FLEXING THE MARGIN: ALTERNATIVE HYPOTHESES FOR FLANK UPLIFT ALONG THE TEXAS GULF OF MEXICO MARGIN

The Texas margin of the Gulf of Mexico provides an opportunity to test the hypothesis that sediment loading can induce uplift along the flanks of passive and rifted margins. Such ‘flexural uplift' models (e.g. Karner and Watts, 1982) are an alternative to ‘thermal subsidence' models and make different predictions on the structural and thermal histories of hydrocarbon-rich basins. The uplifted flank of the Texas Gulf margin is the Llano-Edwards plateau consisting of Mesoproterozoic (Grenville) and Paleozoic (Ouachita) rocks that sit ~800 meters above sea level. The plateau was exhumed from ~2 km depth from the late Triassic through early Jurassic rifting (from apatite fission track work of Corrigan et al., 1998). Roughly 100 m.y. later, in the late Cretaceous, the Gulf margin was buried by ~1 km of sediment marking the beginning of several pulses of sedimentation that formed roughly two-thirds of the Gulf's stratigraphic section. In the sediment-loading hypothesis, the southeastern front of the plateau is bounded by the Balcones fault system, a “hinge” area for plateau uplift. An alternative hypothesis for the Balcones escarpment holds that it is a retreating escarpment. Still another hypothesis holds that the Llano plateau has been relatively passive to sediment transport to the gulf. Hypothesis tests for future work include: more low-temperature thermochronology of the Llano plateau, topographic analysis of the gulf margin, structural analysis of the Balcones fault system, seismic and potential field analysis of the margin (to investigate possible asthenospheric response to flank uplift), and forward modeling of the GoM rift with numerical techniques. Such hypothesis tests can simultaneously shed more light on the crustal and upper mantle composition of the Gulf margin, as formed during Paleozoic orogenic events and Mesozoic rifting.

References

Corrigan, J., Cervany, P. F., Donelick, R., and Bergman, S. C. Postorogenic denudation along the late Paleozoic Ouachita trend, south central United States of America: Magnitude and timing constraints from apatite fission track data. Tectonics 1998, 17, 587-603.

Karner, G.D., and Watts, A.B. On isostasy at Altantic-type continental margins. Journal of Geophysical Research 1982, 87, 2923-2948.