THERMAL MATURITY OF LOWER PALEOZOIC SEDIMENTARY SUCCESSIONS IN ARCTICCANADA

Mean maximum graptolite reflectance values from numerous sections in A rctic Canada range from 0.6% in Cornwallis Island and northwestern Dev on Island to 4.7% in Ellesmere Island. Me attribute this great lateral reflectance variation to differing burial depths of the graptolite-be aring strata beneath thick synorogenic siliciclastic covers. Me attrib ute the low maturity of rocks in northern Cornwallis and eastern Bathu rst islands to a maximum burial of about 2 km. Elsewhere, we used the paleogeographic location and proximity to the Ellesmerian overthrust w edge to interpret the measured reflectance values. In northern Ellesme re Island, where the highest graptolite reflectance values (4.7%) occu r, as much as 9.6 km of synorogenic siliciclastics accumulated on a te ctonically loaded carbonate shelf. Initial synorogenic siliciclastics encountered substantial submarine-to-basin relief, and thus about 2 km of sediment were deposited prior to the initiation of deposition on t he adjacent drowned shelf. Also, the deep-water sequence probably was underlain by attenuated continental crust adjacent to the southeastwar d-advancing Ellesmerian overthrust wedge. Together, these factors caus ed deposition of as much as 7.6 km of sediment in western Melville Isl and and, as much as 9.6 km in northeastern Ellesmere Island. On the dr owned shelf, synorogenic stratal thicknesses were legs, a feature we a ttribute to a thicker, more rigid crustal sequence and greater distanc e from the Ellesmerian tectonic loading. We expect liquid hydrocarbons to be generated from the organic matter in the shales in areas with a graptolite R(o), maximum (GP(o) max) of less than 1.7%. The presence of two types of solid bitumens having different reflectances, morpholo gies, and optical textures suggests that hydrocarbons were generated a nd migrated through the graptolite-bearing strata. Me expect only gase ous hydrocarbons in areas where GR(o) max exceeds 2.0% R(o).