The palaeontologists that taught classes in the university I attended (UPMC, Paris VI), always told us we should be cautious while studying any fossil assemblage because it is important to take “time-averaging”* into consideration. It is very important, they told us, and I thought that I had understood it (as did my classmates). This until last week when I found an article by Michal Kowalewski (1996) on the subject, and I found out that the theory of the matter is very complicated.
I am not going to discuss the details, but what I wanted to put forward is the concept and theoretical work that had to be done in order to establish the notion of time-averaging and how it works. It is indeed quite complicated and shows that it is necessary to work on what I’d call theoretical geology.
*time-averaging: the fossils contained in a single sedimentological layer haven’t died and fossilised synchronously. Also, the different organisms that are found fossilised, don’t have the same fossilisation potential. This can create various problems while studying the assemblages, and the studies that have been carried out concern all the aspects of this phenomenon.