Magnetostratigraphy and tectonic implications of Paleogene-Neogene sediments in the Yinchuan Basin, western North China Craton

Self Cite

The South Ningxia Basin, as the outermost Cenozoic basin on the north‐eastern margin of the Tibetan Plateau, is characterized by a series of convex to the north‐east arcuate structural belts. Constraining the final formation time of the belt has been an ongoing focus in geologic research of the Tibetan Plateau. A set of early Pleistocene conglomerates, the Yumen conglomerate, overlying the folded pre‐Quaternary formations are widely distributed throughout the whole basin, and the latest folded formation is the upper Pliocene Ganhegou Formation, marking the termination of folding uplift in the north‐eastern Tibetan Plateau. Based on 1:50,000 geological mapping, a set of early Pleistocene alluvial fan conglomerates overlying the folded Palaeogene–Neogene strata were recognized and agree well with the Yumen conglomerate. Here, the Yumen conglomerate formation ages were determined to be 0.6–1.04 Ma using cosmic nuclide burial dating. Combined with the upper limit age of the latest strata beneath the unconformity with the latest palaeomagnetic age of 2.77 Ma, the crustal shortening event is restricted to the period 2.77–1.04 Ma, indicating that it is the most intense tectonic shortening event along the north‐eastern margin of the Tibetan Plateau.

Section: Geological Settingsupporting

confidence: 88%

Section: Geological Settingmentioning

confidence: 99%

Yumen conglomerate ages in the South Ningxia Basin, north‐eastern Tibetan Plateau, as constrained by cosmogenic dating

Shi

Chen

et al. 2019

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“…Taking into account the relationships between adjacent basins, several researchers argue that the Shanxi Graben System is not an independent rift but an NE extension of the Weihe Basin, which is formed by the fault depression after the inversion of the early basin (Ning, 1995;Chen, 2017). (Liu et al, 2019;Xu et al, 1993). During the first stage when the western subduction of the Pacific Plate is the main factor of the basin evolution, the Shanxi Graben System has not yet formed.…”

Section: Tectonic Implicationsmentioning

confidence: 99%

Late Cenozoic magnetostratigraphy of the Yuncheng Basin, central North China Craton and its tectonic implications

Yan

Gong

et al. 2020

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Yuncheng Basin, the southernmost basin in the Shanxi Graben System, is considered to be one of the earliest formed in this region. However, due to the insufficient study on the strata and the lack of drilling data, the initial time of the Yuncheng Basin has not been accurately constrained, which heavily restricts our understanding about the formation and evolution of the Shanxi Graben System. In this study, borehole SG-1, which penetrated through the entire Late Cenozoic sediments and reached the basement bedrock, was obtained in the northern part of the Yuncheng Basin, and a detailed magnetostratigraphic study has been carried out on the samples selected from the borehole SG-1. Results show that the borehole SG-1 records 17 normal (N1-N17) and 16 reversed (R1-R16) polarity zones which can correspond to the chron C1n-C4An.1n of the global geomagnetic polarity timescale (GPTS). The bottom of the borehole SG-1 is within chron C4An, and the age of the bottom can be extrapolated to 9.1 Ma according to the sediment accumulation rates calculated by two lowermost major polarity transition boundaries. This age provides precise limitation for the initiation of the Yuncheng Basin and the formation of the Shanxi Graben System. The sediment accumulation rates of the Borehole SG-1 was calculated by major polarity boundaries of chrons and subchrons in the borehole SG-1 and showed significant changes at 9.1, 3.6, and 1.2 Ma. Unlike other basins around the Ordos Block which formed much earlier under the influence of western subduction of the Pacific Ocean, the initiation and evolution of the Shanxi Graben system were mainly controlled by the uplift and outward expansion of the Tibetan Plateau after the Late Miocene. The initiation of the Shanxi Graben System indicates that the far-field effect of the uplift and outward expansion of the Tibetan Plateau reached the central North China Craton by at the latest 9.1 Ma. The effect posed a persistent impact on the evolution of the Yuncheng Basin since 9.1 Ma and led to significant changes of the sediment accumulation rates and sedimentary facies at 9.1, 3.6, and 1.2 Ma in the Yuncheng Basin which correspond well to the prologue of the Qingzang Movement, phase A of the Qingzang Movement, and Kunhuang Movement.

“…Thus, the magnetostratigraphic data of the Sikouzi Formation in the Hejiakouzi valley are referenced from the results of Wang et al (2011) in the Sikouzi section, while the rest are referenced from Shen et al (2001), Jiang et al (2007), and Wang et al (2011). Recently, high-resolution magnetostratigraphic data of the Yinchuan Basin have been reported by Liu et al (2019). Some minor differences between the magnetostratigraphic data published in different studies exist, but it is generally comparable.…”

Section: Cenozoic Stratigraphic Sequencementioning

confidence: 99%

Tectonic evolution of the Qingshuihe Basin since the Late Miocene: Relationship with north‐eastward expansion of the Tibetan Plateau

Tian¹,

Li²,

Liang³

et al. 2019

Southwest Ningxia is located at the tectonic and geographical northeastern edge of the Tibetan Plateau and is an ideal site for studying continental dynamics and plateau building. The Southern Ningxia Arc Tectonic Belt (SNATB) formed during the Cenozoic period as a result of the collision between India and Eurasia and was affected by the Tibetan Plateau uplift. However, the upward growth and expansion processes of the SNATB remain unclear. We investigated the Qingshuihe Basin (a Late Cenozoic basin located between the Tianjingshan and Qingshuihe faults in the northeastern SNATB) using field geological surveys combined with borehole, high-density resistiv