Write a 3 pages paper on geochemistry physics. Mechanical infiltration also plays a vital part in the downward movement of clay sized particles. Carbonate rocks such as limestone are affected by inversion, recrystallisation and grain growth as well. Typical processes that affect carbonate rocks are (sequentially) biochemical degradation, polycondensation and insolubilisation. 2. Why is the smectite to illite transition important in the process of petroleum formation? The smectite to illite transition is an important diagenesis reaction especially for shales with progressive burial. This transformation has the potential to flush hydrocarbons from various shales, accelerating the generation of hydrocarbons, producing high pore fluid pressures and for provision of various cementation agents to different sandstones. 3. How would you expect the alkane/alkene ratio to change as a hydrocarbon mixture matures over geological time, and why? The alkane/alkene ratio would tend to decrease with time as a hydrocarbon mixture matures over geological time. This would take place as the biodegradation process would tend to remove alkanes so that the hydrocarbon mixture moves towards aromatics. 4.