TRACE ELEMENT PROVENANCE DETERMINATIONS FOR MIOCENE LACUSTRINE MUDSTONES: RIDGE BASIN, SOUTHERN CALIFORNIA

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M. Elaine Kennedy, Geoscience Research Institute, located on the campus of Loma Linda University, Loma Linda, CA

Source rocks and source areas were determined for 154 samples assigned to the Cereza Peak Shale Member of the Miocene Peace Valley Formation and associated units exposed in Ridge Basin, California. Information was obtained by x-ray fluorescence analysis of the following 14 trace elements: Ba, Cr, Hf, La, Pb, Ni, Th, U, Y, Sr, Rb, Nb, Ga and Zr. These data were augmented by Fourier transform infrared spectroscopy and x-ray diffraction analyses, plus inductively coupled plasma atomic emission analysis. Bivariate plots, computation of the correlation coefficient (r), 2-way analysis of variance and the Duncan new multiple range test were employed to reduce the resultant data.

The following evidence suggests a northeastern source (Liebre Massif) for the Cereza Peak mudstone samples: (1) Cr strongly correlates with clay content (r = 0.96) and values for the Cr and clay increase basinward from the northeast, (2) Cr, Ni, Nb, Rb, U, Y and Zr values are similar for the Cereza Peak and northeastern-sourced Piru Gorge mudstone samples; however, values for mudstones from the southwestern-sourced Violin Breccia are as much as 2.5 times greater, (3) average La:Th ratios of 3.2 and 3.4 as well as average Hf values of 3.0 and 4.3 ppm for Cereza Peak and Piru Gorge samples, respectively, also indicate a close genetic affinity. These values are consistent with those from granitic Liebre Massif samples (La:Th = 2.7; Hf = 3.4 ppm), but contrast sharply with samples from the Violin Breccia (La:Th = 4.7; Hf = 6.6 ppm).

Published in: American Association of Petroleum Geologists, Annual Convention, Abstracts, 1993, p.127.