anthropogenic origin of siliceous scoria droplets from pleistocene and holocene archaeological sites in northern syria abstract siliceous scoria droplets measuring from 1 to 10 mm from one late pleistocene and four early holocene archaeological sites in northern syria are compared to similar droplets previously suggested to be the result of a cosmic impact at the onset of the younger dryas global cooling event the findings demonstrate that the presence of siliceous scoria droplets are independent of age and thus are not specific to the beginning of the younger dryas occurrences have not been reported from natural deposits but are instead associated with buildings destroyed by fire and thus appear to be restricted to archaeological sites we therefore conclude that melting of building earth in ancient settlements can occur during fires reaching modest temperatures there is no evidence to suggest that siliceous scoria droplets result from very high temperature melting of soil and are the result of a cosmic event

cosmic impact or natural fires at the allerod younger dryas boundary a matter of dating and calibration wittke et al 1 present evidence of a major cosmic impact at the onset of the younger dryas yd episode including some markers found in the top of the well known usselo marker horizon uh this finding is contrary to our extensive radiocarbon dating effort from this horizon 2 which shows that the uh at aalsterhut postdates the onset of the yd furthermore wittke et al 1 misinterpret the origin of the uh this horizon is a well defined paleosoil that formed during the allerod and the early yd in the top part of coversand this coversand was deposited before the allerod during cold and dry conditions and is part of the european sandbelt wildfires were common and occurred throughout this period rather than synchronously with the onset of the yd 3

bayesian chronological analyses consistent with synchronous age of 12 835 12 735 cal b p for younger dryas boundary on four continents the younger dryas impact hypothesis posits that a cosmic impact across much of the northern hemisphere deposited the younger dryas boundary ydb layer containing peak abundances in a variable assemblage of proxies including magnetic and glassy impact related spherules high temperature minerals and melt glass nanodiamonds carbon spherules aciniform carbon platinum and osmium bayesian chronological modeling was applied to 354 dates from 23 stratigraphic sections in 12 countries on four continents to establish a modeled ydb age range for this event of 12 835 12 735 cal b p at 95 probability this range overlaps that of a peak in extraterrestrial platinum in the greenland ice sheet and of the earliest age of the younger dryas climate episode in six proxy records suggesting a causal connection between the ydb impact event and the younger dryas two statistical tests indicate that both modeled and unmodeled ages in the 30 records are consistent with synchronous deposition of the ydb layer within the limits of dating uncertainty 100 y the widespread distribution of the ydb layer suggests that it may serve as a datum layer

greenland pt anomaly may point to noncataclysmic cape york meteorite entry petaev et al 1 tested the suite of hypotheses collectively known as the impact hypothesis that a swarm of impacts or airbursts from comets chondritic or stony asteroids caused an abrupt climate change continental scale wildfires mass extinctions and collapse of the clovis culture at or near the younger dryas boundary ydb the authors identify a large pt anomaly in the greenland ice sheet project 2 gisp2 core and suggest that it hints at an extraterrestrial source because there is no corresponding ir spike petaev et al challenge the impact hypothesis by proposing a highly fractionated iron meteorite the pt anomaly predates ammonimum and nitrate peaks in the gisp2 core by decades eliminating

burning peat and reworking loess contribute to the formation and evolution of a large carolina bay basin abstract carolina bays are nearly ubiquitous along 1300 km of the north american atlantic coastal plain but relatively few bays have been examined in detail making their formation and evolution a topic of controversy the lake mattamuskeet basin eastern north carolina usa is a conglomeration of multiple carolina bays that form a 162 km2 lake the eastern shoreline of the lake is made up of a 2 9 km wide plain of parabolic ridges that recorded rapid shoreface progradation the lower shoreface deposit contains abundant charcoal beds and laminae dated 6465 6863 cal yr bp corresponding with initiation of a lacustrine environment in the eastern part of the lake a core from the western part of the lake sampled a 1541 1633 cal yr bp charcoal bed at the base of the lacustrine unit indicating formation of this part of the basin postdates the eastern basin lake mattamuskeet has no relationship to the younger dryas or a linked impact event because rim accretion significantly postdates 12 000 cal yr bp the shoreline progradation and association of charcoal beds with the oldest lake sediment in both main parts of the basin suggest that fire and subsequent hydrodynamic processes were associated with initial formation of these carolina bays

age models and the younger dryas impact hypothesis israde alcantara et al 1 drew on interpretations of a core from lake cuitzeo mexico to support the younger dryas yd impact hypothesis a key aspect of their study was identifying and dating the yd interval in the sediments the authors stated that they recovered impact indicators from a 10 cm thick zone dating to 12 9 kcal bp but provided no direct numerical age control or chronological uncertainties for this interval depending on the carbon sources 14c ages of bulk lake sediment can be offset by several centuries 2 however even though the study used bulk 14c dates no offset was quantified dating of the section was accomplished by interpolating through 1 m of undated sediment because the six dates in that interval were rejected even so the rejected dates were in stratigraphic order and there seems no a priori basis to exclude them their age model was anchored by a tephra layer identified as the cieneguillas rhyolitic tephra dated elsewhere as 31 kcal bp 3 but no geochemical evidence was provided to support this tephra identification

unsupervised seismic facies analysis via deep convolutional autoencoders abstractone of the most important goals of seismic stratigraphy studies is to interpret the elements of the seismic facies with respect to the geologic environment prestack seismic data carry rich information that can help us get higher resolution and more accurate facies maps therefore it is promising to use prestack seismic data for the seismic facies recognition task however because each identified object changes from the poststack trace vectors to a prestack trace matrix effective feature extraction becomes more challenging we have developed a novel data driven offset temporal feature extraction approach using the deep convolutional autoencoder dcae as an unsupervised deep learning method dcae learns nonlinear discriminant and invariant features from unlabeled data then seismic facies analysis can be accomplished through the use of conventional classification or clustering techniques e g k means or self organizing maps using a physical model and field prestack seismic surveys we c

diamond from the dabie shan metamorphic rocks and its implication for tectonic setting diamond occurs in ultrahigh pressure metamorphic rocks from dabie shan anhui province eastern china diamond bearing rocks include eclogite gamet pyroxenite and jadeitite diamond occurs in a mineral assemblage with coesite and jadeite the diamonds and diamondiferous rocks of dabie shan are interpreted to be the products of ultrahigh pressure metamorphism in the underthrust basement of the yangtze continental plate during the early mesozoic at greater than 4 0 gigapascals and 900 c this interpretation is based on the distribution of rock units the stability field of diamond and isotopic data indicating a crustal origin for the rocks most diamonds occur as euhedral inclusions in garnets and are 10 to 60 micrometers across although some are up to 700 micrometers across

perylene in lake biwa sediments originating from cenococcum geophilum in its catchment area abstract perylene which is composed of five benzene rings is commonly found in sediments throughout the world at concentrations and distributions that are different from those of other polycyclic aromatic hydrocarbons the only information available on the origin of perylene comes from 4 9 dihydroxyperylene 3 10 quinone dhpq which originates from fungal component symbiosis or from parasites on plants however there is no direct evidence of a mechanism of perylene formation in this study we examined the relationship between sedimentary perylene and cenococcum geophilum c geophilum in a catchment area at lake biwa sclerotium grains of c geophilum containing dhpq were found in this catchment area approximately 40 balls kg 1 dried soil for 1 mm and small sclerotium grains were frequently found in the sediment in the sediment sample we also found broken particles containing perylene and they had a porous structure characteristic of sclerotium grains furthermore the particles contained dhpq in different transformation stages to perylene via 3 10 perylenequinone 3 10 pq this finding was consistent with results from elemental analysis oxygen carbon because a remarkable amount of dhpq originating from c geophilum also exists in the humic acids of soils and because the inputs of compounds to the lake depend strongly on the rivers perylene in the lake biwa sediment originates mainly from the dhpq of c geophilum in its catchment area

microdiamond daughter crystals precipitated from supercritical coh silicate fluids included in garnet erzgebirge germany microdiamonds associated with phlogopite quartz paragonite phengite apatite and rutile are found as regular constituents of minute polyphase inclusions in garnet of ultrahigh pressure p metamorphic gneiss lenses within migmatites of the gneiss eclogite unit erzgebirge germany these aggregates are interpreted to represent original inclusions of a supercritical dense coh fluid rich in k na and sio 2 from this fluid diamond was precipitated as a daughter crystal due to cooling at ultrahigh p conditions brittle failure of the garnet host due to overpressure during release of confining pressure is demonstrated by healed radial cracks during further cooling the silicate phase assemblage of the inclusions crystallized at reduced internal pressures outside the stability field of diamond as indicated by the presence of quartz paragonite and plagioclase it is proposed that the mica dominated mineral assemblage of the inclusions formed by reaction between the fluid and the garnet host the previously formed diamond daughter crystals being preserved metastably these diamond bearing inclusions provide an unequivocal record of dense supercritical coh fluids rich in alkalies and silica within subducted continental crust during ultrahigh p metamorphism

transitional changes in arborescent lignophytes at the devonian carboniferous boundary abstract it is usually considered that after the extinction of the devonian tree archaeopteri s no new arborescent lignophytes were established before the late tournaisian a reassessment of this pattern is presented here based on a three fold approach a re evaluation of the taxic diversity of tournaisian lignophyte trees based on descriptions of new plants from palaeotropical latitudes a study of the patterns of phenotypic changes occurring among early lignophytes using a principal coordinate analysis and a phylogenetic analysis of the affinities of the arborescent taxa the best supported results indicate that a substantial taxonomic and phenotypic diversity of arborescent lignophytes was already established in the first part of the tournaisian including some taxa that persisted until the serpukhovian two genera may have originated in the late devonian and crossed the devonian carboniferous boundary fewer originations and a decrease in phenotypic diversity occurred in the visean the phenotypic distinctiveness of tree stems compared with those of other growth forms in the lignophytes is assessed we propose a scenario in which the presence of lignophyte trees is continuous across the devonian carboniferous boundary with arborescent taxa distinct from archaeopteris already present in the latest devonian possibly in upland floras and diversifying significantly soon after the devonian carboniferous boundary supplementary material a list of taxa characters and matrices used in the principal coordinate analysis and phylogenetic analysis is available at http www geolsoc org uk sup18447

terrestrial carbon and nitrogen isotopic ratios from cretaceous tertiary boundary nanodiamonds one hypothesis for the origin of the nanometer size diamonds found at the cretaceous tertiary k t boundary is that they are relict interstellar diamond grains carried by a postulated asteroid the 13 c 12 c and 15 n 14 n ratios of the diamonds from two sites in north america however show that the diamonds are two component mixtures differing in carbon and nitrogen isotopic composition and nitrogen abundance samples from a site from italy show no evidence for either diamond component all the isotopic signatures obtained from the k t boundary are material well distinguished from known meteoritic diamonds particularly the fine grain interstellar diamonds that are abundant in primitive chondrites the k t diamonds were most likely produced during the impact of the asteroid with earth or in a plasma resulting from the associated fireball

frasnian plants from the dra valley southern anti atlas morocco anatomically preserved plant fragments are reported from devonian marine deposits exposed in the dra valley of southern anti atlas morocco associated conodont and tentaculite faunas indicate that the sediments yielding plants which consist of black shales with intercalated calcareous concretions are early frasnian in age and most probably represent zone 2 of the conodont zonation this is the first record of frasnian plants in north africa the specimens found all correspond to decorticated portions of axes six are referable to callixylon the organ genus corresponding to anatomically preserved axes of the progymnosperm tree archaeopteris based on wood characters especially ray structure they are assigned to the species c henkei formerly described from the famennian of europe one single specimen is compared to xenocladia a cladoxylopsid genus previously known from the middle devonian of europe usa and kazakhstan interestingly archaeopteridales and cladoxylopsida are two groups that dominate the younger plant assemblages of famennian age recently described from the eastern anti atlas callixylon henkei type axes occur both in the frasnian and in the famennian deposits of the anti atlas and they are all devoid of growth rings these results are in accordance with a close position of gondwana and euramerica during late devonian times

the climate change caused by the land plant invasion in the devonian land plants invaded continents during the mid paleozoic their spreading and diversification have been compared to the cambrian explosion in terms of intensity and impact on the diversification of life on earth whereas prior studies were focused on the evolution of the root system and its weathering contribution here we used a coupled climate carbon vegetation model to investigate the biophysical impacts of plant colonization on the surface climate through changes in continental albedo roughness thermal properties and potential evaporation from the early to the late devonian our model simulates a significant atmospheric co2 drop from 6300 to 2100ppmv that is due to an increase in the consumption of co2 though continental silicate weathering the continental drift and the climatic changes promoted by land plants explain this trend the simulated co2 drawdown is paradoxically associated with unchanged temperatures we show here that the co2 drop is counteracted by a large warming resulting from the surface albedo reduction caused by the appearance of an extended plant cover if co2 is consensually assumed as the main driver of the phanerozoic climate this paper demonstrates that during land plant invasion the modifications of soil properties could have played in the opposite direction of the carbon dioxide fall hence maintaining warm temperatures during part of the devonian

first record of rellimia leclercq bonamo aneurophytales from gondwana with comments on the earliest lignophytes

carbon nitrogen argon and helium study of impact diamonds from ebeliakh alluvial deposits and popigai crater nineteen diamond aggregate specimens 1 2 mm in size from impactites of popigai crater and five diamond samples 5 7 mm in size from ebeliakh river placers were studied our investigations indicate that samples from ebeliakh were formed in an impact event with the exception of one specimen y7 the carbon isotopic composition of diamonds from popigai varies within the previously reported limits 13c 8 to 22 whereas diamonds from ebeliakh placers show heavier values of 13c 7 to 10 all the specimens studied contain very low amounts of n mostly 20 ppm but a few contained up to 60 ppm for specimens where the quantity of n allowed reliable analysis 15n values were found to be in the range of 3 9 to 11 9 on the basis of combined ar and n study it was concluded that impact diamonds studied here can be a mixture of at least two types of gas carriers e g different diamond components a possible explanation would be involvement of a carbon vapour deposition cvd process or diamond growth in the impact melt in addition to the direct graphite diamond shock transformation the 13c distributions and different n 36ar correlations have indicated a difference between impact diamonds from ebeliakh and diamonds extracted from popigai crater this could be explained by the existence of different diamond populations formed during the popigai impact event on the other hand ebeliakh diamonds could have resulted from a separate impact event to popigai and an alternative crater is yet to be found

nanodiamonds in the younger dryas boundary sediment layer we report abundant nanodiamonds in sediments dating to 12 9 0 1 thousand calendar years before the present at multiple locations across north america selected area electron diffraction patterns reveal two diamond allotropes in this boundary layer but not above or below that interval cubic diamonds form under high temperature pressure regimes and n diamonds also require extraordinary conditions well outside the range of earth9s typical surficial processes but common to cosmic impacts n diamond concentrations range from 10 to 3700 parts per billion by weight comparable to amounts found in known impact layers these diamonds provide strong evidence for earth9s collision with a rare swarm of carbonaceous chondrites or comets at the onset of the younger dryas cool interval producing multiple airbursts and possible surface impacts with severe repercussions for plants animals and humans in north america

black mats spring fed streams and late glacial age recharge in the southern great basin black mats are prominent features of the late pleistocene and holocene stratigraphic record in the southern great basin faunal geochemical and sedimentological evidence shows that the black mats formed in several microenvironments related to spring discharge ranging from wet meadows to shallow ponds small land snails such asgastrocopta tappanianaandvertigo berryiare the most common mollusk taxa present semiaquatic and aquatic taxa are less abundant and include catinellids fossaria parva gyraulus parvus and others living today in and around perennial seeps and ponds the ostracodescypridopsis okeechobiandscottia tumida typical of seeps and low discharge springs today as well as other taxa typical of springs and wetlands are common in the black mats several new species that lived in the saturated subsurface also are present but lacustrine ostracodes are absent the 13c values of organic matter in the black mats range from 12 to 26 reflecting contributions of tissue from both c3 sedges most shrubs and trees and c4 saltbush saltgrass plants carbon 14 dates on the humate fraction of 55 black mats fall between 11 800 to 6300 and 230014c yr b p to modern the total absence of mats in our sample between 6300 and 230014c yr b p likely reflects increased aridity associated with the mid holocene altithermal the oldest black mats date to 11 800 11 60014c yr b p and the peak in the14c black mat distribution falls at 10 00014c yr b p as the formation of black mats is spring related their abundance reflects refilling of valley aquifers starting no later than 11 800 and peaking after 11 00014c yr b p reactivation of spring fed channels shortly before 11 20014c yr b p is also apparent in the stratigraphic records from the las vegas and pahrump valleys this age distribution suggests that black mats and related spring fed channels in part may have formed in response to younger dryas yd age recharge in the region however the inception of black mat formation precedes that of the yd by at least 40014c yr and hydrological change is gradual not rapid

the youngest big impact on earth deduced from geological and historical evidence the comparison of events that followed the great impact at the cretaceous tertiary boundary with those contained within the flood myths suggests an analogous cosmic cause this paper proposes that there is geological evidence to support this thesis which is also indicated by a careful analysis of the natural phenomena described in flood traditions the time the sites the cause the detailed course of the events and the consequences of this catastrophe can hope to be reconstructed

quantifying the distribution of nanodiamonds in pre younger dryas to recent age deposits along bull creek oklahoma panhandle usa high levels of nanodiamonds nds have been used to support the transformative hypothesis that an extraterrestrial et event comet explosion triggered younger dryas changes in temperature flora and fauna assemblages and human adaptations firestone rb et al 2007 proc natl acad sci usa 104 41 16016 16021 we evaluate this hypothesis by establishing the distribution of nds within the bull creek drainage of the beaver river basin in the oklahoma panhandle the earlier report of an abundance spike of nds in the bull creek i younger dryas boundary soil is confirmed although no pure cubic diamonds were identified the lack of hexagonal nds suggests bull creek i is not near any impact site potential hexagonal nds at bull creek were found to be more consistent with graphene graphane an additional nd spike is found in deposits of late holocene through the modern age indicating nds are not unique to the younger dryas boundary nd distributions do not correlate with depositional environment pedogenesis climate perturbations periods of surface stability or cultural activity

age constraint for an earliest famennian forest and its implications for frasnian famennian boundary in west junggar northwest china abstract as one of the five major extinction events in earth history the frasnian famennian boundary ffb crisis caused dramatic reductions in marine and terrestrial diversity the effects of this event on terrestrial ecosystems are not well understood due to the limited preservation of terrestrial sedimentary rocks and the relative scarcity of plant fossils this study generates a robust zircon u pb age 371 5 0 9 ma earliest famennian for a new fossil assemblage containing lycopsida archaeopteridales and cladoxylopsida from the upper zhulumute formation of the west junggar basin nw china these taxa are typical arborescent plants of the late devonian and represent the oldest known forest in china documenting afforestation in west junggar coevally with or just after the upper kellwasser event 372 ma the new u pb ages generated in this study refine the placement of the ffb in west junggar to within the zhulumute formation instead of the hongguleleng formation as previously thought

wood taphonomy in a tropical marine carbonate environment experimental results from lee stocking island bahamas abstract both teredinid bivales and limnorid isopods attacked wood that was deployed experimentally for two years in a carbonate environment on average wood samples collected after one year on the sea floor lost 17 of their original surface area to limnoria and 50 of their original volume to teredinids after two years on the sea floor wood samples lost an average of 39 of their original surface and 74 of their original volume all samples of kiln dried lumber pinus sequoia araucaria magnolia and quercus experienced significantly more attack by teredinids and limnoria than samples of quercus stellata post oak branch wood that experienced terrestrial decomposition in a warm temperate environment for five years before deployment on the sea floor taphonomic loss rates for wood in marine environments based on kiln dried lumber may overestimate loss rates for natural wood entering marine environments after initial decomposition in terrestrial environments burial appears to play an important role in wood taphonomy burial to a depth of 3 cm inhibited destruction by limnoria but not teredinids possibly due to the greater tolerance of molluscs for low o 2 levels and the ability of teredinids to raise their siphons above the wood surface both limnorids and teredinids may contribute to the formation of teredolites disaggregated sediment filled teredinid borings limnorid isopods remove the surface of wood exposing the calcite lined borings of teredinids once their calcite lined borings are exposed teredinid are susceptible to predation and in the aftermath of predation teredinid borings may become sediment filled exposure also causes the calcite lined borings to break and disaggregate leading to the formation of teredolites the fossil record of teredinids reaches back to the jurassic limnoria traces in the surface of wood are distinctive and diagnostic at the species level however limnoria have a sparse fossil record

new constraints on the evolution of carolina bays from ground penetrating radar ground penetrating radar gpr data for the savannah river site srs in the upper coastal plain of south carolina combined with geological archaeological and ecological data place new constraints on the evolution of carolina bays extant srs bay morphology formed mainly during the holocene and did not involve migration of bays across the landscape multiple periods of bay rim accretion with intervening intervals of erosion may characterize the longer term evolution of the bays bay evolution however did not involve significant modification of the upland unit underlying the region during fluctuating but generally open water conditions breaking waves along bay shorelines eroded and transported sediment which was subsequently exposed for deflation during periods of low water deflation and transport of sand into standing vegetation along the margin of the bay depression created a rim in the form of a parabolic dune lacking obvious internal stratification simultaneously infilling occurred by shoreline erosion and transport from adjacent elevated surfaces this coupled with growth of emergent vegetation resulted in decreased hydroperiod wave energy shoreline modification and rim accretion transport of some rim sediments back into the bays via alluvial and colluvial activity created wedges of infilling sediment during waning stages of evolution the apparent contradiction of bay orientation with respect to prevailing winds might reflect seasonal changes in water level and wind direction southwesterly winds during spring high water causes nw se elongation of the bays whereas northwesterly winds during lower water in the fall and winter account for nearshore deflation and rim accretion along the east southeastern bay margins

discovery of metamorphic diamonds in central china an indication of a 4000 km long zone of deep subduction resulting from multiple continental collisions the central orogenic belt cob of china is a major continental collision zone that contains extensive outcrops of deeply subducted and exhumed rocks at both the eastern and the western end of the belt here we report discovery of microdiamonds from both eclogites and felsic gneisses in the north qinling zone in the central portion of the cob this discovery demonstrates that the country rocks of continental affinity shared in the ultra high pressure metamorphic uhpm event and provides a bridge connecting the two previously recognized uhpm terranes thereby establishing the existence of a uhpm belt extending more than 4000 km geochronological dating yields early palaeozoic ages in the west and early mesozoic ages in the east recording two separate continental collisions overprinted within the cob occurrence of uhp metamorphism during recurrent continental collision here and in the alps suggests that deep subduction of continental material during such collisions is probably common rather than exceptional with significant implications for processes of plate tectonic reorganization and mantle mixing over time

geochemistry of carbonaceous impactites from the gardnos impact structure norway abstract the gardnos impact structure in southern norway is one of only two known impact structures among 175 whose impactites contain significant amounts typically 0 2 1 0 wt of carbon or 5 to 10 times the amount present in the target rocks sudbury canada is the other this study extends a previous investigation of the geochemistry and petrology of gardnos impactites french et al 1997 with additional sampling and a detailed investigation of the nature and possible origin of the carbonaceous material present two principal carbon components have been identified in gardnos impactites 1 impact produced diamonds 0 5 to 1 m in size with a cubic crystal structure predominantly hexagonal morphologies with platey layers and an estimated concentration of geochemical data suggests that there are no suitable target rocks that could provide a single source for the carbon in gardnos impactites however raman spectroscopy stable isotope analysis and transmission electron microscopy of the impact diamonds and graphitic carbon suggests that there were at least two episodes of c emplacement in gardnos impactites an impact related incorporation and shock transformation of graphitic material from target rocks followed by later mobilization of c possibly during postimpact cooling or later regional metamorphism

the impact flood connection does it exist in a recent article in terra nova kristan tollmann and tollmann 1994 suggested that the biblical flood can be explained by seven fragments of a comet that impacted the ocean at seven locations on earth at 03 00h c e t on 23 september 9545 yr bp we demonstrate that all the geological proofs that allegedly support their conclusions are not supported by the available data on impact cratering their hypothesis is based on insufficient and ambiguous data selective citation and incomplete comprehension of previous research

diamonds from the iridium rich k t boundary layer at arroyo el mimbral tamaulipas mexico diamonds up to 30 m in size were found in the iridium rich layer from the k t boundary site at arroyo el mimbral and the spherule bed from arroyo el penon northeastern mexico stepped heating experiments indicate two or more isotopically distinct diamond components with carbon isotopic compositions characteristic of a mixture of carbon sources the diamonds crystal form is cubic not the hexagonal polymorph of diamond lonsdaleite which has been used previously to infer formation due to shock transformation of graphite the size crystallography and mineralogic associations of k t diamonds are similar to those of impact produced diamonds from the ries crater in germany where both shock transformation of graphite and a mode of formation by condensation from a vapor plume have been inferred the discovery of impact produced diamonds in association with high ir contents for these sediments supports their impact origin k t age and the inference that their source was from the buried impact crater of chicxulub on the yucatan peninsula mexico

the carbonado diamond conundrum abstract the reviewer presents the results of a literature search on the enigmatic occurrences of carbonado a form but not the only form of polycrystalline diamond which is mined for industrial diamonds the principal occurrences are in brazil the central african republic car and siberia yakutia in the latter the name yakutite has been coined but though there are differences between these polycrystalline diamonds and the brazil car minerals they would seem to be little more significant than differences within the gondwana occurrences and yakutite should probably be regarded as another name for carbonado most occurrences are in placers and the minerals have probably been recycled more than once by sedimentary processes the ultimate source being unknown polycrystalline diamond has been described from the udachnaya pipe yakutia and though it is strictly framesite defined as an eruptive pipe variety of carbonado it differs little from other carbonados the fact that all occurrences known are in areas with kimberlites and gem diamond developments present suggests that carbonado does stem from terrestrial eruptive processes though not necessarily kimberlite pipes nevertheless this can be only a provisional personal conclusion there is much contradictory evidence in the literature the evidence of subjection to radiogenic agencies in car carbonados seems to be unexplained but it may be a secondary effect and not present in all carbonados this is a conundrum which still calls for much more research

the murray springs clovis site pleistocene extinction and the question of extraterrestrial impact some of the evidence for the recent hypothesis of an extraterrestrial impact that caused late pleistocene megafaunal extinctions firestone et al 2007 proc natl acad sci usa 104 16016 16021 was based upon samples collected at murray springs a clovis archaeological site in southeastern arizona here we describe sampling and analyses of magnetic separates from within above and below the lower younger dryas boundary lydb black mat at murray springs as well as radiation measurements from the lydb at murray springs and two other well stratified clovis sites the main magnetic fraction at murray springs is maghemite magnetic microspherules have terrestrial origins but also occur as cosmic dust particles we failed to find iridium or radiation anomalies the evidence for massive biomass burning at murray springs is addressed and found to be lacking we could not substantiate some of the claims by firestone and others but our findings do not preclude a terminal pleistocene cosmic event

microdiamond in high grade metamorphic rocks of the western gneiss region norway three grains of microdiamond were recovered from high grade gneiss exposed in the western gneiss region norway identification and characterization of the diamond grains by raman and infrared spectroscopy indicate the presence of substitutional impurities of h and n primary fluid inclusions in garnet and quartz in the diamond bearing rock demonstrate the evolution of metamorphic volatile fluids from reduced n 2 co 2 compositions during the peak phase of metamorphism to n 2 ch 4 h 2 o bearing compositions during retrograde metamorphism compatible geologic petrologic and fluid composition data imply a metamorphic origin for the microdiamonds if so the metamorphic and fluid conditions recorded by the microdiamonds and gneissic host may be applicable to microdiamond investigations in other high pressure regionally metamorphosed orogens

buried paleoindian age landscapes in stream valleys of the central plains usa abstract a systematic study of late quaternary landscape evolution in the central plains documented widespread deeply buried paleosols that represent paleoindian age landscapes in terrace fills of large streams 5th order in alluvial fans and in draws in areas of western kansas with a thick loess mantle alluvial stratigraphic sections were investigated along a steep bio climatic gradient extending from the moist subhumid forest prairie border of the east central plains to the dry subhumid and semi arid shortgrass prairie of the west central plains radiocarbon ages indicate that most large streams were characterized by slow aggradation accompanied by cumulic soil development from ca 11 500 to 10 000 14c yr b p in the valleys of some large streams such as the ninnescah and saline rivers these processes continued into the early holocene the soil stratigraphic record in the draws of western kansas indicates slow aggradation punctuated by episodes of landscape stability and pedogenesis beginning as early as ca 13 300 14c yr b p and spanning the pleistocene holocene boundary the development record of alluvial fans in western kansas is similar to the record in the draws slow aggradation was punctuated by multiple episodes of soil development between ca 13 000 and 9000 14c yr b p in eastern kansas and nebraska development of alluvial fans was common during the early and middle holocene but evidence shows fan development as early as ca 11 300 14c yr b p buried soils dating between ca 12 600 and 9000 14c yr b p were documented in fans throughout the region in stream valleys across the central plains rapid alluviation after ca 9000 14c yr b p resulted in deeply buried soils that may harbor paleoindian cultural deposits hence the paucity of recorded stratified paleoindian sites in the central plains is probably related to poor visibility i e deep burial in alluvial deposits instead of limited human occupation in the region during the terminal pleistocene and early holocene the thick dark cumulic a horizons of soils representing buried paleoindian age landscapes are targets for future archaeological surveys

wildfire and abrupt ecosystem disruption on california s northern channel islands at the allerod younger dryas boundary 13 0 12 9 ka abstract sedimentary records from california s northern channel islands and the adjacent santa barbara basin sbb indicate intense regional biomass burning wildfire at the allerod younger dryas boundary 13 0 12 9 ka all age ranges in this paper are expressed in thousands of calendar years before present ka radiocarbon ages will be identified and clearly marked 14c years multiproxy records in sbb ocean drilling project odp site 893 indicate that these wildfires coincided with the onset of regional cooling and an abrupt vegetational shift from closed montane forest to more open habitats abrupt ecosystem disruption is evident on the northern channel islands at the allerod younger dryas boundary with the onset of biomass burning and resulting mass sediment wasting of the landscape these wildfires coincide with the extinction of mammuthus exilis pygmy mammoth the earliest evidence for human presence on these islands at 13 1 12 9 ka 11 000 10 900 14c years is followed by an apparent 600 800 year gap in the archaeological record which is followed by indications of a larger scale colonization after 12 2 ka although a number of processes could have contributed to a post 18 ka decline in m exilis populations e g reduction of habitat due to sea level rise and human exploitation of limited insular populations we argue that the ultimate demise of m exilis was more likely a result of continental scale ecosystem disruption that registered across north america at the onset of the younger dryas cooling episode contemporaneous with the extinction of other megafaunal taxa evidence for ecosystem disruption at 13 12 9 ka on these offshore islands is consistent with the younger dryas boundary cosmic impact hypothesis firestone r b west a kennett j p becker l bunch t e revay z s schultz p h belgya t kennett d j erlandson j m dickenson o j goodyear a a harris r s howard g a kloosterman j b lechler p mayewski p a montgomery j poreda r darrah t que hee s s smith a r stich a topping w wittke j h wolbach w s 2007 evidence for an extraterrestrial impact 12 900 years ago that contributed to the megafaunal extinctions and younger dryas cooling proceedings of the national academy of sciences 104 16016 16021

evidence from the northwestern venezuelan andes for extraterrestrial impact the black mat enigma abstract a carbon rich black layer encrusted on a sandy pebbly bed of outwash in the northern venezuelan andes previously considered the result of an alpine grass fire is now recognized as a black mat candidate correlative with clovis age sites in north america falling within the range of black mat dated sites 12 9 ka cal bp as such the bed at site mum7b which dates to 14 c years bp raw dates and appears to be contemporaneous with the younger dryas yd cooling event marks a possibly much more extensive occurrence than previously identified no fossils megafauna or tool assemblages were observed at this newly identified candidate site 3800 a m s l as in the case of the north american sites here evidence is presented for an extraterrestrial impact event at 12 9 ka the impact related andean bed located 20 cm above 13 7 13 3 ka cal bp alluvial and glaciolacustrine deposits falls within the sediment characteristics and age range of black mat dated sites 12 9 ka cal bp in north america site sediment characteristics include carbon glassy spherules magnetic microspherules carbon mat welded onto coarse granular material occasional presence of platinum group metals rh and ru planar deformation features pdfs in fine silt size fragmental grains of quartz as well as orthoclase and monazite with an abundance of rare earth elements rees if the candidate site is black mat correlative with the black mat sites of north america such an extensive occurrence may support the hypothesized airburst impact over the laurentide glacier which led to a reversal of allerod warming and the onset of yd cooling and readvance of glaciers while this finding does not confirm such it merits further investigation which includes the reconnaissance for additional sites in south america furthermore if confirmed such an extensive occurrence may corroborate an impact origin

radiocarbon dating of palaeosol components in moraines in lapland northern sweden abstract accurate geochronologies are the key for comparison of palaeoclimate records in order to clarify problems concerning the geochronology of glacier fluctuations we dated palaeosols in moraines in the kebnekaise mountain region of swedish lapland these palaeosols already have been dated several years ago using bulk samples of the palaeosols and yielded ages of 6180 5790 and 2750 2100 cal yr bp in an attempt to evaluate the sources of contamination associated with bulk samples these soils were re dated by using coleoptera fragments cenococcum geophilum spores humic acids and woody plant tissues the new dates reveal that the two palaeosols found within the moraines represent much longer periods of time than was previously assumed soil formation periods can be distinguished for periods 7800 7580 6300 4080 2450 2000 and 1170 740 cal yr bp these age groups point to differentiated soil formation processes resedimentation bioturbation and or cryoturbation the results show that dated terrestrial macrofossils from glacial moraines indicate climate changes that are in accordance with other proxy records in northern and central scandinavia and in certain times off phase with glacier fluctuations in southern maritime norway this throws light on possible changing interaction of forcing factors during the holocene

a post glacial sea level hinge on the central pacific coast of canada abstract post glacial sea level dynamics during the last 15 000 calendar years are highly variable along the pacific coast of canada during the last glacial maximum the earth s crust was depressed by ice loading along the mainland inner coast and relative sea levels were as much as 200 m higher than today in contrast some outer coastal areas experienced a glacial forebulge uplift effect that caused relative sea levels to drop to as much as 150 m below present levels between these inner and outer coasts we hypothesize that there would have been an area where sea level remained relatively stable despite regional and global trends in sea level change to address this hypothesis we use pond basin coring diatom analysis archaeological site testing sedimentary exposure sampling and radiocarbon dating to construct sea level histories for the hakai passage region our data include 106 newly reported radiocarbon ages from key coastal sites that together support the thesis that this area has experienced a relatively stable sea level over the last 15 000 calendar years these findings are significant in that they indicate a relatively stable coastal environment amenable to long term human occupation and settlement of the area our results will help inform future archaeological investigations in the region

sclerotia as indicators of mid holocene tree limit altitude colorado front range usa studies in the front range of north central colorado have shown that sclerotia of cenococcum geophilum a common ectomycorrhizal fungus are larger beneath spruce fir forest and tree island vegetation than beneath tundra grasses and herbs the presence in alpine tundra soils of c geophilum sclerotia with median diameters that approach or exceed 1 0 mm is evidence that tree limit formerly stood higher than it does today a sediment sample collected 116 m above tree limit on rowe mountain in rocky mountain national park contained charred sclerotia with a median diameter of 1 1 mm wood charcoal particles too large to have been transported by wind were associated radiocarbon dates of 4770 25 yr bp charred sclerotia and 4900 15 yr bp charred spruce twig apply to the wildfire that destroyed forest or tree island vegetation at this locality lack of evidence for post fire regeneration suggests that growing season temperatures had already begun to decline from elevated middle holocene levels

the obolon impact structure ukraine and its ejecta deposits the obolon impact structure 18 km in diameter is situated at the northeastern slope of the ukrainian shield near its margin with the dnieper donets depression the crater was formed in crystalline rocks of the precambrian basement that are overlain by marine carboniferous and continental lower triassic deposits the post impact sediments comprise marine middle jurassic bajocian and bathonian and younger mesozoic and cenozoic deposits today the impact structure is buried beneath an about 300 meter thick sedimentary rock sequence most information on the obolon structure is derived from two boreholes in the western part of the crater the lowest part of the section in the deepest borehole is composed by allogenic breccia of crystalline basement rocks overlain by clast rich impact melt rocks and suevites abundant shock metamorphic effects are planar deformation features pdfs in quartz and feldspars kink bands in biotite etc coesite and impact diamonds were found in clast rich impact melt rocks crater fill deposits are a series of sandstones and breccias with blocks of sedimentary rocks that are covered by a layer of crystalline rock breccia crystalline rock breccias conglomeratic breccias and sandstones with crystalline rock debris have been found in some boreholes around the obolon impact structure to a distance of about 50 km from its center those deposits are always underlain by lower triassic continental red clay and overlain by middle jurassic marine clay the k ar age of impact melt glasses is 169 ma which corresponds to the middle jurassic bajocian age the composition of crater fill rocks within the crater and sediments outside the obolon structure testify to its formation under submarine conditions

large pt anomaly in the greenland ice core points to a cataclysm at the onset of younger dryas one explanation of the abrupt cooling episode known as the younger dryas yd is a cosmic impact or airburst at the yd boundary ydb that triggered cooling and resulted in other calamities including the disappearance of the clovis culture and the extinction of many large mammal species we tested the ydb impact hypothesis by analyzing ice samples from the greenland ice sheet project 2 gisp2 ice core across the bolling allerod yd boundary for major and trace elements we found a large pt anomaly at the ydb not accompanied by a prominent ir anomaly with the pt ir ratios at the pt peak exceeding those in known terrestrial and extraterrestrial materials whereas the highly fractionated pt ir ratio rules out mantle or chondritic sources of the pt anomaly it does not allow positive identification of the source circumstantial evidence such as very high superchondritic pt al ratios associated with the pt anomaly and its timing different from other major events recorded on the gisp2 ice core such as well understood sulfate spikes caused by volcanic activity and the ammonium and nitrate spike due to the biomass destruction hints for an extraterrestrial source of pt such a source could have been a highly differentiated object like an ir poor iron meteorite that is unlikely to result in an airburst or trigger wide wildfires proposed by the ydb impact hypothesis

chronological evidence fails to support claim of an isochronous widespread layer of cosmic impact indicators dated to 12 800 years ago according to the younger dryas impact hypothesis ydih 12 800 calendar years before present north america experienced an extraterrestrial impact that triggered the younger dryas and devastated human populations and biotic communities on this continent and elsewhere this supposed event is reportedly marked by multiple impact indicators but critics have challenged this evidence and considerable controversy now surrounds the ydih proponents of the ydih state that a key test of the hypothesis is whether those indicators are isochronous and securely dated to the younger dryas onset they are not we have examined the age basis of the supposed younger dryas boundary layer at the 29 sites and regions in north and south america europe and the middle east in which proponents report its occurrence several of the sites lack any age control others have radiometric ages that are chronologically irrelevant nearly a dozen have ages inferred by statistically and chronologically flawed age depth interpolations and in several the ages directly on the supposed impact layer are older or younger than 12 800 calendar years ago only 3 of the 29 sites fall within the temporal window of the yd onset as defined by ydih proponents the ydih fails the critical chronological test of an isochronous event at the yd onset which coupled with the many published concerns about the extraterrestrial origin of the purported impact markers renders the ydih unsupported there is no reason or compelling evidence to accept the claim that a cosmic impact occurred 12 800 y ago and caused the younger dryas

comprehensive analysis of nanodiamond evidence relating to the younger dryas impact hypothesis during the end of the last glacial period in the northern hemisphere near 12 9k cal a bp deglacial warming of the bolling allerod interstadial ceased abruptly and the climate returned to glacial conditions for an interval of about 1300 years known as the younger dryas stadial the younger dryas impact hypothesis proposes that the onset of the younger dryas climate reversal pleistocene megafaunal extinctions and disappearance of the clovis paleoindian lithic technology were coeval and caused by continent wide catastrophic effects of impact bolide events in north america while there are no known impact structures dated to the younger dryas onset physical evidence of the impact bolide events is argued to be present in sediments spanning several continents at stratigraphic levels inferred to date to the bolling allerod younger dryas boundary ydb reports of nanometer to submicron sized diamonds in ydb sediments in particular the rare 2h hexagonal polytype of diamond lonsdaleite have been presented as strong evidence for shock processing of crustal materials we review the available data on diamonds in sediments and provide new data we find no evidence for lonsdaleite in ydb sediments and find no evidence of a spike in nanodiamond concentration at the ydb layer to support the impact hypothesis

suspect cubic diamond impact proxy and a suspect lonsdaleite identification the presence of nanometer sized diamonds in purported younger dryas yd boundary dated sediments carbon spherules and greenland ice was cited as evidence of a yd impact event 1 although cubic and hexagonal lonsdaleite diamond have been found in shocked metamorphosed meteorites and are associated with terrestrial impact structures cubic diamonds are well known to occur in terrestrial deposits that have no associations with impact processes for example submicron and smaller cubic diamond crystals have been found recently in carbonaceous spherules isolated in upper soils from various german and belgian sites 2 lacking links to impact structures these diamonds are evidently not products of impact

accumulation of impact markers in desert wetlands and implications for the younger dryas impact hypothesis the younger dryas impact hypothesis contends that an extraterrestrial object exploded over north america at 12 9 ka initiating the younger dryas cold event the extinction of many north american megafauna and the demise of the clovis archeological culture although the exact nature and location of the proposed impact or explosion remain unclear alleged evidence for the fallout comes from multiple sites across north america and a site in belgium at 6 of the 10 original sites excluding the carolina bays elevated concentrations of various impact markers were found in association with black mats that date to the onset of the younger dryas black mats are common features in paleowetland deposits and typically represent shallow marsh environments in this study we investigated black mats ranging in age from approximately 6 to more than 40 ka in the southwestern united states and the atacama desert of northern chile at 10 of 13 sites we found elevated concentrations of iridium in bulk and magnetic sediments magnetic spherules and or titanomagnetite grains within or at the base of black mats regardless of their age or location suggesting that elevated concentrations of these markers arise from processes common to wetland systems and not a catastrophic extraterrestrial impact event

fungus not comet or catastrophe accounts for carbonaceous spherules in the younger dryas impact layer 1 a claim attributes the onset of the younger dryas climate interval and a range of other effects 12 900 years ago to a comet airburst and or impact event one key aspect of this claim centers on the origin of carbonaceous spherules that purportedly formed during intense impact ignited wildfires samples from pleistocene holocene sedimentary sequences in the california channel islands and other sites show that carbon spherules and elongate forms are common in samples dating to before during and well after the 12 900 year time horizon including from modern samples microscopic studies show that carbon spherules have morphologies and internal structures identical to fungal sclerotia such as sclerotium and cenococcum experimental charring of fungal sclerotia shows that their reflectance increases with temperature reflectance measurements of modern and late pleistocene spherules show that the latter indicate at most low intensity burning these data cast further doubt upon the evidence suggesting a catastrophic younger dryas impact event

middle devonian lycopsids from high southern palaeolatitudes of gondwana argentina fossil plants are described from the upper part of the devonian lolen formation sierra de la ventana buenos aires province argentina in the area of estancia las acacias the sequence is composed mainly of dark grey shales and fossils were found in a single horizon where thin inter layered beds of fine reddish brown micaceous sandstones appear where the environment of marine deposition became more shallow the age of the lolen formation is presently established on the basis of brachiopods these being characteristic elements of the malvinokaffric realm from the gondwana lower devonian emsian the fossil plants are remarkably preserved given that they are in rocks that have undergone intense deformation the plants are identified as haplostigma sp and haskinsia cf h colophylla and suggest a middle devonian age givetian for the fossil bearing levels haskinsia identified on the basis of leaf morphology is the first well delimited middle devonian lycopsid genus described from argentina and the record from the most southerly palaeolatitude during the middle devonian haskinsia was distributed in tropical warm temperate and high southern latitude cool temperate zones

implanted radiogenic and other noble gases in crustal diamonds from northern kazakhstan noble gases were extracted in steps from grain size fractions of microdiamonds 15 m the concentration also decreases with the combustion step both results are clear evidence that 4he has been implanted into the diamonds from decaying elements in the surrounding matrix the saturation concentration of 4he 5 6 10 4 cm3 stp g is among the very highest observed in any terrestrial diamonds fission xenon from the spontaneous fission of 238u accompanies the radiogenic 4he the 136xef 4he ratio of 2 5 0 3 10 9 agrees well with the production ratio of 2 3 10 9 expected in a reservoir where th u 3 3 radiogenic 40ar is predominantly 90 set free upon combustion it also resides in the diamonds and appears to have been incorporated into the diamonds upon their formation 3he on the other hand is mainly released during pyrolysis and hence is apparently carried by contaminants the concentration in the diamonds proper is of the order of 4 10 12 cm3 stp g with a 3he 4he ratio of 1 10 8 excess 21ne similarly appears to be present in contaminants as well as in diamonds proper these two nuclides in the contaminants must have a nucleogenic origin but it is difficult to explain their high concentrations

evidence for deposition of 10 million tonnes of impact spherules across four continents 12 800 y ago airbursts impacts by a fragmented comet or asteroid have been proposed at the younger dryas onset 12 80 0 15 ka based on identification of an assemblage of impact related proxies including microspherules nanodiamonds and iridium distributed across four continents at the younger dryas boundary ydb spherule peaks have been independently confirmed in eight studies but unconfirmed in two others resulting in continued dispute about their occurrence distribution and origin to further address this dispute and better identify ydb spherules we present results from one of the largest spherule investigations ever undertaken regarding spherule geochemistry morphologies origins and processes of formation we investigated 18 sites across north america europe and the middle east performing nearly 700 analyses on spherules using energy dispersive x ray spectroscopy for geochemical analyses and scanning electron microscopy for surface microstructural characterization twelve locations rank among the world s premier end pleistocene archaeological sites where the ydb marks a hiatus in human occupation or major changes in site use our results are consistent with melting of sediments to temperatures 2 200 c by the thermal radiation and air shocks produced by passage of an extraterrestrial object through the atmosphere they are inconsistent with volcanic cosmic anthropogenic lightning or authigenic sources we also produced spherules from wood in the laboratory at 1 730 c indicating that impact related incineration of biomass may have contributed to spherule production at 12 8 ka an estimated 10 million tonnes of spherules were distributed across 50 million square kilometers similar to well known impact strewnfields and consistent with a major cosmic impact event

post clovis survival of american mastodon in the southern great lakes region of north america abstract the end of the pleistocene in north america was marked by a wave of extinctions of large mammals with the last known appearances of many species falling between ca 11 000 10 000 14c yr bp temporally this period overlaps with the clovis paleoindian cultural complex 11 190 10 530 14c yr bp and with sudden climatic changes that define the beginning of the younger dryas chronozone ca 11 000 10 000 14c yr bp both of which have been considered as potential proximal causes of this extinction event radiocarbon dating of enamel and filtered bone collagen from an extinct american mastodon mammut americanum from northern indiana usa by accelerator mass spectrometer yielded direct dates of 10 055 40 14c yr bp and 10 032 40 14c yr bp indicating that the animal survived beyond the clovis time period and into the late younger dryas although the late survival of this species in mid continental north america does not remove either humans or climatic change as contributing causes for the late pleistocene extinctions neither clovis hunters nor the climatic perturbations initiating the younger dryas chronozone were immediately responsible for driving mastodons to extinction

evidence from central mexico supporting the younger dryas extraterrestrial impact hypothesis we report the discovery in lake cuitzeo in central mexico of a black carbon rich lacustrine layer containing nanodiamonds microspherules and other unusual materials that date to the early younger dryas and are interpreted to result from an extraterrestrial impact these proxies were found in a 27 m long core as part of an interdisciplinary effort to extract a paleoclimate record back through the previous interglacial our attention focused early on an anomalous 10 cm thick carbon rich layer at a depth of 2 8 m that dates to 12 9 ka and coincides with a suite of anomalous coeval environmental and biotic changes independently recognized in other regional lake sequences collectively these changes have produced the most distinctive boundary layer in the late quaternary record this layer contains a diverse abundant assemblage of impact related markers including nanodiamonds carbon spherules and magnetic spherules with rapid melting quenching textures all reaching synchronous peaks immediately beneath a layer containing the largest peak of charcoal in the core analyses by multiple methods demonstrate the presence of three allotropes of nanodiamond n diamond i carbon and hexagonal nanodiamond lonsdaleite in order of estimated relative abundance this nanodiamond rich layer is consistent with the younger dryas boundary layer found at numerous sites across north america greenland and western europe we have examined multiple hypotheses to account for these observations and find the evidence cannot be explained by any known terrestrial mechanism it is however consistent with the younger dryas boundary impact hypothesis postulating a major extraterrestrial impact involving multiple airburst s and and or ground impact s at 12 9 ka

inconsistent impact hypotheses for the younger dryas israde alcantara et al 1 presented evidence from lake cuitzeo sediments and argued that it supports the younger dryas yd impact hypothesis of firestone et al 2 for a major extraterrestrial impact event involving multiple airburst s and or ground impact s at 12 9 ka firestone et al 2 did not specify the details of the impact but proposed that it had continent wide effects and was most likely a comet the yd hypothesis requires an energy of 107 megatons equivalent to a 4 km wide comet because no late pleistocene craters have been identified firestone et al 2 argue for prior fragmentation of a large impactor and suggest that multiple 2 km objects struck the laurentide ice sheet at oblique angles

the younger dryas impact hypothesis a requiem abstract the younger dryas yd impact hypothesis is a recent theory that suggests that a cometary or meteoritic body or bodies hit and or exploded over north america 12 900 years ago causing the yd climate episode extinction of pleistocene megafauna demise of the clovis archeological culture and a range of other effects since gaining widespread attention in 2007 substantial research has focused on testing the 12 main signatures presented as evidence of a catastrophic extraterrestrial event 12 900 years ago here we present a review of the impact hypothesis including its evolution and current variants and of efforts to test and corroborate the hypothesis the physical evidence interpreted as signatures of an impact event can be separated into two groups the first group consists of evidence that has been largely rejected by the scientific community and is no longer in widespread discussion including particle tracks in archeological chert magnetic nodules in pleistocene bones impact origin of the carolina bays and elevated concentrations of radioactivity iridium and fullerenes enriched in 3 he the second group consists of evidence that has been active in recent research and discussions carbon spheres and elongates magnetic grains and magnetic spherules byproducts of catastrophic wildfire and nanodiamonds over time however these signatures have also seen contrary evidence rather than support recent studies have shown that carbon spheres and elongates do not represent extraterrestrial carbon nor impact induced megafires but are indistinguishable from fungal sclerotia and arthropod fecal material that are a small but common component of many terrestrial deposits magnetic grains and spherules are heterogeneously distributed in sediments but reported measurements of unique peaks in concentrations at the yd onset have yet to be reproduced the magnetic grains are certainly just iron rich detrital grains whereas reported yd magnetic spherules are consistent with the diffuse non catastrophic input of micrometeorite ablation fallout probably augmented by anthropogenic and other terrestrial spherular grains results here also show considerable subjectivity in the reported sampling methods that may explain the purported yd spherule concentration peaks fire is a pervasive earth surface process and reanalyses of the original yd sites and of coeval records show episodic fire on the landscape through the latest pleistocene with no unique fire event at the onset of the yd lastly with yd impact proponents increasingly retreating to nanodiamonds cubic hexagonal lonsdaleite and the proposed n diamond as evidence of impact those data have been called into question the presence of lonsdaleite was reported as proof of impact related shock processes but the evidence presented was inconsistent with lonsdaleite and consistent instead with polycrystalline aggregates of graphene and graphane mixtures that are ubiquitous in carbon forms isolated from sediments ranging from modern to pre yd age important questions remain regarding the origins and distribution of other diamond forms e g cubic nanodiamonds in summary none of the original yd impact signatures have been subsequently corroborated by independent tests of the 12 original lines of evidence seven have so far proven to be non reproducible the remaining signatures instead seem to represent either 1 non catastrophic mechanisms and or 2 terrestrial rather than extraterrestrial or impact related sources in all of these cases sparse but ubiquitous materials seem to have been misreported and misinterpreted as singular peaks at the onset of the yd throughout the arc of this hypothesis recognized and expected impact markers were not found leading to proposed yd impactors and impact processes that were novel self contradictory rapidly changing and sometimes defying the laws of physics the yd impact hypothesis provides a cautionary tale for researchers the scientific community the press and the broader public

carbonado physical and chemical properties a critical evaluation of proposed origins and a revised genetic model abstract carbonado diamond is the most controversial of all diamond types and is found only in brazil and the central african republic bangui neither an affinity to earth s mantle nor an origin in the crust can be unequivocally established carbonado diamond is at least 3 8 ga old an age about 0 5 ga older than the oldest diamonds yet reported in kimberlites and lamproites on earth derived from neo to mid proterozoic meta conglomerates the primary magmatic host rock has not been identified discovered in 1841 the material is polycrystalline robust and coke like and is best described as a strongly bonded micro diamond ceramic it is characteristically porous which precludes an origin at high pressures and high temperatures in earth s deep interior yet it is also typically patinated with a glass like surface that resembles melting with exotic inclusions of highly reduced metals carbides and nitrides the origin of carbonado diamond is made even more challenging but the challenge is important because a new diamondiferous host rock may be involved and the development of a new physical process for generating diamond is possibly assured the combination of micro crystals and random crystal orientation leads to extreme mechanical toughness and a predicable super hardness the physical and chemical properties of carbonado are described with a view to the development of a mimetic strategy to synthesize carbonado and to duplicate its extreme toughness and super hardness textural variations are described with an emphasis on melt like surface features not previously discussed in the literature but having a very clear bearing on the history and genesis of carbonado selected physical properties are presented and the proposed origins diverse in character and imaginatively novel are critically reviewed from our present knowledge of the dynamic earth all indications are that carbonado is unlikely to be of terrestrial origin a revised model for the origin of carbonado is developed based on 1 new observations which show that white dwarf stars can have diamond cores 2 c rich exoplanets may have diamond bearing mantles and 3 new shock wave experiments on methane suggest that diamond may be present in large gaseous planets such as saturn uranus and neptune where diamond in the core is solid and in jupiter where liquid diamond may be present it is proposed that carbonado diamond was delivered to earth from extra solar sources during the episode of late heavy bombardment 4 1 3 8 ga if the currently held view that r process heavy elements were added as a late veneer to earth through the collision of white dwarfs in kilonova explosions then why not carbonado diamond during this epic event

nanocrystalline diamond from the earth s mantle underneath hawaii abstract melt inclusions in a mantle derived garnet pyroxenite xenolith from salt lake crater hawaiian island of oahu have been analysed by means of transmission electron microscopy including energy dispersive x ray analysis electron energy loss spectroscopy and electron diffraction the melt inclusions represent trapped low degree melt that metasomatised the hawaiian mantle lithosphere before the eruption of the host magma the inclusions consist of a c cl s rich glass of basaltic composition an exsolved gas fluid phase mainly co2 with minor amounts of co h2o and some unidentified c h and h s species and or carbonate diamond is the major phase in the glass ranging in size between a few and several hundred nanometres two varieties of nanocrystalline diamonds are identified polycrystalline aggregates of nanometre size diamonds are tentatively explained as pseudomorphs after carbonate while single crystals are suggested to have crystallised from the melt other nanocrystalline phases include native fe and cu fes fes2 zns ags and several ti nb zr ir in pd rich phases of unknown composition overall the observed mineral assemblage suggests that the melt was highly reduced and strongly enriched in volatiles and trace elements of contrasting geochemical affinity our findings are the first evidence for a metasomatic impregnation of the hawaiian mantle by low degree melts here we report the first occurrence of diamond in the modern oceanic mantle

a carbon and nitrogen isotope study of diamond from primitive chondrites diamonds isolated from primitive chondrites of the carbonaceous ordinary and enstatite groups have been analysed by high resolution stepped combustion followed by measurement of their c and n isotopes using a newly adapted technique that allows quantitative measurements of c n ratios the 13c of the diamond is shown to vary between meteorite groups from 32 to 38 0 and the measured c n ratios suggest that the n concentration of diamond ranges over a factor of 7 from 1800 ppm tieschitz to 13 000 ppm adrar 003 the 15n of n released from diamond is constrained to 348 7 the complexity of the c release pattern and c n ratio during combustion implies the presence of more than one component which suggests that either more than one type of diamond is present in the samples or unidentified additional phases are located in the acid resistant residue the components are present in varying proportions between meteorite groups the data are compatible with a model of a mix of different diamond populations some probably presolar and some possibly solar existing in the early solar nebula where each population originally contributed a roughly equal amount to chondrites of every class subsequent metamorphism has resulted in overall variations in 13c and c n ratios in diamond isolated from meteorites of differing petrologic grade without significantly altering the n isotopic composition possible ways for this to be achieved are explored

nanometre size diamonds in the cretaceous tertiary boundary clay of alberta starting with the discovery of an iridium anomaly at the cretaceous tertiary boundary in italy1 the idea that a large asteroid or comet struck the earth at the end of the cretaceous period has gained wide acceptance2 4 although some workers suggest that massive volcanic eruptions can also explain the observations5 the abundance of small diamonds 3 5 nm in size in chondritic meteorites6 7 prompted us to search for such diamonds in the cretaceous tertiary boundary clay of the red deer valley of alberta the knudsen s farm locality dissolution and oxidation of this clay yielded 45 ng g 1 of a white fraction consisting of more than 97 carbon which was absent from rocks above and below the boundary layer we present evidence that this material is indeed diamond which strengthens further the case for an extraterrestrial impact the diamond indium ratio in the boundary clay may constrain the type of impactor our estimate 1 22 1 is close to the value found in type c2 chondritic meteorites2

early proterozoic ultrahigh pressure metamorphism evidence from microdiamonds microdiamonds from the akluil k minette dykes nunavut canada are similar to diamonds formed in subducted metamorphic rocks high concentrations of unaggregated nitrogen and positive 15 n suggest that the microdiamonds formed within rocks subducted to ultrahigh pressures before being sampled by the minette magma 1 8 billion years ago this ultrahigh pressure metamorphism in north america probably related to the trans hudson orogen about 2 billion years ago extends the occurrence of ultrahigh pressure metamorphism from 0 6 billion years to before 1 8 billion years ago and suggests that phanerozoic type subductions were active by the early proterozoic

shock synthesized hexagonal diamonds in younger dryas boundary sediments the long standing controversy regarding the late pleistocene megafaunal extinctions in north america has been invigorated by a hypothesis implicating a cosmic impact at the llerod younger dryas boundary or ydb 12 900 100 cal bp or 10 900 100 14c years abrupt ecosystem disruption caused by this event may have triggered the megafaunal extinctions along with reductions in other animal populations including humans the hypothesis remains controversial due to absence of shocked minerals tektites and impact craters here we report the presence of shock synthesized hexagonal nanodiamonds lonsdaleite in ydb sediments dating to 12 950 50 cal bp at arlington canyon santa rosa island california lonsdaleite is known on earth only in meteorites and impact craters and its presence strongly supports a cosmic impact event further strengthened by its co occurrence with other nanometer sized diamond polymorphs n diamonds and cubics these shock synthesized diamonds are also associated with proxies indicating major biomass burning charcoal carbon spherules and soot this biomass burning at the younger dryas yd onset is regional in extent based on evidence from adjacent santa barbara basin and coeval with broader continent wide biomass burning biomass burning also coincides with abrupt sediment mass wasting and ecological disruption and the last known occurrence of pygmy mammoths mammuthus exilis on the channel islands correlating with broader animal extinctions throughout north america the only previously known co occurrence of nanodiamonds soot and extinction is the cretaceous tertiary k t impact layer these data are consistent with abrupt ecosystem change and megafaunal extinction possibly triggered by a cosmic impact over north america at 12 900 100 cal bp

arborescent lignophytes in the tournaisian vegetation of queensland australia palaeoecological and palaeogeographical significance abstract a middle tournaisian flora comprising several taxa of arborescent lignophytes is documented for the first time in australia it challenges earlier hypotheses considering that the early mississippian vegetation of australia was impoverished and dominated by small to medium sized arborescent lycopsids until the serpukhovian when climatic conditions became favorable to the thriving of the famous lignophyte dominated rhacopteris flora recorded in australia but also south america the present account is based on anatomically preserved fragments of trunks and branches from two localities of queensland in the broken river province and the burdekin basin three taxa are recognized dameria hueberi gen et sp nov the putative progymnosperm species protopitys buchiana goeppert 1850 and a taxon of uncertain affinities characterized by a pitus type of wood but which differs from the latter genus by anatomical traits relative to its primary body the possible occurrence of subtle growth rings in some of the woods from the burdekin basin and the conifer like traits of the dameria wood are interpreted as ecological clues suggesting that these trees may have inhabited drier settings than the wetland habitats generally inferred for the lycopsids this difference in habitats is suggested to explain the rarity of arborescent lignophytes compared to lycopsids in the australian record of plants of early mississippian age the three taxa reported in this paper represent the earliest record of arborescent lignophytes in australia after the global events that affected the vegetation at the devonian carboniferous boundary and the extinction of archaeopteris they show that the successional pattern of arborescent lignophytes around the devonian carboniferous boundary is comparable to that observed in western europe with the evidence of a diversification occurring as early as the middle tournaisian the palaeogeographic and stratigraphic distribution of protopitys and dameria indicates the occurrence of extensive floral exchanges between southern laurussia and north eastern gondwana in the late devonian to mississippian

devonian plants from colombia with discussion of their geological and palaeogeographical context plant fossils are described from the cuche formation eastern cordillera colombia in the area of floresta those identified as colpodexylon cf deatsii banks and cf archaeopteris sp suggest an earliest late devonian frasnian age for the formation these or similar taxa are also found in contemporaneous deposits in western venezuela and other elements of the venezuelan flora are found in a geographically intermediate locality all three devonian plant localities in the northwest of south america are within the colombian eastern cordillera and its northern extension the venezuelan perija range an area that has been integrated as a part of the so called eastern andean terrane or central andean province supposedly accreted to the autochthonous block of the guyana shield during the early jurassic or before although both invertebrates and plants from this terrane have strong affinities to north american and european assemblages and might be interpreted as implying a laurussian origin for the eastern andean terrane the evidence is not yet unequivocal with some authors postulating an in situ development of this province

an antarctic iron meteorite contains preterrestrial impact produced diamond and lonsdaleite of the many meteorites recovered so far from the allan hills antarctica only nine have been irons one of these alha77283 contains troilite fes graphite c schreibersite fe ni 3p cohenite fe3c inclusions rich in the carbonado type diamond lonsdaleite nodules previously described from the canyon diablo meteorite1 2 the canyon diablo arizona meteorite the excavator of meteor crater is the only other iron meteorite known to contain these high pressure minerals and their occurrence in that meteorite has been explained as the result of shock induced transformation of graphite most probably at the moment of terrestrial impact and disintegration of the projectile during crater formation3 6 the suggestion7 that formation was by high gravitational pressure has not been accepted virtually identical diamond lonsdaleite containing material in alha77283 occurs in a meteorite specimen with a well developed heat altered zone produced by atmospheric ablation it seems therefore that the diamond and lonsdaleite were present in the meteoroid before its final ablative passage through the atmosphere and soft landing on the ground the shock event that produced these high pressure phases therefore must have taken place on its parent body or have been associated with the disruption of that body here we present the metallographic and x ray diffraction data on which this conclusion is based

raman micro spectroscopy on diamond graphite and other carbon polymorphs from the ultrahigh pressure metamorphic kimi complex of the rhodope metamorphic province ne greece raman micro spectroscopy was applied on carbon inclusions in garnet porphyroblasts from kyanite biotite garnet schists of the rhodope metamorphic province rmp ne greece diamond and cuboids of poorly to highly ordered graphite were identified either as single phase inclusions or as polyphase inclusions along with co2 and or carbonates calcite magnesian calcite questionable raman bands that may be assigned to other c phases nanodiamond lonsdaleite a different c polymorph have been observed the presence of diamond confirms beyond any doubt the ultrahigh pressure uhp metamorphism reported by mposkos and kostopoulos 1 e mposkos d kostopoulos diamond former coesite and supersilisic garnet in metasedimentary rocks from the greek rhodope a new ultrahigh pressure metamorphic province established earth planet sci lett 192 2001 497 506 in the rmp cuboid graphite showing variable degree of disordering most probably formed after diamond the possible involvement of co2 and or c o h fluids in the formation of diamond is discussed

diamonds from the popigai impact structure russia diamonds were found in impact melt rocks and breccias at the popigai impact structure in siberia the diamonds preserve the crystallographic habit and twinning of graphites in the preimpact target rocks from which they formed by shock transformation secondary and transmission electron microscopy indicate that the samples are polycrystalline and contain abundant very thin lamellae which could represent stacking faults with local hexagonal symmetry or microtwins microcrystalline units are 1 m infrared spectroscopy indicates the presence of solid co 2 and water in microinclusions in the diamonds co 2 being under a pressure greater than 5 gpa at room temperature trace element and isotopic compositions confirm the derivation from graphite precursors

the corossol structure a possible impact crater on the seafloor of the northwestern gulf of st lawrence eastern canada we report on a 4 1 0 2 km diameter and 185 m deep circular submarine structure exposed on the seabed in 40 m water depths in the northwestern gulf of st lawrence eastern canada from the analysis of high resolution multibeam bathymetric and seismic data the presence of a circular form characterized by a central uplift and concentric rings resembles the morphology and geometry of complex meteorite impact structures also other origins such as kimberlites intrusions karsts or diapirs can be eliminated on geological criteria a single 4 cm long breccia fragment recovered from the central uplift has numerous glassy droplets of fluorapatite composition assumed to be impact melts and a single quartz grain with planar intersection features thought to be shock induced planar deformation features pdfs the absolute age of this possible impact structure is unknown but its geological setting indicates that it was formed long after the mid ordovician and before regional pre quaternary sea level lowstands present results outline the need for further examination to confirm an impact origin and to precisely date the formation of the structure

microdiamonds frontier of ultrahigh pressure metamorphism a review abstract this is a comprehensive review paper devoted to microdiamonds from ultrahigh pressure metamorphic uhpm terranes incorporated in orogenic belts formed at convergent plate boundaries in paleozoic mesozoic alpine time when in 1980 the first small diamonds were discovered within amphibolite granulate facies metamorphic rocks it came as a great surprise that buoyant continental crust could be subducted to depths of hundreds of kilometers and then subsequently exhumed since then much progress has been made in understanding the mechanism of these diamonds formation and the number of new diamond bearing uhpm terranes was significantly increased especially within european orogenes moreover new variations in tectonic settings in which uhp rocks can be formed and exhumed came to the attention of geologists simply due to the finding of diamonds in places previously forbidden for their formation e g oceanic islands ophiolites and forearc environments over the past decade the rapidly moving technological advancement has made it possible to examine microdiamonds in detail and to learn that part of them has a polycrystalline nature that they contain nanometric multiphase inclusions of crystalline and fluid phases and that they keep a crustal signature of carbon isotopes scanning and transmission electron microscopy focused ion beam techniques synchrotron infrared spectroscopy micro x ray diffraction and nano secondary ion mass spectrometry studies of these diamonds provide evidence that they keep traces of fluid originated from both crustal and mantle reservoirs and that they probably interacted with deep mantle plumes hypotheses proposed for diamond formation in subduction zones founded on both analytical and experimental studies are discussed the paper also emphasizes that the discovery of these microdiamonds as well as coesite triggered a major revision in the understanding of deep subduction processes leading to a clear realization of how continental materials can be recycled into the earth s mantle and geochemically rejuvenate it

diamond inclusions in garnets from metamorphic rocks a new environment for diamond formation diamonds commonly occur in kimberlites lamproites and alluvial sediments derived from these rocks more recently diamonds or their graphite pseudomorphs have been discovered in ultramafic massifs1 and picrites2 here we report the occurrence of diamonds in situ in crustal rocks highly retrograded high pressure metamorphic garnet pyroxene and pyroxene carbonate garnet rocks biotite gneisses and schists from the kokchetav massif northern kazakhstan ussr the diamonds are cubo octahedral averaging 12 m in size and occur in zircons and with euhedral graphite as inclusions in unzoned garnets we believe that the zircon and garnet matrices protected these diamonds from retrogressive transformation to graphite mica rutile titanite clinopyroxene kyanite and zircon also occur as inclusions in garnet often intergrown with the diamonds equilibration relations of inclusions and host garnets indicate that both diamonds and graphite crystallized from a fluid phase under static conditions at pressures of 40 kbar and temperatures 900 1 000 c

a rift model for the sedimentary diamond deposits of brazil although several hundred kimberlites have been discovered in the past 20 years in brazil the brazilian diamond production has been derived almost entirely from sedimentary deposits diamond bearing conglomerates of different ages and recent alluvials or terraces conglomerates as a source of diamond production may not be very significant in economic terms but are extremely important in geological terms because they are the main known sources of the recent alluvial deposits of brazil in this sense brazil shows a sharp contrast with other large scale producing countries such as south africa botswana russia and australia where the production comes largely from kimberlites it has similarities with angola and india in the former the calonda conglomerates and in the latter the banganapalli conglomerates are as important as sources as are the kimberlites either because diamonds are recovered from them directly or because they feed the alluvials but brazil differs from these countries regarding the age of the oldest diamond finds while in angola they are restricted to the cretaceous and in india to the upper proterozoic in brazil they spread from the lower middle proterozoic to the cretaceous brazil is thus a very privileged area to study diamond sedimentary deposits not only because they are numerous and have economic importance but also and mainly because they occur in sedimentary sequences of at least four different ages the recognition of common geological features in diamond sedimentary sequences of different ages led to the conclusion that their recurrence through time reflect fundamental processes which can be put together in a rift evolutionary model in this study seven different diamondiferous districts in brazil are briefly described and their rift related features are emphasised these features include the position in the sedimentary pile both of the diamond bearing conglomerates and the volcanic events as well as the proximal character in relation to growth faults and the horizontal linear distribution of the conglomerates the proposed model stems from a sedimentary reasoning it links primary diamond sources and related volcanism to rifts and substantiates the idea that kimberlite lamproite extrusions predate tectonic paroxysm such that after erosion diamonds from those extrusions end up in proximal rift infill sediments here the timing of the extrusion of the primary diamond source rocks is similar to the one determined by white et al who produced structural evidence to establish their model

discovery of a nanodiamond rich layer in the greenland ice sheet we report the discovery in the greenland ice sheet of a discrete layer of free nanodiamonds nds in very high abundances implying most likely either an unprecedented influx of extraterrestrial et material or a cosmic impact event that occurred after the last glacial episode from that layer we extracted n diamonds and hexagonal diamonds lonsdaleite an accepted et impact indicator at abundances of up to about 5 10 6 times background levels in adjacent younger and older ice the nds in the concentrated layer are rounded suggesting they most likely formed during a cosmic impact through some process similar to carbon vapor deposition or high explosive detonation this morphology has not been reported previously in cosmic material but has been observed in terrestrial impact material this is the first highly enriched discrete layer of nds observed in glacial ice anywhere and its presence indicates that ice caps are important archives of et events of varying magnitudes using a preliminary ice chronology based on oxygen isotopes and dust stratigraphy the nd rich layer appears to be coeval with nd abundance peaks reported at numerous north american sites in a sedimentary layer the younger dryas boundary layer ydb dating to 12 9 0 1 ka however more investigation is needed to confirm this association

first find of polycrystalline diamond in ultrahigh pressure metamorphic terrane of erzgebirge germany this article describes polycrystalline diamond from the erzgebirge ultrahigh pressure metamorphic uhpm terrane of the bohemian massif related to the variscan 340 ma continent continent collision the foils polycrystalline diamond included in zircon were prepared with focused ion beam fib and studied with transmission electron microscopy tem each domain of the polycrystalline diamond consisted of a series of diamond monocrystals from 1 to 4 up to 15 containing numerous nanometric fluid and crystalline inclusions of sio2 caco3 kcl and kalsi3o8 the integrated chemistry of the nanoinclusions suggests that the polycrystalline diamond was crystallized from a mixture of two end members which includes a carbon rich hydrous silicic fluid containing si al k and a hydrous saline fluid rich in cl k na traces of carbonate sulphate and phosphate coupled with the presence of metallic cations such as fe mg ti cr co zn zr pb as and hg found in the diamond are coherent with the local geochemical diversity of the host metasedimentary rocks the oxidation state of the diamond forming fluid was close to c co buffer for example fo2 6 log units which is at the upper limit of the diamond stability region the presence of dislocation arrays indicating low angle grain boundaries together with zig zag features or kinks at diamond grain boundaries reflects rapid crystallization of the polycrystalline diamond triangular fluid pockets with steps at the surface related to 110 and 111 planes of diamond could promote the formation of c h and c oh bonds that probably could facilitate the process of diamond graphitization the microstructural features of polycrystalline diamond from the erzgebirge uhpm terrane as well as their undisputed formation from crustal organic carbon can be used for better understanding of the origin of any polycrystalline diamond formation from both kimberlitic and alluvial sources including enigmatic polycrystalline black diamond commonly called carbonado

mantle related carbonados geochemical insights from diamonds from the dachine komatiite french guiana abstract carbonado is a unique type of polycrystalline diamond characterised among others by 13c depleted isotope compositions 13c 25 vs pdb little advanced nitrogen aggregation ib iaa and sintered ceramic like diamond grains its origin remains an enigma with models proposing a formation either in the earth s crust or even within an exploding super nova the possibility that carbonado formed in the earth s mantle is often rejected because diamond with carbonado like geochemical features has never been found in rocks such as kimberlites that carry diamonds from the mantle in this study it is shown that the c and n stable isotope compositions nitrogen contents and nitrogen speciation of diamonds from the dachine komatiite french guyana exhibit unambiguous similarities with carbonados these include c isotopes from 32 6 to 0 15 mode at 27 n aggregation only ib iaa diamonds from 2 to 76 of n pairs and n isotopes from 4 1 to 6 9 average 2 1 2 9 which all strikingly match the carbonado data this evidence illustrates that the main geochemical arguments usually called to reject a mantle origin of carbonado are no longer valid a model linking carbonado crystallisation from komatiite volatiles is developed in this model the sintering is produced by the high temperature of the komatiite magma thus accounting for their absence in colder kimberlites the low 13c compositions of carbonados would be inherited from the transition zone 300 km depths which is known to yield diamonds with distinct c isotope distributions compared to most lithospheric diamonds 150 300 km depths this model can account for most available observations of carbonados including their large size sintering photoluminescense cathodoluminescence features and geochemical characteristics

the mysterious onset of the younger dryas abstract the 1300 year long younger dryas cold reversal 12 900 11 600 cal bp is seen most clearly in greenland ice cores contemporaneous changes of climate and environment in more southerly regions were variably expressed the precise timing of the abrupt younger dryas onset is still uncertain it was linked to a sudden increase in 14c manifest as a cliff where 14c dates drop from 11 000 to 10 600 radiocarbon years bp within a century of real time followed by a long plateau changes in ocean and or atmospheric circulation or solar radiation and even a comet impact have been proposed as triggers but the abruptness and severity of yd onset still elude explanation

a search for shocked quartz grains in the allerod younger dryas boundary layer the younger dryas impact hypothesis suggests that multiple airbursts or extraterrestrial impacts occurring at the end of the allerod interstadial resulted in the younger dryas cold period so far no reproducible diagnostic evidence has however been reported quartz grains containing planar deformation features known as shocked quartz grains are considered a reliable indicator for the occurrence of an extraterrestrial impact when found in a geological setting although alleged shocked quartz grains have been reported at a possible allerod younger dryas boundary layer in venezuela the identification of shocked quartz in this layer is ambiguous to test whether shocked quartz is indeed present in the proposed impact layer we investigated the quartz fraction of multiple allerod younger dryas boundary layers from europe and north america where proposed impact markers have been reported grains were analyzed using a combination of light and electron microscopy techniques all samples contained a variable amount of quartz grains with sub planar microstructures often tectonic deformation lamellae a total of one quartz grain containing planar deformation features was found in our samples this shocked quartz grain comes from the usselo palaeosol at geldrop aalsterhut the netherlands scanning electron microscopy cathodoluminescence imaging and transmission electron microscopy imaging however show that the planar deformation features in this grain are healed and thus likely to be older than the allerod younger dryas boundary we suggest that this grain was possibly eroded from an older crater or distal ejecta layer and later redeposited in the european sandbelt the single shocked quartz grain at this moment thus cannot be used to support the younger dryas impact hypothesis