渭河盆地始新世-渐新世沉积物源变化的钻探样品Sr和Nd同位素证据

始新世暖期和始新世-渐新世降温阶段（EOT）在地球气候系统演化中具有代表性，对认识现代全球变暖过程和机制有参考价值。渭河盆地堆积了始新世以来连续的河湖相沉积序列，对其进行沉积物源示踪研究有助于重建渭河流域地貌演化、沉积过程和气候环境变化。本研究对渭河盆地新生代沉积中心固市凹陷荔参1井（钻探井深6535 m）下部的始新世红河组（6527~5529 m）和渐新世白鹿塬组（5315~4759 m）样品进行了Sr和Nd同位素分析，探索古近纪渭河盆地的物源变化过程。结果显示，红河组样品Sr和Nd同位素平均值分别是⁸⁷Sr/⁸⁶Sr=0.716127和ε_Nd=-13.5，白鹿塬组Sr和Nd同位素平均值分别是⁸⁷Sr/⁸⁶Sr=0.720461和ε_Nd=-12.4。分粒级（< 2 μm，2~64 μm和>64 μm）Sr和Nd同位素测试结果表明，粒度效应对渭河盆地始新世-渐新世沉积物硅酸盐矿物的Sr同位素值影响较大，而对Nd同位素影响较小，表明硅酸盐矿物Nd同位素值可作为渭河盆地沉积物物源的指示。结合潜在源区Sr和Nd同位素分布特征，发现渭河盆地始新世和渐新世沉积物主要来自于秦岭造山带和鄂尔多斯地块的贡献，其物源变化与构造抬升和气候演变密切相关。渭河盆地始新世和渐新世沉积物传输和堆积过程与晚新生代相似，具有相对稳定的两端元物源，为利用红河组和白鹿塬组沉积序列重建古气候古环境奠定了良好的基础。

Provenance of the Eocene and Oligocene sediment in the Weihe Basin(Central China): Evidence from strontium and neodymium isotopic composition of silicate from a drill core

The Middle Eocene warm period and Early Oligocene cooling event are representative periods in evolution of Earth's climate system during Cenozoic era, offering valuable insights to understanding processes and mechanisms of modern global warming. Weihe Basin, a Cenozoic basin formed at the Eocene, has accumulated a continuous sequence of fluvio-lacustrine deposits >7000 m since the Middle Eocene. Investigating the sediment sources is helpful for reconstructing geomorphological evolution and paleoclimate and paleoenvironment of the Weihe River drainage, and is of great significance for understanding past regional climate change in warming period. In this study, Sr and Nd isotope analyses were undrtaken on samples from lower Honghe Formation(8 samples, depth of 6527~5529 m) of the Eocene and Bailuyuan Formation(6 samples, depth of 5315~4759 m) of the Oligocene from Lican 1 well(a drilled core (34°44'29.5″N, 109°48'55.7″E) with depth of 6535 m) in the depocenter of the Weihe Basin, aiming to elucidate variations of the Paleogene sediment provenance in the Weihe Basin and bolstering paleoclimate and paleoenvironmental reconstructions. The results reveal that average values of Sr and Nd isotopes for the Honghe Formation samples are 87Sr/86Sr=0.716127 and 143Nd/144Nd(εNd)=-13.5, respectively, while for the Bailuyuan Formation samples, average values are 87Sr/86Sr=0.720461 and 143Nd/144Nd(εNd)=-12.4. Isotopic composition analysis on different grain sizes(< 2 μm, 2~64 μm, and >64 μm) of the samples indicate that grain size distribution has significantly influenced Sr isotope values of the Weihe Basin sediments, while their impact on Nd isotopes is relatively minor. This result suggests that Nd isotope values of silicate minerals can serve as an indicator of sediment sources in the Weihe Basin. Combining characteristics of Sr and Nd isotope values in the potential provenances, we find that the sediment sources in the Weihe Basin during the Eocene and Oligocene were mainly originated from Qinling orogenic belt and Ordos Block, with source variations closely related to tectonic uplift and climate change. The Eocene and Oligocene sediments in the Weihe Basin have relatively stable dual sources, laying a foundation for reconstructing the past climate and environment using these sedimentary sequences.