Rock formation at Lung Lok Shui at Ping Chau

Abstract

The major type of rocks in Ping Chau Island are bedded dolomitic and calcareous siltstone. Lung Lok Shui is a cherty layer and it is rare in Ping Chau. The rock formation at Lung Lok Shui has been a debatable issue. There are three hypotheses to explain its formation and no consensus have been reached so far. The hypotheses of its rock formation include forming by a big bombard from a meteor, acid rain occurred due to super volcanic eruptions causing the increasing of the solubility of silica and dissolution of silica by hot spring through hydrothermal process. The third hypothesis is more reasonable for the formation of Lung Lok Shui. It is believed that the heat flow was derived from the hot spring which was forming by volcanic activities in South China Sea during Palaeogene. The objective of this study is to examine the possible formation of cherty layer. By studying the relevant literature view on geological background of Ping Chau, tectonic setting of Southeast China and Ping Chau Formation to determine the related tectonic setting and depositional environment for the formation of Lung Lok Shui. Also, this research focus on studying different types of cherts and their origins to determine the origin of Lung Lok Shui. The volcanic activities in South China Sea will also be studied to analyze whether the volcanic activities could influence the formation of Lung Lok Shui. Apart from that, field observation will be included in the methodology. A rock sample is collected from Lung Lok Shui to analyze the mineral compositions and microstructures by carrying on thin-section examination. It is concluded that Lung Lok Shui was non-marine chert which formed in the lacustrine environment in alkaline lake water by chemical precipitation. Lung Lok Shui was formed by the hydrothermal fluid derived from hot spring. The hot springs were developed by the volcanic activities in South China during Palaeogene. It is believed the heat flow was derived from the volcanic activities and it dissolved the silica and formed a rich silica layer above the unconsolidated siltstone. It is possible that the heat source derived from the volcanic activities in the northern South China during Paleocene.