A Review and Comparison of Carbonate Rock Magnetization: Leg 133, Queensland Plateau, Australia

A review and summary of carbonate rock magnetics from Leg 133 sites on the Queensland Plateau and comparison with other pure carbonates of similar age are presented to assess the nature and variation of magnetization in large carbonate platforms.A combination of rock-magnetic techniques suggests that the primary carrier of magnetic remanence is ultrafine-grained, singledomain crystals of either magnetite or maghemite.Rock-magnetic, geochemical, and demagnetization results suggest that much of the original magnetite has been oxidized to maghemite and may have been further altered to a "soft" oxyhydroxide phase.A transition to improved preservation of magnetic remanence is coincident with subsidence of the platform and a shift from neritic to bathyal conditions.Comparison with rock-magnetic characteristics from shallow Bahamian platforms confirms a similar source of magnetization, probably biogenic.Variation in the preservation of remanence is perhaps related to local fluid flow and geohistory of the platforms.