mechanics of upward propagation of cover collapse sinkholes cover collapse sinkholes occur by failure of the walls of a soil void above cavernous bedrock i examine conditions for failure in compression by crack propagation and coalescence and for failure by sloughing in which pore water pressure produces a net tension perpendicular to the wall of the void compressive failure without relaxation of stress does not explain observed long term stability of thick soils nor failures in thin residual soils if stress relaxation occurs with compressive failure soil voids tend to stabilize and sinkholes are not predicted sloughing failure is not predicted for steady state pore pressure fields even for a perched water table at the surface over a drained void transient pore pressure conditions that could produce sloughing may result from 1 rapid drawdown causing soil consolidation and transient high pore pressure gradients 2 approach of a wetting front in unsaturated soil with high permeability behind the front 3 dissolution of air from bubbles in the soil and exsolution near the void producing a low permeability zone near the void

pb pb baddeleyite ages of mafic dykes from the western dharwar craton southern india a window into 2 21 2 18 ga global mafic magmatism abstract paleoproterozoic mafic magmatism in the dharwar craton dc is evident by ubiquitous dykes of varied orientations and emplacement ages eight distinct mafic dyke events have been identified in the eastern dharwar craton edc while studies in the western dharwar craton wdc were restricted to a previously dated dandeli dyke precise baddeleyite te tims pb pb ages for five mafic dykes across the wdc reveal emplacement ages of 2212 3 0 8 ma 2212 9 0 4 ma 2208 1 0 8 ma 2205 2 0 8 ma for nw se to nnw sse trending dykes and 1957 3 0 7 ma for ene wsw dyke the ca 1 96 ga mundargi dyke establishes a new episode of mafic magmatism in the dc whereas ca 2 21 ga mafic dykes suggests widespread mafic magmatism across the dc the collective trend of ca 2 21 2 20 ga radiating dykes vary from n100 e in edc to n165 e in wdc converging towards the north western margin of dc fanning angle 65 where a mantle plume appears to be located it is postulated that ca 2 18 ga mahbubnagar dandeli dyke swarm of the dc also originated from a similar plume source but as a distinct pulse within a time span of 35 40 myr present study depicts barcode of the wdc and represents an epitome of correlations with the edc superior slave and greenland cratons widespread ca 2 21 2 18 ga lip event indicates that these cratons were located at proximity and suggests breakup of supercraton sclavia superia the single 1 96 ga mundargi dyke is coeval with the dykes and sills of karelia north china and north atlantic cratons

organic matter oxidation and aragonite diagenesis in a coral reef abstract a combination of field and theoretical work is used to study controls on the saturation state of aragonite inside a coral reef framework a closed system ion speciation model is used to evaluate the effect of organic matter oxidation on the saturation state of aragonite the aragonite saturation state initially drops below 1 but becomes oversaturated during sulfate reduction the c n ratio of the organic matter affects the degree of oversaturation with n poor organic material resulting in a system more corrosive to aragonite precipitation of sulfide as fes strongly affects the aragonite saturation state and systems with much fes formation will have a stronger tendency to become oversaturated with respect to aragonite both precipitation and dissolution of aragonite are predicted at different stages of the organic reaction pathway if the model system is maintained at aragonite saturation field data from a coral reef framework indicate that the system maintains itself at aragonite saturation and model predicted changes in dissolved calcium follow those observed in the interstitial waters of the reef aragonite probably acts as a solid phase buffer in regulating the ph of interstitial waters because interstitial water in the reef has a short residence time the observed equilibration suggests rapid kinetics

three dimensional visualization of orbital forcing and climatic repsonse interactively exploring the pacemaker of the ice ages recent developments in continuous core logging techniques now permit us to recover the high resolution time series necessary for the detailed spectral analyses of paleoclimatic proxy records when applied to long records recovered by scientific drilling 5 10 ma they enable us to look at the long term history and evolution of the ocean s response to orbital forcing a serious limitation in these studies is the need to display the complex multidimensional spatial and temporal interactions of the ocean climate system in an easily comprehensible manner we have addressed this issue by developing a series 3d visualization tools which permit visualization of the role of the orbital parameters in determining the latitudinal variation of insolation as well as the interactive exploration of multidimensional data sets the orbits tool allows us to visualize the effect of orbital eccentricity precession and tilt on the latitudinal distribution of insolation on the earth at the solstices and the equinoxes for any time over the past 5 ma for berger s orbital model or 10 ma for laskar s orbital model the effect of the orbital parameters on insolation can be viewed individually in pairs or all three together by moving the model steadily through time the rate at which orbitally induced changes in insolation occur can also be visualized to look at the ocean s response to orbital forcing we take the long time series generated from our paleoclimatic proxies and calculate their spectrum over a fixed but sliding time window to view the complex multidimensional relationships found in these evolutionary spectral analyses we use another interactive 3d data exploration tool developed at the university of new brunswick canada this tool fledermaus uses a six degrees of freedom input device bat and a series of software modules for color coding shading and rendering complex data sets to allow the user to interactively fly through the multidimensional data through the use of color texture and 3d position as many as six or seven variables can be explored in a simple and intuitive manner with special liquid crystal display glasses the scene can be viewed in true stereo we use these tools to explore the relationship between orbital forcing and the response of the benthic isotope and calcium carbonate record at odp site 846 90 w and 5 s this analysis shows an equatorial pacific carbonate record which has a large component of linear response to tilt but little linear response to precession there is a major shift in response from a carbonate dominated response to an isotope ice volume dominated response at approximately 4 5 ma and as expected there is a large nonlinear response at the lower frequencies 400 and 100 kyr during the past 800 kyr to 1 ma

gamma ray measurements in the kirchrode i and ii boreholes abstract the downhole ray logs in the kirchrode i and ii boreholes through the albian southeast of hannover in northwest germany were used a to correlate the two boreholes b to calculate the clay content of the sediments and c to detect cyclicity in changes in sediment composition the cross correlation of the downhole ray logs of the kirchrode i and ii showed that a shift of the kirchrode ii borehole downwards by 89 m provides the best correlation with the kirchrode i borehole a comparison of the ray log of kirchrode ii with that of the nearby prakla 2 borehole for which biostratigraphic data is available also yields a close correspondence using this correlation of the logs and adopting the stratigraphic subdivision of the prakla 2 borehole by kemper 1989 the upper middle albian and middle lower albian boundaries in kirchrode ii are at depths of 152 and 252 m respectively the ray logs were used to calculate the clay content it varies between 30 and 60 indicating only small lithologic changes this result is in agreement with values derived from analysis of the quartz and caco3 contents of core samples the montmorillonite illite and kaolinite contents of the clay fraction determined by kuhn et al 2001 are the basis for an independent calculation of the clay contents of the core using mean literature values for the thorium and potassium contents of these three clay minerals the periodicities identified by spectral analysis of the ray measurements made every 5 cm throughout the recovered albian sequence can be interpreted in terms of milankovitch cycles sliding window spectral analysis shows that the sedimentation rates were relatively constant during the late albian 8 12 cm ka sedimentation rates of 4 cm ka were determined for the middle albian

orbital forcing in a boreal cretaceous epeiric sea high resolution analysis of core and logging data upper albian of the kirchrode i drill core lower saxony basin nw germany abstract a 245 m 0 245 m subsurface core of upper albian marine sediments from north germany research well kirchrode i was studied to identify sequences and cycles of sedimentation and related forcing mechanisms on sedimentation in an epeiric sea of the sub boreal realm the core consists of monotonous gray marls with an exceptionally high sedimentation rate of 8 12 cm ka 1 in total it represents a period of approximately 2 5 4 ma a silty glauconite rich condensed layer marks a change in the succession at 132 m and is paralleled by the first occurrence of e turriseiffelii and g bentonensis the lower part of the core shows lenticular bedding siderite nodules average caco 3 content of ca 40 and an abundance of inoceramids inoceramus anglicus birostrina lissa actinoceramus sulcatus the upper part is characterised by plane bedding common siderite layers an average caco 3 content of ca 35 and an abundance of aucellinas aucellina gryphaeoides according to lithology and ichnofacies the succession represents a transgressive regressive cycle with distinct bimodality of lithology fossil and trace fossil content together with reworking and redeposition at the base and top we studied well log data sediment composition sediment color and carbonate content and applied various mathematical analysis techniques to these data principal component analysis spectral analysis fourier transform autocorrelation spectral analysis revealed well pronounced periodic cyclicity in the upper part of the upper albian 12 8 4 5 3 4 1 7 m the 12 m eccentricity cycles are the most intense cycles reflecting periodic changes in the terrigenous clastic supply chaotic transitional intervals occur around the middle upper albian upper albian and topmost albian parts of the core they are characterised by non cyclic changes in litho and biofacies mathematically these changes correspond to singularity points they are preceded by non orbital high frequency variations in carbonate content and in ray

emplacement ages of paleoproterozoic mafic dyke swarms in eastern dharwar craton india implications for paleoreconstructions and support for a 30 change in dyke trends from south to north abstract large igneous provinces lips and especially their dyke swarms are pivotal to reconstruction of ancient supercontinents the dharwar craton of southern peninsular india represents a substantial portion of archean crust and has been considered to be a principal constituent of superia sclavia nuna columbia and rodinia supercontinents the craton is intruded by numerous regional scale mafic dyke swarms of which only a few have robustly constrained emplacement ages through this study the lip record of the dharwar craton has been improved by u pb geochronology of 18 dykes which together comprise seven generations of paleoproterozoic dyke swarms with emplacement ages within the 2 37 1 79 ga age interval from oldest to youngest the new ages integrated with u pb ages previously reported for the hampi swarm define the following eight swarms with their currently recommended names ne sw to ese wnw trending ca 2 37 ga bangalore karimnagar swarm n s to nne ssw trending ca 2 25 ga ippaguda dhiburahalli swarm n s to nnw sse trending ca 2 22 ga kandlamadugu swarm nw se to wnw ese trending ca 2 21 ga anantapur kunigal swarm nw se to wnw ese trending ca 2 18 ga mahbubnagar dandeli swarm n s nw se and ene wsw trending ca 2 08 ga devarabanda swarm e w trending 1 88 1 89 ga hampi swarm nw se ca 1 79 ga pebbair swarm comparison of the arcuate trends of some swarms along with an apparent oroclinal bend of ancient geological features such as regional dharwar greenstone belts and the late archean ca 2 5 ga closepet granite batholith have led to the hypothesis that the northern dharwar block has rotated relative to the southern block by restoring a 30 counter clockwise rotation of the northern dharwar block relative to the southern block we show that pre 2 08 ga arcuate and fanning dyke swarms consistently become approximately linear two possible tectonic models for this apparent bending and concomitant dyke rotations are discussed regardless of which deformation mechanisms applies these findings reinforce previous suggestions that the radial patterns of the giant ca 2 37 ga bangalore karimnagar dyke swarm and probably also the ca 2 21 ga anantapur kunigal swarm may not be primary features

mineralogy of the upper albian sediments from the kirchrode i borehole with special emphasis on the clay mineralogy abstract the mineralogy of a 245 m thick section of upper albian marly clay stones to clayey marlstones from the kirchrode i borehole lower saxony basin of nw germany has been studied by x ray diffractometry infrared spectrometry chemical analysis and microscopy the investigations were carried out on bulk samples and grain size fractions the mineralogy of the sediments is characterised by biogenous carbonates mainly calcite by terrigenous detrital components and diagenetic minerals often enriched in concretions the calcite content fluctuates considerably between 20 and 50 most probably because of changes in the marine palaeoenvironment illite montmorillonite and kaolinite are the predominant clay minerals but in changing portions chlorite and alkali feldspars were detected only in traces mixed layer minerals such as illite smectites i s are also present in higher amounts in the lower part and less in the upper part of the core reworked upper carboniferous mudstones and siltstones are interpreted to have delivered part of the well crystallised illite kaolinite chlorite and quartz montmorillonites and mixed layer minerals together with kaolinite and illite may be inherited from weakly consolidated jurassic sediments aptian and albian claystones and marlstones and from palaeosols the increase in the proportion of montmorillonite among the clay minerals in the upper part of the upper albian may be due to redistribution of volcanic sediments after either terrestrial or submarine alteration of volcanic ash volcanic activity is known in this area e g the middle to upper albian flammenmergel at the southern margin of the lower saxony basin and around the north atlantic throughout aptian albian time but in the kirchrode i core ash fall was identified as a source for montmorillonite in only one layer namely at 87 25 m where high zr and nb concentrations were also found the mineralogical composition of the concretionary material is generally a mixture of biogenous calcite siliciclastic debris quartz and clay minerals and microcrystalline diagenetically formed fe mn carbonates rhodochrosite siderite and carbonate fluorapatite francolite rhodochrosite is more abundant in the lower part mn siderite in the upper part of the core concretions with fluorapatite francolite occur sporadically

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

the transformation of amphibolite facies gneiss to charnockite in southern karnataka and northern tamil nadu india amphibolite facies metamorphic grade gives way southward to the granulite grade in southern karnataka as acid gneisses develop charnockite patches and streaks and basic enclaves develop pyroxenes petrologic investigations in the transitional zone south of mysore have established the following points 1 the transition is prograde amphibole bearing gneisses intimately associated with charnockite at kabbal and several similar localities are not retrogressive after charnockite as proved by patchy obliteration of their foliation by transgressive very coarse grained charnockite high fluorine content of biotite and amphibole in gneisses and high large ion lithophile element contents in gneisses and charnockites these features are in contrast to very low fluorine in retrogressive amphiboles and biotites very low large ion lithophile element contents and zonal bleaching of charnockite in clearly retrogressive areas as at bhavani sagar tamil nadu 2 metamorphic temperatures in the transitional areas were 700 800 c pressures were 5 7 kbar and h2o pressures were 0 1 0 3 times total pressures based on thermodynamic calculations using mineral analyses dense co2 rich fluid inclusions in the kabbal rocks confirm the low h2o pressures at the first appearance of orthopyroxene farther to the south in the nilgiri hills and adjacent granulite massif areas peak metamorphic temperatures were 800 900 c pressures were 7 9 kbar and water pressures were very low so that primary biotites and amphiboles those with high f contents are rare 3 the incipient granulite grade metamorphism of the transitional areas was introduced by a wave of anatexis and k metasomatism this process was arrested by drying out under heavy co2 influx charnockites so formed are hybrids of anatectic granite and metabasite of metabasite and immediately adjacent gneiss or are virtually isochemical with pre existing gneiss despite gross recrystallization to granulite mineralogy these features show that partial melting and metasomatism are attendant rather than causative in charnockite development copious co2 from a deep crustal or mantle source pushed ahead of it a wave of more aqueous solutions which promoted anatexis granulite metamorphism of both neosome and paleosome followed the process is very similar to that deduced for the madras granulites by weaver 1980 the massif charnockites for the most part extremely depleted in lithophile minor elements show many evidences of having gone through the same process

preliminary anisotropy of magnetic susceptibility studies on 2367 ma bangalore karimnagar giant dyke swarm southern india implications for magma flow abstract anisotropy of magnetic susceptibility ams fabrics have been studied for the first time on a well constrained paleoproterozoic bangalore karimnagar giant mafic dyke swarm at ca 2367 ma in the dharwar craton south india a total number of 43 samples from nine sites representing five n e trending dykes have been subjected to ams and conventional rock magnetic studies the magnetic fabric is principally ferromagnetic in origin as the magnetic susceptibility values are 10 3 si which is further supported by isothermal remanent magnetization irm studies hysteresis loops isothermal remanent magnetisation irm thermomagnetic properties and optical observations indicate that pseudo single domain psd low titanium magnetite particles dominate the low field susceptibility of samples the magnetic fabrics results correspond well with the comprehensive field studies however the degree of anisotropy results ranges from 0 4 to 12 8 with a mean total anisotropy of 4 7 the principal ams axes for samples from all the sites are tightly clustered on equal area plots and two main fabrics were revealed in the bangalore karimnagar giant dyke swarm in the first the maximum susceptibility axes is sub horizontal and parallel to the dyke walls minimum susceptibility axes plot near the pole of the dyke it is interpreted as the primary magma flow direction a second fabric with maximum susceptibility axis is sub horizontal and perpendicular to the dyke walls and is interpreted as a result of vertical compaction at a late stage of crystallization preliminary results suggest that dyke propagation in the bangalore karimnagar giant dyke swarm preserve a flow induced fabric slightly upwards to the ne and magma flow is sub horizontal

palaeomagnetics and igneous activity of the area adjoining the south westem margin of the cuddapah basin india summary fifty six orientated samples were collected from 13 sites on five dolerite dykes between lat 14 23 n long 77 43 e and lat 14 08 n long 77 49 e which adjoin the south western margin of the cuddapah basin in anantapur district andhra pradesh after af demagnetization two dykes five sites striking ene possess similar magnetic directions 1 d 57 1 69 k 52 95 7 and 2 d 71 i 72 k 260 95 5 again dykes 3 three sites and 4 two sites have similar strike ne and magnetic directions d 64 i 7 k 142 95 8 and d 53 i 8 k 142 95 6 and dyke 5 two sites striking nw shows d 320 i 34 k 68 95 13 remanent directions estimated from total field magnetic anomaly data agree well with these results synthesis of these data with 10 other published palaeomagnetic studies of precambrian dolerite dykes on the indian peninsula suggest that these three systems of dykes adjoining the cuddapah basin had been emplaced prior to the basin formation perhaps representing the initial thermal event responsible for the basin development and also that there have been at least three separate periods of dyke emplacement on this shield the radiometric data however are very sparse and these periods cannot be dated with confidence

the kirchrode i and ii boreholes technical details and evidence on tectonics and the palaeoceanographic development during the albian abstract the technical details of drilling and coring at the kirchrode i and ii sites are presented at these sites a sequence of claystones and marlstones from an albian shelf basin was recovered constraints on the ages of the sediments in the two boreholes are provided by the occurrence of the inoceramid bivalve actinoceramus sulcatus the first appearance of which is used to define the middle upper albian boundary and by observed facies changes that can be correlated to the established lithostratigraphy the cores from the two boreholes provide a rather complete 285 m long sequence of the upper albian with a 155 5 m long overlap analysis of the tectonic structures showed considerable shortening in the middle and lower albian part of the sequence due to normal faulting of the upper albian only the lowermost part is affected by faults the increase in sedimentation rates of terrigenous detritus and of marine biogenic carbonate which occurs in the basal part of the c auritus subzone is interpreted to reflect a regional change to a more humid climate and regional tectonic movements uplift of the rhenish bohemian massif subsidence of the lower saxony basin intensified locally by halokinetic movements the further increase in marine productivity in the latest albian may be related to upwelling of more nutrient rich deep water along submarine relief in this shelf sea identification of milankovitch cyclicity documented by the fluctuating caco3 contents of the sediments is used i to constrain the minimum time represented by the upper albian deposits and ii to determine the duration of the sea level cycles cycle v 1 6 ma cycle vi 2 ma and iii to establish the duration of the late albian ammonite subzones e g callihoplites auritus subzone 2 1 ma average sedimentation rates determined from the identified 100 ka eccentricity cycles show a stepwise increase in sedimentation rates from 1 2 cm 1000 a in the lower albian dark claystones to 7 13 cm 1000 a in the late late albian in addition to the general deepening trend through the late albian two nearly completely documented 3rd order sea level cycles in the upper albian of kirchrode i were recognised plus another one cut short by faulting at the base of the upper albian documented in kirchrode ii these global sea level cycles were identified on the basis a of the sequence of the abundance maxima of selected benthos and plankton groups b of trends in the fluctuations of the caco3 content and c of the abundance of glauconite the transgression periods in this upper albian deep shelf basin are characterised by intensified circulation this intensified circulation is found to have affected first the surface near waters resulting e g in an increase in the abundance of immigrant plankton and nekton species from the tethys at a later stage the deep water was affected supporting then an increased population of suspension feeding benthos and causing condensation and erosion in the sediment at the sea floor

biological response to milankovitch forcing during the late albian kirchrode i borehole northwestern germany abstract we studied the biological response to orbital forcing in marine upper albian sediments recovered from the 245 m long kirchrode i borehole in the lower saxony basin in northwestern germany results from quantitative analysis of planktonic and benthic foraminifera of calcareous nannofossils and radiolaria were used for this study spectral analysis in the depth domain indicates for the high sedimentation rate part of the upper albian dominant periods with wavelengths of 10 13 m 5 6 m and 2 3 m which we interpret to represent the biological response to orbital forcing in the milankovitch frequency bands eccentricity obliquity and precession respectively in addition a low amplitude 40 50 m cycle was found which would represent the long term eccentricity variation of roughly 400 ka microfossil cyclicity does not change significantly within the whole core indicating sedimentation rates of 11 12 cm ka on an average with variations between 3 5 and 13 ka microfossils show greater variability in their abundance changes than the physical and chemical parameters and also greater power in the higher frequency bands obliquity and precession while most of the planktonic foraminifer species studied are dominated by variations in the obliquity most benthic foraminifer species show an additional strong influence of precession these differences in the cyclicity of the abundance changes are interpreted as reflecting a stronger influence of low latitude water in the deep waters of the late albian lower saxony basin than in the shallow waters this basin was part of a wide boreal epicontinental sea which was connected to the tethys to the south via the polish strait and via the paris basin and which was connected with the north atlantic and arctic to the north in analogy to results from analysis of data from the late neogene strong effects of precession interpreted as being more characteristic for changes influences triggered in the low latitudes and those of obliquity to be more characteristic for influences from the high latitudes the presence of a relatively strong eccentricity cycle not only in the compound parameters but also in the abundance changes of single species during the late albian means that there must have been a non linear response to orbital forcing and internal feedbacks

influence of the changing lunar orbit on the astronomical frequencies of pre quaternary insolation patterns the sensitivity of the frequencies of the earth s orbital elements involved in the astronomical theory of paleoclimates obliquity and climatic precession to the earth moon distance and consequently to the length of the day and to the dynamical ellipticity of the earth is investigated for the last billions of years but the new frequencies have been computed for the last 440 million years only a time interval over which data and a model of the earth were available moreover we consider only the impact of the changing precessional parameter assuming that the fundamental frequencies of the planetary motion are steady at the geological time scale under such hypotheses the shortening of the earth moon distance and of the length of the day back in time induces a shortening of the fundamental astronomical periods for obliquity and precession a shortening that is larger for longer periods

u pb baddeleyite ages of the kerns and triangle mountain intrusions nipissing diabase ontario u pb ages have been determined for two diabase intrusions from kerns and hudson townships that are part of the nipissing diabase suite from the proterozoic southern province canada the ages of the kerns and triangle mountain intrusions are 2217 2 4 and 2209 6 3 5 ma respectively based on analysis of primary baddeleyite from both intrusions together with a published u pb age for the castle mine intrusion these data indicate that the nipissing sills were emplaced separately over a time span of 2 8 1 6 ma given by the maximum and minimum overlap of errors on the u pb ages

contrasting high and intermediate pressures of metamorphism in the archaean sargur schists of southern india the archaean karnataka craton of southern india contains eastern and western crustal blocks separated by a major thurst in which sargur schists occur as lenses within tonalitic peninsular gneisses the schist complex comprises pelites quartzitic psammites carbonates and calc silicates iron formations and basic rocks and thus provides many mineral assemblages ideal for the calculation of pt conditions with their gneisses the sargur rocks are unconformably overlain by the dharwar greenstone belts and are generally thought to be older than 3 000 my

intracratonic stability a comparison of paleomagnetic data from the north and the south of dharwar craton india abstract the prominent bend of dharwar craton india was recently suggested to post date the stabilization phase of the craton via a 30 anticlockwise vertical axis intracratonic rotation the prima facie evidence for this rotation was the realignment of dyke trends following correction of the inferred deformation the proposal also appeared to be consistent with the observed structural grain in the host archean basement we argue that using the trend of dyke swarms is not the ideal method to assess intracratonic rotation and instead we use variations in paleomagnetically determined declination data from these dykes we find that multiple early paleoproterozoic dyke swarms the 2367 2216 and 2082 ma generations preserve a systematic offset with a large uncertainty the mean paleomagnetically permissible anticlockwise rotation is 19 17 dykes emplaced during the 1888 ma lip do not show the same offset which suggests that rotation occurred prior to this time therefore the 2082 1888 ma interval brackets the window for any deformation and tectonism required to bend the dharwar craton by about 20 no large scale deformational events are documented in the dharwar craton during this critical interval apart from the earliest stages of cuddapah basin formation we argue that the observed rotation results from biases associated with how trends of dykes and their magnetic directions are compiled when age data are limited the curvature of geological features in dharwar craton is likely the tectonic inheritance of the neoarchean collision between the western dharwar and eastern dharwar cratons

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

the karnataka late cretaceous dykes as products of the marion hot spot at the madagascar india breakup event evidence from 40ar 39ar geochronology and geochemistry two late cretaceous mafic dykes with an ene strike that is orthogonal to the west coast of india and located nearly 200 km inland around huliyardurga karnataka state yield 40ar 39ar plateau ages of 90 0 1 0 and 87 5 0 9 ma these fe ti enriched tholeiites are essentially co eval with at least four other igneous suites widely scattered in southern india namely the south and north kerala dykes the agali anaikatti dykes of central kerala tamil nadu and lavas of st mary islands off the west coast of india the karnataka cretaceous dykes are also co eval and compositionally very similar to the fe ti enriched tholeiitic lavas and dykes around mananjary a major phase of late cretaceous magmatism along the eastern rifted margin of madagascar which are believed to be products of the marion hot spot that extruded at 88 ma synchronous with the india madagascar break up event the age and compositional similarities between these late cretaceous magmatic rocks from india and madagascar constitute a clear evidence for extension of the thermal manifestations deep into the indian peninsula

the southern high grade margin of the dharwar craton the amphibolite facies to granulite facies transition at the southern margin of the dharwar craton has been studied in the krishnagiri satnur halaguru and kushalnagar areas of southern india in all three areas the transition appears to be a progressive metamorphic overprint on cratonal gneisses and their mafic and metasedimentary enclaves without major structural interruption in the kabbal satnur br hills section of karnataka a high grade charnockite massif with pronounced rb depletion is the culmination of an apparently continuous increase of metamorphic grade southward in this and the kushalnagar areas increase of paleopressure from near 6 to near 8 kbar with increasing grade indicates a depth zone relationship of the amphibolite and granulite facies incipient charnockite replacing peninsular gneiss first appears along n s shears parallel to the regional grain of the craton low p h 2 o high co 2 vapors were instrumental in the creation of orthopyroxene introduction from a deep so

palaeosecular variation over the past 5 myr based on a new generalized database summary a generalized database of global palaeomagnetic data from 3719 lava flows and thin dykes of age 0 5 ma has been constructed for use with a relational database management system the database includes all data whose virtual geomagnetic poles vgp lie within 45 of the spin axis and can be used for studies of palaeosecular variation and for geomagnetic field modelling because many of these data were collected and processed more than 15 20 years ago each result has been characterized according to the demagnetization procedures carried out analysis of these data in terms of the latitude variation of the angular dispersion of vgps palaeosecular variation from lavas strongly suggests that careful data selection is required and that many of the older studies may need to be redone using more modern methods differences between the angular dispersions for separate normal and reverse polarity data sets confirm that many older studies have not been adequately cleaned magnetically therefore the use of the database for geomagnetic field modelling should be carried out with some caution using a vgp cut off angle that varies with latitude the best data set consists of 2636 results that show a smooth increase of vgp angular dispersion with latitude model g for palaeosecular variation which is based on modelling of the antisymmetric dipole and symmetric quadrupole dynamo families provides a good fit to these results

modeling 100 000 year climate fluctuations in pre pleistocene time series a number of pre pleistocene climate records exhibit significant fluctuations at the 100 000 year 100 ky eccentricity period before the time of such fluctuations in global ice volume the origin of these fluctuations has been obscure results reported here from a modeling study suggest that such a response can occur over low latitude land areas involved in monsoon fluctuations the twice yearly passage of the sun across the equator and the seasonal timing of perihelion interact to increase both 100 ky and 400 ky power in the modeled temperature field the magnitude of the temperature response is sufficiently large to leave an imprint on the geologic record and simulated fluctuations resemble those found in records of triassic lake levels

paleomagnetism and u pb geochronology of diabase dyke swarms of minto block superior province quebec canada in the first collaborative study of paleomagnetism and precise u pb geochronology in the minto block of the superior province mafic dyke swarms with three widely divergent paleomagnetic signatures and isotopic ages have been identified the 2505 2 ma ptarmigan dykes trend north to northeast and have a virtual geomagnetic pole at 42 s 220 e similar to that of 2473 2446 ma matachewan dykes of the southern superior province the ca 2230 ma maguire dykes trend west to northwest and yield a paleopole at 9 s 267 e similar to those for 2216 8 4 ma senneterre dykes and 2217 2210 ma nipissing sills of the southern superior and southern provinces respectively the 2209 1 ma klotz dykes trend west northwest but do not carry a consistent magnetization direction finally 1998 2 ma minto dykes of west northwest to northwest trend identical in age to the 1998 ma 2 ma purtuniq ophiolite of the cape smith belt have a paleopole at 38 n 174 e the similarity of paleopoles for the ca 2 23 2 21 ga maguire

the albian cenomanian transition and oceanic anoxic event 1d an example from the boreal realm the upper albian to lower cenomanian interval in the hanover area germany is characterized by a well developed lithological transition from upper albian monotonous marly claystones of several hundred metres thickness which become enriched in biosilica in the topmost albian to increasingly caco3 rich marls and limestones in the lower and middle cenomanian this study presents a new 165 m thick composite record spanning the latest albian to mid early cenomanian ca 103 0 to 97 5 ma based on two core drillings at anderten in the central lower saxony basin east of hanover which is a sub basin of the north german basin due to the lack or delayed occurrences of tethyan biostratigraphic markers for the late albian and early cenomanian in the boreal realm the definition of the albian cenomanian boundary as based on the lowest occurrence of thalmanninella globotruncanoides is not applicable in order to overcome this issue an integrated biostratigraphic chemostratigraphic approach has been employed in addition to biostratigraphy calcareous nannofossils ostracods planktonic foraminifera and inoceramids the anderten succession has been studied using sedimentary geochemistry caco3 total organic carbon toc 13c and 18o ray logging and x ray fluorescence core scanning this approach enabled successful correlation of the composite anderten record to european reference sections in england south east france and italy as well as to further low resolution records from the lower saxony basin wunstorf and konrad 101 core this work has made it possible to identify the 13ccarb expression of i the oceanic anoxic event 1d ii the albian cenomanian boundary interval and iii potentially the lower cenomanian event s chemostratigraphic age assignments are supported by biostratigraphic results calcareous nannofossils indicate an extended upper cretaceous 0 uc0 zone upper albian up to uc2 upper lower cenomanian and the occurrence of the ostracod physocythere steghausi supports an early cenomanian age for most of the upper part of the composite record notably influxes of the planktonic foraminifer thalmanninella aff reicheli have previously been described from this area and the first appearance of this taxon is usually used to define the base of the middle cenomanian substage however findings from the anderten cores and elsewhere suggest that this taxon has an apparently earlier first appearance questioning previous age assignments from the boreal realm solely based on planktonic foraminifera due to both moderately well preserved microfossils and high sedimentation rates the drilled succession of anderten is considered as a potential boreal reference section for the albian cenomanian transition this article is protected by copyright all rights reserved

palaeoceanographic and climatic changes during the albian summary of the results from the kirchrode boreholes abstract analysis of the albian sediments from the kirchrode site by different disciplines yielded information about depth productivity and oxygenation of the water in the deeper parts of the lower saxony basin one of the mid latitude shelf sea basins in the northern hemisphere in addition information was obtained about phases during which inflow of water from the neighboring oceans tethys north atlantic and circulation within the basin was intensified about sea level changes as well as about climate changes occurring during the albian in this mid latitude region this information was derived from observations of the effects the changes in the palaeoenvironment had on the fossil and mineral assemblages the sediment facies and the geochemical composition of the sediment the increase in terrigenous input during the upper albian the relative increase in detrital montmorillonite and silt sized minerals e g quartz and zircon reflect tectonic movements e g uplift of the rhenish bohemian massif and subsidence of the lower saxony basin locally intensified by halokinetic movements and long term regional changes in climate a change to a more humid climate occurred approximately at the stratigraphic first occurrence of the calcareous nannofossil genus eiffellithus in this region and at the start of a new transgressional period and it led to increased runoff from the land possibly a second change this time to a more arid climate occurred in the latest albian during times of high sedimentation rates of terrigenous components the marine productivity in the shelf sea is also increased as a consequence of the increased input of dissolved and particulate matter during the latest albian upwelling may have been the cause of a further increase in productivity a global sea level change overlying the effects of these regional and local processes was recognised e g in changes in sedimentation rates in the monotonous deep shelf sediments decreasing during transgression and highstand times increasing during regression and lowstand times global sea level changes are best documented in changes in the abundances of the main plankton and benthos groups and changes in the relative abundance of benthos groups with different feeding strategies suspension feeders and detritus feeders transgressional periods start with an abundance maximum in species that immigrated from the tethys highstand conditions at lower nutrient levels are documented in the sediment record by a maximum in planktonic foraminifera and calcareous nannoplankton when nutrient levels under highstand conditions were higher like at the end of the albian calcareous nannofossils and siliceous plankton dominate milankovitch cyclicity was identified using spectral analysis of the regularly and closely spaced data sets of sedimentological palaeontological and geochemical parameters the higher abundance of terrigenous plant material in the dark parts of the sedimentary cyles in the upper albian suggest a change in humidity was the main climatic change and changes in benthos foraminifera assemblages indicate cyclic productivity changes in at least part of the sequence among planktonic foraminifera species that immigrated from the tethys have a stronger precessional signal in their abundance fluctuations while the boreal species show a stronger obliquity signal for the deep part of the shelf basin the strong precessional signal in the cyclicity of benthic foraminifera abundances suggests that conditions were influenced for most of the upper albian by processes triggered in the low latitudes based on the identified milankovitch cyclicity sedimentation rates were found to increase through the upper albian from 1 5 6 5 to 7 13 cm ka the duration of the callihoplites auritus ammonite subzone was determined to be 2 1 ma and the minimum duration of the late albian 4 ma possibly 4 5 4 8 ma

metamorphism of cordierite gneisses from the bangalore region of the indian archean abstract mineral compositions from cordierite bearing metasedimentary enclaves adjacent to the closepet granite in the bangalore region of the south indian craton indicate peak metamorphism in the range 4 5 5 0 kb 690 730 c p h 2 o is found to decrease towards the south and those assemblages which lie south of the charnockite line are formed under conditions of p h 2 o total 250 km north bangalore andalusite bearing assemblages from the northern margin of the closepet granite indicate peak metamorphic conditions in the range 2 6 3 8 kb 520 620 c the inferred piezotacrmic array is strongly convex towards the temperature axis and may represent a transient geotherm in the upper crust related to the emplacement of the closepet granite or to volatile activity along the margins of the granite

progressive metamorphism of mafic rocks from greenschist to granulite facies in the dharwar craton of south india in the archean dharwar craton of southern india n s trending belts of metabasic rocks are exposed which underwent regional metamorphism at about 2 5 ga ago the progressive changes in the assemblages and mineral chemistry of metabasites was studied in a n s traverse covering the chitradurga and nagaman gala belts the sargur area and the nilgiri hills towards the south with increasing metamorphic grade greenschists chl act ab ep pm carb qtz give way to amphibolites hbl plag pm qtz gar cumm and mafic granulites pyx plag gar pm hbl qtz the amphibole composition changes from actinolite in the greenschist zone to tschermakitic hornblende in the amphibolite zone and pargasitic hastingsitic hornblende in the granulite zone the ti content of the amphiboles systematically increases in this direction the plagioclase composition changes from albite in the greenschist zone to oligoclase andesine in the amphibolite zone and andesine labradorite in the granulite zone almandin

late albian ammonite biostratigraphy of the kirchrode i borehole hannover germany abstract the ammonite biostratigraphy of the 245 m of sediments of late albian age traversed in the kirchrode i 1 91 boring situated in the south eastern suburbs of the city of hannover lower saxony basin is described correlation is made with the actinoceramus birostrina bivalve biostratigraphy in the part of the core of early late albian age and with the inoceramus inoceramus lissa aucellina gryphaeoides succession above the earliest sediments of late albian age are of late dipoloceras cristatum subzone age with a good representation of the hysteroceras orbignyi subzone and an incomplete representation of the hysteroceras varicosum subzone a notable feature of the succession is the presence of a considerable thickness ca 164 m of sediments of callihoplites auritus subzone age sediments of stoliczkaia dispar zone age indicate the representation of the mortoniceras mortoniceras rostratum mortoniceras durnovarites perinflatum and arrhaphoceras praeschloenbachia briacensis subzones the ammonite fauna of the borehole is listed and the ammonite biostratigraphy of the clay sediments traversed is discussed a brief comparison is made with other surface and borehole sections in northern germany and elsewhere and the more cosmopolitan tethyan elements of the fauna are indicated and discussed

foraminiferal response to seasonality modulated by orbital cycles in the cretaceous mid latitudes the albian record from the lower saxony basin abstract the mid cretaceous serves as an excellent laboratory for testing the dynamics of the climate under greenhouse state of the earth this study is focused on the cyclicity record of foraminiferal assemblages in the lower saxony basin during the middle albian the short eccentricity obliquity and precession cycles are consistently recorded in absolute and relative abundance of most opportunistic benthic and planktic foraminifers the question is why foraminifers reacted to orbital cycles and what they actually record in the equable global climate it is suggested that seasonality changes modulated by orbital cycles are responsible for the milankovitch cyclicity records it is well known that the axial obliquity directly influences seasonal contrasts in mid and high latitudes the precession modulated by the eccentricity of the earth orbit further affects the contrast of seasons therefore seasonal dynamics of precipitation runoff and storm tracks patterns and to a lesser extent temperature contrasts are most likely factors controlling milankovitch scale cyclic fluctuations of foraminiferal assemblages and other proxies sensitive to productivity changes it can be deduced that periods of the highest seasonal contrasts were dominated by opportunistic abundant taxa such as benthic valvulineria gyroidinoides group and planktic hedbergellids which record the strongest obliquity signals the lower saxony and adjacent boreal basins were possibly controlled by humid climate with relatively dry summers and wet winter seasons this study confronted with the presented conceptual model and former climate models supports the conclusion that the temperate zone surrounding tethys was sensitive to seasonal changes modulated by orbital cyclicity the mid latitudinal climate of the greenhouse earth seems to be more dynamic and more seasonal than expected

new advances in karst collapse research in china until 2000 more than 1 446 karst collapse events and 45 037 sinkhole pits have been documented in china in this paper focusing on new achievements of karst collapse research in china a large scale model experiment a method of risk assessment and data management of karst collapse based on geographic information system technology are introduced for the region

a 2082 ma radiating dyke swarm in the eastern dharwar craton southern india and its implications to cuddapah basin formation abstract using consistent paleomagnetic data together with precise pb pb baddeleyite ages on a series of mafic dykes occurring over an area of at least 70 000 km2 a 2081 8 1 1 ma weighted mean of 4 dykes dyke swarm was identified intruding the archean basement rocks in the eastern dharwar craton skirting the cuddapah basin on its north northwest and western flanks the geometry of these dykes collectively due to their progressive variation in trend from n134 w to n28 e defines a fan angle of about 162 and forms a spectacular radiating swarm converging toward a focal point beneath the cuddapah basin anisotropy of magnetic susceptibility ams investigations on these dykes based on the orientation of principal eigenvectors indicate magma flow was vertically upward in them suggesting the magma source of these dykes to be proximal to the sampling sites these features together with reported geophysical evidence for high density material below the cuddapah basin suggest that this mafic volcanic province probably formed due to the impact of an asthenospheric mantle upwelling perhaps triggered by a plume head or other causal mechanisms like global warming of mantle or small scale instability like edge driven convection this may have resulted in the domal uplift of the continental lithosphere large scale crustal extension and thinning followed by thermal relaxation and subsidence that may have been responsible for the formation of the intra cratonic cuddapah basin shortly after 2082 ma dyke swarms of this age fort frances dykes 2076 5 4 ma or of slightly younger lac esprit dykes 2069 1 ma and older cauchon lake dykes 2091 1 1 8 2 1 ma ages are fairly wide spread in the superior province however a reconstruction of the paleopositions of dharwar cuddapah dykes 38 n 180 e a95 4 and superior at 2080 ma using paleomagnetic data fort frances dykes p 43 n lp 184 e does not suggest a close proximity for these provinces at that time their disparate locations could therefore suggest these were two distinct nodes of wide spread magmatism between 2080 ma and 2065 ma

organic geochemistry and depositional history of upper albian sediments from the kirchrode i borehole northern germany abstract in the framework of a multidisciplinary research program an organic geochemical study was carried out on a drill core which comprises a 245 m thick sequence of light colored upper albian marlstones that were deposited in the central part of the lower saxony basin northern germany for part of the upper albian sequence high resolution measurements of carbonate contents reveal cycles which can be related to earth orbital forcing based on these data sediment accumulation rates were calculated to be in the order of 15 g m2yr1 these high accumulation rates contrast with very low organic carbon contents and an extremely poor preservation of the autochthonous organic matter most of the sedimentary organic matter is of terrigenous origin and mainly derived from the erosion of older sedimentary rocks organic petrography reveals only a very small fraction of marine organic particles carbon sulphur ratios pristane phytane ratios as well as the predominance of resedimented organic particles over autochthonous organic particles suggest that aerobic degradation processes rather than anaerobic processes sulphate reduction were responsible for the degradation of the organic matter furthermore the scarcity of terrigenous organic particles vitrinite indicates that there was little vegetation on nearby land areas to explain these analytical results a depositional model was developed which could explain the scarcity of organic matter in the upper albian sediments this model is based on downwelling of oxygen rich saline waters of tethyan origin which reduces the nutrient content of surface waters and thus primary bioproductivity while degradation of primary organic matter in the water column is enhanced at the same time these conditions contrast to those which existed in barremian and early aptian times in this basin when limited water exchange with adjacent oceans caused oxygen deficiency and the deposition of numerous organic carbon rich black shales the thick organic matter poor upper albian sequence of northern germany also contrasts with comparatively thin time equivalent deep sea black shales from italy this discrepancy indicates that local and regional oceanographic factors at least in this case have a greater influence on organic matter deposition than global events

precise pb baddeleyite geochronology by the thermal extraction thermal ionization mass spectrometry method abstract the ability to easily obtain precise 0 1 age determinations on mafic rocks can facilitate identification of contemporaneous magmatic events across continents and hence open new avenues of research investigations related to large scale mantle processes we present high precision pb age determinations on baddeleyite zro 2 a common accessory mineral in mafic rocks using the recently developed thermal extraction thermal ionization mass spectrometer te tims procedure for dating of zircon in order to constrain the conditions for thermal extraction of pb from baddeleyite a sequence of sem back scattered electron images were acquired along with energy dispersive x ray spectroscopy spot analysis of baddeleyite grains embedded in silica beads at progressively increasing temperature between 1200 and 1590 c replicate analyses of twelve preheated at 1250 c and silica embedded baddeleyite grains from the paleoproterozoic phalaborwa carbonatite using this procedure have yielded a 207 pb 206 pb weighted mean age of 2060 3 0 4 ma consistent with previously reported 207 pb 206 pb ages for this carbonatite occurrence determined by the conventional u pb isotope dilution thermal ionization mass spectrometry id tims technique fourteen baddeleyite fractions from a large paleoproterozoic n s striking mafic dyke swarm in the dharwar craton yielded a 207 pb 206 pb weighted mean age of 2215 9 0 3 ma also consistent with previously determined conventional ages all data were corrected for mass fractionation of 0 18 amu as determined previously on zircon both data sets scatter outside measurement errors implying an external 2 sigma error of 0 055 in the case of the carbonatite and 0 043 for the mafic dyke which we suggest represents the reproducibility of the fractionation correction our results demonstrate that thermal extraction 207 pb 206 pb ages are comparable with the conventional u pb ages in both accuracy and precision this procedure does not need ultra clean laboratory conditions

sea level changes and organic walled phytoplankton response in a late albian epicontinental setting lower saxony basin nw germany abstract samples from a 245 m long core from the upper albian of nw germany have been analysed palynologically in accordance with the concept of sequence palynology of prauss 1993 two completed cycles of 3rd order sea level change are inferred superimposed by a 2nd order cycle during the 3rd order cycles the response of both the ratio of terrigenous sporomorphs to marine palynomorphs t m index and dinoflagellate diversity shows a gradual decrease within the transgressive systems tracts the quantitative response of certain dinoflagellate taxa however is different within each 3rd order cycle the abundance of skolochorate cysts increases strongly only during the earlier cycle this difference is suggested to be a function of the 2nd order cycle which is transgressive during most of the earlier 3rd order cycle but regressive throughout the later one the layer at about 135 m is interpreted to represent the maximum flooding surface of the 2nd order cycle the succession in peak abundance of the dinoflagellate genera oligosphaeridium surculosphaeridium pterodinium may characterise a transgressive systems tract to early highstand systems tract interval during a 3rd order cycle however the proportions of surculosphaeridium respond much more distinctly to the 2nd order sea level changes being highest during the corresponding maximum flooding surface higher proportions of palaeoperidinium cretaceum may indicate enhanced primary productivity and or estuarine circulation during transgressive and advanced late highstand conditions with respect to water mass characteristics within the photic zone no clear dominance of tethyan or arctic waters is distinguishable based on dinoflagellate taxa a rather mixed water mass dominated by cosmopolitan and boreal taxa seems to be present throughout most of the section the influence of warmer water masses largely indicated by the proportion of skolochorate cysts is enhanced during each transgressive interval of the 3rd order cycles but it is less well developed within the transgressive systems tract at the top of the section it is suggested that a strong tethyan influence in terms of water mass introduction into the nw german basin was predominant only during the transgressive pulse of the 2nd order cycle above 135 m the tethyan or warm water influence is considered largely as a function of oceanic circulation rather than sea level rise but is episodically enhanced during the relatively weak pulses of 3rd order transgressions certain dinoflagellate taxa known from the upper albian arctic region vesperopsis mayii luxadinium primulum l propatulum luxadinium cf l primulum are absent

syntectonic granite emplacement at different structural levels the closepet granite south india abstract the closepet granite in south india is a large 400 km long but only 30 km wide elongate late archaean granitic body structural levels from deep crust to upper levels crop out as evidenced by a shallowing of paleo depths from north to south all along the closepet granite this allows the study of the emplacement of the same granitic body at various crustal levels four zones have been identified a root zone where magmas are collected in active shear zones a transfer zone featuring large scale magma ascent and crystal liquid partitioning in the granitic mush a gap where the mush was filtered allowing only the liquids to rise shallow intrusions filled with this liquid the closepet granite was emplaced syntectonically field work and anisotropy of magnetic susceptibility allowed documentation of steep foliations with subhorizontal lineations both in the root and transfer zones and in the shallow intrusions remote sensing evidenced a network of shear zones bounding the closepet granite in the porphyritic root and transfer zones magmas cooled slowly thus developing strong fabrics during large scale dextral shearing ascent of residual liquids amidst the crystallizing solid framework was not recorded in the fabrics however these liquids were channelised through the gap and infilled the homogeneous shallow intrusions where rapid cooling only permitted the development of feint although wholly consistent fabrics

short term warming events during the boreal albian mid cretaceous pronounced paleotemperature variations associated with the carbon cycle perturbations of oceanic anoxic events oaes 1b and 1d are known to have occurred during the early and latest albian however reliable paleotemperature data spanning the 12 m y between these two events are sparse here we present 18o 13c and mg ca data for the middle to early late albian based on analysis of unusually well preserved glassy foraminifers from a clay rich sequence drilled in the boreal lower saxony basin northwestern germany 45 n paleolatitude our records reveal pronounced variability in planktic 18o 1 5 2 5 on a 100 k y time scale that we interpret to indicate substantial changes in sea surface temperature to 7 c and 18o salinity to 3 psu our findings attest to the climatic sensitivity of marginal basins in these boreal latitudes during the mid cretaceous and suggest that the heat and salt budgets of the lower saxony basin were orbitally conditioned during the albian presumably through atmospheric or oceanic heat transport from lower latitudes where surface waters were warmer than today in response to strong greenhouse gas forcing

precambrian continental strain and shear zone patterns south indian case 1 this study addresses the tectonic and mechanical significance of crustal scale strain and shear zone patterns in the south indian precambrian lithosphere it is based on a tectonic map of the dharwar craton derived from landsat imagery existing documentation and our own field observations we document the contrasted responses of the two main parts of the craton to late archean 2 56 2 51 ga shortening the old 3 ga lithosphere of the western dharwar craton stabilized at 2 61 ga underwent moderate shortening and strain localization along spaced shear zones the eastern dharwar craton rejuvenated by late archean juvenile magmatic accretion responded to shortening by flowing laterally against the western dharwar craton shortening operated without significant thickening because of the high buoyancy of the juvenile crust and the very low strength of its mantle lithosphere the late archean crustal scale shear zone network did not accommodate large displacements and only contributed to smoothing out of strain heterogeneities during the latest stages of flow the shear zone pattern only reflects the symmetry of the regional finite strain field of a wide hot orogen it does not result from terrain amalgamation but accompanies crustal flow and does not compare with those of modern active margins which accommodate unidirectional transpression our analysis further suggests that the shear zones bounding the craton did not record large horizontal displacements during final assembly of gondwana but rather transverse shortening and vertical extrusion

calcareous nannoplankton from the boreal late albian of nw germany kirchrode i borehole its biostratigraphy and cyclicity abstract one hundred and sixty samples from the continuously cored kirchrode i research borehole were examined for calcareous nannoplankton a total of 106 coccolith taxa were identified the state of preservation varied from poor to good mostly moderately good the coccolith assemblages were assigned to the eiffellithus turriseiffelii zone cc9 and prediscosphaera columnata zone cc8 of the upper albian sissingh geol en mijnb 56 1977 37 a count of the taxa was made at 5 m intervals and in certain sections at 1 m intervals this study focuses on the dating of the sequence with calcareous nannofossils and the determination of the fluctuations in the abundance of calcareous nannofossils the cyclicity found in the changes in their abundance was correlated with cycles determined for the changes in the calcium carbonate content of the sediment

a new approach for forecasting the appearance of sinkholes near the jinshazhou tunnel the paper deals with a frequent and known problem of suffusion type of sinkhole formation in soil due to water level oscillations above karstified bedrock the authors measured groundwater pressure oscillations caused by pumping groundwater from the excavated tunnel to determine the reliable indicators for prediction of sudden soil collapse based on risk assessment the statistical analysis was performed to determine suspicious values which reliably predict the soil collapse the results of analysis of monitored values indicate very good time correlation coefficients with the failures the work comprises the following main parts 1 survey of the geologic environment 2 monitoring of hydrodynamic conditions and 3 acquisition of a forecasting criterion based on the statistical analysis of anomalous monitoring data from this research it might be concluded that the appearance time of sinkholes and the abnormal values were strongly linearly dependent with a correlation coefficient of over 99 this conclusion will be a contribution to estimate the risk of karst collapse in a similar environment

spiroplectinata key benthic foraminifer genus for palaeoceanographic reconstruction of the albian lower saxony basin abstract this paper is focused on albian spiroplectinata a morphologically unique benthic agglutinated foraminifer genus and its application for reconstructing changes in the water masses within the lower saxony basin a new interpretation of microhabitat preferences and feeding habit for spiroplectinata is proposed and discussed their functional morphology composition of their tests and their relationships with adherent foraminifera suggest that at least adult individuals of spiroplectinata were epibenthic and were either suspension or deposit feeders the suspension feeding mode is favoured because this genus is associated with adherent suspension feeding foraminifera and it does not correlate with other epibenthic deposit feeders spiroplectinata constructed an elongated uniserial terminal part which probably facilitated an erect position to spread a reticulopodium well above the sediment water interface the distribution of this foraminifer can therefore be used here as a sensitive indicator for the existence of bottom currents four or five periods of intensified bottom water circulation around the early middle albian boundary s 1 middle s 2 late middle to earliest late albian s 3 probably represents two intervals and early late albian s 4 are reconstructed and well marked by maxima of spiroplectinata annectens s complanata and spiroplectinata sp a s annectens is known from strata in the western tethys i e in the late aptian and early albian that are older than those in the boreal realm its first appearance in the lower saxony basin occurs in the late early albian followed by the first maximum just above the early middle albian boundary and probably represents the main immigration event into the lower saxony basin this supports the idea that the deep water in the late early to early late albian boreal epicontinental sea during the spiroplectinata intervals came from the tethys and not from the polar regions if one interprets the plankton benthos foraminifera ratio as reflecting sea level changes it implies that sea level rises may have been responsible for opening and or deepening of boreal tethyan gateways that activated extensive exchange of water masses this late early albian and early late albian invasion of tethyan water can be correlated with a general global warming and shifting of climate zones

responses of cover collapse sinkholes to groundwater changes a case study of early warning of soil cave and sinkhole activity on datansha island in guangzhou china in karst areas of quaternary sediments fissures and solution channels through soluble rocks provide unseen conduits for the vertical movement of surface water into the underlying karst aquifers this downward flow may also transport overburden material which can result in the formation of soil caves and ground loss called cover collapse sinkholes because of the concealed development of such soil caves and generally complicated geological conditions the prediction of soil cave development and sinkhole activity is far from perfect this study focused on the early warning of soil cave and sinkhole development by monitoring groundwater level decline based on the improved terzaghi loosening pressure theory and using excess pore water pressure two types of critical groundwater level decline are discussed the first denoted as 0 is the critical groundwater level decline related to soil cave formation and evolution the second denoted as ht is the critical groundwater level decline related to soil cave roof collapse this method of groundwater monitoring for the early warning of soil cave and sinkhole development is currently being applied on datansha island in guangzhou china

continental scientific drilling project of cretaceous songliao basin scientific objectives and drilling technology abstract the continental scientific drilling project at the cretaceous age songliao basin is a drilling initiative under the framework of the international continental scientific drilling program to recover a nearly complete cretaceous terrestrial sedimentary record in the songliao basin northeastern china the recovered cores will provide unique opportunities for the geosciences community to advance the understanding of climate change in the cretaceous greenhouse world and provide a documentation of geological events relevant to the carbon cycle during this time period this drilling project will address significant geological questions such as the identification of important stratigraphic boundaries and the marine terrestrial correlations of stratigraphy the reasons for the biotic response to the terrestrial environmental changes the terrestrial response to the cretaceous oceanic anoxic events the formation of terrestrial petroleum source rocks and the mechanisms for the cretaceous magnetic normal superchron cns in the first stage of this drilling project the ski drilling rock cores of 2485 89 m in total length were recovered and the recovery ratio reached 96 46 a series of drilling and coring technologies including regular confined directional and sealed coring were utilized to ensure a higher recovery ratio for the core and will be described at the end of this paper well loggings were conducted right after coring core handling and storage were arranged in such a way that the scientific research was conducted on half of each core whereas the other half of each core was preserved for long term storage the upcoming second stage the skii drilling will combine with data from the existing ski to provide complete high resolution climate records of the terrestrial environment for the whole cretaceous time period

review of the advanced monitoring technology of groundwater air pressure enclosed potentiometric for karst collapse studies this paper presents an overview of the groundwater air pressure monitoring technology for karst sinkholes karst collapses often occurred rapidly without prior warning the early warning for potential karst collapses has been one of the most challenging problems around the world in fact many karst collapses are kind of sudden geohazards and mainly induced by abrupt changes of hydrodynamic conditions within karst conduit systems traditionally only groundwater level monitoring was applied to monitoring the karst collapses which did not reflect the hydrodynamic conditions within karst conduit systems the monitoring technology of groundwater air pressure was proposed by the institute of karst geology china in 1998 to study the formation mechanisms monitoring and forecast of karst collapses this technology has been improved in the past 20 years and applied to collapse risk assessment triggering factor evaluation and controlling drawdown of the groundwater levels during underground civil engineering works at 11 study sites this advanced technology is characterized by improved borehole drilling special sealing technique of borehole orifice and high frequency data logging the recommended logging interval is at least 5 20 min to capture the transient changes of groundwater air pressure within karst conduit systems the pressure transducers used in this technique are retrievable and can be reused or recycled

the dharwar craton southern india interpreted as the result of late archaean oblique convergence abstract the dharwar craton comprises two distinct parts separated by a steep n s sinistral shear zone in the western part a pre 2900 ma complex of orthogneisses granodiorites and narrow tracts of supracrustal rocks sargur group forms the basement to volcanic and sedimentary basins of the dharwar supergroup ca 2800 2550 ma late archaean deformation is characterised by ne sw crustal shortening and steep n s sinistral shear zones the eastern part is underlain by parallel steep n s or nw se linear belts of calc alkaline anatectic and juvenile granites and granodiorites dharwar batholith ca 2750 2510 ma with intervening volcanic and sedimentary schist belts ca 2800 2550 ma the plutonic belts are 15 25 km wide up to 150 km long and bounded by steep nw se high strain zones up to 2 km wide with sinistral shear sense except one which is dextral magmatic state fabrics and structures in the plutonic rocks are parallel to solid state sinistral shear fabrics in the high strain zones but diffuse magmatic banding is commonly oblique to these zones and coincides with the plane of instantaneous shortening in sinistral shear magmatic state structures swarms of vertical nw se dykes of granite and the vertical wedge shape of the linear belts are consistent with emplacement of the batholith during sinistral shear when magma pressure exceeded regional horizontal compressive stress upright folds and schistosity steep reverse faults and effects of regional ht lp metamorphism show that deformation was partitioned into ne sw shortening in the schist belts during emplacement of the plutonic belts in the sinistral shear regime the western part of the craton is interpreted as the foreland to an accretionary arc represented by the batholith and schist belts intra arc basins in the east ne sw shortening and sinistral transcurrent displacements in the foreland and arc are consistent with arc normal and arc parallel displacements during oblique convergence analogous to mesozoic cenozoic convergent settings

inorganic geochemistry of albian sediments from the lower saxony basin nw germany palaeoenvironmental constraints and orbital cycles abstract within the international albicore project upper albian sediments from a 245 m core kirchrode i drilled in hannover were studied by inorganic geochemical methods more than 650 samples minimum sample spacing 0 5 m were analysed for major and minor element concentrations this chemical database was used to reconstruct the depositional environment and to investigate the influence of high frequency milankovitch cycles on the chemical composition of the sediments the chemical composition of the sedimentary sequence is primarily controlled by variations in carbonate content corresponding to ca al ratios variations in both ti al and si al ratios are interpreted as fluctuations in detrital composition resulting from increases in smectite and quartz content in the upper section of the core high amounts of reactive iron but low pyrite concentrations the lack of enrichment of redox sensitive trace elements v cr and high mn concentrations indicate oxic bottom water conditions and the absence of an oxygen minimum zone for the upper albian at the kirchrode site the nutrient related trace elements ba p zn suggest a generally oligotrophic setting with slightly elevated productivity only in the uppermost upper albian only one layer was identified as containing volcanogenic material at 87 20 m this layer is characterised by elevated montmorillonite zr and nb mass balance calculations for the entire core suggest that the high mn values cannot be explained by riverine input alone therefore a coastal oxygen minimum zone south of the kirchrode site is postulated as an additional mn source cyclic variations in both carbonate content and al normalised concentrations of predominantly detrital elements like si and ti are seen in a 60 m interval 40 100 m where sedimentological palaeontological and geochemical data suggest stable depositional conditions although carbonate cyclicity cyclicity in detrital input and nutrient related element abundances do not correlate with each other three strong peaks in the results of spectral analysis of these chemical data for this interval appear to correspond to milankovitch frequencies in the eccentricity obliquity and precession bands

paleomagnetism and u pb geochronology of easterly trending dykes in the dharwar craton india feldspar clouding radiating dyke swarms and the position of india at 2 37 ga abstract a u pb baddeleyite age of 2367 1 ma from a diabase dyke together with previously published age data suggests that a major early proterozoic dyke swarm cuts across the structural grain of the archean dharwar craton in india paleomagnetic data suggest the swarm is at least 300 km wide and 300 km long and has a fan angle of at least 30 with convergence to the west it was originally emplaced at high latitudes and together with the widgiemooltha dykes of the yilgarn block of australia may have been a segment of a larger radiating swarm related to a long lived plume event that was active for about 50 my from 2418 to 2367 ma a regional change in the intensity of brown feldspar clouding in the dykes suggests that the dharwar craton was tilted northwards in harmony with previous observations on the structure and metamorphism of the archean rocks towards the south the brown feldspar clouding becomes more intense and locally assumes a blacker more sooty appearance the black clouding whose precise origins remain unknown is accompanied by a remagnetization and appears to coincide closely with a region of carbonatite magmatism at 800 ma and with a shear zone and change in structural trend related to pan african deformation at 550 ma paleomagnetic studies suggest that i the high coercivity part of the remanent magnetization is carried by magnetite exsolved within either brown or black clouded feldspars and ii as a more general observation diabase with brown clouded feldspar can carry a primary magnetization but not if the clouding is black

palaeoenvironmental interpretation of late albian calcareous dinoflagellate cysts from the kirchrode i borehole lower saxony basin nw germany abstract late albian calcareous dinoflagellate cyst assemblages from samples of the kirchrode i borehole contains 38 morphospecies which represent a flora of moderate warm water conditions in an oceanic controlled epicontinental regime the vertical changes of cyst associations reflect sea level fluctuations the regressive phases of the highstand are characterised by the exclusive occurrence of benthic resting cysts while planktonic counterparts joined during transgressive phases floral exchanges via the water masses which were influenced by the tethys were in progress only during phases of relatively strong currents in particular during transgressions in contrast the highstand during which water circulation decreased can be characterised by autochthonous morphotypes reflecting an epicontinental habitat the corresponding cyclic intraspecies change of cyst diameter is interpreted to reflect changes in productivity which were probably controlled by eccentricity cycles

age and tectonic implications of paleoproterozoic mafic dyke swarms for the origin of 2 2 ga enriched lithosphere beneath the ungava peninsula canada abstract mafic dyke swarms represent short lived magmatic events that carry important temporal and chemical constraints for the evolution of the lithospheric mantle five baddeleyite u pb isotopic analyses of paleoproterozoic mafic dyke swarms intruding the ungava peninsula yielded ages of 2508 6 2220 1 2212 3 2199 5 and 2149 3 ma these ages fall within the 2 5 2 0 ga period previously defined by five other swarms which together comprise a magmatic record of more than 500 ma the similar age composition and surface area of two 2 51 ga swarms along with the lack of coeval supracrustal rocks suggest they correspond to failed rifts an important magmatic hiatus of 280 ma follows but ends with the intrusion of numerous dykes between 2 23 and 2 20 ga in the thinnest lithosphere of the northern ungava peninsula these dykes exhibit chemical signatures that vary from enriched older 2229 2212 ma dykes nd t 4 to relatively depleted 2209 2199 ma voluminous younger dykes nd t 1 4 la yb ca 2 21 2 20 ga later dykes emplaced ca 2 17 ga within a rejuvenated paleoproterozoic lithosphere also have depleted chemical compositions and map the extent of rifting coeval with the emplacement of early basalts in the labrador trough dykes emplaced in the 2 15 2 00 ga period further to the south are proximal to coeval continental basalts with which they share enriched isotopic compositions nd t 1 5 to 7 and a positive correlation between la yb and zr nb la yb 4 10 zr nb 7 20 that suggest assimilation of an archean crustal component a progressive decrease in the nd t values of these magmas with decreasing age further implies increasing contamination until the archean lithosphere failed ca 2 0 ga and permitted the eruption of isotopically depleted basalts the ca 2 2 ga depleted northern dykes and the 2 1 1 9 ga povungnituk basalts of the cape smith foldbelt share a negative correlation between zr nb and la yb that is expected for the incorporation of an enriched lithospheric component this component is represented by the alkaline rocks comprised in the circum ungava supracrustal belts carbonatites lamprophyric lavas alkaline basalts and by the lac aigneau lamprophyric dykes 1941 3 ma intruding the ungava peninsula these alkaline magmas collectively have 2 2 2 1 ga depleted mantle nd model ages t dm similar to a 2 15 ga sm nd isochron defined by the basaltic rocks of the supracrustal belts although these nd t dm ages and isochron are 100 300 ma older than magmatic ages they are identical with the ca 2 2 ga mafic dykes of the ungava peninsula this time correlation along with the similar chemical signature of the northern dykes and younger povungnituk basalts suggest that the composition of younger lavas and alkaline magmas was influenced by an enriched component associated with the pervasive metasomatism of the lithosphere coeval with the emplacement of the many ca 2 2 ga dykes

paleomagnetism and geochronological studies on a 450 km long 2216 ma dyke from the dharwar craton southern india abstract paleomagnetic and geochronological studies were carried out on a 450 km long from 17 sites n s striking paleoproterozoic dyke swarm exposed along a natural crustal cross section of about 10 km increasing from north to south in the dharwar craton to study the characteristics of paleomagnetism and geochronology in vertical dimension u pb pb pb dating on baddeleyite gives a crystallisation age of 2216 0 0 9 ma for long dyke akld paleomagnetic data from this well dated 2216 ma dyke swarm in dharwar craton are of excellent quality high coercivity and high blocking temperature components are carried by single domain magnetite and show dual polarity remanence directions combined normal and reverse polarity remanences on akld and other n s dykes define the most reliable paleomagnetic pole for 2216 ma at latitude 36 s and longitude 312 e a95 7 though paleomagnetic data is unavailable on other n s dykes below the cuddapah basin high precision geochronology suggest that they are of similar age within errors though there is a variation in the crustal depth of dharwar craton from north to south consistent pb pb u pb baddeleyite geochronology and paleomagnetic studies along the akld established its continuity and preservation along its entire strike length the virtual geomagnetic poles of these sites confirm a stable remanence and are almost identical to the previously reported paleomagnetic pole and also supported by positive reversal test positive paleomagnetic reversal test on these dykes signify that the remanent magnetization is primary and formed during initial cooling of the intrusions updated apparent polar wander path of dharwar craton indicates relatively low drift rate during 2 21 2 08 ga interval magnetogranulometry and sem studies show that remanent magnetization in this dyke was carried by single domain magnetite residing within silicate minerals

recent investigations of the 0 5 ma geomagnetic field recorded by lava flows we present a synthesis of 0 5 ma paleomagnetic directional data collected from 17 different locations under the collaborative time averaged geomagnetic field initiative tafi when combined with regional compilations from the northwest united states the southwest united states japan new zealand hawaii mexico south pacific and the indian ocean a data set of over 2000 sites with high quality stable polarity and declination and inclination measurements is obtained this is a more than sevenfold increase over similar quality data in the existing paleosecular variation of recent lavas psvrl data set and has greatly improved spatial sampling the new data set spans 78 s to 53 n and has sufficient temporal and spatial sampling to allow characterization of latitudinal variations in the time averaged field taf and paleosecular variation psv for the brunhes and matuyama chrons and for the 0 5 ma interval combined the brunhes and matuyama chrons exhibit different taf geometries notably smaller departures from a geocentric axial dipole field during the brunhes consistent with higher dipole strength observed from paleointensity data geographical variations in psv are also different for the brunhes and matuyama given the high quality of our data set polarity asymmetries in psv and the taf cannot be attributed to viscous overprints but suggest different underlying field behavior perhaps related to the influence of long lived core mantle boundary conditions on core flow psv as measured by dispersion of virtual geomagnetic poles shows less latitudinal variation than predicted by current statistical psv models or by previous data sets in particular the brunhes data reported here are compatible with a wide range of models from those that predict constant dispersion as a function of latitude to those that predict an increase in dispersion with latitude discriminating among such models could be helped by increased numbers of low latitude data and new high northern latitude sites tests with other data sets and with simulations indicate that some of the latitudinal signature previously observed in vgp dispersion can be attributed to the inclusion of low quality insufficiently cleaned data with too few samples per site our matuyama data show a stronger dependence of dispersion on latitude than the brunhes data the taf is examined using the variation of inclination anomaly with latitude best fit two parameter models have axial quadrupole contributions of 2 4 of the axial dipole term and axial octupole contributions of 1 5 approximately 2 of the octupole signature is likely the result of bias incurred by averaging unit vectors