珠江口晚第四纪埋藏风化层及其环境意义*

风化层是沉积间断和环境变迁的明显标志。在珠江三角洲平原以及珠江口海域都见有晚第四纪的埋藏风化层。珠江口外伶仃岛海域2个钻孔岩芯4个样品的AMS年龄表明,在第四系剖面中,MIS 3以来通常有两个风化层。下风化层的年龄为\{31060~\}28754aB.P. ,属于MIS 3; 上风化层为\{14320~\}11500aB.P. ,属于MIS 2。风化层的岩性因地而异,包括粘土、砂质粘土、中细砂和砂砾等。色调为红褐色、褐色或杂色。2个岩芯上、下风化层4个样品的氧化物分析表明,上风化层的风化强度比下风化层大。1个岩芯的硅藻分析表明,风化层主要是陆相层经风化而成,两个风化层分别反映MIS 3和MIS 2的两个陆相—海相的沉积旋回。

BURIED WEATHERING LAYERS OF THE LATE QUATERNARY AND THEIR ENVIRONMENTAL SIGNIFICANCE IN THE ZHUJIANG RIVER ESTUARY

The weathering layer is an obvious index for sedimentary discontinuity and change of environment. The buried weathering layers of the Late Quaternary can be recognized not only in the plain of the Zhujiang Delta but also in the sea area of the estuary of Zhujiang River. The datings of four samples from two cores in the sea area of Wai Lingding Island at the Zhujiang River estuary show that there are generally two weathering layers in the profiles of Late Quaternary since MIS 3. The lower layer is dated about 31060 - 28754aB. P., belonging to MIS 3 and the upper layer 14320 - 11500aB. P., belonging to MIS 2. The lithology of weathering layers, including clay, sandy clay, fine-medium sands and sand-pebbles, etc., varies from place to place. The colour of weathering layers appears reddish brown, brownish, or mottled. The analysis of oxide of four samples from the two cores shows that the weathering intensity of the upper layer is stronger than that of the lower. The diatom analysis of one core shows that the two weathering layers are mainly weathered from terrestrial sediments, showing two depositional cycles from terrestrial to marine during MIS 3 and MIS 2 respectively.