Abstract

The paleogeographical setting, sequence stratigraphy, and timing for six Tertiary brown coal deposits along the southern seaboard of Australia indicate a concentration of major coal-forming phases to periods of significant coastal onlap coupled with frequent sea level oscillations.

Structural settings for thick seam development include grabenlike depressions adjacent to a major basin, embayments often barred from the main marine basinal sedimentation by a barrier sand buildup across the entrance, and paleovalleys incised into hard rock. A correlation also occurs between thick brown coals and warm-temperate to subtropical climatic conditions with evidence for multicyclic stacking of raised mires and ombrotrophic conditions similar 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 sequence cycles TB2.1 to TB2.3 (15.5 to 21.0 Ma).

Knowledge of the timing and disposition of coaly rocks provides useful information to the petroleum explorationist regarding source potential and distribution within these time periods.

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