Pages: 125 - 144
Abstract: A short reverse polarity magnetosubzone, herein defined as the Brodno Subzone, was detected in the upper part of the magnetozone M19n at the locality of Brodno near Zilina (Western Carpathians) using high-resolution magnetostratigraphy. An analogous short reverse polarity magnetosubzone, herein defined as the Kysuca Subzone occurs in the middle part of the magnetozone M20n. Both the magnetosubzones are known from marine profiles but have been detected only sporadically and documented insufficiently in continental outcrops.These two subzones have not yet been detected together in one and the same continental section. Their stratigraphic position in the Brodno section is defined and their interpretation in the other studied section at Stramberk is inferred. In the Brodno section, the Kysuca Subzone represents the basal part of the calpionellid Remanei Subzone of the Crassicollaria Standard Zone (early late Tithionian), its base lies at the level of 55 % of the local thickness of the magnetozone M20n. The Brodno Subzone lies within the calpionellid Alpina Subzone of the Calpionella Standard Zone (earliest Berriasian) and its base in the Brodno section lies at the level of 82 % of the local thickness of the magnetozone M19n. In both the studied sections, the Jurassic/Cretaceous boundary based on calpionellids (base of the Calpionella Standard Zone) lies approximately at the end of the lowermost third of the magnetozone M19n (at the level of 34 % of the local thickness of the magnetozone M19n in the Brodno section). Magnetostratigraphic calibration of calpionellid events proved their isochronous character in the localities of Brodno and Stramberk. The interval of ca. ± 5000 years, during which a transition occurred from normal (reverse) to reverse (normal) polarity of magnetic field of the co-axial geocentric dipole of the Earth, can be determined from an analysis of paleomagnetic directions inferred from samples with intermediate polarity collected from normally and reversely polarized boundary strata at the locality of Brodno and with respect to the sedimentation rate. This value represents the relative accuracy of possible correlations of the boundaries of the detected magnetosubzones with boundaries of analogous subzones at other localities on the Earth using the above given synchronous global event.
Keywords: Jurassic/Cretaceous boundary strata, Tethyan Realm, Brodno and Stramberk sections, high-resolution magnetostratigraphy, two magnetosubzones, calpionellid and magnetostratigraphic correlationDownload PDF document Show Text Version