The Cenomanian-Turonian transgression has been studied in a 220 m cored section using common source rock data, elemental data and conventional biomarker parameters. Differences in the type of organic matter found in these regressive and transgressive offshore marine sediments have been documented and assessed within a sequence stratigraphic framework. The interval of maximum flooding of the Cretaceous seaway shoreline is delineated by discontinuities in the total organic carbon content and Hydrogen Index. The overall transgressive event is also accompanied by (a) an increase in the concentrations of elements such as thorium, vanadium, potassium, barium, sodium...etc., (b) changes in the relative concentrations and the characteristics of the biomarker parameters and (c) changes in the characteristic features of the kerogen. All of these data are consistent with a simultaneous decrease in terrigenous organic matter and increase in marine algal input.