Paleo Heat Flow in North American Late Paleozoic Foreland Basins: Constraints From Permian Basin of West Texas

Alton A. Brown
Consultant, Richardson, TX, USA; [email protected]

North American Late Paleozoic foreland basins are characterized by relatively high thermal maturity that is inconsistent with current burial depth and modern heat flow. Previous studies have explained high thermal maturity by some combination of exhumation, lateral heat transfer by moving groundwater, and elevated heat flow (near igneous bodies). Elevated, basin-scale paleo heat flow has not been proposed, because it is widely believed that basement heat flow on cratons is relative stable through time.
The Eastern Delaware basin and Central Basin platform (west Texas) provides a test for craton heat flow stability, because burial history is well constrained. Paleozoic and early Mesozoic strata are preserved, and later burial history can be reconstructed from nearby areas. Stratigraphic relations prevent significant groundwater flow to the foreland basin and igneous activity is absent. Proximity of platform carbonates and basin siliciclastics allows comparison of assumed conductivity models on thermal maturity.
One-dimensional conductive geohistory models for wells on the carbonate platform and the siliciclastic basin demonstrate that modern heat flow (48 mW/m²) is insufficient to reproduce the observed thermal maturity (vitrinite reflectance) trend, even if exceptionally generous Cretaceous and Cenozoic burial and exhumation are assumed.
Because burial history is well constrained, the only way to explain observed thermal maturity is an elevated heat flow in the past. Early to middle Cenozoic heating is associated with volcanic intrusions in West Texas that extends into the western Delaware basin. Pre-Cretaceous subcrop patterns are consistent with heating in far west Texas associated with formation of a Late Jurassic-early Cretaceous rift. However, the study area is too far east to be affected by either of these events. Late Triassic or Early Jurassic heating is most favorable for developing observed thermal maturity because it is the time of maximum burial. No tectonic events or intrusions are documented at this time.
One possible cause for Late Triassic heating is a deep thermal pulse caused by Hercynian collision that is delayed from reaching the sedimentary basin by transient heat flow. The lag time can be significant for deep heating events. Peak heating in the sedimentary basin by a base-lithosphere (100 km depth) thermal pulse (such as cratonic lithosphere overriding hot mantle) is about 150 My after initiation of base lithosphere heating. Heating at the base of the lithosphere in response to collision and Late Paleozoic plate movements would reach Permian basin strata during the Late Triassic and early Jurassic, coincident with maximum burial. The duration and magnitude of base lithosphere heating can be constrained by the amount of heating needed to match the thermal maturity in the sedimentary basin.

AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands

AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands