关键词: 广州城区, 古环境, 晚全新世, 唐宋时期, 硅藻, 软体动物

Abstract:

This study analyzed the radiocarbon chronology, lithology, and diatom and mollusk shell assemblages obtained from the profile of the Jiefang Middle Road archeological site in Yuexiu District, Guangzhou. It is determined that the Guangzhou Old Town, which lies on the northern bank of the Pearl River, was in a river bed and an estuarine wetland or lowland during the pre-Qin period. Microfossils of organisms with a high salinity tolerance were not observed in the sediment as the inflow of fresh water reduced the estuarine salinity; only estuarine-marine diatom taxa were found, with the mollusk shell fragments being mostly those of freshwater species and a few brackish water species. Therefore, we postulate that the salinity of the water bodies within the Guangzhou region was completely different during the pre-Qin period than during the mid-Holocene. In the former period, the area along the riverbanks of the Pearl River was mainly affected by riverine freshwater discharge and upward tidal convergence. In addition, radiocarbon dating results and the absence of enclosed bivalve mollusk shells in situ suggested that most of the freshwater and brackish water mollusk shells excavated at the site were food waste discarded by the ancient Nanyue people during the period in which their fishing tradition boomed in the pre-Qin (Eastern Zhou Dynasty) period. This also suggested that the shell deposits were relocated to the later strata via constant digs by the Nanyue successors, most probably due to the expansion of the town and restoration of the river, development of agricultural irrigation, or redeposition caused by the flooding that occurred throughout the Tang Dynasty. Since the establishment of the Nanyue Kingdom, signs of frequent human activity–particularly during the Tang Dynasty–can be recognized in the study area, which was then still a wetland or lowland area influenced mainly by fluvial and tidal dynamic forces, with its soil fertility serving as a foundation for the flourishing of agriculture. This is also consistent with the human-driven shoreline reorganization of the Pearl River noted in the Tang historical records. During the period from the late Tang Dynasty to the Five Dynasties, rulers expanded the wetland in the south due to a marked growth in population. Moreover, the region was exposed above water and gradually developed into the Guangzhou Old Town during the Northern Song Dynasty, despite having been affected-to some extent-by multiple flood events, as recorded in the history of the Kaibao reign (AD 968-976) and Zhidao reign (AD 995-997). The expansion and development of the Guangzhou Old Town continued during the Song Dynasty, with the expansion of agricultural and industrial practices, and the shoreline of the Pearl River was pushed farther south. In conclusion, the environmental and urban transformation of the Pearl River Delta region since ca. 2 ka BP were mainly related to the influence of Holocene sea level alterations, the quantity of river sediment being discharged, pressure from human use of the land, and the practice of river restoration. This study also suggests that the archeological records coincide with the historical records and the general course of the progressive transformation of the Pearl River Delta region, thereby providing new evidence for environmental archeological research.

Key words: Guangzhou, paleoenvironment, late Holocene, Tang-Song Era, diatom, mollusk