Colluvial sediments of talus relicts ("talus flatirons") around mesas preserve a record that sheds light on slope-forming processes at temporal scales >103yr. The sedimentology and soil stratigraphy of two groups of talus flatirons in the northeastern hyperarid Negev desert reveal four deposition events in the younger talus and at least two in the older one. Numerical modeling of high-resolution 10Be depth profiles suggests that these taluses were deposited during the middle Pleistocene; the younger talus group first depositional event occurred at 551 -142+80ka and its abandonment occurred at 270 -38+17ka. The abandonment of the older talus group and stabilization of its surface occurred at 497 -114+176ka. These ages indicate that the development of the studied talus sequence is not specifically associated with Pleistocene glacial-interglacial cycles. The 10Be modeled concentrations indicate significant differences in the average inheritance of talus flatirons of different groups. These differences can be attributed to variability in the transport distance and duration of gravel exposure during transport but could also reflect some temporal variability in cliff retreat. Our results also demonstrate that talus slopes in hyperarid areas, despite their steepness, can store sediment for long periods (~500ka) and thus constitute a valuable archive.
Bibliographical noteFunding Information:
This research was supported by the Israel Science Foundation grant 146/08 , the United States–Israel Binational Science Foundation grant 2006-221 and the U.S. Army Research Office grant ( DAAD19-03-1-0159 ). We thank Y. Rephael and A. Muskin for field assistance, Y. Nahmias and S. Mazeh for lab assistance, N. Teutsch for performing the ICP-OES analysis, A. Boroda for figure editing, and E. Morin, M. Tsaserski and Y. Amiel for fruitful discussion. We thank K. Nichols, L. McFadden, B. Harrison, R. Braucher, and A. Gillespie for their thoughtful comments that significantly improved this paper.
- Cosmogenic nuclides
- Hyperarid desert
- Landscape evolution
- Numerical modeling
- Slope processes
- Talus flatirons