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D.P. Adam

Publications and source records attributed to D.P. Adam.

23 records · Page 2Linked to original sources
USGS1983

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.

California↗
USGS1981

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.

Geological Society of America Bulletin↗
USGS1976

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.

California↗
USGS1967

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.

California↗