渤海湾沿岸晚第四纪地层划分及地质意义

摘要

This paper, taking four drilling holes cutting through the upper Pleistocene as an example to classify the late quaternary strata along the coast of Bohai Bay, discussed lithofacies paleogeography and neotectonic characteristics, based on lithology and sedimentary structures, 14C ages of peat and humus mud, micropaleontology and palynology, and the theory of climatic stratigraphy and sequence stratigraphy. Nine units divided are MIS5e (Marine Isotope Stage 5e), MIS5d, MIS5c, MIS5b, MIS5a, MIS4, MIS3, MIS2 and MIS1 in an ascending order. Transgressions occurred in MIS5e, MIS5c, MIS3 and MIS1. Marsh, interfluve and lagoon formed during the MIS5e due to river action equivalent to sea action. Interfluve and river and sand bank-lagoon formed during MIS5c because of river action better than sea action. 7~8 m thick of marine sediment formed when sea level rose at the early stage of MIS3, and then river and sand bank and lagoon formed when sea level fell at the late stage of MIS3 because of river action strengthening. 10 -15 m thick of marine sediment thickness formed in the northern and western coasts; 3 m thick of lagoon sediment formed in the southern coast. The ancient Yellow River deltas had prograded from south to north in the coast of Bohai bay. The hard clay and interfluves formed when sea level fell during MIS5d, MIS5b and MIS2. Marsh formed during the last deglaciation because of sea level rising. The coast of Bohai Bay was characterized by differential subsidence during the Late Quaternary. The differential subsidence rate between southern Huanghua depression and Chengning uplift reached 0. 16 mm/a, while the rate of the northern and middle sections of the Huanghua depression reached 0. 31 mm/a. MIS5c was the period of the tectonic activity.%本文以4个钻透上更新统钻孔为例,以岩性和沉积构造为基础,采用“C、微体和孢粉等分析方法,结合气候地层和层序地层学的理论,对渤海湾晚第四纪地层进行了划分,讨论了岩相古地理和新构造特征.渤海湾沿岸晚第四纪地层可以划分为9组地层,自下而上分别为海洋氧同位素5e(MIS5e)、MIS5d、MIS5c、MIS5b、MIS5a、MIS4、MIS3、MIS2和MIS1阶段地层.MIS5e、MIS5c、MIS3和MIS1时期发生海侵.MIS5e海侵时,河流堆积作用和海侵作用相当；MIS5c海侵时,海侵作用增强,但河流堆积作用更大,多形成河流相.MIS3海侵时,海侵作用较强,形成厚7～8 m海相层,海平面下降时,河流堆积作用增强.MIS1海侵时,北岸和西岸作用最强,形成厚10～15 m的海相层；南岸河流堆积作用较强,仅形成3m的潟湖相.MIS5d、MIS5b和MIS2时期,海平面较低,多形成硬粘土和河间洼地.MIS2的冰消期,多形成泛滥的沼泽洼地.渤海湾晚第四纪差异沉降明显,南岸黄骅坳陷和埕宁隆起的差异沉降速率达0.16 mm/a,黄骅坳陷北部和中部的差异沉降速率达0.31 mm/a.MIS5c为主要构造活动期.