11:15 AM - 11:30 AM
[MIS19-03] The linkage between desertification and tectonism inferred from the provenance change of the terrestrial sediments in the Tarim basin
Keywords:Tarim Basin, provenance change, desertification
The Tarim basin, which locates to the northwest from the Tibetan Plateau, is the area where the most significant aridification was expected as a result of the uplift of the Himalaya and the Tibetan plateau due to the collision between the Indian subcontinent and the Eurasia continent during Cenozoic (e.g. Kitoh, 2005). However, the geological evidence supporting the relationship between the aridification of the Tarim basin and the tectonism in its surrounding areas is not obtained sufficiently. The reason why the difficulty in examining the relationship between the timing of tectonism and aridification arises is that the timing of the onset of aeolian dune deposition in the Tarim basin, which is the good evidence of the aridification, depends on age models and, thus, there is uncertainty in the timing of the desertification. To solve this problem, it is effective to compare the timing of both tectonic and climatic events on the same section.
In this study, the provenance change of the upper Eocene to the middle Miocene fluvial sandstone deposited in the Aertashi section in the southwestern edge of the Tarim basin was examined using the Electron Spin Resonance (ESR) signal intensity and Crystallinity Index (CI) analyses of quartz in the 64-500μm fraction and the thin section observation. The timing of the tectonic movement in the Pamir estimated from the provenance change is compared with the timing of the desertification implied by the lithology to examine the relationship between the tectonism and the desertification.
The result of the ESR signal intensity and the CI analyses indicates that the provenance changes of the fluvial sandstone in the Aertashi section are divided into six stages and the boundary between stages are ca. 35Ma, ca. 33Ma, ca. 26Ma, ca. 21Ma, and ca. 17Ma, respectively. Thin section observation shows that the composition of the fluvial sandstone changes significantly at ca. 17Ma with higher content of lithic fragments with wide variety of the types, and the relatively high content of biotite and mafic minerals after ca. 17Ma.
The significant provenance changes at ca. 33Ma, ca. 26Ma, and ca. 17Ma showen by the ESR signal and the CI data imply that the tectonic movement in the Pamir possibly occurred around these times. Since the onset of desertification in the Tarim basin is estimated around 35Ma based on the lithology, the uplift of the Pamir does not seem to have been the cause of the initial aridification in the Tarim basin.
In this study, the provenance change of the upper Eocene to the middle Miocene fluvial sandstone deposited in the Aertashi section in the southwestern edge of the Tarim basin was examined using the Electron Spin Resonance (ESR) signal intensity and Crystallinity Index (CI) analyses of quartz in the 64-500μm fraction and the thin section observation. The timing of the tectonic movement in the Pamir estimated from the provenance change is compared with the timing of the desertification implied by the lithology to examine the relationship between the tectonism and the desertification.
The result of the ESR signal intensity and the CI analyses indicates that the provenance changes of the fluvial sandstone in the Aertashi section are divided into six stages and the boundary between stages are ca. 35Ma, ca. 33Ma, ca. 26Ma, ca. 21Ma, and ca. 17Ma, respectively. Thin section observation shows that the composition of the fluvial sandstone changes significantly at ca. 17Ma with higher content of lithic fragments with wide variety of the types, and the relatively high content of biotite and mafic minerals after ca. 17Ma.
The significant provenance changes at ca. 33Ma, ca. 26Ma, and ca. 17Ma showen by the ESR signal and the CI data imply that the tectonic movement in the Pamir possibly occurred around these times. Since the onset of desertification in the Tarim basin is estimated around 35Ma based on the lithology, the uplift of the Pamir does not seem to have been the cause of the initial aridification in the Tarim basin.