Imagine layers of time compressed into stone. That is the Cyrtograptusskifer. It is right beneath our feet. This isn’t just any rock. The Cyrtograptusskifer whispers tales from the Early Silurian period. This was about 430 million years ago.
What exactly is the Cyrtograptusskifer? It is an older term for a 60-meter-thick sequence. This sequence features dark gray to light gray clay siltstone. Think of it as a time capsule. It is made of mud and silt.
Interestingly, the Cyrtograptusskifer likely hides beneath much of Denmark. It may even stretch across the Baltic Sea floor. It lies close to Bornholm’s south coast. Yet, it only peeks out in a few spots. Visit Øle Å near its mouth. You can see the youngest Silurian deposit here. You can also find it in Læså’s lower reaches. Both sites are on South Bornholm.
But what makes the Cyrtograptusskifer truly special? It is teeming with fossils. Graptolites steal the show. These fossils belong to the genus Cyrtograptus. They are easily recognized by their spiral-rolled and branched forms. Picture tiny, ancient creatures trapped in stone. Similar shale also appears in Skåne.
Here is a fun fact. Despite its significance, the Cyrtograptusskifer has no official name. This is according to current naming rules.
Bornholm itself has a rich history. It was once a Viking stronghold. For a time, Sweden controlled it. Lübeck, a German city, also had its turn in the 16th century. The Treaty of Roskilde awarded Bornholm to Sweden in 1658. By 1660, it was back in Danish hands. During World War II, Germans occupied it. Russians bombed it in 1945 to speed up the German surrender.
The island’s geology is just as varied. The northern part boasts granite cliffs and wooded areas. The south features sandstone, limestone, and shale.
Bornholm faced a climate disaster 4,900 years ago. A large volcanic eruption darkened skies across Northern Europe. This event coincided with unique sun stone sacrifices. Neolithic people on Bornholm offered engraved stones to appease the gods. They hoped to restore the sunlight.
These sun stones are flat shale pieces. They display engraved patterns and sun motifs. Archaeologists believe they symbolize fertility. The stones were sacrificed to ensure sun and growth. Vasagård West is a key site. Residents deposited sun stones in ditches. Ritual feasts accompanied these offerings. Animal bones and broken pottery marked the occasion around 2,900 BC.
Consider the Cyrtograptusskifer. It is more than just a rock formation. It is a window into deep time. It connects us to ancient seas. It also connects us to the people of Bornholm’s past. The Cyrtograptusskifer whispers secrets of survival.