Floral Influences on the Petroleum Source Potential of New Zealand Coals

New Zealand coals range in age from Cretaceous to Miocene and represent a wide variety of mire floral communities. Chemical and petrographic analysis demonstrate considerable variability in coal properties, and particularly vitrinite chemistry. Although some chemical variability can be attributed to environmental controls such as mire drainage and marine influence, other trends correspond with age, climate and floral assemblage.Mire flora is primarily reconstructed using palynological analysis. Cretaceous and Eocene coals are dominated by gymnosperm and angiosperm pollen respectively. Paleocene sequences exhibit large fluctuations in mire flora and provide ideal sample sets for investigation of potential floral controls on petroleum source potential.Proximate analysis, specific energy, sulphur, palynology and Rock-Eval data presented for 36 coals demonstrate a general increase in petroleum source potential with increasing angiosperm palynomorph dominance. Notable exceptions are coals from immediately beneath the Cretaceous/Tertiary boundary at Greymouth Coalfield, which have moderate to high Rock-Eval yield despite very low angiosperm palynomorph abundance.Pyrolysis-gcros of 3 Paleocene and 2 Cretaceous samples shows generally good oil generative potential, particularly for perhydrous coals. Stepwise pyrolysis-GCMS and bulk kinetic parameters indicate that angiosperm derived coals may generate oil at slightly lower temperatures than gymnosperm derived coals. This difference in generation temperatures is small, however there is evidence that current kinetic models do not account for rank variation in the immature analogues used to predict generation histories. Consequently, actual generation temperatures may be significantly underestimated, and the difference in generation temperatures for gymnosperm vs angiosperm derived coals may be more significant, than current models suggest.