Quaternary Faults and Folds of the Northern Sacramento Valley: Accommodating Transpressional Strain in the Northern Sierra and Southern Cascadia Transition Zone

Date: 4/24/2019

Time: 02:45 PM

Room: Puget Sound

The northern Sacramento Valley is located at the transition between the Sierra Nevada and Cascadia tectonic provinces where geodesy and seismology show crustal deformation is characterized by northwest oriented transpressional shear. The location and rate of individual structures taking up the deformation remains unconstrained. We map geologic structure in the subsurface and at the surface, construct fluvial terrace profiles, and date deformed Quaternary landforms in the northern Sacramento Valley to assess the evidence, style, and rate of Quaternary deformation for a series of previously identified northeast trending faults and folds within the zone of deformation including: 1) the Red Bluff fault, 2) the Inks Creek fold system, 3) the Battle Creek fault zone, and 4) the Bear Creek fault. Geophysical datasets, including a magnetic anomaly map and vintage 2-D seismic reflection profiles, suggest the Red Bluff and Bear Creek faults are deep-seated north-dipping reverse faults that displace and fold shallow strata above, while the Battle Creek is a long-lived south-dipping inverted Cretaceous normal fault. Topographic surface profiles extracted from a 10-meter DEM show each fault and fold to generally display north-side-up displacement and warp early to mid-Quaternary deposits. Longitudinal fluvial terrace profiles constructed from lidar along the Sacramento River show that deformed late Pleistocene fluvial terraces are associated with windgaps and abandoned channel features where the river traverses the Inks Creek fold system and Red Bluff fault. The sum of the observations provide evidence for late Quaternary contractional strain accommodation within the northern Sacramento Valley; however, evidence of lateral motion remains less apparent within the geomorphology. These faults mark the southern-most extent of the northern Sierra and southern Cascadia transition zone. Pending radiocarbon and optically stimulated luminescence analysis of samples collected from the deformed fluvial terraces will help constrain long-term rates of deformation.

Presenting Author: Stephen Angster

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