The Chinese Chang’e-3 mission landed close to the eastern rim of the ~450 m diameter Ziwei crater. Regional stratigraphy of the landing site and impact excavation model suggest that the bulk continuous ejecta deposit...The Chinese Chang’e-3 mission landed close to the eastern rim of the ~450 m diameter Ziwei crater. Regional stratigraphy of the landing site and impact excavation model suggest that the bulk continuous ejecta deposits of the Ziwei crater are composed by Erathothenian-aged mare basalts. Along the traverse of the Yutu rover, the western segment features a gentle topographic uplift(~0.5 m high over ~4 m), which is spatially connected with the structurally-uplifted crater rim. Assuming that this broad topographic uplift has physical properties discontinuous with materials below, we use data returned by the high-frequency lunar penetrating radar onboard the Yutu rover to estimate the possible range of relative permittivity for this topographic uplift. Only when the relative permittivity is ~9 is the observed radar reflection consistent with the observed topography, suggesting that the topographic uplift is composed of basaltic blocks that were excavated by the Ziwei crater. This result is consistent both with the impact excavation model that predicts deeper basaltic materials being deposited closer to the crater rim, and with observation of numerous half-buried boulders on the surface of this hill. We note that this study is the first to use topography and radargram data to estimate the relative permittivity of lunar surface uplifts, an approach that has had many successful applications on Mars. Similar approaches can apply other ground penetrating radar data for the Moon, such as will be available from the ongoing Chang’e-4 mission.展开更多
The six largest known impact craters of the last 250 Myr(≥70 km in diameter),which are capable of causing significant environmental damage,coincide with four times of recognized extinction events at 36(with 2 craters...The six largest known impact craters of the last 250 Myr(≥70 km in diameter),which are capable of causing significant environmental damage,coincide with four times of recognized extinction events at 36(with 2 craters),66,and 145 Myr ago,and possibly with two provisional extinction events at 168 and215 Myr ago.These impact cratering events are accompanied by layers in the geologic record interpreted as impact ejecta.Chance occurrences of impacts and extinctions can be rejected at confidence levels of99.96%(for 4 impact/extinctions)to 99.99%(for 6 impact/extinctions).These results argue that several extinction events over the last 250 Myr may be related to the effects of large-body impacts.展开更多
The presence of glass microspherules enclosing relict grains, shattered quartz and silicon carbide in white sandstone beds near the Jurassic-Cretaceous boundary in west central Sinai indicates a cosmic impact event. C...The presence of glass microspherules enclosing relict grains, shattered quartz and silicon carbide in white sandstone beds near the Jurassic-Cretaceous boundary in west central Sinai indicates a cosmic impact event. Characterization of the impact microspherules and proposing a reasonable scenario for their origin are the aims of this work. Field observations, optical, binocular, scanning electron and high-resolution transmitted electron microscopy investigations and chemical analyses were carried out. The study revealed that glass microspherules have high Al<sub>2</sub>O<sub>3</sub> and FeO contents and low CaO and MgO contents. The high content of Al<sub>2</sub>O<sub>3</sub> indicates that the source of microtektite-like microspherules is attributed to the melting of a clay-rich sandstone and carbonaceous matter, while the high content of FeO indicates admixing with projectile matter. The reaction between silica and carbon was carried out under conditions of high temperature (T > 1000°C) and carbon (C/Si > 1) which resulted in the production of silicon carbide with microdiamond intergrowth. Consequently, this intergrowth is in accordance with the impact origin via rapid condensation and growth within a vapor phase. In spite of the fact that no source crater has been recognized to date in the study area, the authors propose at least a single cosmic impact event scenario for the recorded glass microspherules in west central Sinai. The impact excavated the Paleozoic siliciclastic sedimentary rocks and then the glass microspherules showered the area of study. The deposition of microtektite-like glass particles within the white sandstone beds of the Malha Formation took place in the fluvial plain terrestrial environment. This setting precluded severe post-depositional reworking, yielding preservation of the glass particles in a primary layer. Eventually, lateral migration of the braided channels led to the reworking of the microspherules layer and the spatial dispersal of the shattered quartz.展开更多
The~790 ka Australasian(micro)tektite strewn field is one of the most recent and best-known examples of impact ejecta emplacement as the result of a large-scale cratering event across a considerable part of Earth'...The~790 ka Australasian(micro)tektite strewn field is one of the most recent and best-known examples of impact ejecta emplacement as the result of a large-scale cratering event across a considerable part of Earth's surface(>10%in area).The Australasian strewn field is characterized by a tri-lobe pattern consisting of a large central distribution lobe,and two smaller side lobes extending to the west and east.Here,we report on the discovery of microtektite-like particles in sedimentary traps,containing abundant micrometeorite material,in the Sør Rondane Mountain(SRM)range of East Antarctica.The thirty-three glassy particles display a characteristic pale yellowcolor and are predominantly spherical in shape,except for a single dumbbell-shaped particle.The vitreous spherules range in size from220 to 570μm,with an average diameter of~370μm.This compares relatively well with the size distribution(75–778μm)of Australasian microtektites previously recovered from the TransantarcticMountains(TAM)and located ca.2500–3000 km fromthe SRM.In addition,the chemical composition of the SRM particles exhibits limited variation and is nearly identical to the‘normal-type’(i.e.,<6%MgO)TAM microtektites.The Sr and Nd isotope systematics for a single batch of SRM particles(n=26)strongly support their affiliation with TAMmicrotektites and the Australasian tektite strewn field in general.Furthermore,Sr isotope ratios and Nd model ages suggest that the target material of the SRM particles was composed of a plagioclase-or carbonate-rich lithology derived from a Paleo-or Mesoproterozoic crustal unit.The affiliation to the Australasian strewn field requires long-range transportation,with estimated great circle distances of ca.11,600 km from the hypothetical source crater,provided transportation occurred along the central distribution lobe.This is in agreement with the observations made for the Australasian microtektites recovered from Victoria Land(ca.11,000 km)and Larkman Nunatak(ca.12,000 km),which,on average,decrease in size and alkali concentrations(e.g.,Na and K)as their distance from the source crater increases.The values for the SRMparticles are intermediate to those of the Victoria Land and Larkman Nunatak microtektites for both parameters,thus supporting this observation.We therefore interpret the SRM particles as‘normal-type’Australasian microtektites,which significantly extend the central distribution lobe of the Australasian strewn field westward.Australasian microtektite distribution thus occurred on a continent-wide scale across Antarctica and allows for the identification of new,potential recovery sites on the Antarctic continent as well as the southeastern part of the Indian Ocean.Similar to volcanic ash layers,the~790 ka distal Australasian impact ejecta are thus a record of an instantaneous event that can be used for time-stratigraphic correlation across Antarctica.展开更多
基金supported by the National Natural Science Foundation of China (41773063, 41525015 and 41830214)the Science and Technology Development Fund of Macao (0042/2018/A2)the Opening Fund of the Key Laboratory of Lunar and Deep Space Exploration, CAS (no.ldse201702)
文摘The Chinese Chang’e-3 mission landed close to the eastern rim of the ~450 m diameter Ziwei crater. Regional stratigraphy of the landing site and impact excavation model suggest that the bulk continuous ejecta deposits of the Ziwei crater are composed by Erathothenian-aged mare basalts. Along the traverse of the Yutu rover, the western segment features a gentle topographic uplift(~0.5 m high over ~4 m), which is spatially connected with the structurally-uplifted crater rim. Assuming that this broad topographic uplift has physical properties discontinuous with materials below, we use data returned by the high-frequency lunar penetrating radar onboard the Yutu rover to estimate the possible range of relative permittivity for this topographic uplift. Only when the relative permittivity is ~9 is the observed radar reflection consistent with the observed topography, suggesting that the topographic uplift is composed of basaltic blocks that were excavated by the Ziwei crater. This result is consistent both with the impact excavation model that predicts deeper basaltic materials being deposited closer to the crater rim, and with observation of numerous half-buried boulders on the surface of this hill. We note that this study is the first to use topography and radargram data to estimate the relative permittivity of lunar surface uplifts, an approach that has had many successful applications on Mars. Similar approaches can apply other ground penetrating radar data for the Moon, such as will be available from the ongoing Chang’e-4 mission.
基金Support for Rampino came from an NYU Research Challenge grant
文摘The six largest known impact craters of the last 250 Myr(≥70 km in diameter),which are capable of causing significant environmental damage,coincide with four times of recognized extinction events at 36(with 2 craters),66,and 145 Myr ago,and possibly with two provisional extinction events at 168 and215 Myr ago.These impact cratering events are accompanied by layers in the geologic record interpreted as impact ejecta.Chance occurrences of impacts and extinctions can be rejected at confidence levels of99.96%(for 4 impact/extinctions)to 99.99%(for 6 impact/extinctions).These results argue that several extinction events over the last 250 Myr may be related to the effects of large-body impacts.
文摘The presence of glass microspherules enclosing relict grains, shattered quartz and silicon carbide in white sandstone beds near the Jurassic-Cretaceous boundary in west central Sinai indicates a cosmic impact event. Characterization of the impact microspherules and proposing a reasonable scenario for their origin are the aims of this work. Field observations, optical, binocular, scanning electron and high-resolution transmitted electron microscopy investigations and chemical analyses were carried out. The study revealed that glass microspherules have high Al<sub>2</sub>O<sub>3</sub> and FeO contents and low CaO and MgO contents. The high content of Al<sub>2</sub>O<sub>3</sub> indicates that the source of microtektite-like microspherules is attributed to the melting of a clay-rich sandstone and carbonaceous matter, while the high content of FeO indicates admixing with projectile matter. The reaction between silica and carbon was carried out under conditions of high temperature (T > 1000°C) and carbon (C/Si > 1) which resulted in the production of silicon carbide with microdiamond intergrowth. Consequently, this intergrowth is in accordance with the impact origin via rapid condensation and growth within a vapor phase. In spite of the fact that no source crater has been recognized to date in the study area, the authors propose at least a single cosmic impact event scenario for the recorded glass microspherules in west central Sinai. The impact excavated the Paleozoic siliciclastic sedimentary rocks and then the glass microspherules showered the area of study. The deposition of microtektite-like glass particles within the white sandstone beds of the Malha Formation took place in the fluvial plain terrestrial environment. This setting precluded severe post-depositional reworking, yielding preservation of the glass particles in a primary layer. Eventually, lateral migration of the braided channels led to the reworking of the microspherules layer and the spatial dispersal of the shattered quartz.
基金the Research Foundation Flanders (FWO)for funding this PhD research to BSthe support by the Belgian Science Policy (BELSPO) through BELAM,Amundsen and BAMM projects+2 种基金the Research Foundation-Flanders (FWO–Vlaanderen) and the VUB strategic researchthe support from the FWO–FNRS “Excellence of Science (EoS)” project ET–Ho ME (ID30442502)the FRS–FNRS for support.
文摘The~790 ka Australasian(micro)tektite strewn field is one of the most recent and best-known examples of impact ejecta emplacement as the result of a large-scale cratering event across a considerable part of Earth's surface(>10%in area).The Australasian strewn field is characterized by a tri-lobe pattern consisting of a large central distribution lobe,and two smaller side lobes extending to the west and east.Here,we report on the discovery of microtektite-like particles in sedimentary traps,containing abundant micrometeorite material,in the Sør Rondane Mountain(SRM)range of East Antarctica.The thirty-three glassy particles display a characteristic pale yellowcolor and are predominantly spherical in shape,except for a single dumbbell-shaped particle.The vitreous spherules range in size from220 to 570μm,with an average diameter of~370μm.This compares relatively well with the size distribution(75–778μm)of Australasian microtektites previously recovered from the TransantarcticMountains(TAM)and located ca.2500–3000 km fromthe SRM.In addition,the chemical composition of the SRM particles exhibits limited variation and is nearly identical to the‘normal-type’(i.e.,<6%MgO)TAM microtektites.The Sr and Nd isotope systematics for a single batch of SRM particles(n=26)strongly support their affiliation with TAMmicrotektites and the Australasian tektite strewn field in general.Furthermore,Sr isotope ratios and Nd model ages suggest that the target material of the SRM particles was composed of a plagioclase-or carbonate-rich lithology derived from a Paleo-or Mesoproterozoic crustal unit.The affiliation to the Australasian strewn field requires long-range transportation,with estimated great circle distances of ca.11,600 km from the hypothetical source crater,provided transportation occurred along the central distribution lobe.This is in agreement with the observations made for the Australasian microtektites recovered from Victoria Land(ca.11,000 km)and Larkman Nunatak(ca.12,000 km),which,on average,decrease in size and alkali concentrations(e.g.,Na and K)as their distance from the source crater increases.The values for the SRMparticles are intermediate to those of the Victoria Land and Larkman Nunatak microtektites for both parameters,thus supporting this observation.We therefore interpret the SRM particles as‘normal-type’Australasian microtektites,which significantly extend the central distribution lobe of the Australasian strewn field westward.Australasian microtektite distribution thus occurred on a continent-wide scale across Antarctica and allows for the identification of new,potential recovery sites on the Antarctic continent as well as the southeastern part of the Indian Ocean.Similar to volcanic ash layers,the~790 ka distal Australasian impact ejecta are thus a record of an instantaneous event that can be used for time-stratigraphic correlation across Antarctica.
基金We thank the China National Space Administration for providing access to the lunar sample CE5C0200YJFM00302This work was supported by the Strategic Priority Research Program of Chinese Academy of Sciences(XDB 41000000)+4 种基金the National Natural Science Foundation of China(42273042 and 41931077)the Technical Advanced Research Project of Civil Space(D020201)the Youth Innovation Promotion Association,Chinese Academy of Sciences(2020395)the Key Research Program of Frontier Sciences,Chinese Academy of Sciences(ZDBS-SSWJSC007-10 and QYZDY-SSW-DQC028)China Postdoctoral Science Foundation(2022M720216).
