A review of Tertiary brown coal deposits in Australia - Their depositionalfactors and eustatic correlations

The paleogeographical setting, sequence stratigraphy, and timing for six Te rtiary brown coal deposits along the southern seaboard of Australia indicat e a concentration of major coal-forming phases to periods of significant co astal onlap coupled with frequent sea level oscillations. Structural settings for thick seam development include grabenlike depressio ns adjacent to a major basin, embayments often barred from the main marine basinal sedimentation by a barrier sand buildup across the entrance, and pa leovalleys incised into hard rock. A correlation also occurs between thick brown coals and warm-temperate to subtropical climatic conditions with evid ence for multicyclic stacking of raised mires and ombrotrophic conditions s imilar to the modern tropical peats of Indonesia. Common periods for thick seam development can be tied to the Exxon coastal onlap charts in the late middle Eocene and late Eocene sequence cycles TA3. 5 to TA4.3 (36.0 to 42.5 Ma) and the late early to early middle Miocene seq uence cycles TB2.1 to TB2.3 (15.5 to 21.0 Ma). Knowledge of the timing and disposition of coaly rocks provides useful info rmation to the petroleum explorationist regarding source potential and dist ribution within these time periods.