Witnesses of prehistory

Around 80 million years ago, the Münsterland was part of a large sea. The limestone layers exposed in the quarries around Beckum are sedimentary deposits of this sea. The layers consist of an alternating sequence of clayey marls, marly limestones and marl limestones.

Text by Georg Olbrich, Beckum

What minerals can be found here? The possibilities of finding minerals in the Beckum quarries are strongly related to the mining activities. If fissures are excavated, many beautiful minerals can be found. Fissures are formed by shifting rock plates (plate tectonics) or by earthquakes. In the resulting fissures and cracks, a) hydrothermal; i.e. rising hot waters with dissolved minerals penetrate and crystallise over long periods of time, or b) from above by rainwater, which dissolves minerals from the neighbouring rocks on its way down, thus providing the germs for crystals to grow. Which of the two theories is correct has not yet been clearly clarified.

In my 50 years of collecting, I have been able to identify 7 different types of minerals to date:
1. Calcite (calcium carbonate), CaCO3
2. Strontianite (strontium carbonate), SrCO3
3. Pyrite (sulphide), FeS2
4. Marcasite (sulphide), FeS2
5. Limonite (brown iron ore - hydroxide), FeOOH
6. Manganese oxide (precipitates in the form of dendrites), MnO
7. Barite (sulphate), BaSO4

These minerals occur independently, but also together with other minerals. It can happen that small brass-coloured pyrite crystals grow on or in calcite crystals and snow-white, tree-like strontianite crystals sit between the calcite crystals. This meeting of different minerals on the same parent rock is called paragenesis. If such minerals are found together with the parent rock, these pieces are called mineral specimens.

A special and very rare find was made in 1985 in the Readymix quarry (today Holcim's Kollenbach plant). The mineral baryte, also known as barite, was found in the north-eastern part of the quarry. The barite was grown on calcite crystals, had a tabular shape of about 10 mm in size and was white in colour. It was a unique find and this mineral has not been found again until today.

Anyone who would like to know more about this beautiful and interesting hobby can contact the working group "Mineral and Fossil Friends" of the Beckum Local History Society. The group meets every first Wednesday of the month at 6.30 pm for a round of talks at the Samson restaurant in Beckum. We undertake several organised excursions a year and also warmly invite guests to join us. Attention: Entering the quarries is generally prohibited.

You may only enter the quarries with a written permit and in compliance with the factory regulations and protective equipment. For your own safety, you should never enter the quarry alone!

Fossils

Text and pictures by Ludger Bach

In the marl and limestone layers that are exposed in the Beckum quarries, remains of primeval life from the Cretaceous sea have also been preserved in some layers. Partially preserved fossils can be found with diligence and a little luck, especially in the upper Beckum strata and in the prehelmet strata that are still exposed in some places. Compared to other sites in Germany, these finds are a certain rarity. Above all, the optically unspectacular, straight-growing ammonites called Baculites vertebralis, which are sometimes confused with belemnites, come to light. These thunderbolts (rostrums of former octopuses) are so weather-resistant due to their hardness (calcite) that they can also be picked up on marly fields.

However, the spiral-shaped ammonite shells deserve special attention. They can appear in the area of the local quarries up to a size of 70 centimetres and then require considerable salvage efforts. However, a wide variety of species with diameters averaging 10 centimetres predominate.

The finds from the native stone caves, however, illustrate a far more diverse life in the once subtropical sea. In addition to extremely rare fish finds, various mussels, snails, nautilids, sponges, sea urchins and filigree brittle stars came to light. Another unusual find is the cone of a conifer, as we are dealing with marine sediments here. This part of a land plant was probably washed into this area with submarine mud flows from the southern coastal strip.

These finds also show how exciting excursions to the quarries around Beckum can be, which are also offered by the working group of the local history society thanks to the help of the local cement industry.

Further information on the private websites of Ludger Bach https://bach-fossilien.jimdofree.com and Georg Olbrich https://olbrichgeo.de/
(By clicking on the link you will leave the pages of the city of Beckum)