The evolution of the overburden affects the thermal structure (Table 14.1) and numerous other factors important to a petroleum system during the development of a thrustbelt. In the case of increasing burial, the underlying sediments subside to greater depths with higher temperatures (Fig. 14.1a). In the case of erosion, the underlying sediments are uplifted to shallower depths with lower temperatures.Whether subsidence or uplift occurs depends on depositional rates and erosional rates specific for different environments.

Because the interplay of deposition and erosion in thrustbelts is complex, this discussion will start by investigating their impact on the thermal structure in simple settings, which have equal depositional or erosional rates over large areas before moving progressively to thrustbelt settings.

Role of deposition on thermal regimes

Assuming no erosion, deposition depresses the heat flow, and the depression persists long after sedimentation ceases (De Bremaeker, 1983; Ungerer et al., 1990). The magnitude of the depression depends on the thermal conductivity of the sediments deposited and the rate and duration of deposition (e.g., Jessop and Majorowicz, 1994; Yalcin et al., 1997).

Insight into the effects of deposition, compaction and related pore fluid movement on the thermal regime in tectonically simple oceanic and deep marginal basins (Hutchison, 1985) allows representation of the sediment system by a two-layer model in which horizontal dimensions extend to infinity (Fig. 14.2a). It allows the application of a simplified one-dimensional solution for vertical heat flow.