顺5孔的磁性地层学和早松山世的北京海侵

MAGNETOSTRATIGRAPHY OF THE CORE S-5 AND THE TRANSGRESSION IN THE BEIJING AREA DURING THE EARLY MATUYAMA EPOCH

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.).

Vertically oriented samples collected from the core 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 160 m, 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 as-semblage in dicates the warm, shallow-water, open-sea palaeoecological environments. .According to the ages of magnetostratigraphic sequences, this marine bed composed of silts and sands with foraminiferal fossils marked by classical Hyalinea baltica, has been dated to be about 2.26 m.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 cores from the Beijing Plain. From these facts, it is postulated 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 nan-noplankton, the interval of 2.3-1.6 m.y. is a. distinct 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-Pleistocene boundary in the Beijing Plain at the basal limit of the Matuyama epoch (2.43m.y.).