SDS was the first Subcommission to complete in 1998 the formal definition of chronostratigraphic subdivisions (three series and seven stages) by approved GSSPs (Geological Stratotype Sections and Points; see publication list). The Devonian-Carboniferous boundary was formally defined by an International Working Group and approved by ICS in 1991 (Paproth et al., 1991; see publications). Already in parallel with the search for chronostratigraphic definition, SDS had begun to follow a wide range of other tasks of equal importance for the wider community of geoscientists.

Definition of formal substages

From several reasons it became necessary that some of the defined stages, the Emsian, Givetian, Frasnian, and Famennian, need to be formally subdivided into internationally accepted substages:

Some of the stages had a much longer duration than others (e.g., the Emsian, Frasnian, and Famennian) and, especially, than stages in other systems.
Stage subdivisions are frequently in use in many publications on different topics, but without any common meaning and without allowing a meaningful correlation or integration of data.
Several major biotic crises or global sedimentary perturbations (e.g., black shale events), which provide natural subdivisions, occurred within stages (e.g, within the Emsian, Givetian, Frasnian, and Famennian) and are widely lumped by non-specialists and in crude statistical analysis of data resolved only at the stage level (e.g., in misleading biodiversity studies).
There are classical and widely known subdivisions of stages in key regions (e.g., Emsian of Czechia, Givetian of Belgium and Germany, Frasnian of Belgium and North America, Famennian of Belgium and Germany).
Biostratigraphy and other stratigraphic methods easily allow subdivisions that can be recognized globally – hence SDS feels committed to supply a most precise global time scale.

As agreed with ICS, substages will be formally defined by an index fossil but (currently) not by a GSSP. Instead, regional reference sections that allow global correlation will be designated and compiled. No old terms will be revived and no new chronostratigraphic names will be introduced. Instead, depending on the number of substages, the terms Lower, Middle and Upper, and Uppermost will be employed. As an alternative, the terms Early, Middle, Late, and Latest may be used.

Global recognition of chronostratigraphic units

All Devonian GSSPs were defined in subtropical/tropical pelagic outer shelf facies, which allowed easy global correlation based on cosmopolitan faunas and significant short-termed eustatic pulses. Correlation of GSSP levels into huge near-shore, neritic, terrestrial and boreal Devonian areas has been accomplished in a few cases but is still at an early stage elsewhere. Neritic-pelagic and marine-non-marine correlations have been topics of all recent SDS Business Meetings and of many excursions (see SDS Newsletters). Since 2004, the close partnership between SDS and IGCP 499 on “Devonian land-sea interaction: evolution of ecosystems and climate” emphasizes this approach. The approval of GSSPs is only the first step towards a standardized stratigraphy – exploring, increasing and documenting the correlative potential of GSSP (regional GSSP application) is of equal importance.

A huge amount of geological/stratigraphical literature employs old and regional chronostratigraphic nomenclatures that are not understandable and usable any more if no correlation between the new and global stratigraphic system and traditional, regional subdivisions is achieved. During its regional meetings and based on work by national Subcommissions, this task has been tackled in specific regions (e.g, Belgium, Germany, North America, Russia) and is continuing.

Modern, non-biostratigraphic methods

Stratigraphy is increasingly using new non-biostratigraphic methods of correlation, with important application in basin analysis and exploration. These include sequence stratigraphy, magnetostratigraphy (especially the use of magnetic susceptibility in mostly re-magnetized basins and fold belts), chemostratigraphy, stable isotope stratigraphy, cyclostratigraphy, and quantitative stratigraphy (especially graphic correlation techniques). SDS has devoted in the past special symposia, parts of their excursions and of Business Meetings (see list of Meetings and SDS Newsletters) to progress in these fields and will continue to do so.

Integration of Chronostratigraphy and Geochronology

In the past there has been a significant lack of bio- and chronostratigraphically strictly constrained absolute ages for the Devonian. SDS has coordinated and stimulated the geochronological investigation of well-dated volcanic rocks that has lead to a much approved absolute time scale in recent years. Work by the groups around R. D. Tucker (USA), and especially by B. Kaufmann and E. Trapp (conducted in Münster, Germany), has to be emphasized.

Communication of Devonian stratigraphic progress

Advances in stratigraphy are of little significance if they are not widely communicated to the global scientific community. Results are not only reported regularly to ICS, but also in the annual SDS Newsletter, in a range of SDS publications, including complete GSSP reviews (see SDS Publications), and via this homepage.

Devonian global environmental change

The Devonian was a time of repeated global biotic crisis of different magnitudes, including two 1st mass extinctions at the Frasnian-Famennian boundary (Upper Kellwasser Event) and in the topmost Famennian (Hangenberg Events). SDS has focused within its symposia on sudden extinctions, anoxic, climatic and eustatic events, building up a detailed event stratigraphy that enables non-biostratigraphic correlations.