Evolution of the Upper Yellow River as Revealed by Changes in Heavy-Mineral and Geochemical (REE) Signatures of Fluvial Terraces (Lanzhou, China)

Wang Wang,Hu Hu,Zhang Zhang,Peng Peng,Garzanti Garzanti,Andò Andò,Nie Nie,Pfaff Pfaff,Pan Pan

doi:10.3390/min9100603

Abstract

Despite decades of study, the factors that controlled the formation and evolution of theupper reaches of the Yellow River, including uplift of the northeastern Tibetan Plateau, Pliocene-Pleistocene climate change, and autogenetic processes are still poorly constrained. The stratigraphicrecord of such paleogeographic evolution is recorded in the sequence of nine terraces formed duringprogressive incision of the Yellow River in the last 1.7 Ma. This article investigates in detail forsediment provenance in terraces of the Lanzhou area, based on heavy-mineral and geochemical(REE) signatures. Two main provenance changes are identified, pointing each to a majorpaleogeographic reorganization coupled with expansion of the upper Yellow River catchment andenhanced sediment fluxes. The first change took place between the deposition of terrace T9 (formedaround 1.7 Ma) and terrace T8 (formed around 1.5 Ma), when rapid fluvial incision point to tectoniccontrol and active uplift of northeastern Tibetan Plateau. The second change took place betweendeposition of terrace T4 (formed around 0.86 Ma) and terrace T3 (formed around 0.14 Ma), duringa period of low incision rates and notably enhanced sediment fluxes as a response to enhanced EastAsian Summer Monsoon and consequently increased precipitations, pointing instead chiefly toclimatic control.

Highlights

The Yellow River is the sixth longest river and carries the highest sediment load in the world [1,2].The upper course of the Yellow River drains the central and northeastern Tibetan Plateau, and reconstructing its origin and early history is key to understanding the relationship between fluvial incision, climate variation, and basement uplift [3,4,5,6,7,8,9]
Based on the chronological sequence of the terraces, the Yellow River system was interpreted to have been formed since the middle Pleistocene as a response either to the accelerated tectonic uplift of the northeastern Tibetan Plateau [3,4,6,7,10,11], or to climatically-driven expansion of lake systems breaching topographic barriers [12,13,14]
Different heavy-mineral assemblages in superposed Yellow River terraces of the Lanzhou area, together with varying REE patterns, indicate major provenance changes through time

Summary

Introduction

The Yellow River is the sixth longest river and carries the highest sediment load in the world [1,2].The upper course of the Yellow River drains the central and northeastern Tibetan Plateau, and reconstructing its origin and early history is key to understanding the relationship between fluvial incision, climate variation, and basement uplift [3,4,5,6,7,8,9]. Based on the chronological sequence of the terraces, the Yellow River system was interpreted to have been formed since the middle Pleistocene as a response either to the accelerated tectonic uplift of the northeastern Tibetan Plateau [3,4,6,7,10,11], or to climatically-driven expansion of lake systems breaching topographic barriers [12,13,14]. Previous provenance studies of Yellow River sediments emphasized mainly the spatial differentiation among upper, middle, and lower modern fluvial reaches using zircon and heavy-mineral data [9,15,16,17,18,19,20]. In the complex northeastern Tibetan Plateau area, a considerably higher number of valid zircon ages need to be obtained (≥250 per sample) [22,23] in order to reliably identify subtle provenance differences in the dataset

Results

Discussion

Conclusion