FERROMAGNETIC RESONANCE STRATIGRAPHY AT THE PALEOCENE-EOCENE GSSP, DABABIYA, EGYPT: TESTING THE MAGNETOFOSSIL SPIKE HYPOTHESIS

Recent discovery of abundant magnetofossils in kaolinite clay spanning the Initial Eocene Thermal Maximum (IETM) on the Atlantic coastal plain, New Jersey leaves unanswered the question of whether the magnetofossil spike is a local or global phenomenon. We present results of ferromagnetic resonance (FMR) stratigraphy in 16 samples spanning seven meters across the Paleocene-Eocene (PE) boundary at the Dababiya, Egypt GSSP.

FMR spectra and remanence rock magnetism reveal a low coercivity and positive anisotropic mineral, plausibly magnetite, unindicated by conventional paleomagnetic study. Almost all data fits extant definitions of possible magnetofossils. We suspect, however, that FMR parameters have power to track a wide range of lithofacies changes, including simple magnetofossil abundance. All FMR parameters show stasis below the PE boundary. Anomalies related to high Fe3+ content are present within 10 cm of the carbon isotope excursion; we relate this anomaly to jarosite, rather than goethite or hematite. Interestingly, two apparently identical samples of brown phosphatic shale at the carbon isotopic nadir have similar (but not identical) FMR parameters, distinct from the rest of the sample suite. In every case, FMR favors magnetofossils in the lower TOC sample of the pair, consistent with expectations from younger sediments.

Our results encourage the prospect of using FMR to track subtle environmental changes not readily apparent in outcrop. The PE magnetofossil spike may be a global phenomenon, but in restricted facies at the carbon isotope excursion's nadir.