Oligocene Kugmallit Sequence in the Beaufort-Mackenzie Basin:
Regional Sequence Stratigraphic Framework, Potential Controls on
Sedimentation Cycle and Basin Fill Patterns
Gillian Chi*
Geological Survey of Canada, Calgary, AB
gchi@nrcan.gc.ca
and
ZhuoHeng Cheng and James Dietrich
Geological Survey of Canada, Calgary, AB, Canada
Summary
The Oligocene Kugmallit Sequence is one of the most important offshore oil and gas exploration
targets in the Beaufort-Mackenzie Basin. Sequence stratigraphic analysis of Kugmallit Sequence in
both onshore and offshore areas reveals the presence of two distinct prograding delta systems in
the southwest and southeast, separated by tectonic highs, with different paleo-drainage systems
and provenances. The delta system in the southeast covered a broader area, with thicker sediments
than that in the southwest. Only distal facies are preserved in the southwest, whereas proximal and
distal facies are present in the southeast delta system. It is suggested that orogenesis in the
southwest removed the proximal delta facies and changed the paleo-drainage. An understanding
the origin of the delta system is vital to understanding the context of the whole basin and especially
to the distribution of reservoir rocks in the Oligocene sequence.
Sequence stratigraphic analysis indicates that the Oligocene Kugmallit Sequence is divisible into
four regional sub-sequences, controlled by base-level cycles, paleogeography and tectonic
episodes. The nature of the subsequence boundaries varies in different parts of the basin. In the
southwest the sequence boundaries were generated by tectonic uplift with extensive large scale
submarine erosion, whereas in the southeast they are relatively conformable. In the deep-water
sediments of the north-central part of the basin, deeply eroded boundaries of the subsequences can
be recognized on seismic data. A mechanism to explain these subsequence boundaries is related to
activity on the Tarsiut-Amauligak Fault Zone. Rapid subsidence on the hanging-wall side of the
growth faults resulted in the largest sediment accommodation space and the thickest accumulation
of the oldest subsequece, decreasing in the younger sequences. During sedimentation there was
reduced movement on the faults and the erosion occurred if accommodation was less than zero.
Farther north there was uplift which led to less accommodation space and thin deposits. The
thickest accumulation of deep-water sediments occurs on the hanging-wall side of the growth faults
as do the associated deeply incised, sequence-boundary channels.
AAPG Search and Discovery Article #90170©2013 CSPG/CSEG/CWLS GeoConvention 2008, Calgary, Alberta, Canada, May 12-15, 2008
