Provenance of seashore sediments of the Wu Kai Sha Tsui, Hong Kong : a petrographic study of sand grains

Abstract

Eight sediment samples were collected along the seashore of Wu Kai Sha Tsui, Hong Kong. They were molded into thin sections for investigation of the mineral compositions and lithic fragments under a polarizing microscope. In addition, roundness and undulatory extinction were adopted to study the thin section samples. The main purpose for the study is to identify the source region of the sediment samples in the area. The test results of the samples are shown in detail in Table 1a and 1b. The high feldspar content generally infers that the depositional basin is close to the source of the sediments, and the depositional rate is relatively high. The test results for roundness exhibit that much higher percentages of the angular and subangular sand grains exist in comparison to the percentage of round and subrounded grains. These results also support the foregoing inference for a high depositional rate. The quartz content of the eight sediment samples is high, and therefore, the mineralogical maturity and stability of the study area is thought to be high. The high ratio of quartz to feldspar implies that the source region of the rock is granite, and the high ratio of K-feldspar to plagioclase also indicates that the source region of the sediments was exposed in a humid climate. By means of adopting the undulatory extinction method, it identifies that both the low-rank metamorphic and plutonic regions existed. Furthermore, the ternary diagrams of provenance analysis show that the sediments in Wu Kai Sha Tusi originated from sialic crust (i.e. continental block and recycled orogeny).