尼罗河三角洲全新世海平面变动及其对环境的影响——与长江三角洲的对比

Holocene Nile Delta sea-level fluctuations and its impact on environment——with special reference to the Changjiang River Delta

利用泥炭（33个）和潟湖（65个）14C测年数据重建了尼罗河三角洲全新世海平面的变动过程,结果显示潟湖样品比泥炭更为有效地反映出海平面变动特征:距今7000a时海平面约位于现今-10m,距今5000a时约为-5m,距离2000a时已接近现代.海侵强度和范围受古地貌和区域沉降的影响呈现出东北部大、中部其次、西部最小.随着海平面上升速率减小,三角洲在约距今7000a时开始建造,并广泛发育潟湖、沙坝和平原河流沉积体系.此后,海平面趋于稳定,人类活动增强,导致海岸沉积环境大片萎缩、消亡.同样利用泥炭（45个）测年数据重建了长江三角洲全新世海平面变动,结果与尼罗河的差异较大,可能是两地沉降差异所致.近代长江三角洲人类活动也是导致环境退化的主要原因.

The Holocene sea-level rise of the Nile Delta is reconstructed on the basis of radiocarbon dates that are derived from 33 peat samples and 65 lagoon samples obtained from many boreholes located in the lower delta plain. The result indicates that the lagoonal curve is more reliable than that of the peat curve, the latter is much influenced by the sediment compact. The result also shows that the sea level was about 10 m below the present during 7 000 a B. P., about 5 m below the present in 5 000 a B. P. , and was nearer to the present in 2 000 a B. P. Affected by the paleotopography and regional subsidence of the study area, the largest impact from transgressive intensity and scope tends to occur in the northeastern Nile sector. This influence becomes progressively reduced toward the central and northwestern Nile sectors. A vast Nile Delta Plain dominated by lagoon - sand beach and fluvial plain system had began to build at about 7 000 a B. P. , when rise in sea level started to decelerate and deltaic sedimentation rate overwhelmed the sea contribution. As sea level tends to be stabilized in Late Holocene, human activity, such as reclamation and channelisation, induces environmental deterioration, represented by largely shrunken lagoonal system. A comparable example of the Changjiang Delta is cited in the present study. It is shown that the Holocene Changjiang sea level did not fluctuate coincidentally as the Nile, much likely due to the differences of regional subsidence between the two regions. The fertile delta plain that was formed by the delta-coast construction at about 7 000 a B.P. induced the Neolithic civilization. However, intensifying human activity since 2000 a B.P. also has aggravated the delta-coast environment. Many lakes and drainage networks are diminishing.