MIS3阶段以来黄骅北部地区潮坪地层中的微体生物群

依据渤海湾湾顶南侧、古黄河三角洲河北省黄骅市北部地区13个钻孔岩芯材料微体古生物学研究,以及地球化学背景、沉积构造分析,本文确定了自相当海洋氧同位素MIS3阶段以来中潮坪、高潮坪、淡水注入的潮坪、潮汐通道、分支河道及边滩、牛轭湖、贫营养湖、滨海湿地与富营养湖、泛滥平原一泛滥盆地等不同沉积地层中的微体生物(有孔虫、海相与非海相介形类)分布特征.在MIS3阶段高潮坪一低地沉积之后,河口与相邻低地依然持续或断续出现海相微体生物,个别钻孔中其分布甚至延续到末次盛冰期低海面地层中,但是基本都是广盐种和低盐种.这一现象与沿海构造沉降背景下河口位置长期向陆迁移,微体生物随短暂的强潮及突发的风暴潮搬运、甚至与风、水和鸟的搬运作用有关;远离古河道地点则无此现象.这些海侵事件与全球海面变化和古海面高度无关.与渤海湾顶北侧天津沿海相比,黄骅北部未见天津沿海确定的全新世早期潮下带砂质沉积单元,以及相应的微体生物群,应与当时天津沿海构造沉降速率较高有关.在三角洲与潮坪研究中,微体古生物学发挥了重要作用,而不仅是记述内容之一.

MICROFOSSILS IN TIDAL FLAT STRATA ON THE NORTHERN HUANGHUA AREA SINCE THE MIS 3

Based on the study of micropalaeontology, as well as the analysis of geochemical background and sedimen-tary structure for 13 boreholes in the northern Huanghua area, Hebei Province (south side of the Bohai Bay end and the paleo-Huanghe (Yellow) River deltaic plain), the present paper determined the distribution characteristics of microfossil (Foraminifera and marine-, non-marine Ostracoda) in different sedimentary strata, such as the middle and high tidal flats, tidal flat with fresh-water injecting, tidal channel, river bed, back swamp of distributary channel, oxbow lake, coastal wetland, eutrophic or oligotrophic lakes, fluvial plain and fluvial basin since the marine isotope stage (MIS) 3. Above the high tidal flat and lowland strata of MIS 3, the marine microfossils continuously or discontinuously occur at some horizons of estuary facies and neighbor lowland, even during the Last Glacial Maximum, but only of the euryhaline and low-salinity assemblages generally, which do not extend far from the paleo-river. This feature was related to the estuary shifting toward the land under the coastal plain subsidence setting in a long-term, as well as temporary strong tidal current and abrupt storm influence, even possibly related to the transportation by wind, water and bird. Such transgressive events do not mean global sea-level changes. Unlike the Tianjin coast of the northern end of the Bohai Bay, Early Holocene microfossils and sandy sedimentary unit of the subtidal facies are not found in the studied area, suggesting that the Tianjin coast had higher rate of tectonic subsidence. This study shows that micropaleontology is significant in the research of deltaic or tidal sediments.