Core sampling for palaeomagnetic dating (Népoui, New Caledonia, 2011). © BRGM - L. Alizert

Regolith studies: near-surface geology and planning

02.11.2013
Regolith, which forms the geological layer closest to the surface, is the focus of major environmental issues. It is still unevenly documented in France. Major efforts are required to cater for the increasing interest of users.

Until the late 1990s, regolith units were largely under-assessed or ignored in geological mapping. Sound information on regolith is essential to understand and optimise the management of our environment:

Relevant knowledge on regolith geology can provide answers to most environmental issues that arise in:

  • Good quality in groundwater exploration/production,
  • Low- and medium-enthalpy geothermal potential,
  • Infrastructure works for transport or housing,
  • Inventories of natural hazards,
  • Materials and minerals exploration/production
  •  Waste storage
  • Effects of climate change, soil erosion, etc.

All of these activities imply reliable knowledge on near-surface geology and therefore of the particular geological units collectively known as “superficial formations”, “soil parent materials” or “regolith”.

What is regolith?

The term “regolith” was first coined by Merill (1897) from the Greek rêghos, meaning “cover” and lithos, meaning “rock”, to refer to any material of inland origin, of whatever age, covering hard, sound rock (bedrock), and sometimes including interlayers or inclusions of hard rock in loose or weathered material.

This type of terrain is the “epidermis” of our Earth and results from chemical and physical interactions between the hydrosphere, the atmosphere and the biosphere.  Regolith, which covers most emerged and submerged lands almost continuously, is a system of usually loose rock material formed in situ (weathering profiles, or autochthonous regolith) or transported sedimentary material (allochthonous regolith, with alluvial, colluvial (slope), eolian, lacustrine and/or glacial units).  

Economic and environmental issues involving knowledge of near-surface geology

Regolith terrain supports biological activity; it is the locus of many human activities and the source of usable materials (like clay, sand or gravel) and minerals (such as nickel, iron, manganese, gold and bauxite); it encloses alluvial water tables and is the parent rock of many soils. The properties of regolith unit determine possibilities for establishing settlements and also the constraints to be considered for their rational management.  

Regolith is also a system of geological objects that can provide information on the long history of continental surfaces, the geodynamic events that have governed their formation and evolution and the palaeoclimates that have affected them. Reliable reconstructions of this history and targeted and/or team-based multidisciplinary projects in different contexts are working to:

  • characterise near-surface areas in terms of their physical and chemical parameters,
  • explain the formation of hydrographic networks, soils and weathering profiles, lakes or swamps, and the general evolution of landscapes.
  • locate prospecting guides for certain minerals, some of which are now of strategic interest,
  • propose analogues of climate change effects in terrestrial to coastal environments, especially those linked to greenhouse gases.

Knowledge on regolith in mainland France

The Geological Map of France and the Subsurface Database (BSS), which covers underground engineering works in compliance with the Mining Code, contain most current knowledge on the geology of France.

During the launch of the French Geological Reference Platform, a baseline assessment of knowledge on regolith in mainland France was performed. This showed considerable disparity and sectors where very little information was available.

An integrated approach

Since 2000, BRGM has been strengthening its competences in regolith studies and handles the entire chain from exploration to data acquisition, processing and retrieval and geometric modelling of near-surface geology:

  • Geological and geophysical data acquisition  
  • Detailed characterisation (sedimentology, mineralogy, petrography, etc.) and dating,
  • Data processing and interpretation,
  • Stratigraphic, palaeoenvironmental, palaeographic and palaeoclimatic reconstructions,
  • Data collection and sharing,
  • Knowledge products (reports and scientific publications),
  • Multilayer GIS integration, digital databases and multicriteria analyses,
  • 3D modelling and thematic mapping.

The scale and resolution of the processed data output depends on the quantity and distribution of the data, and especially on the expectations and needs of users. Depending on each case, map scales vary from 1/1 000 000 to 1/5 000 and may be multiple.

Our flagship products and services:

  • Multilayer geological maps and geometric models in 3D,
  • Geological syntheses for scientific or applied uses,
  • Geological core drilling samples and field acquisitions,
  • Detailed characterisation and dating of autochthonous and allochthonous regolith units,
  • Expert studies in France (mainland and overseas) and elsewhere,
  • Field courses
  • Maps of physico-chemical parameters on request, in partnership with other BRGM departments (hydrogeology applications, materials, risks, etc.).

Contact

Your contacts at BRGM for geological data on regolith:

Pierre Nehlig

Head of Geology for Spatial Planning and core-drilling workshop leader

Tel.: +33 (0)2 38 64 32 50

p.nehlig@brgm.fr

Florence Quesnel

Head of the scientific programme on “Regolith formation and characteristics”

Tel.: +33 (0)2 38 64 38 80

f.quesnel@brgm.fr

Caroline Ricordel-Prognon

Head of the project on “Regolith, a substrate for sustainable development: updating knowledge on near-surface geology”

Tel.: +33 (0)2 38 64 38 93

c.prognon@brgm.fr

BRGM - 3 avenue Claude-Guillemin - BP 36009 45060 Orléans Cedex 2 - France Tel.: +33 (0)2 38 64 34 34