ABSTRACT

Difficulties will always arise if we presume to compare conventional stratigraphic columns (macro-lithology) with corresponding geophysical logs (responding to microvariations), because the causative phenomena are of two widely different orders of magnitude.

We should study closely-spaced thin sections, compute data on frequency and maximum apparent grain-size (clasticity index) of the principal microscopic components (detrital and authigenic minerals, benthonic and pelagic microfaunas, physico-chemical properties of the matrix), and plot these as a set: of curves alongside the stratigraphic column for comparison with the geophysical profile and the zonation of the index-fossils.

Several mechanisms of sedimentation have been outlined in numerous Paleozoic and Mesozoic sections of Europe through the investigation of the following problems:

1. Variation of the clasticity and the frequency of detrital minerals.
2. Relations between detrital minerals and authigenic components such as glauconite, silica, and feldspars.
3. Variation of iron compounds with respect to detrital and authigenic minerals.
4. Variation of microfaunas with respect to mineral components.
5. Reciprocal relations between benthonic and pelagic microfaunas.

It is suggested that microscopic investigation should become common practice because numerous processes of sedimentation of fundamental importance for the reconstruction of environments are of small scale and are commonly overlooked.