Geochemical evidence for paleoclimatic variations during deposition of two Late Pliocene sapropels from the Vrica section, Calabria

Abstract

The near-shore paleosetting of the Vrica Pliocene–Pleistocene boundary section provides an expanded sedimentary sequence that is ideal for investigating small-scale variations in sapropel deposition. We analyzed a suite of geochemical parameters in samples from a freshly drilled core that includes sapropelic layers c (1.851 Ma) and d (1.829 Ma) to characterize their depositional variation. Both sapropelic layers differ from background sediment by having higher total organic carbon (TOC) contents, lower δ 15N values, and higher contents of redox-sensitive and chalcophile elements. Layer c consists of a lower sub-layer in which TOC content is less than that of the upper sub-layer. Layer d exists as three sub-layers that are separated by low-TOC sediment. The lowermost sub-layer is weakly expressed and lacks chalcophile element enrichment. The other two sub-layers are strongly developed and illustrate that sapropel-forming conditions can be quickly established and interrupted. The two interruptions within layer d indicate a decrease in continental runoff, verifying the importance of humid conditions over continental borderlands and freshening of Mediterranean surface waters in forming sapropels. Although organic matter production was elevated during deposition of layers c and d, barium contents of sapropels and background sediment are similar, which shows that this paleoproductivity proxy is not suitable for shallow settings like Vrica. Our results confirm that considerable paleoclimatic variation can occur during deposition of an individual sapropel layer and in closely spaced sapropel events.