Description Area

In our Description Area, we characterise the content and structure of sediments. This provides insight into the physical and seismic characteristics of the Dutch subsurface. Our descriptions are foundational to lithostratigraphy and the development of geological models.

Origin and usability of the subsurface

The sediments and their sequences offer information on the depositional environment and its alternation: river, sea, lake, or dune. Or dry, wet, hot, or cold. We also measure the firmness of the subsurface. The measured porosity of the sediment is a measure for its permeability or potential for water or CO2 storage. In this way, we can determine whether locations in the subsurface can be used for applications that contribute to the energy transition. Overview of the Description Area at the Geological Survey of the Netherlands (GDN), which is part of TNO.

Representative materials

We measure and estimate physical characteristics such as grain size. Using chemical reactions, we determine the chemical properties of materials such as clays, loams, sands, gravels, and peats. Lime, for example, reacts with hydrochloric acid. We consistently and meticulously describe sediments from the earth’s surface up to hundreds of metres below it, from quarries, construction pits, and drillings. Drillings can be completely cored or consist of sediment retrieved via air and/or water lift, therefore (usually) making them representative examples of the bulk sediment.

Sediment descriptions

Sediment descriptions consist of a range of information, including the type of sediment (such as clay, loam, sand, gravel, or organic matter) and their percentage proportions, which together characterise the sediment type. We also look at the colour, composition, shape, and size of the grains; admixture of other sediment types (clay chunks in sand, for example); biogenic content (such as shells and plant remains); and sedimentary structures (stratification, erosive contacts, bioturbation, rooting). For practical reasons, we often distinguish between sediments and rocks, despite the fact that rocks have usually also been sediments and may include associated structures and the remains of deceased organisms. Rocks are sediments hardened by various chemical and physical influences.


For our measurements, we use various tools, such as microscopes, binoculars, Munsell colour charts (for sediments and rocks), cutting machines, hydrochloric acid (10%, to detect lime), peroxide (5%, to detect organic material), and a variety of tools, ranging from hammers and chisels to tweezers and preparation needles. We are also able to use various collections that consist of (and are supplemented by) new comparative material for shells from fresh and salt water, gravel types, sediment types, and an extensive collection of rocks.

Learn more about our Description Area

A team of passionate employees works in our Description Area. Interested in more information? Contact Ronald Harting via the blue ‘mail directly’ button below.