**3.1 Sample preparation for particulate organic components analysis**

For analyzing individual organic components, a standard non-oxidative method is applied for the isolation of kerogen [24, 25]. The crushed (2–5 mm) sample is preextracted in the Soxhlet extraction apparatus using dichloromethane (CH2Cl2) for at least 24 hours. The crushed fraction must be treated with HCl and HF acids to remove carbonates and silicates. Heavy solution of ZnCl2 (ρ = 1.95 at 20°C) is applied in order to concentrate the kerogen. The organic residue is sieved through a 10 mm nylon mesh using distilled water, isolated kerogen is the fraction retained in the sieve.

Particulate organic components are separated by size using a set of nylon membranes. Set of nylon membranes with pore diameters ranging from 5 to 200 μm. The sieving process follows the arrangement of the sieves (membranes) in a sequential nest: smallest mesh number (larger aperture, 120 to 200 μm) at the top and largest mesh number (smallest aperture, 20– 100 μm) at the bottom. The set of smallest aperture nylon membranes is used for the filtration process using a Kitasato flask and a vacuum pump. Organic residues separated by size after the filtration process are spread on slides using different solutions (water, detergent, and alcohol). The hand-picking technique is performed on the kerogen concentrate (KC) strewn slide. This slide is placed under the microscope and the organic particles are separated from each other, one by one, with the aid of a histological needle (**Figure 2a**). The components of the heterogeneous mixture are then identified and individually separated from each other (**Figure 2b**–**e**).
