3.10 Morphostratigraphy
3.10.1 General properties and rules
3.10.1.1 Morphostratigraphy -- Morphostratigraphy has to do with stratigraphical classification of geomorphological elements (landforms). The principles of stratigraphy (Section 1.2) are applied to landforms which are placed in a chronological order from older to younger. In Northern Europe, morphostratigraphy has traditions going back to studies of Quaternary ice-contact deposits and shoreline levels in the middle of the last century.
The use of landforms as morphostratigraphical units has been subject to some discussion. Frye & Willman (1962) suggested that such units should be used. Mangerud et al. (1974) argued for their continued use in Northern Europe and, in particular, stressed how practical they were when studies were being undertaken on the retreat of the continental ice-sheets and the history of isostatic recovery. According to American practice (e.g. Frye & Willman 1962), morphostratigraphical units embrace both the shape of the form element and the sediments in it, whereas the Nordic tradition (e.g. Mangerud et al. 1974) allows them to be defined by their abstract shape alone.
Morphostratigraphy is not dealt with by either ISSC (1976) or NACSN (1983). The latter Code does, however, introduce an allostratigraphic classification system. An allostratigraphical unit is defined partly on the basis of its material content, partly on its surface shape and its morphological boundary relationships to adjacent units. As pointed out above, there is no tradition in Norway or other Nordic countries for classifying superficial deposits and geomorphological features in this manner. It is also the opinion of NSK that using a combination of lithological and morphological features as identification criteria is an unfortunate practice. Hence, NSK does not recommend the use of the allostratigraphical classification system. Instead, a morphostratigraphical classification system is advocated, perhaps, if necessary, combined with a lithostratigraphical or biostratigraphical one.
No systematical classification system for morphostratigraphy, or guidelines for naming morphostratigraphical units, have so far been available. Moreover, morphostratigraphy and chronostratigraphy have sometimes been confused (see Section 3.10.2.8). The morphostratigraphical classification system proposed in this Code uses unit terms similar to those used for lithodemic units (Section 3.3). This is done because (1) neither morphostratigraphical nor lithodemic units comply properly with the Law of Superposition (Section 1.2), (2) units in both categories may have a composite mode of formation and need not be laterally continuous, and (3) the unit terms are genetically neutral.
3.10.1.2 Definition -- A morphostratigraphical unit is a landform, or group of landforms, whose boundaries can be delimited, and which constitutes one of several corresponding units that together demonstrate a geological process in time and space. The landforms may result from deposition or erosion, or a combination of both processes. The morphostratigraphical unit is defined independently of material content and the period in time when the landform or landforms constituting it were formed. Figures 25 and 26 show idealized examples.
The individual landform in a morphostratigraphical unit can be defined and named in accordance with the rules given in Section 3.7.1. The material content can be defined as in lithostratigraphical (Section 3.2), lithodemic (Section 3.3) or biostratigraphical units (Section 3.5). The time-span which the morphostratigraphical units represent can be defined geochronometrically (Section 4.4) or diachronously (Section 4.7). It is important to keep these different categories separate when working with morphostratigraphical classification.
3.10.1.3 Nomenclature -- Morphostratigraphical units are named according to the "general rules for naming and defining geological units" (Chap. 2). Formal names are composed of a proper name and the morphostratigraphical unit term, perhaps separated by a term describing the character of the unit (e.g. ice-contact ridge, terrace, beach ridge) (see also Section 3.10.2.6). The proper name is a geographical name for the type locality or type area; old-established proper names may also be used. A morphostratigraphical unit that is derived from a previously erected geological form unit may be given the name of that unit if misunderstanding cannot arise.
3.10.1.4 Units and hierarchy -- Morphostratigraphical units which are integral parts of a hierarchical classification system are, in decreasing order of rank, morphosupersuite, morphosuite and morphodeme. Morphocomplex is a unit without rank in the hierarchy. The morphodeme is the fundamental unit. These terms are introduced and defined for the first time in this Code.
