presence of an iron rich nanophase material in the upper layer of the cretaceous tertiary boundary clay abstract we report new geochemical evidence from ten cretaceous tertiary k t boundary sites in north america and europe indicating the presence of a material remnant of a large asteroid or comet that struck the earth at 65 0 ma mossbauer spectroscopic data reveals that a ubiquitous iron rich nanophase material exists at the uppermost part of the k t boundary layer in the western hemisphere and in europe marine and continental fine grained sedimentary rock the high surface to volume ratio of nanophase material suggests that it may be the carrier of the iridium abundance enhancement that marks the k t boundary even more provocative is the possibility that discovered nanophase material is for the most part composed of the vaporized impactor after the impact generated high temperature vapor plume rose and cooled above the atmosphere introduction in the last two decades an enormous amount of chemical and physical evidence has been gathered that supports the idea that a large asteroid or comet struck earth at

the stratigraphic distribution of ni rich spinels in cretaceous tertiary boundary rocks at el kef tunisia caravaca spain and hole 761c leg 122 abstract ni rich spinels have been found throughhout the world at the cretaceous tertiary boundary these minerals have no counterparts in terrestrial rocks but have been observed in meteoroid ablation material and impact debris suggesting that the cretaceous tertiary boundary spinels result from an extraterrestrial event their stratigraphic distribution which has been observed at the cretaceous tertiary boundary sites of el kef tunisia caravaca spain and hole 761c odp leg 122 indian ocean are markedly different from site to site and are all much less extended than the ir anomalies regional differences in ni rich spinel distibution are entirely explained by a brief event recorded under different bioturbation conditions the wider stratigraphic dispersion of ir is attributed to postdepositional chemical processes at el kef the site which appears to be the least affected by bioturbation and which has the highest sedimentation rate the 1 2 mm thick ni rich spinel spike indicates that the deposition time did not exceed an upper limit of 100 years this upper limit is consistent only with the collision of an asteroid or a comet at the close of the cretaceous

the rotokawa geothermal system new zealand an active epithermal gold depositing environment the rotokawa geothermal system is less than 20 000 yrs old and is situated in a sequence of pleistocene and recent volcanic rocks and underlying mesozoic graywacke basement in the taupo volcanic zone a region dominated by extensional tectonics at lease 12 different hydrothermal explosition breccias are preserved in surface outcrops the largest eruptive site being a crater of 1 5 km in diameter which formed about 6 060 years ago and is presently occupied by an acid lake lake rotokawa with a ph approximately 2 significant bedded sulfur deposits which formed in an earlier crater lake exist beneath the present lake the deep fluids are dilute chloride 0 022 mole kg waters having higher reduced sulfur concentrations h 2 s approximately 7x10 super 3 mole kg than any previously studied active geothermal system a maximum temperature of 320 degrees c has been measured in the system water rock interaction has given rise to a zone of propylitic alteration at depth which is overlain by a region of advanced and intermediate argillic alteration extensive boiling occurs at depth an sulfide minerals such as sphalerite galena chalcopyrite and argentite occur sporadically with ubiquitous pyrite argentiferous alunite occurs in the advanced argillic alteration zone clasts of silicified lake beds in the hydrothermal explosion breccias commonly contain pyrite and carry subeconomic gold values of up to 0 1 g metric ton thermal waters discharging on the northeast shore of the lake are depositing gold ore grade arsenic and antimony sulfide rich muds which also contain high concentrations of tungsten thallium mercury silver and gallium this surface deposit is estimated to contain about 250 kg 8 000 oz of gold and has been deposited during the past 1 800 yrs since the formation 6 060 yrs ago of the large hydrothermal explosion crater in which lake rotokawa is now situated about 12 0 million oz 370 metric tons of gold may have been transported into the environment beneath the crater it is estimated that 1 7 to 3 3 million oz of gold may have been deposited in the upper 300 to 400 m underlying lake rotokawa from hydrothermal fluids initially saturated with gold

chicxulub multiring impact basin size and other characteristics derived from gravity analysis the buried chicxulub impact structure in mexico which is linked to the cretaceous tertiary k t boundary layer may be significantly larger than previously suspected reprocessed gravity data over northern yucatan reveal three major rings and parts of a fourth ring spaced similarly to those observed at multiring impact basins on other planets the outer ring probably corresponding to the basin s topographic rim is almost 300 kilometers in diameter indicating that chicxulub may be one of the largest impact structures produced in the inner solar system since the period of early bombardment ended nearly 4 billion years ago

a sequence of events across the cretaceous tertiary boundary the lithological and biological sequence of events across the cretaceous tertiary k t as developed in thick and complete landbased sections and termed the standard k t event sequence is also found in many i sdp cores from all over the globe microtektite like spherules have been found in almost every core or outcrop with an iridium anomaly forming a worldwide strewnfield these microtektites are an excellent indicator of the k t boundary level the basal paleocene globigerina eugubma zone is nov established in all major ocean basins the difference in faunas between the pacific and tethys atlantic oceans may point to different recovery of the oldest paleocene planktonic foraminiferal assemblages in different ocean basins planktonic foraminifera and nannoplankton apparently show a different extinction recovery pattern at the k t boundary which suggests that the nannoplankton underwent final extinction later and recover later than planktonic foraminifera these patterns may be important for the evaluation of the type and range of environmental stress resulting from the hypothesized impact s at the k t boundary blocking of sunlight by the dust cloud still can account for the clear mass mortality at the k t boundary but seems less likely as explanation for the final nannoplankton extinction as photosynthetic nannoplankton appear to survive 1000 10 000 years into the tertiary

gold quartz veins in metamorphic terranes and their bearing on the role of fluids in faulting gold quartz vein fields in metamorphic terranes such as greenstone belts provide evidence for the involvement of large volumes of fluids during faulting and may be products of seismic processes near the base of the seismogenic regime in the val d or district of the abitibi greenstone belt canada quartz tourmaline carbonate veins form a vein field 30 15 km in the hanging wall of a crustal scale fault zone which was the main channelway for upward migration of the deeply generated fluids the veins occur in small high angle reverse faults and in adjacent horizontal extensional fractures extending up to 75 m in intact rocks they have formed incrementally during active reverse faulting in response to crustal shortening at depths corresponding to those at the base of the seismogenic zone in actively deforming crust detailed structural and fluid inclusion studies provide evidence for generally lithostatic but fluctuating fluid pressures p of the order of 200 mpa and for cyclic stress reversals during vein formation and provide good support for the fault valve model a comparison of vein characteristics with standard earthquake rupture parameters suggests that each slip increment along veins in reverse faults was accompanied by a small earthquake 4 m 3 or less the large vein field thus represents both the extent of fluid dispersion in the hanging wall of a crustal scale channelway and the distribution of small earthquakes integrated over the lifetime of the hydrothermal system it is proposed that such small earthquakes along veins in reverse faults are related to large earthquakes m 6 nucleating near the base of the seismogenic regime along the nearby crustal scale fault either as aftershocks or as a precursory smarm

a meteorite from the cretaceous tertiary boundary cretaceous tertiary boundary sediments are now widely recognized to contain the record of a large asteroid or comet impact event1 probably at the site of the chicxulub crater on the yucatan peninsula2 after nearly two decades of intensive research however much remains unknown about the specific nature of the projectile and of the impact event itself here we describe a 2 5 mm fossil meteorite found in sediments retrieved from the cretaceous tertiary boundary in the north pacific ocean that we infer may be a piece of the projectile responsible for the chicxulub crater geochemical and petrographic analyses of this meteorite indicate that it probably came from a typical metal and sulphide rich carbonaceous chondrite rather than the porous aggregate type of interplanetary dust considered typical of cometary materials3 the fact that meteorite survival should be enhanced by impacts at low asteroidal velocities4 also implies that this meteorite had an asteroidal rather than a cometary origin

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

isotopic evidence for the cretaceous tertiary impactor and its type high precision mass spectrometric analysis of chromium in sediment samples from the cretaceous tertiary k t boundary coincident with the extinction of numerous organisms on earth confirms the cosmic origin of the k t phenomenon the isotopic composition of chromium in k t boundary samples from stevns klint denmark and caravaca spain is different from that of earth and indicates its extraterrestrial source the chromium isotopic signature is consistent with a carbonaceous chondrite type impactor the observed differences in the chromium isotopic composition among various meteorite classes can serve as a diagnostic tool for deciphering the nature of impactors that have collided with earth during its history

spinel bearing spherules condensed from the chicxulub impact vapor plume formation of the giant chicxulub crater off mexico s yucatan peninsula coincided with deposition of the global ir rich cretaceous tertiary k t stratigraphic boundary layer at ca 65 ma the boundary is marked most sharply by abundant spherules containing unaltered grains of magnesioferrite spinel here we predict for the first time the sequential condensation of solids and liquids from the plume of vaporized rock expected from oblique k t impacts we predict highly oxidizing plumes that condense silicate liquid droplets bearing spinel grains whose compositions closely match those marking the actual boundary systematic global variations in spinel composition are consistent with higher condensation temperatures for spinels found at atlantic and european sites than for those in the pacific

size and structure of the chicxulub crater revealed by horizontal gravity gradients and cenotes it is now widely believed that a large impact occurred on the earth at the end of the cretaceous period and that the buried chicxulub structure in yucatan mexico is the resulting crater24 knowledge of the size and internal structure of the chicxulub crater is necessary for quantifying the effects of the impact on the cretaceous environment although much information bearing on the crater s structure is available diameter estimates range from 170 to 300 km refs 1a 7 corresponding to an order of magnitude variation in impact energy here we show the diameter of the crater to be 180 km by examining the horizontal gradient of the bouguer gravity anomaly over the structure this size is confirmed by the distribution of karst features in the yucatan region mainly water filled sinkholes known as cenotes the coincidence of cenotes and peripheral gravity gradient maxima suggests that cenote formation is closely related to the presence of slump faults near the crater rim

chicxulub crater yucatan tektites impact glasses and the geochemistry of target rocks and breccias a comparison of breccias and basement rocks from four drill holes near the chicxulub impact structure yucatan a possible cretaceous tertiary k t boundary crater with black and yellow impact glasses from the haitian k t boundary layer shows that mixtures of andesite like rocks with carbonates and evaporites from chicxulub are compositionally different from the yellow glasses at the time of impact the chicxulub area was covered by evaporitic and carbonate deposits several kilometres thick because impact glasses are generally produced by shock melting of surface rocks a link between the haitian glasses and chicxulub is difficult to understand the 34 s isotopic signature of chicxulub breccias and evaporites is incompatible with that of a continental k t boundary we suggest that the pre impact target stratigraphy at chicxulub as well as the interpretation of the carbonate evaporite rocks as breccias should be revised

nickel rich magnesiowiistite in cretaceous tertiary boundary spherules crystallized from ultramafic refractory silicate liquids we have found trace inclusions of ni rich magnesiowastite within grains of magnesioferrite spinel recovered from cretaceous tertiary boundary sediments from dsdp site 596 south pacific 23 51 20 s 169 39 27 w and dsdp site 577 north pacific 3 6 51 n 157 43 40 e measured compositions of these inclusions range from mg 85ni 74fe 17 o to mg 74ni 09fe 1 7 o coexisting magnesioferrite and magnesiowastite can only crystallize from ultramafic refractory mg rich liquids with mgsi 2 atom ratio such liquid compositions cannot form as a result of fractional crystallization and are unknown to occur as a result of terrestrial igneous processes or meteoroid ablation we infer that these minerals crystallized from liquid droplets that equilibrated with silicate vapor at high temperatures probably 2300 c resulting in fractionation of volatile sio2 from more refractory mgo the most plausible source of this high temperature vapor is in the fireball of the major impact event that terminated the cretaceous

pressure fluctuations phase separation and gold precipitation during seismic fracture propagation gold mineralization at croagh patrick western ireland occurs in quartz veins associated with three synchronous oblique tensile shear systems the veins evolved by progressive thickening of isolated en echelon lensoid tensile fractures that show a power law relation between their length and thickness a change in power law exponent marks the linking of the en echelon arrays by large oblique tensile veins fluid inclusion data show that gold was deposited due to unmixing of an h 2 o co 2 nacl fluid at 320 240 c and 160 30 mpa primarily due to decreases in fluid pressure evidence for phase separation is only observed in the large linking veins and is abundant close to intersections of the vein arrays these sites are where high gold grades occur the distribution of gold is believed to reflect both spatial and temporal variations in fluid pressure fluctuation during seismic fracture propagation controlled by the vein growth mechanism and zones of maximum dilation

size and morphology of the chicxulub impact crater the chicxulub impact in mexico has been linked to the mass extinction of species at the end of the cretaceous period from seismic data collected across the offshore portion of the impact crater the diameter of the transient cavity is determined to be about 100 km this parameter is critical for constraining impact related effects on the cretaceous environment with previous estimates of the cavity diameter spanning an order of magnitude in impact energy the offshore seismic data indicate that the chicxulub crater has a multi ring basin morphology similar to large impact structures observed on other planets such as venus

sar interferometry on a very long time scale a study of the interferometric characteristics of man made features anthropogenic features show up as highly coherent objects even in heavily decorrelated interferograms in order to assess whether the information from such features is still usable the stability of their phase and coherence is analyzed through a series of interferograms the results indicate that these features can remain interferometrically stable over several years

geochemistry of impact glasses from the k t boundary in haiti relation to smectites and a new type of glass we have individually analyzed twelve black and seven yellow glasses from the k t boundary section at beloc haiti plus three smectite mantles around black glasses the main chemical differences between black and yellow glasses are higher s ca mg zn as br sb and au but lower k na and si abundances in the yellow glasses we have found high cao yellow glasses with low s contents 0 08 0 17 wt which may be explained by fusion of carbonate rich sediments microprobe studies of individual glasses show that the black glasses are very homogeneous in their composition at the 10 100 m level while yellow glasses show much more variability and different intra sample elemental correlations one of the black glasses has higher sio2 and k2o abundances but lower concentrations of all other major elements this suggests the existence of a third glass type which we have named the high si k variety hsi k glass the glass shows areas consisting of pure sio2 maybe lechatelierite and some schlieren with lower sio2 content the chemical composition indicates that the hsi k glass may have originated from melting of a sedimentary source rock such as shale or argillite severe changes in major and trace element composition occur during alteration of the glass as documented by analyses of adhering smectites the ree patterns in the glass are similar to average upper crust but the smectites exhibit much lower abundances and flat patterns not unlike the patterns observed in claystones at numerous k t boundary sites the suggestion that the chicxulub structure in yucatan may be the source crater for the k t impact glasses is not fully supported by the currently available data impact glasses and tektites are produced from the surface layers of their targets at chicxulub the target stratigraphy comprised mainly carbonates and evaporites although we cannot exclude chicxulub as a source the present data do not provide any firm chemical evidence for a connection we conclude however that the haiti glasses have formed by impact and have later undergone alteration by low temperature hydrothermal processes to produce clays the boundary claystones at k t boundary sites may very well be alteration products of these impact glasses

impact induced mass wasting at the k t boundary blake nose western north atlantic seismic reflection data combined with results from ocean drilling document regional scale slumping associated with the cretaceous tertiary k t impact event the k t boundary is biostratigraphically complete at three ocean drilling program sites 1049 1050 and 1052 located on blake nose 30 n 75 w off eastern florida in water depths of 1300 2600 m maastrichtian chalk is folded and fractured below the k t boundary at all three sites whereas lowermost paleocene clays and chalks are undeformed deformation is pervasive in maastrichtian at the deepest water site site 1049 whereas at the shallower water sites sites 1050 and 1052 thick intervals of structurally intact maastrichtian chalk are separated by thinner intervals of highly deformed sediments correlation of core to seismic reflection data indicates that the k t boundary immediately overlies seismic facies characteristic of mass wasting that extend across most of the 55 km distance of the depth transect maastrichtian sediments appear to have moved as large slump blocks on the upper part of blake nose but deformed more uniformly in the deeper water parts of the transect we suggest that mass wasting occurred on the blake nose 1600 km from the chicxulub crater in response to the cataclysmic seismicity generated by the impact

rare earth element composition as evidence of the precursor material of cretaceous tertiary boundary sediments at distal sections abstract the chicxulub impact event led to a worldwide deposition of impact materials originated from target rocks and the vaporized bolide relative contributions of both types of material to the k t ejecta deposits vary with distance to the crater site at distal sites e g agost and caravaca in the se of spain a major contribution of extraterrestrial material is indicated by different impact signatures such as os and cr isotope composition abundant microkrystites platinum group elements and other siderophile elements that are typical of extraterrestrial components closer settings to the chicxulub crater for example the blake nose plateau in the north american margin display major continental crustal rock contributions in the ejecta layer ree compositions provide additional evidence for terrestrial vs extraterrestrial rock contributions previous research has not focused specifically on ree concentrations and corresponding c1 and nasc normalized patterns however normalized ree patterns are already generating supplementary insights into the nature of the original material of the k t boundary layer thus blake nose ejecta c1 normalized patterns indicate a derivation from continental crustal target rocks in more distal sections ree compositions point to a probable mafic precursor and confirm that extraterrestrial materials represent a major contribution the ejecta layer

fluid inclusion evidence for p v t x evolution of hydrothermal solutions in late alpine gold quartz veins at brusson val d ayas northwest italian alps

the suevite of drill hole yucatan 6 in the chicxulub impact crater the suevite breccia of the chicxulub impact crater yucatan mexico is more variable and complex in terms of composition and stratigraphy than suevites observed at other craters detailed studies microscope electron microprobe sem xrf have been carried out on a noncontinuous set of samples from the drill hole yucatn 6 y6 located 50 km sw from the center of the impact structure three subunits can be distinguished in the suevite the upper unit is a fine grained carbonate rich suevite breccia with few shocked basement clasts mostly altered melt fragments and formerly melted carbonate material the middle suevite is a coarse grained suevite with shocked basement clasts and altered silicate melt fragments the lower suevite unit is composed of shocked basement and melt fragments and large evaporite clasts the matrix of the suevite is not clastic but recrystallized and composed mainly of feldspar and pyroxene the composition of the upper members of the suevite is dominated by the sedimentary cover of the yucatan target rock with depth in well y6 the amount of carbonate decreases and the proportion of evaporite and silicate basement rocks increases significantly even at the thin section scale melt phases of different chemistry can be identified showing that no widespread homogenization of the melt took place the melt compositions also reflect the heterogeneity of the deep yucatan basement calcite with characteristic feathery texture indicates the existence of formerly pure carbonate melt the proportion of carbonate to evaporite clasts is less than 5 1 except in the lower suevite where large evaporite clasts are present this proportion constrains the amount of co2 and sox released by the impact event