Chemical remanent magnetization due to deep-burial diagenesis in oolitic hematite-bearing ironstones of Alabama

Details Chemical remanent magnetization due to deep-burial diagenesis in oolitic hematite-bearing ironstones of Alabama Chemical remanent magnetization due to deep-burial diagenesis in oolitic hematite-bearing ironstones of Alabama

Mar 1985

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985pepi...37..261h&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 37, Issue 4, p. 261-284.

Physics

6

Scientific paper

Oolitic hematite-bearing ironstones of the Silurian Red Mountain Formation of Alabama are shown to carry a single-component remanence stable enough to have survived major folding (of probable Permian age). Nevertheless, the remanence direction (ten sites yielding a paleopole at 38.0°N, 132.4°E with dm = 3.6°, dp = 1.9°), its reverse polarity and a negative intraformational conglomerate test show that the remanence was very likely acquired during the Pennsylvanian-some 130 Ma after deposition. This remanence is likely a chemical remanent magnetization (CRM) acquired during diagenesis induced by heating due to deep burial under a Pennsylvanian clastic wedge. Two possible mechanisms for acquisition of CRM during deep-burial diagenesis are considered. In hypothesis I, the oolitic hematite transformed from original geothite when heated to about 80°C, acquiring CRM. In hypothesis II, the oolitic hematite originated from ferrihydrite and was too fine-grained to acquire stable CRM until heat raised the solubility of hematite allowing grain growth. Hypothesis I explains the timing of remanence acquisition better, but there is some evidence that oolitic goethites may be stable to considerably more than 80°C. Hypothesis II has some difficulty explaining preliminary paleomagnetic results from oolitic hematite-bearing ironstones of the Silurian Clinton Group, New York State. We prefer hypothesis I but both hypotheses remain plausible. Both hypotheses warn that continental red beds may also acquire CRM during diagenesis induced by deep-burial heating, long after deposition but before folding.
Now at Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, K1A 0E8, Canada.

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