Graptolite Reflectance and Thermal Maturity of Lower Paleozoic Rocks

Abstract Structured marine - derived organic matter such as algae, chitinozoa, graptolites and scolecodonts are common in lower Paleozoic sediments, while vitrinite is sparse or absent. Systematic studies of the optical properties (%Rair max, % Roil max’ refractive and absorptive indices) of graptolite epiderm at 546 nm and also dispersion in visible light at 400-700 nm show progressive changes similar to those undergone by vitrinite with increasing rank. This increase of graptolite reflectance with increasing maturity is related to an increase in the condensed aromatic carbon within its structure. Graptolite reflectance, similar to vitrinite, is sensitive to changes in lithology, weathering, tectonism, hydrothermal mineralization and depth of burial (temperature).