Variaciones de espesor y de contenido en CaCO3 en los pares marga-caliza del Maastrichtiense inferior en Sopelana (Arco Vasco)

Abstract

The Sopelana sea-cliff section exposes, in very good conditions, a continuous marl-limestone alternation from the Lower Maastrichtian in the deep Basque Arc domain. The 55 rhythms studied represent ~1100 ka and correspond to ~60cm/20ka. The marls are thicker than limestone layers and the Fischer diagram detects several shifts of high sedimentation and a well-marked minimum. The spectral analysis of the (%) CaCO3 content of the 30 selected rhythms (179 analysis, 18.74 m), confirms the rhythm with two frequency peaks, which correspond to the precession and eccentricity periods. The high-resolution analysis of four rhythms (<2cm/sample; 117 analysis, 2.04 m) shows a lack of symmetry and a different behaviour among them. The weathering surfaces point out an (%, CaCO3 ) enrichment tendency