Mudflat/distal fan and shallow lake sedimentation (upper Vallesian–Turolian) in the Tianshui Basin, Central China: Evidence against the late Miocene eolian loess

Abstract

a b s t r a c t a r t i c l e i n f o Keywords:Tianshui basin Lake deposits Mudflat Calcretes Eolian deposits NeogeneThe Tianshui Basin in central China contains a thick sedimentary sequence (~1400 m) of continental deposits, Aragonian to Villafranchian (Miocene-Pliocene) in age. Intense Himalayan movements around the Paleogene/Miocene boundary triggered the uplift of mountain ranges around the Tianshui Basin, providing the deposition site for continental sediments. The sedimentary infill of the basin consists of four stratigraphic units (I to IV). This paper focuses on Unit II. Most of the accommodation space was occupied by Unit I, so during the sedimentation of Unit II, the morphology of the basin was relatively flat, promoting the development of wide distal fan/mudflat areas and wide shallow lakes. Deposits include: red mudstones, pedogenic and groundwater calcretes, reworked calcrete deposits, sheet-floods, fluvial channels, rippled sandstones/siltstones, ooidal/peloidal packstones, palustrine limestones, bioturbated marls and intraclastic limestones/marls. The characteristics and organization of the deposits indicate the gradual transition from alluvial to lake environments. Within the distal fan/mudflat, the deposition of reworked calcrete clasts as one of the most striking facies of the basin may be attributed to substantial recycling of calcrete levels and red clays. At the lake margins, the presence of ooids and palustrine limestones suggests the possibility of ramplike margins within different energy settings. The origin of some of the deposits of the basin's QA-I section is under discussion, and their consideration as eolian has been recently proposed. However, we believe this possibility is precluded by the characteristics of the deposits. Our proposal has important implications for revising the interpretation of Miocene paleoclimatic conditions in central Asia.

A magnetostratigraphic record of landscape development in the eastern Ordos Plateau, China: Transition from Late Miocene and Early Pliocene stacked sedimentation to Late Pliocene and Quaternary uplift and incision by the Yellow River

“…4C). The lacustrine genesis in the basin is derived by the aforementioned geomorphological and sedimentological arguments and corresponds with lacustrine deposition as reported by Alonso-Zarza et al (2009).…”

Late Cenozoic orogenic history of Western Qinling inferred from sedimentation of Tianshui basin, northeastern margin of Tibetan Plateau

“…Within the Guyuan Group, lithologies consist of interbedded conglomerate and sandstone or poorly sorted breccia with thicknesses varying from several tens to hundreds of meters. On the basis of sedimentological observations (Alonso-Zarza et al 2009), the abundant fossil mammals (Table 1) and the detailed magnetostratigraphic chronology of Li et al (2006), the Gansu Group has been divided into four lithostratigraphic units (Figs. 1d, 2): (1) Unit I (Aquitanian to lower Tortonian), consisting of orangebrown conglomerate or coarse sandstone interbedded with reddish-brown mudstone in the south basin margin (Fig.…”

A Review of Recent Advances in Red-Clay Environmental Magnetism and Paleoclimate History on the Chinese Loess Plateau

“…Depositional ages of this sequence span from ∼22 to ∼6 Ma and a recent study extended the bottom age of this sequence back to 25 Ma (Qiang et al, 2011). At this time, debates exist about whether "loess sediments" older than 6 Ma are eolian in origin or at least whether they were also affected by fluvial processes after deposition (Ding et al, 1998;Sun et al, 1998;Guo Z. T. et al, 2001;Alonso-Zarza et al, 2009). However, most researchers agree that loess sediments younger than 6 Ma are eolian with little modification from fluvial processes (Ding et al, 1998;Sun et al, 1998;An et al, 2001;Lu et al, 2001).…”