我们对渤海湾北岸177个表层沉积物样品进行了有孔虫分析。经鉴定,未发现浮游有孔虫,底栖有孔虫共计82种,其中包括一新种Jadammina planata He et Li sp.nov.根据不同的环境中沉积物内有孔虫群属种组合不同,大体可归纳为二种组合:一是河口、海滩、泻湖、滨海平原等滨海边缘环境组合,在南堡以东该组合称为厚壁转轮虫——显孔鼓室希望虫组合,南堡以西称为厚壁转轮虫——多变假小九字虫组合,二是分布在水深10米以内的近岸浅海环境组合,称为厚壁转轮虫——缝裂希望虫组合。在不同环境中,有孔虫壳体数量的变化是有规律的,一般在泻湖中有孔虫含量最多,滨岸沙坝处最少,沙坝脊部有时为零,向海方向至近岸浅海共含量又有逐渐增多的趋势。
Vertically oriented samples collected from the care S-5 in the county of Shunyi,Beijing Plain, were measured on an astatic magnetometer, after demagnetized with a peak value of 150 or 200 Oe. The results have shown that the loose sediments up to a thickness of 640 m have recorded the Brunhes-Matuyama boundary at the depth of 160m, the Matuyama-Gauss boundary at the. depth of 468 m, and the short events corresponding to the polarity events during each epoch. 28 species of foraminiferal fossils were isolated from the sample at the depth of 428 m, 31% of this fauna is composed of planktonic foraminifera. Such an assemblage in dicates the warm, shallow-water, open-sea palaeoecological environments.According to the ages of magnetostratigraphic sequences, this marina bed composed of silts and sands with foraminiferal fossils marked by classical HyaliNea baltica,has been dated to be about 2.26 re.y, B.P., approximating the age of FAD of Hyalinea baltica in the section at Santa Maria in Italy (about 2.1 m.y.B. P). Its equivalent is also found in the other coree from the Beijing Plain. From these facts, it is postulatsd that during the early Matuyama epoch, an extensive transgression took place on the Beijing Plain. A new datum level of benthonic and planktonic foraminifera marked by the appearance of Hyalinea baltica has been found in Early Matuyama strata in the Beijing Plain. The first appearance of cold forms in the Vrica Section in Italy has been dated to be about 2:4 m.y.B.P. Based upon the up-to-date reports on calcareous nannoplankton, the interval of 2.3--1.6 m.y. is a distinet alternating stage in their evolution history. The climate in the Northern Hemisphere began to become obviously colder at about 2.5 m.y. ago. From the foregoing discussion, it is reasonable to set the Pliocene-Pleistoecne boundary in the Beijing Plain at the basal limit of the Matuyama epoch (2.43 m.y.).
