In this contribution, we study two meter-scale cycles from the Kimmeridge Clay Formation (cored near Marton, Yorkshire) which shows cyclic organic matter (OM) distribution. Our aim is to try to understand the factors responsile for (OM) accumulation. The first cycle, called lower cycle, shows a total organic carbon (TOC) content between 1 and 10% whereas the second, called upper cycle, shows a TOC content varying between 5 and 35%. The geochemical composition (major elements and trace elements), the organic geochemistry (TOC, HI, palynofacies) and mineralogy of the sediments have been determined. In both cycles, the cyclicity is expressed through variations in the nature and in the relative abundance of the various types of organic-matter constituents. Furthermore, dilution effects by inorganic components of the sediment cannot account for the TOC cyclicity. For lower cycle, the Mo, V and U content is low and little variable as is the intensity of the oxidation which OM suffered from. This indicates that variations in phytoplanktonic productivity may be held responsible for the cyclicity in steady and mildly reducing redox conditions. In the upper cycle, cyclicity also appears to depend on productivity but variations in the concentration of Mo, V and U and in the oxidation state of the OM suggest the environment was temporarily more reducing. It is proposed that larger amounts of H 2S were released into marine bottom waters as a result of initial OM decomposition, forced the oxic-anoxic boundary to rise in the water column and thus favoured OM storage. The main driving force for variations in the OM concentration was the productivity of organic-matter-walled phytoplankton. Redox conditions of the depositional environment could have had a positive action, but only by acting as a positive feedback effect.