Magnetostratigraphic chronology of Borehole HLL01, south coast of Laizhou Bay

Asian marginal seas have played an important role in modulating regional energy and material exchanges and deriving climatic and environmental evolutions. As an effective method, magnetostratigraphy establishes reliable geochronological framework, which is critical for reconstructing long-term history of climatic and environmental changes in the past. Due to the fact that the previous long-term records were mainly located in the west and north Bohai Sea, a new Borehole HLL01, drilled in the Laizhou Bay with a length 452m, was studied. The main results are as follows: ①The HLL01 magnetostratigraphy, containing 272 samples with reliable ChRMs and 10 normal and 9 reverse magnetozones, were identified. ②Comparing with the ATNTS2012, the HLL01 magnetostratigraphy recorded C3An.2n to C1n chrons, and its bottom age was about 6.6Ma. ③Boundaries between the Miocene and Pliocene and between the Pliocene and Pleistocene were located at the depth of 340m and 140m, respectively. ④Through comparison with the previous results from the west and north Bohai Sea, it is inferred that in the period since the Late Miocene the area around the Bohai Basin was predominated by thermal subsidence, but the environmental histories in various subunits were different.