The Use of Boron Concentrations in Fossil Materials as a Paleosalinity Indicator

Citation

Furst, Marian Judith (1979) The Use of Boron Concentrations in Fossil Materials as a Paleosalinity Indicator. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/053m-sr84. https://resolver.caltech.edu/CaltechTHESIS:05132024-183001142

Abstract

The ¹⁰B(n,α) ⁷Li nuclear reaction has been used in conjunction with alpha-sensitive plastic track detectors to determine boron concentrations in various biologically precipitated minerals. A correlation between the boron concentration in the water in which the precipitating organisms grew and the boron concentration in the materials analyzed was found in specimens of Mytilus edulis, related bivalves, diatoms, and siliceous sponge spicules. M. edulis shell boron concentrations in aragonite ranged from about 5 ppm in specimens from 5 ⁰/₀₀ salinity water to about 15 ppm in specimens from 35 ⁰/₀₀ salinity water. Salinities can not be distinguished quantitatively using carbonate shells beyond the general distinction of marine, brackish, or nearly-fresh water. Fossil shells showed evidence for some loss of boron from aragonite. Freshwater diatomites contained less than 10 ppm B, while marine diatomites and unconsolidated marine core samples contained about 100 ppm. Detailed studies of live­ collected sponge spicules established that individual spicules larger than 20-25 microns in diameter can be analyzed, and that there is a correlation with water salinity for sponges from regions of low water temperature and high productivity. Measured concentrations ranged between nearly 0 for fresh-water sponges to 600-700 for marine sponges. However, spicules from sponges from tropical, low-productivity marine locations contained markedly less boron. The exact relationships between B concentration in the spicules and concentration in the water, temperature, nutrient supply, and food sources for the sponges are not known. Pleistocene spicules from deep-sea cores tended to contain somewhat less boron than might be anticipated by comparison with live-collected spicules based on present water temperatures and nutrient supplies. It is uncertain whether the lower concentrations are the result of diagenetic processes or the unknown effects of differences in the food supply and/or environmental conditions. Until the significance of the boron concentration in spicules is understood more fully, paleosalinity determinations will not be possible. If a relationship between boron content and water temperature or nutrient supply can be defined, it may be possible to use boron concentrations in spicules to trace oceanic circulation patterns in the past.

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