very high temperature impact melt products as evidence for cosmic airbursts and impacts 12 900 years ago it has been proposed that fragments of an asteroid or comet impacted earth deposited silica and iron rich microspherules and other proxies across several continents and triggered the younger dryas cooling episode 12 900 years ago although many independent groups have confirmed the impact evidence the hypothesis remains controversial because some groups have failed to do so we examined sediment sequences from 18 dated younger dryas boundary ydb sites across three continents north america europe and asia spanning 12 000 km around nearly one third of the planet all sites display abundant microspherules in the ydb with none or few above and below in addition three sites abu hureyra syria melrose pennsylvania and blackville south carolina display vesicular high temperature siliceous scoria like objects or slos that match the spherules geochemically we compared ydb objects with melt products from a known cosmic impact meteor crater arizona and from the 1945 trinity nuclear airburst in socorro new mexico and found that all of these high energy events produced material that is geochemically and morphologically comparable including i high temperature rapidly quenched microspherules and slos ii corundum mullite and suessite fe3si a rare meteoritic mineral that forms under high temperatures iii melted sio2 glass or lechatelierite with flow textures or schlieren that form at 2 200 c and iv particles with features indicative of high energy interparticle collisions these results are inconsistent with anthropogenic volcanic authigenic and cosmic materials yet consistent with cosmic ejecta supporting the hypothesis of extraterrestrial airbursts impacts 12 900 years ago the wide geographic distribution of slos is consistent with multiple impactors

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

structure of the riddleville basin from cocorp seismic data and implications for reactivation tectonics seismic reflection data collected during cocorp s traverse of the southern appalachians reveal that the triassic riddleville basin is a half graben defined by strong north dipping basal reflections truncated on the north by a major south dipping normal fault lithologies observed in similar basins suggest that these high amplitude continuous reflections may be from lacustrine sediments or basaltic layers the high angle border fault soles into the augusta fault a major south dipping low angle paleozoic thrust geometric relations suggest that formation of the riddleville basin reactivated this older appalachian fault

cocorp seismic profiling of the appalachian orogen beneath the coastal plain of georgia a southeastward extension onto the coastal plain of an earlier cocorp traverse which confirmed large scale thin skinned thrusting of crystalline rocks of the southern appalachians has provided some of the most spectacular reflections yet seen in crustal seismic data most of the reflectors can be interpreted as either fault surfaces or as metamorphosed strata of late precambrian early paleozoic age they are consistent with the hypothesis that a major detachment extends eastward beneath this part of the orogen although other interpretations with a more complex pattern of detachments or sutures are also possible large scale overthrusting provides a mechanism for incorporating sedimentary rocks into the lower crust and may help to explain many of the layered features on crustal seismic data reflections from deep beneath the coastal plain indicate that the structural configuration of the rocks is complex and that the remains of a collision zone are being observed several east dipping horizons which bear strong similarities to thrust faults in valley and ridge sedimentary rocks are seen in the basement at shallow and mid crustal levels beneath the coastal plain the augusta fault for example displays a reflection which extends at a low angle some 80 km or more southeast of its surface position in conjunction with surface geologic information these new data demonstrate that late paleozoic compressive deformation was pervasive and resulted in lateral movements in the upper crust extending from the valley and ridge to the crystalline rocks beneath the coastal plain a distance of 400 km or more a large antiform cresting at about 2 3 sec or about 6 km below the surface and other structures beneath the coastal plain of georgia deserve further consideration for petroleum exploration although metamorphism may have eliminated petroleum from these rocks refracted arrivals and fault geometries indicate two triassic rift basins beneath coastal plain sedimentary rocks one of which has apparently not been recognized previously

the giles county virginia seismic zone a well defined seismic zone recently detected in virginia has an orientation that is not related to the surrounding geologic structures the orientation of the zone appears to be related to features below the appalachian overthrust belt a damaging earthquake that is important in evaluating seismic hazard in the southeastern united states may have occurred in the zone in 1897

in situ stress natural fracture distribution and borehole elongation in the auburn geothermal well auburn new york hydraulic fracturing stress measurements and a borehole televiewer survey were conducted in a 1 6 km deep well at auburn new york this well which was drilled at the outer margin of the appalachian fold and thrust belt in the appalachian plateau penetrates approximately 1540 m of lower paleozoic sedimentary rocks and terminates 60 m into the precambrian marble basement analysis of the hydraulic fracturing tests indicates that the minimum horizontal principal stress increases in a nearly linear fashion from 9 9 0 2 mpa at 593 m to 30 6 0 4 mpa at 1482 m the magnitude of the maximum horizontal principal stress increases in a less regular fashion from 13 8 1 2 mpa to 49 0 2 0 mpa over the same depth range the magnitudes of the horizontal principal stresses relative to the calculated overburden stress are somewhat lower than is the norm for this region and are indicative of a strike slip faulting regime that at some depths is transitional to normal faulting as expected from the relative aseismicity of central new york state however analysis of the magnitudes of the horizontal principal stresses indicates at least to a depth of 1 5 km that frictional failure on favorably oriented preexisting fault planes is unlikely orientations of the hydraulic fractures at 593 and 919 m indicate that the azimuth of the maximum horizontal principal stress at auburn is n83 e 15 in agreement with other stress field indicators for this region the borehole televiewer log revealed a considerable number of planar features in the auburn well the great majority of which are subhorizontal dips 5 and are thought to be bedding plane washouts or drill bit scour marks in addition a smaller number of distinct natural fractures were observed on the borehole televiewer log of these the distinct steeply dipping natural fractures in the lower half of the sedimentary section at auburn tend to strike approximately east west while those in the upper part of the well and in the precambrian basement exhibit no strong preferred orientation the origin of this east west striking fracture set is uncertain as it is parallel both to the contemporary direction of maximum horizontal compression and to a late paleozoic fracture set that has been mapped to the south of auburn in addition to these planar features the borehole televiewer log indicates paired dark bands on diametrically opposite sides of the borehole throughout the auburn well processing of the borehole televiewer data in the time domain revealed these features to be irregular depressions in the borehole wall as these depressions were consistently oriented in a direction at right angles to the direction of maximum horizontal compression we interpret them to be the result of stress induced spalling of the borehole wall breakouts

single crystal elasticity of mg0 9fe0 1 o to 81 gpa ferropericlase is the second most abundant mineral in earth s lower mantle and knowledge of its elastic properties at relevant conditions is needed to adequately interpret seismic observations in terms of the mineralogy and thermal state of the deep earth here we report the complete elastic tensor of mg sub 0 9 fe sub 0 1 o ferropericlase to 81 2 gpa at room temperature measured by brillouin spectroscopy and x ray diffraction in the diamond anvil cell our data indicate that the spin transition of iron between 45 and 63 gpa dramatically affects the longitudinal and off diagonal elements of the elastic stiffness tensor c sub 11 and c sub 12 whereas it leaves the shear constant c sub 44 almost unaffected based on our results the spin transition markedly changes the pressure and temperature dependence of the compressional and bulk sound velocities and must be taken into account in any attempt to match average radial seismic velocity profiles with mineral physics observations the different pressure dependence of compressional and bulk and shear sound velocities across the high spin to low spin hs ls transition implies that the spin transition might be best observed in the v sub p v sub s ratio and its pressure and temperature derivative we also point out the possibility that the spin transitionmore leads to an anti correlated temperature dependence of shear and compressional wave speeds in certain pressure temperature regimes in earth s lower mantle less

recurrence rates of large earthquakes in the south carolina coastal plain based on paleoliquefaction data we present a reanalysis of results of 15 years of paleoliquefaction investigations in the south carolina coastal plain all earlier radiocarbon age data and locations of organic material collected by various investigators were reviewed and recalibrated to obtain a uniform data set the calibrated dates and the spatial extent of the sandblows having similar dates were used to estimate ages and magnitudes of prehistoric earthquake episodes the results of this analysis suggest seven episodes episodes a g of prehistoric liquefaction in the past 6000 years and two possible scenarios for their occurrence in the first scenario three seismic sources exist within the coastal plain of south carolina at charleston a b e and g with magnitudes m 71 georgetown c and f and bluffton d with magnitudes m 6 in the second scenario episodes c and d are combined into one episode episode c9 in this scenario all earthquakes occurred at charleston and with m 71 episodes a and b seem to be more representative of the earthquake cycle and suggest a recurrence time of 500 600 years for m 71 earthquakes at charleston the recurrence times and magnitudes for episodes c and d are estimated at 2000 years and 6 0 respectively the older episodes are less frequent a fact that may be attributable to times of low ground water table before 6000 years b p the ground water table was too low to permit observable liquefaction features to develop at the surface

recent vertical crustal movements near charleston south carolina reevaluation of first order leveling data for the south carolina coastal plain shows evidence of recent vertical crustal movements these movements do not appear to be due to internal systematic errors in the data but rather to external processes such as near surface water withdrawal or neotectonic movements dislocation modeling of the observed movements near charleston provided a nonunique solution thus the geodetic data do not provide a constraint on the tectonic model for the charleston area the movements observed near charleston are aseismic and any tectonic movements are masked by the effects of water withdrawal or are buried within the noise level

seismotectonics of northeastern united states and adjacent canada data for local earthquakes recorded by a network of stations in northeastern united states and adjacent canada were analyzed to study the seismicity the relationship between earthquakes and known faults the state of stress and crustal and upper mantle velocity structure in addition portable seismographs were deployed in the field to study aftershocks as a result accurate locations for about 364 local earthquakes 2 mb 5 and 22 focal mechanism solutions were determined a comparison of the spatial distribution of these events 1970 1979 with historical earthquakes 1534 1959 reveals that seismic activity in the northeast is relatively stationary in space those areas that have had little or no seismicity historically are relatively aseismic today whereas the historically active areas are also active today the instrumental locations historical seismicity and focal mechanism solutions show an internal consistency that help us distinguish two distinct seismogenic provinces 1 the adirondack western quebec province is a northwesterly trending zone of seismic activity about 200 km wide and at least 500 km long extending from the se adirondacks into western quebec canada thrust faulting on planes striking nnw to nw appears to predominate and the inferred axis of maximum horizontal compression is largely uniform and trends wsw nearly parallel to the calculated absolute plate motion of north america little or no seismicity is found where anorthosite outcrops at the surface correlations between gravity anomalies and earthquake locations suggest that seismic activity in this zone is localized to regions of steep ne or sw gradient in bouguer anomalies this zone does not appear to extend southeastward to boston as proposed by some workers 2 the appalachian province is a northeasterly trending zone of seismic activity extending from northern virginia to new brunswick canada highangle reverse or thrust faulting on n to ne trending planes appears to predominate the western margin of this province however appears to be relatively aseismic we attribute this relative lack of activity to one or more of the following the presence of igneous activity postdating rifting of africa from north america the occurrence of intense metamorphism during the acadian orogeny which may have annealed preexisting faults and the predominance of ductile as opposed to brittle deformation in the geologic past the inferred axis of maximum horizontal compression along the eastern margin of the appalachians is rather uniform and trends w wnw almost perpendicular to the magnetic lineations offshore we suggest that this w wnw compression reflects the gravitational force arising from horizontal density variations in the oceanic lithosphere as it cools and moves away from spreading centers

cenozoic faulting in the vicinity of the charleston south carolina 1886 earthquake multichannel seismic reflection profiles in the meizoseismal area of the 1886 charleston earthquake and nearby offshore area show evidence of cenozoic faulting deformation observed on two land profiles defines a northeast striking reverse fault zone named the cooke fault a jurassic age basalt layer at 750 m depth has 50 m vertical displacement southeast side down overlying upper cretaceous and cenozoic beds have decreasing displacement with decreasing depth these displacements coupled with larger 190 m displacements of reflectors below the basalt indicate continuing cenozoic movement of a post basalt flow pre late cretaceous fault into eocene time or later the fault extends into a cluster of 1973 1978 epicenters this suggests a possible causal relationship with seismicity marine multichannel seismic reflection data combined with single channel high resolution reflection profiles reveal cenozoic faulting beneath the continental shelf near charleston a reverse fault 12 km offshore named the helena banks fault extends for at least 30 km and is observed as shallow as 10 m below the sea bottom with the most recent movement in post miocene or pliocene time there is no known seismicity in the area of this fault the reverse movement on the helena banks and cooke faults is consistent with a northwest southeast compressional stress regime elucidation of the relation if any between reactivated triassic or older structures and or a decollement defined by diffractions at 11 4 1 5 km depth on the one hand and seismicity on the other will be important in assessing earthquake risk in many areas of similar tectonic setting outside of the charleston region in the atlantic coastal and continental margin area

extreme heating events and effects in the natural environment implications for environmental geomorphology lightning and cosmic impacts on bedrock sediment cover and vegetation cause and have caused through geologic time almost instantaneous high energy discharges that produce extreme heating to many hundreds or a few thousand degrees celsius the effects of these cataclysmic events leave an imprint in surface material such that much of it becomes physically changed and carbonized primary and secondary minerals become welded together and or coated with carbon providing a food source for microbes which invade the altered material here we present a summary of fired rock and sediment covers from the andes cosmic impact the alps lightning fired rock and southern ontario canada where lightning toppled a red pine pinus resinosa thus altering the cellulose internal fiber and bark electrostatically levitated minerals from the tree roots soil transported upward a considerable distance became embedded in the outside and inside of the bark cellulose quartz and various plagioclases were melted the former producing deformed sheets of si the latter pure metallic na mineral artifacts of extreme heating events catalogued here might be used in environmental reconstruction efforts when problematic bedrock and sediment covers offer no alternative explanation

rift and grain in two granites of the white mountain magma series new england granites commonly have two subperpendicular weakness directions called rift and grain which are exploited during quarrying field and thin section study of granites from the white mountain batholith jurassic and the mount ascutney intrusive cretaceous show that the rift and grain directions are consistently developed parallel to mesozoic joints and suggests that the rift is the result of a preferentially oriented microcrack fabric and topographically controlled near surface in situ stresses the microcrack fabric is made up of fluid inclusion planes and open microfractures fluid inclusions developed during postemplacement cooling and represent healed microfractures open microcracks developed during uplift by recracking fluid inclusion planes so there is a strong similarity of orientation between elements in the microfracture fabric the influence of gravity sets up downslope acting near surface stresses which favor the development of open microfractures striking perpendicular to the downslope stresses joints and microfractures are best developed perpendicular to the local slope directions replotted and field checked data from dale 1923 demonstrate that in 53 turn of the century new england quarries rift and grain are parallel and perpendicular respectively to the direction of topographic slope thus rift and grain in granites of the white mountain batholith jurassic and the mount ascutney intrusive cretaceous result from a combination of a properly oriented microcrack fabric and topographically controlled near surface in situ stresses

strain on the san andreas fault near palmdale california rapid aseismic change frequently repeated strain measurements near palmdale california during the period from 1971 through 1980 indicate that in addition to a uniform accumulation of right lateral shear strain engineering shear 0 35 microradian per year across the san andreas fault a 1 microstrain contraction perpendicular to the fault that accumulated gradually during the interval 1974 through 1978 was aseismically released between february and november 1979 subsequently november 1979 to march 1980 about half of the contraction was recovered this sequence of strain changes can be explained in terms of south southwestward migration of a slip event consisting of the south southwestward movement of the upper crust on a horizontal detachment surface at a depth of 10 to 30 kilometers the large strain change in 1979 corresponds to the passage of the slip event beneath the san andreas fault

the younger dryas impact hypothesis a cosmic catastrophe in this paper we review the evidence for the younger dryas impact hypothesis ydih which proposes that at 12 9k cal a bp north america south america europe and the middle east were subjected to some sort of extraterrestrial event this purported event is proposed as a catastrophic process responsible for terminal pleistocene environmental changes onset of yd cooling continent scale wildfires extinction of late pleistocene mammals and demise of the clovis culture in north america the earliest well documented continent scale settlement of the region the basic physics in the ydih is not in accord with the physics of impacts nor the basic laws of physics no yd boundary ydb crater craters or other direct indicators of an impact are known age control is weak to non existent at 26 of the 29 localities claimed to have evidence for the ydih attempts to reproduce the results of physical and geochemical analyses used to support the ydih have failed or show that many indicators are not unique to an impact nor to 12 9k cal a bp the depositional environments of purported indicators at most sites tend to concentrate particulate matter and probably created many ydb zones geomorphic stratigraphic and fire records show no evidence of any sort of catastrophic changes in the environment at or immediately following the ydb late pleistocene extinctions varied in time and across space archeological data provide no indication of population decline demographic collapse or major adaptive shifts at or just after 12 9 ka the data and the hypotheses generated by ydih proponents are contradictory inconsistent and incoherent copyright 2014 john wiley sons ltd

palynological signal of the younger dryas in the tropical venezuelan andes the occurrence or not of the younger dryas cold reversal in the tropical andes remains a controversial topic this study reports a clear signal for this event in the venezuelan andes employing high resolution palynological analysis of a well dated sediment core from laguna de los anteojos situated around 3900 m elevation within grass paramo vegetation the lake is surrounded by some polylepis forests which are close to their upper distribution limit the section of the core discussed here is 150 cm long and dated between about 14 68 and 9 35 cal kyr bp using a polynomial age depth model based on six ams radiocarbon dates between 12 86 and 11 65 cal kyr bp an abrupt shift occurred in the pollen assemblage manifested by a decline of podocarpus polylepis and huperzia combined with an increase in poaceae and asteraceae the aquatic pteridophyte isoetes also decreased and disappeard and the algae remains show their minimum values pollen assemblages from the younger dryas interval show maximum dissimilarity values compared with today s pollen assemblage and are more similar to modern analogs from superparamo vegetation growing at elevations 400 500 m higher a lowering of vegetation zones of this magnitude corresponds to a temperature decline of between 2 5 and 3 8 c during this colder interval lake levels may have been lower suggesting a decrease in available moisture the vegetation shift documented in anteojos record between 12 86 and 11 65 cal kyr bp is comparable to the el abra stadial in the colombian andes but it differs in magnitude the anteojos shift is better dated and coincides with the younger dryas chron as recorded in the cariaco basin sea surface temperature reconstructions and records of continental runoff as well as in the oxygen isotope measurements from the greenland ice cores when compared to other proxies of quasi immediate response to climate the time lag for the response of vegetation to climate is found to be negligible at a centennial scale the polylepis pollen curve is especially noteworthy as it reproduces the overall pollen trends and matches well with paleoclimatic reconstructions based on other proxies hence polylepis might be used as a reliable paleoclimatic indicator in lake sediments close to its uppermost distribution boundary

age of the crowfoot advance in the canadian rocky mountains a glacial event coeval with the younger dryas oscillation a suite of sediment core samples was recovered from two lakes crowfoot and bow lakes that are adjacent to the crowfoot moraine type locality to identify and radiocarbon date sediments related to the crowfoot advance the crowfoot moraine system widely recognized throughout northwestern north america represents a glacial advance that is post wisconsin and pre mazama tephra in age an interval of inorganic sediments bracketed by accelerator mass spectrometry radiocarbon ages of ca 11 330 and 10 100 sup 14 c yr b p is associated with the crowfoot moraine the crowfoot advance is therefore approximately synchronous with the european younger dryas cold event ca 11 000 10 000 sup 14 c yr b p furthermore the termination of the crowfoot advance also appears to have been abrupt these findings illustrate that the climatic change responsible for the european younger dryas event extended beyond the northern atlantic basin and western europe equilibrium line altitude ela depressions associated with the crowfoot advance are similar to those determined for the little ice age advance whereas younger dryas ela depressions in europe significantly exceed little ice age ela depressions 26 refs 3 figs 1 tab

evidence for a younger dryas glacial advance in the andes of northwestern venezuela abstract deposits of push moraine outwash and glaciolacustrine sediments recovered from two areas in the northwestern venezuelan andes document the latest pleistocene advance of merida ice underlying peats provide maximum ages on till and outwash evidently emplaced during the younger dryas yd climatic event one example recovered from the humboldt massif where the farthest extent of yd ice buried peat in the surface of late glacial till provides a within glacier advance age of 12 4 ka cal bp the peat lies on moraine deposited during a stillstand event when the humboldt glacier retreated to the area of lago verde at 4000 m a s l approximately 0 5 km upvalley toward lago suero yd till buries peat deposited in glaciolacustrine sediments of presumed late glacial age farther north in the mucunuque mucubaji catchment of the eastern cordillera a push moraine of possible yd age buries older till of late glacial age 0 2 km upvalley outwash of yd age buries glaciolacustrine peat and organic rich alluvial sediment dated to 13 7 and 13 3 ka cal bp the latest merida advance documented here is approximately synchronous with the yd cold event of europe and the north atlantic region ca 11 6 12 7 ka cal bp the yd event in both areas of the northwestern venezuelan andes nearly reestablished earlier late glacial ice positions and termination appears to have been abrupt the valleys in both areas were evacuated of yd ice without emplacement of recessional moraines as during the main deglaciation at the humboldt site equilibrium line altitudes ela s for the late glacial were about 50 m lower than during the inferred yd in the mucunuque mucubaji catchment ela s for the late glacial 3900 m a s l are difficult to establish given the absence of lateral moraines

a reevaluation of the evidence for a younger dryas climatic reversal in the tropical andes abstract a review of the evidence for a younger dryas equivalent climatic reversal in the tropical andes shows that a number of hypotheses need to be reassessed assumptions of the el abra cold and humid phase in colombia are compromised by insufficient dating control periods of glacier advance in peru and bolivia lack sufficient dating control to be correlated with the european younger dryas only glaciers on the quelccaya ice cap in peru may have advanced shortly before the onset of the european climatic reversal but even there a correlation is questionable a late glacial advance in the chimborazo area in ecuador is considerably older than previously suggested the same glacier advance has been dated to earlier than 12 000 bp in other areas of ecuador the emerging picture suggests two phases of glacier advances in the tropical andes 13 000 12 000 bp and 9000 10 000 bp both may have been caused by increasing precipitation unequivocal evidence for a cold younger dryas event in the tropical andes has yet to emerge

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

nanodiamond rich layer across three continents consistent with major cosmic impact at 12 800 cal bp abstracta major cosmic impact event has been proposed at the onset of the younger dryas yd cooling episode at 12 800 150 years before present forming the yd boundary ydb layer distributed over 50 million km2 on four continents in 24 dated stratigraphic sections in 10 countries of the northern hemisphere the ydb layer contains a clearly defined abundance peak in nanodiamonds nds a major cosmic impact proxy observed nd polytypes include cubic diamonds lonsdaleite like crystals and diamond like carbon nanoparticles called n diamond and i carbon the nd abundances in bulk ydb sediments ranged up to 500 ppb mean 200 ppb and that in carbon spherules up to 3700 ppb mean 750 ppb 138 of 205 sediment samples 67 contained no detectable nds isotopic evidence indicates that ydb nds were produced from terrestrial carbon as with other impact diamonds and were not derived from the impactor itself the ydb layer is also marked by abundance peaks in other impact related proxies including

viscosity undulations in the lower mantle the dynamical role of iron spin transition a b s t r a c t a proper determination of the lower mantle viscosity profile is fundamental to understanding earth geodynamics based on results coming from different sources several models have been proposed to constrain the variations of viscosity as a function of pressure stress and temperature while some models have proposed a relatively modest viscosity variation across the lower mantle others have proposed variations of several orders of magnitude here we have determined the viscosity of ferropericlase a major mantle mineral and explored the role of the iron high to low spin transition viscosity was described within the elastic strain energy model in which the activation parameters are obtained from the bulk and shear wave velocities those velocities were computed combining first principles total energy calculations and the quasi harmonic approximation as ar esult of a strong elasticity softening across the spin transition there is a large reduction in the activation free energies of the materials creep properties leading to viscosity undulations these results suggest that the variations of the viscosity across the lower mantle resulting from geoid inversion and postglacial rebound studies may be caused by the iron spin transition in mantle minerals implications of the undulated lower mantle viscosity profile exist for both down and up wellings in the mantle we find that a viscosity profile characterized by an activation free energy of g z0 300 400 kj mol based on diffusion creep and dilation factor 0 5b etter fits the observed high velocity layer at mid mantle depths which can be explained by the stagnation and mixing of mantle material our model also accounts for the growth of mantle plume heads up to the size necessary to explain the large igneous provinces that characterize the start of most plume tracks

interaction between jointing and topography a case study at mt ascutney vermont u s a abstract jointing relationships indicate that the cretaceous mt ascutney intrusive complex vermont contains both cooling and unloading joints with similar orientations this orientation pattern appears to be the result of the interaction of a cretaceous joint fabric with topography and very near surface stresses existing joints provide directions of weakness which influence subsequent joint orientations in addition topography controls and is controlled by the joint fabric this study suggests that in the mt ascutney intrusive complex the formation of joints during uplift and unloading is highly dependent on previous episodes of joint development

fired glaciofluvial sediment in the northwestern andes biotic aspects of the black mat abstract fired glaciofluvial beds in outwash considered to date from the onset of the younger dryas event 12 9 ka in the northwestern venezuelan andes are considered equivalent to the black mat deposits described in other areas of north and south america and europe it may be equivalent to sediment recovered from other sites containing beds with spikes of cosmic nuclides and charcoal indicating the presence of widespread fire one of the signatures of the black mat conflagration that followed the proposed breakup of comet encke or an unknown asteroid over the laurentide icesheet at 12 9 ka in the northern andes at site mum7b sediment considered coeval with the black mat contains glassy carbon spherules tri coatings of c welded onto quartz and feldspar covered with fe and mn monazite with excessive concentrations of rees platinum metals including ru and rh possible pdf s and disrupted brecciated and microfractured quartz and feldspar from impacting ejecta and excessive heating summarize the data obtained so far the purpose of this paper is to document the physical character mineralogy and biotic composition of the black mat

gravity anomalies and flexure of the lithosphere at mountain ranges the bouguer gravity anomaly over the himalayan alpine and appalachian mountains is characterized by a generally asymmetric gravity low which spans the mountains and associated foreland basins the minimum of the gravity low is generally systematically displaced from the region of greatest topographic relief and shows no obvious relationship to surface geology in addition the alps and appalachians are associated with a generally symmetric gravity high that is unrelated to the topographic relief together the gravity low and high form a characteristic positive negative anomaly couple the steep gravity gradient between the positive and negative couple correlates with the insubric line and its equivalents in the alps and the brevard zone in the southern appalachians this gravity anomaly couple is interpreted as evidence for flexure of the continental lithosphere by subsurface buried and surface topographic loading the magnitude of the subsurface load is estimated from the integrated excess mass represented by the positive anomaly and the magnitude of the surface load from the topography by combining these loads the flexure of the lithosphere and the associated bouguer gravity anomaly are calculated for different assumed values of the elastic thickness te of continental lithosphere the best fitting value of te for the himalayas is 80 100 km for the alps 25 50 km and for the appalachians 80 130 km the model calculations suggest that the main contribution to the gravity couple in the alps and appalachians arises not from surface loads such as thrust sheets and nappes but from subsurface loads however in the case of the himalayas the topography appears to be a sufficient load to explain the observed asymmetric gravity low when subsurface loads do exist therefore we would not expect a close correlation between mountain topographic relief and depth to the m discontinuity as required by classical models of isostasy rather the m discontinuity is expected to relate to the center of mass of all the loads acting on the lithosphere the surface and subsurface loads inferred from the gravity anomaly play a major role in the development of mountains and foreland basins the emplacement of large subsurface loads represents the primary event in the alps and appalachians while in the himalayas the emplacement of the surface load is the primary event the emplacement of the subsurface load probably marks the initiation of foreland basin development the regional characteristics of the basin are controlled by the primary load while local variations are controlled by the secondary thrust sheet loads subsequent movement of either load will produce migration of the basin depocenter the origin of the subsurface load is not clear but its association with the insubric line in the alps and the brevard zone in the appalachians suggests that it may be related to the obduction of crustal blocks flakes onto the underlying plate during continental collision or possibly to the preloaded crustal structure of the underlying plate

potential glacial evidence for the younger dryas event in the cordillera of north and south america there is debate as to whether or not the younger dryas yd climatic event affected areas outside of the north atlantic region the potential of alpine glacial deposits to record the yd is of interest because alpine glaciers would be likely to leave a morainal record even during minor short lived advances caused by a period of deteriorating climate in the cordilleran ranges of north and south america there are several candidate moraines many bracketed between radiocarbon ages of ca 12 and 10 ka which may be yd in age the best examples are in the canadian and american rockies the ecuadorian peruvian and bolivian andes and around the patagonian ice cap in most cases temporal brackets are not narrow enough and some radiocarbon ages may not be accurate enough to allow correlation at the present time there are two cases of lateglacial readvance whose ages are interpreted to match or fall within the yd interval an advance of the crowfoot glacier in canada is interpreted to have occurred within the period ca 11 3 and 10 14c ka bp and an advance of the reschreiter glacier in ecuador is interpreted to have culminated in the period ca 11 to 10 6 14c ka bp the latter interpretation depends on an assumption that lake level variations were caused by glacier advances and retreats

strong motion seismology although this is the first review on this topic to appear in a quadrennial report the roots of strong motion seismology extend back to at least 1932 when far sighted engineers in the seismological field survey of the u s coast and geodetic survey installed rugged fieldworthy instruments designed to make on scale recordings of large earthquakes carder 1964 these instruments are called accelerographs for their output closely mimics ground acceleration hudson 1979 the original instruments and their offspring have provided a wealth of information about ground motions of direct use to engineers due in large part to the continued devotion of the seismological field survey now part of the branch of engineering seismology and geology at the u s geological survey the number of recordings has increased substantially particularly in the last two decades and multiple recordings of a few california earthquakes have provided the data necessary to begin to unravel the complexities of the ground motions and to predict these motions on an empirical basis although seismologists used accelerograph records in studies of earthquake energy and ground motion attenuation as long ago as 1942 gutenberg and richter 1942 1956 widespread seismological use of the records began with aki s 1968 analysis of the 1966 parkfield earthquake

the 1886 charleston south carolina earthquake and the appalachian detachment several lines of evidence from new and existing data are consistent with an extended fault slip associated with the 1886 earthquake in south carolina back slip over a portion of the appalachian detachment approximately corresponding to the coastal plain of south carolina fits some of the data including coseismic and post seismic strain indicators a small seismic source for the august 31 1886 main shock cannot be ruled out and a large but only partially seismic fault slip is possible during this event intensities of mm viii occurred over a wide area of the coastal plain and are not limited to the charleston summerville area where the traditional small source for this earthquake is located near source effects such as ground fissuring liquefaction changes in line of sight foreshocks and aftershocks occurred over a wide area of the coastal plain and neighboring inner piedmont which we tentatively refer to as the meizoseismal area this area is sharply bounded by the savannah river toward the southwest and approximately by the north carolina south carolina state border toward the northeast these boundaries are not associated with any known structure transverse to the strike of the appalachians during the 14 years prior to 1886 seismicity was concentrated around the extended meizoseismal area while the seismicity within that area was unusually low suggesting a premonitory doughnutlike pattern the intensity distribution in the far and near field of the 1886 event and of the great indian detachment earthquakes e g the 1905 m 8 and the 1934 m 8 3 events are qualitatively and quantitatively similar this is consistent with comparable source dimensions since well known intermediate magnitude earthquakes in india and in eastern north america exhibit similar intensity patterns and indicate similar seismic attenuation in the two cratonic environments several meters of coseismic 1886 northwest compressive strain near summerville are indicated by buckling of rails a large postseismic normal displacement is suggested by releveling data 1935 1968 across the brevard fault zone updip northwest of the presumed 1886 detachment slip these strains are consistent with a southeastward slip of the detached crystalline sheet associated with the 1886 earthquake available data indicate that in the southern appalachians the updip transition from maximum horizontal to least horizontal compressive stress in the dip direction perpendicular to structural trends occurs somewhere in the piedmont and may coincide with the steepest portion of the detachment the stress field may also contain a time dependent component in the sediments of the coastal plain orthogonal sets of subvertical clastic dikes oriented along and across the appalachian strike direction suggest one or more interchange of the principal stress axes we infer from coseismic dry fissuring and liquefaction that clastic dikes filled from above and from below were also generated during the 1886 event prehistoric clastic dikes along with other structures in the sediments may have been generated during prehistoric earthquakes similar to the 1886 event stress reversals corresponding to earthquake cycles may characterize the stress field within detached sheets or wedges that move primarily by great detachment earthquake ruptures appendices are available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j81 008 1 00 payment must accompany order

neotectonism along the atlantic passive continental margin a review abstract an extensive body of geologic data including the modern state of stress historical seismicity surface and subsurface stratigraphy numerical models of crustal deformation surficial geomorphic systems and historical precise leveling and tidal gauge records constrain the style and rate of neotectonic deformation for the appalachians and atlantic passive continental margin there are two major styles of neotectonism in the eastern united states the northeastern united states is dominated by isostatic uplift and northward migration of peripheral bulge collapse in response to deglaciation this locally rapid but decreasing rate of deformation is superimposed upon slower long term deformation along the atlantic margin most of the long term continental margin deformation is attributed to lithospheric flexuring in response to sediment loading in sedimentary basins especially the baltimore canyon trough and carolina trough isostatic deformation in response to continental denudation and water loading of the shelf and stress from far field plate tectonic sources significant deformational features include an uplift anomaly near cape fear n c northward and southward tilting of the coastal plain into the salisbury and southeast georgia embayments respectively seaward tilting of the coastal plain piedmont and a complex pattern of postglacial uplift and later subsidence in the northeast estimates of vertical crustal velocities for similar locations vary over several orders of magnitude measurement interval bias and systematic leveling errors may account for some of the discrepancies evidence for periodic deformation in the eastern united states in substantial and it is possible that historic data indicate a period of accelerated deformation along the atlantic continental margin

evidence for a cosmogenic origin of fired glaciofluvial beds in the northwestern andes correlation with experimentally heated quartz and feldspar abstract fired sediment considered equivalent to the black mat impact of 12 9 ka has been located and analyzed in the andes of northwestern venezuela the black mat refers to possible fallout from the encke comet airburst presumed to have occurred over the laurentide ice sheet the impact spreading ejecta over large portions of north america and europe making it an interhemispheric event of considerable magnitude these possible equivalent beds in the northern andes first considered to result from a lightning induced conflagration adjacent to the retreating late wisconsinan merida glaciation ice are now known to have undergone intense heating upon impact to a temperature much higher than what would occur in a wet first stage successional tundra analyses carried out by sem and fesem in se and bse modes show massive micro disruption on grain surfaces fractures diminishing with depth toward grain interiors and c welded onto quartz and plagioclase minerals bubbles on some grains possibly the result of exclusion of water of crystallization are seen on some samples principally quartz the presence of copious monazite in the carbonaceous coatings is considered part of the incoming ejecta as it is not a common indicator mineral in the local lithology analysis by sem and fesem of quartz and plagioclase subjected experimentally to temperatures ranging from 500 to 900 c shows that intense heating affects resident mineralogies to differing extents with grain disruption more prevalent along cleavage planes deep into grain interiors the intergrowth of carbonaceous black mat material with thermally disrupted and fragmented quartz and feldspar a welded patina of 100 400 nm thickness could only occur with temperatures in excess of 900 c the event interpreted here to be of cosmogenic origin

large scale thin skin tectonics the lithosphere is to a first approximation a layered system generally pressure temperature and composition are strongly dependent on depth and vary relatively little laterally these parameters can affect greatly the response to stress of rocks in the crust and upper mantle and are responsible for the stratification of many characteristics such as seismic response rheology and kinematics in the lithosphere asthemosphere system e g chen and molnar 1983 on a smaller scale lithology which often is also horizontally stratified plays a major role in determining strength e g engelder and geiser 1980 pore pressure can also greatly affect strength hubbert and rubey 1959 suppe 1981

ferrous iron diffusion in ferro periclase across the spin transition we present first principle calculations on absolute diffusion rates of high and low spin ferrous iron in ferro periclase the diffusivity of high and low spin iron depends on the physical conditions pressure and temperature iron concentration and the value of the chosen hubbard u we also find that low spin iron swaps back to high spin during migration our results show that throughout the earth s lower mantle iron diffuses at a faster rate than magnesium up to an order of magnitude thus the effect of the spin transition only has a small impact on the rheology of periclase in the earth s mantle using reasonable vacancy concentrations we find that ferro periclase is much weaker than mgsio3 perovskite throughout the mantle we conclude therefore that ferro periclase controls the viscosity of the mantle in regions where it becomes interconnected such as regions of high strain around slabs or near plumes at very high pressures such as in super earths low spin iron diffusion is expected to become much slower than magnesium eventually making ferro periclase more viscous than pure periclase c 2010 elsevier b v all rights reserved

freshwater outbursts to the oceans from glacial lake agassiz and their role in climate change during the last deglaciation abstract lake agassiz was the largest lake in north america during the last deglaciation as the laurentide ice sheet lis retreated large volumes of water stored in this proglacial lake were episodically released into the oceans these waters were variably routed to the gulf of mexico arctic ocean north atlantic ocean and hudson bay during this period the three largest cooling events in the northern hemisphere closely followed 4 of the 5 largest outbursts from lake agassiz 1 the younger dryas which was preceded by a release of 9500 km 3 2 the preboreal oscillation preceded by releases of 9300 km 3 and 5900 km 3 and 3 the 8 2 ka cold event preceded by a 163 000 km 3 outburst these are respectively fluxes of 0 30 sv 0 29 sv 0 19 sv and 5 2 sv if released in 1 year because the influx of freshwater reaching the north atlantic ocean can inhibit thermohaline circulation partly depending on whether the ocean was in a glacial interglacial or transitional mode of circulation we believe that at least these large outbursts from lake agassiz may have provided the triggers for changes in ocean circulation and in turn for widespread climate change

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

lightning induced mineral chemical changes in red pine pinus resinosa abstract red pine pinus resinosa growing in sandy soil of glacial lake whittlesey age 13 12 ka in the town of waterford ontario canada north of lake erie was struck by lightning in a fierce thunderstorm may 2010 the lightning strike was strong enough to destroy television sets and telephones in nearby houses and two red pines were struck one split down the middle from above the bole to near the crown samples of bark and inner tissue were examined to determine the composition of black silt size specs seen on the severed material in addition to minerals found in abundance in the local soil c clots spherules disrupted cellulose structures blackened tissue fused disfigured si and metallic sheets of na the latter sourced from melted albite na rich plagioclase were analyzed many silt and sand size particles sourced from the local soil were presumably electrically levitated along and within the bark by the lightning discharge iron rich micas other fe minerals and a great range of light minerals moistened by torrential rain were among the silts and sands transported to great height and embedded in the bark

effect of anomalous compressibility on fe diffusion in ferropericlase throughout the spin crossover in the lower mantle abstract the transport of iron in the deep earth is important for understanding chemical equilibration between deep earth phases and between the core and mantle however iron transport modeling is complicated by its changes in spin state with pressure and temperature recent studies saha et al 2011 ammann et al 2011 calculated the diffusivity of iron in ferropericlase as a function of iron s spin state but did not include the coupling of iron migration energetics to the observed anomalous bulk modulus softening associated with the spin transition wentzcovitch et al 2009 crowhurst et al 2008 here we calculate the diffusivity of iron in ferropericlase throughout the lower mantle using a model for both iron s spin and the anomalous bulk modulus softening to provide a complete model of iron diffusion in ferropericlase including the bulk modulus softening increases iron diffusivities by a factor of thirty relative to values without this effect at some depths on the geotherm

geologic evidence for recurrent moderate to large earthquakes near charleston south carolina multiple generations of earthquake induced sand blows in quaternary sediments and soils near charleston south carolina are evidence of recurrent moderate to large earthquakes in that area the large 1886 earthquake the only historic earthquake known to have produced sand blows at charleston probably caused the youngest observed blows older late quaternary sand blows in the charleston area indicate at least two prehistoric earthquakes with shaking severities comparable to the 1886 event

review of major shale dominated detachment and thrust characteristics in the diagenetic zone part ii rock mechanics and microscopic scale abstract characterising large shale thrust zone behaviour down to the diagenetic metamorphic boundary is both simple and complex the task in critical taper analogue and numerical models has been successfully approximated using simple material parameters yet the weakness of shales thrusts on a case by case basis show great variability in key factors across a wide range of scales understanding of these variables and their relationships to different tectonic settings is patchy due to the different objectives of workers studying the various systems e g seismic hazards hydrocarbon exploration structural geology research and the types of available geological and geophysical data early research recognized that megathrusts feature creeping and locked patches which may be described using the rate and state formalism in addition to temperature differential stress and strain rate key controlling factors on thrust weakness are mineralogy amount of weak phase present structure localization mechanisms grain size and shapes porosity permeability and pore fluid pressure the smectite illite transition has been a focus of seismic hazard research due to its coincidence with the top of the seismogenic zone while there may be a relationship other factors such as pore fluid pressure variations or structure localization are also important the critical taper model is a simple means of determining whether basic rock mechanics data e g frictional strength pore fluid pressure is appropriate for natural wedges for example aseismic basal detachments of gravity driven systems smaller critical taper wedges appear to retain higher pore fluid pressures along the basal detachment than seismogenic basal detachments higher critical taper wedges in many continental and deltaic fold and thrust belts high organic carbon content is a very important factor in shale weakness due to 1 the overall more ductile and well cleaved nature of the shale when organic content is high 2 the presence of high overpressures due to maturation of organic material and 3 metamorphism of carbon to low friction graphite this multifaceted influence of organic carbon content is just one example of the diversity of potential influences on shale thrust zone weakness which enable shales to be weak despite considerable lateral deposition related and vertical burial related changes in composition some key variations between different types of fold and thrust belt gravity driven accretionary prism andean himalayan type lie in systematic variations in clay mineralogy magnitudes and origins of overpressures seismic versus aseismic detachments and different structural localization mechanisms further research is required to explore the viability of such distinctions and their impact on structural styles

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

new evidence from a black mat site in the northern andes supporting a cosmic impact 12 800 years ago abstractprevious work has ascribed a cosmic impact origin to black high temperature carbon encrusted beds 2 3 cm thick associated with the younger dryas readvance of ice at 12 8 ka during the late glacial in the northern andes of venezuela the evidence for this includes carbon spherules aluminosilicate melt rocks melted coatings of glass like amorphous carbon and fe mn on sands and clasts derived from local felsic gneiss and granite these sediments have been subjected to renewed investigation using high resolution scanning electron microscopy and energy dispersive spectrometry and new data show that spherules at site mum7b exhibit unique morphologies and compositions molar oxide weight percentages prove the spherules are not volcanic and show little overlap with cosmic materials spherule microstructures display quench melting and thus could not have formed from slow geological authigenic diagenetic or metamorphic processes instead geochemical values for the venezuelan samples plot withi

contemporary tilting in the central atlantic coastal plain geodetic leveling across the cape hatteras arch between norfolk va and new bern nc 240 km suggests an unusually large northward tilting new bern appears to have risen relative to norfolk as much as 18 pm 3 cm between 1932 and 1963 and 26 6 pm 3 cm between 1963 and 1979 although on the basis of geomorphic evidence this area has been interpreted by some as having undergone significant holocene tilting the rates indicated by leveling seem unrealistically large not only with respect to the longer term geologic estimates but also in comparison with contemporary tide gauge estimates of crustal movement a detailed analysis of the leveling results was carried out to evaluate to the extent possible their validity as estimates of neotectonic movement the apparent consistency of repeated resurveys the low topographic relief and the large magnitude of observed tilting argue against certain types of systematic error accumulation loop misclosure analysis is inconclusive however comparison of

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

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

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

rapid ice margin fluctuations during the younger dryas in the tropical andes abstract radiocarbon dated lacustrine sequences in peru show that the chronology of glaciation during the late glacial in the tropical andes was significantly out of phase with the record of climate change in the north atlantic region fluvial incision of glacial lake deposits in the cordillera blanca central peru has exposed a glacial outwash gravel radiocarbon dates from peat stratigraphically bounding the gravel imply that a glacier advance culminated between 11 280 and 10 990 14c yr b p rapid ice recession followed similarly in southern peru ice readvanced between 11 500 and 10 900 14c yr b p as shown by a basal radiocarbon date of 10 870 14c yr b p from a lake within 1 km of the quelccaya ice cap by 10 900 14c yr b p the ice front had retreated to nearly within its modern limits thus glaciers in central and southern peru advanced and retreated in near lockstep with one another the younger dryas in the peruvian andes was apparently marked by retreating ice fronts in spite of the cool conditions that are inferred from the 18o record of sajama ice this retreat was apparently driven by reduced precipitation which is consistent with interpretations of other paleoclimatic indicators from the region and which may have been a nonlinear response to steadily decreasing summer insolation

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

younger dryas black mats and the rancholabrean termination in north america of the 97 geoarchaeological sites of this study that bridge the pleistocene holocene transition last deglaciation approximately two thirds have a black organic rich layer or black mat in the form of mollic paleosols aquolls diatomites or algal mats with radiocarbon ages suggesting they are stratigraphic manifestations of the younger dryas cooling episode 10 900 b p to 9 800 b p radiocarbon years this layer or mat covers the clovis age landscape or surface on which the last remnants of the terminal pleistocene megafauna are recorded stratigraphically and chronologically the extinction appears to have been catastrophic seemingly too sudden and extensive for either human predation or climate change to have been the primary cause this sudden rancholabrean termination at 10 900 50 b p appears to have coincided with the sudden climatic switch from allerod warming to younger dryas cooling recent evidence for extraterrestrial impact although not yet compelling needs further testing because a remarkable major perturbation occurred at 10 900 b p that needs to be explained

characteristics of the western quebec seismic zone a comparison of geological data shows that most of the earthquakes of western quebec lie within or near the eastern and western boundaries of a grenville ca 1000 ma central metasedimentary belt and in the area of the younger fault zone along the ottawa river although most of the earthquakes have occurred within terrain of grenville age or older the younger rift zone is characterized by the larger earthquakes temiskaming m6 2 1935 cornwall massena m5 7 1944 the earthquakes also correlate with gradient zones around two prominent anomalies in the smoothed bouguer gravity field the pattern of aeromagnetic anomalies and drainage channels reflects preeambrian structural trends and indicates the central metasedimentary belt continues beneath paleozoic sediments to lake ontario the strikes of magnetic gravity and drainage features north of lake ontario are parallel to features mapped to the south of the lake geological data and geophysical trends suggest that a cataclastic zone is continuous alon

landslide zoning in a part of the garhwal himalayas the himalayas are undergoing constant rupturing in the thrust belt zone in the garhwal himalayas due to which earthquake and mass movement activity is triggered these processes of mass movement and landslides have been constantly modifying the landscape landslides are one of the indicators of the geomorphological modifications taking place in this active and fragile terrain this work is aimed at providing another example of landslide susceptibility mapping based on geological and geomorphological attributes the data collected from aerial photographs topographic sheets and the image suggests that there is a correlation between the distribution of landslides and some of the geological and geomorphological factors for example the distance from an active fault relative relief and slope parameters like factor of safety altitude relief slope and the distance from the fault lineament have been included in the study a rating system has been applied to the factors for arriving at a quantitative estimate of landslide susceptibility for each physiographic unit since terrain classification forms the foundation of this work the entire study can be grouped into two sequential activities 1 the terrain classification and 2 landslide susceptibility mapping the result is the landslide susceptibility zoning map presented the landslides have not been classified with respect to time and may represent the final result of the on going geological geomorphological and seismic activity since the holocene period or late pleistocene time when the glaciers retreated

seismicity focal mechanisms and tectonics in the last four years there has been a tremendous increase in the detail of tectonic processes reported in the typical seismotectonic study new data from many local and regional networks of seismographs established during the previous four year period plus the now routine application of improved hypocentral location procedures long period body wave modelling and moment tensor inversion using digitally recorded data have increased resolution of both the hypocentral location and the nature of the faulting process consequently research emphasis has been on local tectonics or those aspects of regional and global tectonics requiring high resolution i briefly describe below some of the highlights of these studies

the el abra stadial a younger dryas equivalent in colombia abstract a survey of radiocarbon dated palynological stratigraphical and glacio morphological evidence from colombia is presented showing a cold climatic fluctuation most likely between 10 900 and 10 100 bp immediately preceding the initiation of the holocene this fluctuation called the el abra stadial is characterized by lower temperatures and less precipitation and occurs after the late glacial guantiva interstadial average annual temperature during the guantiva interstadial may have been 2 c lower than today and during the el abra stadial from 4 to 6 c lower than today the upper forest line during the el abra stadial was some 400 to 500 m lower than during the guantiva interstadial and some 600 to 800 m lower than today the guantiva interstadial el abra stadial early holocene sequence is radiocarbon dated by some 45 dates and evidence is shown from 14 areas mostly located at high elevations 2000 4000 m in the eastern and central cordillera and in the sierra nevada de santa marta but some from the tropical low lands although more precise dating of the boundaries is desirable we interpret the guantiva el abra climatic fluctuations as equivalents in time and climatic phenomena to the allerod younger dryas sequence in europe

chronology of quaternary glaciations in east africa abstract a new glacial chronology for equatorial east africa is developed using in situ cosmogenic 36 cl measured in 122 boulders from moraines on mount kenya and kilimanjaro the oldest deposits sampled on kilimanjaro yield a limiting 36 cl age of 360 calendar kyr all 36 cl ages are in calendar years cal kyr or cal yr on mount kenya the oldest moraines give ages of 355 420 kyr liki i and 255 285 kyr teleki given the uncertainty in our 36 cl ages the liki i moraine may correspond to either marine isotope stage 10 or 12 whereas the teleki moraine correlates with stage 8 there is no evidence for stage 6 on either mountain the liki ii moraines on mt kenya and moraines of the fourth glaciation on kilimanjaro give ages of 28 3 kyr and 20 1 kyr respectively they represent the last glacial maximum lgm and correlate with stage 2 of the marine isotope record a series of smaller moraines above the lgm deposits record several readvances that occurred during the late glacial on mt kenya these deposits date to 14 6 1 2 kyr liki iia 10 2 0 5 kyr liki iii 8 6 0 2 kyr liki iiia and 200 yr lewis the corresponding deposits on kilimanjaro have mean ages of 17 3 2 9 kyr fourth glaciation saddle 15 8 2 5 kyr little glaciation saddle and 13 8 2 3 kyr fourth glaciation kibo these data indicate that the climate of the tropics was extremely variable at the end of the last glacial cycle

seismic moment assessment of earthquakes in stable continental regions ii historical seismicity summary this part i study in conjunction with part 11 develops a method to determine within specified uncertainty bounds the seismic moment and thus moment magnitude of all earthquakes of stable continental regions scr for which instrumental or intensity data exist its basis is polynomial regression analysis using a database of scr earthquakes with direct seismic moment determination the independent variables include modern teleseismic magnitudes and regional magnitudes part i and isoseismal areas or number of recording stations part 11 part i11 is an application of the methodology of parts i and i1 to several major historical earthquakes all data used in the regressions are assigned individual uncertainties estimated from the literature or from experience formal confidence limits 68 per cent or 95 per cent on both the regression formulas and the predicted seismic moment values are then possible via error propagation analysis the most complete development is for the teleseismic magnitudes m and mb for both the final regression for log m is a quadratic formula that closely emulates the relationship between amplitude magnitudes and log m expected from dislocation theory and source scaling arguments regressions are also derived for the regional magnitudes mlg and m because there are many scr events mainly pre 1964 that have no teleseismic magnitudes prediction uncertainties from teleseismic magnitudes in moment magnitude units are in the ao 18 0 28 range and from regional magnitudes in the ko 23 0 38 range over a wide magnitude band finally the methodology developed here is generic even though the database is specific application to plate boundary oceanic intraplate or active continental intraplate regions should be straightforward

seismic strain rates in the central and eastern united states seismic strain rates for the entire central and eastern united states are estimated from historical seismicity and from several seismicity models typical strain rates are estimated to be the on the order of 10 12 to 10 11 per year except near historical sites of large earthquakes where higher rates pertain uncertainties in strain rates are large deformation caused by strain rates less than 10 10 yr 1 is very small compared to average denudation rates denudation and deposition may control the rate of earthquake occurrence in some parts of the central and eastern united states by modifying the vertical stress due to load a simple quantitative model predicts the earthquake occurrence rate in the appalachian mountains from an estimate of the regional denudation rate

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

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