Pre-Miocene birth of the Yangtze River

Abstract

The development of fluvial systems in East Asia is closely linked to the evolving topography following India-Eurasia collision. Despite this, the age of the Yangtze River system has been strongly debated, with estimates ranging from 40 to 45 Ma, to a more recent initiation around 2 Ma. Here, we present (40)Ar/(39)Ar ages from basalts interbedded with fluvial sediments from the lower reaches of the Yangtze together with detrital zircon U-Pb ages from sand grains within these sediments. We show that a river containing sediments indistinguishable from the modern river was established before ~23 Ma. We argue that the connection through the Three Gorges must postdate 36.5 Ma because of evaporite and lacustrine sedimentation in the Jianghan Basin before that time. We propose that the present Yangtze River system formed in response to regional extension throughout eastern China, synchronous with the start of strike-slip tectonism and surface uplift in eastern Tibet and fed by strengthened rains caused by the newly intensified summer monsoon.

Keywords: Asian monsoon; Subei Basin; Yangtze gravel; drainage capture; provenance.

Fig. 1.

Topographic map of East Asia, showing major rivers and the locations mentioned in the text. SBSYB, Subei–South Yellow Sea Basin; BHB, Bohai Basin; ECSB, East China Sea Basin; PRB, Pearl River Mouth Basin; YB, Yinggehai Basin; SPG, Songpan Garze; QB, Qiangtang Block. Red circles show locations of Yellow River samples (31). Major faults marked are taken from Replumaz and Tapponnier (59). The black dashed box indicates the location of Fig. 2.

Fig. 2.

(A) Simplified geological map of Nanjing area showing the locations of studied sections. (B) Sedimentary logs from the studied Yangtze gravel sections in the lower reaches of the Yangtze basin in comparison with the lithostratigraphy of Jianghan Basin. (a) Lingyanshan; (b) Xiaopanshan; (c) Guizishan; and (d) Jianghan Basin. Locations of sediments from which zircons were dated are shown together with the age controls. The y axis in the sedimentary logs is in depth; N+Q, Neogene and Pleistocene; E3, Oligocene; E2, Eocene; E1, Paleocene; K2, Late Cretaceous. (C) Sketch showing a cross section (black line in A) of the geology of Nanjing area.

Fig. 3.

KDE diagrams of zircon populations from Yangtze River gravels showing the similarity of the provenance to the modern river at Nanjing, at Wuhan, and the average composition of the delta 3.2 Ma. Note the different spectrum provided by the lower reaches of the Yellow River. Locations of the sampled outcrops are shown on Figs. 1 and 2.

Fig. 4.

Simplified maps showing the development of the Yangtze River in response to tectonic evolution in East Asia, based on the data presented in this paper as well as associated studies discussed in the text. (A) 32 and (B) 16 Ma. Names of basins as in Fig. 1. Maps reflect the progressive extrusion of Indochina and the opening of the South China Sea, but recognize that the continental blocks east of Longmenshan have remained relatively rigid since the Eocene (59). ASRR, Ailao Shan–Red River Fault; LMS, Longmenshan. Shaded river segment indicates the reversed section of the Yangtze River.