Abstract
A shortage of Cenozoic vertebrate fossils in the Tibetan Plateau has been an obstacle in our understanding of biological evolution in response to changes in tectonism, topography, and environment. This is especially true for Paleogene records, so far known by only two sites along the northern rim of the Plateau. We report a Hongyazi Basin in northern Tibetan Plateau that produces at least three mammalian faunas that span Oligocene through late Miocene. Located at the foothills of the Danghe Nanshan and presently connected to the northern margin of the Suganhu Basin through the Greater Haltang River, the intermountain basin is controlled by the tectonics of the Danghe Nanshan to the north and Chahan’ebotu Mountain to the south, making the basin sediments well suited for inferring the evolutionary history of these two mountain ranges. At the bottom of the local section, the Oligocene Haltang Fauna is best compared to the early Oligocene Desmatolagus-Karakoromys decessus assemblage in the Dingdanggou Fauna in Tabenbuluk Basin. The Middle Miocene Ebotu Fauna from the middle Hongyazi section shares many taxa with the late Middle Miocene Tunggur mammal assemblage in Inner Mongolia, such as Heterosminthus orientalis, Megacricetodon sinensis, Democricetodon lindsayi, and Alloptox gobiensis. Toward the top of the section, the Hongyazi Fauna includes late Miocene elements typical of Hipparion faunas of North China. All three faunas are of typical North China-Central Asian characteristics, suggesting a lack of geographic barriers for faunal differentiation through the late Miocene. Sedimentary packages producing these faunas are arrayed from north to south in progressively younger strata, consistent with a compressive regime to accommodate shortening between Danghe Nanshan and Chahan’ebotu Mountain by thrust faults and folds. With additional constraints from vertebrate fossils along the northern flanks of the Danghe Nanshan, an eastward propagation of the Danghe Nanshan is postulated.
Highlights
Cenozoic vertebrate fossils within the Tibetan Plateau have been generally scarce, often for lack of appropriate deposits or difficulties in access to exposures, and for limited paleontological efforts devoted to the plateau exploration [1]
Known fossil sites range from early Miocene to Pliocene [2,3,4,5,6,7,8] and knowledge about early Cenozoic (Oligocene and earlier) has so far remained elusive, except along the northern margins of the plateau [9,10]
The Hongyazi Basin is at the southern foothills of the Danghe Nanshan along the northern margin of the Tibetan Plateau
Summary
Cenozoic vertebrate fossils within the Tibetan Plateau have been generally scarce, often for lack of appropriate deposits or difficulties in access to exposures, and for limited paleontological efforts devoted to the plateau exploration [1]. The Hongyazi Basin is at the southern foothills of the Danghe Nanshan along the northern margin of the Tibetan Plateau. We term this thrust system South Danghe Nanshan thrust (Fig. 1), which locally cuts through sediments of early Oligocene through late Miocene age.
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