Stratigraphy

With regard to stratigraphy, for the description of stratigraphic units (including recent quaternary deposits) we will proceed from the oldest to the most recent term. In the case of legends structured in tectonic units, the order dictated by the structural order can also be maintained in the Explanatory Notes, starting from the geometrically higher tectonic unit, in accordance with the tectonic scheme and the legend of the sheet.

The lithological description of the cartographic units, obviously differentiated according to the type of constituent rock, must be sufficiently wide and in any case never less detailed than that reported in the legend of the sheet. Since in the various chapters will be reported data of extreme importance also for application purposes, it is recommended to expose first the data related to the lithological characters that macroscopically characterize the rocks, then going down in detail. The information should include: constituent lithographs, their lateral and vertical relationships, color, thickness and geometry of the layers and of the unit as a whole, structure, texture, degree of cementation, fossiliferous content, mineralogical and petrographic association, sedimentary and flow structures, mineralizations possibly present and anything else useful to identify the unit under examination. The limits and stratigraphic relationships with the other units will have to be described (if outcropping), with particular regard to the discontinuous ones (both discordant and concordant) and their possible expressions (hard-ground, bauxiti, paleosols, etc.). It will have to be indicated the power of the unit, total or outcrop, estimated or measured in the area or in adjacent areas, with attention to lateral variations.
For sedimentary rocks it is necessary to describe the fossiliferous association (both micro and macro), with the indication of the biozones that characterize the unit. For clastic, volcanic and crystalline rocks large space must be given, as appropriate, to the description of mineralogical, petrographic and chemical characters.
Whenever possible, the lithogenetic environment or the way it is put in place must be described, reporting, if conflicting, alternative interpretations of other Authors.
Finally, the age, derived from geometric, biostratigraphic and/or radiometric data, will be reported.
If deemed necessary, schemes, diagrams, tables, facies charts, etc., can be added, within the limits of what indicated in paragraph 4.2.3 - Illustrations of the Notebook, series III, n. 2 of the SGN. This will also be the location for the description of the survey data.
A last annotation concerns the establishment of new stratigraphic units. To the large number of units already known in the literature, often of local character, sometimes in synonymy with others, mostly not formally defined even if of consolidated use in the literature, are added those recognized and defined with the proceeding of the activities for the survey of the Geological Map at the scale 1:50.000. In order for these units to be usable for cartographic purposes, a certain amount of synthesis and revision work is indispensable, also in consideration of local and regional geological characteristics. For this purpose, the Illustrative Notes can perform a very important function of cartographic homogenization, being able to become the place where to set up new units, redefine those already in use, make correlations, etc.. The Illustrative Notes are therefore the ideal place where to report all the data (including the standard sections) necessary for the definition and formal establishment of the unit, which will be done through the compilation of a worksheet developed by the Italian Commission of Stratigraphy of the Italian Geological Society, as part of the Program Agreement between the National Geological Survey and the CNR.