Cross-shelf colour zonation in northern Great Barrier Reef lagoon surficial sediments

A cross-shelf colour zonation is observed in Great Barrier Reef lagoon surf icial sediments from 12 to 18 degreesS, with colours tending to lighten fro m inner to outer shelf. The phenomenon is particularly well defined south o f Cairns where four zones occur. The colour zonation appears to reflect the abrupt facies changes that occur in the lagoon. Visual estimates of relati ve optical lightness for the zones are strongly related to carbonate conten t, and lightness class boundaries broadly follow carbonate contours, indica ting that the mechanisms leading to the colour zones are related to those g overning carbonate distribution.