A MOLECULAR STRATIGRAPHIC APPROACH TO PALEOENVIRONMENTAL ASSESSMENT AND THE RECOGNITION OF CHANGES IN-SOURCE INPUTS IN MARLS OF THE MULHOUSE BASIN (ALSACE, FRANCE)

Principal components analysis (PCA) has been used to investigate chang es in concentrations of the components of the hydrocarbon fractions ex tracted from 71 marl samples, selected to cover two total organic carb on (TOC) maxima in the lower part of the Salt IV formation, a Lower Ol igocene evaporitic sequence from the Mulhouse Basin, France. The analy sis indicates that the fractions can be ascribed as lying between two end member distributions. The changes in these distributions are gradu al, suggesting that they resulted from fairly gradual changes in the d epositional palaeoenvironment. These changes are related to increased algal productivity associated with the evolution of a restricted lacus trine environment through to one with a greater marine influence. Syst ematic variations in the concentrations of selected components relativ e to the TOC profile point to a repeated sequential evolution in the b iological assemblage during deposition of the sequence.