Insights into the Along-Strike Variation in Structural Style of the Northern Subandean Trend

T. L. Gubbels, J. R. Everett, R. J. Staskowski, J. F. Amos

The Subandean fold-thrust belt and foreland basin lies along the eastern side of the northern Andes of Peru, Ecuador and Colombia and includes the Andean foothills, part of the jungle-covered western Amazon rainforest, and the Llanos region of Colombia. Supergiant discoveries at Cusiana and Cano Limon demonstrate the major hydrocarbon potential of the region. A regional digital geologic interpretation based on a 63-scene geocoded digital Multispectral Scanner (MSS) mosaic extending from 8°S to 8°N provides a guide to exploration strategies in this remote and poorly known region.

Within this region, the Subandean fold-thrust belt is segmented into four discrete zones of characteristic structural style. In the southernmost segment, south of 5°S, active thin-skinned deformation extends over 200 km east of the Andean topographic front and is controlled by a thick interval of Mesozoic salt. Salt diapirism and thickening along anticlinal axes are characteristic of this segment; the impressive width of this belt is likely related to a low-viscosity, subhorizontal salt decollement. The folded zone narrows considerably to the north; between 5° and 1°S, the fold-thrust belt is less than 100 km wide and buried by a thick sequence of slightly deformed Tertiary clastics. Between 1°S and 4°N, the Subandean zone is basement involved and the deformat on front is emergent, with Precambrian basement thrust over the Tertiary. In the northernmost segment, from 4° to 8°N, several thrust-tip folds exceed lengths of 100 km, and a mixture of thick- and thin-skinned styles are present. Segment boundaries are related to paleotectonic controls, rather than dynamic controls imposed by the subducting Nazca plate.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995