Magnetostratigraphy of the Neogene Chaka basin and its implications for mountain building processes in the north‐eastern Tibetan Plateau

Abstract

Magnetostratigraphy of sedimentary rock deposited in the Chaka basin (north-eastern Tibetan Plateau) indicates a late Miocene onset of basin formation and subsequent development of the adjacent Qinghai Nan Shan. Sedimentation in the basin initiated at $11 Ma. In the lower part of the basin ¢ll, a coarsening-upward sequence starting at $9 Ma, as well as rapid sedimentation rates, and northward paleocurrents, are consistent with continued growth of the Ela Shan to the south. In the upper section, several lines of evidence suggest that thrust faulting and topographic development of the Qinghai Nan Shan began at $6.1 Ma. Paleocurrent indicators, preserved in the basin in the proximal footwall of the Qinghai Nan Shan, show a change from northward to southward £ow between 6.5 and 3.8 Ma. At the same location, sediment derived from the Qinghai Nan Shan appears at 6.1 Ma. Finally, the initiation of progressively shallowing dips observed in deformed basin strata and a change to pebbly, £uvial deposits at 6.1 Ma provide a minimum age for the onset of slip on the thrust fault that dips north-east beneath the Qinghai Nan Shan.We interpret a decrease in sediment accumulation rates since $6 Ma to indicate a reduction in Chaka basin accommodation space due to active faulting and folding along the Qinghai Nan Shan and incorporation of the basin into the wedge-top depozone. Declination anomalies indicate the beginning of counter-clockwise rotation since 6.1Ma, which we associate with local deformation, not regional block rotation.The emergence of the Qinghai Nan Shan near the end of the Miocene Epoch partitioned the once contiguous Chaka-Gonghe and Qinghai basin complex. In a regional framework, our study adds to a growing body of evidence that points to widespread initiation and/or reactivation of fault networks during the late Miocene across the northeastern Tibetan Plateau.

The impact of regional uplift of the Tibetan Plateau on the Asian monsoon climate

“…However, other studies suggest that the central TP uplifted earlier than the southern and northern TP (Wang et al, 2008(Wang et al, , 2014. For the northern TP, for example, some studies suggest that this region experienced marked uplift between 25 and 20 Ma (Xiao et al, 2012), while others show a significant uplift as having occurred since the late Miocene (Fang et al, 2005;Lease et al, 2007;Zheng et al, 2010;Zhang et al, 2012a;Li et al, 2014). Seen in this way, there are still some uncertainties in the scenarios of TP uplifts.…”

“…10d and 11). In terms of the uplift time of the northern TP, rapid persistent uplifting mainly started from the late Miocene (Fang et al, 2005;Lease et al, 2007;Zheng et al, 2010;Zhang et al, 2012a;Li et al, 2014). If the intensified East Asian winter monsoon from…”

Evolution of the NE Qinghai–Tibetan Plateau, constrained by the apatite fission track ages of the mountain ranges around the Xining Basin in NW China

“…52-50 Ma (Dai et al, 2006) and the Qaidam Basin formed during 65-50 Ma (Yin et al, 2008b); (2) the basin mechanisms are different: the Xining Basin developed due to the extension and pulling-apart caused by the clockwise rotation of the Central Qilian Block related to the South Qilian Block, and many growth normal faults have recently been found (Dupont-Nivet et al, 2004, and our unpublished data) dating to the Early Cenozoic; and the basin became a compressive one since the Miocene because of the basinward thrusting of the Laji Shan and the Daban Shan, but the Qaidam Basin developed due to thrusting that had been occurring since the beginning of the basin (Yin et al, 2008a(Yin et al, , 2008b; (3) some recent studies have shown that the region between the present Xining Basin and Qaidam Basin (i.e., Ela Shan, Guide Basin and Xunhua Basin) underwent prolonged uplift during the Paleogene; the Ela Shan was once a structural highland shedding clasts into the Qaidam Basin to the west and the Xining Basin to the east, and no sediments of that period are distributed there (Craddock et al, 2011;Lu et al, 2012); in addition, the Chaka and Gonghe Basins located between the Xining Basin and Qaidam Basin developed only since ca. 11-10 Ma (Craddock et al, 2011;Zhang et al, 2012); (4) the sedimentary environments are different: the Qaidam Basin was dominated by fluvial environments during the Paleogene and by a lacustrine environment during the Neogene (Yin et al, 2008b); however, the Xining Basin was in a lacustrine environment during the Paleogene and in a fluvial one during the Neogene (Zhang et al, 2010a,b;our unpublished data).…”

Climatic and tectonic controls on sedimentation and erosion during the Pliocene-Quaternary in the Qaidam Basin (China)

“…Both tectonic uplift and climate change can infl uence sedimentation patterns, and thus any causal interpretation of stratigraphy must account for both tectonic and climatic infl uences. Strata preserved within the Qaidam and other nearby basins in the northeastern Tibetan Plateau record tectonic and climatic changes since at least Paleocene time (Pares et al, 2003;Fang et al, 2003Fang et al, , 2007Horton et al, 2004;Zhou et al, 2006;Yin et al, 2008;Craddock et al, 2011;Zhuang et al, 2011b;H.-P. Zhang et al, 2012). Differentiating the tectonic versus climatic controls on sedimentation at any of these localities, however, is complicated by the competing infl uences of both tectonics and climate on sedimentation.…”

“…This interpretation is consistent with multiple proxy data sets suggesting that the late Pliocene "climate crash" had begun by ca. 3.0 Ma, resulting in a cooler and more arid climate in central Asia (e.g., Thunell and Belyea, 1982;Dwyer et al, 1995;Ravelo et al, 2004;H.-P. Zhang et al, 2012). Global climate change toward cooler, drier conditions may have produced the arid conditions observed (Zheng et al, 2010;H.-P. Zhang et al, 2012).…”