Flatiron

Abstract: Summary. This study provides chronological evidence of the influence of climatic variability in the generation of late Quaternary talus flatiron sequences in Spain. The temporal clustering of the OSL and radiocarbon dates obtained from talus flatiron deposits indicates that warm/wet and cold/dry periods controlled the accumulation and incision processes in the slopes, respectively, that led to the development of talus flatirons. These results strongly suggest that talus flatiron sequences constitute valuable paleoclimatic records. Additional and more accurate geochronological data from Spain and other regions of the world would improve the potential of these poorly-known landforms in paleoenvironmental studies.

Abstract: Cuesta escarpment retreat is a principal mode of exhumation in regions of layered sedimentary rock. On the Colorado Plateau, this process acts as a mechanism for maintaining high-relief topography and facilitating drainage divide migration. Quantitative estimates of cuesta evolution are difficult to evaluate over glacial-interglacial timescales, and thus rates of geomorphic change along individual escarpments have mostly been constrained over millions of years. Several studies have addressed this problem by dating colluvium-mantled talus flatirons. However, this technique has not been applied systematically on the Colorado Plateau. This study quantifies geomorphic change along a single Colorado Plateau cuesta using Cl surface exposure dating. We present 33 ages from a single generation of talus flatirons below the Coal Cliffs of central Utah. Landscape evolution is further constrained using 14 ages from in-situ bedrock, 3 ages from boulders on gully interfluves, and two ages from terrace alluvium. Results suggest a colluvial apron was deposited below the cuesta beginning as early as Marine Isotope Stage 3, and the latest depositional phase occurred near the Last Glacial Maximum. A switch from apron deposition to incision initiated flatiron formation sometime between 19.7 ± 2.5 and 11.8 ± 1.6 ka, broadly coincident with the transition from glacial to interglacial conditions. Our results have several important implications. Climatic changes during the end of the last glacial period appear to have shifted the balance between deposition and erosion below the Coal Cliffs, emptying the sediment reservoir at their base and increasing their height via bedrock incision. The climatic forcing could be imparted by several mechanisms, including local controls on debris generation / mobilization and base level changes exerted by transverse streams. Similar processes may have occurred during previous glacial-interglacial transitions, implying that the escarpment retreat processes may be partially modulated by orbitallycontrolled variations in Earth’s climate over larger timescales. Copyright © 2018 John Wiley & Sons, Ltd.