Morphostratigraphy and facies architecture of sandy barriers along the Eastern Shore of Nova Scotia

Abstract

Linear southeast trending valleys along the Eastern Shore of Nova Scotia were initially formed by fluvial incision and subsequently scoured during Pleistocene glaciations. Estuarine and barrier sedimentation was initiated when the valleys were drowned during the marine transgression of the early- to mid-Holocene. This coast continues to experience transgression, due to relative sea-level rise of 35–40 cm per century. Eastern Shore barriers have formed under a wave-dominated regime. The modal wave is highly energetic, with a height of 1.5–2 m and a 9–10 s period. Tidal range is low mesotidal with maximum spring range of 2.1 m. Fluvial sediment supply to Eastern Shore estuaries is negligible. Four sandy barriers from the Eastern Shore exhibit erosional and progradational morphologies that result from differences in the balance between relative sea-level rise, sediment supply and depositional processes within coastal compartments. Morphological contrasts represent the cyclic nature of barrier and estuarine evolution along the Eastern Shore. During transgression, sedimentation commences with a unit of fine grained central basin deposits overlain by a bed of fine to medium, massive and cross-bedded flood-tidal delta sands. An erosional surface lies at the contact between the flood-tidal delta facies and the overlying nearshore facies of tabular and cross-bedded gravelly sands. In some cases, the nearshore unit may grade upward into a second, younger flood-tidal delta deposit that is in turn incised, and then filled by sandy channel fill facies. The tidal delta facies is overlain by beach sands at the seaward side and washover deposits on the landward side of the barrier. The uppermost facies in the sequence includes a composite unit of upper beach and dune sands. Where sediment supply is sufficient, a beach ridge plain will form, producing a composite barrier stratigraphy with transgressive and regressive elements.