Fluvial landscapes of the Harappan civilization
Fluvial landscapes of the Harappan civilization
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DOI：
10.1073/pnas.1112743109
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发表时间：
2012-06-26
影响因子：
11.1
通讯作者：
Syvitski, James P. M.
中科院分区：
文献类型：
--
作者：
Giosan, Liviu;Clift, Peter D.;Syvitski, James P. M.
作为最早的城市文明之一，青铜时代哈拉帕文明的崩溃至今仍是一个谜。城市主义在印度-恒河平原西部地区繁荣了大约600年，但自大约3900年前以来，总定居面积和定居规模下降，许多遗址被遗弃，并且记录了遗址数量和密度向东方的重大转变。我们报告的形态学和年代学证据表明，哈拉帕地区的河流景观在全新世晚期变得非常稳定，因为该地区在大约5000 BP后干旱化加剧。在冲积平原的上游，旁遮普的大型喜马拉雅河流停止了侵蚀，而在下游，印度河在信德省形成的独特的巨型河流脊的沉积速度减慢。这种河流的平静表明洪水强度的逐渐减少可能在4,500 BP左右刺激了最初的集约化农业并鼓励了城市化。然而，季风降水的进一步减少导致了对洪水和雨水农业不利的条件。与先前的假设相反，一些人认为，在印度河和恒河盆地之间的交汇处，有一条巨大的冰川滋养的喜马拉雅河流，灌溉了哈拉帕的中心地带，我们表明，在全新世期间，只有季风滋养的河流在那里活跃。随着季风减弱，季风性河流逐渐干涸或变得季节性，影响了沿途的宜居性。水文气候压力增加了农业生产的脆弱性，支持了哈拉帕的城市化，导致定居点缩小，作物多样化，以及旁遮普邦、哈里亚纳邦和北方邦较湿润的季风地区的定居点急剧增加。
The collapse of the Bronze Age Harappan, one of the earliest urban civilizations, remains an enigma. Urbanism flourished in the western region of the Indo-Gangetic Plain for approximately 600 y, but since approximately 3,900 y ago, the total settled area and settlement sizes declined, many sites were abandoned, and a significant shift in site numbers and density towards the east is recorded. We report morphologic and chronologic evidence indicating that fluvial landscapes in Harappan territory became remarkably stable during the late Holocene as aridification intensified in the region after approximately 5,000 BP. Upstream on the alluvial plain, the large Himalayan rivers in Punjab stopped incising, while downstream, sedimentation slowed on the distinctive mega-fluvial ridge, which the Indus built in Sindh. This fluvial quiescence suggests a gradual decrease in flood intensity that probably stimulated intensive agriculture initially and encouraged urbanization around 4,500 BP. However, further decline in monsoon precipitation led to conditions adverse to both inundation-and rain-based farming. Contrary to earlier assumptions that a large glacier-fed Himalayan river, identified by some with the mythical Sarasvati, watered the Harappan heartland on the interfluve between the Indus and Ganges basins, we show that only monsoonal-fed rivers were active there during the Holocene. As the monsoon weakened, monsoonal rivers gradually dried or became seasonal, affecting habitability along their courses. Hydroclimatic stress increased the vulnerability of agricultural production supporting Harappan urbanism, leading to settlement downsizing, diversification of crops, and a drastic increase in settlements in the moister monsoon regions of the upper Punjab, Haryana, and Uttar Pradesh.