Widespread chemical remagnetization: Orogenic fluids or burial diagenesis of clays?

Abstract

The results of this study indicate that widespread or pervasive chemical remanent magnetizations (CRMs) can form as a consequence of the burial diagenetic conversion of smectite to illite. Paleomagnetic, rock magnetic, and geochemical evidence supports the CRM-clay diagenesis connection in carbonates of the Vocontian trough in SE-France and rules out another commonly cited mechanism, i.e. orogenic-type fluids. A widespread and pervasive CRM is present throughout the basin where smectite has converted during burial. The CRM is weakly developed or absent where smectite conversion is incomplete, and the only location with a primary magnetization is identified where the clays were not altered during burial. The magnetite content and mean grain size increase downsection and within time intervals across the basin with the degree of smectite alteration. Also, based on geochemical evidence, the widespread CRM is not associated to orogenic-type fluids. Paleomagnetic and rock magnetic trends with clay diagenesis from clastics of the Green River Basin in Wyoming are generally similar to those of the Vocontian trough and are also consistent with magnetite authigenesis and the development of a CRM. Among the benefits in understanding the mechanisms for the development of widespread CRMs are the potential to date diagenetic events paleomagnetically.