ABSTRACT

Leaching in the limestones of the Bowan Park Group (Ordovician) is considered to have selectively dissolved fossils producing various types of fossil molds and possibly some irregular cavities. The tabulate coral Tetradium, a large, inarticulate brachiopod resembling Eodinobolus, the cylindrical labechiid stromatoporoid Alleynodictyon, and gastropods, are the principal fossils affected and it is tentatively suggested that they may have been composed originally of aragonite. Most of the other fossils in the sequence have their internal structure left intact, even when found in assumed leached horizons, and may have been composed of either high or low Mg-calcite.

The solution of limestone and the subsequent filling of cavities with sparry calcite (most common), diagenetic silt, pellets, sand-sized grains, and ?marine sediment altered the original fabric to one of the following: 1) fossil casts in limestone, 2) interconnecting spar-filled vugs in limestone, 3) mottled limestone, or 4) `Stromatactis' limestone. In general, the most common occurrence of solution effects is just beneath erosional surfaces, and is inferred to result from subaerial exposure.