Chemosymbiotic bivalves from Miocene methane-seep carbonates in Italy

Abstract

Abstract.-Eleven species of chemosymbiotic bivalves are reported from middle to late Miocene methane seep deposits ('Calcari a Lucina') in the Italian Apennines, including seven new species and one new genus. The new species are Bathymodiolus (s.l.) moroniae and B. (s.l.) miomediterraneus among the Bathymodiolinae and Archivesica aharoni, A. apenninica, A. strigarum, and 'Pliocardia' italica among the Vesicomyidae; specimens from the middle Miocene of Deruta are reported as Archivesica aff. aharoni. Samiolus iohannesbaptistae new genus new species is introduced for an unusual mytilid with a commarginally ribbed surface, which might be the first non-bathymodiolin mytilid obligate to the seep environment. The two large lucinid species from which these deposits derived their informal name 'Calcari a Lucina' are identified as Meganodontia hoernea (Des Moulins, 1868) and Lucinoma perusina (Sacco, 1901). With Chanellaxinus sp., we report the first thyasirid from a Neogene deep-water seep deposit in Italy and the first fossil occurrence of this genus.

Mollusks (Gastropoda, Bivalvia) from Miocene cold-seep deposits in northern Italy: revisions and additions

“…The only previous records are three specimens assigned to Channelaxinus sp. from the Ca' Cavalmagra site (Kiel & Taviani 2017). This is a remarkable contrast to coeval seep deposits in both the Pacific and the Caribbean regions (Amano et al 2015(Amano et al , 2022Kiel & Hansen 2015;Hryniewicz 2022;Kiel et al 2022), where large thyasirids typically assigned to Conchocele Gabb, 1866 often dominate the assemblages.…”

“…Over the last one-and-a-half decades, we (in different constellations) have published several faunistic and taxonomic updates of the mollusks of the Calcari a Lucina deposits. These included most bivalve groups (Taviani et al 2011;Kiel & Taviani 2017 and various reports on individual new sites or noteworthy taxa (Berti et al 1994;Lucente & Taviani 2005;Sami & Tabanelli 2013;Sami & Taviani 2015;Kiel et al , 2023. The purpose of this study is to revise all species that we have not covered previously (mostly the gastropods), to describe new species, to provide new records of known species from various sites, and to supply new taxonomic data for known species.…”

Messinian seep-carbonates marking the transition to the evaporite deposits in the Romagna sector of the northern Apennines (Italy)

“…An accurate mapping associated with facies, compositional and isotopic analysis shows that they are constituted largely by authigenic, strongly 13 C depleted carbonates, rich in chemosymbiotic taxa (Sami & Taviani, 2015;Kiel & Taviani, 2017), with fluid expulsion structures (vein network, conduits, breccias and other features such as vuggy and mottled fabric). Based on these evidence, they can be interpreted as the product environments by a consortium of methanotrophic archea and sulphate-reducing bacteria (Boetius et al, 2000) as confirmed by the presence of large bivalves belonging to Mytilidae, Lucinidae and Vesicomyidae.…”

“…In the northern Apennines, and precisely in the sector of the spectacular area of the Vena del Gesso, between Senio and Lamone Valleys, the passage between euxinic shales-sapropels mudstones of Ghioli di letto Fm, marking the closure of the Miocene Marnosoarenacea foredeep, and the evaporites is characterized by the presence of numerous outcrops of seep-carbonates, historically named "Lucina limestones" (Sami & Taviani, 2015). These authigenic carbonates are frequently reported in various geological settings of the northern Apennines (Clari et al, 2009;Argentino et al, 2019;Conti et al, 2021a), characterized by densely packed chemosynthetic fauna (Kiel & Taviani, 2017) related to hydrocarbonrich fluids (Conti et al, 2021b cum ref. ).…”

Miocene Seep-Carbonates of the Northern Apennines (Emilia to Umbria, Italy): An Overview

“…Due to the fluxes of reduced carbon and sulfur compounds reaching the seafloor, these environments are inhabited by peculiar microbial consortia and chemosymbiotic macrofaunal assemblages [11][12][13][14][15][16] and marked by specific geochemical imprinting [17,18]. Fossil analogous to modern systems have been recognized in exposed sedimentary successions on all continents (except Antarctica) and have allowed the investigation of the long-term evolution of hydrocarbon seepage in relation to tectonic processes and climate change [12].…”