Back to Exploration – 2008 CSPG CSEG CWLS Convention 758
High Resolution Sequence Stratigraphic Correlation and Coal Seam
Distribution in the Upper Carboniferous Strata of the Central Maritimes Basin
Gillian Chi*
Geological Survey of Canada, Calgary, AB
gchi@nrcan.gc.ca
James Dietrich
Geological Survey of Canada, Calgary, AB, Canada
and
Peter Giles
Geological Survey of Canada, Dartmouth, NS, Canada
Summary
Upper Carboniferous strata in the Magdalen Basin, southern Gulf of St. Lawrence were deposited in
restricted–marine to alluvial environments, with abundant coal seams in the Namurian-Westphalian
succession (Cumberland and Pictou groups). Because the coal measures represent significant
hydrocarbon source rocks, an evaluation of the distribution and thickness of the coal-bearing strata
is essential for assessing petroleum potential in this basin.
High resolution sequence stratigraphic correlations of the coal-bearing strata were conducted using
data from four offshore wells and seven regional seismic reflection cross sections. The correlations
were achieved utilizing the control of base level change on non-marine sequence stratigraphy, basin
fill depositional patterns and coal accumulation. The depositional cycles within the coal - bearing
strata are predominantly asymmetric, leading to thicker sediments in the transgressive system tract
(TST) than in the regressive system tract (RST), they are separated by maximum regressive
surfaces and equivalent erosional unconformities, which can be clearly observed on the seismic
sections.
Nine third-order depositional sequences have been identified in the Upper Carboniferous strata,
with four in the Bradelle (SS1 to SS4), three in the Green Gable (SS5 to SS7), and two in the Cable
Head Formation (SS8 to SS9). Interestingly, the SS4 sequence in the upper part of the Bradelle
Formation was observed only in the central part of the basin.
The interpretation of coal-bearing strata in a sequence stratigraphic framework provides an
improved understanding of the variability in the coal distribution and thickness. The identification of
abundant coal beds and numerous incised channels from the well and seismic data indicates low to
intermediate sediment accommodation rates in this basin. The vertical distribution of the coal-
bearing strata varies in different parts of the basin. In the basin margins represented by the Bradelle
