105b. Niklas, Karl J., Brown, Jr. R. M., and Richard Santos. 1985. Ultrastructural states of preservation in Clarkia angiosperm leaf tissues: implications on modes of fossilization. Late Cenozoic History of the Pacific Northwest. Ed. C. J. Smiley. Pacific Division, AAAS.

105b. Abstract

Ultrastructural analyses of Miocene leaf tissues from the Clarkia flora indicate the preservation of various protoplasmic features such as chloroplasts, mitochondria, and nuclei. Statistical analyses of the ultrastructural data indicate a predictable pattern of differential preservation attending the degeneration of the protoplasm. Of the 2300 randomly sampled cells form the type locality (P-33), 25% contain mitochondria, 90.1% contain chloroplasts, and 4.3% contain nuclei. Comparable analyses of tissues from site P-40 indicate that 34.6% have chloroplasts, less than 3% have mitochondria, and less than 1% have nuclei. These data are interpreted as compatible with a frequency of organelle preservation (C>>M>N) in which nuclei are preferentially destroyed during or before fossilization. Simulated fossilization involving the compression of living leaf tissues and studies of senescent and dehydrated tissues are used to evaluate the probable effects of these factors on the sequence of events leading to the observed ultrastructure of the Clarkia fossils. From these studies we conclude that 63% of the sample tissues appear to have entered the depositional environment as the result of leaf abscission and 15% were detached from their branches as a result of trauma; 89% of the tissues examined show evidence of compression wall failure, while 17% show concertina cell wall distortion similar to that seen in dehydration of living tissues.

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