Problems with permineralization of peat

I must begin by congratulating these three authors on their comprehensive and lucid reviews of the processes of plant permineralization which are both complicated and still, in certain respects, perplexing. There is little in what they say that I am competent to dispute. None the less, I assume it is my prerogative, indeed my obligation, to seek out some areas of contention, lest our discussion should devolve into mere amiable acquiescence. It is perhaps appropriate to start by remarking on the rather obvious fact that the preservation of truly cellular detail in animal fossils is exceedingly rare (setting aside unicells, such as forams, and bone tissue); whereas in plants, even in prokaryotes, preservation of cellular structure in silicate, carbonate or pyrite is not all that uncommon. Such preservation is, inevitably, in some degree concomitant with the possession of cell walls. It is also, for palaeobotanists, one of the huge compensations for the relative rarity of plant fossils, compared with animals, throughout the geological record. However, although permineralized plants have now been studied for over 150 years, we still know remarkably little about the processes resulting in this permineralization. There are two main respects in which we remain ignorant of the permineralization process. First, even now, there is no general agreement about the source, either of the silicon in silicification, or of the cations (calcium, magnesium) in coal balls. There is continuing debate about whether the mineral matter came in each of these rather different cases, from ‘above’ or ‘below’, and indeed whether in each instance a single common process is involved. Secondly, we still have no present-day environment that offers a model for either silicification or calcification resulting in cellular preservation of higher plant tissue in a swamp environment.