Abstract As the late Pleistocene Cordilleran Ice Sheet (CIS) retreated from the southern Puget Lowland and thinned rapidly, marine waters invaded the central and northern lowland, floating the residual ice and causing wholesale collapse of the CIS from southern Whidbey Island to southern British Columbia. Massive, poorly sorted Everson glaciomarine drift was deposited contemporaneously over the entire central and northern lowland. More than 160 14 C dates show that the Everson interval began 12,500 14 C yr B.P. and ended 11,700 14 C yr B.P. Numerous marine strandlines record the drop in relative sea level in the Fraser Lowland from ~180 m (600 ft) at the end of the Everson interval to near present sea level. Following emergence of the Fraser Lowland, a lobe of the CIS advanced from the Fraser Canyon near Sumas to Bellingham during the Sumas Stade. As the ice retreated, at least eight end moraines were built successively across the lowland, each marking a position of ice advance or stillstand that records late Pleistocene climatic fluctuations. About 40 new 14 C dates indicate that the ages of these moraines span the Inter-Allerød–Younger Dryas intervals between 11,700 and 10,000 14 C yr B.P. The 14 C chronology allows correlation of the Sumas moraines with moraines in the Cascade Range, Rocky Mountains, Canada, Scandinavia, the European Alps, New Zealand, South America, and elsewhere. Late in the retreat of the ice, large outburst floods from an ice-dammed lake in British Columbia swept across the Sumas outwash plain, resulting in fluted topography and giant ripples on dune forms.

Abstract The advance of the Cordilleran Ice Sheet (CIS) during the Vashon Stade is limited by 14 C dates from sediments beneath Vashon till, which indicate that ice advanced southward across the Canadian border sometime after ca. 18 ka 14 C yr B.P. and reached the Seattle area soon after 14.5 ka 14 C yr B.P. The Puget lobe underwent sudden, large-scale terminus recession and downwasting not long after 14.5 ka 14 C yr B.P., and backwasted northward from its southern terminus past the Seattle area by ca. 14 ka 14 C yr B.P. Rapid thinning of Vashon ice after the terminus had receded north of Seattle allowed marine water from the Strait of Juan de Fuca to flood the lowland, floating the remaining ice and disintegrating the remaining CIS northward all the way to Canada, except for a narrow band along the eastern margin of the lowland. Everson glaciomarine drift (gmd), consisting mostly of poorly sorted stony clay deposited from floating ice, was deposited essentially contemporaneously over the central and northern Puget Lowland. Unbroken, articulated, marine shells, some in growth positions, indicate that the gmd represents in situ deposition. More than 150 14 C dates from Washington and British Columbia fix the age of the Everson gmd at 11,500 to ca. 12,500 14 C yr B.P., making it a valuable stratigraphic marker over the central and northern Puget Lowland. Ice-contact marine deltas and shorelines were produced on Whidbey Island as the CIS thinned and disintegrated in the central Puget Lowland, allowing marine water from the Strait of Juan de Fuca to penetrate beneath the ice. During this time, the CIS had disintegrated in the deeper water of the inland waterways, but grounded ice remained along the eastern side of the mainland, changing the ice flow direction from N-S to NE-SW, from the grounded ice on the mainland toward the open deep water to the west at the Strait of Juan de Fuca. A well-defined, marine ice-margin existed along the south and west sides of Penn Cove and isostatically raised shorelines and marine deltas were formed at elevations up to ~33 m on southern Whidbey Island and up to ~88 m on northern Whidbey. The shorelines are best preserved along the sides of marine embayments on the island. Following the deposition of Everson gmd and the emergence of the northern Puget Lowland, the CIS readvanced several times, defining four phases of the Sumas Stade: Sumas I represents grounding of the CIS and deposition of till in the western Fraser Lowland. Sumas II consists of a well-defined moraine and meltwater channels deeply incised into Everson gmd. A series of Sumas III moraines that occur in British Columbia shed meltwater that built a broad outwash plain behind the Sumas II moraine. A Sumas IV moraine occurs across a Sumas III meltwater channel at the eastern margin of the Fraser Lowland.

Fission tracks are zones of intense damage that result when fission fragments pass through a solid. 238 U is the only naturally occurring isotope whose decay rate results in a significant number of tracks over geologic time. Spontaneous fission of 238 U occurs at a known rate, and by determining the number of fission tracks and the amount of uranium present in a mineral or glass, its age may be determined. Many geologic materials contain trace amounts of uranium, but because of such factors as uranium abundance and track retention, zircon and glass are the only materials routinely dated in Quaternary samples. Applications of fission-track dating to Quaternary studies include the dating of volcanic ash and archaeological material. The method has also been used to determine the rate of landform development in the Powder River Basin of Wyoming through the dating of clinker formed by the natural burning of coal beds. In the Himalayas of northern Pakistan, fission-track dating of zircon and apatite has shown that uplift rates during the Quaternary were as high as 1 cm/yr, which accounts for the incredible mountainous relief.

Luminescence techniques can provide ages for deposits undatable by routine geochronometric techniques (e.g., 14 C, K-Ar, fission track). Two classes of events can be dated by luminescence methods: (I) growth of a mineral or its last cooling, and (II) the last exposure to sunlight. Within the past few years, significant advances in procedures, technology, and understanding of the thermoluminescence (TL) behavior of minerals have been made that place luminescence dating techniques on the verge of widespread application to Quaternary deposits. Most progress has come from studies of known-age material deposited under known conditions. Within class I, both distal and proximal tephra deposits have been dated, using TL techniques originally developed for pottery dating. Within class II, loess, buried soils, and waterlaid silts have been successfully dated. Means have been demonstrated for isolating and controlling several major sources of error, such as the type of TL instability known as anomalous fading, as well as the effects of uncertainty about the degree of zeroing of the luminescence signal in certain depositional environments. In particular, because of different sensitivities to light of the TL of quartz and feldspars, feldspars have been shown to be the preferred component for dating most unheated sediments. Of the competing TL methods for dating the last exposure to sunlight, the partial bleach (R-Gamma or R-Beta) technique, when properly applied, has been shown to yield the best results in general. Nevertheless, in future dating studies of unheated sediments, this laborious method may be displaced by a novel technique that uses laser light, rather than heat, to stimulate the luminescence that is a measure of the past ionizing radiation absorbed dose. This new optical (OSL) method of dating promises to be simple, sensitive, and speedy.

The geochemistry of amino acids in fossil wood materials appears to be applicable to geological problems such as correlation, relative-age dating, and paleothermometry of sedimentary deposits in the northern Yukon Territory, Canada (Rutter and Crawford, 1984). Activation energies and Arrhenius frequency factors were calculated for the racemization reaction of several bound amino acids (asp, ala, glu, leu). These parameters were obtained by determining elevated temperature rate constants for the bound amino acids isolated from modern and fossil Picea glauca (white spruce). The ratios of dextro to levro stereoisomers (D/L ratio) obtained for bound aspartic acid were found to be the most reliable and yielded values of 18.4 ±2.4 Kcal/mol and 27.6 ±3.0 yr −1 for activation energy and Arrhenius frequency factor ( ρ nA), respectively. Slight differences in kinetic parameters were obtained between fossil and modem wood replicates. Aspartic acid also yielded results correlatable to studies performed on Sequoiadendron giganteum (Engel and others, 1977). These findings suggested that species specific effects may not be significant for proteinaceous material found within wood matrices. Extrapolation of a first-order rate constant for bound aspartic acid in the fossil Picea sp. yielded a value of 9.75 × 10 −7 yr −1 . This constant was derived from the extent of racemization of the dated sample (>53,000 yr B.P.). Rate constants were similarly determined for various fossil localities in the northern Yukon. These rate constants ranged from 9.75 × 10 −7 yr −1 to 3.24 ± 0.2 × 10 −6 yr −1 . As this reaction is temperature dependent, estimations of paleotemperatures that the fossil samples had experienced were calculated. The values obtained (−49°C ± 30°C) were unrealistic since the racemization does not appear to follow simple reversible first-order kinetics. More reasonable results were obtained (−19°C) if the assumption used for calculation was based on the presence of free aspartic acid (complete protein hydrolysis). The apparent rate of racemization of free aspartic acid is characteristically lower than the apparent rates of racemization of protein-bound amino acids.

The aminostratigraphic relationships of approximately 150 coastal Quaternary sites from Nova Scotia to Florida and the Bahamas Islands are reviewed. The broad latitudinal range of the sites provides a useful perspective on the relative kinetics of racemization at substantially different temperatures. Local aminostratigraphic sections are presented for five regions in which present mean annual temperatures differ by 3°C or less. Correlation of these individual aminostratigraphies is accomplished by qualitative comparison of results for overlapping sections and by quantitative kinetic modeling. Correlations based on kinetic modeling with local calibration are compared with available U-series data for coastal plain sites. Using basic aminostratigraphic assumptions about the relationship of present and past temperature gradients, the amino acid data from most of the calibration sites follow logical trends. However, significant conflicts between U-series dates and aminostratigraphic age estimates are recognized for sites in South Carolina and for a group of sites in eastern Virginia (central Chesapeake Bay). Reconciliation of the aminostratigraphic data with all of the Atlantic Coastal Plain U-series coral dates is not possible without invoking extreme (and latitudinally variable) thermal effects on the racemization kinetics.

Measurement of the paleomagnetism of Quaternary sediments does not yield a numerical age as do isotopic dating methods. In order to convert paleomagnetic data into an age, it must be correlated to known conditions of the geomagnetic field that have been dated by some other method. Paleomagnetic data useful for this purpose include magnetic polarity (normal or reversed), field declination and inclination, secular variation, and magnetic susceptibility. Diamictons, such as till, glaciomarine drift, and mudflows, may carry a stable magnetic remanence if they contain enough silt and clay in the matrix of the deposit. Glaciomarine drifts provide good examples of diamictons which, although poorly sorted, retain stable and reliable magnetism. Remanence and anisotropy of magnetic susceptibility in tills may have distinctly different orientations, indicating that remanence is not significantly affected by the preferred orientation of larger grains during shearing. Clay/silt-rich tills in Nebraska, Iowa, and Minnesota give reliable normal and reversed DRMs that record the earth’s magnetic field at the time of deposition, despite anisotropy of susceptibility measurements that show a microfabric from glacial shearing. Thus, some, but not necessarily all, tills may be suitable for reliable paleomagnetic measurements if they have enough fine-grained matrix. Small magnetic grains in some silt/clay-rich tills orient themselves parallel to the earth’s magnetic field within water-filled pore spaces. Magnetic grains have sufficient freedom to rotate into alignment because hydrostatic pore pressure carries part of the glacial load and the pore fluid does not transmit shear stresses that might otherwise result in mechanical grain rotation (Easterbrook, 1983). The DRM is fixed in till when enough pore water is expelled to restrict grain rotation. Supporting evidence is necessary to use polarity changes in sediment for age determination. Boundaries between specific magnetic polarity changes are not identifiable without supporting evidence, because: (1) the change in magnetic polarity may represent any one of several possible reversal boundaries, (2) the change in polarity may belong to one of the many excursions of the magnetic field, and (3) significant erosion of the lower polarity epoch may be followed by deposition of sediment much younger than the beginning of the polarity change. The degree of magnetic foliation in a till may be determined by the principal axes of a susceptibility ellipsoid, which is significantly more spherical for glaciomarine drift than till. Lodgement till deposited in a water-saturated high-shear environment at the base of a glacier may contain a well-defined magnetic fabric that accurately reflects its petrofabric. Massive till-like glaciomarine drift, consisting of clastic particles dropped from floating ice in marine waters, contains elongate particles that are more randomly oriented than those of subglacial till because it lacks the pervasive shear associated with subglacial till. An example of the use of combined paleomagnetic measurements and fission-track dating of Pleistocene deposits in the Central Plains indicates that: (1) “Nebraskan” till is not the oldest drift in the region, (2) “Nebraskan” tills at various classic sections are not the same age, (3) the oldest till is older than 2 Ma, and (4) the early Pleistocene glacial sequence in the region is considerably more complex than previously thought.

Long-term changes in the inclination and declination of the magnetic field at a site are manifestations of geomagnetic secular variation. If a master curve of secular variation is available, then correlation of the paleomagnetic record of undated Quaternary sediments with the master curve can lead to determination of the age of the sediments. Because secular variation is coherent only over distances on the order of a few thousand kilometers, separate master curves must be developed for each region. Historical records, lava flows, and archaeological sites can all provide information about secular variation, but only rapidly deposited sediments can provide the continuous record needed to construct a master curve. The quality of the sedimentary secular variation record depends, however, on the processes by which the sediments acquire their magnetization. These processes create inherent limitations on the agreement in space and time between records. So-called “second-generation” paleomagnetic studies of lacustrine sequences are now yielding credible master curves. These studies are characterized by careful attention to coring procedures, good stratigraphic control, a firm chronologic framework, replicate paleomagnetic sampling, and auxiliary rock magnetic studies. Sediments from lakes in Oregon and Minnesota have provided master curves for western and east-central North America, respectively. Analysis of these master curves shows that dating of sedimentary sequences by geomagnetic secular variation is feasible and that it can provide new opportunities for high-resolution studies of climatologic and sedimentologic processes.

The early Pleistocene history of the Puget Lowland is marked by repeated advances of the Cordilleran ice sheet into the southern Puget Lowland where deposits of at least three glaciations older than 1.0 Ma are recognized: the Orting (oldest), Stuck, and Salmon Springs, separated by the interglacial Alderton (older) and Puyallup Formations. Until recently, the chronology of these stratigraphic units was unknown and correlations were based entirely on relative age considerations. Paleomagnetic analyses of sediments and petrographic, geochemical, and fission-track analyses of associated tephra were undertaken in order to provide a basis for establishing the chronology of the type sections of these stratigraphic units and to develop a standard for correlations throughout the Puget Lowland. Although paleomagnetic overprinting is common in the sediments sampled, primary components of remanent magnetism were successfully isolated during demagnetization. Previous work (Easterbrook and others, 1981; Westgate and others, 1987) identified the Salmon Springs Drift as reversely magnetized and about 1.0 m.y. old. This investigation establishes the reversed magnetization of the pre–Salmon Springs sediments at or close to their type localities and illustrates the use of the Lake Tapps tephra in regional correlations. The 1.0-Ma fission-track age of the Lake Tapps tephra and the reversed magnetic polarity of the Orting Drift, Alderton Formation, Stuck Drift, Puyallup Formation, and Salmon Springs Drift indicate that all were deposited during the Matuyama Reversed Epoch which began about 2.48 Ma and ended about 0.73 Ma.

Abstract Few depositional environments are as varied as those associated with glaciers, resulting in deposits of widely differenting physical characteristics. Sediments deposited directly from glacial ice generally are poorly sorted and unstratified diamictons whereas those indirectly associated with ice via meltwater streams or lakes are sorted and stratified. Recognition of glacial clastic sediments is important because of climatic implications and rapid facies changes associated with glacial deposition. Diamictons The term diamicton is used for poorly sorted, unstratified deposits of unspecific origin. The most common glacial diamictons are till and glaciomarine drift, both deposited more or less directly from ice without the winnowing effects of water. They are characterized by a heterogeneous mixture of sediment sizes, ranging from boulders to clay, and a lack of stratification. Particle size distribution is often bimodal with concentrates in the pebble cobble and silt-clay fractions (Fig. 1). Both types of diamictons are usually massive with only minor stratified intercalations.Glacial till is deposited in direct contact with glacial ice. Although it does not make up substantial sediment thicknesses in the geologic record, till makes a discontinuous cover for as much as 30% of the earth's continental landmasses and forms significant deposits in Precambrian and Permo-Carboniferous rocks of South America, Africa, and North America (Fig 2).Till consists of unsorted, unstratifiedpebbles, cobbles, and boulders in a matrix of sand, silt, and clay. The coarser fraction is mostly pebble size with cobbles and boulders scattered throughout.Many pebbles are rounded to sub-rounded, suggesting that they were incorporated by ice