Paleomagnetic determinations on lithological profiles of two paralleled[( )-275(long )]drilling cores covering the past 130 kyr B.P., GT40 and GT60, from the Yanchi Playa in the arid Northwestern China, indicate that ...Paleomagnetic determinations on lithological profiles of two paralleled[( )-275(long )]drilling cores covering the past 130 kyr B.P., GT40 and GT60, from the Yanchi Playa in the arid Northwestern China, indicate that a series of pronounced paleomagnetic excursions have been documented. By correlating our results with published regional and worldwide reports, 4 excursion events out of 10 apparent reversal signals (labeled from GT-1 to GT-10) were identified as excursion events coeval with the Mono Lake Event ([(28.4)( )]kyr~[(25.8)( )]kyr), Laschamp Event ([(43.3)( )]kyr^40.5 kyr), Gaotai Event (82.8 kyr~[(72.4)25( )]kyr) and the Blake Event (127.4 kyr^113.3 kyr), respectively. GT-9 correlates with the above-mentioned Gaotai Event, GT-7 and GT-6 correspond to two stages of the Laschamp Event and GT-5 to the Mono Lake Event. It is noteworthy that the so-called Gaotai Event has not been reported as a pronounced paleomagnetic excursion in the Northwestern China. Every magnetic excursion event corresponds to paleointensity minima, anteceding those established abrupt paleoclimatic change events, such as the Younger Drays and the Heinrich Events (H1-H6)[(. )-250( )]Here,[( )-250( )]we tentatively[( )-250( )]propose that these geomagnetic excursions/reversals can be viewed as precursors to climate abruptness. During the transitional stages when the earths magnetic field shifted between a temporal normal and a negative period, the earths magnetic paleointensity fell correspondingly to a pair of minima. Although more precise chronology and more convincing rock magnetic parameter determinations are essentially required for further interpretation of their intricate coupling mechanism, these results may have revealed, to some extent, that the earths incessantly changing magnetic field exerts an strong influence on the onset of saw-tooth shaped abrupt climate oscillations through certain feedback chains in arid Central Asia or even North Hemispheric high latitude regions.展开更多
Two reversal geomagnetic excursions are detected by systematically paleomagnetic measurements of the Core NP93-2 from the Prydz Bay, Eastern Antarctica.One is found in 60 to 67.5 cm from the tOP of the core, and the 1...Two reversal geomagnetic excursions are detected by systematically paleomagnetic measurements of the Core NP93-2 from the Prydz Bay, Eastern Antarctica.One is found in 60 to 67.5 cm from the tOP of the core, and the 14C dating age of layer 67.5 cm to 72.5 cm is 10315±800 a B.P.It is estimated that the geomagnetic excursion occurred at 9980-8880 a B.P.,and perhaps was the record of the Gothenburg geomagnetic excursion (about 12000 a B.P.).The other is found in 27.5-32.5 cm,and the 14C dating age is 5390±600 a B.P., with which no generally acknowledgedgeomagnetic excursion can be compared. But a few reports of geomagnetic excursions can be used for comparing with,Zhu et al.reported a geomagnetic excursion at 4980-4770 a B.P.from peat in Beijing, Wang et al.reported a geomagnetic excursion at5120±110 a B.P.from Core NS-89--76 in Nansha Waters and Zhou et al. reported ageomagnetic excursion at 6400-6000 a B.P.from Core QC2 in Yellow Sea. Whetherthe studied geomagnetic excursion does exist or whether those reported geomagnetic excursion are the same one is worth further study.展开更多
Over the past few years, OSL and TCN datings of glacial material from High Asia have come into fashion. To this day, however, these techniques do not permit safe calibration. The intensity of the cosmic ray flux is be...Over the past few years, OSL and TCN datings of glacial material from High Asia have come into fashion. To this day, however, these techniques do not permit safe calibration. The intensity of the cosmic ray flux is being modulated by the solar and terrestrial magnetic fields and their secular fluctuations in the past. So far, these variations cannot be converted into the respective local TCN production rates for High Asia. We have reason to believe that the ages that are being calculated despite these uneertainties are generally overestimated. This assessment is supported by eonventional radiocarbon dates and above＂ all by the glacial chronology developed independently on the basis of the Quaternary geological method. The strongly emerging evidence for a much more extensive LGM glaciation of High Asia is, however, either being ignored or rejected by many authors, solely on the basis of the above-mentioned uncalibrated datings. This self-conceit based on the ＂dating fallacy＂, as we call it, should be avoided since it goes decidedly against the standards of the scientific method established in Quaternary geology and makes a fundamental scientific discussion impossible.展开更多
基金This work is funded by the National Natural Science Foundation of China(NSFC Grant No.94731010).
文摘Paleomagnetic determinations on lithological profiles of two paralleled[( )-275(long )]drilling cores covering the past 130 kyr B.P., GT40 and GT60, from the Yanchi Playa in the arid Northwestern China, indicate that a series of pronounced paleomagnetic excursions have been documented. By correlating our results with published regional and worldwide reports, 4 excursion events out of 10 apparent reversal signals (labeled from GT-1 to GT-10) were identified as excursion events coeval with the Mono Lake Event ([(28.4)( )]kyr~[(25.8)( )]kyr), Laschamp Event ([(43.3)( )]kyr^40.5 kyr), Gaotai Event (82.8 kyr~[(72.4)25( )]kyr) and the Blake Event (127.4 kyr^113.3 kyr), respectively. GT-9 correlates with the above-mentioned Gaotai Event, GT-7 and GT-6 correspond to two stages of the Laschamp Event and GT-5 to the Mono Lake Event. It is noteworthy that the so-called Gaotai Event has not been reported as a pronounced paleomagnetic excursion in the Northwestern China. Every magnetic excursion event corresponds to paleointensity minima, anteceding those established abrupt paleoclimatic change events, such as the Younger Drays and the Heinrich Events (H1-H6)[(. )-250( )]Here,[( )-250( )]we tentatively[( )-250( )]propose that these geomagnetic excursions/reversals can be viewed as precursors to climate abruptness. During the transitional stages when the earths magnetic field shifted between a temporal normal and a negative period, the earths magnetic paleointensity fell correspondingly to a pair of minima. Although more precise chronology and more convincing rock magnetic parameter determinations are essentially required for further interpretation of their intricate coupling mechanism, these results may have revealed, to some extent, that the earths incessantly changing magnetic field exerts an strong influence on the onset of saw-tooth shaped abrupt climate oscillations through certain feedback chains in arid Central Asia or even North Hemispheric high latitude regions.
文摘Two reversal geomagnetic excursions are detected by systematically paleomagnetic measurements of the Core NP93-2 from the Prydz Bay, Eastern Antarctica.One is found in 60 to 67.5 cm from the tOP of the core, and the 14C dating age of layer 67.5 cm to 72.5 cm is 10315±800 a B.P.It is estimated that the geomagnetic excursion occurred at 9980-8880 a B.P.,and perhaps was the record of the Gothenburg geomagnetic excursion (about 12000 a B.P.).The other is found in 27.5-32.5 cm,and the 14C dating age is 5390±600 a B.P., with which no generally acknowledgedgeomagnetic excursion can be compared. But a few reports of geomagnetic excursions can be used for comparing with,Zhu et al.reported a geomagnetic excursion at 4980-4770 a B.P.from peat in Beijing, Wang et al.reported a geomagnetic excursion at5120±110 a B.P.from Core NS-89--76 in Nansha Waters and Zhou et al. reported ageomagnetic excursion at 6400-6000 a B.P.from Core QC2 in Yellow Sea. Whetherthe studied geomagnetic excursion does exist or whether those reported geomagnetic excursion are the same one is worth further study.
文摘Over the past few years, OSL and TCN datings of glacial material from High Asia have come into fashion. To this day, however, these techniques do not permit safe calibration. The intensity of the cosmic ray flux is being modulated by the solar and terrestrial magnetic fields and their secular fluctuations in the past. So far, these variations cannot be converted into the respective local TCN production rates for High Asia. We have reason to believe that the ages that are being calculated despite these uneertainties are generally overestimated. This assessment is supported by eonventional radiocarbon dates and above＂ all by the glacial chronology developed independently on the basis of the Quaternary geological method. The strongly emerging evidence for a much more extensive LGM glaciation of High Asia is, however, either being ignored or rejected by many authors, solely on the basis of the above-mentioned uncalibrated datings. This self-conceit based on the ＂dating fallacy＂, as we call it, should be avoided since it goes decidedly against the standards of the scientific method established in Quaternary geology and makes a fundamental scientific discussion impossible.
