Abstract
AbstractThe Wheeler Ridge anticline, located in the southern San Joaquin Valley of California, USA, is a well-studied and classic example of a laterally growing fault propagation fold. New high-resolution lidar elevation data combined with nine infrared stimulated luminescence (IRSL) ages of discrete geomorphic surfaces that are bounded by prominent transverse wind and river gaps allow for investigation of tectonic topography through time. Luminescence ages from four of the six surfaces yield depositional ages that range from 32 ka to 153 ka, which are broadly consistent with a previously published soil chronosequence. Our graphical modeling indicates an average surface uplift rate of ~2.1 mm/yr and an average along-strike fold propagation rate of ~20 mm/yr. However, our probabilistic modelling and topographic analysis suggest a rate decrease of both uplift and lateral propagation toward the fault tip from ~2.4 to 0.7 mm/yr and from ~49 to 14 mm/yr, respectively. Rate decreases are not progressive but rather occur in punctuated deformational intervals across previously documented structural barriers (tear faults) resulting in a fold that is characterized by discrete segments that exhibit a systematic deformational decrease toward the east. The punctuated tectonic growth of Wheeler Ridge has also locally controlled the topographic evolution of the anticline by effecting the formational timing and position of at least seven wind and river gaps that result from multiple north-flowing antecedent streams that traverse the growing structure. We quantify the timing of wind and river gap formation, based on IRSL results and inferred incision rates, and present a model for the spatiotemporal evolution of transverse drainages and the topographic development of Wheeler Ridge. Our chronology of gap formation broadly correlates with regional Late Pleistocene dry climate intervals suggesting that both tectonics and climate were integral to the geomorphic development of the Wheeler Ridge anticline.
Highlights
The double-restraining bend in the platebounding San Andreas fault system in Southern California has resulted in broad regions of transpressional deformation both north and south of the bend (Figure 1(a))
This paper presents nine new infrared stimulated luminescence (IRSL) ages from uplifted and isolated alluvial fan surfaces, and new geomorphic mapping and topographic analysis based on a high-resolution lidar dataset to better constrain the evolution of this well-known fault propagation fold
We compare our modelled and graphical uplift and lateral propagation rates with a geomorphic model proposed by Hetzel et al [24] to bolster our field mapping and digital topographic analysis of the occurrence of wind gaps that traverse the topography of Wheeler Ridge (Figures 4(a) and 4(b))
Summary
The double-restraining bend (the Big Bend) in the platebounding San Andreas fault system in Southern California has resulted in broad regions of transpressional deformation both north and south of the bend (Figure 1(a)). The onset of transpressional deformation, northward folding, and thrust-related displacement by the buried Pleito thrust fault along the San Emigdio front is estimated to have initiated 450–700 ka [29]. Uplift rates estimated from retrodeformed sedimentary strata identified in hydrocarbon exploration wells suggest northward propagation of the deformational front onto the Wheeler Ridge fault initiated between 250 and 400 ka (Figure 1(b); [20, 29]). Transfer of strain into the foreland would have resulted in a local decrease in slope within the newly formed piggyback basin, thereby setting up a competition between the erosive power of northward flowing streams from the San Emigdio Mountains and the east-propagating tectonic topography of the Wheeler Ridge fault [18]. A fold propagation rate of 25–30 mm/yr has been estimated from the ages of the youngest deformed alluvial fan surfaces at Wheeler Ridge [19, 21]
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