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
The formation of halite in continental basins is intimately linked to lake-level changes.Current research has revealed the connection between lake-level variations and astronomical forcing on a million-year scale.Othe...The formation of halite in continental basins is intimately linked to lake-level changes.Current research has revealed the connection between lake-level variations and astronomical forcing on a million-year scale.Other studies have also highlighted the influence of orbitally-induced climate cycles on halite deposition.However,our understanding of the impact of astronomically-paced lake-level changes on halite formation remains constrained.The Paleogene Dawenkou Formation in the Huanggang Basin of East China provides a continuous salt-bearing sedimentary record to investigate the lake-level changes in halite deposition.Lake-level fluctuations reconstructed by sedimentary noise modeling for the Middle and Upper members of the Dawenkou Formation indicate that the lake-level variations in the Huanggang Basin were linked to astronomical forcing with periods of∼2.4 Myr,∼1.2 Myr and/or∼100 kyr.Our results suggest that astronomical forcing,as a driver of lake-level variations,may have had an impact on halite deposition during the Paleogene.In the initial stage of halite formation within the Middle Member of the Dawenkou Formation,reduced heat and moisture transport during the∼1.2 Myr obliquity minima resulted in low lake levels in mid-to-high latitudes.The prolonged droughts caused by the low amplitude of∼2.4 Myr eccentricity created conditions more favorable for the development of thicker layers of halite.Subsequently,in the next halite-forming stage,a larger amplitude of∼2.4 Myr eccentricity led to a more humid climate.Warm/dry winters and cool summers paced by the∼100 kyr orbital eccentricity minima resulted in enhanced evaporation,relatively lower lake levels,and thinner halite deposition.Nevertheless,the possible transgressions may have contributed to complicated phase relationship between the lake-level change cycles and orbital cycles.This study offers an opportunity to delve deeper into the mechanism of halite deposition by objectively reconstructing lake levels using sedimentary noise modeling.展开更多
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.
基金supported by the Deep Earth Probe and Mineral Resources Exploration—National Science and Technology Major Project of China(No.2024ZD1001105).
文摘The formation of halite in continental basins is intimately linked to lake-level changes.Current research has revealed the connection between lake-level variations and astronomical forcing on a million-year scale.Other studies have also highlighted the influence of orbitally-induced climate cycles on halite deposition.However,our understanding of the impact of astronomically-paced lake-level changes on halite formation remains constrained.The Paleogene Dawenkou Formation in the Huanggang Basin of East China provides a continuous salt-bearing sedimentary record to investigate the lake-level changes in halite deposition.Lake-level fluctuations reconstructed by sedimentary noise modeling for the Middle and Upper members of the Dawenkou Formation indicate that the lake-level variations in the Huanggang Basin were linked to astronomical forcing with periods of∼2.4 Myr,∼1.2 Myr and/or∼100 kyr.Our results suggest that astronomical forcing,as a driver of lake-level variations,may have had an impact on halite deposition during the Paleogene.In the initial stage of halite formation within the Middle Member of the Dawenkou Formation,reduced heat and moisture transport during the∼1.2 Myr obliquity minima resulted in low lake levels in mid-to-high latitudes.The prolonged droughts caused by the low amplitude of∼2.4 Myr eccentricity created conditions more favorable for the development of thicker layers of halite.Subsequently,in the next halite-forming stage,a larger amplitude of∼2.4 Myr eccentricity led to a more humid climate.Warm/dry winters and cool summers paced by the∼100 kyr orbital eccentricity minima resulted in enhanced evaporation,relatively lower lake levels,and thinner halite deposition.Nevertheless,the possible transgressions may have contributed to complicated phase relationship between the lake-level change cycles and orbital cycles.This study offers an opportunity to delve deeper into the mechanism of halite deposition by objectively reconstructing lake levels using sedimentary noise modeling.
