Intercalibration of Boreal and Tethyan time scales: the magnetobiostratigraphy of the Middle Triassic and the latest Early Triassic from Spitsbergen, Arctic Norway

Abstract

An integrated biomagnetostratigraphic study of the latest Early Triassic to the upper parts of the Middle Triassic, at Milne Edwardsfjellet in central Spitsbergen, Svalbard, allows a detailed correlation of Boreal and Tethyan biostratigraphies. The biostratigraphy consists of ammonoid and palynomorph zonations, supported by conodonts, through some 234 m of succession in two adjacent sections. The magnetostratigraphy consists of 10 substantive normal— reverse polarity chrons, defined by sampling at 150 stratigraphic levels. The magnetization is carried by magnetite and an unidentified magnetic sulphide, and is difficult to fully separate from a strong present-day-like magnetization. The biomagnetostratigraphy from the late Olenekian (Vendomdalen Member) is supplemented by data from nearby Vikinghogda. The early and middle Anisian has a high sedimentation rate, comprising over half the ca. 140-m thickness of the Botneheia Formation, whereas the late Anisian and lower Ladinian is condensed into about 20 m. The two latest Boreal Ladinian ammonoid zones are absent as a result of erosional truncation below the Tschermakfjellet Formation. Correlation with Tethyan biomagnetostratigraphies shows the traditional base of the Boreal Anisian (base of the Grambergia taimyrensis Zone) precedes the base of the Anisian (using definitions based on the De? sli Caira section in Romania). The Boreal upper Anisian Gymnotoceras rotelliforme and Frechites nevadanus ammonoid zones correlate with most of the Tethyan Pelsonian and Illyrian substages. The base Ladinian defined in the Tethyan global boundary stratotype and point (GSSP) is closely equivalent to the traditional base of the Boreal Ladinian at the Intornites oleshkoi Zone. The latest Olenekian—early Anisian magnetic polarity time scale is refined using the Spitsbergen data.