海河河口地区全新世环境及其地层

ENVIRONMENT AND STRATIGRAPHY IN THE MOUTHREGION OF HAIHE RIVER DURING THEHOLOCENE EPOCH

全新世初期本区为淡水湖沼或冲积平原，距今9200年前海侵开始影响到本区，约8000年前海面急剧上升，本区成为古渤海的一部分，至7700年前发生海退，嗣后较稳定，大规模海侵发生在6300—5800年前，当时这里成为浅海，5400年前再次海退成陆。5000年以来，海面仍有波动，在环境演变中主要表现为岸线不断地向东退却。全新世下限以距今12000年为宜，本区地层可分上、中、下全新统，下和中全新统又可分为上、下两段。

: Some core samples have been collected from the drilling holes in Junliangcheng and Lizhu- angzi, which are both located at the mouth region of the Haihe River. We have carried ou ana- lysis of lithological properties, microflssils (foraminifera, ostracoda), molluscs, 14C dating for these samples. Based on these analyses, we have shown local relative sealevel changes and the variations of environments of this area. During the initial stage of the Early Holocene, this area was a fresh-water lake, marshy low-land or alluviaI plain. In about 9245±210 Y. B. P., this area was submerged by sea transg- ression. By 8000 Y. B. P., the submerged area ex panded because sealevel rose drastically and this area became a part ot ancient Bohai Sea. Following the regression starting from about 7700 Y. B. P., a relative stable sealevel occurred during 7400-7000 Y. B. P., and the shell. bed was formed in Biaokou. A large-scale transgression took place again during 6300-5800 Y. B. P., and this area was turned into an estuary. After that, there was regression again, the estuary redu- ced in scope and changed into a marshy littoral plain during about 5400 Y. B. P. Since 5000 Y. B. P. environmental variations have been connected with both climate and sealevel fluctuation, as well as with the migration of the Yellow River. For example, this area was turned into littoral plain during about 4200 Y. B. P., this event corresponded to the north- ward movement of the Yellow River in 2278 B. C. After comprehensive research, we set the lower limit of the Holocene at 12000 Y. B. P. The Holocene epoch of this area can be divided into Early, Middle and Late Holocene. correspond- ing to Lower, Middle and Upper Holocene Series. We can further divide Lower and Middle Holocene series each into two sections: Upper section and Lower section. The conditions of each section are arranged in Tab. 2, the Holocene stratigraphic division in the mouth region of the Haihe River.