Abstract

Fluvial channel bodies in the Pennsylvanian Sydney Mines Formation are contained within high-frequency sequences that represent relative sea-level fluctuations, linked to climate change, on a gently subsiding craton. Channel-body style within coastal-plain deposits was controlled by sea-level transit cycles, modulated by climate and substrate resistance. Coarse bed-load systems are deeply incised, multi-storey bodies up to 30 m thick. Some represent valleys backfilled during late lowstand and transgression, probably under a humid climate. Sinuous channel systems display well developed lateral accretion surfaces and ridge-and-swale topography. Distributary systems are narrow channel bodies that cut bayfill deposits. These two groups lie within highstand deposits, and represent the readvance of coastal rivers following maximum transgression. Sand-flat systems consist of plane-bedded sand sheets and downstream-accreting macroforms, laid down under ephemeral flow conditions, adjacent to deep sinuous channels. They are interpreted as channel and valley fills generated during late highstand, falling stage, and lowstand under a strongly seasonal climate. Calcrete caps on some sand-flat bodies suggest that they filled prior to the main lowstand phase of paleosol development. A complex relationship is apparent between channel or valley fills and mature paleosols that bound sequences. Resistant substrates (coals, indurated limestones) influenced channel-body geometry by promoting lateral expansion and localising incision.

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