Quaternary alluvial-fan development, climate and morphologic dating of fault scarps in Laguna Salada, Baja California, Mexico

• Published in: Geomorphology (Amsterdam, Netherlands) Vol. 102; no. 3; pp. 578 - 594
• Main Authors: Spelz, Ronald M., Fletcher, John M., Owen, Lewis A., Caffee, Marc W.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.12.2008; Elsevier
• Subjects: Active tectonics; Baja California; Earth sciences; Earth, ocean, space; Exact sciences and technology; Geochronology; Geomorphology, landform evolution; Isotope geochemistry. Geochronology; Marine and continental quaternary; Paleoclimate; Surficial geology; Terrestrial cosmogenic nuclide (TCN) dating; Mexico; Baja California Mexico; Canada; Paleoclimate; Active tectonics; Terrestrial cosmogenic nuclide (TCN) dating; Baja California; diffusion; alluvial fans; degradation; slopes; upper Quaternary; North America; faults; paleoclimate; fault scarps; middle Pleistocene; aridity; Be-10; dating; tectonics; Cenozoic; climate change; cosmogenic elements; Quaternary; boulders; concentration; upper Pleistocene; diffusivity; exposure age; Phanerozoic; landform evolution; Pleistocene
• ISSN: 0169-555X; 1872-695X
• DOI: 10.1016/j.geomorph.2008.06.001

Late Quaternary slip across the Cañada David detachment has produced an extensive array of Quaternary scarps cutting alluvial-fans along nearly the entire length (~ 60 km) of the range-bounding detachment. Eight regional alluvial-fan surfaces (Q 1 [youngest] to Q 8 [oldest]) are defined and mapped along the entire Sierra el Mayor range-front. Terrestrial cosmogenic nuclide 10Be concentrations from individual boulders on alluvial-fan surfaces Q 4 and Q 7 yield surface exposure ages of 15.5 ± 2.2 ka and 204 ± 11 ka, respectively. Formation of the fans is probably tectonic, but their evolution is strongly moderated by climate, with surfaces developing as the hydrological conditions have changed in response to climate change on Milankovitch timescales. Systematic mapping reveals that the fault scarp array along active range-bounding faults in Sierras Cucapa and El Mayor can be divided into individual rupture zones, based on cross-cutting relationships with alluvial-fans. Quantitative morphological ages of the Laguna Salada fault-scarps, derived from linear diffusive degradation modeling, are consistent with the age of the scarps based on cross-cutting relationships. The weighted means of the maximum mass diffusivity constant for all scarps with offsets < 4 m is 0.051 and 0.066 m 2/ka for the infinite and finite-slope solutions of the diffusion equation, respectively. This estimate is approximately an order of magnitude smaller than the lowest diffusivity constants documented in other regions and it probably reflects the extreme aridity and other microclimatic conditions that characterize the eastern margin of Laguna Salada.