Spatial variation of sediment components in the marine deposits of Hong Kong

The continental shelf of Hong Kong is generally less than 25m deep and is characterized by an extensive blanket marine mud, interrupted locally by sandier deposits associated with tidal channels and areas exposed to high wave energy. The mud blanket is often considered to be uniform in its sedimentology. However, this study has shown that there are distinct, though often subtle, variations in composition and sedimentation rates. Organic matter ranges between 2 and 32%, with most samples containing between 5 and 15%. Carbonate generally comprises 2-25% of the mud, though local coquinas also occur. Biogenic silica is a minor component, with diatoms and sponge spicules dominating. Species diversity and abundance show clear spatial variation. Particle size trends are subtle but distinct. Sedimentation rates reported here range between 0.17 and 0.51cm/a. Attempts to date sediments failed in western Hong Kong, possibly because of bioturbation effects.

香港沿岸的大陸架一般少於25米深，架上被大量海泥覆蓋，只有在潮汐通道或受能量高波浪影響的地區才間中有沙質沉積物。從沉積物學的觀點而言，覆蓋在大陸架上的海泥沉積規律變化不大。但這個研究發現，沉積物的成分及沉積率展示明難以察覺的差異。沉積物中有機物成份約在2-32%之間；而大部分樣本則在5-15%之間。海泥中的碳酸鹽含量約在2-15%之間，間中亦發現有貝殼類物質。此外，海泥中亦發現少量含有硅藻及海綿的生源硅。這些生物的種類及數量有明顯的空間差異，顆粒大小變化不大但很突出其沉積率在每年0.17至0.51厘米之間。可能受到生物混濁效應的影響，在香港西部地區收集的沉積物未能通過年份檢定。