Bull Lake Glaciation Research Articles

Numerical modeling of the Snowmass Creek paleoglacier, Colorado, and climate in the Rocky Mountains during the Bull Lake glaciation (MIS 6)

AbstractWell-preserved moraines from the penultimate, or Bull Lake, glaciation of Snowmass Creek Valley in the Elk Range of Colorado (USA) present an opportunity to examine the character of the high-altitude climate in the Rocky Mountains during Marine Oxygen Isotope Stage 6. This study employs a 2-D coupled mass/energy balance and flow model to assess the magnitudes of temperature and precipitation change that could have sustained the glacier in mass-balance equilibrium at its maximum extent during the Bull Lake glaciation. Variable substrate effects on glacier flow and ice thickness make the modeling somewhat more complex than in geologically simpler settings. Model results indicate that a temperature depression of about 6.7°C compared with the present (1971–2000 AD) would have been necessary to sustain the Snowmass Creek glacier in mass-balance equilibrium during the Bull Lake glaciation, assuming no change in precipitation amount or seasonality. A 50% increase or decrease from modern precipitation would have been coupled with 5.2°C and 9.1°C Bull Lake temperature depressions respectively. Uncertainty in these modeled temperature depressions is about 1°C.

Surface reconstruction and derivation of erosion rates over several glaciations (1 Ma) in an alpine setting (Sinks Canyon, Wyoming, USA)

At middle to high latitudes, many alpine valleys have been shaped by glaciers associated with periods of Pleistocene glaciation. Present glaciated valleys are characterised by broadened valley floors and U-shaped cross sections, continuously formed by glacial activity from initially V-shaped, fluvial cross sections. Sinks Canyon (Wind River Range, USA) is a glaciated valley characterised by a typical U-shaped cross section, containing till from several glacial advances over a range of at least 1Ma. The morphostratigraphic records indicate a fourfold difference in ice surface elevation between the youngest and oldest glacial periods, which is not easily explained by the present-day valley topography. To assess possible evolution scenarios of Sinks Canyon, we modelled the palaeovalley topography using a geographic information system (GIS) filtering technique in combination with temporal reference points from relative and numerically dated glacial deposits. Ice thicknesses were calculated using the shallow ice approximation.In our model, the valley became shallower and the topography smoother with increasing years back in time. The results suggest that valley topography with ages between 640 and 1000ka can clearly be distinguished from the present-day topography. Surfaces with ages of 130–200ka (attributable to MIS 6; Bull Lake glaciation) still could be discerned from present-day topography, but with relatively high uncertainties. The method did not work for topography less than ~100ka or older than ~1Ma. Erosion depths were calculated using the differences between present-day elevation and the modelled surfaces. Calculated erosion rates were within the range of reference values for glacial erosion (0.001 to 1mm a−1). Glacial erosion appears to have removed 0.52 to 0.72mm a−1 of rock within a time frame of 1Ma, assuming 200ka of aggregated glacial flow. If the glacial occupation was longer or the impact of fluvial erosion was not negligible (as assumed), then the calculated rate is lower. If the model assumes a less extended time of glacial flow (<100ka), the rate exceeds 1mm a−1. The method used for surface reconstruction and erosion rates calculation is highly dependent on (i) the reliability of the temporal anchor points and (ii) the assumption of physical glacier conditions (basal shear stress).

Timing of glaciation and last glacial maximum paleoclimate estimates from the Fish Lake Plateau, Utah

The High Plateaus of Utah include seven separate mountain ranges that supported glaciers during the Pleistocene. The Fish Lake Plateau, located on the eastern edge of the High Plateaus, preserves evidence of at least two glacial advances. Four cosmogenic 3He exposure ages of boulders in an older moraine range from 79 to 159 ka with a mean age of 129 ± 39 ka and oldest ages of 152 ± 3 and 159 ± 5 ka. These ages suggest deposition during the type Bull Lake glaciation and Marine Oxygen Isotope Stage (MIS) 6. Twenty boulder exposure ages from four different younger moraines indicate a local last glacial maximum (LGM) of ~ 21.1 ka, coincident with the type Pinedale glaciation and MIS 2. Reconstructed Pinedale-age glaciers from the Fish Lake Plateau have equilibrium-line altitudes ranging from 2950 to 3190 m. LGM summer temperature depressions for the Fish Lake Plateau range from −10.7 to −8.2°C, assuming no change in precipitation. Comparison of the Fish Lake summer temperature depressions to a regional dataset suggests that the Fish Lake Plateau may have had a slight increase (~ 1.5× modern) in precipitation during the LGM. A series of submerged ridges in Fish Lake were identified during a bathymetric survey and are likely Bull Lake age moraines.

Cosmogenic exposure-age chronologies of Pinedale and Bull Lake glaciations in greater Yellowstone and the Teton Range, USA

We have obtained 69 new cosmogenic 10Be surface exposure ages from boulders on moraines deposited by glaciers of the greater Yellowstone glacial system and Teton Range during the middle and late Pleistocene. These new data, combined with 43 previously obtained 3He and 10Be ages from deposits of the northern Yellowstone outlet glacier, establish a high-resolution chronology for the Yellowstone–Teton mountain glacier complexes. Boulders deposited at the southern limit of the penultimate ice advance of the Yellowstone glacial system yield a mean age of 136±1310Beka and oldest ages of ∼151–15710Beka. These ages support a correlation with the Bull Lake of West Yellowstone, with the type Bull Lake of the Wind River Range, and with Marine Isotope Stage (MIS) 6. End moraines marking the maximum Pinedale positions of outlet glaciers around the periphery of the Yellowstone glacial system range in age from 18.8±0.9 to 16.5±1.410Beka, and possibly as young as 14.6±0.710Beka, suggesting differences in response times of the various ice-cap source regions. Moreover, all dated Pinedale terminal moraines in the greater Yellowstone glacial system post-date the Pinedale maximum in the Wind River Range by ∼4–6kyr, indicating a significant phase relationship between glacial maxima in these adjacent ranges. Boulders on the outermost set and an inner set of Pinedale end moraines enclosing Jenny Lake on the eastern Teton front yield mean ages of 14.6±0.7 and 13.5±1.110Beka, respectively. The outer Jenny Lake moraines are partially buried by outwash from ice on the Yellowstone Plateau, hence their age indicates a major standstill of an expanded valley glacier in the Teton Range prior to the Younger Dryas, followed closely by deglaciation of the Yellowstone Plateau. These new glacial chronologies are indicative of spatially variable regional climate forcing and temporally complex patterns of glacier responses in this region of the Rocky Mountains during the Pleistocene.

Cosmogenic 3He exposure ages of Pleistocene debris flows and desert pavements in Capitol Reef National Park, Utah

The Quaternary history of the Capitol Reef area, Utah, is closely linked to the basaltic-andesite boulder deposits that cover much of the landscape. Understanding the age and mode of emplacement of these deposits is crucial to deciphering the Quaternary evolution of this part of the Colorado Plateau. Using cosmogenic 3He exposure age dating, we obtained apparent exposure ages for several key deposits in the Capitol Reef area. Coarse boulder diamicts capping the Johnson Mesa and Carcass Creek Terraces are not associated with the Bull Lake glaciation as previously thought, but were deposited 180±15 to 205±17 ka (minimum age) and are the result of debris flow deposition. Desert pavements on the Johnson Mesa surface give exposure ranging from 97±8 to 159±14 ka and are 34–96 kyears younger than the boulder exposure ages. The offset between the boulder and pavement exposure ages appears to be related to a delay in pavement formation until the penultimate glacial/interglacial transition or periodic burial and exposure of pavement clasts since debris flow deposition. Incision rates for the Capitol Reef reach of the Fremont River calculated from the boulder exposure ages range from 0.40 to 0.43 m kyear −1 (maximum rates) and are some of the highest on the Colorado Plateau.

Reinterpretation of the Cedar Ridge section, Wind River Range, Wyoming: Implications for the glacial chronology of the Rocky Mountains

The Cedar Ridge stratigraphic section in the escarpment north of Bull Lake, Wind River Range, Wyoming, may be the most significant section of Quaternary sediments in the Rocky Mountains. This section contains a thick sequence of Bull Lake till, but its greater significance is as the type section or a reference section for the deposits of three pre–Bull Lake glaciations: Washakie Point (oldest), Cedar Ridge, and Sacagawea Ridge (reference section, type section at Dinwoody Lakes). However, after reexamining the tills, lake sediments, and buried soils in this section, we conclude that the stratigraphic record is best interpreted as the result of two glaciations, not the four of previous investigations. Buried soils are especially useful in deciphering the stratigraphy of this section through the contrast between well-developed interglacial soils and weakly developed interstadial soils. We conclude that only the Bull Lake and Sacagawea Ridge glaciations are represented by deposits in the Cedar Ridge section. Deposits formerly called Cedar Ridge are reinterpreted as representing an early stade of the Sacagawea Ridge glaciation. A paleomagnetic study reveals that all the sediments have normal polarity and thus are probably younger than the Brunhes-Matuyama boundary of ca. 770 ka. Although the deposits of the Cedar Ridge section have been correlated with moraines and terraces, this procedure should be done only by direct tracing or with the use of all available dating control. The best record of Quaternary glaciations in the area, however, is in the river terraces of glacial outwash origin in the Wind River basin, not the moraines and stratigraphic sections along the mountain front.

Soil Relative Dating of Moraine and Outwash-terrace Sequences in the Northern Part of the Upper Arkansas Valley, Central Colorado, U.S.A.

Profile development indices for soils developed in moraines and outwash near Twin Lakes and in outwash near Leadville support the correlation of moraines with subdued morphology and two high outwash terraces with the Bull Lake glaciation (ca. 130–160 ka) and the correlation of hummocky moraines and two low outwash terraces with the Pinedale glaciation (ca. 14–47 ka). Elsewhere in the northern part of the upper Arkansas Valley, glacial sequences are correlated by mapping outwash terraces near the mouths of major tributaries of the Arkansas River. Near Twin Lakes, indices for soils on low, outer lateral moraines suggest that the older Pinedale glaciers extended beyond the margin of high, younger Pinedale lateral moraines with hummocky topography. A few subdued moraines near Twin Lakes and Leadville probably record one or more glaciations significantly older than the Bull Lake. The downvalley extent of Pinedale glaciers in the Mosquito Range on the east side of the Arkansas Valley is uncertain: most likely, Pinedale glaciers were almost as extensive as Bull Lake glaciers but built no prominent terminal moraines at their maximum positions.

Soil Relative Dating of Moraine and Outwash-Terrace Sequences in the Northern Part of the Upper Arkansas Valley, Central Colorado, U.S.A.

Profile development indices for soils developed in moraines and outwash near Twin Lakes and in outwash near Leadville support the correlation of moraines with subdued morphology and two high outwash terraces with the Bull Lake glaciation (ca. 130-160 ka) and the correlation of hummocky moraines and two low outwash terraces with the Pinedale glaciation (ca. 14-47 ka). Elsewhere in the northern part of the upper Arkansas Valley, glacial sequences are correlated by mapping outwash terraces near the mouths of major tributaries of the Arkansas River. Near Twin Lakes, indices for soils on low, outer lateral moraines suggest that the older Pinedale glaciers extended beyond the margin of high, younger Pinedale lateral moraines with hummocky topography. A few subdued moraines near Twin Lakes and Leadville probably record one or more glaciations significantly older than the Bull Lake. The downvalley extent of Pinedale glaciers in the Mosquito Range on the east side of the Arkansas Valley is uncertain: most likely, Pinedale glaciers were almost as extensive as Bull Lake glaciers but built no prominent terminal moraines at their maximum positions.

Soil Evidence for a Glaciation Intermediate between the Bull Lake and Pinedale Glaciations at Fremont Lake, Wind River Range, Wyoming, U.S.A.

Soil Evidence for a Glaciation Intermediate between the Bull Lake and Pinedale Glaciations at Fremont Lake, Wind River Range, Wyoming, U.S.A.

Quaternary evolution of Cedar Creek alluvial fan, montana

Cedar Creek alluvial fan is a textbook example of an alluvial fan because of its fan shape with smooth, concentric contours and excellent symmetry. Similar planimetric shapes have been used to infer uniform fan deposition; however, Cedar Creek alluvial fan is composed of four fan deposits of Quaternary age, Qf1 (oldest) to Qf4 (youngest), indicating that fan deposition was nonuniform in both time and space. Field studies indicate that deposition of Cedar Creek alluvial fan is related to glaciofluvial outwash activity during the Pleistocene and upper-fan entrenchment and lower-fan deposition during the Holocene. Qf1 and Qf2 deposits are sub-horizontally bedded, clast-supported sandy gravels uniformly imbricated upfan. Comparison of soil profiles developed in these deposits to radiogenically-dated chronosequences within the region indicates that Qf1 and Qf2 are correlative with Bull Lake and Pinedale-age deposits, respectively. These relationships are substantiated by physical correlation of Qf1 and Qf2 with Bull Lake and Pinedale moraines, respectively, in the Cedar Creek drainage basin. The sedimentology and timing of Qf1 and Qf2 indicate deposition in high-energy, proglacial, braided streams. Furthermore, the present morphology of Cedar Creek alluvial fan was established largely during aggradation of Qf1 and Qf2 when sediment supply to the fan was sufficient to activate 60% to greater than 90% of the total fan area. During Bull Lake glaciation, the apex of Qf1 deposition formed the apex of Cedar Creek alluvial fan as Qf1 covered more than 90% of the present fan area. During Pinedale glaciation, Qf2 deposition shifted downfan; Qf2 is inset into Qf1 above the intersection point, but below the intersection point it eroded and/or buried Qf1 as it activated as much as 60% of the fan area. Qf3 and Qf4, comprising 21% of the fan area, are inset into Qf2 in the lower fan area. Soil development in Qf3 and Qf4 deposits indicate episodic deposition and entrenchment beginning in early Holocene and continuing to present. A post-glacial decrease in sediment supply to Cedar Creek alluvial fan is indicated by sediment storage within the Cedar Creek drainage basin. Decreased sediment supply to the fan resulted in upper-fan entrenchment of Qf2 and deposition of Qf3 and Qf4 in the lower-fan area.

Soils Developed in the Glacial Deposits of the Type Areas of the Pinedale and Bull Lake Glaciations, Wind River Range, Wyoming, U.S.A.

The degree of soil development in glacial deposits in the Fremont Lake area (FLA) and Bull Lake type area (BLTA) on opposite sides of the Wind River Range of western Wyoming is chiefly influenced by the ages of the parent materials although other soil-forming factors are important. Soil morphology, clay content, and calcium carbonate content are useful in distinguishing moraines of the Bull Lake glaciation (about 140 to 150 ka) from those of the Pinedale glaciation (about 14 to 35 ka) in these areas. In the FLA, soils in Bull Lake deposits have an average Profile Development Index (PDI) of 39 index-cm and average 15% clay and 7% calcium carbonate (CaCO3), and soils in Pinedale deposits have an average PDI of 25 index-cm and average 6% clay and 1% CaCO3. In the BLTA, soils in Bull

Obsidian-hydration dating of fluvially reworked sediments in the West Yellowstone region, Montana

This study evaluates obsidian-hydration dating in postglacial fluvial terraces cut into an outwash plain near West Yellowstone, Montana. Fluvial transport fractures obsidian grains. However, some old hydration rinds may be preserved, thus, a grain may record several fracturing events. The most recent fracturing event at West Yellowstone is recorded in surface sediments from all of the terraces, which were cut in a shorter period of time than the technique can discern. They formed about 19,000 ± 1000 yr ago, using published hydration-rate estimates and a mean rind thickness of 6.34 ± 0.14 μm (1 SE). Alternatively, the application of published hydration-rate constants for the Obsidian Cliff flow with an estimated effective hydration temperature of 1.4°C yield an age of 24,400 ± 1100 yr (1 SE). Thicker rinds record fracturing during Bull Lake glaciation and cooling cracks from the emplacement of several source flows. Much of the observed spread in rind thicknesses (6.34 ± 1.69 μm: 1 SD) is probably the result of chemically induced variations in hydration rate. Terrace ages based on a single rind would range from 13,000 to 39,000 yr (±1 SD). Therefore, it is inappropriate to (1) use a set of hydration-rate constants determined from a single sample to calculate ages for multiple artifacts or geological samples, (2) date an archaeological or geological event on the basis of a single artifact, or (3) generate a chronostratigraphy on the basis of individual dates as a function of depth. Multiple evaluations of source chemistry and hydration rates and multiple rind measurements are required to date fracturing events.

Anderson Canyon – A Classic Area in South-Central Idaho for Teaching Alpine Glacial Geology

The well-preserved record of alpine glacial geology displayed in Anderson Canyon, south-central Idaho, is a potential source of diversity and enrichment for summer field programs that visit the Rocky Mountain west each year. This valley provides a record of regional glacial history within a relatively small area (9 square km or 3.5 square miles), and is suitable for a short student mapping project. The moraines and outwash in Anderson Canyon define two major glaciations (the Copper Basin and Potholes) that are generally equivalent to the Bull Lake and Pinedale glaciations of adjacent Rocky Mountain areas. Associated lacustrine deposits document impoundment and drainage of two glacial lakes. Reconstruction of ice margins, fluvial patterns, and lacustrine systems provides a basis for correlation with regional Pleistocene events. The access road to Anderson Canyon is located midway along an improved road that connects Ketchum-Sun Valley on Idaho 75 with U.S. 93, approximately 27.3 km (17 miles) north of Mack...

The use of hornblende etching, clast weathering, and soils to date alpine glacial and periglacial deposits: A study from southwestern Montana

Many techniques for relative dating of surficial deposits suffer from (1) the need to make judgments and (2) poor reproducibility of data. Furthermore, many of the techniques generate data that do not permit the use of statistical analysis. In contrast, assessing the etching of hornblende grains yields objectively obtained, reproducible data that can be subjected to statistical analysis. In a study of the deposits of the Bear Gulch basin, Tobacco Root Range, southwestern Montana, the hornblende-etching data proved superior to the clast-weathering data and the soil-profile data in making interpretations of age relationships. The mean etching of hornblende grains decreases as a logarithmic function of depth. Hornblende grains from older deposits are more etched, especially near the surfaces of the profiles. The collective evidence supports a record of four first-order glacial and periglacial events, which have been correlated with (1) the youngest pre-Bull Lake glaciation, about 280,000 yr B.P.; (2) the Bull Lake glaciation, about 140,000 yr B.P.; (3) the Pinedale glaciation, consisting of two second-order advances, the first and most extensive between 26,000 and 20,000 yr B.P. and the second about 12,000 yr B.P.; and (4) a mid Neoglacial episode of periglacial activity. In addition, a major landslide blocked the valley in pre-Bull Lake time, and an episode of flood erosion along the valley floor is believed to have truncated the late Pinedale terminal moraine about 1500 yr B.P. In a study area for which numerical ages of the deposits are available, hornblende etching can be expressed mathematically as a function of the time since deposition, with the resulting relationship used to date deposits wherein ages are unknown.

A PINEDALE/BULL LAKE INTERGLACIAL PALEOSOL AND ITS IMPLICATIONS, CENTRAL LEMHI MOUNTAINS, IDAHO

A calcium-rich paleosol, preserved on buried till and buried colluvial surfaces, was discovered at several locations in the central Lemhi Mountains. The strati-graphic and pedologic characteristics of the paleosol assign its formation to the Interglacial between the Pinedale and Bull Lake Glaciations, between about 127,000 and 50,000 years before present. Pollen extracted from the paleosol reveal, in association with pedologic data, the horizons above the B2t level were decapitated by subsequent glacial and colluvial erosion. Interpretation of the pollen assemblage reveals that the lower treeline rose a minimum of 120–150 m during the interglacial, which must have been considerably warmer and drier than at present. [Key words: paleosol, Pinedale/Bull Lake Interglacial, paleoenvironmental reconstruction, pollen analysis, Lemhi Mountains, Idaho.]

Sangamonian(?) and Wisconsinan paleoenvironments in Yellowstone National Park

Pollen and plant macrofossil records from Yellowstone National Park, if combined with dated glacial events, provide a paleoenvironmental record of much of the last glacial-interglacial cycle. Bull Lake glaciation has been dated at ∼140,000 yr B.P. Section EP-6 records a late-glacial to full interglacial sequence which is correlated with the Sangamonian interglacial and estimated to be 127,000 yr old at the peak warm period. A prevailing Pseudotsuga - Pinus flexilis - Pinus ponderosa forest suggests that climate was considerably warmer than any in the Holocene. Section EP-5 is somewhat younger, probably late Sangamonian, and shows a forest dominated by Picea , Abies , Pseudotsuga , and a haploxylon Pinus . Slightly cooler conditions than those of the present are indicated. The warmest phase of the Grassy Lake Reservoir section is considered to be ∼82,000 yr old and records a warm interstadial cycle beginning with tundra. The warming sequence is indicated by change to a Picea - Abies - Pinus albicaulis forest and then to a Pinus contorta forest. The cycle ends with forest destruction and a return to open (tundra?) and, presumably, cold conditions. Extremely low values of arboreal pollen indicate that tundra vegetation and cold conditions continued from ∼70,000 to ∼50,000 yr B.P. One cool and, apparently, short interstadial interrupted this extended period of tundra shortly after 68,000 B.P. when a very open parkland of Picea - Abies - Pinus albicaulis appeared. No records of environment are available between ∼50,000 and 30,000 yr B.P. The Pinedale icecap apparently expanded ∼30,000 yr B.P. and lasted until ∼14,000 yr B.P. Late-glacial Picea - Abies - Pinus albicaulis parklands gave way to Pinus contorta forests that have prevailed with minor variation for ∼10,000 yr.

A statistical method for relative-age dating of moraines in the Sawatch Range, Colorado

A relative-age classification of Pleistocene moraines in the northern Sawatch Range, Colorado, has been developed using information- and graph-theoretic methods applied to moraine morphology and weathering characteristics. At 89 stations on moraines in the study area, measurements were made of the six best age-dependent criteria; listed in order of importance, they are percentage of pitted granite, percentage of fresh granite, depth of pitting, width of moraine crest, surface-boulder frequency, and distal-moraine slope angle. Data were evaluated using computer programs CHARANAL (character analysis) and GRAPH (similarity clustering analysis) to produce an age classification of stations according to similarity with respect to the six criteria. Groups of moraines were then tentatively assigned Rocky Mountain geologic-climate names on the basis of weathering parameters and qualitative consideration of deposit morphology, downvalley position, and soil-profile development. Two pre–Bull Lake(?) glaciations are recognized in the area and tentatively correlated with the Cedar Ridge and Sacagawea Ridge Glaciations described by Richmond (1960, 1962, 1965) in the Rocky Mountains. Early(?) and late Bull Lake(?) glaciers occupied Lake Creek Valley; however, evidence of Bull Lake Glaciation was not found in the valleys of East Brush Creek or Nolan Creek. Early Pinedale glaciers occupied all major valleys in the study area, and most were more extensive than late Bull Lake glaciers, possibly explaining the lack of evidence in some valleys for Bull Lake Glaciation. Most valleys in the northern Sawatch Range were again glaciated during middle and late Pinedale time. The information- and graph-theoretic methods used in this study are useful tools for relative-age dating of Pleistocene deposits. Use of the methods (1) allows more objective age classification of glacial deposits to be made on the basis of qualitative data and measurements of several or many weathering characteristics, (2) may help to determine whether deposits represent different glaciations or phases of the same glaciation, and (3) may aid in correlation of glacial deposits between regions of similar climate and bedrock over great distances.

Obsidian hydration dating and correlation of Bull Lake and Pinedale Glaciations near West Yellowstone, Montana

The ages of the last two glaciations near West Yellowstone, Montana, can be calculated by obsidian hydration techniques that are calibrated by K-Ar dating of obsidian-bearing lava flows. The average age of glacial abrasion of obsidian in the Pinedale terminal moraines is about 30,000 yr, with most age measurements between 20,000 and 35,000 yr. For the Bull Lake moraines, it is about 140,000 yr, with most measurements between 130,000 and 155,000 yr. This age for the Bull Lake moraines is also supported by geologic relations that show that the moraines are older than a rhyolite flow dated by K-Ar as 114,500 ± 7,300 yr old (lσ). These obsidian hydration ages of the Pinedale and Bull Lake Glaciations correlate well with the last two cold intervals of the marine record. The age determined for the Bull Lake Glaciation near West Yellowstone antedates the last interglaciation of the marine record, which is commonly correlated with the Sangamon Interglaciation. Our results suggest correlation of the Pinedale Glaciation near West Yellowstone with much or all of the Wisconsin Glaciation and of the Bull Lake with the late Illinoian. This differs with the commonly accepted correlation of the Pinedale with the late (“classical”) Wisconsin and of the Bull Lake with the early Wisconsin. The correlation of Bull Lake with late Illinoian appears equally or more compatible with traditional criteria for correlation, namely comparative soil development and degree of preservation of morainal morphology.

Obsidian Hydration Dates Glacial Loading?

Three different groups of hydration rinds have been measured on thin sections of obsidian from Obsidian Cliff, Yellowstone National Park, Wyoming. The average thickness of the thickest (oldest) group of hydration rinds is 16.3 micrometers and can be related to the original emplacement of the flow 176,000 years ago (potassium-argon age). In addition to these original surfaces, most thin sections show cracks and surfaces which have average hydration rind thicknesses of 14.5 and 7.9 micrometers. These later two hydration rinds compare closely in thickness with those on obsidian pebbles in the Bull Lake and Pinedale terminal moraines in the West Yellowstone Basin, which are 14 to 15 and 7 to 8 micrometers thick, respectively. The later cracks are thought to have been formed by glacial loading during the Bull Lake and Pinedale glaciations, when an estimated 800 meters of ice covered the Obsidian Cliff flow.

Comparison of the quaternary stratigraphy of the Alps and Rocky Mountains

Comparison of the glacial and periglacial deposits and soils of the Alps and Rocky Mountains suggests the following correlations. The Donau, Günz, and Mindel are correlated with the Washakie Point (Nebraskan), Cedar Ridge (Kansan), and Sacagawea Ridge (Illinoian). These glaciations are separated and followed by interglacials represented by thick deeply weathered soils, the last being the Mindel/Riss, or Sacagawea Ridge/Bull Lake (Sangamon). The Riss I (Paar) and Riss II (type Riss) Glaciations are correlated with the early and late advances of the Bull Lake Glaciation (early Altonian), and are believed to be different glaciations separated and followed by short interglacials represented by soils of intermediate development at these latitudes. The Alt-Würm period of restricted ice in the Alps is represented only by local unnamed deposits in the Rocky Mountains. In the Alps, at least three interstadial soils occur between the Riss/Würm soil and the oldest Main Würm end moraine. These coincide in time respectively with the beginning and end of the Port Talbot II interstadial and with Plum Point interstadial. The three major end moraines of the Main Würm are correlated with three or locally more end moraines of the early and middle stades of the Pinedale (Woodfordian). Moraines of the late stade of the Pinedale are equivalent to the late glacial and early postglacial moraines of post-Würm but pre-Atlantic age in the Alps.K-Ar dating and tephrochronology in the Rockies suggest that the Washakie Point ended about 1.2 m.y. B.P., the Cedar Ridge about 700,000 B.P., the Sacagawea Ridge about 180,000 B.P., the last great interglacial about 130,000 B.P., and the interglacial separating early and late Bull Lake about 80,000 B.P. Radiocarbon dates from the Alps suggest that the Riss/Würm was about 70,000–60,000 B.P., and that Alt-Würm interstadials occurred at &gt;50,000, 45,000–40,000, 34,000–32,000, and 28,000 B.P. Radiocarbon dates from rock shelter deposits in France indicate minor interstadials in the Main Würm at 21,000–20,000 B.P. and about 17,000 B.P. Both the Main Würm and Pinedale ended about 11,800 B.P.