Abstract
Pyrolysis-mass spectrometry of extracted sediments from the Livello Bonarelli, a thinly laminated carbonate-poor sedimentary unit at the Cenomanian-Turonian boundary, indicates significant differences between the samples. Microscopic investigations and pyrolysis-gas chromatography show a main contribution from marine organic matter for all samples. The composition of the extractable hydrocarbons becomes more complex with increasing organic carbon content of the sediments, indicating increasing anoxicity in the environment of sedimentation.
Organic geochemical analyses combined with sedimentological and paleontological data show that the Livello Bonarelli could have been deposited in a paleoenvironment similar to that recently proposed for the Pleistocene Mediterranean sapropels, with an intermittent influx of fresh water leading to stagnation and a high productivity of marine organic matter caused by the transported nutrients.