Chitinozoan, graptolite, and scolecodont reflectance as an alternative to vitrinite and pyrobitumen reflectance in Ordovician and Silurian strata, Anticosti Island, Quebec, Canada

Because of the absence of vitrinite in lower Paleozoic sediments, the reflectance of pyrobitumen is used as an indicator of thermal maturation. A new technique of preparing organic matter permits discrimination among types of zooclasts and solid bitumen, including pyrobitumen, and leads to more precise reflectance-histograms. Studies of organic matter from Ordovician-Silurian strata of Anticosti Island show that reflectance of zooclasts is different from that of solid bitumen, and that each group of the following zooclasts, chitinozoans, graptolites, and scolecodonts, has a specific reflectance evolution path with increasing depth. On a logarithmic scale, the paths of the three groups of zooclasts are linear, highly correlated, and converging. However, reflectance of solid bitumen is not linear throughout the range studied; solid bitumen becomes linear only where the reflectance is greater than 0.75%. Comparing the relations between zooclasts and solid bitumen with the vitrinite-solid bitumen correlation in the literature suggests that a hypothetical vitrinite evolution line in the Anticosti Island basin should be subparallel with that of chitinozoans and graptolites, but 0.4-0.8% lower, in the 1-2% range. However, scolecodonts and vitrinite should have the same reflectance at 1%, but scolecodont reflectance should be slightly (0.2%) higher for a vitrinite reflectance of 2%.