C-13 C-12 RATIO DOUBLE CYCLICITY IN A MIOCENE BROWNCOAL - ISOTOPIC SIGNALS AND ORBITAL FORCING/

A detailed stable carbon isotopic profile of a late Miocene browncoal seam from the Lower Rhine Embayment, Germany, reveals two clear separa te cycles of different frequency: this is the first instance of this t ype of isotopic signature being recognized within coals. The ratio of the two frequencies suggests this isotopic signal possibly resulted fr om climatic or vegetational responses to orbital forcing. The cyclicit y has been enhanced by the application of conventional filtering metho ds on the data set. An analysis of the seam's palynology indicates a c orrelation between heavier isotopic compositions and the presence of S equoiapollenites polyformosus, whose parent plant is believed to have favoured moist climates and higher groundwater tables.