Stratigraphic Guide: Formation vs. Complex

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Stratigraphic Guide: Formation vs. Complex

Postby bzoli » October 11th, 2011, 12:10 pm

Problem: Chapter 5, C.2 states: "Formations are the only formal lithostratigraphic units into which the stratigraphic column everywhere should be divided completely on the basis of lithology."
1. If the words "stratigraphic column" are interpreted in favour of the idea that "formations" are only sedimentary and/or volcanic units intrusive and metamorphic rocks, for which the layering and stratigraphic succession cannot be ascertained, should not be named "formations". This would be in harmony with Chapter 5, F.4, and these rocks can be named among others "complex".
2. On the other hand, Chapter 5, C.8 gives another definition of "complex": "A lithostratigraphic unit composed of diverse types of any class or classes or rocks (sedimentary, igneous, metamorphic) and characterized by irregularly mixed lithology or by highly complicated structural relations".
3. A brief check of the internet reveals that no "granite formations" are mentioned as lithostratigraphic units whereas there are many "granite complexes". This worldwide practice is in harmony with the definition in F.4.
i) In order to avoid the uncertainty ("if") outlined in 1 it would be useful to give in C.1 or C.2 an additional explanation like "the contents of this item is not valid for intrusive and metamorphic rocks (see F.4)".
ii) A revision of the contents of the term "complex" with eliminating the disharmony between the two definitions (C.8 and F.4) is needed. If both meanings of the terms will be preserved it would be desirable to introduce a clear difference between them. For example, "Ófalu Complex" could satisfy C.8 whereas "Ófalu Metamorphic (or Schist) Complex" F.4. The difference would consist in the absence (C.8) or presence (F.4) of a lithological name.
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