Abstract

The Lower Silurian Sayabec Formation represents a peritidal-dominated carbonate ramp that developed at the northern edge of the post-Taconian Gaspé successor basin. In the Late Silurian, during the Salinic disturbance, the Sayabec ramp was subaerially exposed locally. This could have lead to the formation of economically significant secondary dissolution porosity. A detailed diagenetic study of the Sayabec Formation was carried out at selected localities along the Northern Outcrop Belt in the Gaspé Peninsula, where the Salinic unconformity and hydrothermal alteration of the carbonate facies have been documented.

The diagenetic history consists of initial minor marine diagenesis (marine cements in boundstones and neptunian dykes) followed by pervasive burial diagenesis that resulted in the emplacement of various pore- and fracture-filling calcite cements, due to the mixing of basinal brines and hydrothermal fluids. Late Silurian tectonic exhumation of the lithifled carbonate ramp is recorded locally in meteoric-cement-filled fractures that were dissolution-enhanced after early burial. The significance of this event in generating porosity was relatively minor.

Preserved porosity is observed where limestone facies and calcite cements were completely replaced by hydrothermal saddle dolomite. However, the porous dolostone is of geographically limited extent. The hydrothermal event is mostly recorded in high-temperature calcite cements that occlude burial fractures.

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