Abstract

The uranium concentration of two independent carbonate sediment sample suites was studied to establish the effect of fresh water alteration on the redistribution of uranium. Recent carbonate sands and their ancient analogs were studied in Bermuda and along the east coast of the Mediterranean Sea in Israel. The results of the uranium analyses are compared to established indicators of fresh water alteration in carbonate sediments. Interpretation of the data from both areas yields the same conclusions. As the metastable minerals aragonite and Mg-calcite are removed by fresh water from the sediment system and the sample type changes from unconsolidated carbonate sand to consolidated limestone there is a concomitant decrease in uranium content. The uranium and calcite concentrations show an inverse relation and indicate that the product of fresh water alteration, calcite, accepts less uranium than the original aragonite. The relationship between uranium and the stable carbon and oxygen isotopes for the Bermuda suite is inconclusive, whereas the same plots for the Israeli Coast suite show a direct relationship between decreasing uranium content and increasingly negative delta values. The relations between uranium and established indicators of fresh water alteration provide converging lines of evidence indicating that fresh water dissolution and replacement of marine carbonates cause a reduction, up to 50 percent over the Pleistocene samples, in total sample uranium content.

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