|Paper No. 106-0|
|GLACIOPLUVIAL CLIMATE-CYCLE CONTROL OF INSET ALLUVIAL TERRACE DEPOSITS IN THE RIO GRANDE DRAINAGE, NORTH CENTRAL NEW MEXICO|
STONE, Byron D., U.S. Geol Survey, 101 Pitkin Street, East Hartford, CT 06108, email@example.com, COLE, Jim, USGS, MS 913, Denver Federal Center, Denver, CO 80225, and SHROBA, Ralph R., USGS, Box 25046, MS 913, Denver Federal Center, Denver, CO 80225|
Quaternary alluvial terrace deposits are discontinuous along streams of the Rio Grande drainage system and are inset into Tertiary rift-fill deposits of the Albuquerque basin. New mapping, subsurface data, and consistent age controls permit revision of a genetic terrace model correlated with marine 18O glacial stages. Well known regional pluvial-lake records, including nearby Lake Estancia, and ages of ground-water recharge during the last glacial cycle further support the glaciopluvial correlation. Terrace deposits typically consist of basal cobble gravel and overlying channel-fill deposits of sand and granule-pebble gravel, 50-85 m thick. Sand-silt-clay strata predominate in leeward settings. Gravel-clast rock types and sediment types provide local lithologic continuity in these otherwise allostratigraphic units. The highest terrace gravel, 98 m above the Rio Grande flood plain (RGf), is early Quaternary in age (included Bandelier ash 1.6 Ma and 1.2 Ma). Tercero Alto terrace gravel and sand deposits, 90 m above RGf, are 640 ka, late stage 16 (Lava Creek B ash). Segundo Alto terrace deposits, 44 m above RGf, include basal gravel, overlying sand-silt sequences, capped by 7 m of sand and gravel. Interbedded basalt, dated 156 ka, and overlying basalt, dated 140 ka, closely constrain a terrace age of late stage 6. Primero Alto terrace sand and gravel, 21 m above RGf in overlapping terrace deposits, extends across the inner valley beneath the RGf. Cobble-boulder gravel is present 12-20 m below Holocene alluvium. Primero deposits are correlated with late stage 2, the time of high river discharge and high local precipitation that produced ground-water recharge rates 6x the present rate. The strong correlation of dated terrace deposits with 18O glacial stages indicates genetic linkage to the forcing glaciopluvial-climate hemicycle. Each cycle began with cooling, increased effective precipitation and river discharge, and deep river erosional entrenchment for a few thousand years, followed by thousands of years of aggradation of coarse bed load, supplied by slope erosion and small glaciers. Late-glacial warming, and vegetation and hillslope stabilization subsequently decreased gravel loads and discharge, leading to incision recorded by small, low terraces, and the inset modern, interglacial flood-plain alluvium.
GSA Annual Meeting, November 5-8, 2001
General Information for this Meeting
|Session No. 106|
Quaternary Geology/Geomorphology III
Hynes Convention Center: 210
8:00 AM-12:00 PM, Wednesday, November 7, 2001
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