Surface sediments from 120 locations surrounding the Arlington Reef Complex of the Great Barrier Reef of Australia were examined to determine the types and relative abundances of microborers present, to describe the morphology of their excavations, and to plot and interpret their distributional patterns.

The most widespread and abundant microborings found within carbonate particles were those produced by fungi, which appear to be among the first endolithic organisms to attack skeletal debris. A characteristic branching red(?) alga was found to be most abundant at depths in excess of 60 ft (18 m), although it was not restricted to these depths. However, a distinctive endolithic sponge was found only at depths below 60 ft (18 m) and may prove valuable as a paleoecologic guide.

An 8- to 10-μ green alga actively infests carbonate particles of the interior reef platform to depths as great as 100 ft (30 m), although it is generally more abundant at shallower depths. This endolithic alga serves both as a photic zone indicator and sediment tracer within the study area. Its distribution within sediments indicates that net transport is landward from the interior reef platform with little or no sediment being carried seaward. Southward movement of platform-derived sediment along the back-reef axial channel is also suggested.

Endolithic organisms were observed to infest preferentially molluscan fragments, thereby selectively removing them from the carbonate fraction. The distribution and spatial relationships of endolithic organisms within Arlington Reef Complex sediments suggest that microborers may be useful as relative depth indicators in recent, and possibly ancient, carbonates.

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