Linking Tarim Basin sea retreat (west China) and Asian aridification in the late Eocene
Abstract
The Tarim Basin in western China formed the easternmost margin of a shallow epicontinental sea
that extended across Eurasia and was well connected to the western Tethys during the Paleogene.
Climate modelling studies suggest that the westward retreat of this sea from Central Asia may have
been as important as the Tibetan Plateau uplift in forcing aridification and monsoon intensification
in the Asian continental interior due to the redistribution of the land-sea thermal contrast. However,
testing of this hypothesis is hindered by poor constraints on the timing and precise palaeogeographic
dynamics of the retreat. Here, we present an improved integrated bio- and magnetostratigraphic
chronological framework of the previously studied marine to continental transition in the southwest
Tarim Basin along the Pamir and West Kunlun Shan, allowing us to better constrain its timing,
cause and palaeoenvironmental impact. The sea retreat is assigned a latest Lutetian–earliest Bartonian
age (ca. 41 Ma; correlation of the last marine sediments to calcareous nannofossil Zone CP14
and correlation of the first continental red beds to the base of magnetochron C18r). Higher up in the
continental deposits, a major hiatus includes the Eocene–Oligocene transition (ca. 34 Ma). This suggests
the Tarim Basin was hydrologically connected to the Tethyan marine Realm until at least the
earliest Oligocene and had not yet been closed by uplift of the Pamir–Kunlun orogenic system. The
westward sea retreat at ca. 41 Ma and the disconformity at the Eocene–Oligocene transition are both
time-equivalent with reported Asian aridification steps, suggesting that, consistent with climate
modelling results, the sea acted as an important moisture source for the Asian continental interior.