Rock-magnetic properties of the Cretaceous/Tertiary Micara Formation in the Guantánamo area, eastern Cuba
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Abstract
Initial results of a rock-magnetic study of the 35 m thick Calabazas sedimentary section of the Micara Formation, eastern Cuba are reported. Previous studies have interpreted the Cretaceous/Tertiary (K/T) boundary within the Micara Formation, based mainly on analyses of planktonic foraminifera assemblages and lateral correlations. The K/T boundary in sedimentary sections in Gubbio, Italy and Caravaca, Spain is characterized, in addition to the iridium anomaly, by a rock-magnetic anomaly that is related to enrichment of iron oxide minerals (magnetite). Study of rock-magnetic properties in the Calabazas section identifies three horizons characterized by increased abundance of magnetic minerals, which are located at about 4, 12 and 20 m above the base of the outcrop, respectively. The 4 m horizon is characterized by magnetic susceptibility values of about 90 x 10-5 SI, whereas in the rest of the section values are around 20 x 10-5 SI. The corresponding NRM and IRM intensities are about 7 mA/m and 7 A/m, respectively. The 12 m horizon is marked by 22 A/m IRM intensity and 14 mA/m NRM intensity. The 20 m horizon is marked by 16 mA/m NRM intensity and 3 A/m IRM intensity. The magnetic anomaly at 4 m corresponds to the highest concentration of magnetic minerals, likely iron-rich fine-grained magnetites with pseudo-single domain behavior. However, this magnetic anomaly in the Calabazas section displays a wider stratigraphic range than in other K/T boundary sections. The characteristics of the wide magnetic anomaly suggest an alternative interpretation in terms of sedimentary input of magnetic material not related to the hot early impact ejecta. The Calabazas section lies in the Paleocene, and the magnetic peaks observed in the sediments result from fluctuations in the relative contents of magnetic minerals.
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