The Sierra Norte de Sevilla Geopark was first nominated as a Spanish Natural Park in 1989. In 2011, it was declared a European Geopark and later recognized as a UNESCO World Geopark in 2015.
The unique paleontological features and the international recognition of the Early Cambrian trilobite sites within the geopark are briefly presented in this work. Following the discovery of the first trilobite site in 1938, about 20 Early Cambrian trilobite sites have been reported since then. They occur in the Benalija Unit near the municipalities of Cazalla de la Sierra, Guadalcanal, San Nicolás del Puerto and Constantina. These discoveries resulted in several studies published by some of the most renowned Cambrian specialists from the 20th century, namely Richter and Richter (1940), Hupé (1953), Hennigsmoen (1958) and Sdzuy (1961, 1962). See Mayoral et al. (2008) and Mayoral et al. (2020) for more recent studies.
Geological and Stratigraphical Location
The trilobite sites occur in the Ossa-Morena Zone (Iberian Massif; Fig. 1A), in Cambrian outcrops of the northern limb of the Olivenza-Monesterio Antiform (Fig. 1B). More specifically, they are within the Benalija Unit (Fig. 1C). The sites are scattered throughout the stratigraphic succession of the Lower Cambrian Alanís Beds (Fig. 2).
Figure 1. Location of the studied area. A. Ossa-Morena Zone (framed area). B. Cambrian outcrops and location of the Sierra Norte de Sevilla Geopark. C. Main sites with fauna of the Early Cambrian (Benalija Unit) in the Sierra Norte de Sevilla Geopark. Geological map modified from Tragsatec (2011).
Figure 2. Synthetic Lower Cambrian stratigraphy of the area.
Paleontological Relevance of the Trilobite and Associated Fauna Sites
A total of 16 genera and 18 species of trilobites have been recognized in the Sierra Norte de Sevilla Geopark, one of the highest trilobite diversities worldwide for this geological time interval. The geopark also includes the original locations – type area, or locus typicus – where several trilobite genera were defined, namely Alanisia, Saukianda, Perrector, Eops, Strenuaeva and Andalusiana (Fig. 3),as well as those of other species including twelve trilobites, one hyolith, one serpulid and one echinoderm.
In addition, the Sierra Norte de Sevilla Geopark is the type area where the Marianian Stage (from the Latin Mons Mariani = Sierra Morena) was defined. The Marianian is a formal geological unit of reference for the Cambrian Mediterranean Subprovince. The presence of Early Cambrian soft-bodied fossils was evidence to include this Geopark in the list of exceptional Lagerstätten sites, highlighting the scientific value of the sites in terms of natural heritage and the need for their conservation.
From a strictly scientific perspective, one of the most outstanding characteristics of the Geopark is that it allows the possibility of analyzing, both temporally and spatially, the variation in trilobite faunal assemblages and, therefore, to interpret the changes in the communities of successive ecosystems. Furthermore, the Geopark offers the possibility of recognizing different paleoenvironments which range from coastal (Cerro del Hierro event) to marine platforms, with benthic and pelagic fossil fauna present, such as some tiny, pelagic eodiscid trilobites which are characteristic of the Lower Cambrian of both North America and Europe.