wedge above the subduction zone allowing for the effects of the added component from the subducted slab there appears to be no necessity to invoke separate mantle source regions for the two suites of lavas both may have been derived from chemically similar portions of mantle if volcanic arc lavas are derived from the mantle wedge the implication is that such a source lies at relatively shallow depth within the upper mantle the same may therefore apply to the carboniferous continental rift basalts this evidence combined with the fact that there is no evident hot spot trail across the midland valley despite a long period of within plate volcanism and rapid plate movements during the carboniferous suggests that the alkali basalt magmatism is not the product of a deep seated mantle plume rather the volcanism appears to owe more to passive rifting and to diapiric upwelling from a source region within the uppermost mantle

deep lithospheric structure across the central african shear zone in cameroon summary teleseismic p and pkp arrival times recorded by a network of 40 seismic stations deployed along a 300 km profile across the adamawa plateau at the northern end of the volcanic line in central cameroon provide constraints on lithospheric thickness and anisotropy within the subcrustal lithosphere these data indicate a thinned lithosphere beneath the central african shear zone where seismologically defined asthenosphere upwells from a depth of about 190 km to about 120 km in a relatively narrow belt thus it has only a low amplitude effect on the observed gravity anomalies the bouguer gravity high over the garoua rift is consistent with crustal thinning beneath it an abrupt change of the lithospheric thickness beneath the northern boundary fault correlates with both the topographic relief and a distinct change of the orientation of relatively high and low velocity directions which we infer to be due to anisotropy within the subcrustal lithosphere this fault may represent an important accretionary suture zone dividing lithospheric blocks that originated in different tectonic settings and acquired different frozen in anisotropy

direct evidence of ancient shock metamorphism at the site of the 1908 tunguska event abstract shock metamorphism is rarely found at the surface of the earth the most used structures to identify shock metamorphism are true planar deformation features pdfs in quartz now accepted as diagnostic indicators of a meteorite impact here we present several lines of evidence for shock metamorphism and pdfs developed in quartz occurring on samples centered on a circular geological structure on mount stojkovic 60 54 06 n 101 55 40 e which lies within southern surface exposures of the siberian traps the shock event appears to have occurred during the eruption of the surface siberian traps basalts that cover this region curiously mount stojkovic lies within 3 km of the tree fall epicenter of the 1908 tunguska event based on current estimates of the phanerozoic impact distribution there is at most a 1 in 17 000 chance that the 1908 bolide would randomly fall on the site of a previous impact structure capable of creating shocked quartz just as improbable would be an airbust event incapable of creating a small crater that could have produced shock metamorphism our preferred least implausible hypothesis is that the shock metamorphism here was associated with a terrestrial event a hyperexplosive volcanic gas eruption called verneshot

belemnite biomineralization development and geochemistry the complex rostrum of neohibolites minimus abstract belemnites a group of extinct coleoid cephalopods were important components of mesozoic marine ecosystems their calcitic rostra are extensively used in biostratigraphy and geochemistry the preservation state of the rostra is a crucial factor for the interpretation of their geochemical data however their preservation is difficult to assess since no modern cephalopod forms calcitic rostra the biomineralization process of the rostrum which functioned as an internal skeleton is poorly understood for most species this also applies for the epirostrum a late ontogenetic extension of the rostrum which is only present in some belemnite species the primary structure and function of this character are still being debated controversially we have investigated the microstructure stable isotope 13 c 18 o and elemental composition mg ca sr ca fe ca mn ca of both ortho and epirostra of the belemnite species neohibolites minimus early cretaceous albian for comparison we studied argonauts argonauta argo these recent octopuses build a calcitic shell ortho and epirostra of n minimus show microstructural and geochemical differences cathodoluminescence microscopy and the microstructures of belemnites and argonauts indicate that blue orange luminescent growth lines in the studied belemnites are largely a primary biomineralization phenomenon and not solely due to diagenesis based in part on analogy to argonaut shell we suggest that the inner part of the belemnite epirostrum is a continuation of an originally organic apical line the development and evolution of the epirostrum as a potential sexually selected character is discussed well preserved epirostrum calcite has higher element ca ratios than the calcite of the orthorostrum suggesting a vital effect affecting these values we further found evidence for vital effects on the stable isotope signatures due to metabolic and kinetic fractionation our findings suggest a complex mineralization process of the studied rostra different microstructures with distinctive geochemical signatures occur in a single belemnite species vital effects played an important role in the rostrum geochemistry complicating the application of the rostra as paleoclimatic archives

cretaceous sea surface temperature evolution constraints from tex86 and planktonic foraminiferal oxygen isotopes it is well established that greenhouse conditions prevailed during the cretaceous period 145 66 ma determining the exact nature of the greenhouse gas forcing climatic warming and climate sensitivity remains however an active topic of research quantitative and qualitative geochemical and palaeontological proxies provide valuable observational constraints on cretaceous climate in particular reconstructions of cretaceous sea surface temperatures ssts have been revolutionised firstly by the recognition that clay rich sequences can host exceptionally preserved planktonic foraminifera allowing for reliable oxygen isotope analyses and secondly by the development of the organic palaeothermometer tex86 based on the distribution of marine archaeal membrane lipids here we provide a new compilation and synthesis of available planktonic foraminiferal 18o 18opl and tex86 sst proxy data for almost the entire cretaceous period the compilation uses ssts recalculated from published raw data allowing examination of the sensitivity of each proxy to the calculation method e g choice of calibration and places all data on a common timescale overall the compilation shows many similarities with trends present in individual records of cretaceous climate change for example both sst proxies and benthic foraminiferal 18o records indicate maximum warmth in the cenomanian turonian interval our reconstruction of the evolution of latitudinal temperature gradients low 48 palaeolatitudes reveals temporal changes in the valanginian aptian the low to higher mid latitudinal temperature gradient was weak decreasing from 10 17 c in the valanginian to 3 5 c in the aptian based on tex86 ssts in the cenomanian santonian reconstructed latitudinal temperature contrasts are also small relative to modern 14 c based on low latitude tex86 and 18opl ssts minus higher latitude 18opl ssts compared with 20 c for the modern in the mid campanian to end maastrichtian latitudinal temperature gradients strengthened 19 21 c based on low latitude tex86 and 18opl ssts minus higher latitude 18opl ssts with cooling occurring at low middle and higher palaeolatitude sites implying global surface ocean cooling and or changes in ocean heat transport in the late cretaceous these reconstructed long term trends are resilient regardless of the choice of proxy tex86 or 18opl or calibration this new cretaceous sst synthesis provides an up to date target for modelling studies investigating the mechanics of extreme climates

evidence for a composite organic inorganic fabric of belemnite rostra implications for palaeoceanography and palaeoecology carbonate skeletons of fossil marine organisms are widely used to reconstruct palaeoceanographic parameters specifically the geochemistry of jurassic and cretaceous belemnite rostra is traditionally interpreted to represent near sea surface seawater properties more recently an increasing number of workers have reported significant scatter in geochemical data e g 18o 13c element ca ratio when comparing rostra from the same stratigraphic level or within a single belemnite rostrum this scatter is not explained by differential diagenetic overprint alone here we report petrographic evidence on the primary ultrastructure of rostra of megateuthis middle jurassic and belemnitella and gonioteuthis late cretaceous the biogenic ultrastructure consists of a filigree framework of triaxial branches and tetrahedrons of variable size forming a honeycomb like network data presented here suggest that these rostra yielded as much as 50 to 90 primary pore space on the level of a working hypothesis and in analogy with modern cephalopods we propose that the pore space was formerly filled with body fluid and or organic compounds during the life time of these organisms intra rostral porosity was post mortem occluded by earliest diagenetic isopachous calcite cements of a non biogenic origin these may have been precipitated due to increased alkalinity related to the decay of organic matter if this holds true then the resulting fabric represents a composite biogenic abiogenic structure in order to optically separate the two calcite phases forming a single calcite fibre we employed a wide range of state of the art analytical tools to thin sections and ultra thin sections of well preserved specimens pending a verification of these well supported ultrastructural data by means of high resolution geochemical analyses from biogenic and abiogenic phases we suggest that these findings have significance for those using belemnite rostra as archives of their palaeoenvironment

remote telemetry of daily vertical and horizontal movement of nautilus in palau vertical depth migrations by the chambered cephalopod nautilus when moving into shallower waters at night were first documented by wiley1 although unsupported by quantitative data this observation strongly influenced the interpretation of the mode of life of nautilus and of the palaeoecology of fossil chambered cephalopods2 4 to determine whether these migrations do occur we mounted ultrasonic transmitters on four nautilus belauensis in palau the transmitters contained a strain gauge depth sensor that caused the transmitters to emit sonic pulses at intervals that varied with depth so that geographical position and depth could be ascertained our results indicate that at least in this population or geographical area vertical depth changes of up to 200 m per day are common although too soon to make generalizations about other populations of nautilus in the pacific it has been suggested that the morphological position of the siphuncle within the phragmocone of the chambered shell would increase the efficiency of vertical migrations m nautilus if such migrations were found to occur5 6 as similar siphuncle configurations are common in most post triassic nautiloids and some ammonoids6 7 it could be that vertical migration was common in many fossil forms as well

a lithospheric instability origin for the cameroon volcanic line the cameroon volcanic line cvl is an enigmatic structure that defies common dynamic models of melt generation and volcanic activity on earth there magma generation and intrusion has been sustained for more than 70 myr over a 1600 km long chain straddling the ocean continent boundary with no detectable spatial age progression the chain is nearly perpendicular to the coastline and terminates in a y shaped structure that has not been affected by absolute plate motions implying that the mantle upwelling that feeds magmatic activity is attached to the continent we propose that this form of volcanism is due to a new type of instability that may develop within the subcontinental lithospheric mantle at the edge of a continent laboratory experiments document how lithosphere beneath a continental block of finite size can become unstable due to cooling from above the instability pattern is made of linear upwellings and downwellings that converge radially towards the center of the continent in an outer region and an array of polygonal cells in a central region the pattern is characterized by branching structures that are reminiscent of the strike and y shaped outline of the cvl the instability develops over long timescales with small rates of upwelling and melting and is attached to the continent by construction downwellings adjacent to upwellings induce compression in the crust which may account for deformation in the benue trough just before the onset of cvl magmatism

a teleseismic delay time study across the central african shear zone in the adamawa region of cameroon west africa summary p wave relative teleseismic residuals were measured for a network of seismological stations along a 300 km profile across the adamawa plateau and the central african shear zone of central cameroon to determine the variation in crust and upper mantle velocity associated with these structures a plot of the mean relative residuals for the stations shows a long wavelength 300 km variation of amplitude 0 45 s the slowest arrivals are located over and just to the north of the faulted northern margin of the adamawa plateau the residuals do not correlate with topography surface geology or the previously determined crustal structure in any simple way the aki inversion technique has been used to invert the relative residuals into a 3 d model of velocity perturbations from a mean earth model the results show the region is divided roughly into three blocks by two subvertical boundaries striking ene and traversing both the crust and upper mantle down to depths greater than 190km the central block which is 2 per cent slower than the adjacent blocks roughly corresponds to the central african shear zone the adamawa plateau as an individual uplifted area is explained by the interaction of a regional anomalous upper mantle associated with the west african rift system and the central african shear zone which provided a conduit for heat flow to the surface

chemical controls of cathodoluminescence of natural dolomites and calcites new data and review calcites and dolomites from the late precambrian bonahaven formation of scotland exhibit luminescence when mnco3 0 03 wt dolomite or 0 06 wt calcite and feco3 2 2 5 wt dolomite comparison with other published data shows close similarity in the position of fe quenching in dolomite but more variability in the position of mn activation in calcites and dolomites and the onset of fe quenching in calcites these anomalies are thought to relate to chemical controls subsidiary to the dominant factors of fe and mn concentration it is not practical to make a useful comparison between operating conditions of different luminescence instruments because of differences in design and an inability to measure routinely the current actually on the specimen surface

the control of cathodoluminescence in dolomite by iron and manganese variations in the cathodoluminescent properties of carbonates are usually attributed to differing proportions of manganese mn2 as the most important activator and iron fe2 as the main inhibitor of luminescence interactions between manganese and iron concentrations and the luminescent properties of dolomite are demonstrated by petrographic and chemical analyses of 86 samples of dolomite representing a range of depositional environments and ages cambrian to cretaceous and a wide geographical distribution north america and europe iron and manganese are positively correlated in the dolomites with the former showing a greater range of variation very small amounts of manganese are sufficient to activate the luminescence and as little as 100 ppm mn2 is present in highly luminescing samples the intensity of luminescence is not proportional to the manganese concentration iron begins to quench luminescence as its concentration reaches 10 000 ppm above that level luminescence is rapidly lost and total extinction occurs among samples containing more than 15 000 ppm fe2 regardless of the manganese concentration

carbon and oxygen isotope composition of nautilus macromphalus a record of thermocline waters off new caledonia abstract this study investigates the controls on the stable isotope composition of shell nacreous layer of a modern nautilus macromphalus from new caledonia closely spaced samples were taken both along growth lines isochrons and growth axis time series carbon isotope compositions 13 c 0 3 to 1 pdb of the shell decrease in the domains of maximal growth 0 3 and muscle insertion 0 4 maximal 13 c variations of about 1 are recorded in time series a global ontogenetic decrease of 13 c values is observed for both dorsal and ventral areas 0 4 to 0 8 and can be ascribed to a metabolic effect with age or to changes in the food source by contrast oxygen isotope compositions are quite constant 1 1 18 o

trace element and isotopic zonation in vein calcite from the mendip hills uk with spatial process correlation analysis abstract high resolution scanning proton microprobe spm analyses of fissure filling calcite from the mendip hills uk show fine scale chemical zonation patterns in fe and mn concentrations from fissure centre to wall these fluctuations are sharp and steep peaks of 0 01 0 1 mm width with concentrations changing by as much as 8000 ppm zonation in pb and zn is similar to that obtained for mn and fe and maxima in the concentrations of these two elements are correlated with maxima in mn concentration longer wavelength fluctuations 1 0 3 0 mm are evident in data obtained for sr for which changes in concentration are gradual and fluctuate by at most 500 ppm auto correlation calculations show that oscillations in the mn and fe data have a wavelength of 0 9 1 3 mm in contrast to auto correlations and cross correlations with zn and pb which indicate wavelengths of 0 4 mm strontium correlations indicate a peak to trough distance of 4 2 mm which implies a much longer wavelength fluctuation in the sr data cross correlations also clearly show that pb and zn concentrations co vary strongly cross correlation function value of 0 7 at lag 0 but all other cross correlations are weak these computations demonstrate that intrinsic controls on trace element partitioning cannot alone account for the observed patterns long period fluctuations are interpreted to result from a sustained change in the starting composition of the aqueous phase while the high frequency oscillations are interpreted to be caused by mixing reactions among fluids that have reacted with different portions of country rock prior to calcite precipitation analyses of the carbon oxygen and strontium isotopes from these vein calcites have also been completed 18o plotted as a function of 13c results in an inverted triangular array we interpret this along with the trace element data as resulting from three distinct fluids participating in the formation of these fissure fills a low mn fe high sr marine fluid apex at 18o 0 13c 4 both relative to pdb a high mn fe low sr hydrothermal fluid 2 9 5 and a low mn fe low sr meteoric fluid 12 5 the trace element and isotopic compositions of this zoned calcite thus document the following processes in detail 1 the formation of a meteoric fissure system triassic 2 reactions with hotter and more reduced circulating fluids and 3 the subsequent flooding of the system with seawater during transgression of the area rhaetian early jurassic strontium isotopic data from a belemnite located within one of the fissures gives an early jurassic age of approximately 198 ma hot reduced fluids with high metal concentrations were probably forced up into these fissures by seismic pumping during movement on associated regional faults

mollusc and brachiopod skeletal hard parts intricate archives of their marine environment the biogenic carbonate hard parts of fossil bivalves cephalopods and brachiopods are among the most widely exploited marine archives of phanerozoic environmental and climate dynamics research the advent of novel analytical tools has led many workers to explore non traditional geochemical and petrographic proxies and work performed in neighbouring disciplines sheds light on the complex biomineralization strategies applied by these organisms these considerations form a strong motivation to review the potential and problems related to the compilation and interpretation of proxy data from bivalve cephalopod and brachiopod hard parts from the viewpoint of the sedimentologist and palaeoceanographer specific focus is on the complex biomineralization pathways of a given dissolved ion or food particle from its aquatic environment via the digestion and biomineralization apparatus in molluscs and brachiopods and its incorporation into a biomineral given that molluscs and brachiopods do not secrete their hard parts from seawater but rather from their mantle and periostracum this paper evaluates differences and similarities of seawater versus that of body fluids cephalopods bivalves and brachiopods exert a strong biological control on biomineralization that to some degree may buffer their shell geochemistry against secular changes in seawater chemistry disordered amorphous calcium carbonate precursor phases later transformed to crystalline biominerals may be significant in carbonate archive research due to expected geochemical offset relative to the direct precipitation of stable phases a reasonable level of understanding of the related mechanisms is thus crucial for those who use these skeletal hard parts as archives of the palaeo environment the impact of what is commonly referred to as biological factors on the geochemistry of mollusc and brachiopod hard parts is explored for conventional isotope systems such as carbon oxygen strontium and traditionally used element to calcium ratios in particular the often used 13ccarb or the mg ca and sr ca elemental proxies are fraught with problems an interesting new research field represents the analysis calibration and application of non traditional proxies to mollusc and brachiopod hard parts examples include the carbonate clumped isotope 47 approach and the analysis of the isotopes of ca mg n li s or element to ca ratios such as li ca or b ca and rare earth elements based on considerations discussed here a series of do s and don ts in mollusc and brachiopod archive research are proposed and suggestions for future work are presented in essence the suggestions proposed here include experimental work also field experiments making use of recent archive organisms or where possible a reasonable recent analogue in the case of extinct groups moreover the detailed understanding of the architecture of mollusc and brachiopod hard parts and their ultra structures must guide sampling strategies for geochemical analyses where feasible a detailed understanding of the diagenetic pathways and the application of multi proxy and multi archive approaches should form the foundation of fossil carbonate archive research the uncritical compilation of large data sets from various carbonate shelled organisms collected at different locations is not encouraged

ontogeny and habitat change in mesozoic cephalopods revealed by stable isotopes δ18o δ13c abstract stable isotope 18 o and 13 c ratios were measured in successive aragonitic shell sequences of ammonoids class cephalopoda to determine whether their depth distributions changed within ontogeny and whether stable isotope values differ in various morphological groups e g leiostraca vs trachyostraca we concentrate mainly on 18 o for temperature results and added 13 c data to obtain information on the ontogenetic history for which full spiral measurements were undertaken for the first time to obtain valid stable isotope data from ammonoid shells we measured ontogenetic sequences full shell within different genera data sets from the jurassic cadoceras and cretaceous hypacanthoplite s nowakites were chosen due to the pure primary aragonitic shell preservation the study was designed to extract better information on the habitat and life cycle of fossil cephalopods e g ammonoids in comparison with recent cephalopods e g nautilus spirula sepia possessing equivalent or comparable hard parts the data from three genera suggest different modes of life in at least two morphological groups we detected and established two main groups with different ontogenetic strategies based on the 18 o data the wcw type warm cool warm type of cadoceras resembles strategies in nautilus and sepia which migrate from shallow into deeper environments and back in ontogeny wc type warm cool type and the cw type cool warm type of hypacanthoplites resembling the first two migration phases of spirula cwc type which migrates from deeper into shallower and back again into deeper habitats the main three phases revealed by both 18 o and 13 c data sets most probably reflect diet changes in juvenile to mid aged individuals followed by a habitat change for spawning adults in cadoceras the temperatures range from 21 2 c for juveniles down to 12 1 c for mid aged individuals and back up 16 9 c in adults the cw type strategy of hypacanthoplites involves a temperature range of 22 8 c to 28 9 c the respective mean values are 24 2 c juveniles 25 8 c middle phase and 27 8 c adults the 13 c values also revealed three ontogenetic stages in cadoceras and hypacanthoplites including two major shifts from positive to negative and from negative to positive values which probably correspond to sexual maturation the initiation of reproduction and concomitant changes in diet the presented data combined with previous ontogenetic studies e g stable isotopes on spirula nautilus and sepia can be used as proxies to directly correlate the habitats and ontogeny of recent and fossil cephalopods

petrology of the bimodal cenozoic volcanism of the kapsiki plateau northernmost cameroon central africa the kapsiki plateau is the northernmost volcanic zone of the cameroon line the volcanism 27 35 ma is of alkaline type and has a typical bimodal lava series diversity with basalts and hawaiite as mafic lavas and phonolites trachytes and rhyolites as felsic lavas mg rich olivine phenocrysts occur only in basalts the hawaiite contains andesine olivine and ca rich pyroxene phenocrysts and sanidine and quartz xenocrysts the phonolites contain alkali feldspar and na rich clinopyroxene phenocrysts two types of trachytes occur peralkaline trachytes with ti na and f rich aegirine augite richterite arfvedsonite phenocrysts and non peralkaline trachytes with an aenigmatite type undetermined mineral ti rich biotite and zircon phenocrysts similarly two types of rhyolites occur peralkaline with quartz and arfvedsonite phenocrysts and non peralkaline with quartz and biotite phenocrysts differentiation indices thornton and tuttle 1960 of the lavas range from 22 to 97 with a large gap in the range 34 82 some basalts are primitive 530 ppm ni 1100 ppm cr in basaltic lavas phonolites and non peralkaline trachytes and rhyolites zr and nb covary with approximately constant ratios o3 1 zr nb 5 3u however peralkaline trachytes and rhyolites have high concentrations in zr up to 2180 ppm and nb up to 780 ppm with correlative higher zr nb ratios 6 3 8 3 some rhyolites have abnormal ree patterns with kinks depleted in light ree probably resulting from stability of na ree f complexes under hydrothermal conditions despite a large gap between basaltic and felsic lavas major and trace element distributions indicate co magmatism for both the basaltic and felsic lavas the differentiation of the lava series is dominated by crystal fractionation the role of fluids in rhyolite genesis being of minor effect as evidenced by constant values of y ho and zr hf throughout the series the kapsiki plateau basalts are similar in their chemical and isotopic data character to other basalts from both the continental and oceanic sectors of the cameroon line the continental crust appears to have no significant role in their genesis the hawaiite mineralogical and geochemical characteristics are consistent with an origin by mixing of basaltic and felsic phonolitic magmas the kapsiki plateau basaltic magmas may have originated from an infra asthenospheric reservoir similarly to other basaltic magmas generated throughout the cameroon line the sr isotope variations observed in trachytes and rhyolites point to some contamination of the magmas by crustal materials while the nd isotopic composition is only slightly affected q 2000 elsevier science b v all rights reserved

carbonate mineral water interactions in sulfide rich mine tailings the chemical composition and mineralogy of coatings on carbonate minerals from mine tailings have been studied using aqueous geochemical methods time of flight laser ionization mass spectrometry tof lims and transmission electron microscopy tem the goal is to study major and trace element partitioning between the aqueous and solid phase and to infer mechanisms that control the concentrations of elements in the pore water of sulfide rich mine tailings pore water samples and carbonate mineral grains were collected from four geochemically distinct zones within the tailings oxidation of sulfide minerals near the surface results in a large range in pore water ph 3 85 to 6 98 and aqueous concentrations of metals and sulfate with increasing depth in the tailings mineral water interactions lead to increasing ph and decreasing concentrations of metals and sulfate calculated mineral saturation indices trends in the abundance of ca fe mg and mn in tof lims profiles through the secondary coatings and electron diffraction patterns obtained from the coatings suggest that precipitation dissolution of jarosite group minerals gypsum goethite akaganeite amorphous fe oxyhydroxides and siderite control the aqueous ca fe na k and so4 concentrations the occurrence of secondary coatings on primary minerals is widespread and reactions with the secondary minerals rather than the primary mineral substrate probably represent the principal controls on trace element distributions in the pore water the data indicate that adsorption surface complexation and co precipitation reactions are important controls on the concentrations of trace elements in the pore water the occurrence of siderite coatings on the surface of ankerite grains suggests that fe bearing dolomite structure carbonate minerals dissolve incongruently this corroborates inferences made by previous workers that solubility differences between calcite and siderite lead to calcite dissolution and siderite precipitation during acid neutralization the accumulation of secondary coatings will diminish the rate of mineral dissolution reactions involving the primary minerals consequently the use of kinetic rate constants obtained from the literature for simulating the dissolution of primary mineral phases such as the carbonates and alumino silicates will likely overestimate the actual rates

origin of island dolostones a case study from the cayman formation miocene cayman brac british west indies abstract cayman brac the easternmost of the cayman islands is 19 km long 1 5 to 3 km wide and rises 40 m above sea level at its eastern end geographically isolated by the deep oceanic waters of the caribbean sea this island with its thick succession of pervasively dolomitized tertiary rocks is a natural laboratory for assessing the origin of island dolostones dolostones in the miocene cayman formation 100 m thick with most crystals 55 mol caco3 geochemically they are characterised by 13c values of 1 6 to 3 5 18o values of 2 3 4 0 80 279 ppm sr 52 340 ppm fe and 9 82 ppm mn the inverse correlation between 18o and mol caco3 and positive correlation between sr and mol caco3 largely reflect kinetic effects on oxygen isotope fractionation and the sr partition behaviour between dolomite and water dolomite stoichiometry indicates formation from waters with a high mg ca ratio and 18o values corrected for biases associated with dolomite stoichiometry and phosphoric acid fractionation indicate formation from normal seawater like fluids under near surface conditions the 87sr 86sr ratios point to two phases of dolomitization phase i in the late miocene 6 8 ma caused partial dolomitization of the basal part of the cayman formation phase ii during the pliocene to early pleistocene 1 5 ma completed dolomitization of the cayman formation both phases of dolomitization were mediated by similar fluids although available information suggests that dolomitization was probably linked to sea level fluctuations the timing of dolomitization relative to the transgressive regressive cycle remains open to debate

stable isotope data δ18o δ13c of the ammonite genus simbirskites implications for habitat reconstructions of extinct cephalopods abstract the accurate habitats of the extinct ammonites and belemnites are largely unknown most ammonites are thought to have had a pelagic lifestyle while belemnites are often considered to have dwelled in deeper colder waters stable isotope analysis 18o 13c provides a useful method to reconstruct the habitats of these two groups of extinct cephalopods but is at the same time limited by various unknowns including the isotopic composition of the past seawater vital effects and diagenesis in this paper stable isotope data from 12 ammonite shells simbirskites spp from the upper hauterivian of the lower saxony basin northwest germany are presented ontogenetic isotope profiles have been obtained from six of these shells in order to reconstruct habitat changes during their lifetime these new ammonite data are combined with published stable isotope data from belemnites hibolithes jaculoides and tex86 palaeotemperature estimates from the same section the combination of isochronous ammonite and belemnite stable isotope data shows that the resulting values of both groups go along with each other calculated palaeotemperatures of the two groups differ by 5 10 c with belemnites always showing the colder temperatures all juvenile shells show an increase of the 13camm to more positive values throughout their ontogeny they are stable in an adult shell fragment the incorporation of carbon isotopes in the ammonite shell therefore correlates with ontogeny and is influenced by metabolic effects probably linked to the shell growth rate the isotope profiles further suggest vertical habitat changes during the ontogeny of the ammonites indicating that the 13camm values might record a combination of environmental and metabolic signals taking into account studies on oxygen isotope fractionation of recent aragonitic and calcitic mollusc shells a similar pelagic habitat is proposed here for both ammonites and belemnites

the giant pacific oyster crassostrea gigas as a modern analog for fossil ostreoids isotopic ca o c and elemental mg ca sr ca mn ca proxies 1 modern analogs are an essential part of palaeoclimate studies because they provide the basis for the understanding of geochemical signatures of fossils ostreoids are common in many sedimentary sequences and because of their fast growth high temporal resolution sampling of past seasonal variability is possible here two shell structures of modern giant pacific oysters crassostrea gigas the chalky substance and foliate layers have been sampled for trace element distributions mg sr mn and stable isotope variability c o ca oxygen isotopes exhibit a clear seasonal signature mean carbon isotope values of different oysters agree within 0 1 but ontogenic variability is complicated by shell growth patterns and potential small vital effects the calcium isotope ratios are found to be constant throughout ontogeny within analytical precision at a value of 44 40ca 0 68 0 16 2 sd srm 915a which is consistent with other bivalve species calcium isotope ratios in oyster shell material might thus be a possible proxy for palaeo seawater calcium isotope ratios element ca ratios are significantly higher in the chalky substance than in the foliate layers and especially high sr ca and mn ca ratios are observed for the first growth season of the oysters mg ca ratios in the chalky substance show a negative correlation with 18o values compatible with a temperature dependence whereas this correlation is absent in the foliate layers seasonal changes of sr ca are controlled by metabolic processes whereas for mn ca an additional environmental control is evident

isotope paleontology growth and composition of extant calcareous species abstract isotope paleontology uses the isotopic composition of fossil remains of organisms to make inferences about the physical surroundings of growth of the organisms especially temperature and to obtain clues about life history and modes of growth in calcareous fossils oxygen isotopes are mainly used in the former and carbon isotopes in the latter however since physical surroundings and organism response are intimately associated both types of information are contained in each of the isotopic signals to explore the potential of isotope paleontology and to provide a basis for reconstruction a broad range of extant organisms has been studied taking the pioneering work of epstein and associates as a starting point results are summarized for a representative sampling of these studies with emphasis on work at the laboratories of the authors from the mid seventies to the present the organisms considered are nannoplankton benthic algae planktonic and benthic deep sea foraminifera larger foraminifera sponges corals bryozoans polychaetes arthropods bivalves gastropods cephalopods and vertebrates fish otoliths the survey broadly suggests that regarding oxygen isotopes materials tend to be precipitated close to equilibrium with the surrounding seawater as postulated by urey and that for carbon isotopes disequilibrium is the rule life spans growth rates differential seasonal growth and age of reproductive activity can be extracted under favorable circumstances from individual shells and skeletal parts in detail the interpretation of isotope records of individual shells is quite complicated and simple models will fail to give satisfactory results in many or most cases

temperatures and oxygen isotopic composition of phanerozoic oceans abstract the temperature of ancient oceans is an important constraint for understanding the climate history of our planet the classical oxygen isotope paleothermometry on fossil shells while very proficient when applied to the younger cenozoic portion of the geologic record is believed to yield only unreliable results for the phanerozoic deep time either because the empirically well documented secular trend to more negative 18 o values with increasing age was generated by post depositional recrystallization processes or if primary implies ecologically unpalatable hot early oceans here we present a compilation of 18 o measurements for 58 532 low mg calcite marine shells that cover almost the entire phanerozoic eon argue that the secular decline of about 6 is primary propose that it reflects the changing oxygen isotopic composition of sea water and define a new baseline trend for 18 o of paleo sea water the latter providing a new template for calculation of ambient habitat temperatures of fossil specimens the resulting pattern for fossil taxa foraminifera brachiopods belemnites and bivalves mimics their modern counterparts in temperature ranges and modes this conceptual framework enables application of actualistic concepts to ambient habitat temperatures of fossils and provides us with a long overdue tool for interpretation of deep time geologic history

mineralogy and mn geochemistry of laboratory synthesized dolomite abstract dolomite was synthesized in hydrothermal bombs to assess influences on mn partitioning into the mg and ca sites calcite was added to magnesium chloride solutions doped with 0 10 20 or 50 ppm mn runs were made for 8 to 241 hr at 192 and 224 c the calcium content of dolomite increased to 60 64 after 75 hr at 192 c and reverted to stoichiometry thereafter increases in the mn content of the starter solution progressively retarded formation of dolomite for dolomites formed without added mn or formed in less than 40 hr with 10 ppm added mn the esr signals were too broad to permit determination of mn site distribution ratios measurable ratios of mn in the mg site to mn in the ca site vary as a linear function of time from 0 3 to 7 for samples prepared at 192 c and from 3 to 16 for those prepared at 224 c stoichiometric dolomites have higher mn partitioning ratios than nonstoichiometric dolomites as observed in natural systems dolomites formed in supratidal sabkha early groundwater and dorag conditions may differ in their mn signature from those formed during burial diagenesis

past and present circulation of co 2 bearing fluids in the crystalline gran paradiso massif orco valley north western italian alps tectonic and geochemical constraints abstract in the orco valley inside the gran paradiso massif 3 main fault systems are present a e w striking faults dipping at 45 60 to the n b high angle nw se striking faults and c high angle ne sw to nne ssw striking faults the e w striking faults and the interposed nw se faults appear to represent a cogenetic structural association related to a larger scale transtensional shear zone while the ne sw faults are probably inherited by an older discontinuous deformation stage breccia bodies or veins mostly consisting of carbonate siderite ankerite calcite quartz with sulphide au mineralisation recording a multistage mesothermal evolution occur along both e w and nw se fault systems three water types are recognised type i ca 2 hco 3 waters with minor so 4 2 type ii ca 2 na hco 3 waters varying towards na hco 3 cl waters and type iii mg 2 hco 3 waters type i and type iii groundwaters are freshly recharged waters only slightly exchanged with rocks type ii includes waters which come into contact with carbonate fracture fillings and geochemical modelling indicates that dissolution of carbonates along fractures is the main process controlling the groundwater chemistry these waters evolve in a system open to uprising co 2 and their strongly negative 13 c co 2 suggests a substantial organic component in the co 2 discharge in the past co 2 bearing fluids were likely responsible for the formation of fe bearing carbonate fracture fillings the persistence through time of the co 2 flux in the region has important implications for the reconstruction of the alpine tectonic evolution and deep structure

a simple global model of plate dynamics and mantle convection cooling and thickening of lithospheric plates with age and subduction result in large scale horizontal density contrasts tending to drive plate motions and mantle flow we quantify the driving forces associated with these density contrasts to determine if they can drive the observed plate motions first two dimensional models are computed to evaluate the effects of assumed rheologies and boundary conditions we are unable to obtain platelike behavior in viscous models with traction free boundary conditions the piecewise uniform velocities distinctive of plate motion can be imposed as boundary conditions and the dynamic consistency of the models evaluated by determining if the net force on each vanishes if the lithosphere has a newtonian viscous rheology the net force on any plate is a strong function of the effective grid spacing used leading to ambiguities in interpretation incorporating a rigid plastic lithosphere which fails at a critical yield stress into the otherwise viscous model removes these ambiguities the model is extended to the actual three dimensional spherical plate geometry the observed velocities of rigid plastic plates are matched to the solution of the viscous stokes equation at the lithosphere asthenosphere boundary body forces from the seismically observed slabs from the thickening of the lithosphere obtained from the actual lithospheric ages and from the differences in structure between continents and oceans are included interior density contrasts such as those resulting from upwellings from a hot bottom boundary layer are assumed to occur on a scale small compared to plate dimensions and are not included the driving forces from the density contrasts within the plates are calculated and compared to resisting forces resulting from viscous drag computed from the three dimensional global return flow and resistance to deformation at converging boundaries the rms residual torque is 30 of the driving torque the density contrasts within the plates themselves can reasonably account for plate motions body forces from convection in the interior may provide only a small net force on the plates at converging boundaries the lithosphere has a yield stress of 100 bars drag at the base of the plates is 5 bars and resists plate motion the net driving forces from subducting slabs and collisional resistance are localized and approximately balance driving forces from lithospheric thickening are distributed over the areas of the plates as is viscous drag the approximate balance of these two forces predicts plate velocities uncorrelated with plate area as observed the model represents a specific case of boundary layer convection the dynamical results are consistent with either upper mantle or mantle wide convection

impact of diagenetic alteration on brachiopod shell magnesium isotope δ26mg signatures experimental versus field data due to their thermodynamically stable low mg calcite mineralogy the shells of brachiopods are often counted among the most reliable archives of the physicochemical conditions that occurred during the phanerozoic in marine waters consequently traditional and non traditional isotope and elemental proxy data from brachiopod valves have been analyzed in numerous studies and results obtained have been placed in context with ancient seawater properties this paper tests the sensitivity of brachiopod shell magnesium isotope 26mg data to diagenetic alteration we apply a dual approach by i performing hydrothermal alteration experiments using meteoric marine and burial reactive fluids and ii comparing these data to naturally altered ancient brachiopod shells the degree of alteration of individual shells is assessed by a combination of fluorescence and cathodoluminescence microscopy the absence of luminescence might indicate both well preserved shell material but also the secondary enrichment of quenching elements such as iron along diagenetic pathways complementary oxygen isotope data provide insight into the question of open versus closed system behavior of brachiopod shells brachiopod shell magnesium isotope values respond to differential fluid temperature chemistry and experiment durations the patterns observed are complicated by the interplay of kinetic and thermodynamic patterns and the presence of variable amounts of water soluble and water insoluble organic matter within these biominerals generally the range in bulk 26mg from experimentally altered 1 52 and that of bulk samples from ancient diagenetically altered brachiopod valves 1 53 exceed the geochemical variability of 26mgbrachiopod bulk values of most recent specimens 1 26 in the lower and upper range more 26mg enriched 0 8 and more 26mg depleted 0 7 values respectively are found in altered shells in comparison to unaltered ones the data shown here are considered significant for those aiming to reconstruct palaeoenvironmental parameters based on brachiopod archives consequently we propose tentative guidelines for magnesium isotope research applied to ancient carbonates

effect of a jurassic oceanic anoxic event on belemnite ecology and evolution the toarcian oceanic anoxic event t oae 183 million y ago is possibly the most extreme episode of widespread ocean oxygen deficiency in the phanerozoic coinciding with rapid atmospheric pco2 increase and significant loss of biodiversity in marine faunas the event is a unique past tipping point in the earth system where rapid and massive release of isotopically light carbon led to a major perturbation in the global carbon cycle as recorded in organic and inorganic c isotope records modern marine ecosystems are projected to experience major loss in biodiversity in response to enhanced ocean anoxia driven by anthropogenic release of greenhouse gases potential consequences of this anthropogenic forcing can be approximated by studying analog environmental perturbations in the past such as the t oae here we present to our knowledge the first organic carbon isotope record derived from the organic matrix in the calcite rostra of early toarcian belemnites we combine both organic and calcite carbon isotope analyses of individual specimens of these marine predators to obtain a refined reconstruction of the early toarcian global exogenic carbon cycle perturbation and belemnite paleoecology the organic carbon isotope data combined with measurements of oxygen isotope values from the same specimens allow for a more robust interpretation of the interplay between the global carbon cycle perturbation environmental change and biotic response during the t oae we infer that belemnites adapted to environmental change by shifting their habitat from cold bottom waters to warm surface waters in response to expanded seafloor anoxia

evolution of middle to late cretaceous oceans a 55 m y record of earth s temperature and carbon cycle a new 55 m y global compilation of benthic foraminifera 13 c and 18 o for the middle to late cretaceous shows that there was widespread formation of bottom waters with temperatures 20 c during the cretaceous greenhouse world these bottom waters filled the silled north atlantic and probably originated as thermocline or intermediate waters in the tropical oceans carbon burial during the cretaceous oceanic anoxic events produced a positive 13 c shift in global carbon reservoirs but this is not particularly large especially by comparison with the remarkable late paleocene carbon maximum the interbasin 13 c gradient was unusually large during the cretaceous hot greenhouse probably because the north atlantic sills prevented the free exchange of waters in the deep basin the hot greenhouse ended when the equatorial atlantic gateway opened sufficiently to flood the deep north atlantic with relatively cool polar waters formed in the southern ocean

estimating palaeo water depth from the physical rock record abstract palaeo water depth and its change with time is a key factor in environmental analysis and in sedimentology in general the literature published on this topic and on related subjects however is substantial albeit scattered within and between different communities geologists oceanographers engineers physicists etc here i focus on proxies for palaeo bathymetry as obtained from the physical rock record floral faunal and chemical evidence for palaeo water depth being equally important must be dealt with elsewhere an assessment of the main depth related parameters in actualistic settings is presented and their applicability to the fossil sedimentary record discussed the outcome reveals the full complexity of this topic there is for example no such thing as an average wave base depth applicable to a wide range of fossil case settings this because wave and current climates in general and particularly so in neritic and coastal settings are intriguingly complex furthermore observations from modern oceans are not a priori applicable to fossil ones acknowledging these problems and limitations critically evaluated quantitative proposals for depth indicative facies and features in the sedimentary record are presented and error bars discussed

the lake nyos gas disaster chemical and isotopic evidence in waters and dissolved gases from three cameroonian crater lakes nyos monoun and wum abstract to better understand the cause of the nyos gas disaster of august 21 1986 we conducted geochemical and limnological surveys in october 1986 of three lakes nyos monoun and wum which are located in the cameroon volcanic zone that is characterized by a prevalence of young alkaline basalts and basanitoids lake wum was studied as a non active control co2 is dissolved in significant concentrations about 1 5 of saturation in gas active lakes nyos and monoun but is virtually absent in lake wum stable isotopic ratios of total dissolved carbon 13c 3 for nyos and 5 5 for monoun and of helium 5 7 ratm for nyos and 3 6 ratm for monoun indicate a mantle origin of these gases however so42 and cl concentrations are found to be very low concentrations of dissolved chemical species like fe2 mg2 ca2 and hco3 are high in the two gas active lakes whereas they are very low in the gas inactive lake high salinities in the gas active lakes are probably due to dissolution of indigenous mafic rocks and transported lateritic soil in acidic co2 rich warm water the gas active lakes are characterized by increasing temperature and salinity with increasing depth indicating an active influx of heat and dissolved materials at the bottom density estimates show that the lake water is stably stratified in spite of the inverse temperature profile of the lakes on account of dissolved chemical species the concentrations of dissolved carbonate species co2 aq and hco3 are positively correlated with those of ionic dissolved species indicating their common occurrence in the bottom water the august 1986 gas bursts from lake nyos were most likely caused by rapid exsolution of dissolved co2 within the lake an explosive process such as a phreatic eruption or a co2 gas jetting from beneath the bottom is unlikely because of low concentrations of cl and so42 no oxygen isotopic shift low turbidity and no reported perturbation of the bottom sediments exsolution of co2 bubbles could occur if co2 saturated bottom water was displaced upwards by an increased influx of high salinity water from the bottom during the rainy season exsolution of co2 at the upper layers was possibly accelerated by upwelling of a two phase fluid co2 bubbles and solution a mechanism known as a pneumatic lift pump resulting in discharge of a large amount of co2 gas the h2s concentration in the gas cloud must have been kept far below the lethal level because of a high fe2 concentration of the lake water

new type of compositional zoning in calcite insights into crystal growth mechanisms compositional zoning of trace elements is observed in time equivalent regions within 10 overline 1 4 growth sectors of natural and synthetic calcite single crystals and has been called intrasectoral zoning to distinguish it from conventional sectoral zoning differential interference contrast microscopy shows that 101 overline 1 4 faces grow by the spiral mechanism cathodoluminescence microscopy and electron probe microanalyses reveal that trace element partitioning differences on 101 overline 1 4 faces correspond exactly to crystallographically controlled orientations of growth steps effective partitioning of mg and mn varies up to a factor of four between time correlative growth steps spreading in different directions effective sr partitioning varies by approximately 20 and is inversely correlated with enrichment trends of mg and mn preferential incorporation of different aqueous species at different growth steps may provide an explanation for morphological and chemical variation in natural calcites

the jurassic history of the africa antarctica corridor new constraints from magnetic data on the conjugate continental margins abstract finding the best fit for east and west gondwana requires a detailed knowledge of the initial jurassic movements between africa and antarctica this study presents results of systematic and densely spaced aeromagnetic measurements which have been conducted in 2009 2010 across the astrid ridge antarctica and in the western riiser larsen sea to provide constraints for the early seafloor spreading history between both continents the data reveal different magnetic signatures of the northern and southern parts of the astrid ridge which are separated by the astrid fracture zone the southern part is weakly magnetised corresponding to the low amplitude anomaly field of the southwestern riiser larsen sea in contrast the northern astrid ridge bears strong anomalies of positive value furthermore several sets of trends are visible in the data in the mozambique channel we extended the existing magnetic spreading anomaly identifications combined with the spreading anomalies in the conjugate riiser larsen sea they were used to establish a new model of the relative movements of africa and antarctica after the breakup of gondwana in jurassic times a detailed model for the emplacement of the mozambique ridge is now incorporated the model postulates a tight fit between africa and antarctica and two stages of breakup the first of which lasting until 159 ma m33n during this stage antarctica rotated anticlockwise with respect to africa the grunehogna craton cleared the coastal plains of mozambique to a position east of the mozambique fracture zone the southern astrid ridge is interpreted to consist of oceanic crust also formed during this first stage prior to the riiser larsen sea during the second stage antarctica moved southward with respect to africa forming the mozambique basin and the conjugate riiser larsen sea the mozambique ridge and the northern natal valley were formed at different spreading centres being active subsequently

seismicity of the cameroon volcanic line 1982 1990 abstract this paper is dedicated to soba djallo director of irgm who died in 1991 results of seismic monitoring of the continental segment of the cameroon volcanic line for the period 1982 to 1990 are reported mount cameroon continues to be seismically the most active area with a well defined seismicity pattern characterized by single and swarm events with duration magnitudes between 2 and 3 occurring at depths down to 55 km on average the earthquakes here occur at the rate of about 2 events every 3 days further north the seismicity is low except for isolated felt events located along the foumban shear zone which probably controls the location of the earthquakes as well as the volcanic centres making up the volcanic line during this eight year period two fatal carbon dioxide gas emissions from crater lakes occurred in 1984 l monoun and 1986 l nyos causing 37 and 1700 deaths respectively seismic monitoring indicates that no seismic activity was associated with these lakes thus favouring an aseismic cause to the disasters these gas emissions the increased number of felt earthquakes and a recent natural explosion on mount cameroon suggest either a more active phase of the cameroon volcanic line and or a greater awareness by the local population of the phenomena associated with this volcanic province

geophysical evidence of cretaceous volcanics in logone birni basin northern cameroon central africa and consequences for the west and central african rift system abstract detailed analyses and interpretation realized by combining existing 2d reflection seismic and gravity magnetic data of the logone birni basin lbb in the west and central african rift system wcas have revealed the distribution of the main buried volcanic bodies as well as their relationships with the structural and tectonic evolution of this basin the volcanic activity in the lbb is restricted to the cretaceous period three main volcanic episodes are identified and are associated to the neocomian late albian and cenomanian turonian rifting phases respectively the volcanic bodies within the lower cretaceous are either lying directly on basement or are mainly interbedded with the contemporaneous sediments whereas the upper cretaceous bodies are morphologically expressed in the forms of dykes and sills the volcanic activity was more intense in the western region of the central lbb zina sub basin along the cameroon nigeria border whereas it was scanty and scattered in the other parts of the basin the main volcanic dykes are found on the flanks of the major faults bounding basement horsts or in crestal positions in association with syndepositional faults although wcas is associated with large amount of crustal extension and minor volcanism the intense volcanic activity observed in lbb during the cretaceous suggests that the intrusive zone during this period was confined to the basement beneath the study area flanked respectively to the north south and southwest by the lake chad poli and chum triple junctions tensional stresses generated by this localized domal uplift accounts for most of the observed tectonic structures where major faults transected the entire lithosphere thus providing conduits for magma migration

rapid warming and salinity changes of cretaceous surface waters in the subtropical north atlantic paleomarine carbon isotopic records reveal occasional and rapid release of greenhouse gases into the atmosphere the regional consequences on surface ocean properties and time relationships between the atmosphere and the ocean however are still far from understood we observe a sudden 1 5 shift in leaf wax n alkane 13c values at the onset of oceanic anoxic event oae 1b from early albian sediments off northwest africa deep sea drilling project site 545 that is best explained by the rapid release of isotopically light carbon into the cretaceous atmosphere this 1 5 shift in the n alkanes precedes a negative isotope excursion of similar magnitude observed in marine carbonate organic matter and algal steranes a tex86 based record of sea surface temperature sst confirms almost instantaneous warming by 3 5 c along with the marine isotope shifts at site 545 paralleled by an 2 c tex86 sst increase and a freshening of surface water salinity from 43 to 41 at blake nose ocean drilling program site 1049 multiproxy evidence indicates that once established these warm ssts prevailed and were stable during oae 1b suggesting that the emission of 13c depleted carbon started abruptly but then continued over tens of thousands of years the sst cooled by 1 2 c at the end of the event not reaching pre excursion levels the new records provide evidence for a time lag best estimate 1 3 k y between atmospheric and oceanic processes that we interpret as a direct response to changes in the atmospheric greenhouse gas concentrations followed by propagation into the ocean and subsequent heating of surface waters

anomalous bathymetry and palaeobathymetric models of the mozambique basin and riiser larsen sea abstract in this study we introduce a palaeobathymetric model for the conjugate mozambique basin and riiser larsen sea built by employing backstripping techniques compensating for dynamic topography and plate motions the model is presented at 0 2 0 2 grid resolution making it suitable for future oceanographic and climate simulation model experiments aimed at a better understanding of the climatic and oceanographic relevance of oceanic gateways in the southern ocean at the present day the seafloor next to the mozambican continental margin is around 300 m shallower and that in the central mozambique channel is almost 1300 m shallower than their conjugate areas or the predictions of oceanic thermal subsidence models the cause of this anomalous depth is difficult to determine confidently because of sparse data in particular concerning sediment thickness and because of the wide range of amplitudes in modelled present day dynamic topography the distribution of shallow seafloor suggests that it might be attributed to the presence of thicker than usual oceanic crust which in turn can be attributed to the paleogene passage of the quathlamba plume beneath the basin we portray these effects in our palaeobathymetric models in contrast the riiser larsen sea has experienced fairly stable subsidence since its formation in jurassic times with only slight observable changes attributable to the onset of antarctic glaciation and during the middle miocene climate transition both basins display flexure over half wavelengths of 60 80 km with amplitudes of 1500 m towards their continental margins this plays an important role in models of palaeobathymetry for times older than 100 ma near the margins isolated areas of transitional or debatable crustal composition including beira high and gunnerus ridge are depicted to subside in a similar fashion to oceanic crust further into the indian ocean oceanic lithosphere younger than 100 ma on both plates has subsided to depths that are typical of thermal subsidence models finally the new palaeobathymetry had distinct consequences for the current systems in the young southern ocean during the time periods the onset of coast parallel bottom currents and associated contourite deposition in the mozambique channel at palaeo water depths of 3500 4000 m may be a consequence of either an opening of a deep water passage into the south atlantic between southwest indian ridge and agulhas plateau or into the tethys ocean in the late cretaceous

extremely high sea surface temperatures at low latitudes during the middle cretaceous as revealed by archaeal membrane lipids the middle cretaceous 125 88 ma greenhouse world was characterized by high atmospheric co 2 levels the general absence of polar ice caps and much higher global temperatures than at present both 1 8 o based and model based temperature reconstructions indicate extremely high sea surface temperatures ssts at high latitudes however there are a number of uncertainties with sst reconstructions based on 1 8 o isotope data of foraminifera due to diagenetic overprinting effects and tenuous assumptions with respect to the 1 8 o value of cretaceous seawater the paleoecology of middle cretaceous marine organisms and seawater ph here we applied a novel sst proxy i e text tetraether index of 86 carbon atoms based on the membrane lipids of marine crenarchaeota derived from middle cretaceous sedimentary rocks deposited at low latitudes the text proxy indicates that tropical ssts in the proto north atlantic were at 32 36 c during the early albian and late cenomanian early turonian this finding agrees with sst estimates based on 1 8 o paleothermometry of well preserved foraminifera as well as global circulation model calculations the text proxy indicates cooler ssts 27 32 c for the equatorial pacific during the early aptian which is in agreement with sst estimates based on 1 8 o paleothermometry

trace element zoning in dolomite proton microprobe data and thermodynamic constraints on fluid compositions abstract lower cretaceous euhedral dolomite crystals from the gargano peninsula italy have been analyzed by scanning proton microprobe spm for the trace elements sr zn fe mn cu ni y and rb intricate decoupled zoning patterns for fe mn and zn are a ubiquitous feature of the outer 55 microns of the dolomite crystals differences between peak and baseline concentrations are on the order of several hundred parts per million in contrast sr concentrations are nearly constant at 110 ppm the concentrations of the other cations are all low cu 20 ppm y 10 ppm and ni and rb 5 ppm in order to investigate the origin of the gargano dolomite we have used the method of tardy and garrels to estimate equilibrium partition coefficients for divalent cations between aqueous fluids and the dolomite structure 18o measurements on gargano dolomites show that they formed at a maximum temperature of 75 c 7 c estimated equilibrium constants for substitution of the cation m into dolomite calculated baseline molar cation ratios for fluids in equilibrium with gargano dolomite and measured cation ratios for seawater and marine sediment pore fluids at 75 c are as follows m n k eq log10 calculated ratio log10m n measured ratio in seawater log10m n measured ratio marine pore fluids mn mg 1 27 4 62 7 17 2 75 fe mg 12 66 4 77 6 57 3 81 zn mg 6 85 5 27 6 72 4 84 sr ca 0 17 2 94 1 92 1 83 cation ratios of fluids in equilibrium with the baseline concentrations of mn fe and zn in the gargano dolomite samples are bracketed by the cation ratios measured in seawater and in marine sediment pore fluids the factor often discrepancy for sr in the predicted fluid compared with seawater is probably due to nonideal mixing of sr on the ca site the decoupled fluctuations of the mn and fe concentrations in these samples can be explained by eh fluctuations in the reactant fluid zn fluctuations may be a product of ph dependent oxide surface reactions to test this hypothesis of origin unzoned tertiary dolomites from enewetak atoll and from the bahama bank have also been analyzed the homogeneous sr concentration in the gargano dolomite is similar to the sr concentrations measured in the enewetak atoll 175 ppm and bahama bank 150 ppm dolomites samples which in both cases almost certainly grew in equilibrium with seawater gargano baseline mn 20 ppm and fe 80 ppm concentrations are also much the same as the bahama bank dolomite mn 15 ppm and fe 140 ppm concentrations the lack of sr zoning in the gargano samples and the similarity of their sr mn and fe content to dolomite that formed in equilibrium with seawater indicates that the dolomitizing fluid was most likely seawater or a seawater type brine low sr concentrations 12 ppm in pore filling calcite from the gargano suggests that in contrast to the dolomite the calcite precipitated from meteoric fluids

thermal evolution of cretaceous tethyan marine waters inferred from oxygen isotope composition of fish tooth enamels 1 the evolution of subtropical 30 35 n upper ocean temperatures through the cretaceous is inferred from the oxygen isotope compositions of 64 fish teeth enamel coming from the western tethyan platform mean 18o values of 22 at the berriasian valanginian boundary decrease with oscillations to 18 5 around the cenomanian turonian boundary and progressively increase to 21 5 by the end of the cretaceous the similarity of this oxygen isotope curve for bioapatites from platform environments with those for foraminifera and bulk carbonates that were deposited in deeper waters and at other paleolatitudes indicates that they record global climatic signals major cooling events at the million year scale can be distinguished 1 at the berriasian valanginian boundary and 2 during the earliest late valanginian a third cooling event is detected during the earliest aptian these events already proposed as icehouse interludes during the lower cretaceous are also recorded at subtropical latitudes a progressive warming is identified from the aptian to the cenomanian turonian interval that corresponds to a thermal optimum and then upper ocean temperatures decreased to the maastrichtian minimum isotopic temperatures range from 15 c to 28 c assuming a 18oseawater of 1 for an ice free world taking more realistic 18oseawater values of 0 for tropical waters during glacial periods within the berriasian valanginian interval and earliest aptian or with above average salinities possibly the maastrichtian temperatures are increased by 4 5 c temperature differences between climatic extremes of the valanginian and cenomanian turonian are estimated to have been 10 c latitudinal thermal gradients for the albian cenomanian turonian and maastrichtian were 0 2 0 3 c latitude and thus weaker than modern oceanic values at about 0 4 c latitude

demersal habitat of late cretaceous ammonoids evidence from oxygen isotopes for the campanian late cretaceous northwestern pacific thermal structure comparison of oxygen isotope data for exceptionally well preserved cooccurring plankton and benthos from the campanian of hokkaido japan with nine species of ammonoids clearly indicates the demersal nektobenthic habitat of ammonoids unlike nautilus the ammonoids studied did not engage in significant short term vertical migrations in the water column the new foraminiferal isotopic data suggest that sea surface and sea bottom temperatures were 26 and 18 c respectively at 40 n in the campanian northwestern pacific the temperatures were significantly warmer than those in the modern northwest pacific this finding provides the first reliable evidence for the warm late cretaceous mid latitude north pacific isotopic analyses of ammonoids show that the average calcification temperature of all ammonoid shells analyzed was 19 c comparable to those of cooccurring benthos none of these ammonoids display calcification temperatures equivalent to those of planktonic foraminifers

geochemistry of mine waters draining a low sulfide gold quartz vein deposit bralorne british columbia abstract the bralorne and pioneer mines now inactive produced over 4 million ounces of au from an orogenic lode au deposit located on the eastern edge of the coastal mountains of sw british columbia between 2007 and 2009 drainage from a recently developed exploration adit was investigated in order to better understand and anticipate potential environmental management issues associated with the development of this type of deposit in the future portal discharge rate and specific conductance were monitored continuously over a 14 month period during which 36 water samples were collected additional samples were collected from flooded workings within the adit concentrations of as and sb at the portal range as high as 1738 and 316 g l respectively while those in the mine pool reach 3304 and 349 g l respectively effluent chemistry is mildly alkaline ph 8 7 and is dominated by na ca mg hco3 and so4 geochemical inverse modeling of effluent composition indicates weathering of albite 2515 kg a ferroan dolomite 718 kg a pyrite 456 kg a arsenopyrite 23 kg a and stibnite 2 kg a modeled sulfide reaction coefficients normalized by their corresponding host rock concentrations suggest that oxidation of arsenopyrite is 25 times slower than that of pyrite whereas oxidation of stibnite is 1 5 times faster oxidative dissolution of arsenopyrite and stibnite releases 10 6 kg a of as and 1 1 kg a of sb of which 57 and 46 respectively are sorbed to ferrihydrite and gibbsite on the bed of the shallow channel through which the mine pool drains to the portal although mass balance calculations predict the formation of sufficient ferrihydrite to sorb 100 of the as dissolved in the mine pool this attenuation process was ineffective possibly because the precipitated sorbents settled to the bottom of the water column or because of competition for sorption sites from ca and hco3 the dissolved sb as molar ratio in portal effluent 0 082 is much greater than the sb as ratio of the mineralization 0 002 because of slower arsenopyrite oxidation and somewhat lesser sorption of sb

evolution of habitat depth in the jurassic cretaceous ammonoids ammonoids a group of cephalopods with external chambered shells arose in the early devonian and went extinct at the cretaceous paleogene k pg boundary during their 340 million y history ammonoids suffered three major diversity crises at the end of the devonian permian and triassic periods and the terminal extinction event at the k pg boundary because of their rapid morphological evolution and rich fossil record ammonoids have been used to determine the relative age of marine strata and correlation since the dawn of stratigraphy although the morphological analyses of shell materials have provided some insights into ontogeny and evolution their biological nature is poorly understood because of the lack of soft body fossils and close modern relatives for example although one may usually imagine that ammonoids were planktic or nektic organisms within a water column like the nautilus which is the sole surviving cephalopod bearing an external chambered shell there is very little direct evidence showing the habitat depth of ammonoids within an ancient water column

new distribution coefficient for the incorporation of strontium into dolomite and its implications for the formation of ancient dolomites late tertiary dolomites form the bahamas exhibit a strong inverse correlation between sr and mol mgco sub 3 it is proposed that this relation is a result of a distribution coefficient dependent on the concentration of ca in dolomite because these dolomites precipitated from water with a sr sup 2 ca sup 2 ratio similar to that of seawater a distribution coefficient d sub sr sup dolomite of 0 0118 is calculated for sr in stoichiometric dolomite this coefficient increases by about 0 0039 for every additional mol caco sub 3 in nonstoichiometric dolomite these data have three important implication first the new d sub sr sup dolomite is substantially lower than previously suggested second a relation has been established among the sr sup 2 ca sup 2 ratio of dolomite forming waters the major element composition of dolomites and the sr content of dolomites allowing the determination of the sr sup 2 ca sup 2 ratio of fluids involved in the formation of ancient dolomites third some published data sets on dolomites show a similar relation between sr content and major element composition suggesting that these dolomites may also have formed from seawater other data sets deviate from the correlation defined by little bahama bank dolomites indicating either dolomitization in fluids other than seawater or changes ofmore the sr sup 2 ca sup 2 ratio of seawater through time less

the oxygen and carbon isotope distribution in the mediterranean water masses abstract the oxygen and carbon stable isotope compositions of the present day mediterranean waters have been measured in order to evaluate their variability which is related to the specific climatic and hydrological conditions within the basin the experimental equation between the 18 o value and the salinity of water based on 300 measurements on surface intermediate and deep waters sampled during the vicomed 2 and 3 cruises in the western central and eastern mediterranean has a slope of 0 27 a value which is significantly lower than the slope of 0 45 as defined in the northeast atlantic ocean this difference in the 18 o salinity relationship which occurs immediately in the alboran basin is basically a characteristic of the climatic regime of the mediterranean i e of an excess evaporation over fresh water input the largest variations of these two parameters 18 o of water and 13 c of co 2 are observed in the surface waters mostly in the western mediterranean this evolution mirrors the progressive eastward restriction which separates the less evaporated and more productive western basins from the more evaporated and less productive eastern basins the intermediate waters constitute a homogeneous layer however their 18 o values decrease eastward by 0 35 at maximum due to progressive dilution by mixing with overlying and underlying water masses their 13 c values decrease also eastward by 0 35 at maximum due to an increasing input of nutrients issued from the regeneration of sinking organic particles the deep waters have similar 18 o values but slightly higher 13 c values often by less than 0 1 than the overlying intermediate waters indicating generally well ventilated conditions due to active winter convection

a new tectonic model for the cameroon line central africa abstract the cameroon line a major geological feature in central africa has been considered successively as a series of horsts and grabens a continental rift and a mega shear zone it is marked out by about 60 anorogenic complexes and a dozen volcanic centres all of which have alkaline affinity remote sensing allows us recognition of the main lineament trends n70 n s n135 and e w while autocorrelation analysis reveals a major fault zone striking n30 in western cameroon and n15 in the northern region a mega left lateral shear zone is the model that best accounts for the fracture pattern and associated features such as linear and circular structures alignment of subvolcanic complexes syntectonic leucogranites marking out older shear zones and vein dykes the n70 adamawa fault zone a pan african fracture reworked during albian aptian times is the only shear zone of continental scale that could have initiated en echelon mega tension gashes within the cameroon line during a cainozoic left lateral transcurrent movement