Geology topics
D.P. Adam
Publications and source records attributed to D.P. Adam.
Tephrochronologic studies of sediment cores from Walker Lake, Nevada
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Palynology of two upper Quaternary cores from Clear Lake, Lake County, California, with a section on dating
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Pollen data from a 2.93-meter Holocene lacustrine section from Walker Lake, Coconino County, Arizona
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Temperature and precipitation estimates through the last glacial cycle from Clear Lake, California, pollen data
Modern pollen surface samples from six lake and marsh sites in the northern California Coast Ranges establish a linear relation between elevation and the oak/(oak + pine) pollen ratio. Modern temperature and precipitation lapse rates were used to convert variations in the pollen ratio into temperature and precipitation changes. Pollen data from two cores from Clear Lake, Lake County, California, spanning the past 40,000 and 130,000 years were used to estimate temperature and precipitation changes through the last full glacial cycle. The maximum glacial cooling is estimated to be 7° to 8° C; the last full interglacial period was about 1.5° C warmer than the Holocene, and a mid-Holocene interval was warmer than the present. The estimated precipitation changes are probably less reliable than the estimated temperature changes.
Pollen data from a 5-meter upper Pleistocene lacustrine section from Walker Lake, Coconino County, Arizona
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Chrysophyte cysts as potential environmental indicators
Many Chrysophyte algae produce morphologically distinctive, siliceous, microscopic cysts during a resting stage of their life cycles; these cysts are often preserved in sediments. Scanning electron microscopy and Nomarski optics permit much more detailed observation of these cysts than was heretofore possible. We have used an ecologic and biogeographic approach to study the distribution of cyst forms in sediments and have established that many cyst types are found only in specific habitats, such as montane lakes, wet meadows, ephemeral ponds, and Sphagnum bogs. In the samples we have studied, cysts seem to be most common in fluctuating fresh-water habitats of low to moderate pH and some winter freezing. Numerous taxonomic problems have yet to be resolved. We believe that chrysophyte cysts have the potential to become a useful tool for both modern environmental assessments and paleoecological studies of Cenozoic fresh-water lacustrine deposits.
Fish remains from core 8, Clear Lake, Lake County, California
A 21.2-m-long core taken in the northwest part of the Upper Arm or main body of Clear Lake, California, has yielded a continuous record of fish life in this part of the lake during approximately the last 24,500 years. This record provides data concerning faunal changes in the Upper Arm, and also permits reconstruction of fish sizes and growth rates based upon scale remains. Four tables are presented that provide data on sample numbers and their frequency of occurrence and identification of skeletal and scale remains, and the reconstructed lengths and weights of Tule perch ( Hysterocarpus traski Gibbons) based upon remains of the scales of this species. A fifth table presents the mean reconstructed standard lengths and mean ages in years B.P. for slugs 1 through 24, 0-18.3 m. These data provide a unique data base for examination of paleoecologic and paleoclimatic trends in the North Coast Range of California through the Holocene and late Pleistocene. The record augments similar paleoecologic and paleoclimatic trends reconstructed from Core 6 and 7, taken in the Highlands and Oaks Arms of Clear Lake, respectively.
Fish remains from Core 6, Clear Lake, Lake County, California
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Sampling procedures and catalogue of samples for eight boreholes at Clear Lake, Lake County, California
Clear Lake, California, is situated in an area which has been subject to crustal movement, earthquake-generated ground shaking, volcanic eruptions, and climatic fluctuations during late Quaternary time. The U.S. Geological Survey, in cooperation with Lake County, has undertaken a study of the seismic, volcanic, and environmental history recorded in the late Quaternary sediments beneath the floor of the lake (Sims, 1974). This study is based on continuous core samples measuring 12 cm or 15 cm in diameter that were obtained in August-November, 1973, from 8 boreholes measuring 14-113 m in length (Figure 1). Preliminary description of many of these samples and interpretation of ancient seismic events can be found in Sims and Rymer (1975). Over 2,000 multiple samples have been taken from these cores in order to study the environmental record preserved in the lacustrine sediments. Samples were taken for pollen, diatoms, cladocera, bulk mineralogy, fine size analysis, macrofossils, and water-content/organic carbon-content at designated depths. In addition, volcanic ash and radiocarbon samples were removed for correlation studies and age determinations. This report provides a description of the standard sampling procedures designed for sapropelic muds and peat-rich clays, a description of modified sampling procedures developed for sampling sands and coarser sediments, and a catalogue of samples from the Clear Lake cores. Table 2 outlines the steps followed for the standard sampling procedures.
Enclosed bark as a pollen trap
Counts were made of pollen in traps formed by enclosed bark in two remnants of bristlecone pine, Pinus aristata Engelm., from the White Mountains of east-central California. The traps, dated by tree-rings at A.D. 350 and 1300 B.C., contained a major complex of pine-sagebrush pollen and traces of other species, representing the equivalent of the present vegetation.