3.11 Tectonostratigraphical units
3.11.1 General properties and rules
3.11.1.1 Tectonostratigraphy -- Tectonostratigraphy is concerned with the stratigraphical division of bodies of rock which are piled on top of each other and separated by thrusts (Section 3.9.9). A tectonostratigraphical unit is therefore a body of rock which has been displaced along a thrust fault (floor thrust), and may be delimited uppermost by a roof thrust or the erosion surface (Fig. 27). Tectonostratigraphical classification therefore differs fundamentally from lithostratigraphical and lithodemic classifications. A tectonostratigraphical unit may consist of one or more lithostratigraphical and/or lithodemic units.
3.11.1.2 Nomenclature -- Tectonostratigraphical units are given names in accordance with the "general rules for naming and defining geological units" (Chap. 2). Formal names are composed of a geographical name (or an alternative name in the case of the continental shelf) and the tectonostratigraphical unit term. A tectonostratigraphical unit which is defined first after its floor thrust has been given a formal name is to have the same proper name as the floor thrust, and vice versa, a floor thrust is to be given the same proper name as the nappe of which it forms the base.
Many nappes in the Scandinavian mountain chain have old-established names derived from a type area. It should be possible to erect reference sections for the bounding thrusts of such nappes. When erection of a new tectonostratigraphical unit is desirable this should preferably be defined on the basis of a type section, with the possible addition of one or more reference sections, to cover the bounding thrusts. It is particularly important that the floor thrust is included (see Sections 2.4.5 and 3.9.9, and figure 22).
3.11.1.3 Units and hierarchy -- The tectonostratigraphical units forming a hierarchical classification system are, in decreasing order of rank, nappe system and nappe complex, nappe, thrust sheet and small thrust sheet. Thrust sheet (flak or skyveflak) may also be used as a general unit term without rank. Nappe is the fundamental unit. Nappe complex and nappe system have equal rank, but are distinguished from each other on the basis of the relative age differences of movements on the internal thrust faults.
