Geology topics

J.K. Osmond

Publications and source records attributed to J.K. Osmond.

3 recordsLinked to original sources

USGS1978

Uranium-isotope variations in groundwaters of the Floridan aquifer and Boulder Zone of south Florida

Water samples from four wells from the main Floridan aquifer (300-400 m below mean sea level) in southeast Florida exhibit 234 U 233 U activity ratios that are significantly lower than the secular equilibrium value of 1.00. Such anomalous values have been observed previously only in waters from sedimentary aquifers in the near-surface oxidizing environments. These four wells differ from six others, all producing from the same general horizon, in being located in cavernous highly transmissive zones. We hypothesize that the low activity ratios are indicative of a relic circulation pattern whereby water from the surface aquifer was channelled to lower levels when sea level was much lower. At a deeper cavernous level, known as the Boulder Zone (800-1,000 m below mean sea level), the U isotopes, along with other chemical constituents, show progressive changes with increasing distance from an inferred flow source in the Straits of Florida. This tends to support the hypothesized landward flow (though with a more northerly component) of cold seawater in the extensively transmissive Boulder Zone.

Florida↗

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↗

USGS1968

Uranium disequilibrium in groundwater: An isotope dilution approach in hydrologic investigations

The distribution and environmental disequilibrium patterns of naturally occurring uranium isotopes (U 234 and U 238 ) in waters of the Floridan aquifer suggest that variations in the ratios of isotopic activity and concentrations can be used quantitatively to evaluate mixing proportions of waters from differing sources. Uranium is probably unique in its potential for this approach, which seems to have general usefulness in hydrologic investigations.

Florida↗