Origin of the Plio-Pleistocene Vrica laminites: Organic geochemical evidence

Abstract

Organic geochemical properties of samples from lower Pleistocene laminite Layer H at Vrica, Calabria, have been examined for evidence of the origin of these dark-colored sediments. The laminite samples are geochemically distinct from the surrounding gray marly clays. They contain less CaCO3 and more TOC, have higher C/N ratios and lower [delta]13C values, and their hydrocarbon contents indicate larger proportions of land-derived organic matter. The Vrica laminites appear to have originated principally as a consequence of enhanced runoff of land-derived organic matter and clastic sediments from nearby land areas during episodes of wetter regional climate. Freshening of surface waters by the runoff created salinity stratification of the water column, diminished availability of oxygen in near-bottom waters, and improved preservation of organic matter. Marine productivity was probably also enhanced, but not as much as is evident for pelagic sapropels in the eastern Mediterranean.