The progressive co-evolutionary development of the Pan-Tibetan Highlands, the Asian monsoon system and Asian biodiversity

Abstract

Within the ongoing controversy regarding the orogeny of the Tibetan Plateau region, two directly conflicting endmember frameworks have emerged in which either: (1) a high central ‘proto-plateau’ existed before the onset of India–Asia continental collision; or (2) the early Paleogene central Tibet comprised a wide east–west-oriented lowland c. 1–2 km above sea-level, bounded by high (>4.5 km) mountain systems. Reconstructing the development of the plateau correctly is fundamental to running realistic Earth system models that explore monsoon and biodiversity evolution in the region, and understanding the interplay between monsoon dynamics, landscape and biodiversity is critical for future resource management. We explore the strengths and weaknesses of different palaeoaltimetric methodologies as applied across the Tibetan region. Combining methodologies, appreciating the vulnerabilities arising from their underlying assumptions and testing them using numerical climate models produces consilience (agreement), allowing further refinement of both models and proxies. We argue that an east–west-oriented Paleogene Central Tibetan Valley was a cradle and conduit for thermophilic biota, seeding the modern regional biodiversity. The rise of eastern Tibet intensified regional rainfall and erosion, which increased topographic relief and biodiversification. Gradual monsoon development reflected the evolving topography, but modern-like Asian monsoons developed only after a plateau formed in the Miocene.