April 2016    Print this article


Québec’s Stratigraphic Lexicon

Ghyslain Roy, Geologist.
Ministère de l’Énergie et des Ressources naturelles

Stratigraphy and stratigraphic units: What are they?

Stratigraphy is the branch of geology concerned with the order and relative position of geological strata in the Earth’s crust. It plays an important role in producing the geological information on a given area, since it is used among other things to establish the relative positions of rock bodies and prepare models to help understand geological development.

The geological surveys carried out each year by Géologie Québec contribute to this information by adding and defining new geological units. The surveys allow geologists to propose a division of basement rock based largely on lithological features, age and spatial distribution of rocks.

Each zone is known as a “geological unit” or “stratigraphic unit” in cases where sufficient information is available to assign a classification and formal appellation. Classification and appellation of stratigraphic units are governed by the North American Stratigraphic Code, which contains the principles and rules of procedure. The Code was prepared by the North American Commission on Stratigraphic Nomenclature (NACSN) for geologists working in North America.

What about the stratigraphic lexicon?

Québec’s stratigraphic lexicon contains the descriptions of all stratigraphic units identified in Québec. It is also an internal tool used by geologists from Géologie Québec to manage stratigraphic units during fieldwork. The lexicon contains information drawn from geological surveys carried out by Géologie Québec, along with historical data from the literature. Like other similar lexicons throughout the world, it provides the geological community with an important directory and profile of all the stratigraphic units used in Québec.

The stratigraphic units are presented in the form of descriptive files. The file for an individual unit provides full details of all available information including:

A long-term task

Producing the geological map of a territory as immense as Québec is a long-term task, and ensuring stratigraphic coherence can be challenging. Creating a stratigraphic lexicon is also a huge undertaking, one that involves assembling and compiling enormous quantities of data and checking their consistency with the geological map of Québec. So far, Québec has more than 2,000 stratigraphic units, and information on these units is scattered among a variety of documents including reports, theses, scientific papers and previously published stratigraphic lexicons.

A modern lexicon

The stratigraphic lexicon is entirely Web-based, for the convenience of users. Users can search the full texts of stratigraphic files posted on the Web using search engines such as Google to identify all the Web pages referring to the stratigraphic units that fit their search criteria. This is currently not possible with SIGÉOM, which contains static PDF images.


Stratigraphic file

The lexicon also uses the georeferencing applications available in SIGÉOM. Users can, with a single click, display the location of a stratigraphic unit within the territory, by means of an interactive map. It is then possible to compare the unit’s position with the many other layers of information available on the interactive map (regional geography, drilling, geochronological samples, etc.).


Interactive map

The descriptive files also offer other interactive possibilities with the SIGÉOM database and EXAMINE. For example, hyperlinks lead users to photographs, information on geochronological samples and geoscientific documents. Figure 1 shows the main interactions available in a descriptive file from the lexicon.


Photo

The first Web files should be posted online during the spring of 2016. They will refer to 12 stratigraphic units from the geological compilation of the Ungava Orogen (Lamothe, 2007, in French only), which has 21 in all. New files will be added to the lexicon as the data are compiled, and when the first electronic geology report (EGR) is published in the fall of 2016. Like the stratigraphic lexicon, the EGR will contain many links to the SIGÉOM database and applications, including the interactive map and the stratigraphic lexicon (see the article on the EGR in the Québec Mines Bulletin of July 2014).

The mapping work done by Géologie Québec and its predecessors in the last 100 years will therefore be presented in a more easily accessible electronic form, so that specialists and the general public can benefit from the geoscientific knowledge amassed in Québec over the years.

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