Evolution of sedimentary environment at the ZKA01 borehole in the north wing of the Yangtze River Delta since late Quaternary

Abstract

The late Quaternary chronostratigraphic framework and marine transgression have long been research focal points in the Yangtze River Delta. The frequent channel oscillation and river incision in the Yangtze Delta have led to the frequent absence of complete stratigraphic records. Complete marine transgression records have yet to be discovered within the same borehole in this region. Based on lithostratigraphy, biostratigraphy, paleomagnetic chronology, and OSL dating studies of the ZKA01 borehole in the Dongtai area of the northern wing of the Yangtze River Delta region, the stratigraphic chronology framework since Marine Isotope Stage 5 (MIS5) was established. The ZKA01 borehole was found to have comprehensively recorded five marine transgression events in the Yangtze Delta region since late Pleistocene. The results indicate that the B/M boundary of the ZKA01 borehole is located at 108 m, and the M/G boundary is at 300.25 m. The boundary between the Middle and Upper Pleistocene is positioned at the bottom of the third marine transgression layer, precisely at 92.95 m. The boundary between the Upper Pleistocene and Holocene boundaries is located at the bottom of the first marine transgression layer discovered in the borehole, precisely at 16.65 m. The first three transgressions occurred during MIS5 (128–74 ka), of which MIS 5.1 had a larger scale, second only to the scale of the transgressions during the Holocene. The fourth transgression occurred during MIS3 (60–24 ka), equivalent in depth and age to the "II marine phase layer" of MIS3. The fifth transgression occurred during MIS1 (12 ka to present), depositing in a nearshore shallow marine environment, with the largest scale observed. Additionally, it was identified that the first transgression layer (MIS5) is approximately equivalent in burial depth across various regional boreholes, serving as a distinctive stratigraphic marker for stratigraphic division and comparative studies in the Yangtze River Delta. These research findings hold significant importance for Quaternary stratigraphic division and comparative analysis of sedimentary environments in the Yangtze River Delta.

Keywords

• yangtze river delta
• chronology
• stratum
• sedimentary environment
• microfossils
• mis5
• marine transgression