A shift from lithostratigraphic to allostratigraphic classification of Quaternary glacial deposits

Abstract

The bedrock of the northern halves of North America and Europe is covered by Quaternary glacial deposits, forming a surficial overburden that is relatively thin, nonlithified, lithologically variable on a small scale (in terms of grain-size, mineralogy, texture, fabric, structure, and color), and often has a well-preserved depositional topography. These geologically unique characteristics and the fact that the glacial overburden was long considered to be of only restricted economic value have caused it to be treated differently in geological research from the older, regularly lithified strata. Due to the striking geomorphology of these glacial deposits, their investigation has also been incorporated into physical geography research. Thus, the segregation of the Quaternary research community into different schools of geology and geography has created multiple classification approaches and has caused the formal stratigraphic classifications successfully applied in pre-Quaternary geology to be applied less regularly to Quaternary glacial strata. This has led to inefficient use of Quaternary geological data for scientific and socio-economic purposes.The few currently existing national Quaternary stratigraphic frameworks are based on lithostratigraphy. These are poorly suited for describing deposits in glaciated shield areas in particular; we propose a classification for such areas based on the combined use of allostratigraphic and lithostratigraphic data, with alloformations as the fundamental units and lithostratigraphic units filling out the framework where appropriate. This classification would provide a hierarchical framework for glaciogenic deposits that could potentially support stratigraphic information systems, databases, and digital spatial models more effectively than the traditional lithostratigraphic frameworks.

A new Quaternary and Neogene Lithostratigraphical Framework for Great Britain and the Isle of Man

“…Elsewhere, particularly applicable in glaciated terrains (e.g. in Finland), an allostratigraphical scheme has been adopted (Räsänen et al, 2009) in which formations are defined by unconformable boundaries. A similar approach based mainly on seismo-stratigraphy has been utilised for the Quaternary deposits lying offshore the UK (Stoker et al, 2011).…”

A shift from lithostratigraphic to allostratigraphic classification of Quaternary glacial deposits: COMMENT

“…Additionally, Räsänen et al (2009) display a commonly held misunderstanding when they describe the Illinois lithostratigraphy of Willman and Frye (1970), and by implication, Minnesota's, as a sensu latu approach. They claim this because our approaches allow for lithologic variability in the lithostratigraphic unit.…”

“…Indeed, formal lithostratigraphies have been progressively established in most Midwestern states. Räsänen et al (2009) claim that Quaternary units are difficult to map. But in the Midwest, till sheets have been correlated based on texture and grain lithology for hundreds to thousands of kilometers, from the Canadian border through Minnesota to central Iowa, a distance equal to a till sheet stretching from central Finland to Lithuania.…”

“…In the Baltic, seismic profiles shown by Räsänen et al (2009) clearly show unconformities but yield little material characteristics, so alloformations seem appropriate. However, if these deposits were on land, as in Minnesota, the material character would be observable, the unconformities less so, and lithostratigraphy more practical.…”

“…We take issue with how Räsänen et al (2009) characterize the lithostratigraphic work in the Midwest. We can report that the Minnesota Geological Survey (MGS) lithostratigraphic classification is not "freely" applied, nor does it use North American Code of Stratigraphic Nomenclature (NACSN) terminology "loosely."…”