Abstract

The interpretation of prograded gravel as an indicator of tectonic uplift, that is, "syntectonic" deposition, is not necessarily correct. Increases in sediment supply induced by tectonic uplifting did not control the progradation of gravel in the Pine Valley basin, an actively subsiding half graben in northeastern Nevada. Rather, the distribution of lithofacies in the Pine Valley basin is primarily controlled by the uneven distribution of subsidence within the basin. Differences in subsidence along the axis of the basin indicate a strong inverse relationship between the long-term subsidence rate since late Miocene time and the distance of gravel transport out into the basin. Differential progradation of alluvial gravel into the basin from various drainages along the footwall is not related to uplift or lithology of the source area, size of the catchment area, or climate. In addition, the relatively fixed location of the topographic low within the basin through time, as indicated by the distribution of lacustrine deposits and the position of the modern axial drainage, suggests that a balance between basin subsidence and sediment supply to the basin has been generally maintained through time. Thus, if subsidence rates are a measure of tectonic activity, gravel progradation may record times of reduced, not increased, tectonism.

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