An extremely sharp magnetic reversal observed in lacustrine sediments in
central Italy has been interpreted as a record of the Matuyama-Brunhes
geomagnetic polarity reversal that may represent less than a decade (Sagnotti et
al., 2014. 2016). Here, we report new results from the same Sulmona Basin
outcrop that question this interpretation. In particular, we find evidence of
reversed (Matuyama) directions well above the proposed Matuyama-Brunhes
Boundary (MBB). Coercivity spectra of anhysteretic remanent magnetization
(ARM) imply a 3-component magnetic mineralogy: low-, intermediate-, and
high-coercivity. The low-coercivity component is found in all but one of the
samples and carries a strong modern overprint seen throughout the section. The
high-coercivity component is dominated by volcanic material which is prone to
remagnetization. Since it is much more magnetic than the surrounding lacustrine
sediments, it may influence the remanence signal even when present at very low
concentrations. The intermediate-coercivity component is the main carrier of any
true primary remanence, but whether or not this can be isolated depends on the
blocking-temperature and coercivity spectra of individual samples, and on the
demagnetization method used. The complexity of the magnetization, the
reversed zones above the proposed MBB, and the normal zones that Sagnotti and
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colleagues found below it, lead to the conclusion that this section does not carry
a reliable high-resolution record of the geomagnetic field. Thus, we feel that
inferences about the stratigraphic position and duration of the MBB are premature.