Distributions of pigments in the organic matter of marls from the Vena del Gesso evaporitic sequence

The porphyrins and carotenoids of marl horizons within the Messinian evaporitic cycles of the Vena del Gesso basin show variations in abundance and composition throughout a sequence of ten cycles. Significant variations are also apparent within individual marl horizons. The differences in pigment distribution reflect significant changes in the environmental conditions during sediment deposition. The presence of significant amounts of isorenieratene and co-occurrence of an alkyl porphyrin with a C34 skeleton provide evidence for anoxic conditions extending into the photic zone of the palaeo-water column. Variations in the free pigment contents of the marls reflect a regressive trend both during deposition of an individual marl, and over the entire sequence.