Source organisms and formation pathway of the kerogen of the Göynük Oil Shale (Oligocene, Turkey) as revealed by electron microscopy, spectroscopy and pyrolysis

The kerogen of the Göynük Oil Shale (an important, Oligocene, lacustrine deposit in Turkey) was examined by scanning (SEM) and transmission (TEM) electron microscopy, spectroscopy (FTIR, solid state 13C NMR) and pyrolysis. The chemical structure of this immature, Type I, kerogen was shown to be based on long polymethylenic chains up to C31, linked via ether bridges and comprising sterically protected ester and amide functions. EM observations revealed that the organic matter of the oil shale is chiefly composed of ultralaminae. Based on chemical and morphological grounds, these ultralaminae were shown to result from the selective preservation of resistant biomacromolecules (algaenans) occurring in thin outer walls of freshwater microalgae. The selective preservation of such algaenans thus was the main formation pathway of the Göynük Oil Shale and accounts for the typical morphological and chemical features of this large organic matter-rich deposit. In addition, the present results support the general character, suggested by previous studies, of the ultralaminae/nitrile relationship and of the correlation between nitrile distribution and the origin (marine vs lacustrine) of ultralaminae-containing kerogens.