## 5 Discussion
### Paleoclimatic Responses to Regional Tectonic and Global Climatic Events
#### 5.3.2 Responses to Global Climatic Events  
During the Jurassic and Cretaceous, the tectonic regime of the East Asian Plate changed significantly, giving rise to an East Asian convergent tectonic system with intracontinational subduction and orogen. This convergence has led to the formation of the East China Plateau [8; 58; 59; 60]. Furthermore, the Liupanshan Basin began to develop at the Hauterivian-Barremian boundary in the Lower Cretaceous (approximately 130 Ma); it was then already separated from the Great Ordos Basin [16; 29]. In the Aptian-Albian (about 120-110 Ma), the paleo-uplift rose again. The East China Plateau began to collapse at the beginning of the Aptian (125 Ma) [17; 61]. This allowed the airflow previously blocked by the plateau to enter the interior, while the paleo-uplift prevented the airflow from moving further inland. Therefore, as revealed by the Haijiazhuang section, the climate was arid during the early depositional period of the Madongshan Formation. However, during the late depositional period, the environment became warmer and more humid than before. This is likely due to global climate variations [33]. To date, several studies have demonstrated a rapid global cooling event at the Aptian-Albian boundary (or in the Late Aptian). For example, late Aptian glendonites from the Sverdrup Basin, Canadian Arctic, and from Spitsbergen, Norway, indicated near-freezing underwater temperatures [62; 63]. Moreover, [PERSON] et al. utilized the North Atlantic DSDP545 \(\mathrm{TEX_{86}}\) proxy to reconstruct paleo-sea surface temperatures and discovered an obvious cooling event during the upper Aptian. Geochemical and micro paleontological evidence from drill cores of marine sediments suggested that the cooling may have triggered an ecological crisis in the oceans [64]. The global sea level curve showed a rapid sea level drop of at least 50 m at the Aptian-Albian boundary. The whole-rock \(\mathrm{\delta^{18}O}\) data obtained from the Exmouth Plateau, Australia, indicate a co-occurrence of the sea-level drop and a \(\mathrm{\delta^{18}O}\) enrichment of more than 0.8%, even exceeding 1% [24; 65; 66]. In addition, fossils of marine reptiles that live at high latitudes have been discovered in the late Aptian sediments in southeast Australia, indicating a paleoclimate in which the seasonal extreme lows were close to the freezing point [66]. Given all this evidence, the global oceans cooled significantly at the Aptian-Albian boundary (Table 2). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Region** & **Climate Reference** & **Climate Significance** & **Period** \\ \hline Sverdrup Basin, Canadian Arctic, and Spitsbergen, Norway & glendonites & The sea water temperature is close to the freezing point. & Late Aptian \\ North Atlantic & \(\mathrm{TEX_{86}}\) & The surface temperature of the ancient seawater & Late Aptian \\ Southeast Australia & \(\mathrm{Fossils\,of\,marine\, reptiles}\) in high-latitude regions & The paleoclimate conditions during this period were extremely cold seasonally to near freezing point. & Late Aptian \\ Exmouth Plateau, Australia & \(\mathrm{\delta^{18}O}>0.8\%\) & The temperature of seawater & Aptian-Albian boundary \\ Global & The sea level curve is declining. & The temperature of seawater & Aptian-Albian boundary \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Marine environmental conditions at the Aptian-Albian boundary (or in the Late Aptian). According to records found in terrestrial sediments, it is likely that the climate became colder and more humid at this boundary (Table 3). For example, the evolution of the carbonate platform in the Serdj-Bargou region of central Tunisia shows that the coral-gravel-sponge assemblage in biogenic carbonate rocks was replaced by oolitic material in the late Aptian [67]. Similarly, the kaolinite clay content increased in sediments of north Sicily at the Aptian-Albian boundary [68].