Distribution:

Mackenzie Bay strata underlie most of the Beaufort shelf; their southern limit is a truncation edge below the sub-Iperk unconformity. Nowhere are Mackenzie Bay strata known to be exposed in the Yukon or adjacent Northwest Territories. Their southern subcrop edge just reaches the outer part of Mackenzie Delta. Where the Demarcation subbasin has been penetrated by the Edlok N-56 well, the Mackenzie Bay Sequence is seen to be present as part of the sediment fill. Under the central Beaufort shelf the sequence expands basinward from a few hundred metres in thickness to about 1000 m in the vicinity of North Issungnak L-86. However, the thickest development occurs in the western part of the Beaufort-Mackenzie Basin where up to 2000 m, or more, of section are present (Dixon et al., 1992).

Lithology:

Shale is the dominant rock type in the central Beaufort area, where there are the most penetrations of the sequence. A common characteristic of these shales is the abundance of pyrite, commonly in the shape of straight or branching rods. These pyrite rods are generally 1 to 2 mm in diameter and usually only a few millimetres long. Their origin is unknown, although it is possible that they represent replacement of burrow-fill material.They are so characteristic of the sequence that they can be used to identify it with a fair degree of confidence in the absence of other data. However, in places the pyrite rods do extend into the overlying Akpak and underlying Kugmallit sequences and cannot be relied upon entirely. Sand and silt grains are a common component of the cuttings in the shale successions indicating the presence of intercalated thin, sandstone and siltstone beds. In the Netserk and Uviluk wells there are several sandstone units that are thick enough to register on logs. Under the outer Mackenzie Delta, in the Taglu to Ivik wells, there is a thin remnant of the Mackenzie Bay Sequence betwen the Iperk and Kugmallit sequences that is sandstone-rich. These locally preserved sandy successions have been identified as Mackenzie Bay Sequence on the basis of occurrences of foraminifers from the Asterigerina staeschi Interval Zone (Young and McNeil, 1984, where the foraminifers are referred as Cibicides spp.). Log signature and lithological characteristics are very similar to those of the enclosing strata and the exact boundaries of Mackenzie Bay strata in these wells is speculative (Dixon et al., 1992).

Relationship:

The lower contact of the Mackenzie Bay Sequence is erosional over local structural highs (e.g., Adgo Anticline) and along paleoshelf slopes north of the Tarsiut-Amauligak Fault Zone. The upper contact is mostly conformable with Akpak strata, although shelf margin truncation of Mackenzie Bay strata is evident on some seismic profiles. The outer shelf and slope portions of the Mackenzie Bay Sequence are characterized by high amplitude reflections and well developed clinoforms, and are good examples of high amplitude seismic facies developed in shale-dominant shelf sediments. Where Mackenzie Bay shelf strata rest on Kugmallit deltaic deposits, there is a marked lithological contrast between Mackenzie Bay shale and Kugmallit sandstones. Miocene strata are poorly documented in northern Canada, although the Beaufort Formaiton of Banks Island has been indicated as being Miocene and could be correlative with the Mackenzie Bay Sequence. However, the age of the Beaufort Formation is not well defined and ages as old as Early Miocene to as young as Late miocene have been suggested (Hills, 1969; Hills and Fyles, 1973; Hills et al., 1974) for Banks Island strata. If the Beaufort Formation on Banks Island is Early or Middle Miocene, then it is probably correlative with Mackenzie Bay strata; if Late Miocene, then it is more likely to be correlative with the Akpak Sequence. Possible equivalents of the lower Mackenzie Bay Sequences may be present in the Nuwok Member of the Savaganirtok Formation at Carter Creek, on the Alaskan North Slope (approximately 150 km west of the Yukon-Alaska border). The Nuwok Member contains foraminifers of the upper part of the Turrilina alsatica Zone (McNeil and Miller, 1990). Seismic correlations across the Yukon-Alaska border indicate that Mackenzie Bay strata extend into offshore northeastern Alaska (Dixon et al., 1992).

History:

The Mackenzie Bay Sequence is named after the Mackenzie Bay Formation (Young and McNeil, 1984) to which it is essentially equivalent. However, unlike Young and McNeil (op. cit.) Dixon et al. (1992) do not consider their Beaufort Formation to be entirely coeval with Mackenzie Bay strata (Dixon et al., 1992).

Other Citations:

Dixon, 1992c, 1995; Dixon et al., 2008.

References:

Dietrich, J.R., Dixon, J., and McNeil, D.H., 1985. Sequence analysis and nomenclature of Upper Cretaceous to Holocene strata in the Beaufort-Mackenzie Basin; in Current Reseach, Part A, Geological Survey of Canada, Paper 85-1A, p. 613-628.

Dixon, J., 1992c. A Review of Cretaceous and Tertiary Stratigraphy in the Northern Yukon and Adjacent Northwest Territories; Geological Survey of Canada, Paper 92-9, 79 p.

Dixon, J., 1995, ed. Geological atlas of the Beaufort-Mackenzie area; Geological Survey of Canada, Miscellaneous Report 59, Ottawa, Canada, 173 pp.

Dixon, J., Dietrich, J.R., Lane, L.S., and McNeil, D.H., 2008. Geology of the Late Cretaceous to Cenozoic Beaufort-Mackenzie Basin, Canada; in, The sedimentary basins of the United States and Canada, A.D. Miall (ed.); Sedimentary Basins of the World, Volume 5, pages 551-572.

Dixon, J., Dietrich, J.R., McNeil, D.H., 1992. Upper Cretaceous to Pleistocene sequence stratigraphy of the Beaufort-Mackenzie and Banks Island areas, Northwest Canada; Geological Survey of Canada, Bulletin 407, 90 pages.

Dixon, J., McNeil, D.H., Dietrich, J.R., Bujak, J.P., and Davies, E.H., 1984. Geology and biostratigraphy of the Dome Gulf et al. Hunt Kopanoar M-13 well, Beaufort Sea; Geological Survey of Canada, Paper 82-13, 28 p.

Hills, L.V. and Fyles, J.G., 1973. The Beaufort Formation, Canadian Arctic (abstract), p. 11: in Program and Abstracts, Symposium on the Geology of the Canadian Arctic; Canadian Society of Petroleum Geologists, Geological Association of Canada, Saskatoon

Hills, L.V., 1969. Beaufort Formation, northwestern Banks Island, District of Franklin; In Report of Activities, Part A, Geological Survey of Canada, Paper 69-1A, p. 204-207.

Hills, L.V., Sangster, E.V., and Suneby, L.B., 1981. Lexicon of Canadian Stratigraphy, Volume 2, Yukon Territory and District of MacKenzie: Canadian Society of Petroleum Geologists, 240 p.

McIntyre, D.J., 1985. Palynology; In Geology, Biostratigraphy and Organic Geochemistry of Jurassic to Pleistocene Strata, Beaufort-Mackenzie Area, Northwest Canada. J. Dixon, J.R. Dietrich, D.H. McNeil, D.J. McIntyre, L.R. Snowdon, and P. Brooks, Course Notes, Canadian Society of Petroleum Geologists, p. 39-50.

McNeil, D.H. and Miller, K.G., 1990. High latitude application of 87 Sr/ 86 Sr - correlation of Nuwok beds On North Slope, Alaska, to standard Oligocene chronostratigraphy; Geology vol. 18, p. 415-418.

McNeil, D.H., 1989. Foraminiferal zonation and biofacies analysis of Cenozoic strata in the Beaufort-Mackenzie Basin of Arctic Canada; In Current Research, Part G, Geological Survey of Canada, Paper 89-1G, p. 203-223.

Young, F.G. and McNeil, D.H., 1984. Cenozoic stratigraphy of Mackenzie Delta, Northwest Territories: Geological Survey of Canada, Bulletin 336, 63 p.