ABSTRACT

Rhizoliths from the Pleistocene Ironshore Formation are formed of a brown micrite core surrounded by sediment that is well cemented with 1) calcite rhomb chains, 2) isolated calcite rhombs, 3) calcified spherical bodies, 4) Types I and II calcified epilithic and chasmolithic filaments, and 5) grain-coating calcite needle mats. The friable host sediment has significantly less cement and lacks the grain-coating calcite needle mats and Type II calcified filaments of the rhizoliths. The sediment, however, contains calcite needles and a cryptocrystalline cement which do not occur in the rhizolith.

The contrast in the amount and type of cement between the rhizoliths and the encasing sediment points to the significant role that plants can play in carbonate diagenesis. Not only do the plant roots act as conduits for water of varying composition, they also provide sites at which algae, fungi, and bacteria thrive. These microorganisms serve to promote diagenesis in the rhizoliths. The occurrence of the sediments in a coastal setting means that they are subjected to many different types of water ranging from freshwater to saltwater. Such variability along with the associated changes in the water chemistry may be responsible for the considerable variation in the cement associated with the rhizoliths.