Occurrence and preservation of Eocene squamariacean and coralline rhodoliths: Eua, Tonga.

Abstract

Outcrops of Middle Eocene platform limestones on Eua, Tonga, contain mixtures of squamariacean and coralline rhodoliths. Squamariacean rhodoliths from these outcrops are composed of a single algal species and are less frequently encrusted or bored than coralline rhodoliths from the same outcrops. Both coralline algae (originally composed of magnesian calcite) and squamariacean algae (formerly aragonite) are now low-magnesian calcite and both were presumably altered during exposure to fresh water. Surprisingly, microstructural detail is better preversed in the squamariacean rhodoliths than in coralline rhodoliths. -Authors