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The scene was very curious and rather pretty; its beauty, however, entirely depended on the brilliancy of the surroundng colours. The shallow, clear, and still water of the lagoon, resting in its greater part on white sand, is, when illumined by a vertical sun, of the most vivid green. This brilliant expanse, several miles in width, is on all sides divided, either by a line of snow-white breakers from the dark heaving waters of the ocean, or from the blue vault of heaven by the strips of land, crowned by the level tops of the cocoa-nut trees. As a white cloud here and there affords a pleasing contrast with the azure sky, so in the lagoon, bands of living coral darken the emerald green water.
Charles Darwin (Voyage of the Beagle, 1860)


Justification for a separate chapter on the subject of ichnology of marine carbonate - as opposed to terrigeneous - sediments lies in the nature of carbonate grains and the environments in which they are produced, cemented and destroyed. The special properties of carbonate substrates and carbonate depositional environments are reflected by the characteristic trace fossils in several ways. In most respects, however, the ichnology of the shallow marine carbonate environments resembles that of their physical equivalents for terrigeneous sediments (see Chapter 15). The emphasis of this chapter is on carbonate systems of the warmer seas; those of temperate regions are more elastic in nature than their warm-water equivalents, and their ichnology has received little attention.

Aspects of ichnology that are peculiar to carbonate environments belong in three general categories: (i) bioturbation and burrows; (2) pellet formation; (3) bioerosion of carbonate grains (including miente envelope formation), of beachrock and coasts, and of hardgrounds and reefs.

Unbioturbated sediments of beach and restricted subtidal environments tend to be strongly laminated. Thus, the presence of any burrows within the fabric is conspicuous, as also is the complete destruction of the lamination by total bioturbation when it occurs. Absence of bioturbation is much more common, as it is in the same environments in the terrigeneous realm, and usually this may be accounted for by either physical reworking of the sediments or lack of benthos.

In high-energy settings, physical reworking of sediment and the concomitant deposition of thick, single-event units, are frequent and tend to obliterate

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