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[1] We have conducted a detailed magnetic study on 45 chondrules from two carbonaceous chondrites of the CV type: (1) Mokoia and (2) Allende. Allende has been previously extensively studied and is thought to have a high potential of retaining an extra-terrestrial paleofield. Few paleomagnetic studies of Mokoia have previously been undertaken. We report a range of magnetic measurements including hysteresis, first-order reversal curve analysis (FORCs), demagnetization characteristics, and isothermal remanent (IRM) acquisition behavior on both Mokoia and Allende chondrules. The Mokoia chondrules displayed more single domain-like behavior than the Allende chondrules, suggesting smaller grain sizes and higher magnetic stability. The Mokoia chondrules also had higher average concentrations of magnetic minerals and a larger range of magnetic characteristics than the Allende chondrules. IRM acquisition analysis found that both sets of chondrules have the same dominant magnetic mineral, likely to be a FeNi phase (taenite, kamacite, and/or awaruite) contributing to 48% of the Mokoia chondrules and 42% of the Allende chondrule characteristics. FORC analysis revealed that generally the Allende chondrules displayed low-field coercivity distributions with little interactions, and the Mokoia chondrules show clear single-domain like distributions. Paleointensity estimates for the two meteorites using the REMc and Preisach methods yielded estimates between 13 and 60 mT and 3-56 mT, respectively, for Allende and 3-140 mT and 1-110 mT, respectively, for Mokoia. From the data, we suggest that Mokoia chondrules carry a non-primary remagnetization, and while Allende is more likely than Mokoia to retain its primary magnetization, it also displays signs of post accretionary magnetization.

This study combines magnetic experimentation and geochemical analysis on oil sands from Osmington Mills and Mupe Bay, Wessex Basin, UK to investigate the possibility of a relationship between hydrocarbons and magnetic mineralogy. Removal of hydrocarbons by chemical extraction was conducted to allow comparison of (1) oil sands and (2) cleaned sands. Detailed magnetic analysis including low-temperature and high-temperature experimentation revealed that all but one sample was dominated by siderite, identified by the Néel transition at 37–38 K as well as containing large grains of multidomain magnetite (Verwey transition 110 K) and hematite (Morin transition 250 K). Scanning electron microscopy and energy dispersive x-ray analysis confirmed the presence of iron oxides, in particular framboids 500 nm–45 µm in diameter, probably magnetite. Hysteresis parameters showed distinct grouping of oil sands compared to their clean counterparts and a negative linear regression in log space was observed (R2=0.7) between the percentage of extractable organic matter and magnetic susceptibility. These results suggest a relationship exists between magnetic minerals and the alteration of oil due to biodegradation, which is not yet fully understood. Possible mechanisms are suggested to be due to anaerobic bacteria or the transportation of the oil as it migrates through the host rock.

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