seismic stratigraphy and sedimentary processes at the norwegian sea margin northeast of the faeroe islands abstract sedimentary processes on the continental slope north of the faeroe islands during the cenozoic were studied in detail using high resolution multichannel reflection seismic data a wedge shaped succession of cenozoic sediments with a maximum thickness of approximately 2 km overlies the basaltic basement which forms the underlying structure of the slope the sedimentary succession represents four depositional sequences and a contourite deposition also some slump deposits are recognised the oldest sequence which is possibly of eocene late oligocene age was prone to repeated mass movements during the deposition of the sequence at the end of the oligocene the sediments on the slope stabilised and the depositional pattern was strongly influenced by sea level changes in the late pliocene a renewed instability of the slope occurred resulting in mass movements causing erosion at the middle of the slope and creating a major slide escarpment at the base of the slope subsequently the sedimentary processes change from mainly downslope progradational forms to along slope current induced contourite deposition this change most likely marks the formation of a norwegian sea deep water current pattern similar to the present variations of the current strength and sediment supply caused by glacial interglacial cycles probably results in an alternating sedimentation pattern of the contourite deposit another impact from the glaciation of the northern hemisphere is the presence of iceberg turbate at the upper parts of the northeastern faeroes slope

late quaternary sedimentary processes and ocean circulation changes at the southeast greenland margin a study has been made of late quaternary depositional processes and bottom current activity on the southeast greenland margin using seismic sub bottom profiling and deep tow side scan sonar data as well as sediment core information the seabed data demonstrate the occurrence of strong southerly bottom currents prevailing on the slope and rise well defined longitudinal bedforms indicate maximum mean near bottom current velocities of up to at least 1 0 m s at the depth stratum of labrador sea water 800 1500 m similarly strong currents occur in denmark strait overflow water dsow at the base of the slope whereas more basinward the maximum dsow flow speed is lower iceberg plow marks were found down to about 700 m water depth both at the shelf edge and on the lower slope and rise the seafloor morphology is indicative of downslope sediment transport and mass flow deposition which is concluded to be a typically glacial feature after generally more sluggish deep water circulation during the last glacial maximum dsow basin ventilation was re established shortly before 13 3 ka on the shelf in front of the retreating greenland ice margin permanent or semi permanent sea ice conditions prevailed until about 12 5 ka at that time increased irminger current activity had resulted in warming and east greenland current egc controlled iceberg drift increased no evidence was found for a return to extreme glacial conditions or a ceasing of dsow flow during the younger dryas abundant coarse ird collected at greater water depth from shallow sub seabed strata has a provenance mainly in the northern part of east greenland 68 73 n which demonstrates the existence of a pre holocene egc system initially extending to beyond the shelf edge

modelled atmospheric temperatures and global sea levels over the past million years the climate has passed through a series of glacials and interglacials over the past million years but the nature of this cyclicity in terms of temperature ice volume and sea level and the underlying causes are not well known bintanja et al use a new method to deduce a one million year time series of these variables the reconstructed records are much longer than other methods have provided for any of these variables individually the most intense glacial stages were 17 c colder than today and most of the continental ice was present in north america strong cooling in the beginning of glacials was found to precede ice sheet build up these findings may shed light on the causes of ice age cycles marine records of sediment oxygen isotope compositions show that the earth s climate has gone through a succession of glacial and interglacial periods during the past million years but the interpretation of the oxygen isotope records is complicated because both isotope storage in ice sheets and deep water temperature affect the recorded isotopic composition1 2 3 4 5 separating these two effects would require long records of either sea level or deep ocean temperature which are currently not available here we use a coupled model of the northern hemisphere ice sheets6 and ocean temperatures forced to match an oxygen isotope record for the past million years compiled from 57 globally distributed sediment cores to quantify both contributions simultaneously we find that the ice sheet contribution to the variability in oxygen isotope composition varied from ten per cent in the beginning of glacial periods to sixty per cent at glacial maxima suggesting that strong ocean cooling preceded slow ice sheet build up the model yields mutually consistent time series of continental mean surface temperatures between 40 and 80 n ice volume and global sea level we find that during extreme glacial stages air temperatures were 17 1 8 c lower than present with a 120 10 m sea level equivalent of continental ice present

hydrothermally altered impact melt rock and breccia contributions to the soil of mars samples of melt rock and breccia from 12 terrestrial impact craters were examined to identify alteration minerals and their conditions of formation the dominant assemblage in most cases is clay silica k feldspar zeolite indicating hydrothermal alteration at low pressures and temperatures of 100 300 c the clays are predominantly fe chlorites and smectites in most cases depleted in al and enriched in fe and mg relative to their source rocks alteration of impact glass is often complete while alteration of crystalling melt rock is limited to a few percent of the rock volume impact breccia is altered to only a small extent compared to the alteration of glass impact induced hydrothermal alteration is to be expected at martian impact sites if significant quantities of ground ice and or water are present the alteration products are likely to resemble the clays found at terrestrial craters al fe fractionation similar to that observed on earth is strongly suggested by the viking soil analyses the quantitative contribution of hydrothermal clays to the soil of mars is estimated based on a model which predicts the generation of the equivalent of a 61 m thick blanket of impact melt planet wide the inefficiency of melt production in small craters and the inefficiency of alteration in large craters limit the expected production of clay to a few percent of this figure clays produced by impact induced hydrothermal alteration may be expected to contribute to the fines on mars but this contribution is probably not dominant relative to other suggested sources

lithogeochemical patterns related to sedex mineralization sudbury basin canada abstract distal sediments stratigraphically equivalent to sedex zn cu pb deposits at the base of the proterozoic onwatin argillite formation sudbury basin are depleted in s and enriched in mn occurring as kutnohorite manganosiderite and spessartine and in ba in the form of the k ba feldspar hyalophane fluid inclusion data indicate deposition of the distal sediments at 125 c and of the sedex carbonate gangue at 170 c the overlying onwatin argillites deposited at 60 c are characterized by a distinctive pattern of s c org 0 36 indicative of diagenetic s alternating with s c org 0 36 probably reflecting episodic expulsion of s bearing fluids into the water column during the waning stages of hydrothermal activity similar to the s c org pattern are patterns of rhythmically alternating low and high zn pb as re ni and pd values in the onwatin argillite coinciding with the onset of hydrothermal activity 34 s values in pyrite decrease abruptly from 7 at the top of the onaping formation to 3 at the base of the overlying onwatin argillites 13 c values in the carbonate gangue of the sedex deposits 8 9 to 2 4 lie in or close to the range for magmatic carbon in contrast to values of 18 7 to 14 9 in carbonate derived by oxidation of organic carbon in the overlying and underlying rocks low 34 s values in the sedex deposits and basal onwatin rocks and enrichment of the onwatin argillite in s ni re and pd suggest derivation of these metals at least part of the s and possibly cu zn pb from the magmatic ni cu ores and or associated sudbury igneous complex which probably also provided the energy to drive the convective exhalative system responsible for the sedex mineralization the model implies potential for further sedex deposits along the 110 km of the onwatin onaping contact

chicxulub testing for post impact hydrothermal input into the tertiary ocean studies of large terrestrial impact craters indicate that post impact hydrothermal activity is a likely consequence of the crustal deformation and heating induced by such events in the case of the chicxulub basin where marine conditions were re established soon after the impact significant fluxing of seawater through the crust and hydrothermal venting into the water column might be anticipated we have carried out geochemical analyses of tertiary carbonate sediments within the yaxcopoil 1 yax 1 drill hole to test for evidence of such post impact hydrothermal circulation hydrothermal activity is most likely to be found close to thick layers of melt rock inside the collapsed transient cavity and it is estimated that yax 1 is located 20 km outside this cavity consequently the most likely signature of hydrothermal venting into the water column would be geochemical anomalies attributable to fallout of suspended particulate matter from a submarine hydrothermal plume samples of tertiary biomicrites from depths of 794 01 to 777 02 m have high concentrations of manganese iron phosphorous titanium and aluminium and low iron manganese ratios relative to samples from higher in the stratigraphic succession this geochemical anomaly decreases fairly systematically between 793 13 m and 777 02 m above which an abrupt change in geochemistry is observed a mass balance calculation suggests that the anomaly is unlikely to be the result of a decreasing detrital input to the carbonate sediments and the nature of the element enrichments is consistent with expectations for fallout from a distal hydrothermal plume we conclude that a postimpact hydrothermal system did develop at chicxulub which led to the expulsion of hydrothermal fluids into the tertiary water column preliminary biostratigraphic and magnetostratigraphic dating on yax 1 core suggest that this hydrothermal activity lasted for at least 300 ka

distribution characteristics and controlling factors of vertical joint spacing in sand mud interbedded strata abstract nearly 3 600 vertical joints were measured in sand mud interbedded rock masses from 30 outcrops in the yan an area china information such as joint spacing joint aperture and the thickness of sandstone formations was obtained results show that the vertical joints are well developed in the study areas and the fracture spacing tolayer thickness ratio s t can reach 0 79 the joint spacing has a strong positive linear relationship with the thickness of the sandstone layer and presents a lognormal distribution in each sandstone layer however the morphology of the lognormal distribution is related to the degree of joint development the higher the degree of joint development the smaller skewness of the joint spacing distribution in addition although the value of s t for saturate joint is generally 0 8 1 2 the vertical joints may reach saturation at greater s t by penetrating multiple layers of sandstone when the intervening soft layer is thin

retreat patterns and dynamics of the sentralbankrenna glacial system central barents sea accepted manuscript version published version available at https doi org 10 1016 j quascirev 2017 06 004 accepted manuscript version licensed cc by nc nd 4 0

impact induced hydrothermal activity within the haughton impact structure arctic canada generation of a transient warm wet oasis field studies and analytical scanning electron microscopy indicate that a hydrothermal system was created by the interaction of water with hot impact generated rocks following formation of the 24 km diameter 23 ma haughton impact structure hydrothermal alteration is recognized in two settings within polymict impact breccias overlying the central portion of the structure and within localized pipes in impact generated concentric fault systems the intra breccia alteration comprises three varieties of cavity and fracture filling a sulfide with carbonate b sulfate and c carbonate these are accompanied by subordinate celestite barite fluorite quartz and marcasite selenite is also developed particularly in the lower levels of the impact breccia sheet the fault related hydrothermal alteration occurs in 1 7 m diameter subvertical pipes that are exposed for lengths of up 20 m the pipes are defined by a monomict quartz carbonate breccia showing pronounced fe hydroxide alteration associated sulfides include marcasite pyrite and chalcopyrite we propose three distinct stages in the evolution of the hydrothermal system 1 early stage 200 c with the precipitation of quartz vapor phase dominated 2 main stage 200 100 c with the development of a two phase vapor plus liquid zone leading to calcite celestite barite marcasite and fluorite precipitation and 3 late stage 100 c with selenite and fibroferrite development through liquid phase dominated precipitation we estimate that it took several tens of thousands of years to cool below 50 c following impact during this time haughton supported a 14 km diameter crater lake and subsurface water system providing a warmer wetter niche relative to the surrounding terrain the results reveal how understanding the internal structure of impact craters is necessary in order to determine their plumbing and cooling systems

fluxes to sediments underlying the rainbow hydrothermal plume at 36 14 n on the mid atlantic ridge abstract a geochemical investigation has been conducted of a suite of four sediment cores collected from directly beneath the hydrothermal plume at distances of 2 to 25 km from the rainbow hydrothermal field as well as a large biogenic component 80 caco3 these sediments record clear enrichments of the elements fe cu mn v p and as from hydrothermal plume fallout but only minor detrital background material systematic variations in the abundances of hydrothermal elements are observed at increasing distance from the vent site consistent with chemical evolution of the dispersing plume further pronounced ni and cr enrichments at specific levels within each of the two cores collected from closest to the vent site are indicative of discrete episodes of additional input of ultrabasic material at these two near field locations radiocarbon dating reveals mean holocene accumulation rates for all four cores of 2 7 to 3 7 cm kyr 1 with surface mixed layers 7 to 10 cm thick from which a history of deposition from the rainbow hydrothermal plume can be deduced deposition from the plume supplies elements to the underlying sediments that are either directly hydrothermally sourced e g fe mn cu or scavenged from seawater via the hydrothermal plume e g v p as holocene fluxes into to the cores surface mixed layers are presented which typically are an order of magnitude greater than background authigenic fluxes from the open north atlantic one core collected closest to the vent site indicates that both the concentration and flux of hydrothermally derived material increased significantly at some point between 8 and 12 14c kyr ago the preferred explanation is that this variation reflects the initiation intensification of hydrothermal venting at the rainbow hydrothermal field at this time perhaps linked to some specific tectonic event in this fault controlled hydrothermal setting

is the transition impact to post impact rock complete some remarks based on xrf scanning electron microprobe and thin section analyses of the yaxcopoil 1 core in the chicxulub crater the transition from impact to post impact rocks in the yaxcopoil 1 core is marked by a 2 cm thick clay layer characterized by dissolution features the clay overlies a 9 cm thick hardground overlying a 66 cm thick crossbedded unit consisting of dolomite sandstone alternating with thin micro conglomerate layers with litho and bioclasts and the altered remains of impact glass now smectite the micro conglomerates mark erosion surfaces microprobe and backscatter sem analysis of the dolomite rhombs show an early diagenetic complex zoned idiomorphic overgrowth with mn rich zones possibly formed by hot fluids related to cooling melt sheet in the crater the pore spaces are filled with several generations of coelestite barite k feldpar and sparry calcite xrf core scanning analysis detected high mn values in the crossbedded sediments but no anomalous enrichment of the siderophile elements cr co fe and ni in the clay layer shocked quartz occurs in the crossbedded unit but is absent in the clay layer the basal paleocene marls are strongly dissolved and do not contain a basal paleocene fauna the presence of a hardground the lack of siderophile elements shocked quartz or ni rich spinels in the clay layer and the absence of basal paleocene biozones p0 and pa all suggest that the top of the ejecta sequence and a significant part of the lower paleocene is missing due to the high energy sedimentation infill a hiatus at the top of the impactite is not unexpected but there is nothing in the biostratigraphy geochemistry and petrology of the yaxcopoil 1 core that can be used to argue against the synchroneity of the end cretaceous mass extinctions and the chicxulub crater

hf zr and ree partition coefficients between ilmenite and liquid implications for lunar petrogenesis hf zr and ree partition coefficients between ilmenite and coexisting liquid were determined under near lunar conditions ilmenite was synthesized at 1125 c under low oxygen fugacity fo2 10 12 4 from glass of a high ti mare basalt composition doped with 50 100 g g of ree and hf and 500 1000 g g of zr the partition coefficients d of ilmenite for hf and zr obtained by isotope dilution analysis are 0 41 and 0 33 respectively these values are significantly lower than those of ilmenite 3 0 and 1 8 respectively from a kimberlite megacryst fujimaki et al 1984a dree for the synthesized ilmenite are slightly smaller than those of ilmenite from the kimberlite megacryst and the dlu is 0 056 these results suggest that ilmenite may have played an important role in the lu hf evolution of lunar mare basalts using newly determined dlu and dhf for ilmenite the lu hf evolution or lunar cumulates and the coexisting magma was examined for several different crystallization sequences by a model calculation the lu hf variation trend of most high ti mare basalts is well explained by a small degree less than 5 of partial melting of the cumulates however a higher degree of partial melting is required to explain the variation of very low ti basalts green glass and apollo 12 low ti basalts apollo 15 low ti basalts could not be produced by simple partial melting but may require chromite crystallization as well

gale crater and impact processes curiosity s first 364 sols on mars abstract impact processes at all scales have been involved in the formation and subsequent evolution of gale crater small impact craters in the vicinity of the curiosity msl landing site and rover traverse during the 364 sols after landing have been studied both from orbit and the surface evidence for the effect of impacts on basement outcrops may include loose blocks of sandstone and conglomerate and disrupted fractured sedimentary layers which are not obviously displaced by erosion impact ejecta blankets are likely to be present but in the absence of distinct glass or impact melt phases are difficult to distinguish from sedimentary volcaniclastic breccia and conglomerate deposits the occurrence of individual blocks with diverse petrological characteristics including igneous textures have been identified across the surface of bradbury rise and some of these blocks may represent distal ejecta from larger craters in the vicinity of gale distal ejecta may also occur in the form of impact spherules identified in the sediments and drift material possible examples of impactites in the form of shatter cones shocked rocks and ropy textured fragments of materials that may have been molten have been observed but cannot be uniquely confirmed modification by aeolian processes of craters smaller than 40 m in diameter observed in this study are indicated by erosion of crater rims and infill of craters with aeolian and airfall dust deposits estimates for resurfacing suggest that craters less than 15 m in diameter may represent steady state between production and destruction the smallest candidate impact crater observed is 0 6 m in diameter the observed crater record and other data are consistent with a resurfacing rate of the order of 10 mm myr considerably greater than the rate from impact cratering alone but remarkably lower than terrestrial erosion rates

a slope movement in a complex rock formation deformation measurements and dem modelling abstract the case history of a deep seated slope movement in a complex rock formation marly arenaceous formation is analyzed the movement monitored for more than 20 years was recognized after the discovery of intense cracking in the concrete lining of a hydraulic tunnel running across the slope the time history of displacements shows that the ongoing deformation process is essentially a stationary creep phenomenon also influenced by transient variations in pore pressure distribution the shearing zone is mainly formed by tectonized clay gouge and is characterized by a mobilized strength close to residual the slope has been modelled by dem approach as a complex blocky structure defined by several joint sets bedding planes inclined and sub vertical joints different hypotheses about the geometry of the slip surface compatible with field evidences are discussed as well as their influence on the critical friction angle of the slope the type of model adopted for rock mass with continuous or staggered joints influences the pre failure deformation mode but the failure conditions are not as much affected finally the response of dem models to the increase in water level at the toe of the slope and to the rise of the groundwater table inside the slope has been analyzed the results of simplified models without flow calculation and coupled hydro mechanical analyses are compared finding some relevant differences

fluidization and hydrothermal alteration of the suevite deposit at the ries crater west germany and implications for mars the formation cooling and alteration of the impact ejecta deposits at the ries crater are an analog for impact processes and the formation of regoliths and soils on mars we have studied the suevite deposit an impact melt bearing breccia found outside of the crater rim this suevite contains large numbers of chimney like degassing pipes apparently formed by high gas pressures in the hot 500 c fluidized suevite immediately after deposition of the suevite the likely sources of the gas are volatiles from the melted and shocked basement inclusions the suevite outside of the crater rim contains about 15 wt clay indicating a large amount of alteration of the suevite the clay is an fe rich montmorillonite with less than 5 interstratified illite indicating that the temperature at which most of the alteration occurred was less than 100 130 c the duration of this low temperature period may have been extended by additional heating from the exothermal alteration reactions the surfaces of the degassing pipes are not altered to clays however but have a thin fe rich oxide or hydroxide coating the absence of alteration in the pipes suggests that the main alteration event outside the crater occurred under unsaturated conditions such that the walls of the pipes were dry suevite deposits are likely to exist on mars because of the presence of volatile rich target rock martian suevites may have also been fluidized and hydrothermally altered contributing significantly to the formation of the clay like phases inferred to exist in the martian soil

seabed erosion on the lomonosov ridge central arctic ocean a tale of deep draft icebergs in the eurasia basin and the influence of atlantic water inflow on iceberg motion 1 the submarine lomonosov ridge which bisects the arctic ocean is covered by 450 m of hemipelagic sediments high resolution chirp sonar and side scan data have documented erosion of a section of the ridge here we present multichannel seismic and chirp sonar data which show removal of unconsolidated sediments along the eurasia basin side of the lomonosov ridge where the central ridge is shallower than 1000 m the incomplete erosion of the hemipelagic drape and probable topographic control of ice motion suggest that the deepest draft glacier ice which reached the central arctic ocean from the eurasia basin was in the form of armadas of large icebergs embedded in sea ice rather than a single continuous floating ice shelf massive rapid discharge of glacier ice was probably required to produce the deepest draft 800 m icebergs eastward and northward drift trajectories from a likely iceberg source area on the kara barents sea margin would reflect the relative strength of atlantic inflow through the fram strait however only icebergs with drafts exceeding bathymetric thresholds on the lomonosov ridge would leave an erosive imprint on the seabed advection of atlantic water may have been relatively strong at times of discharge from the saalian ice sheet icebergs exiting the arctic ocean caused massive erosion and redeposition of the hemipelagic sediments on top of yermak plateau

relict sea floor ploughmarks record deep keeled antarctic icebergs to 45 s on the argentine margin abstract this paper reports ploughmarks on the argentine continental margin up to 44 50 s the most northerly morphological evidence of giant icebergs in the southern atlantic more than 2500 ploughmarks up to 32 km long 685 m wide and more than 20 m deep have been observed at modern water depths up to 646 m taking into account these iceberg sizes and ocean current directions which appear to have remained similar from the last full glacial to the present interglacial the icebergs that produced the ploughmarks are interpreted to be calved from fast flowing ice streams draining huge basins of the west antarctic ice sheet and the western antarctic peninsula during the last glacial maximum lgm about 20 000 years ago ploughmarks at the deepest water depths correspond to icebergs more than 500 m thick and at least 2 km wide given a sea level rise of 120 m since the lgm the icebergs after having drifted northeast in the antarctic circumpolar current were transported northward by the falklands malvinas current a total distance of 2000 to 4000 km the waters north of the falkland islands in particular were probably several degrees colder than today to prevent rapid iceberg melting and deterioration

constraints on the greenland ice sheet since the last glacial maximum from sea level observations and glacial rebound models abstract geomorphological descriptions of changes in the extent of the greenland ice sheet gis have been combined with glacial isostatic adjustment models to reproduce the sea level history of greenland since the last glacial maximum lgm the contribution to past sea level change around greenland due to ice load changes outside of that region has been considerable 10 s of meters while still contributing a rise of several mm yr 1 today the isostatic contribution to relative sea level around greenland from changes in the gis is found by iteratively perturbing preliminary ice models with different lgm extents and deglaciation starting times the resulting first order model that provides the best agreement between observed and predicted sea level contributes 3 1 and 1 9 m water equivalent of additional ice relative to present day ice volumes at the lgm and younger dryas respectively the gis in most areas does not appear to have extended far onto the continental shelf the exceptions being southern most southwest greenland and northern east greenland as well as at the coalescence of the northwest greenland and innuitian ice sheets changes in ice thickness since the lgm were 500 m along the present day outer coast and 1500 m along some parts of the present day ice margin the observed mid to late holocene fall in sea level to below the present day level and the subsequent transgression seen in some areas implies that the gis retreated behind the present day margin by distances of the order of 40 km before readvancing

mobile element analysis by secondary ion mass spectrometry sims of impactite matrix samples from the yaxcopoil 1 drill core in the chicxulub impact structure the concentrations of the fluid mobile trace elements lithium beryllium boron and barium were measured in samples of the altered matrix of several impactite breccias of the yaxcopoil 1 drill core using secondary ion mass spectrometry sims to determine the extent of transport due to aqueous or hydrothermal processes three of the elements li be and b have higher concentrations in the upper suevite impact breccias than in the lower impact melt deposits by factors of 3 5 2 2 and 1 5 respectively lithium and b are the most enriched elements up section and appear to have had the greatest mobility the similar fractionation of li and b is consistent with fluid transport and alteration under low temperature conditions of less than 150 c based on published experimental studies in contrast to li be and b the concentration of ba in the altered matrix materials decreases upward in the section and the concentration of ba in the matrix is an order of magnitude less than the bulk concentrations likely due to the presence of barite the origin of the elemental variations with depth may be related to different protolith compositions in the upper versus the lower impactite units a different protolith in the altered matrix is suggested by the mg rich composition of the lower units versus the al rich composition of the upper units which largely correlates with the mobile element variations the possibility that vertical transport of mobile elements is due to a postimpact hydrothermal system is supported by published data showing that the sediments immediately overlying the impactites are enriched in mobile elements derived from a hydrothermal system however the mobile elements in the sediments do not have to originate from the underlying impactites in conclusion our data suggests that the impactites at this location did not experience extensive high temperature hydrothermal processing and that only limited transport of some elements including li be and b occurred

geophysical evidence of deep keeled icebergs on the rockall bank northeast atlantic ocean high resolution multibeam swath bathymetric data acquired from the rockall bank reveal an abundance of linear to slightly sinuous seabed incisions these features interpreted as relict iceberg scours provide for the first time evidence that the rockall bank was intensively scoured by iceberg keels while the shallower portion of the rockall bank lacks evidence of iceberg scouring on the western and southern flanks between 250 and 450 m water depth the seabed is almost completely covered by thousands of cross cutting scours more isolated scours up to 800 m wide and 25 km long are also observed down to nearly 600 m water depth based on a full glacial sea level low stand of 120 m these isolated scour marks must have been carved bygigantic icebergs with keels up to 500 m deep and able to create incisions up to 15 m deep in the seabed analysis of scour orientation length width and depth indicates that these mega icebergs were likely calved from large fast flowing ice sheet outlets draining circum north atlantic ice sheets prevailing scour orientations suggest a number of possible ice sheet sources including southeast and southern greenland and the donegal barra ice stream of the last british irish ice sheet the bimodal distribution of the scour depth observed across the rockall bank suggest either different icebergs provenances or physical and climatic controlson icebergs draft

discontinuity frequency and block volume distribution in rock masses abstract the discontinuity spacing density function is theoretically found by applying the first principles of the maximum entropy theory it is shown that this function is the negative exponential probability density function then the analytical relation between rqd and discontinuity frequency that may be derived provided that discontinuity sets follow the negative exponential model is validated against simulation data it is also found that if the discontinuity spacings follow the negative exponential distribution then the number of fractures per length measured along scanlines or drilled cores follow quite well the two parameter weibull distribution function subsequently following the methodology proposed originally by hudson and priest the closed form expression of block volume distribution in a rock mass transected by three mutually orthogonal discontinuity sets is found also the left truncated block volume proportion above a certain block volume size is found analytically the theoretical results referring to discontinuity frequency and block volume distributions are finally successfully validated against measurements carried out on drill cores and exposed walls in a dolomitic marble quarry the methodology presented herein can be applied to rock engineering applications that necessitate the characterization of rock mass discontinuities and discontinuity spacings are reasonably well represented by the negative exponential probability density function the proposed method for the prediction of marble block volume distribution was applied to data from a quarry from drill cores and scanlines on exposed quarry walls

magnetostratigraphy of the impact breccias and post impact carbonates from borehole yaxcopoil 1 chicxulub impact crater yucatan mexico we report the magnetostratigraphy of the sedimentary sequence between the impact breccias and the post impact carbonate sequence conducted on samples recovered by yaxcopoil 1 yax 1 samples of impact breccias show reverse polarities that span up to 56 cm into the post impact carbonate lithologies we correlate these breccias to those of pemex boreholes yucatan 6 and chicxulub 1 from which we tied our magnetostratigraphy to the radiometric age from a melt sample from the yucatan 6 borehole thin section analyses of the carbonate samples showed a significant amount of dark minerals and glass shards that we identified as the magnetic carriers therefore we propose that the mechanism of magnetic acquisition within the carbonate rocks for the interval studied is detrital remanent magnetism drm with these samples we constructed the scale of geomagnetic polarities where we find two polarities within the sequence a reverse polarity event within the impact breccias and the base of the post impact carbonate sequence up to 794 07 m and a normal polarity event in the last 20 cm of the interval studied the polarities recorded in the sequence analyzed are interpreted to span from chron 29r to 29n and we propose that the reverse polarity event lies within the 29r chron the magnetostratigraphy of the sequence studied shows that the horizon at 794 11 m deep interpreted as the k t boundary lies within the geomagnetic chron 29r which contains the k t boundary

giant iceberg plow marks at more than 1 km water depth offshore west greenland abstract during a recent 2006 cruise of rv dana high resolution side scan sonar and sub bottom profiling was carried out on selected shelf and slope transects offshore disko bugt central west greenland available commercial seismic data from the margin indicate here irregular seabed morphology with erosional features locally extending down to c 1100 m water depth the newly acquired side scan sonar data reveal the presence of giant iceberg plow marks extending sub parallel to the slope between about 800 and 1085 m water depth the height difference between bottom of the scours and rim crest is up to 40 m the largest plow marks are about 750 m wide to date no observed modern icebergs including those from antarctica have drafts in excess of c 500 m taking into account maximum glacial sea level lowering of c 120 m the paleo iceberg keel depth was at least 950 m due to the presence of the relatively shallow 1000 m and dimensions of the plow marks are concluded to be exceptional and comparable to glacial scouring features reported from the arctic ocean

impact melt sheet formation on mars and its implication for hydrothermal systems and exobiology abstract hydrothermal deposits are a prime exobiological research target on mars and impact craters are potentially a significant source for these deposits key factors in the longevity of terrestrial impact crater hydrothermal systems are the volume of shock melt produced and the degree to which this melt is quenched by mixing with un melted clasts mixing occurs when the shock melt is smeared along the crater floor and the degree of mixing is inversely proportional to the thickness of this smeared layer to investigate the potential development of thick melt sheets on mars we apply an analytical impact model to asteroid and long period lp comet impacts that produces martian craters with final diameters of 30 640 km we combine our model shock melt volumes with estimates of the surface area of the transient cavity to estimate initial shock melt thickness which we use as a proxy measure of the amount of mixing between shock melt and un melted clasts we calculate this shock melt thickness parameter for a range terrestrial craters with and without thick melt sheets from which we infer the melt sheet characteristics for the model mars craters the results demonstrate that most asteroid impacts on mars do not produce thick clast free melt sheets only asteroid impact craters 580 km in diameter on mars produce shock melt thicknesses comparable to earth s 200 km diameter sudbury crater and martian craters 65 km in diameter produce shock melt thicknesses comparable to terrestrial craters that lack melts sheets entirely lp comet impacts on mars are more likely to produce thick melt sheets lp comet impact craters 280 km in diameter on mars produce shock melt thicknesses comparable to that of the sudbury crater given that lp comet impacts on mars are rare compared to asteroid impacts we conclude that large long lived impact hydrothermal systems are likewise rare on mars comparisons of the mars asteroid impact rate with the potential longevity of impact hydrothermal systems indicate that such systems were active 1 of the time in the last 3 5 ga which raises questions about the exobiological importance of impact crater hydrothermal systems on mars after the noachian

discontinuity modelling and rock block geometry identification to optimize production in dimension stone quarries abstract evaluating the reserves of commercial blocks in dimension stone quarries requires determining in situ block geometry furthermore to extract blocks the planes need to be cut and the intersection between the fracture network and the cutting patterns forms smaller blocks the optimization of the cutting patterns can increase quarrying efficiency resulting in less environmental damage in this paper a numerical algorithm was selected from various algorithms and was developed for in situ block identification the optimization approach was adopted to increase quarry productivity and to investigate quarrying direction on a large scale however on a small scale this approach was employed for checking the distance between the cutting planes according to the algorithms developed 3d quarryoptimizer was programmed in the matlab environment to determine the geometry of the blocks and to optimize extraction based on the quality classification of the blocks formed the algorithms developed have such advantages as the optimization approach and taking the geometry of the blocks into consideration this methodology was applied in a marble quarry and a granite quarry research conducted in the granite quarry showed that the program is a practical tool to determine the geometry of in situ blocks and their quality classification the marble quarry was studied for the optimization phase the large scale optimization indicated a maximum difference of 17 in the yield among several quarrying directions on a small scale however a 120 increase in quarry yield was achieved with the optimal interval between the cutting planes

applying photogrammetry and semi automated joint mapping for rock mass characterization abstract rock engineering in blocky rock masses demands a sound knowledge about the joint network since it consists of planes of weakness than can lead to block instabilities however collecting data about the joint network is time consuming seldom very detailed and depends strongly on the experience of the mapping geologist additionally the characterization is reduced to the identification of the most relevant joint structures with their characteristic orientation and spacing other parameters like the in situ block shape and the block size distribution or the main orientation of the blocks are seldom collected or determined if at all with the emergence and increasing application of digital surface mapping techniques in rock mass characterization like shapemetrix3d or the discontinuity set extractor the time needed on site could be reduced and the degree of detail in the mapping of discontinuities is improved significantly the work presented in this study displays a continuous work flow from the data collection in the field to the determination of the block size and shape distribution generated by the intersection of joint sets for the process a marble quarry in styria austria was digitized using photogrammetry the joint sets are semi automatically identified with the discontinuity set extractor whose results are transferred into the software shapemetrix3d where the joint set spacing along with its standard deviations are determined these parameters are used to generate statistical representation of representative rock mass units using 3dec itasca consulting group inc and determine the block sizes block shapes and main orientation of the blocks in a row of simulations

contribution of giant icebergs to the southern ocean freshwater flux 1 in the period 1979 2003 the mass of giant icebergs icebergs larger than 18 5 km in length calving from antarctica averaged 1089 300 gt yr 1 of ice under half the snow accumulation over the continent given by the intergovernmental panel on climate change 2246 86 gt yr 1 here we combine a database of iceberg tracks from the national ice center and a model of iceberg thermodynamics in order to estimate the amount and distribution of meltwater attributable to giant icebergs by comparing with published modeled meltwater distribution for smaller bergs we show that giant icebergs have a different melting pattern an estimated 35 of giant icebergs mass is exported north of 63 s versus 3 for smaller bergs although giant bergs spend more of the earlier part of their history nearer to the coast we combine both estimates to produce the first iceberg meltwater map that takes into account giant icebergs the average meltwater input is shown to exceed precipitation minus evaporation p e in certain areas and is a nonnegligible term in the balance of freshwater fluxes in the southern ocean the calving of giant icebergs is however episodic this might have implications for their impact on the freshwater budget of the ocean it is estimated that over the period 1987 2003 the meltwater flux in the weddell and ross seas has varied by at least 15 000 m3 s 1 over a month because of the potential sensitivity of the production of deep waters to abrupt changes in the freshwater budget variations in iceberg melt rates of this magnitude might be climatologically significant

iceberg scouring in scoresby sund and on the east greenland continental shelf modern and relict scours produced by iceberg keels have been reported from a number of high latitude continental shelves in the northern hemisphere and antarctica but observations are largely absent from the east greenland shelf about 18 km3 yr 1 of icebergs are calved into the scoresby sund fjord system east greenland these icebergs have submarine keels with drafts up to 550 m modern iceberg contacts with the sea floor are inferred from calculated keel depths and stationary icebergs identified on sequential landsat imagery acoustic profiles parasound 3 5 khz of the sea floor show that scouring is a significant process in water depths 550 m iceberg scouring intensity varies inversely with water depth the most intense scouring occurs at depths of 300 400 m iceberg scours were observed on over 25 000 km2 of the east greenland shelf at 69 72 n and 75 n scours are being actively produced on the modern shelf but relict scours probably dating back to the late weichselian are also present the rate of iceberg production from greenland ice sheet outlet glaciers and iceberg drift tracks on the shelf suggests that iceberg scouring is important over a significant proportion of the 500 000 km2 area above the shelf break around greenland

deep pleistocene iceberg plowmarks on the yermak plateau sidescan and 3 5 khz evidence for thick calving ice fronts and a possible marine ice sheet in the arctic ocean the southern yermak plateau northwest of spitsbergen was investigated with 11 12 khz sidescan sonar and 3 5 khz profiler to test whether thick pleistocene ice streams ever calved into the arctic ocean and or whether a continuous arctic ice sheet existed in either case the ice would have grounded on the plateau crest on its way out of the arctic several distinct sets of relict iceberg plowmarks were discovered at present water depths from less than 450 m to at least 850 m perhaps recording the deepest iceberg keels known the plateau crest 510 530 m is nearly bare of plowmarks perhaps because of beveling by an ice rise formed of grounding shelf ice this implies continuous 400 600 m thick grounded ice consistent with but not proving the postulated existence of an arctic ice sheet most plowmarks are probably late pleistocene products of the calving of barents kara ice sheets into the arctic ocean plowmarks in 450 850 m deep water require unusually deep ice sheet grounding lines e g svyataya anna trough and or drat increasing capsizing events even if sea levels were 100 50 m lower than today at water depths of 800 to 1800 m the sidescan texture and topography suggest bottom currents descending the northeast slope of the plateau

labrador sea boundary currents and the fate of the irminger sea water abstract the general circulation of the labrador sea is studied with a dataset of 53 surface drifters drogued at 15 m and several hydrographic sections done in may 1997 surface drifters indicate three distinct speed regimes fast boundary currents a slower crossover from greenland to labrador and a slow eddy dominated flow in the basin interior mean eulerian velocity maps show several recirculation cells located offshore of the main currents in addition to the cyclonic circulation of the labrador sea above the northern slope of the basin the surface drifters have two preferential paths one between the 1000 m and 2000 m isobaths and the other close to the 3000 m isobath the vertical shear estimated from ctd data supports the presence of two distinct currents around the basin one current more baroclinic flows between the 1000 m and 2000 m isobaths the other one more barotropic flows above the lower continental slope the irminger sea water carried by the boundary currents is altered as it tr

large fluctuations in speed on greenland s jakobshavn isbrae glacier it is important to understand recent changes in the velocity of greenland glaciers because the mass balance of the greenland ice sheet is partly determined by the flow rates of these outlets jakobshavn isbrae is greenland s largest outlet glacier draining about 6 5 per cent of the ice sheet area and it has been surveyed repeatedly since 1991 ref 2 here we use remote sensing data to measure the velocity of jakobshavn isbrae between 1992 and 2003 we detect large variability of the velocity over time including a slowing down from 6 700 m yr 1 in 1985 to 5 700 m yr 1 in 1992 and a subsequent speeding up to 9 400 m yr 1 by 2000 and 12 600 m yr 1 in 2003 these changes are consistent with earlier evidence for thickening of the glacier in the early 1990s and rapid thinning thereafter our observations indicate that fast flowing glaciers can significantly alter ice discharge at sub decadal timescales with at least a potential to respond rapidly to a changing climate

geochemistry of a hydrothermal sediment core from the obs vent field 21 n east pacific rise abstract we report a geochemical investigation of near vent hydrothermal sediment from the east pacific rise collected in a short 11 cm core by submersible from the obs vent site at 21 n the sediment has high concentrations of fe 23 25 cu 10 22 zn 4 13 and s 22 30 but low mn concentrations 108 279 ppm indicating a much fresher sulfidic input than in previously reported near vent sediments from the mid atlantic ridge further studies are required to fully characterise near field hydrothermal sediments but the data in this study allow the first comparisons with similar near vent material collected previously from the mid atlantic ridge as well as ridge flank data from the epr and juan de fuca ridge compared to ridge flank sediments the near field sediments exhibit high ratios of fe mn cu fe and zn fe unlike cu and zn pb is not so significantly enriched pb isotope compositions are indistinguishable from local morb indicating a dominant hydrothermal source for this element in these sediments this may not necessarily be the case for ridge flank sediments however where scavenging from seawater may also be important ree distributions throughout the core exhibit low concentrations and characteristics typical of vent fluids with lree enrichments and pronounced positive eu anomalies these patterns are similar to those of relatively fresh sulfides but there is also evidence for progressive oxidation downward into the core by ingressing seawater

iceberg calving from the amery ice shelf east antarctica we investigate the iceberg calving cycle of the amery ice shelf ais east antarctica using evidence acquired between 1936 and 2000 the most recent major iceberg calving event occurred between late 1963 and early 1964 when a large berg totalling about 10000 km2 in area broke from the ice front the rate of forward advance of the ice front is presently 1300 1400 m a 1 at this rate of advance based on the present ice front position from recent radarsat imagery it would take 20 25 years to attain the 1963 pre calve position suggesting that the ais calving cycle has a period of approximately 60 70 years two longitudinal parallel to flow rifts approximately 25 km apart at the ais front are observed in satellite imagery acquired over the last 14 years these rifts have formed at suture zones in the ice shelf where neighbouring flow bands have separated in association with transverse spreading the rifts were 15 km rift a and 26 km rift b in length in september 2000 and will probably become the sides of a large tabular iceberg 25 km 25 km a transverse perpendicular to flow fracture visible at the upstream end of rift a in 1996 had propagated 6 km towards rift b by september 2000 when it meets rift b the iceberg will calve a satellite image acquired in 1962 shows an embayment of this size in the ais front hence we deduce that this calving pattern also occurred during the last calving cycle and therefore that the calving behaviour of the ais apparently follows a regular pattern

determination of structural domain boundaries in jointed rock masses an example from the songta dam site china abstract this paper presents an application of the kolmogorov smirnov and wilcoxon rank sum nonparametric statistical tests for identifying structural domain boundaries in jointed rock masses in the method the upper hemispherical surface is divided into 100 nearly equal area windows the similarity between two samples of joint orientations is measured by comparing the frequencies or the number of joint poles occurring in the windows over 2400 joints collected from 8 adjacent exploration tunnels at the songta dam site in southwest china are used to demonstrate the method by applying the technique to the study area structural domain boundaries in the rock mass are determined our results suggest that the study area with an area of approximately 17 850 m2 can be classified into four structural domains however the traditional method with the correlation coefficient fails to reveal the structural changes since the correlation coefficient is only a measure of strength of the linear relation between two samples it has limitations in measuring the similarity between joint orientation distributions a comparison between the proposed method and previous methods indicates that the new technique could provide more reliable results besides the new method can be applied to structural populations with small sample sizes

quaternary sedimentation and norwegian sea overflow pathways around bill bailey bank northeastern atlantic abstract using high resolution multi channel sleeve gun seismics and tobi side scan sonar and subbottom profiler acoustic data as well as sediment cores and published hydrographic measurements a study has been made of quaternary sedimentation patterns and depositional processes around bill bailey bank bbb in the northeastern atlantic from the western outlet of the faeroe bank fb channel which is the main conduit of norwegian sea overflow water nsow there is a complex pattern of nsow controlled sediment transport pathways extending to areas north of lousy bank lb the acoustic data and sediment cores reveal the existence of a contour current at water depths exceeding 1000 m flowing from the wyville thomson ridge via the southern rise of fb and bbb into the valley between bbb and lb and further northward towards the area north of bbb we conclude that this contour current is related to intermittent nsow overflow of the wyville thomson ridge the maximum bottom flow speed along this secondary nsow flow pathway is inferred to reach about 0 50 m s bedforms observed in the northeastern part of the study area north of bbb suggest a maximum bottom flow speed of locally at least 1 0 m s the maximum thickness 0 5 s twt of the pliocene quaternary seismic sequence at water depths in excess of 1000 m south of bbb is nearly twice that found north of bbb on average higher accumulation rates in the former area can be ascribed to a hydrographic setting favouring sediment accumulation which especially under glacial conditions markedly differed from conditions north of bbb this applies to both bottom and surface circulation linear bulk sedimentation rates north of bbb were largest during deglacial warming when the rates were about three times higher than the average holocene rate 4 5 cm ka increased fluxes during deglaciation reflect transport and depositional conditions associated with reactivation of the nsow current system south of bbb average linear bulk accumulation rates were persistently higher i e in the range 15 23 cm ka during various late pleistocene stages between 30 and 10 ka

warming and freshening of baffin bay 1916 2003 1 regression analysis of historical hydrographic data is used to determine changes in temperature and salinity in baffin bay for the time period from 1916 to 2003 we find two distinct sets of changes in the baffin first areas affected by the atlantic inflow to baffin bay show substantial and statistically significant warming trends in the more than 2000 m deep basin the warming peaks at 0 11 0 06 c decade at 700 m depth below the 640 m sill depth of davis strait connecting baffin bay to the north atlantic ocean a vertical heat flux divergence of 0 25 w m2 is required to warm baffin bay below 900 m by the amount observed the required heat appears to be advected from the shelf and slope regions of the eastern labrador sea via davis strait along the west greenland shelf break and diffuses vertically and horizontally into the deep central basin the north atlantic oscillation index accounts for about 30 of the interannual variance of temperature fluctuations below the davis strait sill depth second areas affected by arctic inflow to baffin bay show a marginally significant freshening of up to about 0 086 0 039 psu decade this freshening trend extends along the western margin of baffin island to davis strait and into the labrador sea the freshening in the northern reaches of baffin bay is similar in size to that at its southern reaches temporal variability of annual composites between these locations appears to be in phase suggesting a swift transition of arctic waters at 76 n to labrador sea waters at 62 n

development of an assessment system for the blastability of rock masses intact rock properties and the discontinuity structure of a rock mass are among the most important variables influencing blasting results this influence is considered to be a composite intrinsic property of a rock mass and is referred to as the blastability of a rock mass it represents the ease with which a rock mass can be fragmented by blasting this paper outlines an energy block transition model recently proposed by the authors for characterising the blast process a preliminary validation of this model using two sets of field data from the literature is briefly outlined the model is comparable or better than bond s comminution theory at predicting blasting results for cases where intrinsic rock properties are relatively constant to generate a predictive capability for the model a blastability designation bd is designed which reflects the intrinsic resistance of the rock mass to blasting the quantification of bd based on rock engineering systems approaches and consideration of a comprehensive range of intact rock properties and discontinuity structures is illustrated a case study is given which applies the model and the associated assessment system to a highway cutting site confidence as to the potential value of the assessment system and the model is obtained since refinement and improvement on pre existing models can be seen from the new preliminary results

were glacial iceberg surges in the north atlantic triggered by climatic warming high resolution physical mineralogical sedimentological and micropalaeontological studies were carried out on north atlantic cores from the reykjanes ridge at 59degreesn and from the region southwest of the faeroe islands all core sites are situated along the pathway of iceland scotland overflow water isow and the various parameters measured display similar features previously identified carbonate oscillations keigwin and jones 1994 j geophys res 99 12397 12410 in the time span back to the marine isotope stage 5 4 transition and late glacial lithic events bond and lotti 1995 science 267 1005 1010 such as the heinrich ice rafting events are all represented in the core records long term trends and higher frequency changes in isow intensity were reconstructed on the basis of various independent proxy records the long term trends in circulation match theoretical orbitally forced insolation changes our observed links between ice rafted detritus ird input variations in sea surface temperature sst and circulation at greater depth point to the need to re examine the origin of ird events we suggest that these events may have been triggered by enhanced partly sub surface heat transport to the north enhanced northward heat transport may have caused bottom melting of floating outlet glaciers and ice shelves leading to increased iceberg discharge and ice sheet destabilization this discharge resulted in lower sst s and a lower temperature over greenland thus as shown by our records this scenario implies a temporary de coupling of surface processes and circulation at greater depth a key feature is the occurrence of a saw tooth pattern in the marine data which is similar to the greenland ice core records moreover the warming theory of ird events would explain the observed out of phase relationship between the greenland and antarctic ice core records and also the rapid establishment of higher temperatures over greenland immediately after the cold phases stadials of the dansgaard oeschger cycles less

the ree content of some hydrothermal fluids ree concentrations were determined in solutions from submarine hydrothermal vents on the east pacific rise and for the first time from continental geothermal fields in tibet and bulgaria they indicate that in hydrothermal systems ree are immobile at temperatures below 350 c and for water rock ratios of 105 nd values of submarine solutions and anhydrites 4 7 to 6 2 suggests recharge on the sedimentcovered flanks of the ridge carbonate anions as measured by alkalinity appear to increase the solubility of heavy ree somewhat but not to the extent that substantial amounts of ree could be driven out from rocks by hydrothermal activity

dating of a regional hydrothermal system induced by the 1850 ma sudbury impact event new u pb geochronologic data from the sudbury structure directly link extensive hydrothermal activity in crater fill breccias with the 1850 ma impact event and constrain complex impact induced processes to 4 m y semiconformable alteration of breccias in the onaping formation includes silicification albitization chloritization calcitization and complex feldspathization which directly underlies zn cu pb ore deposits geochronologic data demonstrate a middle to lower crustal source for the crater fill deposit that was subsequently affected by the hydrothermal event at 1848 4 3 8 1 8 ma these and other data confirm that the crater fill breccia hydrothermal system sudbury igneous complex and its sublayer ni ore bearing units were emplaced as a result of impact the ages of events associated with the sudbury structure are now more closely constrained than in any other meteorite impact structure

the circulation water masses and sea ice of baffin bay abstract the oceanographic meteorological and sea ice conditions in baffin bay are studied using historical hydrographic satellite and meteorological data and a set of current meter data from a mooring program of the bedford institute of oceanography baffin bay is partially covered by sea ice all year except august and september the interannual variation of the ice extent is shown to be correlated with winter air temperature available hydrographic data were used to study the water masses and the horizontal and vertical distribution of temperature salinity three water masses can be identified arctic water in the upper 100 300 m of all regions except the southeast west greenland intermediate water at 300 800 m in most of the interior of baffin bay and deep baffin bay water in all regions below 1200 m the temperature and salinity in baffin bay have limited seasonal variability except in the upper 300 m of eastern davis strait northern baffin bay and the mouth of lancaster sound summer data have a temperature minimum at 100 m which suggests winter convection does not penetrate deeper than this depth current meter data and results of a circulation model indicate that the mean circulation is cyclonic the seasonal variation of the currents is complex overall summer and fall tend to have stronger currents than winter and spring at all depths among the different regions the largest seasonal variation occurs at the mouth of lancaster sound and the baffin island slope model generated velocity fields show a basic agreement with the observed currents and indicate strong topographic control in the vicinity of davis strait and on the greenland shelves the model also produces a southward counter current on the greenland slope which may explain the observed high horizontal shears over the greenland slope estimates of the volume and fresh water transports through lancaster jones and smith sounds are reviewed transports through davis strait are computed from the current meter data the balance of freshwater budget and sensitivity of the thermohaline circulation to freshwater transport are discussed

foraminiferal biostratigraphy and paleoenvironmental reconstruction at the yaxcopoil 1 drill hole chicxulub crater yucatan peninsula the yaxcopoil 1 yax 1 drill hole comprises cretaceous limestones and calcarenites the k p boundary cocktail unit including impact breccia and a danian marly clay layer overlain by calcareous marls the biostratigraphy paleobathymetry and environmental turnover across the k p interval were inferred after analyzing the planktic and benthic foraminiferal assemblages the cretaceous samples only contain a few poorly preserved planktic foraminifera of a middle campanian to maastrichtian age while low diversity benthic foraminiferal assemblages suggest a sufficient nutrient supply to the sea floor and a shallow neritic occasionally stressed environment the impact breccia and the redeposited suevite are overlain by a 46 cm thick dolomitic calcareous sandstone unit that contains scarce reworked planktic foraminiferal specimens this unit probably represents the uppermost part of the initial infill of the crater the uppermost centimeters of this unit are bioturbated and its top represents a hiatus that spans at least the g cretacea pv eugubina and part of the p pseudobulloides biozones this unit is overlain by a 3 4 cm thick marly clay layer that represents a condensed layer benthic foraminiferal assemblages suggest a low food supply to the sea floor and environmental instability during the deposition of the marly clay layer the increase in diversity of the assemblages indicates that the environmental conditions improved and stabilized from the g compressa biozone toward the a uncinata p2 biozone the danian planktic and benthic foraminiferal assemblages indicate a deeper probably bathyal environment