Ken I. Saunders

The Late Carboniferous Sydney Mines Formation near Sydney, Nova Scotia comprises a succession of cyclothems, each 40 m thick on average, which show a basinwide alternation of red mudstones and grey coal-bearing strata. The Hub Cyclothem (Westphalian D - Stephanian) lies between the Hub coal seam and the Bonar (or Lloyd Cove) seam, and is intermittently exposed along 30 km of depositional strike.

Three facies assemblages constitute the Hub Cyclothem. Assemblage 1 contains coal-bearing floodplain deposits and meandering channel fills; it was deposited under the influence of a humid climate with a low degree of seasonality during a sea-level highstand. Assemblage 2 contains calcretes, vertisols, and fills from deep ephemeral channels; it was deposited under the influence of seasonally semi-arid climate. The calcrete in Assemblage 2 may have formed following a relative fall in sea-level. Assemblage 3 contains calcite cemented floodplain deposits, and anastomosed channel fills; it was deposited under the influence of a strongly seasonal semi-arid climate, with an intense rainy season. Assemblage 3 may have been deposited while sea-level was rising.

In a sequence stratigraphic context, a sequence boundary lies at the top of the calcrete, near the base of Assemblage 2. A maximum flooding surface lies at the top of the thickest split of the Hub Coal seam. A highstand systems tract comprises all of the strata above the thickest split of the Hub seam, and below the top of the calcrete. The remainder of the cyclothem lies in a transgressive systems tract. There is no lowstand systems tract in the exposed part of the Hub Cyclothem; the transgressive surface, therefore, is near-coincident with the sequence boundary.

The Hub Cyclothem is a good source of coal. Petroleum exploration potential is poor in the exposed parts of the basin; offshore areas may be better if suitable source rocks can be found. Coalbed methane potential may be promising in areas where thick channel fills are juxtaposed against coal seams.

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Pages: 183
Supervisor: Martin Gibling