天津—河北沿海钻孔地层中的末次盛冰期下切河谷

INCISED VALLEY OF LAST GLACIAL MAXIMUM STAGE IN THE DRILLING STRATA ON THE TIANJIN-HEBEI COASTAL PLAIN

文章回顾了1965年李四光先生追寻末次冰期对环境影响的讲话,以及40余年来在天津—河北沿海钻孔地层中、末次盛冰期下切河谷的发现过程。在源到汇过程中,起码自晚更新世以来,研究区已经是古黄河沉积区,多处发现的末次盛冰期下切河谷底板多位于30~32m深度,低于全新统底板一般在20m的深度;与长江口地区钻孔末次盛冰期下切河谷深62m相比,研究区下切河谷规模不如前者,也没有一个统一的大河口。末次盛冰期下切河谷最远地点,是距现代海岸约80km的河北省孟村回族自治县县城北侧,即西汉黄河亚三角洲叶瓣顶部。众多钻孔见早全新世快速沉积,只能是黄河支流有这样充足的泥沙供给,在局部顶托了早全新世海侵作用发生。

This paper reviewed the Prof.J.S.Lee’s speech on how the Last Glacial Stage climate affected the environment in 1965,as well as the discovery process of the incised valley of the Last Glacial Maximum(LGM)Stage in the drilling strata on the Tianjin-Hebei coastal plain over 40 years.In the source-to-sink processes,at least since Late Pleistocene the study area had been the palaeo-Huanghe(Yellow)River sedimentary area,and the bottom of incised valley of LGM which had been found at many sites were generally at the depth of 30~32 m,lower than that of 20 m of the common Holocene series in the study area.Compared with the depth of 62 m of LGM incised valley in the Changjiang(Yangtze)River estuary area,the range of LGM incised valley in the study area was not as large as the former and there was no unified large estuary.The farthest LGM incised valley occurred at the north urban area of the Mengcun Hui autonomous county of Hebei Province,80 km from the present coastline,i.e.the top of the Huanghe(Yellow)River sub-delta lobe in Western Han Dynasty.At the same time,the rapid deposition of Early Holocene happened at some drilling holes.It appears that in the study area,only the tributaries of palaeo-Huanghe(Yellow)River could provide such abundant supply,which partly supported the happening of Early Holocene transgression at some areas.