Chitinozoan, graptolite and organic-rich immature Upper Ordovician mudstone was artificially matured using closed hydrous pyrolysis. The pyrolysis was performed at isothermal temperatures of 310-350 degrees C at 10 degrees C increments for 72 h. This temperature range simulates the subsurface thermogenic hydrocarbon generation window based on previous laboratory simulations. The objectives of this study are to (a) qualitatively and quantitatively assess the degree of physicochemical transformation of dispersed organic matter (DOM) and zooclasts in BRF petroleum source rock after artificial maturation; and (b) determine the relationship between graptolite, chitinozoan, vitrinite-like particle and bitumen reflectance (R-o) with increasing pyrolysis temperature and the thermal maturity. Petrographic analysis shows that bituminite and amorphous kerogen were the first organic macerals to thermally decompose after the first pyrolysis temperature. This is followed by liptodetrinite, thin-walled alginite, acritarch, and telalginite as pyrolysis temperature increases. Concurrently, the fluorescence properties of the telalginite shifted from greenish yellow to reddish-orange after the last stage (350 degrees C) pyrolysis. In addition, significant amount of bright fluorescing labile hydrocarbons produced during pyrolysis were observed oozing from pore spaces and on the surface of the rock matrix. Pore -filling, orange to reddish-orange fluorescing solid bitumen were also found in pores spaces created by the thermal decomposition of DOM. The lack of morphological evidence for the thermal decomposition of chitinozoans and graptolites suggests that these zooclasts macerals may have limited or have no contribution to the overall hydrocarbon generation. Nonetheless, their respective reflectance (R-o) increased (0.64% to 1.34% and 0.55% to 1.38%) as the pyrolysis temperature was increased. These R-o values are significantly higher than the vitrinite-like particles (0.49% to 1.07%) and solid bitumen (0.30% to 1.09%). The measured RocK-Eval T-max and solid bitumen vitrinite reflectance equivalent (VRo-eqv) are comparable to the average vitrinite-like particles. The relationship between rate of increase in chitinozoan and graptolite, and vitrinite-like particles R-o, expressed by the equations: Ro-vit-like = 037 R-chi and Ro-vit-like = 0.79 R-grap are comparable to those observed in geologically matured source rocks.