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Rocky Mountain (66th Annual) and Cordilleran (110th Annual) Joint Meeting (19–21 May 2014)

Paper No. 10
Presentation Time: 10:45 AM

WHAT IS THE ROLE OF CLIMATE AND GLACIATION ON LATE PLEISTOCENE SEDIMENT PRODUCTION RECORDED IN ALLUVIAL FANS, LOST RIVER RANGE IDAHO?


RITTENOUR, Tammy1, KENWORTHY, Megan K.2, PIERCE, Jennifer L.2, PIERCE, Kenneth L.3, SUTFIN, Nicholas A.4 and SHARP, Warren5, (1)Department of Geology and Luminescence Laboratory, Utah State University, Logan, UT 84322, (2)Department of Geosciences, Boise State University, Boise, ID 83725, (3)U. S. Geological Survey, NRMSC, 2327 University Way, Box 2, Bozeman, MT 59715, (4)Geosciences, Colorado State University, Campus Delivery 1482, Fort Collins, CO 80523-1482, (5)Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709, tammy.rittenour@usu.edu

We present geomorphic, sedimentologic and geochronologic (OSL and U-series) results from large low-gradient alluvial fans at the base of the Lost River Range (LRR), southeastern Idaho. This research addresses two major questions related to sediment production recorded in LRR alluvial fans:

1. How does the timing of alluvial fan deposition relate to glacial-interglacial climates? Bull’s (1991) hypothesis, based on the southwest US, suggests greatest sediment delivery to streams during transitions between glacial and interglacial climates due to liberation of hillslope sediments generated under wetter glacial regimes. Alternatively, research in the northern Rocky Mountains suggests fluvial aggradation during glacial conditions due to increased sediment production and higher discharges at these times. Strict application of these two hypotheses suggests peak LRR fan deposition in either the earliest Holocene or during the last glacial maximum (LGM).

2. What is the influence of glaciation within the catchment on the timing and volume of sediment delivered to alluvial fans? It is expected that catchments which hosted late Pleistocene glaciers will have greater sediment production and different records than fans at the mouth of non-glaciated catchments. Study catchments ranged from 80% glaciated to non-glaciated.

Results indicate the deposition of broad concordant alluvial fan surfaces at 13-18, 20-30, 35-60 and 95-115 ka. Holocene deposits are restricted to narrow incised channels. Limited LGM-aged deposits and the predominance of MIS 3-4 deposits suggests a disconnect between regional ice extent, catchment-scale sediment production and alluvial fan deposition. Moreover, similarity of alluvial fan records between glaciated and unglaciated basins suggests the extent of catchment glaciation has little influence on the timing or scale of downstream fan deposition. Instead, alluvial-fan sedimentation reflects regional climatic influence on hillslope sediment production.

Session No. 29

T5. Session Honoring Kenneth L. Pierce and the Breadth of His Research in Greater Yellowstone
Wednesday, 21 May 2014: 8:00 AM-12:00 PM
Procrastinator Theater (Montana State University)
Geological Society of America Abstracts with Programs. Vol. 46, No. 5, p.82
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