Redescription of pleurotomaria gerthiweaver, 1931 (gastropoda, vetigastropoda), from the early cretaceous of Argentina: New data on its age, associated palaeoenvironments and palaeobiogeographic affinities

Abstract

Pleurotomaria gerthi Weaver, 1931 (Gastropoda, Vetigastropoda) from the Pilmatue Member of the Agrio Formation is rede-scribed and reillustrated on the basis of 38 newly collected specimens from nine localities in Neuquen Province, Argentina, including its type locality. The holotype housed in the C.E. Weaver collection is also refigured. Pleurotomaria gerthi-bearing levels, dated using a detailed ammonoid zonation, are late Valanginian-early Hauterivian. Taphonomic and sedimentological data gathered at three of the nine studied sections indicate that P. gerthi dwelled in shallow marine settings above the storm-weather wave-base. Associated palaeoenvironments are interpreted as inner shelf and inner carbonate ramp settings deposited under the influence storm currents and waves. The species lived on well-oxygenated soft sandy and patchy bioclastic substrates in normal marine warm-temperate waters within the photic zone, associated with a high-diversity macrofossil assemblage. Our study shows that its preferred habitat was the middle carbonate ramp, below the fair-weather wave-base, under low to moderate energy from episodic storm waves and currents. Pleurotomaria gerthi is endemic to the marine Andean basins of the western margin of southern South America and its oldest record is from theTithonian of the Aconcagua-Central Chile Basin. It bears the closest morphological resemblance to Early Cretaceous species from the Tethyan Realm. During the Berriasian-Barremian interval, Pleurotomaria was a pandemic genus, with records in peri-Tethyan basins of Europe and India, as well as in north and south temperate marine basins in England and the western margin of South America.