New insights into the palaeoenvironmental–palaeoclimatic significance and sedimentary dynamics of carbonate Lagerstätten: The lower Albian of Pietraroja (Southern Italy)

Abstract

This study reports the first high‐resolution, integrated facies analysis of the lowermost Albian Pietraroja Lagerstätten (Apennine Carbonate Platform) which yields the first dinosaur (Scipionyx samniticus) found in Italy and other terrestrial vertebrates and plants. Aiming to clarify the long‐debated palaeoenvironmental significance of the Pietraroja succession, the following have been carried out: (i) a field survey to establish stratigraphic position and number of the fossil Lagerstätten; (ii) the centimetre‐scale facies analysis of a new section, ca 15 m‐thick, consisting of two new lithostratigraphic units, the ‘Cyclically organized Limestones’ and the ‘Cherty Limestones’; (iii) the scanning electron microscopy – energy dispersive X‐ray spectroscopy and backscattered electron – energy dispersive X‐ray spectroscopy analyses of clay mineral proxies for palaeoclimate and non‐carbonate grains; and (iv) the regional and supra‐regional investigation of the event stratigraphical context of the fossil Lagerstätten, in order to elucidate the controls on their formation. The section includes two out of the three observed fossil‐rich Lagerstätten, each up to 1.5 m‐thick. The arrangement of lithofacies and early diagenetic overprint defines shallow‐water depositional cycles suggestive of precession and short‐eccentricity periodicities. The Middle Lagerstätte yielding Scipionyx samniticus consists of three intervals. The lower, paralic interval was deposited during arid conditions and passes gradually to the plant‐rich, coastal wetland carbonaceous marls of the upper interval. The ‘Cherty Limestones’, yielding the Upper Lagerstätte with terrestrial vertebrates, contains two spiculitic intervals suggesting the development of siliceous sponge meadows in a shallow, restricted lagoon. Genetic stratigraphy suggests that the Pietraroja Lagerstätten were formed during glacioeustatic lowstands; interestingly, the Middle Lagerstätte mirrors the earliest Albian sea‐level lowstand (KAl1 event, ca 111.2 Myr), during a semi‐continuous supply of windblown volcaniclastics. Findings herein substantiate the pivotal role of paralic‐continental Lagerstätten for deriving high‐frequency palaeoclimatic dynamics and glacioeustacy from carbonate platform archives. The origin of Tethyan continental bridges between Africa and Europe during the late Aptian–earliest Albian cold interval is discussed.