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.
EoceneOligoceneprovenance of sediments of the Weihe Basinstrotntium-neodymium isotopic compositiondeep drill core
万方数据
维普
