The Bolca Lagerstätten: Shallow Marine Life in the Eocene
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Downloaded from http://jgs.lyellcollection.org/ by guest on September 30, 2021 Review focus Journal of the Geological Society Published Online First https://doi.org/10.1144/jgs2017-164 The Bolca Lagerstätten: shallow marine life in the Eocene Matt Friedman1* & Giorgio Carnevale2 1 Museum of Paleontology and Department of Earth and Environmental Sciences, University of Michigan, 1109 Geddes Ave, Ann Arbor, MI 48109-1079, USA 2 Dipartimento di Scienze della Terra, Università degli Studi di Torino, via Valperga Caluso 35, 10125, Torino, Italy M.F., 0000-0002-0114-7384 * Correspondence: [email protected] Abstract: The Eocene limestones around the Italian village of Bolca occur in a series of distinct localities providing a unique snapshot of marine life in the early Cenozoic. Famous for its fishes, the localities of Bolca also yield diverse invertebrate faunas and a rich, but relatively understudied flora. Most fossils from Bolca derive from the Pesciara and Monte Postale sites, which bear similar fossils but are characterized by slightly different taphonomic and environmental profiles. Although not precisely contemporaneous, the age of these principal localities is well constrained to a narrow interval within the Ypresian Stage, c. 50– 49 Ma. This places Bolca at a critical time in the evolutionary assembly of modern marine fish diversity and of reef communities more generally. Received 22 December 2017; revised 7 March 2018; accepted 8 March 2018 The rich fossil sites near Bolca, Italy provide a picture of life in a contains remains of crocodiles, turtles, snakes and plants. The warm, shallow marine setting during the early Eocene, roughly lignites of Vegroni yield a variety of plants. 50 myr ago. Deposited within an archipelago near the western end of the Tethys Ocean, the major localities of Bolca collectively have yielded over 500 species of terrestrial vertebrates, fishes, insects, Stratigraphy and age marine invertebrates and plants. The outstanding significance of the The Pesciara and Monte Postale successions are among the few Bolca Lagerstätten derives from a unique combination of age (near shallow-water Eocene sequences deposited on the Lessini Shelf the dawn of modern reef ecosystems), location (within an ancient (sensu Bosellini 1989), a palaeogeographical feature of the biodiversity hotspot) and taphonomy (exceptional preservation). Southern Alps that was uplifted during the Alpine orogeny. Upon Here we provide an overview of these sites, discussing history, reaching the photic zone during the early Eocene, the Lessini Shelf geology, fossils and significance. acted as a centre of deposition of shallow-water carbonates (Doglioni & Bosellini 1987; Bosellini 1989; Luciani 1989). Eruptive products of extensive magmatic activity accumulated between the late Geological context Paleocene and the middle Eocene (e.g. Macera et al. 2008). Localities Beginning in the early Eocene, these volcanic and volcanoclastic deposits became intercalated with marls and limestones. The village of Bolca lies on the eastern part of Monti Lessini not far Widespread regional faulting and cross-cutting volcanic units from Verona, northern Italy. Monti Lessini represents a southern hinder stratigraphic studies of the Eocene succession of the Bolca prolongation of the Southern Alps (Carminati et al. 2012). Several area. Consequently, the Eocene carbonates of the Lessini Shelf have productive sites characterized by contrasting fossils are known from been collectively assigned to the ‘Calcari Nummulitici’, an informal the Bolca region (Papazzoni et al. 2014; Fig. 1), and are collectively unit poorly constrained in terms of age and depositional setting. known as ‘Monte Bolca’ in older literature although no such place Pesciara consists of a limestone block surrounded by volcanic exists. We refer to this geographically compact collection of deposits (Fig. 1b). The outcrop is less than 20 m thick, covering an environmentally and stratigraphically distinctive localities as the area of a few hundred square metres, and consists of a rhythmic Bolca Lagerstätten, drawing distinctions between the various sites. alternation of finely laminated micritic limestone with fishes and The most famous representative is Pesciara, which has been plants and grainstone bearing benthic fossils (Papazzoni & exploited since the mid-16th century (Box 1) and yields exquisitely Trevisani 2006). Nearly all the fishes, soft-bodied invertebrates preserved marine fishes, plants and soft-bodied invertebrates. It is and plants collected from Pesciara are from five bands of grey, joined by Monte Postale, located nearby and also famous for marine laminated micritic limestone. The succession of Monte Postale fishes and plants. These two localities are the source of most fossils consists of more than 130 m of grainstone that alternates with from the Bolca area in museums, and have yielded over 100 000 massive coralgal limestone and laminated wackestone with fishes exceptionally preserved fossils (e.g. Blot 1969; Box 1). This review and plants similar to those of Pesciara (e.g. Vescogni et al. 2016; focuses on these two localities. Papazzoni et al. 2017). The laminated limestone varies in thickness There are two additional nearby localities included among the depending on position in the succession. However, most layers are Bolca Lagerstätten: Purga di Bolca and Vegroni. These freshwater about 1 m thick, very similar to those of Pesciara. and brackish deposits are classically considered younger than Both the Pesciara and Monte Postale successions were deposited Pesciara and Monte Postale, but their stratigraphic correlation with in the early late Ypresian. Calcareous nannofossils and larger the more famous horizons is problematic (Papazzoni et al. 2014). benthic Foraminifera indicate that the Pesciara succession corre- Purga di Bolca consists of lignites around a volcanic neck, and sponds to the upper part of that of Monte Postale. Monte Postale © 2018 The Author(s). Published by The Geological Society of London. All rights reserved. For permissions: http://www.geolsoc.org.uk/permissions. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics Downloaded from http://jgs.lyellcollection.org/ by guest on September 30, 2021 M. Friedman & G. Carnevale Fig. 1. Location and geology of Pesciaria and Monte Postale, the principal Lagerstätten of Bolca. (a) Location of Bolca in Italy. (b) Topographic map of region immediately NW of the village of Bolca. Colours indicate different geological units: yellow, Spilecco Limestone; green, laminated and bedded limestone; blue, massive limestone; orange, volcanic rocks. Intensity of shading indicates either rock exposed in outcrop (dark) or inferred (light). Adapted from Trevisani (2015). spans the entire NP 13 and CNE 5 calcareous nannoplankton zones are rare, with palms represented only by fruits (complete palms are (Papazzoni et al. 2017), corresponding to a large part of the Shallow found at Vegroni; Giusberti et al. 2014a). Leaves and leaflets, Benthic Zone (SBZ) 11 in the time interval between c. 50.5 and especially of legumes, are the most common remains of dicots, but 48.96 Ma (see Agnini et al. 2014). This corresponds to the early twigs, fruits and flowers are also known. Specimens of whole plants Eocene climatic optimum (EECO in the sense of Luciani et al. are known, but some of these are regarded as restorations or 2016). Pesciara has been assigned to the uppermost part of SBZ 11, composites (Wilde et al. 2014). In addition to these remains, corresponding to the basal portion of NP 14 and CNE 6, between Pesciara also yields amber (Trevisani et al. 2005). As in the 48.96 and c. 48.5 Ma. macroflora, angiosperms dominate the microflora, with rare gymnosperm pollen and fern spores (Kedves & Zsivin 1970). In drawing comparisons with approximately coeval fossil floras Floral and faunal composition (e.g. lacustrine deposits of Messel), Wilde et al. (2014) noted lower Study of different components of the Bolca fossil assemblages is diversity in the Pesciara–Monte Postale macroflora combined with a uneven. The fishes of Pesciara and Monte Postale have been the distinctive composition in terms of both taxa and organs. They subject of nearly continuous investigation for centuries. The so- attributed these features to a taphonomic filter arising from fluvial called ‘minor fauna’, comprising non-fishes, of Pesciara and Monte transport to the ocean and subsequent shallow marine wave action, Postale are poorly known by comparison (Carnevale et al. 2014; and also acknowledged the potentially important role of storms in Giusberti et al. 2014b). Similarly, relatively little work has built transporting some plant remains. upon foundational palaeobotanical studies from the 19th century (Wilde et al. 2014). Invertebrates Plants Jellyfishes and corals Marine plants and macroalgae Medusae from Pesciara comprise complete specimens preserving delicate features (Giusberti et al. 2014b; Fig. 2d). Corals are a Floating or fully marine monocots such as seagrasses are the most common component of the benthic fauna, represented by broken common elements of the Pesciara–Monte Postale flora (Wilde et al. material in the coarse-grained carbonates intercalated between the 2014; Fig. 2a). Brown and red algae are represented by macrofossils laminites and in the fossiliferous laminated wackestone of Monte and biomarkers (Schwark et al. 2009). Postale (Tang 2002; Marramà et al. 2016a; Fig. 1b and c). Terrestrial plants Ferns are absent, and gymnosperms are limited to long, needle-like