珠江三角洲生物埋葬群与环境变迁

THE THANATOCOENOSIS AND ENVIRONMENT EVOLUTION IN THE ZHUJIANG DELTA

本文将珠江三角洲第四纪环境与现代环境的生物埋葬群进行对照，重建晚更新世中期和全新世中期的古沉积环境，划分出两期的海侵区、海侵波及区、海侵影响区，并对中更新世海侵期表示存疑。

The modern environment in the estuary area of the Zhujiang River can be divided into six types:the delta plain, shallow,tidal estuary, delta front slope. prodelta and shallow sea.The thanatocoenosis composed of foraminfera, ostracoda, diatom and shell in different environmental unit is enumerated.Comparing the thanatocoenosis occured in the Quaternary system with that found from modern environment, two maps of paleoenvironment during the transgression period of Q32-2 and Q42 in Zhujiang Delta are produced respectively. The authors suggest that the environment during transgression period in a estuary includes three units, namely the typical transgression area including prodelta and delta front slope, the area involved by transgression including tidal estuary and shallow, and the area influenced by transgression which is delta plain.According to the feature of fossil group found in the profiles which have been dated,the transgression scope during the period of Q32-2 was mainly distributed along the western and eastern sides of Lingdingyang, but a tidal estuary was involved northwest forward to the central part of the delta such as Daliang and Fushan. There were two estuaries in the southern part of the delta but they were not involved northward so far from sea. During the transgression period of Q42,the paleoenvironmental feature was different from that of Q32-2 mentioned above. An area of about two-thirds of the delta had been submerged by sea water, resulting an extensive scope of prodelta. The limit of prodelta at that time was ranged by a strike of NE-SW along the line of Huangpu-Panyu-Daliang-Xingtan-Nantou-Lile. In other words, the transgression of Q42 is the greatest one since Late Quaternary in the area of Zhujiang Delta. moreover, there were two tidal estuaries which involved to Nanzhuang, Fushan and Zhoubiao north to Guangzhou, Therefore the scope of delta lain was quite small at that time.As for the transgression of Q2, the authors consider that it may be impossible because the sand-pebble deposits found in the northwestern margin of the delta are of alluvial and proluvial features,and the marine sediments of Q2 have only been found on the shelf of the basin of Zhujiang River mouth at an altitude of about -100m at present.