DINOFLAGELLATES AS POTENTIAL PRECURSORS OF 24-NORCHOLESTANES

Occurring widely in oils and ancient sediments,24-norcholestanes are useful to oil-source correlation and petroleum age evaluation.24-norcholestanes mainly derive from diatoms;however,they are also identified unambiguously from dinoflagellates.Abundant 24-norcholestanes occur in oils and source rocks of the Shahejie Formation,but no diatom fossils have been distinguished from the Shahejie Formation.Thus,other potential precursors might be responsible for these 24-norcholestanes.A correlative relationship between 24-norcholestanes and dinocysts or triaromatic dinosteroids has been observed,revealing that dinoflagellates should be potential precursors of 24-norcholestanes.It seems that 24-norcholestanes come from dinoflagellates and diatoms,respectively,for different basins.Notwithstanding the fact that 24-norsterols have low concentrations in contemporary dinoflagella test,it is concluded that dinoflagellates are key contributors to 24-norcholestanes within subtropical lacustrine sediments of the Eocene-Oligocene Jiyang Depression.