Kerogens limits within the Van Krevelen diagram. In dash, approximative limits currently admitted for (H/C)_at. and (O/C)_at. ratio values of BCM: (H/C)_at. ratio values (0.02 < soot < 0.30 < charcoals < 0.60 < chars < 1.00, Hammes et al., 2007), (O/C)_at. ratio values (0.10 < soot < 0.20 < charcoals < 0.40 < chars < 0.60, Godlberg, 1985 in Hedges, 2000, Hammes et al., 2007). In black triangle: various natural or experimental charcoals, fossil charcoals (Kuhlbusch, 1998). Black arrows direction indicates the elemental composition change with increasing thermal processes (during burial and during combustion).