TRACE-ELEMENTS AND CR AND C ISOTOPIC SIGNATURES IN LATE NEOPROTEROZOIC AND EARLIEST CAMBRIAN SEDIMENTARY ORGANIC-MATTER FROM SILICICLASTIC SUCCESSIONS IN THE EAST EUROPEAN PLATFORM

Sedimentary organic matter deriving from tubes of sabelliditids, vendo taenids, sapropelic films and kerogens was extracted by acid processin g from Upper Vendian siliciclastic successions in the East European Pl atform. Elemental composition obtained by instrumental neutron activat ion analysis (INAA) displays the increasing cobalt (Co) concentration from 1 ppm at the bottom of Upper Vendian succession to about 800 ppm in the uppermost part near the Precambrian-Cambrian boundary. This dis tribution is recorded in all studied successions and is not related to resistant minerals that survived acid treatment. The enrichment in Co and other metals in the sedimentary organic matter is inferred to be caused by the bloom of cyanobacterial microbiota, and bonding of metal s in decaying sedimentary organic matter during pre-burial bacterial r eworking and post-burial early diagenesis in a low energy, stagnant de positional basin during Kotlin times. The positive Ce-anom in probable benthic sabelliditids, and the exceptional preservation of sedimentar y organic matter from Kotlinian strata, indicate the anaerobic conditi ons during their sedimentation. Clear correlations between Sr-87/Sr-86 , delta(13)C and Co imply the secondary isotopic signatures of Sr and C in sedimentary organic matter deriving from a restricted epicontinen tal marine basin.