Regional boundary sections: Towards greater precision in correlating with global standard stratotypes
|Category||Paleontology and Stratigraphy|
|Location||International Geological Congress,oslo 2008|
|Holding Date||04 October 2008|
The internationally agreed global stratigraphic chart (ISC), i.e. the sequence of named chronostratigraphic units and their boundaries, is, to a large extent, completed. It shall be used as a global chrono-standard for subdivision of earth history, and for correlating regional or local stratigraphic units in different regions and geological domains. A unified ISC is especially useful at present, when integration of international efforts results in a compilation of geological maps of the world to derive a global geological synthesis. The basic requirement for this goal is the correlation of Global Stratotype Sections and Points (GSSPs) with regional stratigraphic units and boundaries outside of the GSSP area to distant regions, or in different provincial paleogeographic and facies settings.
While working on establishment of GSSPs, reasonably acceptable correlations have already been achieved by comparative analysis of the most complete and well studied candidate sections. However, this remains a difficult, and in some instances, an almost impossible task. This is especially true for Palaeozoic systems such as the Cambrian, Ordovician, and Permian. Most of these have achieved newly compiled sets of global series and stages with new boundary horizons. For others such as the Carboniferous, even if traditional sequence and nomenclature of units remain more or less unchanged, some boundaries have had to be redefined. In order to produce uniform, high quality international geological maps, we need to revise and redefine the ages of our regional mapping units by correlation with units and boundaries fixed in the ISC and GSSPs. This can be facilitated by establishing Regional Stratotype Sections and Points (RSSPs). The first step should be to designate reference sections which coincide as clearly as possible with corresponding GSSPs. In some regions this kind of stratigraphic sections, compatible with the GSSP, have already been studied intensively as former GSSP candidates.
The second type of RSSP concerns regional stratigraphic units that traditionally have been mapping units, or in higher stratigraphic categories, a combination of such units. In a broad sense, such mapping units were originally facies units. In some instances, these have been characterised by description of their lithology and paleontology, but without paying special attention to precise boundary levels. Therefore, it is recommended that in future newly recognized regional units should be established with procedures similar to those used for the GSSPs, keeping in mind that already existing units may be revised in this sense in order to obtain additional real SSPs.
The RSSPs need not be internationally approved, but they should be published and endorsed by the respective national or regional stratigraphic committees, or national or provincial geological surveys.