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.
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.