Lai Chi Chong EarthCache
Hidden : 6/16/2010
Difficulty:
1 out of 5
Terrain:
2 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:


Lai Chi Chong (荔枝莊) – Earth forces and rock strata
(Given coordinate refer to Lai Chi Chong Pier)

*** Recommend to visit during low tide (visit link) ***

Lai Chi Chong located in Sai Kung West Country Park, along to Tolo Channel (赤門海峽) Geo Area, and belong to Hong Kong Geo Park / Hong Kong National Geopark & National GeoPark of China nowadays.
A Lai Chi Chong Geo Trail also established for guide the area, on the shore west of the ferry pier, there is an expanse of thick layered rock with distinctive folds (摺曲), faults (斷層) and bedding (層理). This interesting feature makes Lai Chi Chong an ideal site for geological study. The 5-hectare rock flat was decided of Site of Special Scientific Interest in 1985.

In this region of modest size you can find rocks that are directly related to volcanic activities, as well as different volcanic sedimentary rocks (火山沉積岩). It is also a good place to observe clearly visible and easily identifiable sedimentary composition. It is a striking sight at low tide when the rocks are vastly exposed.

The Lai Chi Chong Formation consists of tuffaceous sandstone (凝灰質砂岩), siltstone(粉砂岩), mudstone and conglomerate (礫岩), as well as rocks directly related with volcanic activities like coarse crystal tuff, fine tuff and porphyritic rhyolite (班狀流紋岩). Volcanoes spewed out heavy volcanic ash and pyroclastic flows which cooled and turned into to tuff. When eruptions ceased, airborne silicon dioxide precipitated with rainfall and settled under water form black silicon chert beds (燧石岩床). There uniquely coloured rock beds, alternating with lighter shade volcanic siltstone, formed volcanic sedimentary rock bed of bold colour contrast. Given intermittent yet dramatic environment changes, these black rock beds vary in thickness, ranging from 10cm to nearly 1m. Occasionally you can detect plant fossils within.

At the seaside by the ferry pier, clearly twisted rock bed can been seen at low tide. Known as folds in geology, these bucking structures are distortions. Fold come in two forms: anticline folds with a swelling centre, and syncline folds which are concave. Both types are generally in continuous alternate patterns, and the folds bands vary in size.

Bedding of the Lai Chi Chong Formation are extremely well developed. These layered structures of sedimentary rock have come into being through variations of colour, grain size, composition and structural vertical orientation. By observing the beddings, you can understand the sedimentary environment and water movement, and at the same time tell whether the attitude of stratum has ever overtuned. Along the Lai Chi Chong coast, you can see graded bedding where the grain size of rock composites changes from coarse in the lower layers to fine in the upper layers. Also present here are current beddings which are formed by water currents flowing at different directions at different times, and convolute bedding in which sediment lamina is bent into folds and cut off by the rock beds on top.

To honor the found log, please email the following to cache owner
- Please estimate the age Lai Chi Chong's geological age
- Please describe the cause of the Convolute bedding (Folds)
& please include a photo with a convolute bedding (folds) of Lai Chi Chong with your GPSr to claim your visit.

Public transport information
Land
By green minibus no.7 from Sai Kung, get off at Pak Sha O, and hike to Lai Chi Chong (visit link)

Sea
By ferry from Ma Liu Shui (University MTR Station)
Ferry timetable (Route 2) (visit link)

*** When exploring, look out of sharp stones and avoid loose, slippery or uneven rock surface to prevent accidents. It is offence to chisel, dig or collect any rocks. ***

Bibliography/Reference
KM Yeung / CY Ng - "Landmark Excursionsz - Agriculture, Fisheries and Conservation Dept / Friends of Country Parks / Cosmos Books Ltd. – 2008 – ISBN 9789882113596
Hong Kong GeoPark (visit link) (visit link)

Additional Hints (No hints available.)



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