Classification of Gamma-ray Data

All of the in situ gamma-ray data collected at sites on the Palos Verdes Peninsula were classified into groups using a maximum likelihood clustering algorithm. These calculations were done to test how well the gamma-ray data discriminate the different geologic units. The data were clustered into four groups based upon the potassium (K), uranium (eU), and thorium (eTh) concentrations. The figure below shows a 3-dimensional representation of the groups and the table lists the mean values and standard deviations for each of the groups. Groups 1 and 3 generally correspond to areas of terrace cover or the lower part of the Altamira Shale. Group 2 may reflect the Valmonte Diatomite although a number of sites classified as group 2 lie within areas mapped as the phosphatic lithofacies of Conrad and Ehlig (1987). Group 4 is probably characteristic of the more uraniferous parts of the phosphatic lithofacies.

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