根据对昆仑山北麓阿羌地区第四纪风成砂尘沉积物的调查、地层对比和107组古地磁标本(321块样品)的测定结果认为,阿羌地层剖面记录了Brunhes时以来我国极端干旱区最完整的风成砂尘堆积序列;剖面中间冰期形成的生草层1PE和细粒风尘堆积29...根据对昆仑山北麓阿羌地区第四纪风成砂尘沉积物的调查、地层对比和107组古地磁标本(321块样品)的测定结果认为,阿羌地层剖面记录了Brunhes时以来我国极端干旱区最完整的风成砂尘堆积序列;剖面中间冰期形成的生草层1PE和细粒风尘堆积29FGL、31FGL、33FGL、35FGL、37FGL、39FGL、42FGL在形成的地质时代上可依次与黄土高原古土壤S_0、S_1、S_2、S_3、S_4、S_5、S_6、S_7进行对比,而与1PE和细粒风尘堆积29FGL、……、42FGL互为叠覆的冰期气候形成的风成极细砂和粗粒风尘堆积则可与黄土高原黄土L_1、……、L_8进行对比。此外,在阿羌剖面砂尘堆积底部42FGL层中发现有0.7 Ma B P前的宇宙尘埃物质,这对于该地风成砂尘下限年代的确定、研究极端干旱区气候的发展历史和晚新生代地外灾变事件的对比具有重要意义。展开更多
The presence of the reversals of the geomagnetic field within the Brunhes is indicated by paleomagnetic stuides on Cenozoic volcanic rocks in the Leizhou Peninsula, loess strata and Quaternary marine sediments in the ...The presence of the reversals of the geomagnetic field within the Brunhes is indicated by paleomagnetic stuides on Cenozoic volcanic rocks in the Leizhou Peninsula, loess strata and Quaternary marine sediments in the Pearl River Mouth basin in China. These regional reversals occured at 0.58±0.13 Ma, 0.45 Ma and 0.47—0.48 Ma respectively according to the results of K-Ar isotopic dating and climatostratigraphic and biostratigraphic analyses. The reversals equivalent to the Emperor Event is suggested.The reversals revealed in different regions with various lithologic characters in China prove that the Emperor Event is a global reversal event rather than a geomagnetic excursion, and its confirmation will permit a precise definition of the Middle/Late Pleistocene boundary.展开更多
Several significant events of a geological nature occurred approximately 800 ka before the present: (1) Australasian tektite fall (AA), (2) Brunhes-Matuyama geomagnetic reversal (BMR), (3) mid-Pleistocene changes in i...Several significant events of a geological nature occurred approximately 800 ka before the present: (1) Australasian tektite fall (AA), (2) Brunhes-Matuyama geomagnetic reversal (BMR), (3) mid-Pleistocene changes in ice age cycles. Add to these the undated fault system (4) in the South-West (SW) of the South China Sea (SCS). Here we offer a unified cause for all four of these in (5), an impact in the SCS of a large, massive cosmic object, likely a comet, obliquely coming from the SW at an extremely shallow angle, striking the Sunda shelf yet unexploded with the shock of its compressed air bow wave, and causing the continual shelf and slope to collapse, resulting in the fault system (4), then traveling almost tangentially to the surface, exploding at impact with the sea surface, ejecting the tektites (1), creating the formation underlying the later atolls of Spratlies Archipelago (6), Nansha Islands in Chinese, & causing the BMR (2). An explanation of event (3) was Richard Muller’s hypothesis of planet Earth passing through an interplanetary dust cloud periodically due to ecliptic precession. Here we hypothesize this cloud actually is a belt of Australasian tektites ejected into space at super-orbital velocities that Earth encounters about every 100 ka.展开更多
Paleomagnetic records of the Gauss-Matuyama reversal were obtained from two loess sections at Baoji on the Chinese Loes Plateau. Stepwise thermal demagnetization shows two obvious magnetization components. A low-tempe...Paleomagnetic records of the Gauss-Matuyama reversal were obtained from two loess sections at Baoji on the Chinese Loes Plateau. Stepwise thermal demagnetization shows two obvious magnetization components. A low-temperature component iso lated between 100 and 200–250℃ is close to the present geomagnetic field direction, and a high-temperature component iso lated above 200–250℃ reveals clearly normal, reversed, and transitional polarities. Magnetostratigraphic results of both sec tions indicated that the Gauss-Matuyama reversal consists of a high-frequency polarity fluctuation zone, but the characteristic remanent magnetization directions during the reversal are clearly inconsistent. Rock magnetic experiments demonstrated tha for all the specimens with normal, reversed, and transitional polarities magnetite and hematite are the main magnetic carriers Anisotropy of magnetic susceptibility indicates that the studied loess sediments have a primary sedimentary fabric. Based on virtual geomagnetic pole latitudes, the Gauss-Matuyama reversal records in the two sections are accompanied by 14 short-lived geomagnetic episodes(15 rapid polarity swings) and 12 short-lived geomagnetic episodes(13 rapid polarity swings), respec tively. Our new records, together with previous ones from lacustrine, marine, and aeolian deposits, suggest that high-frequency polarity swings coexist with the Gauss-Matuyama reversal, and that the Gauss-Matuyama reversal may have taken more than11 kyr to complete. However, we need more detailed analyses of sections across polarity swings during reversals as well a more high-resolution reversal records to understand geomagnetic behavior and inconsistent characteristic remanent magnetiza tion directions during polarity reversals.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
文摘根据对昆仑山北麓阿羌地区第四纪风成砂尘沉积物的调查、地层对比和107组古地磁标本(321块样品)的测定结果认为,阿羌地层剖面记录了Brunhes时以来我国极端干旱区最完整的风成砂尘堆积序列;剖面中间冰期形成的生草层1PE和细粒风尘堆积29FGL、31FGL、33FGL、35FGL、37FGL、39FGL、42FGL在形成的地质时代上可依次与黄土高原古土壤S_0、S_1、S_2、S_3、S_4、S_5、S_6、S_7进行对比,而与1PE和细粒风尘堆积29FGL、……、42FGL互为叠覆的冰期气候形成的风成极细砂和粗粒风尘堆积则可与黄土高原黄土L_1、……、L_8进行对比。此外,在阿羌剖面砂尘堆积底部42FGL层中发现有0.7 Ma B P前的宇宙尘埃物质,这对于该地风成砂尘下限年代的确定、研究极端干旱区气候的发展历史和晚新生代地外灾变事件的对比具有重要意义。
文摘The presence of the reversals of the geomagnetic field within the Brunhes is indicated by paleomagnetic stuides on Cenozoic volcanic rocks in the Leizhou Peninsula, loess strata and Quaternary marine sediments in the Pearl River Mouth basin in China. These regional reversals occured at 0.58±0.13 Ma, 0.45 Ma and 0.47—0.48 Ma respectively according to the results of K-Ar isotopic dating and climatostratigraphic and biostratigraphic analyses. The reversals equivalent to the Emperor Event is suggested.The reversals revealed in different regions with various lithologic characters in China prove that the Emperor Event is a global reversal event rather than a geomagnetic excursion, and its confirmation will permit a precise definition of the Middle/Late Pleistocene boundary.
文摘Several significant events of a geological nature occurred approximately 800 ka before the present: (1) Australasian tektite fall (AA), (2) Brunhes-Matuyama geomagnetic reversal (BMR), (3) mid-Pleistocene changes in ice age cycles. Add to these the undated fault system (4) in the South-West (SW) of the South China Sea (SCS). Here we offer a unified cause for all four of these in (5), an impact in the SCS of a large, massive cosmic object, likely a comet, obliquely coming from the SW at an extremely shallow angle, striking the Sunda shelf yet unexploded with the shock of its compressed air bow wave, and causing the continual shelf and slope to collapse, resulting in the fault system (4), then traveling almost tangentially to the surface, exploding at impact with the sea surface, ejecting the tektites (1), creating the formation underlying the later atolls of Spratlies Archipelago (6), Nansha Islands in Chinese, & causing the BMR (2). An explanation of event (3) was Richard Muller’s hypothesis of planet Earth passing through an interplanetary dust cloud periodically due to ecliptic precession. Here we hypothesize this cloud actually is a belt of Australasian tektites ejected into space at super-orbital velocities that Earth encounters about every 100 ka.
基金supported by the National Natural Science Foundation of China (Grant No. 41172038)the Program for New Century Excellent Talents in University (Grant No. NCET-11-0720)+2 种基金the Fundamental Research Fund for the Central Universities (Grant Nos. 26520100, 2652011110)the Ministry of Education, Culture, Sports, Science, and Technology of Japan (MEXT) (Grant No. 19340151)Part of this study was performed under the cooperative research program of CMCR, Kochi University (Grant Nos. 07A017, A07B027)
文摘Paleomagnetic records of the Gauss-Matuyama reversal were obtained from two loess sections at Baoji on the Chinese Loes Plateau. Stepwise thermal demagnetization shows two obvious magnetization components. A low-temperature component iso lated between 100 and 200–250℃ is close to the present geomagnetic field direction, and a high-temperature component iso lated above 200–250℃ reveals clearly normal, reversed, and transitional polarities. Magnetostratigraphic results of both sec tions indicated that the Gauss-Matuyama reversal consists of a high-frequency polarity fluctuation zone, but the characteristic remanent magnetization directions during the reversal are clearly inconsistent. Rock magnetic experiments demonstrated tha for all the specimens with normal, reversed, and transitional polarities magnetite and hematite are the main magnetic carriers Anisotropy of magnetic susceptibility indicates that the studied loess sediments have a primary sedimentary fabric. Based on virtual geomagnetic pole latitudes, the Gauss-Matuyama reversal records in the two sections are accompanied by 14 short-lived geomagnetic episodes(15 rapid polarity swings) and 12 short-lived geomagnetic episodes(13 rapid polarity swings), respec tively. Our new records, together with previous ones from lacustrine, marine, and aeolian deposits, suggest that high-frequency polarity swings coexist with the Gauss-Matuyama reversal, and that the Gauss-Matuyama reversal may have taken more than11 kyr to complete. However, we need more detailed analyses of sections across polarity swings during reversals as well a more high-resolution reversal records to understand geomagnetic behavior and inconsistent characteristic remanent magnetiza tion directions during polarity reversals.
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.
