persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

planar lamellar substructures in quartz both single and multiple sets of lamellar features in quartz grains can be produced in shock experiments and are observed at known impact sites they can also be produced in static constant strain rate experiments and are observed at known tectonic and explosive volcanic sites the former are strictly planar and parallel and generally conform to rational crystallographic orientations in the quartz crystal structure the latter can also be planar and parallel but sometimes show slight to moderate curvature with lamellar bifurcations and variable lamellar widths their orientations show a variety of forms with in general a broader angular distribution than that of the impact generated lamellae deductions of physical conditions of deformation from optical morphology spacing multiplicity and orientation information alone remain somewhat conjectural full characterization by transmission electron microscopy tem appears to be necessary

extraterrestrial impact events the record in the rocks and the stratigraphic column abstract the known terrestrial impact record is a biased sample of a much larger population of impact events the biases are due to the modifying effects of terrestrial geologic processes coupled with incomplete searches for impact structures and impact related materials terrestrial impact structures have the same basic forms as impact craters on the other planets of the inner solar system but because of post impact modification by terrestrial geologic process are recognised by the occurrence of shock metamorphic effects in some cases siderophile anomalies have been identified in impact lithologies and have been used to estimate the composition of the impacting body similar shock metamorphic effects and a siderophile anomaly in k t boundary materials are indicative of a major impact event which has been correlated with the formation of the chicxulub structure mexico evidence of a small number of other impacts occur in the stratigraphic record most commonly as tektite or microtektite horizons in some cases they are known to be accompanied by geochemical anomalies in other cases a number of ir anomalies have been reported in the stratigraphic record but there is no confirmatory evidence that they are due to impact the majority of known impact events in the stratigraphic record are from relatively recent geologic time logic dictates however that many more impacts must be recorded in terrestrial sediments and model calculations indicate that relatively small impacts d 20 km have the potential to cause atmospheric blow out and thus global dispersion of some of the impact products geochemical detection however of such events may not be easy in some cases because of relatively small absolute signals against the background of the daily infall of cosmic material in addition non chondritic bodies may result in no appreciable geochemical anomaly in view of this any claim to a geochemical signature of impact in the stratigraphic record should be accompanied by a physical search for impact materials although in the case of impacts into oceanic crust this too will be difficult given the k t experience however and the fact that large scale impact on earth is a natural consequence of the character of the solar system the potential of impacts to provide local and global marker horizons can not be ignored similarly the fact that impacts may have the potential to result in short term biologic or climatic excursions can not be dismissed arbitrarily when considering the causes of such phenomena as stable isotope anomalies in the stratigraphic record

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

abrupt cold spells in the northwest mediterranean hitherto unknown abundance peaks of left coiling l c neogloboquadrina pachyderma from a gulf of lions piston core indicate that abrupt cold spells associated with atlantic heinrich events affected the mediterranean n pachyderma l c is typical of sub polar waters in the open ocean the southern edge of its glacial north atlantic bioprovince reached south portugal only trace abundances of n pachyderma l c are known from quaternary mediterranean sediments suggesting that no significant invasions occured via the strait of gibraltar the gulf of lions abundance peaks therefore seem to reflect area specific thriving of a normally rare but indigenous taxon in the western mediterranean through local favorable habitat development the general planktonic foraminiferal record suggests that the basic hydrographic regime in the gulf of lions with wintertime deep convective overturn was relatively stable over the past 60 kyr under these conditions high abundances of n pachyderma l c would essentially imply temperature reductions of the order of 5 8 relative to the present

the circular uneged uul structure east gobi basin mongolia geomorphic and structural evidence for meteorite impact into an unconsolidated coarse clastic target abstract the uneged uul structure is a 10 km circular complex multi ridged domal feature in the unegt subbasin of the east gobi basin southeastern mongolia as revealed by remote sensing and recent field reconnaissance the central part of the uneged uul structure comprises a complex central peak of outward radiating curved ridges composed of stratigraphically uplifted greenschist facies basement schists surrounded by an annular moat the most prominent feature of the structure is a central annular ridge 3 km in diameter composed of pebble boulder conglomerates and gravels of the upper jurassic sharilyn formation surrounded by three outer domal ridges composed of lower cretaceous conglomeratic sandstones and gypsum clays jurassic conglomerates forming the main part of the central annular ridge show effects of severe internal deformation the original population of pebbles cobbles and boulders appears moderately displaced and mostly broken but nowhere aligned along shear planes or foliated primary sedimentary features such as cross lamination or imbrication have been obliterated we explain this penetrative brecciation as a result of dissipative shearing caused by a strong and rapid singular event that in magnitude was beyond the range of the common crustal tectonics recorded elsewhere in this region disrupted and chaotically distributed conglomeratic sandstone beds in the central annular ridge dip in highly variable directions on a local scale but show an apparent se nw trend of bedding plane alignment further outside the tilted and uplifted upper jurassic to lower cretaceous strata of the domal area are overlain by the flat lying upper cretaceous which stratigraphically constrains the timing of deformation at the uneged uul structure to most likely the early cretaceous endogenic formation models such as magmatism and salt gypsum or mud diapirism fail to explain the nature of the uneged uul structure the uneged uul structure bears a set of geomorphic and structural features resembling those at some eroded complex impact structures on earth morphologically similar central peaks are observed at the spider and matt wilson impact structures in australia the central annular ridge reminds of that at gosses bluff in australia the outer domal ridges might correspond to ring like features as known from tin bider in algeria we therefore cautiously propose that an impact may have produced the uneged uul feature causing structural uplift 1000 m of basement rocks at its center so far no convincing evidence for shock metamorphism could be proven by field work and petrographic analyses however it is likely that at the time of the deformation event the unconsolidated conglomerates were highly porous and possibly immersed in groundwater buffering the propagation of sudden stress reducing deformation further studies will be in order to unravel the nature of the uneged uul structure which should be considered a promising possible impact structure

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

the elemental and isotopic composition of sulfur and nitrogen in chinese coals abstract coal combustion is an important atmospheric pollution source in most chinese cities so systematic studies on sulfur and nitrogen in chinese coals are needed the sulfur contents in chinese coals average 0 9 1 0 indicating that most chinese coals are low in sulfur a nearly constant mean 34 s value is observed in low sulfur ts 1 t 3 and j 3 high sulfur chinese coals os 0 8 often found at late carboniferous c 3 and late permian p 2 in southern china had two main sulfur sources original plant sulfur and secondary sulfur the wide variety of 34 s values of chinese coals 15 to 50 is a result of a complex sulfur origin the 15 n values of chinese coals ranged from 6 to 4 showing a lack of correlation with coal ages whereas nitrogen contents are higher in paleozoic coals than in mesozoic coals this may be related to their original precursor plant species high nitrogen pteridophytes for the paleozoic coals and low nitrogen gymnosperms for the mesozoic coals different to 34 s values chinese coals showed higher 15 n values in marine environments than in freshwater environments

multiple sulfur isotope constraints on the modern sulfur cycle we present 28 multiple sulfur isotope measurements of seawater sulfate 34sso4 34sso4 and 33sso4 33sso4 from the modern ocean over a range of water depths and sites along the eastern margin of the pacific ocean the average measured 34sso4 34sso4 is 21 24 0 88 2 0 88 2 with a calculated 33sso4 33sso4 of 0 050 0 050 0 014 2 0 014 2 with these values we use a box model to place constraints on the gross fraction of pyrite burial in modern sediments this model presents an improvement on previous estimates of the global pyrite burial flux because it does not rely on the assumed value of 34spyrite 34spyrite which is poorly constrained but instead uses new information about the relationship between 34s 34s and 33s 33s in global marine sulfate our calculations indicate that the pyrite burial flux from the modern ocean is between 10 and 45 of the total sulfur lost from the oceans with a more probable range between 20 and 35

variability of the large scale general circulation of the mediterranean sea from observations and modelling a review abstract in this paper we present an overview of the most recent findings about the mediterranean sea present day circulation structure both historical observations and numerical model simulations are presented outlining the differences and agreement the model simulations are presented for both an eddy resolving and a coarse resolution numerical model and the results are intercompared the importance of the mesoscales in modifying the large scale flow field is elucidated the critical point is the discovery of the large amplitude interannual variability of the circulation and water mass structure associated with the anomalies of atmospheric forcing over the basin the seasonal variability can be strictly related to changes in heat and momentum fluxes while the interannual variability has a component which is related to the mesoscale field the latter is very intense in the algerian current region and levantine basin but different in structure in the two regions results are shown which confirm the importance of wind driving in establishing the kinetic energy of the flow field by comparing the current transport at the strait of corsica with observations in conclusion the essential characteristics of the present day circulation are associated with the atmospheric forcing and the basin topographic structure results from palaeoceanographic simulations for the last 20 000 years show that changing the atmospheric forcing can cause large changes in the circulation structure which may have affected sapropel formation

insolation cycles as a major control of equatorial indian ocean primary production analysis of a continuous sedimentary record taken in the maldives indicates that strong primary production fluctuations 70 to 390 grams of carbon per square meter per year have occurred in the equatorial indian ocean during the past 910 000 years the record of primary production is coherent and in phase with the february equatorial insolation whereas it shows diverse phase behavior with 18o depending on the orbital frequency eccentricity obliquity or precession examined these observations imply a direct control of productivity in the equatorial oceanic system by insolation in the equatorial indian ocean productivity is driven by the wind intensity of westerlies which is related to the southern oscillation therefore it is suggested that a precession forcing on the southern oscillation is responsible for the observed paleoproductivity dynamics

a new model for atmospheric oxygen over phanerozoic time a mathematical model has been constructed that enables calculation of the level of atmospheric o2 over the past 570 my from rates of burial and weathering of organic carbon c and pyrite sulfur s burial rates as a function of time are calculated from an assumed constant worldwide clastic sedimentation rate and the relative abundance and c and s contents of the three rock types marine sandstones and shales coal basin sediments and other non marine clastics red beds arkoses by our model values of o2 versus time using a constant total sedimentation rate agree with those for variable sedimentation derived from present day rock abundances and estimates of erosional losses since deposition this agreement is the result of our reliance on the idea that any increase in total worldwide sediment burial with consequently faster burial of c and s and greater o2 production must be accompanied by a corresponding increase in erosion and increased exposure of c and s on the continents to o2 consumption via weathering it is the redistribution of sediment between the three different rock types and not total sedimentation rate that is important in o2 control to add stability to the system negative feedback against excessive o2 fluctuation was provided in the modeling by the geologically reasonable assignment of higher weathering rates to younger rocks resulting in rapid recycling of c and s we did not use direct o2 negative feedback on either weathering of c and s or burial of c because weathering rates are assumed to be limited by uplift and erosion and the burial rate of c limited by the rate of sediment deposition the latter assumption is the result of modern sediment studies which show that marine organic matter burial occurs mainly in oxygenated shallow water and is limited by the rate of supply of nutrients to the oceans by rivers results of the modeling indicate that atmospheric o2 probably has varied appreciably over phanerozoic time during the late carboniferous and permian periods o2 was higher than previously because of the rise of vascular land plants and the widespread burial of organic matter in vast coal swamps a large decrease in o2 during the late permian was due probably to the drying up of the coal swamps and deposition of a large proportion of total sediment in c and s free continental red beds sensitivity study shows that major parameters affecting results are the mean c concentration in coal basins and the relative sizes of the reservoirs of young rapidly recycled versus old rocks less sensitivity was found for changes over time in total land area undergoing weathering and the use of direct o2 negative feedback on marine carbon burial good agreement for rates of c burial calculated via our model and via independent models which are based on the use of stable carbon isotopes indicates that the dominant factor that has brought about changes in atmospheric o2 level and the isotopic composition of dissolved inorganic carbon in seawater over phanerozoic time is sedimentation and not weathering or higher temperature phenomena such as basalt seawater reaction

modeling the mediterranean sea interannual variability during 1961 2000 focus on the eastern mediterranean transient 1 this work is dedicated to the study of the climate variability of the mediterranean sea in particular the study of the eastern mediterranean transient emt which occurred in the early 1990s simulations of the 1961 2000 period have been carried out with an eddy permitting ocean general circulation model of the mediterranean sea driven by realistic interannual high resolution air sea fluxes using different databases for the river runoff black sea inflow and atlantic thermohaline characteristics at climatological or interannual scales we assess the effects of the non atmospheric hydrological forcings on the simulation of the interannual variations of the mediterranean circulation the evolution of the basin scale heat content is in very good agreement with the observations especially in the surface and intermediate layers while the agreement is lower for the evolution of the salt content convection events in the aegean sea are noticed in the simulations between 1972 and 1976 in the late 1980s and around the emt period the formation rates of cretan deep water cdw are different during these periods allowing or preventing the spreading of cdw into the eastern mediterranean the sequence of the emt events is well reproduced the high winter oceanic surface cooling and net evaporation over the aegean sea in the early 1990s the high amount of dense cdw formed during these winters and then the overflow and the spreading of this cdw in the eastern mediterranean among the preconditioning processes suggested in the literature we find that changes in the levantine surface circulation possibly induced by the presence in the cretan passage of anticyclonic eddies and a lasting period with reduced net precipitation over the eastern mediterranean lead to an increase of the salt content of the aegean sea changes in the black sea freshwater inflow or in the characteristic of the atlantic water entering at the gibraltar strait also modify the thermohaline state of the aegean sea before the emt but as none of these preconditioning factors has a lasting impact on lowering the vertical stratification of the aegean sea we conclude that concerning the emt the major triggering elements are the atmospheric fluxes and winds occurring in winters 1991 1992 and 1992 1993

late glacial holocene climate variability at the south eastern margin of the aegean sea abstract new micropaleontological palynological and geochemical results from a relatively shallow 500 m sediment core ns 14 in the south eastern aegean sea provide a detailed picture of the regional expression of sapropel s1 formation in this sub basin of the eastern mediterranean sea specifically freshwater input during 10 6 10 0 ka bp has preceded the deposition of s1 further decrease in surface water salinity is evidenced between 10 0 and 8 5 ka bp at the lower part of s1a which in respect to s1b is featured by warmer 19 5 c and more productive surface waters associated with dysoxic bottom conditions a series of coolings detected within the s1 depositional interval may be linked to outbursts of cold northerly air masses and relevant pulses in the deep intermediate water ventilation that caused the s1 interruption between 7 9 and 7 3 ka bp and culminated during the deposition of s1b with the decline of deep chlorophyll maximum dcm at 6 5 ka bp the climate instability and the relevant absence of anoxia weakened the organic matter preservation in the shallow south eastern aegean margin during the s1 times ns 14 record provides evidence for a distinct mid holocene warm up to 25 c and wet phase associated with the deposition of the sapropel like layer smh sapropel mid holocene between 5 4 and 4 3 ka bp the smh layer could represent evidence of on going albeit weak african monsoon forcing only expressed at the south eastern edge of the aegean sea its end is associated with the 4 2 ka bp northern hemisphere mega drought event and the termination of the african humid period at 3 8 ka bp

distinguishing shocked from tectonically deformed quartz by the use of the sem and chemical etching abstract multiple sets of crystallographically oriented planar deformation features pdfs are generated by high strain rate shock waves at pressures of 12 gpa in naturally shocked quartz samples on surfaces pdfs appear as narrow 50 500 nm lamellae filled with amorphosed quartz diaplectic glass which can be etched with hydrofluoric acid or with hydrothermal alkaline solutions in contrast slow strain rate tectonic deformation pressure produces wider semi linear and widely spaced arrays of dislocation loops that are not glass filled etching samples with hf before examination in a scanning electron microscope sem allows for unambiguous visual distinction between glass filled pdfs and glass free tectonic deformation arrays in quartz this etching also reveals the internal pillaring often characteristic of shock induced pdfs this technique is useful for easily distinguishing between shock and tectonic deformation in quartz but does not replace optical techniques for characterizing the shock features

presence of the solar de vries cycle 205 years during the last ice age certain characteristic periodicities in the 14c record from tree rings such as the well known 11 yr schwabe cycle are known to be of solar origin the origin of longer period cycles such as the 205 yr de vries cycle in the 14c record was less certain and it was possible to attribute it either to solar or climatic variability here we demonstrate that the de vries cycle is present in 10be data from the grip ice core during the last ice age 25 to 50 kyr bp analysis of the amplitude of variation of this cycle shows it to be modulated by the geomagnetic field indicating that the de vries cycle is indeed of solar rather than climatic origin

experimental reproduction of tectonic deformation lamellae in quartz and comparison to shock induced planar deformation features planar features can develop in quartz during comparatively slow tectonic deformation and during very fast dynamic shock metamorphism despite their very different structural nature tectonically induced deformation lamellae have sometimes been mistaken as shock induced planar deformation features pdfs to understand the formation of deformation lamellae and to address the substantial differences between them and pdfs we have conducted deformation experiments on single crystals of quartz in a griggs type apparatus at a temperature of 800 c a confining pressure of 12 kbar and a strain rate of 0 7 1 1 x 10 6 the deformed samples were analyzed with transmission electron microscopy tem and compared to natural pdfs from the ries crater germany tem revealed that tectonic deformation lamellae are associated with numerous sub parallel curved subgrain walls across which the orientation of the crystal changes slightly the formation of deformation lamellae is due to glide and climb controlled deformation in the exponential creep regime in contrast the pdfs in shocked quartz from the ries are perfectly planar crystallographically controlled features that originally represented amorphous lamellae due to postshock annealing and hydrothermal activity they are recrystallized and decorated with fluid inclusions

biogeochemical controls on mercury stable isotope compositions of world coal deposits a review abstract coal deposits were important natural hg sinks in the late paleozoic and middle late mesozoic coal combustion since the industrial revolution has emitted more than 35 000 t of hg into the atmosphere environmental geochemistry research on hg in coal is essential to understand the natural hg cycle throughout earth history and the present day hg cycle under human perturbation in this review we summarize the methods of hg isotope measurement in coals and compile recently published hg isotope data of 200 world coal samples according to their locations formation periods carboniferous permian jurassic cretaceous early middle cenozoic and ranks anthracite bituminous coal subbituminous coal lignite and illustrate the controls of sources and biogeochemical processes on hg isotope compositions in coal deposits up to 4 7 variation 3 90 to 0 77 in mass dependent fractionation mdf represented by 202 hg and 1 0 variation 0 63 to 0 34 in mass independent fractionation mif represented by 199 hg are observed in world coal deposit with an average value of 1 16 0 79 1sd and 0 11 0 18 1sd for 202 hg and 199 hg respectively we find that coal 202 hg and 199 hg are broadly controlled by two source materials terrestrial plants biogenic hg and crustal rocks geogenic hg accounting for 37 46 and 54 63 of hg in coals no clear trends are seen in neither 202 hg vs coal forming periods nor 202 hg vs coal ranks which we attribute to important overlapping of 202 hg in the source materials of different coal forming periods and the multidirectional hg mdf during coalification interestingly a step wise increase in total hg and a disappearance of 199 hg are observed along with increasing coal rank suggesting the addition of hydrothermal hg into high rank coals the hydrothermal fluids not only upgraded the coal ranks but also increased the hg concentrations and 199 hg of coals in addition the addition of hydrothermal hg into coal deposits was also partly responsible for the comparatively higher total hg and 199 hg in the late paleozoic coals relative to the mesozoic and cenozoic coals the co variation of atmospheric oxygen levels and 199 hg of coals at different coal forming time widows suggests that the removal of biogenic hg in response to widespread swamp fires may have increased the 199 hg in late paleozoic coals as well our study indicates that coal hg isotopes provide new insights into the biogeochemical cycle of hg in coal deposits and that 199 hg is a robust indicator to trace hg addition removal in coal deposits and biogeochemical processes magmatic intrusion hydrothermal fluids penetration burning of coal swamp occurring during coal deposition

a review of the structure petrology and dynamic deformation characteristics of some enigmatic terrestrial structures abstract we review three categories of enigmatic terrestrial structures that have a variety of macroscopic and microscopic dynamic deformation features the first category includes the midcontinent united states cryptoexplosion structures they are of shallow origin and illustrate the effects that might be expected from a meteorite impact on a sedimentary rock terrane the second category includes the well known vredefort and sudbury plutons or basement uplifts the lesser known precambrian basement uplifts at steen river manson and carswell and the diatreme breccia dikes at the slate islands they are of relatively deep seated origin and illustrate the effects that might be expected from deep crustal or mantle processes of an explosive nature the third category includes the large landslides in areas of crystalline rocks at koefels and langtang the dynamic deformation features at these latter locations appear to be related to high strain rate tectonic processes associated with the landslide itself we conclude that microscopic dynamic deformation features which occur in natural materials may have originated from meteorite impacts from internal explosions or from high strain rate tectonic process

alternating augite plagioclase wedges in basement dolerites of lockne impact structure sweden a new shock wave induced deformation feature this paper reports peculiar alternating augite plagioclase wedges in basement dolerites of lockne impact structure sweden the combined microscopic and spectroscopic studies of the micro nanoscale wedges reveal that these are deformation induced features first samples showing wedges 12 out of 18 studied are distributed in the impact structure within a radius of up to 10 km from the crater center second the margins between the augite and labradorite wedges are sharp and the 110 prismatic cleavage of augite develops into fractures and thereafter into wedges the fractures are filled with molten labradorite pushed from the neighboring bulk labradorite grain third compared to the bulk labradorite the dislocation density and the residual strain in the labradorite wedges are significantly higher a possible mechanism of genesis of the wedges is proposed the mechanism explains that passing of the shock waves in the basement dolerite induced i formation of microfractures in augite and labradorite ii development of the augite prismatic cleavages into the wedges which overprint the microfracture in the labradorite wedges and iii thereafter infilling of microfractures in the augite wedges by labradorite

examples of multiple rock slope collapses from kofels otz valley austria and western norway abstract this paper describes the effects of large massive rock slope failures on subsequent slope stability three examples of large rock slope failures from the austrian alps and norway demonstrate that failure increases the probability of further collapses at kofels austria a holocene rock slope failure several km3 in size filled the otz valley the morphology of the deposits indicates that at least one subsequent failure occurred along the head scarp of the first failure most likely a slide of similar size debris of the second landslide slid over the older deposits forming the famous kofels frictionite at least three rock slope failures all of them in excess of 106 m3 occurred from the same mountainside within the last 6000 8000 years at tafjord in western norway the most recent of these failures in 1934 triggered a destructive tsunami five large failures with volumes 50 000m3 occurred at ramnefjell norway within 50 years two of them caused considerable damage and a large number of death due to the formation of destructive tsunamis two dimensional finite element models of rock slope stability before and after the kofels and tafjord landslides show that massive rock slope failures produce a irregular slopes parts of which are as steep or steeper than the slope before failure and which represent new zones of instability and b zones of weakness related to slow slope deformation and related cracking

electron microscopy study of hyalomylonites evidence for frictional melting in landslides abstract hyalomylonites from langtang nepal and kofels otz valley austria were investigated by transmission electron microscopy tem the matrix is glassy at both localities rarely it is crystallized and devitrified to dendrites and skeletal microlites of plagioclase alkali feldspar and biotite the matrix is chemically heterogeneous with schlieren and formed by partial to almost complete melting of host rocks of granitic to granodioritic composition locally glasses with pure quartz plagioclase and alkalifeldspar composition were found from sio 2 glass minimum temperatures of 1520 c are estimated at both hyalomylonite localities melting appears to be the result of frictional heating on the gliding plane of a large landslide the host rocks were deformed in a brittle mode microstructures typical of plastic deformation at high temperatures are displayed by inclusions and were probably inherited from previous tectonic events

chicxulub crater a possible cretaceous tertiary boundary impact crater on the yucatan peninsula mexico we suggest that a buried 180 km diameter circular structure on the yucatan peninsula mexico is an impact crater its size and shape are revealed by magnetic and gravity field anomalies as well as by oil wells drilled inside and near the structure the stratigraphy of the crater includes a sequence of andesitic igneous rocks and glass interbedded with and overlain by breccias that contain evidence of shock metamorphism the andesitic rocks have chemical and isotopic compositions similar to those of tektites found in cretaceous tertiary k t ejecta a 90 m thick k t boundary breccia also containing evidence of shock metamorphism is present 50 km outside the crater s edge this breccia probably represents the crater s ejecta blanket the age of the crater is not precisely known but a k t boundary age is indicated because the crater is in a thick carbonate sequence shock produced co2 from the impact may have caused a severe greenhouse warming

planar deformation features in shocked quartz a transmission electron microscopy investigation abstract we present a detailed investigation by transmission electron microscopy tem of the fine structure of planar deformation features pdf in quartz grains within which shock metamorphism has been detected optically and which originate from various sites slate islands la malbaie and manicouagan lake canada ries crater germany the toba caldera sumatra the vredefort complex in south africa and the k t boundary at raton basin colorado pdfs appear on tem micrographs as straight and very narrow tem reveals many more pdfs than are optically detected probably because only concentrations of such defects in narrow areas can induce an optically detectable contrast caution should therefore be exercised when applying criteria based on the optical observation of single or multiple sets of pdfs pdfs in samples from slate islands and raton basin exhibit a peculiar morphology a high density of very tiny bubbles precipitated on the dislocation lines comparison with the behavior of wet quartz strongly suggests that these materials experienced lengthy annealing at moderate pressure and temperature

geophysical anomalies and quartz deformation of the warburton west structure central australia abstract this paper reports geophysical anomalies and intra crystalline quartz lamellae in drill cores from the warburton west basin overlapping the border of south australia and the northern territory the pre upper carboniferous 450 300 km large warburton basin north eastern south australia is marked by distinct eastern and western magnetic gravity and low velocity seismic tomography anomalies quartz grains from arenite core samples contain intra crystalline lamellae in carbonate quartz veins and in clastic grains similar to those reported earlier from arenites volcanic rocks and granites from the warburton east basin universal stage measurements of quartz lamellae in both sub basins define miller bravais indices of 10 12 and 10 13 in situ quartz lamellae occur only in pre late carboniferous rocks whereas lamellae bearing clastic quartz grains occur in both pre late carboniferous and post late carboniferous rocks the latter likely redeposited from the pre late carboniferous basement quartz lamellae in clastic quartz grains are mostly curved and bent either due to tectonic deformation or to re deformation of impact generated planar features during crustal rebound or and post impact tectonic deformation seismic tomography low velocity anomalies in both warburton west basin and warburton east basin suggest fracturing of the crust to depths of more than 20 km geophysical modelling of the cooper basin which overlies the eastern warburton east basin suggests existence of a body of high density 2 9 3 0 gr cm 3 and high magnetic susceptibility si 0 012 0 037 at a depth of 6 10 km at the centre of the anomalies in the warburton west basin a large magnetic body of si 0 030 is modelled below 10 km with a large positive gravity anomaly offset to the north of the magnetic anomaly in both the warburton east and warburton west the deep crustal fracturing suggested by the low velocity seismic tomography complicates interpretations of the gravity data universal stage measurements of quartz lamellae suggest presence of both planar deformation features of shock metamorphic derivation and deformed planar lamella the latter may be attributed either to re deformation of impact generated lamella impact rebound deformation or and post impact tectonic deformation the magnetic anomalies in the warburton east and west sub basins are interpreted in terms of 1 presence of deep seated central mafic bodies 2 deep crustal fracturing and 3 removal of devonian and carboniferous strata associated with rebound of a central uplift consequent on large asteroid impact further tests of the warburton structures require deep crustal seismic transects

living coccolithophores from the gulf of sirte southern mediterranean sea during the summer of 2008 the gulf of sirte is a largely unexplored area in the southernmost mediterranean sea we are presenting here 2008 sum mer data on the distribution pattern of living coccolithophores a main phytoplankton calcifying group in 105 samples from 20 stations the survey includes coastal and offshore stations enabling us to provide indications on the dynamics of phytoplankton productivity in relation to oceanographic processes the total coccosphere concentrations show higher values in the offshore stations and lower ones for coastal sites umbellosphaera tenuis emiliania huxleyi florisphaera profunda syracosphaera pulchra hol calyptrosphaera oblonga and rhabdosphaera spp dominate the assemblages the coccolithophore community shows the typical vertical zonation with k strategist taxa among others u tenuis rhabdosphaera spp and discosphaera tubifera in the upper 75 meters depth and lower photic zone taxa dominated by f profunda below the latter species shows its maximum development in the deep chlorophyll maximum layer which occurs in the up per part of the levantine intermediate water where the nutrient content is higher than in the overlying layers the mesoscale oceanographic circulation significantly affects the spatial and vertical distribution of coccolithophores with the thermocline and halocline depth shaping the vertical zonation of coccolithophore taxa and resulting in a strong lateral gradient within the gulf in the eastern sector under the influence of the gulf of sirte anticyclone the dcm is deeper and so is the occurrence of k strat egist taxa and f profunda

holocene periodicity in north atlantic climate and deep ocean flow south of iceland climate fluctuations during the past millennium are relatively well documented1 on a longer timescale there is growing evidence of millennial scale variability of holocene climate at periodicities of 2 500 and 950 years possibly caused by changes in solar flux 2 3 and 1 500 years maybe related to an internal oscillation of the climate system 4 5 6 but the involvement of deep water masses in these holocene climate changes has yet to be established here we use sediment grain size data from the iceland basin to reconstruct past changes in the speed of deep water flow the study site is under the influence of iceland scotland overflow water isow the flow of which is an important component of the thermohaline circulation that modulates european climate flow changes coincide with some known climate events the little ice age and the mediaeval warm period and extend over the entire holocene epoch with aquasi periodicity of 1 500 years the grain size data indicate afaster isow flow when the climate of northern europe is warmer however a second mode of operation is observed in the early holocene when warm climate intervals are associated with slower isow flow at that time the melting remnant of land based glacial age ice may have provided a sufficient source of fresh water to the ocean to reduce isow flow south of iceland

shock metamorphism of quartz in nature and experiment ii significance in geoscience the occurrence of shock metamorphosed quartz is the most common petrographic criterion for the identification of terrestrial impact structures and lithologies its utility is due to its almost ubiquitous occurrence in terrestrial rocks its overall stability and the fact that a variety of shock metamorphic effects occurring over a range of shock pressures have been well documented these shock effects have been generally duplicated in shock recovery experiments and thus serve as shock pressure barometers after reviewing the general character of shock effects in quartz the differences between experimental and natural shock events and their potential effects on the shock metamorphism of quartz are explored the short pulse lengths in experiments may account for the difficulty in synthesizing the high pressure polymorphs coesite and stishovite compared to natural occurrences in addition post shock thermal effects are possible in natural events which can affect shock altered physical properties such as refractive index and cause annealing of shock damage and recrystallization the orientations of planar microstructures however are unaffected by post impact thermal events except if quartz is recrystallized and provide the best natural shock barometer in terms of utility and occurrence the nature of planar microstructures particularly planar deformation features pdfs is discussed in some detail and a scheme of variations in orientations with shock pressure is provided the effect of post impact events on pdfs is generally limited to annealing of the original glass lamellae to produce decorated pdfs resulting from the exsolution of dissolved water during recrystallization basal 0001 pdfs differ from other pdf orientations in that they are multiple mechanical brazil twins which are difficult to detect if not partially annealed and decorated the occurrence and significance of shock metamorphosed quartz and its other phases namely coesite stishovite diaplectic glass and lechatelierite are discussed for terrestrial impact structures in both crystalline non porous and sedimentary porous targets the bulk of past studies have dealt with crystalline targets where variations in recorded shock pressure in quartz have been used to constrain aspects of the cratering process and to estimate crater dimensions at eroded structures in sedimentary targets the effect of pore space results in an inhomogeneous distribution in recorded shock pressure and temperature which requires a different classification scheme for the variation of recorded shock compared to that in crystalline targets this is discussed along with examples of variations in the relative abundances of planar microstructures and their orientations which are attributed to textural variations in sedimentary target rocks examples of the shock metamorphism of quartz in distal ejecta such as at the k t boundary and from nuclear explosions are illustrated and are equivalent to that of known impact structures except with respect to characteristics that are due to long term post shock thermal effects finally the differences between the deformation and phase transformation of quartz by shock and by endogenic tectonic and volcanic processes are discussed we confirm previous conclusions that they are completely dissimilar in character due to the vastly different physical conditions and time scales typical for shock events compared to tectonic and volcanic events well characterized and documented shock effects in quartz are unequivocal indicators of impact in the natural environment

high resolution palaeoenvironmental reconstruction of odp hole 963d sicily channel during the last deglaciation based on calcareous nannofossils abstract a palaeoenvironmental reconstruction of ocean drilling program odp hole 963d sicily channel has been obtained on the basis of quantitative abundance fluctuations in the calcareous nannofossil assemblages the studied hole is characterized by a very high sedimentary resolution and covers the last ca 20 kyr a new palaeoclimatic curve based on the gephyrocapsa muellerae upper photic zone upz group ratio permitted the detection of the rapid climatic fluctuations that characterized the last deglaciation cold water masses occupied the sicily channel during the glacial period and the younger dryas whereas they were generally warm during the bolling allerod and the holocene an approach based on a direct relationship between actualistic data water samples and palaeontological records in the coccolithophores has been attempted in order to obtain the palaeoecological characterization with the proposition of two floristic groups pertaining to the upper photic zone and the lower photic zone lpz further information has been provided by several additional taxa during the investigated time interval stratification in the water column and oligotrophic conditions are always linked to the warm periods while high productivity caused by continuous convection of nutrient fluxes existed during the cold periods finally a simple model with two end members is proposed to explain the relative abundance of the deep dwelling species florisphaera profunda relative to other coccolithophores and to the physical conditions of the photic zone

a dynamic concept for eastern mediterranean circulation and oxygenation during sapropel formation we propose that intermittent bottom water ventilation occurred throughout periods of sapropel deposition and that the recently reported sapropel interruptions represent centennial scale episodes of enhanced frequency intensity of that process in essence the modern high frequency variability in deep water formation affected by climatic variability over the northern basins on seasonal to longer time scales prevailed also at times of sapropel deposition although the overall ventilation state was much reduced this concept is supported by detailed multiple species isotope records for three aegean cores the presence of abundant globorotalia truncatulinoides within especially sapropels s7 and s8 in the western levantine basin observations of three rapid benthic repopulations within sapropel s6 in the deep western levantine basin a report of continuous benthic presence through sapropel s1 at intermediate deep locations offshore libya and further supporting information from the literature in the aegean records concomitant abundance of low oxygen tolerant benthic foraminifera and presence of the more oxyphilic benthic foraminifer uvigerina mediterranea with surface similar 13c values indicate repeated deep water re oxygenation events throughout the deposition of s1 the observations of a continuous benthic presence through s1 offshore from libya imply that no persistent anoxia developed at mid depth levels in that region which is far removed from direct deep ventilation influences the abundance of deep mesopelagic g truncatulinoides through several sapropels from the western levantine basin also suggests the presence of bio available oxygen at many hundreds of meters of depth moreover the rapid intermittent benthic repopulations within sapropels from the deep eastern mediterranean imply that bottom water anoxia was spatially restricted and or of a highly intermittent nature the short time scales of these repopulation events are incompatible with titration of an extensively anoxic water column and subsequent re establishment of water column anoxia we suggest that where anoxic azoic conditions were present they most likely were restricted to a veneer at the sediment water interface the extent of such an anoxic blanket depends on the balance between advective oxygen supply into the deep sea and biological and chemical oxygen demand the demand functions imply a decoupling of oxygenation from water mass advection allowing export production and corg posting rates to the sea floor to delimit the extent of the anoxic blanket in both space and time low productivity regions would develop no anoxic blanket allowing for the observed persistence of deep dwelling planktonic and bottom dwelling benthic faunas

the early paleozoic development of bioturbation evolutionary and geobiological consequences abstract bioturbation the physical and chemical mixing of sediments by burrowing animals is a critical engineering process in modern seafloor environments and exerts an important control on not only benthic ecology and sediment properties but also ocean wide biogeochemical cycling well mixed sediments have long been assumed to appear at the precambrian cambrian boundary with the first occurrence of the index fossil and three dimensional burrow treptichnus pedum however field based analyses synthesizing ichnological stratigraphic sedimentological and taphonomic data collected from lower paleozoic successions worldwide indicate that sediment mixing in marine shelf environments remained limited until at least the late silurian 120 million years after the precambrian cambrian transition in spite of early advances in complex modes of infaunalization mixed layer development had a much more gradual trajectory and did not occur in step with the first appearance of three dimensional burrows the delayed appearance of modern style intensities of sediment reworking postdating both the cambrian explosion and the great ordovician biodiversification event may be due to the late stage radiation of mobile infaunal deposit feeders biological bulldozers the organisms which are in modern marine settings the most efficient bioturbators the protracted development of the sediment mixed layer holds important implications for contemporaneous biogeochemical cycling and oxygenation of the ocean atmosphere system the delayed development of intensive sediment mixing may have also mediated exceptional preservation of both fossilized soft tissues and shallow tier trace fossils and may therefore have contributed to the anomalous preponderance of konservat lagerstatten and exceptionally preserved shallow tier trace fossils and bioglyphs characteristic of the lower paleozoic stratigraphic record

variability in the vertical structure of the water column and paleoproductivity reconstruction in the central western mediterranean during the late pleistocene abstract a sedimentary sequence spanning marine isotope stage mis 6 to mis 2 in core lc07 recovered in the central mediterranean has been investigated in order to produce a high resolution paleoceanographic reconstruction the changes in productivity deduced from calcareous plankton relative abundances and independently confirmed by the ba xs fluctuations are linked to the stability of the water column which is mainly controlled by the water mass temperature during glacial intervals productivity was generally enhanced oligotrophic and warmer water masses with a deepened seasonal thermocline can be inferred for most of mis5 the magnetic properties of the sediment show increased occurrences of north africa dust in the central mediterranean during cold phases likely as a consequence of a more efficient erosive process triggered by southward displacement of the intertropical convergence zone although increases in both productivity and saharan dust occurred during cold periods the atmospheric inputs do not seem to contribute significantly to the fertilization of primary producers a shannon index curve has been used to tentatively synthesize the variations of calcareous nannofossil assemblages through the last 150 kyr the assemblage diversity sharply increased coincident with the transition from the penultimate glacial to the last interglacial subsequently low diversity was gradually reached again in the last glacial

sulfur distribution and isotopic composition in peats from the okefenokee swamp georgia and the everglades florida abstract peat cores from three aquatic environments freshwater brackish and marine have been analyzed for organic pyritic and sulfatic sulfur contents and isotope ratios peat collected from each environment has a unique combination of sulfur content distribution and isotope ratio freshwater peat from the okefenokee swamp contains the least sulfur 0 26 to 0 48 primarily organic sulfur and is vertically uniform in sulfur content and isotope ratio the organic sulfur isotope ratio of the okefenokee pear 12 3 to 12 8 per mil is similar to that of sulfate in associated surface waters cores from presently brackish and marine peats from the florida everglades have high organic pyritic and sulfatic sulfur contents with vertical variability in sulfur content and isotope ration the isotope ratio of organic sulfur in the brackish and marine peat is lighter than that of sulfate associated with their respective peat forming environments organic sulfur in the marine peat is isotopically lighter than in the brackish peat freshwater peats subsequently overlain by sediment associated with brackish to marine waters may have a sulfur content distribution and isotopic ratio indistinguishable from peats derived under brackish or marine conditions the primary source of sulfur in peats is dissolved sulfate associated with the peat forming system the sulfate concentration of the waters in which a peat forms is of major importance in determining the isotopic composition of the sulfur form found in peat the content distribution and isotopic ratio of low and high sulfur peats are similar to those reported for coals indicating that the fundamental sulfur geochemistry of coals may have been established during the peat forming stage of coalification the organic sulfur content and isotope ratio of a coal may be useful in estimating the relative sulfate ion concentration of the waters present during the peat forming stage of coalification where transgressive sequences are not involved the sulfate ion concentration of paleowaters could be used to interpret the paleoenvironment during the peat forming stage of coalification and thus information about the organic sulfur content and isotope ratio of coals may prove useful in helping to assess coal quality in advance of mining

recreating atmospheric sulphur deposition histories from peat stratigraphy diagenetic conditions required for signal preservation and reconstruction of past sulphur deposition in the derbyshire peak district uk three modern pristine and one previously polluted ombrotrophic peat were sampled and analysed to investigate whether the isotopic composition of atmospheric sulphur inputs could be preserved in the organic fraction of ombrotrophic peats without undue alteration through syn depositional or diagenetic effects peat type reflecting the environment of deposition and diagenesis was shown to be critical in determining whether an environmental archive of sulphur deposition could be preserved within the profile of the pristine peats sampled hummock peat from shetland proved to be the most suitable exhibiting a near constant 34s characteristic of the growing vegetation in the organic fraction of peat in the upper 30 cm of the profile however only short to medium term changes 600 years in input are likely to be preserved due to the masking effect produced by incorporation of sulphide derived from bacterial sulphate reduction bsr into the organic fraction at depth the organic fraction of peat sampled from waterlogged pools at forsinard ne scotland was masked by sulphide incorporation throughout the profile while peat from abisko n sweden was exposed to annual freeze thaw cycles which appear to have produced significant decomposition of the organically bound sulphur and loss of the original depositional isotopic signal three peat types were sampled from the southern pennines an area with a gross history of sulphur pollution during the industrial revolution high hummock peat low hummock peat and waterlogged peat from a pool complex in drier high and low hummock peat types diagenesis and decomposition were not found to be significant processes in the upper portions of the peat hence alterations in the isotopic composition of the organic sulphur fraction in the profile reflect that of the depositional environment in the hummock peats organically bound sulphur becomes isotopically lighter at around 1400 ad which may reflect alterations in local sulphur inputs at this time due to the small scale smelting of lead in the area isotopic compositions become progressively lighter still towards the peat surface layers which correlate well with the excesses of sulphur deposition largely from coal burning during the industrial revolution

suborbital climate variability during marine isotopic stage 5 in the central mediterranean basin evidence from calcareous plankton record abstract new faunal and floral records from ocean drilling project hole 963a resolved at 80 year spacing provide evidence of suborbital scale climate variability in the central mediterranean sea throughout marine isotope stage mis 5 cold events in the central mediterranean sea indicated by low abundances of warm species and high abundances of cold species are also evident in a planktonic foraminifera paleoclimatic curve they have been linked to ngrip greenland ice core c events and appear correlative with similar sub millennial climate fluctuations identified in the north atlantic region and in the alboran basin westernmost mediterranean low resolution benthic and planktonic oxygen isotope fluctuations parallel trends in the surface records evidenced by planktonic assemblage fluctuations bolstering their interpretation as climate proxies climate events also occur in the mediterranean between named c events and may be coeval with additional climate events identified recently in the western subtropical atlantic hence we propose that frequent climate oscillations during mis 5 characterize both sides of the mid latitude north atlantic perhaps indicating millennial scale variations in mid latitude atmospheric patterns

radon emanation from giant landslides of koefels tyrol austria and langtang himal nepal the identification of extremely high indoor radon concentrations in the village umhausen tyrol austria initiated a scientific program to get information about the source and distribution of this noble gas the high concentrations can not be related to u anomalies or large scale fault zones the nearby giant landslide of koefels with its highly fractured and crushed orthogneisses are the only possible source of radon despite the fact that the u and ra content of the rocks is by no means exceptional the reasons for the high emanation rates from the landslide are discussed and compared to results gained from a similar examination of the giant landslide of langtang himal nepal the exceptional geologic situation in both cases as well as the spatial distribution of different concentration levels indicate that both landslides must be considered as the production sites of radon independent of the u and ra contents of the rocks the most important factors producing high emanation rates are the production of a high active surface area and circulation pathways for rn enriched soil air by brittle deformation due to the impact of the landslidemass

the dynamics of the sicily strait a comprehensive study from observations and models abstract the dynamics of the sicily strait are investigated in a comprehensive study using recent in situ observations ocean general circulation model ogcm simulations and process model results in particular results of a very high resolution mediterranean model med16 developed in the context of the mercator project are described the circulation in the sicily strait can be described as a two layer exchange of atlantic water aw and eastern mediterranean outflow water eow the algerian current brings aw the upper layer eastwards and splits into two branches at the entrance to the sicily strait one flowing to the tyrrhenian sea the other into the sicily strait the later is composed of two streams referred to as the atlantic ionian stream ais and the atlantic tunisian current atc in winter the atc signature is more pronounced in summer the ais is associated with a number of well known semi permanent features including the intermittent northward extension of the ais called nais at the ionian shelf break which seems to be driven by the surface density contrast between waters of the sicilian and the ionian basins new intermittent patterns are shown by the med16 simulations for example an anticyclonic eddy called mca south of the malta channel and an anticyclonic gyre associated to the nais called naisa upwelling is well developed in august with temperature lower than 24 c along the western and southern coasts of sicily the seasonal transport of the aw through the strait has a maximum value 1 4 sv in winter and a minimum value at the end of summer 0 8 sv in the lower layer at the exit of the sicily strait the eow mainly composed of levantine intermediate water liw outflows into the tyrrhenian sea and veers to the right then as well known the liw flows along the northern coast of sicily before reaching the sardinia channel a new liw path from the sicily strait towards the sardinia channel is shown by the med16 model and is due to intermediate eddy shedding at the exit of the sicily strait the topography of the sill in the sicily strait plays a major role in the circulation a combination of barotropic baroclinic double kelvin waves on both side of the sill provides a mechanism for splitting the algerian current

coccolithophorid distribution in the ionian sea and its relationship to eastern mediterranean circulation during late fall to early winter 1997 subtropical latitude with a general high species diversity and a well defined depth distribution it is in fact possible to recognize an upper photic zone assemblage dominated by e huxleyi and characterized by higher concentration and species diversity and a lower photic zone where typically deep living species i e f profunda g flabellatus a re present these two zones are separated by a transition layer where species of both zones are represented and new ones appear such vertical distribution appears to be strictly related to the local hydrology with the zone boundaries rising and falling as a function of the location of the isotherms in particular the first significant occurrence of f profunda from surface to the deep photic zone corresponds with the start of the thermocline comparison of present plankton data with the surface sediment record although displaying a consistent pattern of species assemblage shows some differences in the presence and relative abundance of some species g oceanica this can be related to seasonal as well as interannual variations in the pattern and intensity of surface circulation in the investigated area index terms 4855 oceanography biological and chemical plankton 4815 oceanography biological and chemical ecosystems structure and dynamics keywords eastern mediterranean sea coccolithophorids ecology phytoplankton citation malinverno e p ziveri and c corselli coccolithophorid distribution in the ionian sea and its relationship to eastern mediterranean circulation during late fall to early winter 1997 j geophys res 108 c9 8115 doi 10 1029 2002jc001346 2003

burial of organic carbon and pyrite sulfur in sediments over phanerozoic time a new theory in present day marine sediments almost all of which are deposited in normal oxygenated seawater rates of burial of organic carbon c and pyrite sulfur s correlate positively and bear a constant ratio to one another c s 3 on a weight basis by contrast calculations based on the isotopic model of garrels and lerman 1981 indicate that at various times during the phanerozoic the worldwide burial ratio must have been considerably different than the present day value this ratio change is caused by the requirement that increases in the worldwide mass of organic carbon must be accompanied by equivalent decreases in the mass of sedimentary pyrite sulfur in order to maintain a roughly constant level of o2 in the atmosphere such apparently contradictory behavior can be explained if the locus of major organic carbon burial has shifted over time from normal marine environments as at present to non marine freshwater or to euxinic environments in the geologic past a shift to predominantly freshwater burial can help explain predicted high c s ratios in permo carboniferous sediments and a shift to euxinic environments can help explain predicted low c s ratios during the early paleozoic it is demonstrated that the three environments today exhibit distinguishably different average c s ratios

primary productivity variability on the atlantic iberian margin over the last 70 000 years evidence from coccolithophores and fossil organic compounds 1 this study analyzes coccolithophore abundance fluctuations e g emiliania huxleyi gephyrocapsa specimens and florisphaera profunda in core md01 2444 sediment strata retrieved at the iberian margin northeastern atlantic ocean coccolithophores are calcareous nannofossils a major component of the oceanic phytoplankton which provide information about past ecological and climatological variability results are supported by data on fossil organic compounds sea surface temperatures alkenones and n hexacosan 1 ol index and geochemical analyses benthic 13ccc and planktonic 18occ isotopes three scenarios are taken into account for this location at centennial scale resolution over the last 70 000 years the holocene and the stadial and interstadial modes the different alternatives are described by means of elements such as nutrients upwelling phenomena temperatures at surface and subsurface level or the arrival of surface turbid fresh and cold waters due to icebergs low sea level increased aridity and dust during the holocene moderate primary productivity was observed mainly concentrated in e huxleyi specimens surface temperatures were at maxima while the water column was highly ventilated by northern sourced polar deep waters and warmer subsurface nutrient poor subtropical waters over most of the last glacial stadials surface productivity weakened higher f profunda and reworked specimen percentages and lower diunsaturated and triunsaturated c37 alkenones the arrival of cold arctic surface waters traced by tetraunsaturated c37 peaks and large e huxleyi together with powerful ventilated southern sourced polar deep waters disturbed in all likelihood the delicate vertical equilibrium while preventing significant upwelling mixing finally during the last glacial interstadials lower f profunda percentages nonreworked material and higher diunsaturated and triunsaturated c37 alkenones a combined signal is observed warm surface temperatures were concurrent with generally low oxygenation of the deep sea floor moderate arrival of northern sourced deep waters and subsurface cold nutrient rich recently upwelled waters probably of polar origin these particular conditions may have promoted vertical mixing while enhancing surface primary productivity mainly of gephyrocapsa specimens

rise in seawater sulphate concentration associated with the paleoproterozoic positive carbon isotope excursion evidence from sulphate evaporites in the 2 2 2 1 gyr shallow marine lucknow formation south africa past oceanic sulphate concentration is important for under standing how the oceansredox state responded to atmospheric oxygen levels the absence of extensive marine sulphate evaporites before 1 2 gyr probably reflects low seawater sulphate and or higher carbonate concentrations sulphate evaporites formed locally during the 2 22 2 06 gyr lomagundi positive d 13 c excursion however the 2 2 2 1 gyr lucknow formation south africa provides the first direct evidence for seawater sulphate precipitation on a carbonate platform with open ocean access and limited terrestrial input these marginal marine deposits contain evidence for evaporite molds pseudomorphs after selenite gypsum and solid inclusions of ca sulphate in quartz carbon and sulphur isotope data match the global record and indicate a marine source of the evaporitic brines the apparent precipitation of gypsum before halite requires 2 5 mm l 1 sulphate concentration higher than cur rent estimates for the paleoproterozoic during the lomagundi event which postdates the 2 32 gyr initial rise in atmospheric oxygen seawater sulphate concentration rose from archean values of 200 lm l 1 but dropped subsequently because of higher pyrite burial rates and a lower oceanic redox state

dynamic deformation of quartz and feldspar clues to causes of some natural crises abstract indications of natural catastrophes and crises are preserved in some geologic strutures and in the stratigraphic record emphasizing the dynamic nature of the earth s evolution the crises may result either from exogenic or endogenic energy sources distinguishing between these sources is a complex multidisciplinary problem in the earth sciences shock deformation by impact has been well studied both in shock recovery experiments and in known impactites but only recently has the possibility of generation of shock waves by high temperature internal explosions been seriously considered an optically based reconaissance survey of microstructures in quartz and feldspar in some explosive silicic volcanics suggests that they may have been induced by dynamic deformation at high temperature in some respects the character of the microstructures differs greatly from those induced by room temperature shock whereas in others the differences are subtle results from recent shock recovery experiments on quartzite preheated to 440 and shocked to 28 gpa support this contention for two classic cretaceous tertiary sections at gubbio italy it is shown that shock mosaicism and shock lamellae occur over a 4 m interval bisected by the boundary in a pattern approximately correlatable with an independently established iridium enrichment these data are incompatible with any single event and are most plausibly interpreted as reflecting a period 0 5 my of intense probably episodic volcanism with a culmination at the k t transition multiple dynamic events may also account for macroscopic and microscopic structures developed during the evolution of the vredefort structure south africa

coupling plankton sediment trap surface sediment coccolithophore regime in the north aegean sea ne mediterranean abstract quantitative coccolithophore analyses were performed on data of 2011 2015 dataset derived from the examination of plankton samples until 100 m water depth the sinking particulate matter collected by a time series sediment trap and surface and core sediments of the north aegean sea sampling site m2 athos basin ne mediterranean the aim was to achieve a better understanding of the potential modifications of the coccolithophore assemblage between the surface waters plankton the water column sidocoenosis and the underlying sediment thanatocoenosis sediment trap calcareous nannoplankton multiannual mean fluxes 20 108 coccoliths m2 day 1 documented similar values to the accumulation rates recorded in the surface sediment 23 6 108 coccoliths m 2 day 1 whereas within the last 500 years the rates have ranged from 2 19 108 to 5 4 108 coccoliths m 2 day 1 the dominant species in all sampling types was emiliania huxleyi reaching in some cases striking relative abundances of 85 90 morphometric analyses on e huxleyi coccoliths documented the presence of a lightly calcified morphotype in the water column and sediment trap samples in addition to the seasonal occurrence of heavier calcified e huxleyi coccoliths indicating enhanced black sea water inflows during may 2011 february 2015 and october 2015 however such a signal was not preserved in the surface sediment assemblage mostly due to processes of diagenetic calcite overgrowth notably florisphaera profunda was not included in the upper water column plankton assemblage but in the sediment traps and surface sediments thus it is presumed to flourish in nutrient enriched layers below the sampled 100 m water column depth several fragile syracosphaeraceae and holococcolithophore species and the delicate algirosphaera robusta were not present in the sinking assemblage or on the seafloor however the main features of the living assemblages were generally preserved the recorded high relative abundances of e huxleyi 60 in the sediment were in accordance with positive north atlantic oscillation nao shifts during recent production of dense water masses in the north aegean

sulfur during early diagenesis in sphagnum peat insights from δ34s ratio profiles in 21pb dated peat cores pb chronologies and depth profiles of stable s isotope ratios 834s and concentrations of organic and inorganic s fractions were determined in peat cores from nine sites in the u s and the czech republic results indicate that depth profiles in s concentrations s accumulation and 634s ratios in peat deposits are affected not only by historical patterns in atmospheric s deposition but also by ongoing depth dependent changes in s reduction oxidation and s immobilization mineralization processes within a peat deposit these processes impart a certain degree of mobility to s in peat bringing into question the validity of reconstructing historical records of s accumulation using dated peat profiles over long term diagenesis isotopically light s may be continually released from deep peat this release may result in redistribution of s and s isotopes in peat and suggests that short term patterns in s accumulation may not persist over much longer time scales

cenozoic record of δ 34 s in foraminiferal calcite implies an early eocene shift to deep ocean sulfide burial understanding the changes in and drivers of isotopic variability of sulfur in seawater sulfate 34sso4 sw over geological time remains a long standing goal particularly because of the coupling between the biogeochemical sulfur and carbon cycles the early cenozoic has remained enigmatic in this regard as the existing seawater sulfate isotopic records appear to be decoupled from the well defined carbon isotope composition of the ocean here we present a new cenozoic record of sulfur isotopes using carbonate associated sulfate hosted in the calcite lattice of single species foraminifera the vastly improved stratigraphy afforded by this record demonstrates that carbon and sulfur cycles as recorded by their isotopes are not fully decoupled in the early cenozoic with a model driven by partial coupling of the carbon and sulfur cycles we demonstrate that a change in sulfur isotopic fractionation of the pyrite burial flux best explains the large increase in 34sso4 sw 53 million years ago ma and the subsequent long steady state we suggest that the locus of pyrite burial changed from shallow epicontinental seas and shelf environments to more open ocean sediments around 53 ma loss of extensive shelf environments corresponds to cretaceous palaeogene sea level changes and tectonic reorganization occurring as the himalayan arc first collided with asia a cenozoic reconstruction of the 34s of marine sulfate suggests a shift in the locus of pyrite burial from shallow seas to the open ocean during the early eocene

sulfur isotopes in coal constrain the evolution of the phanerozoic sulfur cycle sulfate is the second most abundant anion behind chloride in modern seawater and its cycling is intimately coupled to the cycling of organic matter and oxygen at the earth s surface for example the reduction of sulfide by microbes oxidizes vast amounts of organic carbon and the subsequent reaction of sulfide with iron produces pyrite whose burial in sediments is an important oxygen source to the atmosphere the concentrations of seawater sulfate and the operation of sulfur cycle have experienced dynamic changes through earth s history and our understanding of this history is based mainly on interpretations of the isotope record of seawater sulfates and sedimentary pyrites the isotope record however does not give a complete picture of the ancient sulfur cycle this is because in standard isotope mass balance models there are more variables than constraints typically in interpretations of the isotope record and in the absence of better information one assumes that the isotopic composition of the input sulfate to the oceans has remained constant through time it is argued here that this assumption has a constraint over the last 390 ma from the isotopic composition of sulfur in coal indeed these compositions do not deviate substantially from the modern surface water input to the oceans when applied to mass balance models these results support previous interpretations of sulfur cycle operation and counter recent suggestions that sulfate has been a minor player in sulfur cycling through the phanerozoic eon

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

the stable isotope geochemistry of australian coals abstract d h 13 c 12 c 18 o 16 o and 34 s 32 s ratios in the organic matrix and organic solvent extracts of australian coals and in the fluids and minerals associated with these coals are reported and reviewed against similar isotopic data for coals from other regions where coals are immature original isotopic differences between macrolithotypes and between solvent extracts lipid concentrates and insoluble residues are largely preserved however with increasing maturity these characteristic differences particularly those between macrolithotypes are rapidly erased conversely where as indicated by low total sulfur contents coals of cretaceous to permian age were deposited under essentially freshwater conditions 34 s values for the organically bound sulfur remain remarkably constant at 4 3 relative to meteoritic sulfur in similar younger tertiary coals the organic sulfur is markedly enriched in 34 s five distinctive isotopic patterns which may be interpreted in terms of the environment of sulfate reduction can be recognized from 34 s 32 s ratio measurements on the various forms of sulfur in australian coals isotopic studies of seam gas hydrocarbons collected in situ show these to be unexpectedly strongly depleted in the heavier isotopes of hydrogen and carbon relative to natural gases from proposed humic sources furthermore no pronounced increase in the 13 c content in methane with increase in rank of the parent coal was observed in addition several sources of associated carbon dioxide have been delineated including normal maturation processes invasion of the seams by magnetic carbon dioxide and interaction of the coal with intrusive magma isotopic exchange between free seam gases is not accepted as an explanation for some unusual isotopic fractionations seen rather the data suggest that these gases may be formed in a state approaching isotopic equilibrium this argument also satisfactorily explains the isotopic compositions of primary siderite and secondary calcite associated with bituminous coal seams however where seams are invaded and permeated with externally derived carbon dioxide usually of magnetic origin carbonates are frequently absent presumably as a result of the action of carbonic acid

geophysical anomalies and quartz microstructures eastern warburton basin north east south australia tectonic or impact shock metamorphic origin abstract the eastern warburton basin northeast south australia features major geophysical anomalies including a magnetic high of near 200 nt centred on a 25 km wide magnetic low 30 000 km large eastern warburton basin the qz pe include multiple intersecting planar to curved sub planar elements with relic lamellae less than 2 m wide with spacing of 4 5 m qz pe are commonly re deformed displaying bent and wavy patterns accompanied with fluid inclusions u stage measurements of a total of 243 planar sets in 157 quartz grains indicate dominance of 10 12 10 13 and subsidiary 11 22 22 41 m 10 11 and x 51 61 planes transmission electron microscopy tem analysis displays relic narrow 1 m wide lamellae and relic non sub grain boundaries where crystal segments maintain optical continuity extensive sericite alteration of feldspar suggests hydrothermal alteration to a depth of 500 m below the unconformity which overlies the qz pe bearing warburton basin terrain the data are discussed in terms of a tectonic metamorphic deformation and b impact shock metamorphism producing planar deformation features qz pdf deformed qz pe are compared to re deformed qz pdfs in the sudbury vredefort manicouagan and charlevoix impact structures a 4 5 km uplift of the big lake granite suite during 298 295 ma is consistent with missing of upper ordovician to devonian strata and possible impact rebound the occurrence of circular seismic tomography anomalies below the east warburton basin the poolowana basin and the woodleigh impact structure signifies a potential diagnostic nature of circular tomographic anomalies

ocean surface and wind dynamics in the atlantic ocean off northwest africa during the last 140 000 years abstract a combined micropaleontological analysis of core camel 1 from the oligotrophic sierra leone rise area has allowed reconstruction of the paleoclimatic and paleoceanographic history of the region for the last 140 kyr the ratio n between the reticulofenestrids coccolithophore indicators of relatively high nutrient contents versus florisphaera profunda a lower photic zone coccolithophore allowed us to monitor changes in the nutricline depth these results were compared with those obtained for marine diatom and planktic foraminifera assemblages thus a shallow nutricline thermocline and high productivity during stages 6 5d 5b 4 and 2 is proposed this situation can be correlated with maximum input of biosiliceous wind transported particles fresh water diatoms and phytoliths in sea sediments the shallow nutricline is correlated with an intensification in atlantic divergence and or a north equatorial current intensification when the ne trades were enhanced for glacial and stadials cold periods a clear precessional component is observed in the surface water dynamics during the last climatic cycle minima in the n ratio coinciding with minimum insolation during winter in the boreal hemisphere during mis 5 4 and 2 dry conditions were dominant on the northern african continent corresponding to a more intense ne trade wind circulation the increased phytolith concentrations during mis 6 are consistent with a more intense seasonality on the african continent cold planktic foraminifera assemblages show an eccentricity component linked to northern ice sheet dynamics this situation is enhanced in isotope stages 6 and 3 due to an intensification in the north equatorial current the eccentricity component is also observed both in the n ratio coccolithophore related and in the total planktic foraminifera

three sets of crystallographic sub planar structures in quartz formed by tectonic deformation abstract in quartz multiple sets of fine planar deformation microstructures that have specific crystallographic orientations parallel to planes with low miller bravais indices are commonly considered as shock induced planar deformation features pdfs 1 diagnostic of shock metamorphism using polarized light microscopy we demonstrate that up to three sets of tectonically induced sub planar fine extinction bands febs sub parallel to the basal and crystallographic planes are common in vein quartz in low grade tectonometamorphic settings we conclude that the observation of multiple 2 3 sets of fine scale closely spaced crystallographically controlled sub planar microstructures is not sufficient to unambiguously distinguish pdfs from tectonic febs

holocene millennial scale productivity variations in the sicily channel mediterranean sea 1 the calcareous nannofossil assemblages of ocean drilling program hole 963d from the central mediterranean sea have been investigated to document oceanographic changes in surface waters the studied site is located in an area sensitive to large scale atmospheric and climatic systems and to high and low latitude climate connection it is characterized by a high sedimentation rate the achieved mean sampling resolution is 70 years that allowed the sicily channel environmental changes to be examined in great detail over the last 12 ka bp we focused on the species florisphaera profunda that lives in the lower photic zone its distribution pattern shows repeated abundance fluctuations of about 10 15 such variations could be related to different primary production levels given that the study of the distribution of this species on the sicily channel seafloor demonstrates the significant correlation to productivity changes as provided by satellite imagery productivity variations were quantitatively estimated and were interpreted on the basis of the relocation of the nutricline within the photic zone led by the dynamics of the summer thermocline productivity changes were compared with oceanographic atmospheric and cosmogenic nuclide proxies the good match with holocene master records as with ice rafted detritus in the subpolar north atlantic and the near 1500 year periodicity suggest that the sicily channel environment responded to worldwide climate anomalies enhanced northern hemisphere atmospheric circulation which has been reported as one of the most important forcing mechanisms for holocene coolings in previous mediterranean studies had a remarkable impact on the water column dynamics of the sicily channel

volcanism around k t boundary time its role in an impact scenario for k t extinction events abstract a widespread debate on the cretaceous tertiary k t boundary 65 1 ma extinctions has largely revolved around an impact or a volcanic cause evidence for both events is strengthened by recent work impact triggered deccan volcanism or independent impact and mantle plume events have been suggested this review examines evidence for both events and suggests that they overlapped in time but with globally uneven effects the combined effects produced generally inhospitable k t environments leading to mass extinctions although some life forms flourished afterwards volcanic contributions to the k t boundary environment probably include increased platinum group element pge and acid rain fall out particularly from large scale mantle upwellings e g deccan cameroon and coral sea events a previously proposed post k t greenland starting plume apparently already existed in the cretaceous k t features such as the iridium ir anomaly most likely include longer term volcanic as well as sudden meteoritic impact contributions volcanic contributions were greatest from southern hemisphere sources whereas meteorite impacts featured in the northern hemisphere

reworked coccoliths as runoff proxy for the last 400 years the case of gaeta gulf central tyrrhenian sea central italy abstract we present the results of a high resolution study carried out on a shallow water sediment core recovered in the central tyrrhenian sea to reconstruct the runoff history of the catchment basin of volturno and garigliano rivers gulf of gaeta italy over the past 400 years we compared the abundance distribution pattern of reworked coccoliths to the surface runoff model simulation for the volturno and garigliano hydrographic river basins the global historical climatology network index the palmer drought severity index the tevere river discharge anomaly the average summer rainfall in southern italy and the reconstructed north atlantic oscillation signal this comparison suggested that the biotic signal of the reworked coccoliths may be used to detect climatic events from local to global scale the calcareous nannofossil assemblages as well as their diversity index are modulated by oscillation in solar activity where minima in solar activity correspond to minima calcareous nannofossil diversity and vice versa in particular the antiphase correlation between the abundance of reworked coccoliths and the north atlantic oscillation index which modulates winter precipitation suggests that this biotic index could be used as a reliable proxy to reconstruct the variations in the hydrographic basin runoff of the volturno and garigliano rivers in addition power spectral and wavelet analysis carried out on both signals documented the occurrence of climatic cycles of the duration of about 95 yr from 1900 ad upwards a turnover in the periodicity from 95 yr climatic cycles to 22 26 yr cycles occurred in the reworked coccoliths signal suggesting a strong control of solar forcing hale cycle over the last century

synchronous radiocarbon and climate shifts during the last deglaciation radiocarbon data from the cariaco basin provide calibration of the carbon 14 time scale across the period of deglaciation 15 000 to 10 000 years ago with resolution available previously only from holocene tree rings reconstructed changes in atmospheric carbon 14 are larger than previously thought with the largest change occurring simultaneously with the sudden climatic cooling of the younger dryas event carbon 14 and published beryllium 10 data together suggest that concurrent climate and carbon 14 changes were predominantly the result of abrupt shifts in deep ocean ventilation

low temperature intracrystalline deformation microstructures in quartz a review of numerous genetic interpretations of the individual low temperature intracrystalline deformation microstructures in quartz shows that there is no consensus concerning their formation mechanisms therefore we introduce a new purely descriptive terminology for the three categories of intracrystalline deformation microstructures formed in the low quartz stability field fine extinction bands feb wide extinction bands web and localised extinction bands leb the localised extinction bands are further subdivided into blocky bleb straight sleb and granular gleb morphological types a detailed polarised light microscopy study of vein quartz from the low grade metamorphic high ardenne slate belt belgium further reveals a series of particular geometric relationships between these newly defined intracrystalline deformation microstructures these geometric relationships are largely unrecognised or underemphasised in the literature and need to be taken into account in any future genetic interpretation based on our observations and a critical assessment of the current genetic models we argue that the interpretation of the pertinent microstructures in terms of ambient conditions and deformation history should be made with care as long as the genesis of these microstructures is not better confined

stable isotopes reveal human influences on southern new zealand soils abstract a multi isotopic soil study across a southern new zealand transect has been undertaken as part of a geochemical baseline survey to identify human impacts on new zealand s landscape and characterise different land uses and anthropogenic effects carbon nitrogen and sulphur isotopes from two soil depths 0 30 and 50 70 cm were acquired across a variety of land uses including pristine national parks urban centres intensively farmed pastoral land climates dry 6000 mm annual rainfall altitude sea level to 2300 m above sea level and soil parent material lithology sandstone schist basalt detrital organic matter accumulated more in lowlands than at higher altitudes with higher carbon and nitrogen contents found in river valleys carbon isotopes clearly differentiated between drier higher altitude or open pastoral sites more positive values and wetter forested sites more negative values nitrogen isotopes reflect anthropogenic human influence with elevated values around urban and intensively farmed sites and lower values characterising indigenous forests and pristine sites sulphur isotopes either show more positive values typical of fertilisers rain or sea spray in open pastoral sites or more negative values consistent with weathered geological sources such as metamorphic sulphides found in schist in some river valley sites the study demonstrates that regional isotope studies are a potential tool to understand the long and short term impacts on landscapes and may be useful for future mineral exploration urban health studies agricultural site remediation and land use control and regulation

studies of the rooiberg group bushveld complex south africa no evidence for an impact origin abstract it has been suggested that the bushveld complex of south africa could be the result of multiple large meteorite or comet impacts according to this hypothesis part of the lower rooiberg group which forms the roof of the complex represents a sheet of impact melt breccia and other impact breccias the present study is an attempt to test the viability of the impact hypothesis for the bushveld complex by interpreting newly acquired field geochemical petrographic and textural data for rooiberg group and associated rocks extensive field work throughout the rooiberg group and particularly at the contact between this unit and the underlying pretoria group metasediments has failed to identify any material that could be interpreted as impact related the rooiberg group is predominantly composed of individual volcanic flows and pyroclastic units representing several geochemically distinct magma types these volcanic units are interbedded with thin laterally extensive sedimentary units a few of which are sedimentary breccias the presence of needles of quartz that may represent paramorphs after tridymite in some rooiberg group units has been used as evidence to support the contention that these rocks represent superheated impact melt however quartz paramorphs after tridymite have been recognized in terrestrial volcanic provinces e g the north shore volcanic group in northeastern minnesota structural data including dips of rooiberg group strata suggest that the lobate shape of the complex which resembles several closely spaced ring features is the result of post rooiberg group deformation microdeformation features in quartz from bushveld related rocks do not satisfy the criteria of shock metamorphic planar deformation features pdfs which would be characteristic of impact induced shock pressures between 10 and 30 gpa these data especially the absence of macroscopic and microscopic evidence of shock deformation in pre bushveld rocks are inconsistent with formation of the bushveld complex by impact

preservation of primary stable isotope signatures of peat forming plants during early decomposition observation along an altitudinal transect abstract the preservation of the primary stable isotope compositions of peat forming plants in peat was tested along a short

geophysical and structural criteria for the identification of buried impact structures with reference to australia the discovery of large asteroid impact structures likely and possible impact structures onshore and offshore the australian continent woodleigh 120 km 360 ma gnargoo 75 km lower permian upper cretaceous tookoonooka 55 65 km 125 ma talundilly 84 km 125 ma mount ashmore 100 km end eocene and warburton twin structures 400 km pre end carboniferous requires re examination of the diagnostic criteria used for their identification bouguer anomalies of established impact structures chicxulub 170 km 64 98 0 05 ma woodleigh impact structure and gnargoo probable impact structure display a unique structural architecture where pre impact structural ridges are intersected and truncated by the outer ring of the circular structure seismic reflection data outline circular central uplift domes basement plugs and rim synclines sharp circular seismic tomography anomalies indicate low velocity columns under both the woodleigh impact structure and warburton probable impact hinting at deep crustal fracturing deformed curved and clouded intra crystalline planar deformation features in quartz qz pdfs displaying miller indices 10 11 10 12 10 13 diagnostic of shock metamorphism abound around exposed established impact structures vredefort 298 km 2023 4 ma sudbury 250 km 1850 3 ma charlevoix 54 km 342 15 ma manicouagan 100 km 214 1 ma tookoonooka and talundilly deformed qz pdfs allow recognition of shock metamorphism in buried impact structures where original qz pdfs were bent recrystallized and or clouded during formation of the central uplift and hydrothermal activity triggered by the impact planar deformation in quartz can also occur in explosive pyroclastic units but are limited to boehm lamella brazil twins with single lamella sets 0001 it has been suggested that a class of microstructures in quartz referred to as metamorphic deformation lamella qz mdl occur in endogenic tectonic metamorphic terrains however no type locality has been established for qz mdl of non impact origin

forcing of atlantic equatorial and subpolar millennial cycles by precession abundance cycles of the marine alga florisphaera profunda centered on a period of 7600 carbon 14 years 8400 calendar years are present in high resolution records from the equatorial atlantic spanning 0 to 45 000 years ago these cycles correlate with heinrich events 1 through 5 which document rapid changes in continental ice melting around the subpolar north atlantic these variations in f profunda are a direct response to modulation in zonal wind driven divergence produced by a precessional component of orbital variation during a time of reduced eccentricity modulation

a sequence stratigraphic investigation of a miocene formation supported by coal seam quality parameters central paratethys n hungary abstract a stratigraphic investigation of the coal bearing miocene siliciclastic succession in structurally dissected basins of northern hungary was performed based on log correlations and is supported by coal petrology and sulphur data the succession represents the karpatian lower order global eustatic cycle of the paratethys and was dissected into six higher order sedimentary sequences sq 1 sq 6 the coal bearing strata in the nograd basin sq 1 sq3 represent a lowstand systems tract lst prior to the karpatian relative sea level rise the transgressive systems tract tst starts with the oncophora beds sq 4 accumulated above a regional unconformity and containing coal beds in the borsod basin the tst is superimposed by tectonically forced higher order lowstand systems tracts sq 5 sq 6 containing coal beds only in the relatively elevated east borsod basin to support the sequence stratigraphic model the average maceral and sulphur content of coal seams was also interpreted the low sulphur 0 47 content in sq 1 reflects the lowstand environment determined by continental derived freshwater input transitional sulphur contents 0 66 1 02 in the late lowstand sq 2 and sq 3 indicate occasional saline invasions related to relative sea level rises high 2 3 2 6 sulphur contents in the tst sq 4 were caused by regular seawater inundations into the lagoon while decreasing sulphur contents in sq 5 and sq 6 2 28 2 09 reflect the increasing rate of freshwater income in association with the stepwise basinward shifts of the shoreline and the lagoonal facies within the lower to middle miocene salgotarjan lignite formation the analysis of coal seams contributed to the interpretation of relative sea level changes and the sequence stratigraphic context facilitated both the interpretation of sulphur content in coals and the reliable correlation of coal seams

possible solar origin of the 1 470 year glacial climate cycle demonstrated in a coupled model dansgaard oeschger events are rapid climate fluctuations that occurred during and at the end of the last ice age with remarkable regularity there were 23 such events between 110 000 and 23 000 years bp with a periodicity of 1 470 years identify the source of this cycle and it should be possible to say what triggered these events the sun had been excluded as a possible cause because of the lack of a 1 470 year spectral contribution in records of solar variability despite this braun et al present a new hypothesis that convincingly explains the 1 470 year period as the net result of two well known solar cycles the devries and gleissberg cycles with periods of 210 years and 87 years many palaeoclimate records from the north atlantic region show a pattern of rapid climate oscillations the so called dansgaard oeschger events with a quasi periodicity of 1 470 years for the late glacial period1 2 3 4 5 6 various hypotheses have been suggested to explain these rapid temperature shifts including internal oscillations in the climate system and external forcing possibly from the sun7 but whereas pronounced solar cycles of 87 and 210 years are well known8 9 10 11 12 a 1 470 year solar cycle has not been detected8 here we show that an intermediate complexity climate model with glacial climate conditions simulates rapid climate shifts similar to the dansgaard oeschger events with a spacing of 1 470 years when forced by periodic freshwater input into the north atlantic ocean in cycles of 87 and 210 years we attribute the robust 1 470 year response time to the superposition of the two shorter cycles together with strongly nonlinear dynamics and the long characteristic timescale of the thermohaline circulation for holocene conditions similar events do not occur we conclude that the glacial 1 470 year climate cycles could have been triggered by solar forcing despite the absence of a 1 470 year solar cycle

constraints on the late ediacaran sulfur cycle from carbonate associated sulfate we report new sulfur isotope compositions 34s in carbonate associated sulfate cas and pyrite from the lower nama group namibia 550 to 35 is highly unusual in earth history and in the terminal ediacaran is best explained by a high pyrite burial flux pyrite in the nama group is close in isotopic composition to coeval sulfate but the sulfur isotope fractionation between sulfate and pyrite varies widely among different studied basins suggesting highly heterogeneous redox and depositional conditions

mediterranean coccolith ecobiostratigraphy since the penultimate glacial the last 145 000 years and ecobioevent traceability abstract the mediterranean sea is a miniature ocean ideal to test the response of marine ecosystems to amplified orbital and suborbital climate changes here we present coccolith data from a sardinia channel gravity core arcose c 33 analysed over the last 145 000 years with a mean resolution of about 900 years the study highlights that regional phytoplankton assemblages underwent significant modifications between the penultimate glacial and the last interglacial as well as between the last glacial and the holocene the n ratio palaeoproductivity index suggests reduced productivity levels and the development of a deep nutricline during the last interglacial and the holocene within the last glacial period many taxa exhibit abundance fluctuations that parallel oscillations in 18 o values of globigerina bulloides tests heinrich events and stadials seem to be associated with drops in primary productivity levels as already observed in the alboran sea and the sicily channel a total of 19 ecobioevents were identified in the sardinia channel sediments including abundance fluctuations of emiliania huxleyi 4 m florisphaera profunda and gephyrocapsa oceanica the comparison of events across the mediterranean sea suggests that traceability applies to the sicily channel balearic and tyrrhenian seas supporting the adoption of a common ecobiostratigraphic scheme less certain is the correlation with the alboran sea although peaks of helicosphaera carteri and syracosphaera histrica during heinrich events and stadials suggest similar nutrient dynamics in response to suborbital climatic variations in the sicily channel southern tyrrhenian and alboran seas the traceability of events within eastern mediterranean cores is strongly limited possibly due to different physico chemical properties and nutrient dynamics

enso like forcing on oceanic primary production during the late pleistocene late pleistocene changes in oceanic primary productivity along the equator in the indian and pacific oceans are revealed by quantitative changes in nanoplankton communities preserved in nine deep sea cores we show that variations in equatorial productivity are primarily caused by glacial interglacial variability and by precession controlled changes in the east west thermocline slope of the indo pacific the precession controlled variations in productivity are linked to processes similar to the southern oscillation phenomenon and they precede changes in the oxygen isotopic ratio which indicates that they are not the result of ice sheet fluctuations the 30 000 year spectral peak in the tropical indo pacific ocean productivity records is also present in the antarctica atmospheric co2 record suggesting an important role for equatorial biological productivity in modifying atmospheric co2

proximal impact deposits at the cretaceous tertiary boundary in the gulf of mexico a restudy of dsdp leg 77 sites 536 and 540 restudy of deep sea drilling project sites 536 and 540 in the southeast gulf of mexico gives evidence for a giant wave at cretaceous tertiary boundary time five units are recognized 1 cenomanian limestone underlies a hiatus in which the five highest cretaceous stages are missing possibly because of catastrophic k t erosion 2 pebbly mudstone 45 m thick represents a submarine landslide possibly of k t age 3 current bedded sandstone more than 2 5 m thick contains anomalous iridium tektite glass and shocked quartz it is interpreted as ejecta from a nearby impact crater reworked on the deep sea floor by the resulting tsunami 4 a 50 cm interval of calcareous mudstone containing small cretaceous planktic foraminifera and the ir peak is interpreted as the silt size fraction of the cretaceous material suspended by the impact generated wave 5 calcareous mudstone with basal tertiary forams and the uppermost tail of the ir anomaly overlies the disturbed interval dating the impact and wave event as k t boundary age like beloc in haiti and mimbral in mexico sites 536 and 540 are consistent with a large k t age impact at the nearby chicxulub crater

dynamic deformation of volcanic ejecta from the toba caldera possible relevance to cretaceous tertiary boundary phenomena plagioclase and biotite phenocrysts in ignimbrites erupted from the toba caldera sumatra show microstructures and textures indicative of shock stress levels higher than 10 gpa strong dynamic deformation has resulted in intense kinking in biotite and with increasing shock intensity the development of plagioclase of planar features shock mosaicism incipient recrystallization and possible partial melting microstructures in quartz indicative of strong shock deformation are rare however and many shock lamellae if formed may have healed during post shock residence in the hot ignimbrite they might be preserved in ash falls peak shock stresses from explosive silicic volcanism and other endogenous processes may be high and if so would obviate the need for extraterrestrial impacts to produce all dynamically deformed structures possibly including shock features observed near the cretaceous tertiary boundary 38 references 3 figures

a 1400 year high resolution record of atmospheric circulation over the north atlantic and asia major ion series developed from new subannual scale sampling of an ice core from central greenland are calibrated with instrumental series of atmospheric sea level pressure recording major marine icelandic low and terrestrial siberian high atmospheric circulation systems to provide proxy records of atmospheric circulation over the past 1400 years examination of the proxy records reveals major changes in behaviour of these systems c ad 1400 multidecadal and centennial scale periodic components characterization of mean sea level pressure anomaly fields during the little ice age and the mediaeval warm period the potential role of solar forcing coupled ocean atmosphere associations and a perspective within which the characteristics of instrumental era climate can be assessed

comment on searching for giant ancient impact structures on earth the mesoarchaean maniitsoq structure west greenland by garde et al earth planet sci lett 337 338 2012 197 210

sulfur isotopic variations in low sulfur coals from the rocky mountain region abstract the isotopic composition of organic sulfur and disseminated and massive pyrite has been determined in vertical sections from eight low sulfur coals paleocene and cretaceous in age in four coal fields of wyoming and colorado the 34 s values of organic sulfur from five sites in the anderson wyodak coal paleocene of the eastern powder river basin wyoming are more negative than expected for low sulfur coals 18 7 to 3 9 suggesting that organic sulfur was derived from a combination of original plant sulfur and secondary 34 s depleted sulfur the 34 s depleted sulfur was probably produced from bacterial reduction of sulfate which infiltrated from the top and bottom during the peat stage the 34 s of organic sulfur in a paleocene coal from the hanna basin wyoming ranges from 1 6 to 13 1 vertical variation in 34 s here suggests bacterial reduction in a partially closed system of sulfate which infiltrated from the top of the seam a paleocene and a cretaceous coal from the green river coal region in wyoming and colorado both yield 34 s values of organic sulfur 2 4 to 8 1 consistent with what would be expected for original plant sulfur 34 s values of pyrite at all sites varies widely 52 6 to 34 6 the isotope composition of the disseminated pyrite correlates with that of the organic sulfur implying a similar mode and timing of incorporation 34 s of the massive pyrite shows no such correlation

abrupt temperature changes in the western mediterranean over the past 250 000 years a continuous high resolution western mediterranean sea surface temperature sst alkenone record spanning the past 250 000 years shows that abrupt changes were more common at warming than at cooling during marine isotope stage mis 6 sst oscillated following a stadial interstadial pattern but at lower intensities and rates of change than in the dansgaard oeschger events of mis 3 some of the most prominent events occurred over miss 5 and 7 after prolonged warm periods of high stability climate during the whole period was predominantly maintained in interglacial interstadial conditions whereas the duration of stadials was much shorter

δ34s and δ33s records of paleozoic seawater sulfate based on the analysis of carbonate associated sulfate abstract this study updates the 34s and 33s temporal records of paleozoic and early mesozoic seawater sulfate using analysis of carbonate associated sulfate of biogenic and whole rock carbonate the time resolution of carbonate samples studied here is on the order of millions of years which is longer than the timescale for homogenization of seawater sulfate sulfur one tenth of a million years but is comparable to the timescale for isotope evolution of sulfate in the oceans this 34s record confirms the long term decreasing trend that is discernible over the 250 million year timescale of sampling and the 33s record of seawater sulfate for the paleozoic is consistent with an average value of 0 002 0 004 2 540 251 ma that is distinct from the positive 33s observed today and inferred for the rest of the cenozoic both 34s and 33s records of seawater sulfate suggest the presence of shorter timescale variations that occur on timescales of tens of millions of years arguably driven by changes in intensity of sulfide oxidation in cycling of sulfur and or by rapid changes in sulfur influx to the oceans and its associated sulfur isotopes the permian triassic boundary marks a transition in co trajectories of 34s and 33s from in phase to anti phase the biogeochemical forcing that causes this is unclear this newly calibrated record remains consistent with an earlier assertion wu et al 2010 that the sulfur isotope fractionation 34ssw py between oceanic sulfate 34ssw and coeval sedimentary pyrite 34spy was smaller during the paleozoic than in the cenozoic and reached lowest values during the carboniferous the 34sin and 33sin estimates of influx sulfur to the oceans afforded by the isotope mass balance model for each geologic period throughout the paleozoic reveal a change from higher positive values of 34sin more negative values of 33sin approximately 0 030 to lower positive values of 34sin slightly negative values of 33sin approximately 0 003 this change is interpreted to reflect the evolution of the earth surface sulfur pool and the rapid recycling of newly formed evaporite sulfate minerals as arguably supported by our estimates of integrated erosion rates over geologic time for pyrite and evaporite 6 1 6 4 10 9 a 1 and 7 7 7 8 10 9 a 1 respectively

protracted development of bioturbation through the early palaeozoic era mobile organisms first appeared in the fossil record prior to the precambrian cambrian transition sediment textures indicate that the degree of sediment mixing by animal activity remained low for 120 million years following the transition

coccolithophores in the equatorial atlantic ocean response to seasonal and late quaternary surface water variability abstract the present study was initiated to ascertain the significance of coccolithophores as a proxy for paleoceanographic and paleoproductivity studies in the equatorial atlantic data from a range of different samples from the plankton surface sediments as well as sediment cores are shown and compared with each other in general the living coccolithophores in the surface and subsurface waters show considerable variation in cell numbers and distribution patterns cell densities reached a maximum of up to 300 103 coccospheres l in the upwelling area of the equatorial atlantic here emiliania huxleyi is the dominant species with relatively high cell numbers whereas umbellosphaera irregularis and umbellosphaera tenuis are characteristic for oligotrophic surface waters although they are observed in high relative abundances these species only occur in low absolute numbers the lower photic zone is dominated by high abundances and considerable cell numbers of florisphaera profunda the geographical distribution pattern of coccoliths in surface sediments reflects the conditions of the overlying surface water masses however abundances of the oligotrophic species umbellosphaera irregularis and umbellosphaera tenuis are strongly diminished causing an increase in relative abundance of the lower photic zone taxa florisphaera profunda and gladiolithus flabellatus during the past 140 000 years the surface water circulation of the equatorial atlantic has changed drastically as can be seen from changes in the coccolithophore species composition absolute coccolith numbers as well as coccolith accumulation rates significant increases in coccolith numbers and accumulation rates is observed in the southern equatorial atlantic during the last glacial interval oxygen isotope stages 2 4 which we attribute to enhanced upwelling intensities and advection of cool nutrient rich waters at this site in the western equatorial atlantic we observe an opposite trend with decreasing numbers of coccoliths during glacial periods which probably is caused by a deepening of the thermocline

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

coccolithophore export production in guaymas basin gulf of california response to climate forcing abstract the flux and taxonomic composition of coccolithophores has been determined for sediment trap samples collected over a two year period from guaymas basin central gulf of california the gulf of california is a subtropical marginal sea with exceptionally high rates of primary productivity the annual biogenic sediment fluxes are largely dominated by silica with diatoms as the major contributor to the opal flux for the july 1990 through november 1992 study period the total coccolithophore export production in guaymas varied in response to the strength of el nino southern oscillation enso coccolithophore production follows the general surface primary productivity pattern with relatively high fluxes from late fall to late winter and low production in the summer when the water column is highly stratified and nutrient depleted high fluxes of up to 10 9 coccoliths m 2 day 1 and 3 10 6 coccospheres m 2 day 1 indicate that coccolithophores are an important component of the phytoplankton population in guaymas basin the intensification of enso conditions during 1992 altered the typical hydrography of the gulf of california by increasing sst and reducing the strength of spring upwelling this is reflected in reduced opal and diatom fluxes during this period conversely these more oligotrophic conditions resulted in higher total coccolithophore fluxes during spring and summer 1992 gephyrocapsa oceanica is present in the gulf throughout the study period but is dominant during weak or non enso times emiliania huxleyi and to a lesser degree florisphaera profunda are abundant during strong enso periods two major coccolithophore signals are indicative of strong enso conditions and could be used as paleo enso indicators in the gulf of california a the switch in dominance between g oceanica and e huxleyi and b high abundances of the deep dwelling species f profunda the abundance of this latter species shows a strong inverse relationship with opal fluxes a comparison of the annual coccolith flux with coccolith accumulation rates in the surface sediments indicates that only about 10 20 of the coccolith export production is preserved in the anoxic sediments of guaymas basin this very low level of preservation is probably due to bacterial processes on the sea floor which cause acidification of the bottom waters at the sediment water interface coccolith accumulation rates are higher in surface sediments from the western coast of the central gulf suggesting both higher coccolithophore production and better preservation in this region probably associated with lower diatom production tintinnids which agglutinate coccoliths are strongly selective for both coccolith size and species

microscopic lamellar deformation features in quartz discriminative characteristics of shock generated varieties the appearance and orientation of microscopic lamellar deformation features in quartz have been examined in samples from different geologic environments lamellar deformation features from known shock and or impact environments are sharp parallel closely spaced and tend to extend in a continuous manner across entire grains they have specific well documented orientations and occur in multiple sets per grain lamellar deformation features from other geologic environments including tectonic and explosive volcanic only superficially resemble shock features they are generally less well defined slightly curved wider spaced and tend to extend in a discontinuous manner across parts of grains they have relatively random orientations only some of which correspond to known shock orientations and generally occur as single sets per grain on the basis of these observations we conclude that there is a characteristic set of microscopic deformation features produced in quartz by shock these so called planar features differ from microscopic lamellar deformation features produced by other dynamic processes therefore the case for the formation of characteristic planar features in quartz by natural processes other than impact is still not proven