Stratigraphy and sedimentology of the Pennsylvanian Grande Anse Formation, Cumberland Basin, eastern Canada: its relationship to salt tectonics and coeval strata of the Joggins World Heritage Site

Abstract

The Cumberland Basin is one of several sedimentary basins comprising the late Paleozoic Maritimes Basin complex of eastern Canada. Pennsylvanian salt tectonics in the Cumberland Basin caused two salt mini-basins to evolve either side of the Minudie Anticline, a salt wall. South of the wall (Athol Syncline), along the Joggins World Heritage shoreline, an ~ 3000 m succession of strata (Little River, Joggins, Springhill Mines, and Ragged Reef formations) accumulated conformably on the Boss Point Formation. North of the wall (Black Point sub-basin), the biostratigraphically equivalent, but mostly unstudied, ~ 600 m-thick succession of Grande Anse Formation lies in angular unconformity on folded and faulted Boss Point and basal Little River formations.
 Grande Anse Formation sedimentology indicates four lithofacies associations: floodplain (LA1), braided channel (LA2), sheet flood (LA3), and debris flow deposits (LA4). One possible model has the Black Point sub-basin with its own hydrological system, completely separated from the Athol Syncline. A low subsidence rate combined with the low sedimentation rate produced the ~600 m-thick sand- and mud-prone succession that was contemporaneous to the ~ 3 km succession to the south. The second model proposes that north of the salt wall was exposed to erosion during accumulation of Joggins and Springhill Mines formation strata to the south. Subsequently, the sediment of the lithologically similar Ragged Reef and Grande Anse formations either (i) onlapped to the north, unconformably on the folded Boss Point, or (ii) unconformably-disconformably on the underlying strata after a period of time indistinguishable in the biostratigraphic record.

A model for the early diagenesis of humid climate, fluvial strata influenced by adjacent salt deposits: Grande Anse Formation, Cumberland Basin, Canada

“…Previous sedimentological and geochemical studies of the Grande Anse Formation (Allen et al ., 2013; Bahr & Keighley, 2021, 2022) have all supported the interpretation of sedimentation in a tropical, semi‐humid to humid, terrestrial climate. Suttner & Dutta (1986) also developed a bivariate log/log plot of selected detrital components that can assess point‐count data to infer palaeoclimate.…”

“…This stratigraphy collectively comprises >3 km of strata that are disconformable on the Mabou Group (Calder et al ., 2005; Waldron et al ., 2013; Craggs et al ., 2017). A series of biostratigraphic (Utting et al ., 2010), sedimentological and geochemical studies (Bahr & Keighley, 2021, 2022), have also demonstrated that the overlying >900 m thick strata south of the Anticline, previously described as the Ragged Reef Formation by Ryan et al . (1991), has many similarities to the Grande Anse Formation north of Minudie Anticline, which was first mapped by Norman (1941).…”

“…In summary of Craggs et al . (2017) and Bahr & Keighley (2021), on the western side of the Basin, the Minudie Anticline is a salt wall with a core of Viséan strata. These strata comprise interbedded limestone, mudstone and evaporite of the Pugwash Mines and Lime‐kiln Brook formations, which are included in the Windsor Group and interpreted to be of marine and marginal marine origin.…”

“…3). North of the resulting asymmetrical salt wall, in what has been termed the Black Point sub‐basin (Bahr & Keighley, 2021), folds and faults in the Boss Point Formation and overlying basal Little River formations, are truncated by an angular unconformity at the base of the approx. 600 m thick red beds of the Grande Anse Formation (Craggs et al ., 2017).…”

“…This contribution is a petrographic study of part of the Pennsylvanian Cumberland Group succession in the Basin, specifically the Grande Anse Formation, that likely formed a cover sequence on the Minudie Anticline, a wall‐shaped salt diapir, shortly after a major and rapid (approx. 2 Myr) episode of salt evacuation (Bahr & Keighley, 2021, 2022). The research aims to add to the understanding of diagenetic controls on reservoir quality in diapiric and other salt‐influenced geological situations by: (i) describing the paragenetic sequence recorded in sandstones and conglomerates of the Grande Anse Formation; (ii) constraining the conditions affecting precipitation of the authigenic cements; and (iii) highlighting the broader impact of salt‐influenced pore waters and resultant diagenetic phases influencing reservoir quality, particularly during shallow burial.…”