Abstract
A compaction correction for the paleomagnetism of the Nanaimo Group sedimentary rocks: Implications for the Baja British Columbia hypothesis
Department of Earth and Environmental Sciences, Lehigh University, Bethlehem, Pennsylvania, USA
Department of Earth and Environmental Sciences, Lehigh University, Bethlehem, Pennsylvania, USA
A paleomagnetic and magnetic anisotropy study of the Late Cretaceous Northumberland formation on Hornby Island, British Columbia,
was conducted to determine if burial compaction could have caused its anomalously shallow inclinations. The shallow Nanaimo
Group inclinations have been used to support the Baja British Columbia (Baja BC) model of continental dynamics in which superterranes
were transported thousands of kilometers northward along the active North American continental margin in the Cretaceous. A
mean of the site means from the Northumberland formation is D = 5.8°, I = 50.9°, α95 = 7.9° (N = 8). Anisotropy of magnetic susceptibility (AMS) and anisotropy of anhysteretic remanence (AAR) were measured to identify
and correct for any inclination shallowing caused by depositional/compactional processes. Both concretion and fine-grained
rock samples had typical depositional/compactional AMS and AAR fabrics with bedding perpendicular minimum principal axes.
A revised correction equation was used to account for the effects of either triaxial magnetic fabrics or small angular deviations
of principal axes from the bedding plane. The average inclination was increased by 9.6° after the compaction correction (D = 6.1°, I = 60.5°, α95 = 7.1°, N = 8), and the mean inclination of concretion and fine-grained rock sites was significantly steeper than
Received 17 July 2003; accepted 13 November 2003; published 6 February 2004.
Citation: (2004), A compaction correction for the paleomagnetism of the Nanaimo Group sedimentary rocks: Implications for the Baja British Columbia hypothesis, J. Geophys. Res., 109, B02102, doi:10.1029/2003JB002696.
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