Emblematic fossil deposits with historical value for Bulgarian geology – 150 years after Franz Tula‘s first routes in Bulgaria

This year marks the 150th anniversary of the first geological route of the Viennese explorer Franz von Toula (1845–1920) in Bulgaria, who described and illustrated the first Bulgarian fossils. Some of the described fossil deposits remain in the history of Bulgarian geology as geosites of high scientific and educational value, and the presence of specimens in the Viennese museums makes them geosites of international importance. This article examines spatio-temporal and illustrative-descriptive criteria for estimation of fossil sites as geosites of historical value for Bulgarian geology. The first group of criteria includes data on the geographical location and date of publication, and the second one – certain scientific information such as paleontological description and illustrations of the fossil taxa. Some of the first fossil deposits falling within the boundaries of the Bulgarian geoparks “Belogradchik Rocks”, “Iskar Canyon”, and “East Balkan” are examined. The analysis of the earliest publications of Toula (1877a, b) shows that the first Bulgarian fossils were described in NW Bulgaria near the towns of Kula and Dimovo, and the first fossil deposits were those of the Stephanian megaflora from “Zelenigrad” coal mine and fossil fauna from the Triassic “mushelkalk” near the town of Belogradchik. Another important geosite is the fossil deposit near the village of Varbovo, where the presence of the Jurassic system in Bulgaria was proven for the first time. On the territory of the “Iskar Canyon” geopark Toula (1878) described two outcrops that were also assessed as geosites of historical value for Bulgarian geology: the ino­ceramus limestone near the village of Chelopek with the first Upper Cretaceous fossils in Bulgaria, and the Stephanian horsetails, ferns and lepidophytes near the town of Svoge, representative of the Svoge coal basin. On the territory of the “East Balkan” Geopark in Garnyovitsa area near the town of Kotel, Toula (1890) discovered a unique for Bulgaria deposit of corals and hydrozoa in an Upper Triassic olistolith, which are key fossils for the Mesozoic stratigraphy and the correlation of Late Triassic rocks on a global scale. He named three new coral species after the town of Kotel. In the limestones of “belemnitico rosso” type, which are also olistoliths among turbidites of the Kotel Formation, Toula identified Early Jurassic belemnites and crinoids. These key outcrops in the “East Balkan” Geopark are also estimated as geosites of historical value for Bulgarian geology.