Figure F28. Variations of ash alteration state across Subunit IA/IB boundary and Unit I/II boundary. A. Unaltered glass shards in ash layers above 251.54 m CSF-B (Subunit IA). B. First appearance of altered glass in the succession. The appearance of such a degree of ash alteration characterizes strata within Subunit IB. C. Relatively larger degree of alteration to the ash shown in B. D. Reappearance of unaltered ash within Unit II.
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