ABSTRACT

Two major regional trends in the Gulf Coast heat flow have been noted--decreasing temperatures at constant depth in younger, more basinward units and increasing geothermal gradient with depth. These trends are complicated by local heat flow anomalies. While basement heat input may have increased during a Mesozoic rifting episode, it has probably remained essentially constant since the late Jurassic. Therefore, the regional differences in heat flow must be the result of intrinsic sediment properties, sediment deposition, and fluids moving through the sediments. Numerical modeling indicates that the major regional trends can be explained by a moving boundary effect caused by continuous, long-term sediment deposition, coupled with forced convection caused by the compaction of the sediments. Deposition of cool sediments depresses the isotherms until the sediments can be heated to normal levels. Marginward heat advection due to lateral and upward movement of fluids through the more permeable sediments also contributes to the regional trend of higher temperatures in the older, inland sediments. Local perturbations (abnormally high temperatures) are caused by fluid movement focused by either faults or salt dome flanks. Observed thermal anomalies near salt domes may be caused primarily by fluid movement and not the greater thermal conductivity of salt. Finally, theoretical and field evidence indicates the possible occurrence of free convection in the Gulf Coast Basin. This may modify the heat flux on both a regional and a local scale.