Towards a clarification of the provenance of Cenozoic sediments in the northern Qaidam Basin

Abstract

Determining the provenance of sedimentary basin fill in the northern Qaidam Basin is a key step toward understanding the sedimentary system dynamics and mountain-building processes of the surrounding orogenic belts in Tibet. The exceptionally thick (average of 6-8 km) Cenozoic fluvio-lacustrine deposits in the northern Qaidam Basin were once thought to have been eroded from the nearby northern Qaidam Basin margin and the southern Qilian Shan and to reflect the prolonged thrust-related exhumation of these orogenic belts. However, several recent studies, based mainly on paleocurrent and detrital zircon U-Pb age data, suggested that they were derived from the distant East Kunlun Shan to the south, or the Qimen Tagh to the southwest (at least 200 and 350 km from the northern Qaidam Basin, respectively). That model assumed that the East Kunlun Shan and Qimen Tagh formed significant topographic barriers during the earliest sedimentation of Cenozoic strata (e.g., the Lulehe Formation) in the northern Qaidam Basin. Therefore, the tectonic significance of the provenance of the Lulehe Formation remains a fundamental problem in understanding the postcollisional uplift history of the northern Tibetan Plateau. To address this issue, we conducted sedimentological and paleocurrent analyses of the Lulehe Formation and detrital zircon U-Pb dating of Mesozoic strata in the northern Qaidam Basin. The results, in combination with existing paleocurrent and seismic reflection data, collectively indicate that although the source area cannot be specified by matching zircon U-Pb ages in sedimentary rocks with crystalline basement source rocks, other evidence points consistently to a unified proximal northerly source area (the northern Qaidam Basin margin and the southern Qilian Shan). Our results emphasize that noncrystalline basement rocks (e.g., Mesozoic sedimentary rocks) in fold-and-thrust belts should be taken into consideration when seeking potential source areas by correlating zircon U-Pb ages of siliciclastic detritus with related basement rocks. In addition, this study strongly supports the claim that variations in the proportions of age populations should be used with caution when determining source terrane by comparisons of age distributions.

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

“…Compared with the widespread middle Miocene deformation across the entire Qilian Shan, the early Cenozoic deformation is just reported south of the Qaidam Basin (e.g., Clark et al, ; Jolivet et al, , ; D. Liu, Li, et al, ; Mock et al, ; F. Wang, Shi, et al, ; Y. Wang et al, ; Yin et al, ), the northern Qaidam Basin (e.g., F. Cheng et al, ; He et al, ; Jolivet et al, ; Lu et al, ; Yin et al, ; Zhuang et al, ), and parts of the Qilian Shan, such as the Xining‐Lanzhou Basin (Dupont‐Nivet et al, ; Dai et al, ; J. Zhang et al, ; Wang, Zhang, Liu, et al, ), western Qinling (Clark et al, ; Duvall et al, ), and the central‐northern Qilian Shan (e.g., Qi et al, ; He et al, ; Figure b). The Paleocene‐Eocene and widespread middle Miocene deformation suggest that the crustal shortening has extended into the northern Tibetan Plateau to reactive preexisting weaknesses shortly after the India‐Eurasia collision, followed by a phase of extensive crustal shortening across the Qilian Shan since the middle Miocene.…”

“…It is also supported by provenance analyses for the Qaidam Basin, which indicate that early Cenozoic sediments in the northern Qaidam Basin were shed from the Kunlun Shan rather than the southern Qilian Shan, and provenance change occurred during early‐middle Miocene (Bush et al, ; W. Wang, Zheng, Zhang, et al, ). While Lu et al () suggest that Bush et al () may misidentify the underlying Cretaceous Quanyagou formation as the lower part of the Lulehe formation such that produce improper conclusions, they concluded that the Lulehe formation is characterized by proximal alluvial fan deposits that originated from the northern Qaidam Basin and the southern Qilian Shan based on evidence of sedimentology, facies analysis, and seismic reflection profiles (e.g., F. Cheng et al, ; Lu et al, ; Yin et al, ). Cheng et al () suggest that if both the traditional (~50 Ma) and younger (~25.5 Ma) age models are correct, the Qaidam Basin may experience diachronous basin‐fill process and the lithostratigraphic units throughout the basin are time transgressive.…”

“…Compared with the widespread middle Miocene deformation across the entire Qilian Shan, the early Cenozoic deformation is just reported south of the Qaidam Basin (e.g., Clark et al, 2010;Jolivet et al, 1999Jolivet et al, , 2001Mock et al, 1999;F. Wang, Shi, et al, 2017;Yin et al, 2002), the northern Qaidam Basin (e.g., F. Cheng et al, 2019;He et al, 2018;Jolivet et al, 2001;Lu et al, 2018;Yin et al, 2008;Zhuang et al, 2011), and parts of the Qilian Shan, such as the Xining-Lanzhou Basin (Dupont-Nivet et al, 2004;Dai et al, 2006;J. Zhang et al, 2015;, western Qinling Duvall et al, 2011), and the central-northern Qilian Shan (e.g., Qi et al, 2016;He et al, 2017; Figure 9b).…”

Early Cenozoic exhumation in the Qilian Shan, northeastern margin of the Tibetan Plateau: Insights from detrital apatite fission track thermochronology

“…Evidence from previous studies supports the early Cenozoic tectonic exhumation event. Adjacent to the Qilian Shan, the northern Qaidam Basin and the Jiuquan Basin also archive detritus with distinct AFT ages of ~60–50 Ma (He et al., 2017, 2018; Jian et al., 2018; Lin et al., 2019); the deposition of coarse clasts that originated from the Qilian Shan overlying the Cretaceous in unconformable prevail in the northern Qaidam Basin (Ji et al., 2017; Lu et al., 2018; Zhuang et al., 2011), accompanied by the beginning development of synsedimentary thrusting structures and deformation during the Paleocene‐early Eocene (Cheng et al., 2019; Yin et al., 2008); analogously, coarse clast‐dominated sediment rapidly accumulated over the Cretaceous in unconformable in the Xining Basin during the early Eocene (Fang et al., 2019). Early Eocene initiation of rapid exhumation of several terranes in the southern Qilian Shan (Jian et al., 2018; Qi et al., 2016; Cheng et al., 2016; Zhuang et al., 2018) and the northern extension of the Qilian Shan (An et al., 2020) has been revealed by thermochronology.…”

Provenance Analysis of the Paleogene Strata in the Northern Qaidam Basin, China: Evidences from Sediment Distribution, Heavy Mineral Assemblages and Detrital Zircon U‒Pb Geochronology

“…Numerous approaches have been applied to provenance analysis in the Qaidam Basin, including clast composition of conglomerate [1][2][3], sandstone modal analysis [4][5][6][7], detrital mineral U-Pb geochronology [8][9][10][11][12][13], paleocurrent analysis [3,4,[10][11][12][13], heavy mineral analysis [4,5,[14][15][16], and element geochemistry [7,17], etc. However, some discrepancies still exist in previous results of provenance analysis.…”