Santonian (Upper Cretaceous) rudists bearing conglomeratic site on the Majella Massif (Pennapiedimonte, Central Apennine
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GEOSITES
Santonian (Upper Cretaceous) rudists bearing conglomeratic site on the Majella Massif (Pennapiedimonte, Central Apennines, Italy)
Photograph description The Majella National Park (MNP) in Central Italy has a great geological, stratigraphic and paleontological potential (e.g., Collareta et al. 2020). The unique features of the MNP qualify for consideration by United Nations Educational, Scientific and Cultural Organization (UNESCO) Global Geopark (Liberatoscioli et al. 2018). Several geosites have been documented in the MNP area. One of these is the area of Balzolo, close to the village of Pennapiedimonte (CH, Italy) at the mouth of the Avella River Valley. The area is crossed by a mountain path, along which it is possible to find several outcrops with important paleontological and sedimentological features that illustrate the evolution of the Majella complex (Raffi et al. 2016). The path leads to the innermost part of the Majella Massif, in one of the deeper and most hidden valley of the MNP. It cuts the entire stratigraphic succession of the Majella Massif passing by most recent Formations of Santo Spirito and Orfento (Paleogene to Late Cretaceous in age), toward the Tre Grotte Formation (Late Cretaceous in age), which crops out widely at the end of the path. The Tre Grotte Fm consists of several lithofacies such as mudstone–wackestone, bioclastic packstone–grainstone, breccias and megabreccias with platform and pelagic clumps. It is heteropic with coeval shallow water limestone of Cima delle Murelle Fm which crops out at the end of the valley (e.g., Rusciadelli 2005).
Even though the passage from marginal shelf to slope paleoenvironments is common and well known, it is exceptionally displayed in the MNP. Along the road, a 2- to 3-m-thick outcrop made up of a conglomerate level crops out (WGS84 coordinates: long. 42.151944, lat. 14.176667). It is characterized by small, well-rounded, well to poor sorted, and imbricated bioclasts. The majority of the clasts are rudist fragment (Fig. 1a). Among the clasts, some better-preserved rudists are recognizable, together with corals and nerineids. The presence of Vaccinites (Fig. 1b) constrains the outcrop chronostratigraphically (Santonian, Late Cretaceous). Fossil shells, mainly fragmented, are often flowed. The deposit is toughly cemented, but differential weathering and erosion have revealed the clasts in high relief. This rudist-bearing conglomeratic bank appears and disappears abruptly as traced outcrop, so it represents a drastic change in the depositional conditions. These coarse skeletal deposits suggest currents and high marine energy events which reworked more or less fragmented shells long exposed in a marginal open shelf area. Rudists bearing conglomeratic levels are well known and similar examples are present in different Santonian peri-Mediterranean successions, as in Pesco Rosito, southern Italy (Cestari and Sartorio 1995). Every new outcrop is a piece of the puzzle and contributes to understanding this peculiar and important paleoenvironment whic
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