Paleomagnetism and cycle stratigraphy of the Triassic Fleming Fjord and Gipsdalen Formations of East Greenland

Abstract

A 210 m section of Late Triassic Fleming Fjord Formation (the Malmros Klint Member and the lowermost 80m of the overlying Carlsberg Fjord beds of the Ørsted Dal Member) in the Tait Bjerg area of the Jameson Land Basin, East Greenland, was sampled for paleomagnetic study and measured for cycle stratigraphie analysis. Paleomagnetic samples were also taken from the underlying Gipsdalen Formation in the Gipsdalen area. A high stability characteristic magnetization carried by hematite was successfully isolated in 63 sampling levels in the Fleming Fjord Formation and 9 sampling sites in the Gipsdalen Formation using progressive thermal demagnetization. The mean characteristic directions for the Herning Fjord and the Gipsdalen Formations may be be biased by sedimentary inclination error but are consistent with a northward drift of East Greenland of about 10° from the arid (ca. 25° N) to semihumid (ca. 35° N) paleoclimatic belts in the Middle to Late Triassic. Seven normal and reversed polarity intervals are clearly delineated in the Fleming Fjord Formation section. A preferred correlation of the magnetostratigraphy to a cyclostratigraphically calibrated reference polarity sequence recently derived from drill cores in the Newark Basin of eastern North America suggests that the sampled interval represents about a 3.5 m.y. interval of the late Norian. The Malmros Klint Member and the overlying Carlsberg Fjord beds have composite sedimentary cycles that vary in thickness from 25 m to about 1 m and seem to match Milankovitch orbital climatic cyclicity with periods of ~400ky, ~100ky, ~40ky, and ~20ky. The composition and thickness ratio of the cycles suggest that the measured section of the Malmros Klint Member and the Carlsberg Fjord beds represents lacustrine accumulation over about 4 m.y., a duration consistent with the magnetostratigraphic correlations.