Compaction of basin sediments: Modeling based on time‐temperature history

Porosity decrease of sandstones, carbonates, and shales during burial is modeled here in terms of time‐temperature exposure rather than in terms of depth. Loss of porosity (ϕ) in the subsurface is represented by a power function, ϕ = A(M)B, where A and B are constants and M is a measure of integrated time‐temperature history. Regression lines of carbonate and sandstone porosity upon Lopatin's time‐temperature index of thermal maturity (TTI) generally fall within a rather narrow envelope whose axis is approximated by ϕ = 30(TTI)−0.33. This equation is useful for regional modeling of carbonate and sandstone compaction. Dependence of porosity upon integrated time‐temperature history implies that basin sediments are not in equilibrium but compact through geologic time. Calculations show that subsidence resulting from the loss of porosity with increasing time‐temperature exposure (as opposed to deeper burial) can produce a second‐stage, passively formed basin containing many hundreds of meters of sediments.