Development of gully systems under the combined impact of monsoonal climatic shift and neo-tectonic uplift over the Chinese Loess Plateau

Abstract

The surface landscape of the Chinese Loess Plateau features densely developed gully systems. Gully incision and extension are extremely active over the elevated regions of loess hills, ridges and tablelands. This paper presents the results of investigations on major gullying phases over the Loess Plateau during the Quaternary. The objective is to establish a chronology of gullying events and to examine their relations with monsoonal climatic changes and neo-tectonic uplifts. Results from field observations, geomorphologic and pedo-stratigraphic analysis indicate that pre-historical gullying events are recorded by buried palaeogullies and pedo-stratigraphic unconformities preserved in loess sections. There were four major gullying phases identified at the loess to palaeosol transitions of L6/S5, L3/S2, L2/S1, L1/S0 in the stratigraphy over the Loess Plateau. The age of a gullying event is closely related with the bottom unit of the palaeosol series in the overlying loess blanket. The Gullying phases were therefore dated to ca. 600 ka, 240 ka, 125 ka and 11.5 ka, respectively, by loess chronology. This means that gully incision occurred when large-scale monsoonal climatic shift met with coincided neo-tectonic uplift of the land mass. Neo-tectonic uplift provided the gullying with potential for deep down-cutting. Excessive runoff resulted from precipitation brought on by intensified maritime monsoon was a dynamic forcing of the gullying at the transitions of MIS 16/15, 8/7, 6/5 and 2/1. In response to each wave of gully incision and cross-section development occurred the outspreading of the tributary gullies, and a new order of gullies formed. Gully density is therefore increased and the loess land became more dissected hills and ridges. These results provide new insights into history of gully erosion and long-term landscape development in the semi-arid loess regions of the world.