[MIS06-P13] The change in the environment and tectonics from Late Paleocene to Early Miocene in the Northeastern Tibetan Plateau
Keywords:Northeastern Tibet, Uplift, Lanzhou basin, EOT, ESR
We conducted field survey at the Duitinggou section in the northeastern edge of the Tibetan plateau, make a route map and a columnar section, and collected samples for analyses. We correlated our columnar section with a columnar section of Zhang (2015) constructed at the nearby section, and projected their age model, which is constructed based on magnetostratigraphy to our columnar section. We analyzed the grain size distribution of major lithologies to distinguish the sedimentary facies and characterize the lithological units. We also measured Electron Spin Resonance (ESR) intensity of quartz in the two grain size fractions to examine the provenance changes.
According to the result, Duitinggou section can be divided into six sedimentary units from 1 to 6 in ascending order and based on the constructed age model, the age of Duitinggou section ranges from about 57.6 Ma to 18.9 Ma, i.e. from Late Paleocene to Early Miocene.
Based on the result of the grain size analysis, we classify four patterns of the grain size distributions interpreted as fluvial sediments, lacustrine sediments, aeolian deposits and mixed sediments, respectively.
The >63µm sandstone samples were considered to have represented as mostly fluvial sediments. A gradual increase in the ESR intensity of quartz from 50 Ma to 24 Ma is interpreted as the evidence of unroofing in the source area. It seems that the uplift of the source area occurred before 50 Ma. A sudden decrease in the ESR intensity around 24 Ma suggested a major tectonic uplift and exposure of low grade metamorphic rocks occurred at that age, which might be related to the uplift of the northeastern Tibetan Plateau that started around 24Ma.