Thermal maturity of Cambrian to Devonian rocks of northeastern Ellesmere Island

Abstract

Conodont Colour Alteration Index (CAI) values were obtained for 143 conodont collections derived from Upper Cambrian through Lower Devonian strata. The results provide a useful analysis of thermal maturity conditions over the entire report area. Thermal maturity conditions recorded by CAI values in lower Paleozoic rocks of the report area are attributed to depositional loading associated with the accumulation of foreland clastic sediments in the Middle and Late Devonian, and related tectonic loading that ended in the Early Carboniferous. The fore- land wedge is partly preserved on central and southern Ellesmere Island but has been entirely stripped from the report area. The steep thermal maturity gradient associated with the top of the oil window can be explained by dif- ferential loading of the crust during an ancestral phase of slip on the Rawlings Bay Thrust and Judge Daly Fault Zone in Middle Devonian to Early Carboniferous time. The differential load was proportionately greater to the northwest as a consequence of down-to-the-northwest slip on the linked ancestral fault sys- tem. Subsequent vertical displacement on the Rawlings Bay Thrust may be almost 10 km.