The Geology of Hong Kong (Interactive On-line)

Ap Lei Chau Formation - Kra

The type locality of the Ap Lei Chau Formation (Table 5.6) lies along the southwest foreshore of Ap Lei Chau (Figure 5.16). The formation comprises mainly welded fine ash vitric tuffs with interlayered eutaxitic bands, typically defined by chloritized fiamme (Plate 5.27). It also includes tuff breccias, pyroclastic breccias, tuffites and coarse ash tuffs, thin lavas, and impersistent epiclastic layers. On the western side of Hong Kong Island, the formation is variably folded and is at least 1250 m thick, although the base has not been observed (Figure 5.20). A U–Pb zircon age of 142.7 ± 0.2 Ma indicates an Early Cretaceous age for the formation (Davis et al., 1997).

Previously, the Ap Lei Chau Formation was considered to outcrop over much of eastern Kowloon (GCO, 1986b). However, the rocks in this area have now been mainly reassigned to either the Mount Davis Formation or the new Che Kwu Shan Formation on the basis of petrographic interpretation and whole-rock geochemistry (Campbell & Sewell, 1998). Some of the outcrop in eastern Hong Kong Island has also been reassigned to the Mount Davis Formation. A pale buff vitric tuff with small fiamme on the southern flanks of Tai Mo Shan, formerly considered to be the thin northern equivalent of the Ap Lei Chau Formation (Addison, 1986), is now included within the substantially older Shing Mun Formation.