PHOTOS & VIDEO: A megalodon once swam along the Šentil, but another peculiarity was discovered during highway construction

In the area surrounding today’s municipality of Šentilj, a vast expanse of shallow sea once stretched over 20 million years ago, teeming with diverse marine life. This body of water, known as the Pannonian Sea, was characterized by its warm and shallow depths, fostering a rich ecosystem. Over time, sediments accumulated on the seabed, gradually transforming into solid rock formations, specifically, rounded, oval, or elongated shapes called septaria. These structures contained cracks through which minerals were precipitated from heated solutions, resulting in unique geological formations. Well-preserved examples of septaria and other marine organisms, which were part of the Pannonian Sea, can be viewed at the Regional Tourist Centre Septaria near the border with Austria in Šentilj. The centre also showcases life during the Celtic era, offering visitors a glimpse into ancient history. The formation of the Pannonian Sea began as part of the larger Tethys Sea, which covered much of what is now Central Europe. As the landmasses drifted apart due to tectonic activity, the Pannonian Sea emerged. According to local guide Jelko Weldt, who has shared insights on this topic, the region's geological evolution was influenced by the uplift of mountain ranges such as the Alps, Carpathians, and Dinarides. These movements caused the Pannonian basin to deepen, eventually leading to the retreat of the sea. Rivers played a crucial role in this process, carrying sediments into the basin and contributing to the gradual shallowing of the waters. Eventually, the Danube River carved a channel through the Carpathians, allowing the waters to drain into the Balkan lowlands. Today, remnants of the Pannonian Sea can be found in the Black Sea, Caspian Sea, and Aral Sea. The Pannonian Sea once spanned the territory of modern-day Pannonian Basin, extending deep into present-day Slovenia, Hungary, Serbia, Romania, Bulgaria, and even reaching the Black Sea. However, it is important to note that Lake Balaton in Hungary is not a remnant of the Pannonian Sea. Instead, it is a freshwater lake formed by volcanic activity and meteoric water accumulation. Unlike the Pannonian Sea, Balaton lacks the connection to the former marine environment and is instead shaped by human intervention, including the construction of an artificial canal. During the construction of the Šentilj motorway between 1994 and 1996, workers uncovered well-preserved specimens of septaria and other marine fossils. These findings have since been displayed at the Museum of the Pannonian Sea, providing tangible evidence of the region’s ancient past. Septaria are distinguished by their cracked interiors, where crystallization occurred as organic materials decomposed under pressure and heat. The decomposition of living organisms within these structures released gases, creating fissures through which minerals were deposited. Layers of sediment continued to accumulate, forming the complex geological layers observed today. Among the notable finds are marine organisms such as sea urchins, which lived entirely on the ocean floor and were buried in sand or sediment carried by rivers. Other discoveries include various types of shells, snails, and corals. These fossilized remains offer a window into the biodiversity of the Pannonian Sea, highlighting the dynamic interplay between geological processes and biological evolution.