STRATIGRAPHIC ANALYSIS OF THE TERTIARY SEDIMENTS IN THE BOZHONG AREA, BOHAI BAY PEOPLES REPUBLIC OF CHINA

摘要

The Bohai Bay is an intra-continental rift basin in which thick Tertiary lacustrine and fluvial sediments were deposited. In Phillips Bozhong Block CA 11/05 in the Central Bohai Bay, the Tertiary sediments are divided into stratigraphic sequences based on seismic and well data. The definition of individual sequences, however, is different from the Exxon's sequence model. Both regional unconformity and condensational (flooding?) surfaces were used as sequence boundaries. Depositional systems were identified within each sequence. Subdividing individual sequences into systems tracts was not attempted, as each of the sequences is a product of the interplays among tectonism, sediment supply, lake level fluctuations, and climatic changes. Development of individual sequences was mainly controlled by tectonic activity within and outside the basin. Relative sea-level rise in the late Oligocene time may have caused a marine incursion and therefore exerted a significant influence on the development of the Oligocene Shahejie and lower Dongying sequences. However, the role of lake level fluctuations during other time periods is difficult to assess, due to the lack of reliable lake level indicators in the stratigraphic record and uncertainty in the reference datum, though we don't think that lake level fluctuations played a dominant role in the sequence development. The development of Miocene and Pliocene fluvial sequences were primarily controlled by steady thermal subsidence of the basin punctuated by sediment supply episodes related to tectonism and climatic changes in the source terrain.