Petrology of selected carbonaceous limestones and shales in Late Carboniferous coal basins of Atlantic Canada

Abstract

Carbonaceous limestones and shales are associated with coal in Late Carboniferous alluvial to coastal successions of Nova Scotia. The units are thin (< 2 m) but well indurated, and some can be traced for >45 km. They consist of micrite and/or illitic and kaolinitic clay, and some contain abundant bivalves, ostracodes, pyrite (up to 11 vol.%), and phosphatic and sideritic nodules. Trace fossils are scarce to absent. The organic material (2–43% TOC) is characterised as type II/III, and is mainly of terrestrial derivation, predominantly vitrinite and sporinite with lamalginite and telalginite as minor constituents. Vitrinite reflectance measurements indicate immaturity ( R o < 0.5%) but are lower than those of associated coals. Source rock and hydrocarbon recovery potentials are good to very good, and the potentials of some units compare favourably with those of alginite-rich Carboniferous oil shales in adjacent basins. The carbonaceous units were deposited in shallow lakes and/or interdistributary bays with aerobic to anaerobic bottom waters, at times of minimal detrial input.