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The Geology of Hong Kong (Interactive On-line)
Pat Sin Leng Formation - Kp

The Pat Sin Leng Formation crops out mostly on the mainland of Hong Kong, in the northeast New Territories. There, it forms a prominent north-dipping escarpment along Pat Sin Leng from Wong Leng in the west to Kwun Yam Tung in the east (Plate 8.1). The formation is thought to be Early Cretaceous (Lai et al., 1996) and rests unconformably on volcanic rocks of the Tai Mo Shan Formation in the southeast, but is overthrust by these same rocks in the north. The formation has a maximum exposed thickness of 500 m and covers an area of some 30 km2. The designated type section is at Chek Ma Tau (Figure 8.2).

The Pat Sin Leng Formation varies from grey to greyish white, thickly-bedded conglomerate, tuffaceous sandstone, and reddish brown thinly-bedded siltstone in the lower part, through greyish red sandstone and occasional conglomerate in the middle part, to reddish purple, clayey siltstone with sandstone in the upper part. Subround to subangular pebbles, cobbles and boulders mostly comprise red and brown volcanic rocks (Plate 8.2).

Jones (1995) described two main types of deposit at Bluff Head: channel-fill and sheetflood deposits. The channel-fill comprises conglomerates, forming erosively-based units up to a few metres thick, and pebbly sheet sandstones and siltstones. The conglomerates are poorly sorted and matrix supported, with clasts of mainly volcanic granules, intraformational mudstone clasts, and less commonly red sandstone and grey volcanic clasts. The conglomerates form fining-upward sequences. These pass into the sheetflood deposits composed of sheet-like sandstones, up to 0.4 m thick, and siltstones with dessication cracks and intense bioturbation.