<figure><img src="image_6.png" /><figcaption>**Figure 3:** Lithostratigraphy and sedimentary facies of Paleogene sediments from the Xining (Dai et al., 2006), Lanzhou (Yue et al., 2000) and Linxia (Feng et al., 2022a) Basins and their correlation of magnetic polarity stratigraphy to the geomagnetic polarity timescale (GPTS) (Gradstein et al., 2012).</figcaption></figure>
<figure><img src="image_7.png" /><figcaption>**Figure 4:** Field photographs of the Cenozoic strata in the Longzhong Basin.</figcaption></figure>

(a) Angular unconformity between the Xiliugou Formation and the Lower Cretaceous Hekou Group in the Lanzhou Basin (GPS: 36°20′33.84″N, 103°29′25.05″E).

(b) Massive reddish quartziferous, calcareous, and homogeneous coarse sandstone in the Dahejia Section representing the oldest Cenozoic strata in the Linxia Basin (GPS: 35°49′17.92″N, 102°46′30.17″E).

(c) Lithology of the Xiliugou Formation, which represents the oldest Cenozoic strata in the Lanzhou Basin (GPS: 36°16′17.79″N, 103°31′55.70″E), similar to that of the Dahejia Section in the Linxia Basin.

(d) The Yehucheng Formation in the Lanzhou Basin characterized by regular alternations of laterally continuous gypsum layers and red mudstone beds (GPS: 36°21′5.66″N, 103°28′58.56″E).

(e) Lithology of the Mahalagou Formation from the Guanjiashan Section in the Xining Basin (GPS: 36°41′20.77″N, 101°51′59.63″E), similar to that of the Yehucheng Formation in the Lanzhou Basin.

(f) Early Miocene stratigraphic sequence of the Zhongzhuang Formation from the Yangjuangou Section in the Xunhua Basin (GPS: 35°50′17.86″N, 102°29′15.11″E).

(g) Zebra Bed of the Dongxiang Formation characterized by greenish-white marlite and alternative purple red mudstone in the Maogou Section (35°40′1.89″N, 103°19′12.07″E).

(h) The late Late Miocene Liushu Formation characterized by paleosol complexes and mudstones intercalated with multiple layers of coarse sandstones in the Laogou Section (35°28′16.95″N, 103°23′29.91″E).

(i) Quaternary eolian loess in the Lanzhou Basin (36°19′0.91″N, 36°19′0.91″E).

Note that all the photos were taken by Feng Zhantao.
<figure><img src="image_8.png" /><figcaption>**Figure 5:** Stratigraphic divisions and sedimentary facies based on mammal-bearing fossils and paleomagnetic dating of the Neogene sedimentary sequence in the sub-basins of the Longzhong Basin. Note that the sites of the presented 20 sections are marked in Fig. 2. XNB: Xining Basin; LZB: Lanzhou Basin; GDB: Guide Basin; XHB: Xunhua Basin; LXB: Linxia Basin; TSB: Tianshui Basin. 1. Comprehensive integrated section in the Xining Basin (Fang et al., 2019); 2. Xingjiawan section (Ao et al., 2016b); 3. Quantougou section (Zhang P. et al., 2020); 4. Xianshuihe section (Wang W. et al., 2016); 5. Duitinggou section (Zhang P. et al., 2016, 2018; Ao et al., 2020); 6. Xijin drilling (Zhang J., Li et al., 2016); 7. Fanjiaping section (Guo et al., 2018); 8. Fenghuangshan section (Zhang Y.-B. et al., 2014); 9. Comprehensive integrated section in the Guide Basin (Fang et al., 2005); 10. eastern Ashigong section (Wang Z. et al., 2018); 11. Hualong section (Lease et al., 2012); 12. Upper and lower Xunhua section (Hough et al., 2011); 13. Yangjuangou and Xigou section (Ji et al., 2010; Xu, 2016); 14. Heilingding (Wang J. et al., 2010; Fang et al., 2016; Wu et al., 2017); 15. Guonigou section (Fang et al., 2016); 16. Yagou section (Sun et al., 2023); 17. Maogou section (Fang et al., 2003); 18. Wushan-Nanyu-Yinwan sections (Wang X.-X. et al., 2023); 19. Yanwan section (Zhang J. et al., 2013); 20. Lamashan and Yaodian sections (Li J. et al., 2006; Wang X.-X. et al., 2012).</figcaption></figure>
<figure><img src="image_9.png" /><figcaption>**Figure 6:** Geological map of the Xining Basin with mammal fossil localities and typical study sections. 1: Xiejia section and Tashan drilling; 2: East Xining–Shuiwan–Guanjiashan section; 3: Mojiazhuang section; 4: Bingling Shan section (modified from Fang et al., 2019).</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>**Figure 7:** Magnetostratigraphic contrasts of the sections bearing mammalian fauna in the Xining Basin and their correlations with the GPTS 2012 (modified from Fang et al., 2019).</figcaption></figure>
<figure><img src="image_11.png" /><figcaption>**Figure 8:** Geological map of the Lanzhou Basin with mammal fossil localities and typical study sections. 1: Xianshuihe section (Wang W. et al., 2016); 2: Yongdeng section (Yue et al., 2000); 3. Quantougou section (Zhang P. et al., 2020); 4. Duitinggou section (Zhang P. et al., 2016, 2018; Ao et al., 2020); 5. Fenghuangshan section (Zhang Y.-B. et al., 2014); 6. Fanjiaping section (Guo et al., 2018); 7. Nanshan section (Sun et al., 2011); 8. Xijin drilling (Zhang J., Li et al., 2016).</figcaption></figure>
<figure><img src="image_12.png" /><figcaption>**Figure 9:** Magnetostratigraphic contrasts of the sections bearing mammalian fauna in the Lanzhou Basin and their correlations with the GPTS of Gradstein et al. (2012).</figcaption></figure>
<figure><img src="image_13.png" /><figcaption>**Figure 10:** Geological map of the Linxia Basin with mammal fossil localities and typical study sections. 1: Wangjiashan section (Li J. et al., 1997); 2: Maogou section (Fang et al., 2003); 3. Yagou section (Sun et al., 2023); 4. Guonigou section (Fang et al., 2016); 5. Longdan drilling (Zan et al., 2016); 6. Laogou section (Zhang W.-L. et al., 2019); 7. Heilinding section (Wang J. et al., 2010; Fang et al., 2016; Wu et al., 2017); 8. Duikang section (Zhang W.-L. et al., 2020).</figcaption></figure>
<figure><img src="image_14.png" /><figcaption>**Figure 11:** Magnetostratigraphic contrasts of the sections bearing mammalian fauna in the Linxia Basin and their correlations with the GPTS of Gradstein et al. (2012).</figcaption></figure>
<figure><img src="image_15.png" /><figcaption>**Figure 12:** (a) Average ecological scores of mammalian fauna in the Xining, Lanzhou, and Linxia Basins with 50%, 90%, and 95% bootstrap confidence intervals, which are calculated via a “loess” smoothing method and 5,000 bootstrap simulations in Acycle (Li M. et al., 2019). (b) Percentages of shrub and herb taxa in the Lanzhou Basin (Hui et al., 2021c), Linxia Basin (Ma et al., 1998), Tianshui Basin (Hui et al., 2011), and Xunhua Basin (Xu et al., 2015).</figcaption></figure>
<figure><img src="image_16.png" /><figcaption>**Figure 13:** (a) Spatial distribution of the mean annual NDVI in the Longzhong Basin from 2000 to 2020. (b and c) correlations between the NDVI and climate (temperature and precipitation) at the same temporal and spatial scale using Pearson correlation coefficient analysis in R. (d) The contribution rate of precipitation to changes in the NDVI indicates that precipitation contributes more than 50% to the NDVI in most regions. Vegetation data were obtained from the National Tibetan Plateau Science Data Center (Gao et al., 2022), while the climate data were sourced from Peng et al. (2019).</figcaption></figure>

<figure><img src="image_17.png" /><figcaption>**Figure 14:** Changes in reconstructed ecological conditions since the Oligocene based on fossil mammals compared with terrestrial and marine records of the East Asian summer monsoon. (a) The average ecological score of mammal fossils from the Longzhong Basin region. (b–c)</figcaption></figure>
Carbonate oxygen and carbon isotope records of the Xining Basin (Yang et al., 2022). (d) Loess magnetic susceptibility in the western Loess Plateau (Qiang et al., 2011). (e) Eolian flux of ODP Site 1208 in the North Pacific (Zhang W.-F. et al., 2016). (f) CIA values of ODP Site 1148 in the South China Sea (Wei et al., 2006). (g) Global deep-sea $\delta^{18}$O values (Westerhold et al., 2020). (h) Normalization of sedimentation rates from the Linxia Basin (Fang et al., 2016; Wu et al., 2017), Xunhua Basin (Lease et al., 2012), Lanzhou Basin (Wang W. et al., 2016; Zhang et al., 2020), and Xining Basin (Fang et al., 2019).

(a) Late Eocene

<figure><img src="image_18.png" /></figure>

(b) Oligocene to Early Miocene

<figure><img src="image_19.png" /></figure>

(c) Middle Miocene

<figure><img src="image_20.png" /></figure>

(d) Late Miocene to Pliocene

<figure><img src="image_21.png" /></figure>

(e) Quaternary

<figure><img src="image_22.png" /></figure>

**Figure 15:** Block diagrams showing the five-stage landscape and ecological evolution of the Longzhong Basin since the late Eocene.
<caption>**Table 1**</caption>

The paleomagnetic age and average ecological score of faunas in Linxia, Lanzhou and Xining basins

<table><thead><tr><th>Basin</th><th>Fauna</th><th>Age (Ma)</th><th>Ecological Score Average</th></tr></thead><tbody><tr><td rowspan="4">Linxia Basin</td><td>Dzungariotherium</td><td>27/21</td><td>3.67±0.33</td></tr><tr><td>Platybelodon</td><td>12.5-11.1</td><td>4.07±0.33</td></tr><tr><td>Hipparion</td><td>11.5-5.3</td><td>2.79±0.6</td></tr><tr><td>Equus</td><td>2.5-2.2</td><td>2.03±0.46</td></tr><tr><td rowspan="10">Lanzhou Basin</td><td>Nanpoping</td><td>31-30</td><td>2.76±0.52</td></tr><tr><td>Xiagou</td><td>26-25</td><td>2.5±0.5</td></tr><tr><td>Gaolanshan</td><td>25</td><td>2.2±0.46</td></tr><tr><td>Miaozuizi</td><td>24-23.2</td><td>3.06±0.55</td></tr><tr><td>Zhangjiaping</td><td>21.3-20.6</td><td>2.96±0.55</td></tr><tr><td>Duitinggou</td><td>18.9</td><td>3.44±0.38</td></tr><tr><td>Quantougou</td><td>12.8-11.7</td><td>3.28±0.29</td></tr><tr><td>Xingjiawan</td><td>8-6.5</td><td>3.05±0.69</td></tr><tr><td rowspan="5">Xining Basin</td><td>Xiejia</td><td>25</td><td>2.41±0.55</td></tr><tr><td>Chetougou</td><td>22.5-19.5</td><td>-</td></tr><tr><td>Danshuilu</td><td>17-16</td><td>3.5±0.4</td></tr><tr><td>Diaogou</td><td>16-13.8</td><td>4.14±0.38</td></tr><tr><td>Xiamen</td><td>10-8</td><td>2.72±0.64</td></tr></tbody></table>
**Declaration of competing interest**

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
<figure><img src="image_23.png" /><figcaption>Figure 1</figcaption></figure>
<figure><img src="image_24.png" /><figcaption>Figure 2</figcaption></figure>
Xining Basin

Xiejia-Binglingshan Section
(Dai et al., 2006)

GPTS
(2012)
Age
(Ma)

<figure><img src="image_25.png" /></figure>

Mudstone/Siltstone

Fine-grained sandstone

MS

Linxia Basin

Dahejia Section
(Feng et al., 2022)

<figure><img src="image_26.png" /></figure>

Coarse-grained sandstone

Conglomerate

S: Sandstone

Gypsum

Malite

C: Conglomerate

Lanzhou Basin

Xianshuihe Section

Wang W. et al., 2016

GPTS
(2012)
Age
(Ma)

<figure><img src="image_27.png" /></figure>

Polarity

VGP Lat. (°)

-90 0 90

33.2 Ma

Yehucheng Fru.

42.5 Ma

Xilinhot Fru.

Thickness (m)
Lith.

<figure><img src="image_28.png" /></figure>

<figure><img src="image_29.png" /></figure>

<figure><img src="image_30.png" /></figure>

<figure><img src="image_31.png" /></figure>

<figure><img src="image_32.png" /></figure>

<figure><img src="image_33.png" /></figure>

<figure><img src="image_34.png" /></figure>

Figure 3
<figure><img src="image_35.png" /></figure>

<figure><img src="image_36.png" /></figure>

<figure><img src="image_37.png" /></figure>

<figure><img src="image_38.png" /></figure>

<figure><img src="image_39.png" /></figure>

<figure><img src="image_40.png" /></figure>

<figure><img src="image_41.png" /></figure>

<figure><img src="image_42.png" /></figure>

<figure><img src="image_43.png" /><figcaption>Figure 4</figcaption></figure>
<figure><img src="image_44.png" /><figcaption>Figure 5</figcaption></figure>
<figure><img src="image_45.png" /><figcaption>Figure 6</figcaption></figure>
<figure><img src="image_46.png" /><figcaption>Figure 7</figcaption></figure>
<figure><img src="image_47.png" /><figcaption>Figure 8</figcaption></figure>
<figure><img src="image_48.png" /><figcaption>Figure 9</figcaption></figure>
<figure><img src="image_49.png" /><figcaption>Figure 10</figcaption></figure>
<figure><img src="image_50.png" /><figcaption>Figure 11</figcaption></figure>
<table><thead><tr><th colspan="2">Time Scale (2022)</th><th>Europe</th><th>China</th></tr><tr><th>Epoch</th><th>Stage</th><th>Stage/Age</th><th>Stage/Age</th></tr></thead><tbody><tr><td rowspan="4">Pliocene</td><td>Chibanian</td><td></td><td></td></tr><tr><td>Calabrian</td><td>MN 18</td><td>Nihewanian</td></tr><tr><td rowspan="2">Gelasian</td><td>MN 17</td><td>2.6</td></tr><tr><td>MN 16</td><td>Mazegouan</td></tr><tr><td rowspan="4">Miocene</td><td>Messinian</td><td>MN 13</td><td>Baodean</td></tr><tr><td rowspan="3">Tortonian</td><td>MN 12</td><td>7.25</td></tr><tr><td>MN 8</td><td></td></tr><tr><td>MN 11</td><td></td></tr><tr><td rowspan="3">Serravallian</td><td>Vallesian</td><td>MN 10</td><td>Bahean</td></tr><tr><td rowspan="2">Astaracian</td><td>MN 9</td><td></td></tr><tr><td>MN 7</td><td></td></tr><tr><td rowspan="2">Langhian</td><td>MN 8</td><td></td><td></td></tr><tr><td>MN 6</td><td></td><td></td></tr><tr><td rowspan="4">Burdigalian</td><td>Astecian</td><td></td><td></td></tr><tr><td>MN 5</td><td></td><td></td></tr><tr><td>MN 4</td><td></td><td></td></tr><tr><td>MN 3</td><td></td><td></td></tr><tr><td rowspan="4">Aquitanian</td><td>Astecian</td><td></td><td></td></tr><tr><td>MN 2</td><td></td><td></td></tr><tr><td>MN 1</td><td></td><td></td></tr><tr><td></td><td></td><td></td></tr><tr><td rowspan="4">Oligocene</td><td>Chattian</td><td></td><td></td></tr><tr><td>Suevian</td><td>MP 25-30</td><td></td></tr><tr><td rowspan="2">Rupelian</td><td>MP 21-24</td><td></td></tr><tr><td></td><td></td></tr></tbody></table>

<figure><img src="image_51.png" /><figcaption>Figure 12</figcaption></figure>

Polarity Age (Ma)
Chron

<figure><img src="image_52.png" /></figure>
<figure><img src="image_53.png" /><figcaption>Figure 13</figcaption></figure>
<figure><img src="image_54.png" /><figcaption>Figure 14</figcaption></figure>
(a) Late Eocene

<figure><img src="image_55.png" /></figure>

(c) Middle Miocene

<figure><img src="image_56.png" /></figure>

(e) Quaternary

<figure><img src="image_57.png" /></figure>

(b) Oligocene to Early Miocene

<figure><img src="image_58.png" /></figure>

(d) Late Miocene to Pliocene

<figure><img src="image_59.png" /><figcaption>Figure 15</figcaption></figure>