Volcaniclastic sedimentary rock － Lai Chi Chong

Volcaniclastic sedimentary rock － Lai Chi Chong

Background Information

On the southeastern shore of Tolo Channel in the Eastern New Territories, a set of Early Cretaceous volcaniclastic sedimentary rock strata called Lai Chi Chong Formation are distributed around rural Lai Chi Chong and nearby coastal areas. They are “younger” than the sedimentary rock of Ma Shi Chau but “older” than that of Tung Ping Chau. Research has shown that this region has rather complicated geological setting and rock types, with Mesozoic volcaniclastic sedimentary rocks, tuff, rhyolite and Paleozoic sedimentary rocks occurring locally. The uneven stratum on the foreshore near the Lai Chi Chong pier is volcanic ash sedimentary rock. Displaying very distinctive foldings, faults and bedding structure, it is an ideal location for geological study.

Geological Information

Major outcropped sections of Lai Chi Chong Formation can be found on the beach west of Lai Chi Chong pier. Although less than 200m wide, these sections manifest extremely complicated rock properties that include tuffite ,tuffaceous sandstone, siltstone, coarse ash crystal tuff, eutaxitic fine ash tuff and porphyritic rhyolite in current bedding. Bedding development is excellent with a wealth of visible sedimentary structures, such as current bedding, graded bedding, convolute bedding and subaquatic slump. Signs occurring from folding, fault and discordance of strike directions are also clearly noticeable.