Mineralogy of the core YRD-1101 of the Yellow River Delta: Implications for sediment origin and environmental evolution during the last ～1.9Myr

摘要

In this study, we report the high-resolution heavy mineral records from a 200.30 m long borehole (YRD-1101) on the northern coast of modern Yellow River delta (YRD), covering the last similar to 1.90Myr. The results show that the heavy mineral assemblages are dominated by epidote, followed by hornblende, garnet and hematite-limonite. In the Yellow River (YR) sediments, the content of hornblende is higher than the epidote, and the epidote to hornblende ratios (E/H) are lower than the core YRD-1101. The E/H show two distinct lower values at depositional unit (DU) 4-2 (117.9-125.6 m) and DU 4-1 to DU 2 (13.5-99.3 m), indicating the obvious influence of YR sediments. The heavy mineral composition of DU 5 is distinct from YR sediments and interpreted as the result from heterogeneous provenance of the adjacent ancient rivers, while DU 4 to DU 1 resemble the upper-middle reaches of the YR sediments. The different sediment types (mud, sandy silt and silt) of core YRD-1101 do not contain markedly different transparent-heavy-mineral assemblages in terms of concentration and mineral ratios. No matter how sedimentary environment changes, the ratios of epidote and hornblende show very stable values in DU 4-1 and DU 3 due to the influence of YR sediments. The transparent-heavy-minerals such as hornblende, epidote and other stable minerals, which were relatively stable, are controlled primarily by provenance, while the sedimentary environment mostly influences the flaky minerals and the authigenic minerals. This study provides evidence regarding the history of the lower reaches of the YR and YRD since the early Pleistocene, highlighting river's important role for the evolution of the western coast of the Bohai Sea (BS).