THE ULTRAFINE STRUCTURE OF ORGANIC-MATTER FROM KIMMERIDGIAN SOURCE-ROCKS OF YORKSHIRE (UK)

Isolated organic material from sedimentary rocks, after destruction of minerals and observation under optical microscope in transmitted ligh t (palynofacies) shows the existence of various amorphous organic mate rials. This work deals with the identification of this organic materia l. Organic material microsampled with steromicroscope is studied by tr ansmission electron microscopy. Results are interpreted with respect t o the sedimentology of the depositional cycle. The orange amorphous or ganic matter exhibits an internal structure nanoscopically amorphous a nd perfectly homogeneous. It exists as a gelatinous form closely resem bling the lamellar diffuse amorphous organic matter observed in the ul trathin sections of total organic material. As a proof of a phytoplank tonic productivity, it is accompanied by an intense sulphate reduction . It is interpreted as the result of an early gelification process of the original phytoplanktonic material. The brown amorphous organic mat ter is mainly represented by ultralaminae, interpreted as the bio-resi stant parts of planktonic organisms of which the metabolisable fractio n was partly degraded before deposition. The black amorphous organic m atter contains a large diversity of ultra-structures dominated by lign aceous debris. This amorphous organic matter, contains organic materia ls of diverse origin including imprints from coccoliths, quartz and cl ays. The close association with the mineral fraction would suggest tha t this material constitutes the organic fraction of the organo-mineral groundmass of the original rock.