The official 'golden spike' marking 89.8 million years ago. A thin rock layer in Germany where a wave of spiral-shelled sea creatures suddenly vanished during the age of dinosaurs.
Daderot, CC0, via Wikimedia Commons
A planet's official timeline
In a former limestone quarry near Salzgitter-Salder, a small bronze plaque marks a globally significant point in Earth's history. This is a Global Boundary Stratotype Section and Point (GSSP), informally known as a "golden spike." Ratified in May 2021 by the International Union of Geological Sciences, this marker defines the precise start of the Coniacian Age of the Late Cretaceous Period, 89.8 million years ago.
The quarry exposes a 220-meter-thick sequence of rock layers that were once sediments on an ancient sea floor. Around 90 million years ago, this part of Europe was a collection of islands in a warm, shallow sea. The layers of limestone and marl are tilted steeply at an angle of about 70 degrees, pushed upwards by a massive underground salt dome. This geological tilting provides an accessible, book-like cross-section of millions of years of marine history. The rock record is so complete and full of fossils that it was chosen over competing sites in the USA, Poland, and India.
The extinction marker
The golden spike is not defined by a asteroid impact, but by the subtle first appearance of a specific fossil. The boundary is placed at the base of rock layer number 46, which contains the first fossils of the inoceramid bivalve Cremnoceramus deformis erectus. Inoceramids were a family of giant, reef-building bivalves, related to modern oysters and clams. The appearance of this new species marks a faunal turnover event, an important moment in the evolution of life during the Cretaceous.
The layers at Salzgitter-Salder document a diverse marine ecosystem. While the official marker is the appearance of Cremnoceramus, the wider ecosystem included the spiral-shelled ammonites common to the period, along with sea urchins and microscopic foraminifera. The larger inoceramid clams of the Platyceramus genus could grow to enormous sizes, with some fossil specimens reaching three meters in diameter, making them the largest bivalves known. These huge, thin shells often provided shelter for schools of small fish, whose fossilized remains are sometimes found preserved inside the giant clams.
💡Fun Facts
The term "golden spike" is metaphorical; the official marker is a bronze plaque, not solid gold.
The layers of limestone and marl show rhythmic patterns that correspond to Milankovitch cycles—long-term changes in Earth's orbit that influence climate.
Some fossilized *Platyceramus* shells have been found containing pearls.
The quarry is a designated geotope and part of the Harz-Braunschweiger Land-Ostfalen UNESCO Global Geopark.
The former quarry is not freely open to the public for nature conservation reasons. Guided tours may be available on occasion through the UNESCO Geopark.
Admission
Access is restricted. Check with the geopark for tour availability and pricing.
Accessibility
As a former quarry, the terrain is uneven, rocky, and steep. It is not accessible for wheelchairs or those with mobility issues.
