This is a fascinating paper.
Galvez, M.E., Beyssac, O., Benzerara, K., Bernard, S., Menguy,
N., Cox, S.C., Martinez, I., Johnston, M.R. and Brown, G.E., 2012.
Morphological preservation of carbonaceous plant fossils in
blueschist metamorphic rocks from New Zealand. Geobiology,
10(2), pp.118-129.
PDF file at:
https://www.researchgate.net/publication/221800575_Morphological_preservation_of_carbonaceous_plant_fossils_in_blueschist_metamorphic_rocks_from_New_Zealand
Abstract at:
http://onlinelibrary.wiley.com/doi/10.1111/j.1472-4669