山东庙岛群岛全新世黄土

HOLOCENE LOESS OF MIAODAO ISLANDS IN SHANDONG

庙岛群岛横跨渤海海峡,在这些岛屿上发育了第四纪各个阶段的黄土地层。在该区的马兰黄土之上普遍发育了全新世黄土。两者间有一清楚的侵蚀面相隔。全新世早期以浅棕黄色的黄土为特征,粒度较粗,其堆积时间约在10000—8000aB.P.之间。黄土层底部有零星散布的海相砾石和海螺化石。全新世中期为黑垆土发育期,其时间从8000aB.P.持续到2500aB.P.。黑垆土厚约1.5m。全新世晚期又以砂质黄土堆积为特征,厚约30cm。

Miaodao Islands lie across the Bohai Gulf between Jiaodong and Liaodong Peninsulas. They consist of eighteen big or small islands. During the time of lower sea level in Pleistocene and Holocene, thick beds of loess were deposited both on these islands and on the exposed Bohai Plain. The sediments of Late Cenozoic, which are mainly loess and weathered mantle of red clay, are well developed here. The loess here can be divided into brownish red loam of Early Pleistocene, Lishi Loess of Middle Pleistocene, Malan Loess of Late Pleistocene and Holocene Loess. In the Holocene Loess, there are rich remains of Neolithic Culture and those from tombs of different dynasties, such as Qin, Han and Tang. This shows that loess ground here has been the site of important human activities. Holocene Loess, which is widespread over Malan Loess, is light brownish yellow in color, loose and blocky in texture and traversed by vertical joints. Within the Holocene Loess, near the top, there is a well-developed paleosol layer, dark grayish brown in color. It is 1.5m thick. The ^(14)C datings of different samples taken in this layer are 6 790±200 a B.P., 5 620±110 a B.P. and 2 61±105 a B.P. respectively. The total thickness of Holocene Loess, including the paleosol, amounts to 2—2.5m. There is an erosional surface between Holocene and Malan Loess. Near the base of Holocene Loess there are fossil remains: Monodonta labio(L.), Chlorostoma rusticum (Gmelin) and gravels. They might have been eroded from a higher ground representing former higher sea level. They were deposited together with loess. The grain size of Holocene Loess is mainly fine sand and coarse silt. It is well-sorted. Grain size 0.125—0.05 mm(3—4.33φ) accounts for 52—60%; 0.05—0.01 mm (4.33—6.66φ). accounts for only 10—12%; 0.01—0.001 mm (6.66—9.99φ) accounts for 27—34%. Holocene Loess tends to be coarser in the lower and gets finer in the upper part. It is a reworked material by wind from the former beach plain. Holocene Loess of Miaodao Islands may be subdivided into 3 layers: 1) Early Holocene, mainly sandy loess, the age of which is about 10 000—8 000 a B.P.; 2) Middle Holocene, mainly occupied by dark grayish brown paleosol, its age is 8 000—2 500 a B.P.; 3) Late Holocene, the top layer.