## 4 Discussion
### Facies Associations and Depositional Environments  
Based on the integration of field observations and detailed microfacies analyses, the lithofacies of the upper Jiabula (Gyabula) Formation and the Chuangde Formation can be systematically classified into four distinct facies associations, (1) lower slope-basin, (2) lower slope, (3) upper slope, and (4) upper slope-shelf margin, as illustrated in Figures 12 and 13. The lower slope-basin facies association consists mainly of shale and marlstone (MF1), with occasional siltstone or radiolarian chert (MF7-8) interbeds (Figure 12). Within the upper Jiabula Formation (S1 to S25), this facies association is typified by black shales interbedded with cherts, which we interpret as indicative of deposition in basinal environments ([PERSON] and [PERSON], 1995; [PERSON] and [PERSON], 2000) [37, 38]. This facies association is also identified in the upper (S94 to S97 and S106 to S109) Chuangde Formation (Figures 12 and 13A-C), where it is manifested by laterally extensive, parallel-laminated red to cherry red shales, peloidal marlstone (MF1), and radiolarian cherts (MF7-8). The presence of radiolarian cherts (MF7 and MF8) in the upper Chuangde Formation may indicate basinal environments below the carbonate compensation depth (CCD). The lower slope facies association is predominantly characterized by bioclastic wake-stone with variable clast content (MF3-4), interbedded with shale layers, slump blocks, and brecias composed of foraminiferal grainstone (MF6). These facies exhibit a distinctive red to cherry red coloration and are primarily observed in the lower Chuangde Formation (Figures 12 and 13C). In contrast to the basin facies, this association is marked by a higher proportion of carbonate components and, more significantly, the presence of slump blocks and brecias composed of grainstone. The foraminiferal grainstones are interpreted as having originated from the shelf margin and subsequently transported into slope environments via submarine slides or sheet flow deposits (e.g., [PERSON] and [PERSON], 1986; [PERSON] and [PERSON], 1990) [39, 40, 41]. Notably, the slump blocks and brecias are relatively thin and infrequent, leading us to infer that they were deposited in distal or lower slope environments. Figure 13: Field photos showing the combination of some lithofacies and sedimentary structures in the CORBs of the Gyangze–Kangmar basin. (**D**) Microfacies (MF1–MF9) from the upper-near top part of the Chuangde Formation in the Zhangguo section, Gyangze (S100–S113 in Figure 12). (**B**) Microfacies (MF1–MF5) and cherts (MF7–8) from the upper part of the Chuangde Formation in the Zhangguo section, Gyangze (S94–S97 in Figure 12). (**C**) The erosional/scouring contact between megabreccias (MG) of the Zongzhuo Formation and reddish shale and cherts of the Chuangde Formation from the Chuangde section in Gyangze. Notice that in this location, shales above the chert beds are removed by the megabreccia. (**D**) The exposure situation of Cretaceous oceanic red beds (BORBs) in the surrounding areas of Chuangde, Gyangze, with note: multiple repetitions of strata occur due to tectonic activities (folding and faulting). (**E**) Reddish shale and marlstone of the basal Chuangde Formation and its underlying Jiabula Formation from the Daba section in Kangmar. (**F**) Syn-depositional folds (SDF) in slump blocks of the middle Chuangde Formation, Gyangze. The upper slope facies association is predominantly characterized by bioclastic wake-stone (MF3 and MF4) and slump blocks exhibiting breccitation (MF6), which are prominently observed within the middle-upper Chuangde Formation (Figure 12). The slump deposits display partial breccitation at their basal and frontal regions, while internally, they reveal symp depositional folding structures (Figure 13F). Despite the presence of localized deformations, the slump units exhibit significant lateral continuity, which enables them to be consistently traced across the outcrop scale.