oxygen isotope calibration of the onset of ice rafting and history of glaciation in the north atlantic region we report here that dsdp site 552a cored with the hydraulic piston corer on the west flank of rockall bank recovered an undisturbed sequence of alternating white deep sea carbonate oozes and dark coloured layers that are rich in glacial debris oxygen isotope analysis of the sequence together with detailed nannofossil and palaeomagnetic stratigraphy shows that the first major horizon of ice rafting occurred at about 2 4 myr and was preceded by a minor pulse of ice rafting at about 2 5 myr the carbon isotope record shows that the site has been bathed by a water mass of similar characteristics to present day north atlantic deep water at least since 3 5 myr

late neogene atlantic circulation model a hydrodynamical numerical model of the general circulation in the paleo atlantic ocean is applied to the climatological conditions of the period 3 6 to 2 4 m a b p for three different stages of this interval representing the transition from a warmer to a cooler climate the circulation and the temperature fields are calculated generally a tendency towards a weakening of the currents is achieved

strain fabric analysis applied to hydrothermal ore deposits emplaced during changing geodynamical conditions infiernillo and las picazas san rafael massif argentina abstract infiernillo and las picazas are two small hydrothermal ore deposits in the northern san rafael massif argentina they are genetically linked to the permian choiyoi volcanic province which reflects the transition from a convergent plate margin to an extensional regime calc alkaline early permian lower choiyoi magmatism was syntectonic with transpressional deformation of the san rafael orogeny whereas transitional late permian upper choiyoi sequences were emplaced under a transtensional regime during the post san rafael extension infiernillo is a cu mo porphyry type deposit hosted by pyroclastic rocks of the lower choiyoi it consists of a central quartz plug surrounded by a potassic and a phyllic halo and a set of peripheral polymetallic cu pb zn veins cropping out close to the alteration zone the las picazas deposit consists of a group of low sulfidation epithermal galena bearing veins hosted by early palaeozoic meta sediments strain fabric and available 2 d and 3 d kinematic analyses were performed in order to define the relationships between both deposits and the geodynamic scenario these data reveal that a porphyry emplacement at infiernillo occurred during the declination of the san rafael orogeny shortly before the change in stress regime and b las picazas low sulfidation epithermal veins were emplaced during the subsequent transtensional post san rafael regime these results prove that each ore deposit is linked to a different stress regime reflecting the change in geodynamical conditions that prevailed during the emplacement of the choiyoi volcanism thus strain fabric analysis at both ore deposits allows us to confirm that the tectonic regime is a major factor in controlling the mineralization style of hydrothermal ore deposits

shear zones as a new type of palaeostress indicator this paper proposes that shear zones act as palaeostress indicators in much the same way as brittle faults several hundred shear zones from both the limbs of the variscan langland mumblcs anticline south wales are treated using the graphical and numerical methods of fault slip analysis estimated palaeostress directions derived from shear zones are characterized by greater scatter than where brittle faults are used as stress indicators an important reason for this is the fact that on some shear zones the direction of maximum shear stress slip lineation is not perpendicular to the line of s c intersection as a consequence the use of slip lineations produces better solutions than cases where the slip direction is inferred as a line perpendicular to the s c intersection the filtering of data to reduce the scatter in the results produces insignificant improvement and is considered unnecessary

a conceptual model for hydrocarbon accumulation and seepage processes around chapopote asphalt site southern gulf of mexico from high resolution seismic point of view 1 as part of the german r v meteor m67 2 expedition in 2006 to the southern gulf of mexico a set of 2d high resolution seismic profiles was acquired across the chapopote knoll to study seafloor asphalt occurrences on the basis of regional seismostratigraphic studies and dsdp drilling a more highly reflective coarse grained sediment unit of late miocene age is identified as a potential shallow hydrocarbon reservoir although a unit of that age would typically be buried by pliocene and pleistocene sediment cover at chapopote local salt tectonism has highly elevated the structure since the late miocene and the miocene reservoir is locally above present day regional datum the elevation resulted in a thin 100 200 m fine grained sediment cover on the crest of the knoll above the reservoir because oil and gas production can be expected at depth in jurassic cretaceous and tertiary source rocks the presence of high amplitude reflector packages within the reservoir unit is interpreted as an evidence of hydrocarbons this is variously supported by observations of crosscutting reflectors polarity reversal and drops in instantaneous frequency the thin seal above the reservoir unit facilitates leakage of trapped hydrocarbons hydrocarbons apparently invaded into the seal sediments in the wider vicinity around the crest of the knoll even extending beyond the area where seafloor asphalt is known the asphalt site thus may be a currently active spot while the rest of the crest may be temporarily sealed by solid phase hydrocarbons we propose that a shallow large reservoir with deeply sourced relatively heavy petroleum is principally responsible for the formation of asphalts on the seafloor

displaced antarctic diatoms in vema channel sediments late pleistocene holocene fluctuations in aabw flow abstract displaced antarctic diatoms were identified and counted in a suite of 23 giant gravity cores from the east flank of the vema channel providing a semi quantitative index of late pleistocene holocene fluctuations in antarctic bottom water aabw flow twelve species of antarctic diatoms were counted and three of these nitzschia kerguelensis eucampia antarctica and coscinodiscus lentiginosus occur in sufficient quantity for statistically meaningful interpretations the number of diatom specimens per gram of carbonate free sediment was determined for core top last glacial maximum last interglacial and penultimate glacial maximum intervals antarctic diatoms are abundant in cores from depths in excess of 4100 m and disappear abruptly in core tops between approximately 4125 and 3975 m water depth no specimens of antarctic diatoms are present in cores shallower than 3744 m the top of this transition zone corresponds with the isotherms 1 9 c and the isopycnal 4 45 93 that hogg et al 1982 selected as a suitable reference level between northward and southward flow in the vema channel axis the sediments from the vema channel indicate no significant shallowing or deepening of this level during the glacial or interglacial intervals examined displaced antarctic diatoms are generally less abundant during glacial maxima than during interglacials downcore counts of displaced antarctic diatoms reveal two peaks of dramatically increased abundances at the isotopic stage 6 7 and 3 2 boundaries in other cores within the vema channel from below 3965 m late pleistocene hiatuses are common

past climate and the role of ocean heat transport model simulations for the cretaceous a series of general circulation model experiments using global environmental and ecological simulation of interactive systems genesis were executed to evaluate the sensitivity of simulated mid cretaceous climate to small perturbations in ocean heat transport three experiments were performed 1 mixed layer ocean with no ocean heat transport zeroq 2 ocean heat transport specified as required for genesis to best match modern observations oneq and 3 doubled ocean heat transport twoq the oneq experiment represents an ocean heat transport which is actually about 15 of the values given by carissimo et al 1985 from modern observations as a sensitivity experiment these model simulations represent a doubling of the role of the ocean however relative to the observations they represent small perturbations to the total poleward heat transport in the model with the exception of the tropics no major changes in the structure of the general circulation of the atmosphere resulted from the modification of the ocean heat transport however relatively small increases in ocean heat transport resulted in a number of significant differences between simulations including tropical cooling polar warming weakened equator to pole surface temperature gradients weakened midlatitude jets decreased land sea pressure contrast and decreased midlatitude storminess the experiments indicate that changes in ocean heat transport which are well within the realm of possibility for earth history can have significant climatic impact although ocean heat transport may be a significant factor in explaining cretaceous polar warmth the changes specified in these experiments alone are not sufficient to explain the polar warmth of the cretaceous

shallow sediment deformation styles in north western campeche knolls gulf of mexico and their controls on the occurrence of hydrocarbon seepage during german r v meteor m67 2 expedition to campeche knolls southern gulf of mexico a set of 2d high resolution seismic data was acquired to study the near surface sediment structure and its relationship with hydrocarbon seepages in this salt province the comprehensive survey covered 20 individual bathymetric highs or ridges and identified three principle structural types passive type chaopopte type and asymmetric flap type the first type is the result of passive diapirism whereas the latter two were initialized by a regional compressional event in the miocene but are later differently modified by salt tectonism chapopote type structures appear as symmetrical domes with uplifted coarse grained miocene sediments in their cores and rather thin syn kinematic sediments covering the crests asymmetric flap type structures are also first folded as domes or ridges but one flap later subsided together with salt evacuation resulting in single uplifted monoclines with the coarse grained pre kinematic sediments as reservoir units both structural types can focus and accumulate hydrocarbons the geometries of the structures suggest that hydrocarbons are accumulated in the center of the chapopote type structures and in the subsided flaps of the asymmetric flap type structures hydrocarbon leakage from these thinly sealed reservoirs is regarded as the principle mechanism for the seepage in the study area and accordingly the most seepage prone positions are above these reservoirs the seep locations suggested by analysis of sea surface oil slick images of sar satellite data are also examined in this study these independently derived seep locations confirm the seepage prone positions to be above the shallow buried reservoirs this study suggest that the shallow sediment structures control the distribution of the hydrocarbon seeps of the north western campeche knolls although the hydrocarbons are sourced from the greater depth

separation of multiple stress events by fault striation analysis an example from variscan and younger structures at ogmore south wales the study of minor structures in carboniferous and triassic sedimentary rocks at ogmore by sea bridgend reveals that the observed microstructures are the consequence of successive brittle deformation events age relationships can be deduced from sets of structures consisting of conjugate faults oblique slip faults tension gashes and stylolites from which deductions can be made about the orientations of principal stresses corresponding to pre and post triassic events the demonstrable polyphase tectonic history at ogmore and the occurrence of large numbers of striated faults at four sites allow the opportunity of testing a newly proposed strategy for palaeostress analysis from striated faults with complex stress histories the new technique based on the statistical procedure of cluster analysis involves the sorting of fault slip data into coherent dynamic setsasa preliminary stage of formal stress inversion the fault sets separated using this technique yield stresses which are similar to those deduced from field observations four stress configurations are distinguished of which two are pre triassic in age correlations with previously derived stresses are discussed

application of hyperbolic stress strain models for sandstone and shale to fold wavelength in the mexican ridges foldbelt abstract the mexican ridges foldbelt on the continental slope east of mexico has major folds with wavelengths averaging 7 km locally there are also small amplitude near surface folds with wavelengths of 2 km initial dominant wavelength is modelled by the finite element method using the hyperbolic stress strain relationship originally derived for soils hyperbolic stress strain models for sandstone and shale are calibrated using field porosity depth relationships for shale and laboratory one dimensional consolidation data for sand and clay effective tangent young s modulus calculated from hyperbolic stress strain models is generally higher for sandstones than for shales and for both rock types modulus increases substantially with depth the finite element models of dominant wavelength duplicate the two orders of folds observed in the mexican ridges and match their wavelengths in the models fold wavelength is nearly constant for large variations in both sandstone fraction in the folded section and pore pressure magnitude in the overpressured basal shale below the folded section but fold amplification is increased by high pore pressure in the basal shale and by high sandstone fraction in the folded section fold wavelength is affected more by depth distribution of high pore pressure than by pressure magnitude and on the lower continental slope where grain size may be smaller a thicker zone of high pressure would partly explain the modest downslope increase in fold wavelength

deep water circulation in the northeast atlantic and climatic changes during the late neogene dsdp site 141 abstract oxygen and carbon stable isotope data of pyrgo murrhina and flux rates of calcium carbonate in the bio and magnetostratigraphically dated sediment sequence at dsdp site 141 were used for a reconstruction of the deep water circulation in the northeast atlantic during late miocene and pliocene times a distinct change towards reduced advection of deep water recorded near 5 4 ma is contemporaneous with the cessation of the outflow of the saline mediterranean water into the atlantic during the pliocene between 4 5 and 2 75 ma and between 2 1 and 1 8 ma north atlantic deep water nadw circulation was sluggish and site 141 possibly influenced by antarctic bottom water aabw near 2 75 ma the advection of well oxidized nadw was strongly intensified this change is related to an onset of major arctic ice growth and or a major cooling of nadw

kinematic and dynamic fault slip analyses implications from the surface rupture of the 1999 chi chi taiwan earthquake the 1999 chi chi earthquake created a 100 km long surface rupture on the chelungpu thrust fault in taiwan due to convergence between the phillipine sea and eurasian plates fault slip measurements were made by several researchers from the entire length of the rupture directly following the earthquake and can thus be attributed to a single tectonic event conventional fault slip analyses are applied to these data and the results are compared with independent seismological and kinematic observations unlike many fault slip analyses complications due to multiple deformations can be categorically excluded and the results can be evaluated from the seismological and plate movement data kinematic analyses of fault slip data that are weighted by displacement show sub horizontal nw se shortening that is parallel to the plate convergence vector a single fault plane solution satisfies almost all the data right dihedra and trihedra solutions also satisfy almost all the surface rupture measurements and give 1 in a nw se orientation that is similar to the results of stress inversion and to inversion from earthquakes in the chi chi earthquake sequence despite criticisms of fault slip analysis methods these results show that fault slip analyses from data collected along major faults which have not witnessed multiple deformation events can be valid homogeneous strain and stress states exist in the sense that kinematic and dynamic solutions can be found that fit essentially all the data and these solutions have tectonic significance

formation of ferromanganese microcrusts in relation to glacial interglacial stages in pleistocene sediments from ampere seamount subtropical ne atlantic ferromanganese microcrusts were found in oxic sediments that are undisturbed between 60 and 480 cm bsf rhythmic alternations of muddy calcareous ooze and foraminiferal nannofossil ooze make up the sediment sequence which extends to 270 ka at 480 cm bsf where a hiatus of at least 1 3 myr occurs the bottom of the core is pliocene the occurrence of ferromanganese microcrusts mainly formed on foraminifera tests larger than 200 m can be correlated with glacial stages 4 6 and 8 and indicates enhanced metal fluxes they do not form at the expense of carbonate material but derive their metals from the water column by hydrogenetic precipitation manganese was supplied as mn2 mainly from the oxygen minimum zone omz where it is transported via detrital material and brought into solution by weakly reducing conditions promoted by the oxidation of organic matter an enhanced detrital flux during glacials may also cause increased mn availability in the omz during these periods mixing of oxygen rich intermediate water with omz water during the glacial intervals caused mn2 oxidation in the water column underneath the omz

an inverse problem in microtectonics for the determination of stress tensors from fault striation analysis abstract a method is proposed to compute some characteristics of a possible stress tensor related to striations measured in a given faulted area if several tectonic phases are responsible for the striations the method separates and determines the successive stress tensors the iterative algorithm consists of alternatively a sorting the data attributed to a tectonic phase and b computing the characteristics of the stress tensor of this phase the method is tested using an application to synthetic and actual data

model simulation of the cretaceous ocean circulation three dimensional numerical ocean circulation model experiments that were designed to evaluate the circulation characteristics for the mid cretaceous 100 million years ago show that the primary direction of flow through the tethys ocean was eastward in contrast a westward flowing circumglobal tethys current has been a consistent feature of earlier reconstructions of cretaceous ocean circulation the model studies demonstrate that i ocean circulation is sufficiently sensitive to the role of continental positions sea level and climate to limit the application of modern analogs to past circulations and ii reconstructions based on limited biogeographic data may not provide unique surface circulation patterns

late tertiary quaternary magnetostratigraphy and biostratigraphy of vema channel sediments abstract twenty one piston cores in a transect of the vema channel near 31 s were analyzed magnetostratigraphically and biostratigraphically in order to ascertain the depositional continuity in the late tertiary and quaternary the cores span a depth interval of 2941 4235 m and represent three distinct physiographic provinces each of which shows a relatively consistent accumulation pattern the deepest cores are from the broad terraces which flank the vema channel axis on both the west 3650 mm and east 4150 4250 m these cores show the highest accumulation rates in the region 20 m m y 2 and no evidence of unconformities twelve cores from the flanks of the rio grande rise 2941 3950 m show depositional continuity in the late quaternary and normal pelagic accumulation rates 5 10 m m y 2 with evidence in two of the cores for minor erosional hiatuses on a local scale perhaps due to slumping a relatively narrow transition zone between the rio grande rise flanks and the eastern terrace 3950 4150 m shows buried manganese pavements and near outcrops of miocene pliocene strata indicating intermittent erosion during the late tertiary and quaternary perhaps due to episodes of intensified aabw flow modern flow within this transition zone and over the eastern terrace is relatively weak gu 2 cm s 2 and southward the presence of well developed sediment waves on the terrace and buried erosional unconformities upslope to the east suggests substantially higher current velocities during the late tertiary than those present today

the tethyan oyster pycnodonte costeina costei coquand 1869 in the coniacian upper cretaceous of the iberian basin spain taxonomic palaeoecological and palaeobiogeographical implications abstract oysters were among the most important groups of marine invertebrates in late cretaceous biotas of the tethyan realm during the major eustatic sea level highstands of this interval large areas of northern africa and southern europe were characterized by carbonate shelf environments with conditions favourable for the widespread dispersal of highly diverse marine ecosystems which included many ostreid bivalves in this palaeoecological setting pycnodonte costeina costei coquand 1869 is one of the most widespread representatives of the subfamily pycnodonteinae extending from central asia and egypt to southern france and the iberian peninsula this taxon is characterised by a strong convex left valve with an expanded posterior flange suggesting that this species was a free lying recliner on infralittoral soft substrates the species is also remarkable due to its morphological plasticity with ecophenotypes characterised by extremely variable left valve ornamentation the assemblages of p c costei studied herein occur in middle to upper coniacian outer shelf facies within the northern and central sectors of the iberian basin spain associated with transgressive and highstand system tracts the species occurs mostly in autochthonous concentrations of several tens of individuals cemented or oriented side by side and colonised by epizoans and borers endolithic sponges related to the ichnogenus entobia were especially abundant infesting many specimens to a great extent these new finds in the iberian basin also improve the known palaeogeographic range of p c costei its distribution can be related to current circulation along the tethys ocean firstly from its original area in central asia to north african shelves and then to the iberian basin and france across the proto atlantic lusitanian area this dispersal model inferred by these currents also explains much of the tethyan affinities found in the late cretaceous marine faunas of iberia

structural analysis of faults related to a heterogeneous stress history reconstruction of a dismembered gold deposit stawell western lachlan fold belt australia in the internationally significant victorian goldfields a complex system of faults dismembers the 5 million ounce magdala gold deposit these faults represent a combination of neoformed faults and inherited faults that reflect deformation associated with stress tensors of variable orientation and stress shape ratio the fault geometry is strongly controlled by the pre existing rheology faults have propagated around the flanks of an antiformal basalt dome along earlier ductile cleavages and the margins of porphyry dykes many of the faults do not have andersonian geometries and there is no correlation between the orientation of the faults and the palaeostress directions much of the faulting is associated with the emplacement of porphyry dykes additional gold mineralisation related to plutonism and late stage deformation post dating the intrusion of the stawell pluton systematic mapping of extension veins associated with faults striations and conjugate joint sets allowed the construction of a revised and more robust history of brittle deformation this successfully predicted the offset direction of the currently mined magdala ore body beneath the studied system of faults the use of extension veins was a critical aspect of the analysis if striations on the fault surfaces had solely been used the offset direction of the new golden gift orebody would not have been correctly ascertained the palaeostress history was delineated via use of compression and tension dihedra stress inversion of slip data and calculation of theoretical resolved shear stress for faults with orientations similar to those mapped the calculation of theoretical resolved shear stress directions highlights the importance that the intermediate stress has on the slip direction for faults whose pole does not lie in the plane containing 1 and 3

response of deep ocean circulation to initiation of northern hemisphere glaciation 3 2 ma carbon isotopic records from benthic foraminifera are used to map patterns of deep ocean circulation between 3 and 2 million years ago the interval when significant northern hemisphere glaciation began the 18o and 13c data from four atlantic sites 552 607 610 and 704 and one pacific site 677 show that global cooling over this interval was associated with increased suppression of north atlantic deep water nadw formation however the relative strength of nadw production was always greater than is observed during late pleistocene glaciations when extreme decreases in nadw are observed in the deep north atlantic our data indicate that an increase in the equator to pole temperature gradient associated with the onset of northern hemisphere glaciation did not intensify deepwater production in the north atlantic but rather the opposite occurred this is not unexpected as it is the warm high salinity characteristic rather than the low temperature of thermocline waters that is critical to the deepwater formation process in this region today

a stress inversion procedure for polyphase fault slip data sets palaeostress estimation from striated fault data is frequently frustrated by the fact that natural fault data are heterogeneous in the sense that they cannot satisfactorily be explained by reactivation brought about by a single stress tensor in many instances there is clear evidence to show that striation data can record the effects of multiple stress events any attempt to find the tensor which best fits or explains such dynamically mixed data sets risks determining a spurious stress state which is some form of compromise between the real stress states corresponding to different tectonic phases to avoid this problem a strategy is proposed here which involves an initial separation of the raw data into coherent sub sets prior to formal stress inversion this separation is performed by assigning attributes to each fault which describe the fault s compatibility with trial stress tensors using these attributes faults can be grouped into dynamically homogeneous families using the statistical techniques of cluster analysis

determination of sediment volumes accumulation rates and turbidite emplacement frequencies on the madeira abyssal plain ne atlantic a correlation between seismic and borehole data the sedimentary infill history of the madeira abyssal plain map is established from correlation of odp leg 157 drillsites sites 950 952 with an almost regular grid of 7000 km of intermediate resolution seismic reflection profiles covering the central part of the abyssal plain the most conspicuous seismic reflectors bounding the seismostratigraphic units have been identified and mapped correlation between seismic and borehole data using synthetic seismograms allows the lithological attribution and dating of the reflectors and seismostratigraphic units lateral mapping and correlation of seismic units also allows both the volumes and rates of accumulation of sediments within each seismostratigraphic unit and equivalent time periods of deposition to be determined these calculations have been corrected for the effect of compaction calculated at around 40 at the base of the drillholes three main turbidite types have been identified at the drillsites and their emplacement frequency has been calculated for each site and time period our results show that cretaceous oceanic crust was draped with red pelagic clays and the fracture zone valleys were completely infilled and levelled in a geologically rather short time probably during the latest oligocene and early miocene by organic rich turbidites derived from the nw african continental margin at 16 ma the topography was levelled enough to allow large turbidity current flows to cover the entire plain during the middle and late miocene 16 5 9 ma organic rich turbidites were emplaced on the abyssal plain at a low rate of accumulation 12 m my in the uppermost miocene early pliocene 5 9 3 6 ma turbidite emplacement increased markedly in both frequency and accumulation rate e g 26 m my for organic rich turbidites during this time period emplacement of volcanic rich turbidites also increased in volume and frequency a trend that continued into the pliocene increased volcanic rich turbidite emplacement correlates well with increased volcanic activity on the canary islands and increased organic rich turbidite emplacement may correlate with periods of erosion on the nw african continental margin these erosional periods may be related to global cooling and falling sea level intensification of bottom water currents and enhanced upwelling on the margin

oxygen isotope compositions of late jurassic vertebrate remains from lithographic limestones of western europe implications for the ecology of fish turtles and crocodilians oxygen isotopes can be used to reconstruct the palaeoenvironmental conditions in which vertebrates lived and thereby give an indication of their ecology this has been done for faunas from the famous late jurassic lithographic limestones of western urope oxygen isotope compositions of phosphate from apatite were measured in aquatic or semiaquatic vertebrate remains fish turtles and crocodilians deposited in these protected coastal marine environments the unknown water composition in the oxygen isotope fractionation equations between phosphate and water was solved for turtles by assuming that modern relationship between environmental water and turtle bone isotope compositions applies to the past the results show that 1 coastal marine waters were thermally homogenous at the regional scale of western europe 2 oxygen isotope data discriminate between coastal marine and freshwater to brackish water inhabitants 3 the plesiochelyid turtles were coastal marine inhabitants their 18o values allow the calculation of the oxygen isotope compositions of marine waters thus refining the estimate of water temperatures by combining 18o values from fish and 4 the marine isotopic signature and the cranial anatomy of plesiochelyid turtles lead us to propose that they had a salt excreting system i e the fundamental physiological feature that controls osmoregulation in the marine environment these late jurassic turtles are proposed to be the first know marine turtles several tens of million years before the chelonioids or sea turtles

mid cretaceous ocean circulation results from model sensitivity studies a series of ocean general circulation model gcm experiments for mid cretaceous continental paleogeography with atmospheric forcing prescribed from atmospheric gcm experiments are utilized to investigate the nature of the mid cretaceous ocean circulation the experiments illustrate a tethys system of clockwise currents and predominant eastward flow in marked contrast with earlier reconstructions this result is apparently robust for changes in bathymetry and in the degree of planetary warmth changes in sea level have the largest potential to produce alternative circulation characteristics two major current systems outside of tethys dominate the model simulation the site of bottom water formation is the north pacific however in a sensitivity experiment for a warmer climate the eastern tethys became a site of deep water formation

neogene bottom water masses and benthic foraminifera in the ne atlantic ocean modern benthic foraminiferal assemblages show a correlation with oceanic bottom water masses a study of the neogene benthic foraminifera from seven sites to the south and two sites to the north of the azores ridge shows patterns of change which can be interpreted in terms of past water masses an antarctic bottom water aabw influence has been present to the south since the mid miocene but to the north of the azores ridge aabw was present only up to the late pliocene since when it has been absent overlying aabw is north atlantic deep water nadw and north east atlantic deep water neadw the latter shows a spectacular increase in importance from the late pliocene to recent the faunal changes can be correlated with changes in circulation in the late pliocene which heralded the incoming of major glacial events from c 2 4 ma

was there a wind driven tethys circumglobal current in the late cretaceous abstract the problem of the existence of a tethys circumglobal current tcc in the late cretaceous continental geometry campanian is addressed within an ocean model which is expected to strongly overestimate the wind driven tcc volume transport a relatively weak tcc is found for the reconstructed campanian paleogeography used as a measure of the strength of the tcc a circumglobal flow index is introduced this index is based on volume fluxes through meridional sections within the equatorial part of the domain the impact of changes in the paleogeography on the tcc is considered by computing steady flows for different shapes of eurasia the results on the extent of eurasia such that a strong tcc appears provide support that no strong wind driven tcc has existed during the campanian

climate change on tectonic time scales abstract observational and modeling studies relevant to climate change on tectonic time scales are reviewed probably the most significant climate result from this time scale involves inferences about nearly ice free conditions for some intervals of earth history some additional results suggest relatively rapid transitions between climate states modeling studies indicate that although tectonic changes significantly modify the atmosphere and ocean circulation in most cases such modifications do not appear to be sufficient to explain ice free climates increased atmospheric co2 levels 5 10 presentvalues may be needed to completely reconcile models and data although the co2 paradigm has received widespread attention in the last few years the results summarized herein indicate that co2 is only one of several important factors influencing climate i believe the time is appropriate for contemplating climate change on tectonic time scales in terms of a post co2 synthesis in which direct tectonic factors are approximately equal in importance to co2 fluctuations in the last few years modeling studies have progressed from a state of virtually no work on the topic to one where the models are in some respect ahead of the observations in the sense that data have not been compiled to test even some of the most basic model predictions in particular information is needed on past atmospheric co2 levels tropical sea surface temperatures seasonality of continental interiors and locations and production rates of deep waters initial steps are being taken to integrate observational and modeling activities on tectonic time scales and some of these shortcomings may be rectified over the next few years

oceanic circulation as an element in palaeogeographical reconstructions the arenig early ordovician as an example a new conceptual palaeo oceanographical model is outlined in this paper the model differs from previous models by using shifts in hadley circulation caused by orbital variations and the rotation rate of the earth to locate the position of the planetary oceanic low and high pressure systems around which the planetary ocean surface currents flow adapting the model to the arenig early ordovician the temperate low pressure zones were found to be located at 50 latitude and the subtropical high pressure zones at 25 latitude traditionally most palaeozoic palaeogeographical recon structions are reconstructed using palaeomagnetic data supplemented with data from climate sensitive lithofacies and palaeo biogeographical distributions however as a new approach in palaeogeographical reconstructions the con ceptual palaeo oceanographical model is combined with palaeobiogeographical data for the arenig series comple menting the palaeomagnetic data and resulting in a new refined palaeogeographical reconstruction

orientational data on the state of stress in northeastern mexico as inferred from stress induced borehole elongations preferential elongation directions are presented from 46 subvertical wells in northeastern mexico from depth intervals ranging from 161 to 4 912 m the measurements document a remarkably consistent west east to northwest southeast direction of the contemporary least horizontal stress in the upper crust of this intraplate region in the regional neotectonic framework the data suggest that mexico north of the trans mexican volcanic belt is being stretched in west east to northwest southeast direction the measurements from the area of the laramide chihuahua and coahuila fold thrust belts define the southern extend of the basin and range rio grande rift stress province of the southwestern united states into northern mexico the least horizontal in situ stress directions recorded in the gulf coastal plain burgos and tampico misantla basins are oblique to the continental margin of the gulf of mexico but subparallel to the direction measured in the area of the basin and range rio grande rift stress province this suggests that the stress distribution in these basins is not mainly the result of gravitational loading as in the gulf coast stress province of the united states but is controlled by the same lithospheric stress system that characterizes the basin and range rio grande rift stress province this is also supported by the north south trending zone of oligocene quaternary alkaline volcanism that crosses the tampico misantla basin furthermore the data indicate that the active deformation of the mexican ridges fold belt east of the study area in the gulf of mexico cannot be caused by a compressional external tectonic load the direction of the least horizontal in situ stress measured in the area of the laramide sierra madre oriental fold thrust belt in hidalgo and san luis potosi states is consistent with that of the other zones however wellbore elongations were recorded less frequently and show a rather large circular variance which suggests that the minimum and maximum horizontal far field stresses are about equal in this area

bottom current speed in the vema channel recorded by particle size of sediment fine fraction abstract the particle size distribution of the carbonate free silt fraction was determined in forty two core top samples from the east flank of the vema channel in order to allow comparison of the mean particle size with near bottom current speed based on nearby ctd and current meter observations the silt mean particle size fluctuates insignificantly between 1450 3950 m but coarsens markedly below 4000 m under antarctic source bottom currents the top of the zone of coarse sizes approximates the top of lower circumpolar water lcpw at 4000 m the steep gradient to coarsest sizes in the axis of the channel marks the transition to antarctic bottom water aabw the vertical profile of mean particle size on the east flank correlates in general respects with the vertical velocity gradient in the channel axis although the core sites on the east flank are as far as 200 miles from the current meter arrays nevertheless this relationship is used to infer that the non carbonate particle sizes deposited on the east flank of the channel may be an indication of bottom current speed and therefore the mean size is used to reconstruct profiles of mean current speed for three time slices 18 120 and 140 ka b p during glacial isotopic stages 2 and 6 the particle sizes deposited on the east flank of the channel are characterized by finer sizes at nearly all depths and the zone of coarse sizes corresponding to lcpw and aabw deepens during interglacial isotopic stage 5e the particlesize profile is very similar to the modern profile however lcpw and aabw appear to be deeper than at present the finer particle sizes deposited at nearly all depths during glacial periods indicates that the velocity of deep circulation in the atlantic was reduced in response to the ice ages deep circulation during isotopic stage 5e closely resembled modern circulation however aabw production rates may have been less that at present

late neogene changes of paleoclimate and paleoproductivity off northwest africa d s d p site 397 abstract the sediment record of site 397 may provide information about both the causes of changes in coastal productivity in the northeast atlantic and the history of climate in northwest africa during the late neogene this study concentrates on the drastic climatic reversal near 2 4 m y b p near 3 2 m y b p a distinct increase of accumulation rates of terrigenous matter and higher paleo trade wind speeds may suggest increased aridity of the northwest african continent this change was followed by higher paleoproductivity of coastal waters off northwest africa high paleoproductivity may be caused by both fluvial nutrient supply and or upwelling during the beginning and the end of inter glacial times river discharge was dominant whereas during phases of glacial maximum stronger fertility of increased coastal upwelling became more important

stress space striated faults deformation twins and their constraints on paleostress abstract stress space is used to illustrate a discussion of the range of stress tensors theoretically compatible with striated faults and with deformation twinning other than friction laws each of the main constraints placed on stress by such data specifies the magnitude of a component of traction being linear in elements of the stress tensor such a constraint by each datum is represented in stress space by a hyperplane comparison at each level of constraint orientation sense of shear assumption of critical ratio or value of shear stress for faulting twinning is made for a single datum followed by consideration of sets of data and stress tensor reduction at no level of constraint are striated faults and deformation twins equivalent fault data cannot constrain absolute values of stress components data for untwinned crystals within twinned untwinned sets provide the fullest limit to values of deviatoric stresses paleostress estimates from twinned untwinned data are generally preferable to those from striated faults

major element analysis of cyclic black shales paleoceanographic implications for the early cretaceous deep western tethys lower cretaceous sediments are frequently characterized by a well expressed cyclicity while the processes influencing environments above the carbonate compensation depth ccd are reasonably well understood almost nothing is known about the deep ocean cretaceous sub ccd sediments from the tethys and atlantic oceans typically show rhythmic black green shale successions to gain insight into the nature of these black green shale cycles we performed detailed geochemical analyses x ray fluorescence rock eval and reactive iron analysis on a 3 m long section of latest aptian age the major element distribution of the analyzed shale sequence indicates a periodic change from a high productivity and well oxygenated green shale mode to a low productivity oxygen deficient black shale mode it is proposed here that the preservation of organic matter was dependent on the strength of salinity driven deepwater generation furthermore the data show that the corg content covaries with changes in the detrital composition therefore we hypothesize that tethyan deepwater circulation was sensitive to changes in the monsoonal system time series analysis suggests that these changes are periodic in nature although we are currently unable to prove that the dominant periodicity is related to the precession component of the milankovitch frequencies

tectonic forcings of maastrichtian ocean climate evolution a global compilation of deep sea isotopic records suggests that maastrichtian ocean climate evolution tvas tectonically driven during the early maastrichtian the atlantic intermediate deep ocean was isolated from the pacific indian and southern oceans deep water formed in the high latitude north atlantic and north pacific at the early late maastrichtian boundary a major reorganization of oceanic circulation patterns occurred resulting in the development of a thermohaline circulation system similar to that of the modem oceans a combination of isotopic and plate kinematic data suggests that this event was triggered by the final breaching of tectonic sills in the south atlantic and the initiation of north south flow of intermediate and deep water in the atlantic the onset of laramide tectonism during the mid maastrichtian led to the concurrent draining of major epicontinental seaways together these events caused cooling increased latitudinal temperature gradients increased ventilation of the deep ocean and affected a range of marine biota

palaeo stress fields in the variscan foreland during the carboniferous from microstructural analysis in the british isles abstract north of the variscan front the carboniferous series of the british isles is affected by mainly n s trending folds which are almost perpendicular to this e w oriented front flat and unconformable overlying permian strata demonstrate a variscan age for the deformation a microtectonic survey made in dinantian and to a lesser extent namurian calcareous layers has revealed two successive events according to chronological criteria the first event maximum stress e w trending led to the formation of n s folds with local reorientation in the vicinity of major pre existing faults this compression may have been active since the namurian it pre dates a second compressional event orientated n s which is related to the final emplacement of the variscan nappes

the jabal akhdar dome in the oman mountains evolution of a dynamic fracture system the mesozoic succession of the jabal akhdar dome in the oman mountains hosts complex networks of fractures and veins in carbonates which are a clear example of dynamic fracture opening and sealing in a highly overpressured system the area underwent several tectonic events during the late cretaceous and cenozoic including the obduction of the samail ophiolite and hawasina nappes followed by uplift and compression due to the arabia eurasia convergence this study presents the results of an extensive tectonic survey and correlates subseismic scale structures in jabal akhdar faults fractures veins and stylolites with the main tectonic events in the northeastern arabian plate as some of the studied formations host large oil reserves in neighboring areas determining the relative timing of these events in the exhumed rocks is important to understand hydrocarbon distribution and fracture patterns in these reservoirs the formation of early veins and stylolites in the oman mountains is followed by top to the south layer parallel shearing that may be associated with the obduction of the samail and hawasina nappes this compressional tectonic event is followed by normal dip slip to oblique slip faults and veins top to the northeast layer parallel shearing which corresponds to the first stage of exhumation of the autochthonous rocks offsets these structures our new data indicate that this first phase of events is overprinted by complex strike slip networks of veins and fractures as well as by the reactivation and onset of seismic scale faults strike slip structures belong to three distinct events the first one nw se oriented compression is probably associated with the oblique collision of the indian plate against the arabian platform during the late campanian to the mid eocene the second event e w oriented compression is likely to have been formed during the late oligocene middle miocene during uplift the last event ne sw oriented compression probably took place during the miocene pliocene structures of the first two strike slip events have the same orientation as seismic scale faults observed in the subsurface of oman and abu dhabi in addition increasing vein intensity towards the top of the autochthonous formations in the oman mountains as well as the small angle between conjugate vein sets indicate that high fluid pressures that are thought to be present during strike slip deformation

a new variscan deformation map of england and wales collections of bedding orientations from subareas of 550 km 2 are used to define bedding fabrics from the variscan fold belt and foreland in england and wales the bedding fabrics constructed from data taken from published geological maps 1 50 000 scale are analysed in terms of the scheidegger watson orientation tensor the calculated eigenvalues of the orientation tensor define the average structural trends including the best fit fold axis for each subarea the eigenvectors of the tensor allow the original sedimentary fabrics to be distinguished from those modified by deformation the progressive tectonic modification of these fabrics leads to the concept of fabric evolution paths and the extent of the modification is expressed by a deformation parameter although it is emphasised that this parameter is not solely a function of finite strain magnitude its variation is represented on a map which brings out different degrees of variscan tectonic modification of bedding fabrics this map delineates a variscan bedding fabric front corresponding to the northern boundary of a zone of pervasive and strong deformation in the foreland this new analysis allows the variation of variscan trends to be mapped and the significance of these trends to be quantified in terms of deformation magnitude 1999 elsevier science b v all rights reserved

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

late neogene evolution of paleoclimate and paleoceanic circulation in the northern and southern hemispheres a comparison oxygen isotopes and clay minerals grain size and accumulation rates of terrigenous i e mainly eolian sediments from northeast atlantic dsdp sites 141 366 397 and 544b and from southwest pacific dsdp sites 588 590 and 591 were used to assess parallelisms and differences in the evolution of paleoclimate and paleoceanic circulation in the northern and southern hemispheres during the last 7 ma

heat flow through the sea bottom around the yucatan peninsula heat flow studies were conducted in january february 1987 off the atlantic coast of mexico on board the r v akademik nikolai strakhov two areas were surveyed one transecting the salt dome province and the campeche canyon in the gulf of mexico and the other on the eastern flank of the yucatan peninsula conductive heat flow through the bottom sediments was determined as the product of vertical temperature gradient and in situ thermal conductivity measured with a thermal probe using a multithermistor array and real time processing capabilities forward two dimensional modeling allows us to estimate heat flow variations at both sites from local disturbances and to obtain average heat flow values of 51 mw m2 for the transect within the gulf of mexico and 38 and 69 mw m2 for two basins within the yucatan area sea bottom relief has a predominant effect over other environmental factors in the scatter of heat flow determination in the gulf of mexico

geological evaluation of climate general circulation models and model implications for mesozoic cloud cover general circulation models gcms are currently used to predict future global change however the robustness of gcms can and should be evaluated by their ability to simulate past climate regimes their success in retrodiction can then be assessed by reference to the testimony of the geological record geological evidence provides a database which can be used in the estimation of sea surface temperatures and other proxy data useful in palaeoclimatic studies these data can then be used to refine the prescribed boundary conditions for running gcms themselves results of modelling experiments confirm a generally warmer mesozoic earth with arid tropics and convective rainfall higher over the oceans than at present circum polar wetlands are also indicated modelled cloudiness is also higher in the mesozoic contributing to greenhouse conditions and possibly influencing terrestrial biomes and marine ecosystems

tectonic analysis of fault slip data sets using data that include the direction and the sense of motion on individual fault surfaces determined by slickenside lineations it is possible to reconstruct reduced stress tensors that correspond to the orientation of stress axes and to the ratio 2 3 1 3 between principal stress values 1 2 3 compression being positive no assumption is made concerning the orientation of fault planes relative to stress axes so that reactived faults are taken into account as well as newly created ones qualitative and quantitative methods for analysis of fault slip data were developed during the last 10 years the practical limitation of the methods and the necessity for critical field observations are emphasized these methods can be applied to focal mechanisms of earthquakes a more complex analysis of heterogeneous data sets involving an iterative separation of different stress systems is also discussed this analysis enables one to distinguish successive faulting events careful qualitative study in the field is in all cases essential

seismic stratigraphy of veracruz tongue deep southwestern gulf of mexico the veracruz tongue is a region of continental slope and rise sediments bounded bathymetrically by the mexican ridges fold belt to the west and the campeche knolls salt province to the east study of two multichannel seismic lines and single fold sparker data enables five post early miocene seismic stratigraphic sequences to be distinguished in the tongue sedimentary processes responsible for deposition of each sequence are inferred on the basis of external geometry internal reflection configuration and where possible core data the five sequences are each interpreted to consist of turbidites grading laterally into hemipelagites these primary deposits may be modified later by downslope creep or sliding and slumping because bathymetry is a major control on location of turbidity current flows slides and slumps the depositional history of the veracruz tongue provides indirect evidence of tectonic evolution of the mexican ridges fold belt and the campeche knolls salt province salt domes first formed a barrier to turbidity current flow from the east at the close of the middle miocene the mexican ridges fold belt evolved gradually until it formed a complete barrier to turbidity current flow from the west at the close of the pliocene as a result of shift in direction of turbidity current flow through time potentially sand prone miocene turbidites are overlain by hemipelagic clays and clayey oozes a situation favorable to hydrocarbon entrapment

paleodepth distribution of neocene deep sea hiatuses the depth of formation of miocene to middle pliocene deep sea hiatuses nh1 to nh8 has been determined using 152 deep sea drilling project sites in the atlantic pacific and indian oceans megahiatuses representing maxima in deep sea erosion occur at three water depths below 3800 m at intermediate depths between about 2000 and 3000 m and in shallower waters above 1500 m paleodepth both the paleodepths and distribution of these hiatus maxima suggest that flow of antarctic bottom water antarctic intermediate water and north atlantic deep water masses largely caused this erosion correlation of the hiatuses with oxygen isotope carbonate and sea level records indicates that prior to 11 ma brief hiatuses including those resulting from nondeposition in high productivity equatorial regions largely correlate with global cooling episodes high carbonate content and lowstands of sea level during the last 11 m y hiatuses also seem to correlate with cooling episodes but carbonate dissolution is characteristic and sea levels may have been rising or at a lowstand during the nh4 nh7 and nh8 intervals it is possible that a rise in sea level corresponds with polar cooling but there is uncertainty in correlation brief hiatuses during rising sea levels can be explained by basin shelf fractionation of carbonates hiatuses during sea level lowstands and cooling episodes may result from intensified bottom water circulation and increased corrosiveness of bottom water due to higher levels of co2 and increased productivity during increased upwelling supplement appendix 1 is availablewith entire article on microfiche orderfrom american geophysical union 2000florida avenue n w washington dc20009 document p87001 2 50 paymentmust accompany order

paleoclimate of the kimmeridgian tithonian late jurassic world i results using a general circulation model abstract the kimmeridgian tithonian 154 7 145 6 ma middle and late late jurassic was a time of expanded continental rifting increased sea floor spreading and a relatively high eustatic sea level stand these processes collectively caused the fragmentation and flooding of the megacontinent pangea as well as the alteration of the global paleoclimate using a version of the community climate model ccm from the national center for atmospheric research we report two kimmeridgian tithonian paleoclimate seasonal simulations with geologically inferred paleotopography one using a co 2 concentration of 280 ppm pre industrial level and the other 1120 ppm increasing the co 2 four fold warms virtually the entire planet the greatest warming occurs over the higher latitude oceans and the least over the equatorial and subtropical regions simulation of a warmer planet with an elevated greenhouse effect fits the distribution of paleoclimatically sensitive faunas floras and sedimentary rocks model results indicate that sea ice was restricted to the high latitudes of the boreal and austral seas making landfall only in restricted areas the trade winds bring heavy rainfall in december january february to eastern gondwana and in june july august to the tethys sea margins a strong june july august monsoon occurs over southeast asia the distribution of coals correlates to precipitation sufficient to maintain gymnosperm forests and coastal areas where water saturated sediments are a result of eustatic high stands of sea level evaporites are localized to areas of negative precipitation evaporation runoff is restricted to regions of intense precipitation overall the 1120 ppm co 2 simulation provides a reasonable paleoclimate for the kimmeridgian tithonian and provides a standard until a ccm with oceanic heat transport a coupled atmospheric oceanic model or one with a finer grid cell configuration is available the results need further scrutiny in areas with more detailed geologic information

benthic phosphorus regeneration net primary production and ocean anoxia a model of the coupled marine biogeochemical cycles of carbon and phosphorus we examine the relationships between ocean ventilation primary production water column anoxia and benthic regeneration of phosphorus using a mass balance model of the coupled marine biogeochemical cycles of carbon c and phosphorus p the elemental cycles are coupled via the redfield c p ratio of marine phytoplankton and the c p ratio of organic matter preserved in marine sediments the model assumes that on geologic timescales net primary production in the oceans is limited by the upwelling of dissolved phosphorus to the photic zone the model incorporates the dependence on bottom water oxygenation of the regeneration of nutrient phosphorus from particulate matter deposited at the water sediment interface evidence from marine and lacustrine settings modern and ancient demonstrates that sedimentary burial of phosphorus associated with organic matter and ferric oxyhydroxides decreases when bottom water anoxia dysoxia expands steady state simulations show that a reduction in the rate of thermohaline circulation or a decrease of the oxygen content of downwelling water masses intensifies water column anoxia dysoxia and at the same time increases surface water productivity the first effect reflects the declining supply of oxygen to the deeper parts of the ocean the second effect is caused by the enhanced benthic regeneration of phosphorus from organic matter and ferric oxyhydroxides sedimentary burial of organic carbon and authigenic calcium phosphate mineral francolite on the other hand is promoted by reduced ocean ventilation according to the model global scale anoxia dysoxia leads to a more efficient recycling of reactive phosphorus within the ocean system consequently higher rates of primary production and organic carbon burial can be achieved even when the continental supply of reactive phosphorus to the oceans remains unchanged

fault systems and paleo stress tensors in the indus suture zone nw pakistan abstract analysis of fault striations measured in the kohistan part of the indus suture zone nw himalaya pakistan has been carried out to document dynamic evolution during the brittle stage of the collision of india and asia processing of the data with a direct inversion method identified four stress fields which were chronologically ordered from field evidence as sse nnw compression e w compression radial extension and ssw nne compression the last corresponds to the present day stress field defined from seismic activity the earlier stress fields are related to times during the miocene when convergence related stresses were disturbed by the formation of the nearby nanga parbat and indus syntaxes

inferring stress from faulting from early concepts to inverse methods abstract we review the evolution of concepts on and methods of estimating the state of stress from fault movements theories of failure in isotropic materials suggested a simple geometrical construction of optimal principal stress directions from a fault plane and its associated slip these optimal directions align shear stress and slip directions and maximize the difference between shear stress and frictional resistance on the fault plane optimal stress directions for calcite twinning are obtained by a similar construction with the difference that they maximize shear stress force representation of seismic sources independently introduced pressure p and tension t axes at positions that also maximize shear stress on both nodal planes frictional slip theory and the constraint that slip and shear stress directions be parallel allowed to address reactivation of pre existing faults this suggested that stress could also be inverted from reactivated fault and slip data or earthquake focal mechanisms early methods relied on geometrical constructions as a substitute for calculations whereas later methods relied on software as these calculations became tractable with the help of computers similar methods were developed for the inversion of stress from crystal twin gliding with non optimal geometry with a different criterion that relies on a threshold of the component of shear stress along the gliding line even though these methods seek a common stress tensor compatible with fault and slip data their main use is to separate polyphase data into homogeneous subsets and help deciphering complex tectonic histories fault and slip data can also be analyzed to constrain the strain rather than the stress tensor in most cases this involves a summation and yields an average strain for the considered rock volume stress inversion thus appears better suited for differentiating heterogeneous data whereas strain analysis appears better suited for homogenizing them

cretaceous plate tectonic reconstructions abstract plate tectonic reconstructions for each cretaceous stage are produced as base maps for cretaceous paleogeography and for oceanic and continental data both geologic and geophysical data are utilized to determine the relative rotations of cretaceous plates with respect to north america a sea floor spreading history is generated from the relative rotations this history is consistent with data from the deep sea drilling project paleolatitude lines are derived using average paleomagnetic pole positions these reconstructions are significantly more comprehensive than previous global reconstructions although there are still many areas which remain controversial

late pleistocene glacial interglacial changes in planktonic foraminiferal biofacies and carbonate dissolution patterns in the vema channel abstract a suite of closely spaced giant gravity cores between 1500 and 4500 m on the east flank of the vema channel was examined to determine variations in carbonate preservation for the last two interglacials present day and isotopic stage 5e and glacials isotopic stages 2 and 6 as had been previously observed present day sediment dissolution facies i e foraminiferal and sedimentary lysoclines are closely related to hydrographic changes in the major water masses which occupy the vema channel nadw and aawb carbonate preservation is systematically better during interglacials than during glacials throughout the entire depth range of the transect the positions of the foraminiferal and sedimentary lysoclines however appear to have remained relatively constant through the glacial interglacial cycles of the last 140 000 years the lack of any substantial vertical movement of these dissolution facies during the late pleistocene suggests that there has not been any significant change in the position of the water masses flowing through the vema channel during this time interval however the overall poorer preservation of glacial sediments indicates that the glacial equivalents of both nadw and aabw were more corrosive to carbonate than at present this overall increase in dissolution can most simply be attributed to a general stagnation of deep and bottom flow through this region during glacial episodes

atmospheric circulation during warm geologic periods is the equator to pole surface temperature gradient the controlling factor paleoclimatologists have hypothesized that the equator to pole surface temperature gradient is a dominant control on the paleocirculation of the oceans and the atmosphere atmospheric simulations using realistic cretaceous 100 m y ago geography are used to examine quantitatively the relationships between paleogeography surface temperature gradients and the nature of the atmospheric circulation these results raise questions concerning the classical theories and interpretations of warm paleoclimates and suggest that paleogeography is an important factor governing the nature of the circulation

a plea for more caution in fault slip analysis abstract the analysis of fault slip data is a widely used tool in structural geology this method consists of three major steps a data acquisition by measurements in outcrops b data separation into homogeneous subsets and calculation of the principal stress or strain axes with one of several available methods and c data interpretation in a regional tectonic context which includes the assignment of ages and the derivation of regional patterns each one of these three steps may introduce artefacts and misinterpretations the major problem during step a is sampling bias due to unfavourable outcrop geometry or due to neglecting faults with subtle slip sense indicators step b contains numerous possibilities to influence the calculation results e g by arbitrary separation of data into subsets choice of the analysis method and uncritical use of software age assignment in step c can in most cases be made only indirectly e g by the assumption that measured outcrop scale faults have the same age as parallel map scale faults or by the inference that subsets from different sites with parallel oriented principal axes are syngenetic neither assumption is necessarily valid with this paper we want to sharpen researchers awareness of the problems related to fault slip analysis