地质年代的精确确定是我们认识地球演化历史和过程的关键,而如何提高地质年代的精度却一直是个尚待解决的科学难题。最近30年多年来,基于古气候学研究的天文旋回理论获得了普遍认可和广泛应用,尤其是成功应用于天文地质年代校准中。这...地质年代的精确确定是我们认识地球演化历史和过程的关键,而如何提高地质年代的精度却一直是个尚待解决的科学难题。最近30年多年来,基于古气候学研究的天文旋回理论获得了普遍认可和广泛应用,尤其是成功应用于天文地质年代校准中。这种数字定年方法是通过天文调谐获得连续的高分辨率的地质年代,是对传统地质定年方法如古生物、古地磁以及放射性同位素测年方法的一次革新。最新的国际地质年表The Geologic Time Scale 2012(简称GTS2012)中经过天文校准的地质年代已近100%覆盖了新生代,而中生代的天文年代校准还存在着很大挑战。目前应用稳定的405ka的偏心率长周期对中生代地层进行天文地质年代校准,是国际地质年表从GTS2004到GTS2012的一个最大改进。文中将主要介绍天文旋回的基础理论和其在中生代的应用及其研究现状。展开更多
A continuous terrestrial succession was recovered from the Songke-2(SK-2)borehole in the Songliao Basin,Northeastern China.This borehole provides a unique material for further research on the continental paleoclimate ...A continuous terrestrial succession was recovered from the Songke-2(SK-2)borehole in the Songliao Basin,Northeastern China.This borehole provides a unique material for further research on the continental paleoclimate during Cretaceous greenhouse period,following a series of achievements of the Songke-1(SK-1)core.In this study,thorium(Th)logging data were chosen as a paleoclimate proxy to conduct a detailed cyclostratigraphic analysis.The Th series varies quasi-periodically;power spectra and evolutionary fast Fourier transformation(FFT)analysis reveal significant cycles in the Quantou(K2 q),Qingshankou(K2 qn),Yaojia(K2 y)and Nenjiang(K2 n)formations.The ratio of cycle wavelengths in these stratigraphic units is approximately 20:5:2:1,corresponding to long orbital eccentricity(405 kyr),short orbital eccentricity(100 kyr),obliquity(37 kyr),and precession cycles(22.5 kyr and 18.4 kyr).The durations of the K2 n,K2 y,K2 qn and K2 q are estimated as 6.97,1.83,5.30 and 4.52 Myr,respectively,based on the constructed^18.62 Myr"floating"astronomical time scale(ATS).Comparison of the durations between the SK-1 s and SK-2 boreholes exhibits a slight difference of 0.06 Myr and 0.459 Myr for K2 qn and K2 y.Nevertheless,our ATS of K2 n supports the chronostratigraphic frame constructed by the CA-ID-TIMS data of the SK-1 s borehole.This new"floating"ATS provides precise numerical ages for stratigraphic boundaries,biozones and geological events in the Songliao Basin,and can serve as a basis for correlation of strata and events between marine and terrestrial systems.展开更多
The Oligocene-Miocene transition period was characterized by a decrease in global CO2 levels, expansion of polar ice sheet, fall in global sea-level, etc. However, the reasons for, and mechanisms of, this global, extr...The Oligocene-Miocene transition period was characterized by a decrease in global CO2 levels, expansion of polar ice sheet, fall in global sea-level, etc. However, the reasons for, and mechanisms of, this global, extreme-cold climate change event（Mi-1） still remain controversial. Our samples from the core of the Ocean Drilling Program（ODP） Leg 154, Site 926, located in the equatorial Atlantic, mainly consist of light-gray, nannofossil chalk with foraminifers interbedded with greenish-gray, clayey, nannofossil chalk sediments. Color variation from light-gray layers（up to 80% carbonate content） to dark layers（60% carbonate content） was observed to occur cyclically at the meter scale. Therefore, we chose color reflectance lightness（L*） data as the paleoclimate proxy on which to perform cyclostratigraphic analysis because it could reflect carbonate content changes. Based on the recognition of the 405 kyr long eccentricity and 40 kyr obliquity cycles of the L* series, we tuned the series to establish an absolute astronomical time scale using the published age of the Oligocene-Miocene boundary（OMB） as the anchor for an absolute age control point. The power spectra of the tuned L* series showed that the long eccentricity signals became significantly weak, while the obliquity signals became strong, from the Late Oligocene to the Early Miocene. The 405 kyr long eccentricity minimum coincided with the 1.2 Myr obliquity node at the OMB, and similar convergences might be closely related to other extreme-cold events in Earth’s history. In addition, the sedimentation accumulation rate, oxygen isotopes of benthonic foraminifers, and rodents’ per-taxon turnover rate from Central Spain showed the same 2 Myr cyclicity, which indicates the significant influence of Earth-orbital forcing on the Earth system and ecological evolution on the million-year time scale.展开更多
文摘地质年代的精确确定是我们认识地球演化历史和过程的关键,而如何提高地质年代的精度却一直是个尚待解决的科学难题。最近30年多年来,基于古气候学研究的天文旋回理论获得了普遍认可和广泛应用,尤其是成功应用于天文地质年代校准中。这种数字定年方法是通过天文调谐获得连续的高分辨率的地质年代,是对传统地质定年方法如古生物、古地磁以及放射性同位素测年方法的一次革新。最新的国际地质年表The Geologic Time Scale 2012(简称GTS2012)中经过天文校准的地质年代已近100%覆盖了新生代,而中生代的天文年代校准还存在着很大挑战。目前应用稳定的405ka的偏心率长周期对中生代地层进行天文地质年代校准,是国际地质年表从GTS2004到GTS2012的一个最大改进。文中将主要介绍天文旋回的基础理论和其在中生代的应用及其研究现状。
基金supported by the National Natural Science Foundation of China(41790451,41925010,and 41688103)National Key R&D Program of China(2019YFC0605403)the subject development project of RIPED(yjkt2019-3).
文摘A continuous terrestrial succession was recovered from the Songke-2(SK-2)borehole in the Songliao Basin,Northeastern China.This borehole provides a unique material for further research on the continental paleoclimate during Cretaceous greenhouse period,following a series of achievements of the Songke-1(SK-1)core.In this study,thorium(Th)logging data were chosen as a paleoclimate proxy to conduct a detailed cyclostratigraphic analysis.The Th series varies quasi-periodically;power spectra and evolutionary fast Fourier transformation(FFT)analysis reveal significant cycles in the Quantou(K2 q),Qingshankou(K2 qn),Yaojia(K2 y)and Nenjiang(K2 n)formations.The ratio of cycle wavelengths in these stratigraphic units is approximately 20:5:2:1,corresponding to long orbital eccentricity(405 kyr),short orbital eccentricity(100 kyr),obliquity(37 kyr),and precession cycles(22.5 kyr and 18.4 kyr).The durations of the K2 n,K2 y,K2 qn and K2 q are estimated as 6.97,1.83,5.30 and 4.52 Myr,respectively,based on the constructed^18.62 Myr"floating"astronomical time scale(ATS).Comparison of the durations between the SK-1 s and SK-2 boreholes exhibits a slight difference of 0.06 Myr and 0.459 Myr for K2 qn and K2 y.Nevertheless,our ATS of K2 n supports the chronostratigraphic frame constructed by the CA-ID-TIMS data of the SK-1 s borehole.This new"floating"ATS provides precise numerical ages for stratigraphic boundaries,biozones and geological events in the Songliao Basin,and can serve as a basis for correlation of strata and events between marine and terrestrial systems.
基金supported by the National Natural Science Foundation of China (Grant No. 41322013)the Program of Introducing Talents of Discipline to Universities (Grant No. B14031)the National Basic Research Program of China (Grant No. 2012CB822003)
文摘The Oligocene-Miocene transition period was characterized by a decrease in global CO2 levels, expansion of polar ice sheet, fall in global sea-level, etc. However, the reasons for, and mechanisms of, this global, extreme-cold climate change event（Mi-1） still remain controversial. Our samples from the core of the Ocean Drilling Program（ODP） Leg 154, Site 926, located in the equatorial Atlantic, mainly consist of light-gray, nannofossil chalk with foraminifers interbedded with greenish-gray, clayey, nannofossil chalk sediments. Color variation from light-gray layers（up to 80% carbonate content） to dark layers（60% carbonate content） was observed to occur cyclically at the meter scale. Therefore, we chose color reflectance lightness（L*） data as the paleoclimate proxy on which to perform cyclostratigraphic analysis because it could reflect carbonate content changes. Based on the recognition of the 405 kyr long eccentricity and 40 kyr obliquity cycles of the L* series, we tuned the series to establish an absolute astronomical time scale using the published age of the Oligocene-Miocene boundary（OMB） as the anchor for an absolute age control point. The power spectra of the tuned L* series showed that the long eccentricity signals became significantly weak, while the obliquity signals became strong, from the Late Oligocene to the Early Miocene. The 405 kyr long eccentricity minimum coincided with the 1.2 Myr obliquity node at the OMB, and similar convergences might be closely related to other extreme-cold events in Earth’s history. In addition, the sedimentation accumulation rate, oxygen isotopes of benthonic foraminifers, and rodents’ per-taxon turnover rate from Central Spain showed the same 2 Myr cyclicity, which indicates the significant influence of Earth-orbital forcing on the Earth system and ecological evolution on the million-year time scale.
