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The Geology of Hong Kong (Interactive On-line)
Bluff Head Formation - Db


The Bluff Head Formation consists of pale grey, fine- to coarse-grained quartzitic sandstone, with subordinate reddish brown and purple sericitic siltstone and greyish white, quartz - pebble conglomerate (Plate 3.1). The formation has a minimum thickness of 800 m (Lai et al., 1996) and its type section is at Bluff Head at the mouth of Tolo Channel (Figure 3.3).


North of Tolo Channel, the formation occurs as a fault-bounded block between strata of the Early Jurassic Tolo Channel Formation to the south and Mesozoic tuffs and sedimentary rocks to the north. Although the sequence dips steeply to the northwest, fossil evidence indicates that the beds nearest Tolo Channel are dominantly Middle Devonian in age, whereas those adjacent to Plover Cove are of Early Devonian age. It is probable that a fault separates the Early Devonian succession from the Middle Devonian succession. The southern faulted contact adjacent to Tolo Channel appears to be a high-angle reverse fault. The Tolo Channel Formation is present only as fault wedges between the Devonian and the main offshore expression of the Tolo Channel Fault. To the north, the Early Devonian succession is faulted against the Jurassic Tai Mo Shan Formation, but in the northeast, the Middle Devonian sedimentary rocks are in faulted contact with the Cretaceous Pat Sin Leng Formation.


At Bluff Head, the cliffs provide the most complete sequence through the formation. The strata are structurally complex, with the bedding oversteepened and locally overturned adjacent to the southern faulted margin (Plate 3.2). To the north, the strata are tightly folded in a series of northnortheast-plunging anticlines and synclines (Plate 3.3). In places the dip decreases to as little as 30o, though a more normal angle is around 45o to the northwest. This is the only comprehensive section through the sequence and it is possible that the rocks are folded in a similar fashion along the entire peninsula.


In the vicinity of Ma On Shan, Late Devonian sedimentary rocks dip 30o to the southeast and form a succession at least 100 m thick. They were best exposed along a temporary road section excavated during site formation works for the Kwun Hang Water Treatment Works. Minor exposures of the Bluff Head Formation have also been reported from Wu Kwai Sha Tsui (Sewell, 1996). These sedimentary rocks have been correlated with the sequence at Harbour Island and are presumed to be Middle Devonian in age.




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