High-frequency Milankovitch cycles have been identified in the Liassic hemipelagic carbonates of the Basque-Cantabrian basin. The cycles detected are attributed to precession forcing. VVe examined this high frequency cycling using advanced spectral analysis of the secular variation in the CaC03 (wt%) content of the hemipelagic rocks. However, the same spectral analyses applied to the temporal variations of the total organic carbon (TOO and 8*3C of the sediment do not found the same cyclicity. This suggest that the high-frequency orbital forcing may have not been a main control on organic productivity, sea bottom anoxia and/or rate of organic matter burial, which may have been controlled by other intrinsic or extrinsic factors.
The results of this study will be applied to other chemostratigraphic analyses been conducted in the middle-upper Lias hemipelagic rocks of the Basque-Cantabrian basin in order to test if the previously detected palaeoceanic temperature variations may be related to preccesion cycle
