Hong Kong Geology Guide Book Geotechnical Engineering Office ...

Cape Collinson Road, Siu Sai Wan, Hong Kong Island
Chapter 14 – Tuff-breccia and Rhyolitic Crystal Tuff – Che Kwu Shan
Formation (II)
Introduction
The Che Kwu Shan Formation, part of the Repulse Bay Volcanic Group, was
considered to have been deposited by a hot rhyolitic volcanic ash flow (Sewell et al.,
2000). In addition to a streaked appearance that resulted from welding of the very hot
crystal ash particles, the Formation
also comprises a large volume of tuffbreccia.
Along the eastern side of
Hong Kong Island, tuff-breccia and
rhyolitic crystal tuff are common in
coastal outcrops to the east of Cape
Collinson Road, Siu Sai Wan. These
various rock types were previously
assigned to the Shing Mun Formation
by Strange & Shaw (1986). However,
based on U-Pb isotope age dating,
major and trace element geochemistry,
petrographic properties and
stratigraphic relationships, Campbell
& Sewell (1997) later defined the Che
Kwu Shan Formation, which mainly
crops out in the vicinity of the Clear
Water Bay peninsula. However, the
Geological reconnaissance map of Cape Collinson
outcrops near the Cape Collinson
Correctional Institution appear to
differ in several respects from those at Silverstrand Bay, Clear Water Bay peninsula,
which have been assigned to the same Formation. The differences may be due to
variations in depositional processes during volcanic eruption.
How to Get There
The rocks of the Che Kwu Shan Formation are well-exposed along the coast to the
north of the Cape Collinson Correctional Institution. However, the rock cliffs are very
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