impactoclastic density current emplacement of terrestrial meteorite impact ejecta and the formation of dust pellets and accretionary lapilli evidence from stac fada scotland abstractwe present an impactoclastic density current model for terrestrial meteorite impact ejecta emplacement that is based on a hitherto unreported threefold sequence of lithofacies in the recently identified stac fada impact ejecta outflow blanket in scotland massive suevite division a grades seamlessly up into massive suevite containing whole and broken accretionary lapilli division b and this is overlain by a thin layer of clast supported dust pellets division c the sequence closely resembles sequences in accretionary lapilli bearing ignimbrites emplaced by pyroclastic density currents at volcanoes and we deduce similar emplacement mechanisms we propose that 99 of the thickness of the stac fada ejecta blanket as seen at outcrop was deposited from a single depletive spatially decelerating granular fluid based density current that rapidly waxed and then waned a previously unreported thin layer of pellets division c records direct fallout from a residual atmospheric dust plume we pro

kreep glass and the exotic provenance and formation of polymict breccia 66055 polymict breccia 66055 from the apollo 16 site is unique in that it contains abundant brown kreep glass 0 3 0 4 k2o and related brown glassy breccias which have fluid forms during assembly it consisted of hot and cold debris which flowed together most of the rock consists of clasts of poikiloblastic breccia granulitic impactite and mesostasis rich impact melt vha basalt both of which predate the assembly of 66055 in contrast the kreep glass was created in the impact which produced the rock kreep compositions are sparse among glasses in soils and other breccias at the apollo 16 site and the rock would not have formed locally it must be exotic terrains in which 66055 might have formed exist to the west of the landing site suitable igneous target materials for the kreep glass have not positively been identified in 66055 so the petrogenesis of apollo 16 kreep remains enigmatic although the presence of a granitic glass fragment embedded in kreep glass suggests that it is igneous a local volcanic origin is more consistent with the spatial relationships as deduced from orbital geochemical data than is a basin ejecta deposit

chicxulub impact ejecta from albion island belize impact ejecta from the albion formation are exposed in northern belize the ejecta come from the outer portion of the continuous ejecta blanket of the chicxulub crater which is located 360 km to the northwest the basal unit of the albion formation is a 1 m thick clay and dolomite spheroid bed composed of up to four discrete flows the clay spheroids are altered impact glass and the dolomite spheroids are accretionary lapilli the upper unit is a 15 m thick coarse diamictite bed containing altered glass large accretionary blocks striated polished and impacted cobbles and rare shocked quartz the abundance of accretionary clasts evidence for atmospheric drag sorting and the presence of multiple flows in the albion formation indicate that atmospheres play an important role in the formation of the outer portions of continuous ejecta blankets of large craters

the sevětin astrobleme southern bohemia czechoslovakia the geological geomorphological petrological and geophysical data for the 46 km circular structure sev tin 49 05 n 14 35 e southern bohemia are consistent with characteristic of moderately eroded structures that have originated by hypervelocity meteorite impact the astrobleme dated as late cretaceous probably coniac santon 85 75 m y is dissected into radial fault segments which exhibit a variable level of erosion the classification of the sev tin astrobleme as a probable impact structure is based on the geological and geophysical evidence of central scar about 8 km in diameter shock metamorphism in the centre of the structure and relics of silicified impact breccia including globular and suevite types with structural indications of molten material shatter coning and shock metamorphism are documented for several formations and lithologies ranging in age from the hercynian granite of the crystalline basement through stephanian permian to the upper cretaceous lower klikov formation the morphological expression of the crater rim is preserved in the less eroded segments the central uplift d 21 km approximately 0 5 of the total diameter still preserved in part as a positive morphological feature is partly burried under the post impact upper klikov formation the impact event provided the major tectonic geomorphological and paleogeographic resetting which was known for some time in the evolution of the continental upper cretaceous of this area and expressed in the splitting of the klikov formation into two divisions

cretaceous paleogene boundary deposits at loma capiro central cuba evidence for the chicxulub impact a newly discovered upper cretaceous to lower paleogene section at loma capiro central cuba has provided new evidence for a cretaceous paleogene boundary age for the chicxulub impact the studied sediments at loma capiro consist of a foraminifera rich marl and sandstone hemipelagic sequence and a 9 6 m thick intercalated clastic complex planktic foraminifera indicate an upper maastrichtian age for the sediments below the clastic complex and a lowermost danian age for those just above this complex small benthic foraminifera from below and above the clastic complex indicate deposition at middle to lower bathyal depths the fining upward clastic complex consists of a basal breccia that is overlain by microconglomerates and coarse to fine grained sandstones the clastic complex contains reworked foraminifera from different ages and different paleoenvironments and toward the top impact material such as altered microtektites shocked quartz terrestrial chondrules and accretionary lapilli these microfacies suggest deposition from gravity flows that eroded sediments from upper slope and shelf settings and redeposited them in deeper bathyal environments we suggest that the origin of the clastic complex may be linked to the collapse of the cuban platform triggered by the cretaceous paleogene impact at chicxulub

mineralogical constraints on the thermal history of martian regolith breccia northwest africa 8114 abstract martian meteorite northwest africa nwa 8114 a paired stone to nwa 7034 provides an opportunity to examine the thermal history of a martian regolith and study near surface processes and ancient environmental conditions near an impact crater on mars our study reports petrographic and alteration textures and focuses on pyroxene and iron oxide grains some of the pyroxene clasts show exsolution lamellae indicating a high temperature magmatic origin and slow cooling however transmission electron microscopy reveals that other predominantly pyroxene clasts are porous and have partially re crystallised to form magnetite and a k bearing feldspathic glassy material together with relict pyroxene this breakdown event was associated with oxidation with up to 25 fe3 fe in the relict pyroxene measured using fe k xanes by comparison with previous studies this breakdown and oxidation of pyroxene is most likely to be a result of impact shock heating being held at a temperature above 700 c for at least 7 days in an oxidising regolith environment we report an approximate 40ar 39ar maximum age of 1 13 1 25 ga for an individual separated augite clast the disturbed nature of the spectra precludes precise age determination in section this clast is porous and contains iron oxide grains this shows that it has undergone the high temperature partial breakdown seen in other relict pyroxene clasts and has up to 25 fe3 fe we infer that the age corresponds to the impact shock heating event that led to the high temperature breakdown of many of the pyroxenes after consolidation of the impact ejecta blanket high temperatures above 700 c may have been maintained for long enough to remobilise and congruently partially melt some of the alkali feldspar clasts to produce the feldspar veins and aureoles that crosscut and in some cases surround the oxidised pyroxene however the veins could alternatively be the result of a hydrothermal event in the impact regolith a simple fourier cooling model suggests that a regolith of at least five metres depth would be sufficient to maintain temperatures associated with the pyroxene breakdown for over seven days low temperature hydrous alteration took place forming goethite identified via xrd xanes and ftir comparing with previous studies the goethite is likely to be terrestrial alteration pseudomorphing martian pyrite

the role of ph in red stratum mudstone disintegration in the three gorges reservoir area china and the associated micromechanisms abstract the well known slide prone red stratum mudstones in the three gorges reservoir tgr area are currently undergoing sharp changes in i water level driven by the impounding discharging operation of the three gorges dam and ii the rain water h concentration driven by recent rapid industrial agricultural development and these changes are expected to impact geohazards this potential impact emphasizes the importance of understanding the role of ph in the drying wetting disintegration of red stratum mudstones although many investigations have focused on the role of ph in mudstone disintegration the red stratum mudstones in the tgr area differ from mudstones elsewhere and the role of ph has seldom been studied in these rocks this work adds to the limited body of research by 1 experimentally investigating the possible role of ph in red stratum mudstone drying wetting disintegration and 2 revealing the micromechanisms responsible for this role in the experiment six disintegration performance indexes and two mechanical indexes i e particle size gradation slake durability index decay constant surface energy box dimension fractal dimension cohesion and friction angle were monitored throughout the disintegration process a tri piecewise linear fractal model is proposed to better describe the particle size distribution this research shows that the acid enhancements stimulate the disintegration of red stratum mudstones and significantly affect shear strength in comparison alkaline environments inhibit the mudstone fragmentation and slightly degrade the shear strength two possible micromechanisms and three potential effects of acid or alkaline agents are presented to account for the role of ph the findings provide insights into the potential geohazard impacts of sharp changes in the exposure environment i e water level and h concentration of the red stratum mudstones in the tgr area

distribution petrography and shock metamorphism of the ejecta of the ries crater in germany a review abstract the lithologies and distribution of the various ejecta formations from the ries crater germany are described they may be subdivided into 1 low shock level 10 gpa represented by polymict crystalline breccias fall out suevites crater suevite and tektites moldavites the ejecta from the mesozoic sedimentary column do not show effects of shock pressures exceeding 10 gpa and only basement gneisses were shock melted to yield suevite glasses it is therefore concluded that the maximum impact energy was transferred from the impactor to the target rocks at a depth of at least 1000 m below ground level where a complex of gneisses underlies shallower granitic intrusions the estimated depth of the transient crater was about 2700 m and its diameter was 12 13 km bunte breccia megablocks of sedimentary rocks and crystalline breccias and megablocks were ejected in ballistic trajectories and form the earliest ejecta deposits extending up to a radius of 22 km fall out suevites are understood to have been lofted from the transient crater by an expanding plume of vaporized rocks and deposited outside the crater as fluidized turbulent masses on top of the earlier ejecta in contrast the crater suevite never left the crater cavity it represents the main mass of suevite moldavites are understood to have been formed during the first encounter of the impactor with the ground by condensation from vaporized and ionizised tertiary sands covering the surface of the target area

ries crater and suevite revisited observations and modeling part ii modeling we present the results of numerical modeling of the formation of the ries crater utilizing the two hydrocodes sova and isale these standard models allow us to reproduce crater shape size and morphology and composition and extension of the continuous ejecta blanket some of these results cannot however be readily reconciled with observations the impact plume above the crater consists mainly of molten and vaporized sedimentary rocks containing very little material in comparison with the ejecta curtain at the end of the modification stage the crater floor is covered by a thick layer of impact melt with a total volume of 6 11 km3 the thickness of true fallback material from the plume inside the crater does not exceed a couple of meters ejecta from all stratigraphic units of the target are transported ballistically no separation of sedimentary and crystalline rocks as observed between suevites and bunte breccia at ries is noted we also present numerical results quantifying the existing geological hypotheses of ries ejecta emplacement from an impact plume by melt flow or by a pyroclastic density current the results show that none of these mechanisms is consistent with physical constraints and or observations finally we suggest a new hypothesis of suevite formation and emplacement by postimpact interaction of hot impact melt with water or volatile rich sedimentary rocks

catastrophic emplacement of the heart mountain block slide wyoming and montana usa the mechanism that allowed many tens of km of movement of the enormous block slide floored by the rootless heart mountain detachment fault in nw wyoming has long been a puzzle carbonat rich microbreccia that is widespread along the fault and in dikes in the upper plate contains accreted grains indistinguishable from those observed as fallout from volcanic eruption clouds accretionary lapilli and impact ejecta clouds and in intrusive diatremes in these settings and also in industrial processing accreted grains form when particles in a turbulent gaseous suspension containing limited water adhere to a nucleating grain or to each other elongate grains in thick microbreccia have strong but diverse shap preferred orientations unlike those reported from other fault rocks but instead suggestive of turbulent flow and the microbreccia contains layering and other features of sedimentary character that appear to record deposition from suspension rather than frictional processes along a fault we suggest that frictional heating led to dissociation of carbonate rock along the fault producing supercritical co 2 as the suspending medium high co 2 pressure drastically reduced friction along the fault and allowed continuation of catastrophic movement probably initiated by a volcanic or phreatomagmatic explosion resulting in very large displacement on a low dipping surface earlier slower sliding may have occurred but final emplacement was rapid minutes and spectacular

spherule layers records of ancient impacts abstract a large extraterrestrial object striking earth at cosmic velocity melts and vaporizes silicate materials which can condense into highly spheroidal sand size particles that get deposited hundreds to thousands of kilometers from the point of impact these particles known as impact spherules have been detected in great abundance in a relatively small number of thin discrete layers ranging in age from less than a million years to 3 47 billion years unaltered impact spherules consist entirely of glass microtektites or a combination of glass and crystals grown in flight microkrystites impact spherule layers form very rapidly and can be very extensive even global in extent e g the cretaceous tertiary k t boundary layer so they form excellent time stratigraphic markers because they are always found in a stratigraphic context spherule layers are probably superior to terrestrial craters and related structures for assessing the environmental and biotic effects of large impacts a reco

the nature of the groundmass of surficial suevite from the ries impact structure germany and constraints on its origin surficial suevites from the ries impact structure have been investigated in the field and using optical and analytical scanning electron microscopy the groundmass of these suevites comprises calcite clay minerals impact melt glass crystallites plagioclase garnet and pyroxene francolite and ba phillipsite the latter zeolite is a secondary phase abundant textures have been observed intricate flow textures between the various groundmass phases globules of each phase in the other phases spheroids of pyrrhotite in calcite the budding off of clay globules into silicate glass and or calcite euhedral overgrowths of francolite on apatite clasts and quench textured crystallites in the groundmass groundmass forming calcite displays higher feo mno and sio2 contents than limestone target material the composition of suevite clay minerals is highly variable and not always consistent with montmorillonite three types of glasses are distinguished in the groundmass type 1 glasses are sio2 rich and are clearly derived from sandstones in the sedimentary cover while the protoliths of the other two glass types remains unclear analytical data and micro textures indicate that the calcite silicate glass francolite and clay minerals of the groundmass of the ries suevites represent a series of impact generated melts that were molten at the time of and after deposition on cooling plagioclase pyroxene and garnet crystallized from the groundmass these results are at variance with the current traditional descriptive definition of suevite given that ries is the original type occurrence of suevite some modification to the traditional definition may be in order as the results of this study are most consistent with the groundmass of ries surficial suevites representing a mix of several types of impact generated melts we suggest that a possible origin for these suevites is as some form of impact melt flow s that emanated from different regions of the evolving crater

ries crater and suevite revisited observations and modeling part i observations we report results of an interdisciplinary project devoted to the 26 km diameter ries crater and to the genesis of suevite recent laboratory analyses of crater suevite occurring within the central crater basin and of outer suevite on top of the continuous ejecta blanket as well as data accumulated during the past 50 years are interpreted within the boundary conditions imposed by a comprehensive new effort to model the crater formation and its ejecta deposits by computer code calculations artemieva et al 2013 the properties of suevite are considered on all scales from megascopic to submicroscopic in the context of its geological setting in a new approach we reconstruct the minimum maximum volumes of all allochthonous impact formations 108 116 km3 of suevite 14 22 km3 and the total volume of impact melt 4 9 8 0 km3 produced by the ries impact event prior to erosion these volumes are reasonably compatible with corresponding values obtained by numerical modeling taking all data on modal composition texture chemistry and shock metamorphism of suevite and the results of modeling into account we arrive at a new empirical model implying five main consecutive phases of crater formation and ejecta emplacement numerical modeling indicates that only a very small fraction of suevite can be derived from the primary ejecta plume which is possibly represented by the fine grained basal layer of outer suevite the main mass of suevite was deposited from a secondary plume induced by an explosive reaction fuel coolant interaction of impact melt with water and volatile rich sedimentary rocks within a clast laden temporary melt pool both melt pool and plume appear to be heterogeneous in space and time outer suevite appears to be derived from an early formed melt rich and clast poor plume region rich in strongly shocked components melt clasts and originating from an upper more marginal zone of the melt pool crater suevite is obviously deposited from later formed clast rich and melt poor plumes dominated by unshocked and weakly shocked clasts and derived from a deeper central zone of the melt pool genetically we distinguish between primary suevite which includes dike suevite the lower sublayer of crater suevite and possibly a basal layer of outer suevite and secondary suevite represented by the massive upper sublayer of crater suevite and the main mass of outer suevite

accretion dispersal and reaccumulation of the bishunpur ll3 1 brecciated chondrite evidence from troilite silicate metal inclusions and chondrule rims abstract a set of troilite silicate metal tsm inclusions and chondrule rims in the bishunpur ll3 1 chondrite provide information regarding impact brecciation of small bodies in the early solar system the tsm inclusions and chondrule rims consist of numerous angular to subrounded silicate grains that are individually enclosed by fine networks of troilite feni metal also occurs in the troilite matrix the silicates include olivine fo55 98 low ca pyroxene en78 98 and high ca pyroxene en48 68wo11 32 al and si rich glass coexists with the silicates relatively coarse silicate grains are apparently fragments of chondrules typical of petrologic type 3 chondrites troilite fills all available cracks and pores in the silicate grains some of the tsm inclusions and rims are themselves surrounded by fine grained silicate rich rims fgr the tsm inclusions and rims texturally resemble the troilite rich regions in the smyer h chondrite breccia they probably formed by shock induced mobilization of troilite during an impact event on a primitive asteroidal body because silicates in the tsm inclusions and rims have highly unequilibrated compositions their precursor was presumably type 3 chondritic material like bishunpur itself the tsm inclusions and the chondrules with the tsm rims were fragmented and dispersed after the impact induced compaction then reaccreted onto the bishunpur parent body fgr probably formed around the tsm inclusions and rims as well as around some chondrules during the reaccumulation process components of most type 2 and 3 chondrites probably experienced similar processing i e dispersal of unconsolidated materials and subsequent reaccumulation

accretionary dust mantles in cm chondrites evidence for solar nebula processes abstract the texture and modal composition of fourteen carbonaceous chondrites of the cm group were studied in detail to unravel the origin of their various components and the evolution of their parent body ies the analysis and mapping of complete thin sections by scanning electron and optical microscopy revealed textural units in most samples in which all coarse grained primordial chondritic components chondrules chondrule fragments refractory inclusions particles rich in hydrous silicates pcp and various mineral fragments are coated by fine grained serpentine and tochilinite rich dust the dust mantled particles have spheroidal shapes and form a special lithology in which they are densely aggregated and compacted without any interstitial clastic material the dust mantles termed accretionary dust mantles and their host lithology called primary accretionary rock are interpreted as products of accretion processes in the solar nebula an origin by processes on the parent body is excluded for textural and mineralogical reasons most cm chondrites are affected by secondary impact induced brecciation of variable intensity except for yamato 791198 which is composed entirely of a primary accretionary rock obviously unaltered by secondary parent body processes such as aqueous alteration or brecciation the cm chondrites y74662 haripura cold bokkeveld kivesvaara mighei pollen nogoya y793321 alh 83100 murray and murchison consist of clasts of primary accretionary rock embedded in a fine grained clastic matrix derived from primary rock material the volume percentage of the clastic matrix ranges from 5 y74662 to 76 murchison bells and essebi are brecciated and affected by aqueous alteration to an extent that fragments of primary rock are not preserved the evaluation of literature data indicates that solar wind implanted noble gases are absent in the primary accretionary rock component of cm chondrites they are only present in brecciated samples it must be concluded from the relation between the content of trapped solar wind and degree of brecciation that 1 the solar noble gases are residing exclusively in the clastic matrix and 2 some cm chondrites are regolith breccias and others are fragmental or monomict breccias both types were formed on the parent body although the latter were never exposed to the solar wind based on the results of textural chemical and mineralogical investigations we conclude that a major portion of the water bearing phases in cm chondrites were produced by the hydration of refractory phases prior to the formation of dust mantles and prior to the formation of the recent cm parent body this process requires special physicochemical conditions which allow the crystallization of oh bearing silicates e g higher density of the nebula gas or special precursor planetesimals of the cm chondrite parent body

the sudbury impact layer in the paleoproterozoic iron ranges of northern michigan usa a layer of breccia that contains fragments of impact ejecta has been found at 10 sites in the paleoproterozoic iron ranges of northern michigan in the lake superior region of the united states radiometric age constraints from events predating and postdating depo si tion of the breccia are ca 1875 ma and 1830 ma the major bolide impact that occurred at 1850 ma at sudbury ontario 500 700 km east of these sites is the likely causative event the michigan sites described here along with previously described sites in minnesota and ontario defi ne an extensive ejecta bearing deposit throughout the paleoproterozoic iron ranges of the lake superior region that we refer to as the sudbury impact layer the layer at the sites in michigan exhibits a range of thicknesses lithologic characters and sedimentary settings the diversity of rock types and internal stratigraphic details of the layer imply that several different processes of transport and deposition are represented but the detailed investigations needed to document them are incomplete many of the sites had been described and interpreted previously as products of common terrestrial processes but the presence of relict shock induced planar deformation features in quartz indicates that the breccia layer is in fact the product of an extra terrestrial impact at most localities this layer also contains relict fragments of altered devitrifi ed glass and or accretionary lapilli one immediate use of the impact layer is as an ultraprecise time line that ties together the well known stratigraphic sequences of the various geographically separated iron ranges the correlation of which has remained controversial for many decades the sudbury impact layer most commonly lies at a horizon that records a signifi cant change in the character of sediments across the region the impact layer marks the end of a major period of banded iron formation deposition that was succeeded by deposition of ficlastic rocks commonly black shales the impact may have produced regional if not global changes in the environment that resulted in this widespread synchronous change in sedimentation style

comparing two methods to estimate lateral force acting on stabilizing piles for a landslide in the three gorges reservoir china stabilizing piles are used worldwide to stabilize unstable slopes however to date there is little coverage in the scientific literature on the effects of the pore water pressure and the shear strength of the slip zone on the lateral force acting on the piles this paper presents and compares two methods to estimate the lateral force acting on the stabilizing piles these are the limit equilibrium method lem and the finite element shear strength reduction method fe srm for both methods the comsol software was used to model the infiltration of reservoir water and rainfall into the sliding mass the distribution of lateral force was then simulated by the normal stress distribution on the piles with fe srm in plaxis 8 2 software the effect of shear strength of the slip zone on the lateral force and its distribution were also studied the lower ercengyan landslide in the three gorges reservoir was used as study area with four different hydrological scenarios based on the reservoir water level fluctuations and rainfall amounts the results show that the lateral force with the lem method is slightly greater than with the fe srm method the lateral force reaches a peak when the level of the reservoir rises to 175 m combined with high rainfall amount and decreases linearly as the effective shear strength of the slip zone increases the distribution of the lateral force is parabolic and varies with the shear strength parameters of the slip zone in conclusion the lem and fe srm methods can be used to calculate the lateral force acting on the stabilizing piles and estimate the lateral force distribution this technique effectively analyzes the behavior of stabilizing piles for landslides it can be applied in the routine practical design of stabilizing piles in the three gorges reservoir as well as other similar areas

the azuara impact structure spain new insights from geophysical and geological investigations a progress report on geophysical and geological investigations in the 35 40 km diameter azuara probable impact structure northeast spain is given the target is a 10 km thick sequence of palaeozoic mesozoic and cenozoic sediments gravity measurements establish a negative residual anomaly of about 100 m s2 and a mass deficiency of 1 24 1014 kg they suggest the existence of a buried inner ring with half the size of the outer ring the result of preliminary model calculations is compatible with the assumption of a flat structure only a few kilometers deep measurements of the total intensity of the earth s magnetic field do not indicate causative bodies related to the structure geological mapping reveals a tectonic style which is characterized by folds and faults with radial and tangential elements and a strong horizontal component ejecta abundant monomict and polymict breccias dislocated megablocks inverted stratigraphy and a megabreccia up to 80 m thick in the outer ring are evidence for intense and violent deformation networks of typical breccia dikes well known from many impact structure cut through nearly all stratigraphical units various types and generations of breccia dikes occur in addition to previously described shock deformation in quartz and mica we present further evidence of high pressure and high temperature signatures in rocks the age of the impact is estimated to be upper eocene or oligocene we conclude that the formation of the azuara structure is difficult to explain by mechanisms other than impact and we discuss our observations within the scope of the contact compression excavation and modification stages of impact cratering with special attention directed to the peculiarities of the azuara sedimentary target

aggregation in particle rich environments a textural study of examples from volcanic eruptions meteorite impacts and fluidized bed processing aggregation is a common process occurring in many diverse particulate gas mixtures e g those derived from explosive volcanic eruptions meteorite impact events and fluid bed processing it results from the collision and sticking of particles suspended in turbulent gas air to date there is no generalized model of the underlying physical processes here we investigate aggregates from 18 natural deposits 16 volcanic deposits and two meteorite impact deposits as well as aggregates produced experimentally via fluidized bed techniques all aggregates were analyzed for their size internal structuring and constituent particle size distribution commonalities and differences between the aggregate types are then used to infer salient features of the aggregation process average core to rim ratios of internally structured aggregates accretionary lapilli is found to be similar for artificial and volcanic aggregates but up to an order of magnitude different than impact related aggregates rim structures of artificial and volcanic aggregates appear to be physically similar single sub spherical regularly shaped rims whereas impact related aggregates more often show multiple or irregularly shaped rims the particle size distributions psds of all three aggregate types are similar 200 m this proves that in all three environments aggregation occurs under broadly similar conditions despite the significant differences in source conditions particle volume fraction particle size distribution particle composition temperature residence times plume conditions e g humidity and temperature and dynamics of fallout and deposition impact generated and volcanic aggregates share many similarities and in some cases may be indistinguishable without their stratigraphic context

engineering geological problems in the three gorges project on the yangtze china the three gorges project formally commenced in december 1994 geological investigations however have been in progress since the 1950s the scope of this work was comprehensive covering all aspects of reservoir geology regional tectonics and seismicity as well as studies related to site selection and structural foundation conditions and construction materials in this paper a review of the geological studies is conducted with emphasis placed on the principle geological problems the following is concluded the damsite offers an excellent foundation in precambrian granite rocks the tectonic setting for the project is relatively simple the existing level of seismicity is anticipated to remain at the same low level no significant change in the stability of existing bank slopes is expected to occur due to the operation of the reservoir and no slides will endanger the construction and operation of the project

terrestrial chondrules glass spherules and accretionary lapilli from the suevite ries crater germany abstract until recently no terrestrial analogues of meteoritic and lunar chondrules were known only rare glass spherules from the lonar crater india and black magnetic spherules from various localities have been recorded the impact breccia suevite of the no rdlinger ries crater germany contains both chondrules and glass spherules and in addition accretionary lapilli all of which are found imbedded within the fine grained matrix of the suevite the chondrules display many of the textural features characteristic of meteoritic and lunar chondrules lithic chondrules and fluid drop chondrules are present the latter having a composition quite similar to that of glass bombs and glass fragments in the suevite fluid drop chondrules developed from glass spherules by slow devitrification in the hot suevite ejecta masses after deposition on the whole fluid drop chondrules lithic chondrules and glass spherules are rare in the suevite with fluid drop chondrules prevailing detection of chondrules from a terrestrial impact crater supports theories of an impact origin for meteoritic and lunar chondrules accretionary lapilli also represent material formed as a result of impact

petrography of the impact breccias of the enkingen subo 18 drill core southern ries crater germany new estimate of impact melt volume a new drill core subo 18 that intersects a continuous sequence of impact breccias has been obtained at the town of enkingen at the southern edge of the ries inner crater detailed petrographic analysis of this core provides important new information regarding the nature and origin of within crater suevite which is not only relevant for the understanding of the formation of the ries impact structure but has strong implications for impact breccia deposition in general in the enkingen core below 21 m of crater sediment 90 m of impact breccia have been sampled most of this material is what in the past has been referred to as suevite defined as groundmass of clastic material entraining cogenetic melt fragments and target rock clasts only the bottommost 10 m of core are melt dominated impact breccia any relatively thick melt rock intersection along this core is revealed to be composed of individual centimeter to decimeter sized melt bodies best described as agglomerate due to its close resemblance to volcaniclastics of that type detailed macro meso and microscopic petrographic analysis has established that the subo 18 impact breccias cannot be divided into distinct units the groundmass is extensively altered to phyllosilicate smectite or chlorite or carbonate minerals results of a detailed scanning electron microscopic investigation of the groundmasses of samples from all parts of this sequence emphatically support the traditional definition of suevite irrespective of scale modal analysis at macroscopic to submicroscopic scales has shown that the overall average melt content of enkingen suevite is on the order of 48 vol this exceeds by far previous estimates and brings the ries crater melt volume in line with values traditionally suggested from crater and melt volume scaling for similar sized impact structures in crystalline and mixed targets

fe rich and k rich mafic spherules from slumped and channelized chicxulub ejecta deposits in the northern la sierrita area ne mexico spherule deposits commonly interpreted as ejecta from the chicxulub impact at yucatan mexico are present in many k t cretaceous tertiary sections geological mapping of the northern la sierrita area ne mexico revealed the presence of 1 multiple spherule deposits embedded in late maastrichtian marls which are folded or disaggregated breccia like they are up to 6 m thick locally present in two outcrop areas and show limited lateral continuity these deposits consist of mm cm sized spherical to drop shaped vesiculated spherules angular to filamentous ejecta fragments and abundant carbonate they are interpreted as primary ejecta fallout deposits that have been affected by subsequent local slumps slides liquefaction and debris flows welded components suggest an initial ground surge like ejecta dispersion mode 2 a spherule deposit 10 60 cm thick that constitutes the base of a channelized sand siltstone deposit at or close to the k t boundary and is characterized by wide lateral continuity it is of similar petrologic composition to deposit 1 though slightly enriched in terrigeneous detritus thus reflecting influx from proximal shelf areas it is interpreted to result from debris flows and turbidite currents though no size sorting and abrasion of ejecta has been observed petrological mineralogical and geochemical criteria suggest that ejecta components from both types of spherule deposits are similar and originated from the chicxulub impact with multiple deposits produced by subsequent remolding reworking and redeposition spherules and fragments have an fe 25 30 wt al mg rich and si poor 25 wt sio2 composition and are altered to chlorite and iron oxides though rare k rich mafic glass 50 wt sio2 5 8 wt k is also present they contain ti fe k rich schlieren fe mg rich globules and rare m sized metallic and sulfidic ni co rich inclusions carbonate as clasts and within spherules and fragments shows textures indicative of quenching and or liquid immiscibility although potential ejecta fractionation and alteration make accurate evaluation difficult this composition suggests an ejecta origin mainly from mafic lithologies and carbonaceous sediments in addition to a contribution from intermediate felsic rocks and the possibility of meteoritic contamination

ancient aqueous environments at endeavour crater mars opportunity has investigated in detail rocks on the rim of the noachian age endeavour crater where orbital spectral reflectance signatures indicate the presence of fe 3 rich smectites the signatures are associated with fine grained layered rocks containing spherules of diagenetic or impact origin the layered rocks are overlain by breccias and both units are cut by calcium sulfate veins precipitated from fluids that circulated after the endeavour impact compositional data for fractures in the layered rocks suggest formation of al rich smectites by aqueous leaching evidence is thus preserved for water rock interactions before and after the impact with aqueous environments of slightly acidic to circum neutral ph that would have been more favorable for prebiotic chemistry and microorganisms than those recorded by younger sulfate rich rocks at meridiani planum

impact melt products of chondritic material a large variety of objects in chondritic meteorites formed as a result of impact melting shock veins metal troilite mixtures metal and sulfide nodules melt pockets vugs agglutinates glassy and crystalline spherules and numerous types of melt rock clasts the type of object produced in an impact event is related to the interaction of the shock waves with the particular target rock impact melting has also affected large portions of several chondrite breccias many of these contain vugs and patches of silicate glass some workers have suggested that various iron meteorites including groups iab iiicd and iie as well as several ungrouped irons were formed from individual impact melt pools in chondritic regoliths the eagle station trio pallasites and several ungrouped meteorites bencubbin weatherford enon acapulco and allan hills a77081 may have formed from impact melted chondritic material it is also possible that the parent magmas of ureilites were derived from impact melted metal rich carbonaceous chondrite material

a precambrian proximal ejecta blanket from scotland ejecta blankets around impact craters are rarely preserved on earth although impact craters are ubiquitous on solid bodies throughout the solar system on earth they are rapidly effaced and few records exist of the processes that occur during emplacement of ejecta the stac fada member of the precambrian stoer group in scotland has previously been described as volcanic in origin however shocked quartz and biotite provide evidence for high pressure shock metamorphism while chromium isotope values and elevated abundances of platinum group metals and siderophile elements indicate addition of meteoritic material thus the unit is reinterpreted here as having an impact origin the ejecta blanket reaches 20 m in thickness and contains abundant dark green vesicular devitrified glass fragments field observations suggest that the deposit was emplaced as a single fluidized flow that formed as a result of an impact into water saturated sedimentary strata the continental geological setting and presence of groundwater make this deposit an analogue for martian fluidized ejecta blankets

petrography and composition of martian regolith breccia meteorite northwest africa 7475 the northwest africa nwa 7475 meteorite is one of the several stones of paired regolith breccias from mars based on petrography oxygen isotope mineral compositions and bulk rock compositions its inventory of lithic clasts is dominated by vitrophyre impact melts that were emplaced while they were still molten other clast types include crystallized impact melt rocks evolved plutonic rocks possible basalts contact metamorphosed rocks and siltstones impact spherules and vitrophyre shards record airborne transport and accreted dust rims were sintered on most clasts presumably during residence in an ejecta plume the clast assemblage records at least three impact events one that formed an impact melt sheet on mars 4 4 ga ago a second that assembled nwa 7475 from impactites associated with the impact melt sheet at 1 7 1 4 ga and a third that launched nwa 7475 from mars 5 ma ago mildly shocked pyroxene and plagioclase constrain shock metamorphic conditions during launch to 5 and 15 gpa the mild postshock heating that resulted from these shock pressures would have been insufficient to sterilize this water bearing lithology during launch magnetite maghemite and pyrite are likely products of secondary alteration on mars textural relationships suggest that calcium carbonate and goethite are probably of terrestrial origin yet trace element chemistry indicates relatively low terrestrial alteration comparison of mars odyssey gamma ray spectrometer data with the fe and th abundances of nwa 7475 points to a provenance in the ancient southern highlands of mars gratteri crater with an age of 5 ma and an apparent diameter of 6 9 km marks one possible launch site of nwa 7475

early archaean spherule beds in the barberton mountain land south africa no evidence for impact origin abstract detailed petrographical and geochemical studies are reported for several well documented occurrences of spherule rich layers in the barberton mountain land south africa which were previously inferred by lowe and co workers to be the result of early archaean meteorite impacts in contrast we made the following observations the textures of most spherules are not necessarily the result of impact but could instead be the product of radial or intersertal growth of crystals during secondary mineral formation there is no difference in the content of siderophile elements between spherule layers and layers devoid of spherules the siderophile element abundances are high where sulphide minerals e g pyrite gersdorffite and chalcopyrite and or chromite are present independent of the presence or absence of spherules high contents of e g ir up to 2700 ppb ni 0 96 wt and cr 1 6 wt were found in various samples abundances of these elements in chondritic meteorites are approximately 600 ppb 1 4 wt and 0 35 wt respectively resulting in respective meteoritic components in these samples of 450 70 and 460 we do not accept these high concentrations as primary meteoritic signatures impact melt rocks have typically 1 of a meteoritic component furthermore spherules of any kind are very rare in known impact deposits including the k t boundary if present at all they are not usually associated with any significant ir or pge anomaly the high abundances of the siderophile elements in some barberton samples and their enrichment in secondary minerals indicate that these elements have been remobilized and reconcentrated the pge interelement ratios have changed during remobilization as well thus the pge abundance patterns and ratios are not primary and cannot be used as an argument in favour of an impact origin either nickel rich cr spinels which are found in some of the barberton spherule samples have low fe 3 fe total ratios these ratios are incompatible with an extraterrestrial or impact origin because such impact derived spinels including those found at the k t boundary are highly oxidized and also have different chemical compositions there is also no indication of any evidence of shock metamorphism associated with the barberton spherule layers which is the commonly accepted definitive criterion for recognition of an impact origin this is unusual because such evidence is preserved even in heavily altered samples from deeply eroded archaean impact structures we conclude that while these spherule layers are clearly unusual and deserve further attention there is no convincing evidence for an origin by impact we suggest that they were formed by volcanic processes followed by extensive hydrothermal alteration

deformation of the central pier of the permanent shiplock three gorges project china an analysis case study the central pier cp is one of the key structures of the permanent shiplock in the three gorges project on the yangtze river china this paper deals with the study of the rock mass deformation of the cp of the second shiplock under various operation conditions numerical simulations using the 2 d distinct element method and 3 d finite element method are applied to analyze the rock mass deformation also time series analysis and gray system theory are used to predict the trends of rock displacements based on in situ measured data the results can be summarized as follows 1 the main deformation of the rock mass in the cp occurs after excavation completion while the shiplock is in operation the dominant displacements mainly occurring on both sides of the northern chamber developing generally towards the chamber 2 the horizontal displacement varies with the process of excavation and is in a steady state after excavation and during operation of the shiplock the displacement is slightly decreased 3 the horizontal displacement parallel to the axial line of the shiplock occurs downstream and 4 the vertical displacement occurs during excavation and then subsidence with various values takes place in different parts of the cp for different operation conditions

origin of accretionary lapilli within ground hugging density currents evidence from pyroclastic couplets on tenerife aggregation of airborne particles is an important way in which the atmosphere is cleansed of fine dust particles such as following explosive eruptions and meteorite impacts we identify successive stages in the growth history of particle aggregates based upon well preserved ash aggregate bearing pyroclastic layers on tenerife the layers are persistently organized into couplets made up of a lower ignimbrite layer and an upper widespread coignimbrite ash fall layer the upper part of each ignimbrite contains whole and fragmented concentric laminated accretionary lapilli whereas the overlying coignimbrite ash fall layer lacks accretionary lapilli and is composed of framework supported smaller and nonlaminated ash pellets sometimes slightly deformed or partly disaggregated the pellets resemble the cores of the larger accretionary lapilli in the underlying ignimbrite layer these field relations are repeated numerous times in several different successions and they indicate that ash pellets not accretionary lapilli form within the coignimbrite ash plumes some pellets fell directly to the ground producing coignimbrite ash fall layers but others settled into pyroclastic density currents where they accreted successive concentric laminations of fine ash as they circulated through the variously turbulent levels of the stratified current and heat of the lower part of the current dried and partly lithified them into brittle accretionary lapilli the fully formed whole and broken accretionary lapilli were then deposited from the current along with ash and pumice lapilli numerous ignimbrite veneers on tenerife have the form of ash layers a few centimeters thick that drape topography and locally contain matrix supported accretionary lapilli most volcanoes lack laterally continuous field exposure and such accretionary lapilli bearing layers might be mistaken for ash fall deposits we highlight the value of careful distinction between different types of ash aggregate facies when interpreting the origin of pyroclastic deposits for example during hazard assessments

terrestrial impact melt rocks and glasses abstract the effects of meteorite and comet impact on earth are rock brecciation the formation of shock metamorphic features rock melting and the formation of impact structures i e simple craters complex craters and multi ring basins large events such as the 65 ma chicxulub impact are believed to have had catastrophic environmental effects that profoundly influenced the development of life on earth in this review an attempt is made to summarize some of the voluminous literature on impact melting one important aspect of planetary impact provide some comments on this process and to make suggestions for future research the products of impact melting are glasses impact melt rocks and pseudotachylites our treatise deals mainly with the geological setting petrography and major element chemistry of melt rocks and glasses impact glasses in several petrographic aspects are similar to volcanic glasses but they are associated with shock metamorphosed mineral and rock fragments and in places with siderophile element anomalies suggestive of meteoritic contamination they are found in allogenic breccia deposits within fall back suevite and outside fall out suevite impact craters and as spherules in distal ejecta large events such as the k t boundary chicxulub impact are responsible for the formation of worldwide ejecta horizons which are associated with siderophile element anomalies and shock metamorphosed mineral and rock debris impact glasses have a bulk chemical composition that is homogeneous but exemptions to this rule are common on a microscopic scale however impact glasses are commonly strikingly heterogeneous tektites are glasses ejected from craters over large distances they are characterized by very low water and volatile contents and element abundances and ratios that are evidence that tektites formed by melting of upper crustal sedimentary rocks four tektite strewn fields are known three of which can be tied to specific impact craters impact melt rocks form sheets lenses and dike like bodies within or beneath allogenic fallback breccia deposits in the impact crater and possibly on crater terraces and flanks dikes of impact melt rocks also intrude the rocks of the crater floor they commonly contain shock metamorphosed target rock and mineral fragments in various stages of assimilation and are glassy or fine to coarse grained chemically they are strikingly homogeneous but as with impact glasses exemptions to this rule do exist large and thick melt bodies such as the sudbury igneous complex sic are differentiated or may represent a combination of impact melt rocks sensu strictu and impact triggered deep crustal melts a concerted multidisciplinary approach to future research on impact melting and on other aspects of meteorite and comet impact is advocated impact models are models only and uncritical reliance on their validity will not lead to a better understanding of impact processes especially of melting excavation and deposition of allogenic breccias and the spatial position of breccias in relation to sheets and lenses of melt rocks within the crater impact triggered pressure release melting of target rocks beneath the excavation cavity may be responsible for the existence of melt rocks beneath the impact melt rocks sensu strictu this controversial idea needs to be tested by a re evaluation of existing data and models be they based on field or laboratory research only a relatively small number of terrestrial impact structures has been investigated in sufficient detail as it relates to geological and geophysical mapping in this review we summarize observations made on impact melt rocks and impact glasses in a number of north american brent haughton manicouagan new quebec sudbury wanapitei all in canada asian popigai russia zhamanshin kazakhstan two south african structures morokweng and vredefort the henbury crater field of australia and one european crater ries germany our tables listing major element chemical compositions of impact glasses and melt rocks however include also data from structures not dealt with in further detail

geochemistry and mineralogy of early archean spherule beds barberton mountain land south africa evidence for origin by impact doubtful abstract spherule layers in the 3 4 ga barberton greenstone belt south africa have been interpreted as being the result of large asteroid or comet impacts on the early earth this interpretation was based among other arguments on the enrichment of siderophile elements especially the platinum group elements we made a detailed mineralogical petrological and geochemical study of spherule bed samples taken from drill cores and underground exposures at the princeton mt morgan and sheba gold mines as well as surface localities the macrostructure of each sample from within different spherule layer units shows evidence for multiple more than five events over about 30 cm this would require multiple impacts within a few million years which is unlikely the mineral phases are almost exclusively of secondary origin the mineralogy provides evidence for extensive hydrothermal and metasomatic alterations of the spherule beds geochemical analyses of alternating spherule shale and chert layers show no correlation between the siderophile elements e g ir co ni and au contrary to that which would be expected if the siderophile elements had an extraterrestrial source furthermore no significant variation in the content of the siderophile elements was detected between spherule layers and shale layers however siderophile element contents are high only in layers containing abundant sulphide minerals and having high as sb se and cr contents we suggest that complex mineralizations similar to those that have formed the barberton archean gold deposits or the bon accord deposit were responsible for the siderophile element enrichments in the spherule beds the mineralogical and geochemical data provide no direct evidence in favour of their initial origin by impact nowhere else in the world have such multiple or even single spherule beds been observed and none of the numerous known impact crates or the cretaceous tertiary boundary is associated with comparable spherule beds known impact debris usually contains

a dual layer chicxulub ejecta sequence with shocked carbonates from the cretaceous paleogene k pg boundary demerara rise western atlantic abstract an up to 2 cm thick chicxulub ejecta deposit marking the cretaceous paleogene k pg boundary the k t boundary was recovered in six holes drilled during odp leg 207 demerara rise tropical western atlantic stunning features of this deposit are its uniformity over an area of 30 km2 and the total absence of bioturbation allowing documentation of the original sedimentary sequence high resolution mineralogical petrological elemental isotopic sr nd and rock magnetic data reveal a distinct microstratigraphy and a range of ejecta components the deposit is normally graded and composed predominantly of rounded 0 1 to max 1 mm sized spherules spherules are altered to dioctahedral aluminous smectite though occasionally relict si al rich hydrated glass is also present suggesting acidic precursor lithologies spherule textures vary from hollow to vesicle rich to massive some show in situ collapse others include distinct fe mg ca ti rich melt globules and lath shaped al rich quench crystals both altered glass spherules and the clay matrix site 1259b display strongly negative e nd t 65 ma values 17 indicating uptake of nd from contemporaneous ocean water during alteration finally fe mg rich spherules shocked quartz and feldspar grains few lithic clasts as well as abundant accretionary and porous carbonate clasts are concentrated in the uppermost 0 5 0 7 mm of the deposit the carbonate clasts display in part very unusual textures which are interpreted to be of shock metamorphic origin the preservation of delicate spherule textures normal grading with lack of evidence for traction transport and sub millimeter scale compositional trends provide evidence for this spherule deposit representing a primary air fall deposit not affected by significant reworking the odp leg 207 spherule deposit is the first known dual layer k pg boundary in marine settings it incorporates compositional and stratigraphic aspects of both proximal and distal marine sites its stratigraphy strongly resembles the dual layer k pg boundary deposits in the terrestrial western interior of north america although there carbonate phases are not preserved the occurrence of a dual ejecta layer in these quite different sedimentary environments separated by several thousands of kilometers provides additional evidence for an original sedimentary sequence therefore the layered nature of the deposit may document compositional differences between ballistic chicxulub ejecta forming the majority of the spherule deposit and material falling out from the vapor ejecta plume which is concentrated in the uppermost part

textural constraints on the formation of impact spherules a case study from the dales gorge bif paleoproterozoic hamersley group of western australia impact ejecta about 2 5 gyr old in the ds4 layer of the dales gorge bif hamersley group western australia are so well preserved that many original textures such as vesicles and microlites are faithfully preserved about 65 of the particles in the layer originated as impact ejecta of which 81 are splash forms the remaining 19 are angular but the splash forms and angular particles have the same composition mainly diagenetic stilpnomelane and k feldspar and share a common suite of internal textures some particles contain randomly oriented microlites texturally identical to plagioclase in basalts most splash forms have rims of inward growing crystals that may have formed from the melt perhaps nucleated by impinging dust or via thermal devitrification the rims clearly formed in flight because in broken particles which make up about 13 of the splash forms they are generally not present on broken surfaces the origin of the angular particles is uncertain but they may represent solid ejecta given the large sizes and variable shapes of the splash forms they are probably droplets of impact melt emplaced ballistically this is largely by analogy to the k t boundary layer but ds4 splash forms differ from k t spherules in important ways suggesting the k t model is not universal the occurrence of basaltic ejecta from a large impact highlights its scarcity in the stratigraphic record despite the areal abundance of oceanic crust the diverse textures formed via in flight crystallization suggest particle paths in the plume are more complex than is generally appreciated

suevite of the ries crater germany source rocks and implications for cratering mechanics suevites are impact breccias with a montmorillonitic matrix that contains shocked and unshocked mineral and rock fragments from the crystalline basement glass inclusions and a small amount of sedimentary clasts data are given of the modal composition of fall out suevites deposited at isolated points around the crater and crater suevite forming a layer below post impact lake sediments in the crater cavity fall out suevites contain aerodynamically shaped bombs which are absent in crater suevite taking into account not only large glass fragments and bombs but also the finer fractions the glass content of fall out and crater suevites amounts to 47 and 29 vol respectively crystalline clasts in suevites consist of all igneous and metamorphic rock types that constitute the local basement which consists of an upper layer of igneous rocks mainly granites and a lower series of gneisses and amphibolite based on a collection of 1 200 clasts from 13 suevite occurrences the average crystalline clast population of suevites was determined suevites contain on the average 46 igneous and 54 metamorphic clasts in constrast weakly shocked and unshocked crystalline ejecta of the ries structure consist of 82 igneous and 18 metamorphic rocks

carbonate silicate liquid immiscibility upon impact melting ries crater germany the 24 km diameter ries impact crater in southern germany is one of the most studied impact structures on earth the ries impactor struck a triassic to upper jurassic sedimentary sequence overlying hercynian crystalline basement at the time of impact 14 87 0 36 ma storzer et al 1995 the 350 m thick malm limestone was present only to the south and east of the impact site to the north and west the malm had been eroded away exposing the underlying dogger and lias the largest proportion of shocked target material is in the impact melt bearing breccia suevite the suevite had been believed to be derived entirely from the crystalline basement calcite in the suevite has been interpreted as a postimpact hydrothermal deposit from optical inspection of 540 thin sections of suevite from 32 sites i find that calcite in the suevite shows textural evidence of liquid immiscibility with the silicate impact melt textural evidence of liquid immiscibility between silicate and carbonate melt in the ries suevite includes carbonate globules within silicate glass silicate globules embedded in carbonate deformable and coalescing carbonate spheres within silicate glass sharp menisci or cusps and budding between silicate and carbonate melt fluidal textures and gas vesicles in carbonate schlieren a quench crystallization sequence of the carbonate spinifex textured quenched carbonate separate carbonate spherules in the suevite mineral fragment matrix and inclusions of mineral fragments suspended in carbonate blebs given this evidence of liquid immiscibility the carbonate in the suevite therefore has like the silicate melt a primary origin by impact shock melting evidence of carbonate silicate liquid immiscibility is abundant in the suevites from the southwest to east of the ries crater the rarer suevites to the west to northeast of the crater are nearly devoid of carbonate melts this correspondence between the occurrence of outcropping limestones at the target surface and the formation of carbonate melt indicates that the malm limestones are the source rocks of the carbonate impact melt this correspondence shows that the suevites preserve a compositional memory of their source rocks from the regional distribution of suevites with or without immiscible carbonate melts it is inferred that the ries impactor hit the steep albtrauf escarpment at its toe in an oblique impact from the north

petrology of impactites from el gygytgyn crater breccias in icdp drill core 1c glassy impact melt rocks and spherules el gygytgyn is a 18 km diameter 3 6 ma old impact crater in ne siberia international continental scientific drilling program el gygytgyn hole 1c was drilled on the frozen crater lake 2 3 km from the crater center to a final depth of 517 m below the lake floor petrographic and geochemical analyses of 26 drill core samples three impact melt rocks from the surface and seven glass spherules from surface deposits outside the crater are used to characterize the impactite inventory at el gygytgyn the bottom 98 m of hole 1c intersected monomict brecciated unshocked rhyolitic ignimbrite with minor intercalations of polymict breccia and mafic inclusions these lithologies are overlain by 89 m of polymict breccia whose components occasionally exhibit scarce low degree shock metamorphic features this unit is succeeded by 10 m of suevite that contains about 1 vol glassy impact melt shards 1 cm in size and a low amount of shock metamorphosed lithic clasts the suevite is capped by a reworked fallout deposit that constitutes a transition over 4 m into lacustrine sedimentation a higher abundance of shock metamorphosed lithic clasts and glass spherules some with ni rich spinel and admixture of an ultramafic component characterize this unit we tentatively interpret this impactite section as allochthonous breccia in the vicinity of el gygytgyn s central ring uplift the geochemical compositions of seven glass spherules from terrace deposits 2 km outside the crater and eight spherules from the reworked fallout deposit in hole 1c show far greater variability than the composition of impact melt shards and impact melt rocks some of these spherules also show strong enrichments in siderophile elements