Sequence stratigraphy of the Late Permian Coal Measures in the Sydney Basin

Abstract

In the Late Permian Newcastle, Tomago and Illawarra Coal Measures of the foreland Sydney Basin, eight 3rd‐order depositional sequences form three sequence sets. The sequence sets constitute the highstand systems tract of a 2nd‐order sequence. Up‐sequence decreasing marine shale thickness and increasing incised‐valley‐fill thickness, coupled with an overall regressive trend from marine to dominantly alluvial environments, indicate that sedimentation was influenced by 3rd‐order relative sea‐level cyclicity superimposed on 2nd‐order falling relative sea‐level. The correlation of sequence boundaries and their overlying incised‐valley‐fills from well to well across the basin implies repeated basin‐wide relative sea‐level falls (involving uplift and/or eustatic sea‐level falls). Angular unconformities coincident with the Sequence D, Sequence E, and end‐Permian sequence boundaries indicate periods of accelerated structural movement during relative sea‐level falls. Basin‐wide coal seams were formed at the top of the lowstand systems tract from peat growing above 3rd‐order incised‐valley‐fills and on interfluves. In this foreland ramp basin, thick coal‐bearing coastal plain facies developed landward of relatively thinner marine facies as a result of faster subsidence rates in the landward direction.