MULTIPLE PALAEOECOLOGICAL PROXIES CONSTRAIN THE INTERPLAY BETWEEN TIBETAN PLATEAU GROWTH, THE PROTO-MONSOONS AND FLORAL DISPERSAL DURING THE EARLY INDIA-ASIA COLLISION
Résumé
The interplay between tectonics, monsoonal climate regimes, and
biodiversity of the Tibetan Plateau has been the recent focus of
much investigation. However, the linkages between orogeny and
climate, as well as their impacts on floral diversity, are still unclear.
The Nangqian Basin of east-central Tibet holds a key Paleocene–
Eocene record of deformation and environmental change during
the early stage of the India-Asia collision, the development of the
Tibetan Plateau, and the proto-monsoons. Here, we examine new
palynoassemblages recovered from this basin and apply Fourier
Transform Infrared (FTIR) microspectroscopy to quantify ultraviolet
irradiance based on pollen chemistry, in combination with plant
leaf wax biomarkers. Although the studied section was previously
assigned a mid-Cretaceous age based on ostracods, this new palynological
evidence combined with magnetostratigraphy rather indicates
a Paleogene age. Volcanic intrusives and extrusives crosscut
the lacustrine to alluvial Cenozoic Nangqian strata, providing a
minimum age constraint at ca. 37 Ma. In the context of a proto-Tibetan
Plateau established early in the Cenozoic, the abundance of
high-altitude bisaccates from the Nangqian section is of particular
interest. It largely predates the spread of high-altitude elements to
the North in Central Asia from 36 Ma, and their diversification after
the 34 Ma Eocene–Oligocene transition cooling. These observations
are in line with a growing body of evidence that parts of the Tibetan
Plateau had attained high elevations similar to modern conditions
soon after the India-Asia collision. The outward growth from this elevated
central part of the Tibetan Plateau, with associated effects on
the monsoons, is envisioned to have had major effects on dispersal
and speciation of the Pinophyta across Asia during the Paleogene.