Pelagosite revisited: The origin and significance of a laminated aragonitic encrustation of Mediterranean supralittoral rocks
Alessandro Montanari, David M. Bice, A.J. Timothy Jull, Anatoliy B. Kudryavtsev, Jennifer L. Macalady, Irene Schaperdoth, Warren D. Sharp, David Shimabukuro, William J. Schopf, Visnja Vucetić, "Pelagosite revisited: The origin and significance of a laminated aragonitic encrustation of Mediterranean supralittoral rocks", 250 Million Years of Earth History in Central Italy: Celebrating 25 Years of the Geological Observatory of Coldigioco, Christian Koeberl, David M. Bice
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n this paper, we review ~140 yr of investigations about pelagosite, a usually black aragonitic encrustation with a vitreous luster that forms in the splash zone of Mediterranean rocky coasts. Prior to the mid-1920s, the geologic community considered pelagosite to be a separate mineral of uncertain composition, but then in 1926, Italian mineralogist Ettore Onorato determined that pelagosite has the same structure as aragonite (orthorhombic CaCO3), and also that it contained cells of blue-green algae (i.e., cyanobacteria). Once pelagosite was declassed from the status of a mineral, and its name was eliminated from catalogues and textbooks, Onorato’s documentation of the cyanobacterial cells contained in this encrustation seems to have fallen into almost total oblivion during the rest of the twentieth century. We revisited pelagosite in its original type locality, the remote southern Adriatic island of Pelagosa (today’s Croatian island of Palagruža), as well as in the Dalmatian island of Hvar. Using modern analytical methods and techniques, we redefined the mineralogical and geochemical composition of pelagosite, the nature and significance of its microbial content, and the origin of its pisolitic “tree-ring” internal structure, which probably reflects cyclic climate changes.
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250 Million Years of Earth History in Central Italy: Celebrating 25 Years of the Geological Observatory of Coldigioco
Central Italy has been a cradle of geology for centuries. For more than 100 years, studies at the Umbria and Marche Apennines have led to new ideas and a better understanding of the past, such as the Cretaceous–Paleogene (K-Pg) boundary event, or the events across the Eocene–Oligocene transition from a greenhouse to an icehouse world. The Umbria-Marche Apennines are entirely made of marine sedimentary rocks, representing a continuous record of the geotectonic evolution of an epeiric sea from the Early Triassic to the Pleistocene. The book includes reviews and original research works accomplished with the support of the Geological Observatory of Coldigioco, an independent research and educational center, which was founded in an abandoned medieval hamlet near Apiro in 1992.