ABSTRACT

The Atlantic-type passive margin of the northeast Gulf of Mexico consists of a thick section of Mesozoic and Cenozoic sedimentary strata. Tectonic subsidence curves calculated by backstripping stratigraphic columns acquired from deep well data in Mississippi, Alabama and Florida compare well with theoretical subsidence curves for uniform extension of the lithosphere. Results support an interpretation of rift-related lithospheric extension during the Early/Middle Jurassic followed by a long period of thermal subsidence. Subsidence patterns indicate that the lithosphere is unattenuated north of the peripheral fault zones and thins southwards. Crustal thinning reached maxima in the deep Mississippi Salt Basin and in state waters west of Mobile Bay. Present-day crustal thicknesses estimated from tectonic subsidence curves agree well with seismic refraction data and show that thick transitional crust underlies the northeast Gulf margin. Using the one-dimensional heat flow equation and including effects of sedimentation rate, compaction, and radiogenic heat production, the thermal history of the sediment fill was determined. Constraints for the model were provided by geochemical data, bottom hole temperatures and heat flow measurements. Model results show that the Jurassic Smackover Formation, the regional source rock, entered the oil window during Early to Late Cretaceous. Calculated thermal maturities suggest that the Smackover may reach maturity levels sufficient to generate liquid hydrocarbons at burial depths as shallow as 3 km and become overmature at a minimum depth of approximately 5 km.