FROM COMBINED GLACIAL ALLO- AND LITHOSTRATIGRAPHY TO GLACIAL SEQUENCE STRATIGRAPHY

Formal stratigraphic classification is a fundamental scientific tool for developing a regional knowledge of the geologic evolution of any period in the Earth’s history. For the subfield of Quaternary geology, the selection of stratigraphic classification criteria is as important a paradigmal decision as was the adoption of sequence stratigraphy for petroleum geology in the 1980s.

The few currently existing national Quaternary stratigraphic frameworks are based on lithostratigraphy. As the true nature of the Quaternary depositional units especially in glaciated shield areas is often that they are arranged in unconformity-bounded, lithologically varying packages, allostratigraphy may be regarded as the most promising descriptive approach for stratigraphic classification. A classification based on the combined use of allostratigraphic and lithostratigraphic data should fit better for such areas, with alloformations as the fundamental units and lithostratigraphic units filling out the framework where appropriate. Lithostratigraphy is undoubtedly applicable, but it should be applied in a stricter manner than it has been used.

The combined use of allo- and lithostratigraphy provides a hierarchical classification system for glacigenic deposits and creates a basis for sequence stratigraphic interpretations. It supports detailed chronostratigraphic and diachronic work in order to improve our understanding of the complicated Quaternary couplings of astronomic forcing, climatic change and continental glacial dynamics that have determined the distribution and nature of glacial depositional and erosional products. The classification would provide a hierarchical framework for glacigenic deposits, which could potentially support stratigraphic information systems, databases and digital spatial models more effectively than the traditional lithostratigraphic frameworks.

In the presentation practical recent field examples on the application of the combined use of allo- and lithostratigraphy are discussed.