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Geology topics

Charles W. Holmes

Publications and source records attributed to Charles W. Holmes.

24 records · Page 2Linked to original sources
USGS1983

Sedimentology of Southwestern Roads region, U.S. Virgin Islands: origin and rate of sediment accumulation

Sand deposits on southern insular shelf of St. Thomas, U.S. Virgin Islands, were investigated to determine their origin, environmental processes and accumulation rates. Sea-floor samples show that the sand has been derived (in situ) mainly from calcareous algae and molluscs. Zonation of the dominant sand producers is related to the present environmental setting; water depth has the greatest influence. Carbon-14 data (bulk sample) of cores indicate accumulation rates of slightly less than 1 mm/year for the last 5,000 years. Faunal studies show that the climate has remained constant over the past 5,000 years. The only changes in environmental conditions appear to have been an increase in water depth, changes in the patterns of water movement, and an increase in water temperature.

Virgin Islands↗
USGS1981

210 Pb method for estimating the rate of carbonate sand sedimentation

The plot of 210 Pb activity against depth in carbonate sands on the Virgin Island Bank is a negative asymmetric hyperbolic curve. As depth increases, an initial rapid decrease in 210 Pb activity caused by the decay of unsupported 210 Pb and 226 Ra is followed by increasing activity as a result of 210 Pb achieving equilibrium with in growing 230 Th. As this curve is time dependent, an estimate of the relative ages in carbonate sequences and the rates of net carbonate accumulation can be made. The ease of 210 Pb activity determinations makes this procedure an attractive method in obtaining carbonate sand accumulation rates.

Geo-Marine Letters↗
USGS1977

Effects of dredged channels on trace-metal migration in an estuary

Determination of trace-metal levels in the sediments of the Matagorda Bay system revealed anomalously high mercury values. The distribution of the mercury-rich sediment deposits is the result of the sedimentological regime of the bay system produced by the tidal currents in the dredged channel. According to this model, the oxygenated open gulf water pushed into the bay by tidal currents activates the mercury and reintroduces it into the sediment regime of the bay in an area where the turbidity maximum is most prevalent. Within this region, the absorption sites are at a maximum, tying up the mercury. The mercury-enriched suspended material is then transported and deposited according to the hydraulic regime within the bay system.

Texas↗
USGS1972

Distribution and isotopic composition of uranium in lower Nueces River, Nueces Bay and Corpus Christi Bay, Texas

The uranium concentration and isotopic composition of water and suspended sediment from the Nueces River, Nueces Bay and Corpus Christi Bay were determined by alpha-spectroscopy. The average dissolved uranium concentration and radioactivity ratio (U 234 /U 238 ) of Nueces River water were determined to be 2.44 µg/1 and 1.15 respectively. Water from a tributary of the Nueces River, Cayamon Creek, was found to contain an average dissolved uranium concentration of 42.8 µg/1 with an isotopic radioactivity ratio of 1.56. Close inspection of the lateral concentration and isotopic activity ratio of uranium revealed an increase below the confluence of Cayamon Creek with the Nueces River. A model was derived based on equations used in isotopic dilution analysis, which predicts these increases within analytical error. This model may be useful in future studies to locate anomalous uranium within the hydrologic environment.

Texas↗
USGS1968

The geochronology of foraminiferal ooze deposits in the "Southern Ocean"

Many cores raised from the Drake Passage are characterized by alternating zones of foraminiferal ooze and sandysilt. Cores raised from the East Pacific Rise are foraminiferal ooze or alternating siliceous and carbonate ooze. The uranium and thorium concentrations and isotopic ratios in foraminifers separated from these cores were measured by alpha-spectroscopy. 230 Th in foraminiferal tests is found to be out of equilibrium with its parent ( 234 U), enabling the “excess 230 Th” method to be used in estimating sedimentation rates. The uranium concentration of the tests is constant, suggesting constant uranium concentrations in the sea and thus constant production of 230 Th during periods of foraminiferal production. 232 Th concentration is 2.1 ± 0.7 ppm in the Drake Passage and below the level of detection in tests from the East Pacific Rise. Within each core the 232 Th is constant, varying closely with distance from the source. Based on the degree of disequilibrium of 230 Th, correlations between cores can be made. Age estimates of the foraminiferal zones indicate deposition occurred between 8 000 and 120 000 and between 190 000 and 280 000 years before present. Reported dates of high stands of the sea fall between the ages estimated for the foraminiferal zones, suggesting these zones were deposited during northern hemisphere glacial maxima.

Earth and Planetary Science Letters↗