SEDIMENTOLOGY OF THE BOSS POINT FORMATION (PENNSYLVANIAN), CUMBERLAND BASIN, NOVA SCOTIA

The 1,144-m-thick Boss Point Formation (Pennsylvanian) was deposited in the Cumberland Basin of Atlantic Canada. Although the type section comprises ~25% of the stratigraphic thickness of the Joggins Fossil Cliffs UNESCO World Heritage Site, significant portions of this unit have not been studied in detail. Previous studies focused on the alternating braidplain and lacustrine/deltaic cycles in the middle part of the formation and ignored the redbed-dominated intervals in the upper 234 m and lower 80 m. This study represents the first analysis of the entire thickness of the Boss Point Formation at the type section; we provide new information about depositional environments, the nature of cyclicity, and the first detailed measured section through the entire formation.

The Boss Point Formation is dominated by multistory sandstone channel bodies (57% of total formation thickness; average = 41 m thick) separated by fine-grained packages of floodplain and lacustrine strata (43% of total thickness; avg. = 24 m thick). Channel bodies are dominantly composed of fine- to medium-grained sandstone. Conglomeratic lags define stories that are 10-15 m thick; lags are composed of intra- and extraformational clasts and transported logs. Well-drained floodplain deposits make up the majority (66%) of the exposed, non-channel facies (19% of total thickness; 212 m total). These intervals are composed of red to reddish-brown, blocky to platy mudrocks, rare micritic limestone, and scattered calcareous paleosols. Redbeds are particularly abundant in the undescribed parts of the formation. Poorly drained floodplain deposits comprise 24% of the exposed, non-channel facies (6% of total thickness; 78 m total). They occur as 5-10 m thick packages of gray to gray green, blocky to platy mudrocks within scattered organic-rich horizons and a single 0.06 m thick coal bed. Lacustrine facies comprise 10% of the exposed non-channel facies (3% total thickness; 30 m total); they are composed of gray/black shale, blocky to platy gray mudrocks, and organic-rich limestones.

The redbed-dominated intervals at the top and bottom of the formation record the transition into, and out of, typical cyclic Boss Point facies. The abundance of redbeds within the type section may record a paleotopographic high atop the salt-cored Minudie Anticline.