Pleistocene incision rates in the western United States calibrated using Lava Creek B tephra

Authors
Citation
Dp. Dethier, Pleistocene incision rates in the western United States calibrated using Lava Creek B tephra, GEOLOGY, 29(9), 2001, pp. 783-786
Citations number
36
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Earth Sciences
Journal title
GEOLOGY
ISSN journal
0091-7613 → ACNP
Volume
29
Issue
9
Year of publication
2001
Pages
783 - 786
Database
ISI
SICI code
0091-7613(200109)29:9<783:PIRITW>2.0.ZU;2-F
Abstract
The Lava Creek B ash bed, erupted from the Yellowstone caldera ca. 0.64 Ma, provides a datum for measuring long-term fluvial incision west of the Miss issippi River. The ash is widely preserved due to its substantial volume, b road initial dispersal, and the aggrading environment into which the ash fe ll. Drainages incised soon after Lava Creek B deposition, isolating the ash from fluvial erosion and preserving it in fill terraces. Calculated rates of incision since ca. 0.60 Ma range from less than or equal to2 to similar to 30 cm. k.y.(-1). Rates are high in most areas near the Rocky Mountains a nd downstream along rivers draining mountainous terrain, and are lowest eas t of the High Plains and along the Snake River. Incision rates along many r ivers decrease downstream. Rates of downcutting increased in the late Pleis tocene along several major rivers, indicating that climate change altered s ediment budgets. Regional and temporal data suggest that fluvial incision r ecords increased middle and late Pleistocene runoff from the southern Rocky Mountains, rather than epeirogenic uplift, but regional rock uplift cannot be excluded as a significant factor.