Temporal variations in Holocene slip rate along the central Garlock fault, Pilot Knob Valley, California

Average geologic slip rates along the central Garlock fault, in eastern California, are thought to have been relatively steady at 5-7 mm/yr since at least the Late Pleistocene, yet present-day rates inferred from geodetic velocity fields are indistinguishable from zero. We evaluate the possibility of non-steady slip over millennial timescales using displaced Late Holocene alluvium along the central Garlock fault in Pilot Knob Valley. Truncation of a Late Holocene alluvial fan deposit against a shutter ridge requires a minimum of 30-37 m of displacement since deposition of the fan; maximum allowable displacement is 43-50 m. The extent of soil development atop the fan surface and optically stimulated luminescence ages bracket fan deposition between 3.5 and 4.5 ka. Together, these data require that slip rates during the Late Holocene were ̃7-14 mm/yr, with a preferred rate of ̃11-13 mm/yr. Our results, in conjunction with previous estimates of displacement over the past ̃15 ka, require significant temporal variations in strain release along the Garlock fault and confirm previous suggestions that interactions among fault systems in eastern California give rise to alternating periods of fault activity and quiescence

Late MIS 3 stabilization of dunes in the eastern Central Great Plains, USA

Extensive luminescence and 14C dating of aeolian sand dunes and sheets in the Central Great Plains (CGP) have been biased toward the western part of the region, targeted relatively large dune fields, and produced primarily Holocene (Marine Isotope Stage (MIS) 1) and latest Pleistocene (MIS 2) ages. This research luminescence dated a small discontinuous dune field perched on the high terrace of the Kansas River valley, situated on the eastern side of the CGP. These dunes have been stable since at least 30–28 ka, indicating that they are among the oldest recognizable dunes preserved in the CGP, as well as the entire North American Great Plains. The inferred stabilization of these dunes was coeval with pedogenesis and low sediment accumulation rates in upland loess, playa lunettes, and alluvial sequences in the CGP, in a time period with maximum summer insolation and relatively warm conditions. Source of the sand is presumed to have been fluvial sediments from the adjacent Kansas River, now preserved as the Buck Creek Terrace. Sand-mobilizing winds were southerly to southwesterly given that the dunes mantle only the high-terrace remnants on the north side of the valley. Long-term dune stability after MIS 3 appears to indicate that latest-Pleistocene and Holocene megadroughts were not sufficiently severe and eastward penetrating to reactivate these eastern CGP dunes