Stephen Bigg

The LaHave Platform is a relatively stable segment of the continental margin of Nova Scotia, developed along the flank of the Scotian Basin. The latest Cretaceous through Tertiary part of the succession, designated the Wyandot and Banquereau formations, is the subject of this study. At least three mappable seismic 'packages' that approximate seismic sequences are identifiable in the study interval. The packages and their bounding surfaces were mapped using industry seismic reflection profiles acquired in the 1970s and 1980s. Faults were relatively uncommon in the study area/interval, except near the shelf edge, where the horizons begin to be offset by minor normal faults. Here also, canyons have been incised that continue to the southeast onto the slope.

Ties between the seismic and eight wells show that the seismic packages correspond to at least two successive transgressive-regressive cycles that deposited alternating units of mudstone (during transgression) and sandstone (during regression) from the early Campanian to Miocene. The Wyandot Formation represents the maximum transgression near the base of the interval, during the Santonian to early Campanian. The Wyandot is followed by regression during the Campanian to Paleocene portion of the Banquereau Formation. The regression is characterized in the well logs as mudstone grading to sandstone, and in the seismic by progradational seismic horizons of seismic package 1 and most of package 2. The maximum regression occurred during the Maastrichtian-Paleocene, and is represented by sandstones up to 225 m thick. Another transgressional episode and subsequent regression during the Eocene-Oligocene and Miocene are represented as mainly mudstone and sandstone, respectively, and further progradational seismic packages (the remainder of seismic package 2 and package 3). Erosion on top of the Wyandot was also observed, possibly representing an additional regressive event before the beginning of the Banquereau Formation deposition.

The geometry of the seismic packages and canyons in the study area indicate the location of the main depocentres and sediment transport directions. The thickest accumulation of Campanian-Paleocene mudstones and sandstones (450 m) was deposited near the centre of the study interval, in the area between the Ojibwa, Oneida, and Demascota wells. If transported over the paleoshelf edge, significant accumulations of sandstone-dominated units may be expected on the slope adjacent to this depocentre. The depocentre of the Eocene-Miocene sandstones (up to 274 m) was slightly seaward of the Oneida well. The thickest accumulation of later Tertiary (Oligocene-Miocene) sandstones should therefore occur on the slope beyond Oneida. Furthermore, canyons in the southwest portion of the study area were infilled during the both the Maastrichtian-Paleocene and Miocene transgressions, implying that coeval prograding sandstones may have been intermittently transported through the canyons and onto the slope. Future oil and gas exploration efforts should concentrate on these areas as sites of potentially significant hydrocarbon reservoirs, especially in the interval of the Maastrichtian-Paleocene and Oligocene-Miocene sands on the shelf.

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Pages: 167
Supervisor: Andrew MacRae