Diagenetic evolution of a Late Silurian reef platform, Gaspé Basin, Quebec, based on cathodoluminescence petrography

Carbonate units of two facie of the platformal upper reef complex of the Late Silurian West Point Formation, Gaspé Peninsula, Quebec, were studied to decipher their diagenetic evolution. The two facies were a reef-margin facies and a back-reef to lagoonal facies. Under the light microscope, only three broad cement phases were recognized. In contrast, cathodoluminescence observation revealed seven distinct generations of cements and a plethora of additional diagenetic features such as fracturing, internal brecciation, sulfatization, and stylolitization. The first four generations of cement were early marine and confined to the reef-margin facies. The subsequent three cement generations evolved in shallow to deeper burial environments and affected the reef-margin facies and the back-reef to lagoonal facies. C and O stable-isotope data support these deductions. Fracturing, internal brecciation, stylolitization, sulfatization, and the generation of the latest cements occurred during compaction and postcompaction stages. Lithification of the facies was rapid, with the pores completely occluded before a maximum burial depth of about 1 km was attained (based on conodont colour-alteration indices, organic-matter maturation data, and overall post-Silurian paleogeography).