Peter W. Birkeland

Reevaluation of multiparameter relative dating techniques and their application to the glacial sequence along the eastern escarpment of the Sierra Nevada, California

Four valleys, recently studied by other workers, were examined along the eastern Sierra Nevada to refine relative-dating techniques. A variety of weathering parameters and soil properties fail to delineate more than two major post-Sherwin Pleistocene glaciations. We correlate these two glaciations with the Tahoe and Tioga Glaciations. Type Mono Basin Till, usually considered to be pre-Tahoe, exhibits the following weathering similarities with Tahoe Till, if both are under sagebrush: (1) grusification of subsurface granitic boulders; (2) degree of pitting, mineral relief, and rind development on surface granitic boulders; and (3) very slight clay increase in the B horizon. Type Casa Diablo Till also has weathering characteristics similar to Tahoe Till, except a slightly more developed Bt horizon is present. Hence, dates on basalt of 0.126 ± 0.025 and 0.062 ± 0.013 my Casa Diablo Till also has weathering characteristics similar to Tahoe Till, except a slightly more developed Bt horizon is present. Hence, dates on basalt of 0.126 ± 0.025 and 0.062 ± 0.013 my (Bailey et al. 1976), which bracket type Casa Diablo, may provide age control on the Tahoe glaciation. In addition, we are unable to demonstrate that the Tenaya is a separate glaciation. In three of the four valleys studied our weathering data for Tenaya Till are equivalent with those for Tioga Till, but with those for Tahoe Till in the fourth valley. We were not satisfied with our ability to differentiate the Casa Diablo, Mono Basin, and Tenaya as separate glaciations even though data were collected in the type areas for two of these deposits. Reasons for suggesting a change back to a two-fold Tahoe-Tioga glacial sequence, rather than the present five-fold sequence, are that we have measured a greater number of parameters than has been done previously, soils were submitted to detailed laboratory analyses, and surface weathering features were studied under consistent present vegetation cover to avoid possible problems induced by ancient forest fires. Nevertheless our relative-dating scheme does not rule out the possibility of a more detailed glacial sequence.

Integrating soils and geomorphology in mountains—an example from the Front Range of Colorado

Soil distribution in high mountains reflects the impact of several soil-forming factors. Soil geomorphologists use key pedological properties to estimate ages of Quaternary deposits of various depositional environments, estimate long-term stability and instability of landscapes, and make inferences on past climatic change. Once the influence of the soil-forming factors is known, soils can be used to help interpret some aspects of landscape evolution that otherwise might go undetected. The Front Range of Colorado rises from the plains of the Colorado Piedmont at about 1700 m past a widespread, dissected Tertiary erosion surface between 2300 and 2800 m up to an alpine Continental Divide at 3600 to over 4000 m. Pleistocene valley glaciers reached the western edge of the erosion surface. Parent rocks are broadly uniform (granitic and gneissic). Climate varies from 46 cm mean annual precipitation (MAP) and 11 jC mean annual temperature (MAT) in the plains to 102 cm and � 4 jC, respectively, near the range crest. Vegetation follows climate with grassland in the plains, forest in the mountains, and tundra above 3450 m. Soils reflect the bioclimatic transect from plains to divide: A/Bw or Bt/Bk or K (grassland) to A/E/Bw or Bt/C (forest) to A/Bw/C (tundra). Corresponding soil pH values decrease from 8 to less than 5 with increasing elevation. The pedogenic clay minerals dominant in each major vegetation zone are: smectite (grassland), vermiculite (forest), and 1.0–1.8 nm mixed-layer clays (tundra). Within the lower forested zone, the topographic factor (aspect) results in more leached, colder soils, with relatively thin O horizons, well-expressed E horizons and Bt horizons (Alfisols) on N-facing slopes, whereas soils with thicker A horizons, less developed or no E horizons, and Bw or Bt horizons (Mollisols) are more common on S-facing slopes. The topographic factor in the tundra results in soil patterns as a consequence of wind-redistributed snow and the amount of time it lingers on the landscape. An important parent material factor is airborne dust, which results in fine-grained surface horizons and, if infiltrated, contributes to clay accumulation in some Bt horizons. The time factor is evaluated by soil chronosequence studies of Quaternary deposits in tundra, upper forest, and plains grassland. Few soils in the study area are >10,000 years old in the tundra, >100,000 years old in the forest, and >2 million years old in the grassland. Stages of granite weathering vary with distance from the Continental Divide and the best developed is grus near the sedimentary/granitic rock contact just west of the mountain front. Grus takes a minimum of 100,000 years to form.

Suggested terminology for Quaternary dating methods

Abstract Classification of Quaternary dating methods should be based on the level of quantitative information and the degree of confidence contained in the age estimates produced by the dating methods. We recommend the use of the terms numerical-age, calibrated-age, relative-age , and correlated-age to describe these levels. We also classify dating methods by type into sideral, isotopic, radiogenic, chemical and biological, geomorphic, and correlation methods. The use of “absolute” is inappropriate for most dating methods, and should be replaced by “numerical.” The use of “date” should be minimized in favor of “age” or “age estimate.” We recommend use of the abbreviations ka and Ma for most ages; calender dates can be used where appropriate and yr B.P. can be used for radiocarbon ages.

Soil-geomorphic research ― a selective overview

Abstract Much soil-geomorphologic research involves tracking the development of soils with time, otherwise known as soil chronosequences. Most of these have been undertaken on landforms underlain by Quaternary depsits of varying ages. In general, there is a predictable variation in both soil-horizon sequence and amounts of constituents such as clay, Fe, and CaCO 3 with time. The rate at which these constituents accumulate in the soil is a function of parent material, bioclimate and atmospheric dust influx, and because of the latter, soils in aridic regions can form at rapid rates. Profile properties can be used to estimate the ages of deposits and faulting events, but the error on the estimated age can be ±50% or greater. The position of salt accumulations in soil profiles is one of the best indications of climatic change, and these can be modelled to compare with various climatic parameters, present and past. Profile characteristics due to pedogenic thresholds, however, can mimic those due to climatic change, so close dating is necessary to differentiate the effects of both. Soil-geomorphic data are essential to understand the origin of ancient paleosols in the sedimentary rock records, but a major problem still is one of recognition of these features as soils, and to separate the effects of pedogenesis from those of diagenesis.

Pedogenic gradients for iron and aluminum accumulation and phosphorus depletion in arctic and alpine soils as a function of time and climate

Pedogenically significant chemical extracts of iron, aluminum, and phosphorus are related mainly to time in chronosequences from Baffin Island (Canadian Arctic), the alpine Sierra Nevada and Wind River Range (western United States), the alpine Khumbu Glacier area (Himalaya, Nepal), and the alpine Southern Alps (New Zealand). Based on the accumulation index for Fe and Al, and the depletion index for P in each region, the following ranking of chemical pedogenic development is obtained: Southern Alps > Khumbu Glacier area ≅ Wind River Range > Sierra Nevada > coastal Baffin Island > inland Baffin Island. The ranking mainly follows regional climate, with the greatest accumulation and depletion to the warmest and wettest environment, and the least accumulation and depletion in the coldest and driest environment.

Subdivision of Holocene glacial deposits, Ben Ohau Range, New Zealand, using relative-dating methods

Relative-dating methods measure post-depositional alteration of surficial deposits. Measured in this study are the size of the yellow-green Rhizocarpon lichen, percent lichen cover, weathering-rind thickness, quartz-vein height, surface oxidation, and pitting of clasts. The data are used to subdivide Holocene deposits in the Ben Ohau Range and to suggest correlation with moraines in other parts of the Southern Alps. Glacial and/or rock-glacier deposits of five different ages are identified in the Ben Ohau Range. Ages can be approximated mainly from the rind-development curve of Chinn (1981). From youngest to oldest the deposits are: Dun Fiunary (∼ 100 yr); Whale Stream (∼ 250 yr); Jacks Stream (∼ 3,000 yr); Ferintosh (∼ 4,000 yr); and Birch Hill (∼ 9,000 yr). All but the Whale Stream have been previously named, but data presented here result in improved definitions of mapping units and more accurate age assignment. The present climate of the Ben Ohau Range is increasingly continental to the south. A similar climatic gradient existed for much of the post-Birch Hill Holocene, as shown by the glacial depositional facies: moraines are common to the north, whereas rock glaciers, especially of Jacks Stream and Ferintosh ages, are common to the south. In some areas, rock glaciers that have long been inactive have recently been reactivated. Data from moraines in the Waimakariri Drainage and the Mount Cook, Cameron Valley, and Rakaia River areas improve previous correlations, as relative-dating methods provide age information where 14C ages are either lacking or limiting, or when a single relative-dating method is subject to erroneous interpretation.

Nomenclature of alpine glacial deposits, or, What's in a name?

The most useful and objective classification for alpine glacial deposits, as well as for many other Quaternary deposits, appears to be one based on parameters which vary with age as a result of postdepositional modifications. In areas and units for which radiometrically datable materials are rare, age information is gained primarily from these postdepositional modifications by what are here called relative-dating (RD) methods. In order for alpine glacial deposits to be subdivided and formally named, sufficient field data for consistent recognition and mapping need to be collected. These data include measurements of age-dependent parameters such as soil properties, rock-weathering characteristics, and landform changes. Subdivision and naming of glacial deposits should be no more detailed than the resolution of the RD methods, which generally decreases with time. Only when deposits have been objectively characterized by these relative-dating methods can correlations with deposits in other areas or with other types of records be substantiated.

Status of correlation of Quaternary stratigraphic units in the western conterminous United States

Abstract Deposits of Quaternary age from the Rocky Mountains to the Pacific Coast in the western conterminous United States represent a great variety of environments. The deposits include those of continental and alpine glaciers, glacial meltwater streams, nonglacial streams, pluvial lakes, marine environments, eolian environments, and masswasting environments. On two charts we have attempted to correlate representative sequences of deposits of many of these environments, based on published sources and recent unpublished investigations. Evidence for correlation is based mainly on stratigraphic sequence, soil characteristics, the amount of subsequent erosion and interlayered volcanic ash beds identifiable as to source. Chronologic control is based on numerous radiocarbon dates, U-series dates on marine fossils, and K-Ar dates on volcanic rocks. The Bishop volcanic ash bed and one of the Pearlette-like volcanic ash beds appear to represent significant regional key horizons, respectively about 700,000 and 600,000 years old. Rock magnetism is shown to suggest the paleomagnetic polarity at the time of rock deposition. Assigned land-mammal ages of included fossils help to put limits on the age of some units.

Mean Velocities and Boulder Transport During Tahoe–Age Floods of the Truckee River, California–Nevada

In Truckee River glacial outwash deposits of the Tahoe Glaciation, boulders and gravel bars indicate discharges and velocities far greater than those of the present river. Collapse of unstable glacier dams near Lake Tahoes outlet would have been necessary to release quickly the large volumes of impounded water that produced the above features. A mean flood velocity, using the Manning formula, near 30 feet per second, probably was attained along the valley as far downstream as Verdi, Nevada. A velocity of slightly more than 10 feet per second was possible farther downstream. A reasonable tractive force can be estimated for the movement of most of the observed boulders. It is concluded that a tractive force of from 20 to 30 pounds per square foot was sufficient to move the largest boulder, measuring 40 × 20 × 10 feet above ground surface, in a 40-to 80-foot-deep flood moving nearly 30 feet per second on a slope of 0.007.

Radiocarbon dates on deglaciation, cordillera central, Northern Peruvian Andes

Abstract Three radiocarbon dates along with relative-dating criteria place limits on the deglaciation history of Manachaque Valley, Cordillera Central. Ice retreated from the late-glacial maximum by at least 12,100 yr B.P. During ice retreat numerous moraines were deposited throughout the valley. Glacier cover was reduced to about half that of the last glacial maximum by at least 9700 yr B.P. and to less than a tenth by at least 6450 yr B.P. Because all dates are minimum, the dates and field data are consistent with little or no ice remaining by early Holocene. No unambiguous Younger Dryas moraines are present.