ABSTRACT

Stromatactis calcilutite mounds from Upper Silurian rocks of Gaspe Peninsula, Quebec, Canada. are important constituents of a reef complex in the southern part of the peninsula. They reach thicknesses up to 115 m and had paleoslopes of about 40°. Stromatactis constitutes up to 30 percent of the rock volume. The microfacies of the calcilutite consists of agglomerates of pelletlike bodies forming a pelletoidal network surrounded by uniform mudstone. Sponge spicules are ubiquitous. By analogy with textural features of a well-documented sponge, Malumispongium hartnageli (Clark 1924) which occurs slightly above the mounds. it is suggested that the pelletoidal network of the mound calcilutite represents a former sponge network that underwent very early dingenetic change and cemen ation. Stromatactis would have originated as early marine cementation of growth cavities in the sponge network and of cavities created by decay of local uncemented sponge tissues.