Fault scarp colluvium
Colluvial wedges, which consist of sediment eroded from a fault scarp following surface faulting, are often ideal targets for paleoseismic research because they are deposited the closest in time to the rupture event. However, colluvium is often avoided for OSL dating because of the short transport distance and likelihood of incomplete resetting of a residual/prior burial dose. To limit the sampling of only partially bleached sediment from the foot wall (e.g., sediment transported only a limited distance), one should sample the toe of colluvial wedges (most distal) and not deposits immediately abutting the fault plane. Single-grain dating is almost always used for fault-scarp colluvium, which minimizes averaging of various luminescence signals from multi-grain aliquots.
fault plane. Single-grain dating is almost always used for fault-scarp colluvium, which minimizes averaging of various luminescence signals from multi-grain aliquots.
Schematic of normal faulting rupture event along a shallow hillslope surface.
Sediemtn accumulates in the newly created scarp between the hanging wall and the footwall.
This sediment is transported a short distance,possibly rapidly and likely contains many non-bleached grains.
If sampling a colluvial wedge, it is best to target the most distal point (toe).
Other OSL targets in a paleoseismic trench include the last unit deposited prior to the rupture event, taking care not to sample bioturbated sedimetns. Additionally, post-rupture sediments overlying the colluvial wedge may be sampled to help bracket the surface rupture event.
Send samples to:
USU Luminescence Lab
1770 North Research Parkway, Suite 123
North Logan, UT 84341
All samples should be labeled 'Light-sensitive mineral samples for geologic analysis. All material will be consumed in analysis. No monetary value'.
International samples: Send via international shipping company such as UPS, FedEx, DHL, TNT, do not use local postal service.
Email tracking number to Tammy or Michelle.