Low-latitude Oxfordian position of the Oravic crustal segment (Pieniny Klippen Belt, Western Carpathians): Palaeogeographic implications
Abstract The Bajocian and the Oxfordian–Kimmeridgian crinoidal limestones of the Pieniny Klippen Belt (PKB), Western Carpathians and the Bathonian–Callovian neptunian dykes which cut them were sampled for rock magnetic and palaeomagnetic study. The sampled sections were: Babina, Mestecko, Vrsatec, Bolesovska dolina and Szaflary. SIRM(T) curves show that the limestone and the dykes from Mestecko contain hematite with blocking temperature T b about 650–670 °C. Babina limestone and dykes contain magnetite with T b between 470 and 570 °C, usually accompanied by small hematite tail. Sometimes goethite with T b about 80–100 °C is seen. Dykes and limestone from Vrsatec contain magnetite with T b of 570 °C or hematite with unblocking temperature of 670 °C. After cleaning of recent soft component by a temperature of 200 °C and a field of 10–20 mT, the hard component was revealed. After tilt correction the locality-mean directions found in limestones have scattered declination but similar reversed inclination between −35° and –40° for the Bajocian and between −35° and −49° for the Oxfordian–Kimmeridgian. An exception was the mean direction for the Bajocian limestone from Bolesovska dolina which has normal polarity. Fold test for inclination only showed pre-folding inclinations for the Bajocian and Oxfordian–Kimmeridgian limestones and scattered inclinations for the in situ and tilt corrected directions for the dykes. The mean palaeoinclination calculated for Bajocian and Oxfordian–Kimmeridgian by means of “inclination-only” test are −38.5° +/−3° and −42.5° +/−11.2°, respectively, which corresponds to 21.7 +/−1.5°N and 24.6 +/−5.6°N of palaeolatitude. This is about 10°–15° lower than the value of inclination expected for that age for the Pieniny Klippen Belt from the Jurassic poles for Stable Europe. As positive inclination only fold test proves pre-folding age of isolating directions other possibility — flattening of inclination should be considered. Anisotropy of magnetic susceptibility (AMS) and magnetic unhysteretic remanent magnetisation (AARM) can be used for the evaluation of origin and for the deviation of natural remanent magnetisation NRM. The axes of AMS are scattered for all localities. The degree of anisotropy is low. The shape parameter T shows equal distribution of oblate and prolate fabric. On the contrary, the ARM maximum axes are well clustered, especially for Mestecko and Vrsatec. The maximum axes are distributed in a vertical plane for Mestecko and in horizontal plane for Babina and Vrsatec. This evidences that the AARM fabric is not related to sedimentation and compaction. The anisotropy axes are not close to the NRM directions. For Mestecko they are steeper. This excludes an effect of shallowing of NRM. On this basis we can assume that more southern palaeolatitude of the Pieniny Klippen Belt than expected is a demonstration of palaeogeography and tectonics and points to a close vicinity of the PKB to the African plate in the Jurassic. The results from the Polish part of PKB which emerged in the latest years showed the same palaeolatitude for the Callovian–Kimmeridgian limestones. The low palaeomagnetic inclinations measured in the Bajocian crinoidal limestones show that the southward drift may have started earlier than previously expected.