The palaeomagnetism of Late Permian‐Early Triassic and Late Triassic deposits on Timor: an Australian origin?

Abstract

Palaeomagnetic studies have been carried out on sediments from two formations in Western Timor; (a) red, crinoid‐bearing limestones of the Maubisse Formation of Late Permian‐Early Triassic age and (b) reddish calcilutites and red shales of the Aituto Formation of Late Triassic age. The crinoid‐bearing limestones occur in both a non‐recrystallized and a recrystallized, slightly marmorized facies. Natural Remanent Magnetization (NRM) was analysed by means of progressive demagnetization both using alternating magnetic fields and by heating. The determination of acquisition remanence and remanent coercive force demonstrated that in a large number of sites high‐temperature (volcanic) haematite is the main carrier of remanence. A few sites from the non‐recrystallized Maubisse Limestones revealed magnetite as the main remanence carrier. The recrystallized Maubisse Limestones were found to have a secondary remanence with a very high coercivity and a high blocking temperature. Characteristic Remanent Magnetization (ChRM) directions could be obtained both from the non‐recrystallized limestones of the Maubisse Formation and from the Aituto Formation. For the plate tectonic interpretation of the data only the ChRM inclination values have been used, because of the complicated, often chaotic tectonism on Timor. Palaeolatitudinal positions of 39° and 33° have been derived from the Late Permian‐Early Triassic Maubisse Formation and the Late Triassic Aituto Formation, respectively. This points to the presence on the island of Timor of a displaced terrane of Australian origin. Copyright © 1990, Wiley Blackwell. All rights reserved