BROOKS RANGE OF ALASKA AND EAST-VENEZUELAN CORDILLERA: REVISED COMPARISON

The Brooks Range and east-Venezuelan segments of the Cordillera both contain fold-thrust belts of mid-Tertiary completion age, and both contain cover sheets of pre-emplaced ophiolitic, basaltic, and metasedimentary composition. Both involve marine passive-margin series (2 and 5 km thick) and foredeep fill (12 and 6 km thick), and both are associated with aging world-class petroleum reserves. Both frontal fold-thrust belts contain late structural traps beneath piggybacked tectonic surface units. Both involve hydrocarbon systems of the passive margin and/or the foredeep fill. Both areas face deep-basin uncertainties, limits to drilling, and environmental restrictions.

In the Macal area (East Venezuela), two deep exploration wells re-define a narrow Dahlstromian imbricate zone within a section of older detached folds. This limits the prospectivity of the frontal belt mountainward. Based on surface geology, well data, and 2D seismic data, the frontal belt has been described in 8 new structure cross sections.

Juxtaposing the Venezuelan Cordillera with the TACT model of the Brooks Range displays similarities in geology and in data coverage. Both zones of seismogenic coupling between lower crust and subducting slab are implied, but not documented. Reflection-seismic events suggest a 10 to 20 km thick layer of mobilized lower crust transmitting and strain-partitioning subductive shear to the surface. Both Cordilleran main bodies are vast terranes highlighted by active lineaments.