Late Oligocene–Early Miocene magnetochronology of the mammalian faunas in the Lanzhou Basin–environmental changes in the NE margin of the Tibetan Plateau

Abstract

A large number of terrestrial mammalian fossils were reported in the well-exposed Paleogene and Neogene fluvio-lacustrine strata in Western China. Their accurate ages are crucial to understand the mammalian and environmental evolution associated with the step-wise uplift of the Tibetan Plateau. At present their ages are surprisingly poorly constrained. Here, we present a high-resolution magnetostratigraphic dating of the Late Oligocene–Early Miocene mammal assemblages from a 233-m thick fluvio-lacustrine section in the Lanzhou Basin located at the northeastern margin of the Tibetan Plateau, China. The results suggest that the section spans from the polarity subchron C6Cn.2r to C5En, i.e. ranging from ca 23 to 18 Ma. This magnetochronology provides considerably more robust ages for three associated land mammalian faunal assemblages. Updated ages end the debate on existing ambiguous and distinctly different magnetostratigraphic correlations for those Late Oligocene–Early Miocene assemblages. The new ages now enable precise correlation of these faunas to the European Land Mammal and North American Land Mammal Ages. The faunal assemblages further suggest a mixed setting of woodlands and grasslands associated with a humid environment in the Lanzhou Basin during the Late Oligocene–Early Miocene, in contrast to its modern poor vegetation cover and arid environment.

Orbital climate variability on the northeastern Tibetan Plateau across the Eocene–Oligocene transition

“…3). The overlying Oligocene-Miocene Xianshuihe Formation consists mainly of light red mudstones that are intercalated with sandstone or conglomerate packages 37,38 , while the underlying early Eocene Xiliugou Formation consists of red massive sandstones ( Supplementary Fig. 3).…”

“…Late Eocene to early Oligocene magneto-astrochronology from the Lanzhou Basin. Constrained by mammal and pollen biostratigraphy, the Xianshuihe Formation magnetostratigraphy 37,38 in the Duitinggou section (0-383 m) has been documented to range from polarity chron C5En down to uppermost chron C12r, with ages from~18 to 31 Ma ( Supplementary Fig. 4).…”

“…The Lanzhou Basin presents a relatively small area of roughly 300 km 2 that is filled with a thick (>1500 m) and mostly continuous sequence of Eocene – Miocene playa-palaeolake sediments that were transported primarily from the surrounding highlands 35 . Composed mostly of red fine-grained deposits, they provide an important early Eocene to Miocene regional climate archive 35 – 38 .…”

“…4 ). Combining the established chronology of the concordantly overlying Xianshuihe Formation 37 , 38 , detailed palaeomagnetic analysis (Supplementary Note 1 ; Supplementary Figs. 4 – 6 ) provides a downward magnetostratigraphic continuation from polarity chrons C12r to C16n.1n for the Yehucheng Formation, with magnetostratigraphic ages of ~31–35.7 Ma according to the 2012 geomagnetic polarity time scale (GPTS) 41 (Fig.…”

A Pedogenic Model for the Magnetic Enhancement of Late Miocene Fluvial‐Lacustrine Sediments From the Xining Basin, NE Tibetan Plateau

“…These continental sedimentary sequences contain abundant faunal assemblages and were deposited nearly continuously during the Cenozoic (Dai et al, ; Dettman et al, ; Dupont‐Nivet et al, ; Fang et al, , ; Fu et al, ; Hou et al, ; Jiang et al, ; Lease et al, ; Miao et al, ; Xiao et al, ; Zhuang et al, ). Recently, high‐resolution magnetostratigraphic analysis yielded a reliable age model for the fluvio‐lacustrine sediments in the main sedimentary basins (Ao et al, ; Dupont‐Nivet et al, ; Yang et al, ; Zan, Fang, Yan, et al, ; P. Zhang et al, ; Zhang et al, ). Thus, they provide a good opportunity to improve our understanding of the tectonic uplift and paleoenvironmental evolution of the NE TP.…”