Physical Research Laboratory, Navrangpura, Ahmedabad, 380 009, India.
Department of Geology, Presidency University, Kolkata, 700 073, India.
Sci Rep. 2019 Nov 20;9(1):17221. doi: 10.1038/s41598-019-53489-4.
The legendary river Saraswati of Indian mythology has often been hypothesized to be an ancient perennial channel of the seasonal river Ghaggar that flowed through the heartland of the Bronze Age Harappan civilization in north-western India. Despite the discovery of abundant settlements along a major paleo-channel of the Ghaggar, many believed that the Harappans depended solely on monsoonal rains, because no proof existed for the river's uninterrupted flow during the zenith of the civilization. Here, we present unequivocal evidence for the Ghaggar's perennial past by studying temporal changes of sediment provenance along a 300 km stretch of the river basin. This is achieved using Ar/Ar ages of detrital muscovite and Sr-Nd isotopic ratios of siliciclastic sediment in fluvial sequences, dated by radiocarbon and luminescence methods. We establish that during 80-20 ka and 9-4.5 ka the river was perennial and was receiving sediments from the Higher and Lesser Himalayas. The latter phase can be attributed to the reactivation of the river by the distributaries of the Sutlej. This revived perennial condition of the Ghaggar, which can be correlated with the Saraswati, likely facilitated development of the early Harappan settlements along its banks. The timing of the eventual decline of the river, which led to the collapse of the civilization, approximately coincides with the commencement of the Meghalayan Stage.
印度神话中的传奇河流 Saraswati 曾被假设为季节性 Ghaggar 河的一条古老常年河道，该河道流经印度西北部青铜时代哈拉帕文明的中心地带。尽管在 Ghaggar 的一条主要古河道沿线发现了丰富的定居点，但许多人认为哈拉帕人仅依赖季风降雨，因为在文明鼎盛时期，没有证据表明该河流的水流是不间断的。在这里，我们通过研究河流流域 300 公里长的一段河流沉积物物源的时间变化，提供了 Ghaggar 具有常年历史的明确证据。这是通过放射性碳和发光方法对碎屑白云母的 Ar/Ar 年龄和河流序列中硅质碎屑沉积物的 Sr-Nd 同位素比值进行研究来实现的。我们确定，在 80-20 千年前和 9-4.5 千年前，这条河是常年的，并且从喜马拉雅山脉的高山和低山接收沉积物。后一阶段可归因于 Sutlej 河的支流对河流的重新激活。这种 Ghaggar 的恢复性常年状态，与 Saraswati 河有关，可能促进了其河岸早期哈拉帕定居点的发展。最终导致文明崩溃的河流的衰落时间与 Meghalayan 阶段的开始大致吻合。
