Magnetic susceptibility and gamma ray spectrometry in the Tré Maroua section (Tithonian/Berriasian, SE France) – terrigenous input and comparison with Tethyan record

Abstract

Field magnetic susceptibility (MS) and gamma ray spectrometry (GRS) measurements were performed in the Jurassic/Cretaceous boundary interval in the Tré Maroua section (SE France). The 24 m thick section covers the interval from the upper Tithonian magnetozone M20n (Chitinoidella Zone) to the lower Berriasian M17r magnetozone (Calpionella elliptica Subzone). The micritic limestones reveal a very low content of terrigenous impurities (0.0–0.2% K and 0.2–2.0 ppm Th) and low MS values (–5 to 15 × 10–6 SI). Despite low intensity of both MS and GRS signal, a consistent trend of terrigenous input is observed: decreasing values in the upper Tithonian and increasing tendency in the upper part of the lower Berriasian. The long-term trends are quite similar to those documented in some Western Tethyan sections and the Polish Basin, indicating that variations of terrigenous input might be controlled by large-scale palaeoclimatic variations and relative sea-level changes. Decrease of Conusphaera and increase of Nannoconus frequencies fall in the lower part of M19n2n in the uppermost Tithonian. These events correlate with large decrease of terrigenous input and widespread oligotrophication in the Western Tethyan domain.