Report No. : GEO Report No. 356

Report Title : Updating of Hong Kong Geological Survey 1:20,000-scale Maps Major Findings and Revisions Map Sheet 6 - Yuen Long (2022), 67 p.

Author : K.W.F. So & R.J. Sewell

Abstract

There have been new data available since the first edition of 1:20,000-scale geological maps were surveyed and published by the Hong Kong Geological Survey of the Geotechnical Engineering Office. Consequently, the Hong Kong Geological Survey Section of the Planning Division has embarked on a programme to update the 1:20,000-scale maps and to release them in both printed and digital forms. This programme will make these geological maps more easily accessible to the public, and more useful to engineers and planners.

The map updating work is being digitised on a GIS platform using a standard GIS template, and the maps are being published and disseminated in ArcReader format.

Sheet 6 - Yuen Long is the fourth map updated under the programme. The first edition of Sheet 6 was surveyed between 1984 and 1987, and was published in 1988. Reliability of the geological maps has been improved after incorporation of the vast amount of new information that has accumulated over the past thirty years, and advances in the understanding Hong Kong's geology since the published maps were first surveyed.

The key findings and revisions to Sheet 6 are described in this report. They include: new interpretation of the solid geology covered by superficial deposits, revision of the stratigraphy of the Carboniferous San Tin Group, reassignment of sedimentary units to Jurassic formations, revision of the nomenclature and classification of volcanic stratigraphy and intrusive rocks, improved accuracy of the alignment of concealed major faults and geological boundaries, revision of a fold model, revision of the type and extent of metamorphism, reinterpretation of onshore and offshore superficial deposits, and updating of the reclamation history. A whole-territory geodatabase has been developed, within which geological data of various aspects are arranged in multiple GIS data layers. A further major improvement is the addition of a solid-only GIS layer, which includes the first interpretation of the offshore solid geology based on geophysical and borehole data, and a large number of additional GIS layers containing geological and related information.

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