This is a preliminary study on the microtektites that were found in large numbers from the interval between 7.80 and 8.10 m depth of core S095-17957-2 (10°53.9’N, 115°18.3’E, water depth 2 195 m), northern...This is a preliminary study on the microtektites that were found in large numbers from the interval between 7.80 and 8.10 m depth of core S095-17957-2 (10°53.9’N, 115°18.3’E, water depth 2 195 m), northern Nansha area of the South China Sea. The microtektites vary in shape, with spherules predominating, and are commonly less than 1 mm in diameter, transparent or semitransparent, brownish in color, with bubbles inside. Based on coarse fraction stratigraphy and foraminifera/nanofossil biostratigraphical events the microtektite layer was assigned to nearly the Bm-hes/Matuyama magnetic reversal boundary (some 0.78 MaBP). Obviously, the present microtektites, and those found from the middle Pleistocene of the Indian Ocean, Australia and loess of northern China, were products of the same impact event and therefore, are useful as a reliable mark in Quaternary stratigraphy, as well as in paleoclimatic studies.展开更多
The present study confirms the stratigraphical position of microtektite layer being clearly located below the Brunhes/Matuyama (B/M) boundary. Based on the sedimentation rate derived from the stable isotopic and magne...The present study confirms the stratigraphical position of microtektite layer being clearly located below the Brunhes/Matuyama (B/M) boundary. Based on the sedimentation rate derived from the stable isotopic and magnetic data of ODP Site 772A, cores 17957 and 17959 in the South China Sea, the age of the mid-Pleistocene impact event was estimated at 10-12 ka earlier than the Brunhes-Matuyama polarity reversal. However, the microtektites were found above the measured B/M boundary in the loess profile due to the downward deviation of the measured B/M boundary from its true position. This demonstrates the complexity of paleo-magnetic records in the loess profiles which, in turn, causes the confusion in the sea-land stratigraphic correlation.展开更多
Dongling Mountain is the highest one of the Beijing West Mountains. There is a layer of subalpine meadow soil about 0.50 m thick at the top of the mountain, of which the basement rock is the Jurassic andesite. A secti...Dongling Mountain is the highest one of the Beijing West Mountains. There is a layer of subalpine meadow soil about 0.50 m thick at the top of the mountain, of which the basement rock is the Jurassic andesite. A section was artificially dug out and some samples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展开更多
Two sediment cores, MD06-3050 and MD06-3047, were analyzed to study the Quaternary calcareous nannofossil and microtektite records. We dated bioevents and the microtektite impact event by calibrating with oxygen isoto...Two sediment cores, MD06-3050 and MD06-3047, were analyzed to study the Quaternary calcareous nannofossil and microtektite records. We dated bioevents and the microtektite impact event by calibrating with oxygen isotope stratigraphy. Seven calcareous nannofossil bioevents were identified over the past 2.36 Ma including the last appearance of data for Discoaster brouweri, Calcidiscus macintyrei, large Gephyrocapsa and Pseudoemiliania lacunosa, the first appearance of data for large Gephyrocapsa and Emiliania huxleyi, and the abrupt increase in the abundance of Gephyrocapsa caribbeanica. In addition, we fortunately observed that Australasian microtektites were distributed in core MD06-3050 from 1340 to 1374 cm.展开更多
It is first in continental sediment-loess that 16 microtektites and 3 ablated glassy Si-Mg microspherules were found. They occur only in the upper layer of L8, a 40—70-cm horizon above the B/M boundary. The age of de...It is first in continental sediment-loess that 16 microtektites and 3 ablated glassy Si-Mg microspherules were found. They occur only in the upper layer of L8, a 40—70-cm horizon above the B/M boundary. The age of deposition is about 0.72 Ma. Microtektites in loess are usually sphere, speroid, kidney-form, tear-drop and irregular debris in shape. They are transparent and translucent, and some have the shade of green, amber and yellow in color. Their sizes range from 65 to 220μm. Most of microtektites were badly pitted and corroded, but there remain bubbles, cavities and scorious and flow microstructure in some ones. On the basis of their major oxide compositions, microtektites in loess may be divided into three chemical groups that are described as normal, bottle-green and high-aluminium microtektite. They are similar in chemical composition to microtektites in deep-sea cores. Geochemistry of trace elements show that the origin of microtektite is very complicated and their parent materials are from multiple sources. On the basis of geographical location, deposition age, stratigraphic occurrence, physical property and chemical composition, microtektites found in loess at Luochuan may fall into the Australia-Southeast Asian tektite strewn field.展开更多
Loess and paleosol have been regarded as an excellent geological body for reestablishment of the past 2.4 Ma paleoclimatic history.The discovery and study of microtektites in Luochuan loess section imply that the infl...Loess and paleosol have been regarded as an excellent geological body for reestablishment of the past 2.4 Ma paleoclimatic history.The discovery and study of microtektites in Luochuan loess section imply that the influence of impact event展开更多
Ⅰ. RESEARCHED PROFILEIn China, the most detailed study on loess was carried out in the Heimugou loess profile located at Luochuan County, Shaanxi Province, where the loess has a thickness of 135m. According to the li...Ⅰ. RESEARCHED PROFILEIn China, the most detailed study on loess was carried out in the Heimugou loess profile located at Luochuan County, Shaanxi Province, where the loess has a thickness of 135m. According to the lithologic character, loess of this section can be divided into Pouto loess, Malan loess, Lishi loess and Wucheng loess. The layer of red clay,展开更多
The thick loess strata in the Loess Plateau of China, which have not been essentially reformed by internal and external agents, are one of the optimum continental deposits preserving the extraterrestrial materials in ...The thick loess strata in the Loess Plateau of China, which have not been essentially reformed by internal and external agents, are one of the optimum continental deposits preserving the extraterrestrial materials in the last 2.5 Ma. Thus, combining the records with the detailed data of the loess-paleosol sequence, the ages and environmental impacts of the astrogeologic events can be determined.展开更多
Anomalies of content of Ir, noble metals and other trace elements are usually regarded as crucial evidence of impact event. A large number of microtektites have been found in deep-sea sediments since the 1960s, but an...Anomalies of content of Ir, noble metals and other trace elements are usually regarded as crucial evidence of impact event. A large number of microtektites have been found in deep-sea sediments since the 1960s, but analyses of trace elements in microtektitebearing layers have seldom been reported, with the exception that Asaro et al. stated that microtektite-bearing layers in Caribbean Gulf exhibited anomaly of Ir (?). The展开更多
Geologic marks related to extraterrestrial impact events, such as impact split gravels, impact brecciate layers, impact dikes, microirghizites, microtektites, especially meteoritic residues, were discovered on the bou...Geologic marks related to extraterrestrial impact events, such as impact split gravels, impact brecciate layers, impact dikes, microirghizites, microtektites, especially meteoritic residues, were discovered on the boundary between Sinian/Cambrian at Tianmenshan of Western Hunan, which may possibly demonstrate that an extraterrestrial impact event has ever occurred there on the S/C boundary.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 49676287, 49732060).
文摘This is a preliminary study on the microtektites that were found in large numbers from the interval between 7.80 and 8.10 m depth of core S095-17957-2 (10°53.9’N, 115°18.3’E, water depth 2 195 m), northern Nansha area of the South China Sea. The microtektites vary in shape, with spherules predominating, and are commonly less than 1 mm in diameter, transparent or semitransparent, brownish in color, with bubbles inside. Based on coarse fraction stratigraphy and foraminifera/nanofossil biostratigraphical events the microtektite layer was assigned to nearly the Bm-hes/Matuyama magnetic reversal boundary (some 0.78 MaBP). Obviously, the present microtektites, and those found from the middle Pleistocene of the Indian Ocean, Australia and loess of northern China, were products of the same impact event and therefore, are useful as a reliable mark in Quaternary stratigraphy, as well as in paleoclimatic studies.
文摘The present study confirms the stratigraphical position of microtektite layer being clearly located below the Brunhes/Matuyama (B/M) boundary. Based on the sedimentation rate derived from the stable isotopic and magnetic data of ODP Site 772A, cores 17957 and 17959 in the South China Sea, the age of the mid-Pleistocene impact event was estimated at 10-12 ka earlier than the Brunhes-Matuyama polarity reversal. However, the microtektites were found above the measured B/M boundary in the loess profile due to the downward deviation of the measured B/M boundary from its true position. This demonstrates the complexity of paleo-magnetic records in the loess profiles which, in turn, causes the confusion in the sea-land stratigraphic correlation.
文摘Dongling Mountain is the highest one of the Beijing West Mountains. There is a layer of subalpine meadow soil about 0.50 m thick at the top of the mountain, of which the basement rock is the Jurassic andesite. A section was artificially dug out and some samples
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
基金supported by the Pilot Project of the National Knowledge Innovation Program of the Chinese Academy of Sciences (KZCX2-YW-221)the National Natural Science Foundation of China (40906030,40976026and40906038)the National Basic Research Program of China (2007CB815903)
文摘Two sediment cores, MD06-3050 and MD06-3047, were analyzed to study the Quaternary calcareous nannofossil and microtektite records. We dated bioevents and the microtektite impact event by calibrating with oxygen isotope stratigraphy. Seven calcareous nannofossil bioevents were identified over the past 2.36 Ma including the last appearance of data for Discoaster brouweri, Calcidiscus macintyrei, large Gephyrocapsa and Pseudoemiliania lacunosa, the first appearance of data for large Gephyrocapsa and Emiliania huxleyi, and the abrupt increase in the abundance of Gephyrocapsa caribbeanica. In addition, we fortunately observed that Australasian microtektites were distributed in core MD06-3050 from 1340 to 1374 cm.
基金Project supported by the National Natural Science Foundation of China, and Lab of Loess and Quaternary Geology at Xi'an, Academia Sinica.
文摘It is first in continental sediment-loess that 16 microtektites and 3 ablated glassy Si-Mg microspherules were found. They occur only in the upper layer of L8, a 40—70-cm horizon above the B/M boundary. The age of deposition is about 0.72 Ma. Microtektites in loess are usually sphere, speroid, kidney-form, tear-drop and irregular debris in shape. They are transparent and translucent, and some have the shade of green, amber and yellow in color. Their sizes range from 65 to 220μm. Most of microtektites were badly pitted and corroded, but there remain bubbles, cavities and scorious and flow microstructure in some ones. On the basis of their major oxide compositions, microtektites in loess may be divided into three chemical groups that are described as normal, bottle-green and high-aluminium microtektite. They are similar in chemical composition to microtektites in deep-sea cores. Geochemistry of trace elements show that the origin of microtektite is very complicated and their parent materials are from multiple sources. On the basis of geographical location, deposition age, stratigraphic occurrence, physical property and chemical composition, microtektites found in loess at Luochuan may fall into the Australia-Southeast Asian tektite strewn field.
基金Project supported by the National Natural Science Foundation of China.
文摘Loess and paleosol have been regarded as an excellent geological body for reestablishment of the past 2.4 Ma paleoclimatic history.The discovery and study of microtektites in Luochuan loess section imply that the influence of impact event
基金Project supported by the National Natural Science Foundation of China.
文摘Ⅰ. RESEARCHED PROFILEIn China, the most detailed study on loess was carried out in the Heimugou loess profile located at Luochuan County, Shaanxi Province, where the loess has a thickness of 135m. According to the lithologic character, loess of this section can be divided into Pouto loess, Malan loess, Lishi loess and Wucheng loess. The layer of red clay,
基金Project sponsored by the foundation of Xi'an Laboratory of Loess and Quaternary, Academia Sinica and by the foundation of the Laboratory of Geomechanics Ministry of Geology and Mineral Resources PRC
文摘The thick loess strata in the Loess Plateau of China, which have not been essentially reformed by internal and external agents, are one of the optimum continental deposits preserving the extraterrestrial materials in the last 2.5 Ma. Thus, combining the records with the detailed data of the loess-paleosol sequence, the ages and environmental impacts of the astrogeologic events can be determined.
基金Project supported by the National Natural Science Foundation of China
文摘Anomalies of content of Ir, noble metals and other trace elements are usually regarded as crucial evidence of impact event. A large number of microtektites have been found in deep-sea sediments since the 1960s, but analyses of trace elements in microtektitebearing layers have seldom been reported, with the exception that Asaro et al. stated that microtektite-bearing layers in Caribbean Gulf exhibited anomaly of Ir (?). The
基金financially supported by China National Natural Science Foundation(Grant No.40172078).
文摘Geologic marks related to extraterrestrial impact events, such as impact split gravels, impact brecciate layers, impact dikes, microirghizites, microtektites, especially meteoritic residues, were discovered on the boundary between Sinian/Cambrian at Tianmenshan of Western Hunan, which may possibly demonstrate that an extraterrestrial impact event has ever occurred there on the S/C boundary.
