In situ metal-staining of biological membranes in sediments

Decomposition of organic matter in sediments is principally mediated by bacteria and burrowing organisms. During this process, organic matter undergoes a series of structural chances in which heavy metals and minerals actively participate 1–4 . Metal–organic complexes arise which are instrumental in crystal seed formation and growth of authigenic minerals such as sulphides, phosphates, oxides and carbonates. By means of transmission electron microscopy, modern organic-rich sediments from the Black Sea and Lake Tanganyka and samples from Eocene Messel oil shale in Germany were studied for the presence of heavy metal stained biological membranes. We report here that during early diagenesis heavy metals seem to supplant hydrogen, alkali and alkaline-earth ions placed at the surfaces of membranes in living organisms. The resulting patterns are the same as those found in organic tissues which before electron microscopy were stained with lead, uranium and osmium salts. In sediments, naturally stained membranes can further act as templates for mineral deposition and may—in certain environmental conditions—lead to strata-bound ore deposits.