Quaternary geology and ecology of the greater Yellowstone area (original) (raw)
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Climate, Tectonics or...?: Speculations on the Recent Paleolimnology of Yellowstone Lake
2013
The sediments of Yellowstone Lake may reveal the paleoecological history of this lake over the last few centuries. These sediments contain up to 60 % biogenic silica derived from diatom frustules settling out from the overlying water. The sediment record reveals large variations in the diatom deposition over the last ~350 years. Some of these variations appear to correlate extremely well with independent climate records, particularly mean annual winter temperature and precipitation, derived from tree ring data extrapolations. A strong correlation occurs, for example, during an extended period of below-normal winter temperatures and above-normal precipitation seen during the late 1800s. Below-normal winter temperatures can significantly extend winter ice cover and shorten the icefree, isothermal period during which the spring diatom bloom occurs. Rapid thermal stratification following prolonged ice cover may reduce annual diatom production and the subsequent silica deposition. Yet th...
PhD Dissertation, University of New Mexico, 1993
The Yellowstone fires of 1988 provided an opportunity to observe the geomorphic impact of widespread, intense forest fires on a mountain environment. Post-1988 fire-related sedimentation events also served as geomorphological and sedimentological analogs which were used to interpret a Holocene stratigraphic record of fire-related alluvial activity. Research focused primarily on the steep-walled glacial trough valley of Soda Butte Creek, and parts of the Slough Creek and Lamar River drainages in northeastern Yellowstone. All of the examined major post-1988 fire-related sedimentation events involved the generation of widespread surface runoff from brief, intense summer convective-storm precipitation on steep slopes in intensely burned basins. Sheetwash and rillflow entrained large quantities of fme soil-surface sediment. Where runoff became concentrated in low-order channels, deep incision and progressive sediment bulking occurred, with most smaller basins ( <2 km2) producing debris flows in initial phases of early postfire events. Deposition occurred mainly on alluvial fans along the sides of trough valleys. The depositional sequence in each event implied a progression from higher- to lower-sediment concentration flows. The relative importance of flow processes in an event is partly determined by basin characteristics such as area, relief, percentage of exposed bedrock, lithology, and available sediment. Later events were dominated by dilute flows, probably because of (1) flushing of channel storage in prior events, and/or (2) compaction of burned soil surfaces, thus reduced fine sediment availability even in previously inactive basins. In general, debris-flow dominated events caused fan aggradation, whereas more erosive streamflow-dominated events caused progradation of fans. Post-1988 fire-related debris-flow deposits commonly displayed an abundance of mud-rich matrix bearing coarse charcoal. Similar charcoal-rich fire-related debris-flow facies were identified in Holocene alluvial fan stratigraphic sections and dated by 14C methods, calibrated to calendar years. Charcoal is typically scarce in fire-related hyperconcentrated-flow and streamflow sediments, but units of these facies were interpreted as probable fire-related sediments where they overlie well-preserved charred 0 horizons (soil surface layers), also 14C-datable. vii An estimated 30% of the late Holocene fan alluvium in the Soda Butte drainage consists of fire-related debris-flow and probable fire-related sediments. Fire-related depositional events cluster strongly within the intervals of ca. 6500-6100 BC, 4500-4000 BC, 3500-2400 BC, 800 BC-350 AD, and 650-1200 AD. A major peak in fire-related debris-flow activity occurred at the height of the globally-recognized Medieval Warm Period ca. 1050-1200 AD, and notable correspondence exists between other warm and dry periods in high-resolution climate proxy records and fire-related sedimentation. Historical climate analogs imply that convective-storm activity during warmer periods is increased, but that high interannual variability of summer precipitation at such times may enhance the potential for both severe short-term drought and storm-generated fan deposition in northeastern Yellowstone. Along lower Soda Butte Creek, fill-cut terrace surfaces are created by extensive lateral erosion of channels and concurrent accumulation of overbank sediments. Overbank aggradation occurred ca. 7300(?)-6700 BC (terrace level Tla), 5800-4500 BC (Tlb), 1400-800 BC (T2), 100 BC-650 AD (T3), and 1200-1700 AD (T4). Local paleoclimatic indicators imply effectively wetter conditions during these intervals. Because most present-day runoff, overbank flow, and suspended sediment yield occurs during the snowmelt period, floodplain widening and overbank sedimentation probably occurs during periods of generally cooler and wetter climate with higher winter precipitation. In transitions to drier intervals, reduced average runoff results in meanderbelt narrowing, and incision may be driven by extreme flood discharges during warm rain-on-snow events. Alluvial systems in northeastern Yellowstone show a clear response to millennial-scale Holocene climatic cycles, where alluvial fan aggradation and progradation over valley floors during drier periods alternates with floodplain construction and trimming back of fans by axial streams during wetter periods. "Small-scale" climatic fluctuations of the Holocene thus had substantial impact on postglacial landscapes in northeastern Yellowstone.
Glacial limits in the middle and southern Rocky Mountains, USA, south of the Yellowstone Ice Cap
Developments in Quaternary Science, 2004
This chapter includes the mapped limits for glacial deposits of the Middle and Southern Rocky Mountains of the USA except Yellowstone National Park and the immediately adjacent ranges in Wyoming, Montana, and Idaho. Map units include: (1) the maximum limits of Pleistocene glaciation, (2) the limits of Pinedale glaciation, (3) the limits of Bull Lake glaciation, and (4) the limits of deposits that are presently thought to correlate to the European Younger Dryas climate event. Few map units that are identified in this region unequivocally correspond to the early-middle Wisconsin period. Numbers discussed in superscript refer to localities that are important to the Quaternary interpretations of this region and the location of each is indicated on the accompanying map. The chapter also discusses that the model for the glacial succession in Rocky mountain region was established. Early mapping recognized deposits that corresponded to two alpine glaciations in many ranges. Later maps delineated deposits that corresponded to three glaciations. It reviews that each of these glaciations subsequently has been subdivided, with subdivisions based on relative age and numeric age-data. It identified deposits corresponding to three Pleistocene glaciations in the Wind River Range: the Pinedale, Bull Lake, and Buffalo drifts.
MBMG Special Publication 122: Geology of Montana, vol. 1: Geologic History, 2020
The Neogene Sixmile Creek Formation fi lls many grabens south of the Lewis and Clark Tectonic Zone in western Montana, preserving a stratigraphic record of the outbreak and passage of the Yellowstone hotspot from ~17 Ma to ~2.5 Ma. The grabens were formed on a broad dome centered on the hotspot outbreak area in southwest Idaho and southeast Oregon, producing an angular unconformity as the underlying Renova Formation and older rocks were tilted, eroded, and buried by graben fi ll of the Sixmile Creek Formation. Where these grabens were connected to drainages from the hotspot bulge, the Sixmile Creek consists of three spatially and temporally interleaved lithostratigraphic members. From oldest to youngest, they are the Sweetwater Creek, Anderson Ranch, and Big Hole River members, and are best exposed in the Ruby and Be averhead grabens in southwest Montana. Early in the evolution of the grabens, debris and fl uvial fl ows surged down from horst blocks and accumulated in the grabens. They captured runoff from the hotspot dome, resulting in thick deposits of inter-bedded fl uvially deposited silicic tephra and far-traveled river gravel. As the hotspot track propagated northeast-ward along the eastern Snake River Plain, the northeasterly gradient increased, resulting in more gravel input and increasingly larger clast sizes. On the plains, northeasterly fl owing braided rivers draining the Rocky Mountains to the west deposited widespread gravel called the Flaxville Formation. Around 4 Ma, the middle Miocene grabens were crosscut by northwest-trending Pliocene grabens as crustal stresses changed with the northeasterly passage of volcanic centers along the hotspot track. Some drainages were diverted into the new grabens, creating the present drainage system in southwest Montana.