FACIES AND EARLY DIAGENETIC INFLUENCE ON THE DEPOSITIONAL MAGNETIZATION OF CARBONATES

Rock-magnetic data from a core (Clino) on the margin of Great Bahama B ank show that both depositional facies and early diagenesis contribute to preservation of depositional remanent magnetization. This primary magnetization, carried by single-domain magnetite, and resultant direc tional data recorded in carbonates are influenced by diagenetic altera tion that is largely controlled by facies and to a lesser degree relat ive sea level, Although polarity does not change, there is usually inc lination shallowing relative to the axial dipole value, and the inclin ation values are more dispersed as a result of cementation, Four magne to-diagenetic zones were identified in Clino: from top down, these are (I) a low-Mg calcite, a cemented, shallow-water facies with dispersed inclinations, relatively high remanence coercivity, and magnetostatic interaction; (II) an upper-slope facies, moderately cemented, that ha s original aragonite mineralogy, produced more statistically consisten t inclination angles, lower magnetostatic interactions and coercivity, and higher remanence intensity; (III) a cemented, lower-slope facies having characteristics of both the overlying zones, but containing som e dolomite and abundant fractures; and (IV) a partially dolomitized, b asal lower-slope interval with magnetic characteristics (dispersed inc lination, weaker intensity, higher coercivity, higher magnetostatic in teraction) similar to the shallow-water facies. The relatively uncompl icated diagenetic history, excellent age control, and depositional fac ies provide a spectrum of magnetization destructive processes and char acterization of polarity data from platform carbonates.