Martin Gibling¹
(1) Dalhousie University, Halifax, NS

Abstract: Sequence framework for the Upper Carboniferous Sydney Coalfield, Atlantic Canada

The Sydney Mines Formation comprises twelve sequences that probably reflect glacioeustatic events in a low-subsidence setting. Strata change upward from mainly coastal to alluvial. Sequence boundaries are marked by mature calcretes or calcic vertisols, and the maximum flooding surface (MFS) lies within dark limestones or shales above major coals. Five lower sequences 8-30 m thick are dominated by the highstand systems tract (HST) with minor coals: the MFS is virtually coincident with the sequence boundary in several sequences. However, the transgressive systems tract (TST) is prominent in the thickest sequences, which commence with alluvial strata (well-drained paleosols and splays) that pass upward into relatively thick coals. We infer that high-accommodation events promoted floodplain storage in coastal rivers and peat accumulation in wetlands. Immature calcic paleosols underlie sequence boundaries in several sequences, and may represent the effects of forced regression. Three higher sequences are thicker (~70 m) and have similar stratal patterns to those below, but are dominated by alluvial redbeds. The coals represent rare highstands that inundated this landward setting. Although thick redbeds may indicate floodplain storage during transgression, we suggest that the alluvium lay landward of most transgressive influence and passes basinward into multiple thin sequences, such as those lower in the formation. Coal maceral assemblages resemble those of lower delta plains elsewhere, and change little through the formation.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana