摘要:
在渭河流域东部老官台(LGT)全新世黄土-古土壤剖面中,系统采集了15个黄土释光测年样品,应用单片再生剂量法(SAR)对这些样品的细颗粒混合矿物进行了光释光(OSL)测年,测定结果表明:红外之后蓝光释光([post-IR]OSL)的年龄偏大,红外释光(IRSL)的年龄偏小或与蓝光释光(BLSL)的年龄基本一致,应用IRSL和BLSL信号测定的OSL年龄整体偏小可能与测定样品中长石矿物的异常衰退有关,而[post-IR]OSL信号由于很少发生异常衰退问题,使得其年龄可靠性更高。基于测定的[post-IR]OSL年龄,结合该剖面的磁化率和粒度指标,进一步探讨了渭河流域东部自全新世以来发生的两期土壤侵蚀事件,第1期土壤侵蚀事件发生在约12.40~9.34kaBP,即全新世大暖期来临之前的气候转暖期间;第2期土壤侵蚀事件发生在约4.60~3.76kaBP,即全新世大暖期即将结束、气候开始出现恶化、黄河中游地区夏文化发展的时期,这为深入探索夏代发生的大洪水事件及其气候背景提供了科学依据,本区两期显著的土壤侵蚀事件的发现,揭示了东亚季风系统的不稳定性,表现为千年到百年尺度上的快速变化。
Abstract:
Fifteen loess samples were collected from Laoguantai (LGT) Holocene loess-paleosol profile in the eastern Guanzhong basin, and then optically stimulated luminescence (OSL) dating for polymineral fine grains of these samples were made by application of single-aliquot regenerative-dose (SAR) protocol. The measured results show that OSL ages estimated from[post-IR] OSL signals are maximums, and that ages estimated from IRSL signals are minimum or consistent with those estimated from BLSL signals. The generally younger OSL ages estimated from IRSL and BLSL signals may originate from abnormal decay of feldspar within polymineral fine grains. There is no such problem in the[-post-IR] OSL signals, so the OSL ages estimated from the[-post-IR] OSL signals have more credibility. Based on the[-post-IR] OSL ages and the measured magnetic susceptibility and grain-size of the profile, the study has discovered two soil erosion periods due to increased sheetwash. The first stage of soil erosion event took place about 9.34-12.40 ka, in which the climate became warmer to the Holocene Megathermal in this area. The second stage of soil erosion event took place about 3.76-4.60 ka, in which the Holocene Megathermal would soon be ended and the worsening of climate was beginning in this area, which provides scientific evidence for exploring the Flood Event and its climate background took place in the early Xia Dynasty of China. The two soil erosion events discovered in this area indicate that the East Asian monsoon was not stable during the Holocene, showing rapid fluctuations on millennial to sub-millennial timescales.
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