Multi-stratigraphic study and response to sea-level fluctuations since the last deglaciation detected from BZK0402 core in the Shuiyang River basin, Yangtze River

This paper is the result of environmental geological survey engineering.

Objective To carry out multi-stratigraphic research on the borehole BZK0402 located in the Shuiyang River basin, and explore the sea-level fluctuations since the last deglaciation and the origin of the Paleo-Danyang Lake formation.

Methods Based on the lithostratigraphical classification and the magnetostratigraphic and chronostratigraphical constraints, the multi-stratigraphic study on the BZK0402 core was carried out. Comparative analysis was also been made between the BZK0402 core and the cores which located in the Yangtze River valley and the Yangtze River delta.

Results The analysis divided the BZK0402 core within Quarternary era into two units, namely the Middle-Upper Pelistocene Daqiaozhen Formation and the Holocene Wuhu Formation. The sediments through the western margin of the Yangtze River delta where the BZK0402 core lies in, also furthers our understanding of the general pattern of sea-level change since the Last Glacial Maximum (LGM), with these changes divided into four stages as follows: (1) The LGM was associated with a period of gravel and sand dominated deposition as a result of steep slopes and significant strong fluvial erosion within the Middle and Lower Reaches of the Yangtze River. (2) The Early Holocene saw a decrease in the grainsize of the sediments being deposited, with sedimentary facies changing from fluvial to lacustrine environments as a result of post-glacial transgression. This period also saw the development of pteridophyte undergrowth-dominated coniferous forest vegetation along with lakes and bog and swamp areas. (3) The Middle Holocene transgressive maximum was associated with the deposition of lacustrine clays that contain coniferous broad-leaved mixed forest vegetation. (4) These sediments are overlain by disturbed Late Holocene to present sediments, with this disturbance caused by uncertain factors.

Conclusions The sediments in the Shuiyang River, which is a tributary of Yangzte River, not only formed within Holecene, but also formed in Pleistocene. The Paleo-Danyang Lake located within the Shuiyang River Valley formed during the Early Holocene, and the period of the lake formation consistent with the Holocene transgression.