Estella B. Leopold

Abrupt uplift within the past 1700 years at Southern Puget Sound, Washington

Shorelines rose as much as 7 meters along southern Puget Sound and Hood Canal between 500 and 1700 years ago. Evidence for this uplift consists of elevated wave-cut shore platforms near Seattle and emerged, peat-covered tidal flats as much as 60 kilometers to the southwest. The uplift was too rapid for waves to leave intermediate shorelines on even the best preserved platform. The tidal flats also emerged abruptly; they changed into freshwater swamps and meadows without first becoming tidal marshes. Where uplift was greatest, it adjoined an inferred fault that crosses Puget Sound at Seattle and it probably accompanied reverse slip on that fault 1000 to 1100 years ago. The uplift and probable fault slip show that the crust of the North America plate contains potential sources of damaging earthquakes in the Puget Sound region.

An 18 million year record of vegetation and climate change in northwestern Canada and Alaska: Tectonic and global climatic correlates

Abstract We reconstruct long-term vegetation/paleoclimatic trends, spanning the last 18 million years, in Alaska, Yukon and far western Northwest Territories. Twenty-one average percentage spectra for pollen and spores are assembled from eight surface/subsurface sections. The sections are dated independently or by correlation. Pollen and spore ratios indicate the direction of change in vegetation and climatic parameters — growing season temperature (Test), tree canopy density (Cest) and paludification at study sites (Pest). A global warm peak ca. 15 Ma is shown by the abundance of thermophilous taxa, including Fagus and Quercus. A temperature decline immediately following 15 Ma parallels climatic reconstructions based on marine oxygen isotopes. Subsequent declines correlate to the Messinian event and the onset of late Pliocene-Pleistocene glaciation. After 7 Ma herbs and shrubs become more important elements of the palynological assemblages, suggesting a more continental, colder/drier climate. However, a late Pliocene warm interval is evident. Vegetation/climatic changes during the early to late Miocene show synchrony with, and are most economically attributable to, global events. After 7 Ma, vegetation/climate change is attributed primarily to latest Miocene-to-Pleistocene uplift of the Alaska Range and St. Elias Mts. The continuing influence of global climatic patterns is shown in the late Pliocene warm interval, despite uplift to the south. The opening of the Bering Strait ca. 3 Ma may have moderated the climate in the study area.

Lignin geochemistry of a Late Quaternary sediment core from Lake Washington

Long-term lignin stability and paleovegetation patterns were investigated using CuO oxidation products of sediments from an 11 m core of Late Quaternary sediment collected from the mid-basin of Lake Washington, Washington State. Relatively constant yields of lignin-derived phenols (normalized to organic carbon) from the entire core indicate minimal in situ lignin degradation over the last 13,000 years. Compositional patterns within the phenolic suite and increased corresponding yields from baseextracted sediments indicate that sedimentary lignins are present predominantly as well preserved plant tissue fragments. Abundance patterns of vanillyl, syringyl, and cinnamyl phenols record four distinct sequences within the core characterized by: 1. (a) high concentrations of gymnosperm wood in a basal horizon of glacial flour, 11-10 m; 2. (b) an essentially pure mixture of nonwoody angiosperm tissues in late Pleistocene sediments, 10-8 m; 3. (c) relatively high concentrations of angiosperm woods in the bottom half of a limnic peat sequence deposited approximately 10,000–7,000 years B.P., 8-4 m; and 4. (d) a progressive enrichment in gymnosperm woods at the expense of angiosperm woods over the last 7,000 years in the upper limnic peat, 4-0 m. Vascular plant tissues account for less than half the total sedimentary organic carbon throughout the core.

Pollen and lignin records of late quaternary vegetation, lake washington.

Analyses of lignin oxidation products and pollen for an 11-meter core from Lake Washington provide independent but similar reconstructions of the late Quaternary vegetation in the Puget Lowland. An exception is in sediments of the late Pleistocene where pollen percentages and influx values suggest conifer forest whereas lignin compositions suggest a treeless source region. This dissimilarity appears to result from different major provenances: eolian transport of pollen to the lake from adjacent or downstream drainage basins as opposed to fluvial transport of lignified plant debris only from the Lake Washington drainage basin.

Mineral magnetic studies of lake sediments

This review outlines the origin and environmental significance of magnetic minerals in lake sediments. Attention is drawn to situations where the patterns of mineral magnetic variation is a reflection of processes other than changing erosion rates and fire incidence. The use of mineral magnetic techniques in sediment source tracing, palaeoclimatic studies and the reconstruction of particulate pollution history is illustrated by means of case studies from Britain and N. America. The value of magnetic susceptibility as an on-site core logging technique is shown by reference to data from Lake Washington.

A long pollen sequence of Neogene age, Alaska Range

Abstract A thick sediment sequence (∼590 m) of Neogene age, exposed in the Nenana coal field, Alaska, at a latitude of 63.5°N provides an extensive pollen and spore record spanning most of the Miocene and probably part of the early Pliocene. The sediments of the upper Usibelli Group (Miocene) and overlying Nenana Gravel (Pliocene?) are the basis of this study. The flora from both leaves and pollen of the Usibelli Group connotes a vegetation similar to the mixed northern hardwood forest of northeastern United States, and the northern part of East China, northern Korea and southern Hokkaido. The warmest pollen and leaf assemblages of the Miocene occur in the Suntrana Formation in the lower third of the unit, and these correlate very well with flora of the upper Seldovian stage as the reference section on Cook Inlet, which is of late-early to early-middle Miocene age. Shifts in forest composition from Suntrana Formation sediments (upper Seldovian Stage) into the overlying sediments of the Lignite Creek and Grubstake Formations connote a cooling with minor changes of vegetation and climate. These cooler phases are correlative with the Homerian and Clamgulchian Stages of Cook Inlet. Mean annual temperature (MAT) estimate based on fossil pollen and leaves from the lower Suntrana Formation is ca. 9° C, and summers were consistently warm and wet. In the cooler phases of the late Miocene the MAT probably dropped to about 5° C.

Paleoecology of a Miocene flora from the Shanwang formation, Shandong province, northern East China

Abstract The Shanwang Formation, which is late Early to early Middle Miocene based on radiometric dates and vertebrate fossils, was deposited in a small intermontane lake basin (N. Lat. 36.5°) and contains a rich assemblage of plant and animal fossils. The chief plant families represented by pollen taxa are Fagaceae, Juglandaceae, Betulaceae, Ulmaceae, Hamamelidaceae and Pinaceae. The combined pollen and leaf data indicate that the Miocene vegetation of the Shanwang area was mixed deciduous and evergreen broad‐leaved forest with a humid warm‐temperate to subtropical climate. In contrast, the modern vegetation is a deciduous broadleaved forest, that contains very few subtropical elements. The average annual temperature at Shanwang was similar to that of today. The main difference between the modern and Miocene climates is that the annual temperature range has increased (colder winters), and precipitation which was evenly distributed is now highly seasonal (winter dry). A comparison between the fossil polle...

Sedimentary Belts in Lagoon of Kapingamarangi Atoll

Systematic bottom sampling in the lagoon of Kapingamarangi Atoll indicates that sediments accumulating there are of six principal types, each characteristic of and largely restricted to definite depth limits. These types of sediment form facies belts that encircle the deepest parts (240 feet) of the approximately 6-by-8-mile lagoon and, on a smaller scale, extend around each of the patch reefs in the lagoon. The facies belts, from the reef inward toward greater depths, are composed of the following materials: (1) medium-grained calcium carbonate sand formed largely of Foraminifera (Amphistegina madagascariensis and Marginopora vertebralis), (2) fine-grained calcium carbonate sand formed largely of fragments of mollusks, (3) debris from branch corals growing in thickets ne rby, (4) accumulations of algal segments of the genus Halimeda, (5) calcium carbonate sand composed largely of a Foraminifera species (Amphistegina lessonii) different from those in shallow water, and (6) calcium carbonate mud. Mechanical analyses indicate that in areas of shallow water, sediments are progressively finer with depth and a gradation lagoonward occurs from foraminiferal sand into shell sand, the effect of waves and tides. Below the belt of branch corals, at depths greater than about 90 feet, however, sediments of the three inner facies belts show virtually no mixing. Where strong currents from the sea enter the lagoon on its southern side, a silt formed from shell and coral fragments has developed a tongue that projects lagoonward for about a mile and disturbs the pattern of facies belts that normally parallel the peripheral reef. The abundance of Foraminifera in most of the sediments at Kapingamarangi Atoll permits a quantitative study of their relation to depth of water and to facies belts. Five large species are important foraminiferal constituents of the sediments. Two occur abundantly in shallow waters up to the crest of the peripheral reef, and three occur in waters from 100 to 200 feet in depth. Other Foraminifera from the atoll are much smaller, occur more sparsely, and are much less important as rock formers; collectively they form in most places less than one per cent of the volume of a sample. Foraminiferal content of samples from each of the six different facies is distinctive. Relations are apparent between the Foraminifera present, the type of sediment, the depth of water, and the amount of wave a tion. Quantitative analysis of microfossils in bottom sediments of the lagoon shows that (1) diatoms and sponge spicules are accumulating in greatest numbers in sediments of the relatively deep, quiet water of the center, and are rare in sediments adjacent to the lagoon beaches; (2) microforaminifers are present in all the major sediment facies of the lagoon, but are particularly numerous on bottoms where water is either very shallow or very deep; concentration in deep areas probably is, in part, the result of environmentally induced dwarfing of otherwise larger forms; (3) pollen and spores in the sediments are locally derived, and their extreme scarcity probably reflects the limited number of End_Page 501------------------------------ local source plants; (4) dinoflagellate cysts in the sediments increase in number with depth, and were not found in sediments from water shallower than 150 feet; bathymetric stratification of the adult planktonic forms may be responsible. Possible factors controlling organisms represented in each facies belt are variations in type of bottom, turbulence, and temperature which control the faunas at various depths, and light may determine the lower limit of the algal Halimeda. Other factors of possible significance such as chemical composition, pH, salinity, and density seem to be similar at all depths represented and probably are not important controls. Depth-controlled facies belts, or bathymetric zones, comparable with those at Kapingamarangi, are recognized in some ancient sedimentary deposits, especially in rocks of late Paleozoic age. Certain reefs of several Paleozoic systems are believed to be similar in many respects to the peripheral reef and others to the patch reefs of this atoll.

WARM CLIMATE IN THE LATE MIOCENE OF THE SOUTH COAST OF ALASKA AND THE OCCURRENCE OF PODOCARPACEAE POLLEN

Abstract A study of the Homerian type section in the upper Beluga Formation (Upper Miocene) of the Kenai Group of southern Alaska has yielded two surprising discoveries: (1) warmth-loving taxa and (2) the presence in Alaska of a ‘new’ gymnosperm family, Podocarpaceae. A well-preserved pollen and spore flora is present in Upper Miocene coal beds of the Kenai lowland, near Homer, Alaska. Stump horizons, abundant wood fragments, wood grain, and amber within the coal attest to a forested swamp. Pollen assemblages from the Homerian type section include elements of both Mixed Northern Hardwood and warm-temperate Mesophytic forests and are far richer than the flora previously defining the Homerian type section, which had suggested a less diverse, cooler assemblage. Within the Homerian type section, the flora exhibits no definite taxonomic chronology; in general, Alnus dominates, with up to 45% of the total counts, followed by Pinaceae and Taxodiaceae pollen types (30 to 35%) and thermophiles (c. 14%). At least 36 genera are represented, including Carya type, Corylus, Ilex, Juglans, Myrica, Ostrya/Carpinus, Pterocarya, Quercus/Quercus-type, and Ulmus/Zelkova, eight dicot genera have not previously been reported from the type Homerian. Presence of these hardwoods in moderate to minor amounts suggests that the climate during the Homerian (Late Miocene) was only slightly cooler than that of the Seldovian (Early to Middle Miocene). Unexpectedly, Dacrydium and Podocarpus are present as minor elements in most of the samples. They apparently coexisted with the other Miocene taxa, because the pre-Paleogene Kenai–Chugach terrane to the southeast, which supplied sediments to the Kenai Group, is mostly of oceanic plate provenance and is unlikely to have been the source of the pollen. A uniform orange fluorescence of all the pollen, including the podocarps and any potentially reworked pollen, also suggests a contemporaneous origin for all the taxa. The flora from the Homerian type section may precede or coincide with uplift of the Alaska Range to the north. Thus, further comparison with Homerian taxa at localities north and south of the Alaska Range will be important as it may reveal a possible rain shadow effect.

Pre-Olympia Pleistocene Stratigraphy and Chronology in the Central Puget Lowland, Washington

Drifts of two pre-Olympia glaciations separated by nonglacial sediments are widespread in the central Puget Lowland of western Washington. The Double Bluff Drift (older) and Possession Drift represent advances of the Puget lobe of the Cordilleran ice sheet more than 40,000 years ago. The nonglacial Whidbey Formation between the drifts was formed in streams and lakes. During its deposition, climate was initially cool and moist, as inferred from pollen in peat beds, but subsequently it became much like that of the present in the lowland. The Possession Drift is tentatively correlated with glacial deposits of Salmon Springs age in the southern part of the lowland. The Whidbey Formation may correlate with nonglacial deposits between two Salmon Springs Drifts or with the Puyallup Formation.