A New Sediment Accumulation Model of Cenozoic Depositional Ages From the Qaidam Basin, Tibetan Plateau

Abstract

Two debated age models, with a basal age of ~50 Ma versus ~30 Ma, are proposed for the depositional age of Cenozoic strata within the Qaidam basin result in a diverse understanding of the initial pattern of deformation in the northern Tibetan Plateau. To evaluate these age models, we integrated isopach maps within the basin with published thermochronology data from surrounding ranges to balance the sediments preserved in the basin with materials eroded in the drainage area. When following the traditional ~50 Ma age model, the total volume of material eroded from the surrounding source area is 4.4 ± 0.3 × 105 km3. Using instead the ~30 Ma age model for the basal Lulehe Formation and related revisions to the basin chronology, the volume of eroded material is calculated at 3.5 ± 0.2 × 105 km3, which provides a better match to the calculated total volume of solid grains that are preserved in the basin (2.8 ± 0.1 × 105 km3). However, growth strata revealed in seismic profiles along the Southern Qaidam Thrust suggest reverse‐faulting began during the deposition of Oligocene‐Miocene strata. Following the ~50 Ma age model, the onset time of faulting along the Southern Qaidam Thrust is ~35.5 Ma, consistent with previous thermochronology results. If both age models are correct, then this requires a significant time‐transgressive nature to basin fill that allows for older ages of deposition in the southern part of the basin. This study highlights the need for further effort to determine the depositional age of the strata in the southern and western parts of the Qaidam basin.

Miocene Range Growth Along the Altyn Tagh Fault: Insights From Apatite Fission Track and (U‐Th)/He Thermochronometry in the Western Danghenan Shan, China

“…This is supported by thermochronological data in the Qimen Tagh (Jolivet et al, 1999;, eastern Kunlun Shan Mock et al, 1999;F. Wang, Shi, et al, 2017), and northern margin of the Qaidam Basin (He et al, 2018;Jolivet et al, 2001), and estimation on the sediments preserved in the Qaidam Basin and materials eroded in the surrounding drainage area (Cheng et al, 2018). However, recent published magnetostratigraphy and mammalian biostratigraphy refine the onset of basin fill in the Qaidam Basin to~25.5 Ma and reveal that the detritus shed from the southern Qilian Shan occurred at 12 Ma, suggesting that the deformation in the southern Qilian Shan is significantly later than previously…”

“…If this traditional age model is correct, the northern and southern margins of the Qaidam Basin have received sediments from the adjacent mountains, such as the southern Qilian Shan and/or eastern Kunlun Shan in the early Cenozoic, which may derive from tectonic exhumation then. This is supported by thermochronological data in the Qimen Tagh (Jolivet et al, ; D. Liu, Li, et al, ; Y. Wang et al, ), eastern Kunlun Shan (Clark et al, ; Mock et al, ; F. Wang, Shi, et al, ), and northern margin of the Qaidam Basin (He et al, ; Jolivet et al, ), and estimation on the sediments preserved in the Qaidam Basin and materials eroded in the surrounding drainage area (Cheng et al, ). However, recent published magnetostratigraphy and mammalian biostratigraphy refine the onset of basin fill in the Qaidam Basin to ~25.5 Ma and reveal that the detritus shed from the southern Qilian Shan occurred at ~12 Ma, suggesting that the deformation in the southern Qilian Shan is significantly later than previously estimated (W. Wang, Zheng, Zhang, et al, ).…”

“…However, the age of the Lulehe formation, which marks the initiation of Cenozoic sedimentation in the Qaidam basin, remains highly debated. It was considered that the Lulehe formation was deposited during Paleocene and early Eocene (~50 Ma) based on magnetostratigraphy, spore and pollen assemblages, and regional lithostratigraphic correction (e.g., GBGMR, ; F. Cheng et al, ; Fang et al, ; Yin et al, ). If this traditional age model is correct, the northern and southern margins of the Qaidam Basin have received sediments from the adjacent mountains, such as the southern Qilian Shan and/or eastern Kunlun Shan in the early Cenozoic, which may derive from tectonic exhumation then.…”

“…However, the age of the Lulehe formation, which marks the initiation of Cenozoic sedimentation in the Qaidam basin, remains highly debated. It was considered that the Lulehe formation was deposited during Paleocene and early Eocene (~50 Ma) based on magnetostratigraphy, spore and pollen assemblages, and regional lithostratigraphic correction (e.g., GBGMR, 1989;F. Cheng et al, 2018;Fang et al, 2007;Yin et al, 2008).…”

Tectonics of the Eastern Kunlun Range: Cenozoic Reactivation of a Paleozoic‐Early Mesozoic Orogen

“…Oligocene lacustrine strata are interpreted to have been deposited within a single depression, much larger than the modern Qaidam basin, which was subsequently partitioned by uplift associated with the Qimen Tagh thrust belt (Yin et al, ). Growth strata relationships indicate that deformation along the Eastern Kunlun margin of the basin commenced at circa 29–24 Ma (e.g., Cheng, Fu, et al, ; Cheng et al, ; X. Cheng, Fu, et al, ; Wu et al, ; Yin et al, , ).…”